Re: [rfc-i] Evolving document sources over a long time (Re: Comments on draft-roach-bis-documents-00)

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Thanks to everyone for their suggestions.   Now that I've followed up on many of them, I'd like to tell everybody what I've found so that people can consider the implicationss for Adam's document and for the processing of upcoming updates to RFC5661.   In particular, use of the existing v1 tools has proved quite helpful although it is not a panacea.

So what I've found is that:
  • Even with the v1 xml2rfc, the .xml that I have gotten for RFC5661 from the RFC editor cannot be successfully processed.   Whether you use the existing v2 xml2rfc  or the v1 xml2rfc available on the web, considerable effort is required to get to an xml that can be processed successfully.   The xml file I received from the RFC editor is attached as rfc5661Base.xml while the one I arrived at is attached as rfc5661Ready.xml.
  • Processing of the best xml that I have been able to arrive at for rfc5661 using the current v2 xml2rfc results in a document which, when compared with rfc5661 using rfcdiff,  has a large number of differences which might be considered spurious.  Although I don't feel any of these are in fact spurious, they are numerous enough that it might be hard to make this determination quickly.  The largest part of these differences concern text tables which rfcdiff flags as different even in cases in which the tables seem identical.   Also, there re small formtting differences that resul from the use of the v2 xml2rfc as well as issues arsing from different handling policies for hyphenated words.  I've attached the resulting .txt file as rfc5661Ready.txt so that people can rfcdiff it against rfc5661.
  • Processing of the best xml that I have been able to arrive at for rfc5661 using the v1 xml2rfc available on the web results in a document which, when compared with rfc5661 using rfcdiff, shows a small number of differences but is not identical to rfc5661.   Besides the small set of difference mentioned below, common to both v1 and v2 xml2rfc, the main issue concerns a number of cases in which the xml (and rfc5661) has two spaces following a period while the v1 xml2rfc has only a single space.   This is a formatting change but if it is considered "spurious", then that spurious change is unavoidable when using the v1 xml2rfc.  It can be avoided using the v2 xml2rfc but that causes many more differences with rfc5661, as discusssed above.   I've attached the resulting .txt file as rfc5661ReadyV1.txt so that people can rfcdiff it against rfc5661.
  • In addition there are a few differences that appear whether the v1 or v2 xml2rfc is used.   
    • One source of these concerrns the capitalization (or not) of the words "profile" and "type" in the titles of many stringprep-related sections.  Since RFC5661 uses different forms in the section itself and in the table-of-contents, it is impossible to avoid one of those being different from RFC5661.  
    • Other problems arise from the different lengths of xml2rfc-generated introductory material before the table of contents.   The page count is different for v1 and v2 but both differ from rfc5661.
    • References to ancohor are handled differently in v1 and v2 but neither can be made to match the results in rfc5661.   
    • Another problem is that rfcdiff appears to have a bug resulting in it showing that a significant piece of the definition of CB_COMPOUND is missing, even though the .txt file shows no such difference :-(
Based on my experences, I'd like to suggest:
  • That the following addition be made to item 3 in section 3.1 of Adam's document.
In evaluating whether such disqualifying changes have occurred, it is intended that changes due solely to changes in the tools used to generate RFC .txt files be allowed.  In addition, issues resulting from changes made by the RFC editor but not reflected in the xml file for the RFC not interfere with IESG consideration of the document and can be made, if necessary, by the RFC editor after the revised documment is approved for publication.
  • That the following addition be made to item 6 in section 3.1 of Adam's document.
This will include the AD's determination that the requirements of item 3 above have been met.
  • That, if possible, somebody should fix the bug in rfcdiff noted above.

On Mon, May 13, 2019 at 5:22 AM David Noveck <davenoveck@xxxxxxxxx> wrote:
>> For RFC5661 and documents derived from it using Adam’s procedure, that ship has already sailed :-(.

> As the references section needs to be updated anyway (for the DOIs), I’m not sure this is really true.  Or, if it is, 
> RFC 5661 maybe isn’t really a candidate for this process, because it may be impractical to re-generate the exact 
> numbering that RFC 5661 used.

I had been assuming that you could turn off sortrefs and construct a reference section in the exact order that the
v1 tool.   I'll try some experientsto validate that approach.

.> > > Since RFC 5661, we also got DOIs on RFCs, so it is inevitable there are a lot of diffs.  
>> 
>> It is not inevitable as shown by the fact that I didn't run into that issue.   It's kind of nice to know that there was an issue out there that I didn't run into :-)
>> 
>> For reasons I  really don't understand, the xml for rfc5661 does not include rfc reference from external libraries.   It includes them inline, so a new rfc derived from that xml  file will not include DOIs.  

> Yes.  All these RFC references would be updated by the RFC editor into current references..

That's not a problem for Adam's procedure :-).   The RFC candidate considred by the IESG would still match
rfc5661.   Then, during RFC editing, the reference section could be revised to include the DOI's.

>> That is not a problem for Adam's procedure, but it may be for the IESG or the RFC editor.   I hope that, in processing RFC’s using Adam's procedure, people will overlook the lack of DOIs in the same way that they overlook other aspects of the document that would prevent a new document of that form from being published.

>AFAICT, they can’t, as the RFC editor has committed to providing DOIs.  

Please see above:
  • The IESG doesn't have to deal with the DOI diffs, since it won't see them.
  • The RFC editor would create DOI diffs but not be bound by Adam's procedure in doing so.
Where this might be a problem is in document where the existing xml uses external reference libraries.   That avoids the need for the RFC to do anything to provide the DOI's other that updating the libraries.   However the IESG will see the diffs resulting from the inclusion of DOI's so I would hope that Adam's document is clear thar they should not be considered "spurous".


On Sun, May 12, 2019 at 12:57 PM Carsten Bormann <cabo@xxxxxxx> wrote:
Hi Julian,

> FWIW, I disagree (but I realize that I'm probably in a minority). The
> problem with Markdown is that the simple things are easy, but everything
> else gets messy. I'm looking forward to see how you kram (pun intended)
> the V3 features into your tool…

Do I have to?

If an author wants to use a V3 feature that does not lend itself to authoring in markdown, they can always put the XML tags right into their markdown source.

>>>> but that was the way things were done in 2010.
>>>
>>> I’m prepared to stick with that, unless there is something better about the alternatives.
>>
>> Right, for a minor update, digging out the v1 tools and finding a platform where they can still run may actually be the best way to proceed.
>
> All you need is a TCL processor. Works fine over here on a newly
> installed notebook with Windows 10 and Cygwin.

Haven’t tried that in a while… 
Works for me, too (macOS 10.13.6, on a small document, with the usual formatting differences from v2…). 
Good to know.
(Although I have heard people have had problems on other platforms recently..)

Grüße, Carsten



Internet Engineering Task Force (IETF)                   S. Shepler, Ed.
Request for Comments: 5661                               Storspeed, Inc.
Category: Standards Track                                 M. Eisler, Ed.
ISSN: 2070-1721                                           D. Noveck, Ed.
                                                                  NetApp
                                                            January 2010


      Network File System (NFS) Version 4 Minor Version 1 Protocol

Abstract

   This document describes the Network File System (NFS) version 4 minor
   version 1, including features retained from the base protocol (NFS
   version 4 minor version 0, which is specified in RFC 3530) and
   protocol extensions made subsequently.  Major extensions introduced
   in NFS version 4 minor version 1 include Sessions, Directory
   Delegations, and parallel NFS (pNFS).  NFS version 4 minor version 1
   has no dependencies on NFS version 4 minor version 0, and it is
   considered a separate protocol.  Thus, this document neither updates
   nor obsoletes RFC 3530.  NFS minor version 1 is deemed superior to
   NFS minor version 0 with no loss of functionality, and its use is
   preferred over version 0.  Both NFS minor versions 0 and 1 can be
   used simultaneously on the same network, between the same client and
   server.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5661.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   8
     1.1.   The NFS Version 4 Minor Version 1 Protocol . . . . . . .   8
     1.2.   Requirements Language  . . . . . . . . . . . . . . . . .   8
     1.3.   Scope of This Document . . . . . . . . . . . . . . . . .   8
     1.4.   NFSv4 Goals  . . . . . . . . . . . . . . . . . . . . . .   8
     1.5.   NFSv4.1 Goals  . . . . . . . . . . . . . . . . . . . . .   9
     1.6.   General Definitions  . . . . . . . . . . . . . . . . . .  10
     1.7.   Overview of NFSv4.1 Features . . . . . . . . . . . . . .  12
     1.8.   Differences from NFSv4.0 . . . . . . . . . . . . . . . .  16
   2.  Core Infrastructure . . . . . . . . . . . . . . . . . . . . .  17
     2.1.   Introduction . . . . . . . . . . . . . . . . . . . . . .  17
     2.2.   RPC and XDR  . . . . . . . . . . . . . . . . . . . . . .  17
     2.3.   COMPOUND and CB_COMPOUND . . . . . . . . . . . . . . . .  20
     2.4.   Client Identifiers and Client Owners . . . . . . . . . .  21
     2.5.   Server Owners  . . . . . . . . . . . . . . . . . . . . .  27
     2.6.   Security Service Negotiation . . . . . . . . . . . . . .  27
     2.7.   Minor Versioning . . . . . . . . . . . . . . . . . . . .  33
     2.8.   Non-RPC-Based Security Services  . . . . . . . . . . . .  35
     2.9.   Transport Layers . . . . . . . . . . . . . . . . . . . .  36
     2.10.  Session  . . . . . . . . . . . . . . . . . . . . . . . .  38
   3.  Protocol Constants and Data Types . . . . . . . . . . . . . .  84
     3.1.   Basic Constants  . . . . . . . . . . . . . . . . . . . .  84
     3.2.   Basic Data Types . . . . . . . . . . . . . . . . . . . .  85
     3.3.   Structured Data Types  . . . . . . . . . . . . . . . . .  87
   4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . . .  95
     4.1.   Obtaining the First Filehandle . . . . . . . . . . . . .  96
     4.2.   Filehandle Types . . . . . . . . . . . . . . . . . . . .  97
     4.3.   One Method of Constructing a Volatile Filehandle . . . .  99
     4.4.   Client Recovery from Filehandle Expiration . . . . . . . 100
   5.  File Attributes . . . . . . . . . . . . . . . . . . . . . . . 101
     5.1.   REQUIRED Attributes  . . . . . . . . . . . . . . . . . . 102
     5.2.   RECOMMENDED Attributes . . . . . . . . . . . . . . . . . 102
     5.3.   Named Attributes . . . . . . . . . . . . . . . . . . . . 103
     5.4.   Classification of Attributes . . . . . . . . . . . . . . 104
     5.5.   Set-Only and Get-Only Attributes . . . . . . . . . . . . 105
     5.6.   REQUIRED Attributes - List and Definition References . . 105
     5.7.   RECOMMENDED Attributes - List and Definition
            References . . . . . . . . . . . . . . . . . . . . . . . 106
     5.8.   Attribute Definitions  . . . . . . . . . . . . . . . . . 108



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     5.9.   Interpreting owner and owner_group . . . . . . . . . . . 117
     5.10.  Character Case Attributes  . . . . . . . . . . . . . . . 119
     5.11.  Directory Notification Attributes  . . . . . . . . . . . 119
     5.12.  pNFS Attribute Definitions . . . . . . . . . . . . . . . 119
     5.13.  Retention Attributes . . . . . . . . . . . . . . . . . . 121
   6.  Access Control Attributes . . . . . . . . . . . . . . . . . . 124
     6.1.   Goals  . . . . . . . . . . . . . . . . . . . . . . . . . 124
     6.2.   File Attributes Discussion . . . . . . . . . . . . . . . 125
     6.3.   Common Methods . . . . . . . . . . . . . . . . . . . . . 142
     6.4.   Requirements . . . . . . . . . . . . . . . . . . . . . . 144
   7.  Single-Server Namespace . . . . . . . . . . . . . . . . . . . 151
     7.1.   Server Exports . . . . . . . . . . . . . . . . . . . . . 151
     7.2.   Browsing Exports . . . . . . . . . . . . . . . . . . . . 151
     7.3.   Server Pseudo File System  . . . . . . . . . . . . . . . 152
     7.4.   Multiple Roots . . . . . . . . . . . . . . . . . . . . . 152
     7.5.   Filehandle Volatility  . . . . . . . . . . . . . . . . . 152
     7.6.   Exported Root  . . . . . . . . . . . . . . . . . . . . . 153
     7.7.   Mount Point Crossing . . . . . . . . . . . . . . . . . . 153
     7.8.   Security Policy and Namespace Presentation . . . . . . . 154
   8.  State Management  . . . . . . . . . . . . . . . . . . . . . . 155
     8.1.   Client and Session ID  . . . . . . . . . . . . . . . . . 155
     8.2.   Stateid Definition . . . . . . . . . . . . . . . . . . . 156
     8.3.   Lease Renewal  . . . . . . . . . . . . . . . . . . . . . 164
     8.4.   Crash Recovery . . . . . . . . . . . . . . . . . . . . . 167
     8.5.   Server Revocation of Locks . . . . . . . . . . . . . . . 178
     8.6.   Short and Long Leases  . . . . . . . . . . . . . . . . . 179
     8.7.   Clocks, Propagation Delay, and Calculating Lease
            Expiration . . . . . . . . . . . . . . . . . . . . . . . 179
     8.8.   Obsolete Locking Infrastructure from NFSv4.0 . . . . . . 180
   9.  File Locking and Share Reservations . . . . . . . . . . . . . 181
     9.1.   Opens and Byte-Range Locks . . . . . . . . . . . . . . . 181
     9.2.   Lock Ranges  . . . . . . . . . . . . . . . . . . . . . . 185
     9.3.   Upgrading and Downgrading Locks  . . . . . . . . . . . . 185
     9.4.   Stateid Seqid Values and Byte-Range Locks  . . . . . . . 186
     9.5.   Issues with Multiple Open-Owners . . . . . . . . . . . . 186
     9.6.   Blocking Locks . . . . . . . . . . . . . . . . . . . . . 187
     9.7.   Share Reservations . . . . . . . . . . . . . . . . . . . 188
     9.8.   OPEN/CLOSE Operations  . . . . . . . . . . . . . . . . . 189
     9.9.   Open Upgrade and Downgrade . . . . . . . . . . . . . . . 189
     9.10.  Parallel OPENs . . . . . . . . . . . . . . . . . . . . . 190
     9.11.  Reclaim of Open and Byte-Range Locks . . . . . . . . . . 191
   10. Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 191
     10.1.  Performance Challenges for Client-Side Caching . . . . . 192
     10.2.  Delegation and Callbacks . . . . . . . . . . . . . . . . 193
     10.3.  Data Caching . . . . . . . . . . . . . . . . . . . . . . 197
     10.4.  Open Delegation  . . . . . . . . . . . . . . . . . . . . 202
     10.5.  Data Caching and Revocation  . . . . . . . . . . . . . . 213
     10.6.  Attribute Caching  . . . . . . . . . . . . . . . . . . . 215



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     10.7.  Data and Metadata Caching and Memory Mapped Files  . . . 217
     10.8.  Name and Directory Caching without Directory
            Delegations  . . . . . . . . . . . . . . . . . . . . . . 219
     10.9.  Directory Delegations  . . . . . . . . . . . . . . . . . 221
   11. Multi-Server Namespace  . . . . . . . . . . . . . . . . . . . 225
     11.1.  Location Attributes  . . . . . . . . . . . . . . . . . . 225
     11.2.  File System Presence or Absence  . . . . . . . . . . . . 225
     11.3.  Getting Attributes for an Absent File System . . . . . . 227
     11.4.  Uses of Location Information . . . . . . . . . . . . . . 229
     11.5.  Location Entries and Server Identity . . . . . . . . . . 233
     11.6.  Additional Client-Side Considerations  . . . . . . . . . 233
     11.7.  Effecting File System Transitions  . . . . . . . . . . . 234
     11.8.  Effecting File System Referrals  . . . . . . . . . . . . 248
     11.9.  The Attribute fs_locations . . . . . . . . . . . . . . . 254
     11.10. The Attribute fs_locations_info  . . . . . . . . . . . . 257
     11.11. The Attribute fs_status  . . . . . . . . . . . . . . . . 269
   12. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 273
     12.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . 273
     12.2.  pNFS Definitions . . . . . . . . . . . . . . . . . . . . 274
     12.3.  pNFS Operations  . . . . . . . . . . . . . . . . . . . . 280
     12.4.  pNFS Attributes  . . . . . . . . . . . . . . . . . . . . 281
     12.5.  Layout Semantics . . . . . . . . . . . . . . . . . . . . 281
     12.6.  pNFS Mechanics . . . . . . . . . . . . . . . . . . . . . 296
     12.7.  Recovery . . . . . . . . . . . . . . . . . . . . . . . . 298
     12.8.  Metadata and Storage Device Roles  . . . . . . . . . . . 303
     12.9.  Security Considerations for pNFS . . . . . . . . . . . . 303
   13. NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type . 304
     13.1.  Client ID and Session Considerations . . . . . . . . . . 305
     13.2.  File Layout Definitions  . . . . . . . . . . . . . . . . 307
     13.3.  File Layout Data Types . . . . . . . . . . . . . . . . . 308
     13.4.  Interpreting the File Layout . . . . . . . . . . . . . . 312
     13.5.  Data Server Multipathing . . . . . . . . . . . . . . . . 319
     13.6.  Operations Sent to NFSv4.1 Data Servers  . . . . . . . . 320
     13.7.  COMMIT through Metadata Server . . . . . . . . . . . . . 322
     13.8.  The Layout Iomode  . . . . . . . . . . . . . . . . . . . 324
     13.9.  Metadata and Data Server State Coordination  . . . . . . 324
     13.10. Data Server Component File Size  . . . . . . . . . . . . 327
     13.11. Layout Revocation and Fencing  . . . . . . . . . . . . . 328
     13.12. Security Considerations for the File Layout Type . . . . 329
   14. Internationalization  . . . . . . . . . . . . . . . . . . . . 330
     14.1.  Stringprep Profile for the utf8str_cs Type . . . . . . . 331
     14.2.  Stringprep Profile for the utf8str_cis Type  . . . . . . 332
     14.3.  Stringprep Profile for the utf8str_mixed Type  . . . . . 333
     14.4.  UTF-8 Capabilities . . . . . . . . . . . . . . . . . . . 335
     14.5.  UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 335
   15. Error Values  . . . . . . . . . . . . . . . . . . . . . . . . 336
     15.1.  Error Definitions  . . . . . . . . . . . . . . . . . . . 336
     15.2.  Operations and Their Valid Errors  . . . . . . . . . . . 355



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     15.3.  Callback Operations and Their Valid Errors . . . . . . . 372
     15.4.  Errors and the Operations That Use Them  . . . . . . . . 375
   16. NFSv4.1 Procedures  . . . . . . . . . . . . . . . . . . . . . 391
     16.1.  Procedure 0: NULL - No Operation . . . . . . . . . . . . 391
     16.2.  Procedure 1: COMPOUND - Compound Operations  . . . . . . 392
   17. Operations: REQUIRED, RECOMMENDED, or OPTIONAL  . . . . . . . 403
   18. NFSv4.1 Operations  . . . . . . . . . . . . . . . . . . . . . 406
     18.1.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 406
     18.2.  Operation 4: CLOSE - Close File  . . . . . . . . . . . . 412
     18.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 413
     18.4.  Operation 6: CREATE - Create a Non-Regular File Object . 416
     18.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . . . . . . . . . . . . 419
     18.6.  Operation 8: DELEGRETURN - Return Delegation . . . . . . 420
     18.7.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 420
     18.8.  Operation 10: GETFH - Get Current Filehandle . . . . . . 422
     18.9.  Operation 11: LINK - Create Link to a File . . . . . . . 423
     18.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 426
     18.11. Operation 13: LOCKT - Test for Lock  . . . . . . . . . . 431
     18.12. Operation 14: LOCKU - Unlock File  . . . . . . . . . . . 432
     18.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 434
     18.14. Operation 16: LOOKUPP - Lookup Parent Directory  . . . . 435
     18.15. Operation 17: NVERIFY - Verify Difference in
            Attributes . . . . . . . . . . . . . . . . . . . . . . . 437
     18.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 438
     18.17. Operation 19: OPENATTR - Open Named Attribute
            Directory  . . . . . . . . . . . . . . . . . . . . . . . 457
     18.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 459
     18.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 460
     18.20. Operation 23: PUTPUBFH - Set Public Filehandle . . . . . 461
     18.21. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 463
     18.22. Operation 25: READ - Read from File  . . . . . . . . . . 463
     18.23. Operation 26: READDIR - Read Directory . . . . . . . . . 466
     18.24. Operation 27: READLINK - Read Symbolic Link  . . . . . . 469
     18.25. Operation 28: REMOVE - Remove File System Object . . . . 470
     18.26. Operation 29: RENAME - Rename Directory Entry  . . . . . 473
     18.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 476
     18.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 477
     18.29. Operation 33: SECINFO - Obtain Available Security  . . . 478
     18.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 482
     18.31. Operation 37: VERIFY - Verify Same Attributes  . . . . . 485
     18.32. Operation 38: WRITE - Write to File  . . . . . . . . . . 486
     18.33. Operation 40: BACKCHANNEL_CTL - Backchannel Control  . . 491
     18.34. Operation 41: BIND_CONN_TO_SESSION - Associate
            Connection with Session  . . . . . . . . . . . . . . . . 492
     18.35. Operation 42: EXCHANGE_ID - Instantiate Client ID  . . . 495
     18.36. Operation 43: CREATE_SESSION - Create New Session and
            Confirm Client ID  . . . . . . . . . . . . . . . . . . . 513



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     18.37. Operation 44: DESTROY_SESSION - Destroy a Session  . . . 523
     18.38. Operation 45: FREE_STATEID - Free Stateid with No
            Locks  . . . . . . . . . . . . . . . . . . . . . . . . . 525
     18.39. Operation 46: GET_DIR_DELEGATION - Get a Directory
            Delegation . . . . . . . . . . . . . . . . . . . . . . . 526
     18.40. Operation 47: GETDEVICEINFO - Get Device Information . . 530
     18.41. Operation 48: GETDEVICELIST - Get All Device Mappings
            for a File System  . . . . . . . . . . . . . . . . . . . 533
     18.42. Operation 49: LAYOUTCOMMIT - Commit Writes Made Using
            a Layout . . . . . . . . . . . . . . . . . . . . . . . . 534
     18.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 538
     18.44. Operation 51: LAYOUTRETURN - Release Layout
            Information  . . . . . . . . . . . . . . . . . . . . . . 548
     18.45. Operation 52: SECINFO_NO_NAME - Get Security on
            Unnamed Object . . . . . . . . . . . . . . . . . . . . . 553
     18.46. Operation 53: SEQUENCE - Supply Per-Procedure
            Sequencing and Control . . . . . . . . . . . . . . . . . 554
     18.47. Operation 54: SET_SSV - Update SSV for a Client ID . . . 560
     18.48. Operation 55: TEST_STATEID - Test Stateids for
            Validity . . . . . . . . . . . . . . . . . . . . . . . . 562
     18.49. Operation 56: WANT_DELEGATION - Request Delegation . . . 564
     18.50. Operation 57: DESTROY_CLIENTID - Destroy a Client ID . . 568
     18.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims
            Finished . . . . . . . . . . . . . . . . . . . . . . . . 568
     18.52. Operation 10044: ILLEGAL - Illegal Operation . . . . . . 571
   19. NFSv4.1 Callback Procedures . . . . . . . . . . . . . . . . . 571
     19.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 572
     19.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 572
   20. NFSv4.1 Callback Operations . . . . . . . . . . . . . . . . . 576
     20.1.  Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 576
     20.2.  Operation 4: CB_RECALL - Recall a Delegation . . . . . . 577
     20.3.  Operation 5: CB_LAYOUTRECALL - Recall Layout from
            Client . . . . . . . . . . . . . . . . . . . . . . . . . 578
     20.4.  Operation 6: CB_NOTIFY - Notify Client of Directory
            Changes  . . . . . . . . . . . . . . . . . . . . . . . . 582
     20.5.  Operation 7: CB_PUSH_DELEG - Offer Previously
            Requested Delegation to Client . . . . . . . . . . . . . 586
     20.6.  Operation 8: CB_RECALL_ANY - Keep Any N Recallable
            Objects  . . . . . . . . . . . . . . . . . . . . . . . . 587
     20.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal
            Resources for Recallable Objects . . . . . . . . . . . . 590
     20.8.  Operation 10: CB_RECALL_SLOT - Change Flow Control
            Limits . . . . . . . . . . . . . . . . . . . . . . . . . 591
     20.9.  Operation 11: CB_SEQUENCE - Supply Backchannel
            Sequencing and Control . . . . . . . . . . . . . . . . . 592
     20.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending
            Delegation Wants . . . . . . . . . . . . . . . . . . . . 594
     20.11. Operation 13: CB_NOTIFY_LOCK - Notify Client of



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            Possible Lock Availability . . . . . . . . . . . . . . . 595
     20.12. Operation 14: CB_NOTIFY_DEVICEID - Notify Client of
            Device ID Changes  . . . . . . . . . . . . . . . . . . . 597
     20.13. Operation 10044: CB_ILLEGAL - Illegal Callback
            Operation  . . . . . . . . . . . . . . . . . . . . . . . 599
   21. Security Considerations . . . . . . . . . . . . . . . . . . . 599
   22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 601
     22.1.  Named Attribute Definitions  . . . . . . . . . . . . . . 601
     22.2.  Device ID Notifications  . . . . . . . . . . . . . . . . 602
     22.3.  Object Recall Types  . . . . . . . . . . . . . . . . . . 604
     22.4.  Layout Types . . . . . . . . . . . . . . . . . . . . . . 605
     22.5.  Path Variable Definitions  . . . . . . . . . . . . . . . 608
   23. References  . . . . . . . . . . . . . . . . . . . . . . . . . 612
     23.1.  Normative References . . . . . . . . . . . . . . . . . . 612
     23.2.  Informative References . . . . . . . . . . . . . . . . . 614
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . 616



































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1.  Introduction

1.1.  The NFS Version 4 Minor Version 1 Protocol

   The NFS version 4 minor version 1 (NFSv4.1) protocol is the second
   minor version of the NFS version 4 (NFSv4) protocol.  The first minor
   version, NFSv4.0, is described in [30].  It generally follows the
   guidelines for minor versioning that are listed in Section 10 of RFC
   3530.  However, it diverges from guidelines 11 ("a client and server
   that support minor version X must support minor versions 0 through
   X-1") and 12 ("no new features may be introduced as mandatory in a
   minor version").  These divergences are due to the introduction of
   the sessions model for managing non-idempotent operations and the
   RECLAIM_COMPLETE operation.  These two new features are
   infrastructural in nature and simplify implementation of existing and
   other new features.  Making them anything but REQUIRED would add
   undue complexity to protocol definition and implementation.  NFSv4.1
   accordingly updates the minor versioning guidelines (Section 2.7).

   As a minor version, NFSv4.1 is consistent with the overall goals for
   NFSv4, but extends the protocol so as to better meet those goals,
   based on experiences with NFSv4.0.  In addition, NFSv4.1 has adopted
   some additional goals, which motivate some of the major extensions in
   NFSv4.1.

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

1.3.  Scope of This Document

   This document describes the NFSv4.1 protocol.  With respect to
   NFSv4.0, this document does not:

   o  describe the NFSv4.0 protocol, except where needed to contrast
      with NFSv4.1.

   o  modify the specification of the NFSv4.0 protocol.

   o  clarify the NFSv4.0 protocol.

1.4.  NFSv4 Goals

   The NFSv4 protocol is a further revision of the NFS protocol defined
   already by NFSv3 [31].  It retains the essential characteristics of
   previous versions: easy recovery; independence of transport



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   protocols, operating systems, and file systems; simplicity; and good
   performance.  NFSv4 has the following goals:

   o  Improved access and good performance on the Internet

      The protocol is designed to transit firewalls easily, perform well
      where latency is high and bandwidth is low, and scale to very
      large numbers of clients per server.

   o  Strong security with negotiation built into the protocol

      The protocol builds on the work of the ONCRPC working group in
      supporting the RPCSEC_GSS protocol.  Additionally, the NFSv4.1
      protocol provides a mechanism to allow clients and servers the
      ability to negotiate security and require clients and servers to
      support a minimal set of security schemes.

   o  Good cross-platform interoperability

      The protocol features a file system model that provides a useful,
      common set of features that does not unduly favor one file system
      or operating system over another.

   o  Designed for protocol extensions

      The protocol is designed to accept standard extensions within a
      framework that enables and encourages backward compatibility.

1.5.  NFSv4.1 Goals

   NFSv4.1 has the following goals, within the framework established by
   the overall NFSv4 goals.

   o  To correct significant structural weaknesses and oversights
      discovered in the base protocol.

   o  To add clarity and specificity to areas left unaddressed or not
      addressed in sufficient detail in the base protocol.  However, as
      stated in Section 1.3, it is not a goal to clarify the NFSv4.0
      protocol in the NFSv4.1 specification.

   o  To add specific features based on experience with the existing
      protocol and recent industry developments.

   o  To provide protocol support to take advantage of clustered server
      deployments including the ability to provide scalable parallel
      access to files distributed among multiple servers.




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1.6.  General Definitions

   The following definitions provide an appropriate context for the
   reader.

   Byte:  In this document, a byte is an octet, i.e., a datum exactly 8
      bits in length.

   Client:  The client is the entity that accesses the NFS server's
      resources.  The client may be an application that contains the
      logic to access the NFS server directly.  The client may also be
      the traditional operating system client that provides remote file
      system services for a set of applications.

      A client is uniquely identified by a client owner.

      With reference to byte-range locking, the client is also the
      entity that maintains a set of locks on behalf of one or more
      applications.  This client is responsible for crash or failure
      recovery for those locks it manages.

      Note that multiple clients may share the same transport and
      connection and multiple clients may exist on the same network
      node.

   Client ID:  The client ID is a 64-bit quantity used as a unique,
      short-hand reference to a client-supplied verifier and client
      owner.  The server is responsible for supplying the client ID.

   Client Owner:  The client owner is a unique string, opaque to the
      server, that identifies a client.  Multiple network connections
      and source network addresses originating from those connections
      may share a client owner.  The server is expected to treat
      requests from connections with the same client owner as coming
      from the same client.

   File System:  The file system is the collection of objects on a
      server (as identified by the major identifier of a server owner,
      which is defined later in this section) that share the same fsid
      attribute (see Section 5.8.1.9).

   Lease:  A lease is an interval of time defined by the server for
      which the client is irrevocably granted locks.  At the end of a
      lease period, locks may be revoked if the lease has not been
      extended.  A lock must be revoked if a conflicting lock has been
      granted after the lease interval.

      A server grants a client a single lease for all state.



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   Lock:  The term "lock" is used to refer to byte-range (in UNIX
      environments, also known as record) locks, share reservations,
      delegations, or layouts unless specifically stated otherwise.

   Secret State Verifier (SSV):  The SSV is a unique secret key shared
      between a client and server.  The SSV serves as the secret key for
      an internal (that is, internal to NFSv4.1) Generic Security
      Services (GSS) mechanism (the SSV GSS mechanism; see
      Section 2.10.9).  The SSV GSS mechanism uses the SSV to compute
      message integrity code (MIC) and Wrap tokens.  See
      Section 2.10.8.3 for more details on how NFSv4.1 uses the SSV and
      the SSV GSS mechanism.

   Server:  The Server is the entity responsible for coordinating client
      access to a set of file systems and is identified by a server
      owner.  A server can span multiple network addresses.

   Server Owner:  The server owner identifies the server to the client.
      The server owner consists of a major identifier and a minor
      identifier.  When the client has two connections each to a peer
      with the same major identifier, the client assumes that both peers
      are the same server (the server namespace is the same via each
      connection) and that lock state is sharable across both
      connections.  When each peer has both the same major and minor
      identifiers, the client assumes that each connection might be
      associable with the same session.

   Stable Storage:  Stable storage is storage from which data stored by
      an NFSv4.1 server can be recovered without data loss from multiple
      power failures (including cascading power failures, that is,
      several power failures in quick succession), operating system
      failures, and/or hardware failure of components other than the
      storage medium itself (such as disk, nonvolatile RAM, flash
      memory, etc.).

      Some examples of stable storage that are allowable for an NFS
      server include:

      1.  Media commit of data; that is, the modified data has been
          successfully written to the disk media, for example, the disk
          platter.

      2.  An immediate reply disk drive with battery-backed, on-drive
          intermediate storage or uninterruptible power system (UPS).

      3.  Server commit of data with battery-backed intermediate storage
          and recovery software.




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      4.  Cache commit with uninterruptible power system (UPS) and
          recovery software.

   Stateid:  A stateid is a 128-bit quantity returned by a server that
      uniquely defines the open and locking states provided by the
      server for a specific open-owner or lock-owner/open-owner pair for
      a specific file and type of lock.

   Verifier:  A verifier is a 64-bit quantity generated by the client
      that the server can use to determine if the client has restarted
      and lost all previous lock state.

1.7.  Overview of NFSv4.1 Features

   The major features of the NFSv4.1 protocol will be reviewed in brief.
   This will be done to provide an appropriate context for both the
   reader who is familiar with the previous versions of the NFS protocol
   and the reader who is new to the NFS protocols.  For the reader new
   to the NFS protocols, there is still a set of fundamental knowledge
   that is expected.  The reader should be familiar with the External
   Data Representation (XDR) and Remote Procedure Call (RPC) protocols
   as described in [2] and [3].  A basic knowledge of file systems and
   distributed file systems is expected as well.

   In general, this specification of NFSv4.1 will not distinguish those
   features added in minor version 1 from those present in the base
   protocol but will treat NFSv4.1 as a unified whole.  See Section 1.8
   for a summary of the differences between NFSv4.0 and NFSv4.1.

1.7.1.  RPC and Security

   As with previous versions of NFS, the External Data Representation
   (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFSv4.1
   protocol are those defined in [2] and [3].  To meet end-to-end
   security requirements, the RPCSEC_GSS framework [4] is used to extend
   the basic RPC security.  With the use of RPCSEC_GSS, various
   mechanisms can be provided to offer authentication, integrity, and
   privacy to the NFSv4 protocol.  Kerberos V5 is used as described in
   [5] to provide one security framework.  With the use of RPCSEC_GSS,
   other mechanisms may also be specified and used for NFSv4.1 security.

   To enable in-band security negotiation, the NFSv4.1 protocol has
   operations that provide the client a method of querying the server
   about its policies regarding which security mechanisms must be used
   for access to the server's file system resources.  With this, the
   client can securely match the security mechanism that meets the
   policies specified at both the client and server.




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   NFSv4.1 introduces parallel access (see Section 1.7.2.2), which is
   called pNFS.  The security framework described in this section is
   significantly modified by the introduction of pNFS (see
   Section 12.9), because data access is sometimes not over RPC.  The
   level of significance varies with the storage protocol (see
   Section 12.2.5) and can be as low as zero impact (see Section 13.12).

1.7.2.  Protocol Structure

1.7.2.1.  Core Protocol

   Unlike NFSv3, which used a series of ancillary protocols (e.g., NLM,
   NSM (Network Status Monitor), MOUNT), within all minor versions of
   NFSv4 a single RPC protocol is used to make requests to the server.
   Facilities that had been separate protocols, such as locking, are now
   integrated within a single unified protocol.

1.7.2.2.  Parallel Access

   Minor version 1 supports high-performance data access to a clustered
   server implementation by enabling a separation of metadata access and
   data access, with the latter done to multiple servers in parallel.

   Such parallel data access is controlled by recallable objects known
   as "layouts", which are integrated into the protocol locking model.
   Clients direct requests for data access to a set of data servers
   specified by the layout via a data storage protocol which may be
   NFSv4.1 or may be another protocol.

   Because the protocols used for parallel data access are not
   necessarily RPC-based, the RPC-based security model (Section 1.7.1)
   is obviously impacted (see Section 12.9).  The degree of impact
   varies with the storage protocol (see Section 12.2.5) used for data
   access, and can be as low as zero (see Section 13.12).

1.7.3.  File System Model

   The general file system model used for the NFSv4.1 protocol is the
   same as previous versions.  The server file system is hierarchical
   with the regular files contained within being treated as opaque byte
   streams.  In a slight departure, file and directory names are encoded
   with UTF-8 to deal with the basics of internationalization.

   The NFSv4.1 protocol does not require a separate protocol to provide
   for the initial mapping between path name and filehandle.  All file
   systems exported by a server are presented as a tree so that all file
   systems are reachable from a special per-server global root
   filehandle.  This allows LOOKUP operations to be used to perform



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   functions previously provided by the MOUNT protocol.  The server
   provides any necessary pseudo file systems to bridge any gaps that
   arise due to unexported gaps between exported file systems.

1.7.3.1.  Filehandles

   As in previous versions of the NFS protocol, opaque filehandles are
   used to identify individual files and directories.  Lookup-type and
   create operations translate file and directory names to filehandles,
   which are then used to identify objects in subsequent operations.

   The NFSv4.1 protocol provides support for persistent filehandles,
   guaranteed to be valid for the lifetime of the file system object
   designated.  In addition, it provides support to servers to provide
   filehandles with more limited validity guarantees, called volatile
   filehandles.

1.7.3.2.  File Attributes

   The NFSv4.1 protocol has a rich and extensible file object attribute
   structure, which is divided into REQUIRED, RECOMMENDED, and named
   attributes (see Section 5).

   Several (but not all) of the REQUIRED attributes are derived from the
   attributes of NFSv3 (see the definition of the fattr3 data type in
   [31]).  An example of a REQUIRED attribute is the file object's type
   (Section 5.8.1.2) so that regular files can be distinguished from
   directories (also known as folders in some operating environments)
   and other types of objects.  REQUIRED attributes are discussed in
   Section 5.1.

   An example of three RECOMMENDED attributes are acl, sacl, and dacl.
   These attributes define an Access Control List (ACL) on a file object
   (Section 6).  An ACL provides directory and file access control
   beyond the model used in NFSv3.  The ACL definition allows for
   specification of specific sets of permissions for individual users
   and groups.  In addition, ACL inheritance allows propagation of
   access permissions and restrictions down a directory tree as file
   system objects are created.  RECOMMENDED attributes are discussed in
   Section 5.2.

   A named attribute is an opaque byte stream that is associated with a
   directory or file and referred to by a string name.  Named attributes
   are meant to be used by client applications as a method to associate
   application-specific data with a regular file or directory.  NFSv4.1
   modifies named attributes relative to NFSv4.0 by tightening the
   allowed operations in order to prevent the development of non-
   interoperable implementations.  Named attributes are discussed in



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   Section 5.3.

1.7.3.3.  Multi-Server Namespace

   NFSv4.1 contains a number of features to allow implementation of
   namespaces that cross server boundaries and that allow and facilitate
   a non-disruptive transfer of support for individual file systems
   between servers.  They are all based upon attributes that allow one
   file system to specify alternate or new locations for that file
   system.

   These attributes may be used together with the concept of absent file
   systems, which provide specifications for additional locations but no
   actual file system content.  This allows a number of important
   facilities:

   o  Location attributes may be used with absent file systems to
      implement referrals whereby one server may direct the client to a
      file system provided by another server.  This allows extensive
      multi-server namespaces to be constructed.

   o  Location attributes may be provided for present file systems to
      provide the locations of alternate file system instances or
      replicas to be used in the event that the current file system
      instance becomes unavailable.

   o  Location attributes may be provided when a previously present file
      system becomes absent.  This allows non-disruptive migration of
      file systems to alternate servers.

1.7.4.  Locking Facilities

   As mentioned previously, NFSv4.1 is a single protocol that includes
   locking facilities.  These locking facilities include support for
   many types of locks including a number of sorts of recallable locks.
   Recallable locks such as delegations allow the client to be assured
   that certain events will not occur so long as that lock is held.
   When circumstances change, the lock is recalled via a callback
   request.  The assurances provided by delegations allow more extensive
   caching to be done safely when circumstances allow it.

   The types of locks are:

   o  Share reservations as established by OPEN operations.

   o  Byte-range locks.





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   o  File delegations, which are recallable locks that assure the
      holder that inconsistent opens and file changes cannot occur so
      long as the delegation is held.

   o  Directory delegations, which are recallable locks that assure the
      holder that inconsistent directory modifications cannot occur so
      long as the delegation is held.

   o  Layouts, which are recallable objects that assure the holder that
      direct access to the file data may be performed directly by the
      client and that no change to the data's location that is
      inconsistent with that access may be made so long as the layout is
      held.

   All locks for a given client are tied together under a single client-
   wide lease.  All requests made on sessions associated with the client
   renew that lease.  When the client's lease is not promptly renewed,
   the client's locks are subject to revocation.  In the event of server
   restart, clients have the opportunity to safely reclaim their locks
   within a special grace period.

1.8.  Differences from NFSv4.0

   The following summarizes the major differences between minor version
   1 and the base protocol:

   o  Implementation of the sessions model (Section 2.10).

   o  Parallel access to data (Section 12).

   o  Addition of the RECLAIM_COMPLETE operation to better structure the
      lock reclamation process (Section 18.51).

   o  Enhanced delegation support as follows.

      *  Delegations on directories and other file types in addition to
         regular files (Section 18.39, Section 18.49).

      *  Operations to optimize acquisition of recalled or denied
         delegations (Section 18.49, Section 20.5, Section 20.7).

      *  Notifications of changes to files and directories
         (Section 18.39, Section 20.4).

      *  A method to allow a server to indicate that it is recalling one
         or more delegations for resource management reasons, and thus a
         method to allow the client to pick which delegations to return
         (Section 20.6).



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   o  Attributes can be set atomically during exclusive file create via
      the OPEN operation (see the new EXCLUSIVE4_1 creation method in
      Section 18.16).

   o  Open files can be preserved if removed and the hard link count
      ("hard link" is defined in an Open Group [6] standard) goes to
      zero, thus obviating the need for clients to rename deleted files
      to partially hidden names -- colloquially called "silly rename"
      (see the new OPEN4_RESULT_PRESERVE_UNLINKED reply flag in
      Section 18.16).

   o  Improved compatibility with Microsoft Windows for Access Control
      Lists (Section 6.2.3, Section 6.2.2, Section 6.4.3.2).

   o  Data retention (Section 5.13).

   o  Identification of the implementation of the NFS client and server
      (Section 18.35).

   o  Support for notification of the availability of byte-range locks
      (see the new OPEN4_RESULT_MAY_NOTIFY_LOCK reply flag in
      Section 18.16 and see Section 20.11).

   o  In NFSv4.1, LIPKEY and SPKM-3 are not required security mechanisms
      [32].

2.  Core Infrastructure

2.1.  Introduction

   NFSv4.1 relies on core infrastructure common to nearly every
   operation.  This core infrastructure is described in the remainder of
   this section.

2.2.  RPC and XDR

   The NFSv4.1 protocol is a Remote Procedure Call (RPC) application
   that uses RPC version 2 and the corresponding eXternal Data
   Representation (XDR) as defined in [3] and [2].

2.2.1.  RPC-Based Security

   Previous NFS versions have been thought of as having a host-based
   authentication model, where the NFS server authenticates the NFS
   client, and trusts the client to authenticate all users.  Actually,
   NFS has always depended on RPC for authentication.  One of the first
   forms of RPC authentication, AUTH_SYS, had no strong authentication
   and required a host-based authentication approach.  NFSv4.1 also



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   depends on RPC for basic security services and mandates RPC support
   for a user-based authentication model.  The user-based authentication
   model has user principals authenticated by a server, and in turn the
   server authenticated by user principals.  RPC provides some basic
   security services that are used by NFSv4.1.

2.2.1.1.  RPC Security Flavors

   As described in Section 7.2 ("Authentication") of [3], RPC security
   is encapsulated in the RPC header, via a security or authentication
   flavor, and information specific to the specified security flavor.
   Every RPC header conveys information used to identify and
   authenticate a client and server.  As discussed in Section 2.2.1.1.1,
   some security flavors provide additional security services.

   NFSv4.1 clients and servers MUST implement RPCSEC_GSS.  (This
   requirement to implement is not a requirement to use.)  Other
   flavors, such as AUTH_NONE and AUTH_SYS, MAY be implemented as well.

2.2.1.1.1.  RPCSEC_GSS and Security Services

   RPCSEC_GSS [4] uses the functionality of GSS-API [7].  This allows
   for the use of various security mechanisms by the RPC layer without
   the additional implementation overhead of adding RPC security
   flavors.

2.2.1.1.1.1.  Identification, Authentication, Integrity, Privacy

   Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
   users on clients to servers, and servers to users.  It can also
   perform integrity checking on the entire RPC message, including the
   RPC header, and on the arguments or results.  Finally, privacy,
   usually via encryption, is a service available with RPCSEC_GSS.
   Privacy is performed on the arguments and results.  Note that if
   privacy is selected, integrity, authentication, and identification
   are enabled.  If privacy is not selected, but integrity is selected,
   authentication and identification are enabled.  If integrity and
   privacy are not selected, but authentication is enabled,
   identification is enabled.  RPCSEC_GSS does not provide
   identification as a separate service.

   Although GSS-API has an authentication service distinct from its
   privacy and integrity services, GSS-API's authentication service is
   not used for RPCSEC_GSS's authentication service.  Instead, each RPC
   request and response header is integrity protected with the GSS-API
   integrity service, and this allows RPCSEC_GSS to offer per-RPC
   authentication and identity.  See [4] for more information.




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   NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and
   authentication service.  NFSv4.1 servers MUST support RPCSEC_GSS's
   privacy service.  NFSv4.1 clients SHOULD support RPCSEC_GSS's privacy
   service.

2.2.1.1.1.2.  Security Mechanisms for NFSv4.1

   RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide
   security services.  Therefore, NFSv4.1 clients and servers MUST
   support the Kerberos V5 security mechanism.

   The use of RPCSEC_GSS requires selection of mechanism, quality of
   protection (QOP), and service (authentication, integrity, privacy).
   For the mandated security mechanisms, NFSv4.1 specifies that a QOP of
   zero is used, leaving it up to the mechanism or the mechanism's
   configuration to map QOP zero to an appropriate level of protection.
   Each mandated mechanism specifies a minimum set of cryptographic
   algorithms for implementing integrity and privacy.  NFSv4.1 clients
   and servers MUST be implemented on operating environments that comply
   with the REQUIRED cryptographic algorithms of each REQUIRED
   mechanism.

2.2.1.1.1.2.1.  Kerberos V5

   The Kerberos V5 GSS-API mechanism as described in [5] MUST be
   implemented with the RPCSEC_GSS services as specified in the
   following table:


      column descriptions:
      1 == number of pseudo flavor
      2 == name of pseudo flavor
      3 == mechanism's OID
      4 == RPCSEC_GSS service
      5 == NFSv4.1 clients MUST support
      6 == NFSv4.1 servers MUST support

      1      2        3                    4                     5   6
      ------------------------------------------------------------------
      390003 krb5     1.2.840.113554.1.2.2 rpc_gss_svc_none      yes yes
      390004 krb5i    1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
      390005 krb5p    1.2.840.113554.1.2.2 rpc_gss_svc_privacy    no yes

   Note that the number and name of the pseudo flavor are presented here
   as a mapping aid to the implementor.  Because the NFSv4.1 protocol
   includes a method to negotiate security and it understands the GSS-
   API mechanism, the pseudo flavor is not needed.  The pseudo flavor is
   needed for the NFSv3 since the security negotiation is done via the



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   MOUNT protocol as described in [33].

   At the time NFSv4.1 was specified, the Advanced Encryption Standard
   (AES) with HMAC-SHA1 was a REQUIRED algorithm set for Kerberos V5.
   In contrast, when NFSv4.0 was specified, weaker algorithm sets were
   REQUIRED for Kerberos V5, and were REQUIRED in the NFSv4.0
   specification, because the Kerberos V5 specification at the time did
   not specify stronger algorithms.  The NFSv4.1 specification does not
   specify REQUIRED algorithms for Kerberos V5, and instead, the
   implementor is expected to track the evolution of the Kerberos V5
   standard if and when stronger algorithms are specified.

2.2.1.1.1.2.1.1.  Security Considerations for Cryptographic Algorithms
                  in Kerberos V5

   When deploying NFSv4.1, the strength of the security achieved depends
   on the existing Kerberos V5 infrastructure.  The algorithms of
   Kerberos V5 are not directly exposed to or selectable by the client
   or server, so there is some due diligence required by the user of
   NFSv4.1 to ensure that security is acceptable where needed.

2.2.1.1.1.3.  GSS Server Principal

   Regardless of what security mechanism under RPCSEC_GSS is being used,
   the NFS server MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
   names are of the form:

        service@hostname

   For NFS, the "service" element is

        nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms.  For Kerberos V5, the following form is
   RECOMMENDED:

        nfs/hostname

2.3.  COMPOUND and CB_COMPOUND

   A significant departure from the versions of the NFS protocol before
   NFSv4 is the introduction of the COMPOUND procedure.  For the NFSv4
   protocol, in all minor versions, there are exactly two RPC
   procedures, NULL and COMPOUND.  The COMPOUND procedure is defined as
   a series of individual operations and these operations perform the
   sorts of functions performed by traditional NFS procedures.



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   The operations combined within a COMPOUND request are evaluated in
   order by the server, without any atomicity guarantees.  A limited set
   of facilities exist to pass results from one operation to another.
   Once an operation returns a failing result, the evaluation ends and
   the results of all evaluated operations are returned to the client.

   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, multi-component look up requests can be
   constructed by combining multiple LOOKUP operations.  Those can be
   further combined with operations such as GETATTR, READDIR, or OPEN
   plus READ to do more complicated sets of operation without incurring
   additional latency.

   NFSv4.1 also contains a considerable set of callback operations in
   which the server makes an RPC directed at the client.  Callback RPCs
   have a similar structure to that of the normal server requests.  In
   all minor versions of the NFSv4 protocol, there are two callback RPC
   procedures: CB_NULL and CB_COMPOUND.  The CB_COMPOUND procedure is
   defined in an analogous fashion to that of COMPOUND with its own set
   of callback operations.

   The addition of new server and callback operations within the
   COMPOUND and CB_COMPOUND request framework provides a means of
   extending the protocol in subsequent minor versions.

   Except for a small number of operations needed for session creation,
   server requests and callback requests are performed within the
   context of a session.  Sessions provide a client context for every
   request and support robust reply protection for non-idempotent
   requests.

2.4.  Client Identifiers and Client Owners

   For each operation that obtains or depends on locking state, the
   specific client needs to be identifiable by the server.

   Each distinct client instance is represented by a client ID.  A
   client ID is a 64-bit identifier representing a specific client at a
   given time.  The client ID is changed whenever the client re-
   initializes, and may change when the server re-initializes.  Client
   IDs are used to support lock identification and crash recovery.

   During steady state operation, the client ID associated with each
   operation is derived from the session (see Section 2.10) on which the
   operation is sent.  A session is associated with a client ID when the
   session is created.



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   Unlike NFSv4.0, the only NFSv4.1 operations possible before a client
   ID is established are those needed to establish the client ID.

   A sequence of an EXCHANGE_ID operation followed by a CREATE_SESSION
   operation using that client ID (eir_clientid as returned from
   EXCHANGE_ID) is required to establish and confirm the client ID on
   the server.  Establishment of identification by a new incarnation of
   the client also has the effect of immediately releasing any locking
   state that a previous incarnation of that same client might have had
   on the server.  Such released state would include all byte-range
   lock, share reservation, layout state, and -- where the server
   supports neither the CLAIM_DELEGATE_PREV nor CLAIM_DELEG_CUR_FH claim
   types -- all delegation state associated with the same client with
   the same identity.  For discussion of delegation state recovery, see
   Section 10.2.1.  For discussion of layout state recovery, see
   Section 12.7.1.

   Releasing such state requires that the server be able to determine
   that one client instance is the successor of another.  Where this
   cannot be done, for any of a number of reasons, the locking state
   will remain for a time subject to lease expiration (see Section 8.3)
   and the new client will need to wait for such state to be removed, if
   it makes conflicting lock requests.

   Client identification is encapsulated in the following client owner
   data type:


   struct client_owner4 {
           verifier4       co_verifier;
           opaque          co_ownerid<NFS4_OPAQUE_LIMIT>;
   };

   The first field, co_verifier, is a client incarnation verifier.  The
   server will start the process of canceling the client's leased state
   if co_verifier is different than what the server has previously
   recorded for the identified client (as specified in the co_ownerid
   field).

   The second field, co_ownerid, is a variable length string that
   uniquely defines the client so that subsequent instances of the same
   client bear the same co_ownerid with a different verifier.

   There are several considerations for how the client generates the
   co_ownerid string:

   o  The string should be unique so that multiple clients do not
      present the same string.  The consequences of two clients



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      presenting the same string range from one client getting an error
      to one client having its leased state abruptly and unexpectedly
      cancelled.

   o  The string should be selected so that subsequent incarnations
      (e.g., restarts) of the same client cause the client to present
      the same string.  The implementor is cautioned from an approach
      that requires the string to be recorded in a local file because
      this precludes the use of the implementation in an environment
      where there is no local disk and all file access is from an
      NFSv4.1 server.

   o  The string should be the same for each server network address that
      the client accesses.  This way, if a server has multiple
      interfaces, the client can trunk traffic over multiple network
      paths as described in Section 2.10.5.  (Note: the precise opposite
      was advised in the NFSv4.0 specification [30].)

   o  The algorithm for generating the string should not assume that the
      client's network address will not change, unless the client
      implementation knows it is using statically assigned network
      addresses.  This includes changes between client incarnations and
      even changes while the client is still running in its current
      incarnation.  Thus, with dynamic address assignment, if the client
      includes just the client's network address in the co_ownerid
      string, there is a real risk that after the client gives up the
      network address, another client, using a similar algorithm for
      generating the co_ownerid string, would generate a conflicting
      co_ownerid string.

   Given the above considerations, an example of a well-generated
   co_ownerid string is one that includes:

   o  If applicable, the client's statically assigned network address.

   o  Additional information that tends to be unique, such as one or
      more of:

      *  The client machine's serial number (for privacy reasons, it is
         best to perform some one-way function on the serial number).

      *  A Media Access Control (MAC) address (again, a one-way function
         should be performed).

      *  The timestamp of when the NFSv4.1 software was first installed
         on the client (though this is subject to the previously
         mentioned caution about using information that is stored in a
         file, because the file might only be accessible over NFSv4.1).



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      *  A true random number.  However, since this number ought to be
         the same between client incarnations, this shares the same
         problem as that of using the timestamp of the software
         installation.

   o  For a user-level NFSv4.1 client, it should contain additional
      information to distinguish the client from other user-level
      clients running on the same host, such as a process identifier or
      other unique sequence.

   The client ID is assigned by the server (the eir_clientid result from
   EXCHANGE_ID) and should be chosen so that it will not conflict with a
   client ID previously assigned by the server.  This applies across
   server restarts.

   In the event of a server restart, a client may find out that its
   current client ID is no longer valid when it receives an
   NFS4ERR_STALE_CLIENTID error.  The precise circumstances depend on
   the characteristics of the sessions involved, specifically whether
   the session is persistent (see Section 2.10.6.5), but in each case
   the client will receive this error when it attempts to establish a
   new session with the existing client ID and receives the error
   NFS4ERR_STALE_CLIENTID, indicating that a new client ID needs to be
   obtained via EXCHANGE_ID and the new session established with that
   client ID.

   When a session is not persistent, the client will find out that it
   needs to create a new session as a result of getting an
   NFS4ERR_BADSESSION, since the session in question was lost as part of
   a server restart.  When the existing client ID is presented to a
   server as part of creating a session and that client ID is not
   recognized, as would happen after a server restart, the server will
   reject the request with the error NFS4ERR_STALE_CLIENTID.

   In the case of the session being persistent, the client will re-
   establish communication using the existing session after the restart.
   This session will be associated with the existing client ID but may
   only be used to retransmit operations that the client previously
   transmitted and did not see replies to.  Replies to operations that
   the server previously performed will come from the reply cache;
   otherwise, NFS4ERR_DEADSESSION will be returned.  Hence, such a
   session is referred to as "dead".  In this situation, in order to
   perform new operations, the client needs to establish a new session.
   If an attempt is made to establish this new session with the existing
   client ID, the server will reject the request with
   NFS4ERR_STALE_CLIENTID.

   When NFS4ERR_STALE_CLIENTID is received in either of these



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   situations, the client needs to obtain a new client ID by use of the
   EXCHANGE_ID operation, then use that client ID as the basis of a new
   session, and then proceed to any other necessary recovery for the
   server restart case (see Section 8.4.2).

   See the descriptions of EXCHANGE_ID (Section 18.35) and
   CREATE_SESSION (Section 18.36) for a complete specification of these
   operations.

2.4.1.  Upgrade from NFSv4.0 to NFSv4.1

   To facilitate upgrade from NFSv4.0 to NFSv4.1, a server may compare a
   value of data type client_owner4 in an EXCHANGE_ID with a value of
   data type nfs_client_id4 that was established using the SETCLIENTID
   operation of NFSv4.0.  A server that does so will allow an upgraded
   client to avoid waiting until the lease (i.e., the lease established
   by the NFSv4.0 instance client) expires.  This requires that the
   value of data type client_owner4 be constructed the same way as the
   value of data type nfs_client_id4.  If the latter's contents included
   the server's network address (per the recommendations of the NFSv4.0
   specification [30]), and the NFSv4.1 client does not wish to use a
   client ID that prevents trunking, it should send two EXCHANGE_ID
   operations.  The first EXCHANGE_ID will have a client_owner4 equal to
   the nfs_client_id4.  This will clear the state created by the NFSv4.0
   client.  The second EXCHANGE_ID will not have the server's network
   address.  The state created for the second EXCHANGE_ID will not have
   to wait for lease expiration, because there will be no state to
   expire.

2.4.2.  Server Release of Client ID

   NFSv4.1 introduces a new operation called DESTROY_CLIENTID
   (Section 18.50), which the client SHOULD use to destroy a client ID
   it no longer needs.  This permits graceful, bilateral release of a
   client ID.  The operation cannot be used if there are sessions
   associated with the client ID, or state with an unexpired lease.

   If the server determines that the client holds no associated state
   for its client ID (associated state includes unrevoked sessions,
   opens, locks, delegations, layouts, and wants), the server MAY choose
   to unilaterally release the client ID in order to conserve resources.
   If the client contacts the server after this release, the server MUST
   ensure that the client receives the appropriate error so that it will
   use the EXCHANGE_ID/CREATE_SESSION sequence to establish a new client
   ID.  The server ought to be very hesitant to release a client ID
   since the resulting work on the client to recover from such an event
   will be the same burden as if the server had failed and restarted.
   Typically, a server would not release a client ID unless there had



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   been no activity from that client for many minutes.  As long as there
   are sessions, opens, locks, delegations, layouts, or wants, the
   server MUST NOT release the client ID.  See Section 2.10.13.1.4 for
   discussion on releasing inactive sessions.

2.4.3.  Resolving Client Owner Conflicts

   When the server gets an EXCHANGE_ID for a client owner that currently
   has no state, or that has state but the lease has expired, the server
   MUST allow the EXCHANGE_ID and confirm the new client ID if followed
   by the appropriate CREATE_SESSION.

   When the server gets an EXCHANGE_ID for a new incarnation of a client
   owner that currently has an old incarnation with state and an
   unexpired lease, the server is allowed to dispose of the state of the
   previous incarnation of the client owner if one of the following is
   true:

   o  The principal that created the client ID for the client owner is
      the same as the principal that is sending the EXCHANGE_ID
      operation.  Note that if the client ID was created with
      SP4_MACH_CRED state protection (Section 18.35), the principal MUST
      be based on RPCSEC_GSS authentication, the RPCSEC_GSS service used
      MUST be integrity or privacy, and the same GSS mechanism and
      principal MUST be used as that used when the client ID was
      created.

   o  The client ID was established with SP4_SSV protection
      (Section 18.35, Section 2.10.8.3) and the client sends the
      EXCHANGE_ID with the security flavor set to RPCSEC_GSS using the
      GSS SSV mechanism (Section 2.10.9).

   o  The client ID was established with SP4_SSV protection, and under
      the conditions described herein, the EXCHANGE_ID was sent with
      SP4_MACH_CRED state protection.  Because the SSV might not persist
      across client and server restart, and because the first time a
      client sends EXCHANGE_ID to a server it does not have an SSV, the
      client MAY send the subsequent EXCHANGE_ID without an SSV
      RPCSEC_GSS handle.  Instead, as with SP4_MACH_CRED protection, the
      principal MUST be based on RPCSEC_GSS authentication, the
      RPCSEC_GSS service used MUST be integrity or privacy, and the same
      GSS mechanism and principal MUST be used as that used when the
      client ID was created.

   If none of the above situations apply, the server MUST return
   NFS4ERR_CLID_INUSE.

   If the server accepts the principal and co_ownerid as matching that



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   which created the client ID, and the co_verifier in the EXCHANGE_ID
   differs from the co_verifier used when the client ID was created,
   then after the server receives a CREATE_SESSION that confirms the
   client ID, the server deletes state.  If the co_verifier values are
   the same (e.g., the client either is updating properties of the
   client ID (Section 18.35) or is attempting trunking (Section 2.10.5),
   the server MUST NOT delete state.

2.5.  Server Owners

   The server owner is similar to a client owner (Section 2.4), but
   unlike the client owner, there is no shorthand server ID.  The server
   owner is defined in the following data type:


   struct server_owner4 {
    uint64_t       so_minor_id;
    opaque         so_major_id<NFS4_OPAQUE_LIMIT>;
   };

   The server owner is returned from EXCHANGE_ID.  When the so_major_id
   fields are the same in two EXCHANGE_ID results, the connections that
   each EXCHANGE_ID were sent over can be assumed to address the same
   server (as defined in Section 1.6).  If the so_minor_id fields are
   also the same, then not only do both connections connect to the same
   server, but the session can be shared across both connections.  The
   reader is cautioned that multiple servers may deliberately or
   accidentally claim to have the same so_major_id or so_major_id/
   so_minor_id; the reader should examine Sections 2.10.5 and 18.35 in
   order to avoid acting on falsely matching server owner values.

   The considerations for generating a so_major_id are similar to that
   for generating a co_ownerid string (see Section 2.4).  The
   consequences of two servers generating conflicting so_major_id values
   are less dire than they are for co_ownerid conflicts because the
   client can use RPCSEC_GSS to compare the authenticity of each server
   (see Section 2.10.5).

2.6.  Security Service Negotiation

   With the NFSv4.1 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its file system namespace
   that are available for use by NFS clients.  These points can be
   considered security policy boundaries, and, in some NFS
   implementations, are tied to NFS export points.  In turn, the NFS
   server may be configured such that each of these security policy



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   boundaries may have different or multiple security mechanisms in use.

   The security negotiation between client and server SHOULD be done
   with a secure channel to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.
   See Section 21 for further discussion.

2.6.1.  NFSv4.1 Security Tuples

   An NFS server can assign one or more "security tuples" to each
   security policy boundary in its namespace.  Each security tuple
   consists of a security flavor (see Section 2.2.1.1) and, if the
   flavor is RPCSEC_GSS, a GSS-API mechanism Object Identifier (OID), a
   GSS-API quality of protection, and an RPCSEC_GSS service.

2.6.2.  SECINFO and SECINFO_NO_NAME

   The SECINFO and SECINFO_NO_NAME operations allow the client to
   determine, on a per-filehandle basis, what security tuple is to be
   used for server access.  In general, the client will not have to use
   either operation except during initial communication with the server
   or when the client crosses security policy boundaries at the server.
   However, the server's policies may also change at any time and force
   the client to negotiate a new security tuple.

   Where the use of different security tuples would affect the type of
   access that would be allowed if a request was sent over the same
   connection used for the SECINFO or SECINFO_NO_NAME operation (e.g.,
   read-only vs. read-write) access, security tuples that allow greater
   access should be presented first.  Where the general level of access
   is the same and different security flavors limit the range of
   principals whose privileges are recognized (e.g., allowing or
   disallowing root access), flavors supporting the greatest range of
   principals should be listed first.

2.6.3.  Security Error

   Based on the assumption that each NFSv4.1 client and server MUST
   support a minimum set of security (i.e., Kerberos V5 under
   RPCSEC_GSS), the NFS client will initiate file access to the server
   with one of the minimal security tuples.  During communication with
   the server, the client may receive an NFS error of NFS4ERR_WRONGSEC.
   This error allows the server to notify the client that the security
   tuple currently being used contravenes the server's security policy.
   The client is then responsible for determining (see Section 2.6.3.1)
   what security tuples are available at the server and choosing one
   that is appropriate for the client.



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2.6.3.1.  Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME

   This section explains the mechanics of NFSv4.1 security negotiation.

2.6.3.1.1.  Put Filehandle Operations

   The term "put filehandle operation" refers to PUTROOTFH, PUTPUBFH,
   PUTFH, and RESTOREFH.  Each of the subsections herein describes how
   the server handles a subseries of operations that starts with a put
   filehandle operation.

2.6.3.1.1.1.  Put Filehandle Operation + SAVEFH

   The client is saving a filehandle for a future RESTOREFH, LINK, or
   RENAME.  SAVEFH MUST NOT return NFS4ERR_WRONGSEC.  To determine
   whether or not the put filehandle operation returns NFS4ERR_WRONGSEC,
   the server implementation pretends SAVEFH is not in the series of
   operations and examines which of the situations described in the
   other subsections of Section 2.6.3.1.1 apply.

2.6.3.1.1.2.  Two or More Put Filehandle Operations

   For a series of N put filehandle operations, the server MUST NOT
   return NFS4ERR_WRONGSEC to the first N-1 put filehandle operations.
   The Nth put filehandle operation is handled as if it is the first in
   a subseries of operations.  For example, if the server received a
   COMPOUND request with this series of operations -- PUTFH, PUTROOTFH,
   LOOKUP -- then the PUTFH operation is ignored for NFS4ERR_WRONGSEC
   purposes, and the PUTROOTFH, LOOKUP subseries is processed as
   according to Section 2.6.3.1.1.3.

2.6.3.1.1.3.  Put Filehandle Operation + LOOKUP (or OPEN of an Existing
              Name)

   This situation also applies to a put filehandle operation followed by
   a LOOKUP or an OPEN operation that specifies an existing component
   name.

   In this situation, the client is potentially crossing a security
   policy boundary, and the set of security tuples the parent directory
   supports may differ from those of the child.  The server
   implementation may decide whether to impose any restrictions on
   security policy administration.  There are at least three approaches
   (sec_policy_child is the tuple set of the child export,
   sec_policy_parent is that of the parent).






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   (a)  sec_policy_child <= sec_policy_parent (<= for subset).  This
        means that the set of security tuples specified on the security
        policy of a child directory is always a subset of its parent
        directory.

   (b)  sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
        {} for the empty set).  This means that the set of security
        tuples specified on the security policy of a child directory
        always has a non-empty intersection with that of the parent.

   (c)  sec_policy_child ^ sec_policy_parent == {}.  This means that the
        set of security tuples specified on the security policy of a
        child directory may not intersect with that of the parent.  In
        other words, there are no restrictions on how the system
        administrator may set up these tuples.

   In order for a server to support approaches (b) (for the case when a
   client chooses a flavor that is not a member of sec_policy_parent)
   and (c), the put filehandle operation cannot return NFS4ERR_WRONGSEC
   when there is a security tuple mismatch.  Instead, it should be
   returned from the LOOKUP (or OPEN by existing component name) that
   follows.

   Since the above guideline does not contradict approach (a), it should
   be followed in general.  Even if approach (a) is implemented, it is
   possible for the security tuple used to be acceptable for the target
   of LOOKUP but not for the filehandles used in the put filehandle
   operation.  The put filehandle operation could be a PUTROOTFH or
   PUTPUBFH, where the client cannot know the security tuples for the
   root or public filehandle.  Or the security policy for the filehandle
   used by the put filehandle operation could have changed since the
   time the filehandle was obtained.

   Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in
   response to the put filehandle operation if the operation is
   immediately followed by a LOOKUP or an OPEN by component name.

2.6.3.1.1.4.  Put Filehandle Operation + LOOKUPP

   Since SECINFO only works its way down, there is no way LOOKUPP can
   return NFS4ERR_WRONGSEC without SECINFO_NO_NAME.  SECINFO_NO_NAME
   solves this issue via style SECINFO_STYLE4_PARENT, which works in the
   opposite direction as SECINFO.  As with Section 2.6.3.1.1.3, a put
   filehandle operation that is followed by a LOOKUPP MUST NOT return
   NFS4ERR_WRONGSEC.  If the server does not support SECINFO_NO_NAME,
   the client's only recourse is to send the put filehandle operation,
   LOOKUPP, GETFH sequence of operations with every security tuple it
   supports.



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   Regardless of whether SECINFO_NO_NAME is supported, an NFSv4.1 server
   MUST NOT return NFS4ERR_WRONGSEC in response to a put filehandle
   operation if the operation is immediately followed by a LOOKUPP.

2.6.3.1.1.5.  Put Filehandle Operation + SECINFO/SECINFO_NO_NAME

   A security-sensitive client is allowed to choose a strong security
   tuple when querying a server to determine a file object's permitted
   security tuples.  The security tuple chosen by the client does not
   have to be included in the tuple list of the security policy of
   either the parent directory indicated in the put filehandle operation
   or the child file object indicated in SECINFO (or any parent
   directory indicated in SECINFO_NO_NAME).  Of course, the server has
   to be configured for whatever security tuple the client selects;
   otherwise, the request will fail at the RPC layer with an appropriate
   authentication error.

   In theory, there is no connection between the security flavor used by
   SECINFO or SECINFO_NO_NAME and those supported by the security
   policy.  But in practice, the client may start looking for strong
   flavors from those supported by the security policy, followed by
   those in the REQUIRED set.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a put
   filehandle operation that is immediately followed by SECINFO or
   SECINFO_NO_NAME.  The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC
   from SECINFO or SECINFO_NO_NAME.

2.6.3.1.1.6.  Put Filehandle Operation + Nothing

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.

2.6.3.1.1.7.  Put Filehandle Operation + Anything Else

   "Anything Else" includes OPEN by filehandle.

   The security policy enforcement applies to the filehandle specified
   in the put filehandle operation.  Therefore, the put filehandle
   operation MUST return NFS4ERR_WRONGSEC when there is a security tuple
   mismatch.  This avoids the complexity of adding NFS4ERR_WRONGSEC as
   an allowable error to every other operation.

   A COMPOUND containing the series put filehandle operation +
   SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an efficient way
   for the client to recover from NFS4ERR_WRONGSEC.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to any operation
   other than a put filehandle operation, LOOKUP, LOOKUPP, and OPEN (by



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   component name).

2.6.3.1.1.8.  Operations after SECINFO and SECINFO_NO_NAME

   Suppose a client sends a COMPOUND procedure containing the series
   SEQUENCE, PUTFH, SECINFO_NONAME, READ, and suppose the security tuple
   used does not match that required for the target file.  By rule (see
   Section 2.6.3.1.1.5), neither PUTFH nor SECINFO_NO_NAME can return
   NFS4ERR_WRONGSEC.  By rule (see Section 2.6.3.1.1.7), READ cannot
   return NFS4ERR_WRONGSEC.  The issue is resolved by the fact that
   SECINFO and SECINFO_NO_NAME consume the current filehandle (note that
   this is a change from NFSv4.0).  This leaves no current filehandle
   for READ to use, and READ returns NFS4ERR_NOFILEHANDLE.

2.6.3.1.2.  LINK and RENAME

   The LINK and RENAME operations use both the current and saved
   filehandles.  Technically, the server MAY return NFS4ERR_WRONGSEC
   from LINK or RENAME if the security policy of the saved filehandle
   rejects the security flavor used in the COMPOUND request's
   credentials.  If the server does so, then if there is no intersection
   between the security policies of saved and current filehandles, this
   means that it will be impossible for the client to perform the
   intended LINK or RENAME operation.

   For example, suppose the client sends this COMPOUND request:
   SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH, RENAME "c" "d", where
   filehandles bFH and aFH refer to different directories.  Suppose no
   common security tuple exists between the security policies of aFH and
   bFH.  If the client sends the request using credentials acceptable to
   bFH's security policy but not aFH's policy, then the PUTFH aFH
   operation will fail with NFS4ERR_WRONGSEC.  After a SECINFO_NO_NAME
   request, the client sends SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH,
   RENAME "c" "d", using credentials acceptable to aFH's security policy
   but not bFH's policy.  The server returns NFS4ERR_WRONGSEC on the
   RENAME operation.

   To prevent a client from an endless sequence of a request containing
   LINK or RENAME, followed by a request containing SECINFO_NO_NAME or
   SECINFO, the server MUST detect when the security policies of the
   current and saved filehandles have no mutually acceptable security
   tuple, and MUST NOT return NFS4ERR_WRONGSEC from LINK or RENAME in
   that situation.  Instead the server MUST do one of two things:

   o  The server can return NFS4ERR_XDEV.

   o  The server can allow the security policy of the current filehandle
      to override that of the saved filehandle, and so return NFS4_OK.



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2.7.  Minor Versioning

   To address the requirement of an NFS protocol that can evolve as the
   need arises, the NFSv4.1 protocol contains the rules and framework to
   allow for future minor changes or versioning.

   The base assumption with respect to minor versioning is that any
   future accepted minor version will be documented in one or more
   Standards Track RFCs.  Minor version 0 of the NFSv4 protocol is
   represented by [30], and minor version 1 is represented by this RFC.
   The COMPOUND and CB_COMPOUND procedures support the encoding of the
   minor version being requested by the client.

   The following items represent the basic rules for the development of
   minor versions.  Note that a future minor version may modify or add
   to the following rules as part of the minor version definition.

   1.   Procedures are not added or deleted.

        To maintain the general RPC model, NFSv4 minor versions will not
        add to or delete procedures from the NFS program.

   2.   Minor versions may add operations to the COMPOUND and
        CB_COMPOUND procedures.

        The addition of operations to the COMPOUND and CB_COMPOUND
        procedures does not affect the RPC model.

        *  Minor versions may append attributes to the bitmap4 that
           represents sets of attributes and to the fattr4 that
           represents sets of attribute values.

           This allows for the expansion of the attribute model to allow
           for future growth or adaptation.

        *  Minor version X must append any new attributes after the last
           documented attribute.

           Since attribute results are specified as an opaque array of
           per-attribute, XDR-encoded results, the complexity of adding
           new attributes in the midst of the current definitions would
           be too burdensome.

   3.   Minor versions must not modify the structure of an existing
        operation's arguments or results.

        Again, the complexity of handling multiple structure definitions
        for a single operation is too burdensome.  New operations should



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        be added instead of modifying existing structures for a minor
        version.

        This rule does not preclude the following adaptations in a minor
        version:

        *  adding bits to flag fields, such as new attributes to
           GETATTR's bitmap4 data type, and providing corresponding
           variants of opaque arrays, such as a notify4 used together
           with such bitmaps

        *  adding bits to existing attributes like ACLs that have flag
           words

        *  extending enumerated types (including NFS4ERR_*) with new
           values

        *  adding cases to a switched union

   4.   Minor versions must not modify the structure of existing
        attributes.

   5.   Minor versions must not delete operations.

        This prevents the potential reuse of a particular operation
        "slot" in a future minor version.

   6.   Minor versions must not delete attributes.

   7.   Minor versions must not delete flag bits or enumeration values.

   8.   Minor versions may declare an operation MUST NOT be implemented.

        Specifying that an operation MUST NOT be implemented is
        equivalent to obsoleting an operation.  For the client, it means
        that the operation MUST NOT be sent to the server.  For the
        server, an NFS error can be returned as opposed to "dropping"
        the request as an XDR decode error.  This approach allows for
        the obsolescence of an operation while maintaining its structure
        so that a future minor version can reintroduce the operation.

        1.  Minor versions may declare that an attribute MUST NOT be
            implemented.

        2.  Minor versions may declare that a flag bit or enumeration
            value MUST NOT be implemented.





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   9.   Minor versions may downgrade features from REQUIRED to
        RECOMMENDED, or RECOMMENDED to OPTIONAL.

   10.  Minor versions may upgrade features from OPTIONAL to
        RECOMMENDED, or RECOMMENDED to REQUIRED.

   11.  A client and server that support minor version X SHOULD support
        minor versions zero through X-1 as well.

   12.  Except for infrastructural changes, a minor version must not
        introduce REQUIRED new features.

        This rule allows for the introduction of new functionality and
        forces the use of implementation experience before designating a
        feature as REQUIRED.  On the other hand, some classes of
        features are infrastructural and have broad effects.  Allowing
        infrastructural features to be RECOMMENDED or OPTIONAL
        complicates implementation of the minor version.

   13.  A client MUST NOT attempt to use a stateid, filehandle, or
        similar returned object from the COMPOUND procedure with minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

2.8.  Non-RPC-Based Security Services

   As described in Section 2.2.1.1.1.1, NFSv4.1 relies on RPC for
   identification, authentication, integrity, and privacy.  NFSv4.1
   itself provides or enables additional security services as described
   in the next several subsections.

2.8.1.  Authorization

   Authorization to access a file object via an NFSv4.1 operation is
   ultimately determined by the NFSv4.1 server.  A client can
   predetermine its access to a file object via the OPEN (Section 18.16)
   and the ACCESS (Section 18.1) operations.

   Principals with appropriate access rights can modify the
   authorization on a file object via the SETATTR (Section 18.30)
   operation.  Attributes that affect access rights include mode, owner,
   owner_group, acl, dacl, and sacl.  See Section 5.

2.8.2.  Auditing

   NFSv4.1 provides auditing on a per-file object basis, via the acl and
   sacl attributes as described in Section 6.  It is outside the scope
   of this specification to specify audit log formats or management



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   policies.

2.8.3.  Intrusion Detection

   NFSv4.1 provides alarm control on a per-file object basis, via the
   acl and sacl attributes as described in Section 6.  Alarms may serve
   as the basis for intrusion detection.  It is outside the scope of
   this specification to specify heuristics for detecting intrusion via
   alarms.

2.9.  Transport Layers

2.9.1.  REQUIRED and RECOMMENDED Properties of Transports

   NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-
   based transports with the following attributes:

   o  The transport supports reliable delivery of data, which NFSv4.1
      requires but neither NFSv4.1 nor RPC has facilities for ensuring
      [34].

   o  The transport delivers data in the order it was sent.  Ordered
      delivery simplifies detection of transmit errors, and simplifies
      the sending of arbitrary sized requests and responses via the
      record marking protocol [3].

   Where an NFSv4.1 implementation supports operation over the IP
   network protocol, any transport used between NFS and IP MUST be among
   the IETF-approved congestion control transport protocols.  At the
   time this document was written, the only two transports that had the
   above attributes were TCP and the Stream Control Transmission
   Protocol (SCTP).  To enhance the possibilities for interoperability,
   an NFSv4.1 implementation MUST support operation over the TCP
   transport protocol.

   Even if NFSv4.1 is used over a non-IP network protocol, it is
   RECOMMENDED that the transport support congestion control.

   It is permissible for a connectionless transport to be used under
   NFSv4.1; however, reliable and in-order delivery of data combined
   with congestion control by the connectionless transport is REQUIRED.
   As a consequence, UDP by itself MUST NOT be used as an NFSv4.1
   transport.  NFSv4.1 assumes that a client transport address and
   server transport address used to send data over a transport together
   constitute a connection, even if the underlying transport eschews the
   concept of a connection.





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2.9.2.  Client and Server Transport Behavior

   If a connection-oriented transport (e.g., TCP) is used, the client
   and server SHOULD use long-lived connections for at least three
   reasons:

   1.  This will prevent the weakening of the transport's congestion
       control mechanisms via short-lived connections.

   2.  This will improve performance for the WAN environment by
       eliminating the need for connection setup handshakes.

   3.  The NFSv4.1 callback model differs from NFSv4.0, and requires the
       client and server to maintain a client-created backchannel (see
       Section 2.10.3.1) for the server to use.

   In order to reduce congestion, if a connection-oriented transport is
   used, and the request is not the NULL procedure:

   o  A requester MUST NOT retry a request unless the connection the
      request was sent over was lost before the reply was received.

   o  A replier MUST NOT silently drop a request, even if the request is
      a retry.  (The silent drop behavior of RPCSEC_GSS [4] does not
      apply because this behavior happens at the RPCSEC_GSS layer, a
      lower layer in the request processing.)  Instead, the replier
      SHOULD return an appropriate error (see Section 2.10.6.1), or it
      MAY disconnect the connection.

   When sending a reply, the replier MUST send the reply to the same
   full network address (e.g., if using an IP-based transport, the
   source port of the requester is part of the full network address)
   from which the requester sent the request.  If using a connection-
   oriented transport, replies MUST be sent on the same connection from
   which the request was received.

   If a connection is dropped after the replier receives the request but
   before the replier sends the reply, the replier might have a pending
   reply.  If a connection is established with the same source and
   destination full network address as the dropped connection, then the
   replier MUST NOT send the reply until the requester retries the
   request.  The reason for this prohibition is that the requester MAY
   retry a request over a different connection (provided that connection
   is associated with the original request's session).

   When using RDMA transports, there are other reasons for not
   tolerating retries over the same connection:




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   o  RDMA transports use "credits" to enforce flow control, where a
      credit is a right to a peer to transmit a message.  If one peer
      were to retransmit a request (or reply), it would consume an
      additional credit.  If the replier retransmitted a reply, it would
      certainly result in an RDMA connection loss, since the requester
      would typically only post a single receive buffer for each
      request.  If the requester retransmitted a request, the additional
      credit consumed on the server might lead to RDMA connection
      failure unless the client accounted for it and decreased its
      available credit, leading to wasted resources.

   o  RDMA credits present a new issue to the reply cache in NFSv4.1.
      The reply cache may be used when a connection within a session is
      lost, such as after the client reconnects.  Credit information is
      a dynamic property of the RDMA connection, and stale values must
      not be replayed from the cache.  This implies that the reply cache
      contents must not be blindly used when replies are sent from it,
      and credit information appropriate to the channel must be
      refreshed by the RPC layer.

   In addition, as described in Section 2.10.6.2, while a session is
   active, the NFSv4.1 requester MUST NOT stop waiting for a reply.

2.9.3.  Ports

   Historically, NFSv3 servers have listened over TCP port 2049.  The
   registered port 2049 [35] for the NFS protocol should be the default
   configuration.  NFSv4.1 clients SHOULD NOT use the RPC binding
   protocols as described in [36].

2.10.  Session

   NFSv4.1 clients and servers MUST support and MUST use the session
   feature as described in this section.

2.10.1.  Motivation and Overview

   Previous versions and minor versions of NFS have suffered from the
   following:

   o  Lack of support for Exactly Once Semantics (EOS).  This includes
      lack of support for EOS through server failure and recovery.

   o  Limited callback support, including no support for sending
      callbacks through firewalls, and races between replies to normal
      requests and callbacks.





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   o  Limited trunking over multiple network paths.

   o  Requiring machine credentials for fully secure operation.

   Through the introduction of a session, NFSv4.1 addresses the above
   shortfalls with practical solutions:

   o  EOS is enabled by a reply cache with a bounded size, making it
      feasible to keep the cache in persistent storage and enable EOS
      through server failure and recovery.  One reason that previous
      revisions of NFS did not support EOS was because some EOS
      approaches often limited parallelism.  As will be explained in
      Section 2.10.6, NFSv4.1 supports both EOS and unlimited
      parallelism.

   o  The NFSv4.1 client (defined in Section 1.6, Paragraph 2) creates
      transport connections and provides them to the server to use for
      sending callback requests, thus solving the firewall issue
      (Section 18.34).  Races between responses from client requests and
      callbacks caused by the requests are detected via the session's
      sequencing properties that are a consequence of EOS
      (Section 2.10.6.3).

   o  The NFSv4.1 client can associate an arbitrary number of
      connections with the session, and thus provide trunking
      (Section 2.10.5).

   o  The NFSv4.1 client and server produces a session key independent
      of client and server machine credentials which can be used to
      compute a digest for protecting critical session management
      operations (Section 2.10.8.3).

   o  The NFSv4.1 client can also create secure RPCSEC_GSS contexts for
      use by the session's backchannel that do not require the server to
      authenticate to a client machine principal (Section 2.10.8.2).

   A session is a dynamically created, long-lived server object created
   by a client and used over time from one or more transport
   connections.  Its function is to maintain the server's state relative
   to the connection(s) belonging to a client instance.  This state is
   entirely independent of the connection itself, and indeed the state
   exists whether or not the connection exists.  A client may have one
   or more sessions associated with it so that client-associated state
   may be accessed using any of the sessions associated with that
   client's client ID, when connections are associated with those
   sessions.  When no connections are associated with any of a client
   ID's sessions for an extended time, such objects as locks, opens,
   delegations, layouts, etc. are subject to expiration.  The session



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   serves as an object representing a means of access by a client to the
   associated client state on the server, independent of the physical
   means of access to that state.

   A single client may create multiple sessions.  A single session MUST
   NOT serve multiple clients.

2.10.2.  NFSv4 Integration

   Sessions are part of NFSv4.1 and not NFSv4.0.  Normally, a major
   infrastructure change such as sessions would require a new major
   version number to an Open Network Computing (ONC) RPC program like
   NFS.  However, because NFSv4 encapsulates its functionality in a
   single procedure, COMPOUND, and because COMPOUND can support an
   arbitrary number of operations, sessions have been added to NFSv4.1
   with little difficulty.  COMPOUND includes a minor version number
   field, and for NFSv4.1 this minor version is set to 1.  When the
   NFSv4 server processes a COMPOUND with the minor version set to 1, it
   expects a different set of operations than it does for NFSv4.0.
   NFSv4.1 defines the SEQUENCE operation, which is required for every
   COMPOUND that operates over an established session, with the
   exception of some session administration operations, such as
   DESTROY_SESSION (Section 18.37).

2.10.2.1.  SEQUENCE and CB_SEQUENCE

   In NFSv4.1, when the SEQUENCE operation is present, it MUST be the
   first operation in the COMPOUND procedure.  The primary purpose of
   SEQUENCE is to carry the session identifier.  The session identifier
   associates all other operations in the COMPOUND procedure with a
   particular session.  SEQUENCE also contains required information for
   maintaining EOS (see Section 2.10.6).  Session-enabled NFSv4.1
   COMPOUND requests thus have the form:

       +-----+--------------+-----------+------------+-----------+----
       | tag | minorversion | numops    |SEQUENCE op | op + args | ...
       |     |   (== 1)     | (limited) |  + args    |           |
       +-----+--------------+-----------+------------+-----------+----

   and the replies have the form:

       +------------+-----+--------+-------------------------------+--//
       |last status | tag | numres |status + SEQUENCE op + results |  //
       +------------+-----+--------+-------------------------------+--//
               //-----------------------+----
               // status + op + results | ...
               //-----------------------+----




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   A CB_COMPOUND procedure request and reply has a similar form to
   COMPOUND, but instead of a SEQUENCE operation, there is a CB_SEQUENCE
   operation.  CB_COMPOUND also has an additional field called
   "callback_ident", which is superfluous in NFSv4.1 and MUST be ignored
   by the client.  CB_SEQUENCE has the same information as SEQUENCE, and
   also includes other information needed to resolve callback races
   (Section 2.10.6.3).

2.10.2.2.  Client ID and Session Association

   Each client ID (Section 2.4) can have zero or more active sessions.
   A client ID and associated session are required to perform file
   access in NFSv4.1.  Each time a session is used (whether by a client
   sending a request to the server or the client replying to a callback
   request from the server), the state leased to its associated client
   ID is automatically renewed.

   State (which can consist of share reservations, locks, delegations,
   and layouts (Section 1.7.4)) is tied to the client ID.  Client state
   is not tied to any individual session.  Successive state changing
   operations from a given state owner MAY go over different sessions,
   provided the session is associated with the same client ID.  A
   callback MAY arrive over a different session than that of the request
   that originally acquired the state pertaining to the callback.  For
   example, if session A is used to acquire a delegation, a request to
   recall the delegation MAY arrive over session B if both sessions are
   associated with the same client ID.  Sections 2.10.8.1 and 2.10.8.2
   discuss the security considerations around callbacks.

2.10.3.  Channels

   A channel is not a connection.  A channel represents the direction
   ONC RPC requests are sent.

   Each session has one or two channels: the fore channel and the
   backchannel.  Because there are at most two channels per session, and
   because each channel has a distinct purpose, channels are not
   assigned identifiers.

   The fore channel is used for ordinary requests from the client to the
   server, and carries COMPOUND requests and responses.  A session
   always has a fore channel.

   The backchannel is used for callback requests from server to client,
   and carries CB_COMPOUND requests and responses.  Whether or not there
   is a backchannel is a decision made by the client; however, many
   features of NFSv4.1 require a backchannel.  NFSv4.1 servers MUST
   support backchannels.



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   Each session has resources for each channel, including separate reply
   caches (see Section 2.10.6.1).  Note that even the backchannel
   requires a reply cache (or, at least, a slot table in order to detect
   retries) because some callback operations are nonidempotent.

2.10.3.1.  Association of Connections, Channels, and Sessions

   Each channel is associated with zero or more transport connections
   (whether of the same transport protocol or different transport
   protocols).  A connection can be associated with one channel or both
   channels of a session; the client and server negotiate whether a
   connection will carry traffic for one channel or both channels via
   the CREATE_SESSION (Section 18.36) and the BIND_CONN_TO_SESSION
   (Section 18.34) operations.  When a session is created via
   CREATE_SESSION, the connection that transported the CREATE_SESSION
   request is automatically associated with the fore channel, and
   optionally the backchannel.  If the client specifies no state
   protection (Section 18.35) when the session is created, then when
   SEQUENCE is transmitted on a different connection, the connection is
   automatically associated with the fore channel of the session
   specified in the SEQUENCE operation.

   A connection's association with a session is not exclusive.  A
   connection associated with the channel(s) of one session may be
   simultaneously associated with the channel(s) of other sessions
   including sessions associated with other client IDs.

   It is permissible for connections of multiple transport types to be
   associated with the same channel.  For example, both TCP and RDMA
   connections can be associated with the fore channel.  In the event an
   RDMA and non-RDMA connection are associated with the same channel,
   the maximum number of slots SHOULD be at least one more than the
   total number of RDMA credits (Section 2.10.6.1).  This way, if all
   RDMA credits are used, the non-RDMA connection can have at least one
   outstanding request.  If a server supports multiple transport types,
   it MUST allow a client to associate connections from each transport
   to a channel.

   It is permissible for a connection of one type of transport to be
   associated with the fore channel, and a connection of a different
   type to be associated with the backchannel.

2.10.4.  Server Scope

   Servers each specify a server scope value in the form of an opaque
   string eir_server_scope returned as part of the results of an
   EXCHANGE_ID operation.  The purpose of the server scope is to allow a
   group of servers to indicate to clients that a set of servers sharing



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   the same server scope value has arranged to use compatible values of
   otherwise opaque identifiers.  Thus, the identifiers generated by one
   server of that set may be presented to another of that same scope.

   The use of such compatible values does not imply that a value
   generated by one server will always be accepted by another.  In most
   cases, it will not.  However, a server will not accept a value
   generated by another inadvertently.  When it does accept it, it will
   be because it is recognized as valid and carrying the same meaning as
   on another server of the same scope.

   When servers are of the same server scope, this compatibility of
   values applies to the follow identifiers:

   o  Filehandle values.  A filehandle value accepted by two servers of
      the same server scope denotes the same object.  A WRITE operation
      sent to one server is reflected immediately in a READ sent to the
      other, and locks obtained on one server conflict with those
      requested on the other.

   o  Session ID values.  A session ID value accepted by two servers of
      the same server scope denotes the same session.

   o  Client ID values.  A client ID value accepted as valid by two
      servers of the same server scope is associated with two clients
      with the same client owner and verifier.

   o  State ID values.  A state ID value is recognized as valid when the
      corresponding client ID is recognized as valid.  If the same
      stateid value is accepted as valid on two servers of the same
      scope and the client IDs on the two servers represent the same
      client owner and verifier, then the two stateid values designate
      the same set of locks and are for the same file.

   o  Server owner values.  When the server scope values are the same,
      server owner value may be validly compared.  In cases where the
      server scope values are different, server owner values are treated
      as different even if they contain all identical bytes.

   The coordination among servers required to provide such compatibility
   can be quite minimal, and limited to a simple partition of the ID
   space.  The recognition of common values requires additional
   implementation, but this can be tailored to the specific situations
   in which that recognition is desired.

   Clients will have occasion to compare the server scope values of
   multiple servers under a number of circumstances, each of which will
   be discussed under the appropriate functional section:



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   o  When server owner values received in response to EXCHANGE_ID
      operations sent to multiple network addresses are compared for the
      purpose of determining the validity of various forms of trunking,
      as described in Section 2.10.5.

   o  When network or server reconfiguration causes the same network
      address to possibly be directed to different servers, with the
      necessity for the client to determine when lock reclaim should be
      attempted, as described in Section 8.4.2.1.

   o  When file system migration causes the transfer of responsibility
      for a file system between servers and the client needs to
      determine whether state has been transferred with the file system
      (as described in Section 11.7.7) or whether the client needs to
      reclaim state on a similar basis as in the case of server restart,
      as described in Section 8.4.2.

   When two replies from EXCHANGE_ID, each from two different server
   network addresses, have the same server scope, there are a number of
   ways a client can validate that the common server scope is due to two
   servers cooperating in a group.

   o  If both EXCHANGE_ID requests were sent with RPCSEC_GSS
      authentication and the server principal is the same for both
      targets, the equality of server scope is validated.  It is
      RECOMMENDED that two servers intending to share the same server
      scope also share the same principal name.

   o  The client may accept the appearance of the second server in the
      fs_locations or fs_locations_info attribute for a relevant file
      system.  For example, if there is a migration event for a
      particular file system or there are locks to be reclaimed on a
      particular file system, the attributes for that particular file
      system may be used.  The client sends the GETATTR request to the
      first server for the fs_locations or fs_locations_info attribute
      with RPCSEC_GSS authentication.  It may need to do this in advance
      of the need to verify the common server scope.  If the client
      successfully authenticates the reply to GETATTR, and the GETATTR
      request and reply containing the fs_locations or fs_locations_info
      attribute refers to the second server, then the equality of server
      scope is supported.  A client may choose to limit the use of this
      form of support to information relevant to the specific file
      system involved (e.g. a file system being migrated).








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2.10.5.  Trunking

   Trunking is the use of multiple connections between a client and
   server in order to increase the speed of data transfer.  NFSv4.1
   supports two types of trunking: session trunking and client ID
   trunking.

   NFSv4.1 servers MUST support both forms of trunking within the
   context of a single server network address and MUST support both
   forms within the context of the set of network addresses used to
   access a single server.  NFSv4.1 servers in a clustered configuration
   MAY allow network addresses for different servers to use client ID
   trunking.

   Clients may use either form of trunking as long as they do not, when
   trunking between different server network addresses, violate the
   servers' mandates as to the kinds of trunking to be allowed (see
   below).  With regard to callback channels, the client MUST allow the
   server to choose among all callback channels valid for a given client
   ID and MUST support trunking when the connections supporting the
   backchannel allow session or client ID trunking to be used for
   callbacks.

   Session trunking is essentially the association of multiple
   connections, each with potentially different target and/or source
   network addresses, to the same session.  When the target network
   addresses (server addresses) of the two connections are the same, the
   server MUST support such session trunking.  When the target network
   addresses are different, the server MAY indicate such support using
   the data returned by the EXCHANGE_ID operation (see below).

   Client ID trunking is the association of multiple sessions to the
   same client ID.  Servers MUST support client ID trunking for two
   target network addresses whenever they allow session trunking for
   those same two network addresses.  In addition, a server MAY, by
   presenting the same major server owner ID (Section 2.5) and server
   scope (Section 2.10.4), allow an additional case of client ID
   trunking.  When two servers return the same major server owner and
   server scope, it means that the two servers are cooperating on
   locking state management, which is a prerequisite for client ID
   trunking.

   Distinguishing when the client is allowed to use session and client
   ID trunking requires understanding how the results of the EXCHANGE_ID
   (Section 18.35) operation identify a server.  Suppose a client sends
   EXCHANGE_IDs over two different connections, each with a possibly
   different target network address, but each EXCHANGE_ID operation has
   the same value in the eia_clientowner field.  If the same NFSv4.1



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   server is listening over each connection, then each EXCHANGE_ID
   result MUST return the same values of eir_clientid,
   eir_server_owner.so_major_id, and eir_server_scope.  The client can
   then treat each connection as referring to the same server (subject
   to verification; see Section 2.10.5.1 later in this section), and it
   can use each connection to trunk requests and replies.  The client's
   choice is whether session trunking or client ID trunking applies.

   Session Trunking.  If the eia_clientowner argument is the same in two
      different EXCHANGE_ID requests, and the eir_clientid,
      eir_server_owner.so_major_id, eir_server_owner.so_minor_id, and
      eir_server_scope results match in both EXCHANGE_ID results, then
      the client is permitted to perform session trunking.  If the
      client has no session mapping to the tuple of eir_clientid,
      eir_server_owner.so_major_id, eir_server_scope, and
      eir_server_owner.so_minor_id, then it creates the session via a
      CREATE_SESSION operation over one of the connections, which
      associates the connection to the session.  If there is a session
      for the tuple, the client can send BIND_CONN_TO_SESSION to
      associate the connection to the session.

      Of course, if the client does not desire to use session trunking,
      it is not required to do so.  It can invoke CREATE_SESSION on the
      connection.  This will result in client ID trunking as described
      below.  It can also decide to drop the connection if it does not
      choose to use trunking.


   Client ID Trunking.  If the eia_clientowner argument is the same in
      two different EXCHANGE_ID requests, and the eir_clientid,
      eir_server_owner.so_major_id, and eir_server_scope results match
      in both EXCHANGE_ID results, then the client is permitted to
      perform client ID trunking (regardless of whether the
      eir_server_owner.so_minor_id results match).  The client can
      associate each connection with different sessions, where each
      session is associated with the same server.

      The client completes the act of client ID trunking by invoking
      CREATE_SESSION on each connection, using the same client ID that
      was returned in eir_clientid.  These invocations create two
      sessions and also associate each connection with its respective
      session.  The client is free to decline to use client ID trunking
      by simply dropping the connection at this point.

      When doing client ID trunking, locking state is shared across
      sessions associated with that same client ID.  This requires the
      server to coordinate state across sessions.




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   The client should be prepared for the possibility that
   eir_server_owner values may be different on subsequent EXCHANGE_ID
   requests made to the same network address, as a result of various
   sorts of reconfiguration events.  When this happens and the changes
   result in the invalidation of previously valid forms of trunking, the
   client should cease to use those forms, either by dropping
   connections or by adding sessions.  For a discussion of lock reclaim
   as it relates to such reconfiguration events, see Section 8.4.2.1.

2.10.5.1.  Verifying Claims of Matching Server Identity

   When two servers over two connections claim matching or partially
   matching eir_server_owner, eir_server_scope, and eir_clientid values,
   the client does not have to trust the servers' claims.  The client
   may verify these claims before trunking traffic in the following
   ways:

   o  For session trunking, clients SHOULD reliably verify if
      connections between different network paths are in fact associated
      with the same NFSv4.1 server and usable on the same session, and
      servers MUST allow clients to perform reliable verification.  When
      a client ID is created, the client SHOULD specify that
      BIND_CONN_TO_SESSION is to be verified according to the SP4_SSV or
      SP4_MACH_CRED (Section 18.35) state protection options.  For
      SP4_SSV, reliable verification depends on a shared secret (the
      SSV) that is established via the SET_SSV (Section 18.47)
      operation.

      When a new connection is associated with the session (via the
      BIND_CONN_TO_SESSION operation, see Section 18.34), if the client
      specified SP4_SSV state protection for the BIND_CONN_TO_SESSION
      operation, the client MUST send the BIND_CONN_TO_SESSION with
      RPCSEC_GSS protection, using integrity or privacy, and an
      RPCSEC_GSS handle created with the GSS SSV mechanism
      (Section 2.10.9).

      If the client mistakenly tries to associate a connection to a
      session of a wrong server, the server will either reject the
      attempt because it is not aware of the session identifier of the
      BIND_CONN_TO_SESSION arguments, or it will reject the attempt
      because the RPCSEC_GSS authentication fails.  Even if the server
      mistakenly or maliciously accepts the connection association
      attempt, the RPCSEC_GSS verifier it computes in the response will
      not be verified by the client, so the client will know it cannot
      use the connection for trunking the specified session.

      If the client specified SP4_MACH_CRED state protection, the
      BIND_CONN_TO_SESSION operation will use RPCSEC_GSS integrity or



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      privacy, using the same credential that was used when the client
      ID was created.  Mutual authentication via RPCSEC_GSS assures the
      client that the connection is associated with the correct session
      of the correct server.


   o  For client ID trunking, the client has at least two options for
      verifying that the same client ID obtained from two different
      EXCHANGE_ID operations came from the same server.  The first
      option is to use RPCSEC_GSS authentication when sending each
      EXCHANGE_ID operation.  Each time an EXCHANGE_ID is sent with
      RPCSEC_GSS authentication, the client notes the principal name of
      the GSS target.  If the EXCHANGE_ID results indicate that client
      ID trunking is possible, and the GSS targets' principal names are
      the same, the servers are the same and client ID trunking is
      allowed.

      The second option for verification is to use SP4_SSV protection.
      When the client sends EXCHANGE_ID, it specifies SP4_SSV
      protection.  The first EXCHANGE_ID the client sends always has to
      be confirmed by a CREATE_SESSION call.  The client then sends
      SET_SSV.  Later, the client sends EXCHANGE_ID to a second
      destination network address different from the one the first
      EXCHANGE_ID was sent to.  The client checks that each EXCHANGE_ID
      reply has the same eir_clientid, eir_server_owner.so_major_id, and
      eir_server_scope.  If so, the client verifies the claim by sending
      a CREATE_SESSION operation to the second destination address,
      protected with RPCSEC_GSS integrity using an RPCSEC_GSS handle
      returned by the second EXCHANGE_ID.  If the server accepts the
      CREATE_SESSION request, and if the client verifies the RPCSEC_GSS
      verifier and integrity codes, then the client has proof the second
      server knows the SSV, and thus the two servers are cooperating for
      the purposes of specifying server scope and client ID trunking.

2.10.6.  Exactly Once Semantics

   Via the session, NFSv4.1 offers exactly once semantics (EOS) for
   requests sent over a channel.  EOS is supported on both the fore
   channel and backchannel.

   Each COMPOUND or CB_COMPOUND request that is sent with a leading
   SEQUENCE or CB_SEQUENCE operation MUST be executed by the receiver
   exactly once.  This requirement holds regardless of whether the
   request is sent with reply caching specified (see
   Section 2.10.6.1.3).  The requirement holds even if the requester is
   sending the request over a session created between a pNFS data client
   and pNFS data server.  To understand the rationale for this
   requirement, divide the requests into three classifications:



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   o  Non-idempotent requests.

   o  Idempotent modifying requests.

   o  Idempotent non-modifying requests.

   An example of a non-idempotent request is RENAME.  Obviously, if a
   replier executes the same RENAME request twice, and the first
   execution succeeds, the re-execution will fail.  If the replier
   returns the result from the re-execution, this result is incorrect.
   Therefore, EOS is required for non-idempotent requests.

   An example of an idempotent modifying request is a COMPOUND request
   containing a WRITE operation.  Repeated execution of the same WRITE
   has the same effect as execution of that WRITE a single time.
   Nevertheless, enforcing EOS for WRITEs and other idempotent modifying
   requests is necessary to avoid data corruption.

   Suppose a client sends WRITE A to a noncompliant server that does not
   enforce EOS, and receives no response, perhaps due to a network
   partition.  The client reconnects to the server and re-sends WRITE A.
   Now, the server has outstanding two instances of A. The server can be
   in a situation in which it executes and replies to the retry of A,
   while the first A is still waiting in the server's internal I/O
   system for some resource.  Upon receiving the reply to the second
   attempt of WRITE A, the client believes its WRITE is done so it is
   free to send WRITE B, which overlaps the byte-range of A. When the
   original A is dispatched from the server's I/O system and executed
   (thus the second time A will have been written), then what has been
   written by B can be overwritten and thus corrupted.

   An example of an idempotent non-modifying request is a COMPOUND
   containing SEQUENCE, PUTFH, READLINK, and nothing else.  The re-
   execution of such a request will not cause data corruption or produce
   an incorrect result.  Nonetheless, to keep the implementation simple,
   the replier MUST enforce EOS for all requests, whether or not
   idempotent and non-modifying.

   Note that true and complete EOS is not possible unless the server
   persists the reply cache in stable storage, and unless the server is
   somehow implemented to never require a restart (indeed, if such a
   server exists, the distinction between a reply cache kept in stable
   storage versus one that is not is one without meaning).  See
   Section 2.10.6.5 for a discussion of persistence in the reply cache.
   Regardless, even if the server does not persist the reply cache, EOS
   improves robustness and correctness over previous versions of NFS
   because the legacy duplicate request/reply caches were based on the
   ONC RPC transaction identifier (XID).  Section 2.10.6.1 explains the



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   shortcomings of the XID as a basis for a reply cache and describes
   how NFSv4.1 sessions improve upon the XID.

2.10.6.1.  Slot Identifiers and Reply Cache

   The RPC layer provides a transaction ID (XID), which, while required
   to be unique, is not convenient for tracking requests for two
   reasons.  First, the XID is only meaningful to the requester; it
   cannot be interpreted by the replier except to test for equality with
   previously sent requests.  When consulting an RPC-based duplicate
   request cache, the opaqueness of the XID requires a computationally
   expensive look up (often via a hash that includes XID and source
   address).  NFSv4.1 requests use a non-opaque slot ID, which is an
   index into a slot table, which is far more efficient.  Second,
   because RPC requests can be executed by the replier in any order,
   there is no bound on the number of requests that may be outstanding
   at any time.  To achieve perfect EOS, using ONC RPC would require
   storing all replies in the reply cache.  XIDs are 32 bits; storing
   over four billion (2^32) replies in the reply cache is not practical.
   In practice, previous versions of NFS have chosen to store a fixed
   number of replies in the cache, and to use a least recently used
   (LRU) approach to replacing cache entries with new entries when the
   cache is full.  In NFSv4.1, the number of outstanding requests is
   bounded by the size of the slot table, and a sequence ID per slot is
   used to tell the replier when it is safe to delete a cached reply.

   In the NFSv4.1 reply cache, when the requester sends a new request,
   it selects a slot ID in the range 0..N, where N is the replier's
   current maximum slot ID granted to the requester on the session over
   which the request is to be sent.  The value of N starts out as equal
   to ca_maxrequests - 1 (Section 18.36), but can be adjusted by the
   response to SEQUENCE or CB_SEQUENCE as described later in this
   section.  The slot ID must be unused by any of the requests that the
   requester has already active on the session.  "Unused" here means the
   requester has no outstanding request for that slot ID.

   A slot contains a sequence ID and the cached reply corresponding to
   the request sent with that sequence ID.  The sequence ID is a 32-bit
   unsigned value, and is therefore in the range 0..0xFFFFFFFF (2^32 -
   1).  The first time a slot is used, the requester MUST specify a
   sequence ID of one (Section 18.36).  Each time a slot is reused, the
   request MUST specify a sequence ID that is one greater than that of
   the previous request on the slot.  If the previous sequence ID was
   0xFFFFFFFF, then the next request for the slot MUST have the sequence
   ID set to zero (i.e., (2^32 - 1) + 1 mod 2^32).

   The sequence ID accompanies the slot ID in each request.  It is for
   the critical check at the replier: it used to efficiently determine



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   whether a request using a certain slot ID is a retransmit or a new,
   never-before-seen request.  It is not feasible for the requester to
   assert that it is retransmitting to implement this, because for any
   given request the requester cannot know whether the replier has seen
   it unless the replier actually replies.  Of course, if the requester
   has seen the reply, the requester would not retransmit.

   The replier compares each received request's sequence ID with the
   last one previously received for that slot ID, to see if the new
   request is:

   o  A new request, in which the sequence ID is one greater than that
      previously seen in the slot (accounting for sequence wraparound).
      The replier proceeds to execute the new request, and the replier
      MUST increase the slot's sequence ID by one.

   o  A retransmitted request, in which the sequence ID is equal to that
      currently recorded in the slot.  If the original request has
      executed to completion, the replier returns the cached reply.  See
      Section 2.10.6.2 for direction on how the replier deals with
      retries of requests that are still in progress.

   o  A misordered retry, in which the sequence ID is less than
      (accounting for sequence wraparound) that previously seen in the
      slot.  The replier MUST return NFS4ERR_SEQ_MISORDERED (as the
      result from SEQUENCE or CB_SEQUENCE).

   o  A misordered new request, in which the sequence ID is two or more
      than (accounting for sequence wraparound) that previously seen in
      the slot.  Note that because the sequence ID MUST wrap around to
      zero once it reaches 0xFFFFFFFF, a misordered new request and a
      misordered retry cannot be distinguished.  Thus, the replier MUST
      return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
      CB_SEQUENCE).

   Unlike the XID, the slot ID is always within a specific range; this
   has two implications.  The first implication is that for a given
   session, the replier need only cache the results of a limited number
   of COMPOUND requests.  The second implication derives from the first,
   which is that unlike XID-indexed reply caches (also known as
   duplicate request caches - DRCs), the slot ID-based reply cache
   cannot be overflowed.  Through use of the sequence ID to identify
   retransmitted requests, the replier does not need to actually cache
   the request itself, reducing the storage requirements of the reply
   cache further.  These facilities make it practical to maintain all
   the required entries for an effective reply cache.

   The slot ID, sequence ID, and session ID therefore take over the



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   traditional role of the XID and source network address in the
   replier's reply cache implementation.  This approach is considerably
   more portable and completely robust -- it is not subject to the
   reassignment of ports as clients reconnect over IP networks.  In
   addition, the RPC XID is not used in the reply cache, enhancing
   robustness of the cache in the face of any rapid reuse of XIDs by the
   requester.  While the replier does not care about the XID for the
   purposes of reply cache management (but the replier MUST return the
   same XID that was in the request), nonetheless there are
   considerations for the XID in NFSv4.1 that are the same as all other
   previous versions of NFS.  The RPC XID remains in each message and
   needs to be formulated in NFSv4.1 requests as in any other ONC RPC
   request.  The reasons include:

   o  The RPC layer retains its existing semantics and implementation.

   o  The requester and replier must be able to interoperate at the RPC
      layer, prior to the NFSv4.1 decoding of the SEQUENCE or
      CB_SEQUENCE operation.

   o  If an operation is being used that does not start with SEQUENCE or
      CB_SEQUENCE (e.g., BIND_CONN_TO_SESSION), then the RPC XID is
      needed for correct operation to match the reply to the request.

   o  The SEQUENCE or CB_SEQUENCE operation may generate an error.  If
      so, the embedded slot ID, sequence ID, and session ID (if present)
      in the request will not be in the reply, and the requester has
      only the XID to match the reply to the request.

   Given that well-formulated XIDs continue to be required, this begs
   the question: why do SEQUENCE and CB_SEQUENCE replies have a session
   ID, slot ID, and sequence ID?  Having the session ID in the reply
   means that the requester does not have to use the XID to look up the
   session ID, which would be necessary if the connection were
   associated with multiple sessions.  Having the slot ID and sequence
   ID in the reply means that the requester does not have to use the XID
   to look up the slot ID and sequence ID.  Furthermore, since the XID
   is only 32 bits, it is too small to guarantee the re-association of a
   reply with its request [37]; having session ID, slot ID, and sequence
   ID in the reply allows the client to validate that the reply in fact
   belongs to the matched request.

   The SEQUENCE (and CB_SEQUENCE) operation also carries a
   "highest_slotid" value, which carries additional requester slot usage
   information.  The requester MUST always indicate the slot ID
   representing the outstanding request with the highest-numbered slot
   value.  The requester should in all cases provide the most
   conservative value possible, although it can be increased somewhat



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   above the actual instantaneous usage to maintain some minimum or
   optimal level.  This provides a way for the requester to yield unused
   request slots back to the replier, which in turn can use the
   information to reallocate resources.

   The replier responds with both a new target highest_slotid and an
   enforced highest_slotid, described as follows:

   o  The target highest_slotid is an indication to the requester of the
      highest_slotid the replier wishes the requester to be using.  This
      permits the replier to withdraw (or add) resources from a
      requester that has been found to not be using them, in order to
      more fairly share resources among a varying level of demand from
      other requesters.  The requester must always comply with the
      replier's value updates, since they indicate newly established
      hard limits on the requester's access to session resources.
      However, because of request pipelining, the requester may have
      active requests in flight reflecting prior values; therefore, the
      replier must not immediately require the requester to comply.


   o  The enforced highest_slotid indicates the highest slot ID the
      requester is permitted to use on a subsequent SEQUENCE or
      CB_SEQUENCE operation.  The replier's enforced highest_slotid
      SHOULD be no less than the highest_slotid the requester indicated
      in the SEQUENCE or CB_SEQUENCE arguments.

      A requester can be intransigent with respect to lowering its
      highest_slotid argument to a Sequence operation, i.e. the
      requester continues to ignore the target highest_slotid in the
      response to a Sequence operation, and continues to set its
      highest_slotid argument to be higher than the target
      highest_slotid.  This can be considered particularly egregious
      behavior when the replier knows there are no outstanding requests
      with slot IDs higher than its target highest_slotid.  When faced
      with such intransigence, the replier is free to take more forceful
      action, and MAY reply with a new enforced highest_slotid that is
      less than its previous enforced highest_slotid.  Thereafter, if
      the requester continues to send requests with a highest_slotid
      that is greater than the replier's new enforced highest_slotid,
      the server MAY return NFS4ERR_BAD_HIGH_SLOT, unless the slot ID in
      the request is greater than the new enforced highest_slotid and
      the request is a retry.

      The replier SHOULD retain the slots it wants to retire until the
      requester sends a request with a highest_slotid less than or equal
      to the replier's new enforced highest_slotid.




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      The requester can also be intransigent with respect to sending
      non-retry requests that have a slot ID that exceeds the replier's
      highest_slotid.  Once the replier has forcibly lowered the
      enforced highest_slotid, the requester is only allowed to send
      retries on slots that exceed the replier's highest_slotid.  If a
      request is received with a slot ID that is higher than the new
      enforced highest_slotid, and the sequence ID is one higher than
      what is in the slot's reply cache, then the server can both retire
      the slot and return NFS4ERR_BADSLOT (however, the server MUST NOT
      do one and not the other).  The reason it is safe to retire the
      slot is because by using the next sequence ID, the requester is
      indicating it has received the previous reply for the slot.


   o  The requester SHOULD use the lowest available slot when sending a
      new request.  This way, the replier may be able to retire slot
      entries faster.  However, where the replier is actively adjusting
      its granted highest_slotid, it will not be able to use only the
      receipt of the slot ID and highest_slotid in the request.  Neither
      the slot ID nor the highest_slotid used in a request may reflect
      the replier's current idea of the requester's session limit,
      because the request may have been sent from the requester before
      the update was received.  Therefore, in the downward adjustment
      case, the replier may have to retain a number of reply cache
      entries at least as large as the old value of maximum requests
      outstanding, until it can infer that the requester has seen a
      reply containing the new granted highest_slotid.  The replier can
      infer that the requester has seen such a reply when it receives a
      new request with the same slot ID as the request replied to and
      the next higher sequence ID.

2.10.6.1.1.  Caching of SEQUENCE and CB_SEQUENCE Replies

   When a SEQUENCE or CB_SEQUENCE operation is successfully executed,
   its reply MUST always be cached.  Specifically, session ID, sequence
   ID, and slot ID MUST be cached in the reply cache.  The reply from
   SEQUENCE also includes the highest slot ID, target highest slot ID,
   and status flags.  Instead of caching these values, the server MAY
   re-compute the values from the current state of the fore channel,
   session, and/or client ID as appropriate.  Similarly, the reply from
   CB_SEQUENCE includes a highest slot ID and target highest slot ID.
   The client MAY re-compute the values from the current state of the
   session as appropriate.

   Regardless of whether or not a replier is re-computing highest slot
   ID, target slot ID, and status on replies to retries, the requester
   MUST NOT assume that the values are being re-computed whenever it
   receives a reply after a retry is sent, since it has no way of



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   knowing whether the reply it has received was sent by the replier in
   response to the retry or is a delayed response to the original
   request.  Therefore, it may be the case that highest slot ID, target
   slot ID, or status bits may reflect the state of affairs when the
   request was first executed.  Although acting based on such delayed
   information is valid, it may cause the receiver of the reply to do
   unneeded work.  Requesters MAY choose to send additional requests to
   get the current state of affairs or use the state of affairs reported
   by subsequent requests, in preference to acting immediately on data
   that might be out of date.

2.10.6.1.2.  Errors from SEQUENCE and CB_SEQUENCE

   Any time SEQUENCE or CB_SEQUENCE returns an error, the sequence ID of
   the slot MUST NOT change.  The replier MUST NOT modify the reply
   cache entry for the slot whenever an error is returned from SEQUENCE
   or CB_SEQUENCE.

2.10.6.1.3.  Optional Reply Caching

   On a per-request basis, the requester can choose to direct the
   replier to cache the reply to all operations after the first
   operation (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or
   csa_cachethis fields of the arguments to SEQUENCE or CB_SEQUENCE.
   The reason it would not direct the replier to cache the entire reply
   is that the request is composed of all idempotent operations [34].
   Caching the reply may offer little benefit.  If the reply is too
   large (see Section 2.10.6.4), it may not be cacheable anyway.  Even
   if the reply to idempotent request is small enough to cache,
   unnecessarily caching the reply slows down the server and increases
   RPC latency.

   Whether or not the requester requests the reply to be cached has no
   effect on the slot processing.  If the results of SEQUENCE or
   CB_SEQUENCE are NFS4_OK, then the slot's sequence ID MUST be
   incremented by one.  If a requester does not direct the replier to
   cache the reply, the replier MUST do one of following:

   o  The replier can cache the entire original reply.  Even though
      sa_cachethis or csa_cachethis is FALSE, the replier is always free
      to cache.  It may choose this approach in order to simplify
      implementation.

   o  The replier enters into its reply cache a reply consisting of the
      original results to the SEQUENCE or CB_SEQUENCE operation, and
      with the next operation in COMPOUND or CB_COMPOUND having the
      error NFS4ERR_RETRY_UNCACHED_REP.  Thus, if the requester later
      retries the request, it will get NFS4ERR_RETRY_UNCACHED_REP.  If a



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      replier receives a retried Sequence operation where the reply to
      the COMPOUND or CB_COMPOUND was not cached, then the replier,

      *  MAY return NFS4ERR_RETRY_UNCACHED_REP in reply to a Sequence
         operation if the Sequence operation is not the first operation
         (granted, a requester that does so is in violation of the
         NFSv4.1 protocol).

      *  MUST NOT return NFS4ERR_RETRY_UNCACHED_REP in reply to a
         Sequence operation if the Sequence operation is the first
         operation.

   o  If the second operation is an illegal operation, or an operation
      that was legal in a previous minor version of NFSv4 and MUST NOT
      be supported in the current minor version (e.g., SETCLIENTID), the
      replier MUST NOT ever return NFS4ERR_RETRY_UNCACHED_REP.  Instead
      the replier MUST return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
      NFS4ERR_NOTSUPP as appropriate.

   o  If the second operation can result in another error status, the
      replier MAY return a status other than NFS4ERR_RETRY_UNCACHED_REP,
      provided the operation is not executed in such a way that the
      state of the replier is changed.  Examples of such an error status
      include: NFS4ERR_NOTSUPP returned for an operation that is legal
      but not REQUIRED in the current minor versions, and thus not
      supported by the replier; NFS4ERR_SEQUENCE_POS; and
      NFS4ERR_REQ_TOO_BIG.

   The discussion above assumes that the retried request matches the
   original one.  Section 2.10.6.1.3.1 discusses what the replier might
   do, and MUST do when original and retried requests do not match.
   Since the replier may only cache a small amount of the information
   that would be required to determine whether this is a case of a false
   retry, the replier may send to the client any of the following
   responses:

   o  The cached reply to the original request (if the replier has
      cached it in its entirety and the users of the original request
      and retry match).

   o  A reply that consists only of the Sequence operation with the
      error NFS4ERR_FALSE_RETRY.

   o  A reply consisting of the response to Sequence with the status
      NFS4_OK, together with the second operation as it appeared in the
      retried request with an error of NFS4ERR_RETRY_UNCACHED_REP or
      other error as described above.




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   o  A reply that consists of the response to Sequence with the status
      NFS4_OK, together with the second operation as it appeared in the
      original request with an error of NFS4ERR_RETRY_UNCACHED_REP or
      other error as described above.

2.10.6.1.3.1.  False Retry

   If a requester sent a Sequence operation with a slot ID and sequence
   ID that are in the reply cache but the replier detected that the
   retried request is not the same as the original request, including a
   retry that has different operations or different arguments in the
   operations from the original and a retry that uses a different
   principal in the RPC request's credential field that translates to a
   different user, then this is a false retry.  When the replier detects
   a false retry, it is permitted (but not always obligated) to return
   NFS4ERR_FALSE_RETRY in response to the Sequence operation when it
   detects a false retry.

   Translations of particularly privileged user values to other users
   due to the lack of appropriately secure credentials, as configured on
   the replier, should be applied before determining whether the users
   are the same or different.  If the replier determines the users are
   different between the original request and a retry, then the replier
   MUST return NFS4ERR_FALSE_RETRY.

   If an operation of the retry is an illegal operation, or an operation
   that was legal in a previous minor version of NFSv4 and MUST NOT be
   supported in the current minor version (e.g., SETCLIENTID), the
   replier MAY return NFS4ERR_FALSE_RETRY (and MUST do so if the users
   of the original request and retry differ).  Otherwise, the replier
   MAY return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or NFS4ERR_NOTSUPP as
   appropriate.  Note that the handling is in contrast for how the
   replier deals with retries requests with no cached reply.  The
   difference is due to NFS4ERR_FALSE_RETRY being a valid error for only
   Sequence operations, whereas NFS4ERR_RETRY_UNCACHED_REP is a valid
   error for all operations except illegal operations and operations
   that MUST NOT be supported in the current minor version of NFSv4.

2.10.6.2.  Retry and Replay of Reply

   A requester MUST NOT retry a request, unless the connection it used
   to send the request disconnects.  The requester can then reconnect
   and re-send the request, or it can re-send the request over a
   different connection that is associated with the same session.

   If the requester is a server wanting to re-send a callback operation
   over the backchannel of a session, the requester of course cannot
   reconnect because only the client can associate connections with the



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   backchannel.  The server can re-send the request over another
   connection that is bound to the same session's backchannel.  If there
   is no such connection, the server MUST indicate that the session has
   no backchannel by setting the SEQ4_STATUS_CB_PATH_DOWN_SESSION flag
   bit in the response to the next SEQUENCE operation from the client.
   The client MUST then associate a connection with the session (or
   destroy the session).

   Note that it is not fatal for a requester to retry without a
   disconnect between the request and retry.  However, the retry does
   consume resources, especially with RDMA, where each request, retry or
   not, consumes a credit.  Retries for no reason, especially retries
   sent shortly after the previous attempt, are a poor use of network
   bandwidth and defeat the purpose of a transport's inherent congestion
   control system.

   A requester MUST wait for a reply to a request before using the slot
   for another request.  If it does not wait for a reply, then the
   requester does not know what sequence ID to use for the slot on its
   next request.  For example, suppose a requester sends a request with
   sequence ID 1, and does not wait for the response.  The next time it
   uses the slot, it sends the new request with sequence ID 2.  If the
   replier has not seen the request with sequence ID 1, then the replier
   is not expecting sequence ID 2, and rejects the requester's new
   request with NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
   CB_SEQUENCE).

   RDMA fabrics do not guarantee that the memory handles (Steering Tags)
   within each RPC/RDMA "chunk" [8] are valid on a scope outside that of
   a single connection.  Therefore, handles used by the direct
   operations become invalid after connection loss.  The server must
   ensure that any RDMA operations that must be replayed from the reply
   cache use the newly provided handle(s) from the most recent request.

   A retry might be sent while the original request is still in progress
   on the replier.  The replier SHOULD deal with the issue by returning
   NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE operation, but
   implementations MAY return NFS4ERR_MISORDERED.  Since errors from
   SEQUENCE and CB_SEQUENCE are never recorded in the reply cache, this
   approach allows the results of the execution of the original request
   to be properly recorded in the reply cache (assuming that the
   requester specified the reply to be cached).

2.10.6.3.  Resolving Server Callback Races

   It is possible for server callbacks to arrive at the client before
   the reply from related fore channel operations.  For example, a
   client may have been granted a delegation to a file it has opened,



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   but the reply to the OPEN (informing the client of the granting of
   the delegation) may be delayed in the network.  If a conflicting
   operation arrives at the server, it will recall the delegation using
   the backchannel, which may be on a different transport connection,
   perhaps even a different network, or even a different session
   associated with the same client ID.

   The presence of a session between the client and server alleviates
   this issue.  When a session is in place, each client request is
   uniquely identified by its { session ID, slot ID, sequence ID }
   triple.  By the rules under which slot entries (reply cache entries)
   are retired, the server has knowledge whether the client has "seen"
   each of the server's replies.  The server can therefore provide
   sufficient information to the client to allow it to disambiguate
   between an erroneous or conflicting callback race condition.

   For each client operation that might result in some sort of server
   callback, the server SHOULD "remember" the { session ID, slot ID,
   sequence ID } triple of the client request until the slot ID
   retirement rules allow the server to determine that the client has,
   in fact, seen the server's reply.  Until the time the { session ID,
   slot ID, sequence ID } request triple can be retired, any recalls of
   the associated object MUST carry an array of these referring
   identifiers (in the CB_SEQUENCE operation's arguments), for the
   benefit of the client.  After this time, it is not necessary for the
   server to provide this information in related callbacks, since it is
   certain that a race condition can no longer occur.

   The CB_SEQUENCE operation that begins each server callback carries a
   list of "referring" { session ID, slot ID, sequence ID } triples.  If
   the client finds the request corresponding to the referring session
   ID, slot ID, and sequence ID to be currently outstanding (i.e., the
   server's reply has not been seen by the client), it can determine
   that the callback has raced the reply, and act accordingly.  If the
   client does not find the request corresponding to the referring
   triple to be outstanding (including the case of a session ID
   referring to a destroyed session), then there is no race with respect
   to this triple.  The server SHOULD limit the referring triples to
   requests that refer to just those that apply to the objects referred
   to in the CB_COMPOUND procedure.

   The client must not simply wait forever for the expected server reply
   to arrive before responding to the CB_COMPOUND that won the race,
   because it is possible that it will be delayed indefinitely.  The
   client should assume the likely case that the reply will arrive
   within the average round-trip time for COMPOUND requests to the
   server, and wait that period of time.  If that period of time
   expires, it can respond to the CB_COMPOUND with NFS4ERR_DELAY.  There



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   are other scenarios under which callbacks may race replies.  Among
   them are pNFS layout recalls as described in Section 12.5.5.2.

2.10.6.4.  COMPOUND and CB_COMPOUND Construction Issues

   Very large requests and replies may pose both buffer management
   issues (especially with RDMA) and reply cache issues.  When the
   session is created (Section 18.36), for each channel (fore and back),
   the client and server negotiate the maximum-sized request they will
   send or process (ca_maxrequestsize), the maximum-sized reply they
   will return or process (ca_maxresponsesize), and the maximum-sized
   reply they will store in the reply cache (ca_maxresponsesize_cached).

   If a request exceeds ca_maxrequestsize, the reply will have the
   status NFS4ERR_REQ_TOO_BIG.  A replier MAY return NFS4ERR_REQ_TOO_BIG
   as the status for the first operation (SEQUENCE or CB_SEQUENCE) in
   the request (which means that no operations in the request executed
   and that the state of the slot in the reply cache is unchanged), or
   it MAY opt to return it on a subsequent operation in the same
   COMPOUND or CB_COMPOUND request (which means that at least one
   operation did execute and that the state of the slot in the reply
   cache does change).  The replier SHOULD set NFS4ERR_REQ_TOO_BIG on
   the operation that exceeds ca_maxrequestsize.

   If a reply exceeds ca_maxresponsesize, the reply will have the status
   NFS4ERR_REP_TOO_BIG.  A replier MAY return NFS4ERR_REP_TOO_BIG as the
   status for the first operation (SEQUENCE or CB_SEQUENCE) in the
   request, or it MAY opt to return it on a subsequent operation (in the
   same COMPOUND or CB_COMPOUND reply).  A replier MAY return
   NFS4ERR_REP_TOO_BIG in the reply to SEQUENCE or CB_SEQUENCE, even if
   the response would still exceed ca_maxresponsesize.

   If sa_cachethis or csa_cachethis is TRUE, then the replier MUST cache
   a reply except if an error is returned by the SEQUENCE or CB_SEQUENCE
   operation (see Section 2.10.6.1.2).  If the reply exceeds
   ca_maxresponsesize_cached (and sa_cachethis or csa_cachethis is
   TRUE), then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE.
   Even if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that
   matter) is returned on an operation other than the first operation
   (SEQUENCE or CB_SEQUENCE), then the reply MUST be cached if
   sa_cachethis or csa_cachethis is TRUE.  For example, if a COMPOUND
   has eleven operations, including SEQUENCE, the fifth operation is a
   RENAME, and the tenth operation is a READ for one million bytes, the
   server may return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth
   operation.  Since the server executed several operations, especially
   the non-idempotent RENAME, the client's request to cache the reply
   needs to be honored in order for the correct operation of exactly
   once semantics.  If the client retries the request, the server will



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   have cached a reply that contains results for ten of the eleven
   requested operations, with the tenth operation having a status of
   NFS4ERR_REP_TOO_BIG_TO_CACHE.

   A client needs to take care that when sending operations that change
   the current filehandle (except for PUTFH, PUTPUBFH, PUTROOTFH, and
   RESTOREFH), it not exceed the maximum reply buffer before the GETFH
   operation.  Otherwise, the client will have to retry the operation
   that changed the current filehandle, in order to obtain the desired
   filehandle.  For the OPEN operation (see Section 18.16), retry is not
   always available as an option.  The following guidelines for the
   handling of filehandle-changing operations are advised:

   o  Within the same COMPOUND procedure, a client SHOULD send GETFH
      immediately after a current filehandle-changing operation.  A
      client MUST send GETFH after a current filehandle-changing
      operation that is also non-idempotent (e.g., the OPEN operation),
      unless the operation is RESTOREFH.  RESTOREFH is an exception,
      because even though it is non-idempotent, the filehandle RESTOREFH
      produced originated from an operation that is either idempotent
      (e.g., PUTFH, LOOKUP), or non-idempotent (e.g., OPEN, CREATE).  If
      the origin is non-idempotent, then because the client MUST send
      GETFH after the origin operation, the client can recover if
      RESTOREFH returns an error.

   o  A server MAY return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle-changing operation if the reply would be too large on
      the next operation.

   o  A server SHOULD return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle-changing, non-idempotent operation if the reply would
      be too large on the next operation, especially if the operation is
      OPEN.

   o  A server MAY return NFS4ERR_UNSAFE_COMPOUND to a non-idempotent
      current filehandle-changing operation, if it looks at the next
      operation (in the same COMPOUND procedure) and finds it is not
      GETFH.  The server SHOULD do this if it is unable to determine in
      advance whether the total response size would exceed
      ca_maxresponsesize_cached or ca_maxresponsesize.

2.10.6.5.  Persistence

   Since the reply cache is bounded, it is practical for the reply cache
   to persist across server restarts.  The replier MUST persist the
   following information if it agreed to persist the session (when the



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   session was created; see Section 18.36):

   o  The session ID.

   o  The slot table including the sequence ID and cached reply for each
      slot.

   The above are sufficient for a replier to provide EOS semantics for
   any requests that were sent and executed before the server restarted.
   If the replier is a client, then there is no need for it to persist
   any more information, unless the client will be persisting all other
   state across client restart, in which case, the server will never see
   any NFSv4.1-level protocol manifestation of a client restart.  If the
   replier is a server, with just the slot table and session ID
   persisting, any requests the client retries after the server restart
   will return the results that are cached in the reply cache, and any
   new requests (i.e., the sequence ID is one greater than the slot's
   sequence ID) MUST be rejected with NFS4ERR_DEADSESSION (returned by
   SEQUENCE).  Such a session is considered dead.  A server MAY re-
   animate a session after a server restart so that the session will
   accept new requests as well as retries.  To re-animate a session, the
   server needs to persist additional information through server
   restart:

   o  The client ID.  This is a prerequisite to let the client create
      more sessions associated with the same client ID as the re-
      animated session.

   o  The client ID's sequence ID that is used for creating sessions
      (see Sections 18.35 and 18.36).  This is a prerequisite to let the
      client create more sessions.

   o  The principal that created the client ID.  This allows the server
      to authenticate the client when it sends EXCHANGE_ID.

   o  The SSV, if SP4_SSV state protection was specified when the client
      ID was created (see Section 18.35).  This lets the client create
      new sessions, and associate connections with the new and existing
      sessions.

   o  The properties of the client ID as defined in Section 18.35.

   A persistent reply cache places certain demands on the server.  The
   execution of the sequence of operations (starting with SEQUENCE) and
   placement of its results in the persistent cache MUST be atomic.  If
   a client retries a sequence of operations that was previously
   executed on the server, the only acceptable outcomes are either the
   original cached reply or an indication that the client ID or session



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   has been lost (indicating a catastrophic loss of the reply cache or a
   session that has been deleted because the client failed to use the
   session for an extended period of time).

   A server could fail and restart in the middle of a COMPOUND procedure
   that contains one or more non-idempotent or idempotent-but-modifying
   operations.  This creates an even higher challenge for atomic
   execution and placement of results in the reply cache.  One way to
   view the problem is as a single transaction consisting of each
   operation in the COMPOUND followed by storing the result in
   persistent storage, then finally a transaction commit.  If there is a
   failure before the transaction is committed, then the server rolls
   back the transaction.  If the server itself fails, then when it
   restarts, its recovery logic could roll back the transaction before
   starting the NFSv4.1 server.

   While the description of the implementation for atomic execution of
   the request and caching of the reply is beyond the scope of this
   document, an example implementation for NFSv2 [38] is described in
   [39].

2.10.7.  RDMA Considerations

   A complete discussion of the operation of RPC-based protocols over
   RDMA transports is in [8].  A discussion of the operation of NFSv4,
   including NFSv4.1, over RDMA is in [9].  Where RDMA is considered,
   this specification assumes the use of such a layering; it addresses
   only the upper-layer issues relevant to making best use of RPC/RDMA.

2.10.7.1.  RDMA Connection Resources

   RDMA requires its consumers to register memory and post buffers of a
   specific size and number for receive operations.

   Registration of memory can be a relatively high-overhead operation,
   since it requires pinning of buffers, assignment of attributes (e.g.,
   readable/writable), and initialization of hardware translation.
   Preregistration is desirable to reduce overhead.  These registrations
   are specific to hardware interfaces and even to RDMA connection
   endpoints; therefore, negotiation of their limits is desirable to
   manage resources effectively.

   Following basic registration, these buffers must be posted by the RPC
   layer to handle receives.  These buffers remain in use by the RPC/
   NFSv4.1 implementation; the size and number of them must be known to
   the remote peer in order to avoid RDMA errors that would cause a
   fatal error on the RDMA connection.




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   NFSv4.1 manages slots as resources on a per-session basis (see
   Section 2.10), while RDMA connections manage credits on a per-
   connection basis.  This means that in order for a peer to send data
   over RDMA to a remote buffer, it has to have both an NFSv4.1 slot and
   an RDMA credit.  If multiple RDMA connections are associated with a
   session, then if the total number of credits across all RDMA
   connections associated with the session is X, and the number of slots
   in the session is Y, then the maximum number of outstanding requests
   is the lesser of X and Y.

2.10.7.2.  Flow Control

   Previous versions of NFS do not provide flow control; instead, they
   rely on the windowing provided by transports like TCP to throttle
   requests.  This does not work with RDMA, which provides no operation
   flow control and will terminate a connection in error when limits are
   exceeded.  Limits such as maximum number of requests outstanding are
   therefore negotiated when a session is created (see the
   ca_maxrequests field in Section 18.36).  These limits then provide
   the maxima within which each connection associated with the session's
   channel(s) must remain.  RDMA connections are managed within these
   limits as described in Section 3.3 of [8]; if there are multiple RDMA
   connections, then the maximum number of requests for a channel will
   be divided among the RDMA connections.  Put a different way, the onus
   is on the replier to ensure that the total number of RDMA credits
   across all connections associated with the replier's channel does
   exceed the channel's maximum number of outstanding requests.

   The limits may also be modified dynamically at the replier's choosing
   by manipulating certain parameters present in each NFSv4.1 reply.  In
   addition, the CB_RECALL_SLOT callback operation (see Section 20.8)
   can be sent by a server to a client to return RDMA credits to the
   server, thereby lowering the maximum number of requests a client can
   have outstanding to the server.

2.10.7.3.  Padding

   Header padding is requested by each peer at session initiation (see
   the ca_headerpadsize argument to CREATE_SESSION in Section 18.36),
   and subsequently used by the RPC RDMA layer, as described in [8].
   Zero padding is permitted.

   Padding leverages the useful property that RDMA preserve alignment of
   data, even when they are placed into anonymous (untagged) buffers.
   If requested, client inline writes will insert appropriate pad bytes
   within the request header to align the data payload on the specified
   boundary.  The client is encouraged to add sufficient padding (up to
   the negotiated size) so that the "data" field of the WRITE operation



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   is aligned.  Most servers can make good use of such padding, which
   allows them to chain receive buffers in such a way that any data
   carried by client requests will be placed into appropriate buffers at
   the server, ready for file system processing.  The receiver's RPC
   layer encounters no overhead from skipping over pad bytes, and the
   RDMA layer's high performance makes the insertion and transmission of
   padding on the sender a significant optimization.  In this way, the
   need for servers to perform RDMA Read to satisfy all but the largest
   client writes is obviated.  An added benefit is the reduction of
   message round trips on the network -- a potentially good trade, where
   latency is present.

   The value to choose for padding is subject to a number of criteria.
   A primary source of variable-length data in the RPC header is the
   authentication information, the form of which is client-determined,
   possibly in response to server specification.  The contents of
   COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
   go into the determination of a maximal NFSv4.1 request size and
   therefore minimal buffer size.  The client must select its offered
   value carefully, so as to avoid overburdening the server, and vice
   versa.  The benefit of an appropriate padding value is higher
   performance.

                    Sender gather:
        |RPC Request|Pad  bytes|Length| -> |User data...|
        \------+----------------------/      \
                \                             \
                 \    Receiver scatter:        \-----------+- ...
            /-----+----------------\            \           \
            |RPC Request|Pad|Length|   ->  |FS buffer|->|FS buffer|->...

   In the above case, the server may recycle unused buffers to the next
   posted receive if unused by the actual received request, or may pass
   the now-complete buffers by reference for normal write processing.
   For a server that can make use of it, this removes any need for data
   copies of incoming data, without resorting to complicated end-to-end
   buffer advertisement and management.  This includes most kernel-based
   and integrated server designs, among many others.  The client may
   perform similar optimizations, if desired.

2.10.7.4.  Dual RDMA and Non-RDMA Transports

   Some RDMA transports (e.g., RFC 5040 [10]) permit a "streaming" (non-
   RDMA) phase, where ordinary traffic might flow before "stepping up"
   to RDMA mode, commencing RDMA traffic.  Some RDMA transports start
   connections always in RDMA mode.  NFSv4.1 allows, but does not
   assume, a streaming phase before RDMA mode.  When a connection is
   associated with a session, the client and server negotiate whether



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   the connection is used in RDMA or non-RDMA mode (see Sections 18.36
   and 18.34).

2.10.8.  Session Security

2.10.8.1.  Session Callback Security

   Via session/connection association, NFSv4.1 improves security over
   that provided by NFSv4.0 for the backchannel.  The connection is
   client-initiated (see Section 18.34) and subject to the same firewall
   and routing checks as the fore channel.  At the client's option (see
   Section 18.35), connection association is fully authenticated before
   being activated (see Section 18.34).  Traffic from the server over
   the backchannel is authenticated exactly as the client specifies (see
   Section 2.10.8.2).

2.10.8.2.  Backchannel RPC Security

   When the NFSv4.1 client establishes the backchannel, it informs the
   server of the security flavors and principals to use when sending
   requests.  If the security flavor is RPCSEC_GSS, the client expresses
   the principal in the form of an established RPCSEC_GSS context.  The
   server is free to use any of the flavor/principal combinations the
   client offers, but it MUST NOT use unoffered combinations.  This way,
   the client need not provide a target GSS principal for the
   backchannel as it did with NFSv4.0, nor does the server have to
   implement an RPCSEC_GSS initiator as it did with NFSv4.0 [30].

   The CREATE_SESSION (Section 18.36) and BACKCHANNEL_CTL
   (Section 18.33) operations allow the client to specify flavor/
   principal combinations.

   Also note that the SP4_SSV state protection mode (see Sections 18.35
   and 2.10.8.3) has the side benefit of providing SSV-derived
   RPCSEC_GSS contexts (Section 2.10.9).

2.10.8.3.  Protection from Unauthorized State Changes

   As described to this point in the specification, the state model of
   NFSv4.1 is vulnerable to an attacker that sends a SEQUENCE operation
   with a forged session ID and with a slot ID that it expects the
   legitimate client to use next.  When the legitimate client uses the
   slot ID with the same sequence number, the server returns the
   attacker's result from the reply cache, which disrupts the legitimate
   client and thus denies service to it.  Similarly, an attacker could
   send a CREATE_SESSION with a forged client ID to create a new session
   associated with the client ID.  The attacker could send requests
   using the new session that change locking state, such as LOCKU



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   operations to release locks the legitimate client has acquired.
   Setting a security policy on the file that requires RPCSEC_GSS
   credentials when manipulating the file's state is one potential work
   around, but has the disadvantage of preventing a legitimate client
   from releasing state when RPCSEC_GSS is required to do so, but a GSS
   context cannot be obtained (possibly because the user has logged off
   the client).

   NFSv4.1 provides three options to a client for state protection,
   which are specified when a client creates a client ID via EXCHANGE_ID
   (Section 18.35).

   The first (SP4_NONE) is to simply waive state protection.

   The other two options (SP4_MACH_CRED and SP4_SSV) share several
   traits:

   o  An RPCSEC_GSS-based credential is used to authenticate client ID
      and session maintenance operations, including creating and
      destroying a session, associating a connection with the session,
      and destroying the client ID.

   o  Because RPCSEC_GSS is used to authenticate client ID and session
      maintenance, the attacker cannot associate a rogue connection with
      a legitimate session, or associate a rogue session with a
      legitimate client ID in order to maliciously alter the client ID's
      lock state via CLOSE, LOCKU, DELEGRETURN, LAYOUTRETURN, etc.

   o  In cases where the server's security policies on a portion of its
      namespace require RPCSEC_GSS authentication, a client may have to
      use an RPCSEC_GSS credential to remove per-file state (e.g.,
      LOCKU, CLOSE, etc.).  The server may require that the principal
      that removes the state match certain criteria (e.g., the principal
      might have to be the same as the one that acquired the state).
      However, the client might not have an RPCSEC_GSS context for such
      a principal, and might not be able to create such a context
      (perhaps because the user has logged off).  When the client
      establishes SP4_MACH_CRED or SP4_SSV protection, it can specify a
      list of operations that the server MUST allow using the machine
      credential (if SP4_MACH_CRED is used) or the SSV credential (if
      SP4_SSV is used).

   The SP4_MACH_CRED state protection option uses a machine credential
   where the principal that creates the client ID MUST also be the
   principal that performs client ID and session maintenance operations.
   The security of the machine credential state protection approach
   depends entirely on safe guarding the per-machine credential.
   Assuming a proper safeguard using the per-machine credential for



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   operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
   DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker from
   associating a rogue connection with a session, or associating a rogue
   session with a client ID.

   There are at least three scenarios for the SP4_MACH_CRED option:

   1.  The system administrator configures a unique, permanent per-
       machine credential for one of the mandated GSS mechanisms (e.g.,
       if Kerberos V5 is used, a "keytab" containing a principal derived
       from a client host name could be used).

   2.  The client is used by a single user, and so the client ID and its
       sessions are used by just that user.  If the user's credential
       expires, then session and client ID maintenance cannot occur, but
       since the client has a single user, only that user is
       inconvenienced.

   3.  The physical client has multiple users, but the client
       implementation has a unique client ID for each user.  This is
       effectively the same as the second scenario, but a disadvantage
       is that each user needs to be allocated at least one session
       each, so the approach suffers from lack of economy.

   The SP4_SSV protection option uses the SSV (Section 1.6), via
   RPCSEC_GSS and the SSV GSS mechanism (Section 2.10.9), to protect
   state from attack.  The SP4_SSV protection option is intended for the
   situation comprised of a client that has multiple active users and a
   system administrator who wants to avoid the burden of installing a
   permanent machine credential on each client.  The SSV is established
   and updated on the server via SET_SSV (see Section 18.47).  To
   prevent eavesdropping, a client SHOULD send SET_SSV via RPCSEC_GSS
   with the privacy service.  Several aspects of the SSV make it
   intractable for an attacker to guess the SSV, and thus associate
   rogue connections with a session, and rogue sessions with a client
   ID:

   o  The arguments to and results of SET_SSV include digests of the old
      and new SSV, respectively.

   o  Because the initial value of the SSV is zero, therefore known, the
      client that opts for SP4_SSV protection and opts to apply SP4_SSV
      protection to BIND_CONN_TO_SESSION and CREATE_SESSION MUST send at
      least one SET_SSV operation before the first BIND_CONN_TO_SESSION
      operation or before the second CREATE_SESSION operation on a
      client ID.  If it does not, the SSV mechanism will not generate
      tokens (Section 2.10.9).  A client SHOULD send SET_SSV as soon as
      a session is created.



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   o  A SET_SSV request does not replace the SSV with the argument to
      SET_SSV.  Instead, the current SSV on the server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.  Each time a
      new principal uses a client ID for the first time, the client
      SHOULD send a SET_SSV with that principal's RPCSEC_GSS
      credentials, with RPCSEC_GSS service set to RPC_GSS_SVC_PRIVACY.

   Here are the types of attacks that can be attempted by an attacker
   named Eve on a victim named Bob, and how SP4_SSV protection foils
   each attack:

   o  Suppose Eve is the first user to log into a legitimate client.
      Eve's use of an NFSv4.1 file system will cause the legitimate
      client to create a client ID with SP4_SSV protection, specifying
      that the BIND_CONN_TO_SESSION operation MUST use the SSV
      credential.  Eve's use of the file system also causes an SSV to be
      created.  The SET_SSV operation that creates the SSV will be
      protected by the RPCSEC_GSS context created by the legitimate
      client, which uses Eve's GSS principal and credentials.  Eve can
      eavesdrop on the network while her RPCSEC_GSS context is created
      and the SET_SSV using her context is sent.  Even if the legitimate
      client sends the SET_SSV with RPC_GSS_SVC_PRIVACY, because Eve
      knows her own credentials, she can decrypt the SSV.  Eve can
      compute an RPCSEC_GSS credential that BIND_CONN_TO_SESSION will
      accept, and so associate a new connection with the legitimate
      session.  Eve can change the slot ID and sequence state of a
      legitimate session, and/or the SSV state, in such a way that when
      Bob accesses the server via the same legitimate client, the
      legitimate client will be unable to use the session.

      The client's only recourse is to create a new client ID for Bob to
      use, and establish a new SSV for the client ID.  The client will
      be unable to delete the old client ID, and will let the lease on
      the old client ID expire.

      Once the legitimate client establishes an SSV over the new session
      using Bob's RPCSEC_GSS context, Eve can use the new session via
      the legitimate client, but she cannot disrupt Bob. Moreover,
      because the client SHOULD have modified the SSV due to Eve using
      the new session, Bob cannot get revenge on Eve by associating a
      rogue connection with the session.

      The question is how did the legitimate client detect that Eve has
      hijacked the old session?  When the client detects that a new
      principal, Bob, wants to use the session, it SHOULD have sent a
      SET_SSV, which leads to the following sub-scenarios:





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      *  Let us suppose that from the rogue connection, Eve sent a
         SET_SSV with the same slot ID and sequence ID that the
         legitimate client later uses.  The server will assume the
         SET_SSV sent with Bob's credentials is a retry, and return to
         the legitimate client the reply it sent Eve. However, unless
         Eve can correctly guess the SSV the legitimate client will use,
         the digest verification checks in the SET_SSV response will
         fail.  That is an indication to the client that the session has
         apparently been hijacked.


      *  Alternatively, Eve sent a SET_SSV with a different slot ID than
         the legitimate client uses for its SET_SSV.  Then the digest
         verification of the SET_SSV sent with Bob's credentials fails
         on the server, and the error returned to the client makes it
         apparent that the session has been hijacked.


      *  Alternatively, Eve sent an operation other than SET_SSV, but
         with the same slot ID and sequence that the legitimate client
         uses for its SET_SSV.  The server returns to the legitimate
         client the response it sent Eve. The client sees that the
         response is not at all what it expects.  The client assumes
         either session hijacking or a server bug, and either way
         destroys the old session.


   o  Eve associates a rogue connection with the session as above, and
      then destroys the session.  Again, Bob goes to use the server from
      the legitimate client, which sends a SET_SSV using Bob's
      credentials.  The client receives an error that indicates that the
      session does not exist.  When the client tries to create a new
      session, this will fail because the SSV it has does not match that
      which the server has, and now the client knows the session was
      hijacked.  The legitimate client establishes a new client ID.


   o  If Eve creates a connection before the legitimate client
      establishes an SSV, because the initial value of the SSV is zero
      and therefore known, Eve can send a SET_SSV that will pass the
      digest verification check.  However, because the new connection
      has not been associated with the session, the SET_SSV is rejected
      for that reason.


   In summary, an attacker's disruption of state when SP4_SSV protection
   is in use is limited to the formative period of a client ID, its
   first session, and the establishment of the SSV.  Once a non-



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   malicious user uses the client ID, the client quickly detects any
   hijack and rectifies the situation.  Once a non-malicious user
   successfully modifies the SSV, the attacker cannot use NFSv4.1
   operations to disrupt the non-malicious user.

   Note that neither the SP4_MACH_CRED nor SP4_SSV protection approaches
   prevent hijacking of a transport connection that has previously been
   associated with a session.  If the goal of a counter-threat strategy
   is to prevent connection hijacking, the use of IPsec is RECOMMENDED.

   If a connection hijack occurs, the hijacker could in theory change
   locking state and negatively impact the service to legitimate
   clients.  However, if the server is configured to require the use of
   RPCSEC_GSS with integrity or privacy on the affected file objects,
   and if EXCHGID4_FLAG_BIND_PRINC_STATEID capability (Section 18.35) is
   in force, this will thwart unauthorized attempts to change locking
   state.

2.10.9.  The Secret State Verifier (SSV) GSS Mechanism

   The SSV provides the secret key for a GSS mechanism internal to
   NFSv4.1 that NFSv4.1 uses for state protection.  Contexts for this
   mechanism are not established via the RPCSEC_GSS protocol.  Instead,
   the contexts are automatically created when EXCHANGE_ID specifies
   SP4_SSV protection.  The only tokens defined are the PerMsgToken
   (emitted by GSS_GetMIC) and the SealedMessage token (emitted by
   GSS_Wrap).

   The mechanism OID for the SSV mechanism is
   iso.org.dod.internet.private.enterprise.Michael Eisler.nfs.ssv_mech
   (1.3.6.1.4.1.28882.1.1).  While the SSV mechanism does not define any
   initial context tokens, the OID can be used to let servers indicate
   that the SSV mechanism is acceptable whenever the client sends a
   SECINFO or SECINFO_NO_NAME operation (see Section 2.6).

   The SSV mechanism defines four subkeys derived from the SSV value.
   Each time SET_SSV is invoked, the subkeys are recalculated by the
   client and server.  The calculation of each of the four subkeys
   depends on each of the four respective ssv_subkey4 enumerated values.
   The calculation uses the HMAC [11] algorithm, using the current SSV
   as the key, the one-way hash algorithm as negotiated by EXCHANGE_ID,
   and the input text as represented by the XDR encoded enumeration
   value for that subkey of data type ssv_subkey4.  If the length of the
   output of the HMAC algorithm exceeds the length of key of the
   encryption algorithm (which is also negotiated by EXCHANGE_ID), then
   the subkey MUST be truncated from the HMAC output, i.e., if the
   subkey is of N bytes long, then the first N bytes of the HMAC output
   MUST be used for the subkey.  The specification of EXCHANGE_ID states



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   that the length of the output of the HMAC algorithm MUST NOT be less
   than the length of subkey needed for the encryption algorithm (see
   Section 18.35).


   /* Input for computing subkeys */
   enum ssv_subkey4 {
           SSV4_SUBKEY_MIC_I2T     = 1,
           SSV4_SUBKEY_MIC_T2I     = 2,
           SSV4_SUBKEY_SEAL_I2T    = 3,
           SSV4_SUBKEY_SEAL_T2I    = 4
   };


   The subkey derived from SSV4_SUBKEY_MIC_I2T is used for calculating
   message integrity codes (MICs) that originate from the NFSv4.1
   client, whether as part of a request over the fore channel or a
   response over the backchannel.  The subkey derived from
   SSV4_SUBKEY_MIC_T2I is used for MICs originating from the NFSv4.1
   server.  The subkey derived from SSV4_SUBKEY_SEAL_I2T is used for
   encryption text originating from the NFSv4.1 client, and the subkey
   derived from SSV4_SUBKEY_SEAL_T2I is used for encryption text
   originating from the NFSv4.1 server.

   The PerMsgToken description is based on an XDR definition:


   /* Input for computing smt_hmac */
   struct ssv_mic_plain_tkn4 {
     uint32_t        smpt_ssv_seq;
     opaque          smpt_orig_plain<>;
   };




   /* SSV GSS PerMsgToken token */
   struct ssv_mic_tkn4 {
     uint32_t        smt_ssv_seq;
     opaque          smt_hmac<>;
   };


   The field smt_hmac is an HMAC calculated by using the subkey derived
   from SSV4_SUBKEY_MIC_I2T or SSV4_SUBKEY_MIC_T2I as the key, the one-
   way hash algorithm as negotiated by EXCHANGE_ID, and the input text
   as represented by data of type ssv_mic_plain_tkn4.  The field
   smpt_ssv_seq is the same as smt_ssv_seq.  The field smpt_orig_plain



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   is the "message" input passed to GSS_GetMIC() (see Section 2.3.1 of
   [7]).  The caller of GSS_GetMIC() provides a pointer to a buffer
   containing the plain text.  The SSV mechanism's entry point for
   GSS_GetMIC() encodes this into an opaque array, and the encoding will
   include an initial four-byte length, plus any necessary padding.
   Prepended to this will be the XDR encoded value of smpt_ssv_seq, thus
   making up an XDR encoding of a value of data type ssv_mic_plain_tkn4,
   which in turn is the input into the HMAC.

   The token emitted by GSS_GetMIC() is XDR encoded and of XDR data type
   ssv_mic_tkn4.  The field smt_ssv_seq comes from the SSV sequence
   number, which is equal to one after SET_SSV (Section 18.47) is called
   the first time on a client ID.  Thereafter, the SSV sequence number
   is incremented on each SET_SSV.  Thus, smt_ssv_seq represents the
   version of the SSV at the time GSS_GetMIC() was called.  As noted in
   Section 18.35, the client and server can maintain multiple concurrent
   versions of the SSV.  This allows the SSV to be changed without
   serializing all RPC calls that use the SSV mechanism with SET_SSV
   operations.  Once the HMAC is calculated, it is XDR encoded into
   smt_hmac, which will include an initial four-byte length, and any
   necessary padding.  Prepended to this will be the XDR encoded value
   of smt_ssv_seq.

   The SealedMessage description is based on an XDR definition:


   /* Input for computing ssct_encr_data and ssct_hmac */
   struct ssv_seal_plain_tkn4 {
     opaque          sspt_confounder<>;
     uint32_t        sspt_ssv_seq;
     opaque          sspt_orig_plain<>;
     opaque          sspt_pad<>;
   };




   /* SSV GSS SealedMessage token */
   struct ssv_seal_cipher_tkn4 {
     uint32_t      ssct_ssv_seq;
     opaque        ssct_iv<>;
     opaque        ssct_encr_data<>;
     opaque        ssct_hmac<>;
   };


   The token emitted by GSS_Wrap() is XDR encoded and of XDR data type
   ssv_seal_cipher_tkn4.



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   The ssct_ssv_seq field has the same meaning as smt_ssv_seq.

   The ssct_encr_data field is the result of encrypting a value of the
   XDR encoded data type ssv_seal_plain_tkn4.  The encryption key is the
   subkey derived from SSV4_SUBKEY_SEAL_I2T or SSV4_SUBKEY_SEAL_T2I, and
   the encryption algorithm is that negotiated by EXCHANGE_ID.

   The ssct_iv field is the initialization vector (IV) for the
   encryption algorithm (if applicable) and is sent in clear text.  The
   content and size of the IV MUST comply with the specification of the
   encryption algorithm.  For example, the id-aes256-CBC algorithm MUST
   use a 16-byte initialization vector (IV), which MUST be unpredictable
   for each instance of a value of data type ssv_seal_plain_tkn4 that is
   encrypted with a particular SSV key.

   The ssct_hmac field is the result of computing an HMAC using the
   value of the XDR encoded data type ssv_seal_plain_tkn4 as the input
   text.  The key is the subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I, and the one-way hash algorithm is that
   negotiated by EXCHANGE_ID.

   The sspt_confounder field is a random value.

   The sspt_ssv_seq field is the same as ssvt_ssv_seq.

   The field sspt_orig_plain field is the original plaintext and is the
   "input_message" input passed to GSS_Wrap() (see Section 2.3.3 of
   [7]).  As with the handling of the plaintext by the SSV mechanism's
   GSS_GetMIC() entry point, the entry point for GSS_Wrap() expects a
   pointer to the plaintext, and will XDR encode an opaque array into
   sspt_orig_plain representing the plain text, along with the other
   fields of an instance of data type ssv_seal_plain_tkn4.

   The sspt_pad field is present to support encryption algorithms that
   require inputs to be in fixed-sized blocks.  The content of sspt_pad
   is zero filled except for the length.  Beware that the XDR encoding
   of ssv_seal_plain_tkn4 contains three variable-length arrays, and so
   each array consumes four bytes for an array length, and each array
   that follows the length is always padded to a multiple of four bytes
   per the XDR standard.

   For example, suppose the encryption algorithm uses 16-byte blocks,
   and the sspt_confounder is three bytes long, and the sspt_orig_plain
   field is 15 bytes long.  The XDR encoding of sspt_confounder uses
   eight bytes (4 + 3 + 1 byte pad), the XDR encoding of sspt_ssv_seq
   uses four bytes, the XDR encoding of sspt_orig_plain uses 20 bytes (4
   + 15 + 1 byte pad), and the smallest XDR encoding of the sspt_pad
   field is four bytes.  This totals 36 bytes.  The next multiple of 16



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   is 48; thus, the length field of sspt_pad needs to be set to 12
   bytes, or a total encoding of 16 bytes.  The total number of XDR
   encoded bytes is thus 8 + 4 + 20 + 16 = 48.

   GSS_Wrap() emits a token that is an XDR encoding of a value of data
   type ssv_seal_cipher_tkn4.  Note that regardless of whether or not
   the caller of GSS_Wrap() requests confidentiality, the token always
   has confidentiality.  This is because the SSV mechanism is for
   RPCSEC_GSS, and RPCSEC_GSS never produces GSS_wrap() tokens without
   confidentiality.

   There is one SSV per client ID.  There is a single GSS context for a
   client ID / SSV pair.  All SSV mechanism RPCSEC_GSS handles of a
   client ID / SSV pair share the same GSS context.  SSV GSS contexts do
   not expire except when the SSV is destroyed (causes would include the
   client ID being destroyed or a server restart).  Since one purpose of
   context expiration is to replace keys that have been in use for "too
   long", hence vulnerable to compromise by brute force or accident, the
   client can replace the SSV key by sending periodic SET_SSV
   operations, which is done by cycling through different users'
   RPCSEC_GSS credentials.  This way, the SSV is replaced without
   destroying the SSV's GSS contexts.

   SSV RPCSEC_GSS handles can be expired or deleted by the server at any
   time, and the EXCHANGE_ID operation can be used to create more SSV
   RPCSEC_GSS handles.  Expiration of SSV RPCSEC_GSS handles does not
   imply that the SSV or its GSS context has expired.

   The client MUST establish an SSV via SET_SSV before the SSV GSS
   context can be used to emit tokens from GSS_Wrap() and GSS_GetMIC().
   If SET_SSV has not been successfully called, attempts to emit tokens
   MUST fail.

   The SSV mechanism does not support replay detection and sequencing in
   its tokens because RPCSEC_GSS does not use those features (See
   Section 5.2.2, "Context Creation Requests", in [4]).  However,
   Section 2.10.10 discusses special considerations for the SSV
   mechanism when used with RPCSEC_GSS.

2.10.10.  Security Considerations for RPCSEC_GSS When Using the SSV
          Mechanism

   When a client ID is created with SP4_SSV state protection (see
   Section 18.35), the client is permitted to associate multiple
   RPCSEC_GSS handles with the single SSV GSS context (see
   Section 2.10.9).  Because of the way RPCSEC_GSS (both version 1 and
   version 2, see [4] and [12]) calculate the verifier of the reply,
   special care must be taken by the implementation of the NFSv4.1



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   client to prevent attacks by a man-in-the-middle.  The verifier of an
   RPCSEC_GSS reply is the output of GSS_GetMIC() applied to the input
   value of the seq_num field of the RPCSEC_GSS credential (data type
   rpc_gss_cred_ver_1_t) (see Section 5.3.3.2 of [4]).  If multiple
   RPCSEC_GSS handles share the same GSS context, then if one handle is
   used to send a request with the same seq_num value as another handle,
   an attacker could block the reply, and replace it with the verifier
   used for the other handle.

   There are multiple ways to prevent the attack on the SSV RPCSEC_GSS
   verifier in the reply.  The simplest is believed to be as follows.

   o  Each time one or more new SSV RPCSEC_GSS handles are created via
      EXCHANGE_ID, the client SHOULD send a SET_SSV operation to modify
      the SSV.  By changing the SSV, the new handles will not result in
      the re-use of an SSV RPCSEC_GSS verifier in a reply.

   o  When a requester decides to use N SSV RPCSEC_GSS handles, it
      SHOULD assign a unique and non-overlapping range of seq_nums to
      each SSV RPCSEC_GSS handle.  The size of each range SHOULD be
      equal to MAXSEQ / N (see Section 5 of [4] for the definition of
      MAXSEQ).  When an SSV RPCSEC_GSS handle reaches its maximum, it
      SHOULD force the replier to destroy the handle by sending a NULL
      RPC request with seq_num set to MAXSEQ + 1 (see Section 5.3.3.3 of
      [4]).

   o  When the requester wants to increase or decrease N, it SHOULD
      force the replier to destroy all N handles by sending a NULL RPC
      request on each handle with seq_num set to MAXSEQ + 1.  If the
      requester is the client, it SHOULD send a SET_SSV operation before
      using new handles.  If the requester is the server, then the
      client SHOULD send a SET_SSV operation when it detects that the
      server has forced it to destroy a backchannel's SSV RPCSEC_GSS
      handle.  By sending a SET_SSV operation, the SSV will change, and
      so the attacker will be unavailable to successfully replay a
      previous verifier in a reply to the requester.

   Note that if the replier carefully creates the SSV RPCSEC_GSS
   handles, the related risk of a man-in-the-middle splicing a forged
   SSV RPCSEC_GSS credential with a verifier for another handle does not
   exist.  This is because the verifier in an RPCSEC_GSS request is
   computed from input that includes both the RPCSEC_GSS handle and
   seq_num (see Section 5.3.1 of [4]).  Provided the replier takes care
   to avoid re-using the value of an RPCSEC_GSS handle that it creates,
   such as by including a generation number in the handle, the man-in-
   the-middle will not be able to successfully replay a previous
   verifier in the request to a replier.




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2.10.11.  Session Mechanics - Steady State

2.10.11.1.  Obligations of the Server

   The server has the primary obligation to monitor the state of
   backchannel resources that the client has created for the server
   (RPCSEC_GSS contexts and backchannel connections).  If these
   resources vanish, the server takes action as specified in
   Section 2.10.13.2.

2.10.11.2.  Obligations of the Client

   The client SHOULD honor the following obligations in order to utilize
   the session:

   o  Keep a necessary session from going idle on the server.  A client
      that requires a session but nonetheless is not sending operations
      risks having the session be destroyed by the server.  This is
      because sessions consume resources, and resource limitations may
      force the server to cull an inactive session.  A server MAY
      consider a session to be inactive if the client has not used the
      session before the session inactivity timer (Section 2.10.12) has
      expired.

   o  Destroy the session when not needed.  If a client has multiple
      sessions, one of which has no requests waiting for replies, and
      has been idle for some period of time, it SHOULD destroy the
      session.

   o  Maintain GSS contexts and RPCSEC_GSS handles for the backchannel.
      If the client requires the server to use the RPCSEC_GSS security
      flavor for callbacks, then it needs to be sure the RPCSEC_GSS
      handles and/or their GSS contexts that are handed to the server
      via BACKCHANNEL_CTL or CREATE_SESSION are unexpired.

   o  Preserve a connection for a backchannel.  The server requires a
      backchannel in order to gracefully recall recallable state or
      notify the client of certain events.  Note that if the connection
      is not being used for the fore channel, there is no way for the
      client to tell if the connection is still alive (e.g., the server
      restarted without sending a disconnect).  The onus is on the
      server, not the client, to determine if the backchannel's
      connection is alive, and to indicate in the response to a SEQUENCE
      operation when the last connection associated with a session's
      backchannel has disconnected.






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2.10.11.3.  Steps the Client Takes to Establish a Session

   If the client does not have a client ID, the client sends EXCHANGE_ID
   to establish a client ID.  If it opts for SP4_MACH_CRED or SP4_SSV
   protection, in the spo_must_enforce list of operations, it SHOULD at
   minimum specify CREATE_SESSION, DESTROY_SESSION,
   BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID.  If it
   opts for SP4_SSV protection, the client needs to ask for SSV-based
   RPCSEC_GSS handles.

   The client uses the client ID to send a CREATE_SESSION on a
   connection to the server.  The results of CREATE_SESSION indicate
   whether or not the server will persist the session reply cache
   through a server that has restarted, and the client notes this for
   future reference.

   If the client specified SP4_SSV state protection when the client ID
   was created, then it SHOULD send SET_SSV in the first COMPOUND after
   the session is created.  Each time a new principal goes to use the
   client ID, it SHOULD send a SET_SSV again.

   If the client wants to use delegations, layouts, directory
   notifications, or any other state that requires a backchannel, then
   it needs to add a connection to the backchannel if CREATE_SESSION did
   not already do so.  The client creates a connection, and calls
   BIND_CONN_TO_SESSION to associate the connection with the session and
   the session's backchannel.  If CREATE_SESSION did not already do so,
   the client MUST tell the server what security is required in order
   for the client to accept callbacks.  The client does this via
   BACKCHANNEL_CTL.  If the client selected SP4_MACH_CRED or SP4_SSV
   protection when it called EXCHANGE_ID, then the client SHOULD specify
   that the backchannel use RPCSEC_GSS contexts for security.

   If the client wants to use additional connections for the
   backchannel, then it needs to call BIND_CONN_TO_SESSION on each
   connection it wants to use with the session.  If the client wants to
   use additional connections for the fore channel, then it needs to
   call BIND_CONN_TO_SESSION if it specified SP4_SSV or SP4_MACH_CRED
   state protection when the client ID was created.

   At this point, the session has reached steady state.

2.10.12.  Session Inactivity Timer

   The server MAY maintain a session inactivity timer for each session.
   If the session inactivity timer expires, then the server MAY destroy
   the session.  To avoid losing a session due to inactivity, the client
   MUST renew the session inactivity timer.  The length of session



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   inactivity timer MUST NOT be less than the lease_time attribute
   (Section 5.8.1.11).  As with lease renewal (Section 8.3), when the
   server receives a SEQUENCE operation, it resets the session
   inactivity timer, and MUST NOT allow the timer to expire while the
   rest of the operations in the COMPOUND procedure's request are still
   executing.  Once the last operation has finished, the server MUST set
   the session inactivity timer to expire no sooner than the sum of the
   current time and the value of the lease_time attribute.

2.10.13.  Session Mechanics - Recovery

2.10.13.1.  Events Requiring Client Action

   The following events require client action to recover.

2.10.13.1.1.  RPCSEC_GSS Context Loss by Callback Path

   If all RPCSEC_GSS handles granted by the client to the server for
   callback use have expired, the client MUST establish a new handle via
   BACKCHANNEL_CTL.  The sr_status_flags field of the SEQUENCE results
   indicates when callback handles are nearly expired, or fully expired
   (see Section 18.46.3).

2.10.13.1.2.  Connection Loss

   If the client loses the last connection of the session and wants to
   retain the session, then it needs to create a new connection, and if,
   when the client ID was created, BIND_CONN_TO_SESSION was specified in
   the spo_must_enforce list, the client MUST use BIND_CONN_TO_SESSION
   to associate the connection with the session.

   If there was a request outstanding at the time of connection loss,
   then if the client wants to continue to use the session, it MUST
   retry the request, as described in Section 2.10.6.2.  Note that it is
   not necessary to retry requests over a connection with the same
   source network address or the same destination network address as the
   lost connection.  As long as the session ID, slot ID, and sequence ID
   in the retry match that of the original request, the server will
   recognize the request as a retry if it executed the request prior to
   disconnect.

   If the connection that was lost was the last one associated with the
   backchannel, and the client wants to retain the backchannel and/or
   prevent revocation of recallable state, the client needs to
   reconnect, and if it does, it MUST associate the connection to the
   session and backchannel via BIND_CONN_TO_SESSION.  The server SHOULD
   indicate when it has no callback connection via the sr_status_flags
   result from SEQUENCE.



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2.10.13.1.3.  Backchannel GSS Context Loss

   Via the sr_status_flags result of the SEQUENCE operation or other
   means, the client will learn if some or all of the RPCSEC_GSS
   contexts it assigned to the backchannel have been lost.  If the
   client wants to retain the backchannel and/or not put recallable
   state subject to revocation, the client needs to use BACKCHANNEL_CTL
   to assign new contexts.

2.10.13.1.4.  Loss of Session

   The replier might lose a record of the session.  Causes include:

   o  Replier failure and restart.

   o  A catastrophe that causes the reply cache to be corrupted or lost
      on the media on which it was stored.  This applies even if the
      replier indicated in the CREATE_SESSION results that it would
      persist the cache.

   o  The server purges the session of a client that has been inactive
      for a very extended period of time.

   o  As a result of configuration changes among a set of clustered
      servers, a network address previously connected to one server
      becomes connected to a different server that has no knowledge of
      the session in question.  Such a configuration change will
      generally only happen when the original server ceases to function
      for a time.

   Loss of reply cache is equivalent to loss of session.  The replier
   indicates loss of session to the requester by returning
   NFS4ERR_BADSESSION on the next operation that uses the session ID
   that refers to the lost session.

   After an event like a server restart, the client may have lost its
   connections.  The client assumes for the moment that the session has
   not been lost.  It reconnects, and if it specified connection
   association enforcement when the session was created, it invokes
   BIND_CONN_TO_SESSION using the session ID.  Otherwise, it invokes
   SEQUENCE.  If BIND_CONN_TO_SESSION or SEQUENCE returns
   NFS4ERR_BADSESSION, the client knows the session is not available to
   it when communicating with that network address.  If the connection
   survives session loss, then the next SEQUENCE operation the client
   sends over the connection will get back NFS4ERR_BADSESSION.  The
   client again knows the session was lost.

   Here is one suggested algorithm for the client when it gets



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   NFS4ERR_BADSESSION.  It is not obligatory in that, if a client does
   not want to take advantage of such features as trunking, it may omit
   parts of it.  However, it is a useful example that draws attention to
   various possible recovery issues:

   1.  If the client has other connections to other server network
       addresses associated with the same session, attempt a COMPOUND
       with a single operation, SEQUENCE, on each of the other
       connections.

   2.  If the attempts succeed, the session is still alive, and this is
       a strong indicator that the server's network address has moved.
       The client might send an EXCHANGE_ID on the connection that
       returned NFS4ERR_BADSESSION to see if there are opportunities for
       client ID trunking (i.e., the same client ID and so_major are
       returned).  The client might use DNS to see if the moved network
       address was replaced with another, so that the performance and
       availability benefits of session trunking can continue.

   3.  If the SEQUENCE requests fail with NFS4ERR_BADSESSION, then the
       session no longer exists on any of the server network addresses
       for which the client has connections associated with that session
       ID.  It is possible the session is still alive and available on
       other network addresses.  The client sends an EXCHANGE_ID on all
       the connections to see if the server owner is still listening on
       those network addresses.  If the same server owner is returned
       but a new client ID is returned, this is a strong indicator of a
       server restart.  If both the same server owner and same client ID
       are returned, then this is a strong indication that the server
       did delete the session, and the client will need to send a
       CREATE_SESSION if it has no other sessions for that client ID.
       If a different server owner is returned, the client can use DNS
       to find other network addresses.  If it does not, or if DNS does
       not find any other addresses for the server, then the client will
       be unable to provide NFSv4.1 service, and fatal errors should be
       returned to processes that were using the server.  If the client
       is using a "mount" paradigm, unmounting the server is advised.

   4.  If the client knows of no other connections associated with the
       session ID and server network addresses that are, or have been,
       associated with the session ID, then the client can use DNS to
       find other network addresses.  If it does not, or if DNS does not
       find any other addresses for the server, then the client will be
       unable to provide NFSv4.1 service, and fatal errors should be
       returned to processes that were using the server.  If the client
       is using a "mount" paradigm, unmounting the server is advised.

   If there is a reconfiguration event that results in the same network



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   address being assigned to servers where the eir_server_scope value is
   different, it cannot be guaranteed that a session ID generated by the
   first will be recognized as invalid by the first.  Therefore, in
   managing server reconfigurations among servers with different server
   scope values, it is necessary to make sure that all clients have
   disconnected from the first server before effecting the
   reconfiguration.  Nonetheless, clients should not assume that servers
   will always adhere to this requirement; clients MUST be prepared to
   deal with unexpected effects of server reconfigurations.  Even where
   a session ID is inappropriately recognized as valid, it is likely
   either that the connection will not be recognized as valid or that a
   sequence value for a slot will not be correct.  Therefore, when a
   client receives results indicating such unexpected errors, the use of
   EXCHANGE_ID to determine the current server configuration is
   RECOMMENDED.

   A variation on the above is that after a server's network address
   moves, there is no NFSv4.1 server listening, e.g., no listener on
   port 2049.  In this example, one of the following occur: the NFSv4
   server returns NFS4ERR_MINOR_VERS_MISMATCH, the NFS server returns a
   PROG_MISMATCH error, the RPC listener on 2049 returns PROG_UNVAIL, or
   attempts to reconnect to the network address timeout.  These SHOULD
   be treated as equivalent to SEQUENCE returning NFS4ERR_BADSESSION for
   these purposes.

   When the client detects session loss, it needs to call CREATE_SESSION
   to recover.  Any non-idempotent operations that were in progress
   might have been performed on the server at the time of session loss.
   The client has no general way to recover from this.

   Note that loss of session does not imply loss of byte-range lock,
   open, delegation, or layout state because locks, opens, delegations,
   and layouts are tied to the client ID and depend on the client ID,
   not the session.  Nor does loss of byte-range lock, open, delegation,
   or layout state imply loss of session state, because the session
   depends on the client ID; loss of client ID however does imply loss
   of session, byte-range lock, open, delegation, and layout state.  See
   Section 8.4.2.  A session can survive a server restart, but lock
   recovery may still be needed.

   It is possible that CREATE_SESSION will fail with
   NFS4ERR_STALE_CLIENTID (e.g., the server restarts and does not
   preserve client ID state).  If so, the client needs to call
   EXCHANGE_ID, followed by CREATE_SESSION.







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2.10.13.2.  Events Requiring Server Action

   The following events require server action to recover.

2.10.13.2.1.  Client Crash and Restart

   As described in Section 18.35, a restarted client sends EXCHANGE_ID
   in such a way that it causes the server to delete any sessions it
   had.

2.10.13.2.2.  Client Crash with No Restart

   If a client crashes and never comes back, it will never send
   EXCHANGE_ID with its old client owner.  Thus, the server has session
   state that will never be used again.  After an extended period of
   time, and if the server has resource constraints, it MAY destroy the
   old session as well as locking state.

2.10.13.2.3.  Extended Network Partition

   To the server, the extended network partition may be no different
   from a client crash with no restart (see Section 2.10.13.2.2).
   Unless the server can discern that there is a network partition, it
   is free to treat the situation as if the client has crashed
   permanently.

2.10.13.2.4.  Backchannel Connection Loss

   If there were callback requests outstanding at the time of a
   connection loss, then the server MUST retry the requests, as
   described in Section 2.10.6.2.  Note that it is not necessary to
   retry requests over a connection with the same source network address
   or the same destination network address as the lost connection.  As
   long as the session ID, slot ID, and sequence ID in the retry match
   that of the original request, the callback target will recognize the
   request as a retry even if it did see the request prior to
   disconnect.

   If the connection lost is the last one associated with the
   backchannel, then the server MUST indicate that in the
   sr_status_flags field of every SEQUENCE reply until the backchannel
   is re-established.  There are two situations, each of which uses
   different status flags: no connectivity for the session's backchannel
   and no connectivity for any session backchannel of the client.  See
   Section 18.46 for a description of the appropriate flags in
   sr_status_flags.





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2.10.13.2.5.  GSS Context Loss

   The server SHOULD monitor when the number of RPCSEC_GSS handles
   assigned to the backchannel reaches one, and when that one handle is
   near expiry (i.e., between one and two periods of lease time), and
   indicate so in the sr_status_flags field of all SEQUENCE replies.
   The server MUST indicate when all of the backchannel's assigned
   RPCSEC_GSS handles have expired via the sr_status_flags field of all
   SEQUENCE replies.

2.10.14.  Parallel NFS and Sessions

   A client and server can potentially be a non-pNFS implementation, a
   metadata server implementation, a data server implementation, or two
   or three types of implementations.  The EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags (not
   mutually exclusive) are passed in the EXCHANGE_ID arguments and
   results to allow the client to indicate how it wants to use sessions
   created under the client ID, and to allow the server to indicate how
   it will allow the sessions to be used.  See Section 13.1 for pNFS
   sessions considerations.

3.  Protocol Constants and Data Types

   The syntax and semantics to describe the data types of the NFSv4.1
   protocol are defined in the XDR RFC 4506 [2] and RPC RFC 5531 [3]
   documents.  The next sections build upon the XDR data types to define
   constants, types, and structures specific to this protocol.  The full
   list of XDR data types is in [13].

3.1.  Basic Constants

   const NFS4_FHSIZE               = 128;
   const NFS4_VERIFIER_SIZE        = 8;
   const NFS4_OPAQUE_LIMIT         = 1024;
   const NFS4_SESSIONID_SIZE       = 16;

   const NFS4_INT64_MAX            = 0x7fffffffffffffff;
   const NFS4_UINT64_MAX           = 0xffffffffffffffff;
   const NFS4_INT32_MAX            = 0x7fffffff;
   const NFS4_UINT32_MAX           = 0xffffffff;

   const NFS4_MAXFILELEN           = 0xffffffffffffffff;
   const NFS4_MAXFILEOFF           = 0xfffffffffffffffe;

   Except where noted, all these constants are defined in bytes.





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   o  NFS4_FHSIZE is the maximum size of a filehandle.

   o  NFS4_VERIFIER_SIZE is the fixed size of a verifier.

   o  NFS4_OPAQUE_LIMIT is the maximum size of certain opaque
      information.

   o  NFS4_SESSIONID_SIZE is the fixed size of a session identifier.

   o  NFS4_INT64_MAX is the maximum value of a signed 64-bit integer.

   o  NFS4_UINT64_MAX is the maximum value of an unsigned 64-bit
      integer.

   o  NFS4_INT32_MAX is the maximum value of a signed 32-bit integer.

   o  NFS4_UINT32_MAX is the maximum value of an unsigned 32-bit
      integer.

   o  NFS4_MAXFILELEN is the maximum length of a regular file.

   o  NFS4_MAXFILEOFF is the maximum offset into a regular file.

3.2.  Basic Data Types

   These are the base NFSv4.1 data types.

   +---------------+---------------------------------------------------+
   | Data Type     | Definition                                        |
   +---------------+---------------------------------------------------+
   | int32_t       | typedef int int32_t;                              |
   | uint32_t      | typedef unsigned int uint32_t;                    |
   | int64_t       | typedef hyper int64_t;                            |
   | uint64_t      | typedef unsigned hyper uint64_t;                  |
   | attrlist4     | typedef opaque attrlist4<>;                       |
   |               | Used for file/directory attributes.               |
   | bitmap4       | typedef uint32_t bitmap4<>;                       |
   |               | Used in attribute array encoding.                 |
   | changeid4     | typedef uint64_t changeid4;                       |
   |               | Used in the definition of change_info4.           |
   | clientid4     | typedef uint64_t clientid4;                       |
   |               | Shorthand reference to client identification.     |
   | count4        | typedef uint32_t count4;                          |
   |               | Various count parameters (READ, WRITE, COMMIT).   |
   | length4       | typedef uint64_t length4;                         |
   |               | The length of a byte-range within a file.         |
   | mode4         | typedef uint32_t mode4;                           |
   |               | Mode attribute data type.                         |



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   | nfs_cookie4   | typedef uint64_t nfs_cookie4;                     |
   |               | Opaque cookie value for READDIR.                  |
   | nfs_fh4       | typedef opaque nfs_fh4<NFS4_FHSIZE>;              |
   |               | Filehandle definition.                            |
   | nfs_ftype4    | enum nfs_ftype4;                                  |
   |               | Various defined file types.                       |
   | nfsstat4      | enum nfsstat4;                                    |
   |               | Return value for operations.                      |
   | offset4       | typedef uint64_t offset4;                         |
   |               | Various offset designations (READ, WRITE, LOCK,   |
   |               | COMMIT).                                          |
   | qop4          | typedef uint32_t qop4;                            |
   |               | Quality of protection designation in SECINFO.     |
   | sec_oid4      | typedef opaque sec_oid4<>;                        |
   |               | Security Object Identifier.  The sec_oid4 data    |
   |               | type is not really opaque.  Instead, it contains  |
   |               | an ASN.1 OBJECT IDENTIFIER as used by GSS-API in  |
   |               | the mech_type argument to GSS_Init_sec_context.   |
   |               | See [7] for details.                              |
   | sequenceid4   | typedef uint32_t sequenceid4;                     |
   |               | Sequence number used for various session          |
   |               | operations (EXCHANGE_ID, CREATE_SESSION,          |
   |               | SEQUENCE, CB_SEQUENCE).                           |
   | seqid4        | typedef uint32_t seqid4;                          |
   |               | Sequence identifier used for locking.             |
   | sessionid4    | typedef opaque sessionid4[NFS4_SESSIONID_SIZE];   |
   |               | Session identifier.                               |
   | slotid4       | typedef uint32_t slotid4;                         |
   |               | Sequencing artifact for various session           |
   |               | operations (SEQUENCE, CB_SEQUENCE).               |
   | utf8string    | typedef opaque utf8string<>;                      |
   |               | UTF-8 encoding for strings.                       |
   | utf8str_cis   | typedef utf8string utf8str_cis;                   |
   |               | Case-insensitive UTF-8 string.                    |
   | utf8str_cs    | typedef utf8string utf8str_cs;                    |
   |               | Case-sensitive UTF-8 string.                      |
   | utf8str_mixed | typedef utf8string utf8str_mixed;                 |
   |               | UTF-8 strings with a case-sensitive prefix and a  |
   |               | case-insensitive suffix.                          |
   | component4    | typedef utf8str_cs component4;                    |
   |               | Represents pathname components.                   |
   | linktext4     | typedef utf8str_cs linktext4;                     |
   |               | Symbolic link contents ("symbolic link" is        |
   |               | defined in an Open Group [14] standard).          |
   | pathname4     | typedef component4 pathname4<>;                   |
   |               | Represents pathname for fs_locations.             |
   | verifier4     | typedef opaque verifier4[NFS4_VERIFIER_SIZE];     |




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   |               | Verifier used for various operations (COMMIT,     |
   |               | CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE)        |
   |               | NFS4_VERIFIER_SIZE is defined as 8.               |
   +---------------+---------------------------------------------------+

                          End of Base Data Types

                                  Table 1

3.3.  Structured Data Types

3.3.1.  nfstime4

   struct nfstime4 {
           int64_t         seconds;
           uint32_t        nseconds;
   };

   The nfstime4 data type gives the number of seconds and nanoseconds
   since midnight or zero hour January 1, 1970 Coordinated Universal
   Time (UTC).  Values greater than zero for the seconds field denote
   dates after the zero hour January 1, 1970.  Values less than zero for
   the seconds field denote dates before the zero hour January 1, 1970.
   In both cases, the nseconds field is to be added to the seconds field
   for the final time representation.  For example, if the time to be
   represented is one-half second before zero hour January 1, 1970, the
   seconds field would have a value of negative one (-1) and the
   nseconds field would have a value of one-half second (500000000).
   Values greater than 999,999,999 for nseconds are invalid.

   This data type is used to pass time and date information.  A server
   converts to and from its local representation of time when processing
   time values, preserving as much accuracy as possible.  If the
   precision of timestamps stored for a file system object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is RECOMMENDED to reduce client and server time skew.

3.3.2.  time_how4

   enum time_how4 {
           SET_TO_SERVER_TIME4 = 0,
           SET_TO_CLIENT_TIME4 = 1
   };








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3.3.3.  settime4

   union settime4 switch (time_how4 set_it) {
    case SET_TO_CLIENT_TIME4:
            nfstime4       time;
    default:
            void;
   };

   The time_how4 and settime4 data types are used for setting timestamps
   in file object attributes.  If set_it is SET_TO_SERVER_TIME4, then
   the server uses its local representation of time for the time value.

3.3.4.  specdata4

   struct specdata4 {
    uint32_t specdata1; /* major device number */
    uint32_t specdata2; /* minor device number */
   };

   This data type represents the device numbers for the device file
   types NF4CHR and NF4BLK.

3.3.5.  fsid4

   struct fsid4 {
           uint64_t        major;
           uint64_t        minor;
   };

3.3.6.  change_policy4

   struct change_policy4 {
           uint64_t        cp_major;
           uint64_t        cp_minor;
   };

   The change_policy4 data type is used for the change_policy
   RECOMMENDED attribute.  It provides change sequencing indication
   analogous to the change attribute.  To enable the server to present a
   value valid across server re-initialization without requiring
   persistent storage, two 64-bit quantities are used, allowing one to
   be a server instance ID and the second to be incremented non-
   persistently, within a given server instance.







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3.3.7.  fattr4

   struct fattr4 {
           bitmap4         attrmask;
           attrlist4       attr_vals;
   };

   The fattr4 data type is used to represent file and directory
   attributes.

   The bitmap is a counted array of 32-bit integers used to contain bit
   values.  The position of the integer in the array that contains bit n
   can be computed from the expression (n / 32), and its bit within that
   integer is (n mod 32).


   0            1
   +-----------+-----------+-----------+--
   |  count    | 31  ..  0 | 63  .. 32 |
   +-----------+-----------+-----------+--

3.3.8.  change_info4

   struct change_info4 {
           bool            atomic;
           changeid4       before;
           changeid4       after;
   };

   This data type is used with the CREATE, LINK, OPEN, REMOVE, and
   RENAME operations to let the client know the value of the change
   attribute for the directory in which the target file system object
   resides.

3.3.9.  netaddr4

   struct netaddr4 {
           /* see struct rpcb in RFC 1833 */
           string na_r_netid<>; /* network id */
           string na_r_addr<>;  /* universal address */
   };

   The netaddr4 data type is used to identify network transport
   endpoints.  The r_netid and r_addr fields respectively contain a
   netid and uaddr.  The netid and uaddr concepts are defined in [15].
   The netid and uaddr formats for TCP over IPv4 and TCP over IPv6 are
   defined in [15], specifically Tables 2 and 3 and Sections 5.2.3.3 and
   5.2.3.4.



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3.3.10.  state_owner4

   struct state_owner4 {
           clientid4       clientid;
           opaque          owner<NFS4_OPAQUE_LIMIT>;
   };

   typedef state_owner4 open_owner4;
   typedef state_owner4 lock_owner4;

   The state_owner4 data type is the base type for the open_owner4
   (Section 3.3.10.1) and lock_owner4 (Section 3.3.10.2).

3.3.10.1.  open_owner4

   This data type is used to identify the owner of OPEN state.

3.3.10.2.  lock_owner4

   This structure is used to identify the owner of byte-range locking
   state.

3.3.11.  open_to_lock_owner4

   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };

   This data type is used for the first LOCK operation done for an
   open_owner4.  It provides both the open_stateid and lock_owner, such
   that the transition is made from a valid open_stateid sequence to
   that of the new lock_stateid sequence.  Using this mechanism avoids
   the confirmation of the lock_owner/lock_seqid pair since it is tied
   to established state in the form of the open_stateid/open_seqid.

3.3.12.  stateid4

   struct stateid4 {
           uint32_t        seqid;
           opaque          other[12];
   };

   This data type is used for the various state sharing mechanisms
   between the client and server.  The client never modifies a value of
   data type stateid.  The starting value of the "seqid" field is



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   undefined.  The server is required to increment the "seqid" field by
   one at each transition of the stateid.  This is important since the
   client will inspect the seqid in OPEN stateids to determine the order
   of OPEN processing done by the server.

3.3.13.  layouttype4

   enum layouttype4 {
           LAYOUT4_NFSV4_1_FILES   = 0x1,
           LAYOUT4_OSD2_OBJECTS    = 0x2,
           LAYOUT4_BLOCK_VOLUME    = 0x3
   };

   This data type indicates what type of layout is being used.  The file
   server advertises the layout types it supports through the
   fs_layout_type file system attribute (Section 5.12.1).  A client asks
   for layouts of a particular type in LAYOUTGET, and processes those
   layouts in its layout-type-specific logic.

   The layouttype4 data type is 32 bits in length.  The range
   represented by the layout type is split into three parts.  Type 0x0
   is reserved.  Types within the range 0x00000001-0x7FFFFFFF are
   globally unique and are assigned according to the description in
   Section 22.4; they are maintained by IANA.  Types within the range
   0x80000000-0xFFFFFFFF are site specific and for private use only.

   The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1 file
   layout type, as defined in Section 13, is to be used.  The
   LAYOUT4_OSD2_OBJECTS enumeration specifies that the object layout, as
   defined in [40], is to be used.  Similarly, the LAYOUT4_BLOCK_VOLUME
   enumeration specifies that the block/volume layout, as defined in
   [41], is to be used.

3.3.14.  deviceid4

   const NFS4_DEVICEID4_SIZE = 16;

   typedef opaque  deviceid4[NFS4_DEVICEID4_SIZE];

   Layout information includes device IDs that specify a storage device
   through a compact handle.  Addressing and type information is
   obtained with the GETDEVICEINFO operation.  Device IDs are not
   guaranteed to be valid across metadata server restarts.  A device ID
   is unique per client ID and layout type.  See Section 12.2.10 for
   more details.






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3.3.15.  device_addr4

   struct device_addr4 {
           layouttype4             da_layout_type;
           opaque                  da_addr_body<>;
   };

   The device address is used to set up a communication channel with the
   storage device.  Different layout types will require different data
   types to define how they communicate with storage devices.  The
   opaque da_addr_body field is interpreted based on the specified
   da_layout_type field.

   This document defines the device address for the NFSv4.1 file layout
   (see Section 13.3), which identifies a storage device by network IP
   address and port number.  This is sufficient for the clients to
   communicate with the NFSv4.1 storage devices, and may be sufficient
   for other layout types as well.  Device types for object-based
   storage devices and block storage devices (e.g., Small Computer
   System Interface (SCSI) volume labels) are defined by their
   respective layout specifications.

3.3.16.  layout_content4

   struct layout_content4 {
           layouttype4 loc_type;
           opaque      loc_body<>;
   };

   The loc_body field is interpreted based on the layout type
   (loc_type).  This document defines the loc_body for the NFSv4.1 file
   layout type; see Section 13.3 for its definition.

3.3.17.  layout4

   struct layout4 {
           offset4                 lo_offset;
           length4                 lo_length;
           layoutiomode4           lo_iomode;
           layout_content4         lo_content;
   };

   The layout4 data type defines a layout for a file.  The layout type
   specific data is opaque within lo_content.  Since layouts are sub-
   dividable, the offset and length together with the file's filehandle,
   the client ID, iomode, and layout type identify the layout.





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3.3.18.  layoutupdate4

   struct layoutupdate4 {
           layouttype4             lou_type;
           opaque                  lou_body<>;
   };

   The layoutupdate4 data type is used by the client to return updated
   layout information to the metadata server via the LAYOUTCOMMIT
   (Section 18.42) operation.  This data type provides a channel to pass
   layout type specific information (in field lou_body) back to the
   metadata server.  For example, for the block/volume layout type, this
   could include the list of reserved blocks that were written.  The
   contents of the opaque lou_body argument are determined by the layout
   type.  The NFSv4.1 file-based layout does not use this data type; if
   lou_type is LAYOUT4_NFSV4_1_FILES, the lou_body field MUST have a
   zero length.

3.3.19.  layouthint4

   struct layouthint4 {
           layouttype4             loh_type;
           opaque                  loh_body<>;
   };

   The layouthint4 data type is used by the client to pass in a hint
   about the type of layout it would like created for a particular file.
   It is the data type specified by the layout_hint attribute described
   in Section 5.12.4.  The metadata server may ignore the hint or may
   selectively ignore fields within the hint.  This hint should be
   provided at create time as part of the initial attributes within
   OPEN.  The loh_body field is specific to the type of layout
   (loh_type).  The NFSv4.1 file-based layout uses the
   nfsv4_1_file_layouthint4 data type as defined in Section 13.3.

3.3.20.  layoutiomode4

   enum layoutiomode4 {
           LAYOUTIOMODE4_READ      = 1,
           LAYOUTIOMODE4_RW        = 2,
           LAYOUTIOMODE4_ANY       = 3
   };

   The iomode specifies whether the client intends to just read or both
   read and write the data represented by the layout.  While the
   LAYOUTIOMODE4_ANY iomode MUST NOT be used in the arguments to the
   LAYOUTGET operation, it MAY be used in the arguments to the
   LAYOUTRETURN and CB_LAYOUTRECALL operations.  The LAYOUTIOMODE4_ANY



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   iomode specifies that layouts pertaining to both LAYOUTIOMODE4_READ
   and LAYOUTIOMODE4_RW iomodes are being returned or recalled,
   respectively.  The metadata server's use of the iomode may depend on
   the layout type being used.  The storage devices MAY validate I/O
   accesses against the iomode and reject invalid accesses.

3.3.21.  nfs_impl_id4

   struct nfs_impl_id4 {
           utf8str_cis   nii_domain;
           utf8str_cs    nii_name;
           nfstime4      nii_date;
   };

   This data type is used to identify client and server implementation
   details.  The nii_domain field is the DNS domain name with which the
   implementor is associated.  The nii_name field is the product name of
   the implementation and is completely free form.  It is RECOMMENDED
   that the nii_name be used to distinguish machine architecture,
   machine platforms, revisions, versions, and patch levels.  The
   nii_date field is the timestamp of when the software instance was
   published or built.

3.3.22.  threshold_item4

   struct threshold_item4 {
           layouttype4     thi_layout_type;
           bitmap4         thi_hintset;
           opaque          thi_hintlist<>;
   };

   This data type contains a list of hints specific to a layout type for
   helping the client determine when it should send I/O directly through
   the metadata server versus the storage devices.  The data type
   consists of the layout type (thi_layout_type), a bitmap (thi_hintset)
   describing the set of hints supported by the server (they may differ
   based on the layout type), and a list of hints (thi_hintlist) whose
   content is determined by the hintset bitmap.  See the mdsthreshold
   attribute for more details.

   The thi_hintset field is a bitmap of the following values:










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   +-------------------------+---+---------+---------------------------+
   | name                    | # | Data    | Description               |
   |                         |   | Type    |                           |
   +-------------------------+---+---------+---------------------------+
   | threshold4_read_size    | 0 | length4 | If a file's length is     |
   |                         |   |         | less than the value of    |
   |                         |   |         | threshold4_read_size,     |
   |                         |   |         | then it is RECOMMENDED    |
   |                         |   |         | that the client read from |
   |                         |   |         | the file via the MDS and  |
   |                         |   |         | not a storage device.     |
   | threshold4_write_size   | 1 | length4 | If a file's length is     |
   |                         |   |         | less than the value of    |
   |                         |   |         | threshold4_write_size,    |
   |                         |   |         | then it is RECOMMENDED    |
   |                         |   |         | that the client write to  |
   |                         |   |         | the file via the MDS and  |
   |                         |   |         | not a storage device.     |
   | threshold4_read_iosize  | 2 | length4 | For read I/O sizes below  |
   |                         |   |         | this threshold, it is     |
   |                         |   |         | RECOMMENDED to read data  |
   |                         |   |         | through the MDS.          |
   | threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
   |                         |   |         | this threshold, it is     |
   |                         |   |         | RECOMMENDED to write data |
   |                         |   |         | through the MDS.          |
   +-------------------------+---+---------+---------------------------+

3.3.23.  mdsthreshold4

   struct mdsthreshold4 {
           threshold_item4 mth_hints<>;
   };

   This data type holds an array of elements of data type
   threshold_item4, each of which is valid for a particular layout type.
   An array is necessary because a server can support multiple layout
   types for a single file.

4.  Filehandles

   The filehandle in the NFS protocol is a per-server unique identifier
   for a file system object.  The contents of the filehandle are opaque
   to the client.  Therefore, the server is responsible for translating
   the filehandle to an internal representation of the file system
   object.





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4.1.  Obtaining the First Filehandle

   The operations of the NFS protocol are defined in terms of one or
   more filehandles.  Therefore, the client needs a filehandle to
   initiate communication with the server.  With the NFSv3 protocol (RFC
   1813 [31]), there exists an ancillary protocol to obtain this first
   filehandle.  The MOUNT protocol, RPC program number 100005, provides
   the mechanism of translating a string-based file system pathname to a
   filehandle, which can then be used by the NFS protocols.

   The MOUNT protocol has deficiencies in the area of security and use
   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in RFC 2054 [42] and RFC 2055 [43].  With
   the use of the public filehandle in combination with the LOOKUP
   operation in the NFSv3 protocol, it has been demonstrated that the
   MOUNT protocol is unnecessary for viable interaction between NFS
   client and server.

   Therefore, the NFSv4.1 protocol will not use an ancillary protocol
   for translation from string-based pathnames to a filehandle.  Two
   special filehandles will be used as starting points for the NFS
   client.

4.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the file system namespace
   at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of the server's file tree.  Once this PUTROOTFH operation is
   used, the client can then traverse the entirety of the server's file
   tree with the LOOKUP operation.  A complete discussion of the server
   namespace is in Section 7.

4.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may be bound or represent an
   arbitrary file system object at the server.  The server is
   responsible for this binding.  It may be that the PUBLIC filehandle
   and the ROOT filehandle refer to the same file system object.
   However, it is up to the administrative software at the server and
   the policies of the server administrator to define the binding of the
   PUBLIC filehandle and server file system object.  The client may not
   make any assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.




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4.2.  Filehandle Types

   In the NFSv3 protocol, there was one type of filehandle with a single
   set of semantics.  This type of filehandle is termed "persistent" in
   NFSv4.1.  The semantics of a persistent filehandle remain the same as
   before.  A new type of filehandle introduced in NFSv4.1 is the
   "volatile" filehandle, which attempts to accommodate certain server
   environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues that make correct
   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a file-system-level invariant that can be
   used to construct a persistent filehandle.  The underlying server
   file system may not provide the invariant or the server's file system
   programming interfaces may not provide access to the needed
   invariant.  Volatile filehandles may ease the implementation of
   server functionality such as hierarchical storage management or file
   system reorganization or migration.  However, the volatile filehandle
   increases the implementation burden for the client.

   Since the client will need to handle persistent and volatile
   filehandles differently, a file attribute is defined that may be used
   by the client to determine the filehandle types being returned by the
   server.

4.2.1.  General Properties of a Filehandle

   The filehandle contains all the information the server needs to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use in a later request and
   can compare two filehandles from the same server for equality by
   doing a byte-by-byte comparison.  However, the client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the same server are equal, they MUST refer to the same file.
   Servers SHOULD try to maintain a one-to-one correspondence between
   filehandles and files, but this is not required.  Clients MUST use
   filehandle comparisons only to improve performance, not for correct
   behavior.  All clients need to be prepared for situations in which it
   cannot be determined whether two filehandles denote the same object
   and in such cases, avoid making invalid assumptions that might cause
   incorrect behavior.  Further discussion of filehandle and attribute
   comparison in the context of data caching is presented in
   Section 10.3.4.

   As an example, in the case that two different pathnames when
   traversed at the server terminate at the same file system object, the
   server SHOULD return the same filehandle for each path.  This can



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   occur if a hard link (see [6]) is used to create two file names that
   refer to the same underlying file object and associated data.  For
   example, if paths /a/b/c and /a/d/c refer to the same file, the
   server SHOULD return the same filehandle for both pathnames'
   traversals.

4.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value for the
   lifetime of the file system object to which it refers.  Once the
   server creates the filehandle for a file system object, the server
   MUST accept the same filehandle for the object for the lifetime of
   the object.  If the server restarts, the NFS server MUST honor the
   same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the file system is migrated, the new
   NFS server MUST honor the same filehandle as the old NFS server.

   The persistent filehandle will be become stale or invalid when the
   file system object is removed.  When the server is presented with a
   persistent filehandle that refers to a deleted object, it MUST return
   an error of NFS4ERR_STALE.  A filehandle may become stale when the
   file system containing the object is no longer available.  The file
   system may become unavailable if it exists on removable media and the
   media is no longer available at the server or the file system in
   whole has been destroyed or the file system has simply been removed
   from the server's namespace (i.e., unmounted in a UNIX environment).

4.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of a persistent filehandle.  The server may determine
   that a volatile filehandle is no longer valid at many different
   points in time.  If the server can definitively determine that a
   volatile filehandle refers to an object that has been removed, the
   server should return NFS4ERR_STALE to the client (as is the case for
   persistent filehandles).  In all other cases where the server
   determines that a volatile filehandle can no longer be used, it
   should return an error of NFS4ERR_FHEXPIRED.

   The REQUIRED attribute "fh_expire_type" is used by the client to
   determine what type of filehandle the server is providing for a
   particular file system.  This attribute is a bitmask with the
   following values:








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   FH4_PERSISTENT  The value of FH4_PERSISTENT is used to indicate a
      persistent filehandle, which is valid until the object is removed
      from the file system.  The server will not return
      NFS4ERR_FHEXPIRED for this filehandle.  FH4_PERSISTENT is defined
      as a value in which none of the bits specified below are set.

   FH4_VOLATILE_ANY  The filehandle may expire at any time, except as
      specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).

   FH4_NOEXPIRE_WITH_OPEN  May only be set when FH4_VOLATILE_ANY is set.
      If this bit is set, then the meaning of FH4_VOLATILE_ANY is
      qualified to exclude any expiration of the filehandle when it is
      open.

   FH4_VOL_MIGRATION  The filehandle will expire as a result of a file
      system transition (migration or replication), in those cases in
      which the continuity of filehandle use is not specified by handle
      class information within the fs_locations_info attribute.  When
      this bit is set, clients without access to fs_locations_info
      information should assume that filehandles will expire on file
      system transitions.

   FH4_VOL_RENAME  The filehandle will expire during rename.  This
      includes a rename by the requesting client or a rename by any
      other client.  If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.

   Servers that provide volatile filehandles that can expire while open
   require special care as regards handling of RENAMEs and REMOVEs.
   This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is
   set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN is not
   set, or if a non-read-only file system has a transition target in a
   different handle class.  In these cases, the server should deny a
   RENAME or REMOVE that would affect an OPEN file of any of the
   components leading to the OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period, in order
   to make sure that reclaims of files where filehandles may have
   expired do not do a reclaim for the wrong file.

   Volatile filehandles are especially suitable for implementation of
   the pseudo file systems used to bridge exports.  See Section 7.5 for
   a discussion of this.

4.3.  One Method of Constructing a Volatile Filehandle

   A volatile filehandle, while opaque to the client, could contain:






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   [volatile bit = 1 | server boot time | slot | generation number]
   o  slot is an index in the server volatile filehandle table


   o  generation number is the generation number for the table entry/
      slot

   When the client presents a volatile filehandle, the server makes the
   following checks, which assume that the check for the volatile bit
   has passed.  If the server boot time is less than the current server
   boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
   NFS4ERR_BADHANDLE.  If the generation number does not match, return
   NFS4ERR_FHEXPIRED.

   When the server restarts, the table is gone (it is volatile).

   If the volatile bit is 0, then it is a persistent filehandle with a
   different structure following it.

4.4.  Client Recovery from Filehandle Expiration

   If possible, the client SHOULD recover from the receipt of an
   NFS4ERR_FHEXPIRED error.  The client must take on additional
   responsibility so that it may prepare itself to recover from the
   expiration of a volatile filehandle.  If the server returns
   persistent filehandles, the client does not need these additional
   steps.

   For volatile filehandles, most commonly the client will need to store
   the component names leading up to and including the file system
   object in question.  With these names, the client should be able to
   recover by finding a filehandle in the namespace that is still
   available or by starting at the root of the server's file system
   namespace.

   If the expired filehandle refers to an object that has been removed
   from the file system, obviously the client will not be able to
   recover from the expired filehandle.

   It is also possible that the expired filehandle refers to a file that
   has been renamed.  If the file was renamed by another client, again
   it is possible that the original client will not be able to recover.
   However, in the case that the client itself is renaming the file and
   the file is open, it is possible that the client may be able to
   recover.  The client can determine the new pathname based on the
   processing of the rename request.  The client can then regenerate the
   new filehandle based on the new pathname.  The client could also use
   the COMPOUND procedure to construct a series of operations like:



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             RENAME A B
             LOOKUP B
             GETFH

   Note that the COMPOUND procedure does not provide atomicity.  This
   example only reduces the overhead of recovering from an expired
   filehandle.

5.  File Attributes

   To meet the requirements of extensibility and increased
   interoperability with non-UNIX platforms, attributes need to be
   handled in a flexible manner.  The NFSv3 fattr3 structure contains a
   fixed list of attributes that not all clients and servers are able to
   support or care about.  The fattr3 structure cannot be extended as
   new needs arise and it provides no way to indicate non-support.  With
   the NFSv4.1 protocol, the client is able to query what attributes the
   server supports and construct requests with only those supported
   attributes (or a subset thereof).

   To this end, attributes are divided into three groups: REQUIRED,
   RECOMMENDED, and named.  Both REQUIRED and RECOMMENDED attributes are
   supported in the NFSv4.1 protocol by a specific and well-defined
   encoding and are identified by number.  They are requested by setting
   a bit in the bit vector sent in the GETATTR request; the server
   response includes a bit vector to list what attributes were returned
   in the response.  New REQUIRED or RECOMMENDED attributes may be added
   to the NFSv4 protocol as part of a new minor version by publishing a
   Standards Track RFC that allocates a new attribute number value and
   defines the encoding for the attribute.  See Section 2.7 for further
   discussion.

   Named attributes are accessed by the new OPENATTR operation, which
   accesses a hidden directory of attributes associated with a file
   system object.  OPENATTR takes a filehandle for the object and
   returns the filehandle for the attribute hierarchy.  The filehandle
   for the named attributes is a directory object accessible by LOOKUP
   or READDIR and contains files whose names represent the named
   attributes and whose data bytes are the value of the attribute.  For
   example:











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        +----------+-----------+---------------------------------+
        | LOOKUP   | "foo"     | ; look up file                  |
        | GETATTR  | attrbits  |                                 |
        | OPENATTR |           | ; access foo's named attributes |
        | LOOKUP   | "x11icon" | ; look up specific attribute    |
        | READ     | 0,4096    | ; read stream of bytes          |
        +----------+-----------+---------------------------------+

   Named attributes are intended for data needed by applications rather
   than by an NFS client implementation.  NFS implementors are strongly
   encouraged to define their new attributes as RECOMMENDED attributes
   by bringing them to the IETF Standards Track process.

   The set of attributes that are classified as REQUIRED is deliberately
   small since servers need to do whatever it takes to support them.  A
   server should support as many of the RECOMMENDED attributes as
   possible but, by their definition, the server is not required to
   support all of them.  Attributes are deemed REQUIRED if the data is
   both needed by a large number of clients and is not otherwise
   reasonably computable by the client when support is not provided on
   the server.

   Note that the hidden directory returned by OPENATTR is a convenience
   for protocol processing.  The client should not make any assumptions
   about the server's implementation of named attributes and whether or
   not the underlying file system at the server has a named attribute
   directory.  Therefore, operations such as SETATTR and GETATTR on the
   named attribute directory are undefined.

5.1.  REQUIRED Attributes

   These MUST be supported by every NFSv4.1 client and server in order
   to ensure a minimum level of interoperability.  The server MUST store
   and return these attributes, and the client MUST be able to function
   with an attribute set limited to these attributes.  With just the
   REQUIRED attributes some client functionality may be impaired or
   limited in some ways.  A client may ask for any of these attributes
   to be returned by setting a bit in the GETATTR request, and the
   server MUST return their value.

5.2.  RECOMMENDED Attributes

   These attributes are understood well enough to warrant support in the
   NFSv4.1 protocol.  However, they may not be supported on all clients
   and servers.  A client may ask for any of these attributes to be
   returned by setting a bit in the GETATTR request but must handle the
   case where the server does not return them.  A client MAY ask for the
   set of attributes the server supports and SHOULD NOT request



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   attributes the server does not support.  A server should be tolerant
   of requests for unsupported attributes and simply not return them
   rather than considering the request an error.  It is expected that
   servers will support all attributes they comfortably can and only
   fail to support attributes that are difficult to support in their
   operating environments.  A server should provide attributes whenever
   they don't have to "tell lies" to the client.  For example, a file
   modification time should be either an accurate time or should not be
   supported by the server.  At times this will be difficult for
   clients, but a client is better positioned to decide whether and how
   to fabricate or construct an attribute or whether to do without the
   attribute.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the NFSv4
   protocol but are accessed by string names rather than numbers and
   correspond to an uninterpreted stream of bytes that are stored with
   the file system object.  The namespace for these attributes may be
   accessed by using the OPENATTR operation.  The OPENATTR operation
   returns a filehandle for a virtual "named attribute directory", and
   further perusal and modification of the namespace may be done using
   operations that work on more typical directories.  In particular,
   READDIR may be used to get a list of such named attributes, and
   LOOKUP and OPEN may select a particular attribute.  Creation of a new
   named attribute may be the result of an OPEN specifying file
   creation.

   Once an OPEN is done, named attributes may be examined and changed by
   normal READ and WRITE operations using the filehandles and stateids
   returned by OPEN.

   Named attributes and the named attribute directory may have their own
   (non-named) attributes.  Each of these objects MUST have all of the
   REQUIRED attributes and may have additional RECOMMENDED attributes.
   However, the set of attributes for named attributes and the named
   attribute directory need not be, and typically will not be, as large
   as that for other objects in that file system.

   Named attributes and the named attribute directory might be the
   target of delegations (in the case of the named attribute directory,
   these will be directory delegations).  However, since granting
   delegations is at the server's discretion, a server need not support
   delegations on named attributes or the named attribute directory.

   It is RECOMMENDED that servers support arbitrary named attributes.  A
   client should not depend on the ability to store any named attributes
   in the server's file system.  If a server does support named



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   attributes, a client that is also able to handle them should be able
   to copy a file's data and metadata with complete transparency from
   one location to another; this would imply that names allowed for
   regular directory entries are valid for named attribute names as
   well.

   In NFSv4.1, the structure of named attribute directories is
   restricted in a number of ways, in order to prevent the development
   of non-interoperable implementations in which some servers support a
   fully general hierarchical directory structure for named attributes
   while others support a limited but adequate structure for named
   attributes.  In such an environment, clients or applications might
   come to depend on non-portable extensions.  The restrictions are:

   o  CREATE is not allowed in a named attribute directory.  Thus, such
      objects as symbolic links and special files are not allowed to be
      named attributes.  Further, directories may not be created in a
      named attribute directory, so no hierarchical structure of named
      attributes for a single object is allowed.

   o  If OPENATTR is done on a named attribute directory or on a named
      attribute, the server MUST return NFS4ERR_WRONG_TYPE.

   o  Doing a RENAME of a named attribute to a different named attribute
      directory or to an ordinary (i.e., non-named-attribute) directory
      is not allowed.

   o  Creating hard links between named attribute directories or between
      named attribute directories and ordinary directories is not
      allowed.

   Names of attributes will not be controlled by this document or other
   IETF Standards Track documents.  See Section 22.1 for further
   discussion.

5.4.  Classification of Attributes

   Each of the REQUIRED and RECOMMENDED attributes can be classified in
   one of three categories: per server (i.e., the value of the attribute
   will be the same for all file objects that share the same server
   owner; see Section 2.5 for a definition of server owner), per file
   system (i.e., the value of the attribute will be the same for some or
   all file objects that share the same fsid attribute (Section 5.8.1.9)
   and server owner), or per file system object.  Note that it is
   possible that some per file system attributes may vary within the
   file system, depending on the value of the "homogeneous"
   (Section 5.8.2.16) attribute.  Note that the attributes
   time_access_set and time_modify_set are not listed in this section



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   because they are write-only attributes corresponding to time_access
   and time_modify, and are used in a special instance of SETATTR.

   o  The per-server attribute is:

         lease_time

   o  The per-file system attributes are:

         supported_attrs, suppattr_exclcreat, fh_expire_type,
         link_support, symlink_support, unique_handles, aclsupport,
         cansettime, case_insensitive, case_preserving,
         chown_restricted, files_avail, files_free, files_total,
         fs_locations, homogeneous, maxfilesize, maxname, maxread,
         maxwrite, no_trunc, space_avail, space_free, space_total,
         time_delta, change_policy, fs_status, fs_layout_type,
         fs_locations_info, fs_charset_cap

   o  The per-file system object attributes are:

         type, change, size, named_attr, fsid, rdattr_error, filehandle,
         acl, archive, fileid, hidden, maxlink, mimetype, mode,
         numlinks, owner, owner_group, rawdev, space_used, system,
         time_access, time_backup, time_create, time_metadata,
         time_modify, mounted_on_fileid, dir_notif_delay,
         dirent_notif_delay, dacl, sacl, layout_type, layout_hint,
         layout_blksize, layout_alignment, mdsthreshold, retention_get,
         retention_set, retentevt_get, retentevt_set, retention_hold,
         mode_set_masked

   For quota_avail_hard, quota_avail_soft, and quota_used, see their
   definitions below for the appropriate classification.

5.5.  Set-Only and Get-Only Attributes

   Some REQUIRED and RECOMMENDED attributes are set-only; i.e., they can
   be set via SETATTR but not retrieved via GETATTR.  Similarly, some
   REQUIRED and RECOMMENDED attributes are get-only; i.e., they can be
   retrieved via GETATTR but not set via SETATTR.  If a client attempts
   to set a get-only attribute or get a set-only attributes, the server
   MUST return NFS4ERR_INVAL.

5.6.  REQUIRED Attributes - List and Definition References

   The list of REQUIRED attributes appears in Table 2.  The meaning of
   the columns of the table are:





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   o  Name: The name of the attribute.

   o  Id: The number assigned to the attribute.  In the event of
      conflicts between the assigned number and [13], the latter is
      likely authoritative, but should be resolved with Errata to this
      document and/or [13].  See [44] for the Errata process.

   o  Data Type: The XDR data type of the attribute.

   o  Acc: Access allowed to the attribute.  R means read-only (GETATTR
      may retrieve, SETATTR may not set).  W means write-only (SETATTR
      may set, GETATTR may not retrieve).  R W means read/write (GETATTR
      may retrieve, SETATTR may set).

   o  Defined in: The section of this specification that describes the
      attribute.

     +--------------------+----+------------+-----+------------------+
     | Name               | Id | Data Type  | Acc | Defined in:      |
     +--------------------+----+------------+-----+------------------+
     | supported_attrs    | 0  | bitmap4    | R   | Section 5.8.1.1  |
     | type               | 1  | nfs_ftype4 | R   | Section 5.8.1.2  |
     | fh_expire_type     | 2  | uint32_t   | R   | Section 5.8.1.3  |
     | change             | 3  | uint64_t   | R   | Section 5.8.1.4  |
     | size               | 4  | uint64_t   | R W | Section 5.8.1.5  |
     | link_support       | 5  | bool       | R   | Section 5.8.1.6  |
     | symlink_support    | 6  | bool       | R   | Section 5.8.1.7  |
     | named_attr         | 7  | bool       | R   | Section 5.8.1.8  |
     | fsid               | 8  | fsid4      | R   | Section 5.8.1.9  |
     | unique_handles     | 9  | bool       | R   | Section 5.8.1.10 |
     | lease_time         | 10 | nfs_lease4 | R   | Section 5.8.1.11 |
     | rdattr_error       | 11 | enum       | R   | Section 5.8.1.12 |
     | filehandle         | 19 | nfs_fh4    | R   | Section 5.8.1.13 |
     | suppattr_exclcreat | 75 | bitmap4    | R   | Section 5.8.1.14 |
     +--------------------+----+------------+-----+------------------+

                                  Table 2

5.7.  RECOMMENDED Attributes - List and Definition References

   The RECOMMENDED attributes are defined in Table 3.  The meanings of
   the column headers are the same as Table 2; see Section 5.6 for the
   meanings.

   +--------------------+----+----------------+-----+------------------+
   | Name               | Id | Data Type      | Acc | Defined in:      |
   +--------------------+----+----------------+-----+------------------+
   | acl                | 12 | nfsace4<>      | R W | Section 6.2.1    |



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   | aclsupport         | 13 | uint32_t       | R   | Section 6.2.1.2  |
   | archive            | 14 | bool           | R W | Section 5.8.2.1  |
   | cansettime         | 15 | bool           | R   | Section 5.8.2.2  |
   | case_insensitive   | 16 | bool           | R   | Section 5.8.2.3  |
   | case_preserving    | 17 | bool           | R   | Section 5.8.2.4  |
   | change_policy      | 60 | chg_policy4    | R   | Section 5.8.2.5  |
   | chown_restricted   | 18 | bool           | R   | Section 5.8.2.6  |
   | dacl               | 58 | nfsacl41       | R W | Section 6.2.2    |
   | dir_notif_delay    | 56 | nfstime4       | R   | Section 5.11.1   |
   | dirent_notif_delay | 57 | nfstime4       | R   | Section 5.11.2   |
   | fileid             | 20 | uint64_t       | R   | Section 5.8.2.7  |
   | files_avail        | 21 | uint64_t       | R   | Section 5.8.2.8  |
   | files_free         | 22 | uint64_t       | R   | Section 5.8.2.9  |
   | files_total        | 23 | uint64_t       | R   | Section 5.8.2.10 |
   | fs_charset_cap     | 76 | uint32_t       | R   | Section 5.8.2.11 |
   | fs_layout_type     | 62 | layouttype4<>  | R   | Section 5.12.1   |
   | fs_locations       | 24 | fs_locations   | R   | Section 5.8.2.12 |
   | fs_locations_info  | 67 | *              | R   | Section 5.8.2.13 |
   | fs_status          | 61 | fs4_status     | R   | Section 5.8.2.14 |
   | hidden             | 25 | bool           | R W | Section 5.8.2.15 |
   | homogeneous        | 26 | bool           | R   | Section 5.8.2.16 |
   | layout_alignment   | 66 | uint32_t       | R   | Section 5.12.2   |
   | layout_blksize     | 65 | uint32_t       | R   | Section 5.12.3   |
   | layout_hint        | 63 | layouthint4    |   W | Section 5.12.4   |
   | layout_type        | 64 | layouttype4<>  | R   | Section 5.12.5   |
   | maxfilesize        | 27 | uint64_t       | R   | Section 5.8.2.17 |
   | maxlink            | 28 | uint32_t       | R   | Section 5.8.2.18 |
   | maxname            | 29 | uint32_t       | R   | Section 5.8.2.19 |
   | maxread            | 30 | uint64_t       | R   | Section 5.8.2.20 |
   | maxwrite           | 31 | uint64_t       | R   | Section 5.8.2.21 |
   | mdsthreshold       | 68 | mdsthreshold4  | R   | Section 5.12.6   |
   | mimetype           | 32 | utf8str_cs     | R W | Section 5.8.2.22 |
   | mode               | 33 | mode4          | R W | Section 6.2.4    |
   | mode_set_masked    | 74 | mode_masked4   |   W | Section 6.2.5    |
   | mounted_on_fileid  | 55 | uint64_t       | R   | Section 5.8.2.23 |
   | no_trunc           | 34 | bool           | R   | Section 5.8.2.24 |
   | numlinks           | 35 | uint32_t       | R   | Section 5.8.2.25 |
   | owner              | 36 | utf8str_mixed  | R W | Section 5.8.2.26 |
   | owner_group        | 37 | utf8str_mixed  | R W | Section 5.8.2.27 |
   | quota_avail_hard   | 38 | uint64_t       | R   | Section 5.8.2.28 |
   | quota_avail_soft   | 39 | uint64_t       | R   | Section 5.8.2.29 |
   | quota_used         | 40 | uint64_t       | R   | Section 5.8.2.30 |
   | rawdev             | 41 | specdata4      | R   | Section 5.8.2.31 |
   | retentevt_get      | 71 | retention_get4 | R   | Section 5.13.3   |
   | retentevt_set      | 72 | retention_set4 |   W | Section 5.13.4   |
   | retention_get      | 69 | retention_get4 | R   | Section 5.13.1   |
   | retention_hold     | 73 | uint64_t       | R W | Section 5.13.5   |
   | retention_set      | 70 | retention_set4 |   W | Section 5.13.2   |



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   | sacl               | 59 | nfsacl41       | R W | Section 6.2.3    |
   | space_avail        | 42 | uint64_t       | R   | Section 5.8.2.32 |
   | space_free         | 43 | uint64_t       | R   | Section 5.8.2.33 |
   | space_total        | 44 | uint64_t       | R   | Section 5.8.2.34 |
   | space_used         | 45 | uint64_t       | R   | Section 5.8.2.35 |
   | system             | 46 | bool           | R W | Section 5.8.2.36 |
   | time_access        | 47 | nfstime4       | R   | Section 5.8.2.37 |
   | time_access_set    | 48 | settime4       |   W | Section 5.8.2.38 |
   | time_backup        | 49 | nfstime4       | R W | Section 5.8.2.39 |
   | time_create        | 50 | nfstime4       | R W | Section 5.8.2.40 |
   | time_delta         | 51 | nfstime4       | R   | Section 5.8.2.41 |
   | time_metadata      | 52 | nfstime4       | R   | Section 5.8.2.42 |
   | time_modify        | 53 | nfstime4       | R   | Section 5.8.2.43 |
   | time_modify_set    | 54 | settime4       |   W | Section 5.8.2.44 |
   +--------------------+----+----------------+-----+------------------+

                                  Table 3

   * fs_locations_info4

5.8.  Attribute Definitions

5.8.1.  Definitions of REQUIRED Attributes

5.8.1.1.  Attribute 0: supported_attrs

   The bit vector that would retrieve all REQUIRED and RECOMMENDED
   attributes that are supported for this object.  The scope of this
   attribute applies to all objects with a matching fsid.

5.8.1.2.  Attribute 1: type

   Designates the type of an object in terms of one of a number of
   special constants:

   o  NF4REG designates a regular file.

   o  NF4DIR designates a directory.

   o  NF4BLK designates a block device special file.

   o  NF4CHR designates a character device special file.

   o  NF4LNK designates a symbolic link.

   o  NF4SOCK designates a named socket special file.





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   o  NF4FIFO designates a fifo special file.

   o  NF4ATTRDIR designates a named attribute directory.

   o  NF4NAMEDATTR designates a named attribute.

   Within the explanatory text and operation descriptions, the following
   phrases will be used with the meanings given below:

   o  The phrase "is a directory" means that the object's type attribute
      is NF4DIR or NF4ATTRDIR.

   o  The phrase "is a special file" means that the object's type
      attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.

   o  The phrases "is an ordinary file" and "is a regular file" mean
      that the object's type attribute is NF4REG or NF4NAMEDATTR.

5.8.1.3.  Attribute 2: fh_expire_type

   Server uses this to specify filehandle expiration behavior to the
   client.  See Section 4 for additional description.

5.8.1.4.  Attribute 3: change

   A value created by the server that the client can use to determine if
   file data, directory contents, or attributes of the object have been
   modified.  The server may return the object's time_metadata attribute
   for this attribute's value, but only if the file system object cannot
   be updated more frequently than the resolution of time_metadata.

5.8.1.5.  Attribute 4: size

   The size of the object in bytes.

5.8.1.6.  Attribute 5: link_support

   TRUE, if the object's file system supports hard links.

5.8.1.7.  Attribute 6: symlink_support

   TRUE, if the object's file system supports symbolic links.

5.8.1.8.  Attribute 7: named_attr

   TRUE, if this object has named attributes.  In other words, object
   has a non-empty named attribute directory.




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5.8.1.9.  Attribute 8: fsid

   Unique file system identifier for the file system holding this
   object.  The fsid attribute has major and minor components, each of
   which are of data type uint64_t.

5.8.1.10.  Attribute 9: unique_handles

   TRUE, if two distinct filehandles are guaranteed to refer to two
   different file system objects.

5.8.1.11.  Attribute 10: lease_time

   Duration of the lease at server in seconds.

5.8.1.12.  Attribute 11: rdattr_error

   Error returned from an attempt to retrieve attributes during a
   READDIR operation.

5.8.1.13.  Attribute 19: filehandle

   The filehandle of this object (primarily for READDIR requests).

5.8.1.14.  Attribute 75: suppattr_exclcreat

   The bit vector that would set all REQUIRED and RECOMMENDED attributes
   that are supported by the EXCLUSIVE4_1 method of file creation via
   the OPEN operation.  The scope of this attribute applies to all
   objects with a matching fsid.

5.8.2.  Definitions of Uncategorized RECOMMENDED Attributes

   The definitions of most of the RECOMMENDED attributes follow.
   Collections that share a common category are defined in other
   sections.

5.8.2.1.  Attribute 14: archive

   TRUE, if this file has been archived since the time of last
   modification (deprecated in favor of time_backup).

5.8.2.2.  Attribute 15: cansettime

   TRUE, if the server is able to change the times for a file system
   object as specified in a SETATTR operation.





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5.8.2.3.  Attribute 16: case_insensitive

   TRUE, if file name comparisons on this file system are case
   insensitive.

5.8.2.4.  Attribute 17: case_preserving

   TRUE, if file name case on this file system is preserved.

5.8.2.5.  Attribute 60: change_policy

   A value created by the server that the client can use to determine if
   some server policy related to the current file system has been
   subject to change.  If the value remains the same, then the client
   can be sure that the values of the attributes related to fs location
   and the fss_type field of the fs_status attribute have not changed.
   On the other hand, a change in this value does necessarily imply a
   change in policy.  It is up to the client to interrogate the server
   to determine if some policy relevant to it has changed.  See
   Section 3.3.6 for details.

   This attribute MUST change when the value returned by the
   fs_locations or fs_locations_info attribute changes, when a file
   system goes from read-only to writable or vice versa, or when the
   allowable set of security flavors for the file system or any part
   thereof is changed.

5.8.2.6.  Attribute 18: chown_restricted

   If TRUE, the server will reject any request to change either the
   owner or the group associated with a file if the caller is not a
   privileged user (for example, "root" in UNIX operating environments
   or, in Windows 2000, the "Take Ownership" privilege).

5.8.2.7.  Attribute 20: fileid

   A number uniquely identifying the file within the file system.

5.8.2.8.  Attribute 21: files_avail

   File slots available to this user on the file system containing this
   object -- this should be the smallest relevant limit.

5.8.2.9.  Attribute 22: files_free

   Free file slots on the file system containing this object -- this
   should be the smallest relevant limit.




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5.8.2.10.  Attribute 23: files_total

   Total file slots on the file system containing this object.

5.8.2.11.  Attribute 76: fs_charset_cap

   Character set capabilities for this file system.  See Section 14.4.

5.8.2.12.  Attribute 24: fs_locations

   Locations where this file system may be found.  If the server returns
   NFS4ERR_MOVED as an error, this attribute MUST be supported.  See
   Section 11.9 for more details.

5.8.2.13.  Attribute 67: fs_locations_info

   Full function file system location.  See Section 11.10 for more
   details.

5.8.2.14.  Attribute 61: fs_status

   Generic file system type information.  See Section 11.11 for more
   details.

5.8.2.15.  Attribute 25: hidden

   TRUE, if the file is considered hidden with respect to the Windows
   API.

5.8.2.16.  Attribute 26: homogeneous

   TRUE, if this object's file system is homogeneous; i.e., all objects
   in the file system (all objects on the server with the same fsid)
   have common values for all per-file-system attributes.

5.8.2.17.  Attribute 27: maxfilesize

   Maximum supported file size for the file system of this object.

5.8.2.18.  Attribute 28: maxlink

   Maximum number of links for this object.

5.8.2.19.  Attribute 29: maxname

   Maximum file name size supported for this object.





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5.8.2.20.  Attribute 30: maxread

   Maximum amount of data the READ operation will return for this
   object.

5.8.2.21.  Attribute 31: maxwrite

   Maximum amount of data the WRITE operation will accept for this
   object.  This attribute SHOULD be supported if the file is writable.
   Lack of this attribute can lead to the client either wasting
   bandwidth or not receiving the best performance.

5.8.2.22.  Attribute 32: mimetype

   MIME body type/subtype of this object.

5.8.2.23.  Attribute 55: mounted_on_fileid

   Like fileid, but if the target filehandle is the root of a file
   system, this attribute represents the fileid of the underlying
   directory.

   UNIX-based operating environments connect a file system into the
   namespace by connecting (mounting) the file system onto the existing
   file object (the mount point, usually a directory) of an existing
   file system.  When the mount point's parent directory is read via an
   API like readdir(), the return results are directory entries, each
   with a component name and a fileid.  The fileid of the mount point's
   directory entry will be different from the fileid that the stat()
   system call returns.  The stat() system call is returning the fileid
   of the root of the mounted file system, whereas readdir() is
   returning the fileid that stat() would have returned before any file
   systems were mounted on the mount point.

   Unlike NFSv3, NFSv4.1 allows a client's LOOKUP request to cross other
   file systems.  The client detects the file system crossing whenever
   the filehandle argument of LOOKUP has an fsid attribute different
   from that of the filehandle returned by LOOKUP.  A UNIX-based client
   will consider this a "mount point crossing".  UNIX has a legacy
   scheme for allowing a process to determine its current working
   directory.  This relies on readdir() of a mount point's parent and
   stat() of the mount point returning fileids as previously described.
   The mounted_on_fileid attribute corresponds to the fileid that
   readdir() would have returned as described previously.

   While the NFSv4.1 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if the server
   does not support mounted_on_fileid, the client has no choice), there



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   is a risk that the client will generate a fileid that conflicts with
   one that is already assigned to another object in the file system.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this area is eliminated.

   If the server detects that there is no mounted point at the target
   file object, then the value for mounted_on_fileid that it returns is
   the same as that of the fileid attribute.

   The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
   provide it if possible, and for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will be requested during
   a READDIR operation, in which case it is trivial (at least for UNIX-
   based servers) to return mounted_on_fileid since it is equal to the
   fileid of a directory entry returned by readdir().  If
   mounted_on_fileid is requested in a GETATTR operation, the server
   should obey an invariant that has it returning a value that is equal
   to the file object's entry in the object's parent directory, i.e.,
   what readdir() would have returned.  Some operating environments
   allow a series of two or more file systems to be mounted onto a
   single mount point.  In this case, for the server to obey the
   aforementioned invariant, it will need to find the base mount point,
   and not the intermediate mount points.

5.8.2.24.  Attribute 34: no_trunc

   If this attribute is TRUE, then if the client uses a file name longer
   than name_max, an error will be returned instead of the name being
   truncated.

5.8.2.25.  Attribute 35: numlinks

   Number of hard links to this object.

5.8.2.26.  Attribute 36: owner

   The string name of the owner of this object.

5.8.2.27.  Attribute 37: owner_group

   The string name of the group ownership of this object.

5.8.2.28.  Attribute 38: quota_avail_hard

   The value in bytes that represents the amount of additional disk
   space beyond the current allocation that can be allocated to this
   file or directory before further allocations will be refused.  It is
   understood that this space may be consumed by allocations to other



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   files or directories.

5.8.2.29.  Attribute 39: quota_avail_soft

   The value in bytes that represents the amount of additional disk
   space that can be allocated to this file or directory before the user
   may reasonably be warned.  It is understood that this space may be
   consumed by allocations to other files or directories though there is
   a rule as to which other files or directories.

5.8.2.30.  Attribute 40: quota_used

   The value in bytes that represents the amount of disk space used by
   this file or directory and possibly a number of other similar files
   or directories, where the set of "similar" meets at least the
   criterion that allocating space to any file or directory in the set
   will reduce the "quota_avail_hard" of every other file or directory
   in the set.

   Note that there may be a number of distinct but overlapping sets of
   files or directories for which a quota_used value is maintained,
   e.g., "all files with a given owner", "all files with a given group
   owner", etc.  The server is at liberty to choose any of those sets
   when providing the content of the quota_used attribute, but should do
   so in a repeatable way.  The rule may be configured per file system
   or may be "choose the set with the smallest quota".

5.8.2.31.  Attribute 41: rawdev

   Raw device number of file of type NF4BLK or NF4CHR.  The device
   number is split into major and minor numbers.  If the file's type
   attribute is not NF4BLK or NF4CHR, the value returned SHOULD NOT be
   considered useful.

5.8.2.32.  Attribute 42: space_avail

   Disk space in bytes available to this user on the file system
   containing this object -- this should be the smallest relevant limit.

5.8.2.33.  Attribute 43: space_free

   Free disk space in bytes on the file system containing this object --
   this should be the smallest relevant limit.

5.8.2.34.  Attribute 44: space_total

   Total disk space in bytes on the file system containing this object.




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5.8.2.35.  Attribute 45: space_used

   Number of file system bytes allocated to this object.

5.8.2.36.  Attribute 46: system

   This attribute is TRUE if this file is a "system" file with respect
   to the Windows operating environment.

5.8.2.37.  Attribute 47: time_access

   The time_access attribute represents the time of last access to the
   object by a READ operation sent to the server.  The notion of what is
   an "access" depends on the server's operating environment and/or the
   server's file system semantics.  For example, for servers obeying
   Portable Operating System Interface (POSIX) semantics, time_access
   would be updated only by the READ and READDIR operations and not any
   of the operations that modify the content of the object [16], [17],
   [18].  Of course, setting the corresponding time_access_set attribute
   is another way to modify the time_access attribute.

   Whenever the file object resides on a writable file system, the
   server should make its best efforts to record time_access into stable
   storage.  However, to mitigate the performance effects of doing so,
   and most especially whenever the server is satisfying the read of the
   object's content from its cache, the server MAY cache access time
   updates and lazily write them to stable storage.  It is also
   acceptable to give administrators of the server the option to disable
   time_access updates.

5.8.2.38.  Attribute 48: time_access_set

   Sets the time of last access to the object.  SETATTR use only.

5.8.2.39.  Attribute 49: time_backup

   The time of last backup of the object.

5.8.2.40.  Attribute 50: time_create

   The time of creation of the object.  This attribute does not have any
   relation to the traditional UNIX file attribute "ctime" or "change
   time".

5.8.2.41.  Attribute 51: time_delta

   Smallest useful server time granularity.




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5.8.2.42.  Attribute 52: time_metadata

   The time of last metadata modification of the object.

5.8.2.43.  Attribute 53: time_modify

   The time of last modification to the object.

5.8.2.44.  Attribute 54: time_modify_set

   Sets the time of last modification to the object.  SETATTR use only.

5.9.  Interpreting owner and owner_group

   The RECOMMENDED attributes "owner" and "owner_group" (and also users
   and groups within the "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that is tied to a particular
   underlying implementation at the client or server, the use of the
   UTF-8 string has been chosen.  Note that Section 6.1 of RFC 2624 [45]
   provides additional rationale.  It is expected that the client and
   server will have their own local representation of owner and
   owner_group that is used for local storage or presentation to the end
   user.  Therefore, it is expected that when these attributes are
   transferred between the client and server, the local representation
   is translated to a syntax of the form "user@dns_domain".  This will
   allow for a client and server that do not use the same local
   representation the ability to translate to a common syntax that can
   be interpreted by both.

   Similarly, security principals may be represented in different ways
   by different security mechanisms.  Servers normally translate these
   representations into a common format, generally that used by local
   storage, to serve as a means of identifying the users corresponding
   to these security principals.  When these local identifiers are
   translated to the form of the owner attribute, associated with files
   created by such principals, they identify, in a common format, the
   users associated with each corresponding set of security principals.

   The translation used to interpret owner and group strings is not
   specified as part of the protocol.  This allows various solutions to
   be employed.  For example, a local translation table may be consulted
   that maps a numeric identifier to the user@dns_domain syntax.  A name
   service may also be used to accomplish the translation.  A server may
   provide a more general service, not limited by any particular
   translation (which would only translate a limited set of possible
   strings) by storing the owner and owner_group attributes in local
   storage without any translation or it may augment a translation
   method by storing the entire string for attributes for which no



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   translation is available while using the local representation for
   those cases in which a translation is available.

   Servers that do not provide support for all possible values of the
   owner and owner_group attributes SHOULD return an error
   (NFS4ERR_BADOWNER) when a string is presented that has no
   translation, as the value to be set for a SETATTR of the owner,
   owner_group, or acl attributes.  When a server does accept an owner
   or owner_group value as valid on a SETATTR (and similarly for the
   owner and group strings in an acl), it is promising to return that
   same string when a corresponding GETATTR is done.  Configuration
   changes (including changes from the mapping of the string to the
   local representation) and ill-constructed name translations (those
   that contain aliasing) may make that promise impossible to honor.
   Servers should make appropriate efforts to avoid a situation in which
   these attributes have their values changed when no real change to
   ownership has occurred.

   The "dns_domain" portion of the owner string is meant to be a DNS
   domain name, for example, user@xxxxxxxxxxx.  Servers should accept as
   valid a set of users for at least one domain.  A server may treat
   other domains as having no valid translations.  A more general
   service is provided when a server is capable of accepting users for
   multiple domains, or for all domains, subject to security
   constraints.

   In the case where there is no translation available to the client or
   server, the attribute value will be constructed without the "@".
   Therefore, the absence of the @ from the owner or owner_group
   attribute signifies that no translation was available at the sender
   and that the receiver of the attribute should not use that string as
   a basis for translation into its own internal format.  Even though
   the attribute value cannot be translated, it may still be useful.  In
   the case of a client, the attribute string may be used for local
   display of ownership.

   To provide a greater degree of compatibility with NFSv3, which
   identified users and groups by 32-bit unsigned user identifiers and
   group identifiers, owner and group strings that consist of decimal
   numeric values with no leading zeros can be given a special
   interpretation by clients and servers that choose to provide such
   support.  The receiver may treat such a user or group string as
   representing the same user as would be represented by an NFSv3 uid or
   gid having the corresponding numeric value.  A server is not
   obligated to accept such a string, but may return an NFS4ERR_BADOWNER
   instead.  To avoid this mechanism being used to subvert user and
   group translation, so that a client might pass all of the owners and
   groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER



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   error when there is a valid translation for the user or owner
   designated in this way.  In that case, the client must use the
   appropriate name@domain string and not the special form for
   compatibility.

   The owner string "nobody" may be used to designate an anonymous user,
   which will be associated with a file created by a security principal
   that cannot be mapped through normal means to the owner attribute.
   Users and implementations of NFSv4.1 SHOULD NOT use "nobody" to
   designate a real user whose access is not anonymous.

5.10.  Character Case Attributes

   With respect to the case_insensitive and case_preserving attributes,
   each UCS-4 character (which UTF-8 encodes) can be mapped according to
   Appendix B.2 of RFC 3454 [19].  For general character handling and
   internationalization issues, see Section 14.

5.11.  Directory Notification Attributes

   As described in Section 18.39, the client can request a minimum delay
   for notifications of changes to attributes, but the server is free to
   ignore what the client requests.  The client can determine in advance
   what notification delays the server will accept by sending a GETATTR
   operation for either or both of two directory notification
   attributes.  When the client calls the GET_DIR_DELEGATION operation
   and asks for attribute change notifications, it should request
   notification delays that are no less than the values in the server-
   provided attributes.

5.11.1.  Attribute 56: dir_notif_delay

   The dir_notif_delay attribute is the minimum number of seconds the
   server will delay before notifying the client of a change to the
   directory's attributes.

5.11.2.  Attribute 57: dirent_notif_delay

   The dirent_notif_delay attribute is the minimum number of seconds the
   server will delay before notifying the client of a change to a file
   object that has an entry in the directory.

5.12.  pNFS Attribute Definitions

5.12.1.  Attribute 62: fs_layout_type

   The fs_layout_type attribute (see Section 3.3.13) applies to a file
   system and indicates what layout types are supported by the file



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   system.  When the client encounters a new fsid, the client SHOULD
   obtain the value for the fs_layout_type attribute associated with the
   new file system.  This attribute is used by the client to determine
   if the layout types supported by the server match any of the client's
   supported layout types.

5.12.2.  Attribute 66: layout_alignment

   When a client holds layouts on files of a file system, the
   layout_alignment attribute indicates the preferred alignment for I/O
   to files on that file system.  Where possible, the client should send
   READ and WRITE operations with offsets that are whole multiples of
   the layout_alignment attribute.

5.12.3.  Attribute 65: layout_blksize

   When a client holds layouts on files of a file system, the
   layout_blksize attribute indicates the preferred block size for I/O
   to files on that file system.  Where possible, the client should send
   READ operations with a count argument that is a whole multiple of
   layout_blksize, and WRITE operations with a data argument of size
   that is a whole multiple of layout_blksize.

5.12.4.  Attribute 63: layout_hint

   The layout_hint attribute (see Section 3.3.19) may be set on newly
   created files to influence the metadata server's choice for the
   file's layout.  If possible, this attribute is one of those set in
   the initial attributes within the OPEN operation.  The metadata
   server may choose to ignore this attribute.  The layout_hint
   attribute is a subset of the layout structure returned by LAYOUTGET.
   For example, instead of specifying particular devices, this would be
   used to suggest the stripe width of a file.  The server
   implementation determines which fields within the layout will be
   used.

5.12.5.  Attribute 64: layout_type

   This attribute lists the layout type(s) available for a file.  The
   value returned by the server is for informational purposes only.  The
   client will use the LAYOUTGET operation to obtain the information
   needed in order to perform I/O, for example, the specific device
   information for the file and its layout.

5.12.6.  Attribute 68: mdsthreshold

   This attribute is a server-provided hint used to communicate to the
   client when it is more efficient to send READ and WRITE operations to



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   the metadata server or the data server.  The two types of thresholds
   described are file size thresholds and I/O size thresholds.  If a
   file's size is smaller than the file size threshold, data accesses
   SHOULD be sent to the metadata server.  If an I/O request has a
   length that is below the I/O size threshold, the I/O SHOULD be sent
   to the metadata server.  Each threshold type is specified separately
   for read and write.

   The server MAY provide both types of thresholds for a file.  If both
   file size and I/O size are provided, the client SHOULD reach or
   exceed both thresholds before sending its read or write requests to
   the data server.  Alternatively, if only one of the specified
   thresholds is reached or exceeded, the I/O requests are sent to the
   metadata server.

   For each threshold type, a value of zero indicates no READ or WRITE
   should be sent to the metadata server, while a value of all ones
   indicates that all READs or WRITEs should be sent to the metadata
   server.

   The attribute is available on a per-filehandle basis.  If the current
   filehandle refers to a non-pNFS file or directory, the metadata
   server should return an attribute that is representative of the
   filehandle's file system.  It is suggested that this attribute is
   queried as part of the OPEN operation.  Due to dynamic system
   changes, the client should not assume that the attribute will remain
   constant for any specific time period; thus, it should be
   periodically refreshed.

5.13.  Retention Attributes

   Retention is a concept whereby a file object can be placed in an
   immutable, undeletable, unrenamable state for a fixed or infinite
   duration of time.  Once in this "retained" state, the file cannot be
   moved out of the state until the duration of retention has been
   reached.

   When retention is enabled, retention MUST extend to the data of the
   file, and the name of file.  The server MAY extend retention to any
   other property of the file, including any subset of REQUIRED,
   RECOMMENDED, and named attributes, with the exceptions noted in this
   section.

   Servers MAY support or not support retention on any file object type.

   The five retention attributes are explained in the next subsections.





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5.13.1.  Attribute 69: retention_get

   If retention is enabled for the associated file, this attribute's
   value represents the retention begin time of the file object.  This
   attribute's value is only readable with the GETATTR operation and
   MUST NOT be modified by the SETATTR operation (Section 5.5).  The
   value of the attribute consists of:

   const RET4_DURATION_INFINITE    = 0xffffffffffffffff;
   struct retention_get4 {
           uint64_t        rg_duration;
           nfstime4        rg_begin_time<1>;
   };

   The field rg_duration is the duration in seconds indicating how long
   the file will be retained once retention is enabled.  The field
   rg_begin_time is an array of up to one absolute time value.  If the
   array is zero length, no beginning retention time has been
   established, and retention is not enabled.  If rg_duration is equal
   to RET4_DURATION_INFINITE, the file, once retention is enabled, will
   be retained for an infinite duration.

   If (as soon as) rg_duration is zero, then rg_begin_time will be of
   zero length, and again, retention is not (no longer) enabled.

5.13.2.  Attribute 70: retention_set

   This attribute is used to set the retention duration and optionally
   enable retention for the associated file object.  This attribute is
   only modifiable via the SETATTR operation and MUST NOT be retrieved
   by the GETATTR operation (Section 5.5).  This attribute corresponds
   to retention_get.  The value of the attribute consists of:

   struct retention_set4 {
           bool            rs_enable;
           uint64_t        rs_duration<1>;
   };

   If the client sets rs_enable to TRUE, then it is enabling retention
   on the file object with the begin time of retention starting from the
   server's current time and date.  The duration of the retention can
   also be provided if the rs_duration array is of length one.  The
   duration is the time in seconds from the begin time of retention, and
   if set to RET4_DURATION_INFINITE, the file is to be retained forever.
   If retention is enabled, with no duration specified in either this
   SETATTR or a previous SETATTR, the duration defaults to zero seconds.
   The server MAY restrict the enabling of retention or the duration of
   retention on the basis of the ACE4_WRITE_RETENTION ACL permission.



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   The enabling of retention MUST NOT prevent the enabling of event-
   based retention or the modification of the retention_hold attribute.

   The following rules apply to both the retention_set and retentevt_set
   attributes.

   o  As long as retention is not enabled, the client is permitted to
      decrease the duration.

   o  The duration can always be set to an equal or higher value, even
      if retention is enabled.  Note that once retention is enabled, the
      actual duration (as returned by the retention_get or retentevt_get
      attributes; see Section 5.13.1 or Section 5.13.3) is constantly
      counting down to zero (one unit per second), unless the duration
      was set to RET4_DURATION_INFINITE.  Thus, it will not be possible
      for the client to precisely extend the duration on a file that has
      retention enabled.

   o  While retention is enabled, attempts to disable retention or
      decrease the retention's duration MUST fail with the error
      NFS4ERR_INVAL.

   o  If the principal attempting to change retention_set or
      retentevt_set does not have ACE4_WRITE_RETENTION permissions, the
      attempt MUST fail with NFS4ERR_ACCESS.

5.13.3.  Attribute 71: retentevt_get

   Gets the event-based retention duration, and if enabled, the event-
   based retention begin time of the file object.  This attribute is
   like retention_get, but refers to event-based retention.  The event
   that triggers event-based retention is not defined by the NFSv4.1
   specification.

5.13.4.  Attribute 72: retentevt_set

   Sets the event-based retention duration, and optionally enables
   event-based retention on the file object.  This attribute corresponds
   to retentevt_get and is like retention_set, but refers to event-based
   retention.  When event-based retention is set, the file MUST be
   retained even if non-event-based retention has been set, and the
   duration of non-event-based retention has been reached.  Conversely,
   when non-event-based retention has been set, the file MUST be
   retained even if event-based retention has been set, and the duration
   of event-based retention has been reached.  The server MAY restrict
   the enabling of event-based retention or the duration of event-based
   retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
   The enabling of event-based retention MUST NOT prevent the enabling



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   of non-event-based retention or the modification of the
   retention_hold attribute.

5.13.5.  Attribute 73: retention_hold

   Gets or sets administrative retention holds, one hold per bit
   position.

   This attribute allows one to 64 administrative holds, one hold per
   bit on the attribute.  If retention_hold is not zero, then the file
   MUST NOT be deleted, renamed, or modified, even if the duration on
   enabled event or non-event-based retention has been reached.  The
   server MAY restrict the modification of retention_hold on the basis
   of the ACE4_WRITE_RETENTION_HOLD ACL permission.  The enabling of
   administration retention holds does not prevent the enabling of
   event-based or non-event-based retention.

   If the principal attempting to change retention_hold does not have
   ACE4_WRITE_RETENTION_HOLD permissions, the attempt MUST fail with
   NFS4ERR_ACCESS.

6.  Access Control Attributes

   Access Control Lists (ACLs) are file attributes that specify fine-
   grained access control.  This section covers the "acl", "dacl",
   "sacl", "aclsupport", "mode", and "mode_set_masked" file attributes
   and their interactions.  Note that file attributes may apply to any
   file system object.

6.1.  Goals

   ACLs and modes represent two well-established models for specifying
   permissions.  This section specifies requirements that attempt to
   meet the following goals:

   o  If a server supports the mode attribute, it should provide
      reasonable semantics to clients that only set and retrieve the
      mode attribute.

   o  If a server supports ACL attributes, it should provide reasonable
      semantics to clients that only set and retrieve those attributes.

   o  On servers that support the mode attribute, if ACL attributes have
      never been set on an object, via inheritance or explicitly, the
      behavior should be traditional UNIX-like behavior.

   o  On servers that support the mode attribute, if the ACL attributes
      have been previously set on an object, either explicitly or via



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      inheritance:

      *  Setting only the mode attribute should effectively control the
         traditional UNIX-like permissions of read, write, and execute
         on owner, owner_group, and other.

      *  Setting only the mode attribute should provide reasonable
         security.  For example, setting a mode of 000 should be enough
         to ensure that future OPEN operations for
         OPEN4_SHARE_ACCESS_READ or OPEN4_SHARE_ACCESS_WRITE by any
         principal fail, regardless of a previously existing or
         inherited ACL.

   o  NFSv4.1 may introduce different semantics relating to the mode and
      ACL attributes, but it does not render invalid any previously
      existing implementations.  Additionally, this section provides
      clarifications based on previous implementations and discussions
      around them.

   o  On servers that support both the mode and the acl or dacl
      attributes, the server must keep the two consistent with each
      other.  The value of the mode attribute (with the exception of the
      three high-order bits described in Section 6.2.4) must be
      determined entirely by the value of the ACL, so that use of the
      mode is never required for anything other than setting the three
      high-order bits.  See Section 6.4.1 for exact requirements.

   o  When a mode attribute is set on an object, the ACL attributes may
      need to be modified in order to not conflict with the new mode.
      In such cases, it is desirable that the ACL keep as much
      information as possible.  This includes information about
      inheritance, AUDIT and ALARM ACEs, and permissions granted and
      denied that do not conflict with the new mode.

6.2.  File Attributes Discussion

6.2.1.  Attribute 12: acl

   The NFSv4.1 ACL attribute contains an array of Access Control Entries
   (ACEs) that are associated with the file system object.  Although the
   client can set and get the acl attribute, the server is responsible
   for using the ACL to perform access control.  The client can use the
   OPEN or ACCESS operations to check access without modifying or
   reading data or metadata.

   The NFS ACE structure is defined as follows:

   typedef uint32_t        acetype4;



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   typedef uint32_t aceflag4;


   typedef uint32_t        acemask4;


   struct nfsace4 {
           acetype4        type;
           aceflag4        flag;
           acemask4        access_mask;
           utf8str_mixed   who;
   };

   To determine if a request succeeds, the server processes each nfsace4
   entry in order.  Only ACEs that have a "who" that matches the
   requester are considered.  Each ACE is processed until all of the
   bits of the requester's access have been ALLOWED.  Once a bit (see
   below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
   considered in the processing of later ACEs.  If an ACCESS_DENIED_ACE
   is encountered where the requester's access still has unALLOWED bits
   in common with the "access_mask" of the ACE, the request is denied.
   When the ACL is fully processed, if there are bits in the requester's
   mask that have not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  Therefore, AUDIT
   and ALARM ACEs are processed only after processing ALLOW and DENY
   ACEs.

   The NFSv4.1 ACL model is quite rich.  Some server platforms may
   provide access-control functionality that goes beyond the UNIX-style
   mode attribute, but that is not as rich as the NFS ACL model.  So
   that users can take advantage of this more limited functionality, the
   server may support the acl attributes by mapping between its ACL
   model and the NFSv4.1 ACL model.  Servers must ensure that the ACL
   they actually store or enforce is at least as strict as the NFSv4 ACL
   that was set.  It is tempting to accomplish this by rejecting any ACL
   that falls outside the small set that can be represented accurately.
   However, such an approach can render ACLs unusable without special
   client-side knowledge of the server's mapping, which defeats the
   purpose of having a common NFSv4 ACL protocol.  Therefore, servers
   should accept every ACL that they can without compromising security.
   To help accomplish this, servers may make a special exception, in the
   case of unsupported permission bits, to the rule that bits not
   ALLOWED or DENIED by an ACL must be denied.  For example, a UNIX-
   style server might choose to silently allow read attribute
   permissions even though an ACL does not explicitly allow those



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   permissions.  (An ACL that explicitly denies permission to read
   attributes should still be rejected.)

   The situation is complicated by the fact that a server may have
   multiple modules that enforce ACLs.  For example, the enforcement for
   NFSv4.1 access may be different from, but not weaker than, the
   enforcement for local access, and both may be different from the
   enforcement for access through other protocols such as SMB (Server
   Message Block).  So it may be useful for a server to accept an ACL
   even if not all of its modules are able to support it.

   The guiding principle with regard to NFSv4 access is that the server
   must not accept ACLs that appear to make access to the file more
   restrictive than it really is.

6.2.1.1.  ACE Type

   The constants used for the type field (acetype4) are as follows:

   const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
   const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
   const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
   const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;

   Only the ALLOWED and DENIED bits may be used in the dacl attribute,
   and only the AUDIT and ALARM bits may be used in the sacl attribute.
   All four are permitted in the acl attribute.

   +------------------------------+--------------+---------------------+
   | Value                        | Abbreviation | Description         |
   +------------------------------+--------------+---------------------+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | Log (in a           |
   |                              |              | system-dependent    |
   |                              |              | way) any access     |
   |                              |              | attempt to a file   |
   |                              |              | or directory that   |
   |                              |              | uses any of the     |
   |                              |              | access methods      |
   |                              |              | specified in        |
   |                              |              | acemask4.           |



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   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate an alarm   |
   |                              |              | (in a               |
   |                              |              | system-dependent    |
   |                              |              | way) when any       |
   |                              |              | access attempt is   |
   |                              |              | made to a file or   |
   |                              |              | directory for the   |
   |                              |              | access methods      |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

   The "Abbreviation" column denotes how the types will be referred to
   throughout the rest of this section.

6.2.1.2.  Attribute 13: aclsupport

   A server need not support all of the above ACE types.  This attribute
   indicates which ACE types are supported for the current file system.
   The bitmask constants used to represent the above definitions within
   the aclsupport attribute are as follows:

   const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
   const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
   const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
   const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;

   Servers that support either the ALLOW or DENY ACE type SHOULD support
   both ALLOW and DENY ACE types.

   Clients should not attempt to set an ACE unless the server claims
   support for that ACE type.  If the server receives a request to set
   an ACE that it cannot store, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE
   that it can store but cannot enforce, the server SHOULD reject the
   request with NFS4ERR_ATTRNOTSUPP.

   Support for any of the ACL attributes is optional (albeit
   RECOMMENDED).  However, a server that supports either of the new ACL
   attributes (dacl or sacl) MUST allow use of the new ACL attributes to
   access all of the ACE types that it supports.  In other words, if
   such a server supports ALLOW or DENY ACEs, then it MUST support the
   dacl attribute, and if it supports AUDIT or ALARM ACEs, then it MUST
   support the sacl attribute.







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6.2.1.3.  ACE Access Mask

   The bitmask constants used for the access mask field are as follows:

   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
   const ACE4_WRITE_RETENTION      = 0x00000200;
   const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Note that some masks have coincident values, for example,
   ACE4_READ_DATA and ACE4_LIST_DIRECTORY.  The mask entries
   ACE4_LIST_DIRECTORY, ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
   intended to be used with directory objects, while ACE4_READ_DATA,
   ACE4_WRITE_DATA, and ACE4_APPEND_DATA are intended to be used with
   non-directory objects.

6.2.1.3.1.  Discussion of Mask Attributes

   ACE4_READ_DATA

      Operation(s) affected:

         READ

         OPEN

      Discussion:

         Permission to read the data of the file.

         Servers SHOULD allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.



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   ACE4_LIST_DIRECTORY

      Operation(s) affected:

         READDIR

      Discussion:

         Permission to list the contents of a directory.

   ACE4_WRITE_DATA

      Operation(s) affected:

         WRITE

         OPEN

         SETATTR of size

      Discussion:

         Permission to modify a file's data.

   ACE4_ADD_FILE

      Operation(s) affected:

         CREATE

         LINK

         OPEN

         RENAME

      Discussion:

         Permission to add a new file in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
         NF4CHR, NF4SOCK, or NF4FIFO.  (NF4DIR is not listed because it
         is covered by ACE4_ADD_SUBDIRECTORY.)  OPEN is affected when
         used to create a regular file.  LINK and RENAME are always
         affected.







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   ACE4_APPEND_DATA

      Operation(s) affected:

         WRITE

         OPEN

         SETATTR of size

      Discussion:

         The ability to modify a file's data, but only starting at EOF.
         This allows for the notion of append-only files, by allowing
         ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the same user
         or group.  If a file has an ACL such as the one described above
         and a WRITE request is made for somewhere other than EOF, the
         server SHOULD return NFS4ERR_ACCESS.

   ACE4_ADD_SUBDIRECTORY

      Operation(s) affected:

         CREATE

         RENAME

      Discussion:

         Permission to create a subdirectory in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4DIR.  The RENAME
         operation is always affected.

   ACE4_READ_NAMED_ATTRS

      Operation(s) affected:

         OPENATTR

      Discussion:

         Permission to read the named attributes of a file or to look up
         the named attribute directory.  OPENATTR is affected when it is
         not used to create a named attribute directory.  This is when
         1) createdir is TRUE, but a named attribute directory already
         exists, or 2) createdir is FALSE.





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   ACE4_WRITE_NAMED_ATTRS

      Operation(s) affected:

         OPENATTR



      Discussion:

         Permission to write the named attributes of a file or to create
         a named attribute directory.  OPENATTR is affected when it is
         used to create a named attribute directory.  This is when
         createdir is TRUE and no named attribute directory exists.  The
         ability to check whether or not a named attribute directory
         exists depends on the ability to look it up; therefore, users
         also need the ACE4_READ_NAMED_ATTRS permission in order to
         create a named attribute directory.

   ACE4_EXECUTE

      Operation(s) affected:

         READ

         OPEN

         REMOVE

         RENAME

         LINK

         CREATE

      Discussion:

         Permission to execute a file.

         Servers SHOULD allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.
         This is because there is no way to execute a file without
         reading the contents.  Though a server may treat ACE4_EXECUTE
         and ACE4_READ_DATA bits identically when deciding to permit a
         READ operation, it SHOULD still allow the two bits to be set
         independently in ACLs, and MUST distinguish between them when
         replying to ACCESS operations.  In particular, servers SHOULD
         NOT silently turn on one of the two bits when the other is set,



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         as that would make it impossible for the client to correctly
         enforce the distinction between read and execute permissions.

         As an example, following a SETATTR of the following ACL:

         nfsuser:ACE4_EXECUTE:ALLOW

         A subsequent GETATTR of ACL for that file SHOULD return:

         nfsuser:ACE4_EXECUTE:ALLOW

         Rather than:

         nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

   ACE4_EXECUTE

      Operation(s) affected:

         LOOKUP

      Discussion:

         Permission to traverse/search a directory.

   ACE4_DELETE_CHILD

      Operation(s) affected:

         REMOVE

         RENAME

      Discussion:

         Permission to delete a file or directory within a directory.
         See Section 6.2.1.3.2 for information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ATTRIBUTES

      Operation(s) affected:

         GETATTR of file system object attributes







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         VERIFY

         NVERIFY

         READDIR

      Discussion:

         The ability to read basic attributes (non-ACLs) of a file.  On
         a UNIX system, basic attributes can be thought of as the stat-
         level attributes.  Allowing this access mask bit would mean
         that the entity can execute "ls -l" and stat.  If a READDIR
         operation requests attributes, this mask must be allowed for
         the READDIR to succeed.

   ACE4_WRITE_ATTRIBUTES

      Operation(s) affected:

         SETATTR of time_access_set, time_backup,

         time_create, time_modify_set, mimetype, hidden, system

      Discussion:

         Permission to change the times associated with a file or
         directory to an arbitrary value.  Also permission to change the
         mimetype, hidden, and system attributes.  A user having
         ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to set
         the times associated with a file to the current server time.

   ACE4_WRITE_RETENTION

      Operation(s) affected:

         SETATTR of retention_set, retentevt_set.

      Discussion:

         Permission to modify the durations of event and non-event-based
         retention.  Also permission to enable event and non-event-based
         retention.  A server MAY behave such that setting
         ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.








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   ACE4_WRITE_RETENTION_HOLD

      Operation(s) affected:

         SETATTR of retention_hold.

      Discussion:

         Permission to modify the administration retention holds.  A
         server MAY map ACE4_WRITE_ATTRIBUTES to
         ACE_WRITE_RETENTION_HOLD.

   ACE4_DELETE

      Operation(s) affected:

         REMOVE

      Discussion:

         Permission to delete the file or directory.  See
         Section 6.2.1.3.2 for information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ACL

      Operation(s) affected:

         GETATTR of acl, dacl, or sacl

         NVERIFY

         VERIFY

      Discussion:

         Permission to read the ACL.

   ACE4_WRITE_ACL

      Operation(s) affected:

         SETATTR of acl and mode








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      Discussion:

         Permission to write the acl and mode attributes.

   ACE4_WRITE_OWNER

      Operation(s) affected:

         SETATTR of owner and owner_group

      Discussion:

         Permission to write the owner and owner_group attributes.  On
         UNIX systems, this is the ability to execute chown() and
         chgrp().

   ACE4_SYNCHRONIZE

      Operation(s) affected:

         NONE

      Discussion:

         Permission to use the file object as a synchronization
         primitive for interprocess communication.  This permission is
         not enforced or interpreted by the NFSv4.1 server on behalf of
         the client.

         Typically, the ACE4_SYNCHRONIZE permission is only meaningful
         on local file systems, i.e., file systems not accessed via
         NFSv4.1.  The reason that the permission bit exists is that
         some operating environments, such as Windows, use
         ACE4_SYNCHRONIZE.

         For example, if a client copies a file that has
         ACE4_SYNCHRONIZE set from a local file system to an NFSv4.1
         server, and then later copies the file from the NFSv4.1 server
         to a local file system, it is likely that if ACE4_SYNCHRONIZE
         was set in the original file, the client will want it set in
         the second copy.  The first copy will not have the permission
         set unless the NFSv4.1 server has the means to set the
         ACE4_SYNCHRONIZE bit.  The second copy will not have the
         permission set unless the NFSv4.1 server has the means to
         retrieve the ACE4_SYNCHRONIZE bit.

   Server implementations need not provide the granularity of control
   that is implied by this list of masks.  For example, POSIX-based



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   systems might not distinguish ACE4_APPEND_DATA (the ability to append
   to a file) from ACE4_WRITE_DATA (the ability to modify existing
   contents); both masks would be tied to a single "write" permission
   [20].  When such a server returns attributes to the client, it would
   show both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the
   write permission is enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should err in the direction of more restricted access,
   except in the previously discussed cases of execute and read.  For
   example, suppose a server cannot distinguish overwriting data from
   appending new data, as described in the previous paragraph.  If a
   client submits an ALLOW ACE where ACE4_APPEND_DATA is set but
   ACE4_WRITE_DATA is not (or vice versa), the server should either turn
   off ACE4_APPEND_DATA or reject the request with NFS4ERR_ATTRNOTSUPP.

6.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits govern the ability to delete a directory entry:
   ACE4_DELETE on the object itself (the "target") and ACE4_DELETE_CHILD
   on the containing directory (the "parent").

   Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
   to allow unlink only to a user that owns either the target or the
   parent; on some such systems the decision also depends on whether the
   target is writable.

   Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
   target, or ACE4_DELETE_CHILD is permitted on the parent.  (Note that
   this is true even if the parent or target explicitly denies one of
   these permissions.)

   If the ACLs in question neither explicitly ALLOW nor DENY either of
   the above, and if MODE4_SVTX is not set on the parent, then the
   server SHOULD allow the removal if and only if ACE4_ADD_FILE is
   permitted.  In the case where MODE4_SVTX is set, the server may also
   require the remover to own either the parent or the target, or may
   require the target to be writable.

   This allows servers to support something close to traditional UNIX-
   like semantics, with ACE4_ADD_FILE taking the place of the write bit.

6.2.1.4.  ACE flag

   The bitmask constants used for the flag field are as follows:






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   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;
   const ACE4_INHERITED_ACE                = 0x00000080;

   A server need not support any of these flags.  If the server supports
   flags that are similar to, but not exactly the same as, these flags,
   the implementation may define a mapping between the protocol-defined
   flags and the implementation-defined flags.

   For example, suppose a client tries to set an ACE with
   ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
   server does not support any form of ACL inheritance, the server
   should reject the request with NFS4ERR_ATTRNOTSUPP.  If the server
   supports a single "inherit ACE" flag that applies to both files and
   directories, the server may reject the request (i.e., requiring the
   client to set both the file and directory inheritance flags).  The
   server may also accept the request and silently turn on the
   ACE4_DIRECTORY_INHERIT_ACE flag.

6.2.1.4.1.  Discussion of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Any non-directory file in any sub-directory will get this ACE
      inherited.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new directory created.
      If this flag is set in an ACE in an ACL attribute to be set on a
      non-directory file system object, the operation attempting to set
      the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  This flag tells the server that
      inheritance of this ACE should stop at newly created child
      directories.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and



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      directories as specified by the ACE4_FILE_INHERIT_ACE and
      ACE4_DIRECTORY_INHERIT_ACE flags.

      If this flag is present on an ACE, but neither
      ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
      then an operation attempting to set such an attribute SHOULD fail
      with NFS4ERR_ATTRNOTSUPP.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG

   ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits may be set only on
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's ACL,
      the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the
      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, it then notes if the operation succeeded or failed.
      If the operation succeeded, and if the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM
      event occurs.  If the operation failed, and if the FAILED flag was
      set for the matching AUDIT or ALARM ACE, then the appropriate
      AUDIT or ALARM event occurs.  Either or both of the SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies to ACCESS operations
      even when they return NFS4_OK.  For the purposes of AUDIT and
      ALARM, we consider an ACCESS operation to be a "failure" if it
      fails to return a bit that was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX
      or a GROUP ACCOUNT as defined under Windows.  Clients and servers
      MUST ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of the special identifiers outlined in
      Section 6.2.1.5.

   ACE4_INHERITED_ACE
      Indicates that this ACE is inherited from a parent directory.  A
      server that supports automatic inheritance will place this flag on
      any ACEs inherited from the parent directory when creating a new
      object.  Client applications will use this to perform automatic
      inheritance.  Clients and servers MUST clear this bit in the acl
      attribute; it may only be used in the dacl and sacl attributes.




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6.2.1.5.  ACE Who

   The "who" field of an ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a
   user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers that need to be understood
   universally, rather than in the context of a particular DNS domain.
   Some of these identifiers cannot be understood when an NFS client
   accesses the server, but have meaning when a local process accesses
   the file.  The ability to display and modify these permissions is
   permitted over NFS, even if none of the access methods on the server
   understands the identifiers.

   +---------------+--------------------------------------------------+
   | Who           | Description                                      |
   +---------------+--------------------------------------------------+
   | OWNER         | The owner of the file.                           |
   | GROUP         | The group associated with the file.              |
   | EVERYONE      | The world, including the owner and owning group. |
   | INTERACTIVE   | Accessed from an interactive terminal.           |
   | NETWORK       | Accessed via the network.                        |
   | DIALUP        | Accessed as a dialup user to the server.         |
   | BATCH         | Accessed from a batch job.                       |
   | ANONYMOUS     | Accessed without any authentication.             |
   | AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS).  |
   | SERVICE       | Access from a system service.                    |
   +---------------+--------------------------------------------------+

                                  Table 4

   To avoid conflict, these special identifiers are distinguished by an
   appended "@" and should appear in the form "xxxx@" (with no domain
   name after the "@"), for example, ANONYMOUS@.

   The ACE4_IDENTIFIER_GROUP flag MUST be ignored on entries with these
   special identifiers.  When encoding entries with these special
   identifiers, the ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.

6.2.1.5.1.  Discussion of EVERYONE@

   It is important to note that "EVERYONE@" is not equivalent to the
   UNIX "other" entity.  This is because, by definition, UNIX "other"
   does not include the owner or owning group of a file.  "EVERYONE@"
   means literally everyone, including the owner or owning group.





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6.2.2.  Attribute 58: dacl

   The dacl attribute is like the acl attribute, but dacl allows just
   ALLOW and DENY ACEs.  The dacl attribute supports automatic
   inheritance (see Section 6.4.3.2).

6.2.3.  Attribute 59: sacl

   The sacl attribute is like the acl attribute, but sacl allows just
   AUDIT and ALARM ACEs.  The sacl attribute supports automatic
   inheritance (see Section 6.4.3.2).

6.2.4.  Attribute 33: mode

   The NFSv4.1 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:

   const MODE4_SUID = 0x800;  /* set user id on execution */
   const MODE4_SGID = 0x400;  /* set group id on execution */
   const MODE4_SVTX = 0x200;  /* save text even after use */
   const MODE4_RUSR = 0x100;  /* read permission: owner */
   const MODE4_WUSR = 0x080;  /* write permission: owner */
   const MODE4_XUSR = 0x040;  /* execute permission: owner */
   const MODE4_RGRP = 0x020;  /* read permission: group */
   const MODE4_WGRP = 0x010;  /* write permission: group */
   const MODE4_XGRP = 0x008;  /* execute permission: group */
   const MODE4_ROTH = 0x004;  /* read permission: other */
   const MODE4_WOTH = 0x002;  /* write permission: other */
   const MODE4_XOTH = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP apply to principals identified in the owner_group
   attribute but who are not identified in the owner attribute.  Bits
   MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH apply to any principal that
   does not match that in the owner attribute and does not have a group
   matching that of the owner_group attribute.

   Bits within a mode other than those specified above are not defined
   by this protocol.  A server MUST NOT return bits other than those
   defined above in a GETATTR or READDIR operation, and it MUST return
   NFS4ERR_INVAL if bits other than those defined above are set in a
   SETATTR, CREATE, OPEN, VERIFY, or NVERIFY operation.

6.2.5.  Attribute 74: mode_set_masked

   The mode_set_masked attribute is a write-only attribute that allows
   individual bits in the mode attribute to be set or reset, without



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   changing others.  It allows, for example, the bits MODE4_SUID,
   MODE4_SGID, and MODE4_SVTX to be modified while leaving unmodified
   any of the nine low-order mode bits devoted to permissions.

   In such instances that the nine low-order bits are left unmodified,
   then neither the acl nor the dacl attribute should be automatically
   modified as discussed in Section 6.4.1.

   The mode_set_masked attribute consists of two words, each in the form
   of a mode4.  The first consists of the value to be applied to the
   current mode value and the second is a mask.  Only bits set to one in
   the mask word are changed (set or reset) in the file's mode.  All
   other bits in the mode remain unchanged.  Bits in the first word that
   correspond to bits that are zero in the mask are ignored, except that
   undefined bits are checked for validity and can result in
   NFS4ERR_INVAL as described below.

   The mode_set_masked attribute is only valid in a SETATTR operation.
   If it is used in a CREATE or OPEN operation, the server MUST return
   NFS4ERR_INVAL.

   Bits not defined as valid in the mode attribute are not valid in
   either word of the mode_set_masked attribute.  The server MUST return
   NFS4ERR_INVAL if any such bits are set to one in a SETATTR.  If the
   mode and mode_set_masked attributes are both specified in the same
   SETATTR, the server MUST also return NFS4ERR_INVAL.

6.3.  Common Methods

   The requirements in this section will be referred to in future
   sections, especially Section 6.4.

6.3.1.  Interpreting an ACL

6.3.1.1.  Server Considerations

   The server uses the algorithm described in Section 6.2.1 to determine
   whether an ACL allows access to an object.  However, the ACL might
   not be the sole determiner of access.  For example:

   o  In the case of a file system exported as read-only, the server may
      deny write access even though an object's ACL grants it.

   o  Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
      permissions to prevent a situation from arising in which there is
      no valid way to ever modify the ACL.





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   o  All servers will allow a user the ability to read the data of the
      file when only the execute permission is granted (i.e., if the ACL
      denies the user the ACE4_READ_DATA access and allows the user
      ACE4_EXECUTE, the server will allow the user to read the data of
      the file).

   o  Many servers have the notion of owner-override in which the owner
      of the object is allowed to override accesses that are denied by
      the ACL.  This may be helpful, for example, to allow users
      continued access to open files on which the permissions have
      changed.

   o  Many servers have the notion of a "superuser" that has privileges
      beyond an ordinary user.  The superuser may be able to read or
      write data or metadata in ways that would not be permitted by the
      ACL.

   o  A retention attribute might also block access otherwise allowed by
      ACLs (see Section 5.13).

6.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own access checks based on their
   interpretation of the ACL, but rather use the OPEN and ACCESS
   operations to do access checks.  This allows the client to act on the
   results of having the server determine whether or not access should
   be granted based on its interpretation of the ACL.

   Clients must be aware of situations in which an object's ACL will
   define a certain access even though the server will not enforce it.
   In general, but especially in these situations, the client needs to
   do its part in the enforcement of access as defined by the ACL.  To
   do this, the client MAY send the appropriate ACCESS operation prior
   to servicing the request of the user or application in order to
   determine whether the user or application should be granted the
   access requested.  For examples in which the ACL may define accesses
   that the server doesn't enforce, see Section 6.3.1.1.

6.3.2.  Computing a Mode Attribute from an ACL

   The following method can be used to calculate the MODE4_R*, MODE4_W*,
   and MODE4_X* bits of a mode attribute, based upon an ACL.

   First, for each of the special identifiers OWNER@, GROUP@, and
   EVERYONE@, evaluate the ACL in order, considering only ALLOW and DENY
   ACEs for the identifier EVERYONE@ and for the identifier under
   consideration.  The result of the evaluation will be an NFSv4 ACL
   mask showing exactly which bits are permitted to that identifier.



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   Then translate the calculated mask for OWNER@, GROUP@, and EVERYONE@
   into mode bits for, respectively, the user, group, and other, as
   follows:

   1.  Set the read bit (MODE4_RUSR, MODE4_RGRP, or MODE4_ROTH) if and
       only if ACE4_READ_DATA is set in the corresponding mask.

   2.  Set the write bit (MODE4_WUSR, MODE4_WGRP, or MODE4_WOTH) if and
       only if ACE4_WRITE_DATA and ACE4_APPEND_DATA are both set in the
       corresponding mask.

   3.  Set the execute bit (MODE4_XUSR, MODE4_XGRP, or MODE4_XOTH), if
       and only if ACE4_EXECUTE is set in the corresponding mask.

6.3.2.1.  Discussion

   Some server implementations also add bits permitted to named users
   and groups to the group bits (MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP).

   Implementations are discouraged from doing this, because it has been
   found to cause confusion for users who see members of a file's group
   denied access that the mode bits appear to allow.  (The presence of
   DENY ACEs may also lead to such behavior, but DENY ACEs are expected
   to be more rarely used.)

   The same user confusion seen when fetching the mode also results if
   setting the mode does not effectively control permissions for the
   owner, group, and other users; this motivates some of the
   requirements that follow.

6.4.  Requirements

   The server that supports both mode and ACL must take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs that have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@".  This way, the client can see if semantically equivalent
   access permissions exist whether the client asks for the owner,
   owner_group, and mode attributes or for just the ACL.

   In this section, much is made of the methods in Section 6.3.2.  Many
   requirements refer to this section.  But note that the methods have
   behaviors specified with "SHOULD".  This is intentional, to avoid
   invalidating existing implementations that compute the mode according
   to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions on owner, group, and other.





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6.4.1.  Setting the Mode and/or ACL Attributes

   In the case where a server supports the sacl or dacl attribute, in
   addition to the acl attribute, the server MUST fail a request to set
   the acl attribute simultaneously with a dacl or sacl attribute.  The
   error to be given is NFS4ERR_ATTRNOTSUPP.

6.4.1.1.  Setting Mode and not ACL

   When any of the nine low-order mode bits are subject to change,
   either because the mode attribute was set or because the
   mode_set_masked attribute was set and the mask included one or more
   bits from the nine low-order mode bits, and no ACL attribute is
   explicitly set, the acl and dacl attributes must be modified in
   accordance with the updated value of those bits.  This must happen
   even if the value of the low-order bits is the same after the mode is
   set as before.

   Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl
   attribute) are unaffected by changes to the mode.

   In cases in which the permissions bits are subject to change, the acl
   and dacl attributes MUST be modified such that the mode computed via
   the method in Section 6.3.2 yields the low-order nine bits (MODE4_R*,
   MODE4_W*, MODE4_X*) of the mode attribute as modified by the
   attribute change.  The ACL attributes SHOULD also be modified such
   that:

   1.  If MODE4_RGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA or ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

   Access mask bits other than those listed above, appearing in ALLOW
   ACEs, MAY also be disabled.

   Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect
   the permissions of the ACL itself, nor do ACEs of the type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the ACL attributes.




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   Also note that the requirement may be met by discarding the acl and
   dacl, in favor of an ACL that represents the mode and only the mode.
   This is permitted, but it is preferable for a server to preserve as
   much of the ACL as possible without violating the above requirements.
   Discarding the ACL makes it effectively impossible for a file created
   with a mode attribute to inherit an ACL (see Section 6.4.3).

6.4.1.2.  Setting ACL and Not Mode

   When setting the acl or dacl and not setting the mode or
   mode_set_masked attributes, the permission bits of the mode need to
   be derived from the ACL.  In this case, the ACL attribute SHOULD be
   set as given.  The nine low-order bits of the mode attribute
   (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result
   of the method in Section 6.3.2.  The three high-order bits of the
   mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.

6.4.1.3.  Setting Both ACL and Mode

   When setting both the mode (includes use of either the mode attribute
   or the mode_set_masked attribute) and the acl or dacl attributes in
   the same operation, the attributes MUST be applied in this order:
   mode (or mode_set_masked), then ACL.  The mode-related attribute is
   set as given, then the ACL attribute is set as given, possibly
   changing the final mode, as described above in Section 6.4.1.2.

6.4.2.  Retrieving the Mode and/or ACL Attributes

   This section applies only to servers that support both the mode and
   ACL attributes.

   Some server implementations may have a concept of "objects without
   ACLs", meaning that all permissions are granted and denied according
   to the mode attribute and that no ACL attribute is stored for that
   object.  If an ACL attribute is requested of such a server, the
   server SHOULD return an ACL that does not conflict with the mode;
   that is to say, the ACL returned SHOULD represent the nine low-order
   bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 6.3.2.

   For other server implementations, the ACL attribute is always present
   for every object.  Such servers SHOULD store at least the three high-
   order bits of the mode attribute (MODE4_SUID, MODE4_SGID,
   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and the low-order nine bits of the mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in
   Section 6.3.2 to the ACL attribute.




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6.4.3.  Creating New Objects

   If a server supports any ACL attributes, it may use the ACL
   attributes on the parent directory to compute an initial ACL
   attribute for a newly created object.  This will be referred to as
   the inherited ACL within this section.  The act of adding one or more
   ACEs to the inherited ACL that are based upon ACEs in the parent
   directory's ACL will be referred to as inheriting an ACE within this
   section.

   Implementors should standardize what the behavior of CREATE and OPEN
   must be depending on the presence or absence of the mode and ACL
   attributes.

   1.  If just the mode is given in the call:

       In this case, inheritance SHOULD take place, but the mode MUST be
       applied to the inherited ACL as described in Section 6.4.1.1,
       thereby modifying the ACL.

   2.  If just the ACL is given in the call:

       In this case, inheritance SHOULD NOT take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification,
       and the mode modified as in Section 6.4.1.2.

   3.  If both mode and ACL are given in the call:

       In this case, inheritance SHOULD NOT take place, and both
       attributes will be set as described in Section 6.4.1.3.

   4.  If neither mode nor ACL is given in the call:

       In the case where an object is being created without any initial
       attributes at all, e.g., an OPEN operation with an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place (note that EXCLUSIVE4_1 is a better choice of
       createmode4, since it does permit initial attributes).  Instead,
       the server SHOULD set permissions to deny all access to the newly
       created object.  It is expected that the appropriate client will
       set the desired attributes in a subsequent SETATTR operation, and
       the server SHOULD allow that operation to succeed, regardless of
       what permissions the object is created with.  For example, an
       empty ACL denies all permissions, but the server should allow the
       owner's SETATTR to succeed even though WRITE_ACL is implicitly
       denied.

       In other cases, inheritance SHOULD take place, and no



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       modifications to the ACL will happen.  The mode attribute, if
       supported, MUST be as computed in Section 6.3.2, with the
       MODE4_SUID, MODE4_SGID, and MODE4_SVTX bits clear.  If no
       inheritable ACEs exist on the parent directory, the rules for
       creating acl, dacl, or sacl attributes are implementation
       defined.  If either the dacl or sacl attribute is supported, then
       the ACL4_DEFAULTED flag SHOULD be set on the newly created
       attributes.


6.4.3.1.  The Inherited ACL

   If the object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the parent directory ACL unless the
   ACE4_FILE_INHERIT_FLAG is set.

   If the object being created is a directory, the inherited ACL should
   inherit all inheritable ACEs from the parent directory, that is,
   those that have the ACE4_FILE_INHERIT_ACE or
   ACE4_DIRECTORY_INHERIT_ACE flag set.  If the inheritable ACE has
   ACE4_FILE_INHERIT_ACE set but ACE4_DIRECTORY_INHERIT_ACE is clear,
   the inherited ACE on the newly created directory MUST have the
   ACE4_INHERIT_ONLY_ACE flag set to prevent the directory from being
   affected by ACEs meant for non-directories.

   When a new directory is created, the server MAY split any inherited
   ACE that is both inheritable and effective (in other words, that has
   neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE set),
   into two ACEs, one with no inheritance flags and one with
   ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or sacl attribute,
   both of those ACEs SHOULD also have the ACE4_INHERITED_ACE flag set.)
   This makes it simpler to modify the effective permissions on the
   directory without modifying the ACE that is to be inherited to the
   new directory's children.

6.4.3.2.  Automatic Inheritance

   The acl attribute consists only of an array of ACEs, but the sacl
   (Section 6.2.3) and dacl (Section 6.2.2) attributes also include an
   additional flag field.

   struct nfsacl41 {
           aclflag4        na41_flag;
           nfsace4         na41_aces<>;
   };

   The flag field applies to the entire sacl or dacl; three flag values
   are defined:



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   const ACL4_AUTO_INHERIT         = 0x00000001;
   const ACL4_PROTECTED            = 0x00000002;
   const ACL4_DEFAULTED            = 0x00000004;

   and all other bits must be cleared.  The ACE4_INHERITED_ACE flag may
   be set in the ACEs of the sacl or dacl (whereas it must always be
   cleared in the acl).

   Together these features allow a server to support automatic
   inheritance, which we now explain in more detail.

   Inheritable ACEs are normally inherited by child objects only at the
   time that the child objects are created; later modifications to
   inheritable ACEs do not result in modifications to inherited ACEs on
   descendants.

   However, the dacl and sacl provide an OPTIONAL mechanism that allows
   a client application to propagate changes to inheritable ACEs to an
   entire directory hierarchy.

   A server that supports this performs inheritance at object creation
   time in the normal way, and SHOULD set the ACE4_INHERITED_ACE flag on
   any inherited ACEs as they are added to the new object.

   A client application such as an ACL editor may then propagate changes
   to inheritable ACEs on a directory by recursively traversing that
   directory's descendants and modifying each ACL encountered to remove
   any ACEs with the ACE4_INHERITED_ACE flag and to replace them by the
   new inheritable ACEs (also with the ACE4_INHERITED_ACE flag set).  It
   uses the existing ACE inheritance flags in the obvious way to decide
   which ACEs to propagate.  (Note that it may encounter further
   inheritable ACEs when descending the directory hierarchy and that
   those will also need to be taken into account when propagating
   inheritable ACEs to further descendants.)

   The reach of this propagation may be limited in two ways: first,
   automatic inheritance is not performed from any directory ACL that
   has the ACL4_AUTO_INHERIT flag cleared; and second, automatic
   inheritance stops wherever an ACL with the ACL4_PROTECTED flag is
   set, preventing modification of that ACL and also (if the ACL is set
   on a directory) of the ACL on any of the object's descendants.

   This propagation is performed independently for the sacl and the dacl
   attributes; thus, the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may
   be independently set for the sacl and the dacl, and propagation of
   one type of acl may continue down a hierarchy even where propagation
   of the other acl has stopped.




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   New objects should be created with a dacl and a sacl that both have
   the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to
   the same value as that on, respectively, the sacl or dacl of the
   parent object.

   Both the dacl and sacl attributes are RECOMMENDED, and a server may
   support one without supporting the other.

   A server that supports both the old acl attribute and one or both of
   the new dacl or sacl attributes must do so in such a way as to keep
   all three attributes consistent with each other.  Thus, the ACEs
   reported in the acl attribute should be the union of the ACEs
   reported in the dacl and sacl attributes, except that the
   ACE4_INHERITED_ACE flag must be cleared from the ACEs in the acl.
   And of course a client that queries only the acl will be unable to
   determine the values of the sacl or dacl flag fields.

   When a client performs a SETATTR for the acl attribute, the server
   SHOULD set the ACL4_PROTECTED flag to true on both the sacl and the
   dacl.  By using the acl attribute, as opposed to the dacl or sacl
   attributes, the client signals that it may not understand automatic
   inheritance, and thus cannot be trusted to set an ACL for which
   automatic inheritance would make sense.

   When a client application queries an ACL, modifies it, and sets it
   again, it should leave any ACEs marked with ACE4_INHERITED_ACE
   unchanged, in their original order, at the end of the ACL.  If the
   application is unable to do this, it should set the ACL4_PROTECTED
   flag.  This behavior is not enforced by servers, but violations of
   this rule may lead to unexpected results when applications perform
   automatic inheritance.

   If a server also supports the mode attribute, it SHOULD set the mode
   in such a way that leaves inherited ACEs unchanged, in their original
   order, at the end of the ACL.  If it is unable to do so, it SHOULD
   set the ACL4_PROTECTED flag on the file's dacl.

   Finally, in the case where the request that creates a new file or
   directory does not also set permissions for that file or directory,
   and there are also no ACEs to inherit from the parent's directory,
   then the server's choice of ACL for the new object is implementation-
   dependent.  In this case, the server SHOULD set the ACL4_DEFAULTED
   flag on the ACL it chooses for the new object.  An application
   performing automatic inheritance takes the ACL4_DEFAULTED flag as a
   sign that the ACL should be completely replaced by one generated
   using the automatic inheritance rules.





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7.  Single-Server Namespace

   This section describes the NFSv4 single-server namespace.  Single-
   server namespaces may be presented directly to clients, or they may
   be used as a basis to form larger multi-server namespaces (e.g.,
   site-wide or organization-wide) to be presented to clients, as
   described in Section 11.

7.1.  Server Exports

   On a UNIX server, the namespace describes all the files reachable by
   pathnames under the root directory or "/".  On a Windows server, the
   namespace constitutes all the files on disks named by mapped disk
   letters.  NFS server administrators rarely make the entire server's
   file system namespace available to NFS clients.  More often, portions
   of the namespace are made available via an "export" feature.  In
   previous versions of the NFS protocol, the root filehandle for each
   export is obtained through the MOUNT protocol; the client sent a
   string that identified the export name within the namespace and the
   server returned the root filehandle for that export.  The MOUNT
   protocol also provided an EXPORTS procedure that enumerated the
   server's exports.

7.2.  Browsing Exports

   The NFSv4.1 protocol provides a root filehandle that clients can use
   to obtain filehandles for the exports of a particular server, via a
   series of LOOKUP operations within a COMPOUND, to traverse a path.  A
   common user experience is to use a graphical user interface (perhaps
   a file "Open" dialog window) to find a file via progressive browsing
   through a directory tree.  The client must be able to move from one
   export to another export via single-component, progressive LOOKUP
   operations.

   This style of browsing is not well supported by the NFSv3 protocol.
   In NFSv3, the client expects all LOOKUP operations to remain within a
   single server file system.  For example, the device attribute will
   not change.  This prevents a client from taking namespace paths that
   span exports.

   In the case of NFSv3, an automounter on the client can obtain a
   snapshot of the server's namespace using the EXPORTS procedure of the
   MOUNT protocol.  If it understands the server's pathname syntax, it
   can create an image of the server's namespace on the client.  The
   parts of the namespace that are not exported by the server are filled
   in with directories that might be constructed similarly to an NFSv4.1
   "pseudo file system" (see Section 7.3) that allows the user to browse
   from one mounted file system to another.  There is a drawback to this



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   representation of the server's namespace on the client: it is static.
   If the server administrator adds a new export, the client will be
   unaware of it.

7.3.  Server Pseudo File System

   NFSv4.1 servers avoid this namespace inconsistency by presenting all
   the exports for a given server within the framework of a single
   namespace for that server.  An NFSv4.1 client uses LOOKUP and READDIR
   operations to browse seamlessly from one export to another.

   Where there are portions of the server namespace that are not
   exported, clients require some way of traversing those portions to
   reach actual exported file systems.  A technique that servers may use
   to provide for this is to bridge the unexported portion of the
   namespace via a "pseudo file system" that provides a view of exported
   directories only.  A pseudo file system has a unique fsid and behaves
   like a normal, read-only file system.

   Based on the construction of the server's namespace, it is possible
   that multiple pseudo file systems may exist.  For example,

           /a              pseudo file system
           /a/b            real file system
           /a/b/c          pseudo file system
           /a/b/c/d        real file system

   Each of the pseudo file systems is considered a separate entity and
   therefore MUST have its own fsid, unique among all the fsids for that
   server.

7.4.  Multiple Roots

   Certain operating environments are sometimes described as having
   "multiple roots".  In such environments, individual file systems are
   commonly represented by disk or volume names.  NFSv4 servers for
   these platforms can construct a pseudo file system above these root
   names so that disk letters or volume names are simply directory names
   in the pseudo root.

7.5.  Filehandle Volatility

   The nature of the server's pseudo file system is that it is a logical
   representation of file system(s) available from the server.
   Therefore, the pseudo file system is most likely constructed
   dynamically when the server is first instantiated.  It is expected
   that the pseudo file system may not have an on-disk counterpart from
   which persistent filehandles could be constructed.  Even though it is



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   preferable that the server provide persistent filehandles for the
   pseudo file system, the NFS client should expect that pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles in
   question.  If the filehandles are volatile, the NFS client must be
   prepared to recover a filehandle value (e.g., with a series of LOOKUP
   operations) when receiving an error of NFS4ERR_FHEXPIRED.

   Because it is quite likely that servers will implement pseudo file
   systems using volatile filehandles, clients need to be prepared for
   them, rather than assuming that all filehandles will be persistent.

7.6.  Exported Root

   If the server's root file system is exported, one might conclude that
   a pseudo file system is unneeded.  This is not necessarily so.
   Assume the following file systems on a server:

           /       fs1  (exported)
           /a      fs2  (not exported)
           /a/b    fs3  (exported)

   Because fs2 is not exported, fs3 cannot be reached with simple
   LOOKUPs.  The server must bridge the gap with a pseudo file system.

7.7.  Mount Point Crossing

   The server file system environment may be constructed in such a way
   that one file system contains a directory that is 'covered' or
   mounted upon by a second file system.  For example:

           /a/b            (file system 1)
           /a/b/c/d        (file system 2)

   The pseudo file system for this server may be constructed to look
   like:

           /               (place holder/not exported)
           /a/b            (file system 1)
           /a/b/c/d        (file system 2)

   It is the server's responsibility to present the pseudo file system
   that is complete to the client.  If the client sends a LOOKUP request
   for the path /a/b/c/d, the server's response is the filehandle of the
   root of the file system /a/b/c/d.  In previous versions of the NFS
   protocol, the server would respond with the filehandle of directory
   /a/b/c/d within the file system /a/b.




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   The NFS client will be able to determine if it crosses a server mount
   point by a change in the value of the "fsid" attribute.

7.8.  Security Policy and Namespace Presentation

   Because NFSv4 clients possess the ability to change the security
   mechanisms used, after determining what is allowed, by using SECINFO
   and SECINFO_NONAME, the server SHOULD NOT present a different view of
   the namespace based on the security mechanism being used by a client.
   Instead, it should present a consistent view and return
   NFS4ERR_WRONGSEC if an attempt is made to access data with an
   inappropriate security mechanism.

   If security considerations make it necessary to hide the existence of
   a particular file system, as opposed to all of the data within it,
   the server can apply the security policy of a shared resource in the
   server's namespace to components of the resource's ancestors.  For
   example:

           /                           (place holder/not exported)
           /a/b                        (file system 1)
           /a/b/MySecretProject        (file system 2)


   The /a/b/MySecretProject directory is a real file system and is the
   shared resource.  Suppose the security policy for /a/b/
   MySecretProject is Kerberos with integrity and it is desired to limit
   knowledge of the existence of this file system.  In this case, the
   server should apply the same security policy to /a/b.  This allows
   for knowledge of the existence of a file system to be secured when
   desirable.

   For the case of the use of multiple, disjoint security mechanisms in
   the server's resources, applying that sort of policy would result in
   the higher-level file system not being accessible using any security
   flavor.  Therefore, that sort of configuration is not compatible with
   hiding the existence (as opposed to the contents) from clients using
   multiple disjoint sets of security flavors.

   In other circumstances, a desirable policy is for the security of a
   particular object in the server's namespace to include the union of
   all security mechanisms of all direct descendants.  A common and
   convenient practice, unless strong security requirements dictate
   otherwise, is to make the entire the pseudo file system accessible by
   all of the valid security mechanisms.

   Where there is concern about the security of data on the network,
   clients should use strong security mechanisms to access the pseudo



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   file system in order to prevent man-in-the-middle attacks.

8.  State Management

   Integrating locking into the NFS protocol necessarily causes it to be
   stateful.  With the inclusion of such features as share reservations,
   file and directory delegations, recallable layouts, and support for
   mandatory byte-range locking, the protocol becomes substantially more
   dependent on proper management of state than the traditional
   combination of NFS and NLM (Network Lock Manager) [46].  These
   features include expanded locking facilities, which provide some
   measure of inter-client exclusion, but the state also offers features
   not readily providable using a stateless model.  There are three
   components to making this state manageable:

   o  clear division between client and server

   o  ability to reliably detect inconsistency in state between client
      and server

   o  simple and robust recovery mechanisms

   In this model, the server owns the state information.  The client
   requests changes in locks and the server responds with the changes
   made.  Non-client-initiated changes in locking state are infrequent.
   The client receives prompt notification of such changes and can
   adjust its view of the locking state to reflect the server's changes.

   Individual pieces of state created by the server and passed to the
   client at its request are represented by 128-bit stateids.  These
   stateids may represent a particular open file, a set of byte-range
   locks held by a particular owner, or a recallable delegation of
   privileges to access a file in particular ways or at a particular
   location.

   In all cases, there is a transition from the most general information
   that represents a client as a whole to the eventual lightweight
   stateid used for most client and server locking interactions.  The
   details of this transition will vary with the type of object but it
   always starts with a client ID.

8.1.  Client and Session ID

   A client must establish a client ID (see Section 2.4) and then one or
   more sessionids (see Section 2.10) before performing any operations
   to open, byte-range lock, delegate, or obtain a layout for a file
   object.  Each session ID is associated with a specific client ID, and
   thus serves as a shorthand reference to an NFSv4.1 client.



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   For some types of locking interactions, the client will represent
   some number of internal locking entities called "owners", which
   normally correspond to processes internal to the client.  For other
   types of locking-related objects, such as delegations and layouts, no
   such intermediate entities are provided for, and the locking-related
   objects are considered to be transferred directly between the server
   and a unitary client.

8.2.  Stateid Definition

   When the server grants a lock of any type (including opens, byte-
   range locks, delegations, and layouts), it responds with a unique
   stateid that represents a set of locks (often a single lock) for the
   same file, of the same type, and sharing the same ownership
   characteristics.  Thus, opens of the same file by different open-
   owners each have an identifying stateid.  Similarly, each set of
   byte-range locks on a file owned by a specific lock-owner has its own
   identifying stateid.  Delegations and layouts also have associated
   stateids by which they may be referenced.  The stateid is used as a
   shorthand reference to a lock or set of locks, and given a stateid,
   the server can determine the associated state-owner or state-owners
   (in the case of an open-owner/lock-owner pair) and the associated
   filehandle.  When stateids are used, the current filehandle must be
   the one associated with that stateid.

   All stateids associated with a given client ID are associated with a
   common lease that represents the claim of those stateids and the
   objects they represent to be maintained by the server.  See
   Section 8.3 for a discussion of the lease.

   The server may assign stateids independently for different clients.
   A stateid with the same bit pattern for one client may designate an
   entirely different set of locks for a different client.  The stateid
   is always interpreted with respect to the client ID associated with
   the current session.  Stateids apply to all sessions associated with
   the given client ID, and the client may use a stateid obtained from
   one session on another session associated with the same client ID.

8.2.1.  Stateid Types

   With the exception of special stateids (see Section 8.2.3), each
   stateid represents locking objects of one of a set of types defined
   by the NFSv4.1 protocol.  Note that in all these cases, where we
   speak of guarantee, it is understood there are situations such as a
   client restart, or lock revocation, that allow the guarantee to be
   voided.





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   o  Stateids may represent opens of files.

      Each stateid in this case represents the OPEN state for a given
      client ID/open-owner/filehandle triple.  Such stateids are subject
      to change (with consequent incrementing of the stateid's seqid) in
      response to OPENs that result in upgrade and OPEN_DOWNGRADE
      operations.

   o  Stateids may represent sets of byte-range locks.

      All locks held on a particular file by a particular owner and
      gotten under the aegis of a particular open file are associated
      with a single stateid with the seqid being incremented whenever
      LOCK and LOCKU operations affect that set of locks.

   o  Stateids may represent file delegations, which are recallable
      guarantees by the server to the client that other clients will not
      reference or modify a particular file, until the delegation is
      returned.  In NFSv4.1, file delegations may be obtained on both
      regular and non-regular files.

      A stateid represents a single delegation held by a client for a
      particular filehandle.

   o  Stateids may represent directory delegations, which are recallable
      guarantees by the server to the client that other clients will not
      modify the directory, until the delegation is returned.

      A stateid represents a single delegation held by a client for a
      particular directory filehandle.

   o  Stateids may represent layouts, which are recallable guarantees by
      the server to the client that particular files may be accessed via
      an alternate data access protocol at specific locations.  Such
      access is limited to particular sets of byte-ranges and may
      proceed until those byte-ranges are reduced or the layout is
      returned.

      A stateid represents the set of all layouts held by a particular
      client for a particular filehandle with a given layout type.  The
      seqid is updated as the layouts of that set of byte-ranges change,
      via layout stateid changing operations such as LAYOUTGET and
      LAYOUTRETURN.








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8.2.2.  Stateid Structure

   Stateids are divided into two fields, a 96-bit "other" field
   identifying the specific set of locks and a 32-bit "seqid" sequence
   value.  Except in the case of special stateids (see Section 8.2.3), a
   particular value of the "other" field denotes a set of locks of the
   same type (for example, byte-range locks, opens, delegations, or
   layouts), for a specific file or directory, and sharing the same
   ownership characteristics.  The seqid designates a specific instance
   of such a set of locks, and is incremented to indicate changes in
   such a set of locks, either by the addition or deletion of locks from
   the set, a change in the byte-range they apply to, or an upgrade or
   downgrade in the type of one or more locks.

   When such a set of locks is first created, the server returns a
   stateid with seqid value of one.  On subsequent operations that
   modify the set of locks, the server is required to increment the
   "seqid" field by one whenever it returns a stateid for the same
   state-owner/file/type combination and there is some change in the set
   of locks actually designated.  In this case, the server will return a
   stateid with an "other" field the same as previously used for that
   state-owner/file/type combination, with an incremented "seqid" field.
   This pattern continues until the seqid is incremented past
   NFS4_UINT32_MAX, and one (not zero) is the next seqid value.

   The purpose of the incrementing of the seqid is to allow the server
   to communicate to the client the order in which operations that
   modified locking state associated with a stateid have been processed
   and to make it possible for the client to send requests that are
   conditional on the set of locks not having changed since the stateid
   in question was returned.

   Except for layout stateids (Section 12.5.3), when a client sends a
   stateid to the server, it has two choices with regard to the seqid
   sent.  It may set the seqid to zero to indicate to the server that it
   wishes the most up-to-date seqid for that stateid's "other" field to
   be used.  This would be the common choice in the case of a stateid
   sent with a READ or WRITE operation.  It also may set a non-zero
   value, in which case the server checks if that seqid is the correct
   one.  In that case, the server is required to return
   NFS4ERR_OLD_STATEID if the seqid is lower than the most current value
   and NFS4ERR_BAD_STATEID if the seqid is greater than the most current
   value.  This would be the common choice in the case of stateids sent
   with a CLOSE or OPEN_DOWNGRADE.  Because OPENs may be sent in
   parallel for the same owner, a client might close a file without
   knowing that an OPEN upgrade had been done by the server, changing
   the lock in question.  If CLOSE were sent with a zero seqid, the OPEN
   upgrade would be cancelled before the client even received an



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   indication that an upgrade had happened.

   When a stateid is sent by the server to the client as part of a
   callback operation, it is not subject to checking for a current seqid
   and returning NFS4ERR_OLD_STATEID.  This is because the client is not
   in a position to know the most up-to-date seqid and thus cannot
   verify it.  Unless specially noted, the seqid value for a stateid
   sent by the server to the client as part of a callback is required to
   be zero with NFS4ERR_BAD_STATEID returned if it is not.

   In making comparisons between seqids, both by the client in
   determining the order of operations and by the server in determining
   whether the NFS4ERR_OLD_STATEID is to be returned, the possibility of
   the seqid being swapped around past the NFS4_UINT32_MAX value needs
   to be taken into account.  When two seqid values are being compared,
   the total count of slots for all sessions associated with the current
   client is used to do this.  When one seqid value is less than this
   total slot count and another seqid value is greater than
   NFS4_UINT32_MAX minus the total slot count, the former is to be
   treated as lower than the latter, despite the fact that it is
   numerically greater.

8.2.3.  Special Stateids

   Stateid values whose "other" field is either all zeros or all ones
   are reserved.  They may not be assigned by the server but have
   special meanings defined by the protocol.  The particular meaning
   depends on whether the "other" field is all zeros or all ones and the
   specific value of the "seqid" field.

   The following combinations of "other" and "seqid" are defined in
   NFSv4.1:

   o  When "other" and "seqid" are both zero, the stateid is treated as
      a special anonymous stateid, which can be used in READ, WRITE, and
      SETATTR requests to indicate the absence of any OPEN state
      associated with the request.  When an anonymous stateid value is
      used and an existing open denies the form of access requested,
      then access will be denied to the request.  This stateid MUST NOT
      be used on operations to data servers (Section 13.6).

   o  When "other" and "seqid" are both all ones, the stateid is a
      special READ bypass stateid.  When this value is used in WRITE or
      SETATTR, it is treated like the anonymous value.  When used in
      READ, the server MAY grant access, even if access would normally
      be denied to READ operations.  This stateid MUST NOT be used on
      operations to data servers.




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   o  When "other" is zero and "seqid" is one, the stateid represents
      the current stateid, which is whatever value is the last stateid
      returned by an operation within the COMPOUND.  In the case of an
      OPEN, the stateid returned for the open file and not the
      delegation is used.  The stateid passed to the operation in place
      of the special value has its "seqid" value set to zero, except
      when the current stateid is used by the operation CLOSE or
      OPEN_DOWNGRADE.  If there is no operation in the COMPOUND that has
      returned a stateid value, the server MUST return the error
      NFS4ERR_BAD_STATEID.  As illustrated in Figure 6, if the value of
      a current stateid is a special stateid and the stateid of an
      operation's arguments has "other" set to zero and "seqid" set to
      one, then the server MUST return the error NFS4ERR_BAD_STATEID.

   o  When "other" is zero and "seqid" is NFS4_UINT32_MAX, the stateid
      represents a reserved stateid value defined to be invalid.  When
      this stateid is used, the server MUST return the error
      NFS4ERR_BAD_STATEID.

   If a stateid value is used that has all zeros or all ones in the
   "other" field but does not match one of the cases above, the server
   MUST return the error NFS4ERR_BAD_STATEID.

   Special stateids, unlike other stateids, are not associated with
   individual client IDs or filehandles and can be used with all valid
   client IDs and filehandles.  In the case of a special stateid
   designating the current stateid, the current stateid value
   substituted for the special stateid is associated with a particular
   client ID and filehandle, and so, if it is used where the current
   filehandle does not match that associated with the current stateid,
   the operation to which the stateid is passed will return
   NFS4ERR_BAD_STATEID.

8.2.4.  Stateid Lifetime and Validation

   Stateids must remain valid until either a client restart or a server
   restart or until the client returns all of the locks associated with
   the stateid by means of an operation such as CLOSE or DELEGRETURN.
   If the locks are lost due to revocation, as long as the client ID is
   valid, the stateid remains a valid designation of that revoked state
   until the client frees it by using FREE_STATEID.  Stateids associated
   with byte-range locks are an exception.  They remain valid even if a
   LOCKU frees all remaining locks, so long as the open file with which
   they are associated remains open, unless the client frees the
   stateids via the FREE_STATEID operation.

   It should be noted that there are situations in which the client's
   locks become invalid, without the client requesting they be returned.



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   These include lease expiration and a number of forms of lock
   revocation within the lease period.  It is important to note that in
   these situations, the stateid remains valid and the client can use it
   to determine the disposition of the associated lost locks.

   An "other" value must never be reused for a different purpose (i.e.,
   different filehandle, owner, or type of locks) within the context of
   a single client ID.  A server may retain the "other" value for the
   same purpose beyond the point where it may otherwise be freed, but if
   it does so, it must maintain "seqid" continuity with previous values.

   One mechanism that may be used to satisfy the requirement that the
   server recognize invalid and out-of-date stateids is for the server
   to divide the "other" field of the stateid into two fields.

   o  an index into a table of locking-state structures.

   o  a generation number that is incremented on each allocation of a
      table entry for a particular use.

   And then store in each table entry,

   o  the client ID with which the stateid is associated.

   o  the current generation number for the (at most one) valid stateid
      sharing this index value.

   o  the filehandle of the file on which the locks are taken.

   o  an indication of the type of stateid (open, byte-range lock, file
      delegation, directory delegation, layout).

   o  the last "seqid" value returned corresponding to the current
      "other" value.

   o  an indication of the current status of the locks associated with
      this stateid, in particular, whether these have been revoked and
      if so, for what reason.

   With this information, an incoming stateid can be validated and the
   appropriate error returned when necessary.  Special and non-special
   stateids are handled separately.  (See Section 8.2.3 for a discussion
   of special stateids.)

   Note that stateids are implicitly qualified by the current client ID,
   as derived from the client ID associated with the current session.
   Note, however, that the semantics of the session will prevent
   stateids associated with a previous client or server instance from



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   being analyzed by this procedure.

   If server restart has resulted in an invalid client ID or a session
   ID that is invalid, SEQUENCE will return an error and the operation
   that takes a stateid as an argument will never be processed.

   If there has been a server restart where there is a persistent
   session and all leased state has been lost, then the session in
   question will, although valid, be marked as dead, and any operation
   not satisfied by means of the reply cache will receive the error
   NFS4ERR_DEADSESSION, and thus not be processed as indicated below.

   When a stateid is being tested and the "other" field is all zeros or
   all ones, a check that the "other" and "seqid" fields match a defined
   combination for a special stateid is done and the results determined
   as follows:

   o  If the "other" and "seqid" fields do not match a defined
      combination associated with a special stateid, the error
      NFS4ERR_BAD_STATEID is returned.

   o  If the special stateid is one designating the current stateid and
      there is a current stateid, then the current stateid is
      substituted for the special stateid and the checks appropriate to
      non-special stateids are performed.

   o  If the combination is valid in general but is not appropriate to
      the context in which the stateid is used (e.g., an all-zero
      stateid is used when an OPEN stateid is required in a LOCK
      operation), the error NFS4ERR_BAD_STATEID is also returned.

   o  Otherwise, the check is completed and the special stateid is
      accepted as valid.

   When a stateid is being tested, and the "other" field is neither all
   zeros nor all ones, the following procedure could be used to validate
   an incoming stateid and return an appropriate error, when necessary,
   assuming that the "other" field would be divided into a table index
   and an entry generation.

   o  If the table index field is outside the range of the associated
      table, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry is of a different generation than that
      specified in the incoming stateid, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry does not match the current filehandle,
      return NFS4ERR_BAD_STATEID.



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   o  If the client ID in the table entry does not match the client ID
      associated with the current session, return NFS4ERR_BAD_STATEID.

   o  If the stateid represents revoked state, then return
      NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED,
      as appropriate.

   o  If the stateid type is not valid for the context in which the
      stateid appears, return NFS4ERR_BAD_STATEID.  Note that a stateid
      may be valid in general, as would be reported by the TEST_STATEID
      operation, but be invalid for a particular operation, as, for
      example, when a stateid that doesn't represent byte-range locks is
      passed to the non-from_open case of LOCK or to LOCKU, or when a
      stateid that does not represent an open is passed to CLOSE or
      OPEN_DOWNGRADE.  In such cases, the server MUST return
      NFS4ERR_BAD_STATEID.

   o  If the "seqid" field is not zero and it is greater than the
      current sequence value corresponding to the current "other" field,
      return NFS4ERR_BAD_STATEID.

   o  If the "seqid" field is not zero and it is less than the current
      sequence value corresponding to the current "other" field, return
      NFS4ERR_OLD_STATEID.

   o  Otherwise, the stateid is valid and the table entry should contain
      any additional information about the type of stateid and
      information associated with that particular type of stateid, such
      as the associated set of locks, e.g., open-owner and lock-owner
      information, as well as information on the specific locks, e.g.,
      open modes and byte-ranges.

8.2.5.  Stateid Use for I/O Operations

   Clients performing I/O operations need to select an appropriate
   stateid based on the locks (including opens and delegations) held by
   the client and the various types of state-owners sending the I/O
   requests.  SETATTR operations that change the file size are treated
   like I/O operations in this regard.

   The following rules, applied in order of decreasing priority, govern
   the selection of the appropriate stateid.  In following these rules,
   the client will only consider locks of which it has actually received
   notification by an appropriate operation response or callback.  Note
   that the rules are slightly different in the case of I/O to data
   servers when file layouts are being used (see Section 13.9.1).





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   o  If the client holds a delegation for the file in question, the
      delegation stateid SHOULD be used.

   o  Otherwise, if the entity corresponding to the lock-owner (e.g., a
      process) sending the I/O has a byte-range lock stateid for the
      associated open file, then the byte-range lock stateid for that
      lock-owner and open file SHOULD be used.

   o  If there is no byte-range lock stateid, then the OPEN stateid for
      the open file in question SHOULD be used.

   o  Finally, if none of the above apply, then a special stateid SHOULD
      be used.

   Ignoring these rules may result in situations in which the server
   does not have information necessary to properly process the request.
   For example, when mandatory byte-range locks are in effect, if the
   stateid does not indicate the proper lock-owner, via a lock stateid,
   a request might be avoidably rejected.

   The server however should not try to enforce these ordering rules and
   should use whatever information is available to properly process I/O
   requests.  In particular, when a client has a delegation for a given
   file, it SHOULD take note of this fact in processing a request, even
   if it is sent with a special stateid.

8.2.6.  Stateid Use for SETATTR Operations

   Because each operation is associated with a session ID and from that
   the clientid can be determined, operations do not need to include a
   stateid for the server to be able to determine whether they should
   cause a delegation to be recalled or are to be treated as done within
   the scope of the delegation.

   In the case of SETATTR operations, a stateid is present.  In cases
   other than those that set the file size, the client may send either a
   special stateid or, when a delegation is held for the file in
   question, a delegation stateid.  While the server SHOULD validate the
   stateid and may use the stateid to optimize the determination as to
   whether a delegation is held, it SHOULD note the presence of a
   delegation even when a special stateid is sent, and MUST accept a
   valid delegation stateid when sent.

8.3.  Lease Renewal

   Each client/server pair, as represented by a client ID, has a single
   lease.  The purpose of the lease is to allow the client to indicate
   to the server, in a low-overhead way, that it is active, and thus



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   that the server is to retain the client's locks.  This arrangement
   allows the server to remove stale locking-related objects that are
   held by a client that has crashed or is otherwise unreachable, once
   the relevant lease expires.  This in turn allows other clients to
   obtain conflicting locks without being delayed indefinitely by
   inactive or unreachable clients.  It is not a mechanism for cache
   consistency and lease renewals may not be denied if the lease
   interval has not expired.

   Since each session is associated with a specific client (identified
   by the client's client ID), any operation sent on that session is an
   indication that the associated client is reachable.  When a request
   is sent for a given session, successful execution of a SEQUENCE
   operation (or successful retrieval of the result of SEQUENCE from the
   reply cache) on an unexpired lease will result in the lease being
   implicitly renewed, for the standard renewal period (equal to the
   lease_time attribute).

   If the client ID's lease has not expired when the server receives a
   SEQUENCE operation, then the server MUST renew the lease.  If the
   client ID's lease has expired when the server receives a SEQUENCE
   operation, the server MAY renew the lease; this depends on whether
   any state was revoked as a result of the client's failure to renew
   the lease before expiration.

   Absent other activity that would renew the lease, a COMPOUND
   consisting of a single SEQUENCE operation will suffice.  The client
   should also take communication-related delays into account and take
   steps to ensure that the renewal messages actually reach the server
   in good time.  For example:

   o  When trunking is in effect, the client should consider sending
      multiple requests on different connections, in order to ensure
      that renewal occurs, even in the event of blockage in the path
      used for one of those connections.

   o  Transport retransmission delays might become so large as to
      approach or exceed the length of the lease period.  This may be
      particularly likely when the server is unresponsive due to a
      restart; see Section 8.4.2.1.  If the client implementation is not
      careful, transport retransmission delays can result in the client
      failing to detect a server restart before the grace period ends.
      The scenario is that the client is using a transport with
      exponential backoff, such that the maximum retransmission timeout
      exceeds both the grace period and the lease_time attribute.  A
      network partition causes the client's connection's retransmission
      interval to back off, and even after the partition heals, the next
      transport-level retransmission is sent after the server has



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      restarted and its grace period ends.

      The client MUST either recover from the ensuing NFS4ERR_NO_GRACE
      errors or it MUST ensure that, despite transport-level
      retransmission intervals that exceed the lease_time, a SEQUENCE
      operation is sent that renews the lease before expiration.  The
      client can achieve this by associating a new connection with the
      session, and sending a SEQUENCE operation on it.  However, if the
      attempt to establish a new connection is delayed for some reason
      (e.g., exponential backoff of the connection establishment
      packets), the client will have to abort the connection
      establishment attempt before the lease expires, and attempt to
      reconnect.

   If the server renews the lease upon receiving a SEQUENCE operation,
   the server MUST NOT allow the lease to expire while the rest of the
   operations in the COMPOUND procedure's request are still executing.
   Once the last operation has finished, and the response to COMPOUND
   has been sent, the server MUST set the lease to expire no sooner than
   the sum of current time and the value of the lease_time attribute.

   A client ID's lease can expire when it has been at least the lease
   interval (lease_time) since the last lease-renewing SEQUENCE
   operation was sent on any of the client ID's sessions and there are
   no active COMPOUND operations on any such sessions.

   Because the SEQUENCE operation is the basic mechanism to renew a
   lease, and because it must be done at least once for each lease
   period, it is the natural mechanism whereby the server will inform
   the client of changes in the lease status that the client needs to be
   informed of.  The client should inspect the status flags
   (sr_status_flags) returned by sequence and take the appropriate
   action (see Section 18.46.3 for details).

   o  The status bits SEQ4_STATUS_CB_PATH_DOWN and
      SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with the
      backchannel that the client may need to address in order to
      receive callback requests.

   o  The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
      SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicate problems with GSS
      contexts or RPCSEC_GSS handles for the backchannel that the client
      might have to address in order to allow callback requests to be
      sent.

   o  The status bits SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
      SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED,
      SEQ4_STATUS_ADMIN_STATE_REVOKED, and



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      SEQ4_STATUS_RECALLABLE_STATE_REVOKED notify the client of lock
      revocation events.  When these bits are set, the client should use
      TEST_STATEID to find what stateids have been revoked and use
      FREE_STATEID to acknowledge loss of the associated state.

   o  The status bit SEQ4_STATUS_LEASE_MOVE indicates that
      responsibility for lease renewal has been transferred to one or
      more new servers.

   o  The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED indicates that
      due to server restart the client must reclaim locking state.

   o  The status bit SEQ4_STATUS_BACKCHANNEL_FAULT indicates that the
      server has encountered an unrecoverable fault with the backchannel
      (e.g., it has lost track of a sequence ID for a slot in the
      backchannel).

8.4.  Crash Recovery

   A critical requirement in crash recovery is that both the client and
   the server know when the other has failed.  Additionally, it is
   required that a client sees a consistent view of data across server
   restarts.  All READ and WRITE operations that may have been queued
   within the client or network buffers must wait until the client has
   successfully recovered the locks protecting the READ and WRITE
   operations.  Any that reach the server before the server can safely
   determine that the client has recovered enough locking state to be
   sure that such operations can be safely processed must be rejected.
   This will happen because either:

   o  The state presented is no longer valid since it is associated with
      a now invalid client ID.  In this case, the client will receive
      either an NFS4ERR_BADSESSION or NFS4ERR_DEADSESSION error, and any
      attempt to attach a new session to that invalid client ID will
      result in an NFS4ERR_STALE_CLIENTID error.

   o  Subsequent recovery of locks may make execution of the operation
      inappropriate (NFS4ERR_GRACE).

8.4.1.  Client Failure and Recovery

   In the event that a client fails, the server may release the client's
   locks when the associated lease has expired.  Conflicting locks from
   another client may only be granted after this lease expiration.  As
   discussed in Section 8.3, when a client has not failed and re-
   establishes its lease before expiration occurs, requests for
   conflicting locks will not be granted.




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   To minimize client delay upon restart, lock requests are associated
   with an instance of the client by a client-supplied verifier.  This
   verifier is part of the client_owner4 sent in the initial EXCHANGE_ID
   call made by the client.  The server returns a client ID as a result
   of the EXCHANGE_ID operation.  The client then confirms the use of
   the client ID by establishing a session associated with that client
   ID (see Section 18.36.3 for a description of how this is done).  All
   locks, including opens, byte-range locks, delegations, and layouts
   obtained by sessions using that client ID, are associated with that
   client ID.

   Since the verifier will be changed by the client upon each
   initialization, the server can compare a new verifier to the verifier
   associated with currently held locks and determine that they do not
   match.  This signifies the client's new instantiation and subsequent
   loss (upon confirmation of the new client ID) of locking state.  As a
   result, the server is free to release all locks held that are
   associated with the old client ID that was derived from the old
   verifier.  At this point, conflicting locks from other clients, kept
   waiting while the lease had not yet expired, can be granted.  In
   addition, all stateids associated with the old client ID can also be
   freed, as they are no longer reference-able.

   Note that the verifier must have the same uniqueness properties as
   the verifier for the COMMIT operation.

8.4.2.  Server Failure and Recovery

   If the server loses locking state (usually as a result of a restart),
   it must allow clients time to discover this fact and re-establish the
   lost locking state.  The client must be able to re-establish the
   locking state without having the server deny valid requests because
   the server has granted conflicting access to another client.
   Likewise, if there is a possibility that clients have not yet re-
   established their locking state for a file and that such locking
   state might make it invalid to perform READ or WRITE operations.  For
   example, if mandatory locks are a possibility, the server must
   disallow READ and WRITE operations for that file.

   A client can determine that loss of locking state has occurred via
   several methods.

   1.  When a SEQUENCE (most common) or other operation returns
       NFS4ERR_BADSESSION, this may mean that the session has been
       destroyed but the client ID is still valid.  The client sends a
       CREATE_SESSION request with the client ID to re-establish the
       session.  If CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
       the client must establish a new client ID (see Section 8.1) and



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       re-establish its lock state with the new client ID, after the
       CREATE_SESSION operation succeeds (see Section 8.4.2.1).

   2.  When a SEQUENCE (most common) or other operation on a persistent
       session returns NFS4ERR_DEADSESSION, this indicates that a
       session is no longer usable for new, i.e., not satisfied from the
       reply cache, operations.  Once all pending operations are
       determined to be either performed before the retry or not
       performed, the client sends a CREATE_SESSION request with the
       client ID to re-establish the session.  If CREATE_SESSION fails
       with NFS4ERR_STALE_CLIENTID, the client must establish a new
       client ID (see Section 8.1) and re-establish its lock state after
       the CREATE_SESSION, with the new client ID, succeeds
       (Section 8.4.2.1).

   3.  When an operation, neither SEQUENCE nor preceded by SEQUENCE (for
       example, CREATE_SESSION, DESTROY_SESSION), returns
       NFS4ERR_STALE_CLIENTID, the client MUST establish a new client ID
       (Section 8.1) and re-establish its lock state (Section 8.4.2.1).

8.4.2.1.  State Reclaim

   When state information and the associated locks are lost as a result
   of a server restart, the protocol must provide a way to cause that
   state to be re-established.  The approach used is to define, for most
   types of locking state (layouts are an exception), a request whose
   function is to allow the client to re-establish on the server a lock
   first obtained from a previous instance.  Generally, these requests
   are variants of the requests normally used to create locks of that
   type and are referred to as "reclaim-type" requests, and the process
   of re-establishing such locks is referred to as "reclaiming" them.

   Because each client must have an opportunity to reclaim all of the
   locks that it has without the possibility that some other client will
   be granted a conflicting lock, a "grace period" is devoted to the
   reclaim process.  During this period, requests creating client IDs
   and sessions are handled normally, but locking requests are subject
   to special restrictions.  Only reclaim-type locking requests are
   allowed, unless the server can reliably determine (through state
   persistently maintained across restart instances) that granting any
   such lock cannot possibly conflict with a subsequent reclaim.  When a
   request is made to obtain a new lock (i.e., not a reclaim-type
   request) during the grace period and such a determination cannot be
   made, the server must return the error NFS4ERR_GRACE.

   Once a session is established using the new client ID, the client
   will use reclaim-type locking requests (e.g., LOCK operations with
   reclaim set to TRUE and OPEN operations with a claim type of



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   CLAIM_PREVIOUS; see Section 9.11) to re-establish its locking state.
   Once this is done, or if there is no such locking state to reclaim,
   the client sends a global RECLAIM_COMPLETE operation, i.e., one with
   the rca_one_fs argument set to FALSE, to indicate that it has
   reclaimed all of the locking state that it will reclaim.  Once a
   client sends such a RECLAIM_COMPLETE operation, it may attempt non-
   reclaim locking operations, although it might get an NFS4ERR_GRACE
   status result from each such operation until the period of special
   handling is over.  See Section 11.7.7 for a discussion of the
   analogous handling lock reclamation in the case of file systems
   transitioning from server to server.

   During the grace period, the server must reject READ and WRITE
   operations and non-reclaim locking requests (i.e., other LOCK and
   OPEN operations) with an error of NFS4ERR_GRACE, unless it can
   guarantee that these may be done safely, as described below.

   The grace period may last until all clients that are known to
   possibly have had locks have done a global RECLAIM_COMPLETE
   operation, indicating that they have finished reclaiming the locks
   they held before the server restart.  This means that a client that
   has done a RECLAIM_COMPLETE must be prepared to receive an
   NFS4ERR_GRACE when attempting to acquire new locks.  In order for the
   server to know that all clients with possible prior lock state have
   done a RECLAIM_COMPLETE, the server must maintain in stable storage a
   list clients that may have such locks.  The server may also terminate
   the grace period before all clients have done a global
   RECLAIM_COMPLETE.  The server SHOULD NOT terminate the grace period
   before a time equal to the lease period in order to give clients an
   opportunity to find out about the server restart, as a result of
   sending requests on associated sessions with a frequency governed by
   the lease time.  Note that when a client does not send such requests
   (or they are sent by the client but not received by the server), it
   is possible for the grace period to expire before the client finds
   out that the server restart has occurred.

   Some additional time in order to allow a client to establish a new
   client ID and session and to effect lock reclaims may be added to the
   lease time.  Note that analogous rules apply to file system-specific
   grace periods discussed in Section 11.7.7.

   If the server can reliably determine that granting a non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned even within the
   grace period, although NFS4ERR_GRACE must always be returned to
   clients attempting a non-reclaim lock request before doing their own
   global RECLAIM_COMPLETE.  For the server to be able to service READ
   and WRITE operations during the grace period, it must again be able



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   to guarantee that no possible conflict could arise between a
   potential reclaim locking request and the READ or WRITE operation.
   If the server is unable to offer that guarantee, the NFS4ERR_GRACE
   error must be returned to the client.

   For a server to provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, a server may keep information about
   granted locks in stable storage.  With this information, the server
   could determine if a locking, READ or WRITE operation can be safely
   processed.

   For example, if the server maintained on stable storage summary
   information on whether mandatory locks exist, either mandatory byte-
   range locks, or share reservations specifying deny modes, many
   requests could be allowed during the grace period.  If it is known
   that no such share reservations exist, OPEN request that do not
   specify deny modes may be safely granted.  If, in addition, it is
   known that no mandatory byte-range locks exist, either through
   information stored on stable storage or simply because the server
   does not support such locks, READ and WRITE operations may be safely
   processed during the grace period.  Another important case is where
   it is known that no mandatory byte-range locks exist, either because
   the server does not provide support for them or because their absence
   is known from persistently recorded data.  In this case, READ and
   WRITE operations specifying stateids derived from reclaim-type
   operations may be validly processed during the grace period because
   of the fact that the valid reclaim ensures that no lock subsequently
   granted can prevent the I/O.

   To reiterate, for a server that allows non-reclaim lock and I/O
   requests to be processed during the grace period, it MUST determine
   that no lock subsequently reclaimed will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during the grace period.

   Clients should be prepared for the return of NFS4ERR_GRACE errors for
   non-reclaim lock and I/O requests.  In this case, the client should
   employ a retry mechanism for the request.  A delay (on the order of
   several seconds) between retries should be used to avoid overwhelming
   the server.  Further discussion of the general issue is included in
   [47].  The client must account for the server that can perform I/O
   and non-reclaim locking requests within the grace period as well as
   those that cannot do so.

   A reclaim-type locking request outside the server's grace period can
   only succeed if the server can guarantee that no conflicting lock or



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   I/O request has been granted since restart.

   A server may, upon restart, establish a new value for the lease
   period.  Therefore, clients should, once a new client ID is
   established, refetch the lease_time attribute and use it as the basis
   for lease renewal for the lease associated with that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period for the previous server
   instantiation.  This allows the client state obtained during the
   previous server instance to be reliably re-established.

   The possibility exists that, because of server configuration events,
   the client will be communicating with a server different than the one
   on which the locks were obtained, as shown by the combination of
   eir_server_scope and eir_server_owner.  This leads to the issue of if
   and when the client should attempt to reclaim locks previously
   obtained on what is being reported as a different server.  The rules
   to resolve this question are as follows:

   o  If the server scope is different, the client should not attempt to
      reclaim locks.  In this situation, no lock reclaim is possible.
      Any attempt to re-obtain the locks with non-reclaim operations is
      problematic since there is no guarantee that the existing
      filehandles will be recognized by the new server, or that if
      recognized, they denote the same objects.  It is best to treat the
      locks as having been revoked by the reconfiguration event.

   o  If the server scope is the same, the client should attempt to
      reclaim locks, even if the eir_server_owner value is different.
      In this situation, it is the responsibility of the server to
      return NFS4ERR_NO_GRACE if it cannot provide correct support for
      lock reclaim operations, including the prevention of edge
      conditions.

   The eir_server_owner field is not used in making this determination.
   Its function is to specify trunking possibilities for the client (see
   Section 2.10.5) and not to control lock reclaim.

8.4.2.1.1.  Security Considerations for State Reclaim

   During the grace period, a client can reclaim state that it believes
   or asserts it had before the server restarted.  Unless the server
   maintained a complete record of all the state the client had, the
   server has little choice but to trust the client.  (Of course, if the
   server maintained a complete record, then it would not have to force
   the client to reclaim state after server restart.)  While the server
   has to trust the client to tell the truth, such trust does not have
   any negative consequences for security.  The fundamental rule for the



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   server when processing reclaim requests is that it MUST NOT grant the
   reclaim if an equivalent non-reclaim request would not be granted
   during steady state due to access control or access conflict issues.
   For example, an OPEN request during a reclaim will be refused with
   NFS4ERR_ACCESS if the principal making the request does not have
   access to open the file according to the discretionary ACL
   (Section 6.2.2) on the file.

   Nonetheless, it is possible that a client operating in error or
   maliciously could, during reclaim, prevent another client from
   reclaiming access to state.  For example, an attacker could send an
   OPEN reclaim operation with a deny mode that prevents another client
   from reclaiming the OPEN state it had before the server restarted.
   The attacker could perform the same denial of service during steady
   state prior to server restart, as long as the attacker had
   permissions.  Given that the attack vectors are equivalent, the grace
   period does not offer any additional opportunity for denial of
   service, and any concerns about this attack vector, whether during
   grace or steady state, are addressed the same way: use RPCSEC_GSS for
   authentication and limit access to the file only to principals that
   the owner of the file trusts.

   Note that if prior to restart the server had client IDs with the
   EXCHGID4_FLAG_BIND_PRINC_STATEID (Section 18.35) capability set, then
   the server SHOULD record in stable storage the client owner and the
   principal that established the client ID via EXCHANGE_ID.  If the
   server does not, then there is a risk a client will be unable to
   reclaim state if it does not have a credential for a principal that
   was originally authorized to establish the state.

8.4.3.  Network Partitions and Recovery

   If the duration of a network partition is greater than the lease
   period provided by the server, the server will not have received a
   lease renewal from the client.  If this occurs, the server may free
   all locks held for the client or it may allow the lock state to
   remain for a considerable period, subject to the constraint that if a
   request for a conflicting lock is made, locks associated with an
   expired lease do not prevent such a conflicting lock from being
   granted but MUST be revoked as necessary so as to avoid interfering
   with such conflicting requests.

   If the server chooses to delay freeing of lock state until there is a
   conflict, it may either free all of the client's locks once there is
   a conflict or it may only revoke the minimum set of locks necessary
   to allow conflicting requests.  When it adopts the finer-grained
   approach, it must revoke all locks associated with a given stateid,
   even if the conflict is with only a subset of locks.



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   When the server chooses to free all of a client's lock state, either
   immediately upon lease expiration or as a result of the first attempt
   to obtain a conflicting a lock, the server may report the loss of
   lock state in a number of ways.

   The server may choose to invalidate the session and the associated
   client ID.  In this case, once the client can communicate with the
   server, it will receive an NFS4ERR_BADSESSION error.  Upon attempting
   to create a new session, it would get an NFS4ERR_STALE_CLIENTID.
   Upon creating the new client ID and new session, the client will
   attempt to reclaim locks.  Normally, the server will not allow the
   client to reclaim locks, because the server will not be in its
   recovery grace period.

   Another possibility is for the server to maintain the session and
   client ID but for all stateids held by the client to become invalid
   or stale.  Once the client can reach the server after such a network
   partition, the status returned by the SEQUENCE operation will
   indicate a loss of locking state; i.e., the flag
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED will be set in sr_status_flags.
   In addition, all I/O submitted by the client with the now invalid
   stateids will fail with the server returning the error
   NFS4ERR_EXPIRED.  Once the client learns of the loss of locking
   state, it will suitably notify the applications that held the
   invalidated locks.  The client should then take action to free
   invalidated stateids, either by establishing a new client ID using a
   new verifier or by doing a FREE_STATEID operation to release each of
   the invalidated stateids.

   When the server adopts a finer-grained approach to revocation of
   locks when a client's lease has expired, only a subset of stateids
   will normally become invalid during a network partition.  When the
   client can communicate with the server after such a network partition
   heals, the status returned by the SEQUENCE operation will indicate a
   partial loss of locking state
   (SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED).  In addition, operations,
   including I/O submitted by the client, with the now invalid stateids
   will fail with the server returning the error NFS4ERR_EXPIRED.  Once
   the client learns of the loss of locking state, it will use the
   TEST_STATEID operation on all of its stateids to determine which
   locks have been lost and then suitably notify the applications that
   held the invalidated locks.  The client can then release the
   invalidated locking state and acknowledge the revocation of the
   associated locks by doing a FREE_STATEID operation on each of the
   invalidated stateids.

   When a network partition is combined with a server restart, there are
   edge conditions that place requirements on the server in order to



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   avoid silent data corruption following the server restart.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition arises as a result of the scenarios such as
   the following:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.

   3.  Client A's lease expires, and the server releases the lock.

   4.  Client B acquires a lock that would have conflicted with that of
       client A.

   5.  Client B releases its lock.

   6.  Server restarts.

   7.  Network partition between client A and server heals.

   8.  Client A connects to a new server instance and finds out about
       server restart.

   9.  Client A reclaims its lock within the server's grace period.

   Thus, at the final step, the server has erroneously granted client
   A's lock reclaim.  If client B modified the object the lock was
   protecting, client A will experience object corruption.

   The second known edge condition arises in situations such as the
   following:

   1.   Client A acquires one or more locks.

   2.   Server restarts.

   3.   Client A and server experience mutual network partition, such
        that client A is unable to reclaim all of its locks within the
        grace period.

   4.   Server's reclaim grace period ends.  Client A has either no
        locks or an incomplete set of locks known to the server.

   5.   Client B acquires a lock that would have conflicted with a lock
        of client A that was not reclaimed.




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   6.   Client B releases the lock.

   7.   Server restarts a second time.

   8.   Network partition between client A and server heals.

   9.   Client A connects to new server instance and finds out about
        server restart.

   10.  Client A reclaims its lock within the server's grace period.

   As with the first edge condition, the final step of the scenario of
   the second edge condition has the server erroneously granting client
   A's lock reclaim.

   Solving the first and second edge conditions requires either that the
   server always assumes after it restarts that some edge condition
   occurs, and thus returns NFS4ERR_NO_GRACE for all reclaim attempts,
   or that the server record some information in stable storage.  The
   amount of information the server records in stable storage is in
   inverse proportion to how harsh the server intends to be whenever
   edge conditions arise.  The server that is completely tolerant of all
   edge conditions will record in stable storage every lock that is
   acquired, removing the lock record from stable storage only when the
   lock is released.  For the two edge conditions discussed above, the
   harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage some
   minimal information.  For example, a server implementation could, for
   each client, save in stable storage a record containing:

   o  the co_ownerid field from the client_owner4 presented in the
      EXCHANGE_ID operation.

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see Section 8.5) to revoke a
      byte-range lock, share reservation, or delegation and there has
      been no acknowledgment, via FREE_STATEID, of such revocation.

   o  a boolean that indicates whether the client may have locks that it
      believes to be reclaimable in situations in which the grace period
      was terminated, making the server's view of lock reclaimability
      suspect.  The server will set this for any client record in stable
      storage where the client has not done a suitable RECLAIM_COMPLETE
      (global or file system-specific depending on the target of the
      lock request) before it grants any new (i.e., not reclaimed) lock
      to any client.

   Assuming the above record keeping, for the first edge condition,



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   after the server restarts, the record that client A's lease expired
   means that another client could have acquired a conflicting byte-
   range lock, share reservation, or delegation.  Hence, the server must
   reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   For the second edge condition, after the server restarts for a second
   time, the indication that the client had not completed its reclaims
   at the time at which the grace period ended means that the server
   must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   When either edge condition occurs, the client's attempt to reclaim
   locks will result in the error NFS4ERR_NO_GRACE.  When this is
   received, or after the client restarts with no lock state, the client
   will send a global RECLAIM_COMPLETE.  When the RECLAIM_COMPLETE is
   received, the server and client are again in agreement regarding
   reclaimable locks and both booleans in persistent storage can be
   reset, to be set again only when there is a subsequent event that
   causes lock reclaim operations to be questionable.

   Regardless of the level and approach to record keeping, the server
   MUST implement one of the following strategies (which apply to
   reclaims of share reservations, byte-range locks, and delegations):

   1.  Reject all reclaims with NFS4ERR_NO_GRACE.  This is extremely
       unforgiving, but necessary if the server does not record lock
       state in stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server restart, including the two noted
       in this section, are detected.  It is acceptable to erroneously
       recognize an edge condition and not allow a reclaim, when, with
       sufficient knowledge, it would be allowed.  The error the server
       would return in this case is NFS4ERR_NO_GRACE.  Note that it is
       not known if there are other edge conditions.

       In the event that, after a server restart, the server determines
       there is unrecoverable damage or corruption to the information in
       stable storage, then for all clients and/or locks that may be
       affected, the server MUST return NFS4ERR_NO_GRACE.

   A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
   outside the scope of this specification, since the strategies for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute of the objects for which the client is trying to
   reclaim state, and use that to determine whether to re-establish the



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   state via normal OPEN or LOCK operations.  This is acceptable
   provided that the client's operating environment allows it.  In other
   words, the client implementor is advised to document for his users
   the behavior.  The client could also inform the application that its
   byte-range lock or share reservations (whether or not they were
   delegated) have been lost, such as via a UNIX signal, a Graphical
   User Interface (GUI) pop-up window, etc.  See Section 10.5 for a
   discussion of what the client should do for dealing with unreclaimed
   delegations on client state.

   For further discussion of revocation of locks, see Section 8.5.

8.5.  Server Revocation of Locks

   At any point, the server can revoke locks held by a client, and the
   client must be prepared for this event.  When the client detects that
   its locks have been or may have been revoked, the client is
   responsible for validating the state information between itself and
   the server.  Validating locking state for the client means that it
   must verify or reclaim state for each lock currently held.

   The first occasion of lock revocation is upon server restart.  Note
   that this includes situations in which sessions are persistent and
   locking state is lost.  In this class of instances, the client will
   receive an error (NFS4ERR_STALE_CLIENTID) on an operation that takes
   client ID, usually as part of recovery in response to a problem with
   the current session), and the client will proceed with normal crash
   recovery as described in the Section 8.4.2.1.

   The second occasion of lock revocation is the inability to renew the
   lease before expiration, as discussed in Section 8.4.3.  While this
   is considered a rare or unusual event, the client must be prepared to
   recover.  The server is responsible for determining the precise
   consequences of the lease expiration, informing the client of the
   scope of the lock revocation decided upon.  The client then uses the
   status information provided by the server in the SEQUENCE results
   (field sr_status_flags, see Section 18.46.3) to synchronize its
   locking state with that of the server, in order to recover.

   The third occasion of lock revocation can occur as a result of
   revocation of locks within the lease period, either because of
   administrative intervention or because a recallable lock (a
   delegation or layout) was not returned within the lease period after
   having been recalled.  While these are considered rare events, they
   are possible, and the client must be prepared to deal with them.
   When either of these events occurs, the client finds out about the
   situation through the status returned by the SEQUENCE operation.  Any
   use of stateids associated with locks revoked during the lease period



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   will receive the error NFS4ERR_ADMIN_REVOKED or
   NFS4ERR_DELEG_REVOKED, as appropriate.

   In all situations in which a subset of locking state may have been
   revoked, which include all cases in which locking state is revoked
   within the lease period, it is up to the client to determine which
   locks have been revoked and which have not.  It does this by using
   the TEST_STATEID operation on the appropriate set of stateids.  Once
   the set of revoked locks has been determined, the applications can be
   notified, and the invalidated stateids can be freed and lock
   revocation acknowledged by using FREE_STATEID.

8.6.  Short and Long Leases

   When determining the time period for the server lease, the usual
   lease tradeoffs apply.  A short lease is good for fast server
   recovery at a cost of increased operations to effect lease renewal
   (when there are no other operations during the period to effect lease
   renewal as a side effect).  A long lease is certainly kinder and
   gentler to servers trying to handle very large numbers of clients.
   The number of extra requests to effect lock renewal drops in inverse
   proportion to the lease time.  The disadvantages of a long lease
   include the possibility of slower recovery after certain failures.
   After server failure, a longer grace period may be required when some
   clients do not promptly reclaim their locks and do a global
   RECLAIM_COMPLETE.  In the event of client failure, the longer period
   for a lease to expire will force conflicting requests to wait longer.

   A long lease is practical if the server can store lease state in
   stable storage.  Upon recovery, the server can reconstruct the lease
   state from its stable storage and continue operation with its
   clients.

8.7.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by
   the server as a time delta.  However, there is a requirement that the
   client and server clocks do not drift excessively over the duration
   of the lease.  There is also the issue of propagation delay across
   the network, which could easily be several hundred milliseconds, as
   well as the possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the client should subtract it
   from lease times (e.g., if the client estimates the one-way
   propagation delay as 200 milliseconds, then it can assume that the
   lease is already 200 milliseconds old when it gets it).  In addition,
   it will take another 200 milliseconds to get a response back to the



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   server.  So the client must send a lease renewal or write data back
   to the server at least 400 milliseconds before the lease would
   expire.  If the propagation delay varies over the life of the lease
   (e.g., the client is on a mobile host), the client will need to
   continuously subtract the increase in propagation delay from the
   lease times.

   The server's lease period configuration should take into account the
   network distance of the clients that will be accessing the server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate lease period, the
   server's administrator may have to tune the lease period.

8.8.  Obsolete Locking Infrastructure from NFSv4.0

   There are a number of operations and fields within existing
   operations that no longer have a function in NFSv4.1.  In one way or
   another, these changes are all due to the implementation of sessions
   that provide client context and exactly once semantics as a base
   feature of the protocol, separate from locking itself.

   The following NFSv4.0 operations MUST NOT be implemented in NFSv4.1.
   The server MUST return NFS4ERR_NOTSUPP if these operations are found
   in an NFSv4.1 COMPOUND.

   o  SETCLIENTID since its function has been replaced by EXCHANGE_ID.

   o  SETCLIENTID_CONFIRM since client ID confirmation now happens by
      means of CREATE_SESSION.

   o  OPEN_CONFIRM because state-owner-based seqids have been replaced
      by the sequence ID in the SEQUENCE operation.

   o  RELEASE_LOCKOWNER because lock-owners with no associated locks do
      not have any sequence-related state and so can be deleted by the
      server at will.

   o  RENEW because every SEQUENCE operation for a session causes lease
      renewal, making a separate operation superfluous.

   Also, there are a number of fields, present in existing operations,
   related to locking that have no use in minor version 1.  They were
   used in minor version 0 to perform functions now provided in a
   different fashion.





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   o  Sequence ids used to sequence requests for a given state-owner and
      to provide retry protection, now provided via sessions.

   o  Client IDs used to identify the client associated with a given
      request.  Client identification is now available using the client
      ID associated with the current session, without needing an
      explicit client ID field.

   Such vestigial fields in existing operations have no function in
   NFSv4.1 and are ignored by the server.  Note that client IDs in
   operations new to NFSv4.1 (such as CREATE_SESSION and
   DESTROY_CLIENTID) are not ignored.

9.  File Locking and Share Reservations

   To support Win32 share reservations, it is necessary to provide
   operations that atomically open or create files.  Having a separate
   share/unshare operation would not allow correct implementation of the
   Win32 OpenFile API.  In order to correctly implement share semantics,
   the previous NFS protocol mechanisms used when a file is opened or
   created (LOOKUP, CREATE, ACCESS) need to be replaced.  The NFSv4.1
   protocol defines an OPEN operation that is capable of atomically
   looking up, creating, and locking a file on the server.

9.1.  Opens and Byte-Range Locks

   It is assumed that manipulating a byte-range lock is rare when
   compared to READ and WRITE operations.  It is also assumed that
   server restarts and network partitions are relatively rare.
   Therefore, it is important that the READ and WRITE operations have a
   lightweight mechanism to indicate if they possess a held lock.  A
   LOCK operation contains the heavyweight information required to
   establish a byte-range lock and uniquely define the owner of the
   lock.

9.1.1.  State-Owner Definition

   When opening a file or requesting a byte-range lock, the client must
   specify an identifier that represents the owner of the requested
   lock.  This identifier is in the form of a state-owner, represented
   in the protocol by a state_owner4, a variable-length opaque array
   that, when concatenated with the current client ID, uniquely defines
   the owner of a lock managed by the client.  This may be a thread ID,
   process ID, or other unique value.

   Owners of opens and owners of byte-range locks are separate entities
   and remain separate even if the same opaque arrays are used to
   designate owners of each.  The protocol distinguishes between open-



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   owners (represented by open_owner4 structures) and lock-owners
   (represented by lock_owner4 structures).

   Each open is associated with a specific open-owner while each byte-
   range lock is associated with a lock-owner and an open-owner, the
   latter being the open-owner associated with the open file under which
   the LOCK operation was done.  Delegations and layouts, on the other
   hand, are not associated with a specific owner but are associated
   with the client as a whole (identified by a client ID).

9.1.2.  Use of the Stateid and Locking

   All READ, WRITE, and SETATTR operations contain a stateid.  For the
   purposes of this section, SETATTR operations that change the size
   attribute of a file are treated as if they are writing the area
   between the old and new sizes (i.e., the byte-range truncated or
   added to the file by means of the SETATTR), even where SETATTR is not
   explicitly mentioned in the text.  The stateid passed to one of these
   operations must be one that represents an open, a set of byte-range
   locks, or a delegation, or it may be a special stateid representing
   anonymous access or the special bypass stateid.

   If the state-owner performs a READ or WRITE operation in a situation
   in which it has established a byte-range lock or share reservation on
   the server (any OPEN constitutes a share reservation), the stateid
   (previously returned by the server) must be used to indicate what
   locks, including both byte-range locks and share reservations, are
   held by the state-owner.  If no state is established by the client,
   either a byte-range lock or a share reservation, a special stateid
   for anonymous state (zero as the value for "other" and "seqid") is
   used.  (See Section 8.2.3 for a description of 'special' stateids in
   general.)  Regardless of whether a stateid for anonymous state or a
   stateid returned by the server is used, if there is a conflicting
   share reservation or mandatory byte-range lock held on the file, the
   server MUST refuse to service the READ or WRITE operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the OPEN denies READ or WRITE
   operations, that denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Byte-range locks may be implemented by
   the server as either mandatory or advisory, or the choice of
   mandatory or advisory behavior may be determined by the server on the
   basis of the file being accessed (for example, some UNIX-based
   servers support a "mandatory lock bit" on the mode attribute such
   that if set, byte-range locks are required on the file before I/O is
   possible).  When byte-range locks are advisory, they only prevent the
   granting of conflicting lock requests and have no effect on READs or
   WRITEs.  Mandatory byte-range locks, however, prevent conflicting I/O



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   operations.  When they are attempted, they are rejected with
   NFS4ERR_LOCKED.  When the client gets NFS4ERR_LOCKED on a file for
   which it knows it has the proper share reservation, it will need to
   send a LOCK operation on the byte-range of the file that includes the
   byte-range the I/O was to be performed on, with an appropriate
   locktype field of the LOCK operation's arguments (i.e., READ*_LT for
   a READ operation, WRITE*_LT for a WRITE operation).

   Note that for UNIX environments that support mandatory byte-range
   locking, the distinction between advisory and mandatory locking is
   subtle.  In fact, advisory and mandatory byte-range locks are exactly
   the same as far as the APIs and requirements on implementation.  If
   the mandatory lock attribute is set on the file, the server checks to
   see if the lock-owner has an appropriate shared (READ_LT) or
   exclusive (WRITE_LT) byte-range lock on the byte-range it wishes to
   READ from or WRITE to.  If there is no appropriate lock, the server
   checks if there is a conflicting lock (which can be done by
   attempting to acquire the conflicting lock on behalf of the lock-
   owner, and if successful, release the lock after the READ or WRITE
   operation is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, byte-range locks are always mandatory, so
   the server always checks for byte-range locks during I/O requests.

   Thus, the LOCK operation does not need to distinguish between
   advisory and mandatory byte-range locks.  It is the server's
   processing of the READ and WRITE operations that introduces the
   distinction.

   Every stateid that is validly passed to READ, WRITE, or SETATTR, with
   the exception of special stateid values, defines an access mode for
   the file (i.e., OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
   OPEN4_SHARE_ACCESS_BOTH).

   o  For stateids associated with opens, this is the mode defined by
      the original OPEN that caused the allocation of the OPEN stateid
      and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
      same open-owner/file pair.

   o  For stateids returned by byte-range LOCK operations, the
      appropriate mode is the access mode for the OPEN stateid
      associated with the lock set represented by the stateid.

   o  For delegation stateids, the access mode is based on the type of
      delegation.

   When a READ, WRITE, or SETATTR (that specifies the size attribute)



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   operation is done, the operation is subject to checking against the
   access mode to verify that the operation is appropriate given the
   stateid with which the operation is associated.

   In the case of WRITE-type operations (i.e., WRITEs and SETATTRs that
   set size), the server MUST verify that the access mode allows writing
   and MUST return an NFS4ERR_OPENMODE error if it does not.  In the
   case of READ, the server may perform the corresponding check on the
   access mode, or it may choose to allow READ on OPENs for
   OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
   implementation may unavoidably do reads (e.g., due to buffer cache
   constraints).  However, even if READs are allowed in these
   circumstances, the server MUST still check for locks that conflict
   with the READ (e.g., another OPEN specified OPEN4_SHARE_DENY_READ or
   OPEN4_SHARE_DENY_BOTH).  Note that a server that does enforce the
   access mode check on READs need not explicitly check for conflicting
   share reservations since the existence of OPEN for
   OPEN4_SHARE_ACCESS_READ guarantees that no conflicting share
   reservation can exist.

   The READ bypass special stateid (all bits of "other" and "seqid" set
   to one) indicates a desire to bypass locking checks.  The server MAY
   allow READ operations to bypass locking checks at the server, when
   this special stateid is used.  However, WRITE operations with this
   special stateid value MUST NOT bypass locking checks and are treated
   exactly the same as if a special stateid for anonymous state were
   used.

   A lock may not be granted while a READ or WRITE operation using one
   of the special stateids is being performed and the scope of the lock
   to be granted would conflict with the READ or WRITE operation.  This
   can occur when:

   o  A mandatory byte-range lock is requested with a byte-range that
      conflicts with the byte-range of the READ or WRITE operation.  For
      the purposes of this paragraph, a conflict occurs when a shared
      lock is requested and a WRITE operation is being performed, or an
      exclusive lock is requested and either a READ or a WRITE operation
      is being performed.

   o  A share reservation is requested that denies reading and/or
      writing and the corresponding operation is being performed.

   o  A delegation is to be granted and the delegation type would
      prevent the I/O operation, i.e., READ and WRITE conflict with an
      OPEN_DELEGATE_WRITE delegation and WRITE conflicts with an
      OPEN_DELEGATE_READ delegation.




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   When a client holds a delegation, it needs to ensure that the stateid
   sent conveys the association of operation with the delegation, to
   avoid the delegation from being avoidably recalled.  When the
   delegation stateid, a stateid open associated with that delegation,
   or a stateid representing byte-range locks derived from such an open
   is used, the server knows that the READ, WRITE, or SETATTR does not
   conflict with the delegation but is sent under the aegis of the
   delegation.  Even though it is possible for the server to determine
   from the client ID (via the session ID) that the client does in fact
   have a delegation, the server is not obliged to check this, so using
   a special stateid can result in avoidable recall of the delegation.

9.2.  Lock Ranges

   The protocol allows a lock-owner to request a lock with a byte-range
   and then either upgrade, downgrade, or unlock a sub-range of the
   initial lock, or a byte-range that overlaps -- fully or partially --
   either with that initial lock or a combination of a set of existing
   locks for the same lock-owner.  It is expected that this will be an
   uncommon type of request.  In any case, servers or server file
   systems may not be able to support sub-range lock semantics.  In the
   event that a server receives a locking request that represents a sub-
   range of current locking state for the lock-owner, the server is
   allowed to return the error NFS4ERR_LOCK_RANGE to signify that it
   does not support sub-range lock operations.  Therefore, the client
   should be prepared to receive this error and, if appropriate, report
   the error to the requesting application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server may not support sub-range requests for reasons related to the
   recovery of byte-range locking state in the event of server failure.
   As discussed in Section 8.4.2, the server may employ certain
   optimizations during recovery that work effectively only when the
   client's behavior during lock recovery is similar to the client's
   locking behavior prior to server failure.

9.3.  Upgrading and Downgrading Locks

   If a client has a WRITE_LT lock on a byte-range, it can request an
   atomic downgrade of the lock to a READ_LT lock via the LOCK
   operation, by setting the type to READ_LT.  If the server supports
   atomic downgrade, the request will succeed.  If not, it will return
   NFS4ERR_LOCK_NOTSUPP.  The client should be prepared to receive this
   error and, if appropriate, report the error to the requesting
   application.

   If a client has a READ_LT lock on a byte-range, it can request an



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   atomic upgrade of the lock to a WRITE_LT lock via the LOCK operation
   by setting the type to WRITE_LT or WRITEW_LT.  If the server does not
   support atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the
   upgrade can be achieved without an existing conflict, the request
   will succeed.  Otherwise, the server will return either
   NFS4ERR_DENIED or NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is
   returned if the client sent the LOCK operation with the type set to
   WRITEW_LT and the server has detected a deadlock.  The client should
   be prepared to receive such errors and, if appropriate, report the
   error to the requesting application.

9.4.  Stateid Seqid Values and Byte-Range Locks

   When a LOCK or LOCKU operation is performed, the stateid returned has
   the same "other" value as the argument's stateid, and a "seqid" value
   that is incremented (relative to the argument's stateid) to reflect
   the occurrence of the LOCK or LOCKU operation.  The server MUST
   increment the value of the "seqid" field whenever there is any change
   to the locking status of any byte offset as described by any of the
   locks covered by the stateid.  A change in locking status includes a
   change from locked to unlocked or the reverse or a change from being
   locked for READ_LT to being locked for WRITE_LT or the reverse.

   When there is no such change, as, for example, when a range already
   locked for WRITE_LT is locked again for WRITE_LT, the server MAY
   increment the "seqid" value.

9.5.  Issues with Multiple Open-Owners

   When the same file is opened by multiple open-owners, a client will
   have multiple OPEN stateids for that file, each associated with a
   different open-owner.  In that case, there can be multiple LOCK and
   LOCKU requests for the same lock-owner sent using the different OPEN
   stateids, and so a situation may arise in which there are multiple
   stateids, each representing byte-range locks on the same file and
   held by the same lock-owner but each associated with a different
   open-owner.

   In such a situation, the locking status of each byte (i.e., whether
   it is locked, the READ_LT or WRITE_LT type of the lock, and the lock-
   owner holding the lock) MUST reflect the last LOCK or LOCKU operation
   done for the lock-owner in question, independent of the stateid
   through which the request was sent.

   When a byte is locked by the lock-owner in question, the open-owner
   to which that byte-range lock is assigned SHOULD be that of the open-
   owner associated with the stateid through which the last LOCK of that
   byte was done.  When there is a change in the open-owner associated



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   with locks for the stateid through which a LOCK or LOCKU was done,
   the "seqid" field of the stateid MUST be incremented, even if the
   locking, in terms of lock-owners has not changed.  When there is a
   change to the set of locked bytes associated with a different stateid
   for the same lock-owner, i.e., associated with a different open-
   owner, the "seqid" value for that stateid MUST NOT be incremented.

9.6.  Blocking Locks

   Some clients require the support of blocking locks.  While NFSv4.1
   provides a callback when a previously unavailable lock becomes
   available, this is an OPTIONAL feature and clients cannot depend on
   its presence.  Clients need to be prepared to continually poll for
   the lock.  This presents a fairness problem.  Two of the lock types,
   READW_LT and WRITEW_LT, are used to indicate to the server that the
   client is requesting a blocking lock.  When the callback is not used,
   the server should maintain an ordered list of pending blocking locks.
   When the conflicting lock is released, the server may wait for the
   period of time equal to lease_time for the first waiting client to
   re-request the lock.  After the lease period expires, the next
   waiting client request is allowed the lock.  Clients are required to
   poll at an interval sufficiently small that it is likely to acquire
   the lock in a timely manner.  The server is not required to maintain
   a list of pending blocked locks as it is used to increase fairness
   and not correct operation.  Because of the unordered nature of crash
   recovery, storing of lock state to stable storage would be required
   to guarantee ordered granting of blocking locks.

   Servers may also note the lock types and delay returning denial of
   the request to allow extra time for a conflicting lock to be
   released, allowing a successful return.  In this way, clients can
   avoid the burden of needless frequent polling for blocking locks.
   The server should take care in the length of delay in the event the
   client retransmits the request.

   If a server receives a blocking LOCK operation, denies it, and then
   later receives a nonblocking request for the same lock, which is also
   denied, then it should remove the lock in question from its list of
   pending blocking locks.  Clients should use such a nonblocking
   request to indicate to the server that this is the last time they
   intend to poll for the lock, as may happen when the process
   requesting the lock is interrupted.  This is a courtesy to the
   server, to prevent it from unnecessarily waiting a lease period
   before granting other LOCK operations.  However, clients are not
   required to perform this courtesy, and servers must not depend on
   them doing so.  Also, clients must be prepared for the possibility
   that this final locking request will be accepted.




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   When a server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK,
   that CB_NOTIFY_LOCK callbacks might be done for the current open
   file, the client should take notice of this, but, since this is a
   hint, cannot rely on a CB_NOTIFY_LOCK always being done.  A client
   may reasonably reduce the frequency with which it polls for a denied
   lock, since the greater latency that might occur is likely to be
   eliminated given a prompt callback, but it still needs to poll.  When
   it receives a CB_NOTIFY_LOCK, it should promptly try to obtain the
   lock, but it should be aware that other clients may be polling and
   that the server is under no obligation to reserve the lock for that
   particular client.

9.7.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from byte-range locking.
   When a client opens a file, it sends an OPEN operation to the server
   specifying the type of access required (READ, WRITE, or BOTH) and the
   type of access to deny others (OPEN4_SHARE_DENY_NONE,
   OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
   OPEN4_SHARE_DENY_BOTH).  If the OPEN fails, the client will fail the
   application's open request.

   Pseudo-code definition of the semantics:

           if (request.access == 0) {
             return (NFS4ERR_INVAL)
           } else {
             if ((request.access & file_state.deny)) ||
                (request.deny & file_state.access)) {
               return (NFS4ERR_SHARE_DENIED)
           }
           return (NFS4ERR_OK);

   When doing this checking of share reservations on OPEN, the current
   file_state used in the algorithm includes bits that reflect all
   current opens, including those for the open-owner making the new OPEN
   request.

   The constants used for the OPEN and OPEN_DOWNGRADE operations for the
   access and deny fields are as follows:










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   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

9.8.  OPEN/CLOSE Operations

   To provide correct share semantics, a client MUST use the OPEN
   operation to obtain the initial filehandle and indicate the desired
   access and what access, if any, to deny.  Even if the client intends
   to use a special stateid for anonymous state or READ bypass, it must
   still obtain the filehandle for the regular file with the OPEN
   operation so the appropriate share semantics can be applied.  Clients
   that do not have a deny mode built into their programming interfaces
   for opening a file should request a deny mode of
   OPEN4_SHARE_DENY_NONE.

   The OPEN operation with the CREATE flag also subsumes the CREATE
   operation for regular files as used in previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the open-
   owner on that file.  If byte-range locks are held, the client SHOULD
   release all locks before sending a CLOSE operation.  The server MAY
   free all outstanding locks on CLOSE, but some servers may not support
   the CLOSE of a file that still has byte-range locks held.  The server
   MUST return failure, NFS4ERR_LOCKS_HELD, if any locks would exist
   after the CLOSE.

   The LOOKUP operation will return a filehandle without establishing
   any lock state on the server.  Without a valid stateid, the server
   will assume that the client has the least access.  For example, if
   one client opened a file with OPEN4_SHARE_DENY_BOTH and another
   client accesses the file via a filehandle obtained through LOOKUP,
   the second client could only read the file using the special read
   bypass stateid.  The second client could not WRITE the file at all
   because it would not have a valid stateid from OPEN and the special
   anonymous stateid would not be allowed access.

9.9.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the open-owner for which the OPEN
   is being done already has the file open, the result is to upgrade the
   open file status maintained on the server to include the access and



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   deny bits specified by the new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the
   protocol is concerned, and it includes the union of the access and
   deny bits for all of the OPEN requests completed.  The OPEN is
   represented by a single stateid whose "other" value matches that of
   the original open, and whose "seqid" value is incremented to reflect
   the occurrence of the upgrade.  The increment is required in cases in
   which the "upgrade" results in no change to the open mode (e.g., an
   OPEN is done for read when the existing open file is opened for
   OPEN4_SHARE_ACCESS_BOTH).  Only a single CLOSE will be done to reset
   the effects of both OPENs.  The client may use the stateid returned
   by the OPEN effecting the upgrade or with a stateid sharing the same
   "other" field and a seqid of zero, although care needs to be taken as
   far as upgrades that happen while the CLOSE is pending.  Note that
   the client, when sending the OPEN, may not know that the same file is
   in fact being opened.  The above only applies if both OPENs result in
   the OPENed object being designated by the same filehandle.

   When the server chooses to export multiple filehandles corresponding
   to the same file object and returns different filehandles on two
   different OPENs of the same file object, the server MUST NOT "OR"
   together the access and deny bits and coalesce the two open files.
   Instead, the server must maintain separate OPENs with separate
   stateids and will require separate CLOSEs to free them.

   When multiple open files on the client are merged into a single OPEN
   file object on the server, the close of one of the open files (on the
   client) may necessitate change of the access and deny status of the
   open file on the server.  This is because the union of the access and
   deny bits for the remaining opens may be smaller (i.e., a proper
   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the necessary change and the client should use it to update the
   server so that share reservation requests by other clients are
   handled properly.  The stateid returned has the same "other" field as
   that passed to the server.  The "seqid" value in the returned stateid
   MUST be incremented, even in situations in which there is no change
   to the access and deny bits for the file.

9.10.  Parallel OPENs

   Unlike the case of NFSv4.0, in which OPEN operations for the same
   open-owner are inherently serialized because of the owner-based
   seqid, multiple OPENs for the same open-owner may be done in
   parallel.  When clients do this, they may encounter situations in
   which, because of the existence of hard links, two OPEN operations
   may turn out to open the same file, with a later OPEN performed being
   an upgrade of the first, with this fact only visible to the client
   once the operations complete.



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   In this situation, clients may determine the order in which the OPENs
   were performed by examining the stateids returned by the OPENs.
   Stateids that share a common value of the "other" field can be
   recognized as having opened the same file, with the order of the
   operations determinable from the order of the "seqid" fields, mod any
   possible wraparound of the 32-bit field.

   When the possibility exists that the client will send multiple OPENs
   for the same open-owner in parallel, it may be the case that an open
   upgrade may happen without the client knowing beforehand that this
   could happen.  Because of this possibility, CLOSEs and
   OPEN_DOWNGRADEs should generally be sent with a non-zero seqid in the
   stateid, to avoid the possibility that the status change associated
   with an open upgrade is not inadvertently lost.

9.11.  Reclaim of Open and Byte-Range Locks

   Special forms of the LOCK and OPEN operations are provided when it is
   necessary to re-establish byte-range locks or opens after a server
   failure.

   o  To reclaim existing opens, an OPEN operation is performed using a
      CLAIM_PREVIOUS.  Because the client, in this type of situation,
      will have already opened the file and have the filehandle of the
      target file, this operation requires that the current filehandle
      be the target file, rather than a directory, and no file name is
      specified.

   o  To reclaim byte-range locks, a LOCK operation with the reclaim
      parameter set to true is used.

   Reclaims of opens associated with delegations are discussed in
   Section 10.2.1.

10.  Client-Side Caching

   Client-side caching of data, of file attributes, and of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem, and
   previous versions of the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a lack of coherence poses for users.
   These techniques have not been clearly defined by earlier protocol
   specifications, and it is often unclear what is valid or invalid
   client behavior.

   The NFSv4.1 protocol uses many techniques similar to those that have
   been used in previous protocol versions.  The NFSv4.1 protocol does



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   not provide distributed cache coherence.  However, it defines a more
   limited set of caching guarantees to allow locks and share
   reservations to be used without destructive interference from client-
   side caching.

   In addition, the NFSv4.1 protocol introduces a delegation mechanism,
   which allows many decisions normally made by the server to be made
   locally by clients.  This mechanism provides efficient support of the
   common cases where sharing is infrequent or where sharing is read-
   only.

10.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges can arise when those techniques are used with
   very large numbers of clients.  This is particularly true when
   clients are geographically distributed, which classically increases
   the latency for cache revalidation requests.

   The previous versions of the NFS protocol repeat their file data
   cache validation requests at the time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a file is only accessed by a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated references to the server to find that no
   conflicts exist are expensive.  A better option with regards to
   performance is to allow a client that repeatedly opens a file to do
   so without reference to the server.  This is done until potentially
   conflicting operations from another client actually occur.

   A similar situation arises in connection with byte-range locking.
   Sending LOCK and LOCKU operations as well as the READ and WRITE
   operations necessary to make data caching consistent with the locking
   semantics (see Section 10.3.2) can severely limit performance.  When
   locking is used to provide protection against infrequent conflicts, a
   large penalty is incurred.  This penalty may discourage the use of
   byte-range locking by applications.

   The NFSv4.1 protocol provides more aggressive caching strategies with
   the following design goals:

   o  Compatibility with a large range of server semantics.

   o  Providing the same caching benefits as previous versions of the
      NFS protocol when unable to support the more aggressive model.




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   o  Requirements for aggressive caching are organized so that a large
      portion of the benefit can be obtained even when not all of the
      requirements can be met.

   The appropriate requirements for the server are discussed in later
   sections in which specific forms of caching are covered (see
   Section 10.4).

10.2.  Delegation and Callbacks

   Recallable delegation of server responsibilities for a file to a
   client improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client engages in sharing of a
   delegated file.

   A delegation is passed from the server to the client, specifying the
   object of the delegation and the type of delegation.  There are
   different types of delegations, but each type contains a stateid to
   be used to represent the delegation when performing operations that
   depend on the delegation.  This stateid is similar to those
   associated with locks and share reservations but differs in that the
   stateid for a delegation is associated with a client ID and may be
   used on behalf of all the open-owners for the given client.  A
   delegation is made to the client as a whole and not to any specific
   process or thread of control within it.

   The backchannel is established by CREATE_SESSION and
   BIND_CONN_TO_SESSION, and the client is required to maintain it.
   Because the backchannel may be down, even temporarily, correct
   protocol operation does not depend on them.  Preliminary testing of
   backchannel functionality by means of a CB_COMPOUND procedure with a
   single operation, CB_SEQUENCE, can be used to check the continuity of
   the backchannel.  A server avoids delegating responsibilities until
   it has determined that the backchannel exists.  Because the granting
   of a delegation is always conditional upon the absence of conflicting
   access, clients MUST NOT assume that a delegation will be granted and
   they MUST always be prepared for OPENs, WANT_DELEGATIONs, and
   GET_DIR_DELEGATIONs to be processed without any delegations being
   granted.

   Unlike locks, an operation by a second client to a delegated file
   will cause the server to recall a delegation through a callback.  For
   individual operations, we will describe, under IMPLEMENTATION, when
   such operations are required to effect a recall.  A number of points
   should be noted, however.




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   o  The server is free to recall a delegation whenever it feels it is
      desirable and may do so even if no operations requiring recall are
      being done.

   o  Operations done outside the NFSv4.1 protocol, due to, for example,
      access by other protocols, or by local access, also need to result
      in delegation recall when they make analogous changes to file
      system data.  What is crucial is if the change would invalidate
      the guarantees provided by the delegation.  When this is possible,
      the delegation needs to be recalled and MUST be returned or
      revoked before allowing the operation to proceed.

   o  The semantics of the file system are crucial in defining when
      delegation recall is required.  If a particular change within a
      specific implementation causes change to a file attribute, then
      delegation recall is required, whether that operation has been
      specifically listed as requiring delegation recall.  Again, what
      is critical is whether the guarantees provided by the delegation
      are being invalidated.

   Despite those caveats, the implementation sections for a number of
   operations describe situations in which delegation recall would be
   required under some common circumstances:

   o  For GETATTR, see Section 18.7.4.

   o  For OPEN, see Section 18.16.4.

   o  For READ, see Section 18.22.4.

   o  For REMOVE, see Section 18.25.4.

   o  For RENAME, see Section 18.26.4.

   o  For SETATTR, see Section 18.30.4.

   o  For WRITE, see Section 18.32.4.

   On recall, the client holding the delegation needs to flush modified
   state (such as modified data) to the server and return the
   delegation.  The conflicting request will not be acted on until the
   recall is complete.  The recall is considered complete when the
   client returns the delegation or the server times its wait for the
   delegation to be returned and revokes the delegation as a result of
   the timeout.  In the interim, the server will either delay responding
   to conflicting requests or respond to them with NFS4ERR_DELAY.
   Following the resolution of the recall, the server has the
   information necessary to grant or deny the second client's request.



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   At the time the client receives a delegation recall, it may have
   substantial state that needs to be flushed to the server.  Therefore,
   the server should allow sufficient time for the delegation to be
   returned since it may involve numerous RPCs to the server.  If the
   server is able to determine that the client is diligently flushing
   state to the server as a result of the recall, the server may extend
   the usual time allowed for a recall.  However, the time allowed for
   recall completion should not be unbounded.

   An example of this is when responsibility to mediate opens on a given
   file is delegated to a client (see Section 10.4).  The server will
   not know what opens are in effect on the client.  Without this
   knowledge, the server will be unable to determine if the access and
   deny states for the file allow any particular open until the
   delegation for the file has been returned.

   A client failure or a network partition can result in failure to
   respond to a recall callback.  In this case, the server will revoke
   the delegation, which in turn will render useless any modified state
   still on the client.

10.2.1.  Delegation Recovery

   There are three situations that delegation recovery needs to deal
   with:

   o  client restart

   o  server restart

   o  network partition (full or backchannel-only)

   In the event the client restarts, the failure to renew the lease will
   result in the revocation of byte-range locks and share reservations.
   Delegations, however, may be treated a bit differently.

   There will be situations in which delegations will need to be re-
   established after a client restarts.  The reason for this is that the
   client may have file data stored locally and this data was associated
   with the previously held delegations.  The client will need to re-
   establish the appropriate file state on the server.

   To allow for this type of client recovery, the server MAY extend the
   period for delegation recovery beyond the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because the normal recall
   process may require significant time for the client to flush changed
   state to the server, other clients need be prepared for delays that



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   occur because of a conflicting delegation.  This longer interval
   would increase the window for clients to restart and consult stable
   storage so that the delegations can be reclaimed.  For OPEN
   delegations, such delegations are reclaimed using OPEN with a claim
   type of CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH (see Sections 10.5
   and 18.16 for discussion of OPEN delegation and the details of OPEN,
   respectively).

   A server MAY support claim types of CLAIM_DELEGATE_PREV and
   CLAIM_DELEG_PREV_FH, and if it does, it MUST NOT remove delegations
   upon a CREATE_SESSION that confirm a client ID created by
   EXCHANGE_ID.  Instead, the server MUST, for a period of time no less
   than that of the value of the lease_time attribute, maintain the
   client's delegations to allow time for the client to send
   CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH requests.  The server
   that supports CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH MUST
   support the DELEGPURGE operation.

   When the server restarts, delegations are reclaimed (using the OPEN
   operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
   locks and share reservations.  However, there is a slight semantic
   difference.  In the normal case, if the server decides that a
   delegation should not be granted, it performs the requested action
   (e.g., OPEN) without granting any delegation.  For reclaim, the
   server grants the delegation but a special designation is applied so
   that the client treats the delegation as having been granted but
   recalled by the server.  Because of this, the client has the duty to
   write all modified state to the server and then return the
   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFSv4.1 protocol:

   o  Upon reclaim, a client reporting resources assigned to it by an
      earlier server instance must be granted those resources.

   o  The server has unquestionable authority to determine whether
      delegations are to be granted and, once granted, whether they are
      to be continued.

   o  The use of callbacks should not be depended upon until the client
      has proven its ability to receive them.

   When a client needs to reclaim a delegation and there is no
   associated open, the client may use the CLAIM_PREVIOUS variant of the
   WANT_DELEGATION operation.  However, since the server is not required
   to support this operation, an alternative is to reclaim via a dummy
   OPEN together with the delegation using an OPEN of type
   CLAIM_PREVIOUS.  The dummy open file can be released using a CLOSE to
   re-establish the original state to be reclaimed, a delegation without



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   an associated open.

   When a client has more than a single open associated with a
   delegation, state for those additional opens can be established using
   OPEN operations of type CLAIM_DELEGATE_CUR.  When these are used to
   establish opens associated with reclaimed delegations, the server
   MUST allow them when made within the grace period.

   When a network partition occurs, delegations are subject to freeing
   by the server when the lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the server may extend the period in which conflicting
   requests are held off.  Eventually, the occurrence of a conflicting
   request from another client will cause revocation of the delegation.
   A loss of the backchannel (e.g., by later network configuration
   change) will have the same effect.  A recall request will fail and
   revocation of the delegation will result.

   A client normally finds out about revocation of a delegation when it
   uses a stateid associated with a delegation and receives one of the
   errors NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or
   NFS4ERR_DELEG_REVOKED.  It also may find out about delegation
   revocation after a client restart when it attempts to reclaim a
   delegation and receives that same error.  Note that in the case of a
   revoked OPEN_DELEGATE_WRITE delegation, there are issues because data
   may have been modified by the client whose delegation is revoked and
   separately by other clients.  See Section 10.5.1 for a discussion of
   such issues.  Note also that when delegations are revoked,
   information about the revoked delegation will be written by the
   server to stable storage (as described in Section 8.4.3).  This is
   done to deal with the case in which a server restarts after revoking
   a delegation but before the client holding the revoked delegation is
   notified about the revocation.

10.3.  Data Caching

   When applications share access to a set of files, they need to be
   implemented so as to take account of the possibility of conflicting
   access by another application.  This is true whether the applications
   in question execute on different clients or reside on the same
   client.

   Share reservations and byte-range locks are the facilities the
   NFSv4.1 protocol provides to allow applications to coordinate access
   by using mutual exclusion facilities.  The NFSv4.1 protocol's data
   caching must be implemented such that it does not invalidate the
   assumptions on which those using these facilities depend.




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10.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions on which
   applications rely, NFSv4.1 clients should not provide cached data to
   applications or modify it on behalf of an application when it would
   not be valid to obtain or modify that same data via a READ or WRITE
   operation.

   Furthermore, in the absence of an OPEN delegation (see Section 10.4),
   two additional rules apply.  Note that these rules are obeyed in
   practice by many NFSv3 clients.

   o  First, cached data present on a client must be revalidated after
      doing an OPEN.  Revalidating means that the client fetches the
      change attribute from the server, compares it with the cached
      change attribute, and if different, declares the cached data (as
      well as the cached attributes) as invalid.  This is to ensure that
      the data for the OPENed file is still correctly reflected in the
      client's cache.  This validation must be done at least when the
      client's OPEN operation includes a deny of OPEN4_SHARE_DENY_WRITE
      or OPEN4_SHARE_DENY_BOTH, thus terminating a period in which other
      clients may have had the opportunity to open the file with
      OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH access.  Clients
      may choose to do the revalidation more often (i.e., at OPENs
      specifying a deny mode of OPEN4_SHARE_DENY_NONE) to parallel the
      NFSv3 protocol's practice for the benefit of users assuming this
      degree of cache revalidation.

      Since the change attribute is updated for data and metadata
      modifications, some client implementors may be tempted to use the
      time_modify attribute and not the change attribute to validate
      cached data, so that metadata changes do not spuriously invalidate
      clean data.  The implementor is cautioned in this approach.  The
      change attribute is guaranteed to change for each update to the
      file, whereas time_modify is guaranteed to change only at the
      granularity of the time_delta attribute.  Use by the client's data
      cache validation logic of time_modify and not change runs the risk
      of the client incorrectly marking stale data as valid.  Thus, any
      cache validation approach by the client MUST include the use of
      the change attribute.

   o  Second, modified data must be flushed to the server before closing
      a file OPENed for OPEN4_SHARE_ACCESS_WRITE.  This is complementary
      to the first rule.  If the data is not flushed at CLOSE, the
      revalidation done after the client OPENs a file is unable to
      achieve its purpose.  The other aspect to flushing the data before
      close is that the data must be committed to stable storage, at the
      server, before the CLOSE operation is requested by the client.  In



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      the case of a server restart and a CLOSEd file, it may not be
      possible to retransmit the data to be written to the file, hence,
      this requirement.

10.3.2.  Data Caching and File Locking

   For those applications that choose to use byte-range locking instead
   of share reservations to exclude inconsistent file access, there is
   an analogous set of constraints that apply to client-side data
   caching.  These rules are effective only if the byte-range locking is
   used in a way that matches in an equivalent way the actual READ and
   WRITE operations executed.  This is as opposed to byte-range locking
   that is based on pure convention.  For example, it is possible to
   manipulate a two-megabyte file by dividing the file into two one-
   megabyte ranges and protecting access to the two byte-ranges by byte-
   range locks on bytes zero and one.  A WRITE_LT lock on byte zero of
   the file would represent the right to perform READ and WRITE
   operations on the first byte-range.  A WRITE_LT lock on byte one of
   the file would represent the right to perform READ and WRITE
   operations on the second byte-range.  As long as all applications
   manipulating the file obey this convention, they will work on a local
   file system.  However, they may not work with the NFSv4.1 protocol
   unless clients refrain from data caching.

   The rules for data caching in the byte-range locking environment are:

   o  First, when a client obtains a byte-range lock for a particular
      byte-range, the data cache corresponding to that byte-range (if
      any cache data exists) must be revalidated.  If the change
      attribute indicates that the file may have been updated since the
      cached data was obtained, the client must flush or invalidate the
      cached data for the newly locked byte-range.  A client might
      choose to invalidate all of the non-modified cached data that it
      has for the file, but the only requirement for correct operation
      is to invalidate all of the data in the newly locked byte-range.

   o  Second, before releasing a WRITE_LT lock for a byte-range, all
      modified data for that byte-range must be flushed to the server.
      The modified data must also be written to stable storage.

   Note that flushing data to the server and the invalidation of cached
   data must reflect the actual byte-ranges locked or unlocked.
   Rounding these up or down to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half of that block is within an area being
   unlocked may cause invalid modification to the byte-range outside the
   unlocked area.  This, in turn, may be part of a byte-range locked by
   another client.  Clients can avoid this situation by synchronously



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   performing portions of WRITE operations that overlap that portion
   (initial or final) that is not a full block.  Similarly, invalidating
   a locked area that is not an integral number of full buffer blocks
   would require the client to read one or two partial blocks from the
   server if the revalidation procedure shows that the data that the
   client possesses may not be valid.

   The data that is written to the server as a prerequisite to the
   unlocking of a byte-range must be written, at the server, to stable
   storage.  The client may accomplish this either with synchronous
   writes or by following asynchronous writes with a COMMIT operation.
   This is required because retransmission of the modified data after a
   server restart might conflict with a lock held by another client.

   A client implementation may choose to accommodate applications that
   use byte-range locking in non-standard ways (e.g., using a byte-range
   lock as a global semaphore) by flushing to the server more data upon
   a LOCKU than is covered by the locked range.  This may include
   modified data within files other than the one for which the unlocks
   are being done.  In such cases, the client must not interfere with
   applications whose READs and WRITEs are being done only within the
   bounds of byte-range locks that the application holds.  For example,
   an application locks a single byte of a file and proceeds to write
   that single byte.  A client that chose to handle a LOCKU by flushing
   all modified data to the server could validly write that single byte
   in response to an unrelated LOCKU operation.  However, it would not
   be valid to write the entire block in which that single written byte
   was located since it includes an area that is not locked and might be
   locked by another client.  Client implementations can avoid this
   problem by dividing files with modified data into those for which all
   modifications are done to areas covered by an appropriate byte-range
   lock and those for which there are modifications not covered by a
   byte-range lock.  Any writes done for the former class of files must
   not include areas not locked and thus not modified on the client.

10.3.3.  Data Caching and Mandatory File Locking

   Client-side data caching needs to respect mandatory byte-range
   locking when it is in effect.  The presence of mandatory byte-range
   locking for a given file is indicated when the client gets back
   NFS4ERR_LOCKED from a READ or WRITE operation on a file for which it
   has an appropriate share reservation.  When mandatory locking is in
   effect for a file, the client must check for an appropriate byte-
   range lock for data being read or written.  If a byte-range lock
   exists for the range being read or written, the client may satisfy
   the request using the client's validated cache.  If an appropriate
   byte-range lock is not held for the range of the read or write, the
   read or write request must not be satisfied by the client's cache and



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   the request must be sent to the server for processing.  When a read
   or write request partially overlaps a locked byte-range, the request
   should be subdivided into multiple pieces with each byte-range
   (locked or not) treated appropriately.

10.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the file system object to which the data belongs.  For
   NFSv3 clients, the typical practice has been to assume for the
   purpose of caching that distinct filehandles represent distinct file
   system objects.  The client then has the choice to organize and
   maintain the data cache on this basis.

   In the NFSv4.1 protocol, there is now the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle may be constructed on the basis of the object's
   pathname.  Therefore, clients need a reliable method to determine if
   two filehandles designate the same file system object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the distinct client-side objects
   that mapped to the same server-side object.

   By providing a method to differentiate filehandles, the NFSv4.1
   protocol alleviates a potential functional regression in comparison
   with the NFSv3 protocol.  Without this method, caching
   inconsistencies within the same client could occur, and this has not
   been present in previous versions of the NFS protocol.  Note that it
   is possible to have such inconsistencies with applications executing
   on multiple clients, but that is not the issue being addressed here.

   For the purposes of data caching, the following steps allow an
   NFSv4.1 client to determine whether two distinct filehandles denote
   the same server-side object:

   o  If GETATTR directed to two filehandles returns different values of
      the fsid attribute, then the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the fsid of the
      two filehandles in question returns a unique_handles attribute
      with a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed to the two filehandles does not return the
      fileid attribute for both of the handles, then it cannot be
      determined whether the two objects are the same.  Therefore,
      operations that depend on that knowledge (e.g., client-side data



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      caching) cannot be done reliably.  Note that if GETATTR does not
      return the fileid attribute for both filehandles, it will return
      it for neither of the filehandles, since the fsid for both
      filehandles is the same.

   o  If GETATTR directed to the two filehandles returns different
      values for the fileid attribute, then they are distinct objects.

   o  Otherwise, they are the same object.

10.4.  Open Delegation

   When a file is being OPENed, the server may delegate further handling
   of opens and closes for that file to the opening client.  Any such
   delegation is recallable since the circumstances that allowed for the
   delegation are subject to change.  In particular, if the server
   receives a conflicting OPEN from another client, the server must
   recall the delegation before deciding whether the OPEN from the other
   client may be granted.  Making a delegation is up to the server, and
   clients should not assume that any particular OPEN either will or
   will not result in an OPEN delegation.  The following is a typical
   set of conditions that servers might use in deciding whether an OPEN
   should be delegated:

   o  The client must be able to respond to the server's callback
      requests.  If a backchannel has been established, the server will
      send a CB_COMPOUND request, containing a single operation,
      CB_SEQUENCE, for a test of backchannel availability.

   o  The client must have responded properly to previous recalls.

   o  There must be no current OPEN conflicting with the requested
      delegation.

   o  There should be no current delegation that conflicts with the
      delegation being requested.

   o  The probability of future conflicting open requests should be low
      based on the recent history of the file.

   o  The existence of any server-specific semantics of OPEN/CLOSE that
      would make the required handling incompatible with the prescribed
      handling that the delegated client would apply (see below).

   There are two types of OPEN delegations: OPEN_DELEGATE_READ and
   OPEN_DELEGATE_WRITE.  An OPEN_DELEGATE_READ delegation allows a
   client to handle, on its own, requests to open a file for reading
   that do not deny OPEN4_SHARE_ACCESS_READ access to others.  Multiple



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   OPEN_DELEGATE_READ delegations may be outstanding simultaneously and
   do not conflict.  An OPEN_DELEGATE_WRITE delegation allows the client
   to handle, on its own, all opens.  Only OPEN_DELEGATE_WRITE
   delegation may exist for a given file at a given time, and it is
   inconsistent with any OPEN_DELEGATE_READ delegations.

   When a client has an OPEN_DELEGATE_READ delegation, it is assured
   that neither the contents, the attributes (with the exception of
   time_access), nor the names of any links to the file will change
   without its knowledge, so long as the delegation is held.  When a
   client has an OPEN_DELEGATE_WRITE delegation, it may modify the file
   data locally since no other client will be accessing the file's data.
   The client holding an OPEN_DELEGATE_WRITE delegation may only locally
   affect file attributes that are intimately connected with the file
   data: size, change, time_access, time_metadata, and time_modify.  All
   other attributes must be reflected on the server.

   When a client has an OPEN delegation, it does not need to send OPENs
   or CLOSEs to the server.  Instead, the client may update the
   appropriate status internally.  For an OPEN_DELEGATE_READ delegation,
   opens that cannot be handled locally (opens that are for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH or that deny
   OPEN4_SHARE_ACCESS_READ access) must be sent to the server.

   When an OPEN delegation is made, the reply to the OPEN contains an
   OPEN delegation structure that specifies the following:

   o  the type of delegation (OPEN_DELEGATE_READ or
      OPEN_DELEGATE_WRITE).

   o  space limitation information to control flushing of data on close
      (OPEN_DELEGATE_WRITE delegation only; see Section 10.4.1)

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation

   The delegation stateid is separate and distinct from the stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock-owner and will continue
   to be valid after the delegation is recalled and the file remains
   open.

   When a request internal to the client is made to open a file and an
   OPEN delegation is in effect, it will be accepted or rejected solely
   on the basis of the following conditions.  Any requirement for other
   checks to be made by the delegate should result in the OPEN
   delegation being denied so that the checks can be made by the server



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   itself.

   o  The access and deny bits for the request and the file as described
      in Section 9.7.

   o  The read and write permissions as determined below.

   The nfsace4 passed with delegation can be used to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If the nfsace4 indicates that the open may be done, then it should
      be granted without reference to the server.

   o  If the nfsace4 indicates that the open may not be done, then an
      ACCESS request must be sent to the server to obtain the definitive
      answer.

   The server may return an nfsace4 that is more restrictive than the
   actual ACL of the file.  This includes an nfsace4 that specifies
   denial of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" (see
   Section 5.9) may make it incorrect to return the actual ACL of the
   file in the delegation response.

   The use of a delegation together with various other forms of caching
   creates the possibility that no server authentication and
   authorization will ever be performed for a given user since all of
   the user's requests might be satisfied locally.  Where the client is
   depending on the server for authentication and authorization, the
   client should be sure authentication and authorization occurs for
   each user by use of the ACCESS operation.  This should be the case
   even if an ACCESS operation would not be required otherwise.  As
   mentioned before, the server may enforce frequent authentication by
   returning an nfsace4 denying all access with every OPEN delegation.

10.4.1.  Open Delegation and Data Caching

   An OPEN delegation allows much of the message overhead associated
   with the opening and closing files to be eliminated.  An open when an
   OPEN delegation is in effect does not require that a validation
   message be sent to the server.  The continued endurance of the
   "OPEN_DELEGATE_READ delegation" provides a guarantee that no OPEN for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, and thus no write,
   has occurred.  Similarly, when closing a file opened for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH and if an
   OPEN_DELEGATE_WRITE delegation is in effect, the data written does
   not have to be written to the server until the OPEN delegation is
   recalled.  The continued endurance of the OPEN delegation provides a



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   guarantee that no open, and thus no READ or WRITE, has been done by
   another client.

   For the purposes of OPEN delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  Although a client SHOULD NOT use special stateids when
   an open exists, delegation handling on the server can use the client
   ID associated with the current session to determine if the operation
   has been done by the holder of the delegation (in which case, no
   recall is necessary) or by another client (in which case, the
   delegation must be recalled and I/O not proceed until the delegation
   is recalled or revoked).

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and,
   through normal accounting, the server is able to determine if the
   available file system space for the data has been exceeded (i.e., the
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that an
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   write modified data to the server of a size equal to that provided in
   the original delegation.  The server must make this assurance for all
   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data, taking
   into account available file system space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available file system space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas, or available file system space,
   the server may grant OPEN_DELEGATE_WRITE delegations with very
   restrictive space limitations.  The limitations may be defined in a
   way that will always force modified data to be flushed to the server
   on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client, and unexpired
   authentication credentials may not be present.  In this case, the



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   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

10.4.2.  Open Delegation and File Locks

   When a client holds an OPEN_DELEGATE_WRITE delegation, lock
   operations are performed locally.  This includes those required for
   mandatory byte-range locking.  This can be done since the delegation
   implies that there can be no conflicting locks.  Similarly, all of
   the revalidations that would normally be associated with obtaining
   locks and the flushing of data associated with the releasing of locks
   need not be done.

   When a client holds an OPEN_DELEGATE_READ delegation, lock operations
   are not performed locally.  All lock operations, including those
   requesting non-exclusive locks, are sent to the server for
   resolution.

10.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where the
   target is a file that has an OPEN_DELEGATE_WRITE delegation in
   effect.  The reason for this is that the client holding the
   OPEN_DELEGATE_WRITE delegation may have modified the data, and the
   server needs to reflect this change to the second client that
   submitted the GETATTR.  Therefore, the client holding the
   OPEN_DELEGATE_WRITE delegation needs to be interrogated.  The server
   will use the CB_GETATTR operation.  The only attributes that the
   server can reliably query via CB_GETATTR are size and change.

   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the
   delegation has a modified version of the file.  If the client's copy
   of the delegated file is not modified (data or size), the server can
   satisfy the second client's GETATTR request from the attributes
   stored locally at the server.  If the file is modified, the server
   only needs to know about this modified state.  If the server
   determines that the file is currently modified, it will respond to
   the second client's GETATTR as if the file had been modified locally
   at the server.

   Since the form of the change attribute is determined by the server
   and is opaque to the client, the client and server need to agree on a
   method of communicating the modified state of the file.  For the size
   attribute, the client will report its current view of the file size.



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   For the change attribute, the handling is more involved.

   For the client, the following steps will be taken when receiving an
   OPEN_DELEGATE_WRITE delegation:

   o  The value of the change attribute will be obtained from the server
      and cached.  Let this value be represented by c.

   o  The client will create a value greater than c that will be used
      for communicating that modified data is held at the client.  Let
      this value be represented by d.

   o  When the client is queried via CB_GETATTR for the change
      attribute, it checks to see if it holds modified data.  If the
      file is modified, the value d is returned for the change attribute
      value.  If this file is not currently modified, the client returns
      the value c for the change attribute.

   For simplicity of implementation, the client MAY for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, the client again modifies the file's data or
   metadata in its cache.  The client can return the same value because
   the only requirement is that the client be able to indicate to the
   server that the client holds modified data.  Therefore, the value of
   d may always be c + 1.

   While the change attribute is opaque to the client in the sense that
   it has no idea what units of time, if any, the server is counting
   change with, it is not opaque in that the client has to treat it as
   an unsigned integer, and the server has to be able to see the results
   of the client's changes to that integer.  Therefore, the server MUST
   encode the change attribute in network order when sending it to the
   client.  The client MUST decode it from network order to its native
   order when receiving it, and the client MUST encode it in network
   order when sending it to the server.  For this reason, change is
   defined as an unsigned integer rather than an opaque array of bytes.

   For the server, the following steps will be taken when providing an
   OPEN_DELEGATE_WRITE delegation:

   o  Upon providing an OPEN_DELEGATE_WRITE delegation, the server will
      cache a copy of the change attribute in the data structure it uses
      to record the delegation.  Let this value be represented by sc.

   o  When a second client sends a GETATTR operation on the same file to
      the server, the server obtains the change attribute from the first
      client.  Let this value be cc.




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   o  If the value cc is equal to sc, the file is not modified and the
      server returns the current values for change, time_metadata, and
      time_modify (for example) to the second client.

   o  If the value cc is NOT equal to sc, the file is currently modified
      at the first client and most likely will be modified at the server
      at a future time.  The server then uses its current time to
      construct attribute values for time_metadata and time_modify.  A
      new value of sc, which we will call nsc, is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values to the
      requester.  The server replaces sc in the delegation record with
      nsc.  To prevent the possibility of time_modify, time_metadata,
      and change from appearing to go backward (which would happen if
      the client holding the delegation fails to write its modified data
      to the server before the delegation is revoked or returned), the
      server SHOULD update the file's metadata record with the
      constructed attribute values.  For reasons of reasonable
      performance, committing the constructed attribute values to stable
      storage is OPTIONAL.

   As discussed earlier in this section, the client MAY return the same
   cc value on subsequent CB_GETATTR calls, even if the file was
   modified in the client's cache yet again between successive
   CB_GETATTR calls.  Therefore, the server must assume that the file
   has been modified yet again, and MUST take care to ensure that the
   new nsc it constructs and returns is greater than the previous nsc it
   returned.  An example implementation's delegation record would
   satisfy this mandate by including a boolean field (let us call it
   "modified") that is set to FALSE when the delegation is granted, and
   an sc value set at the time of grant to the change attribute value.
   The modified field would be set to TRUE the first time cc != sc, and
   would stay TRUE until the delegation is returned or revoked.  The
   processing for constructing nsc, time_modify, and time_metadata would
   use this pseudo code:
















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       if (!modified) {
           do CB_GETATTR for change and size;

           if (cc != sc)
               modified = TRUE;
       } else {
           do CB_GETATTR for size;
       }

       if (modified) {
           sc = sc + 1;
           time_modify = time_metadata = current_time;
           update sc, time_modify, time_metadata into file's metadata;
       }


   This would return to the client (that sent GETATTR) the attributes it
   requested, but make sure size comes from what CB_GETATTR returned.
   The server would not update the file's metadata with the client's
   modified size.

   In the case that the file attribute size is different than the
   server's current value, the server treats this as a modification
   regardless of the value of the change attribute retrieved via
   CB_GETATTR and responds to the second client as in the last step.

   This methodology resolves issues of clock differences between client
   and server and other scenarios where the use of CB_GETATTR break
   down.

   It should be noted that the server is under no obligation to use
   CB_GETATTR, and therefore the server MAY simply recall the delegation
   to avoid its use.

10.4.4.  Recall of Open Delegation

   The following events necessitate recall of an OPEN delegation:

   o  potentially conflicting OPEN request (or a READ or WRITE operation
      done with a special stateid)

   o  SETATTR sent by another client

   o  REMOVE request for the file

   o  RENAME request for the file as either the source or target of the
      RENAME




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   Whether a RENAME of a directory in the path leading to the file
   results in recall of an OPEN delegation depends on the semantics of
   the server's file system.  If that file system denies such RENAMEs
   when a file is open, the recall must be performed to determine
   whether the file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   OPEN delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.

   When a client receives a recall for an OPEN delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will no longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see Section 18.16, which describes the OPEN operation, for
      details.)

   o  If there are granted byte-range locks, the corresponding LOCK
      operations need to be performed.  This applies to the
      OPEN_DELEGATE_WRITE delegation case only.

   o  For an OPEN_DELEGATE_WRITE delegation, if at the time of recall
      the file is not open for OPEN4_SHARE_ACCESS_WRITE/
      OPEN4_SHARE_ACCESS_BOTH, all modified data for the file must be
      flushed to the server.  If the delegation had not existed, the
      client would have done this data flush before the CLOSE operation.

   o  For an OPEN_DELEGATE_WRITE delegation when a file is still open at
      the time of recall, any modified data for the file needs to be
      flushed to the server.

   o  With the OPEN_DELEGATE_WRITE delegation in place, it is possible
      that the file was truncated during the duration of the delegation.
      For example, the truncation could have occurred as a result of an



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      OPEN UNCHECKED with a size attribute value of zero.  Therefore, if
      a truncation of the file has occurred and this operation has not
      been propagated to the server, the truncation must occur before
      any modified data is written to the server.

   In the case of OPEN_DELEGATE_WRITE delegation, byte-range locking
   imposes some additional requirements.  To precisely maintain the
   associated invariant, it is required to flush any modified data in
   any byte-range for which a WRITE_LT lock was released while the
   OPEN_DELEGATE_WRITE delegation was in effect.  However, because the
   OPEN_DELEGATE_WRITE delegation implies no other locking by other
   clients, a simpler implementation is to flush all modified data for
   the file (as described just above) if any WRITE_LT lock has been
   released while the OPEN_DELEGATE_WRITE delegation was in effect.

   An implementation need not wait until delegation recall (or the
   decision to voluntarily return a delegation) to perform any of the
   above actions, if implementation considerations (e.g., resource
   availability constraints) make that desirable.  Generally, however,
   the fact that the actual OPEN state of the file may continue to
   change makes it not worthwhile to send information about opens and
   closes to the server, except as part of delegation return.  An
   exception is when the client has no more internal opens of the file.
   In this case, sending a CLOSE is useful because it reduces resource
   utilization on the client and server.  Regardless of the client's
   choices on scheduling these actions, all must be performed before the
   delegation is returned, including (when applicable) the close that
   corresponds to the OPEN that resulted in the delegation.  These
   actions can be performed either in previous requests or in previous
   operations in the same COMPOUND request.

10.4.5.  Clients That Fail to Honor Delegation Recalls

   A client may fail to respond to a recall for various reasons, such as
   a failure of the backchannel from server to the client.  The client
   may be unaware of a failure in the backchannel.  This lack of
   awareness could result in the client finding out long after the
   failure that its delegation has been revoked, and another client has
   modified the data for which the client had a delegation.  This is
   especially a problem for the client that held an OPEN_DELEGATE_WRITE
   delegation.

   Status bits returned by SEQUENCE operations help to provide an
   alternate way of informing the client of issues regarding the status
   of the backchannel and of recalled delegations.  When the backchannel
   is not available, the server returns the status bit
   SEQ4_STATUS_CB_PATH_DOWN on SEQUENCE operations.  The client can
   react by attempting to re-establish the backchannel and by returning



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   recallable objects if a backchannel cannot be successfully re-
   established.

   Whether the backchannel is functioning or not, it may be that the
   recalled delegation is not returned.  Note that the client's lease
   might still be renewed, even though the recalled delegation is not
   returned.  In this situation, servers SHOULD revoke delegations that
   are not returned in a period of time equal to the lease period.  This
   period of time should allow the client time to note the backchannel-
   down status and re-establish the backchannel.

   When delegations are revoked, the server will return with the
   SEQ4_STATUS_RECALLABLE_STATE_REVOKED status bit set on subsequent
   SEQUENCE operations.  The client should note this and then use
   TEST_STATEID to find which delegations have been revoked.

10.4.6.  Delegation Revocation

   At the point a delegation is revoked, if there are associated opens
   on the client, these opens may or may not be revoked.  If no byte-
   range lock or open is granted that is inconsistent with the existing
   open, the stateid for the open may remain valid and be disconnected
   from the revoked delegation, just as would be the case if the
   delegation were returned.

   For example, if an OPEN for OPEN4_SHARE_ACCESS_BOTH with a deny of
   OPEN4_SHARE_DENY_NONE is associated with the delegation, granting of
   another such OPEN to a different client will revoke the delegation
   but need not revoke the OPEN, since the two OPENs are consistent with
   each other.  On the other hand, if an OPEN denying write access is
   granted, then the existing OPEN must be revoked.

   When opens and/or locks are revoked, the applications holding these
   opens or locks need to be notified.  This notification usually occurs
   by returning errors for READ/WRITE operations or when a close is
   attempted for the open file.

   If no opens exist for the file at the point the delegation is
   revoked, then notification of the revocation is unnecessary.
   However, if there is modified data present at the client for the
   file, the user of the application should be notified.  Unfortunately,
   it may not be possible to notify the user since active applications
   may not be present at the client.  See Section 10.5.1 for additional
   details.







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10.4.7.  Delegations via WANT_DELEGATION

   In addition to providing delegations as part of the reply to OPEN
   operations, servers MAY provide delegations separate from open, via
   the OPTIONAL WANT_DELEGATION operation.  This allows delegations to
   be obtained in advance of an OPEN that might benefit from them, for
   objects that are not a valid target of OPEN, or to deal with cases in
   which a delegation has been recalled and the client wants to make an
   attempt to re-establish it if the absence of use by other clients
   allows that.

   The WANT_DELEGATION operation may be performed on any type of file
   object other than a directory.

   When a delegation is obtained using WANT_DELEGATION, any open files
   for the same filehandle held by that client are to be treated as
   subordinate to the delegation, just as if they had been created using
   an OPEN of type CLAIM_DELEGATE_CUR.  They are otherwise unchanged as
   to seqid, access and deny modes, and the relationship with byte-range
   locks.  Similarly, because existing byte-range locks are subordinate
   to an open, those byte-range locks also become indirectly subordinate
   to that new delegation.

   The WANT_DELEGATION operation provides for delivery of delegations
   via callbacks, when the delegations are not immediately available.
   When a requested delegation is available, it is delivered to the
   client via a CB_PUSH_DELEG operation.  When this happens, open files
   for the same filehandle become subordinate to the new delegation at
   the point at which the delegation is delivered, just as if they had
   been created using an OPEN of type CLAIM_DELEGATE_CUR.  Similarly,
   this occurs for existing byte-range locks subordinate to an open.

10.5.  Data Caching and Revocation

   When locks and delegations are revoked, the assumptions upon which
   successful caching depends are no longer guaranteed.  For any locks
   or share reservations that have been revoked, the corresponding
   state-owner needs to be notified.  This notification includes
   applications with a file open that has a corresponding delegation
   that has been revoked.  Cached data associated with the revocation
   must be removed from the client.  In the case of modified data
   existing in the client's cache, that data must be removed from the
   client without being written to the server.  As mentioned, the
   assumptions made by the client are no longer valid at the point when
   a lock or delegation has been revoked.  For example, another client
   may have been granted a conflicting byte-range lock after the
   revocation of the byte-range lock at the first client.  Therefore,
   the data within the lock range may have been modified by the other



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   client.  Obviously, the first client is unable to guarantee to the
   application what has occurred to the file in the case of revocation.

   Notification to a state-owner will in many cases consist of simply
   returning an error on the next and all subsequent READs/WRITEs to the
   open file or on the close.  Where the methods available to a client
   make such notification impossible because errors for certain
   operations may not be returned, more drastic action such as signals
   or process termination may be appropriate.  The justification here is
   that an invariant on which an application depends may be violated.
   Depending on how errors are typically treated for the client-
   operating environment, further levels of notification including
   logging, console messages, and GUI pop-ups may be appropriate.

10.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the
   special issue of modified data in the client cache while the file is
   not open.  In this situation, any client that does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the file system namespace to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of the
   file in question, such a saved copy of the client's view of the file
   may be of particular value for recovery.  In another case, recovery
   using a copy of the file based partially on the client's cached data
   and partially on the server's copy as modified by other clients will
   be anything but straightforward, so clients may avoid saving file
   contents in these situations or specially mark the results to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target file system.
   Such saving may also be restricted to situations when the client has
   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target file system.





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10.6.  Attribute Caching

   This section pertains to the caching of a file's attributes on a
   client when that client does not hold a delegation on the file.

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files, and
   caching of the data for these needs to be handled just as data
   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory (as well as the directory's contents) are to be
   cached on the same basis as any other pathnames.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   should not be cached.  The exception to this are modifications to
   attributes that are intimately connected with data caching.
   Therefore, extending a file by writing data to the local data cache
   is reflected immediately in the size as seen on the client without
   this change being immediately reflected on the server.  Normally,
   such changes are not propagated directly to the server, but when the
   modified data is flushed to the server, analogous attribute changes
   are made on the server.  When OPEN delegation is in effect, the
   modified attributes may be returned to the server in reaction to a
   CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on another client.

   The typical file system application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherencies mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.

   o  When operations are performed that change attributes at the
      server, the updated attribute set is requested as part of the



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      containing RPC.  This includes directory operations that update
      attributes indirectly.  This is accomplished by following the
      modifying operation with a GETATTR operation and then using the
      results of the GETATTR to update the client's cached attributes.

   Note that if the full set of attributes to be cached is requested by
   READDIR, the results can be cached by the client on the same basis as
   attributes obtained via GETATTR.

   A client may validate its cached version of attributes for a file by
   fetching both the change and time_access attributes and assuming that
   if the change attribute has the same value as it did when the
   attributes were cached, then no attributes other than time_access
   have changed.  The reason why time_access is also fetched is because
   many servers operate in environments where the operation that updates
   change does not update time_access.  For example, POSIX file
   semantics do not update access time when a file is modified by the
   write system call [18].  Therefore, the client that wants a current
   time_access value should fetch it with change during the attribute
   cache validation processing and update its cached time_access.

   The client may maintain a cache of modified attributes for those
   attributes intimately connected with data of modified regular files
   (size, time_modify, and change).  Other than those three attributes,
   the client MUST NOT maintain a cache of modified attributes.
   Instead, attribute changes are immediately sent to the server.

   In some operating environments, the equivalent to time_access is
   expected to be implicitly updated by each read of the content of the
   file object.  If an NFS client is caching the content of a file
   object, whether it is a regular file, directory, or symbolic link,
   the client SHOULD NOT update the time_access attribute (via SETATTR
   or a small READ or READDIR request) on the server with each read that
   is satisfied from cache.  The reason is that this can defeat the
   performance benefits of caching content, especially since an explicit
   SETATTR of time_access may alter the change attribute on the server.
   If the change attribute changes, clients that are caching the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged to maintain a modified
   version of time_access in its cache, since the client either would
   eventually have to write the access time to the server with bad
   performance effects or never update the server's time_access, thereby
   resulting in a situation where an application that caches access time
   between a close and open of the same file observes the access time
   oscillating between the past and present.  The time_access attribute
   always means the time of last access to a file by a read that was
   satisfied by the server.  This way clients will tend to see only
   time_access changes that go forward in time.



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10.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include the capability for an application
   to map a file's content into the application's address space.  Each
   time the application accesses a memory location that corresponds to a
   block that has not been loaded into the address space, a page fault
   occurs and the file is read (or if the block does not exist in the
   file, the block is allocated and then instantiated in the
   application's address space).

   As long as each memory-mapped access to the file requires a page
   fault, the relevant attributes of the file that are used to detect
   access and modification (time_access, time_metadata, time_modify, and
   change) will be updated.  However, in many operating environments,
   when page faults are not required, these attributes will not be
   updated on reads or updates to the file via memory access (regardless
   of whether the file is local or is accessed remotely).  A client or
   server MAY fail to update attributes of a file that is being accessed
   via memory-mapped I/O. This has several implications:

   o  If there is an application on the server that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value of the change attribute to determine
      whether or not its cache is stale.  A server that knows that the
      file is memory-mapped could always pessimistically return updated
      values for change so as to force the application to always get the
      most up-to-date data and metadata for the file.  However, due to
      the negative performance implications of this, such behavior is
      OPTIONAL.

   o  If the memory-mapped file is not being modified on the server, and
      instead is just being read by an application via the memory-mapped
      interface, the client will not see an updated time_access
      attribute.  However, in many operating environments, neither will
      any process running on the server.  Thus, NFS clients are at no
      disadvantage with respect to local processes.

   o  If there is another client that is memory mapping the file, and if
      that client is holding an OPEN_DELEGATE_WRITE delegation, the same
      set of issues as discussed in the previous two bullet points
      apply.  So, when a server does a CB_GETATTR to a file that the
      client has modified in its cache, the reply from CB_GETATTR will
      not necessarily be accurate.  As discussed earlier, the client's
      obligation is to report that the file has been modified since the
      delegation was granted, not whether it has been modified again
      between successive CB_GETATTR calls, and the server MUST assume
      that any file the client has modified in cache has been modified
      again between successive CB_GETATTR calls.  Depending on the



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      nature of the client's memory management system, this weak
      obligation may not be possible.  A client MAY return stale
      information in CB_GETATTR whenever the file is memory-mapped.

   o  The mixture of memory mapping and byte-range locking on the same
      file is problematic.  Consider the following scenario, where a
      page size on each client is 8192 bytes.

      *  Client A memory maps the first page (8192 bytes) of file X.

      *  Client B memory maps the first page (8192 bytes) of file X.

      *  Client A WRITE_LT locks the first 4096 bytes.

      *  Client B WRITE_LT locks the second 4096 bytes.

      *  Client A, via a STORE instruction, modifies part of its locked
         byte-range.

      *  Simultaneous to client A, client B executes a STORE on part of
         its locked byte-range.

   Here the challenge is for each client to resynchronize to get a
   correct view of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, not that a subset of the page corresponding to the
   respective lock byte-ranges has been modified.  So it is not possible
   for each client to do the right thing, which is to write to the
   server only that portion of the page that is locked.  For example, if
   client A simply writes out the page, and then client B writes out the
   page, client A's data is lost.

   Moreover, if mandatory locking is enabled on the file, then we have a
   different problem.  When clients A and B execute the STORE
   instructions, the resulting page faults require a byte-range lock on
   the entire page.  Each client then tries to extend their locked range
   to the entire page, which results in a deadlock.  Communicating the
   NFS4ERR_DEADLOCK error to a STORE instruction is difficult at best.

   If a client is locking the entire memory-mapped file, there is no
   problem with advisory or mandatory byte-range locking, at least until
   the client unlocks a byte-range in the middle of the file.

   Given the above issues, the following are permitted:

   o  Clients and servers MAY deny memory mapping a file for which they
      know there are byte-range locks.




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   o  Clients and servers MAY deny a byte-range lock on a file they know
      is memory-mapped.

   o  A client MAY deny memory mapping a file that it knows requires
      mandatory locking for I/O. If mandatory locking is enabled after
      the file is opened and mapped, the client MAY deny the application
      further access to its mapped file.

10.8.  Name and Directory Caching without Directory Delegations

   The NFSv4.1 directory delegation facility (described in Section 10.9
   below) is OPTIONAL for servers to implement.  Even where it is
   implemented, it may not always be functional because of resource
   availability issues or other constraints.  Thus, it is important to
   understand how name and directory caching are done in the absence of
   directory delegations.  These topics are discussed in the next two
   subsections.

10.8.1.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical file system APIs, an upper time boundary is
   maintained for how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client.

   When a client is not making changes to a directory for which there
   exist name cache entries, the client needs to periodically fetch
   attributes for that directory to ensure that it is not being
   modified.  After determining that no modification has occurred, the
   expiration time for the associated name cache entries may be updated
   to be the current time plus the name cache staleness bound.

   When a client is making changes to a given directory, it needs to
   determine whether there have been changes made to the directory by
   other clients.  It does this by using the change attribute as
   reported before and after the directory operation in the associated
   change_info4 value returned for the operation.  The server is able to
   communicate to the client whether the change_info4 data is provided
   atomically with respect to the directory operation.  If the change
   values are provided atomically, the client has a basis for
   determining, given proper care, whether other clients are modifying
   the directory in question.

   The simplest way to enable the client to make this determination is



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   for the client to serialize all changes made to a specific directory.
   When this is done, and the server provides before and after values of
   the change attribute atomically, the client can simply compare the
   after value of the change attribute from one operation on a directory
   with the before value on the subsequent operation modifying that
   directory.  When these are equal, the client is assured that no other
   client is modifying the directory in question.

   When such serialization is not used, and there may be multiple
   simultaneous outstanding operations modifying a single directory sent
   from a single client, making this sort of determination can be more
   complicated.  If two such operations complete in a different order
   than they were actually performed, that might give an appearance
   consistent with modification being made by another client.  Where
   this appears to happen, the client needs to await the completion of
   all such modifications that were started previously, to see if the
   outstanding before and after change numbers can be sorted into a
   chain such that the before value of one change number matches the
   after value of a previous one, in a chain consistent with this client
   being the only one modifying the directory.

   In either of these cases, the client is able to determine whether the
   directory is being modified by another client.  If the comparison
   indicates that the directory was updated by another client, the name
   cache associated with the modified directory is purged from the
   client.  If the comparison indicates no modification, the name cache
   can be updated on the client to reflect the directory operation and
   the associated timeout can be extended.  The post-operation change
   value needs to be saved as the basis for future change_info4
   comparisons.

   As demonstrated by the scenario above, name caching requires that the
   client revalidate name cache data by inspecting the change attribute
   of a directory at the point when the name cache item was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre- and
   post-operation change attribute values atomically.  When the server
   is unable to report the before and after values atomically with
   respect to the directory operation, the server must indicate that
   fact in the change_info4 return value.  When the information is not
   atomically reported, the client should not assume that other clients
   have not changed the directory.







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10.8.2.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical file system APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory that is not obtained in
      a single READDIR operation must always be a consistent snapshot of
      directory contents.  This is determined by using a GETATTR before
      the first READDIR and after the last READDIR that contributes to
      the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre- and
   post-operation change attribute values atomically.  When the server
   is unable to report the before and after values atomically with
   respect to the directory operation, the server must indicate that
   fact in the change_info4 return value.  When the information is not
   atomically reported, the client should not assume that other clients
   have not changed the directory.

10.9.  Directory Delegations







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10.9.1.  Introduction to Directory Delegations

   Directory caching for the NFSv4.1 protocol, as previously described,
   is similar to file caching in previous versions.  Clients typically
   cache directory information for a duration determined by the client.
   At the end of a predefined timeout, the client will query the server
   to see if the directory has been updated.  By caching attributes,
   clients reduce the number of GETATTR calls made to the server to
   validate attributes.  Furthermore, frequently accessed files and
   directories, such as the current working directory, have their
   attributes cached on the client so that some NFS operations can be
   performed without having to make an RPC call.  By caching name and
   inode information about most recently looked up entries in a
   Directory Name Lookup Cache (DNLC), clients do not need to send
   LOOKUP calls to the server every time these files are accessed.

   This caching approach works reasonably well at reducing network
   traffic in many environments.  However, it does not address
   environments where there are numerous queries for files that do not
   exist.  In these cases of "misses", the client sends requests to the
   server in order to provide reasonable application semantics and
   promptly detect the creation of new directory entries.  Examples of
   high miss activity are compilation in software development
   environments.  The current behavior of NFS limits its potential
   scalability and wide-area sharing effectiveness in these types of
   environments.  Other distributed stateful file system architectures
   such as AFS and DFS have proven that adding state around directory
   contents can greatly reduce network traffic in high-miss
   environments.

   Delegation of directory contents is an OPTIONAL feature of NFSv4.1.
   Directory delegations provide similar traffic reduction benefits as
   with file delegations.  By allowing clients to cache directory
   contents (in a read-only fashion) while being notified of changes,
   the client can avoid making frequent requests to interrogate the
   contents of slowly-changing directories, reducing network traffic and
   improving client performance.  It can also simplify the task of
   determining whether other clients are making changes to the directory
   when the client itself is making many changes to the directory and
   changes are not serialized.

   Directory delegations allow improved namespace cache consistency to
   be achieved through delegations and synchronous recalls, in the
   absence of notifications.  In addition, if time-based consistency is
   sufficient, asynchronous notifications can provide performance
   benefits for the client, and possibly the server, under some common
   operating conditions such as slowly-changing and/or very large
   directories.



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10.9.2.  Directory Delegation Design

   NFSv4.1 introduces the GET_DIR_DELEGATION (Section 18.39) operation
   to allow the client to ask for a directory delegation.  The
   delegation covers directory attributes and all entries in the
   directory.  If either of these change, the delegation will be
   recalled synchronously.  The operation causing the recall will have
   to wait before the recall is complete.  Any changes to directory
   entry attributes will not cause the delegation to be recalled.

   In addition to asking for delegations, a client can also ask for
   notifications for certain events.  These events include changes to
   the directory's attributes and/or its contents.  If a client asks for
   notification for a certain event, the server will notify the client
   when that event occurs.  This will not result in the delegation being
   recalled for that client.  The notifications are asynchronous and
   provide a way of avoiding recalls in situations where a directory is
   changing enough that the pure recall model may not be effective while
   trying to allow the client to get substantial benefit.  In the
   absence of notifications, once the delegation is recalled the client
   has to refresh its directory cache; this might not be very efficient
   for very large directories.

   The delegation is read-only and the client may not make changes to
   the directory other than by performing NFSv4.1 operations that modify
   the directory or the associated file attributes so that the server
   has knowledge of these changes.  In order to keep the client's
   namespace synchronized with the server, the server will notify the
   delegation-holding client (assuming it has requested notifications)
   of the changes made as a result of that client's directory-modifying
   operations.  This is to avoid any need for that client to send
   subsequent GETATTR or READDIR operations to the server.  If a single
   client is holding the delegation and that client makes any changes to
   the directory (i.e., the changes are made via operations sent on a
   session associated with the client ID holding the delegation), the
   delegation will not be recalled.  Multiple clients may hold a
   delegation on the same directory, but if any such client modifies the
   directory, the server MUST recall the delegation from the other
   clients, unless those clients have made provisions to be notified of
   that sort of modification.

   Delegations can be recalled by the server at any time.  Normally, the
   server will recall the delegation when the directory changes in a way
   that is not covered by the notification, or when the directory
   changes and notifications have not been requested.  If another client
   removes the directory for which a delegation has been granted, the
   server will recall the delegation.




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10.9.3.  Attributes in Support of Directory Notifications

   See Section 5.11 for a description of the attributes associated with
   directory notifications.

10.9.4.  Directory Delegation Recall

   The server will recall the directory delegation by sending a callback
   to the client.  It will use the same callback procedure as used for
   recalling file delegations.  The server will recall the delegation
   when the directory changes in a way that is not covered by the
   notification.  However, the server need not recall the delegation if
   attributes of an entry within the directory change.

   If the server notices that handing out a delegation for a directory
   is causing too many notifications to be sent out, it may decide to
   not hand out delegations for that directory and/or recall those
   already granted.  If a client tries to remove the directory for which
   a delegation has been granted, the server will recall all associated
   delegations.

   The implementation sections for a number of operations describe
   situations in which notification or delegation recall would be
   required under some common circumstances.  In this regard, a similar
   set of caveats to those listed in Section 10.2 apply.

   o  For CREATE, see Section 18.4.4.

   o  For LINK, see Section 18.9.4.

   o  For OPEN, see Section 18.16.4.

   o  For REMOVE, see Section 18.25.4.

   o  For RENAME, see Section 18.26.4.

   o  For SETATTR, see Section 18.30.4.

10.9.5.  Directory Delegation Recovery

   Recovery from client or server restart for state on regular files has
   two main goals: avoiding the necessity of breaking application
   guarantees with respect to locked files and delivery of updates
   cached at the client.  Neither of these goals applies to directories
   protected by OPEN_DELEGATE_READ delegations and notifications.  Thus,
   no provision is made for reclaiming directory delegations in the
   event of client or server restart.  The client can simply establish a
   directory delegation in the same fashion as was done initially.



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11.  Multi-Server Namespace

   NFSv4.1 supports attributes that allow a namespace to extend beyond
   the boundaries of a single server.  It is RECOMMENDED that clients
   and servers support construction of such multi-server namespaces.
   Use of such multi-server namespaces is OPTIONAL, however, and for
   many purposes, single-server namespaces are perfectly acceptable.
   Use of multi-server namespaces can provide many advantages, however,
   by separating a file system's logical position in a namespace from
   the (possibly changing) logistical and administrative considerations
   that result in particular file systems being located on particular
   servers.

11.1.  Location Attributes

   NFSv4.1 contains RECOMMENDED attributes that allow file systems on
   one server to be associated with one or more instances of that file
   system on other servers.  These attributes specify such file system
   instances by specifying a server address target (either as a DNS name
   representing one or more IP addresses or as a literal IP address)
   together with the path of that file system within the associated
   single-server namespace.

   The fs_locations_info RECOMMENDED attribute allows specification of
   one or more file system instance locations where the data
   corresponding to a given file system may be found.  This attribute
   provides to the client, in addition to information about file system
   instance locations, significant information about the various file
   system instance choices (e.g., priority for use, writability,
   currency, etc.).  It also includes information to help the client
   efficiently effect as seamless a transition as possible among
   multiple file system instances, when and if that should be necessary.

   The fs_locations RECOMMENDED attribute is inherited from NFSv4.0 and
   only allows specification of the file system locations where the data
   corresponding to a given file system may be found.  Servers SHOULD
   make this attribute available whenever fs_locations_info is
   supported, but client use of fs_locations_info is to be preferred.

11.2.  File System Presence or Absence

   A given location in an NFSv4.1 namespace (typically but not
   necessarily a multi-server namespace) can have a number of file
   system instance locations associated with it (via the fs_locations or
   fs_locations_info attribute).  There may also be an actual current
   file system at that location, accessible via normal namespace
   operations (e.g., LOOKUP).  In this case, the file system is said to
   be "present" at that position in the namespace, and clients will



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   typically use it, reserving use of additional locations specified via
   the location-related attributes to situations in which the principal
   location is no longer available.

   When there is no actual file system at the namespace location in
   question, the file system is said to be "absent".  An absent file
   system contains no files or directories other than the root.  Any
   reference to it, except to access a small set of attributes useful in
   determining alternate locations, will result in an error,
   NFS4ERR_MOVED.  Note that if the server ever returns the error
   NFS4ERR_MOVED, it MUST support the fs_locations attribute and SHOULD
   support the fs_locations_info and fs_status attributes.

   While the error name suggests that we have a case of a file system
   that once was present, and has only become absent later, this is only
   one possibility.  A position in the namespace may be permanently
   absent with the set of file system(s) designated by the location
   attributes being the only realization.  The name NFS4ERR_MOVED
   reflects an earlier, more limited conception of its function, but
   this error will be returned whenever the referenced file system is
   absent, whether it has moved or not.

   Except in the case of GETATTR-type operations (to be discussed
   later), when the current filehandle at the start of an operation is
   within an absent file system, that operation is not performed and the
   error NFS4ERR_MOVED is returned, to indicate that the file system is
   absent on the current server.

   Because a GETFH cannot succeed if the current filehandle is within an
   absent file system, filehandles within an absent file system cannot
   be transferred to the client.  When a client does have filehandles
   within an absent file system, it is the result of obtaining them when
   the file system was present, and having the file system become absent
   subsequently.

   It should be noted that because the check for the current filehandle
   being within an absent file system happens at the start of every
   operation, operations that change the current filehandle so that it
   is within an absent file system will not result in an error.  This
   allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
   used to get attribute information, particularly location attribute
   information, as discussed below.

   The RECOMMENDED file system attribute fs_status can be used to
   interrogate the present/absent status of a given file system.






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11.3.  Getting Attributes for an Absent File System

   When a file system is absent, most attributes are not available, but
   it is necessary to allow the client access to the small set of
   attributes that are available, and most particularly those that give
   information about the correct current locations for this file system:
   fs_locations and fs_locations_info.

11.3.1.  GETATTR within an Absent File System

   As mentioned above, an exception is made for GETATTR in that
   attributes may be obtained for a filehandle within an absent file
   system.  This exception only applies if the attribute mask contains
   at least one attribute bit that indicates the client is interested in
   a result regarding an absent file system: fs_locations,
   fs_locations_info, or fs_status.  If none of these attributes is
   requested, GETATTR will result in an NFS4ERR_MOVED error.

   When a GETATTR is done on an absent file system, the set of supported
   attributes is very limited.  Many attributes, including those that
   are normally REQUIRED, will not be available on an absent file
   system.  In addition to the attributes mentioned above (fs_locations,
   fs_locations_info, fs_status), the following attributes SHOULD be
   available on absent file systems.  In the case of RECOMMENDED
   attributes, they should be available at least to the same degree that
   they are available on present file systems.

   change_policy:  This attribute is useful for absent file systems and
      can be helpful in summarizing to the client when any of the
      location-related attributes change.

   fsid:  This attribute should be provided so that the client can
      determine file system boundaries, including, in particular, the
      boundary between present and absent file systems.  This value must
      be different from any other fsid on the current server and need
      have no particular relationship to fsids on any particular
      destination to which the client might be directed.

   mounted_on_fileid:  For objects at the top of an absent file system,
      this attribute needs to be available.  Since the fileid is within
      the present parent file system, there should be no need to
      reference the absent file system to provide this information.

   Other attributes SHOULD NOT be made available for absent file
   systems, even when it is possible to provide them.  The server should
   not assume that more information is always better and should avoid
   gratuitously providing additional information.




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   When a GETATTR operation includes a bit mask for one of the
   attributes fs_locations, fs_locations_info, or fs_status, but where
   the bit mask includes attributes that are not supported, GETATTR will
   not return an error, but will return the mask of the actual
   attributes supported with the results.

   Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
   attribute mask does not include fs_locations, fs_locations_info, or
   fs_status, the error NFS4ERR_MOVED will result.  It differs in that
   any appearance in the attribute mask of an attribute not supported
   for an absent file system (and note that this will include some
   normally REQUIRED attributes) will also cause an NFS4ERR_MOVED
   result.

11.3.2.  READDIR and Absent File Systems

   A READDIR performed when the current filehandle is within an absent
   file system will result in an NFS4ERR_MOVED error, since, unlike the
   case of GETATTR, no such exception is made for READDIR.

   Attributes for an absent file system may be fetched via a READDIR for
   a directory in a present file system, when that directory contains
   the root directories of one or more absent file systems.  In this
   case, the handling is as follows:

   o  If the attribute set requested includes one of the attributes
      fs_locations, fs_locations_info, or fs_status, then fetching of
      attributes proceeds normally and no NFS4ERR_MOVED indication is
      returned, even when the rdattr_error attribute is requested.

   o  If the attribute set requested does not include one of the
      attributes fs_locations, fs_locations_info, or fs_status, then if
      the rdattr_error attribute is requested, each directory entry for
      the root of an absent file system will report NFS4ERR_MOVED as the
      value of the rdattr_error attribute.

   o  If the attribute set requested does not include any of the
      attributes fs_locations, fs_locations_info, fs_status, or
      rdattr_error, then the occurrence of the root of an absent file
      system within the directory will result in the READDIR failing
      with an NFS4ERR_MOVED error.

   o  The unavailability of an attribute because of a file system's
      absence, even one that is ordinarily REQUIRED, does not result in
      any error indication.  The set of attributes returned for the root
      directory of the absent file system in that case is simply
      restricted to those actually available.




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11.4.  Uses of Location Information

   The location-bearing attributes (fs_locations and fs_locations_info),
   together with the possibility of absent file systems, provide a
   number of important facilities in providing reliable, manageable, and
   scalable data access.

   When a file system is present, these attributes can provide
   alternative locations, to be used to access the same data, in the
   event of server failures, communications problems, or other
   difficulties that make continued access to the current file system
   impossible or otherwise impractical.  Under some circumstances,
   multiple alternative locations may be used simultaneously to provide
   higher-performance access to the file system in question.  Provision
   of such alternate locations is referred to as "replication" although
   there are cases in which replicated sets of data are not in fact
   present, and the replicas are instead different paths to the same
   data.

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location.  In this case, a continued attempt to use the
   data in the now-absent file system will result in an NFS4ERR_MOVED
   error and, at that point, the successor locations (typically only one
   although multiple choices are possible) can be fetched and used to
   continue access.  Transfer of the file system contents to the new
   location is referred to as "migration", but it should be kept in mind
   that there are cases in which this term can be used, like
   "replication", when there is no actual data migration per se.

   Where a file system was not previously present, specification of file
   system location provides a means by which file systems located on one
   server can be associated with a namespace defined by another server,
   thus allowing a general multi-server namespace facility.  A
   designation of such a location, in place of an absent file system, is
   called a "referral".

   Because client support for location-related attributes is OPTIONAL, a
   server may (but is not required to) take action to hide migration and
   referral events from such clients, by acting as a proxy, for example.
   The server can determine the presence of client support from the
   arguments of the EXCHANGE_ID operation (see Section 18.35.3).

11.4.1.  File System Replication

   The fs_locations and fs_locations_info attributes provide alternative
   locations, to be used to access data in place of or in addition to
   the current file system instance.  On first access to a file system,



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   the client should obtain the value of the set of alternate locations
   by interrogating the fs_locations or fs_locations_info attribute,
   with the latter being preferred.

   In the event that server failures, communications problems, or other
   difficulties make continued access to the current file system
   impossible or otherwise impractical, the client can use the alternate
   locations as a way to get continued access to its data.  Depending on
   specific attributes of these alternate locations, as indicated within
   the fs_locations_info attribute, multiple locations may be used
   simultaneously, to provide higher performance through the
   exploitation of multiple paths between client and target file system.

   The alternate locations may be physical replicas of the (typically
   read-only) file system data, or they may reflect alternate paths to
   the same server or provide for the use of various forms of server
   clustering in which multiple servers provide alternate ways of
   accessing the same physical file system.  How these different modes
   of file system transition are represented within the fs_locations and
   fs_locations_info attributes and how the client deals with file
   system transition issues will be discussed in detail below.

   Multiple server addresses, whether they are derived from a single
   entry with a DNS name representing a set of IP addresses or from
   multiple entries each with its own server address, may correspond to
   the same actual server.  The fact that two addresses correspond to
   the same server is shown by a common so_major_id field within the
   eir_server_owner field returned by EXCHANGE_ID (see Section 18.35.3).
   For a detailed discussion of how server address targets interact with
   the determination of server identity specified by the server owner
   field, see Section 11.5.

11.4.2.  File System Migration

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location, as specified by the fs_locations or
   fs_locations_info attribute.  Typically, a client will be accessing
   the file system in question, get an NFS4ERR_MOVED error, and then use
   the fs_locations or fs_locations_info attribute to determine the new
   location of the data.  When fs_locations_info is used, additional
   information will be available that will define the nature of the
   client's handling of the transition to a new server.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the file
   system will be moved between servers.  It is anticipated that a
   number of different server-to-server transfer mechanisms might be



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   used with the choice left to the server implementor.  The NFSv4.1
   protocol specifies the method used to communicate the migration event
   between client and server.

   The new location may be an alternate communication path to the same
   server or, in the case of various forms of server clustering, another
   server providing access to the same physical file system.  The
   client's responsibilities in dealing with this transition depend on
   the specific nature of the new access path as well as how and whether
   data was in fact migrated.  These issues will be discussed in detail
   below.

   When multiple server addresses correspond to the same actual server,
   as shown by a common value for the so_major_id field of the
   eir_server_owner field returned by EXCHANGE_ID, the location or
   locations may designate alternate server addresses in the form of
   specific server network addresses.  These can be used to access the
   file system in question at those addresses and when it is no longer
   accessible at the original address.

   Although a single successor location is typical, multiple locations
   may be provided, together with information that allows priority among
   the choices to be indicated, via information in the fs_locations_info
   attribute.  Where suitable, clustering mechanisms make it possible to
   provide multiple identical file systems or paths to them; this allows
   the client the opportunity to deal with any resource or
   communications issues that might limit data availability.

   When an alternate location is designated as the target for migration,
   it must designate the same data (with metadata being the same to the
   degree indicated by the fs_locations_info attribute).  Where file
   systems are writable, a change made on the original file system must
   be visible on all migration targets.  Where a file system is not
   writable but represents a read-only copy (possibly periodically
   updated) of a writable file system, similar requirements apply to the
   propagation of updates.  Any change visible in the original file
   system must already be effected on all migration targets, to avoid
   any possibility that a client, in effecting a transition to the
   migration target, will see any reversion in file system state.

11.4.3.  Referrals

   Referrals provide a way of placing a file system in a location within
   the namespace essentially without respect to its physical location on
   a given server.  This allows a single server or a set of servers to
   present a multi-server namespace that encompasses file systems
   located on multiple servers.  Some likely uses of this include
   establishment of site-wide or organization-wide namespaces, or even



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   knitting such together into a truly global namespace.

   Referrals occur when a client determines, upon first referencing a
   position in the current namespace, that it is part of a new file
   system and that the file system is absent.  When this occurs,
   typically by receiving the error NFS4ERR_MOVED, the actual location
   or locations of the file system can be determined by fetching the
   fs_locations or fs_locations_info attribute.

   The locations-related attribute may designate a single file system
   location or multiple file system locations, to be selected based on
   the needs of the client.  The server, in the fs_locations_info
   attribute, may specify priorities to be associated with various file
   system location choices.  The server may assign different priorities
   to different locations as reported to individual clients, in order to
   adapt to client physical location or to effect load balancing.  When
   both read-only and read-write file systems are present, some of the
   read-only locations might not be absolutely up-to-date (as they would
   have to be in the case of replication and migration).  Servers may
   also specify file system locations that include client-substituted
   variables so that different clients are referred to different file
   systems (with different data contents) based on client attributes
   such as CPU architecture.

   When the fs_locations_info attribute indicates that there are
   multiple possible targets listed, the relationships among them may be
   important to the client in selecting which one to use.  The same
   rules specified in Section 11.4.1 defining the appropriate standards
   for the data propagation apply to these multiple replicas as well.
   For example, the client might prefer a writable target on a server
   that has additional writable replicas to which it subsequently might
   switch.  Note that, as distinguished from the case of replication,
   there is no need to deal with the case of propagation of updates made
   by the current client, since the current client has not accessed the
   file system in question.

   Use of multi-server namespaces is enabled by NFSv4.1 but is not
   required.  The use of multi-server namespaces and their scope will
   depend on the applications used and system administration
   preferences.

   Multi-server namespaces can be established by a single server
   providing a large set of referrals to all of the included file
   systems.  Alternatively, a single multi-server namespace may be
   administratively segmented with separate referral file systems (on
   separate servers) for each separately administered portion of the
   namespace.  The top-level referral file system or any segment may use
   replicated referral file systems for higher availability.



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   Generally, multi-server namespaces are for the most part uniform, in
   that the same data made available to one client at a given location
   in the namespace is made available to all clients at that location.
   However, there are facilities provided that allow different clients
   to be directed to different sets of data, so as to adapt to such
   client characteristics as CPU architecture.

11.5.  Location Entries and Server Identity

   As mentioned above, a single location entry may have a server address
   target in the form of a DNS name that may represent multiple IP
   addresses, while multiple location entries may have their own server
   address targets that reference the same server.  Whether two IP
   addresses designate the same server is indicated by the existence of
   a common so_major_id field within the eir_server_owner field returned
   by EXCHANGE_ID (see Section 18.35.3), subject to further verification
   (for details see Section 2.10.5).

   When multiple addresses for the same server exist, the client may
   assume that for each file system in the namespace of a given server
   network address, there exist file systems at corresponding namespace
   locations for each of the other server network addresses.  It may do
   this even in the absence of explicit listing in fs_locations and
   fs_locations_info.  Such corresponding file system locations can be
   used as alternate locations, just as those explicitly specified via
   the fs_locations and fs_locations_info attributes.  Where these
   specific addresses are explicitly designated in the fs_locations_info
   attribute, the conditions of use specified in this attribute (e.g.,
   priorities, specification of simultaneous use) may limit the client's
   use of these alternate locations.

   If a single location entry designates multiple server IP addresses,
   the client cannot assume that these addresses are multiple paths to
   the same server.  In most cases, they will be, but the client MUST
   verify that before acting on that assumption.  When two server
   addresses are designated by a single location entry and they
   correspond to different servers, this normally indicates some sort of
   misconfiguration, and so the client should avoid using such location
   entries when alternatives are available.  When they are not, clients
   should pick one of IP addresses and use it, without using others that
   are not directed to the same server.

11.6.  Additional Client-Side Considerations

   When clients make use of servers that implement referrals,
   replication, and migration, care should be taken that a user who
   mounts a given file system that includes a referral or a relocated
   file system continues to see a coherent picture of that user-side



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   file system despite the fact that it contains a number of server-side
   file systems that may be on different servers.

   One important issue is upward navigation from the root of a server-
   side file system to its parent (specified as ".." in UNIX), in the
   case in which it transitions to that file system as a result of
   referral, migration, or a transition as a result of replication.
   When the client is at such a point, and it needs to ascend to the
   parent, it must go back to the parent as seen within the multi-server
   namespace rather than sending a LOOKUPP operation to the server,
   which would result in the parent within that server's single-server
   namespace.  In order to do this, the client needs to remember the
   filehandles that represent such file system roots and use these
   instead of sending a LOOKUPP operation to the current server.  This
   will allow the client to present to applications a consistent
   namespace, where upward navigation and downward navigation are
   consistent.

   Another issue concerns refresh of referral locations.  When referrals
   are used extensively, they may change as server configurations
   change.  It is expected that clients will cache information related
   to traversing referrals so that future client-side requests are
   resolved locally without server communication.  This is usually
   rooted in client-side name look up caching.  Clients should
   periodically purge this data for referral points in order to detect
   changes in location information.  When the change_policy attribute
   changes for directories that hold referral entries or for the
   referral entries themselves, clients should consider any associated
   cached referral information to be out of date.

11.7.  Effecting File System Transitions

   Transitions between file system instances, whether due to switching
   between replicas upon server unavailability or to server-initiated
   migration events, are best dealt with together.  This is so even
   though, for the server, pragmatic considerations will normally force
   different implementation strategies for planned and unplanned
   transitions.  Even though the prototypical use cases of replication
   and migration contain distinctive sets of features, when all
   possibilities for these operations are considered, there is an
   underlying unity of these operations, from the client's point of
   view, that makes treating them together desirable.

   A number of methods are possible for servers to replicate data and to
   track client state in order to allow clients to transition between
   file system instances with a minimum of disruption.  Such methods
   vary between those that use inter-server clustering techniques to
   limit the changes seen by the client, to those that are less



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   aggressive, use more standard methods of replicating data, and impose
   a greater burden on the client to adapt to the transition.

   The NFSv4.1 protocol does not impose choices on clients and servers
   with regard to that spectrum of transition methods.  In fact, there
   are many valid choices, depending on client and application
   requirements and their interaction with server implementation
   choices.  The NFSv4.1 protocol does define the specific choices that
   can be made, how these choices are communicated to the client, and
   how the client is to deal with any discontinuities.

   In the sections below, references will be made to various possible
   server implementation choices as a way of illustrating the transition
   scenarios that clients may deal with.  The intent here is not to
   define or limit server implementations but rather to illustrate the
   range of issues that clients may face.

   In the discussion below, references will be made to a file system
   having a particular property or to two file systems (typically the
   source and destination) belonging to a common class of any of several
   types.  Two file systems that belong to such a class share some
   important aspects of file system behavior that clients may depend
   upon when present, to easily effect a seamless transition between
   file system instances.  Conversely, where the file systems do not
   belong to such a common class, the client has to deal with various
   sorts of implementation discontinuities that may cause performance or
   other issues in effecting a transition.

   Where the fs_locations_info attribute is available, such file system
   classification data will be made directly available to the client
   (see Section 11.10 for details).  When only fs_locations is
   available, default assumptions with regard to such classifications
   have to be inferred (see Section 11.9 for details).

   In cases in which one server is expected to accept opaque values from
   the client that originated from another server, the servers SHOULD
   encode the "opaque" values in big-endian byte order.  If this is
   done, servers acting as replicas or immigrating file systems will be
   able to parse values like stateids, directory cookies, filehandles,
   etc., even if their native byte order is different from that of other
   servers cooperating in the replication and migration of the file
   system.

11.7.1.  File System Transitions and Simultaneous Access

   When a single file system may be accessed at multiple locations,
   either because of an indication of file system identity as reported
   by the fs_locations or fs_locations_info attributes or because two



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   file system instances have corresponding locations on server
   addresses that connect to the same server (as indicated by a common
   so_major_id field in the eir_server_owner field returned by
   EXCHANGE_ID), the client will, depending on specific circumstances as
   discussed below, either:

   o  Access multiple instances simultaneously, each of which represents
      an alternate path to the same data and metadata.

   o  Access one instance (or set of instances) and then transition to
      an alternative instance (or set of instances) as a result of
      network issues, server unresponsiveness, or server-directed
      migration.  The transition may involve changes in filehandles,
      fileids, the change attribute, and/or locking state, depending on
      the attributes of the source and destination file system
      instances, as specified in the fs_locations_info attribute.

   Which of these choices is possible, and how a transition is effected,
   is governed by equivalence classes of file system instances as
   reported by the fs_locations_info attribute, and for file system
   instances in the same location within a multi-homed single-server
   namespace, as indicated by the value of the so_major_id field of the
   eir_server_owner field returned by EXCHANGE_ID.

11.7.2.  Simultaneous Use and Transparent Transitions

   When two file system instances have the same location within their
   respective single-server namespaces and those two server network
   addresses designate the same server (as indicated by the same value
   of the so_major_id field of the eir_server_owner field returned in
   response to EXCHANGE_ID), those file system instances can be treated
   as the same, and either used together simultaneously or serially with
   no transition activity required on the part of the client.  In this
   case, we refer to the transition as "transparent", and the client in
   transferring access from one to the other is acting as it would in
   the event that communication is interrupted, with a new connection
   and possibly a new session being established to continue access to
   the same file system.

   Whether simultaneous use of the two file system instances is valid is
   controlled by whether the fs_locations_info attribute shows the two
   instances as having the same simultaneous-use class.  See
   Section 11.10.1 for information about the definition of the various
   use classes, including the simultaneous-use class.

   Note that for two such file systems, any information within the
   fs_locations_info attribute that indicates the need for special
   transition activity, i.e., the appearance of the two file system



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   instances with different handle, fileid, write-verifier, change, and
   readdir classes, indicates a serious problem.  The client, if it
   allows transition to the file system instance at all, must not treat
   this as a transparent transition.  The server SHOULD NOT indicate
   that these instances belong to different handle, fileid, write-
   verifier, change, and readdir classes, whether or not the two
   instances are shown belonging to the same simultaneous-use class.

   Where these conditions do not apply, a non-transparent file system
   instance transition is required with the details depending on the
   respective handle, fileid, write-verifier, change, and readdir
   classes of the two file system instances, and whether the two
   servers' addresses in question have the same eir_server_scope value
   as reported by EXCHANGE_ID.

11.7.2.1.  Simultaneous Use of File System Instances

   When the conditions in Section 11.7.2 hold, in either of the
   following two cases, the client may use the two file system instances
   simultaneously.

   o  The fs_locations_info attribute does not contain separate per-
      network-address entries for file system instances at the distinct
      network addresses.  This includes the case in which the
      fs_locations_info attribute is unavailable.  In this case, the
      fact that the two server addresses connect to the same server (as
      indicated by the two addresses sharing the same the so_major_id
      value and subsequently confirmed as described in Section 2.10.5)
      justifies simultaneous use, and there is no fs_locations_info
      attribute information contradicting that.

   o  The fs_locations_info attribute indicates that two file system
      instances belong to the same simultaneous-use class.

   In this case, the client may use both file system instances
   simultaneously, as representations of the same file system, whether
   that happens because the two network addresses connect to the same
   physical server or because different servers connect to clustered
   file systems and export their data in common.  When simultaneous use
   is in effect, any change made to one file system instance must be
   immediately reflected in the other file system instance(s).  Locks
   are treated as part of a common lease, associated with a common
   client ID.  Depending on the details of the eir_server_owner returned
   by EXCHANGE_ID, the two server instances may be accessed by different
   sessions or a single session in common.






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11.7.2.2.  Transparent File System Transitions

   When the conditions in Section 11.7.2.1 hold and the
   fs_locations_info attribute explicitly shows the file system
   instances for these distinct network addresses as belonging to
   different simultaneous-use classes, the file system instances should
   not be used by the client simultaneously.  Rather, they should be
   used serially with one being used unless and until communication
   difficulties, lack of responsiveness, or an explicit migration event
   causes another file system instance (or set of file system instances
   sharing a common simultaneous-use class) to be used.

   When a change of file system instance is to be done, the client will
   use the same client ID already in effect.  If the client already has
   connections to the new server address, these will be used.
   Otherwise, new connections to existing sessions or new sessions
   associated with the existing client ID are established as indicated
   by the eir_server_owner returned by EXCHANGE_ID.

   In all such transparent transition cases, the following apply:

   o  If filehandles are persistent, they stay the same.  If filehandles
      are volatile, they either stay the same or expire, but the reason
      for expiration is not due to the file system transition.

   o  Fileid values do not change across the transition.

   o  The file system will have the same fsid in both the old and new
      locations.

   o  Change attribute values are consistent across the transition and
      do not have to be refetched.  When change attributes indicate that
      a cached object is still valid, it can remain cached.

   o  Client and state identifiers retain their validity across the
      transition, except where their staleness is recognized and
      reported by the new server.  Except where such staleness requires
      it, no lock reclamation is needed.  Any such staleness is an
      indication that the server should be considered to have restarted
      and is reported as discussed in Section 8.4.2.

   o  Write verifiers are presumed to retain their validity and can be
      used to compare with verifiers returned by COMMIT on the new
      server.  If COMMIT on the new server returns an identical
      verifier, then it is expected that the new server has all of the
      data that was written unstably to the original server and has
      committed that data to stable storage as requested.




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   o  Readdir cookies are presumed to retain their validity and can be
      presented to subsequent READDIR requests together with the readdir
      verifier with which they are associated.  When the verifier is
      accepted as valid, the cookie will continue the READDIR operation
      so that the entire directory can be obtained by the client.

11.7.3.  Filehandles and File System Transitions

   There are a number of ways in which filehandles can be handled across
   a file system transition.  These can be divided into two broad
   classes depending upon whether the two file systems across which the
   transition happens share sufficient state to effect some sort of
   continuity of file system handling.

   When there is no such cooperation in filehandle assignment, the two
   file systems are reported as being in different handle classes.  In
   this case, all filehandles are assumed to expire as part of the file
   system transition.  Note that this behavior does not depend on the
   fh_expire_type attribute and supersedes the specification of the
   FH4_VOL_MIGRATION bit, which only affects behavior when
   fs_locations_info is not available.

   When there is cooperation in filehandle assignment, the two file
   systems are reported as being in the same handle classes.  In this
   case, persistent filehandles remain valid after the file system
   transition, while volatile filehandles (excluding those that are only
   volatile due to the FH4_VOL_MIGRATION bit) are subject to expiration
   on the target server.

11.7.4.  Fileids and File System Transitions

   In NFSv4.0, the issue of continuity of fileids in the event of a file
   system transition was not addressed.  The general expectation had
   been that in situations in which the two file system instances are
   created by a single vendor using some sort of file system image copy,
   fileids will be consistent across the transition, while in the
   analogous multi-vendor transitions they will not.  This poses
   difficulties, especially for the client without special knowledge of
   the transition mechanisms adopted by the server.  Note that although
   fileid is not a REQUIRED attribute, many servers support fileids and
   many clients provide APIs that depend on fileids.

   It is important to note that while clients themselves may have no
   trouble with a fileid changing as a result of a file system
   transition event, applications do typically have access to the fileid
   (e.g., via stat).  The result is that an application may work
   perfectly well if there is no file system instance transition or if
   any such transition is among instances created by a single vendor,



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   yet be unable to deal with the situation in which a multi-vendor
   transition occurs at the wrong time.

   Providing the same fileids in a multi-vendor (multiple server
   vendors) environment has generally been held to be quite difficult.
   While there is work to be done, it needs to be pointed out that this
   difficulty is partly self-imposed.  Servers have typically identified
   fileid with inode number, i.e. with a quantity used to find the file
   in question.  This identification poses special difficulties for
   migration of a file system between vendors where assigning the same
   index to a given file may not be possible.  Note here that a fileid
   is not required to be useful to find the file in question, only that
   it is unique within the given file system.  Servers prepared to
   accept a fileid as a single piece of metadata and store it apart from
   the value used to index the file information can relatively easily
   maintain a fileid value across a migration event, allowing a truly
   transparent migration event.

   In any case, where servers can provide continuity of fileids, they
   should, and the client should be able to find out that such
   continuity is available and take appropriate action.  Information
   about the continuity (or lack thereof) of fileids across a file
   system transition is represented by specifying whether the file
   systems in question are of the same fileid class.

   Note that when consistent fileids do not exist across a transition
   (either because there is no continuity of fileids or because fileid
   is not a supported attribute on one of instances involved), and there
   are no reliable filehandles across a transition event (either because
   there is no filehandle continuity or because the filehandles are
   volatile), the client is in a position where it cannot verify that
   files it was accessing before the transition are the same objects.
   It is forced to assume that no object has been renamed, and, unless
   there are guarantees that provide this (e.g., the file system is
   read-only), problems for applications may occur.  Therefore, use of
   such configurations should be limited to situations where the
   problems that this may cause can be tolerated.

11.7.5.  Fsids and File System Transitions

   Since fsids are generally only unique within a per-server basis, it
   is likely that they will change during a file system transition.  One
   exception is the case of transparent transitions, but in that case we
   have multiple network addresses that are defined as the same server
   (as specified by a common value of the so_major_id field of
   eir_server_owner).  Clients should not make the fsids received from
   the server visible to applications since they may not be globally
   unique, and because they may change during a file system transition



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   event.  Applications are best served if they are isolated from such
   transitions to the extent possible.

   Although normally a single source file system will transition to a
   single target file system, there is a provision for splitting a
   single source file system into multiple target file systems, by
   specifying the FSLI4F_MULTI_FS flag.

11.7.5.1.  File System Splitting

   When a file system transition is made and the fs_locations_info
   indicates that the file system in question may be split into multiple
   file systems (via the FSLI4F_MULTI_FS flag), the client SHOULD do
   GETATTRs to determine the fsid attribute on all known objects within
   the file system undergoing transition to determine the new file
   system boundaries.

   Clients may maintain the fsids passed to existing applications by
   mapping all of the fsids for the descendant file systems to the
   common fsid used for the original file system.

   Splitting a file system may be done on a transition between file
   systems of the same fileid class, since the fact that fileids are
   unique within the source file system ensure they will be unique in
   each of the target file systems.

11.7.6.  The Change Attribute and File System Transitions

   Since the change attribute is defined as a server-specific one,
   change attributes fetched from one server are normally presumed to be
   invalid on another server.  Such a presumption is troublesome since
   it would invalidate all cached change attributes, requiring
   refetching.  Even more disruptive, the absence of any assured
   continuity for the change attribute means that even if the same value
   is retrieved on refetch, no conclusions can be drawn as to whether
   the object in question has changed.  The identical change attribute
   could be merely an artifact of a modified file with a different
   change attribute construction algorithm, with that new algorithm just
   happening to result in an identical change value.

   When the two file systems have consistent change attribute formats,
   and this fact is communicated to the client by reporting in the same
   change class, the client may assume a continuity of change attribute
   construction and handle this situation just as it would be handled
   without any file system transition.






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11.7.7.  Lock State and File System Transitions

   In a file system transition, the client needs to handle cases in
   which the two servers have cooperated in state management and in
   which they have not.  Cooperation by two servers in state management
   requires coordination of client IDs.  Before the client attempts to
   use a client ID associated with one server in a request to the server
   of the other file system, it must eliminate the possibility that two
   non-cooperating servers have assigned the same client ID by accident.
   The client needs to compare the eir_server_scope values returned by
   each server.  If the scope values do not match, then the servers have
   not cooperated in state management.  If the scope values match, then
   this indicates the servers have cooperated in assigning client IDs to
   the point that they will reject client IDs that refer to state they
   do not know about.  See Section 2.10.4 for more information about the
   use of server scope.

   In the case of migration, the servers involved in the migration of a
   file system SHOULD transfer all server state from the original to the
   new server.  When this is done, it must be done in a way that is
   transparent to the client.  With replication, such a degree of common
   state is typically not the case.  Clients, however, should use the
   information provided by the eir_server_scope returned by EXCHANGE_ID
   (as modified by the validation procedures described in
   Section 2.10.4) to determine whether such sharing may be in effect,
   rather than making assumptions based on the reason for the
   transition.

   This state transfer will reduce disruption to the client when a file
   system transition occurs.  If the servers are successful in
   transferring all state, the client can attempt to establish sessions
   associated with the client ID used for the source file system
   instance.  If the server accepts that as a valid client ID, then the
   client may use the existing stateids associated with that client ID
   for the old file system instance in connection with that same client
   ID in connection with the transitioned file system instance.  If the
   client in question already had a client ID on the target system, it
   may interrogate the stateid values from the source system under that
   new client ID, with the assurance that if they are accepted as valid,
   then they represent validly transferred lock state for the source
   file system, which has been transferred to the target server.

   When the two servers belong to the same server scope, it does not
   mean that when dealing with the transition, the client will not have
   to reclaim state.  However, it does mean that the client may proceed
   using its current client ID when establishing communication with the
   new server, and the new server will either recognize the client ID as
   valid or reject it, in which case locks must be reclaimed by the



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   client.

   File systems cooperating in state management may actually share state
   or simply divide the identifier space so as to recognize (and reject
   as stale) each other's stateids and client IDs.  Servers that do
   share state may not do so under all conditions or at all times.  If
   the server cannot be sure when accepting a client ID that it reflects
   the locks the client was given, the server must treat all associated
   state as stale and report it as such to the client.

   When the two file system instances are on servers that do not share a
   server scope value, the client must establish a new client ID on the
   destination, if it does not have one already, and reclaim locks if
   allowed by the server.  In this case, old stateids and client IDs
   should not be presented to the new server since there is no assurance
   that they will not conflict with IDs valid on that server.  Note that
   in this case, lock reclaim may be attempted even when the servers
   involved in the transfer have different server scope values (see
   Section 8.4.2.1 for the contrary case of reclaim after server
   reboot).  Servers with different server scope values may cooperate to
   allow reclaim for locks associated with the transfer of a file system
   even if they do not cooperate sufficiently to share a server scope.

   In either case, when actual locks are not known to be maintained, the
   destination server may establish a grace period specific to the given
   file system, with non-reclaim locks being rejected for that file
   system, even though normal locks are being granted for other file
   systems.  Clients should not infer the absence of a grace period for
   file systems being transitioned to a server from responses to
   requests for other file systems.

   In the case of lock reclamation for a given file system after a file
   system transition, edge conditions can arise similar to those for
   reclaim after server restart (although in the case of the planned
   state transfer associated with migration, these can be avoided by
   securely recording lock state as part of state migration).  Unless
   the destination server can guarantee that locks will not be
   incorrectly granted, the destination server should not allow lock
   reclaims and should avoid establishing a grace period.

   Once all locks have been reclaimed, or there were no locks to
   reclaim, the client indicates that there are no more reclaims to be
   done for the file system in question by sending a RECLAIM_COMPLETE
   operation with the rca_one_fs parameter set to true.  Once this has
   been done, non-reclaim locking operations may be done, and any
   subsequent request to do reclaims will be rejected with the error
   NFS4ERR_NO_GRACE.




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   Information about client identity may be propagated between servers
   in the form of client_owner4 and associated verifiers, under the
   assumption that the client presents the same values to all the
   servers with which it deals.

   Servers are encouraged to provide facilities to allow locks to be
   reclaimed on the new server after a file system transition.  Often,
   however, in cases in which the two servers do not share a server
   scope value, such facilities may not be available and the client
   should be prepared to re-obtain locks, even though it is possible
   that the client may have its LOCK or OPEN request denied due to a
   conflicting lock.

   The consequences of having no facilities available to reclaim locks
   on the new server will depend on the type of environment.  In some
   environments, such as the transition between read-only file systems,
   such denial of locks should not pose large difficulties in practice.
   When an attempt to re-establish a lock on a new server is denied, the
   client should treat the situation as if its original lock had been
   revoked.  Note that when the lock is granted, the client cannot
   assume that no conflicting lock could have been granted in the
   interim.  Where change attribute continuity is present, the client
   may check the change attribute to check for unwanted file
   modifications.  Where even this is not available, and the file system
   is not read-only, a client may reasonably treat all pending locks as
   having been revoked.

11.7.7.1.  Leases and File System Transitions

   In the case of lease renewal, the client may not be submitting
   requests for a file system that has been transferred to another
   server.  This can occur because of the lease renewal mechanism.  The
   client renews the lease associated with all file systems when
   submitting a request on an associated session, regardless of the
   specific file system being referenced.

   In order for the client to schedule renewal of its lease where there
   is locking state that may have been relocated to the new server, the
   client must find out about lease relocation before that lease expire.
   To accomplish this, the SEQUENCE operation will return the status bit
   SEQ4_STATUS_LEASE_MOVED if responsibility for any of the renewed
   locking state has been transferred to a new server.  This will
   continue until the client receives an NFS4ERR_MOVED error for each of
   the file systems for which there has been locking state relocation.

   When a client receives an SEQ4_STATUS_LEASE_MOVED indication from a
   server, for each file system of the server for which the client has
   locking state, the client should perform an operation.  For



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   simplicity, the client may choose to reference all file systems, but
   what is important is that it must reference all file systems for
   which there was locking state where that state has moved.  Once the
   client receives an NFS4ERR_MOVED error for each such file system, the
   server will clear the SEQ4_STATUS_LEASE_MOVED indication.  The client
   can terminate the process of checking file systems once this
   indication is cleared (but only if the client has received a reply
   for all outstanding SEQUENCE requests on all sessions it has with the
   server), since there are no others for which locking state has moved.

   A client may use GETATTR of the fs_status (or fs_locations_info)
   attribute on all of the file systems to get absence indications in a
   single (or a few) request(s), since absent file systems will not
   cause an error in this context.  However, it still must do an
   operation that receives NFS4ERR_MOVED on each file system, in order
   to clear the SEQ4_STATUS_LEASE_MOVED indication.

   Once the set of file systems with transferred locking state has been
   determined, the client can follow the normal process to obtain the
   new server information (through the fs_locations and
   fs_locations_info attributes) and perform renewal of that lease on
   the new server, unless information in the fs_locations_info attribute
   shows that no state could have been transferred.  If the server has
   not had state transferred to it transparently, the client will
   receive NFS4ERR_STALE_CLIENTID from the new server, as described
   above, and the client can then reclaim locks as is done in the event
   of server failure.

11.7.7.2.  Transitions and the Lease_time Attribute

   In order that the client may appropriately manage its lease in the
   case of a file system transition, the destination server must
   establish proper values for the lease_time attribute.

   When state is transferred transparently, that state should include
   the correct value of the lease_time attribute.  The lease_time
   attribute on the destination server must never be less than that on
   the source, since this would result in premature expiration of a
   lease granted by the source server.  Upon transitions in which state
   is transferred transparently, the client is under no obligation to
   refetch the lease_time attribute and may continue to use the value
   previously fetched (on the source server).

   If state has not been transferred transparently, either because the
   associated servers are shown as having different eir_server_scope
   strings or because the client ID is rejected when presented to the
   new server, the client should fetch the value of lease_time on the
   new (i.e., destination) server, and use it for subsequent locking



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   requests.  However, the server must respect a grace period of at
   least as long as the lease_time on the source server, in order to
   ensure that clients have ample time to reclaim their lock before
   potentially conflicting non-reclaimed locks are granted.

11.7.8.  Write Verifiers and File System Transitions

   In a file system transition, the two file systems may be clustered in
   the handling of unstably written data.  When this is the case, and
   the two file systems belong to the same write-verifier class, write
   verifiers returned from one system may be compared to those returned
   by the other and superfluous writes avoided.

   When two file systems belong to different write-verifier classes, any
   verifier generated by one must not be compared to one provided by the
   other.  Instead, it should be treated as not equal even when the
   values are identical.

11.7.9.  Readdir Cookies and Verifiers and File System Transitions

   In a file system transition, the two file systems may be consistent
   in their handling of READDIR cookies and verifiers.  When this is the
   case, and the two file systems belong to the same readdir class,
   READDIR cookies and verifiers from one system may be recognized by
   the other and READDIR operations started on one server may be validly
   continued on the other, simply by presenting the cookie and verifier
   returned by a READDIR operation done on the first file system to the
   second.

   When two file systems belong to different readdir classes, any
   READDIR cookie and verifier generated by one is not valid on the
   second, and must not be presented to that server by the client.  The
   client should act as if the verifier was rejected.

11.7.10.  File System Data and File System Transitions

   When multiple replicas exist and are used simultaneously or in
   succession by a client, applications using them will normally expect
   that they contain either the same data or data that is consistent
   with the normal sorts of changes that are made by other clients
   updating the data of the file system (with metadata being the same to
   the degree indicated by the fs_locations_info attribute).  However,
   when multiple file systems are presented as replicas of one another,
   the precise relationship between the data of one and the data of
   another is not, as a general matter, specified by the NFSv4.1
   protocol.  It is quite possible to present as replicas file systems
   where the data of those file systems is sufficiently different that
   some applications have problems dealing with the transition between



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   replicas.  The namespace will typically be constructed so that
   applications can choose an appropriate level of support, so that in
   one position in the namespace a varied set of replicas will be
   listed, while in another only those that are up-to-date may be
   considered replicas.  The protocol does define four special cases of
   the relationship among replicas to be specified by the server and
   relied upon by clients:

   o  When multiple server addresses correspond to the same actual
      server, as indicated by a common so_major_id field within the
      eir_server_owner field returned by EXCHANGE_ID, the client may
      depend on the fact that changes to data, metadata, or locks made
      on one file system are immediately reflected on others.

   o  When multiple replicas exist and are used simultaneously by a
      client (see the FSLIB4_CLSIMUL definition within
      fs_locations_info), they must designate the same data.  Where file
      systems are writable, a change made on one instance must be
      visible on all instances, immediately upon the earlier of the
      return of the modifying requester or the visibility of that change
      on any of the associated replicas.  This allows a client to use
      these replicas simultaneously without any special adaptation to
      the fact that there are multiple replicas.  In this case, locks
      (whether share reservations or byte-range locks) and delegations
      obtained on one replica are immediately reflected on all replicas,
      even though these locks will be managed under a set of client IDs.

   o  When one replica is designated as the successor instance to
      another existing instance after return NFS4ERR_MOVED (i.e., the
      case of migration), the client may depend on the fact that all
      changes written to stable storage on the original instance are
      written to stable storage of the successor (uncommitted writes are
      dealt with in Section 11.7.8).

   o  Where a file system is not writable but represents a read-only
      copy (possibly periodically updated) of a writable file system,
      clients have similar requirements with regard to the propagation
      of updates.  They may need a guarantee that any change visible on
      the original file system instance must be immediately visible on
      any replica before the client transitions access to that replica,
      in order to avoid any possibility that a client, in effecting a
      transition to a replica, will see any reversion in file system
      state.  The specific means of this guarantee varies based on the
      value of the fss_type field that is reported as part of the
      fs_status attribute (see Section 11.11).  Since these file systems
      are presumed to be unsuitable for simultaneous use, there is no
      specification of how locking is handled; in general, locks
      obtained on one file system will be separate from those on others.



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      Since these are going to be read-only file systems, this is not
      expected to pose an issue for clients or applications.

11.8.  Effecting File System Referrals

   Referrals are effected when an absent file system is encountered and
   one or more alternate locations are made available by the
   fs_locations or fs_locations_info attributes.  The client will
   typically get an NFS4ERR_MOVED error, fetch the appropriate location
   information, and proceed to access the file system on a different
   server, even though it retains its logical position within the
   original namespace.  Referrals differ from migration events in that
   they happen only when the client has not previously referenced the
   file system in question (so there is nothing to transition).
   Referrals can only come into effect when an absent file system is
   encountered at its root.

   The examples given in the sections below are somewhat artificial in
   that an actual client will not typically do a multi-component look
   up, but will have cached information regarding the upper levels of
   the name hierarchy.  However, these example are chosen to make the
   required behavior clear and easy to put within the scope of a small
   number of requests, without getting unduly into details of how
   specific clients might choose to cache things.

11.8.1.  Referral Example (LOOKUP)

   Let us suppose that the following COMPOUND is sent in an environment
   in which /this/is/the/path is absent from the target server.  This
   may be for a number of reasons.  It may be that the file system has
   moved, or it may be that the target server is functioning mainly, or
   solely, to refer clients to the servers on which various file systems
   are located.

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  LOOKUP "path"

   o  GETFH

   o  GETATTR (fsid, fileid, size, time_modify)




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   Under the given circumstances, the following will be the result.

   o  PUTROOTFH --> NFS_OK.  The current fh is now the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  LOOKUP "path" --> NFS_OK.  The current fh is for /this/is/the/path
      and is within a new, absent file system, but ... the client will
      never see the value of that fh.

   o  GETFH --> NFS4ERR_MOVED.  Fails because current fh is in an absent
      file system at the start of the operation, and the specification
      makes no exception for GETFH.

   o  GETATTR (fsid, fileid, size, time_modify).  Not executed because
      the failure of the GETFH stops processing of the COMPOUND.

   Given the failure of the GETFH, the client has the job of determining
   the root of the absent file system and where to find that file
   system, i.e., the server and path relative to that server's root fh.
   Note that in this example, the client did not obtain filehandles and
   attribute information (e.g., fsid) for the intermediate directories,
   so that it would not be sure where the absent file system starts.  It
   could be the case, for example, that /this/is/the is the root of the
   moved file system and that the reason that the look up of "path"
   succeeded is that the file system was not absent on that operation
   but was moved between the last LOOKUP and the GETFH (since COMPOUND
   is not atomic).  Even if we had the fsids for all of the intermediate
   directories, we could have no way of knowing that /this/is/the/path
   was the root of a new file system, since we don't yet have its fsid.

   In order to get the necessary information, let us re-send the chain
   of LOOKUPs with GETFHs and GETATTRs to at least get the fsids so we
   can be sure where the appropriate file system boundaries are.  The
   client could choose to get fs_locations_info at the same time but in
   most cases the client will have a good guess as to where file system
   boundaries are (because of where NFS4ERR_MOVED was, and was not,
   received) making fetching of fs_locations_info unnecessary.





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   OP01:  PUTROOTFH --> NFS_OK

   -  Current fh is root of pseudo-fs.

   OP02:  GETATTR(fsid) --> NFS_OK

   -  Just for completeness.  Normally, clients will know the fsid of
      the pseudo-fs as soon as they establish communication with a
      server.

   OP03:  LOOKUP "this" --> NFS_OK

   OP04:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP05:  GETFH --> NFS_OK

   -  Current fh is for /this and is within pseudo-fs.

   OP06:  LOOKUP "is" --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP07:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP08:  GETFH --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP09:  LOOKUP "the" --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP10:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.






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   OP11:  GETFH --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP12:  LOOKUP "path" --> NFS_OK

   -  Current fh is for /this/is/the/path and is within a new, absent
      file system, but ...

   -  The client will never see the value of that fh.

   OP13:  GETATTR(fsid, fs_locations_info) --> NFS_OK

   -  We are getting the fsid to know where the file system boundaries
      are.  In this operation, the fsid will be different than that of
      the parent directory (which in turn was retrieved in OP10).  Note
      that the fsid we are given will not necessarily be preserved at
      the new location.  That fsid might be different, and in fact the
      fsid we have for this file system might be a valid fsid of a
      different file system on that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /this/is/the/path rather than /this/is/the since we have
      the fsid of the latter and it is that of the pseudo-fs, which
      presumably cannot move.  However, in other examples, we might not
      have this kind of information to rely on (e.g., /this/is/the might
      be a non-pseudo file system separate from /this/is/the/path), so
      we need to have other reliable source information on the boundary
      of the file system that is moved.  If, for example, the file
      system /this/is had moved, we would have a case of migration
      rather than referral, and once the boundaries of the migrated file
      system was clear we could fetch fs_locations_info.

   -  We are fetching fs_locations_info because the fact that we got an
      NFS4ERR_MOVED at this point means that it is most likely that this
      is a referral and we need the destination.  Even if it is the case
      that /this/is/the is a file system that has migrated, we will
      still need the location information for that file system.

   OP14:  GETFH --> NFS4ERR_MOVED

   -  Fails because current fh is in an absent file system at the start
      of the operation, and the specification makes no exception for
      GETFH.  Note that this means the server will never send the client
      a filehandle from within an absent file system.

   Given the above, the client knows where the root of the absent file
   system is (/this/is/the/path) by noting where the change of fsid



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   occurred (between "the" and "path").  The fs_locations_info attribute
   also gives the client the actual location of the absent file system,
   so that the referral can proceed.  The server gives the client the
   bare minimum of information about the absent file system so that
   there will be very little scope for problems of conflict between
   information sent by the referring server and information of the file
   system's home.  No filehandles and very few attributes are present on
   the referring server, and the client can treat those it receives as
   transient information with the function of enabling the referral.

11.8.2.  Referral Example (READDIR)

   Another context in which a client may encounter referrals is when it
   does a READDIR on a directory in which some of the sub-directories
   are the roots of absent file systems.

   Suppose such a directory is read as follows:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (fsid, size, time_modify, mounted_on_fileid)

   In this case, because rdattr_error is not requested,
   fs_locations_info is not requested, and some of the attributes cannot
   be provided, the result will be an NFS4ERR_MOVED error on the
   READDIR, with the detailed results as follows:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (fsid, size, time_modify, mounted_on_fileid) -->
      NFS4ERR_MOVED.  Note that the same error would have been returned
      if /this/is/the had migrated, but it is returned because the



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      directory contains the root of an absent file system.

   So now suppose that we re-send with rdattr_error:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)

   The results will be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
      --> NFS_OK.  The attributes for directory entry with the component
      named "path" will only contain rdattr_error with the value
      NFS4ERR_MOVED, together with an fsid value and a value for
      mounted_on_fileid.

   So suppose we do another READDIR to get fs_locations_info (although
   we could have used a GETATTR directly, as in Section 11.8.1).

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, time_modify)




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   The results would be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, time_modify) --> NFS_OK.  The attributes will be as shown
      below.

   The attributes for the directory entry with the component named
   "path" will only contain:

   o  rdattr_error (value: NFS_OK)

   o  fs_locations_info

   o  mounted_on_fileid (value: unique fileid within referring file
      system)

   o  fsid (value: unique value within referring server)

   The attributes for entry "path" will not contain size or time_modify
   because these attributes are not available within an absent file
   system.

11.9.  The Attribute fs_locations

   The fs_locations attribute is structured in the following way:


   struct fs_location4 {
           utf8str_cis     server<>;
           pathname4       rootpath;
   };


   struct fs_locations4 {
           pathname4       fs_root;
           fs_location4    locations<>;



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   };

   The fs_location4 data type is used to represent the location of a
   file system by providing a server name and the path to the root of
   the file system within that server's namespace.  When a set of
   servers have corresponding file systems at the same path within their
   namespaces, an array of server names may be provided.  An entry in
   the server array is a UTF-8 string and represents one of a
   traditional DNS host name, IPv4 address, IPv6 address, or a zero-
   length string.  An IPv4 or IPv6 address is represented as a universal
   address (see Section 3.3.9 and [15]), minus the netid, and either
   with or without the trailing ".p1.p2" suffix that represents the port
   number.  If the suffix is omitted, then the default port, 2049,
   SHOULD be assumed.  A zero-length string SHOULD be used to indicate
   the current address being used for the RPC call.  It is not a
   requirement that all servers that share the same rootpath be listed
   in one fs_location4 instance.  The array of server names is provided
   for convenience.  Servers that share the same rootpath may also be
   listed in separate fs_location4 entries in the fs_locations
   attribute.

   The fs_locations4 data type and fs_locations attribute contain an
   array of such locations.  Since the namespace of each server may be
   constructed differently, the "fs_root" field is provided.  The path
   represented by fs_root represents the location of the file system in
   the current server's namespace, i.e., that of the server from which
   the fs_locations attribute was obtained.  The fs_root path is meant
   to aid the client by clearly referencing the root of the file system
   whose locations are being reported, no matter what object within the
   current file system the current filehandle designates.  The fs_root
   is simply the pathname the client used to reach the object on the
   current server (i.e., the object to which the fs_locations attribute
   applies).

   When the fs_locations attribute is interrogated and there are no
   alternate file system locations, the server SHOULD return a zero-
   length array of fs_location4 structures, together with a valid
   fs_root.

   As an example, suppose there is a replicated file system located at
   two servers (servA and servB).  At servA, the file system is located
   at path /a/b/c.  At, servB the file system is located at path /x/y/z.
   If the client were to obtain the fs_locations value for the directory
   at /a/b/c/d, it might not necessarily know that the file system's
   root is located in servA's namespace at /a/b/c.  When the client
   switches to servB, it will need to determine that the directory it
   first referenced at servA is now represented by the path /x/y/z/d on
   servB.  To facilitate this, the fs_locations attribute provided by



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   servA would have an fs_root value of /a/b/c and two entries in
   fs_locations.  One entry in fs_locations will be for itself (servA)
   and the other will be for servB with a path of /x/y/z.  With this
   information, the client is able to substitute /x/y/z for the /a/b/c
   at the beginning of its access path and construct /x/y/z/d to use for
   the new server.

   Note that there is no requirement that the number of components in
   each rootpath be the same; there is no relation between the number of
   components in rootpath or fs_root, and none of the components in a
   rootpath and fs_root have to be the same.  In the above example, we
   could have had a third element in the locations array, with server
   equal to "servC" and rootpath equal to "/I/II", and a fourth element
   in locations with server equal to "servD" and rootpath equal to
   "/aleph/beth/gimel/daleth/he".

   The relationship between fs_root to a rootpath is that the client
   replaces the pathname indicated in fs_root for the current server for
   the substitute indicated in rootpath for the new server.

   For an example of a referred or migrated file system, suppose there
   is a file system located at serv1.  At serv1, the file system is
   located at /az/buky/vedi/glagoli.  The client finds that object at
   glagoli has migrated (or is a referral).  The client gets the
   fs_locations attribute, which contains an fs_root of /az/buky/vedi/
   glagoli, and one element in the locations array, with server equal to
   serv2, and rootpath equal to /izhitsa/fita.  The client replaces /az/
   buky/vedi/glagoli with /izhitsa/fita, and uses the latter pathname on
   serv2.

   Thus, the server MUST return an fs_root that is equal to the path the
   client used to reach the object to which the fs_locations attribute
   applies.  Otherwise, the client cannot determine the new path to use
   on the new server.

   Since the fs_locations attribute lacks information defining various
   attributes of the various file system choices presented, it SHOULD
   only be interrogated and used when fs_locations_info is not
   available.  When fs_locations is used, information about the specific
   locations should be assumed based on the following rules.

   The following rules are general and apply irrespective of the
   context.

   o  All listed file system instances should be considered as of the
      same handle class, if and only if, the current fh_expire_type
      attribute does not include the FH4_VOL_MIGRATION bit.  Note that
      in the case of referral, filehandle issues do not apply since



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      there can be no filehandles known within the current file system,
      nor is there any access to the fh_expire_type attribute on the
      referring (absent) file system.

   o  All listed file system instances should be considered as of the
      same fileid class if and only if the fh_expire_type attribute
      indicates persistent filehandles and does not include the
      FH4_VOL_MIGRATION bit.  Note that in the case of referral, fileid
      issues do not apply since there can be no fileids known within the
      referring (absent) file system, nor is there any access to the
      fh_expire_type attribute.

   o  All file system instances servers should be considered as of
      different change classes.

   For other class assignments, handling of file system transitions
   depends on the reasons for the transition:

   o  When the transition is due to migration, that is, the client was
      directed to a new file system after receiving an NFS4ERR_MOVED
      error, the target should be treated as being of the same write-
      verifier class as the source.

   o  When the transition is due to failover to another replica, that
      is, the client selected another replica without receiving an
      NFS4ERR_MOVED error, the target should be treated as being of a
      different write-verifier class from the source.

   The specific choices reflect typical implementation patterns for
   failover and controlled migration, respectively.  Since other choices
   are possible and useful, this information is better obtained by using
   fs_locations_info.  When a server implementation needs to communicate
   other choices, it MUST support the fs_locations_info attribute.

   See Section 21 for a discussion on the recommendations for the
   security flavor to be used by any GETATTR operation that requests the
   "fs_locations" attribute.

11.10.  The Attribute fs_locations_info

   The fs_locations_info attribute is intended as a more functional
   replacement for fs_locations that will continue to exist and be
   supported.  Clients can use it to get a more complete set of
   information about alternative file system locations.  When the server
   does not support fs_locations_info, fs_locations can be used to get a
   subset of the information.  A server that supports fs_locations_info
   MUST support fs_locations as well.




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   There is additional information present in fs_locations_info, that is
   not available in fs_locations:

   o  Attribute continuity information.  This information will allow a
      client to select a location that meets the transparency
      requirements of the applications accessing the data and to
      leverage optimizations due to the server guarantees of attribute
      continuity (e.g., if between multiple server locations the change
      attribute of a file of the file system is continuous, the client
      does not have to invalidate the file's cache if the change
      attribute is the same among all locations).

   o  File system identity information that indicates when multiple
      replicas, from the client's point of view, correspond to the same
      target file system, allowing them to be used interchangeably,
      without disruption, as multiple paths to the same thing.

   o  Information that will bear on the suitability of various replicas,
      depending on the use that the client intends.  For example, many
      applications need an absolutely up-to-date copy (e.g., those that
      write), while others may only need access to the most up-to-date
      copy reasonably available.

   o  Server-derived preference information for replicas, which can be
      used to implement load-balancing while giving the client the
      entire file system list to be used in case the primary fails.

   The fs_locations_info attribute is structured similarly to the
   fs_locations attribute.  A top-level structure (fs_locations_info4)
   contains the entire attribute including the root pathname of the file
   system and an array of lower-level structures that define replicas
   that share a common rootpath on their respective servers.  The lower-
   level structure in turn (fs_locations_item4) contains a specific
   pathname and information on one or more individual server replicas.
   For that last lowest-level, fs_locations_info has an
   fs_locations_server4 structure that contains per-server-replica
   information in addition to the server name.  This per-server-replica
   information includes a nominally opaque array, fls_info, in which
   specific pieces of information are located at the specific indices
   listed below.

   The attribute will always contain at least a single
   fs_locations_server entry.  Typically, this will be an entry with the
   FS4LIGF_CUR_REQ flag set, although in the case of a referral there
   will be no entry with that flag set.

   It should be noted that fs_locations_info attributes returned by
   servers for various replicas may differ for various reasons.  One



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   server may know about a set of replicas that are not known to other
   servers.  Further, compatibility attributes may differ.  Filehandles
   might be of the same class going from replica A to replica B but not
   going in the reverse direction.  This might happen because the
   filehandles are the same, but replica B's server implementation might
   not have provision to note and report that equivalence.

   The fs_locations_info attribute consists of a root pathname
   (fli_fs_root, just like fs_root in the fs_locations attribute),
   together with an array of fs_location_item4 structures.  The
   fs_location_item4 structures in turn consist of a root pathname
   (fli_rootpath) together with an array (fli_entries) of elements of
   data type fs_locations_server4, all defined as follows.

   /*
    * Defines an individual server replica
    */
   struct  fs_locations_server4 {
           int32_t         fls_currency;
           opaque          fls_info<>;
           utf8str_cis     fls_server;
   };

   /*
    * Byte indices of items within
    * fls_info: flag fields, class numbers,
    * bytes indicating ranks and orders.
    */
   const FSLI4BX_GFLAGS            = 0;
   const FSLI4BX_TFLAGS            = 1;

   const FSLI4BX_CLSIMUL           = 2;
   const FSLI4BX_CLHANDLE          = 3;
   const FSLI4BX_CLFILEID          = 4;
   const FSLI4BX_CLWRITEVER        = 5;
   const FSLI4BX_CLCHANGE          = 6;
   const FSLI4BX_CLREADDIR         = 7;

   const FSLI4BX_READRANK          = 8;
   const FSLI4BX_WRITERANK         = 9;
   const FSLI4BX_READORDER         = 10;
   const FSLI4BX_WRITEORDER        = 11;

   /*
    * Bits defined within the general flag byte.
    */
   const FSLI4GF_WRITABLE          = 0x01;
   const FSLI4GF_CUR_REQ           = 0x02;



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   const FSLI4GF_ABSENT            = 0x04;
   const FSLI4GF_GOING             = 0x08;
   const FSLI4GF_SPLIT             = 0x10;

   /*
    * Bits defined within the transport flag byte.
    */
   const FSLI4TF_RDMA              = 0x01;

   /*
    * Defines a set of replicas sharing
    * a common value of the rootpath
    * with in the corresponding
    * single-server namespaces.
    */
   struct  fs_locations_item4 {
           fs_locations_server4    fli_entries<>;
           pathname4               fli_rootpath;
   };

   /*
    * Defines the overall structure of
    * the fs_locations_info attribute.
    */
   struct  fs_locations_info4 {
           uint32_t                fli_flags;
           int32_t                 fli_valid_for;
           pathname4               fli_fs_root;
           fs_locations_item4      fli_items<>;
   };

   /*
    * Flag bits in fli_flags.
    */
   const FSLI4IF_VAR_SUB           = 0x00000001;

   typedef fs_locations_info4 fattr4_fs_locations_info;

   As noted above, the fs_locations_info attribute, when supported, may
   be requested of absent file systems without causing NFS4ERR_MOVED to
   be returned.  It is generally expected that it will be available for
   both present and absent file systems even if only a single
   fs_locations_server4 entry is present, designating the current
   (present) file system, or two fs_locations_server4 entries
   designating the previous location of an absent file system (the one
   just referenced) and its successor location.  Servers are strongly
   urged to support this attribute on all file systems if they support
   it on any file system.



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   The data presented in the fs_locations_info attribute may be obtained
   by the server in any number of ways, including specification by the
   administrator or by current protocols for transferring data among
   replicas and protocols not yet developed.  NFSv4.1 only defines how
   this information is presented by the server to the client.

11.10.1.  The fs_locations_server4 Structure

   The fs_locations_server4 structure consists of the following items:

   o  An indication of how up-to-date the file system is (fls_currency)
      in seconds.  This value is relative to the master copy.  A
      negative value indicates that the server is unable to give any
      reasonably useful value here.  A value of zero indicates that the
      file system is the actual writable data or a reliably coherent and
      fully up-to-date copy.  Positive values indicate how out-of-date
      this copy can normally be before it is considered for update.
      Such a value is not a guarantee that such updates will always be
      performed on the required schedule but instead serves as a hint
      about how far the copy of the data would be expected to be behind
      the most up-to-date copy.

   o  A counted array of one-byte values (fls_info) containing
      information about the particular file system instance.  This data
      includes general flags, transport capability flags, file system
      equivalence class information, and selection priority information.
      The encoding will be discussed below.

   o  The server string (fls_server).  For the case of the replica
      currently being accessed (via GETATTR), a zero-length string MAY
      be used to indicate the current address being used for the RPC
      call.  The fls_server field can also be an IPv4 or IPv6 address,
      formatted the same way as an IPv4 or IPv6 address in the "server"
      field of the fs_location4 data type (see Section 11.9).

   Data within the fls_info array is in the form of 8-bit data items
   with constants giving the offsets within the array of various values
   describing this particular file system instance.  This style of
   definition was chosen, in preference to explicit XDR structure
   definitions for these values, for a number of reasons.

   o  The kinds of data in the fls_info array, representing flags, file
      system classes, and priorities among sets of file systems
      representing the same data, are such that 8 bits provide a quite
      acceptable range of values.  Even where there might be more than
      256 such file system instances, having more than 256 distinct
      classes or priorities is unlikely.




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   o  Explicit definition of the various specific data items within XDR
      would limit expandability in that any extension within a
      subsequent minor version would require yet another attribute,
      leading to specification and implementation clumsiness.

   o  Such explicit definitions would also make it impossible to propose
      Standards Track extensions apart from a full minor version.

   This encoding scheme can be adapted to the specification of multi-
   byte numeric values, even though none are currently defined.  If
   extensions are made via Standards Track RFCs, multi-byte quantities
   will be encoded as a range of bytes with a range of indices, with the
   byte interpreted in big-endian byte order.  Further, any such index
   assignments are constrained so that the relevant quantities will not
   cross XDR word boundaries.

   The set of fls_info data is subject to expansion in a future minor
   version, or in a Standards Track RFC, within the context of a single
   minor version.  The server SHOULD NOT send and the client MUST NOT
   use indices within the fls_info array that are not defined in
   Standards Track RFCs.

   The fls_info array contains:

   o  Two 8-bit flag fields, one devoted to general file-system
      characteristics and a second reserved for transport-related
      capabilities.

   o  Six 8-bit class values that define various file system equivalence
      classes as explained below.

   o  Four 8-bit priority values that govern file system selection as
      explained below.

   The general file system characteristics flag (at byte index
   FSLI4BX_GFLAGS) has the following bits defined within it:

   o  FSLI4GF_WRITABLE indicates that this file system target is
      writable, allowing it to be selected by clients that may need to
      write on this file system.  When the current file system instance
      is writable and is defined as of the same simultaneous use class
      (as specified by the value at index FSLI4BX_CLSIMUL) to which the
      client was previously writing, then it must incorporate within its
      data any committed write made on the source file system instance.
      See Section 11.7.8, which discusses the write-verifier class.
      While there is no harm in not setting this flag for a file system
      that turns out to be writable, turning the flag on for a read-only
      file system can cause problems for clients that select a migration



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      or replication target based on the flag and then find themselves
      unable to write.

   o  FSLI4GF_CUR_REQ indicates that this replica is the one on which
      the request is being made.  Only a single server entry may have
      this flag set and, in the case of a referral, no entry will have
      it.

   o  FSLI4GF_ABSENT indicates that this entry corresponds to an absent
      file system replica.  It can only be set if FSLI4GF_CUR_REQ is
      set.  When both such bits are set, it indicates that a file system
      instance is not usable but that the information in the entry can
      be used to determine the sorts of continuity available when
      switching from this replica to other possible replicas.  Since
      this bit can only be true if FSLI4GF_CUR_REQ is true, the value
      could be determined using the fs_status attribute, but the
      information is also made available here for the convenience of the
      client.  An entry with this bit, since it represents a true file
      system (albeit absent), does not appear in the event of a
      referral, but only when a file system has been accessed at this
      location and has subsequently been migrated.

   o  FSLI4GF_GOING indicates that a replica, while still available,
      should not be used further.  The client, if using it, should make
      an orderly transfer to another file system instance as
      expeditiously as possible.  It is expected that file systems going
      out of service will be announced as FSLI4GF_GOING some time before
      the actual loss of service.  It is also expected that the
      fli_valid_for value will be sufficiently small to allow clients to
      detect and act on scheduled events, while large enough that the
      cost of the requests to fetch the fs_locations_info values will
      not be excessive.  Values on the order of ten minutes seem
      reasonable.

      When this flag is seen as part of a transition into a new file
      system, a client might choose to transfer immediately to another
      replica, or it may reference the current file system and only
      transition when a migration event occurs.  Similarly, when this
      flag appears as a replica in the referral, clients would likely
      avoid being referred to this instance whenever there is another
      choice.

   o  FSLI4GF_SPLIT indicates that when a transition occurs from the
      current file system instance to this one, the replacement may
      consist of multiple file systems.  In this case, the client has to
      be prepared for the possibility that objects on the same file
      system before migration will be on different ones after.  Note
      that FSLI4GF_SPLIT is not incompatible with the file systems



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      belonging to the same fileid class since, if one has a set of
      fileids that are unique within a file system, each subset assigned
      to a smaller file system after migration would not have any
      conflicts internal to that file system.

      A client, in the case of a split file system, will interrogate
      existing files with which it has continuing connection (it is free
      to simply forget cached filehandles).  If the client remembers the
      directory filehandle associated with each open file, it may
      proceed upward using LOOKUPP to find the new file system
      boundaries.  Note that in the event of a referral, there will not
      be any such files and so these actions will not be performed.
      Instead, a reference to a portion of the original file system now
      split off into other file systems will encounter an fsid change
      and possibly a further referral.

      Once the client recognizes that one file system has been split
      into two, it can prevent the disruption of running applications by
      presenting the two file systems as a single one until a convenient
      point to recognize the transition, such as a restart.  This would
      require a mapping from the server's fsids to fsids as seen by the
      client, but this is already necessary for other reasons.  As noted
      above, existing fileids within the two descendant file systems
      will not conflict.  Providing non-conflicting fileids for newly
      created files on the split file systems is the responsibility of
      the server (or servers working in concert).  The server can encode
      filehandles such that filehandles generated before the split event
      can be discerned from those generated after the split, allowing
      the server to determine when the need for emulating two file
      systems as one is over.

      Although it is possible for this flag to be present in the event
      of referral, it would generally be of little interest to the
      client, since the client is not expected to have information
      regarding the current contents of the absent file system.

   The transport-flag field (at byte index FSLI4BX_TFLAGS) contains the
   following bits related to the transport capabilities of the specific
   file system.

   o  FSLI4TF_RDMA indicates that this file system provides NFSv4.1 file
      system access using an RDMA-capable transport.

   Attribute continuity and file system identity information are
   expressed by defining equivalence relations on the sets of file
   systems presented to the client.  Each such relation is expressed as
   a set of file system equivalence classes.  For each relation, a file
   system has an 8-bit class number.  Two file systems belong to the



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   same class if both have identical non-zero class numbers.  Zero is
   treated as non-matching.  Most often, the relevant question for the
   client will be whether a given replica is identical to / continuous
   with the current one in a given respect, but the information should
   be available also as to whether two other replicas match in that
   respect as well.

   The following fields specify the file system's class numbers for the
   equivalence relations used in determining the nature of file system
   transitions.  See Section 11.7 and its various subsections for
   details about how this information is to be used.  Servers may assign
   these values as they wish, so long as file system instances that
   share the same value have the specified relationship to one another;
   conversely, file systems that have the specified relationship to one
   another share a common class value.  As each instance entry is added,
   the relationships of this instance to previously entered instances
   can be consulted, and if one is found that bears the specified
   relationship, that entry's class value can be copied to the new
   entry.  When no such previous entry exists, a new value for that byte
   index (not previously used) can be selected, most likely by
   incrementing the value of the last class value assigned for that
   index.

   o  The field with byte index FSLI4BX_CLSIMUL defines the
      simultaneous-use class for the file system.

   o  The field with byte index FSLI4BX_CLHANDLE defines the handle
      class for the file system.

   o  The field with byte index FSLI4BX_CLFILEID defines the fileid
      class for the file system.

   o  The field with byte index FSLI4BX_CLWRITEVER defines the write-
      verifier class for the file system.

   o  The field with byte index FSLI4BX_CLCHANGE defines the change
      class for the file system.

   o  The field with byte index FSLI4BX_CLREADDIR defines the readdir
      class for the file system.

   Server-specified preference information is also provided via 8-bit
   values within the fls_info array.  The values provide a rank and an
   order (see below) to be used with separate values specifiable for the
   cases of read-only and writable file systems.  These values are
   compared for different file systems to establish the server-specified
   preference, with lower values indicating "more preferred".




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   Rank is used to express a strict server-imposed ordering on clients,
   with lower values indicating "more preferred".  Clients should
   attempt to use all replicas with a given rank before they use one
   with a higher rank.  Only if all of those file systems are
   unavailable should the client proceed to those of a higher rank.
   Because specifying a rank will override client preferences, servers
   should be conservative about using this mechanism, particularly when
   the environment is one in which client communication characteristics
   are neither tightly controlled nor visible to the server.

   Within a rank, the order value is used to specify the server's
   preference to guide the client's selection when the client's own
   preferences are not controlling, with lower values of order
   indicating "more preferred".  If replicas are approximately equal in
   all respects, clients should defer to the order specified by the
   server.  When clients look at server latency as part of their
   selection, they are free to use this criterion but it is suggested
   that when latency differences are not significant, the server-
   specified order should guide selection.

   o  The field at byte index FSLI4BX_READRANK gives the rank value to
      be used for read-only access.

   o  The field at byte index FSLI4BX_READORDER gives the order value to
      be used for read-only access.

   o  The field at byte index FSLI4BX_WRITERANK gives the rank value to
      be used for writable access.

   o  The field at byte index FSLI4BX_WRITEORDER gives the order value
      to be used for writable access.

   Depending on the potential need for write access by a given client,
   one of the pairs of rank and order values is used.  The read rank and
   order should only be used if the client knows that only reading will
   ever be done or if it is prepared to switch to a different replica in
   the event that any write access capability is required in the future.

11.10.2.  The fs_locations_info4 Structure

   The fs_locations_info4 structure, encoding the fs_locations_info
   attribute, contains the following:

   o  The fli_flags field, which contains general flags that affect the
      interpretation of this fs_locations_info4 structure and all
      fs_locations_item4 structures within it.  The only flag currently
      defined is FSLI4IF_VAR_SUB.  All bits in the fli_flags field that
      are not defined should always be returned as zero.



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   o  The fli_fs_root field, which contains the pathname of the root of
      the current file system on the current server, just as it does in
      the fs_locations4 structure.

   o  An array called fli_items of fs_locations4_item structures, which
      contain information about replicas of the current file system.
      Where the current file system is actually present, or has been
      present, i.e., this is not a referral situation, one of the
      fs_locations_item4 structures will contain an fs_locations_server4
      for the current server.  This structure will have FSLI4GF_ABSENT
      set if the current file system is absent, i.e., normal access to
      it will return NFS4ERR_MOVED.

   o  The fli_valid_for field specifies a time in seconds for which it
      is reasonable for a client to use the fs_locations_info attribute
      without refetch.  The fli_valid_for value does not provide a
      guarantee of validity since servers can unexpectedly go out of
      service or become inaccessible for any number of reasons.  Clients
      are well-advised to refetch this information for an actively
      accessed file system at every fli_valid_for seconds.  This is
      particularly important when file system replicas may go out of
      service in a controlled way using the FSLI4GF_GOING flag to
      communicate an ongoing change.  The server should set
      fli_valid_for to a value that allows well-behaved clients to
      notice the FSLI4GF_GOING flag and make an orderly switch before
      the loss of service becomes effective.  If this value is zero,
      then no refetch interval is appropriate and the client need not
      refetch this data on any particular schedule.  In the event of a
      transition to a new file system instance, a new value of the
      fs_locations_info attribute will be fetched at the destination.
      It is to be expected that this may have a different fli_valid_for
      value, which the client should then use in the same fashion as the
      previous value.

   The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
   substitution is to be enabled.  See Section 11.10.3 for an
   explanation of variable substitution.

11.10.3.  The fs_locations_item4 Structure

   The fs_locations_item4 structure contains a pathname (in the field
   fli_rootpath) that encodes the path of the target file system
   replicas on the set of servers designated by the included
   fs_locations_server4 entries.  The precise manner in which this
   target location is specified depends on the value of the
   FSLI4IF_VAR_SUB flag within the associated fs_locations_info4
   structure.




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   If this flag is not set, then fli_rootpath simply designates the
   location of the target file system within each server's single-server
   namespace just as it does for the rootpath within the fs_location4
   structure.  When this bit is set, however, component entries of a
   certain form are subject to client-specific variable substitution so
   as to allow a degree of namespace non-uniformity in order to
   accommodate the selection of client-specific file system targets to
   adapt to different client architectures or other characteristics.

   When such substitution is in effect, a variable beginning with the
   string "${" and ending with the string "}" and containing a colon is
   to be replaced by the client-specific value associated with that
   variable.  The string "unknown" should be used by the client when it
   has no value for such a variable.  The pathname resulting from such
   substitutions is used to designate the target file system, so that
   different clients may have different file systems, corresponding to
   that location in the multi-server namespace.

   As mentioned above, such substituted pathname variables contain a
   colon.  The part before the colon is to be a DNS domain name, and the
   part after is to be a case-insensitive alphanumeric string.

   Where the domain is "ietf.org", only variable names defined in this
   document or subsequent Standards Track RFCs are subject to such
   substitution.  Organizations are free to use their domain names to
   create their own sets of client-specific variables, to be subject to
   such substitution.  In cases where such variables are intended to be
   used more broadly than a single organization, publication of an
   Informational RFC defining such variables is RECOMMENDED.

   The variable ${ietf.org:CPU_ARCH} is used to denote that the CPU
   architecture object files are compiled.  This specification does not
   limit the acceptable values (except that they must be valid UTF-8
   strings), but such values as "x86", "x86_64", and "sparc" would be
   expected to be used in line with industry practice.

   The variable ${ietf.org:OS_TYPE} is used to denote the operating
   system, and thus the kernel and library APIs, for which code might be
   compiled.  This specification does not limit the acceptable values
   (except that they must be valid UTF-8 strings), but such values as
   "linux" and "freebsd" would be expected to be used in line with
   industry practice.

   The variable ${ietf.org:OS_VERSION} is used to denote the operating
   system version, and thus the specific details of versioned
   interfaces, for which code might be compiled.  This specification
   does not limit the acceptable values (except that they must be valid
   UTF-8 strings).  However, combinations of numbers and letters with



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   interspersed dots would be expected to be used in line with industry
   practice, with the details of the version format depending on the
   specific value of the variable ${ietf.org:OS_TYPE} with which it is
   used.

   Use of these variables could result in the direction of different
   clients to different file systems on the same server, as appropriate
   to particular clients.  In cases in which the target file systems are
   located on different servers, a single server could serve as a
   referral point so that each valid combination of variable values
   would designate a referral hosted on a single server, with the
   targets of those referrals on a number of different servers.

   Because namespace administration is affected by the values selected
   to substitute for various variables, clients should provide
   convenient means of determining what variable substitutions a client
   will implement, as well as, where appropriate, providing means to
   control the substitutions to be used.  The exact means by which this
   will be done is outside the scope of this specification.

   Although variable substitution is most suitable for use in the
   context of referrals, it may be used in the context of replication
   and migration.  If it is used in these contexts, the server must
   ensure that no matter what values the client presents for the
   substituted variables, the result is always a valid successor file
   system instance to that from which a transition is occurring, i.e.,
   that the data is identical or represents a later image of a writable
   file system.

   Note that when fli_rootpath is a null pathname (that is, one with
   zero components), the file system designated is at the root of the
   specified server, whether or not the FSLI4IF_VAR_SUB flag within the
   associated fs_locations_info4 structure is set.

11.11.  The Attribute fs_status

   In an environment in which multiple copies of the same basic set of
   data are available, information regarding the particular source of
   such data and the relationships among different copies can be very
   helpful in providing consistent data to applications.











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   enum fs4_status_type {
           STATUS4_FIXED = 1,
           STATUS4_UPDATED = 2,
           STATUS4_VERSIONED = 3,
           STATUS4_WRITABLE = 4,
           STATUS4_REFERRAL = 5
   };

   struct fs4_status {
           bool            fss_absent;
           fs4_status_type fss_type;
           utf8str_cs      fss_source;
           utf8str_cs      fss_current;
           int32_t         fss_age;
           nfstime4        fss_version;
   };

   The boolean fss_absent indicates whether the file system is currently
   absent.  This value will be set if the file system was previously
   present and becomes absent, or if the file system has never been
   present and the type is STATUS4_REFERRAL.  When this boolean is set
   and the type is not STATUS4_REFERRAL, the remaining information in
   the fs4_status reflects that last valid when the file system was
   present.

   The fss_type field indicates the kind of file system image
   represented.  This is of particular importance when using the version
   values to determine appropriate succession of file system images.
   When fss_absent is set, and the file system was previously present,
   the value of fss_type reflected is that when the file was last
   present.  Five values are distinguished:

   o  STATUS4_FIXED, which indicates a read-only image in the sense that
      it will never change.  The possibility is allowed that, as a
      result of migration or switch to a different image, changed data
      can be accessed, but within the confines of this instance, no
      change is allowed.  The client can use this fact to cache
      aggressively.

   o  STATUS4_VERSIONED, which indicates that the image, like the
      STATUS4_UPDATED case, is updated externally, but it provides a
      guarantee that the server will carefully update an associated
      version value so that the client can protect itself from a
      situation in which it reads data from one version of the file
      system and then later reads data from an earlier version of the
      same file system.  See below for a discussion of how this can be
      done.




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   o  STATUS4_UPDATED, which indicates an image that cannot be updated
      by the user writing to it but that may be changed externally,
      typically because it is a periodically updated copy of another
      writable file system somewhere else.  In this case, version
      information is not provided, and the client does not have the
      responsibility of making sure that this version only advances upon
      a file system instance transition.  In this case, it is the
      responsibility of the server to make sure that the data presented
      after a file system instance transition is a proper successor
      image and includes all changes seen by the client and any change
      made before all such changes.

   o  STATUS4_WRITABLE, which indicates that the file system is an
      actual writable one.  The client need not, of course, actually
      write to the file system, but once it does, it should not accept a
      transition to anything other than a writable instance of that same
      file system.

   o  STATUS4_REFERRAL, which indicates that the file system in question
      is absent and has never been present on this server.

   Note that in the STATUS4_UPDATED and STATUS4_VERSIONED cases, the
   server is responsible for the appropriate handling of locks that are
   inconsistent with external changes to delegations.  If a server gives
   out delegations, they SHOULD be recalled before an inconsistent
   change is made to the data, and MUST be revoked if this is not
   possible.  Similarly, if an OPEN is inconsistent with data that is
   changed (the OPEN has OPEN4_SHARE_DENY_WRITE/OPEN4_SHARE_DENY_BOTH
   and the data is changed), that OPEN SHOULD be considered
   administratively revoked.

   The opaque strings fss_source and fss_current provide a way of
   presenting information about the source of the file system image
   being present.  It is not intended that the client do anything with
   this information other than make it available to administrative
   tools.  It is intended that this information be helpful when
   researching possible problems with a file system image that might
   arise when it is unclear if the correct image is being accessed and,
   if not, how that image came to be made.  This kind of diagnostic
   information will be helpful, if, as seems likely, copies of file
   systems are made in many different ways (e.g., simple user-level
   copies, file-system-level point-in-time copies, clones of the
   underlying storage), under a variety of administrative arrangements.
   In such environments, determining how a given set of data was
   constructed can be very helpful in resolving problems.

   The opaque string fss_source is used to indicate the source of a
   given file system with the expectation that tools capable of creating



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   a file system image propagate this information, when possible.  It is
   understood that this may not always be possible since a user-level
   copy may be thought of as creating a new data set and the tools used
   may have no mechanism to propagate this data.  When a file system is
   initially created, it is desirable to associate with it data
   regarding how the file system was created, where it was created, who
   created it, etc.  Making this information available in this attribute
   in a human-readable string will be helpful for applications and
   system administrators and will also serve to make it available when
   the original file system is used to make subsequent copies.

   The opaque string fss_current should provide whatever information is
   available about the source of the current copy.  Such information
   includes the tool creating it, any relevant parameters to that tool,
   the time at which the copy was done, the user making the change, the
   server on which the change was made, etc.  All information should be
   in a human-readable string.

   The field fss_age provides an indication of how out-of-date the file
   system currently is with respect to its ultimate data source (in case
   of cascading data updates).  This complements the fls_currency field
   of fs_locations_server4 (see Section 11.10) in the following way: the
   information in fls_currency gives a bound for how out of date the
   data in a file system might typically get, while the value in fss_age
   gives a bound on how out-of-date that data actually is.  Negative
   values imply that no information is available.  A zero means that
   this data is known to be current.  A positive value means that this
   data is known to be no older than that number of seconds with respect
   to the ultimate data source.  Using this value, the client may be
   able to decide that a data copy is too old, so that it may search for
   a newer version to use.

   The fss_version field provides a version identification, in the form
   of a time value, such that successive versions always have later time
   values.  When the fs_type is anything other than STATUS4_VERSIONED,
   the server may provide such a value, but there is no guarantee as to
   its validity and clients will not use it except to provide additional
   information to add to fss_source and fss_current.

   When fss_type is STATUS4_VERSIONED, servers SHOULD provide a value of
   fss_version that progresses monotonically whenever any new version of
   the data is established.  This allows the client, if reliable image
   progression is important to it, to fetch this attribute as part of
   each COMPOUND where data or metadata from the file system is used.

   When it is important to the client to make sure that only valid
   successor images are accepted, it must make sure that it does not
   read data or metadata from the file system without updating its sense



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   of the current state of the image.  This is to avoid the possibility
   that the fs_status that the client holds will be one for an earlier
   image, which would cause the client to accept a new file system
   instance that is later than that but still earlier than the updated
   data read by the client.

   In order to accept valid images reliably, the client must do a
   GETATTR of the fs_status attribute that follows any interrogation of
   data or metadata within the file system in question.  Often this is
   most conveniently done by appending such a GETATTR after all other
   operations that reference a given file system.  When errors occur
   between reading file system data and performing such a GETATTR, care
   must be exercised to make sure that the data in question is not used
   before obtaining the proper fs_status value.  In this connection,
   when an OPEN is done within such a versioned file system and the
   associated GETATTR of fs_status is not successfully completed, the
   open file in question must not be accessed until that fs_status is
   fetched.

   The procedure above will ensure that before using any data from the
   file system the client has in hand a newly-fetched current version of
   the file system image.  Multiple values for multiple requests in
   flight can be resolved by assembling them into the required partial
   order (and the elements should form a total order within the partial
   order) and using the last.  The client may then, when switching among
   file system instances, decline to use an instance that does not have
   an fss_type of STATUS4_VERSIONED or whose fss_version field is
   earlier than the last one obtained from the predecessor file system
   instance.

12.  Parallel NFS (pNFS)

12.1.  Introduction

   pNFS is an OPTIONAL feature within NFSv4.1; the pNFS feature set
   allows direct client access to the storage devices containing file
   data.  When file data for a single NFSv4 server is stored on multiple
   and/or higher-throughput storage devices (by comparison to the
   server's throughput capability), the result can be significantly
   better file access performance.  The relationship among multiple
   clients, a single server, and multiple storage devices for pNFS
   (server and clients have access to all storage devices) is shown in
   Figure 1.








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       +-----------+
       |+-----------+                                 +-----------+
       ||+-----------+                                |           |
       |||           |        NFSv4.1 + pNFS          |           |
       +||  Clients  |<------------------------------>|   Server  |
        +|           |                                |           |
         +-----------+                                |           |
              |||                                     +-----------+
              |||                                           |
              |||                                           |
              ||| Storage        +-----------+              |
              ||| Protocol       |+-----------+             |
              ||+----------------||+-----------+  Control   |
              |+-----------------|||           |    Protocol|
              +------------------+||  Storage  |------------+
                                  +|  Devices  |
                                   +-----------+

                                 Figure 1

   In this model, the clients, server, and storage devices are
   responsible for managing file access.  This is in contrast to NFSv4
   without pNFS, where it is primarily the server's responsibility; some
   of this responsibility may be delegated to the client under strictly
   specified conditions.  See Section 12.2.5 for a discussion of the
   Storage Protocol.  See Section 12.2.6 for a discussion of the Control
   Protocol.

   pNFS takes the form of OPTIONAL operations that manage protocol
   objects called 'layouts' (Section 12.2.7) that contain a byte-range
   and storage location information.  The layout is managed in a similar
   fashion as NFSv4.1 data delegations.  For example, the layout is
   leased, recallable, and revocable.  However, layouts are distinct
   abstractions and are manipulated with new operations.  When a client
   holds a layout, it is granted the ability to directly access the
   byte-range at the storage location specified in the layout.

   There are interactions between layouts and other NFSv4.1 abstractions
   such as data delegations and byte-range locking.  Delegation issues
   are discussed in Section 12.5.5.  Byte-range locking issues are
   discussed in Sections 12.2.9 and 12.5.1.

12.2.  pNFS Definitions

   NFSv4.1's pNFS feature provides parallel data access to a file system
   that stripes its content across multiple storage servers.  The first
   instantiation of pNFS, as part of NFSv4.1, separates the file system
   protocol processing into two parts: metadata processing and data



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   processing.  Data consist of the contents of regular files that are
   striped across storage servers.  Data striping occurs in at least two
   ways: on a file-by-file basis and, within sufficiently large files,
   on a block-by-block basis.  In contrast, striped access to metadata
   by pNFS clients is not provided in NFSv4.1, even though the file
   system back end of a pNFS server might stripe metadata.  Metadata
   consist of everything else, including the contents of non-regular
   files (e.g., directories); see Section 12.2.1.  The metadata
   functionality is implemented by an NFSv4.1 server that supports pNFS
   and the operations described in Section 18; such a server is called a
   metadata server (Section 12.2.2).

   The data functionality is implemented by one or more storage devices,
   each of which are accessed by the client via a storage protocol.  A
   subset (defined in Section 13.6) of NFSv4.1 is one such storage
   protocol.  New terms are introduced to the NFSv4.1 nomenclature and
   existing terms are clarified to allow for the description of the pNFS
   feature.

12.2.1.  Metadata

   Information about a file system object, such as its name, location
   within the namespace, owner, ACL, and other attributes.  Metadata may
   also include storage location information, and this will vary based
   on the underlying storage mechanism that is used.

12.2.2.  Metadata Server

   An NFSv4.1 server that supports the pNFS feature.  A variety of
   architectural choices exist for the metadata server and its use of
   file system information held at the server.  Some servers may contain
   metadata only for file objects residing at the metadata server, while
   the file data resides on associated storage devices.  Other metadata
   servers may hold both metadata and a varying degree of file data.

12.2.3.  pNFS Client

   An NFSv4.1 client that supports pNFS operations and supports at least
   one storage protocol for performing I/O to storage devices.

12.2.4.  Storage Device

   A storage device stores a regular file's data, but leaves metadata
   management to the metadata server.  A storage device could be another
   NFSv4.1 server, an object-based storage device (OSD), a block device
   accessed over a System Area Network (SAN, e.g., either FiberChannel
   or iSCSI SAN), or some other entity.




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12.2.5.  Storage Protocol

   As noted in Figure 1, the storage protocol is the method used by the
   client to store and retrieve data directly from the storage devices.

   The NFSv4.1 pNFS feature has been structured to allow for a variety
   of storage protocols to be defined and used.  One example storage
   protocol is NFSv4.1 itself (as documented in Section 13).  Other
   options for the storage protocol are described elsewhere and include:

   o  Block/volume protocols such as Internet SCSI (iSCSI) [48] and FCP
      [49].  The block/volume protocol support can be independent of the
      addressing structure of the block/volume protocol used, allowing
      more than one protocol to access the same file data and enabling
      extensibility to other block/volume protocols.  See [41] for a
      layout specification that allows pNFS to use block/volume storage
      protocols.

   o  Object protocols such as OSD over iSCSI or Fibre Channel [50].
      See [40] for a layout specification that allows pNFS to use object
      storage protocols.

   It is possible that various storage protocols are available to both
   client and server and it may be possible that a client and server do
   not have a matching storage protocol available to them.  Because of
   this, the pNFS server MUST support normal NFSv4.1 access to any file
   accessible by the pNFS feature; this will allow for continued
   interoperability between an NFSv4.1 client and server.

12.2.6.  Control Protocol

   As noted in Figure 1, the control protocol is used by the exported
   file system between the metadata server and storage devices.
   Specification of such protocols is outside the scope of the NFSv4.1
   protocol.  Such control protocols would be used to control activities
   such as the allocation and deallocation of storage, the management of
   state required by the storage devices to perform client access
   control, and, depending on the storage protocol, the enforcement of
   authentication and authorization so that restrictions that would be
   enforced by the metadata server are also enforced by the storage
   device.

   A particular control protocol is not REQUIRED by NFSv4.1 but
   requirements are placed on the control protocol for maintaining
   attributes like modify time, the change attribute, and the end-of-
   file (EOF) position.  Note that if pNFS is layered over a clustered,
   parallel file system (e.g., PVFS [51]), the mechanisms that enable
   clustering and parallelism in that file system can be considered the



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   control protocol.

12.2.7.  Layout Types

   A layout describes the mapping of a file's data to the storage
   devices that hold the data.  A layout is said to belong to a specific
   layout type (data type layouttype4, see Section 3.3.13).  The layout
   type allows for variants to handle different storage protocols, such
   as those associated with block/volume [41], object [40], and file
   (Section 13) layout types.  A metadata server, along with its control
   protocol, MUST support at least one layout type.  A private sub-range
   of the layout type namespace is also defined.  Values from the
   private layout type range MAY be used for internal testing or
   experimentation (see Section 3.3.13).

   As an example, the organization of the file layout type could be an
   array of tuples (e.g., device ID, filehandle), along with a
   definition of how the data is stored across the devices (e.g.,
   striping).  A block/volume layout might be an array of tuples that
   store <device ID, block number, block count> along with information
   about block size and the associated file offset of the block number.
   An object layout might be an array of tuples <device ID, object ID>
   and an additional structure (i.e., the aggregation map) that defines
   how the logical byte sequence of the file data is serialized into the
   different objects.  Note that the actual layouts are typically more
   complex than these simple expository examples.

   Requests for pNFS-related operations will often specify a layout
   type.  Examples of such operations are GETDEVICEINFO and LAYOUTGET.
   The response for these operations will include structures such as a
   device_addr4 or a layout4, each of which includes a layout type
   within it.  The layout type sent by the server MUST always be the
   same one requested by the client.  When a server sends a response
   that includes a different layout type, the client SHOULD ignore the
   response and behave as if the server had returned an error response.

12.2.8.  Layout

   A layout defines how a file's data is organized on one or more
   storage devices.  There are many potential layout types; each of the
   layout types are differentiated by the storage protocol used to
   access data and by the aggregation scheme that lays out the file data
   on the underlying storage devices.  A layout is precisely identified
   by the tuple <client ID, filehandle, layout type, iomode, range>,
   where filehandle refers to the filehandle of the file on the metadata
   server.

   It is important to define when layouts overlap and/or conflict with



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   each other.  For two layouts with overlapping byte-ranges to actually
   overlap each other, both layouts must be of the same layout type,
   correspond to the same filehandle, and have the same iomode.  Layouts
   conflict when they overlap and differ in the content of the layout
   (i.e., the storage device/file mapping parameters differ).  Note that
   differing iomodes do not lead to conflicting layouts.  It is
   permissible for layouts with different iomodes, pertaining to the
   same byte-range, to be held by the same client.  An example of this
   would be copy-on-write functionality for a block/volume layout type.

12.2.9.  Layout Iomode

   The layout iomode (data type layoutiomode4, see Section 3.3.20)
   indicates to the metadata server the client's intent to perform
   either just READ operations or a mixture containing READ and WRITE
   operations.  For certain layout types, it is useful for a client to
   specify this intent at the time it sends LAYOUTGET (Section 18.43).
   For example, for block/volume-based protocols, block allocation could
   occur when a LAYOUTIOMODE4_RW iomode is specified.  A special
   LAYOUTIOMODE4_ANY iomode is defined and can only be used for
   LAYOUTRETURN and CB_LAYOUTRECALL, not for LAYOUTGET.  It specifies
   that layouts pertaining to both LAYOUTIOMODE4_READ and
   LAYOUTIOMODE4_RW iomodes are being returned or recalled,
   respectively.

   A storage device may validate I/O with regard to the iomode; this is
   dependent upon storage device implementation and layout type.  Thus,
   if the client's layout iomode is inconsistent with the I/O being
   performed, the storage device may reject the client's I/O with an
   error indicating that a new layout with the correct iomode should be
   obtained via LAYOUTGET.  For example, if a client gets a layout with
   a LAYOUTIOMODE4_READ iomode and performs a WRITE to a storage device,
   the storage device is allowed to reject that WRITE.

   The use of the layout iomode does not conflict with OPEN share modes
   or byte-range LOCK operations; open share mode and byte-range lock
   conflicts are enforced as they are without the use of pNFS and are
   logically separate from the pNFS layout level.  Open share modes and
   byte-range locks are the preferred method for restricting user access
   to data files.  For example, an OPEN of OPEN4_SHARE_ACCESS_WRITE does
   not conflict with a LAYOUTGET containing an iomode of
   LAYOUTIOMODE4_RW performed by another client.  Applications that
   depend on writing into the same file concurrently may use byte-range
   locking to serialize their accesses.







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12.2.10.  Device IDs

   The device ID (data type deviceid4, see Section 3.3.14) identifies a
   group of storage devices.  The scope of a device ID is the pair
   <client ID, layout type>.  In practice, a significant amount of
   information may be required to fully address a storage device.
   Rather than embedding all such information in a layout, layouts embed
   device IDs.  The NFSv4.1 operation GETDEVICEINFO (Section 18.40) is
   used to retrieve the complete address information (including all
   device addresses for the device ID) regarding the storage device
   according to its layout type and device ID.  For example, the address
   of an NFSv4.1 data server or of an object-based storage device could
   be an IP address and port.  The address of a block storage device
   could be a volume label.

   Clients cannot expect the mapping between a device ID and its storage
   device address(es) to persist across metadata server restart.  See
   Section 12.7.4 for a description of how recovery works in that
   situation.

   A device ID lives as long as there is a layout referring to the
   device ID.  If there are no layouts referring to the device ID, the
   server is free to delete the device ID any time.  Once a device ID is
   deleted by the server, the server MUST NOT reuse the device ID for
   the same layout type and client ID again.  This requirement is
   feasible because the device ID is 16 bytes long, leaving sufficient
   room to store a generation number if the server's implementation
   requires most of the rest of the device ID's content to be reused.
   This requirement is necessary because otherwise the race conditions
   between asynchronous notification of device ID addition and deletion
   would be too difficult to sort out.

   Device ID to device address mappings are not leased, and can be
   changed at any time.  (Note that while device ID to device address
   mappings are likely to change after the metadata server restarts, the
   server is not required to change the mappings.)  A server has two
   choices for changing mappings.  It can recall all layouts referring
   to the device ID or it can use a notification mechanism.

   The NFSv4.1 protocol has no optimal way to recall all layouts that
   referred to a particular device ID (unless the server associates a
   single device ID with a single fsid or a single client ID; in which
   case, CB_LAYOUTRECALL has options for recalling all layouts
   associated with the fsid, client ID pair, or just the client ID).

   Via a notification mechanism (see Section 20.12), device ID to device
   address mappings can change over the duration of server operation
   without recalling or revoking the layouts that refer to device ID.



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   The notification mechanism can also delete a device ID, but only if
   the client has no layouts referring to the device ID.  A notification
   of a change to a device ID to device address mapping will immediately
   or eventually invalidate some or all of the device ID's mappings.
   The server MUST support notifications and the client must request
   them before they can be used.  For further information about the
   notification types Section 20.12.

12.3.  pNFS Operations

   NFSv4.1 has several operations that are needed for pNFS servers,
   regardless of layout type or storage protocol.  These operations are
   all sent to a metadata server and summarized here.  While pNFS is an
   OPTIONAL feature, if pNFS is implemented, some operations are
   REQUIRED in order to comply with pNFS.  See Section 17.

   These are the fore channel pNFS operations:

   GETDEVICEINFO  (Section 18.40), as noted previously
      (Section 12.2.10), returns the mapping of device ID to storage
      device address.

   GETDEVICELIST  (Section 18.41) allows clients to fetch all device IDs
      for a specific file system.

   LAYOUTGET  (Section 18.43) is used by a client to get a layout for a
      file.

   LAYOUTCOMMIT  (Section 18.42) is used to inform the metadata server
      of the client's intent to commit data that has been written to the
      storage device (the storage device as originally indicated in the
      return value of LAYOUTGET).

   LAYOUTRETURN  (Section 18.44) is used to return layouts for a file, a
      file system ID (FSID), or a client ID.

   These are the backchannel pNFS operations:

   CB_LAYOUTRECALL  (Section 20.3) recalls a layout, all layouts
      belonging to a file system, or all layouts belonging to a client
      ID.

   CB_RECALL_ANY  (Section 20.6) tells a client that it needs to return
      some number of recallable objects, including layouts, to the
      metadata server.






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   CB_RECALLABLE_OBJ_AVAIL  (Section 20.7) tells a client that a
      recallable object that it was denied (in case of pNFS, a layout
      denied by LAYOUTGET) due to resource exhaustion is now available.

   CB_NOTIFY_DEVICEID  (Section 20.12) notifies the client of changes to
      device IDs.

12.4.  pNFS Attributes

   A number of attributes specific to pNFS are listed and described in
   Section 5.12.

12.5.  Layout Semantics

12.5.1.  Guarantees Provided by Layouts

   Layouts grant to the client the ability to access data located at a
   storage device with the appropriate storage protocol.  The client is
   guaranteed the layout will be recalled when one of two things occur:
   either a conflicting layout is requested or the state encapsulated by
   the layout becomes invalid (this can happen when an event directly or
   indirectly modifies the layout).  When a layout is recalled and
   returned by the client, the client continues with the ability to
   access file data with normal NFSv4.1 operations through the metadata
   server.  Only the ability to access the storage devices is affected.

   The requirement of NFSv4.1 that all user access rights MUST be
   obtained through the appropriate OPEN, LOCK, and ACCESS operations is
   not modified with the existence of layouts.  Layouts are provided to
   NFSv4.1 clients, and user access still follows the rules of the
   protocol as if they did not exist.  It is a requirement that for a
   client to access a storage device, a layout must be held by the
   client.  If a storage device receives an I/O request for a byte-range
   for which the client does not hold a layout, the storage device
   SHOULD reject that I/O request.  Note that the act of modifying a
   file for which a layout is held does not necessarily conflict with
   the holding of the layout that describes the file being modified.
   Therefore, it is the requirement of the storage protocol or layout
   type that determines the necessary behavior.  For example, block/
   volume layout types require that the layout's iomode agree with the
   type of I/O being performed.

   Depending upon the layout type and storage protocol in use, storage
   device access permissions may be granted by LAYOUTGET and may be
   encoded within the type-specific layout.  For an example of storage
   device access permissions, see an object-based protocol such as [50].
   If access permissions are encoded within the layout, the metadata
   server SHOULD recall the layout when those permissions become invalid



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   for any reason -- for example, when a file becomes unwritable or
   inaccessible to a client.  Note, clients are still required to
   perform the appropriate OPEN, LOCK, and ACCESS operations as
   described above.  The degree to which it is possible for the client
   to circumvent these operations and the consequences of doing so must
   be clearly specified by the individual layout type specifications.
   In addition, these specifications must be clear about the
   requirements and non-requirements for the checking performed by the
   server.

   In the presence of pNFS functionality, mandatory byte-range locks
   MUST behave as they would without pNFS.  Therefore, if mandatory file
   locks and layouts are provided simultaneously, the storage device
   MUST be able to enforce the mandatory byte-range locks.  For example,
   if one client obtains a mandatory byte-range lock and a second client
   accesses the storage device, the storage device MUST appropriately
   restrict I/O for the range of the mandatory byte-range lock.  If the
   storage device is incapable of providing this check in the presence
   of mandatory byte-range locks, then the metadata server MUST NOT
   grant layouts and mandatory byte-range locks simultaneously.

12.5.2.  Getting a Layout

   A client obtains a layout with the LAYOUTGET operation.  The metadata
   server will grant layouts of a particular type (e.g., block/volume,
   object, or file).  The client selects an appropriate layout type that
   the server supports and the client is prepared to use.  The layout
   returned to the client might not exactly match the requested byte-
   range as described in Section 18.43.3.  As needed a client may send
   multiple LAYOUTGET operations; these might result in multiple
   overlapping, non-conflicting layouts (see Section 12.2.8).

   In order to get a layout, the client must first have opened the file
   via the OPEN operation.  When a client has no layout on a file, it
   MUST present an open stateid, a delegation stateid, or a byte-range
   lock stateid in the loga_stateid argument.  A successful LAYOUTGET
   result includes a layout stateid.  The first successful LAYOUTGET
   processed by the server using a non-layout stateid as an argument
   MUST have the "seqid" field of the layout stateid in the response set
   to one.  Thereafter, the client MUST use a layout stateid (see
   Section 12.5.3) on future invocations of LAYOUTGET on the file, and
   the "seqid" MUST NOT be set to zero.  Once the layout has been
   retrieved, it can be held across multiple OPEN and CLOSE sequences.
   Therefore, a client may hold a layout for a file that is not
   currently open by any user on the client.  This allows for the
   caching of layouts beyond CLOSE.

   The storage protocol used by the client to access the data on the



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   storage device is determined by the layout's type.  The client is
   responsible for matching the layout type with an available method to
   interpret and use the layout.  The method for this layout type
   selection is outside the scope of the pNFS functionality.

   Although the metadata server is in control of the layout for a file,
   the pNFS client can provide hints to the server when a file is opened
   or created about the preferred layout type and aggregation schemes.
   pNFS introduces a layout_hint attribute (Section 5.12.4) that the
   client can set at file creation time to provide a hint to the server
   for new files.  Setting this attribute separately, after the file has
   been created might make it difficult, or impossible, for the server
   implementation to comply.

   Because the EXCLUSIVE4 createmode4 does not allow the setting of
   attributes at file creation time, NFSv4.1 introduces the EXCLUSIVE4_1
   createmode4, which does allow attributes to be set at file creation
   time.  In addition, if the session is created with persistent reply
   caches, EXCLUSIVE4_1 is neither necessary nor allowed.  Instead,
   GUARDED4 both works better and is prescribed.  Table 10 in
   Section 18.16.3 summarizes how a client is allowed to send an
   exclusive create.

12.5.3.  Layout Stateid

   As with all other stateids, the layout stateid consists of a "seqid"
   and "other" field.  Once a layout stateid is established, the "other"
   field will stay constant unless the stateid is revoked or the client
   returns all layouts on the file and the server disposes of the
   stateid.  The "seqid" field is initially set to one, and is never
   zero on any NFSv4.1 operation that uses layout stateids, whether it
   is a fore channel or backchannel operation.  After the layout stateid
   is established, the server increments by one the value of the "seqid"
   in each subsequent LAYOUTGET and LAYOUTRETURN response, and in each
   CB_LAYOUTRECALL request.

   Given the design goal of pNFS to provide parallelism, the layout
   stateid differs from other stateid types in that the client is
   expected to send LAYOUTGET and LAYOUTRETURN operations in parallel.
   The "seqid" value is used by the client to properly sort responses to
   LAYOUTGET and LAYOUTRETURN.  The "seqid" is also used to prevent race
   conditions between LAYOUTGET and CB_LAYOUTRECALL.  Given that the
   processing rules differ from layout stateids and other stateid types,
   only the pNFS sections of this document should be considered to
   determine proper layout stateid handling.

   Once the client receives a layout stateid, it MUST use the correct
   "seqid" for subsequent LAYOUTGET or LAYOUTRETURN operations.  The



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   correct "seqid" is defined as the highest "seqid" value from
   responses of fully processed LAYOUTGET or LAYOUTRETURN operations or
   arguments of a fully processed CB_LAYOUTRECALL operation.  Since the
   server is incrementing the "seqid" value on each layout operation,
   the client may determine the order of operation processing by
   inspecting the "seqid" value.  In the case of overlapping layout
   ranges, the ordering information will provide the client the
   knowledge of which layout ranges are held.  Note that overlapping
   layout ranges may occur because of the client's specific requests or
   because the server is allowed to expand the range of a requested
   layout and notify the client in the LAYOUTRETURN results.  Additional
   layout stateid sequencing requirements are provided in
   Section 12.5.5.2.

   The client's receipt of a "seqid" is not sufficient for subsequent
   use.  The client must fully process the operations before the "seqid"
   can be used.  For LAYOUTGET results, if the client is not using the
   forgetful model (Section 12.5.5.1), it MUST first update its record
   of what ranges of the file's layout it has before using the seqid.
   For LAYOUTRETURN results, the client MUST delete the range from its
   record of what ranges of the file's layout it had before using the
   seqid.  For CB_LAYOUTRECALL arguments, the client MUST send a
   response to the recall before using the seqid.  The fundamental
   requirement in client processing is that the "seqid" is used to
   provide the order of processing.  LAYOUTGET results may be processed
   in parallel.  LAYOUTRETURN results may be processed in parallel.
   LAYOUTGET and LAYOUTRETURN responses may be processed in parallel as
   long as the ranges do not overlap.  CB_LAYOUTRECALL request
   processing MUST be processed in "seqid" order at all times.

   Once a client has no more layouts on a file, the layout stateid is no
   longer valid and MUST NOT be used.  Any attempt to use such a layout
   stateid will result in NFS4ERR_BAD_STATEID.

12.5.4.  Committing a Layout

   Allowing for varying storage protocol capabilities, the pNFS protocol
   does not require the metadata server and storage devices to have a
   consistent view of file attributes and data location mappings.  Data
   location mapping refers to aspects such as which offsets store data
   as opposed to storing holes (see Section 13.4.4 for a discussion).
   Related issues arise for storage protocols where a layout may hold
   provisionally allocated blocks where the allocation of those blocks
   does not survive a complete restart of both the client and server.
   Because of this inconsistency, it is necessary to resynchronize the
   client with the metadata server and its storage devices and make any
   potential changes available to other clients.  This is accomplished
   by use of the LAYOUTCOMMIT operation.



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   The LAYOUTCOMMIT operation is responsible for committing a modified
   layout to the metadata server.  The data should be written and
   committed to the appropriate storage devices before the LAYOUTCOMMIT
   occurs.  The scope of the LAYOUTCOMMIT operation depends on the
   storage protocol in use.  It is important to note that the level of
   synchronization is from the point of view of the client that sent the
   LAYOUTCOMMIT.  The updated state on the metadata server need only
   reflect the state as of the client's last operation previous to the
   LAYOUTCOMMIT.  The metadata server is not REQUIRED to maintain a
   global view that accounts for other clients' I/O that may have
   occurred within the same time frame.

   For block/volume-based layouts, LAYOUTCOMMIT may require updating the
   block list that comprises the file and committing this layout to
   stable storage.  For file-based layouts, synchronization of
   attributes between the metadata and storage devices, primarily the
   size attribute, is required.

   The control protocol is free to synchronize the attributes before it
   receives a LAYOUTCOMMIT; however, upon successful completion of a
   LAYOUTCOMMIT, state that exists on the metadata server that describes
   the file MUST be synchronized with the state that exists on the
   storage devices that comprise that file as of the client's last sent
   operation.  Thus, a client that queries the size of a file between a
   WRITE to a storage device and the LAYOUTCOMMIT might observe a size
   that does not reflect the actual data written.

   The client MUST have a layout in order to send a LAYOUTCOMMIT
   operation.

12.5.4.1.  LAYOUTCOMMIT and change/time_modify

   The change and time_modify attributes may be updated by the server
   when the LAYOUTCOMMIT operation is processed.  The reason for this is
   that some layout types do not support the update of these attributes
   when the storage devices process I/O operations.  If a client has a
   layout with the LAYOUTIOMODE4_RW iomode on the file, the client MAY
   provide a suggested value to the server for time_modify within the
   arguments to LAYOUTCOMMIT.  Based on the layout type, the provided
   value may or may not be used.  The server should sanity-check the
   client-provided values before they are used.  For example, the server
   should ensure that time does not flow backwards.  The client always
   has the option to set time_modify through an explicit SETATTR
   operation.

   For some layout protocols, the storage device is able to notify the
   metadata server of the occurrence of an I/O; as a result, the change
   and time_modify attributes may be updated at the metadata server.



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   For a metadata server that is capable of monitoring updates to the
   change and time_modify attributes, LAYOUTCOMMIT processing is not
   required to update the change attribute.  In this case, the metadata
   server must ensure that no further update to the data has occurred
   since the last update of the attributes; file-based protocols may
   have enough information to make this determination or may update the
   change attribute upon each file modification.  This also applies for
   the time_modify attribute.  If the server implementation is able to
   determine that the file has not been modified since the last
   time_modify update, the server need not update time_modify at
   LAYOUTCOMMIT.  At LAYOUTCOMMIT completion, the updated attributes
   should be visible if that file was modified since the latest previous
   LAYOUTCOMMIT or LAYOUTGET.

12.5.4.2.  LAYOUTCOMMIT and size

   The size of a file may be updated when the LAYOUTCOMMIT operation is
   used by the client.  One of the fields in the argument to
   LAYOUTCOMMIT is loca_last_write_offset; this field indicates the
   highest byte offset written but not yet committed with the
   LAYOUTCOMMIT operation.  The data type of loca_last_write_offset is
   newoffset4 and is switched on a boolean value, no_newoffset, that
   indicates if a previous write occurred or not.  If no_newoffset is
   FALSE, an offset is not given.  If the client has a layout with
   LAYOUTIOMODE4_RW iomode on the file, with a byte-range (denoted by
   the values of lo_offset and lo_length) that overlaps
   loca_last_write_offset, then the client MAY set no_newoffset to TRUE
   and provide an offset that will update the file size.  Keep in mind
   that offset is not the same as length, though they are related.  For
   example, a loca_last_write_offset value of zero means that one byte
   was written at offset zero, and so the length of the file is at least
   one byte.

   The metadata server may do one of the following:

   1.  Update the file's size using the last write offset provided by
       the client as either the true file size or as a hint of the file
       size.  If the metadata server has a method available, any new
       value for file size should be sanity-checked.  For example, the
       file must not be truncated if the client presents a last write
       offset less than the file's current size.

   2.  Ignore the client-provided last write offset; the metadata server
       must have sufficient knowledge from other sources to determine
       the file's size.  For example, the metadata server queries the
       storage devices with the control protocol.

   The method chosen to update the file's size will depend on the



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   storage device's and/or the control protocol's capabilities.  For
   example, if the storage devices are block devices with no knowledge
   of file size, the metadata server must rely on the client to set the
   last write offset appropriately.

   The results of LAYOUTCOMMIT contain a new size value in the form of a
   newsize4 union data type.  If the file's size is set as a result of
   LAYOUTCOMMIT, the metadata server must reply with the new size;
   otherwise, the new size is not provided.  If the file size is
   updated, the metadata server SHOULD update the storage devices such
   that the new file size is reflected when LAYOUTCOMMIT processing is
   complete.  For example, the client should be able to read up to the
   new file size.

   The client can extend the length of a file or truncate a file by
   sending a SETATTR operation to the metadata server with the size
   attribute specified.  If the size specified is larger than the
   current size of the file, the file is "zero extended", i.e., zeros
   are implicitly added between the file's previous EOF and the new EOF.
   (In many implementations, the zero-extended byte-range of the file
   consists of unallocated holes in the file.)  When the client writes
   past EOF via WRITE, the SETATTR operation does not need to be used.

12.5.4.3.  LAYOUTCOMMIT and layoutupdate

   The LAYOUTCOMMIT argument contains a loca_layoutupdate field
   (Section 18.42.1) of data type layoutupdate4 (Section 3.3.18).  This
   argument is a layout-type-specific structure.  The structure can be
   used to pass arbitrary layout-type-specific information from the
   client to the metadata server at LAYOUTCOMMIT time.  For example, if
   using a block/volume layout, the client can indicate to the metadata
   server which reserved or allocated blocks the client used or did not
   use.  The content of loca_layoutupdate (field lou_body) need not be
   the same layout-type-specific content returned by LAYOUTGET
   (Section 18.43.2) in the loc_body field of the lo_content field of
   the logr_layout field.  The content of loca_layoutupdate is defined
   by the layout type specification and is opaque to LAYOUTCOMMIT.

12.5.5.  Recalling a Layout

   Since a layout protects a client's access to a file via a direct
   client-storage-device path, a layout need only be recalled when it is
   semantically unable to serve this function.  Typically, this occurs
   when the layout no longer encapsulates the true location of the file
   over the byte-range it represents.  Any operation or action, such as
   server-driven restriping or load balancing, that changes the layout
   will result in a recall of the layout.  A layout is recalled by the
   CB_LAYOUTRECALL callback operation (see Section 20.3) and returned



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   with LAYOUTRETURN (see Section 18.44).  The CB_LAYOUTRECALL operation
   may recall a layout identified by a byte-range, all layouts
   associated with a file system ID (FSID), or all layouts associated
   with a client ID.  Section 12.5.5.2 discusses sequencing issues
   surrounding the getting, returning, and recalling of layouts.

   An iomode is also specified when recalling a layout.  Generally, the
   iomode in the recall request must match the layout being returned;
   for example, a recall with an iomode of LAYOUTIOMODE4_RW should cause
   the client to only return LAYOUTIOMODE4_RW layouts and not
   LAYOUTIOMODE4_READ layouts.  However, a special LAYOUTIOMODE4_ANY
   enumeration is defined to enable recalling a layout of any iomode; in
   other words, the client must return both LAYOUTIOMODE4_READ and
   LAYOUTIOMODE4_RW layouts.

   A REMOVE operation SHOULD cause the metadata server to recall the
   layout to prevent the client from accessing a non-existent file and
   to reclaim state stored on the client.  Since a REMOVE may be delayed
   until the last close of the file has occurred, the recall may also be
   delayed until this time.  After the last reference on the file has
   been released and the file has been removed, the client should no
   longer be able to perform I/O using the layout.  In the case of a
   file-based layout, the data server SHOULD return NFS4ERR_STALE in
   response to any operation on the removed file.

   Once a layout has been returned, the client MUST NOT send I/Os to the
   storage devices for the file, byte-range, and iomode represented by
   the returned layout.  If a client does send an I/O to a storage
   device for which it does not hold a layout, the storage device SHOULD
   reject the I/O.

   Although pNFS does not alter the file data caching capabilities of
   clients, or their semantics, it recognizes that some clients may
   perform more aggressive write-behind caching to optimize the benefits
   provided by pNFS.  However, write-behind caching may negatively
   affect the latency in returning a layout in response to a
   CB_LAYOUTRECALL; this is similar to file delegations and the impact
   that file data caching has on DELEGRETURN.  Client implementations
   SHOULD limit the amount of unwritten data they have outstanding at
   any one time in order to prevent excessively long responses to
   CB_LAYOUTRECALL.  Once a layout is recalled, a server MUST wait one
   lease period before taking further action.  As soon as a lease period
   has passed, the server may choose to fence the client's access to the
   storage devices if the server perceives the client has taken too long
   to return a layout.  However, just as in the case of data delegation
   and DELEGRETURN, the server may choose to wait, given that the client
   is showing forward progress on its way to returning the layout.  This
   forward progress can take the form of successful interaction with the



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   storage devices or of sub-portions of the layout being returned by
   the client.  The server can also limit exposure to these problems by
   limiting the byte-ranges initially provided in the layouts and thus
   the amount of outstanding modified data.

12.5.5.1.  Layout Recall Callback Robustness

   It has been assumed thus far that pNFS client state (layout ranges
   and iomode) for a file exactly matches that of the pNFS server for
   that file.  This assumption leads to the implication that any
   callback results in a LAYOUTRETURN or set of LAYOUTRETURNs that
   exactly match the range in the callback, since both client and server
   agree about the state being maintained.  However, it can be useful if
   this assumption does not always hold.  For example:

   o  If conflicts that require callbacks are very rare, and a server
      can use a multi-file callback to recover per-client resources
      (e.g., via an FSID recall or a multi-file recall within a single
      CB_COMPOUND), the result may be significantly less client-server
      pNFS traffic.

   o  It may be useful for servers to maintain information about what
      ranges are held by a client on a coarse-grained basis, leading to
      the server's layout ranges being beyond those actually held by the
      client.  In the extreme, a server could manage conflicts on a per-
      file basis, only sending whole-file callbacks even though clients
      may request and be granted sub-file ranges.

   o  It may be useful for clients to "forget" details about what
      layouts and ranges the client actually has, leading to the
      server's layout ranges being beyond those that the client "thinks"
      it has.  As long as the client does not assume it has layouts that
      are beyond what the server has granted, this is a safe practice.
      When a client forgets what ranges and layouts it has, and it
      receives a CB_LAYOUTRECALL operation, the client MUST follow up
      with a LAYOUTRETURN for what the server recalled, or alternatively
      return the NFS4ERR_NOMATCHING_LAYOUT error if it has no layout to
      return in the recalled range.

   o  In order to avoid errors, it is vital that a client not assign
      itself layout permissions beyond what the server has granted, and
      that the server not forget layout permissions that have been
      granted.  On the other hand, if a server believes that a client
      holds a layout that the client does not know about, it is useful
      for the client to cleanly indicate completion of the requested
      recall either by sending a LAYOUTRETURN operation for the entire
      requested range or by returning an NFS4ERR_NOMATCHING_LAYOUT error
      to the CB_LAYOUTRECALL.



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   Thus, in light of the above, it is useful for a server to be able to
   send callbacks for layout ranges it has not granted to a client, and
   for a client to return ranges it does not hold.  A pNFS client MUST
   always return layouts that comprise the full range specified by the
   recall.  Note, the full recalled layout range need not be returned as
   part of a single operation, but may be returned in portions.  This
   allows the client to stage the flushing of dirty data and commits and
   returns of layouts.  Also, it indicates to the metadata server that
   the client is making progress.

   When a layout is returned, the client MUST NOT have any outstanding
   I/O requests to the storage devices involved in the layout.
   Rephrasing, the client MUST NOT return the layout while it has
   outstanding I/O requests to the storage device.

   Even with this requirement for the client, it is possible that I/O
   requests may be presented to a storage device no longer allowed to
   perform them.  Since the server has no strict control as to when the
   client will return the layout, the server may later decide to
   unilaterally revoke the client's access to the storage devices as
   provided by the layout.  In choosing to revoke access, the server
   must deal with the possibility of lingering I/O requests, i.e., I/O
   requests that are still in flight to storage devices identified by
   the revoked layout.  All layout type specifications MUST define
   whether unilateral layout revocation by the metadata server is
   supported; if it is, the specification must also describe how
   lingering writes are processed.  For example, storage devices
   identified by the revoked layout could be fenced off from the client
   that held the layout.

   In order to ensure client/server convergence with regard to layout
   state, the final LAYOUTRETURN operation in a sequence of LAYOUTRETURN
   operations for a particular recall MUST specify the entire range
   being recalled, echoing the recalled layout type, iomode, recall/
   return type (FILE, FSID, or ALL), and byte-range, even if layouts
   pertaining to partial ranges were previously returned.  In addition,
   if the client holds no layouts that overlap the range being recalled,
   the client should return the NFS4ERR_NOMATCHING_LAYOUT error code to
   CB_LAYOUTRECALL.  This allows the server to update its view of the
   client's layout state.

12.5.5.2.  Sequencing of Layout Operations

   As with other stateful operations, pNFS requires the correct
   sequencing of layout operations. pNFS uses the "seqid" in the layout
   stateid to provide the correct sequencing between regular operations
   and callbacks.  It is the server's responsibility to avoid
   inconsistencies regarding the layouts provided and the client's



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   responsibility to properly serialize its layout requests and layout
   returns.

12.5.5.2.1.  Layout Recall and Return Sequencing

   One critical issue with regard to layout operations sequencing
   concerns callbacks.  The protocol must defend against races between
   the reply to a LAYOUTGET or LAYOUTRETURN operation and a subsequent
   CB_LAYOUTRECALL.  A client MUST NOT process a CB_LAYOUTRECALL that
   implies one or more outstanding LAYOUTGET or LAYOUTRETURN operations
   to which the client has not yet received a reply.  The client detects
   such a CB_LAYOUTRECALL by examining the "seqid" field of the recall's
   layout stateid.  If the "seqid" is not exactly one higher than what
   the client currently has recorded, and the client has at least one
   LAYOUTGET and/or LAYOUTRETURN operation outstanding, the client knows
   the server sent the CB_LAYOUTRECALL after sending a response to an
   outstanding LAYOUTGET or LAYOUTRETURN.  The client MUST wait before
   processing such a CB_LAYOUTRECALL until it processes all replies for
   outstanding LAYOUTGET and LAYOUTRETURN operations for the
   corresponding file with seqid less than the seqid given by
   CB_LAYOUTRECALL (lor_stateid; see Section 20.3.)

   In addition to the seqid-based mechanism, Section 2.10.6.3 describes
   the sessions mechanism for allowing the client to detect callback
   race conditions and delay processing such a CB_LAYOUTRECALL.  The
   server MAY reference conflicting operations in the CB_SEQUENCE that
   precedes the CB_LAYOUTRECALL.  Because the server has already sent
   replies for these operations before sending the callback, the replies
   may race with the CB_LAYOUTRECALL.  The client MUST wait for all the
   referenced calls to complete and update its view of the layout state
   before processing the CB_LAYOUTRECALL.

12.5.5.2.1.1.  Get/Return Sequencing

   The protocol allows the client to send concurrent LAYOUTGET and
   LAYOUTRETURN operations to the server.  The protocol does not provide
   any means for the server to process the requests in the same order in
   which they were created.  However, through the use of the "seqid"
   field in the layout stateid, the client can determine the order in
   which parallel outstanding operations were processed by the server.
   Thus, when a layout retrieved by an outstanding LAYOUTGET operation
   intersects with a layout returned by an outstanding LAYOUTRETURN on
   the same file, the order in which the two conflicting operations are
   processed determines the final state of the overlapping layout.  The
   order is determined by the "seqid" returned in each operation: the
   operation with the higher seqid was executed later.

   It is permissible for the client to send multiple parallel LAYOUTGET



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   operations for the same file or multiple parallel LAYOUTRETURN
   operations for the same file or a mix of both.

   It is permissible for the client to use the current stateid (see
   Section 16.2.3.1.2) for LAYOUTGET operations, for example, when
   compounding LAYOUTGETs or compounding OPEN and LAYOUTGETs.  It is
   also permissible to use the current stateid when compounding
   LAYOUTRETURNs.

   It is permissible for the client to use the current stateid when
   combining LAYOUTRETURN and LAYOUTGET operations for the same file in
   the same COMPOUND request since the server MUST process these in
   order.  However, if a client does send such COMPOUND requests, it
   MUST NOT have more than one outstanding for the same file at the same
   time, and it MUST NOT have other LAYOUTGET or LAYOUTRETURN operations
   outstanding at the same time for that same file.

12.5.5.2.1.2.  Client Considerations

   Consider a pNFS client that has sent a LAYOUTGET, and before it
   receives the reply to LAYOUTGET, it receives a CB_LAYOUTRECALL for
   the same file with an overlapping range.  There are two
   possibilities, which the client can distinguish via the layout
   stateid in the recall.

   1.  The server processed the LAYOUTGET before sending the recall, so
       the LAYOUTGET must be waited for because it may be carrying
       layout information that will need to be returned to deal with the
       CB_LAYOUTRECALL.

   2.  The server sent the callback before receiving the LAYOUTGET.  The
       server will not respond to the LAYOUTGET until the
       CB_LAYOUTRECALL is processed.

   If these possibilities cannot be distinguished, a deadlock could
   result, as the client must wait for the LAYOUTGET response before
   processing the recall in the first case, but that response will not
   arrive until after the recall is processed in the second case.  Note
   that in the first case, the "seqid" in the layout stateid of the
   recall is two greater than what the client has recorded; in the
   second case, the "seqid" is one greater than what the client has
   recorded.  This allows the client to disambiguate between the two
   cases.  The client thus knows precisely which possibility applies.

   In case 1, the client knows it needs to wait for the LAYOUTGET
   response before processing the recall (or the client can return
   NFS4ERR_DELAY).




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   In case 2, the client will not wait for the LAYOUTGET response before
   processing the recall because waiting would cause deadlock.
   Therefore, the action at the client will only require waiting in the
   case that the client has not yet seen the server's earlier responses
   to the LAYOUTGET operation(s).

   The recall process can be considered completed when the final
   LAYOUTRETURN operation for the recalled range is completed.  The
   LAYOUTRETURN uses the layout stateid (with seqid) specified in
   CB_LAYOUTRECALL.  If the client uses multiple LAYOUTRETURNs in
   processing the recall, the first LAYOUTRETURN will use the layout
   stateid as specified in CB_LAYOUTRECALL.  Subsequent LAYOUTRETURNs
   will use the highest seqid as is the usual case.

12.5.5.2.1.3.  Server Considerations

   Consider a race from the metadata server's point of view.  The
   metadata server has sent a CB_LAYOUTRECALL and receives an
   overlapping LAYOUTGET for the same file before the LAYOUTRETURN(s)
   that respond to the CB_LAYOUTRECALL.  There are three cases:

   1.  The client sent the LAYOUTGET before processing the
       CB_LAYOUTRECALL.  The "seqid" in the layout stateid of the
       arguments of LAYOUTGET is one less than the "seqid" in
       CB_LAYOUTRECALL.  The server returns NFS4ERR_RECALLCONFLICT to
       the client, which indicates to the client that there is a pending
       recall.

   2.  The client sent the LAYOUTGET after processing the
       CB_LAYOUTRECALL, but the LAYOUTGET arrived before the
       LAYOUTRETURN and the response to CB_LAYOUTRECALL that completed
       that processing.  The "seqid" in the layout stateid of LAYOUTGET
       is equal to or greater than that of the "seqid" in
       CB_LAYOUTRECALL.  The server has not received a response to the
       CB_LAYOUTRECALL, so it returns NFS4ERR_RECALLCONFLICT.

   3.  The client sent the LAYOUTGET after processing the
       CB_LAYOUTRECALL; the server received the CB_LAYOUTRECALL
       response, but the LAYOUTGET arrived before the LAYOUTRETURN that
       completed that processing.  The "seqid" in the layout stateid of
       LAYOUTGET is equal to that of the "seqid" in CB_LAYOUTRECALL.
       The server has received a response to the CB_LAYOUTRECALL, so it
       returns NFS4ERR_RETURNCONFLICT.








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12.5.5.2.1.4.  Wraparound and Validation of Seqid

   The rules for layout stateid processing differ from other stateids in
   the protocol because the "seqid" value cannot be zero and the
   stateid's "seqid" value changes in a CB_LAYOUTRECALL operation.  The
   non-zero requirement combined with the inherent parallelism of layout
   operations means that a set of LAYOUTGET and LAYOUTRETURN operations
   may contain the same value for "seqid".  The server uses a slightly
   modified version of the modulo arithmetic as described in
   Section 2.10.6.1 when incrementing the layout stateid's "seqid".  The
   difference is that zero is not a valid value for "seqid"; when the
   value of a "seqid" is 0xFFFFFFFF, the next valid value will be
   0x00000001.  The modulo arithmetic is also used for the comparisons
   of "seqid" values in the processing of CB_LAYOUTRECALL events as
   described above in Section 12.5.5.2.1.3.

   Just as the server validates the "seqid" in the event of
   CB_LAYOUTRECALL usage, as described in Section 12.5.5.2.1.3, the
   server also validates the "seqid" value to ensure that it is within
   an appropriate range.  This range represents the degree of
   parallelism the server supports for layout stateids.  If the client
   is sending multiple layout operations to the server in parallel, by
   definition, the "seqid" value in the supplied stateid will not be the
   current "seqid" as held by the server.  The range of parallelism
   spans from the highest or current "seqid" to a "seqid" value in the
   past.  To assist in the discussion, the server's current "seqid"
   value for a layout stateid is defined as SERVER_CURRENT_SEQID.  The
   lowest "seqid" value that is acceptable to the server is represented
   by PAST_SEQID.  And the value for the range of valid "seqid"s or
   range of parallelism is VALID_SEQID_RANGE.  Therefore, the following
   holds: VALID_SEQID_RANGE = SERVER_CURRENT_SEQID - PAST_SEQID.  In the
   following, all arithmetic is the modulo arithmetic as described
   above.

   The server MUST support a minimum VALID_SEQID_RANGE.  The minimum is
   defined as: VALID_SEQID_RANGE = summation over 1..N of
   (ca_maxoperations(i) - 1), where N is the number of session fore
   channels and ca_maxoperations(i) is the value of the ca_maxoperations
   returned from CREATE_SESSION of the i'th session.  The reason for "-
   1" is to allow for the required SEQUENCE operation.  The server MAY
   support a VALID_SEQID_RANGE value larger than the minimum.  The
   maximum VALID_SEQID_RANGE is (2 ^ 32 - 2) (accounting for zero not
   being a valid "seqid" value).

   If the server finds the "seqid" is zero, the NFS4ERR_BAD_STATEID
   error is returned to the client.  The server further validates the
   "seqid" to ensure it is within the range of parallelism,
   VALID_SEQID_RANGE.  If the "seqid" value is outside of that range,



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   the error NFS4ERR_OLD_STATEID is returned to the client.  Upon
   receipt of NFS4ERR_OLD_STATEID, the client updates the stateid in the
   layout request based on processing of other layout requests and re-
   sends the operation to the server.

12.5.5.2.1.5.  Bulk Recall and Return

   pNFS supports recalling and returning all layouts that are for files
   belonging to a particular fsid (LAYOUTRECALL4_FSID,
   LAYOUTRETURN4_FSID) or client ID (LAYOUTRECALL4_ALL,
   LAYOUTRETURN4_ALL).  There are no "bulk" stateids, so detection of
   races via the seqid is not possible.  The server MUST NOT initiate
   bulk recall while another recall is in progress, or the corresponding
   LAYOUTRETURN is in progress or pending.  In the event the server
   sends a bulk recall while the client has a pending or in-progress
   LAYOUTRETURN, CB_LAYOUTRECALL, or LAYOUTGET, the client returns
   NFS4ERR_DELAY.  In the event the client sends a LAYOUTGET or
   LAYOUTRETURN while a bulk recall is in progress, the server returns
   NFS4ERR_RECALLCONFLICT.  If the client sends a LAYOUTGET or
   LAYOUTRETURN after the server receives NFS4ERR_DELAY from a bulk
   recall, then to ensure forward progress, the server MAY return
   NFS4ERR_RECALLCONFLICT.

   Once a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL is sent, the server MUST
   NOT allow the client to use any layout stateid except for
   LAYOUTCOMMIT operations.  Once the client receives a CB_LAYOUTRECALL
   of LAYOUTRECALL4_ALL, it MUST NOT use any layout stateid except for
   LAYOUTCOMMIT operations.  Once a LAYOUTRETURN of LAYOUTRETURN4_ALL is
   sent, all layout stateids granted to the client ID are freed.  The
   client MUST NOT use the layout stateids again.  It MUST use LAYOUTGET
   to obtain new layout stateids.

   Once a CB_LAYOUTRECALL of LAYOUTRECALL4_FSID is sent, the server MUST
   NOT allow the client to use any layout stateid that refers to a file
   with the specified fsid except for LAYOUTCOMMIT operations.  Once the
   client receives a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL, it MUST NOT
   use any layout stateid that refers to a file with the specified fsid
   except for LAYOUTCOMMIT operations.  Once a LAYOUTRETURN of
   LAYOUTRETURN4_FSID is sent, all layout stateids granted to the
   referenced fsid are freed.  The client MUST NOT use those freed
   layout stateids for files with the referenced fsid again.
   Subsequently, for any file with the referenced fsid, to use a layout,
   the client MUST first send a LAYOUTGET operation in order to obtain a
   new layout stateid for that file.

   If the server has sent a bulk CB_LAYOUTRECALL and receives a
   LAYOUTGET, or a LAYOUTRETURN with a stateid, the server MUST return
   NFS4ERR_RECALLCONFLICT.  If the server has sent a bulk



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   CB_LAYOUTRECALL and receives a LAYOUTRETURN with an lr_returntype
   that is not equal to the lor_recalltype of the CB_LAYOUTRECALL, the
   server MUST return NFS4ERR_RECALLCONFLICT.

12.5.6.  Revoking Layouts

   Parallel NFS permits servers to revoke layouts from clients that fail
   to respond to recalls and/or fail to renew their lease in time.
   Depending on the layout type, the server might revoke the layout and
   might take certain actions with respect to the client's I/O to data
   servers.

12.5.7.  Metadata Server Write Propagation

   Asynchronous writes written through the metadata server may be
   propagated lazily to the storage devices.  For data written
   asynchronously through the metadata server, a client performing a
   read at the appropriate storage device is not guaranteed to see the
   newly written data until a COMMIT occurs at the metadata server.
   While the write is pending, reads to the storage device may give out
   either the old data, the new data, or a mixture of new and old.  Upon
   completion of a synchronous WRITE or COMMIT (for asynchronously
   written data), the metadata server MUST ensure that storage devices
   give out the new data and that the data has been written to stable
   storage.  If the server implements its storage in any way such that
   it cannot obey these constraints, then it MUST recall the layouts to
   prevent reads being done that cannot be handled correctly.  Note that
   the layouts MUST be recalled prior to the server responding to the
   associated WRITE operations.

12.6.  pNFS Mechanics

   This section describes the operations flow taken by a pNFS client to
   a metadata server and storage device.

   When a pNFS client encounters a new FSID, it sends a GETATTR to the
   NFSv4.1 server for the fs_layout_type (Section 5.12.1) attribute.  If
   the attribute returns at least one layout type, and the layout types
   returned are among the set supported by the client, the client knows
   that pNFS is a possibility for the file system.  If, from the server
   that returned the new FSID, the client does not have a client ID that
   came from an EXCHANGE_ID result that returned
   EXCHGID4_FLAG_USE_PNFS_MDS, it MUST send an EXCHANGE_ID to the server
   with the EXCHGID4_FLAG_USE_PNFS_MDS bit set.  If the server's
   response does not have EXCHGID4_FLAG_USE_PNFS_MDS, then contrary to
   what the fs_layout_type attribute said, the server does not support
   pNFS, and the client will not be able use pNFS to that server; in
   this case, the server MUST return NFS4ERR_NOTSUPP in response to any



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   pNFS operation.

   The client then creates a session, requesting a persistent session,
   so that exclusive creates can be done with single round trip via the
   createmode4 of GUARDED4.  If the session ends up not being
   persistent, the client will use EXCLUSIVE4_1 for exclusive creates.

   If a file is to be created on a pNFS-enabled file system, the client
   uses the OPEN operation.  With the normal set of attributes that may
   be provided upon OPEN used for creation, there is an OPTIONAL
   layout_hint attribute.  The client's use of layout_hint allows the
   client to express its preference for a layout type and its associated
   layout details.  The use of a createmode4 of UNCHECKED4, GUARDED4, or
   EXCLUSIVE4_1 will allow the client to provide the layout_hint
   attribute at create time.  The client MUST NOT use EXCLUSIVE4 (see
   Table 10).  The client is RECOMMENDED to combine a GETATTR operation
   after the OPEN within the same COMPOUND.  The GETATTR may then
   retrieve the layout_type attribute for the newly created file.  The
   client will then know what layout type the server has chosen for the
   file and therefore what storage protocol the client must use.

   If the client wants to open an existing file, then it also includes a
   GETATTR to determine what layout type the file supports.

   The GETATTR in either the file creation or plain file open case can
   also include the layout_blksize and layout_alignment attributes so
   that the client can determine optimal offsets and lengths for I/O on
   the file.

   Assuming the client supports the layout type returned by GETATTR and
   it chooses to use pNFS for data access, it then sends LAYOUTGET using
   the filehandle and stateid returned by OPEN, specifying the range it
   wants to do I/O on.  The response is a layout, which may be a subset
   of the range for which the client asked.  It also includes device IDs
   and a description of how data is organized (or in the case of
   writing, how data is to be organized) across the devices.  The device
   IDs and data description are encoded in a format that is specific to
   the layout type, but the client is expected to understand.

   When the client wants to send an I/O, it determines to which device
   ID it needs to send the I/O command by examining the data description
   in the layout.  It then sends a GETDEVICEINFO to find the device
   address(es) of the device ID.  The client then sends the I/O request
   to one of device ID's device addresses, using the storage protocol
   defined for the layout type.  Note that if a client has multiple I/Os
   to send, these I/O requests may be done in parallel.

   If the I/O was a WRITE, then at some point the client may want to use



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   LAYOUTCOMMIT to commit the modification time and the new size of the
   file (if it believes it extended the file size) to the metadata
   server and the modified data to the file system.

12.7.  Recovery

   Recovery is complicated by the distributed nature of the pNFS
   protocol.  In general, crash recovery for layouts is similar to crash
   recovery for delegations in the base NFSv4.1 protocol.  However, the
   client's ability to perform I/O without contacting the metadata
   server introduces subtleties that must be handled correctly if the
   possibility of file system corruption is to be avoided.

12.7.1.  Recovery from Client Restart

   Client recovery for layouts is similar to client recovery for other
   lock and delegation state.  When a pNFS client restarts, it will lose
   all information about the layouts that it previously owned.  There
   are two methods by which the server can reclaim these resources and
   allow otherwise conflicting layouts to be provided to other clients.

   The first is through the expiry of the client's lease.  If the client
   recovery time is longer than the lease period, the client's lease
   will expire and the server will know that state may be released.  For
   layouts, the server may release the state immediately upon lease
   expiry or it may allow the layout to persist, awaiting possible lease
   revival, as long as no other layout conflicts.

   The second is through the client restarting in less time than it
   takes for the lease period to expire.  In such a case, the client
   will contact the server through the standard EXCHANGE_ID protocol.
   The server will find that the client's co_ownerid matches the
   co_ownerid of the previous client invocation, but that the verifier
   is different.  The server uses this as a signal to release all layout
   state associated with the client's previous invocation.  In this
   scenario, the data written by the client but not covered by a
   successful LAYOUTCOMMIT is in an undefined state; it may have been
   written or it may now be lost.  This is acceptable behavior and it is
   the client's responsibility to use LAYOUTCOMMIT to achieve the
   desired level of stability.

12.7.2.  Dealing with Lease Expiration on the Client

   If a client believes its lease has expired, it MUST NOT send I/O to
   the storage device until it has validated its lease.  The client can
   send a SEQUENCE operation to the metadata server.  If the SEQUENCE
   operation is successful, but sr_status_flag has
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,



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   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
   SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST NOT use
   currently held layouts.  The client has two choices to recover from
   the lease expiration.  First, for all modified but uncommitted data,
   the client writes it to the metadata server using the FILE_SYNC4 flag
   for the WRITEs, or WRITE and COMMIT.  Second, the client re-
   establishes a client ID and session with the server and obtains new
   layouts and device-ID-to-device-address mappings for the modified
   data ranges and then writes the data to the storage devices with the
   newly obtained layouts.

   If sr_status_flags from the metadata server has
   SEQ4_STATUS_RESTART_RECLAIM_NEEDED set (or SEQUENCE returns
   NFS4ERR_BAD_SESSION and CREATE_SESSION returns
   NFS4ERR_STALE_CLIENTID), then the metadata server has restarted, and
   the client SHOULD recover using the methods described in
   Section 12.7.4.

   If sr_status_flags from the metadata server has
   SEQ4_STATUS_LEASE_MOVED set, then the client recovers by following
   the procedure described in Section 11.7.7.1.  After that, the client
   may get an indication that the layout state was not moved with the
   file system.  The client recovers as in the other applicable
   situations discussed in the first two paragraphs of this section.

   If sr_status_flags reports no loss of state, then the lease for the
   layouts that the client has are valid and renewed, and the client can
   once again send I/O requests to the storage devices.

   While clients SHOULD NOT send I/Os to storage devices that may extend
   past the lease expiration time period, this is not always possible,
   for example, an extended network partition that starts after the I/O
   is sent and does not heal until the I/O request is received by the
   storage device.  Thus, the metadata server and/or storage devices are
   responsible for protecting themselves from I/Os that are both sent
   before the lease expires and arrive after the lease expires.  See
   Section 12.7.3.

12.7.3.  Dealing with Loss of Layout State on the Metadata Server

   This is a description of the case where all of the following are
   true:

   o  the metadata server has not restarted

   o  a pNFS client's layouts have been discarded (usually because the
      client's lease expired) and are invalid




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   o  an I/O from the pNFS client arrives at the storage device

   The metadata server and its storage devices MUST solve this by
   fencing the client.  In other words, they MUST solve this by
   preventing the execution of I/O operations from the client to the
   storage devices after layout state loss.  The details of how fencing
   is done are specific to the layout type.  The solution for NFSv4.1
   file-based layouts is described in (Section 13.11), and solutions for
   other layout types are in their respective external specification
   documents.

12.7.4.  Recovery from Metadata Server Restart

   The pNFS client will discover that the metadata server has restarted
   via the methods described in Section 8.4.2 and discussed in a pNFS-
   specific context in Paragraph 2.  The client MUST stop using layouts
   and delete the device ID to device address mappings it previously
   received from the metadata server.  Having done that, if the client
   wrote data to the storage device without committing the layouts via
   LAYOUTCOMMIT, then the client has additional work to do in order to
   have the client, metadata server, and storage device(s) all
   synchronized on the state of the data.

   o  If the client has data still modified and unwritten in the
      client's memory, the client has only two choices.

      1.  The client can obtain a layout via LAYOUTGET after the
          server's grace period and write the data to the storage
          devices.

      2.  The client can WRITE that data through the metadata server
          using the WRITE (Section 18.32) operation, and then obtain
          layouts as desired.

   o  If the client asynchronously wrote data to the storage device, but
      still has a copy of the data in its memory, then it has available
      to it the recovery options listed above in the previous bullet
      point.  If the metadata server is also in its grace period, the
      client has available to it the options below in the next bullet
      point.

   o  The client does not have a copy of the data in its memory and the
      metadata server is still in its grace period.  The client cannot
      use LAYOUTGET (within or outside the grace period) to reclaim a
      layout because the contents of the response from LAYOUTGET may not
      match what it had previously.  The range might be different or the
      client might get the same range but the content of the layout
      might be different.  Even if the content of the layout appears to



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      be the same, the device IDs may map to different device addresses,
      and even if the device addresses are the same, the device
      addresses could have been assigned to a different storage device.
      The option of retrieving the data from the storage device and
      writing it to the metadata server per the recovery scenario
      described above is not available because, again, the mappings of
      range to device ID, device ID to device address, and device
      address to physical device are stale, and new mappings via new
      LAYOUTGET do not solve the problem.

      The only recovery option for this scenario is to send a
      LAYOUTCOMMIT in reclaim mode, which the metadata server will
      accept as long as it is in its grace period.  The use of
      LAYOUTCOMMIT in reclaim mode informs the metadata server that the
      layout has changed.  It is critical that the metadata server
      receive this information before its grace period ends, and thus
      before it starts allowing updates to the file system.

      To send LAYOUTCOMMIT in reclaim mode, the client sets the
      loca_reclaim field of the operation's arguments (Section 18.42.1)
      to TRUE.  During the metadata server's recovery grace period (and
      only during the recovery grace period) the metadata server is
      prepared to accept LAYOUTCOMMIT requests with the loca_reclaim
      field set to TRUE.

      When loca_reclaim is TRUE, the client is attempting to commit
      changes to the layout that occurred prior to the restart of the
      metadata server.  The metadata server applies some consistency
      checks on the loca_layoutupdate field of the arguments to
      determine whether the client can commit the data written to the
      storage device to the file system.  The loca_layoutupdate field is
      of data type layoutupdate4 and contains layout-type-specific
      content (in the lou_body field of loca_layoutupdate).  The layout-
      type-specific information that loca_layoutupdate might have is
      discussed in Section 12.5.4.3.  If the metadata server's
      consistency checks on loca_layoutupdate succeed, then the metadata
      server MUST commit the data (as described by the loca_offset,
      loca_length, and loca_layoutupdate fields of the arguments) that
      was written to the storage device.  If the metadata server's
      consistency checks on loca_layoutupdate fail, the metadata server
      rejects the LAYOUTCOMMIT operation and makes no changes to the
      file system.  However, any time LAYOUTCOMMIT with loca_reclaim
      TRUE fails, the pNFS client has lost all the data in the range
      defined by <loca_offset, loca_length>.  A client can defend
      against this risk by caching all data, whether written
      synchronously or asynchronously in its memory, and by not
      releasing the cached data until a successful LAYOUTCOMMIT.  This
      condition does not hold true for all layout types; for example,



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      file-based storage devices need not suffer from this limitation.

   o  The client does not have a copy of the data in its memory and the
      metadata server is no longer in its grace period; i.e., the
      metadata server returns NFS4ERR_NO_GRACE.  As with the scenario in
      the above bullet point, the failure of LAYOUTCOMMIT means the data
      in the range <loca_offset, loca_length> lost.  The defense against
      the risk is the same -- cache all written data on the client until
      a successful LAYOUTCOMMIT.

12.7.5.  Operations during Metadata Server Grace Period

   Some of the recovery scenarios thus far noted that some operations
   (namely, WRITE and LAYOUTGET) might be permitted during the metadata
   server's grace period.  The metadata server may allow these
   operations during its grace period.  For LAYOUTGET, the metadata
   server must reliably determine that servicing such a request will not
   conflict with an impending LAYOUTCOMMIT reclaim request.  For WRITE,
   the metadata server must reliably determine that servicing the
   request will not conflict with an impending OPEN or with a LOCK where
   the file has mandatory byte-range locking enabled.

   As mentioned previously, for expediency, the metadata server might
   reject some operations (namely, WRITE and LAYOUTGET) during its grace
   period, because the simplest correct approach is to reject all non-
   reclaim pNFS requests and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, depending on the storage protocol
   (which is specific to the layout type) and metadata server
   implementation, the metadata server may be able to determine that a
   particular request is safe.  For example, a metadata server may save
   provisional allocation mappings for each file to stable storage, as
   well as information about potentially conflicting OPEN share modes
   and mandatory byte-range locks that might have been in effect at the
   time of restart, and the metadata server may use this information
   during the recovery grace period to determine that a WRITE request is
   safe.

12.7.6.  Storage Device Recovery

   Recovery from storage device restart is mostly dependent upon the
   layout type in use.  However, there are a few general techniques a
   client can use if it discovers a storage device has crashed while
   holding modified, uncommitted data that was asynchronously written.
   First and foremost, it is important to realize that the client is the
   only one that has the information necessary to recover non-committed
   data since it holds the modified data and probably nothing else does.
   Second, the best solution is for the client to err on the side of
   caution and attempt to rewrite the modified data through another



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   path.

   The client SHOULD immediately WRITE the data to the metadata server,
   with the stable field in the WRITE4args set to FILE_SYNC4.  Once it
   does this, there is no need to wait for the original storage device.

12.8.  Metadata and Storage Device Roles

   If the same physical hardware is used to implement both a metadata
   server and storage device, then the same hardware entity is to be
   understood to be implementing two distinct roles and it is important
   that it be clearly understood on behalf of which role the hardware is
   executing at any given time.

   Two sub-cases can be distinguished.

   1.  The storage device uses NFSv4.1 as the storage protocol, i.e.,
       the same physical hardware is used to implement both a metadata
       and data server.  See Section 13.1 for a description of how
       multiple roles are handled.

   2.  The storage device does not use NFSv4.1 as the storage protocol,
       and the same physical hardware is used to implement both a
       metadata and storage device.  Whether distinct network addresses
       are used to access the metadata server and storage device is
       immaterial.  This is because it is always clear to the pNFS
       client and server, from the upper-layer protocol being used
       (NFSv4.1 or non-NFSv4.1), to which role the request to the common
       server network address is directed.

12.9.  Security Considerations for pNFS

   pNFS separates file system metadata and data and provides access to
   both.  There are pNFS-specific operations (listed in Section 12.3)
   that provide access to the metadata; all existing NFSv4.1
   conventional (non-pNFS) security mechanisms and features apply to
   accessing the metadata.  The combination of components in a pNFS
   system (see Figure 1) is required to preserve the security properties
   of NFSv4.1 with respect to an entity that is accessing a storage
   device from a client, including security countermeasures to defend
   against threats for which NFSv4.1 provides defenses in environments
   where these threats are considered significant.

   In some cases, the security countermeasures for connections to
   storage devices may take the form of physical isolation or a
   recommendation to avoid the use of pNFS in an environment.  For
   example, it may be impractical to provide confidentiality protection
   for some storage protocols to protect against eavesdropping.  In



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   environments where eavesdropping on such protocols is of sufficient
   concern to require countermeasures, physical isolation of the
   communication channel (e.g., via direct connection from client(s) to
   storage device(s)) and/or a decision to forgo use of pNFS (e.g., and
   fall back to conventional NFSv4.1) may be appropriate courses of
   action.

   Where communication with storage devices is subject to the same
   threats as client-to-metadata server communication, the protocols
   used for that communication need to provide security mechanisms as
   strong as or no weaker than those available via RPCSEC_GSS for
   NFSv4.1.  Except for the storage protocol used for the
   LAYOUT4_NFSV4_1_FILES layout (see Section 13), i.e., except for
   NFSv4.1, it is beyond the scope of this document to specify the
   security mechanisms for storage access protocols.

   pNFS implementations MUST NOT remove NFSv4.1's access controls.  The
   combination of clients, storage devices, and the metadata server are
   responsible for ensuring that all client-to-storage-device file data
   access respects NFSv4.1's ACLs and file open modes.  This entails
   performing both of these checks on every access in the client, the
   storage device, or both (as applicable; when the storage device is an
   NFSv4.1 server, the storage device is ultimately responsible for
   controlling access as described in Section 13.9.2).  If a pNFS
   configuration performs these checks only in the client, the risk of a
   misbehaving client obtaining unauthorized access is an important
   consideration in determining when it is appropriate to use such a
   pNFS configuration.  Such layout types SHOULD NOT be used when
   client-only access checks do not provide sufficient assurance that
   NFSv4.1 access control is being applied correctly.  (This is not a
   problem for the file layout type described in Section 13 because the
   storage access protocol for LAYOUT4_NFSV4_1_FILES is NFSv4.1, and
   thus the security model for storage device access via
   LAYOUT4_NFSv4_1_FILES is the same as that of the metadata server.)
   For handling of access control specific to a layout, the reader
   should examine the layout specification, such as the NFSv4.1/
   file-based layout (Section 13) of this document, the blocks layout
   [41], and objects layout [40].

13.  NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type

   This section describes the semantics and format of NFSv4.1 file-based
   layouts for pNFS.  NFSv4.1 file-based layouts use the
   LAYOUT4_NFSV4_1_FILES layout type.  The LAYOUT4_NFSV4_1_FILES type
   defines striping data across multiple NFSv4.1 data servers.






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13.1.  Client ID and Session Considerations

   Sessions are a REQUIRED feature of NFSv4.1, and this extends to both
   the metadata server and file-based (NFSv4.1-based) data servers.

   The role a server plays in pNFS is determined by the result it
   returns from EXCHANGE_ID.  The roles are:

   o  Metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result
      eir_flags).

   o  Data server (EXCHGID4_FLAG_USE_PNFS_DS).

   o  Non-metadata server (EXCHGID4_FLAG_USE_NON_PNFS).  This is an
      NFSv4.1 server that does not support operations (e.g., LAYOUTGET)
      or attributes that pertain to pNFS.

   The client MAY request zero or more of EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_DS, or EXCHGID4_FLAG_USE_PNFS_MDS, even though
   some combinations (e.g., EXCHGID4_FLAG_USE_NON_PNFS |
   EXCHGID4_FLAG_USE_PNFS_MDS) are contradictory.  However, the server
   MUST only return the following acceptable combinations:

        +--------------------------------------------------------+
        | Acceptable Results from EXCHANGE_ID                    |
        +--------------------------------------------------------+
        | EXCHGID4_FLAG_USE_PNFS_MDS                             |
        | EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS |
        | EXCHGID4_FLAG_USE_PNFS_DS                              |
        | EXCHGID4_FLAG_USE_NON_PNFS                             |
        | EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS |
        +--------------------------------------------------------+

   As the above table implies, a server can have one or two roles.  A
   server can be both a metadata server and a data server, or it can be
   both a data server and non-metadata server.  In addition to returning
   two roles in the EXCHANGE_ID's results, and thus serving both roles
   via a common client ID, a server can serve two roles by returning a
   unique client ID and server owner for each role in each of two
   EXCHANGE_ID results, with each result indicating each role.

   In the case of a server with concurrent pNFS roles that are served by
   a common client ID, if the EXCHANGE_ID request from the client has
   zero or a combination of the bits set in eia_flags, the server result
   should set bits that represent the higher of the acceptable
   combination of the server roles, with a preference to match the roles
   requested by the client.  Thus, if a client request has
   (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS |



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   EXCHGID4_FLAG_USE_PNFS_DS) flags set, and the server is both a
   metadata server and a data server, serving both the roles by a common
   client ID, the server SHOULD return with (EXCHGID4_FLAG_USE_PNFS_MDS
   | EXCHGID4_FLAG_USE_PNFS_DS) set.

   In the case of a server that has multiple concurrent pNFS roles, each
   role served by a unique client ID, if the client specifies zero or a
   combination of roles in the request, the server results SHOULD return
   only one of the roles from the combination specified by the client
   request.  If the role specified by the server result does not match
   the intended use by the client, the client should send the
   EXCHANGE_ID specifying just the interested pNFS role.

   If a pNFS metadata client gets a layout that refers it to an NFSv4.1
   data server, it needs a client ID on that data server.  If it does
   not yet have a client ID from the server that had the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the EXCHANGE_ID results, then
   the client needs to send an EXCHANGE_ID to the data server, using the
   same co_ownerid as it sent to the metadata server, with the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the arguments.  If the server's
   EXCHANGE_ID results have EXCHGID4_FLAG_USE_PNFS_DS set, then the
   client may use the client ID to create sessions that will exchange
   pNFS data operations.  The client ID returned by the data server has
   no relationship with the client ID returned by a metadata server
   unless the client IDs are equal, and the server owners and server
   scopes of the data server and metadata server are equal.

   In NFSv4.1, the session ID in the SEQUENCE operation implies the
   client ID, which in turn might be used by the server to map the
   stateid to the right client/server pair.  However, when a data server
   is presented with a READ or WRITE operation with a stateid, because
   the stateid is associated with a client ID on a metadata server, and
   because the session ID in the preceding SEQUENCE operation is tied to
   the client ID of the data server, the data server has no obvious way
   to determine the metadata server from the COMPOUND procedure, and
   thus has no way to validate the stateid.  One RECOMMENDED approach is
   for pNFS servers to encode metadata server routing and/or identity
   information in the data server filehandles as returned in the layout.

   If metadata server routing and/or identity information is encoded in
   data server filehandles, when the metadata server identity or
   location changes, the data server filehandles it gave out will become
   invalid (stale), and so the metadata server MUST first recall the
   layouts.  Invalidating a data server filehandle does not render the
   NFS client's data cache invalid.  The client's cache should map a
   data server filehandle to a metadata server filehandle, and a
   metadata server filehandle to cached data.




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   If a server is both a metadata server and a data server, the server
   might need to distinguish operations on files that are directed to
   the metadata server from those that are directed to the data server.
   It is RECOMMENDED that the values of the filehandles returned by the
   LAYOUTGET operation be different than the value of the filehandle
   returned by the OPEN of the same file.

   Another scenario is for the metadata server and the storage device to
   be distinct from one client's point of view, and the roles reversed
   from another client's point of view.  For example, in the cluster
   file system model, a metadata server to one client might be a data
   server to another client.  If NFSv4.1 is being used as the storage
   protocol, then pNFS servers need to encode the values of filehandles
   according to their specific roles.

13.1.1.  Sessions Considerations for Data Servers

   Section 2.10.11.2 states that a client has to keep its lease renewed
   in order to prevent a session from being deleted by the server.  If
   the reply to EXCHANGE_ID has just the EXCHGID4_FLAG_USE_PNFS_DS role
   set, then (as noted in Section 13.6) the client will not be able to
   determine the data server's lease_time attribute because GETATTR will
   not be permitted.  Instead, the rule is that any time a client
   receives a layout referring it to a data server that returns just the
   EXCHGID4_FLAG_USE_PNFS_DS role, the client MAY assume that the
   lease_time attribute from the metadata server that returned the
   layout applies to the data server.  Thus, the data server MUST be
   aware of the values of all lease_time attributes of all metadata
   servers for which it is providing I/O, and it MUST use the maximum of
   all such lease_time values as the lease interval for all client IDs
   and sessions established on it.

   For example, if one metadata server has a lease_time attribute of 20
   seconds, and a second metadata server has a lease_time attribute of
   10 seconds, then if both servers return layouts that refer to an
   EXCHGID4_FLAG_USE_PNFS_DS-only data server, the data server MUST
   renew a client's lease if the interval between two SEQUENCE
   operations on different COMPOUND requests is less than 20 seconds.

13.2.  File Layout Definitions

   The following definitions apply to the LAYOUT4_NFSV4_1_FILES layout
   type and may be applicable to other layout types.

   Unit.  A unit is a fixed-size quantity of data written to a data
      server.





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   Pattern.  A pattern is a method of distributing one or more equal
      sized units across a set of data servers.  A pattern is iterated
      one or more times.

   Stripe.  A stripe is a set of data distributed across a set of data
      servers in a pattern before that pattern repeats.

   Stripe Count.  A stripe count is the number of units in a pattern.

   Stripe Width.  A stripe width is the size of a stripe in bytes.  The
      stripe width = the stripe count * the size of the stripe unit.

   Hereafter, this document will refer to a unit that is a written in a
   pattern as a "stripe unit".

   A pattern may have more stripe units than data servers.  If so, some
   data servers will have more than one stripe unit per stripe.  A data
   server that has multiple stripe units per stripe MAY store each unit
   in a different data file (and depending on the implementation, will
   possibly assign a unique data filehandle to each data file).

13.3.  File Layout Data Types

   The high level NFSv4.1 layout types are nfsv4_1_file_layouthint4,
   nfsv4_1_file_layout_ds_addr4, and nfsv4_1_file_layout4.

   The SETATTR operation supports a layout hint attribute
   (Section 5.12.4).  When the client sets a layout hint (data type
   layouthint4) with a layout type of LAYOUT4_NFSV4_1_FILES (the
   loh_type field), the loh_body field contains a value of data type
   nfsv4_1_file_layouthint4.

   const NFL4_UFLG_MASK            = 0x0000003F;
   const NFL4_UFLG_DENSE           = 0x00000001;
   const NFL4_UFLG_COMMIT_THRU_MDS = 0x00000002;
   const NFL4_UFLG_STRIPE_UNIT_SIZE_MASK
                                   = 0xFFFFFFC0;

   typedef uint32_t nfl_util4;












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   enum filelayout_hint_care4 {
           NFLH4_CARE_DENSE        = NFL4_UFLG_DENSE,

           NFLH4_CARE_COMMIT_THRU_MDS
                                   = NFL4_UFLG_COMMIT_THRU_MDS,

           NFLH4_CARE_STRIPE_UNIT_SIZE
                                   = 0x00000040,

           NFLH4_CARE_STRIPE_COUNT = 0x00000080
   };

   /* Encoded in the loh_body field of data type layouthint4: */

   struct nfsv4_1_file_layouthint4 {
           uint32_t        nflh_care;
           nfl_util4       nflh_util;
           count4          nflh_stripe_count;
   };

   The generic layout hint structure is described in Section 3.3.19.
   The client uses the layout hint in the layout_hint (Section 5.12.4)
   attribute to indicate the preferred type of layout to be used for a
   newly created file.  The LAYOUT4_NFSV4_1_FILES layout-type-specific
   content for the layout hint is composed of three fields.  The first
   field, nflh_care, is a set of flags indicating which values of the
   hint the client cares about.  If the NFLH4_CARE_DENSE flag is set,
   then the client indicates in the second field, nflh_util, a
   preference for how the data file is packed (Section 13.4.4), which is
   controlled by the value of the expression nflh_util & NFL4_UFLG_DENSE
   ("&" represents the bitwise AND operator).  If the
   NFLH4_CARE_COMMIT_THRU_MDS flag is set, then the client indicates a
   preference for whether the client should send COMMIT operations to
   the metadata server or data server (Section 13.7), which is
   controlled by the value of nflh_util & NFL4_UFLG_COMMIT_THRU_MDS.  If
   the NFLH4_CARE_STRIPE_UNIT_SIZE flag is set, the client indicates its
   preferred stripe unit size, which is indicated in nflh_util &
   NFL4_UFLG_STRIPE_UNIT_SIZE_MASK (thus, the stripe unit size MUST be a
   multiple of 64 bytes).  The minimum stripe unit size is 64 bytes.  If
   the NFLH4_CARE_STRIPE_COUNT flag is set, the client indicates in the
   third field, nflh_stripe_count, the stripe count.  The stripe count
   multiplied by the stripe unit size is the stripe width.

   When LAYOUTGET returns a LAYOUT4_NFSV4_1_FILES layout (indicated in
   the loc_type field of the lo_content field), the loc_body field of
   the lo_content field contains a value of data type
   nfsv4_1_file_layout4.  Among other content, nfsv4_1_file_layout4 has
   a storage device ID (field nfl_deviceid) of data type deviceid4.  The



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   GETDEVICEINFO operation maps a device ID to a storage device address
   (type device_addr4).  When GETDEVICEINFO returns a device address
   with a layout type of LAYOUT4_NFSV4_1_FILES (the da_layout_type
   field), the da_addr_body field contains a value of data type
   nfsv4_1_file_layout_ds_addr4.


   typedef netaddr4 multipath_list4<>;

   /*
    * Encoded in the da_addr_body field of
    * data type device_addr4:
    */
   struct nfsv4_1_file_layout_ds_addr4 {
           uint32_t        nflda_stripe_indices<>;
           multipath_list4 nflda_multipath_ds_list<>;
   };

   The nfsv4_1_file_layout_ds_addr4 data type represents the device
   address.  It is composed of two fields:

   1.  nflda_multipath_ds_list: An array of lists of data servers, where
       each list can be one or more elements, and each element
       represents a data server address that may serve equally as the
       target of I/O operations (see Section 13.5).  The length of this
       array might be different than the stripe count.

   2.  nflda_stripe_indices: An array of indices used to index into
       nflda_multipath_ds_list.  The value of each element of
       nflda_stripe_indices MUST be less than the number of elements in
       nflda_multipath_ds_list.  Each element of nflda_multipath_ds_list
       SHOULD be referred to by one or more elements of
       nflda_stripe_indices.  The number of elements in
       nflda_stripe_indices is always equal to the stripe count.



   /*
    * Encoded in the loc_body field of
    * data type layout_content4:
    */
   struct nfsv4_1_file_layout4 {
            deviceid4      nfl_deviceid;
            nfl_util4      nfl_util;
            uint32_t       nfl_first_stripe_index;
            offset4        nfl_pattern_offset;
            nfs_fh4        nfl_fh_list<>;
   };



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   The nfsv4_1_file_layout4 data type represents the layout.  It is
   composed of the following fields:

   1.  nfl_deviceid: The device ID that maps to a value of type
       nfsv4_1_file_layout_ds_addr4.

   2.  nfl_util: Like the nflh_util field of data type
       nfsv4_1_file_layouthint4, a compact representation of how the
       data on a file on each data server is packed, whether the client
       should send COMMIT operations to the metadata server or data
       server, and the stripe unit size.  If a server returns two or
       more overlapping layouts, each stripe unit size in each
       overlapping layout MUST be the same.

   3.  nfl_first_stripe_index: The index into the first element of the
       nflda_stripe_indices array to use.

   4.  nfl_pattern_offset: This field is the logical offset into the
       file where the striping pattern starts.  It is required for
       converting the client's logical I/O offset (e.g., the current
       offset in a POSIX file descriptor before the read() or write()
       system call is sent) into the stripe unit number (see
       Section 13.4.1).

       If dense packing is used, then nfl_pattern_offset is also needed
       to convert the client's logical I/O offset to an offset on the
       file on the data server corresponding to the stripe unit number
       (see Section 13.4.4).

       Note that nfl_pattern_offset is not always the same as lo_offset.
       For example, via the LAYOUTGET operation, a client might request
       a layout starting at offset 1000 of a file that has its striping
       pattern start at offset zero.


   5.  nfl_fh_list: An array of data server filehandles for each list of
       data servers in each element of the nflda_multipath_ds_list
       array.  The number of elements in nfl_fh_list depends on whether
       sparse or dense packing is being used.

       *  If sparse packing is being used, the number of elements in
          nfl_fh_list MUST be one of three values:

          +  Zero.  This means that filehandles used for each data
             server are the same as the filehandle returned by the OPEN
             operation from the metadata server.





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          +  One. This means that every data server uses the same
             filehandle: what is specified in nfl_fh_list[0].

          +  The same number of elements in nflda_multipath_ds_list.
             Thus, in this case, when sending an I/O operation to any
             data server in nflda_multipath_ds_list[X], the filehandle
             in nfl_fh_list[X] MUST be used.

          See the discussion on sparse packing in Section 13.4.4.


       *  If dense packing is being used, the number of elements in
          nfl_fh_list MUST be the same as the number of elements in
          nflda_stripe_indices.  Thus, when sending an I/O operation to
          any data server in
          nflda_multipath_ds_list[nflda_stripe_indices[Y]], the
          filehandle in nfl_fh_list[Y] MUST be used.  In addition, any
          time there exists i and j, (i != j), such that the
          intersection of
          nflda_multipath_ds_list[nflda_stripe_indices[i]] and
          nflda_multipath_ds_list[nflda_stripe_indices[j]] is not empty,
          then nfl_fh_list[i] MUST NOT equal nfl_fh_list[j].  In other
          words, when dense packing is being used, if a data server
          appears in two or more units of a striping pattern, each
          reference to the data server MUST use a different filehandle.

          Indeed, if there are multiple striping patterns, as indicated
          by the presence of multiple objects of data type layout4
          (either returned in one or multiple LAYOUTGET operations), and
          a data server is the target of a unit of one pattern and
          another unit of another pattern, then each reference to each
          data server MUST use a different filehandle.

          See the discussion on dense packing in Section 13.4.4.

   The details on the interpretation of the layout are in Section 13.4.

13.4.  Interpreting the File Layout

13.4.1.  Determining the Stripe Unit Number

   To find the stripe unit number that corresponds to the client's
   logical file offset, the pattern offset will also be used.  The i'th
   stripe unit (SUi) is:

       relative_offset = file_offset - nfl_pattern_offset;
       SUi = floor(relative_offset / stripe_unit_size);




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13.4.2.  Interpreting the File Layout Using Sparse Packing

   When sparse packing is used, the algorithm for determining the
   filehandle and set of data-server network addresses to write stripe
   unit i (SUi) to is:


      stripe_count = number of elements in nflda_stripe_indices;

      j = (SUi + nfl_first_stripe_index) % stripe_count;

      idx = nflda_stripe_indices[j];

      fh_count = number of elements in nfl_fh_list;
      ds_count = number of elements in nflda_multipath_ds_list;

      switch (fh_count) {
        case ds_count:
          fh = nfl_fh_list[idx];
          break;

        case 1:
          fh = nfl_fh_list[0];
          break;

        case 0:
          fh = filehandle returned by OPEN;
          break;

        default:
          throw a fatal exception;
          break;
      }

      address_list = nflda_multipath_ds_list[idx];


   The client would then select a data server from address_list, and
   send a READ or WRITE operation using the filehandle specified in fh.

   Consider the following example:

   Suppose we have a device address consisting of seven data servers,
   arranged in three equivalence (Section 13.5) classes:

      { A, B, C, D }, { E }, { F, G }

   where A through G are network addresses.



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   Then

      nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }

   i.e.,

      nflda_multipath_ds_list[0] = { A, B, C, D }

      nflda_multipath_ds_list[1] = { E }

      nflda_multipath_ds_list[2] = { F, G }

   Suppose the striping index array is:

      nflda_stripe_indices<> = { 2, 0, 1, 0 }

   Now suppose the client gets a layout that has a device ID that maps
   to the above device address.  The initial index contains

      nfl_first_stripe_index = 2,

   and the filehandle list is

      nfl_fh_list = { 0x36, 0x87, 0x67 }.

   If the client wants to write to SU0, the set of valid { network
   address, filehandle } combinations for SUi are determined by:

      nfl_first_stripe_index = 2

   So

      idx = nflda_stripe_indices[(0 + 2) % 4]

         = nflda_stripe_indices[2]

         = 1

   So

      nflda_multipath_ds_list[1] = { E }

   and

      nfl_fh_list[1] = { 0x87 }

   The client can thus write SU0 to { 0x87, { E } }.




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   The destinations of the first 13 storage units are:

                    +-----+------------+--------------+
                    | SUi | filehandle | data servers |
                    +-----+------------+--------------+
                    | 0   | 87         | E            |
                    | 1   | 36         | A,B,C,D      |
                    | 2   | 67         | F,G          |
                    | 3   | 36         | A,B,C,D      |
                    | 4   | 87         | E            |
                    | 5   | 36         | A,B,C,D      |
                    | 6   | 67         | F,G          |
                    | 7   | 36         | A,B,C,D      |
                    | 8   | 87         | E            |
                    | 9   | 36         | A,B,C,D      |
                    | 10  | 67         | F,G          |
                    | 11  | 36         | A,B,C,D      |
                    | 12  | 87         | E            |
                    +-----+------------+--------------+

13.4.3.  Interpreting the File Layout Using Dense Packing

   When dense packing is used, the algorithm for determining the
   filehandle and set of data server network addresses to write stripe
   unit i (SUi) to is:

      stripe_count = number of elements in nflda_stripe_indices;

      j = (SUi + nfl_first_stripe_index) % stripe_count;

      idx = nflda_stripe_indices[j];

      fh_count = number of elements in nfl_fh_list;
      ds_count = number of elements in nflda_multipath_ds_list;

      switch (fh_count) {
        case stripe_count:
          fh = nfl_fh_list[j];
          break;

        default:
          throw a fatal exception;
          break;
      }

      address_list = nflda_multipath_ds_list[idx];





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   The client would then select a data server from address_list, and
   send a READ or WRITE operation using the filehandle specified in fh.

   Consider the following example (which is the same as the sparse
   packing example, except for the filehandle list):

   Suppose we have a device address consisting of seven data servers,
   arranged in three equivalence (Section 13.5) classes:

      { A, B, C, D }, { E }, { F, G }

   where A through G are network addresses.

   Then

      nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }

   i.e.,

      nflda_multipath_ds_list[0] = { A, B, C, D }

      nflda_multipath_ds_list[1] = { E }

      nflda_multipath_ds_list[2] = { F, G }

   Suppose the striping index array is:

      nflda_stripe_indices<> = { 2, 0, 1, 0 }

   Now suppose the client gets a layout that has a device ID that maps
   to the above device address.  The initial index contains

      nfl_first_stripe_index = 2,

   and

      nfl_fh_list = { 0x67, 0x37, 0x87, 0x36 }.

   The interesting examples for dense packing are SU1 and SU3 because
   each stripe unit refers to the same data server list, yet each stripe
   unit MUST use a different filehandle.  If the client wants to write
   to SU1, the set of valid { network address, filehandle } combinations
   for SUi are determined by:

      nfl_first_stripe_index = 2

   So




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      j = (1 + 2) % 4 = 3

         idx = nflda_stripe_indices[j]

         = nflda_stripe_indices[3]

         = 0

   So

      nflda_multipath_ds_list[0] = { A, B, C, D }

   and

      nfl_fh_list[3] = { 0x36 }

   The client can thus write SU1 to { 0x36, { A, B, C, D } }.

   For SU3, j = (3 + 2) % 4 = 1, and nflda_stripe_indices[1] = 0.  Then
   nflda_multipath_ds_list[0] = { A, B, C, D }, and nfl_fh_list[1] =
   0x37.  The client can thus write SU3 to { 0x37, { A, B, C, D } }.

   The destinations of the first 13 storage units are:

                    +-----+------------+--------------+
                    | SUi | filehandle | data servers |
                    +-----+------------+--------------+
                    | 0   | 87         | E            |
                    | 1   | 36         | A,B,C,D      |
                    | 2   | 67         | F,G          |
                    | 3   | 37         | A,B,C,D      |
                    | 4   | 87         | E            |
                    | 5   | 36         | A,B,C,D      |
                    | 6   | 67         | F,G          |
                    | 7   | 37         | A,B,C,D      |
                    | 8   | 87         | E            |
                    | 9   | 36         | A,B,C,D      |
                    | 10  | 67         | F,G          |
                    | 11  | 37         | A,B,C,D      |
                    | 12  | 87         | E            |
                    +-----+------------+--------------+

13.4.4.  Sparse and Dense Stripe Unit Packing

   The flag NFL4_UFLG_DENSE of the nfl_util4 data type (field nflh_util
   of the data type nfsv4_1_file_layouthint4 and field nfl_util of data
   type nfsv4_1_file_layout_ds_addr4) specifies how the data is packed
   within the data file on a data server.  It allows for two different



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   data packings: sparse and dense.  The packing type determines the
   calculation that will be made to map the client-visible file offset
   to the offset within the data file located on the data server.

   If nfl_util & NFL4_UFLG_DENSE is zero, this means that sparse packing
   is being used.  Hence, the logical offsets of the file as viewed by a
   client sending READs and WRITEs directly to the metadata server are
   the same offsets each data server uses when storing a stripe unit.
   The effect then, for striping patterns consisting of at least two
   stripe units, is for each data server file to be sparse or "holey".
   So for example, suppose there is a pattern with three stripe units,
   the stripe unit size is 4096 bytes, and there are three data servers
   in the pattern.  Then, the file in data server 1 will have stripe
   units 0, 3, 6, 9, ... filled; data server 2's file will have stripe
   units 1, 4, 7, 10, ... filled; and data server 3's file will have
   stripe units 2, 5, 8, 11, ... filled.  The unfilled stripe units of
   each file will be holes; hence, the files in each data server are
   sparse.

   If sparse packing is being used and a client attempts I/O to one of
   the holes, then an error MUST be returned by the data server.  Using
   the above example, if data server 3 received a READ or WRITE
   operation for block 4, the data server would return
   NFS4ERR_PNFS_IO_HOLE.  Thus, data servers need to understand the
   striping pattern in order to support sparse packing.

   If nfl_util & NFL4_UFLG_DENSE is one, this means that dense packing
   is being used, and the data server files have no holes.  Dense
   packing might be selected because the data server does not
   (efficiently) support holey files or because the data server cannot
   recognize read-ahead unless there are no holes.  If dense packing is
   indicated in the layout, the data files will be packed.  Using the
   same striping pattern and stripe unit size that were used for the
   sparse packing example, the corresponding dense packing example would
   have all stripe units of all data files filled as follows:

   o  Logical stripe units 0, 3, 6, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 1.

   o  Logical stripe units 1, 4, 7, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 2.

   o  Logical stripe units 2, 5, 8, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 3.

   Because dense packing does not leave holes on the data servers, the
   pNFS client is allowed to write to any offset of any data file of any
   data server in the stripe.  Thus, the data servers need not know the



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   file's striping pattern.

   The calculation to determine the byte offset within the data file for
   dense data server layouts is:

      stripe_width = stripe_unit_size * N;
         where N = number of elements in nflda_stripe_indices.

      relative_offset = file_offset - nfl_pattern_offset;

      data_file_offset = floor(relative_offset / stripe_width)
         * stripe_unit_size
         + relative_offset % stripe_unit_size

   If dense packing is being used, and a data server appears more than
   once in a striping pattern, then to distinguish one stripe unit from
   another, the data server MUST use a different filehandle.  Let's
   suppose there are two data servers.  Logical stripe units 0, 3, 6 are
   served by data server 1; logical stripe units 1, 4, 7 are served by
   data server 2; and logical stripe units 2, 5, 8 are also served by
   data server 2.  Unless data server 2 has two filehandles (each
   referring to a different data file), then, for example, a write to
   logical stripe unit 1 overwrites the write to logical stripe unit 2
   because both logical stripe units are located in the same stripe unit
   (0) of data server 2.

13.5.  Data Server Multipathing

   The NFSv4.1 file layout supports multipathing to multiple data server
   addresses.  Data-server-level multipathing is used for bandwidth
   scaling via trunking (Section 2.10.5) and for higher availability of
   use in the case of a data-server failure.  Multipathing allows the
   client to switch to another data server address which may be that of
   another data server that is exporting the same data stripe unit,
   without having to contact the metadata server for a new layout.

   To support data server multipathing, each element of the
   nflda_multipath_ds_list contains an array of one more data server
   network addresses.  This array (data type multipath_list4) represents
   a list of data servers (each identified by a network address), with
   the possibility that some data servers will appear in the list
   multiple times.

   The client is free to use any of the network addresses as a
   destination to send data server requests.  If some network addresses
   are less optimal paths to the data than others, then the MDS SHOULD
   NOT include those network addresses in an element of
   nflda_multipath_ds_list.  If less optimal network addresses exist to



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   provide failover, the RECOMMENDED method to offer the addresses is to
   provide them in a replacement device-ID-to-device-address mapping, or
   a replacement device ID.  When a client finds that no data server in
   an element of nflda_multipath_ds_list responds, it SHOULD send a
   GETDEVICEINFO to attempt to replace the existing device-ID-to-device-
   address mappings.  If the MDS detects that all data servers
   represented by an element of nflda_multipath_ds_list are unavailable,
   the MDS SHOULD send a CB_NOTIFY_DEVICEID (if the client has indicated
   it wants device ID notifications for changed device IDs) to change
   the device-ID-to-device-address mappings to the available data
   servers.  If the device ID itself will be replaced, the MDS SHOULD
   recall all layouts with the device ID, and thus force the client to
   get new layouts and device ID mappings via LAYOUTGET and
   GETDEVICEINFO.

   Generally, if two network addresses appear in an element of
   nflda_multipath_ds_list, they will designate the same data server,
   and the two data server addresses will support the implementation of
   client ID or session trunking (the latter is RECOMMENDED) as defined
   in Section 2.10.5.  The two data server addresses will share the same
   server owner or major ID of the server owner.  It is not always
   necessary for the two data server addresses to designate the same
   server with trunking being used.  For example, the data could be
   read-only, and the data consist of exact replicas.

13.6.  Operations Sent to NFSv4.1 Data Servers

   Clients accessing data on an NFSv4.1 data server MUST send only the
   NULL procedure and COMPOUND procedures whose operations are taken
   only from two restricted subsets of the operations defined as valid
   NFSv4.1 operations.  Clients MUST use the filehandle specified by the
   layout when accessing data on NFSv4.1 data servers.

   The first of these operation subsets consists of management
   operations.  This subset consists of the BACKCHANNEL_CTL,
   BIND_CONN_TO_SESSION, CREATE_SESSION, DESTROY_CLIENTID,
   DESTROY_SESSION, EXCHANGE_ID, SECINFO_NO_NAME, SET_SSV, and SEQUENCE
   operations.  The client may use these operations in order to set up
   and maintain the appropriate client IDs, sessions, and security
   contexts involved in communication with the data server.  Henceforth,
   these will be referred to as data-server housekeeping operations.

   The second subset consists of COMMIT, READ, WRITE, and PUTFH.  These
   operations MUST be used with a current filehandle specified by the
   layout.  In the case of PUTFH, the new current filehandle MUST be one
   taken from the layout.  Henceforth, these will be referred to as
   data-server I/O operations.  As described in Section 12.5.1, a client
   MUST NOT send an I/O to a data server for which it does not hold a



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   valid layout; the data server MUST reject such an I/O.

   Unless the server has a concurrent non-data-server personality --
   i.e., EXCHANGE_ID results returned (EXCHGID4_FLAG_USE_PNFS_DS |
   EXCHGID4_FLAG_USE_PNFS_MDS) or (EXCHGID4_FLAG_USE_PNFS_DS |
   EXCHGID4_FLAG_USE_NON_PNFS) see Section 13.1 -- any attempted use of
   operations against a data server other than those specified in the
   two subsets above MUST return NFS4ERR_NOTSUPP to the client.

   When the server has concurrent data-server and non-data-server
   personalities, each COMPOUND sent by the client MUST be constructed
   so that it is appropriate to one of the two personalities, and it
   MUST NOT contain operations directed to a mix of those personalities.
   The server MUST enforce this.  To understand the constraints,
   operations within a COMPOUND are divided into the following three
   classes:

   1.  An operation that is ambiguous regarding its personality
       assignment.  This includes all of the data-server housekeeping
       operations.  Additionally, if the server has assigned filehandles
       so that the ones defined by the layout are the same as those used
       by the metadata server, all operations using such filehandles are
       within this class, with the following exception.  The exception
       is that if the operation uses a stateid that is incompatible with
       a data-server personality (e.g., a special stateid or the stateid
       has a non-zero "seqid" field, see Section 13.9.1), the operation
       is in class 3, as described below.  A COMPOUND containing
       multiple class 1 operations (and operations of no other class)
       MAY be sent to a server with multiple concurrent data server and
       non-data-server personalities.

   2.  An operation that is unambiguously referable to the data-server
       personality.  This includes data-server I/O operations where the
       filehandle is one that can only be validly directed to the data-
       server personality.

   3.  An operation that is unambiguously referable to the non-data-
       server personality.  This includes all COMPOUND operations that
       are neither data-server housekeeping nor data-server I/O
       operations, plus data-server I/O operations where the current fh
       (or the one to be made the current fh in the case of PUTFH) is
       only valid on the metadata server or where a stateid is used that
       is incompatible with the data server, i.e., is a special stateid
       or has a non-zero seqid value.

   When a COMPOUND first executes an operation from class 3 above, it
   acts as a normal COMPOUND on any other server, and the data-server
   personality ceases to be relevant.  There are no special restrictions



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   on the operations in the COMPOUND to limit them to those for a data
   server.  When a PUTFH is done, filehandles derived from the layout
   are not valid.  If their format is not normally acceptable, then
   NFS4ERR_BADHANDLE MUST result.  Similarly, current filehandles for
   other operations do not accept filehandles derived from layouts and
   are not normally usable on the metadata server.  Using these will
   result in NFS4ERR_STALE.

   When a COMPOUND first executes an operation from class 2, which would
   be PUTFH where the filehandle is one from a layout, the COMPOUND
   henceforth is interpreted with respect to the data-server
   personality.  Operations outside the two classes discussed above MUST
   result in NFS4ERR_NOTSUPP.  Filehandles are validated using the rules
   of the data server, resulting in NFS4ERR_BADHANDLE and/or
   NFS4ERR_STALE even when they would not normally do so when addressed
   to the non-data-server personality.  Stateids must obey the rules of
   the data server in that any use of special stateids or stateids with
   non-zero seqid values must result in NFS4ERR_BAD_STATEID.

   Until the server first executes an operation from class 2 or class 3,
   the client MUST NOT depend on the operation being executed by either
   the data-server or the non-data-server personality.  The server MUST
   pick one personality consistently for a given COMPOUND, with the only
   possible transition being a single one when the first operation from
   class 2 or class 3 is executed.

   Because of the complexity induced by assigning filehandles so they
   can be used on both a data server and a metadata server, it is
   RECOMMENDED that where the same server can have both personalities,
   the server assign separate unique filehandles to both personalities.
   This makes it unambiguous for which server a given request is
   intended.

   GETATTR and SETATTR MUST be directed to the metadata server.  In the
   case of a SETATTR of the size attribute, the control protocol is
   responsible for propagating size updates/truncations to the data
   servers.  In the case of extending WRITEs to the data servers, the
   new size must be visible on the metadata server once a LAYOUTCOMMIT
   has completed (see Section 12.5.4.2).  Section 13.10 describes the
   mechanism by which the client is to handle data-server files that do
   not reflect the metadata server's size.

13.7.  COMMIT through Metadata Server

   The file layout provides two alternate means of providing for the
   commit of data written through data servers.  The flag
   NFL4_UFLG_COMMIT_THRU_MDS in the field nfl_util of the file layout
   (data type nfsv4_1_file_layout4) is an indication from the metadata



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   server to the client of the REQUIRED way of performing COMMIT, either
   by sending the COMMIT to the data server or the metadata server.
   These two methods of dealing with the issue correspond to broad
   styles of implementation for a pNFS server supporting the file layout
   type.

   o  When the flag is FALSE, COMMIT operations MUST to be sent to the
      data server to which the corresponding WRITE operations were sent.
      This approach is sometimes useful when file striping is
      implemented within the pNFS server (instead of the file system),
      with the individual data servers each implementing their own file
      systems.

   o  When the flag is TRUE, COMMIT operations MUST be sent to the
      metadata server, rather than to the individual data servers.  This
      approach is sometimes useful when file striping is implemented
      within the clustered file system that is the backend to the pNFS
      server.  In such an implementation, each COMMIT to each data
      server might result in repeated writes of metadata blocks to the
      detriment of write performance.  Sending a single COMMIT to the
      metadata server can be more efficient when there exists a
      clustered file system capable of implementing such a coordinated
      COMMIT.

      If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is TRUE, then in order to
      maintain the current NFSv4.1 commit and recovery model, the data
      servers MUST return a common writeverf verifier in all WRITE
      responses for a given file layout, and the metadata server's
      COMMIT implementation must return the same writeverf.  The value
      of the writeverf verifier MUST be changed at the metadata server
      or any data server that is referenced in the layout, whenever
      there is a server event that can possibly lead to loss of
      uncommitted data.  The scope of the verifier can be for a file or
      for the entire pNFS server.  It might be more difficult for the
      server to maintain the verifier at the file level, but the benefit
      is that only events that impact a given file will require recovery
      action.

   Note that if the layout specified dense packing, then the offset used
   to a COMMIT to the MDS may differ than that of an offset used to a
   COMMIT to the data server.

   The single COMMIT to the metadata server will return a verifier, and
   the client should compare it to all the verifiers from the WRITEs and
   fail the COMMIT if there are any mismatched verifiers.  If COMMIT to
   the metadata server fails, the client should re-send WRITEs for all
   the modified data in the file.  The client should treat modified data
   with a mismatched verifier as a WRITE failure and try to recover by



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   resending the WRITEs to the original data server or using another
   path to that data if the layout has not been recalled.
   Alternatively, the client can obtain a new layout or it could rewrite
   the data directly to the metadata server.  If nfl_util &
   NFL4_UFLG_COMMIT_THRU_MDS is FALSE, sending a COMMIT to the metadata
   server might have no effect.  If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS
   is FALSE, a COMMIT sent to the metadata server should be used only to
   commit data that was written to the metadata server.  See
   Section 12.7.6 for recovery options.

13.8.  The Layout Iomode

   The layout iomode need not be used by the metadata server when
   servicing NFSv4.1 file-based layouts, although in some circumstances
   it may be useful.  For example, if the server implementation supports
   reading from read-only replicas or mirrors, it would be useful for
   the server to return a layout enabling the client to do so.  As such,
   the client SHOULD set the iomode based on its intent to read or write
   the data.  The client may default to an iomode of LAYOUTIOMODE4_RW.
   The iomode need not be checked by the data servers when clients
   perform I/O. However, the data servers SHOULD still validate that the
   client holds a valid layout and return an error if the client does
   not.

13.9.  Metadata and Data Server State Coordination

13.9.1.  Global Stateid Requirements

   When the client sends I/O to a data server, the stateid used MUST NOT
   be a layout stateid as returned by LAYOUTGET or sent by
   CB_LAYOUTRECALL.  Permitted stateids are based on one of the
   following: an OPEN stateid (the stateid field of data type OPEN4resok
   as returned by OPEN), a delegation stateid (the stateid field of data
   types open_read_delegation4 and open_write_delegation4 as returned by
   OPEN or WANT_DELEGATION, or as sent by CB_PUSH_DELEG), or a stateid
   returned by the LOCK or LOCKU operations.  The stateid sent to the
   data server MUST be sent with the seqid set to zero, indicating the
   most current version of that stateid, rather than indicating a
   specific non-zero seqid value.  In no case is the use of special
   stateid values allowed.

   The stateid used for I/O MUST have the same effect and be subject to
   the same validation on a data server as it would if the I/O was being
   performed on the metadata server itself in the absence of pNFS.  This
   has the implication that stateids are globally valid on both the
   metadata and data servers.  This requires the metadata server to
   propagate changes in LOCK and OPEN state to the data servers, so that
   the data servers can validate I/O accesses.  This is discussed



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   further in Section 13.9.2.  Depending on when stateids are
   propagated, the existence of a valid stateid on the data server may
   act as proof of a valid layout.

   Clients performing I/O operations need to select an appropriate
   stateid based on the locks (including opens and delegations) held by
   the client and the various types of state-owners sending the I/O
   requests.  The rules for doing so when referencing data servers are
   somewhat different from those discussed in Section 8.2.5, which apply
   when accessing metadata servers.

   The following rules, applied in order of decreasing priority, govern
   the selection of the appropriate stateid:

   o  If the client holds a delegation for the file in question, the
      delegation stateid should be used.

   o  Otherwise, there must be an OPEN stateid for the current open-
      owner, and that OPEN stateid for the open file in question is
      used, unless mandatory locking prevents that.  See below.

   o  If the data server had previously responded with NFS4ERR_LOCKED to
      use of the OPEN stateid, then the client should use the byte-range
      lock stateid whenever one exists for that open file with the
      current lock-owner.

   o  Special stateids should never be used.  If they are used, the data
      server MUST reject the I/O with an NFS4ERR_BAD_STATEID error.

13.9.2.  Data Server State Propagation

   Since the metadata server, which handles byte-range lock and open-
   mode state changes as well as ACLs, might not be co-located with the
   data servers where I/O accesses are validated, the server
   implementation MUST take care of propagating changes of this state to
   the data servers.  Once the propagation to the data servers is
   complete, the full effect of those changes MUST be in effect at the
   data servers.  However, some state changes need not be propagated
   immediately, although all changes SHOULD be propagated promptly.
   These state propagations have an impact on the design of the control
   protocol, even though the control protocol is outside of the scope of
   this specification.  Immediate propagation refers to the synchronous
   propagation of state from the metadata server to the data server(s);
   the propagation must be complete before returning to the client.







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13.9.2.1.  Lock State Propagation

   If the pNFS server supports mandatory byte-range locking, any
   mandatory byte-range locks on a file MUST be made effective at the
   data servers before the request that establishes them returns to the
   caller.  The effect MUST be the same as if the mandatory byte-range
   lock state were synchronously propagated to the data servers, even
   though the details of the control protocol may avoid actual transfer
   of the state under certain circumstances.

   On the other hand, since advisory byte-range lock state is not used
   for checking I/O accesses at the data servers, there is no semantic
   reason for propagating advisory byte-range lock state to the data
   servers.  Since updates to advisory locks neither confer nor remove
   privileges, these changes need not be propagated immediately, and may
   not need to be propagated promptly.  The updates to advisory locks
   need only be propagated when the data server needs to resolve a
   question about a stateid.  In fact, if byte-range locking is not
   mandatory (i.e., is advisory) the clients are advised to avoid using
   the byte-range lock-based stateids for I/O. The stateids returned by
   OPEN are sufficient and eliminate overhead for this kind of state
   propagation.

   If a client gets back an NFS4ERR_LOCKED error from a data server,
   this is an indication that mandatory byte-range locking is in force.
   The client recovers from this by getting a byte-range lock that
   covers the affected range and re-sends the I/O with the stateid of
   the byte-range lock.

13.9.2.2.  Open and Deny Mode Validation

   Open and deny mode validation MUST be performed against the open and
   deny mode(s) held by the data servers.  When access is reduced or a
   deny mode made more restrictive (because of CLOSE or OPEN_DOWNGRADE),
   the data server MUST prevent any I/Os that would be denied if
   performed on the metadata server.  When access is expanded, the data
   server MUST make sure that no requests are subsequently rejected
   because of open or deny issues that no longer apply, given the
   previous relaxation.

13.9.2.3.  File Attributes

   Since the SETATTR operation has the ability to modify state that is
   visible on both the metadata and data servers (e.g., the size), care
   must be taken to ensure that the resultant state across the set of
   data servers is consistent, especially when truncating or growing the
   file.




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   As described earlier, the LAYOUTCOMMIT operation is used to ensure
   that the metadata is synchronized with changes made to the data
   servers.  For the NFSv4.1-based data storage protocol, it is
   necessary to re-synchronize state such as the size attribute, and the
   setting of mtime/change/atime.  See Section 12.5.4 for a full
   description of the semantics regarding LAYOUTCOMMIT and attribute
   synchronization.  It should be noted that by using an NFSv4.1-based
   layout type, it is possible to synchronize this state before
   LAYOUTCOMMIT occurs.  For example, the control protocol can be used
   to query the attributes present on the data servers.

   Any changes to file attributes that control authorization or access
   as reflected by ACCESS calls or READs and WRITEs on the metadata
   server, MUST be propagated to the data servers for enforcement on
   READ and WRITE I/O calls.  If the changes made on the metadata server
   result in more restrictive access permissions for any user, those
   changes MUST be propagated to the data servers synchronously.

   The OPEN operation (Section 18.16.4) does not impose any requirement
   that I/O operations on an open file have the same credentials as the
   OPEN itself (unless EXCHGID4_FLAG_BIND_PRINC_STATEID is set when
   EXCHANGE_ID creates the client ID), and so it requires the server's
   READ and WRITE operations to perform appropriate access checking.
   Changes to ACLs also require new access checking by READ and WRITE on
   the server.  The propagation of access-right changes due to changes
   in ACLs may be asynchronous only if the server implementation is able
   to determine that the updated ACL is not more restrictive for any
   user specified in the old ACL.  Due to the relative infrequency of
   ACL updates, it is suggested that all changes be propagated
   synchronously.

13.10.  Data Server Component File Size

   A potential problem exists when a component data file on a particular
   data server has grown past EOF; the problem exists for both dense and
   sparse layouts.  Imagine the following scenario: a client creates a
   new file (size == 0) and writes to byte 131072; the client then seeks
   to the beginning of the file and reads byte 100.  The client should
   receive zeroes back as a result of the READ.  However, if the
   striping pattern directs the client to send the READ to a data server
   other than the one that received the client's original WRITE, the
   data server servicing the READ may believe that the file's size is
   still 0 bytes.  In that event, the data server's READ response will
   contain zero bytes and an indication of EOF.  The data server can
   only return zeroes if it knows that the file's size has been
   extended.  This would require the immediate propagation of the file's
   size to all data servers, which is potentially very costly.
   Therefore, the client that has initiated the extension of the file's



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   size MUST be prepared to deal with these EOF conditions.  When the
   offset in the arguments to READ is less than the client's view of the
   file size, if the READ response indicates EOF and/or contains fewer
   bytes than requested, the client will interpret such a response as a
   hole in the file, and the NFS client will substitute zeroes for the
   data.

   The NFSv4.1 protocol only provides close-to-open file data cache
   semantics; meaning that when the file is closed, all modified data is
   written to the server.  When a subsequent OPEN of the file is done,
   the change attribute is inspected for a difference from a cached
   value for the change attribute.  For the case above, this means that
   a LAYOUTCOMMIT will be done at close (along with the data WRITEs) and
   will update the file's size and change attribute.  Access from
   another client after that point will result in the appropriate size
   being returned.

13.11.  Layout Revocation and Fencing

   As described in Section 12.7, the layout-type-specific storage
   protocol is responsible for handling the effects of I/Os that started
   before lease expiration and extend through lease expiration.  The
   LAYOUT4_NFSV4_1_FILES layout type can prevent all I/Os to data
   servers from being executed after lease expiration (this prevention
   is called "fencing"), without relying on a precise client lease timer
   and without requiring data servers to maintain lease timers.  The
   LAYOUT4_NFSV4_1_FILES pNFS server has the flexibility to revoke
   individual layouts, and thus fence I/O on a per-file basis.

   In addition to lease expiration, the reasons a layout can be revoked
   include: client fails to respond to a CB_LAYOUTRECALL, the metadata
   server restarts, or administrative intervention.  Regardless of the
   reason, once a client's layout has been revoked, the pNFS server MUST
   prevent the client from sending I/O for the affected file from and to
   all data servers; in other words, it MUST fence the client from the
   affected file on the data servers.

   Fencing works as follows.  As described in Section 13.1, in COMPOUND
   procedure requests to the data server, the data filehandle provided
   by the PUTFH operation and the stateid in the READ or WRITE operation
   are used to ensure that the client has a valid layout for the I/O
   being performed; if it does not, the I/O is rejected with
   NFS4ERR_PNFS_NO_LAYOUT.  The server can simply check the stateid and,
   additionally, make the data filehandle stale if the layout specified
   a data filehandle that is different from the metadata server's
   filehandle for the file (see the nfl_fh_list description in
   Section 13.3).




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   Before the metadata server takes any action to revoke layout state
   given out by a previous instance, it must make sure that all layout
   state from that previous instance are invalidated at the data
   servers.  This has the following implications.

   o  The metadata server must not restripe a file until it has
      contacted all of the data servers to invalidate the layouts from
      the previous instance.

   o  The metadata server must not give out mandatory locks that
      conflict with layouts from the previous instance without either
      doing a specific layout invalidation (as it would have to do
      anyway) or doing a global data server invalidation.

13.12.  Security Considerations for the File Layout Type

   The NFSv4.1 file layout type MUST adhere to the security
   considerations outlined in Section 12.9.  NFSv4.1 data servers MUST
   make all of the required access checks on each READ or WRITE I/O as
   determined by the NFSv4.1 protocol.  If the metadata server would
   deny a READ or WRITE operation on a file due to its ACL, mode
   attribute, open access mode, open deny mode, mandatory byte-range
   lock state, or any other attributes and state, the data server MUST
   also deny the READ or WRITE operation.  This impacts the control
   protocol and the propagation of state from the metadata server to the
   data servers; see Section 13.9.2 for more details.

   The methods for authentication, integrity, and privacy for data
   servers based on the LAYOUT4_NFSV4_1_FILES layout type are the same
   as those used by metadata servers.  Metadata and data servers use ONC
   RPC security flavors to authenticate, and SECINFO and SECINFO_NO_NAME
   to negotiate the security mechanism and services to be used.  Thus,
   when using the LAYOUT4_NFSV4_1_FILES layout type, the impact on the
   RPC-based security model due to pNFS (as alluded to in Sections 1.7.1
   and 1.7.2.2) is zero.

   For a given file object, a metadata server MAY require different
   security parameters (secinfo4 value) than the data server.  For a
   given file object with multiple data servers, the secinfo4 value
   SHOULD be the same across all data servers.  If the secinfo4 values
   across a metadata server and its data servers differ for a specific
   file, the mapping of the principal to the server's internal user
   identifier MUST be the same in order for the access-control checks
   based on ACL, mode, open and deny mode, and mandatory locking to be
   consistent across on the pNFS server.

   If an NFSv4.1 implementation supports pNFS and supports NFSv4.1 file
   layouts, then the implementation MUST support the SECINFO_NO_NAME



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   operation on both the metadata and data servers.

14.  Internationalization

   The primary issue in which NFSv4.1 needs to deal with
   internationalization, or I18N, is with respect to file names and
   other strings as used within the protocol.  The choice of string
   representation must allow reasonable name/string access to clients
   that use various languages.  The UTF-8 encoding of the UCS (Universal
   Multiple-Octet Coded Character Set) as defined by ISO10646 [21]
   allows for this type of access and follows the policy described in
   "IETF Policy on Character Sets and Languages", RFC 2277 [22].

   RFC 3454 [19], otherwise know as "stringprep", documents a framework
   for using Unicode/UTF-8 in networking protocols so as "to increase
   the likelihood that string input and string comparison work in ways
   that make sense for typical users throughout the world".  A protocol
   must define a profile of stringprep "in order to fully specify the
   processing options".  The remainder of this section defines the
   NFSv4.1 stringprep profiles.  Much of the terminology used for the
   remainder of this section comes from stringprep.

   There are three UTF-8 string types defined for NFSv4.1: utf8str_cs,
   utf8str_cis, and utf8str_mixed.  Separate profiles are defined for
   each.  Each profile defines the following, as required by stringprep:

   o  The intended applicability of the profile.

   o  The character repertoire that is the input and output to
      stringprep (which is Unicode 3.2 for the referenced version of
      stringprep).  However, NFSv4.1 implementations are not limited to
      3.2.

   o  The mapping tables from stringprep used (as described in Section 3
      of stringprep).

   o  Any additional mapping tables specific to the profile.

   o  The Unicode normalization used, if any (as described in Section 4
      of stringprep).

   o  The tables from the stringprep listing of characters that are
      prohibited as output (as described in Section 5 of stringprep).

   o  The bidirectional string testing used, if any (as described in
      Section 6 of stringprep).





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   o  Any additional characters that are prohibited as output specific
      to the profile.

   Stringprep discusses Unicode characters, whereas NFSv4.1 renders
   UTF-8 characters.  Since there is a one-to-one mapping from UTF-8 to
   Unicode, when the remainder of this document refers to Unicode, the
   reader should assume UTF-8.

   Much of the text for the profiles comes from RFC 3491 [23].

14.1.  Stringprep Profile for the utf8str_cs Type

   Every use of the utf8str_cs type definition in the NFSv4 protocol
   specification follows the profile named nfs4_cs_prep.

14.1.1.  Intended Applicability of the nfs4_cs_prep Profile

   The utf8str_cs type is a case-sensitive string of UTF-8 characters.
   Its primary use in NFSv4.1 is for naming components and pathnames.
   Components and pathnames are stored on the server's file system.  Two
   valid distinct UTF-8 strings might be the same after processing via
   the utf8str_cs profile.  If the strings are two names inside a
   directory, the NFSv4.1 server will need to either:

   o  disallow the creation of a second name if its post-processed form
      collides with that of an existing name, or

   o  allow the creation of the second name, but arrange so that after
      post-processing, the second name is different than the post-
      processed form of the first name.

14.1.2.  Character Repertoire of nfs4_cs_prep

   The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
   Appendix A.1.  However, NFSv4.1 implementations are not limited to
   3.2.

14.1.3.  Mapping Used by nfs4_cs_prep

   The nfs4_cs_prep profile specifies mapping using the following tables
   from stringprep:

      Table B.1

   Table B.2 is normally not part of the nfs4_cs_prep profile as it is
   primarily for dealing with case-insensitive comparisons.  However, if
   the NFSv4.1 file server supports the case_insensitive file system
   attribute, and if case_insensitive is TRUE, the NFSv4.1 server MUST



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   use Table B.2 (in addition to Table B1) when processing utf8str_cs
   strings, and the NFSv4.1 client MUST assume Table B.2 (in addition to
   Table B.1) is being used.

   If the case_preserving attribute is present and set to FALSE, then
   the NFSv4.1 server MUST use Table B.2 to map case when processing
   utf8str_cs strings.  Whether the server maps from lower to upper case
   or from upper to lower case is an implementation dependency.

14.1.4.  Normalization used by nfs4_cs_prep

   The nfs4_cs_prep profile does not specify a normalization form.  A
   later revision of this specification may specify a particular
   normalization form.  Therefore, the server and client can expect that
   they may receive unnormalized characters within protocol requests and
   responses.  If the operating environment requires normalization, then
   the implementation must normalize utf8str_cs strings within the
   protocol before presenting the information to an application (at the
   client) or local file system (at the server).

14.1.5.  Prohibited Output for nfs4_cs_prep

   The nfs4_cs_prep profile RECOMMENDS prohibiting the use of the
   following tables from stringprep:

      Table C.5

      Table C.6

14.1.6.  Bidirectional Output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking of
   bidirectional strings.

14.2.  Stringprep Profile for the utf8str_cis Type

   Every use of the utf8str_cis type definition in the NFSv4.1 protocol
   specification follows the profile named nfs4_cis_prep.

14.2.1.  Intended Applicability of the nfs4_cis_prep Profile

   The utf8str_cis type is a case-insensitive string of UTF-8
   characters.  Its primary use in NFSv4.1 is for naming NFS servers.

14.2.2.  Character Repertoire of nfs4_cis_prep

   The nfs4_cis_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1.  However, NFSv4.1 implementations are not



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   limited to 3.2.

14.2.3.  Mapping Used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies mapping using the following
   tables from stringprep:

      Table B.1

      Table B.2

14.2.4.  Normalization Used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies using Unicode normalization form
   KC, as described in stringprep.

14.2.5.  Prohibited Output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

14.2.6.  Bidirectional Output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies checking bidirectional strings as
   described in stringprep's Section 6.

14.3.  Stringprep Profile for the utf8str_mixed Type

   Every use of the utf8str_mixed type definition in the NFSv4.1
   protocol specification follows the profile named nfs4_mixed_prep.



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14.3.1.  Intended Applicability of the nfs4_mixed_prep Profile

   The utf8str_mixed type is a string of UTF-8 characters, with a prefix
   that is case sensitive, a separator equal to '@', and a suffix that
   is a fully qualified domain name.  Its primary use in NFSv4.1 is for
   naming principals identified in an Access Control Entry.

14.3.2.  Character Repertoire of nfs4_mixed_prep

   The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1.  However, NFSv4.1 implementations are not
   limited to 3.2.

14.3.3.  Mapping Used by nfs4_cis_prep

   For the prefix and the separator of a utf8str_mixed string, the
   nfs4_mixed_prep profile specifies mapping using the following table
   from stringprep:

      Table B.1

   For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
   specifies mapping using the following tables from stringprep:

      Table B.1

      Table B.2

14.3.4.  Normalization Used by nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies using Unicode normalization
   form KC, as described in stringprep.

14.3.5.  Prohibited Output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2

      Table C.3

      Table C.4

      Table C.5




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      Table C.6

      Table C.7

      Table C.8

      Table C.9

14.3.6.  Bidirectional Output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies checking bidirectional strings
   as described in stringprep's Section 6.

14.4.  UTF-8 Capabilities

   const FSCHARSET_CAP4_CONTAINS_NON_UTF8  = 0x1;
   const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8   = 0x2;

   typedef uint32_t        fs_charset_cap4;

   Because some operating environments and file systems do not enforce
   character set encodings, NFSv4.1 supports the fs_charset_cap
   attribute (Section 5.8.2.11) that indicates to the client a file
   system's UTF-8 capabilities.  The attribute is an integer containing
   a pair of flags.  The first flag is FSCHARSET_CAP4_CONTAINS_NON_UTF8,
   which, if set to one, tells the client that the file system contains
   non-UTF-8 characters, and the server will not convert non-UTF
   characters to UTF-8 if the client reads a symlink or directory,
   neither will operations with component names or pathnames in the
   arguments convert the strings to UTF-8.  The second flag is
   FSCHARSET_CAP4_ALLOWS_ONLY_UTF8, which, if set to one, indicates that
   the server will accept (and generate) only UTF-8 characters on the
   file system.  If FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set to one,
   FSCHARSET_CAP4_CONTAINS_NON_UTF8 MUST be set to zero.
   FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 SHOULD always be set to one.

14.5.  UTF-8 Related Errors

   Where the client sends an invalid UTF-8 string, the server should
   return NFS4ERR_INVAL (see Table 5).  This includes cases in which
   inappropriate prefixes are detected and where the count includes
   trailing bytes that do not constitute a full UCS character.

   Where the client-supplied string is valid UTF-8 but contains
   characters that are not supported by the server as a value for that
   string (e.g., names containing characters outside of Unicode plane 0
   on file systems that fail to support such characters despite their
   presence in the Unicode standard), the server should return



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   NFS4ERR_BADCHAR.

   Where a UTF-8 string is used as a file name, and the file system
   (while supporting all of the characters within the name) does not
   allow that particular name to be used, the server should return the
   error NFS4ERR_BADNAME (Table 5).  This includes situations in which
   the server file system imposes a normalization constraint on name
   strings, but will also include such situations as file system
   prohibitions of "." and ".." as file names for certain operations,
   and other such constraints.

15.  Error Values

   NFS error numbers are assigned to failed operations within a Compound
   (COMPOUND or CB_COMPOUND) request.  A Compound request contains a
   number of NFS operations that have their results encoded in sequence
   in a Compound reply.  The results of successful operations will
   consist of an NFS4_OK status followed by the encoded results of the
   operation.  If an NFS operation fails, an error status will be
   entered in the reply and the Compound request will be terminated.

15.1.  Error Definitions

                        Protocol Error Definitions

    +-----------------------------------+--------+-------------------+
    | Error                             | Number | Description       |
    +-----------------------------------+--------+-------------------+
    | NFS4_OK                           | 0      | Section 15.1.3.1  |
    | NFS4ERR_ACCESS                    | 13     | Section 15.1.6.1  |
    | NFS4ERR_ATTRNOTSUPP               | 10032  | Section 15.1.15.1 |
    | NFS4ERR_ADMIN_REVOKED             | 10047  | Section 15.1.5.1  |
    | NFS4ERR_BACK_CHAN_BUSY            | 10057  | Section 15.1.12.1 |
    | NFS4ERR_BADCHAR                   | 10040  | Section 15.1.7.1  |
    | NFS4ERR_BADHANDLE                 | 10001  | Section 15.1.2.1  |
    | NFS4ERR_BADIOMODE                 | 10049  | Section 15.1.10.1 |
    | NFS4ERR_BADLAYOUT                 | 10050  | Section 15.1.10.2 |
    | NFS4ERR_BADNAME                   | 10041  | Section 15.1.7.2  |
    | NFS4ERR_BADOWNER                  | 10039  | Section 15.1.15.2 |
    | NFS4ERR_BADSESSION                | 10052  | Section 15.1.11.1 |
    | NFS4ERR_BADSLOT                   | 10053  | Section 15.1.11.2 |
    | NFS4ERR_BADTYPE                   | 10007  | Section 15.1.4.1  |
    | NFS4ERR_BADXDR                    | 10036  | Section 15.1.1.1  |
    | NFS4ERR_BAD_COOKIE                | 10003  | Section 15.1.1.2  |
    | NFS4ERR_BAD_HIGH_SLOT             | 10077  | Section 15.1.11.3 |
    | NFS4ERR_BAD_RANGE                 | 10042  | Section 15.1.8.1  |
    | NFS4ERR_BAD_SEQID                 | 10026  | Section 15.1.16.1 |
    | NFS4ERR_BAD_SESSION_DIGEST        | 10051  | Section 15.1.12.2 |



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    | NFS4ERR_BAD_STATEID               | 10025  | Section 15.1.5.2  |
    | NFS4ERR_CB_PATH_DOWN              | 10048  | Section 15.1.11.4 |
    | NFS4ERR_CLID_INUSE                | 10017  | Section 15.1.13.2 |
    | NFS4ERR_CLIENTID_BUSY             | 10074  | Section 15.1.13.1 |
    | NFS4ERR_COMPLETE_ALREADY          | 10054  | Section 15.1.9.1  |
    | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055  | Section 15.1.11.6 |
    | NFS4ERR_DEADLOCK                  | 10045  | Section 15.1.8.2  |
    | NFS4ERR_DEADSESSION               | 10078  | Section 15.1.11.5 |
    | NFS4ERR_DELAY                     | 10008  | Section 15.1.1.3  |
    | NFS4ERR_DELEG_ALREADY_WANTED      | 10056  | Section 15.1.14.1 |
    | NFS4ERR_DELEG_REVOKED             | 10087  | Section 15.1.5.3  |
    | NFS4ERR_DENIED                    | 10010  | Section 15.1.8.3  |
    | NFS4ERR_DIRDELEG_UNAVAIL          | 10084  | Section 15.1.14.2 |
    | NFS4ERR_DQUOT                     | 69     | Section 15.1.4.2  |
    | NFS4ERR_ENCR_ALG_UNSUPP           | 10079  | Section 15.1.13.3 |
    | NFS4ERR_EXIST                     | 17     | Section 15.1.4.3  |
    | NFS4ERR_EXPIRED                   | 10011  | Section 15.1.5.4  |
    | NFS4ERR_FBIG                      | 27     | Section 15.1.4.4  |
    | NFS4ERR_FHEXPIRED                 | 10014  | Section 15.1.2.2  |
    | NFS4ERR_FILE_OPEN                 | 10046  | Section 15.1.4.5  |
    | NFS4ERR_GRACE                     | 10013  | Section 15.1.9.2  |
    | NFS4ERR_HASH_ALG_UNSUPP           | 10072  | Section 15.1.13.4 |
    | NFS4ERR_INVAL                     | 22     | Section 15.1.1.4  |
    | NFS4ERR_IO                        | 5      | Section 15.1.4.6  |
    | NFS4ERR_ISDIR                     | 21     | Section 15.1.2.3  |
    | NFS4ERR_LAYOUTTRYLATER            | 10058  | Section 15.1.10.3 |
    | NFS4ERR_LAYOUTUNAVAILABLE         | 10059  | Section 15.1.10.4 |
    | NFS4ERR_LEASE_MOVED               | 10031  | Section 15.1.16.2 |
    | NFS4ERR_LOCKED                    | 10012  | Section 15.1.8.4  |
    | NFS4ERR_LOCKS_HELD                | 10037  | Section 15.1.8.5  |
    | NFS4ERR_LOCK_NOTSUPP              | 10043  | Section 15.1.8.6  |
    | NFS4ERR_LOCK_RANGE                | 10028  | Section 15.1.8.7  |
    | NFS4ERR_MINOR_VERS_MISMATCH       | 10021  | Section 15.1.3.2  |
    | NFS4ERR_MLINK                     | 31     | Section 15.1.4.7  |
    | NFS4ERR_MOVED                     | 10019  | Section 15.1.2.4  |
    | NFS4ERR_NAMETOOLONG               | 63     | Section 15.1.7.3  |
    | NFS4ERR_NOENT                     | 2      | Section 15.1.4.8  |
    | NFS4ERR_NOFILEHANDLE              | 10020  | Section 15.1.2.5  |
    | NFS4ERR_NOMATCHING_LAYOUT         | 10060  | Section 15.1.10.5 |
    | NFS4ERR_NOSPC                     | 28     | Section 15.1.4.9  |
    | NFS4ERR_NOTDIR                    | 20     | Section 15.1.2.6  |
    | NFS4ERR_NOTEMPTY                  | 66     | Section 15.1.4.10 |
    | NFS4ERR_NOTSUPP                   | 10004  | Section 15.1.1.5  |
    | NFS4ERR_NOT_ONLY_OP               | 10081  | Section 15.1.3.3  |
    | NFS4ERR_NOT_SAME                  | 10027  | Section 15.1.15.3 |
    | NFS4ERR_NO_GRACE                  | 10033  | Section 15.1.9.3  |
    | NFS4ERR_NXIO                      | 6      | Section 15.1.16.3 |
    | NFS4ERR_OLD_STATEID               | 10024  | Section 15.1.5.5  |



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    | NFS4ERR_OPENMODE                  | 10038  | Section 15.1.8.8  |
    | NFS4ERR_OP_ILLEGAL                | 10044  | Section 15.1.3.4  |
    | NFS4ERR_OP_NOT_IN_SESSION         | 10071  | Section 15.1.3.5  |
    | NFS4ERR_PERM                      | 1      | Section 15.1.6.2  |
    | NFS4ERR_PNFS_IO_HOLE              | 10075  | Section 15.1.10.6 |
    | NFS4ERR_PNFS_NO_LAYOUT            | 10080  | Section 15.1.10.7 |
    | NFS4ERR_RECALLCONFLICT            | 10061  | Section 15.1.14.3 |
    | NFS4ERR_RECLAIM_BAD               | 10034  | Section 15.1.9.4  |
    | NFS4ERR_RECLAIM_CONFLICT          | 10035  | Section 15.1.9.5  |
    | NFS4ERR_REJECT_DELEG              | 10085  | Section 15.1.14.4 |
    | NFS4ERR_REP_TOO_BIG               | 10066  | Section 15.1.3.6  |
    | NFS4ERR_REP_TOO_BIG_TO_CACHE      | 10067  | Section 15.1.3.7  |
    | NFS4ERR_REQ_TOO_BIG               | 10065  | Section 15.1.3.8  |
    | NFS4ERR_RESTOREFH                 | 10030  | Section 15.1.16.4 |
    | NFS4ERR_RETRY_UNCACHED_REP        | 10068  | Section 15.1.3.9  |
    | NFS4ERR_RETURNCONFLICT            | 10086  | Section 15.1.10.8 |
    | NFS4ERR_ROFS                      | 30     | Section 15.1.4.11 |
    | NFS4ERR_SAME                      | 10009  | Section 15.1.15.4 |
    | NFS4ERR_SHARE_DENIED              | 10015  | Section 15.1.8.9  |
    | NFS4ERR_SEQUENCE_POS              | 10064  | Section 15.1.3.10 |
    | NFS4ERR_SEQ_FALSE_RETRY           | 10076  | Section 15.1.11.7 |
    | NFS4ERR_SEQ_MISORDERED            | 10063  | Section 15.1.11.8 |
    | NFS4ERR_SERVERFAULT               | 10006  | Section 15.1.1.6  |
    | NFS4ERR_STALE                     | 70     | Section 15.1.2.7  |
    | NFS4ERR_STALE_CLIENTID            | 10022  | Section 15.1.13.5 |
    | NFS4ERR_STALE_STATEID             | 10023  | Section 15.1.16.5 |
    | NFS4ERR_SYMLINK                   | 10029  | Section 15.1.2.8  |
    | NFS4ERR_TOOSMALL                  | 10005  | Section 15.1.1.7  |
    | NFS4ERR_TOO_MANY_OPS              | 10070  | Section 15.1.3.11 |
    | NFS4ERR_UNKNOWN_LAYOUTTYPE        | 10062  | Section 15.1.10.9 |
    | NFS4ERR_UNSAFE_COMPOUND           | 10069  | Section 15.1.3.12 |
    | NFS4ERR_WRONGSEC                  | 10016  | Section 15.1.6.3  |
    | NFS4ERR_WRONG_CRED                | 10082  | Section 15.1.6.4  |
    | NFS4ERR_WRONG_TYPE                | 10083  | Section 15.1.2.9  |
    | NFS4ERR_XDEV                      | 18     | Section 15.1.4.12 |
    +-----------------------------------+--------+-------------------+

                                  Table 5

15.1.1.  General Errors

   This section deals with errors that are applicable to a broad set of
   different purposes.

15.1.1.1.  NFS4ERR_BADXDR (Error Code 10036)

   The arguments for this operation do not match those specified in the
   XDR definition.  This includes situations in which the request ends



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   before all the arguments have been seen.  Note that this error
   applies when fixed enumerations (these include booleans) have a value
   within the input stream that is not valid for the enum.  A replier
   may pre-parse all operations for a Compound procedure before doing
   any operation execution and return RPC-level XDR errors in that case.

15.1.1.2.  NFS4ERR_BAD_COOKIE (Error Code 10003)

   Used for operations that provide a set of information indexed by some
   quantity provided by the client or cookie sent by the server for an
   earlier invocation.  Where the value cannot be used for its intended
   purpose, this error results.

15.1.1.3.  NFS4ERR_DELAY (Error Code 10008)

   For any of a number of reasons, the replier could not process this
   operation in what was deemed a reasonable time.  The client should
   wait and then try the request with a new slot and sequence value.

   Some examples of scenarios that might lead to this situation:

   o  A server that supports hierarchical storage receives a request to
      process a file that had been migrated.

   o  An operation requires a delegation recall to proceed, and waiting
      for this delegation recall makes processing this request in a
      timely fashion impossible.

   In such cases, the error NFS4ERR_DELAY allows these preparatory
   operations to proceed without holding up client resources such as a
   session slot.  After delaying for period of time, the client can then
   re-send the operation in question (but not with the same slot ID and
   sequence ID; one or both MUST be different on the re-send).

   Note that without the ability to return NFS4ERR_DELAY and the
   client's willingness to re-send when receiving it, deadlock might
   result.  For example, if a recall is done, and if the delegation
   return or operations preparatory to delegation return are held up by
   other operations that need the delegation to be returned, session
   slots might not be available.  The result could be deadlock.

15.1.1.4.  NFS4ERR_INVAL (Error Code 22)

   The arguments for this operation are not valid for some reason, even
   though they do match those specified in the XDR definition for the
   request.





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15.1.1.5.  NFS4ERR_NOTSUPP (Error Code 10004)

   Operation not supported, either because the operation is an OPTIONAL
   one and is not supported by this server or because the operation MUST
   NOT be implemented in the current minor version.

15.1.1.6.  NFS4ERR_SERVERFAULT (Error Code 10006)

   An error occurred on the server that does not map to any of the
   specific legal NFSv4.1 protocol error values.  The client should
   translate this into an appropriate error.  UNIX clients may choose to
   translate this to EIO.

15.1.1.7.  NFS4ERR_TOOSMALL (Error Code 10005)

   Used where an operation returns a variable amount of data, with a
   limit specified by the client.  Where the data returned cannot be fit
   within the limit specified by the client, this error results.

15.1.2.  Filehandle Errors

   These errors deal with the situation in which the current or saved
   filehandle, or the filehandle passed to PUTFH intended to become the
   current filehandle, is invalid in some way.  This includes situations
   in which the filehandle is a valid filehandle in general but is not
   of the appropriate object type for the current operation.

   Where the error description indicates a problem with the current or
   saved filehandle, it is to be understood that filehandles are only
   checked for the condition if they are implicit arguments of the
   operation in question.

15.1.2.1.  NFS4ERR_BADHANDLE (Error Code 10001)

   Illegal NFS filehandle for the current server.  The current file
   handle failed internal consistency checks.  Once accepted as valid
   (by PUTFH), no subsequent status change can cause the filehandle to
   generate this error.

15.1.2.2.  NFS4ERR_FHEXPIRED (Error Code 10014)

   A current or saved filehandle that is an argument to the current
   operation is volatile and has expired at the server.

15.1.2.3.  NFS4ERR_ISDIR (Error Code 21)

   The current or saved filehandle designates a directory when the
   current operation does not allow a directory to be accepted as the



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   target of this operation.

15.1.2.4.  NFS4ERR_MOVED (Error Code 10019)

   The file system that contains the current filehandle object is not
   present at the server.  It may have been relocated or migrated to
   another server, or it may have never been present.  The client may
   obtain the new file system location by obtaining the "fs_locations"
   or "fs_locations_info" attribute for the current filehandle.  For
   further discussion, refer to Section 11.2.

15.1.2.5.  NFS4ERR_NOFILEHANDLE (Error Code 10020)

   The logical current or saved filehandle value is required by the
   current operation and is not set.  This may be a result of a
   malformed COMPOUND operation (i.e., no PUTFH or PUTROOTFH before an
   operation that requires the current filehandle be set).

15.1.2.6.  NFS4ERR_NOTDIR (Error Code 20)

   The current (or saved) filehandle designates an object that is not a
   directory for an operation in which a directory is required.

15.1.2.7.  NFS4ERR_STALE (Error Code 70)

   The current or saved filehandle value designating an argument to the
   current operation is invalid.  The file referred to by that
   filehandle no longer exists or access to it has been revoked.

15.1.2.8.  NFS4ERR_SYMLINK (Error Code 10029)

   The current filehandle designates a symbolic link when the current
   operation does not allow a symbolic link as the target.

15.1.2.9.  NFS4ERR_WRONG_TYPE (Error Code 10083)

   The current (or saved) filehandle designates an object that is of an
   invalid type for the current operation, and there is no more specific
   error (such as NFS4ERR_ISDIR or NFS4ERR_SYMLINK) that applies.  Note
   that in NFSv4.0, such situations generally resulted in the less-
   specific error NFS4ERR_INVAL.

15.1.3.  Compound Structure Errors

   This section deals with errors that relate to the overall structure
   of a Compound request (by which we mean to include both COMPOUND and
   CB_COMPOUND), rather than to particular operations.




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   There are a number of basic constraints on the operations that may
   appear in a Compound request.  Sessions add to these basic
   constraints by requiring a Sequence operation (either SEQUENCE or
   CB_SEQUENCE) at the start of the Compound.

15.1.3.1.  NFS_OK (Error code 0)

   Indicates the operation completed successfully, in that all of the
   constituent operations completed without error.

15.1.3.2.  NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)

   The minor version specified is not one that the current listener
   supports.  This value is returned in the overall status for the
   Compound but is not associated with a specific operation since the
   results will specify a result count of zero.

15.1.3.3.  NFS4ERR_NOT_ONLY_OP (Error Code 10081)

   Certain operations, which are allowed to be executed outside of a
   session, MUST be the only operation within a Compound whenever the
   Compound does not start with a Sequence operation.  This error
   results when that constraint is not met.

15.1.3.4.  NFS4ERR_OP_ILLEGAL (Error Code 10044)

   The operation code is not a valid one for the current Compound
   procedure.  The opcode in the result stream matched with this error
   is the ILLEGAL value, although the value that appears in the request
   stream may be different.  Where an illegal value appears and the
   replier pre-parses all operations for a Compound procedure before
   doing any operation execution, an RPC-level XDR error may be
   returned.

15.1.3.5.  NFS4ERR_OP_NOT_IN_SESSION (Error Code 10071)

   Most forward operations and all callback operations are only valid
   within the context of a session, so that the Compound request in
   question MUST begin with a Sequence operation.  If an attempt is made
   to execute these operations outside the context of session, this
   error results.

15.1.3.6.  NFS4ERR_REP_TOO_BIG (Error Code 10066)

   The reply to a Compound would exceed the channel's negotiated maximum
   response size.





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15.1.3.7.  NFS4ERR_REP_TOO_BIG_TO_CACHE (Error Code 10067)

   The reply to a Compound would exceed the channel's negotiated maximum
   size for replies cached in the reply cache when the Sequence for the
   current request specifies that this request is to be cached.

15.1.3.8.  NFS4ERR_REQ_TOO_BIG (Error Code 10065)

   The Compound request exceeds the channel's negotiated maximum size
   for requests.

15.1.3.9.  NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)

   The requester has attempted a retry of a Compound that it previously
   requested not be placed in the reply cache.

15.1.3.10.  NFS4ERR_SEQUENCE_POS (Error Code 10064)

   A Sequence operation appeared in a position other than the first
   operation of a Compound request.

15.1.3.11.  NFS4ERR_TOO_MANY_OPS (Error Code 10070)

   The Compound request has too many operations, exceeding the count
   negotiated when the session was created.

15.1.3.12.  NFS4ERR_UNSAFE_COMPOUND (Error Code 10068)

   The client has sent a COMPOUND request with an unsafe mix of
   operations -- specifically, with a non-idempotent operation that
   changes the current filehandle and that is not followed by a GETFH.

15.1.4.  File System Errors

   These errors describe situations that occurred in the underlying file
   system implementation rather than in the protocol or any NFSv4.x
   feature.

15.1.4.1.  NFS4ERR_BADTYPE (Error Code 10007)

   An attempt was made to create an object with an inappropriate type
   specified to CREATE.  This may be because the type is undefined,
   because the type is not supported by the server, or because the type
   is not intended to be created by CREATE (such as a regular file or
   named attribute, for which OPEN is used to do the file creation).






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15.1.4.2.  NFS4ERR_DQUOT (Error Code 19)

   Resource (quota) hard limit exceeded.  The user's resource limit on
   the server has been exceeded.

15.1.4.3.  NFS4ERR_EXIST (Error Code 17)

   A file of the specified target name (when creating, renaming, or
   linking) already exists.

15.1.4.4.  NFS4ERR_FBIG (Error Code 27)

   The file is too large.  The operation would have caused the file to
   grow beyond the server's limit.

15.1.4.5.  NFS4ERR_FILE_OPEN (Error Code 10046)

   The operation is not allowed because a file involved in the operation
   is currently open.  Servers may, but are not required to, disallow
   linking-to, removing, or renaming open files.

15.1.4.6.  NFS4ERR_IO (Error Code 5)

   Indicates that an I/O error occurred for which the file system was
   unable to provide recovery.

15.1.4.7.  NFS4ERR_MLINK (Error Code 31)

   The request would have caused the server's limit for the number of
   hard links a file may have to be exceeded.

15.1.4.8.  NFS4ERR_NOENT (Error Code 2)

   Indicates no such file or directory.  The file or directory name
   specified does not exist.

15.1.4.9.  NFS4ERR_NOSPC (Error Code 28)

   Indicates there is no space left on the device.  The operation would
   have caused the server's file system to exceed its limit.

15.1.4.10.  NFS4ERR_NOTEMPTY (Error Code 66)

   An attempt was made to remove a directory that was not empty.







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15.1.4.11.  NFS4ERR_ROFS (Error Code 30)

   Indicates a read-only file system.  A modifying operation was
   attempted on a read-only file system.

15.1.4.12.  NFS4ERR_XDEV (Error Code 18)

   Indicates an attempt to do an operation, such as linking, that
   inappropriately crosses a boundary.  This may be due to such
   boundaries as:

   o  that between file systems (where the fsids are different).

   o  that between different named attribute directories or between a
      named attribute directory and an ordinary directory.

   o  that between byte-ranges of a file system that the file system
      implementation treats as separate (for example, for space
      accounting purposes), and where cross-connection between the byte-
      ranges are not allowed.

15.1.5.  State Management Errors

   These errors indicate problems with the stateid (or one of the
   stateids) passed to a given operation.  This includes situations in
   which the stateid is invalid as well as situations in which the
   stateid is valid but designates locking state that has been revoked.
   Depending on the operation, the stateid when valid may designate
   opens, byte-range locks, file or directory delegations, layouts, or
   device maps.

15.1.5.1.  NFS4ERR_ADMIN_REVOKED (Error Code 10047)

   A stateid designates locking state of any type that has been revoked
   due to administrative interaction, possibly while the lease is valid.

15.1.5.2.  NFS4ERR_BAD_STATEID (Error Code 10026)

   A stateid does not properly designate any valid state.  See Sections
   8.2.4 and 8.2.3 for a discussion of how stateids are validated.

15.1.5.3.  NFS4ERR_DELEG_REVOKED (Error Code 10087)

   A stateid designates recallable locking state of any type (delegation
   or layout) that has been revoked due to the failure of the client to
   return the lock when it was recalled.





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15.1.5.4.  NFS4ERR_EXPIRED (Error Code 10011)

   A stateid designates locking state of any type that has been revoked
   due to expiration of the client's lease, either immediately upon
   lease expiration, or following a later request for a conflicting
   lock.

15.1.5.5.  NFS4ERR_OLD_STATEID (Error Code 10024)

   A stateid with a non-zero seqid value does match the current seqid
   for the state designated by the user.

15.1.6.  Security Errors

   These are the various permission-related errors in NFSv4.1.

15.1.6.1.  NFS4ERR_ACCESS (Error Code 13)

   Indicates permission denied.  The caller does not have the correct
   permission to perform the requested operation.  Contrast this with
   NFS4ERR_PERM (Section 15.1.6.2), which restricts itself to owner or
   privileged-user permission failures, and NFS4ERR_WRONG_CRED
   (Section 15.1.6.4), which deals with appropriate permission to delete
   or modify transient objects based on the credentials of the user that
   created them.

15.1.6.2.  NFS4ERR_PERM (Error Code 1)

   Indicates requester is not the owner.  The operation was not allowed
   because the caller is neither a privileged user (root) nor the owner
   of the target of the operation.

15.1.6.3.  NFS4ERR_WRONGSEC (Error Code 10016)

   Indicates that the security mechanism being used by the client for
   the operation does not match the server's security policy.  The
   client should change the security mechanism being used and re-send
   the operation (but not with the same slot ID and sequence ID; one or
   both MUST be different on the re-send).  SECINFO and SECINFO_NO_NAME
   can be used to determine the appropriate mechanism.

15.1.6.4.  NFS4ERR_WRONG_CRED (Error Code 10082)

   An operation that manipulates state was attempted by a principal that
   was not allowed to modify that piece of state.






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15.1.7.  Name Errors

   Names in NFSv4 are UTF-8 strings.  When the strings are not valid
   UTF-8 or are of length zero, the error NFS4ERR_INVAL results.
   Besides this, there are a number of other errors to indicate specific
   problems with names.

15.1.7.1.  NFS4ERR_BADCHAR (Error Code 10040)

   A UTF-8 string contains a character that is not supported by the
   server in the context in which it being used.

15.1.7.2.  NFS4ERR_BADNAME (Error Code 10041)

   A name string in a request consisted of valid UTF-8 characters
   supported by the server, but the name is not supported by the server
   as a valid name for the current operation.  An example might be
   creating a file or directory named ".." on a server whose file system
   uses that name for links to parent directories.

15.1.7.3.  NFS4ERR_NAMETOOLONG (Error Code 63)

   Returned when the filename in an operation exceeds the server's
   implementation limit.

15.1.8.  Locking Errors

   This section deals with errors related to locking, both as to share
   reservations and byte-range locking.  It does not deal with errors
   specific to the process of reclaiming locks.  Those are dealt with in
   Section 15.1.9.

15.1.8.1.  NFS4ERR_BAD_RANGE (Error Code 10042)

   The byte-range of a LOCK, LOCKT, or LOCKU operation is not allowed by
   the server.  For example, this error results when a server that only
   supports 32-bit ranges receives a range that cannot be handled by
   that server.  (See Section 18.10.3.)

15.1.8.2.  NFS4ERR_DEADLOCK (Error Code 10045)

   The server has been able to determine a byte-range locking deadlock
   condition for a READW_LT or WRITEW_LT LOCK operation.

15.1.8.3.  NFS4ERR_DENIED (Error Code 10010)

   An attempt to lock a file is denied.  Since this may be a temporary
   condition, the client is encouraged to re-send the lock request (but



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   not with the same slot ID and sequence ID; one or both MUST be
   different on the re-send) until the lock is accepted.  See
   Section 9.6 for a discussion of the re-send.

15.1.8.4.  NFS4ERR_LOCKED (Error Code 10012)

   A READ or WRITE operation was attempted on a file where there was a
   conflict between the I/O and an existing lock:

   o  There is a share reservation inconsistent with the I/O being done.

   o  The range to be read or written intersects an existing mandatory
      byte-range lock.

15.1.8.5.  NFS4ERR_LOCKS_HELD (Error Code 10037)

   An operation was prevented by the unexpected presence of locks.

15.1.8.6.  NFS4ERR_LOCK_NOTSUPP (Error Code 10043)

   A LOCK operation was attempted that would require the upgrade or
   downgrade of a byte-range lock range already held by the owner, and
   the server does not support atomic upgrade or downgrade of locks.

15.1.8.7.  NFS4ERR_LOCK_RANGE (Error Code 10028)

   A LOCK operation is operating on a range that overlaps in part a
   currently held byte-range lock for the current lock-owner and does
   not precisely match a single such byte-range lock where the server
   does not support this type of request, and thus does not implement
   POSIX locking semantics [24].  See Sections 18.10.4, 18.11.4, and
   18.12.4 for a discussion of how this applies to LOCK, LOCKT, and
   LOCKU respectively.

15.1.8.8.  NFS4ERR_OPENMODE (Error Code 10038)

   The client attempted a READ, WRITE, LOCK, or other operation not
   sanctioned by the stateid passed (e.g., writing to a file opened for
   read-only access).

15.1.8.9.  NFS4ERR_SHARE_DENIED (Error Code 10015)

   An attempt to OPEN a file with a share reservation has failed because
   of a share conflict.







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15.1.9.  Reclaim Errors

   These errors relate to the process of reclaiming locks after a server
   restart.

15.1.9.1.  NFS4ERR_COMPLETE_ALREADY (Error Code 10054)

   The client previously sent a successful RECLAIM_COMPLETE operation.
   An additional RECLAIM_COMPLETE operation is not necessary and results
   in this error.

15.1.9.2.  NFS4ERR_GRACE (Error Code 10013)

   The server was in its recovery or grace period.  The locking request
   was not a reclaim request and so could not be granted during that
   period.

15.1.9.3.  NFS4ERR_NO_GRACE (Error Code 10033)

   A reclaim of client state was attempted in circumstances in which the
   server cannot guarantee that conflicting state has not been provided
   to another client.  This can occur because the reclaim has been done
   outside of the grace period of the server, after the client has done
   a RECLAIM_COMPLETE operation, or because previous operations have
   created a situation in which the server is not able to determine that
   a reclaim-interfering edge condition does not exist.

15.1.9.4.  NFS4ERR_RECLAIM_BAD (Error Code 10034)

   The server has determined that a reclaim attempted by the client is
   not valid, i.e. the lock specified as being reclaimed could not
   possibly have existed before the server restart.  A server is not
   obliged to make this determination and will typically rely on the
   client to only reclaim locks that the client was granted prior to
   restart.  However, when a server does have reliable information to
   enable it make this determination, this error indicates that the
   reclaim has been rejected as invalid.  This is as opposed to the
   error NFS4ERR_RECLAIM_CONFLICT (see Section 15.1.9.5) where the
   server can only determine that there has been an invalid reclaim, but
   cannot determine which request is invalid.

15.1.9.5.  NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)

   The reclaim attempted by the client has encountered a conflict and
   cannot be satisfied.  Potentially indicates a misbehaving client,
   although not necessarily the one receiving the error.  The
   misbehavior might be on the part of the client that established the
   lock with which this client conflicted.  See also Section 15.1.9.4



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   for the related error, NFS4ERR_RECLAIM_BAD.

15.1.10.  pNFS Errors

   This section deals with pNFS-related errors including those that are
   associated with using NFSv4.1 to communicate with a data server.

15.1.10.1.  NFS4ERR_BADIOMODE (Error Code 10049)

   An invalid or inappropriate layout iomode was specified.  For example
   an inappropriate layout iomode, suppose a client's LAYOUTGET
   operation specified an iomode of LAYOUTIOMODE4_RW, and the server is
   neither able nor willing to let the client send write requests to
   data servers; the server can reply with NFS4ERR_BADIOMODE.  The
   client would then send another LAYOUTGET with an iomode of
   LAYOUTIOMODE4_READ.

15.1.10.2.  NFS4ERR_BADLAYOUT (Error Code 10050)

   The layout specified is invalid in some way.  For LAYOUTCOMMIT, this
   indicates that the specified layout is not held by the client or is
   not of mode LAYOUTIOMODE4_RW.  For LAYOUTGET, it indicates that a
   layout matching the client's specification as to minimum length
   cannot be granted.

15.1.10.3.  NFS4ERR_LAYOUTTRYLATER (Error Code 10058)

   Layouts are temporarily unavailable for the file.  The client should
   re-send later (but not with the same slot ID and sequence ID; one or
   both MUST be different on the re-send).

15.1.10.4.  NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)

   Returned when layouts are not available for the current file system
   or the particular specified file.

15.1.10.5.  NFS4ERR_NOMATCHING_LAYOUT (Error Code 10060)

   Returned when layouts are recalled and the client has no layouts
   matching the specification of the layouts being recalled.

15.1.10.6.  NFS4ERR_PNFS_IO_HOLE (Error Code 10075)

   The pNFS client has attempted to read from or write to an illegal
   hole of a file of a data server that is using sparse packing.  See
   Section 13.4.4.





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15.1.10.7.  NFS4ERR_PNFS_NO_LAYOUT (Error Code 10080)

   The pNFS client has attempted to read from or write to a file (using
   a request to a data server) without holding a valid layout.  This
   includes the case where the client had a layout, but the iomode does
   not allow a WRITE.

15.1.10.8.  NFS4ERR_RETURNCONFLICT (Error Code 10086)

   A layout is unavailable due to an attempt to perform the LAYOUTGET
   before a pending LAYOUTRETURN on the file has been received.  See
   Section 12.5.5.2.1.3.

15.1.10.9.  NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)

   The client has specified a layout type that is not supported by the
   server.

15.1.11.  Session Use Errors

   This section deals with errors encountered when using sessions, that
   is, errors encountered when a request uses a Sequence (i.e., either
   SEQUENCE or CB_SEQUENCE) operation.

15.1.11.1.  NFS4ERR_BADSESSION (Error Code 10052)

   The specified session ID is unknown to the server to which the
   operation is addressed.

15.1.11.2.  NFS4ERR_BADSLOT (Error Code 10053)

   The requester sent a Sequence operation that attempted to use a slot
   the replier does not have in its slot table.  It is possible the slot
   may have been retired.

15.1.11.3.  NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)

   The highest_slot argument in a Sequence operation exceeds the
   replier's enforced highest_slotid.

15.1.11.4.  NFS4ERR_CB_PATH_DOWN (Error Code 10048)

   There is a problem contacting the client via the callback path.  The
   function of this error has been mostly superseded by the use of
   status flags in the reply to the SEQUENCE operation (see
   Section 18.46).





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15.1.11.5.  NFS4ERR_DEADSESSION (Error Code 10078)

   The specified session is a persistent session that is dead and does
   not accept new requests or perform new operations on existing
   requests (in the case in which a request was partially executed
   before server restart).

15.1.11.6.  NFS4ERR_CONN_NOT_BOUND_TO_SESSION (Error Code 10055)

   A Sequence operation was sent on a connection that has not been
   associated with the specified session, where the client specified
   that connection association was to be enforced with SP4_MACH_CRED or
   SP4_SSV state protection.

15.1.11.7.  NFS4ERR_SEQ_FALSE_RETRY (Error Code 10076)

   The requester sent a Sequence operation with a slot ID and sequence
   ID that are in the reply cache, but the replier has detected that the
   retried request is not the same as the original request.  See
   Section 2.10.6.1.3.1.

15.1.11.8.  NFS4ERR_SEQ_MISORDERED (Error Code 10063)

   The requester sent a Sequence operation with an invalid sequence ID.

15.1.12.  Session Management Errors

   This section deals with errors associated with requests used in
   session management.

15.1.12.1.  NFS4ERR_BACK_CHAN_BUSY (Error Code 10057)

   An attempt was made to destroy a session when the session cannot be
   destroyed because the server has callback requests outstanding.

15.1.12.2.  NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)

   The digest used in a SET_SSV request is not valid.

15.1.13.  Client Management Errors

   This section deals with errors associated with requests used to
   create and manage client IDs.

15.1.13.1.  NFS4ERR_CLIENTID_BUSY (Error Code 10074)

   The DESTROY_CLIENTID operation has found there are sessions and/or
   unexpired state associated with the client ID to be destroyed.



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15.1.13.2.  NFS4ERR_CLID_INUSE (Error Code 10017)

   While processing an EXCHANGE_ID operation, the server was presented
   with a co_ownerid field that matches an existing client with valid
   leased state, but the principal sending the EXCHANGE_ID operation
   differs from the principal that established the existing client.
   This indicates a collision (most likely due to chance) between
   clients.  The client should recover by changing the co_ownerid and
   re-sending EXCHANGE_ID (but not with the same slot ID and sequence
   ID; one or both MUST be different on the re-send).

15.1.13.3.  NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)

   An EXCHANGE_ID was sent that specified state protection via SSV, and
   where the set of encryption algorithms presented by the client did
   not include any supported by the server.

15.1.13.4.  NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)

   An EXCHANGE_ID was sent that specified state protection via SSV, and
   where the set of hashing algorithms presented by the client did not
   include any supported by the server.

15.1.13.5.  NFS4ERR_STALE_CLIENTID (Error Code 10022)

   A client ID not recognized by the server was passed to an operation.
   Note that unlike the case of NFSv4.0, client IDs are not passed
   explicitly to the server in ordinary locking operations and cannot
   result in this error.  Instead, when there is a server restart, it is
   first manifested through an error on the associated session, and the
   staleness of the client ID is detected when trying to associate a
   client ID with a new session.

15.1.14.  Delegation Errors

   This section deals with errors associated with requesting and
   returning delegations.

15.1.14.1.  NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)

   The client has requested a delegation when it had already registered
   that it wants that same delegation.

15.1.14.2.  NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)

   This error is returned when the server is unable or unwilling to
   provide a requested directory delegation.




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15.1.14.3.  NFS4ERR_RECALLCONFLICT (Error Code 10061)

   A recallable object (i.e., a layout or delegation) is unavailable due
   to a conflicting recall operation that is currently in progress for
   that object.

15.1.14.4.  NFS4ERR_REJECT_DELEG (Error Code 10085)

   The callback operation invoked to deal with a new delegation has
   rejected it.

15.1.15.  Attribute Handling Errors

   This section deals with errors specific to attribute handling within
   NFSv4.

15.1.15.1.  NFS4ERR_ATTRNOTSUPP (Error Code 10032)

   An attribute specified is not supported by the server.  This error
   MUST NOT be returned by the GETATTR operation.

15.1.15.2.  NFS4ERR_BADOWNER (Error Code 10039)

   This error is returned when an owner or owner_group attribute value
   or the who field of an ACE within an ACL attribute value cannot be
   translated to a local representation.

15.1.15.3.  NFS4ERR_NOT_SAME (Error Code 10027)

   This error is returned by the VERIFY operation to signify that the
   attributes compared were not the same as those provided in the
   client's request.

15.1.15.4.  NFS4ERR_SAME (Error Code 10009)

   This error is returned by the NVERIFY operation to signify that the
   attributes compared were the same as those provided in the client's
   request.

15.1.16.  Obsoleted Errors

   These errors MUST NOT be generated by any NFSv4.1 operation.  This
   can be for a number of reasons.

   o  The function provided by the error has been superseded by one of
      the status bits returned by the SEQUENCE operation.





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   o  The new session structure and associated change in locking have
      made the error unnecessary.

   o  There has been a restructuring of some errors for NFSv4.1 that
      resulted in the elimination of certain errors.

15.1.16.1.  NFS4ERR_BAD_SEQID (Error Code 10026)

   The sequence number (seqid) in a locking request is neither the next
   expected number or the last number processed.  These seqids are
   ignored in NFSv4.1.

15.1.16.2.  NFS4ERR_LEASE_MOVED (Error Code 10031)

   A lease being renewed is associated with a file system that has been
   migrated to a new server.  The error has been superseded by the
   SEQ4_STATUS_LEASE_MOVED status bit (see Section 18.46).

15.1.16.3.  NFS4ERR_NXIO (Error Code 5)

   I/O error.  No such device or address.  This error is for errors
   involving block and character device access, but because NFSv4.1 is
   not a device-access protocol, this error is not applicable.

15.1.16.4.  NFS4ERR_RESTOREFH (Error Code 10030)

   The RESTOREFH operation does not have a saved filehandle (identified
   by SAVEFH) to operate upon.  In NFSv4.1, this error has been
   superseded by NFS4ERR_NOFILEHANDLE.

15.1.16.5.  NFS4ERR_STALE_STATEID (Error Code 10023)

   A stateid generated by an earlier server instance was used.  This
   error is moot in NFSv4.1 because all operations that take a stateid
   MUST be preceded by the SEQUENCE operation, and the earlier server
   instance is detected by the session infrastructure that supports
   SEQUENCE.

15.2.  Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each protocol operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   operations with two important exceptions:

   o  The operations that MUST NOT be implemented: OPEN_CONFIRM,
      RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and SETCLIENTID_CONFIRM.




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   o  The invalid operation: ILLEGAL.

              Valid Error Returns for Each Protocol Operation

   +----------------------+--------------------------------------------+
   | Operation            | Errors                                     |
   +----------------------+--------------------------------------------+
   | ACCESS               | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   | BACKCHANNEL_CTL      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_NOENT, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   | BIND_CONN_TO_SESSION | NFS4ERR_BADSESSION, NFS4ERR_BADXDR,        |
   |                      | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_NOT_ONLY_OP,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |















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   | CLOSE                | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_LOCKS_HELD,     |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | COMMIT               | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_IO,             |
   |                      | NFS4ERR_ISDIR, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | CREATE               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADNAME,          |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BADTYPE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_DQUOT,              |
   |                      | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MLINK,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_OP_NOT_IN_SESSION, |
   |                      | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG,         |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND                    |








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   | CREATE_SESSION       | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE,        |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_NOENT,              |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_NOSPC,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SEQ_MISORDERED,                    |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID, NFS4ERR_TOOSMALL,  |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | DELEGPURGE           | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONG_CRED                         |
   | DELEGRETURN          | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | DESTROY_CLIENTID     | NFS4ERR_BADXDR, NFS4ERR_CLIENTID_BUSY,     |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_REP_TOO_BIG,  |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |







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   | DESTROY_SESSION      | NFS4ERR_BACK_CHAN_BUSY,                    |
   |                      | NFS4ERR_BADSESSION, NFS4ERR_BADXDR,        |
   |                      | NFS4ERR_CB_PATH_DOWN,                      |
   |                      | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_REP_TOO_BIG,  |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | EXCHANGE_ID          | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_CLID_INUSE, NFS4ERR_DEADSESSION,   |
   |                      | NFS4ERR_DELAY, NFS4ERR_ENCR_ALG_UNSUPP,    |
   |                      | NFS4ERR_HASH_ALG_UNSUPP, NFS4ERR_INVAL,    |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOT_ONLY_OP,        |
   |                      | NFS4ERR_NOT_SAME, NFS4ERR_REP_TOO_BIG,     |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |
   | FREE_STATEID         | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_LOCKS_HELD, NFS4ERR_OLD_STATEID,   |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONG_CRED                         |
   | GET_DIR_DELEGATION   | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DIRDELEG_UNAVAIL,                  |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |





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RFC 5661                         NFSv4.1                    January 2010


   | GETATTR              | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   | GETDEVICEINFO        | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOOSMALL,     |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | GETDEVICELIST        | NFS4ERR_BADXDR, NFS4ERR_BAD_COOKIE,        |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_NOFILEHANDLE,          |
   |                      | NFS4ERR_NOTSUPP, NFS4ERR_NOT_SAME,         |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   | GETFH                | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED,          |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_STALE   |
   | ILLEGAL              | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL         |












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   | LAYOUTCOMMIT         | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADIOMODE,    |
   |                      | NFS4ERR_BADLAYOUT, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,    |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_ISDIR NFS4ERR_MOVED,               |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_CRED                         |
   | LAYOUTGET            | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADIOMODE, NFS4ERR_BADLAYOUT,      |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO,                 |
   |                      | NFS4ERR_LAYOUTTRYLATER,                    |
   |                      | NFS4ERR_LAYOUTUNAVAILABLE, NFS4ERR_LOCKED, |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOSPC, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECALLCONFLICT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOOSMALL, NFS4ERR_TOO_MANY_OPS,    |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |








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RFC 5661                         NFSv4.1                    January 2010


   | LAYOUTRETURN         | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE     |
   | LINK                 | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_IO, NFS4ERR_MLINK,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP,           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONGSEC, NFS4ERR_WRONG_TYPE,      |
   |                      | NFS4ERR_XDEV                               |















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RFC 5661                         NFSv4.1                    January 2010


   | LOCK                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE,         |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADLOCK,     |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DENIED, NFS4ERR_EXPIRED,           |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LOCK_NOTSUPP, NFS4ERR_LOCK_RANGE,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,     |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE     |
   | LOCKT                | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_BAD_RANGE, NFS4ERR_DEADSESSION,    |
   |                      | NFS4ERR_DELAY, NFS4ERR_DENIED,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LOCK_RANGE, NFS4ERR_MOVED,         |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_STALE, NFS4ERR_SYMLINK,            |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED,  |
   |                      | NFS4ERR_WRONG_TYPE                         |















Shepler, et al.              Standards Track                  [Page 363]

RFC 5661                         NFSv4.1                    January 2010


   | LOCKU                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE,         |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_LOCK_RANGE, NFS4ERR_MOVED,         |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID, |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | LOOKUP               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONGSEC                           |
   | LOOKUPP              | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONGSEC                           |










Shepler, et al.              Standards Track                  [Page 364]

RFC 5661                         NFSv4.1                    January 2010


   | NVERIFY              | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_SAME,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | OPEN                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADOWNER,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_ALREADY_WANTED,              |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_EXIST, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NO_GRACE,          |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_SHARE_DENIED, |
   |                      | NFS4ERR_STALE, NFS4ERR_SYMLINK,            |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_WRONGSEC, |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | OPEN_CONFIRM         | NFS4ERR_NOTSUPP                            |








Shepler, et al.              Standards Track                  [Page 365]

RFC 5661                         NFSv4.1                    January 2010


   | OPEN_DOWNGRADE       | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   | OPENATTR             | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | PUTFH                | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_MOVED, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC     |
   | PUTPUBFH             | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONGSEC                           |






Shepler, et al.              Standards Track                  [Page 366]

RFC 5661                         NFSv4.1                    January 2010


   | PUTROOTFH            | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONGSEC                           |
   | READ                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,    |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR, NFS4ERR_IO,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID, |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_PNFS_IO_HOLE,                      |
   |                      | NFS4ERR_PNFS_NO_LAYOUT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | READDIR              | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_BAD_COOKIE, NFS4ERR_DEADSESSION,   |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOT_SAME,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOOSMALL, NFS4ERR_TOO_MANY_OPS     |











Shepler, et al.              Standards Track                  [Page 367]

RFC 5661                         NFSv4.1                    January 2010


   | READLINK             | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   | RECLAIM_COMPLETE     | NFS4ERR_BADXDR, NFS4ERR_COMPLETE_ALREADY,  |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED,  |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | RELEASE_LOCKOWNER    | NFS4ERR_NOTSUPP                            |
   | REMOVE               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |












Shepler, et al.              Standards Track                  [Page 368]

RFC 5661                         NFSv4.1                    January 2010


   | RENAME               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_MLINK, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC,    |
   |                      | NFS4ERR_XDEV                               |
   | RENEW                | NFS4ERR_NOTSUPP                            |
   | RESTOREFH            | NFS4ERR_DEADSESSION, NFS4ERR_FHEXPIRED,    |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC     |
   | SAVEFH               | NFS4ERR_DEADSESSION, NFS4ERR_FHEXPIRED,    |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |














Shepler, et al.              Standards Track                  [Page 369]

RFC 5661                         NFSv4.1                    January 2010


   | SECINFO              | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_OP_NOT_IN_SESSION, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   | SECINFO_NO_NAME      | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOENT,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   | SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,       |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,     |
   |                      | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SEQUENCE_POS,                      |
   |                      | NFS4ERR_SEQ_FALSE_RETRY,                   |
   |                      | NFS4ERR_SEQ_MISORDERED,                    |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   | SET_SSV              | NFS4ERR_BADXDR,                            |
   |                      | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_TOO_MANY_OPS                       |




Shepler, et al.              Standards Track                  [Page 370]

RFC 5661                         NFSv4.1                    January 2010


   | SETATTR              | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BADXDR,          |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   | SETCLIENTID          | NFS4ERR_NOTSUPP                            |
   | SETCLIENTID_CONFIRM  | NFS4ERR_NOTSUPP                            |
   | TEST_STATEID         | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |
   | VERIFY               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOT_SAME,    |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |







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RFC 5661                         NFSv4.1                    January 2010


   | WANT_DELEGATION      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY,                             |
   |                      | NFS4ERR_DELEG_ALREADY_WANTED,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECALLCONFLICT,                    |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   | WRITE                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FBIG,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_PNFS_IO_HOLE,                      |
   |                      | NFS4ERR_PNFS_NO_LAYOUT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   +----------------------+--------------------------------------------+

                                  Table 6

15.3.  Callback Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each callback operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   callback operations with the exception of CB_ILLEGAL.




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RFC 5661                         NFSv4.1                    January 2010


         Valid Error Returns for Each Protocol Callback Operation

   +-------------------------+-----------------------------------------+
   | Callback Operation      | Errors                                  |
   +-------------------------+-----------------------------------------+
   | CB_GETATTR              | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   | CB_ILLEGAL              | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL      |
   | CB_LAYOUTRECALL         | NFS4ERR_BADHANDLE, NFS4ERR_BADIOMODE,   |
   |                         | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,    |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_NOMATCHING_LAYOUT,              |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_UNKNOWN_LAYOUTTYPE,             |
   |                         | NFS4ERR_WRONG_TYPE                      |
   | CB_NOTIFY               | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_NOTIFY_DEVICEID      | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |




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RFC 5661                         NFSv4.1                    January 2010


   | CB_NOTIFY_LOCK          | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_PUSH_DELEG           | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REJECT_DELEG,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_WRONG_TYPE                      |
   | CB_RECALL               | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_RECALL_ANY           | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL,                          |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_RECALLABLE_OBJ_AVAIL | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |



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RFC 5661                         NFSv4.1                    January 2010


   | CB_RECALL_SLOT          | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,  |
   |                         | NFS4ERR_DELAY,                          |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,    |
   |                         | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,  |
   |                         | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_REP_TOO_BIG,     |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SEQUENCE_POS,                   |
   |                         | NFS4ERR_SEQ_FALSE_RETRY,                |
   |                         | NFS4ERR_SEQ_MISORDERED,                 |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   | CB_WANTS_CANCELLED      | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   +-------------------------+-----------------------------------------+

                                  Table 7

15.4.  Errors and the Operations That Use Them

   +-----------------------------------+-------------------------------+
   | Error                             | Operations                    |
   +-----------------------------------+-------------------------------+
   | NFS4ERR_ACCESS                    | ACCESS, COMMIT, CREATE,       |
   |                                   | GETATTR, GET_DIR_DELEGATION,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LINK, LOCK, LOCKT, LOCKU,     |
   |                                   | LOOKUP, LOOKUPP, NVERIFY,     |
   |                                   | OPEN, OPENATTR, READ,         |
   |                                   | READDIR, READLINK, REMOVE,    |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WRITE                 |




Shepler, et al.              Standards Track                  [Page 375]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_ADMIN_REVOKED             | CLOSE, DELEGRETURN,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_ATTRNOTSUPP               | CREATE, LAYOUTCOMMIT,         |
   |                                   | NVERIFY, OPEN, SETATTR,       |
   |                                   | VERIFY                        |
   | NFS4ERR_BACK_CHAN_BUSY            | DESTROY_SESSION               |
   | NFS4ERR_BADCHAR                   | CREATE, EXCHANGE_ID, LINK,    |
   |                                   | LOOKUP, NVERIFY, OPEN,        |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SETATTR, VERIFY               |
   | NFS4ERR_BADHANDLE                 | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY, CB_NOTIFY_LOCK,    |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | PUTFH                         |
   | NFS4ERR_BADIOMODE                 | CB_LAYOUTRECALL,              |
   |                                   | LAYOUTCOMMIT, LAYOUTGET       |
   | NFS4ERR_BADLAYOUT                 | LAYOUTCOMMIT, LAYOUTGET       |
   | NFS4ERR_BADNAME                   | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO       |
   | NFS4ERR_BADOWNER                  | CREATE, OPEN, SETATTR         |
   | NFS4ERR_BADSESSION                | BIND_CONN_TO_SESSION,         |
   |                                   | CB_SEQUENCE, DESTROY_SESSION, |
   |                                   | SEQUENCE                      |
   | NFS4ERR_BADSLOT                   | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_BADTYPE                   | CREATE                        |























Shepler, et al.              Standards Track                  [Page 376]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_BADXDR                    | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_ILLEGAL,       |
   |                                   | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION, ILLEGAL,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | OPEN_DOWNGRADE, PUTFH, READ,  |
   |                                   | READDIR, RECLAIM_COMPLETE,    |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME, SEQUENCE,    |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_BAD_COOKIE                | GETDEVICELIST, READDIR        |
   | NFS4ERR_BAD_HIGH_SLOT             | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | SEQUENCE                      |
   | NFS4ERR_BAD_RANGE                 | LOCK, LOCKT, LOCKU            |
   | NFS4ERR_BAD_SESSION_DIGEST        | BIND_CONN_TO_SESSION, SET_SSV |
   | NFS4ERR_BAD_STATEID               | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_LOCK, CB_RECALL,    |
   |                                   | CLOSE, DELEGRETURN,           |
   |                                   | FREE_STATEID, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_CB_PATH_DOWN              | DESTROY_SESSION               |
   | NFS4ERR_CLID_INUSE                | CREATE_SESSION, EXCHANGE_ID   |
   | NFS4ERR_CLIENTID_BUSY             | DESTROY_CLIENTID              |
   | NFS4ERR_COMPLETE_ALREADY          | RECLAIM_COMPLETE              |
   | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, DESTROY_SESSION, |
   |                                   | SEQUENCE                      |



Shepler, et al.              Standards Track                  [Page 377]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_DEADLOCK                  | LOCK                          |
   | NFS4ERR_DEADSESSION               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION, CLOSE,  |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |



























Shepler, et al.              Standards Track                  [Page 378]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_DELAY                     | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SEQUENCE,    |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_DELEG_ALREADY_WANTED      | OPEN, WANT_DELEGATION         |
   | NFS4ERR_DELEG_REVOKED             | DELEGRETURN, LAYOUTCOMMIT,    |
   |                                   | LAYOUTGET, LAYOUTRETURN,      |
   |                                   | OPEN, READ, SETATTR, WRITE    |
   | NFS4ERR_DENIED                    | LOCK, LOCKT                   |
   | NFS4ERR_DIRDELEG_UNAVAIL          | GET_DIR_DELEGATION            |
   | NFS4ERR_DQUOT                     | CREATE, LAYOUTGET, LINK,      |
   |                                   | OPEN, OPENATTR, RENAME,       |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_ENCR_ALG_UNSUPP           | EXCHANGE_ID                   |
   | NFS4ERR_EXIST                     | CREATE, LINK, OPEN, RENAME    |
   | NFS4ERR_EXPIRED                   | CLOSE, DELEGRETURN,           |
   |                                   | LAYOUTCOMMIT, LAYOUTRETURN,   |
   |                                   | LOCK, LOCKU, OPEN,            |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | SETATTR, WRITE                |



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RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_FBIG                      | LAYOUTCOMMIT, OPEN, SETATTR,  |
   |                                   | WRITE                         |
   | NFS4ERR_FHEXPIRED                 | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_FILE_OPEN                 | LINK, REMOVE, RENAME          |
   | NFS4ERR_GRACE                     | GETATTR, GET_DIR_DELEGATION,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, NVERIFY, OPEN, READ,   |
   |                                   | REMOVE, RENAME, SETATTR,      |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_HASH_ALG_UNSUPP           | EXCHANGE_ID                   |

























Shepler, et al.              Standards Track                  [Page 380]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_INVAL                     | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_PUSH_DELEG,                |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY, CREATE,        |
   |                                   | CREATE_SESSION, DELEGRETURN,  |
   |                                   | EXCHANGE_ID, GETATTR,         |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | NVERIFY, OPEN,                |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | READDIR, READLINK,            |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | SET_SSV, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_IO                        | ACCESS, COMMIT, CREATE,       |
   |                                   | GETATTR, GETDEVICELIST,       |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LINK, LOOKUP, LOOKUPP,        |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | REMOVE, RENAME, SETATTR,      |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_ISDIR                     | COMMIT, LAYOUTCOMMIT,         |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, OPEN, READ, WRITE      |
   | NFS4ERR_LAYOUTTRYLATER            | LAYOUTGET                     |
   | NFS4ERR_LAYOUTUNAVAILABLE         | LAYOUTGET                     |
   | NFS4ERR_LOCKED                    | LAYOUTGET, READ, SETATTR,     |
   |                                   | WRITE                         |
   | NFS4ERR_LOCKS_HELD                | CLOSE, FREE_STATEID           |
   | NFS4ERR_LOCK_NOTSUPP              | LOCK                          |
   | NFS4ERR_LOCK_RANGE                | LOCK, LOCKT, LOCKU            |
   | NFS4ERR_MLINK                     | CREATE, LINK, RENAME          |







Shepler, et al.              Standards Track                  [Page 381]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_MOVED                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, RECLAIM_COMPLETE,   |
   |                                   | REMOVE, RENAME, RESTOREFH,    |
   |                                   | SAVEFH, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_NAMETOOLONG               | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO       |
   | NFS4ERR_NOENT                     | BACKCHANNEL_CTL,              |
   |                                   | CREATE_SESSION, EXCHANGE_ID,  |
   |                                   | GETDEVICEINFO, LOOKUP,        |
   |                                   | LOOKUPP, OPEN, OPENATTR,      |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME               |
   | NFS4ERR_NOFILEHANDLE              | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_NOMATCHING_LAYOUT         | CB_LAYOUTRECALL               |
   | NFS4ERR_NOSPC                     | CREATE, CREATE_SESSION,       |
   |                                   | LAYOUTGET, LINK, OPEN,        |
   |                                   | OPENATTR, RENAME, SETATTR,    |
   |                                   | WRITE                         |
   | NFS4ERR_NOTDIR                    | CREATE, GET_DIR_DELEGATION,   |
   |                                   | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | READDIR, REMOVE, RENAME,      |
   |                                   | SECINFO, SECINFO_NO_NAME      |
   | NFS4ERR_NOTEMPTY                  | REMOVE, RENAME                |



Shepler, et al.              Standards Track                  [Page 382]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_NOTSUPP                   | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG,                |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_WANTS_CANCELLED,           |
   |                                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, OPENATTR, |
   |                                   | OPEN_CONFIRM,                 |
   |                                   | RELEASE_LOCKOWNER, RENEW,     |
   |                                   | SECINFO_NO_NAME, SETCLIENTID, |
   |                                   | SETCLIENTID_CONFIRM,          |
   |                                   | WANT_DELEGATION               |
   | NFS4ERR_NOT_ONLY_OP               | BIND_CONN_TO_SESSION,         |
   |                                   | CREATE_SESSION,               |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID  |
   | NFS4ERR_NOT_SAME                  | EXCHANGE_ID, GETDEVICELIST,   |
   |                                   | READDIR, VERIFY               |
   | NFS4ERR_NO_GRACE                  | LAYOUTCOMMIT, LAYOUTRETURN,   |
   |                                   | LOCK, OPEN, WANT_DELEGATION   |
   | NFS4ERR_OLD_STATEID               | CLOSE, DELEGRETURN,           |
   |                                   | FREE_STATEID, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_OPENMODE                  | LAYOUTGET, LOCK, READ,        |
   |                                   | SETATTR, WRITE                |
   | NFS4ERR_OP_ILLEGAL                | CB_ILLEGAL, ILLEGAL           |



















Shepler, et al.              Standards Track                  [Page 383]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_OP_NOT_IN_SESSION         | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT,               |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE, DELEGPURGE,   |
   |                                   | DELEGRETURN, FREE_STATEID,    |
   |                                   | GETATTR, GETDEVICEINFO,       |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_PERM                      | CREATE, OPEN, SETATTR         |
   | NFS4ERR_PNFS_IO_HOLE              | READ, WRITE                   |
   | NFS4ERR_PNFS_NO_LAYOUT            | READ, WRITE                   |
   | NFS4ERR_RECALLCONFLICT            | LAYOUTGET, WANT_DELEGATION    |
   | NFS4ERR_RECLAIM_BAD               | LAYOUTCOMMIT, LOCK, OPEN,     |
   |                                   | WANT_DELEGATION               |
   | NFS4ERR_RECLAIM_CONFLICT          | LAYOUTCOMMIT, LOCK, OPEN,     |
   |                                   | WANT_DELEGATION               |
   | NFS4ERR_REJECT_DELEG              | CB_PUSH_DELEG                 |














Shepler, et al.              Standards Track                  [Page 384]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_REP_TOO_BIG               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |



















Shepler, et al.              Standards Track                  [Page 385]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_REP_TOO_BIG_TO_CACHE      | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |



















Shepler, et al.              Standards Track                  [Page 386]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_REQ_TOO_BIG               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |



















Shepler, et al.              Standards Track                  [Page 387]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_RETRY_UNCACHED_REP        | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_ROFS                      | CREATE, LINK, LOCK, LOCKT,    |
   |                                   | OPEN, OPENATTR,               |
   |                                   | OPEN_DOWNGRADE, REMOVE,       |
   |                                   | RENAME, SETATTR, WRITE        |
   | NFS4ERR_SAME                      | NVERIFY                       |
   | NFS4ERR_SEQUENCE_POS              | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_SEQ_FALSE_RETRY           | CB_SEQUENCE, SEQUENCE         |
   | NFS4ERR_SEQ_MISORDERED            | CB_SEQUENCE, CREATE_SESSION,  |
   |                                   | SEQUENCE                      |










Shepler, et al.              Standards Track                  [Page 388]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_SERVERFAULT               | ACCESS, BIND_CONN_TO_SESSION, |
   |                                   | CB_GETATTR, CB_NOTIFY,        |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKU, LOOKUP, LOOKUPP,       |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | OPEN_DOWNGRADE, PUTFH,        |
   |                                   | PUTPUBFH, PUTROOTFH, READ,    |
   |                                   | READDIR, READLINK,            |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, TEST_STATEID,        |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_SHARE_DENIED              | OPEN                          |
   | NFS4ERR_STALE                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, RECLAIM_COMPLETE,   |
   |                                   | REMOVE, RENAME, RESTOREFH,    |
   |                                   | SAVEFH, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_STALE_CLIENTID            | CREATE_SESSION,               |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION               |




Shepler, et al.              Standards Track                  [Page 389]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_SYMLINK                   | COMMIT, LAYOUTCOMMIT, LINK,   |
   |                                   | LOCK, LOCKT, LOOKUP, LOOKUPP, |
   |                                   | OPEN, READ, WRITE             |
   | NFS4ERR_TOOSMALL                  | CREATE_SESSION,               |
   |                                   | GETDEVICEINFO, LAYOUTGET,     |
   |                                   | READDIR                       |
   | NFS4ERR_TOO_MANY_OPS              | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   | NFS4ERR_UNKNOWN_LAYOUTTYPE        | CB_LAYOUTRECALL,              |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, NVERIFY,        |
   |                                   | SETATTR, VERIFY               |
   | NFS4ERR_UNSAFE_COMPOUND           | CREATE, OPEN, OPENATTR        |
   | NFS4ERR_WRONGSEC                  | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | RENAME, RESTOREFH             |




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   | NFS4ERR_WRONG_CRED                | CLOSE, CREATE_SESSION,        |
   |                                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION,              |
   |                                   | FREE_STATEID, LAYOUTCOMMIT,   |
   |                                   | LAYOUTRETURN, LOCK, LOCKT,    |
   |                                   | LOCKU, OPEN_DOWNGRADE,        |
   |                                   | RECLAIM_COMPLETE              |
   | NFS4ERR_WRONG_TYPE                | CB_LAYOUTRECALL,              |
   |                                   | CB_PUSH_DELEG, COMMIT,        |
   |                                   | GETATTR, LAYOUTGET,           |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, NVERIFY, OPEN,         |
   |                                   | OPENATTR, READ, READLINK,     |
   |                                   | RECLAIM_COMPLETE, SETATTR,    |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   | NFS4ERR_XDEV                      | LINK, RENAME                  |
   +-----------------------------------+-------------------------------+

                                  Table 8

16.  NFSv4.1 Procedures

   Both procedures, NULL and COMPOUND, MUST be implemented.

16.1.  Procedure 0: NULL - No Operation

16.1.1.  ARGUMENTS

   void;

16.1.2.  RESULTS

   void;

16.1.3.  DESCRIPTION

   This is the standard NULL procedure with the standard void argument
   and void response.  This procedure has no functionality associated
   with it.  Because of this, it is sometimes used to measure the
   overhead of processing a service request.  Therefore, the server
   SHOULD ensure that no unnecessary work is done in servicing this
   procedure.







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16.1.4.  ERRORS

   None.

16.2.  Procedure 1: COMPOUND - Compound Operations

16.2.1.  ARGUMENTS

   enum nfs_opnum4 {
    OP_ACCESS              = 3,
    OP_CLOSE               = 4,
    OP_COMMIT              = 5,
    OP_CREATE              = 6,
    OP_DELEGPURGE          = 7,
    OP_DELEGRETURN         = 8,
    OP_GETATTR             = 9,
    OP_GETFH               = 10,
    OP_LINK                = 11,
    OP_LOCK                = 12,
    OP_LOCKT               = 13,
    OP_LOCKU               = 14,
    OP_LOOKUP              = 15,
    OP_LOOKUPP             = 16,
    OP_NVERIFY             = 17,
    OP_OPEN                = 18,
    OP_OPENATTR            = 19,
    OP_OPEN_CONFIRM        = 20, /* Mandatory not-to-implement */
    OP_OPEN_DOWNGRADE      = 21,
    OP_PUTFH               = 22,
    OP_PUTPUBFH            = 23,
    OP_PUTROOTFH           = 24,
    OP_READ                = 25,
    OP_READDIR             = 26,
    OP_READLINK            = 27,
    OP_REMOVE              = 28,
    OP_RENAME              = 29,
    OP_RENEW               = 30, /* Mandatory not-to-implement */
    OP_RESTOREFH           = 31,
    OP_SAVEFH              = 32,
    OP_SECINFO             = 33,
    OP_SETATTR             = 34,
    OP_SETCLIENTID         = 35, /* Mandatory not-to-implement */
    OP_SETCLIENTID_CONFIRM = 36, /* Mandatory not-to-implement */
    OP_VERIFY              = 37,
    OP_WRITE               = 38,
    OP_RELEASE_LOCKOWNER   = 39, /* Mandatory not-to-implement */

   /* new operations for NFSv4.1 */



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    OP_BACKCHANNEL_CTL     = 40,
    OP_BIND_CONN_TO_SESSION = 41,
    OP_EXCHANGE_ID         = 42,
    OP_CREATE_SESSION      = 43,
    OP_DESTROY_SESSION     = 44,
    OP_FREE_STATEID        = 45,
    OP_GET_DIR_DELEGATION  = 46,
    OP_GETDEVICEINFO       = 47,
    OP_GETDEVICELIST       = 48,
    OP_LAYOUTCOMMIT        = 49,
    OP_LAYOUTGET           = 50,
    OP_LAYOUTRETURN        = 51,
    OP_SECINFO_NO_NAME     = 52,
    OP_SEQUENCE            = 53,
    OP_SET_SSV             = 54,
    OP_TEST_STATEID        = 55,
    OP_WANT_DELEGATION     = 56,
    OP_DESTROY_CLIENTID    = 57,
    OP_RECLAIM_COMPLETE    = 58,
    OP_ILLEGAL             = 10044
   };


   union nfs_argop4 switch (nfs_opnum4 argop) {
    case OP_ACCESS:        ACCESS4args opaccess;
    case OP_CLOSE:         CLOSE4args opclose;
    case OP_COMMIT:        COMMIT4args opcommit;
    case OP_CREATE:        CREATE4args opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
    case OP_GETATTR:       GETATTR4args opgetattr;
    case OP_GETFH:         void;
    case OP_LINK:          LINK4args oplink;
    case OP_LOCK:          LOCK4args oplock;
    case OP_LOCKT:         LOCKT4args oplockt;
    case OP_LOCKU:         LOCKU4args oplocku;
    case OP_LOOKUP:        LOOKUP4args oplookup;
    case OP_LOOKUPP:       void;
    case OP_NVERIFY:       NVERIFY4args opnverify;
    case OP_OPEN:          OPEN4args opopen;
    case OP_OPENATTR:      OPENATTR4args opopenattr;

    /* Not for NFSv4.1 */
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;

    case OP_OPEN_DOWNGRADE:
                           OPEN_DOWNGRADE4args opopen_downgrade;




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    case OP_PUTFH:         PUTFH4args opputfh;
    case OP_PUTPUBFH:      void;
    case OP_PUTROOTFH:     void;
    case OP_READ:          READ4args opread;
    case OP_READDIR:       READDIR4args opreaddir;
    case OP_READLINK:      void;
    case OP_REMOVE:        REMOVE4args opremove;
    case OP_RENAME:        RENAME4args oprename;

    /* Not for NFSv4.1 */
    case OP_RENEW:         RENEW4args oprenew;

    case OP_RESTOREFH:     void;
    case OP_SAVEFH:        void;
    case OP_SECINFO:       SECINFO4args opsecinfo;
    case OP_SETATTR:       SETATTR4args opsetattr;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
                                   opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4args opverify;
    case OP_WRITE:         WRITE4args opwrite;

    /* Not for NFSv4.1 */
    case OP_RELEASE_LOCKOWNER:
                           RELEASE_LOCKOWNER4args
                           oprelease_lockowner;

    /* Operations new to NFSv4.1 */
    case OP_BACKCHANNEL_CTL:
                           BACKCHANNEL_CTL4args opbackchannel_ctl;

    case OP_BIND_CONN_TO_SESSION:
                           BIND_CONN_TO_SESSION4args
                           opbind_conn_to_session;

    case OP_EXCHANGE_ID:   EXCHANGE_ID4args opexchange_id;

    case OP_CREATE_SESSION:
                           CREATE_SESSION4args opcreate_session;

    case OP_DESTROY_SESSION:
                           DESTROY_SESSION4args opdestroy_session;

    case OP_FREE_STATEID:  FREE_STATEID4args opfree_stateid;



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    case OP_GET_DIR_DELEGATION:
                           GET_DIR_DELEGATION4args
                                   opget_dir_delegation;

    case OP_GETDEVICEINFO: GETDEVICEINFO4args opgetdeviceinfo;
    case OP_GETDEVICELIST: GETDEVICELIST4args opgetdevicelist;
    case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4args oplayoutcommit;
    case OP_LAYOUTGET:     LAYOUTGET4args oplayoutget;
    case OP_LAYOUTRETURN:  LAYOUTRETURN4args oplayoutreturn;

    case OP_SECINFO_NO_NAME:
                           SECINFO_NO_NAME4args opsecinfo_no_name;

    case OP_SEQUENCE:      SEQUENCE4args opsequence;
    case OP_SET_SSV:       SET_SSV4args opset_ssv;
    case OP_TEST_STATEID:  TEST_STATEID4args optest_stateid;

    case OP_WANT_DELEGATION:
                           WANT_DELEGATION4args opwant_delegation;

    case OP_DESTROY_CLIENTID:
                           DESTROY_CLIENTID4args
                                   opdestroy_clientid;

    case OP_RECLAIM_COMPLETE:
                           RECLAIM_COMPLETE4args
                                   opreclaim_complete;

    /* Operations not new to NFSv4.1 */
    case OP_ILLEGAL:       void;
   };


   struct COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           nfs_argop4      argarray<>;
   };

16.2.2.  RESULTS

   union nfs_resop4 switch (nfs_opnum4 resop) {
    case OP_ACCESS:        ACCESS4res opaccess;
    case OP_CLOSE:         CLOSE4res opclose;
    case OP_COMMIT:        COMMIT4res opcommit;
    case OP_CREATE:        CREATE4res opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;



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    case OP_GETATTR:       GETATTR4res opgetattr;
    case OP_GETFH:         GETFH4res opgetfh;
    case OP_LINK:          LINK4res oplink;
    case OP_LOCK:          LOCK4res oplock;
    case OP_LOCKT:         LOCKT4res oplockt;
    case OP_LOCKU:         LOCKU4res oplocku;
    case OP_LOOKUP:        LOOKUP4res oplookup;
    case OP_LOOKUPP:       LOOKUPP4res oplookupp;
    case OP_NVERIFY:       NVERIFY4res opnverify;
    case OP_OPEN:          OPEN4res opopen;
    case OP_OPENATTR:      OPENATTR4res opopenattr;
    /* Not for NFSv4.1 */
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;

    case OP_OPEN_DOWNGRADE:
                           OPEN_DOWNGRADE4res
                                   opopen_downgrade;

    case OP_PUTFH:         PUTFH4res opputfh;
    case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
    case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
    case OP_READ:          READ4res opread;
    case OP_READDIR:       READDIR4res opreaddir;
    case OP_READLINK:      READLINK4res opreadlink;
    case OP_REMOVE:        REMOVE4res opremove;
    case OP_RENAME:        RENAME4res oprename;
    /* Not for NFSv4.1 */
    case OP_RENEW:         RENEW4res oprenew;
    case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
    case OP_SAVEFH:        SAVEFH4res opsavefh;
    case OP_SECINFO:       SECINFO4res opsecinfo;
    case OP_SETATTR:       SETATTR4res opsetattr;
    /* Not for NFSv4.1 */
    case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID_CONFIRM:
                           SETCLIENTID_CONFIRM4res
                                   opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4res opverify;
    case OP_WRITE:         WRITE4res opwrite;

    /* Not for NFSv4.1 */
    case OP_RELEASE_LOCKOWNER:
                           RELEASE_LOCKOWNER4res
                                   oprelease_lockowner;

    /* Operations new to NFSv4.1 */



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    case OP_BACKCHANNEL_CTL:
                           BACKCHANNEL_CTL4res
                                   opbackchannel_ctl;

    case OP_BIND_CONN_TO_SESSION:
                           BIND_CONN_TO_SESSION4res
                                    opbind_conn_to_session;

    case OP_EXCHANGE_ID:   EXCHANGE_ID4res opexchange_id;

    case OP_CREATE_SESSION:
                           CREATE_SESSION4res
                                   opcreate_session;

    case OP_DESTROY_SESSION:
                           DESTROY_SESSION4res
                                   opdestroy_session;

    case OP_FREE_STATEID:  FREE_STATEID4res
                                   opfree_stateid;

    case OP_GET_DIR_DELEGATION:
                           GET_DIR_DELEGATION4res
                                   opget_dir_delegation;

    case OP_GETDEVICEINFO: GETDEVICEINFO4res
                                   opgetdeviceinfo;

    case OP_GETDEVICELIST: GETDEVICELIST4res
                                   opgetdevicelist;

    case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4res oplayoutcommit;
    case OP_LAYOUTGET:     LAYOUTGET4res oplayoutget;
    case OP_LAYOUTRETURN:  LAYOUTRETURN4res oplayoutreturn;

    case OP_SECINFO_NO_NAME:
                           SECINFO_NO_NAME4res
                                   opsecinfo_no_name;

    case OP_SEQUENCE:      SEQUENCE4res opsequence;
    case OP_SET_SSV:       SET_SSV4res opset_ssv;
    case OP_TEST_STATEID:  TEST_STATEID4res optest_stateid;

    case OP_WANT_DELEGATION:
                           WANT_DELEGATION4res
                                   opwant_delegation;

    case OP_DESTROY_CLIENTID:



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                           DESTROY_CLIENTID4res
                                   opdestroy_clientid;

    case OP_RECLAIM_COMPLETE:
                           RECLAIM_COMPLETE4res
                                   opreclaim_complete;

    /* Operations not new to NFSv4.1 */
    case OP_ILLEGAL:       ILLEGAL4res opillegal;
   };


   struct COMPOUND4res {
           nfsstat4        status;
           utf8str_cs      tag;
           nfs_resop4      resarray<>;
   };

16.2.3.  DESCRIPTION

   The COMPOUND procedure is used to combine one or more NFSv4
   operations into a single RPC request.  The server interprets each of
   the operations in turn.  If an operation is executed by the server
   and the status of that operation is NFS4_OK, then the next operation
   in the COMPOUND procedure is executed.  The server continues this
   process until there are no more operations to be executed or until
   one of the operations has a status value other than NFS4_OK.

   In the processing of the COMPOUND procedure, the server may find that
   it does not have the available resources to execute any or all of the
   operations within the COMPOUND sequence.  See Section 2.10.6.4 for a
   more detailed discussion.

   The server will generally choose between two methods of decoding the
   client's request.  The first would be the traditional one-pass XDR
   decode.  If there is an XDR decoding error in this case, the RPC XDR
   decode error would be returned.  The second method would be to make
   an initial pass to decode the basic COMPOUND request and then to XDR
   decode the individual operations; the most interesting is the decode
   of attributes.  In this case, the server may encounter an XDR decode
   error during the second pass.  If it does, the server would return
   the error NFS4ERR_BADXDR to signify the decode error.

   The COMPOUND arguments contain a "minorversion" field.  For NFSv4.1,
   the value for this field is 1.  If the server receives a COMPOUND
   procedure with a minorversion field value that it does not support,
   the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH and a
   zero-length resultdata array.



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   Contained within the COMPOUND results is a "status" field.  If the
   results array length is non-zero, this status must be equivalent to
   the status of the last operation that was executed within the
   COMPOUND procedure.  Therefore, if an operation incurred an error
   then the "status" value will be the same error value as is being
   returned for the operation that failed.

   Note that operations zero and one are not defined for the COMPOUND
   procedure.  Operation 2 is not defined and is reserved for future
   definition and use with minor versioning.  If the server receives an
   operation array that contains operation 2 and the minorversion field
   has a value of zero, an error of NFS4ERR_OP_ILLEGAL, as described in
   the next paragraph, is returned to the client.  If an operation array
   contains an operation 2 and the minorversion field is non-zero and
   the server does not support the minor version, the server returns an
   error of NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
   NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
   errors.

   It is possible that the server receives a request that contains an
   operation that is less than the first legal operation (OP_ACCESS) or
   greater than the last legal operation (OP_RELEASE_LOCKOWNER).  In
   this case, the server's response will encode the opcode OP_ILLEGAL
   rather than the illegal opcode of the request.  The status field in
   the ILLEGAL return results will be set to NFS4ERR_OP_ILLEGAL.  The
   COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.

   The definition of the "tag" in the request is left to the
   implementor.  It may be used to summarize the content of the Compound
   request for the benefit of packet-sniffers and engineers debugging
   implementations.  However, the value of "tag" in the response SHOULD
   be the same value as provided in the request.  This applies to the
   tag field of the CB_COMPOUND procedure as well.

16.2.3.1.  Current Filehandle and Stateid

   The COMPOUND procedure offers a simple environment for the execution
   of the operations specified by the client.  The first two relate to
   the filehandle while the second two relate to the current stateid.

16.2.3.1.1.  Current Filehandle

   The current and saved filehandles are used throughout the protocol.
   Most operations implicitly use the current filehandle as an argument,
   and many set the current filehandle as part of the results.  The
   combination of client-specified sequences of operations and current
   and saved filehandle arguments and results allows for greater
   protocol flexibility.  The best or easiest example of current



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   filehandle usage is a sequence like the following:


         PUTFH fh1              {fh1}
         LOOKUP "compA"         {fh2}
         GETATTR                {fh2}
         LOOKUP "compB"         {fh3}
         GETATTR                {fh3}
         LOOKUP "compC"         {fh4}
         GETATTR                {fh4}
         GETFH

                                 Figure 2

   In this example, the PUTFH (Section 18.19) operation explicitly sets
   the current filehandle value while the result of each LOOKUP
   operation sets the current filehandle value to the resultant file
   system object.  Also, the client is able to insert GETATTR operations
   using the current filehandle as an argument.

   The PUTROOTFH (Section 18.21) and PUTPUBFH (Section 18.20) operations
   also set the current filehandle.  The above example would replace
   "PUTFH fh1" with PUTROOTFH or PUTPUBFH with no filehandle argument in
   order to achieve the same effect (on the assumption that "compA" is
   directly below the root of the namespace).

   Along with the current filehandle, there is a saved filehandle.
   While the current filehandle is set as the result of operations like
   LOOKUP, the saved filehandle must be set directly with the use of the
   SAVEFH operation.  The SAVEFH operation copies the current filehandle
   value to the saved value.  The saved filehandle value is used in
   combination with the current filehandle value for the LINK and RENAME
   operations.  The RESTOREFH operation will copy the saved filehandle
   value to the current filehandle value; as a result, the saved
   filehandle value may be used a sort of "scratch" area for the
   client's series of operations.

16.2.3.1.2.  Current Stateid

   With NFSv4.1, additions of a current stateid and a saved stateid have
   been made to the COMPOUND processing environment; this allows for the
   passing of stateids between operations.  There are no changes to the
   syntax of the protocol, only changes to the semantics of a few
   operations.

   A "current stateid" is the stateid that is associated with the
   current filehandle.  The current stateid may only be changed by an
   operation that modifies the current filehandle or returns a stateid.



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   If an operation returns a stateid, it MUST set the current stateid to
   the returned value.  If an operation sets the current filehandle but
   does not return a stateid, the current stateid MUST be set to the
   all-zeros special stateid, i.e., (seqid, other) = (0, 0).  If an
   operation uses a stateid as an argument but does not return a
   stateid, the current stateid MUST NOT be changed.  For example,
   PUTFH, PUTROOTFH, and PUTPUBFH will change the current server state
   from {ocfh, (osid)} to {cfh, (0, 0)}, while LOCK will change the
   current state from {cfh, (osid} to {cfh, (nsid)}.  Operations like
   LOOKUP that transform a current filehandle and component name into a
   new current filehandle will also change the current state to {0, 0}.
   The SAVEFH and RESTOREFH operations will save and restore both the
   current filehandle and the current stateid as a set.

   The following example is the common case of a simple READ operation
   with a normal stateid showing that the PUTFH initializes the current
   stateid to (0, 0).  The subsequent READ with stateid (sid1) leaves
   the current stateid unchanged.

       PUTFH fh1                             - -> {fh1, (0, 0)}
       READ (sid1), 0, 1024      {fh1, (0, 0)} -> {fh1, (0, 0)}

                                 Figure 3

   This next example performs an OPEN with the root filehandle and, as a
   result, generates stateid (sid1).  The next operation specifies the
   READ with the argument stateid set such that (seqid, other) are equal
   to (1, 0), but the current stateid set by the previous operation is
   actually used when the operation is evaluated.  This allows correct
   interaction with any existing, potentially conflicting, locks.

       PUTROOTFH                             - -> {fh1, (0, 0)}
       OPEN "compA"              {fh1, (0, 0)} -> {fh2, (sid1)}
       READ (1, 0), 0, 1024      {fh2, (sid1)} -> {fh2, (sid1)}
       CLOSE (1, 0)              {fh2, (sid1)} -> {fh2, (sid2)}

                                 Figure 4

   This next example is similar to the second in how it passes the
   stateid sid2 generated by the LOCK operation to the next READ
   operation.  This allows the client to explicitly surround a single
   I/O operation with a lock and its appropriate stateid to guarantee
   correctness with other client locks.  The example also shows how
   SAVEFH and RESTOREFH can save and later reuse a filehandle and
   stateid, passing them as the current filehandle and stateid to a READ
   operation.





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       PUTFH fh1                             - -> {fh1, (0, 0)}
       LOCK 0, 1024, (sid1)      {fh1, (sid1)} -> {fh1, (sid2)}
       READ (1, 0), 0, 1024      {fh1, (sid2)} -> {fh1, (sid2)}
       LOCKU 0, 1024, (1, 0)     {fh1, (sid2)} -> {fh1, (sid3)}
       SAVEFH                    {fh1, (sid3)} -> {fh1, (sid3)}

       PUTFH fh2                 {fh1, (sid3)} -> {fh2, (0, 0)}
       WRITE (1, 0), 0, 1024     {fh2, (0, 0)} -> {fh2, (0, 0)}

       RESTOREFH                 {fh2, (0, 0)} -> {fh1, (sid3)}
       READ (1, 0), 1024, 1024   {fh1, (sid3)} -> {fh1, (sid3)}

                                 Figure 5

   The final example shows a disallowed use of the current stateid.  The
   client is attempting to implicitly pass an anonymous special stateid,
   (0,0), to the READ operation.  The server MUST return
   NFS4ERR_BAD_STATEID in the reply to the READ operation.

       PUTFH fh1                             - -> {fh1, (0, 0)}
       READ (1, 0), 0, 1024      {fh1, (0, 0)} -> NFS4ERR_BAD_STATEID

                                 Figure 6

16.2.4.  ERRORS

   COMPOUND will of course return every error that each operation on the
   fore channel can return (see Table 6).  However, if COMPOUND returns
   zero operations, obviously the error returned by COMPOUND has nothing
   to do with an error returned by an operation.  The list of errors
   COMPOUND will return if it processes zero operations include:




















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                          COMPOUND Error Returns

   +------------------------------+------------------------------------+
   | Error                        | Notes                              |
   +------------------------------+------------------------------------+
   | NFS4ERR_BADCHAR              | The tag argument has a character   |
   |                              | the replier does not support.      |
   | NFS4ERR_BADXDR               |                                    |
   | NFS4ERR_DELAY                |                                    |
   | NFS4ERR_INVAL                | The tag argument is not in UTF-8   |
   |                              | encoding.                          |
   | NFS4ERR_MINOR_VERS_MISMATCH  |                                    |
   | NFS4ERR_SERVERFAULT          |                                    |
   | NFS4ERR_TOO_MANY_OPS         |                                    |
   | NFS4ERR_REP_TOO_BIG          |                                    |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE |                                    |
   | NFS4ERR_REQ_TOO_BIG          |                                    |
   +------------------------------+------------------------------------+

                                  Table 9

17.  Operations: REQUIRED, RECOMMENDED, or OPTIONAL

   The following tables summarize the operations of the NFSv4.1 protocol
   and the corresponding designation of REQUIRED, RECOMMENDED, and
   OPTIONAL to implement or MUST NOT implement.  The designation of MUST
   NOT implement is reserved for those operations that were defined in
   NFSv4.0 and MUST NOT be implemented in NFSv4.1.

   For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
   for operations sent by the client is for the server implementation.
   The client is generally required to implement the operations needed
   for the operating environment for which it serves.  For example, a
   read-only NFSv4.1 client would have no need to implement the WRITE
   operation and is not required to do so.

   The REQUIRED or OPTIONAL designation for callback operations sent by
   the server is for both the client and server.  Generally, the client
   has the option of creating the backchannel and sending the operations
   on the fore channel that will be a catalyst for the server sending
   callback operations.  A partial exception is CB_RECALL_SLOT; the only
   way the client can avoid supporting this operation is by not creating
   a backchannel.

   Since this is a summary of the operations and their designation,
   there are subtleties that are not presented here.  Therefore, if
   there is a question of the requirements of implementation, the
   operation descriptions themselves must be consulted along with other



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   relevant explanatory text within this specification.

   The abbreviations used in the second and third columns of the table
   are defined as follows.

   REQ  REQUIRED to implement

   REC  RECOMMEND to implement

   OPT  OPTIONAL to implement

   MNI  MUST NOT implement

   For the NFSv4.1 features that are OPTIONAL, the operations that
   support those features are OPTIONAL, and the server would return
   NFS4ERR_NOTSUPP in response to the client's use of those operations.
   If an OPTIONAL feature is supported, it is possible that a set of
   operations related to the feature become REQUIRED to implement.  The
   third column of the table designates the feature(s) and if the
   operation is REQUIRED or OPTIONAL in the presence of support for the
   feature.

   The OPTIONAL features identified and their abbreviations are as
   follows:

   pNFS  Parallel NFS

   FDELG  File Delegations

   DDELG  Directory Delegations

                                Operations

   +----------------------+------------+--------------+----------------+
   | Operation            | REQ, REC,  | Feature      | Definition     |
   |                      | OPT, or    | (REQ, REC,   |                |
   |                      | MNI        | or OPT)      |                |
   +----------------------+------------+--------------+----------------+
   | ACCESS               | REQ        |              | Section 18.1   |
   | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
   | BIND_CONN_TO_SESSION | REQ        |              | Section 18.34  |
   | CLOSE                | REQ        |              | Section 18.2   |
   | COMMIT               | REQ        |              | Section 18.3   |
   | CREATE               | REQ        |              | Section 18.4   |
   | CREATE_SESSION       | REQ        |              | Section 18.36  |
   | DELEGPURGE           | OPT        | FDELG (REQ)  | Section 18.5   |





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   | DELEGRETURN          | OPT        | FDELG,       | Section 18.6   |
   |                      |            | DDELG, pNFS  |                |
   |                      |            | (REQ)        |                |
   | DESTROY_CLIENTID     | REQ        |              | Section 18.50  |
   | DESTROY_SESSION      | REQ        |              | Section 18.37  |
   | EXCHANGE_ID          | REQ        |              | Section 18.35  |
   | FREE_STATEID         | REQ        |              | Section 18.38  |
   | GETATTR              | REQ        |              | Section 18.7   |
   | GETDEVICEINFO        | OPT        | pNFS (REQ)   | Section 18.40  |
   | GETDEVICELIST        | OPT        | pNFS (OPT)   | Section 18.41  |
   | GETFH                | REQ        |              | Section 18.8   |
   | GET_DIR_DELEGATION   | OPT        | DDELG (REQ)  | Section 18.39  |
   | LAYOUTCOMMIT         | OPT        | pNFS (REQ)   | Section 18.42  |
   | LAYOUTGET            | OPT        | pNFS (REQ)   | Section 18.43  |
   | LAYOUTRETURN         | OPT        | pNFS (REQ)   | Section 18.44  |
   | LINK                 | OPT        |              | Section 18.9   |
   | LOCK                 | REQ        |              | Section 18.10  |
   | LOCKT                | REQ        |              | Section 18.11  |
   | LOCKU                | REQ        |              | Section 18.12  |
   | LOOKUP               | REQ        |              | Section 18.13  |
   | LOOKUPP              | REQ        |              | Section 18.14  |
   | NVERIFY              | REQ        |              | Section 18.15  |
   | OPEN                 | REQ        |              | Section 18.16  |
   | OPENATTR             | OPT        |              | Section 18.17  |
   | OPEN_CONFIRM         | MNI        |              | N/A            |
   | OPEN_DOWNGRADE       | REQ        |              | Section 18.18  |
   | PUTFH                | REQ        |              | Section 18.19  |
   | PUTPUBFH             | REQ        |              | Section 18.20  |
   | PUTROOTFH            | REQ        |              | Section 18.21  |
   | READ                 | REQ        |              | Section 18.22  |
   | READDIR              | REQ        |              | Section 18.23  |
   | READLINK             | OPT        |              | Section 18.24  |
   | RECLAIM_COMPLETE     | REQ        |              | Section 18.51  |
   | RELEASE_LOCKOWNER    | MNI        |              | N/A            |
   | REMOVE               | REQ        |              | Section 18.25  |
   | RENAME               | REQ        |              | Section 18.26  |
   | RENEW                | MNI        |              | N/A            |
   | RESTOREFH            | REQ        |              | Section 18.27  |
   | SAVEFH               | REQ        |              | Section 18.28  |
   | SECINFO              | REQ        |              | Section 18.29  |
   | SECINFO_NO_NAME      | REC        | pNFS file    | Section 18.45, |
   |                      |            | layout (REQ) | Section 13.12  |
   | SEQUENCE             | REQ        |              | Section 18.46  |
   | SETATTR              | REQ        |              | Section 18.30  |
   | SETCLIENTID          | MNI        |              | N/A            |
   | SETCLIENTID_CONFIRM  | MNI        |              | N/A            |
   | SET_SSV              | REQ        |              | Section 18.47  |
   | TEST_STATEID         | REQ        |              | Section 18.48  |



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   | VERIFY               | REQ        |              | Section 18.31  |
   | WANT_DELEGATION      | OPT        | FDELG (OPT)  | Section 18.49  |
   | WRITE                | REQ        |              | Section 18.32  |
   +----------------------+------------+--------------+----------------+

                            Callback Operations

   +-------------------------+-----------+-------------+---------------+
   | Operation               | REQ, REC, | Feature     | Definition    |
   |                         | OPT, or   | (REQ, REC,  |               |
   |                         | MNI       | or OPT)     |               |
   +-------------------------+-----------+-------------+---------------+
   | CB_GETATTR              | OPT       | FDELG (REQ) | Section 20.1  |
   | CB_LAYOUTRECALL         | OPT       | pNFS (REQ)  | Section 20.3  |
   | CB_NOTIFY               | OPT       | DDELG (REQ) | Section 20.4  |
   | CB_NOTIFY_DEVICEID      | OPT       | pNFS (OPT)  | Section 20.12 |
   | CB_NOTIFY_LOCK          | OPT       |             | Section 20.11 |
   | CB_PUSH_DELEG           | OPT       | FDELG (OPT) | Section 20.5  |
   | CB_RECALL               | OPT       | FDELG,      | Section 20.2  |
   |                         |           | DDELG, pNFS |               |
   |                         |           | (REQ)       |               |
   | CB_RECALL_ANY           | OPT       | FDELG,      | Section 20.6  |
   |                         |           | DDELG, pNFS |               |
   |                         |           | (REQ)       |               |
   | CB_RECALL_SLOT          | REQ       |             | Section 20.8  |
   | CB_RECALLABLE_OBJ_AVAIL | OPT       | DDELG, pNFS | Section 20.7  |
   |                         |           | (REQ)       |               |
   | CB_SEQUENCE             | OPT       | FDELG,      | Section 20.9  |
   |                         |           | DDELG, pNFS |               |
   |                         |           | (REQ)       |               |
   | CB_WANTS_CANCELLED      | OPT       | FDELG,      | Section 20.10 |
   |                         |           | DDELG, pNFS |               |
   |                         |           | (REQ)       |               |
   +-------------------------+-----------+-------------+---------------+

18.  NFSv4.1 Operations

18.1.  Operation 3: ACCESS - Check Access Rights













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18.1.1.  ARGUMENTS


   const ACCESS4_READ      = 0x00000001;
   const ACCESS4_LOOKUP    = 0x00000002;
   const ACCESS4_MODIFY    = 0x00000004;
   const ACCESS4_EXTEND    = 0x00000008;
   const ACCESS4_DELETE    = 0x00000010;
   const ACCESS4_EXECUTE   = 0x00000020;

   struct ACCESS4args {
           /* CURRENT_FH: object */
           uint32_t        access;
   };


18.1.2.  RESULTS

   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };

   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };


18.1.3.  DESCRIPTION

   ACCESS determines the access rights that a user, as identified by the
   credentials in the RPC request, has with respect to the file system
   object specified by the current filehandle.  The client encodes the
   set of access rights that are to be checked in the bit mask "access".
   The server checks the permissions encoded in the bit mask.  If a
   status of NFS4_OK is returned, two bit masks are included in the
   response.  The first, "supported", represents the access rights for
   which the server can verify reliably.  The second, "access",
   represents the access rights available to the user for the filehandle
   provided.  On success, the current filehandle retains its value.

   Note that the reply's supported and access fields MUST NOT contain
   more values than originally set in the request's access field.  For
   example, if the client sends an ACCESS operation with just the
   ACCESS4_READ value set and the server supports this value, the server



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   MUST NOT set more than ACCESS4_READ in the supported field even if it
   could have reliably checked other values.

   The reply's access field MUST NOT contain more values than the
   supported field.

   The results of this operation are necessarily advisory in nature.  A
   return status of NFS4_OK and the appropriate bit set in the bit mask
   do not imply that such access will be allowed to the file system
   object in the future.  This is because access rights can be revoked
   by the server at any time.

   The following access permissions may be requested:

   ACCESS4_READ  Read data from file or read a directory.

   ACCESS4_LOOKUP  Look up a name in a directory (no meaning for non-
      directory objects).

   ACCESS4_MODIFY  Rewrite existing file data or modify existing
      directory entries.

   ACCESS4_EXTEND  Write new data or add directory entries.

   ACCESS4_DELETE  Delete an existing directory entry.

   ACCESS4_EXECUTE  Execute a regular file (no meaning for a directory).

   On success, the current filehandle retains its value.

   ACCESS4_EXECUTE is a challenging semantic to implement because NFS
   provides remote file access, not remote execution.  This leads to the
   following:

   o  Whether or not a regular file is executable ought to be the
      responsibility of the NFS client and not the server.  And yet the
      ACCESS operation is specified to seemingly require a server to own
      that responsibility.

   o  When a client executes a regular file, it has to read the file
      from the server.  Strictly speaking, the server should not allow
      the client to read a file being executed unless the user has read
      permissions on the file.  Requiring explicit read permissions on
      executable files in order to access them over NFS is not going to
      be acceptable to some users and storage administrators.
      Historically, NFS servers have allowed a user to READ a file if
      the user has execute access to the file.




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   As a practical example, the UNIX specification [52] states that an
   implementation claiming conformance to UNIX may indicate in the
   access() programming interface's result that a privileged user has
   execute rights, even if no execute permission bits are set on the
   regular file's attributes.  It is possible to claim conformance to
   the UNIX specification and instead not indicate execute rights in
   that situation, which is true for some operating environments.
   Suppose the operating environments of the client and server are
   implementing the access() semantics for privileged users differently,
   and the ACCESS operation implementations of the client and server
   follow their respective access() semantics.  This can cause undesired
   behavior:

   o  Suppose the client's access() interface returns X_OK if the user
      is privileged and no execute permission bits are set on the
      regular file's attribute, and the server's access() interface does
      not return X_OK in that situation.  Then the client will be unable
      to execute files stored on the NFS server that could be executed
      if stored on a non-NFS file system.

   o  Suppose the client's access() interface does not return X_OK if
      the user is privileged, and no execute permission bits are set on
      the regular file's attribute, and the server's access() interface
      does return X_OK in that situation.  Then:

      *  The client will be able to execute files stored on the NFS
         server that could be executed if stored on a non-NFS file
         system, unless the client's execution subsystem also checks for
         execute permission bits.

      *  Even if the execution subsystem is checking for execute
         permission bits, there are more potential issues.  For example,
         suppose the client is invoking access() to build a "path search
         table" of all executable files in the user's "search path",
         where the path is a list of directories each containing
         executable files.  Suppose there are two files each in separate
         directories of the search path, such that files have the same
         component name.  In the first directory the file has no execute
         permission bits set, and in the second directory the file has
         execute bits set.  The path search table will indicate that the
         first directory has the executable file, but the execute
         subsystem will fail to execute it.  The command shell might
         fail to try the second file in the second directory.  And even
         if it did, this is a potential performance issue.  Clearly, the
         desired outcome for the client is for the path search table to
         not contain the first file.

   To deal with the problems described above, the "smart client, stupid



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   server" principle is used.  The client owns overall responsibility
   for determining execute access and relies on the server to parse the
   execution permissions within the file's mode, acl, and dacl
   attributes.  The rules for the client and server follow:

   o  If the client is sending ACCESS in order to determine if the user
      can read the file, the client SHOULD set ACCESS4_READ in the
      request's access field.

   o  If the client's operating environment only grants execution to the
      user if the user has execute access according to the execute
      permissions in the mode, acl, and dacl attributes, then if the
      client wants to determine execute access, the client SHOULD send
      an ACCESS request with ACCESS4_EXECUTE bit set in the request's
      access field.

   o  If the client's operating environment grants execution to the user
      even if the user does not have execute access according to the
      execute permissions in the mode, acl, and dacl attributes, then if
      the client wants to determine execute access, it SHOULD send an
      ACCESS request with both the ACCESS4_EXECUTE and ACCESS4_READ bits
      set in the request's access field.  This way, if any read or
      execute permission grants the user read or execute access (or if
      the server interprets the user as privileged), as indicated by the
      presence of ACCESS4_EXECUTE and/or ACCESS4_READ in the reply's
      access field, the client will be able to grant the user execute
      access to the file.

   o  If the server supports execute permission bits, or some other
      method for denoting executability (e.g., the suffix of the name of
      the file might indicate execute), it MUST check only execute
      permissions, not read permissions, when determining whether or not
      the reply will have ACCESS4_EXECUTE set in the access field.  The
      server MUST NOT also examine read permission bits when determining
      whether or not the reply will have ACCESS4_EXECUTE set in the
      access field.  Even if the server's operating environment would
      grant execute access to the user (e.g., the user is privileged),
      the server MUST NOT reply with ACCESS4_EXECUTE set in reply's
      access field unless there is at least one execute permission bit
      set in the mode, acl, or dacl attributes.  In the case of acl and
      dacl, the "one execute permission bit" MUST be an ACE4_EXECUTE bit
      set in an ALLOW ACE.

   o  If the server does not support execute permission bits or some
      other method for denoting executability, it MUST NOT set
      ACCESS4_EXECUTE in the reply's supported and access fields.  If
      the client set ACCESS4_EXECUTE in the ACCESS request's access
      field, and ACCESS4_EXECUTE is not set in the reply's supported



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      field, then the client will have to send an ACCESS request with
      the ACCESS4_READ bit set in the request's access field.

   o  If the server supports read permission bits, it MUST only check
      for read permissions in the mode, acl, and dacl attributes when it
      receives an ACCESS request with ACCESS4_READ set in the access
      field.  The server MUST NOT also examine execute permission bits
      when determining whether the reply will have ACCESS4_READ set in
      the access field or not.

   Note that if the ACCESS reply has ACCESS4_READ or ACCESS_EXECUTE set,
   then the user also has permissions to OPEN (Section 18.16) or READ
   (Section 18.22) the file.  In other words, if the client sends an
   ACCESS request with the ACCESS4_READ and ACCESS_EXECUTE set in the
   access field (or two separate requests, one with ACCESS4_READ set and
   the other with ACCESS4_EXECUTE set), and the reply has just
   ACCESS4_EXECUTE set in the access field (or just one reply has
   ACCESS4_EXECUTE set), then the user has authorization to OPEN or READ
   the file.

18.1.4.  IMPLEMENTATION

   In general, it is not sufficient for the client to attempt to deduce
   access permissions by inspecting the uid, gid, and mode fields in the
   file attributes or by attempting to interpret the contents of the ACL
   attribute.  This is because the server may perform uid or gid mapping
   or enforce additional access-control restrictions.  It is also
   possible that the server may not be in the same ID space as the
   client.  In these cases (and perhaps others), the client cannot
   reliably perform an access check with only current file attributes.

   In the NFSv2 protocol, the only reliable way to determine whether an
   operation was allowed was to try it and see if it succeeded or
   failed.  Using the ACCESS operation in the NFSv4.1 protocol, the
   client can ask the server to indicate whether or not one or more
   classes of operations are permitted.  The ACCESS operation is
   provided to allow clients to check before doing a series of
   operations that will result in an access failure.  The OPEN operation
   provides a point where the server can verify access to the file
   object and a method to return that information to the client.  The
   ACCESS operation is still useful for directory operations or for use
   in the case that the UNIX interface access() is used on the client.

   The information returned by the server in response to an ACCESS call
   is not permanent.  It was correct at the exact time that the server
   performed the checks, but not necessarily afterwards.  The server can
   revoke access permission at any time.




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   The client should use the effective credentials of the user to build
   the authentication information in the ACCESS request used to
   determine access rights.  It is the effective user and group
   credentials that are used in subsequent READ and WRITE operations.

   Many implementations do not directly support the ACCESS4_DELETE
   permission.  Operating systems like UNIX will ignore the
   ACCESS4_DELETE bit if set on an access request on a non-directory
   object.  In these systems, delete permission on a file is determined
   by the access permissions on the directory in which the file resides,
   instead of being determined by the permissions of the file itself.
   Therefore, the mask returned enumerating which access rights can be
   determined will have the ACCESS4_DELETE value set to 0.  This
   indicates to the client that the server was unable to check that
   particular access right.  The ACCESS4_DELETE bit in the access mask
   returned will then be ignored by the client.

18.2.  Operation 4: CLOSE - Close File

18.2.1.  ARGUMENTS

   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid;
           stateid4        open_stateid;
   };


18.2.2.  RESULTS

   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:
            stateid4       open_stateid;
    default:
            void;
   };


18.2.3.  DESCRIPTION

   The CLOSE operation releases share reservations for the regular or
   named attribute file as specified by the current filehandle.  The
   share reservations and other state information released at the server
   as a result of this CLOSE are only those associated with the supplied
   stateid.  State associated with other OPENs is not affected.

   If byte-range locks are held, the client SHOULD release all locks
   before sending a CLOSE.  The server MAY free all outstanding locks on



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   CLOSE, but some servers may not support the CLOSE of a file that
   still has byte-range locks held.  The server MUST return failure if
   any locks would exist after the CLOSE.

   The argument seqid MAY have any value, and the server MUST ignore
   seqid.

   On success, the current filehandle retains its value.

   The server MAY require that the combination of principal, security
   flavor, and, if applicable, GSS mechanism that sent the OPEN request
   also be the one to CLOSE the file.  This might not be possible if
   credentials for the principal are no longer available.  The server
   MAY allow the machine credential or SSV credential (see
   Section 18.35) to send CLOSE.

18.2.4.  IMPLEMENTATION

   Even though CLOSE returns a stateid, this stateid is not useful to
   the client and should be treated as deprecated.  CLOSE "shuts down"
   the state associated with all OPENs for the file by a single open-
   owner.  As noted above, CLOSE will either release all file-locking
   state or return an error.  Therefore, the stateid returned by CLOSE
   is not useful for operations that follow.  To help find any uses of
   this stateid by clients, the server SHOULD return the invalid special
   stateid (the "other" value is zero and the "seqid" field is
   NFS4_UINT32_MAX, see Section 8.2.3).

   A CLOSE operation may make delegations grantable where they were not
   previously.  Servers may choose to respond immediately if there are
   pending delegation want requests or may respond to the situation at a
   later time.

18.3.  Operation 5: COMMIT - Commit Cached Data

18.3.1.  ARGUMENTS

   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };









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18.3.2.  RESULTS

   struct COMMIT4resok {
           verifier4       writeverf;
   };

   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };


18.3.3.  DESCRIPTION

   The COMMIT operation forces or flushes uncommitted, modified data to
   stable storage for the file specified by the current filehandle.  The
   flushed data is that which was previously written with one or more
   WRITE operations that had the "committed" field of their results
   field set to UNSTABLE4.

   The offset specifies the position within the file where the flush is
   to begin.  An offset value of zero means to flush data starting at
   the beginning of the file.  The count specifies the number of bytes
   of data to flush.  If the count is zero, a flush from the offset to
   the end of the file is done.

   The server returns a write verifier upon successful completion of the
   COMMIT.  The write verifier is used by the client to determine if the
   server has restarted between the initial WRITE operations and the
   COMMIT.  The client does this by comparing the write verifier
   returned from the initial WRITE operations and the verifier returned
   by the COMMIT operation.  The server must vary the value of the write
   verifier at each server event or instantiation that may lead to a
   loss of uncommitted data.  Most commonly this occurs when the server
   is restarted; however, other events at the server may result in
   uncommitted data loss as well.

   On success, the current filehandle retains its value.

18.3.4.  IMPLEMENTATION

   The COMMIT operation is similar in operation and semantics to the
   POSIX fsync() [25] system interface that synchronizes a file's state
   with the disk (file data and metadata is flushed to disk or stable
   storage).  COMMIT performs the same operation for a client, flushing
   any unsynchronized data and metadata on the server to the server's



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   disk or stable storage for the specified file.  Like fsync(), it may
   be that there is some modified data or no modified data to
   synchronize.  The data may have been synchronized by the server's
   normal periodic buffer synchronization activity.  COMMIT should
   return NFS4_OK, unless there has been an unexpected error.

   COMMIT differs from fsync() in that it is possible for the client to
   flush a range of the file (most likely triggered by a buffer-
   reclamation scheme on the client before the file has been completely
   written).

   The server implementation of COMMIT is reasonably simple.  If the
   server receives a full file COMMIT request, that is, starting at
   offset zero and count zero, it should do the equivalent of applying
   fsync() to the entire file.  Otherwise, it should arrange to have the
   modified data in the range specified by offset and count to be
   flushed to stable storage.  In both cases, any metadata associated
   with the file must be flushed to stable storage before returning.  It
   is not an error for there to be nothing to flush on the server.  This
   means that the data and metadata that needed to be flushed have
   already been flushed or lost during the last server failure.

   The client implementation of COMMIT is a little more complex.  There
   are two reasons for wanting to commit a client buffer to stable
   storage.  The first is that the client wants to reuse a buffer.  In
   this case, the offset and count of the buffer are sent to the server
   in the COMMIT request.  The server then flushes any modified data
   based on the offset and count, and flushes any modified metadata
   associated with the file.  It then returns the status of the flush
   and the write verifier.  The second reason for the client to generate
   a COMMIT is for a full file flush, such as may be done at close.  In
   this case, the client would gather all of the buffers for this file
   that contain uncommitted data, do the COMMIT operation with an offset
   of zero and count of zero, and then free all of those buffers.  Any
   other dirty buffers would be sent to the server in the normal
   fashion.

   After a buffer is written (via the WRITE operation) by the client
   with the "committed" field in the result of WRITE set to UNSTABLE4,
   the buffer must be considered as modified by the client until the
   buffer has either been flushed via a COMMIT operation or written via
   a WRITE operation with the "committed" field in the result set to
   FILE_SYNC4 or DATA_SYNC4.  This is done to prevent the buffer from
   being freed and reused before the data can be flushed to stable
   storage on the server.

   When a response is returned from either a WRITE or a COMMIT operation
   and it contains a write verifier that differs from that previously



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   returned by the server, the client will need to retransmit all of the
   buffers containing uncommitted data to the server.  How this is to be
   done is up to the implementor.  If there is only one buffer of
   interest, then it should be sent in a WRITE request with the
   FILE_SYNC4 stable parameter.  If there is more than one buffer, it
   might be worthwhile retransmitting all of the buffers in WRITE
   operations with the stable parameter set to UNSTABLE4 and then
   retransmitting the COMMIT operation to flush all of the data on the
   server to stable storage.  However, if the server repeatably returns
   from COMMIT a verifier that differs from that returned by WRITE, the
   only way to ensure progress is to retransmit all of the buffers with
   WRITE requests with the FILE_SYNC4 stable parameter.

   The above description applies to page-cache-based systems as well as
   buffer-cache-based systems.  In the former systems, the virtual
   memory system will need to be modified instead of the buffer cache.

18.4.  Operation 6: CREATE - Create a Non-Regular File Object

18.4.1.  ARGUMENTS

   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4 linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4 devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
    default:
            void;  /* server should return NFS4ERR_BADTYPE */
   };

   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;
   };










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18.4.2.  RESULTS

   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */
   };

   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            /* new CURRENTFH: created object */
            CREATE4resok resok4;
    default:
            void;
   };


18.4.3.  DESCRIPTION

   The CREATE operation creates a file object other than an ordinary
   file in a directory with a given name.  The OPEN operation MUST be
   used to create a regular file or a named attribute.

   The current filehandle must be a directory: an object of type NF4DIR.
   If the current filehandle is an attribute directory (type
   NF4ATTRDIR), the error NFS4ERR_WRONG_TYPE is returned.  If the
   current file handle designates any other type of object, the error
   NFS4ERR_NOTDIR results.

   The objname specifies the name for the new object.  The objtype
   determines the type of object to be created: directory, symlink, etc.
   If the object type specified is that of an ordinary file, a named
   attribute, or a named attribute directory, the error NFS4ERR_BADTYPE
   results.

   If an object of the same name already exists in the directory, the
   server will return the error NFS4ERR_EXIST.

   For the directory where the new file object was created, the server
   returns change_info4 information in cinfo.  With the atomic field of
   the change_info4 data type, the server will indicate if the before
   and after change attributes were obtained atomically with respect to
   the file object creation.

   If the objname has a length of zero, or if objname does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   The current filehandle is replaced by that of the new object.




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   The createattrs specifies the initial set of attributes for the
   object.  The set of attributes may include any writable attribute
   valid for the object type.  When the operation is successful, the
   server will return to the client an attribute mask signifying which
   attributes were successfully set for the object.

   If createattrs includes neither the owner attribute nor an ACL with
   an ACE for the owner, and if the server's file system both supports
   and requires an owner attribute (or an owner ACE), then the server
   MUST derive the owner (or the owner ACE).  This would typically be
   from the principal indicated in the RPC credentials of the call, but
   the server's operating environment or file system semantics may
   dictate other methods of derivation.  Similarly, if createattrs
   includes neither the group attribute nor a group ACE, and if the
   server's file system both supports and requires the notion of a group
   attribute (or group ACE), the server MUST derive the group attribute
   (or the corresponding owner ACE) for the file.  This could be from
   the RPC call's credentials, such as the group principal if the
   credentials include it (such as with AUTH_SYS), from the group
   identifier associated with the principal in the credentials (e.g.,
   POSIX systems have a user database [26] that has a group identifier
   for every user identifier), inherited from the directory in which the
   object is created, or whatever else the server's operating
   environment or file system semantics dictate.  This applies to the
   OPEN operation too.

   Conversely, it is possible that the client will specify in
   createattrs an owner attribute, group attribute, or ACL that the
   principal indicated the RPC call's credentials does not have
   permissions to create files for.  The error to be returned in this
   instance is NFS4ERR_PERM.  This applies to the OPEN operation too.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the delegation is
   such that the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the CREATE operation MUST NOT
   proceed until the delegation is returned or revoked.  Except where
   this happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations
   request such notifications, NOTIFY4_ADD_ENTRY will be generated as a
   result of this operation.

   If the capability FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set
   (Section 14.4), and a symbolic link is being created, then the
   content of the symbolic link MUST be in UTF-8 encoding.



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18.4.4.  IMPLEMENTATION

   If the client desires to set attribute values after the create, a
   SETATTR operation can be added to the COMPOUND request so that the
   appropriate attributes will be set.

18.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

18.5.1.  ARGUMENTS

   struct DELEGPURGE4args {
           clientid4       clientid;
   };


18.5.2.  RESULTS

   struct DELEGPURGE4res {
           nfsstat4        status;
   };


18.5.3.  DESCRIPTION

   This operation purges all of the delegations awaiting recovery for a
   given client.  This is useful for clients that do not commit
   delegation information to stable storage to indicate that conflicting
   requests need not be delayed by the server awaiting recovery of
   delegation information.

   The client is NOT specified by the clientid field of the request.
   The client SHOULD set the client field to zero, and the server MUST
   ignore the clientid field.  Instead, the server MUST derive the
   client ID from the value of the session ID in the arguments of the
   SEQUENCE operation that precedes DELEGPURGE in the COMPOUND request.

   The DELEGPURGE operation should be used by clients that record
   delegation information on stable storage on the client.  In this
   case, after the client recovers all delegations it knows of, it
   should immediately send a DELEGPURGE operation.  Doing so will notify
   the server that no additional delegations for the client will be
   recovered allowing it to free resources, and avoid delaying other
   clients which make requests that conflict with the unrecovered
   delegations.  The set of delegations known to the server and the
   client might be different.  The reason for this is that after sending
   a request that resulted in a delegation, the client might experience
   a failure before it both received the delegation and committed the
   delegation to the client's stable storage.



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   The server MAY support DELEGPURGE, but if it does not, it MUST NOT
   support CLAIM_DELEGATE_PREV and MUST NOT support CLAIM_DELEG_PREV_FH.

18.6.  Operation 8: DELEGRETURN - Return Delegation

18.6.1.  ARGUMENTS

   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated object */
           stateid4        deleg_stateid;
   };


18.6.2.  RESULTS

   struct DELEGRETURN4res {
           nfsstat4        status;
   };


18.6.3.  DESCRIPTION

   The DELEGRETURN operation returns the delegation represented by the
   current filehandle and stateid.

   Delegations may be returned voluntarily (i.e., before the server has
   recalled them) or when recalled.  In either case, the client must
   properly propagate state changed under the context of the delegation
   to the server before returning the delegation.

   The server MAY require that the principal, security flavor, and if
   applicable, the GSS mechanism, combination that acquired the
   delegation also be the one to send DELEGRETURN on the file.  This
   might not be possible if credentials for the principal are no longer
   available.  The server MAY allow the machine credential or SSV
   credential (see Section 18.35) to send DELEGRETURN.

18.7.  Operation 9: GETATTR - Get Attributes

18.7.1.  ARGUMENTS

   struct GETATTR4args {
           /* CURRENT_FH: object */
           bitmap4         attr_request;
   };






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18.7.2.  RESULTS

   struct GETATTR4resok {
           fattr4          obj_attributes;
   };

   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };


18.7.3.  DESCRIPTION

   The GETATTR operation will obtain attributes for the file system
   object specified by the current filehandle.  The client sets a bit in
   the bitmap argument for each attribute value that it would like the
   server to return.  The server returns an attribute bitmap that
   indicates the attribute values that it was able to return, which will
   include all attributes requested by the client that are attributes
   supported by the server for the target file system.  This bitmap is
   followed by the attribute values ordered lowest attribute number
   first.

   The server MUST return a value for each attribute that the client
   requests if the attribute is supported by the server for the target
   file system.  If the server does not support a particular attribute
   on the target file system, then it MUST NOT return the attribute
   value and MUST NOT set the attribute bit in the result bitmap.  The
   server MUST return an error if it supports an attribute on the target
   but cannot obtain its value.  In that case, no attribute values will
   be returned.

   File systems that are absent should be treated as having support for
   a very small set of attributes as described in Section 11.3.1, even
   if previously, when the file system was present, more attributes were
   supported.

   All servers MUST support the REQUIRED attributes as specified in
   Section 5.6, for all file systems, with the exception of absent file
   systems.

   On success, the current filehandle retains its value.






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18.7.4.  IMPLEMENTATION

   Suppose there is an OPEN_DELEGATE_WRITE delegation held by another
   client for the file in question and size and/or change are among the
   set of attributes being interrogated.  The server has two choices.
   First, the server can obtain the actual current value of these
   attributes from the client holding the delegation by using the
   CB_GETATTR callback.  Second, the server, particularly when the
   delegated client is unresponsive, can recall the delegation in
   question.  The GETATTR MUST NOT proceed until one of the following
   occurs:

   o  The requested attribute values are returned in the response to
      CB_GETATTR.

   o  The OPEN_DELEGATE_WRITE delegation is returned.

   o  The OPEN_DELEGATE_WRITE delegation is revoked.

   Unless one of the above happens very quickly, one or more
   NFS4ERR_DELAY errors will be returned while a delegation is
   outstanding.

18.8.  Operation 10: GETFH - Get Current Filehandle

18.8.1.  ARGUMENTS

   /* CURRENT_FH: */
   void;

18.8.2.  RESULTS

   struct GETFH4resok {
           nfs_fh4         object;
   };

   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };









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18.8.3.  DESCRIPTION

   This operation returns the current filehandle value.

   On success, the current filehandle retains its value.

   As described in Section 2.10.6.4, GETFH is REQUIRED or RECOMMENDED to
   immediately follow certain operations, and servers are free to reject
   such operations if the client fails to insert GETFH in the request as
   REQUIRED or RECOMMENDED.  Section 18.16.4.1 provides additional
   justification for why GETFH MUST follow OPEN.

18.8.4.  IMPLEMENTATION

   Operations that change the current filehandle like LOOKUP or CREATE
   do not automatically return the new filehandle as a result.  For
   instance, if a client needs to look up a directory entry and obtain
   its filehandle, then the following request is needed.

      PUTFH (directory filehandle)

      LOOKUP (entry name)

      GETFH

18.9.  Operation 11: LINK - Create Link to a File

18.9.1.  ARGUMENTS

   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };

















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18.9.2.  RESULTS

   struct LINK4resok {
           change_info4    cinfo;
   };

   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };


18.9.3.  DESCRIPTION

   The LINK operation creates an additional newname for the file
   represented by the saved filehandle, as set by the SAVEFH operation,
   in the directory represented by the current filehandle.  The existing
   file and the target directory must reside within the same file system
   on the server.  On success, the current filehandle will continue to
   be the target directory.  If an object exists in the target directory
   with the same name as newname, the server must return NFS4ERR_EXIST.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 data type, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   If the newname has a length of zero, or if newname does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

18.9.4.  IMPLEMENTATION

   The server MAY impose restrictions on the LINK operation such that
   LINK may not be done when the file is open or when that open is done
   by particular protocols, or with particular options or access modes.
   When LINK is rejected because of such restrictions, the error
   NFS4ERR_FILE_OPEN is returned.

   If a server does implement such restrictions and those restrictions
   include cases of NFSv4 opens preventing successful execution of a
   link, the server needs to recall any delegations that could hide the
   existence of opens relevant to that decision.  The reason is that
   when a client holds a delegation, the server might not have an
   accurate account of the opens for that client, since the client may
   execute OPENs and CLOSEs locally.  The LINK operation must be delayed
   only until a definitive result can be obtained.  For example, suppose



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   there are multiple delegations and one of them establishes an open
   whose presence would prevent the link.  Given the server's semantics,
   NFS4ERR_FILE_OPEN may be returned to the caller as soon as that
   delegation is returned without waiting for other delegations to be
   returned.  Similarly, if such opens are not associated with
   delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
   delegation recall being done.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the delegation is
   such that the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the operation cannot be
   performed successfully until the delegation is returned or revoked.
   Except where this happens very quickly, one or more NFS4ERR_DELAY
   errors will be returned to requests made while delegation remains
   outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations
   request such notifications, instead of a recall, NOTIFY4_ADD_ENTRY
   will be generated as a result of the LINK operation.

   If the current file system supports the numlinks attribute, and other
   clients have delegations to the file being linked, then those
   delegations MUST be recalled and the LINK operation MUST NOT proceed
   until all delegations are returned or revoked.  Except where this
   happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   Changes to any property of the "hard" linked files are reflected in
   all of the linked files.  When a link is made to a file, the
   attributes for the file should have a value for numlinks that is one
   greater than the value before the LINK operation.

   The statement "file and the target directory must reside within the
   same file system on the server" means that the fsid fields in the
   attributes for the objects are the same.  If they reside on different
   file systems, the error NFS4ERR_XDEV is returned.  This error may be
   returned by some servers when there is an internal partitioning of a
   file system that the LINK operation would violate.

   On some servers, "." and ".." are illegal values for newname and the
   error NFS4ERR_BADNAME will be returned if they are specified.

   When the current filehandle designates a named attribute directory
   and the object to be linked (the saved filehandle) is not a named
   attribute for the same object, the error NFS4ERR_XDEV MUST be
   returned.  When the saved filehandle designates a named attribute and



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   the current filehandle is not the appropriate named attribute
   directory, the error NFS4ERR_XDEV MUST also be returned.

   When the current filehandle designates a named attribute directory
   and the object to be linked (the saved filehandle) is a named
   attribute within that directory, the server may return the error
   NFS4ERR_NOTSUPP.

   In the case that newname is already linked to the file represented by
   the saved filehandle, the server will return NFS4ERR_EXIST.

   Note that symbolic links are created with the CREATE operation.

18.10.  Operation 12: LOCK - Create Lock





































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18.10.1.  ARGUMENTS

   /*
    * For LOCK, transition from open_stateid and lock_owner
    * to a lock stateid.
    */
   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };

   /*
    * For LOCK, existing lock stateid continues to request new
    * file lock for the same lock_owner and open_stateid.
    */
   struct exist_lock_owner4 {
           stateid4        lock_stateid;
           seqid4          lock_seqid;
   };

   union locker4 switch (bool new_lock_owner) {
    case TRUE:
           open_to_lock_owner4     open_owner;
    case FALSE:
           exist_lock_owner4       lock_owner;
   };

   /*
    * LOCK/LOCKT/LOCKU: Record lock management
    */
   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };











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18.10.2.  RESULTS

   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };

   struct LOCK4resok {
           stateid4        lock_stateid;
   };

   union LOCK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LOCK4resok     resok4;
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    default:
            void;
   };


18.10.3.  DESCRIPTION

   The LOCK operation requests a byte-range lock for the byte-range
   specified by the offset and length parameters, and lock type
   specified in the locktype parameter.  If this is a reclaim request,
   the reclaim parameter will be TRUE.

   Bytes in a file may be locked even if those bytes are not currently
   allocated to the file.  To lock the file from a specific offset
   through the end-of-file (no matter how long the file actually is) use
   a length field equal to NFS4_UINT64_MAX.  The server MUST return
   NFS4ERR_INVAL under the following combinations of length and offset:

   o  Length is equal to zero.

   o  Length is not equal to NFS4_UINT64_MAX, and the sum of length and
      offset exceeds NFS4_UINT64_MAX.

   32-bit servers are servers that support locking for byte offsets that
   fit within 32 bits (i.e., less than or equal to NFS4_UINT32_MAX).  If
   the client specifies a range that overlaps one or more bytes beyond
   offset NFS4_UINT32_MAX but does not end at offset NFS4_UINT64_MAX,
   then such a 32-bit server MUST return the error NFS4ERR_BAD_RANGE.

   If the server returns NFS4ERR_DENIED, the owner, offset, and length



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   of a conflicting lock are returned.

   The locker argument specifies the lock-owner that is associated with
   the LOCK operation.  The locker4 structure is a switched union that
   indicates whether the client has already created byte-range locking
   state associated with the current open file and lock-owner.  In the
   case in which it has, the argument is just a stateid representing the
   set of locks associated with that open file and lock-owner, together
   with a lock_seqid value that MAY be any value and MUST be ignored by
   the server.  In the case where no byte-range locking state has been
   established, or the client does not have the stateid available, the
   argument contains the stateid of the open file with which this lock
   is to be associated, together with the lock-owner with which the lock
   is to be associated.  The open_to_lock_owner case covers the very
   first lock done by a lock-owner for a given open file and offers a
   method to use the established state of the open_stateid to transition
   to the use of a lock stateid.

   The following fields of the locker parameter MAY be set to any value
   by the client and MUST be ignored by the server:

   o  The clientid field of the lock_owner field of the open_owner field
      (locker.open_owner.lock_owner.clientid).  The reason the server
      MUST ignore the clientid field is that the server MUST derive the
      client ID from the session ID from the SEQUENCE operation of the
      COMPOUND request.

   o  The open_seqid and lock_seqid fields of the open_owner field
      (locker.open_owner.open_seqid and locker.open_owner.lock_seqid).

   o  The lock_seqid field of the lock_owner field
      (locker.lock_owner.lock_seqid).

   Note that the client ID appearing in a LOCK4denied structure is the
   actual client associated with the conflicting lock, whether this is
   the client ID associated with the current session or a different one.
   Thus, if the server returns NFS4ERR_DENIED, it MUST set the clientid
   field of the owner field of the denied field.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.





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18.10.4.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting byte-range lock, the same offset and length that were
   provided in the arguments should be returned in the denied results.

   LOCK operations are subject to permission checks and to checks
   against the access type of the associated file.  However, the
   specific right and modes required for various types of locks reflect
   the semantics of the server-exported file system, and are not
   specified by the protocol.  For example, Windows 2000 allows a write
   lock of a file open for read access, while a POSIX-compliant system
   does not.

   When the client sends a LOCK operation that corresponds to a range
   that the lock-owner has locked already (with the same or different
   lock type), or to a sub-range of such a range, or to a byte-range
   that includes multiple locks already granted to that lock-owner, in
   whole or in part, and the server does not support such locking
   operations (i.e., does not support POSIX locking semantics), the
   server will return the error NFS4ERR_LOCK_RANGE.  In that case, the
   client may return an error, or it may emulate the required
   operations, using only LOCK for ranges that do not include any bytes
   already locked by that lock-owner and LOCKU of locks held by that
   lock-owner (specifying an exactly matching range and type).
   Similarly, when the client sends a LOCK operation that amounts to
   upgrading (changing from a READ_LT lock to a WRITE_LT lock) or
   downgrading (changing from WRITE_LT lock to a READ_LT lock) an
   existing byte-range lock, and the server does not support such a
   lock, the server will return NFS4ERR_LOCK_NOTSUPP.  Such operations
   may not perfectly reflect the required semantics in the face of
   conflicting LOCK operations from other clients.

   When a client holds an OPEN_DELEGATE_WRITE delegation, the client
   holding that delegation is assured that there are no opens by other
   clients.  Thus, there can be no conflicting LOCK operations from such
   clients.  Therefore, the client may be handling locking requests
   locally, without doing LOCK operations on the server.  If it does
   that, it must be prepared to update the lock status on the server, by
   sending appropriate LOCK and LOCKU operations before returning the
   delegation.

   When one or more clients hold OPEN_DELEGATE_READ delegations, any
   LOCK operation where the server is implementing mandatory locking
   semantics MUST result in the recall of all such delegations.  The
   LOCK operation may not be granted until all such delegations are
   returned or revoked.  Except where this happens very quickly, one or
   more NFS4ERR_DELAY errors will be returned to requests made while the



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   delegation remains outstanding.

18.11.  Operation 13: LOCKT - Test for Lock

18.11.1.  ARGUMENTS

   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };


18.11.2.  RESULTS

   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };


18.11.3.  DESCRIPTION

   The LOCKT operation tests the lock as specified in the arguments.  If
   a conflicting lock exists, the owner, offset, length, and type of the
   conflicting lock are returned.  The owner field in the results
   includes the client ID of the owner of the conflicting lock, whether
   this is the client ID associated with the current session or a
   different client ID.  If no lock is held, nothing other than NFS4_OK
   is returned.  Lock types READ_LT and READW_LT are processed in the
   same way in that a conflicting lock test is done without regard to
   blocking or non-blocking.  The same is true for WRITE_LT and
   WRITEW_LT.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   The clientid field of the owner MAY be set to any value by the client
   and MUST be ignored by the server.  The reason the server MUST ignore
   the clientid field is that the server MUST derive the client ID from
   the session ID from the SEQUENCE operation of the COMPOUND request.



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   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.

18.11.4.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.

   LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
   identify the owner.  This is because the client does not have to open
   the file to test for the existence of a lock, so a stateid might not
   be available.

   As noted in Section 18.10.4, some servers may return
   NFS4ERR_LOCK_RANGE to certain (otherwise non-conflicting) LOCK
   operations that overlap ranges already granted to the current lock-
   owner.

   The LOCKT operation's test for conflicting locks SHOULD exclude locks
   for the current lock-owner, and thus should return NFS4_OK in such
   cases.  Note that this means that a server might return NFS4_OK to a
   LOCKT request even though a LOCK operation for the same range and
   lock-owner would fail with NFS4ERR_LOCK_RANGE.

   When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
   (see Section 18.10.4) to handle LOCK requests locally.  In such a
   case, LOCKT requests will similarly be handled locally.

18.12.  Operation 14: LOCKU - Unlock File

18.12.1.  ARGUMENTS

   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        lock_stateid;
           offset4         offset;
           length4         length;
   };





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18.12.2.  RESULTS

   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       lock_stateid;
    default:
            void;
   };


18.12.3.  DESCRIPTION

   The LOCKU operation unlocks the byte-range lock specified by the
   parameters.  The client may set the locktype field to any value that
   is legal for the nfs_lock_type4 enumerated type, and the server MUST
   accept any legal value for locktype.  Any legal value for locktype
   has no effect on the success or failure of the LOCKU operation.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   The seqid parameter MAY be any value and the server MUST ignore it.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.

   The server MAY require that the principal, security flavor, and if
   applicable, the GSS mechanism, combination that sent a LOCK operation
   also be the one to send LOCKU on the file.  This might not be
   possible if credentials for the principal are no longer available.
   The server MAY allow the machine credential or SSV credential (see
   Section 18.35) to send LOCKU.

18.12.4.  IMPLEMENTATION

   If the area to be unlocked does not correspond exactly to a lock
   actually held by the lock-owner, the server may return the error
   NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
   locked, where the area is a sub-range of the area locked, where it
   overlaps the area locked without matching exactly, or the area
   specified includes multiple locks held by the lock-owner.  In all of
   these cases, allowed by POSIX locking [24] semantics, a client



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   receiving this error should, if it desires support for such
   operations, simulate the operation using LOCKU on ranges
   corresponding to locks it actually holds, possibly followed by LOCK
   operations for the sub-ranges not being unlocked.

   When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
   (see Section 18.10.4) to handle LOCK requests locally.  In such a
   case, LOCKU operations will similarly be handled locally.

18.13.  Operation 15: LOOKUP - Lookup Filename

18.13.1.  ARGUMENTS

   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };


18.13.2.  RESULTS

   struct LOOKUP4res {
           /* New CURRENT_FH: object */
           nfsstat4        status;
   };


18.13.3.  DESCRIPTION

   The LOOKUP operation looks up or finds a file system object using the
   directory specified by the current filehandle.  LOOKUP evaluates the
   component and if the object exists, the current filehandle is
   replaced with the component's filehandle.

   If the component cannot be evaluated either because it does not exist
   or because the client does not have permission to evaluate the
   component, then an error will be returned and the current filehandle
   will be unchanged.

   If the component is a zero-length string or if any component does not
   obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

18.13.4.  IMPLEMENTATION

   If the client wants to achieve the effect of a multi-component look
   up, it may construct a COMPOUND request such as (and obtain each
   filehandle):




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         PUTFH  (directory filehandle)
         LOOKUP "pub"
         GETFH
         LOOKUP "foo"
         GETFH
         LOOKUP "bar"
         GETFH

   Unlike NFSv3, NFSv4.1 allows LOOKUP requests to cross mountpoints on
   the server.  The client can detect a mountpoint crossing by comparing
   the fsid attribute of the directory with the fsid attribute of the
   directory looked up.  If the fsids are different, then the new
   directory is a server mountpoint.  UNIX clients that detect a
   mountpoint crossing will need to mount the server's file system.
   This needs to be done to maintain the file object identity checking
   mechanisms common to UNIX clients.

   Servers that limit NFS access to "shared" or "exported" file systems
   should provide a pseudo file system into which the exported file
   systems can be integrated, so that clients can browse the server's
   namespace.  The clients view of a pseudo file system will be limited
   to paths that lead to exported file systems.

   Note: previous versions of the protocol assigned special semantics to
   the names "." and "..".  NFSv4.1 assigns no special semantics to
   these names.  The LOOKUPP operator must be used to look up a parent
   directory.

   Note that this operation does not follow symbolic links.  The client
   is responsible for all parsing of filenames including filenames that
   are modified by symbolic links encountered during the look up
   process.

   If the current filehandle supplied is not a directory but a symbolic
   link, the error NFS4ERR_SYMLINK is returned as the error.  For all
   other non-directory file types, the error NFS4ERR_NOTDIR is returned.

18.14.  Operation 16: LOOKUPP - Lookup Parent Directory

18.14.1.  ARGUMENTS

   /* CURRENT_FH: object */
   void;








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18.14.2.  RESULTS

   struct LOOKUPP4res {
           /* new CURRENT_FH: parent directory */
           nfsstat4        status;
   };


18.14.3.  DESCRIPTION

   The current filehandle is assumed to refer to a regular directory or
   a named attribute directory.  LOOKUPP assigns the filehandle for its
   parent directory to be the current filehandle.  If there is no parent
   directory, an NFS4ERR_NOENT error must be returned.  Therefore,
   NFS4ERR_NOENT will be returned by the server when the current
   filehandle is at the root or top of the server's file tree.

   As is the case with LOOKUP, LOOKUPP will also cross mountpoints.

   If the current filehandle is not a directory or named attribute
   directory, the error NFS4ERR_NOTDIR is returned.

   If the requester's security flavor does not match that configured for
   the parent directory, then the server SHOULD return NFS4ERR_WRONGSEC
   (a future minor revision of NFSv4 may upgrade this to MUST) in the
   LOOKUPP response.  However, if the server does so, it MUST support
   the SECINFO_NO_NAME operation (Section 18.45), so that the client can
   gracefully determine the correct security flavor.

   If the current filehandle is a named attribute directory that is
   associated with a file system object via OPENATTR (i.e., not a sub-
   directory of a named attribute directory), LOOKUPP SHOULD return the
   filehandle of the associated file system object.

18.14.4.  IMPLEMENTATION

   An issue to note is upward navigation from named attribute
   directories.  The named attribute directories are essentially
   detached from the namespace, and this property should be safely
   represented in the client operating environment.  LOOKUPP on a named
   attribute directory may return the filehandle of the associated file,
   and conveying this to applications might be unsafe as many
   applications expect the parent of an object to always be a directory.
   Therefore, the client may want to hide the parent of named attribute
   directories (represented as ".." in UNIX) or represent the named
   attribute directory as its own parent (as is typically done for the
   file system root directory in UNIX).




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18.15.  Operation 17: NVERIFY - Verify Difference in Attributes

18.15.1.  ARGUMENTS

   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };


18.15.2.  RESULTS

   struct NVERIFY4res {
           nfsstat4        status;
   };


18.15.3.  DESCRIPTION

   This operation is used to prefix a sequence of operations to be
   performed if one or more attributes have changed on some file system
   object.  If all the attributes match, then the error NFS4ERR_SAME
   MUST be returned.

   On success, the current filehandle retains its value.

18.15.4.  IMPLEMENTATION

   This operation is useful as a cache validation operator.  If the
   object to which the attributes belong has changed, then the following
   operations may obtain new data associated with that object, for
   instance, to check if a file has been changed and obtain new data if
   it has:

         SEQUENCE
         PUTFH fh
         NVERIFY attrbits attrs
         READ 0 32767

   Contrast this with NFSv3, which would first send a GETATTR in one
   request/reply round trip, and then if attributes indicated that the
   client's cache was stale, then send a READ in another request/reply
   round trip.

   In the case that a RECOMMENDED attribute is specified in the NVERIFY
   operation and the server does not support that attribute for the file
   system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.



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   When the attribute rdattr_error or any set-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.

18.16.  Operation 18: OPEN - Open a Regular File

18.16.1.  ARGUMENTS

   /*
    * Various definitions for OPEN
    */
   enum createmode4 {
           UNCHECKED4      = 0,
           GUARDED4        = 1,
           /* Deprecated in NFSv4.1. */
           EXCLUSIVE4      = 2,
           /*
            * New to NFSv4.1. If session is persistent,
            * GUARDED4 MUST be used.  Otherwise, use
            * EXCLUSIVE4_1 instead of EXCLUSIVE4.
            */
           EXCLUSIVE4_1    = 3
   };

   struct creatverfattr {
            verifier4      cva_verf;
            fattr4         cva_attrs;
   };

   union createhow4 switch (createmode4 mode) {
    case UNCHECKED4:
    case GUARDED4:
            fattr4         createattrs;
    case EXCLUSIVE4:
            verifier4      createverf;
    case EXCLUSIVE4_1:
            creatverfattr  ch_createboth;
   };

   enum opentype4 {
           OPEN4_NOCREATE  = 0,
           OPEN4_CREATE    = 1
   };

   union openflag4 switch (opentype4 opentype) {
    case OPEN4_CREATE:
            createhow4     how;
    default:



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            void;
   };

   /* Next definitions used for OPEN delegation */
   enum limit_by4 {
           NFS_LIMIT_SIZE          = 1,
           NFS_LIMIT_BLOCKS        = 2
           /* others as needed */
   };

   struct nfs_modified_limit4 {
           uint32_t        num_blocks;
           uint32_t        bytes_per_block;
   };

   union nfs_space_limit4 switch (limit_by4 limitby) {
    /* limit specified as file size */
    case NFS_LIMIT_SIZE:
            uint64_t               filesize;
    /* limit specified by number of blocks */
    case NFS_LIMIT_BLOCKS:
            nfs_modified_limit4    mod_blocks;
   } ;

   /*
    * Share Access and Deny constants for open argument
    */
   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;


   /* new flags for share_access field of OPEN4args */
   const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK        = 0xFF00;
   const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE     = 0x0000;
   const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x0100;
   const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x0200;
   const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0300;
   const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x0400;
   const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x0500;

   const
    OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL



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    = 0x10000;

   const
    OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
    = 0x20000;

   enum open_delegation_type4 {
           OPEN_DELEGATE_NONE      = 0,
           OPEN_DELEGATE_READ      = 1,
           OPEN_DELEGATE_WRITE     = 2,
           OPEN_DELEGATE_NONE_EXT  = 3 /* new to v4.1 */
   };

   enum open_claim_type4 {
           /*
            * Not a reclaim.
            */
           CLAIM_NULL              = 0,

           CLAIM_PREVIOUS          = 1,
           CLAIM_DELEGATE_CUR      = 2,
           CLAIM_DELEGATE_PREV     = 3,

           /*
            * Not a reclaim.
            *
            * Like CLAIM_NULL, but object identified
            * by the current filehandle.
            */
           CLAIM_FH                = 4, /* new to v4.1 */

           /*
            * Like CLAIM_DELEGATE_CUR, but object identified
            * by current filehandle.
            */
           CLAIM_DELEG_CUR_FH      = 5, /* new to v4.1 */

           /*
            * Like CLAIM_DELEGATE_PREV, but object identified
            * by current filehandle.
            */
           CLAIM_DELEG_PREV_FH     = 6 /* new to v4.1 */
   };

   struct open_claim_delegate_cur4 {
           stateid4        delegate_stateid;
           component4      file;
   };



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   union open_claim4 switch (open_claim_type4 claim) {
    /*
     * No special rights to file.
     * Ordinary OPEN of the specified file.
     */
    case CLAIM_NULL:
           /* CURRENT_FH: directory */
           component4      file;
    /*
     * Right to the file established by an
     * open previous to server reboot.  File
     * identified by filehandle obtained at
     * that time rather than by name.
     */
    case CLAIM_PREVIOUS:
           /* CURRENT_FH: file being reclaimed */
           open_delegation_type4   delegate_type;

    /*
     * Right to file based on a delegation
     * granted by the server.  File is
     * specified by name.
     */
    case CLAIM_DELEGATE_CUR:
           /* CURRENT_FH: directory */
           open_claim_delegate_cur4        delegate_cur_info;

    /*
     * Right to file based on a delegation
     * granted to a previous boot instance
     * of the client.  File is specified by name.
     */
    case CLAIM_DELEGATE_PREV:
            /* CURRENT_FH: directory */
           component4      file_delegate_prev;

    /*
     * Like CLAIM_NULL.  No special rights
     * to file.  Ordinary OPEN of the
     * specified file by current filehandle.
     */
    case CLAIM_FH: /* new to v4.1 */
           /* CURRENT_FH: regular file to open */
           void;

    /*
     * Like CLAIM_DELEGATE_PREV.  Right to file based on a
     * delegation granted to a previous boot



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     * instance of the client.  File is identified by
     * by filehandle.
     */
    case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
           /* CURRENT_FH: file being opened */
           void;

    /*
     * Like CLAIM_DELEGATE_CUR.  Right to file based on
     * a delegation granted by the server.
     * File is identified by filehandle.
     */
    case CLAIM_DELEG_CUR_FH: /* new to v4.1 */
            /* CURRENT_FH: file being opened */
            stateid4       oc_delegate_stateid;

   };

   /*
    * OPEN: Open a file, potentially receiving an OPEN delegation
    */
   struct OPEN4args {
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
           open_owner4     owner;
           openflag4       openhow;
           open_claim4     claim;
   };


18.16.2.  RESULTS

   struct open_read_delegation4 {
    stateid4 stateid;    /* Stateid for delegation*/
    bool     recall;     /* Pre-recalled flag for
                            delegations obtained
                            by reclaim (CLAIM_PREVIOUS) */

    nfsace4 permissions; /* Defines users who don't
                            need an ACCESS call to
                            open for read */
   };

   struct open_write_delegation4 {
    stateid4 stateid;      /* Stateid for delegation */
    bool     recall;       /* Pre-recalled flag for
                              delegations obtained



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                              by reclaim
                              (CLAIM_PREVIOUS) */

    nfs_space_limit4
              space_limit; /* Defines condition that
                              the client must check to
                              determine whether the
                              file needs to be flushed
                              to the server on close.  */

    nfsace4   permissions; /* Defines users who don't
                              need an ACCESS call as
                              part of a delegated
                              open. */
   };


   enum why_no_delegation4 { /* new to v4.1 */
           WND4_NOT_WANTED         = 0,
           WND4_CONTENTION         = 1,
           WND4_RESOURCE           = 2,
           WND4_NOT_SUPP_FTYPE     = 3,
           WND4_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
           WND4_NOT_SUPP_UPGRADE   = 5,
           WND4_NOT_SUPP_DOWNGRADE = 6,
           WND4_CANCELLED          = 7,
           WND4_IS_DIR             = 8
   };

   union open_none_delegation4 /* new to v4.1 */
   switch (why_no_delegation4 ond_why) {
           case WND4_CONTENTION:
                   bool ond_server_will_push_deleg;
           case WND4_RESOURCE:
                   bool ond_server_will_signal_avail;
           default:
                   void;
   };

   union open_delegation4
   switch (open_delegation_type4 delegation_type) {
           case OPEN_DELEGATE_NONE:
                   void;
           case OPEN_DELEGATE_READ:
                   open_read_delegation4 read;
           case OPEN_DELEGATE_WRITE:
                   open_write_delegation4 write;
           case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */



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                   open_none_delegation4 od_whynone;
   };

   /*
    * Result flags
    */

   /* Client must confirm open */
   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   /* Type of file locking behavior at the server */
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
   /* Server will preserve file if removed while open */
   const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;

   /*
    * Server may use CB_NOTIFY_LOCK on locks
    * derived from this open
    */
   const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;

   struct OPEN4resok {
    stateid4       stateid;      /* Stateid for open */
    change_info4   cinfo;        /* Directory Change Info */
    uint32_t       rflags;       /* Result flags */
    bitmap4        attrset;      /* attribute set for create*/
    open_delegation4 delegation; /* Info on any open
                                    delegation */
   };

   union OPEN4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* New CURRENT_FH: opened file */
           OPEN4resok      resok4;
    default:
           void;
   };


18.16.3.  DESCRIPTION

   The OPEN operation opens a regular file in a directory with the
   provided name or filehandle.  OPEN can also create a file if a name
   is provided, and the client specifies it wants to create a file.
   Specification of whether or not a file is to be created, and the
   method of creation is via the openhow parameter.  The openhow
   parameter consists of a switched union (data type opengflag4), which
   switches on the value of opentype (OPEN4_NOCREATE or OPEN4_CREATE).
   If OPEN4_CREATE is specified, this leads to another switched union



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   (data type createhow4) that supports four cases of creation methods:
   UNCHECKED4, GUARDED4, EXCLUSIVE4, or EXCLUSIVE4_1.  If opentype is
   OPEN4_CREATE, then the claim field of the claim field MUST be one of
   CLAIM_NULL, CLAIM_DELEGATE_CUR, or CLAIM_DELEGATE_PREV, because these
   claim methods include a component of a file name.

   Upon success (which might entail creation of a new file), the current
   filehandle is replaced by that of the created or existing object.

   If the current filehandle is a named attribute directory, OPEN will
   then create or open a named attribute file.  Note that exclusive
   create of a named attribute is not supported.  If the createmode is
   EXCLUSIVE4 or EXCLUSIVE4_1 and the current filehandle is a named
   attribute directory, the server will return EINVAL.

   UNCHECKED4 means that the file should be created if a file of that
   name does not exist and encountering an existing regular file of that
   name is not an error.  For this type of create, createattrs specifies
   the initial set of attributes for the file.  The set of attributes
   may include any writable attribute valid for regular files.  When an
   UNCHECKED4 create encounters an existing file, the attributes
   specified by createattrs are not used, except that when createattrs
   specifies the size attribute with a size of zero, the existing file
   is truncated.

   If GUARDED4 is specified, the server checks for the presence of a
   duplicate object by name before performing the create.  If a
   duplicate exists, NFS4ERR_EXIST is returned.  If the object does not
   exist, the request is performed as described for UNCHECKED4.

   For the UNCHECKED4 and GUARDED4 cases, where the operation is
   successful, the server will return to the client an attribute mask
   signifying which attributes were successfully set for the object.

   EXCLUSIVE4_1 and EXCLUSIVE4 specify that the server is to follow
   exclusive creation semantics, using the verifier to ensure exclusive
   creation of the target.  The server should check for the presence of
   a duplicate object by name.  If the object does not exist, the server
   creates the object and stores the verifier with the object.  If the
   object does exist and the stored verifier matches the client provided
   verifier, the server uses the existing object as the newly created
   object.  If the stored verifier does not match, then an error of
   NFS4ERR_EXIST is returned.

   If using EXCLUSIVE4, and if the server uses attributes to store the
   exclusive create verifier, the server will signify which attributes
   it used by setting the appropriate bits in the attribute mask that is
   returned in the results.  Unlike UNCHECKED4, GUARDED4, and



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   EXCLUSIVE4_1, EXCLUSIVE4 does not support the setting of attributes
   at file creation, and after a successful OPEN via EXCLUSIVE4, the
   client MUST send a SETATTR to set attributes to a known state.

   In NFSv4.1, EXCLUSIVE4 has been deprecated in favor of EXCLUSIVE4_1.
   Unlike EXCLUSIVE4, attributes may be provided in the EXCLUSIVE4_1
   case, but because the server may use attributes of the target object
   to store the verifier, the set of allowable attributes may be fewer
   than the set of attributes SETATTR allows.  The allowable attributes
   for EXCLUSIVE4_1 are indicated in the suppattr_exclcreat
   (Section 5.8.1.14) attribute.  If the client attempts to set in
   cva_attrs an attribute that is not in suppattr_exclcreat, the server
   MUST return NFS4ERR_INVAL.  The response field, attrset, indicates
   both which attributes the server set from cva_attrs and which
   attributes the server used to store the verifier.  As described in
   Section 18.16.4, the client can compare cva_attrs.attrmask with
   attrset to determine which attributes were used to store the
   verifier.

   With the addition of persistent sessions and pNFS, under some
   conditions EXCLUSIVE4 MUST NOT be used by the client or supported by
   the server.  The following table summarizes the appropriate and
   mandated exclusive create methods for implementations of NFSv4.1:

                   Required methods for exclusive create

   +----------------+-----------+---------------+----------------------+
   | Persistent     | Server    | Server        | Client Allowed       |
   | Reply Cache    | Supports  | REQUIRED      |                      |
   | Enabled        | pNFS      |               |                      |
   +----------------+-----------+---------------+----------------------+
   | no             | no        | EXCLUSIVE4_1  | EXCLUSIVE4_1         |
   |                |           | and           | (SHOULD) or          |
   |                |           | EXCLUSIVE4    | EXCLUSIVE4 (SHOULD   |
   |                |           |               | NOT)                 |
   | no             | yes       | EXCLUSIVE4_1  | EXCLUSIVE4_1         |
   | yes            | no        | GUARDED4      | GUARDED4             |
   | yes            | yes       | GUARDED4      | GUARDED4             |
   +----------------+-----------+---------------+----------------------+

                                 Table 10

   If CREATE_SESSION4_FLAG_PERSIST is set in the results of
   CREATE_SESSION, the reply cache is persistent (see Section 18.36).
   If the EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the results from
   EXCHANGE_ID, the server is a pNFS server (see Section 18.35).  If the
   client attempts to use EXCLUSIVE4 on a persistent session, or a
   session derived from an EXCHGID4_FLAG_USE_PNFS_MDS client ID, the



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   server MUST return NFS4ERR_INVAL.

   With persistent sessions, exclusive create semantics are fully
   achievable via GUARDED4, and so EXCLUSIVE4 or EXCLUSIVE4_1 MUST NOT
   be used.  When pNFS is being used, the layout_hint attribute might
   not be supported after the file is created.  Only the EXCLUSIVE4_1
   and GUARDED methods of exclusive file creation allow the atomic
   setting of attributes.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 data type, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   The OPEN operation provides for Windows share reservation capability
   with the use of the share_access and share_deny fields of the OPEN
   arguments.  The client specifies at OPEN the required share_access
   and share_deny modes.  For clients that do not directly support
   SHAREs (i.e., UNIX), the expected deny value is
   OPEN4_SHARE_DENY_NONE.  In the case that there is an existing SHARE
   reservation that conflicts with the OPEN request, the server returns
   the error NFS4ERR_SHARE_DENIED.  For additional discussion of SHARE
   semantics, see Section 9.7.

   For each OPEN, the client provides a value for the owner field of the
   OPEN argument.  The owner field is of data type open_owner4, and
   contains a field called clientid and a field called owner.  The
   client can set the clientid field to any value and the server MUST
   ignore it.  Instead, the server MUST derive the client ID from the
   session ID of the SEQUENCE operation of the COMPOUND request.

   The "seqid" field of the request is not used in NFSv4.1, but it MAY
   be any value and the server MUST ignore it.

   In the case that the client is recovering state from a server
   failure, the claim field of the OPEN argument is used to signify that
   the request is meant to reclaim state previously held.

   The "claim" field of the OPEN argument is used to specify the file to
   be opened and the state information that the client claims to
   possess.  There are seven claim types as follows:










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   +----------------------+--------------------------------------------+
   | open type            | description                                |
   +----------------------+--------------------------------------------+
   | CLAIM_NULL, CLAIM_FH | For the client, this is a new OPEN request |
   |                      | and there is no previous state associated  |
   |                      | with the file for the client.  With        |
   |                      | CLAIM_NULL, the file is identified by the  |
   |                      | current filehandle and the specified       |
   |                      | component name.  With CLAIM_FH (new to     |
   |                      | NFSv4.1), the file is identified by just   |
   |                      | the current filehandle.                    |
   | CLAIM_PREVIOUS       | The client is claiming basic OPEN state    |
   |                      | for a file that was held previous to a     |
   |                      | server restart.  Generally used when a     |
   |                      | server is returning persistent             |
   |                      | filehandles; the client may not have the   |
   |                      | file name to reclaim the OPEN.             |
   | CLAIM_DELEGATE_CUR,  | The client is claiming a delegation for    |
   | CLAIM_DELEG_CUR_FH   | OPEN as granted by the server.  Generally, |
   |                      | this is done as part of recalling a        |
   |                      | delegation.  With CLAIM_DELEGATE_CUR, the  |
   |                      | file is identified by the current          |
   |                      | filehandle and the specified component     |
   |                      | name.  With CLAIM_DELEG_CUR_FH (new to     |
   |                      | NFSv4.1), the file is identified by just   |
   |                      | the current filehandle.                    |
   | CLAIM_DELEGATE_PREV, | The client is claiming a delegation        |
   | CLAIM_DELEG_PREV_FH  | granted to a previous client instance;     |
   |                      | used after the client restarts.  The       |
   |                      | server MAY support CLAIM_DELEGATE_PREV     |
   |                      | and/or CLAIM_DELEG_PREV_FH (new to         |
   |                      | NFSv4.1).  If it does support either claim |
   |                      | type, CREATE_SESSION MUST NOT remove the   |
   |                      | client's delegation state, and the server  |
   |                      | MUST support the DELEGPURGE operation.     |
   +----------------------+--------------------------------------------+

   For OPEN requests that reach the server during the grace period, the
   server returns an error of NFS4ERR_GRACE.  The following claim types
   are exceptions:

   o  OPEN requests specifying the claim type CLAIM_PREVIOUS are devoted
      to reclaiming opens after a server restart and are typically only
      valid during the grace period.

   o  OPEN requests specifying the claim types CLAIM_DELEGATE_CUR and
      CLAIM_DELEG_CUR_FH are valid both during and after the grace
      period.  Since the granting of the delegation that they are



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      subordinate to assures that there is no conflict with locks to be
      reclaimed by other clients, the server need not return
      NFS4ERR_GRACE when these are received during the grace period.

   For any OPEN request, the server may return an OPEN delegation, which
   allows further opens and closes to be handled locally on the client
   as described in Section 10.4.  Note that delegation is up to the
   server to decide.  The client should never assume that delegation
   will or will not be granted in a particular instance.  It should
   always be prepared for either case.  A partial exception is the
   reclaim (CLAIM_PREVIOUS) case, in which a delegation type is claimed.
   In this case, delegation will always be granted, although the server
   may specify an immediate recall in the delegation structure.

   The rflags returned by a successful OPEN allow the server to return
   information governing how the open file is to be handled.

   o  OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned by an
      NFSv4.1 server.

   o  OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's byte-range
      locking behavior supports the complete set of POSIX locking
      techniques [24].  From this, the client can choose to manage byte-
      range locking state in a way to handle a mismatch of byte-range
      locking management.

   o  OPEN4_RESULT_PRESERVE_UNLINKED indicates that the server will
      preserve the open file if the client (or any other client) removes
      the file as long as it is open.  Furthermore, the server promises
      to preserve the file through the grace period after server
      restart, thereby giving the client the opportunity to reclaim its
      open.

   o  OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
      CB_NOTIFY_LOCK callbacks for locks on this file.  This flag is a
      hint only, and may be safely ignored by the client.

   If the component is of zero length, NFS4ERR_INVAL will be returned.
   The component is also subject to the normal UTF-8, character support,
   and name checks.  See Section 14.5 for further discussion.

   When an OPEN is done and the specified open-owner already has the
   resulting filehandle open, the result is to "OR" together the new
   share and deny status together with the existing status.  In this
   case, only a single CLOSE need be done, even though multiple OPENs
   were completed.  When such an OPEN is done, checking of share
   reservations for the new OPEN proceeds normally, with no exception
   for the existing OPEN held by the same open-owner.  In this case, the



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   stateid returned as an "other" field that matches that of the
   previous open while the "seqid" field is incremented to reflect the
   change status due to the new open.

   If the underlying file system at the server is only accessible in a
   read-only mode and the OPEN request has specified ACCESS_WRITE or
   ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
   only file system.

   As with the CREATE operation, the server MUST derive the owner, owner
   ACE, group, or group ACE if any of the four attributes are required
   and supported by the server's file system.  For an OPEN with the
   EXCLUSIVE4 createmode, the server has no choice, since such OPEN
   calls do not include the createattrs field.  Conversely, if
   createattrs (UNCHECKED4 or GUARDED4) or cva_attrs (EXCLUSIVE4_1) is
   specified, and includes an owner, owner_group, or ACE that the
   principal in the RPC call's credentials does not have authorization
   to create files for, then the server may return NFS4ERR_PERM.

   In the case of an OPEN that specifies a size of zero (e.g.,
   truncation) and the file has named attributes, the named attributes
   are left as is and are not removed.

   NFSv4.1 gives more precise control to clients over acquisition of
   delegations via the following new flags for the share_access field of
   OPEN4args:

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL

   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED

   If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
   then the client will have specified one and only one of:

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG






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   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   Otherwise, the client is neither indicating a desire nor a non-desire
   for a delegation, and the server MAY or MAY not return a delegation
   in the OPEN response.

   If the server supports the new _WANT_ flags and the client sends one
   or more of the new flags, then in the event the server does not
   return a delegation, it MUST return a delegation type of
   OPEN_DELEGATE_NONE_EXT.  The field ond_why in the reply indicates why
   no delegation was returned and will be one of:

   WND4_NOT_WANTED  The client specified
      OPEN4_SHARE_ACCESS_WANT_NO_DELEG.

   WND4_CONTENTION  There is a conflicting delegation or open on the
      file.

   WND4_RESOURCE  Resource limitations prevent the server from granting
      a delegation.

   WND4_NOT_SUPP_FTYPE  The server does not support delegations on this
      file type.

   WND4_WRITE_DELEG_NOT_SUPP_FTYPE  The server does not support
      OPEN_DELEGATE_WRITE delegations on this file type.

   WND4_NOT_SUPP_UPGRADE  The server does not support atomic upgrade of
      an OPEN_DELEGATE_READ delegation to an OPEN_DELEGATE_WRITE
      delegation.

   WND4_NOT_SUPP_DOWNGRADE  The server does not support atomic downgrade
      of an OPEN_DELEGATE_WRITE delegation to an OPEN_DELEGATE_READ
      delegation.

   WND4_CANCELED  The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL
      and now any "want" for this file object is cancelled.

   WND4_IS_DIR  The specified file object is a directory, and the
      operation is OPEN or WANT_DELEGATION, which do not support
      delegations on directories.




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   OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
   OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
   OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the client wants
   an OPEN_DELEGATE_READ, OPEN_DELEGATE_WRITE, or any delegation
   regardless which of OPEN4_SHARE_ACCESS_READ,
   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH is set.  If the
   client has an OPEN_DELEGATE_READ delegation on a file and requests an
   OPEN_DELEGATE_WRITE delegation, then the client is requesting atomic
   upgrade of its OPEN_DELEGATE_READ delegation to an
   OPEN_DELEGATE_WRITE delegation.  If the client has an
   OPEN_DELEGATE_WRITE delegation on a file and requests an
   OPEN_DELEGATE_READ delegation, then the client is requesting atomic
   downgrade to an OPEN_DELEGATE_READ delegation.  A server MAY support
   atomic upgrade or downgrade.  If it does, then the returned
   delegation_type of OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE that is
   different from the delegation type the client currently has,
   indicates successful upgrade or downgrade.  If the server does not
   support atomic delegation upgrade or downgrade, then ond_why will be
   set to WND4_NOT_SUPP_UPGRADE or WND4_NOT_SUPP_DOWNGRADE.

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG means that the client wants no
   delegation.

   OPEN4_SHARE_ACCESS_WANT_CANCEL means that the client wants no
   delegation and wants to cancel any previously registered "want" for a
   delegation.

   The client may set one or both of
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED.  However, they
   will have no effect unless one of following is set:

   o  OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to insufficient resources, the server MAY later inform
   the client, via the CB_RECALLABLE_OBJ_AVAIL operation, that the
   resource limitation condition has eased.  The server will tell the
   client that it intends to send a future CB_RECALLABLE_OBJ_AVAIL
   operation by setting delegation_type in the results to
   OPEN_DELEGATE_NONE_EXT, ond_why to WND4_RESOURCE, and



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   ond_server_will_signal_avail set to TRUE.  If
   ond_server_will_signal_avail is set to TRUE, the server MUST later
   send a CB_RECALLABLE_OBJ_AVAIL operation.

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to contention, the server MAY later inform the client,
   via the CB_PUSH_DELEG operation, that the contention condition has
   eased.  The server will tell the client that it intends to send a
   future CB_PUSH_DELEG operation by setting delegation_type in the
   results to OPEN_DELEGATE_NONE_EXT, ond_why to WND4_CONTENTION, and
   ond_server_will_push_deleg to TRUE.  If ond_server_will_push_deleg is
   TRUE, the server MUST later send a CB_PUSH_DELEG operation.

   If the client has previously registered a want for a delegation on a
   file, and then sends a request to register a want for a delegation on
   the same file, the server MUST return a new error:
   NFS4ERR_DELEG_ALREADY_WANTED.  If the client wishes to register a
   different type of delegation want for the same file, it MUST cancel
   the existing delegation WANT.

18.16.4.  IMPLEMENTATION

   In absence of a persistent session, the client invokes exclusive
   create by setting the how parameter to EXCLUSIVE4 or EXCLUSIVE4_1.
   In these cases, the client provides a verifier that can reasonably be
   expected to be unique.  A combination of a client identifier, perhaps
   the client network address, and a unique number generated by the
   client, perhaps the RPC transaction identifier, may be appropriate.

   If the object does not exist, the server creates the object and
   stores the verifier in stable storage.  For file systems that do not
   provide a mechanism for the storage of arbitrary file attributes, the
   server may use one or more elements of the object's metadata to store
   the verifier.  The verifier MUST be stored in stable storage to
   prevent erroneous failure on retransmission of the request.  It is
   assumed that an exclusive create is being performed because exclusive
   semantics are critical to the application.  Because of the expected
   usage, exclusive CREATE does not rely solely on the server's reply
   cache for storage of the verifier.  A nonpersistent reply cache does
   not survive a crash and the session and reply cache may be deleted
   after a network partition that exceeds the lease time, thus opening
   failure windows.

   An NFSv4.1 server SHOULD NOT store the verifier in any of the file's
   RECOMMENDED or REQUIRED attributes.  If it does, the server SHOULD



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   use time_modify_set or time_access_set to store the verifier.  The
   server SHOULD NOT store the verifier in the following attributes:

      acl (it is desirable for access control to be established at
      creation),

      dacl (ditto),

      mode (ditto),

      owner (ditto),

      owner_group (ditto),

      retentevt_set (it may be desired to establish retention at
      creation)

      retention_hold (ditto),

      retention_set (ditto),

      sacl (it is desirable for auditing control to be established at
      creation),

      size (on some servers, size may have a limited range of values),

      mode_set_masked (as with mode),

         and

      time_creation (a meaningful file creation should be set when the
      file is created).

   Another alternative for the server is to use a named attribute to
   store the verifier.

   Because the EXCLUSIVE4 create method does not specify initial
   attributes when processing an EXCLUSIVE4 create, the server

   o  SHOULD set the owner of the file to that corresponding to the
      credential of request's RPC header.

   o  SHOULD NOT leave the file's access control to anyone but the owner
      of the file.

   If the server cannot support exclusive create semantics, possibly
   because of the requirement to commit the verifier to stable storage,
   it should fail the OPEN request with the error NFS4ERR_NOTSUPP.



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   During an exclusive CREATE request, if the object already exists, the
   server reconstructs the object's verifier and compares it with the
   verifier in the request.  If they match, the server treats the
   request as a success.  The request is presumed to be a duplicate of
   an earlier, successful request for which the reply was lost and that
   the server duplicate request cache mechanism did not detect.  If the
   verifiers do not match, the request is rejected with the status
   NFS4ERR_EXIST.

   After the client has performed a successful exclusive create, the
   attrset response indicates which attributes were used to store the
   verifier.  If EXCLUSIVE4 was used, the attributes set in attrset were
   used for the verifier.  If EXCLUSIVE4_1 was used, the client
   determines the attributes used for the verifier by comparing attrset
   with cva_attrs.attrmask; any bits set in the former but not the
   latter identify the attributes used to store the verifier.  The
   client MUST immediately send a SETATTR to set attributes used to
   store the verifier.  Until it does so, the attributes used to store
   the verifier cannot be relied upon.  The subsequent SETATTR MUST NOT
   occur in the same COMPOUND request as the OPEN.

   Unless a persistent session is used, use of the GUARDED4 attribute
   does not provide exactly once semantics.  In particular, if a reply
   is lost and the server does not detect the retransmission of the
   request, the operation can fail with NFS4ERR_EXIST, even though the
   create was performed successfully.  The client would use this
   behavior in the case that the application has not requested an
   exclusive create but has asked to have the file truncated when the
   file is opened.  In the case of the client timing out and
   retransmitting the create request, the client can use GUARDED4 to
   prevent against a sequence like create, write, create (retransmitted)
   from occurring.

   For SHARE reservations, the value of the expression (share_access &
   ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) MUST be one of
   OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
   OPEN4_SHARE_ACCESS_BOTH.  If not, the server MUST return
   NFS4ERR_INVAL.  The value of share_deny MUST be one of
   OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE,
   or OPEN4_SHARE_DENY_BOTH.  If not, the server MUST return
   NFS4ERR_INVAL.

   Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH), the client
   should check that the requester has the proper access rights to
   perform the specified operation.  This would generally be the results
   of applying the ACL access rules to the file for the current
   requester.  However, just as with the ACCESS operation, the client



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   should not attempt to second-guess the server's decisions, as access
   rights may change and may be subject to server administrative
   controls outside the ACL framework.  If the requester's READ or WRITE
   operation is not authorized (depending on the share_access value),
   the server MUST return NFS4ERR_ACCESS.

   Note that if the client ID was not created with the
   EXCHGID4_FLAG_BIND_PRINC_STATEID capability set in the reply to
   EXCHANGE_ID, then the server MUST NOT impose any requirement that
   READs and WRITEs sent for an open file have the same credentials as
   the OPEN itself, and the server is REQUIRED to perform access
   checking on the READs and WRITEs themselves.  Otherwise, if the reply
   to EXCHANGE_ID did have EXCHGID4_FLAG_BIND_PRINC_STATEID set, then
   with one exception, the credentials used in the OPEN request MUST
   match those used in the READs and WRITEs, and the stateids in the
   READs and WRITEs MUST match, or be derived from the stateid from the
   reply to OPEN.  The exception is if SP4_SSV or SP4_MACH_CRED state
   protection is used, and the spo_must_allow result of EXCHANGE_ID
   includes the READ and/or WRITE operations.  In that case, the machine
   or SSV credential will be allowed to send READ and/or WRITE.  See
   Section 18.35.

   If the component provided to OPEN is a symbolic link, the error
   NFS4ERR_SYMLINK will be returned to the client, while if it is a
   directory the error NFS4ERR_ISDIR will be returned.  If the component
   is neither of those but not an ordinary file, the error
   NFS4ERR_WRONG_TYPE is returned.  If the current filehandle is not a
   directory, the error NFS4ERR_NOTDIR will be returned.

   The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows a
   client to avoid the common implementation practice of renaming an
   open file to ".nfs<unique value>" after it removes the file.  After
   the server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client sends
   a REMOVE operation that would reduce the file's link count to zero,
   the server SHOULD report a value of zero for the numlinks attribute
   on the file.

   If another client has a delegation of the file being opened that
   conflicts with open being done (sometimes depending on the
   share_access or share_deny value specified), the delegation(s) MUST
   be recalled, and the operation cannot proceed until each such
   delegation is returned or revoked.  Except where this happens very
   quickly, one or more NFS4ERR_DELAY errors will be returned to
   requests made while delegation remains outstanding.  In the case of
   an OPEN_DELEGATE_WRITE delegation, any open by a different client
   will conflict, while for an OPEN_DELEGATE_READ delegation, only opens
   with one of the following characteristics will be considered
   conflicting:



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   o  The value of share_access includes the bit
      OPEN4_SHARE_ACCESS_WRITE.

   o  The value of share_deny specifies OPEN4_SHARE_DENY_READ or
      OPEN4_SHARE_DENY_BOTH.

   o  OPEN4_CREATE is specified together with UNCHECKED4, the size
      attribute is specified as zero (for truncation), and an existing
      file is truncated.

   If OPEN4_CREATE is specified and the file does not exist and the
   current filehandle designates a directory for which another client
   holds a directory delegation, then, unless the delegation is such
   that the situation can be resolved by sending a notification, the
   delegation MUST be recalled, and the operation cannot proceed until
   the delegation is returned or revoked.  Except where this happens
   very quickly, one or more NFS4ERR_DELAY errors will be returned to
   requests made while delegation remains outstanding.

   If OPEN4_CREATE is specified and the file does not exist and the
   current filehandle designates a directory for which one or more
   directory delegations exist, then, when those delegations request
   such notifications, NOTIFY4_ADD_ENTRY will be generated as a result
   of this operation.

18.16.4.1.  Warning to Client Implementors

   OPEN resembles LOOKUP in that it generates a filehandle for the
   client to use.  Unlike LOOKUP though, OPEN creates server state on
   the filehandle.  In normal circumstances, the client can only release
   this state with a CLOSE operation.  CLOSE uses the current filehandle
   to determine which file to close.  Therefore, the client MUST follow
   every OPEN operation with a GETFH operation in the same COMPOUND
   procedure.  This will supply the client with the filehandle such that
   CLOSE can be used appropriately.

   Simply waiting for the lease on the file to expire is insufficient
   because the server may maintain the state indefinitely as long as
   another client does not attempt to make a conflicting access to the
   same file.

   See also Section 2.10.6.4.

18.17.  Operation 19: OPENATTR - Open Named Attribute Directory







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18.17.1.  ARGUMENTS

   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };


18.17.2.  RESULTS

   struct OPENATTR4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: named attribute
            *                   directory
            */
           nfsstat4        status;
   };


18.17.3.  DESCRIPTION

   The OPENATTR operation is used to obtain the filehandle of the named
   attribute directory associated with the current filehandle.  The
   result of the OPENATTR will be a filehandle to an object of type
   NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
   be used to obtain filehandles for the various named attributes
   associated with the original file system object.  Filehandles
   returned within the named attribute directory will designate objects
   of type of NF4NAMEDATTR.

   The createdir argument allows the client to signify if a named
   attribute directory should be created as a result of the OPENATTR
   operation.  Some clients may use the OPENATTR operation with a value
   of FALSE for createdir to determine if any named attributes exist for
   the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
   createdir has a value of TRUE and no named attribute directory
   exists, one is created and its filehandle becomes the current
   filehandle.  On the other hand, if createdir has a value of TRUE and
   the named attribute directory already exists, no error results and
   the filehandle of the existing directory becomes the current
   filehandle.  The creation of a named attribute directory assumes that
   the server has implemented named attribute support in this fashion
   and is not required to do so by this definition.

   If the current file handle designates an object of type NF4NAMEDATTR
   (a named attribute) or NF4ATTRDIR (a named attribute directory), an
   error of NFS4ERR_WRONG_TYPE is returned to the client.  Named



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   attributes or a named attribute directory MUST NOT have their own
   named attributes.

18.17.4.  IMPLEMENTATION

   If the server does not support named attributes for the current
   filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
   client.

18.18.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

18.18.1.  ARGUMENTS

   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };


18.18.2.  RESULTS

   struct OPEN_DOWNGRADE4resok {
           stateid4        open_stateid;
   };

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
            void;
   };


18.18.3.  DESCRIPTION

   This operation is used to adjust the access and deny states for a
   given open.  This is necessary when a given open-owner opens the same
   file multiple times with different access and deny values.  In this
   situation, a close of one of the opens may change the appropriate
   share_access and share_deny flags to remove bits associated with
   opens no longer in effect.

   Valid values for the expression (share_access &
   ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) are OPEN4_SHARE_ACCESS_READ,
   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH.  If the client



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   specifies other values, the server MUST reply with NFS4ERR_INVAL.

   Valid values for the share_deny field are OPEN4_SHARE_DENY_NONE,
   OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
   OPEN4_SHARE_DENY_BOTH.  If the client specifies other values, the
   server MUST reply with NFS4ERR_INVAL.

   After checking for valid values of share_access and share_deny, the
   server replaces the current access and deny modes on the file with
   share_access and share_deny subject to the following constraints:

   o  The bits in share_access SHOULD equal the union of the
      share_access bits (not including OPEN4_SHARE_WANT_* bits)
      specified for some subset of the OPENs in effect for the current
      open-owner on the current file.

   o  The bits in share_deny SHOULD equal the union of the share_deny
      bits specified for some subset of the OPENs in effect for the
      current open-owner on the current file.

   If the above constraints are not respected, the server SHOULD return
   the error NFS4ERR_INVAL.  Since share_access and share_deny bits
   should be subsets of those already granted, short of a defect in the
   client or server implementation, it is not possible for the
   OPEN_DOWNGRADE request to be denied because of conflicting share
   reservations.

   The seqid argument is not used in NFSv4.1, MAY be any value, and MUST
   be ignored by the server.

   On success, the current filehandle retains its value.

18.18.4.  IMPLEMENTATION

   An OPEN_DOWNGRADE operation may make OPEN_DELEGATE_READ delegations
   grantable where they were not previously.  Servers may choose to
   respond immediately if there are pending delegation want requests or
   may respond to the situation at a later time.

18.19.  Operation 22: PUTFH - Set Current Filehandle

18.19.1.  ARGUMENTS

   struct PUTFH4args {
           nfs_fh4         object;
   };





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18.19.2.  RESULTS

   struct PUTFH4res {
           /*
            * If status is NFS4_OK,
            *    new CURRENT_FH: argument to PUTFH
            */
           nfsstat4        status;
   };


18.19.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   provided as an argument.  It clears the current stateid.

   If the security mechanism used by the requester does not meet the
   requirements of the filehandle provided to this operation, the server
   MUST return NFS4ERR_WRONGSEC.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.19.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.

18.20.  Operation 23: PUTPUBFH - Set Public Filehandle

18.20.1.  ARGUMENT

   void;

18.20.2.  RESULT

   struct PUTPUBFH4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: public fh
            */
           nfsstat4        status;
   };







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18.20.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   that represents the public filehandle of the server's namespace.
   This filehandle may be different from the "root" filehandle that may
   be associated with some other directory on the server.

   PUTPUBFH also clears the current stateid.

   The public filehandle represents the concepts embodied in RFC 2054
   [42], RFC 2055 [43], and RFC 2224 [53].  The intent for NFSv4.1 is
   that the public filehandle (represented by the PUTPUBFH operation) be
   used as a method of providing WebNFS server compatibility with NFSv3.

   The public filehandle and the root filehandle (represented by the
   PUTROOTFH operation) SHOULD be equivalent.  If the public and root
   filehandles are not equivalent, then the directory corresponding to
   the public filehandle MUST be a descendant of the directory
   corresponding to the root filehandle.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.20.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.

   With the NFSv3 public filehandle, the client is able to specify
   whether the pathname provided in the LOOKUP should be evaluated as
   either an absolute path relative to the server's root or relative to
   the public filehandle.  RFC 2224 [53] contains further discussion of
   the functionality.  With NFSv4.1, that type of specification is not
   directly available in the LOOKUP operation.  The reason for this is
   because the component separators needed to specify absolute vs.
   relative are not allowed in NFSv4.  Therefore, the client is
   responsible for constructing its request such that the use of either
   PUTROOTFH or PUTPUBFH signifies absolute or relative evaluation of an
   NFS URL, respectively.

   Note that there are warnings mentioned in RFC 2224 [53] with respect
   to the use of absolute evaluation and the restrictions the server may
   place on that evaluation with respect to how much of its namespace
   has been made available.  These same warnings apply to NFSv4.1.  It
   is likely, therefore, that because of server implementation details,
   an NFSv3 absolute public filehandle look up may behave differently
   than an NFSv4.1 absolute resolution.



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   There is a form of security negotiation as described in RFC 2755 [54]
   that uses the public filehandle and an overloading of the pathname.
   This method is not available with NFSv4.1 as filehandles are not
   overloaded with special meaning and therefore do not provide the same
   framework as NFSv3.  Clients should therefore use the security
   negotiation mechanisms described in Section 2.6.

18.21.  Operation 24: PUTROOTFH - Set Root Filehandle

18.21.1.  ARGUMENTS

   void;

18.21.2.  RESULTS

   struct PUTROOTFH4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: root fh
            */
           nfsstat4        status;
   };


18.21.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   that represents the root of the server's namespace.  From this
   filehandle, a LOOKUP operation can locate any other filehandle on the
   server.  This filehandle may be different from the "public"
   filehandle that may be associated with some other directory on the
   server.

   PUTROOTFH also clears the current stateid.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.21.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.

18.22.  Operation 25: READ - Read from File






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18.22.1.  ARGUMENTS

   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };


18.22.2.  RESULTS

   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };

   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };


18.22.3.  DESCRIPTION

   The READ operation reads data from the regular file identified by the
   current filehandle.

   The client provides an offset of where the READ is to start and a
   count of how many bytes are to be read.  An offset of zero means to
   read data starting at the beginning of the file.  If offset is
   greater than or equal to the size of the file, the status NFS4_OK is
   returned with a data length set to zero and eof is set to TRUE.  The
   READ is subject to access permissions checking.

   If the client specifies a count value of zero, the READ succeeds and
   returns zero bytes of data again subject to access permissions
   checking.  The server may choose to return fewer bytes than specified
   by the client.  The client needs to check for this condition and
   handle the condition appropriately.

   Except when special stateids are used, the stateid value for a READ
   request represents a value returned from a previous byte-range lock
   or share reservation request or the stateid associated with a
   delegation.  The stateid identifies the associated owners if any and
   is used by the server to verify that the associated locks are still



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   valid (e.g., have not been revoked).

   If the read ended at the end-of-file (formally, in a correctly formed
   READ operation, if offset + count is equal to the size of the file),
   or the READ operation extends beyond the size of the file (if offset
   + count is greater than the size of the file), eof is returned as
   TRUE; otherwise, it is FALSE.  A successful READ of an empty file
   will always return eof as TRUE.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   For a READ with a stateid value of all bits equal to zero, the server
   MAY allow the READ to be serviced subject to mandatory byte-range
   locks or the current share deny modes for the file.  For a READ with
   a stateid value of all bits equal to one, the server MAY allow READ
   operations to bypass locking checks at the server.

   On success, the current filehandle retains its value.

18.22.4.  IMPLEMENTATION

   If the server returns a "short read" (i.e., fewer data than requested
   and eof is set to FALSE), the client should send another READ to get
   the remaining data.  A server may return less data than requested
   under several circumstances.  The file may have been truncated by
   another client or perhaps on the server itself, changing the file
   size from what the requesting client believes to be the case.  This
   would reduce the actual amount of data available to the client.  It
   is possible that the server reduce the transfer size and so return a
   short read result.  Server resource exhaustion may also occur in a
   short read.

   If mandatory byte-range locking is in effect for the file, and if the
   byte-range corresponding to the data to be read from the file is
   WRITE_LT locked by an owner not associated with the stateid, the
   server will return the NFS4ERR_LOCKED error.  The client should try
   to get the appropriate READ_LT via the LOCK operation before re-
   attempting the READ.  When the READ completes, the client should
   release the byte-range lock via LOCKU.

   If another client has an OPEN_DELEGATE_WRITE delegation for the file
   being read, the delegation must be recalled, and the operation cannot
   proceed until that delegation is returned or revoked.  Except where
   this happens very quickly, one or more NFS4ERR_DELAY errors will be



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   returned to requests made while the delegation remains outstanding.
   Normally, delegations will not be recalled as a result of a READ
   operation since the recall will occur as a result of an earlier OPEN.
   However, since it is possible for a READ to be done with a special
   stateid, the server needs to check for this case even though the
   client should have done an OPEN previously.

18.23.  Operation 26: READDIR - Read Directory

18.23.1.  ARGUMENTS

   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };


18.23.2.  RESULTS

   struct entry4 {
           nfs_cookie4     cookie;
           component4      name;
           fattr4          attrs;
           entry4          *nextentry;
   };

   struct dirlist4 {
           entry4          *entries;
           bool            eof;
   };

   struct READDIR4resok {
           verifier4       cookieverf;
           dirlist4        reply;
   };


   union READDIR4res switch (nfsstat4 status) {
    case NFS4_OK:
            READDIR4resok  resok4;
    default:
            void;
   };




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18.23.3.  DESCRIPTION

   The READDIR operation retrieves a variable number of entries from a
   file system directory and returns client-requested attributes for
   each entry along with information to allow the client to request
   additional directory entries in a subsequent READDIR.

   The arguments contain a cookie value that represents where the
   READDIR should start within the directory.  A value of zero for the
   cookie is used to start reading at the beginning of the directory.
   For subsequent READDIR requests, the client specifies a cookie value
   that is provided by the server on a previous READDIR request.

   The request's cookieverf field should be set to 0 zero) when the
   request's cookie field is zero (first read of the directory).  On
   subsequent requests, the cookieverf field must match the cookieverf
   returned by the READDIR in which the cookie was acquired.  If the
   server determines that the cookieverf is no longer valid for the
   directory, the error NFS4ERR_NOT_SAME must be returned.

   The dircount field of the request is a hint of the maximum number of
   bytes of directory information that should be returned.  This value
   represents the total length of the names of the directory entries and
   the cookie value for these entries.  This length represents the XDR
   encoding of the data (names and cookies) and not the length in the
   native format of the server.

   The maxcount field of the request represents the maximum total size
   of all of the data being returned within the READDIR4resok structure
   and includes the XDR overhead.  The server MAY return less data.  If
   the server is unable to return a single directory entry within the
   maxcount limit, the error NFS4ERR_TOOSMALL MUST be returned to the
   client.

   Finally, the request's attr_request field represents the list of
   attributes to be returned for each directory entry supplied by the
   server.

   A successful reply consists of a list of directory entries.  Each of
   these entries contains the name of the directory entry, a cookie
   value for that entry, and the associated attributes as requested.
   The "eof" flag has a value of TRUE if there are no more entries in
   the directory.

   The cookie value is only meaningful to the server and is used as a
   cursor for the directory entry.  As mentioned, this cookie is used by
   the client for subsequent READDIR operations so that it may continue
   reading a directory.  The cookie is similar in concept to a READ



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   offset but MUST NOT be interpreted as such by the client.  Ideally,
   the cookie value SHOULD NOT change if the directory is modified since
   the client may be caching these values.

   In some cases, the server may encounter an error while obtaining the
   attributes for a directory entry.  Instead of returning an error for
   the entire READDIR operation, the server can instead return the
   attribute rdattr_error (Section 5.8.1.12).  With this, the server is
   able to communicate the failure to the client and not fail the entire
   operation in the instance of what might be a transient failure.
   Obviously, the client must request the fattr4_rdattr_error attribute
   for this method to work properly.  If the client does not request the
   attribute, the server has no choice but to return failure for the
   entire READDIR operation.

   For some file system environments, the directory entries "." and ".."
   have special meaning, and in other environments, they do not.  If the
   server supports these special entries within a directory, they SHOULD
   NOT be returned to the client as part of the READDIR response.  To
   enable some client environments, the cookie values of zero, 1, and 2
   are to be considered reserved.  Note that the UNIX client will use
   these values when combining the server's response and local
   representations to enable a fully formed UNIX directory presentation
   to the application.

   For READDIR arguments, cookie values of one and two SHOULD NOT be
   used, and for READDIR results, cookie values of zero, one, and two
   SHOULD NOT be returned.

   On success, the current filehandle retains its value.

18.23.4.  IMPLEMENTATION

   The server's file system directory representations can differ
   greatly.  A client's programming interfaces may also be bound to the
   local operating environment in a way that does not translate well
   into the NFS protocol.  Therefore, the use of the dircount and
   maxcount fields are provided to enable the client to provide hints to
   the server.  If the client is aggressive about attribute collection
   during a READDIR, the server has an idea of how to limit the encoded
   response.

   If dircount is zero, the server bounds the reply's size based on the
   request's maxcount field.

   The cookieverf may be used by the server to help manage cookie values
   that may become stale.  It should be a rare occurrence that a server
   is unable to continue properly reading a directory with the provided



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   cookie/cookieverf pair.  The server SHOULD make every effort to avoid
   this condition since the application at the client might be unable to
   properly handle this type of failure.

   The use of the cookieverf will also protect the client from using
   READDIR cookie values that might be stale.  For example, if the file
   system has been migrated, the server might or might not be able to
   use the same cookie values to service READDIR as the previous server
   used.  With the client providing the cookieverf, the server is able
   to provide the appropriate response to the client.  This prevents the
   case where the server accepts a cookie value but the underlying
   directory has changed and the response is invalid from the client's
   context of its previous READDIR.

   Since some servers will not be returning "." and ".." entries as has
   been done with previous versions of the NFS protocol, the client that
   requires these entries be present in READDIR responses must fabricate
   them.

18.24.  Operation 27: READLINK - Read Symbolic Link

18.24.1.  ARGUMENTS

   /* CURRENT_FH: symlink */
   void;

18.24.2.  RESULTS

   struct READLINK4resok {
           linktext4       link;
   };

   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };


18.24.3.  DESCRIPTION

   READLINK reads the data associated with a symbolic link.  Depending
   on the value of the UTF-8 capability attribute (Section 14.4), the
   data is encoded in UTF-8.  Whether created by an NFS client or
   created locally on the server, the data in a symbolic link is not
   interpreted (except possibly to check for proper UTF-8 encoding) when
   created, but is simply stored.



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   On success, the current filehandle retains its value.

18.24.4.  IMPLEMENTATION

   A symbolic link is nominally a pointer to another file.  The data is
   not necessarily interpreted by the server, just stored in the file.
   It is possible for a client implementation to store a pathname that
   is not meaningful to the server operating system in a symbolic link.
   A READLINK operation returns the data to the client for
   interpretation.  If different implementations want to share access to
   symbolic links, then they must agree on the interpretation of the
   data in the symbolic link.

   The READLINK operation is only allowed on objects of type NF4LNK.
   The server should return the error NFS4ERR_WRONG_TYPE if the object
   is not of type NF4LNK.

18.25.  Operation 28: REMOVE - Remove File System Object

18.25.1.  ARGUMENTS

   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4      target;
   };


18.25.2.  RESULTS

   struct REMOVE4resok {
           change_info4    cinfo;
   };

   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   };


18.25.3.  DESCRIPTION

   The REMOVE operation removes (deletes) a directory entry named by
   filename from the directory corresponding to the current filehandle.
   If the entry in the directory was the last reference to the
   corresponding file system object, the object may be destroyed.  The
   directory may be either of type NF4DIR or NF4ATTRDIR.



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   For the directory where the filename was removed, the server returns
   change_info4 information in cinfo.  With the atomic field of the
   change_info4 data type, the server will indicate if the before and
   after change attributes were obtained atomically with respect to the
   removal.

   If the target has a length of zero, or if the target does not obey
   the UTF-8 definition (and the server is enforcing UTF-8 encoding; see
   Section 14.4), the error NFS4ERR_INVAL will be returned.

   On success, the current filehandle retains its value.

18.25.4.  IMPLEMENTATION

   NFSv3 required a different operator RMDIR for directory removal and
   REMOVE for non-directory removal.  This allowed clients to skip
   checking the file type when being passed a non-directory delete
   system call (e.g., unlink() [27] in POSIX) to remove a directory, as
   well as the converse (e.g., a rmdir() on a non-directory) because
   they knew the server would check the file type.  NFSv4.1 REMOVE can
   be used to delete any directory entry independent of its file type.
   The implementor of an NFSv4.1 client's entry points from the unlink()
   and rmdir() system calls should first check the file type against the
   types the system call is allowed to remove before sending a REMOVE
   operation.  Alternatively, the implementor can produce a COMPOUND
   call that includes a LOOKUP/VERIFY sequence of operations to verify
   the file type before a REMOVE operation in the same COMPOUND call.

   The concept of last reference is server specific.  However, if the
   numlinks field in the previous attributes of the object had the value
   1, the client should not rely on referring to the object via a
   filehandle.  Likewise, the client should not rely on the resources
   (disk space, directory entry, and so on) formerly associated with the
   object becoming immediately available.  Thus, if a client needs to be
   able to continue to access a file after using REMOVE to remove it,
   the client should take steps to make sure that the file will still be
   accessible.  While the traditional mechanism used is to RENAME the
   file from its old name to a new hidden name, the NFSv4.1 OPEN
   operation MAY return a result flag, OPEN4_RESULT_PRESERVE_UNLINKED,
   which indicates to the client that the file will be preserved if the
   file has an outstanding open (see Section 18.16).

   If the server finds that the file is still open when the REMOVE
   arrives:

   o  The server SHOULD NOT delete the file's directory entry if the
      file was opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH.



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   o  If the file was not opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
      directory entry.  However, until last CLOSE of the file, the
      server MAY continue to allow access to the file via its
      filehandle.

   o  The server MUST NOT delete the directory entry if the reply from
      OPEN had the flag OPEN4_RESULT_PRESERVE_UNLINKED set.

   The server MAY implement its own restrictions on removal of a file
   while it is open.  The server might disallow such a REMOVE (or a
   removal that occurs as part of RENAME).  The conditions that
   influence the restrictions on removal of a file while it is still
   open include:

   o  Whether certain access protocols (i.e., not just NFS) are holding
      the file open.

   o  Whether particular options, access modes, or policies on the
      server are enabled.

   If a file has an outstanding OPEN and this prevents the removal of
   the file's directory entry, the error NFS4ERR_FILE_OPEN is returned.

   Where the determination above cannot be made definitively because
   delegations are being held, they MUST be recalled to allow processing
   of the REMOVE to continue.  When a delegation is held, the server has
   no reliable knowledge of the status of OPENs for that client, so
   unless there are files opened with the particular deny modes by
   clients without delegations, the determination cannot be made until
   delegations are recalled, and the operation cannot proceed until each
   sufficient delegation has been returned or revoked to allow the
   server to make a correct determination.

   In all cases in which delegations are recalled, the server is likely
   to return one or more NFS4ERR_DELAY errors while delegations remain
   outstanding.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the situation can
   be resolved by sending a notification, the directory delegation MUST
   be recalled, and the operation MUST NOT proceed until the delegation
   is returned or revoked.  Except where this happens very quickly, one
   or more NFS4ERR_DELAY errors will be returned to requests made while
   delegation remains outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations



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   request such notifications, NOTIFY4_REMOVE_ENTRY will be generated as
   a result of this operation.

   Note that when a remove occurs as a result of a RENAME,
   NOTIFY4_REMOVE_ENTRY will only be generated if the removal happens as
   a separate operation.  In the case in which the removal is integrated
   and atomic with RENAME, the notification of the removal is integrated
   with notification for the RENAME.  See the discussion of the
   NOTIFY4_RENAME_ENTRY notification in Section 20.4.

18.26.  Operation 29: RENAME - Rename Directory Entry

18.26.1.  ARGUMENTS

   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */
           component4      newname;
   };


18.26.2.  RESULTS

   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };

   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
           RENAME4resok    resok4;
    default:
           void;
   };


18.26.3.  DESCRIPTION

   The RENAME operation renames the object identified by oldname in the
   source directory corresponding to the saved filehandle, as set by the
   SAVEFH operation, to newname in the target directory corresponding to
   the current filehandle.  The operation is required to be atomic to
   the client.  Source and target directories MUST reside on the same
   file system on the server.  On success, the current filehandle will
   continue to be the target directory.

   If the target directory already contains an entry with the name



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   newname, the source object MUST be compatible with the target: either
   both are non-directories or both are directories and the target MUST
   be empty.  If compatible, the existing target is removed before the
   rename occurs or, preferably, the target is removed atomically as
   part of the rename.  See Section 18.25.4 for client and server
   actions whenever a target is removed.  Note however that when the
   removal is performed atomically with the rename, certain parts of the
   removal described there are integrated with the rename.  For example,
   notification of the removal will not be via a NOTIFY4_REMOVE_ENTRY
   but will be indicated as part of the NOTIFY4_ADD_ENTRY or
   NOTIFY4_RENAME_ENTRY generated by the rename.

   If the source object and the target are not compatible or if the
   target is a directory but not empty, the server will return the error
   NFS4ERR_EXIST.

   If oldname and newname both refer to the same file (e.g., they might
   be hard links of each other), then unless the file is open (see
   Section 18.26.4), RENAME MUST perform no action and return NFS4_OK.

   For both directories involved in the RENAME, the server returns
   change_info4 information.  With the atomic field of the change_info4
   data type, the server will indicate if the before and after change
   attributes were obtained atomically with respect to the rename.

   If oldname refers to a named attribute and the saved and current
   filehandles refer to different file system objects, the server will
   return NFS4ERR_XDEV just as if the saved and current filehandles
   represented directories on different file systems.

   If oldname or newname has a length of zero, or if oldname or newname
   does not obey the UTF-8 definition, the error NFS4ERR_INVAL will be
   returned.

18.26.4.  IMPLEMENTATION

   The server MAY impose restrictions on the RENAME operation such that
   RENAME may not be done when the file being renamed is open or when
   that open is done by particular protocols, or with particular options
   or access modes.  Similar restrictions may be applied when a file
   exists with the target name and is open.  When RENAME is rejected
   because of such restrictions, the error NFS4ERR_FILE_OPEN is
   returned.

   When oldname and rename refer to the same file and that file is open
   in a fashion such that RENAME would normally be rejected with
   NFS4ERR_FILE_OPEN if oldname and newname were different files, then
   RENAME SHOULD be rejected with NFS4ERR_FILE_OPEN.



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   If a server does implement such restrictions and those restrictions
   include cases of NFSv4 opens preventing successful execution of a
   rename, the server needs to recall any delegations that could hide
   the existence of opens relevant to that decision.  This is because
   when a client holds a delegation, the server might not have an
   accurate account of the opens for that client, since the client may
   execute OPENs and CLOSEs locally.  The RENAME operation need only be
   delayed until a definitive result can be obtained.  For example, if
   there are multiple delegations and one of them establishes an open
   whose presence would prevent the rename, given the server's
   semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon as
   that delegation is returned without waiting for other delegations to
   be returned.  Similarly, if such opens are not associated with
   delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
   delegation recall being done.

   If the current filehandle or the saved filehandle designates a
   directory for which another client holds a directory delegation,
   then, unless the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the operation cannot proceed
   until the delegation is returned or revoked.  Except where this
   happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   When the current and saved filehandles are the same and they
   designate a directory for which one or more directory delegations
   exist, then, when those delegations request such notifications, a
   notification of type NOTIFY4_RENAME_ENTRY will be generated as a
   result of this operation.  When oldname and rename refer to the same
   file, no notification is generated (because, as Section 18.26.3
   states, the server MUST take no action).  When a file is removed
   because it has the same name as the target, if that removal is done
   atomically with the rename, a NOTIFY4_REMOVE_ENTRY notification will
   not be generated.  Instead, the deletion of the file will be reported
   as part of the NOTIFY4_RENAME_ENTRY notification.

   When the current and saved filehandles are not the same:

   o  If the current filehandle designates a directory for which one or
      more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated as
      a result of this operation.  When a file is removed because it has
      the same name as the target, if that removal is done atomically
      with the rename, a NOTIFY4_REMOVE_ENTRY notification will not be
      generated.  Instead, the deletion of the file will be reported as
      part of the NOTIFY4_ADD_ENTRY notification.





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   o  If the saved filehandle designates a directory for which one or
      more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_REMOVE_ENTRY will be generated
      as a result of this operation.

   If the object being renamed has file delegations held by clients
   other than the one doing the RENAME, the delegations MUST be
   recalled, and the operation cannot proceed until each such delegation
   is returned or revoked.  Note that in the case of multiply linked
   files, the delegation recall requirement applies even if the
   delegation was obtained through a different name than the one being
   renamed.  In all cases in which delegations are recalled, the server
   is likely to return one or more NFS4ERR_DELAY errors while the
   delegation(s) remains outstanding, although it might not do that if
   the delegations are returned quickly.

   The RENAME operation must be atomic to the client.  The statement
   "source and target directories MUST reside on the same file system on
   the server" means that the fsid fields in the attributes for the
   directories are the same.  If they reside on different file systems,
   the error NFS4ERR_XDEV is returned.

   Based on the value of the fh_expire_type attribute for the object,
   the filehandle may or may not expire on a RENAME.  However, server
   implementors are strongly encouraged to attempt to keep filehandles
   from expiring in this fashion.

   On some servers, the file names "." and ".." are illegal as either
   oldname or newname, and will result in the error NFS4ERR_BADNAME.  In
   addition, on many servers the case of oldname or newname being an
   alias for the source directory will be checked for.  Such servers
   will return the error NFS4ERR_INVAL in these cases.

   If either of the source or target filehandles are not directories,
   the server will return NFS4ERR_NOTDIR.

18.27.  Operation 31: RESTOREFH - Restore Saved Filehandle

18.27.1.  ARGUMENTS

   /* SAVED_FH: */
   void;









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18.27.2.  RESULTS

   struct RESTOREFH4res {
           /*
            * If status is NFS4_OK,
            *     new CURRENT_FH: value of saved fh
            */
           nfsstat4        status;
   };


18.27.3.  DESCRIPTION

   The RESTOREFH operation sets the current filehandle and stateid to
   the values in the saved filehandle and stateid.  If there is no saved
   filehandle, then the server will return the error
   NFS4ERR_NOFILEHANDLE.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.27.4.  IMPLEMENTATION

   Operations like OPEN and LOOKUP use the current filehandle to
   represent a directory and replace it with a new filehandle.  Assuming
   that the previous filehandle was saved with a SAVEFH operator, the
   previous filehandle can be restored as the current filehandle.  This
   is commonly used to obtain post-operation attributes for the
   directory, e.g.,

         PUTFH (directory filehandle)
         SAVEFH
         GETATTR attrbits     (pre-op dir attrs)
         CREATE optbits "foo" attrs
         GETATTR attrbits     (file attributes)
         RESTOREFH
         GETATTR attrbits     (post-op dir attrs)

18.28.  Operation 32: SAVEFH - Save Current Filehandle

18.28.1.  ARGUMENTS

   /* CURRENT_FH: */
   void;






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18.28.2.  RESULTS

   struct SAVEFH4res {
           /*
            * If status is NFS4_OK,
            *    new SAVED_FH: value of current fh
            */
           nfsstat4        status;
   };


18.28.3.  DESCRIPTION

   The SAVEFH operation saves the current filehandle and stateid.  If a
   previous filehandle was saved, then it is no longer accessible.  The
   saved filehandle can be restored as the current filehandle with the
   RESTOREFH operator.

   On success, the current filehandle retains its value.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.28.4.  IMPLEMENTATION

18.29.  Operation 33: SECINFO - Obtain Available Security

18.29.1.  ARGUMENTS

   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4      name;
   };

















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18.29.2.  RESULTS

   /*
    * From RFC 2203
    */
   enum rpc_gss_svc_t {
           RPC_GSS_SVC_NONE        = 1,
           RPC_GSS_SVC_INTEGRITY   = 2,
           RPC_GSS_SVC_PRIVACY     = 3
   };

   struct rpcsec_gss_info {
           sec_oid4        oid;
           qop4            qop;
           rpc_gss_svc_t   service;
   };

   /* RPCSEC_GSS has a value of '6' - See RFC 2203 */
   union secinfo4 switch (uint32_t flavor) {
    case RPCSEC_GSS:
            rpcsec_gss_info        flavor_info;
    default:
            void;
   };

   typedef secinfo4 SECINFO4resok<>;

   union SECINFO4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* CURRENTFH: consumed */
            SECINFO4resok resok4;
    default:
            void;
   };


18.29.3.  DESCRIPTION

   The SECINFO operation is used by the client to obtain a list of valid
   RPC authentication flavors for a specific directory filehandle, file
   name pair.  SECINFO should apply the same access methodology used for
   LOOKUP when evaluating the name.  Therefore, if the requester does
   not have the appropriate access to LOOKUP the name, then SECINFO MUST
   behave the same way and return NFS4ERR_ACCESS.

   The result will contain an array that represents the security
   mechanisms available, with an order corresponding to the server's
   preferences, the most preferred being first in the array.  The client



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   is free to pick whatever security mechanism it both desires and
   supports, or to pick in the server's preference order the first one
   it supports.  The array entries are represented by the secinfo4
   structure.  The field 'flavor' will contain a value of AUTH_NONE,
   AUTH_SYS (as defined in RFC 5531 [3]), or RPCSEC_GSS (as defined in
   RFC 2203 [4]).  The field flavor can also be any other security
   flavor registered with IANA.

   For the flavors AUTH_NONE and AUTH_SYS, no additional security
   information is returned.  The same is true of many (if not most)
   other security flavors, including AUTH_DH.  For a return value of
   RPCSEC_GSS, a security triple is returned that contains the mechanism
   object identifier (OID, as defined in RFC 2743 [7]), the quality of
   protection (as defined in RFC 2743 [7]), and the service type (as
   defined in RFC 2203 [4]).  It is possible for SECINFO to return
   multiple entries with flavor equal to RPCSEC_GSS with different
   security triple values.

   On success, the current filehandle is consumed (see
   Section 2.6.3.1.1.8), and if the next operation after SECINFO tries
   to use the current filehandle, that operation will fail with the
   status NFS4ERR_NOFILEHANDLE.

   If the name has a length of zero, or if the name does not obey the
   UTF-8 definition (assuming UTF-8 capabilities are enabled; see
   Section 14.4), the error NFS4ERR_INVAL will be returned.

   See Section 2.6 for additional information on the use of SECINFO.

18.29.4.  IMPLEMENTATION

   The SECINFO operation is expected to be used by the NFS client when
   the error value of NFS4ERR_WRONGSEC is returned from another NFS
   operation.  This signifies to the client that the server's security
   policy is different from what the client is currently using.  At this
   point, the client is expected to obtain a list of possible security
   flavors and choose what best suits its policies.

   As mentioned, the server's security policies will determine when a
   client request receives NFS4ERR_WRONGSEC.  See Table 8 for a list of
   operations that can return NFS4ERR_WRONGSEC.  In addition, when
   READDIR returns attributes, the rdattr_error (Section 5.8.1.12) can
   contain NFS4ERR_WRONGSEC.  Note that CREATE and REMOVE MUST NOT
   return NFS4ERR_WRONGSEC.  The rationale for CREATE is that unless the
   target name exists, it cannot have a separate security policy from
   the parent directory, and the security policy of the parent was
   checked when its filehandle was injected into the COMPOUND request's
   operations stream (for similar reasons, an OPEN operation that



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   creates the target MUST NOT return NFS4ERR_WRONGSEC).  If the target
   name exists, while it might have a separate security policy, that is
   irrelevant because CREATE MUST return NFS4ERR_EXIST.  The rationale
   for REMOVE is that while that target might have a separate security
   policy, the target is going to be removed, and so the security policy
   of the parent trumps that of the object being removed.  RENAME and
   LINK MAY return NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error
   applies only to the saved filehandle (see Section 2.6.3.1.2).  Any
   NFS4ERR_WRONGSEC error on the current filehandle used by LINK and
   RENAME MUST be returned by the PUTFH, PUTPUBFH, PUTROOTFH, or
   RESTOREFH operation that injected the current filehandle.

   With the exception of LINK and RENAME, the set of operations that can
   return NFS4ERR_WRONGSEC represents the point at which the client can
   inject a filehandle into the "current filehandle" at the server.  The
   filehandle is either provided by the client (PUTFH, PUTPUBFH,
   PUTROOTFH), generated as a result of a name-to-filehandle translation
   (LOOKUP and OPEN), or generated from the saved filehandle via
   RESTOREFH.  As Section 2.6.3.1.1.1 states, a put filehandle operation
   followed by SAVEFH MUST NOT return NFS4ERR_WRONGSEC.  Thus, the
   RESTOREFH operation, under certain conditions (see
   Section 2.6.3.1.1), is permitted to return NFS4ERR_WRONGSEC so that
   security policies can be honored.

   The READDIR operation will not directly return the NFS4ERR_WRONGSEC
   error.  However, if the READDIR request included a request for
   attributes, it is possible that the READDIR request's security triple
   did not match that of a directory entry.  If this is the case and the
   client has requested the rdattr_error attribute, the server will
   return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.

   To resolve an error return of NFS4ERR_WRONGSEC, the client does the
   following:

   o  For LOOKUP and OPEN, the client will use SECINFO with the same
      current filehandle and name as provided in the original LOOKUP or
      OPEN to enumerate the available security triples.

   o  For the rdattr_error, the client will use SECINFO with the same
      current filehandle as provided in the original READDIR.  The name
      passed to SECINFO will be that of the directory entry (as returned
      from READDIR) that had the NFS4ERR_WRONGSEC error in the
      rdattr_error attribute.

   o  For PUTFH, PUTROOTFH, PUTPUBFH, RESTOREFH, LINK, and RENAME, the
      client will use SECINFO_NO_NAME { style =
      SECINFO_STYLE4_CURRENT_FH }.  The client will prefix the
      SECINFO_NO_NAME operation with the appropriate PUTFH, PUTPUBFH, or



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      PUTROOTFH operation that provides the filehandle originally
      provided by the PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH
      operation.

      NOTE: In NFSv4.0, the client was required to use SECINFO, and had
      to reconstruct the parent of the original filehandle and the
      component name of the original filehandle.  The introduction in
      NFSv4.1 of SECINFO_NO_NAME obviates the need for reconstruction.

   o  For LOOKUPP, the client will use SECINFO_NO_NAME { style =
      SECINFO_STYLE4_PARENT } and provide the filehandle that equals the
      filehandle originally provided to LOOKUPP.

   See Section 21 for a discussion on the recommendations for the
   security flavor used by SECINFO and SECINFO_NO_NAME.

18.30.  Operation 34: SETATTR - Set Attributes

18.30.1.  ARGUMENTS

   struct SETATTR4args {
           /* CURRENT_FH: target object */
           stateid4        stateid;
           fattr4          obj_attributes;
   };


18.30.2.  RESULTS

   struct SETATTR4res {
           nfsstat4        status;
           bitmap4         attrsset;
   };


18.30.3.  DESCRIPTION

   The SETATTR operation changes one or more of the attributes of a file
   system object.  The new attributes are specified with a bitmap and
   the attributes that follow the bitmap in bit order.

   The stateid argument for SETATTR is used to provide byte-range
   locking context that is necessary for SETATTR requests that set the
   size attribute.  Since setting the size attribute modifies the file's
   data, it has the same locking requirements as a corresponding WRITE.
   Any SETATTR that sets the size attribute is incompatible with a share
   reservation that specifies OPEN4_SHARE_DENY_WRITE.  The area between
   the old end-of-file and the new end-of-file is considered to be



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   modified just as would have been the case had the area in question
   been specified as the target of WRITE, for the purpose of checking
   conflicts with byte-range locks, for those cases in which a server is
   implementing mandatory byte-range locking behavior.  A valid stateid
   SHOULD always be specified.  When the file size attribute is not set,
   the special stateid consisting of all bits equal to zero MAY be
   passed.

   On either success or failure of the operation, the server will return
   the attrsset bitmask to represent what (if any) attributes were
   successfully set.  The attrsset in the response is a subset of the
   attrmask field of the obj_attributes field in the argument.

   On success, the current filehandle retains its value.

18.30.4.  IMPLEMENTATION

   If the request specifies the owner attribute to be set, the server
   SHOULD allow the operation to succeed if the current owner of the
   object matches the value specified in the request.  Some servers may
   be implemented in a way as to prohibit the setting of the owner
   attribute unless the requester has privilege to do so.  If the server
   is lenient in this one case of matching owner values, the client
   implementation may be simplified in cases of creation of an object
   (e.g., an exclusive create via OPEN) followed by a SETATTR.

   The file size attribute is used to request changes to the size of a
   file.  A value of zero causes the file to be truncated, a value less
   than the current size of the file causes data from new size to the
   end of the file to be discarded, and a size greater than the current
   size of the file causes logically zeroed data bytes to be added to
   the end of the file.  Servers are free to implement this using
   unallocated bytes (holes) or allocated data bytes set to zero.
   Clients should not make any assumptions regarding a server's
   implementation of this feature, beyond that the bytes in the affected
   byte-range returned by READ will be zeroed.  Servers MUST support
   extending the file size via SETATTR.

   SETATTR is not guaranteed to be atomic.  A failed SETATTR may
   partially change a file's attributes, hence the reason why the reply
   always includes the status and the list of attributes that were set.

   If the object whose attributes are being changed has a file
   delegation that is held by a client other than the one doing the
   SETATTR, the delegation(s) must be recalled, and the operation cannot
   proceed to actually change an attribute until each such delegation is
   returned or revoked.  In all cases in which delegations are recalled,
   the server is likely to return one or more NFS4ERR_DELAY errors while



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   the delegation(s) remains outstanding, although it might not do that
   if the delegations are returned quickly.

   If the object whose attributes are being set is a directory and
   another client holds a directory delegation for that directory, then
   if enabled, asynchronous notifications will be generated when the set
   of attributes changed has a non-null intersection with the set of
   attributes for which notification is requested.  Notifications of
   type NOTIFY4_CHANGE_DIR_ATTRS will be sent to the appropriate
   client(s), but the SETATTR is not delayed by waiting for these
   notifications to be sent.

   If the object whose attributes are being set is a member of the
   directory for which another client holds a directory delegation, then
   asynchronous notifications will be generated when the set of
   attributes changed has a non-null intersection with the set of
   attributes for which notification is requested.  Notifications of
   type NOTIFY4_CHANGE_CHILD_ATTRS will be sent to the appropriate
   clients, but the SETATTR is not delayed by waiting for these
   notifications to be sent.

   Changing the size of a file with SETATTR indirectly changes the
   time_modify and change attributes.  A client must account for this as
   size changes can result in data deletion.

   The attributes time_access_set and time_modify_set are write-only
   attributes constructed as a switched union so the client can direct
   the server in setting the time values.  If the switched union
   specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
   be used for the operation.  If the switch union does not specify
   SET_TO_CLIENT_TIME4, the server is to use its current time for the
   SETATTR operation.

   If server and client times differ, programs that compare client time
   to file times can break.  A time synchronization protocol should be
   used to limit client/server time skew.

   Use of a COMPOUND containing a VERIFY operation specifying only the
   change attribute, immediately followed by a SETATTR, provides a means
   whereby a client may specify a request that emulates the
   functionality of the SETATTR guard mechanism of NFSv3.  Since the
   function of the guard mechanism is to avoid changes to the file
   attributes based on stale information, delays between checking of the
   guard condition and the setting of the attributes have the potential
   to compromise this function, as would the corresponding delay in the
   NFSv4 emulation.  Therefore, NFSv4.1 servers SHOULD take care to
   avoid such delays, to the degree possible, when executing such a
   request.



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   If the server does not support an attribute as requested by the
   client, the server SHOULD return NFS4ERR_ATTRNOTSUPP.

   A mask of the attributes actually set is returned by SETATTR in all
   cases.  That mask MUST NOT include attribute bits not requested to be
   set by the client.  If the attribute masks in the request and reply
   are equal, the status field in the reply MUST be NFS4_OK.

18.31.  Operation 37: VERIFY - Verify Same Attributes

18.31.1.  ARGUMENTS

   struct VERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };


18.31.2.  RESULTS

   struct VERIFY4res {
           nfsstat4        status;
   };


18.31.3.  DESCRIPTION

   The VERIFY operation is used to verify that attributes have the value
   assumed by the client before proceeding with the following operations
   in the COMPOUND request.  If any of the attributes do not match, then
   the error NFS4ERR_NOT_SAME must be returned.  The current filehandle
   retains its value after successful completion of the operation.

18.31.4.  IMPLEMENTATION

   One possible use of the VERIFY operation is the following series of
   operations.  With this, the client is attempting to verify that the
   file being removed will match what the client expects to be removed.
   This series can help prevent the unintended deletion of a file.

         PUTFH (directory filehandle)
         LOOKUP (file name)
         VERIFY (filehandle == fh)
         PUTFH (directory filehandle)
         REMOVE (file name)

   This series does not prevent a second client from removing and
   creating a new file in the middle of this sequence, but it does help



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   avoid the unintended result.

   In the case that a RECOMMENDED attribute is specified in the VERIFY
   operation and the server does not support that attribute for the file
   system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any set-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.

18.32.  Operation 38: WRITE - Write to File

18.32.1.  ARGUMENTS

   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };

   struct WRITE4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           stable_how4     stable;
           opaque          data<>;
   };


18.32.2.  RESULTS

   struct WRITE4resok {
           count4          count;
           stable_how4     committed;
           verifier4       writeverf;
   };

   union WRITE4res switch (nfsstat4 status) {
    case NFS4_OK:
            WRITE4resok    resok4;
    default:
            void;
   };







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18.32.3.  DESCRIPTION

   The WRITE operation is used to write data to a regular file.  The
   target file is specified by the current filehandle.  The offset
   specifies the offset where the data should be written.  An offset of
   zero specifies that the write should start at the beginning of the
   file.  The count, as encoded as part of the opaque data parameter,
   represents the number of bytes of data that are to be written.  If
   the count is zero, the WRITE will succeed and return a count of zero
   subject to permissions checking.  The server MAY write fewer bytes
   than requested by the client.

   The client specifies with the stable parameter the method of how the
   data is to be processed by the server.  If stable is FILE_SYNC4, the
   server MUST commit the data written plus all file system metadata to
   stable storage before returning results.  This corresponds to the
   NFSv2 protocol semantics.  Any other behavior constitutes a protocol
   violation.  If stable is DATA_SYNC4, then the server MUST commit all
   of the data to stable storage and enough of the metadata to retrieve
   the data before returning.  The server implementor is free to
   implement DATA_SYNC4 in the same fashion as FILE_SYNC4, but with a
   possible performance drop.  If stable is UNSTABLE4, the server is
   free to commit any part of the data and the metadata to stable
   storage, including all or none, before returning a reply to the
   client.  There is no guarantee whether or when any uncommitted data
   will subsequently be committed to stable storage.  The only
   guarantees made by the server are that it will not destroy any data
   without changing the value of writeverf and that it will not commit
   the data and metadata at a level less than that requested by the
   client.

   Except when special stateids are used, the stateid value for a WRITE
   request represents a value returned from a previous byte-range LOCK
   or OPEN request or the stateid associated with a delegation.  The
   stateid identifies the associated owners if any and is used by the
   server to verify that the associated locks are still valid (e.g.,
   have not been revoked).

   Upon successful completion, the following results are returned.  The
   count result is the number of bytes of data written to the file.  The
   server may write fewer bytes than requested.  If so, the actual
   number of bytes written starting at location, offset, is returned.

   The server also returns an indication of the level of commitment of
   the data and metadata via committed.  Per Table 11,

   o  The server MAY commit the data at a stronger level than requested.




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   o  The server MUST commit the data at a level at least as high as
      that committed.

   Valid combinations of the fields stable in the request and committed
                               in the reply.

            +------------+-----------------------------------+
            | stable     | committed                         |
            +------------+-----------------------------------+
            | UNSTABLE4  | FILE_SYNC4, DATA_SYNC4, UNSTABLE4 |
            | DATA_SYNC4 | FILE_SYNC4, DATA_SYNC4            |
            | FILE_SYNC4 | FILE_SYNC4                        |
            +------------+-----------------------------------+

                                 Table 11

   The final portion of the result is the field writeverf.  This field
   is the write verifier and is a cookie that the client can use to
   determine whether a server has changed instance state (e.g., server
   restart) between a call to WRITE and a subsequent call to either
   WRITE or COMMIT.  This cookie MUST be unchanged during a single
   instance of the NFSv4.1 server and MUST be unique between instances
   of the NFSv4.1 server.  If the cookie changes, then the client MUST
   assume that any data written with an UNSTABLE4 value for committed
   and an old writeverf in the reply has been lost and will need to be
   recovered.

   If a client writes data to the server with the stable argument set to
   UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
   UNSTABLE4, the client will follow up some time in the future with a
   COMMIT operation to synchronize outstanding asynchronous data and
   metadata with the server's stable storage, barring client error.  It
   is possible that due to client crash or other error that a subsequent
   COMMIT will not be received by the server.

   For a WRITE with a stateid value of all bits equal to zero, the
   server MAY allow the WRITE to be serviced subject to mandatory byte-
   range locks or the current share deny modes for the file.  For a
   WRITE with a stateid value of all bits equal to 1, the server MUST
   NOT allow the WRITE operation to bypass locking checks at the server
   and otherwise is treated as if a stateid of all bits equal to zero
   were used.

   On success, the current filehandle retains its value.







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18.32.4.  IMPLEMENTATION

   It is possible for the server to write fewer bytes of data than
   requested by the client.  In this case, the server SHOULD NOT return
   an error unless no data was written at all.  If the server writes
   less than the number of bytes specified, the client will need to send
   another WRITE to write the remaining data.

   It is assumed that the act of writing data to a file will cause the
   time_modified and change attributes of the file to be updated.
   However, these attributes SHOULD NOT be changed unless the contents
   of the file are changed.  Thus, a WRITE request with count set to
   zero SHOULD NOT cause the time_modified and change attributes of the
   file to be updated.

   Stable storage is persistent storage that survives:

   1.  Repeated power failures.

   2.  Hardware failures (of any board, power supply, etc.).

   3.  Repeated software crashes and restarts.

   This definition does not address failure of the stable storage module
   itself.

   The verifier is defined to allow a client to detect different
   instances of an NFSv4.1 protocol server over which cached,
   uncommitted data may be lost.  In the most likely case, the verifier
   allows the client to detect server restarts.  This information is
   required so that the client can safely determine whether the server
   could have lost cached data.  If the server fails unexpectedly and
   the client has uncommitted data from previous WRITE requests (done
   with the stable argument set to UNSTABLE4 and in which the result
   committed was returned as UNSTABLE4 as well), the server might not
   have flushed cached data to stable storage.  The burden of recovery
   is on the client, and the client will need to retransmit the data to
   the server.

   A suggested verifier would be to use the time that the server was
   last started (if restarting the server results in lost buffers).

   The reply's committed field allows the client to do more effective
   caching.  If the server is committing all WRITE requests to stable
   storage, then it SHOULD return with committed set to FILE_SYNC4,
   regardless of the value of the stable field in the arguments.  A
   server that uses an NVRAM accelerator may choose to implement this
   policy.  The client can use this to increase the effectiveness of the



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   cache by discarding cached data that has already been committed on
   the server.

   Some implementations may return NFS4ERR_NOSPC instead of
   NFS4ERR_DQUOT when a user's quota is exceeded.

   In the case that the current filehandle is of type NF4DIR, the server
   will return NFS4ERR_ISDIR.  If the current file is a symbolic link,
   the error NFS4ERR_SYMLINK will be returned.  Otherwise, if the
   current filehandle does not designate an ordinary file, the server
   will return NFS4ERR_WRONG_TYPE.

   If mandatory byte-range locking is in effect for the file, and the
   corresponding byte-range of the data to be written to the file is
   READ_LT or WRITE_LT locked by an owner that is not associated with
   the stateid, the server MUST return NFS4ERR_LOCKED.  If so, the
   client MUST check if the owner corresponding to the stateid used with
   the WRITE operation has a conflicting READ_LT lock that overlaps with
   the byte-range that was to be written.  If the stateid's owner has no
   conflicting READ_LT lock, then the client SHOULD try to get the
   appropriate write byte-range lock via the LOCK operation before re-
   attempting the WRITE.  When the WRITE completes, the client SHOULD
   release the byte-range lock via LOCKU.

   If the stateid's owner had a conflicting READ_LT lock, then the
   client has no choice but to return an error to the application that
   attempted the WRITE.  The reason is that since the stateid's owner
   had a READ_LT lock, either the server attempted to temporarily
   effectively upgrade this READ_LT lock to a WRITE_LT lock or the
   server has no upgrade capability.  If the server attempted to upgrade
   the READ_LT lock and failed, it is pointless for the client to re-
   attempt the upgrade via the LOCK operation, because there might be
   another client also trying to upgrade.  If two clients are blocked
   trying to upgrade the same lock, the clients deadlock.  If the server
   has no upgrade capability, then it is pointless to try a LOCK
   operation to upgrade.

   If one or more other clients have delegations for the file being
   written, those delegations MUST be recalled, and the operation cannot
   proceed until those delegations are returned or revoked.  Except
   where this happens very quickly, one or more NFS4ERR_DELAY errors
   will be returned to requests made while the delegation remains
   outstanding.  Normally, delegations will not be recalled as a result
   of a WRITE operation since the recall will occur as a result of an
   earlier OPEN.  However, since it is possible for a WRITE to be done
   with a special stateid, the server needs to check for this case even
   though the client should have done an OPEN previously.




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18.33.  Operation 40: BACKCHANNEL_CTL - Backchannel Control

18.33.1.  ARGUMENT

   typedef opaque gsshandle4_t<>;

   struct gss_cb_handles4 {
           rpc_gss_svc_t           gcbp_service; /* RFC 2203 */
           gsshandle4_t            gcbp_handle_from_server;
           gsshandle4_t            gcbp_handle_from_client;
   };

   union callback_sec_parms4 switch (uint32_t cb_secflavor) {
   case AUTH_NONE:
           void;
   case AUTH_SYS:
           authsys_parms   cbsp_sys_cred; /* RFC 1831 */
   case RPCSEC_GSS:
           gss_cb_handles4 cbsp_gss_handles;
   };

   struct BACKCHANNEL_CTL4args {
           uint32_t                bca_cb_program;
           callback_sec_parms4     bca_sec_parms<>;
   };


18.33.2.  RESULT

   struct BACKCHANNEL_CTL4res {
           nfsstat4                bcr_status;
   };


18.33.3.  DESCRIPTION

   The BACKCHANNEL_CTL operation replaces the backchannel's callback
   program number and adds (not replaces) RPCSEC_GSS handles for use by
   the backchannel.

   The arguments of the BACKCHANNEL_CTL call are a subset of the
   CREATE_SESSION parameters.  In the arguments of BACKCHANNEL_CTL, the
   bca_cb_program field and bca_sec_parms fields correspond respectively
   to the csa_cb_program and csa_sec_parms fields of the arguments of
   CREATE_SESSION (Section 18.36).

   BACKCHANNEL_CTL MUST appear in a COMPOUND that starts with SEQUENCE.




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   If the RPCSEC_GSS handle identified by gcbp_handle_from_server does
   not exist on the server, the server MUST return NFS4ERR_NOENT.

   If an RPCSEC_GSS handle is using the SSV context (see
   Section 2.10.9), then because each SSV RPCSEC_GSS handle shares a
   common SSV GSS context, there are security considerations specific to
   this situation discussed in Section 2.10.10.

18.34.  Operation 41: BIND_CONN_TO_SESSION - Associate Connection with
        Session

18.34.1.  ARGUMENT

   enum channel_dir_from_client4 {
    CDFC4_FORE             = 0x1,
    CDFC4_BACK             = 0x2,
    CDFC4_FORE_OR_BOTH     = 0x3,
    CDFC4_BACK_OR_BOTH     = 0x7
   };

   struct BIND_CONN_TO_SESSION4args {
    sessionid4     bctsa_sessid;

    channel_dir_from_client4
                   bctsa_dir;

    bool           bctsa_use_conn_in_rdma_mode;
   };























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18.34.2.  RESULT

   enum channel_dir_from_server4 {
    CDFS4_FORE     = 0x1,
    CDFS4_BACK     = 0x2,
    CDFS4_BOTH     = 0x3
   };

   struct BIND_CONN_TO_SESSION4resok {
    sessionid4     bctsr_sessid;

    channel_dir_from_server4
                   bctsr_dir;

    bool           bctsr_use_conn_in_rdma_mode;
   };

   union BIND_CONN_TO_SESSION4res
    switch (nfsstat4 bctsr_status) {

    case NFS4_OK:
     BIND_CONN_TO_SESSION4resok
                   bctsr_resok4;

    default:       void;
   };


18.34.3.  DESCRIPTION

   BIND_CONN_TO_SESSION is used to associate additional connections with
   a session.  It MUST be used on the connection being associated with
   the session.  It MUST be the only operation in the COMPOUND
   procedure.  If SP4_NONE (Section 18.35) state protection is used, any
   principal, security flavor, or RPCSEC_GSS context MAY be used to
   invoke the operation.  If SP4_MACH_CRED is used, RPCSEC_GSS MUST be
   used with the integrity or privacy services, using the principal that
   created the client ID.  If SP4_SSV is used, RPCSEC_GSS with the SSV
   GSS mechanism (Section 2.10.9) and integrity or privacy MUST be used.

   If, when the client ID was created, the client opted for SP4_NONE
   state protection, the client is not required to use
   BIND_CONN_TO_SESSION to associate the connection with the session,
   unless the client wishes to associate the connection with the
   backchannel.  When SP4_NONE protection is used, simply sending a
   COMPOUND request with a SEQUENCE operation is sufficient to associate
   the connection with the session specified in SEQUENCE.




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   The field bctsa_dir indicates whether the client wants to associate
   the connection with the fore channel or the backchannel or both
   channels.  The value CDFC4_FORE_OR_BOTH indicates that the client
   wants to associate the connection with both the fore channel and
   backchannel, but will accept the connection being associated to just
   the fore channel.  The value CDFC4_BACK_OR_BOTH indicates that the
   client wants to associate with both the fore channel and backchannel,
   but will accept the connection being associated with just the
   backchannel.  The server replies in bctsr_dir which channel(s) the
   connection is associated with.  If the client specified CDFC4_FORE,
   the server MUST return CDFS4_FORE.  If the client specified
   CDFC4_BACK, the server MUST return CDFS4_BACK.  If the client
   specified CDFC4_FORE_OR_BOTH, the server MUST return CDFS4_FORE or
   CDFS4_BOTH.  If the client specified CDFC4_BACK_OR_BOTH, the server
   MUST return CDFS4_BACK or CDFS4_BOTH.

   See the CREATE_SESSION operation (Section 18.36), and the description
   of the argument csa_use_conn_in_rdma_mode to understand
   bctsa_use_conn_in_rdma_mode, and the description of
   csr_use_conn_in_rdma_mode to understand bctsr_use_conn_in_rdma_mode.

   Invoking BIND_CONN_TO_SESSION on a connection already associated with
   the specified session has no effect, and the server MUST respond with
   NFS4_OK, unless the client is demanding changes to the set of
   channels the connection is associated with.  If so, the server MUST
   return NFS4ERR_INVAL.

18.34.4.  IMPLEMENTATION

   If a session's channel loses all connections, depending on the client
   ID's state protection and type of channel, the client might need to
   use BIND_CONN_TO_SESSION to associate a new connection.  If the
   server restarted and does not keep the reply cache in stable storage,
   the server will not recognize the session ID.  The client will
   ultimately have to invoke EXCHANGE_ID to create a new client ID and
   session.

   Suppose SP4_SSV state protection is being used, and
   BIND_CONN_TO_SESSION is among the operations included in the
   spo_must_enforce set when the client ID was created (Section 18.35).
   If so, there is an issue if SET_SSV is sent, no response is returned,
   and the last connection associated with the client ID drops.  The
   client, per the sessions model, MUST retry the SET_SSV.  But it needs
   a new connection to do so, and MUST associate that connection with
   the session via a BIND_CONN_TO_SESSION authenticated with the SSV GSS
   mechanism.  The problem is that the RPCSEC_GSS message integrity
   codes use a subkey derived from the SSV as the key and the SSV may
   have changed.  While there are multiple recovery strategies, a



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   single, general strategy is described here.

   o  The client reconnects.

   o  The client assumes that the SET_SSV was executed, and so sends
      BIND_CONN_TO_SESSION with the subkey (derived from the new SSV,
      i.e., what SET_SSV would have set the SSV to) used as the key for
      the RPCSEC_GSS credential message integrity codes.

   o  If the request succeeds, this means that the original attempted
      SET_SSV did execute successfully.  The client re-sends the
      original SET_SSV, which the server will reply to via the reply
      cache.

   o  If the server returns an RPC authentication error, this means that
      the server's current SSV was not changed (and the SET_SSV was
      likely not executed).  The client then tries BIND_CONN_TO_SESSION
      with the subkey derived from the old SSV as the key for the
      RPCSEC_GSS message integrity codes.

   o  The attempted BIND_CONN_TO_SESSION with the old SSV should
      succeed.  If so, the client re-sends the original SET_SSV.  If the
      original SET_SSV was not executed, then the server executes it.
      If the original SET_SSV was executed but failed, the server will
      return the SET_SSV from the reply cache.

18.35.  Operation 42: EXCHANGE_ID - Instantiate Client ID

   The EXCHANGE_ID exchanges long-hand client and server identifiers
   (owners), and creates a client ID.

18.35.1.  ARGUMENT



















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   const EXCHGID4_FLAG_SUPP_MOVED_REFER    = 0x00000001;
   const EXCHGID4_FLAG_SUPP_MOVED_MIGR     = 0x00000002;

   const EXCHGID4_FLAG_BIND_PRINC_STATEID  = 0x00000100;

   const EXCHGID4_FLAG_USE_NON_PNFS        = 0x00010000;
   const EXCHGID4_FLAG_USE_PNFS_MDS        = 0x00020000;
   const EXCHGID4_FLAG_USE_PNFS_DS         = 0x00040000;

   const EXCHGID4_FLAG_MASK_PNFS           = 0x00070000;

   const EXCHGID4_FLAG_UPD_CONFIRMED_REC_A = 0x40000000;
   const EXCHGID4_FLAG_CONFIRMED_R         = 0x80000000;

   struct state_protect_ops4 {
           bitmap4 spo_must_enforce;
           bitmap4 spo_must_allow;
   };

   struct ssv_sp_parms4 {
           state_protect_ops4      ssp_ops;
           sec_oid4                ssp_hash_algs<>;
           sec_oid4                ssp_encr_algs<>;
           uint32_t                ssp_window;
           uint32_t                ssp_num_gss_handles;
   };

   enum state_protect_how4 {
           SP4_NONE = 0,
           SP4_MACH_CRED = 1,
           SP4_SSV = 2
   };

   union state_protect4_a switch(state_protect_how4 spa_how) {
           case SP4_NONE:
                   void;
           case SP4_MACH_CRED:
                   state_protect_ops4      spa_mach_ops;
           case SP4_SSV:
                   ssv_sp_parms4           spa_ssv_parms;
   };

   struct EXCHANGE_ID4args {
           client_owner4           eia_clientowner;
           uint32_t                eia_flags;
           state_protect4_a        eia_state_protect;
           nfs_impl_id4            eia_client_impl_id<1>;
   };



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18.35.2.  RESULT

   struct ssv_prot_info4 {
    state_protect_ops4     spi_ops;
    uint32_t               spi_hash_alg;
    uint32_t               spi_encr_alg;
    uint32_t               spi_ssv_len;
    uint32_t               spi_window;
    gsshandle4_t           spi_handles<>;
   };

   union state_protect4_r switch(state_protect_how4 spr_how) {
    case SP4_NONE:
            void;
    case SP4_MACH_CRED:
            state_protect_ops4     spr_mach_ops;
    case SP4_SSV:
            ssv_prot_info4         spr_ssv_info;
   };

   struct EXCHANGE_ID4resok {
    clientid4        eir_clientid;
    sequenceid4      eir_sequenceid;
    uint32_t         eir_flags;
    state_protect4_r eir_state_protect;
    server_owner4    eir_server_owner;
    opaque           eir_server_scope<NFS4_OPAQUE_LIMIT>;
    nfs_impl_id4     eir_server_impl_id<1>;
   };

   union EXCHANGE_ID4res switch (nfsstat4 eir_status) {
   case NFS4_OK:
    EXCHANGE_ID4resok      eir_resok4;

   default:
    void;
   };


18.35.3.  DESCRIPTION

   The client uses the EXCHANGE_ID operation to register a particular
   client owner with the server.  The client ID returned from this
   operation will be necessary for requests that create state on the
   server and will serve as a parent object to sessions created by the
   client.  In order to confirm the client ID it must first be used,
   along with the returned eir_sequenceid, as arguments to
   CREATE_SESSION.  If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the



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   result, eir_flags, then eir_sequenceid MUST be ignored, as it has no
   relevancy.

   EXCHANGE_ID MAY be sent in a COMPOUND procedure that starts with
   SEQUENCE.  However, when a client communicates with a server for the
   first time, it will not have a session, so using SEQUENCE will not be
   possible.  If EXCHANGE_ID is sent without a preceding SEQUENCE, then
   it MUST be the only operation in the COMPOUND procedure's request.
   If it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.

   The eia_clientowner field is composed of a co_verifier field and a
   co_ownerid string.  As noted in Section 2.4, the co_ownerid describes
   the client, and the co_verifier is the incarnation of the client.  An
   EXCHANGE_ID sent with a new incarnation of the client will lead to
   the server removing lock state of the old incarnation.  Whereas an
   EXCHANGE_ID sent with the current incarnation and co_ownerid will
   result in an error or an update of the client ID's properties,
   depending on the arguments to EXCHANGE_ID.

   A server MUST NOT use the same client ID for two different
   incarnations of an eir_clientowner.

   In addition to the client ID and sequence ID, the server returns a
   server owner (eir_server_owner) and server scope (eir_server_scope).
   The former field is used for network trunking as described in
   Section 2.10.5.  The latter field is used to allow clients to
   determine when client IDs sent by one server may be recognized by
   another in the event of file system migration (see Section 11.7.7).

   The client ID returned by EXCHANGE_ID is only unique relative to the
   combination of eir_server_owner.so_major_id and eir_server_scope.
   Thus, if two servers return the same client ID, the onus is on the
   client to distinguish the client IDs on the basis of
   eir_server_owner.so_major_id and eir_server_scope.  In the event two
   different servers claim matching server_owner.so_major_id and
   eir_server_scope, the client can use the verification techniques
   discussed in Section 2.10.5 to determine if the servers are distinct.
   If they are distinct, then the client will need to note the
   destination network addresses of the connections used with each
   server, and use the network address as the final discriminator.

   The server, as defined by the unique identity expressed in the
   so_major_id of the server owner and the server scope, needs to track
   several properties of each client ID it hands out.  The properties
   apply to the client ID and all sessions associated with the client
   ID.  The properties are derived from the arguments and results of
   EXCHANGE_ID.  The client ID properties include:




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   o  The capabilities expressed by the following bits, which come from
      the results of EXCHANGE_ID:

      *  EXCHGID4_FLAG_SUPP_MOVED_REFER

      *  EXCHGID4_FLAG_SUPP_MOVED_MIGR

      *  EXCHGID4_FLAG_BIND_PRINC_STATEID

      *  EXCHGID4_FLAG_USE_NON_PNFS

      *  EXCHGID4_FLAG_USE_PNFS_MDS

      *  EXCHGID4_FLAG_USE_PNFS_DS

      These properties may be updated by subsequent EXCHANGE_ID requests
      on confirmed client IDs though the server MAY refuse to change
      them.

   o  The state protection method used, one of SP4_NONE, SP4_MACH_CRED,
      or SP4_SSV, as set by the spa_how field of the arguments to
      EXCHANGE_ID.  Once the client ID is confirmed, this property
      cannot be updated by subsequent EXCHANGE_ID requests.

   o  For SP4_MACH_CRED or SP4_SSV state protection:

      *  The list of operations (spo_must_enforce) that MUST use the
         specified state protection.  This list comes from the results
         of EXCHANGE_ID.

      *  The list of operations (spo_must_allow) that MAY use the
         specified state protection.  This list comes from the results
         of EXCHANGE_ID.

      Once the client ID is confirmed, these properties cannot be
      updated by subsequent EXCHANGE_ID requests.

   o  For SP4_SSV protection:

      *  The OID of the hash algorithm.  This property is represented by
         one of the algorithms in the ssp_hash_algs field of the
         EXCHANGE_ID arguments.  Once the client ID is confirmed, this
         property cannot be updated by subsequent EXCHANGE_ID requests.

      *  The OID of the encryption algorithm.  This property is
         represented by one of the algorithms in the ssp_encr_algs field
         of the EXCHANGE_ID arguments.  Once the client ID is confirmed,
         this property cannot be updated by subsequent EXCHANGE_ID



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         requests.

      *  The length of the SSV.  This property is represented by the
         spi_ssv_len field in the EXCHANGE_ID results.  Once the client
         ID is confirmed, this property cannot be updated by subsequent
         EXCHANGE_ID requests.

         There are REQUIRED and RECOMMENDED relationships among the
         length of the key of the encryption algorithm ("key length"),
         the length of the output of hash algorithm ("hash length"), and
         the length of the SSV ("SSV length").

         +  key length MUST be <= hash length.  This is because the keys
            used for the encryption algorithm are actually subkeys
            derived from the SSV, and the derivation is via the hash
            algorithm.  The selection of an encryption algorithm with a
            key length that exceeded the length of the output of the
            hash algorithm would require padding, and thus weaken the
            use of the encryption algorithm.

         +  hash length SHOULD be <= SSV length.  This is because the
            SSV is a key used to derive subkeys via an HMAC, and it is
            recommended that the key used as input to an HMAC be at
            least as long as the length of the HMAC's hash algorithm's
            output (see Section 3 of RFC2104 [11]).

         +  key length SHOULD be <= SSV length.  This is a transitive
            result of the above two invariants.

         +  key length SHOULD be >= hash length / 2.  This is because
            the subkey derivation is via an HMAC and it is recommended
            that if the HMAC has to be truncated, it should not be
            truncated to less than half the hash length (see Section 4
            of RFC2104 [11]).

      *  Number of concurrent versions of the SSV the client and server
         will support (Section 2.10.9).  This property is represented by
         spi_window in the EXCHANGE_ID results.  The property may be
         updated by subsequent EXCHANGE_ID requests.

   o  The client's implementation ID as represented by the
      eia_client_impl_id field of the arguments.  The property may be
      updated by subsequent EXCHANGE_ID requests.

   o  The server's implementation ID as represented by the
      eir_server_impl_id field of the reply.  The property may be
      updated by replies to subsequent EXCHANGE_ID requests.




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   The eia_flags passed as part of the arguments and the eir_flags
   results allow the client and server to inform each other of their
   capabilities as well as indicate how the client ID will be used.
   Whether a bit is set or cleared on the arguments' flags does not
   force the server to set or clear the same bit on the results' side.
   Bits not defined above cannot be set in the eia_flags field.  If they
   are, the server MUST reject the operation with NFS4ERR_INVAL.

   The EXCHGID4_FLAG_UPD_CONFIRMED_REC_A bit can only be set in
   eia_flags; it is always off in eir_flags.  The
   EXCHGID4_FLAG_CONFIRMED_R bit can only be set in eir_flags; it is
   always off in eia_flags.  If the server recognizes the co_ownerid and
   co_verifier as mapping to a confirmed client ID, it sets
   EXCHGID4_FLAG_CONFIRMED_R in eir_flags.  The
   EXCHGID4_FLAG_CONFIRMED_R flag allows a client to tell if the client
   ID it is trying to create already exists and is confirmed.

   If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set in eia_flags, this means
   that the client is attempting to update properties of an existing
   confirmed client ID (if the client wants to update properties of an
   unconfirmed client ID, it MUST NOT set
   EXCHGID4_FLAG_UPD_CONFIRMED_REC_A).  If so, it is RECOMMENDED that
   the client send the update EXCHANGE_ID operation in the same COMPOUND
   as a SEQUENCE so that the EXCHANGE_ID is executed exactly once.
   Whether the client can update the properties of client ID depends on
   the state protection it selected when the client ID was created, and
   the principal and security flavor it uses when sending the
   EXCHANGE_ID request.  The situations described in items 6, 7, 8, or 9
   of the second numbered list of Section 18.35.4 will apply.  Note that
   if the operation succeeds and returns a client ID that is already
   confirmed, the server MUST set the EXCHGID4_FLAG_CONFIRMED_R bit in
   eir_flags.

   If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags, this
   means that the client is trying to establish a new client ID; it is
   attempting to trunk data communication to the server
   (Section 2.10.5); or it is attempting to update properties of an
   unconfirmed client ID.  The situations described in items 1, 2, 3, 4,
   or 5 of the second numbered list of Section 18.35.4 will apply.  Note
   that if the operation succeeds and returns a client ID that was
   previously confirmed, the server MUST set the
   EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.

   When the EXCHGID4_FLAG_SUPP_MOVED_REFER flag bit is set, the client
   indicates that it is capable of dealing with an NFS4ERR_MOVED error
   as part of a referral sequence.  When this bit is not set, it is
   still legal for the server to perform a referral sequence.  However,
   a server may use the fact that the client is incapable of correctly



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   responding to a referral, by avoiding it for that particular client.
   It may, for instance, act as a proxy for that particular file system,
   at some cost in performance, although it is not obligated to do so.
   If the server will potentially perform a referral, it MUST set
   EXCHGID4_FLAG_SUPP_MOVED_REFER in eir_flags.

   When the EXCHGID4_FLAG_SUPP_MOVED_MIGR is set, the client indicates
   that it is capable of dealing with an NFS4ERR_MOVED error as part of
   a file system migration sequence.  When this bit is not set, it is
   still legal for the server to indicate that a file system has moved,
   when this in fact happens.  However, a server may use the fact that
   the client is incapable of correctly responding to a migration in its
   scheduling of file systems to migrate so as to avoid migration of
   file systems being actively used.  It may also hide actual migrations
   from clients unable to deal with them by acting as a proxy for a
   migrated file system for particular clients, at some cost in
   performance, although it is not obligated to do so.  If the server
   will potentially perform a migration, it MUST set
   EXCHGID4_FLAG_SUPP_MOVED_MIGR in eir_flags.

   When EXCHGID4_FLAG_BIND_PRINC_STATEID is set, the client indicates
   that it wants the server to bind the stateid to the principal.  This
   means that when a principal creates a stateid, it has to be the one
   to use the stateid.  If the server will perform binding, it will
   return EXCHGID4_FLAG_BIND_PRINC_STATEID.  The server MAY return
   EXCHGID4_FLAG_BIND_PRINC_STATEID even if the client does not request
   it.  If an update to the client ID changes the value of
   EXCHGID4_FLAG_BIND_PRINC_STATEID's client ID property, the effect
   applies only to new stateids.  Existing stateids (and all stateids
   with the same "other" field) that were created with stateid to
   principal binding in force will continue to have binding in force.
   Existing stateids (and all stateids with the same "other" field) that
   were created with stateid to principal not in force will continue to
   have binding not in force.

   The EXCHGID4_FLAG_USE_NON_PNFS, EXCHGID4_FLAG_USE_PNFS_MDS, and
   EXCHGID4_FLAG_USE_PNFS_DS bits are described in Section 13.1 and
   convey roles the client ID is to be used for in a pNFS environment.
   The server MUST set one of the acceptable combinations of these bits
   (roles) in eir_flags, as specified in Section 13.1.  Note that the
   same client owner/server owner pair can have multiple roles.
   Multiple roles can be associated with the same client ID or with
   different client IDs.  Thus, if a client sends EXCHANGE_ID from the
   same client owner to the same server owner multiple times, but
   specifies different pNFS roles each time, the server might return
   different client IDs.  Given that different pNFS roles might have
   different client IDs, the client may ask for different properties for
   each role/client ID.



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   The spa_how field of the eia_state_protect field specifies how the
   client wants to protect its client, locking, and session states from
   unauthorized changes (Section 2.10.8.3):

   o  SP4_NONE.  The client does not request the NFSv4.1 server to
      enforce state protection.  The NFSv4.1 server MUST NOT enforce
      state protection for the returned client ID.

   o  SP4_MACH_CRED.  If spa_how is SP4_MACH_CRED, then the client MUST
      send the EXCHANGE_ID request with RPCSEC_GSS as the security
      flavor, and with a service of RPC_GSS_SVC_INTEGRITY or
      RPC_GSS_SVC_PRIVACY.  If SP4_MACH_CRED is specified, then the
      client wants to use an RPCSEC_GSS-based machine credential to
      protect its state.  The server MUST note the principal the
      EXCHANGE_ID operation was sent with, and the GSS mechanism used.
      These notes collectively comprise the machine credential.

      After the client ID is confirmed, as long as the lease associated
      with the client ID is unexpired, a subsequent EXCHANGE_ID
      operation that uses the same eia_clientowner.co_owner as the first
      EXCHANGE_ID MUST also use the same machine credential as the first
      EXCHANGE_ID.  The server returns the same client ID for the
      subsequent EXCHANGE_ID as that returned from the first
      EXCHANGE_ID.

   o  SP4_SSV.  If spa_how is SP4_SSV, then the client MUST send the
      EXCHANGE_ID request with RPCSEC_GSS as the security flavor, and
      with a service of RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY.
      If SP4_SSV is specified, then the client wants to use the SSV to
      protect its state.  The server records the credential used in the
      request as the machine credential (as defined above) for the
      eia_clientowner.co_owner.  The CREATE_SESSION operation that
      confirms the client ID MUST use the same machine credential.

   When a client specifies SP4_MACH_CRED or SP4_SSV, it also provides
   two lists of operations (each expressed as a bitmap).  The first list
   is spo_must_enforce and consists of those operations the client MUST
   send (subject to the server confirming the list of operations in the
   result of EXCHANGE_ID) with the machine credential (if SP4_MACH_CRED
   protection is specified) or the SSV-based credential (if SP4_SSV
   protection is used).  The client MUST send the operations with
   RPCSEC_GSS credentials that specify the RPC_GSS_SVC_INTEGRITY or
   RPC_GSS_SVC_PRIVACY security service.  Typically, the first list of
   operations includes EXCHANGE_ID, CREATE_SESSION, DELEGPURGE,
   DESTROY_SESSION, BIND_CONN_TO_SESSION, and DESTROY_CLIENTID.  The
   client SHOULD NOT specify in this list any operations that require a
   filehandle because the server's access policies MAY conflict with the
   client's choice, and thus the client would then be unable to access a



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   subset of the server's namespace.

   Note that if SP4_SSV protection is specified, and the client
   indicates that CREATE_SESSION must be protected with SP4_SSV, because
   the SSV cannot exist without a confirmed client ID, the first
   CREATE_SESSION MUST instead be sent using the machine credential, and
   the server MUST accept the machine credential.

   There is a corresponding result, also called spo_must_enforce, of the
   operations for which the server will require SP4_MACH_CRED or SP4_SSV
   protection.  Normally, the server's result equals the client's
   argument, but the result MAY be different.  If the client requests
   one or more operations in the set { EXCHANGE_ID, CREATE_SESSION,
   DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION, DESTROY_CLIENTID
   }, then the result spo_must_enforce MUST include the operations the
   client requested from that set.

   If spo_must_enforce in the results has BIND_CONN_TO_SESSION set, then
   connection binding enforcement is enabled, and the client MUST use
   the machine (if SP4_MACH_CRED protection is used) or SSV (if SP4_SSV
   protection is used) credential on calls to BIND_CONN_TO_SESSION.

   The second list is spo_must_allow and consists of those operations
   the client wants to have the option of sending with the machine
   credential or the SSV-based credential, even if the object the
   operations are performed on is not owned by the machine or SSV
   credential.

   The corresponding result, also called spo_must_allow, consists of the
   operations the server will allow the client to use SP4_SSV or
   SP4_MACH_CRED credentials with.  Normally, the server's result equals
   the client's argument, but the result MAY be different.

   The purpose of spo_must_allow is to allow clients to solve the
   following conundrum.  Suppose the client ID is confirmed with
   EXCHGID4_FLAG_BIND_PRINC_STATEID, and it calls OPEN with the
   RPCSEC_GSS credentials of a normal user.  Now suppose the user's
   credentials expire, and cannot be renewed (e.g., a Kerberos ticket
   granting ticket expires, and the user has logged off and will not be
   acquiring a new ticket granting ticket).  The client will be unable
   to send CLOSE without the user's credentials, which is to say the
   client has to either leave the state on the server or re-send
   EXCHANGE_ID with a new verifier to clear all state, that is, unless
   the client includes CLOSE on the list of operations in spo_must_allow
   and the server agrees.

   The SP4_SSV protection parameters also have:




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   ssp_hash_algs:

      This is the set of algorithms the client supports for the purpose
      of computing the digests needed for the internal SSV GSS mechanism
      and for the SET_SSV operation.  Each algorithm is specified as an
      object identifier (OID).  The REQUIRED algorithms for a server are
      id-sha1, id-sha224, id-sha256, id-sha384, and id-sha512 [28].  The
      algorithm the server selects among the set is indicated in
      spi_hash_alg, a field of spr_ssv_prot_info.  The field
      spi_hash_alg is an index into the array ssp_hash_algs.  If the
      server does not support any of the offered algorithms, it returns
      NFS4ERR_HASH_ALG_UNSUPP.  If ssp_hash_algs is empty, the server
      MUST return NFS4ERR_INVAL.

   ssp_encr_algs:

      This is the set of algorithms the client supports for the purpose
      of providing privacy protection for the internal SSV GSS
      mechanism.  Each algorithm is specified as an OID.  The REQUIRED
      algorithm for a server is id-aes256-CBC.  The RECOMMENDED
      algorithms are id-aes192-CBC and id-aes128-CBC [29].  The selected
      algorithm is returned in spi_encr_alg, an index into
      ssp_encr_algs.  If the server does not support any of the offered
      algorithms, it returns NFS4ERR_ENCR_ALG_UNSUPP.  If ssp_encr_algs
      is empty, the server MUST return NFS4ERR_INVAL.  Note that due to
      previously stated requirements and recommendations on the
      relationships between key length and hash length, some
      combinations of RECOMMENDED and REQUIRED encryption algorithm and
      hash algorithm either SHOULD NOT or MUST NOT be used.  Table 12
      summarizes the illegal and discouraged combinations.

   ssp_window:

      This is the number of SSV versions the client wants the server to
      maintain (i.e., each successful call to SET_SSV produces a new
      version of the SSV).  If ssp_window is zero, the server MUST
      return NFS4ERR_INVAL.  The server responds with spi_window, which
      MUST NOT exceed ssp_window, and MUST be at least one.  Any
      requests on the backchannel or fore channel that are using a
      version of the SSV that is outside the window will fail with an
      ONC RPC authentication error, and the requester will have to retry
      them with the same slot ID and sequence ID.

   ssp_num_gss_handles:







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      This is the number of RPCSEC_GSS handles the server should create
      that are based on the GSS SSV mechanism (Section 2.10.9).  It is
      not the total number of RPCSEC_GSS handles for the client ID.
      Indeed, subsequent calls to EXCHANGE_ID will add RPCSEC_GSS
      handles.  The server responds with a list of handles in
      spi_handles.  If the client asks for at least one handle and the
      server cannot create it, the server MUST return an error.  The
      handles in spi_handles are not available for use until the client
      ID is confirmed, which could be immediately if EXCHANGE_ID returns
      EXCHGID4_FLAG_CONFIRMED_R, or upon successful confirmation from
      CREATE_SESSION.

      While a client ID can span all the connections that are connected
      to a server sharing the same eir_server_owner.so_major_id, the
      RPCSEC_GSS handles returned in spi_handles can only be used on
      connections connected to a server that returns the same the
      eir_server_owner.so_major_id and eir_server_owner.so_minor_id on
      each connection.  It is permissible for the client to set
      ssp_num_gss_handles to zero; the client can create more handles
      with another EXCHANGE_ID call.

      Because each SSV RPCSEC_GSS handle shares a common SSV GSS
      context, there are security considerations specific to this
      situation discussed in Section 2.10.10.

      The seq_window (see Section 5.2.3.1 of RFC2203 [4]) of each
      RPCSEC_GSS handle in spi_handle MUST be the same as the seq_window
      of the RPCSEC_GSS handle used for the credential of the RPC
      request that the EXCHANGE_ID request was sent with.

   +-------------------+----------------------+------------------------+
   | Encryption        | MUST NOT be combined | SHOULD NOT be combined |
   | Algorithm         | with                 | with                   |
   +-------------------+----------------------+------------------------+
   | id-aes128-CBC     |                      | id-sha384, id-sha512   |
   | id-aes192-CBC     | id-sha1              | id-sha512              |
   | id-aes256-CBC     | id-sha1, id-sha224   |                        |
   +-------------------+----------------------+------------------------+

                                 Table 12

   The arguments include an array of up to one element in length called
   eia_client_impl_id.  If eia_client_impl_id is present, it contains
   the information identifying the implementation of the client.
   Similarly, the results include an array of up to one element in
   length called eir_server_impl_id that identifies the implementation
   of the server.  Servers MUST accept a zero-length eia_client_impl_id
   array, and clients MUST accept a zero-length eir_server_impl_id



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   array.

   An example use for implementation identifiers would be diagnostic
   software that extracts this information in an attempt to identify
   interoperability problems, performance workload behaviors, or general
   usage statistics.  Since the intent of having access to this
   information is for planning or general diagnosis only, the client and
   server MUST NOT interpret this implementation identity information in
   a way that affects interoperational behavior of the implementation.
   The reason is that if clients and servers did such a thing, they
   might use fewer capabilities of the protocol than the peer can
   support, or the client and server might refuse to interoperate.

   Because it is possible that some implementations will violate the
   protocol specification and interpret the identity information,
   implementations MUST allow the users of the NFSv4 client and server
   to set the contents of the sent nfs_impl_id structure to any value.

18.35.4.  IMPLEMENTATION

   A server's client record is a 5-tuple:

   1.  co_ownerid

          The client identifier string, from the eia_clientowner
          structure of the EXCHANGE_ID4args structure.

   2.  co_verifier:

          A client-specific value used to indicate incarnations (where a
          client restart represents a new incarnation), from the
          eia_clientowner structure of the EXCHANGE_ID4args structure.

   3.  principal:

          The principal that was defined in the RPC header's credential
          and/or verifier at the time the client record was established.

   4.  client ID:

          The shorthand client identifier, generated by the server and
          returned via the eir_clientid field in the EXCHANGE_ID4resok
          structure.

   5.  confirmed:

          A private field on the server indicating whether or not a
          client record has been confirmed.  A client record is



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          confirmed if there has been a successful CREATE_SESSION
          operation to confirm it.  Otherwise, it is unconfirmed.  An
          unconfirmed record is established by an EXCHANGE_ID call.  Any
          unconfirmed record that is not confirmed within a lease period
          SHOULD be removed.

   The following identifiers represent special values for the fields in
   the records.

   ownerid_arg:

      The value of the eia_clientowner.co_ownerid subfield of the
      EXCHANGE_ID4args structure of the current request.

   verifier_arg:

      The value of the eia_clientowner.co_verifier subfield of the
      EXCHANGE_ID4args structure of the current request.

   old_verifier_arg:

      A value of the eia_clientowner.co_verifier field of a client
      record received in a previous request; this is distinct from
      verifier_arg.

   principal_arg:

      The value of the RPCSEC_GSS principal for the current request.

   old_principal_arg:

      A value of the principal of a client record as defined by the RPC
      header's credential or verifier of a previous request.  This is
      distinct from principal_arg.

   clientid_ret:

      The value of the eir_clientid field the server will return in the
      EXCHANGE_ID4resok structure for the current request.

   old_clientid_ret:

      The value of the eir_clientid field the server returned in the
      EXCHANGE_ID4resok structure for a previous request.  This is
      distinct from clientid_ret.






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   confirmed:

      The client ID has been confirmed.

   unconfirmed:

      The client ID has not been confirmed.

   Since EXCHANGE_ID is a non-idempotent operation, we must consider the
   possibility that retries occur as a result of a client restart,
   network partition, malfunctioning router, etc.  Retries are
   identified by the value of the eia_clientowner field of
   EXCHANGE_ID4args, and the method for dealing with them is outlined in
   the scenarios below.

   The scenarios are described in terms of the client record(s) a server
   has for a given co_ownerid.  Note that if the client ID was created
   specifying SP4_SSV state protection and EXCHANGE_ID as the one of the
   operations in spo_must_allow, then the server MUST authorize
   EXCHANGE_IDs with the SSV principal in addition to the principal that
   created the client ID.

   1.  New Owner ID

          If the server has no client records with
          eia_clientowner.co_ownerid matching ownerid_arg, and
          EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in the
          EXCHANGE_ID, then a new shorthand client ID (let us call it
          clientid_ret) is generated, and the following unconfirmed
          record is added to the server's state.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }

          Subsequently, the server returns clientid_ret.



   2.  Non-Update on Existing Client ID

          If the server has the following confirmed record, and the
          request does not have EXCHGID4_FLAG_UPD_CONFIRMED_REC_A set,
          then the request is the result of a retried request due to a
          faulty router or lost connection, or the client is trying to
          determine if it can perform trunking.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          confirmed }



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          Since the record has been confirmed, the client must have
          received the server's reply from the initial EXCHANGE_ID
          request.  Since the server has a confirmed record, and since
          EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, with the
          possible exception of eir_server_owner.so_minor_id, the server
          returns the same result it did when the client ID's properties
          were last updated (or if never updated, the result when the
          client ID was created).  The confirmed record is unchanged.

   3.  Client Collision

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
          server has the following confirmed record, then this request
          is likely the result of a chance collision between the values
          of the eia_clientowner.co_ownerid subfield of EXCHANGE_ID4args
          for two different clients.

          { ownerid_arg, *, old_principal_arg, old_clientid_ret,
          confirmed }

          If there is currently no state associated with
          old_clientid_ret, or if there is state but the lease has
          expired, then this case is effectively equivalent to the New
          Owner ID case of Paragraph 1.  The confirmed record is
          deleted, the old_clientid_ret and its lock state are deleted,
          a new shorthand client ID is generated, and the following
          unconfirmed record is added to the server's state.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }

          Subsequently, the server returns clientid_ret.


          If old_clientid_ret has an unexpired lease with state, then no
          state of old_clientid_ret is changed or deleted.  The server
          returns NFS4ERR_CLID_INUSE to indicate that the client should
          retry with a different value for the
          eia_clientowner.co_ownerid subfield of EXCHANGE_ID4args.  The
          client record is not changed.

   4.  Replacement of Unconfirmed Record

          If the EXCHGID4_FLAG_UPD_CONFIRMED_REC_A flag is not set, and
          the server has the following unconfirmed record, then the
          client is attempting EXCHANGE_ID again on an unconfirmed
          client ID, perhaps due to a retry, a client restart before
          client ID confirmation (i.e., before CREATE_SESSION was



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          called), or some other reason.

          { ownerid_arg, *, *, old_clientid_ret, unconfirmed }

          It is possible that the properties of old_clientid_ret are
          different than those specified in the current EXCHANGE_ID.
          Whether or not the properties are being updated, to eliminate
          ambiguity, the server deletes the unconfirmed record,
          generates a new client ID (clientid_ret), and establishes the
          following unconfirmed record:

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }


   5.  Client Restart

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
          server has the following confirmed client record, then this
          request is likely from a previously confirmed client that has
          restarted.

          { ownerid_arg, old_verifier_arg, principal_arg,
          old_clientid_ret, confirmed }

          Since the previous incarnation of the same client will no
          longer be making requests, once the new client ID is confirmed
          by CREATE_SESSION, byte-range locks and share reservations
          should be released immediately rather than forcing the new
          incarnation to wait for the lease time on the previous
          incarnation to expire.  Furthermore, session state should be
          removed since if the client had maintained that information
          across restart, this request would not have been sent.  If the
          server supports neither the CLAIM_DELEGATE_PREV nor
          CLAIM_DELEG_PREV_FH claim types, associated delegations should
          be purged as well; otherwise, delegations are retained and
          recovery proceeds according to Section 10.2.1.

          After processing, clientid_ret is returned to the client and
          this client record is added:

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }


          The previously described confirmed record continues to exist,
          and thus the same ownerid_arg exists in both a confirmed and
          unconfirmed state at the same time.  The number of states can



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          collapse to one once the server receives an applicable
          CREATE_SESSION or EXCHANGE_ID.

          +  If the server subsequently receives a successful
             CREATE_SESSION that confirms clientid_ret, then the server
             atomically destroys the confirmed record and makes the
             unconfirmed record confirmed as described in
             Section 18.36.4.

          +  If the server instead subsequently receives an EXCHANGE_ID
             with the client owner equal to ownerid_arg, one strategy is
             to simply delete the unconfirmed record, and process the
             EXCHANGE_ID as described in the entirety of
             Section 18.35.4.

   6.  Update

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          attempt at an update.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          confirmed }

          Since the record has been confirmed, the client must have
          received the server's reply from the initial EXCHANGE_ID
          request.  The server allows the update, and the client record
          is left intact.

   7.  Update but No Confirmed Record

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has no confirmed record corresponding ownerid_arg, then the
          server returns NFS4ERR_NOENT and leaves any unconfirmed record
          intact.

   8.  Update but Wrong Verifier

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          illegal attempt at an update, perhaps because of a retry from
          a previous client incarnation.

          { ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }

          The server returns NFS4ERR_NOT_SAME and leaves the client
          record intact.




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   9.  Update but Wrong Principal

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          illegal attempt at an update by an unauthorized principal.

          { ownerid_arg, verifier_arg, old_principal_arg, clientid_ret,
          confirmed }

          The server returns NFS4ERR_PERM and leaves the client record
          intact.

18.36.  Operation 43: CREATE_SESSION - Create New Session and Confirm
        Client ID

18.36.1.  ARGUMENT

   struct channel_attrs4 {
           count4                  ca_headerpadsize;
           count4                  ca_maxrequestsize;
           count4                  ca_maxresponsesize;
           count4                  ca_maxresponsesize_cached;
           count4                  ca_maxoperations;
           count4                  ca_maxrequests;
           uint32_t                ca_rdma_ird<1>;
   };

   const CREATE_SESSION4_FLAG_PERSIST              = 0x00000001;
   const CREATE_SESSION4_FLAG_CONN_BACK_CHAN       = 0x00000002;
   const CREATE_SESSION4_FLAG_CONN_RDMA            = 0x00000004;

   struct CREATE_SESSION4args {
           clientid4               csa_clientid;
           sequenceid4             csa_sequence;

           uint32_t                csa_flags;

           channel_attrs4          csa_fore_chan_attrs;
           channel_attrs4          csa_back_chan_attrs;

           uint32_t                csa_cb_program;
           callback_sec_parms4     csa_sec_parms<>;
   };








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18.36.2.  RESULT

   struct CREATE_SESSION4resok {
           sessionid4              csr_sessionid;
           sequenceid4             csr_sequence;

           uint32_t                csr_flags;

           channel_attrs4          csr_fore_chan_attrs;
           channel_attrs4          csr_back_chan_attrs;
   };

   union CREATE_SESSION4res switch (nfsstat4 csr_status) {
   case NFS4_OK:
           CREATE_SESSION4resok    csr_resok4;
   default:
           void;
   };


18.36.3.  DESCRIPTION

   This operation is used by the client to create new session objects on
   the server.

   CREATE_SESSION can be sent with or without a preceding SEQUENCE
   operation in the same COMPOUND procedure.  If CREATE_SESSION is sent
   with a preceding SEQUENCE operation, any session created by
   CREATE_SESSION has no direct relation to the session specified in the
   SEQUENCE operation, although the two sessions might be associated
   with the same client ID.  If CREATE_SESSION is sent without a
   preceding SEQUENCE, then it MUST be the only operation in the
   COMPOUND procedure's request.  If it is not, the server MUST return
   NFS4ERR_NOT_ONLY_OP.

   In addition to creating a session, CREATE_SESSION has the following
   effects:

   o  The first session created with a new client ID serves to confirm
      the creation of that client's state on the server.  The server
      returns the parameter values for the new session.

   o  The connection CREATE_SESSION that is sent over is associated with
      the session's fore channel.

   The arguments and results of CREATE_SESSION are described as follows:





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   csa_clientid:

      This is the client ID with which the new session will be
      associated.  The corresponding result is csr_sessionid, the
      session ID of the new session.

   csa_sequence:

      Each client ID serializes CREATE_SESSION via a per-client ID
      sequence number (see Section 18.36.4).  The corresponding result
      is csr_sequence, which MUST be equal to csa_sequence.

   In the next three arguments, the client offers a value that is to be
   a property of the session.  Except where stated otherwise, it is
   RECOMMENDED that the server accept the value.  If it is not
   acceptable, the server MAY use a different value.  Regardless, the
   server MUST return the value the session will use (which will be
   either what the client offered, or what the server is insisting on)
   to the client.

   csa_flags:

      The csa_flags field contains a list of the following flag bits:

      CREATE_SESSION4_FLAG_PERSIST:

         If CREATE_SESSION4_FLAG_PERSIST is set, the client wants the
         server to provide a persistent reply cache.  For sessions in
         which only idempotent operations will be used (e.g., a read-
         only session), clients SHOULD NOT set
         CREATE_SESSION4_FLAG_PERSIST.  If the server does not or cannot
         provide a persistent reply cache, the server MUST NOT set
         CREATE_SESSION4_FLAG_PERSIST in the field csr_flags.

         If the server is a pNFS metadata server, for reasons described
         in Section 12.5.2 it SHOULD support
         CREATE_SESSION4_FLAG_PERSIST if it supports the layout_hint
         (Section 5.12.4) attribute.

      CREATE_SESSION4_FLAG_CONN_BACK_CHAN:

         If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags, the
         client is requesting that the connection over which the
         CREATE_SESSION operation arrived be associated with the
         session's backchannel in addition to its fore channel.  If the
         server agrees, it sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN in
         the result field csr_flags.  If
         CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,



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         then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set in
         csr_flags.

      CREATE_SESSION4_FLAG_CONN_RDMA:

         If CREATE_SESSION4_FLAG_CONN_RDMA is set in csa_flags, and if
         the connection over which the CREATE_SESSION operation arrived
         is currently in non-RDMA mode but has the capability to operate
         in RDMA mode, then the client is requesting that the server
         "step up" to RDMA mode on the connection.  If the server
         agrees, it sets CREATE_SESSION4_FLAG_CONN_RDMA in the result
         field csr_flags.  If CREATE_SESSION4_FLAG_CONN_RDMA is not set
         in csa_flags, then CREATE_SESSION4_FLAG_CONN_RDMA MUST NOT be
         set in csr_flags.  Note that once the server agrees to step up,
         it and the client MUST exchange all future traffic on the
         connection with RPC RDMA framing and not Record Marking ([8]).

   csa_fore_chan_attrs, csa_fore_chan_attrs:

      The csa_fore_chan_attrs and csa_back_chan_attrs fields apply to
      attributes of the fore channel (which conveys requests originating
      from the client to the server), and the backchannel (the channel
      that conveys callback requests originating from the server to the
      client), respectively.  The results are in corresponding
      structures called csr_fore_chan_attrs and csr_back_chan_attrs.
      The results establish attributes for each channel, and on all
      subsequent use of each channel of the session.  Each structure has
      the following fields:

      ca_headerpadsize:

         The maximum amount of padding the requester is willing to apply
         to ensure that write payloads are aligned on some boundary at
         the replier.  For each channel, the server

         +  will reply in ca_headerpadsize with its preferred value, or
            zero if padding is not in use, and

         +  MAY decrease this value but MUST NOT increase it.

      ca_maxrequestsize:

         The maximum size of a COMPOUND or CB_COMPOUND request that will
         be sent.  This size represents the XDR encoded size of the
         request, including the RPC headers (including security flavor
         credentials and verifiers) but excludes any RPC transport
         framing headers.  Imagine a request coming over a non-RDMA
         TCP/IP connection, and that it has a single Record Marking



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         header preceding it.  The maximum allowable count encoded in
         the header will be ca_maxrequestsize.  If a requester sends a
         request that exceeds ca_maxrequestsize, the error
         NFS4ERR_REQ_TOO_BIG will be returned per the description in
         Section 2.10.6.4.  For each channel, the server MAY decrease
         this value but MUST NOT increase it.

      ca_maxresponsesize:

         The maximum size of a COMPOUND or CB_COMPOUND reply that the
         requester will accept from the replier including RPC headers
         (see the ca_maxrequestsize definition).  For each channel, the
         server MAY decrease this value, but MUST NOT increase it.
         However, if the client selects a value for ca_maxresponsesize
         such that a replier on a channel could never send a response,
         the server SHOULD return NFS4ERR_TOOSMALL in the CREATE_SESSION
         reply.  After the session is created, if a requester sends a
         request for which the size of the reply would exceed this
         value, the replier will return NFS4ERR_REP_TOO_BIG, per the
         description in Section 2.10.6.4.

      ca_maxresponsesize_cached:

         Like ca_maxresponsesize, but the maximum size of a reply that
         will be stored in the reply cache (Section 2.10.6.1).  For each
         channel, the server MAY decrease this value, but MUST NOT
         increase it.  If, in the reply to CREATE_SESSION, the value of
         ca_maxresponsesize_cached of a channel is less than the value
         of ca_maxresponsesize of the same channel, then this is an
         indication to the requester that it needs to be selective about
         which replies it directs the replier to cache; for example,
         large replies from nonidempotent operations (e.g., COMPOUND
         requests with a READ operation) should not be cached.  The
         requester decides which replies to cache via an argument to the
         SEQUENCE (the sa_cachethis field, see Section 18.46) or
         CB_SEQUENCE (the csa_cachethis field, see Section 20.9)
         operations.  After the session is created, if a requester sends
         a request for which the size of the reply would exceed
         ca_maxresponsesize_cached, the replier will return
         NFS4ERR_REP_TOO_BIG_TO_CACHE, per the description in
         Section 2.10.6.4.

      ca_maxoperations:

         The maximum number of operations the replier will accept in a
         COMPOUND or CB_COMPOUND.  For the backchannel, the server MUST
         NOT change the value the client offers.  For the fore channel,
         the server MAY change the requested value.  After the session



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         is created, if a requester sends a COMPOUND or CB_COMPOUND with
         more operations than ca_maxoperations, the replier MUST return
         NFS4ERR_TOO_MANY_OPS.

      ca_maxrequests:

         The maximum number of concurrent COMPOUND or CB_COMPOUND
         requests the requester will send on the session.  Subsequent
         requests will each be assigned a slot identifier by the
         requester within the range zero to ca_maxrequests - 1
         inclusive.  For the backchannel, the server MUST NOT change the
         value the client offers.  For the fore channel, the server MAY
         change the requested value.

      ca_rdma_ird:

         This array has a maximum of one element.  If this array has one
         element, then the element contains the inbound RDMA read queue
         depth (IRD).  For each channel, the server MAY decrease this
         value, but MUST NOT increase it.

   csa_cb_program

      This is the ONC RPC program number the server MUST use in any
      callbacks sent through the backchannel to the client.  The server
      MUST specify an ONC RPC program number equal to csa_cb_program and
      an ONC RPC version number equal to 4 in callbacks sent to the
      client.  If a CB_COMPOUND is sent to the client, the server MUST
      use a minor version number of 1.  There is no corresponding
      result.

   csa_sec_parms

      The field csa_sec_parms is an array of acceptable security
      credentials the server can use on the session's backchannel.
      Three security flavors are supported: AUTH_NONE, AUTH_SYS, and
      RPCSEC_GSS.  If AUTH_NONE is specified for a credential, then this
      says the client is authorizing the server to use AUTH_NONE on all
      callbacks for the session.  If AUTH_SYS is specified, then the
      client is authorizing the server to use AUTH_SYS on all callbacks,
      using the credential specified cbsp_sys_cred.  If RPCSEC_GSS is
      specified, then the server is allowed to use the RPCSEC_GSS
      context specified in cbsp_gss_parms as the RPCSEC_GSS context in
      the credential of the RPC header of callbacks to the client.
      There is no corresponding result.

      The RPCSEC_GSS context for the backchannel is specified via a pair
      of values of data type gsshandle4_t.  The data type gsshandle4_t



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      represents an RPCSEC_GSS handle, and is precisely the same as the
      data type of the "handle" field of the rpc_gss_init_res data type
      defined in Section 5.2.3.1, "Context Creation Response -
      Successful Acceptance", of [4].

      The first RPCSEC_GSS handle, gcbp_handle_from_server, is the fore
      handle the server returned to the client (either in the handle
      field of data type rpc_gss_init_res or as one of the elements of
      the spi_handles field returned in the reply to EXCHANGE_ID) when
      the RPCSEC_GSS context was created on the server.  The second
      handle, gcbp_handle_from_client, is the back handle to which the
      client will map the RPCSEC_GSS context.  The server can
      immediately use the value of gcbp_handle_from_client in the
      RPCSEC_GSS credential in callback RPCs.  That is, the value in
      gcbp_handle_from_client can be used as the value of the field
      "handle" in data type rpc_gss_cred_t (see Section 5, "Elements of
      the RPCSEC_GSS Security Protocol", of [4]) in callback RPCs.  The
      server MUST use the RPCSEC_GSS security service specified in
      gcbp_service, i.e., it MUST set the "service" field of the
      rpc_gss_cred_t data type in RPCSEC_GSS credential to the value of
      gcbp_service (see Section 5.3.1, "RPC Request Header", of [4]).

      If the RPCSEC_GSS handle identified by gcbp_handle_from_server
      does not exist on the server, the server will return
      NFS4ERR_NOENT.

      Within each element of csa_sec_parms, the fore and back RPCSEC_GSS
      contexts MUST share the same GSS context and MUST have the same
      seq_window (see Section 5.2.3.1 of RFC2203 [4]).  The fore and
      back RPCSEC_GSS context state are independent of each other as far
      as the RPCSEC_GSS sequence number (see the seq_num field in the
      rpc_gss_cred_t data type of Sections 5 and 5.3.1 of [4]).

      If an RPCSEC_GSS handle is using the SSV context (see
      Section 2.10.9), then because each SSV RPCSEC_GSS handle shares a
      common SSV GSS context, there are security considerations specific
      to this situation discussed in Section 2.10.10.


   Once the session is created, the first SEQUENCE or CB_SEQUENCE
   received on a slot MUST have a sequence ID equal to 1; if not, the
   replier MUST return NFS4ERR_SEQ_MISORDERED.

18.36.4.  IMPLEMENTATION

   To describe a possible implementation, the same notation for client
   records introduced in the description of EXCHANGE_ID is used with the
   following addition:



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      clientid_arg: The value of the csa_clientid field of the
      CREATE_SESSION4args structure of the current request.

   Since CREATE_SESSION is a non-idempotent operation, we need to
   consider the possibility that retries may occur as a result of a
   client restart, network partition, malfunctioning router, etc.  For
   each client ID created by EXCHANGE_ID, the server maintains a
   separate reply cache (called the CREATE_SESSION reply cache) similar
   to the session reply cache used for SEQUENCE operations, with two
   distinctions.

   o  First, this is a reply cache just for detecting and processing
      CREATE_SESSION requests for a given client ID.

   o  Second, the size of the client ID reply cache is of one slot (and
      as a result, the CREATE_SESSION request does not carry a slot
      number).  This means that at most one CREATE_SESSION request for a
      given client ID can be outstanding.

   As previously stated, CREATE_SESSION can be sent with or without a
   preceding SEQUENCE operation.  Even if a SEQUENCE precedes
   CREATE_SESSION, the server MUST maintain the CREATE_SESSION reply
   cache, which is separate from the reply cache for the session
   associated with a SEQUENCE.  If CREATE_SESSION was originally sent by
   itself, the client MAY send a retry of the CREATE_SESSION operation
   within a COMPOUND preceded by a SEQUENCE.  If CREATE_SESSION was
   originally sent in a COMPOUND that started with a SEQUENCE, then the
   client SHOULD send a retry in a COMPOUND that starts with a SEQUENCE
   that has the same session ID as the SEQUENCE of the original request.
   However, the client MAY send a retry in a COMPOUND that either has no
   preceding SEQUENCE, or has a preceding SEQUENCE that refers to a
   different session than the original CREATE_SESSION.  This might be
   necessary if the client sends a CREATE_SESSION in a COMPOUND preceded
   by a SEQUENCE with session ID X, and session X no longer exists.
   Regardless, any retry of CREATE_SESSION, with or without a preceding
   SEQUENCE, MUST use the same value of csa_sequence as the original.

   After the client received a reply to an EXCHANGE_ID operation that
   contains a new, unconfirmed client ID, the server expects the client
   to follow with a CREATE_SESSION operation to confirm the client ID.
   The server expects value of csa_sequenceid in the arguments to that
   CREATE_SESSION to be to equal the value of the field eir_sequenceid
   that was returned in results of the EXCHANGE_ID that returned the
   unconfirmed client ID.  Before the server replies to that EXCHANGE_ID
   operation, it initializes the client ID slot to be equal to
   eir_sequenceid - 1 (accounting for underflow), and records a
   contrived CREATE_SESSION result with a "cached" result of
   NFS4ERR_SEQ_MISORDERED.  With the client ID slot thus initialized,



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   the processing of the CREATE_SESSION operation is divided into four
   phases:

   1.  Client record look up.  The server looks up the client ID in its
       client record table.  If the server contains no records with
       client ID equal to clientid_arg, then most likely the client's
       state has been purged during a period of inactivity, possibly due
       to a loss of connectivity.  NFS4ERR_STALE_CLIENTID is returned,
       and no changes are made to any client records on the server.
       Otherwise, the server goes to phase 2.

   2.  Sequence ID processing.  If csa_sequenceid is equal to the
       sequence ID in the client ID's slot, then this is a replay of the
       previous CREATE_SESSION request, and the server returns the
       cached result.  If csa_sequenceid is not equal to the sequence ID
       in the slot, and is more than one greater (accounting for
       wraparound), then the server returns the error
       NFS4ERR_SEQ_MISORDERED, and does not change the slot.  If
       csa_sequenceid is equal to the slot's sequence ID + 1 (accounting
       for wraparound), then the slot's sequence ID is set to
       csa_sequenceid, and the CREATE_SESSION processing goes to the
       next phase.  A subsequent new CREATE_SESSION call over the same
       client ID MUST use a csa_sequenceid that is one greater than the
       sequence ID in the slot.

   3.  Client ID confirmation.  If this would be the first session for
       the client ID, the CREATE_SESSION operation serves to confirm the
       client ID.  Otherwise, the client ID confirmation phase is
       skipped and only the session creation phase occurs.  Any case in
       which there is more than one record with identical values for
       client ID represents a server implementation error.  Operation in
       the potential valid cases is summarized as follows.

       *  Successful Confirmation

             If the server has the following unconfirmed record, then
             this is the expected confirmation of an unconfirmed record.

             { ownerid, verifier, principal_arg, clientid_arg,
             unconfirmed }

             As noted in Section 18.35.4, the server might also have the
             following confirmed record.

             { ownerid, old_verifier, principal_arg, old_clientid,
             confirmed }





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             The server schedules the replacement of both records with:

             { ownerid, verifier, principal_arg, clientid_arg, confirmed
             }

             The processing of CREATE_SESSION continues on to session
             creation.  Once the session is successfully created, the
             scheduled client record replacement is committed.  If the
             session is not successfully created, then no changes are
             made to any client records on the server.

       *  Unsuccessful Confirmation

             If the server has the following record, then the client has
             changed principals after the previous EXCHANGE_ID request,
             or there has been a chance collision between shorthand
             client identifiers.

             { *, *, old_principal_arg, clientid_arg, * }

             Neither of these cases is permissible.  Processing stops
             and NFS4ERR_CLID_INUSE is returned to the client.  No
             changes are made to any client records on the server.

   4.  Session creation.  The server confirmed the client ID, either in
       this CREATE_SESSION operation, or a previous CREATE_SESSION
       operation.  The server examines the remaining fields of the
       arguments.

       The server creates the session by recording the parameter values
       used (including whether the CREATE_SESSION4_FLAG_PERSIST flag is
       set and has been accepted by the server) and allocating space for
       the session reply cache (if there is not enough space, the server
       returns NFS4ERR_NOSPC).  For each slot in the reply cache, the
       server sets the sequence ID to zero, and records an entry
       containing a COMPOUND reply with zero operations and the error
       NFS4ERR_SEQ_MISORDERED.  This way, if the first SEQUENCE request
       sent has a sequence ID equal to zero, the server can simply
       return what is in the reply cache: NFS4ERR_SEQ_MISORDERED.  The
       client initializes its reply cache for receiving callbacks in the
       same way, and similarly, the first CB_SEQUENCE operation on a
       slot after session creation MUST have a sequence ID of one.

       If the session state is created successfully, the server
       associates the session with the client ID provided by the client.

       When a request that had CREATE_SESSION4_FLAG_CONN_RDMA set needs
       to be retried, the retry MUST be done on a new connection that is



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       in non-RDMA mode.  If properties of the new connection are
       different enough that the arguments to CREATE_SESSION need to
       change, then a non-retry MUST be sent.  The server will
       eventually dispose of any session that was created on the
       original connection.

   On the backchannel, the client and server might wish to have many
   slots, in some cases perhaps more that the fore channel, in order to
   deal with the situations where the network link has high latency and
   is the primary bottleneck for response to recalls.  If so, and if the
   client provides too few slots to the backchannel, the server might
   limit the number of recallable objects it gives to the client.

   Implementing RPCSEC_GSS callback support requires changes to both the
   client and server implementations of RPCSEC_GSS.  One possible set of
   changes includes:

   o  Adding a data structure that wraps the GSS-API context with a
      reference count.

   o  New functions to increment and decrement the reference count.  If
      the reference count is decremented to zero, the wrapper data
      structure and the GSS-API context it refers to would be freed.

   o  Change RPCSEC_GSS to create the wrapper data structure upon
      receiving GSS-API context from gss_accept_sec_context() and
      gss_init_sec_context().  The reference count would be initialized
      to 1.

   o  Adding a function to map an existing RPCSEC_GSS handle to a
      pointer to the wrapper data structure.  The reference count would
      be incremented.

   o  Adding a function to create a new RPCSEC_GSS handle from a pointer
      to the wrapper data structure.  The reference count would be
      incremented.

   o  Replacing calls from RPCSEC_GSS that free GSS-API contexts, with
      calls to decrement the reference count on the wrapper data
      structure.

18.37.  Operation 44: DESTROY_SESSION - Destroy a Session

18.37.1.  ARGUMENT

   struct DESTROY_SESSION4args {
           sessionid4      dsa_sessionid;
   };



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18.37.2.  RESULT

   struct DESTROY_SESSION4res {
           nfsstat4        dsr_status;
   };


18.37.3.  DESCRIPTION

   The DESTROY_SESSION operation closes the session and discards the
   session's reply cache, if any.  Any remaining connections associated
   with the session are immediately disassociated.  If the connection
   has no remaining associated sessions, the connection MAY be closed by
   the server.  Locks, delegations, layouts, wants, and the lease, which
   are all tied to the client ID, are not affected by DESTROY_SESSION.

   DESTROY_SESSION MUST be invoked on a connection that is associated
   with the session being destroyed.  In addition, if SP4_MACH_CRED
   state protection was specified when the client ID was created, the
   RPCSEC_GSS principal that created the session MUST be the one that
   destroys the session, using RPCSEC_GSS privacy or integrity.  If
   SP4_SSV state protection was specified when the client ID was
   created, RPCSEC_GSS using the SSV mechanism (Section 2.10.9) MUST be
   used, with integrity or privacy.

   If the COMPOUND request starts with SEQUENCE, and if the sessionids
   specified in SEQUENCE and DESTROY_SESSION are the same, then

   o  DESTROY_SESSION MUST be the final operation in the COMPOUND
      request.

   o  It is advisable to avoid placing DESTROY_SESSION in a COMPOUND
      request with other state-modifying operations, because the
      DESTROY_SESSION will destroy the reply cache.

   o  Because the session and its reply cache are destroyed, a client
      that retries the request may receive an error in reply to the
      retry, even though the original request was successful.

   If the COMPOUND request starts with SEQUENCE, and if the sessionids
   specified in SEQUENCE and DESTROY_SESSION are different, then
   DESTROY_SESSION can appear in any position of the COMPOUND request
   (except for the first position).  The two sessionids can belong to
   different client IDs.

   If the COMPOUND request does not start with SEQUENCE, and if
   DESTROY_SESSION is not the sole operation, then server MUST return
   NFS4ERR_NOT_ONLY_OP.



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   If there is a backchannel on the session and the server has
   outstanding CB_COMPOUND operations for the session which have not
   been replied to, then the server MAY refuse to destroy the session
   and return an error.  If so, then in the event the backchannel is
   down, the server SHOULD return NFS4ERR_CB_PATH_DOWN to inform the
   client that the backchannel needs to be repaired before the server
   will allow the session to be destroyed.  Otherwise, the error
   CB_BACK_CHAN_BUSY SHOULD be returned to indicate that there are
   CB_COMPOUNDs that need to be replied to.  The client SHOULD reply to
   all outstanding CB_COMPOUNDs before re-sending DESTROY_SESSION.

18.38.  Operation 45: FREE_STATEID - Free Stateid with No Locks

18.38.1.  ARGUMENT

   struct FREE_STATEID4args {
           stateid4        fsa_stateid;
   };


18.38.2.  RESULT

   struct FREE_STATEID4res {
           nfsstat4        fsr_status;
   };


18.38.3.  DESCRIPTION

   The FREE_STATEID operation is used to free a stateid that no longer
   has any associated locks (including opens, byte-range locks,
   delegations, and layouts).  This may be because of client LOCKU
   operations or because of server revocation.  If there are valid locks
   (of any kind) associated with the stateid in question, the error
   NFS4ERR_LOCKS_HELD will be returned, and the associated stateid will
   not be freed.

   When a stateid is freed that had been associated with revoked locks,
   by sending the FREE_STATEID operation, the client acknowledges the
   loss of those locks.  This allows the server, once all such revoked
   state is acknowledged, to allow that client again to reclaim locks,
   without encountering the edge conditions discussed in Section 8.4.2.

   Once a successful FREE_STATEID is done for a given stateid, any
   subsequent use of that stateid will result in an NFS4ERR_BAD_STATEID
   error.





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18.39.  Operation 46: GET_DIR_DELEGATION - Get a Directory Delegation

18.39.1.  ARGUMENT


   typedef nfstime4 attr_notice4;

   struct GET_DIR_DELEGATION4args {
           /* CURRENT_FH: delegated directory */
           bool            gdda_signal_deleg_avail;
           bitmap4         gdda_notification_types;
           attr_notice4    gdda_child_attr_delay;
           attr_notice4    gdda_dir_attr_delay;
           bitmap4         gdda_child_attributes;
           bitmap4         gdda_dir_attributes;
   };



































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18.39.2.  RESULT

   struct GET_DIR_DELEGATION4resok {
           verifier4       gddr_cookieverf;
           /* Stateid for get_dir_delegation */
           stateid4        gddr_stateid;
           /* Which notifications can the server support */
           bitmap4         gddr_notification;
           bitmap4         gddr_child_attributes;
           bitmap4         gddr_dir_attributes;
   };

   enum gddrnf4_status {
           GDD4_OK         = 0,
           GDD4_UNAVAIL    = 1
   };

   union GET_DIR_DELEGATION4res_non_fatal
    switch (gddrnf4_status gddrnf_status) {
    case GDD4_OK:
     GET_DIR_DELEGATION4resok      gddrnf_resok4;
    case GDD4_UNAVAIL:
     bool                          gddrnf_will_signal_deleg_avail;
   };

   union GET_DIR_DELEGATION4res
    switch (nfsstat4 gddr_status) {
    case NFS4_OK:
     GET_DIR_DELEGATION4res_non_fatal      gddr_res_non_fatal4;
    default:
     void;
   };


18.39.3.  DESCRIPTION

   The GET_DIR_DELEGATION operation is used by a client to request a
   directory delegation.  The directory is represented by the current
   filehandle.  The client also specifies whether it wants the server to
   notify it when the directory changes in certain ways by setting one
   or more bits in a bitmap.  The server may refuse to grant the
   delegation.  In that case, the server will return
   NFS4ERR_DIRDELEG_UNAVAIL.  If the server decides to hand out the
   delegation, it will return a cookie verifier for that directory.  If
   the cookie verifier changes when the client is holding the
   delegation, the delegation will be recalled unless the client has
   asked for notification for this event.




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   The server will also return a directory delegation stateid,
   gddr_stateid, as a result of the GET_DIR_DELEGATION operation.  This
   stateid will appear in callback messages related to the delegation,
   such as notifications and delegation recalls.  The client will use
   this stateid to return the delegation voluntarily or upon recall.  A
   delegation is returned by calling the DELEGRETURN operation.

   The server might not be able to support notifications of certain
   events.  If the client asks for such notifications, the server MUST
   inform the client of its inability to do so as part of the
   GET_DIR_DELEGATION reply by not setting the appropriate bits in the
   supported notifications bitmask, gddr_notification, contained in the
   reply.  The server MUST NOT add bits to gddr_notification that the
   client did not request.

   The GET_DIR_DELEGATION operation can be used for both normal and
   named attribute directories.

   If client sets gdda_signal_deleg_avail to TRUE, then it is
   registering with the client a "want" for a directory delegation.  If
   the delegation is not available, and the server supports and will
   honor the "want", the results will have
   gddrnf_will_signal_deleg_avail set to TRUE and no error will be
   indicated on return.  If so, the client should expect a future
   CB_RECALLABLE_OBJ_AVAIL operation to indicate that a directory
   delegation is available.  If the server does not wish to honor the
   "want" or is not able to do so, it returns the error
   NFS4ERR_DIRDELEG_UNAVAIL.  If the delegation is immediately
   available, the server SHOULD return it with the response to the
   operation, rather than via a callback.

   When a client makes a request for a directory delegation while it
   already holds a directory delegation for that directory (including
   the case where it has been recalled but not yet returned by the
   client or revoked by the server), the server MUST reply with the
   value of gddr_status set to NFS4_OK, the value of gddrnf_status set
   to GDD4_UNAVAIL, and the value of gddrnf_will_signal_deleg_avail set
   to FALSE.  The delegation the client held before the request remains
   intact, and its state is unchanged.  The current stateid is not
   changed (see Section 16.2.3.1.2 for a description of the current
   stateid).

18.39.4.  IMPLEMENTATION

   Directory delegations provide the benefit of improving cache
   consistency of namespace information.  This is done through
   synchronous callbacks.  A server must support synchronous callbacks
   in order to support directory delegations.  In addition to that,



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   asynchronous notifications provide a way to reduce network traffic as
   well as improve client performance in certain conditions.

   Notifications are specified in terms of potential changes to the
   directory.  A client can ask to be notified of events by setting one
   or more bits in gdda_notification_types.  The client can ask for
   notifications on addition of entries to a directory (by setting the
   NOTIFY4_ADD_ENTRY in gdda_notification_types), notifications on entry
   removal (NOTIFY4_REMOVE_ENTRY), renames (NOTIFY4_RENAME_ENTRY),
   directory attribute changes (NOTIFY4_CHANGE_DIR_ATTRIBUTES), and
   cookie verifier changes (NOTIFY4_CHANGE_COOKIE_VERIFIER) by setting
   one or more corresponding bits in the gdda_notification_types field.

   The client can also ask for notifications of changes to attributes of
   directory entries (NOTIFY4_CHANGE_CHILD_ATTRIBUTES) in order to keep
   its attribute cache up to date.  However, any changes made to child
   attributes do not cause the delegation to be recalled.  If a client
   is interested in directory entry caching or negative name caching, it
   can set the gdda_notification_types appropriately to its particular
   need and the server will notify it of all changes that would
   otherwise invalidate its name cache.  The kind of notification a
   client asks for may depend on the directory size, its rate of change,
   and the applications being used to access that directory.  The
   enumeration of the conditions under which a client might ask for a
   notification is out of the scope of this specification.

   For attribute notifications, the client will set bits in the
   gdda_dir_attributes bitmap to indicate which attributes it wants to
   be notified of.  If the server does not support notifications for
   changes to a certain attribute, it SHOULD NOT set that attribute in
   the supported attribute bitmap specified in the reply
   (gddr_dir_attributes).  The client will also set in the
   gdda_child_attributes bitmap the attributes of directory entries it
   wants to be notified of, and the server will indicate in
   gddr_child_attributes which attributes of directory entries it will
   notify the client of.

   The client will also let the server know if it wants to get the
   notification as soon as the attribute change occurs or after a
   certain delay by setting a delay factor; gdda_child_attr_delay is for
   attribute changes to directory entries and gdda_dir_attr_delay is for
   attribute changes to the directory.  If this delay factor is set to
   zero, that indicates to the server that the client wants to be
   notified of any attribute changes as soon as they occur.  If the
   delay factor is set to N seconds, the server will make a best-effort
   guarantee that attribute updates are synchronized within N seconds.
   If the client asks for a delay factor that the server does not
   support or that may cause significant resource consumption on the



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   server by causing the server to send a lot of notifications, the
   server should not commit to sending out notifications for attributes
   and therefore must not set the appropriate bit in the
   gddr_child_attributes and gddr_dir_attributes bitmaps in the
   response.

   The client MUST use a security tuple (Section 2.6.1) that the
   directory or its applicable ancestor (Section 2.6) is exported with.
   If not, the server MUST return NFS4ERR_WRONGSEC to the operation that
   both precedes GET_DIR_DELEGATION and sets the current filehandle (see
   Section 2.6.3.1).

   The directory delegation covers all the entries in the directory
   except the parent entry.  That means if a directory and its parent
   both hold directory delegations, any changes to the parent will not
   cause a notification to be sent for the child even though the child's
   parent entry points to the parent directory.

18.40.  Operation 47: GETDEVICEINFO - Get Device Information

18.40.1.  ARGUMENT

   struct GETDEVICEINFO4args {
           deviceid4       gdia_device_id;
           layouttype4     gdia_layout_type;
           count4          gdia_maxcount;
           bitmap4         gdia_notify_types;
   };


18.40.2.  RESULT

   struct GETDEVICEINFO4resok {
           device_addr4    gdir_device_addr;
           bitmap4         gdir_notification;
   };

   union GETDEVICEINFO4res switch (nfsstat4 gdir_status) {
   case NFS4_OK:
           GETDEVICEINFO4resok     gdir_resok4;
   case NFS4ERR_TOOSMALL:
           count4                  gdir_mincount;
   default:
           void;
   };






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18.40.3.  DESCRIPTION

   The GETDEVICEINFO operation returns pNFS storage device address
   information for the specified device ID.  The client identifies the
   device information to be returned by providing the gdia_device_id and
   gdia_layout_type that uniquely identify the device.  The client
   provides gdia_maxcount to limit the number of bytes for the result.
   This maximum size represents all of the data being returned within
   the GETDEVICEINFO4resok structure and includes the XDR overhead.  The
   server may return less data.  If the server is unable to return any
   information within the gdia_maxcount limit, the error
   NFS4ERR_TOOSMALL will be returned.  However, if gdia_maxcount is
   zero, NFS4ERR_TOOSMALL MUST NOT be returned.

   The da_layout_type field of the gdir_device_addr returned by the
   server MUST be equal to the gdia_layout_type specified by the client.
   If it is not equal, the client SHOULD ignore the response as invalid
   and behave as if the server returned an error, even if the client
   does have support for the layout type returned.

   The client also provides a notification bitmap, gdia_notify_types,
   for the device ID mapping notification for which it is interested in
   receiving; the server must support device ID notifications for the
   notification request to have affect.  The notification mask is
   composed in the same manner as the bitmap for file attributes
   (Section 3.3.7).  The numbers of bit positions are listed in the
   notify_device_type4 enumeration type (Section 20.12).  Only two
   enumerated values of notify_device_type4 currently apply to
   GETDEVICEINFO: NOTIFY_DEVICEID4_CHANGE and NOTIFY_DEVICEID4_DELETE
   (see Section 20.12).

   The notification bitmap applies only to the specified device ID.  If
   a client sends a GETDEVICEINFO operation on a deviceID multiple
   times, the last notification bitmap is used by the server for
   subsequent notifications.  If the bitmap is zero or empty, then the
   device ID's notifications are turned off.

   If the client wants to just update or turn off notifications, it MAY
   send a GETDEVICEINFO operation with gdia_maxcount set to zero.  In
   that event, if the device ID is valid, the reply's da_addr_body field
   of the gdir_device_addr field will be of zero length.

   If an unknown device ID is given in gdia_device_id, the server
   returns NFS4ERR_NOENT.  Otherwise, the device address information is
   returned in gdir_device_addr.  Finally, if the server supports
   notifications for device ID mappings, the gdir_notification result
   will contain a bitmap of which notifications it will actually send to
   the client (via CB_NOTIFY_DEVICEID, see Section 20.12).



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   If NFS4ERR_TOOSMALL is returned, the results also contain
   gdir_mincount.  The value of gdir_mincount represents the minimum
   size necessary to obtain the device information.

18.40.4.  IMPLEMENTATION

   Aside from updating or turning off notifications, another use case
   for gdia_maxcount being set to zero is to validate a device ID.

   The client SHOULD request a notification for changes or deletion of a
   device ID to device address mapping so that the server can allow the
   client gracefully use a new mapping, without having pending I/O fail
   abruptly, or force layouts using the device ID to be recalled or
   revoked.

   It is possible that GETDEVICEINFO (and GETDEVICELIST) will race with
   CB_NOTIFY_DEVICEID, i.e., CB_NOTIFY_DEVICEID arrives before the
   client gets and processes the response to GETDEVICEINFO or
   GETDEVICELIST.  The analysis of the race leverages the fact that the
   server MUST NOT delete a device ID that is referred to by a layout
   the client has.

   o  CB_NOTIFY_DEVICEID deletes a device ID.  If the client believes it
      has layouts that refer to the device ID, then it is possible that
      layouts referring to the deleted device ID have been revoked.  The
      client should send a TEST_STATEID request using the stateid for
      each layout that might have been revoked.  If TEST_STATEID
      indicates that any layouts have been revoked, the client must
      recover from layout revocation as described in Section 12.5.6.  If
      TEST_STATEID indicates that at least one layout has not been
      revoked, the client should send a GETDEVICEINFO operation on the
      supposedly deleted device ID to verify that the device ID has been
      deleted.

      If GETDEVICEINFO indicates that the device ID does not exist, then
      the client assumes the server is faulty and recovers by sending an
      EXCHANGE_ID operation.  If GETDEVICEINFO indicates that the device
      ID does exist, then while the server is faulty for sending an
      erroneous device ID deletion notification, the degree to which it
      is faulty does not require the client to create a new client ID.

      If the client does not have layouts that refer to the device ID,
      no harm is done.  The client should mark the device ID as deleted,
      and when GETDEVICEINFO or GETDEVICELIST results are received that
      indicate that the device ID has been in fact deleted, the device
      ID should be removed from the client's cache.





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   o  CB_NOTIFY_DEVICEID indicates that a device ID's device addressing
      mappings have changed.  The client should assume that the results
      from the in-progress GETDEVICEINFO will be stale for the device ID
      once received, and so it should send another GETDEVICEINFO on the
      device ID.

18.41.  Operation 48: GETDEVICELIST - Get All Device Mappings for a File
        System

18.41.1.  ARGUMENT

   struct GETDEVICELIST4args {
           /* CURRENT_FH: object belonging to the file system */
           layouttype4     gdla_layout_type;

           /* number of deviceIDs to return */
           count4          gdla_maxdevices;

           nfs_cookie4     gdla_cookie;
           verifier4       gdla_cookieverf;
   };


18.41.2.  RESULT

   struct GETDEVICELIST4resok {
           nfs_cookie4             gdlr_cookie;
           verifier4               gdlr_cookieverf;
           deviceid4               gdlr_deviceid_list<>;
           bool                    gdlr_eof;
   };

   union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
   case NFS4_OK:
           GETDEVICELIST4resok     gdlr_resok4;
   default:
           void;
   };


18.41.3.  DESCRIPTION

   This operation is used by the client to enumerate all of the device
   IDs that a server's file system uses.

   The client provides a current filehandle of a file object that
   belongs to the file system (i.e., all file objects sharing the same
   fsid as that of the current filehandle) and the layout type in



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   gdia_layout_type.  Since this operation might require multiple calls
   to enumerate all the device IDs (and is thus similar to the READDIR
   (Section 18.23) operation), the client also provides gdia_cookie and
   gdia_cookieverf to specify the current cursor position in the list.
   When the client wants to read from the beginning of the file system's
   device mappings, it sets gdla_cookie to zero.  The field
   gdla_cookieverf MUST be ignored by the server when gdla_cookie is
   zero.  The client provides gdla_maxdevices to limit the number of
   device IDs in the result.  If gdla_maxdevices is zero, the server
   MUST return NFS4ERR_INVAL.  The server MAY return fewer device IDs.

   The successful response to the operation will contain the cookie,
   gdlr_cookie, and the cookie verifier, gdlr_cookieverf, to be used on
   the subsequent GETDEVICELIST.  A gdlr_eof value of TRUE signifies
   that there are no remaining entries in the server's device list.
   Each element of gdlr_deviceid_list contains a device ID.

18.41.4.  IMPLEMENTATION

   An example of the use of this operation is for pNFS clients and
   servers that use LAYOUT4_BLOCK_VOLUME layouts.  In these environments
   it may be helpful for a client to determine device accessibility upon
   first file system access.

18.42.  Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a Layout


























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18.42.1.  ARGUMENT

   union newtime4 switch (bool nt_timechanged) {
   case TRUE:
           nfstime4           nt_time;
   case FALSE:
           void;
   };

   union newoffset4 switch (bool no_newoffset) {
   case TRUE:
           offset4           no_offset;
   case FALSE:
           void;
   };

   struct LAYOUTCOMMIT4args {
           /* CURRENT_FH: file */
           offset4                 loca_offset;
           length4                 loca_length;
           bool                    loca_reclaim;
           stateid4                loca_stateid;
           newoffset4              loca_last_write_offset;
           newtime4                loca_time_modify;
           layoutupdate4           loca_layoutupdate;
   };

18.42.2.  RESULT

   union newsize4 switch (bool ns_sizechanged) {
   case TRUE:
           length4         ns_size;
   case FALSE:
           void;
   };

   struct LAYOUTCOMMIT4resok {
           newsize4                locr_newsize;
   };

   union LAYOUTCOMMIT4res switch (nfsstat4 locr_status) {
   case NFS4_OK:
           LAYOUTCOMMIT4resok      locr_resok4;
   default:
           void;
   };





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18.42.3.  DESCRIPTION

   The LAYOUTCOMMIT operation commits changes in the layout represented
   by the current filehandle, client ID (derived from the session ID in
   the preceding SEQUENCE operation), byte-range, and stateid.  Since
   layouts are sub-dividable, a smaller portion of a layout, retrieved
   via LAYOUTGET, can be committed.  The byte-range being committed is
   specified through the byte-range (loca_offset and loca_length).  This
   byte-range MUST overlap with one or more existing layouts previously
   granted via LAYOUTGET (Section 18.43), each with an iomode of
   LAYOUTIOMODE4_RW.  In the case where the iomode of any held layout
   segment is not LAYOUTIOMODE4_RW, the server should return the error
   NFS4ERR_BAD_IOMODE.  For the case where the client does not hold
   matching layout segment(s) for the defined byte-range, the server
   should return the error NFS4ERR_BAD_LAYOUT.

   The LAYOUTCOMMIT operation indicates that the client has completed
   writes using a layout obtained by a previous LAYOUTGET.  The client
   may have only written a subset of the data range it previously
   requested.  LAYOUTCOMMIT allows it to commit or discard provisionally
   allocated space and to update the server with a new end-of-file.  The
   layout referenced by LAYOUTCOMMIT is still valid after the operation
   completes and can be continued to be referenced by the client ID,
   filehandle, byte-range, layout type, and stateid.

   If the loca_reclaim field is set to TRUE, this indicates that the
   client is attempting to commit changes to a layout after the restart
   of the metadata server during the metadata server's recovery grace
   period (see Section 12.7.4).  This type of request may be necessary
   when the client has uncommitted writes to provisionally allocated
   byte-ranges of a file that were sent to the storage devices before
   the restart of the metadata server.  In this case, the layout
   provided by the client MUST be a subset of a writable layout that the
   client held immediately before the restart of the metadata server.
   The value of the field loca_stateid MUST be a value that the metadata
   server returned before it restarted.  The metadata server is free to
   accept or reject this request based on its own internal metadata
   consistency checks.  If the metadata server finds that the layout
   provided by the client does not pass its consistency checks, it MUST
   reject the request with the status NFS4ERR_RECLAIM_BAD.  The
   successful completion of the LAYOUTCOMMIT request with loca_reclaim
   set to TRUE does NOT provide the client with a layout for the file.
   It simply commits the changes to the layout specified in the
   loca_layoutupdate field.  To obtain a layout for the file, the client
   must send a LAYOUTGET request to the server after the server's grace
   period has expired.  If the metadata server receives a LAYOUTCOMMIT
   request with loca_reclaim set to TRUE when the metadata server is not
   in its recovery grace period, it MUST reject the request with the



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   status NFS4ERR_NO_GRACE.

   Setting the loca_reclaim field to TRUE is required if and only if the
   committed layout was acquired before the metadata server restart.  If
   the client is committing a layout that was acquired during the
   metadata server's grace period, it MUST set the "reclaim" field to
   FALSE.

   The loca_stateid is a layout stateid value as returned by previously
   successful layout operations (see Section 12.5.3).

   The loca_last_write_offset field specifies the offset of the last
   byte written by the client previous to the LAYOUTCOMMIT.  Note that
   this value is never equal to the file's size (at most it is one byte
   less than the file's size) and MUST be less than or equal to
   NFS4_MAXFILEOFF.  Also, loca_last_write_offset MUST overlap the range
   described by loca_offset and loca_length.  The metadata server may
   use this information to determine whether the file's size needs to be
   updated.  If the metadata server updates the file's size as the
   result of the LAYOUTCOMMIT operation, it must return the new size
   (locr_newsize.ns_size) as part of the results.

   The loca_time_modify field allows the client to suggest a
   modification time it would like the metadata server to set.  The
   metadata server may use the suggestion or it may use the time of the
   LAYOUTCOMMIT operation to set the modification time.  If the metadata
   server uses the client-provided modification time, it should ensure
   that time does not flow backwards.  If the client wants to force the
   metadata server to set an exact time, the client should use a SETATTR
   operation in a COMPOUND right after LAYOUTCOMMIT.  See Section 12.5.4
   for more details.  If the client desires the resultant modification
   time, it should construct the COMPOUND so that a GETATTR follows the
   LAYOUTCOMMIT.

   The loca_layoutupdate argument to LAYOUTCOMMIT provides a mechanism
   for a client to provide layout-specific updates to the metadata
   server.  For example, the layout update can describe what byte-ranges
   of the original layout have been used and what byte-ranges can be
   deallocated.  There is no NFSv4.1 file layout-specific layoutupdate4
   structure.

   The layout information is more verbose for block devices than for
   objects and files because the latter two hide the details of block
   allocation behind their storage protocols.  At the minimum, the
   client needs to communicate changes to the end-of-file location back
   to the server, and, if desired, its view of the file's modification
   time.  For block/volume layouts, it needs to specify precisely which
   blocks have been used.



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   If the layout identified in the arguments does not exist, the error
   NFS4ERR_BADLAYOUT is returned.  The layout being committed may also
   be rejected if it does not correspond to an existing layout with an
   iomode of LAYOUTIOMODE4_RW.

   On success, the current filehandle retains its value and the current
   stateid retains its value.

18.42.4.  IMPLEMENTATION

   The client MAY also use LAYOUTCOMMIT with the loca_reclaim field set
   to TRUE to convey hints to modified file attributes or to report
   layout-type specific information such as I/O errors for object-based
   storage layouts, as normally done during normal operation.  Doing so
   may help the metadata server to recover files more efficiently after
   restart.  For example, some file system implementations may require
   expansive recovery of file system objects if the metadata server does
   not get a positive indication from all clients holding a
   LAYOUTIOMODE4_RW layout that they have successfully completed all
   their writes.  Sending a LAYOUTCOMMIT (if required) and then
   following with LAYOUTRETURN can provide such an indication and allow
   for graceful and efficient recovery.

   If loca_reclaim is TRUE, the metadata server is free to either
   examine or ignore the value in the field loca_stateid.  The metadata
   server implementation might or might not encode in its layout stateid
   information that allows the metadate server to perform a consistency
   check on the LAYOUTCOMMIT request.

18.43.  Operation 50: LAYOUTGET - Get Layout Information

18.43.1.  ARGUMENT

   struct LAYOUTGET4args {
           /* CURRENT_FH: file */
           bool                    loga_signal_layout_avail;
           layouttype4             loga_layout_type;
           layoutiomode4           loga_iomode;
           offset4                 loga_offset;
           length4                 loga_length;
           length4                 loga_minlength;
           stateid4                loga_stateid;
           count4                  loga_maxcount;
   };







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18.43.2.  RESULT

   struct LAYOUTGET4resok {
           bool               logr_return_on_close;
           stateid4           logr_stateid;
           layout4            logr_layout<>;
   };

   union LAYOUTGET4res switch (nfsstat4 logr_status) {
   case NFS4_OK:
           LAYOUTGET4resok     logr_resok4;
   case NFS4ERR_LAYOUTTRYLATER:
           bool                logr_will_signal_layout_avail;
   default:
           void;
   };


18.43.3.  DESCRIPTION

   The LAYOUTGET operation requests a layout from the metadata server
   for reading or writing the file given by the filehandle at the byte-
   range specified by offset and length.  Layouts are identified by the
   client ID (derived from the session ID in the preceding SEQUENCE
   operation), current filehandle, layout type (loga_layout_type), and
   the layout stateid (loga_stateid).  The use of the loga_iomode field
   depends upon the layout type, but should reflect the client's data
   access intent.

   If the metadata server is in a grace period, and does not persist
   layouts and device ID to device address mappings, then it MUST return
   NFS4ERR_GRACE (see Section 8.4.2.1).

   The LAYOUTGET operation returns layout information for the specified
   byte-range: a layout.  The client actually specifies two ranges, both
   starting at the offset in the loga_offset field.  The first range is
   between loga_offset and loga_offset + loga_length - 1 inclusive.
   This range indicates the desired range the client wants the layout to
   cover.  The second range is between loga_offset and loga_offset +
   loga_minlength - 1 inclusive.  This range indicates the required
   range the client needs the layout to cover.  Thus, loga_minlength
   MUST be less than or equal to loga_length.

   When a length field is set to NFS4_UINT64_MAX, this indicates a
   desire (when loga_length is NFS4_UINT64_MAX) or requirement (when
   loga_minlength is NFS4_UINT64_MAX) to get a layout from loga_offset
   through the end-of-file, regardless of the file's length.




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   The following rules govern the relationships among, and the minima
   of, loga_length, loga_minlength, and loga_offset.

   o  If loga_length is less than loga_minlength, the metadata server
      MUST return NFS4ERR_INVAL.

   o  If loga_minlength is zero, this is an indication to the metadata
      server that the client desires any layout at offset loga_offset or
      less that the metadata server has "readily available".  Readily is
      subjective, and depends on the layout type and the pNFS server
      implementation.  For example, some metadata servers might have to
      pre-allocate stable storage when they receive a request for a
      range of a file that goes beyond the file's current length.  If
      loga_minlength is zero and loga_length is greater than zero, this
      tells the metadata server what range of the layout the client
      would prefer to have.  If loga_length and loga_minlength are both
      zero, then the client is indicating that it desires a layout of
      any length with the ending offset of the range no less than the
      value specified loga_offset, and the starting offset at or below
      loga_offset.  If the metadata server does not have a layout that
      is readily available, then it MUST return NFS4ERR_LAYOUTTRYLATER.

   o  If the sum of loga_offset and loga_minlength exceeds
      NFS4_UINT64_MAX, and loga_minlength is not NFS4_UINT64_MAX, the
      error NFS4ERR_INVAL MUST result.

   o  If the sum of loga_offset and loga_length exceeds NFS4_UINT64_MAX,
      and loga_length is not NFS4_UINT64_MAX, the error NFS4ERR_INVAL
      MUST result.

   After the metadata server has performed the above checks on
   loga_offset, loga_minlength, and loga_offset, the metadata server
   MUST return a layout according to the rules in Table 13.


















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         Acceptable layouts based on loga_minlength.  Note: u64m =
     NFS4_UINT64_MAX; a_off = loga_offset; a_minlen = loga_minlength.

   +-----------+-----------+----------+----------+---------------------+
   | Layout    | Layout    | Layout   | Layout   | Layout length of    |
   | iomode of | a_minlen  | iomode   | offset   | reply               |
   | request   | of        | of reply | of reply |                     |
   |           | request   |          |          |                     |
   +-----------+-----------+----------+----------+---------------------+
   | _READ     | u64m      | MAY be   | MUST be  | MUST be >= file     |
   |           |           | _READ    | <= a_off | length - layout     |
   |           |           |          |          | offset              |
   | _READ     | u64m      | MAY be   | MUST be  | MUST be u64m        |
   |           |           | _RW      | <= a_off |                     |
   | _READ     | > 0 and < | MAY be   | MUST be  | MUST be >= MIN(file |
   |           | u64m      | _READ    | <= a_off | length, a_minlen +  |
   |           |           |          |          | a_off) - layout     |
   |           |           |          |          | offset              |
   | _READ     | > 0 and < | MAY be   | MUST be  | MUST be >= a_off -  |
   |           | u64m      | _RW      | <= a_off | layout offset +     |
   |           |           |          |          | a_minlen            |
   | _READ     | 0         | MAY be   | MUST be  | MUST be > 0         |
   |           |           | _READ    | <= a_off |                     |
   | _READ     | 0         | MAY be   | MUST be  | MUST be > 0         |
   |           |           | _RW      | <= a_off |                     |
   | _RW       | u64m      | MUST be  | MUST be  | MUST be u64m        |
   |           |           | _RW      | <= a_off |                     |
   | _RW       | > 0 and < | MUST be  | MUST be  | MUST be >= a_off -  |
   |           | u64m      | _RW      | <= a_off | layout offset +     |
   |           |           |          |          | a_minlen            |
   | _RW       | 0         | MUST be  | MUST be  | MUST be > 0         |
   |           |           | _RW      | <= a_off |                     |
   +-----------+-----------+----------+----------+---------------------+

                                 Table 13

   If loga_minlength is not zero and the metadata server cannot return a
   layout according to the rules in Table 13, then the metadata server
   MUST return the error NFS4ERR_BADLAYOUT.  If loga_minlength is zero
   and the metadata server cannot or will not return a layout according
   to the rules in Table 13, then the metadata server MUST return the
   error NFS4ERR_LAYOUTTRYLATER.  Assuming that loga_length is greater
   than loga_minlength or equal to zero, the metadata server SHOULD
   return a layout according to the rules in Table 14.







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   Desired layouts based on loga_length.  The rules of Table 13 MUST be
    applied first.  Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
                           a_len = loga_length.

   +------------+------------+-----------+-----------+-----------------+
   | Layout     | Layout     | Layout    | Layout    | Layout length   |
   | iomode of  | a_len of   | iomode of | offset of | of reply        |
   | request    | request    | reply     | reply     |                 |
   +------------+------------+-----------+-----------+-----------------+
   | _READ      | u64m       | MAY be    | MUST be   | SHOULD be u64m  |
   |            |            | _READ     | <= a_off  |                 |
   | _READ      | u64m       | MAY be    | MUST be   | SHOULD be u64m  |
   |            |            | _RW       | <= a_off  |                 |
   | _READ      | > 0 and <  | MAY be    | MUST be   | SHOULD be >=    |
   |            | u64m       | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _READ      | > 0 and <  | MAY be    | MUST be   | SHOULD be >=    |
   |            | u64m       | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _READ      | 0          | MAY be    | MUST be   | SHOULD be >     |
   |            |            | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   | _READ      | 0          | MAY be    | MUST be   | SHOULD be >     |
   |            |            | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   | _RW        | u64m       | MUST be   | MUST be   | SHOULD be u64m  |
   |            |            | _RW       | <= a_off  |                 |
   | _RW        | > 0 and <  | MUST be   | MUST be   | SHOULD be >=    |
   |            | u64m       | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _RW        | 0          | MUST be   | MUST be   | SHOULD be >     |
   |            |            | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   +------------+------------+-----------+-----------+-----------------+

                                 Table 14

   The loga_stateid field specifies a valid stateid.  If a layout is not
   currently held by the client, the loga_stateid field represents a
   stateid reflecting the correspondingly valid open, byte-range lock,
   or delegation stateid.  Once a layout is held on the file by the
   client, the loga_stateid field MUST be a stateid as returned from a
   previous LAYOUTGET or LAYOUTRETURN operation or provided by a
   CB_LAYOUTRECALL operation (see Section 12.5.3).

   The loga_maxcount field specifies the maximum layout size (in bytes)
   that the client can handle.  If the size of the layout structure
   exceeds the size specified by maxcount, the metadata server will



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   return the NFS4ERR_TOOSMALL error.

   The returned layout is expressed as an array, logr_layout, with each
   element of type layout4.  If a file has a single striping pattern,
   then logr_layout SHOULD contain just one entry.  Otherwise, if the
   requested range overlaps more than one striping pattern, logr_layout
   will contain the required number of entries.  The elements of
   logr_layout MUST be sorted in ascending order of the value of the
   lo_offset field of each element.  There MUST be no gaps or overlaps
   in the range between two successive elements of logr_layout.  The
   lo_iomode field in each element of logr_layout MUST be the same.

   Table 13 and Table 14 both refer to a returned layout iomode, offset,
   and length.  Because the returned layout is encoded in the
   logr_layout array, more description is required.

   iomode

      The value of the returned layout iomode listed in Table 13 and
      Table 14 is equal to the value of the lo_iomode field in each
      element of logr_layout.  As shown in Table 13 and Table 14, the
      metadata server MAY return a layout with an lo_iomode different
      from the requested iomode (field loga_iomode of the request).  If
      it does so, it MUST ensure that the lo_iomode is more permissive
      than the loga_iomode requested.  For example, this behavior allows
      an implementation to upgrade LAYOUTIOMODE4_READ requests to
      LAYOUTIOMODE4_RW requests at its discretion, within the limits of
      the layout type specific protocol.  A lo_iomode of either
      LAYOUTIOMODE4_READ or LAYOUTIOMODE4_RW MUST be returned.

   offset

      The value of the returned layout offset listed in Table 13 and
      Table 14 is always equal to the lo_offset field of the first
      element logr_layout.

   length

      When setting the value of the returned layout length, the
      situation is complicated by the possibility that the special
      layout length value NFS4_UINT64_MAX is involved.  For a
      logr_layout array of N elements, the lo_length field in the first
      N-1 elements MUST NOT be NFS4_UINT64_MAX.  The lo_length field of
      the last element of logr_layout can be NFS4_UINT64_MAX under some
      conditions as described in the following list.

      *  If an applicable rule of Table 13 states that the metadata
         server MUST return a layout of length NFS4_UINT64_MAX, then the



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         lo_length field of the last element of logr_layout MUST be
         NFS4_UINT64_MAX.

      *  If an applicable rule of Table 13 states that the metadata
         server MUST NOT return a layout of length NFS4_UINT64_MAX, then
         the lo_length field of the last element of logr_layout MUST NOT
         be NFS4_UINT64_MAX.

      *  If an applicable rule of Table 14 states that the metadata
         server SHOULD return a layout of length NFS4_UINT64_MAX, then
         the lo_length field of the last element of logr_layout SHOULD
         be NFS4_UINT64_MAX.

      *  When the value of the returned layout length of Table 13 and
         Table 14 is not NFS4_UINT64_MAX, then the returned layout
         length is equal to the sum of the lo_length fields of each
         element of logr_layout.

   The logr_return_on_close result field is a directive to return the
   layout before closing the file.  When the metadata server sets this
   return value to TRUE, it MUST be prepared to recall the layout in the
   case in which the client fails to return the layout before close.
   For the metadata server that knows a layout must be returned before a
   close of the file, this return value can be used to communicate the
   desired behavior to the client and thus remove one extra step from
   the client's and metadata server's interaction.

   The logr_stateid stateid is returned to the client for use in
   subsequent layout related operations.  See Sections 8.2, 12.5.3, and
   12.5.5.2 for a further discussion and requirements.

   The format of the returned layout (lo_content) is specific to the
   layout type.  The value of the layout type (lo_content.loc_type) for
   each of the elements of the array of layouts returned by the metadata
   server (logr_layout) MUST be equal to the loga_layout_type specified
   by the client.  If it is not equal, the client SHOULD ignore the
   response as invalid and behave as if the metadata server returned an
   error, even if the client does have support for the layout type
   returned.

   If neither the requested file nor its containing file system support
   layouts, the metadata server MUST return NFS4ERR_LAYOUTUNAVAILABLE.
   If the layout type is not supported, the metadata server MUST return
   NFS4ERR_UNKNOWN_LAYOUTTYPE.  If layouts are supported but no layout
   matches the client provided layout identification, the metadata
   server MUST return NFS4ERR_BADLAYOUT.  If an invalid loga_iomode is
   specified, or a loga_iomode of LAYOUTIOMODE4_ANY is specified, the
   metadata server MUST return NFS4ERR_BADIOMODE.



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   If the layout for the file is unavailable due to transient
   conditions, e.g., file sharing prohibits layouts, the metadata server
   MUST return NFS4ERR_LAYOUTTRYLATER.

   If the layout request is rejected due to an overlapping layout
   recall, the metadata server MUST return NFS4ERR_RECALLCONFLICT.  See
   Section 12.5.5.2 for details.

   If the layout conflicts with a mandatory byte-range lock held on the
   file, and if the storage devices have no method of enforcing
   mandatory locks, other than through the restriction of layouts, the
   metadata server SHOULD return NFS4ERR_LOCKED.

   If client sets loga_signal_layout_avail to TRUE, then it is
   registering with the client a "want" for a layout in the event the
   layout cannot be obtained due to resource exhaustion.  If the
   metadata server supports and will honor the "want", the results will
   have logr_will_signal_layout_avail set to TRUE.  If so, the client
   should expect a CB_RECALLABLE_OBJ_AVAIL operation to indicate that a
   layout is available.

   On success, the current filehandle retains its value and the current
   stateid is updated to match the value as returned in the results.

18.43.4.  IMPLEMENTATION

   Typically, LAYOUTGET will be called as part of a COMPOUND request
   after an OPEN operation and results in the client having location
   information for the file.  This requires that loga_stateid be set to
   the special stateid that tells the metadata server to use the current
   stateid, which is set by OPEN (see Section 16.2.3.1.2).  A client may
   also hold a layout across multiple OPENs.  The client specifies a
   layout type that limits what kind of layout the metadata server will
   return.  This prevents metadata servers from granting layouts that
   are unusable by the client.

   As indicated by Table 13 and Table 14, the specification of LAYOUTGET
   allows a pNFS client and server considerable flexibility.  A pNFS
   client can take several strategies for sending LAYOUTGET.  Some
   examples are as follows.

   o  If LAYOUTGET is preceded by OPEN in the same COMPOUND request and
      the OPEN requests OPEN4_SHARE_ACCESS_READ access, the client might
      opt to request a _READ layout with loga_offset set to zero,
      loga_minlength set to zero, and loga_length set to
      NFS4_UINT64_MAX.  If the file has space allocated to it, that
      space is striped over one or more storage devices, and there is
      either no conflicting layout or the concept of a conflicting



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      layout does not apply to the pNFS server's layout type or
      implementation, then the metadata server might return a layout
      with a starting offset of zero, and a length equal to the length
      of the file, if not NFS4_UINT64_MAX.  If the length of the file is
      not a multiple of the pNFS server's stripe width (see Section 13.2
      for a formal definition), the metadata server might round up the
      returned layout's length.

   o  If LAYOUTGET is preceded by OPEN in the same COMPOUND request, and
      the OPEN requests OPEN4_SHARE_ACCESS_WRITE access and does not
      truncate the file, the client might opt to request a _RW layout
      with loga_offset set to zero, loga_minlength set to zero, and
      loga_length set to the file's current length (if known), or
      NFS4_UINT64_MAX.  As with the previous case, under some conditions
      the metadata server might return a layout that covers the entire
      length of the file or beyond.

   o  This strategy is as above, but the OPEN truncates the file.  In
      this case, the client might anticipate it will be writing to the
      file from offset zero, and so loga_offset and loga_minlength are
      set to zero, and loga_length is set to the value of
      threshold4_write_iosize.  The metadata server might return a
      layout from offset zero with a length at least as long as
      threshold4_write_iosize.

   o  A process on the client invokes a request to read from offset
      10000 for length 50000.  The client is using buffered I/O, and has
      buffer sizes of 4096 bytes.  The client intends to map the request
      of the process into a series of READ requests starting at offset
      8192.  The end offset needs to be higher than 10000 + 50000 =
      60000, and the next offset that is a multiple of 4096 is 61440.
      The difference between 61440 and that starting offset of the
      layout is 53248 (which is the product of 4096 and 15).  The value
      of threshold4_read_iosize is less than 53248, so the client sends
      a LAYOUTGET request with loga_offset set to 8192, loga_minlength
      set to 53248, and loga_length set to the file's length (if known)
      minus 8192 or NFS4_UINT64_MAX (if the file's length is not known).
      Since this LAYOUTGET request exceeds the metadata server's
      threshold, it grants the layout, possibly with an initial offset
      of zero, with an end offset of at least 8192 + 53248 - 1 = 61439,
      but preferably a layout with an offset aligned on the stripe width
      and a length that is a multiple of the stripe width.

   o  This strategy is as above, but the client is not using buffered
      I/O, and instead all internal I/O requests are sent directly to
      the server.  The LAYOUTGET request has loga_offset equal to 10000
      and loga_minlength set to 50000.  The value of loga_length is set
      to the length of the file.  The metadata server is free to return



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      a layout that fully overlaps the requested range, with a starting
      offset and length aligned on the stripe width.

   o  Again, a process on the client invokes a request to read from
      offset 10000 for length 50000 (i.e. a range with a starting offset
      of 10000 and an ending offset of 69999), and buffered I/O is in
      use.  The client is expecting that the server might not be able to
      return the layout for the full I/O range.  The client intends to
      map the request of the process into a series of thirteen READ
      requests starting at offset 8192, each with length 4096, with a
      total length of 53248 (which equals 13 * 4096), which fully
      contains the range that client's process wants to read.  Because
      the value of threshold4_read_iosize is equal to 4096, it is
      practical and reasonable for the client to use several LAYOUTGET
      operations to complete the series of READs.  The client sends a
      LAYOUTGET request with loga_offset set to 8192, loga_minlength set
      to 4096, and loga_length set to 53248 or higher.  The server will
      grant a layout possibly with an initial offset of zero, with an
      end offset of at least 8192 + 4096 - 1 = 12287, but preferably a
      layout with an offset aligned on the stripe width and a length
      that is a multiple of the stripe width.  This will allow the
      client to make forward progress, possibly sending more LAYOUTGET
      operations for the remainder of the range.

   o  An NFS client detects a sequential read pattern, and so sends a
      LAYOUTGET operation that goes well beyond any current or pending
      read requests to the server.  The server might likewise detect
      this pattern, and grant the LAYOUTGET request.  Once the client
      reads from an offset of the file that represents 50% of the way
      through the range of the last layout it received, in order to
      avoid stalling I/O that would wait for a layout, the client sends
      more operations from an offset of the file that represents 50% of
      the way through the last layout it received.  The client continues
      to request layouts with byte-ranges that are well in advance of
      the byte-ranges of recent and/or read requests of processes
      running on the client.

   o  This strategy is as above, but the client fails to detect the
      pattern, but the server does.  The next time the metadata server
      gets a LAYOUTGET, it returns a layout with a length that is well
      beyond loga_minlength.

   o  A client is using buffered I/O, and has a long queue of write-
      behinds to process and also detects a sequential write pattern.
      It sends a LAYOUTGET for a layout that spans the range of the
      queued write-behinds and well beyond, including ranges beyond the
      filer's current length.  The client continues to send LAYOUTGET
      operations once the write-behind queue reaches 50% of the maximum



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      queue length.

   Once the client has obtained a layout referring to a particular
   device ID, the metadata server MUST NOT delete the device ID until
   the layout is returned or revoked.

   CB_NOTIFY_DEVICEID can race with LAYOUTGET.  One race scenario is
   that LAYOUTGET returns a device ID for which the client does not have
   device address mappings, and the metadata server sends a
   CB_NOTIFY_DEVICEID to add the device ID to the client's awareness and
   meanwhile the client sends GETDEVICEINFO on the device ID.  This
   scenario is discussed in Section 18.40.4.  Another scenario is that
   the CB_NOTIFY_DEVICEID is processed by the client before it processes
   the results from LAYOUTGET.  The client will send a GETDEVICEINFO on
   the device ID.  If the results from GETDEVICEINFO are received before
   the client gets results from LAYOUTGET, then there is no longer a
   race.  If the results from LAYOUTGET are received before the results
   from GETDEVICEINFO, the client can either wait for results of
   GETDEVICEINFO or send another one to get possibly more up-to-date
   device address mappings for the device ID.

18.44.  Operation 51: LAYOUTRETURN - Release Layout Information





























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18.44.1.  ARGUMENT


   /* Constants used for LAYOUTRETURN and CB_LAYOUTRECALL */
   const LAYOUT4_RET_REC_FILE      = 1;
   const LAYOUT4_RET_REC_FSID      = 2;
   const LAYOUT4_RET_REC_ALL       = 3;

   enum layoutreturn_type4 {
           LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
           LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
           LAYOUTRETURN4_ALL  = LAYOUT4_RET_REC_ALL
   };

   struct layoutreturn_file4 {
           offset4         lrf_offset;
           length4         lrf_length;
           stateid4        lrf_stateid;
           /* layouttype4 specific data */
           opaque          lrf_body<>;
   };

   union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
           case LAYOUTRETURN4_FILE:
                   layoutreturn_file4      lr_layout;
           default:
                   void;
   };




   struct LAYOUTRETURN4args {
           /* CURRENT_FH: file */
           bool                    lora_reclaim;
           layouttype4             lora_layout_type;
           layoutiomode4           lora_iomode;
           layoutreturn4           lora_layoutreturn;
   };












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18.44.2.  RESULT

   union layoutreturn_stateid switch (bool lrs_present) {
   case TRUE:
           stateid4                lrs_stateid;
   case FALSE:
           void;
   };

   union LAYOUTRETURN4res switch (nfsstat4 lorr_status) {
   case NFS4_OK:
           layoutreturn_stateid    lorr_stateid;
   default:
           void;
   };


18.44.3.  DESCRIPTION

   This operation returns from the client to the server one or more
   layouts represented by the client ID (derived from the session ID in
   the preceding SEQUENCE operation), lora_layout_type, and lora_iomode.
   When lr_returntype is LAYOUTRETURN4_FILE, the returned layout is
   further identified by the current filehandle, lrf_offset, lrf_length,
   and lrf_stateid.  If the lrf_length field is NFS4_UINT64_MAX, all
   bytes of the layout, starting at lrf_offset, are returned.  When
   lr_returntype is LAYOUTRETURN4_FSID, the current filehandle is used
   to identify the file system and all layouts matching the client ID,
   the fsid of the file system, lora_layout_type, and lora_iomode are
   returned.  When lr_returntype is LAYOUTRETURN4_ALL, all layouts
   matching the client ID, lora_layout_type, and lora_iomode are
   returned and the current filehandle is not used.  After this call,
   the client MUST NOT use the returned layout(s) and the associated
   storage protocol to access the file data.

   If the set of layouts designated in the case of LAYOUTRETURN4_FSID or
   LAYOUTRETURN4_ALL is empty, then no error results.  In the case of
   LAYOUTRETURN4_FILE, the byte-range specified is returned even if it
   is a subdivision of a layout previously obtained with LAYOUTGET, a
   combination of multiple layouts previously obtained with LAYOUTGET,
   or a combination including some layouts previously obtained with
   LAYOUTGET, and one or more subdivisions of such layouts.  When the
   byte-range does not designate any bytes for which a layout is held
   for the specified file, client ID, layout type and mode, no error
   results.  See Section 12.5.5.2.1.5 for considerations with "bulk"
   return of layouts.

   The layout being returned may be a subset or superset of a layout



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   specified by CB_LAYOUTRECALL.  However, if it is a subset, the recall
   is not complete until the full recalled scope has been returned.
   Recalled scope refers to the byte-range in the case of
   LAYOUTRETURN4_FILE, the use of LAYOUTRETURN4_FSID, or the use of
   LAYOUTRETURN4_ALL.  There must be a LAYOUTRETURN with a matching
   scope to complete the return even if all current layout ranges have
   been previously individually returned.

   For all lr_returntype values, an iomode of LAYOUTIOMODE4_ANY
   specifies that all layouts that match the other arguments to
   LAYOUTRETURN (i.e., client ID, lora_layout_type, and one of current
   filehandle and range; fsid derived from current filehandle; or
   LAYOUTRETURN4_ALL) are being returned.

   In the case that lr_returntype is LAYOUTRETURN4_FILE, the lrf_stateid
   provided by the client is a layout stateid as returned from previous
   layout operations.  Note that the "seqid" field of lrf_stateid MUST
   NOT be zero.  See Sections 8.2, 12.5.3, and 12.5.5.2 for a further
   discussion and requirements.

   Return of a layout or all layouts does not invalidate the mapping of
   storage device ID to a storage device address.  The mapping remains
   in effect until specifically changed or deleted via device ID
   notification callbacks.  Of course if there are no remaining layouts
   that refer to a previously used device ID, the server is free to
   delete a device ID without a notification callback, which will be the
   case when notifications are not in effect.

   If the lora_reclaim field is set to TRUE, the client is attempting to
   return a layout that was acquired before the restart of the metadata
   server during the metadata server's grace period.  When returning
   layouts that were acquired during the metadata server's grace period,
   the client MUST set the lora_reclaim field to FALSE.  The
   lora_reclaim field MUST be set to FALSE also when lr_layoutreturn is
   LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL.  See LAYOUTCOMMIT
   (Section 18.42) for more details.

   Layouts may be returned when recalled or voluntarily (i.e., before
   the server has recalled them).  In either case, the client must
   properly propagate state changed under the context of the layout to
   the storage device(s) or to the metadata server before returning the
   layout.

   If the client returns the layout in response to a CB_LAYOUTRECALL
   where the lor_recalltype field of the clora_recall field was
   LAYOUTRECALL4_FILE, the client should use the lor_stateid value from
   CB_LAYOUTRECALL as the value for lrf_stateid.  Otherwise, it should
   use logr_stateid (from a previous LAYOUTGET result) or lorr_stateid



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   (from a previous LAYRETURN result).  This is done to indicate the
   point in time (in terms of layout stateid transitions) when the
   recall was sent.  The client uses the precise lora_recallstateid
   value and MUST NOT set the stateid's seqid to zero; otherwise,
   NFS4ERR_BAD_STATEID MUST be returned.  NFS4ERR_OLD_STATEID can be
   returned if the client is using an old seqid, and the server knows
   the client should not be using the old seqid.  For example, the
   client uses the seqid on slot 1 of the session, receives the response
   with the new seqid, and uses the slot to send another request with
   the old seqid.

   If a client fails to return a layout in a timely manner, then the
   metadata server SHOULD use its control protocol with the storage
   devices to fence the client from accessing the data referenced by the
   layout.  See Section 12.5.5 for more details.

   If the LAYOUTRETURN request sets the lora_reclaim field to TRUE after
   the metadata server's grace period, NFS4ERR_NO_GRACE is returned.

   If the LAYOUTRETURN request sets the lora_reclaim field to TRUE and
   lr_returntype is set to LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL,
   NFS4ERR_INVAL is returned.

   If the client sets the lr_returntype field to LAYOUTRETURN4_FILE,
   then the lrs_stateid field will represent the layout stateid as
   updated for this operation's processing; the current stateid will
   also be updated to match the returned value.  If the last byte of any
   layout for the current file, client ID, and layout type is being
   returned and there are no remaining pending CB_LAYOUTRECALL
   operations for which a LAYOUTRETURN operation must be done,
   lrs_present MUST be FALSE, and no stateid will be returned.  In
   addition, the COMPOUND request's current stateid will be set to the
   all-zeroes special stateid (see Section 16.2.3.1.2).  The server MUST
   reject with NFS4ERR_BAD_STATEID any further use of the current
   stateid in that COMPOUND until the current stateid is re-established
   by a later stateid-returning operation.

   On success, the current filehandle retains its value.

   If the EXCHGID4_FLAG_BIND_PRINC_STATEID capability is set on the
   client ID (see Section 18.35), the server will require that the
   principal, security flavor, and if applicable, the GSS mechanism,
   combination that acquired the layout also be the one to send
   LAYOUTRETURN.  This might not be possible if credentials for the
   principal are no longer available.  The server will allow the machine
   credential or SSV credential (see Section 18.35) to send LAYOUTRETURN
   if LAYOUTRETURN's operation code was set in the spo_must_allow result
   of EXCHANGE_ID.



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18.44.4.  IMPLEMENTATION

   The final LAYOUTRETURN operation in response to a CB_LAYOUTRECALL
   callback MUST be serialized with any outstanding, intersecting
   LAYOUTRETURN operations.  Note that it is possible that while a
   client is returning the layout for some recalled range, the server
   may recall a superset of that range (e.g., LAYOUTRECALL4_ALL); the
   final return operation for the latter must block until the former
   layout recall is done.

   Returning all layouts in a file system using LAYOUTRETURN4_FSID is
   typically done in response to a CB_LAYOUTRECALL for that file system
   as the final return operation.  Similarly, LAYOUTRETURN4_ALL is used
   in response to a recall callback for all layouts.  It is possible
   that the client already returned some outstanding layouts via
   individual LAYOUTRETURN calls and the call for LAYOUTRETURN4_FSID or
   LAYOUTRETURN4_ALL marks the end of the LAYOUTRETURN sequence.  See
   Section 12.5.5.1 for more details.

   Once the client has returned all layouts referring to a particular
   device ID, the server MAY delete the device ID.

18.45.  Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object

18.45.1.  ARGUMENT

   enum secinfo_style4 {
           SECINFO_STYLE4_CURRENT_FH       = 0,
           SECINFO_STYLE4_PARENT           = 1
   };

   /* CURRENT_FH: object or child directory */
   typedef secinfo_style4 SECINFO_NO_NAME4args;


18.45.2.  RESULT

   /* CURRENTFH: consumed if status is NFS4_OK */
   typedef SECINFO4res SECINFO_NO_NAME4res;


18.45.3.  DESCRIPTION

   Like the SECINFO operation, SECINFO_NO_NAME is used by the client to
   obtain a list of valid RPC authentication flavors for a specific file
   object.  Unlike SECINFO, SECINFO_NO_NAME only works with objects that
   are accessed by filehandle.




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   There are two styles of SECINFO_NO_NAME, as determined by the value
   of the secinfo_style4 enumeration.  If SECINFO_STYLE4_CURRENT_FH is
   passed, then SECINFO_NO_NAME is querying for the required security
   for the current filehandle.  If SECINFO_STYLE4_PARENT is passed, then
   SECINFO_NO_NAME is querying for the required security of the current
   filehandle's parent.  If the style selected is SECINFO_STYLE4_PARENT,
   then SECINFO should apply the same access methodology used for
   LOOKUPP when evaluating the traversal to the parent directory.
   Therefore, if the requester does not have the appropriate access to
   LOOKUPP the parent, then SECINFO_NO_NAME must behave the same way and
   return NFS4ERR_ACCESS.

   If PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH returns NFS4ERR_WRONGSEC,
   then the client resolves the situation by sending a COMPOUND request
   that consists of PUTFH, PUTPUBFH, or PUTROOTFH immediately followed
   by SECINFO_NO_NAME, style SECINFO_STYLE4_CURRENT_FH.  See Section 2.6
   for instructions on dealing with NFS4ERR_WRONGSEC error returns from
   PUTFH, PUTROOTFH, PUTPUBFH, or RESTOREFH.

   If SECINFO_STYLE4_PARENT is specified and there is no parent
   directory, SECINFO_NO_NAME MUST return NFS4ERR_NOENT.

   On success, the current filehandle is consumed (see
   Section 2.6.3.1.1.8), and if the next operation after SECINFO_NO_NAME
   tries to use the current filehandle, that operation will fail with
   the status NFS4ERR_NOFILEHANDLE.

   Everything else about SECINFO_NO_NAME is the same as SECINFO.  See
   the discussion on SECINFO (Section 18.29.3).

18.45.4.  IMPLEMENTATION

   See the discussion on SECINFO (Section 18.29.4).

18.46.  Operation 53: SEQUENCE - Supply Per-Procedure Sequencing and
        Control

18.46.1.  ARGUMENT

   struct SEQUENCE4args {
           sessionid4     sa_sessionid;
           sequenceid4    sa_sequenceid;
           slotid4        sa_slotid;
           slotid4        sa_highest_slotid;
           bool           sa_cachethis;
   };





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18.46.2.  RESULT

   const SEQ4_STATUS_CB_PATH_DOWN                  = 0x00000001;
   const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING      = 0x00000002;
   const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED       = 0x00000004;
   const SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED     = 0x00000008;
   const SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED    = 0x00000010;
   const SEQ4_STATUS_ADMIN_STATE_REVOKED           = 0x00000020;
   const SEQ4_STATUS_RECALLABLE_STATE_REVOKED      = 0x00000040;
   const SEQ4_STATUS_LEASE_MOVED                   = 0x00000080;
   const SEQ4_STATUS_RESTART_RECLAIM_NEEDED        = 0x00000100;
   const SEQ4_STATUS_CB_PATH_DOWN_SESSION          = 0x00000200;
   const SEQ4_STATUS_BACKCHANNEL_FAULT             = 0x00000400;
   const SEQ4_STATUS_DEVID_CHANGED                 = 0x00000800;
   const SEQ4_STATUS_DEVID_DELETED                 = 0x00001000;

   struct SEQUENCE4resok {
           sessionid4      sr_sessionid;
           sequenceid4     sr_sequenceid;
           slotid4         sr_slotid;
           slotid4         sr_highest_slotid;
           slotid4         sr_target_highest_slotid;
           uint32_t        sr_status_flags;
   };

   union SEQUENCE4res switch (nfsstat4 sr_status) {
   case NFS4_OK:
           SEQUENCE4resok  sr_resok4;
   default:
           void;
   };


18.46.3.  DESCRIPTION

   The SEQUENCE operation is used by the server to implement session
   request control and the reply cache semantics.

   SEQUENCE MUST appear as the first operation of any COMPOUND in which
   it appears.  The error NFS4ERR_SEQUENCE_POS will be returned when it
   is found in any position in a COMPOUND beyond the first.  Operations
   other than SEQUENCE, BIND_CONN_TO_SESSION, EXCHANGE_ID,
   CREATE_SESSION, and DESTROY_SESSION, MUST NOT appear as the first
   operation in a COMPOUND.  Such operations MUST yield the error
   NFS4ERR_OP_NOT_IN_SESSION if they do appear at the start of a
   COMPOUND.

   If SEQUENCE is received on a connection not associated with the



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   session via CREATE_SESSION or BIND_CONN_TO_SESSION, and connection
   association enforcement is enabled (see Section 18.35), then the
   server returns NFS4ERR_CONN_NOT_BOUND_TO_SESSION.

   The sa_sessionid argument identifies the session to which this
   request applies.  The sr_sessionid result MUST equal sa_sessionid.

   The sa_slotid argument is the index in the reply cache for the
   request.  The sa_sequenceid field is the sequence number of the
   request for the reply cache entry (slot).  The sr_slotid result MUST
   equal sa_slotid.  The sr_sequenceid result MUST equal sa_sequenceid.

   The sa_highest_slotid argument is the highest slot ID for which the
   client has a request outstanding; it could be equal to sa_slotid.
   The server returns two "highest_slotid" values: sr_highest_slotid and
   sr_target_highest_slotid.  The former is the highest slot ID the
   server will accept in future SEQUENCE operation, and SHOULD NOT be
   less than the value of sa_highest_slotid (but see Section 2.10.6.1
   for an exception).  The latter is the highest slot ID the server
   would prefer the client use on a future SEQUENCE operation.

   If sa_cachethis is TRUE, then the client is requesting that the
   server cache the entire reply in the server's reply cache; therefore,
   the server MUST cache the reply (see Section 2.10.6.1.3).  The server
   MAY cache the reply if sa_cachethis is FALSE.  If the server does not
   cache the entire reply, it MUST still record that it executed the
   request at the specified slot and sequence ID.

   The response to the SEQUENCE operation contains a word of status
   flags (sr_status_flags) that can provide to the client information
   related to the status of the client's lock state and communications
   paths.  Note that any status bits relating to lock state MAY be reset
   when lock state is lost due to a server restart (even if the session
   is persistent across restarts; session persistence does not imply
   lock state persistence) or the establishment of a new client
   instance.

   SEQ4_STATUS_CB_PATH_DOWN
      When set, indicates that the client has no operational backchannel
      path for any session associated with the client ID, making it
      necessary for the client to re-establish one.  This bit remains
      set on all SEQUENCE responses on all sessions associated with the
      client ID until at least one backchannel is available on any
      session associated with the client ID.  If the client fails to re-
      establish a backchannel for the client ID, it is subject to having
      recallable state revoked.





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   SEQ4_STATUS_CB_PATH_DOWN_SESSION
      When set, indicates that the session has no operational
      backchannel.  There are two reasons why
      SEQ4_STATUS_CB_PATH_DOWN_SESSION may be set and not
      SEQ4_STATUS_CB_PATH_DOWN.  First is that a callback operation that
      applies specifically to the session (e.g., CB_RECALL_SLOT, see
      Section 20.8) needs to be sent.  Second is that the server did
      send a callback operation, but the connection was lost before the
      reply.  The server cannot be sure whether or not the client
      received the callback operation, and so, per rules on request
      retry, the server MUST retry the callback operation over the same
      session.  The SEQ4_STATUS_CB_PATH_DOWN_SESSION bit is the
      indication to the client that it needs to associate a connection
      to the session's backchannel.  This bit remains set on all
      SEQUENCE responses of the session until a connection is associated
      with the session's a backchannel.  If the client fails to re-
      establish a backchannel for the session, it is subject to having
      recallable state revoked.

   SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING
      When set, indicates that all GSS contexts or RPCSEC_GSS handles
      assigned to the session's backchannel will expire within a period
      equal to the lease time.  This bit remains set on all SEQUENCE
      replies until at least one of the following are true:

      *  All SSV RPCSEC_GSS handles on the session's backchannel have
         been destroyed and all non-SSV GSS contexts have expired.

      *  At least one more SSV RPCSEC_GSS handle has been added to the
         backchannel.

      *  The expiration time of at least one non-SSV GSS context of an
         RPCSEC_GSS handle is beyond the lease period from the current
         time (relative to the time of when a SEQUENCE response was
         sent)

   SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED
      When set, indicates all non-SSV GSS contexts and all SSV
      RPCSEC_GSS handles assigned to the session's backchannel have
      expired or have been destroyed.  This bit remains set on all
      SEQUENCE replies until at least one non-expired non-SSV GSS
      context for the session's backchannel has been established or at
      least one SSV RPCSEC_GSS handle has been assigned to the
      backchannel.







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   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED
      When set, indicates that the lease has expired and as a result the
      server released all of the client's locking state.  This status
      bit remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID (see
      Section 18.38), or by establishing a new client instance by
      destroying all sessions (via DESTROY_SESSION), the client ID (via
      DESTROY_CLIENTID), and then invoking EXCHANGE_ID and
      CREATE_SESSION to establish a new client ID.

   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
      When set, indicates that some subset of the client's locks have
      been revoked due to expiration of the lease period followed by
      another client's conflicting LOCK operation.  This status bit
      remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID.

   SEQ4_STATUS_ADMIN_STATE_REVOKED
      When set, indicates that one or more locks have been revoked
      without expiration of the lease period, due to administrative
      action.  This status bit remains set on all SEQUENCE replies until
      the loss of all such locks has been acknowledged by use of
      FREE_STATEID.

   SEQ4_STATUS_RECALLABLE_STATE_REVOKED
      When set, indicates that one or more recallable objects have been
      revoked without expiration of the lease period, due to the
      client's failure to return them when recalled, which may be a
      consequence of there being no working backchannel and the client
      failing to re-establish a backchannel per the
      SEQ4_STATUS_CB_PATH_DOWN, SEQ4_STATUS_CB_PATH_DOWN_SESSION, or
      SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED status flags.  This status bit
      remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID.

   SEQ4_STATUS_LEASE_MOVED
      When set, indicates that responsibility for lease renewal has been
      transferred to one or more new servers.  This condition will
      continue until the client receives an NFS4ERR_MOVED error and the
      server receives the subsequent GETATTR for the fs_locations or
      fs_locations_info attribute for an access to each file system for
      which a lease has been moved to a new server.  See
      Section 11.7.7.1.

   SEQ4_STATUS_RESTART_RECLAIM_NEEDED
      When set, indicates that due to server restart, the client must
      reclaim locking state.  Until the client sends a global
      RECLAIM_COMPLETE (Section 18.51), every SEQUENCE operation will



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      return SEQ4_STATUS_RESTART_RECLAIM_NEEDED.

   SEQ4_STATUS_BACKCHANNEL_FAULT
      The server has encountered an unrecoverable fault with the
      backchannel (e.g., it has lost track of the sequence ID for a slot
      in the backchannel).  The client MUST stop sending more requests
      on the session's fore channel, wait for all outstanding requests
      to complete on the fore and back channel, and then destroy the
      session.

   SEQ4_STATUS_DEVID_CHANGED
      The client is using device ID notifications and the server has
      changed a device ID mapping held by the client.  This flag will
      stay present until the client has obtained the new mapping with
      GETDEVICEINFO.

   SEQ4_STATUS_DEVID_DELETED
      The client is using device ID notifications and the server has
      deleted a device ID mapping held by the client.  This flag will
      stay in effect until the client sends a GETDEVICEINFO on the
      device ID with a null value in the argument gdia_notify_types.

   The value of the sa_sequenceid argument relative to the cached
   sequence ID on the slot falls into one of three cases.

   o  If the difference between sa_sequenceid and the server's cached
      sequence ID at the slot ID is two (2) or more, or if sa_sequenceid
      is less than the cached sequence ID (accounting for wraparound of
      the unsigned sequence ID value), then the server MUST return
      NFS4ERR_SEQ_MISORDERED.

   o  If sa_sequenceid and the cached sequence ID are the same, this is
      a retry, and the server replies with what is recorded in the reply
      cache.  The lease is possibly renewed as described below.

   o  If sa_sequenceid is one greater (accounting for wraparound) than
      the cached sequence ID, then this is a new request, and the slot's
      sequence ID is incremented.  The operations subsequent to
      SEQUENCE, if any, are processed.  If there are no other
      operations, the only other effects are to cache the SEQUENCE reply
      in the slot, maintain the session's activity, and possibly renew
      the lease.

   If the client reuses a slot ID and sequence ID for a completely
   different request, the server MAY treat the request as if it is a
   retry of what it has already executed.  The server MAY however detect
   the client's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.




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   If SEQUENCE returns an error, then the state of the slot (sequence
   ID, cached reply) MUST NOT change, and the associated lease MUST NOT
   be renewed.

   If SEQUENCE returns NFS4_OK, then the associated lease MUST be
   renewed (see Section 8.3), except if
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is returned in sr_status_flags.

18.46.4.  IMPLEMENTATION

   The server MUST maintain a mapping of session ID to client ID in
   order to validate any operations that follow SEQUENCE that take a
   stateid as an argument and/or result.

   If the client establishes a persistent session, then a SEQUENCE
   received after a server restart might encounter requests performed
   and recorded in a persistent reply cache before the server restart.
   In this case, SEQUENCE will be processed successfully, while requests
   that were not previously performed and recorded are rejected with
   NFS4ERR_DEADSESSION.

   Depending on which of the operations within the COMPOUND were
   successfully performed before the server restart, these operations
   will also have replies sent from the server reply cache.  Note that
   when these operations establish locking state, it is locking state
   that applies to the previous server instance and to the previous
   client ID, even though the server restart, which logically happened
   after these operations, eliminated that state.  In the case of a
   partially executed COMPOUND, processing may reach an operation not
   processed during the earlier server instance, making this operation a
   new one and not performable on the existing session.  In this case,
   NFS4ERR_DEADSESSION will be returned from that operation.

18.47.  Operation 54: SET_SSV - Update SSV for a Client ID

18.47.1.  ARGUMENT

   struct ssa_digest_input4 {
           SEQUENCE4args sdi_seqargs;
   };

   struct SET_SSV4args {
           opaque          ssa_ssv<>;
           opaque          ssa_digest<>;
   };






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18.47.2.  RESULT

   struct ssr_digest_input4 {
           SEQUENCE4res sdi_seqres;
   };

   struct SET_SSV4resok {
           opaque          ssr_digest<>;
   };

   union SET_SSV4res switch (nfsstat4 ssr_status) {
   case NFS4_OK:
           SET_SSV4resok   ssr_resok4;
   default:
           void;
   };


18.47.3.  DESCRIPTION

   This operation is used to update the SSV for a client ID.  Before
   SET_SSV is called the first time on a client ID, the SSV is zero.
   The SSV is the key used for the SSV GSS mechanism (Section 2.10.9)

   SET_SSV MUST be preceded by a SEQUENCE operation in the same
   COMPOUND.  It MUST NOT be used if the client did not opt for SP4_SSV
   state protection when the client ID was created (see Section 18.35);
   the server returns NFS4ERR_INVAL in that case.

   The field ssa_digest is computed as the output of the HMAC (RFC 2104
   [11]) using the subkey derived from the SSV4_SUBKEY_MIC_I2T and
   current SSV as the key (see Section 2.10.9 for a description of
   subkeys), and an XDR encoded value of data type ssa_digest_input4.
   The field sdi_seqargs is equal to the arguments of the SEQUENCE
   operation for the COMPOUND procedure that SET_SSV is within.

   The argument ssa_ssv is XORed with the current SSV to produce the new
   SSV.  The argument ssa_ssv SHOULD be generated randomly.

   In the response, ssr_digest is the output of the HMAC using the
   subkey derived from SSV4_SUBKEY_MIC_T2I and new SSV as the key, and
   an XDR encoded value of data type ssr_digest_input4.  The field
   sdi_seqres is equal to the results of the SEQUENCE operation for the
   COMPOUND procedure that SET_SSV is within.

   As noted in Section 18.35, the client and server can maintain
   multiple concurrent versions of the SSV.  The client and server each
   MUST maintain an internal SSV version number, which is set to one the



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   first time SET_SSV executes on the server and the client receives the
   first SET_SSV reply.  Each subsequent SET_SSV increases the internal
   SSV version number by one.  The value of this version number
   corresponds to the smpt_ssv_seq, smt_ssv_seq, sspt_ssv_seq, and
   ssct_ssv_seq fields of the SSV GSS mechanism tokens (see
   Section 2.10.9).

18.47.4.  IMPLEMENTATION

   When the server receives ssa_digest, it MUST verify the digest by
   computing the digest the same way the client did and comparing it
   with ssa_digest.  If the server gets a different result, this is an
   error, NFS4ERR_BAD_SESSION_DIGEST.  This error might be the result of
   another SET_SSV from the same client ID changing the SSV.  If so, the
   client recovers by sending a SET_SSV operation again with a
   recomputed digest based on the subkey of the new SSV.  If the
   transport connection is dropped after the SET_SSV request is sent,
   but before the SET_SSV reply is received, then there are special
   considerations for recovery if the client has no more connections
   associated with sessions associated with the client ID of the SSV.
   See Section 18.34.4.

   Clients SHOULD NOT send an ssa_ssv that is equal to a previous
   ssa_ssv, nor equal to a previous or current SSV (including an ssa_ssv
   equal to zero since the SSV is initialized to zero when the client ID
   is created).

   Clients SHOULD send SET_SSV with RPCSEC_GSS privacy.  Servers MUST
   support RPCSEC_GSS with privacy for any COMPOUND that has { SEQUENCE,
   SET_SSV }.

   A client SHOULD NOT send SET_SSV with the SSV GSS mechanism's
   credential because the purpose of SET_SSV is to seed the SSV from
   non-SSV credentials.  Instead, SET_SSV SHOULD be sent with the
   credential of a user that is accessing the client ID for the first
   time (Section 2.10.8.3).  However, if the client does send SET_SSV
   with SSV credentials, the digest protecting the arguments uses the
   value of the SSV before ssa_ssv is XORed in, and the digest
   protecting the results uses the value of the SSV after the ssa_ssv is
   XORed in.

18.48.  Operation 55: TEST_STATEID - Test Stateids for Validity

18.48.1.  ARGUMENT

   struct TEST_STATEID4args {
           stateid4        ts_stateids<>;
   };



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18.48.2.  RESULT

   struct TEST_STATEID4resok {
           nfsstat4        tsr_status_codes<>;
   };

   union TEST_STATEID4res switch (nfsstat4 tsr_status) {
       case NFS4_OK:
           TEST_STATEID4resok tsr_resok4;
       default:
           void;
   };


18.48.3.  DESCRIPTION

   The TEST_STATEID operation is used to check the validity of a set of
   stateids.  It can be used at any time, but the client should
   definitely use it when it receives an indication that one or more of
   its stateids have been invalidated due to lock revocation.  This
   occurs when the SEQUENCE operation returns with one of the following
   sr_status_flags set:

   o  SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED

   o  SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED

   o  SEQ4_STATUS_EXPIRED_RECALLABLE_STATE_REVOKED

   The client can use TEST_STATEID one or more times to test the
   validity of its stateids.  Each use of TEST_STATEID allows a large
   set of such stateids to be tested and avoids problems with earlier
   stateids in a COMPOUND request from interfering with the checking of
   subsequent stateids, as would happen if individual stateids were
   tested by a series of corresponding by operations in a COMPOUND
   request.

   For each stateid, the server returns the status code that would be
   returned if that stateid were to be used in normal operation.
   Returning such a status indication is not an error and does not cause
   COMPOUND processing to terminate.  Checks for the validity of the
   stateid proceed as they would for normal operations with a number of
   exceptions:

   o  There is no check for the type of stateid object, as would be the
      case for normal use of a stateid.





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   o  There is no reference to the current filehandle.

   o  Special stateids are always considered invalid (they result in the
      error code NFS4ERR_BAD_STATEID).

   All stateids are interpreted as being associated with the client for
   the current session.  Any possible association with a previous
   instance of the client (as stale stateids) is not considered.

   The valid status values in the returned status_code array are
   NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID,
   NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.

18.48.4.  IMPLEMENTATION

   See Sections 8.2.2 and 8.2.4 for a discussion of stateid structure,
   lifetime, and validation.

18.49.  Operation 56: WANT_DELEGATION - Request Delegation
































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18.49.1.  ARGUMENT

   union deleg_claim4 switch (open_claim_type4 dc_claim) {
   /*
    * No special rights to object.  Ordinary delegation
    * request of the specified object.  Object identified
    * by filehandle.
    */
   case CLAIM_FH: /* new to v4.1 */
           /* CURRENT_FH: object being delegated */
           void;

   /*
    * Right to file based on a delegation granted
    * to a previous boot instance of the client.
    * File is specified by filehandle.
    */
   case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
           /* CURRENT_FH: object being delegated */
           void;

   /*
    * Right to the file established by an open previous
    * to server reboot.  File identified by filehandle.
    * Used during server reclaim grace period.
    */
   case CLAIM_PREVIOUS:
           /* CURRENT_FH: object being reclaimed */
           open_delegation_type4   dc_delegate_type;
   };

   struct WANT_DELEGATION4args {
           uint32_t        wda_want;
           deleg_claim4    wda_claim;
   };


18.49.2.  RESULT

   union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
   case NFS4_OK:
           open_delegation4 wdr_resok4;
   default:
           void;
   };






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18.49.3.  DESCRIPTION

   Where this description mandates the return of a specific error code
   for a specific condition, and where multiple conditions apply, the
   server MAY return any of the mandated error codes.

   This operation allows a client to:

   o  Get a delegation on all types of files except directories.

   o  Register a "want" for a delegation for the specified file object,
      and be notified via a callback when the delegation is available.
      The server MAY support notifications of availability via
      callbacks.  If the server does not support registration of wants,
      it MUST NOT return an error to indicate that, and instead MUST
      return with ond_why set to WND4_CONTENTION or WND4_RESOURCE and
      ond_server_will_push_deleg or ond_server_will_signal_avail set to
      FALSE.  When the server indicates that it will notify the client
      by means of a callback, it will either provide the delegation
      using a CB_PUSH_DELEG operation or cancel its promise by sending a
      CB_WANTS_CANCELLED operation.

   o  Cancel a want for a delegation.

   The client SHOULD NOT set OPEN4_SHARE_ACCESS_READ and SHOULD NOT set
   OPEN4_SHARE_ACCESS_WRITE in wda_want.  If it does, the server MUST
   ignore them.

   The meanings of the following flags in wda_want are the same as they
   are in OPEN, except as noted below.

   o  OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_NO_DELEG.  Unlike the OPEN operation, this
      flag SHOULD NOT be set by the client in the arguments to
      WANT_DELEGATION, and MUST be ignored by the server.

   o  OPEN4_SHARE_ACCESS_WANT_CANCEL

   o  OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL

   o  OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED

   The handling of the above flags in WANT_DELEGATION is the same as in



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   OPEN.  Information about the delegation and/or the promises the
   server is making regarding future callbacks are the same as those
   described in the open_delegation4 structure.

   The successful results of WANT_DELEGATION are of data type
   open_delegation4, which is the same data type as the "delegation"
   field in the results of the OPEN operation (see Section 18.16.3).
   The server constructs wdr_resok4 the same way it constructs OPEN's
   "delegation" with one difference: WANT_DELEGATION MUST NOT return a
   delegation type of OPEN_DELEGATE_NONE.

   If ((wda_want & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) &
   ~OPEN4_SHARE_ACCESS_WANT_NO_DELEG) is zero, then the client is
   indicating no explicit desire or non-desire for a delegation and the
   server MUST return NFS4ERR_INVAL.

   The client uses the OPEN4_SHARE_ACCESS_WANT_CANCEL flag in the
   WANT_DELEGATION operation to cancel a previously requested want for a
   delegation.  Note that if the server is in the process of sending the
   delegation (via CB_PUSH_DELEG) at the time the client sends a
   cancellation of the want, the delegation might still be pushed to the
   client.

   If WANT_DELEGATION fails to return a delegation, and the server
   returns NFS4_OK, the server MUST set the delegation type to
   OPEN4_DELEGATE_NONE_EXT, and set od_whynone, as described in
   Section 18.16.  Write delegations are not available for file types
   that are not writable.  This includes file objects of types NF4BLK,
   NF4CHR, NF4LNK, NF4SOCK, and NF4FIFO.  If the client requests
   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG without
   OPEN4_SHARE_ACCESS_WANT_READ_DELEG on an object with one of the
   aforementioned file types, the server must set
   wdr_resok4.od_whynone.ond_why to WND4_WRITE_DELEG_NOT_SUPP_FTYPE.

18.49.4.  IMPLEMENTATION

   A request for a conflicting delegation is not normally intended to
   trigger the recall of the existing delegation.  Servers may choose to
   treat some clients as having higher priority such that their wants
   will trigger recall of an existing delegation, although that is
   expected to be an unusual situation.

   Servers will generally recall delegations assigned by WANT_DELEGATION
   on the same basis as those assigned by OPEN.  CB_RECALL will
   generally be done only when other clients perform operations
   inconsistent with the delegation.  The normal response to aging of
   delegations is to use CB_RECALL_ANY, in order to give the client the
   opportunity to keep the delegations most useful from its point of



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   view.

18.50.  Operation 57: DESTROY_CLIENTID - Destroy a Client ID

18.50.1.  ARGUMENT

   struct DESTROY_CLIENTID4args {
           clientid4       dca_clientid;
   };


18.50.2.  RESULT

   struct DESTROY_CLIENTID4res {
           nfsstat4        dcr_status;
   };


18.50.3.  DESCRIPTION

   The DESTROY_CLIENTID operation destroys the client ID.  If there are
   sessions (both idle and non-idle), opens, locks, delegations,
   layouts, and/or wants (Section 18.49) associated with the unexpired
   lease of the client ID, the server MUST return NFS4ERR_CLIENTID_BUSY.
   DESTROY_CLIENTID MAY be preceded with a SEQUENCE operation as long as
   the client ID derived from the session ID of SEQUENCE is not the same
   as the client ID to be destroyed.  If the client IDs are the same,
   then the server MUST return NFS4ERR_CLIENTID_BUSY.

   If DESTROY_CLIENTID is not prefixed by SEQUENCE, it MUST be the only
   operation in the COMPOUND request (otherwise, the server MUST return
   NFS4ERR_NOT_ONLY_OP).  If the operation is sent without a SEQUENCE
   preceding it, a client that retransmits the request may receive an
   error in response, because the original request might have been
   successfully executed.

18.50.4.  IMPLEMENTATION

   DESTROY_CLIENTID allows a server to immediately reclaim the resources
   consumed by an unused client ID, and also to forget that it ever
   generated the client ID.  By forgetting that it ever generated the
   client ID, the server can safely reuse the client ID on a future
   EXCHANGE_ID operation.

18.51.  Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished






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18.51.1.  ARGUMENT

   struct RECLAIM_COMPLETE4args {
           /*
            * If rca_one_fs TRUE,
            *
            *    CURRENT_FH: object in
            *    file system reclaim is
            *    complete for.
            */
           bool            rca_one_fs;
   };


18.51.2.  RESULTS

   struct RECLAIM_COMPLETE4res {
           nfsstat4        rcr_status;
   };


18.51.3.  DESCRIPTION

   A RECLAIM_COMPLETE operation is used to indicate that the client has
   reclaimed all of the locking state that it will recover, when it is
   recovering state due to either a server restart or the transfer of a
   file system to another server.  There are two types of
   RECLAIM_COMPLETE operations:

   o  When rca_one_fs is FALSE, a global RECLAIM_COMPLETE is being done.
      This indicates that recovery of all locks that the client held on
      the previous server instance have been completed.

   o  When rca_one_fs is TRUE, a file system-specific RECLAIM_COMPLETE
      is being done.  This indicates that recovery of locks for a single
      fs (the one designated by the current filehandle) due to a file
      system transition have been completed.  Presence of a current
      filehandle is only required when rca_one_fs is set to TRUE.

   Once a RECLAIM_COMPLETE is done, there can be no further reclaim
   operations for locks whose scope is defined as having completed
   recovery.  Once the client sends RECLAIM_COMPLETE, the server will
   not allow the client to do subsequent reclaims of locking state for
   that scope and, if these are attempted, will return NFS4ERR_NO_GRACE.

   Whenever a client establishes a new client ID and before it does the
   first non-reclaim operation that obtains a lock, it MUST send a
   RECLAIM_COMPLETE with rca_one_fs set to FALSE, even if there are no



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   locks to reclaim.  If non-reclaim locking operations are done before
   the RECLAIM_COMPLETE, an NFS4ERR_GRACE error will be returned.

   Similarly, when the client accesses a file system on a new server,
   before it sends the first non-reclaim operation that obtains a lock
   on this new server, it MUST send a RECLAIM_COMPLETE with rca_one_fs
   set to TRUE and current filehandle within that file system, even if
   there are no locks to reclaim.  If non-reclaim locking operations are
   done on that file system before the RECLAIM_COMPLETE, an
   NFS4ERR_GRACE error will be returned.

   Any locks not reclaimed at the point at which RECLAIM_COMPLETE is
   done become non-reclaimable.  The client MUST NOT attempt to reclaim
   them, either during the current server instance or in any subsequent
   server instance, or on another server to which responsibility for
   that file system is transferred.  If the client were to do so, it
   would be violating the protocol by representing itself as owning
   locks that it does not own, and so has no right to reclaim.  See
   Section 8.4.3 for a discussion of edge conditions related to lock
   reclaim.

   By sending a RECLAIM_COMPLETE, the client indicates readiness to
   proceed to do normal non-reclaim locking operations.  The client
   should be aware that such operations may temporarily result in
   NFS4ERR_GRACE errors until the server is ready to terminate its grace
   period.

18.51.4.  IMPLEMENTATION

   Servers will typically use the information as to when reclaim
   activity is complete to reduce the length of the grace period.  When
   the server maintains in persistent storage a list of clients that
   might have had locks, it is in a position to use the fact that all
   such clients have done a RECLAIM_COMPLETE to terminate the grace
   period and begin normal operations (i.e., grant requests for new
   locks) sooner than it might otherwise.

   Latency can be minimized by doing a RECLAIM_COMPLETE as part of the
   COMPOUND request in which the last lock-reclaiming operation is done.
   When there are no reclaims to be done, RECLAIM_COMPLETE should be
   done immediately in order to allow the grace period to end as soon as
   possible.

   RECLAIM_COMPLETE should only be done once for each server instance or
   occasion of the transition of a file system.  If it is done a second
   time, the error NFS4ERR_COMPLETE_ALREADY will result.  Note that
   because of the session feature's retry protection, retries of
   COMPOUND requests containing RECLAIM_COMPLETE operation will not



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   result in this error.

   When a RECLAIM_COMPLETE is sent, the client effectively acknowledges
   any locks not yet reclaimed as lost.  This allows the server to re-
   enable the client to recover locks if the occurrence of edge
   conditions, as described in Section 8.4.3, had caused the server to
   disable the client from recovering locks.

18.52.  Operation 10044: ILLEGAL - Illegal Operation

18.52.1.  ARGUMENTS

   void;

18.52.2.  RESULTS

   struct ILLEGAL4res {
           nfsstat4        status;
   };


18.52.3.  DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the client sending an operation code within COMPOUND that is
   not supported.  See the COMPOUND procedure description for more
   details.

   The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

18.52.4.  IMPLEMENTATION

   A client will probably not send an operation with code OP_ILLEGAL but
   if it does, the response will be ILLEGAL4res just as it would be with
   any other invalid operation code.  Note that if the server gets an
   illegal operation code that is not OP_ILLEGAL, and if the server
   checks for legal operation codes during the XDR decode phase, then
   the ILLEGAL4res would not be returned.

19.  NFSv4.1 Callback Procedures

   The procedures used for callbacks are defined in the following
   sections.  In the interest of clarity, the terms "client" and
   "server" refer to NFS clients and servers, despite the fact that for
   an individual callback RPC, the sense of these terms would be
   precisely the opposite.

   Both procedures, CB_NULL and CB_COMPOUND, MUST be implemented.



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19.1.  Procedure 0: CB_NULL - No Operation

19.1.1.  ARGUMENTS

   void;

19.1.2.  RESULTS

   void;

19.1.3.  DESCRIPTION

   CB_NULL is the standard ONC RPC NULL procedure, with the standard
   void argument and void response.  Even though there is no direct
   functionality associated with this procedure, the server will use
   CB_NULL to confirm the existence of a path for RPCs from the server
   to client.

19.1.4.  ERRORS

   None.

19.2.  Procedure 1: CB_COMPOUND - Compound Operations

19.2.1.  ARGUMENTS


   enum nfs_cb_opnum4 {
           OP_CB_GETATTR           = 3,
           OP_CB_RECALL            = 4,
   /* Callback operations new to NFSv4.1 */
           OP_CB_LAYOUTRECALL      = 5,
           OP_CB_NOTIFY            = 6,
           OP_CB_PUSH_DELEG        = 7,
           OP_CB_RECALL_ANY        = 8,
           OP_CB_RECALLABLE_OBJ_AVAIL = 9,
           OP_CB_RECALL_SLOT       = 10,
           OP_CB_SEQUENCE          = 11,
           OP_CB_WANTS_CANCELLED   = 12,
           OP_CB_NOTIFY_LOCK       = 13,
           OP_CB_NOTIFY_DEVICEID   = 14,

           OP_CB_ILLEGAL           = 10044
   };







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   union nfs_cb_argop4 switch (unsigned argop) {
    case OP_CB_GETATTR:
         CB_GETATTR4args           opcbgetattr;
    case OP_CB_RECALL:
         CB_RECALL4args            opcbrecall;
    case OP_CB_LAYOUTRECALL:
         CB_LAYOUTRECALL4args      opcblayoutrecall;
    case OP_CB_NOTIFY:
         CB_NOTIFY4args            opcbnotify;
    case OP_CB_PUSH_DELEG:
         CB_PUSH_DELEG4args        opcbpush_deleg;
    case OP_CB_RECALL_ANY:
         CB_RECALL_ANY4args        opcbrecall_any;
    case OP_CB_RECALLABLE_OBJ_AVAIL:
         CB_RECALLABLE_OBJ_AVAIL4args opcbrecallable_obj_avail;
    case OP_CB_RECALL_SLOT:
         CB_RECALL_SLOT4args       opcbrecall_slot;
    case OP_CB_SEQUENCE:
         CB_SEQUENCE4args          opcbsequence;
    case OP_CB_WANTS_CANCELLED:
         CB_WANTS_CANCELLED4args   opcbwants_cancelled;
    case OP_CB_NOTIFY_LOCK:
         CB_NOTIFY_LOCK4args       opcbnotify_lock;
    case OP_CB_NOTIFY_DEVICEID:
         CB_NOTIFY_DEVICEID4args   opcbnotify_deviceid;
    case OP_CB_ILLEGAL:            void;
   };


   struct CB_COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           uint32_t        callback_ident;
           nfs_cb_argop4   argarray<>;
   };
















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19.2.2.  RESULTS

   union nfs_cb_resop4 switch (unsigned resop) {
    case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;

    /* new NFSv4.1 operations */
    case OP_CB_LAYOUTRECALL:
                           CB_LAYOUTRECALL4res
                                           opcblayoutrecall;

    case OP_CB_NOTIFY:     CB_NOTIFY4res   opcbnotify;

    case OP_CB_PUSH_DELEG: CB_PUSH_DELEG4res
                                           opcbpush_deleg;

    case OP_CB_RECALL_ANY: CB_RECALL_ANY4res
                                           opcbrecall_any;

    case OP_CB_RECALLABLE_OBJ_AVAIL:
                           CB_RECALLABLE_OBJ_AVAIL4res
                                   opcbrecallable_obj_avail;

    case OP_CB_RECALL_SLOT:
                           CB_RECALL_SLOT4res
                                           opcbrecall_slot;

    case OP_CB_SEQUENCE:   CB_SEQUENCE4res opcbsequence;

    case OP_CB_WANTS_CANCELLED:
                           CB_WANTS_CANCELLED4res
                                   opcbwants_cancelled;

    case OP_CB_NOTIFY_LOCK:
                           CB_NOTIFY_LOCK4res
                                           opcbnotify_lock;

    case OP_CB_NOTIFY_DEVICEID:
                           CB_NOTIFY_DEVICEID4res
                                           opcbnotify_deviceid;

    /* Not new operation */
    case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
   };







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   struct CB_COMPOUND4res {
           nfsstat4 status;
           utf8str_cs      tag;
           nfs_cb_resop4   resarray<>;
   };

19.2.3.  DESCRIPTION

   The CB_COMPOUND procedure is used to combine one or more of the
   callback procedures into a single RPC request.  The main callback RPC
   program has two main procedures: CB_NULL and CB_COMPOUND.  All other
   operations use the CB_COMPOUND procedure as a wrapper.

   During the processing of the CB_COMPOUND procedure, the client may
   find that it does not have the available resources to execute any or
   all of the operations within the CB_COMPOUND sequence.  Refer to
   Section 2.10.6.4 for details.

   The minorversion field of the arguments MUST be the same as the
   minorversion of the COMPOUND procedure used to create the client ID
   and session.  For NFSv4.1, minorversion MUST be set to 1.

   Contained within the CB_COMPOUND results is a "status" field.  This
   status MUST be equal to the status of the last operation that was
   executed within the CB_COMPOUND procedure.  Therefore, if an
   operation incurred an error, then the "status" value will be the same
   error value as is being returned for the operation that failed.

   The "tag" field is handled the same way as that of the COMPOUND
   procedure (see Section 16.2.3).

   Illegal operation codes are handled in the same way as they are
   handled for the COMPOUND procedure.

19.2.4.  IMPLEMENTATION

   The CB_COMPOUND procedure is used to combine individual operations
   into a single RPC request.  The client interprets each of the
   operations in turn.  If an operation is executed by the client and
   the status of that operation is NFS4_OK, then the next operation in
   the CB_COMPOUND procedure is executed.  The client continues this
   process until there are no more operations to be executed or one of
   the operations has a status value other than NFS4_OK.

19.2.5.  ERRORS

   CB_COMPOUND will of course return every error that each operation on
   the backchannel can return (see Table 7).  However, if CB_COMPOUND



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   returns zero operations, obviously the error returned by COMPOUND has
   nothing to do with an error returned by an operation.  The list of
   errors CB_COMPOUND will return if it processes zero operations
   includes:

                         CB_COMPOUND error returns

   +------------------------------+------------------------------------+
   | Error                        | Notes                              |
   +------------------------------+------------------------------------+
   | NFS4ERR_BADCHAR              | The tag argument has a character   |
   |                              | the replier does not support.      |
   | NFS4ERR_BADXDR               |                                    |
   | NFS4ERR_DELAY                |                                    |
   | NFS4ERR_INVAL                | The tag argument is not in UTF-8   |
   |                              | encoding.                          |
   | NFS4ERR_MINOR_VERS_MISMATCH  |                                    |
   | NFS4ERR_SERVERFAULT          |                                    |
   | NFS4ERR_TOO_MANY_OPS         |                                    |
   | NFS4ERR_REP_TOO_BIG          |                                    |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE |                                    |
   | NFS4ERR_REQ_TOO_BIG          |                                    |
   +------------------------------+------------------------------------+

                                 Table 15

20.  NFSv4.1 Callback Operations

20.1.  Operation 3: CB_GETATTR - Get Attributes

20.1.1.  ARGUMENT

   struct CB_GETATTR4args {
           nfs_fh4 fh;
           bitmap4 attr_request;
   };















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20.1.2.  RESULT

   struct CB_GETATTR4resok {
           fattr4  obj_attributes;
   };

   union CB_GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            CB_GETATTR4resok       resok4;
    default:
            void;
   };


20.1.3.  DESCRIPTION

   The CB_GETATTR operation is used by the server to obtain the current
   modified state of a file that has been OPEN_DELEGATE_WRITE delegated.
   The size and change attributes are the only ones guaranteed to be
   serviced by the client.  See Section 10.4.3 for a full description of
   how the client and server are to interact with the use of CB_GETATTR.

   If the filehandle specified is not one for which the client holds an
   OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error is
   returned.

20.1.4.  IMPLEMENTATION

   The client returns attrmask bits and the associated attribute values
   only for the change attribute, and attributes that it may change
   (time_modify, and size).

20.2.  Operation 4: CB_RECALL - Recall a Delegation

20.2.1.  ARGUMENT

   struct CB_RECALL4args {
           stateid4        stateid;
           bool            truncate;
           nfs_fh4         fh;
   };










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20.2.2.  RESULT

   struct CB_RECALL4res {
           nfsstat4        status;
   };


20.2.3.  DESCRIPTION

   The CB_RECALL operation is used to begin the process of recalling a
   delegation and returning it to the server.

   The truncate flag is used to optimize recall for a file object that
   is a regular file and is about to be truncated to zero.  When it is
   TRUE, the client is freed of the obligation to propagate modified
   data for the file to the server, since this data is irrelevant.

   If the handle specified is not one for which the client holds a
   delegation, an NFS4ERR_BADHANDLE error is returned.

   If the stateid specified is not one corresponding to an OPEN
   delegation for the file specified by the filehandle, an
   NFS4ERR_BAD_STATEID is returned.

20.2.4.  IMPLEMENTATION

   The client SHOULD reply to the callback immediately.  Replying does
   not complete the recall except when the value of the reply's status
   field is neither NFS4ERR_DELAY nor NFS4_OK.  The recall is not
   complete until the delegation is returned using a DELEGRETURN
   operation.

20.3.  Operation 5: CB_LAYOUTRECALL - Recall Layout from Client


















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20.3.1.  ARGUMENT

   /*
    * NFSv4.1 callback arguments and results
    */

   enum layoutrecall_type4 {
           LAYOUTRECALL4_FILE = LAYOUT4_RET_REC_FILE,
           LAYOUTRECALL4_FSID = LAYOUT4_RET_REC_FSID,
           LAYOUTRECALL4_ALL  = LAYOUT4_RET_REC_ALL
   };

   struct layoutrecall_file4 {
           nfs_fh4         lor_fh;
           offset4         lor_offset;
           length4         lor_length;
           stateid4        lor_stateid;
   };

   union layoutrecall4 switch(layoutrecall_type4 lor_recalltype) {
   case LAYOUTRECALL4_FILE:
           layoutrecall_file4 lor_layout;
   case LAYOUTRECALL4_FSID:
           fsid4              lor_fsid;
   case LAYOUTRECALL4_ALL:
           void;
   };

   struct CB_LAYOUTRECALL4args {
           layouttype4             clora_type;
           layoutiomode4           clora_iomode;
           bool                    clora_changed;
           layoutrecall4           clora_recall;
   };

20.3.2.  RESULT

   struct CB_LAYOUTRECALL4res {
           nfsstat4        clorr_status;
   };


20.3.3.  DESCRIPTION

   The CB_LAYOUTRECALL operation is used by the server to recall layouts
   from the client; as a result, the client will begin the process of
   returning layouts via LAYOUTRETURN.  The CB_LAYOUTRECALL operation
   specifies one of three forms of recall processing with the value of



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   layoutrecall_type4.  The recall is for one of the following: a
   specific layout of a specific file (LAYOUTRECALL4_FILE), an entire
   file system ID (LAYOUTRECALL4_FSID), or all file systems
   (LAYOUTRECALL4_ALL).

   The behavior of the operation varies based on the value of the
   layoutrecall_type4.  The value and behaviors are:

   LAYOUTRECALL4_FILE

      For a layout to match the recall request, the values of the
      following fields must match those of the layout: clora_type,
      clora_iomode, lor_fh, and the byte-range specified by lor_offset
      and lor_length.  The clora_iomode field may have a special value
      of LAYOUTIOMODE4_ANY.  The special value LAYOUTIOMODE4_ANY will
      match any iomode originally returned in a layout; therefore, it
      acts as a wild card.  The other special value used is for
      lor_length.  If lor_length has a value of NFS4_UINT64_MAX, the
      lor_length field means the maximum possible file size.  If a
      matching layout is found, it MUST be returned using the
      LAYOUTRETURN operation (see Section 18.44).  An example of the
      field's special value use is if clora_iomode is LAYOUTIOMODE4_ANY,
      lor_offset is zero, and lor_length is NFS4_UINT64_MAX, then the
      entire layout is to be returned.

      The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
      client does not hold layouts for the file or if the client does
      not have any overlapping layouts for the specification in the
      layout recall.

   LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL

      If LAYOUTRECALL4_FSID is specified, the fsid specifies the file
      system for which any outstanding layouts MUST be returned.  If
      LAYOUTRECALL4_ALL is specified, all outstanding layouts MUST be
      returned.  In addition, LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL
      specify that all the storage device ID to storage device address
      mappings in the affected file system(s) are also recalled.  The
      respective LAYOUTRETURN with either LAYOUTRETURN4_FSID or
      LAYOUTRETURN4_ALL acknowledges to the server that the client
      invalidated the said device mappings.  See Section 12.5.5.2.1.5
      for considerations with "bulk" recall of layouts.

      The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
      client does not hold layouts and does not have valid deviceid
      mappings.

   In processing the layout recall request, the client also varies its



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   behavior based on the value of the clora_changed field.  This field
   is used by the server to provide additional context for the reason
   why the layout is being recalled.  A FALSE value for clora_changed
   indicates that no change in the layout is expected and the client may
   write modified data to the storage devices involved; this must be
   done prior to returning the layout via LAYOUTRETURN.  A TRUE value
   for clora_changed indicates that the server is changing the layout.
   Examples of layout changes and reasons for a TRUE indication are the
   following: the metadata server is restriping the file or a permanent
   error has occurred on a storage device and the metadata server would
   like to provide a new layout for the file.  Therefore, a
   clora_changed value of TRUE indicates some level of change for the
   layout and the client SHOULD NOT write and commit modified data to
   the storage devices.  In this case, the client writes and commits
   data through the metadata server.

   See Section 12.5.3 for a description of how the lor_stateid field in
   the arguments is to be constructed.  Note that the "seqid" field of
   lor_stateid MUST NOT be zero.  See Sections 8.2, 12.5.3, and 12.5.5.2
   for a further discussion and requirements.

20.3.4.  IMPLEMENTATION

   The client's processing for CB_LAYOUTRECALL is similar to CB_RECALL
   (recall of file delegations) in that the client responds to the
   request before actually returning layouts via the LAYOUTRETURN
   operation.  While the client responds to the CB_LAYOUTRECALL
   immediately, the operation is not considered complete (i.e.,
   considered pending) until all affected layouts are returned to the
   server via the LAYOUTRETURN operation.

   Before returning the layout to the server via LAYOUTRETURN, the
   client should wait for the response from in-process or in-flight
   READ, WRITE, or COMMIT operations that use the recalled layout.

   If the client is holding modified data that is affected by a recalled
   layout, the client has various options for writing the data to the
   server.  As always, the client may write the data through the
   metadata server.  In fact, the client may not have a choice other
   than writing to the metadata server when the clora_changed argument
   is TRUE and a new layout is unavailable from the server.  However,
   the client may be able to write the modified data to the storage
   device if the clora_changed argument is FALSE; this needs to be done
   before returning the layout via LAYOUTRETURN.  If the client were to
   obtain a new layout covering the modified data's byte-range, then
   writing to the storage devices is an available alternative.  Note
   that before obtaining a new layout, the client must first return the
   original layout.



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   In the case of modified data being written while the layout is held,
   the client must use LAYOUTCOMMIT operations at the appropriate time;
   as required LAYOUTCOMMIT must be done before the LAYOUTRETURN.  If a
   large amount of modified data is outstanding, the client may send
   LAYOUTRETURNs for portions of the recalled layout; this allows the
   server to monitor the client's progress and adherence to the original
   recall request.  However, the last LAYOUTRETURN in a sequence of
   returns MUST specify the full range being recalled (see
   Section 12.5.5.1 for details).

   If a server needs to delete a device ID and there are layouts
   referring to the device ID, CB_LAYOUTRECALL MUST be invoked to cause
   the client to return all layouts referring to the device ID before
   the server can delete the device ID.  If the client does not return
   the affected layouts, the server MAY revoke the layouts.

20.4.  Operation 6: CB_NOTIFY - Notify Client of Directory Changes

20.4.1.  ARGUMENT

   /*
    * Directory notification types.
    */
   enum notify_type4 {
           NOTIFY4_CHANGE_CHILD_ATTRS = 0,
           NOTIFY4_CHANGE_DIR_ATTRS = 1,
           NOTIFY4_REMOVE_ENTRY = 2,
           NOTIFY4_ADD_ENTRY = 3,
           NOTIFY4_RENAME_ENTRY = 4,
           NOTIFY4_CHANGE_COOKIE_VERIFIER = 5
   };

   /* Changed entry information.  */
   struct notify_entry4 {
           component4      ne_file;
           fattr4          ne_attrs;
   };

   /* Previous entry information */
   struct prev_entry4 {
           notify_entry4   pe_prev_entry;
           /* what READDIR returned for this entry */
           nfs_cookie4     pe_prev_entry_cookie;
   };

   struct notify_remove4 {
           notify_entry4   nrm_old_entry;
           nfs_cookie4     nrm_old_entry_cookie;



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   };

   struct notify_add4 {
           /*
            * Information on object
            * possibly renamed over.
            */
           notify_remove4      nad_old_entry<1>;
           notify_entry4       nad_new_entry;
           /* what READDIR would have returned for this entry */
           nfs_cookie4         nad_new_entry_cookie<1>;
           prev_entry4         nad_prev_entry<1>;
           bool                nad_last_entry;
   };

   struct notify_attr4 {
           notify_entry4   na_changed_entry;
   };

   struct notify_rename4 {
           notify_remove4  nrn_old_entry;
           notify_add4     nrn_new_entry;
   };

   struct notify_verifier4 {
           verifier4       nv_old_cookieverf;
           verifier4       nv_new_cookieverf;
   };

   /*
    * Objects of type notify_<>4 and
    * notify_device_<>4 are encoded in this.
    */
   typedef opaque notifylist4<>;

   struct notify4 {
           /* composed from notify_type4 or notify_deviceid_type4 */
           bitmap4         notify_mask;
           notifylist4     notify_vals;
   };

   struct CB_NOTIFY4args {
           stateid4    cna_stateid;
           nfs_fh4     cna_fh;
           notify4     cna_changes<>;
   };





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20.4.2.  RESULT

   struct CB_NOTIFY4res {
           nfsstat4    cnr_status;
   };


20.4.3.  DESCRIPTION

   The CB_NOTIFY operation is used by the server to send notifications
   to clients about changes to delegated directories.  The registration
   of notifications for the directories occurs when the delegation is
   established using GET_DIR_DELEGATION.  These notifications are sent
   over the backchannel.  The notification is sent once the original
   request has been processed on the server.  The server will send an
   array of notifications for changes that might have occurred in the
   directory.  The notifications are sent as list of pairs of bitmaps
   and values.  See Section 3.3.7 for a description of how NFSv4.1
   bitmaps work.

   If the server has more notifications than can fit in the CB_COMPOUND
   request, it SHOULD send a sequence of serial CB_COMPOUND requests so
   that the client's view of the directory does not become confused.
   For example, if the server indicates that a file named "foo" is added
   and that the file "foo" is removed, the order in which the client
   receives these notifications needs to be the same as the order in
   which the corresponding operations occurred on the server.

   If the client holding the delegation makes any changes in the
   directory that cause files or sub-directories to be added or removed,
   the server will notify that client of the resulting change(s).  If
   the client holding the delegation is making attribute or cookie
   verifier changes only, the server does not need to send notifications
   to that client.  The server will send the following information for
   each operation:

   NOTIFY4_ADD_ENTRY
      The server will send information about the new directory entry
      being created along with the cookie for that entry.  The entry
      information (data type notify_add4) includes the component name of
      the entry and attributes.  The server will send this type of entry
      when a file is actually being created, when an entry is being
      added to a directory as a result of a rename across directories
      (see below), and when a hard link is being created to an existing
      file.  If this entry is added to the end of the directory, the
      server will set the nad_last_entry flag to TRUE.  If the file is
      added such that there is at least one entry before it, the server
      will also return the previous entry information (nad_prev_entry, a



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      variable-length array of up to one element.  If the array is of
      zero length, there is no previous entry), along with its cookie.
      This is to help clients find the right location in their file name
      caches and directory caches where this entry should be cached.  If
      the new entry's cookie is available, it will be in the
      nad_new_entry_cookie (another variable-length array of up to one
      element) field.  If the addition of the entry causes another entry
      to be deleted (which can only happen in the rename case)
      atomically with the addition, then information on this entry is
      reported in nad_old_entry.

   NOTIFY4_REMOVE_ENTRY
      The server will send information about the directory entry being
      deleted.  The server will also send the cookie value for the
      deleted entry so that clients can get to the cached information
      for this entry.

   NOTIFY4_RENAME_ENTRY
      The server will send information about both the old entry and the
      new entry.  This includes the name and attributes for each entry.
      In addition, if the rename causes the deletion of an entry (i.e.,
      the case of a file renamed over), then this is reported in
      nrn_new_new_entry.nad_old_entry.  This notification is only sent
      if both entries are in the same directory.  If the rename is
      across directories, the server will send a remove notification to
      one directory and an add notification to the other directory,
      assuming both have a directory delegation.

   NOTIFY4_CHANGE_CHILD_ATTRS/NOTIFY4_CHANGE_DIR_ATTRS
      The client will use the attribute mask to inform the server of
      attributes for which it wants to receive notifications.  This
      change notification can be requested for changes to the attributes
      of the directory as well as changes to any file's attributes in
      the directory by using two separate attribute masks.  The client
      cannot ask for change attribute notification for a specific file.
      One attribute mask covers all the files in the directory.  Upon
      any attribute change, the server will send back the values of
      changed attributes.  Notifications might not make sense for some
      file system-wide attributes, and it is up to the server to decide
      which subset it wants to support.  The client can negotiate the
      frequency of attribute notifications by letting the server know
      how often it wants to be notified of an attribute change.  The
      server will return supported notification frequencies or an
      indication that no notification is permitted for directory or
      child attributes by setting the dir_notif_delay and
      dir_entry_notif_delay attributes, respectively.





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   NOTIFY4_CHANGE_COOKIE_VERIFIER
      If the cookie verifier changes while a client is holding a
      delegation, the server will notify the client so that it can
      invalidate its cookies and re-send a READDIR to get the new set of
      cookies.

20.5.  Operation 7: CB_PUSH_DELEG - Offer Previously Requested
       Delegation to Client

20.5.1.  ARGUMENT

   struct CB_PUSH_DELEG4args {
           nfs_fh4          cpda_fh;
           open_delegation4 cpda_delegation;

   };


20.5.2.  RESULT

   struct CB_PUSH_DELEG4res {
           nfsstat4 cpdr_status;
   };


20.5.3.  DESCRIPTION

   CB_PUSH_DELEG is used by the server both to signal to the client that
   the delegation it wants (previously indicated via a want established
   from an OPEN or WANT_DELEGATION operation) is available and to
   simultaneously offer the delegation to the client.  The client has
   the choice of accepting the delegation by returning NFS4_OK to the
   server, delaying the decision to accept the offered delegation by
   returning NFS4ERR_DELAY, or permanently rejecting the offer of the
   delegation by returning NFS4ERR_REJECT_DELEG.  When a delegation is
   rejected in this fashion, the want previously established is
   permanently deleted and the delegation is subject to acquisition by
   another client.

20.5.4.  IMPLEMENTATION

   If the client does return NFS4ERR_DELAY and there is a conflicting
   delegation request, the server MAY process it at the expense of the
   client that returned NFS4ERR_DELAY.  The client's want will not be
   cancelled, but MAY be processed behind other delegation requests or
   registered wants.

   When a client returns a status other than NFS4_OK, NFS4ERR_DELAY, or



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   NFS4ERR_REJECT_DELAY, the want remains pending, although servers may
   decide to cancel the want by sending a CB_WANTS_CANCELLED.

20.6.  Operation 8: CB_RECALL_ANY - Keep Any N Recallable Objects

20.6.1.  ARGUMENT

   const RCA4_TYPE_MASK_RDATA_DLG          = 0;
   const RCA4_TYPE_MASK_WDATA_DLG          = 1;
   const RCA4_TYPE_MASK_DIR_DLG            = 2;
   const RCA4_TYPE_MASK_FILE_LAYOUT        = 3;
   const RCA4_TYPE_MASK_BLK_LAYOUT         = 4;
   const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN     = 8;
   const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX     = 9;
   const RCA4_TYPE_MASK_OTHER_LAYOUT_MIN   = 12;
   const RCA4_TYPE_MASK_OTHER_LAYOUT_MAX   = 15;

   struct  CB_RECALL_ANY4args      {
           uint32_t        craa_objects_to_keep;
           bitmap4         craa_type_mask;
   };


20.6.2.  RESULT

   struct CB_RECALL_ANY4res {
           nfsstat4        crar_status;
   };


20.6.3.  DESCRIPTION

   The server may decide that it cannot hold all of the state for
   recallable objects, such as delegations and layouts, without running
   out of resources.  In such a case, while not optimal, the server is
   free to recall individual objects to reduce the load.

   Because the general purpose of such recallable objects as delegations
   is to eliminate client interaction with the server, the server cannot
   interpret lack of recent use as indicating that the object is no
   longer useful.  The absence of visible use is consistent with a
   delegation keeping potential operations from being sent to the
   server.  In the case of layouts, while it is true that the usefulness
   of a layout is indicated by the use of the layout when storage
   devices receive I/O requests, because there is no mandate that a
   storage device indicate to the metadata server any past or present
   use of a layout, the metadata server is not likely to know which
   layouts are good candidates to recall in response to low resources.



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   In order to implement an effective reclaim scheme for such objects,
   the server's knowledge of available resources must be used to
   determine when objects must be recalled with the clients selecting
   the actual objects to be returned.

   Server implementations may differ in their resource allocation
   requirements.  For example, one server may share resources among all
   classes of recallable objects, whereas another may use separate
   resource pools for layouts and for delegations, or further separate
   resources by types of delegations.

   When a given resource pool is over-utilized, the server can send a
   CB_RECALL_ANY to clients holding recallable objects of the types
   involved, allowing it to keep a certain number of such objects and
   return any excess.  A mask specifies which types of objects are to be
   limited.  The client chooses, based on its own knowledge of current
   usefulness, which of the objects in that class should be returned.

   A number of bits are defined.  For some of these, ranges are defined
   and it is up to the definition of the storage protocol to specify how
   these are to be used.  There are ranges reserved for object-based
   storage protocols and for other experimental storage protocols.  An
   RFC defining such a storage protocol needs to specify how particular
   bits within its range are to be used.  For example, it may specify a
   mapping between attributes of the layout (read vs. write, size of
   area) and the bit to be used, or it may define a field in the layout
   where the associated bit position is made available by the server to
   the client.

   RCA4_TYPE_MASK_RDATA_DLG

      The client is to return OPEN_DELEGATE_READ delegations on non-
      directory file objects.

   RCA4_TYPE_MASK_WDATA_DLG

      The client is to return OPEN_DELEGATE_WRITE delegations on regular
      file objects.

   RCA4_TYPE_MASK_DIR_DLG

      The client is to return directory delegations.

   RCA4_TYPE_MASK_FILE_LAYOUT







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      The client is to return layouts of type LAYOUT4_NFSV4_1_FILES.

   RCA4_TYPE_MASK_BLK_LAYOUT

      See [41] for a description.

   RCA4_TYPE_MASK_OBJ_LAYOUT_MIN to RCA4_TYPE_MASK_OBJ_LAYOUT_MAX

      See [40] for a description.

   RCA4_TYPE_MASK_OTHER_LAYOUT_MIN to RCA4_TYPE_MASK_OTHER_LAYOUT_MAX

      This range is reserved for telling the client to recall layouts of
      experimental or site-specific layout types (see Section 3.3.13).

   When a bit is set in the type mask that corresponds to an undefined
   type of recallable object, NFS4ERR_INVAL MUST be returned.  When a
   bit is set that corresponds to a defined type of object but the
   client does not support an object of the type, NFS4ERR_INVAL MUST NOT
   be returned.  Future minor versions of NFSv4 may expand the set of
   valid type mask bits.

   CB_RECALL_ANY specifies a count of objects that the client may keep
   as opposed to a count that the client must return.  This is to avoid
   a potential race between a CB_RECALL_ANY that had a count of objects
   to free with a set of client-originated operations to return layouts
   or delegations.  As a result of the race, the client and server would
   have differing ideas as to how many objects to return.  Hence, the
   client could mistakenly free too many.

   If resource demands prompt it, the server may send another
   CB_RECALL_ANY with a lower count, even if it has not yet received an
   acknowledgment from the client for a previous CB_RECALL_ANY with the
   same type mask.  Although the possibility exists that these will be
   received by the client in an order different from the order in which
   they were sent, any such permutation of the callback stream is
   harmless.  It is the job of the client to bring down the size of the
   recallable object set in line with each CB_RECALL_ANY received, and
   until that obligation is met, it cannot be cancelled or modified by
   any subsequent CB_RECALL_ANY for the same type mask.  Thus, if the
   server sends two CB_RECALL_ANYs, the effect will be the same as if
   the lower count was sent, whatever the order of recall receipt.  Note
   that this means that a server may not cancel the effect of a
   CB_RECALL_ANY by sending another recall with a higher count.  When a
   CB_RECALL_ANY is received and the count is already within the limit
   set or is above a limit that the client is working to get down to,
   that callback has no effect.




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   Servers are generally free to deny recallable objects when
   insufficient resources are available.  Note that the effect of such a
   policy is implicitly to give precedence to existing objects relative
   to requested ones, with the result that resources might not be
   optimally used.  To prevent this, servers are well advised to make
   the point at which they start sending CB_RECALL_ANY callbacks
   somewhat below that at which they cease to give out new delegations
   and layouts.  This allows the client to purge its less-used objects
   whenever appropriate and so continue to have its subsequent requests
   given new resources freed up by object returns.

20.6.4.  IMPLEMENTATION

   The client can choose to return any type of object specified by the
   mask.  If a server wishes to limit the use of objects of a specific
   type, it should only specify that type in the mask it sends.  Should
   the client fail to return requested objects, it is up to the server
   to handle this situation, typically by sending specific recalls
   (i.e., sending CB_RECALL operations) to properly limit resource
   usage.  The server should give the client enough time to return
   objects before proceeding to specific recalls.  This time should not
   be less than the lease period.

20.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for
       Recallable Objects

20.7.1.  ARGUMENT

   typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;


20.7.2.  RESULT

   struct CB_RECALLABLE_OBJ_AVAIL4res {
           nfsstat4        croa_status;
   };


20.7.3.  DESCRIPTION

   CB_RECALLABLE_OBJ_AVAIL is used by the server to signal the client
   that the server has resources to grant recallable objects that might
   previously have been denied by OPEN, WANT_DELEGATION, GET_DIR_DELEG,
   or LAYOUTGET.

   The argument craa_objects_to_keep means the total number of
   recallable objects of the types indicated in the argument type_mask
   that the server believes it can allow the client to have, including



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   the number of such objects the client already has.  A client that
   tries to acquire more recallable objects than the server informs it
   can have runs the risk of having objects recalled.

   The server is not obligated to reserve the difference between the
   number of the objects the client currently has and the value of
   craa_objects_to_keep, nor does delaying the reply to
   CB_RECALLABLE_OBJ_AVAIL prevent the server from using the resources
   of the recallable objects for another purpose.  Indeed, if a client
   responds slowly to CB_RECALLABLE_OBJ_AVAIL, the server might
   interpret the client as having reduced capability to manage
   recallable objects, and so cancel or reduce any reservation it is
   maintaining on behalf of the client.  Thus, if the client desires to
   acquire more recallable objects, it needs to reply quickly to
   CB_RECALLABLE_OBJ_AVAIL, and then send the appropriate operations to
   acquire recallable objects.

20.8.  Operation 10: CB_RECALL_SLOT - Change Flow Control Limits

20.8.1.  ARGUMENT

   struct CB_RECALL_SLOT4args {
           slotid4       rsa_target_highest_slotid;
   };


20.8.2.  RESULT

   struct CB_RECALL_SLOT4res {
           nfsstat4   rsr_status;
   };


20.8.3.  DESCRIPTION

   The CB_RECALL_SLOT operation requests the client to return session
   slots, and if applicable, transport credits (e.g., RDMA credits for
   connections associated with the operations channel) of the session's
   fore channel.  CB_RECALL_SLOT specifies rsa_target_highest_slotid,
   the value of the target highest slot ID the server wants for the
   session.  The client MUST then progress toward reducing the session's
   highest slot ID to the target value.

   If the session has only non-RDMA connections associated with its
   operations channel, then the client need only wait for all
   outstanding requests with a slot ID > rsa_target_highest_slotid to
   complete, then send a single COMPOUND consisting of a single SEQUENCE
   operation, with the sa_highestslot field set to



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   rsa_target_highest_slotid.  If there are RDMA-based connections
   associated with operation channel, then the client needs to also send
   enough zero-length "RDMA Send" messages to take the total RDMA credit
   count to rsa_target_highest_slotid + 1 or below.

20.8.4.  IMPLEMENTATION

   If the client fails to reduce highest slot it has on the fore channel
   to what the server requests, the server can force the issue by
   asserting flow control on the receive side of all connections bound
   to the fore channel, and then finish servicing all outstanding
   requests that are in slots greater than rsa_target_highest_slotid.
   Once that is done, the server can then open the flow control, and any
   time the client sends a new request on a slot greater than
   rsa_target_highest_slotid, the server can return NFS4ERR_BADSLOT.

20.9.  Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing and
       Control

20.9.1.  ARGUMENT

   struct referring_call4 {
           sequenceid4     rc_sequenceid;
           slotid4         rc_slotid;
   };

   struct referring_call_list4 {
           sessionid4      rcl_sessionid;
           referring_call4 rcl_referring_calls<>;
   };

   struct CB_SEQUENCE4args {
           sessionid4           csa_sessionid;
           sequenceid4          csa_sequenceid;
           slotid4              csa_slotid;
           slotid4              csa_highest_slotid;
           bool                 csa_cachethis;
           referring_call_list4 csa_referring_call_lists<>;
   };












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20.9.2.  RESULT

   struct CB_SEQUENCE4resok {
           sessionid4         csr_sessionid;
           sequenceid4        csr_sequenceid;
           slotid4            csr_slotid;
           slotid4            csr_highest_slotid;
           slotid4            csr_target_highest_slotid;
   };

   union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
   case NFS4_OK:
           CB_SEQUENCE4resok   csr_resok4;
   default:
           void;
   };


20.9.3.  DESCRIPTION

   The CB_SEQUENCE operation is used to manage operational accounting
   for the backchannel of the session on which a request is sent.  The
   contents include the session ID to which this request belongs, the
   slot ID and sequence ID used by the server to implement session
   request control and exactly once semantics, and exchanged slot ID
   maxima that are used to adjust the size of the reply cache.  In each
   CB_COMPOUND request, CB_SEQUENCE MUST appear once and MUST be the
   first operation.  The error NFS4ERR_SEQUENCE_POS MUST be returned
   when CB_SEQUENCE is found in any position in a CB_COMPOUND beyond the
   first.  If any other operation is in the first position of
   CB_COMPOUND, NFS4ERR_OP_NOT_IN_SESSION MUST be returned.

   See Section 18.46.3 for a description of how slots are processed.

   If csa_cachethis is TRUE, then the server is requesting that the
   client cache the reply in the callback reply cache.  The client MUST
   cache the reply (see Section 2.10.6.1.3).

   The csa_referring_call_lists array is the list of COMPOUND requests,
   identified by session ID, slot ID, and sequence ID.  These are
   requests that the client previously sent to the server.  These
   previous requests created state that some operation(s) in the same
   CB_COMPOUND as the csa_referring_call_lists are identifying.  A
   session ID is included because leased state is tied to a client ID,
   and a client ID can have multiple sessions.  See Section 2.10.6.3.

   The value of the csa_sequenceid argument relative to the cached
   sequence ID on the slot falls into one of three cases.



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   o  If the difference between csa_sequenceid and the client's cached
      sequence ID at the slot ID is two (2) or more, or if
      csa_sequenceid is less than the cached sequence ID (accounting for
      wraparound of the unsigned sequence ID value), then the client
      MUST return NFS4ERR_SEQ_MISORDERED.

   o  If csa_sequenceid and the cached sequence ID are the same, this is
      a retry, and the client returns the CB_COMPOUND request's cached
      reply.

   o  If csa_sequenceid is one greater (accounting for wraparound) than
      the cached sequence ID, then this is a new request, and the slot's
      sequence ID is incremented.  The operations subsequent to
      CB_SEQUENCE, if any, are processed.  If there are no other
      operations, the only other effects are to cache the CB_SEQUENCE
      reply in the slot, maintain the session's activity, and when the
      server receives the CB_SEQUENCE reply, renew the lease of state
      related to the client ID.

   If the server reuses a slot ID and sequence ID for a completely
   different request, the client MAY treat the request as if it is a
   retry of what it has already executed.  The client MAY however detect
   the server's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.

   If CB_SEQUENCE returns an error, then the state of the slot (sequence
   ID, cached reply) MUST NOT change.  See Section 2.10.6.1.3 for the
   conditions when the error NFS4ERR_RETRY_UNCACHED_REP might be
   returned.

   The client returns two "highest_slotid" values: csr_highest_slotid
   and csr_target_highest_slotid.  The former is the highest slot ID the
   client will accept in a future CB_SEQUENCE operation, and SHOULD NOT
   be less than the value of csa_highest_slotid (but see
   Section 2.10.6.1 for an exception).  The latter is the highest slot
   ID the client would prefer the server use on a future CB_SEQUENCE
   operation.

20.10.  Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation
        Wants

20.10.1.  ARGUMENT

   struct CB_WANTS_CANCELLED4args {
           bool cwca_contended_wants_cancelled;
           bool cwca_resourced_wants_cancelled;
   };





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20.10.2.  RESULT

   struct CB_WANTS_CANCELLED4res {
           nfsstat4        cwcr_status;
   };


20.10.3.  DESCRIPTION

   The CB_WANTS_CANCELLED operation is used to notify the client that
   some or all of the wants it registered for recallable delegations and
   layouts have been cancelled.

   If cwca_contended_wants_cancelled is TRUE, this indicates that the
   server will not be pushing to the client any delegations that become
   available after contention passes.

   If cwca_resourced_wants_cancelled is TRUE, this indicates that the
   server will not notify the client when there are resources on the
   server to grant delegations or layouts.

   After receiving a CB_WANTS_CANCELLED operation, the client is free to
   attempt to acquire the delegations or layouts it was waiting for, and
   possibly re-register wants.

20.10.4.  IMPLEMENTATION

   When a client has an OPEN, WANT_DELEGATION, or GET_DIR_DELEGATION
   request outstanding, when a CB_WANTS_CANCELLED is sent, the server
   may need to make clear to the client whether a promise to signal
   delegation availability happened before the CB_WANTS_CANCELLED and is
   thus covered by it, or after the CB_WANTS_CANCELLED in which case it
   was not covered by it.  The server can make this distinction by
   putting the appropriate requests into the list of referring calls in
   the associated CB_SEQUENCE.

20.11.  Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible Lock
        Availability

20.11.1.  ARGUMENT

   struct CB_NOTIFY_LOCK4args {
       nfs_fh4     cnla_fh;
       lock_owner4 cnla_lock_owner;
   };






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20.11.2.  RESULT

   struct CB_NOTIFY_LOCK4res {
           nfsstat4        cnlr_status;
   };


20.11.3.  DESCRIPTION

   The server can use this operation to indicate that a byte-range lock
   for the given file and lock-owner, previously requested by the client
   via an unsuccessful LOCK operation, might be available.

   This callback is meant to be used by servers to help reduce the
   latency of blocking locks in the case where they recognize that a
   client that has been polling for a blocking byte-range lock may now
   be able to acquire the lock.  If the server supports this callback
   for a given file, it MUST set the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
   when responding to successful opens for that file.  This does not
   commit the server to the use of CB_NOTIFY_LOCK, but the client may
   use this as a hint to decide how frequently to poll for locks derived
   from that open.

   If an OPEN operation results in an upgrade, in which the stateid
   returned has an "other" value matching that of a stateid already
   allocated, with a new "seqid" indicating a change in the lock being
   represented, then the value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
   when responding to that new OPEN controls handling from that point
   going forward.  When parallel OPENs are done on the same file and
   open-owner, the ordering of the "seqid" fields of the returned
   stateids (subject to wraparound) are to be used to select the
   controlling value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.

20.11.4.  IMPLEMENTATION

   The server MUST NOT grant the byte-range lock to the client unless
   and until it receives a LOCK operation from the client.  Similarly,
   the client receiving this callback cannot assume that it now has the
   lock or that a subsequent LOCK operation for the lock will be
   successful.

   The server is not required to implement this callback, and even if it
   does, it is not required to use it in any particular case.
   Therefore, the client must still rely on polling for blocking locks,
   as described in Section 9.6.

   Similarly, the client is not required to implement this callback, and
   even it does, is still free to ignore it.  Therefore, the server MUST



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   NOT assume that the client will act based on the callback.

20.12.  Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device ID
        Changes

20.12.1.  ARGUMENT

   /*
    * Device notification types.
    */
   enum notify_deviceid_type4 {
           NOTIFY_DEVICEID4_CHANGE = 1,
           NOTIFY_DEVICEID4_DELETE = 2
   };

   /* For NOTIFY4_DEVICEID4_DELETE */
   struct notify_deviceid_delete4 {
           layouttype4     ndd_layouttype;
           deviceid4       ndd_deviceid;
   };

   /* For NOTIFY4_DEVICEID4_CHANGE */
   struct notify_deviceid_change4 {
           layouttype4     ndc_layouttype;
           deviceid4       ndc_deviceid;
           bool            ndc_immediate;
   };

   struct CB_NOTIFY_DEVICEID4args {
           notify4 cnda_changes<>;
   };


20.12.2.  RESULT

   struct CB_NOTIFY_DEVICEID4res {
           nfsstat4        cndr_status;
   };


20.12.3.  DESCRIPTION

   The CB_NOTIFY_DEVICEID operation is used by the server to send
   notifications to clients about changes to pNFS device IDs.  The
   registration of device ID notifications is optional and is done via
   GETDEVICEINFO.  These notifications are sent over the backchannel
   once the original request has been processed on the server.  The
   server will send an array of notifications, cnda_changes, as a list



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   of pairs of bitmaps and values.  See Section 3.3.7 for a description
   of how NFSv4.1 bitmaps work.

   As with CB_NOTIFY (Section 20.4.3), it is possible the server has
   more notifications than can fit in a CB_COMPOUND, thus requiring
   multiple CB_COMPOUNDs.  Unlike CB_NOTIFY, serialization is not an
   issue because unlike directory entries, device IDs cannot be re-used
   after being deleted (Section 12.2.10).

   All device ID notifications contain a device ID and a layout type.
   The layout type is necessary because two different layout types can
   share the same device ID, and the common device ID can have
   completely different mappings for each layout type.

   The server will send the following notifications:

   NOTIFY_DEVICEID4_CHANGE
      A previously provided device-ID-to-device-address mapping has
      changed and the client uses GETDEVICEINFO to obtain the updated
      mapping.  The notification is encoded in a value of data type
      notify_deviceid_change4.  This data type also contains a boolean
      field, ndc_immediate, which if TRUE indicates that the change will
      be enforced immediately, and so the client might not be able to
      complete any pending I/O to the device ID.  If ndc_immediate is
      FALSE, then for an indefinite time, the client can complete
      pending I/O. After pending I/O is complete, the client SHOULD get
      the new device-ID-to-device-address mappings before sending new
      I/O requests to the storage devices addressed by the device ID.

   NOTIFY4_DEVICEID_DELETE
      Deletes a device ID from the mappings.  This notification MUST NOT
      be sent if the client has a layout that refers to the device ID.
      In other words, if the server is sending a delete device ID
      notification, one of the following is true for layouts associated
      with the layout type:

      *  The client never had a layout referring to that device ID.

      *  The client has returned all layouts referring to that device
         ID.

      *  The server has revoked all layouts referring to that device ID.

      The notification is encoded in a value of data type
      notify_deviceid_delete4.  After a server deletes a device ID, it
      MUST NOT reuse that device ID for the same layout type until the
      client ID is deleted.




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20.13.  Operation 10044: CB_ILLEGAL - Illegal Callback Operation

20.13.1.  ARGUMENT

           void;

20.13.2.  RESULT

   /*
    * CB_ILLEGAL: Response for illegal operation numbers
    */
   struct CB_ILLEGAL4res {
           nfsstat4        status;
   };


20.13.3.  DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the server sending an operation code within CB_COMPOUND that
   is not defined in the NFSv4.1 specification.  See Section 19.2.3 for
   more details.

   The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

20.13.4.  IMPLEMENTATION

   A server will probably not send an operation with code OP_CB_ILLEGAL,
   but if it does, the response will be CB_ILLEGAL4res just as it would
   be with any other invalid operation code.  Note that if the client
   gets an illegal operation code that is not OP_ILLEGAL, and if the
   client checks for legal operation codes during the XDR decode phase,
   then an instance of data type CB_ILLEGAL4res will not be returned.

21.  Security Considerations

   Historically, the authentication model of NFS was based on the entire
   machine being the NFS client, with the NFS server trusting the NFS
   client to authenticate the end-user.  The NFS server in turn shared
   its files only to specific clients, as identified by the client's
   source network address.  Given this model, the AUTH_SYS RPC security
   flavor simply identified the end-user using the client to the NFS
   server.  When processing NFS responses, the client ensured that the
   responses came from the same network address and port number to which
   the request was sent.  While such a model is easy to implement and
   simple to deploy and use, it is unsafe.  Thus, NFSv4.1
   implementations are REQUIRED to support a security model that uses
   end-to-end authentication, where an end-user on a client mutually



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   authenticates (via cryptographic schemes that do not expose passwords
   or keys in the clear on the network) to a principal on an NFS server.
   Consideration is also given to the integrity and privacy of NFS
   requests and responses.  The issues of end-to-end mutual
   authentication, integrity, and privacy are discussed in
   Section 2.2.1.1.1.  There are specific considerations when using
   Kerberos V5 as described in Section 2.2.1.1.1.2.1.1.

   Note that being REQUIRED to implement does not mean REQUIRED to use;
   AUTH_SYS can be used by NFSv4.1 clients and servers.  However,
   AUTH_SYS is merely an OPTIONAL security flavor in NFSv4.1, and so
   interoperability via AUTH_SYS is not assured.

   For reasons of reduced administration overhead, better performance,
   and/or reduction of CPU utilization, users of NFSv4.1 implementations
   might decline to use security mechanisms that enable integrity
   protection on each remote procedure call and response.  The use of
   mechanisms without integrity leaves the user vulnerable to a man-in-
   the-middle of the NFS client and server that modifies the RPC request
   and/or the response.  While implementations are free to provide the
   option to use weaker security mechanisms, there are three operations
   in particular that warrant the implementation overriding user
   choices.

   o  The first two such operations are SECINFO and SECINFO_NO_NAME.  It
      is RECOMMENDED that the client send both operations such that they
      are protected with a security flavor that has integrity
      protection, such as RPCSEC_GSS with either the
      rpc_gss_svc_integrity or rpc_gss_svc_privacy service.  Without
      integrity protection encapsulating SECINFO and SECINFO_NO_NAME and
      their results, a man-in-the-middle could modify results such that
      the client might select a weaker algorithm in the set allowed by
      the server, making the client and/or server vulnerable to further
      attacks.

   o  The third operation that SHOULD use integrity protection is any
      GETATTR for the fs_locations and fs_locations_info attributes, in
      order to mitigate the severity of a man-in-the-middle attack.  The
      attack has two steps.  First the attacker modifies the unprotected
      results of some operation to return NFS4ERR_MOVED.  Second, when
      the client follows up with a GETATTR for the fs_locations or
      fs_locations_info attributes, the attacker modifies the results to
      cause the client to migrate its traffic to a server controlled by
      the attacker.  With integrity protection, this attack is
      mitigated.

   Relative to previous NFS versions, NFSv4.1 has additional security
   considerations for pNFS (see Sections 12.9 and 13.12), locking and



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   session state (see Section 2.10.8.3), and state recovery during grace
   period (see Section 8.4.2.1.1).  With respect to locking and session
   state, if SP4_SSV state protection is being used, Section 2.10.10 has
   specific security considerations for the NFSv4.1 client and server.

22.  IANA Considerations

   This section uses terms that are defined in [55].

22.1.  Named Attribute Definitions

   IANA created a registry called the "NFSv4 Named Attribute Definitions
   Registry".

   The NFSv4.1 protocol supports the association of a file with zero or
   more named attributes.  The namespace identifiers for these
   attributes are defined as string names.  The protocol does not define
   the specific assignment of the namespace for these file attributes.
   The IANA registry promotes interoperability where common interests
   exist.  While application developers are allowed to define and use
   attributes as needed, they are encouraged to register the attributes
   with IANA.

   Such registered named attributes are presumed to apply to all minor
   versions of NFSv4, including those defined subsequently to the
   registration.  If the named attribute is intended to be limited to
   specific minor versions, this will be clearly stated in the
   registry's assignment.

   All assignments to the registry are made on a First Come First Served
   basis, per Section 4.1 of [55].  The policy for each assignment is
   Specification Required, per Section 4.1 of [55].

   Under the NFSv4.1 specification, the name of a named attribute can in
   theory be up to 2^32 - 1 bytes in length, but in practice NFSv4.1
   clients and servers will be unable to handle a string that long.
   IANA should reject any assignment request with a named attribute that
   exceeds 128 UTF-8 characters.  To give the IESG the flexibility to
   set up bases of assignment of Experimental Use and Standards Action,
   the prefixes of "EXPE" and "STDS" are Reserved.  The named attribute
   with a zero-length name is Reserved.

   The prefix "PRIV" is designated for Private Use. A site that wants to
   make use of unregistered named attributes without risk of conflicting
   with an assignment in IANA's registry should use the prefix "PRIV" in
   all of its named attributes.

   Because some NFSv4.1 clients and servers have case-insensitive



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   semantics, the fifteen additional lower case and mixed case
   permutations of each of "EXPE", "PRIV", and "STDS" are Reserved
   (e.g., "expe", "expE", "exPe", etc. are Reserved).  Similarly, IANA
   must not allow two assignments that would conflict if both named
   attributes were converted to a common case.

   The registry of named attributes is a list of assignments, each
   containing three fields for each assignment.

   1.  A US-ASCII string name that is the actual name of the attribute.
       This name must be unique.  This string name can be 1 to 128 UTF-8
       characters long.

   2.  A reference to the specification of the named attribute.  The
       reference can consume up to 256 bytes (or more if IANA permits).

   3.  The point of contact of the registrant.  The point of contact can
       consume up to 256 bytes (or more if IANA permits).

22.1.1.  Initial Registry

   There is no initial registry.

22.1.2.  Updating Registrations

   The registrant is always permitted to update the point of contact
   field.  Any other change will require Expert Review or IESG Approval.

22.2.  Device ID Notifications

   IANA created a registry called the "NFSv4 Device ID Notifications
   Registry".

   The potential exists for new notification types to be added to the
   CB_NOTIFY_DEVICEID operation (see Section 20.12).  This can be done
   via changes to the operations that register notifications, or by
   adding new operations to NFSv4.  This requires a new minor version of
   NFSv4, and requires a Standards Track document from the IETF.
   Another way to add a notification is to specify a new layout type
   (see Section 22.4).

   Hence, all assignments to the registry are made on a Standards Action
   basis per Section 4.1 of [55], with Expert Review required.

   The registry is a list of assignments, each containing five fields
   per assignment.





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   1.  The name of the notification type.  This name must have the
       prefix "NOTIFY_DEVICEID4_".  This name must be unique.

   2.  The value of the notification.  IANA will assign this number, and
       the request from the registrant will use TBD1 instead of an
       actual value.  IANA MUST use a whole number that can be no higher
       than 2^32-1, and should be the next available value.  The value
       assigned must be unique.  A Designated Expert must be used to
       ensure that when the name of the notification type and its value
       are added to the NFSv4.1 notify_deviceid_type4 enumerated data
       type in the NFSv4.1 XDR description ([13]), the result continues
       to be a valid XDR description.

   3.  The Standards Track RFC(s) that describe the notification.  If
       the RFC(s) have not yet been published, the registrant will use
       RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.

   4.  How the RFC introduces the notification.  This is indicated by a
       single US-ASCII value.  If the value is N, it means a minor
       revision to the NFSv4 protocol.  If the value is L, it means a
       new pNFS layout type.  Other values can be used with IESG
       Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       notification.  While these are numeric values, IANA will not
       allocate and assign them; the author of the relevant RFCs with
       IESG Approval assigns these numbers.  Each time there is a new
       minor version of NFSv4 approved, a Designated Expert should
       review the registry to make recommended updates as needed.

22.2.1.  Initial Registry

   The initial registry is in Table 16.  Note that the next available
   value is zero.

   +-------------------------+-------+---------+-----+----------------+
   | Notification Name       | Value | RFC     | How | Minor Versions |
   +-------------------------+-------+---------+-----+----------------+
   | NOTIFY_DEVICEID4_CHANGE | 1     | RFC5661 | N   | 1              |
   | NOTIFY_DEVICEID4_DELETE | 2     | RFC5661 | N   | 1              |
   +-------------------------+-------+---------+-----+----------------+

           Table 16: Initial Device ID Notification Assignments








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22.2.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.

22.3.  Object Recall Types

   IANA created a registry called the "NFSv4 Recallable Object Types
   Registry".

   The potential exists for new object types to be added to the
   CB_RECALL_ANY operation (see Section 20.6).  This can be done via
   changes to the operations that add recallable types, or by adding new
   operations to NFSv4.  This requires a new minor version of NFSv4, and
   requires a Standards Track document from IETF.  Another way to add a
   new recallable object is to specify a new layout type (see
   Section 22.4).

   All assignments to the registry are made on a Standards Action basis
   per Section 4.1 of [55], with Expert Review required.

   Recallable object types are 32-bit unsigned numbers.  There are no
   Reserved values.  Values in the range 12 through 15, inclusive, are
   designated for Private Use.

   The registry is a list of assignments, each containing five fields
   per assignment.

   1.  The name of the recallable object type.  This name must have the
       prefix "RCA4_TYPE_MASK_".  The name must be unique.

   2.  The value of the recallable object type.  IANA will assign this
       number, and the request from the registrant will use TBD1 instead
       of an actual value.  IANA MUST use a whole number that can be no
       higher than 2^32-1, and should be the next available value.  The
       value must be unique.  A Designated Expert must be used to ensure
       that when the name of the recallable type and its value are added
       to the NFSv4 XDR description [13], the result continues to be a
       valid XDR description.

   3.  The Standards Track RFC(s) that describe the recallable object
       type.  If the RFC(s) have not yet been published, the registrant
       will use RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.

   4.  How the RFC introduces the recallable object type.  This is
       indicated by a single US-ASCII value.  If the value is N, it
       means a minor revision to the NFSv4 protocol.  If the value is L,
       it means a new pNFS layout type.  Other values can be used with



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       IESG Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       recallable object type.  While these are numeric values, IANA
       will not allocate and assign them; the author of the relevant
       RFCs with IESG Approval assigns these numbers.  Each time there
       is a new minor version of NFSv4 approved, a Designated Expert
       should review the registry to make recommended updates as needed.

22.3.1.  Initial Registry

   The initial registry is in Table 17.  Note that the next available
   value is five.

   +-------------------------------+-------+--------+-----+------------+
   | Recallable Object Type Name   | Value | RFC    | How | Minor      |
   |                               |       |        |     | Versions   |
   +-------------------------------+-------+--------+-----+------------+
   | RCA4_TYPE_MASK_RDATA_DLG      | 0     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_WDATA_DLG      | 1     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_DIR_DLG        | 2     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_FILE_LAYOUT    | 3     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_BLK_LAYOUT     | 4     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_OBJ_LAYOUT_MIN | 8     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_OBJ_LAYOUT_MAX | 9     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   +-------------------------------+-------+--------+-----+------------+

           Table 17: Initial Recallable Object Type Assignments

22.3.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.

22.4.  Layout Types

   IANA created a registry called the "pNFS Layout Types Registry".

   All assignments to the registry are made on a Standards Action basis,
   with Expert Review required.




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   Layout types are 32-bit numbers.  The value zero is Reserved.  Values
   in the range 0x80000000 to 0xFFFFFFFF inclusive are designated for
   Private Use. IANA will assign numbers from the range 0x00000001 to
   0x7FFFFFFF inclusive.

   The registry is a list of assignments, each containing five fields.

   1.  The name of the layout type.  This name must have the prefix
       "LAYOUT4_".  The name must be unique.

   2.  The value of the layout type.  IANA will assign this number, and
       the request from the registrant will use TBD1 instead of an
       actual value.  The value assigned must be unique.  A Designated
       Expert must be used to ensure that when the name of the layout
       type and its value are added to the NFSv4.1 layouttype4
       enumerated data type in the NFSv4.1 XDR description ([13]), the
       result continues to be a valid XDR description.

   3.  The Standards Track RFC(s) that describe the notification.  If
       the RFC(s) have not yet been published, the registrant will use
       RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.
       Collectively, the RFC(s) must adhere to the guidelines listed in
       Section 22.4.3.

   4.  How the RFC introduces the layout type.  This is indicated by a
       single US-ASCII value.  If the value is N, it means a minor
       revision to the NFSv4 protocol.  If the value is L, it means a
       new pNFS layout type.  Other values can be used with IESG
       Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       notification.  While these are numeric values, IANA will not
       allocate and assign them; the author of the relevant RFCs with
       IESG Approval assigns these numbers.  Each time there is a new
       minor version of NFSv4 approved, a Designated Expert should
       review the registry to make recommended updates as needed.

22.4.1.  Initial Registry

   The initial registry is in Table 18.











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    +-----------------------+-------+----------+-----+----------------+
    | Layout Type Name      | Value | RFC      | How | Minor Versions |
    +-----------------------+-------+----------+-----+----------------+
    | LAYOUT4_NFSV4_1_FILES | 0x1   | RFC 5661 | N   | 1              |
    | LAYOUT4_OSD2_OBJECTS  | 0x2   | RFC 5664 | L   | 1              |
    | LAYOUT4_BLOCK_VOLUME  | 0x3   | RFC 5663 | L   | 1              |
    +-----------------------+-------+----------+-----+----------------+

                 Table 18: Initial Layout Type Assignments

22.4.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.

22.4.3.  Guidelines for Writing Layout Type Specifications

   The author of a new pNFS layout specification must follow these steps
   to obtain acceptance of the layout type as a Standards Track RFC:

   1.  The author devises the new layout specification.

   2.  The new layout type specification MUST, at a minimum:

       *  Define the contents of the layout-type-specific fields of the
          following data types:

          +  the da_addr_body field of the device_addr4 data type;

          +  the loh_body field of the layouthint4 data type;

          +  the loc_body field of layout_content4 data type (which in
             turn is the lo_content field of the layout4 data type);

          +  the lou_body field of the layoutupdate4 data type;

       *  Describe or define the storage access protocol used to access
          the storage devices.

       *  Describe whether revocation of layouts is supported.

       *  At a minimum, describe the methods of recovery from:

          1.  Failure and restart for client, server, storage device.

          2.  Lease expiration from perspective of the active client,
              server, storage device.




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          3.  Loss of layout state resulting in fencing of client access
              to storage devices (for an example, see Section 12.7.3).

       *  Include an IANA considerations section, which will in turn
          include:

          +  A request to IANA for a new layout type per Section 22.4.

          +  A list of requests to IANA for any new recallable object
             types for CB_RECALL_ANY; each entry is to be presented in
             the form described in Section 22.3.

          +  A list of requests to IANA for any new notification values
             for CB_NOTIFY_DEVICEID; each entry is to be presented in
             the form described in Section 22.2.

       *  Include a security considerations section.  This section MUST
          explain how the NFSv4.1 authentication, authorization, and
          access-control models are preserved.  That is, if a metadata
          server would restrict a READ or WRITE operation, how would
          pNFS via the layout similarly restrict a corresponding input
          or output operation?

   3.  The author documents the new layout specification as an Internet-
       Draft.

   4.  The author submits the Internet-Draft for review through the IETF
       standards process as defined in "The Internet Standards Process--
       Revision 3" (BCP 9).  The new layout specification will be
       submitted for eventual publication as a Standards Track RFC.

   5.  The layout specification progresses through the IETF standards
       process.

22.5.  Path Variable Definitions

   This section deals with the IANA considerations associated with the
   variable substitution feature for location names as described in
   Section 11.10.3.  As described there, variables subject to
   substitution consist of a domain name and a specific name within that
   domain, with the two separated by a colon.  There are two sets of
   IANA considerations here:

   1.  The list of variable names.

   2.  For each variable name, the list of possible values.

   Thus, there will be one registry for the list of variable names, and



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   possibly one registry for listing the values of each variable name.

22.5.1.  Path Variables Registry

   IANA created a registry called the "NFSv4 Path Variables Registry".

22.5.1.1.  Path Variable Values

   Variable names are of the form "${", followed by a domain name,
   followed by a colon (":"), followed by a domain-specific portion of
   the variable name, followed by "}".  When the domain name is
   "ietf.org", all variables names must be registered with IANA on a
   Standards Action basis, with Expert Review required.  Path variables
   with registered domain names neither part of nor equal to ietf.org
   are assigned on a Hierarchical Allocation basis (delegating to the
   domain owner) and thus of no concern to IANA, unless the domain owner
   chooses to register a variable name from his domain.  If the domain
   owner chooses to do so, IANA will do so on a First Come First Serve
   basis.  To accommodate registrants who do not have their own domain,
   IANA will accept requests to register variables with the prefix
   "${FCFS.ietf.org:" on a First Come First Served basis.  Assignments
   on a First Come First Basis do not require Expert Review, unless the
   registrant also wants IANA to establish a registry for the values of
   the registered variable.

   The registry is a list of assignments, each containing three fields.

   1.  The name of the variable.  The name of this variable must start
       with a "${" followed by a registered domain name, followed by
       ":", or it must start with "${FCFS.ietf.org".  The name must be
       no more than 64 UTF-8 characters long.  The name must be unique.

   2.  For assignments made on Standards Action basis, the Standards
       Track RFC(s) that describe the variable.  If the RFC(s) have not
       yet been published, the registrant will use RFCTBD1, RFCTBD2,
       etc. instead of an actual RFC number.  Note that the RFCs do not
       have to be a part of an NFS minor version.  For assignments made
       on a First Come First Serve basis, an explanation (consuming no
       more than 1024 bytes, or more if IANA permits) of the purpose of
       the variable.  A reference to the explanation can be substituted.

   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).
       For assignments made on a Standards Action basis, the point of
       contact is always IESG.






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22.5.1.1.1.  Initial Registry

   The initial registry is in Table 19.

         +------------------------+----------+------------------+
         | Variable Name          | RFC      | Point of Contact |
         +------------------------+----------+------------------+
         | ${ietf.org:CPU_ARCH}   | RFC 5661 | IESG             |
         | ${ietf.org:OS_TYPE}    | RFC 5661 | IESG             |
         | ${ietf.org:OS_VERSION} | RFC 5661 | IESG             |
         +------------------------+----------+------------------+

                 Table 19: Initial List of Path Variables

   IANA has created registries for the values of the variable names
   ${ietf.org:CPU_ARCH} and ${ietf.org:OS_TYPE}.  See Sections 22.5.2
   and 22.5.3.

   For the values of the variable ${ietf.org:OS_VERSION}, no registry is
   needed as the specifics of the values of the variable will vary with
   the value of ${ietf.org:OS_TYPE}.  Thus, values for ${ietf.org:
   OS_VERSION} are on a Hierarchical Allocation basis and are of no
   concern to IANA.

22.5.1.1.2.  Updating Registrations

   The update of an assignment made on a Standards Action basis will
   require IESG Approval on the advice of a Designated Expert.

   The registrant can always update the point of contact of an
   assignment made on a First Come First Serve basis.  Any other update
   will require Expert Review.

22.5.2.  Values for the ${ietf.org:CPU_ARCH} Variable

   IANA created a registry called the "NFSv4 ${ietf.org:CPU_ARCH} Value
   Registry".

   Assignments to the registry are made on a First Come First Serve
   basis.  The zero-length value of ${ietf.org:CPU_ARCH} is Reserved.
   Values with a prefix of "PRIV" are designated for Private Use.

   The registry is a list of assignments, each containing three fields.

   1.  A value of the ${ietf.org:CPU_ARCH} variable.  The value must be
       1 to 32 UTF-8 characters long.  The value must be unique.





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   2.  An explanation (consuming no more than 1024 bytes, or more if
       IANA permits) of what CPU architecture the value denotes.  A
       reference to the explanation can be substituted.

   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).

22.5.2.1.  Initial Registry

   There is no initial registry.

22.5.2.2.  Updating Registrations

   The registrant is free to update the assignment, i.e., change the
   explanation and/or point-of-contact fields.

22.5.3.  Values for the ${ietf.org:OS_TYPE} Variable

   IANA created a registry called the "NFSv4 ${ietf.org:OS_TYPE} Value
   Registry".

   Assignments to the registry are made on a First Come First Serve
   basis.  The zero-length value of ${ietf.org:OS_TYPE} is Reserved.
   Values with a prefix of "PRIV" are designated for Private Use.

   The registry is a list of assignments, each containing three fields.

   1.  A value of the ${ietf.org:OS_TYPE} variable.  The value must be 1
       to 32 UTF-8 characters long.  The value must be unique.

   2.  An explanation (consuming no more than 1024 bytes, or more if
       IANA permits) of what CPU architecture the value denotes.  A
       reference to the explanation can be substituted.

   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).

22.5.3.1.  Initial Registry

   There is no initial registry.

22.5.3.2.  Updating Registrations

   The registrant is free to update the assignment, i.e., change the
   explanation and/or point of contact fields.

23.  References




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23.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Eisler, M., Ed., "XDR: External Data Representation Standard",
         STD 67, RFC 4506, May 2006.

   [3]   Thurlow, R., "RPC: Remote Procedure Call Protocol Specification
         Version 2", RFC 5531, May 2009.

   [4]   Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
         Specification", RFC 2203, September 1997.

   [5]   Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos Version
         5 Generic Security Service Application Program Interface (GSS-
         API) Mechanism Version 2", RFC 4121, July 2005.

   [6]   The Open Group, "Section 3.191 of Chapter 3 of Base Definitions
         of The Open Group Base Specifications Issue 6 IEEE Std 1003.1,
         2004 Edition, HTML Version (www.opengroup.org), ISBN
         1931624232", 2004.

   [7]   Linn, J., "Generic Security Service Application Program
         Interface Version 2, Update 1", RFC 2743, January 2000.

   [8]   Talpey, T. and B. Callaghan, "Remote Direct Memory Access
         Transport for Remote Procedure Call", RFC 5666, October 2009.

   [9]   Talpey, T. and B. Callaghan, "Network File System (NFS) Direct
         Data Placement", RFC 5667, January 2010.

   [10]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D. Garcia,
         "A Remote Direct Memory Access Protocol Specification",
         RFC 5040, October 2007.

   [11]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
         for Message Authentication", RFC 2104, February 1997.

   [12]  Eisler, M., "RPCSEC_GSS Version 2", RFC 5403, February 2009.

   [13]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., "Network
         File System (NFS) Version 4 Minor Version 1 External Data
         Representation Standard (XDR) Description", RFC 5662,
         January 2010.

   [14]  The Open Group, "Section 3.372 of Chapter 3 of Base Definitions
         of The Open Group Base Specifications Issue 6 IEEE Std 1003.1,



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         2004 Edition, HTML Version (www.opengroup.org), ISBN
         1931624232", 2004.

   [15]  Eisler, M., "IANA Considerations for Remote Procedure Call
         (RPC) Network Identifiers and Universal Address Formats",
         RFC 5665, January 2010.

   [16]  The Open Group, "Section 'read()' of System Interfaces of The
         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [17]  The Open Group, "Section 'readdir()' of System Interfaces of
         The Open Group Base Specifications Issue 6 IEEE Std 1003.1,
         2004 Edition, HTML Version (www.opengroup.org), ISBN
         1931624232", 2004.

   [18]  The Open Group, "Section 'write()' of System Interfaces of The
         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [19]  Hoffman, P. and M. Blanchet, "Preparation of Internationalized
         Strings ("stringprep")", RFC 3454, December 2002.

   [20]  The Open Group, "Section 'chmod()' of System Interfaces of The
         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [21]  International Organization for Standardization, "Information
         Technology - Universal Multiple-octet coded Character Set (UCS)
         - Part 1: Architecture and Basic Multilingual Plane",
         ISO Standard 10646-1, May 1993.

   [22]  Alvestrand, H., "IETF Policy on Character Sets and Languages",
         BCP 18, RFC 2277, January 1998.

   [23]  Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile
         for Internationalized Domain Names (IDN)", RFC 3491,
         March 2003.

   [24]  The Open Group, "Section 'fcntl()' of System Interfaces of The
         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [25]  The Open Group, "Section 'fsync()' of System Interfaces of The



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         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [26]  The Open Group, "Section 'getpwnam()' of System Interfaces of
         The Open Group Base Specifications Issue 6 IEEE Std 1003.1,
         2004 Edition, HTML Version (www.opengroup.org), ISBN
         1931624232", 2004.

   [27]  The Open Group, "Section 'unlink()' of System Interfaces of The
         Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004
         Edition, HTML Version (www.opengroup.org), ISBN 1931624232",
         2004.

   [28]  Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms
         and Identifiers for RSA Cryptography for use in the Internet
         X.509 Public Key Infrastructure Certificate and Certificate
         Revocation List (CRL) Profile", RFC 4055, June 2005.

   [29]  National Institute of Standards and Technology, "Cryptographic
         Algorithm Object Registration", URL http://csrc.nist.gov/
         groups/ST/crypto_apps_infra/csor/algorithms.html,
         November 2007.

23.2.  Informative References

   [30]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., Beame,
         C., Eisler, M., and D. Noveck, "Network File System (NFS)
         version 4 Protocol", RFC 3530, April 2003.

   [31]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS Version 3
         Protocol Specification", RFC 1813, June 1995.

   [32]  Eisler, M., "LIPKEY - A Low Infrastructure Public Key Mechanism
         Using SPKM", RFC 2847, June 2000.

   [33]  Eisler, M., "NFS Version 2 and Version 3 Security Issues and
         the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
         RFC 2623, June 1999.

   [34]  Juszczak, C., "Improving the Performance and Correctness of an
         NFS Server", USENIX Conference Proceedings , June 1990.

   [35]  Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced by
         an On-line Database", RFC 3232, January 2002.

   [36]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
         RFC 1833, August 1995.



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   [37]  Werme, R., "RPC XID Issues", USENIX Conference Proceedings ,
         February 1996.

   [38]  Nowicki, B., "NFS: Network File System Protocol specification",
         RFC 1094, March 1989.

   [39]  Bhide, A., Elnozahy, E., and S. Morgan, "A Highly Available
         Network Server", USENIX Conference Proceedings , January 1991.

   [40]  Halevy, B., Welch, B., and J. Zelenka, "Object-Based Parallel
         NFS (pNFS) Operations", RFC 5664, January 2010.

   [41]  Black, D., Glasgow, J., and S. Fridella, "Parallel NFS (pNFS)
         Block/Volume Layout", RFC 5663, January 2010.

   [42]  Callaghan, B., "WebNFS Client Specification", RFC 2054,
         October 1996.

   [43]  Callaghan, B., "WebNFS Server Specification", RFC 2055,
         October 1996.

   [44]  IESG, "IESG Processing of RFC Errata for the IETF Stream",
         July 2008.

   [45]  Shepler, S., "NFS Version 4 Design Considerations", RFC 2624,
         June 1999.

   [46]  The Open Group, "Protocols for Interworking: XNFS, Version 3W,
         ISBN 1-85912-184-5", February 1998.

   [47]  Floyd, S. and V. Jacobson, "The Synchronization of Periodic
         Routing Messages", IEEE/ACM Transactions on Networking 2(2),
         pp. 122-136, April 1994.

   [48]  Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M., and E.
         Zeidner, "Internet Small Computer Systems Interface (iSCSI)",
         RFC 3720, April 2004.

   [49]  Snively, R., "Fibre Channel Protocol for SCSI, 2nd Version
         (FCP-2)", ANSI/INCITS 350-2003, Oct 2003.

   [50]  Weber, R., "Object-Based Storage Device Commands (OSD)", ANSI/
         INCITS 400-2004, July 2004,
         <http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf>.

   [51]  Carns, P., Ligon III, W., Ross, R., and R. Thakur, "PVFS: A
         Parallel File System for Linux Clusters.", Proceedings of the
         4th Annual Linux Showcase and Conference , 2000.



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   [52]  The Open Group, "The Open Group Base Specifications Issue 6,
         IEEE Std 1003.1, 2004 Edition", 2004.

   [53]  Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.

   [54]  Chiu, A., Eisler, M., and B. Callaghan, "Security Negotiation
         for WebNFS", RFC 2755, January 2000.

   [55]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
         Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.

Appendix A.  Acknowledgments

   The initial text for the SECINFO extensions were edited by Mike
   Eisler with contributions from Peng Dai, Sergey Klyushin, and Carl
   Burnett.

   The initial text for the SESSIONS extensions were edited by Tom
   Talpey, Spencer Shepler, Jon Bauman with contributions from Charles
   Antonelli, Brent Callaghan, Mike Eisler, John Howard, Chet Juszczak,
   Trond Myklebust, Dave Noveck, John Scott, Mike Stolarchuk, and Mark
   Wittle.

   Initial text relating to multi-server namespace features, including
   the concept of referrals, were contributed by Dave Noveck, Carl
   Burnett, and Charles Fan with contributions from Ted Anderson, Neil
   Brown, and Jon Haswell.

   The initial text for the Directory Delegations support were
   contributed by Saadia Khan with input from Dave Noveck, Mike Eisler,
   Carl Burnett, Ted Anderson, and Tom Talpey.

   The initial text for the ACL explanations were contributed by Sam
   Falkner and Lisa Week.

   The pNFS work was inspired by the NASD and OSD work done by Garth
   Gibson.  Gary Grider has also been a champion of high-performance
   parallel I/O. Garth Gibson and Peter Corbett started the pNFS effort
   with a problem statement document for the IETF that formed the basis
   for the pNFS work in NFSv4.1.

   The initial text for the parallel NFS support was edited by Brent
   Welch and Garth Goodson.  Additional authors for those documents were
   Benny Halevy, David Black, and Andy Adamson.  Additional input came
   from the informal group that contributed to the construction of the
   initial pNFS drafts; specific acknowledgment goes to Gary Grider,
   Peter Corbett, Dave Noveck, Peter Honeyman, and Stephen Fridella.




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   Fredric Isaman found several errors in draft versions of the ONC RPC
   XDR description of the NFSv4.1 protocol.

   Audrey Van Belleghem provided, in numerous ways, essential co-
   ordination and management of the process of editing the specification
   documents.

   Richard Jernigan gave feedback on the file layout's striping pattern
   design.

   Several formal inspection teams were formed to review various areas
   of the protocol.  All the inspections found significant errors and
   room for improvement.  NFSv4.1's inspection teams were:

   o  ACLs, with the following inspectors: Sam Falkner, Bruce Fields,
      Rahul Iyer, Saadia Khan, Dave Noveck, Lisa Week, Mario Wurzl, and
      Alan Yoder.

   o  Sessions, with the following inspectors: William Brown, Tom
      Doeppner, Robert Gordon, Benny Halevy, Fredric Isaman, Rick
      Macklem, Trond Myklebust, Dave Noveck, Karen Rochford, John Scott,
      and Peter Shah.

   o  Initial pNFS inspection, with the following inspectors: Andy
      Adamson, David Black, Mike Eisler, Marc Eshel, Sam Falkner, Garth
      Goodson, Benny Halevy, Rahul Iyer, Trond Myklebust, Spencer
      Shepler, and Lisa Week.

   o  Global namespace, with the following inspectors: Mike Eisler, Dan
      Ellard, Craig Everhart, Fredric Isaman, Trond Myklebust, Dave
      Noveck, Theresa Raj, Spencer Shepler, Renu Tewari, and Robert
      Thurlow.

   o  NFSv4.1 file layout type, with the following inspectors: Andy
      Adamson, Marc Eshel, Sam Falkner, Garth Goodson, Rahul Iyer, Trond
      Myklebust, and Lisa Week.

   o  NFSv4.1 locking and directory delegations, with the following
      inspectors: Mike Eisler, Pranoop Erasani, Robert Gordon, Saadia
      Khan, Eric Kustarz, Dave Noveck, Spencer Shepler, and Amy Weaver.

   o  EXCHANGE_ID and DESTROY_CLIENTID, with the following inspectors:
      Mike Eisler, Pranoop Erasani, Robert Gordon, Benny Halevy, Fredric
      Isaman, Saadia Khan, Ricardo Labiaga, Rick Macklem, Trond
      Myklebust, Spencer Shepler, and Brent Welch.

   o  Final pNFS inspection, with the following inspectors: Andy
      Adamson, Mike Eisler, Mark Eshel, Sam Falkner, Jason Glasgow,



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      Garth Goodson, Robert Gordon, Benny Halevy, Dean Hildebrand, Rahul
      Iyer, Suchit Kaura, Trond Myklebust, Anatoly Pinchuk, Spencer
      Shepler, Renu Tewari, Lisa Week, and Brent Welch.

   A review team worked together to generate the tables of assignments
   of error sets to operations and make sure that each such assignment
   had two or more people validating it.  Participating in the process
   were Andy Adamson, Mike Eisler, Sam Falkner, Garth Goodson, Robert
   Gordon, Trond Myklebust, Dave Noveck, Spencer Shepler, Tom Talpey,
   Amy Weaver, and Lisa Week.

   Jari Arkko, David Black, Scott Bradner, Lisa Dusseault, Lars Eggert,
   Chris Newman, and Tim Polk provided valuable review and guidance.

   Olga Kornievskaia found several errors in the SSV specification.

   Ricardo Labiaga found several places where the use of RPCSEC_GSS was
   underspecified.

   Those who provided miscellaneous comments include: Andy Adamson,
   Sunil Bhargo, Alex Burlyga, Pranoop Erasani, Bruce Fields, Vadim
   Finkelstein, Jason Goldschmidt, Vijay K. Gurbani, Sergey Klyushin,
   Ricardo Labiaga, James Lentini, Anshul Madan, Daniel Muntz, Daniel
   Picken, Archana Ramani, Jim Rees, Mahesh Siddheshwar, Tom Talpey, and
   Peter Varga.

Authors' Addresses

   Spencer Shepler (editor)
   Storspeed, Inc.
   7808 Moonflower Drive
   Austin, TX  78750
   USA

   Phone: +1-512-402-5811 ext 8530
   EMail: shepler@xxxxxxxxxxxxx


   Mike Eisler (editor)
   NetApp
   5765 Chase Point Circle
   Colorado Springs, CO  80919
   USA

   Phone: +1-719-599-9026
   EMail: mike@xxxxxxxxxx
   URI:   http://www.eisler.com




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   David Noveck (editor)
   NetApp
   1601 Trapelo Road, Suite 16
   Waltham, MA  02451
   USA

   Phone: +1-781-768-5347
   EMail: dnoveck@xxxxxxxxxx











































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Internet Engineering Task Force (IETF)                   S. Shepler, Ed.
Request for Comments: 5661                               Storspeed, Inc.
Category: Standards Track                                 M. Eisler, Ed.
ISSN: 2070-1721                                           D. Noveck, Ed.
                                                                  NetApp
                                                            January 2010


      Network File System (NFS) Version 4 Minor Version 1 Protocol

Abstract

   This document describes the Network File System (NFS) version 4 minor
   version 1, including features retained from the base protocol (NFS
   version 4 minor version 0, which is specified in RFC 3530) and
   protocol extensions made subsequently.  Major extensions introduced
   in NFS version 4 minor version 1 include Sessions, Directory
   Delegations, and parallel NFS (pNFS).  NFS version 4 minor version 1
   has no dependencies on NFS version 4 minor version 0, and it is
   considered a separate protocol.  Thus, this document neither updates
   nor obsoletes RFC 3530.  NFS minor version 1 is deemed superior to
   NFS minor version 0 with no loss of functionality, and its use is
   preferred over version 0.  Both NFS minor versions 0 and 1 can be
   used simultaneously on the same network, between the same client and
   server.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5661.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.1.  The NFS Version 4 Minor Version 1 Protocol  . . . . . . .   7
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   7
     1.3.  Scope of This Document  . . . . . . . . . . . . . . . . .   7
     1.4.  NFSv4 Goals . . . . . . . . . . . . . . . . . . . . . . .   8
     1.5.  NFSv4.1 Goals . . . . . . . . . . . . . . . . . . . . . .   8
     1.6.  General Definitions . . . . . . . . . . . . . . . . . . .   9
     1.7.  Overview of NFSv4.1 Features  . . . . . . . . . . . . . .  11
     1.8.  Differences from NFSv4.0  . . . . . . . . . . . . . . . .  15
   2.  Core Infrastructure . . . . . . . . . . . . . . . . . . . . .  16
     2.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .  16
     2.2.  RPC and XDR . . . . . . . . . . . . . . . . . . . . . . .  17
     2.3.  COMPOUND and CB_COMPOUND  . . . . . . . . . . . . . . . .  20
     2.4.  Client Identifiers and Client Owners  . . . . . . . . . .  21
     2.5.  Server Owners . . . . . . . . . . . . . . . . . . . . . .  26
     2.6.  Security Service Negotiation  . . . . . . . . . . . . . .  27
     2.7.  Minor Versioning  . . . . . . . . . . . . . . . . . . . .  32
     2.8.  Non-RPC-Based Security Services . . . . . . . . . . . . .  34
     2.9.  Transport Layers  . . . . . . . . . . . . . . . . . . . .  35
     2.10. Session . . . . . . . . . . . . . . . . . . . . . . . . .  38
   3.  Protocol Constants and Data Types . . . . . . . . . . . . . .  84
     3.1.  Basic Constants . . . . . . . . . . . . . . . . . . . . .  84
     3.2.  Basic Data Types  . . . . . . . . . . . . . . . . . . . .  85
     3.3.  Structured Data Types . . . . . . . . . . . . . . . . . .  87
   4.  Filehandles . . . . . . . . . . . . . . . . . . . . . . . . .  95
     4.1.  Obtaining the First Filehandle  . . . . . . . . . . . . .  96
     4.2.  Filehandle Types  . . . . . . . . . . . . . . . . . . . .  97
     4.3.  One Method of Constructing a Volatile Filehandle  . . . .  99
     4.4.  Client Recovery from Filehandle Expiration  . . . . . . . 100
   5.  File Attributes . . . . . . . . . . . . . . . . . . . . . . . 101
     5.1.  REQUIRED Attributes . . . . . . . . . . . . . . . . . . . 102
     5.2.  RECOMMENDED Attributes  . . . . . . . . . . . . . . . . . 102
     5.3.  Named Attributes  . . . . . . . . . . . . . . . . . . . . 103
     5.4.  Classification of Attributes  . . . . . . . . . . . . . . 104
     5.5.  Set-Only and Get-Only Attributes  . . . . . . . . . . . . 105
     5.6.  REQUIRED Attributes - List and Definition References  . . 105
     5.7.  RECOMMENDED Attributes - List and Definition References . 106
     5.8.  Attribute        Definitions  . . . . . . . . . . . . . . 108
     5.9.  Interpreting owner and owner_group  . . . . . . . . . . . 117



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     5.10. Character Case Attributes . . . . . . . . . . . . . . . . 119
     5.11. Directory Notification Attributes . . . . . . . . . . . . 119
     5.12. pNFS Attribute Definitions  . . . . . . . . . . . . . . . 120
     5.13. Retention Attributes  . . . . . . . . . . . . . . . . . . 121
   6.  Access Control Attributes . . . . . . . . . . . . . . . . . . 124
     6.1.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 124
     6.2.  File Attributes Discussion  . . . . . . . . . . . . . . . 125
     6.3.  Common Methods  . . . . . . . . . . . . . . . . . . . . . 142
     6.4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . 144
   7.  Single-Server Namespace . . . . . . . . . . . . . . . . . . . 151
     7.1.  Server Exports  . . . . . . . . . . . . . . . . . . . . . 151
     7.2.  Browsing Exports  . . . . . . . . . . . . . . . . . . . . 151
     7.3.  Server Pseudo File System . . . . . . . . . . . . . . . . 152
     7.4.  Multiple Roots  . . . . . . . . . . . . . . . . . . . . . 152
     7.5.  Filehandle Volatility . . . . . . . . . . . . . . . . . . 153
     7.6.  Exported Root . . . . . . . . . . . . . . . . . . . . . . 153
     7.7.  Mount Point Crossing  . . . . . . . . . . . . . . . . . . 153
     7.8.  Security Policy and Namespace Presentation  . . . . . . . 154
   8.  State Management  . . . . . . . . . . . . . . . . . . . . . . 155
     8.1.  Client and Session ID . . . . . . . . . . . . . . . . . . 156
     8.2.  Stateid Definition  . . . . . . . . . . . . . . . . . . . 156
     8.3.  Lease Renewal . . . . . . . . . . . . . . . . . . . . . . 165
     8.4.  Crash Recovery  . . . . . . . . . . . . . . . . . . . . . 167
     8.5.  Server Revocation of Locks  . . . . . . . . . . . . . . . 178
     8.6.  Short and Long Leases . . . . . . . . . . . . . . . . . . 179
     8.7.  Clocks, Propagation Delay, and Calculating Lease
           Expiration  . . . . . . . . . . . . . . . . . . . . . . . 180
     8.8.  Obsolete Locking Infrastructure from NFSv4.0  . . . . . . 180
   9.  File Locking and Share Reservations . . . . . . . . . . . . . 181
     9.1.  Opens and Byte-Range Locks  . . . . . . . . . . . . . . . 181
     9.2.  Lock Ranges . . . . . . . . . . . . . . . . . . . . . . . 185
     9.3.  Upgrading and Downgrading Locks . . . . . . . . . . . . . 186
     9.4.  Stateid Seqid Values and Byte-Range Locks . . . . . . . . 186
     9.5.  Issues with Multiple Open-Owners  . . . . . . . . . . . . 186
     9.6.  Blocking Locks  . . . . . . . . . . . . . . . . . . . . . 187
     9.7.  Share Reservations  . . . . . . . . . . . . . . . . . . . 188
     9.8.  OPEN/CLOSE Operations . . . . . . . . . . . . . . . . . . 189
     9.9.  Open Upgrade and Downgrade  . . . . . . . . . . . . . . . 190
     9.10. Parallel OPENs  . . . . . . . . . . . . . . . . . . . . . 191
     9.11. Reclaim of Open and Byte-Range Locks  . . . . . . . . . . 191
   10. Client-Side Caching . . . . . . . . . . . . . . . . . . . . . 192
     10.1.  Performance Challenges for Client-Side Caching . . . . . 192
     10.2.  Delegation and Callbacks . . . . . . . . . . . . . . . . 193
     10.3.  Data Caching . . . . . . . . . . . . . . . . . . . . . . 198
     10.4.  Open Delegation  . . . . . . . . . . . . . . . . . . . . 202
     10.5.  Data Caching and Revocation  . . . . . . . . . . . . . . 213
     10.6.  Attribute Caching  . . . . . . . . . . . . . . . . . . . 215
     10.7.  Data and Metadata Caching and Memory Mapped Files  . . . 217



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     10.8.  Name and Directory Caching without Directory Delegations 219
     10.9.  Directory Delegations  . . . . . . . . . . . . . . . . . 221
   11. Multi-Server Namespace  . . . . . . . . . . . . . . . . . . . 225
     11.1.  Location Attributes  . . . . . . . . . . . . . . . . . . 225
     11.2.  File System Presence or Absence  . . . . . . . . . . . . 225
     11.3.  Getting Attributes for an Absent File System . . . . . . 227
     11.4.  Uses of Location Information . . . . . . . . . . . . . . 229
     11.5.  Location Entries and Server Identity . . . . . . . . . . 233
     11.6.  Additional Client-Side Considerations  . . . . . . . . . 234
     11.7.  Effecting File System Transitions  . . . . . . . . . . . 234
     11.8.  Effecting File System Referrals  . . . . . . . . . . . . 248
     11.9.  The Attribute fs_locations . . . . . . . . . . . . . . . 254
     11.10. The Attribute fs_locations_info  . . . . . . . . . . . . 257
     11.11. The Attribute fs_status  . . . . . . . . . . . . . . . . 269
   12. Parallel NFS (pNFS) . . . . . . . . . . . . . . . . . . . . . 273
     12.1.  Introduction . . . . . . . . . . . . . . . . . . . . . . 273
     12.2.  pNFS Definitions . . . . . . . . . . . . . . . . . . . . 274
     12.3.  pNFS Operations  . . . . . . . . . . . . . . . . . . . . 280
     12.4.  pNFS Attributes  . . . . . . . . . . . . . . . . . . . . 281
     12.5.  Layout Semantics . . . . . . . . . . . . . . . . . . . . 281
     12.6.  pNFS Mechanics . . . . . . . . . . . . . . . . . . . . . 296
     12.7.  Recovery . . . . . . . . . . . . . . . . . . . . . . . . 298
     12.8.  Metadata and Storage Device Roles  . . . . . . . . . . . 303
     12.9.  Security Considerations for pNFS . . . . . . . . . . . . 303
   13. NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type . 305
     13.1.  Client ID and Session Considerations . . . . . . . . . . 305
     13.2.  File Layout Definitions  . . . . . . . . . . . . . . . . 308
     13.3.  File Layout Data Types . . . . . . . . . . . . . . . . . 308
     13.4.  Interpreting the File Layout . . . . . . . . . . . . . . 312
     13.5.  Data Server Multipathing . . . . . . . . . . . . . . . . 320
     13.6.  Operations Sent to NFSv4.1 Data Servers  . . . . . . . . 321
     13.7.  COMMIT through Metadata Server . . . . . . . . . . . . . 323
     13.8.  The Layout Iomode  . . . . . . . . . . . . . . . . . . . 324
     13.9.  Metadata and Data Server State Coordination  . . . . . . 325
     13.10. Data Server Component File Size  . . . . . . . . . . . . 328
     13.11. Layout Revocation and Fencing  . . . . . . . . . . . . . 328
     13.12. Security Considerations for the File Layout Type . . . . 329
   14. Internationalization  . . . . . . . . . . . . . . . . . . . . 330
     14.1.  Stringprep Profile for the utf8str_cs Type . . . . . . . 331
     14.2.  Stringprep Profile for the utf8str_cis Type  . . . . . . 333
     14.3.  Stringprep Profile for the utf8str_mixed Type  . . . . . 334
     14.4.  UTF-8 Capabilities . . . . . . . . . . . . . . . . . . . 336
     14.5.  UTF-8 Related Errors . . . . . . . . . . . . . . . . . . 336
   15. Error Values  . . . . . . . . . . . . . . . . . . . . . . . . 337
     15.1.  Error Definitions  . . . . . . . . . . . . . . . . . . . 337
     15.2.  Operations and Their Valid Errors  . . . . . . . . . . . 356
     15.3.  Callback Operations and Their Valid Errors . . . . . . . 372
     15.4.  Errors and the Operations That Use Them  . . . . . . . . 375



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   16. NFSv4.1 Procedures  . . . . . . . . . . . . . . . . . . . . . 390
     16.1.  Procedure 0: NULL - No Operation . . . . . . . . . . . . 390
     16.2.  Procedure 1: COMPOUND - Compound Operations  . . . . . . 390
   17. Operations: REQUIRED, RECOMMENDED, or OPTIONAL  . . . . . . . 402
   18. NFSv4.1 Operations  . . . . . . . . . . . . . . . . . . . . . 405
     18.1.  Operation 3: ACCESS - Check Access Rights  . . . . . . . 405
     18.2.  Operation 4: CLOSE - Close File  . . . . . . . . . . . . 411
     18.3.  Operation 5: COMMIT - Commit Cached Data . . . . . . . . 412
     18.4.  Operation 6: CREATE - Create a Non-Regular File Object . 415
     18.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting
            Recovery . . . . . . . . . . . . . . . . . . . . . . . . 418
     18.6.  Operation 8: DELEGRETURN - Return Delegation . . . . . . 419
     18.7.  Operation 9: GETATTR - Get Attributes  . . . . . . . . . 419
     18.8.  Operation 10: GETFH - Get Current Filehandle . . . . . . 421
     18.9.  Operation 11: LINK - Create Link to a File . . . . . . . 422
     18.10. Operation 12: LOCK - Create Lock . . . . . . . . . . . . 425
     18.11. Operation 13: LOCKT - Test for Lock  . . . . . . . . . . 430
     18.12. Operation 14: LOCKU - Unlock File  . . . . . . . . . . . 431
     18.13. Operation 15: LOOKUP - Lookup Filename . . . . . . . . . 433
     18.14. Operation 16: LOOKUPP - Lookup Parent Directory  . . . . 435
     18.15. Operation 17: NVERIFY - Verify Difference in Attributes  436
     18.16. Operation 18: OPEN - Open a Regular File . . . . . . . . 437
     18.17. Operation 19: OPENATTR - Open Named Attribute Directory  457
     18.18. Operation 21: OPEN_DOWNGRADE - Reduce Open File Access . 459
     18.19. Operation 22: PUTFH - Set Current Filehandle . . . . . . 460
     18.20. Operation 23: PUTPUBFH - Set   Public Filehandle . . . . 461
     18.21. Operation 24: PUTROOTFH - Set Root Filehandle  . . . . . 463
     18.22. Operation 25: READ - Read from File  . . . . . . . . . . 464
     18.23. Operation 26: READDIR - Read Directory . . . . . . . . . 466
     18.24. Operation 27: READLINK - Read Symbolic Link  . . . . . . 470
     18.25. Operation 28: REMOVE - Remove File System Object . . . . 471
     18.26. Operation 29: RENAME - Rename Directory Entry  . . . . . 474
     18.27. Operation 31: RESTOREFH - Restore Saved Filehandle . . . 477
     18.28. Operation 32: SAVEFH - Save Current Filehandle . . . . . 478
     18.29. Operation 33: SECINFO - Obtain Available Security  . . . 479
     18.30. Operation 34: SETATTR - Set Attributes . . . . . . . . . 483
     18.31. Operation 37: VERIFY - Verify Same Attributes  . . . . . 486
     18.32. Operation 38: WRITE - Write to File  . . . . . . . . . . 487
     18.33. Operation 40: BACKCHANNEL_CTL - Backchannel Control  . . 492
     18.34. Operation 41: BIND_CONN_TO_SESSION - Associate
            Connection with Session  . . . . . . . . . . . . . . . . 493
     18.35. Operation 42: EXCHANGE_ID - Instantiate Client ID  . . . 496
     18.36. Operation 43: CREATE_SESSION - Create New Session and
            Confirm Client ID  . . . . . . . . . . . . . . . . . . . 514
     18.37. Operation 44: DESTROY_SESSION - Destroy a Session  . . . 524
     18.38. Operation 45: FREE_STATEID - Free Stateid with No Locks  526
     18.39. Operation 46: GET_DIR_DELEGATION - Get a Directory
            Delegation . . . . . . . . . . . . . . . . . . . . . . . 527



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     18.40. Operation 47: GETDEVICEINFO - Get Device Information . . 531
     18.41. Operation 48: GETDEVICELIST - Get All Device Mappings
            for a File System  . . . . . . . . . . . . . . . . . . . 534
     18.42. Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a
            Layout . . . . . . . . . . . . . . . . . . . . . . . . . 535
     18.43. Operation 50: LAYOUTGET - Get Layout Information . . . . 539
     18.44. Operation 51: LAYOUTRETURN - Release Layout Information  549
     18.45. Operation 52: SECINFO_NO_NAME - Get Security on Unnamed
            Object . . . . . . . . . . . . . . . . . . . . . . . . . 554
     18.46. Operation 53: SEQUENCE - Supply Per-Procedure Sequencing
            and Control  . . . . . . . . . . . . . . . . . . . . . . 555
     18.47. Operation 54: SET_SSV - Update SSV for a Client ID . . . 561
     18.48. Operation 55: TEST_STATEID - Test Stateids for Validity  563
     18.49. Operation 56: WANT_DELEGATION - Request Delegation . . . 565
     18.50. Operation 57: DESTROY_CLIENTID - Destroy a Client ID . . 569
     18.51. Operation 58: RECLAIM_COMPLETE - Indicates Reclaims
            Finished . . . . . . . . . . . . . . . . . . . . . . . . 570
     18.52. Operation 10044: ILLEGAL - Illegal Operation . . . . . . 572
   19. NFSv4.1 Callback Procedures . . . . . . . . . . . . . . . . . 572
     19.1.  Procedure 0: CB_NULL - No Operation  . . . . . . . . . . 573
     19.2.  Procedure 1: CB_COMPOUND - Compound Operations . . . . . 573
   20. NFSv4.1 Callback Operations . . . . . . . . . . . . . . . . . 578
     20.1.  Operation 3: CB_GETATTR - Get Attributes . . . . . . . . 578
     20.2.  Operation 4: CB_RECALL - Recall a Delegation . . . . . . 579
     20.3.  Operation 5: CB_LAYOUTRECALL - Recall Layout from Client 580
     20.4.  Operation 6: CB_NOTIFY - Notify Client of Directory
            Changes  . . . . . . . . . . . . . . . . . . . . . . . . 583
     20.5.  Operation 7: CB_PUSH_DELEG - Offer Previously Requested
            Delegation to Client . . . . . . . . . . . . . . . . . . 587
     20.6.  Operation 8: CB_RECALL_ANY - Keep Any N Recallable
            Objects  . . . . . . . . . . . . . . . . . . . . . . . . 588
     20.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources
            for Recallable Objects . . . . . . . . . . . . . . . . . 591
     20.8.  Operation 10: CB_RECALL_SLOT - Change Flow Control
            Limits . . . . . . . . . . . . . . . . . . . . . . . . . 592
     20.9.  Operation 11: CB_SEQUENCE - Supply Backchannel
            Sequencing and Control . . . . . . . . . . . . . . . . . 593
     20.10. Operation 12: CB_WANTS_CANCELLED - Cancel Pending
            Delegation Wants . . . . . . . . . . . . . . . . . . . . 596
     20.11. Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible
            Lock Availability  . . . . . . . . . . . . . . . . . . . 597
     20.12. Operation 14: CB_NOTIFY_DEVICEID - Notify Client of
            Device ID Changes  . . . . . . . . . . . . . . . . . . . 598
     20.13. Operation 10044: CB_ILLEGAL - Illegal Callback Operation 600
   21. Security Considerations . . . . . . . . . . . . . . . . . . . 601
   22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 603
     22.1.  Named Attribute Definitions  . . . . . . . . . . . . . . 603
     22.2.  Device ID Notifications  . . . . . . . . . . . . . . . . 604



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     22.3.  Object Recall Types  . . . . . . . . . . . . . . . . . . 606
     22.4.  Layout Types . . . . . . . . . . . . . . . . . . . . . . 607
     22.5.  Path Variable Definitions  . . . . . . . . . . . . . . . 610
   23. References  . . . . . . . . . . . . . . . . . . . . . . . . . 613
     23.1.  Normative References . . . . . . . . . . . . . . . . . . 614
     23.2.  Informative References . . . . . . . . . . . . . . . . . 616
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . . 619
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 621

1.  Introduction

1.1.  The NFS Version 4 Minor Version 1 Protocol

   The NFS version 4 minor version 1 (NFSv4.1) protocol is the second
   minor version of the NFS version 4 (NFSv4) protocol.  The first minor
   version, NFSv4.0, is described in [30].  It generally follows the
   guidelines for minor versioning that are listed in Section 10 of RFC
   3530.  However, it diverges from guidelines 11 ("a client and server
   that support minor version X must support minor versions 0 through
   X-1") and 12 ("no new features may be introduced as mandatory in a
   minor version").  These divergences are due to the introduction of
   the sessions model for managing non-idempotent operations and the
   RECLAIM_COMPLETE operation.  These two new features are
   infrastructural in nature and simplify implementation of existing and
   other new features.  Making them anything but REQUIRED would add
   undue complexity to protocol definition and implementation.  NFSv4.1
   accordingly updates the minor versioning guidelines (Section 2.7).

   As a minor version, NFSv4.1 is consistent with the overall goals for
   NFSv4, but extends the protocol so as to better meet those goals,
   based on experiences with NFSv4.0.  In addition, NFSv4.1 has adopted
   some additional goals, which motivate some of the major extensions in
   NFSv4.1.

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

1.3.  Scope of This Document

   This document describes the NFSv4.1 protocol.  With respect to
   NFSv4.0, this document does not:

   o  describe the NFSv4.0 protocol, except where needed to contrast
      with NFSv4.1.




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   o  modify the specification of the NFSv4.0 protocol.

   o  clarify the NFSv4.0 protocol.

1.4.  NFSv4 Goals

   The NFSv4 protocol is a further revision of the NFS protocol defined
   already by NFSv3 [31].  It retains the essential characteristics of
   previous versions: easy recovery; independence of transport
   protocols, operating systems, and file systems; simplicity; and good
   performance.  NFSv4 has the following goals:

   o  Improved access and good performance on the Internet

      The protocol is designed to transit firewalls easily, perform well
      where latency is high and bandwidth is low, and scale to very
      large numbers of clients per server.

   o  Strong security with negotiation built into the protocol

      The protocol builds on the work of the ONCRPC working group in
      supporting the RPCSEC_GSS protocol.  Additionally, the NFSv4.1
      protocol provides a mechanism to allow clients and servers the
      ability to negotiate security and require clients and servers to
      support a minimal set of security schemes.

   o  Good cross-platform interoperability

      The protocol features a file system model that provides a useful,
      common set of features that does not unduly favor one file system
      or operating system over another.

   o  Designed for protocol extensions

      The protocol is designed to accept standard extensions within a
      framework that enables and encourages backward compatibility.

1.5.  NFSv4.1 Goals

   NFSv4.1 has the following goals, within the framework established by
   the overall NFSv4 goals.

   o  To correct significant structural weaknesses and oversights
      discovered in the base protocol.

   o  To add clarity and specificity to areas left unaddressed or not
      addressed in sufficient detail in the base protocol.  However, as




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      stated in Section 1.3, it is not a goal to clarify the NFSv4.0
      protocol in the NFSv4.1 specification.

   o  To add specific features based on experience with the existing
      protocol and recent industry developments.

   o  To provide protocol support to take advantage of clustered server
      deployments including the ability to provide scalable parallel
      access to files distributed among multiple servers.

1.6.  General Definitions

   The following definitions provide an appropriate context for the
   reader.

   Byte:  In this document, a byte is an octet, i.e., a datum exactly 8
      bits in length.

   Client:  The client is the entity that accesses the NFS server's
      resources.  The client may be an application that contains the
      logic to access the NFS server directly.  The client may also be
      the traditional operating system client that provides remote file
      system services for a set of applications.

      A client is uniquely identified by a client owner.

      With reference to byte-range locking, the client is also the
      entity that maintains a set of locks on behalf of one or more
      applications.  This client is responsible for crash or failure
      recovery for those locks it manages.

      Note that multiple clients may share the same transport and
      connection and multiple clients may exist on the same network
      node.

   Client ID:  The client ID is a 64-bit quantity used as a unique,
      short-hand reference to a client-supplied verifier and client
      owner.  The server is responsible for supplying the client ID.

   Client Owner:  The client owner is a unique string, opaque to the
      server, that identifies a client.  Multiple network connections
      and source network addresses originating from those connections
      may share a client owner.  The server is expected to treat
      requests from connections with the same client owner as coming
      from the same client.

   File System:  The file system is the collection of objects on a
      server (as identified by the major identifier of a server owner,



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      which is defined later in this section) that share the same fsid
      attribute (see Section 5.8.1.9).

   Lease:  A lease is an interval of time defined by the server for
      which the client is irrevocably granted locks.  At the end of a
      lease period, locks may be revoked if the lease has not been
      extended.  A lock must be revoked if a conflicting lock has been
      granted after the lease interval.

      A server grants a client a single lease for all state.

   Lock:  The term "lock" is used to refer to byte-range (in UNIX
      environments, also known as record) locks, share reservations,
      delegations, or layouts unless specifically stated otherwise.

   Secret State Verifier (SSV):  The SSV is a unique secret key shared
      between a client and server.  The SSV serves as the secret key for
      an internal (that is, internal to NFSv4.1) Generic Security
      Services (GSS) mechanism (the SSV GSS mechanism; see
      Section 2.10.9).  The SSV GSS mechanism uses the SSV to compute
      message integrity code (MIC) and Wrap tokens.  See
      Section 2.10.8.3 for more details on how NFSv4.1 uses the SSV and
      the SSV GSS mechanism.

   Server:  The Server is the entity responsible for coordinating client
      access to a set of file systems and is identified by a server
      owner.  A server can span multiple network addresses.

   Server Owner:  The server owner identifies the server to the client.
      The server owner consists of a major identifier and a minor
      identifier.  When the client has two connections each to a peer
      with the same major identifier, the client assumes that both peers
      are the same server (the server namespace is the same via each
      connection) and that lock state is sharable across both
      connections.  When each peer has both the same major and minor
      identifiers, the client assumes that each connection might be
      associable with the same session.

   Stable Storage:  Stable storage is storage from which data stored by
      an NFSv4.1 server can be recovered without data loss from multiple
      power failures (including cascading power failures, that is,
      several power failures in quick succession), operating system
      failures, and/or hardware failure of components other than the
      storage medium itself (such as disk, nonvolatile RAM, flash
      memory, etc.).

      Some examples of stable storage that are allowable for an NFS
      server include:



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      1.  Media commit of data; that is, the modified data has been
          successfully written to the disk media, for example, the disk
          platter.

      2.  An immediate reply disk drive with battery-backed, on-drive
          intermediate storage or uninterruptible power system (UPS).

      3.  Server commit of data with battery-backed intermediate storage
          and recovery software.

      4.  Cache commit with uninterruptible power system (UPS) and
          recovery software.

   Stateid:  A stateid is a 128-bit quantity returned by a server that
      uniquely defines the open and locking states provided by the
      server for a specific open-owner or lock-owner/open-owner pair for
      a specific file and type of lock.

   Verifier:  A verifier is a 64-bit quantity generated by the client
      that the server can use to determine if the client has restarted
      and lost all previous lock state.

1.7.  Overview of NFSv4.1 Features

   The major features of the NFSv4.1 protocol will be reviewed in brief.
   This will be done to provide an appropriate context for both the
   reader who is familiar with the previous versions of the NFS protocol
   and the reader who is new to the NFS protocols.  For the reader new
   to the NFS protocols, there is still a set of fundamental knowledge
   that is expected.  The reader should be familiar with the External
   Data Representation (XDR) and Remote Procedure Call (RPC) protocols
   as described in [2] and [3].  A basic knowledge of file systems and
   distributed file systems is expected as well.

   In general, this specification of NFSv4.1 will not distinguish those
   features added in minor version 1 from those present in the base
   protocol but will treat NFSv4.1 as a unified whole.  See Section 1.8
   for a summary of the differences between NFSv4.0 and NFSv4.1.

1.7.1.  RPC and Security

   As with previous versions of NFS, the External Data Representation
   (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFSv4.1
   protocol are those defined in [2] and [3].  To meet end-to-end
   security requirements, the RPCSEC_GSS framework [4] is used to extend
   the basic RPC security.  With the use of RPCSEC_GSS, various
   mechanisms can be provided to offer authentication, integrity, and
   privacy to the NFSv4 protocol.  Kerberos V5 is used as described in



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   [5] to provide one security framework.  With the use of RPCSEC_GSS,
   other mechanisms may also be specified and used for NFSv4.1 security.

   To enable in-band security negotiation, the NFSv4.1 protocol has
   operations that provide the client a method of querying the server
   about its policies regarding which security mechanisms must be used
   for access to the server's file system resources.  With this, the
   client can securely match the security mechanism that meets the
   policies specified at both the client and server.

   NFSv4.1 introduces parallel access (see Section 1.7.2.2), which is
   called pNFS.  The security framework described in this section is
   significantly modified by the introduction of pNFS (see
   Section 12.9), because data access is sometimes not over RPC.  The
   level of significance varies with the storage protocol (see
   Section 12.2.5) and can be as low as zero impact (see Section 13.12).

1.7.2.  Protocol Structure

1.7.2.1.  Core Protocol

   Unlike NFSv3, which used a series of ancillary protocols (e.g., NLM,
   NSM (Network Status Monitor), MOUNT), within all minor versions of
   NFSv4 a single RPC protocol is used to make requests to the server.
   Facilities that had been separate protocols, such as locking, are now
   integrated within a single unified protocol.

1.7.2.2.  Parallel Access

   Minor version 1 supports high-performance data access to a clustered
   server implementation by enabling a separation of metadata access and
   data access, with the latter done to multiple servers in parallel.

   Such parallel data access is controlled by recallable objects known
   as "layouts", which are integrated into the protocol locking model.
   Clients direct requests for data access to a set of data servers
   specified by the layout via a data storage protocol which may be
   NFSv4.1 or may be another protocol.

   Because the protocols used for parallel data access are not
   necessarily RPC-based, the RPC-based security model (Section 1.7.1)
   is obviously impacted (see Section 12.9).  The degree of impact
   varies with the storage protocol (see Section 12.2.5) used for data
   access, and can be as low as zero (see Section 13.12).







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1.7.3.  File System Model

   The general file system model used for the NFSv4.1 protocol is the
   same as previous versions.  The server file system is hierarchical
   with the regular files contained within being treated as opaque byte
   streams.  In a slight departure, file and directory names are encoded
   with UTF-8 to deal with the basics of internationalization.

   The NFSv4.1 protocol does not require a separate protocol to provide
   for the initial mapping between path name and filehandle.  All file
   systems exported by a server are presented as a tree so that all file
   systems are reachable from a special per-server global root
   filehandle.  This allows LOOKUP operations to be used to perform
   functions previously provided by the MOUNT protocol.  The server
   provides any necessary pseudo file systems to bridge any gaps that
   arise due to unexported gaps between exported file systems.

1.7.3.1.  Filehandles

   As in previous versions of the NFS protocol, opaque filehandles are
   used to identify individual files and directories.  Lookup-type and
   create operations translate file and directory names to filehandles,
   which are then used to identify objects in subsequent operations.

   The NFSv4.1 protocol provides support for persistent filehandles,
   guaranteed to be valid for the lifetime of the file system object
   designated.  In addition, it provides support to servers to provide
   filehandles with more limited validity guarantees, called volatile
   filehandles.

1.7.3.2.  File Attributes

   The NFSv4.1 protocol has a rich and extensible file object attribute
   structure, which is divided into REQUIRED, RECOMMENDED, and named
   attributes (see Section 5).

   Several (but not all) of the REQUIRED attributes are derived from the
   attributes of NFSv3 (see the definition of the fattr3 data type in
   [31]).  An example of a REQUIRED attribute is the file object's type
   (Section 5.8.1.2) so that regular files can be distinguished from
   directories (also known as folders in some operating environments)
   and other types of objects.  REQUIRED attributes are discussed in
   Section 5.1.

   An example of three RECOMMENDED attributes are acl, sacl, and dacl.
   These attributes define an Access Control List (ACL) on a file object
   (Section 6).  An ACL provides directory and file access control
   beyond the model used in NFSv3.  The ACL definition allows for



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   specification of specific sets of permissions for individual users
   and groups.  In addition, ACL inheritance allows propagation of
   access permissions and restrictions down a directory tree as file
   system objects are created.  RECOMMENDED attributes are discussed in
   Section 5.2.

   A named attribute is an opaque byte stream that is associated with a
   directory or file and referred to by a string name.  Named attributes
   are meant to be used by client applications as a method to associate
   application-specific data with a regular file or directory.  NFSv4.1
   modifies named attributes relative to NFSv4.0 by tightening the
   allowed operations in order to prevent the development of non-
   interoperable implementations.  Named attributes are discussed in
   Section 5.3.

1.7.3.3.  Multi-Server Namespace

   NFSv4.1 contains a number of features to allow implementation of
   namespaces that cross server boundaries and that allow and facilitate
   a non-disruptive transfer of support for individual file systems
   between servers.  They are all based upon attributes that allow one
   file system to specify alternate or new locations for that file
   system.

   These attributes may be used together with the concept of absent file
   systems, which provide specifications for additional locations but no
   actual file system content.  This allows a number of important
   facilities:

   o  Location attributes may be used with absent file systems to
      implement referrals whereby one server may direct the client to a
      file system provided by another server.  This allows extensive
      multi-server namespaces to be constructed.

   o  Location attributes may be provided for present file systems to
      provide the locations of alternate file system instances or
      replicas to be used in the event that the current file system
      instance becomes unavailable.

   o  Location attributes may be provided when a previously present file
      system becomes absent.  This allows non-disruptive migration of
      file systems to alternate servers.

1.7.4.  Locking Facilities

   As mentioned previously, NFSv4.1 is a single protocol that includes
   locking facilities.  These locking facilities include support for
   many types of locks including a number of sorts of recallable locks.



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   Recallable locks such as delegations allow the client to be assured
   that certain events will not occur so long as that lock is held.
   When circumstances change, the lock is recalled via a callback
   request.  The assurances provided by delegations allow more extensive
   caching to be done safely when circumstances allow it.

   The types of locks are:

   o  Share reservations as established by OPEN operations.

   o  Byte-range locks.

   o  File delegations, which are recallable locks that assure the
      holder that inconsistent opens and file changes cannot occur so
      long as the delegation is held.

   o  Directory delegations, which are recallable locks that assure the
      holder that inconsistent directory modifications cannot occur so
      long as the delegation is held.

   o  Layouts, which are recallable objects that assure the holder that
      direct access to the file data may be performed directly by the
      client and that no change to the data's location that is
      inconsistent with that access may be made so long as the layout is
      held.

   All locks for a given client are tied together under a single client-
   wide lease.  All requests made on sessions associated with the client
   renew that lease.  When the client's lease is not promptly renewed,
   the client's locks are subject to revocation.  In the event of server
   restart, clients have the opportunity to safely reclaim their locks
   within a special grace period.

1.8.  Differences from NFSv4.0

   The following summarizes the major differences between minor version
   1 and the base protocol:

   o  Implementation of the sessions model (Section 2.10).

   o  Parallel access to data (Section 12).

   o  Addition of the RECLAIM_COMPLETE operation to better structure the
      lock reclamation process (Section 18.51).

   o  Enhanced delegation support as follows.





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      *  Delegations on directories and other file types in addition to
         regular files (Section 18.39, Section 18.49).

      *  Operations to optimize acquisition of recalled or denied
         delegations (Section 18.49, Section 20.5, Section 20.7).

      *  Notifications of changes to files and directories
         (Section 18.39, Section 20.4).

      *  A method to allow a server to indicate that it is recalling one
         or more delegations for resource management reasons, and thus a
         method to allow the client to pick which delegations to return
         (Section 20.6).

   o  Attributes can be set atomically during exclusive file create via
      the OPEN operation (see the new EXCLUSIVE4_1 creation method in
      Section 18.16).

   o  Open files can be preserved if removed and the hard link count
      ("hard link" is defined in an Open Group [6] standard) goes to
      zero, thus obviating the need for clients to rename deleted files
      to partially hidden names -- colloquially called "silly rename"
      (see the new OPEN4_RESULT_PRESERVE_UNLINKED reply flag in
      Section 18.16).

   o  Improved compatibility with Microsoft Windows for Access Control
      Lists (Section 6.2.3, Section 6.2.2, Section 6.4.3.2).

   o  Data retention (Section 5.13).

   o  Identification of the implementation of the NFS client and server
      (Section 18.35).

   o  Support for notification of the availability of byte-range locks
      (see the new OPEN4_RESULT_MAY_NOTIFY_LOCK reply flag in
      Section 18.16 and see Section 20.11).

   o  In NFSv4.1, LIPKEY and SPKM-3 are not required security mechanisms
      [32].

2.  Core Infrastructure

2.1.  Introduction

   NFSv4.1 relies on core infrastructure common to nearly every
   operation.  This core infrastructure is described in the remainder of
   this section.




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2.2.  RPC and XDR

   The NFSv4.1 protocol is a Remote Procedure Call (RPC) application
   that uses RPC version 2 and the corresponding eXternal Data
   Representation (XDR) as defined in [3] and [2].

2.2.1.  RPC-Based Security

   Previous NFS versions have been thought of as having a host-based
   authentication model, where the NFS server authenticates the NFS
   client, and trusts the client to authenticate all users.  Actually,
   NFS has always depended on RPC for authentication.  One of the first
   forms of RPC authentication, AUTH_SYS, had no strong authentication
   and required a host-based authentication approach.  NFSv4.1 also
   depends on RPC for basic security services and mandates RPC support
   for a user-based authentication model.  The user-based authentication
   model has user principals authenticated by a server, and in turn the
   server authenticated by user principals.  RPC provides some basic
   security services that are used by NFSv4.1.

2.2.1.1.  RPC Security Flavors

   As described in Section 7.2 ("Authentication") of [3], RPC security
   is encapsulated in the RPC header, via a security or authentication
   flavor, and information specific to the specified security flavor.
   Every RPC header conveys information used to identify and
   authenticate a client and server.  As discussed in Section 2.2.1.1.1,
   some security flavors provide additional security services.

   NFSv4.1 clients and servers MUST implement RPCSEC_GSS.  (This
   requirement to implement is not a requirement to use.)  Other
   flavors, such as AUTH_NONE and AUTH_SYS, MAY be implemented as well.

2.2.1.1.1.  RPCSEC_GSS and Security Services

   RPCSEC_GSS [4] uses the functionality of GSS-API [7].  This allows
   for the use of various security mechanisms by the RPC layer without
   the additional implementation overhead of adding RPC security
   flavors.

2.2.1.1.1.1.  Identification, Authentication, Integrity, Privacy

   Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
   users on clients to servers, and servers to users.  It can also
   perform integrity checking on the entire RPC message, including the
   RPC header, and on the arguments or results.  Finally, privacy,
   usually via encryption, is a service available with RPCSEC_GSS.
   Privacy is performed on the arguments and results.  Note that if



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   privacy is selected, integrity, authentication, and identification
   are enabled.  If privacy is not selected, but integrity is selected,
   authentication and identification are enabled.  If integrity and
   privacy are not selected, but authentication is enabled,
   identification is enabled.  RPCSEC_GSS does not provide
   identification as a separate service.

   Although GSS-API has an authentication service distinct from its
   privacy and integrity services, GSS-API's authentication service is
   not used for RPCSEC_GSS's authentication service.  Instead, each RPC
   request and response header is integrity protected with the GSS-API
   integrity service, and this allows RPCSEC_GSS to offer per-RPC
   authentication and identity.  See [4] for more information.

   NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and
   authentication service.  NFSv4.1 servers MUST support RPCSEC_GSS's
   privacy service.  NFSv4.1 clients SHOULD support RPCSEC_GSS's privacy
   service.

2.2.1.1.1.2.  Security Mechanisms for NFSv4.1

   RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that provide
   security services.  Therefore, NFSv4.1 clients and servers MUST
   support the Kerberos V5 security mechanism.

   The use of RPCSEC_GSS requires selection of mechanism, quality of
   protection (QOP), and service (authentication, integrity, privacy).
   For the mandated security mechanisms, NFSv4.1 specifies that a QOP of
   zero is used, leaving it up to the mechanism or the mechanism's
   configuration to map QOP zero to an appropriate level of protection.
   Each mandated mechanism specifies a minimum set of cryptographic
   algorithms for implementing integrity and privacy.  NFSv4.1 clients
   and servers MUST be implemented on operating environments that comply
   with the REQUIRED cryptographic algorithms of each REQUIRED
   mechanism.

2.2.1.1.1.2.1.  Kerberos V5

   The Kerberos V5 GSS-API mechanism as described in [5] MUST be
   implemented with the RPCSEC_GSS services as specified in the
   following table:










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      column descriptions:
      1 == number of pseudo flavor
      2 == name of pseudo flavor
      3 == mechanism's OID
      4 == RPCSEC_GSS service
      5 == NFSv4.1 clients MUST support
      6 == NFSv4.1 servers MUST support

      1      2        3                    4                     5   6
      ------------------------------------------------------------------
      390003 krb5     1.2.840.113554.1.2.2 rpc_gss_svc_none      yes yes
      390004 krb5i    1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
      390005 krb5p    1.2.840.113554.1.2.2 rpc_gss_svc_privacy    no yes

   Note that the number and name of the pseudo flavor are presented here
   as a mapping aid to the implementor.  Because the NFSv4.1 protocol
   includes a method to negotiate security and it understands the GSS-
   API mechanism, the pseudo flavor is not needed.  The pseudo flavor is
   needed for the NFSv3 since the security negotiation is done via the
   MOUNT protocol as described in [33].

   At the time NFSv4.1 was specified, the Advanced Encryption Standard
   (AES) with HMAC-SHA1 was a REQUIRED algorithm set for Kerberos V5.
   In contrast, when NFSv4.0 was specified, weaker algorithm sets were
   REQUIRED for Kerberos V5, and were REQUIRED in the NFSv4.0
   specification, because the Kerberos V5 specification at the time did
   not specify stronger algorithms.  The NFSv4.1 specification does not
   specify REQUIRED algorithms for Kerberos V5, and instead, the
   implementor is expected to track the evolution of the Kerberos V5
   standard if and when stronger algorithms are specified.

2.2.1.1.1.2.1.1.  Security Considerations for Cryptographic Algorithms
                  in Kerberos V5

   When deploying NFSv4.1, the strength of the security achieved depends
   on the existing Kerberos V5 infrastructure.  The algorithms of
   Kerberos V5 are not directly exposed to or selectable by the client
   or server, so there is some due diligence required by the user of
   NFSv4.1 to ensure that security is acceptable where needed.

2.2.1.1.1.3.  GSS Server Principal

   Regardless of what security mechanism under RPCSEC_GSS is being used,
   the NFS server MUST identify itself in GSS-API via a
   GSS_C_NT_HOSTBASED_SERVICE name type.  GSS_C_NT_HOSTBASED_SERVICE
   names are of the form:

        service@hostname



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   For NFS, the "service" element is

        nfs

   Implementations of security mechanisms will convert nfs@hostname to
   various different forms.  For Kerberos V5, the following form is
   RECOMMENDED:

        nfs/hostname

2.3.  COMPOUND and CB_COMPOUND

   A significant departure from the versions of the NFS protocol before
   NFSv4 is the introduction of the COMPOUND procedure.  For the NFSv4
   protocol, in all minor versions, there are exactly two RPC
   procedures, NULL and COMPOUND.  The COMPOUND procedure is defined as
   a series of individual operations and these operations perform the
   sorts of functions performed by traditional NFS procedures.

   The operations combined within a COMPOUND request are evaluated in
   order by the server, without any atomicity guarantees.  A limited set
   of facilities exist to pass results from one operation to another.
   Once an operation returns a failing result, the evaluation ends and
   the results of all evaluated operations are returned to the client.

   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, multi-component look up requests can be
   constructed by combining multiple LOOKUP operations.  Those can be
   further combined with operations such as GETATTR, READDIR, or OPEN
   plus READ to do more complicated sets of operation without incurring
   additional latency.

   NFSv4.1 also contains a considerable set of callback operations in
   which the server makes an RPC directed at the client.  Callback RPCs
   have a similar structure to that of the normal server requests.  In
   all minor versions of the NFSv4 protocol, there are two callback RPC
   procedures: CB_NULL and CB_COMPOUND.  The CB_COMPOUND procedure is
   defined in an analogous fashion to that of COMPOUND with its own set
   of callback operations.

   The addition of new server and callback operations within the
   COMPOUND and CB_COMPOUND request framework provides a means of
   extending the protocol in subsequent minor versions.

   Except for a small number of operations needed for session creation,
   server requests and callback requests are performed within the



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   context of a session.  Sessions provide a client context for every
   request and support robust reply protection for non-idempotent
   requests.

2.4.  Client Identifiers and Client Owners

   For each operation that obtains or depends on locking state, the
   specific client needs to be identifiable by the server.

   Each distinct client instance is represented by a client ID.  A
   client ID is a 64-bit identifier representing a specific client at a
   given time.  The client ID is changed whenever the client re-
   initializes, and may change when the server re-initializes.  Client
   IDs are used to support lock identification and crash recovery.

   During steady state operation, the client ID associated with each
   operation is derived from the session (see Section 2.10) on which the
   operation is sent.  A session is associated with a client ID when the
   session is created.

   Unlike NFSv4.0, the only NFSv4.1 operations possible before a client
   ID is established are those needed to establish the client ID.

   A sequence of an EXCHANGE_ID operation followed by a CREATE_SESSION
   operation using that client ID (eir_clientid as returned from
   EXCHANGE_ID) is required to establish and confirm the client ID on
   the server.  Establishment of identification by a new incarnation of
   the client also has the effect of immediately releasing any locking
   state that a previous incarnation of that same client might have had
   on the server.  Such released state would include all byte-range
   lock, share reservation, layout state, and -- where the server
   supports neither the CLAIM_DELEGATE_PREV nor CLAIM_DELEG_CUR_FH claim
   types -- all delegation state associated with the same client with
   the same identity.  For discussion of delegation state recovery, see
   Section 10.2.1.  For discussion of layout state recovery, see
   Section 12.7.1.

   Releasing such state requires that the server be able to determine
   that one client instance is the successor of another.  Where this
   cannot be done, for any of a number of reasons, the locking state
   will remain for a time subject to lease expiration (see Section 8.3)
   and the new client will need to wait for such state to be removed, if
   it makes conflicting lock requests.

   Client identification is encapsulated in the following client owner
   data type:





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   struct client_owner4 {
           verifier4       co_verifier;
           opaque          co_ownerid<NFS4_OPAQUE_LIMIT>;
   };

   The first field, co_verifier, is a client incarnation verifier.  The
   server will start the process of canceling the client's leased state
   if co_verifier is different than what the server has previously
   recorded for the identified client (as specified in the co_ownerid
   field).

   The second field, co_ownerid, is a variable length string that
   uniquely defines the client so that subsequent instances of the same
   client bear the same co_ownerid with a different verifier.

   There are several considerations for how the client generates the
   co_ownerid string:

   o  The string should be unique so that multiple clients do not
      present the same string.  The consequences of two clients
      presenting the same string range from one client getting an error
      to one client having its leased state abruptly and unexpectedly
      cancelled.

   o  The string should be selected so that subsequent incarnations
      (e.g., restarts) of the same client cause the client to present
      the same string.  The implementor is cautioned from an approach
      that requires the string to be recorded in a local file because
      this precludes the use of the implementation in an environment
      where there is no local disk and all file access is from an
      NFSv4.1 server.

   o  The string should be the same for each server network address that
      the client accesses.  This way, if a server has multiple
      interfaces, the client can trunk traffic over multiple network
      paths as described in Section 2.10.5.  (Note: the precise opposite
      was advised in the NFSv4.0 specification [30].)

   o  The algorithm for generating the string should not assume that the
      client's network address will not change, unless the client
      implementation knows it is using statically assigned network
      addresses.  This includes changes between client incarnations and
      even changes while the client is still running in its current
      incarnation.  Thus, with dynamic address assignment, if the client
      includes just the client's network address in the co_ownerid
      string, there is a real risk that after the client gives up the
      network address, another client, using a similar algorithm for




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      generating the co_ownerid string, would generate a conflicting
      co_ownerid string.

   Given the above considerations, an example of a well-generated
   co_ownerid string is one that includes:

   o  If applicable, the client's statically assigned network address.

   o  Additional information that tends to be unique, such as one or
      more of:

      *  The client machine's serial number (for privacy reasons, it is
         best to perform some one-way function on the serial number).

      *  A Media Access Control (MAC) address (again, a one-way function
         should be performed).

      *  The timestamp of when the NFSv4.1 software was first installed
         on the client (though this is subject to the previously
         mentioned caution about using information that is stored in a
         file, because the file might only be accessible over NFSv4.1).

      *  A true random number.  However, since this number ought to be
         the same between client incarnations, this shares the same
         problem as that of using the timestamp of the software
         installation.

   o  For a user-level NFSv4.1 client, it should contain additional
      information to distinguish the client from other user-level
      clients running on the same host, such as a process identifier or
      other unique sequence.

   The client ID is assigned by the server (the eir_clientid result from
   EXCHANGE_ID) and should be chosen so that it will not conflict with a
   client ID previously assigned by the server.  This applies across
   server restarts.

   In the event of a server restart, a client may find out that its
   current client ID is no longer valid when it receives an
   NFS4ERR_STALE_CLIENTID error.  The precise circumstances depend on
   the characteristics of the sessions involved, specifically whether
   the session is persistent (see Section 2.10.6.5), but in each case
   the client will receive this error when it attempts to establish a
   new session with the existing client ID and receives the error
   NFS4ERR_STALE_CLIENTID, indicating that a new client ID needs to be
   obtained via EXCHANGE_ID and the new session established with that
   client ID.




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   When a session is not persistent, the client will find out that it
   needs to create a new session as a result of getting an
   NFS4ERR_BADSESSION, since the session in question was lost as part of
   a server restart.  When the existing client ID is presented to a
   server as part of creating a session and that client ID is not
   recognized, as would happen after a server restart, the server will
   reject the request with the error NFS4ERR_STALE_CLIENTID.

   In the case of the session being persistent, the client will re-
   establish communication using the existing session after the restart.
   This session will be associated with the existing client ID but may
   only be used to retransmit operations that the client previously
   transmitted and did not see replies to.  Replies to operations that
   the server previously performed will come from the reply cache;
   otherwise, NFS4ERR_DEADSESSION will be returned.  Hence, such a
   session is referred to as "dead".  In this situation, in order to
   perform new operations, the client needs to establish a new session.
   If an attempt is made to establish this new session with the existing
   client ID, the server will reject the request with
   NFS4ERR_STALE_CLIENTID.

   When NFS4ERR_STALE_CLIENTID is received in either of these
   situations, the client needs to obtain a new client ID by use of the
   EXCHANGE_ID operation, then use that client ID as the basis of a new
   session, and then proceed to any other necessary recovery for the
   server restart case (see Section 8.4.2).

   See the descriptions of EXCHANGE_ID (Section 18.35) and
   CREATE_SESSION (Section 18.36) for a complete specification of these
   operations.

2.4.1.  Upgrade from NFSv4.0 to NFSv4.1

   To facilitate upgrade from NFSv4.0 to NFSv4.1, a server may compare a
   value of data type client_owner4 in an EXCHANGE_ID with a value of
   data type nfs_client_id4 that was established using the SETCLIENTID
   operation of NFSv4.0.  A server that does so will allow an upgraded
   client to avoid waiting until the lease (i.e., the lease established
   by the NFSv4.0 instance client) expires.  This requires that the
   value of data type client_owner4 be constructed the same way as the
   value of data type nfs_client_id4.  If the latter's contents included
   the server's network address (per the recommendations of the NFSv4.0
   specification [30]), and the NFSv4.1 client does not wish to use a
   client ID that prevents trunking, it should send two EXCHANGE_ID
   operations.  The first EXCHANGE_ID will have a client_owner4 equal to
   the nfs_client_id4.  This will clear the state created by the NFSv4.0
   client.  The second EXCHANGE_ID will not have the server's network
   address.  The state created for the second EXCHANGE_ID will not have



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   to wait for lease expiration, because there will be no state to
   expire.

2.4.2.  Server Release of Client ID

   NFSv4.1 introduces a new operation called DESTROY_CLIENTID
   (Section 18.50), which the client SHOULD use to destroy a client ID
   it no longer needs.  This permits graceful, bilateral release of a
   client ID.  The operation cannot be used if there are sessions
   associated with the client ID, or state with an unexpired lease.

   If the server determines that the client holds no associated state
   for its client ID (associated state includes unrevoked sessions,
   opens, locks, delegations, layouts, and wants), the server MAY choose
   to unilaterally release the client ID in order to conserve resources.
   If the client contacts the server after this release, the server MUST
   ensure that the client receives the appropriate error so that it will
   use the EXCHANGE_ID/CREATE_SESSION sequence to establish a new client
   ID.  The server ought to be very hesitant to release a client ID
   since the resulting work on the client to recover from such an event
   will be the same burden as if the server had failed and restarted.
   Typically, a server would not release a client ID unless there had
   been no activity from that client for many minutes.  As long as there
   are sessions, opens, locks, delegations, layouts, or wants, the
   server MUST NOT release the client ID.  See Section 2.10.13.1.4 for
   discussion on releasing inactive sessions.

2.4.3.  Resolving Client Owner Conflicts

   When the server gets an EXCHANGE_ID for a client owner that currently
   has no state, or that has state but the lease has expired, the server
   MUST allow the EXCHANGE_ID and confirm the new client ID if followed
   by the appropriate CREATE_SESSION.

   When the server gets an EXCHANGE_ID for a new incarnation of a client
   owner that currently has an old incarnation with state and an
   unexpired lease, the server is allowed to dispose of the state of the
   previous incarnation of the client owner if one of the following is
   true:

   o  The principal that created the client ID for the client owner is
      the same as the principal that is sending the EXCHANGE_ID
      operation.  Note that if the client ID was created with
      SP4_MACH_CRED state protection (Section 18.35), the principal MUST
      be based on RPCSEC_GSS authentication, the RPCSEC_GSS service used
      MUST be integrity or privacy, and the same GSS mechanism and
      principal MUST be used as that used when the client ID was
      created.



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   o  The client ID was established with SP4_SSV protection
      (Section 18.35, Section 2.10.8.3) and the client sends the
      EXCHANGE_ID with the security flavor set to RPCSEC_GSS using the
      GSS SSV mechanism (Section 2.10.9).

   o  The client ID was established with SP4_SSV protection, and under
      the conditions described herein, the EXCHANGE_ID was sent with
      SP4_MACH_CRED state protection.  Because the SSV might not persist
      across client and server restart, and because the first time a
      client sends EXCHANGE_ID to a server it does not have an SSV, the
      client MAY send the subsequent EXCHANGE_ID without an SSV
      RPCSEC_GSS handle.  Instead, as with SP4_MACH_CRED protection, the
      principal MUST be based on RPCSEC_GSS authentication, the
      RPCSEC_GSS service used MUST be integrity or privacy, and the same
      GSS mechanism and principal MUST be used as that used when the
      client ID was created.

   If none of the above situations apply, the server MUST return
   NFS4ERR_CLID_INUSE.

   If the server accepts the principal and co_ownerid as matching that
   which created the client ID, and the co_verifier in the EXCHANGE_ID
   differs from the co_verifier used when the client ID was created,
   then after the server receives a CREATE_SESSION that confirms the
   client ID, the server deletes state.  If the co_verifier values are
   the same (e.g., the client either is updating properties of the
   client ID (Section 18.35) or is attempting trunking (Section 2.10.5),
   the server MUST NOT delete state.

2.5.  Server Owners

   The server owner is similar to a client owner (Section 2.4), but
   unlike the client owner, there is no shorthand server ID.  The server
   owner is defined in the following data type:

   struct server_owner4 {
    uint64_t       so_minor_id;
    opaque         so_major_id<NFS4_OPAQUE_LIMIT>;
   };

   The server owner is returned from EXCHANGE_ID.  When the so_major_id
   fields are the same in two EXCHANGE_ID results, the connections that
   each EXCHANGE_ID were sent over can be assumed to address the same
   server (as defined in Section 1.6).  If the so_minor_id fields are
   also the same, then not only do both connections connect to the same
   server, but the session can be shared across both connections.  The
   reader is cautioned that multiple servers may deliberately or
   accidentally claim to have the same so_major_id or so_major_id/



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   so_minor_id; the reader should examine Sections 2.10.5 and 18.35 in
   order to avoid acting on falsely matching server owner values.

   The considerations for generating a so_major_id are similar to that
   for generating a co_ownerid string (see Section 2.4).  The
   consequences of two servers generating conflicting so_major_id values
   are less dire than they are for co_ownerid conflicts because the
   client can use RPCSEC_GSS to compare the authenticity of each server
   (see Section 2.10.5).

2.6.  Security Service Negotiation

   With the NFSv4.1 server potentially offering multiple security
   mechanisms, the client needs a method to determine or negotiate which
   mechanism is to be used for its communication with the server.  The
   NFS server may have multiple points within its file system namespace
   that are available for use by NFS clients.  These points can be
   considered security policy boundaries, and, in some NFS
   implementations, are tied to NFS export points.  In turn, the NFS
   server may be configured such that each of these security policy
   boundaries may have different or multiple security mechanisms in use.

   The security negotiation between client and server SHOULD be done
   with a secure channel to eliminate the possibility of a third party
   intercepting the negotiation sequence and forcing the client and
   server to choose a lower level of security than required or desired.
   See Section 21 for further discussion.

2.6.1.  NFSv4.1 Security Tuples

   An NFS server can assign one or more "security tuples" to each
   security policy boundary in its namespace.  Each security tuple
   consists of a security flavor (see Section 2.2.1.1) and, if the
   flavor is RPCSEC_GSS, a GSS-API mechanism Object Identifier (OID), a
   GSS-API quality of protection, and an RPCSEC_GSS service.

2.6.2.  SECINFO and SECINFO_NO_NAME

   The SECINFO and SECINFO_NO_NAME operations allow the client to
   determine, on a per-filehandle basis, what security tuple is to be
   used for server access.  In general, the client will not have to use
   either operation except during initial communication with the server
   or when the client crosses security policy boundaries at the server.
   However, the server's policies may also change at any time and force
   the client to negotiate a new security tuple.

   Where the use of different security tuples would affect the type of
   access that would be allowed if a request was sent over the same



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   connection used for the SECINFO or SECINFO_NO_NAME operation (e.g.,
   read-only vs. read-write) access, security tuples that allow greater
   access should be presented first.  Where the general level of access
   is the same and different security flavors limit the range of
   principals whose privileges are recognized (e.g., allowing or
   disallowing root access), flavors supporting the greatest range of
   principals should be listed first.

2.6.3.  Security Error

   Based on the assumption that each NFSv4.1 client and server MUST
   support a minimum set of security (i.e., Kerberos V5 under
   RPCSEC_GSS), the NFS client will initiate file access to the server
   with one of the minimal security tuples.  During communication with
   the server, the client may receive an NFS error of NFS4ERR_WRONGSEC.
   This error allows the server to notify the client that the security
   tuple currently being used contravenes the server's security policy.
   The client is then responsible for determining (see Section 2.6.3.1)
   what security tuples are available at the server and choosing one
   that is appropriate for the client.

2.6.3.1.  Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME

   This section explains the mechanics of NFSv4.1 security negotiation.

2.6.3.1.1.  Put Filehandle Operations

   The term "put filehandle operation" refers to PUTROOTFH, PUTPUBFH,
   PUTFH, and RESTOREFH.  Each of the subsections herein describes how
   the server handles a subseries of operations that starts with a put
   filehandle operation.

2.6.3.1.1.1.  Put Filehandle Operation + SAVEFH

   The client is saving a filehandle for a future RESTOREFH, LINK, or
   RENAME.  SAVEFH MUST NOT return NFS4ERR_WRONGSEC.  To determine
   whether or not the put filehandle operation returns NFS4ERR_WRONGSEC,
   the server implementation pretends SAVEFH is not in the series of
   operations and examines which of the situations described in the
   other subsections of Section 2.6.3.1.1 apply.

2.6.3.1.1.2.  Two or More Put Filehandle Operations

   For a series of N put filehandle operations, the server MUST NOT
   return NFS4ERR_WRONGSEC to the first N-1 put filehandle operations.
   The Nth put filehandle operation is handled as if it is the first in
   a subseries of operations.  For example, if the server received a
   COMPOUND request with this series of operations -- PUTFH, PUTROOTFH,



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   LOOKUP -- then the PUTFH operation is ignored for NFS4ERR_WRONGSEC
   purposes, and the PUTROOTFH, LOOKUP subseries is processed as
   according to Section 2.6.3.1.1.3.

2.6.3.1.1.3.  Put Filehandle Operation + LOOKUP (or OPEN of an Existing
              Name)

   This situation also applies to a put filehandle operation followed by
   a LOOKUP or an OPEN operation that specifies an existing component
   name.

   In this situation, the client is potentially crossing a security
   policy boundary, and the set of security tuples the parent directory
   supports may differ from those of the child.  The server
   implementation may decide whether to impose any restrictions on
   security policy administration.  There are at least three approaches
   (sec_policy_child is the tuple set of the child export,
   sec_policy_parent is that of the parent).

   (a)  sec_policy_child <= sec_policy_parent (<= for subset).  This
        means that the set of security tuples specified on the security
        policy of a child directory is always a subset of its parent
        directory.

   (b)  sec_policy_child ^ sec_policy_parent != {} (^ for intersection,
        {} for the empty set).  This means that the set of security
        tuples specified on the security policy of a child directory
        always has a non-empty intersection with that of the parent.

   (c)  sec_policy_child ^ sec_policy_parent == {}.  This means that the
        set of security tuples specified on the security policy of a
        child directory may not intersect with that of the parent.  In
        other words, there are no restrictions on how the system
        administrator may set up these tuples.

   In order for a server to support approaches (b) (for the case when a
   client chooses a flavor that is not a member of sec_policy_parent)
   and (c), the put filehandle operation cannot return NFS4ERR_WRONGSEC
   when there is a security tuple mismatch.  Instead, it should be
   returned from the LOOKUP (or OPEN by existing component name) that
   follows.

   Since the above guideline does not contradict approach (a), it should
   be followed in general.  Even if approach (a) is implemented, it is
   possible for the security tuple used to be acceptable for the target
   of LOOKUP but not for the filehandles used in the put filehandle
   operation.  The put filehandle operation could be a PUTROOTFH or
   PUTPUBFH, where the client cannot know the security tuples for the



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   root or public filehandle.  Or the security policy for the filehandle
   used by the put filehandle operation could have changed since the
   time the filehandle was obtained.

   Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC in
   response to the put filehandle operation if the operation is
   immediately followed by a LOOKUP or an OPEN by component name.

2.6.3.1.1.4.  Put Filehandle Operation + LOOKUPP

   Since SECINFO only works its way down, there is no way LOOKUPP can
   return NFS4ERR_WRONGSEC without SECINFO_NO_NAME.  SECINFO_NO_NAME
   solves this issue via style SECINFO_STYLE4_PARENT, which works in the
   opposite direction as SECINFO.  As with Section 2.6.3.1.1.3, a put
   filehandle operation that is followed by a LOOKUPP MUST NOT return
   NFS4ERR_WRONGSEC.  If the server does not support SECINFO_NO_NAME,
   the client's only recourse is to send the put filehandle operation,
   LOOKUPP, GETFH sequence of operations with every security tuple it
   supports.

   Regardless of whether SECINFO_NO_NAME is supported, an NFSv4.1 server
   MUST NOT return NFS4ERR_WRONGSEC in response to a put filehandle
   operation if the operation is immediately followed by a LOOKUPP.

2.6.3.1.1.5.  Put Filehandle Operation + SECINFO/SECINFO_NO_NAME

   A security-sensitive client is allowed to choose a strong security
   tuple when querying a server to determine a file object's permitted
   security tuples.  The security tuple chosen by the client does not
   have to be included in the tuple list of the security policy of
   either the parent directory indicated in the put filehandle operation
   or the child file object indicated in SECINFO (or any parent
   directory indicated in SECINFO_NO_NAME).  Of course, the server has
   to be configured for whatever security tuple the client selects;
   otherwise, the request will fail at the RPC layer with an appropriate
   authentication error.

   In theory, there is no connection between the security flavor used by
   SECINFO or SECINFO_NO_NAME and those supported by the security
   policy.  But in practice, the client may start looking for strong
   flavors from those supported by the security policy, followed by
   those in the REQUIRED set.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a put
   filehandle operation that is immediately followed by SECINFO or
   SECINFO_NO_NAME.  The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC
   from SECINFO or SECINFO_NO_NAME.




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2.6.3.1.1.6.  Put Filehandle Operation + Nothing

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.

2.6.3.1.1.7.  Put Filehandle Operation + Anything Else

   "Anything Else" includes OPEN by filehandle.

   The security policy enforcement applies to the filehandle specified
   in the put filehandle operation.  Therefore, the put filehandle
   operation MUST return NFS4ERR_WRONGSEC when there is a security tuple
   mismatch.  This avoids the complexity of adding NFS4ERR_WRONGSEC as
   an allowable error to every other operation.

   A COMPOUND containing the series put filehandle operation +
   SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an efficient way
   for the client to recover from NFS4ERR_WRONGSEC.

   The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to any operation
   other than a put filehandle operation, LOOKUP, LOOKUPP, and OPEN (by
   component name).

2.6.3.1.1.8.  Operations after SECINFO and SECINFO_NO_NAME

   Suppose a client sends a COMPOUND procedure containing the series
   SEQUENCE, PUTFH, SECINFO_NONAME, READ, and suppose the security tuple
   used does not match that required for the target file.  By rule (see
   Section 2.6.3.1.1.5), neither PUTFH nor SECINFO_NO_NAME can return
   NFS4ERR_WRONGSEC.  By rule (see Section 2.6.3.1.1.7), READ cannot
   return NFS4ERR_WRONGSEC.  The issue is resolved by the fact that
   SECINFO and SECINFO_NO_NAME consume the current filehandle (note that
   this is a change from NFSv4.0).  This leaves no current filehandle
   for READ to use, and READ returns NFS4ERR_NOFILEHANDLE.

2.6.3.1.2.  LINK and RENAME

   The LINK and RENAME operations use both the current and saved
   filehandles.  Technically, the server MAY return NFS4ERR_WRONGSEC
   from LINK or RENAME if the security policy of the saved filehandle
   rejects the security flavor used in the COMPOUND request's
   credentials.  If the server does so, then if there is no intersection
   between the security policies of saved and current filehandles, this
   means that it will be impossible for the client to perform the
   intended LINK or RENAME operation.

   For example, suppose the client sends this COMPOUND request:
   SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH, RENAME "c" "d", where
   filehandles bFH and aFH refer to different directories.  Suppose no



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   common security tuple exists between the security policies of aFH and
   bFH.  If the client sends the request using credentials acceptable to
   bFH's security policy but not aFH's policy, then the PUTFH aFH
   operation will fail with NFS4ERR_WRONGSEC.  After a SECINFO_NO_NAME
   request, the client sends SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH,
   RENAME "c" "d", using credentials acceptable to aFH's security policy
   but not bFH's policy.  The server returns NFS4ERR_WRONGSEC on the
   RENAME operation.

   To prevent a client from an endless sequence of a request containing
   LINK or RENAME, followed by a request containing SECINFO_NO_NAME or
   SECINFO, the server MUST detect when the security policies of the
   current and saved filehandles have no mutually acceptable security
   tuple, and MUST NOT return NFS4ERR_WRONGSEC from LINK or RENAME in
   that situation.  Instead the server MUST do one of two things:

   o  The server can return NFS4ERR_XDEV.

   o  The server can allow the security policy of the current filehandle
      to override that of the saved filehandle, and so return NFS4_OK.

2.7.  Minor Versioning

   To address the requirement of an NFS protocol that can evolve as the
   need arises, the NFSv4.1 protocol contains the rules and framework to
   allow for future minor changes or versioning.

   The base assumption with respect to minor versioning is that any
   future accepted minor version will be documented in one or more
   Standards Track RFCs.  Minor version 0 of the NFSv4 protocol is
   represented by [30], and minor version 1 is represented by this RFC.
   The COMPOUND and CB_COMPOUND procedures support the encoding of the
   minor version being requested by the client.

   The following items represent the basic rules for the development of
   minor versions.  Note that a future minor version may modify or add
   to the following rules as part of the minor version definition.

   1.   Procedures are not added or deleted.

        To maintain the general RPC model, NFSv4 minor versions will not
        add to or delete procedures from the NFS program.

   2.   Minor versions may add operations to the COMPOUND and
        CB_COMPOUND procedures.

        The addition of operations to the COMPOUND and CB_COMPOUND
        procedures does not affect the RPC model.



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        *  Minor versions may append attributes to the bitmap4 that
           represents sets of attributes and to the fattr4 that
           represents sets of attribute values.

           This allows for the expansion of the attribute model to allow
           for future growth or adaptation.

        *  Minor version X must append any new attributes after the last
           documented attribute.

           Since attribute results are specified as an opaque array of
           per-attribute, XDR-encoded results, the complexity of adding
           new attributes in the midst of the current definitions would
           be too burdensome.

   3.   Minor versions must not modify the structure of an existing
        operation's arguments or results.

        Again, the complexity of handling multiple structure definitions
        for a single operation is too burdensome.  New operations should
        be added instead of modifying existing structures for a minor
        version.

        This rule does not preclude the following adaptations in a minor
        version:

        *  adding bits to flag fields, such as new attributes to
           GETATTR's bitmap4 data type, and providing corresponding
           variants of opaque arrays, such as a notify4 used together
           with such bitmaps

        *  adding bits to existing attributes like ACLs that have flag
           words

        *  extending enumerated types (including NFS4ERR_*) with new
           values

        *  adding cases to a switched union

   4.   Minor versions must not modify the structure of existing
        attributes.

   5.   Minor versions must not delete operations.

        This prevents the potential reuse of a particular operation
        "slot" in a future minor version.

   6.   Minor versions must not delete attributes.



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   7.   Minor versions must not delete flag bits or enumeration values.

   8.   Minor versions may declare an operation MUST NOT be implemented.

        Specifying that an operation MUST NOT be implemented is
        equivalent to obsoleting an operation.  For the client, it means
        that the operation MUST NOT be sent to the server.  For the
        server, an NFS error can be returned as opposed to "dropping"
        the request as an XDR decode error.  This approach allows for
        the obsolescence of an operation while maintaining its structure
        so that a future minor version can reintroduce the operation.

        1.  Minor versions may declare that an attribute MUST NOT be
            implemented.

        2.  Minor versions may declare that a flag bit or enumeration
            value MUST NOT be implemented.

   9.   Minor versions may downgrade features from REQUIRED to
        RECOMMENDED, or RECOMMENDED to OPTIONAL.

   10.  Minor versions may upgrade features from OPTIONAL to
        RECOMMENDED, or RECOMMENDED to REQUIRED.

   11.  A client and server that support minor version X SHOULD support
        minor versions zero through X-1 as well.

   12.  Except for infrastructural changes, a minor version must not
        introduce REQUIRED new features.

        This rule allows for the introduction of new functionality and
        forces the use of implementation experience before designating a
        feature as REQUIRED.  On the other hand, some classes of
        features are infrastructural and have broad effects.  Allowing
        infrastructural features to be RECOMMENDED or OPTIONAL
        complicates implementation of the minor version.

   13.  A client MUST NOT attempt to use a stateid, filehandle, or
        similar returned object from the COMPOUND procedure with minor
        version X for another COMPOUND procedure with minor version Y,
        where X != Y.

2.8.  Non-RPC-Based Security Services

   As described in Section 2.2.1.1.1.1, NFSv4.1 relies on RPC for
   identification, authentication, integrity, and privacy.  NFSv4.1
   itself provides or enables additional security services as described
   in the next several subsections.



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2.8.1.  Authorization

   Authorization to access a file object via an NFSv4.1 operation is
   ultimately determined by the NFSv4.1 server.  A client can
   predetermine its access to a file object via the OPEN (Section 18.16)
   and the ACCESS (Section 18.1) operations.

   Principals with appropriate access rights can modify the
   authorization on a file object via the SETATTR (Section 18.30)
   operation.  Attributes that affect access rights include mode, owner,
   owner_group, acl, dacl, and sacl.  See Section 5.

2.8.2.  Auditing

   NFSv4.1 provides auditing on a per-file object basis, via the acl and
   sacl attributes as described in Section 6.  It is outside the scope
   of this specification to specify audit log formats or management
   policies.

2.8.3.  Intrusion Detection

   NFSv4.1 provides alarm control on a per-file object basis, via the
   acl and sacl attributes as described in Section 6.  Alarms may serve
   as the basis for intrusion detection.  It is outside the scope of
   this specification to specify heuristics for detecting intrusion via
   alarms.

2.9.  Transport Layers

2.9.1.  REQUIRED and RECOMMENDED Properties of Transports

   NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-
   based transports with the following attributes:

   o  The transport supports reliable delivery of data, which NFSv4.1
      requires but neither NFSv4.1 nor RPC has facilities for ensuring
      [34].

   o  The transport delivers data in the order it was sent.  Ordered
      delivery simplifies detection of transmit errors, and simplifies
      the sending of arbitrary sized requests and responses via the
      record marking protocol [3].

   Where an NFSv4.1 implementation supports operation over the IP
   network protocol, any transport used between NFS and IP MUST be among
   the IETF-approved congestion control transport protocols.  At the
   time this document was written, the only two transports that had the
   above attributes were TCP and the Stream Control Transmission



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   Protocol (SCTP).  To enhance the possibilities for interoperability,
   an NFSv4.1 implementation MUST support operation over the TCP
   transport protocol.

   Even if NFSv4.1 is used over a non-IP network protocol, it is
   RECOMMENDED that the transport support congestion control.

   It is permissible for a connectionless transport to be used under
   NFSv4.1; however, reliable and in-order delivery of data combined
   with congestion control by the connectionless transport is REQUIRED.
   As a consequence, UDP by itself MUST NOT be used as an NFSv4.1
   transport.  NFSv4.1 assumes that a client transport address and
   server transport address used to send data over a transport together
   constitute a connection, even if the underlying transport eschews the
   concept of a connection.

2.9.2.  Client and Server Transport Behavior

   If a connection-oriented transport (e.g., TCP) is used, the client
   and server SHOULD use long-lived connections for at least three
   reasons:

   1.  This will prevent the weakening of the transport's congestion
       control mechanisms via short-lived connections.

   2.  This will improve performance for the WAN environment by
       eliminating the need for connection setup handshakes.

   3.  The NFSv4.1 callback model differs from NFSv4.0, and requires the
       client and server to maintain a client-created backchannel (see
       Section 2.10.3.1) for the server to use.

   In order to reduce congestion, if a connection-oriented transport is
   used, and the request is not the NULL procedure:

   o  A requester MUST NOT retry a request unless the connection the
      request was sent over was lost before the reply was received.

   o  A replier MUST NOT silently drop a request, even if the request is
      a retry.  (The silent drop behavior of RPCSEC_GSS [4] does not
      apply because this behavior happens at the RPCSEC_GSS layer, a
      lower layer in the request processing.)  Instead, the replier
      SHOULD return an appropriate error (see Section 2.10.6.1), or it
      MAY disconnect the connection.

   When sending a reply, the replier MUST send the reply to the same
   full network address (e.g., if using an IP-based transport, the
   source port of the requester is part of the full network address)



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   from which the requester sent the request.  If using a connection-
   oriented transport, replies MUST be sent on the same connection from
   which the request was received.

   If a connection is dropped after the replier receives the request but
   before the replier sends the reply, the replier might have a pending
   reply.  If a connection is established with the same source and
   destination full network address as the dropped connection, then the
   replier MUST NOT send the reply until the requester retries the
   request.  The reason for this prohibition is that the requester MAY
   retry a request over a different connection (provided that connection
   is associated with the original request's session).

   When using RDMA transports, there are other reasons for not
   tolerating retries over the same connection:

   o  RDMA transports use "credits" to enforce flow control, where a
      credit is a right to a peer to transmit a message.  If one peer
      were to retransmit a request (or reply), it would consume an
      additional credit.  If the replier retransmitted a reply, it would
      certainly result in an RDMA connection loss, since the requester
      would typically only post a single receive buffer for each
      request.  If the requester retransmitted a request, the additional
      credit consumed on the server might lead to RDMA connection
      failure unless the client accounted for it and decreased its
      available credit, leading to wasted resources.

   o  RDMA credits present a new issue to the reply cache in NFSv4.1.
      The reply cache may be used when a connection within a session is
      lost, such as after the client reconnects.  Credit information is
      a dynamic property of the RDMA connection, and stale values must
      not be replayed from the cache.  This implies that the reply cache
      contents must not be blindly used when replies are sent from it,
      and credit information appropriate to the channel must be
      refreshed by the RPC layer.

   In addition, as described in Section 2.10.6.2, while a session is
   active, the NFSv4.1 requester MUST NOT stop waiting for a reply.

2.9.3.  Ports

   Historically, NFSv3 servers have listened over TCP port 2049.  The
   registered port 2049 [35] for the NFS protocol should be the default
   configuration.  NFSv4.1 clients SHOULD NOT use the RPC binding
   protocols as described in [36].






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2.10.  Session

   NFSv4.1 clients and servers MUST support and MUST use the session
   feature as described in this section.

2.10.1.  Motivation and Overview

   Previous versions and minor versions of NFS have suffered from the
   following:

   o  Lack of support for Exactly Once Semantics (EOS).  This includes
      lack of support for EOS through server failure and recovery.

   o  Limited callback support, including no support for sending
      callbacks through firewalls, and races between replies to normal
      requests and callbacks.

   o  Limited trunking over multiple network paths.

   o  Requiring machine credentials for fully secure operation.

   Through the introduction of a session, NFSv4.1 addresses the above
   shortfalls with practical solutions:

   o  EOS is enabled by a reply cache with a bounded size, making it
      feasible to keep the cache in persistent storage and enable EOS
      through server failure and recovery.  One reason that previous
      revisions of NFS did not support EOS was because some EOS
      approaches often limited parallelism.  As will be explained in
      Section 2.10.6, NFSv4.1 supports both EOS and unlimited
      parallelism.

   o  The NFSv4.1 client (defined in Section 1.6, Paragraph 2) creates
      transport connections and provides them to the server to use for
      sending callback requests, thus solving the firewall issue
      (Section 18.34).  Races between responses from client requests and
      callbacks caused by the requests are detected via the session's
      sequencing properties that are a consequence of EOS
      (Section 2.10.6.3).

   o  The NFSv4.1 client can associate an arbitrary number of
      connections with the session, and thus provide trunking
      (Section 2.10.5).

   o  The NFSv4.1 client and server produces a session key independent
      of client and server machine credentials which can be used to
      compute a digest for protecting critical session management
      operations (Section 2.10.8.3).



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   o  The NFSv4.1 client can also create secure RPCSEC_GSS contexts for
      use by the session's backchannel that do not require the server to
      authenticate to a client machine principal (Section 2.10.8.2).

   A session is a dynamically created, long-lived server object created
   by a client and used over time from one or more transport
   connections.  Its function is to maintain the server's state relative
   to the connection(s) belonging to a client instance.  This state is
   entirely independent of the connection itself, and indeed the state
   exists whether or not the connection exists.  A client may have one
   or more sessions associated with it so that client-associated state
   may be accessed using any of the sessions associated with that
   client's client ID, when connections are associated with those
   sessions.  When no connections are associated with any of a client
   ID's sessions for an extended time, such objects as locks, opens,
   delegations, layouts, etc. are subject to expiration.  The session
   serves as an object representing a means of access by a client to the
   associated client state on the server, independent of the physical
   means of access to that state.

   A single client may create multiple sessions.  A single session MUST
   NOT serve multiple clients.

2.10.2.  NFSv4 Integration

   Sessions are part of NFSv4.1 and not NFSv4.0.  Normally, a major
   infrastructure change such as sessions would require a new major
   version number to an Open Network Computing (ONC) RPC program like
   NFS.  However, because NFSv4 encapsulates its functionality in a
   single procedure, COMPOUND, and because COMPOUND can support an
   arbitrary number of operations, sessions have been added to NFSv4.1
   with little difficulty.  COMPOUND includes a minor version number
   field, and for NFSv4.1 this minor version is set to 1.  When the
   NFSv4 server processes a COMPOUND with the minor version set to 1, it
   expects a different set of operations than it does for NFSv4.0.
   NFSv4.1 defines the SEQUENCE operation, which is required for every
   COMPOUND that operates over an established session, with the
   exception of some session administration operations, such as
   DESTROY_SESSION (Section 18.37).

2.10.2.1.  SEQUENCE and CB_SEQUENCE

   In NFSv4.1, when the SEQUENCE operation is present, it MUST be the
   first operation in the COMPOUND procedure.  The primary purpose of
   SEQUENCE is to carry the session identifier.  The session identifier
   associates all other operations in the COMPOUND procedure with a
   particular session.  SEQUENCE also contains required information for




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   maintaining EOS (see Section 2.10.6).  Session-enabled NFSv4.1
   COMPOUND requests thus have the form:

       +-----+--------------+-----------+------------+-----------+----
       | tag | minorversion | numops    |SEQUENCE op | op + args | ...
       |     |   (== 1)     | (limited) |  + args    |           |
       +-----+--------------+-----------+------------+-----------+----

   and the replies have the form:

       +------------+-----+--------+-------------------------------+--//
       |last status | tag | numres |status + SEQUENCE op + results |  //
       +------------+-----+--------+-------------------------------+--//
               //-----------------------+----
               // status + op + results | ...
               //-----------------------+----

   A CB_COMPOUND procedure request and reply has a similar form to
   COMPOUND, but instead of a SEQUENCE operation, there is a CB_SEQUENCE
   operation.  CB_COMPOUND also has an additional field called
   "callback_ident", which is superfluous in NFSv4.1 and MUST be ignored
   by the client.  CB_SEQUENCE has the same information as SEQUENCE, and
   also includes other information needed to resolve callback races
   (Section 2.10.6.3).

2.10.2.2.  Client ID and Session Association

   Each client ID (Section 2.4) can have zero or more active sessions.
   A client ID and associated session are required to perform file
   access in NFSv4.1.  Each time a session is used (whether by a client
   sending a request to the server or the client replying to a callback
   request from the server), the state leased to its associated client
   ID is automatically renewed.

   State (which can consist of share reservations, locks, delegations,
   and layouts (Section 1.7.4)) is tied to the client ID.  Client state
   is not tied to any individual session.  Successive state changing
   operations from a given state owner MAY go over different sessions,
   provided the session is associated with the same client ID.  A
   callback MAY arrive over a different session than that of the request
   that originally acquired the state pertaining to the callback.  For
   example, if session A is used to acquire a delegation, a request to
   recall the delegation MAY arrive over session B if both sessions are
   associated with the same client ID.  Sections 2.10.8.1 and 2.10.8.2
   discuss the security considerations around callbacks.






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2.10.3.  Channels

   A channel is not a connection.  A channel represents the direction
   ONC RPC requests are sent.

   Each session has one or two channels: the fore channel and the
   backchannel.  Because there are at most two channels per session, and
   because each channel has a distinct purpose, channels are not
   assigned identifiers.

   The fore channel is used for ordinary requests from the client to the
   server, and carries COMPOUND requests and responses.  A session
   always has a fore channel.

   The backchannel is used for callback requests from server to client,
   and carries CB_COMPOUND requests and responses.  Whether or not there
   is a backchannel is a decision made by the client; however, many
   features of NFSv4.1 require a backchannel.  NFSv4.1 servers MUST
   support backchannels.

   Each session has resources for each channel, including separate reply
   caches (see Section 2.10.6.1).  Note that even the backchannel
   requires a reply cache (or, at least, a slot table in order to detect
   retries) because some callback operations are nonidempotent.

2.10.3.1.  Association of Connections, Channels, and Sessions

   Each channel is associated with zero or more transport connections
   (whether of the same transport protocol or different transport
   protocols).  A connection can be associated with one channel or both
   channels of a session; the client and server negotiate whether a
   connection will carry traffic for one channel or both channels via
   the CREATE_SESSION (Section 18.36) and the BIND_CONN_TO_SESSION
   (Section 18.34) operations.  When a session is created via
   CREATE_SESSION, the connection that transported the CREATE_SESSION
   request is automatically associated with the fore channel, and
   optionally the backchannel.  If the client specifies no state
   protection (Section 18.35) when the session is created, then when
   SEQUENCE is transmitted on a different connection, the connection is
   automatically associated with the fore channel of the session
   specified in the SEQUENCE operation.

   A connection's association with a session is not exclusive.  A
   connection associated with the channel(s) of one session may be
   simultaneously associated with the channel(s) of other sessions
   including sessions associated with other client IDs.





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   It is permissible for connections of multiple transport types to be
   associated with the same channel.  For example, both TCP and RDMA
   connections can be associated with the fore channel.  In the event an
   RDMA and non-RDMA connection are associated with the same channel,
   the maximum number of slots SHOULD be at least one more than the
   total number of RDMA credits (Section 2.10.6.1).  This way, if all
   RDMA credits are used, the non-RDMA connection can have at least one
   outstanding request.  If a server supports multiple transport types,
   it MUST allow a client to associate connections from each transport
   to a channel.

   It is permissible for a connection of one type of transport to be
   associated with the fore channel, and a connection of a different
   type to be associated with the backchannel.

2.10.4.  Server Scope

   Servers each specify a server scope value in the form of an opaque
   string eir_server_scope returned as part of the results of an
   EXCHANGE_ID operation.  The purpose of the server scope is to allow a
   group of servers to indicate to clients that a set of servers sharing
   the same server scope value has arranged to use compatible values of
   otherwise opaque identifiers.  Thus, the identifiers generated by one
   server of that set may be presented to another of that same scope.

   The use of such compatible values does not imply that a value
   generated by one server will always be accepted by another.  In most
   cases, it will not.  However, a server will not accept a value
   generated by another inadvertently.  When it does accept it, it will
   be because it is recognized as valid and carrying the same meaning as
   on another server of the same scope.

   When servers are of the same server scope, this compatibility of
   values applies to the follow identifiers:

   o  Filehandle values.  A filehandle value accepted by two servers of
      the same server scope denotes the same object.  A WRITE operation
      sent to one server is reflected immediately in a READ sent to the
      other, and locks obtained on one server conflict with those
      requested on the other.

   o  Session ID values.  A session ID value accepted by two servers of
      the same server scope denotes the same session.

   o  Client ID values.  A client ID value accepted as valid by two
      servers of the same server scope is associated with two clients
      with the same client owner and verifier.




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   o  State ID values.  A state ID value is recognized as valid when the
      corresponding client ID is recognized as valid.  If the same
      stateid value is accepted as valid on two servers of the same
      scope and the client IDs on the two servers represent the same
      client owner and verifier, then the two stateid values designate
      the same set of locks and are for the same file.

   o  Server owner values.  When the server scope values are the same,
      server owner value may be validly compared.  In cases where the
      server scope values are different, server owner values are treated
      as different even if they contain all identical bytes.

   The coordination among servers required to provide such compatibility
   can be quite minimal, and limited to a simple partition of the ID
   space.  The recognition of common values requires additional
   implementation, but this can be tailored to the specific situations
   in which that recognition is desired.

   Clients will have occasion to compare the server scope values of
   multiple servers under a number of circumstances, each of which will
   be discussed under the appropriate functional section:

   o  When server owner values received in response to EXCHANGE_ID
      operations sent to multiple network addresses are compared for the
      purpose of determining the validity of various forms of trunking,
      as described in Section 2.10.5.

   o  When network or server reconfiguration causes the same network
      address to possibly be directed to different servers, with the
      necessity for the client to determine when lock reclaim should be
      attempted, as described in Section 8.4.2.1.

   o  When file system migration causes the transfer of responsibility
      for a file system between servers and the client needs to
      determine whether state has been transferred with the file system
      (as described in Section 11.7.7) or whether the client needs to
      reclaim state on a similar basis as in the case of server restart,
      as described in Section 8.4.2.

   When two replies from EXCHANGE_ID, each from two different server
   network addresses, have the same server scope, there are a number of
   ways a client can validate that the common server scope is due to two
   servers cooperating in a group.

   o  If both EXCHANGE_ID requests were sent with RPCSEC_GSS
      authentication and the server principal is the same for both
      targets, the equality of server scope is validated.  It is




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      RECOMMENDED that two servers intending to share the same server
      scope also share the same principal name.

   o  The client may accept the appearance of the second server in the
      fs_locations or fs_locations_info attribute for a relevant file
      system.  For example, if there is a migration event for a
      particular file system or there are locks to be reclaimed on a
      particular file system, the attributes for that particular file
      system may be used.  The client sends the GETATTR request to the
      first server for the fs_locations or fs_locations_info attribute
      with RPCSEC_GSS authentication.  It may need to do this in advance
      of the need to verify the common server scope.  If the client
      successfully authenticates the reply to GETATTR, and the GETATTR
      request and reply containing the fs_locations or fs_locations_info
      attribute refers to the second server, then the equality of server
      scope is supported.  A client may choose to limit the use of this
      form of support to information relevant to the specific file
      system involved (e.g. a file system being migrated).

2.10.5.  Trunking

   Trunking is the use of multiple connections between a client and
   server in order to increase the speed of data transfer.  NFSv4.1
   supports two types of trunking: session trunking and client ID
   trunking.

   NFSv4.1 servers MUST support both forms of trunking within the
   context of a single server network address and MUST support both
   forms within the context of the set of network addresses used to
   access a single server.  NFSv4.1 servers in a clustered configuration
   MAY allow network addresses for different servers to use client ID
   trunking.

   Clients may use either form of trunking as long as they do not, when
   trunking between different server network addresses, violate the
   servers' mandates as to the kinds of trunking to be allowed (see
   below).  With regard to callback channels, the client MUST allow the
   server to choose among all callback channels valid for a given client
   ID and MUST support trunking when the connections supporting the
   backchannel allow session or client ID trunking to be used for
   callbacks.

   Session trunking is essentially the association of multiple
   connections, each with potentially different target and/or source
   network addresses, to the same session.  When the target network
   addresses (server addresses) of the two connections are the same, the
   server MUST support such session trunking.  When the target network




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   addresses are different, the server MAY indicate such support using
   the data returned by the EXCHANGE_ID operation (see below).

   Client ID trunking is the association of multiple sessions to the
   same client ID.  Servers MUST support client ID trunking for two
   target network addresses whenever they allow session trunking for
   those same two network addresses.  In addition, a server MAY, by
   presenting the same major server owner ID (Section 2.5) and server
   scope (Section 2.10.4), allow an additional case of client ID
   trunking.  When two servers return the same major server owner and
   server scope, it means that the two servers are cooperating on
   locking state management, which is a prerequisite for client ID
   trunking.

   Distinguishing when the client is allowed to use session and client
   ID trunking requires understanding how the results of the EXCHANGE_ID
   (Section 18.35) operation identify a server.  Suppose a client sends
   EXCHANGE_IDs over two different connections, each with a possibly
   different target network address, but each EXCHANGE_ID operation has
   the same value in the eia_clientowner field.  If the same NFSv4.1
   server is listening over each connection, then each EXCHANGE_ID
   result MUST return the same values of eir_clientid,
   eir_server_owner.so_major_id, and eir_server_scope.  The client can
   then treat each connection as referring to the same server (subject
   to verification; see Section 2.10.5.1 later in this section), and it
   can use each connection to trunk requests and replies.  The client's
   choice is whether session trunking or client ID trunking applies.

   Session Trunking.  If the eia_clientowner argument is the same in two
      different EXCHANGE_ID requests, and the eir_clientid,
      eir_server_owner.so_major_id, eir_server_owner.so_minor_id, and
      eir_server_scope results match in both EXCHANGE_ID results, then
      the client is permitted to perform session trunking.  If the
      client has no session mapping to the tuple of eir_clientid,
      eir_server_owner.so_major_id, eir_server_scope, and
      eir_server_owner.so_minor_id, then it creates the session via a
      CREATE_SESSION operation over one of the connections, which
      associates the connection to the session.  If there is a session
      for the tuple, the client can send BIND_CONN_TO_SESSION to
      associate the connection to the session.

      Of course, if the client does not desire to use session trunking,
      it is not required to do so.  It can invoke CREATE_SESSION on the
      connection.  This will result in client ID trunking as described
      below.  It can also decide to drop the connection if it does not
      choose to use trunking.





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   Client ID Trunking.  If the eia_clientowner argument is the same in
      two different EXCHANGE_ID requests, and the eir_clientid,
      eir_server_owner.so_major_id, and eir_server_scope results match
      in both EXCHANGE_ID results, then the client is permitted to
      perform client ID trunking (regardless of whether the
      eir_server_owner.so_minor_id results match).  The client can
      associate each connection with different sessions, where each
      session is associated with the same server.

      The client completes the act of client ID trunking by invoking
      CREATE_SESSION on each connection, using the same client ID that
      was returned in eir_clientid.  These invocations create two
      sessions and also associate each connection with its respective
      session.  The client is free to decline to use client ID trunking
      by simply dropping the connection at this point.

      When doing client ID trunking, locking state is shared across
      sessions associated with that same client ID.  This requires the
      server to coordinate state across sessions.

   The client should be prepared for the possibility that
   eir_server_owner values may be different on subsequent EXCHANGE_ID
   requests made to the same network address, as a result of various
   sorts of reconfiguration events.  When this happens and the changes
   result in the invalidation of previously valid forms of trunking, the
   client should cease to use those forms, either by dropping
   connections or by adding sessions.  For a discussion of lock reclaim
   as it relates to such reconfiguration events, see Section 8.4.2.1.

2.10.5.1.  Verifying Claims of Matching Server Identity

   When two servers over two connections claim matching or partially
   matching eir_server_owner, eir_server_scope, and eir_clientid values,
   the client does not have to trust the servers' claims.  The client
   may verify these claims before trunking traffic in the following
   ways:

   o  For session trunking, clients SHOULD reliably verify if
      connections between different network paths are in fact associated
      with the same NFSv4.1 server and usable on the same session, and
      servers MUST allow clients to perform reliable verification.  When
      a client ID is created, the client SHOULD specify that
      BIND_CONN_TO_SESSION is to be verified according to the SP4_SSV or
      SP4_MACH_CRED (Section 18.35) state protection options.  For
      SP4_SSV, reliable verification depends on a shared secret (the
      SSV) that is established via the SET_SSV (Section 18.47)
      operation.




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      When a new connection is associated with the session (via the
      BIND_CONN_TO_SESSION operation, see Section 18.34), if the client
      specified SP4_SSV state protection for the BIND_CONN_TO_SESSION
      operation, the client MUST send the BIND_CONN_TO_SESSION with
      RPCSEC_GSS protection, using integrity or privacy, and an
      RPCSEC_GSS handle created with the GSS SSV mechanism
      (Section 2.10.9).

      If the client mistakenly tries to associate a connection to a
      session of a wrong server, the server will either reject the
      attempt because it is not aware of the session identifier of the
      BIND_CONN_TO_SESSION arguments, or it will reject the attempt
      because the RPCSEC_GSS authentication fails.  Even if the server
      mistakenly or maliciously accepts the connection association
      attempt, the RPCSEC_GSS verifier it computes in the response will
      not be verified by the client, so the client will know it cannot
      use the connection for trunking the specified session.

      If the client specified SP4_MACH_CRED state protection, the
      BIND_CONN_TO_SESSION operation will use RPCSEC_GSS integrity or
      privacy, using the same credential that was used when the client
      ID was created.  Mutual authentication via RPCSEC_GSS assures the
      client that the connection is associated with the correct session
      of the correct server.



   o  For client ID trunking, the client has at least two options for
      verifying that the same client ID obtained from two different
      EXCHANGE_ID operations came from the same server.  The first
      option is to use RPCSEC_GSS authentication when sending each
      EXCHANGE_ID operation.  Each time an EXCHANGE_ID is sent with
      RPCSEC_GSS authentication, the client notes the principal name of
      the GSS target.  If the EXCHANGE_ID results indicate that client
      ID trunking is possible, and the GSS targets' principal names are
      the same, the servers are the same and client ID trunking is
      allowed.

      The second option for verification is to use SP4_SSV protection.
      When the client sends EXCHANGE_ID, it specifies SP4_SSV
      protection.  The first EXCHANGE_ID the client sends always has to
      be confirmed by a CREATE_SESSION call.  The client then sends
      SET_SSV.  Later, the client sends EXCHANGE_ID to a second
      destination network address different from the one the first
      EXCHANGE_ID was sent to.  The client checks that each EXCHANGE_ID
      reply has the same eir_clientid, eir_server_owner.so_major_id, and
      eir_server_scope.  If so, the client verifies the claim by sending
      a CREATE_SESSION operation to the second destination address,



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      protected with RPCSEC_GSS integrity using an RPCSEC_GSS handle
      returned by the second EXCHANGE_ID.  If the server accepts the
      CREATE_SESSION request, and if the client verifies the RPCSEC_GSS
      verifier and integrity codes, then the client has proof the second
      server knows the SSV, and thus the two servers are cooperating for
      the purposes of specifying server scope and client ID trunking.

2.10.6.  Exactly Once Semantics

   Via the session, NFSv4.1 offers exactly once semantics (EOS) for
   requests sent over a channel.  EOS is supported on both the fore
   channel and backchannel.

   Each COMPOUND or CB_COMPOUND request that is sent with a leading
   SEQUENCE or CB_SEQUENCE operation MUST be executed by the receiver
   exactly once.  This requirement holds regardless of whether the
   request is sent with reply caching specified (see
   Section 2.10.6.1.3).  The requirement holds even if the requester is
   sending the request over a session created between a pNFS data client
   and pNFS data server.  To understand the rationale for this
   requirement, divide the requests into three classifications:

   o  Non-idempotent requests.

   o  Idempotent modifying requests.

   o  Idempotent non-modifying requests.

   An example of a non-idempotent request is RENAME.  Obviously, if a
   replier executes the same RENAME request twice, and the first
   execution succeeds, the re-execution will fail.  If the replier
   returns the result from the re-execution, this result is incorrect.
   Therefore, EOS is required for non-idempotent requests.

   An example of an idempotent modifying request is a COMPOUND request
   containing a WRITE operation.  Repeated execution of the same WRITE
   has the same effect as execution of that WRITE a single time.
   Nevertheless, enforcing EOS for WRITEs and other idempotent modifying
   requests is necessary to avoid data corruption.

   Suppose a client sends WRITE A to a noncompliant server that does not
   enforce EOS, and receives no response, perhaps due to a network
   partition.  The client reconnects to the server and re-sends WRITE A.
   Now, the server has outstanding two instances of A.  The server can
   be in a situation in which it executes and replies to the retry of A,
   while the first A is still waiting in the server's internal I/O
   system for some resource.  Upon receiving the reply to the second
   attempt of WRITE A, the client believes its WRITE is done so it is



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   free to send WRITE B, which overlaps the byte-range of A.  When the
   original A is dispatched from the server's I/O system and executed
   (thus the second time A will have been written), then what has been
   written by B can be overwritten and thus corrupted.

   An example of an idempotent non-modifying request is a COMPOUND
   containing SEQUENCE, PUTFH, READLINK, and nothing else.  The re-
   execution of such a request will not cause data corruption or produce
   an incorrect result.  Nonetheless, to keep the implementation simple,
   the replier MUST enforce EOS for all requests, whether or not
   idempotent and non-modifying.

   Note that true and complete EOS is not possible unless the server
   persists the reply cache in stable storage, and unless the server is
   somehow implemented to never require a restart (indeed, if such a
   server exists, the distinction between a reply cache kept in stable
   storage versus one that is not is one without meaning).  See
   Section 2.10.6.5 for a discussion of persistence in the reply cache.
   Regardless, even if the server does not persist the reply cache, EOS
   improves robustness and correctness over previous versions of NFS
   because the legacy duplicate request/reply caches were based on the
   ONC RPC transaction identifier (XID).  Section 2.10.6.1 explains the
   shortcomings of the XID as a basis for a reply cache and describes
   how NFSv4.1 sessions improve upon the XID.

2.10.6.1.  Slot Identifiers and Reply Cache

   The RPC layer provides a transaction ID (XID), which, while required
   to be unique, is not convenient for tracking requests for two
   reasons.  First, the XID is only meaningful to the requester; it
   cannot be interpreted by the replier except to test for equality with
   previously sent requests.  When consulting an RPC-based duplicate
   request cache, the opaqueness of the XID requires a computationally
   expensive look up (often via a hash that includes XID and source
   address).  NFSv4.1 requests use a non-opaque slot ID, which is an
   index into a slot table, which is far more efficient.  Second,
   because RPC requests can be executed by the replier in any order,
   there is no bound on the number of requests that may be outstanding
   at any time.  To achieve perfect EOS, using ONC RPC would require
   storing all replies in the reply cache.  XIDs are 32 bits; storing
   over four billion (2^32) replies in the reply cache is not practical.
   In practice, previous versions of NFS have chosen to store a fixed
   number of replies in the cache, and to use a least recently used
   (LRU) approach to replacing cache entries with new entries when the
   cache is full.  In NFSv4.1, the number of outstanding requests is
   bounded by the size of the slot table, and a sequence ID per slot is
   used to tell the replier when it is safe to delete a cached reply.




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   In the NFSv4.1 reply cache, when the requester sends a new request,
   it selects a slot ID in the range 0..N, where N is the replier's
   current maximum slot ID granted to the requester on the session over
   which the request is to be sent.  The value of N starts out as equal
   to ca_maxrequests - 1 (Section 18.36), but can be adjusted by the
   response to SEQUENCE or CB_SEQUENCE as described later in this
   section.  The slot ID must be unused by any of the requests that the
   requester has already active on the session.  "Unused" here means the
   requester has no outstanding request for that slot ID.

   A slot contains a sequence ID and the cached reply corresponding to
   the request sent with that sequence ID.  The sequence ID is a 32-bit
   unsigned value, and is therefore in the range 0..0xFFFFFFFF (2^32 -
   1).  The first time a slot is used, the requester MUST specify a
   sequence ID of one (Section 18.36).  Each time a slot is reused, the
   request MUST specify a sequence ID that is one greater than that of
   the previous request on the slot.  If the previous sequence ID was
   0xFFFFFFFF, then the next request for the slot MUST have the sequence
   ID set to zero (i.e., (2^32 - 1) + 1 mod 2^32).

   The sequence ID accompanies the slot ID in each request.  It is for
   the critical check at the replier: it used to efficiently determine
   whether a request using a certain slot ID is a retransmit or a new,
   never-before-seen request.  It is not feasible for the requester to
   assert that it is retransmitting to implement this, because for any
   given request the requester cannot know whether the replier has seen
   it unless the replier actually replies.  Of course, if the requester
   has seen the reply, the requester would not retransmit.

   The replier compares each received request's sequence ID with the
   last one previously received for that slot ID, to see if the new
   request is:

   o  A new request, in which the sequence ID is one greater than that
      previously seen in the slot (accounting for sequence wraparound).
      The replier proceeds to execute the new request, and the replier
      MUST increase the slot's sequence ID by one.

   o  A retransmitted request, in which the sequence ID is equal to that
      currently recorded in the slot.  If the original request has
      executed to completion, the replier returns the cached reply.  See
      Section 2.10.6.2 for direction on how the replier deals with
      retries of requests that are still in progress.

   o  A misordered retry, in which the sequence ID is less than
      (accounting for sequence wraparound) that previously seen in the
      slot.  The replier MUST return NFS4ERR_SEQ_MISORDERED (as the
      result from SEQUENCE or CB_SEQUENCE).



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   o  A misordered new request, in which the sequence ID is two or more
      than (accounting for sequence wraparound) that previously seen in
      the slot.  Note that because the sequence ID MUST wrap around to
      zero once it reaches 0xFFFFFFFF, a misordered new request and a
      misordered retry cannot be distinguished.  Thus, the replier MUST
      return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
      CB_SEQUENCE).

   Unlike the XID, the slot ID is always within a specific range; this
   has two implications.  The first implication is that for a given
   session, the replier need only cache the results of a limited number
   of COMPOUND requests.  The second implication derives from the first,
   which is that unlike XID-indexed reply caches (also known as
   duplicate request caches - DRCs), the slot ID-based reply cache
   cannot be overflowed.  Through use of the sequence ID to identify
   retransmitted requests, the replier does not need to actually cache
   the request itself, reducing the storage requirements of the reply
   cache further.  These facilities make it practical to maintain all
   the required entries for an effective reply cache.

   The slot ID, sequence ID, and session ID therefore take over the
   traditional role of the XID and source network address in the
   replier's reply cache implementation.  This approach is considerably
   more portable and completely robust -- it is not subject to the
   reassignment of ports as clients reconnect over IP networks.  In
   addition, the RPC XID is not used in the reply cache, enhancing
   robustness of the cache in the face of any rapid reuse of XIDs by the
   requester.  While the replier does not care about the XID for the
   purposes of reply cache management (but the replier MUST return the
   same XID that was in the request), nonetheless there are
   considerations for the XID in NFSv4.1 that are the same as all other
   previous versions of NFS.  The RPC XID remains in each message and
   needs to be formulated in NFSv4.1 requests as in any other ONC RPC
   request.  The reasons include:

   o  The RPC layer retains its existing semantics and implementation.

   o  The requester and replier must be able to interoperate at the RPC
      layer, prior to the NFSv4.1 decoding of the SEQUENCE or
      CB_SEQUENCE operation.

   o  If an operation is being used that does not start with SEQUENCE or
      CB_SEQUENCE (e.g., BIND_CONN_TO_SESSION), then the RPC XID is
      needed for correct operation to match the reply to the request.

   o  The SEQUENCE or CB_SEQUENCE operation may generate an error.  If
      so, the embedded slot ID, sequence ID, and session ID (if present)




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      in the request will not be in the reply, and the requester has
      only the XID to match the reply to the request.

   Given that well-formulated XIDs continue to be required, this begs
   the question: why do SEQUENCE and CB_SEQUENCE replies have a session
   ID, slot ID, and sequence ID?  Having the session ID in the reply
   means that the requester does not have to use the XID to look up the
   session ID, which would be necessary if the connection were
   associated with multiple sessions.  Having the slot ID and sequence
   ID in the reply means that the requester does not have to use the XID
   to look up the slot ID and sequence ID.  Furthermore, since the XID
   is only 32 bits, it is too small to guarantee the re-association of a
   reply with its request [37]; having session ID, slot ID, and sequence
   ID in the reply allows the client to validate that the reply in fact
   belongs to the matched request.

   The SEQUENCE (and CB_SEQUENCE) operation also carries a
   "highest_slotid" value, which carries additional requester slot usage
   information.  The requester MUST always indicate the slot ID
   representing the outstanding request with the highest-numbered slot
   value.  The requester should in all cases provide the most
   conservative value possible, although it can be increased somewhat
   above the actual instantaneous usage to maintain some minimum or
   optimal level.  This provides a way for the requester to yield unused
   request slots back to the replier, which in turn can use the
   information to reallocate resources.

   The replier responds with both a new target highest_slotid and an
   enforced highest_slotid, described as follows:

   o  The target highest_slotid is an indication to the requester of the
      highest_slotid the replier wishes the requester to be using.  This
      permits the replier to withdraw (or add) resources from a
      requester that has been found to not be using them, in order to
      more fairly share resources among a varying level of demand from
      other requesters.  The requester must always comply with the
      replier's value updates, since they indicate newly established
      hard limits on the requester's access to session resources.
      However, because of request pipelining, the requester may have
      active requests in flight reflecting prior values; therefore, the
      replier must not immediately require the requester to comply.



   o  The enforced highest_slotid indicates the highest slot ID the
      requester is permitted to use on a subsequent SEQUENCE or
      CB_SEQUENCE operation.  The replier's enforced highest_slotid




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      SHOULD be no less than the highest_slotid the requester indicated
      in the SEQUENCE or CB_SEQUENCE arguments.

      A requester can be intransigent with respect to lowering its
      highest_slotid argument to a Sequence operation, i.e. the
      requester continues to ignore the target highest_slotid in the
      response to a Sequence operation, and continues to set its
      highest_slotid argument to be higher than the target
      highest_slotid.  This can be considered particularly egregious
      behavior when the replier knows there are no outstanding requests
      with slot IDs higher than its target highest_slotid.  When faced
      with such intransigence, the replier is free to take more forceful
      action, and MAY reply with a new enforced highest_slotid that is
      less than its previous enforced highest_slotid.  Thereafter, if
      the requester continues to send requests with a highest_slotid
      that is greater than the replier's new enforced highest_slotid,
      the server MAY return NFS4ERR_BAD_HIGH_SLOT, unless the slot ID in
      the request is greater than the new enforced highest_slotid and
      the request is a retry.

      The replier SHOULD retain the slots it wants to retire until the
      requester sends a request with a highest_slotid less than or equal
      to the replier's new enforced highest_slotid.

      The requester can also be intransigent with respect to sending
      non-retry requests that have a slot ID that exceeds the replier's
      highest_slotid.  Once the replier has forcibly lowered the
      enforced highest_slotid, the requester is only allowed to send
      retries on slots that exceed the replier's highest_slotid.  If a
      request is received with a slot ID that is higher than the new
      enforced highest_slotid, and the sequence ID is one higher than
      what is in the slot's reply cache, then the server can both retire
      the slot and return NFS4ERR_BADSLOT (however, the server MUST NOT
      do one and not the other).  The reason it is safe to retire the
      slot is because by using the next sequence ID, the requester is
      indicating it has received the previous reply for the slot.



   o  The requester SHOULD use the lowest available slot when sending a
      new request.  This way, the replier may be able to retire slot
      entries faster.  However, where the replier is actively adjusting
      its granted highest_slotid, it will not be able to use only the
      receipt of the slot ID and highest_slotid in the request.  Neither
      the slot ID nor the highest_slotid used in a request may reflect
      the replier's current idea of the requester's session limit,
      because the request may have been sent from the requester before
      the update was received.  Therefore, in the downward adjustment



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      case, the replier may have to retain a number of reply cache
      entries at least as large as the old value of maximum requests
      outstanding, until it can infer that the requester has seen a
      reply containing the new granted highest_slotid.  The replier can
      infer that the requester has seen such a reply when it receives a
      new request with the same slot ID as the request replied to and
      the next higher sequence ID.

2.10.6.1.1.  Caching of SEQUENCE and CB_SEQUENCE Replies

   When a SEQUENCE or CB_SEQUENCE operation is successfully executed,
   its reply MUST always be cached.  Specifically, session ID, sequence
   ID, and slot ID MUST be cached in the reply cache.  The reply from
   SEQUENCE also includes the highest slot ID, target highest slot ID,
   and status flags.  Instead of caching these values, the server MAY
   re-compute the values from the current state of the fore channel,
   session, and/or client ID as appropriate.  Similarly, the reply from
   CB_SEQUENCE includes a highest slot ID and target highest slot ID.
   The client MAY re-compute the values from the current state of the
   session as appropriate.

   Regardless of whether or not a replier is re-computing highest slot
   ID, target slot ID, and status on replies to retries, the requester
   MUST NOT assume that the values are being re-computed whenever it
   receives a reply after a retry is sent, since it has no way of
   knowing whether the reply it has received was sent by the replier in
   response to the retry or is a delayed response to the original
   request.  Therefore, it may be the case that highest slot ID, target
   slot ID, or status bits may reflect the state of affairs when the
   request was first executed.  Although acting based on such delayed
   information is valid, it may cause the receiver of the reply to do
   unneeded work.  Requesters MAY choose to send additional requests to
   get the current state of affairs or use the state of affairs reported
   by subsequent requests, in preference to acting immediately on data
   that might be out of date.

2.10.6.1.2.  Errors from SEQUENCE and CB_SEQUENCE

   Any time SEQUENCE or CB_SEQUENCE returns an error, the sequence ID of
   the slot MUST NOT change.  The replier MUST NOT modify the reply
   cache entry for the slot whenever an error is returned from SEQUENCE
   or CB_SEQUENCE.

2.10.6.1.3.  Optional Reply Caching

   On a per-request basis, the requester can choose to direct the
   replier to cache the reply to all operations after the first
   operation (SEQUENCE or CB_SEQUENCE) via the sa_cachethis or



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   csa_cachethis fields of the arguments to SEQUENCE or CB_SEQUENCE.
   The reason it would not direct the replier to cache the entire reply
   is that the request is composed of all idempotent operations [34].
   Caching the reply may offer little benefit.  If the reply is too
   large (see Section 2.10.6.4), it may not be cacheable anyway.  Even
   if the reply to idempotent request is small enough to cache,
   unnecessarily caching the reply slows down the server and increases
   RPC latency.

   Whether or not the requester requests the reply to be cached has no
   effect on the slot processing.  If the results of SEQUENCE or
   CB_SEQUENCE are NFS4_OK, then the slot's sequence ID MUST be
   incremented by one.  If a requester does not direct the replier to
   cache the reply, the replier MUST do one of following:

   o  The replier can cache the entire original reply.  Even though
      sa_cachethis or csa_cachethis is FALSE, the replier is always free
      to cache.  It may choose this approach in order to simplify
      implementation.

   o  The replier enters into its reply cache a reply consisting of the
      original results to the SEQUENCE or CB_SEQUENCE operation, and
      with the next operation in COMPOUND or CB_COMPOUND having the
      error NFS4ERR_RETRY_UNCACHED_REP.  Thus, if the requester later
      retries the request, it will get NFS4ERR_RETRY_UNCACHED_REP.  If a
      replier receives a retried Sequence operation where the reply to
      the COMPOUND or CB_COMPOUND was not cached, then the replier,

      *  MAY return NFS4ERR_RETRY_UNCACHED_REP in reply to a Sequence
         operation if the Sequence operation is not the first operation
         (granted, a requester that does so is in violation of the
         NFSv4.1 protocol).

      *  MUST NOT return NFS4ERR_RETRY_UNCACHED_REP in reply to a
         Sequence operation if the Sequence operation is the first
         operation.

   o  If the second operation is an illegal operation, or an operation
      that was legal in a previous minor version of NFSv4 and MUST NOT
      be supported in the current minor version (e.g., SETCLIENTID), the
      replier MUST NOT ever return NFS4ERR_RETRY_UNCACHED_REP.  Instead
      the replier MUST return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
      NFS4ERR_NOTSUPP as appropriate.

   o  If the second operation can result in another error status, the
      replier MAY return a status other than NFS4ERR_RETRY_UNCACHED_REP,
      provided the operation is not executed in such a way that the
      state of the replier is changed.  Examples of such an error status



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      include: NFS4ERR_NOTSUPP returned for an operation that is legal
      but not REQUIRED in the current minor versions, and thus not
      supported by the replier; NFS4ERR_SEQUENCE_POS; and
      NFS4ERR_REQ_TOO_BIG.

   The discussion above assumes that the retried request matches the
   original one.  Section 2.10.6.1.3.1 discusses what the replier might
   do, and MUST do when original and retried requests do not match.
   Since the replier may only cache a small amount of the information
   that would be required to determine whether this is a case of a false
   retry, the replier may send to the client any of the following
   responses:

   o  The cached reply to the original request (if the replier has
      cached it in its entirety and the users of the original request
      and retry match).

   o  A reply that consists only of the Sequence operation with the
      error NFS4ERR_FALSE_RETRY.

   o  A reply consisting of the response to Sequence with the status
      NFS4_OK, together with the second operation as it appeared in the
      retried request with an error of NFS4ERR_RETRY_UNCACHED_REP or
      other error as described above.

   o  A reply that consists of the response to Sequence with the status
      NFS4_OK, together with the second operation as it appeared in the
      original request with an error of NFS4ERR_RETRY_UNCACHED_REP or
      other error as described above.

2.10.6.1.3.1.  False Retry

   If a requester sent a Sequence operation with a slot ID and sequence
   ID that are in the reply cache but the replier detected that the
   retried request is not the same as the original request, including a
   retry that has different operations or different arguments in the
   operations from the original and a retry that uses a different
   principal in the RPC request's credential field that translates to a
   different user, then this is a false retry.  When the replier detects
   a false retry, it is permitted (but not always obligated) to return
   NFS4ERR_FALSE_RETRY in response to the Sequence operation when it
   detects a false retry.

   Translations of particularly privileged user values to other users
   due to the lack of appropriately secure credentials, as configured on
   the replier, should be applied before determining whether the users
   are the same or different.  If the replier determines the users are




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   different between the original request and a retry, then the replier
   MUST return NFS4ERR_FALSE_RETRY.

   If an operation of the retry is an illegal operation, or an operation
   that was legal in a previous minor version of NFSv4 and MUST NOT be
   supported in the current minor version (e.g., SETCLIENTID), the
   replier MAY return NFS4ERR_FALSE_RETRY (and MUST do so if the users
   of the original request and retry differ).  Otherwise, the replier
   MAY return NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or NFS4ERR_NOTSUPP as
   appropriate.  Note that the handling is in contrast for how the
   replier deals with retries requests with no cached reply.  The
   difference is due to NFS4ERR_FALSE_RETRY being a valid error for only
   Sequence operations, whereas NFS4ERR_RETRY_UNCACHED_REP is a valid
   error for all operations except illegal operations and operations
   that MUST NOT be supported in the current minor version of NFSv4.

2.10.6.2.  Retry and Replay of Reply

   A requester MUST NOT retry a request, unless the connection it used
   to send the request disconnects.  The requester can then reconnect
   and re-send the request, or it can re-send the request over a
   different connection that is associated with the same session.

   If the requester is a server wanting to re-send a callback operation
   over the backchannel of a session, the requester of course cannot
   reconnect because only the client can associate connections with the
   backchannel.  The server can re-send the request over another
   connection that is bound to the same session's backchannel.  If there
   is no such connection, the server MUST indicate that the session has
   no backchannel by setting the SEQ4_STATUS_CB_PATH_DOWN_SESSION flag
   bit in the response to the next SEQUENCE operation from the client.
   The client MUST then associate a connection with the session (or
   destroy the session).

   Note that it is not fatal for a requester to retry without a
   disconnect between the request and retry.  However, the retry does
   consume resources, especially with RDMA, where each request, retry or
   not, consumes a credit.  Retries for no reason, especially retries
   sent shortly after the previous attempt, are a poor use of network
   bandwidth and defeat the purpose of a transport's inherent congestion
   control system.

   A requester MUST wait for a reply to a request before using the slot
   for another request.  If it does not wait for a reply, then the
   requester does not know what sequence ID to use for the slot on its
   next request.  For example, suppose a requester sends a request with
   sequence ID 1, and does not wait for the response.  The next time it
   uses the slot, it sends the new request with sequence ID 2.  If the



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   replier has not seen the request with sequence ID 1, then the replier
   is not expecting sequence ID 2, and rejects the requester's new
   request with NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or
   CB_SEQUENCE).

   RDMA fabrics do not guarantee that the memory handles (Steering Tags)
   within each RPC/RDMA "chunk" [8] are valid on a scope outside that of
   a single connection.  Therefore, handles used by the direct
   operations become invalid after connection loss.  The server must
   ensure that any RDMA operations that must be replayed from the reply
   cache use the newly provided handle(s) from the most recent request.

   A retry might be sent while the original request is still in progress
   on the replier.  The replier SHOULD deal with the issue by returning
   NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE operation, but
   implementations MAY return NFS4ERR_MISORDERED.  Since errors from
   SEQUENCE and CB_SEQUENCE are never recorded in the reply cache, this
   approach allows the results of the execution of the original request
   to be properly recorded in the reply cache (assuming that the
   requester specified the reply to be cached).

2.10.6.3.  Resolving Server Callback Races

   It is possible for server callbacks to arrive at the client before
   the reply from related fore channel operations.  For example, a
   client may have been granted a delegation to a file it has opened,
   but the reply to the OPEN (informing the client of the granting of
   the delegation) may be delayed in the network.  If a conflicting
   operation arrives at the server, it will recall the delegation using
   the backchannel, which may be on a different transport connection,
   perhaps even a different network, or even a different session
   associated with the same client ID.

   The presence of a session between the client and server alleviates
   this issue.  When a session is in place, each client request is
   uniquely identified by its { session ID, slot ID, sequence ID }
   triple.  By the rules under which slot entries (reply cache entries)
   are retired, the server has knowledge whether the client has "seen"
   each of the server's replies.  The server can therefore provide
   sufficient information to the client to allow it to disambiguate
   between an erroneous or conflicting callback race condition.

   For each client operation that might result in some sort of server
   callback, the server SHOULD "remember" the { session ID, slot ID,
   sequence ID } triple of the client request until the slot ID
   retirement rules allow the server to determine that the client has,
   in fact, seen the server's reply.  Until the time the { session ID,
   slot ID, sequence ID } request triple can be retired, any recalls of



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   the associated object MUST carry an array of these referring
   identifiers (in the CB_SEQUENCE operation's arguments), for the
   benefit of the client.  After this time, it is not necessary for the
   server to provide this information in related callbacks, since it is
   certain that a race condition can no longer occur.

   The CB_SEQUENCE operation that begins each server callback carries a
   list of "referring" { session ID, slot ID, sequence ID } triples.  If
   the client finds the request corresponding to the referring session
   ID, slot ID, and sequence ID to be currently outstanding (i.e., the
   server's reply has not been seen by the client), it can determine
   that the callback has raced the reply, and act accordingly.  If the
   client does not find the request corresponding to the referring
   triple to be outstanding (including the case of a session ID
   referring to a destroyed session), then there is no race with respect
   to this triple.  The server SHOULD limit the referring triples to
   requests that refer to just those that apply to the objects referred
   to in the CB_COMPOUND procedure.

   The client must not simply wait forever for the expected server reply
   to arrive before responding to the CB_COMPOUND that won the race,
   because it is possible that it will be delayed indefinitely.  The
   client should assume the likely case that the reply will arrive
   within the average round-trip time for COMPOUND requests to the
   server, and wait that period of time.  If that period of time
   expires, it can respond to the CB_COMPOUND with NFS4ERR_DELAY.  There
   are other scenarios under which callbacks may race replies.  Among
   them are pNFS layout recalls as described in Section 12.5.5.2.

2.10.6.4.  COMPOUND and CB_COMPOUND Construction Issues

   Very large requests and replies may pose both buffer management
   issues (especially with RDMA) and reply cache issues.  When the
   session is created (Section 18.36), for each channel (fore and back),
   the client and server negotiate the maximum-sized request they will
   send or process (ca_maxrequestsize), the maximum-sized reply they
   will return or process (ca_maxresponsesize), and the maximum-sized
   reply they will store in the reply cache (ca_maxresponsesize_cached).

   If a request exceeds ca_maxrequestsize, the reply will have the
   status NFS4ERR_REQ_TOO_BIG.  A replier MAY return NFS4ERR_REQ_TOO_BIG
   as the status for the first operation (SEQUENCE or CB_SEQUENCE) in
   the request (which means that no operations in the request executed
   and that the state of the slot in the reply cache is unchanged), or
   it MAY opt to return it on a subsequent operation in the same
   COMPOUND or CB_COMPOUND request (which means that at least one
   operation did execute and that the state of the slot in the reply




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   cache does change).  The replier SHOULD set NFS4ERR_REQ_TOO_BIG on
   the operation that exceeds ca_maxrequestsize.

   If a reply exceeds ca_maxresponsesize, the reply will have the status
   NFS4ERR_REP_TOO_BIG.  A replier MAY return NFS4ERR_REP_TOO_BIG as the
   status for the first operation (SEQUENCE or CB_SEQUENCE) in the
   request, or it MAY opt to return it on a subsequent operation (in the
   same COMPOUND or CB_COMPOUND reply).  A replier MAY return
   NFS4ERR_REP_TOO_BIG in the reply to SEQUENCE or CB_SEQUENCE, even if
   the response would still exceed ca_maxresponsesize.

   If sa_cachethis or csa_cachethis is TRUE, then the replier MUST cache
   a reply except if an error is returned by the SEQUENCE or CB_SEQUENCE
   operation (see Section 2.10.6.1.2).  If the reply exceeds
   ca_maxresponsesize_cached (and sa_cachethis or csa_cachethis is
   TRUE), then the server MUST return NFS4ERR_REP_TOO_BIG_TO_CACHE.
   Even if NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for that
   matter) is returned on an operation other than the first operation
   (SEQUENCE or CB_SEQUENCE), then the reply MUST be cached if
   sa_cachethis or csa_cachethis is TRUE.  For example, if a COMPOUND
   has eleven operations, including SEQUENCE, the fifth operation is a
   RENAME, and the tenth operation is a READ for one million bytes, the
   server may return NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth
   operation.  Since the server executed several operations, especially
   the non-idempotent RENAME, the client's request to cache the reply
   needs to be honored in order for the correct operation of exactly
   once semantics.  If the client retries the request, the server will
   have cached a reply that contains results for ten of the eleven
   requested operations, with the tenth operation having a status of
   NFS4ERR_REP_TOO_BIG_TO_CACHE.

   A client needs to take care that when sending operations that change
   the current filehandle (except for PUTFH, PUTPUBFH, PUTROOTFH, and
   RESTOREFH), it not exceed the maximum reply buffer before the GETFH
   operation.  Otherwise, the client will have to retry the operation
   that changed the current filehandle, in order to obtain the desired
   filehandle.  For the OPEN operation (see Section 18.16), retry is not
   always available as an option.  The following guidelines for the
   handling of filehandle-changing operations are advised:

   o  Within the same COMPOUND procedure, a client SHOULD send GETFH
      immediately after a current filehandle-changing operation.  A
      client MUST send GETFH after a current filehandle-changing
      operation that is also non-idempotent (e.g., the OPEN operation),
      unless the operation is RESTOREFH.  RESTOREFH is an exception,
      because even though it is non-idempotent, the filehandle RESTOREFH
      produced originated from an operation that is either idempotent
      (e.g., PUTFH, LOOKUP), or non-idempotent (e.g., OPEN, CREATE).  If



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      the origin is non-idempotent, then because the client MUST send
      GETFH after the origin operation, the client can recover if
      RESTOREFH returns an error.

   o  A server MAY return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle-changing operation if the reply would be too large on
      the next operation.

   o  A server SHOULD return NFS4ERR_REP_TOO_BIG or
      NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE) on a
      filehandle-changing, non-idempotent operation if the reply would
      be too large on the next operation, especially if the operation is
      OPEN.

   o  A server MAY return NFS4ERR_UNSAFE_COMPOUND to a non-idempotent
      current filehandle-changing operation, if it looks at the next
      operation (in the same COMPOUND procedure) and finds it is not
      GETFH.  The server SHOULD do this if it is unable to determine in
      advance whether the total response size would exceed
      ca_maxresponsesize_cached or ca_maxresponsesize.

2.10.6.5.  Persistence

   Since the reply cache is bounded, it is practical for the reply cache
   to persist across server restarts.  The replier MUST persist the
   following information if it agreed to persist the session (when the
   session was created; see Section 18.36):

   o  The session ID.

   o  The slot table including the sequence ID and cached reply for each
      slot.

   The above are sufficient for a replier to provide EOS semantics for
   any requests that were sent and executed before the server restarted.
   If the replier is a client, then there is no need for it to persist
   any more information, unless the client will be persisting all other
   state across client restart, in which case, the server will never see
   any NFSv4.1-level protocol manifestation of a client restart.  If the
   replier is a server, with just the slot table and session ID
   persisting, any requests the client retries after the server restart
   will return the results that are cached in the reply cache, and any
   new requests (i.e., the sequence ID is one greater than the slot's
   sequence ID) MUST be rejected with NFS4ERR_DEADSESSION (returned by
   SEQUENCE).  Such a session is considered dead.  A server MAY re-
   animate a session after a server restart so that the session will
   accept new requests as well as retries.  To re-animate a session, the



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   server needs to persist additional information through server
   restart:

   o  The client ID.  This is a prerequisite to let the client create
      more sessions associated with the same client ID as the re-
      animated session.

   o  The client ID's sequence ID that is used for creating sessions
      (see Sections 18.35 and 18.36).  This is a prerequisite to let the
      client create more sessions.

   o  The principal that created the client ID.  This allows the server
      to authenticate the client when it sends EXCHANGE_ID.

   o  The SSV, if SP4_SSV state protection was specified when the client
      ID was created (see Section 18.35).  This lets the client create
      new sessions, and associate connections with the new and existing
      sessions.

   o  The properties of the client ID as defined in Section 18.35.

   A persistent reply cache places certain demands on the server.  The
   execution of the sequence of operations (starting with SEQUENCE) and
   placement of its results in the persistent cache MUST be atomic.  If
   a client retries a sequence of operations that was previously
   executed on the server, the only acceptable outcomes are either the
   original cached reply or an indication that the client ID or session
   has been lost (indicating a catastrophic loss of the reply cache or a
   session that has been deleted because the client failed to use the
   session for an extended period of time).

   A server could fail and restart in the middle of a COMPOUND procedure
   that contains one or more non-idempotent or idempotent-but-modifying
   operations.  This creates an even higher challenge for atomic
   execution and placement of results in the reply cache.  One way to
   view the problem is as a single transaction consisting of each
   operation in the COMPOUND followed by storing the result in
   persistent storage, then finally a transaction commit.  If there is a
   failure before the transaction is committed, then the server rolls
   back the transaction.  If the server itself fails, then when it
   restarts, its recovery logic could roll back the transaction before
   starting the NFSv4.1 server.

   While the description of the implementation for atomic execution of
   the request and caching of the reply is beyond the scope of this
   document, an example implementation for NFSv2 [38] is described in
   [39].




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2.10.7.  RDMA Considerations

   A complete discussion of the operation of RPC-based protocols over
   RDMA transports is in [8].  A discussion of the operation of NFSv4,
   including NFSv4.1, over RDMA is in [9].  Where RDMA is considered,
   this specification assumes the use of such a layering; it addresses
   only the upper-layer issues relevant to making best use of RPC/RDMA.

2.10.7.1.  RDMA Connection Resources

   RDMA requires its consumers to register memory and post buffers of a
   specific size and number for receive operations.

   Registration of memory can be a relatively high-overhead operation,
   since it requires pinning of buffers, assignment of attributes (e.g.,
   readable/writable), and initialization of hardware translation.
   Preregistration is desirable to reduce overhead.  These registrations
   are specific to hardware interfaces and even to RDMA connection
   endpoints; therefore, negotiation of their limits is desirable to
   manage resources effectively.

   Following basic registration, these buffers must be posted by the RPC
   layer to handle receives.  These buffers remain in use by the RPC/
   NFSv4.1 implementation; the size and number of them must be known to
   the remote peer in order to avoid RDMA errors that would cause a
   fatal error on the RDMA connection.

   NFSv4.1 manages slots as resources on a per-session basis (see
   Section 2.10), while RDMA connections manage credits on a per-
   connection basis.  This means that in order for a peer to send data
   over RDMA to a remote buffer, it has to have both an NFSv4.1 slot and
   an RDMA credit.  If multiple RDMA connections are associated with a
   session, then if the total number of credits across all RDMA
   connections associated with the session is X, and the number of slots
   in the session is Y, then the maximum number of outstanding requests
   is the lesser of X and Y.

2.10.7.2.  Flow Control

   Previous versions of NFS do not provide flow control; instead, they
   rely on the windowing provided by transports like TCP to throttle
   requests.  This does not work with RDMA, which provides no operation
   flow control and will terminate a connection in error when limits are
   exceeded.  Limits such as maximum number of requests outstanding are
   therefore negotiated when a session is created (see the
   ca_maxrequests field in Section 18.36).  These limits then provide
   the maxima within which each connection associated with the session's
   channel(s) must remain.  RDMA connections are managed within these



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   limits as described in Section 3.3 of [8]; if there are multiple RDMA
   connections, then the maximum number of requests for a channel will
   be divided among the RDMA connections.  Put a different way, the onus
   is on the replier to ensure that the total number of RDMA credits
   across all connections associated with the replier's channel does
   exceed the channel's maximum number of outstanding requests.

   The limits may also be modified dynamically at the replier's choosing
   by manipulating certain parameters present in each NFSv4.1 reply.  In
   addition, the CB_RECALL_SLOT callback operation (see Section 20.8)
   can be sent by a server to a client to return RDMA credits to the
   server, thereby lowering the maximum number of requests a client can
   have outstanding to the server.

2.10.7.3.  Padding

   Header padding is requested by each peer at session initiation (see
   the ca_headerpadsize argument to CREATE_SESSION in Section 18.36),
   and subsequently used by the RPC RDMA layer, as described in [8].
   Zero padding is permitted.

   Padding leverages the useful property that RDMA preserve alignment of
   data, even when they are placed into anonymous (untagged) buffers.
   If requested, client inline writes will insert appropriate pad bytes
   within the request header to align the data payload on the specified
   boundary.  The client is encouraged to add sufficient padding (up to
   the negotiated size) so that the "data" field of the WRITE operation
   is aligned.  Most servers can make good use of such padding, which
   allows them to chain receive buffers in such a way that any data
   carried by client requests will be placed into appropriate buffers at
   the server, ready for file system processing.  The receiver's RPC
   layer encounters no overhead from skipping over pad bytes, and the
   RDMA layer's high performance makes the insertion and transmission of
   padding on the sender a significant optimization.  In this way, the
   need for servers to perform RDMA Read to satisfy all but the largest
   client writes is obviated.  An added benefit is the reduction of
   message round trips on the network -- a potentially good trade, where
   latency is present.

   The value to choose for padding is subject to a number of criteria.
   A primary source of variable-length data in the RPC header is the
   authentication information, the form of which is client-determined,
   possibly in response to server specification.  The contents of
   COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
   go into the determination of a maximal NFSv4.1 request size and
   therefore minimal buffer size.  The client must select its offered
   value carefully, so as to avoid overburdening the server, and vice




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   versa.  The benefit of an appropriate padding value is higher
   performance.

                    Sender gather:
        |RPC Request|Pad  bytes|Length| -> |User data...|
        \------+----------------------/      \
                \                             \
                 \    Receiver scatter:        \-----------+- ...
            /-----+----------------\            \           \
            |RPC Request|Pad|Length|   ->  |FS buffer|->|FS buffer|->...

   In the above case, the server may recycle unused buffers to the next
   posted receive if unused by the actual received request, or may pass
   the now-complete buffers by reference for normal write processing.
   For a server that can make use of it, this removes any need for data
   copies of incoming data, without resorting to complicated end-to-end
   buffer advertisement and management.  This includes most kernel-based
   and integrated server designs, among many others.  The client may
   perform similar optimizations, if desired.

2.10.7.4.  Dual RDMA and Non-RDMA Transports

   Some RDMA transports (e.g., RFC 5040 [10]) permit a "streaming" (non-
   RDMA) phase, where ordinary traffic might flow before "stepping up"
   to RDMA mode, commencing RDMA traffic.  Some RDMA transports start
   connections always in RDMA mode.  NFSv4.1 allows, but does not
   assume, a streaming phase before RDMA mode.  When a connection is
   associated with a session, the client and server negotiate whether
   the connection is used in RDMA or non-RDMA mode (see Sections 18.36
   and 18.34).

2.10.8.  Session Security

2.10.8.1.  Session Callback Security

   Via session/connection association, NFSv4.1 improves security over
   that provided by NFSv4.0 for the backchannel.  The connection is
   client-initiated (see Section 18.34) and subject to the same firewall
   and routing checks as the fore channel.  At the client's option (see
   Section 18.35), connection association is fully authenticated before
   being activated (see Section 18.34).  Traffic from the server over
   the backchannel is authenticated exactly as the client specifies (see
   Section 2.10.8.2).








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2.10.8.2.  Backchannel RPC Security

   When the NFSv4.1 client establishes the backchannel, it informs the
   server of the security flavors and principals to use when sending
   requests.  If the security flavor is RPCSEC_GSS, the client expresses
   the principal in the form of an established RPCSEC_GSS context.  The
   server is free to use any of the flavor/principal combinations the
   client offers, but it MUST NOT use unoffered combinations.  This way,
   the client need not provide a target GSS principal for the
   backchannel as it did with NFSv4.0, nor does the server have to
   implement an RPCSEC_GSS initiator as it did with NFSv4.0 [30].

   The CREATE_SESSION (Section 18.36) and BACKCHANNEL_CTL
   (Section 18.33) operations allow the client to specify flavor/
   principal combinations.

   Also note that the SP4_SSV state protection mode (see Sections 18.35
   and 2.10.8.3) has the side benefit of providing SSV-derived
   RPCSEC_GSS contexts (Section 2.10.9).

2.10.8.3.  Protection from Unauthorized State Changes

   As described to this point in the specification, the state model of
   NFSv4.1 is vulnerable to an attacker that sends a SEQUENCE operation
   with a forged session ID and with a slot ID that it expects the
   legitimate client to use next.  When the legitimate client uses the
   slot ID with the same sequence number, the server returns the
   attacker's result from the reply cache, which disrupts the legitimate
   client and thus denies service to it.  Similarly, an attacker could
   send a CREATE_SESSION with a forged client ID to create a new session
   associated with the client ID.  The attacker could send requests
   using the new session that change locking state, such as LOCKU
   operations to release locks the legitimate client has acquired.
   Setting a security policy on the file that requires RPCSEC_GSS
   credentials when manipulating the file's state is one potential work
   around, but has the disadvantage of preventing a legitimate client
   from releasing state when RPCSEC_GSS is required to do so, but a GSS
   context cannot be obtained (possibly because the user has logged off
   the client).

   NFSv4.1 provides three options to a client for state protection,
   which are specified when a client creates a client ID via EXCHANGE_ID
   (Section 18.35).

   The first (SP4_NONE) is to simply waive state protection.

   The other two options (SP4_MACH_CRED and SP4_SSV) share several
   traits:



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   o  An RPCSEC_GSS-based credential is used to authenticate client ID
      and session maintenance operations, including creating and
      destroying a session, associating a connection with the session,
      and destroying the client ID.

   o  Because RPCSEC_GSS is used to authenticate client ID and session
      maintenance, the attacker cannot associate a rogue connection with
      a legitimate session, or associate a rogue session with a
      legitimate client ID in order to maliciously alter the client ID's
      lock state via CLOSE, LOCKU, DELEGRETURN, LAYOUTRETURN, etc.

   o  In cases where the server's security policies on a portion of its
      namespace require RPCSEC_GSS authentication, a client may have to
      use an RPCSEC_GSS credential to remove per-file state (e.g.,
      LOCKU, CLOSE, etc.).  The server may require that the principal
      that removes the state match certain criteria (e.g., the principal
      might have to be the same as the one that acquired the state).
      However, the client might not have an RPCSEC_GSS context for such
      a principal, and might not be able to create such a context
      (perhaps because the user has logged off).  When the client
      establishes SP4_MACH_CRED or SP4_SSV protection, it can specify a
      list of operations that the server MUST allow using the machine
      credential (if SP4_MACH_CRED is used) or the SSV credential (if
      SP4_SSV is used).

   The SP4_MACH_CRED state protection option uses a machine credential
   where the principal that creates the client ID MUST also be the
   principal that performs client ID and session maintenance operations.
   The security of the machine credential state protection approach
   depends entirely on safe guarding the per-machine credential.
   Assuming a proper safeguard using the per-machine credential for
   operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
   DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker from
   associating a rogue connection with a session, or associating a rogue
   session with a client ID.

   There are at least three scenarios for the SP4_MACH_CRED option:

   1.  The system administrator configures a unique, permanent per-
       machine credential for one of the mandated GSS mechanisms (e.g.,
       if Kerberos V5 is used, a "keytab" containing a principal derived
       from a client host name could be used).

   2.  The client is used by a single user, and so the client ID and its
       sessions are used by just that user.  If the user's credential
       expires, then session and client ID maintenance cannot occur, but
       since the client has a single user, only that user is
       inconvenienced.



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   3.  The physical client has multiple users, but the client
       implementation has a unique client ID for each user.  This is
       effectively the same as the second scenario, but a disadvantage
       is that each user needs to be allocated at least one session
       each, so the approach suffers from lack of economy.

   The SP4_SSV protection option uses the SSV (Section 1.6), via
   RPCSEC_GSS and the SSV GSS mechanism (Section 2.10.9), to protect
   state from attack.  The SP4_SSV protection option is intended for the
   situation comprised of a client that has multiple active users and a
   system administrator who wants to avoid the burden of installing a
   permanent machine credential on each client.  The SSV is established
   and updated on the server via SET_SSV (see Section 18.47).  To
   prevent eavesdropping, a client SHOULD send SET_SSV via RPCSEC_GSS
   with the privacy service.  Several aspects of the SSV make it
   intractable for an attacker to guess the SSV, and thus associate
   rogue connections with a session, and rogue sessions with a client
   ID:

   o  The arguments to and results of SET_SSV include digests of the old
      and new SSV, respectively.

   o  Because the initial value of the SSV is zero, therefore known, the
      client that opts for SP4_SSV protection and opts to apply SP4_SSV
      protection to BIND_CONN_TO_SESSION and CREATE_SESSION MUST send at
      least one SET_SSV operation before the first BIND_CONN_TO_SESSION
      operation or before the second CREATE_SESSION operation on a
      client ID.  If it does not, the SSV mechanism will not generate
      tokens (Section 2.10.9).  A client SHOULD send SET_SSV as soon as
      a session is created.

   o  A SET_SSV request does not replace the SSV with the argument to
      SET_SSV.  Instead, the current SSV on the server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.  Each time a
      new principal uses a client ID for the first time, the client
      SHOULD send a SET_SSV with that principal's RPCSEC_GSS
      credentials, with RPCSEC_GSS service set to RPC_GSS_SVC_PRIVACY.

   Here are the types of attacks that can be attempted by an attacker
   named Eve on a victim named Bob, and how SP4_SSV protection foils
   each attack:

   o  Suppose Eve is the first user to log into a legitimate client.
      Eve's use of an NFSv4.1 file system will cause the legitimate
      client to create a client ID with SP4_SSV protection, specifying
      that the BIND_CONN_TO_SESSION operation MUST use the SSV
      credential.  Eve's use of the file system also causes an SSV to be
      created.  The SET_SSV operation that creates the SSV will be



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      protected by the RPCSEC_GSS context created by the legitimate
      client, which uses Eve's GSS principal and credentials.  Eve can
      eavesdrop on the network while her RPCSEC_GSS context is created
      and the SET_SSV using her context is sent.  Even if the legitimate
      client sends the SET_SSV with RPC_GSS_SVC_PRIVACY, because Eve
      knows her own credentials, she can decrypt the SSV.  Eve can
      compute an RPCSEC_GSS credential that BIND_CONN_TO_SESSION will
      accept, and so associate a new connection with the legitimate
      session.  Eve can change the slot ID and sequence state of a
      legitimate session, and/or the SSV state, in such a way that when
      Bob accesses the server via the same legitimate client, the
      legitimate client will be unable to use the session.

      The client's only recourse is to create a new client ID for Bob to
      use, and establish a new SSV for the client ID.  The client will
      be unable to delete the old client ID, and will let the lease on
      the old client ID expire.

      Once the legitimate client establishes an SSV over the new session
      using Bob's RPCSEC_GSS context, Eve can use the new session via
      the legitimate client, but she cannot disrupt Bob.  Moreover,
      because the client SHOULD have modified the SSV due to Eve using
      the new session, Bob cannot get revenge on Eve by associating a
      rogue connection with the session.

      The question is how did the legitimate client detect that Eve has
      hijacked the old session?  When the client detects that a new
      principal, Bob, wants to use the session, it SHOULD have sent a
      SET_SSV, which leads to the following sub-scenarios:



      *  Let us suppose that from the rogue connection, Eve sent a
         SET_SSV with the same slot ID and sequence ID that the
         legitimate client later uses.  The server will assume the
         SET_SSV sent with Bob's credentials is a retry, and return to
         the legitimate client the reply it sent Eve.  However, unless
         Eve can correctly guess the SSV the legitimate client will use,
         the digest verification checks in the SET_SSV response will
         fail.  That is an indication to the client that the session has
         apparently been hijacked.



      *  Alternatively, Eve sent a SET_SSV with a different slot ID than
         the legitimate client uses for its SET_SSV.  Then the digest
         verification of the SET_SSV sent with Bob's credentials fails




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         on the server, and the error returned to the client makes it
         apparent that the session has been hijacked.



      *  Alternatively, Eve sent an operation other than SET_SSV, but
         with the same slot ID and sequence that the legitimate client
         uses for its SET_SSV.  The server returns to the legitimate
         client the response it sent Eve.  The client sees that the
         response is not at all what it expects.  The client assumes
         either session hijacking or a server bug, and either way
         destroys the old session.



   o  Eve associates a rogue connection with the session as above, and
      then destroys the session.  Again, Bob goes to use the server from
      the legitimate client, which sends a SET_SSV using Bob's
      credentials.  The client receives an error that indicates that the
      session does not exist.  When the client tries to create a new
      session, this will fail because the SSV it has does not match that
      which the server has, and now the client knows the session was
      hijacked.  The legitimate client establishes a new client ID.



   o  If Eve creates a connection before the legitimate client
      establishes an SSV, because the initial value of the SSV is zero
      and therefore known, Eve can send a SET_SSV that will pass the
      digest verification check.  However, because the new connection
      has not been associated with the session, the SET_SSV is rejected
      for that reason.



   In summary, an attacker's disruption of state when SP4_SSV protection
   is in use is limited to the formative period of a client ID, its
   first session, and the establishment of the SSV.  Once a non-
   malicious user uses the client ID, the client quickly detects any
   hijack and rectifies the situation.  Once a non-malicious user
   successfully modifies the SSV, the attacker cannot use NFSv4.1
   operations to disrupt the non-malicious user.

   Note that neither the SP4_MACH_CRED nor SP4_SSV protection approaches
   prevent hijacking of a transport connection that has previously been
   associated with a session.  If the goal of a counter-threat strategy
   is to prevent connection hijacking, the use of IPsec is RECOMMENDED.




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   If a connection hijack occurs, the hijacker could in theory change
   locking state and negatively impact the service to legitimate
   clients.  However, if the server is configured to require the use of
   RPCSEC_GSS with integrity or privacy on the affected file objects,
   and if EXCHGID4_FLAG_BIND_PRINC_STATEID capability (Section 18.35) is
   in force, this will thwart unauthorized attempts to change locking
   state.

2.10.9.  The Secret State Verifier (SSV) GSS Mechanism

   The SSV provides the secret key for a GSS mechanism internal to
   NFSv4.1 that NFSv4.1 uses for state protection.  Contexts for this
   mechanism are not established via the RPCSEC_GSS protocol.  Instead,
   the contexts are automatically created when EXCHANGE_ID specifies
   SP4_SSV protection.  The only tokens defined are the PerMsgToken
   (emitted by GSS_GetMIC) and the SealedMessage token (emitted by
   GSS_Wrap).

   The mechanism OID for the SSV mechanism is
   iso.org.dod.internet.private.enterprise.Michael Eisler.nfs.ssv_mech
   (1.3.6.1.4.1.28882.1.1).  While the SSV mechanism does not define any
   initial context tokens, the OID can be used to let servers indicate
   that the SSV mechanism is acceptable whenever the client sends a
   SECINFO or SECINFO_NO_NAME operation (see Section 2.6).

   The SSV mechanism defines four subkeys derived from the SSV value.
   Each time SET_SSV is invoked, the subkeys are recalculated by the
   client and server.  The calculation of each of the four subkeys
   depends on each of the four respective ssv_subkey4 enumerated values.
   The calculation uses the HMAC [11] algorithm, using the current SSV
   as the key, the one-way hash algorithm as negotiated by EXCHANGE_ID,
   and the input text as represented by the XDR encoded enumeration
   value for that subkey of data type ssv_subkey4.  If the length of the
   output of the HMAC algorithm exceeds the length of key of the
   encryption algorithm (which is also negotiated by EXCHANGE_ID), then
   the subkey MUST be truncated from the HMAC output, i.e., if the
   subkey is of N bytes long, then the first N bytes of the HMAC output
   MUST be used for the subkey.  The specification of EXCHANGE_ID states
   that the length of the output of the HMAC algorithm MUST NOT be less
   than the length of subkey needed for the encryption algorithm (see
   Section 18.35).










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   /* Input for computing subkeys */
   enum ssv_subkey4 {
           SSV4_SUBKEY_MIC_I2T     = 1,
           SSV4_SUBKEY_MIC_T2I     = 2,
           SSV4_SUBKEY_SEAL_I2T    = 3,
           SSV4_SUBKEY_SEAL_T2I    = 4
   };


   The subkey derived from SSV4_SUBKEY_MIC_I2T is used for calculating
   message integrity codes (MICs) that originate from the NFSv4.1
   client, whether as part of a request over the fore channel or a
   response over the backchannel.  The subkey derived from
   SSV4_SUBKEY_MIC_T2I is used for MICs originating from the NFSv4.1
   server.  The subkey derived from SSV4_SUBKEY_SEAL_I2T is used for
   encryption text originating from the NFSv4.1 client, and the subkey
   derived from SSV4_SUBKEY_SEAL_T2I is used for encryption text
   originating from the NFSv4.1 server.

   The PerMsgToken description is based on an XDR definition:


   /* Input for computing smt_hmac */
   struct ssv_mic_plain_tkn4 {
     uint32_t        smpt_ssv_seq;
     opaque          smpt_orig_plain<>;
   };



   /* SSV GSS PerMsgToken token */
   struct ssv_mic_tkn4 {
     uint32_t        smt_ssv_seq;
     opaque          smt_hmac<>;
   };


   The field smt_hmac is an HMAC calculated by using the subkey derived
   from SSV4_SUBKEY_MIC_I2T or SSV4_SUBKEY_MIC_T2I as the key, the one-
   way hash algorithm as negotiated by EXCHANGE_ID, and the input text
   as represented by data of type ssv_mic_plain_tkn4.  The field
   smpt_ssv_seq is the same as smt_ssv_seq.  The field smpt_orig_plain
   is the "message" input passed to GSS_GetMIC() (see Section 2.3.1 of
   [7]).  The caller of GSS_GetMIC() provides a pointer to a buffer
   containing the plain text.  The SSV mechanism's entry point for
   GSS_GetMIC() encodes this into an opaque array, and the encoding will
   include an initial four-byte length, plus any necessary padding.
   Prepended to this will be the XDR encoded value of smpt_ssv_seq, thus



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   making up an XDR encoding of a value of data type ssv_mic_plain_tkn4,
   which in turn is the input into the HMAC.

   The token emitted by GSS_GetMIC() is XDR encoded and of XDR data type
   ssv_mic_tkn4.  The field smt_ssv_seq comes from the SSV sequence
   number, which is equal to one after SET_SSV (Section 18.47) is called
   the first time on a client ID.  Thereafter, the SSV sequence number
   is incremented on each SET_SSV.  Thus, smt_ssv_seq represents the
   version of the SSV at the time GSS_GetMIC() was called.  As noted in
   Section 18.35, the client and server can maintain multiple concurrent
   versions of the SSV.  This allows the SSV to be changed without
   serializing all RPC calls that use the SSV mechanism with SET_SSV
   operations.  Once the HMAC is calculated, it is XDR encoded into
   smt_hmac, which will include an initial four-byte length, and any
   necessary padding.  Prepended to this will be the XDR encoded value
   of smt_ssv_seq.

   The SealedMessage description is based on an XDR definition:


   /* Input for computing ssct_encr_data and ssct_hmac */
   struct ssv_seal_plain_tkn4 {
     opaque          sspt_confounder<>;
     uint32_t        sspt_ssv_seq;
     opaque          sspt_orig_plain<>;
     opaque          sspt_pad<>;
   };



   /* SSV GSS SealedMessage token */
   struct ssv_seal_cipher_tkn4 {
     uint32_t      ssct_ssv_seq;
     opaque        ssct_iv<>;
     opaque        ssct_encr_data<>;
     opaque        ssct_hmac<>;
   };


   The token emitted by GSS_Wrap() is XDR encoded and of XDR data type
   ssv_seal_cipher_tkn4.

   The ssct_ssv_seq field has the same meaning as smt_ssv_seq.

   The ssct_encr_data field is the result of encrypting a value of the
   XDR encoded data type ssv_seal_plain_tkn4.  The encryption key is the
   subkey derived from SSV4_SUBKEY_SEAL_I2T or SSV4_SUBKEY_SEAL_T2I, and
   the encryption algorithm is that negotiated by EXCHANGE_ID.



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   The ssct_iv field is the initialization vector (IV) for the
   encryption algorithm (if applicable) and is sent in clear text.  The
   content and size of the IV MUST comply with the specification of the
   encryption algorithm.  For example, the id-aes256-CBC algorithm MUST
   use a 16-byte initialization vector (IV), which MUST be unpredictable
   for each instance of a value of data type ssv_seal_plain_tkn4 that is
   encrypted with a particular SSV key.

   The ssct_hmac field is the result of computing an HMAC using the
   value of the XDR encoded data type ssv_seal_plain_tkn4 as the input
   text.  The key is the subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I, and the one-way hash algorithm is that
   negotiated by EXCHANGE_ID.

   The sspt_confounder field is a random value.

   The sspt_ssv_seq field is the same as ssvt_ssv_seq.

   The field sspt_orig_plain field is the original plaintext and is the
   "input_message" input passed to GSS_Wrap() (see Section 2.3.3 of
   [7]).  As with the handling of the plaintext by the SSV mechanism's
   GSS_GetMIC() entry point, the entry point for GSS_Wrap() expects a
   pointer to the plaintext, and will XDR encode an opaque array into
   sspt_orig_plain representing the plain text, along with the other
   fields of an instance of data type ssv_seal_plain_tkn4.

   The sspt_pad field is present to support encryption algorithms that
   require inputs to be in fixed-sized blocks.  The content of sspt_pad
   is zero filled except for the length.  Beware that the XDR encoding
   of ssv_seal_plain_tkn4 contains three variable-length arrays, and so
   each array consumes four bytes for an array length, and each array
   that follows the length is always padded to a multiple of four bytes
   per the XDR standard.

   For example, suppose the encryption algorithm uses 16-byte blocks,
   and the sspt_confounder is three bytes long, and the sspt_orig_plain
   field is 15 bytes long.  The XDR encoding of sspt_confounder uses
   eight bytes (4 + 3 + 1 byte pad), the XDR encoding of sspt_ssv_seq
   uses four bytes, the XDR encoding of sspt_orig_plain uses 20 bytes (4
   + 15 + 1 byte pad), and the smallest XDR encoding of the sspt_pad
   field is four bytes.  This totals 36 bytes.  The next multiple of 16
   is 48; thus, the length field of sspt_pad needs to be set to 12
   bytes, or a total encoding of 16 bytes.  The total number of XDR
   encoded bytes is thus 8 + 4 + 20 + 16 = 48.

   GSS_Wrap() emits a token that is an XDR encoding of a value of data
   type ssv_seal_cipher_tkn4.  Note that regardless of whether or not
   the caller of GSS_Wrap() requests confidentiality, the token always



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   has confidentiality.  This is because the SSV mechanism is for
   RPCSEC_GSS, and RPCSEC_GSS never produces GSS_wrap() tokens without
   confidentiality.

   There is one SSV per client ID.  There is a single GSS context for a
   client ID / SSV pair.  All SSV mechanism RPCSEC_GSS handles of a
   client ID / SSV pair share the same GSS context.  SSV GSS contexts do
   not expire except when the SSV is destroyed (causes would include the
   client ID being destroyed or a server restart).  Since one purpose of
   context expiration is to replace keys that have been in use for "too
   long", hence vulnerable to compromise by brute force or accident, the
   client can replace the SSV key by sending periodic SET_SSV
   operations, which is done by cycling through different users'
   RPCSEC_GSS credentials.  This way, the SSV is replaced without
   destroying the SSV's GSS contexts.

   SSV RPCSEC_GSS handles can be expired or deleted by the server at any
   time, and the EXCHANGE_ID operation can be used to create more SSV
   RPCSEC_GSS handles.  Expiration of SSV RPCSEC_GSS handles does not
   imply that the SSV or its GSS context has expired.

   The client MUST establish an SSV via SET_SSV before the SSV GSS
   context can be used to emit tokens from GSS_Wrap() and GSS_GetMIC().
   If SET_SSV has not been successfully called, attempts to emit tokens
   MUST fail.

   The SSV mechanism does not support replay detection and sequencing in
   its tokens because RPCSEC_GSS does not use those features (See
   Section 5.2.2, "Context Creation Requests", in [4]).  However,
   Section 2.10.10 discusses special considerations for the SSV
   mechanism when used with RPCSEC_GSS.

2.10.10.  Security Considerations for RPCSEC_GSS When Using the SSV
          Mechanism

   When a client ID is created with SP4_SSV state protection (see
   Section 18.35), the client is permitted to associate multiple
   RPCSEC_GSS handles with the single SSV GSS context (see
   Section 2.10.9).  Because of the way RPCSEC_GSS (both version 1 and
   version 2, see [4] and [12]) calculate the verifier of the reply,
   special care must be taken by the implementation of the NFSv4.1
   client to prevent attacks by a man-in-the-middle.  The verifier of an
   RPCSEC_GSS reply is the output of GSS_GetMIC() applied to the input
   value of the seq_num field of the RPCSEC_GSS credential (data type
   rpc_gss_cred_ver_1_t) (see Section 5.3.3.2 of [4]).  If multiple
   RPCSEC_GSS handles share the same GSS context, then if one handle is
   used to send a request with the same seq_num value as another handle,




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   an attacker could block the reply, and replace it with the verifier
   used for the other handle.

   There are multiple ways to prevent the attack on the SSV RPCSEC_GSS
   verifier in the reply.  The simplest is believed to be as follows.

   o  Each time one or more new SSV RPCSEC_GSS handles are created via
      EXCHANGE_ID, the client SHOULD send a SET_SSV operation to modify
      the SSV.  By changing the SSV, the new handles will not result in
      the re-use of an SSV RPCSEC_GSS verifier in a reply.

   o  When a requester decides to use N SSV RPCSEC_GSS handles, it
      SHOULD assign a unique and non-overlapping range of seq_nums to
      each SSV RPCSEC_GSS handle.  The size of each range SHOULD be
      equal to MAXSEQ / N (see Section 5 of [4] for the definition of
      MAXSEQ).  When an SSV RPCSEC_GSS handle reaches its maximum, it
      SHOULD force the replier to destroy the handle by sending a NULL
      RPC request with seq_num set to MAXSEQ + 1 (see Section 5.3.3.3 of
      [4]).

   o  When the requester wants to increase or decrease N, it SHOULD
      force the replier to destroy all N handles by sending a NULL RPC
      request on each handle with seq_num set to MAXSEQ + 1.  If the
      requester is the client, it SHOULD send a SET_SSV operation before
      using new handles.  If the requester is the server, then the
      client SHOULD send a SET_SSV operation when it detects that the
      server has forced it to destroy a backchannel's SSV RPCSEC_GSS
      handle.  By sending a SET_SSV operation, the SSV will change, and
      so the attacker will be unavailable to successfully replay a
      previous verifier in a reply to the requester.

   Note that if the replier carefully creates the SSV RPCSEC_GSS
   handles, the related risk of a man-in-the-middle splicing a forged
   SSV RPCSEC_GSS credential with a verifier for another handle does not
   exist.  This is because the verifier in an RPCSEC_GSS request is
   computed from input that includes both the RPCSEC_GSS handle and
   seq_num (see Section 5.3.1 of [4]).  Provided the replier takes care
   to avoid re-using the value of an RPCSEC_GSS handle that it creates,
   such as by including a generation number in the handle, the man-in-
   the-middle will not be able to successfully replay a previous
   verifier in the request to a replier.

2.10.11.  Session Mechanics - Steady State








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2.10.11.1.  Obligations of the Server

   The server has the primary obligation to monitor the state of
   backchannel resources that the client has created for the server
   (RPCSEC_GSS contexts and backchannel connections).  If these
   resources vanish, the server takes action as specified in
   Section 2.10.13.2.

2.10.11.2.  Obligations of the Client

   The client SHOULD honor the following obligations in order to utilize
   the session:

   o  Keep a necessary session from going idle on the server.  A client
      that requires a session but nonetheless is not sending operations
      risks having the session be destroyed by the server.  This is
      because sessions consume resources, and resource limitations may
      force the server to cull an inactive session.  A server MAY
      consider a session to be inactive if the client has not used the
      session before the session inactivity timer (Section 2.10.12) has
      expired.

   o  Destroy the session when not needed.  If a client has multiple
      sessions, one of which has no requests waiting for replies, and
      has been idle for some period of time, it SHOULD destroy the
      session.

   o  Maintain GSS contexts and RPCSEC_GSS handles for the backchannel.
      If the client requires the server to use the RPCSEC_GSS security
      flavor for callbacks, then it needs to be sure the RPCSEC_GSS
      handles and/or their GSS contexts that are handed to the server
      via BACKCHANNEL_CTL or CREATE_SESSION are unexpired.

   o  Preserve a connection for a backchannel.  The server requires a
      backchannel in order to gracefully recall recallable state or
      notify the client of certain events.  Note that if the connection
      is not being used for the fore channel, there is no way for the
      client to tell if the connection is still alive (e.g., the server
      restarted without sending a disconnect).  The onus is on the
      server, not the client, to determine if the backchannel's
      connection is alive, and to indicate in the response to a SEQUENCE
      operation when the last connection associated with a session's
      backchannel has disconnected.








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2.10.11.3.  Steps the Client Takes to Establish a Session

   If the client does not have a client ID, the client sends EXCHANGE_ID
   to establish a client ID.  If it opts for SP4_MACH_CRED or SP4_SSV
   protection, in the spo_must_enforce list of operations, it SHOULD at
   minimum specify CREATE_SESSION, DESTROY_SESSION,
   BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID.  If it
   opts for SP4_SSV protection, the client needs to ask for SSV-based
   RPCSEC_GSS handles.

   The client uses the client ID to send a CREATE_SESSION on a
   connection to the server.  The results of CREATE_SESSION indicate
   whether or not the server will persist the session reply cache
   through a server that has restarted, and the client notes this for
   future reference.

   If the client specified SP4_SSV state protection when the client ID
   was created, then it SHOULD send SET_SSV in the first COMPOUND after
   the session is created.  Each time a new principal goes to use the
   client ID, it SHOULD send a SET_SSV again.

   If the client wants to use delegations, layouts, directory
   notifications, or any other state that requires a backchannel, then
   it needs to add a connection to the backchannel if CREATE_SESSION did
   not already do so.  The client creates a connection, and calls
   BIND_CONN_TO_SESSION to associate the connection with the session and
   the session's backchannel.  If CREATE_SESSION did not already do so,
   the client MUST tell the server what security is required in order
   for the client to accept callbacks.  The client does this via
   BACKCHANNEL_CTL.  If the client selected SP4_MACH_CRED or SP4_SSV
   protection when it called EXCHANGE_ID, then the client SHOULD specify
   that the backchannel use RPCSEC_GSS contexts for security.

   If the client wants to use additional connections for the
   backchannel, then it needs to call BIND_CONN_TO_SESSION on each
   connection it wants to use with the session.  If the client wants to
   use additional connections for the fore channel, then it needs to
   call BIND_CONN_TO_SESSION if it specified SP4_SSV or SP4_MACH_CRED
   state protection when the client ID was created.

   At this point, the session has reached steady state.

2.10.12.  Session Inactivity Timer

   The server MAY maintain a session inactivity timer for each session.
   If the session inactivity timer expires, then the server MAY destroy
   the session.  To avoid losing a session due to inactivity, the client
   MUST renew the session inactivity timer.  The length of session



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   inactivity timer MUST NOT be less than the lease_time attribute
   (Section 5.8.1.11).  As with lease renewal (Section 8.3), when the
   server receives a SEQUENCE operation, it resets the session
   inactivity timer, and MUST NOT allow the timer to expire while the
   rest of the operations in the COMPOUND procedure's request are still
   executing.  Once the last operation has finished, the server MUST set
   the session inactivity timer to expire no sooner than the sum of the
   current time and the value of the lease_time attribute.

2.10.13.  Session Mechanics - Recovery

2.10.13.1.  Events Requiring Client Action

   The following events require client action to recover.

2.10.13.1.1.  RPCSEC_GSS Context Loss by Callback Path

   If all RPCSEC_GSS handles granted by the client to the server for
   callback use have expired, the client MUST establish a new handle via
   BACKCHANNEL_CTL.  The sr_status_flags field of the SEQUENCE results
   indicates when callback handles are nearly expired, or fully expired
   (see Section 18.46.3).

2.10.13.1.2.  Connection Loss

   If the client loses the last connection of the session and wants to
   retain the session, then it needs to create a new connection, and if,
   when the client ID was created, BIND_CONN_TO_SESSION was specified in
   the spo_must_enforce list, the client MUST use BIND_CONN_TO_SESSION
   to associate the connection with the session.

   If there was a request outstanding at the time of connection loss,
   then if the client wants to continue to use the session, it MUST
   retry the request, as described in Section 2.10.6.2.  Note that it is
   not necessary to retry requests over a connection with the same
   source network address or the same destination network address as the
   lost connection.  As long as the session ID, slot ID, and sequence ID
   in the retry match that of the original request, the server will
   recognize the request as a retry if it executed the request prior to
   disconnect.

   If the connection that was lost was the last one associated with the
   backchannel, and the client wants to retain the backchannel and/or
   prevent revocation of recallable state, the client needs to
   reconnect, and if it does, it MUST associate the connection to the
   session and backchannel via BIND_CONN_TO_SESSION.  The server SHOULD
   indicate when it has no callback connection via the sr_status_flags
   result from SEQUENCE.



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2.10.13.1.3.  Backchannel GSS Context Loss

   Via the sr_status_flags result of the SEQUENCE operation or other
   means, the client will learn if some or all of the RPCSEC_GSS
   contexts it assigned to the backchannel have been lost.  If the
   client wants to retain the backchannel and/or not put recallable
   state subject to revocation, the client needs to use BACKCHANNEL_CTL
   to assign new contexts.

2.10.13.1.4.  Loss of Session

   The replier might lose a record of the session.  Causes include:

   o  Replier failure and restart.

   o  A catastrophe that causes the reply cache to be corrupted or lost
      on the media on which it was stored.  This applies even if the
      replier indicated in the CREATE_SESSION results that it would
      persist the cache.

   o  The server purges the session of a client that has been inactive
      for a very extended period of time.

   o  As a result of configuration changes among a set of clustered
      servers, a network address previously connected to one server
      becomes connected to a different server that has no knowledge of
      the session in question.  Such a configuration change will
      generally only happen when the original server ceases to function
      for a time.

   Loss of reply cache is equivalent to loss of session.  The replier
   indicates loss of session to the requester by returning
   NFS4ERR_BADSESSION on the next operation that uses the session ID
   that refers to the lost session.

   After an event like a server restart, the client may have lost its
   connections.  The client assumes for the moment that the session has
   not been lost.  It reconnects, and if it specified connection
   association enforcement when the session was created, it invokes
   BIND_CONN_TO_SESSION using the session ID.  Otherwise, it invokes
   SEQUENCE.  If BIND_CONN_TO_SESSION or SEQUENCE returns
   NFS4ERR_BADSESSION, the client knows the session is not available to
   it when communicating with that network address.  If the connection
   survives session loss, then the next SEQUENCE operation the client
   sends over the connection will get back NFS4ERR_BADSESSION.  The
   client again knows the session was lost.





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   Here is one suggested algorithm for the client when it gets
   NFS4ERR_BADSESSION.  It is not obligatory in that, if a client does
   not want to take advantage of such features as trunking, it may omit
   parts of it.  However, it is a useful example that draws attention to
   various possible recovery issues:

   1.  If the client has other connections to other server network
       addresses associated with the same session, attempt a COMPOUND
       with a single operation, SEQUENCE, on each of the other
       connections.

   2.  If the attempts succeed, the session is still alive, and this is
       a strong indicator that the server's network address has moved.
       The client might send an EXCHANGE_ID on the connection that
       returned NFS4ERR_BADSESSION to see if there are opportunities for
       client ID trunking (i.e., the same client ID and so_major are
       returned).  The client might use DNS to see if the moved network
       address was replaced with another, so that the performance and
       availability benefits of session trunking can continue.

   3.  If the SEQUENCE requests fail with NFS4ERR_BADSESSION, then the
       session no longer exists on any of the server network addresses
       for which the client has connections associated with that session
       ID.  It is possible the session is still alive and available on
       other network addresses.  The client sends an EXCHANGE_ID on all
       the connections to see if the server owner is still listening on
       those network addresses.  If the same server owner is returned
       but a new client ID is returned, this is a strong indicator of a
       server restart.  If both the same server owner and same client ID
       are returned, then this is a strong indication that the server
       did delete the session, and the client will need to send a
       CREATE_SESSION if it has no other sessions for that client ID.
       If a different server owner is returned, the client can use DNS
       to find other network addresses.  If it does not, or if DNS does
       not find any other addresses for the server, then the client will
       be unable to provide NFSv4.1 service, and fatal errors should be
       returned to processes that were using the server.  If the client
       is using a "mount" paradigm, unmounting the server is advised.

   4.  If the client knows of no other connections associated with the
       session ID and server network addresses that are, or have been,
       associated with the session ID, then the client can use DNS to
       find other network addresses.  If it does not, or if DNS does not
       find any other addresses for the server, then the client will be
       unable to provide NFSv4.1 service, and fatal errors should be
       returned to processes that were using the server.  If the client
       is using a "mount" paradigm, unmounting the server is advised.




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   If there is a reconfiguration event that results in the same network
   address being assigned to servers where the eir_server_scope value is
   different, it cannot be guaranteed that a session ID generated by the
   first will be recognized as invalid by the first.  Therefore, in
   managing server reconfigurations among servers with different server
   scope values, it is necessary to make sure that all clients have
   disconnected from the first server before effecting the
   reconfiguration.  Nonetheless, clients should not assume that servers
   will always adhere to this requirement; clients MUST be prepared to
   deal with unexpected effects of server reconfigurations.  Even where
   a session ID is inappropriately recognized as valid, it is likely
   either that the connection will not be recognized as valid or that a
   sequence value for a slot will not be correct.  Therefore, when a
   client receives results indicating such unexpected errors, the use of
   EXCHANGE_ID to determine the current server configuration is
   RECOMMENDED.

   A variation on the above is that after a server's network address
   moves, there is no NFSv4.1 server listening, e.g., no listener on
   port 2049.  In this example, one of the following occur: the NFSv4
   server returns NFS4ERR_MINOR_VERS_MISMATCH, the NFS server returns a
   PROG_MISMATCH error, the RPC listener on 2049 returns PROG_UNVAIL, or
   attempts to reconnect to the network address timeout.  These SHOULD
   be treated as equivalent to SEQUENCE returning NFS4ERR_BADSESSION for
   these purposes.

   When the client detects session loss, it needs to call CREATE_SESSION
   to recover.  Any non-idempotent operations that were in progress
   might have been performed on the server at the time of session loss.
   The client has no general way to recover from this.

   Note that loss of session does not imply loss of byte-range lock,
   open, delegation, or layout state because locks, opens, delegations,
   and layouts are tied to the client ID and depend on the client ID,
   not the session.  Nor does loss of byte-range lock, open, delegation,
   or layout state imply loss of session state, because the session
   depends on the client ID; loss of client ID however does imply loss
   of session, byte-range lock, open, delegation, and layout state.  See
   Section 8.4.2.  A session can survive a server restart, but lock
   recovery may still be needed.

   It is possible that CREATE_SESSION will fail with
   NFS4ERR_STALE_CLIENTID (e.g., the server restarts and does not
   preserve client ID state).  If so, the client needs to call
   EXCHANGE_ID, followed by CREATE_SESSION.






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2.10.13.2.  Events Requiring Server Action

   The following events require server action to recover.

2.10.13.2.1.  Client Crash and Restart

   As described in Section 18.35, a restarted client sends EXCHANGE_ID
   in such a way that it causes the server to delete any sessions it
   had.

2.10.13.2.2.  Client Crash with No Restart

   If a client crashes and never comes back, it will never send
   EXCHANGE_ID with its old client owner.  Thus, the server has session
   state that will never be used again.  After an extended period of
   time, and if the server has resource constraints, it MAY destroy the
   old session as well as locking state.

2.10.13.2.3.  Extended Network Partition

   To the server, the extended network partition may be no different
   from a client crash with no restart (see Section 2.10.13.2.2).
   Unless the server can discern that there is a network partition, it
   is free to treat the situation as if the client has crashed
   permanently.

2.10.13.2.4.  Backchannel Connection Loss

   If there were callback requests outstanding at the time of a
   connection loss, then the server MUST retry the requests, as
   described in Section 2.10.6.2.  Note that it is not necessary to
   retry requests over a connection with the same source network address
   or the same destination network address as the lost connection.  As
   long as the session ID, slot ID, and sequence ID in the retry match
   that of the original request, the callback target will recognize the
   request as a retry even if it did see the request prior to
   disconnect.

   If the connection lost is the last one associated with the
   backchannel, then the server MUST indicate that in the
   sr_status_flags field of every SEQUENCE reply until the backchannel
   is re-established.  There are two situations, each of which uses
   different status flags: no connectivity for the session's backchannel
   and no connectivity for any session backchannel of the client.  See
   Section 18.46 for a description of the appropriate flags in
   sr_status_flags.





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2.10.13.2.5.  GSS Context Loss

   The server SHOULD monitor when the number of RPCSEC_GSS handles
   assigned to the backchannel reaches one, and when that one handle is
   near expiry (i.e., between one and two periods of lease time), and
   indicate so in the sr_status_flags field of all SEQUENCE replies.
   The server MUST indicate when all of the backchannel's assigned
   RPCSEC_GSS handles have expired via the sr_status_flags field of all
   SEQUENCE replies.

2.10.14.  Parallel NFS and Sessions

   A client and server can potentially be a non-pNFS implementation, a
   metadata server implementation, a data server implementation, or two
   or three types of implementations.  The EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags (not
   mutually exclusive) are passed in the EXCHANGE_ID arguments and
   results to allow the client to indicate how it wants to use sessions
   created under the client ID, and to allow the server to indicate how
   it will allow the sessions to be used.  See Section 13.1 for pNFS
   sessions considerations.

3.  Protocol Constants and Data Types

   The syntax and semantics to describe the data types of the NFSv4.1
   protocol are defined in the XDR RFC 4506 [2] and RPC RFC 5531 [3]
   documents.  The next sections build upon the XDR data types to define
   constants, types, and structures specific to this protocol.  The full
   list of XDR data types is in [13].

3.1.  Basic Constants

   const NFS4_FHSIZE               = 128;
   const NFS4_VERIFIER_SIZE        = 8;
   const NFS4_OPAQUE_LIMIT         = 1024;
   const NFS4_SESSIONID_SIZE       = 16;

   const NFS4_INT64_MAX            = 0x7fffffffffffffff;
   const NFS4_UINT64_MAX           = 0xffffffffffffffff;
   const NFS4_INT32_MAX            = 0x7fffffff;
   const NFS4_UINT32_MAX           = 0xffffffff;

   const NFS4_MAXFILELEN           = 0xffffffffffffffff;
   const NFS4_MAXFILEOFF           = 0xfffffffffffffffe;

   Except where noted, all these constants are defined in bytes.

   o  NFS4_FHSIZE is the maximum size of a filehandle.



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   o  NFS4_VERIFIER_SIZE is the fixed size of a verifier.

   o  NFS4_OPAQUE_LIMIT is the maximum size of certain opaque
      information.

   o  NFS4_SESSIONID_SIZE is the fixed size of a session identifier.

   o  NFS4_INT64_MAX is the maximum value of a signed 64-bit integer.

   o  NFS4_UINT64_MAX is the maximum value of an unsigned 64-bit
      integer.

   o  NFS4_INT32_MAX is the maximum value of a signed 32-bit integer.

   o  NFS4_UINT32_MAX is the maximum value of an unsigned 32-bit
      integer.

   o  NFS4_MAXFILELEN is the maximum length of a regular file.

   o  NFS4_MAXFILEOFF is the maximum offset into a regular file.

3.2.  Basic Data Types

   These are the base NFSv4.1 data types.

   +---------------+---------------------------------------------------+
   | Data Type     | Definition                                        |
   +---------------+---------------------------------------------------+
   | int32_t       | typedef int int32_t;                              |
   | uint32_t      | typedef unsigned int uint32_t;                    |
   | int64_t       | typedef hyper int64_t;                            |
   | uint64_t      | typedef unsigned hyper uint64_t;                  |
   | attrlist4     | typedef opaque attrlist4<>;                       |
   |               | Used for file/directory attributes.               |
   | bitmap4       | typedef uint32_t bitmap4<>;                       |
   |               | Used in attribute array encoding.                 |
   | changeid4     | typedef uint64_t changeid4;                       |
   |               | Used in the definition of change_info4.           |
   | clientid4     | typedef uint64_t clientid4;                       |
   |               | Shorthand reference to client identification.     |
   | count4        | typedef uint32_t count4;                          |
   |               | Various count parameters (READ, WRITE, COMMIT).   |
   | length4       | typedef uint64_t length4;                         |
   |               | The length of a byte-range within a file.         |
   | mode4         | typedef uint32_t mode4;                           |
   |               | Mode attribute data type.                         |
   | nfs_cookie4   | typedef uint64_t nfs_cookie4;                     |
   |               | Opaque cookie value for READDIR.                  |



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   | nfs_fh4       | typedef opaque nfs_fh4<NFS4_FHSIZE>;              |
   |               | Filehandle definition.                            |
   | nfs_ftype4    | enum nfs_ftype4;                                  |
   |               | Various defined file types.                       |
   | nfsstat4      | enum nfsstat4;                                    |
   |               | Return value for operations.                      |
   | offset4       | typedef uint64_t offset4;                         |
   |               | Various offset designations (READ, WRITE, LOCK,   |
   |               | COMMIT).                                          |
   | qop4          | typedef uint32_t qop4;                            |
   |               | Quality of protection designation in SECINFO.     |
   | sec_oid4      | typedef opaque sec_oid4<>;                        |
   |               | Security Object Identifier.  The sec_oid4 data    |
   |               | type is not really opaque.  Instead, it contains  |
   |               | an ASN.1 OBJECT IDENTIFIER as used by GSS-API in  |
   |               | the mech_type argument to GSS_Init_sec_context.   |
   |               | See [7] for details.                              |
   | sequenceid4   | typedef uint32_t sequenceid4;                     |
   |               | Sequence number used for various session          |
   |               | operations (EXCHANGE_ID, CREATE_SESSION,          |
   |               | SEQUENCE, CB_SEQUENCE).                           |
   | seqid4        | typedef uint32_t seqid4;                          |
   |               | Sequence identifier used for locking.             |
   | sessionid4    | typedef opaque sessionid4[NFS4_SESSIONID_SIZE];   |
   |               | Session identifier.                               |
   | slotid4       | typedef uint32_t slotid4;                         |
   |               | Sequencing artifact for various session           |
   |               | operations (SEQUENCE, CB_SEQUENCE).               |
   | utf8string    | typedef opaque utf8string<>;                      |
   |               | UTF-8 encoding for strings.                       |
   | utf8str_cis   | typedef utf8string utf8str_cis;                   |
   |               | Case-insensitive UTF-8 string.                    |
   | utf8str_cs    | typedef utf8string utf8str_cs;                    |
   |               | Case-sensitive UTF-8 string.                      |
   | utf8str_mixed | typedef utf8string utf8str_mixed;                 |
   |               | UTF-8 strings with a case-sensitive prefix and a  |
   |               | case-insensitive suffix.                          |
   | component4    | typedef utf8str_cs component4;                    |
   |               | Represents pathname components.                   |
   | linktext4     | typedef utf8str_cs linktext4;                     |
   |               | Symbolic link contents ("symbolic link" is        |
   |               | defined in an Open Group [14] standard).          |
   | pathname4     | typedef component4 pathname4<>;                   |
   |               | Represents pathname for fs_locations.             |
   | verifier4     | typedef opaque verifier4[NFS4_VERIFIER_SIZE];     |
   |               | Verifier used for various operations (COMMIT,     |
   |               | CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE)        |
   |               | NFS4_VERIFIER_SIZE is defined as 8.               |



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   +---------------+---------------------------------------------------+

                          End of Base Data Types

                                  Table 1

3.3.  Structured Data Types

3.3.1.  nfstime4

   struct nfstime4 {
           int64_t         seconds;
           uint32_t        nseconds;
   };

   The nfstime4 data type gives the number of seconds and nanoseconds
   since midnight or zero hour January 1, 1970 Coordinated Universal
   Time (UTC).  Values greater than zero for the seconds field denote
   dates after the zero hour January 1, 1970.  Values less than zero for
   the seconds field denote dates before the zero hour January 1, 1970.
   In both cases, the nseconds field is to be added to the seconds field
   for the final time representation.  For example, if the time to be
   represented is one-half second before zero hour January 1, 1970, the
   seconds field would have a value of negative one (-1) and the
   nseconds field would have a value of one-half second (500000000).
   Values greater than 999,999,999 for nseconds are invalid.

   This data type is used to pass time and date information.  A server
   converts to and from its local representation of time when processing
   time values, preserving as much accuracy as possible.  If the
   precision of timestamps stored for a file system object is less than
   defined, loss of precision can occur.  An adjunct time maintenance
   protocol is RECOMMENDED to reduce client and server time skew.

3.3.2.  time_how4

   enum time_how4 {
           SET_TO_SERVER_TIME4 = 0,
           SET_TO_CLIENT_TIME4 = 1
   };

3.3.3.  settime4









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   union settime4 switch (time_how4 set_it) {
    case SET_TO_CLIENT_TIME4:
            nfstime4       time;
    default:
            void;
   };

   The time_how4 and settime4 data types are used for setting timestamps
   in file object attributes.  If set_it is SET_TO_SERVER_TIME4, then
   the server uses its local representation of time for the time value.

3.3.4.  specdata4

   struct specdata4 {
    uint32_t specdata1; /* major device number */
    uint32_t specdata2; /* minor device number */
   };

   This data type represents the device numbers for the device file
   types NF4CHR and NF4BLK.

3.3.5.  fsid4

   struct fsid4 {
           uint64_t        major;
           uint64_t        minor;
   };

3.3.6.  change_policy4

   struct change_policy4 {
           uint64_t        cp_major;
           uint64_t        cp_minor;
   };

   The change_policy4 data type is used for the change_policy
   RECOMMENDED attribute.  It provides change sequencing indication
   analogous to the change attribute.  To enable the server to present a
   value valid across server re-initialization without requiring
   persistent storage, two 64-bit quantities are used, allowing one to
   be a server instance ID and the second to be incremented non-
   persistently, within a given server instance.

3.3.7.  fattr4







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   struct fattr4 {
           bitmap4         attrmask;
           attrlist4       attr_vals;
   };

   The fattr4 data type is used to represent file and directory
   attributes.

   The bitmap is a counted array of 32-bit integers used to contain bit
   values.  The position of the integer in the array that contains bit n
   can be computed from the expression (n / 32), and its bit within that
   integer is (n mod 32).

   0            1
   +-----------+-----------+-----------+--
   |  count    | 31  ..  0 | 63  .. 32 |
   +-----------+-----------+-----------+--

3.3.8.  change_info4

   struct change_info4 {
           bool            atomic;
           changeid4       before;
           changeid4       after;
   };

   This data type is used with the CREATE, LINK, OPEN, REMOVE, and
   RENAME operations to let the client know the value of the change
   attribute for the directory in which the target file system object
   resides.

3.3.9.  netaddr4

   struct netaddr4 {
           /* see struct rpcb in RFC 1833 */
           string na_r_netid<>; /* network id */
           string na_r_addr<>;  /* universal address */
   };

   The netaddr4 data type is used to identify network transport
   endpoints.  The r_netid and r_addr fields respectively contain a
   netid and uaddr.  The netid and uaddr concepts are defined in [15].
   The netid and uaddr formats for TCP over IPv4 and TCP over IPv6 are
   defined in [15], specifically Tables 2 and 3 and Sections 5.2.3.3 and
   5.2.3.4.






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3.3.10.  state_owner4

   struct state_owner4 {
           clientid4       clientid;
           opaque          owner<NFS4_OPAQUE_LIMIT>;
   };

   typedef state_owner4 open_owner4;
   typedef state_owner4 lock_owner4;

   The state_owner4 data type is the base type for the open_owner4
   (Section 3.3.10.1) and lock_owner4 (Section 3.3.10.2).

3.3.10.1.  open_owner4

   This data type is used to identify the owner of OPEN state.

3.3.10.2.  lock_owner4

   This structure is used to identify the owner of byte-range locking
   state.

3.3.11.  open_to_lock_owner4

   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };

   This data type is used for the first LOCK operation done for an
   open_owner4.  It provides both the open_stateid and lock_owner, such
   that the transition is made from a valid open_stateid sequence to
   that of the new lock_stateid sequence.  Using this mechanism avoids
   the confirmation of the lock_owner/lock_seqid pair since it is tied
   to established state in the form of the open_stateid/open_seqid.

3.3.12.  stateid4

   struct stateid4 {
           uint32_t        seqid;
           opaque          other[12];
   };

   This data type is used for the various state sharing mechanisms
   between the client and server.  The client never modifies a value of
   data type stateid.  The starting value of the "seqid" field is



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   undefined.  The server is required to increment the "seqid" field by
   one at each transition of the stateid.  This is important since the
   client will inspect the seqid in OPEN stateids to determine the order
   of OPEN processing done by the server.

3.3.13.  layouttype4

   enum layouttype4 {
           LAYOUT4_NFSV4_1_FILES   = 0x1,
           LAYOUT4_OSD2_OBJECTS    = 0x2,
           LAYOUT4_BLOCK_VOLUME    = 0x3
   };

   This data type indicates what type of layout is being used.  The file
   server advertises the layout types it supports through the
   fs_layout_type file system attribute (Section 5.12.1).  A client asks
   for layouts of a particular type in LAYOUTGET, and processes those
   layouts in its layout-type-specific logic.

   The layouttype4 data type is 32 bits in length.  The range
   represented by the layout type is split into three parts.  Type 0x0
   is reserved.  Types within the range 0x00000001-0x7FFFFFFF are
   globally unique and are assigned according to the description in
   Section 22.4; they are maintained by IANA.  Types within the range
   0x80000000-0xFFFFFFFF are site specific and for private use only.

   The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1 file
   layout type, as defined in Section 13, is to be used.  The
   LAYOUT4_OSD2_OBJECTS enumeration specifies that the object layout, as
   defined in [40], is to be used.  Similarly, the LAYOUT4_BLOCK_VOLUME
   enumeration specifies that the block/volume layout, as defined in
   [41], is to be used.

3.3.14.  deviceid4

   const NFS4_DEVICEID4_SIZE = 16;

   typedef opaque  deviceid4[NFS4_DEVICEID4_SIZE];

   Layout information includes device IDs that specify a storage device
   through a compact handle.  Addressing and type information is
   obtained with the GETDEVICEINFO operation.  Device IDs are not
   guaranteed to be valid across metadata server restarts.  A device ID
   is unique per client ID and layout type.  See Section 12.2.10 for
   more details.






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3.3.15.  device_addr4

   struct device_addr4 {
           layouttype4             da_layout_type;
           opaque                  da_addr_body<>;
   };

   The device address is used to set up a communication channel with the
   storage device.  Different layout types will require different data
   types to define how they communicate with storage devices.  The
   opaque da_addr_body field is interpreted based on the specified
   da_layout_type field.

   This document defines the device address for the NFSv4.1 file layout
   (see Section 13.3), which identifies a storage device by network IP
   address and port number.  This is sufficient for the clients to
   communicate with the NFSv4.1 storage devices, and may be sufficient
   for other layout types as well.  Device types for object-based
   storage devices and block storage devices (e.g., Small Computer
   System Interface (SCSI) volume labels) are defined by their
   respective layout specifications.

3.3.16.  layout_content4

   struct layout_content4 {
           layouttype4 loc_type;
           opaque      loc_body<>;
   };

   The loc_body field is interpreted based on the layout type
   (loc_type).  This document defines the loc_body for the NFSv4.1 file
   layout type; see Section 13.3 for its definition.

3.3.17.  layout4

   struct layout4 {
           offset4                 lo_offset;
           length4                 lo_length;
           layoutiomode4           lo_iomode;
           layout_content4         lo_content;
   };

   The layout4 data type defines a layout for a file.  The layout type
   specific data is opaque within lo_content.  Since layouts are sub-
   dividable, the offset and length together with the file's filehandle,
   the client ID, iomode, and layout type identify the layout.





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3.3.18.  layoutupdate4

   struct layoutupdate4 {
           layouttype4             lou_type;
           opaque                  lou_body<>;
   };

   The layoutupdate4 data type is used by the client to return updated
   layout information to the metadata server via the LAYOUTCOMMIT
   (Section 18.42) operation.  This data type provides a channel to pass
   layout type specific information (in field lou_body) back to the
   metadata server.  For example, for the block/volume layout type, this
   could include the list of reserved blocks that were written.  The
   contents of the opaque lou_body argument are determined by the layout
   type.  The NFSv4.1 file-based layout does not use this data type; if
   lou_type is LAYOUT4_NFSV4_1_FILES, the lou_body field MUST have a
   zero length.

3.3.19.  layouthint4

   struct layouthint4 {
           layouttype4             loh_type;
           opaque                  loh_body<>;
   };

   The layouthint4 data type is used by the client to pass in a hint
   about the type of layout it would like created for a particular file.
   It is the data type specified by the layout_hint attribute described
   in Section 5.12.4.  The metadata server may ignore the hint or may
   selectively ignore fields within the hint.  This hint should be
   provided at create time as part of the initial attributes within
   OPEN.  The loh_body field is specific to the type of layout
   (loh_type).  The NFSv4.1 file-based layout uses the
   nfsv4_1_file_layouthint4 data type as defined in Section 13.3.

3.3.20.  layoutiomode4

   enum layoutiomode4 {
           LAYOUTIOMODE4_READ      = 1,
           LAYOUTIOMODE4_RW        = 2,
           LAYOUTIOMODE4_ANY       = 3
   };

   The iomode specifies whether the client intends to just read or both
   read and write the data represented by the layout.  While the
   LAYOUTIOMODE4_ANY iomode MUST NOT be used in the arguments to the
   LAYOUTGET operation, it MAY be used in the arguments to the
   LAYOUTRETURN and CB_LAYOUTRECALL operations.  The LAYOUTIOMODE4_ANY



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   iomode specifies that layouts pertaining to both LAYOUTIOMODE4_READ
   and LAYOUTIOMODE4_RW iomodes are being returned or recalled,
   respectively.  The metadata server's use of the iomode may depend on
   the layout type being used.  The storage devices MAY validate I/O
   accesses against the iomode and reject invalid accesses.

3.3.21.  nfs_impl_id4

   struct nfs_impl_id4 {
           utf8str_cis   nii_domain;
           utf8str_cs    nii_name;
           nfstime4      nii_date;
   };

   This data type is used to identify client and server implementation
   details.  The nii_domain field is the DNS domain name with which the
   implementor is associated.  The nii_name field is the product name of
   the implementation and is completely free form.  It is RECOMMENDED
   that the nii_name be used to distinguish machine architecture,
   machine platforms, revisions, versions, and patch levels.  The
   nii_date field is the timestamp of when the software instance was
   published or built.

3.3.22.  threshold_item4

   struct threshold_item4 {
           layouttype4     thi_layout_type;
           bitmap4         thi_hintset;
           opaque          thi_hintlist<>;
   };

   This data type contains a list of hints specific to a layout type for
   helping the client determine when it should send I/O directly through
   the metadata server versus the storage devices.  The data type
   consists of the layout type (thi_layout_type), a bitmap (thi_hintset)
   describing the set of hints supported by the server (they may differ
   based on the layout type), and a list of hints (thi_hintlist) whose
   content is determined by the hintset bitmap.  See the mdsthreshold
   attribute for more details.

   The thi_hintset field is a bitmap of the following values:










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   +-------------------------+---+---------+---------------------------+
   | name                    | # | Data    | Description               |
   |                         |   | Type    |                           |
   +-------------------------+---+---------+---------------------------+
   | threshold4_read_size    | 0 | length4 | If a file's length is     |
   |                         |   |         | less than the value of    |
   |                         |   |         | threshold4_read_size,     |
   |                         |   |         | then it is RECOMMENDED    |
   |                         |   |         | that the client read from |
   |                         |   |         | the file via the MDS and  |
   |                         |   |         | not a storage device.     |
   | threshold4_write_size   | 1 | length4 | If a file's length is     |
   |                         |   |         | less than the value of    |
   |                         |   |         | threshold4_write_size,    |
   |                         |   |         | then it is RECOMMENDED    |
   |                         |   |         | that the client write to  |
   |                         |   |         | the file via the MDS and  |
   |                         |   |         | not a storage device.     |
   | threshold4_read_iosize  | 2 | length4 | For read I/O sizes below  |
   |                         |   |         | this threshold, it is     |
   |                         |   |         | RECOMMENDED to read data  |
   |                         |   |         | through the MDS.          |
   | threshold4_write_iosize | 3 | length4 | For write I/O sizes below |
   |                         |   |         | this threshold, it is     |
   |                         |   |         | RECOMMENDED to write data |
   |                         |   |         | through the MDS.          |
   +-------------------------+---+---------+---------------------------+

3.3.23.  mdsthreshold4

   struct mdsthreshold4 {
           threshold_item4 mth_hints<>;
   };

   This data type holds an array of elements of data type
   threshold_item4, each of which is valid for a particular layout type.
   An array is necessary because a server can support multiple layout
   types for a single file.

4.  Filehandles

   The filehandle in the NFS protocol is a per-server unique identifier
   for a file system object.  The contents of the filehandle are opaque
   to the client.  Therefore, the server is responsible for translating
   the filehandle to an internal representation of the file system
   object.





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4.1.  Obtaining the First Filehandle

   The operations of the NFS protocol are defined in terms of one or
   more filehandles.  Therefore, the client needs a filehandle to
   initiate communication with the server.  With the NFSv3 protocol (RFC
   1813 [31]), there exists an ancillary protocol to obtain this first
   filehandle.  The MOUNT protocol, RPC program number 100005, provides
   the mechanism of translating a string-based file system pathname to a
   filehandle, which can then be used by the NFS protocols.

   The MOUNT protocol has deficiencies in the area of security and use
   via firewalls.  This is one reason that the use of the public
   filehandle was introduced in RFC 2054 [42] and RFC 2055 [43].  With
   the use of the public filehandle in combination with the LOOKUP
   operation in the NFSv3 protocol, it has been demonstrated that the
   MOUNT protocol is unnecessary for viable interaction between NFS
   client and server.

   Therefore, the NFSv4.1 protocol will not use an ancillary protocol
   for translation from string-based pathnames to a filehandle.  Two
   special filehandles will be used as starting points for the NFS
   client.

4.1.1.  Root Filehandle

   The first of the special filehandles is the ROOT filehandle.  The
   ROOT filehandle is the "conceptual" root of the file system namespace
   at the NFS server.  The client uses or starts with the ROOT
   filehandle by employing the PUTROOTFH operation.  The PUTROOTFH
   operation instructs the server to set the "current" filehandle to the
   ROOT of the server's file tree.  Once this PUTROOTFH operation is
   used, the client can then traverse the entirety of the server's file
   tree with the LOOKUP operation.  A complete discussion of the server
   namespace is in Section 7.

4.1.2.  Public Filehandle

   The second special filehandle is the PUBLIC filehandle.  Unlike the
   ROOT filehandle, the PUBLIC filehandle may be bound or represent an
   arbitrary file system object at the server.  The server is
   responsible for this binding.  It may be that the PUBLIC filehandle
   and the ROOT filehandle refer to the same file system object.
   However, it is up to the administrative software at the server and
   the policies of the server administrator to define the binding of the
   PUBLIC filehandle and server file system object.  The client may not
   make any assumptions about this binding.  The client uses the PUBLIC
   filehandle via the PUTPUBFH operation.




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4.2.  Filehandle Types

   In the NFSv3 protocol, there was one type of filehandle with a single
   set of semantics.  This type of filehandle is termed "persistent" in
   NFSv4.1.  The semantics of a persistent filehandle remain the same as
   before.  A new type of filehandle introduced in NFSv4.1 is the
   "volatile" filehandle, which attempts to accommodate certain server
   environments.

   The volatile filehandle type was introduced to address server
   functionality or implementation issues that make correct
   implementation of a persistent filehandle infeasible.  Some server
   environments do not provide a file-system-level invariant that can be
   used to construct a persistent filehandle.  The underlying server
   file system may not provide the invariant or the server's file system
   programming interfaces may not provide access to the needed
   invariant.  Volatile filehandles may ease the implementation of
   server functionality such as hierarchical storage management or file
   system reorganization or migration.  However, the volatile filehandle
   increases the implementation burden for the client.

   Since the client will need to handle persistent and volatile
   filehandles differently, a file attribute is defined that may be used
   by the client to determine the filehandle types being returned by the
   server.

4.2.1.  General Properties of a Filehandle

   The filehandle contains all the information the server needs to
   distinguish an individual file.  To the client, the filehandle is
   opaque.  The client stores filehandles for use in a later request and
   can compare two filehandles from the same server for equality by
   doing a byte-by-byte comparison.  However, the client MUST NOT
   otherwise interpret the contents of filehandles.  If two filehandles
   from the same server are equal, they MUST refer to the same file.
   Servers SHOULD try to maintain a one-to-one correspondence between
   filehandles and files, but this is not required.  Clients MUST use
   filehandle comparisons only to improve performance, not for correct
   behavior.  All clients need to be prepared for situations in which it
   cannot be determined whether two filehandles denote the same object
   and in such cases, avoid making invalid assumptions that might cause
   incorrect behavior.  Further discussion of filehandle and attribute
   comparison in the context of data caching is presented in
   Section 10.3.4.

   As an example, in the case that two different pathnames when
   traversed at the server terminate at the same file system object, the
   server SHOULD return the same filehandle for each path.  This can



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   occur if a hard link (see [6]) is used to create two file names that
   refer to the same underlying file object and associated data.  For
   example, if paths /a/b/c and /a/d/c refer to the same file, the
   server SHOULD return the same filehandle for both pathnames'
   traversals.

4.2.2.  Persistent Filehandle

   A persistent filehandle is defined as having a fixed value for the
   lifetime of the file system object to which it refers.  Once the
   server creates the filehandle for a file system object, the server
   MUST accept the same filehandle for the object for the lifetime of
   the object.  If the server restarts, the NFS server MUST honor the
   same filehandle value as it did in the server's previous
   instantiation.  Similarly, if the file system is migrated, the new
   NFS server MUST honor the same filehandle as the old NFS server.

   The persistent filehandle will be become stale or invalid when the
   file system object is removed.  When the server is presented with a
   persistent filehandle that refers to a deleted object, it MUST return
   an error of NFS4ERR_STALE.  A filehandle may become stale when the
   file system containing the object is no longer available.  The file
   system may become unavailable if it exists on removable media and the
   media is no longer available at the server or the file system in
   whole has been destroyed or the file system has simply been removed
   from the server's namespace (i.e., unmounted in a UNIX environment).

4.2.3.  Volatile Filehandle

   A volatile filehandle does not share the same longevity
   characteristics of a persistent filehandle.  The server may determine
   that a volatile filehandle is no longer valid at many different
   points in time.  If the server can definitively determine that a
   volatile filehandle refers to an object that has been removed, the
   server should return NFS4ERR_STALE to the client (as is the case for
   persistent filehandles).  In all other cases where the server
   determines that a volatile filehandle can no longer be used, it
   should return an error of NFS4ERR_FHEXPIRED.

   The REQUIRED attribute "fh_expire_type" is used by the client to
   determine what type of filehandle the server is providing for a
   particular file system.  This attribute is a bitmask with the
   following values:

   FH4_PERSISTENT  The value of FH4_PERSISTENT is used to indicate a
      persistent filehandle, which is valid until the object is removed
      from the file system.  The server will not return




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      NFS4ERR_FHEXPIRED for this filehandle.  FH4_PERSISTENT is defined
      as a value in which none of the bits specified below are set.

   FH4_VOLATILE_ANY  The filehandle may expire at any time, except as
      specifically excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).

   FH4_NOEXPIRE_WITH_OPEN  May only be set when FH4_VOLATILE_ANY is set.
      If this bit is set, then the meaning of FH4_VOLATILE_ANY is
      qualified to exclude any expiration of the filehandle when it is
      open.

   FH4_VOL_MIGRATION  The filehandle will expire as a result of a file
      system transition (migration or replication), in those cases in
      which the continuity of filehandle use is not specified by handle
      class information within the fs_locations_info attribute.  When
      this bit is set, clients without access to fs_locations_info
      information should assume that filehandles will expire on file
      system transitions.

   FH4_VOL_RENAME  The filehandle will expire during rename.  This
      includes a rename by the requesting client or a rename by any
      other client.  If FH4_VOL_ANY is set, FH4_VOL_RENAME is redundant.

   Servers that provide volatile filehandles that can expire while open
   require special care as regards handling of RENAMEs and REMOVEs.
   This situation can arise if FH4_VOL_MIGRATION or FH4_VOL_RENAME is
   set, if FH4_VOLATILE_ANY is set and FH4_NOEXPIRE_WITH_OPEN is not
   set, or if a non-read-only file system has a transition target in a
   different handle class.  In these cases, the server should deny a
   RENAME or REMOVE that would affect an OPEN file of any of the
   components leading to the OPEN file.  In addition, the server should
   deny all RENAME or REMOVE requests during the grace period, in order
   to make sure that reclaims of files where filehandles may have
   expired do not do a reclaim for the wrong file.

   Volatile filehandles are especially suitable for implementation of
   the pseudo file systems used to bridge exports.  See Section 7.5 for
   a discussion of this.

4.3.  One Method of Constructing a Volatile Filehandle

   A volatile filehandle, while opaque to the client, could contain:









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   [volatile bit = 1 | server boot time | slot | generation number]
   o  slot is an index in the server volatile filehandle table


   o  generation number is the generation number for the table entry/
      slot

   When the client presents a volatile filehandle, the server makes the
   following checks, which assume that the check for the volatile bit
   has passed.  If the server boot time is less than the current server
   boot time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
   NFS4ERR_BADHANDLE.  If the generation number does not match, return
   NFS4ERR_FHEXPIRED.

   When the server restarts, the table is gone (it is volatile).

   If the volatile bit is 0, then it is a persistent filehandle with a
   different structure following it.

4.4.  Client Recovery from Filehandle Expiration

   If possible, the client SHOULD recover from the receipt of an
   NFS4ERR_FHEXPIRED error.  The client must take on additional
   responsibility so that it may prepare itself to recover from the
   expiration of a volatile filehandle.  If the server returns
   persistent filehandles, the client does not need these additional
   steps.

   For volatile filehandles, most commonly the client will need to store
   the component names leading up to and including the file system
   object in question.  With these names, the client should be able to
   recover by finding a filehandle in the namespace that is still
   available or by starting at the root of the server's file system
   namespace.

   If the expired filehandle refers to an object that has been removed
   from the file system, obviously the client will not be able to
   recover from the expired filehandle.

   It is also possible that the expired filehandle refers to a file that
   has been renamed.  If the file was renamed by another client, again
   it is possible that the original client will not be able to recover.
   However, in the case that the client itself is renaming the file and
   the file is open, it is possible that the client may be able to
   recover.  The client can determine the new pathname based on the
   processing of the rename request.  The client can then regenerate the
   new filehandle based on the new pathname.  The client could also use
   the COMPOUND procedure to construct a series of operations like:



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             RENAME A B
             LOOKUP B
             GETFH

   Note that the COMPOUND procedure does not provide atomicity.  This
   example only reduces the overhead of recovering from an expired
   filehandle.

5.  File Attributes

   To meet the requirements of extensibility and increased
   interoperability with non-UNIX platforms, attributes need to be
   handled in a flexible manner.  The NFSv3 fattr3 structure contains a
   fixed list of attributes that not all clients and servers are able to
   support or care about.  The fattr3 structure cannot be extended as
   new needs arise and it provides no way to indicate non-support.  With
   the NFSv4.1 protocol, the client is able to query what attributes the
   server supports and construct requests with only those supported
   attributes (or a subset thereof).

   To this end, attributes are divided into three groups: REQUIRED,
   RECOMMENDED, and named.  Both REQUIRED and RECOMMENDED attributes are
   supported in the NFSv4.1 protocol by a specific and well-defined
   encoding and are identified by number.  They are requested by setting
   a bit in the bit vector sent in the GETATTR request; the server
   response includes a bit vector to list what attributes were returned
   in the response.  New REQUIRED or RECOMMENDED attributes may be added
   to the NFSv4 protocol as part of a new minor version by publishing a
   Standards Track RFC that allocates a new attribute number value and
   defines the encoding for the attribute.  See Section 2.7 for further
   discussion.

   Named attributes are accessed by the new OPENATTR operation, which
   accesses a hidden directory of attributes associated with a file
   system object.  OPENATTR takes a filehandle for the object and
   returns the filehandle for the attribute hierarchy.  The filehandle
   for the named attributes is a directory object accessible by LOOKUP
   or READDIR and contains files whose names represent the named
   attributes and whose data bytes are the value of the attribute.  For
   example:

        +----------+-----------+---------------------------------+
        | LOOKUP   | "foo"     | ; look up file                  |
        | GETATTR  | attrbits  |                                 |
        | OPENATTR |           | ; access foo's named attributes |
        | LOOKUP   | "x11icon" | ; look up specific attribute    |
        | READ     | 0,4096    | ; read stream of bytes          |
        +----------+-----------+---------------------------------+



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   Named attributes are intended for data needed by applications rather
   than by an NFS client implementation.  NFS implementors are strongly
   encouraged to define their new attributes as RECOMMENDED attributes
   by bringing them to the IETF Standards Track process.

   The set of attributes that are classified as REQUIRED is deliberately
   small since servers need to do whatever it takes to support them.  A
   server should support as many of the RECOMMENDED attributes as
   possible but, by their definition, the server is not required to
   support all of them.  Attributes are deemed REQUIRED if the data is
   both needed by a large number of clients and is not otherwise
   reasonably computable by the client when support is not provided on
   the server.

   Note that the hidden directory returned by OPENATTR is a convenience
   for protocol processing.  The client should not make any assumptions
   about the server's implementation of named attributes and whether or
   not the underlying file system at the server has a named attribute
   directory.  Therefore, operations such as SETATTR and GETATTR on the
   named attribute directory are undefined.

5.1.  REQUIRED Attributes

   These MUST be supported by every NFSv4.1 client and server in order
   to ensure a minimum level of interoperability.  The server MUST store
   and return these attributes, and the client MUST be able to function
   with an attribute set limited to these attributes.  With just the
   REQUIRED attributes some client functionality may be impaired or
   limited in some ways.  A client may ask for any of these attributes
   to be returned by setting a bit in the GETATTR request, and the
   server MUST return their value.

5.2.  RECOMMENDED Attributes

   These attributes are understood well enough to warrant support in the
   NFSv4.1 protocol.  However, they may not be supported on all clients
   and servers.  A client may ask for any of these attributes to be
   returned by setting a bit in the GETATTR request but must handle the
   case where the server does not return them.  A client MAY ask for the
   set of attributes the server supports and SHOULD NOT request
   attributes the server does not support.  A server should be tolerant
   of requests for unsupported attributes and simply not return them
   rather than considering the request an error.  It is expected that
   servers will support all attributes they comfortably can and only
   fail to support attributes that are difficult to support in their
   operating environments.  A server should provide attributes whenever
   they don't have to "tell lies" to the client.  For example, a file
   modification time should be either an accurate time or should not be



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   supported by the server.  At times this will be difficult for
   clients, but a client is better positioned to decide whether and how
   to fabricate or construct an attribute or whether to do without the
   attribute.

5.3.  Named Attributes

   These attributes are not supported by direct encoding in the NFSv4
   protocol but are accessed by string names rather than numbers and
   correspond to an uninterpreted stream of bytes that are stored with
   the file system object.  The namespace for these attributes may be
   accessed by using the OPENATTR operation.  The OPENATTR operation
   returns a filehandle for a virtual "named attribute directory", and
   further perusal and modification of the namespace may be done using
   operations that work on more typical directories.  In particular,
   READDIR may be used to get a list of such named attributes, and
   LOOKUP and OPEN may select a particular attribute.  Creation of a new
   named attribute may be the result of an OPEN specifying file
   creation.

   Once an OPEN is done, named attributes may be examined and changed by
   normal READ and WRITE operations using the filehandles and stateids
   returned by OPEN.

   Named attributes and the named attribute directory may have their own
   (non-named) attributes.  Each of these objects MUST have all of the
   REQUIRED attributes and may have additional RECOMMENDED attributes.
   However, the set of attributes for named attributes and the named
   attribute directory need not be, and typically will not be, as large
   as that for other objects in that file system.

   Named attributes and the named attribute directory might be the
   target of delegations (in the case of the named attribute directory,
   these will be directory delegations).  However, since granting
   delegations is at the server's discretion, a server need not support
   delegations on named attributes or the named attribute directory.

   It is RECOMMENDED that servers support arbitrary named attributes.  A
   client should not depend on the ability to store any named attributes
   in the server's file system.  If a server does support named
   attributes, a client that is also able to handle them should be able
   to copy a file's data and metadata with complete transparency from
   one location to another; this would imply that names allowed for
   regular directory entries are valid for named attribute names as
   well.

   In NFSv4.1, the structure of named attribute directories is
   restricted in a number of ways, in order to prevent the development



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   of non-interoperable implementations in which some servers support a
   fully general hierarchical directory structure for named attributes
   while others support a limited but adequate structure for named
   attributes.  In such an environment, clients or applications might
   come to depend on non-portable extensions.  The restrictions are:

   o  CREATE is not allowed in a named attribute directory.  Thus, such
      objects as symbolic links and special files are not allowed to be
      named attributes.  Further, directories may not be created in a
      named attribute directory, so no hierarchical structure of named
      attributes for a single object is allowed.

   o  If OPENATTR is done on a named attribute directory or on a named
      attribute, the server MUST return NFS4ERR_WRONG_TYPE.

   o  Doing a RENAME of a named attribute to a different named attribute
      directory or to an ordinary (i.e., non-named-attribute) directory
      is not allowed.

   o  Creating hard links between named attribute directories or between
      named attribute directories and ordinary directories is not
      allowed.

   Names of attributes will not be controlled by this document or other
   IETF Standards Track documents.  See Section 22.1 for further
   discussion.

5.4.  Classification of Attributes

   Each of the REQUIRED and RECOMMENDED attributes can be classified in
   one of three categories: per server (i.e., the value of the attribute
   will be the same for all file objects that share the same server
   owner; see Section 2.5 for a definition of server owner), per file
   system (i.e., the value of the attribute will be the same for some or
   all file objects that share the same fsid attribute (Section 5.8.1.9)
   and server owner), or per file system object.  Note that it is
   possible that some per file system attributes may vary within the
   file system, depending on the value of the "homogeneous"
   (Section 5.8.2.16) attribute.  Note that the attributes
   time_access_set and time_modify_set are not listed in this section
   because they are write-only attributes corresponding to time_access
   and time_modify, and are used in a special instance of SETATTR.

   o  The per-server attribute is:

         lease_time

   o  The per-file system attributes are:



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         supported_attrs, suppattr_exclcreat, fh_expire_type,
         link_support, symlink_support, unique_handles, aclsupport,
         cansettime, case_insensitive, case_preserving,
         chown_restricted, files_avail, files_free, files_total,
         fs_locations, homogeneous, maxfilesize, maxname, maxread,
         maxwrite, no_trunc, space_avail, space_free, space_total,
         time_delta, change_policy, fs_status, fs_layout_type,
         fs_locations_info, fs_charset_cap

   o  The per-file system object attributes are:

         type, change, size, named_attr, fsid, rdattr_error, filehandle,
         acl, archive, fileid, hidden, maxlink, mimetype, mode,
         numlinks, owner, owner_group, rawdev, space_used, system,
         time_access, time_backup, time_create, time_metadata,
         time_modify, mounted_on_fileid, dir_notif_delay,
         dirent_notif_delay, dacl, sacl, layout_type, layout_hint,
         layout_blksize, layout_alignment, mdsthreshold, retention_get,
         retention_set, retentevt_get, retentevt_set, retention_hold,
         mode_set_masked

   For quota_avail_hard, quota_avail_soft, and quota_used, see their
   definitions below for the appropriate classification.

5.5.  Set-Only and Get-Only Attributes

   Some REQUIRED and RECOMMENDED attributes are set-only; i.e., they can
   be set via SETATTR but not retrieved via GETATTR.  Similarly, some
   REQUIRED and RECOMMENDED attributes are get-only; i.e., they can be
   retrieved via GETATTR but not set via SETATTR.  If a client attempts
   to set a get-only attribute or get a set-only attributes, the server
   MUST return NFS4ERR_INVAL.

5.6.  REQUIRED Attributes - List and Definition References

   The list of REQUIRED attributes appears in Table 2.  The meaning of
   the columns of the table are:

   o  Name: The name of the attribute.

   o  Id: The number assigned to the attribute.  In the event of
      conflicts between the assigned number and [13], the latter is
      likely authoritative, but should be resolved with Errata to this
      document and/or [13].  See [44] for the Errata process.

   o  Data Type: The XDR data type of the attribute.





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   o  Acc: Access allowed to the attribute.  R means read-only (GETATTR
      may retrieve, SETATTR may not set).  W means write-only (SETATTR
      may set, GETATTR may not retrieve).  R W means read/write (GETATTR
      may retrieve, SETATTR may set).

   o  Defined in: The section of this specification that describes the
      attribute.

    +--------------------+----+------------+-----+-------------------+
    | Name               | Id | Data Type  | Acc | Defined in:       |
    +--------------------+----+------------+-----+-------------------+
    | supported_attrs    | 0  | bitmap4    | R   | Section 5.8.1.1   |
    | type               | 1  | nfs_ftype4 | R   | Section 5.8.1.2   |
    | fh_expire_type     | 2  | uint32_t   | R   | Section 5.8.1.3   |
    | change             | 3  | uint64_t   | R   | Section 5.8.1.4   |
    | size               | 4  | uint64_t   | R W | Section 5.8.1.5   |
    | link_support       | 5  | bool       | R   | Section 5.8.1.6   |
    | symlink_support    | 6  | bool       | R   | Section 5.8.1.7   |
    | named_attr         | 7  | bool       | R   | Section 5.8.1.8   |
    | fsid               | 8  | fsid4      | R   | Section 5.8.1.9   |
    | unique_handles     | 9  | bool       | R   | Section 5.8.1.10  |
    | lease_time         | 10 | nfs_lease4 | R   | Section 5.8.1.11  |
    | rdattr_error       | 11 | enum       | R   | Section 5.8.1.12  |
    | filehandle         | 19 | nfs_fh4    | R   | Section 5.8.1.13  |
    | suppattr_exclcreat | 75 | bitmap4    | R   | Section 5.8.1.14  |
    +--------------------+----+------------+-----+-------------------+

                                  Table 2

5.7.  RECOMMENDED Attributes - List and Definition References

   The RECOMMENDED attributes are defined in Table 3.  The meanings of
   the column headers are the same as Table 2; see Section 5.6 for the
   meanings.

   +--------------------+----+----------------+-----+------------------+
   | Name               | Id | Data Type      | Acc | Defined in:      |
   +--------------------+----+----------------+-----+------------------+
   | acl                | 12 | nfsace4<>      | R W | Section 6.2.1    |
   | aclsupport         | 13 | uint32_t       | R   | Section 6.2.1.2  |
   | archive            | 14 | bool           | R W | Section 5.8.2.1  |
   | cansettime         | 15 | bool           | R   | Section 5.8.2.2  |
   | case_insensitive   | 16 | bool           | R   | Section 5.8.2.3  |
   | case_preserving    | 17 | bool           | R   | Section 5.8.2.4  |
   | change_policy      | 60 | chg_policy4    | R   | Section 5.8.2.5  |
   | chown_restricted   | 18 | bool           | R   | Section 5.8.2.6  |
   | dacl               | 58 | nfsacl41       | R W | Section 6.2.2    |
   | dir_notif_delay    | 56 | nfstime4       | R   | Section 5.11.1   |



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   | dirent_notif_delay | 57 | nfstime4       | R   | Section 5.11.2   |
   | fileid             | 20 | uint64_t       | R   | Section 5.8.2.7  |
   | files_avail        | 21 | uint64_t       | R   | Section 5.8.2.8  |
   | files_free         | 22 | uint64_t       | R   | Section 5.8.2.9  |
   | files_total        | 23 | uint64_t       | R   | Section 5.8.2.10 |
   | fs_charset_cap     | 76 | uint32_t       | R   | Section 5.8.2.11 |
   | fs_layout_type     | 62 | layouttype4<>  | R   | Section 5.12.1   |
   | fs_locations       | 24 | fs_locations   | R   | Section 5.8.2.12 |
   | fs_locations_info  | 67 | *              | R   | Section 5.8.2.13 |
   | fs_status          | 61 | fs4_status     | R   | Section 5.8.2.14 |
   | hidden             | 25 | bool           | R W | Section 5.8.2.15 |
   | homogeneous        | 26 | bool           | R   | Section 5.8.2.16 |
   | layout_alignment   | 66 | uint32_t       | R   | Section 5.12.2   |
   | layout_blksize     | 65 | uint32_t       | R   | Section 5.12.3   |
   | layout_hint        | 63 | layouthint4    | W   | Section 5.12.4   |
   | layout_type        | 64 | layouttype4<>  | R   | Section 5.12.5   |
   | maxfilesize        | 27 | uint64_t       | R   | Section 5.8.2.17 |
   | maxlink            | 28 | uint32_t       | R   | Section 5.8.2.18 |
   | maxname            | 29 | uint32_t       | R   | Section 5.8.2.19 |
   | maxread            | 30 | uint64_t       | R   | Section 5.8.2.20 |
   | maxwrite           | 31 | uint64_t       | R   | Section 5.8.2.21 |
   | mdsthreshold       | 68 | mdsthreshold4  | R   | Section 5.12.6   |
   | mimetype           | 32 | utf8str_cs     | R W | Section 5.8.2.22 |
   | mode               | 33 | mode4          | R W | Section 6.2.4    |
   | mode_set_masked    | 74 | mode_masked4   | W   | Section 6.2.5    |
   | mounted_on_fileid  | 55 | uint64_t       | R   | Section 5.8.2.23 |
   | no_trunc           | 34 | bool           | R   | Section 5.8.2.24 |
   | numlinks           | 35 | uint32_t       | R   | Section 5.8.2.25 |
   | owner              | 36 | utf8str_mixed  | R W | Section 5.8.2.26 |
   | owner_group        | 37 | utf8str_mixed  | R W | Section 5.8.2.27 |
   | quota_avail_hard   | 38 | uint64_t       | R   | Section 5.8.2.28 |
   | quota_avail_soft   | 39 | uint64_t       | R   | Section 5.8.2.29 |
   | quota_used         | 40 | uint64_t       | R   | Section 5.8.2.30 |
   | rawdev             | 41 | specdata4      | R   | Section 5.8.2.31 |
   | retentevt_get      | 71 | retention_get4 | R   | Section 5.13.3   |
   | retentevt_set      | 72 | retention_set4 | W   | Section 5.13.4   |
   | retention_get      | 69 | retention_get4 | R   | Section 5.13.1   |
   | retention_hold     | 73 | uint64_t       | R W | Section 5.13.5   |
   | retention_set      | 70 | retention_set4 | W   | Section 5.13.2   |
   | sacl               | 59 | nfsacl41       | R W | Section 6.2.3    |
   | space_avail        | 42 | uint64_t       | R   | Section 5.8.2.32 |
   | space_free         | 43 | uint64_t       | R   | Section 5.8.2.33 |
   | space_total        | 44 | uint64_t       | R   | Section 5.8.2.34 |
   | space_used         | 45 | uint64_t       | R   | Section 5.8.2.35 |
   | system             | 46 | bool           | R W | Section 5.8.2.36 |
   | time_access        | 47 | nfstime4       | R   | Section 5.8.2.37 |
   | time_access_set    | 48 | settime4       | W   | Section 5.8.2.38 |
   | time_backup        | 49 | nfstime4       | R W | Section 5.8.2.39 |



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   | time_create        | 50 | nfstime4       | R W | Section 5.8.2.40 |
   | time_delta         | 51 | nfstime4       | R   | Section 5.8.2.41 |
   | time_metadata      | 52 | nfstime4       | R   | Section 5.8.2.42 |
   | time_modify        | 53 | nfstime4       | R   | Section 5.8.2.43 |
   | time_modify_set    | 54 | settime4       | W   | Section 5.8.2.44 |
   +--------------------+----+----------------+-----+------------------+

                                  Table 3

   * fs_locations_info4

5.8.  Attribute Definitions

5.8.1.  Definitions of REQUIRED Attributes

5.8.1.1.  Attribute 0: supported_attrs

   The bit vector that would retrieve all REQUIRED and RECOMMENDED
   attributes that are supported for this object.  The scope of this
   attribute applies to all objects with a matching fsid.

5.8.1.2.  Attribute 1: type

   Designates the type of an object in terms of one of a number of
   special constants:

   o  NF4REG designates a regular file.

   o  NF4DIR designates a directory.

   o  NF4BLK designates a block device special file.

   o  NF4CHR designates a character device special file.

   o  NF4LNK designates a symbolic link.

   o  NF4SOCK designates a named socket special file.

   o  NF4FIFO designates a fifo special file.

   o  NF4ATTRDIR designates a named attribute directory.

   o  NF4NAMEDATTR designates a named attribute.

   Within the explanatory text and operation descriptions, the following
   phrases will be used with the meanings given below:





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   o  The phrase "is a directory" means that the object's type attribute
      is NF4DIR or NF4ATTRDIR.

   o  The phrase "is a special file" means that the object's type
      attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO.

   o  The phrases "is an ordinary file" and "is a regular file" mean
      that the object's type attribute is NF4REG or NF4NAMEDATTR.

5.8.1.3.  Attribute 2: fh_expire_type

   Server uses this to specify filehandle expiration behavior to the
   client.  See Section 4 for additional description.

5.8.1.4.  Attribute 3: change

   A value created by the server that the client can use to determine if
   file data, directory contents, or attributes of the object have been
   modified.  The server may return the object's time_metadata attribute
   for this attribute's value, but only if the file system object cannot
   be updated more frequently than the resolution of time_metadata.

5.8.1.5.  Attribute 4: size

   The size of the object in bytes.

5.8.1.6.  Attribute 5: link_support

   TRUE, if the object's file system supports hard links.

5.8.1.7.  Attribute 6: symlink_support

   TRUE, if the object's file system supports symbolic links.

5.8.1.8.  Attribute 7: named_attr

   TRUE, if this object has named attributes.  In other words, object
   has a non-empty named attribute directory.

5.8.1.9.  Attribute 8: fsid

   Unique file system identifier for the file system holding this
   object.  The fsid attribute has major and minor components, each of
   which are of data type uint64_t.







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5.8.1.10.  Attribute 9: unique_handles

   TRUE, if two distinct filehandles are guaranteed to refer to two
   different file system objects.

5.8.1.11.  Attribute 10: lease_time

   Duration of the lease at server in seconds.

5.8.1.12.  Attribute 11: rdattr_error

   Error returned from an attempt to retrieve attributes during a
   READDIR operation.

5.8.1.13.  Attribute 19: filehandle

   The filehandle of this object (primarily for READDIR requests).

5.8.1.14.  Attribute 75: suppattr_exclcreat

   The bit vector that would set all REQUIRED and RECOMMENDED attributes
   that are supported by the EXCLUSIVE4_1 method of file creation via
   the OPEN operation.  The scope of this attribute applies to all
   objects with a matching fsid.

5.8.2.  Definitions of Uncategorized RECOMMENDED Attributes

   The definitions of most of the RECOMMENDED attributes follow.
   Collections that share a common category are defined in other
   sections.

5.8.2.1.  Attribute 14: archive

   TRUE, if this file has been archived since the time of last
   modification (deprecated in favor of time_backup).

5.8.2.2.  Attribute 15: cansettime

   TRUE, if the server is able to change the times for a file system
   object as specified in a SETATTR operation.

5.8.2.3.  Attribute 16: case_insensitive

   TRUE, if file name comparisons on this file system are case
   insensitive.






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5.8.2.4.  Attribute 17: case_preserving

   TRUE, if file name case on this file system is preserved.

5.8.2.5.  Attribute 60: change_policy

   A value created by the server that the client can use to determine if
   some server policy related to the current file system has been
   subject to change.  If the value remains the same, then the client
   can be sure that the values of the attributes related to fs location
   and the fss_type field of the fs_status attribute have not changed.
   On the other hand, a change in this value does necessarily imply a
   change in policy.  It is up to the client to interrogate the server
   to determine if some policy relevant to it has changed.  See
   Section 3.3.6 for details.

   This attribute MUST change when the value returned by the
   fs_locations or fs_locations_info attribute changes, when a file
   system goes from read-only to writable or vice versa, or when the
   allowable set of security flavors for the file system or any part
   thereof is changed.

5.8.2.6.  Attribute 18: chown_restricted

   If TRUE, the server will reject any request to change either the
   owner or the group associated with a file if the caller is not a
   privileged user (for example, "root" in UNIX operating environments
   or, in Windows 2000, the "Take Ownership" privilege).

5.8.2.7.  Attribute 20: fileid

   A number uniquely identifying the file within the file system.

5.8.2.8.  Attribute 21: files_avail

   File slots available to this user on the file system containing this
   object -- this should be the smallest relevant limit.

5.8.2.9.  Attribute 22: files_free

   Free file slots on the file system containing this object -- this
   should be the smallest relevant limit.

5.8.2.10.  Attribute 23: files_total

   Total file slots on the file system containing this object.





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5.8.2.11.  Attribute 76: fs_charset_cap

   Character set capabilities for this file system.  See Section 14.4.

5.8.2.12.  Attribute 24: fs_locations

   Locations where this file system may be found.  If the server returns
   NFS4ERR_MOVED as an error, this attribute MUST be supported.  See
   Section 11.9 for more details.

5.8.2.13.  Attribute 67: fs_locations_info

   Full function file system location.  See Section 11.10 for more
   details.

5.8.2.14.  Attribute 61: fs_status

   Generic file system type information.  See Section 11.11 for more
   details.

5.8.2.15.  Attribute 25: hidden

   TRUE, if the file is considered hidden with respect to the Windows
   API.

5.8.2.16.  Attribute 26: homogeneous

   TRUE, if this object's file system is homogeneous; i.e., all objects
   in the file system (all objects on the server with the same fsid)
   have common values for all per-file-system attributes.

5.8.2.17.  Attribute 27: maxfilesize

   Maximum supported file size for the file system of this object.

5.8.2.18.  Attribute 28: maxlink

   Maximum number of links for this object.

5.8.2.19.  Attribute 29: maxname

   Maximum file name size supported for this object.

5.8.2.20.  Attribute 30: maxread

   Maximum amount of data the READ operation will return for this
   object.




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5.8.2.21.  Attribute 31: maxwrite

   Maximum amount of data the WRITE operation will accept for this
   object.  This attribute SHOULD be supported if the file is writable.
   Lack of this attribute can lead to the client either wasting
   bandwidth or not receiving the best performance.

5.8.2.22.  Attribute 32: mimetype

   MIME body type/subtype of this object.

5.8.2.23.  Attribute 55: mounted_on_fileid

   Like fileid, but if the target filehandle is the root of a file
   system, this attribute represents the fileid of the underlying
   directory.

   UNIX-based operating environments connect a file system into the
   namespace by connecting (mounting) the file system onto the existing
   file object (the mount point, usually a directory) of an existing
   file system.  When the mount point's parent directory is read via an
   API like readdir(), the return results are directory entries, each
   with a component name and a fileid.  The fileid of the mount point's
   directory entry will be different from the fileid that the stat()
   system call returns.  The stat() system call is returning the fileid
   of the root of the mounted file system, whereas readdir() is
   returning the fileid that stat() would have returned before any file
   systems were mounted on the mount point.

   Unlike NFSv3, NFSv4.1 allows a client's LOOKUP request to cross other
   file systems.  The client detects the file system crossing whenever
   the filehandle argument of LOOKUP has an fsid attribute different
   from that of the filehandle returned by LOOKUP.  A UNIX-based client
   will consider this a "mount point crossing".  UNIX has a legacy
   scheme for allowing a process to determine its current working
   directory.  This relies on readdir() of a mount point's parent and
   stat() of the mount point returning fileids as previously described.
   The mounted_on_fileid attribute corresponds to the fileid that
   readdir() would have returned as described previously.

   While the NFSv4.1 client could simply fabricate a fileid
   corresponding to what mounted_on_fileid provides (and if the server
   does not support mounted_on_fileid, the client has no choice), there
   is a risk that the client will generate a fileid that conflicts with
   one that is already assigned to another object in the file system.
   Instead, if the server can provide the mounted_on_fileid, the
   potential for client operational problems in this area is eliminated.




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   If the server detects that there is no mounted point at the target
   file object, then the value for mounted_on_fileid that it returns is
   the same as that of the fileid attribute.

   The mounted_on_fileid attribute is RECOMMENDED, so the server SHOULD
   provide it if possible, and for a UNIX-based server, this is
   straightforward.  Usually, mounted_on_fileid will be requested during
   a READDIR operation, in which case it is trivial (at least for UNIX-
   based servers) to return mounted_on_fileid since it is equal to the
   fileid of a directory entry returned by readdir().  If
   mounted_on_fileid is requested in a GETATTR operation, the server
   should obey an invariant that has it returning a value that is equal
   to the file object's entry in the object's parent directory, i.e.,
   what readdir() would have returned.  Some operating environments
   allow a series of two or more file systems to be mounted onto a
   single mount point.  In this case, for the server to obey the
   aforementioned invariant, it will need to find the base mount point,
   and not the intermediate mount points.

5.8.2.24.  Attribute 34: no_trunc

   If this attribute is TRUE, then if the client uses a file name longer
   than name_max, an error will be returned instead of the name being
   truncated.

5.8.2.25.  Attribute 35: numlinks

   Number of hard links to this object.

5.8.2.26.  Attribute 36: owner

   The string name of the owner of this object.

5.8.2.27.  Attribute 37: owner_group

   The string name of the group ownership of this object.

5.8.2.28.  Attribute 38: quota_avail_hard

   The value in bytes that represents the amount of additional disk
   space beyond the current allocation that can be allocated to this
   file or directory before further allocations will be refused.  It is
   understood that this space may be consumed by allocations to other
   files or directories.







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5.8.2.29.  Attribute 39: quota_avail_soft

   The value in bytes that represents the amount of additional disk
   space that can be allocated to this file or directory before the user
   may reasonably be warned.  It is understood that this space may be
   consumed by allocations to other files or directories though there is
   a rule as to which other files or directories.

5.8.2.30.  Attribute 40: quota_used

   The value in bytes that represents the amount of disk space used by
   this file or directory and possibly a number of other similar files
   or directories, where the set of "similar" meets at least the
   criterion that allocating space to any file or directory in the set
   will reduce the "quota_avail_hard" of every other file or directory
   in the set.

   Note that there may be a number of distinct but overlapping sets of
   files or directories for which a quota_used value is maintained,
   e.g., "all files with a given owner", "all files with a given group
   owner", etc.  The server is at liberty to choose any of those sets
   when providing the content of the quota_used attribute, but should do
   so in a repeatable way.  The rule may be configured per file system
   or may be "choose the set with the smallest quota".

5.8.2.31.  Attribute 41: rawdev

   Raw device number of file of type NF4BLK or NF4CHR.  The device
   number is split into major and minor numbers.  If the file's type
   attribute is not NF4BLK or NF4CHR, the value returned SHOULD NOT be
   considered useful.

5.8.2.32.  Attribute 42: space_avail

   Disk space in bytes available to this user on the file system
   containing this object -- this should be the smallest relevant limit.

5.8.2.33.  Attribute 43: space_free

   Free disk space in bytes on the file system containing this object --
   this should be the smallest relevant limit.

5.8.2.34.  Attribute 44: space_total

   Total disk space in bytes on the file system containing this object.






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5.8.2.35.  Attribute 45: space_used

   Number of file system bytes allocated to this object.

5.8.2.36.  Attribute 46: system

   This attribute is TRUE if this file is a "system" file with respect
   to the Windows operating environment.

5.8.2.37.  Attribute 47: time_access

   The time_access attribute represents the time of last access to the
   object by a READ operation sent to the server.  The notion of what is
   an "access" depends on the server's operating environment and/or the
   server's file system semantics.  For example, for servers obeying
   Portable Operating System Interface (POSIX) semantics, time_access
   would be updated only by the READ and READDIR operations and not any
   of the operations that modify the content of the object [16], [17],
   [18].  Of course, setting the corresponding time_access_set attribute
   is another way to modify the time_access attribute.

   Whenever the file object resides on a writable file system, the
   server should make its best efforts to record time_access into stable
   storage.  However, to mitigate the performance effects of doing so,
   and most especially whenever the server is satisfying the read of the
   object's content from its cache, the server MAY cache access time
   updates and lazily write them to stable storage.  It is also
   acceptable to give administrators of the server the option to disable
   time_access updates.

5.8.2.38.  Attribute 48: time_access_set

   Sets the time of last access to the object.  SETATTR use only.

5.8.2.39.  Attribute 49: time_backup

   The time of last backup of the object.

5.8.2.40.  Attribute 50: time_create

   The time of creation of the object.  This attribute does not have any
   relation to the traditional UNIX file attribute "ctime" or "change
   time".








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5.8.2.41.  Attribute 51: time_delta

   Smallest useful server time granularity.

5.8.2.42.  Attribute 52: time_metadata

   The time of last metadata modification of the object.

5.8.2.43.  Attribute 53: time_modify

   The time of last modification to the object.

5.8.2.44.  Attribute 54: time_modify_set

   Sets the time of last modification to the object.  SETATTR use only.

5.9.  Interpreting owner and owner_group

   The RECOMMENDED attributes "owner" and "owner_group" (and also users
   and groups within the "acl" attribute) are represented in terms of a
   UTF-8 string.  To avoid a representation that is tied to a particular
   underlying implementation at the client or server, the use of the
   UTF-8 string has been chosen.  Note that Section 6.1 of RFC 2624 [45]
   provides additional rationale.  It is expected that the client and
   server will have their own local representation of owner and
   owner_group that is used for local storage or presentation to the end
   user.  Therefore, it is expected that when these attributes are
   transferred between the client and server, the local representation
   is translated to a syntax of the form "user@dns_domain".  This will
   allow for a client and server that do not use the same local
   representation the ability to translate to a common syntax that can
   be interpreted by both.

   Similarly, security principals may be represented in different ways
   by different security mechanisms.  Servers normally translate these
   representations into a common format, generally that used by local
   storage, to serve as a means of identifying the users corresponding
   to these security principals.  When these local identifiers are
   translated to the form of the owner attribute, associated with files
   created by such principals, they identify, in a common format, the
   users associated with each corresponding set of security principals.

   The translation used to interpret owner and group strings is not
   specified as part of the protocol.  This allows various solutions to
   be employed.  For example, a local translation table may be consulted
   that maps a numeric identifier to the user@dns_domain syntax.  A name
   service may also be used to accomplish the translation.  A server may
   provide a more general service, not limited by any particular



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   translation (which would only translate a limited set of possible
   strings) by storing the owner and owner_group attributes in local
   storage without any translation or it may augment a translation
   method by storing the entire string for attributes for which no
   translation is available while using the local representation for
   those cases in which a translation is available.

   Servers that do not provide support for all possible values of the
   owner and owner_group attributes SHOULD return an error
   (NFS4ERR_BADOWNER) when a string is presented that has no
   translation, as the value to be set for a SETATTR of the owner,
   owner_group, or acl attributes.  When a server does accept an owner
   or owner_group value as valid on a SETATTR (and similarly for the
   owner and group strings in an acl), it is promising to return that
   same string when a corresponding GETATTR is done.  Configuration
   changes (including changes from the mapping of the string to the
   local representation) and ill-constructed name translations (those
   that contain aliasing) may make that promise impossible to honor.
   Servers should make appropriate efforts to avoid a situation in which
   these attributes have their values changed when no real change to
   ownership has occurred.

   The "dns_domain" portion of the owner string is meant to be a DNS
   domain name, for example, user@xxxxxxxxxxx.  Servers should accept as
   valid a set of users for at least one domain.  A server may treat
   other domains as having no valid translations.  A more general
   service is provided when a server is capable of accepting users for
   multiple domains, or for all domains, subject to security
   constraints.

   In the case where there is no translation available to the client or
   server, the attribute value will be constructed without the "@".
   Therefore, the absence of the @ from the owner or owner_group
   attribute signifies that no translation was available at the sender
   and that the receiver of the attribute should not use that string as
   a basis for translation into its own internal format.  Even though
   the attribute value cannot be translated, it may still be useful.  In
   the case of a client, the attribute string may be used for local
   display of ownership.

   To provide a greater degree of compatibility with NFSv3, which
   identified users and groups by 32-bit unsigned user identifiers and
   group identifiers, owner and group strings that consist of decimal
   numeric values with no leading zeros can be given a special
   interpretation by clients and servers that choose to provide such
   support.  The receiver may treat such a user or group string as
   representing the same user as would be represented by an NFSv3 uid or
   gid having the corresponding numeric value.  A server is not



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   obligated to accept such a string, but may return an NFS4ERR_BADOWNER
   instead.  To avoid this mechanism being used to subvert user and
   group translation, so that a client might pass all of the owners and
   groups in numeric form, a server SHOULD return an NFS4ERR_BADOWNER
   error when there is a valid translation for the user or owner
   designated in this way.  In that case, the client must use the
   appropriate name@domain string and not the special form for
   compatibility.

   The owner string "nobody" may be used to designate an anonymous user,
   which will be associated with a file created by a security principal
   that cannot be mapped through normal means to the owner attribute.
   Users and implementations of NFSv4.1 SHOULD NOT use "nobody" to
   designate a real user whose access is not anonymous.

5.10.  Character Case Attributes

   With respect to the case_insensitive and case_preserving attributes,
   each UCS-4 character (which UTF-8 encodes) can be mapped according to
   Appendix B.2 of RFC 3454 [19].  For general character handling and
   internationalization issues, see Section 14.

5.11.  Directory Notification Attributes

   As described in Section 18.39, the client can request a minimum delay
   for notifications of changes to attributes, but the server is free to
   ignore what the client requests.  The client can determine in advance
   what notification delays the server will accept by sending a GETATTR
   operation for either or both of two directory notification
   attributes.  When the client calls the GET_DIR_DELEGATION operation
   and asks for attribute change notifications, it should request
   notification delays that are no less than the values in the server-
   provided attributes.

5.11.1.  Attribute 56: dir_notif_delay

   The dir_notif_delay attribute is the minimum number of seconds the
   server will delay before notifying the client of a change to the
   directory's attributes.

5.11.2.  Attribute 57: dirent_notif_delay

   The dirent_notif_delay attribute is the minimum number of seconds the
   server will delay before notifying the client of a change to a file
   object that has an entry in the directory.






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5.12.  pNFS Attribute Definitions

5.12.1.  Attribute 62: fs_layout_type

   The fs_layout_type attribute (see Section 3.3.13) applies to a file
   system and indicates what layout types are supported by the file
   system.  When the client encounters a new fsid, the client SHOULD
   obtain the value for the fs_layout_type attribute associated with the
   new file system.  This attribute is used by the client to determine
   if the layout types supported by the server match any of the client's
   supported layout types.

5.12.2.  Attribute 66: layout_alignment

   When a client holds layouts on files of a file system, the
   layout_alignment attribute indicates the preferred alignment for I/O
   to files on that file system.  Where possible, the client should send
   READ and WRITE operations with offsets that are whole multiples of
   the layout_alignment attribute.

5.12.3.  Attribute 65: layout_blksize

   When a client holds layouts on files of a file system, the
   layout_blksize attribute indicates the preferred block size for I/O
   to files on that file system.  Where possible, the client should send
   READ operations with a count argument that is a whole multiple of
   layout_blksize, and WRITE operations with a data argument of size
   that is a whole multiple of layout_blksize.

5.12.4.  Attribute 63: layout_hint

   The layout_hint attribute (see Section 3.3.19) may be set on newly
   created files to influence the metadata server's choice for the
   file's layout.  If possible, this attribute is one of those set in
   the initial attributes within the OPEN operation.  The metadata
   server may choose to ignore this attribute.  The layout_hint
   attribute is a subset of the layout structure returned by LAYOUTGET.
   For example, instead of specifying particular devices, this would be
   used to suggest the stripe width of a file.  The server
   implementation determines which fields within the layout will be
   used.

5.12.5.  Attribute 64: layout_type

   This attribute lists the layout type(s) available for a file.  The
   value returned by the server is for informational purposes only.  The
   client will use the LAYOUTGET operation to obtain the information




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   needed in order to perform I/O, for example, the specific device
   information for the file and its layout.

5.12.6.  Attribute 68: mdsthreshold

   This attribute is a server-provided hint used to communicate to the
   client when it is more efficient to send READ and WRITE operations to
   the metadata server or the data server.  The two types of thresholds
   described are file size thresholds and I/O size thresholds.  If a
   file's size is smaller than the file size threshold, data accesses
   SHOULD be sent to the metadata server.  If an I/O request has a
   length that is below the I/O size threshold, the I/O SHOULD be sent
   to the metadata server.  Each threshold type is specified separately
   for read and write.

   The server MAY provide both types of thresholds for a file.  If both
   file size and I/O size are provided, the client SHOULD reach or
   exceed both thresholds before sending its read or write requests to
   the data server.  Alternatively, if only one of the specified
   thresholds is reached or exceeded, the I/O requests are sent to the
   metadata server.

   For each threshold type, a value of zero indicates no READ or WRITE
   should be sent to the metadata server, while a value of all ones
   indicates that all READs or WRITEs should be sent to the metadata
   server.

   The attribute is available on a per-filehandle basis.  If the current
   filehandle refers to a non-pNFS file or directory, the metadata
   server should return an attribute that is representative of the
   filehandle's file system.  It is suggested that this attribute is
   queried as part of the OPEN operation.  Due to dynamic system
   changes, the client should not assume that the attribute will remain
   constant for any specific time period; thus, it should be
   periodically refreshed.

5.13.  Retention Attributes

   Retention is a concept whereby a file object can be placed in an
   immutable, undeletable, unrenamable state for a fixed or infinite
   duration of time.  Once in this "retained" state, the file cannot be
   moved out of the state until the duration of retention has been
   reached.

   When retention is enabled, retention MUST extend to the data of the
   file, and the name of file.  The server MAY extend retention to any
   other property of the file, including any subset of REQUIRED,




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   RECOMMENDED, and named attributes, with the exceptions noted in this
   section.

   Servers MAY support or not support retention on any file object type.

   The five retention attributes are explained in the next subsections.

5.13.1.  Attribute 69: retention_get

   If retention is enabled for the associated file, this attribute's
   value represents the retention begin time of the file object.  This
   attribute's value is only readable with the GETATTR operation and
   MUST NOT be modified by the SETATTR operation (Section 5.5).  The
   value of the attribute consists of:

   const RET4_DURATION_INFINITE    = 0xffffffffffffffff;
   struct retention_get4 {
           uint64_t        rg_duration;
           nfstime4        rg_begin_time<1>;
   };

   The field rg_duration is the duration in seconds indicating how long
   the file will be retained once retention is enabled.  The field
   rg_begin_time is an array of up to one absolute time value.  If the
   array is zero length, no beginning retention time has been
   established, and retention is not enabled.  If rg_duration is equal
   to RET4_DURATION_INFINITE, the file, once retention is enabled, will
   be retained for an infinite duration.

   If (as soon as) rg_duration is zero, then rg_begin_time will be of
   zero length, and again, retention is not (no longer) enabled.

5.13.2.  Attribute 70: retention_set

   This attribute is used to set the retention duration and optionally
   enable retention for the associated file object.  This attribute is
   only modifiable via the SETATTR operation and MUST NOT be retrieved
   by the GETATTR operation (Section 5.5).  This attribute corresponds
   to retention_get.  The value of the attribute consists of:

   struct retention_set4 {
           bool            rs_enable;
           uint64_t        rs_duration<1>;
   };

   If the client sets rs_enable to TRUE, then it is enabling retention
   on the file object with the begin time of retention starting from the
   server's current time and date.  The duration of the retention can



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   also be provided if the rs_duration array is of length one.  The
   duration is the time in seconds from the begin time of retention, and
   if set to RET4_DURATION_INFINITE, the file is to be retained forever.
   If retention is enabled, with no duration specified in either this
   SETATTR or a previous SETATTR, the duration defaults to zero seconds.
   The server MAY restrict the enabling of retention or the duration of
   retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
   The enabling of retention MUST NOT prevent the enabling of event-
   based retention or the modification of the retention_hold attribute.

   The following rules apply to both the retention_set and retentevt_set
   attributes.

   o  As long as retention is not enabled, the client is permitted to
      decrease the duration.

   o  The duration can always be set to an equal or higher value, even
      if retention is enabled.  Note that once retention is enabled, the
      actual duration (as returned by the retention_get or retentevt_get
      attributes; see Section 5.13.1 or Section 5.13.3) is constantly
      counting down to zero (one unit per second), unless the duration
      was set to RET4_DURATION_INFINITE.  Thus, it will not be possible
      for the client to precisely extend the duration on a file that has
      retention enabled.

   o  While retention is enabled, attempts to disable retention or
      decrease the retention's duration MUST fail with the error
      NFS4ERR_INVAL.

   o  If the principal attempting to change retention_set or
      retentevt_set does not have ACE4_WRITE_RETENTION permissions, the
      attempt MUST fail with NFS4ERR_ACCESS.

5.13.3.  Attribute 71: retentevt_get

   Gets the event-based retention duration, and if enabled, the event-
   based retention begin time of the file object.  This attribute is
   like retention_get, but refers to event-based retention.  The event
   that triggers event-based retention is not defined by the NFSv4.1
   specification.

5.13.4.  Attribute 72: retentevt_set

   Sets the event-based retention duration, and optionally enables
   event-based retention on the file object.  This attribute corresponds
   to retentevt_get and is like retention_set, but refers to event-based
   retention.  When event-based retention is set, the file MUST be
   retained even if non-event-based retention has been set, and the



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   duration of non-event-based retention has been reached.  Conversely,
   when non-event-based retention has been set, the file MUST be
   retained even if event-based retention has been set, and the duration
   of event-based retention has been reached.  The server MAY restrict
   the enabling of event-based retention or the duration of event-based
   retention on the basis of the ACE4_WRITE_RETENTION ACL permission.
   The enabling of event-based retention MUST NOT prevent the enabling
   of non-event-based retention or the modification of the
   retention_hold attribute.

5.13.5.  Attribute 73: retention_hold

   Gets or sets administrative retention holds, one hold per bit
   position.

   This attribute allows one to 64 administrative holds, one hold per
   bit on the attribute.  If retention_hold is not zero, then the file
   MUST NOT be deleted, renamed, or modified, even if the duration on
   enabled event or non-event-based retention has been reached.  The
   server MAY restrict the modification of retention_hold on the basis
   of the ACE4_WRITE_RETENTION_HOLD ACL permission.  The enabling of
   administration retention holds does not prevent the enabling of
   event-based or non-event-based retention.

   If the principal attempting to change retention_hold does not have
   ACE4_WRITE_RETENTION_HOLD permissions, the attempt MUST fail with
   NFS4ERR_ACCESS.

6.  Access Control Attributes

   Access Control Lists (ACLs) are file attributes that specify fine-
   grained access control.  This section covers the "acl", "dacl",
   "sacl", "aclsupport", "mode", and "mode_set_masked" file attributes
   and their interactions.  Note that file attributes may apply to any
   file system object.

6.1.  Goals

   ACLs and modes represent two well-established models for specifying
   permissions.  This section specifies requirements that attempt to
   meet the following goals:

   o  If a server supports the mode attribute, it should provide
      reasonable semantics to clients that only set and retrieve the
      mode attribute.

   o  If a server supports ACL attributes, it should provide reasonable
      semantics to clients that only set and retrieve those attributes.



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   o  On servers that support the mode attribute, if ACL attributes have
      never been set on an object, via inheritance or explicitly, the
      behavior should be traditional UNIX-like behavior.

   o  On servers that support the mode attribute, if the ACL attributes
      have been previously set on an object, either explicitly or via
      inheritance:

      *  Setting only the mode attribute should effectively control the
         traditional UNIX-like permissions of read, write, and execute
         on owner, owner_group, and other.

      *  Setting only the mode attribute should provide reasonable
         security.  For example, setting a mode of 000 should be enough
         to ensure that future OPEN operations for
         OPEN4_SHARE_ACCESS_READ or OPEN4_SHARE_ACCESS_WRITE by any
         principal fail, regardless of a previously existing or
         inherited ACL.

   o  NFSv4.1 may introduce different semantics relating to the mode and
      ACL attributes, but it does not render invalid any previously
      existing implementations.  Additionally, this section provides
      clarifications based on previous implementations and discussions
      around them.

   o  On servers that support both the mode and the acl or dacl
      attributes, the server must keep the two consistent with each
      other.  The value of the mode attribute (with the exception of the
      three high-order bits described in Section 6.2.4) must be
      determined entirely by the value of the ACL, so that use of the
      mode is never required for anything other than setting the three
      high-order bits.  See Section 6.4.1 for exact requirements.

   o  When a mode attribute is set on an object, the ACL attributes may
      need to be modified in order to not conflict with the new mode.
      In such cases, it is desirable that the ACL keep as much
      information as possible.  This includes information about
      inheritance, AUDIT and ALARM ACEs, and permissions granted and
      denied that do not conflict with the new mode.

6.2.  File Attributes Discussion

6.2.1.  Attribute 12: acl

   The NFSv4.1 ACL attribute contains an array of Access Control Entries
   (ACEs) that are associated with the file system object.  Although the
   client can set and get the acl attribute, the server is responsible
   for using the ACL to perform access control.  The client can use the



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   OPEN or ACCESS operations to check access without modifying or
   reading data or metadata.

   The NFS ACE structure is defined as follows:

   typedef uint32_t        acetype4;

   typedef uint32_t aceflag4;

   typedef uint32_t        acemask4;

   struct nfsace4 {
           acetype4        type;
           aceflag4        flag;
           acemask4        access_mask;
           utf8str_mixed   who;
   };

   To determine if a request succeeds, the server processes each nfsace4
   entry in order.  Only ACEs that have a "who" that matches the
   requester are considered.  Each ACE is processed until all of the
   bits of the requester's access have been ALLOWED.  Once a bit (see
   below) has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer
   considered in the processing of later ACEs.  If an ACCESS_DENIED_ACE
   is encountered where the requester's access still has unALLOWED bits
   in common with the "access_mask" of the ACE, the request is denied.
   When the ACL is fully processed, if there are bits in the requester's
   mask that have not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  Therefore, AUDIT
   and ALARM ACEs are processed only after processing ALLOW and DENY
   ACEs.

   The NFSv4.1 ACL model is quite rich.  Some server platforms may
   provide access-control functionality that goes beyond the UNIX-style
   mode attribute, but that is not as rich as the NFS ACL model.  So
   that users can take advantage of this more limited functionality, the
   server may support the acl attributes by mapping between its ACL
   model and the NFSv4.1 ACL model.  Servers must ensure that the ACL
   they actually store or enforce is at least as strict as the NFSv4 ACL
   that was set.  It is tempting to accomplish this by rejecting any ACL
   that falls outside the small set that can be represented accurately.
   However, such an approach can render ACLs unusable without special
   client-side knowledge of the server's mapping, which defeats the
   purpose of having a common NFSv4 ACL protocol.  Therefore, servers
   should accept every ACL that they can without compromising security.



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   To help accomplish this, servers may make a special exception, in the
   case of unsupported permission bits, to the rule that bits not
   ALLOWED or DENIED by an ACL must be denied.  For example, a UNIX-
   style server might choose to silently allow read attribute
   permissions even though an ACL does not explicitly allow those
   permissions.  (An ACL that explicitly denies permission to read
   attributes should still be rejected.)

   The situation is complicated by the fact that a server may have
   multiple modules that enforce ACLs.  For example, the enforcement for
   NFSv4.1 access may be different from, but not weaker than, the
   enforcement for local access, and both may be different from the
   enforcement for access through other protocols such as SMB (Server
   Message Block).  So it may be useful for a server to accept an ACL
   even if not all of its modules are able to support it.

   The guiding principle with regard to NFSv4 access is that the server
   must not accept ACLs that appear to make access to the file more
   restrictive than it really is.

6.2.1.1.  ACE Type

   The constants used for the type field (acetype4) are as follows:

   const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
   const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
   const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
   const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;

   Only the ALLOWED and DENIED bits may be used in the dacl attribute,
   and only the AUDIT and ALARM bits may be used in the sacl attribute.
   All four are permitted in the acl attribute.



















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   +------------------------------+--------------+---------------------+
   | Value                        | Abbreviation | Description         |
   +------------------------------+--------------+---------------------+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              |              | the access defined  |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | Log (in a system-   |
   |                              |              | dependent way) any  |
   |                              |              | access attempt to a |
   |                              |              | file or directory   |
   |                              |              | that uses any of    |
   |                              |              | the access methods  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generate an alarm   |
   |                              |              | (in a system-       |
   |                              |              | dependent way) when |
   |                              |              | any access attempt  |
   |                              |              | is made to a file   |
   |                              |              | or directory for    |
   |                              |              | the access methods  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

   The "Abbreviation" column denotes how the types will be referred to
   throughout the rest of this section.

6.2.1.2.  Attribute 13: aclsupport

   A server need not support all of the above ACE types.  This attribute
   indicates which ACE types are supported for the current file system.
   The bitmask constants used to represent the above definitions within
   the aclsupport attribute are as follows:

   const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
   const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
   const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
   const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;

   Servers that support either the ALLOW or DENY ACE type SHOULD support
   both ALLOW and DENY ACE types.




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   Clients should not attempt to set an ACE unless the server claims
   support for that ACE type.  If the server receives a request to set
   an ACE that it cannot store, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server receives a request to set an ACE
   that it can store but cannot enforce, the server SHOULD reject the
   request with NFS4ERR_ATTRNOTSUPP.

   Support for any of the ACL attributes is optional (albeit
   RECOMMENDED).  However, a server that supports either of the new ACL
   attributes (dacl or sacl) MUST allow use of the new ACL attributes to
   access all of the ACE types that it supports.  In other words, if
   such a server supports ALLOW or DENY ACEs, then it MUST support the
   dacl attribute, and if it supports AUDIT or ALARM ACEs, then it MUST
   support the sacl attribute.

6.2.1.3.  ACE Access Mask

   The bitmask constants used for the access mask field are as follows:

   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
   const ACE4_WRITE_RETENTION      = 0x00000200;
   const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Note that some masks have coincident values, for example,
   ACE4_READ_DATA and ACE4_LIST_DIRECTORY.  The mask entries
   ACE4_LIST_DIRECTORY, ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
   intended to be used with directory objects, while ACE4_READ_DATA,
   ACE4_WRITE_DATA, and ACE4_APPEND_DATA are intended to be used with
   non-directory objects.





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6.2.1.3.1.  Discussion of Mask Attributes

   ACE4_READ_DATA

      Operation(s) affected:

         READ

         OPEN

      Discussion:

         Permission to read the data of the file.

         Servers SHOULD allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.

   ACE4_LIST_DIRECTORY

      Operation(s) affected:

         READDIR

      Discussion:

         Permission to list the contents of a directory.

   ACE4_WRITE_DATA

      Operation(s) affected:

         WRITE

         OPEN

         SETATTR of size

      Discussion:

         Permission to modify a file's data.

   ACE4_ADD_FILE

      Operation(s) affected:

         CREATE

         LINK



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         OPEN

         RENAME

      Discussion:

         Permission to add a new file in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
         NF4CHR, NF4SOCK, or NF4FIFO.  (NF4DIR is not listed because it
         is covered by ACE4_ADD_SUBDIRECTORY.)  OPEN is affected when
         used to create a regular file.  LINK and RENAME are always
         affected.

   ACE4_APPEND_DATA

      Operation(s) affected:

         WRITE

         OPEN

         SETATTR of size

      Discussion:

         The ability to modify a file's data, but only starting at EOF.
         This allows for the notion of append-only files, by allowing
         ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the same user
         or group.  If a file has an ACL such as the one described above
         and a WRITE request is made for somewhere other than EOF, the
         server SHOULD return NFS4ERR_ACCESS.

   ACE4_ADD_SUBDIRECTORY

      Operation(s) affected:

         CREATE

         RENAME

      Discussion:

         Permission to create a subdirectory in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4DIR.  The RENAME
         operation is always affected.

   ACE4_READ_NAMED_ATTRS




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      Operation(s) affected:

         OPENATTR

      Discussion:

         Permission to read the named attributes of a file or to look up
         the named attribute directory.  OPENATTR is affected when it is
         not used to create a named attribute directory.  This is when
         1) createdir is TRUE, but a named attribute directory already
         exists, or 2) createdir is FALSE.

   ACE4_WRITE_NAMED_ATTRS

      Operation(s) affected:

         OPENATTR



      Discussion:

         Permission to write the named attributes of a file or to create
         a named attribute directory.  OPENATTR is affected when it is
         used to create a named attribute directory.  This is when
         createdir is TRUE and no named attribute directory exists.  The
         ability to check whether or not a named attribute directory
         exists depends on the ability to look it up; therefore, users
         also need the ACE4_READ_NAMED_ATTRS permission in order to
         create a named attribute directory.

   ACE4_EXECUTE

      Operation(s) affected:

         READ

         OPEN

         REMOVE

         RENAME

         LINK

         CREATE

      Discussion:



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         Permission to execute a file.

         Servers SHOULD allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.
         This is because there is no way to execute a file without
         reading the contents.  Though a server may treat ACE4_EXECUTE
         and ACE4_READ_DATA bits identically when deciding to permit a
         READ operation, it SHOULD still allow the two bits to be set
         independently in ACLs, and MUST distinguish between them when
         replying to ACCESS operations.  In particular, servers SHOULD
         NOT silently turn on one of the two bits when the other is set,
         as that would make it impossible for the client to correctly
         enforce the distinction between read and execute permissions.

         As an example, following a SETATTR of the following ACL:

         nfsuser:ACE4_EXECUTE:ALLOW

         A subsequent GETATTR of ACL for that file SHOULD return:

         nfsuser:ACE4_EXECUTE:ALLOW

         Rather than:

         nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

   ACE4_EXECUTE

      Operation(s) affected:

         LOOKUP

      Discussion:

         Permission to traverse/search a directory.

   ACE4_DELETE_CHILD

      Operation(s) affected:

         REMOVE

         RENAME

      Discussion:






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         Permission to delete a file or directory within a directory.
         See Section 6.2.1.3.2 for information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ATTRIBUTES

      Operation(s) affected:

         GETATTR of file system object attributes

         VERIFY

         NVERIFY

         READDIR

      Discussion:

         The ability to read basic attributes (non-ACLs) of a file.  On
         a UNIX system, basic attributes can be thought of as the stat-
         level attributes.  Allowing this access mask bit would mean
         that the entity can execute "ls -l" and stat.  If a READDIR
         operation requests attributes, this mask must be allowed for
         the READDIR to succeed.

   ACE4_WRITE_ATTRIBUTES

      Operation(s) affected:

         SETATTR of time_access_set, time_backup,

         time_create, time_modify_set, mimetype, hidden, system

      Discussion:

         Permission to change the times associated with a file or
         directory to an arbitrary value.  Also permission to change the
         mimetype, hidden, and system attributes.  A user having
         ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be allowed to set
         the times associated with a file to the current server time.

   ACE4_WRITE_RETENTION

      Operation(s) affected:

         SETATTR of retention_set, retentevt_set.

      Discussion:



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         Permission to modify the durations of event and non-event-based
         retention.  Also permission to enable event and non-event-based
         retention.  A server MAY behave such that setting
         ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.

   ACE4_WRITE_RETENTION_HOLD

      Operation(s) affected:

         SETATTR of retention_hold.

      Discussion:

         Permission to modify the administration retention holds.  A
         server MAY map ACE4_WRITE_ATTRIBUTES to
         ACE_WRITE_RETENTION_HOLD.

   ACE4_DELETE

      Operation(s) affected:

         REMOVE

      Discussion:

         Permission to delete the file or directory.  See
         Section 6.2.1.3.2 for information on ACE4_DELETE and
         ACE4_DELETE_CHILD interact.

   ACE4_READ_ACL

      Operation(s) affected:

         GETATTR of acl, dacl, or sacl

         NVERIFY

         VERIFY

      Discussion:

         Permission to read the ACL.

   ACE4_WRITE_ACL

      Operation(s) affected:

         SETATTR of acl and mode



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      Discussion:

         Permission to write the acl and mode attributes.

   ACE4_WRITE_OWNER

      Operation(s) affected:

         SETATTR of owner and owner_group

      Discussion:

         Permission to write the owner and owner_group attributes.  On
         UNIX systems, this is the ability to execute chown() and
         chgrp().

   ACE4_SYNCHRONIZE

      Operation(s) affected:

         NONE

      Discussion:

         Permission to use the file object as a synchronization
         primitive for interprocess communication.  This permission is
         not enforced or interpreted by the NFSv4.1 server on behalf of
         the client.

         Typically, the ACE4_SYNCHRONIZE permission is only meaningful
         on local file systems, i.e., file systems not accessed via
         NFSv4.1.  The reason that the permission bit exists is that
         some operating environments, such as Windows, use
         ACE4_SYNCHRONIZE.

         For example, if a client copies a file that has
         ACE4_SYNCHRONIZE set from a local file system to an NFSv4.1
         server, and then later copies the file from the NFSv4.1 server
         to a local file system, it is likely that if ACE4_SYNCHRONIZE
         was set in the original file, the client will want it set in
         the second copy.  The first copy will not have the permission
         set unless the NFSv4.1 server has the means to set the
         ACE4_SYNCHRONIZE bit.  The second copy will not have the
         permission set unless the NFSv4.1 server has the means to
         retrieve the ACE4_SYNCHRONIZE bit.

   Server implementations need not provide the granularity of control
   that is implied by this list of masks.  For example, POSIX-based



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   systems might not distinguish ACE4_APPEND_DATA (the ability to append
   to a file) from ACE4_WRITE_DATA (the ability to modify existing
   contents); both masks would be tied to a single "write" permission
   [20].  When such a server returns attributes to the client, it would
   show both ACE4_APPEND_DATA and ACE4_WRITE_DATA if and only if the
   write permission is enabled.

   If a server receives a SETATTR request that it cannot accurately
   implement, it should err in the direction of more restricted access,
   except in the previously discussed cases of execute and read.  For
   example, suppose a server cannot distinguish overwriting data from
   appending new data, as described in the previous paragraph.  If a
   client submits an ALLOW ACE where ACE4_APPEND_DATA is set but
   ACE4_WRITE_DATA is not (or vice versa), the server should either turn
   off ACE4_APPEND_DATA or reject the request with NFS4ERR_ATTRNOTSUPP.

6.2.1.3.2.  ACE4_DELETE vs. ACE4_DELETE_CHILD

   Two access mask bits govern the ability to delete a directory entry:
   ACE4_DELETE on the object itself (the "target") and ACE4_DELETE_CHILD
   on the containing directory (the "parent").

   Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
   to allow unlink only to a user that owns either the target or the
   parent; on some such systems the decision also depends on whether the
   target is writable.

   Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
   target, or ACE4_DELETE_CHILD is permitted on the parent.  (Note that
   this is true even if the parent or target explicitly denies one of
   these permissions.)

   If the ACLs in question neither explicitly ALLOW nor DENY either of
   the above, and if MODE4_SVTX is not set on the parent, then the
   server SHOULD allow the removal if and only if ACE4_ADD_FILE is
   permitted.  In the case where MODE4_SVTX is set, the server may also
   require the remover to own either the parent or the target, or may
   require the target to be writable.

   This allows servers to support something close to traditional UNIX-
   like semantics, with ACE4_ADD_FILE taking the place of the write bit.

6.2.1.4.  ACE flag

   The bitmask constants used for the flag field are as follows:






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   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;
   const ACE4_INHERITED_ACE                = 0x00000080;

   A server need not support any of these flags.  If the server supports
   flags that are similar to, but not exactly the same as, these flags,
   the implementation may define a mapping between the protocol-defined
   flags and the implementation-defined flags.

   For example, suppose a client tries to set an ACE with
   ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.  If the
   server does not support any form of ACL inheritance, the server
   should reject the request with NFS4ERR_ATTRNOTSUPP.  If the server
   supports a single "inherit ACE" flag that applies to both files and
   directories, the server may reject the request (i.e., requiring the
   client to set both the file and directory inheritance flags).  The
   server may also accept the request and silently turn on the
   ACE4_DIRECTORY_INHERIT_ACE flag.

6.2.1.4.1.  Discussion of Flag Bits

   ACE4_FILE_INHERIT_ACE
      Any non-directory file in any sub-directory will get this ACE
      inherited.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE should be
      added to each new directory created.
      If this flag is set in an ACE in an ACL attribute to be set on a
      non-directory file system object, the operation attempting to set
      the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  This flag tells the server that
      inheritance of this ACE should stop at newly created child
      directories.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and



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      directories as specified by the ACE4_FILE_INHERIT_ACE and
      ACE4_DIRECTORY_INHERIT_ACE flags.

      If this flag is present on an ACE, but neither
      ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
      then an operation attempting to set such an attribute SHOULD fail
      with NFS4ERR_ATTRNOTSUPP.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG


   ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits may be set only on
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's ACL,
      the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the
      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, it then notes if the operation succeeded or failed.
      If the operation succeeded, and if the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM
      event occurs.  If the operation failed, and if the FAILED flag was
      set for the matching AUDIT or ALARM ACE, then the appropriate
      AUDIT or ALARM event occurs.  Either or both of the SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies to ACCESS operations
      even when they return NFS4_OK.  For the purposes of AUDIT and
      ALARM, we consider an ACCESS operation to be a "failure" if it
      fails to return a bit that was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX
      or a GROUP ACCOUNT as defined under Windows.  Clients and servers
      MUST ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of the special identifiers outlined in
      Section 6.2.1.5.

   ACE4_INHERITED_ACE
      Indicates that this ACE is inherited from a parent directory.  A
      server that supports automatic inheritance will place this flag on
      any ACEs inherited from the parent directory when creating a new
      object.  Client applications will use this to perform automatic
      inheritance.  Clients and servers MUST clear this bit in the acl
      attribute; it may only be used in the dacl and sacl attributes.



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6.2.1.5.  ACE Who

   The "who" field of an ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a
   user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
   which.

   There are several special identifiers that need to be understood
   universally, rather than in the context of a particular DNS domain.
   Some of these identifiers cannot be understood when an NFS client
   accesses the server, but have meaning when a local process accesses
   the file.  The ability to display and modify these permissions is
   permitted over NFS, even if none of the access methods on the server
   understands the identifiers.

   +---------------+---------------------------------------------------+
   | Who           | Description                                       |
   +---------------+---------------------------------------------------+
   | OWNER         | The owner of the file.                            |
   | GROUP         | The group associated with the file.               |
   | EVERYONE      | The world, including the owner and owning group.  |
   | INTERACTIVE   | Accessed from an interactive terminal.            |
   | NETWORK       | Accessed via the network.                         |
   | DIALUP        | Accessed as a dialup user to the server.          |
   | BATCH         | Accessed from a batch job.                        |
   | ANONYMOUS     | Accessed without any authentication.              |
   | AUTHENTICATED | Any authenticated user (opposite of ANONYMOUS).   |
   | SERVICE       | Access from a system service.                     |
   +---------------+---------------------------------------------------+

                                  Table 4

   To avoid conflict, these special identifiers are distinguished by an
   appended "@" and should appear in the form "xxxx@" (with no domain
   name after the "@"), for example, ANONYMOUS@.

   The ACE4_IDENTIFIER_GROUP flag MUST be ignored on entries with these
   special identifiers.  When encoding entries with these special
   identifiers, the ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.

6.2.1.5.1.  Discussion of EVERYONE@

   It is important to note that "EVERYONE@" is not equivalent to the
   UNIX "other" entity.  This is because, by definition, UNIX "other"
   does not include the owner or owning group of a file.  "EVERYONE@"
   means literally everyone, including the owner or owning group.





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6.2.2.  Attribute 58: dacl

   The dacl attribute is like the acl attribute, but dacl allows just
   ALLOW and DENY ACEs.  The dacl attribute supports automatic
   inheritance (see Section 6.4.3.2).

6.2.3.  Attribute 59: sacl

   The sacl attribute is like the acl attribute, but sacl allows just
   AUDIT and ALARM ACEs.  The sacl attribute supports automatic
   inheritance (see Section 6.4.3.2).

6.2.4.  Attribute 33: mode

   The NFSv4.1 mode attribute is based on the UNIX mode bits.  The
   following bits are defined:

   const MODE4_SUID = 0x800;  /* set user id on execution */
   const MODE4_SGID = 0x400;  /* set group id on execution */
   const MODE4_SVTX = 0x200;  /* save text even after use */
   const MODE4_RUSR = 0x100;  /* read permission: owner */
   const MODE4_WUSR = 0x080;  /* write permission: owner */
   const MODE4_XUSR = 0x040;  /* execute permission: owner */
   const MODE4_RGRP = 0x020;  /* read permission: group */
   const MODE4_WGRP = 0x010;  /* write permission: group */
   const MODE4_XGRP = 0x008;  /* execute permission: group */
   const MODE4_ROTH = 0x004;  /* read permission: other */
   const MODE4_WOTH = 0x002;  /* write permission: other */
   const MODE4_XOTH = 0x001;  /* execute permission: other */

   Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the principal
   identified in the owner attribute.  Bits MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP apply to principals identified in the owner_group
   attribute but who are not identified in the owner attribute.  Bits
   MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH apply to any principal that
   does not match that in the owner attribute and does not have a group
   matching that of the owner_group attribute.

   Bits within a mode other than those specified above are not defined
   by this protocol.  A server MUST NOT return bits other than those
   defined above in a GETATTR or READDIR operation, and it MUST return
   NFS4ERR_INVAL if bits other than those defined above are set in a
   SETATTR, CREATE, OPEN, VERIFY, or NVERIFY operation.








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6.2.5.  Attribute 74: mode_set_masked

   The mode_set_masked attribute is a write-only attribute that allows
   individual bits in the mode attribute to be set or reset, without
   changing others.  It allows, for example, the bits MODE4_SUID,
   MODE4_SGID, and MODE4_SVTX to be modified while leaving unmodified
   any of the nine low-order mode bits devoted to permissions.

   In such instances that the nine low-order bits are left unmodified,
   then neither the acl nor the dacl attribute should be automatically
   modified as discussed in Section 6.4.1.

   The mode_set_masked attribute consists of two words, each in the form
   of a mode4.  The first consists of the value to be applied to the
   current mode value and the second is a mask.  Only bits set to one in
   the mask word are changed (set or reset) in the file's mode.  All
   other bits in the mode remain unchanged.  Bits in the first word that
   correspond to bits that are zero in the mask are ignored, except that
   undefined bits are checked for validity and can result in
   NFS4ERR_INVAL as described below.

   The mode_set_masked attribute is only valid in a SETATTR operation.
   If it is used in a CREATE or OPEN operation, the server MUST return
   NFS4ERR_INVAL.

   Bits not defined as valid in the mode attribute are not valid in
   either word of the mode_set_masked attribute.  The server MUST return
   NFS4ERR_INVAL if any such bits are set to one in a SETATTR.  If the
   mode and mode_set_masked attributes are both specified in the same
   SETATTR, the server MUST also return NFS4ERR_INVAL.

6.3.  Common Methods

   The requirements in this section will be referred to in future
   sections, especially Section 6.4.

6.3.1.  Interpreting an ACL

6.3.1.1.  Server Considerations

   The server uses the algorithm described in Section 6.2.1 to determine
   whether an ACL allows access to an object.  However, the ACL might
   not be the sole determiner of access.  For example:

   o  In the case of a file system exported as read-only, the server may
      deny write access even though an object's ACL grants it.





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   o  Server implementations MAY grant ACE4_WRITE_ACL and ACE4_READ_ACL
      permissions to prevent a situation from arising in which there is
      no valid way to ever modify the ACL.

   o  All servers will allow a user the ability to read the data of the
      file when only the execute permission is granted (i.e., if the ACL
      denies the user the ACE4_READ_DATA access and allows the user
      ACE4_EXECUTE, the server will allow the user to read the data of
      the file).

   o  Many servers have the notion of owner-override in which the owner
      of the object is allowed to override accesses that are denied by
      the ACL.  This may be helpful, for example, to allow users
      continued access to open files on which the permissions have
      changed.

   o  Many servers have the notion of a "superuser" that has privileges
      beyond an ordinary user.  The superuser may be able to read or
      write data or metadata in ways that would not be permitted by the
      ACL.

   o  A retention attribute might also block access otherwise allowed by
      ACLs (see Section 5.13).

6.3.1.2.  Client Considerations

   Clients SHOULD NOT do their own access checks based on their
   interpretation of the ACL, but rather use the OPEN and ACCESS
   operations to do access checks.  This allows the client to act on the
   results of having the server determine whether or not access should
   be granted based on its interpretation of the ACL.

   Clients must be aware of situations in which an object's ACL will
   define a certain access even though the server will not enforce it.
   In general, but especially in these situations, the client needs to
   do its part in the enforcement of access as defined by the ACL.  To
   do this, the client MAY send the appropriate ACCESS operation prior
   to servicing the request of the user or application in order to
   determine whether the user or application should be granted the
   access requested.  For examples in which the ACL may define accesses
   that the server doesn't enforce, see Section 6.3.1.1.

6.3.2.  Computing a Mode Attribute from an ACL

   The following method can be used to calculate the MODE4_R*, MODE4_W*,
   and MODE4_X* bits of a mode attribute, based upon an ACL.





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   First, for each of the special identifiers OWNER@, GROUP@, and
   EVERYONE@, evaluate the ACL in order, considering only ALLOW and DENY
   ACEs for the identifier EVERYONE@ and for the identifier under
   consideration.  The result of the evaluation will be an NFSv4 ACL
   mask showing exactly which bits are permitted to that identifier.

   Then translate the calculated mask for OWNER@, GROUP@, and EVERYONE@
   into mode bits for, respectively, the user, group, and other, as
   follows:

   1.  Set the read bit (MODE4_RUSR, MODE4_RGRP, or MODE4_ROTH) if and
       only if ACE4_READ_DATA is set in the corresponding mask.

   2.  Set the write bit (MODE4_WUSR, MODE4_WGRP, or MODE4_WOTH) if and
       only if ACE4_WRITE_DATA and ACE4_APPEND_DATA are both set in the
       corresponding mask.

   3.  Set the execute bit (MODE4_XUSR, MODE4_XGRP, or MODE4_XOTH), if
       and only if ACE4_EXECUTE is set in the corresponding mask.

6.3.2.1.  Discussion

   Some server implementations also add bits permitted to named users
   and groups to the group bits (MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP).

   Implementations are discouraged from doing this, because it has been
   found to cause confusion for users who see members of a file's group
   denied access that the mode bits appear to allow.  (The presence of
   DENY ACEs may also lead to such behavior, but DENY ACEs are expected
   to be more rarely used.)

   The same user confusion seen when fetching the mode also results if
   setting the mode does not effectively control permissions for the
   owner, group, and other users; this motivates some of the
   requirements that follow.

6.4.  Requirements

   The server that supports both mode and ACL must take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs that have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@".  This way, the client can see if semantically equivalent
   access permissions exist whether the client asks for the owner,
   owner_group, and mode attributes or for just the ACL.

   In this section, much is made of the methods in Section 6.3.2.  Many
   requirements refer to this section.  But note that the methods have



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   behaviors specified with "SHOULD".  This is intentional, to avoid
   invalidating existing implementations that compute the mode according
   to the withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
   actual permissions on owner, group, and other.

6.4.1.  Setting the Mode and/or ACL Attributes

   In the case where a server supports the sacl or dacl attribute, in
   addition to the acl attribute, the server MUST fail a request to set
   the acl attribute simultaneously with a dacl or sacl attribute.  The
   error to be given is NFS4ERR_ATTRNOTSUPP.

6.4.1.1.  Setting Mode and not ACL

   When any of the nine low-order mode bits are subject to change,
   either because the mode attribute was set or because the
   mode_set_masked attribute was set and the mask included one or more
   bits from the nine low-order mode bits, and no ACL attribute is
   explicitly set, the acl and dacl attributes must be modified in
   accordance with the updated value of those bits.  This must happen
   even if the value of the low-order bits is the same after the mode is
   set as before.

   Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl
   attribute) are unaffected by changes to the mode.

   In cases in which the permissions bits are subject to change, the acl
   and dacl attributes MUST be modified such that the mode computed via
   the method in Section 6.3.2 yields the low-order nine bits (MODE4_R*,
   MODE4_W*, MODE4_X*) of the mode attribute as modified by the
   attribute change.  The ACL attributes SHOULD also be modified such
   that:

   1.  If MODE4_RGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA or ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

   Access mask bits other than those listed above, appearing in ALLOW
   ACEs, MAY also be disabled.




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   Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect
   the permissions of the ACL itself, nor do ACEs of the type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the ACL attributes.

   Also note that the requirement may be met by discarding the acl and
   dacl, in favor of an ACL that represents the mode and only the mode.
   This is permitted, but it is preferable for a server to preserve as
   much of the ACL as possible without violating the above requirements.
   Discarding the ACL makes it effectively impossible for a file created
   with a mode attribute to inherit an ACL (see Section 6.4.3).

6.4.1.2.  Setting ACL and Not Mode

   When setting the acl or dacl and not setting the mode or
   mode_set_masked attributes, the permission bits of the mode need to
   be derived from the ACL.  In this case, the ACL attribute SHOULD be
   set as given.  The nine low-order bits of the mode attribute
   (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result
   of the method in Section 6.3.2.  The three high-order bits of the
   mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.

6.4.1.3.  Setting Both ACL and Mode

   When setting both the mode (includes use of either the mode attribute
   or the mode_set_masked attribute) and the acl or dacl attributes in
   the same operation, the attributes MUST be applied in this order:
   mode (or mode_set_masked), then ACL.  The mode-related attribute is
   set as given, then the ACL attribute is set as given, possibly
   changing the final mode, as described above in Section 6.4.1.2.

6.4.2.  Retrieving the Mode and/or ACL Attributes

   This section applies only to servers that support both the mode and
   ACL attributes.

   Some server implementations may have a concept of "objects without
   ACLs", meaning that all permissions are granted and denied according
   to the mode attribute and that no ACL attribute is stored for that
   object.  If an ACL attribute is requested of such a server, the
   server SHOULD return an ACL that does not conflict with the mode;
   that is to say, the ACL returned SHOULD represent the nine low-order
   bits of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
   described in Section 6.3.2.

   For other server implementations, the ACL attribute is always present
   for every object.  Such servers SHOULD store at least the three high-
   order bits of the mode attribute (MODE4_SUID, MODE4_SGID,



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   MODE4_SVTX).  The server SHOULD return a mode attribute if one is
   requested, and the low-order nine bits of the mode (MODE4_R*,
   MODE4_W*, MODE4_X*) MUST match the result of applying the method in
   Section 6.3.2 to the ACL attribute.

6.4.3.  Creating New Objects

   If a server supports any ACL attributes, it may use the ACL
   attributes on the parent directory to compute an initial ACL
   attribute for a newly created object.  This will be referred to as
   the inherited ACL within this section.  The act of adding one or more
   ACEs to the inherited ACL that are based upon ACEs in the parent
   directory's ACL will be referred to as inheriting an ACE within this
   section.

   Implementors should standardize what the behavior of CREATE and OPEN
   must be depending on the presence or absence of the mode and ACL
   attributes.

   1.  If just the mode is given in the call:

       In this case, inheritance SHOULD take place, but the mode MUST be
       applied to the inherited ACL as described in Section 6.4.1.1,
       thereby modifying the ACL.

   2.  If just the ACL is given in the call:

       In this case, inheritance SHOULD NOT take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification,
       and the mode modified as in Section 6.4.1.2.

   3.  If both mode and ACL are given in the call:

       In this case, inheritance SHOULD NOT take place, and both
       attributes will be set as described in Section 6.4.1.3.

   4.  If neither mode nor ACL is given in the call:

       In the case where an object is being created without any initial
       attributes at all, e.g., an OPEN operation with an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place (note that EXCLUSIVE4_1 is a better choice of
       createmode4, since it does permit initial attributes).  Instead,
       the server SHOULD set permissions to deny all access to the newly
       created object.  It is expected that the appropriate client will
       set the desired attributes in a subsequent SETATTR operation, and
       the server SHOULD allow that operation to succeed, regardless of
       what permissions the object is created with.  For example, an



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       empty ACL denies all permissions, but the server should allow the
       owner's SETATTR to succeed even though WRITE_ACL is implicitly
       denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to the ACL will happen.  The mode attribute, if
       supported, MUST be as computed in Section 6.3.2, with the
       MODE4_SUID, MODE4_SGID, and MODE4_SVTX bits clear.  If no
       inheritable ACEs exist on the parent directory, the rules for
       creating acl, dacl, or sacl attributes are implementation
       defined.  If either the dacl or sacl attribute is supported, then
       the ACL4_DEFAULTED flag SHOULD be set on the newly created
       attributes.



6.4.3.1.  The Inherited ACL

   If the object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the parent directory ACL unless the
   ACE4_FILE_INHERIT_FLAG is set.

   If the object being created is a directory, the inherited ACL should
   inherit all inheritable ACEs from the parent directory, that is,
   those that have the ACE4_FILE_INHERIT_ACE or
   ACE4_DIRECTORY_INHERIT_ACE flag set.  If the inheritable ACE has
   ACE4_FILE_INHERIT_ACE set but ACE4_DIRECTORY_INHERIT_ACE is clear,
   the inherited ACE on the newly created directory MUST have the
   ACE4_INHERIT_ONLY_ACE flag set to prevent the directory from being
   affected by ACEs meant for non-directories.

   When a new directory is created, the server MAY split any inherited
   ACE that is both inheritable and effective (in other words, that has
   neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE set),
   into two ACEs, one with no inheritance flags and one with
   ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or sacl attribute,
   both of those ACEs SHOULD also have the ACE4_INHERITED_ACE flag set.)
   This makes it simpler to modify the effective permissions on the
   directory without modifying the ACE that is to be inherited to the
   new directory's children.

6.4.3.2.  Automatic Inheritance

   The acl attribute consists only of an array of ACEs, but the sacl
   (Section 6.2.3) and dacl (Section 6.2.2) attributes also include an
   additional flag field.





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   struct nfsacl41 {
           aclflag4        na41_flag;
           nfsace4         na41_aces<>;
   };

   The flag field applies to the entire sacl or dacl; three flag values
   are defined:

   const ACL4_AUTO_INHERIT         = 0x00000001;
   const ACL4_PROTECTED            = 0x00000002;
   const ACL4_DEFAULTED            = 0x00000004;

   and all other bits must be cleared.  The ACE4_INHERITED_ACE flag may
   be set in the ACEs of the sacl or dacl (whereas it must always be
   cleared in the acl).

   Together these features allow a server to support automatic
   inheritance, which we now explain in more detail.

   Inheritable ACEs are normally inherited by child objects only at the
   time that the child objects are created; later modifications to
   inheritable ACEs do not result in modifications to inherited ACEs on
   descendants.

   However, the dacl and sacl provide an OPTIONAL mechanism that allows
   a client application to propagate changes to inheritable ACEs to an
   entire directory hierarchy.

   A server that supports this performs inheritance at object creation
   time in the normal way, and SHOULD set the ACE4_INHERITED_ACE flag on
   any inherited ACEs as they are added to the new object.

   A client application such as an ACL editor may then propagate changes
   to inheritable ACEs on a directory by recursively traversing that
   directory's descendants and modifying each ACL encountered to remove
   any ACEs with the ACE4_INHERITED_ACE flag and to replace them by the
   new inheritable ACEs (also with the ACE4_INHERITED_ACE flag set).  It
   uses the existing ACE inheritance flags in the obvious way to decide
   which ACEs to propagate.  (Note that it may encounter further
   inheritable ACEs when descending the directory hierarchy and that
   those will also need to be taken into account when propagating
   inheritable ACEs to further descendants.)

   The reach of this propagation may be limited in two ways: first,
   automatic inheritance is not performed from any directory ACL that
   has the ACL4_AUTO_INHERIT flag cleared; and second, automatic
   inheritance stops wherever an ACL with the ACL4_PROTECTED flag is




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   set, preventing modification of that ACL and also (if the ACL is set
   on a directory) of the ACL on any of the object's descendants.

   This propagation is performed independently for the sacl and the dacl
   attributes; thus, the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may
   be independently set for the sacl and the dacl, and propagation of
   one type of acl may continue down a hierarchy even where propagation
   of the other acl has stopped.

   New objects should be created with a dacl and a sacl that both have
   the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to
   the same value as that on, respectively, the sacl or dacl of the
   parent object.

   Both the dacl and sacl attributes are RECOMMENDED, and a server may
   support one without supporting the other.

   A server that supports both the old acl attribute and one or both of
   the new dacl or sacl attributes must do so in such a way as to keep
   all three attributes consistent with each other.  Thus, the ACEs
   reported in the acl attribute should be the union of the ACEs
   reported in the dacl and sacl attributes, except that the
   ACE4_INHERITED_ACE flag must be cleared from the ACEs in the acl.
   And of course a client that queries only the acl will be unable to
   determine the values of the sacl or dacl flag fields.

   When a client performs a SETATTR for the acl attribute, the server
   SHOULD set the ACL4_PROTECTED flag to true on both the sacl and the
   dacl.  By using the acl attribute, as opposed to the dacl or sacl
   attributes, the client signals that it may not understand automatic
   inheritance, and thus cannot be trusted to set an ACL for which
   automatic inheritance would make sense.

   When a client application queries an ACL, modifies it, and sets it
   again, it should leave any ACEs marked with ACE4_INHERITED_ACE
   unchanged, in their original order, at the end of the ACL.  If the
   application is unable to do this, it should set the ACL4_PROTECTED
   flag.  This behavior is not enforced by servers, but violations of
   this rule may lead to unexpected results when applications perform
   automatic inheritance.

   If a server also supports the mode attribute, it SHOULD set the mode
   in such a way that leaves inherited ACEs unchanged, in their original
   order, at the end of the ACL.  If it is unable to do so, it SHOULD
   set the ACL4_PROTECTED flag on the file's dacl.

   Finally, in the case where the request that creates a new file or
   directory does not also set permissions for that file or directory,



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   and there are also no ACEs to inherit from the parent's directory,
   then the server's choice of ACL for the new object is implementation-
   dependent.  In this case, the server SHOULD set the ACL4_DEFAULTED
   flag on the ACL it chooses for the new object.  An application
   performing automatic inheritance takes the ACL4_DEFAULTED flag as a
   sign that the ACL should be completely replaced by one generated
   using the automatic inheritance rules.

7.  Single-Server Namespace

   This section describes the NFSv4 single-server namespace.  Single-
   server namespaces may be presented directly to clients, or they may
   be used as a basis to form larger multi-server namespaces (e.g.,
   site-wide or organization-wide) to be presented to clients, as
   described in Section 11.

7.1.  Server Exports

   On a UNIX server, the namespace describes all the files reachable by
   pathnames under the root directory or "/".  On a Windows server, the
   namespace constitutes all the files on disks named by mapped disk
   letters.  NFS server administrators rarely make the entire server's
   file system namespace available to NFS clients.  More often, portions
   of the namespace are made available via an "export" feature.  In
   previous versions of the NFS protocol, the root filehandle for each
   export is obtained through the MOUNT protocol; the client sent a
   string that identified the export name within the namespace and the
   server returned the root filehandle for that export.  The MOUNT
   protocol also provided an EXPORTS procedure that enumerated the
   server's exports.

7.2.  Browsing Exports

   The NFSv4.1 protocol provides a root filehandle that clients can use
   to obtain filehandles for the exports of a particular server, via a
   series of LOOKUP operations within a COMPOUND, to traverse a path.  A
   common user experience is to use a graphical user interface (perhaps
   a file "Open" dialog window) to find a file via progressive browsing
   through a directory tree.  The client must be able to move from one
   export to another export via single-component, progressive LOOKUP
   operations.

   This style of browsing is not well supported by the NFSv3 protocol.
   In NFSv3, the client expects all LOOKUP operations to remain within a
   single server file system.  For example, the device attribute will
   not change.  This prevents a client from taking namespace paths that
   span exports.




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   In the case of NFSv3, an automounter on the client can obtain a
   snapshot of the server's namespace using the EXPORTS procedure of the
   MOUNT protocol.  If it understands the server's pathname syntax, it
   can create an image of the server's namespace on the client.  The
   parts of the namespace that are not exported by the server are filled
   in with directories that might be constructed similarly to an NFSv4.1
   "pseudo file system" (see Section 7.3) that allows the user to browse
   from one mounted file system to another.  There is a drawback to this
   representation of the server's namespace on the client: it is static.
   If the server administrator adds a new export, the client will be
   unaware of it.

7.3.  Server Pseudo File System

   NFSv4.1 servers avoid this namespace inconsistency by presenting all
   the exports for a given server within the framework of a single
   namespace for that server.  An NFSv4.1 client uses LOOKUP and READDIR
   operations to browse seamlessly from one export to another.

   Where there are portions of the server namespace that are not
   exported, clients require some way of traversing those portions to
   reach actual exported file systems.  A technique that servers may use
   to provide for this is to bridge the unexported portion of the
   namespace via a "pseudo file system" that provides a view of exported
   directories only.  A pseudo file system has a unique fsid and behaves
   like a normal, read-only file system.

   Based on the construction of the server's namespace, it is possible
   that multiple pseudo file systems may exist.  For example,

           /a              pseudo file system
           /a/b            real file system
           /a/b/c          pseudo file system
           /a/b/c/d        real file system

   Each of the pseudo file systems is considered a separate entity and
   therefore MUST have its own fsid, unique among all the fsids for that
   server.

7.4.  Multiple Roots

   Certain operating environments are sometimes described as having
   "multiple roots".  In such environments, individual file systems are
   commonly represented by disk or volume names.  NFSv4 servers for
   these platforms can construct a pseudo file system above these root
   names so that disk letters or volume names are simply directory names
   in the pseudo root.




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7.5.  Filehandle Volatility

   The nature of the server's pseudo file system is that it is a logical
   representation of file system(s) available from the server.
   Therefore, the pseudo file system is most likely constructed
   dynamically when the server is first instantiated.  It is expected
   that the pseudo file system may not have an on-disk counterpart from
   which persistent filehandles could be constructed.  Even though it is
   preferable that the server provide persistent filehandles for the
   pseudo file system, the NFS client should expect that pseudo file
   system filehandles are volatile.  This can be confirmed by checking
   the associated "fh_expire_type" attribute for those filehandles in
   question.  If the filehandles are volatile, the NFS client must be
   prepared to recover a filehandle value (e.g., with a series of LOOKUP
   operations) when receiving an error of NFS4ERR_FHEXPIRED.

   Because it is quite likely that servers will implement pseudo file
   systems using volatile filehandles, clients need to be prepared for
   them, rather than assuming that all filehandles will be persistent.

7.6.  Exported Root

   If the server's root file system is exported, one might conclude that
   a pseudo file system is unneeded.  This is not necessarily so.
   Assume the following file systems on a server:

           /       fs1  (exported)
           /a      fs2  (not exported)
           /a/b    fs3  (exported)

   Because fs2 is not exported, fs3 cannot be reached with simple
   LOOKUPs.  The server must bridge the gap with a pseudo file system.

7.7.  Mount Point Crossing

   The server file system environment may be constructed in such a way
   that one file system contains a directory that is 'covered' or
   mounted upon by a second file system.  For example:

           /a/b            (file system 1)
           /a/b/c/d        (file system 2)

   The pseudo file system for this server may be constructed to look
   like:

           /               (place holder/not exported)
           /a/b            (file system 1)
           /a/b/c/d        (file system 2)



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   It is the server's responsibility to present the pseudo file system
   that is complete to the client.  If the client sends a LOOKUP request
   for the path /a/b/c/d, the server's response is the filehandle of the
   root of the file system /a/b/c/d.  In previous versions of the NFS
   protocol, the server would respond with the filehandle of directory
   /a/b/c/d within the file system /a/b.

   The NFS client will be able to determine if it crosses a server mount
   point by a change in the value of the "fsid" attribute.

7.8.  Security Policy and Namespace Presentation

   Because NFSv4 clients possess the ability to change the security
   mechanisms used, after determining what is allowed, by using SECINFO
   and SECINFO_NONAME, the server SHOULD NOT present a different view of
   the namespace based on the security mechanism being used by a client.
   Instead, it should present a consistent view and return
   NFS4ERR_WRONGSEC if an attempt is made to access data with an
   inappropriate security mechanism.

   If security considerations make it necessary to hide the existence of
   a particular file system, as opposed to all of the data within it,
   the server can apply the security policy of a shared resource in the
   server's namespace to components of the resource's ancestors.  For
   example:

           /                           (place holder/not exported)
           /a/b                        (file system 1)
           /a/b/MySecretProject        (file system 2)


   The /a/b/MySecretProject directory is a real file system and is the
   shared resource.  Suppose the security policy for /a/b/
   MySecretProject is Kerberos with integrity and it is desired to limit
   knowledge of the existence of this file system.  In this case, the
   server should apply the same security policy to /a/b.  This allows
   for knowledge of the existence of a file system to be secured when
   desirable.

   For the case of the use of multiple, disjoint security mechanisms in
   the server's resources, applying that sort of policy would result in
   the higher-level file system not being accessible using any security
   flavor.  Therefore, that sort of configuration is not compatible with
   hiding the existence (as opposed to the contents) from clients using
   multiple disjoint sets of security flavors.

   In other circumstances, a desirable policy is for the security of a
   particular object in the server's namespace to include the union of



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   all security mechanisms of all direct descendants.  A common and
   convenient practice, unless strong security requirements dictate
   otherwise, is to make the entire the pseudo file system accessible by
   all of the valid security mechanisms.

   Where there is concern about the security of data on the network,
   clients should use strong security mechanisms to access the pseudo
   file system in order to prevent man-in-the-middle attacks.

8.  State Management

   Integrating locking into the NFS protocol necessarily causes it to be
   stateful.  With the inclusion of such features as share reservations,
   file and directory delegations, recallable layouts, and support for
   mandatory byte-range locking, the protocol becomes substantially more
   dependent on proper management of state than the traditional
   combination of NFS and NLM (Network Lock Manager) [46].  These
   features include expanded locking facilities, which provide some
   measure of inter-client exclusion, but the state also offers features
   not readily providable using a stateless model.  There are three
   components to making this state manageable:

   o  clear division between client and server

   o  ability to reliably detect inconsistency in state between client
      and server

   o  simple and robust recovery mechanisms

   In this model, the server owns the state information.  The client
   requests changes in locks and the server responds with the changes
   made.  Non-client-initiated changes in locking state are infrequent.
   The client receives prompt notification of such changes and can
   adjust its view of the locking state to reflect the server's changes.

   Individual pieces of state created by the server and passed to the
   client at its request are represented by 128-bit stateids.  These
   stateids may represent a particular open file, a set of byte-range
   locks held by a particular owner, or a recallable delegation of
   privileges to access a file in particular ways or at a particular
   location.

   In all cases, there is a transition from the most general information
   that represents a client as a whole to the eventual lightweight
   stateid used for most client and server locking interactions.  The
   details of this transition will vary with the type of object but it
   always starts with a client ID.




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8.1.  Client and Session ID

   A client must establish a client ID (see Section 2.4) and then one or
   more sessionids (see Section 2.10) before performing any operations
   to open, byte-range lock, delegate, or obtain a layout for a file
   object.  Each session ID is associated with a specific client ID, and
   thus serves as a shorthand reference to an NFSv4.1 client.

   For some types of locking interactions, the client will represent
   some number of internal locking entities called "owners", which
   normally correspond to processes internal to the client.  For other
   types of locking-related objects, such as delegations and layouts, no
   such intermediate entities are provided for, and the locking-related
   objects are considered to be transferred directly between the server
   and a unitary client.

8.2.  Stateid Definition

   When the server grants a lock of any type (including opens, byte-
   range locks, delegations, and layouts), it responds with a unique
   stateid that represents a set of locks (often a single lock) for the
   same file, of the same type, and sharing the same ownership
   characteristics.  Thus, opens of the same file by different open-
   owners each have an identifying stateid.  Similarly, each set of
   byte-range locks on a file owned by a specific lock-owner has its own
   identifying stateid.  Delegations and layouts also have associated
   stateids by which they may be referenced.  The stateid is used as a
   shorthand reference to a lock or set of locks, and given a stateid,
   the server can determine the associated state-owner or state-owners
   (in the case of an open-owner/lock-owner pair) and the associated
   filehandle.  When stateids are used, the current filehandle must be
   the one associated with that stateid.

   All stateids associated with a given client ID are associated with a
   common lease that represents the claim of those stateids and the
   objects they represent to be maintained by the server.  See
   Section 8.3 for a discussion of the lease.

   The server may assign stateids independently for different clients.
   A stateid with the same bit pattern for one client may designate an
   entirely different set of locks for a different client.  The stateid
   is always interpreted with respect to the client ID associated with
   the current session.  Stateids apply to all sessions associated with
   the given client ID, and the client may use a stateid obtained from
   one session on another session associated with the same client ID.






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8.2.1.  Stateid Types

   With the exception of special stateids (see Section 8.2.3), each
   stateid represents locking objects of one of a set of types defined
   by the NFSv4.1 protocol.  Note that in all these cases, where we
   speak of guarantee, it is understood there are situations such as a
   client restart, or lock revocation, that allow the guarantee to be
   voided.

   o  Stateids may represent opens of files.

      Each stateid in this case represents the OPEN state for a given
      client ID/open-owner/filehandle triple.  Such stateids are subject
      to change (with consequent incrementing of the stateid's seqid) in
      response to OPENs that result in upgrade and OPEN_DOWNGRADE
      operations.

   o  Stateids may represent sets of byte-range locks.

      All locks held on a particular file by a particular owner and
      gotten under the aegis of a particular open file are associated
      with a single stateid with the seqid being incremented whenever
      LOCK and LOCKU operations affect that set of locks.

   o  Stateids may represent file delegations, which are recallable
      guarantees by the server to the client that other clients will not
      reference or modify a particular file, until the delegation is
      returned.  In NFSv4.1, file delegations may be obtained on both
      regular and non-regular files.

      A stateid represents a single delegation held by a client for a
      particular filehandle.

   o  Stateids may represent directory delegations, which are recallable
      guarantees by the server to the client that other clients will not
      modify the directory, until the delegation is returned.

      A stateid represents a single delegation held by a client for a
      particular directory filehandle.

   o  Stateids may represent layouts, which are recallable guarantees by
      the server to the client that particular files may be accessed via
      an alternate data access protocol at specific locations.  Such
      access is limited to particular sets of byte-ranges and may
      proceed until those byte-ranges are reduced or the layout is
      returned.





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      A stateid represents the set of all layouts held by a particular
      client for a particular filehandle with a given layout type.  The
      seqid is updated as the layouts of that set of byte-ranges change,
      via layout stateid changing operations such as LAYOUTGET and
      LAYOUTRETURN.

8.2.2.  Stateid Structure

   Stateids are divided into two fields, a 96-bit "other" field
   identifying the specific set of locks and a 32-bit "seqid" sequence
   value.  Except in the case of special stateids (see Section 8.2.3), a
   particular value of the "other" field denotes a set of locks of the
   same type (for example, byte-range locks, opens, delegations, or
   layouts), for a specific file or directory, and sharing the same
   ownership characteristics.  The seqid designates a specific instance
   of such a set of locks, and is incremented to indicate changes in
   such a set of locks, either by the addition or deletion of locks from
   the set, a change in the byte-range they apply to, or an upgrade or
   downgrade in the type of one or more locks.

   When such a set of locks is first created, the server returns a
   stateid with seqid value of one.  On subsequent operations that
   modify the set of locks, the server is required to increment the
   "seqid" field by one whenever it returns a stateid for the same
   state-owner/file/type combination and there is some change in the set
   of locks actually designated.  In this case, the server will return a
   stateid with an "other" field the same as previously used for that
   state-owner/file/type combination, with an incremented "seqid" field.
   This pattern continues until the seqid is incremented past
   NFS4_UINT32_MAX, and one (not zero) is the next seqid value.

   The purpose of the incrementing of the seqid is to allow the server
   to communicate to the client the order in which operations that
   modified locking state associated with a stateid have been processed
   and to make it possible for the client to send requests that are
   conditional on the set of locks not having changed since the stateid
   in question was returned.

   Except for layout stateids (Section 12.5.3), when a client sends a
   stateid to the server, it has two choices with regard to the seqid
   sent.  It may set the seqid to zero to indicate to the server that it
   wishes the most up-to-date seqid for that stateid's "other" field to
   be used.  This would be the common choice in the case of a stateid
   sent with a READ or WRITE operation.  It also may set a non-zero
   value, in which case the server checks if that seqid is the correct
   one.  In that case, the server is required to return
   NFS4ERR_OLD_STATEID if the seqid is lower than the most current value
   and NFS4ERR_BAD_STATEID if the seqid is greater than the most current



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   value.  This would be the common choice in the case of stateids sent
   with a CLOSE or OPEN_DOWNGRADE.  Because OPENs may be sent in
   parallel for the same owner, a client might close a file without
   knowing that an OPEN upgrade had been done by the server, changing
   the lock in question.  If CLOSE were sent with a zero seqid, the OPEN
   upgrade would be cancelled before the client even received an
   indication that an upgrade had happened.

   When a stateid is sent by the server to the client as part of a
   callback operation, it is not subject to checking for a current seqid
   and returning NFS4ERR_OLD_STATEID.  This is because the client is not
   in a position to know the most up-to-date seqid and thus cannot
   verify it.  Unless specially noted, the seqid value for a stateid
   sent by the server to the client as part of a callback is required to
   be zero with NFS4ERR_BAD_STATEID returned if it is not.

   In making comparisons between seqids, both by the client in
   determining the order of operations and by the server in determining
   whether the NFS4ERR_OLD_STATEID is to be returned, the possibility of
   the seqid being swapped around past the NFS4_UINT32_MAX value needs
   to be taken into account.  When two seqid values are being compared,
   the total count of slots for all sessions associated with the current
   client is used to do this.  When one seqid value is less than this
   total slot count and another seqid value is greater than
   NFS4_UINT32_MAX minus the total slot count, the former is to be
   treated as lower than the latter, despite the fact that it is
   numerically greater.

8.2.3.  Special Stateids

   Stateid values whose "other" field is either all zeros or all ones
   are reserved.  They may not be assigned by the server but have
   special meanings defined by the protocol.  The particular meaning
   depends on whether the "other" field is all zeros or all ones and the
   specific value of the "seqid" field.

   The following combinations of "other" and "seqid" are defined in
   NFSv4.1:

   o  When "other" and "seqid" are both zero, the stateid is treated as
      a special anonymous stateid, which can be used in READ, WRITE, and
      SETATTR requests to indicate the absence of any OPEN state
      associated with the request.  When an anonymous stateid value is
      used and an existing open denies the form of access requested,
      then access will be denied to the request.  This stateid MUST NOT
      be used on operations to data servers (Section 13.6).





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   o  When "other" and "seqid" are both all ones, the stateid is a
      special READ bypass stateid.  When this value is used in WRITE or
      SETATTR, it is treated like the anonymous value.  When used in
      READ, the server MAY grant access, even if access would normally
      be denied to READ operations.  This stateid MUST NOT be used on
      operations to data servers.

   o  When "other" is zero and "seqid" is one, the stateid represents
      the current stateid, which is whatever value is the last stateid
      returned by an operation within the COMPOUND.  In the case of an
      OPEN, the stateid returned for the open file and not the
      delegation is used.  The stateid passed to the operation in place
      of the special value has its "seqid" value set to zero, except
      when the current stateid is used by the operation CLOSE or
      OPEN_DOWNGRADE.  If there is no operation in the COMPOUND that has
      returned a stateid value, the server MUST return the error
      NFS4ERR_BAD_STATEID.  As illustrated in Figure 6, if the value of
      a current stateid is a special stateid and the stateid of an
      operation's arguments has "other" set to zero and "seqid" set to
      one, then the server MUST return the error NFS4ERR_BAD_STATEID.

   o  When "other" is zero and "seqid" is NFS4_UINT32_MAX, the stateid
      represents a reserved stateid value defined to be invalid.  When
      this stateid is used, the server MUST return the error
      NFS4ERR_BAD_STATEID.

   If a stateid value is used that has all zeros or all ones in the
   "other" field but does not match one of the cases above, the server
   MUST return the error NFS4ERR_BAD_STATEID.

   Special stateids, unlike other stateids, are not associated with
   individual client IDs or filehandles and can be used with all valid
   client IDs and filehandles.  In the case of a special stateid
   designating the current stateid, the current stateid value
   substituted for the special stateid is associated with a particular
   client ID and filehandle, and so, if it is used where the current
   filehandle does not match that associated with the current stateid,
   the operation to which the stateid is passed will return
   NFS4ERR_BAD_STATEID.

8.2.4.  Stateid Lifetime and Validation

   Stateids must remain valid until either a client restart or a server
   restart or until the client returns all of the locks associated with
   the stateid by means of an operation such as CLOSE or DELEGRETURN.
   If the locks are lost due to revocation, as long as the client ID is
   valid, the stateid remains a valid designation of that revoked state
   until the client frees it by using FREE_STATEID.  Stateids associated



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   with byte-range locks are an exception.  They remain valid even if a
   LOCKU frees all remaining locks, so long as the open file with which
   they are associated remains open, unless the client frees the
   stateids via the FREE_STATEID operation.

   It should be noted that there are situations in which the client's
   locks become invalid, without the client requesting they be returned.
   These include lease expiration and a number of forms of lock
   revocation within the lease period.  It is important to note that in
   these situations, the stateid remains valid and the client can use it
   to determine the disposition of the associated lost locks.

   An "other" value must never be reused for a different purpose (i.e.,
   different filehandle, owner, or type of locks) within the context of
   a single client ID.  A server may retain the "other" value for the
   same purpose beyond the point where it may otherwise be freed, but if
   it does so, it must maintain "seqid" continuity with previous values.

   One mechanism that may be used to satisfy the requirement that the
   server recognize invalid and out-of-date stateids is for the server
   to divide the "other" field of the stateid into two fields.

   o  an index into a table of locking-state structures.

   o  a generation number that is incremented on each allocation of a
      table entry for a particular use.

   And then store in each table entry,

   o  the client ID with which the stateid is associated.

   o  the current generation number for the (at most one) valid stateid
      sharing this index value.

   o  the filehandle of the file on which the locks are taken.

   o  an indication of the type of stateid (open, byte-range lock, file
      delegation, directory delegation, layout).

   o  the last "seqid" value returned corresponding to the current
      "other" value.

   o  an indication of the current status of the locks associated with
      this stateid, in particular, whether these have been revoked and
      if so, for what reason.

   With this information, an incoming stateid can be validated and the
   appropriate error returned when necessary.  Special and non-special



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   stateids are handled separately.  (See Section 8.2.3 for a discussion
   of special stateids.)

   Note that stateids are implicitly qualified by the current client ID,
   as derived from the client ID associated with the current session.
   Note, however, that the semantics of the session will prevent
   stateids associated with a previous client or server instance from
   being analyzed by this procedure.

   If server restart has resulted in an invalid client ID or a session
   ID that is invalid, SEQUENCE will return an error and the operation
   that takes a stateid as an argument will never be processed.

   If there has been a server restart where there is a persistent
   session and all leased state has been lost, then the session in
   question will, although valid, be marked as dead, and any operation
   not satisfied by means of the reply cache will receive the error
   NFS4ERR_DEADSESSION, and thus not be processed as indicated below.

   When a stateid is being tested and the "other" field is all zeros or
   all ones, a check that the "other" and "seqid" fields match a defined
   combination for a special stateid is done and the results determined
   as follows:

   o  If the "other" and "seqid" fields do not match a defined
      combination associated with a special stateid, the error
      NFS4ERR_BAD_STATEID is returned.

   o  If the special stateid is one designating the current stateid and
      there is a current stateid, then the current stateid is
      substituted for the special stateid and the checks appropriate to
      non-special stateids are performed.

   o  If the combination is valid in general but is not appropriate to
      the context in which the stateid is used (e.g., an all-zero
      stateid is used when an OPEN stateid is required in a LOCK
      operation), the error NFS4ERR_BAD_STATEID is also returned.

   o  Otherwise, the check is completed and the special stateid is
      accepted as valid.

   When a stateid is being tested, and the "other" field is neither all
   zeros nor all ones, the following procedure could be used to validate
   an incoming stateid and return an appropriate error, when necessary,
   assuming that the "other" field would be divided into a table index
   and an entry generation.





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   o  If the table index field is outside the range of the associated
      table, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry is of a different generation than that
      specified in the incoming stateid, return NFS4ERR_BAD_STATEID.

   o  If the selected table entry does not match the current filehandle,
      return NFS4ERR_BAD_STATEID.

   o  If the client ID in the table entry does not match the client ID
      associated with the current session, return NFS4ERR_BAD_STATEID.

   o  If the stateid represents revoked state, then return
      NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED,
      as appropriate.

   o  If the stateid type is not valid for the context in which the
      stateid appears, return NFS4ERR_BAD_STATEID.  Note that a stateid
      may be valid in general, as would be reported by the TEST_STATEID
      operation, but be invalid for a particular operation, as, for
      example, when a stateid that doesn't represent byte-range locks is
      passed to the non-from_open case of LOCK or to LOCKU, or when a
      stateid that does not represent an open is passed to CLOSE or
      OPEN_DOWNGRADE.  In such cases, the server MUST return
      NFS4ERR_BAD_STATEID.

   o  If the "seqid" field is not zero and it is greater than the
      current sequence value corresponding to the current "other" field,
      return NFS4ERR_BAD_STATEID.

   o  If the "seqid" field is not zero and it is less than the current
      sequence value corresponding to the current "other" field, return
      NFS4ERR_OLD_STATEID.

   o  Otherwise, the stateid is valid and the table entry should contain
      any additional information about the type of stateid and
      information associated with that particular type of stateid, such
      as the associated set of locks, e.g., open-owner and lock-owner
      information, as well as information on the specific locks, e.g.,
      open modes and byte-ranges.

8.2.5.  Stateid Use for I/O Operations

   Clients performing I/O operations need to select an appropriate
   stateid based on the locks (including opens and delegations) held by
   the client and the various types of state-owners sending the I/O
   requests.  SETATTR operations that change the file size are treated
   like I/O operations in this regard.



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   The following rules, applied in order of decreasing priority, govern
   the selection of the appropriate stateid.  In following these rules,
   the client will only consider locks of which it has actually received
   notification by an appropriate operation response or callback.  Note
   that the rules are slightly different in the case of I/O to data
   servers when file layouts are being used (see Section 13.9.1).

   o  If the client holds a delegation for the file in question, the
      delegation stateid SHOULD be used.

   o  Otherwise, if the entity corresponding to the lock-owner (e.g., a
      process) sending the I/O has a byte-range lock stateid for the
      associated open file, then the byte-range lock stateid for that
      lock-owner and open file SHOULD be used.

   o  If there is no byte-range lock stateid, then the OPEN stateid for
      the open file in question SHOULD be used.

   o  Finally, if none of the above apply, then a special stateid SHOULD
      be used.

   Ignoring these rules may result in situations in which the server
   does not have information necessary to properly process the request.
   For example, when mandatory byte-range locks are in effect, if the
   stateid does not indicate the proper lock-owner, via a lock stateid,
   a request might be avoidably rejected.

   The server however should not try to enforce these ordering rules and
   should use whatever information is available to properly process I/O
   requests.  In particular, when a client has a delegation for a given
   file, it SHOULD take note of this fact in processing a request, even
   if it is sent with a special stateid.

8.2.6.  Stateid Use for SETATTR Operations

   Because each operation is associated with a session ID and from that
   the clientid can be determined, operations do not need to include a
   stateid for the server to be able to determine whether they should
   cause a delegation to be recalled or are to be treated as done within
   the scope of the delegation.

   In the case of SETATTR operations, a stateid is present.  In cases
   other than those that set the file size, the client may send either a
   special stateid or, when a delegation is held for the file in
   question, a delegation stateid.  While the server SHOULD validate the
   stateid and may use the stateid to optimize the determination as to
   whether a delegation is held, it SHOULD note the presence of a




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   delegation even when a special stateid is sent, and MUST accept a
   valid delegation stateid when sent.

8.3.  Lease Renewal

   Each client/server pair, as represented by a client ID, has a single
   lease.  The purpose of the lease is to allow the client to indicate
   to the server, in a low-overhead way, that it is active, and thus
   that the server is to retain the client's locks.  This arrangement
   allows the server to remove stale locking-related objects that are
   held by a client that has crashed or is otherwise unreachable, once
   the relevant lease expires.  This in turn allows other clients to
   obtain conflicting locks without being delayed indefinitely by
   inactive or unreachable clients.  It is not a mechanism for cache
   consistency and lease renewals may not be denied if the lease
   interval has not expired.

   Since each session is associated with a specific client (identified
   by the client's client ID), any operation sent on that session is an
   indication that the associated client is reachable.  When a request
   is sent for a given session, successful execution of a SEQUENCE
   operation (or successful retrieval of the result of SEQUENCE from the
   reply cache) on an unexpired lease will result in the lease being
   implicitly renewed, for the standard renewal period (equal to the
   lease_time attribute).

   If the client ID's lease has not expired when the server receives a
   SEQUENCE operation, then the server MUST renew the lease.  If the
   client ID's lease has expired when the server receives a SEQUENCE
   operation, the server MAY renew the lease; this depends on whether
   any state was revoked as a result of the client's failure to renew
   the lease before expiration.

   Absent other activity that would renew the lease, a COMPOUND
   consisting of a single SEQUENCE operation will suffice.  The client
   should also take communication-related delays into account and take
   steps to ensure that the renewal messages actually reach the server
   in good time.  For example:

   o  When trunking is in effect, the client should consider sending
      multiple requests on different connections, in order to ensure
      that renewal occurs, even in the event of blockage in the path
      used for one of those connections.

   o  Transport retransmission delays might become so large as to
      approach or exceed the length of the lease period.  This may be
      particularly likely when the server is unresponsive due to a
      restart; see Section 8.4.2.1.  If the client implementation is not



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      careful, transport retransmission delays can result in the client
      failing to detect a server restart before the grace period ends.
      The scenario is that the client is using a transport with
      exponential backoff, such that the maximum retransmission timeout
      exceeds both the grace period and the lease_time attribute.  A
      network partition causes the client's connection's retransmission
      interval to back off, and even after the partition heals, the next
      transport-level retransmission is sent after the server has
      restarted and its grace period ends.

      The client MUST either recover from the ensuing NFS4ERR_NO_GRACE
      errors or it MUST ensure that, despite transport-level
      retransmission intervals that exceed the lease_time, a SEQUENCE
      operation is sent that renews the lease before expiration.  The
      client can achieve this by associating a new connection with the
      session, and sending a SEQUENCE operation on it.  However, if the
      attempt to establish a new connection is delayed for some reason
      (e.g., exponential backoff of the connection establishment
      packets), the client will have to abort the connection
      establishment attempt before the lease expires, and attempt to
      reconnect.

   If the server renews the lease upon receiving a SEQUENCE operation,
   the server MUST NOT allow the lease to expire while the rest of the
   operations in the COMPOUND procedure's request are still executing.
   Once the last operation has finished, and the response to COMPOUND
   has been sent, the server MUST set the lease to expire no sooner than
   the sum of current time and the value of the lease_time attribute.

   A client ID's lease can expire when it has been at least the lease
   interval (lease_time) since the last lease-renewing SEQUENCE
   operation was sent on any of the client ID's sessions and there are
   no active COMPOUND operations on any such sessions.

   Because the SEQUENCE operation is the basic mechanism to renew a
   lease, and because it must be done at least once for each lease
   period, it is the natural mechanism whereby the server will inform
   the client of changes in the lease status that the client needs to be
   informed of.  The client should inspect the status flags
   (sr_status_flags) returned by sequence and take the appropriate
   action (see Section 18.46.3 for details).

   o  The status bits SEQ4_STATUS_CB_PATH_DOWN and
      SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with the
      backchannel that the client may need to address in order to
      receive callback requests.





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   o  The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
      SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicate problems with GSS
      contexts or RPCSEC_GSS handles for the backchannel that the client
      might have to address in order to allow callback requests to be
      sent.

   o  The status bits SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
      SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED,
      SEQ4_STATUS_ADMIN_STATE_REVOKED, and
      SEQ4_STATUS_RECALLABLE_STATE_REVOKED notify the client of lock
      revocation events.  When these bits are set, the client should use
      TEST_STATEID to find what stateids have been revoked and use
      FREE_STATEID to acknowledge loss of the associated state.

   o  The status bit SEQ4_STATUS_LEASE_MOVE indicates that
      responsibility for lease renewal has been transferred to one or
      more new servers.

   o  The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED indicates that
      due to server restart the client must reclaim locking state.

   o  The status bit SEQ4_STATUS_BACKCHANNEL_FAULT indicates that the
      server has encountered an unrecoverable fault with the backchannel
      (e.g., it has lost track of a sequence ID for a slot in the
      backchannel).

8.4.  Crash Recovery

   A critical requirement in crash recovery is that both the client and
   the server know when the other has failed.  Additionally, it is
   required that a client sees a consistent view of data across server
   restarts.  All READ and WRITE operations that may have been queued
   within the client or network buffers must wait until the client has
   successfully recovered the locks protecting the READ and WRITE
   operations.  Any that reach the server before the server can safely
   determine that the client has recovered enough locking state to be
   sure that such operations can be safely processed must be rejected.
   This will happen because either:

   o  The state presented is no longer valid since it is associated with
      a now invalid client ID.  In this case, the client will receive
      either an NFS4ERR_BADSESSION or NFS4ERR_DEADSESSION error, and any
      attempt to attach a new session to that invalid client ID will
      result in an NFS4ERR_STALE_CLIENTID error.

   o  Subsequent recovery of locks may make execution of the operation
      inappropriate (NFS4ERR_GRACE).




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8.4.1.  Client Failure and Recovery

   In the event that a client fails, the server may release the client's
   locks when the associated lease has expired.  Conflicting locks from
   another client may only be granted after this lease expiration.  As
   discussed in Section 8.3, when a client has not failed and re-
   establishes its lease before expiration occurs, requests for
   conflicting locks will not be granted.

   To minimize client delay upon restart, lock requests are associated
   with an instance of the client by a client-supplied verifier.  This
   verifier is part of the client_owner4 sent in the initial EXCHANGE_ID
   call made by the client.  The server returns a client ID as a result
   of the EXCHANGE_ID operation.  The client then confirms the use of
   the client ID by establishing a session associated with that client
   ID (see Section 18.36.3 for a description of how this is done).  All
   locks, including opens, byte-range locks, delegations, and layouts
   obtained by sessions using that client ID, are associated with that
   client ID.

   Since the verifier will be changed by the client upon each
   initialization, the server can compare a new verifier to the verifier
   associated with currently held locks and determine that they do not
   match.  This signifies the client's new instantiation and subsequent
   loss (upon confirmation of the new client ID) of locking state.  As a
   result, the server is free to release all locks held that are
   associated with the old client ID that was derived from the old
   verifier.  At this point, conflicting locks from other clients, kept
   waiting while the lease had not yet expired, can be granted.  In
   addition, all stateids associated with the old client ID can also be
   freed, as they are no longer reference-able.

   Note that the verifier must have the same uniqueness properties as
   the verifier for the COMMIT operation.

8.4.2.  Server Failure and Recovery

   If the server loses locking state (usually as a result of a restart),
   it must allow clients time to discover this fact and re-establish the
   lost locking state.  The client must be able to re-establish the
   locking state without having the server deny valid requests because
   the server has granted conflicting access to another client.
   Likewise, if there is a possibility that clients have not yet re-
   established their locking state for a file and that such locking
   state might make it invalid to perform READ or WRITE operations.  For
   example, if mandatory locks are a possibility, the server must
   disallow READ and WRITE operations for that file.




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   A client can determine that loss of locking state has occurred via
   several methods.

   1.  When a SEQUENCE (most common) or other operation returns
       NFS4ERR_BADSESSION, this may mean that the session has been
       destroyed but the client ID is still valid.  The client sends a
       CREATE_SESSION request with the client ID to re-establish the
       session.  If CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
       the client must establish a new client ID (see Section 8.1) and
       re-establish its lock state with the new client ID, after the
       CREATE_SESSION operation succeeds (see Section 8.4.2.1).

   2.  When a SEQUENCE (most common) or other operation on a persistent
       session returns NFS4ERR_DEADSESSION, this indicates that a
       session is no longer usable for new, i.e., not satisfied from the
       reply cache, operations.  Once all pending operations are
       determined to be either performed before the retry or not
       performed, the client sends a CREATE_SESSION request with the
       client ID to re-establish the session.  If CREATE_SESSION fails
       with NFS4ERR_STALE_CLIENTID, the client must establish a new
       client ID (see Section 8.1) and re-establish its lock state after
       the CREATE_SESSION, with the new client ID, succeeds
       (Section 8.4.2.1).

   3.  When an operation, neither SEQUENCE nor preceded by SEQUENCE (for
       example, CREATE_SESSION, DESTROY_SESSION), returns
       NFS4ERR_STALE_CLIENTID, the client MUST establish a new client ID
       (Section 8.1) and re-establish its lock state (Section 8.4.2.1).

8.4.2.1.  State Reclaim

   When state information and the associated locks are lost as a result
   of a server restart, the protocol must provide a way to cause that
   state to be re-established.  The approach used is to define, for most
   types of locking state (layouts are an exception), a request whose
   function is to allow the client to re-establish on the server a lock
   first obtained from a previous instance.  Generally, these requests
   are variants of the requests normally used to create locks of that
   type and are referred to as "reclaim-type" requests, and the process
   of re-establishing such locks is referred to as "reclaiming" them.

   Because each client must have an opportunity to reclaim all of the
   locks that it has without the possibility that some other client will
   be granted a conflicting lock, a "grace period" is devoted to the
   reclaim process.  During this period, requests creating client IDs
   and sessions are handled normally, but locking requests are subject
   to special restrictions.  Only reclaim-type locking requests are
   allowed, unless the server can reliably determine (through state



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   persistently maintained across restart instances) that granting any
   such lock cannot possibly conflict with a subsequent reclaim.  When a
   request is made to obtain a new lock (i.e., not a reclaim-type
   request) during the grace period and such a determination cannot be
   made, the server must return the error NFS4ERR_GRACE.

   Once a session is established using the new client ID, the client
   will use reclaim-type locking requests (e.g., LOCK operations with
   reclaim set to TRUE and OPEN operations with a claim type of
   CLAIM_PREVIOUS; see Section 9.11) to re-establish its locking state.
   Once this is done, or if there is no such locking state to reclaim,
   the client sends a global RECLAIM_COMPLETE operation, i.e., one with
   the rca_one_fs argument set to FALSE, to indicate that it has
   reclaimed all of the locking state that it will reclaim.  Once a
   client sends such a RECLAIM_COMPLETE operation, it may attempt non-
   reclaim locking operations, although it might get an NFS4ERR_GRACE
   status result from each such operation until the period of special
   handling is over.  See Section 11.7.7 for a discussion of the
   analogous handling lock reclamation in the case of file systems
   transitioning from server to server.

   During the grace period, the server must reject READ and WRITE
   operations and non-reclaim locking requests (i.e., other LOCK and
   OPEN operations) with an error of NFS4ERR_GRACE, unless it can
   guarantee that these may be done safely, as described below.

   The grace period may last until all clients that are known to
   possibly have had locks have done a global RECLAIM_COMPLETE
   operation, indicating that they have finished reclaiming the locks
   they held before the server restart.  This means that a client that
   has done a RECLAIM_COMPLETE must be prepared to receive an
   NFS4ERR_GRACE when attempting to acquire new locks.  In order for the
   server to know that all clients with possible prior lock state have
   done a RECLAIM_COMPLETE, the server must maintain in stable storage a
   list clients that may have such locks.  The server may also terminate
   the grace period before all clients have done a global
   RECLAIM_COMPLETE.  The server SHOULD NOT terminate the grace period
   before a time equal to the lease period in order to give clients an
   opportunity to find out about the server restart, as a result of
   sending requests on associated sessions with a frequency governed by
   the lease time.  Note that when a client does not send such requests
   (or they are sent by the client but not received by the server), it
   is possible for the grace period to expire before the client finds
   out that the server restart has occurred.

   Some additional time in order to allow a client to establish a new
   client ID and session and to effect lock reclaims may be added to the




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   lease time.  Note that analogous rules apply to file system-specific
   grace periods discussed in Section 11.7.7.

   If the server can reliably determine that granting a non-reclaim
   request will not conflict with reclamation of locks by other clients,
   the NFS4ERR_GRACE error does not have to be returned even within the
   grace period, although NFS4ERR_GRACE must always be returned to
   clients attempting a non-reclaim lock request before doing their own
   global RECLAIM_COMPLETE.  For the server to be able to service READ
   and WRITE operations during the grace period, it must again be able
   to guarantee that no possible conflict could arise between a
   potential reclaim locking request and the READ or WRITE operation.
   If the server is unable to offer that guarantee, the NFS4ERR_GRACE
   error must be returned to the client.

   For a server to provide simple, valid handling during the grace
   period, the easiest method is to simply reject all non-reclaim
   locking requests and READ and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, a server may keep information about
   granted locks in stable storage.  With this information, the server
   could determine if a locking, READ or WRITE operation can be safely
   processed.

   For example, if the server maintained on stable storage summary
   information on whether mandatory locks exist, either mandatory byte-
   range locks, or share reservations specifying deny modes, many
   requests could be allowed during the grace period.  If it is known
   that no such share reservations exist, OPEN request that do not
   specify deny modes may be safely granted.  If, in addition, it is
   known that no mandatory byte-range locks exist, either through
   information stored on stable storage or simply because the server
   does not support such locks, READ and WRITE operations may be safely
   processed during the grace period.  Another important case is where
   it is known that no mandatory byte-range locks exist, either because
   the server does not provide support for them or because their absence
   is known from persistently recorded data.  In this case, READ and
   WRITE operations specifying stateids derived from reclaim-type
   operations may be validly processed during the grace period because
   of the fact that the valid reclaim ensures that no lock subsequently
   granted can prevent the I/O.

   To reiterate, for a server that allows non-reclaim lock and I/O
   requests to be processed during the grace period, it MUST determine
   that no lock subsequently reclaimed will be rejected and that no lock
   subsequently reclaimed would have prevented any I/O operation
   processed during the grace period.





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   Clients should be prepared for the return of NFS4ERR_GRACE errors for
   non-reclaim lock and I/O requests.  In this case, the client should
   employ a retry mechanism for the request.  A delay (on the order of
   several seconds) between retries should be used to avoid overwhelming
   the server.  Further discussion of the general issue is included in
   [47].  The client must account for the server that can perform I/O
   and non-reclaim locking requests within the grace period as well as
   those that cannot do so.

   A reclaim-type locking request outside the server's grace period can
   only succeed if the server can guarantee that no conflicting lock or
   I/O request has been granted since restart.

   A server may, upon restart, establish a new value for the lease
   period.  Therefore, clients should, once a new client ID is
   established, refetch the lease_time attribute and use it as the basis
   for lease renewal for the lease associated with that server.
   However, the server must establish, for this restart event, a grace
   period at least as long as the lease period for the previous server
   instantiation.  This allows the client state obtained during the
   previous server instance to be reliably re-established.

   The possibility exists that, because of server configuration events,
   the client will be communicating with a server different than the one
   on which the locks were obtained, as shown by the combination of
   eir_server_scope and eir_server_owner.  This leads to the issue of if
   and when the client should attempt to reclaim locks previously
   obtained on what is being reported as a different server.  The rules
   to resolve this question are as follows:

   o  If the server scope is different, the client should not attempt to
      reclaim locks.  In this situation, no lock reclaim is possible.
      Any attempt to re-obtain the locks with non-reclaim operations is
      problematic since there is no guarantee that the existing
      filehandles will be recognized by the new server, or that if
      recognized, they denote the same objects.  It is best to treat the
      locks as having been revoked by the reconfiguration event.

   o  If the server scope is the same, the client should attempt to
      reclaim locks, even if the eir_server_owner value is different.
      In this situation, it is the responsibility of the server to
      return NFS4ERR_NO_GRACE if it cannot provide correct support for
      lock reclaim operations, including the prevention of edge
      conditions.

   The eir_server_owner field is not used in making this determination.
   Its function is to specify trunking possibilities for the client (see
   Section 2.10.5) and not to control lock reclaim.



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8.4.2.1.1.  Security Considerations for State Reclaim

   During the grace period, a client can reclaim state that it believes
   or asserts it had before the server restarted.  Unless the server
   maintained a complete record of all the state the client had, the
   server has little choice but to trust the client.  (Of course, if the
   server maintained a complete record, then it would not have to force
   the client to reclaim state after server restart.)  While the server
   has to trust the client to tell the truth, such trust does not have
   any negative consequences for security.  The fundamental rule for the
   server when processing reclaim requests is that it MUST NOT grant the
   reclaim if an equivalent non-reclaim request would not be granted
   during steady state due to access control or access conflict issues.
   For example, an OPEN request during a reclaim will be refused with
   NFS4ERR_ACCESS if the principal making the request does not have
   access to open the file according to the discretionary ACL
   (Section 6.2.2) on the file.

   Nonetheless, it is possible that a client operating in error or
   maliciously could, during reclaim, prevent another client from
   reclaiming access to state.  For example, an attacker could send an
   OPEN reclaim operation with a deny mode that prevents another client
   from reclaiming the OPEN state it had before the server restarted.
   The attacker could perform the same denial of service during steady
   state prior to server restart, as long as the attacker had
   permissions.  Given that the attack vectors are equivalent, the grace
   period does not offer any additional opportunity for denial of
   service, and any concerns about this attack vector, whether during
   grace or steady state, are addressed the same way: use RPCSEC_GSS for
   authentication and limit access to the file only to principals that
   the owner of the file trusts.

   Note that if prior to restart the server had client IDs with the
   EXCHGID4_FLAG_BIND_PRINC_STATEID (Section 18.35) capability set, then
   the server SHOULD record in stable storage the client owner and the
   principal that established the client ID via EXCHANGE_ID.  If the
   server does not, then there is a risk a client will be unable to
   reclaim state if it does not have a credential for a principal that
   was originally authorized to establish the state.

8.4.3.  Network Partitions and Recovery

   If the duration of a network partition is greater than the lease
   period provided by the server, the server will not have received a
   lease renewal from the client.  If this occurs, the server may free
   all locks held for the client or it may allow the lock state to
   remain for a considerable period, subject to the constraint that if a
   request for a conflicting lock is made, locks associated with an



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   expired lease do not prevent such a conflicting lock from being
   granted but MUST be revoked as necessary so as to avoid interfering
   with such conflicting requests.

   If the server chooses to delay freeing of lock state until there is a
   conflict, it may either free all of the client's locks once there is
   a conflict or it may only revoke the minimum set of locks necessary
   to allow conflicting requests.  When it adopts the finer-grained
   approach, it must revoke all locks associated with a given stateid,
   even if the conflict is with only a subset of locks.

   When the server chooses to free all of a client's lock state, either
   immediately upon lease expiration or as a result of the first attempt
   to obtain a conflicting a lock, the server may report the loss of
   lock state in a number of ways.

   The server may choose to invalidate the session and the associated
   client ID.  In this case, once the client can communicate with the
   server, it will receive an NFS4ERR_BADSESSION error.  Upon attempting
   to create a new session, it would get an NFS4ERR_STALE_CLIENTID.
   Upon creating the new client ID and new session, the client will
   attempt to reclaim locks.  Normally, the server will not allow the
   client to reclaim locks, because the server will not be in its
   recovery grace period.

   Another possibility is for the server to maintain the session and
   client ID but for all stateids held by the client to become invalid
   or stale.  Once the client can reach the server after such a network
   partition, the status returned by the SEQUENCE operation will
   indicate a loss of locking state; i.e., the flag
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED will be set in sr_status_flags.
   In addition, all I/O submitted by the client with the now invalid
   stateids will fail with the server returning the error
   NFS4ERR_EXPIRED.  Once the client learns of the loss of locking
   state, it will suitably notify the applications that held the
   invalidated locks.  The client should then take action to free
   invalidated stateids, either by establishing a new client ID using a
   new verifier or by doing a FREE_STATEID operation to release each of
   the invalidated stateids.

   When the server adopts a finer-grained approach to revocation of
   locks when a client's lease has expired, only a subset of stateids
   will normally become invalid during a network partition.  When the
   client can communicate with the server after such a network partition
   heals, the status returned by the SEQUENCE operation will indicate a
   partial loss of locking state
   (SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED).  In addition, operations,
   including I/O submitted by the client, with the now invalid stateids



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   will fail with the server returning the error NFS4ERR_EXPIRED.  Once
   the client learns of the loss of locking state, it will use the
   TEST_STATEID operation on all of its stateids to determine which
   locks have been lost and then suitably notify the applications that
   held the invalidated locks.  The client can then release the
   invalidated locking state and acknowledge the revocation of the
   associated locks by doing a FREE_STATEID operation on each of the
   invalidated stateids.

   When a network partition is combined with a server restart, there are
   edge conditions that place requirements on the server in order to
   avoid silent data corruption following the server restart.  Two of
   these edge conditions are known, and are discussed below.

   The first edge condition arises as a result of the scenarios such as
   the following:

   1.  Client A acquires a lock.

   2.  Client A and server experience mutual network partition, such
       that client A is unable to renew its lease.

   3.  Client A's lease expires, and the server releases the lock.

   4.  Client B acquires a lock that would have conflicted with that of
       client A.

   5.  Client B releases its lock.

   6.  Server restarts.

   7.  Network partition between client A and server heals.

   8.  Client A connects to a new server instance and finds out about
       server restart.

   9.  Client A reclaims its lock within the server's grace period.

   Thus, at the final step, the server has erroneously granted client
   A's lock reclaim.  If client B modified the object the lock was
   protecting, client A will experience object corruption.

   The second known edge condition arises in situations such as the
   following:

   1.   Client A acquires one or more locks.

   2.   Server restarts.



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   3.   Client A and server experience mutual network partition, such
        that client A is unable to reclaim all of its locks within the
        grace period.

   4.   Server's reclaim grace period ends.  Client A has either no
        locks or an incomplete set of locks known to the server.

   5.   Client B acquires a lock that would have conflicted with a lock
        of client A that was not reclaimed.

   6.   Client B releases the lock.

   7.   Server restarts a second time.

   8.   Network partition between client A and server heals.

   9.   Client A connects to new server instance and finds out about
        server restart.

   10.  Client A reclaims its lock within the server's grace period.

   As with the first edge condition, the final step of the scenario of
   the second edge condition has the server erroneously granting client
   A's lock reclaim.

   Solving the first and second edge conditions requires either that the
   server always assumes after it restarts that some edge condition
   occurs, and thus returns NFS4ERR_NO_GRACE for all reclaim attempts,
   or that the server record some information in stable storage.  The
   amount of information the server records in stable storage is in
   inverse proportion to how harsh the server intends to be whenever
   edge conditions arise.  The server that is completely tolerant of all
   edge conditions will record in stable storage every lock that is
   acquired, removing the lock record from stable storage only when the
   lock is released.  For the two edge conditions discussed above, the
   harshest a server can be, and still support a grace period for
   reclaims, requires that the server record in stable storage some
   minimal information.  For example, a server implementation could, for
   each client, save in stable storage a record containing:

   o  the co_ownerid field from the client_owner4 presented in the
      EXCHANGE_ID operation.

   o  a boolean that indicates if the client's lease expired or if there
      was administrative intervention (see Section 8.5) to revoke a
      byte-range lock, share reservation, or delegation and there has
      been no acknowledgment, via FREE_STATEID, of such revocation.




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   o  a boolean that indicates whether the client may have locks that it
      believes to be reclaimable in situations in which the grace period
      was terminated, making the server's view of lock reclaimability
      suspect.  The server will set this for any client record in stable
      storage where the client has not done a suitable RECLAIM_COMPLETE
      (global or file system-specific depending on the target of the
      lock request) before it grants any new (i.e., not reclaimed) lock
      to any client.

   Assuming the above record keeping, for the first edge condition,
   after the server restarts, the record that client A's lease expired
   means that another client could have acquired a conflicting byte-
   range lock, share reservation, or delegation.  Hence, the server must
   reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   For the second edge condition, after the server restarts for a second
   time, the indication that the client had not completed its reclaims
   at the time at which the grace period ended means that the server
   must reject a reclaim from client A with the error NFS4ERR_NO_GRACE.

   When either edge condition occurs, the client's attempt to reclaim
   locks will result in the error NFS4ERR_NO_GRACE.  When this is
   received, or after the client restarts with no lock state, the client
   will send a global RECLAIM_COMPLETE.  When the RECLAIM_COMPLETE is
   received, the server and client are again in agreement regarding
   reclaimable locks and both booleans in persistent storage can be
   reset, to be set again only when there is a subsequent event that
   causes lock reclaim operations to be questionable.

   Regardless of the level and approach to record keeping, the server
   MUST implement one of the following strategies (which apply to
   reclaims of share reservations, byte-range locks, and delegations):

   1.  Reject all reclaims with NFS4ERR_NO_GRACE.  This is extremely
       unforgiving, but necessary if the server does not record lock
       state in stable storage.

   2.  Record sufficient state in stable storage such that all known
       edge conditions involving server restart, including the two noted
       in this section, are detected.  It is acceptable to erroneously
       recognize an edge condition and not allow a reclaim, when, with
       sufficient knowledge, it would be allowed.  The error the server
       would return in this case is NFS4ERR_NO_GRACE.  Note that it is
       not known if there are other edge conditions.

       In the event that, after a server restart, the server determines
       there is unrecoverable damage or corruption to the information in




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       stable storage, then for all clients and/or locks that may be
       affected, the server MUST return NFS4ERR_NO_GRACE.

   A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
   outside the scope of this specification, since the strategies for
   such handling are very dependent on the client's operating
   environment.  However, one potential approach is described below.

   When the client receives NFS4ERR_NO_GRACE, it could examine the
   change attribute of the objects for which the client is trying to
   reclaim state, and use that to determine whether to re-establish the
   state via normal OPEN or LOCK operations.  This is acceptable
   provided that the client's operating environment allows it.  In other
   words, the client implementor is advised to document for his users
   the behavior.  The client could also inform the application that its
   byte-range lock or share reservations (whether or not they were
   delegated) have been lost, such as via a UNIX signal, a Graphical
   User Interface (GUI) pop-up window, etc.  See Section 10.5 for a
   discussion of what the client should do for dealing with unreclaimed
   delegations on client state.

   For further discussion of revocation of locks, see Section 8.5.

8.5.  Server Revocation of Locks

   At any point, the server can revoke locks held by a client, and the
   client must be prepared for this event.  When the client detects that
   its locks have been or may have been revoked, the client is
   responsible for validating the state information between itself and
   the server.  Validating locking state for the client means that it
   must verify or reclaim state for each lock currently held.

   The first occasion of lock revocation is upon server restart.  Note
   that this includes situations in which sessions are persistent and
   locking state is lost.  In this class of instances, the client will
   receive an error (NFS4ERR_STALE_CLIENTID) on an operation that takes
   client ID, usually as part of recovery in response to a problem with
   the current session), and the client will proceed with normal crash
   recovery as described in the Section 8.4.2.1.

   The second occasion of lock revocation is the inability to renew the
   lease before expiration, as discussed in Section 8.4.3.  While this
   is considered a rare or unusual event, the client must be prepared to
   recover.  The server is responsible for determining the precise
   consequences of the lease expiration, informing the client of the
   scope of the lock revocation decided upon.  The client then uses the
   status information provided by the server in the SEQUENCE results




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   (field sr_status_flags, see Section 18.46.3) to synchronize its
   locking state with that of the server, in order to recover.

   The third occasion of lock revocation can occur as a result of
   revocation of locks within the lease period, either because of
   administrative intervention or because a recallable lock (a
   delegation or layout) was not returned within the lease period after
   having been recalled.  While these are considered rare events, they
   are possible, and the client must be prepared to deal with them.
   When either of these events occurs, the client finds out about the
   situation through the status returned by the SEQUENCE operation.  Any
   use of stateids associated with locks revoked during the lease period
   will receive the error NFS4ERR_ADMIN_REVOKED or
   NFS4ERR_DELEG_REVOKED, as appropriate.

   In all situations in which a subset of locking state may have been
   revoked, which include all cases in which locking state is revoked
   within the lease period, it is up to the client to determine which
   locks have been revoked and which have not.  It does this by using
   the TEST_STATEID operation on the appropriate set of stateids.  Once
   the set of revoked locks has been determined, the applications can be
   notified, and the invalidated stateids can be freed and lock
   revocation acknowledged by using FREE_STATEID.

8.6.  Short and Long Leases

   When determining the time period for the server lease, the usual
   lease tradeoffs apply.  A short lease is good for fast server
   recovery at a cost of increased operations to effect lease renewal
   (when there are no other operations during the period to effect lease
   renewal as a side effect).  A long lease is certainly kinder and
   gentler to servers trying to handle very large numbers of clients.
   The number of extra requests to effect lock renewal drops in inverse
   proportion to the lease time.  The disadvantages of a long lease
   include the possibility of slower recovery after certain failures.
   After server failure, a longer grace period may be required when some
   clients do not promptly reclaim their locks and do a global
   RECLAIM_COMPLETE.  In the event of client failure, the longer period
   for a lease to expire will force conflicting requests to wait longer.

   A long lease is practical if the server can store lease state in
   stable storage.  Upon recovery, the server can reconstruct the lease
   state from its stable storage and continue operation with its
   clients.







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8.7.  Clocks, Propagation Delay, and Calculating Lease Expiration

   To avoid the need for synchronized clocks, lease times are granted by
   the server as a time delta.  However, there is a requirement that the
   client and server clocks do not drift excessively over the duration
   of the lease.  There is also the issue of propagation delay across
   the network, which could easily be several hundred milliseconds, as
   well as the possibility that requests will be lost and need to be
   retransmitted.

   To take propagation delay into account, the client should subtract it
   from lease times (e.g., if the client estimates the one-way
   propagation delay as 200 milliseconds, then it can assume that the
   lease is already 200 milliseconds old when it gets it).  In addition,
   it will take another 200 milliseconds to get a response back to the
   server.  So the client must send a lease renewal or write data back
   to the server at least 400 milliseconds before the lease would
   expire.  If the propagation delay varies over the life of the lease
   (e.g., the client is on a mobile host), the client will need to
   continuously subtract the increase in propagation delay from the
   lease times.

   The server's lease period configuration should take into account the
   network distance of the clients that will be accessing the server's
   resources.  It is expected that the lease period will take into
   account the network propagation delays and other network delay
   factors for the client population.  Since the protocol does not allow
   for an automatic method to determine an appropriate lease period, the
   server's administrator may have to tune the lease period.

8.8.  Obsolete Locking Infrastructure from NFSv4.0

   There are a number of operations and fields within existing
   operations that no longer have a function in NFSv4.1.  In one way or
   another, these changes are all due to the implementation of sessions
   that provide client context and exactly once semantics as a base
   feature of the protocol, separate from locking itself.

   The following NFSv4.0 operations MUST NOT be implemented in NFSv4.1.
   The server MUST return NFS4ERR_NOTSUPP if these operations are found
   in an NFSv4.1 COMPOUND.

   o  SETCLIENTID since its function has been replaced by EXCHANGE_ID.

   o  SETCLIENTID_CONFIRM since client ID confirmation now happens by
      means of CREATE_SESSION.





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   o  OPEN_CONFIRM because state-owner-based seqids have been replaced
      by the sequence ID in the SEQUENCE operation.

   o  RELEASE_LOCKOWNER because lock-owners with no associated locks do
      not have any sequence-related state and so can be deleted by the
      server at will.

   o  RENEW because every SEQUENCE operation for a session causes lease
      renewal, making a separate operation superfluous.

   Also, there are a number of fields, present in existing operations,
   related to locking that have no use in minor version 1.  They were
   used in minor version 0 to perform functions now provided in a
   different fashion.

   o  Sequence ids used to sequence requests for a given state-owner and
      to provide retry protection, now provided via sessions.

   o  Client IDs used to identify the client associated with a given
      request.  Client identification is now available using the client
      ID associated with the current session, without needing an
      explicit client ID field.

   Such vestigial fields in existing operations have no function in
   NFSv4.1 and are ignored by the server.  Note that client IDs in
   operations new to NFSv4.1 (such as CREATE_SESSION and
   DESTROY_CLIENTID) are not ignored.

9.  File Locking and Share Reservations

   To support Win32 share reservations, it is necessary to provide
   operations that atomically open or create files.  Having a separate
   share/unshare operation would not allow correct implementation of the
   Win32 OpenFile API.  In order to correctly implement share semantics,
   the previous NFS protocol mechanisms used when a file is opened or
   created (LOOKUP, CREATE, ACCESS) need to be replaced.  The NFSv4.1
   protocol defines an OPEN operation that is capable of atomically
   looking up, creating, and locking a file on the server.

9.1.  Opens and Byte-Range Locks

   It is assumed that manipulating a byte-range lock is rare when
   compared to READ and WRITE operations.  It is also assumed that
   server restarts and network partitions are relatively rare.
   Therefore, it is important that the READ and WRITE operations have a
   lightweight mechanism to indicate if they possess a held lock.  A
   LOCK operation contains the heavyweight information required to




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   establish a byte-range lock and uniquely define the owner of the
   lock.

9.1.1.  State-Owner Definition

   When opening a file or requesting a byte-range lock, the client must
   specify an identifier that represents the owner of the requested
   lock.  This identifier is in the form of a state-owner, represented
   in the protocol by a state_owner4, a variable-length opaque array
   that, when concatenated with the current client ID, uniquely defines
   the owner of a lock managed by the client.  This may be a thread ID,
   process ID, or other unique value.

   Owners of opens and owners of byte-range locks are separate entities
   and remain separate even if the same opaque arrays are used to
   designate owners of each.  The protocol distinguishes between open-
   owners (represented by open_owner4 structures) and lock-owners
   (represented by lock_owner4 structures).

   Each open is associated with a specific open-owner while each byte-
   range lock is associated with a lock-owner and an open-owner, the
   latter being the open-owner associated with the open file under which
   the LOCK operation was done.  Delegations and layouts, on the other
   hand, are not associated with a specific owner but are associated
   with the client as a whole (identified by a client ID).

9.1.2.  Use of the Stateid and Locking

   All READ, WRITE, and SETATTR operations contain a stateid.  For the
   purposes of this section, SETATTR operations that change the size
   attribute of a file are treated as if they are writing the area
   between the old and new sizes (i.e., the byte-range truncated or
   added to the file by means of the SETATTR), even where SETATTR is not
   explicitly mentioned in the text.  The stateid passed to one of these
   operations must be one that represents an open, a set of byte-range
   locks, or a delegation, or it may be a special stateid representing
   anonymous access or the special bypass stateid.

   If the state-owner performs a READ or WRITE operation in a situation
   in which it has established a byte-range lock or share reservation on
   the server (any OPEN constitutes a share reservation), the stateid
   (previously returned by the server) must be used to indicate what
   locks, including both byte-range locks and share reservations, are
   held by the state-owner.  If no state is established by the client,
   either a byte-range lock or a share reservation, a special stateid
   for anonymous state (zero as the value for "other" and "seqid") is
   used.  (See Section 8.2.3 for a description of 'special' stateids in
   general.)  Regardless of whether a stateid for anonymous state or a



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   stateid returned by the server is used, if there is a conflicting
   share reservation or mandatory byte-range lock held on the file, the
   server MUST refuse to service the READ or WRITE operation.

   Share reservations are established by OPEN operations and by their
   nature are mandatory in that when the OPEN denies READ or WRITE
   operations, that denial results in such operations being rejected
   with error NFS4ERR_LOCKED.  Byte-range locks may be implemented by
   the server as either mandatory or advisory, or the choice of
   mandatory or advisory behavior may be determined by the server on the
   basis of the file being accessed (for example, some UNIX-based
   servers support a "mandatory lock bit" on the mode attribute such
   that if set, byte-range locks are required on the file before I/O is
   possible).  When byte-range locks are advisory, they only prevent the
   granting of conflicting lock requests and have no effect on READs or
   WRITEs.  Mandatory byte-range locks, however, prevent conflicting I/O
   operations.  When they are attempted, they are rejected with
   NFS4ERR_LOCKED.  When the client gets NFS4ERR_LOCKED on a file for
   which it knows it has the proper share reservation, it will need to
   send a LOCK operation on the byte-range of the file that includes the
   byte-range the I/O was to be performed on, with an appropriate
   locktype field of the LOCK operation's arguments (i.e., READ*_LT for
   a READ operation, WRITE*_LT for a WRITE operation).

   Note that for UNIX environments that support mandatory byte-range
   locking, the distinction between advisory and mandatory locking is
   subtle.  In fact, advisory and mandatory byte-range locks are exactly
   the same as far as the APIs and requirements on implementation.  If
   the mandatory lock attribute is set on the file, the server checks to
   see if the lock-owner has an appropriate shared (READ_LT) or
   exclusive (WRITE_LT) byte-range lock on the byte-range it wishes to
   READ from or WRITE to.  If there is no appropriate lock, the server
   checks if there is a conflicting lock (which can be done by
   attempting to acquire the conflicting lock on behalf of the lock-
   owner, and if successful, release the lock after the READ or WRITE
   operation is done), and if there is, the server returns
   NFS4ERR_LOCKED.

   For Windows environments, byte-range locks are always mandatory, so
   the server always checks for byte-range locks during I/O requests.

   Thus, the LOCK operation does not need to distinguish between
   advisory and mandatory byte-range locks.  It is the server's
   processing of the READ and WRITE operations that introduces the
   distinction.

   Every stateid that is validly passed to READ, WRITE, or SETATTR, with
   the exception of special stateid values, defines an access mode for



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   the file (i.e., OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
   OPEN4_SHARE_ACCESS_BOTH).

   o  For stateids associated with opens, this is the mode defined by
      the original OPEN that caused the allocation of the OPEN stateid
      and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
      same open-owner/file pair.

   o  For stateids returned by byte-range LOCK operations, the
      appropriate mode is the access mode for the OPEN stateid
      associated with the lock set represented by the stateid.

   o  For delegation stateids, the access mode is based on the type of
      delegation.

   When a READ, WRITE, or SETATTR (that specifies the size attribute)
   operation is done, the operation is subject to checking against the
   access mode to verify that the operation is appropriate given the
   stateid with which the operation is associated.

   In the case of WRITE-type operations (i.e., WRITEs and SETATTRs that
   set size), the server MUST verify that the access mode allows writing
   and MUST return an NFS4ERR_OPENMODE error if it does not.  In the
   case of READ, the server may perform the corresponding check on the
   access mode, or it may choose to allow READ on OPENs for
   OPEN4_SHARE_ACCESS_WRITE, to accommodate clients whose WRITE
   implementation may unavoidably do reads (e.g., due to buffer cache
   constraints).  However, even if READs are allowed in these
   circumstances, the server MUST still check for locks that conflict
   with the READ (e.g., another OPEN specified OPEN4_SHARE_DENY_READ or
   OPEN4_SHARE_DENY_BOTH).  Note that a server that does enforce the
   access mode check on READs need not explicitly check for conflicting
   share reservations since the existence of OPEN for
   OPEN4_SHARE_ACCESS_READ guarantees that no conflicting share
   reservation can exist.

   The READ bypass special stateid (all bits of "other" and "seqid" set
   to one) indicates a desire to bypass locking checks.  The server MAY
   allow READ operations to bypass locking checks at the server, when
   this special stateid is used.  However, WRITE operations with this
   special stateid value MUST NOT bypass locking checks and are treated
   exactly the same as if a special stateid for anonymous state were
   used.

   A lock may not be granted while a READ or WRITE operation using one
   of the special stateids is being performed and the scope of the lock
   to be granted would conflict with the READ or WRITE operation.  This
   can occur when:



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   o  A mandatory byte-range lock is requested with a byte-range that
      conflicts with the byte-range of the READ or WRITE operation.  For
      the purposes of this paragraph, a conflict occurs when a shared
      lock is requested and a WRITE operation is being performed, or an
      exclusive lock is requested and either a READ or a WRITE operation
      is being performed.

   o  A share reservation is requested that denies reading and/or
      writing and the corresponding operation is being performed.

   o  A delegation is to be granted and the delegation type would
      prevent the I/O operation, i.e., READ and WRITE conflict with an
      OPEN_DELEGATE_WRITE delegation and WRITE conflicts with an
      OPEN_DELEGATE_READ delegation.

   When a client holds a delegation, it needs to ensure that the stateid
   sent conveys the association of operation with the delegation, to
   avoid the delegation from being avoidably recalled.  When the
   delegation stateid, a stateid open associated with that delegation,
   or a stateid representing byte-range locks derived from such an open
   is used, the server knows that the READ, WRITE, or SETATTR does not
   conflict with the delegation but is sent under the aegis of the
   delegation.  Even though it is possible for the server to determine
   from the client ID (via the session ID) that the client does in fact
   have a delegation, the server is not obliged to check this, so using
   a special stateid can result in avoidable recall of the delegation.

9.2.  Lock Ranges

   The protocol allows a lock-owner to request a lock with a byte-range
   and then either upgrade, downgrade, or unlock a sub-range of the
   initial lock, or a byte-range that overlaps -- fully or partially --
   either with that initial lock or a combination of a set of existing
   locks for the same lock-owner.  It is expected that this will be an
   uncommon type of request.  In any case, servers or server file
   systems may not be able to support sub-range lock semantics.  In the
   event that a server receives a locking request that represents a sub-
   range of current locking state for the lock-owner, the server is
   allowed to return the error NFS4ERR_LOCK_RANGE to signify that it
   does not support sub-range lock operations.  Therefore, the client
   should be prepared to receive this error and, if appropriate, report
   the error to the requesting application.

   The client is discouraged from combining multiple independent locking
   ranges that happen to be adjacent into a single request since the
   server may not support sub-range requests for reasons related to the
   recovery of byte-range locking state in the event of server failure.
   As discussed in Section 8.4.2, the server may employ certain



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   optimizations during recovery that work effectively only when the
   client's behavior during lock recovery is similar to the client's
   locking behavior prior to server failure.

9.3.  Upgrading and Downgrading Locks

   If a client has a WRITE_LT lock on a byte-range, it can request an
   atomic downgrade of the lock to a READ_LT lock via the LOCK
   operation, by setting the type to READ_LT.  If the server supports
   atomic downgrade, the request will succeed.  If not, it will return
   NFS4ERR_LOCK_NOTSUPP.  The client should be prepared to receive this
   error and, if appropriate, report the error to the requesting
   application.

   If a client has a READ_LT lock on a byte-range, it can request an
   atomic upgrade of the lock to a WRITE_LT lock via the LOCK operation
   by setting the type to WRITE_LT or WRITEW_LT.  If the server does not
   support atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the
   upgrade can be achieved without an existing conflict, the request
   will succeed.  Otherwise, the server will return either
   NFS4ERR_DENIED or NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is
   returned if the client sent the LOCK operation with the type set to
   WRITEW_LT and the server has detected a deadlock.  The client should
   be prepared to receive such errors and, if appropriate, report the
   error to the requesting application.

9.4.  Stateid Seqid Values and Byte-Range Locks

   When a LOCK or LOCKU operation is performed, the stateid returned has
   the same "other" value as the argument's stateid, and a "seqid" value
   that is incremented (relative to the argument's stateid) to reflect
   the occurrence of the LOCK or LOCKU operation.  The server MUST
   increment the value of the "seqid" field whenever there is any change
   to the locking status of any byte offset as described by any of the
   locks covered by the stateid.  A change in locking status includes a
   change from locked to unlocked or the reverse or a change from being
   locked for READ_LT to being locked for WRITE_LT or the reverse.

   When there is no such change, as, for example, when a range already
   locked for WRITE_LT is locked again for WRITE_LT, the server MAY
   increment the "seqid" value.

9.5.  Issues with Multiple Open-Owners

   When the same file is opened by multiple open-owners, a client will
   have multiple OPEN stateids for that file, each associated with a
   different open-owner.  In that case, there can be multiple LOCK and
   LOCKU requests for the same lock-owner sent using the different OPEN



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   stateids, and so a situation may arise in which there are multiple
   stateids, each representing byte-range locks on the same file and
   held by the same lock-owner but each associated with a different
   open-owner.

   In such a situation, the locking status of each byte (i.e., whether
   it is locked, the READ_LT or WRITE_LT type of the lock, and the lock-
   owner holding the lock) MUST reflect the last LOCK or LOCKU operation
   done for the lock-owner in question, independent of the stateid
   through which the request was sent.

   When a byte is locked by the lock-owner in question, the open-owner
   to which that byte-range lock is assigned SHOULD be that of the open-
   owner associated with the stateid through which the last LOCK of that
   byte was done.  When there is a change in the open-owner associated
   with locks for the stateid through which a LOCK or LOCKU was done,
   the "seqid" field of the stateid MUST be incremented, even if the
   locking, in terms of lock-owners has not changed.  When there is a
   change to the set of locked bytes associated with a different stateid
   for the same lock-owner, i.e., associated with a different open-
   owner, the "seqid" value for that stateid MUST NOT be incremented.

9.6.  Blocking Locks

   Some clients require the support of blocking locks.  While NFSv4.1
   provides a callback when a previously unavailable lock becomes
   available, this is an OPTIONAL feature and clients cannot depend on
   its presence.  Clients need to be prepared to continually poll for
   the lock.  This presents a fairness problem.  Two of the lock types,
   READW_LT and WRITEW_LT, are used to indicate to the server that the
   client is requesting a blocking lock.  When the callback is not used,
   the server should maintain an ordered list of pending blocking locks.
   When the conflicting lock is released, the server may wait for the
   period of time equal to lease_time for the first waiting client to
   re-request the lock.  After the lease period expires, the next
   waiting client request is allowed the lock.  Clients are required to
   poll at an interval sufficiently small that it is likely to acquire
   the lock in a timely manner.  The server is not required to maintain
   a list of pending blocked locks as it is used to increase fairness
   and not correct operation.  Because of the unordered nature of crash
   recovery, storing of lock state to stable storage would be required
   to guarantee ordered granting of blocking locks.

   Servers may also note the lock types and delay returning denial of
   the request to allow extra time for a conflicting lock to be
   released, allowing a successful return.  In this way, clients can
   avoid the burden of needless frequent polling for blocking locks.




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   The server should take care in the length of delay in the event the
   client retransmits the request.

   If a server receives a blocking LOCK operation, denies it, and then
   later receives a nonblocking request for the same lock, which is also
   denied, then it should remove the lock in question from its list of
   pending blocking locks.  Clients should use such a nonblocking
   request to indicate to the server that this is the last time they
   intend to poll for the lock, as may happen when the process
   requesting the lock is interrupted.  This is a courtesy to the
   server, to prevent it from unnecessarily waiting a lease period
   before granting other LOCK operations.  However, clients are not
   required to perform this courtesy, and servers must not depend on
   them doing so.  Also, clients must be prepared for the possibility
   that this final locking request will be accepted.

   When a server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK,
   that CB_NOTIFY_LOCK callbacks might be done for the current open
   file, the client should take notice of this, but, since this is a
   hint, cannot rely on a CB_NOTIFY_LOCK always being done.  A client
   may reasonably reduce the frequency with which it polls for a denied
   lock, since the greater latency that might occur is likely to be
   eliminated given a prompt callback, but it still needs to poll.  When
   it receives a CB_NOTIFY_LOCK, it should promptly try to obtain the
   lock, but it should be aware that other clients may be polling and
   that the server is under no obligation to reserve the lock for that
   particular client.

9.7.  Share Reservations

   A share reservation is a mechanism to control access to a file.  It
   is a separate and independent mechanism from byte-range locking.
   When a client opens a file, it sends an OPEN operation to the server
   specifying the type of access required (READ, WRITE, or BOTH) and the
   type of access to deny others (OPEN4_SHARE_DENY_NONE,
   OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
   OPEN4_SHARE_DENY_BOTH).  If the OPEN fails, the client will fail the
   application's open request.

   Pseudo-code definition of the semantics:











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           if (request.access == 0) {
             return (NFS4ERR_INVAL)
           } else {
             if ((request.access & file_state.deny)) ||
                (request.deny & file_state.access)) {
               return (NFS4ERR_SHARE_DENIED)
           }
           return (NFS4ERR_OK);

   When doing this checking of share reservations on OPEN, the current
   file_state used in the algorithm includes bits that reflect all
   current opens, including those for the open-owner making the new OPEN
   request.

   The constants used for the OPEN and OPEN_DOWNGRADE operations for the
   access and deny fields are as follows:

   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;

9.8.  OPEN/CLOSE Operations

   To provide correct share semantics, a client MUST use the OPEN
   operation to obtain the initial filehandle and indicate the desired
   access and what access, if any, to deny.  Even if the client intends
   to use a special stateid for anonymous state or READ bypass, it must
   still obtain the filehandle for the regular file with the OPEN
   operation so the appropriate share semantics can be applied.  Clients
   that do not have a deny mode built into their programming interfaces
   for opening a file should request a deny mode of
   OPEN4_SHARE_DENY_NONE.

   The OPEN operation with the CREATE flag also subsumes the CREATE
   operation for regular files as used in previous versions of the NFS
   protocol.  This allows a create with a share to be done atomically.

   The CLOSE operation removes all share reservations held by the open-
   owner on that file.  If byte-range locks are held, the client SHOULD
   release all locks before sending a CLOSE operation.  The server MAY
   free all outstanding locks on CLOSE, but some servers may not support
   the CLOSE of a file that still has byte-range locks held.  The server




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   MUST return failure, NFS4ERR_LOCKS_HELD, if any locks would exist
   after the CLOSE.

   The LOOKUP operation will return a filehandle without establishing
   any lock state on the server.  Without a valid stateid, the server
   will assume that the client has the least access.  For example, if
   one client opened a file with OPEN4_SHARE_DENY_BOTH and another
   client accesses the file via a filehandle obtained through LOOKUP,
   the second client could only read the file using the special read
   bypass stateid.  The second client could not WRITE the file at all
   because it would not have a valid stateid from OPEN and the special
   anonymous stateid would not be allowed access.

9.9.  Open Upgrade and Downgrade

   When an OPEN is done for a file and the open-owner for which the OPEN
   is being done already has the file open, the result is to upgrade the
   open file status maintained on the server to include the access and
   deny bits specified by the new OPEN as well as those for the existing
   OPEN.  The result is that there is one open file, as far as the
   protocol is concerned, and it includes the union of the access and
   deny bits for all of the OPEN requests completed.  The OPEN is
   represented by a single stateid whose "other" value matches that of
   the original open, and whose "seqid" value is incremented to reflect
   the occurrence of the upgrade.  The increment is required in cases in
   which the "upgrade" results in no change to the open mode (e.g., an
   OPEN is done for read when the existing open file is opened for
   OPEN4_SHARE_ACCESS_BOTH).  Only a single CLOSE will be done to reset
   the effects of both OPENs.  The client may use the stateid returned
   by the OPEN effecting the upgrade or with a stateid sharing the same
   "other" field and a seqid of zero, although care needs to be taken as
   far as upgrades that happen while the CLOSE is pending.  Note that
   the client, when sending the OPEN, may not know that the same file is
   in fact being opened.  The above only applies if both OPENs result in
   the OPENed object being designated by the same filehandle.

   When the server chooses to export multiple filehandles corresponding
   to the same file object and returns different filehandles on two
   different OPENs of the same file object, the server MUST NOT "OR"
   together the access and deny bits and coalesce the two open files.
   Instead, the server must maintain separate OPENs with separate
   stateids and will require separate CLOSEs to free them.

   When multiple open files on the client are merged into a single OPEN
   file object on the server, the close of one of the open files (on the
   client) may necessitate change of the access and deny status of the
   open file on the server.  This is because the union of the access and
   deny bits for the remaining opens may be smaller (i.e., a proper



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   subset) than previously.  The OPEN_DOWNGRADE operation is used to
   make the necessary change and the client should use it to update the
   server so that share reservation requests by other clients are
   handled properly.  The stateid returned has the same "other" field as
   that passed to the server.  The "seqid" value in the returned stateid
   MUST be incremented, even in situations in which there is no change
   to the access and deny bits for the file.

9.10.  Parallel OPENs

   Unlike the case of NFSv4.0, in which OPEN operations for the same
   open-owner are inherently serialized because of the owner-based
   seqid, multiple OPENs for the same open-owner may be done in
   parallel.  When clients do this, they may encounter situations in
   which, because of the existence of hard links, two OPEN operations
   may turn out to open the same file, with a later OPEN performed being
   an upgrade of the first, with this fact only visible to the client
   once the operations complete.

   In this situation, clients may determine the order in which the OPENs
   were performed by examining the stateids returned by the OPENs.
   Stateids that share a common value of the "other" field can be
   recognized as having opened the same file, with the order of the
   operations determinable from the order of the "seqid" fields, mod any
   possible wraparound of the 32-bit field.

   When the possibility exists that the client will send multiple OPENs
   for the same open-owner in parallel, it may be the case that an open
   upgrade may happen without the client knowing beforehand that this
   could happen.  Because of this possibility, CLOSEs and
   OPEN_DOWNGRADEs should generally be sent with a non-zero seqid in the
   stateid, to avoid the possibility that the status change associated
   with an open upgrade is not inadvertently lost.

9.11.  Reclaim of Open and Byte-Range Locks

   Special forms of the LOCK and OPEN operations are provided when it is
   necessary to re-establish byte-range locks or opens after a server
   failure.

   o  To reclaim existing opens, an OPEN operation is performed using a
      CLAIM_PREVIOUS.  Because the client, in this type of situation,
      will have already opened the file and have the filehandle of the
      target file, this operation requires that the current filehandle
      be the target file, rather than a directory, and no file name is
      specified.





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   o  To reclaim byte-range locks, a LOCK operation with the reclaim
      parameter set to true is used.

   Reclaims of opens associated with delegations are discussed in
   Section 10.2.1.

10.  Client-Side Caching

   Client-side caching of data, of file attributes, and of file names is
   essential to providing good performance with the NFS protocol.
   Providing distributed cache coherence is a difficult problem, and
   previous versions of the NFS protocol have not attempted it.
   Instead, several NFS client implementation techniques have been used
   to reduce the problems that a lack of coherence poses for users.
   These techniques have not been clearly defined by earlier protocol
   specifications, and it is often unclear what is valid or invalid
   client behavior.

   The NFSv4.1 protocol uses many techniques similar to those that have
   been used in previous protocol versions.  The NFSv4.1 protocol does
   not provide distributed cache coherence.  However, it defines a more
   limited set of caching guarantees to allow locks and share
   reservations to be used without destructive interference from client-
   side caching.

   In addition, the NFSv4.1 protocol introduces a delegation mechanism,
   which allows many decisions normally made by the server to be made
   locally by clients.  This mechanism provides efficient support of the
   common cases where sharing is infrequent or where sharing is read-
   only.

10.1.  Performance Challenges for Client-Side Caching

   Caching techniques used in previous versions of the NFS protocol have
   been successful in providing good performance.  However, several
   scalability challenges can arise when those techniques are used with
   very large numbers of clients.  This is particularly true when
   clients are geographically distributed, which classically increases
   the latency for cache revalidation requests.

   The previous versions of the NFS protocol repeat their file data
   cache validation requests at the time the file is opened.  This
   behavior can have serious performance drawbacks.  A common case is
   one in which a file is only accessed by a single client.  Therefore,
   sharing is infrequent.

   In this case, repeated references to the server to find that no
   conflicts exist are expensive.  A better option with regards to



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   performance is to allow a client that repeatedly opens a file to do
   so without reference to the server.  This is done until potentially
   conflicting operations from another client actually occur.

   A similar situation arises in connection with byte-range locking.
   Sending LOCK and LOCKU operations as well as the READ and WRITE
   operations necessary to make data caching consistent with the locking
   semantics (see Section 10.3.2) can severely limit performance.  When
   locking is used to provide protection against infrequent conflicts, a
   large penalty is incurred.  This penalty may discourage the use of
   byte-range locking by applications.

   The NFSv4.1 protocol provides more aggressive caching strategies with
   the following design goals:

   o  Compatibility with a large range of server semantics.

   o  Providing the same caching benefits as previous versions of the
      NFS protocol when unable to support the more aggressive model.

   o  Requirements for aggressive caching are organized so that a large
      portion of the benefit can be obtained even when not all of the
      requirements can be met.

   The appropriate requirements for the server are discussed in later
   sections in which specific forms of caching are covered (see
   Section 10.4).

10.2.  Delegation and Callbacks

   Recallable delegation of server responsibilities for a file to a
   client improves performance by avoiding repeated requests to the
   server in the absence of inter-client conflict.  With the use of a
   "callback" RPC from server to client, a server recalls delegated
   responsibilities when another client engages in sharing of a
   delegated file.

   A delegation is passed from the server to the client, specifying the
   object of the delegation and the type of delegation.  There are
   different types of delegations, but each type contains a stateid to
   be used to represent the delegation when performing operations that
   depend on the delegation.  This stateid is similar to those
   associated with locks and share reservations but differs in that the
   stateid for a delegation is associated with a client ID and may be
   used on behalf of all the open-owners for the given client.  A
   delegation is made to the client as a whole and not to any specific
   process or thread of control within it.




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   The backchannel is established by CREATE_SESSION and
   BIND_CONN_TO_SESSION, and the client is required to maintain it.
   Because the backchannel may be down, even temporarily, correct
   protocol operation does not depend on them.  Preliminary testing of
   backchannel functionality by means of a CB_COMPOUND procedure with a
   single operation, CB_SEQUENCE, can be used to check the continuity of
   the backchannel.  A server avoids delegating responsibilities until
   it has determined that the backchannel exists.  Because the granting
   of a delegation is always conditional upon the absence of conflicting
   access, clients MUST NOT assume that a delegation will be granted and
   they MUST always be prepared for OPENs, WANT_DELEGATIONs, and
   GET_DIR_DELEGATIONs to be processed without any delegations being
   granted.

   Unlike locks, an operation by a second client to a delegated file
   will cause the server to recall a delegation through a callback.  For
   individual operations, we will describe, under IMPLEMENTATION, when
   such operations are required to effect a recall.  A number of points
   should be noted, however.

   o  The server is free to recall a delegation whenever it feels it is
      desirable and may do so even if no operations requiring recall are
      being done.

   o  Operations done outside the NFSv4.1 protocol, due to, for example,
      access by other protocols, or by local access, also need to result
      in delegation recall when they make analogous changes to file
      system data.  What is crucial is if the change would invalidate
      the guarantees provided by the delegation.  When this is possible,
      the delegation needs to be recalled and MUST be returned or
      revoked before allowing the operation to proceed.

   o  The semantics of the file system are crucial in defining when
      delegation recall is required.  If a particular change within a
      specific implementation causes change to a file attribute, then
      delegation recall is required, whether that operation has been
      specifically listed as requiring delegation recall.  Again, what
      is critical is whether the guarantees provided by the delegation
      are being invalidated.

   Despite those caveats, the implementation sections for a number of
   operations describe situations in which delegation recall would be
   required under some common circumstances:

   o  For GETATTR, see Section 18.7.4.

   o  For OPEN, see Section 18.16.4.




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   o  For READ, see Section 18.22.4.

   o  For REMOVE, see Section 18.25.4.

   o  For RENAME, see Section 18.26.4.

   o  For SETATTR, see Section 18.30.4.

   o  For WRITE, see Section 18.32.4.

   On recall, the client holding the delegation needs to flush modified
   state (such as modified data) to the server and return the
   delegation.  The conflicting request will not be acted on until the
   recall is complete.  The recall is considered complete when the
   client returns the delegation or the server times its wait for the
   delegation to be returned and revokes the delegation as a result of
   the timeout.  In the interim, the server will either delay responding
   to conflicting requests or respond to them with NFS4ERR_DELAY.
   Following the resolution of the recall, the server has the
   information necessary to grant or deny the second client's request.

   At the time the client receives a delegation recall, it may have
   substantial state that needs to be flushed to the server.  Therefore,
   the server should allow sufficient time for the delegation to be
   returned since it may involve numerous RPCs to the server.  If the
   server is able to determine that the client is diligently flushing
   state to the server as a result of the recall, the server may extend
   the usual time allowed for a recall.  However, the time allowed for
   recall completion should not be unbounded.

   An example of this is when responsibility to mediate opens on a given
   file is delegated to a client (see Section 10.4).  The server will
   not know what opens are in effect on the client.  Without this
   knowledge, the server will be unable to determine if the access and
   deny states for the file allow any particular open until the
   delegation for the file has been returned.

   A client failure or a network partition can result in failure to
   respond to a recall callback.  In this case, the server will revoke
   the delegation, which in turn will render useless any modified state
   still on the client.

10.2.1.  Delegation Recovery

   There are three situations that delegation recovery needs to deal
   with:

   o  client restart



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   o  server restart

   o  network partition (full or backchannel-only)

   In the event the client restarts, the failure to renew the lease will
   result in the revocation of byte-range locks and share reservations.
   Delegations, however, may be treated a bit differently.

   There will be situations in which delegations will need to be re-
   established after a client restarts.  The reason for this is that the
   client may have file data stored locally and this data was associated
   with the previously held delegations.  The client will need to re-
   establish the appropriate file state on the server.

   To allow for this type of client recovery, the server MAY extend the
   period for delegation recovery beyond the typical lease expiration
   period.  This implies that requests from other clients that conflict
   with these delegations will need to wait.  Because the normal recall
   process may require significant time for the client to flush changed
   state to the server, other clients need be prepared for delays that
   occur because of a conflicting delegation.  This longer interval
   would increase the window for clients to restart and consult stable
   storage so that the delegations can be reclaimed.  For OPEN
   delegations, such delegations are reclaimed using OPEN with a claim
   type of CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH (see Sections 10.5
   and 18.16 for discussion of OPEN delegation and the details of OPEN,
   respectively).

   A server MAY support claim types of CLAIM_DELEGATE_PREV and
   CLAIM_DELEG_PREV_FH, and if it does, it MUST NOT remove delegations
   upon a CREATE_SESSION that confirm a client ID created by
   EXCHANGE_ID.  Instead, the server MUST, for a period of time no less
   than that of the value of the lease_time attribute, maintain the
   client's delegations to allow time for the client to send
   CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH requests.  The server
   that supports CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH MUST
   support the DELEGPURGE operation.

   When the server restarts, delegations are reclaimed (using the OPEN
   operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
   locks and share reservations.  However, there is a slight semantic
   difference.  In the normal case, if the server decides that a
   delegation should not be granted, it performs the requested action
   (e.g., OPEN) without granting any delegation.  For reclaim, the
   server grants the delegation but a special designation is applied so
   that the client treats the delegation as having been granted but
   recalled by the server.  Because of this, the client has the duty to
   write all modified state to the server and then return the



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   delegation.  This process of handling delegation reclaim reconciles
   three principles of the NFSv4.1 protocol:

   o  Upon reclaim, a client reporting resources assigned to it by an
      earlier server instance must be granted those resources.

   o  The server has unquestionable authority to determine whether
      delegations are to be granted and, once granted, whether they are
      to be continued.

   o  The use of callbacks should not be depended upon until the client
      has proven its ability to receive them.

   When a client needs to reclaim a delegation and there is no
   associated open, the client may use the CLAIM_PREVIOUS variant of the
   WANT_DELEGATION operation.  However, since the server is not required
   to support this operation, an alternative is to reclaim via a dummy
   OPEN together with the delegation using an OPEN of type
   CLAIM_PREVIOUS.  The dummy open file can be released using a CLOSE to
   re-establish the original state to be reclaimed, a delegation without
   an associated open.

   When a client has more than a single open associated with a
   delegation, state for those additional opens can be established using
   OPEN operations of type CLAIM_DELEGATE_CUR.  When these are used to
   establish opens associated with reclaimed delegations, the server
   MUST allow them when made within the grace period.

   When a network partition occurs, delegations are subject to freeing
   by the server when the lease renewal period expires.  This is similar
   to the behavior for locks and share reservations.  For delegations,
   however, the server may extend the period in which conflicting
   requests are held off.  Eventually, the occurrence of a conflicting
   request from another client will cause revocation of the delegation.
   A loss of the backchannel (e.g., by later network configuration
   change) will have the same effect.  A recall request will fail and
   revocation of the delegation will result.

   A client normally finds out about revocation of a delegation when it
   uses a stateid associated with a delegation and receives one of the
   errors NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or
   NFS4ERR_DELEG_REVOKED.  It also may find out about delegation
   revocation after a client restart when it attempts to reclaim a
   delegation and receives that same error.  Note that in the case of a
   revoked OPEN_DELEGATE_WRITE delegation, there are issues because data
   may have been modified by the client whose delegation is revoked and
   separately by other clients.  See Section 10.5.1 for a discussion of
   such issues.  Note also that when delegations are revoked,



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   information about the revoked delegation will be written by the
   server to stable storage (as described in Section 8.4.3).  This is
   done to deal with the case in which a server restarts after revoking
   a delegation but before the client holding the revoked delegation is
   notified about the revocation.

10.3.  Data Caching

   When applications share access to a set of files, they need to be
   implemented so as to take account of the possibility of conflicting
   access by another application.  This is true whether the applications
   in question execute on different clients or reside on the same
   client.

   Share reservations and byte-range locks are the facilities the
   NFSv4.1 protocol provides to allow applications to coordinate access
   by using mutual exclusion facilities.  The NFSv4.1 protocol's data
   caching must be implemented such that it does not invalidate the
   assumptions on which those using these facilities depend.

10.3.1.  Data Caching and OPENs

   In order to avoid invalidating the sharing assumptions on which
   applications rely, NFSv4.1 clients should not provide cached data to
   applications or modify it on behalf of an application when it would
   not be valid to obtain or modify that same data via a READ or WRITE
   operation.

   Furthermore, in the absence of an OPEN delegation (see Section 10.4),
   two additional rules apply.  Note that these rules are obeyed in
   practice by many NFSv3 clients.

   o  First, cached data present on a client must be revalidated after
      doing an OPEN.  Revalidating means that the client fetches the
      change attribute from the server, compares it with the cached
      change attribute, and if different, declares the cached data (as
      well as the cached attributes) as invalid.  This is to ensure that
      the data for the OPENed file is still correctly reflected in the
      client's cache.  This validation must be done at least when the
      client's OPEN operation includes a deny of OPEN4_SHARE_DENY_WRITE
      or OPEN4_SHARE_DENY_BOTH, thus terminating a period in which other
      clients may have had the opportunity to open the file with
      OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH access.  Clients
      may choose to do the revalidation more often (i.e., at OPENs
      specifying a deny mode of OPEN4_SHARE_DENY_NONE) to parallel the
      NFSv3 protocol's practice for the benefit of users assuming this
      degree of cache revalidation.




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      Since the change attribute is updated for data and metadata
      modifications, some client implementors may be tempted to use the
      time_modify attribute and not the change attribute to validate
      cached data, so that metadata changes do not spuriously invalidate
      clean data.  The implementor is cautioned in this approach.  The
      change attribute is guaranteed to change for each update to the
      file, whereas time_modify is guaranteed to change only at the
      granularity of the time_delta attribute.  Use by the client's data
      cache validation logic of time_modify and not change runs the risk
      of the client incorrectly marking stale data as valid.  Thus, any
      cache validation approach by the client MUST include the use of
      the change attribute.

   o  Second, modified data must be flushed to the server before closing
      a file OPENed for OPEN4_SHARE_ACCESS_WRITE.  This is complementary
      to the first rule.  If the data is not flushed at CLOSE, the
      revalidation done after the client OPENs a file is unable to
      achieve its purpose.  The other aspect to flushing the data before
      close is that the data must be committed to stable storage, at the
      server, before the CLOSE operation is requested by the client.  In
      the case of a server restart and a CLOSEd file, it may not be
      possible to retransmit the data to be written to the file, hence,
      this requirement.

10.3.2.  Data Caching and File Locking

   For those applications that choose to use byte-range locking instead
   of share reservations to exclude inconsistent file access, there is
   an analogous set of constraints that apply to client-side data
   caching.  These rules are effective only if the byte-range locking is
   used in a way that matches in an equivalent way the actual READ and
   WRITE operations executed.  This is as opposed to byte-range locking
   that is based on pure convention.  For example, it is possible to
   manipulate a two-megabyte file by dividing the file into two one-
   megabyte ranges and protecting access to the two byte-ranges by byte-
   range locks on bytes zero and one.  A WRITE_LT lock on byte zero of
   the file would represent the right to perform READ and WRITE
   operations on the first byte-range.  A WRITE_LT lock on byte one of
   the file would represent the right to perform READ and WRITE
   operations on the second byte-range.  As long as all applications
   manipulating the file obey this convention, they will work on a local
   file system.  However, they may not work with the NFSv4.1 protocol
   unless clients refrain from data caching.

   The rules for data caching in the byte-range locking environment are:

   o  First, when a client obtains a byte-range lock for a particular
      byte-range, the data cache corresponding to that byte-range (if



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      any cache data exists) must be revalidated.  If the change
      attribute indicates that the file may have been updated since the
      cached data was obtained, the client must flush or invalidate the
      cached data for the newly locked byte-range.  A client might
      choose to invalidate all of the non-modified cached data that it
      has for the file, but the only requirement for correct operation
      is to invalidate all of the data in the newly locked byte-range.

   o  Second, before releasing a WRITE_LT lock for a byte-range, all
      modified data for that byte-range must be flushed to the server.
      The modified data must also be written to stable storage.

   Note that flushing data to the server and the invalidation of cached
   data must reflect the actual byte-ranges locked or unlocked.
   Rounding these up or down to reflect client cache block boundaries
   will cause problems if not carefully done.  For example, writing a
   modified block when only half of that block is within an area being
   unlocked may cause invalid modification to the byte-range outside the
   unlocked area.  This, in turn, may be part of a byte-range locked by
   another client.  Clients can avoid this situation by synchronously
   performing portions of WRITE operations that overlap that portion
   (initial or final) that is not a full block.  Similarly, invalidating
   a locked area that is not an integral number of full buffer blocks
   would require the client to read one or two partial blocks from the
   server if the revalidation procedure shows that the data that the
   client possesses may not be valid.

   The data that is written to the server as a prerequisite to the
   unlocking of a byte-range must be written, at the server, to stable
   storage.  The client may accomplish this either with synchronous
   writes or by following asynchronous writes with a COMMIT operation.
   This is required because retransmission of the modified data after a
   server restart might conflict with a lock held by another client.

   A client implementation may choose to accommodate applications that
   use byte-range locking in non-standard ways (e.g., using a byte-range
   lock as a global semaphore) by flushing to the server more data upon
   a LOCKU than is covered by the locked range.  This may include
   modified data within files other than the one for which the unlocks
   are being done.  In such cases, the client must not interfere with
   applications whose READs and WRITEs are being done only within the
   bounds of byte-range locks that the application holds.  For example,
   an application locks a single byte of a file and proceeds to write
   that single byte.  A client that chose to handle a LOCKU by flushing
   all modified data to the server could validly write that single byte
   in response to an unrelated LOCKU operation.  However, it would not
   be valid to write the entire block in which that single written byte
   was located since it includes an area that is not locked and might be



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   locked by another client.  Client implementations can avoid this
   problem by dividing files with modified data into those for which all
   modifications are done to areas covered by an appropriate byte-range
   lock and those for which there are modifications not covered by a
   byte-range lock.  Any writes done for the former class of files must
   not include areas not locked and thus not modified on the client.

10.3.3.  Data Caching and Mandatory File Locking

   Client-side data caching needs to respect mandatory byte-range
   locking when it is in effect.  The presence of mandatory byte-range
   locking for a given file is indicated when the client gets back
   NFS4ERR_LOCKED from a READ or WRITE operation on a file for which it
   has an appropriate share reservation.  When mandatory locking is in
   effect for a file, the client must check for an appropriate byte-
   range lock for data being read or written.  If a byte-range lock
   exists for the range being read or written, the client may satisfy
   the request using the client's validated cache.  If an appropriate
   byte-range lock is not held for the range of the read or write, the
   read or write request must not be satisfied by the client's cache and
   the request must be sent to the server for processing.  When a read
   or write request partially overlaps a locked byte-range, the request
   should be subdivided into multiple pieces with each byte-range
   (locked or not) treated appropriately.

10.3.4.  Data Caching and File Identity

   When clients cache data, the file data needs to be organized
   according to the file system object to which the data belongs.  For
   NFSv3 clients, the typical practice has been to assume for the
   purpose of caching that distinct filehandles represent distinct file
   system objects.  The client then has the choice to organize and
   maintain the data cache on this basis.

   In the NFSv4.1 protocol, there is now the possibility to have
   significant deviations from a "one filehandle per object" model
   because a filehandle may be constructed on the basis of the object's
   pathname.  Therefore, clients need a reliable method to determine if
   two filehandles designate the same file system object.  If clients
   were simply to assume that all distinct filehandles denote distinct
   objects and proceed to do data caching on this basis, caching
   inconsistencies would arise between the distinct client-side objects
   that mapped to the same server-side object.

   By providing a method to differentiate filehandles, the NFSv4.1
   protocol alleviates a potential functional regression in comparison
   with the NFSv3 protocol.  Without this method, caching
   inconsistencies within the same client could occur, and this has not



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   been present in previous versions of the NFS protocol.  Note that it
   is possible to have such inconsistencies with applications executing
   on multiple clients, but that is not the issue being addressed here.

   For the purposes of data caching, the following steps allow an
   NFSv4.1 client to determine whether two distinct filehandles denote
   the same server-side object:

   o  If GETATTR directed to two filehandles returns different values of
      the fsid attribute, then the filehandles represent distinct
      objects.

   o  If GETATTR for any file with an fsid that matches the fsid of the
      two filehandles in question returns a unique_handles attribute
      with a value of TRUE, then the two objects are distinct.

   o  If GETATTR directed to the two filehandles does not return the
      fileid attribute for both of the handles, then it cannot be
      determined whether the two objects are the same.  Therefore,
      operations that depend on that knowledge (e.g., client-side data
      caching) cannot be done reliably.  Note that if GETATTR does not
      return the fileid attribute for both filehandles, it will return
      it for neither of the filehandles, since the fsid for both
      filehandles is the same.

   o  If GETATTR directed to the two filehandles returns different
      values for the fileid attribute, then they are distinct objects.

   o  Otherwise, they are the same object.

10.4.  Open Delegation

   When a file is being OPENed, the server may delegate further handling
   of opens and closes for that file to the opening client.  Any such
   delegation is recallable since the circumstances that allowed for the
   delegation are subject to change.  In particular, if the server
   receives a conflicting OPEN from another client, the server must
   recall the delegation before deciding whether the OPEN from the other
   client may be granted.  Making a delegation is up to the server, and
   clients should not assume that any particular OPEN either will or
   will not result in an OPEN delegation.  The following is a typical
   set of conditions that servers might use in deciding whether an OPEN
   should be delegated:

   o  The client must be able to respond to the server's callback
      requests.  If a backchannel has been established, the server will
      send a CB_COMPOUND request, containing a single operation,
      CB_SEQUENCE, for a test of backchannel availability.



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   o  The client must have responded properly to previous recalls.

   o  There must be no current OPEN conflicting with the requested
      delegation.

   o  There should be no current delegation that conflicts with the
      delegation being requested.

   o  The probability of future conflicting open requests should be low
      based on the recent history of the file.

   o  The existence of any server-specific semantics of OPEN/CLOSE that
      would make the required handling incompatible with the prescribed
      handling that the delegated client would apply (see below).

   There are two types of OPEN delegations: OPEN_DELEGATE_READ and
   OPEN_DELEGATE_WRITE.  An OPEN_DELEGATE_READ delegation allows a
   client to handle, on its own, requests to open a file for reading
   that do not deny OPEN4_SHARE_ACCESS_READ access to others.  Multiple
   OPEN_DELEGATE_READ delegations may be outstanding simultaneously and
   do not conflict.  An OPEN_DELEGATE_WRITE delegation allows the client
   to handle, on its own, all opens.  Only OPEN_DELEGATE_WRITE
   delegation may exist for a given file at a given time, and it is
   inconsistent with any OPEN_DELEGATE_READ delegations.

   When a client has an OPEN_DELEGATE_READ delegation, it is assured
   that neither the contents, the attributes (with the exception of
   time_access), nor the names of any links to the file will change
   without its knowledge, so long as the delegation is held.  When a
   client has an OPEN_DELEGATE_WRITE delegation, it may modify the file
   data locally since no other client will be accessing the file's data.
   The client holding an OPEN_DELEGATE_WRITE delegation may only locally
   affect file attributes that are intimately connected with the file
   data: size, change, time_access, time_metadata, and time_modify.  All
   other attributes must be reflected on the server.

   When a client has an OPEN delegation, it does not need to send OPENs
   or CLOSEs to the server.  Instead, the client may update the
   appropriate status internally.  For an OPEN_DELEGATE_READ delegation,
   opens that cannot be handled locally (opens that are for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH or that deny
   OPEN4_SHARE_ACCESS_READ access) must be sent to the server.

   When an OPEN delegation is made, the reply to the OPEN contains an
   OPEN delegation structure that specifies the following:

   o  the type of delegation (OPEN_DELEGATE_READ or
      OPEN_DELEGATE_WRITE).



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   o  space limitation information to control flushing of data on close
      (OPEN_DELEGATE_WRITE delegation only; see Section 10.4.1)

   o  an nfsace4 specifying read and write permissions

   o  a stateid to represent the delegation

   The delegation stateid is separate and distinct from the stateid for
   the OPEN proper.  The standard stateid, unlike the delegation
   stateid, is associated with a particular lock-owner and will continue
   to be valid after the delegation is recalled and the file remains
   open.

   When a request internal to the client is made to open a file and an
   OPEN delegation is in effect, it will be accepted or rejected solely
   on the basis of the following conditions.  Any requirement for other
   checks to be made by the delegate should result in the OPEN
   delegation being denied so that the checks can be made by the server
   itself.

   o  The access and deny bits for the request and the file as described
      in Section 9.7.

   o  The read and write permissions as determined below.

   The nfsace4 passed with delegation can be used to avoid frequent
   ACCESS calls.  The permission check should be as follows:

   o  If the nfsace4 indicates that the open may be done, then it should
      be granted without reference to the server.

   o  If the nfsace4 indicates that the open may not be done, then an
      ACCESS request must be sent to the server to obtain the definitive
      answer.

   The server may return an nfsace4 that is more restrictive than the
   actual ACL of the file.  This includes an nfsace4 that specifies
   denial of all access.  Note that some common practices such as
   mapping the traditional user "root" to the user "nobody" (see
   Section 5.9) may make it incorrect to return the actual ACL of the
   file in the delegation response.

   The use of a delegation together with various other forms of caching
   creates the possibility that no server authentication and
   authorization will ever be performed for a given user since all of
   the user's requests might be satisfied locally.  Where the client is
   depending on the server for authentication and authorization, the
   client should be sure authentication and authorization occurs for



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   each user by use of the ACCESS operation.  This should be the case
   even if an ACCESS operation would not be required otherwise.  As
   mentioned before, the server may enforce frequent authentication by
   returning an nfsace4 denying all access with every OPEN delegation.

10.4.1.  Open Delegation and Data Caching

   An OPEN delegation allows much of the message overhead associated
   with the opening and closing files to be eliminated.  An open when an
   OPEN delegation is in effect does not require that a validation
   message be sent to the server.  The continued endurance of the
   "OPEN_DELEGATE_READ delegation" provides a guarantee that no OPEN for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, and thus no write,
   has occurred.  Similarly, when closing a file opened for
   OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH and if an
   OPEN_DELEGATE_WRITE delegation is in effect, the data written does
   not have to be written to the server until the OPEN delegation is
   recalled.  The continued endurance of the OPEN delegation provides a
   guarantee that no open, and thus no READ or WRITE, has been done by
   another client.

   For the purposes of OPEN delegation, READs and WRITEs done without an
   OPEN are treated as the functional equivalents of a corresponding
   type of OPEN.  Although a client SHOULD NOT use special stateids when
   an open exists, delegation handling on the server can use the client
   ID associated with the current session to determine if the operation
   has been done by the holder of the delegation (in which case, no
   recall is necessary) or by another client (in which case, the
   delegation must be recalled and I/O not proceed until the delegation
   is recalled or revoked).

   With delegations, a client is able to avoid writing data to the
   server when the CLOSE of a file is serviced.  The file close system
   call is the usual point at which the client is notified of a lack of
   stable storage for the modified file data generated by the
   application.  At the close, file data is written to the server and,
   through normal accounting, the server is able to determine if the
   available file system space for the data has been exceeded (i.e., the
   server returns NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting
   includes quotas.  The introduction of delegations requires that an
   alternative method be in place for the same type of communication to
   occur between client and server.

   In the delegation response, the server provides either the limit of
   the size of the file or the number of modified blocks and associated
   block size.  The server must ensure that the client will be able to
   write modified data to the server of a size equal to that provided in
   the original delegation.  The server must make this assurance for all



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   outstanding delegations.  Therefore, the server must be careful in
   its management of available space for new or modified data, taking
   into account available file system space and any applicable quotas.
   The server can recall delegations as a result of managing the
   available file system space.  The client should abide by the server's
   state space limits for delegations.  If the client exceeds the stated
   limits for the delegation, the server's behavior is undefined.

   Based on server conditions, quotas, or available file system space,
   the server may grant OPEN_DELEGATE_WRITE delegations with very
   restrictive space limitations.  The limitations may be defined in a
   way that will always force modified data to be flushed to the server
   on close.

   With respect to authentication, flushing modified data to the server
   after a CLOSE has occurred may be problematic.  For example, the user
   of the application may have logged off the client, and unexpired
   authentication credentials may not be present.  In this case, the
   client may need to take special care to ensure that local unexpired
   credentials will in fact be available.  This may be accomplished by
   tracking the expiration time of credentials and flushing data well in
   advance of their expiration or by making private copies of
   credentials to assure their availability when needed.

10.4.2.  Open Delegation and File Locks

   When a client holds an OPEN_DELEGATE_WRITE delegation, lock
   operations are performed locally.  This includes those required for
   mandatory byte-range locking.  This can be done since the delegation
   implies that there can be no conflicting locks.  Similarly, all of
   the revalidations that would normally be associated with obtaining
   locks and the flushing of data associated with the releasing of locks
   need not be done.

   When a client holds an OPEN_DELEGATE_READ delegation, lock operations
   are not performed locally.  All lock operations, including those
   requesting non-exclusive locks, are sent to the server for
   resolution.

10.4.3.  Handling of CB_GETATTR

   The server needs to employ special handling for a GETATTR where the
   target is a file that has an OPEN_DELEGATE_WRITE delegation in
   effect.  The reason for this is that the client holding the
   OPEN_DELEGATE_WRITE delegation may have modified the data, and the
   server needs to reflect this change to the second client that
   submitted the GETATTR.  Therefore, the client holding the
   OPEN_DELEGATE_WRITE delegation needs to be interrogated.  The server



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   will use the CB_GETATTR operation.  The only attributes that the
   server can reliably query via CB_GETATTR are size and change.

   Since CB_GETATTR is being used to satisfy another client's GETATTR
   request, the server only needs to know if the client holding the
   delegation has a modified version of the file.  If the client's copy
   of the delegated file is not modified (data or size), the server can
   satisfy the second client's GETATTR request from the attributes
   stored locally at the server.  If the file is modified, the server
   only needs to know about this modified state.  If the server
   determines that the file is currently modified, it will respond to
   the second client's GETATTR as if the file had been modified locally
   at the server.

   Since the form of the change attribute is determined by the server
   and is opaque to the client, the client and server need to agree on a
   method of communicating the modified state of the file.  For the size
   attribute, the client will report its current view of the file size.
   For the change attribute, the handling is more involved.

   For the client, the following steps will be taken when receiving an
   OPEN_DELEGATE_WRITE delegation:

   o  The value of the change attribute will be obtained from the server
      and cached.  Let this value be represented by c.

   o  The client will create a value greater than c that will be used
      for communicating that modified data is held at the client.  Let
      this value be represented by d.

   o  When the client is queried via CB_GETATTR for the change
      attribute, it checks to see if it holds modified data.  If the
      file is modified, the value d is returned for the change attribute
      value.  If this file is not currently modified, the client returns
      the value c for the change attribute.

   For simplicity of implementation, the client MAY for each CB_GETATTR
   return the same value d.  This is true even if, between successive
   CB_GETATTR operations, the client again modifies the file's data or
   metadata in its cache.  The client can return the same value because
   the only requirement is that the client be able to indicate to the
   server that the client holds modified data.  Therefore, the value of
   d may always be c + 1.

   While the change attribute is opaque to the client in the sense that
   it has no idea what units of time, if any, the server is counting
   change with, it is not opaque in that the client has to treat it as
   an unsigned integer, and the server has to be able to see the results



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   of the client's changes to that integer.  Therefore, the server MUST
   encode the change attribute in network order when sending it to the
   client.  The client MUST decode it from network order to its native
   order when receiving it, and the client MUST encode it in network
   order when sending it to the server.  For this reason, change is
   defined as an unsigned integer rather than an opaque array of bytes.

   For the server, the following steps will be taken when providing an
   OPEN_DELEGATE_WRITE delegation:

   o  Upon providing an OPEN_DELEGATE_WRITE delegation, the server will
      cache a copy of the change attribute in the data structure it uses
      to record the delegation.  Let this value be represented by sc.

   o  When a second client sends a GETATTR operation on the same file to
      the server, the server obtains the change attribute from the first
      client.  Let this value be cc.

   o  If the value cc is equal to sc, the file is not modified and the
      server returns the current values for change, time_metadata, and
      time_modify (for example) to the second client.

   o  If the value cc is NOT equal to sc, the file is currently modified
      at the first client and most likely will be modified at the server
      at a future time.  The server then uses its current time to
      construct attribute values for time_metadata and time_modify.  A
      new value of sc, which we will call nsc, is computed by the
      server, such that nsc >= sc + 1.  The server then returns the
      constructed time_metadata, time_modify, and nsc values to the
      requester.  The server replaces sc in the delegation record with
      nsc.  To prevent the possibility of time_modify, time_metadata,
      and change from appearing to go backward (which would happen if
      the client holding the delegation fails to write its modified data
      to the server before the delegation is revoked or returned), the
      server SHOULD update the file's metadata record with the
      constructed attribute values.  For reasons of reasonable
      performance, committing the constructed attribute values to stable
      storage is OPTIONAL.

   As discussed earlier in this section, the client MAY return the same
   cc value on subsequent CB_GETATTR calls, even if the file was
   modified in the client's cache yet again between successive
   CB_GETATTR calls.  Therefore, the server must assume that the file
   has been modified yet again, and MUST take care to ensure that the
   new nsc it constructs and returns is greater than the previous nsc it
   returned.  An example implementation's delegation record would
   satisfy this mandate by including a boolean field (let us call it
   "modified") that is set to FALSE when the delegation is granted, and



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   an sc value set at the time of grant to the change attribute value.
   The modified field would be set to TRUE the first time cc != sc, and
   would stay TRUE until the delegation is returned or revoked.  The
   processing for constructing nsc, time_modify, and time_metadata would
   use this pseudo code:

       if (!modified) {
           do CB_GETATTR for change and size;

           if (cc != sc)
               modified = TRUE;
       } else {
           do CB_GETATTR for size;
       }

       if (modified) {
           sc = sc + 1;
           time_modify = time_metadata = current_time;
           update sc, time_modify, time_metadata into file's metadata;
       }


   This would return to the client (that sent GETATTR) the attributes it
   requested, but make sure size comes from what CB_GETATTR returned.
   The server would not update the file's metadata with the client's
   modified size.

   In the case that the file attribute size is different than the
   server's current value, the server treats this as a modification
   regardless of the value of the change attribute retrieved via
   CB_GETATTR and responds to the second client as in the last step.

   This methodology resolves issues of clock differences between client
   and server and other scenarios where the use of CB_GETATTR break
   down.

   It should be noted that the server is under no obligation to use
   CB_GETATTR, and therefore the server MAY simply recall the delegation
   to avoid its use.

10.4.4.  Recall of Open Delegation

   The following events necessitate recall of an OPEN delegation:

   o  potentially conflicting OPEN request (or a READ or WRITE operation
      done with a special stateid)

   o  SETATTR sent by another client



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   o  REMOVE request for the file

   o  RENAME request for the file as either the source or target of the
      RENAME

   Whether a RENAME of a directory in the path leading to the file
   results in recall of an OPEN delegation depends on the semantics of
   the server's file system.  If that file system denies such RENAMEs
   when a file is open, the recall must be performed to determine
   whether the file in question is, in fact, open.

   In addition to the situations above, the server may choose to recall
   OPEN delegations at any time if resource constraints make it
   advisable to do so.  Clients should always be prepared for the
   possibility of recall.

   When a client receives a recall for an OPEN delegation, it needs to
   update state on the server before returning the delegation.  These
   same updates must be done whenever a client chooses to return a
   delegation voluntarily.  The following items of state need to be
   dealt with:

   o  If the file associated with the delegation is no longer open and
      no previous CLOSE operation has been sent to the server, a CLOSE
      operation must be sent to the server.

   o  If a file has other open references at the client, then OPEN
      operations must be sent to the server.  The appropriate stateids
      will be provided by the server for subsequent use by the client
      since the delegation stateid will no longer be valid.  These OPEN
      requests are done with the claim type of CLAIM_DELEGATE_CUR.  This
      will allow the presentation of the delegation stateid so that the
      client can establish the appropriate rights to perform the OPEN.
      (see Section 18.16, which describes the OPEN operation, for
      details.)

   o  If there are granted byte-range locks, the corresponding LOCK
      operations need to be performed.  This applies to the
      OPEN_DELEGATE_WRITE delegation case only.

   o  For an OPEN_DELEGATE_WRITE delegation, if at the time of recall
      the file is not open for OPEN4_SHARE_ACCESS_WRITE/
      OPEN4_SHARE_ACCESS_BOTH, all modified data for the file must be
      flushed to the server.  If the delegation had not existed, the
      client would have done this data flush before the CLOSE operation.






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   o  For an OPEN_DELEGATE_WRITE delegation when a file is still open at
      the time of recall, any modified data for the file needs to be
      flushed to the server.

   o  With the OPEN_DELEGATE_WRITE delegation in place, it is possible
      that the file was truncated during the duration of the delegation.
      For example, the truncation could have occurred as a result of an
      OPEN UNCHECKED with a size attribute value of zero.  Therefore, if
      a truncation of the file has occurred and this operation has not
      been propagated to the server, the truncation must occur before
      any modified data is written to the server.

   In the case of OPEN_DELEGATE_WRITE delegation, byte-range locking
   imposes some additional requirements.  To precisely maintain the
   associated invariant, it is required to flush any modified data in
   any byte-range for which a WRITE_LT lock was released while the
   OPEN_DELEGATE_WRITE delegation was in effect.  However, because the
   OPEN_DELEGATE_WRITE delegation implies no other locking by other
   clients, a simpler implementation is to flush all modified data for
   the file (as described just above) if any WRITE_LT lock has been
   released while the OPEN_DELEGATE_WRITE delegation was in effect.

   An implementation need not wait until delegation recall (or the
   decision to voluntarily return a delegation) to perform any of the
   above actions, if implementation considerations (e.g., resource
   availability constraints) make that desirable.  Generally, however,
   the fact that the actual OPEN state of the file may continue to
   change makes it not worthwhile to send information about opens and
   closes to the server, except as part of delegation return.  An
   exception is when the client has no more internal opens of the file.
   In this case, sending a CLOSE is useful because it reduces resource
   utilization on the client and server.  Regardless of the client's
   choices on scheduling these actions, all must be performed before the
   delegation is returned, including (when applicable) the close that
   corresponds to the OPEN that resulted in the delegation.  These
   actions can be performed either in previous requests or in previous
   operations in the same COMPOUND request.

10.4.5.  Clients That Fail to Honor Delegation Recalls

   A client may fail to respond to a recall for various reasons, such as
   a failure of the backchannel from server to the client.  The client
   may be unaware of a failure in the backchannel.  This lack of
   awareness could result in the client finding out long after the
   failure that its delegation has been revoked, and another client has
   modified the data for which the client had a delegation.  This is
   especially a problem for the client that held an OPEN_DELEGATE_WRITE
   delegation.



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   Status bits returned by SEQUENCE operations help to provide an
   alternate way of informing the client of issues regarding the status
   of the backchannel and of recalled delegations.  When the backchannel
   is not available, the server returns the status bit
   SEQ4_STATUS_CB_PATH_DOWN on SEQUENCE operations.  The client can
   react by attempting to re-establish the backchannel and by returning
   recallable objects if a backchannel cannot be successfully re-
   established.

   Whether the backchannel is functioning or not, it may be that the
   recalled delegation is not returned.  Note that the client's lease
   might still be renewed, even though the recalled delegation is not
   returned.  In this situation, servers SHOULD revoke delegations that
   are not returned in a period of time equal to the lease period.  This
   period of time should allow the client time to note the backchannel-
   down status and re-establish the backchannel.

   When delegations are revoked, the server will return with the
   SEQ4_STATUS_RECALLABLE_STATE_REVOKED status bit set on subsequent
   SEQUENCE operations.  The client should note this and then use
   TEST_STATEID to find which delegations have been revoked.

10.4.6.  Delegation Revocation

   At the point a delegation is revoked, if there are associated opens
   on the client, these opens may or may not be revoked.  If no byte-
   range lock or open is granted that is inconsistent with the existing
   open, the stateid for the open may remain valid and be disconnected
   from the revoked delegation, just as would be the case if the
   delegation were returned.

   For example, if an OPEN for OPEN4_SHARE_ACCESS_BOTH with a deny of
   OPEN4_SHARE_DENY_NONE is associated with the delegation, granting of
   another such OPEN to a different client will revoke the delegation
   but need not revoke the OPEN, since the two OPENs are consistent with
   each other.  On the other hand, if an OPEN denying write access is
   granted, then the existing OPEN must be revoked.

   When opens and/or locks are revoked, the applications holding these
   opens or locks need to be notified.  This notification usually occurs
   by returning errors for READ/WRITE operations or when a close is
   attempted for the open file.

   If no opens exist for the file at the point the delegation is
   revoked, then notification of the revocation is unnecessary.
   However, if there is modified data present at the client for the
   file, the user of the application should be notified.  Unfortunately,
   it may not be possible to notify the user since active applications



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   may not be present at the client.  See Section 10.5.1 for additional
   details.

10.4.7.  Delegations via WANT_DELEGATION

   In addition to providing delegations as part of the reply to OPEN
   operations, servers MAY provide delegations separate from open, via
   the OPTIONAL WANT_DELEGATION operation.  This allows delegations to
   be obtained in advance of an OPEN that might benefit from them, for
   objects that are not a valid target of OPEN, or to deal with cases in
   which a delegation has been recalled and the client wants to make an
   attempt to re-establish it if the absence of use by other clients
   allows that.

   The WANT_DELEGATION operation may be performed on any type of file
   object other than a directory.

   When a delegation is obtained using WANT_DELEGATION, any open files
   for the same filehandle held by that client are to be treated as
   subordinate to the delegation, just as if they had been created using
   an OPEN of type CLAIM_DELEGATE_CUR.  They are otherwise unchanged as
   to seqid, access and deny modes, and the relationship with byte-range
   locks.  Similarly, because existing byte-range locks are subordinate
   to an open, those byte-range locks also become indirectly subordinate
   to that new delegation.

   The WANT_DELEGATION operation provides for delivery of delegations
   via callbacks, when the delegations are not immediately available.
   When a requested delegation is available, it is delivered to the
   client via a CB_PUSH_DELEG operation.  When this happens, open files
   for the same filehandle become subordinate to the new delegation at
   the point at which the delegation is delivered, just as if they had
   been created using an OPEN of type CLAIM_DELEGATE_CUR.  Similarly,
   this occurs for existing byte-range locks subordinate to an open.

10.5.  Data Caching and Revocation

   When locks and delegations are revoked, the assumptions upon which
   successful caching depends are no longer guaranteed.  For any locks
   or share reservations that have been revoked, the corresponding
   state-owner needs to be notified.  This notification includes
   applications with a file open that has a corresponding delegation
   that has been revoked.  Cached data associated with the revocation
   must be removed from the client.  In the case of modified data
   existing in the client's cache, that data must be removed from the
   client without being written to the server.  As mentioned, the
   assumptions made by the client are no longer valid at the point when
   a lock or delegation has been revoked.  For example, another client



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   may have been granted a conflicting byte-range lock after the
   revocation of the byte-range lock at the first client.  Therefore,
   the data within the lock range may have been modified by the other
   client.  Obviously, the first client is unable to guarantee to the
   application what has occurred to the file in the case of revocation.

   Notification to a state-owner will in many cases consist of simply
   returning an error on the next and all subsequent READs/WRITEs to the
   open file or on the close.  Where the methods available to a client
   make such notification impossible because errors for certain
   operations may not be returned, more drastic action such as signals
   or process termination may be appropriate.  The justification here is
   that an invariant on which an application depends may be violated.
   Depending on how errors are typically treated for the client-
   operating environment, further levels of notification including
   logging, console messages, and GUI pop-ups may be appropriate.

10.5.1.  Revocation Recovery for Write Open Delegation

   Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the
   special issue of modified data in the client cache while the file is
   not open.  In this situation, any client that does not flush modified
   data to the server on each close must ensure that the user receives
   appropriate notification of the failure as a result of the
   revocation.  Since such situations may require human action to
   correct problems, notification schemes in which the appropriate user
   or administrator is notified may be necessary.  Logging and console
   messages are typical examples.

   If there is modified data on the client, it must not be flushed
   normally to the server.  A client may attempt to provide a copy of
   the file data as modified during the delegation under a different
   name in the file system namespace to ease recovery.  Note that when
   the client can determine that the file has not been modified by any
   other client, or when the client has a complete cached copy of the
   file in question, such a saved copy of the client's view of the file
   may be of particular value for recovery.  In another case, recovery
   using a copy of the file based partially on the client's cached data
   and partially on the server's copy as modified by other clients will
   be anything but straightforward, so clients may avoid saving file
   contents in these situations or specially mark the results to warn
   users of possible problems.

   Saving of such modified data in delegation revocation situations may
   be limited to files of a certain size or might be used only when
   sufficient disk space is available within the target file system.
   Such saving may also be restricted to situations when the client has




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   sufficient buffering resources to keep the cached copy available
   until it is properly stored to the target file system.

10.6.  Attribute Caching

   This section pertains to the caching of a file's attributes on a
   client when that client does not hold a delegation on the file.

   The attributes discussed in this section do not include named
   attributes.  Individual named attributes are analogous to files, and
   caching of the data for these needs to be handled just as data
   caching is for ordinary files.  Similarly, LOOKUP results from an
   OPENATTR directory (as well as the directory's contents) are to be
   cached on the same basis as any other pathnames.

   Clients may cache file attributes obtained from the server and use
   them to avoid subsequent GETATTR requests.  Such caching is write
   through in that modification to file attributes is always done by
   means of requests to the server and should not be done locally and
   should not be cached.  The exception to this are modifications to
   attributes that are intimately connected with data caching.
   Therefore, extending a file by writing data to the local data cache
   is reflected immediately in the size as seen on the client without
   this change being immediately reflected on the server.  Normally,
   such changes are not propagated directly to the server, but when the
   modified data is flushed to the server, analogous attribute changes
   are made on the server.  When OPEN delegation is in effect, the
   modified attributes may be returned to the server in reaction to a
   CB_RECALL call.

   The result of local caching of attributes is that the attribute
   caches maintained on individual clients will not be coherent.
   Changes made in one order on the server may be seen in a different
   order on one client and in a third order on another client.

   The typical file system application programming interfaces do not
   provide means to atomically modify or interrogate attributes for
   multiple files at the same time.  The following rules provide an
   environment where the potential incoherencies mentioned above can be
   reasonably managed.  These rules are derived from the practice of
   previous NFS protocols.

   o  All attributes for a given file (per-fsid attributes excepted) are
      cached as a unit at the client so that no non-serializability can
      arise within the context of a single file.

   o  An upper time boundary is maintained on how long a client cache
      entry can be kept without being refreshed from the server.



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   o  When operations are performed that change attributes at the
      server, the updated attribute set is requested as part of the
      containing RPC.  This includes directory operations that update
      attributes indirectly.  This is accomplished by following the
      modifying operation with a GETATTR operation and then using the
      results of the GETATTR to update the client's cached attributes.

   Note that if the full set of attributes to be cached is requested by
   READDIR, the results can be cached by the client on the same basis as
   attributes obtained via GETATTR.

   A client may validate its cached version of attributes for a file by
   fetching both the change and time_access attributes and assuming that
   if the change attribute has the same value as it did when the
   attributes were cached, then no attributes other than time_access
   have changed.  The reason why time_access is also fetched is because
   many servers operate in environments where the operation that updates
   change does not update time_access.  For example, POSIX file
   semantics do not update access time when a file is modified by the
   write system call [18].  Therefore, the client that wants a current
   time_access value should fetch it with change during the attribute
   cache validation processing and update its cached time_access.

   The client may maintain a cache of modified attributes for those
   attributes intimately connected with data of modified regular files
   (size, time_modify, and change).  Other than those three attributes,
   the client MUST NOT maintain a cache of modified attributes.
   Instead, attribute changes are immediately sent to the server.

   In some operating environments, the equivalent to time_access is
   expected to be implicitly updated by each read of the content of the
   file object.  If an NFS client is caching the content of a file
   object, whether it is a regular file, directory, or symbolic link,
   the client SHOULD NOT update the time_access attribute (via SETATTR
   or a small READ or READDIR request) on the server with each read that
   is satisfied from cache.  The reason is that this can defeat the
   performance benefits of caching content, especially since an explicit
   SETATTR of time_access may alter the change attribute on the server.
   If the change attribute changes, clients that are caching the content
   will think the content has changed, and will re-read unmodified data
   from the server.  Nor is the client encouraged to maintain a modified
   version of time_access in its cache, since the client either would
   eventually have to write the access time to the server with bad
   performance effects or never update the server's time_access, thereby
   resulting in a situation where an application that caches access time
   between a close and open of the same file observes the access time
   oscillating between the past and present.  The time_access attribute
   always means the time of last access to a file by a read that was



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   satisfied by the server.  This way clients will tend to see only
   time_access changes that go forward in time.

10.7.  Data and Metadata Caching and Memory Mapped Files

   Some operating environments include the capability for an application
   to map a file's content into the application's address space.  Each
   time the application accesses a memory location that corresponds to a
   block that has not been loaded into the address space, a page fault
   occurs and the file is read (or if the block does not exist in the
   file, the block is allocated and then instantiated in the
   application's address space).

   As long as each memory-mapped access to the file requires a page
   fault, the relevant attributes of the file that are used to detect
   access and modification (time_access, time_metadata, time_modify, and
   change) will be updated.  However, in many operating environments,
   when page faults are not required, these attributes will not be
   updated on reads or updates to the file via memory access (regardless
   of whether the file is local or is accessed remotely).  A client or
   server MAY fail to update attributes of a file that is being accessed
   via memory-mapped I/O.  This has several implications:

   o  If there is an application on the server that has memory mapped a
      file that a client is also accessing, the client may not be able
      to get a consistent value of the change attribute to determine
      whether or not its cache is stale.  A server that knows that the
      file is memory-mapped could always pessimistically return updated
      values for change so as to force the application to always get the
      most up-to-date data and metadata for the file.  However, due to
      the negative performance implications of this, such behavior is
      OPTIONAL.

   o  If the memory-mapped file is not being modified on the server, and
      instead is just being read by an application via the memory-mapped
      interface, the client will not see an updated time_access
      attribute.  However, in many operating environments, neither will
      any process running on the server.  Thus, NFS clients are at no
      disadvantage with respect to local processes.

   o  If there is another client that is memory mapping the file, and if
      that client is holding an OPEN_DELEGATE_WRITE delegation, the same
      set of issues as discussed in the previous two bullet points
      apply.  So, when a server does a CB_GETATTR to a file that the
      client has modified in its cache, the reply from CB_GETATTR will
      not necessarily be accurate.  As discussed earlier, the client's
      obligation is to report that the file has been modified since the
      delegation was granted, not whether it has been modified again



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      between successive CB_GETATTR calls, and the server MUST assume
      that any file the client has modified in cache has been modified
      again between successive CB_GETATTR calls.  Depending on the
      nature of the client's memory management system, this weak
      obligation may not be possible.  A client MAY return stale
      information in CB_GETATTR whenever the file is memory-mapped.

   o  The mixture of memory mapping and byte-range locking on the same
      file is problematic.  Consider the following scenario, where a
      page size on each client is 8192 bytes.

      *  Client A memory maps the first page (8192 bytes) of file X.

      *  Client B memory maps the first page (8192 bytes) of file X.

      *  Client A WRITE_LT locks the first 4096 bytes.

      *  Client B WRITE_LT locks the second 4096 bytes.

      *  Client A, via a STORE instruction, modifies part of its locked
         byte-range.

      *  Simultaneous to client A, client B executes a STORE on part of
         its locked byte-range.

   Here the challenge is for each client to resynchronize to get a
   correct view of the first page.  In many operating environments, the
   virtual memory management systems on each client only know a page is
   modified, not that a subset of the page corresponding to the
   respective lock byte-ranges has been modified.  So it is not possible
   for each client to do the right thing, which is to write to the
   server only that portion of the page that is locked.  For example, if
   client A simply writes out the page, and then client B writes out the
   page, client A's data is lost.

   Moreover, if mandatory locking is enabled on the file, then we have a
   different problem.  When clients A and B execute the STORE
   instructions, the resulting page faults require a byte-range lock on
   the entire page.  Each client then tries to extend their locked range
   to the entire page, which results in a deadlock.  Communicating the
   NFS4ERR_DEADLOCK error to a STORE instruction is difficult at best.

   If a client is locking the entire memory-mapped file, there is no
   problem with advisory or mandatory byte-range locking, at least until
   the client unlocks a byte-range in the middle of the file.

   Given the above issues, the following are permitted:




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   o  Clients and servers MAY deny memory mapping a file for which they
      know there are byte-range locks.

   o  Clients and servers MAY deny a byte-range lock on a file they know
      is memory-mapped.

   o  A client MAY deny memory mapping a file that it knows requires
      mandatory locking for I/O.  If mandatory locking is enabled after
      the file is opened and mapped, the client MAY deny the application
      further access to its mapped file.

10.8.  Name and Directory Caching without Directory Delegations

   The NFSv4.1 directory delegation facility (described in Section 10.9
   below) is OPTIONAL for servers to implement.  Even where it is
   implemented, it may not always be functional because of resource
   availability issues or other constraints.  Thus, it is important to
   understand how name and directory caching are done in the absence of
   directory delegations.  These topics are discussed in the next two
   subsections.

10.8.1.  Name Caching

   The results of LOOKUP and READDIR operations may be cached to avoid
   the cost of subsequent LOOKUP operations.  Just as in the case of
   attribute caching, inconsistencies may arise among the various client
   caches.  To mitigate the effects of these inconsistencies and given
   the context of typical file system APIs, an upper time boundary is
   maintained for how long a client name cache entry can be kept without
   verifying that the entry has not been made invalid by a directory
   change operation performed by another client.

   When a client is not making changes to a directory for which there
   exist name cache entries, the client needs to periodically fetch
   attributes for that directory to ensure that it is not being
   modified.  After determining that no modification has occurred, the
   expiration time for the associated name cache entries may be updated
   to be the current time plus the name cache staleness bound.

   When a client is making changes to a given directory, it needs to
   determine whether there have been changes made to the directory by
   other clients.  It does this by using the change attribute as
   reported before and after the directory operation in the associated
   change_info4 value returned for the operation.  The server is able to
   communicate to the client whether the change_info4 data is provided
   atomically with respect to the directory operation.  If the change
   values are provided atomically, the client has a basis for




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   determining, given proper care, whether other clients are modifying
   the directory in question.

   The simplest way to enable the client to make this determination is
   for the client to serialize all changes made to a specific directory.
   When this is done, and the server provides before and after values of
   the change attribute atomically, the client can simply compare the
   after value of the change attribute from one operation on a directory
   with the before value on the subsequent operation modifying that
   directory.  When these are equal, the client is assured that no other
   client is modifying the directory in question.

   When such serialization is not used, and there may be multiple
   simultaneous outstanding operations modifying a single directory sent
   from a single client, making this sort of determination can be more
   complicated.  If two such operations complete in a different order
   than they were actually performed, that might give an appearance
   consistent with modification being made by another client.  Where
   this appears to happen, the client needs to await the completion of
   all such modifications that were started previously, to see if the
   outstanding before and after change numbers can be sorted into a
   chain such that the before value of one change number matches the
   after value of a previous one, in a chain consistent with this client
   being the only one modifying the directory.

   In either of these cases, the client is able to determine whether the
   directory is being modified by another client.  If the comparison
   indicates that the directory was updated by another client, the name
   cache associated with the modified directory is purged from the
   client.  If the comparison indicates no modification, the name cache
   can be updated on the client to reflect the directory operation and
   the associated timeout can be extended.  The post-operation change
   value needs to be saved as the basis for future change_info4
   comparisons.

   As demonstrated by the scenario above, name caching requires that the
   client revalidate name cache data by inspecting the change attribute
   of a directory at the point when the name cache item was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre- and
   post-operation change attribute values atomically.  When the server
   is unable to report the before and after values atomically with
   respect to the directory operation, the server must indicate that
   fact in the change_info4 return value.  When the information is not
   atomically reported, the client should not assume that other clients
   have not changed the directory.



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10.8.2.  Directory Caching

   The results of READDIR operations may be used to avoid subsequent
   READDIR operations.  Just as in the cases of attribute and name
   caching, inconsistencies may arise among the various client caches.
   To mitigate the effects of these inconsistencies, and given the
   context of typical file system APIs, the following rules should be
   followed:

   o  Cached READDIR information for a directory that is not obtained in
      a single READDIR operation must always be a consistent snapshot of
      directory contents.  This is determined by using a GETATTR before
      the first READDIR and after the last READDIR that contributes to
      the cache.

   o  An upper time boundary is maintained to indicate the length of
      time a directory cache entry is considered valid before the client
      must revalidate the cached information.

   The revalidation technique parallels that discussed in the case of
   name caching.  When the client is not changing the directory in
   question, checking the change attribute of the directory with GETATTR
   is adequate.  The lifetime of the cache entry can be extended at
   these checkpoints.  When a client is modifying the directory, the
   client needs to use the change_info4 data to determine whether there
   are other clients modifying the directory.  If it is determined that
   no other client modifications are occurring, the client may update
   its directory cache to reflect its own changes.

   As demonstrated previously, directory caching requires that the
   client revalidate directory cache data by inspecting the change
   attribute of a directory at the point when the directory was cached.
   This requires that the server update the change attribute for
   directories when the contents of the corresponding directory is
   modified.  For a client to use the change_info4 information
   appropriately and correctly, the server must report the pre- and
   post-operation change attribute values atomically.  When the server
   is unable to report the before and after values atomically with
   respect to the directory operation, the server must indicate that
   fact in the change_info4 return value.  When the information is not
   atomically reported, the client should not assume that other clients
   have not changed the directory.

10.9.  Directory Delegations







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10.9.1.  Introduction to Directory Delegations

   Directory caching for the NFSv4.1 protocol, as previously described,
   is similar to file caching in previous versions.  Clients typically
   cache directory information for a duration determined by the client.
   At the end of a predefined timeout, the client will query the server
   to see if the directory has been updated.  By caching attributes,
   clients reduce the number of GETATTR calls made to the server to
   validate attributes.  Furthermore, frequently accessed files and
   directories, such as the current working directory, have their
   attributes cached on the client so that some NFS operations can be
   performed without having to make an RPC call.  By caching name and
   inode information about most recently looked up entries in a
   Directory Name Lookup Cache (DNLC), clients do not need to send
   LOOKUP calls to the server every time these files are accessed.

   This caching approach works reasonably well at reducing network
   traffic in many environments.  However, it does not address
   environments where there are numerous queries for files that do not
   exist.  In these cases of "misses", the client sends requests to the
   server in order to provide reasonable application semantics and
   promptly detect the creation of new directory entries.  Examples of
   high miss activity are compilation in software development
   environments.  The current behavior of NFS limits its potential
   scalability and wide-area sharing effectiveness in these types of
   environments.  Other distributed stateful file system architectures
   such as AFS and DFS have proven that adding state around directory
   contents can greatly reduce network traffic in high-miss
   environments.

   Delegation of directory contents is an OPTIONAL feature of NFSv4.1.
   Directory delegations provide similar traffic reduction benefits as
   with file delegations.  By allowing clients to cache directory
   contents (in a read-only fashion) while being notified of changes,
   the client can avoid making frequent requests to interrogate the
   contents of slowly-changing directories, reducing network traffic and
   improving client performance.  It can also simplify the task of
   determining whether other clients are making changes to the directory
   when the client itself is making many changes to the directory and
   changes are not serialized.

   Directory delegations allow improved namespace cache consistency to
   be achieved through delegations and synchronous recalls, in the
   absence of notifications.  In addition, if time-based consistency is
   sufficient, asynchronous notifications can provide performance
   benefits for the client, and possibly the server, under some common
   operating conditions such as slowly-changing and/or very large
   directories.



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10.9.2.  Directory Delegation Design

   NFSv4.1 introduces the GET_DIR_DELEGATION (Section 18.39) operation
   to allow the client to ask for a directory delegation.  The
   delegation covers directory attributes and all entries in the
   directory.  If either of these change, the delegation will be
   recalled synchronously.  The operation causing the recall will have
   to wait before the recall is complete.  Any changes to directory
   entry attributes will not cause the delegation to be recalled.

   In addition to asking for delegations, a client can also ask for
   notifications for certain events.  These events include changes to
   the directory's attributes and/or its contents.  If a client asks for
   notification for a certain event, the server will notify the client
   when that event occurs.  This will not result in the delegation being
   recalled for that client.  The notifications are asynchronous and
   provide a way of avoiding recalls in situations where a directory is
   changing enough that the pure recall model may not be effective while
   trying to allow the client to get substantial benefit.  In the
   absence of notifications, once the delegation is recalled the client
   has to refresh its directory cache; this might not be very efficient
   for very large directories.

   The delegation is read-only and the client may not make changes to
   the directory other than by performing NFSv4.1 operations that modify
   the directory or the associated file attributes so that the server
   has knowledge of these changes.  In order to keep the client's
   namespace synchronized with the server, the server will notify the
   delegation-holding client (assuming it has requested notifications)
   of the changes made as a result of that client's directory-modifying
   operations.  This is to avoid any need for that client to send
   subsequent GETATTR or READDIR operations to the server.  If a single
   client is holding the delegation and that client makes any changes to
   the directory (i.e., the changes are made via operations sent on a
   session associated with the client ID holding the delegation), the
   delegation will not be recalled.  Multiple clients may hold a
   delegation on the same directory, but if any such client modifies the
   directory, the server MUST recall the delegation from the other
   clients, unless those clients have made provisions to be notified of
   that sort of modification.

   Delegations can be recalled by the server at any time.  Normally, the
   server will recall the delegation when the directory changes in a way
   that is not covered by the notification, or when the directory
   changes and notifications have not been requested.  If another client
   removes the directory for which a delegation has been granted, the
   server will recall the delegation.




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10.9.3.  Attributes in Support of Directory Notifications

   See Section 5.11 for a description of the attributes associated with
   directory notifications.

10.9.4.  Directory Delegation Recall

   The server will recall the directory delegation by sending a callback
   to the client.  It will use the same callback procedure as used for
   recalling file delegations.  The server will recall the delegation
   when the directory changes in a way that is not covered by the
   notification.  However, the server need not recall the delegation if
   attributes of an entry within the directory change.

   If the server notices that handing out a delegation for a directory
   is causing too many notifications to be sent out, it may decide to
   not hand out delegations for that directory and/or recall those
   already granted.  If a client tries to remove the directory for which
   a delegation has been granted, the server will recall all associated
   delegations.

   The implementation sections for a number of operations describe
   situations in which notification or delegation recall would be
   required under some common circumstances.  In this regard, a similar
   set of caveats to those listed in Section 10.2 apply.

   o  For CREATE, see Section 18.4.4.

   o  For LINK, see Section 18.9.4.

   o  For OPEN, see Section 18.16.4.

   o  For REMOVE, see Section 18.25.4.

   o  For RENAME, see Section 18.26.4.

   o  For SETATTR, see Section 18.30.4.

10.9.5.  Directory Delegation Recovery

   Recovery from client or server restart for state on regular files has
   two main goals: avoiding the necessity of breaking application
   guarantees with respect to locked files and delivery of updates
   cached at the client.  Neither of these goals applies to directories
   protected by OPEN_DELEGATE_READ delegations and notifications.  Thus,
   no provision is made for reclaiming directory delegations in the
   event of client or server restart.  The client can simply establish a
   directory delegation in the same fashion as was done initially.



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11.  Multi-Server Namespace

   NFSv4.1 supports attributes that allow a namespace to extend beyond
   the boundaries of a single server.  It is RECOMMENDED that clients
   and servers support construction of such multi-server namespaces.
   Use of such multi-server namespaces is OPTIONAL, however, and for
   many purposes, single-server namespaces are perfectly acceptable.
   Use of multi-server namespaces can provide many advantages, however,
   by separating a file system's logical position in a namespace from
   the (possibly changing) logistical and administrative considerations
   that result in particular file systems being located on particular
   servers.

11.1.  Location Attributes

   NFSv4.1 contains RECOMMENDED attributes that allow file systems on
   one server to be associated with one or more instances of that file
   system on other servers.  These attributes specify such file system
   instances by specifying a server address target (either as a DNS name
   representing one or more IP addresses or as a literal IP address)
   together with the path of that file system within the associated
   single-server namespace.

   The fs_locations_info RECOMMENDED attribute allows specification of
   one or more file system instance locations where the data
   corresponding to a given file system may be found.  This attribute
   provides to the client, in addition to information about file system
   instance locations, significant information about the various file
   system instance choices (e.g., priority for use, writability,
   currency, etc.).  It also includes information to help the client
   efficiently effect as seamless a transition as possible among
   multiple file system instances, when and if that should be necessary.

   The fs_locations RECOMMENDED attribute is inherited from NFSv4.0 and
   only allows specification of the file system locations where the data
   corresponding to a given file system may be found.  Servers SHOULD
   make this attribute available whenever fs_locations_info is
   supported, but client use of fs_locations_info is to be preferred.

11.2.  File System Presence or Absence

   A given location in an NFSv4.1 namespace (typically but not
   necessarily a multi-server namespace) can have a number of file
   system instance locations associated with it (via the fs_locations or
   fs_locations_info attribute).  There may also be an actual current
   file system at that location, accessible via normal namespace
   operations (e.g., LOOKUP).  In this case, the file system is said to
   be "present" at that position in the namespace, and clients will



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   typically use it, reserving use of additional locations specified via
   the location-related attributes to situations in which the principal
   location is no longer available.

   When there is no actual file system at the namespace location in
   question, the file system is said to be "absent".  An absent file
   system contains no files or directories other than the root.  Any
   reference to it, except to access a small set of attributes useful in
   determining alternate locations, will result in an error,
   NFS4ERR_MOVED.  Note that if the server ever returns the error
   NFS4ERR_MOVED, it MUST support the fs_locations attribute and SHOULD
   support the fs_locations_info and fs_status attributes.

   While the error name suggests that we have a case of a file system
   that once was present, and has only become absent later, this is only
   one possibility.  A position in the namespace may be permanently
   absent with the set of file system(s) designated by the location
   attributes being the only realization.  The name NFS4ERR_MOVED
   reflects an earlier, more limited conception of its function, but
   this error will be returned whenever the referenced file system is
   absent, whether it has moved or not.

   Except in the case of GETATTR-type operations (to be discussed
   later), when the current filehandle at the start of an operation is
   within an absent file system, that operation is not performed and the
   error NFS4ERR_MOVED is returned, to indicate that the file system is
   absent on the current server.

   Because a GETFH cannot succeed if the current filehandle is within an
   absent file system, filehandles within an absent file system cannot
   be transferred to the client.  When a client does have filehandles
   within an absent file system, it is the result of obtaining them when
   the file system was present, and having the file system become absent
   subsequently.

   It should be noted that because the check for the current filehandle
   being within an absent file system happens at the start of every
   operation, operations that change the current filehandle so that it
   is within an absent file system will not result in an error.  This
   allows such combinations as PUTFH-GETATTR and LOOKUP-GETATTR to be
   used to get attribute information, particularly location attribute
   information, as discussed below.

   The RECOMMENDED file system attribute fs_status can be used to
   interrogate the present/absent status of a given file system.






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11.3.  Getting Attributes for an Absent File System

   When a file system is absent, most attributes are not available, but
   it is necessary to allow the client access to the small set of
   attributes that are available, and most particularly those that give
   information about the correct current locations for this file system:
   fs_locations and fs_locations_info.

11.3.1.  GETATTR within an Absent File System

   As mentioned above, an exception is made for GETATTR in that
   attributes may be obtained for a filehandle within an absent file
   system.  This exception only applies if the attribute mask contains
   at least one attribute bit that indicates the client is interested in
   a result regarding an absent file system: fs_locations,
   fs_locations_info, or fs_status.  If none of these attributes is
   requested, GETATTR will result in an NFS4ERR_MOVED error.

   When a GETATTR is done on an absent file system, the set of supported
   attributes is very limited.  Many attributes, including those that
   are normally REQUIRED, will not be available on an absent file
   system.  In addition to the attributes mentioned above (fs_locations,
   fs_locations_info, fs_status), the following attributes SHOULD be
   available on absent file systems.  In the case of RECOMMENDED
   attributes, they should be available at least to the same degree that
   they are available on present file systems.

   change_policy:  This attribute is useful for absent file systems and
      can be helpful in summarizing to the client when any of the
      location-related attributes change.

   fsid:  This attribute should be provided so that the client can
      determine file system boundaries, including, in particular, the
      boundary between present and absent file systems.  This value must
      be different from any other fsid on the current server and need
      have no particular relationship to fsids on any particular
      destination to which the client might be directed.

   mounted_on_fileid:  For objects at the top of an absent file system,
      this attribute needs to be available.  Since the fileid is within
      the present parent file system, there should be no need to
      reference the absent file system to provide this information.

   Other attributes SHOULD NOT be made available for absent file
   systems, even when it is possible to provide them.  The server should
   not assume that more information is always better and should avoid
   gratuitously providing additional information.




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   When a GETATTR operation includes a bit mask for one of the
   attributes fs_locations, fs_locations_info, or fs_status, but where
   the bit mask includes attributes that are not supported, GETATTR will
   not return an error, but will return the mask of the actual
   attributes supported with the results.

   Handling of VERIFY/NVERIFY is similar to GETATTR in that if the
   attribute mask does not include fs_locations, fs_locations_info, or
   fs_status, the error NFS4ERR_MOVED will result.  It differs in that
   any appearance in the attribute mask of an attribute not supported
   for an absent file system (and note that this will include some
   normally REQUIRED attributes) will also cause an NFS4ERR_MOVED
   result.

11.3.2.  READDIR and Absent File Systems

   A READDIR performed when the current filehandle is within an absent
   file system will result in an NFS4ERR_MOVED error, since, unlike the
   case of GETATTR, no such exception is made for READDIR.

   Attributes for an absent file system may be fetched via a READDIR for
   a directory in a present file system, when that directory contains
   the root directories of one or more absent file systems.  In this
   case, the handling is as follows:

   o  If the attribute set requested includes one of the attributes
      fs_locations, fs_locations_info, or fs_status, then fetching of
      attributes proceeds normally and no NFS4ERR_MOVED indication is
      returned, even when the rdattr_error attribute is requested.

   o  If the attribute set requested does not include one of the
      attributes fs_locations, fs_locations_info, or fs_status, then if
      the rdattr_error attribute is requested, each directory entry for
      the root of an absent file system will report NFS4ERR_MOVED as the
      value of the rdattr_error attribute.

   o  If the attribute set requested does not include any of the
      attributes fs_locations, fs_locations_info, fs_status, or
      rdattr_error, then the occurrence of the root of an absent file
      system within the directory will result in the READDIR failing
      with an NFS4ERR_MOVED error.

   o  The unavailability of an attribute because of a file system's
      absence, even one that is ordinarily REQUIRED, does not result in
      any error indication.  The set of attributes returned for the root
      directory of the absent file system in that case is simply
      restricted to those actually available.




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11.4.  Uses of Location Information

   The location-bearing attributes (fs_locations and fs_locations_info),
   together with the possibility of absent file systems, provide a
   number of important facilities in providing reliable, manageable, and
   scalable data access.

   When a file system is present, these attributes can provide
   alternative locations, to be used to access the same data, in the
   event of server failures, communications problems, or other
   difficulties that make continued access to the current file system
   impossible or otherwise impractical.  Under some circumstances,
   multiple alternative locations may be used simultaneously to provide
   higher-performance access to the file system in question.  Provision
   of such alternate locations is referred to as "replication" although
   there are cases in which replicated sets of data are not in fact
   present, and the replicas are instead different paths to the same
   data.

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location.  In this case, a continued attempt to use the
   data in the now-absent file system will result in an NFS4ERR_MOVED
   error and, at that point, the successor locations (typically only one
   although multiple choices are possible) can be fetched and used to
   continue access.  Transfer of the file system contents to the new
   location is referred to as "migration", but it should be kept in mind
   that there are cases in which this term can be used, like
   "replication", when there is no actual data migration per se.

   Where a file system was not previously present, specification of file
   system location provides a means by which file systems located on one
   server can be associated with a namespace defined by another server,
   thus allowing a general multi-server namespace facility.  A
   designation of such a location, in place of an absent file system, is
   called a "referral".

   Because client support for location-related attributes is OPTIONAL, a
   server may (but is not required to) take action to hide migration and
   referral events from such clients, by acting as a proxy, for example.
   The server can determine the presence of client support from the
   arguments of the EXCHANGE_ID operation (see Section 18.35.3).

11.4.1.  File System Replication

   The fs_locations and fs_locations_info attributes provide alternative
   locations, to be used to access data in place of or in addition to
   the current file system instance.  On first access to a file system,



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   the client should obtain the value of the set of alternate locations
   by interrogating the fs_locations or fs_locations_info attribute,
   with the latter being preferred.

   In the event that server failures, communications problems, or other
   difficulties make continued access to the current file system
   impossible or otherwise impractical, the client can use the alternate
   locations as a way to get continued access to its data.  Depending on
   specific attributes of these alternate locations, as indicated within
   the fs_locations_info attribute, multiple locations may be used
   simultaneously, to provide higher performance through the
   exploitation of multiple paths between client and target file system.

   The alternate locations may be physical replicas of the (typically
   read-only) file system data, or they may reflect alternate paths to
   the same server or provide for the use of various forms of server
   clustering in which multiple servers provide alternate ways of
   accessing the same physical file system.  How these different modes
   of file system transition are represented within the fs_locations and
   fs_locations_info attributes and how the client deals with file
   system transition issues will be discussed in detail below.

   Multiple server addresses, whether they are derived from a single
   entry with a DNS name representing a set of IP addresses or from
   multiple entries each with its own server address, may correspond to
   the same actual server.  The fact that two addresses correspond to
   the same server is shown by a common so_major_id field within the
   eir_server_owner field returned by EXCHANGE_ID (see Section 18.35.3).
   For a detailed discussion of how server address targets interact with
   the determination of server identity specified by the server owner
   field, see Section 11.5.

11.4.2.  File System Migration

   When a file system is present and becomes absent, clients can be
   given the opportunity to have continued access to their data, at an
   alternate location, as specified by the fs_locations or
   fs_locations_info attribute.  Typically, a client will be accessing
   the file system in question, get an NFS4ERR_MOVED error, and then use
   the fs_locations or fs_locations_info attribute to determine the new
   location of the data.  When fs_locations_info is used, additional
   information will be available that will define the nature of the
   client's handling of the transition to a new server.

   Such migration can be helpful in providing load balancing or general
   resource reallocation.  The protocol does not specify how the file
   system will be moved between servers.  It is anticipated that a
   number of different server-to-server transfer mechanisms might be



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   used with the choice left to the server implementor.  The NFSv4.1
   protocol specifies the method used to communicate the migration event
   between client and server.

   The new location may be an alternate communication path to the same
   server or, in the case of various forms of server clustering, another
   server providing access to the same physical file system.  The
   client's responsibilities in dealing with this transition depend on
   the specific nature of the new access path as well as how and whether
   data was in fact migrated.  These issues will be discussed in detail
   below.

   When multiple server addresses correspond to the same actual server,
   as shown by a common value for the so_major_id field of the
   eir_server_owner field returned by EXCHANGE_ID, the location or
   locations may designate alternate server addresses in the form of
   specific server network addresses.  These can be used to access the
   file system in question at those addresses and when it is no longer
   accessible at the original address.

   Although a single successor location is typical, multiple locations
   may be provided, together with information that allows priority among
   the choices to be indicated, via information in the fs_locations_info
   attribute.  Where suitable, clustering mechanisms make it possible to
   provide multiple identical file systems or paths to them; this allows
   the client the opportunity to deal with any resource or
   communications issues that might limit data availability.

   When an alternate location is designated as the target for migration,
   it must designate the same data (with metadata being the same to the
   degree indicated by the fs_locations_info attribute).  Where file
   systems are writable, a change made on the original file system must
   be visible on all migration targets.  Where a file system is not
   writable but represents a read-only copy (possibly periodically
   updated) of a writable file system, similar requirements apply to the
   propagation of updates.  Any change visible in the original file
   system must already be effected on all migration targets, to avoid
   any possibility that a client, in effecting a transition to the
   migration target, will see any reversion in file system state.

11.4.3.  Referrals

   Referrals provide a way of placing a file system in a location within
   the namespace essentially without respect to its physical location on
   a given server.  This allows a single server or a set of servers to
   present a multi-server namespace that encompasses file systems
   located on multiple servers.  Some likely uses of this include




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   establishment of site-wide or organization-wide namespaces, or even
   knitting such together into a truly global namespace.

   Referrals occur when a client determines, upon first referencing a
   position in the current namespace, that it is part of a new file
   system and that the file system is absent.  When this occurs,
   typically by receiving the error NFS4ERR_MOVED, the actual location
   or locations of the file system can be determined by fetching the
   fs_locations or fs_locations_info attribute.

   The locations-related attribute may designate a single file system
   location or multiple file system locations, to be selected based on
   the needs of the client.  The server, in the fs_locations_info
   attribute, may specify priorities to be associated with various file
   system location choices.  The server may assign different priorities
   to different locations as reported to individual clients, in order to
   adapt to client physical location or to effect load balancing.  When
   both read-only and read-write file systems are present, some of the
   read-only locations might not be absolutely up-to-date (as they would
   have to be in the case of replication and migration).  Servers may
   also specify file system locations that include client-substituted
   variables so that different clients are referred to different file
   systems (with different data contents) based on client attributes
   such as CPU architecture.

   When the fs_locations_info attribute indicates that there are
   multiple possible targets listed, the relationships among them may be
   important to the client in selecting which one to use.  The same
   rules specified in Section 11.4.1 defining the appropriate standards
   for the data propagation apply to these multiple replicas as well.
   For example, the client might prefer a writable target on a server
   that has additional writable replicas to which it subsequently might
   switch.  Note that, as distinguished from the case of replication,
   there is no need to deal with the case of propagation of updates made
   by the current client, since the current client has not accessed the
   file system in question.

   Use of multi-server namespaces is enabled by NFSv4.1 but is not
   required.  The use of multi-server namespaces and their scope will
   depend on the applications used and system administration
   preferences.

   Multi-server namespaces can be established by a single server
   providing a large set of referrals to all of the included file
   systems.  Alternatively, a single multi-server namespace may be
   administratively segmented with separate referral file systems (on
   separate servers) for each separately administered portion of the




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   namespace.  The top-level referral file system or any segment may use
   replicated referral file systems for higher availability.

   Generally, multi-server namespaces are for the most part uniform, in
   that the same data made available to one client at a given location
   in the namespace is made available to all clients at that location.
   However, there are facilities provided that allow different clients
   to be directed to different sets of data, so as to adapt to such
   client characteristics as CPU architecture.

11.5.  Location Entries and Server Identity

   As mentioned above, a single location entry may have a server address
   target in the form of a DNS name that may represent multiple IP
   addresses, while multiple location entries may have their own server
   address targets that reference the same server.  Whether two IP
   addresses designate the same server is indicated by the existence of
   a common so_major_id field within the eir_server_owner field returned
   by EXCHANGE_ID (see Section 18.35.3), subject to further verification
   (for details see Section 2.10.5).

   When multiple addresses for the same server exist, the client may
   assume that for each file system in the namespace of a given server
   network address, there exist file systems at corresponding namespace
   locations for each of the other server network addresses.  It may do
   this even in the absence of explicit listing in fs_locations and
   fs_locations_info.  Such corresponding file system locations can be
   used as alternate locations, just as those explicitly specified via
   the fs_locations and fs_locations_info attributes.  Where these
   specific addresses are explicitly designated in the fs_locations_info
   attribute, the conditions of use specified in this attribute (e.g.,
   priorities, specification of simultaneous use) may limit the client's
   use of these alternate locations.

   If a single location entry designates multiple server IP addresses,
   the client cannot assume that these addresses are multiple paths to
   the same server.  In most cases, they will be, but the client MUST
   verify that before acting on that assumption.  When two server
   addresses are designated by a single location entry and they
   correspond to different servers, this normally indicates some sort of
   misconfiguration, and so the client should avoid using such location
   entries when alternatives are available.  When they are not, clients
   should pick one of IP addresses and use it, without using others that
   are not directed to the same server.







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11.6.  Additional Client-Side Considerations

   When clients make use of servers that implement referrals,
   replication, and migration, care should be taken that a user who
   mounts a given file system that includes a referral or a relocated
   file system continues to see a coherent picture of that user-side
   file system despite the fact that it contains a number of server-side
   file systems that may be on different servers.

   One important issue is upward navigation from the root of a server-
   side file system to its parent (specified as ".." in UNIX), in the
   case in which it transitions to that file system as a result of
   referral, migration, or a transition as a result of replication.
   When the client is at such a point, and it needs to ascend to the
   parent, it must go back to the parent as seen within the multi-server
   namespace rather than sending a LOOKUPP operation to the server,
   which would result in the parent within that server's single-server
   namespace.  In order to do this, the client needs to remember the
   filehandles that represent such file system roots and use these
   instead of sending a LOOKUPP operation to the current server.  This
   will allow the client to present to applications a consistent
   namespace, where upward navigation and downward navigation are
   consistent.

   Another issue concerns refresh of referral locations.  When referrals
   are used extensively, they may change as server configurations
   change.  It is expected that clients will cache information related
   to traversing referrals so that future client-side requests are
   resolved locally without server communication.  This is usually
   rooted in client-side name look up caching.  Clients should
   periodically purge this data for referral points in order to detect
   changes in location information.  When the change_policy attribute
   changes for directories that hold referral entries or for the
   referral entries themselves, clients should consider any associated
   cached referral information to be out of date.

11.7.  Effecting File System Transitions

   Transitions between file system instances, whether due to switching
   between replicas upon server unavailability or to server-initiated
   migration events, are best dealt with together.  This is so even
   though, for the server, pragmatic considerations will normally force
   different implementation strategies for planned and unplanned
   transitions.  Even though the prototypical use cases of replication
   and migration contain distinctive sets of features, when all
   possibilities for these operations are considered, there is an
   underlying unity of these operations, from the client's point of
   view, that makes treating them together desirable.



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   A number of methods are possible for servers to replicate data and to
   track client state in order to allow clients to transition between
   file system instances with a minimum of disruption.  Such methods
   vary between those that use inter-server clustering techniques to
   limit the changes seen by the client, to those that are less
   aggressive, use more standard methods of replicating data, and impose
   a greater burden on the client to adapt to the transition.

   The NFSv4.1 protocol does not impose choices on clients and servers
   with regard to that spectrum of transition methods.  In fact, there
   are many valid choices, depending on client and application
   requirements and their interaction with server implementation
   choices.  The NFSv4.1 protocol does define the specific choices that
   can be made, how these choices are communicated to the client, and
   how the client is to deal with any discontinuities.

   In the sections below, references will be made to various possible
   server implementation choices as a way of illustrating the transition
   scenarios that clients may deal with.  The intent here is not to
   define or limit server implementations but rather to illustrate the
   range of issues that clients may face.

   In the discussion below, references will be made to a file system
   having a particular property or to two file systems (typically the
   source and destination) belonging to a common class of any of several
   types.  Two file systems that belong to such a class share some
   important aspects of file system behavior that clients may depend
   upon when present, to easily effect a seamless transition between
   file system instances.  Conversely, where the file systems do not
   belong to such a common class, the client has to deal with various
   sorts of implementation discontinuities that may cause performance or
   other issues in effecting a transition.

   Where the fs_locations_info attribute is available, such file system
   classification data will be made directly available to the client
   (see Section 11.10 for details).  When only fs_locations is
   available, default assumptions with regard to such classifications
   have to be inferred (see Section 11.9 for details).

   In cases in which one server is expected to accept opaque values from
   the client that originated from another server, the servers SHOULD
   encode the "opaque" values in big-endian byte order.  If this is
   done, servers acting as replicas or immigrating file systems will be
   able to parse values like stateids, directory cookies, filehandles,
   etc., even if their native byte order is different from that of other
   servers cooperating in the replication and migration of the file
   system.




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11.7.1.  File System Transitions and Simultaneous Access

   When a single file system may be accessed at multiple locations,
   either because of an indication of file system identity as reported
   by the fs_locations or fs_locations_info attributes or because two
   file system instances have corresponding locations on server
   addresses that connect to the same server (as indicated by a common
   so_major_id field in the eir_server_owner field returned by
   EXCHANGE_ID), the client will, depending on specific circumstances as
   discussed below, either:

   o  Access multiple instances simultaneously, each of which represents
      an alternate path to the same data and metadata.

   o  Access one instance (or set of instances) and then transition to
      an alternative instance (or set of instances) as a result of
      network issues, server unresponsiveness, or server-directed
      migration.  The transition may involve changes in filehandles,
      fileids, the change attribute, and/or locking state, depending on
      the attributes of the source and destination file system
      instances, as specified in the fs_locations_info attribute.

   Which of these choices is possible, and how a transition is effected,
   is governed by equivalence classes of file system instances as
   reported by the fs_locations_info attribute, and for file system
   instances in the same location within a multi-homed single-server
   namespace, as indicated by the value of the so_major_id field of the
   eir_server_owner field returned by EXCHANGE_ID.

11.7.2.  Simultaneous Use and Transparent Transitions

   When two file system instances have the same location within their
   respective single-server namespaces and those two server network
   addresses designate the same server (as indicated by the same value
   of the so_major_id field of the eir_server_owner field returned in
   response to EXCHANGE_ID), those file system instances can be treated
   as the same, and either used together simultaneously or serially with
   no transition activity required on the part of the client.  In this
   case, we refer to the transition as "transparent", and the client in
   transferring access from one to the other is acting as it would in
   the event that communication is interrupted, with a new connection
   and possibly a new session being established to continue access to
   the same file system.

   Whether simultaneous use of the two file system instances is valid is
   controlled by whether the fs_locations_info attribute shows the two
   instances as having the same simultaneous-use class.  See




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   Section 11.10.1 for information about the definition of the various
   use classes, including the simultaneous-use class.

   Note that for two such file systems, any information within the
   fs_locations_info attribute that indicates the need for special
   transition activity, i.e., the appearance of the two file system
   instances with different handle, fileid, write-verifier, change, and
   readdir classes, indicates a serious problem.  The client, if it
   allows transition to the file system instance at all, must not treat
   this as a transparent transition.  The server SHOULD NOT indicate
   that these instances belong to different handle, fileid, write-
   verifier, change, and readdir classes, whether or not the two
   instances are shown belonging to the same simultaneous-use class.

   Where these conditions do not apply, a non-transparent file system
   instance transition is required with the details depending on the
   respective handle, fileid, write-verifier, change, and readdir
   classes of the two file system instances, and whether the two
   servers' addresses in question have the same eir_server_scope value
   as reported by EXCHANGE_ID.

11.7.2.1.  Simultaneous Use of File System Instances

   When the conditions in Section 11.7.2 hold, in either of the
   following two cases, the client may use the two file system instances
   simultaneously.

   o  The fs_locations_info attribute does not contain separate per-
      network-address entries for file system instances at the distinct
      network addresses.  This includes the case in which the
      fs_locations_info attribute is unavailable.  In this case, the
      fact that the two server addresses connect to the same server (as
      indicated by the two addresses sharing the same the so_major_id
      value and subsequently confirmed as described in Section 2.10.5)
      justifies simultaneous use, and there is no fs_locations_info
      attribute information contradicting that.

   o  The fs_locations_info attribute indicates that two file system
      instances belong to the same simultaneous-use class.

   In this case, the client may use both file system instances
   simultaneously, as representations of the same file system, whether
   that happens because the two network addresses connect to the same
   physical server or because different servers connect to clustered
   file systems and export their data in common.  When simultaneous use
   is in effect, any change made to one file system instance must be
   immediately reflected in the other file system instance(s).  Locks
   are treated as part of a common lease, associated with a common



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   client ID.  Depending on the details of the eir_server_owner returned
   by EXCHANGE_ID, the two server instances may be accessed by different
   sessions or a single session in common.

11.7.2.2.  Transparent File System Transitions

   When the conditions in Section 11.7.2.1 hold and the
   fs_locations_info attribute explicitly shows the file system
   instances for these distinct network addresses as belonging to
   different simultaneous-use classes, the file system instances should
   not be used by the client simultaneously.  Rather, they should be
   used serially with one being used unless and until communication
   difficulties, lack of responsiveness, or an explicit migration event
   causes another file system instance (or set of file system instances
   sharing a common simultaneous-use class) to be used.

   When a change of file system instance is to be done, the client will
   use the same client ID already in effect.  If the client already has
   connections to the new server address, these will be used.
   Otherwise, new connections to existing sessions or new sessions
   associated with the existing client ID are established as indicated
   by the eir_server_owner returned by EXCHANGE_ID.

   In all such transparent transition cases, the following apply:

   o  If filehandles are persistent, they stay the same.  If filehandles
      are volatile, they either stay the same or expire, but the reason
      for expiration is not due to the file system transition.

   o  Fileid values do not change across the transition.

   o  The file system will have the same fsid in both the old and new
      locations.

   o  Change attribute values are consistent across the transition and
      do not have to be refetched.  When change attributes indicate that
      a cached object is still valid, it can remain cached.

   o  Client and state identifiers retain their validity across the
      transition, except where their staleness is recognized and
      reported by the new server.  Except where such staleness requires
      it, no lock reclamation is needed.  Any such staleness is an
      indication that the server should be considered to have restarted
      and is reported as discussed in Section 8.4.2.

   o  Write verifiers are presumed to retain their validity and can be
      used to compare with verifiers returned by COMMIT on the new
      server.  If COMMIT on the new server returns an identical



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      verifier, then it is expected that the new server has all of the
      data that was written unstably to the original server and has
      committed that data to stable storage as requested.

   o  Readdir cookies are presumed to retain their validity and can be
      presented to subsequent READDIR requests together with the readdir
      verifier with which they are associated.  When the verifier is
      accepted as valid, the cookie will continue the READDIR operation
      so that the entire directory can be obtained by the client.

11.7.3.  Filehandles and File System Transitions

   There are a number of ways in which filehandles can be handled across
   a file system transition.  These can be divided into two broad
   classes depending upon whether the two file systems across which the
   transition happens share sufficient state to effect some sort of
   continuity of file system handling.

   When there is no such cooperation in filehandle assignment, the two
   file systems are reported as being in different handle classes.  In
   this case, all filehandles are assumed to expire as part of the file
   system transition.  Note that this behavior does not depend on the
   fh_expire_type attribute and supersedes the specification of the
   FH4_VOL_MIGRATION bit, which only affects behavior when
   fs_locations_info is not available.

   When there is cooperation in filehandle assignment, the two file
   systems are reported as being in the same handle classes.  In this
   case, persistent filehandles remain valid after the file system
   transition, while volatile filehandles (excluding those that are only
   volatile due to the FH4_VOL_MIGRATION bit) are subject to expiration
   on the target server.

11.7.4.  Fileids and File System Transitions

   In NFSv4.0, the issue of continuity of fileids in the event of a file
   system transition was not addressed.  The general expectation had
   been that in situations in which the two file system instances are
   created by a single vendor using some sort of file system image copy,
   fileids will be consistent across the transition, while in the
   analogous multi-vendor transitions they will not.  This poses
   difficulties, especially for the client without special knowledge of
   the transition mechanisms adopted by the server.  Note that although
   fileid is not a REQUIRED attribute, many servers support fileids and
   many clients provide APIs that depend on fileids.

   It is important to note that while clients themselves may have no
   trouble with a fileid changing as a result of a file system



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   transition event, applications do typically have access to the fileid
   (e.g., via stat).  The result is that an application may work
   perfectly well if there is no file system instance transition or if
   any such transition is among instances created by a single vendor,
   yet be unable to deal with the situation in which a multi-vendor
   transition occurs at the wrong time.

   Providing the same fileids in a multi-vendor (multiple server
   vendors) environment has generally been held to be quite difficult.
   While there is work to be done, it needs to be pointed out that this
   difficulty is partly self-imposed.  Servers have typically identified
   fileid with inode number, i.e. with a quantity used to find the file
   in question.  This identification poses special difficulties for
   migration of a file system between vendors where assigning the same
   index to a given file may not be possible.  Note here that a fileid
   is not required to be useful to find the file in question, only that
   it is unique within the given file system.  Servers prepared to
   accept a fileid as a single piece of metadata and store it apart from
   the value used to index the file information can relatively easily
   maintain a fileid value across a migration event, allowing a truly
   transparent migration event.

   In any case, where servers can provide continuity of fileids, they
   should, and the client should be able to find out that such
   continuity is available and take appropriate action.  Information
   about the continuity (or lack thereof) of fileids across a file
   system transition is represented by specifying whether the file
   systems in question are of the same fileid class.

   Note that when consistent fileids do not exist across a transition
   (either because there is no continuity of fileids or because fileid
   is not a supported attribute on one of instances involved), and there
   are no reliable filehandles across a transition event (either because
   there is no filehandle continuity or because the filehandles are
   volatile), the client is in a position where it cannot verify that
   files it was accessing before the transition are the same objects.
   It is forced to assume that no object has been renamed, and, unless
   there are guarantees that provide this (e.g., the file system is
   read-only), problems for applications may occur.  Therefore, use of
   such configurations should be limited to situations where the
   problems that this may cause can be tolerated.

11.7.5.  Fsids and File System Transitions

   Since fsids are generally only unique within a per-server basis, it
   is likely that they will change during a file system transition.  One
   exception is the case of transparent transitions, but in that case we
   have multiple network addresses that are defined as the same server



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   (as specified by a common value of the so_major_id field of
   eir_server_owner).  Clients should not make the fsids received from
   the server visible to applications since they may not be globally
   unique, and because they may change during a file system transition
   event.  Applications are best served if they are isolated from such
   transitions to the extent possible.

   Although normally a single source file system will transition to a
   single target file system, there is a provision for splitting a
   single source file system into multiple target file systems, by
   specifying the FSLI4F_MULTI_FS flag.

11.7.5.1.  File System Splitting

   When a file system transition is made and the fs_locations_info
   indicates that the file system in question may be split into multiple
   file systems (via the FSLI4F_MULTI_FS flag), the client SHOULD do
   GETATTRs to determine the fsid attribute on all known objects within
   the file system undergoing transition to determine the new file
   system boundaries.

   Clients may maintain the fsids passed to existing applications by
   mapping all of the fsids for the descendant file systems to the
   common fsid used for the original file system.

   Splitting a file system may be done on a transition between file
   systems of the same fileid class, since the fact that fileids are
   unique within the source file system ensure they will be unique in
   each of the target file systems.

11.7.6.  The Change Attribute and File System Transitions

   Since the change attribute is defined as a server-specific one,
   change attributes fetched from one server are normally presumed to be
   invalid on another server.  Such a presumption is troublesome since
   it would invalidate all cached change attributes, requiring
   refetching.  Even more disruptive, the absence of any assured
   continuity for the change attribute means that even if the same value
   is retrieved on refetch, no conclusions can be drawn as to whether
   the object in question has changed.  The identical change attribute
   could be merely an artifact of a modified file with a different
   change attribute construction algorithm, with that new algorithm just
   happening to result in an identical change value.

   When the two file systems have consistent change attribute formats,
   and this fact is communicated to the client by reporting in the same
   change class, the client may assume a continuity of change attribute




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   construction and handle this situation just as it would be handled
   without any file system transition.

11.7.7.  Lock State and File System Transitions

   In a file system transition, the client needs to handle cases in
   which the two servers have cooperated in state management and in
   which they have not.  Cooperation by two servers in state management
   requires coordination of client IDs.  Before the client attempts to
   use a client ID associated with one server in a request to the server
   of the other file system, it must eliminate the possibility that two
   non-cooperating servers have assigned the same client ID by accident.
   The client needs to compare the eir_server_scope values returned by
   each server.  If the scope values do not match, then the servers have
   not cooperated in state management.  If the scope values match, then
   this indicates the servers have cooperated in assigning client IDs to
   the point that they will reject client IDs that refer to state they
   do not know about.  See Section 2.10.4 for more information about the
   use of server scope.

   In the case of migration, the servers involved in the migration of a
   file system SHOULD transfer all server state from the original to the
   new server.  When this is done, it must be done in a way that is
   transparent to the client.  With replication, such a degree of common
   state is typically not the case.  Clients, however, should use the
   information provided by the eir_server_scope returned by EXCHANGE_ID
   (as modified by the validation procedures described in
   Section 2.10.4) to determine whether such sharing may be in effect,
   rather than making assumptions based on the reason for the
   transition.

   This state transfer will reduce disruption to the client when a file
   system transition occurs.  If the servers are successful in
   transferring all state, the client can attempt to establish sessions
   associated with the client ID used for the source file system
   instance.  If the server accepts that as a valid client ID, then the
   client may use the existing stateids associated with that client ID
   for the old file system instance in connection with that same client
   ID in connection with the transitioned file system instance.  If the
   client in question already had a client ID on the target system, it
   may interrogate the stateid values from the source system under that
   new client ID, with the assurance that if they are accepted as valid,
   then they represent validly transferred lock state for the source
   file system, which has been transferred to the target server.

   When the two servers belong to the same server scope, it does not
   mean that when dealing with the transition, the client will not have
   to reclaim state.  However, it does mean that the client may proceed



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   using its current client ID when establishing communication with the
   new server, and the new server will either recognize the client ID as
   valid or reject it, in which case locks must be reclaimed by the
   client.

   File systems cooperating in state management may actually share state
   or simply divide the identifier space so as to recognize (and reject
   as stale) each other's stateids and client IDs.  Servers that do
   share state may not do so under all conditions or at all times.  If
   the server cannot be sure when accepting a client ID that it reflects
   the locks the client was given, the server must treat all associated
   state as stale and report it as such to the client.

   When the two file system instances are on servers that do not share a
   server scope value, the client must establish a new client ID on the
   destination, if it does not have one already, and reclaim locks if
   allowed by the server.  In this case, old stateids and client IDs
   should not be presented to the new server since there is no assurance
   that they will not conflict with IDs valid on that server.  Note that
   in this case, lock reclaim may be attempted even when the servers
   involved in the transfer have different server scope values (see
   Section 8.4.2.1 for the contrary case of reclaim after server
   reboot).  Servers with different server scope values may cooperate to
   allow reclaim for locks associated with the transfer of a file system
   even if they do not cooperate sufficiently to share a server scope.

   In either case, when actual locks are not known to be maintained, the
   destination server may establish a grace period specific to the given
   file system, with non-reclaim locks being rejected for that file
   system, even though normal locks are being granted for other file
   systems.  Clients should not infer the absence of a grace period for
   file systems being transitioned to a server from responses to
   requests for other file systems.

   In the case of lock reclamation for a given file system after a file
   system transition, edge conditions can arise similar to those for
   reclaim after server restart (although in the case of the planned
   state transfer associated with migration, these can be avoided by
   securely recording lock state as part of state migration).  Unless
   the destination server can guarantee that locks will not be
   incorrectly granted, the destination server should not allow lock
   reclaims and should avoid establishing a grace period.

   Once all locks have been reclaimed, or there were no locks to
   reclaim, the client indicates that there are no more reclaims to be
   done for the file system in question by sending a RECLAIM_COMPLETE
   operation with the rca_one_fs parameter set to true.  Once this has
   been done, non-reclaim locking operations may be done, and any



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   subsequent request to do reclaims will be rejected with the error
   NFS4ERR_NO_GRACE.

   Information about client identity may be propagated between servers
   in the form of client_owner4 and associated verifiers, under the
   assumption that the client presents the same values to all the
   servers with which it deals.

   Servers are encouraged to provide facilities to allow locks to be
   reclaimed on the new server after a file system transition.  Often,
   however, in cases in which the two servers do not share a server
   scope value, such facilities may not be available and the client
   should be prepared to re-obtain locks, even though it is possible
   that the client may have its LOCK or OPEN request denied due to a
   conflicting lock.

   The consequences of having no facilities available to reclaim locks
   on the new server will depend on the type of environment.  In some
   environments, such as the transition between read-only file systems,
   such denial of locks should not pose large difficulties in practice.
   When an attempt to re-establish a lock on a new server is denied, the
   client should treat the situation as if its original lock had been
   revoked.  Note that when the lock is granted, the client cannot
   assume that no conflicting lock could have been granted in the
   interim.  Where change attribute continuity is present, the client
   may check the change attribute to check for unwanted file
   modifications.  Where even this is not available, and the file system
   is not read-only, a client may reasonably treat all pending locks as
   having been revoked.

11.7.7.1.  Leases and File System Transitions

   In the case of lease renewal, the client may not be submitting
   requests for a file system that has been transferred to another
   server.  This can occur because of the lease renewal mechanism.  The
   client renews the lease associated with all file systems when
   submitting a request on an associated session, regardless of the
   specific file system being referenced.

   In order for the client to schedule renewal of its lease where there
   is locking state that may have been relocated to the new server, the
   client must find out about lease relocation before that lease expire.
   To accomplish this, the SEQUENCE operation will return the status bit
   SEQ4_STATUS_LEASE_MOVED if responsibility for any of the renewed
   locking state has been transferred to a new server.  This will
   continue until the client receives an NFS4ERR_MOVED error for each of
   the file systems for which there has been locking state relocation.




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   When a client receives an SEQ4_STATUS_LEASE_MOVED indication from a
   server, for each file system of the server for which the client has
   locking state, the client should perform an operation.  For
   simplicity, the client may choose to reference all file systems, but
   what is important is that it must reference all file systems for
   which there was locking state where that state has moved.  Once the
   client receives an NFS4ERR_MOVED error for each such file system, the
   server will clear the SEQ4_STATUS_LEASE_MOVED indication.  The client
   can terminate the process of checking file systems once this
   indication is cleared (but only if the client has received a reply
   for all outstanding SEQUENCE requests on all sessions it has with the
   server), since there are no others for which locking state has moved.

   A client may use GETATTR of the fs_status (or fs_locations_info)
   attribute on all of the file systems to get absence indications in a
   single (or a few) request(s), since absent file systems will not
   cause an error in this context.  However, it still must do an
   operation that receives NFS4ERR_MOVED on each file system, in order
   to clear the SEQ4_STATUS_LEASE_MOVED indication.

   Once the set of file systems with transferred locking state has been
   determined, the client can follow the normal process to obtain the
   new server information (through the fs_locations and
   fs_locations_info attributes) and perform renewal of that lease on
   the new server, unless information in the fs_locations_info attribute
   shows that no state could have been transferred.  If the server has
   not had state transferred to it transparently, the client will
   receive NFS4ERR_STALE_CLIENTID from the new server, as described
   above, and the client can then reclaim locks as is done in the event
   of server failure.

11.7.7.2.  Transitions and the Lease_time Attribute

   In order that the client may appropriately manage its lease in the
   case of a file system transition, the destination server must
   establish proper values for the lease_time attribute.

   When state is transferred transparently, that state should include
   the correct value of the lease_time attribute.  The lease_time
   attribute on the destination server must never be less than that on
   the source, since this would result in premature expiration of a
   lease granted by the source server.  Upon transitions in which state
   is transferred transparently, the client is under no obligation to
   refetch the lease_time attribute and may continue to use the value
   previously fetched (on the source server).

   If state has not been transferred transparently, either because the
   associated servers are shown as having different eir_server_scope



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   strings or because the client ID is rejected when presented to the
   new server, the client should fetch the value of lease_time on the
   new (i.e., destination) server, and use it for subsequent locking
   requests.  However, the server must respect a grace period of at
   least as long as the lease_time on the source server, in order to
   ensure that clients have ample time to reclaim their lock before
   potentially conflicting non-reclaimed locks are granted.

11.7.8.  Write Verifiers and File System Transitions

   In a file system transition, the two file systems may be clustered in
   the handling of unstably written data.  When this is the case, and
   the two file systems belong to the same write-verifier class, write
   verifiers returned from one system may be compared to those returned
   by the other and superfluous writes avoided.

   When two file systems belong to different write-verifier classes, any
   verifier generated by one must not be compared to one provided by the
   other.  Instead, it should be treated as not equal even when the
   values are identical.

11.7.9.  Readdir Cookies and Verifiers and File System Transitions

   In a file system transition, the two file systems may be consistent
   in their handling of READDIR cookies and verifiers.  When this is the
   case, and the two file systems belong to the same readdir class,
   READDIR cookies and verifiers from one system may be recognized by
   the other and READDIR operations started on one server may be validly
   continued on the other, simply by presenting the cookie and verifier
   returned by a READDIR operation done on the first file system to the
   second.

   When two file systems belong to different readdir classes, any
   READDIR cookie and verifier generated by one is not valid on the
   second, and must not be presented to that server by the client.  The
   client should act as if the verifier was rejected.

11.7.10.  File System Data and File System Transitions

   When multiple replicas exist and are used simultaneously or in
   succession by a client, applications using them will normally expect
   that they contain either the same data or data that is consistent
   with the normal sorts of changes that are made by other clients
   updating the data of the file system (with metadata being the same to
   the degree indicated by the fs_locations_info attribute).  However,
   when multiple file systems are presented as replicas of one another,
   the precise relationship between the data of one and the data of
   another is not, as a general matter, specified by the NFSv4.1



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   protocol.  It is quite possible to present as replicas file systems
   where the data of those file systems is sufficiently different that
   some applications have problems dealing with the transition between
   replicas.  The namespace will typically be constructed so that
   applications can choose an appropriate level of support, so that in
   one position in the namespace a varied set of replicas will be
   listed, while in another only those that are up-to-date may be
   considered replicas.  The protocol does define four special cases of
   the relationship among replicas to be specified by the server and
   relied upon by clients:

   o  When multiple server addresses correspond to the same actual
      server, as indicated by a common so_major_id field within the
      eir_server_owner field returned by EXCHANGE_ID, the client may
      depend on the fact that changes to data, metadata, or locks made
      on one file system are immediately reflected on others.

   o  When multiple replicas exist and are used simultaneously by a
      client (see the FSLIB4_CLSIMUL definition within
      fs_locations_info), they must designate the same data.  Where file
      systems are writable, a change made on one instance must be
      visible on all instances, immediately upon the earlier of the
      return of the modifying requester or the visibility of that change
      on any of the associated replicas.  This allows a client to use
      these replicas simultaneously without any special adaptation to
      the fact that there are multiple replicas.  In this case, locks
      (whether share reservations or byte-range locks) and delegations
      obtained on one replica are immediately reflected on all replicas,
      even though these locks will be managed under a set of client IDs.

   o  When one replica is designated as the successor instance to
      another existing instance after return NFS4ERR_MOVED (i.e., the
      case of migration), the client may depend on the fact that all
      changes written to stable storage on the original instance are
      written to stable storage of the successor (uncommitted writes are
      dealt with in Section 11.7.8).

   o  Where a file system is not writable but represents a read-only
      copy (possibly periodically updated) of a writable file system,
      clients have similar requirements with regard to the propagation
      of updates.  They may need a guarantee that any change visible on
      the original file system instance must be immediately visible on
      any replica before the client transitions access to that replica,
      in order to avoid any possibility that a client, in effecting a
      transition to a replica, will see any reversion in file system
      state.  The specific means of this guarantee varies based on the
      value of the fss_type field that is reported as part of the
      fs_status attribute (see Section 11.11).  Since these file systems



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      are presumed to be unsuitable for simultaneous use, there is no
      specification of how locking is handled; in general, locks
      obtained on one file system will be separate from those on others.
      Since these are going to be read-only file systems, this is not
      expected to pose an issue for clients or applications.

11.8.  Effecting File System Referrals

   Referrals are effected when an absent file system is encountered and
   one or more alternate locations are made available by the
   fs_locations or fs_locations_info attributes.  The client will
   typically get an NFS4ERR_MOVED error, fetch the appropriate location
   information, and proceed to access the file system on a different
   server, even though it retains its logical position within the
   original namespace.  Referrals differ from migration events in that
   they happen only when the client has not previously referenced the
   file system in question (so there is nothing to transition).
   Referrals can only come into effect when an absent file system is
   encountered at its root.

   The examples given in the sections below are somewhat artificial in
   that an actual client will not typically do a multi-component look
   up, but will have cached information regarding the upper levels of
   the name hierarchy.  However, these example are chosen to make the
   required behavior clear and easy to put within the scope of a small
   number of requests, without getting unduly into details of how
   specific clients might choose to cache things.

11.8.1.  Referral Example (LOOKUP)

   Let us suppose that the following COMPOUND is sent in an environment
   in which /this/is/the/path is absent from the target server.  This
   may be for a number of reasons.  It may be that the file system has
   moved, or it may be that the target server is functioning mainly, or
   solely, to refer clients to the servers on which various file systems
   are located.

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  LOOKUP "path"

   o  GETFH



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   o  GETATTR (fsid, fileid, size, time_modify)

   Under the given circumstances, the following will be the result.

   o  PUTROOTFH --> NFS_OK.  The current fh is now the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  LOOKUP "path" --> NFS_OK.  The current fh is for /this/is/the/path
      and is within a new, absent file system, but ... the client will
      never see the value of that fh.

   o  GETFH --> NFS4ERR_MOVED.  Fails because current fh is in an absent
      file system at the start of the operation, and the specification
      makes no exception for GETFH.

   o  GETATTR (fsid, fileid, size, time_modify).  Not executed because
      the failure of the GETFH stops processing of the COMPOUND.

   Given the failure of the GETFH, the client has the job of determining
   the root of the absent file system and where to find that file
   system, i.e., the server and path relative to that server's root fh.
   Note that in this example, the client did not obtain filehandles and
   attribute information (e.g., fsid) for the intermediate directories,
   so that it would not be sure where the absent file system starts.  It
   could be the case, for example, that /this/is/the is the root of the
   moved file system and that the reason that the look up of "path"
   succeeded is that the file system was not absent on that operation
   but was moved between the last LOOKUP and the GETFH (since COMPOUND
   is not atomic).  Even if we had the fsids for all of the intermediate
   directories, we could have no way of knowing that /this/is/the/path
   was the root of a new file system, since we don't yet have its fsid.

   In order to get the necessary information, let us re-send the chain
   of LOOKUPs with GETFHs and GETATTRs to at least get the fsids so we
   can be sure where the appropriate file system boundaries are.  The
   client could choose to get fs_locations_info at the same time but in
   most cases the client will have a good guess as to where file system
   boundaries are (because of where NFS4ERR_MOVED was, and was not,
   received) making fetching of fs_locations_info unnecessary.



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   OP01:  PUTROOTFH --> NFS_OK

   -  Current fh is root of pseudo-fs.

   OP02:  GETATTR(fsid) --> NFS_OK

   -  Just for completeness.  Normally, clients will know the fsid of
      the pseudo-fs as soon as they establish communication with a
      server.

   OP03:  LOOKUP "this" --> NFS_OK

   OP04:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP05:  GETFH --> NFS_OK

   -  Current fh is for /this and is within pseudo-fs.

   OP06:  LOOKUP "is" --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP07:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP08:  GETFH --> NFS_OK

   -  Current fh is for /this/is and is within pseudo-fs.

   OP09:  LOOKUP "the" --> NFS_OK

   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP10:  GETATTR(fsid) --> NFS_OK

   -  Get current fsid to see where file system boundaries are.  The
      fsid will be that for the pseudo-fs in this example, so no
      boundary.

   OP11:  GETFH --> NFS_OK




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   -  Current fh is for /this/is/the and is within pseudo-fs.

   OP12:  LOOKUP "path" --> NFS_OK

   -  Current fh is for /this/is/the/path and is within a new, absent
      file system, but ...

   -  The client will never see the value of that fh.

   OP13:  GETATTR(fsid, fs_locations_info) --> NFS_OK

   -  We are getting the fsid to know where the file system boundaries
      are.  In this operation, the fsid will be different than that of
      the parent directory (which in turn was retrieved in OP10).  Note
      that the fsid we are given will not necessarily be preserved at
      the new location.  That fsid might be different, and in fact the
      fsid we have for this file system might be a valid fsid of a
      different file system on that new server.

   -  In this particular case, we are pretty sure anyway that what has
      moved is /this/is/the/path rather than /this/is/the since we have
      the fsid of the latter and it is that of the pseudo-fs, which
      presumably cannot move.  However, in other examples, we might not
      have this kind of information to rely on (e.g., /this/is/the might
      be a non-pseudo file system separate from /this/is/the/path), so
      we need to have other reliable source information on the boundary
      of the file system that is moved.  If, for example, the file
      system /this/is had moved, we would have a case of migration
      rather than referral, and once the boundaries of the migrated file
      system was clear we could fetch fs_locations_info.

   -  We are fetching fs_locations_info because the fact that we got an
      NFS4ERR_MOVED at this point means that it is most likely that this
      is a referral and we need the destination.  Even if it is the case
      that /this/is/the is a file system that has migrated, we will
      still need the location information for that file system.

   OP14:  GETFH --> NFS4ERR_MOVED

   -  Fails because current fh is in an absent file system at the start
      of the operation, and the specification makes no exception for
      GETFH.  Note that this means the server will never send the client
      a filehandle from within an absent file system.

   Given the above, the client knows where the root of the absent file
   system is (/this/is/the/path) by noting where the change of fsid
   occurred (between "the" and "path").  The fs_locations_info attribute
   also gives the client the actual location of the absent file system,



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   so that the referral can proceed.  The server gives the client the
   bare minimum of information about the absent file system so that
   there will be very little scope for problems of conflict between
   information sent by the referring server and information of the file
   system's home.  No filehandles and very few attributes are present on
   the referring server, and the client can treat those it receives as
   transient information with the function of enabling the referral.

11.8.2.  Referral Example (READDIR)

   Another context in which a client may encounter referrals is when it
   does a READDIR on a directory in which some of the sub-directories
   are the roots of absent file systems.

   Suppose such a directory is read as follows:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (fsid, size, time_modify, mounted_on_fileid)

   In this case, because rdattr_error is not requested,
   fs_locations_info is not requested, and some of the attributes cannot
   be provided, the result will be an NFS4ERR_MOVED error on the
   READDIR, with the detailed results as follows:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (fsid, size, time_modify, mounted_on_fileid) -->
      NFS4ERR_MOVED.  Note that the same error would have been returned
      if /this/is/the had migrated, but it is returned because the
      directory contains the root of an absent file system.




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   So now suppose that we re-send with rdattr_error:

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)

   The results will be:

   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
      --> NFS_OK.  The attributes for directory entry with the component
      named "path" will only contain rdattr_error with the value
      NFS4ERR_MOVED, together with an fsid value and a value for
      mounted_on_fileid.

   So suppose we do another READDIR to get fs_locations_info (although
   we could have used a GETATTR directly, as in Section 11.8.1).

   o  PUTROOTFH

   o  LOOKUP "this"

   o  LOOKUP "is"

   o  LOOKUP "the"

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, time_modify)

   The results would be:




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   o  PUTROOTFH --> NFS_OK.  The current fh is at the root of the
      pseudo-fs.

   o  LOOKUP "this" --> NFS_OK.  The current fh is for /this and is
      within the pseudo-fs.

   o  LOOKUP "is" --> NFS_OK.  The current fh is for /this/is and is
      within the pseudo-fs.

   o  LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the and
      is within the pseudo-fs.

   o  READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
      size, time_modify) --> NFS_OK.  The attributes will be as shown
      below.

   The attributes for the directory entry with the component named
   "path" will only contain:

   o  rdattr_error (value: NFS_OK)

   o  fs_locations_info

   o  mounted_on_fileid (value: unique fileid within referring file
      system)

   o  fsid (value: unique value within referring server)

   The attributes for entry "path" will not contain size or time_modify
   because these attributes are not available within an absent file
   system.

11.9.  The Attribute fs_locations

   The fs_locations attribute is structured in the following way:

   struct fs_location4 {
           utf8str_cis     server<>;
           pathname4       rootpath;
   };

   struct fs_locations4 {
           pathname4       fs_root;
           fs_location4    locations<>;
   };

   The fs_location4 data type is used to represent the location of a
   file system by providing a server name and the path to the root of



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   the file system within that server's namespace.  When a set of
   servers have corresponding file systems at the same path within their
   namespaces, an array of server names may be provided.  An entry in
   the server array is a UTF-8 string and represents one of a
   traditional DNS host name, IPv4 address, IPv6 address, or a zero-
   length string.  An IPv4 or IPv6 address is represented as a universal
   address (see Section 3.3.9 and [15]), minus the netid, and either
   with or without the trailing ".p1.p2" suffix that represents the port
   number.  If the suffix is omitted, then the default port, 2049,
   SHOULD be assumed.  A zero-length string SHOULD be used to indicate
   the current address being used for the RPC call.  It is not a
   requirement that all servers that share the same rootpath be listed
   in one fs_location4 instance.  The array of server names is provided
   for convenience.  Servers that share the same rootpath may also be
   listed in separate fs_location4 entries in the fs_locations
   attribute.

   The fs_locations4 data type and fs_locations attribute contain an
   array of such locations.  Since the namespace of each server may be
   constructed differently, the "fs_root" field is provided.  The path
   represented by fs_root represents the location of the file system in
   the current server's namespace, i.e., that of the server from which
   the fs_locations attribute was obtained.  The fs_root path is meant
   to aid the client by clearly referencing the root of the file system
   whose locations are being reported, no matter what object within the
   current file system the current filehandle designates.  The fs_root
   is simply the pathname the client used to reach the object on the
   current server (i.e., the object to which the fs_locations attribute
   applies).

   When the fs_locations attribute is interrogated and there are no
   alternate file system locations, the server SHOULD return a zero-
   length array of fs_location4 structures, together with a valid
   fs_root.

   As an example, suppose there is a replicated file system located at
   two servers (servA and servB).  At servA, the file system is located
   at path /a/b/c.  At, servB the file system is located at path /x/y/z.
   If the client were to obtain the fs_locations value for the directory
   at /a/b/c/d, it might not necessarily know that the file system's
   root is located in servA's namespace at /a/b/c.  When the client
   switches to servB, it will need to determine that the directory it
   first referenced at servA is now represented by the path /x/y/z/d on
   servB.  To facilitate this, the fs_locations attribute provided by
   servA would have an fs_root value of /a/b/c and two entries in
   fs_locations.  One entry in fs_locations will be for itself (servA)
   and the other will be for servB with a path of /x/y/z.  With this
   information, the client is able to substitute /x/y/z for the /a/b/c



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   at the beginning of its access path and construct /x/y/z/d to use for
   the new server.

   Note that there is no requirement that the number of components in
   each rootpath be the same; there is no relation between the number of
   components in rootpath or fs_root, and none of the components in a
   rootpath and fs_root have to be the same.  In the above example, we
   could have had a third element in the locations array, with server
   equal to "servC" and rootpath equal to "/I/II", and a fourth element
   in locations with server equal to "servD" and rootpath equal to
   "/aleph/beth/gimel/daleth/he".

   The relationship between fs_root to a rootpath is that the client
   replaces the pathname indicated in fs_root for the current server for
   the substitute indicated in rootpath for the new server.

   For an example of a referred or migrated file system, suppose there
   is a file system located at serv1.  At serv1, the file system is
   located at /az/buky/vedi/glagoli.  The client finds that object at
   glagoli has migrated (or is a referral).  The client gets the
   fs_locations attribute, which contains an fs_root of /az/buky/vedi/
   glagoli, and one element in the locations array, with server equal to
   serv2, and rootpath equal to /izhitsa/fita.  The client replaces
   /az/buky/vedi/glagoli with /izhitsa/fita, and uses the latter
   pathname on serv2.

   Thus, the server MUST return an fs_root that is equal to the path the
   client used to reach the object to which the fs_locations attribute
   applies.  Otherwise, the client cannot determine the new path to use
   on the new server.

   Since the fs_locations attribute lacks information defining various
   attributes of the various file system choices presented, it SHOULD
   only be interrogated and used when fs_locations_info is not
   available.  When fs_locations is used, information about the specific
   locations should be assumed based on the following rules.

   The following rules are general and apply irrespective of the
   context.

   o  All listed file system instances should be considered as of the
      same handle class, if and only if, the current fh_expire_type
      attribute does not include the FH4_VOL_MIGRATION bit.  Note that
      in the case of referral, filehandle issues do not apply since
      there can be no filehandles known within the current file system,
      nor is there any access to the fh_expire_type attribute on the
      referring (absent) file system.




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   o  All listed file system instances should be considered as of the
      same fileid class if and only if the fh_expire_type attribute
      indicates persistent filehandles and does not include the
      FH4_VOL_MIGRATION bit.  Note that in the case of referral, fileid
      issues do not apply since there can be no fileids known within the
      referring (absent) file system, nor is there any access to the
      fh_expire_type attribute.

   o  All file system instances servers should be considered as of
      different change classes.

   For other class assignments, handling of file system transitions
   depends on the reasons for the transition:

   o  When the transition is due to migration, that is, the client was
      directed to a new file system after receiving an NFS4ERR_MOVED
      error, the target should be treated as being of the same write-
      verifier class as the source.

   o  When the transition is due to failover to another replica, that
      is, the client selected another replica without receiving an
      NFS4ERR_MOVED error, the target should be treated as being of a
      different write-verifier class from the source.

   The specific choices reflect typical implementation patterns for
   failover and controlled migration, respectively.  Since other choices
   are possible and useful, this information is better obtained by using
   fs_locations_info.  When a server implementation needs to communicate
   other choices, it MUST support the fs_locations_info attribute.

   See Section 21 for a discussion on the recommendations for the
   security flavor to be used by any GETATTR operation that requests the
   "fs_locations" attribute.

11.10.  The Attribute fs_locations_info

   The fs_locations_info attribute is intended as a more functional
   replacement for fs_locations that will continue to exist and be
   supported.  Clients can use it to get a more complete set of
   information about alternative file system locations.  When the server
   does not support fs_locations_info, fs_locations can be used to get a
   subset of the information.  A server that supports fs_locations_info
   MUST support fs_locations as well.

   There is additional information present in fs_locations_info, that is
   not available in fs_locations:





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   o  Attribute continuity information.  This information will allow a
      client to select a location that meets the transparency
      requirements of the applications accessing the data and to
      leverage optimizations due to the server guarantees of attribute
      continuity (e.g., if between multiple server locations the change
      attribute of a file of the file system is continuous, the client
      does not have to invalidate the file's cache if the change
      attribute is the same among all locations).

   o  File system identity information that indicates when multiple
      replicas, from the client's point of view, correspond to the same
      target file system, allowing them to be used interchangeably,
      without disruption, as multiple paths to the same thing.

   o  Information that will bear on the suitability of various replicas,
      depending on the use that the client intends.  For example, many
      applications need an absolutely up-to-date copy (e.g., those that
      write), while others may only need access to the most up-to-date
      copy reasonably available.

   o  Server-derived preference information for replicas, which can be
      used to implement load-balancing while giving the client the
      entire file system list to be used in case the primary fails.

   The fs_locations_info attribute is structured similarly to the
   fs_locations attribute.  A top-level structure (fs_locations_info4)
   contains the entire attribute including the root pathname of the file
   system and an array of lower-level structures that define replicas
   that share a common rootpath on their respective servers.  The lower-
   level structure in turn (fs_locations_item4) contains a specific
   pathname and information on one or more individual server replicas.
   For that last lowest-level, fs_locations_info has an
   fs_locations_server4 structure that contains per-server-replica
   information in addition to the server name.  This per-server-replica
   information includes a nominally opaque array, fls_info, in which
   specific pieces of information are located at the specific indices
   listed below.

   The attribute will always contain at least a single
   fs_locations_server entry.  Typically, this will be an entry with the
   FS4LIGF_CUR_REQ flag set, although in the case of a referral there
   will be no entry with that flag set.

   It should be noted that fs_locations_info attributes returned by
   servers for various replicas may differ for various reasons.  One
   server may know about a set of replicas that are not known to other
   servers.  Further, compatibility attributes may differ.  Filehandles
   might be of the same class going from replica A to replica B but not



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   going in the reverse direction.  This might happen because the
   filehandles are the same, but replica B's server implementation might
   not have provision to note and report that equivalence.

   The fs_locations_info attribute consists of a root pathname
   (fli_fs_root, just like fs_root in the fs_locations attribute),
   together with an array of fs_location_item4 structures.  The
   fs_location_item4 structures in turn consist of a root pathname
   (fli_rootpath) together with an array (fli_entries) of elements of
   data type fs_locations_server4, all defined as follows.

   /*
    * Defines an individual server replica
    */
   struct  fs_locations_server4 {
           int32_t         fls_currency;
           opaque          fls_info<>;
           utf8str_cis     fls_server;
   };

   /*
    * Byte indices of items within
    * fls_info: flag fields, class numbers,
    * bytes indicating ranks and orders.
    */
   const FSLI4BX_GFLAGS            = 0;
   const FSLI4BX_TFLAGS            = 1;

   const FSLI4BX_CLSIMUL           = 2;
   const FSLI4BX_CLHANDLE          = 3;
   const FSLI4BX_CLFILEID          = 4;
   const FSLI4BX_CLWRITEVER        = 5;
   const FSLI4BX_CLCHANGE          = 6;
   const FSLI4BX_CLREADDIR         = 7;

   const FSLI4BX_READRANK          = 8;
   const FSLI4BX_WRITERANK         = 9;
   const FSLI4BX_READORDER         = 10;
   const FSLI4BX_WRITEORDER        = 11;

   /*
    * Bits defined within the general flag byte.
    */
   const FSLI4GF_WRITABLE          = 0x01;
   const FSLI4GF_CUR_REQ           = 0x02;
   const FSLI4GF_ABSENT            = 0x04;
   const FSLI4GF_GOING             = 0x08;
   const FSLI4GF_SPLIT             = 0x10;



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   /*
    * Bits defined within the transport flag byte.
    */
   const FSLI4TF_RDMA              = 0x01;

   /*
    * Defines a set of replicas sharing
    * a common value of the rootpath
    * with in the corresponding
    * single-server namespaces.
    */
   struct  fs_locations_item4 {
           fs_locations_server4    fli_entries<>;
           pathname4               fli_rootpath;
   };

   /*
    * Defines the overall structure of
    * the fs_locations_info attribute.
    */
   struct  fs_locations_info4 {
           uint32_t                fli_flags;
           int32_t                 fli_valid_for;
           pathname4               fli_fs_root;
           fs_locations_item4      fli_items<>;
   };

   /*
    * Flag bits in fli_flags.
    */
   const FSLI4IF_VAR_SUB           = 0x00000001;

   typedef fs_locations_info4 fattr4_fs_locations_info;

   As noted above, the fs_locations_info attribute, when supported, may
   be requested of absent file systems without causing NFS4ERR_MOVED to
   be returned.  It is generally expected that it will be available for
   both present and absent file systems even if only a single
   fs_locations_server4 entry is present, designating the current
   (present) file system, or two fs_locations_server4 entries
   designating the previous location of an absent file system (the one
   just referenced) and its successor location.  Servers are strongly
   urged to support this attribute on all file systems if they support
   it on any file system.

   The data presented in the fs_locations_info attribute may be obtained
   by the server in any number of ways, including specification by the
   administrator or by current protocols for transferring data among



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   replicas and protocols not yet developed.  NFSv4.1 only defines how
   this information is presented by the server to the client.

11.10.1.  The fs_locations_server4 Structure

   The fs_locations_server4 structure consists of the following items:

   o  An indication of how up-to-date the file system is (fls_currency)
      in seconds.  This value is relative to the master copy.  A
      negative value indicates that the server is unable to give any
      reasonably useful value here.  A value of zero indicates that the
      file system is the actual writable data or a reliably coherent and
      fully up-to-date copy.  Positive values indicate how out-of-date
      this copy can normally be before it is considered for update.
      Such a value is not a guarantee that such updates will always be
      performed on the required schedule but instead serves as a hint
      about how far the copy of the data would be expected to be behind
      the most up-to-date copy.

   o  A counted array of one-byte values (fls_info) containing
      information about the particular file system instance.  This data
      includes general flags, transport capability flags, file system
      equivalence class information, and selection priority information.
      The encoding will be discussed below.

   o  The server string (fls_server).  For the case of the replica
      currently being accessed (via GETATTR), a zero-length string MAY
      be used to indicate the current address being used for the RPC
      call.  The fls_server field can also be an IPv4 or IPv6 address,
      formatted the same way as an IPv4 or IPv6 address in the "server"
      field of the fs_location4 data type (see Section 11.9).

   Data within the fls_info array is in the form of 8-bit data items
   with constants giving the offsets within the array of various values
   describing this particular file system instance.  This style of
   definition was chosen, in preference to explicit XDR structure
   definitions for these values, for a number of reasons.

   o  The kinds of data in the fls_info array, representing flags, file
      system classes, and priorities among sets of file systems
      representing the same data, are such that 8 bits provide a quite
      acceptable range of values.  Even where there might be more than
      256 such file system instances, having more than 256 distinct
      classes or priorities is unlikely.

   o  Explicit definition of the various specific data items within XDR
      would limit expandability in that any extension within a




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      subsequent minor version would require yet another attribute,
      leading to specification and implementation clumsiness.

   o  Such explicit definitions would also make it impossible to propose
      Standards Track extensions apart from a full minor version.

   This encoding scheme can be adapted to the specification of multi-
   byte numeric values, even though none are currently defined.  If
   extensions are made via Standards Track RFCs, multi-byte quantities
   will be encoded as a range of bytes with a range of indices, with the
   byte interpreted in big-endian byte order.  Further, any such index
   assignments are constrained so that the relevant quantities will not
   cross XDR word boundaries.

   The set of fls_info data is subject to expansion in a future minor
   version, or in a Standards Track RFC, within the context of a single
   minor version.  The server SHOULD NOT send and the client MUST NOT
   use indices within the fls_info array that are not defined in
   Standards Track RFCs.

   The fls_info array contains:

   o  Two 8-bit flag fields, one devoted to general file-system
      characteristics and a second reserved for transport-related
      capabilities.

   o  Six 8-bit class values that define various file system equivalence
      classes as explained below.

   o  Four 8-bit priority values that govern file system selection as
      explained below.

   The general file system characteristics flag (at byte index
   FSLI4BX_GFLAGS) has the following bits defined within it:

   o  FSLI4GF_WRITABLE indicates that this file system target is
      writable, allowing it to be selected by clients that may need to
      write on this file system.  When the current file system instance
      is writable and is defined as of the same simultaneous use class
      (as specified by the value at index FSLI4BX_CLSIMUL) to which the
      client was previously writing, then it must incorporate within its
      data any committed write made on the source file system instance.
      See Section 11.7.8, which discusses the write-verifier class.
      While there is no harm in not setting this flag for a file system
      that turns out to be writable, turning the flag on for a read-only
      file system can cause problems for clients that select a migration
      or replication target based on the flag and then find themselves
      unable to write.



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   o  FSLI4GF_CUR_REQ indicates that this replica is the one on which
      the request is being made.  Only a single server entry may have
      this flag set and, in the case of a referral, no entry will have
      it.

   o  FSLI4GF_ABSENT indicates that this entry corresponds to an absent
      file system replica.  It can only be set if FSLI4GF_CUR_REQ is
      set.  When both such bits are set, it indicates that a file system
      instance is not usable but that the information in the entry can
      be used to determine the sorts of continuity available when
      switching from this replica to other possible replicas.  Since
      this bit can only be true if FSLI4GF_CUR_REQ is true, the value
      could be determined using the fs_status attribute, but the
      information is also made available here for the convenience of the
      client.  An entry with this bit, since it represents a true file
      system (albeit absent), does not appear in the event of a
      referral, but only when a file system has been accessed at this
      location and has subsequently been migrated.

   o  FSLI4GF_GOING indicates that a replica, while still available,
      should not be used further.  The client, if using it, should make
      an orderly transfer to another file system instance as
      expeditiously as possible.  It is expected that file systems going
      out of service will be announced as FSLI4GF_GOING some time before
      the actual loss of service.  It is also expected that the
      fli_valid_for value will be sufficiently small to allow clients to
      detect and act on scheduled events, while large enough that the
      cost of the requests to fetch the fs_locations_info values will
      not be excessive.  Values on the order of ten minutes seem
      reasonable.

      When this flag is seen as part of a transition into a new file
      system, a client might choose to transfer immediately to another
      replica, or it may reference the current file system and only
      transition when a migration event occurs.  Similarly, when this
      flag appears as a replica in the referral, clients would likely
      avoid being referred to this instance whenever there is another
      choice.

   o  FSLI4GF_SPLIT indicates that when a transition occurs from the
      current file system instance to this one, the replacement may
      consist of multiple file systems.  In this case, the client has to
      be prepared for the possibility that objects on the same file
      system before migration will be on different ones after.  Note
      that FSLI4GF_SPLIT is not incompatible with the file systems
      belonging to the same fileid class since, if one has a set of
      fileids that are unique within a file system, each subset assigned




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      to a smaller file system after migration would not have any
      conflicts internal to that file system.

      A client, in the case of a split file system, will interrogate
      existing files with which it has continuing connection (it is free
      to simply forget cached filehandles).  If the client remembers the
      directory filehandle associated with each open file, it may
      proceed upward using LOOKUPP to find the new file system
      boundaries.  Note that in the event of a referral, there will not
      be any such files and so these actions will not be performed.
      Instead, a reference to a portion of the original file system now
      split off into other file systems will encounter an fsid change
      and possibly a further referral.

      Once the client recognizes that one file system has been split
      into two, it can prevent the disruption of running applications by
      presenting the two file systems as a single one until a convenient
      point to recognize the transition, such as a restart.  This would
      require a mapping from the server's fsids to fsids as seen by the
      client, but this is already necessary for other reasons.  As noted
      above, existing fileids within the two descendant file systems
      will not conflict.  Providing non-conflicting fileids for newly
      created files on the split file systems is the responsibility of
      the server (or servers working in concert).  The server can encode
      filehandles such that filehandles generated before the split event
      can be discerned from those generated after the split, allowing
      the server to determine when the need for emulating two file
      systems as one is over.

      Although it is possible for this flag to be present in the event
      of referral, it would generally be of little interest to the
      client, since the client is not expected to have information
      regarding the current contents of the absent file system.

   The transport-flag field (at byte index FSLI4BX_TFLAGS) contains the
   following bits related to the transport capabilities of the specific
   file system.

   o  FSLI4TF_RDMA indicates that this file system provides NFSv4.1 file
      system access using an RDMA-capable transport.

   Attribute continuity and file system identity information are
   expressed by defining equivalence relations on the sets of file
   systems presented to the client.  Each such relation is expressed as
   a set of file system equivalence classes.  For each relation, a file
   system has an 8-bit class number.  Two file systems belong to the
   same class if both have identical non-zero class numbers.  Zero is
   treated as non-matching.  Most often, the relevant question for the



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   client will be whether a given replica is identical to / continuous
   with the current one in a given respect, but the information should
   be available also as to whether two other replicas match in that
   respect as well.

   The following fields specify the file system's class numbers for the
   equivalence relations used in determining the nature of file system
   transitions.  See Section 11.7 and its various subsections for
   details about how this information is to be used.  Servers may assign
   these values as they wish, so long as file system instances that
   share the same value have the specified relationship to one another;
   conversely, file systems that have the specified relationship to one
   another share a common class value.  As each instance entry is added,
   the relationships of this instance to previously entered instances
   can be consulted, and if one is found that bears the specified
   relationship, that entry's class value can be copied to the new
   entry.  When no such previous entry exists, a new value for that byte
   index (not previously used) can be selected, most likely by
   incrementing the value of the last class value assigned for that
   index.

   o  The field with byte index FSLI4BX_CLSIMUL defines the
      simultaneous-use class for the file system.

   o  The field with byte index FSLI4BX_CLHANDLE defines the handle
      class for the file system.

   o  The field with byte index FSLI4BX_CLFILEID defines the fileid
      class for the file system.

   o  The field with byte index FSLI4BX_CLWRITEVER defines the write-
      verifier class for the file system.

   o  The field with byte index FSLI4BX_CLCHANGE defines the change
      class for the file system.

   o  The field with byte index FSLI4BX_CLREADDIR defines the readdir
      class for the file system.

   Server-specified preference information is also provided via 8-bit
   values within the fls_info array.  The values provide a rank and an
   order (see below) to be used with separate values specifiable for the
   cases of read-only and writable file systems.  These values are
   compared for different file systems to establish the server-specified
   preference, with lower values indicating "more preferred".

   Rank is used to express a strict server-imposed ordering on clients,
   with lower values indicating "more preferred".  Clients should



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   attempt to use all replicas with a given rank before they use one
   with a higher rank.  Only if all of those file systems are
   unavailable should the client proceed to those of a higher rank.
   Because specifying a rank will override client preferences, servers
   should be conservative about using this mechanism, particularly when
   the environment is one in which client communication characteristics
   are neither tightly controlled nor visible to the server.

   Within a rank, the order value is used to specify the server's
   preference to guide the client's selection when the client's own
   preferences are not controlling, with lower values of order
   indicating "more preferred".  If replicas are approximately equal in
   all respects, clients should defer to the order specified by the
   server.  When clients look at server latency as part of their
   selection, they are free to use this criterion but it is suggested
   that when latency differences are not significant, the server-
   specified order should guide selection.

   o  The field at byte index FSLI4BX_READRANK gives the rank value to
      be used for read-only access.

   o  The field at byte index FSLI4BX_READORDER gives the order value to
      be used for read-only access.

   o  The field at byte index FSLI4BX_WRITERANK gives the rank value to
      be used for writable access.

   o  The field at byte index FSLI4BX_WRITEORDER gives the order value
      to be used for writable access.

   Depending on the potential need for write access by a given client,
   one of the pairs of rank and order values is used.  The read rank and
   order should only be used if the client knows that only reading will
   ever be done or if it is prepared to switch to a different replica in
   the event that any write access capability is required in the future.

11.10.2.  The fs_locations_info4 Structure

   The fs_locations_info4 structure, encoding the fs_locations_info
   attribute, contains the following:

   o  The fli_flags field, which contains general flags that affect the
      interpretation of this fs_locations_info4 structure and all
      fs_locations_item4 structures within it.  The only flag currently
      defined is FSLI4IF_VAR_SUB.  All bits in the fli_flags field that
      are not defined should always be returned as zero.





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   o  The fli_fs_root field, which contains the pathname of the root of
      the current file system on the current server, just as it does in
      the fs_locations4 structure.

   o  An array called fli_items of fs_locations4_item structures, which
      contain information about replicas of the current file system.
      Where the current file system is actually present, or has been
      present, i.e., this is not a referral situation, one of the
      fs_locations_item4 structures will contain an fs_locations_server4
      for the current server.  This structure will have FSLI4GF_ABSENT
      set if the current file system is absent, i.e., normal access to
      it will return NFS4ERR_MOVED.

   o  The fli_valid_for field specifies a time in seconds for which it
      is reasonable for a client to use the fs_locations_info attribute
      without refetch.  The fli_valid_for value does not provide a
      guarantee of validity since servers can unexpectedly go out of
      service or become inaccessible for any number of reasons.  Clients
      are well-advised to refetch this information for an actively
      accessed file system at every fli_valid_for seconds.  This is
      particularly important when file system replicas may go out of
      service in a controlled way using the FSLI4GF_GOING flag to
      communicate an ongoing change.  The server should set
      fli_valid_for to a value that allows well-behaved clients to
      notice the FSLI4GF_GOING flag and make an orderly switch before
      the loss of service becomes effective.  If this value is zero,
      then no refetch interval is appropriate and the client need not
      refetch this data on any particular schedule.  In the event of a
      transition to a new file system instance, a new value of the
      fs_locations_info attribute will be fetched at the destination.
      It is to be expected that this may have a different fli_valid_for
      value, which the client should then use in the same fashion as the
      previous value.

   The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
   substitution is to be enabled.  See Section 11.10.3 for an
   explanation of variable substitution.

11.10.3.  The fs_locations_item4 Structure

   The fs_locations_item4 structure contains a pathname (in the field
   fli_rootpath) that encodes the path of the target file system
   replicas on the set of servers designated by the included
   fs_locations_server4 entries.  The precise manner in which this
   target location is specified depends on the value of the
   FSLI4IF_VAR_SUB flag within the associated fs_locations_info4
   structure.




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   If this flag is not set, then fli_rootpath simply designates the
   location of the target file system within each server's single-server
   namespace just as it does for the rootpath within the fs_location4
   structure.  When this bit is set, however, component entries of a
   certain form are subject to client-specific variable substitution so
   as to allow a degree of namespace non-uniformity in order to
   accommodate the selection of client-specific file system targets to
   adapt to different client architectures or other characteristics.

   When such substitution is in effect, a variable beginning with the
   string "${" and ending with the string "}" and containing a colon is
   to be replaced by the client-specific value associated with that
   variable.  The string "unknown" should be used by the client when it
   has no value for such a variable.  The pathname resulting from such
   substitutions is used to designate the target file system, so that
   different clients may have different file systems, corresponding to
   that location in the multi-server namespace.

   As mentioned above, such substituted pathname variables contain a
   colon.  The part before the colon is to be a DNS domain name, and the
   part after is to be a case-insensitive alphanumeric string.

   Where the domain is "ietf.org", only variable names defined in this
   document or subsequent Standards Track RFCs are subject to such
   substitution.  Organizations are free to use their domain names to
   create their own sets of client-specific variables, to be subject to
   such substitution.  In cases where such variables are intended to be
   used more broadly than a single organization, publication of an
   Informational RFC defining such variables is RECOMMENDED.

   The variable ${ietf.org:CPU_ARCH} is used to denote that the CPU
   architecture object files are compiled.  This specification does not
   limit the acceptable values (except that they must be valid UTF-8
   strings), but such values as "x86", "x86_64", and "sparc" would be
   expected to be used in line with industry practice.

   The variable ${ietf.org:OS_TYPE} is used to denote the operating
   system, and thus the kernel and library APIs, for which code might be
   compiled.  This specification does not limit the acceptable values
   (except that they must be valid UTF-8 strings), but such values as
   "linux" and "freebsd" would be expected to be used in line with
   industry practice.

   The variable ${ietf.org:OS_VERSION} is used to denote the operating
   system version, and thus the specific details of versioned
   interfaces, for which code might be compiled.  This specification
   does not limit the acceptable values (except that they must be valid
   UTF-8 strings).  However, combinations of numbers and letters with



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   interspersed dots would be expected to be used in line with industry
   practice, with the details of the version format depending on the
   specific value of the variable ${ietf.org:OS_TYPE} with which it is
   used.

   Use of these variables could result in the direction of different
   clients to different file systems on the same server, as appropriate
   to particular clients.  In cases in which the target file systems are
   located on different servers, a single server could serve as a
   referral point so that each valid combination of variable values
   would designate a referral hosted on a single server, with the
   targets of those referrals on a number of different servers.

   Because namespace administration is affected by the values selected
   to substitute for various variables, clients should provide
   convenient means of determining what variable substitutions a client
   will implement, as well as, where appropriate, providing means to
   control the substitutions to be used.  The exact means by which this
   will be done is outside the scope of this specification.

   Although variable substitution is most suitable for use in the
   context of referrals, it may be used in the context of replication
   and migration.  If it is used in these contexts, the server must
   ensure that no matter what values the client presents for the
   substituted variables, the result is always a valid successor file
   system instance to that from which a transition is occurring, i.e.,
   that the data is identical or represents a later image of a writable
   file system.

   Note that when fli_rootpath is a null pathname (that is, one with
   zero components), the file system designated is at the root of the
   specified server, whether or not the FSLI4IF_VAR_SUB flag within the
   associated fs_locations_info4 structure is set.

11.11.  The Attribute fs_status

   In an environment in which multiple copies of the same basic set of
   data are available, information regarding the particular source of
   such data and the relationships among different copies can be very
   helpful in providing consistent data to applications.











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   enum fs4_status_type {
           STATUS4_FIXED = 1,
           STATUS4_UPDATED = 2,
           STATUS4_VERSIONED = 3,
           STATUS4_WRITABLE = 4,
           STATUS4_REFERRAL = 5
   };

   struct fs4_status {
           bool            fss_absent;
           fs4_status_type fss_type;
           utf8str_cs      fss_source;
           utf8str_cs      fss_current;
           int32_t         fss_age;
           nfstime4        fss_version;
   };

   The boolean fss_absent indicates whether the file system is currently
   absent.  This value will be set if the file system was previously
   present and becomes absent, or if the file system has never been
   present and the type is STATUS4_REFERRAL.  When this boolean is set
   and the type is not STATUS4_REFERRAL, the remaining information in
   the fs4_status reflects that last valid when the file system was
   present.

   The fss_type field indicates the kind of file system image
   represented.  This is of particular importance when using the version
   values to determine appropriate succession of file system images.
   When fss_absent is set, and the file system was previously present,
   the value of fss_type reflected is that when the file was last
   present.  Five values are distinguished:

   o  STATUS4_FIXED, which indicates a read-only image in the sense that
      it will never change.  The possibility is allowed that, as a
      result of migration or switch to a different image, changed data
      can be accessed, but within the confines of this instance, no
      change is allowed.  The client can use this fact to cache
      aggressively.

   o  STATUS4_VERSIONED, which indicates that the image, like the
      STATUS4_UPDATED case, is updated externally, but it provides a
      guarantee that the server will carefully update an associated
      version value so that the client can protect itself from a
      situation in which it reads data from one version of the file
      system and then later reads data from an earlier version of the
      same file system.  See below for a discussion of how this can be
      done.




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   o  STATUS4_UPDATED, which indicates an image that cannot be updated
      by the user writing to it but that may be changed externally,
      typically because it is a periodically updated copy of another
      writable file system somewhere else.  In this case, version
      information is not provided, and the client does not have the
      responsibility of making sure that this version only advances upon
      a file system instance transition.  In this case, it is the
      responsibility of the server to make sure that the data presented
      after a file system instance transition is a proper successor
      image and includes all changes seen by the client and any change
      made before all such changes.

   o  STATUS4_WRITABLE, which indicates that the file system is an
      actual writable one.  The client need not, of course, actually
      write to the file system, but once it does, it should not accept a
      transition to anything other than a writable instance of that same
      file system.

   o  STATUS4_REFERRAL, which indicates that the file system in question
      is absent and has never been present on this server.

   Note that in the STATUS4_UPDATED and STATUS4_VERSIONED cases, the
   server is responsible for the appropriate handling of locks that are
   inconsistent with external changes to delegations.  If a server gives
   out delegations, they SHOULD be recalled before an inconsistent
   change is made to the data, and MUST be revoked if this is not
   possible.  Similarly, if an OPEN is inconsistent with data that is
   changed (the OPEN has OPEN4_SHARE_DENY_WRITE/OPEN4_SHARE_DENY_BOTH
   and the data is changed), that OPEN SHOULD be considered
   administratively revoked.

   The opaque strings fss_source and fss_current provide a way of
   presenting information about the source of the file system image
   being present.  It is not intended that the client do anything with
   this information other than make it available to administrative
   tools.  It is intended that this information be helpful when
   researching possible problems with a file system image that might
   arise when it is unclear if the correct image is being accessed and,
   if not, how that image came to be made.  This kind of diagnostic
   information will be helpful, if, as seems likely, copies of file
   systems are made in many different ways (e.g., simple user-level
   copies, file-system-level point-in-time copies, clones of the
   underlying storage), under a variety of administrative arrangements.
   In such environments, determining how a given set of data was
   constructed can be very helpful in resolving problems.

   The opaque string fss_source is used to indicate the source of a
   given file system with the expectation that tools capable of creating



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   a file system image propagate this information, when possible.  It is
   understood that this may not always be possible since a user-level
   copy may be thought of as creating a new data set and the tools used
   may have no mechanism to propagate this data.  When a file system is
   initially created, it is desirable to associate with it data
   regarding how the file system was created, where it was created, who
   created it, etc.  Making this information available in this attribute
   in a human-readable string will be helpful for applications and
   system administrators and will also serve to make it available when
   the original file system is used to make subsequent copies.

   The opaque string fss_current should provide whatever information is
   available about the source of the current copy.  Such information
   includes the tool creating it, any relevant parameters to that tool,
   the time at which the copy was done, the user making the change, the
   server on which the change was made, etc.  All information should be
   in a human-readable string.

   The field fss_age provides an indication of how out-of-date the file
   system currently is with respect to its ultimate data source (in case
   of cascading data updates).  This complements the fls_currency field
   of fs_locations_server4 (see Section 11.10) in the following way: the
   information in fls_currency gives a bound for how out of date the
   data in a file system might typically get, while the value in fss_age
   gives a bound on how out-of-date that data actually is.  Negative
   values imply that no information is available.  A zero means that
   this data is known to be current.  A positive value means that this
   data is known to be no older than that number of seconds with respect
   to the ultimate data source.  Using this value, the client may be
   able to decide that a data copy is too old, so that it may search for
   a newer version to use.

   The fss_version field provides a version identification, in the form
   of a time value, such that successive versions always have later time
   values.  When the fs_type is anything other than STATUS4_VERSIONED,
   the server may provide such a value, but there is no guarantee as to
   its validity and clients will not use it except to provide additional
   information to add to fss_source and fss_current.

   When fss_type is STATUS4_VERSIONED, servers SHOULD provide a value of
   fss_version that progresses monotonically whenever any new version of
   the data is established.  This allows the client, if reliable image
   progression is important to it, to fetch this attribute as part of
   each COMPOUND where data or metadata from the file system is used.

   When it is important to the client to make sure that only valid
   successor images are accepted, it must make sure that it does not
   read data or metadata from the file system without updating its sense



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   of the current state of the image.  This is to avoid the possibility
   that the fs_status that the client holds will be one for an earlier
   image, which would cause the client to accept a new file system
   instance that is later than that but still earlier than the updated
   data read by the client.

   In order to accept valid images reliably, the client must do a
   GETATTR of the fs_status attribute that follows any interrogation of
   data or metadata within the file system in question.  Often this is
   most conveniently done by appending such a GETATTR after all other
   operations that reference a given file system.  When errors occur
   between reading file system data and performing such a GETATTR, care
   must be exercised to make sure that the data in question is not used
   before obtaining the proper fs_status value.  In this connection,
   when an OPEN is done within such a versioned file system and the
   associated GETATTR of fs_status is not successfully completed, the
   open file in question must not be accessed until that fs_status is
   fetched.

   The procedure above will ensure that before using any data from the
   file system the client has in hand a newly-fetched current version of
   the file system image.  Multiple values for multiple requests in
   flight can be resolved by assembling them into the required partial
   order (and the elements should form a total order within the partial
   order) and using the last.  The client may then, when switching among
   file system instances, decline to use an instance that does not have
   an fss_type of STATUS4_VERSIONED or whose fss_version field is
   earlier than the last one obtained from the predecessor file system
   instance.

12.  Parallel NFS (pNFS)

12.1.  Introduction

   pNFS is an OPTIONAL feature within NFSv4.1; the pNFS feature set
   allows direct client access to the storage devices containing file
   data.  When file data for a single NFSv4 server is stored on multiple
   and/or higher-throughput storage devices (by comparison to the
   server's throughput capability), the result can be significantly
   better file access performance.  The relationship among multiple
   clients, a single server, and multiple storage devices for pNFS
   (server and clients have access to all storage devices) is shown in
   Figure 1.








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       +-----------+
       |+-----------+                                 +-----------+
       ||+-----------+                                |           |
       |||           |        NFSv4.1 + pNFS          |           |
       +||  Clients  |<------------------------------>|   Server  |
        +|           |                                |           |
         +-----------+                                |           |
              |||                                     +-----------+
              |||                                           |
              |||                                           |
              ||| Storage        +-----------+              |
              ||| Protocol       |+-----------+             |
              ||+----------------||+-----------+  Control   |
              |+-----------------|||           |    Protocol|
              +------------------+||  Storage  |------------+
                                  +|  Devices  |
                                   +-----------+

                                 Figure 1

   In this model, the clients, server, and storage devices are
   responsible for managing file access.  This is in contrast to NFSv4
   without pNFS, where it is primarily the server's responsibility; some
   of this responsibility may be delegated to the client under strictly
   specified conditions.  See Section 12.2.5 for a discussion of the
   Storage Protocol.  See Section 12.2.6 for a discussion of the Control
   Protocol.

   pNFS takes the form of OPTIONAL operations that manage protocol
   objects called 'layouts' (Section 12.2.7) that contain a byte-range
   and storage location information.  The layout is managed in a similar
   fashion as NFSv4.1 data delegations.  For example, the layout is
   leased, recallable, and revocable.  However, layouts are distinct
   abstractions and are manipulated with new operations.  When a client
   holds a layout, it is granted the ability to directly access the
   byte-range at the storage location specified in the layout.

   There are interactions between layouts and other NFSv4.1 abstractions
   such as data delegations and byte-range locking.  Delegation issues
   are discussed in Section 12.5.5.  Byte-range locking issues are
   discussed in Sections 12.2.9 and 12.5.1.

12.2.  pNFS Definitions

   NFSv4.1's pNFS feature provides parallel data access to a file system
   that stripes its content across multiple storage servers.  The first
   instantiation of pNFS, as part of NFSv4.1, separates the file system
   protocol processing into two parts: metadata processing and data



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   processing.  Data consist of the contents of regular files that are
   striped across storage servers.  Data striping occurs in at least two
   ways: on a file-by-file basis and, within sufficiently large files,
   on a block-by-block basis.  In contrast, striped access to metadata
   by pNFS clients is not provided in NFSv4.1, even though the file
   system back end of a pNFS server might stripe metadata.  Metadata
   consist of everything else, including the contents of non-regular
   files (e.g., directories); see Section 12.2.1.  The metadata
   functionality is implemented by an NFSv4.1 server that supports pNFS
   and the operations described in Section 18; such a server is called a
   metadata server (Section 12.2.2).

   The data functionality is implemented by one or more storage devices,
   each of which are accessed by the client via a storage protocol.  A
   subset (defined in Section 13.6) of NFSv4.1 is one such storage
   protocol.  New terms are introduced to the NFSv4.1 nomenclature and
   existing terms are clarified to allow for the description of the pNFS
   feature.

12.2.1.  Metadata

   Information about a file system object, such as its name, location
   within the namespace, owner, ACL, and other attributes.  Metadata may
   also include storage location information, and this will vary based
   on the underlying storage mechanism that is used.

12.2.2.  Metadata Server

   An NFSv4.1 server that supports the pNFS feature.  A variety of
   architectural choices exist for the metadata server and its use of
   file system information held at the server.  Some servers may contain
   metadata only for file objects residing at the metadata server, while
   the file data resides on associated storage devices.  Other metadata
   servers may hold both metadata and a varying degree of file data.

12.2.3.  pNFS Client

   An NFSv4.1 client that supports pNFS operations and supports at least
   one storage protocol for performing I/O to storage devices.

12.2.4.  Storage Device

   A storage device stores a regular file's data, but leaves metadata
   management to the metadata server.  A storage device could be another
   NFSv4.1 server, an object-based storage device (OSD), a block device
   accessed over a System Area Network (SAN, e.g., either FiberChannel
   or iSCSI SAN), or some other entity.




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12.2.5.  Storage Protocol

   As noted in Figure 1, the storage protocol is the method used by the
   client to store and retrieve data directly from the storage devices.

   The NFSv4.1 pNFS feature has been structured to allow for a variety
   of storage protocols to be defined and used.  One example storage
   protocol is NFSv4.1 itself (as documented in Section 13).  Other
   options for the storage protocol are described elsewhere and include:

   o  Block/volume protocols such as Internet SCSI (iSCSI) [48] and FCP
      [49].  The block/volume protocol support can be independent of the
      addressing structure of the block/volume protocol used, allowing
      more than one protocol to access the same file data and enabling
      extensibility to other block/volume protocols.  See [41] for a
      layout specification that allows pNFS to use block/volume storage
      protocols.

   o  Object protocols such as OSD over iSCSI or Fibre Channel [50].
      See [40] for a layout specification that allows pNFS to use object
      storage protocols.

   It is possible that various storage protocols are available to both
   client and server and it may be possible that a client and server do
   not have a matching storage protocol available to them.  Because of
   this, the pNFS server MUST support normal NFSv4.1 access to any file
   accessible by the pNFS feature; this will allow for continued
   interoperability between an NFSv4.1 client and server.

12.2.6.  Control Protocol

   As noted in Figure 1, the control protocol is used by the exported
   file system between the metadata server and storage devices.
   Specification of such protocols is outside the scope of the NFSv4.1
   protocol.  Such control protocols would be used to control activities
   such as the allocation and deallocation of storage, the management of
   state required by the storage devices to perform client access
   control, and, depending on the storage protocol, the enforcement of
   authentication and authorization so that restrictions that would be
   enforced by the metadata server are also enforced by the storage
   device.

   A particular control protocol is not REQUIRED by NFSv4.1 but
   requirements are placed on the control protocol for maintaining
   attributes like modify time, the change attribute, and the end-of-
   file (EOF) position.  Note that if pNFS is layered over a clustered,
   parallel file system (e.g., PVFS [51]), the mechanisms that enable




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   clustering and parallelism in that file system can be considered the
   control protocol.

12.2.7.  Layout Types

   A layout describes the mapping of a file's data to the storage
   devices that hold the data.  A layout is said to belong to a specific
   layout type (data type layouttype4, see Section 3.3.13).  The layout
   type allows for variants to handle different storage protocols, such
   as those associated with block/volume [41], object [40], and file
   (Section 13) layout types.  A metadata server, along with its control
   protocol, MUST support at least one layout type.  A private sub-range
   of the layout type namespace is also defined.  Values from the
   private layout type range MAY be used for internal testing or
   experimentation (see Section 3.3.13).

   As an example, the organization of the file layout type could be an
   array of tuples (e.g., device ID, filehandle), along with a
   definition of how the data is stored across the devices (e.g.,
   striping).  A block/volume layout might be an array of tuples that
   store <device ID, block number, block count> along with information
   about block size and the associated file offset of the block number.
   An object layout might be an array of tuples <device ID, object ID>
   and an additional structure (i.e., the aggregation map) that defines
   how the logical byte sequence of the file data is serialized into the
   different objects.  Note that the actual layouts are typically more
   complex than these simple expository examples.

   Requests for pNFS-related operations will often specify a layout
   type.  Examples of such operations are GETDEVICEINFO and LAYOUTGET.
   The response for these operations will include structures such as a
   device_addr4 or a layout4, each of which includes a layout type
   within it.  The layout type sent by the server MUST always be the
   same one requested by the client.  When a server sends a response
   that includes a different layout type, the client SHOULD ignore the
   response and behave as if the server had returned an error response.

12.2.8.  Layout

   A layout defines how a file's data is organized on one or more
   storage devices.  There are many potential layout types; each of the
   layout types are differentiated by the storage protocol used to
   access data and by the aggregation scheme that lays out the file data
   on the underlying storage devices.  A layout is precisely identified
   by the tuple <client ID, filehandle, layout type, iomode, range>,
   where filehandle refers to the filehandle of the file on the metadata
   server.




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   It is important to define when layouts overlap and/or conflict with
   each other.  For two layouts with overlapping byte-ranges to actually
   overlap each other, both layouts must be of the same layout type,
   correspond to the same filehandle, and have the same iomode.  Layouts
   conflict when they overlap and differ in the content of the layout
   (i.e., the storage device/file mapping parameters differ).  Note that
   differing iomodes do not lead to conflicting layouts.  It is
   permissible for layouts with different iomodes, pertaining to the
   same byte-range, to be held by the same client.  An example of this
   would be copy-on-write functionality for a block/volume layout type.

12.2.9.  Layout Iomode

   The layout iomode (data type layoutiomode4, see Section 3.3.20)
   indicates to the metadata server the client's intent to perform
   either just READ operations or a mixture containing READ and WRITE
   operations.  For certain layout types, it is useful for a client to
   specify this intent at the time it sends LAYOUTGET (Section 18.43).
   For example, for block/volume-based protocols, block allocation could
   occur when a LAYOUTIOMODE4_RW iomode is specified.  A special
   LAYOUTIOMODE4_ANY iomode is defined and can only be used for
   LAYOUTRETURN and CB_LAYOUTRECALL, not for LAYOUTGET.  It specifies
   that layouts pertaining to both LAYOUTIOMODE4_READ and
   LAYOUTIOMODE4_RW iomodes are being returned or recalled,
   respectively.

   A storage device may validate I/O with regard to the iomode; this is
   dependent upon storage device implementation and layout type.  Thus,
   if the client's layout iomode is inconsistent with the I/O being
   performed, the storage device may reject the client's I/O with an
   error indicating that a new layout with the correct iomode should be
   obtained via LAYOUTGET.  For example, if a client gets a layout with
   a LAYOUTIOMODE4_READ iomode and performs a WRITE to a storage device,
   the storage device is allowed to reject that WRITE.

   The use of the layout iomode does not conflict with OPEN share modes
   or byte-range LOCK operations; open share mode and byte-range lock
   conflicts are enforced as they are without the use of pNFS and are
   logically separate from the pNFS layout level.  Open share modes and
   byte-range locks are the preferred method for restricting user access
   to data files.  For example, an OPEN of OPEN4_SHARE_ACCESS_WRITE does
   not conflict with a LAYOUTGET containing an iomode of
   LAYOUTIOMODE4_RW performed by another client.  Applications that
   depend on writing into the same file concurrently may use byte-range
   locking to serialize their accesses.






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12.2.10.  Device IDs

   The device ID (data type deviceid4, see Section 3.3.14) identifies a
   group of storage devices.  The scope of a device ID is the pair
   <client ID, layout type>.  In practice, a significant amount of
   information may be required to fully address a storage device.
   Rather than embedding all such information in a layout, layouts embed
   device IDs.  The NFSv4.1 operation GETDEVICEINFO (Section 18.40) is
   used to retrieve the complete address information (including all
   device addresses for the device ID) regarding the storage device
   according to its layout type and device ID.  For example, the address
   of an NFSv4.1 data server or of an object-based storage device could
   be an IP address and port.  The address of a block storage device
   could be a volume label.

   Clients cannot expect the mapping between a device ID and its storage
   device address(es) to persist across metadata server restart.  See
   Section 12.7.4 for a description of how recovery works in that
   situation.

   A device ID lives as long as there is a layout referring to the
   device ID.  If there are no layouts referring to the device ID, the
   server is free to delete the device ID any time.  Once a device ID is
   deleted by the server, the server MUST NOT reuse the device ID for
   the same layout type and client ID again.  This requirement is
   feasible because the device ID is 16 bytes long, leaving sufficient
   room to store a generation number if the server's implementation
   requires most of the rest of the device ID's content to be reused.
   This requirement is necessary because otherwise the race conditions
   between asynchronous notification of device ID addition and deletion
   would be too difficult to sort out.

   Device ID to device address mappings are not leased, and can be
   changed at any time.  (Note that while device ID to device address
   mappings are likely to change after the metadata server restarts, the
   server is not required to change the mappings.)  A server has two
   choices for changing mappings.  It can recall all layouts referring
   to the device ID or it can use a notification mechanism.

   The NFSv4.1 protocol has no optimal way to recall all layouts that
   referred to a particular device ID (unless the server associates a
   single device ID with a single fsid or a single client ID; in which
   case, CB_LAYOUTRECALL has options for recalling all layouts
   associated with the fsid, client ID pair, or just the client ID).

   Via a notification mechanism (see Section 20.12), device ID to device
   address mappings can change over the duration of server operation
   without recalling or revoking the layouts that refer to device ID.



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   The notification mechanism can also delete a device ID, but only if
   the client has no layouts referring to the device ID.  A notification
   of a change to a device ID to device address mapping will immediately
   or eventually invalidate some or all of the device ID's mappings.
   The server MUST support notifications and the client must request
   them before they can be used.  For further information about the
   notification types Section 20.12.

12.3.  pNFS Operations

   NFSv4.1 has several operations that are needed for pNFS servers,
   regardless of layout type or storage protocol.  These operations are
   all sent to a metadata server and summarized here.  While pNFS is an
   OPTIONAL feature, if pNFS is implemented, some operations are
   REQUIRED in order to comply with pNFS.  See Section 17.

   These are the fore channel pNFS operations:

   GETDEVICEINFO  (Section 18.40), as noted previously
      (Section 12.2.10), returns the mapping of device ID to storage
      device address.

   GETDEVICELIST  (Section 18.41) allows clients to fetch all device IDs
      for a specific file system.

   LAYOUTGET  (Section 18.43) is used by a client to get a layout for a
      file.

   LAYOUTCOMMIT  (Section 18.42) is used to inform the metadata server
      of the client's intent to commit data that has been written to the
      storage device (the storage device as originally indicated in the
      return value of LAYOUTGET).

   LAYOUTRETURN  (Section 18.44) is used to return layouts for a file, a
      file system ID (FSID), or a client ID.

   These are the backchannel pNFS operations:

   CB_LAYOUTRECALL  (Section 20.3) recalls a layout, all layouts
      belonging to a file system, or all layouts belonging to a client
      ID.

   CB_RECALL_ANY  (Section 20.6) tells a client that it needs to return
      some number of recallable objects, including layouts, to the
      metadata server.






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   CB_RECALLABLE_OBJ_AVAIL  (Section 20.7) tells a client that a
      recallable object that it was denied (in case of pNFS, a layout
      denied by LAYOUTGET) due to resource exhaustion is now available.

   CB_NOTIFY_DEVICEID  (Section 20.12) notifies the client of changes to
      device IDs.

12.4.  pNFS Attributes

   A number of attributes specific to pNFS are listed and described in
   Section 5.12.

12.5.  Layout Semantics

12.5.1.  Guarantees Provided by Layouts

   Layouts grant to the client the ability to access data located at a
   storage device with the appropriate storage protocol.  The client is
   guaranteed the layout will be recalled when one of two things occur:
   either a conflicting layout is requested or the state encapsulated by
   the layout becomes invalid (this can happen when an event directly or
   indirectly modifies the layout).  When a layout is recalled and
   returned by the client, the client continues with the ability to
   access file data with normal NFSv4.1 operations through the metadata
   server.  Only the ability to access the storage devices is affected.

   The requirement of NFSv4.1 that all user access rights MUST be
   obtained through the appropriate OPEN, LOCK, and ACCESS operations is
   not modified with the existence of layouts.  Layouts are provided to
   NFSv4.1 clients, and user access still follows the rules of the
   protocol as if they did not exist.  It is a requirement that for a
   client to access a storage device, a layout must be held by the
   client.  If a storage device receives an I/O request for a byte-range
   for which the client does not hold a layout, the storage device
   SHOULD reject that I/O request.  Note that the act of modifying a
   file for which a layout is held does not necessarily conflict with
   the holding of the layout that describes the file being modified.
   Therefore, it is the requirement of the storage protocol or layout
   type that determines the necessary behavior.  For example, block/
   volume layout types require that the layout's iomode agree with the
   type of I/O being performed.

   Depending upon the layout type and storage protocol in use, storage
   device access permissions may be granted by LAYOUTGET and may be
   encoded within the type-specific layout.  For an example of storage
   device access permissions, see an object-based protocol such as [50].
   If access permissions are encoded within the layout, the metadata
   server SHOULD recall the layout when those permissions become invalid



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   for any reason -- for example, when a file becomes unwritable or
   inaccessible to a client.  Note, clients are still required to
   perform the appropriate OPEN, LOCK, and ACCESS operations as
   described above.  The degree to which it is possible for the client
   to circumvent these operations and the consequences of doing so must
   be clearly specified by the individual layout type specifications.
   In addition, these specifications must be clear about the
   requirements and non-requirements for the checking performed by the
   server.

   In the presence of pNFS functionality, mandatory byte-range locks
   MUST behave as they would without pNFS.  Therefore, if mandatory file
   locks and layouts are provided simultaneously, the storage device
   MUST be able to enforce the mandatory byte-range locks.  For example,
   if one client obtains a mandatory byte-range lock and a second client
   accesses the storage device, the storage device MUST appropriately
   restrict I/O for the range of the mandatory byte-range lock.  If the
   storage device is incapable of providing this check in the presence
   of mandatory byte-range locks, then the metadata server MUST NOT
   grant layouts and mandatory byte-range locks simultaneously.

12.5.2.  Getting a Layout

   A client obtains a layout with the LAYOUTGET operation.  The metadata
   server will grant layouts of a particular type (e.g., block/volume,
   object, or file).  The client selects an appropriate layout type that
   the server supports and the client is prepared to use.  The layout
   returned to the client might not exactly match the requested byte-
   range as described in Section 18.43.3.  As needed a client may send
   multiple LAYOUTGET operations; these might result in multiple
   overlapping, non-conflicting layouts (see Section 12.2.8).

   In order to get a layout, the client must first have opened the file
   via the OPEN operation.  When a client has no layout on a file, it
   MUST present an open stateid, a delegation stateid, or a byte-range
   lock stateid in the loga_stateid argument.  A successful LAYOUTGET
   result includes a layout stateid.  The first successful LAYOUTGET
   processed by the server using a non-layout stateid as an argument
   MUST have the "seqid" field of the layout stateid in the response set
   to one.  Thereafter, the client MUST use a layout stateid (see
   Section 12.5.3) on future invocations of LAYOUTGET on the file, and
   the "seqid" MUST NOT be set to zero.  Once the layout has been
   retrieved, it can be held across multiple OPEN and CLOSE sequences.
   Therefore, a client may hold a layout for a file that is not
   currently open by any user on the client.  This allows for the
   caching of layouts beyond CLOSE.





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   The storage protocol used by the client to access the data on the
   storage device is determined by the layout's type.  The client is
   responsible for matching the layout type with an available method to
   interpret and use the layout.  The method for this layout type
   selection is outside the scope of the pNFS functionality.

   Although the metadata server is in control of the layout for a file,
   the pNFS client can provide hints to the server when a file is opened
   or created about the preferred layout type and aggregation schemes.
   pNFS introduces a layout_hint attribute (Section 5.12.4) that the
   client can set at file creation time to provide a hint to the server
   for new files.  Setting this attribute separately, after the file has
   been created might make it difficult, or impossible, for the server
   implementation to comply.

   Because the EXCLUSIVE4 createmode4 does not allow the setting of
   attributes at file creation time, NFSv4.1 introduces the EXCLUSIVE4_1
   createmode4, which does allow attributes to be set at file creation
   time.  In addition, if the session is created with persistent reply
   caches, EXCLUSIVE4_1 is neither necessary nor allowed.  Instead,
   GUARDED4 both works better and is prescribed.  Table 10 in
   Section 18.16.3 summarizes how a client is allowed to send an
   exclusive create.

12.5.3.  Layout Stateid

   As with all other stateids, the layout stateid consists of a "seqid"
   and "other" field.  Once a layout stateid is established, the "other"
   field will stay constant unless the stateid is revoked or the client
   returns all layouts on the file and the server disposes of the
   stateid.  The "seqid" field is initially set to one, and is never
   zero on any NFSv4.1 operation that uses layout stateids, whether it
   is a fore channel or backchannel operation.  After the layout stateid
   is established, the server increments by one the value of the "seqid"
   in each subsequent LAYOUTGET and LAYOUTRETURN response, and in each
   CB_LAYOUTRECALL request.

   Given the design goal of pNFS to provide parallelism, the layout
   stateid differs from other stateid types in that the client is
   expected to send LAYOUTGET and LAYOUTRETURN operations in parallel.
   The "seqid" value is used by the client to properly sort responses to
   LAYOUTGET and LAYOUTRETURN.  The "seqid" is also used to prevent race
   conditions between LAYOUTGET and CB_LAYOUTRECALL.  Given that the
   processing rules differ from layout stateids and other stateid types,
   only the pNFS sections of this document should be considered to
   determine proper layout stateid handling.





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   Once the client receives a layout stateid, it MUST use the correct
   "seqid" for subsequent LAYOUTGET or LAYOUTRETURN operations.  The
   correct "seqid" is defined as the highest "seqid" value from
   responses of fully processed LAYOUTGET or LAYOUTRETURN operations or
   arguments of a fully processed CB_LAYOUTRECALL operation.  Since the
   server is incrementing the "seqid" value on each layout operation,
   the client may determine the order of operation processing by
   inspecting the "seqid" value.  In the case of overlapping layout
   ranges, the ordering information will provide the client the
   knowledge of which layout ranges are held.  Note that overlapping
   layout ranges may occur because of the client's specific requests or
   because the server is allowed to expand the range of a requested
   layout and notify the client in the LAYOUTRETURN results.  Additional
   layout stateid sequencing requirements are provided in
   Section 12.5.5.2.

   The client's receipt of a "seqid" is not sufficient for subsequent
   use.  The client must fully process the operations before the "seqid"
   can be used.  For LAYOUTGET results, if the client is not using the
   forgetful model (Section 12.5.5.1), it MUST first update its record
   of what ranges of the file's layout it has before using the seqid.
   For LAYOUTRETURN results, the client MUST delete the range from its
   record of what ranges of the file's layout it had before using the
   seqid.  For CB_LAYOUTRECALL arguments, the client MUST send a
   response to the recall before using the seqid.  The fundamental
   requirement in client processing is that the "seqid" is used to
   provide the order of processing.  LAYOUTGET results may be processed
   in parallel.  LAYOUTRETURN results may be processed in parallel.
   LAYOUTGET and LAYOUTRETURN responses may be processed in parallel as
   long as the ranges do not overlap.  CB_LAYOUTRECALL request
   processing MUST be processed in "seqid" order at all times.

   Once a client has no more layouts on a file, the layout stateid is no
   longer valid and MUST NOT be used.  Any attempt to use such a layout
   stateid will result in NFS4ERR_BAD_STATEID.

12.5.4.  Committing a Layout

   Allowing for varying storage protocol capabilities, the pNFS protocol
   does not require the metadata server and storage devices to have a
   consistent view of file attributes and data location mappings.  Data
   location mapping refers to aspects such as which offsets store data
   as opposed to storing holes (see Section 13.4.4 for a discussion).
   Related issues arise for storage protocols where a layout may hold
   provisionally allocated blocks where the allocation of those blocks
   does not survive a complete restart of both the client and server.
   Because of this inconsistency, it is necessary to resynchronize the
   client with the metadata server and its storage devices and make any



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   potential changes available to other clients.  This is accomplished
   by use of the LAYOUTCOMMIT operation.

   The LAYOUTCOMMIT operation is responsible for committing a modified
   layout to the metadata server.  The data should be written and
   committed to the appropriate storage devices before the LAYOUTCOMMIT
   occurs.  The scope of the LAYOUTCOMMIT operation depends on the
   storage protocol in use.  It is important to note that the level of
   synchronization is from the point of view of the client that sent the
   LAYOUTCOMMIT.  The updated state on the metadata server need only
   reflect the state as of the client's last operation previous to the
   LAYOUTCOMMIT.  The metadata server is not REQUIRED to maintain a
   global view that accounts for other clients' I/O that may have
   occurred within the same time frame.

   For block/volume-based layouts, LAYOUTCOMMIT may require updating the
   block list that comprises the file and committing this layout to
   stable storage.  For file-based layouts, synchronization of
   attributes between the metadata and storage devices, primarily the
   size attribute, is required.

   The control protocol is free to synchronize the attributes before it
   receives a LAYOUTCOMMIT; however, upon successful completion of a
   LAYOUTCOMMIT, state that exists on the metadata server that describes
   the file MUST be synchronized with the state that exists on the
   storage devices that comprise that file as of the client's last sent
   operation.  Thus, a client that queries the size of a file between a
   WRITE to a storage device and the LAYOUTCOMMIT might observe a size
   that does not reflect the actual data written.

   The client MUST have a layout in order to send a LAYOUTCOMMIT
   operation.

12.5.4.1.  LAYOUTCOMMIT and change/time_modify

   The change and time_modify attributes may be updated by the server
   when the LAYOUTCOMMIT operation is processed.  The reason for this is
   that some layout types do not support the update of these attributes
   when the storage devices process I/O operations.  If a client has a
   layout with the LAYOUTIOMODE4_RW iomode on the file, the client MAY
   provide a suggested value to the server for time_modify within the
   arguments to LAYOUTCOMMIT.  Based on the layout type, the provided
   value may or may not be used.  The server should sanity-check the
   client-provided values before they are used.  For example, the server
   should ensure that time does not flow backwards.  The client always
   has the option to set time_modify through an explicit SETATTR
   operation.




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   For some layout protocols, the storage device is able to notify the
   metadata server of the occurrence of an I/O; as a result, the change
   and time_modify attributes may be updated at the metadata server.
   For a metadata server that is capable of monitoring updates to the
   change and time_modify attributes, LAYOUTCOMMIT processing is not
   required to update the change attribute.  In this case, the metadata
   server must ensure that no further update to the data has occurred
   since the last update of the attributes; file-based protocols may
   have enough information to make this determination or may update the
   change attribute upon each file modification.  This also applies for
   the time_modify attribute.  If the server implementation is able to
   determine that the file has not been modified since the last
   time_modify update, the server need not update time_modify at
   LAYOUTCOMMIT.  At LAYOUTCOMMIT completion, the updated attributes
   should be visible if that file was modified since the latest previous
   LAYOUTCOMMIT or LAYOUTGET.

12.5.4.2.  LAYOUTCOMMIT and size

   The size of a file may be updated when the LAYOUTCOMMIT operation is
   used by the client.  One of the fields in the argument to
   LAYOUTCOMMIT is loca_last_write_offset; this field indicates the
   highest byte offset written but not yet committed with the
   LAYOUTCOMMIT operation.  The data type of loca_last_write_offset is
   newoffset4 and is switched on a boolean value, no_newoffset, that
   indicates if a previous write occurred or not.  If no_newoffset is
   FALSE, an offset is not given.  If the client has a layout with
   LAYOUTIOMODE4_RW iomode on the file, with a byte-range (denoted by
   the values of lo_offset and lo_length) that overlaps
   loca_last_write_offset, then the client MAY set no_newoffset to TRUE
   and provide an offset that will update the file size.  Keep in mind
   that offset is not the same as length, though they are related.  For
   example, a loca_last_write_offset value of zero means that one byte
   was written at offset zero, and so the length of the file is at least
   one byte.

   The metadata server may do one of the following:

   1.  Update the file's size using the last write offset provided by
       the client as either the true file size or as a hint of the file
       size.  If the metadata server has a method available, any new
       value for file size should be sanity-checked.  For example, the
       file must not be truncated if the client presents a last write
       offset less than the file's current size.

   2.  Ignore the client-provided last write offset; the metadata server
       must have sufficient knowledge from other sources to determine




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       the file's size.  For example, the metadata server queries the
       storage devices with the control protocol.

   The method chosen to update the file's size will depend on the
   storage device's and/or the control protocol's capabilities.  For
   example, if the storage devices are block devices with no knowledge
   of file size, the metadata server must rely on the client to set the
   last write offset appropriately.

   The results of LAYOUTCOMMIT contain a new size value in the form of a
   newsize4 union data type.  If the file's size is set as a result of
   LAYOUTCOMMIT, the metadata server must reply with the new size;
   otherwise, the new size is not provided.  If the file size is
   updated, the metadata server SHOULD update the storage devices such
   that the new file size is reflected when LAYOUTCOMMIT processing is
   complete.  For example, the client should be able to read up to the
   new file size.

   The client can extend the length of a file or truncate a file by
   sending a SETATTR operation to the metadata server with the size
   attribute specified.  If the size specified is larger than the
   current size of the file, the file is "zero extended", i.e., zeros
   are implicitly added between the file's previous EOF and the new EOF.
   (In many implementations, the zero-extended byte-range of the file
   consists of unallocated holes in the file.)  When the client writes
   past EOF via WRITE, the SETATTR operation does not need to be used.

12.5.4.3.  LAYOUTCOMMIT and layoutupdate

   The LAYOUTCOMMIT argument contains a loca_layoutupdate field
   (Section 18.42.1) of data type layoutupdate4 (Section 3.3.18).  This
   argument is a layout-type-specific structure.  The structure can be
   used to pass arbitrary layout-type-specific information from the
   client to the metadata server at LAYOUTCOMMIT time.  For example, if
   using a block/volume layout, the client can indicate to the metadata
   server which reserved or allocated blocks the client used or did not
   use.  The content of loca_layoutupdate (field lou_body) need not be
   the same layout-type-specific content returned by LAYOUTGET
   (Section 18.43.2) in the loc_body field of the lo_content field of
   the logr_layout field.  The content of loca_layoutupdate is defined
   by the layout type specification and is opaque to LAYOUTCOMMIT.

12.5.5.  Recalling a Layout

   Since a layout protects a client's access to a file via a direct
   client-storage-device path, a layout need only be recalled when it is
   semantically unable to serve this function.  Typically, this occurs
   when the layout no longer encapsulates the true location of the file



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   over the byte-range it represents.  Any operation or action, such as
   server-driven restriping or load balancing, that changes the layout
   will result in a recall of the layout.  A layout is recalled by the
   CB_LAYOUTRECALL callback operation (see Section 20.3) and returned
   with LAYOUTRETURN (see Section 18.44).  The CB_LAYOUTRECALL operation
   may recall a layout identified by a byte-range, all layouts
   associated with a file system ID (FSID), or all layouts associated
   with a client ID.  Section 12.5.5.2 discusses sequencing issues
   surrounding the getting, returning, and recalling of layouts.

   An iomode is also specified when recalling a layout.  Generally, the
   iomode in the recall request must match the layout being returned;
   for example, a recall with an iomode of LAYOUTIOMODE4_RW should cause
   the client to only return LAYOUTIOMODE4_RW layouts and not
   LAYOUTIOMODE4_READ layouts.  However, a special LAYOUTIOMODE4_ANY
   enumeration is defined to enable recalling a layout of any iomode; in
   other words, the client must return both LAYOUTIOMODE4_READ and
   LAYOUTIOMODE4_RW layouts.

   A REMOVE operation SHOULD cause the metadata server to recall the
   layout to prevent the client from accessing a non-existent file and
   to reclaim state stored on the client.  Since a REMOVE may be delayed
   until the last close of the file has occurred, the recall may also be
   delayed until this time.  After the last reference on the file has
   been released and the file has been removed, the client should no
   longer be able to perform I/O using the layout.  In the case of a
   file-based layout, the data server SHOULD return NFS4ERR_STALE in
   response to any operation on the removed file.

   Once a layout has been returned, the client MUST NOT send I/Os to the
   storage devices for the file, byte-range, and iomode represented by
   the returned layout.  If a client does send an I/O to a storage
   device for which it does not hold a layout, the storage device SHOULD
   reject the I/O.

   Although pNFS does not alter the file data caching capabilities of
   clients, or their semantics, it recognizes that some clients may
   perform more aggressive write-behind caching to optimize the benefits
   provided by pNFS.  However, write-behind caching may negatively
   affect the latency in returning a layout in response to a
   CB_LAYOUTRECALL; this is similar to file delegations and the impact
   that file data caching has on DELEGRETURN.  Client implementations
   SHOULD limit the amount of unwritten data they have outstanding at
   any one time in order to prevent excessively long responses to
   CB_LAYOUTRECALL.  Once a layout is recalled, a server MUST wait one
   lease period before taking further action.  As soon as a lease period
   has passed, the server may choose to fence the client's access to the
   storage devices if the server perceives the client has taken too long



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   to return a layout.  However, just as in the case of data delegation
   and DELEGRETURN, the server may choose to wait, given that the client
   is showing forward progress on its way to returning the layout.  This
   forward progress can take the form of successful interaction with the
   storage devices or of sub-portions of the layout being returned by
   the client.  The server can also limit exposure to these problems by
   limiting the byte-ranges initially provided in the layouts and thus
   the amount of outstanding modified data.

12.5.5.1.  Layout Recall Callback Robustness

   It has been assumed thus far that pNFS client state (layout ranges
   and iomode) for a file exactly matches that of the pNFS server for
   that file.  This assumption leads to the implication that any
   callback results in a LAYOUTRETURN or set of LAYOUTRETURNs that
   exactly match the range in the callback, since both client and server
   agree about the state being maintained.  However, it can be useful if
   this assumption does not always hold.  For example:

   o  If conflicts that require callbacks are very rare, and a server
      can use a multi-file callback to recover per-client resources
      (e.g., via an FSID recall or a multi-file recall within a single
      CB_COMPOUND), the result may be significantly less client-server
      pNFS traffic.

   o  It may be useful for servers to maintain information about what
      ranges are held by a client on a coarse-grained basis, leading to
      the server's layout ranges being beyond those actually held by the
      client.  In the extreme, a server could manage conflicts on a per-
      file basis, only sending whole-file callbacks even though clients
      may request and be granted sub-file ranges.

   o  It may be useful for clients to "forget" details about what
      layouts and ranges the client actually has, leading to the
      server's layout ranges being beyond those that the client "thinks"
      it has.  As long as the client does not assume it has layouts that
      are beyond what the server has granted, this is a safe practice.
      When a client forgets what ranges and layouts it has, and it
      receives a CB_LAYOUTRECALL operation, the client MUST follow up
      with a LAYOUTRETURN for what the server recalled, or alternatively
      return the NFS4ERR_NOMATCHING_LAYOUT error if it has no layout to
      return in the recalled range.

   o  In order to avoid errors, it is vital that a client not assign
      itself layout permissions beyond what the server has granted, and
      that the server not forget layout permissions that have been
      granted.  On the other hand, if a server believes that a client
      holds a layout that the client does not know about, it is useful



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      for the client to cleanly indicate completion of the requested
      recall either by sending a LAYOUTRETURN operation for the entire
      requested range or by returning an NFS4ERR_NOMATCHING_LAYOUT error
      to the CB_LAYOUTRECALL.

   Thus, in light of the above, it is useful for a server to be able to
   send callbacks for layout ranges it has not granted to a client, and
   for a client to return ranges it does not hold.  A pNFS client MUST
   always return layouts that comprise the full range specified by the
   recall.  Note, the full recalled layout range need not be returned as
   part of a single operation, but may be returned in portions.  This
   allows the client to stage the flushing of dirty data and commits and
   returns of layouts.  Also, it indicates to the metadata server that
   the client is making progress.

   When a layout is returned, the client MUST NOT have any outstanding
   I/O requests to the storage devices involved in the layout.
   Rephrasing, the client MUST NOT return the layout while it has
   outstanding I/O requests to the storage device.

   Even with this requirement for the client, it is possible that I/O
   requests may be presented to a storage device no longer allowed to
   perform them.  Since the server has no strict control as to when the
   client will return the layout, the server may later decide to
   unilaterally revoke the client's access to the storage devices as
   provided by the layout.  In choosing to revoke access, the server
   must deal with the possibility of lingering I/O requests, i.e., I/O
   requests that are still in flight to storage devices identified by
   the revoked layout.  All layout type specifications MUST define
   whether unilateral layout revocation by the metadata server is
   supported; if it is, the specification must also describe how
   lingering writes are processed.  For example, storage devices
   identified by the revoked layout could be fenced off from the client
   that held the layout.

   In order to ensure client/server convergence with regard to layout
   state, the final LAYOUTRETURN operation in a sequence of LAYOUTRETURN
   operations for a particular recall MUST specify the entire range
   being recalled, echoing the recalled layout type, iomode, recall/
   return type (FILE, FSID, or ALL), and byte-range, even if layouts
   pertaining to partial ranges were previously returned.  In addition,
   if the client holds no layouts that overlap the range being recalled,
   the client should return the NFS4ERR_NOMATCHING_LAYOUT error code to
   CB_LAYOUTRECALL.  This allows the server to update its view of the
   client's layout state.






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12.5.5.2.  Sequencing of Layout Operations

   As with other stateful operations, pNFS requires the correct
   sequencing of layout operations. pNFS uses the "seqid" in the layout
   stateid to provide the correct sequencing between regular operations
   and callbacks.  It is the server's responsibility to avoid
   inconsistencies regarding the layouts provided and the client's
   responsibility to properly serialize its layout requests and layout
   returns.

12.5.5.2.1.  Layout Recall and Return Sequencing

   One critical issue with regard to layout operations sequencing
   concerns callbacks.  The protocol must defend against races between
   the reply to a LAYOUTGET or LAYOUTRETURN operation and a subsequent
   CB_LAYOUTRECALL.  A client MUST NOT process a CB_LAYOUTRECALL that
   implies one or more outstanding LAYOUTGET or LAYOUTRETURN operations
   to which the client has not yet received a reply.  The client detects
   such a CB_LAYOUTRECALL by examining the "seqid" field of the recall's
   layout stateid.  If the "seqid" is not exactly one higher than what
   the client currently has recorded, and the client has at least one
   LAYOUTGET and/or LAYOUTRETURN operation outstanding, the client knows
   the server sent the CB_LAYOUTRECALL after sending a response to an
   outstanding LAYOUTGET or LAYOUTRETURN.  The client MUST wait before
   processing such a CB_LAYOUTRECALL until it processes all replies for
   outstanding LAYOUTGET and LAYOUTRETURN operations for the
   corresponding file with seqid less than the seqid given by
   CB_LAYOUTRECALL (lor_stateid; see Section 20.3.)

   In addition to the seqid-based mechanism, Section 2.10.6.3 describes
   the sessions mechanism for allowing the client to detect callback
   race conditions and delay processing such a CB_LAYOUTRECALL.  The
   server MAY reference conflicting operations in the CB_SEQUENCE that
   precedes the CB_LAYOUTRECALL.  Because the server has already sent
   replies for these operations before sending the callback, the replies
   may race with the CB_LAYOUTRECALL.  The client MUST wait for all the
   referenced calls to complete and update its view of the layout state
   before processing the CB_LAYOUTRECALL.

12.5.5.2.1.1.  Get/Return Sequencing

   The protocol allows the client to send concurrent LAYOUTGET and
   LAYOUTRETURN operations to the server.  The protocol does not provide
   any means for the server to process the requests in the same order in
   which they were created.  However, through the use of the "seqid"
   field in the layout stateid, the client can determine the order in
   which parallel outstanding operations were processed by the server.
   Thus, when a layout retrieved by an outstanding LAYOUTGET operation



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   intersects with a layout returned by an outstanding LAYOUTRETURN on
   the same file, the order in which the two conflicting operations are
   processed determines the final state of the overlapping layout.  The
   order is determined by the "seqid" returned in each operation: the
   operation with the higher seqid was executed later.

   It is permissible for the client to send multiple parallel LAYOUTGET
   operations for the same file or multiple parallel LAYOUTRETURN
   operations for the same file or a mix of both.

   It is permissible for the client to use the current stateid (see
   Section 16.2.3.1.2) for LAYOUTGET operations, for example, when
   compounding LAYOUTGETs or compounding OPEN and LAYOUTGETs.  It is
   also permissible to use the current stateid when compounding
   LAYOUTRETURNs.

   It is permissible for the client to use the current stateid when
   combining LAYOUTRETURN and LAYOUTGET operations for the same file in
   the same COMPOUND request since the server MUST process these in
   order.  However, if a client does send such COMPOUND requests, it
   MUST NOT have more than one outstanding for the same file at the same
   time, and it MUST NOT have other LAYOUTGET or LAYOUTRETURN operations
   outstanding at the same time for that same file.

12.5.5.2.1.2.  Client Considerations

   Consider a pNFS client that has sent a LAYOUTGET, and before it
   receives the reply to LAYOUTGET, it receives a CB_LAYOUTRECALL for
   the same file with an overlapping range.  There are two
   possibilities, which the client can distinguish via the layout
   stateid in the recall.

   1.  The server processed the LAYOUTGET before sending the recall, so
       the LAYOUTGET must be waited for because it may be carrying
       layout information that will need to be returned to deal with the
       CB_LAYOUTRECALL.

   2.  The server sent the callback before receiving the LAYOUTGET.  The
       server will not respond to the LAYOUTGET until the
       CB_LAYOUTRECALL is processed.

   If these possibilities cannot be distinguished, a deadlock could
   result, as the client must wait for the LAYOUTGET response before
   processing the recall in the first case, but that response will not
   arrive until after the recall is processed in the second case.  Note
   that in the first case, the "seqid" in the layout stateid of the
   recall is two greater than what the client has recorded; in the
   second case, the "seqid" is one greater than what the client has



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   recorded.  This allows the client to disambiguate between the two
   cases.  The client thus knows precisely which possibility applies.

   In case 1, the client knows it needs to wait for the LAYOUTGET
   response before processing the recall (or the client can return
   NFS4ERR_DELAY).

   In case 2, the client will not wait for the LAYOUTGET response before
   processing the recall because waiting would cause deadlock.
   Therefore, the action at the client will only require waiting in the
   case that the client has not yet seen the server's earlier responses
   to the LAYOUTGET operation(s).

   The recall process can be considered completed when the final
   LAYOUTRETURN operation for the recalled range is completed.  The
   LAYOUTRETURN uses the layout stateid (with seqid) specified in
   CB_LAYOUTRECALL.  If the client uses multiple LAYOUTRETURNs in
   processing the recall, the first LAYOUTRETURN will use the layout
   stateid as specified in CB_LAYOUTRECALL.  Subsequent LAYOUTRETURNs
   will use the highest seqid as is the usual case.

12.5.5.2.1.3.  Server Considerations

   Consider a race from the metadata server's point of view.  The
   metadata server has sent a CB_LAYOUTRECALL and receives an
   overlapping LAYOUTGET for the same file before the LAYOUTRETURN(s)
   that respond to the CB_LAYOUTRECALL.  There are three cases:

   1.  The client sent the LAYOUTGET before processing the
       CB_LAYOUTRECALL.  The "seqid" in the layout stateid of the
       arguments of LAYOUTGET is one less than the "seqid" in
       CB_LAYOUTRECALL.  The server returns NFS4ERR_RECALLCONFLICT to
       the client, which indicates to the client that there is a pending
       recall.

   2.  The client sent the LAYOUTGET after processing the
       CB_LAYOUTRECALL, but the LAYOUTGET arrived before the
       LAYOUTRETURN and the response to CB_LAYOUTRECALL that completed
       that processing.  The "seqid" in the layout stateid of LAYOUTGET
       is equal to or greater than that of the "seqid" in
       CB_LAYOUTRECALL.  The server has not received a response to the
       CB_LAYOUTRECALL, so it returns NFS4ERR_RECALLCONFLICT.

   3.  The client sent the LAYOUTGET after processing the
       CB_LAYOUTRECALL; the server received the CB_LAYOUTRECALL
       response, but the LAYOUTGET arrived before the LAYOUTRETURN that
       completed that processing.  The "seqid" in the layout stateid of
       LAYOUTGET is equal to that of the "seqid" in CB_LAYOUTRECALL.



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       The server has received a response to the CB_LAYOUTRECALL, so it
       returns NFS4ERR_RETURNCONFLICT.

12.5.5.2.1.4.  Wraparound and Validation of Seqid

   The rules for layout stateid processing differ from other stateids in
   the protocol because the "seqid" value cannot be zero and the
   stateid's "seqid" value changes in a CB_LAYOUTRECALL operation.  The
   non-zero requirement combined with the inherent parallelism of layout
   operations means that a set of LAYOUTGET and LAYOUTRETURN operations
   may contain the same value for "seqid".  The server uses a slightly
   modified version of the modulo arithmetic as described in
   Section 2.10.6.1 when incrementing the layout stateid's "seqid".  The
   difference is that zero is not a valid value for "seqid"; when the
   value of a "seqid" is 0xFFFFFFFF, the next valid value will be
   0x00000001.  The modulo arithmetic is also used for the comparisons
   of "seqid" values in the processing of CB_LAYOUTRECALL events as
   described above in Section 12.5.5.2.1.3.

   Just as the server validates the "seqid" in the event of
   CB_LAYOUTRECALL usage, as described in Section 12.5.5.2.1.3, the
   server also validates the "seqid" value to ensure that it is within
   an appropriate range.  This range represents the degree of
   parallelism the server supports for layout stateids.  If the client
   is sending multiple layout operations to the server in parallel, by
   definition, the "seqid" value in the supplied stateid will not be the
   current "seqid" as held by the server.  The range of parallelism
   spans from the highest or current "seqid" to a "seqid" value in the
   past.  To assist in the discussion, the server's current "seqid"
   value for a layout stateid is defined as SERVER_CURRENT_SEQID.  The
   lowest "seqid" value that is acceptable to the server is represented
   by PAST_SEQID.  And the value for the range of valid "seqid"s or
   range of parallelism is VALID_SEQID_RANGE.  Therefore, the following
   holds: VALID_SEQID_RANGE = SERVER_CURRENT_SEQID - PAST_SEQID.  In the
   following, all arithmetic is the modulo arithmetic as described
   above.

   The server MUST support a minimum VALID_SEQID_RANGE.  The minimum is
   defined as: VALID_SEQID_RANGE = summation over 1..N of
   (ca_maxoperations(i) - 1), where N is the number of session fore
   channels and ca_maxoperations(i) is the value of the ca_maxoperations
   returned from CREATE_SESSION of the i'th session.  The reason for "-
   1" is to allow for the required SEQUENCE operation.  The server MAY
   support a VALID_SEQID_RANGE value larger than the minimum.  The
   maximum VALID_SEQID_RANGE is (2 ^ 32 - 2) (accounting for zero not
   being a valid "seqid" value).





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   If the server finds the "seqid" is zero, the NFS4ERR_BAD_STATEID
   error is returned to the client.  The server further validates the
   "seqid" to ensure it is within the range of parallelism,
   VALID_SEQID_RANGE.  If the "seqid" value is outside of that range,
   the error NFS4ERR_OLD_STATEID is returned to the client.  Upon
   receipt of NFS4ERR_OLD_STATEID, the client updates the stateid in the
   layout request based on processing of other layout requests and re-
   sends the operation to the server.

12.5.5.2.1.5.  Bulk Recall and Return

   pNFS supports recalling and returning all layouts that are for files
   belonging to a particular fsid (LAYOUTRECALL4_FSID,
   LAYOUTRETURN4_FSID) or client ID (LAYOUTRECALL4_ALL,
   LAYOUTRETURN4_ALL).  There are no "bulk" stateids, so detection of
   races via the seqid is not possible.  The server MUST NOT initiate
   bulk recall while another recall is in progress, or the corresponding
   LAYOUTRETURN is in progress or pending.  In the event the server
   sends a bulk recall while the client has a pending or in-progress
   LAYOUTRETURN, CB_LAYOUTRECALL, or LAYOUTGET, the client returns
   NFS4ERR_DELAY.  In the event the client sends a LAYOUTGET or
   LAYOUTRETURN while a bulk recall is in progress, the server returns
   NFS4ERR_RECALLCONFLICT.  If the client sends a LAYOUTGET or
   LAYOUTRETURN after the server receives NFS4ERR_DELAY from a bulk
   recall, then to ensure forward progress, the server MAY return
   NFS4ERR_RECALLCONFLICT.

   Once a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL is sent, the server MUST
   NOT allow the client to use any layout stateid except for
   LAYOUTCOMMIT operations.  Once the client receives a CB_LAYOUTRECALL
   of LAYOUTRECALL4_ALL, it MUST NOT use any layout stateid except for
   LAYOUTCOMMIT operations.  Once a LAYOUTRETURN of LAYOUTRETURN4_ALL is
   sent, all layout stateids granted to the client ID are freed.  The
   client MUST NOT use the layout stateids again.  It MUST use LAYOUTGET
   to obtain new layout stateids.

   Once a CB_LAYOUTRECALL of LAYOUTRECALL4_FSID is sent, the server MUST
   NOT allow the client to use any layout stateid that refers to a file
   with the specified fsid except for LAYOUTCOMMIT operations.  Once the
   client receives a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL, it MUST NOT
   use any layout stateid that refers to a file with the specified fsid
   except for LAYOUTCOMMIT operations.  Once a LAYOUTRETURN of
   LAYOUTRETURN4_FSID is sent, all layout stateids granted to the
   referenced fsid are freed.  The client MUST NOT use those freed
   layout stateids for files with the referenced fsid again.
   Subsequently, for any file with the referenced fsid, to use a layout,
   the client MUST first send a LAYOUTGET operation in order to obtain a
   new layout stateid for that file.



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   If the server has sent a bulk CB_LAYOUTRECALL and receives a
   LAYOUTGET, or a LAYOUTRETURN with a stateid, the server MUST return
   NFS4ERR_RECALLCONFLICT.  If the server has sent a bulk
   CB_LAYOUTRECALL and receives a LAYOUTRETURN with an lr_returntype
   that is not equal to the lor_recalltype of the CB_LAYOUTRECALL, the
   server MUST return NFS4ERR_RECALLCONFLICT.

12.5.6.  Revoking Layouts

   Parallel NFS permits servers to revoke layouts from clients that fail
   to respond to recalls and/or fail to renew their lease in time.
   Depending on the layout type, the server might revoke the layout and
   might take certain actions with respect to the client's I/O to data
   servers.

12.5.7.  Metadata Server Write Propagation

   Asynchronous writes written through the metadata server may be
   propagated lazily to the storage devices.  For data written
   asynchronously through the metadata server, a client performing a
   read at the appropriate storage device is not guaranteed to see the
   newly written data until a COMMIT occurs at the metadata server.
   While the write is pending, reads to the storage device may give out
   either the old data, the new data, or a mixture of new and old.  Upon
   completion of a synchronous WRITE or COMMIT (for asynchronously
   written data), the metadata server MUST ensure that storage devices
   give out the new data and that the data has been written to stable
   storage.  If the server implements its storage in any way such that
   it cannot obey these constraints, then it MUST recall the layouts to
   prevent reads being done that cannot be handled correctly.  Note that
   the layouts MUST be recalled prior to the server responding to the
   associated WRITE operations.

12.6.  pNFS Mechanics

   This section describes the operations flow taken by a pNFS client to
   a metadata server and storage device.

   When a pNFS client encounters a new FSID, it sends a GETATTR to the
   NFSv4.1 server for the fs_layout_type (Section 5.12.1) attribute.  If
   the attribute returns at least one layout type, and the layout types
   returned are among the set supported by the client, the client knows
   that pNFS is a possibility for the file system.  If, from the server
   that returned the new FSID, the client does not have a client ID that
   came from an EXCHANGE_ID result that returned
   EXCHGID4_FLAG_USE_PNFS_MDS, it MUST send an EXCHANGE_ID to the server
   with the EXCHGID4_FLAG_USE_PNFS_MDS bit set.  If the server's
   response does not have EXCHGID4_FLAG_USE_PNFS_MDS, then contrary to



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   what the fs_layout_type attribute said, the server does not support
   pNFS, and the client will not be able use pNFS to that server; in
   this case, the server MUST return NFS4ERR_NOTSUPP in response to any
   pNFS operation.

   The client then creates a session, requesting a persistent session,
   so that exclusive creates can be done with single round trip via the
   createmode4 of GUARDED4.  If the session ends up not being
   persistent, the client will use EXCLUSIVE4_1 for exclusive creates.

   If a file is to be created on a pNFS-enabled file system, the client
   uses the OPEN operation.  With the normal set of attributes that may
   be provided upon OPEN used for creation, there is an OPTIONAL
   layout_hint attribute.  The client's use of layout_hint allows the
   client to express its preference for a layout type and its associated
   layout details.  The use of a createmode4 of UNCHECKED4, GUARDED4, or
   EXCLUSIVE4_1 will allow the client to provide the layout_hint
   attribute at create time.  The client MUST NOT use EXCLUSIVE4 (see
   Table 10).  The client is RECOMMENDED to combine a GETATTR operation
   after the OPEN within the same COMPOUND.  The GETATTR may then
   retrieve the layout_type attribute for the newly created file.  The
   client will then know what layout type the server has chosen for the
   file and therefore what storage protocol the client must use.

   If the client wants to open an existing file, then it also includes a
   GETATTR to determine what layout type the file supports.

   The GETATTR in either the file creation or plain file open case can
   also include the layout_blksize and layout_alignment attributes so
   that the client can determine optimal offsets and lengths for I/O on
   the file.

   Assuming the client supports the layout type returned by GETATTR and
   it chooses to use pNFS for data access, it then sends LAYOUTGET using
   the filehandle and stateid returned by OPEN, specifying the range it
   wants to do I/O on.  The response is a layout, which may be a subset
   of the range for which the client asked.  It also includes device IDs
   and a description of how data is organized (or in the case of
   writing, how data is to be organized) across the devices.  The device
   IDs and data description are encoded in a format that is specific to
   the layout type, but the client is expected to understand.

   When the client wants to send an I/O, it determines to which device
   ID it needs to send the I/O command by examining the data description
   in the layout.  It then sends a GETDEVICEINFO to find the device
   address(es) of the device ID.  The client then sends the I/O request
   to one of device ID's device addresses, using the storage protocol




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   defined for the layout type.  Note that if a client has multiple I/Os
   to send, these I/O requests may be done in parallel.

   If the I/O was a WRITE, then at some point the client may want to use
   LAYOUTCOMMIT to commit the modification time and the new size of the
   file (if it believes it extended the file size) to the metadata
   server and the modified data to the file system.

12.7.  Recovery

   Recovery is complicated by the distributed nature of the pNFS
   protocol.  In general, crash recovery for layouts is similar to crash
   recovery for delegations in the base NFSv4.1 protocol.  However, the
   client's ability to perform I/O without contacting the metadata
   server introduces subtleties that must be handled correctly if the
   possibility of file system corruption is to be avoided.

12.7.1.  Recovery from Client Restart

   Client recovery for layouts is similar to client recovery for other
   lock and delegation state.  When a pNFS client restarts, it will lose
   all information about the layouts that it previously owned.  There
   are two methods by which the server can reclaim these resources and
   allow otherwise conflicting layouts to be provided to other clients.

   The first is through the expiry of the client's lease.  If the client
   recovery time is longer than the lease period, the client's lease
   will expire and the server will know that state may be released.  For
   layouts, the server may release the state immediately upon lease
   expiry or it may allow the layout to persist, awaiting possible lease
   revival, as long as no other layout conflicts.

   The second is through the client restarting in less time than it
   takes for the lease period to expire.  In such a case, the client
   will contact the server through the standard EXCHANGE_ID protocol.
   The server will find that the client's co_ownerid matches the
   co_ownerid of the previous client invocation, but that the verifier
   is different.  The server uses this as a signal to release all layout
   state associated with the client's previous invocation.  In this
   scenario, the data written by the client but not covered by a
   successful LAYOUTCOMMIT is in an undefined state; it may have been
   written or it may now be lost.  This is acceptable behavior and it is
   the client's responsibility to use LAYOUTCOMMIT to achieve the
   desired level of stability.







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12.7.2.  Dealing with Lease Expiration on the Client

   If a client believes its lease has expired, it MUST NOT send I/O to
   the storage device until it has validated its lease.  The client can
   send a SEQUENCE operation to the metadata server.  If the SEQUENCE
   operation is successful, but sr_status_flag has
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
   SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST NOT use
   currently held layouts.  The client has two choices to recover from
   the lease expiration.  First, for all modified but uncommitted data,
   the client writes it to the metadata server using the FILE_SYNC4 flag
   for the WRITEs, or WRITE and COMMIT.  Second, the client re-
   establishes a client ID and session with the server and obtains new
   layouts and device-ID-to-device-address mappings for the modified
   data ranges and then writes the data to the storage devices with the
   newly obtained layouts.

   If sr_status_flags from the metadata server has
   SEQ4_STATUS_RESTART_RECLAIM_NEEDED set (or SEQUENCE returns
   NFS4ERR_BAD_SESSION and CREATE_SESSION returns
   NFS4ERR_STALE_CLIENTID), then the metadata server has restarted, and
   the client SHOULD recover using the methods described in
   Section 12.7.4.

   If sr_status_flags from the metadata server has
   SEQ4_STATUS_LEASE_MOVED set, then the client recovers by following
   the procedure described in Section 11.7.7.1.  After that, the client
   may get an indication that the layout state was not moved with the
   file system.  The client recovers as in the other applicable
   situations discussed in the first two paragraphs of this section.

   If sr_status_flags reports no loss of state, then the lease for the
   layouts that the client has are valid and renewed, and the client can
   once again send I/O requests to the storage devices.

   While clients SHOULD NOT send I/Os to storage devices that may extend
   past the lease expiration time period, this is not always possible,
   for example, an extended network partition that starts after the I/O
   is sent and does not heal until the I/O request is received by the
   storage device.  Thus, the metadata server and/or storage devices are
   responsible for protecting themselves from I/Os that are both sent
   before the lease expires and arrive after the lease expires.  See
   Section 12.7.3.







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12.7.3.  Dealing with Loss of Layout State on the Metadata Server

   This is a description of the case where all of the following are
   true:

   o  the metadata server has not restarted

   o  a pNFS client's layouts have been discarded (usually because the
      client's lease expired) and are invalid

   o  an I/O from the pNFS client arrives at the storage device

   The metadata server and its storage devices MUST solve this by
   fencing the client.  In other words, they MUST solve this by
   preventing the execution of I/O operations from the client to the
   storage devices after layout state loss.  The details of how fencing
   is done are specific to the layout type.  The solution for NFSv4.1
   file-based layouts is described in (Section 13.11), and solutions for
   other layout types are in their respective external specification
   documents.

12.7.4.  Recovery from Metadata Server Restart

   The pNFS client will discover that the metadata server has restarted
   via the methods described in Section 8.4.2 and discussed in a pNFS-
   specific context in Section 12.7.2, Paragraph 2.  The client MUST
   stop using layouts and delete the device ID to device address
   mappings it previously received from the metadata server.  Having
   done that, if the client wrote data to the storage device without
   committing the layouts via LAYOUTCOMMIT, then the client has
   additional work to do in order to have the client, metadata server,
   and storage device(s) all synchronized on the state of the data.

   o  If the client has data still modified and unwritten in the
      client's memory, the client has only two choices.

      1.  The client can obtain a layout via LAYOUTGET after the
          server's grace period and write the data to the storage
          devices.

      2.  The client can WRITE that data through the metadata server
          using the WRITE (Section 18.32) operation, and then obtain
          layouts as desired.

   o  If the client asynchronously wrote data to the storage device, but
      still has a copy of the data in its memory, then it has available
      to it the recovery options listed above in the previous bullet
      point.  If the metadata server is also in its grace period, the



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      client has available to it the options below in the next bullet
      point.

   o  The client does not have a copy of the data in its memory and the
      metadata server is still in its grace period.  The client cannot
      use LAYOUTGET (within or outside the grace period) to reclaim a
      layout because the contents of the response from LAYOUTGET may not
      match what it had previously.  The range might be different or the
      client might get the same range but the content of the layout
      might be different.  Even if the content of the layout appears to
      be the same, the device IDs may map to different device addresses,
      and even if the device addresses are the same, the device
      addresses could have been assigned to a different storage device.
      The option of retrieving the data from the storage device and
      writing it to the metadata server per the recovery scenario
      described above is not available because, again, the mappings of
      range to device ID, device ID to device address, and device
      address to physical device are stale, and new mappings via new
      LAYOUTGET do not solve the problem.

      The only recovery option for this scenario is to send a
      LAYOUTCOMMIT in reclaim mode, which the metadata server will
      accept as long as it is in its grace period.  The use of
      LAYOUTCOMMIT in reclaim mode informs the metadata server that the
      layout has changed.  It is critical that the metadata server
      receive this information before its grace period ends, and thus
      before it starts allowing updates to the file system.

      To send LAYOUTCOMMIT in reclaim mode, the client sets the
      loca_reclaim field of the operation's arguments (Section 18.42.1)
      to TRUE.  During the metadata server's recovery grace period (and
      only during the recovery grace period) the metadata server is
      prepared to accept LAYOUTCOMMIT requests with the loca_reclaim
      field set to TRUE.

      When loca_reclaim is TRUE, the client is attempting to commit
      changes to the layout that occurred prior to the restart of the
      metadata server.  The metadata server applies some consistency
      checks on the loca_layoutupdate field of the arguments to
      determine whether the client can commit the data written to the
      storage device to the file system.  The loca_layoutupdate field is
      of data type layoutupdate4 and contains layout-type-specific
      content (in the lou_body field of loca_layoutupdate).  The layout-
      type-specific information that loca_layoutupdate might have is
      discussed in Section 12.5.4.3.  If the metadata server's
      consistency checks on loca_layoutupdate succeed, then the metadata
      server MUST commit the data (as described by the loca_offset,
      loca_length, and loca_layoutupdate fields of the arguments) that



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      was written to the storage device.  If the metadata server's
      consistency checks on loca_layoutupdate fail, the metadata server
      rejects the LAYOUTCOMMIT operation and makes no changes to the
      file system.  However, any time LAYOUTCOMMIT with loca_reclaim
      TRUE fails, the pNFS client has lost all the data in the range
      defined by <loca_offset, loca_length>.  A client can defend
      against this risk by caching all data, whether written
      synchronously or asynchronously in its memory, and by not
      releasing the cached data until a successful LAYOUTCOMMIT.  This
      condition does not hold true for all layout types; for example,
      file-based storage devices need not suffer from this limitation.

   o  The client does not have a copy of the data in its memory and the
      metadata server is no longer in its grace period; i.e., the
      metadata server returns NFS4ERR_NO_GRACE.  As with the scenario in
      the above bullet point, the failure of LAYOUTCOMMIT means the data
      in the range <loca_offset, loca_length> lost.  The defense against
      the risk is the same -- cache all written data on the client until
      a successful LAYOUTCOMMIT.

12.7.5.  Operations during Metadata Server Grace Period

   Some of the recovery scenarios thus far noted that some operations
   (namely, WRITE and LAYOUTGET) might be permitted during the metadata
   server's grace period.  The metadata server may allow these
   operations during its grace period.  For LAYOUTGET, the metadata
   server must reliably determine that servicing such a request will not
   conflict with an impending LAYOUTCOMMIT reclaim request.  For WRITE,
   the metadata server must reliably determine that servicing the
   request will not conflict with an impending OPEN or with a LOCK where
   the file has mandatory byte-range locking enabled.

   As mentioned previously, for expediency, the metadata server might
   reject some operations (namely, WRITE and LAYOUTGET) during its grace
   period, because the simplest correct approach is to reject all non-
   reclaim pNFS requests and WRITE operations by returning the
   NFS4ERR_GRACE error.  However, depending on the storage protocol
   (which is specific to the layout type) and metadata server
   implementation, the metadata server may be able to determine that a
   particular request is safe.  For example, a metadata server may save
   provisional allocation mappings for each file to stable storage, as
   well as information about potentially conflicting OPEN share modes
   and mandatory byte-range locks that might have been in effect at the
   time of restart, and the metadata server may use this information
   during the recovery grace period to determine that a WRITE request is
   safe.





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12.7.6.  Storage Device Recovery

   Recovery from storage device restart is mostly dependent upon the
   layout type in use.  However, there are a few general techniques a
   client can use if it discovers a storage device has crashed while
   holding modified, uncommitted data that was asynchronously written.
   First and foremost, it is important to realize that the client is the
   only one that has the information necessary to recover non-committed
   data since it holds the modified data and probably nothing else does.
   Second, the best solution is for the client to err on the side of
   caution and attempt to rewrite the modified data through another
   path.

   The client SHOULD immediately WRITE the data to the metadata server,
   with the stable field in the WRITE4args set to FILE_SYNC4.  Once it
   does this, there is no need to wait for the original storage device.

12.8.  Metadata and Storage Device Roles

   If the same physical hardware is used to implement both a metadata
   server and storage device, then the same hardware entity is to be
   understood to be implementing two distinct roles and it is important
   that it be clearly understood on behalf of which role the hardware is
   executing at any given time.

   Two sub-cases can be distinguished.

   1.  The storage device uses NFSv4.1 as the storage protocol, i.e.,
       the same physical hardware is used to implement both a metadata
       and data server.  See Section 13.1 for a description of how
       multiple roles are handled.

   2.  The storage device does not use NFSv4.1 as the storage protocol,
       and the same physical hardware is used to implement both a
       metadata and storage device.  Whether distinct network addresses
       are used to access the metadata server and storage device is
       immaterial.  This is because it is always clear to the pNFS
       client and server, from the upper-layer protocol being used
       (NFSv4.1 or non-NFSv4.1), to which role the request to the common
       server network address is directed.

12.9.  Security Considerations for pNFS

   pNFS separates file system metadata and data and provides access to
   both.  There are pNFS-specific operations (listed in Section 12.3)
   that provide access to the metadata; all existing NFSv4.1
   conventional (non-pNFS) security mechanisms and features apply to
   accessing the metadata.  The combination of components in a pNFS



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   system (see Figure 1) is required to preserve the security properties
   of NFSv4.1 with respect to an entity that is accessing a storage
   device from a client, including security countermeasures to defend
   against threats for which NFSv4.1 provides defenses in environments
   where these threats are considered significant.

   In some cases, the security countermeasures for connections to
   storage devices may take the form of physical isolation or a
   recommendation to avoid the use of pNFS in an environment.  For
   example, it may be impractical to provide confidentiality protection
   for some storage protocols to protect against eavesdropping.  In
   environments where eavesdropping on such protocols is of sufficient
   concern to require countermeasures, physical isolation of the
   communication channel (e.g., via direct connection from client(s) to
   storage device(s)) and/or a decision to forgo use of pNFS (e.g., and
   fall back to conventional NFSv4.1) may be appropriate courses of
   action.

   Where communication with storage devices is subject to the same
   threats as client-to-metadata server communication, the protocols
   used for that communication need to provide security mechanisms as
   strong as or no weaker than those available via RPCSEC_GSS for
   NFSv4.1.  Except for the storage protocol used for the
   LAYOUT4_NFSV4_1_FILES layout (see Section 13), i.e., except for
   NFSv4.1, it is beyond the scope of this document to specify the
   security mechanisms for storage access protocols.

   pNFS implementations MUST NOT remove NFSv4.1's access controls.  The
   combination of clients, storage devices, and the metadata server are
   responsible for ensuring that all client-to-storage-device file data
   access respects NFSv4.1's ACLs and file open modes.  This entails
   performing both of these checks on every access in the client, the
   storage device, or both (as applicable; when the storage device is an
   NFSv4.1 server, the storage device is ultimately responsible for
   controlling access as described in Section 13.9.2).  If a pNFS
   configuration performs these checks only in the client, the risk of a
   misbehaving client obtaining unauthorized access is an important
   consideration in determining when it is appropriate to use such a
   pNFS configuration.  Such layout types SHOULD NOT be used when
   client-only access checks do not provide sufficient assurance that
   NFSv4.1 access control is being applied correctly.  (This is not a
   problem for the file layout type described in Section 13 because the
   storage access protocol for LAYOUT4_NFSV4_1_FILES is NFSv4.1, and
   thus the security model for storage device access via
   LAYOUT4_NFSv4_1_FILES is the same as that of the metadata server.)
   For handling of access control specific to a layout, the reader
   should examine the layout specification, such as the NFSv4.1/file-




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   based layout (Section 13) of this document, the blocks layout [41],
   and objects layout [40].

13.  NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type

   This section describes the semantics and format of NFSv4.1 file-based
   layouts for pNFS.  NFSv4.1 file-based layouts use the
   LAYOUT4_NFSV4_1_FILES layout type.  The LAYOUT4_NFSV4_1_FILES type
   defines striping data across multiple NFSv4.1 data servers.

13.1.  Client ID and Session Considerations

   Sessions are a REQUIRED feature of NFSv4.1, and this extends to both
   the metadata server and file-based (NFSv4.1-based) data servers.

   The role a server plays in pNFS is determined by the result it
   returns from EXCHANGE_ID.  The roles are:

   o  Metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result
      eir_flags).

   o  Data server (EXCHGID4_FLAG_USE_PNFS_DS).

   o  Non-metadata server (EXCHGID4_FLAG_USE_NON_PNFS).  This is an
      NFSv4.1 server that does not support operations (e.g., LAYOUTGET)
      or attributes that pertain to pNFS.

   The client MAY request zero or more of EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_DS, or EXCHGID4_FLAG_USE_PNFS_MDS, even though
   some combinations (e.g., EXCHGID4_FLAG_USE_NON_PNFS |
   EXCHGID4_FLAG_USE_PNFS_MDS) are contradictory.  However, the server
   MUST only return the following acceptable combinations:

        +---------------------------------------------------------+
        | Acceptable Results from EXCHANGE_ID                     |
        +---------------------------------------------------------+
        | EXCHGID4_FLAG_USE_PNFS_MDS                              |
        | EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS  |
        | EXCHGID4_FLAG_USE_PNFS_DS                               |
        | EXCHGID4_FLAG_USE_NON_PNFS                              |
        | EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS  |
        +---------------------------------------------------------+

   As the above table implies, a server can have one or two roles.  A
   server can be both a metadata server and a data server, or it can be
   both a data server and non-metadata server.  In addition to returning
   two roles in the EXCHANGE_ID's results, and thus serving both roles
   via a common client ID, a server can serve two roles by returning a



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   unique client ID and server owner for each role in each of two
   EXCHANGE_ID results, with each result indicating each role.

   In the case of a server with concurrent pNFS roles that are served by
   a common client ID, if the EXCHANGE_ID request from the client has
   zero or a combination of the bits set in eia_flags, the server result
   should set bits that represent the higher of the acceptable
   combination of the server roles, with a preference to match the roles
   requested by the client.  Thus, if a client request has
   (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS |
   EXCHGID4_FLAG_USE_PNFS_DS) flags set, and the server is both a
   metadata server and a data server, serving both the roles by a common
   client ID, the server SHOULD return with
   (EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS) set.

   In the case of a server that has multiple concurrent pNFS roles, each
   role served by a unique client ID, if the client specifies zero or a
   combination of roles in the request, the server results SHOULD return
   only one of the roles from the combination specified by the client
   request.  If the role specified by the server result does not match
   the intended use by the client, the client should send the
   EXCHANGE_ID specifying just the interested pNFS role.

   If a pNFS metadata client gets a layout that refers it to an NFSv4.1
   data server, it needs a client ID on that data server.  If it does
   not yet have a client ID from the server that had the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the EXCHANGE_ID results, then
   the client needs to send an EXCHANGE_ID to the data server, using the
   same co_ownerid as it sent to the metadata server, with the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the arguments.  If the server's
   EXCHANGE_ID results have EXCHGID4_FLAG_USE_PNFS_DS set, then the
   client may use the client ID to create sessions that will exchange
   pNFS data operations.  The client ID returned by the data server has
   no relationship with the client ID returned by a metadata server
   unless the client IDs are equal, and the server owners and server
   scopes of the data server and metadata server are equal.

   In NFSv4.1, the session ID in the SEQUENCE operation implies the
   client ID, which in turn might be used by the server to map the
   stateid to the right client/server pair.  However, when a data server
   is presented with a READ or WRITE operation with a stateid, because
   the stateid is associated with a client ID on a metadata server, and
   because the session ID in the preceding SEQUENCE operation is tied to
   the client ID of the data server, the data server has no obvious way
   to determine the metadata server from the COMPOUND procedure, and
   thus has no way to validate the stateid.  One RECOMMENDED approach is
   for pNFS servers to encode metadata server routing and/or identity
   information in the data server filehandles as returned in the layout.



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   If metadata server routing and/or identity information is encoded in
   data server filehandles, when the metadata server identity or
   location changes, the data server filehandles it gave out will become
   invalid (stale), and so the metadata server MUST first recall the
   layouts.  Invalidating a data server filehandle does not render the
   NFS client's data cache invalid.  The client's cache should map a
   data server filehandle to a metadata server filehandle, and a
   metadata server filehandle to cached data.

   If a server is both a metadata server and a data server, the server
   might need to distinguish operations on files that are directed to
   the metadata server from those that are directed to the data server.
   It is RECOMMENDED that the values of the filehandles returned by the
   LAYOUTGET operation be different than the value of the filehandle
   returned by the OPEN of the same file.

   Another scenario is for the metadata server and the storage device to
   be distinct from one client's point of view, and the roles reversed
   from another client's point of view.  For example, in the cluster
   file system model, a metadata server to one client might be a data
   server to another client.  If NFSv4.1 is being used as the storage
   protocol, then pNFS servers need to encode the values of filehandles
   according to their specific roles.

13.1.1.  Sessions Considerations for Data Servers

   Section 2.10.11.2 states that a client has to keep its lease renewed
   in order to prevent a session from being deleted by the server.  If
   the reply to EXCHANGE_ID has just the EXCHGID4_FLAG_USE_PNFS_DS role
   set, then (as noted in Section 13.6) the client will not be able to
   determine the data server's lease_time attribute because GETATTR will
   not be permitted.  Instead, the rule is that any time a client
   receives a layout referring it to a data server that returns just the
   EXCHGID4_FLAG_USE_PNFS_DS role, the client MAY assume that the
   lease_time attribute from the metadata server that returned the
   layout applies to the data server.  Thus, the data server MUST be
   aware of the values of all lease_time attributes of all metadata
   servers for which it is providing I/O, and it MUST use the maximum of
   all such lease_time values as the lease interval for all client IDs
   and sessions established on it.

   For example, if one metadata server has a lease_time attribute of 20
   seconds, and a second metadata server has a lease_time attribute of
   10 seconds, then if both servers return layouts that refer to an
   EXCHGID4_FLAG_USE_PNFS_DS-only data server, the data server MUST
   renew a client's lease if the interval between two SEQUENCE
   operations on different COMPOUND requests is less than 20 seconds.




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13.2.  File Layout Definitions

   The following definitions apply to the LAYOUT4_NFSV4_1_FILES layout
   type and may be applicable to other layout types.

   Unit.  A unit is a fixed-size quantity of data written to a data
      server.

   Pattern.  A pattern is a method of distributing one or more equal
      sized units across a set of data servers.  A pattern is iterated
      one or more times.

   Stripe.  A stripe is a set of data distributed across a set of data
      servers in a pattern before that pattern repeats.

   Stripe Count.  A stripe count is the number of units in a pattern.

   Stripe Width.  A stripe width is the size of a stripe in bytes.  The
      stripe width = the stripe count * the size of the stripe unit.

   Hereafter, this document will refer to a unit that is a written in a
   pattern as a "stripe unit".

   A pattern may have more stripe units than data servers.  If so, some
   data servers will have more than one stripe unit per stripe.  A data
   server that has multiple stripe units per stripe MAY store each unit
   in a different data file (and depending on the implementation, will
   possibly assign a unique data filehandle to each data file).

13.3.  File Layout Data Types

   The high level NFSv4.1 layout types are nfsv4_1_file_layouthint4,
   nfsv4_1_file_layout_ds_addr4, and nfsv4_1_file_layout4.

   The SETATTR operation supports a layout hint attribute
   (Section 5.12.4).  When the client sets a layout hint (data type
   layouthint4) with a layout type of LAYOUT4_NFSV4_1_FILES (the
   loh_type field), the loh_body field contains a value of data type
   nfsv4_1_file_layouthint4.

   const NFL4_UFLG_MASK            = 0x0000003F;
   const NFL4_UFLG_DENSE           = 0x00000001;
   const NFL4_UFLG_COMMIT_THRU_MDS = 0x00000002;
   const NFL4_UFLG_STRIPE_UNIT_SIZE_MASK
                                   = 0xFFFFFFC0;

   typedef uint32_t nfl_util4;




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   enum filelayout_hint_care4 {
           NFLH4_CARE_DENSE        = NFL4_UFLG_DENSE,

           NFLH4_CARE_COMMIT_THRU_MDS
                                   = NFL4_UFLG_COMMIT_THRU_MDS,

           NFLH4_CARE_STRIPE_UNIT_SIZE
                                   = 0x00000040,

           NFLH4_CARE_STRIPE_COUNT = 0x00000080
   };

   /* Encoded in the loh_body field of data type layouthint4: */

   struct nfsv4_1_file_layouthint4 {
           uint32_t        nflh_care;
           nfl_util4       nflh_util;
           count4          nflh_stripe_count;
   };

   The generic layout hint structure is described in Section 3.3.19.
   The client uses the layout hint in the layout_hint (Section 5.12.4)
   attribute to indicate the preferred type of layout to be used for a
   newly created file.  The LAYOUT4_NFSV4_1_FILES layout-type-specific
   content for the layout hint is composed of three fields.  The first
   field, nflh_care, is a set of flags indicating which values of the
   hint the client cares about.  If the NFLH4_CARE_DENSE flag is set,
   then the client indicates in the second field, nflh_util, a
   preference for how the data file is packed (Section 13.4.4), which is
   controlled by the value of the expression nflh_util & NFL4_UFLG_DENSE
   ("&" represents the bitwise AND operator).  If the
   NFLH4_CARE_COMMIT_THRU_MDS flag is set, then the client indicates a
   preference for whether the client should send COMMIT operations to
   the metadata server or data server (Section 13.7), which is
   controlled by the value of nflh_util & NFL4_UFLG_COMMIT_THRU_MDS.  If
   the NFLH4_CARE_STRIPE_UNIT_SIZE flag is set, the client indicates its
   preferred stripe unit size, which is indicated in nflh_util &
   NFL4_UFLG_STRIPE_UNIT_SIZE_MASK (thus, the stripe unit size MUST be a
   multiple of 64 bytes).  The minimum stripe unit size is 64 bytes.  If
   the NFLH4_CARE_STRIPE_COUNT flag is set, the client indicates in the
   third field, nflh_stripe_count, the stripe count.  The stripe count
   multiplied by the stripe unit size is the stripe width.

   When LAYOUTGET returns a LAYOUT4_NFSV4_1_FILES layout (indicated in
   the loc_type field of the lo_content field), the loc_body field of
   the lo_content field contains a value of data type
   nfsv4_1_file_layout4.  Among other content, nfsv4_1_file_layout4 has
   a storage device ID (field nfl_deviceid) of data type deviceid4.  The



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   GETDEVICEINFO operation maps a device ID to a storage device address
   (type device_addr4).  When GETDEVICEINFO returns a device address
   with a layout type of LAYOUT4_NFSV4_1_FILES (the da_layout_type
   field), the da_addr_body field contains a value of data type
   nfsv4_1_file_layout_ds_addr4.


   typedef netaddr4 multipath_list4<>;

   /*
    * Encoded in the da_addr_body field of
    * data type device_addr4:
    */
   struct nfsv4_1_file_layout_ds_addr4 {
           uint32_t        nflda_stripe_indices<>;
           multipath_list4 nflda_multipath_ds_list<>;
   };

   The nfsv4_1_file_layout_ds_addr4 data type represents the device
   address.  It is composed of two fields:

   1.  nflda_multipath_ds_list: An array of lists of data servers, where
       each list can be one or more elements, and each element
       represents a data server address that may serve equally as the
       target of I/O operations (see Section 13.5).  The length of this
       array might be different than the stripe count.

   2.  nflda_stripe_indices: An array of indices used to index into
       nflda_multipath_ds_list.  The value of each element of
       nflda_stripe_indices MUST be less than the number of elements in
       nflda_multipath_ds_list.  Each element of nflda_multipath_ds_list
       SHOULD be referred to by one or more elements of
       nflda_stripe_indices.  The number of elements in
       nflda_stripe_indices is always equal to the stripe count.


   /*
    * Encoded in the loc_body field of
    * data type layout_content4:
    */
   struct nfsv4_1_file_layout4 {
            deviceid4      nfl_deviceid;
            nfl_util4      nfl_util;
            uint32_t       nfl_first_stripe_index;
            offset4        nfl_pattern_offset;
            nfs_fh4        nfl_fh_list<>;
   };




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   The nfsv4_1_file_layout4 data type represents the layout.  It is
   composed of the following fields:

   1.  nfl_deviceid: The device ID that maps to a value of type
       nfsv4_1_file_layout_ds_addr4.

   2.  nfl_util: Like the nflh_util field of data type
       nfsv4_1_file_layouthint4, a compact representation of how the
       data on a file on each data server is packed, whether the client
       should send COMMIT operations to the metadata server or data
       server, and the stripe unit size.  If a server returns two or
       more overlapping layouts, each stripe unit size in each
       overlapping layout MUST be the same.

   3.  nfl_first_stripe_index: The index into the first element of the
       nflda_stripe_indices array to use.

   4.  nfl_pattern_offset: This field is the logical offset into the
       file where the striping pattern starts.  It is required for
       converting the client's logical I/O offset (e.g., the current
       offset in a POSIX file descriptor before the read() or write()
       system call is sent) into the stripe unit number (see
       Section 13.4.1).

       If dense packing is used, then nfl_pattern_offset is also needed
       to convert the client's logical I/O offset to an offset on the
       file on the data server corresponding to the stripe unit number
       (see Section 13.4.4).

       Note that nfl_pattern_offset is not always the same as lo_offset.
       For example, via the LAYOUTGET operation, a client might request
       a layout starting at offset 1000 of a file that has its striping
       pattern start at offset zero.



   5.  nfl_fh_list: An array of data server filehandles for each list of
       data servers in each element of the nflda_multipath_ds_list
       array.  The number of elements in nfl_fh_list depends on whether
       sparse or dense packing is being used.

       *  If sparse packing is being used, the number of elements in
          nfl_fh_list MUST be one of three values:

          +  Zero.  This means that filehandles used for each data
             server are the same as the filehandle returned by the OPEN
             operation from the metadata server.




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          +  One.  This means that every data server uses the same
             filehandle: what is specified in nfl_fh_list[0].

          +  The same number of elements in nflda_multipath_ds_list.
             Thus, in this case, when sending an I/O operation to any
             data server in nflda_multipath_ds_list[X], the filehandle
             in nfl_fh_list[X] MUST be used.

          See the discussion on sparse packing in Section 13.4.4.



       *  If dense packing is being used, the number of elements in
          nfl_fh_list MUST be the same as the number of elements in
          nflda_stripe_indices.  Thus, when sending an I/O operation to
          any data server in
          nflda_multipath_ds_list[nflda_stripe_indices[Y]], the
          filehandle in nfl_fh_list[Y] MUST be used.  In addition, any
          time there exists i and j, (i != j), such that the
          intersection of
          nflda_multipath_ds_list[nflda_stripe_indices[i]] and
          nflda_multipath_ds_list[nflda_stripe_indices[j]] is not empty,
          then nfl_fh_list[i] MUST NOT equal nfl_fh_list[j].  In other
          words, when dense packing is being used, if a data server
          appears in two or more units of a striping pattern, each
          reference to the data server MUST use a different filehandle.

          Indeed, if there are multiple striping patterns, as indicated
          by the presence of multiple objects of data type layout4
          (either returned in one or multiple LAYOUTGET operations), and
          a data server is the target of a unit of one pattern and
          another unit of another pattern, then each reference to each
          data server MUST use a different filehandle.

          See the discussion on dense packing in Section 13.4.4.

   The details on the interpretation of the layout are in Section 13.4.

13.4.  Interpreting the File Layout

13.4.1.  Determining the Stripe Unit Number

   To find the stripe unit number that corresponds to the client's
   logical file offset, the pattern offset will also be used.  The i'th
   stripe unit (SUi) is:

       relative_offset = file_offset - nfl_pattern_offset;
       SUi = floor(relative_offset / stripe_unit_size);



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13.4.2.  Interpreting the File Layout Using Sparse Packing

   When sparse packing is used, the algorithm for determining the
   filehandle and set of data-server network addresses to write stripe
   unit i (SUi) to is:


      stripe_count = number of elements in nflda_stripe_indices;

      j = (SUi + nfl_first_stripe_index) % stripe_count;

      idx = nflda_stripe_indices[j];

      fh_count = number of elements in nfl_fh_list;
      ds_count = number of elements in nflda_multipath_ds_list;

      switch (fh_count) {
        case ds_count:
          fh = nfl_fh_list[idx];
          break;

        case 1:
          fh = nfl_fh_list[0];
          break;

        case 0:
          fh = filehandle returned by OPEN;
          break;

        default:
          throw a fatal exception;
          break;
      }

      address_list = nflda_multipath_ds_list[idx];


   The client would then select a data server from address_list, and
   send a READ or WRITE operation using the filehandle specified in fh.

   Consider the following example:

   Suppose we have a device address consisting of seven data servers,
   arranged in three equivalence (Section 13.5) classes:

      { A, B, C, D }, { E }, { F, G }

   where A through G are network addresses.



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   Then

      nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }

   i.e.,

      nflda_multipath_ds_list[0] = { A, B, C, D }

      nflda_multipath_ds_list[1] = { E }

      nflda_multipath_ds_list[2] = { F, G }

   Suppose the striping index array is:

      nflda_stripe_indices<> = { 2, 0, 1, 0 }

   Now suppose the client gets a layout that has a device ID that maps
   to the above device address.  The initial index contains

      nfl_first_stripe_index = 2,

   and the filehandle list is

      nfl_fh_list = { 0x36, 0x87, 0x67 }.

   If the client wants to write to SU0, the set of valid { network
   address, filehandle } combinations for SUi are determined by:

      nfl_first_stripe_index = 2

   So

      idx = nflda_stripe_indices[(0 + 2) % 4]

         = nflda_stripe_indices[2]

         = 1

   So

      nflda_multipath_ds_list[1] = { E }

   and

      nfl_fh_list[1] = { 0x87 }

   The client can thus write SU0 to { 0x87, { E } }.




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   The destinations of the first 13 storage units are:

                    +-----+------------+--------------+
                    | SUi | filehandle | data servers |
                    +-----+------------+--------------+
                    | 0   | 87         | E            |
                    | 1   | 36         | A,B,C,D      |
                    | 2   | 67         | F,G          |
                    | 3   | 36         | A,B,C,D      |
                    |     |            |              |
                    | 4   | 87         | E            |
                    | 5   | 36         | A,B,C,D      |
                    | 6   | 67         | F,G          |
                    | 7   | 36         | A,B,C,D      |
                    |     |            |              |
                    | 8   | 87         | E            |
                    | 9   | 36         | A,B,C,D      |
                    | 10  | 67         | F,G          |
                    | 11  | 36         | A,B,C,D      |
                    |     |            |              |
                    | 12  | 87         | E            |
                    +-----+------------+--------------+

13.4.3.  Interpreting the File Layout Using Dense Packing

   When dense packing is used, the algorithm for determining the
   filehandle and set of data server network addresses to write stripe
   unit i (SUi) to is:























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      stripe_count = number of elements in nflda_stripe_indices;

      j = (SUi + nfl_first_stripe_index) % stripe_count;

      idx = nflda_stripe_indices[j];

      fh_count = number of elements in nfl_fh_list;
      ds_count = number of elements in nflda_multipath_ds_list;

      switch (fh_count) {
        case stripe_count:
          fh = nfl_fh_list[j];
          break;

        default:
          throw a fatal exception;
          break;
      }

      address_list = nflda_multipath_ds_list[idx];


   The client would then select a data server from address_list, and
   send a READ or WRITE operation using the filehandle specified in fh.

   Consider the following example (which is the same as the sparse
   packing example, except for the filehandle list):

   Suppose we have a device address consisting of seven data servers,
   arranged in three equivalence (Section 13.5) classes:

      { A, B, C, D }, { E }, { F, G }

   where A through G are network addresses.

   Then

      nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }

   i.e.,

      nflda_multipath_ds_list[0] = { A, B, C, D }

      nflda_multipath_ds_list[1] = { E }

      nflda_multipath_ds_list[2] = { F, G }

   Suppose the striping index array is:



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      nflda_stripe_indices<> = { 2, 0, 1, 0 }

   Now suppose the client gets a layout that has a device ID that maps
   to the above device address.  The initial index contains

      nfl_first_stripe_index = 2,

   and

      nfl_fh_list = { 0x67, 0x37, 0x87, 0x36 }.

   The interesting examples for dense packing are SU1 and SU3 because
   each stripe unit refers to the same data server list, yet each stripe
   unit MUST use a different filehandle.  If the client wants to write
   to SU1, the set of valid { network address, filehandle } combinations
   for SUi are determined by:

      nfl_first_stripe_index = 2

   So

      j = (1 + 2) % 4 = 3

         idx = nflda_stripe_indices[j]

         = nflda_stripe_indices[3]

         = 0

   So

      nflda_multipath_ds_list[0] = { A, B, C, D }

   and

      nfl_fh_list[3] = { 0x36 }

   The client can thus write SU1 to { 0x36, { A, B, C, D } }.

   For SU3, j = (3 + 2) % 4 = 1, and nflda_stripe_indices[1] = 0.  Then
   nflda_multipath_ds_list[0] = { A, B, C, D }, and nfl_fh_list[1] =
   0x37.  The client can thus write SU3 to { 0x37, { A, B, C, D } }.

   The destinations of the first 13 storage units are:







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                    +-----+------------+--------------+
                    | SUi | filehandle | data servers |
                    +-----+------------+--------------+
                    | 0   | 87         | E            |
                    | 1   | 36         | A,B,C,D      |
                    | 2   | 67         | F,G          |
                    | 3   | 37         | A,B,C,D      |
                    |     |            |              |
                    | 4   | 87         | E            |
                    | 5   | 36         | A,B,C,D      |
                    | 6   | 67         | F,G          |
                    | 7   | 37         | A,B,C,D      |
                    |     |            |              |
                    | 8   | 87         | E            |
                    | 9   | 36         | A,B,C,D      |
                    | 10  | 67         | F,G          |
                    | 11  | 37         | A,B,C,D      |
                    |     |            |              |
                    | 12  | 87         | E            |
                    +-----+------------+--------------+

13.4.4.  Sparse and Dense Stripe Unit Packing

   The flag NFL4_UFLG_DENSE of the nfl_util4 data type (field nflh_util
   of the data type nfsv4_1_file_layouthint4 and field nfl_util of data
   type nfsv4_1_file_layout_ds_addr4) specifies how the data is packed
   within the data file on a data server.  It allows for two different
   data packings: sparse and dense.  The packing type determines the
   calculation that will be made to map the client-visible file offset
   to the offset within the data file located on the data server.

   If nfl_util & NFL4_UFLG_DENSE is zero, this means that sparse packing
   is being used.  Hence, the logical offsets of the file as viewed by a
   client sending READs and WRITEs directly to the metadata server are
   the same offsets each data server uses when storing a stripe unit.
   The effect then, for striping patterns consisting of at least two
   stripe units, is for each data server file to be sparse or "holey".
   So for example, suppose there is a pattern with three stripe units,
   the stripe unit size is 4096 bytes, and there are three data servers
   in the pattern.  Then, the file in data server 1 will have stripe
   units 0, 3, 6, 9, ... filled; data server 2's file will have stripe
   units 1, 4, 7, 10, ... filled; and data server 3's file will have
   stripe units 2, 5, 8, 11, ... filled.  The unfilled stripe units of
   each file will be holes; hence, the files in each data server are
   sparse.

   If sparse packing is being used and a client attempts I/O to one of
   the holes, then an error MUST be returned by the data server.  Using



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   the above example, if data server 3 received a READ or WRITE
   operation for block 4, the data server would return
   NFS4ERR_PNFS_IO_HOLE.  Thus, data servers need to understand the
   striping pattern in order to support sparse packing.

   If nfl_util & NFL4_UFLG_DENSE is one, this means that dense packing
   is being used, and the data server files have no holes.  Dense
   packing might be selected because the data server does not
   (efficiently) support holey files or because the data server cannot
   recognize read-ahead unless there are no holes.  If dense packing is
   indicated in the layout, the data files will be packed.  Using the
   same striping pattern and stripe unit size that were used for the
   sparse packing example, the corresponding dense packing example would
   have all stripe units of all data files filled as follows:

   o  Logical stripe units 0, 3, 6, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 1.

   o  Logical stripe units 1, 4, 7, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 2.

   o  Logical stripe units 2, 5, 8, ... of the file would live on stripe
      units 0, 1, 2, ... of the file of data server 3.

   Because dense packing does not leave holes on the data servers, the
   pNFS client is allowed to write to any offset of any data file of any
   data server in the stripe.  Thus, the data servers need not know the
   file's striping pattern.

   The calculation to determine the byte offset within the data file for
   dense data server layouts is:

      stripe_width = stripe_unit_size * N;
         where N = number of elements in nflda_stripe_indices.

      relative_offset = file_offset - nfl_pattern_offset;

      data_file_offset = floor(relative_offset / stripe_width)
         * stripe_unit_size
         + relative_offset % stripe_unit_size

   If dense packing is being used, and a data server appears more than
   once in a striping pattern, then to distinguish one stripe unit from
   another, the data server MUST use a different filehandle.  Let's
   suppose there are two data servers.  Logical stripe units 0, 3, 6 are
   served by data server 1; logical stripe units 1, 4, 7 are served by
   data server 2; and logical stripe units 2, 5, 8 are also served by
   data server 2.  Unless data server 2 has two filehandles (each



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   referring to a different data file), then, for example, a write to
   logical stripe unit 1 overwrites the write to logical stripe unit 2
   because both logical stripe units are located in the same stripe unit
   (0) of data server 2.

13.5.  Data Server Multipathing

   The NFSv4.1 file layout supports multipathing to multiple data server
   addresses.  Data-server-level multipathing is used for bandwidth
   scaling via trunking (Section 2.10.5) and for higher availability of
   use in the case of a data-server failure.  Multipathing allows the
   client to switch to another data server address which may be that of
   another data server that is exporting the same data stripe unit,
   without having to contact the metadata server for a new layout.

   To support data server multipathing, each element of the
   nflda_multipath_ds_list contains an array of one more data server
   network addresses.  This array (data type multipath_list4) represents
   a list of data servers (each identified by a network address), with
   the possibility that some data servers will appear in the list
   multiple times.

   The client is free to use any of the network addresses as a
   destination to send data server requests.  If some network addresses
   are less optimal paths to the data than others, then the MDS SHOULD
   NOT include those network addresses in an element of
   nflda_multipath_ds_list.  If less optimal network addresses exist to
   provide failover, the RECOMMENDED method to offer the addresses is to
   provide them in a replacement device-ID-to-device-address mapping, or
   a replacement device ID.  When a client finds that no data server in
   an element of nflda_multipath_ds_list responds, it SHOULD send a
   GETDEVICEINFO to attempt to replace the existing device-ID-to-device-
   address mappings.  If the MDS detects that all data servers
   represented by an element of nflda_multipath_ds_list are unavailable,
   the MDS SHOULD send a CB_NOTIFY_DEVICEID (if the client has indicated
   it wants device ID notifications for changed device IDs) to change
   the device-ID-to-device-address mappings to the available data
   servers.  If the device ID itself will be replaced, the MDS SHOULD
   recall all layouts with the device ID, and thus force the client to
   get new layouts and device ID mappings via LAYOUTGET and
   GETDEVICEINFO.

   Generally, if two network addresses appear in an element of
   nflda_multipath_ds_list, they will designate the same data server,
   and the two data server addresses will support the implementation of
   client ID or session trunking (the latter is RECOMMENDED) as defined
   in Section 2.10.5.  The two data server addresses will share the same
   server owner or major ID of the server owner.  It is not always



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   necessary for the two data server addresses to designate the same
   server with trunking being used.  For example, the data could be
   read-only, and the data consist of exact replicas.

13.6.  Operations Sent to NFSv4.1 Data Servers

   Clients accessing data on an NFSv4.1 data server MUST send only the
   NULL procedure and COMPOUND procedures whose operations are taken
   only from two restricted subsets of the operations defined as valid
   NFSv4.1 operations.  Clients MUST use the filehandle specified by the
   layout when accessing data on NFSv4.1 data servers.

   The first of these operation subsets consists of management
   operations.  This subset consists of the BACKCHANNEL_CTL,
   BIND_CONN_TO_SESSION, CREATE_SESSION, DESTROY_CLIENTID,
   DESTROY_SESSION, EXCHANGE_ID, SECINFO_NO_NAME, SET_SSV, and SEQUENCE
   operations.  The client may use these operations in order to set up
   and maintain the appropriate client IDs, sessions, and security
   contexts involved in communication with the data server.  Henceforth,
   these will be referred to as data-server housekeeping operations.

   The second subset consists of COMMIT, READ, WRITE, and PUTFH.  These
   operations MUST be used with a current filehandle specified by the
   layout.  In the case of PUTFH, the new current filehandle MUST be one
   taken from the layout.  Henceforth, these will be referred to as
   data-server I/O operations.  As described in Section 12.5.1, a client
   MUST NOT send an I/O to a data server for which it does not hold a
   valid layout; the data server MUST reject such an I/O.

   Unless the server has a concurrent non-data-server personality --
   i.e., EXCHANGE_ID results returned (EXCHGID4_FLAG_USE_PNFS_DS |
   EXCHGID4_FLAG_USE_PNFS_MDS) or (EXCHGID4_FLAG_USE_PNFS_DS |
   EXCHGID4_FLAG_USE_NON_PNFS) see Section 13.1 -- any attempted use of
   operations against a data server other than those specified in the
   two subsets above MUST return NFS4ERR_NOTSUPP to the client.

   When the server has concurrent data-server and non-data-server
   personalities, each COMPOUND sent by the client MUST be constructed
   so that it is appropriate to one of the two personalities, and it
   MUST NOT contain operations directed to a mix of those personalities.
   The server MUST enforce this.  To understand the constraints,
   operations within a COMPOUND are divided into the following three
   classes:

   1.  An operation that is ambiguous regarding its personality
       assignment.  This includes all of the data-server housekeeping
       operations.  Additionally, if the server has assigned filehandles
       so that the ones defined by the layout are the same as those used



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       by the metadata server, all operations using such filehandles are
       within this class, with the following exception.  The exception
       is that if the operation uses a stateid that is incompatible with
       a data-server personality (e.g., a special stateid or the stateid
       has a non-zero "seqid" field, see Section 13.9.1), the operation
       is in class 3, as described below.  A COMPOUND containing
       multiple class 1 operations (and operations of no other class)
       MAY be sent to a server with multiple concurrent data server and
       non-data-server personalities.

   2.  An operation that is unambiguously referable to the data-server
       personality.  This includes data-server I/O operations where the
       filehandle is one that can only be validly directed to the data-
       server personality.

   3.  An operation that is unambiguously referable to the non-data-
       server personality.  This includes all COMPOUND operations that
       are neither data-server housekeeping nor data-server I/O
       operations, plus data-server I/O operations where the current fh
       (or the one to be made the current fh in the case of PUTFH) is
       only valid on the metadata server or where a stateid is used that
       is incompatible with the data server, i.e., is a special stateid
       or has a non-zero seqid value.

   When a COMPOUND first executes an operation from class 3 above, it
   acts as a normal COMPOUND on any other server, and the data-server
   personality ceases to be relevant.  There are no special restrictions
   on the operations in the COMPOUND to limit them to those for a data
   server.  When a PUTFH is done, filehandles derived from the layout
   are not valid.  If their format is not normally acceptable, then
   NFS4ERR_BADHANDLE MUST result.  Similarly, current filehandles for
   other operations do not accept filehandles derived from layouts and
   are not normally usable on the metadata server.  Using these will
   result in NFS4ERR_STALE.

   When a COMPOUND first executes an operation from class 2, which would
   be PUTFH where the filehandle is one from a layout, the COMPOUND
   henceforth is interpreted with respect to the data-server
   personality.  Operations outside the two classes discussed above MUST
   result in NFS4ERR_NOTSUPP.  Filehandles are validated using the rules
   of the data server, resulting in NFS4ERR_BADHANDLE and/or
   NFS4ERR_STALE even when they would not normally do so when addressed
   to the non-data-server personality.  Stateids must obey the rules of
   the data server in that any use of special stateids or stateids with
   non-zero seqid values must result in NFS4ERR_BAD_STATEID.

   Until the server first executes an operation from class 2 or class 3,
   the client MUST NOT depend on the operation being executed by either



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   the data-server or the non-data-server personality.  The server MUST
   pick one personality consistently for a given COMPOUND, with the only
   possible transition being a single one when the first operation from
   class 2 or class 3 is executed.

   Because of the complexity induced by assigning filehandles so they
   can be used on both a data server and a metadata server, it is
   RECOMMENDED that where the same server can have both personalities,
   the server assign separate unique filehandles to both personalities.
   This makes it unambiguous for which server a given request is
   intended.

   GETATTR and SETATTR MUST be directed to the metadata server.  In the
   case of a SETATTR of the size attribute, the control protocol is
   responsible for propagating size updates/truncations to the data
   servers.  In the case of extending WRITEs to the data servers, the
   new size must be visible on the metadata server once a LAYOUTCOMMIT
   has completed (see Section 12.5.4.2).  Section 13.10 describes the
   mechanism by which the client is to handle data-server files that do
   not reflect the metadata server's size.

13.7.  COMMIT through Metadata Server

   The file layout provides two alternate means of providing for the
   commit of data written through data servers.  The flag
   NFL4_UFLG_COMMIT_THRU_MDS in the field nfl_util of the file layout
   (data type nfsv4_1_file_layout4) is an indication from the metadata
   server to the client of the REQUIRED way of performing COMMIT, either
   by sending the COMMIT to the data server or the metadata server.
   These two methods of dealing with the issue correspond to broad
   styles of implementation for a pNFS server supporting the file layout
   type.

   o  When the flag is FALSE, COMMIT operations MUST to be sent to the
      data server to which the corresponding WRITE operations were sent.
      This approach is sometimes useful when file striping is
      implemented within the pNFS server (instead of the file system),
      with the individual data servers each implementing their own file
      systems.

   o  When the flag is TRUE, COMMIT operations MUST be sent to the
      metadata server, rather than to the individual data servers.  This
      approach is sometimes useful when file striping is implemented
      within the clustered file system that is the backend to the pNFS
      server.  In such an implementation, each COMMIT to each data
      server might result in repeated writes of metadata blocks to the
      detriment of write performance.  Sending a single COMMIT to the
      metadata server can be more efficient when there exists a



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      clustered file system capable of implementing such a coordinated
      COMMIT.

      If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is TRUE, then in order to
      maintain the current NFSv4.1 commit and recovery model, the data
      servers MUST return a common writeverf verifier in all WRITE
      responses for a given file layout, and the metadata server's
      COMMIT implementation must return the same writeverf.  The value
      of the writeverf verifier MUST be changed at the metadata server
      or any data server that is referenced in the layout, whenever
      there is a server event that can possibly lead to loss of
      uncommitted data.  The scope of the verifier can be for a file or
      for the entire pNFS server.  It might be more difficult for the
      server to maintain the verifier at the file level, but the benefit
      is that only events that impact a given file will require recovery
      action.

   Note that if the layout specified dense packing, then the offset used
   to a COMMIT to the MDS may differ than that of an offset used to a
   COMMIT to the data server.

   The single COMMIT to the metadata server will return a verifier, and
   the client should compare it to all the verifiers from the WRITEs and
   fail the COMMIT if there are any mismatched verifiers.  If COMMIT to
   the metadata server fails, the client should re-send WRITEs for all
   the modified data in the file.  The client should treat modified data
   with a mismatched verifier as a WRITE failure and try to recover by
   resending the WRITEs to the original data server or using another
   path to that data if the layout has not been recalled.
   Alternatively, the client can obtain a new layout or it could rewrite
   the data directly to the metadata server.  If nfl_util &
   NFL4_UFLG_COMMIT_THRU_MDS is FALSE, sending a COMMIT to the metadata
   server might have no effect.  If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS
   is FALSE, a COMMIT sent to the metadata server should be used only to
   commit data that was written to the metadata server.  See
   Section 12.7.6 for recovery options.

13.8.  The Layout Iomode

   The layout iomode need not be used by the metadata server when
   servicing NFSv4.1 file-based layouts, although in some circumstances
   it may be useful.  For example, if the server implementation supports
   reading from read-only replicas or mirrors, it would be useful for
   the server to return a layout enabling the client to do so.  As such,
   the client SHOULD set the iomode based on its intent to read or write
   the data.  The client may default to an iomode of LAYOUTIOMODE4_RW.
   The iomode need not be checked by the data servers when clients
   perform I/O.  However, the data servers SHOULD still validate that



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   the client holds a valid layout and return an error if the client
   does not.

13.9.  Metadata and Data Server State Coordination

13.9.1.  Global Stateid Requirements

   When the client sends I/O to a data server, the stateid used MUST NOT
   be a layout stateid as returned by LAYOUTGET or sent by
   CB_LAYOUTRECALL.  Permitted stateids are based on one of the
   following: an OPEN stateid (the stateid field of data type OPEN4resok
   as returned by OPEN), a delegation stateid (the stateid field of data
   types open_read_delegation4 and open_write_delegation4 as returned by
   OPEN or WANT_DELEGATION, or as sent by CB_PUSH_DELEG), or a stateid
   returned by the LOCK or LOCKU operations.  The stateid sent to the
   data server MUST be sent with the seqid set to zero, indicating the
   most current version of that stateid, rather than indicating a
   specific non-zero seqid value.  In no case is the use of special
   stateid values allowed.

   The stateid used for I/O MUST have the same effect and be subject to
   the same validation on a data server as it would if the I/O was being
   performed on the metadata server itself in the absence of pNFS.  This
   has the implication that stateids are globally valid on both the
   metadata and data servers.  This requires the metadata server to
   propagate changes in LOCK and OPEN state to the data servers, so that
   the data servers can validate I/O accesses.  This is discussed
   further in Section 13.9.2.  Depending on when stateids are
   propagated, the existence of a valid stateid on the data server may
   act as proof of a valid layout.

   Clients performing I/O operations need to select an appropriate
   stateid based on the locks (including opens and delegations) held by
   the client and the various types of state-owners sending the I/O
   requests.  The rules for doing so when referencing data servers are
   somewhat different from those discussed in Section 8.2.5, which apply
   when accessing metadata servers.

   The following rules, applied in order of decreasing priority, govern
   the selection of the appropriate stateid:

   o  If the client holds a delegation for the file in question, the
      delegation stateid should be used.

   o  Otherwise, there must be an OPEN stateid for the current open-
      owner, and that OPEN stateid for the open file in question is
      used, unless mandatory locking prevents that.  See below.




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   o  If the data server had previously responded with NFS4ERR_LOCKED to
      use of the OPEN stateid, then the client should use the byte-range
      lock stateid whenever one exists for that open file with the
      current lock-owner.

   o  Special stateids should never be used.  If they are used, the data
      server MUST reject the I/O with an NFS4ERR_BAD_STATEID error.

13.9.2.  Data Server State Propagation

   Since the metadata server, which handles byte-range lock and open-
   mode state changes as well as ACLs, might not be co-located with the
   data servers where I/O accesses are validated, the server
   implementation MUST take care of propagating changes of this state to
   the data servers.  Once the propagation to the data servers is
   complete, the full effect of those changes MUST be in effect at the
   data servers.  However, some state changes need not be propagated
   immediately, although all changes SHOULD be propagated promptly.
   These state propagations have an impact on the design of the control
   protocol, even though the control protocol is outside of the scope of
   this specification.  Immediate propagation refers to the synchronous
   propagation of state from the metadata server to the data server(s);
   the propagation must be complete before returning to the client.

13.9.2.1.  Lock State Propagation

   If the pNFS server supports mandatory byte-range locking, any
   mandatory byte-range locks on a file MUST be made effective at the
   data servers before the request that establishes them returns to the
   caller.  The effect MUST be the same as if the mandatory byte-range
   lock state were synchronously propagated to the data servers, even
   though the details of the control protocol may avoid actual transfer
   of the state under certain circumstances.

   On the other hand, since advisory byte-range lock state is not used
   for checking I/O accesses at the data servers, there is no semantic
   reason for propagating advisory byte-range lock state to the data
   servers.  Since updates to advisory locks neither confer nor remove
   privileges, these changes need not be propagated immediately, and may
   not need to be propagated promptly.  The updates to advisory locks
   need only be propagated when the data server needs to resolve a
   question about a stateid.  In fact, if byte-range locking is not
   mandatory (i.e., is advisory) the clients are advised to avoid using
   the byte-range lock-based stateids for I/O.  The stateids returned by
   OPEN are sufficient and eliminate overhead for this kind of state
   propagation.





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   If a client gets back an NFS4ERR_LOCKED error from a data server,
   this is an indication that mandatory byte-range locking is in force.
   The client recovers from this by getting a byte-range lock that
   covers the affected range and re-sends the I/O with the stateid of
   the byte-range lock.

13.9.2.2.  Open and Deny Mode Validation

   Open and deny mode validation MUST be performed against the open and
   deny mode(s) held by the data servers.  When access is reduced or a
   deny mode made more restrictive (because of CLOSE or OPEN_DOWNGRADE),
   the data server MUST prevent any I/Os that would be denied if
   performed on the metadata server.  When access is expanded, the data
   server MUST make sure that no requests are subsequently rejected
   because of open or deny issues that no longer apply, given the
   previous relaxation.

13.9.2.3.  File Attributes

   Since the SETATTR operation has the ability to modify state that is
   visible on both the metadata and data servers (e.g., the size), care
   must be taken to ensure that the resultant state across the set of
   data servers is consistent, especially when truncating or growing the
   file.

   As described earlier, the LAYOUTCOMMIT operation is used to ensure
   that the metadata is synchronized with changes made to the data
   servers.  For the NFSv4.1-based data storage protocol, it is
   necessary to re-synchronize state such as the size attribute, and the
   setting of mtime/change/atime.  See Section 12.5.4 for a full
   description of the semantics regarding LAYOUTCOMMIT and attribute
   synchronization.  It should be noted that by using an NFSv4.1-based
   layout type, it is possible to synchronize this state before
   LAYOUTCOMMIT occurs.  For example, the control protocol can be used
   to query the attributes present on the data servers.

   Any changes to file attributes that control authorization or access
   as reflected by ACCESS calls or READs and WRITEs on the metadata
   server, MUST be propagated to the data servers for enforcement on
   READ and WRITE I/O calls.  If the changes made on the metadata server
   result in more restrictive access permissions for any user, those
   changes MUST be propagated to the data servers synchronously.

   The OPEN operation (Section 18.16.4) does not impose any requirement
   that I/O operations on an open file have the same credentials as the
   OPEN itself (unless EXCHGID4_FLAG_BIND_PRINC_STATEID is set when
   EXCHANGE_ID creates the client ID), and so it requires the server's
   READ and WRITE operations to perform appropriate access checking.



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   Changes to ACLs also require new access checking by READ and WRITE on
   the server.  The propagation of access-right changes due to changes
   in ACLs may be asynchronous only if the server implementation is able
   to determine that the updated ACL is not more restrictive for any
   user specified in the old ACL.  Due to the relative infrequency of
   ACL updates, it is suggested that all changes be propagated
   synchronously.

13.10.  Data Server Component File Size

   A potential problem exists when a component data file on a particular
   data server has grown past EOF; the problem exists for both dense and
   sparse layouts.  Imagine the following scenario: a client creates a
   new file (size == 0) and writes to byte 131072; the client then seeks
   to the beginning of the file and reads byte 100.  The client should
   receive zeroes back as a result of the READ.  However, if the
   striping pattern directs the client to send the READ to a data server
   other than the one that received the client's original WRITE, the
   data server servicing the READ may believe that the file's size is
   still 0 bytes.  In that event, the data server's READ response will
   contain zero bytes and an indication of EOF.  The data server can
   only return zeroes if it knows that the file's size has been
   extended.  This would require the immediate propagation of the file's
   size to all data servers, which is potentially very costly.
   Therefore, the client that has initiated the extension of the file's
   size MUST be prepared to deal with these EOF conditions.  When the
   offset in the arguments to READ is less than the client's view of the
   file size, if the READ response indicates EOF and/or contains fewer
   bytes than requested, the client will interpret such a response as a
   hole in the file, and the NFS client will substitute zeroes for the
   data.

   The NFSv4.1 protocol only provides close-to-open file data cache
   semantics; meaning that when the file is closed, all modified data is
   written to the server.  When a subsequent OPEN of the file is done,
   the change attribute is inspected for a difference from a cached
   value for the change attribute.  For the case above, this means that
   a LAYOUTCOMMIT will be done at close (along with the data WRITEs) and
   will update the file's size and change attribute.  Access from
   another client after that point will result in the appropriate size
   being returned.

13.11.  Layout Revocation and Fencing

   As described in Section 12.7, the layout-type-specific storage
   protocol is responsible for handling the effects of I/Os that started
   before lease expiration and extend through lease expiration.  The
   LAYOUT4_NFSV4_1_FILES layout type can prevent all I/Os to data



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   servers from being executed after lease expiration (this prevention
   is called "fencing"), without relying on a precise client lease timer
   and without requiring data servers to maintain lease timers.  The
   LAYOUT4_NFSV4_1_FILES pNFS server has the flexibility to revoke
   individual layouts, and thus fence I/O on a per-file basis.

   In addition to lease expiration, the reasons a layout can be revoked
   include: client fails to respond to a CB_LAYOUTRECALL, the metadata
   server restarts, or administrative intervention.  Regardless of the
   reason, once a client's layout has been revoked, the pNFS server MUST
   prevent the client from sending I/O for the affected file from and to
   all data servers; in other words, it MUST fence the client from the
   affected file on the data servers.

   Fencing works as follows.  As described in Section 13.1, in COMPOUND
   procedure requests to the data server, the data filehandle provided
   by the PUTFH operation and the stateid in the READ or WRITE operation
   are used to ensure that the client has a valid layout for the I/O
   being performed; if it does not, the I/O is rejected with
   NFS4ERR_PNFS_NO_LAYOUT.  The server can simply check the stateid and,
   additionally, make the data filehandle stale if the layout specified
   a data filehandle that is different from the metadata server's
   filehandle for the file (see the nfl_fh_list description in
   Section 13.3).

   Before the metadata server takes any action to revoke layout state
   given out by a previous instance, it must make sure that all layout
   state from that previous instance are invalidated at the data
   servers.  This has the following implications.

   o  The metadata server must not restripe a file until it has
      contacted all of the data servers to invalidate the layouts from
      the previous instance.

   o  The metadata server must not give out mandatory locks that
      conflict with layouts from the previous instance without either
      doing a specific layout invalidation (as it would have to do
      anyway) or doing a global data server invalidation.

13.12.  Security Considerations for the File Layout Type

   The NFSv4.1 file layout type MUST adhere to the security
   considerations outlined in Section 12.9.  NFSv4.1 data servers MUST
   make all of the required access checks on each READ or WRITE I/O as
   determined by the NFSv4.1 protocol.  If the metadata server would
   deny a READ or WRITE operation on a file due to its ACL, mode
   attribute, open access mode, open deny mode, mandatory byte-range
   lock state, or any other attributes and state, the data server MUST



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   also deny the READ or WRITE operation.  This impacts the control
   protocol and the propagation of state from the metadata server to the
   data servers; see Section 13.9.2 for more details.

   The methods for authentication, integrity, and privacy for data
   servers based on the LAYOUT4_NFSV4_1_FILES layout type are the same
   as those used by metadata servers.  Metadata and data servers use ONC
   RPC security flavors to authenticate, and SECINFO and SECINFO_NO_NAME
   to negotiate the security mechanism and services to be used.  Thus,
   when using the LAYOUT4_NFSV4_1_FILES layout type, the impact on the
   RPC-based security model due to pNFS (as alluded to in Sections 1.7.1
   and 1.7.2.2) is zero.

   For a given file object, a metadata server MAY require different
   security parameters (secinfo4 value) than the data server.  For a
   given file object with multiple data servers, the secinfo4 value
   SHOULD be the same across all data servers.  If the secinfo4 values
   across a metadata server and its data servers differ for a specific
   file, the mapping of the principal to the server's internal user
   identifier MUST be the same in order for the access-control checks
   based on ACL, mode, open and deny mode, and mandatory locking to be
   consistent across on the pNFS server.

   If an NFSv4.1 implementation supports pNFS and supports NFSv4.1 file
   layouts, then the implementation MUST support the SECINFO_NO_NAME
   operation on both the metadata and data servers.

14.  Internationalization

   The primary issue in which NFSv4.1 needs to deal with
   internationalization, or I18N, is with respect to file names and
   other strings as used within the protocol.  The choice of string
   representation must allow reasonable name/string access to clients
   that use various languages.  The UTF-8 encoding of the UCS (Universal
   Multiple-Octet Coded Character Set) as defined by ISO10646 [21]
   allows for this type of access and follows the policy described in
   "IETF Policy on Character Sets and Languages", RFC 2277 [22].

   RFC 3454 [19], otherwise know as "stringprep", documents a framework
   for using Unicode/UTF-8 in networking protocols so as "to increase
   the likelihood that string input and string comparison work in ways
   that make sense for typical users throughout the world".  A protocol
   must define a profile of stringprep "in order to fully specify the
   processing options".  The remainder of this section defines the
   NFSv4.1 stringprep profiles.  Much of the terminology used for the
   remainder of this section comes from stringprep.





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   There are three UTF-8 string types defined for NFSv4.1: utf8str_cs,
   utf8str_cis, and utf8str_mixed.  Separate profiles are defined for
   each.  Each profile defines the following, as required by stringprep:

   o  The intended applicability of the profile.

   o  The character repertoire that is the input and output to
      stringprep (which is Unicode 3.2 for the referenced version of
      stringprep).  However, NFSv4.1 implementations are not limited to
      3.2.

   o  The mapping tables from stringprep used (as described in Section 3
      of stringprep).

   o  Any additional mapping tables specific to the profile.

   o  The Unicode normalization used, if any (as described in Section 4
      of stringprep).

   o  The tables from the stringprep listing of characters that are
      prohibited as output (as described in Section 5 of stringprep).

   o  The bidirectional string testing used, if any (as described in
      Section 6 of stringprep).

   o  Any additional characters that are prohibited as output specific
      to the profile.

   Stringprep discusses Unicode characters, whereas NFSv4.1 renders
   UTF-8 characters.  Since there is a one-to-one mapping from UTF-8 to
   Unicode, when the remainder of this document refers to Unicode, the
   reader should assume UTF-8.

   Much of the text for the profiles comes from RFC 3491 [23].

14.1.  Stringprep Profile for the utf8str_cs Type

   Every use of the utf8str_cs type definition in the NFSv4 protocol
   specification follows the profile named nfs4_cs_prep.

14.1.1.  Intended Applicability of the nfs4_cs_prep Profile

   The utf8str_cs type is a case-sensitive string of UTF-8 characters.
   Its primary use in NFSv4.1 is for naming components and pathnames.
   Components and pathnames are stored on the server's file system.  Two
   valid distinct UTF-8 strings might be the same after processing via
   the utf8str_cs profile.  If the strings are two names inside a
   directory, the NFSv4.1 server will need to either:



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   o  disallow the creation of a second name if its post-processed form
      collides with that of an existing name, or

   o  allow the creation of the second name, but arrange so that after
      post-processing, the second name is different than the post-
      processed form of the first name.

14.1.2.  Character Repertoire of nfs4_cs_prep

   The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
   Appendix A.1.  However, NFSv4.1 implementations are not limited to
   3.2.

14.1.3.  Mapping Used by nfs4_cs_prep

   The nfs4_cs_prep profile specifies mapping using the following tables
   from stringprep:

      Table B.1

   Table B.2 is normally not part of the nfs4_cs_prep profile as it is
   primarily for dealing with case-insensitive comparisons.  However, if
   the NFSv4.1 file server supports the case_insensitive file system
   attribute, and if case_insensitive is TRUE, the NFSv4.1 server MUST
   use Table B.2 (in addition to Table B1) when processing utf8str_cs
   strings, and the NFSv4.1 client MUST assume Table B.2 (in addition to
   Table B.1) is being used.

   If the case_preserving attribute is present and set to FALSE, then
   the NFSv4.1 server MUST use Table B.2 to map case when processing
   utf8str_cs strings.  Whether the server maps from lower to upper case
   or from upper to lower case is an implementation dependency.

14.1.4.  Normalization used by nfs4_cs_prep

   The nfs4_cs_prep profile does not specify a normalization form.  A
   later revision of this specification may specify a particular
   normalization form.  Therefore, the server and client can expect that
   they may receive unnormalized characters within protocol requests and
   responses.  If the operating environment requires normalization, then
   the implementation must normalize utf8str_cs strings within the
   protocol before presenting the information to an application (at the
   client) or local file system (at the server).








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14.1.5.  Prohibited Output for nfs4_cs_prep

   The nfs4_cs_prep profile RECOMMENDS prohibiting the use of the
   following tables from stringprep:

      Table C.5

      Table C.6

14.1.6.  Bidirectional Output for nfs4_cs_prep

   The nfs4_cs_prep profile does not specify any checking of
   bidirectional strings.

14.2.  Stringprep Profile for the utf8str_cis Type

   Every use of the utf8str_cis type definition in the NFSv4.1 protocol
   specification follows the profile named nfs4_cis_prep.

14.2.1.  Intended Applicability of the nfs4_cis_prep Profile

   The utf8str_cis type is a case-insensitive string of UTF-8
   characters.  Its primary use in NFSv4.1 is for naming NFS servers.

14.2.2.  Character Repertoire of nfs4_cis_prep

   The nfs4_cis_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1.  However, NFSv4.1 implementations are not
   limited to 3.2.

14.2.3.  Mapping Used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies mapping using the following
   tables from stringprep:

      Table B.1

      Table B.2

14.2.4.  Normalization Used by nfs4_cis_prep

   The nfs4_cis_prep profile specifies using Unicode normalization form
   KC, as described in stringprep.








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14.2.5.  Prohibited Output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

14.2.6.  Bidirectional Output for nfs4_cis_prep

   The nfs4_cis_prep profile specifies checking bidirectional strings as
   described in stringprep's Section 6.

14.3.  Stringprep Profile for the utf8str_mixed Type

   Every use of the utf8str_mixed type definition in the NFSv4.1
   protocol specification follows the profile named nfs4_mixed_prep.

14.3.1.  Intended Applicability of the nfs4_mixed_prep Profile

   The utf8str_mixed type is a string of UTF-8 characters, with a prefix
   that is case sensitive, a separator equal to '@', and a suffix that
   is a fully qualified domain name.  Its primary use in NFSv4.1 is for
   naming principals identified in an Access Control Entry.

14.3.2.  Character Repertoire of nfs4_mixed_prep

   The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
   stringprep's Appendix A.1.  However, NFSv4.1 implementations are not
   limited to 3.2.






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14.3.3.  Mapping Used by nfs4_cis_prep

   For the prefix and the separator of a utf8str_mixed string, the
   nfs4_mixed_prep profile specifies mapping using the following table
   from stringprep:

      Table B.1

   For the suffix of a utf8str_mixed string, the nfs4_mixed_prep profile
   specifies mapping using the following tables from stringprep:

      Table B.1

      Table B.2

14.3.4.  Normalization Used by nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies using Unicode normalization
   form KC, as described in stringprep.

14.3.5.  Prohibited Output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies prohibiting using the following
   tables from stringprep:

      Table C.1.2

      Table C.2.2

      Table C.3

      Table C.4

      Table C.5

      Table C.6

      Table C.7

      Table C.8

      Table C.9

14.3.6.  Bidirectional Output for nfs4_mixed_prep

   The nfs4_mixed_prep profile specifies checking bidirectional strings
   as described in stringprep's Section 6.




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14.4.  UTF-8 Capabilities

   const FSCHARSET_CAP4_CONTAINS_NON_UTF8  = 0x1;
   const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8   = 0x2;

   typedef uint32_t        fs_charset_cap4;

   Because some operating environments and file systems do not enforce
   character set encodings, NFSv4.1 supports the fs_charset_cap
   attribute (Section 5.8.2.11) that indicates to the client a file
   system's UTF-8 capabilities.  The attribute is an integer containing
   a pair of flags.  The first flag is FSCHARSET_CAP4_CONTAINS_NON_UTF8,
   which, if set to one, tells the client that the file system contains
   non-UTF-8 characters, and the server will not convert non-UTF
   characters to UTF-8 if the client reads a symlink or directory,
   neither will operations with component names or pathnames in the
   arguments convert the strings to UTF-8.  The second flag is
   FSCHARSET_CAP4_ALLOWS_ONLY_UTF8, which, if set to one, indicates that
   the server will accept (and generate) only UTF-8 characters on the
   file system.  If FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set to one,
   FSCHARSET_CAP4_CONTAINS_NON_UTF8 MUST be set to zero.
   FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 SHOULD always be set to one.

14.5.  UTF-8 Related Errors

   Where the client sends an invalid UTF-8 string, the server should
   return NFS4ERR_INVAL (see Table 5).  This includes cases in which
   inappropriate prefixes are detected and where the count includes
   trailing bytes that do not constitute a full UCS character.

   Where the client-supplied string is valid UTF-8 but contains
   characters that are not supported by the server as a value for that
   string (e.g., names containing characters outside of Unicode plane 0
   on file systems that fail to support such characters despite their
   presence in the Unicode standard), the server should return
   NFS4ERR_BADCHAR.

   Where a UTF-8 string is used as a file name, and the file system
   (while supporting all of the characters within the name) does not
   allow that particular name to be used, the server should return the
   error NFS4ERR_BADNAME (Table 5).  This includes situations in which
   the server file system imposes a normalization constraint on name
   strings, but will also include such situations as file system
   prohibitions of "." and ".." as file names for certain operations,
   and other such constraints.






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15.  Error Values

   NFS error numbers are assigned to failed operations within a Compound
   (COMPOUND or CB_COMPOUND) request.  A Compound request contains a
   number of NFS operations that have their results encoded in sequence
   in a Compound reply.  The results of successful operations will
   consist of an NFS4_OK status followed by the encoded results of the
   operation.  If an NFS operation fails, an error status will be
   entered in the reply and the Compound request will be terminated.

15.1.  Error Definitions

                        Protocol Error Definitions

    +-----------------------------------+--------+-------------------+
    | Error                             | Number | Description       |
    +-----------------------------------+--------+-------------------+
    | NFS4_OK                           | 0      | Section 15.1.3.1  |
    | NFS4ERR_ACCESS                    | 13     | Section 15.1.6.1  |
    | NFS4ERR_ATTRNOTSUPP               | 10032  | Section 15.1.15.1 |
    | NFS4ERR_ADMIN_REVOKED             | 10047  | Section 15.1.5.1  |
    | NFS4ERR_BACK_CHAN_BUSY            | 10057  | Section 15.1.12.1 |
    | NFS4ERR_BADCHAR                   | 10040  | Section 15.1.7.1  |
    | NFS4ERR_BADHANDLE                 | 10001  | Section 15.1.2.1  |
    | NFS4ERR_BADIOMODE                 | 10049  | Section 15.1.10.1 |
    | NFS4ERR_BADLAYOUT                 | 10050  | Section 15.1.10.2 |
    | NFS4ERR_BADNAME                   | 10041  | Section 15.1.7.2  |
    | NFS4ERR_BADOWNER                  | 10039  | Section 15.1.15.2 |
    | NFS4ERR_BADSESSION                | 10052  | Section 15.1.11.1 |
    | NFS4ERR_BADSLOT                   | 10053  | Section 15.1.11.2 |
    | NFS4ERR_BADTYPE                   | 10007  | Section 15.1.4.1  |
    | NFS4ERR_BADXDR                    | 10036  | Section 15.1.1.1  |
    | NFS4ERR_BAD_COOKIE                | 10003  | Section 15.1.1.2  |
    | NFS4ERR_BAD_HIGH_SLOT             | 10077  | Section 15.1.11.3 |
    | NFS4ERR_BAD_RANGE                 | 10042  | Section 15.1.8.1  |
    | NFS4ERR_BAD_SEQID                 | 10026  | Section 15.1.16.1 |
    | NFS4ERR_BAD_SESSION_DIGEST        | 10051  | Section 15.1.12.2 |
    | NFS4ERR_BAD_STATEID               | 10025  | Section 15.1.5.2  |
    | NFS4ERR_CB_PATH_DOWN              | 10048  | Section 15.1.11.4 |
    | NFS4ERR_CLID_INUSE                | 10017  | Section 15.1.13.2 |
    | NFS4ERR_CLIENTID_BUSY             | 10074  | Section 15.1.13.1 |
    | NFS4ERR_COMPLETE_ALREADY          | 10054  | Section 15.1.9.1  |
    | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | 10055  | Section 15.1.11.6 |
    | NFS4ERR_DEADLOCK                  | 10045  | Section 15.1.8.2  |
    | NFS4ERR_DEADSESSION               | 10078  | Section 15.1.11.5 |
    | NFS4ERR_DELAY                     | 10008  | Section 15.1.1.3  |
    | NFS4ERR_DELEG_ALREADY_WANTED      | 10056  | Section 15.1.14.1 |
    | NFS4ERR_DELEG_REVOKED             | 10087  | Section 15.1.5.3  |



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    | NFS4ERR_DENIED                    | 10010  | Section 15.1.8.3  |
    | NFS4ERR_DIRDELEG_UNAVAIL          | 10084  | Section 15.1.14.2 |
    | NFS4ERR_DQUOT                     | 69     | Section 15.1.4.2  |
    | NFS4ERR_ENCR_ALG_UNSUPP           | 10079  | Section 15.1.13.3 |
    | NFS4ERR_EXIST                     | 17     | Section 15.1.4.3  |
    | NFS4ERR_EXPIRED                   | 10011  | Section 15.1.5.4  |
    | NFS4ERR_FBIG                      | 27     | Section 15.1.4.4  |
    | NFS4ERR_FHEXPIRED                 | 10014  | Section 15.1.2.2  |
    | NFS4ERR_FILE_OPEN                 | 10046  | Section 15.1.4.5  |
    | NFS4ERR_GRACE                     | 10013  | Section 15.1.9.2  |
    | NFS4ERR_HASH_ALG_UNSUPP           | 10072  | Section 15.1.13.4 |
    | NFS4ERR_INVAL                     | 22     | Section 15.1.1.4  |
    | NFS4ERR_IO                        | 5      | Section 15.1.4.6  |
    | NFS4ERR_ISDIR                     | 21     | Section 15.1.2.3  |
    | NFS4ERR_LAYOUTTRYLATER            | 10058  | Section 15.1.10.3 |
    | NFS4ERR_LAYOUTUNAVAILABLE         | 10059  | Section 15.1.10.4 |
    | NFS4ERR_LEASE_MOVED               | 10031  | Section 15.1.16.2 |
    | NFS4ERR_LOCKED                    | 10012  | Section 15.1.8.4  |
    | NFS4ERR_LOCKS_HELD                | 10037  | Section 15.1.8.5  |
    | NFS4ERR_LOCK_NOTSUPP              | 10043  | Section 15.1.8.6  |
    | NFS4ERR_LOCK_RANGE                | 10028  | Section 15.1.8.7  |
    | NFS4ERR_MINOR_VERS_MISMATCH       | 10021  | Section 15.1.3.2  |
    | NFS4ERR_MLINK                     | 31     | Section 15.1.4.7  |
    | NFS4ERR_MOVED                     | 10019  | Section 15.1.2.4  |
    | NFS4ERR_NAMETOOLONG               | 63     | Section 15.1.7.3  |
    | NFS4ERR_NOENT                     | 2      | Section 15.1.4.8  |
    | NFS4ERR_NOFILEHANDLE              | 10020  | Section 15.1.2.5  |
    | NFS4ERR_NOMATCHING_LAYOUT         | 10060  | Section 15.1.10.5 |
    | NFS4ERR_NOSPC                     | 28     | Section 15.1.4.9  |
    | NFS4ERR_NOTDIR                    | 20     | Section 15.1.2.6  |
    | NFS4ERR_NOTEMPTY                  | 66     | Section 15.1.4.10 |
    | NFS4ERR_NOTSUPP                   | 10004  | Section 15.1.1.5  |
    | NFS4ERR_NOT_ONLY_OP               | 10081  | Section 15.1.3.3  |
    | NFS4ERR_NOT_SAME                  | 10027  | Section 15.1.15.3 |
    | NFS4ERR_NO_GRACE                  | 10033  | Section 15.1.9.3  |
    | NFS4ERR_NXIO                      | 6      | Section 15.1.16.3 |
    | NFS4ERR_OLD_STATEID               | 10024  | Section 15.1.5.5  |
    | NFS4ERR_OPENMODE                  | 10038  | Section 15.1.8.8  |
    | NFS4ERR_OP_ILLEGAL                | 10044  | Section 15.1.3.4  |
    | NFS4ERR_OP_NOT_IN_SESSION         | 10071  | Section 15.1.3.5  |
    | NFS4ERR_PERM                      | 1      | Section 15.1.6.2  |
    | NFS4ERR_PNFS_IO_HOLE              | 10075  | Section 15.1.10.6 |
    | NFS4ERR_PNFS_NO_LAYOUT            | 10080  | Section 15.1.10.7 |
    | NFS4ERR_RECALLCONFLICT            | 10061  | Section 15.1.14.3 |
    | NFS4ERR_RECLAIM_BAD               | 10034  | Section 15.1.9.4  |
    | NFS4ERR_RECLAIM_CONFLICT          | 10035  | Section 15.1.9.5  |
    | NFS4ERR_REJECT_DELEG              | 10085  | Section 15.1.14.4 |
    | NFS4ERR_REP_TOO_BIG               | 10066  | Section 15.1.3.6  |



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    | NFS4ERR_REP_TOO_BIG_TO_CACHE      | 10067  | Section 15.1.3.7  |
    | NFS4ERR_REQ_TOO_BIG               | 10065  | Section 15.1.3.8  |
    | NFS4ERR_RESTOREFH                 | 10030  | Section 15.1.16.4 |
    | NFS4ERR_RETRY_UNCACHED_REP        | 10068  | Section 15.1.3.9  |
    | NFS4ERR_RETURNCONFLICT            | 10086  | Section 15.1.10.8 |
    | NFS4ERR_ROFS                      | 30     | Section 15.1.4.11 |
    | NFS4ERR_SAME                      | 10009  | Section 15.1.15.4 |
    | NFS4ERR_SHARE_DENIED              | 10015  | Section 15.1.8.9  |
    | NFS4ERR_SEQUENCE_POS              | 10064  | Section 15.1.3.10 |
    | NFS4ERR_SEQ_FALSE_RETRY           | 10076  | Section 15.1.11.7 |
    | NFS4ERR_SEQ_MISORDERED            | 10063  | Section 15.1.11.8 |
    | NFS4ERR_SERVERFAULT               | 10006  | Section 15.1.1.6  |
    | NFS4ERR_STALE                     | 70     | Section 15.1.2.7  |
    | NFS4ERR_STALE_CLIENTID            | 10022  | Section 15.1.13.5 |
    | NFS4ERR_STALE_STATEID             | 10023  | Section 15.1.16.5 |
    | NFS4ERR_SYMLINK                   | 10029  | Section 15.1.2.8  |
    | NFS4ERR_TOOSMALL                  | 10005  | Section 15.1.1.7  |
    | NFS4ERR_TOO_MANY_OPS              | 10070  | Section 15.1.3.11 |
    | NFS4ERR_UNKNOWN_LAYOUTTYPE        | 10062  | Section 15.1.10.9 |
    | NFS4ERR_UNSAFE_COMPOUND           | 10069  | Section 15.1.3.12 |
    | NFS4ERR_WRONGSEC                  | 10016  | Section 15.1.6.3  |
    | NFS4ERR_WRONG_CRED                | 10082  | Section 15.1.6.4  |
    | NFS4ERR_WRONG_TYPE                | 10083  | Section 15.1.2.9  |
    | NFS4ERR_XDEV                      | 18     | Section 15.1.4.12 |
    +-----------------------------------+--------+-------------------+

                                  Table 5

15.1.1.  General Errors

   This section deals with errors that are applicable to a broad set of
   different purposes.

15.1.1.1.  NFS4ERR_BADXDR (Error Code 10036)

   The arguments for this operation do not match those specified in the
   XDR definition.  This includes situations in which the request ends
   before all the arguments have been seen.  Note that this error
   applies when fixed enumerations (these include booleans) have a value
   within the input stream that is not valid for the enum.  A replier
   may pre-parse all operations for a Compound procedure before doing
   any operation execution and return RPC-level XDR errors in that case.

15.1.1.2.  NFS4ERR_BAD_COOKIE (Error Code 10003)

   Used for operations that provide a set of information indexed by some
   quantity provided by the client or cookie sent by the server for an




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   earlier invocation.  Where the value cannot be used for its intended
   purpose, this error results.

15.1.1.3.  NFS4ERR_DELAY (Error Code 10008)

   For any of a number of reasons, the replier could not process this
   operation in what was deemed a reasonable time.  The client should
   wait and then try the request with a new slot and sequence value.

   Some examples of scenarios that might lead to this situation:

   o  A server that supports hierarchical storage receives a request to
      process a file that had been migrated.

   o  An operation requires a delegation recall to proceed, and waiting
      for this delegation recall makes processing this request in a
      timely fashion impossible.

   In such cases, the error NFS4ERR_DELAY allows these preparatory
   operations to proceed without holding up client resources such as a
   session slot.  After delaying for period of time, the client can then
   re-send the operation in question (but not with the same slot ID and
   sequence ID; one or both MUST be different on the re-send).

   Note that without the ability to return NFS4ERR_DELAY and the
   client's willingness to re-send when receiving it, deadlock might
   result.  For example, if a recall is done, and if the delegation
   return or operations preparatory to delegation return are held up by
   other operations that need the delegation to be returned, session
   slots might not be available.  The result could be deadlock.

15.1.1.4.  NFS4ERR_INVAL (Error Code 22)

   The arguments for this operation are not valid for some reason, even
   though they do match those specified in the XDR definition for the
   request.

15.1.1.5.  NFS4ERR_NOTSUPP (Error Code 10004)

   Operation not supported, either because the operation is an OPTIONAL
   one and is not supported by this server or because the operation MUST
   NOT be implemented in the current minor version.

15.1.1.6.  NFS4ERR_SERVERFAULT (Error Code 10006)

   An error occurred on the server that does not map to any of the
   specific legal NFSv4.1 protocol error values.  The client should




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   translate this into an appropriate error.  UNIX clients may choose to
   translate this to EIO.

15.1.1.7.  NFS4ERR_TOOSMALL (Error Code 10005)

   Used where an operation returns a variable amount of data, with a
   limit specified by the client.  Where the data returned cannot be fit
   within the limit specified by the client, this error results.

15.1.2.  Filehandle Errors

   These errors deal with the situation in which the current or saved
   filehandle, or the filehandle passed to PUTFH intended to become the
   current filehandle, is invalid in some way.  This includes situations
   in which the filehandle is a valid filehandle in general but is not
   of the appropriate object type for the current operation.

   Where the error description indicates a problem with the current or
   saved filehandle, it is to be understood that filehandles are only
   checked for the condition if they are implicit arguments of the
   operation in question.

15.1.2.1.  NFS4ERR_BADHANDLE (Error Code 10001)

   Illegal NFS filehandle for the current server.  The current file
   handle failed internal consistency checks.  Once accepted as valid
   (by PUTFH), no subsequent status change can cause the filehandle to
   generate this error.

15.1.2.2.  NFS4ERR_FHEXPIRED (Error Code 10014)

   A current or saved filehandle that is an argument to the current
   operation is volatile and has expired at the server.

15.1.2.3.  NFS4ERR_ISDIR (Error Code 21)

   The current or saved filehandle designates a directory when the
   current operation does not allow a directory to be accepted as the
   target of this operation.

15.1.2.4.  NFS4ERR_MOVED (Error Code 10019)

   The file system that contains the current filehandle object is not
   present at the server.  It may have been relocated or migrated to
   another server, or it may have never been present.  The client may
   obtain the new file system location by obtaining the "fs_locations"
   or "fs_locations_info" attribute for the current filehandle.  For
   further discussion, refer to Section 11.2.



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15.1.2.5.  NFS4ERR_NOFILEHANDLE (Error Code 10020)

   The logical current or saved filehandle value is required by the
   current operation and is not set.  This may be a result of a
   malformed COMPOUND operation (i.e., no PUTFH or PUTROOTFH before an
   operation that requires the current filehandle be set).

15.1.2.6.  NFS4ERR_NOTDIR (Error Code 20)

   The current (or saved) filehandle designates an object that is not a
   directory for an operation in which a directory is required.

15.1.2.7.  NFS4ERR_STALE (Error Code 70)

   The current or saved filehandle value designating an argument to the
   current operation is invalid.  The file referred to by that
   filehandle no longer exists or access to it has been revoked.

15.1.2.8.  NFS4ERR_SYMLINK (Error Code 10029)

   The current filehandle designates a symbolic link when the current
   operation does not allow a symbolic link as the target.

15.1.2.9.  NFS4ERR_WRONG_TYPE (Error Code 10083)

   The current (or saved) filehandle designates an object that is of an
   invalid type for the current operation, and there is no more specific
   error (such as NFS4ERR_ISDIR or NFS4ERR_SYMLINK) that applies.  Note
   that in NFSv4.0, such situations generally resulted in the less-
   specific error NFS4ERR_INVAL.

15.1.3.  Compound Structure Errors

   This section deals with errors that relate to the overall structure
   of a Compound request (by which we mean to include both COMPOUND and
   CB_COMPOUND), rather than to particular operations.

   There are a number of basic constraints on the operations that may
   appear in a Compound request.  Sessions add to these basic
   constraints by requiring a Sequence operation (either SEQUENCE or
   CB_SEQUENCE) at the start of the Compound.

15.1.3.1.  NFS_OK (Error code 0)

   Indicates the operation completed successfully, in that all of the
   constituent operations completed without error.





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15.1.3.2.  NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)

   The minor version specified is not one that the current listener
   supports.  This value is returned in the overall status for the
   Compound but is not associated with a specific operation since the
   results will specify a result count of zero.

15.1.3.3.  NFS4ERR_NOT_ONLY_OP (Error Code 10081)

   Certain operations, which are allowed to be executed outside of a
   session, MUST be the only operation within a Compound whenever the
   Compound does not start with a Sequence operation.  This error
   results when that constraint is not met.

15.1.3.4.  NFS4ERR_OP_ILLEGAL (Error Code 10044)

   The operation code is not a valid one for the current Compound
   procedure.  The opcode in the result stream matched with this error
   is the ILLEGAL value, although the value that appears in the request
   stream may be different.  Where an illegal value appears and the
   replier pre-parses all operations for a Compound procedure before
   doing any operation execution, an RPC-level XDR error may be
   returned.

15.1.3.5.  NFS4ERR_OP_NOT_IN_SESSION (Error Code 10071)

   Most forward operations and all callback operations are only valid
   within the context of a session, so that the Compound request in
   question MUST begin with a Sequence operation.  If an attempt is made
   to execute these operations outside the context of session, this
   error results.

15.1.3.6.  NFS4ERR_REP_TOO_BIG (Error Code 10066)

   The reply to a Compound would exceed the channel's negotiated maximum
   response size.

15.1.3.7.  NFS4ERR_REP_TOO_BIG_TO_CACHE (Error Code 10067)

   The reply to a Compound would exceed the channel's negotiated maximum
   size for replies cached in the reply cache when the Sequence for the
   current request specifies that this request is to be cached.

15.1.3.8.  NFS4ERR_REQ_TOO_BIG (Error Code 10065)

   The Compound request exceeds the channel's negotiated maximum size
   for requests.




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15.1.3.9.  NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)

   The requester has attempted a retry of a Compound that it previously
   requested not be placed in the reply cache.

15.1.3.10.  NFS4ERR_SEQUENCE_POS (Error Code 10064)

   A Sequence operation appeared in a position other than the first
   operation of a Compound request.

15.1.3.11.  NFS4ERR_TOO_MANY_OPS (Error Code 10070)

   The Compound request has too many operations, exceeding the count
   negotiated when the session was created.

15.1.3.12.  NFS4ERR_UNSAFE_COMPOUND (Error Code 10068)

   The client has sent a COMPOUND request with an unsafe mix of
   operations -- specifically, with a non-idempotent operation that
   changes the current filehandle and that is not followed by a GETFH.

15.1.4.  File System Errors

   These errors describe situations that occurred in the underlying file
   system implementation rather than in the protocol or any NFSv4.x
   feature.

15.1.4.1.  NFS4ERR_BADTYPE (Error Code 10007)

   An attempt was made to create an object with an inappropriate type
   specified to CREATE.  This may be because the type is undefined,
   because the type is not supported by the server, or because the type
   is not intended to be created by CREATE (such as a regular file or
   named attribute, for which OPEN is used to do the file creation).

15.1.4.2.  NFS4ERR_DQUOT (Error Code 19)

   Resource (quota) hard limit exceeded.  The user's resource limit on
   the server has been exceeded.

15.1.4.3.  NFS4ERR_EXIST (Error Code 17)

   A file of the specified target name (when creating, renaming, or
   linking) already exists.







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15.1.4.4.  NFS4ERR_FBIG (Error Code 27)

   The file is too large.  The operation would have caused the file to
   grow beyond the server's limit.

15.1.4.5.  NFS4ERR_FILE_OPEN (Error Code 10046)

   The operation is not allowed because a file involved in the operation
   is currently open.  Servers may, but are not required to, disallow
   linking-to, removing, or renaming open files.

15.1.4.6.  NFS4ERR_IO (Error Code 5)

   Indicates that an I/O error occurred for which the file system was
   unable to provide recovery.

15.1.4.7.  NFS4ERR_MLINK (Error Code 31)

   The request would have caused the server's limit for the number of
   hard links a file may have to be exceeded.

15.1.4.8.  NFS4ERR_NOENT (Error Code 2)

   Indicates no such file or directory.  The file or directory name
   specified does not exist.

15.1.4.9.  NFS4ERR_NOSPC (Error Code 28)

   Indicates there is no space left on the device.  The operation would
   have caused the server's file system to exceed its limit.

15.1.4.10.  NFS4ERR_NOTEMPTY (Error Code 66)

   An attempt was made to remove a directory that was not empty.

15.1.4.11.  NFS4ERR_ROFS (Error Code 30)

   Indicates a read-only file system.  A modifying operation was
   attempted on a read-only file system.

15.1.4.12.  NFS4ERR_XDEV (Error Code 18)

   Indicates an attempt to do an operation, such as linking, that
   inappropriately crosses a boundary.  This may be due to such
   boundaries as:

   o  that between file systems (where the fsids are different).




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   o  that between different named attribute directories or between a
      named attribute directory and an ordinary directory.

   o  that between byte-ranges of a file system that the file system
      implementation treats as separate (for example, for space
      accounting purposes), and where cross-connection between the byte-
      ranges are not allowed.

15.1.5.  State Management Errors

   These errors indicate problems with the stateid (or one of the
   stateids) passed to a given operation.  This includes situations in
   which the stateid is invalid as well as situations in which the
   stateid is valid but designates locking state that has been revoked.
   Depending on the operation, the stateid when valid may designate
   opens, byte-range locks, file or directory delegations, layouts, or
   device maps.

15.1.5.1.  NFS4ERR_ADMIN_REVOKED (Error Code 10047)

   A stateid designates locking state of any type that has been revoked
   due to administrative interaction, possibly while the lease is valid.

15.1.5.2.  NFS4ERR_BAD_STATEID (Error Code 10026)

   A stateid does not properly designate any valid state.  See Sections
   8.2.4 and 8.2.3 for a discussion of how stateids are validated.

15.1.5.3.  NFS4ERR_DELEG_REVOKED (Error Code 10087)

   A stateid designates recallable locking state of any type (delegation
   or layout) that has been revoked due to the failure of the client to
   return the lock when it was recalled.

15.1.5.4.  NFS4ERR_EXPIRED (Error Code 10011)

   A stateid designates locking state of any type that has been revoked
   due to expiration of the client's lease, either immediately upon
   lease expiration, or following a later request for a conflicting
   lock.

15.1.5.5.  NFS4ERR_OLD_STATEID (Error Code 10024)

   A stateid with a non-zero seqid value does match the current seqid
   for the state designated by the user.






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15.1.6.  Security Errors

   These are the various permission-related errors in NFSv4.1.

15.1.6.1.  NFS4ERR_ACCESS (Error Code 13)

   Indicates permission denied.  The caller does not have the correct
   permission to perform the requested operation.  Contrast this with
   NFS4ERR_PERM (Section 15.1.6.2), which restricts itself to owner or
   privileged-user permission failures, and NFS4ERR_WRONG_CRED
   (Section 15.1.6.4), which deals with appropriate permission to delete
   or modify transient objects based on the credentials of the user that
   created them.

15.1.6.2.  NFS4ERR_PERM (Error Code 1)

   Indicates requester is not the owner.  The operation was not allowed
   because the caller is neither a privileged user (root) nor the owner
   of the target of the operation.

15.1.6.3.  NFS4ERR_WRONGSEC (Error Code 10016)

   Indicates that the security mechanism being used by the client for
   the operation does not match the server's security policy.  The
   client should change the security mechanism being used and re-send
   the operation (but not with the same slot ID and sequence ID; one or
   both MUST be different on the re-send).  SECINFO and SECINFO_NO_NAME
   can be used to determine the appropriate mechanism.

15.1.6.4.  NFS4ERR_WRONG_CRED (Error Code 10082)

   An operation that manipulates state was attempted by a principal that
   was not allowed to modify that piece of state.

15.1.7.  Name Errors

   Names in NFSv4 are UTF-8 strings.  When the strings are not valid
   UTF-8 or are of length zero, the error NFS4ERR_INVAL results.
   Besides this, there are a number of other errors to indicate specific
   problems with names.

15.1.7.1.  NFS4ERR_BADCHAR (Error Code 10040)

   A UTF-8 string contains a character that is not supported by the
   server in the context in which it being used.






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15.1.7.2.  NFS4ERR_BADNAME (Error Code 10041)

   A name string in a request consisted of valid UTF-8 characters
   supported by the server, but the name is not supported by the server
   as a valid name for the current operation.  An example might be
   creating a file or directory named ".." on a server whose file system
   uses that name for links to parent directories.

15.1.7.3.  NFS4ERR_NAMETOOLONG (Error Code 63)

   Returned when the filename in an operation exceeds the server's
   implementation limit.

15.1.8.  Locking Errors

   This section deals with errors related to locking, both as to share
   reservations and byte-range locking.  It does not deal with errors
   specific to the process of reclaiming locks.  Those are dealt with in
   Section 15.1.9.

15.1.8.1.  NFS4ERR_BAD_RANGE (Error Code 10042)

   The byte-range of a LOCK, LOCKT, or LOCKU operation is not allowed by
   the server.  For example, this error results when a server that only
   supports 32-bit ranges receives a range that cannot be handled by
   that server.  (See Section 18.10.3.)

15.1.8.2.  NFS4ERR_DEADLOCK (Error Code 10045)

   The server has been able to determine a byte-range locking deadlock
   condition for a READW_LT or WRITEW_LT LOCK operation.

15.1.8.3.  NFS4ERR_DENIED (Error Code 10010)

   An attempt to lock a file is denied.  Since this may be a temporary
   condition, the client is encouraged to re-send the lock request (but
   not with the same slot ID and sequence ID; one or both MUST be
   different on the re-send) until the lock is accepted.  See
   Section 9.6 for a discussion of the re-send.

15.1.8.4.  NFS4ERR_LOCKED (Error Code 10012)

   A READ or WRITE operation was attempted on a file where there was a
   conflict between the I/O and an existing lock:

   o  There is a share reservation inconsistent with the I/O being done.





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   o  The range to be read or written intersects an existing mandatory
      byte-range lock.

15.1.8.5.  NFS4ERR_LOCKS_HELD (Error Code 10037)

   An operation was prevented by the unexpected presence of locks.

15.1.8.6.  NFS4ERR_LOCK_NOTSUPP (Error Code 10043)

   A LOCK operation was attempted that would require the upgrade or
   downgrade of a byte-range lock range already held by the owner, and
   the server does not support atomic upgrade or downgrade of locks.

15.1.8.7.  NFS4ERR_LOCK_RANGE (Error Code 10028)

   A LOCK operation is operating on a range that overlaps in part a
   currently held byte-range lock for the current lock-owner and does
   not precisely match a single such byte-range lock where the server
   does not support this type of request, and thus does not implement
   POSIX locking semantics [24].  See Sections 18.10.4, 18.11.4, and
   18.12.4 for a discussion of how this applies to LOCK, LOCKT, and
   LOCKU respectively.

15.1.8.8.  NFS4ERR_OPENMODE (Error Code 10038)

   The client attempted a READ, WRITE, LOCK, or other operation not
   sanctioned by the stateid passed (e.g., writing to a file opened for
   read-only access).

15.1.8.9.  NFS4ERR_SHARE_DENIED (Error Code 10015)

   An attempt to OPEN a file with a share reservation has failed because
   of a share conflict.

15.1.9.  Reclaim Errors

   These errors relate to the process of reclaiming locks after a server
   restart.

15.1.9.1.  NFS4ERR_COMPLETE_ALREADY (Error Code 10054)

   The client previously sent a successful RECLAIM_COMPLETE operation.
   An additional RECLAIM_COMPLETE operation is not necessary and results
   in this error.







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15.1.9.2.  NFS4ERR_GRACE (Error Code 10013)

   The server was in its recovery or grace period.  The locking request
   was not a reclaim request and so could not be granted during that
   period.

15.1.9.3.  NFS4ERR_NO_GRACE (Error Code 10033)

   A reclaim of client state was attempted in circumstances in which the
   server cannot guarantee that conflicting state has not been provided
   to another client.  This can occur because the reclaim has been done
   outside of the grace period of the server, after the client has done
   a RECLAIM_COMPLETE operation, or because previous operations have
   created a situation in which the server is not able to determine that
   a reclaim-interfering edge condition does not exist.

15.1.9.4.  NFS4ERR_RECLAIM_BAD (Error Code 10034)

   The server has determined that a reclaim attempted by the client is
   not valid, i.e. the lock specified as being reclaimed could not
   possibly have existed before the server restart.  A server is not
   obliged to make this determination and will typically rely on the
   client to only reclaim locks that the client was granted prior to
   restart.  However, when a server does have reliable information to
   enable it make this determination, this error indicates that the
   reclaim has been rejected as invalid.  This is as opposed to the
   error NFS4ERR_RECLAIM_CONFLICT (see Section 15.1.9.5) where the
   server can only determine that there has been an invalid reclaim, but
   cannot determine which request is invalid.

15.1.9.5.  NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)

   The reclaim attempted by the client has encountered a conflict and
   cannot be satisfied.  Potentially indicates a misbehaving client,
   although not necessarily the one receiving the error.  The
   misbehavior might be on the part of the client that established the
   lock with which this client conflicted.  See also Section 15.1.9.4
   for the related error, NFS4ERR_RECLAIM_BAD.

15.1.10.  pNFS Errors

   This section deals with pNFS-related errors including those that are
   associated with using NFSv4.1 to communicate with a data server.








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15.1.10.1.  NFS4ERR_BADIOMODE (Error Code 10049)

   An invalid or inappropriate layout iomode was specified.  For example
   an inappropriate layout iomode, suppose a client's LAYOUTGET
   operation specified an iomode of LAYOUTIOMODE4_RW, and the server is
   neither able nor willing to let the client send write requests to
   data servers; the server can reply with NFS4ERR_BADIOMODE.  The
   client would then send another LAYOUTGET with an iomode of
   LAYOUTIOMODE4_READ.

15.1.10.2.  NFS4ERR_BADLAYOUT (Error Code 10050)

   The layout specified is invalid in some way.  For LAYOUTCOMMIT, this
   indicates that the specified layout is not held by the client or is
   not of mode LAYOUTIOMODE4_RW.  For LAYOUTGET, it indicates that a
   layout matching the client's specification as to minimum length
   cannot be granted.

15.1.10.3.  NFS4ERR_LAYOUTTRYLATER (Error Code 10058)

   Layouts are temporarily unavailable for the file.  The client should
   re-send later (but not with the same slot ID and sequence ID; one or
   both MUST be different on the re-send).

15.1.10.4.  NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)

   Returned when layouts are not available for the current file system
   or the particular specified file.

15.1.10.5.  NFS4ERR_NOMATCHING_LAYOUT (Error Code 10060)

   Returned when layouts are recalled and the client has no layouts
   matching the specification of the layouts being recalled.

15.1.10.6.  NFS4ERR_PNFS_IO_HOLE (Error Code 10075)

   The pNFS client has attempted to read from or write to an illegal
   hole of a file of a data server that is using sparse packing.  See
   Section 13.4.4.

15.1.10.7.  NFS4ERR_PNFS_NO_LAYOUT (Error Code 10080)

   The pNFS client has attempted to read from or write to a file (using
   a request to a data server) without holding a valid layout.  This
   includes the case where the client had a layout, but the iomode does
   not allow a WRITE.





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15.1.10.8.  NFS4ERR_RETURNCONFLICT (Error Code 10086)

   A layout is unavailable due to an attempt to perform the LAYOUTGET
   before a pending LAYOUTRETURN on the file has been received.  See
   Section 12.5.5.2.1.3.

15.1.10.9.  NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)

   The client has specified a layout type that is not supported by the
   server.

15.1.11.  Session Use Errors

   This section deals with errors encountered when using sessions, that
   is, errors encountered when a request uses a Sequence (i.e., either
   SEQUENCE or CB_SEQUENCE) operation.

15.1.11.1.  NFS4ERR_BADSESSION (Error Code 10052)

   The specified session ID is unknown to the server to which the
   operation is addressed.

15.1.11.2.  NFS4ERR_BADSLOT (Error Code 10053)

   The requester sent a Sequence operation that attempted to use a slot
   the replier does not have in its slot table.  It is possible the slot
   may have been retired.

15.1.11.3.  NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)

   The highest_slot argument in a Sequence operation exceeds the
   replier's enforced highest_slotid.

15.1.11.4.  NFS4ERR_CB_PATH_DOWN (Error Code 10048)

   There is a problem contacting the client via the callback path.  The
   function of this error has been mostly superseded by the use of
   status flags in the reply to the SEQUENCE operation (see
   Section 18.46).

15.1.11.5.  NFS4ERR_DEADSESSION (Error Code 10078)

   The specified session is a persistent session that is dead and does
   not accept new requests or perform new operations on existing
   requests (in the case in which a request was partially executed
   before server restart).





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15.1.11.6.  NFS4ERR_CONN_NOT_BOUND_TO_SESSION (Error Code 10055)

   A Sequence operation was sent on a connection that has not been
   associated with the specified session, where the client specified
   that connection association was to be enforced with SP4_MACH_CRED or
   SP4_SSV state protection.

15.1.11.7.  NFS4ERR_SEQ_FALSE_RETRY (Error Code 10076)

   The requester sent a Sequence operation with a slot ID and sequence
   ID that are in the reply cache, but the replier has detected that the
   retried request is not the same as the original request.  See
   Section 2.10.6.1.3.1.

15.1.11.8.  NFS4ERR_SEQ_MISORDERED (Error Code 10063)

   The requester sent a Sequence operation with an invalid sequence ID.

15.1.12.  Session Management Errors

   This section deals with errors associated with requests used in
   session management.

15.1.12.1.  NFS4ERR_BACK_CHAN_BUSY (Error Code 10057)

   An attempt was made to destroy a session when the session cannot be
   destroyed because the server has callback requests outstanding.

15.1.12.2.  NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)

   The digest used in a SET_SSV request is not valid.

15.1.13.  Client Management Errors

   This section deals with errors associated with requests used to
   create and manage client IDs.

15.1.13.1.  NFS4ERR_CLIENTID_BUSY (Error Code 10074)

   The DESTROY_CLIENTID operation has found there are sessions and/or
   unexpired state associated with the client ID to be destroyed.

15.1.13.2.  NFS4ERR_CLID_INUSE (Error Code 10017)

   While processing an EXCHANGE_ID operation, the server was presented
   with a co_ownerid field that matches an existing client with valid
   leased state, but the principal sending the EXCHANGE_ID operation
   differs from the principal that established the existing client.



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   This indicates a collision (most likely due to chance) between
   clients.  The client should recover by changing the co_ownerid and
   re-sending EXCHANGE_ID (but not with the same slot ID and sequence
   ID; one or both MUST be different on the re-send).

15.1.13.3.  NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)

   An EXCHANGE_ID was sent that specified state protection via SSV, and
   where the set of encryption algorithms presented by the client did
   not include any supported by the server.

15.1.13.4.  NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)

   An EXCHANGE_ID was sent that specified state protection via SSV, and
   where the set of hashing algorithms presented by the client did not
   include any supported by the server.

15.1.13.5.  NFS4ERR_STALE_CLIENTID (Error Code 10022)

   A client ID not recognized by the server was passed to an operation.
   Note that unlike the case of NFSv4.0, client IDs are not passed
   explicitly to the server in ordinary locking operations and cannot
   result in this error.  Instead, when there is a server restart, it is
   first manifested through an error on the associated session, and the
   staleness of the client ID is detected when trying to associate a
   client ID with a new session.

15.1.14.  Delegation Errors

   This section deals with errors associated with requesting and
   returning delegations.

15.1.14.1.  NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)

   The client has requested a delegation when it had already registered
   that it wants that same delegation.

15.1.14.2.  NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)

   This error is returned when the server is unable or unwilling to
   provide a requested directory delegation.

15.1.14.3.  NFS4ERR_RECALLCONFLICT (Error Code 10061)

   A recallable object (i.e., a layout or delegation) is unavailable due
   to a conflicting recall operation that is currently in progress for
   that object.




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15.1.14.4.  NFS4ERR_REJECT_DELEG (Error Code 10085)

   The callback operation invoked to deal with a new delegation has
   rejected it.

15.1.15.  Attribute Handling Errors

   This section deals with errors specific to attribute handling within
   NFSv4.

15.1.15.1.  NFS4ERR_ATTRNOTSUPP (Error Code 10032)

   An attribute specified is not supported by the server.  This error
   MUST NOT be returned by the GETATTR operation.

15.1.15.2.  NFS4ERR_BADOWNER (Error Code 10039)

   This error is returned when an owner or owner_group attribute value
   or the who field of an ACE within an ACL attribute value cannot be
   translated to a local representation.

15.1.15.3.  NFS4ERR_NOT_SAME (Error Code 10027)

   This error is returned by the VERIFY operation to signify that the
   attributes compared were not the same as those provided in the
   client's request.

15.1.15.4.  NFS4ERR_SAME (Error Code 10009)

   This error is returned by the NVERIFY operation to signify that the
   attributes compared were the same as those provided in the client's
   request.

15.1.16.  Obsoleted Errors

   These errors MUST NOT be generated by any NFSv4.1 operation.  This
   can be for a number of reasons.

   o  The function provided by the error has been superseded by one of
      the status bits returned by the SEQUENCE operation.

   o  The new session structure and associated change in locking have
      made the error unnecessary.

   o  There has been a restructuring of some errors for NFSv4.1 that
      resulted in the elimination of certain errors.





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15.1.16.1.  NFS4ERR_BAD_SEQID (Error Code 10026)

   The sequence number (seqid) in a locking request is neither the next
   expected number or the last number processed.  These seqids are
   ignored in NFSv4.1.

15.1.16.2.  NFS4ERR_LEASE_MOVED (Error Code 10031)

   A lease being renewed is associated with a file system that has been
   migrated to a new server.  The error has been superseded by the
   SEQ4_STATUS_LEASE_MOVED status bit (see Section 18.46).

15.1.16.3.  NFS4ERR_NXIO (Error Code 5)

   I/O error.  No such device or address.  This error is for errors
   involving block and character device access, but because NFSv4.1 is
   not a device-access protocol, this error is not applicable.

15.1.16.4.  NFS4ERR_RESTOREFH (Error Code 10030)

   The RESTOREFH operation does not have a saved filehandle (identified
   by SAVEFH) to operate upon.  In NFSv4.1, this error has been
   superseded by NFS4ERR_NOFILEHANDLE.

15.1.16.5.  NFS4ERR_STALE_STATEID (Error Code 10023)

   A stateid generated by an earlier server instance was used.  This
   error is moot in NFSv4.1 because all operations that take a stateid
   MUST be preceded by the SEQUENCE operation, and the earlier server
   instance is detected by the session infrastructure that supports
   SEQUENCE.

15.2.  Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each protocol operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   operations with two important exceptions:

   o  The operations that MUST NOT be implemented: OPEN_CONFIRM,
      RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and SETCLIENTID_CONFIRM.

   o  The invalid operation: ILLEGAL.

              Valid Error Returns for Each Protocol Operation

   +----------------------+--------------------------------------------+
   | Operation            | Errors                                     |



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   +----------------------+--------------------------------------------+
   | ACCESS               | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | BACKCHANNEL_CTL      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_NOENT, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | BIND_CONN_TO_SESSION | NFS4ERR_BADSESSION, NFS4ERR_BADXDR,        |
   |                      | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_NOT_ONLY_OP,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |
   |                      |                                            |
   | CLOSE                | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_LOCKS_HELD,     |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | COMMIT               | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |



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   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_IO,             |
   |                      | NFS4ERR_ISDIR, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | CREATE               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADNAME,          |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BADTYPE,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_DQUOT,              |
   |                      | NFS4ERR_EXIST, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MLINK,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_OP_NOT_IN_SESSION, |
   |                      | NFS4ERR_PERM, NFS4ERR_REP_TOO_BIG,         |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND                    |
   |                      |                                            |
   | CREATE_SESSION       | NFS4ERR_BADXDR, NFS4ERR_CLID_INUSE,        |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_NOENT,              |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_NOSPC,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SEQ_MISORDERED,                    |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID, NFS4ERR_TOOSMALL,  |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | DELEGPURGE           | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |



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   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONG_CRED                         |
   |                      |                                            |
   | DELEGRETURN          | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | DESTROY_CLIENTID     | NFS4ERR_BADXDR, NFS4ERR_CLIENTID_BUSY,     |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_REP_TOO_BIG,  |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | DESTROY_SESSION      | NFS4ERR_BACK_CHAN_BUSY,                    |
   |                      | NFS4ERR_BADSESSION, NFS4ERR_BADXDR,        |
   |                      | NFS4ERR_CB_PATH_DOWN,                      |
   |                      | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_NOT_ONLY_OP, NFS4ERR_REP_TOO_BIG,  |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT,                       |
   |                      | NFS4ERR_STALE_CLIENTID,                    |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | EXCHANGE_ID          | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_CLID_INUSE, NFS4ERR_DEADSESSION,   |
   |                      | NFS4ERR_DELAY, NFS4ERR_ENCR_ALG_UNSUPP,    |
   |                      | NFS4ERR_HASH_ALG_UNSUPP, NFS4ERR_INVAL,    |



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   |                      | NFS4ERR_NOENT, NFS4ERR_NOT_ONLY_OP,        |
   |                      | NFS4ERR_NOT_SAME, NFS4ERR_REP_TOO_BIG,     |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |
   |                      |                                            |
   | FREE_STATEID         | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_LOCKS_HELD, NFS4ERR_OLD_STATEID,   |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONG_CRED                         |
   |                      |                                            |
   | GET_DIR_DELEGATION   | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DIRDELEG_UNAVAIL,                  |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | GETATTR              | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   |                      |                                            |
   | GETDEVICEINFO        | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_INVAL,              |



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RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_NOENT, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOOSMALL,     |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   |                      |                                            |
   | GETDEVICELIST        | NFS4ERR_BADXDR, NFS4ERR_BAD_COOKIE,        |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_NOFILEHANDLE,          |
   |                      | NFS4ERR_NOTSUPP, NFS4ERR_NOT_SAME,         |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE                 |
   |                      |                                            |
   | GETFH                | NFS4ERR_FHEXPIRED, NFS4ERR_MOVED,          |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_STALE   |
   |                      |                                            |
   | ILLEGAL              | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL         |
   |                      |                                            |
   | LAYOUTCOMMIT         | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADIOMODE,    |
   |                      | NFS4ERR_BADLAYOUT, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,    |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_ISDIR NFS4ERR_MOVED,               |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |



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RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_CRED                         |
   |                      |                                            |
   | LAYOUTGET            | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADIOMODE, NFS4ERR_BADLAYOUT,      |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO,                 |
   |                      | NFS4ERR_LAYOUTTRYLATER,                    |
   |                      | NFS4ERR_LAYOUTUNAVAILABLE, NFS4ERR_LOCKED, |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOSPC, NFS4ERR_NOTSUPP,            |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECALLCONFLICT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOOSMALL, NFS4ERR_TOO_MANY_OPS,    |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | LAYOUTRETURN         | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FHEXPIRED,        |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE     |
   |                      |                                            |
   | LINK                 | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |



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RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_IO, NFS4ERR_MLINK,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTSUPP,           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONGSEC, NFS4ERR_WRONG_TYPE,      |
   |                      | NFS4ERR_XDEV                               |
   |                      |                                            |
   | LOCK                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE,         |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADLOCK,     |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DENIED, NFS4ERR_EXPIRED,           |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LOCK_NOTSUPP, NFS4ERR_LOCK_RANGE,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NO_GRACE, NFS4ERR_OLD_STATEID,     |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_CRED, NFS4ERR_WRONG_TYPE     |
   |                      |                                            |
   | LOCKT                | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_BAD_RANGE, NFS4ERR_DEADSESSION,    |
   |                      | NFS4ERR_DELAY, NFS4ERR_DENIED,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR,              |
   |                      | NFS4ERR_LOCK_RANGE, NFS4ERR_MOVED,         |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |



Shepler, et al.              Standards Track                  [Page 363]

RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_STALE, NFS4ERR_SYMLINK,            |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED,  |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | LOCKU                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_RANGE,         |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_LOCK_RANGE, NFS4ERR_MOVED,         |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID, |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | LOOKUP               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED,                 |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONGSEC                           |
   |                      |                                            |
   | LOOKUPP              | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |



Shepler, et al.              Standards Track                  [Page 364]

RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_WRONGSEC                           |
   |                      |                                            |
   | NVERIFY              | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_SAME,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | OPEN                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADOWNER,         |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_ALREADY_WANTED,              |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_EXIST, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL,              |
   |                      | NFS4ERR_ISDIR, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NO_GRACE,          |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_SHARE_DENIED, |
   |                      | NFS4ERR_STALE, NFS4ERR_SYMLINK,            |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND, NFS4ERR_WRONGSEC, |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | OPEN_CONFIRM         | NFS4ERR_NOTSUPP                            |
   |                      |                                            |



Shepler, et al.              Standards Track                  [Page 365]

RFC 5661                         NFSv4.1                    January 2010


   | OPEN_DOWNGRADE       | NFS4ERR_ADMIN_REVOKED, NFS4ERR_BADXDR,     |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OLD_STATEID,                       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED   |
   |                      |                                            |
   | OPENATTR             | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_IO, NFS4ERR_MOVED, NFS4ERR_NOENT,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNSAFE_COMPOUND,                   |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | PUTFH                | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_MOVED, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC     |
   |                      |                                            |
   | PUTPUBFH             | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONGSEC                           |



Shepler, et al.              Standards Track                  [Page 366]

RFC 5661                         NFSv4.1                    January 2010


   |                      |                                            |
   | PUTROOTFH            | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS, |
   |                      | NFS4ERR_WRONGSEC                           |
   |                      |                                            |
   | READ                 | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_EXPIRED,    |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_ISDIR, NFS4ERR_IO,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_OLD_STATEID, |
   |                      | NFS4ERR_OPENMODE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_PNFS_IO_HOLE,                      |
   |                      | NFS4ERR_PNFS_NO_LAYOUT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | READDIR              | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_BAD_COOKIE, NFS4ERR_DEADSESSION,   |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOT_SAME,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOOSMALL, NFS4ERR_TOO_MANY_OPS     |
   |                      |                                            |
   | READLINK             | NFS4ERR_ACCESS, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_FHEXPIRED,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE,                      |



Shepler, et al.              Standards Track                  [Page 367]

RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   |                      |                                            |
   | RECLAIM_COMPLETE     | NFS4ERR_BADXDR, NFS4ERR_COMPLETE_ALREADY,  |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_CRED,  |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | RELEASE_LOCKOWNER    | NFS4ERR_NOTSUPP                            |
   |                      |                                            |
   | REMOVE               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | RENAME               | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXIST,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_FILE_OPEN,      |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_MLINK, NFS4ERR_MOVED,              |
   |                      | NFS4ERR_NAMETOOLONG, NFS4ERR_NOENT,        |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |



Shepler, et al.              Standards Track                  [Page 368]

RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_NOTDIR, NFS4ERR_NOTEMPTY,          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC,    |
   |                      | NFS4ERR_XDEV                               |
   |                      |                                            |
   | RENEW                | NFS4ERR_NOTSUPP                            |
   |                      |                                            |
   | RESTOREFH            | NFS4ERR_DEADSESSION, NFS4ERR_FHEXPIRED,    |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONGSEC     |
   |                      |                                            |
   | SAVEFH               | NFS4ERR_DEADSESSION, NFS4ERR_FHEXPIRED,    |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | SECINFO              | NFS4ERR_ACCESS, NFS4ERR_BADCHAR,           |
   |                      | NFS4ERR_BADNAME, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NAMETOOLONG,        |
   |                      | NFS4ERR_NOENT, NFS4ERR_NOFILEHANDLE,       |
   |                      | NFS4ERR_NOTDIR, NFS4ERR_OP_NOT_IN_SESSION, |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | SECINFO_NO_NAME      | NFS4ERR_ACCESS, NFS4ERR_BADXDR,            |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |



Shepler, et al.              Standards Track                  [Page 369]

RFC 5661                         NFSv4.1                    January 2010


   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_INVAL,          |
   |                      | NFS4ERR_MOVED, NFS4ERR_NOENT,              |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTDIR,      |
   |                      | NFS4ERR_NOTSUPP,                           |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,       |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,     |
   |                      | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,         |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SEQUENCE_POS,                      |
   |                      | NFS4ERR_SEQ_FALSE_RETRY,                   |
   |                      | NFS4ERR_SEQ_MISORDERED,                    |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | SET_SSV              | NFS4ERR_BADXDR,                            |
   |                      | NFS4ERR_BAD_SESSION_DIGEST,                |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_INVAL, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_TOO_MANY_OPS                       |
   |                      |                                            |
   | SETATTR              | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_ATTRNOTSUPP, NFS4ERR_BADCHAR,      |
   |                      | NFS4ERR_BADOWNER, NFS4ERR_BADXDR,          |
   |                      | NFS4ERR_BAD_STATEID, NFS4ERR_DEADSESSION,  |
   |                      | NFS4ERR_DELAY, NFS4ERR_DELEG_REVOKED,      |
   |                      | NFS4ERR_DQUOT, NFS4ERR_EXPIRED,            |
   |                      | NFS4ERR_FBIG, NFS4ERR_FHEXPIRED,           |
   |                      | NFS4ERR_GRACE, NFS4ERR_INVAL, NFS4ERR_IO,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION, NFS4ERR_PERM,   |
   |                      | NFS4ERR_REP_TOO_BIG,                       |



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   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | SETCLIENTID          | NFS4ERR_NOTSUPP                            |
   |                      |                                            |
   | SETCLIENTID_CONFIRM  | NFS4ERR_NOTSUPP                            |
   |                      |                                            |
   | TEST_STATEID         | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY, NFS4ERR_OP_NOT_IN_SESSION,  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_TOO_MANY_OPS  |
   |                      |                                            |
   | VERIFY               | NFS4ERR_ACCESS, NFS4ERR_ATTRNOTSUPP,       |
   |                      | NFS4ERR_BADCHAR, NFS4ERR_BADXDR,           |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOT_SAME,    |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS,                      |
   |                      | NFS4ERR_UNKNOWN_LAYOUTTYPE,                |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   | WANT_DELEGATION      | NFS4ERR_BADXDR, NFS4ERR_DEADSESSION,       |
   |                      | NFS4ERR_DELAY,                             |
   |                      | NFS4ERR_DELEG_ALREADY_WANTED,              |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_MOVED,  |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOTSUPP,     |
   |                      | NFS4ERR_NO_GRACE,                          |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_RECALLCONFLICT,                    |
   |                      | NFS4ERR_RECLAIM_BAD,                       |
   |                      | NFS4ERR_RECLAIM_CONFLICT,                  |
   |                      | NFS4ERR_REP_TOO_BIG,                       |



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   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP,                |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_TOO_MANY_OPS, NFS4ERR_WRONG_TYPE   |
   |                      |                                            |
   | WRITE                | NFS4ERR_ACCESS, NFS4ERR_ADMIN_REVOKED,     |
   |                      | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,       |
   |                      | NFS4ERR_DEADSESSION, NFS4ERR_DELAY,        |
   |                      | NFS4ERR_DELEG_REVOKED, NFS4ERR_DQUOT,      |
   |                      | NFS4ERR_EXPIRED, NFS4ERR_FBIG,             |
   |                      | NFS4ERR_FHEXPIRED, NFS4ERR_GRACE,          |
   |                      | NFS4ERR_INVAL, NFS4ERR_IO, NFS4ERR_ISDIR,  |
   |                      | NFS4ERR_LOCKED, NFS4ERR_MOVED,             |
   |                      | NFS4ERR_NOFILEHANDLE, NFS4ERR_NOSPC,       |
   |                      | NFS4ERR_OLD_STATEID, NFS4ERR_OPENMODE,     |
   |                      | NFS4ERR_OP_NOT_IN_SESSION,                 |
   |                      | NFS4ERR_PNFS_IO_HOLE,                      |
   |                      | NFS4ERR_PNFS_NO_LAYOUT,                    |
   |                      | NFS4ERR_REP_TOO_BIG,                       |
   |                      | NFS4ERR_REP_TOO_BIG_TO_CACHE,              |
   |                      | NFS4ERR_REQ_TOO_BIG,                       |
   |                      | NFS4ERR_RETRY_UNCACHED_REP, NFS4ERR_ROFS,  |
   |                      | NFS4ERR_SERVERFAULT, NFS4ERR_STALE,        |
   |                      | NFS4ERR_SYMLINK, NFS4ERR_TOO_MANY_OPS,     |
   |                      | NFS4ERR_WRONG_TYPE                         |
   |                      |                                            |
   +----------------------+--------------------------------------------+

                                  Table 6

15.3.  Callback Operations and Their Valid Errors

   This section contains a table that gives the valid error returns for
   each callback operation.  The error code NFS4_OK (indicating no
   error) is not listed but should be understood to be returnable by all
   callback operations with the exception of CB_ILLEGAL.

         Valid Error Returns for Each Protocol Callback Operation

   +-------------------------+-----------------------------------------+
   | Callback Operation      | Errors                                  |
   +-------------------------+-----------------------------------------+
   | CB_GETATTR              | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |



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   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         |                                         |
   | CB_ILLEGAL              | NFS4ERR_BADXDR, NFS4ERR_OP_ILLEGAL      |
   |                         |                                         |
   | CB_LAYOUTRECALL         | NFS4ERR_BADHANDLE, NFS4ERR_BADIOMODE,   |
   |                         | NFS4ERR_BADXDR, NFS4ERR_BAD_STATEID,    |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_NOMATCHING_LAYOUT,              |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_UNKNOWN_LAYOUTTYPE,             |
   |                         | NFS4ERR_WRONG_TYPE                      |
   |                         |                                         |
   | CB_NOTIFY               | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_NOTIFY_DEVICEID      | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_NOTIFY_LOCK          | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |



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   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_PUSH_DELEG           | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_INVAL,           |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REJECT_DELEG,                   |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS,                   |
   |                         | NFS4ERR_WRONG_TYPE                      |
   |                         |                                         |
   | CB_RECALL               | NFS4ERR_BADHANDLE, NFS4ERR_BADXDR,      |
   |                         | NFS4ERR_BAD_STATEID, NFS4ERR_DELAY,     |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_RECALL_ANY           | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL,                          |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_RECALLABLE_OBJ_AVAIL | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_INVAL, NFS4ERR_NOTSUPP,         |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_RECALL_SLOT          | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,  |



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RFC 5661                         NFSv4.1                    January 2010


   |                         | NFS4ERR_DELAY,                          |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_SEQUENCE             | NFS4ERR_BADSESSION, NFS4ERR_BADSLOT,    |
   |                         | NFS4ERR_BADXDR, NFS4ERR_BAD_HIGH_SLOT,  |
   |                         | NFS4ERR_CONN_NOT_BOUND_TO_SESSION,      |
   |                         | NFS4ERR_DELAY, NFS4ERR_REP_TOO_BIG,     |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SEQUENCE_POS,                   |
   |                         | NFS4ERR_SEQ_FALSE_RETRY,                |
   |                         | NFS4ERR_SEQ_MISORDERED,                 |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   | CB_WANTS_CANCELLED      | NFS4ERR_BADXDR, NFS4ERR_DELAY,          |
   |                         | NFS4ERR_NOTSUPP,                        |
   |                         | NFS4ERR_OP_NOT_IN_SESSION,              |
   |                         | NFS4ERR_REP_TOO_BIG,                    |
   |                         | NFS4ERR_REP_TOO_BIG_TO_CACHE,           |
   |                         | NFS4ERR_REQ_TOO_BIG,                    |
   |                         | NFS4ERR_RETRY_UNCACHED_REP,             |
   |                         | NFS4ERR_SERVERFAULT,                    |
   |                         | NFS4ERR_TOO_MANY_OPS                    |
   |                         |                                         |
   +-------------------------+-----------------------------------------+

                                  Table 7

15.4.  Errors and the Operations That Use Them

   +-----------------------------------+-------------------------------+
   | Error                             | Operations                    |
   +-----------------------------------+-------------------------------+
   | NFS4ERR_ACCESS                    | ACCESS, COMMIT, CREATE,       |
   |                                   | GETATTR, GET_DIR_DELEGATION,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LINK, LOCK, LOCKT, LOCKU,     |
   |                                   | LOOKUP, LOOKUPP, NVERIFY,     |
   |                                   | OPEN, OPENATTR, READ,         |
   |                                   | READDIR, READLINK, REMOVE,    |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |



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RFC 5661                         NFSv4.1                    January 2010


   |                                   | VERIFY, WRITE                 |
   |                                   |                               |
   | NFS4ERR_ADMIN_REVOKED             | CLOSE, DELEGRETURN,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_ATTRNOTSUPP               | CREATE, LAYOUTCOMMIT,         |
   |                                   | NVERIFY, OPEN, SETATTR,       |
   |                                   | VERIFY                        |
   |                                   |                               |
   | NFS4ERR_BACK_CHAN_BUSY            | DESTROY_SESSION               |
   |                                   |                               |
   | NFS4ERR_BADCHAR                   | CREATE, EXCHANGE_ID, LINK,    |
   |                                   | LOOKUP, NVERIFY, OPEN,        |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SETATTR, VERIFY               |
   |                                   |                               |
   | NFS4ERR_BADHANDLE                 | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY, CB_NOTIFY_LOCK,    |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | PUTFH                         |
   |                                   |                               |
   | NFS4ERR_BADIOMODE                 | CB_LAYOUTRECALL,              |
   |                                   | LAYOUTCOMMIT, LAYOUTGET       |
   |                                   |                               |
   | NFS4ERR_BADLAYOUT                 | LAYOUTCOMMIT, LAYOUTGET       |
   |                                   |                               |
   | NFS4ERR_BADNAME                   | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO       |
   |                                   |                               |
   | NFS4ERR_BADOWNER                  | CREATE, OPEN, SETATTR         |
   |                                   |                               |
   | NFS4ERR_BADSESSION                | BIND_CONN_TO_SESSION,         |
   |                                   | CB_SEQUENCE, DESTROY_SESSION, |
   |                                   | SEQUENCE                      |
   |                                   |                               |
   | NFS4ERR_BADSLOT                   | CB_SEQUENCE, SEQUENCE         |
   |                                   |                               |
   | NFS4ERR_BADTYPE                   | CREATE                        |
   |                                   |                               |
   | NFS4ERR_BADXDR                    | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_ILLEGAL,       |
   |                                   | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |



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RFC 5661                         NFSv4.1                    January 2010


   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION, ILLEGAL,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | OPEN_DOWNGRADE, PUTFH, READ,  |
   |                                   | READDIR, RECLAIM_COMPLETE,    |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME, SEQUENCE,    |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_BAD_COOKIE                | GETDEVICELIST, READDIR        |
   |                                   |                               |
   | NFS4ERR_BAD_HIGH_SLOT             | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | SEQUENCE                      |
   |                                   |                               |
   | NFS4ERR_BAD_RANGE                 | LOCK, LOCKT, LOCKU            |
   |                                   |                               |
   | NFS4ERR_BAD_SESSION_DIGEST        | BIND_CONN_TO_SESSION, SET_SSV |
   |                                   |                               |
   | NFS4ERR_BAD_STATEID               | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_LOCK, CB_RECALL,    |
   |                                   | CLOSE, DELEGRETURN,           |
   |                                   | FREE_STATEID, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_CB_PATH_DOWN              | DESTROY_SESSION               |
   |                                   |                               |
   | NFS4ERR_CLID_INUSE                | CREATE_SESSION, EXCHANGE_ID   |
   |                                   |                               |
   | NFS4ERR_CLIENTID_BUSY             | DESTROY_CLIENTID              |
   |                                   |                               |



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RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_COMPLETE_ALREADY          | RECLAIM_COMPLETE              |
   |                                   |                               |
   | NFS4ERR_CONN_NOT_BOUND_TO_SESSION | CB_SEQUENCE, DESTROY_SESSION, |
   |                                   | SEQUENCE                      |
   |                                   |                               |
   | NFS4ERR_DEADLOCK                  | LOCK                          |
   |                                   |                               |
   | NFS4ERR_DEADSESSION               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION, CLOSE,  |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_DELAY                     | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |



Shepler, et al.              Standards Track                  [Page 378]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SEQUENCE,    |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_DELEG_ALREADY_WANTED      | OPEN, WANT_DELEGATION         |
   |                                   |                               |
   | NFS4ERR_DELEG_REVOKED             | DELEGRETURN, LAYOUTCOMMIT,    |
   |                                   | LAYOUTGET, LAYOUTRETURN,      |
   |                                   | OPEN, READ, SETATTR, WRITE    |
   |                                   |                               |
   | NFS4ERR_DENIED                    | LOCK, LOCKT                   |
   |                                   |                               |
   | NFS4ERR_DIRDELEG_UNAVAIL          | GET_DIR_DELEGATION            |
   |                                   |                               |
   | NFS4ERR_DQUOT                     | CREATE, LAYOUTGET, LINK,      |
   |                                   | OPEN, OPENATTR, RENAME,       |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_ENCR_ALG_UNSUPP           | EXCHANGE_ID                   |
   |                                   |                               |
   | NFS4ERR_EXIST                     | CREATE, LINK, OPEN, RENAME    |
   |                                   |                               |
   | NFS4ERR_EXPIRED                   | CLOSE, DELEGRETURN,           |
   |                                   | LAYOUTCOMMIT, LAYOUTRETURN,   |
   |                                   | LOCK, LOCKU, OPEN,            |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_FBIG                      | LAYOUTCOMMIT, OPEN, SETATTR,  |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_FHEXPIRED                 | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |



Shepler, et al.              Standards Track                  [Page 379]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_FILE_OPEN                 | LINK, REMOVE, RENAME          |
   |                                   |                               |
   | NFS4ERR_GRACE                     | GETATTR, GET_DIR_DELEGATION,  |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, NVERIFY, OPEN, READ,   |
   |                                   | REMOVE, RENAME, SETATTR,      |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_HASH_ALG_UNSUPP           | EXCHANGE_ID                   |
   |                                   |                               |
   | NFS4ERR_INVAL                     | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_PUSH_DELEG,                |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY, CREATE,        |
   |                                   | CREATE_SESSION, DELEGRETURN,  |
   |                                   | EXCHANGE_ID, GETATTR,         |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | NVERIFY, OPEN,                |
   |                                   | OPEN_DOWNGRADE, READ,         |
   |                                   | READDIR, READLINK,            |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | SET_SSV, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_IO                        | ACCESS, COMMIT, CREATE,       |



Shepler, et al.              Standards Track                  [Page 380]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | GETATTR, GETDEVICELIST,       |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LINK, LOOKUP, LOOKUPP,        |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | REMOVE, RENAME, SETATTR,      |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_ISDIR                     | COMMIT, LAYOUTCOMMIT,         |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, OPEN, READ, WRITE      |
   |                                   |                               |
   | NFS4ERR_LAYOUTTRYLATER            | LAYOUTGET                     |
   |                                   |                               |
   | NFS4ERR_LAYOUTUNAVAILABLE         | LAYOUTGET                     |
   |                                   |                               |
   | NFS4ERR_LOCKED                    | LAYOUTGET, READ, SETATTR,     |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_LOCKS_HELD                | CLOSE, FREE_STATEID           |
   |                                   |                               |
   | NFS4ERR_LOCK_NOTSUPP              | LOCK                          |
   |                                   |                               |
   | NFS4ERR_LOCK_RANGE                | LOCK, LOCKT, LOCKU            |
   |                                   |                               |
   | NFS4ERR_MLINK                     | CREATE, LINK, RENAME          |
   |                                   |                               |
   | NFS4ERR_MOVED                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, RECLAIM_COMPLETE,   |
   |                                   | REMOVE, RENAME, RESTOREFH,    |
   |                                   | SAVEFH, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_NAMETOOLONG               | CREATE, LINK, LOOKUP, OPEN,   |
   |                                   | REMOVE, RENAME, SECINFO       |
   |                                   |                               |



Shepler, et al.              Standards Track                  [Page 381]

RFC 5661                         NFSv4.1                    January 2010


   | NFS4ERR_NOENT                     | BACKCHANNEL_CTL,              |
   |                                   | CREATE_SESSION, EXCHANGE_ID,  |
   |                                   | GETDEVICEINFO, LOOKUP,        |
   |                                   | LOOKUPP, OPEN, OPENATTR,      |
   |                                   | REMOVE, RENAME, SECINFO,      |
   |                                   | SECINFO_NO_NAME               |
   |                                   |                               |
   | NFS4ERR_NOFILEHANDLE              | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, VERIFY,              |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_NOMATCHING_LAYOUT         | CB_LAYOUTRECALL               |
   |                                   |                               |
   | NFS4ERR_NOSPC                     | CREATE, CREATE_SESSION,       |
   |                                   | LAYOUTGET, LINK, OPEN,        |
   |                                   | OPENATTR, RENAME, SETATTR,    |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_NOTDIR                    | CREATE, GET_DIR_DELEGATION,   |
   |                                   | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | READDIR, REMOVE, RENAME,      |
   |                                   | SECINFO, SECINFO_NO_NAME      |
   |                                   |                               |
   | NFS4ERR_NOTEMPTY                  | REMOVE, RENAME                |
   |                                   |                               |
   | NFS4ERR_NOTSUPP                   | CB_LAYOUTRECALL, CB_NOTIFY,   |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG,                |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_WANTS_CANCELLED,           |
   |                                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, OPENATTR, |



Shepler, et al.              Standards Track                  [Page 382]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | OPEN_CONFIRM,                 |
   |                                   | RELEASE_LOCKOWNER, RENEW,     |
   |                                   | SECINFO_NO_NAME, SETCLIENTID, |
   |                                   | SETCLIENTID_CONFIRM,          |
   |                                   | WANT_DELEGATION               |
   |                                   |                               |
   | NFS4ERR_NOT_ONLY_OP               | BIND_CONN_TO_SESSION,         |
   |                                   | CREATE_SESSION,               |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID  |
   |                                   |                               |
   | NFS4ERR_NOT_SAME                  | EXCHANGE_ID, GETDEVICELIST,   |
   |                                   | READDIR, VERIFY               |
   |                                   |                               |
   | NFS4ERR_NO_GRACE                  | LAYOUTCOMMIT, LAYOUTRETURN,   |
   |                                   | LOCK, OPEN, WANT_DELEGATION   |
   |                                   |                               |
   | NFS4ERR_OLD_STATEID               | CLOSE, DELEGRETURN,           |
   |                                   | FREE_STATEID, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LOCK, LOCKU,    |
   |                                   | OPEN, OPEN_DOWNGRADE, READ,   |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_OPENMODE                  | LAYOUTGET, LOCK, READ,        |
   |                                   | SETATTR, WRITE                |
   |                                   |                               |
   | NFS4ERR_OP_ILLEGAL                | CB_ILLEGAL, ILLEGAL           |
   |                                   |                               |
   | NFS4ERR_OP_NOT_IN_SESSION         | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT,               |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE, DELEGPURGE,   |
   |                                   | DELEGRETURN, FREE_STATEID,    |
   |                                   | GETATTR, GETDEVICEINFO,       |
   |                                   | GETDEVICELIST, GETFH,         |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |



Shepler, et al.              Standards Track                  [Page 383]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, SET_SSV,             |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_PERM                      | CREATE, OPEN, SETATTR         |
   |                                   |                               |
   | NFS4ERR_PNFS_IO_HOLE              | READ, WRITE                   |
   |                                   |                               |
   | NFS4ERR_PNFS_NO_LAYOUT            | READ, WRITE                   |
   |                                   |                               |
   | NFS4ERR_RECALLCONFLICT            | LAYOUTGET, WANT_DELEGATION    |
   |                                   |                               |
   | NFS4ERR_RECLAIM_BAD               | LAYOUTCOMMIT, LOCK, OPEN,     |
   |                                   | WANT_DELEGATION               |
   |                                   |                               |
   | NFS4ERR_RECLAIM_CONFLICT          | LAYOUTCOMMIT, LOCK, OPEN,     |
   |                                   | WANT_DELEGATION               |
   |                                   |                               |
   | NFS4ERR_REJECT_DELEG              | CB_PUSH_DELEG                 |
   |                                   |                               |
   | NFS4ERR_REP_TOO_BIG               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |



Shepler, et al.              Standards Track                  [Page 384]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE      | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_REQ_TOO_BIG               | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |



Shepler, et al.              Standards Track                  [Page 385]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_RETRY_UNCACHED_REP        | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |



Shepler, et al.              Standards Track                  [Page 386]

RFC 5661                         NFSv4.1                    January 2010


   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_ROFS                      | CREATE, LINK, LOCK, LOCKT,    |
   |                                   | OPEN, OPENATTR,               |
   |                                   | OPEN_DOWNGRADE, REMOVE,       |
   |                                   | RENAME, SETATTR, WRITE        |
   |                                   |                               |
   | NFS4ERR_SAME                      | NVERIFY                       |
   |                                   |                               |
   | NFS4ERR_SEQUENCE_POS              | CB_SEQUENCE, SEQUENCE         |
   |                                   |                               |
   | NFS4ERR_SEQ_FALSE_RETRY           | CB_SEQUENCE, SEQUENCE         |
   |                                   |                               |
   | NFS4ERR_SEQ_MISORDERED            | CB_SEQUENCE, CREATE_SESSION,  |
   |                                   | SEQUENCE                      |
   |                                   |                               |
   | NFS4ERR_SERVERFAULT               | ACCESS, BIND_CONN_TO_SESSION, |
   |                                   | CB_GETATTR, CB_NOTIFY,        |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKU, LOOKUP, LOOKUPP,       |
   |                                   | NVERIFY, OPEN, OPENATTR,      |
   |                                   | OPEN_DOWNGRADE, PUTFH,        |
   |                                   | PUTPUBFH, PUTROOTFH, READ,    |



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   |                                   | READDIR, READLINK,            |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SETATTR, TEST_STATEID,        |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_SHARE_DENIED              | OPEN                          |
   |                                   |                               |
   | NFS4ERR_STALE                     | ACCESS, CLOSE, COMMIT,        |
   |                                   | CREATE, DELEGRETURN, GETATTR, |
   |                                   | GETFH, GET_DIR_DELEGATION,    |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, READ, READDIR,         |
   |                                   | READLINK, RECLAIM_COMPLETE,   |
   |                                   | REMOVE, RENAME, RESTOREFH,    |
   |                                   | SAVEFH, SECINFO,              |
   |                                   | SECINFO_NO_NAME, SETATTR,     |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_STALE_CLIENTID            | CREATE_SESSION,               |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION               |
   |                                   |                               |
   | NFS4ERR_SYMLINK                   | COMMIT, LAYOUTCOMMIT, LINK,   |
   |                                   | LOCK, LOCKT, LOOKUP, LOOKUPP, |
   |                                   | OPEN, READ, WRITE             |
   |                                   |                               |
   | NFS4ERR_TOOSMALL                  | CREATE_SESSION,               |
   |                                   | GETDEVICEINFO, LAYOUTGET,     |
   |                                   | READDIR                       |
   |                                   |                               |
   | NFS4ERR_TOO_MANY_OPS              | ACCESS, BACKCHANNEL_CTL,      |
   |                                   | BIND_CONN_TO_SESSION,         |
   |                                   | CB_GETATTR, CB_LAYOUTRECALL,  |
   |                                   | CB_NOTIFY,                    |
   |                                   | CB_NOTIFY_DEVICEID,           |
   |                                   | CB_NOTIFY_LOCK,               |
   |                                   | CB_PUSH_DELEG, CB_RECALL,     |
   |                                   | CB_RECALLABLE_OBJ_AVAIL,      |
   |                                   | CB_RECALL_ANY,                |
   |                                   | CB_RECALL_SLOT, CB_SEQUENCE,  |



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   |                                   | CB_WANTS_CANCELLED, CLOSE,    |
   |                                   | COMMIT, CREATE,               |
   |                                   | CREATE_SESSION, DELEGPURGE,   |
   |                                   | DELEGRETURN,                  |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION, EXCHANGE_ID, |
   |                                   | FREE_STATEID, GETATTR,        |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | GET_DIR_DELEGATION,           |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |
   |                                   | LOCKT, LOCKU, LOOKUP,         |
   |                                   | LOOKUPP, NVERIFY, OPEN,       |
   |                                   | OPENATTR, OPEN_DOWNGRADE,     |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | READ, READDIR, READLINK,      |
   |                                   | RECLAIM_COMPLETE, REMOVE,     |
   |                                   | RENAME, RESTOREFH, SAVEFH,    |
   |                                   | SECINFO, SECINFO_NO_NAME,     |
   |                                   | SEQUENCE, SETATTR, SET_SSV,   |
   |                                   | TEST_STATEID, VERIFY,         |
   |                                   | WANT_DELEGATION, WRITE        |
   |                                   |                               |
   | NFS4ERR_UNKNOWN_LAYOUTTYPE        | CB_LAYOUTRECALL,              |
   |                                   | GETDEVICEINFO, GETDEVICELIST, |
   |                                   | LAYOUTCOMMIT, LAYOUTGET,      |
   |                                   | LAYOUTRETURN, NVERIFY,        |
   |                                   | SETATTR, VERIFY               |
   |                                   |                               |
   | NFS4ERR_UNSAFE_COMPOUND           | CREATE, OPEN, OPENATTR        |
   |                                   |                               |
   | NFS4ERR_WRONGSEC                  | LINK, LOOKUP, LOOKUPP, OPEN,  |
   |                                   | PUTFH, PUTPUBFH, PUTROOTFH,   |
   |                                   | RENAME, RESTOREFH             |
   |                                   |                               |
   | NFS4ERR_WRONG_CRED                | CLOSE, CREATE_SESSION,        |
   |                                   | DELEGPURGE, DELEGRETURN,      |
   |                                   | DESTROY_CLIENTID,             |
   |                                   | DESTROY_SESSION,              |
   |                                   | FREE_STATEID, LAYOUTCOMMIT,   |
   |                                   | LAYOUTRETURN, LOCK, LOCKT,    |
   |                                   | LOCKU, OPEN_DOWNGRADE,        |
   |                                   | RECLAIM_COMPLETE              |
   |                                   |                               |
   | NFS4ERR_WRONG_TYPE                | CB_LAYOUTRECALL,              |
   |                                   | CB_PUSH_DELEG, COMMIT,        |
   |                                   | GETATTR, LAYOUTGET,           |
   |                                   | LAYOUTRETURN, LINK, LOCK,     |



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   |                                   | LOCKT, NVERIFY, OPEN,         |
   |                                   | OPENATTR, READ, READLINK,     |
   |                                   | RECLAIM_COMPLETE, SETATTR,    |
   |                                   | VERIFY, WANT_DELEGATION,      |
   |                                   | WRITE                         |
   |                                   |                               |
   | NFS4ERR_XDEV                      | LINK, RENAME                  |
   |                                   |                               |
   +-----------------------------------+-------------------------------+

                                  Table 8

16.  NFSv4.1 Procedures

   Both procedures, NULL and COMPOUND, MUST be implemented.

16.1.  Procedure 0: NULL - No Operation

16.1.1.  ARGUMENTS

   void;

16.1.2.  RESULTS

   void;

16.1.3.  DESCRIPTION

   This is the standard NULL procedure with the standard void argument
   and void response.  This procedure has no functionality associated
   with it.  Because of this, it is sometimes used to measure the
   overhead of processing a service request.  Therefore, the server
   SHOULD ensure that no unnecessary work is done in servicing this
   procedure.

16.1.4.  ERRORS

   None.

16.2.  Procedure 1: COMPOUND - Compound Operations

16.2.1.  ARGUMENTS

   enum nfs_opnum4 {
    OP_ACCESS              = 3,
    OP_CLOSE               = 4,
    OP_COMMIT              = 5,
    OP_CREATE              = 6,



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    OP_DELEGPURGE          = 7,
    OP_DELEGRETURN         = 8,
    OP_GETATTR             = 9,
    OP_GETFH               = 10,
    OP_LINK                = 11,
    OP_LOCK                = 12,
    OP_LOCKT               = 13,
    OP_LOCKU               = 14,
    OP_LOOKUP              = 15,
    OP_LOOKUPP             = 16,
    OP_NVERIFY             = 17,
    OP_OPEN                = 18,
    OP_OPENATTR            = 19,
    OP_OPEN_CONFIRM        = 20, /* Mandatory not-to-implement */
    OP_OPEN_DOWNGRADE      = 21,
    OP_PUTFH               = 22,
    OP_PUTPUBFH            = 23,
    OP_PUTROOTFH           = 24,
    OP_READ                = 25,
    OP_READDIR             = 26,
    OP_READLINK            = 27,
    OP_REMOVE              = 28,
    OP_RENAME              = 29,
    OP_RENEW               = 30, /* Mandatory not-to-implement */
    OP_RESTOREFH           = 31,
    OP_SAVEFH              = 32,
    OP_SECINFO             = 33,
    OP_SETATTR             = 34,
    OP_SETCLIENTID         = 35, /* Mandatory not-to-implement */
    OP_SETCLIENTID_CONFIRM = 36, /* Mandatory not-to-implement */
    OP_VERIFY              = 37,
    OP_WRITE               = 38,
    OP_RELEASE_LOCKOWNER   = 39, /* Mandatory not-to-implement */

   /* new operations for NFSv4.1 */

    OP_BACKCHANNEL_CTL     = 40,
    OP_BIND_CONN_TO_SESSION = 41,
    OP_EXCHANGE_ID         = 42,
    OP_CREATE_SESSION      = 43,
    OP_DESTROY_SESSION     = 44,
    OP_FREE_STATEID        = 45,
    OP_GET_DIR_DELEGATION  = 46,
    OP_GETDEVICEINFO       = 47,
    OP_GETDEVICELIST       = 48,
    OP_LAYOUTCOMMIT        = 49,
    OP_LAYOUTGET           = 50,
    OP_LAYOUTRETURN        = 51,



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    OP_SECINFO_NO_NAME     = 52,
    OP_SEQUENCE            = 53,
    OP_SET_SSV             = 54,
    OP_TEST_STATEID        = 55,
    OP_WANT_DELEGATION     = 56,
    OP_DESTROY_CLIENTID    = 57,
    OP_RECLAIM_COMPLETE    = 58,
    OP_ILLEGAL             = 10044
   };

   union nfs_argop4 switch (nfs_opnum4 argop) {
    case OP_ACCESS:        ACCESS4args opaccess;
    case OP_CLOSE:         CLOSE4args opclose;
    case OP_COMMIT:        COMMIT4args opcommit;
    case OP_CREATE:        CREATE4args opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
    case OP_GETATTR:       GETATTR4args opgetattr;
    case OP_GETFH:         void;
    case OP_LINK:          LINK4args oplink;
    case OP_LOCK:          LOCK4args oplock;
    case OP_LOCKT:         LOCKT4args oplockt;
    case OP_LOCKU:         LOCKU4args oplocku;
    case OP_LOOKUP:        LOOKUP4args oplookup;
    case OP_LOOKUPP:       void;
    case OP_NVERIFY:       NVERIFY4args opnverify;
    case OP_OPEN:          OPEN4args opopen;
    case OP_OPENATTR:      OPENATTR4args opopenattr;

    /* Not for NFSv4.1 */
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;

    case OP_OPEN_DOWNGRADE:
                           OPEN_DOWNGRADE4args opopen_downgrade;

    case OP_PUTFH:         PUTFH4args opputfh;
    case OP_PUTPUBFH:      void;
    case OP_PUTROOTFH:     void;
    case OP_READ:          READ4args opread;
    case OP_READDIR:       READDIR4args opreaddir;
    case OP_READLINK:      void;
    case OP_REMOVE:        REMOVE4args opremove;
    case OP_RENAME:        RENAME4args oprename;

    /* Not for NFSv4.1 */
    case OP_RENEW:         RENEW4args oprenew;

    case OP_RESTOREFH:     void;



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    case OP_SAVEFH:        void;
    case OP_SECINFO:       SECINFO4args opsecinfo;
    case OP_SETATTR:       SETATTR4args opsetattr;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
                                   opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4args opverify;
    case OP_WRITE:         WRITE4args opwrite;

    /* Not for NFSv4.1 */
    case OP_RELEASE_LOCKOWNER:
                           RELEASE_LOCKOWNER4args
                           oprelease_lockowner;

    /* Operations new to NFSv4.1 */
    case OP_BACKCHANNEL_CTL:
                           BACKCHANNEL_CTL4args opbackchannel_ctl;

    case OP_BIND_CONN_TO_SESSION:
                           BIND_CONN_TO_SESSION4args
                           opbind_conn_to_session;

    case OP_EXCHANGE_ID:   EXCHANGE_ID4args opexchange_id;

    case OP_CREATE_SESSION:
                           CREATE_SESSION4args opcreate_session;

    case OP_DESTROY_SESSION:
                           DESTROY_SESSION4args opdestroy_session;

    case OP_FREE_STATEID:  FREE_STATEID4args opfree_stateid;

    case OP_GET_DIR_DELEGATION:
                           GET_DIR_DELEGATION4args
                                   opget_dir_delegation;

    case OP_GETDEVICEINFO: GETDEVICEINFO4args opgetdeviceinfo;
    case OP_GETDEVICELIST: GETDEVICELIST4args opgetdevicelist;
    case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4args oplayoutcommit;
    case OP_LAYOUTGET:     LAYOUTGET4args oplayoutget;
    case OP_LAYOUTRETURN:  LAYOUTRETURN4args oplayoutreturn;

    case OP_SECINFO_NO_NAME:
                           SECINFO_NO_NAME4args opsecinfo_no_name;



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    case OP_SEQUENCE:      SEQUENCE4args opsequence;
    case OP_SET_SSV:       SET_SSV4args opset_ssv;
    case OP_TEST_STATEID:  TEST_STATEID4args optest_stateid;

    case OP_WANT_DELEGATION:
                           WANT_DELEGATION4args opwant_delegation;

    case OP_DESTROY_CLIENTID:
                           DESTROY_CLIENTID4args
                                   opdestroy_clientid;

    case OP_RECLAIM_COMPLETE:
                           RECLAIM_COMPLETE4args
                                   opreclaim_complete;

    /* Operations not new to NFSv4.1 */
    case OP_ILLEGAL:       void;
   };

   struct COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           nfs_argop4      argarray<>;
   };

16.2.2.  RESULTS

   union nfs_resop4 switch (nfs_opnum4 resop) {
    case OP_ACCESS:        ACCESS4res opaccess;
    case OP_CLOSE:         CLOSE4res opclose;
    case OP_COMMIT:        COMMIT4res opcommit;
    case OP_CREATE:        CREATE4res opcreate;
    case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
    case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;
    case OP_GETATTR:       GETATTR4res opgetattr;
    case OP_GETFH:         GETFH4res opgetfh;
    case OP_LINK:          LINK4res oplink;
    case OP_LOCK:          LOCK4res oplock;
    case OP_LOCKT:         LOCKT4res oplockt;
    case OP_LOCKU:         LOCKU4res oplocku;
    case OP_LOOKUP:        LOOKUP4res oplookup;
    case OP_LOOKUPP:       LOOKUPP4res oplookupp;
    case OP_NVERIFY:       NVERIFY4res opnverify;
    case OP_OPEN:          OPEN4res opopen;
    case OP_OPENATTR:      OPENATTR4res opopenattr;
    /* Not for NFSv4.1 */
    case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;




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    case OP_OPEN_DOWNGRADE:
                           OPEN_DOWNGRADE4res
                                   opopen_downgrade;

    case OP_PUTFH:         PUTFH4res opputfh;
    case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
    case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
    case OP_READ:          READ4res opread;
    case OP_READDIR:       READDIR4res opreaddir;
    case OP_READLINK:      READLINK4res opreadlink;
    case OP_REMOVE:        REMOVE4res opremove;
    case OP_RENAME:        RENAME4res oprename;
    /* Not for NFSv4.1 */
    case OP_RENEW:         RENEW4res oprenew;
    case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
    case OP_SAVEFH:        SAVEFH4res opsavefh;
    case OP_SECINFO:       SECINFO4res opsecinfo;
    case OP_SETATTR:       SETATTR4res opsetattr;
    /* Not for NFSv4.1 */
    case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;

    /* Not for NFSv4.1 */
    case OP_SETCLIENTID_CONFIRM:
                           SETCLIENTID_CONFIRM4res
                                   opsetclientid_confirm;
    case OP_VERIFY:        VERIFY4res opverify;
    case OP_WRITE:         WRITE4res opwrite;

    /* Not for NFSv4.1 */
    case OP_RELEASE_LOCKOWNER:
                           RELEASE_LOCKOWNER4res
                                   oprelease_lockowner;

    /* Operations new to NFSv4.1 */
    case OP_BACKCHANNEL_CTL:
                           BACKCHANNEL_CTL4res
                                   opbackchannel_ctl;

    case OP_BIND_CONN_TO_SESSION:
                           BIND_CONN_TO_SESSION4res
                                    opbind_conn_to_session;

    case OP_EXCHANGE_ID:   EXCHANGE_ID4res opexchange_id;

    case OP_CREATE_SESSION:
                           CREATE_SESSION4res
                                   opcreate_session;




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    case OP_DESTROY_SESSION:
                           DESTROY_SESSION4res
                                   opdestroy_session;

    case OP_FREE_STATEID:  FREE_STATEID4res
                                   opfree_stateid;

    case OP_GET_DIR_DELEGATION:
                           GET_DIR_DELEGATION4res
                                   opget_dir_delegation;

    case OP_GETDEVICEINFO: GETDEVICEINFO4res
                                   opgetdeviceinfo;

    case OP_GETDEVICELIST: GETDEVICELIST4res
                                   opgetdevicelist;

    case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4res oplayoutcommit;
    case OP_LAYOUTGET:     LAYOUTGET4res oplayoutget;
    case OP_LAYOUTRETURN:  LAYOUTRETURN4res oplayoutreturn;

    case OP_SECINFO_NO_NAME:
                           SECINFO_NO_NAME4res
                                   opsecinfo_no_name;

    case OP_SEQUENCE:      SEQUENCE4res opsequence;
    case OP_SET_SSV:       SET_SSV4res opset_ssv;
    case OP_TEST_STATEID:  TEST_STATEID4res optest_stateid;

    case OP_WANT_DELEGATION:
                           WANT_DELEGATION4res
                                   opwant_delegation;

    case OP_DESTROY_CLIENTID:
                           DESTROY_CLIENTID4res
                                   opdestroy_clientid;

    case OP_RECLAIM_COMPLETE:
                           RECLAIM_COMPLETE4res
                                   opreclaim_complete;

    /* Operations not new to NFSv4.1 */
    case OP_ILLEGAL:       ILLEGAL4res opillegal;
   };







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   struct COMPOUND4res {
           nfsstat4        status;
           utf8str_cs      tag;
           nfs_resop4      resarray<>;
   };

16.2.3.  DESCRIPTION

   The COMPOUND procedure is used to combine one or more NFSv4
   operations into a single RPC request.  The server interprets each of
   the operations in turn.  If an operation is executed by the server
   and the status of that operation is NFS4_OK, then the next operation
   in the COMPOUND procedure is executed.  The server continues this
   process until there are no more operations to be executed or until
   one of the operations has a status value other than NFS4_OK.

   In the processing of the COMPOUND procedure, the server may find that
   it does not have the available resources to execute any or all of the
   operations within the COMPOUND sequence.  See Section 2.10.6.4 for a
   more detailed discussion.

   The server will generally choose between two methods of decoding the
   client's request.  The first would be the traditional one-pass XDR
   decode.  If there is an XDR decoding error in this case, the RPC XDR
   decode error would be returned.  The second method would be to make
   an initial pass to decode the basic COMPOUND request and then to XDR
   decode the individual operations; the most interesting is the decode
   of attributes.  In this case, the server may encounter an XDR decode
   error during the second pass.  If it does, the server would return
   the error NFS4ERR_BADXDR to signify the decode error.

   The COMPOUND arguments contain a "minorversion" field.  For NFSv4.1,
   the value for this field is 1.  If the server receives a COMPOUND
   procedure with a minorversion field value that it does not support,
   the server MUST return an error of NFS4ERR_MINOR_VERS_MISMATCH and a
   zero-length resultdata array.

   Contained within the COMPOUND results is a "status" field.  If the
   results array length is non-zero, this status must be equivalent to
   the status of the last operation that was executed within the
   COMPOUND procedure.  Therefore, if an operation incurred an error
   then the "status" value will be the same error value as is being
   returned for the operation that failed.

   Note that operations zero and one are not defined for the COMPOUND
   procedure.  Operation 2 is not defined and is reserved for future
   definition and use with minor versioning.  If the server receives an
   operation array that contains operation 2 and the minorversion field



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   has a value of zero, an error of NFS4ERR_OP_ILLEGAL, as described in
   the next paragraph, is returned to the client.  If an operation array
   contains an operation 2 and the minorversion field is non-zero and
   the server does not support the minor version, the server returns an
   error of NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
   NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
   errors.

   It is possible that the server receives a request that contains an
   operation that is less than the first legal operation (OP_ACCESS) or
   greater than the last legal operation (OP_RELEASE_LOCKOWNER).  In
   this case, the server's response will encode the opcode OP_ILLEGAL
   rather than the illegal opcode of the request.  The status field in
   the ILLEGAL return results will be set to NFS4ERR_OP_ILLEGAL.  The
   COMPOUND procedure's return results will also be NFS4ERR_OP_ILLEGAL.

   The definition of the "tag" in the request is left to the
   implementor.  It may be used to summarize the content of the Compound
   request for the benefit of packet-sniffers and engineers debugging
   implementations.  However, the value of "tag" in the response SHOULD
   be the same value as provided in the request.  This applies to the
   tag field of the CB_COMPOUND procedure as well.

16.2.3.1.  Current Filehandle and Stateid

   The COMPOUND procedure offers a simple environment for the execution
   of the operations specified by the client.  The first two relate to
   the filehandle while the second two relate to the current stateid.

16.2.3.1.1.  Current Filehandle

   The current and saved filehandles are used throughout the protocol.
   Most operations implicitly use the current filehandle as an argument,
   and many set the current filehandle as part of the results.  The
   combination of client-specified sequences of operations and current
   and saved filehandle arguments and results allows for greater
   protocol flexibility.  The best or easiest example of current
   filehandle usage is a sequence like the following:













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         PUTFH fh1              {fh1}
         LOOKUP "compA"         {fh2}
         GETATTR                {fh2}
         LOOKUP "compB"         {fh3}
         GETATTR                {fh3}
         LOOKUP "compC"         {fh4}
         GETATTR                {fh4}
         GETFH

                                 Figure 2

   In this example, the PUTFH (Section 18.19) operation explicitly sets
   the current filehandle value while the result of each LOOKUP
   operation sets the current filehandle value to the resultant file
   system object.  Also, the client is able to insert GETATTR operations
   using the current filehandle as an argument.

   The PUTROOTFH (Section 18.21) and PUTPUBFH (Section 18.20) operations
   also set the current filehandle.  The above example would replace
   "PUTFH fh1" with PUTROOTFH or PUTPUBFH with no filehandle argument in
   order to achieve the same effect (on the assumption that "compA" is
   directly below the root of the namespace).

   Along with the current filehandle, there is a saved filehandle.
   While the current filehandle is set as the result of operations like
   LOOKUP, the saved filehandle must be set directly with the use of the
   SAVEFH operation.  The SAVEFH operation copies the current filehandle
   value to the saved value.  The saved filehandle value is used in
   combination with the current filehandle value for the LINK and RENAME
   operations.  The RESTOREFH operation will copy the saved filehandle
   value to the current filehandle value; as a result, the saved
   filehandle value may be used a sort of "scratch" area for the
   client's series of operations.

16.2.3.1.2.  Current Stateid

   With NFSv4.1, additions of a current stateid and a saved stateid have
   been made to the COMPOUND processing environment; this allows for the
   passing of stateids between operations.  There are no changes to the
   syntax of the protocol, only changes to the semantics of a few
   operations.

   A "current stateid" is the stateid that is associated with the
   current filehandle.  The current stateid may only be changed by an
   operation that modifies the current filehandle or returns a stateid.
   If an operation returns a stateid, it MUST set the current stateid to
   the returned value.  If an operation sets the current filehandle but
   does not return a stateid, the current stateid MUST be set to the



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   all-zeros special stateid, i.e., (seqid, other) = (0, 0).  If an
   operation uses a stateid as an argument but does not return a
   stateid, the current stateid MUST NOT be changed.  For example,
   PUTFH, PUTROOTFH, and PUTPUBFH will change the current server state
   from {ocfh, (osid)} to {cfh, (0, 0)}, while LOCK will change the
   current state from {cfh, (osid} to {cfh, (nsid)}.  Operations like
   LOOKUP that transform a current filehandle and component name into a
   new current filehandle will also change the current state to {0, 0}.
   The SAVEFH and RESTOREFH operations will save and restore both the
   current filehandle and the current stateid as a set.

   The following example is the common case of a simple READ operation
   with a normal stateid showing that the PUTFH initializes the current
   stateid to (0, 0).  The subsequent READ with stateid (sid1) leaves
   the current stateid unchanged.

       PUTFH fh1                             - -> {fh1, (0, 0)}
       READ (sid1), 0, 1024      {fh1, (0, 0)} -> {fh1, (0, 0)}

                                 Figure 3

   This next example performs an OPEN with the root filehandle and, as a
   result, generates stateid (sid1).  The next operation specifies the
   READ with the argument stateid set such that (seqid, other) are equal
   to (1, 0), but the current stateid set by the previous operation is
   actually used when the operation is evaluated.  This allows correct
   interaction with any existing, potentially conflicting, locks.

       PUTROOTFH                             - -> {fh1, (0, 0)}
       OPEN "compA"              {fh1, (0, 0)} -> {fh2, (sid1)}
       READ (1, 0), 0, 1024      {fh2, (sid1)} -> {fh2, (sid1)}
       CLOSE (1, 0)              {fh2, (sid1)} -> {fh2, (sid2)}

                                 Figure 4

   This next example is similar to the second in how it passes the
   stateid sid2 generated by the LOCK operation to the next READ
   operation.  This allows the client to explicitly surround a single I/
   O operation with a lock and its appropriate stateid to guarantee
   correctness with other client locks.  The example also shows how
   SAVEFH and RESTOREFH can save and later reuse a filehandle and
   stateid, passing them as the current filehandle and stateid to a READ
   operation.








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       PUTFH fh1                             - -> {fh1, (0, 0)}
       LOCK 0, 1024, (sid1)      {fh1, (sid1)} -> {fh1, (sid2)}
       READ (1, 0), 0, 1024      {fh1, (sid2)} -> {fh1, (sid2)}
       LOCKU 0, 1024, (1, 0)     {fh1, (sid2)} -> {fh1, (sid3)}
       SAVEFH                    {fh1, (sid3)} -> {fh1, (sid3)}

       PUTFH fh2                 {fh1, (sid3)} -> {fh2, (0, 0)}
       WRITE (1, 0), 0, 1024     {fh2, (0, 0)} -> {fh2, (0, 0)}

       RESTOREFH                 {fh2, (0, 0)} -> {fh1, (sid3)}
       READ (1, 0), 1024, 1024   {fh1, (sid3)} -> {fh1, (sid3)}

                                 Figure 5

   The final example shows a disallowed use of the current stateid.  The
   client is attempting to implicitly pass an anonymous special stateid,
   (0,0), to the READ operation.  The server MUST return
   NFS4ERR_BAD_STATEID in the reply to the READ operation.

       PUTFH fh1                             - -> {fh1, (0, 0)}
       READ (1, 0), 0, 1024      {fh1, (0, 0)} -> NFS4ERR_BAD_STATEID

                                 Figure 6

16.2.4.  ERRORS

   COMPOUND will of course return every error that each operation on the
   fore channel can return (see Table 6).  However, if COMPOUND returns
   zero operations, obviously the error returned by COMPOUND has nothing
   to do with an error returned by an operation.  The list of errors
   COMPOUND will return if it processes zero operations include:




















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                          COMPOUND Error Returns

   +------------------------------+------------------------------------+
   | Error                        | Notes                              |
   +------------------------------+------------------------------------+
   | NFS4ERR_BADCHAR              | The tag argument has a character   |
   |                              | the replier does not support.      |
   | NFS4ERR_BADXDR               |                                    |
   | NFS4ERR_DELAY                |                                    |
   | NFS4ERR_INVAL                | The tag argument is not in UTF-8   |
   |                              | encoding.                          |
   | NFS4ERR_MINOR_VERS_MISMATCH  |                                    |
   | NFS4ERR_SERVERFAULT          |                                    |
   | NFS4ERR_TOO_MANY_OPS         |                                    |
   | NFS4ERR_REP_TOO_BIG          |                                    |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE |                                    |
   | NFS4ERR_REQ_TOO_BIG          |                                    |
   +------------------------------+------------------------------------+

                                  Table 9

17.  Operations: REQUIRED, RECOMMENDED, or OPTIONAL

   The following tables summarize the operations of the NFSv4.1 protocol
   and the corresponding designation of REQUIRED, RECOMMENDED, and
   OPTIONAL to implement or MUST NOT implement.  The designation of MUST
   NOT implement is reserved for those operations that were defined in
   NFSv4.0 and MUST NOT be implemented in NFSv4.1.

   For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation
   for operations sent by the client is for the server implementation.
   The client is generally required to implement the operations needed
   for the operating environment for which it serves.  For example, a
   read-only NFSv4.1 client would have no need to implement the WRITE
   operation and is not required to do so.

   The REQUIRED or OPTIONAL designation for callback operations sent by
   the server is for both the client and server.  Generally, the client
   has the option of creating the backchannel and sending the operations
   on the fore channel that will be a catalyst for the server sending
   callback operations.  A partial exception is CB_RECALL_SLOT; the only
   way the client can avoid supporting this operation is by not creating
   a backchannel.

   Since this is a summary of the operations and their designation,
   there are subtleties that are not presented here.  Therefore, if
   there is a question of the requirements of implementation, the




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   operation descriptions themselves must be consulted along with other
   relevant explanatory text within this specification.

   The abbreviations used in the second and third columns of the table
   are defined as follows.

   REQ  REQUIRED to implement

   REC  RECOMMEND to implement

   OPT  OPTIONAL to implement

   MNI  MUST NOT implement

   For the NFSv4.1 features that are OPTIONAL, the operations that
   support those features are OPTIONAL, and the server would return
   NFS4ERR_NOTSUPP in response to the client's use of those operations.
   If an OPTIONAL feature is supported, it is possible that a set of
   operations related to the feature become REQUIRED to implement.  The
   third column of the table designates the feature(s) and if the
   operation is REQUIRED or OPTIONAL in the presence of support for the
   feature.

   The OPTIONAL features identified and their abbreviations are as
   follows:

   pNFS  Parallel NFS

   FDELG  File Delegations

   DDELG  Directory Delegations

                                Operations

   +----------------------+------------+--------------+----------------+
   | Operation            | REQ, REC,  | Feature      | Definition     |
   |                      | OPT, or    | (REQ, REC,   |                |
   |                      | MNI        | or OPT)      |                |
   +----------------------+------------+--------------+----------------+
   | ACCESS               | REQ        |              | Section 18.1   |
   | BACKCHANNEL_CTL      | REQ        |              | Section 18.33  |
   | BIND_CONN_TO_SESSION | REQ        |              | Section 18.34  |
   | CLOSE                | REQ        |              | Section 18.2   |
   | COMMIT               | REQ        |              | Section 18.3   |
   | CREATE               | REQ        |              | Section 18.4   |
   | CREATE_SESSION       | REQ        |              | Section 18.36  |
   | DELEGPURGE           | OPT        | FDELG (REQ)  | Section 18.5   |
   | DELEGRETURN          | OPT        | FDELG,       | Section 18.6   |



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   |                      |            | DDELG, pNFS  |                |
   |                      |            | (REQ)        |                |
   | DESTROY_CLIENTID     | REQ        |              | Section 18.50  |
   | DESTROY_SESSION      | REQ        |              | Section 18.37  |
   | EXCHANGE_ID          | REQ        |              | Section 18.35  |
   | FREE_STATEID         | REQ        |              | Section 18.38  |
   | GETATTR              | REQ        |              | Section 18.7   |
   | GETDEVICEINFO        | OPT        | pNFS (REQ)   | Section 18.40  |
   | GETDEVICELIST        | OPT        | pNFS (OPT)   | Section 18.41  |
   | GETFH                | REQ        |              | Section 18.8   |
   | GET_DIR_DELEGATION   | OPT        | DDELG (REQ)  | Section 18.39  |
   | LAYOUTCOMMIT         | OPT        | pNFS (REQ)   | Section 18.42  |
   | LAYOUTGET            | OPT        | pNFS (REQ)   | Section 18.43  |
   | LAYOUTRETURN         | OPT        | pNFS (REQ)   | Section 18.44  |
   | LINK                 | OPT        |              | Section 18.9   |
   | LOCK                 | REQ        |              | Section 18.10  |
   | LOCKT                | REQ        |              | Section 18.11  |
   | LOCKU                | REQ        |              | Section 18.12  |
   | LOOKUP               | REQ        |              | Section 18.13  |
   | LOOKUPP              | REQ        |              | Section 18.14  |
   | NVERIFY              | REQ        |              | Section 18.15  |
   | OPEN                 | REQ        |              | Section 18.16  |
   | OPENATTR             | OPT        |              | Section 18.17  |
   | OPEN_CONFIRM         | MNI        |              | N/A            |
   | OPEN_DOWNGRADE       | REQ        |              | Section 18.18  |
   | PUTFH                | REQ        |              | Section 18.19  |
   | PUTPUBFH             | REQ        |              | Section 18.20  |
   | PUTROOTFH            | REQ        |              | Section 18.21  |
   | READ                 | REQ        |              | Section 18.22  |
   | READDIR              | REQ        |              | Section 18.23  |
   | READLINK             | OPT        |              | Section 18.24  |
   | RECLAIM_COMPLETE     | REQ        |              | Section 18.51  |
   | RELEASE_LOCKOWNER    | MNI        |              | N/A            |
   | REMOVE               | REQ        |              | Section 18.25  |
   | RENAME               | REQ        |              | Section 18.26  |
   | RENEW                | MNI        |              | N/A            |
   | RESTOREFH            | REQ        |              | Section 18.27  |
   | SAVEFH               | REQ        |              | Section 18.28  |
   | SECINFO              | REQ        |              | Section 18.29  |
   | SECINFO_NO_NAME      | REC        | pNFS file    | Section 18.45, |
   |                      |            | layout (REQ) | Section 13.12  |
   | SEQUENCE             | REQ        |              | Section 18.46  |
   | SETATTR              | REQ        |              | Section 18.30  |
   | SETCLIENTID          | MNI        |              | N/A            |
   | SETCLIENTID_CONFIRM  | MNI        |              | N/A            |
   | SET_SSV              | REQ        |              | Section 18.47  |
   | TEST_STATEID         | REQ        |              | Section 18.48  |
   | VERIFY               | REQ        |              | Section 18.31  |



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   | WANT_DELEGATION      | OPT        | FDELG (OPT)  | Section 18.49  |
   | WRITE                | REQ        |              | Section 18.32  |
   +----------------------+------------+--------------+----------------+

                            Callback Operations

   +-------------------------+------------+---------------+------------+
   | Operation               | REQ, REC,  | Feature (REQ, | Definition |
   |                         | OPT, or    | REC, or OPT)  |            |
   |                         | MNI        |               |            |
   +-------------------------+------------+---------------+------------+
   | CB_GETATTR              | OPT        | FDELG (REQ)   | Section    |
   |                         |            |               | 20.1       |
   | CB_LAYOUTRECALL         | OPT        | pNFS (REQ)    | Section    |
   |                         |            |               | 20.3       |
   | CB_NOTIFY               | OPT        | DDELG (REQ)   | Section    |
   |                         |            |               | 20.4       |
   | CB_NOTIFY_DEVICEID      | OPT        | pNFS (OPT)    | Section    |
   |                         |            |               | 20.12      |
   | CB_NOTIFY_LOCK          | OPT        |               | Section    |
   |                         |            |               | 20.11      |
   | CB_PUSH_DELEG           | OPT        | FDELG (OPT)   | Section    |
   |                         |            |               | 20.5       |
   | CB_RECALL               | OPT        | FDELG, DDELG, | Section    |
   |                         |            | pNFS (REQ)    | 20.2       |
   | CB_RECALL_ANY           | OPT        | FDELG, DDELG, | Section    |
   |                         |            | pNFS (REQ)    | 20.6       |
   | CB_RECALL_SLOT          | REQ        |               | Section    |
   |                         |            |               | 20.8       |
   | CB_RECALLABLE_OBJ_AVAIL | OPT        | DDELG, pNFS   | Section    |
   |                         |            | (REQ)         | 20.7       |
   | CB_SEQUENCE             | OPT        | FDELG, DDELG, | Section    |
   |                         |            | pNFS (REQ)    | 20.9       |
   | CB_WANTS_CANCELLED      | OPT        | FDELG, DDELG, | Section    |
   |                         |            | pNFS (REQ)    | 20.10      |
   +-------------------------+------------+---------------+------------+

18.  NFSv4.1 Operations

18.1.  Operation 3: ACCESS - Check Access Rights

18.1.1.  ARGUMENTS









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   const ACCESS4_READ      = 0x00000001;
   const ACCESS4_LOOKUP    = 0x00000002;
   const ACCESS4_MODIFY    = 0x00000004;
   const ACCESS4_EXTEND    = 0x00000008;
   const ACCESS4_DELETE    = 0x00000010;
   const ACCESS4_EXECUTE   = 0x00000020;

   struct ACCESS4args {
           /* CURRENT_FH: object */
           uint32_t        access;
   };


18.1.2.  RESULTS

   struct ACCESS4resok {
           uint32_t        supported;
           uint32_t        access;
   };

   union ACCESS4res switch (nfsstat4 status) {
    case NFS4_OK:
            ACCESS4resok   resok4;
    default:
            void;
   };


18.1.3.  DESCRIPTION

   ACCESS determines the access rights that a user, as identified by the
   credentials in the RPC request, has with respect to the file system
   object specified by the current filehandle.  The client encodes the
   set of access rights that are to be checked in the bit mask "access".
   The server checks the permissions encoded in the bit mask.  If a
   status of NFS4_OK is returned, two bit masks are included in the
   response.  The first, "supported", represents the access rights for
   which the server can verify reliably.  The second, "access",
   represents the access rights available to the user for the filehandle
   provided.  On success, the current filehandle retains its value.

   Note that the reply's supported and access fields MUST NOT contain
   more values than originally set in the request's access field.  For
   example, if the client sends an ACCESS operation with just the
   ACCESS4_READ value set and the server supports this value, the server
   MUST NOT set more than ACCESS4_READ in the supported field even if it
   could have reliably checked other values.




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   The reply's access field MUST NOT contain more values than the
   supported field.

   The results of this operation are necessarily advisory in nature.  A
   return status of NFS4_OK and the appropriate bit set in the bit mask
   do not imply that such access will be allowed to the file system
   object in the future.  This is because access rights can be revoked
   by the server at any time.

   The following access permissions may be requested:

   ACCESS4_READ  Read data from file or read a directory.

   ACCESS4_LOOKUP  Look up a name in a directory (no meaning for non-
      directory objects).

   ACCESS4_MODIFY  Rewrite existing file data or modify existing
      directory entries.

   ACCESS4_EXTEND  Write new data or add directory entries.

   ACCESS4_DELETE  Delete an existing directory entry.

   ACCESS4_EXECUTE  Execute a regular file (no meaning for a directory).

   On success, the current filehandle retains its value.

   ACCESS4_EXECUTE is a challenging semantic to implement because NFS
   provides remote file access, not remote execution.  This leads to the
   following:

   o  Whether or not a regular file is executable ought to be the
      responsibility of the NFS client and not the server.  And yet the
      ACCESS operation is specified to seemingly require a server to own
      that responsibility.

   o  When a client executes a regular file, it has to read the file
      from the server.  Strictly speaking, the server should not allow
      the client to read a file being executed unless the user has read
      permissions on the file.  Requiring explicit read permissions on
      executable files in order to access them over NFS is not going to
      be acceptable to some users and storage administrators.
      Historically, NFS servers have allowed a user to READ a file if
      the user has execute access to the file.

   As a practical example, the UNIX specification [52] states that an
   implementation claiming conformance to UNIX may indicate in the
   access() programming interface's result that a privileged user has



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   execute rights, even if no execute permission bits are set on the
   regular file's attributes.  It is possible to claim conformance to
   the UNIX specification and instead not indicate execute rights in
   that situation, which is true for some operating environments.
   Suppose the operating environments of the client and server are
   implementing the access() semantics for privileged users differently,
   and the ACCESS operation implementations of the client and server
   follow their respective access() semantics.  This can cause undesired
   behavior:

   o  Suppose the client's access() interface returns X_OK if the user
      is privileged and no execute permission bits are set on the
      regular file's attribute, and the server's access() interface does
      not return X_OK in that situation.  Then the client will be unable
      to execute files stored on the NFS server that could be executed
      if stored on a non-NFS file system.

   o  Suppose the client's access() interface does not return X_OK if
      the user is privileged, and no execute permission bits are set on
      the regular file's attribute, and the server's access() interface
      does return X_OK in that situation.  Then:

      *  The client will be able to execute files stored on the NFS
         server that could be executed if stored on a non-NFS file
         system, unless the client's execution subsystem also checks for
         execute permission bits.

      *  Even if the execution subsystem is checking for execute
         permission bits, there are more potential issues.  For example,
         suppose the client is invoking access() to build a "path search
         table" of all executable files in the user's "search path",
         where the path is a list of directories each containing
         executable files.  Suppose there are two files each in separate
         directories of the search path, such that files have the same
         component name.  In the first directory the file has no execute
         permission bits set, and in the second directory the file has
         execute bits set.  The path search table will indicate that the
         first directory has the executable file, but the execute
         subsystem will fail to execute it.  The command shell might
         fail to try the second file in the second directory.  And even
         if it did, this is a potential performance issue.  Clearly, the
         desired outcome for the client is for the path search table to
         not contain the first file.

   To deal with the problems described above, the "smart client, stupid
   server" principle is used.  The client owns overall responsibility
   for determining execute access and relies on the server to parse the




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   execution permissions within the file's mode, acl, and dacl
   attributes.  The rules for the client and server follow:

   o  If the client is sending ACCESS in order to determine if the user
      can read the file, the client SHOULD set ACCESS4_READ in the
      request's access field.

   o  If the client's operating environment only grants execution to the
      user if the user has execute access according to the execute
      permissions in the mode, acl, and dacl attributes, then if the
      client wants to determine execute access, the client SHOULD send
      an ACCESS request with ACCESS4_EXECUTE bit set in the request's
      access field.

   o  If the client's operating environment grants execution to the user
      even if the user does not have execute access according to the
      execute permissions in the mode, acl, and dacl attributes, then if
      the client wants to determine execute access, it SHOULD send an
      ACCESS request with both the ACCESS4_EXECUTE and ACCESS4_READ bits
      set in the request's access field.  This way, if any read or
      execute permission grants the user read or execute access (or if
      the server interprets the user as privileged), as indicated by the
      presence of ACCESS4_EXECUTE and/or ACCESS4_READ in the reply's
      access field, the client will be able to grant the user execute
      access to the file.

   o  If the server supports execute permission bits, or some other
      method for denoting executability (e.g., the suffix of the name of
      the file might indicate execute), it MUST check only execute
      permissions, not read permissions, when determining whether or not
      the reply will have ACCESS4_EXECUTE set in the access field.  The
      server MUST NOT also examine read permission bits when determining
      whether or not the reply will have ACCESS4_EXECUTE set in the
      access field.  Even if the server's operating environment would
      grant execute access to the user (e.g., the user is privileged),
      the server MUST NOT reply with ACCESS4_EXECUTE set in reply's
      access field unless there is at least one execute permission bit
      set in the mode, acl, or dacl attributes.  In the case of acl and
      dacl, the "one execute permission bit" MUST be an ACE4_EXECUTE bit
      set in an ALLOW ACE.

   o  If the server does not support execute permission bits or some
      other method for denoting executability, it MUST NOT set
      ACCESS4_EXECUTE in the reply's supported and access fields.  If
      the client set ACCESS4_EXECUTE in the ACCESS request's access
      field, and ACCESS4_EXECUTE is not set in the reply's supported
      field, then the client will have to send an ACCESS request with
      the ACCESS4_READ bit set in the request's access field.



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   o  If the server supports read permission bits, it MUST only check
      for read permissions in the mode, acl, and dacl attributes when it
      receives an ACCESS request with ACCESS4_READ set in the access
      field.  The server MUST NOT also examine execute permission bits
      when determining whether the reply will have ACCESS4_READ set in
      the access field or not.

   Note that if the ACCESS reply has ACCESS4_READ or ACCESS_EXECUTE set,
   then the user also has permissions to OPEN (Section 18.16) or READ
   (Section 18.22) the file.  In other words, if the client sends an
   ACCESS request with the ACCESS4_READ and ACCESS_EXECUTE set in the
   access field (or two separate requests, one with ACCESS4_READ set and
   the other with ACCESS4_EXECUTE set), and the reply has just
   ACCESS4_EXECUTE set in the access field (or just one reply has
   ACCESS4_EXECUTE set), then the user has authorization to OPEN or READ
   the file.

18.1.4.  IMPLEMENTATION

   In general, it is not sufficient for the client to attempt to deduce
   access permissions by inspecting the uid, gid, and mode fields in the
   file attributes or by attempting to interpret the contents of the ACL
   attribute.  This is because the server may perform uid or gid mapping
   or enforce additional access-control restrictions.  It is also
   possible that the server may not be in the same ID space as the
   client.  In these cases (and perhaps others), the client cannot
   reliably perform an access check with only current file attributes.

   In the NFSv2 protocol, the only reliable way to determine whether an
   operation was allowed was to try it and see if it succeeded or
   failed.  Using the ACCESS operation in the NFSv4.1 protocol, the
   client can ask the server to indicate whether or not one or more
   classes of operations are permitted.  The ACCESS operation is
   provided to allow clients to check before doing a series of
   operations that will result in an access failure.  The OPEN operation
   provides a point where the server can verify access to the file
   object and a method to return that information to the client.  The
   ACCESS operation is still useful for directory operations or for use
   in the case that the UNIX interface access() is used on the client.

   The information returned by the server in response to an ACCESS call
   is not permanent.  It was correct at the exact time that the server
   performed the checks, but not necessarily afterwards.  The server can
   revoke access permission at any time.

   The client should use the effective credentials of the user to build
   the authentication information in the ACCESS request used to




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   determine access rights.  It is the effective user and group
   credentials that are used in subsequent READ and WRITE operations.

   Many implementations do not directly support the ACCESS4_DELETE
   permission.  Operating systems like UNIX will ignore the
   ACCESS4_DELETE bit if set on an access request on a non-directory
   object.  In these systems, delete permission on a file is determined
   by the access permissions on the directory in which the file resides,
   instead of being determined by the permissions of the file itself.
   Therefore, the mask returned enumerating which access rights can be
   determined will have the ACCESS4_DELETE value set to 0.  This
   indicates to the client that the server was unable to check that
   particular access right.  The ACCESS4_DELETE bit in the access mask
   returned will then be ignored by the client.

18.2.  Operation 4: CLOSE - Close File

18.2.1.  ARGUMENTS

   struct CLOSE4args {
           /* CURRENT_FH: object */
           seqid4          seqid;
           stateid4        open_stateid;
   };


18.2.2.  RESULTS

   union CLOSE4res switch (nfsstat4 status) {
    case NFS4_OK:
            stateid4       open_stateid;
    default:
            void;
   };


18.2.3.  DESCRIPTION

   The CLOSE operation releases share reservations for the regular or
   named attribute file as specified by the current filehandle.  The
   share reservations and other state information released at the server
   as a result of this CLOSE are only those associated with the supplied
   stateid.  State associated with other OPENs is not affected.

   If byte-range locks are held, the client SHOULD release all locks
   before sending a CLOSE.  The server MAY free all outstanding locks on
   CLOSE, but some servers may not support the CLOSE of a file that




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   still has byte-range locks held.  The server MUST return failure if
   any locks would exist after the CLOSE.

   The argument seqid MAY have any value, and the server MUST ignore
   seqid.

   On success, the current filehandle retains its value.

   The server MAY require that the combination of principal, security
   flavor, and, if applicable, GSS mechanism that sent the OPEN request
   also be the one to CLOSE the file.  This might not be possible if
   credentials for the principal are no longer available.  The server
   MAY allow the machine credential or SSV credential (see
   Section 18.35) to send CLOSE.

18.2.4.  IMPLEMENTATION

   Even though CLOSE returns a stateid, this stateid is not useful to
   the client and should be treated as deprecated.  CLOSE "shuts down"
   the state associated with all OPENs for the file by a single open-
   owner.  As noted above, CLOSE will either release all file-locking
   state or return an error.  Therefore, the stateid returned by CLOSE
   is not useful for operations that follow.  To help find any uses of
   this stateid by clients, the server SHOULD return the invalid special
   stateid (the "other" value is zero and the "seqid" field is
   NFS4_UINT32_MAX, see Section 8.2.3).

   A CLOSE operation may make delegations grantable where they were not
   previously.  Servers may choose to respond immediately if there are
   pending delegation want requests or may respond to the situation at a
   later time.

18.3.  Operation 5: COMMIT - Commit Cached Data

18.3.1.  ARGUMENTS

   struct COMMIT4args {
           /* CURRENT_FH: file */
           offset4         offset;
           count4          count;
   };


18.3.2.  RESULTS







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   struct COMMIT4resok {
           verifier4       writeverf;
   };

   union COMMIT4res switch (nfsstat4 status) {
    case NFS4_OK:
            COMMIT4resok   resok4;
    default:
            void;
   };


18.3.3.  DESCRIPTION

   The COMMIT operation forces or flushes uncommitted, modified data to
   stable storage for the file specified by the current filehandle.  The
   flushed data is that which was previously written with one or more
   WRITE operations that had the "committed" field of their results
   field set to UNSTABLE4.

   The offset specifies the position within the file where the flush is
   to begin.  An offset value of zero means to flush data starting at
   the beginning of the file.  The count specifies the number of bytes
   of data to flush.  If the count is zero, a flush from the offset to
   the end of the file is done.

   The server returns a write verifier upon successful completion of the
   COMMIT.  The write verifier is used by the client to determine if the
   server has restarted between the initial WRITE operations and the
   COMMIT.  The client does this by comparing the write verifier
   returned from the initial WRITE operations and the verifier returned
   by the COMMIT operation.  The server must vary the value of the write
   verifier at each server event or instantiation that may lead to a
   loss of uncommitted data.  Most commonly this occurs when the server
   is restarted; however, other events at the server may result in
   uncommitted data loss as well.

   On success, the current filehandle retains its value.

18.3.4.  IMPLEMENTATION

   The COMMIT operation is similar in operation and semantics to the
   POSIX fsync() [25] system interface that synchronizes a file's state
   with the disk (file data and metadata is flushed to disk or stable
   storage).  COMMIT performs the same operation for a client, flushing
   any unsynchronized data and metadata on the server to the server's
   disk or stable storage for the specified file.  Like fsync(), it may
   be that there is some modified data or no modified data to



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   synchronize.  The data may have been synchronized by the server's
   normal periodic buffer synchronization activity.  COMMIT should
   return NFS4_OK, unless there has been an unexpected error.

   COMMIT differs from fsync() in that it is possible for the client to
   flush a range of the file (most likely triggered by a buffer-
   reclamation scheme on the client before the file has been completely
   written).

   The server implementation of COMMIT is reasonably simple.  If the
   server receives a full file COMMIT request, that is, starting at
   offset zero and count zero, it should do the equivalent of applying
   fsync() to the entire file.  Otherwise, it should arrange to have the
   modified data in the range specified by offset and count to be
   flushed to stable storage.  In both cases, any metadata associated
   with the file must be flushed to stable storage before returning.  It
   is not an error for there to be nothing to flush on the server.  This
   means that the data and metadata that needed to be flushed have
   already been flushed or lost during the last server failure.

   The client implementation of COMMIT is a little more complex.  There
   are two reasons for wanting to commit a client buffer to stable
   storage.  The first is that the client wants to reuse a buffer.  In
   this case, the offset and count of the buffer are sent to the server
   in the COMMIT request.  The server then flushes any modified data
   based on the offset and count, and flushes any modified metadata
   associated with the file.  It then returns the status of the flush
   and the write verifier.  The second reason for the client to generate
   a COMMIT is for a full file flush, such as may be done at close.  In
   this case, the client would gather all of the buffers for this file
   that contain uncommitted data, do the COMMIT operation with an offset
   of zero and count of zero, and then free all of those buffers.  Any
   other dirty buffers would be sent to the server in the normal
   fashion.

   After a buffer is written (via the WRITE operation) by the client
   with the "committed" field in the result of WRITE set to UNSTABLE4,
   the buffer must be considered as modified by the client until the
   buffer has either been flushed via a COMMIT operation or written via
   a WRITE operation with the "committed" field in the result set to
   FILE_SYNC4 or DATA_SYNC4.  This is done to prevent the buffer from
   being freed and reused before the data can be flushed to stable
   storage on the server.

   When a response is returned from either a WRITE or a COMMIT operation
   and it contains a write verifier that differs from that previously
   returned by the server, the client will need to retransmit all of the
   buffers containing uncommitted data to the server.  How this is to be



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   done is up to the implementor.  If there is only one buffer of
   interest, then it should be sent in a WRITE request with the
   FILE_SYNC4 stable parameter.  If there is more than one buffer, it
   might be worthwhile retransmitting all of the buffers in WRITE
   operations with the stable parameter set to UNSTABLE4 and then
   retransmitting the COMMIT operation to flush all of the data on the
   server to stable storage.  However, if the server repeatably returns
   from COMMIT a verifier that differs from that returned by WRITE, the
   only way to ensure progress is to retransmit all of the buffers with
   WRITE requests with the FILE_SYNC4 stable parameter.

   The above description applies to page-cache-based systems as well as
   buffer-cache-based systems.  In the former systems, the virtual
   memory system will need to be modified instead of the buffer cache.

18.4.  Operation 6: CREATE - Create a Non-Regular File Object

18.4.1.  ARGUMENTS

   union createtype4 switch (nfs_ftype4 type) {
    case NF4LNK:
            linktext4 linkdata;
    case NF4BLK:
    case NF4CHR:
            specdata4 devdata;
    case NF4SOCK:
    case NF4FIFO:
    case NF4DIR:
            void;
    default:
            void;  /* server should return NFS4ERR_BADTYPE */
   };

   struct CREATE4args {
           /* CURRENT_FH: directory for creation */
           createtype4     objtype;
           component4      objname;
           fattr4          createattrs;
   };


18.4.2.  RESULTS









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   struct CREATE4resok {
           change_info4    cinfo;
           bitmap4         attrset;        /* attributes set */
   };

   union CREATE4res switch (nfsstat4 status) {
    case NFS4_OK:
            /* new CURRENTFH: created object */
            CREATE4resok resok4;
    default:
            void;
   };


18.4.3.  DESCRIPTION

   The CREATE operation creates a file object other than an ordinary
   file in a directory with a given name.  The OPEN operation MUST be
   used to create a regular file or a named attribute.

   The current filehandle must be a directory: an object of type NF4DIR.
   If the current filehandle is an attribute directory (type
   NF4ATTRDIR), the error NFS4ERR_WRONG_TYPE is returned.  If the
   current file handle designates any other type of object, the error
   NFS4ERR_NOTDIR results.

   The objname specifies the name for the new object.  The objtype
   determines the type of object to be created: directory, symlink, etc.
   If the object type specified is that of an ordinary file, a named
   attribute, or a named attribute directory, the error NFS4ERR_BADTYPE
   results.

   If an object of the same name already exists in the directory, the
   server will return the error NFS4ERR_EXIST.

   For the directory where the new file object was created, the server
   returns change_info4 information in cinfo.  With the atomic field of
   the change_info4 data type, the server will indicate if the before
   and after change attributes were obtained atomically with respect to
   the file object creation.

   If the objname has a length of zero, or if objname does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

   The current filehandle is replaced by that of the new object.

   The createattrs specifies the initial set of attributes for the
   object.  The set of attributes may include any writable attribute



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   valid for the object type.  When the operation is successful, the
   server will return to the client an attribute mask signifying which
   attributes were successfully set for the object.

   If createattrs includes neither the owner attribute nor an ACL with
   an ACE for the owner, and if the server's file system both supports
   and requires an owner attribute (or an owner ACE), then the server
   MUST derive the owner (or the owner ACE).  This would typically be
   from the principal indicated in the RPC credentials of the call, but
   the server's operating environment or file system semantics may
   dictate other methods of derivation.  Similarly, if createattrs
   includes neither the group attribute nor a group ACE, and if the
   server's file system both supports and requires the notion of a group
   attribute (or group ACE), the server MUST derive the group attribute
   (or the corresponding owner ACE) for the file.  This could be from
   the RPC call's credentials, such as the group principal if the
   credentials include it (such as with AUTH_SYS), from the group
   identifier associated with the principal in the credentials (e.g.,
   POSIX systems have a user database [26] that has a group identifier
   for every user identifier), inherited from the directory in which the
   object is created, or whatever else the server's operating
   environment or file system semantics dictate.  This applies to the
   OPEN operation too.

   Conversely, it is possible that the client will specify in
   createattrs an owner attribute, group attribute, or ACL that the
   principal indicated the RPC call's credentials does not have
   permissions to create files for.  The error to be returned in this
   instance is NFS4ERR_PERM.  This applies to the OPEN operation too.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the delegation is
   such that the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the CREATE operation MUST NOT
   proceed until the delegation is returned or revoked.  Except where
   this happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations
   request such notifications, NOTIFY4_ADD_ENTRY will be generated as a
   result of this operation.

   If the capability FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set
   (Section 14.4), and a symbolic link is being created, then the
   content of the symbolic link MUST be in UTF-8 encoding.





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18.4.4.  IMPLEMENTATION

   If the client desires to set attribute values after the create, a
   SETATTR operation can be added to the COMPOUND request so that the
   appropriate attributes will be set.

18.5.  Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery

18.5.1.  ARGUMENTS

   struct DELEGPURGE4args {
           clientid4       clientid;
   };


18.5.2.  RESULTS

   struct DELEGPURGE4res {
           nfsstat4        status;
   };


18.5.3.  DESCRIPTION

   This operation purges all of the delegations awaiting recovery for a
   given client.  This is useful for clients that do not commit
   delegation information to stable storage to indicate that conflicting
   requests need not be delayed by the server awaiting recovery of
   delegation information.

   The client is NOT specified by the clientid field of the request.
   The client SHOULD set the client field to zero, and the server MUST
   ignore the clientid field.  Instead, the server MUST derive the
   client ID from the value of the session ID in the arguments of the
   SEQUENCE operation that precedes DELEGPURGE in the COMPOUND request.

   The DELEGPURGE operation should be used by clients that record
   delegation information on stable storage on the client.  In this
   case, after the client recovers all delegations it knows of, it
   should immediately send a DELEGPURGE operation.  Doing so will notify
   the server that no additional delegations for the client will be
   recovered allowing it to free resources, and avoid delaying other
   clients which make requests that conflict with the unrecovered
   delegations.  The set of delegations known to the server and the
   client might be different.  The reason for this is that after sending
   a request that resulted in a delegation, the client might experience
   a failure before it both received the delegation and committed the
   delegation to the client's stable storage.



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   The server MAY support DELEGPURGE, but if it does not, it MUST NOT
   support CLAIM_DELEGATE_PREV and MUST NOT support CLAIM_DELEG_PREV_FH.

18.6.  Operation 8: DELEGRETURN - Return Delegation

18.6.1.  ARGUMENTS

   struct DELEGRETURN4args {
           /* CURRENT_FH: delegated object */
           stateid4        deleg_stateid;
   };


18.6.2.  RESULTS

   struct DELEGRETURN4res {
           nfsstat4        status;
   };


18.6.3.  DESCRIPTION

   The DELEGRETURN operation returns the delegation represented by the
   current filehandle and stateid.

   Delegations may be returned voluntarily (i.e., before the server has
   recalled them) or when recalled.  In either case, the client must
   properly propagate state changed under the context of the delegation
   to the server before returning the delegation.

   The server MAY require that the principal, security flavor, and if
   applicable, the GSS mechanism, combination that acquired the
   delegation also be the one to send DELEGRETURN on the file.  This
   might not be possible if credentials for the principal are no longer
   available.  The server MAY allow the machine credential or SSV
   credential (see Section 18.35) to send DELEGRETURN.

18.7.  Operation 9: GETATTR - Get Attributes

18.7.1.  ARGUMENTS

   struct GETATTR4args {
           /* CURRENT_FH: object */
           bitmap4         attr_request;
   };






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18.7.2.  RESULTS

   struct GETATTR4resok {
           fattr4          obj_attributes;
   };

   union GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            GETATTR4resok  resok4;
    default:
            void;
   };


18.7.3.  DESCRIPTION

   The GETATTR operation will obtain attributes for the file system
   object specified by the current filehandle.  The client sets a bit in
   the bitmap argument for each attribute value that it would like the
   server to return.  The server returns an attribute bitmap that
   indicates the attribute values that it was able to return, which will
   include all attributes requested by the client that are attributes
   supported by the server for the target file system.  This bitmap is
   followed by the attribute values ordered lowest attribute number
   first.

   The server MUST return a value for each attribute that the client
   requests if the attribute is supported by the server for the target
   file system.  If the server does not support a particular attribute
   on the target file system, then it MUST NOT return the attribute
   value and MUST NOT set the attribute bit in the result bitmap.  The
   server MUST return an error if it supports an attribute on the target
   but cannot obtain its value.  In that case, no attribute values will
   be returned.

   File systems that are absent should be treated as having support for
   a very small set of attributes as described in Section 11.3.1, even
   if previously, when the file system was present, more attributes were
   supported.

   All servers MUST support the REQUIRED attributes as specified in
   Section 5.6, for all file systems, with the exception of absent file
   systems.

   On success, the current filehandle retains its value.






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18.7.4.  IMPLEMENTATION

   Suppose there is an OPEN_DELEGATE_WRITE delegation held by another
   client for the file in question and size and/or change are among the
   set of attributes being interrogated.  The server has two choices.
   First, the server can obtain the actual current value of these
   attributes from the client holding the delegation by using the
   CB_GETATTR callback.  Second, the server, particularly when the
   delegated client is unresponsive, can recall the delegation in
   question.  The GETATTR MUST NOT proceed until one of the following
   occurs:

   o  The requested attribute values are returned in the response to
      CB_GETATTR.

   o  The OPEN_DELEGATE_WRITE delegation is returned.

   o  The OPEN_DELEGATE_WRITE delegation is revoked.

   Unless one of the above happens very quickly, one or more
   NFS4ERR_DELAY errors will be returned while a delegation is
   outstanding.

18.8.  Operation 10: GETFH - Get Current Filehandle

18.8.1.  ARGUMENTS

   /* CURRENT_FH: */
   void;

18.8.2.  RESULTS

   struct GETFH4resok {
           nfs_fh4         object;
   };

   union GETFH4res switch (nfsstat4 status) {
    case NFS4_OK:
           GETFH4resok     resok4;
    default:
           void;
   };









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18.8.3.  DESCRIPTION

   This operation returns the current filehandle value.

   On success, the current filehandle retains its value.

   As described in Section 2.10.6.4, GETFH is REQUIRED or RECOMMENDED to
   immediately follow certain operations, and servers are free to reject
   such operations if the client fails to insert GETFH in the request as
   REQUIRED or RECOMMENDED.  Section 18.16.4.1 provides additional
   justification for why GETFH MUST follow OPEN.

18.8.4.  IMPLEMENTATION

   Operations that change the current filehandle like LOOKUP or CREATE
   do not automatically return the new filehandle as a result.  For
   instance, if a client needs to look up a directory entry and obtain
   its filehandle, then the following request is needed.

      PUTFH (directory filehandle)

      LOOKUP (entry name)

      GETFH

18.9.  Operation 11: LINK - Create Link to a File

18.9.1.  ARGUMENTS

   struct LINK4args {
           /* SAVED_FH: source object */
           /* CURRENT_FH: target directory */
           component4      newname;
   };


18.9.2.  RESULTS














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   struct LINK4resok {
           change_info4    cinfo;
   };

   union LINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LINK4resok resok4;
    default:
            void;
   };


18.9.3.  DESCRIPTION

   The LINK operation creates an additional newname for the file
   represented by the saved filehandle, as set by the SAVEFH operation,
   in the directory represented by the current filehandle.  The existing
   file and the target directory must reside within the same file system
   on the server.  On success, the current filehandle will continue to
   be the target directory.  If an object exists in the target directory
   with the same name as newname, the server must return NFS4ERR_EXIST.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 data type, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   If the newname has a length of zero, or if newname does not obey the
   UTF-8 definition, the error NFS4ERR_INVAL will be returned.

18.9.4.  IMPLEMENTATION

   The server MAY impose restrictions on the LINK operation such that
   LINK may not be done when the file is open or when that open is done
   by particular protocols, or with particular options or access modes.
   When LINK is rejected because of such restrictions, the error
   NFS4ERR_FILE_OPEN is returned.

   If a server does implement such restrictions and those restrictions
   include cases of NFSv4 opens preventing successful execution of a
   link, the server needs to recall any delegations that could hide the
   existence of opens relevant to that decision.  The reason is that
   when a client holds a delegation, the server might not have an
   accurate account of the opens for that client, since the client may
   execute OPENs and CLOSEs locally.  The LINK operation must be delayed
   only until a definitive result can be obtained.  For example, suppose
   there are multiple delegations and one of them establishes an open
   whose presence would prevent the link.  Given the server's semantics,



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   NFS4ERR_FILE_OPEN may be returned to the caller as soon as that
   delegation is returned without waiting for other delegations to be
   returned.  Similarly, if such opens are not associated with
   delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
   delegation recall being done.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the delegation is
   such that the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the operation cannot be
   performed successfully until the delegation is returned or revoked.
   Except where this happens very quickly, one or more NFS4ERR_DELAY
   errors will be returned to requests made while delegation remains
   outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations
   request such notifications, instead of a recall, NOTIFY4_ADD_ENTRY
   will be generated as a result of the LINK operation.

   If the current file system supports the numlinks attribute, and other
   clients have delegations to the file being linked, then those
   delegations MUST be recalled and the LINK operation MUST NOT proceed
   until all delegations are returned or revoked.  Except where this
   happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   Changes to any property of the "hard" linked files are reflected in
   all of the linked files.  When a link is made to a file, the
   attributes for the file should have a value for numlinks that is one
   greater than the value before the LINK operation.

   The statement "file and the target directory must reside within the
   same file system on the server" means that the fsid fields in the
   attributes for the objects are the same.  If they reside on different
   file systems, the error NFS4ERR_XDEV is returned.  This error may be
   returned by some servers when there is an internal partitioning of a
   file system that the LINK operation would violate.

   On some servers, "." and ".." are illegal values for newname and the
   error NFS4ERR_BADNAME will be returned if they are specified.

   When the current filehandle designates a named attribute directory
   and the object to be linked (the saved filehandle) is not a named
   attribute for the same object, the error NFS4ERR_XDEV MUST be
   returned.  When the saved filehandle designates a named attribute and
   the current filehandle is not the appropriate named attribute
   directory, the error NFS4ERR_XDEV MUST also be returned.



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   When the current filehandle designates a named attribute directory
   and the object to be linked (the saved filehandle) is a named
   attribute within that directory, the server may return the error
   NFS4ERR_NOTSUPP.

   In the case that newname is already linked to the file represented by
   the saved filehandle, the server will return NFS4ERR_EXIST.

   Note that symbolic links are created with the CREATE operation.

18.10.  Operation 12: LOCK - Create Lock

18.10.1.  ARGUMENTS






































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   /*
    * For LOCK, transition from open_stateid and lock_owner
    * to a lock stateid.
    */
   struct open_to_lock_owner4 {
           seqid4          open_seqid;
           stateid4        open_stateid;
           seqid4          lock_seqid;
           lock_owner4     lock_owner;
   };

   /*
    * For LOCK, existing lock stateid continues to request new
    * file lock for the same lock_owner and open_stateid.
    */
   struct exist_lock_owner4 {
           stateid4        lock_stateid;
           seqid4          lock_seqid;
   };

   union locker4 switch (bool new_lock_owner) {
    case TRUE:
           open_to_lock_owner4     open_owner;
    case FALSE:
           exist_lock_owner4       lock_owner;
   };

   /*
    * LOCK/LOCKT/LOCKU: Record lock management
    */
   struct LOCK4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           bool            reclaim;
           offset4         offset;
           length4         length;
           locker4         locker;
   };


18.10.2.  RESULTS










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   struct LOCK4denied {
           offset4         offset;
           length4         length;
           nfs_lock_type4  locktype;
           lock_owner4     owner;
   };

   struct LOCK4resok {
           stateid4        lock_stateid;
   };

   union LOCK4res switch (nfsstat4 status) {
    case NFS4_OK:
            LOCK4resok     resok4;
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    default:
            void;
   };


18.10.3.  DESCRIPTION

   The LOCK operation requests a byte-range lock for the byte-range
   specified by the offset and length parameters, and lock type
   specified in the locktype parameter.  If this is a reclaim request,
   the reclaim parameter will be TRUE.

   Bytes in a file may be locked even if those bytes are not currently
   allocated to the file.  To lock the file from a specific offset
   through the end-of-file (no matter how long the file actually is) use
   a length field equal to NFS4_UINT64_MAX.  The server MUST return
   NFS4ERR_INVAL under the following combinations of length and offset:

   o  Length is equal to zero.

   o  Length is not equal to NFS4_UINT64_MAX, and the sum of length and
      offset exceeds NFS4_UINT64_MAX.

   32-bit servers are servers that support locking for byte offsets that
   fit within 32 bits (i.e., less than or equal to NFS4_UINT32_MAX).  If
   the client specifies a range that overlaps one or more bytes beyond
   offset NFS4_UINT32_MAX but does not end at offset NFS4_UINT64_MAX,
   then such a 32-bit server MUST return the error NFS4ERR_BAD_RANGE.

   If the server returns NFS4ERR_DENIED, the owner, offset, and length
   of a conflicting lock are returned.




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   The locker argument specifies the lock-owner that is associated with
   the LOCK operation.  The locker4 structure is a switched union that
   indicates whether the client has already created byte-range locking
   state associated with the current open file and lock-owner.  In the
   case in which it has, the argument is just a stateid representing the
   set of locks associated with that open file and lock-owner, together
   with a lock_seqid value that MAY be any value and MUST be ignored by
   the server.  In the case where no byte-range locking state has been
   established, or the client does not have the stateid available, the
   argument contains the stateid of the open file with which this lock
   is to be associated, together with the lock-owner with which the lock
   is to be associated.  The open_to_lock_owner case covers the very
   first lock done by a lock-owner for a given open file and offers a
   method to use the established state of the open_stateid to transition
   to the use of a lock stateid.

   The following fields of the locker parameter MAY be set to any value
   by the client and MUST be ignored by the server:

   o  The clientid field of the lock_owner field of the open_owner field
      (locker.open_owner.lock_owner.clientid).  The reason the server
      MUST ignore the clientid field is that the server MUST derive the
      client ID from the session ID from the SEQUENCE operation of the
      COMPOUND request.

   o  The open_seqid and lock_seqid fields of the open_owner field
      (locker.open_owner.open_seqid and locker.open_owner.lock_seqid).

   o  The lock_seqid field of the lock_owner field
      (locker.lock_owner.lock_seqid).

   Note that the client ID appearing in a LOCK4denied structure is the
   actual client associated with the conflicting lock, whether this is
   the client ID associated with the current session or a different one.
   Thus, if the server returns NFS4ERR_DENIED, it MUST set the clientid
   field of the owner field of the denied field.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.







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18.10.4.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting byte-range lock, the same offset and length that were
   provided in the arguments should be returned in the denied results.

   LOCK operations are subject to permission checks and to checks
   against the access type of the associated file.  However, the
   specific right and modes required for various types of locks reflect
   the semantics of the server-exported file system, and are not
   specified by the protocol.  For example, Windows 2000 allows a write
   lock of a file open for read access, while a POSIX-compliant system
   does not.

   When the client sends a LOCK operation that corresponds to a range
   that the lock-owner has locked already (with the same or different
   lock type), or to a sub-range of such a range, or to a byte-range
   that includes multiple locks already granted to that lock-owner, in
   whole or in part, and the server does not support such locking
   operations (i.e., does not support POSIX locking semantics), the
   server will return the error NFS4ERR_LOCK_RANGE.  In that case, the
   client may return an error, or it may emulate the required
   operations, using only LOCK for ranges that do not include any bytes
   already locked by that lock-owner and LOCKU of locks held by that
   lock-owner (specifying an exactly matching range and type).
   Similarly, when the client sends a LOCK operation that amounts to
   upgrading (changing from a READ_LT lock to a WRITE_LT lock) or
   downgrading (changing from WRITE_LT lock to a READ_LT lock) an
   existing byte-range lock, and the server does not support such a
   lock, the server will return NFS4ERR_LOCK_NOTSUPP.  Such operations
   may not perfectly reflect the required semantics in the face of
   conflicting LOCK operations from other clients.

   When a client holds an OPEN_DELEGATE_WRITE delegation, the client
   holding that delegation is assured that there are no opens by other
   clients.  Thus, there can be no conflicting LOCK operations from such
   clients.  Therefore, the client may be handling locking requests
   locally, without doing LOCK operations on the server.  If it does
   that, it must be prepared to update the lock status on the server, by
   sending appropriate LOCK and LOCKU operations before returning the
   delegation.

   When one or more clients hold OPEN_DELEGATE_READ delegations, any
   LOCK operation where the server is implementing mandatory locking
   semantics MUST result in the recall of all such delegations.  The
   LOCK operation may not be granted until all such delegations are
   returned or revoked.  Except where this happens very quickly, one or




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   more NFS4ERR_DELAY errors will be returned to requests made while the
   delegation remains outstanding.

18.11.  Operation 13: LOCKT - Test for Lock

18.11.1.  ARGUMENTS

   struct LOCKT4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           offset4         offset;
           length4         length;
           lock_owner4     owner;
   };


18.11.2.  RESULTS

   union LOCKT4res switch (nfsstat4 status) {
    case NFS4ERR_DENIED:
            LOCK4denied    denied;
    case NFS4_OK:
            void;
    default:
            void;
   };


18.11.3.  DESCRIPTION

   The LOCKT operation tests the lock as specified in the arguments.  If
   a conflicting lock exists, the owner, offset, length, and type of the
   conflicting lock are returned.  The owner field in the results
   includes the client ID of the owner of the conflicting lock, whether
   this is the client ID associated with the current session or a
   different client ID.  If no lock is held, nothing other than NFS4_OK
   is returned.  Lock types READ_LT and READW_LT are processed in the
   same way in that a conflicting lock test is done without regard to
   blocking or non-blocking.  The same is true for WRITE_LT and
   WRITEW_LT.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   The clientid field of the owner MAY be set to any value by the client
   and MUST be ignored by the server.  The reason the server MUST ignore




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   the clientid field is that the server MUST derive the client ID from
   the session ID from the SEQUENCE operation of the COMPOUND request.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.

18.11.4.  IMPLEMENTATION

   If the server is unable to determine the exact offset and length of
   the conflicting lock, the same offset and length that were provided
   in the arguments should be returned in the denied results.

   LOCKT uses a lock_owner4 rather a stateid4, as is used in LOCK to
   identify the owner.  This is because the client does not have to open
   the file to test for the existence of a lock, so a stateid might not
   be available.

   As noted in Section 18.10.4, some servers may return
   NFS4ERR_LOCK_RANGE to certain (otherwise non-conflicting) LOCK
   operations that overlap ranges already granted to the current lock-
   owner.

   The LOCKT operation's test for conflicting locks SHOULD exclude locks
   for the current lock-owner, and thus should return NFS4_OK in such
   cases.  Note that this means that a server might return NFS4_OK to a
   LOCKT request even though a LOCK operation for the same range and
   lock-owner would fail with NFS4ERR_LOCK_RANGE.

   When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
   (see Section 18.10.4) to handle LOCK requests locally.  In such a
   case, LOCKT requests will similarly be handled locally.

18.12.  Operation 14: LOCKU - Unlock File

18.12.1.  ARGUMENTS











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   struct LOCKU4args {
           /* CURRENT_FH: file */
           nfs_lock_type4  locktype;
           seqid4          seqid;
           stateid4        lock_stateid;
           offset4         offset;
           length4         length;
   };


18.12.2.  RESULTS

   union LOCKU4res switch (nfsstat4 status) {
    case   NFS4_OK:
            stateid4       lock_stateid;
    default:
            void;
   };


18.12.3.  DESCRIPTION

   The LOCKU operation unlocks the byte-range lock specified by the
   parameters.  The client may set the locktype field to any value that
   is legal for the nfs_lock_type4 enumerated type, and the server MUST
   accept any legal value for locktype.  Any legal value for locktype
   has no effect on the success or failure of the LOCKU operation.

   The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
   NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
   for LOCK.

   The seqid parameter MAY be any value and the server MUST ignore it.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   On success, the current filehandle retains its value.

   The server MAY require that the principal, security flavor, and if
   applicable, the GSS mechanism, combination that sent a LOCK operation
   also be the one to send LOCKU on the file.  This might not be
   possible if credentials for the principal are no longer available.
   The server MAY allow the machine credential or SSV credential (see
   Section 18.35) to send LOCKU.



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18.12.4.  IMPLEMENTATION

   If the area to be unlocked does not correspond exactly to a lock
   actually held by the lock-owner, the server may return the error
   NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
   locked, where the area is a sub-range of the area locked, where it
   overlaps the area locked without matching exactly, or the area
   specified includes multiple locks held by the lock-owner.  In all of
   these cases, allowed by POSIX locking [24] semantics, a client
   receiving this error should, if it desires support for such
   operations, simulate the operation using LOCKU on ranges
   corresponding to locks it actually holds, possibly followed by LOCK
   operations for the sub-ranges not being unlocked.

   When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose
   (see Section 18.10.4) to handle LOCK requests locally.  In such a
   case, LOCKU operations will similarly be handled locally.

18.13.  Operation 15: LOOKUP - Lookup Filename

18.13.1.  ARGUMENTS

   struct LOOKUP4args {
           /* CURRENT_FH: directory */
           component4      objname;
   };


18.13.2.  RESULTS

   struct LOOKUP4res {
           /* New CURRENT_FH: object */
           nfsstat4        status;
   };


18.13.3.  DESCRIPTION

   The LOOKUP operation looks up or finds a file system object using the
   directory specified by the current filehandle.  LOOKUP evaluates the
   component and if the object exists, the current filehandle is
   replaced with the component's filehandle.

   If the component cannot be evaluated either because it does not exist
   or because the client does not have permission to evaluate the
   component, then an error will be returned and the current filehandle
   will be unchanged.




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   If the component is a zero-length string or if any component does not
   obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.

18.13.4.  IMPLEMENTATION

   If the client wants to achieve the effect of a multi-component look
   up, it may construct a COMPOUND request such as (and obtain each
   filehandle):

         PUTFH  (directory filehandle)
         LOOKUP "pub"
         GETFH
         LOOKUP "foo"
         GETFH
         LOOKUP "bar"
         GETFH

   Unlike NFSv3, NFSv4.1 allows LOOKUP requests to cross mountpoints on
   the server.  The client can detect a mountpoint crossing by comparing
   the fsid attribute of the directory with the fsid attribute of the
   directory looked up.  If the fsids are different, then the new
   directory is a server mountpoint.  UNIX clients that detect a
   mountpoint crossing will need to mount the server's file system.
   This needs to be done to maintain the file object identity checking
   mechanisms common to UNIX clients.

   Servers that limit NFS access to "shared" or "exported" file systems
   should provide a pseudo file system into which the exported file
   systems can be integrated, so that clients can browse the server's
   namespace.  The clients view of a pseudo file system will be limited
   to paths that lead to exported file systems.

   Note: previous versions of the protocol assigned special semantics to
   the names "." and "..".  NFSv4.1 assigns no special semantics to
   these names.  The LOOKUPP operator must be used to look up a parent
   directory.

   Note that this operation does not follow symbolic links.  The client
   is responsible for all parsing of filenames including filenames that
   are modified by symbolic links encountered during the look up
   process.

   If the current filehandle supplied is not a directory but a symbolic
   link, the error NFS4ERR_SYMLINK is returned as the error.  For all
   other non-directory file types, the error NFS4ERR_NOTDIR is returned.






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18.14.  Operation 16: LOOKUPP - Lookup Parent Directory

18.14.1.  ARGUMENTS

   /* CURRENT_FH: object */
   void;

18.14.2.  RESULTS

   struct LOOKUPP4res {
           /* new CURRENT_FH: parent directory */
           nfsstat4        status;
   };


18.14.3.  DESCRIPTION

   The current filehandle is assumed to refer to a regular directory or
   a named attribute directory.  LOOKUPP assigns the filehandle for its
   parent directory to be the current filehandle.  If there is no parent
   directory, an NFS4ERR_NOENT error must be returned.  Therefore,
   NFS4ERR_NOENT will be returned by the server when the current
   filehandle is at the root or top of the server's file tree.

   As is the case with LOOKUP, LOOKUPP will also cross mountpoints.

   If the current filehandle is not a directory or named attribute
   directory, the error NFS4ERR_NOTDIR is returned.

   If the requester's security flavor does not match that configured for
   the parent directory, then the server SHOULD return NFS4ERR_WRONGSEC
   (a future minor revision of NFSv4 may upgrade this to MUST) in the
   LOOKUPP response.  However, if the server does so, it MUST support
   the SECINFO_NO_NAME operation (Section 18.45), so that the client can
   gracefully determine the correct security flavor.

   If the current filehandle is a named attribute directory that is
   associated with a file system object via OPENATTR (i.e., not a sub-
   directory of a named attribute directory), LOOKUPP SHOULD return the
   filehandle of the associated file system object.

18.14.4.  IMPLEMENTATION

   An issue to note is upward navigation from named attribute
   directories.  The named attribute directories are essentially
   detached from the namespace, and this property should be safely
   represented in the client operating environment.  LOOKUPP on a named
   attribute directory may return the filehandle of the associated file,



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   and conveying this to applications might be unsafe as many
   applications expect the parent of an object to always be a directory.
   Therefore, the client may want to hide the parent of named attribute
   directories (represented as ".." in UNIX) or represent the named
   attribute directory as its own parent (as is typically done for the
   file system root directory in UNIX).

18.15.  Operation 17: NVERIFY - Verify Difference in Attributes

18.15.1.  ARGUMENTS

   struct NVERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };


18.15.2.  RESULTS

   struct NVERIFY4res {
           nfsstat4        status;
   };


18.15.3.  DESCRIPTION

   This operation is used to prefix a sequence of operations to be
   performed if one or more attributes have changed on some file system
   object.  If all the attributes match, then the error NFS4ERR_SAME
   MUST be returned.

   On success, the current filehandle retains its value.

18.15.4.  IMPLEMENTATION

   This operation is useful as a cache validation operator.  If the
   object to which the attributes belong has changed, then the following
   operations may obtain new data associated with that object, for
   instance, to check if a file has been changed and obtain new data if
   it has:

         SEQUENCE
         PUTFH fh
         NVERIFY attrbits attrs
         READ 0 32767

   Contrast this with NFSv3, which would first send a GETATTR in one
   request/reply round trip, and then if attributes indicated that the



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   client's cache was stale, then send a READ in another request/reply
   round trip.

   In the case that a RECOMMENDED attribute is specified in the NVERIFY
   operation and the server does not support that attribute for the file
   system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any set-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.

18.16.  Operation 18: OPEN - Open a Regular File

18.16.1.  ARGUMENTS

   /*
    * Various definitions for OPEN
    */
   enum createmode4 {
           UNCHECKED4      = 0,
           GUARDED4        = 1,
           /* Deprecated in NFSv4.1. */
           EXCLUSIVE4      = 2,
           /*
            * New to NFSv4.1. If session is persistent,
            * GUARDED4 MUST be used.  Otherwise, use
            * EXCLUSIVE4_1 instead of EXCLUSIVE4.
            */
           EXCLUSIVE4_1    = 3
   };

   struct creatverfattr {
            verifier4      cva_verf;
            fattr4         cva_attrs;
   };

   union createhow4 switch (createmode4 mode) {
    case UNCHECKED4:
    case GUARDED4:
            fattr4         createattrs;
    case EXCLUSIVE4:
            verifier4      createverf;
    case EXCLUSIVE4_1:
            creatverfattr  ch_createboth;
   };

   enum opentype4 {



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           OPEN4_NOCREATE  = 0,
           OPEN4_CREATE    = 1
   };

   union openflag4 switch (opentype4 opentype) {
    case OPEN4_CREATE:
            createhow4     how;
    default:
            void;
   };

   /* Next definitions used for OPEN delegation */
   enum limit_by4 {
           NFS_LIMIT_SIZE          = 1,
           NFS_LIMIT_BLOCKS        = 2
           /* others as needed */
   };

   struct nfs_modified_limit4 {
           uint32_t        num_blocks;
           uint32_t        bytes_per_block;
   };

   union nfs_space_limit4 switch (limit_by4 limitby) {
    /* limit specified as file size */
    case NFS_LIMIT_SIZE:
            uint64_t               filesize;
    /* limit specified by number of blocks */
    case NFS_LIMIT_BLOCKS:
            nfs_modified_limit4    mod_blocks;
   } ;

   /*
    * Share Access and Deny constants for open argument
    */
   const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
   const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
   const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

   const OPEN4_SHARE_DENY_NONE     = 0x00000000;
   const OPEN4_SHARE_DENY_READ     = 0x00000001;
   const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
   const OPEN4_SHARE_DENY_BOTH     = 0x00000003;


   /* new flags for share_access field of OPEN4args */
   const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK        = 0xFF00;
   const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE     = 0x0000;



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   const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x0100;
   const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x0200;
   const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0300;
   const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x0400;
   const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x0500;

   const
    OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
    = 0x10000;

   const
    OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
    = 0x20000;

   enum open_delegation_type4 {
           OPEN_DELEGATE_NONE      = 0,
           OPEN_DELEGATE_READ      = 1,
           OPEN_DELEGATE_WRITE     = 2,
           OPEN_DELEGATE_NONE_EXT  = 3 /* new to v4.1 */
   };

   enum open_claim_type4 {
           /*
            * Not a reclaim.
            */
           CLAIM_NULL              = 0,

           CLAIM_PREVIOUS          = 1,
           CLAIM_DELEGATE_CUR      = 2,
           CLAIM_DELEGATE_PREV     = 3,

           /*
            * Not a reclaim.
            *
            * Like CLAIM_NULL, but object identified
            * by the current filehandle.
            */
           CLAIM_FH                = 4, /* new to v4.1 */

           /*
            * Like CLAIM_DELEGATE_CUR, but object identified
            * by current filehandle.
            */
           CLAIM_DELEG_CUR_FH      = 5, /* new to v4.1 */

           /*
            * Like CLAIM_DELEGATE_PREV, but object identified
            * by current filehandle.



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            */
           CLAIM_DELEG_PREV_FH     = 6 /* new to v4.1 */
   };

   struct open_claim_delegate_cur4 {
           stateid4        delegate_stateid;
           component4      file;
   };

   union open_claim4 switch (open_claim_type4 claim) {
    /*
     * No special rights to file.
     * Ordinary OPEN of the specified file.
     */
    case CLAIM_NULL:
           /* CURRENT_FH: directory */
           component4      file;
    /*
     * Right to the file established by an
     * open previous to server reboot.  File
     * identified by filehandle obtained at
     * that time rather than by name.
     */
    case CLAIM_PREVIOUS:
           /* CURRENT_FH: file being reclaimed */
           open_delegation_type4   delegate_type;

    /*
     * Right to file based on a delegation
     * granted by the server.  File is
     * specified by name.
     */
    case CLAIM_DELEGATE_CUR:
           /* CURRENT_FH: directory */
           open_claim_delegate_cur4        delegate_cur_info;

    /*
     * Right to file based on a delegation
     * granted to a previous boot instance
     * of the client.  File is specified by name.
     */
    case CLAIM_DELEGATE_PREV:
            /* CURRENT_FH: directory */
           component4      file_delegate_prev;

    /*
     * Like CLAIM_NULL.  No special rights
     * to file.  Ordinary OPEN of the



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     * specified file by current filehandle.
     */
    case CLAIM_FH: /* new to v4.1 */
           /* CURRENT_FH: regular file to open */
           void;

    /*
     * Like CLAIM_DELEGATE_PREV.  Right to file based on a
     * delegation granted to a previous boot
     * instance of the client.  File is identified by
     * by filehandle.
     */
    case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
           /* CURRENT_FH: file being opened */
           void;

    /*
     * Like CLAIM_DELEGATE_CUR.  Right to file based on
     * a delegation granted by the server.
     * File is identified by filehandle.
     */
    case CLAIM_DELEG_CUR_FH: /* new to v4.1 */
            /* CURRENT_FH: file being opened */
            stateid4       oc_delegate_stateid;

   };

   /*
    * OPEN: Open a file, potentially receiving an OPEN delegation
    */
   struct OPEN4args {
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
           open_owner4     owner;
           openflag4       openhow;
           open_claim4     claim;
   };


18.16.2.  RESULTS

   struct open_read_delegation4 {
    stateid4 stateid;    /* Stateid for delegation*/
    bool     recall;     /* Pre-recalled flag for
                            delegations obtained
                            by reclaim (CLAIM_PREVIOUS) */




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    nfsace4 permissions; /* Defines users who don't
                            need an ACCESS call to
                            open for read */
   };

   struct open_write_delegation4 {
    stateid4 stateid;      /* Stateid for delegation */
    bool     recall;       /* Pre-recalled flag for
                              delegations obtained
                              by reclaim
                              (CLAIM_PREVIOUS) */

    nfs_space_limit4
              space_limit; /* Defines condition that
                              the client must check to
                              determine whether the
                              file needs to be flushed
                              to the server on close.  */

    nfsace4   permissions; /* Defines users who don't
                              need an ACCESS call as
                              part of a delegated
                              open. */
   };


   enum why_no_delegation4 { /* new to v4.1 */
           WND4_NOT_WANTED         = 0,
           WND4_CONTENTION         = 1,
           WND4_RESOURCE           = 2,
           WND4_NOT_SUPP_FTYPE     = 3,
           WND4_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
           WND4_NOT_SUPP_UPGRADE   = 5,
           WND4_NOT_SUPP_DOWNGRADE = 6,
           WND4_CANCELLED          = 7,
           WND4_IS_DIR             = 8
   };

   union open_none_delegation4 /* new to v4.1 */
   switch (why_no_delegation4 ond_why) {
           case WND4_CONTENTION:
                   bool ond_server_will_push_deleg;
           case WND4_RESOURCE:
                   bool ond_server_will_signal_avail;
           default:
                   void;
   };




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   union open_delegation4
   switch (open_delegation_type4 delegation_type) {
           case OPEN_DELEGATE_NONE:
                   void;
           case OPEN_DELEGATE_READ:
                   open_read_delegation4 read;
           case OPEN_DELEGATE_WRITE:
                   open_write_delegation4 write;
           case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
                   open_none_delegation4 od_whynone;
   };

   /*
    * Result flags
    */

   /* Client must confirm open */
   const OPEN4_RESULT_CONFIRM      = 0x00000002;
   /* Type of file locking behavior at the server */
   const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
   /* Server will preserve file if removed while open */
   const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;

   /*
    * Server may use CB_NOTIFY_LOCK on locks
    * derived from this open
    */
   const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;

   struct OPEN4resok {
    stateid4       stateid;      /* Stateid for open */
    change_info4   cinfo;        /* Directory Change Info */
    uint32_t       rflags;       /* Result flags */
    bitmap4        attrset;      /* attribute set for create*/
    open_delegation4 delegation; /* Info on any open
                                    delegation */
   };

   union OPEN4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* New CURRENT_FH: opened file */
           OPEN4resok      resok4;
    default:
           void;
   };






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18.16.3.  DESCRIPTION

   The OPEN operation opens a regular file in a directory with the
   provided name or filehandle.  OPEN can also create a file if a name
   is provided, and the client specifies it wants to create a file.
   Specification of whether or not a file is to be created, and the
   method of creation is via the openhow parameter.  The openhow
   parameter consists of a switched union (data type opengflag4), which
   switches on the value of opentype (OPEN4_NOCREATE or OPEN4_CREATE).
   If OPEN4_CREATE is specified, this leads to another switched union
   (data type createhow4) that supports four cases of creation methods:
   UNCHECKED4, GUARDED4, EXCLUSIVE4, or EXCLUSIVE4_1.  If opentype is
   OPEN4_CREATE, then the claim field of the claim field MUST be one of
   CLAIM_NULL, CLAIM_DELEGATE_CUR, or CLAIM_DELEGATE_PREV, because these
   claim methods include a component of a file name.

   Upon success (which might entail creation of a new file), the current
   filehandle is replaced by that of the created or existing object.

   If the current filehandle is a named attribute directory, OPEN will
   then create or open a named attribute file.  Note that exclusive
   create of a named attribute is not supported.  If the createmode is
   EXCLUSIVE4 or EXCLUSIVE4_1 and the current filehandle is a named
   attribute directory, the server will return EINVAL.

   UNCHECKED4 means that the file should be created if a file of that
   name does not exist and encountering an existing regular file of that
   name is not an error.  For this type of create, createattrs specifies
   the initial set of attributes for the file.  The set of attributes
   may include any writable attribute valid for regular files.  When an
   UNCHECKED4 create encounters an existing file, the attributes
   specified by createattrs are not used, except that when createattrs
   specifies the size attribute with a size of zero, the existing file
   is truncated.

   If GUARDED4 is specified, the server checks for the presence of a
   duplicate object by name before performing the create.  If a
   duplicate exists, NFS4ERR_EXIST is returned.  If the object does not
   exist, the request is performed as described for UNCHECKED4.

   For the UNCHECKED4 and GUARDED4 cases, where the operation is
   successful, the server will return to the client an attribute mask
   signifying which attributes were successfully set for the object.

   EXCLUSIVE4_1 and EXCLUSIVE4 specify that the server is to follow
   exclusive creation semantics, using the verifier to ensure exclusive
   creation of the target.  The server should check for the presence of
   a duplicate object by name.  If the object does not exist, the server



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   creates the object and stores the verifier with the object.  If the
   object does exist and the stored verifier matches the client provided
   verifier, the server uses the existing object as the newly created
   object.  If the stored verifier does not match, then an error of
   NFS4ERR_EXIST is returned.

   If using EXCLUSIVE4, and if the server uses attributes to store the
   exclusive create verifier, the server will signify which attributes
   it used by setting the appropriate bits in the attribute mask that is
   returned in the results.  Unlike UNCHECKED4, GUARDED4, and
   EXCLUSIVE4_1, EXCLUSIVE4 does not support the setting of attributes
   at file creation, and after a successful OPEN via EXCLUSIVE4, the
   client MUST send a SETATTR to set attributes to a known state.

   In NFSv4.1, EXCLUSIVE4 has been deprecated in favor of EXCLUSIVE4_1.
   Unlike EXCLUSIVE4, attributes may be provided in the EXCLUSIVE4_1
   case, but because the server may use attributes of the target object
   to store the verifier, the set of allowable attributes may be fewer
   than the set of attributes SETATTR allows.  The allowable attributes
   for EXCLUSIVE4_1 are indicated in the suppattr_exclcreat
   (Section 5.8.1.14) attribute.  If the client attempts to set in
   cva_attrs an attribute that is not in suppattr_exclcreat, the server
   MUST return NFS4ERR_INVAL.  The response field, attrset, indicates
   both which attributes the server set from cva_attrs and which
   attributes the server used to store the verifier.  As described in
   Section 18.16.4, the client can compare cva_attrs.attrmask with
   attrset to determine which attributes were used to store the
   verifier.

   With the addition of persistent sessions and pNFS, under some
   conditions EXCLUSIVE4 MUST NOT be used by the client or supported by
   the server.  The following table summarizes the appropriate and
   mandated exclusive create methods for implementations of NFSv4.1:


















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                   Required methods for exclusive create

   +----------------+-----------+---------------+----------------------+
   | Persistent     | Server    | Server        | Client Allowed       |
   | Reply Cache    | Supports  | REQUIRED      |                      |
   | Enabled        | pNFS      |               |                      |
   +----------------+-----------+---------------+----------------------+
   | no             | no        | EXCLUSIVE4_1  | EXCLUSIVE4_1         |
   |                |           | and           | (SHOULD) or          |
   |                |           | EXCLUSIVE4    | EXCLUSIVE4 (SHOULD   |
   |                |           |               | NOT)                 |
   | no             | yes       | EXCLUSIVE4_1  | EXCLUSIVE4_1         |
   | yes            | no        | GUARDED4      | GUARDED4             |
   | yes            | yes       | GUARDED4      | GUARDED4             |
   +----------------+-----------+---------------+----------------------+

                                 Table 10

   If CREATE_SESSION4_FLAG_PERSIST is set in the results of
   CREATE_SESSION, the reply cache is persistent (see Section 18.36).
   If the EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the results from
   EXCHANGE_ID, the server is a pNFS server (see Section 18.35).  If the
   client attempts to use EXCLUSIVE4 on a persistent session, or a
   session derived from an EXCHGID4_FLAG_USE_PNFS_MDS client ID, the
   server MUST return NFS4ERR_INVAL.

   With persistent sessions, exclusive create semantics are fully
   achievable via GUARDED4, and so EXCLUSIVE4 or EXCLUSIVE4_1 MUST NOT
   be used.  When pNFS is being used, the layout_hint attribute might
   not be supported after the file is created.  Only the EXCLUSIVE4_1
   and GUARDED methods of exclusive file creation allow the atomic
   setting of attributes.

   For the target directory, the server returns change_info4 information
   in cinfo.  With the atomic field of the change_info4 data type, the
   server will indicate if the before and after change attributes were
   obtained atomically with respect to the link creation.

   The OPEN operation provides for Windows share reservation capability
   with the use of the share_access and share_deny fields of the OPEN
   arguments.  The client specifies at OPEN the required share_access
   and share_deny modes.  For clients that do not directly support
   SHAREs (i.e., UNIX), the expected deny value is
   OPEN4_SHARE_DENY_NONE.  In the case that there is an existing SHARE
   reservation that conflicts with the OPEN request, the server returns
   the error NFS4ERR_SHARE_DENIED.  For additional discussion of SHARE
   semantics, see Section 9.7.




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   For each OPEN, the client provides a value for the owner field of the
   OPEN argument.  The owner field is of data type open_owner4, and
   contains a field called clientid and a field called owner.  The
   client can set the clientid field to any value and the server MUST
   ignore it.  Instead, the server MUST derive the client ID from the
   session ID of the SEQUENCE operation of the COMPOUND request.

   The "seqid" field of the request is not used in NFSv4.1, but it MAY
   be any value and the server MUST ignore it.

   In the case that the client is recovering state from a server
   failure, the claim field of the OPEN argument is used to signify that
   the request is meant to reclaim state previously held.

   The "claim" field of the OPEN argument is used to specify the file to
   be opened and the state information that the client claims to
   possess.  There are seven claim types as follows:


































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   +----------------------+--------------------------------------------+
   | open type            | description                                |
   +----------------------+--------------------------------------------+
   | CLAIM_NULL, CLAIM_FH | For the client, this is a new OPEN request |
   |                      | and there is no previous state associated  |
   |                      | with the file for the client.  With        |
   |                      | CLAIM_NULL, the file is identified by the  |
   |                      | current filehandle and the specified       |
   |                      | component name.  With CLAIM_FH (new to     |
   |                      | NFSv4.1), the file is identified by just   |
   |                      | the current filehandle.                    |
   | CLAIM_PREVIOUS       | The client is claiming basic OPEN state    |
   |                      | for a file that was held previous to a     |
   |                      | server restart.  Generally used when a     |
   |                      | server is returning persistent             |
   |                      | filehandles; the client may not have the   |
   |                      | file name to reclaim the OPEN.             |
   | CLAIM_DELEGATE_CUR,  | The client is claiming a delegation for    |
   | CLAIM_DELEG_CUR_FH   | OPEN as granted by the server.  Generally, |
   |                      | this is done as part of recalling a        |
   |                      | delegation.  With CLAIM_DELEGATE_CUR, the  |
   |                      | file is identified by the current          |
   |                      | filehandle and the specified component     |
   |                      | name.  With CLAIM_DELEG_CUR_FH (new to     |
   |                      | NFSv4.1), the file is identified by just   |
   |                      | the current filehandle.                    |
   | CLAIM_DELEGATE_PREV, | The client is claiming a delegation        |
   | CLAIM_DELEG_PREV_FH  | granted to a previous client instance;     |
   |                      | used after the client restarts. The server |
   |                      | MAY support CLAIM_DELEGATE_PREV and/or     |
   |                      | CLAIM_DELEG_PREV_FH (new to NFSv4.1).  If  |
   |                      | it does support either claim type,         |
   |                      | CREATE_SESSION MUST NOT remove the         |
   |                      | client's delegation state, and the server  |
   |                      | MUST support the DELEGPURGE operation.     |
   +----------------------+--------------------------------------------+

   For OPEN requests that reach the server during the grace period, the
   server returns an error of NFS4ERR_GRACE.  The following claim types
   are exceptions:

   o  OPEN requests specifying the claim type CLAIM_PREVIOUS are devoted
      to reclaiming opens after a server restart and are typically only
      valid during the grace period.

   o  OPEN requests specifying the claim types CLAIM_DELEGATE_CUR and
      CLAIM_DELEG_CUR_FH are valid both during and after the grace
      period.  Since the granting of the delegation that they are



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      subordinate to assures that there is no conflict with locks to be
      reclaimed by other clients, the server need not return
      NFS4ERR_GRACE when these are received during the grace period.

   For any OPEN request, the server may return an OPEN delegation, which
   allows further opens and closes to be handled locally on the client
   as described in Section 10.4.  Note that delegation is up to the
   server to decide.  The client should never assume that delegation
   will or will not be granted in a particular instance.  It should
   always be prepared for either case.  A partial exception is the
   reclaim (CLAIM_PREVIOUS) case, in which a delegation type is claimed.
   In this case, delegation will always be granted, although the server
   may specify an immediate recall in the delegation structure.

   The rflags returned by a successful OPEN allow the server to return
   information governing how the open file is to be handled.

   o  OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned by an
      NFSv4.1 server.

   o  OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's byte-range
      locking behavior supports the complete set of POSIX locking
      techniques [24].  From this, the client can choose to manage byte-
      range locking state in a way to handle a mismatch of byte-range
      locking management.

   o  OPEN4_RESULT_PRESERVE_UNLINKED indicates that the server will
      preserve the open file if the client (or any other client) removes
      the file as long as it is open.  Furthermore, the server promises
      to preserve the file through the grace period after server
      restart, thereby giving the client the opportunity to reclaim its
      open.

   o  OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
      CB_NOTIFY_LOCK callbacks for locks on this file.  This flag is a
      hint only, and may be safely ignored by the client.

   If the component is of zero length, NFS4ERR_INVAL will be returned.
   The component is also subject to the normal UTF-8, character support,
   and name checks.  See Section 14.5 for further discussion.

   When an OPEN is done and the specified open-owner already has the
   resulting filehandle open, the result is to "OR" together the new
   share and deny status together with the existing status.  In this
   case, only a single CLOSE need be done, even though multiple OPENs
   were completed.  When such an OPEN is done, checking of share
   reservations for the new OPEN proceeds normally, with no exception
   for the existing OPEN held by the same open-owner.  In this case, the



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   stateid returned as an "other" field that matches that of the
   previous open while the "seqid" field is incremented to reflect the
   change status due to the new open.

   If the underlying file system at the server is only accessible in a
   read-only mode and the OPEN request has specified ACCESS_WRITE or
   ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a read-
   only file system.

   As with the CREATE operation, the server MUST derive the owner, owner
   ACE, group, or group ACE if any of the four attributes are required
   and supported by the server's file system.  For an OPEN with the
   EXCLUSIVE4 createmode, the server has no choice, since such OPEN
   calls do not include the createattrs field.  Conversely, if
   createattrs (UNCHECKED4 or GUARDED4) or cva_attrs (EXCLUSIVE4_1) is
   specified, and includes an owner, owner_group, or ACE that the
   principal in the RPC call's credentials does not have authorization
   to create files for, then the server may return NFS4ERR_PERM.

   In the case of an OPEN that specifies a size of zero (e.g.,
   truncation) and the file has named attributes, the named attributes
   are left as is and are not removed.

   NFSv4.1 gives more precise control to clients over acquisition of
   delegations via the following new flags for the share_access field of
   OPEN4args:

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL

   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED

   If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is not zero,
   then the client will have specified one and only one of:

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG




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   OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG

   OPEN4_SHARE_ACCESS_WANT_CANCEL

   Otherwise, the client is neither indicating a desire nor a non-desire
   for a delegation, and the server MAY or MAY not return a delegation
   in the OPEN response.

   If the server supports the new _WANT_ flags and the client sends one
   or more of the new flags, then in the event the server does not
   return a delegation, it MUST return a delegation type of
   OPEN_DELEGATE_NONE_EXT.  The field ond_why in the reply indicates why
   no delegation was returned and will be one of:

   WND4_NOT_WANTED  The client specified
      OPEN4_SHARE_ACCESS_WANT_NO_DELEG.

   WND4_CONTENTION  There is a conflicting delegation or open on the
      file.

   WND4_RESOURCE  Resource limitations prevent the server from granting
      a delegation.

   WND4_NOT_SUPP_FTYPE  The server does not support delegations on this
      file type.

   WND4_WRITE_DELEG_NOT_SUPP_FTYPE  The server does not support
      OPEN_DELEGATE_WRITE delegations on this file type.

   WND4_NOT_SUPP_UPGRADE  The server does not support atomic upgrade of
      an OPEN_DELEGATE_READ delegation to an OPEN_DELEGATE_WRITE
      delegation.

   WND4_NOT_SUPP_DOWNGRADE  The server does not support atomic downgrade
      of an OPEN_DELEGATE_WRITE delegation to an OPEN_DELEGATE_READ
      delegation.

   WND4_CANCELED  The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL
      and now any "want" for this file object is cancelled.

   WND4_IS_DIR  The specified file object is a directory, and the
      operation is OPEN or WANT_DELEGATION, which do not support
      delegations on directories.

   OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
   OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or



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   OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the client wants
   an OPEN_DELEGATE_READ, OPEN_DELEGATE_WRITE, or any delegation
   regardless which of OPEN4_SHARE_ACCESS_READ,
   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH is set.  If the
   client has an OPEN_DELEGATE_READ delegation on a file and requests an
   OPEN_DELEGATE_WRITE delegation, then the client is requesting atomic
   upgrade of its OPEN_DELEGATE_READ delegation to an
   OPEN_DELEGATE_WRITE delegation.  If the client has an
   OPEN_DELEGATE_WRITE delegation on a file and requests an
   OPEN_DELEGATE_READ delegation, then the client is requesting atomic
   downgrade to an OPEN_DELEGATE_READ delegation.  A server MAY support
   atomic upgrade or downgrade.  If it does, then the returned
   delegation_type of OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE that is
   different from the delegation type the client currently has,
   indicates successful upgrade or downgrade.  If the server does not
   support atomic delegation upgrade or downgrade, then ond_why will be
   set to WND4_NOT_SUPP_UPGRADE or WND4_NOT_SUPP_DOWNGRADE.

   OPEN4_SHARE_ACCESS_WANT_NO_DELEG means that the client wants no
   delegation.

   OPEN4_SHARE_ACCESS_WANT_CANCEL means that the client wants no
   delegation and wants to cancel any previously registered "want" for a
   delegation.

   The client may set one or both of
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
   OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED.  However, they
   will have no effect unless one of following is set:

   o  OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to insufficient resources, the server MAY later inform
   the client, via the CB_RECALLABLE_OBJ_AVAIL operation, that the
   resource limitation condition has eased.  The server will tell the
   client that it intends to send a future CB_RECALLABLE_OBJ_AVAIL
   operation by setting delegation_type in the results to
   OPEN_DELEGATE_NONE_EXT, ond_why to WND4_RESOURCE, and
   ond_server_will_signal_avail set to TRUE.  If




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   ond_server_will_signal_avail is set to TRUE, the server MUST later
   send a CB_RECALLABLE_OBJ_AVAIL operation.

   If the client specifies
   OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it wishes
   to register a "want" for a delegation, in the event the OPEN results
   do not include a delegation.  If so and the server denies the
   delegation due to contention, the server MAY later inform the client,
   via the CB_PUSH_DELEG operation, that the contention condition has
   eased.  The server will tell the client that it intends to send a
   future CB_PUSH_DELEG operation by setting delegation_type in the
   results to OPEN_DELEGATE_NONE_EXT, ond_why to WND4_CONTENTION, and
   ond_server_will_push_deleg to TRUE.  If ond_server_will_push_deleg is
   TRUE, the server MUST later send a CB_PUSH_DELEG operation.

   If the client has previously registered a want for a delegation on a
   file, and then sends a request to register a want for a delegation on
   the same file, the server MUST return a new error:
   NFS4ERR_DELEG_ALREADY_WANTED.  If the client wishes to register a
   different type of delegation want for the same file, it MUST cancel
   the existing delegation WANT.

18.16.4.  IMPLEMENTATION

   In absence of a persistent session, the client invokes exclusive
   create by setting the how parameter to EXCLUSIVE4 or EXCLUSIVE4_1.
   In these cases, the client provides a verifier that can reasonably be
   expected to be unique.  A combination of a client identifier, perhaps
   the client network address, and a unique number generated by the
   client, perhaps the RPC transaction identifier, may be appropriate.

   If the object does not exist, the server creates the object and
   stores the verifier in stable storage.  For file systems that do not
   provide a mechanism for the storage of arbitrary file attributes, the
   server may use one or more elements of the object's metadata to store
   the verifier.  The verifier MUST be stored in stable storage to
   prevent erroneous failure on retransmission of the request.  It is
   assumed that an exclusive create is being performed because exclusive
   semantics are critical to the application.  Because of the expected
   usage, exclusive CREATE does not rely solely on the server's reply
   cache for storage of the verifier.  A nonpersistent reply cache does
   not survive a crash and the session and reply cache may be deleted
   after a network partition that exceeds the lease time, thus opening
   failure windows.

   An NFSv4.1 server SHOULD NOT store the verifier in any of the file's
   RECOMMENDED or REQUIRED attributes.  If it does, the server SHOULD




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   use time_modify_set or time_access_set to store the verifier.  The
   server SHOULD NOT store the verifier in the following attributes:

      acl (it is desirable for access control to be established at
      creation),

      dacl (ditto),

      mode (ditto),

      owner (ditto),

      owner_group (ditto),

      retentevt_set (it may be desired to establish retention at
      creation)

      retention_hold (ditto),

      retention_set (ditto),

      sacl (it is desirable for auditing control to be established at
      creation),

      size (on some servers, size may have a limited range of values),

      mode_set_masked (as with mode),

         and

      time_creation (a meaningful file creation should be set when the
      file is created).

   Another alternative for the server is to use a named attribute to
   store the verifier.

   Because the EXCLUSIVE4 create method does not specify initial
   attributes when processing an EXCLUSIVE4 create, the server

   o  SHOULD set the owner of the file to that corresponding to the
      credential of request's RPC header.

   o  SHOULD NOT leave the file's access control to anyone but the owner
      of the file.

   If the server cannot support exclusive create semantics, possibly
   because of the requirement to commit the verifier to stable storage,
   it should fail the OPEN request with the error NFS4ERR_NOTSUPP.



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   During an exclusive CREATE request, if the object already exists, the
   server reconstructs the object's verifier and compares it with the
   verifier in the request.  If they match, the server treats the
   request as a success.  The request is presumed to be a duplicate of
   an earlier, successful request for which the reply was lost and that
   the server duplicate request cache mechanism did not detect.  If the
   verifiers do not match, the request is rejected with the status
   NFS4ERR_EXIST.

   After the client has performed a successful exclusive create, the
   attrset response indicates which attributes were used to store the
   verifier.  If EXCLUSIVE4 was used, the attributes set in attrset were
   used for the verifier.  If EXCLUSIVE4_1 was used, the client
   determines the attributes used for the verifier by comparing attrset
   with cva_attrs.attrmask; any bits set in the former but not the
   latter identify the attributes used to store the verifier.  The
   client MUST immediately send a SETATTR to set attributes used to
   store the verifier.  Until it does so, the attributes used to store
   the verifier cannot be relied upon.  The subsequent SETATTR MUST NOT
   occur in the same COMPOUND request as the OPEN.

   Unless a persistent session is used, use of the GUARDED4 attribute
   does not provide exactly once semantics.  In particular, if a reply
   is lost and the server does not detect the retransmission of the
   request, the operation can fail with NFS4ERR_EXIST, even though the
   create was performed successfully.  The client would use this
   behavior in the case that the application has not requested an
   exclusive create but has asked to have the file truncated when the
   file is opened.  In the case of the client timing out and
   retransmitting the create request, the client can use GUARDED4 to
   prevent against a sequence like create, write, create (retransmitted)
   from occurring.

   For SHARE reservations, the value of the expression (share_access &
   ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) MUST be one of
   OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
   OPEN4_SHARE_ACCESS_BOTH.  If not, the server MUST return
   NFS4ERR_INVAL.  The value of share_deny MUST be one of
   OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE,
   or OPEN4_SHARE_DENY_BOTH.  If not, the server MUST return
   NFS4ERR_INVAL.

   Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH), the client
   should check that the requester has the proper access rights to
   perform the specified operation.  This would generally be the results
   of applying the ACL access rules to the file for the current
   requester.  However, just as with the ACCESS operation, the client



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   should not attempt to second-guess the server's decisions, as access
   rights may change and may be subject to server administrative
   controls outside the ACL framework.  If the requester's READ or WRITE
   operation is not authorized (depending on the share_access value),
   the server MUST return NFS4ERR_ACCESS.

   Note that if the client ID was not created with the
   EXCHGID4_FLAG_BIND_PRINC_STATEID capability set in the reply to
   EXCHANGE_ID, then the server MUST NOT impose any requirement that
   READs and WRITEs sent for an open file have the same credentials as
   the OPEN itself, and the server is REQUIRED to perform access
   checking on the READs and WRITEs themselves.  Otherwise, if the reply
   to EXCHANGE_ID did have EXCHGID4_FLAG_BIND_PRINC_STATEID set, then
   with one exception, the credentials used in the OPEN request MUST
   match those used in the READs and WRITEs, and the stateids in the
   READs and WRITEs MUST match, or be derived from the stateid from the
   reply to OPEN.  The exception is if SP4_SSV or SP4_MACH_CRED state
   protection is used, and the spo_must_allow result of EXCHANGE_ID
   includes the READ and/or WRITE operations.  In that case, the machine
   or SSV credential will be allowed to send READ and/or WRITE.  See
   Section 18.35.

   If the component provided to OPEN is a symbolic link, the error
   NFS4ERR_SYMLINK will be returned to the client, while if it is a
   directory the error NFS4ERR_ISDIR will be returned.  If the component
   is neither of those but not an ordinary file, the error
   NFS4ERR_WRONG_TYPE is returned.  If the current filehandle is not a
   directory, the error NFS4ERR_NOTDIR will be returned.

   The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows a
   client to avoid the common implementation practice of renaming an
   open file to ".nfs<unique value>" after it removes the file.  After
   the server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client sends
   a REMOVE operation that would reduce the file's link count to zero,
   the server SHOULD report a value of zero for the numlinks attribute
   on the file.

   If another client has a delegation of the file being opened that
   conflicts with open being done (sometimes depending on the
   share_access or share_deny value specified), the delegation(s) MUST
   be recalled, and the operation cannot proceed until each such
   delegation is returned or revoked.  Except where this happens very
   quickly, one or more NFS4ERR_DELAY errors will be returned to
   requests made while delegation remains outstanding.  In the case of
   an OPEN_DELEGATE_WRITE delegation, any open by a different client
   will conflict, while for an OPEN_DELEGATE_READ delegation, only opens
   with one of the following characteristics will be considered
   conflicting:



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   o  The value of share_access includes the bit
      OPEN4_SHARE_ACCESS_WRITE.

   o  The value of share_deny specifies OPEN4_SHARE_DENY_READ or
      OPEN4_SHARE_DENY_BOTH.

   o  OPEN4_CREATE is specified together with UNCHECKED4, the size
      attribute is specified as zero (for truncation), and an existing
      file is truncated.

   If OPEN4_CREATE is specified and the file does not exist and the
   current filehandle designates a directory for which another client
   holds a directory delegation, then, unless the delegation is such
   that the situation can be resolved by sending a notification, the
   delegation MUST be recalled, and the operation cannot proceed until
   the delegation is returned or revoked.  Except where this happens
   very quickly, one or more NFS4ERR_DELAY errors will be returned to
   requests made while delegation remains outstanding.

   If OPEN4_CREATE is specified and the file does not exist and the
   current filehandle designates a directory for which one or more
   directory delegations exist, then, when those delegations request
   such notifications, NOTIFY4_ADD_ENTRY will be generated as a result
   of this operation.

18.16.4.1.  Warning to Client Implementors

   OPEN resembles LOOKUP in that it generates a filehandle for the
   client to use.  Unlike LOOKUP though, OPEN creates server state on
   the filehandle.  In normal circumstances, the client can only release
   this state with a CLOSE operation.  CLOSE uses the current filehandle
   to determine which file to close.  Therefore, the client MUST follow
   every OPEN operation with a GETFH operation in the same COMPOUND
   procedure.  This will supply the client with the filehandle such that
   CLOSE can be used appropriately.

   Simply waiting for the lease on the file to expire is insufficient
   because the server may maintain the state indefinitely as long as
   another client does not attempt to make a conflicting access to the
   same file.

   See also Section 2.10.6.4.

18.17.  Operation 19: OPENATTR - Open Named Attribute Directory







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18.17.1.  ARGUMENTS

   struct OPENATTR4args {
           /* CURRENT_FH: object */
           bool    createdir;
   };


18.17.2.  RESULTS

   struct OPENATTR4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: named attribute
            *                   directory
            */
           nfsstat4        status;
   };


18.17.3.  DESCRIPTION

   The OPENATTR operation is used to obtain the filehandle of the named
   attribute directory associated with the current filehandle.  The
   result of the OPENATTR will be a filehandle to an object of type
   NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
   be used to obtain filehandles for the various named attributes
   associated with the original file system object.  Filehandles
   returned within the named attribute directory will designate objects
   of type of NF4NAMEDATTR.

   The createdir argument allows the client to signify if a named
   attribute directory should be created as a result of the OPENATTR
   operation.  Some clients may use the OPENATTR operation with a value
   of FALSE for createdir to determine if any named attributes exist for
   the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
   createdir has a value of TRUE and no named attribute directory
   exists, one is created and its filehandle becomes the current
   filehandle.  On the other hand, if createdir has a value of TRUE and
   the named attribute directory already exists, no error results and
   the filehandle of the existing directory becomes the current
   filehandle.  The creation of a named attribute directory assumes that
   the server has implemented named attribute support in this fashion
   and is not required to do so by this definition.

   If the current file handle designates an object of type NF4NAMEDATTR
   (a named attribute) or NF4ATTRDIR (a named attribute directory), an
   error of NFS4ERR_WRONG_TYPE is returned to the client.  Named



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   attributes or a named attribute directory MUST NOT have their own
   named attributes.

18.17.4.  IMPLEMENTATION

   If the server does not support named attributes for the current
   filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
   client.

18.18.  Operation 21: OPEN_DOWNGRADE - Reduce Open File Access

18.18.1.  ARGUMENTS

   struct OPEN_DOWNGRADE4args {
           /* CURRENT_FH: opened file */
           stateid4        open_stateid;
           seqid4          seqid;
           uint32_t        share_access;
           uint32_t        share_deny;
   };


18.18.2.  RESULTS

   struct OPEN_DOWNGRADE4resok {
           stateid4        open_stateid;
   };

   union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
    case NFS4_OK:
           OPEN_DOWNGRADE4resok    resok4;
    default:
            void;
   };


18.18.3.  DESCRIPTION

   This operation is used to adjust the access and deny states for a
   given open.  This is necessary when a given open-owner opens the same
   file multiple times with different access and deny values.  In this
   situation, a close of one of the opens may change the appropriate
   share_access and share_deny flags to remove bits associated with
   opens no longer in effect.

   Valid values for the expression (share_access &
   ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) are OPEN4_SHARE_ACCESS_READ,




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   OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH.  If the client
   specifies other values, the server MUST reply with NFS4ERR_INVAL.

   Valid values for the share_deny field are OPEN4_SHARE_DENY_NONE,
   OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or
   OPEN4_SHARE_DENY_BOTH.  If the client specifies other values, the
   server MUST reply with NFS4ERR_INVAL.

   After checking for valid values of share_access and share_deny, the
   server replaces the current access and deny modes on the file with
   share_access and share_deny subject to the following constraints:

   o  The bits in share_access SHOULD equal the union of the
      share_access bits (not including OPEN4_SHARE_WANT_* bits)
      specified for some subset of the OPENs in effect for the current
      open-owner on the current file.

   o  The bits in share_deny SHOULD equal the union of the share_deny
      bits specified for some subset of the OPENs in effect for the
      current open-owner on the current file.

   If the above constraints are not respected, the server SHOULD return
   the error NFS4ERR_INVAL.  Since share_access and share_deny bits
   should be subsets of those already granted, short of a defect in the
   client or server implementation, it is not possible for the
   OPEN_DOWNGRADE request to be denied because of conflicting share
   reservations.

   The seqid argument is not used in NFSv4.1, MAY be any value, and MUST
   be ignored by the server.

   On success, the current filehandle retains its value.

18.18.4.  IMPLEMENTATION

   An OPEN_DOWNGRADE operation may make OPEN_DELEGATE_READ delegations
   grantable where they were not previously.  Servers may choose to
   respond immediately if there are pending delegation want requests or
   may respond to the situation at a later time.

18.19.  Operation 22: PUTFH - Set Current Filehandle

18.19.1.  ARGUMENTS

   struct PUTFH4args {
           nfs_fh4         object;
   };




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18.19.2.  RESULTS

   struct PUTFH4res {
           /*
            * If status is NFS4_OK,
            *    new CURRENT_FH: argument to PUTFH
            */
           nfsstat4        status;
   };


18.19.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   provided as an argument.  It clears the current stateid.

   If the security mechanism used by the requester does not meet the
   requirements of the filehandle provided to this operation, the server
   MUST return NFS4ERR_WRONGSEC.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.19.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.

18.20.  Operation 23: PUTPUBFH - Set Public Filehandle

18.20.1.  ARGUMENT

   void;

18.20.2.  RESULT

   struct PUTPUBFH4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: public fh
            */
           nfsstat4        status;
   };







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18.20.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   that represents the public filehandle of the server's namespace.
   This filehandle may be different from the "root" filehandle that may
   be associated with some other directory on the server.

   PUTPUBFH also clears the current stateid.

   The public filehandle represents the concepts embodied in RFC 2054
   [42], RFC 2055 [43], and RFC 2224 [53].  The intent for NFSv4.1 is
   that the public filehandle (represented by the PUTPUBFH operation) be
   used as a method of providing WebNFS server compatibility with NFSv3.

   The public filehandle and the root filehandle (represented by the
   PUTROOTFH operation) SHOULD be equivalent.  If the public and root
   filehandles are not equivalent, then the directory corresponding to
   the public filehandle MUST be a descendant of the directory
   corresponding to the root filehandle.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.20.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.

   With the NFSv3 public filehandle, the client is able to specify
   whether the pathname provided in the LOOKUP should be evaluated as
   either an absolute path relative to the server's root or relative to
   the public filehandle.  RFC 2224 [53] contains further discussion of
   the functionality.  With NFSv4.1, that type of specification is not
   directly available in the LOOKUP operation.  The reason for this is
   because the component separators needed to specify absolute vs.
   relative are not allowed in NFSv4.  Therefore, the client is
   responsible for constructing its request such that the use of either
   PUTROOTFH or PUTPUBFH signifies absolute or relative evaluation of an
   NFS URL, respectively.

   Note that there are warnings mentioned in RFC 2224 [53] with respect
   to the use of absolute evaluation and the restrictions the server may
   place on that evaluation with respect to how much of its namespace
   has been made available.  These same warnings apply to NFSv4.1.  It
   is likely, therefore, that because of server implementation details,
   an NFSv3 absolute public filehandle look up may behave differently
   than an NFSv4.1 absolute resolution.



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   There is a form of security negotiation as described in RFC 2755 [54]
   that uses the public filehandle and an overloading of the pathname.
   This method is not available with NFSv4.1 as filehandles are not
   overloaded with special meaning and therefore do not provide the same
   framework as NFSv3.  Clients should therefore use the security
   negotiation mechanisms described in Section 2.6.

18.21.  Operation 24: PUTROOTFH - Set Root Filehandle

18.21.1.  ARGUMENTS

   void;

18.21.2.  RESULTS

   struct PUTROOTFH4res {
           /*
            * If status is NFS4_OK,
            *   new CURRENT_FH: root fh
            */
           nfsstat4        status;
   };


18.21.3.  DESCRIPTION

   This operation replaces the current filehandle with the filehandle
   that represents the root of the server's namespace.  From this
   filehandle, a LOOKUP operation can locate any other filehandle on the
   server.  This filehandle may be different from the "public"
   filehandle that may be associated with some other directory on the
   server.

   PUTROOTFH also clears the current stateid.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.21.4.  IMPLEMENTATION

   This operation is used in an NFS request to set the context for file
   accessing operations that follow in the same COMPOUND request.








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18.22.  Operation 25: READ - Read from File

18.22.1.  ARGUMENTS

   struct READ4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           count4          count;
   };


18.22.2.  RESULTS

   struct READ4resok {
           bool            eof;
           opaque          data<>;
   };

   union READ4res switch (nfsstat4 status) {
    case NFS4_OK:
            READ4resok     resok4;
    default:
            void;
   };


18.22.3.  DESCRIPTION

   The READ operation reads data from the regular file identified by the
   current filehandle.

   The client provides an offset of where the READ is to start and a
   count of how many bytes are to be read.  An offset of zero means to
   read data starting at the beginning of the file.  If offset is
   greater than or equal to the size of the file, the status NFS4_OK is
   returned with a data length set to zero and eof is set to TRUE.  The
   READ is subject to access permissions checking.

   If the client specifies a count value of zero, the READ succeeds and
   returns zero bytes of data again subject to access permissions
   checking.  The server may choose to return fewer bytes than specified
   by the client.  The client needs to check for this condition and
   handle the condition appropriately.

   Except when special stateids are used, the stateid value for a READ
   request represents a value returned from a previous byte-range lock
   or share reservation request or the stateid associated with a



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   delegation.  The stateid identifies the associated owners if any and
   is used by the server to verify that the associated locks are still
   valid (e.g., have not been revoked).

   If the read ended at the end-of-file (formally, in a correctly formed
   READ operation, if offset + count is equal to the size of the file),
   or the READ operation extends beyond the size of the file (if offset
   + count is greater than the size of the file), eof is returned as
   TRUE; otherwise, it is FALSE.  A successful READ of an empty file
   will always return eof as TRUE.

   If the current filehandle is not an ordinary file, an error will be
   returned to the client.  In the case that the current filehandle
   represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.  If
   the current filehandle designates a symbolic link, NFS4ERR_SYMLINK is
   returned.  In all other cases, NFS4ERR_WRONG_TYPE is returned.

   For a READ with a stateid value of all bits equal to zero, the server
   MAY allow the READ to be serviced subject to mandatory byte-range
   locks or the current share deny modes for the file.  For a READ with
   a stateid value of all bits equal to one, the server MAY allow READ
   operations to bypass locking checks at the server.

   On success, the current filehandle retains its value.

18.22.4.  IMPLEMENTATION

   If the server returns a "short read" (i.e., fewer data than requested
   and eof is set to FALSE), the client should send another READ to get
   the remaining data.  A server may return less data than requested
   under several circumstances.  The file may have been truncated by
   another client or perhaps on the server itself, changing the file
   size from what the requesting client believes to be the case.  This
   would reduce the actual amount of data available to the client.  It
   is possible that the server reduce the transfer size and so return a
   short read result.  Server resource exhaustion may also occur in a
   short read.

   If mandatory byte-range locking is in effect for the file, and if the
   byte-range corresponding to the data to be read from the file is
   WRITE_LT locked by an owner not associated with the stateid, the
   server will return the NFS4ERR_LOCKED error.  The client should try
   to get the appropriate READ_LT via the LOCK operation before re-
   attempting the READ.  When the READ completes, the client should
   release the byte-range lock via LOCKU.

   If another client has an OPEN_DELEGATE_WRITE delegation for the file
   being read, the delegation must be recalled, and the operation cannot



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   proceed until that delegation is returned or revoked.  Except where
   this happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while the delegation remains outstanding.
   Normally, delegations will not be recalled as a result of a READ
   operation since the recall will occur as a result of an earlier OPEN.
   However, since it is possible for a READ to be done with a special
   stateid, the server needs to check for this case even though the
   client should have done an OPEN previously.

18.23.  Operation 26: READDIR - Read Directory

18.23.1.  ARGUMENTS

   struct READDIR4args {
           /* CURRENT_FH: directory */
           nfs_cookie4     cookie;
           verifier4       cookieverf;
           count4          dircount;
           count4          maxcount;
           bitmap4         attr_request;
   };


18.23.2.  RESULTS



























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   struct entry4 {
           nfs_cookie4     cookie;
           component4      name;
           fattr4          attrs;
           entry4          *nextentry;
   };

   struct dirlist4 {
           entry4          *entries;
           bool            eof;
   };

   struct READDIR4resok {
           verifier4       cookieverf;
           dirlist4        reply;
   };


   union READDIR4res switch (nfsstat4 status) {
    case NFS4_OK:
            READDIR4resok  resok4;
    default:
            void;
   };



18.23.3.  DESCRIPTION

   The READDIR operation retrieves a variable number of entries from a
   file system directory and returns client-requested attributes for
   each entry along with information to allow the client to request
   additional directory entries in a subsequent READDIR.

   The arguments contain a cookie value that represents where the
   READDIR should start within the directory.  A value of zero for the
   cookie is used to start reading at the beginning of the directory.
   For subsequent READDIR requests, the client specifies a cookie value
   that is provided by the server on a previous READDIR request.

   The request's cookieverf field should be set to 0 zero) when the
   request's cookie field is zero (first read of the directory).  On
   subsequent requests, the cookieverf field must match the cookieverf
   returned by the READDIR in which the cookie was acquired.  If the
   server determines that the cookieverf is no longer valid for the
   directory, the error NFS4ERR_NOT_SAME must be returned.





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   The dircount field of the request is a hint of the maximum number of
   bytes of directory information that should be returned.  This value
   represents the total length of the names of the directory entries and
   the cookie value for these entries.  This length represents the XDR
   encoding of the data (names and cookies) and not the length in the
   native format of the server.

   The maxcount field of the request represents the maximum total size
   of all of the data being returned within the READDIR4resok structure
   and includes the XDR overhead.  The server MAY return less data.  If
   the server is unable to return a single directory entry within the
   maxcount limit, the error NFS4ERR_TOOSMALL MUST be returned to the
   client.

   Finally, the request's attr_request field represents the list of
   attributes to be returned for each directory entry supplied by the
   server.

   A successful reply consists of a list of directory entries.  Each of
   these entries contains the name of the directory entry, a cookie
   value for that entry, and the associated attributes as requested.
   The "eof" flag has a value of TRUE if there are no more entries in
   the directory.

   The cookie value is only meaningful to the server and is used as a
   cursor for the directory entry.  As mentioned, this cookie is used by
   the client for subsequent READDIR operations so that it may continue
   reading a directory.  The cookie is similar in concept to a READ
   offset but MUST NOT be interpreted as such by the client.  Ideally,
   the cookie value SHOULD NOT change if the directory is modified since
   the client may be caching these values.

   In some cases, the server may encounter an error while obtaining the
   attributes for a directory entry.  Instead of returning an error for
   the entire READDIR operation, the server can instead return the
   attribute rdattr_error (Section 5.8.1.12).  With this, the server is
   able to communicate the failure to the client and not fail the entire
   operation in the instance of what might be a transient failure.
   Obviously, the client must request the fattr4_rdattr_error attribute
   for this method to work properly.  If the client does not request the
   attribute, the server has no choice but to return failure for the
   entire READDIR operation.

   For some file system environments, the directory entries "." and ".."
   have special meaning, and in other environments, they do not.  If the
   server supports these special entries within a directory, they SHOULD
   NOT be returned to the client as part of the READDIR response.  To
   enable some client environments, the cookie values of zero, 1, and 2



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   are to be considered reserved.  Note that the UNIX client will use
   these values when combining the server's response and local
   representations to enable a fully formed UNIX directory presentation
   to the application.

   For READDIR arguments, cookie values of one and two SHOULD NOT be
   used, and for READDIR results, cookie values of zero, one, and two
   SHOULD NOT be returned.

   On success, the current filehandle retains its value.

18.23.4.  IMPLEMENTATION

   The server's file system directory representations can differ
   greatly.  A client's programming interfaces may also be bound to the
   local operating environment in a way that does not translate well
   into the NFS protocol.  Therefore, the use of the dircount and
   maxcount fields are provided to enable the client to provide hints to
   the server.  If the client is aggressive about attribute collection
   during a READDIR, the server has an idea of how to limit the encoded
   response.

   If dircount is zero, the server bounds the reply's size based on the
   request's maxcount field.

   The cookieverf may be used by the server to help manage cookie values
   that may become stale.  It should be a rare occurrence that a server
   is unable to continue properly reading a directory with the provided
   cookie/cookieverf pair.  The server SHOULD make every effort to avoid
   this condition since the application at the client might be unable to
   properly handle this type of failure.

   The use of the cookieverf will also protect the client from using
   READDIR cookie values that might be stale.  For example, if the file
   system has been migrated, the server might or might not be able to
   use the same cookie values to service READDIR as the previous server
   used.  With the client providing the cookieverf, the server is able
   to provide the appropriate response to the client.  This prevents the
   case where the server accepts a cookie value but the underlying
   directory has changed and the response is invalid from the client's
   context of its previous READDIR.

   Since some servers will not be returning "." and ".." entries as has
   been done with previous versions of the NFS protocol, the client that
   requires these entries be present in READDIR responses must fabricate
   them.





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18.24.  Operation 27: READLINK - Read Symbolic Link

18.24.1.  ARGUMENTS

   /* CURRENT_FH: symlink */
   void;

18.24.2.  RESULTS

   struct READLINK4resok {
           linktext4       link;
   };

   union READLINK4res switch (nfsstat4 status) {
    case NFS4_OK:
            READLINK4resok resok4;
    default:
            void;
   };


18.24.3.  DESCRIPTION

   READLINK reads the data associated with a symbolic link.  Depending
   on the value of the UTF-8 capability attribute (Section 14.4), the
   data is encoded in UTF-8.  Whether created by an NFS client or
   created locally on the server, the data in a symbolic link is not
   interpreted (except possibly to check for proper UTF-8 encoding) when
   created, but is simply stored.

   On success, the current filehandle retains its value.

18.24.4.  IMPLEMENTATION

   A symbolic link is nominally a pointer to another file.  The data is
   not necessarily interpreted by the server, just stored in the file.
   It is possible for a client implementation to store a pathname that
   is not meaningful to the server operating system in a symbolic link.
   A READLINK operation returns the data to the client for
   interpretation.  If different implementations want to share access to
   symbolic links, then they must agree on the interpretation of the
   data in the symbolic link.

   The READLINK operation is only allowed on objects of type NF4LNK.
   The server should return the error NFS4ERR_WRONG_TYPE if the object
   is not of type NF4LNK.





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18.25.  Operation 28: REMOVE - Remove File System Object

18.25.1.  ARGUMENTS

   struct REMOVE4args {
           /* CURRENT_FH: directory */
           component4      target;
   };


18.25.2.  RESULTS

   struct REMOVE4resok {
           change_info4    cinfo;
   };

   union REMOVE4res switch (nfsstat4 status) {
    case NFS4_OK:
            REMOVE4resok   resok4;
    default:
            void;
   };


18.25.3.  DESCRIPTION

   The REMOVE operation removes (deletes) a directory entry named by
   filename from the directory corresponding to the current filehandle.
   If the entry in the directory was the last reference to the
   corresponding file system object, the object may be destroyed.  The
   directory may be either of type NF4DIR or NF4ATTRDIR.

   For the directory where the filename was removed, the server returns
   change_info4 information in cinfo.  With the atomic field of the
   change_info4 data type, the server will indicate if the before and
   after change attributes were obtained atomically with respect to the
   removal.

   If the target has a length of zero, or if the target does not obey
   the UTF-8 definition (and the server is enforcing UTF-8 encoding; see
   Section 14.4), the error NFS4ERR_INVAL will be returned.

   On success, the current filehandle retains its value.








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18.25.4.  IMPLEMENTATION

   NFSv3 required a different operator RMDIR for directory removal and
   REMOVE for non-directory removal.  This allowed clients to skip
   checking the file type when being passed a non-directory delete
   system call (e.g., unlink() [27] in POSIX) to remove a directory, as
   well as the converse (e.g., a rmdir() on a non-directory) because
   they knew the server would check the file type.  NFSv4.1 REMOVE can
   be used to delete any directory entry independent of its file type.
   The implementor of an NFSv4.1 client's entry points from the unlink()
   and rmdir() system calls should first check the file type against the
   types the system call is allowed to remove before sending a REMOVE
   operation.  Alternatively, the implementor can produce a COMPOUND
   call that includes a LOOKUP/VERIFY sequence of operations to verify
   the file type before a REMOVE operation in the same COMPOUND call.

   The concept of last reference is server specific.  However, if the
   numlinks field in the previous attributes of the object had the value
   1, the client should not rely on referring to the object via a
   filehandle.  Likewise, the client should not rely on the resources
   (disk space, directory entry, and so on) formerly associated with the
   object becoming immediately available.  Thus, if a client needs to be
   able to continue to access a file after using REMOVE to remove it,
   the client should take steps to make sure that the file will still be
   accessible.  While the traditional mechanism used is to RENAME the
   file from its old name to a new hidden name, the NFSv4.1 OPEN
   operation MAY return a result flag, OPEN4_RESULT_PRESERVE_UNLINKED,
   which indicates to the client that the file will be preserved if the
   file has an outstanding open (see Section 18.16).

   If the server finds that the file is still open when the REMOVE
   arrives:

   o  The server SHOULD NOT delete the file's directory entry if the
      file was opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH.

   o  If the file was not opened with OPEN4_SHARE_DENY_WRITE or
      OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's
      directory entry.  However, until last CLOSE of the file, the
      server MAY continue to allow access to the file via its
      filehandle.

   o  The server MUST NOT delete the directory entry if the reply from
      OPEN had the flag OPEN4_RESULT_PRESERVE_UNLINKED set.

   The server MAY implement its own restrictions on removal of a file
   while it is open.  The server might disallow such a REMOVE (or a



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   removal that occurs as part of RENAME).  The conditions that
   influence the restrictions on removal of a file while it is still
   open include:

   o  Whether certain access protocols (i.e., not just NFS) are holding
      the file open.

   o  Whether particular options, access modes, or policies on the
      server are enabled.

   If a file has an outstanding OPEN and this prevents the removal of
   the file's directory entry, the error NFS4ERR_FILE_OPEN is returned.

   Where the determination above cannot be made definitively because
   delegations are being held, they MUST be recalled to allow processing
   of the REMOVE to continue.  When a delegation is held, the server has
   no reliable knowledge of the status of OPENs for that client, so
   unless there are files opened with the particular deny modes by
   clients without delegations, the determination cannot be made until
   delegations are recalled, and the operation cannot proceed until each
   sufficient delegation has been returned or revoked to allow the
   server to make a correct determination.

   In all cases in which delegations are recalled, the server is likely
   to return one or more NFS4ERR_DELAY errors while delegations remain
   outstanding.

   If the current filehandle designates a directory for which another
   client holds a directory delegation, then, unless the situation can
   be resolved by sending a notification, the directory delegation MUST
   be recalled, and the operation MUST NOT proceed until the delegation
   is returned or revoked.  Except where this happens very quickly, one
   or more NFS4ERR_DELAY errors will be returned to requests made while
   delegation remains outstanding.

   When the current filehandle designates a directory for which one or
   more directory delegations exist, then, when those delegations
   request such notifications, NOTIFY4_REMOVE_ENTRY will be generated as
   a result of this operation.

   Note that when a remove occurs as a result of a RENAME,
   NOTIFY4_REMOVE_ENTRY will only be generated if the removal happens as
   a separate operation.  In the case in which the removal is integrated
   and atomic with RENAME, the notification of the removal is integrated
   with notification for the RENAME.  See the discussion of the
   NOTIFY4_RENAME_ENTRY notification in Section 20.4.





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18.26.  Operation 29: RENAME - Rename Directory Entry

18.26.1.  ARGUMENTS

   struct RENAME4args {
           /* SAVED_FH: source directory */
           component4      oldname;
           /* CURRENT_FH: target directory */
           component4      newname;
   };


18.26.2.  RESULTS

   struct RENAME4resok {
           change_info4    source_cinfo;
           change_info4    target_cinfo;
   };

   union RENAME4res switch (nfsstat4 status) {
    case NFS4_OK:
           RENAME4resok    resok4;
    default:
           void;
   };


18.26.3.  DESCRIPTION

   The RENAME operation renames the object identified by oldname in the
   source directory corresponding to the saved filehandle, as set by the
   SAVEFH operation, to newname in the target directory corresponding to
   the current filehandle.  The operation is required to be atomic to
   the client.  Source and target directories MUST reside on the same
   file system on the server.  On success, the current filehandle will
   continue to be the target directory.

   If the target directory already contains an entry with the name
   newname, the source object MUST be compatible with the target: either
   both are non-directories or both are directories and the target MUST
   be empty.  If compatible, the existing target is removed before the
   rename occurs or, preferably, the target is removed atomically as
   part of the rename.  See Section 18.25.4 for client and server
   actions whenever a target is removed.  Note however that when the
   removal is performed atomically with the rename, certain parts of the
   removal described there are integrated with the rename.  For example,
   notification of the removal will not be via a NOTIFY4_REMOVE_ENTRY




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   but will be indicated as part of the NOTIFY4_ADD_ENTRY or
   NOTIFY4_RENAME_ENTRY generated by the rename.

   If the source object and the target are not compatible or if the
   target is a directory but not empty, the server will return the error
   NFS4ERR_EXIST.

   If oldname and newname both refer to the same file (e.g., they might
   be hard links of each other), then unless the file is open (see
   Section 18.26.4), RENAME MUST perform no action and return NFS4_OK.

   For both directories involved in the RENAME, the server returns
   change_info4 information.  With the atomic field of the change_info4
   data type, the server will indicate if the before and after change
   attributes were obtained atomically with respect to the rename.

   If oldname refers to a named attribute and the saved and current
   filehandles refer to different file system objects, the server will
   return NFS4ERR_XDEV just as if the saved and current filehandles
   represented directories on different file systems.

   If oldname or newname has a length of zero, or if oldname or newname
   does not obey the UTF-8 definition, the error NFS4ERR_INVAL will be
   returned.

18.26.4.  IMPLEMENTATION

   The server MAY impose restrictions on the RENAME operation such that
   RENAME may not be done when the file being renamed is open or when
   that open is done by particular protocols, or with particular options
   or access modes.  Similar restrictions may be applied when a file
   exists with the target name and is open.  When RENAME is rejected
   because of such restrictions, the error NFS4ERR_FILE_OPEN is
   returned.

   When oldname and rename refer to the same file and that file is open
   in a fashion such that RENAME would normally be rejected with
   NFS4ERR_FILE_OPEN if oldname and newname were different files, then
   RENAME SHOULD be rejected with NFS4ERR_FILE_OPEN.

   If a server does implement such restrictions and those restrictions
   include cases of NFSv4 opens preventing successful execution of a
   rename, the server needs to recall any delegations that could hide
   the existence of opens relevant to that decision.  This is because
   when a client holds a delegation, the server might not have an
   accurate account of the opens for that client, since the client may
   execute OPENs and CLOSEs locally.  The RENAME operation need only be
   delayed until a definitive result can be obtained.  For example, if



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   there are multiple delegations and one of them establishes an open
   whose presence would prevent the rename, given the server's
   semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon as
   that delegation is returned without waiting for other delegations to
   be returned.  Similarly, if such opens are not associated with
   delegations, NFS4ERR_FILE_OPEN can be returned immediately with no
   delegation recall being done.

   If the current filehandle or the saved filehandle designates a
   directory for which another client holds a directory delegation,
   then, unless the situation can be resolved by sending a notification,
   the delegation MUST be recalled, and the operation cannot proceed
   until the delegation is returned or revoked.  Except where this
   happens very quickly, one or more NFS4ERR_DELAY errors will be
   returned to requests made while delegation remains outstanding.

   When the current and saved filehandles are the same and they
   designate a directory for which one or more directory delegations
   exist, then, when those delegations request such notifications, a
   notification of type NOTIFY4_RENAME_ENTRY will be generated as a
   result of this operation.  When oldname and rename refer to the same
   file, no notification is generated (because, as Section 18.26.3
   states, the server MUST take no action).  When a file is removed
   because it has the same name as the target, if that removal is done
   atomically with the rename, a NOTIFY4_REMOVE_ENTRY notification will
   not be generated.  Instead, the deletion of the file will be reported
   as part of the NOTIFY4_RENAME_ENTRY notification.

   When the current and saved filehandles are not the same:

   o  If the current filehandle designates a directory for which one or
      more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated as
      a result of this operation.  When a file is removed because it has
      the same name as the target, if that removal is done atomically
      with the rename, a NOTIFY4_REMOVE_ENTRY notification will not be
      generated.  Instead, the deletion of the file will be reported as
      part of the NOTIFY4_ADD_ENTRY notification.

   o  If the saved filehandle designates a directory for which one or
      more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_REMOVE_ENTRY will be generated
      as a result of this operation.

   If the object being renamed has file delegations held by clients
   other than the one doing the RENAME, the delegations MUST be
   recalled, and the operation cannot proceed until each such delegation
   is returned or revoked.  Note that in the case of multiply linked



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   files, the delegation recall requirement applies even if the
   delegation was obtained through a different name than the one being
   renamed.  In all cases in which delegations are recalled, the server
   is likely to return one or more NFS4ERR_DELAY errors while the
   delegation(s) remains outstanding, although it might not do that if
   the delegations are returned quickly.

   The RENAME operation must be atomic to the client.  The statement
   "source and target directories MUST reside on the same file system on
   the server" means that the fsid fields in the attributes for the
   directories are the same.  If they reside on different file systems,
   the error NFS4ERR_XDEV is returned.

   Based on the value of the fh_expire_type attribute for the object,
   the filehandle may or may not expire on a RENAME.  However, server
   implementors are strongly encouraged to attempt to keep filehandles
   from expiring in this fashion.

   On some servers, the file names "." and ".." are illegal as either
   oldname or newname, and will result in the error NFS4ERR_BADNAME.  In
   addition, on many servers the case of oldname or newname being an
   alias for the source directory will be checked for.  Such servers
   will return the error NFS4ERR_INVAL in these cases.

   If either of the source or target filehandles are not directories,
   the server will return NFS4ERR_NOTDIR.

18.27.  Operation 31: RESTOREFH - Restore Saved Filehandle

18.27.1.  ARGUMENTS

   /* SAVED_FH: */
   void;

18.27.2.  RESULTS

   struct RESTOREFH4res {
           /*
            * If status is NFS4_OK,
            *     new CURRENT_FH: value of saved fh
            */
           nfsstat4        status;
   };








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18.27.3.  DESCRIPTION

   The RESTOREFH operation sets the current filehandle and stateid to
   the values in the saved filehandle and stateid.  If there is no saved
   filehandle, then the server will return the error
   NFS4ERR_NOFILEHANDLE.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.27.4.  IMPLEMENTATION

   Operations like OPEN and LOOKUP use the current filehandle to
   represent a directory and replace it with a new filehandle.  Assuming
   that the previous filehandle was saved with a SAVEFH operator, the
   previous filehandle can be restored as the current filehandle.  This
   is commonly used to obtain post-operation attributes for the
   directory, e.g.,

         PUTFH (directory filehandle)
         SAVEFH
         GETATTR attrbits     (pre-op dir attrs)
         CREATE optbits "foo" attrs
         GETATTR attrbits     (file attributes)
         RESTOREFH
         GETATTR attrbits     (post-op dir attrs)

18.28.  Operation 32: SAVEFH - Save Current Filehandle

18.28.1.  ARGUMENTS

   /* CURRENT_FH: */
   void;

18.28.2.  RESULTS

   struct SAVEFH4res {
           /*
            * If status is NFS4_OK,
            *    new SAVED_FH: value of current fh
            */
           nfsstat4        status;
   };







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18.28.3.  DESCRIPTION

   The SAVEFH operation saves the current filehandle and stateid.  If a
   previous filehandle was saved, then it is no longer accessible.  The
   saved filehandle can be restored as the current filehandle with the
   RESTOREFH operator.

   On success, the current filehandle retains its value.

   See Section 16.2.3.1.1 for more details on the current filehandle.

   See Section 16.2.3.1.2 for more details on the current stateid.

18.28.4.  IMPLEMENTATION

18.29.  Operation 33: SECINFO - Obtain Available Security

18.29.1.  ARGUMENTS

   struct SECINFO4args {
           /* CURRENT_FH: directory */
           component4      name;
   };


18.29.2.  RESULTS

























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   /*
    * From RFC 2203
    */
   enum rpc_gss_svc_t {
           RPC_GSS_SVC_NONE        = 1,
           RPC_GSS_SVC_INTEGRITY   = 2,
           RPC_GSS_SVC_PRIVACY     = 3
   };

   struct rpcsec_gss_info {
           sec_oid4        oid;
           qop4            qop;
           rpc_gss_svc_t   service;
   };

   /* RPCSEC_GSS has a value of '6' - See RFC 2203 */
   union secinfo4 switch (uint32_t flavor) {
    case RPCSEC_GSS:
            rpcsec_gss_info        flavor_info;
    default:
            void;
   };

   typedef secinfo4 SECINFO4resok<>;

   union SECINFO4res switch (nfsstat4 status) {
    case NFS4_OK:
           /* CURRENTFH: consumed */
            SECINFO4resok resok4;
    default:
            void;
   };


18.29.3.  DESCRIPTION

   The SECINFO operation is used by the client to obtain a list of valid
   RPC authentication flavors for a specific directory filehandle, file
   name pair.  SECINFO should apply the same access methodology used for
   LOOKUP when evaluating the name.  Therefore, if the requester does
   not have the appropriate access to LOOKUP the name, then SECINFO MUST
   behave the same way and return NFS4ERR_ACCESS.

   The result will contain an array that represents the security
   mechanisms available, with an order corresponding to the server's
   preferences, the most preferred being first in the array.  The client
   is free to pick whatever security mechanism it both desires and
   supports, or to pick in the server's preference order the first one



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   it supports.  The array entries are represented by the secinfo4
   structure.  The field 'flavor' will contain a value of AUTH_NONE,
   AUTH_SYS (as defined in RFC 5531 [3]), or RPCSEC_GSS (as defined in
   RFC 2203 [4]).  The field flavor can also be any other security
   flavor registered with IANA.

   For the flavors AUTH_NONE and AUTH_SYS, no additional security
   information is returned.  The same is true of many (if not most)
   other security flavors, including AUTH_DH.  For a return value of
   RPCSEC_GSS, a security triple is returned that contains the mechanism
   object identifier (OID, as defined in RFC 2743 [7]), the quality of
   protection (as defined in RFC 2743 [7]), and the service type (as
   defined in RFC 2203 [4]).  It is possible for SECINFO to return
   multiple entries with flavor equal to RPCSEC_GSS with different
   security triple values.

   On success, the current filehandle is consumed (see
   Section 2.6.3.1.1.8), and if the next operation after SECINFO tries
   to use the current filehandle, that operation will fail with the
   status NFS4ERR_NOFILEHANDLE.

   If the name has a length of zero, or if the name does not obey the
   UTF-8 definition (assuming UTF-8 capabilities are enabled; see
   Section 14.4), the error NFS4ERR_INVAL will be returned.

   See Section 2.6 for additional information on the use of SECINFO.

18.29.4.  IMPLEMENTATION

   The SECINFO operation is expected to be used by the NFS client when
   the error value of NFS4ERR_WRONGSEC is returned from another NFS
   operation.  This signifies to the client that the server's security
   policy is different from what the client is currently using.  At this
   point, the client is expected to obtain a list of possible security
   flavors and choose what best suits its policies.

   As mentioned, the server's security policies will determine when a
   client request receives NFS4ERR_WRONGSEC.  See Table 8 for a list of
   operations that can return NFS4ERR_WRONGSEC.  In addition, when
   READDIR returns attributes, the rdattr_error (Section 5.8.1.12) can
   contain NFS4ERR_WRONGSEC.  Note that CREATE and REMOVE MUST NOT
   return NFS4ERR_WRONGSEC.  The rationale for CREATE is that unless the
   target name exists, it cannot have a separate security policy from
   the parent directory, and the security policy of the parent was
   checked when its filehandle was injected into the COMPOUND request's
   operations stream (for similar reasons, an OPEN operation that
   creates the target MUST NOT return NFS4ERR_WRONGSEC).  If the target
   name exists, while it might have a separate security policy, that is



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   irrelevant because CREATE MUST return NFS4ERR_EXIST.  The rationale
   for REMOVE is that while that target might have a separate security
   policy, the target is going to be removed, and so the security policy
   of the parent trumps that of the object being removed.  RENAME and
   LINK MAY return NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error
   applies only to the saved filehandle (see Section 2.6.3.1.2).  Any
   NFS4ERR_WRONGSEC error on the current filehandle used by LINK and
   RENAME MUST be returned by the PUTFH, PUTPUBFH, PUTROOTFH, or
   RESTOREFH operation that injected the current filehandle.

   With the exception of LINK and RENAME, the set of operations that can
   return NFS4ERR_WRONGSEC represents the point at which the client can
   inject a filehandle into the "current filehandle" at the server.  The
   filehandle is either provided by the client (PUTFH, PUTPUBFH,
   PUTROOTFH), generated as a result of a name-to-filehandle translation
   (LOOKUP and OPEN), or generated from the saved filehandle via
   RESTOREFH.  As Section 2.6.3.1.1.1 states, a put filehandle operation
   followed by SAVEFH MUST NOT return NFS4ERR_WRONGSEC.  Thus, the
   RESTOREFH operation, under certain conditions (see
   Section 2.6.3.1.1), is permitted to return NFS4ERR_WRONGSEC so that
   security policies can be honored.

   The READDIR operation will not directly return the NFS4ERR_WRONGSEC
   error.  However, if the READDIR request included a request for
   attributes, it is possible that the READDIR request's security triple
   did not match that of a directory entry.  If this is the case and the
   client has requested the rdattr_error attribute, the server will
   return the NFS4ERR_WRONGSEC error in rdattr_error for the entry.

   To resolve an error return of NFS4ERR_WRONGSEC, the client does the
   following:

   o  For LOOKUP and OPEN, the client will use SECINFO with the same
      current filehandle and name as provided in the original LOOKUP or
      OPEN to enumerate the available security triples.

   o  For the rdattr_error, the client will use SECINFO with the same
      current filehandle as provided in the original READDIR.  The name
      passed to SECINFO will be that of the directory entry (as returned
      from READDIR) that had the NFS4ERR_WRONGSEC error in the
      rdattr_error attribute.

   o  For PUTFH, PUTROOTFH, PUTPUBFH, RESTOREFH, LINK, and RENAME, the
      client will use SECINFO_NO_NAME { style =
      SECINFO_STYLE4_CURRENT_FH }.  The client will prefix the
      SECINFO_NO_NAME operation with the appropriate PUTFH, PUTPUBFH, or
      PUTROOTFH operation that provides the filehandle originally




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      provided by the PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH
      operation.

      NOTE: In NFSv4.0, the client was required to use SECINFO, and had
      to reconstruct the parent of the original filehandle and the
      component name of the original filehandle.  The introduction in
      NFSv4.1 of SECINFO_NO_NAME obviates the need for reconstruction.

   o  For LOOKUPP, the client will use SECINFO_NO_NAME { style =
      SECINFO_STYLE4_PARENT } and provide the filehandle that equals the
      filehandle originally provided to LOOKUPP.

   See Section 21 for a discussion on the recommendations for the
   security flavor used by SECINFO and SECINFO_NO_NAME.

18.30.  Operation 34: SETATTR - Set Attributes

18.30.1.  ARGUMENTS

   struct SETATTR4args {
           /* CURRENT_FH: target object */
           stateid4        stateid;
           fattr4          obj_attributes;
   };


18.30.2.  RESULTS

   struct SETATTR4res {
           nfsstat4        status;
           bitmap4         attrsset;
   };


18.30.3.  DESCRIPTION

   The SETATTR operation changes one or more of the attributes of a file
   system object.  The new attributes are specified with a bitmap and
   the attributes that follow the bitmap in bit order.

   The stateid argument for SETATTR is used to provide byte-range
   locking context that is necessary for SETATTR requests that set the
   size attribute.  Since setting the size attribute modifies the file's
   data, it has the same locking requirements as a corresponding WRITE.
   Any SETATTR that sets the size attribute is incompatible with a share
   reservation that specifies OPEN4_SHARE_DENY_WRITE.  The area between
   the old end-of-file and the new end-of-file is considered to be
   modified just as would have been the case had the area in question



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   been specified as the target of WRITE, for the purpose of checking
   conflicts with byte-range locks, for those cases in which a server is
   implementing mandatory byte-range locking behavior.  A valid stateid
   SHOULD always be specified.  When the file size attribute is not set,
   the special stateid consisting of all bits equal to zero MAY be
   passed.

   On either success or failure of the operation, the server will return
   the attrsset bitmask to represent what (if any) attributes were
   successfully set.  The attrsset in the response is a subset of the
   attrmask field of the obj_attributes field in the argument.

   On success, the current filehandle retains its value.

18.30.4.  IMPLEMENTATION

   If the request specifies the owner attribute to be set, the server
   SHOULD allow the operation to succeed if the current owner of the
   object matches the value specified in the request.  Some servers may
   be implemented in a way as to prohibit the setting of the owner
   attribute unless the requester has privilege to do so.  If the server
   is lenient in this one case of matching owner values, the client
   implementation may be simplified in cases of creation of an object
   (e.g., an exclusive create via OPEN) followed by a SETATTR.

   The file size attribute is used to request changes to the size of a
   file.  A value of zero causes the file to be truncated, a value less
   than the current size of the file causes data from new size to the
   end of the file to be discarded, and a size greater than the current
   size of the file causes logically zeroed data bytes to be added to
   the end of the file.  Servers are free to implement this using
   unallocated bytes (holes) or allocated data bytes set to zero.
   Clients should not make any assumptions regarding a server's
   implementation of this feature, beyond that the bytes in the affected
   byte-range returned by READ will be zeroed.  Servers MUST support
   extending the file size via SETATTR.

   SETATTR is not guaranteed to be atomic.  A failed SETATTR may
   partially change a file's attributes, hence the reason why the reply
   always includes the status and the list of attributes that were set.

   If the object whose attributes are being changed has a file
   delegation that is held by a client other than the one doing the
   SETATTR, the delegation(s) must be recalled, and the operation cannot
   proceed to actually change an attribute until each such delegation is
   returned or revoked.  In all cases in which delegations are recalled,
   the server is likely to return one or more NFS4ERR_DELAY errors while




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   the delegation(s) remains outstanding, although it might not do that
   if the delegations are returned quickly.

   If the object whose attributes are being set is a directory and
   another client holds a directory delegation for that directory, then
   if enabled, asynchronous notifications will be generated when the set
   of attributes changed has a non-null intersection with the set of
   attributes for which notification is requested.  Notifications of
   type NOTIFY4_CHANGE_DIR_ATTRS will be sent to the appropriate
   client(s), but the SETATTR is not delayed by waiting for these
   notifications to be sent.

   If the object whose attributes are being set is a member of the
   directory for which another client holds a directory delegation, then
   asynchronous notifications will be generated when the set of
   attributes changed has a non-null intersection with the set of
   attributes for which notification is requested.  Notifications of
   type NOTIFY4_CHANGE_CHILD_ATTRS will be sent to the appropriate
   clients, but the SETATTR is not delayed by waiting for these
   notifications to be sent.

   Changing the size of a file with SETATTR indirectly changes the
   time_modify and change attributes.  A client must account for this as
   size changes can result in data deletion.

   The attributes time_access_set and time_modify_set are write-only
   attributes constructed as a switched union so the client can direct
   the server in setting the time values.  If the switched union
   specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
   be used for the operation.  If the switch union does not specify
   SET_TO_CLIENT_TIME4, the server is to use its current time for the
   SETATTR operation.

   If server and client times differ, programs that compare client time
   to file times can break.  A time synchronization protocol should be
   used to limit client/server time skew.

   Use of a COMPOUND containing a VERIFY operation specifying only the
   change attribute, immediately followed by a SETATTR, provides a means
   whereby a client may specify a request that emulates the
   functionality of the SETATTR guard mechanism of NFSv3.  Since the
   function of the guard mechanism is to avoid changes to the file
   attributes based on stale information, delays between checking of the
   guard condition and the setting of the attributes have the potential
   to compromise this function, as would the corresponding delay in the
   NFSv4 emulation.  Therefore, NFSv4.1 servers SHOULD take care to
   avoid such delays, to the degree possible, when executing such a
   request.



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   If the server does not support an attribute as requested by the
   client, the server SHOULD return NFS4ERR_ATTRNOTSUPP.

   A mask of the attributes actually set is returned by SETATTR in all
   cases.  That mask MUST NOT include attribute bits not requested to be
   set by the client.  If the attribute masks in the request and reply
   are equal, the status field in the reply MUST be NFS4_OK.

18.31.  Operation 37: VERIFY - Verify Same Attributes

18.31.1.  ARGUMENTS

   struct VERIFY4args {
           /* CURRENT_FH: object */
           fattr4          obj_attributes;
   };


18.31.2.  RESULTS

   struct VERIFY4res {
           nfsstat4        status;
   };


18.31.3.  DESCRIPTION

   The VERIFY operation is used to verify that attributes have the value
   assumed by the client before proceeding with the following operations
   in the COMPOUND request.  If any of the attributes do not match, then
   the error NFS4ERR_NOT_SAME must be returned.  The current filehandle
   retains its value after successful completion of the operation.

18.31.4.  IMPLEMENTATION

   One possible use of the VERIFY operation is the following series of
   operations.  With this, the client is attempting to verify that the
   file being removed will match what the client expects to be removed.
   This series can help prevent the unintended deletion of a file.

         PUTFH (directory filehandle)
         LOOKUP (file name)
         VERIFY (filehandle == fh)
         PUTFH (directory filehandle)
         REMOVE (file name)






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   This series does not prevent a second client from removing and
   creating a new file in the middle of this sequence, but it does help
   avoid the unintended result.

   In the case that a RECOMMENDED attribute is specified in the VERIFY
   operation and the server does not support that attribute for the file
   system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
   client.

   When the attribute rdattr_error or any set-only attribute (e.g.,
   time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
   the client.

18.32.  Operation 38: WRITE - Write to File

18.32.1.  ARGUMENTS

   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
   };

   struct WRITE4args {
           /* CURRENT_FH: file */
           stateid4        stateid;
           offset4         offset;
           stable_how4     stable;
           opaque          data<>;
   };


18.32.2.  RESULTS

   struct WRITE4resok {
           count4          count;
           stable_how4     committed;
           verifier4       writeverf;
   };

   union WRITE4res switch (nfsstat4 status) {
    case NFS4_OK:
            WRITE4resok    resok4;
    default:
            void;
   };





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18.32.3.  DESCRIPTION

   The WRITE operation is used to write data to a regular file.  The
   target file is specified by the current filehandle.  The offset
   specifies the offset where the data should be written.  An offset of
   zero specifies that the write should start at the beginning of the
   file.  The count, as encoded as part of the opaque data parameter,
   represents the number of bytes of data that are to be written.  If
   the count is zero, the WRITE will succeed and return a count of zero
   subject to permissions checking.  The server MAY write fewer bytes
   than requested by the client.

   The client specifies with the stable parameter the method of how the
   data is to be processed by the server.  If stable is FILE_SYNC4, the
   server MUST commit the data written plus all file system metadata to
   stable storage before returning results.  This corresponds to the
   NFSv2 protocol semantics.  Any other behavior constitutes a protocol
   violation.  If stable is DATA_SYNC4, then the server MUST commit all
   of the data to stable storage and enough of the metadata to retrieve
   the data before returning.  The server implementor is free to
   implement DATA_SYNC4 in the same fashion as FILE_SYNC4, but with a
   possible performance drop.  If stable is UNSTABLE4, the server is
   free to commit any part of the data and the metadata to stable
   storage, including all or none, before returning a reply to the
   client.  There is no guarantee whether or when any uncommitted data
   will subsequently be committed to stable storage.  The only
   guarantees made by the server are that it will not destroy any data
   without changing the value of writeverf and that it will not commit
   the data and metadata at a level less than that requested by the
   client.

   Except when special stateids are used, the stateid value for a WRITE
   request represents a value returned from a previous byte-range LOCK
   or OPEN request or the stateid associated with a delegation.  The
   stateid identifies the associated owners if any and is used by the
   server to verify that the associated locks are still valid (e.g.,
   have not been revoked).

   Upon successful completion, the following results are returned.  The
   count result is the number of bytes of data written to the file.  The
   server may write fewer bytes than requested.  If so, the actual
   number of bytes written starting at location, offset, is returned.

   The server also returns an indication of the level of commitment of
   the data and metadata via committed.  Per Table 11,

   o  The server MAY commit the data at a stronger level than requested.




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   o  The server MUST commit the data at a level at least as high as
      that committed.

   Valid combinations of the fields stable in the request and committed
                               in the reply.

            +------------+-----------------------------------+
            | stable     | committed                         |
            +------------+-----------------------------------+
            | UNSTABLE4  | FILE_SYNC4, DATA_SYNC4, UNSTABLE4 |
            | DATA_SYNC4 | FILE_SYNC4, DATA_SYNC4            |
            | FILE_SYNC4 | FILE_SYNC4                        |
            +------------+-----------------------------------+

                                 Table 11

   The final portion of the result is the field writeverf.  This field
   is the write verifier and is a cookie that the client can use to
   determine whether a server has changed instance state (e.g., server
   restart) between a call to WRITE and a subsequent call to either
   WRITE or COMMIT.  This cookie MUST be unchanged during a single
   instance of the NFSv4.1 server and MUST be unique between instances
   of the NFSv4.1 server.  If the cookie changes, then the client MUST
   assume that any data written with an UNSTABLE4 value for committed
   and an old writeverf in the reply has been lost and will need to be
   recovered.

   If a client writes data to the server with the stable argument set to
   UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
   UNSTABLE4, the client will follow up some time in the future with a
   COMMIT operation to synchronize outstanding asynchronous data and
   metadata with the server's stable storage, barring client error.  It
   is possible that due to client crash or other error that a subsequent
   COMMIT will not be received by the server.

   For a WRITE with a stateid value of all bits equal to zero, the
   server MAY allow the WRITE to be serviced subject to mandatory byte-
   range locks or the current share deny modes for the file.  For a
   WRITE with a stateid value of all bits equal to 1, the server MUST
   NOT allow the WRITE operation to bypass locking checks at the server
   and otherwise is treated as if a stateid of all bits equal to zero
   were used.

   On success, the current filehandle retains its value.







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18.32.4.  IMPLEMENTATION

   It is possible for the server to write fewer bytes of data than
   requested by the client.  In this case, the server SHOULD NOT return
   an error unless no data was written at all.  If the server writes
   less than the number of bytes specified, the client will need to send
   another WRITE to write the remaining data.

   It is assumed that the act of writing data to a file will cause the
   time_modified and change attributes of the file to be updated.
   However, these attributes SHOULD NOT be changed unless the contents
   of the file are changed.  Thus, a WRITE request with count set to
   zero SHOULD NOT cause the time_modified and change attributes of the
   file to be updated.

   Stable storage is persistent storage that survives:

   1.  Repeated power failures.

   2.  Hardware failures (of any board, power supply, etc.).

   3.  Repeated software crashes and restarts.

   This definition does not address failure of the stable storage module
   itself.

   The verifier is defined to allow a client to detect different
   instances of an NFSv4.1 protocol server over which cached,
   uncommitted data may be lost.  In the most likely case, the verifier
   allows the client to detect server restarts.  This information is
   required so that the client can safely determine whether the server
   could have lost cached data.  If the server fails unexpectedly and
   the client has uncommitted data from previous WRITE requests (done
   with the stable argument set to UNSTABLE4 and in which the result
   committed was returned as UNSTABLE4 as well), the server might not
   have flushed cached data to stable storage.  The burden of recovery
   is on the client, and the client will need to retransmit the data to
   the server.

   A suggested verifier would be to use the time that the server was
   last started (if restarting the server results in lost buffers).

   The reply's committed field allows the client to do more effective
   caching.  If the server is committing all WRITE requests to stable
   storage, then it SHOULD return with committed set to FILE_SYNC4,
   regardless of the value of the stable field in the arguments.  A
   server that uses an NVRAM accelerator may choose to implement this
   policy.  The client can use this to increase the effectiveness of the



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   cache by discarding cached data that has already been committed on
   the server.

   Some implementations may return NFS4ERR_NOSPC instead of
   NFS4ERR_DQUOT when a user's quota is exceeded.

   In the case that the current filehandle is of type NF4DIR, the server
   will return NFS4ERR_ISDIR.  If the current file is a symbolic link,
   the error NFS4ERR_SYMLINK will be returned.  Otherwise, if the
   current filehandle does not designate an ordinary file, the server
   will return NFS4ERR_WRONG_TYPE.

   If mandatory byte-range locking is in effect for the file, and the
   corresponding byte-range of the data to be written to the file is
   READ_LT or WRITE_LT locked by an owner that is not associated with
   the stateid, the server MUST return NFS4ERR_LOCKED.  If so, the
   client MUST check if the owner corresponding to the stateid used with
   the WRITE operation has a conflicting READ_LT lock that overlaps with
   the byte-range that was to be written.  If the stateid's owner has no
   conflicting READ_LT lock, then the client SHOULD try to get the
   appropriate write byte-range lock via the LOCK operation before re-
   attempting the WRITE.  When the WRITE completes, the client SHOULD
   release the byte-range lock via LOCKU.

   If the stateid's owner had a conflicting READ_LT lock, then the
   client has no choice but to return an error to the application that
   attempted the WRITE.  The reason is that since the stateid's owner
   had a READ_LT lock, either the server attempted to temporarily
   effectively upgrade this READ_LT lock to a WRITE_LT lock or the
   server has no upgrade capability.  If the server attempted to upgrade
   the READ_LT lock and failed, it is pointless for the client to re-
   attempt the upgrade via the LOCK operation, because there might be
   another client also trying to upgrade.  If two clients are blocked
   trying to upgrade the same lock, the clients deadlock.  If the server
   has no upgrade capability, then it is pointless to try a LOCK
   operation to upgrade.

   If one or more other clients have delegations for the file being
   written, those delegations MUST be recalled, and the operation cannot
   proceed until those delegations are returned or revoked.  Except
   where this happens very quickly, one or more NFS4ERR_DELAY errors
   will be returned to requests made while the delegation remains
   outstanding.  Normally, delegations will not be recalled as a result
   of a WRITE operation since the recall will occur as a result of an
   earlier OPEN.  However, since it is possible for a WRITE to be done
   with a special stateid, the server needs to check for this case even
   though the client should have done an OPEN previously.




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18.33.  Operation 40: BACKCHANNEL_CTL - Backchannel Control

18.33.1.  ARGUMENT

   typedef opaque gsshandle4_t<>;

   struct gss_cb_handles4 {
           rpc_gss_svc_t           gcbp_service; /* RFC 2203 */
           gsshandle4_t            gcbp_handle_from_server;
           gsshandle4_t            gcbp_handle_from_client;
   };

   union callback_sec_parms4 switch (uint32_t cb_secflavor) {
   case AUTH_NONE:
           void;
   case AUTH_SYS:
           authsys_parms   cbsp_sys_cred; /* RFC 1831 */
   case RPCSEC_GSS:
           gss_cb_handles4 cbsp_gss_handles;
   };

   struct BACKCHANNEL_CTL4args {
           uint32_t                bca_cb_program;
           callback_sec_parms4     bca_sec_parms<>;
   };


18.33.2.  RESULT

   struct BACKCHANNEL_CTL4res {
           nfsstat4                bcr_status;
   };


18.33.3.  DESCRIPTION

   The BACKCHANNEL_CTL operation replaces the backchannel's callback
   program number and adds (not replaces) RPCSEC_GSS handles for use by
   the backchannel.

   The arguments of the BACKCHANNEL_CTL call are a subset of the
   CREATE_SESSION parameters.  In the arguments of BACKCHANNEL_CTL, the
   bca_cb_program field and bca_sec_parms fields correspond respectively
   to the csa_cb_program and csa_sec_parms fields of the arguments of
   CREATE_SESSION (Section 18.36).

   BACKCHANNEL_CTL MUST appear in a COMPOUND that starts with SEQUENCE.




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   If the RPCSEC_GSS handle identified by gcbp_handle_from_server does
   not exist on the server, the server MUST return NFS4ERR_NOENT.

   If an RPCSEC_GSS handle is using the SSV context (see
   Section 2.10.9), then because each SSV RPCSEC_GSS handle shares a
   common SSV GSS context, there are security considerations specific to
   this situation discussed in Section 2.10.10.

18.34.  Operation 41: BIND_CONN_TO_SESSION - Associate Connection with
        Session

18.34.1.  ARGUMENT

   enum channel_dir_from_client4 {
    CDFC4_FORE             = 0x1,
    CDFC4_BACK             = 0x2,
    CDFC4_FORE_OR_BOTH     = 0x3,
    CDFC4_BACK_OR_BOTH     = 0x7
   };

   struct BIND_CONN_TO_SESSION4args {
    sessionid4     bctsa_sessid;

    channel_dir_from_client4
                   bctsa_dir;

    bool           bctsa_use_conn_in_rdma_mode;
   };


18.34.2.  RESULT




















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   enum channel_dir_from_server4 {
    CDFS4_FORE     = 0x1,
    CDFS4_BACK     = 0x2,
    CDFS4_BOTH     = 0x3
   };

   struct BIND_CONN_TO_SESSION4resok {
    sessionid4     bctsr_sessid;

    channel_dir_from_server4
                   bctsr_dir;

    bool           bctsr_use_conn_in_rdma_mode;
   };

   union BIND_CONN_TO_SESSION4res
    switch (nfsstat4 bctsr_status) {

    case NFS4_OK:
     BIND_CONN_TO_SESSION4resok
                   bctsr_resok4;

    default:       void;
   };


18.34.3.  DESCRIPTION

   BIND_CONN_TO_SESSION is used to associate additional connections with
   a session.  It MUST be used on the connection being associated with
   the session.  It MUST be the only operation in the COMPOUND
   procedure.  If SP4_NONE (Section 18.35) state protection is used, any
   principal, security flavor, or RPCSEC_GSS context MAY be used to
   invoke the operation.  If SP4_MACH_CRED is used, RPCSEC_GSS MUST be
   used with the integrity or privacy services, using the principal that
   created the client ID.  If SP4_SSV is used, RPCSEC_GSS with the SSV
   GSS mechanism (Section 2.10.9) and integrity or privacy MUST be used.

   If, when the client ID was created, the client opted for SP4_NONE
   state protection, the client is not required to use
   BIND_CONN_TO_SESSION to associate the connection with the session,
   unless the client wishes to associate the connection with the
   backchannel.  When SP4_NONE protection is used, simply sending a
   COMPOUND request with a SEQUENCE operation is sufficient to associate
   the connection with the session specified in SEQUENCE.

   The field bctsa_dir indicates whether the client wants to associate
   the connection with the fore channel or the backchannel or both



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   channels.  The value CDFC4_FORE_OR_BOTH indicates that the client
   wants to associate the connection with both the fore channel and
   backchannel, but will accept the connection being associated to just
   the fore channel.  The value CDFC4_BACK_OR_BOTH indicates that the
   client wants to associate with both the fore channel and backchannel,
   but will accept the connection being associated with just the
   backchannel.  The server replies in bctsr_dir which channel(s) the
   connection is associated with.  If the client specified CDFC4_FORE,
   the server MUST return CDFS4_FORE.  If the client specified
   CDFC4_BACK, the server MUST return CDFS4_BACK.  If the client
   specified CDFC4_FORE_OR_BOTH, the server MUST return CDFS4_FORE or
   CDFS4_BOTH.  If the client specified CDFC4_BACK_OR_BOTH, the server
   MUST return CDFS4_BACK or CDFS4_BOTH.

   See the CREATE_SESSION operation (Section 18.36), and the description
   of the argument csa_use_conn_in_rdma_mode to understand
   bctsa_use_conn_in_rdma_mode, and the description of
   csr_use_conn_in_rdma_mode to understand bctsr_use_conn_in_rdma_mode.

   Invoking BIND_CONN_TO_SESSION on a connection already associated with
   the specified session has no effect, and the server MUST respond with
   NFS4_OK, unless the client is demanding changes to the set of
   channels the connection is associated with.  If so, the server MUST
   return NFS4ERR_INVAL.

18.34.4.  IMPLEMENTATION

   If a session's channel loses all connections, depending on the client
   ID's state protection and type of channel, the client might need to
   use BIND_CONN_TO_SESSION to associate a new connection.  If the
   server restarted and does not keep the reply cache in stable storage,
   the server will not recognize the session ID.  The client will
   ultimately have to invoke EXCHANGE_ID to create a new client ID and
   session.

   Suppose SP4_SSV state protection is being used, and
   BIND_CONN_TO_SESSION is among the operations included in the
   spo_must_enforce set when the client ID was created (Section 18.35).
   If so, there is an issue if SET_SSV is sent, no response is returned,
   and the last connection associated with the client ID drops.  The
   client, per the sessions model, MUST retry the SET_SSV.  But it needs
   a new connection to do so, and MUST associate that connection with
   the session via a BIND_CONN_TO_SESSION authenticated with the SSV GSS
   mechanism.  The problem is that the RPCSEC_GSS message integrity
   codes use a subkey derived from the SSV as the key and the SSV may
   have changed.  While there are multiple recovery strategies, a
   single, general strategy is described here.




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   o  The client reconnects.

   o  The client assumes that the SET_SSV was executed, and so sends
      BIND_CONN_TO_SESSION with the subkey (derived from the new SSV,
      i.e., what SET_SSV would have set the SSV to) used as the key for
      the RPCSEC_GSS credential message integrity codes.

   o  If the request succeeds, this means that the original attempted
      SET_SSV did execute successfully.  The client re-sends the
      original SET_SSV, which the server will reply to via the reply
      cache.

   o  If the server returns an RPC authentication error, this means that
      the server's current SSV was not changed (and the SET_SSV was
      likely not executed).  The client then tries BIND_CONN_TO_SESSION
      with the subkey derived from the old SSV as the key for the
      RPCSEC_GSS message integrity codes.

   o  The attempted BIND_CONN_TO_SESSION with the old SSV should
      succeed.  If so, the client re-sends the original SET_SSV.  If the
      original SET_SSV was not executed, then the server executes it.
      If the original SET_SSV was executed but failed, the server will
      return the SET_SSV from the reply cache.

18.35.  Operation 42: EXCHANGE_ID - Instantiate Client ID

   The EXCHANGE_ID exchanges long-hand client and server identifiers
   (owners), and creates a client ID.

18.35.1.  ARGUMENT

   const EXCHGID4_FLAG_SUPP_MOVED_REFER    = 0x00000001;
   const EXCHGID4_FLAG_SUPP_MOVED_MIGR     = 0x00000002;

   const EXCHGID4_FLAG_BIND_PRINC_STATEID  = 0x00000100;

   const EXCHGID4_FLAG_USE_NON_PNFS        = 0x00010000;
   const EXCHGID4_FLAG_USE_PNFS_MDS        = 0x00020000;
   const EXCHGID4_FLAG_USE_PNFS_DS         = 0x00040000;

   const EXCHGID4_FLAG_MASK_PNFS           = 0x00070000;

   const EXCHGID4_FLAG_UPD_CONFIRMED_REC_A = 0x40000000;
   const EXCHGID4_FLAG_CONFIRMED_R         = 0x80000000;

   struct state_protect_ops4 {
           bitmap4 spo_must_enforce;
           bitmap4 spo_must_allow;



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   };

   struct ssv_sp_parms4 {
           state_protect_ops4      ssp_ops;
           sec_oid4                ssp_hash_algs<>;
           sec_oid4                ssp_encr_algs<>;
           uint32_t                ssp_window;
           uint32_t                ssp_num_gss_handles;
   };

   enum state_protect_how4 {
           SP4_NONE = 0,
           SP4_MACH_CRED = 1,
           SP4_SSV = 2
   };

   union state_protect4_a switch(state_protect_how4 spa_how) {
           case SP4_NONE:
                   void;
           case SP4_MACH_CRED:
                   state_protect_ops4      spa_mach_ops;
           case SP4_SSV:
                   ssv_sp_parms4           spa_ssv_parms;
   };

   struct EXCHANGE_ID4args {
           client_owner4           eia_clientowner;
           uint32_t                eia_flags;
           state_protect4_a        eia_state_protect;
           nfs_impl_id4            eia_client_impl_id<1>;
   };


18.35.2.  RESULT

















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   struct ssv_prot_info4 {
    state_protect_ops4     spi_ops;
    uint32_t               spi_hash_alg;
    uint32_t               spi_encr_alg;
    uint32_t               spi_ssv_len;
    uint32_t               spi_window;
    gsshandle4_t           spi_handles<>;
   };

   union state_protect4_r switch(state_protect_how4 spr_how) {
    case SP4_NONE:
            void;
    case SP4_MACH_CRED:
            state_protect_ops4     spr_mach_ops;
    case SP4_SSV:
            ssv_prot_info4         spr_ssv_info;
   };

   struct EXCHANGE_ID4resok {
    clientid4        eir_clientid;
    sequenceid4      eir_sequenceid;
    uint32_t         eir_flags;
    state_protect4_r eir_state_protect;
    server_owner4    eir_server_owner;
    opaque           eir_server_scope<NFS4_OPAQUE_LIMIT>;
    nfs_impl_id4     eir_server_impl_id<1>;
   };

   union EXCHANGE_ID4res switch (nfsstat4 eir_status) {
   case NFS4_OK:
    EXCHANGE_ID4resok      eir_resok4;

   default:
    void;
   };


18.35.3.  DESCRIPTION

   The client uses the EXCHANGE_ID operation to register a particular
   client owner with the server.  The client ID returned from this
   operation will be necessary for requests that create state on the
   server and will serve as a parent object to sessions created by the
   client.  In order to confirm the client ID it must first be used,
   along with the returned eir_sequenceid, as arguments to
   CREATE_SESSION.  If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the
   result, eir_flags, then eir_sequenceid MUST be ignored, as it has no
   relevancy.



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   EXCHANGE_ID MAY be sent in a COMPOUND procedure that starts with
   SEQUENCE.  However, when a client communicates with a server for the
   first time, it will not have a session, so using SEQUENCE will not be
   possible.  If EXCHANGE_ID is sent without a preceding SEQUENCE, then
   it MUST be the only operation in the COMPOUND procedure's request.
   If it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.

   The eia_clientowner field is composed of a co_verifier field and a
   co_ownerid string.  As noted in Section 2.4, the co_ownerid describes
   the client, and the co_verifier is the incarnation of the client.  An
   EXCHANGE_ID sent with a new incarnation of the client will lead to
   the server removing lock state of the old incarnation.  Whereas an
   EXCHANGE_ID sent with the current incarnation and co_ownerid will
   result in an error or an update of the client ID's properties,
   depending on the arguments to EXCHANGE_ID.

   A server MUST NOT use the same client ID for two different
   incarnations of an eir_clientowner.

   In addition to the client ID and sequence ID, the server returns a
   server owner (eir_server_owner) and server scope (eir_server_scope).
   The former field is used for network trunking as described in
   Section 2.10.5.  The latter field is used to allow clients to
   determine when client IDs sent by one server may be recognized by
   another in the event of file system migration (see Section 11.7.7).

   The client ID returned by EXCHANGE_ID is only unique relative to the
   combination of eir_server_owner.so_major_id and eir_server_scope.
   Thus, if two servers return the same client ID, the onus is on the
   client to distinguish the client IDs on the basis of
   eir_server_owner.so_major_id and eir_server_scope.  In the event two
   different servers claim matching server_owner.so_major_id and
   eir_server_scope, the client can use the verification techniques
   discussed in Section 2.10.5 to determine if the servers are distinct.
   If they are distinct, then the client will need to note the
   destination network addresses of the connections used with each
   server, and use the network address as the final discriminator.

   The server, as defined by the unique identity expressed in the
   so_major_id of the server owner and the server scope, needs to track
   several properties of each client ID it hands out.  The properties
   apply to the client ID and all sessions associated with the client
   ID.  The properties are derived from the arguments and results of
   EXCHANGE_ID.  The client ID properties include:

   o  The capabilities expressed by the following bits, which come from
      the results of EXCHANGE_ID:




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      *  EXCHGID4_FLAG_SUPP_MOVED_REFER

      *  EXCHGID4_FLAG_SUPP_MOVED_MIGR

      *  EXCHGID4_FLAG_BIND_PRINC_STATEID

      *  EXCHGID4_FLAG_USE_NON_PNFS

      *  EXCHGID4_FLAG_USE_PNFS_MDS

      *  EXCHGID4_FLAG_USE_PNFS_DS

      These properties may be updated by subsequent EXCHANGE_ID requests
      on confirmed client IDs though the server MAY refuse to change
      them.

   o  The state protection method used, one of SP4_NONE, SP4_MACH_CRED,
      or SP4_SSV, as set by the spa_how field of the arguments to
      EXCHANGE_ID.  Once the client ID is confirmed, this property
      cannot be updated by subsequent EXCHANGE_ID requests.

   o  For SP4_MACH_CRED or SP4_SSV state protection:

      *  The list of operations (spo_must_enforce) that MUST use the
         specified state protection.  This list comes from the results
         of EXCHANGE_ID.

      *  The list of operations (spo_must_allow) that MAY use the
         specified state protection.  This list comes from the results
         of EXCHANGE_ID.

      Once the client ID is confirmed, these properties cannot be
      updated by subsequent EXCHANGE_ID requests.

   o  For SP4_SSV protection:

      *  The OID of the hash algorithm.  This property is represented by
         one of the algorithms in the ssp_hash_algs field of the
         EXCHANGE_ID arguments.  Once the client ID is confirmed, this
         property cannot be updated by subsequent EXCHANGE_ID requests.

      *  The OID of the encryption algorithm.  This property is
         represented by one of the algorithms in the ssp_encr_algs field
         of the EXCHANGE_ID arguments.  Once the client ID is confirmed,
         this property cannot be updated by subsequent EXCHANGE_ID
         requests.





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      *  The length of the SSV.  This property is represented by the
         spi_ssv_len field in the EXCHANGE_ID results.  Once the client
         ID is confirmed, this property cannot be updated by subsequent
         EXCHANGE_ID requests.

         There are REQUIRED and RECOMMENDED relationships among the
         length of the key of the encryption algorithm ("key length"),
         the length of the output of hash algorithm ("hash length"), and
         the length of the SSV ("SSV length").

         +  key length MUST be <= hash length.  This is because the keys
            used for the encryption algorithm are actually subkeys
            derived from the SSV, and the derivation is via the hash
            algorithm.  The selection of an encryption algorithm with a
            key length that exceeded the length of the output of the
            hash algorithm would require padding, and thus weaken the
            use of the encryption algorithm.

         +  hash length SHOULD be <= SSV length.  This is because the
            SSV is a key used to derive subkeys via an HMAC, and it is
            recommended that the key used as input to an HMAC be at
            least as long as the length of the HMAC's hash algorithm's
            output (see Section 3 of RFC2104 [11]).

         +  key length SHOULD be <= SSV length.  This is a transitive
            result of the above two invariants.

         +  key length SHOULD be >= hash length / 2.  This is because
            the subkey derivation is via an HMAC and it is recommended
            that if the HMAC has to be truncated, it should not be
            truncated to less than half the hash length (see Section 4
            of RFC2104 [11]).

      *  Number of concurrent versions of the SSV the client and server
         will support (Section 2.10.9).  This property is represented by
         spi_window in the EXCHANGE_ID results.  The property may be
         updated by subsequent EXCHANGE_ID requests.

   o  The client's implementation ID as represented by the
      eia_client_impl_id field of the arguments.  The property may be
      updated by subsequent EXCHANGE_ID requests.

   o  The server's implementation ID as represented by the
      eir_server_impl_id field of the reply.  The property may be
      updated by replies to subsequent EXCHANGE_ID requests.

   The eia_flags passed as part of the arguments and the eir_flags
   results allow the client and server to inform each other of their



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   capabilities as well as indicate how the client ID will be used.
   Whether a bit is set or cleared on the arguments' flags does not
   force the server to set or clear the same bit on the results' side.
   Bits not defined above cannot be set in the eia_flags field.  If they
   are, the server MUST reject the operation with NFS4ERR_INVAL.

   The EXCHGID4_FLAG_UPD_CONFIRMED_REC_A bit can only be set in
   eia_flags; it is always off in eir_flags.  The
   EXCHGID4_FLAG_CONFIRMED_R bit can only be set in eir_flags; it is
   always off in eia_flags.  If the server recognizes the co_ownerid and
   co_verifier as mapping to a confirmed client ID, it sets
   EXCHGID4_FLAG_CONFIRMED_R in eir_flags.  The
   EXCHGID4_FLAG_CONFIRMED_R flag allows a client to tell if the client
   ID it is trying to create already exists and is confirmed.

   If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set in eia_flags, this means
   that the client is attempting to update properties of an existing
   confirmed client ID (if the client wants to update properties of an
   unconfirmed client ID, it MUST NOT set
   EXCHGID4_FLAG_UPD_CONFIRMED_REC_A).  If so, it is RECOMMENDED that
   the client send the update EXCHANGE_ID operation in the same COMPOUND
   as a SEQUENCE so that the EXCHANGE_ID is executed exactly once.
   Whether the client can update the properties of client ID depends on
   the state protection it selected when the client ID was created, and
   the principal and security flavor it uses when sending the
   EXCHANGE_ID request.  The situations described in items 6, 7, 8, or 9
   of the second numbered list of Section 18.35.4 will apply.  Note that
   if the operation succeeds and returns a client ID that is already
   confirmed, the server MUST set the EXCHGID4_FLAG_CONFIRMED_R bit in
   eir_flags.

   If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags, this
   means that the client is trying to establish a new client ID; it is
   attempting to trunk data communication to the server
   (Section 2.10.5); or it is attempting to update properties of an
   unconfirmed client ID.  The situations described in items 1, 2, 3, 4,
   or 5 of the second numbered list of Section 18.35.4 will apply.  Note
   that if the operation succeeds and returns a client ID that was
   previously confirmed, the server MUST set the
   EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.

   When the EXCHGID4_FLAG_SUPP_MOVED_REFER flag bit is set, the client
   indicates that it is capable of dealing with an NFS4ERR_MOVED error
   as part of a referral sequence.  When this bit is not set, it is
   still legal for the server to perform a referral sequence.  However,
   a server may use the fact that the client is incapable of correctly
   responding to a referral, by avoiding it for that particular client.
   It may, for instance, act as a proxy for that particular file system,



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   at some cost in performance, although it is not obligated to do so.
   If the server will potentially perform a referral, it MUST set
   EXCHGID4_FLAG_SUPP_MOVED_REFER in eir_flags.

   When the EXCHGID4_FLAG_SUPP_MOVED_MIGR is set, the client indicates
   that it is capable of dealing with an NFS4ERR_MOVED error as part of
   a file system migration sequence.  When this bit is not set, it is
   still legal for the server to indicate that a file system has moved,
   when this in fact happens.  However, a server may use the fact that
   the client is incapable of correctly responding to a migration in its
   scheduling of file systems to migrate so as to avoid migration of
   file systems being actively used.  It may also hide actual migrations
   from clients unable to deal with them by acting as a proxy for a
   migrated file system for particular clients, at some cost in
   performance, although it is not obligated to do so.  If the server
   will potentially perform a migration, it MUST set
   EXCHGID4_FLAG_SUPP_MOVED_MIGR in eir_flags.

   When EXCHGID4_FLAG_BIND_PRINC_STATEID is set, the client indicates
   that it wants the server to bind the stateid to the principal.  This
   means that when a principal creates a stateid, it has to be the one
   to use the stateid.  If the server will perform binding, it will
   return EXCHGID4_FLAG_BIND_PRINC_STATEID.  The server MAY return
   EXCHGID4_FLAG_BIND_PRINC_STATEID even if the client does not request
   it.  If an update to the client ID changes the value of
   EXCHGID4_FLAG_BIND_PRINC_STATEID's client ID property, the effect
   applies only to new stateids.  Existing stateids (and all stateids
   with the same "other" field) that were created with stateid to
   principal binding in force will continue to have binding in force.
   Existing stateids (and all stateids with the same "other" field) that
   were created with stateid to principal not in force will continue to
   have binding not in force.

   The EXCHGID4_FLAG_USE_NON_PNFS, EXCHGID4_FLAG_USE_PNFS_MDS, and
   EXCHGID4_FLAG_USE_PNFS_DS bits are described in Section 13.1 and
   convey roles the client ID is to be used for in a pNFS environment.
   The server MUST set one of the acceptable combinations of these bits
   (roles) in eir_flags, as specified in Section 13.1.  Note that the
   same client owner/server owner pair can have multiple roles.
   Multiple roles can be associated with the same client ID or with
   different client IDs.  Thus, if a client sends EXCHANGE_ID from the
   same client owner to the same server owner multiple times, but
   specifies different pNFS roles each time, the server might return
   different client IDs.  Given that different pNFS roles might have
   different client IDs, the client may ask for different properties for
   each role/client ID.





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   The spa_how field of the eia_state_protect field specifies how the
   client wants to protect its client, locking, and session states from
   unauthorized changes (Section 2.10.8.3):

   o  SP4_NONE.  The client does not request the NFSv4.1 server to
      enforce state protection.  The NFSv4.1 server MUST NOT enforce
      state protection for the returned client ID.

   o  SP4_MACH_CRED.  If spa_how is SP4_MACH_CRED, then the client MUST
      send the EXCHANGE_ID request with RPCSEC_GSS as the security
      flavor, and with a service of RPC_GSS_SVC_INTEGRITY or
      RPC_GSS_SVC_PRIVACY.  If SP4_MACH_CRED is specified, then the
      client wants to use an RPCSEC_GSS-based machine credential to
      protect its state.  The server MUST note the principal the
      EXCHANGE_ID operation was sent with, and the GSS mechanism used.
      These notes collectively comprise the machine credential.

      After the client ID is confirmed, as long as the lease associated
      with the client ID is unexpired, a subsequent EXCHANGE_ID
      operation that uses the same eia_clientowner.co_owner as the first
      EXCHANGE_ID MUST also use the same machine credential as the first
      EXCHANGE_ID.  The server returns the same client ID for the
      subsequent EXCHANGE_ID as that returned from the first
      EXCHANGE_ID.

   o  SP4_SSV.  If spa_how is SP4_SSV, then the client MUST send the
      EXCHANGE_ID request with RPCSEC_GSS as the security flavor, and
      with a service of RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY.
      If SP4_SSV is specified, then the client wants to use the SSV to
      protect its state.  The server records the credential used in the
      request as the machine credential (as defined above) for the
      eia_clientowner.co_owner.  The CREATE_SESSION operation that
      confirms the client ID MUST use the same machine credential.

   When a client specifies SP4_MACH_CRED or SP4_SSV, it also provides
   two lists of operations (each expressed as a bitmap).  The first list
   is spo_must_enforce and consists of those operations the client MUST
   send (subject to the server confirming the list of operations in the
   result of EXCHANGE_ID) with the machine credential (if SP4_MACH_CRED
   protection is specified) or the SSV-based credential (if SP4_SSV
   protection is used).  The client MUST send the operations with
   RPCSEC_GSS credentials that specify the RPC_GSS_SVC_INTEGRITY or
   RPC_GSS_SVC_PRIVACY security service.  Typically, the first list of
   operations includes EXCHANGE_ID, CREATE_SESSION, DELEGPURGE,
   DESTROY_SESSION, BIND_CONN_TO_SESSION, and DESTROY_CLIENTID.  The
   client SHOULD NOT specify in this list any operations that require a
   filehandle because the server's access policies MAY conflict with the




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   client's choice, and thus the client would then be unable to access a
   subset of the server's namespace.

   Note that if SP4_SSV protection is specified, and the client
   indicates that CREATE_SESSION must be protected with SP4_SSV, because
   the SSV cannot exist without a confirmed client ID, the first
   CREATE_SESSION MUST instead be sent using the machine credential, and
   the server MUST accept the machine credential.

   There is a corresponding result, also called spo_must_enforce, of the
   operations for which the server will require SP4_MACH_CRED or SP4_SSV
   protection.  Normally, the server's result equals the client's
   argument, but the result MAY be different.  If the client requests
   one or more operations in the set { EXCHANGE_ID, CREATE_SESSION,
   DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION, DESTROY_CLIENTID
   }, then the result spo_must_enforce MUST include the operations the
   client requested from that set.

   If spo_must_enforce in the results has BIND_CONN_TO_SESSION set, then
   connection binding enforcement is enabled, and the client MUST use
   the machine (if SP4_MACH_CRED protection is used) or SSV (if SP4_SSV
   protection is used) credential on calls to BIND_CONN_TO_SESSION.

   The second list is spo_must_allow and consists of those operations
   the client wants to have the option of sending with the machine
   credential or the SSV-based credential, even if the object the
   operations are performed on is not owned by the machine or SSV
   credential.

   The corresponding result, also called spo_must_allow, consists of the
   operations the server will allow the client to use SP4_SSV or
   SP4_MACH_CRED credentials with.  Normally, the server's result equals
   the client's argument, but the result MAY be different.

   The purpose of spo_must_allow is to allow clients to solve the
   following conundrum.  Suppose the client ID is confirmed with
   EXCHGID4_FLAG_BIND_PRINC_STATEID, and it calls OPEN with the
   RPCSEC_GSS credentials of a normal user.  Now suppose the user's
   credentials expire, and cannot be renewed (e.g., a Kerberos ticket
   granting ticket expires, and the user has logged off and will not be
   acquiring a new ticket granting ticket).  The client will be unable
   to send CLOSE without the user's credentials, which is to say the
   client has to either leave the state on the server or re-send
   EXCHANGE_ID with a new verifier to clear all state, that is, unless
   the client includes CLOSE on the list of operations in spo_must_allow
   and the server agrees.

   The SP4_SSV protection parameters also have:



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   ssp_hash_algs:

      This is the set of algorithms the client supports for the purpose
      of computing the digests needed for the internal SSV GSS mechanism
      and for the SET_SSV operation.  Each algorithm is specified as an
      object identifier (OID).  The REQUIRED algorithms for a server are
      id-sha1, id-sha224, id-sha256, id-sha384, and id-sha512 [28].  The
      algorithm the server selects among the set is indicated in
      spi_hash_alg, a field of spr_ssv_prot_info.  The field
      spi_hash_alg is an index into the array ssp_hash_algs.  If the
      server does not support any of the offered algorithms, it returns
      NFS4ERR_HASH_ALG_UNSUPP.  If ssp_hash_algs is empty, the server
      MUST return NFS4ERR_INVAL.

   ssp_encr_algs:

      This is the set of algorithms the client supports for the purpose
      of providing privacy protection for the internal SSV GSS
      mechanism.  Each algorithm is specified as an OID.  The REQUIRED
      algorithm for a server is id-aes256-CBC.  The RECOMMENDED
      algorithms are id-aes192-CBC and id-aes128-CBC [29].  The selected
      algorithm is returned in spi_encr_alg, an index into
      ssp_encr_algs.  If the server does not support any of the offered
      algorithms, it returns NFS4ERR_ENCR_ALG_UNSUPP.  If ssp_encr_algs
      is empty, the server MUST return NFS4ERR_INVAL.  Note that due to
      previously stated requirements and recommendations on the
      relationships between key length and hash length, some
      combinations of RECOMMENDED and REQUIRED encryption algorithm and
      hash algorithm either SHOULD NOT or MUST NOT be used.  Table 12
      summarizes the illegal and discouraged combinations.

   ssp_window:

      This is the number of SSV versions the client wants the server to
      maintain (i.e., each successful call to SET_SSV produces a new
      version of the SSV).  If ssp_window is zero, the server MUST
      return NFS4ERR_INVAL.  The server responds with spi_window, which
      MUST NOT exceed ssp_window, and MUST be at least one.  Any
      requests on the backchannel or fore channel that are using a
      version of the SSV that is outside the window will fail with an
      ONC RPC authentication error, and the requester will have to retry
      them with the same slot ID and sequence ID.

   ssp_num_gss_handles:

      This is the number of RPCSEC_GSS handles the server should create
      that are based on the GSS SSV mechanism (Section 2.10.9).  It is
      not the total number of RPCSEC_GSS handles for the client ID.



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      Indeed, subsequent calls to EXCHANGE_ID will add RPCSEC_GSS
      handles.  The server responds with a list of handles in
      spi_handles.  If the client asks for at least one handle and the
      server cannot create it, the server MUST return an error.  The
      handles in spi_handles are not available for use until the client
      ID is confirmed, which could be immediately if EXCHANGE_ID returns
      EXCHGID4_FLAG_CONFIRMED_R, or upon successful confirmation from
      CREATE_SESSION.

      While a client ID can span all the connections that are connected
      to a server sharing the same eir_server_owner.so_major_id, the
      RPCSEC_GSS handles returned in spi_handles can only be used on
      connections connected to a server that returns the same the
      eir_server_owner.so_major_id and eir_server_owner.so_minor_id on
      each connection.  It is permissible for the client to set
      ssp_num_gss_handles to zero; the client can create more handles
      with another EXCHANGE_ID call.

      Because each SSV RPCSEC_GSS handle shares a common SSV GSS
      context, there are security considerations specific to this
      situation discussed in Section 2.10.10.

      The seq_window (see Section 5.2.3.1 of RFC2203 [4]) of each
      RPCSEC_GSS handle in spi_handle MUST be the same as the seq_window
      of the RPCSEC_GSS handle used for the credential of the RPC
      request that the EXCHANGE_ID request was sent with.

   +-------------------+----------------------+------------------------+
   | Encryption        | MUST NOT be combined | SHOULD NOT be combined |
   | Algorithm         | with                 | with                   |
   +-------------------+----------------------+------------------------+
   | id-aes128-CBC     |                      | id-sha384, id-sha512   |
   | id-aes192-CBC     | id-sha1              | id-sha512              |
   | id-aes256-CBC     | id-sha1, id-sha224   |                        |
   +-------------------+----------------------+------------------------+

                                 Table 12

   The arguments include an array of up to one element in length called
   eia_client_impl_id.  If eia_client_impl_id is present, it contains
   the information identifying the implementation of the client.
   Similarly, the results include an array of up to one element in
   length called eir_server_impl_id that identifies the implementation
   of the server.  Servers MUST accept a zero-length eia_client_impl_id
   array, and clients MUST accept a zero-length eir_server_impl_id
   array.





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   An example use for implementation identifiers would be diagnostic
   software that extracts this information in an attempt to identify
   interoperability problems, performance workload behaviors, or general
   usage statistics.  Since the intent of having access to this
   information is for planning or general diagnosis only, the client and
   server MUST NOT interpret this implementation identity information in
   a way that affects interoperational behavior of the implementation.
   The reason is that if clients and servers did such a thing, they
   might use fewer capabilities of the protocol than the peer can
   support, or the client and server might refuse to interoperate.

   Because it is possible that some implementations will violate the
   protocol specification and interpret the identity information,
   implementations MUST allow the users of the NFSv4 client and server
   to set the contents of the sent nfs_impl_id structure to any value.

18.35.4.  IMPLEMENTATION

   A server's client record is a 5-tuple:

   1.  co_ownerid

          The client identifier string, from the eia_clientowner
          structure of the EXCHANGE_ID4args structure.

   2.  co_verifier:

          A client-specific value used to indicate incarnations (where a
          client restart represents a new incarnation), from the
          eia_clientowner structure of the EXCHANGE_ID4args structure.

   3.  principal:

          The principal that was defined in the RPC header's credential
          and/or verifier at the time the client record was established.

   4.  client ID:

          The shorthand client identifier, generated by the server and
          returned via the eir_clientid field in the EXCHANGE_ID4resok
          structure.

   5.  confirmed:

          A private field on the server indicating whether or not a
          client record has been confirmed.  A client record is
          confirmed if there has been a successful CREATE_SESSION
          operation to confirm it.  Otherwise, it is unconfirmed.  An



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          unconfirmed record is established by an EXCHANGE_ID call.  Any
          unconfirmed record that is not confirmed within a lease period
          SHOULD be removed.

   The following identifiers represent special values for the fields in
   the records.

   ownerid_arg:

      The value of the eia_clientowner.co_ownerid subfield of the
      EXCHANGE_ID4args structure of the current request.

   verifier_arg:

      The value of the eia_clientowner.co_verifier subfield of the
      EXCHANGE_ID4args structure of the current request.

   old_verifier_arg:

      A value of the eia_clientowner.co_verifier field of a client
      record received in a previous request; this is distinct from
      verifier_arg.

   principal_arg:

      The value of the RPCSEC_GSS principal for the current request.

   old_principal_arg:

      A value of the principal of a client record as defined by the RPC
      header's credential or verifier of a previous request.  This is
      distinct from principal_arg.

   clientid_ret:

      The value of the eir_clientid field the server will return in the
      EXCHANGE_ID4resok structure for the current request.

   old_clientid_ret:

      The value of the eir_clientid field the server returned in the
      EXCHANGE_ID4resok structure for a previous request.  This is
      distinct from clientid_ret.

   confirmed:

      The client ID has been confirmed.




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   unconfirmed:

      The client ID has not been confirmed.

   Since EXCHANGE_ID is a non-idempotent operation, we must consider the
   possibility that retries occur as a result of a client restart,
   network partition, malfunctioning router, etc.  Retries are
   identified by the value of the eia_clientowner field of
   EXCHANGE_ID4args, and the method for dealing with them is outlined in
   the scenarios below.

   The scenarios are described in terms of the client record(s) a server
   has for a given co_ownerid.  Note that if the client ID was created
   specifying SP4_SSV state protection and EXCHANGE_ID as the one of the
   operations in spo_must_allow, then the server MUST authorize
   EXCHANGE_IDs with the SSV principal in addition to the principal that
   created the client ID.

   1.  New Owner ID

          If the server has no client records with
          eia_clientowner.co_ownerid matching ownerid_arg, and
          EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in the
          EXCHANGE_ID, then a new shorthand client ID (let us call it
          clientid_ret) is generated, and the following unconfirmed
          record is added to the server's state.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }

          Subsequently, the server returns clientid_ret.





   2.  Non-Update on Existing Client ID

          If the server has the following confirmed record, and the
          request does not have EXCHGID4_FLAG_UPD_CONFIRMED_REC_A set,
          then the request is the result of a retried request due to a
          faulty router or lost connection, or the client is trying to
          determine if it can perform trunking.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          confirmed }





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          Since the record has been confirmed, the client must have
          received the server's reply from the initial EXCHANGE_ID
          request.  Since the server has a confirmed record, and since
          EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, with the
          possible exception of eir_server_owner.so_minor_id, the server
          returns the same result it did when the client ID's properties
          were last updated (or if never updated, the result when the
          client ID was created).  The confirmed record is unchanged.

   3.  Client Collision

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
          server has the following confirmed record, then this request
          is likely the result of a chance collision between the values
          of the eia_clientowner.co_ownerid subfield of EXCHANGE_ID4args
          for two different clients.

          { ownerid_arg, *, old_principal_arg, old_clientid_ret,
          confirmed }

          If there is currently no state associated with
          old_clientid_ret, or if there is state but the lease has
          expired, then this case is effectively equivalent to the New
          Owner ID case of Paragraph 1.  The confirmed record is
          deleted, the old_clientid_ret and its lock state are deleted,
          a new shorthand client ID is generated, and the following
          unconfirmed record is added to the server's state.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }

          Subsequently, the server returns clientid_ret.



          If old_clientid_ret has an unexpired lease with state, then no
          state of old_clientid_ret is changed or deleted.  The server
          returns NFS4ERR_CLID_INUSE to indicate that the client should
          retry with a different value for the
          eia_clientowner.co_ownerid subfield of EXCHANGE_ID4args.  The
          client record is not changed.

   4.  Replacement of Unconfirmed Record

          If the EXCHGID4_FLAG_UPD_CONFIRMED_REC_A flag is not set, and
          the server has the following unconfirmed record, then the
          client is attempting EXCHANGE_ID again on an unconfirmed
          client ID, perhaps due to a retry, a client restart before



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          client ID confirmation (i.e., before CREATE_SESSION was
          called), or some other reason.

          { ownerid_arg, *, *, old_clientid_ret, unconfirmed }

          It is possible that the properties of old_clientid_ret are
          different than those specified in the current EXCHANGE_ID.
          Whether or not the properties are being updated, to eliminate
          ambiguity, the server deletes the unconfirmed record,
          generates a new client ID (clientid_ret), and establishes the
          following unconfirmed record:

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }



   5.  Client Restart

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and if the
          server has the following confirmed client record, then this
          request is likely from a previously confirmed client that has
          restarted.

          { ownerid_arg, old_verifier_arg, principal_arg,
          old_clientid_ret, confirmed }

          Since the previous incarnation of the same client will no
          longer be making requests, once the new client ID is confirmed
          by CREATE_SESSION, byte-range locks and share reservations
          should be released immediately rather than forcing the new
          incarnation to wait for the lease time on the previous
          incarnation to expire.  Furthermore, session state should be
          removed since if the client had maintained that information
          across restart, this request would not have been sent.  If the
          server supports neither the CLAIM_DELEGATE_PREV nor
          CLAIM_DELEG_PREV_FH claim types, associated delegations should
          be purged as well; otherwise, delegations are retained and
          recovery proceeds according to Section 10.2.1.

          After processing, clientid_ret is returned to the client and
          this client record is added:

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          unconfirmed }






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          The previously described confirmed record continues to exist,
          and thus the same ownerid_arg exists in both a confirmed and
          unconfirmed state at the same time.  The number of states can
          collapse to one once the server receives an applicable
          CREATE_SESSION or EXCHANGE_ID.

          +  If the server subsequently receives a successful
             CREATE_SESSION that confirms clientid_ret, then the server
             atomically destroys the confirmed record and makes the
             unconfirmed record confirmed as described in
             Section 18.36.4.

          +  If the server instead subsequently receives an EXCHANGE_ID
             with the client owner equal to ownerid_arg, one strategy is
             to simply delete the unconfirmed record, and process the
             EXCHANGE_ID as described in the entirety of
             Section 18.35.4.

   6.  Update

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          attempt at an update.

          { ownerid_arg, verifier_arg, principal_arg, clientid_ret,
          confirmed }

          Since the record has been confirmed, the client must have
          received the server's reply from the initial EXCHANGE_ID
          request.  The server allows the update, and the client record
          is left intact.

   7.  Update but No Confirmed Record

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has no confirmed record corresponding ownerid_arg, then the
          server returns NFS4ERR_NOENT and leaves any unconfirmed record
          intact.

   8.  Update but Wrong Verifier

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          illegal attempt at an update, perhaps because of a retry from
          a previous client incarnation.

          { ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }




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          The server returns NFS4ERR_NOT_SAME and leaves the client
          record intact.

   9.  Update but Wrong Principal

          If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the server
          has the following confirmed record, then this request is an
          illegal attempt at an update by an unauthorized principal.

          { ownerid_arg, verifier_arg, old_principal_arg, clientid_ret,
          confirmed }

          The server returns NFS4ERR_PERM and leaves the client record
          intact.

18.36.  Operation 43: CREATE_SESSION - Create New Session and Confirm
        Client ID

18.36.1.  ARGUMENT

   struct channel_attrs4 {
           count4                  ca_headerpadsize;
           count4                  ca_maxrequestsize;
           count4                  ca_maxresponsesize;
           count4                  ca_maxresponsesize_cached;
           count4                  ca_maxoperations;
           count4                  ca_maxrequests;
           uint32_t                ca_rdma_ird<1>;
   };

   const CREATE_SESSION4_FLAG_PERSIST              = 0x00000001;
   const CREATE_SESSION4_FLAG_CONN_BACK_CHAN       = 0x00000002;
   const CREATE_SESSION4_FLAG_CONN_RDMA            = 0x00000004;

   struct CREATE_SESSION4args {
           clientid4               csa_clientid;
           sequenceid4             csa_sequence;

           uint32_t                csa_flags;

           channel_attrs4          csa_fore_chan_attrs;
           channel_attrs4          csa_back_chan_attrs;

           uint32_t                csa_cb_program;
           callback_sec_parms4     csa_sec_parms<>;
   };





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18.36.2.  RESULT

   struct CREATE_SESSION4resok {
           sessionid4              csr_sessionid;
           sequenceid4             csr_sequence;

           uint32_t                csr_flags;

           channel_attrs4          csr_fore_chan_attrs;
           channel_attrs4          csr_back_chan_attrs;
   };

   union CREATE_SESSION4res switch (nfsstat4 csr_status) {
   case NFS4_OK:
           CREATE_SESSION4resok    csr_resok4;
   default:
           void;
   };


18.36.3.  DESCRIPTION

   This operation is used by the client to create new session objects on
   the server.

   CREATE_SESSION can be sent with or without a preceding SEQUENCE
   operation in the same COMPOUND procedure.  If CREATE_SESSION is sent
   with a preceding SEQUENCE operation, any session created by
   CREATE_SESSION has no direct relation to the session specified in the
   SEQUENCE operation, although the two sessions might be associated
   with the same client ID.  If CREATE_SESSION is sent without a
   preceding SEQUENCE, then it MUST be the only operation in the
   COMPOUND procedure's request.  If it is not, the server MUST return
   NFS4ERR_NOT_ONLY_OP.

   In addition to creating a session, CREATE_SESSION has the following
   effects:

   o  The first session created with a new client ID serves to confirm
      the creation of that client's state on the server.  The server
      returns the parameter values for the new session.

   o  The connection CREATE_SESSION that is sent over is associated with
      the session's fore channel.

   The arguments and results of CREATE_SESSION are described as follows:

   csa_clientid:



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      This is the client ID with which the new session will be
      associated.  The corresponding result is csr_sessionid, the
      session ID of the new session.

   csa_sequence:

      Each client ID serializes CREATE_SESSION via a per-client ID
      sequence number (see Section 18.36.4).  The corresponding result
      is csr_sequence, which MUST be equal to csa_sequence.

   In the next three arguments, the client offers a value that is to be
   a property of the session.  Except where stated otherwise, it is
   RECOMMENDED that the server accept the value.  If it is not
   acceptable, the server MAY use a different value.  Regardless, the
   server MUST return the value the session will use (which will be
   either what the client offered, or what the server is insisting on)
   to the client.

   csa_flags:

      The csa_flags field contains a list of the following flag bits:

      CREATE_SESSION4_FLAG_PERSIST:

         If CREATE_SESSION4_FLAG_PERSIST is set, the client wants the
         server to provide a persistent reply cache.  For sessions in
         which only idempotent operations will be used (e.g., a read-
         only session), clients SHOULD NOT set
         CREATE_SESSION4_FLAG_PERSIST.  If the server does not or cannot
         provide a persistent reply cache, the server MUST NOT set
         CREATE_SESSION4_FLAG_PERSIST in the field csr_flags.

         If the server is a pNFS metadata server, for reasons described
         in Section 12.5.2 it SHOULD support
         CREATE_SESSION4_FLAG_PERSIST if it supports the layout_hint
         (Section 5.12.4) attribute.

      CREATE_SESSION4_FLAG_CONN_BACK_CHAN:

         If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags, the
         client is requesting that the connection over which the
         CREATE_SESSION operation arrived be associated with the
         session's backchannel in addition to its fore channel.  If the
         server agrees, it sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN in
         the result field csr_flags.  If
         CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,
         then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set in
         csr_flags.



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      CREATE_SESSION4_FLAG_CONN_RDMA:

         If CREATE_SESSION4_FLAG_CONN_RDMA is set in csa_flags, and if
         the connection over which the CREATE_SESSION operation arrived
         is currently in non-RDMA mode but has the capability to operate
         in RDMA mode, then the client is requesting that the server
         "step up" to RDMA mode on the connection.  If the server
         agrees, it sets CREATE_SESSION4_FLAG_CONN_RDMA in the result
         field csr_flags.  If CREATE_SESSION4_FLAG_CONN_RDMA is not set
         in csa_flags, then CREATE_SESSION4_FLAG_CONN_RDMA MUST NOT be
         set in csr_flags.  Note that once the server agrees to step up,
         it and the client MUST exchange all future traffic on the
         connection with RPC RDMA framing and not Record Marking ([8]).

   csa_fore_chan_attrs, csa_fore_chan_attrs:

      The csa_fore_chan_attrs and csa_back_chan_attrs fields apply to
      attributes of the fore channel (which conveys requests originating
      from the client to the server), and the backchannel (the channel
      that conveys callback requests originating from the server to the
      client), respectively.  The results are in corresponding
      structures called csr_fore_chan_attrs and csr_back_chan_attrs.
      The results establish attributes for each channel, and on all
      subsequent use of each channel of the session.  Each structure has
      the following fields:

      ca_headerpadsize:

         The maximum amount of padding the requester is willing to apply
         to ensure that write payloads are aligned on some boundary at
         the replier.  For each channel, the server

         +  will reply in ca_headerpadsize with its preferred value, or
            zero if padding is not in use, and

         +  MAY decrease this value but MUST NOT increase it.

      ca_maxrequestsize:

         The maximum size of a COMPOUND or CB_COMPOUND request that will
         be sent.  This size represents the XDR encoded size of the
         request, including the RPC headers (including security flavor
         credentials and verifiers) but excludes any RPC transport
         framing headers.  Imagine a request coming over a non-RDMA TCP/
         IP connection, and that it has a single Record Marking header
         preceding it.  The maximum allowable count encoded in the
         header will be ca_maxrequestsize.  If a requester sends a
         request that exceeds ca_maxrequestsize, the error



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         NFS4ERR_REQ_TOO_BIG will be returned per the description in
         Section 2.10.6.4.  For each channel, the server MAY decrease
         this value but MUST NOT increase it.

      ca_maxresponsesize:

         The maximum size of a COMPOUND or CB_COMPOUND reply that the
         requester will accept from the replier including RPC headers
         (see the ca_maxrequestsize definition).  For each channel, the
         server MAY decrease this value, but MUST NOT increase it.
         However, if the client selects a value for ca_maxresponsesize
         such that a replier on a channel could never send a response,
         the server SHOULD return NFS4ERR_TOOSMALL in the CREATE_SESSION
         reply.  After the session is created, if a requester sends a
         request for which the size of the reply would exceed this
         value, the replier will return NFS4ERR_REP_TOO_BIG, per the
         description in Section 2.10.6.4.

      ca_maxresponsesize_cached:

         Like ca_maxresponsesize, but the maximum size of a reply that
         will be stored in the reply cache (Section 2.10.6.1).  For each
         channel, the server MAY decrease this value, but MUST NOT
         increase it.  If, in the reply to CREATE_SESSION, the value of
         ca_maxresponsesize_cached of a channel is less than the value
         of ca_maxresponsesize of the same channel, then this is an
         indication to the requester that it needs to be selective about
         which replies it directs the replier to cache; for example,
         large replies from nonidempotent operations (e.g., COMPOUND
         requests with a READ operation) should not be cached.  The
         requester decides which replies to cache via an argument to the
         SEQUENCE (the sa_cachethis field, see Section 18.46) or
         CB_SEQUENCE (the csa_cachethis field, see Section 20.9)
         operations.  After the session is created, if a requester sends
         a request for which the size of the reply would exceed
         ca_maxresponsesize_cached, the replier will return
         NFS4ERR_REP_TOO_BIG_TO_CACHE, per the description in
         Section 2.10.6.4.

      ca_maxoperations:

         The maximum number of operations the replier will accept in a
         COMPOUND or CB_COMPOUND.  For the backchannel, the server MUST
         NOT change the value the client offers.  For the fore channel,
         the server MAY change the requested value.  After the session
         is created, if a requester sends a COMPOUND or CB_COMPOUND with
         more operations than ca_maxoperations, the replier MUST return
         NFS4ERR_TOO_MANY_OPS.



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      ca_maxrequests:

         The maximum number of concurrent COMPOUND or CB_COMPOUND
         requests the requester will send on the session.  Subsequent
         requests will each be assigned a slot identifier by the
         requester within the range zero to ca_maxrequests - 1
         inclusive.  For the backchannel, the server MUST NOT change the
         value the client offers.  For the fore channel, the server MAY
         change the requested value.

      ca_rdma_ird:

         This array has a maximum of one element.  If this array has one
         element, then the element contains the inbound RDMA read queue
         depth (IRD).  For each channel, the server MAY decrease this
         value, but MUST NOT increase it.

   csa_cb_program

      This is the ONC RPC program number the server MUST use in any
      callbacks sent through the backchannel to the client.  The server
      MUST specify an ONC RPC program number equal to csa_cb_program and
      an ONC RPC version number equal to 4 in callbacks sent to the
      client.  If a CB_COMPOUND is sent to the client, the server MUST
      use a minor version number of 1.  There is no corresponding
      result.

   csa_sec_parms

      The field csa_sec_parms is an array of acceptable security
      credentials the server can use on the session's backchannel.
      Three security flavors are supported: AUTH_NONE, AUTH_SYS, and
      RPCSEC_GSS.  If AUTH_NONE is specified for a credential, then this
      says the client is authorizing the server to use AUTH_NONE on all
      callbacks for the session.  If AUTH_SYS is specified, then the
      client is authorizing the server to use AUTH_SYS on all callbacks,
      using the credential specified cbsp_sys_cred.  If RPCSEC_GSS is
      specified, then the server is allowed to use the RPCSEC_GSS
      context specified in cbsp_gss_parms as the RPCSEC_GSS context in
      the credential of the RPC header of callbacks to the client.
      There is no corresponding result.

      The RPCSEC_GSS context for the backchannel is specified via a pair
      of values of data type gsshandle4_t.  The data type gsshandle4_t
      represents an RPCSEC_GSS handle, and is precisely the same as the
      data type of the "handle" field of the rpc_gss_init_res data type
      defined in Section 5.2.3.1, "Context Creation Response -
      Successful Acceptance", of [4].



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      The first RPCSEC_GSS handle, gcbp_handle_from_server, is the fore
      handle the server returned to the client (either in the handle
      field of data type rpc_gss_init_res or as one of the elements of
      the spi_handles field returned in the reply to EXCHANGE_ID) when
      the RPCSEC_GSS context was created on the server.  The second
      handle, gcbp_handle_from_client, is the back handle to which the
      client will map the RPCSEC_GSS context.  The server can
      immediately use the value of gcbp_handle_from_client in the
      RPCSEC_GSS credential in callback RPCs.  That is, the value in
      gcbp_handle_from_client can be used as the value of the field
      "handle" in data type rpc_gss_cred_t (see Section 5, "Elements of
      the RPCSEC_GSS Security Protocol", of [4]) in callback RPCs.  The
      server MUST use the RPCSEC_GSS security service specified in
      gcbp_service, i.e., it MUST set the "service" field of the
      rpc_gss_cred_t data type in RPCSEC_GSS credential to the value of
      gcbp_service (see Section 5.3.1, "RPC Request Header", of [4]).

      If the RPCSEC_GSS handle identified by gcbp_handle_from_server
      does not exist on the server, the server will return
      NFS4ERR_NOENT.

      Within each element of csa_sec_parms, the fore and back RPCSEC_GSS
      contexts MUST share the same GSS context and MUST have the same
      seq_window (see Section 5.2.3.1 of RFC2203 [4]).  The fore and
      back RPCSEC_GSS context state are independent of each other as far
      as the RPCSEC_GSS sequence number (see the seq_num field in the
      rpc_gss_cred_t data type of Sections 5 and 5.3.1 of [4]).

      If an RPCSEC_GSS handle is using the SSV context (see
      Section 2.10.9), then because each SSV RPCSEC_GSS handle shares a
      common SSV GSS context, there are security considerations specific
      to this situation discussed in Section 2.10.10.



   Once the session is created, the first SEQUENCE or CB_SEQUENCE
   received on a slot MUST have a sequence ID equal to 1; if not, the
   replier MUST return NFS4ERR_SEQ_MISORDERED.

18.36.4.  IMPLEMENTATION

   To describe a possible implementation, the same notation for client
   records introduced in the description of EXCHANGE_ID is used with the
   following addition:

      clientid_arg: The value of the csa_clientid field of the
      CREATE_SESSION4args structure of the current request.




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   Since CREATE_SESSION is a non-idempotent operation, we need to
   consider the possibility that retries may occur as a result of a
   client restart, network partition, malfunctioning router, etc.  For
   each client ID created by EXCHANGE_ID, the server maintains a
   separate reply cache (called the CREATE_SESSION reply cache) similar
   to the session reply cache used for SEQUENCE operations, with two
   distinctions.

   o  First, this is a reply cache just for detecting and processing
      CREATE_SESSION requests for a given client ID.

   o  Second, the size of the client ID reply cache is of one slot (and
      as a result, the CREATE_SESSION request does not carry a slot
      number).  This means that at most one CREATE_SESSION request for a
      given client ID can be outstanding.

   As previously stated, CREATE_SESSION can be sent with or without a
   preceding SEQUENCE operation.  Even if a SEQUENCE precedes
   CREATE_SESSION, the server MUST maintain the CREATE_SESSION reply
   cache, which is separate from the reply cache for the session
   associated with a SEQUENCE.  If CREATE_SESSION was originally sent by
   itself, the client MAY send a retry of the CREATE_SESSION operation
   within a COMPOUND preceded by a SEQUENCE.  If CREATE_SESSION was
   originally sent in a COMPOUND that started with a SEQUENCE, then the
   client SHOULD send a retry in a COMPOUND that starts with a SEQUENCE
   that has the same session ID as the SEQUENCE of the original request.
   However, the client MAY send a retry in a COMPOUND that either has no
   preceding SEQUENCE, or has a preceding SEQUENCE that refers to a
   different session than the original CREATE_SESSION.  This might be
   necessary if the client sends a CREATE_SESSION in a COMPOUND preceded
   by a SEQUENCE with session ID X, and session X no longer exists.
   Regardless, any retry of CREATE_SESSION, with or without a preceding
   SEQUENCE, MUST use the same value of csa_sequence as the original.

   After the client received a reply to an EXCHANGE_ID operation that
   contains a new, unconfirmed client ID, the server expects the client
   to follow with a CREATE_SESSION operation to confirm the client ID.
   The server expects value of csa_sequenceid in the arguments to that
   CREATE_SESSION to be to equal the value of the field eir_sequenceid
   that was returned in results of the EXCHANGE_ID that returned the
   unconfirmed client ID.  Before the server replies to that EXCHANGE_ID
   operation, it initializes the client ID slot to be equal to
   eir_sequenceid - 1 (accounting for underflow), and records a
   contrived CREATE_SESSION result with a "cached" result of
   NFS4ERR_SEQ_MISORDERED.  With the client ID slot thus initialized,
   the processing of the CREATE_SESSION operation is divided into four
   phases:




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   1.  Client record look up.  The server looks up the client ID in its
       client record table.  If the server contains no records with
       client ID equal to clientid_arg, then most likely the client's
       state has been purged during a period of inactivity, possibly due
       to a loss of connectivity.  NFS4ERR_STALE_CLIENTID is returned,
       and no changes are made to any client records on the server.
       Otherwise, the server goes to phase 2.

   2.  Sequence ID processing.  If csa_sequenceid is equal to the
       sequence ID in the client ID's slot, then this is a replay of the
       previous CREATE_SESSION request, and the server returns the
       cached result.  If csa_sequenceid is not equal to the sequence ID
       in the slot, and is more than one greater (accounting for
       wraparound), then the server returns the error
       NFS4ERR_SEQ_MISORDERED, and does not change the slot.  If
       csa_sequenceid is equal to the slot's sequence ID + 1 (accounting
       for wraparound), then the slot's sequence ID is set to
       csa_sequenceid, and the CREATE_SESSION processing goes to the
       next phase.  A subsequent new CREATE_SESSION call over the same
       client ID MUST use a csa_sequenceid that is one greater than the
       sequence ID in the slot.

   3.  Client ID confirmation.  If this would be the first session for
       the client ID, the CREATE_SESSION operation serves to confirm the
       client ID.  Otherwise, the client ID confirmation phase is
       skipped and only the session creation phase occurs.  Any case in
       which there is more than one record with identical values for
       client ID represents a server implementation error.  Operation in
       the potential valid cases is summarized as follows.

       *  Successful Confirmation

             If the server has the following unconfirmed record, then
             this is the expected confirmation of an unconfirmed record.

             { ownerid, verifier, principal_arg, clientid_arg,
             unconfirmed }

             As noted in Section 18.35.4, the server might also have the
             following confirmed record.

             { ownerid, old_verifier, principal_arg, old_clientid,
             confirmed }

             The server schedules the replacement of both records with:

             { ownerid, verifier, principal_arg, clientid_arg, confirmed
             }



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             The processing of CREATE_SESSION continues on to session
             creation.  Once the session is successfully created, the
             scheduled client record replacement is committed.  If the
             session is not successfully created, then no changes are
             made to any client records on the server.

       *  Unsuccessful Confirmation

             If the server has the following record, then the client has
             changed principals after the previous EXCHANGE_ID request,
             or there has been a chance collision between shorthand
             client identifiers.

             { *, *, old_principal_arg, clientid_arg, * }

             Neither of these cases is permissible.  Processing stops
             and NFS4ERR_CLID_INUSE is returned to the client.  No
             changes are made to any client records on the server.

   4.  Session creation.  The server confirmed the client ID, either in
       this CREATE_SESSION operation, or a previous CREATE_SESSION
       operation.  The server examines the remaining fields of the
       arguments.

       The server creates the session by recording the parameter values
       used (including whether the CREATE_SESSION4_FLAG_PERSIST flag is
       set and has been accepted by the server) and allocating space for
       the session reply cache (if there is not enough space, the server
       returns NFS4ERR_NOSPC).  For each slot in the reply cache, the
       server sets the sequence ID to zero, and records an entry
       containing a COMPOUND reply with zero operations and the error
       NFS4ERR_SEQ_MISORDERED.  This way, if the first SEQUENCE request
       sent has a sequence ID equal to zero, the server can simply
       return what is in the reply cache: NFS4ERR_SEQ_MISORDERED.  The
       client initializes its reply cache for receiving callbacks in the
       same way, and similarly, the first CB_SEQUENCE operation on a
       slot after session creation MUST have a sequence ID of one.

       If the session state is created successfully, the server
       associates the session with the client ID provided by the client.

       When a request that had CREATE_SESSION4_FLAG_CONN_RDMA set needs
       to be retried, the retry MUST be done on a new connection that is
       in non-RDMA mode.  If properties of the new connection are
       different enough that the arguments to CREATE_SESSION need to
       change, then a non-retry MUST be sent.  The server will
       eventually dispose of any session that was created on the
       original connection.



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   On the backchannel, the client and server might wish to have many
   slots, in some cases perhaps more that the fore channel, in order to
   deal with the situations where the network link has high latency and
   is the primary bottleneck for response to recalls.  If so, and if the
   client provides too few slots to the backchannel, the server might
   limit the number of recallable objects it gives to the client.

   Implementing RPCSEC_GSS callback support requires changes to both the
   client and server implementations of RPCSEC_GSS.  One possible set of
   changes includes:

   o  Adding a data structure that wraps the GSS-API context with a
      reference count.

   o  New functions to increment and decrement the reference count.  If
      the reference count is decremented to zero, the wrapper data
      structure and the GSS-API context it refers to would be freed.

   o  Change RPCSEC_GSS to create the wrapper data structure upon
      receiving GSS-API context from gss_accept_sec_context() and
      gss_init_sec_context().  The reference count would be initialized
      to 1.

   o  Adding a function to map an existing RPCSEC_GSS handle to a
      pointer to the wrapper data structure.  The reference count would
      be incremented.

   o  Adding a function to create a new RPCSEC_GSS handle from a pointer
      to the wrapper data structure.  The reference count would be
      incremented.

   o  Replacing calls from RPCSEC_GSS that free GSS-API contexts, with
      calls to decrement the reference count on the wrapper data
      structure.

18.37.  Operation 44: DESTROY_SESSION - Destroy a Session

18.37.1.  ARGUMENT

   struct DESTROY_SESSION4args {
           sessionid4      dsa_sessionid;
   };









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18.37.2.  RESULT

   struct DESTROY_SESSION4res {
           nfsstat4        dsr_status;
   };


18.37.3.  DESCRIPTION

   The DESTROY_SESSION operation closes the session and discards the
   session's reply cache, if any.  Any remaining connections associated
   with the session are immediately disassociated.  If the connection
   has no remaining associated sessions, the connection MAY be closed by
   the server.  Locks, delegations, layouts, wants, and the lease, which
   are all tied to the client ID, are not affected by DESTROY_SESSION.

   DESTROY_SESSION MUST be invoked on a connection that is associated
   with the session being destroyed.  In addition, if SP4_MACH_CRED
   state protection was specified when the client ID was created, the
   RPCSEC_GSS principal that created the session MUST be the one that
   destroys the session, using RPCSEC_GSS privacy or integrity.  If
   SP4_SSV state protection was specified when the client ID was
   created, RPCSEC_GSS using the SSV mechanism (Section 2.10.9) MUST be
   used, with integrity or privacy.

   If the COMPOUND request starts with SEQUENCE, and if the sessionids
   specified in SEQUENCE and DESTROY_SESSION are the same, then

   o  DESTROY_SESSION MUST be the final operation in the COMPOUND
      request.

   o  It is advisable to avoid placing DESTROY_SESSION in a COMPOUND
      request with other state-modifying operations, because the
      DESTROY_SESSION will destroy the reply cache.

   o  Because the session and its reply cache are destroyed, a client
      that retries the request may receive an error in reply to the
      retry, even though the original request was successful.

   If the COMPOUND request starts with SEQUENCE, and if the sessionids
   specified in SEQUENCE and DESTROY_SESSION are different, then
   DESTROY_SESSION can appear in any position of the COMPOUND request
   (except for the first position).  The two sessionids can belong to
   different client IDs.

   If the COMPOUND request does not start with SEQUENCE, and if
   DESTROY_SESSION is not the sole operation, then server MUST return
   NFS4ERR_NOT_ONLY_OP.



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   If there is a backchannel on the session and the server has
   outstanding CB_COMPOUND operations for the session which have not
   been replied to, then the server MAY refuse to destroy the session
   and return an error.  If so, then in the event the backchannel is
   down, the server SHOULD return NFS4ERR_CB_PATH_DOWN to inform the
   client that the backchannel needs to be repaired before the server
   will allow the session to be destroyed.  Otherwise, the error
   CB_BACK_CHAN_BUSY SHOULD be returned to indicate that there are
   CB_COMPOUNDs that need to be replied to.  The client SHOULD reply to
   all outstanding CB_COMPOUNDs before re-sending DESTROY_SESSION.

18.38.  Operation 45: FREE_STATEID - Free Stateid with No Locks

18.38.1.  ARGUMENT

   struct FREE_STATEID4args {
           stateid4        fsa_stateid;
   };


18.38.2.  RESULT

   struct FREE_STATEID4res {
           nfsstat4        fsr_status;
   };


18.38.3.  DESCRIPTION

   The FREE_STATEID operation is used to free a stateid that no longer
   has any associated locks (including opens, byte-range locks,
   delegations, and layouts).  This may be because of client LOCKU
   operations or because of server revocation.  If there are valid locks
   (of any kind) associated with the stateid in question, the error
   NFS4ERR_LOCKS_HELD will be returned, and the associated stateid will
   not be freed.

   When a stateid is freed that had been associated with revoked locks,
   by sending the FREE_STATEID operation, the client acknowledges the
   loss of those locks.  This allows the server, once all such revoked
   state is acknowledged, to allow that client again to reclaim locks,
   without encountering the edge conditions discussed in Section 8.4.2.

   Once a successful FREE_STATEID is done for a given stateid, any
   subsequent use of that stateid will result in an NFS4ERR_BAD_STATEID
   error.





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18.39.  Operation 46: GET_DIR_DELEGATION - Get a Directory Delegation

18.39.1.  ARGUMENT


   typedef nfstime4 attr_notice4;

   struct GET_DIR_DELEGATION4args {
           /* CURRENT_FH: delegated directory */
           bool            gdda_signal_deleg_avail;
           bitmap4         gdda_notification_types;
           attr_notice4    gdda_child_attr_delay;
           attr_notice4    gdda_dir_attr_delay;
           bitmap4         gdda_child_attributes;
           bitmap4         gdda_dir_attributes;
   };

18.39.2.  RESULT

































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   struct GET_DIR_DELEGATION4resok {
           verifier4       gddr_cookieverf;
           /* Stateid for get_dir_delegation */
           stateid4        gddr_stateid;
           /* Which notifications can the server support */
           bitmap4         gddr_notification;
           bitmap4         gddr_child_attributes;
           bitmap4         gddr_dir_attributes;
   };

   enum gddrnf4_status {
           GDD4_OK         = 0,
           GDD4_UNAVAIL    = 1
   };

   union GET_DIR_DELEGATION4res_non_fatal
    switch (gddrnf4_status gddrnf_status) {
    case GDD4_OK:
     GET_DIR_DELEGATION4resok      gddrnf_resok4;
    case GDD4_UNAVAIL:
     bool                          gddrnf_will_signal_deleg_avail;
   };

   union GET_DIR_DELEGATION4res
    switch (nfsstat4 gddr_status) {
    case NFS4_OK:
     GET_DIR_DELEGATION4res_non_fatal      gddr_res_non_fatal4;
    default:
     void;
   };


18.39.3.  DESCRIPTION

   The GET_DIR_DELEGATION operation is used by a client to request a
   directory delegation.  The directory is represented by the current
   filehandle.  The client also specifies whether it wants the server to
   notify it when the directory changes in certain ways by setting one
   or more bits in a bitmap.  The server may refuse to grant the
   delegation.  In that case, the server will return
   NFS4ERR_DIRDELEG_UNAVAIL.  If the server decides to hand out the
   delegation, it will return a cookie verifier for that directory.  If
   the cookie verifier changes when the client is holding the
   delegation, the delegation will be recalled unless the client has
   asked for notification for this event.

   The server will also return a directory delegation stateid,
   gddr_stateid, as a result of the GET_DIR_DELEGATION operation.  This



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   stateid will appear in callback messages related to the delegation,
   such as notifications and delegation recalls.  The client will use
   this stateid to return the delegation voluntarily or upon recall.  A
   delegation is returned by calling the DELEGRETURN operation.

   The server might not be able to support notifications of certain
   events.  If the client asks for such notifications, the server MUST
   inform the client of its inability to do so as part of the
   GET_DIR_DELEGATION reply by not setting the appropriate bits in the
   supported notifications bitmask, gddr_notification, contained in the
   reply.  The server MUST NOT add bits to gddr_notification that the
   client did not request.

   The GET_DIR_DELEGATION operation can be used for both normal and
   named attribute directories.

   If client sets gdda_signal_deleg_avail to TRUE, then it is
   registering with the client a "want" for a directory delegation.  If
   the delegation is not available, and the server supports and will
   honor the "want", the results will have
   gddrnf_will_signal_deleg_avail set to TRUE and no error will be
   indicated on return.  If so, the client should expect a future
   CB_RECALLABLE_OBJ_AVAIL operation to indicate that a directory
   delegation is available.  If the server does not wish to honor the
   "want" or is not able to do so, it returns the error
   NFS4ERR_DIRDELEG_UNAVAIL.  If the delegation is immediately
   available, the server SHOULD return it with the response to the
   operation, rather than via a callback.

   When a client makes a request for a directory delegation while it
   already holds a directory delegation for that directory (including
   the case where it has been recalled but not yet returned by the
   client or revoked by the server), the server MUST reply with the
   value of gddr_status set to NFS4_OK, the value of gddrnf_status set
   to GDD4_UNAVAIL, and the value of gddrnf_will_signal_deleg_avail set
   to FALSE.  The delegation the client held before the request remains
   intact, and its state is unchanged.  The current stateid is not
   changed (see Section 16.2.3.1.2 for a description of the current
   stateid).

18.39.4.  IMPLEMENTATION

   Directory delegations provide the benefit of improving cache
   consistency of namespace information.  This is done through
   synchronous callbacks.  A server must support synchronous callbacks
   in order to support directory delegations.  In addition to that,
   asynchronous notifications provide a way to reduce network traffic as
   well as improve client performance in certain conditions.



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   Notifications are specified in terms of potential changes to the
   directory.  A client can ask to be notified of events by setting one
   or more bits in gdda_notification_types.  The client can ask for
   notifications on addition of entries to a directory (by setting the
   NOTIFY4_ADD_ENTRY in gdda_notification_types), notifications on entry
   removal (NOTIFY4_REMOVE_ENTRY), renames (NOTIFY4_RENAME_ENTRY),
   directory attribute changes (NOTIFY4_CHANGE_DIR_ATTRIBUTES), and
   cookie verifier changes (NOTIFY4_CHANGE_COOKIE_VERIFIER) by setting
   one or more corresponding bits in the gdda_notification_types field.

   The client can also ask for notifications of changes to attributes of
   directory entries (NOTIFY4_CHANGE_CHILD_ATTRIBUTES) in order to keep
   its attribute cache up to date.  However, any changes made to child
   attributes do not cause the delegation to be recalled.  If a client
   is interested in directory entry caching or negative name caching, it
   can set the gdda_notification_types appropriately to its particular
   need and the server will notify it of all changes that would
   otherwise invalidate its name cache.  The kind of notification a
   client asks for may depend on the directory size, its rate of change,
   and the applications being used to access that directory.  The
   enumeration of the conditions under which a client might ask for a
   notification is out of the scope of this specification.

   For attribute notifications, the client will set bits in the
   gdda_dir_attributes bitmap to indicate which attributes it wants to
   be notified of.  If the server does not support notifications for
   changes to a certain attribute, it SHOULD NOT set that attribute in
   the supported attribute bitmap specified in the reply
   (gddr_dir_attributes).  The client will also set in the
   gdda_child_attributes bitmap the attributes of directory entries it
   wants to be notified of, and the server will indicate in
   gddr_child_attributes which attributes of directory entries it will
   notify the client of.

   The client will also let the server know if it wants to get the
   notification as soon as the attribute change occurs or after a
   certain delay by setting a delay factor; gdda_child_attr_delay is for
   attribute changes to directory entries and gdda_dir_attr_delay is for
   attribute changes to the directory.  If this delay factor is set to
   zero, that indicates to the server that the client wants to be
   notified of any attribute changes as soon as they occur.  If the
   delay factor is set to N seconds, the server will make a best-effort
   guarantee that attribute updates are synchronized within N seconds.
   If the client asks for a delay factor that the server does not
   support or that may cause significant resource consumption on the
   server by causing the server to send a lot of notifications, the
   server should not commit to sending out notifications for attributes
   and therefore must not set the appropriate bit in the



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   gddr_child_attributes and gddr_dir_attributes bitmaps in the
   response.

   The client MUST use a security tuple (Section 2.6.1) that the
   directory or its applicable ancestor (Section 2.6) is exported with.
   If not, the server MUST return NFS4ERR_WRONGSEC to the operation that
   both precedes GET_DIR_DELEGATION and sets the current filehandle (see
   Section 2.6.3.1).

   The directory delegation covers all the entries in the directory
   except the parent entry.  That means if a directory and its parent
   both hold directory delegations, any changes to the parent will not
   cause a notification to be sent for the child even though the child's
   parent entry points to the parent directory.

18.40.  Operation 47: GETDEVICEINFO - Get Device Information

18.40.1.  ARGUMENT

   struct GETDEVICEINFO4args {
           deviceid4       gdia_device_id;
           layouttype4     gdia_layout_type;
           count4          gdia_maxcount;
           bitmap4         gdia_notify_types;
   };


18.40.2.  RESULT

   struct GETDEVICEINFO4resok {
           device_addr4    gdir_device_addr;
           bitmap4         gdir_notification;
   };

   union GETDEVICEINFO4res switch (nfsstat4 gdir_status) {
   case NFS4_OK:
           GETDEVICEINFO4resok     gdir_resok4;
   case NFS4ERR_TOOSMALL:
           count4                  gdir_mincount;
   default:
           void;
   };









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18.40.3.  DESCRIPTION

   The GETDEVICEINFO operation returns pNFS storage device address
   information for the specified device ID.  The client identifies the
   device information to be returned by providing the gdia_device_id and
   gdia_layout_type that uniquely identify the device.  The client
   provides gdia_maxcount to limit the number of bytes for the result.
   This maximum size represents all of the data being returned within
   the GETDEVICEINFO4resok structure and includes the XDR overhead.  The
   server may return less data.  If the server is unable to return any
   information within the gdia_maxcount limit, the error
   NFS4ERR_TOOSMALL will be returned.  However, if gdia_maxcount is
   zero, NFS4ERR_TOOSMALL MUST NOT be returned.

   The da_layout_type field of the gdir_device_addr returned by the
   server MUST be equal to the gdia_layout_type specified by the client.
   If it is not equal, the client SHOULD ignore the response as invalid
   and behave as if the server returned an error, even if the client
   does have support for the layout type returned.

   The client also provides a notification bitmap, gdia_notify_types,
   for the device ID mapping notification for which it is interested in
   receiving; the server must support device ID notifications for the
   notification request to have affect.  The notification mask is
   composed in the same manner as the bitmap for file attributes
   (Section 3.3.7).  The numbers of bit positions are listed in the
   notify_device_type4 enumeration type (Section 20.12).  Only two
   enumerated values of notify_device_type4 currently apply to
   GETDEVICEINFO: NOTIFY_DEVICEID4_CHANGE and NOTIFY_DEVICEID4_DELETE
   (see Section 20.12).

   The notification bitmap applies only to the specified device ID.  If
   a client sends a GETDEVICEINFO operation on a deviceID multiple
   times, the last notification bitmap is used by the server for
   subsequent notifications.  If the bitmap is zero or empty, then the
   device ID's notifications are turned off.

   If the client wants to just update or turn off notifications, it MAY
   send a GETDEVICEINFO operation with gdia_maxcount set to zero.  In
   that event, if the device ID is valid, the reply's da_addr_body field
   of the gdir_device_addr field will be of zero length.

   If an unknown device ID is given in gdia_device_id, the server
   returns NFS4ERR_NOENT.  Otherwise, the device address information is
   returned in gdir_device_addr.  Finally, if the server supports
   notifications for device ID mappings, the gdir_notification result
   will contain a bitmap of which notifications it will actually send to
   the client (via CB_NOTIFY_DEVICEID, see Section 20.12).



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   If NFS4ERR_TOOSMALL is returned, the results also contain
   gdir_mincount.  The value of gdir_mincount represents the minimum
   size necessary to obtain the device information.

18.40.4.  IMPLEMENTATION

   Aside from updating or turning off notifications, another use case
   for gdia_maxcount being set to zero is to validate a device ID.

   The client SHOULD request a notification for changes or deletion of a
   device ID to device address mapping so that the server can allow the
   client gracefully use a new mapping, without having pending I/O fail
   abruptly, or force layouts using the device ID to be recalled or
   revoked.

   It is possible that GETDEVICEINFO (and GETDEVICELIST) will race with
   CB_NOTIFY_DEVICEID, i.e., CB_NOTIFY_DEVICEID arrives before the
   client gets and processes the response to GETDEVICEINFO or
   GETDEVICELIST.  The analysis of the race leverages the fact that the
   server MUST NOT delete a device ID that is referred to by a layout
   the client has.

   o  CB_NOTIFY_DEVICEID deletes a device ID.  If the client believes it
      has layouts that refer to the device ID, then it is possible that
      layouts referring to the deleted device ID have been revoked.  The
      client should send a TEST_STATEID request using the stateid for
      each layout that might have been revoked.  If TEST_STATEID
      indicates that any layouts have been revoked, the client must
      recover from layout revocation as described in Section 12.5.6.  If
      TEST_STATEID indicates that at least one layout has not been
      revoked, the client should send a GETDEVICEINFO operation on the
      supposedly deleted device ID to verify that the device ID has been
      deleted.

      If GETDEVICEINFO indicates that the device ID does not exist, then
      the client assumes the server is faulty and recovers by sending an
      EXCHANGE_ID operation.  If GETDEVICEINFO indicates that the device
      ID does exist, then while the server is faulty for sending an
      erroneous device ID deletion notification, the degree to which it
      is faulty does not require the client to create a new client ID.

      If the client does not have layouts that refer to the device ID,
      no harm is done.  The client should mark the device ID as deleted,
      and when GETDEVICEINFO or GETDEVICELIST results are received that
      indicate that the device ID has been in fact deleted, the device
      ID should be removed from the client's cache.





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   o  CB_NOTIFY_DEVICEID indicates that a device ID's device addressing
      mappings have changed.  The client should assume that the results
      from the in-progress GETDEVICEINFO will be stale for the device ID
      once received, and so it should send another GETDEVICEINFO on the
      device ID.

18.41.  Operation 48: GETDEVICELIST - Get All Device Mappings for a File
        System

18.41.1.  ARGUMENT

   struct GETDEVICELIST4args {
           /* CURRENT_FH: object belonging to the file system */
           layouttype4     gdla_layout_type;

           /* number of deviceIDs to return */
           count4          gdla_maxdevices;

           nfs_cookie4     gdla_cookie;
           verifier4       gdla_cookieverf;
   };


18.41.2.  RESULT

   struct GETDEVICELIST4resok {
           nfs_cookie4             gdlr_cookie;
           verifier4               gdlr_cookieverf;
           deviceid4               gdlr_deviceid_list<>;
           bool                    gdlr_eof;
   };

   union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
   case NFS4_OK:
           GETDEVICELIST4resok     gdlr_resok4;
   default:
           void;
   };


18.41.3.  DESCRIPTION

   This operation is used by the client to enumerate all of the device
   IDs that a server's file system uses.

   The client provides a current filehandle of a file object that
   belongs to the file system (i.e., all file objects sharing the same
   fsid as that of the current filehandle) and the layout type in



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   gdia_layout_type.  Since this operation might require multiple calls
   to enumerate all the device IDs (and is thus similar to the READDIR
   (Section 18.23) operation), the client also provides gdia_cookie and
   gdia_cookieverf to specify the current cursor position in the list.
   When the client wants to read from the beginning of the file system's
   device mappings, it sets gdla_cookie to zero.  The field
   gdla_cookieverf MUST be ignored by the server when gdla_cookie is
   zero.  The client provides gdla_maxdevices to limit the number of
   device IDs in the result.  If gdla_maxdevices is zero, the server
   MUST return NFS4ERR_INVAL.  The server MAY return fewer device IDs.

   The successful response to the operation will contain the cookie,
   gdlr_cookie, and the cookie verifier, gdlr_cookieverf, to be used on
   the subsequent GETDEVICELIST.  A gdlr_eof value of TRUE signifies
   that there are no remaining entries in the server's device list.
   Each element of gdlr_deviceid_list contains a device ID.

18.41.4.  IMPLEMENTATION

   An example of the use of this operation is for pNFS clients and
   servers that use LAYOUT4_BLOCK_VOLUME layouts.  In these environments
   it may be helpful for a client to determine device accessibility upon
   first file system access.

18.42.  Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a Layout

18.42.1.  ARGUMENT
























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   union newtime4 switch (bool nt_timechanged) {
   case TRUE:
           nfstime4           nt_time;
   case FALSE:
           void;
   };

   union newoffset4 switch (bool no_newoffset) {
   case TRUE:
           offset4           no_offset;
   case FALSE:
           void;
   };

   struct LAYOUTCOMMIT4args {
           /* CURRENT_FH: file */
           offset4                 loca_offset;
           length4                 loca_length;
           bool                    loca_reclaim;
           stateid4                loca_stateid;
           newoffset4              loca_last_write_offset;
           newtime4                loca_time_modify;
           layoutupdate4           loca_layoutupdate;
   };

18.42.2.  RESULT

   union newsize4 switch (bool ns_sizechanged) {
   case TRUE:
           length4         ns_size;
   case FALSE:
           void;
   };

   struct LAYOUTCOMMIT4resok {
           newsize4                locr_newsize;
   };

   union LAYOUTCOMMIT4res switch (nfsstat4 locr_status) {
   case NFS4_OK:
           LAYOUTCOMMIT4resok      locr_resok4;
   default:
           void;
   };







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18.42.3.  DESCRIPTION

   The LAYOUTCOMMIT operation commits changes in the layout represented
   by the current filehandle, client ID (derived from the session ID in
   the preceding SEQUENCE operation), byte-range, and stateid.  Since
   layouts are sub-dividable, a smaller portion of a layout, retrieved
   via LAYOUTGET, can be committed.  The byte-range being committed is
   specified through the byte-range (loca_offset and loca_length).  This
   byte-range MUST overlap with one or more existing layouts previously
   granted via LAYOUTGET (Section 18.43), each with an iomode of
   LAYOUTIOMODE4_RW.  In the case where the iomode of any held layout
   segment is not LAYOUTIOMODE4_RW, the server should return the error
   NFS4ERR_BAD_IOMODE.  For the case where the client does not hold
   matching layout segment(s) for the defined byte-range, the server
   should return the error NFS4ERR_BAD_LAYOUT.

   The LAYOUTCOMMIT operation indicates that the client has completed
   writes using a layout obtained by a previous LAYOUTGET.  The client
   may have only written a subset of the data range it previously
   requested.  LAYOUTCOMMIT allows it to commit or discard provisionally
   allocated space and to update the server with a new end-of-file.  The
   layout referenced by LAYOUTCOMMIT is still valid after the operation
   completes and can be continued to be referenced by the client ID,
   filehandle, byte-range, layout type, and stateid.

   If the loca_reclaim field is set to TRUE, this indicates that the
   client is attempting to commit changes to a layout after the restart
   of the metadata server during the metadata server's recovery grace
   period (see Section 12.7.4).  This type of request may be necessary
   when the client has uncommitted writes to provisionally allocated
   byte-ranges of a file that were sent to the storage devices before
   the restart of the metadata server.  In this case, the layout
   provided by the client MUST be a subset of a writable layout that the
   client held immediately before the restart of the metadata server.
   The value of the field loca_stateid MUST be a value that the metadata
   server returned before it restarted.  The metadata server is free to
   accept or reject this request based on its own internal metadata
   consistency checks.  If the metadata server finds that the layout
   provided by the client does not pass its consistency checks, it MUST
   reject the request with the status NFS4ERR_RECLAIM_BAD.  The
   successful completion of the LAYOUTCOMMIT request with loca_reclaim
   set to TRUE does NOT provide the client with a layout for the file.
   It simply commits the changes to the layout specified in the
   loca_layoutupdate field.  To obtain a layout for the file, the client
   must send a LAYOUTGET request to the server after the server's grace
   period has expired.  If the metadata server receives a LAYOUTCOMMIT
   request with loca_reclaim set to TRUE when the metadata server is not




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   in its recovery grace period, it MUST reject the request with the
   status NFS4ERR_NO_GRACE.

   Setting the loca_reclaim field to TRUE is required if and only if the
   committed layout was acquired before the metadata server restart.  If
   the client is committing a layout that was acquired during the
   metadata server's grace period, it MUST set the "reclaim" field to
   FALSE.

   The loca_stateid is a layout stateid value as returned by previously
   successful layout operations (see Section 12.5.3).

   The loca_last_write_offset field specifies the offset of the last
   byte written by the client previous to the LAYOUTCOMMIT.  Note that
   this value is never equal to the file's size (at most it is one byte
   less than the file's size) and MUST be less than or equal to
   NFS4_MAXFILEOFF.  Also, loca_last_write_offset MUST overlap the range
   described by loca_offset and loca_length.  The metadata server may
   use this information to determine whether the file's size needs to be
   updated.  If the metadata server updates the file's size as the
   result of the LAYOUTCOMMIT operation, it must return the new size
   (locr_newsize.ns_size) as part of the results.

   The loca_time_modify field allows the client to suggest a
   modification time it would like the metadata server to set.  The
   metadata server may use the suggestion or it may use the time of the
   LAYOUTCOMMIT operation to set the modification time.  If the metadata
   server uses the client-provided modification time, it should ensure
   that time does not flow backwards.  If the client wants to force the
   metadata server to set an exact time, the client should use a SETATTR
   operation in a COMPOUND right after LAYOUTCOMMIT.  See Section 12.5.4
   for more details.  If the client desires the resultant modification
   time, it should construct the COMPOUND so that a GETATTR follows the
   LAYOUTCOMMIT.

   The loca_layoutupdate argument to LAYOUTCOMMIT provides a mechanism
   for a client to provide layout-specific updates to the metadata
   server.  For example, the layout update can describe what byte-ranges
   of the original layout have been used and what byte-ranges can be
   deallocated.  There is no NFSv4.1 file layout-specific layoutupdate4
   structure.

   The layout information is more verbose for block devices than for
   objects and files because the latter two hide the details of block
   allocation behind their storage protocols.  At the minimum, the
   client needs to communicate changes to the end-of-file location back
   to the server, and, if desired, its view of the file's modification




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   time.  For block/volume layouts, it needs to specify precisely which
   blocks have been used.

   If the layout identified in the arguments does not exist, the error
   NFS4ERR_BADLAYOUT is returned.  The layout being committed may also
   be rejected if it does not correspond to an existing layout with an
   iomode of LAYOUTIOMODE4_RW.

   On success, the current filehandle retains its value and the current
   stateid retains its value.

18.42.4.  IMPLEMENTATION

   The client MAY also use LAYOUTCOMMIT with the loca_reclaim field set
   to TRUE to convey hints to modified file attributes or to report
   layout-type specific information such as I/O errors for object-based
   storage layouts, as normally done during normal operation.  Doing so
   may help the metadata server to recover files more efficiently after
   restart.  For example, some file system implementations may require
   expansive recovery of file system objects if the metadata server does
   not get a positive indication from all clients holding a
   LAYOUTIOMODE4_RW layout that they have successfully completed all
   their writes.  Sending a LAYOUTCOMMIT (if required) and then
   following with LAYOUTRETURN can provide such an indication and allow
   for graceful and efficient recovery.

   If loca_reclaim is TRUE, the metadata server is free to either
   examine or ignore the value in the field loca_stateid.  The metadata
   server implementation might or might not encode in its layout stateid
   information that allows the metadate server to perform a consistency
   check on the LAYOUTCOMMIT request.

18.43.  Operation 50: LAYOUTGET - Get Layout Information

18.43.1.  ARGUMENT

   struct LAYOUTGET4args {
           /* CURRENT_FH: file */
           bool                    loga_signal_layout_avail;
           layouttype4             loga_layout_type;
           layoutiomode4           loga_iomode;
           offset4                 loga_offset;
           length4                 loga_length;
           length4                 loga_minlength;
           stateid4                loga_stateid;
           count4                  loga_maxcount;
   };




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18.43.2.  RESULT

   struct LAYOUTGET4resok {
           bool               logr_return_on_close;
           stateid4           logr_stateid;
           layout4            logr_layout<>;
   };

   union LAYOUTGET4res switch (nfsstat4 logr_status) {
   case NFS4_OK:
           LAYOUTGET4resok     logr_resok4;
   case NFS4ERR_LAYOUTTRYLATER:
           bool                logr_will_signal_layout_avail;
   default:
           void;
   };


18.43.3.  DESCRIPTION

   The LAYOUTGET operation requests a layout from the metadata server
   for reading or writing the file given by the filehandle at the byte-
   range specified by offset and length.  Layouts are identified by the
   client ID (derived from the session ID in the preceding SEQUENCE
   operation), current filehandle, layout type (loga_layout_type), and
   the layout stateid (loga_stateid).  The use of the loga_iomode field
   depends upon the layout type, but should reflect the client's data
   access intent.

   If the metadata server is in a grace period, and does not persist
   layouts and device ID to device address mappings, then it MUST return
   NFS4ERR_GRACE (see Section 8.4.2.1).

   The LAYOUTGET operation returns layout information for the specified
   byte-range: a layout.  The client actually specifies two ranges, both
   starting at the offset in the loga_offset field.  The first range is
   between loga_offset and loga_offset + loga_length - 1 inclusive.
   This range indicates the desired range the client wants the layout to
   cover.  The second range is between loga_offset and loga_offset +
   loga_minlength - 1 inclusive.  This range indicates the required
   range the client needs the layout to cover.  Thus, loga_minlength
   MUST be less than or equal to loga_length.

   When a length field is set to NFS4_UINT64_MAX, this indicates a
   desire (when loga_length is NFS4_UINT64_MAX) or requirement (when
   loga_minlength is NFS4_UINT64_MAX) to get a layout from loga_offset
   through the end-of-file, regardless of the file's length.




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   The following rules govern the relationships among, and the minima
   of, loga_length, loga_minlength, and loga_offset.

   o  If loga_length is less than loga_minlength, the metadata server
      MUST return NFS4ERR_INVAL.

   o  If loga_minlength is zero, this is an indication to the metadata
      server that the client desires any layout at offset loga_offset or
      less that the metadata server has "readily available".  Readily is
      subjective, and depends on the layout type and the pNFS server
      implementation.  For example, some metadata servers might have to
      pre-allocate stable storage when they receive a request for a
      range of a file that goes beyond the file's current length.  If
      loga_minlength is zero and loga_length is greater than zero, this
      tells the metadata server what range of the layout the client
      would prefer to have.  If loga_length and loga_minlength are both
      zero, then the client is indicating that it desires a layout of
      any length with the ending offset of the range no less than the
      value specified loga_offset, and the starting offset at or below
      loga_offset.  If the metadata server does not have a layout that
      is readily available, then it MUST return NFS4ERR_LAYOUTTRYLATER.

   o  If the sum of loga_offset and loga_minlength exceeds
      NFS4_UINT64_MAX, and loga_minlength is not NFS4_UINT64_MAX, the
      error NFS4ERR_INVAL MUST result.

   o  If the sum of loga_offset and loga_length exceeds NFS4_UINT64_MAX,
      and loga_length is not NFS4_UINT64_MAX, the error NFS4ERR_INVAL
      MUST result.

   After the metadata server has performed the above checks on
   loga_offset, loga_minlength, and loga_offset, the metadata server
   MUST return a layout according to the rules in Table 13.


















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         Acceptable layouts based on loga_minlength.  Note: u64m =
     NFS4_UINT64_MAX; a_off = loga_offset; a_minlen = loga_minlength.

   +-----------+-----------+----------+----------+---------------------+
   | Layout    | Layout    | Layout   | Layout   | Layout length of    |
   | iomode of | a_minlen  | iomode   | offset   | reply               |
   | request   | of        | of reply | of reply |                     |
   |           | request   |          |          |                     |
   +-----------+-----------+----------+----------+---------------------+
   | _READ     | u64m      | MAY be   | MUST be  | MUST be >= file     |
   |           |           | _READ    | <= a_off | length - layout     |
   |           |           |          |          | offset              |
   | _READ     | u64m      | MAY be   | MUST be  | MUST be u64m        |
   |           |           | _RW      | <= a_off |                     |
   | _READ     | > 0 and < | MAY be   | MUST be  | MUST be >= MIN(file |
   |           | u64m      | _READ    | <= a_off | length, a_minlen +  |
   |           |           |          |          | a_off) - layout     |
   |           |           |          |          | offset              |
   | _READ     | > 0 and < | MAY be   | MUST be  | MUST be >= a_off -  |
   |           | u64m      | _RW      | <= a_off | layout offset +     |
   |           |           |          |          | a_minlen            |
   | _READ     | 0         | MAY be   | MUST be  | MUST be > 0         |
   |           |           | _READ    | <= a_off |                     |
   | _READ     | 0         | MAY be   | MUST be  | MUST be > 0         |
   |           |           | _RW      | <= a_off |                     |
   | _RW       | u64m      | MUST be  | MUST be  | MUST be u64m        |
   |           |           | _RW      | <= a_off |                     |
   | _RW       | > 0 and < | MUST be  | MUST be  | MUST be >= a_off -  |
   |           | u64m      | _RW      | <= a_off | layout offset +     |
   |           |           |          |          | a_minlen            |
   | _RW       | 0         | MUST be  | MUST be  | MUST be > 0         |
   |           |           | _RW      | <= a_off |                     |
   +-----------+-----------+----------+----------+---------------------+

                                 Table 13

   If loga_minlength is not zero and the metadata server cannot return a
   layout according to the rules in Table 13, then the metadata server
   MUST return the error NFS4ERR_BADLAYOUT.  If loga_minlength is zero
   and the metadata server cannot or will not return a layout according
   to the rules in Table 13, then the metadata server MUST return the
   error NFS4ERR_LAYOUTTRYLATER.  Assuming that loga_length is greater
   than loga_minlength or equal to zero, the metadata server SHOULD
   return a layout according to the rules in Table 14.







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   Desired layouts based on loga_length.  The rules of Table 13 MUST be
    applied first.  Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
                           a_len = loga_length.

   +------------+------------+-----------+-----------+-----------------+
   | Layout     | Layout     | Layout    | Layout    | Layout length   |
   | iomode of  | a_len of   | iomode of | offset of | of reply        |
   | request    | request    | reply     | reply     |                 |
   +------------+------------+-----------+-----------+-----------------+
   | _READ      | u64m       | MAY be    | MUST be   | SHOULD be u64m  |
   |            |            | _READ     | <= a_off  |                 |
   | _READ      | u64m       | MAY be    | MUST be   | SHOULD be u64m  |
   |            |            | _RW       | <= a_off  |                 |
   | _READ      | > 0 and <  | MAY be    | MUST be   | SHOULD be >=    |
   |            | u64m       | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _READ      | > 0 and <  | MAY be    | MUST be   | SHOULD be >=    |
   |            | u64m       | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _READ      | 0          | MAY be    | MUST be   | SHOULD be >     |
   |            |            | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   | _READ      | 0          | MAY be    | MUST be   | SHOULD be >     |
   |            |            | _READ     | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   | _RW        | u64m       | MUST be   | MUST be   | SHOULD be u64m  |
   |            |            | _RW       | <= a_off  |                 |
   | _RW        | > 0 and <  | MUST be   | MUST be   | SHOULD be >=    |
   |            | u64m       | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset + a_len  |
   | _RW        | 0          | MUST be   | MUST be   | SHOULD be >     |
   |            |            | _RW       | <= a_off  | a_off - layout  |
   |            |            |           |           | offset          |
   +------------+------------+-----------+-----------+-----------------+

                                 Table 14

   The loga_stateid field specifies a valid stateid.  If a layout is not
   currently held by the client, the loga_stateid field represents a
   stateid reflecting the correspondingly valid open, byte-range lock,
   or delegation stateid.  Once a layout is held on the file by the
   client, the loga_stateid field MUST be a stateid as returned from a
   previous LAYOUTGET or LAYOUTRETURN operation or provided by a
   CB_LAYOUTRECALL operation (see Section 12.5.3).

   The loga_maxcount field specifies the maximum layout size (in bytes)
   that the client can handle.  If the size of the layout structure




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   exceeds the size specified by maxcount, the metadata server will
   return the NFS4ERR_TOOSMALL error.

   The returned layout is expressed as an array, logr_layout, with each
   element of type layout4.  If a file has a single striping pattern,
   then logr_layout SHOULD contain just one entry.  Otherwise, if the
   requested range overlaps more than one striping pattern, logr_layout
   will contain the required number of entries.  The elements of
   logr_layout MUST be sorted in ascending order of the value of the
   lo_offset field of each element.  There MUST be no gaps or overlaps
   in the range between two successive elements of logr_layout.  The
   lo_iomode field in each element of logr_layout MUST be the same.

   Table 13 and Table 14 both refer to a returned layout iomode, offset,
   and length.  Because the returned layout is encoded in the
   logr_layout array, more description is required.

   iomode

      The value of the returned layout iomode listed in Table 13 and
      Table 14 is equal to the value of the lo_iomode field in each
      element of logr_layout.  As shown in Table 13 and Table 14, the
      metadata server MAY return a layout with an lo_iomode different
      from the requested iomode (field loga_iomode of the request).  If
      it does so, it MUST ensure that the lo_iomode is more permissive
      than the loga_iomode requested.  For example, this behavior allows
      an implementation to upgrade LAYOUTIOMODE4_READ requests to
      LAYOUTIOMODE4_RW requests at its discretion, within the limits of
      the layout type specific protocol.  A lo_iomode of either
      LAYOUTIOMODE4_READ or LAYOUTIOMODE4_RW MUST be returned.

   offset

      The value of the returned layout offset listed in Table 13 and
      Table 14 is always equal to the lo_offset field of the first
      element logr_layout.

   length

      When setting the value of the returned layout length, the
      situation is complicated by the possibility that the special
      layout length value NFS4_UINT64_MAX is involved.  For a
      logr_layout array of N elements, the lo_length field in the first
      N-1 elements MUST NOT be NFS4_UINT64_MAX.  The lo_length field of
      the last element of logr_layout can be NFS4_UINT64_MAX under some
      conditions as described in the following list.





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      *  If an applicable rule of Table 13 states that the metadata
         server MUST return a layout of length NFS4_UINT64_MAX, then the
         lo_length field of the last element of logr_layout MUST be
         NFS4_UINT64_MAX.

      *  If an applicable rule of Table 13 states that the metadata
         server MUST NOT return a layout of length NFS4_UINT64_MAX, then
         the lo_length field of the last element of logr_layout MUST NOT
         be NFS4_UINT64_MAX.

      *  If an applicable rule of Table 14 states that the metadata
         server SHOULD return a layout of length NFS4_UINT64_MAX, then
         the lo_length field of the last element of logr_layout SHOULD
         be NFS4_UINT64_MAX.

      *  When the value of the returned layout length of Table 13 and
         Table 14 is not NFS4_UINT64_MAX, then the returned layout
         length is equal to the sum of the lo_length fields of each
         element of logr_layout.

   The logr_return_on_close result field is a directive to return the
   layout before closing the file.  When the metadata server sets this
   return value to TRUE, it MUST be prepared to recall the layout in the
   case in which the client fails to return the layout before close.
   For the metadata server that knows a layout must be returned before a
   close of the file, this return value can be used to communicate the
   desired behavior to the client and thus remove one extra step from
   the client's and metadata server's interaction.

   The logr_stateid stateid is returned to the client for use in
   subsequent layout related operations.  See Sections 8.2, 12.5.3, and
   12.5.5.2 for a further discussion and requirements.

   The format of the returned layout (lo_content) is specific to the
   layout type.  The value of the layout type (lo_content.loc_type) for
   each of the elements of the array of layouts returned by the metadata
   server (logr_layout) MUST be equal to the loga_layout_type specified
   by the client.  If it is not equal, the client SHOULD ignore the
   response as invalid and behave as if the metadata server returned an
   error, even if the client does have support for the layout type
   returned.

   If neither the requested file nor its containing file system support
   layouts, the metadata server MUST return NFS4ERR_LAYOUTUNAVAILABLE.
   If the layout type is not supported, the metadata server MUST return
   NFS4ERR_UNKNOWN_LAYOUTTYPE.  If layouts are supported but no layout
   matches the client provided layout identification, the metadata
   server MUST return NFS4ERR_BADLAYOUT.  If an invalid loga_iomode is



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   specified, or a loga_iomode of LAYOUTIOMODE4_ANY is specified, the
   metadata server MUST return NFS4ERR_BADIOMODE.

   If the layout for the file is unavailable due to transient
   conditions, e.g., file sharing prohibits layouts, the metadata server
   MUST return NFS4ERR_LAYOUTTRYLATER.

   If the layout request is rejected due to an overlapping layout
   recall, the metadata server MUST return NFS4ERR_RECALLCONFLICT.  See
   Section 12.5.5.2 for details.

   If the layout conflicts with a mandatory byte-range lock held on the
   file, and if the storage devices have no method of enforcing
   mandatory locks, other than through the restriction of layouts, the
   metadata server SHOULD return NFS4ERR_LOCKED.

   If client sets loga_signal_layout_avail to TRUE, then it is
   registering with the client a "want" for a layout in the event the
   layout cannot be obtained due to resource exhaustion.  If the
   metadata server supports and will honor the "want", the results will
   have logr_will_signal_layout_avail set to TRUE.  If so, the client
   should expect a CB_RECALLABLE_OBJ_AVAIL operation to indicate that a
   layout is available.

   On success, the current filehandle retains its value and the current
   stateid is updated to match the value as returned in the results.

18.43.4.  IMPLEMENTATION

   Typically, LAYOUTGET will be called as part of a COMPOUND request
   after an OPEN operation and results in the client having location
   information for the file.  This requires that loga_stateid be set to
   the special stateid that tells the metadata server to use the current
   stateid, which is set by OPEN (see Section 16.2.3.1.2).  A client may
   also hold a layout across multiple OPENs.  The client specifies a
   layout type that limits what kind of layout the metadata server will
   return.  This prevents metadata servers from granting layouts that
   are unusable by the client.

   As indicated by Table 13 and Table 14, the specification of LAYOUTGET
   allows a pNFS client and server considerable flexibility.  A pNFS
   client can take several strategies for sending LAYOUTGET.  Some
   examples are as follows.

   o  If LAYOUTGET is preceded by OPEN in the same COMPOUND request and
      the OPEN requests OPEN4_SHARE_ACCESS_READ access, the client might
      opt to request a _READ layout with loga_offset set to zero,
      loga_minlength set to zero, and loga_length set to



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      NFS4_UINT64_MAX.  If the file has space allocated to it, that
      space is striped over one or more storage devices, and there is
      either no conflicting layout or the concept of a conflicting
      layout does not apply to the pNFS server's layout type or
      implementation, then the metadata server might return a layout
      with a starting offset of zero, and a length equal to the length
      of the file, if not NFS4_UINT64_MAX.  If the length of the file is
      not a multiple of the pNFS server's stripe width (see Section 13.2
      for a formal definition), the metadata server might round up the
      returned layout's length.

   o  If LAYOUTGET is preceded by OPEN in the same COMPOUND request, and
      the OPEN requests OPEN4_SHARE_ACCESS_WRITE access and does not
      truncate the file, the client might opt to request a _RW layout
      with loga_offset set to zero, loga_minlength set to zero, and
      loga_length set to the file's current length (if known), or
      NFS4_UINT64_MAX.  As with the previous case, under some conditions
      the metadata server might return a layout that covers the entire
      length of the file or beyond.

   o  This strategy is as above, but the OPEN truncates the file.  In
      this case, the client might anticipate it will be writing to the
      file from offset zero, and so loga_offset and loga_minlength are
      set to zero, and loga_length is set to the value of
      threshold4_write_iosize.  The metadata server might return a
      layout from offset zero with a length at least as long as
      threshold4_write_iosize.

   o  A process on the client invokes a request to read from offset
      10000 for length 50000.  The client is using buffered I/O, and has
      buffer sizes of 4096 bytes.  The client intends to map the request
      of the process into a series of READ requests starting at offset
      8192.  The end offset needs to be higher than 10000 + 50000 =
      60000, and the next offset that is a multiple of 4096 is 61440.
      The difference between 61440 and that starting offset of the
      layout is 53248 (which is the product of 4096 and 15).  The value
      of threshold4_read_iosize is less than 53248, so the client sends
      a LAYOUTGET request with loga_offset set to 8192, loga_minlength
      set to 53248, and loga_length set to the file's length (if known)
      minus 8192 or NFS4_UINT64_MAX (if the file's length is not known).
      Since this LAYOUTGET request exceeds the metadata server's
      threshold, it grants the layout, possibly with an initial offset
      of zero, with an end offset of at least 8192 + 53248 - 1 = 61439,
      but preferably a layout with an offset aligned on the stripe width
      and a length that is a multiple of the stripe width.

   o  This strategy is as above, but the client is not using buffered I/
      O, and instead all internal I/O requests are sent directly to the



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      server.  The LAYOUTGET request has loga_offset equal to 10000 and
      loga_minlength set to 50000.  The value of loga_length is set to
      the length of the file.  The metadata server is free to return a
      layout that fully overlaps the requested range, with a starting
      offset and length aligned on the stripe width.

   o  Again, a process on the client invokes a request to read from
      offset 10000 for length 50000 (i.e. a range with a starting offset
      of 10000 and an ending offset of 69999), and buffered I/O is in
      use.  The client is expecting that the server might not be able to
      return the layout for the full I/O range.  The client intends to
      map the request of the process into a series of thirteen READ
      requests starting at offset 8192, each with length 4096, with a
      total length of 53248 (which equals 13 * 4096), which fully
      contains the range that client's process wants to read.  Because
      the value of threshold4_read_iosize is equal to 4096, it is
      practical and reasonable for the client to use several LAYOUTGET
      operations to complete the series of READs.  The client sends a
      LAYOUTGET request with loga_offset set to 8192, loga_minlength set
      to 4096, and loga_length set to 53248 or higher.  The server will
      grant a layout possibly with an initial offset of zero, with an
      end offset of at least 8192 + 4096 - 1 = 12287, but preferably a
      layout with an offset aligned on the stripe width and a length
      that is a multiple of the stripe width.  This will allow the
      client to make forward progress, possibly sending more LAYOUTGET
      operations for the remainder of the range.

   o  An NFS client detects a sequential read pattern, and so sends a
      LAYOUTGET operation that goes well beyond any current or pending
      read requests to the server.  The server might likewise detect
      this pattern, and grant the LAYOUTGET request.  Once the client
      reads from an offset of the file that represents 50% of the way
      through the range of the last layout it received, in order to
      avoid stalling I/O that would wait for a layout, the client sends
      more operations from an offset of the file that represents 50% of
      the way through the last layout it received.  The client continues
      to request layouts with byte-ranges that are well in advance of
      the byte-ranges of recent and/or read requests of processes
      running on the client.

   o  This strategy is as above, but the client fails to detect the
      pattern, but the server does.  The next time the metadata server
      gets a LAYOUTGET, it returns a layout with a length that is well
      beyond loga_minlength.

   o  A client is using buffered I/O, and has a long queue of write-
      behinds to process and also detects a sequential write pattern.
      It sends a LAYOUTGET for a layout that spans the range of the



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      queued write-behinds and well beyond, including ranges beyond the
      filer's current length.  The client continues to send LAYOUTGET
      operations once the write-behind queue reaches 50% of the maximum
      queue length.

   Once the client has obtained a layout referring to a particular
   device ID, the metadata server MUST NOT delete the device ID until
   the layout is returned or revoked.

   CB_NOTIFY_DEVICEID can race with LAYOUTGET.  One race scenario is
   that LAYOUTGET returns a device ID for which the client does not have
   device address mappings, and the metadata server sends a
   CB_NOTIFY_DEVICEID to add the device ID to the client's awareness and
   meanwhile the client sends GETDEVICEINFO on the device ID.  This
   scenario is discussed in Section 18.40.4.  Another scenario is that
   the CB_NOTIFY_DEVICEID is processed by the client before it processes
   the results from LAYOUTGET.  The client will send a GETDEVICEINFO on
   the device ID.  If the results from GETDEVICEINFO are received before
   the client gets results from LAYOUTGET, then there is no longer a
   race.  If the results from LAYOUTGET are received before the results
   from GETDEVICEINFO, the client can either wait for results of
   GETDEVICEINFO or send another one to get possibly more up-to-date
   device address mappings for the device ID.

18.44.  Operation 51: LAYOUTRETURN - Release Layout Information

18.44.1.  ARGUMENT
























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   /* Constants used for LAYOUTRETURN and CB_LAYOUTRECALL */
   const LAYOUT4_RET_REC_FILE      = 1;
   const LAYOUT4_RET_REC_FSID      = 2;
   const LAYOUT4_RET_REC_ALL       = 3;

   enum layoutreturn_type4 {
           LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
           LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
           LAYOUTRETURN4_ALL  = LAYOUT4_RET_REC_ALL
   };

   struct layoutreturn_file4 {
           offset4         lrf_offset;
           length4         lrf_length;
           stateid4        lrf_stateid;
           /* layouttype4 specific data */
           opaque          lrf_body<>;
   };

   union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
           case LAYOUTRETURN4_FILE:
                   layoutreturn_file4      lr_layout;
           default:
                   void;
   };



   struct LAYOUTRETURN4args {
           /* CURRENT_FH: file */
           bool                    lora_reclaim;
           layouttype4             lora_layout_type;
           layoutiomode4           lora_iomode;
           layoutreturn4           lora_layoutreturn;
   };



18.44.2.  RESULT












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   union layoutreturn_stateid switch (bool lrs_present) {
   case TRUE:
           stateid4                lrs_stateid;
   case FALSE:
           void;
   };

   union LAYOUTRETURN4res switch (nfsstat4 lorr_status) {
   case NFS4_OK:
           layoutreturn_stateid    lorr_stateid;
   default:
           void;
   };


18.44.3.  DESCRIPTION

   This operation returns from the client to the server one or more
   layouts represented by the client ID (derived from the session ID in
   the preceding SEQUENCE operation), lora_layout_type, and lora_iomode.
   When lr_returntype is LAYOUTRETURN4_FILE, the returned layout is
   further identified by the current filehandle, lrf_offset, lrf_length,
   and lrf_stateid.  If the lrf_length field is NFS4_UINT64_MAX, all
   bytes of the layout, starting at lrf_offset, are returned.  When
   lr_returntype is LAYOUTRETURN4_FSID, the current filehandle is used
   to identify the file system and all layouts matching the client ID,
   the fsid of the file system, lora_layout_type, and lora_iomode are
   returned.  When lr_returntype is LAYOUTRETURN4_ALL, all layouts
   matching the client ID, lora_layout_type, and lora_iomode are
   returned and the current filehandle is not used.  After this call,
   the client MUST NOT use the returned layout(s) and the associated
   storage protocol to access the file data.

   If the set of layouts designated in the case of LAYOUTRETURN4_FSID or
   LAYOUTRETURN4_ALL is empty, then no error results.  In the case of
   LAYOUTRETURN4_FILE, the byte-range specified is returned even if it
   is a subdivision of a layout previously obtained with LAYOUTGET, a
   combination of multiple layouts previously obtained with LAYOUTGET,
   or a combination including some layouts previously obtained with
   LAYOUTGET, and one or more subdivisions of such layouts.  When the
   byte-range does not designate any bytes for which a layout is held
   for the specified file, client ID, layout type and mode, no error
   results.  See Section 12.5.5.2.1.5 for considerations with "bulk"
   return of layouts.

   The layout being returned may be a subset or superset of a layout
   specified by CB_LAYOUTRECALL.  However, if it is a subset, the recall
   is not complete until the full recalled scope has been returned.



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   Recalled scope refers to the byte-range in the case of
   LAYOUTRETURN4_FILE, the use of LAYOUTRETURN4_FSID, or the use of
   LAYOUTRETURN4_ALL.  There must be a LAYOUTRETURN with a matching
   scope to complete the return even if all current layout ranges have
   been previously individually returned.

   For all lr_returntype values, an iomode of LAYOUTIOMODE4_ANY
   specifies that all layouts that match the other arguments to
   LAYOUTRETURN (i.e., client ID, lora_layout_type, and one of current
   filehandle and range; fsid derived from current filehandle; or
   LAYOUTRETURN4_ALL) are being returned.

   In the case that lr_returntype is LAYOUTRETURN4_FILE, the lrf_stateid
   provided by the client is a layout stateid as returned from previous
   layout operations.  Note that the "seqid" field of lrf_stateid MUST
   NOT be zero.  See Sections 8.2, 12.5.3, and 12.5.5.2 for a further
   discussion and requirements.

   Return of a layout or all layouts does not invalidate the mapping of
   storage device ID to a storage device address.  The mapping remains
   in effect until specifically changed or deleted via device ID
   notification callbacks.  Of course if there are no remaining layouts
   that refer to a previously used device ID, the server is free to
   delete a device ID without a notification callback, which will be the
   case when notifications are not in effect.

   If the lora_reclaim field is set to TRUE, the client is attempting to
   return a layout that was acquired before the restart of the metadata
   server during the metadata server's grace period.  When returning
   layouts that were acquired during the metadata server's grace period,
   the client MUST set the lora_reclaim field to FALSE.  The
   lora_reclaim field MUST be set to FALSE also when lr_layoutreturn is
   LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL.  See LAYOUTCOMMIT
   (Section 18.42) for more details.

   Layouts may be returned when recalled or voluntarily (i.e., before
   the server has recalled them).  In either case, the client must
   properly propagate state changed under the context of the layout to
   the storage device(s) or to the metadata server before returning the
   layout.

   If the client returns the layout in response to a CB_LAYOUTRECALL
   where the lor_recalltype field of the clora_recall field was
   LAYOUTRECALL4_FILE, the client should use the lor_stateid value from
   CB_LAYOUTRECALL as the value for lrf_stateid.  Otherwise, it should
   use logr_stateid (from a previous LAYOUTGET result) or lorr_stateid
   (from a previous LAYRETURN result).  This is done to indicate the
   point in time (in terms of layout stateid transitions) when the



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   recall was sent.  The client uses the precise lora_recallstateid
   value and MUST NOT set the stateid's seqid to zero; otherwise,
   NFS4ERR_BAD_STATEID MUST be returned.  NFS4ERR_OLD_STATEID can be
   returned if the client is using an old seqid, and the server knows
   the client should not be using the old seqid.  For example, the
   client uses the seqid on slot 1 of the session, receives the response
   with the new seqid, and uses the slot to send another request with
   the old seqid.

   If a client fails to return a layout in a timely manner, then the
   metadata server SHOULD use its control protocol with the storage
   devices to fence the client from accessing the data referenced by the
   layout.  See Section 12.5.5 for more details.

   If the LAYOUTRETURN request sets the lora_reclaim field to TRUE after
   the metadata server's grace period, NFS4ERR_NO_GRACE is returned.

   If the LAYOUTRETURN request sets the lora_reclaim field to TRUE and
   lr_returntype is set to LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL,
   NFS4ERR_INVAL is returned.

   If the client sets the lr_returntype field to LAYOUTRETURN4_FILE,
   then the lrs_stateid field will represent the layout stateid as
   updated for this operation's processing; the current stateid will
   also be updated to match the returned value.  If the last byte of any
   layout for the current file, client ID, and layout type is being
   returned and there are no remaining pending CB_LAYOUTRECALL
   operations for which a LAYOUTRETURN operation must be done,
   lrs_present MUST be FALSE, and no stateid will be returned.  In
   addition, the COMPOUND request's current stateid will be set to the
   all-zeroes special stateid (see Section 16.2.3.1.2).  The server MUST
   reject with NFS4ERR_BAD_STATEID any further use of the current
   stateid in that COMPOUND until the current stateid is re-established
   by a later stateid-returning operation.

   On success, the current filehandle retains its value.

   If the EXCHGID4_FLAG_BIND_PRINC_STATEID capability is set on the
   client ID (see Section 18.35), the server will require that the
   principal, security flavor, and if applicable, the GSS mechanism,
   combination that acquired the layout also be the one to send
   LAYOUTRETURN.  This might not be possible if credentials for the
   principal are no longer available.  The server will allow the machine
   credential or SSV credential (see Section 18.35) to send LAYOUTRETURN
   if LAYOUTRETURN's operation code was set in the spo_must_allow result
   of EXCHANGE_ID.





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18.44.4.  IMPLEMENTATION

   The final LAYOUTRETURN operation in response to a CB_LAYOUTRECALL
   callback MUST be serialized with any outstanding, intersecting
   LAYOUTRETURN operations.  Note that it is possible that while a
   client is returning the layout for some recalled range, the server
   may recall a superset of that range (e.g., LAYOUTRECALL4_ALL); the
   final return operation for the latter must block until the former
   layout recall is done.

   Returning all layouts in a file system using LAYOUTRETURN4_FSID is
   typically done in response to a CB_LAYOUTRECALL for that file system
   as the final return operation.  Similarly, LAYOUTRETURN4_ALL is used
   in response to a recall callback for all layouts.  It is possible
   that the client already returned some outstanding layouts via
   individual LAYOUTRETURN calls and the call for LAYOUTRETURN4_FSID or
   LAYOUTRETURN4_ALL marks the end of the LAYOUTRETURN sequence.  See
   Section 12.5.5.1 for more details.

   Once the client has returned all layouts referring to a particular
   device ID, the server MAY delete the device ID.

18.45.  Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object

18.45.1.  ARGUMENT

   enum secinfo_style4 {
           SECINFO_STYLE4_CURRENT_FH       = 0,
           SECINFO_STYLE4_PARENT           = 1
   };

   /* CURRENT_FH: object or child directory */
   typedef secinfo_style4 SECINFO_NO_NAME4args;


18.45.2.  RESULT

   /* CURRENTFH: consumed if status is NFS4_OK */
   typedef SECINFO4res SECINFO_NO_NAME4res;


18.45.3.  DESCRIPTION

   Like the SECINFO operation, SECINFO_NO_NAME is used by the client to
   obtain a list of valid RPC authentication flavors for a specific file
   object.  Unlike SECINFO, SECINFO_NO_NAME only works with objects that
   are accessed by filehandle.




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   There are two styles of SECINFO_NO_NAME, as determined by the value
   of the secinfo_style4 enumeration.  If SECINFO_STYLE4_CURRENT_FH is
   passed, then SECINFO_NO_NAME is querying for the required security
   for the current filehandle.  If SECINFO_STYLE4_PARENT is passed, then
   SECINFO_NO_NAME is querying for the required security of the current
   filehandle's parent.  If the style selected is SECINFO_STYLE4_PARENT,
   then SECINFO should apply the same access methodology used for
   LOOKUPP when evaluating the traversal to the parent directory.
   Therefore, if the requester does not have the appropriate access to
   LOOKUPP the parent, then SECINFO_NO_NAME must behave the same way and
   return NFS4ERR_ACCESS.

   If PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH returns NFS4ERR_WRONGSEC,
   then the client resolves the situation by sending a COMPOUND request
   that consists of PUTFH, PUTPUBFH, or PUTROOTFH immediately followed
   by SECINFO_NO_NAME, style SECINFO_STYLE4_CURRENT_FH.  See Section 2.6
   for instructions on dealing with NFS4ERR_WRONGSEC error returns from
   PUTFH, PUTROOTFH, PUTPUBFH, or RESTOREFH.

   If SECINFO_STYLE4_PARENT is specified and there is no parent
   directory, SECINFO_NO_NAME MUST return NFS4ERR_NOENT.

   On success, the current filehandle is consumed (see
   Section 2.6.3.1.1.8), and if the next operation after SECINFO_NO_NAME
   tries to use the current filehandle, that operation will fail with
   the status NFS4ERR_NOFILEHANDLE.

   Everything else about SECINFO_NO_NAME is the same as SECINFO.  See
   the discussion on SECINFO (Section 18.29.3).

18.45.4.  IMPLEMENTATION

   See the discussion on SECINFO (Section 18.29.4).

18.46.  Operation 53: SEQUENCE - Supply Per-Procedure Sequencing and
        Control

18.46.1.  ARGUMENT

   struct SEQUENCE4args {
           sessionid4     sa_sessionid;
           sequenceid4    sa_sequenceid;
           slotid4        sa_slotid;
           slotid4        sa_highest_slotid;
           bool           sa_cachethis;
   };





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18.46.2.  RESULT

   const SEQ4_STATUS_CB_PATH_DOWN                  = 0x00000001;
   const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING      = 0x00000002;
   const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED       = 0x00000004;
   const SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED     = 0x00000008;
   const SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED    = 0x00000010;
   const SEQ4_STATUS_ADMIN_STATE_REVOKED           = 0x00000020;
   const SEQ4_STATUS_RECALLABLE_STATE_REVOKED      = 0x00000040;
   const SEQ4_STATUS_LEASE_MOVED                   = 0x00000080;
   const SEQ4_STATUS_RESTART_RECLAIM_NEEDED        = 0x00000100;
   const SEQ4_STATUS_CB_PATH_DOWN_SESSION          = 0x00000200;
   const SEQ4_STATUS_BACKCHANNEL_FAULT             = 0x00000400;
   const SEQ4_STATUS_DEVID_CHANGED                 = 0x00000800;
   const SEQ4_STATUS_DEVID_DELETED                 = 0x00001000;

   struct SEQUENCE4resok {
           sessionid4      sr_sessionid;
           sequenceid4     sr_sequenceid;
           slotid4         sr_slotid;
           slotid4         sr_highest_slotid;
           slotid4         sr_target_highest_slotid;
           uint32_t        sr_status_flags;
   };

   union SEQUENCE4res switch (nfsstat4 sr_status) {
   case NFS4_OK:
           SEQUENCE4resok  sr_resok4;
   default:
           void;
   };


18.46.3.  DESCRIPTION

   The SEQUENCE operation is used by the server to implement session
   request control and the reply cache semantics.

   SEQUENCE MUST appear as the first operation of any COMPOUND in which
   it appears.  The error NFS4ERR_SEQUENCE_POS will be returned when it
   is found in any position in a COMPOUND beyond the first.  Operations
   other than SEQUENCE, BIND_CONN_TO_SESSION, EXCHANGE_ID,
   CREATE_SESSION, and DESTROY_SESSION, MUST NOT appear as the first
   operation in a COMPOUND.  Such operations MUST yield the error
   NFS4ERR_OP_NOT_IN_SESSION if they do appear at the start of a
   COMPOUND.





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   If SEQUENCE is received on a connection not associated with the
   session via CREATE_SESSION or BIND_CONN_TO_SESSION, and connection
   association enforcement is enabled (see Section 18.35), then the
   server returns NFS4ERR_CONN_NOT_BOUND_TO_SESSION.

   The sa_sessionid argument identifies the session to which this
   request applies.  The sr_sessionid result MUST equal sa_sessionid.

   The sa_slotid argument is the index in the reply cache for the
   request.  The sa_sequenceid field is the sequence number of the
   request for the reply cache entry (slot).  The sr_slotid result MUST
   equal sa_slotid.  The sr_sequenceid result MUST equal sa_sequenceid.

   The sa_highest_slotid argument is the highest slot ID for which the
   client has a request outstanding; it could be equal to sa_slotid.
   The server returns two "highest_slotid" values: sr_highest_slotid and
   sr_target_highest_slotid.  The former is the highest slot ID the
   server will accept in future SEQUENCE operation, and SHOULD NOT be
   less than the value of sa_highest_slotid (but see Section 2.10.6.1
   for an exception).  The latter is the highest slot ID the server
   would prefer the client use on a future SEQUENCE operation.

   If sa_cachethis is TRUE, then the client is requesting that the
   server cache the entire reply in the server's reply cache; therefore,
   the server MUST cache the reply (see Section 2.10.6.1.3).  The server
   MAY cache the reply if sa_cachethis is FALSE.  If the server does not
   cache the entire reply, it MUST still record that it executed the
   request at the specified slot and sequence ID.

   The response to the SEQUENCE operation contains a word of status
   flags (sr_status_flags) that can provide to the client information
   related to the status of the client's lock state and communications
   paths.  Note that any status bits relating to lock state MAY be reset
   when lock state is lost due to a server restart (even if the session
   is persistent across restarts; session persistence does not imply
   lock state persistence) or the establishment of a new client
   instance.

   SEQ4_STATUS_CB_PATH_DOWN
      When set, indicates that the client has no operational backchannel
      path for any session associated with the client ID, making it
      necessary for the client to re-establish one.  This bit remains
      set on all SEQUENCE responses on all sessions associated with the
      client ID until at least one backchannel is available on any
      session associated with the client ID.  If the client fails to re-
      establish a backchannel for the client ID, it is subject to having
      recallable state revoked.




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   SEQ4_STATUS_CB_PATH_DOWN_SESSION
      When set, indicates that the session has no operational
      backchannel.  There are two reasons why
      SEQ4_STATUS_CB_PATH_DOWN_SESSION may be set and not
      SEQ4_STATUS_CB_PATH_DOWN.  First is that a callback operation that
      applies specifically to the session (e.g., CB_RECALL_SLOT, see
      Section 20.8) needs to be sent.  Second is that the server did
      send a callback operation, but the connection was lost before the
      reply.  The server cannot be sure whether or not the client
      received the callback operation, and so, per rules on request
      retry, the server MUST retry the callback operation over the same
      session.  The SEQ4_STATUS_CB_PATH_DOWN_SESSION bit is the
      indication to the client that it needs to associate a connection
      to the session's backchannel.  This bit remains set on all
      SEQUENCE responses of the session until a connection is associated
      with the session's a backchannel.  If the client fails to re-
      establish a backchannel for the session, it is subject to having
      recallable state revoked.

   SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING
      When set, indicates that all GSS contexts or RPCSEC_GSS handles
      assigned to the session's backchannel will expire within a period
      equal to the lease time.  This bit remains set on all SEQUENCE
      replies until at least one of the following are true:

      *  All SSV RPCSEC_GSS handles on the session's backchannel have
         been destroyed and all non-SSV GSS contexts have expired.

      *  At least one more SSV RPCSEC_GSS handle has been added to the
         backchannel.

      *  The expiration time of at least one non-SSV GSS context of an
         RPCSEC_GSS handle is beyond the lease period from the current
         time (relative to the time of when a SEQUENCE response was
         sent)

   SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED
      When set, indicates all non-SSV GSS contexts and all SSV
      RPCSEC_GSS handles assigned to the session's backchannel have
      expired or have been destroyed.  This bit remains set on all
      SEQUENCE replies until at least one non-expired non-SSV GSS
      context for the session's backchannel has been established or at
      least one SSV RPCSEC_GSS handle has been assigned to the
      backchannel.

   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED
      When set, indicates that the lease has expired and as a result the
      server released all of the client's locking state.  This status



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      bit remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID (see
      Section 18.38), or by establishing a new client instance by
      destroying all sessions (via DESTROY_SESSION), the client ID (via
      DESTROY_CLIENTID), and then invoking EXCHANGE_ID and
      CREATE_SESSION to establish a new client ID.

   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
      When set, indicates that some subset of the client's locks have
      been revoked due to expiration of the lease period followed by
      another client's conflicting LOCK operation.  This status bit
      remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID.

   SEQ4_STATUS_ADMIN_STATE_REVOKED
      When set, indicates that one or more locks have been revoked
      without expiration of the lease period, due to administrative
      action.  This status bit remains set on all SEQUENCE replies until
      the loss of all such locks has been acknowledged by use of
      FREE_STATEID.

   SEQ4_STATUS_RECALLABLE_STATE_REVOKED
      When set, indicates that one or more recallable objects have been
      revoked without expiration of the lease period, due to the
      client's failure to return them when recalled, which may be a
      consequence of there being no working backchannel and the client
      failing to re-establish a backchannel per the
      SEQ4_STATUS_CB_PATH_DOWN, SEQ4_STATUS_CB_PATH_DOWN_SESSION, or
      SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED status flags.  This status bit
      remains set on all SEQUENCE replies until the loss of all such
      locks has been acknowledged by use of FREE_STATEID.

   SEQ4_STATUS_LEASE_MOVED
      When set, indicates that responsibility for lease renewal has been
      transferred to one or more new servers.  This condition will
      continue until the client receives an NFS4ERR_MOVED error and the
      server receives the subsequent GETATTR for the fs_locations or
      fs_locations_info attribute for an access to each file system for
      which a lease has been moved to a new server.  See
      Section 11.7.7.1.

   SEQ4_STATUS_RESTART_RECLAIM_NEEDED
      When set, indicates that due to server restart, the client must
      reclaim locking state.  Until the client sends a global
      RECLAIM_COMPLETE (Section 18.51), every SEQUENCE operation will
      return SEQ4_STATUS_RESTART_RECLAIM_NEEDED.

   SEQ4_STATUS_BACKCHANNEL_FAULT



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      The server has encountered an unrecoverable fault with the
      backchannel (e.g., it has lost track of the sequence ID for a slot
      in the backchannel).  The client MUST stop sending more requests
      on the session's fore channel, wait for all outstanding requests
      to complete on the fore and back channel, and then destroy the
      session.

   SEQ4_STATUS_DEVID_CHANGED
      The client is using device ID notifications and the server has
      changed a device ID mapping held by the client.  This flag will
      stay present until the client has obtained the new mapping with
      GETDEVICEINFO.

   SEQ4_STATUS_DEVID_DELETED
      The client is using device ID notifications and the server has
      deleted a device ID mapping held by the client.  This flag will
      stay in effect until the client sends a GETDEVICEINFO on the
      device ID with a null value in the argument gdia_notify_types.

   The value of the sa_sequenceid argument relative to the cached
   sequence ID on the slot falls into one of three cases.

   o  If the difference between sa_sequenceid and the server's cached
      sequence ID at the slot ID is two (2) or more, or if sa_sequenceid
      is less than the cached sequence ID (accounting for wraparound of
      the unsigned sequence ID value), then the server MUST return
      NFS4ERR_SEQ_MISORDERED.

   o  If sa_sequenceid and the cached sequence ID are the same, this is
      a retry, and the server replies with what is recorded in the reply
      cache.  The lease is possibly renewed as described below.

   o  If sa_sequenceid is one greater (accounting for wraparound) than
      the cached sequence ID, then this is a new request, and the slot's
      sequence ID is incremented.  The operations subsequent to
      SEQUENCE, if any, are processed.  If there are no other
      operations, the only other effects are to cache the SEQUENCE reply
      in the slot, maintain the session's activity, and possibly renew
      the lease.

   If the client reuses a slot ID and sequence ID for a completely
   different request, the server MAY treat the request as if it is a
   retry of what it has already executed.  The server MAY however detect
   the client's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.

   If SEQUENCE returns an error, then the state of the slot (sequence
   ID, cached reply) MUST NOT change, and the associated lease MUST NOT
   be renewed.



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   If SEQUENCE returns NFS4_OK, then the associated lease MUST be
   renewed (see Section 8.3), except if
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is returned in sr_status_flags.

18.46.4.  IMPLEMENTATION

   The server MUST maintain a mapping of session ID to client ID in
   order to validate any operations that follow SEQUENCE that take a
   stateid as an argument and/or result.

   If the client establishes a persistent session, then a SEQUENCE
   received after a server restart might encounter requests performed
   and recorded in a persistent reply cache before the server restart.
   In this case, SEQUENCE will be processed successfully, while requests
   that were not previously performed and recorded are rejected with
   NFS4ERR_DEADSESSION.

   Depending on which of the operations within the COMPOUND were
   successfully performed before the server restart, these operations
   will also have replies sent from the server reply cache.  Note that
   when these operations establish locking state, it is locking state
   that applies to the previous server instance and to the previous
   client ID, even though the server restart, which logically happened
   after these operations, eliminated that state.  In the case of a
   partially executed COMPOUND, processing may reach an operation not
   processed during the earlier server instance, making this operation a
   new one and not performable on the existing session.  In this case,
   NFS4ERR_DEADSESSION will be returned from that operation.

18.47.  Operation 54: SET_SSV - Update SSV for a Client ID

18.47.1.  ARGUMENT

   struct ssa_digest_input4 {
           SEQUENCE4args sdi_seqargs;
   };

   struct SET_SSV4args {
           opaque          ssa_ssv<>;
           opaque          ssa_digest<>;
   };


18.47.2.  RESULT







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   struct ssr_digest_input4 {
           SEQUENCE4res sdi_seqres;
   };

   struct SET_SSV4resok {
           opaque          ssr_digest<>;
   };

   union SET_SSV4res switch (nfsstat4 ssr_status) {
   case NFS4_OK:
           SET_SSV4resok   ssr_resok4;
   default:
           void;
   };


18.47.3.  DESCRIPTION

   This operation is used to update the SSV for a client ID.  Before
   SET_SSV is called the first time on a client ID, the SSV is zero.
   The SSV is the key used for the SSV GSS mechanism (Section 2.10.9)

   SET_SSV MUST be preceded by a SEQUENCE operation in the same
   COMPOUND.  It MUST NOT be used if the client did not opt for SP4_SSV
   state protection when the client ID was created (see Section 18.35);
   the server returns NFS4ERR_INVAL in that case.

   The field ssa_digest is computed as the output of the HMAC (RFC 2104
   [11]) using the subkey derived from the SSV4_SUBKEY_MIC_I2T and
   current SSV as the key (see Section 2.10.9 for a description of
   subkeys), and an XDR encoded value of data type ssa_digest_input4.
   The field sdi_seqargs is equal to the arguments of the SEQUENCE
   operation for the COMPOUND procedure that SET_SSV is within.

   The argument ssa_ssv is XORed with the current SSV to produce the new
   SSV.  The argument ssa_ssv SHOULD be generated randomly.

   In the response, ssr_digest is the output of the HMAC using the
   subkey derived from SSV4_SUBKEY_MIC_T2I and new SSV as the key, and
   an XDR encoded value of data type ssr_digest_input4.  The field
   sdi_seqres is equal to the results of the SEQUENCE operation for the
   COMPOUND procedure that SET_SSV is within.

   As noted in Section 18.35, the client and server can maintain
   multiple concurrent versions of the SSV.  The client and server each
   MUST maintain an internal SSV version number, which is set to one the
   first time SET_SSV executes on the server and the client receives the
   first SET_SSV reply.  Each subsequent SET_SSV increases the internal



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   SSV version number by one.  The value of this version number
   corresponds to the smpt_ssv_seq, smt_ssv_seq, sspt_ssv_seq, and
   ssct_ssv_seq fields of the SSV GSS mechanism tokens (see
   Section 2.10.9).

18.47.4.  IMPLEMENTATION

   When the server receives ssa_digest, it MUST verify the digest by
   computing the digest the same way the client did and comparing it
   with ssa_digest.  If the server gets a different result, this is an
   error, NFS4ERR_BAD_SESSION_DIGEST.  This error might be the result of
   another SET_SSV from the same client ID changing the SSV.  If so, the
   client recovers by sending a SET_SSV operation again with a
   recomputed digest based on the subkey of the new SSV.  If the
   transport connection is dropped after the SET_SSV request is sent,
   but before the SET_SSV reply is received, then there are special
   considerations for recovery if the client has no more connections
   associated with sessions associated with the client ID of the SSV.
   See Section 18.34.4.

   Clients SHOULD NOT send an ssa_ssv that is equal to a previous
   ssa_ssv, nor equal to a previous or current SSV (including an ssa_ssv
   equal to zero since the SSV is initialized to zero when the client ID
   is created).

   Clients SHOULD send SET_SSV with RPCSEC_GSS privacy.  Servers MUST
   support RPCSEC_GSS with privacy for any COMPOUND that has { SEQUENCE,
   SET_SSV }.

   A client SHOULD NOT send SET_SSV with the SSV GSS mechanism's
   credential because the purpose of SET_SSV is to seed the SSV from
   non-SSV credentials.  Instead, SET_SSV SHOULD be sent with the
   credential of a user that is accessing the client ID for the first
   time (Section 2.10.8.3).  However, if the client does send SET_SSV
   with SSV credentials, the digest protecting the arguments uses the
   value of the SSV before ssa_ssv is XORed in, and the digest
   protecting the results uses the value of the SSV after the ssa_ssv is
   XORed in.

18.48.  Operation 55: TEST_STATEID - Test Stateids for Validity

18.48.1.  ARGUMENT

   struct TEST_STATEID4args {
           stateid4        ts_stateids<>;
   };





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18.48.2.  RESULT

   struct TEST_STATEID4resok {
           nfsstat4        tsr_status_codes<>;
   };

   union TEST_STATEID4res switch (nfsstat4 tsr_status) {
       case NFS4_OK:
           TEST_STATEID4resok tsr_resok4;
       default:
           void;
   };


18.48.3.  DESCRIPTION

   The TEST_STATEID operation is used to check the validity of a set of
   stateids.  It can be used at any time, but the client should
   definitely use it when it receives an indication that one or more of
   its stateids have been invalidated due to lock revocation.  This
   occurs when the SEQUENCE operation returns with one of the following
   sr_status_flags set:

   o  SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED

   o  SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED

   o  SEQ4_STATUS_EXPIRED_RECALLABLE_STATE_REVOKED

   The client can use TEST_STATEID one or more times to test the
   validity of its stateids.  Each use of TEST_STATEID allows a large
   set of such stateids to be tested and avoids problems with earlier
   stateids in a COMPOUND request from interfering with the checking of
   subsequent stateids, as would happen if individual stateids were
   tested by a series of corresponding by operations in a COMPOUND
   request.

   For each stateid, the server returns the status code that would be
   returned if that stateid were to be used in normal operation.
   Returning such a status indication is not an error and does not cause
   COMPOUND processing to terminate.  Checks for the validity of the
   stateid proceed as they would for normal operations with a number of
   exceptions:

   o  There is no check for the type of stateid object, as would be the
      case for normal use of a stateid.

   o  There is no reference to the current filehandle.



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   o  Special stateids are always considered invalid (they result in the
      error code NFS4ERR_BAD_STATEID).

   All stateids are interpreted as being associated with the client for
   the current session.  Any possible association with a previous
   instance of the client (as stale stateids) is not considered.

   The valid status values in the returned status_code array are
   NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID,
   NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.

18.48.4.  IMPLEMENTATION

   See Sections 8.2.2 and 8.2.4 for a discussion of stateid structure,
   lifetime, and validation.

18.49.  Operation 56: WANT_DELEGATION - Request Delegation

18.49.1.  ARGUMENT
































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   union deleg_claim4 switch (open_claim_type4 dc_claim) {
   /*
    * No special rights to object.  Ordinary delegation
    * request of the specified object.  Object identified
    * by filehandle.
    */
   case CLAIM_FH: /* new to v4.1 */
           /* CURRENT_FH: object being delegated */
           void;

   /*
    * Right to file based on a delegation granted
    * to a previous boot instance of the client.
    * File is specified by filehandle.
    */
   case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
           /* CURRENT_FH: object being delegated */
           void;

   /*
    * Right to the file established by an open previous
    * to server reboot.  File identified by filehandle.
    * Used during server reclaim grace period.
    */
   case CLAIM_PREVIOUS:
           /* CURRENT_FH: object being reclaimed */
           open_delegation_type4   dc_delegate_type;
   };

   struct WANT_DELEGATION4args {
           uint32_t        wda_want;
           deleg_claim4    wda_claim;
   };


18.49.2.  RESULT

   union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
   case NFS4_OK:
           open_delegation4 wdr_resok4;
   default:
           void;
   };








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18.49.3.  DESCRIPTION

   Where this description mandates the return of a specific error code
   for a specific condition, and where multiple conditions apply, the
   server MAY return any of the mandated error codes.

   This operation allows a client to:

   o  Get a delegation on all types of files except directories.

   o  Register a "want" for a delegation for the specified file object,
      and be notified via a callback when the delegation is available.
      The server MAY support notifications of availability via
      callbacks.  If the server does not support registration of wants,
      it MUST NOT return an error to indicate that, and instead MUST
      return with ond_why set to WND4_CONTENTION or WND4_RESOURCE and
      ond_server_will_push_deleg or ond_server_will_signal_avail set to
      FALSE.  When the server indicates that it will notify the client
      by means of a callback, it will either provide the delegation
      using a CB_PUSH_DELEG operation or cancel its promise by sending a
      CB_WANTS_CANCELLED operation.

   o  Cancel a want for a delegation.

   The client SHOULD NOT set OPEN4_SHARE_ACCESS_READ and SHOULD NOT set
   OPEN4_SHARE_ACCESS_WRITE in wda_want.  If it does, the server MUST
   ignore them.

   The meanings of the following flags in wda_want are the same as they
   are in OPEN, except as noted below.

   o  OPEN4_SHARE_ACCESS_WANT_READ_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_ANY_DELEG

   o  OPEN4_SHARE_ACCESS_WANT_NO_DELEG.  Unlike the OPEN operation, this
      flag SHOULD NOT be set by the client in the arguments to
      WANT_DELEGATION, and MUST be ignored by the server.

   o  OPEN4_SHARE_ACCESS_WANT_CANCEL

   o  OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL

   o  OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED





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   The handling of the above flags in WANT_DELEGATION is the same as in
   OPEN.  Information about the delegation and/or the promises the
   server is making regarding future callbacks are the same as those
   described in the open_delegation4 structure.

   The successful results of WANT_DELEGATION are of data type
   open_delegation4, which is the same data type as the "delegation"
   field in the results of the OPEN operation (see Section 18.16.3).
   The server constructs wdr_resok4 the same way it constructs OPEN's
   "delegation" with one difference: WANT_DELEGATION MUST NOT return a
   delegation type of OPEN_DELEGATE_NONE.

   If ((wda_want & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) &
   ~OPEN4_SHARE_ACCESS_WANT_NO_DELEG) is zero, then the client is
   indicating no explicit desire or non-desire for a delegation and the
   server MUST return NFS4ERR_INVAL.

   The client uses the OPEN4_SHARE_ACCESS_WANT_CANCEL flag in the
   WANT_DELEGATION operation to cancel a previously requested want for a
   delegation.  Note that if the server is in the process of sending the
   delegation (via CB_PUSH_DELEG) at the time the client sends a
   cancellation of the want, the delegation might still be pushed to the
   client.

   If WANT_DELEGATION fails to return a delegation, and the server
   returns NFS4_OK, the server MUST set the delegation type to
   OPEN4_DELEGATE_NONE_EXT, and set od_whynone, as described in
   Section 18.16.  Write delegations are not available for file types
   that are not writable.  This includes file objects of types NF4BLK,
   NF4CHR, NF4LNK, NF4SOCK, and NF4FIFO.  If the client requests
   OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG without
   OPEN4_SHARE_ACCESS_WANT_READ_DELEG on an object with one of the
   aforementioned file types, the server must set
   wdr_resok4.od_whynone.ond_why to WND4_WRITE_DELEG_NOT_SUPP_FTYPE.

18.49.4.  IMPLEMENTATION

   A request for a conflicting delegation is not normally intended to
   trigger the recall of the existing delegation.  Servers may choose to
   treat some clients as having higher priority such that their wants
   will trigger recall of an existing delegation, although that is
   expected to be an unusual situation.

   Servers will generally recall delegations assigned by WANT_DELEGATION
   on the same basis as those assigned by OPEN.  CB_RECALL will
   generally be done only when other clients perform operations
   inconsistent with the delegation.  The normal response to aging of
   delegations is to use CB_RECALL_ANY, in order to give the client the



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   opportunity to keep the delegations most useful from its point of
   view.

18.50.  Operation 57: DESTROY_CLIENTID - Destroy a Client ID

18.50.1.  ARGUMENT

   struct DESTROY_CLIENTID4args {
           clientid4       dca_clientid;
   };


18.50.2.  RESULT

   struct DESTROY_CLIENTID4res {
           nfsstat4        dcr_status;
   };


18.50.3.  DESCRIPTION

   The DESTROY_CLIENTID operation destroys the client ID.  If there are
   sessions (both idle and non-idle), opens, locks, delegations,
   layouts, and/or wants (Section 18.49) associated with the unexpired
   lease of the client ID, the server MUST return NFS4ERR_CLIENTID_BUSY.
   DESTROY_CLIENTID MAY be preceded with a SEQUENCE operation as long as
   the client ID derived from the session ID of SEQUENCE is not the same
   as the client ID to be destroyed.  If the client IDs are the same,
   then the server MUST return NFS4ERR_CLIENTID_BUSY.

   If DESTROY_CLIENTID is not prefixed by SEQUENCE, it MUST be the only
   operation in the COMPOUND request (otherwise, the server MUST return
   NFS4ERR_NOT_ONLY_OP).  If the operation is sent without a SEQUENCE
   preceding it, a client that retransmits the request may receive an
   error in response, because the original request might have been
   successfully executed.

18.50.4.  IMPLEMENTATION

   DESTROY_CLIENTID allows a server to immediately reclaim the resources
   consumed by an unused client ID, and also to forget that it ever
   generated the client ID.  By forgetting that it ever generated the
   client ID, the server can safely reuse the client ID on a future
   EXCHANGE_ID operation.







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18.51.  Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished

18.51.1.  ARGUMENT

   struct RECLAIM_COMPLETE4args {
           /*
            * If rca_one_fs TRUE,
            *
            *    CURRENT_FH: object in
            *    file system reclaim is
            *    complete for.
            */
           bool            rca_one_fs;
   };


18.51.2.  RESULTS

   struct RECLAIM_COMPLETE4res {
           nfsstat4        rcr_status;
   };


18.51.3.  DESCRIPTION

   A RECLAIM_COMPLETE operation is used to indicate that the client has
   reclaimed all of the locking state that it will recover, when it is
   recovering state due to either a server restart or the transfer of a
   file system to another server.  There are two types of
   RECLAIM_COMPLETE operations:

   o  When rca_one_fs is FALSE, a global RECLAIM_COMPLETE is being done.
      This indicates that recovery of all locks that the client held on
      the previous server instance have been completed.

   o  When rca_one_fs is TRUE, a file system-specific RECLAIM_COMPLETE
      is being done.  This indicates that recovery of locks for a single
      fs (the one designated by the current filehandle) due to a file
      system transition have been completed.  Presence of a current
      filehandle is only required when rca_one_fs is set to TRUE.

   Once a RECLAIM_COMPLETE is done, there can be no further reclaim
   operations for locks whose scope is defined as having completed
   recovery.  Once the client sends RECLAIM_COMPLETE, the server will
   not allow the client to do subsequent reclaims of locking state for
   that scope and, if these are attempted, will return NFS4ERR_NO_GRACE.





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   Whenever a client establishes a new client ID and before it does the
   first non-reclaim operation that obtains a lock, it MUST send a
   RECLAIM_COMPLETE with rca_one_fs set to FALSE, even if there are no
   locks to reclaim.  If non-reclaim locking operations are done before
   the RECLAIM_COMPLETE, an NFS4ERR_GRACE error will be returned.

   Similarly, when the client accesses a file system on a new server,
   before it sends the first non-reclaim operation that obtains a lock
   on this new server, it MUST send a RECLAIM_COMPLETE with rca_one_fs
   set to TRUE and current filehandle within that file system, even if
   there are no locks to reclaim.  If non-reclaim locking operations are
   done on that file system before the RECLAIM_COMPLETE, an
   NFS4ERR_GRACE error will be returned.

   Any locks not reclaimed at the point at which RECLAIM_COMPLETE is
   done become non-reclaimable.  The client MUST NOT attempt to reclaim
   them, either during the current server instance or in any subsequent
   server instance, or on another server to which responsibility for
   that file system is transferred.  If the client were to do so, it
   would be violating the protocol by representing itself as owning
   locks that it does not own, and so has no right to reclaim.  See
   Section 8.4.3 for a discussion of edge conditions related to lock
   reclaim.

   By sending a RECLAIM_COMPLETE, the client indicates readiness to
   proceed to do normal non-reclaim locking operations.  The client
   should be aware that such operations may temporarily result in
   NFS4ERR_GRACE errors until the server is ready to terminate its grace
   period.

18.51.4.  IMPLEMENTATION

   Servers will typically use the information as to when reclaim
   activity is complete to reduce the length of the grace period.  When
   the server maintains in persistent storage a list of clients that
   might have had locks, it is in a position to use the fact that all
   such clients have done a RECLAIM_COMPLETE to terminate the grace
   period and begin normal operations (i.e., grant requests for new
   locks) sooner than it might otherwise.

   Latency can be minimized by doing a RECLAIM_COMPLETE as part of the
   COMPOUND request in which the last lock-reclaiming operation is done.
   When there are no reclaims to be done, RECLAIM_COMPLETE should be
   done immediately in order to allow the grace period to end as soon as
   possible.

   RECLAIM_COMPLETE should only be done once for each server instance or
   occasion of the transition of a file system.  If it is done a second



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   time, the error NFS4ERR_COMPLETE_ALREADY will result.  Note that
   because of the session feature's retry protection, retries of
   COMPOUND requests containing RECLAIM_COMPLETE operation will not
   result in this error.

   When a RECLAIM_COMPLETE is sent, the client effectively acknowledges
   any locks not yet reclaimed as lost.  This allows the server to re-
   enable the client to recover locks if the occurrence of edge
   conditions, as described in Section 8.4.3, had caused the server to
   disable the client from recovering locks.

18.52.  Operation 10044: ILLEGAL - Illegal Operation

18.52.1.  ARGUMENTS

   void;

18.52.2.  RESULTS

   struct ILLEGAL4res {
           nfsstat4        status;
   };


18.52.3.  DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the client sending an operation code within COMPOUND that is
   not supported.  See the COMPOUND procedure description for more
   details.

   The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

18.52.4.  IMPLEMENTATION

   A client will probably not send an operation with code OP_ILLEGAL but
   if it does, the response will be ILLEGAL4res just as it would be with
   any other invalid operation code.  Note that if the server gets an
   illegal operation code that is not OP_ILLEGAL, and if the server
   checks for legal operation codes during the XDR decode phase, then
   the ILLEGAL4res would not be returned.

19.  NFSv4.1 Callback Procedures

   The procedures used for callbacks are defined in the following
   sections.  In the interest of clarity, the terms "client" and
   "server" refer to NFS clients and servers, despite the fact that for




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   an individual callback RPC, the sense of these terms would be
   precisely the opposite.

   Both procedures, CB_NULL and CB_COMPOUND, MUST be implemented.

19.1.  Procedure 0: CB_NULL - No Operation

19.1.1.  ARGUMENTS

   void;

19.1.2.  RESULTS

   void;

19.1.3.  DESCRIPTION

   CB_NULL is the standard ONC RPC NULL procedure, with the standard
   void argument and void response.  Even though there is no direct
   functionality associated with this procedure, the server will use
   CB_NULL to confirm the existence of a path for RPCs from the server
   to client.

19.1.4.  ERRORS

   None.

19.2.  Procedure 1: CB_COMPOUND - Compound Operations

19.2.1.  ARGUMENTS





















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   enum nfs_cb_opnum4 {
           OP_CB_GETATTR           = 3,
           OP_CB_RECALL            = 4,
   /* Callback operations new to NFSv4.1 */
           OP_CB_LAYOUTRECALL      = 5,
           OP_CB_NOTIFY            = 6,
           OP_CB_PUSH_DELEG        = 7,
           OP_CB_RECALL_ANY        = 8,
           OP_CB_RECALLABLE_OBJ_AVAIL = 9,
           OP_CB_RECALL_SLOT       = 10,
           OP_CB_SEQUENCE          = 11,
           OP_CB_WANTS_CANCELLED   = 12,
           OP_CB_NOTIFY_LOCK       = 13,
           OP_CB_NOTIFY_DEVICEID   = 14,

           OP_CB_ILLEGAL           = 10044
   };

   union nfs_cb_argop4 switch (unsigned argop) {
    case OP_CB_GETATTR:
         CB_GETATTR4args           opcbgetattr;
    case OP_CB_RECALL:
         CB_RECALL4args            opcbrecall;
    case OP_CB_LAYOUTRECALL:
         CB_LAYOUTRECALL4args      opcblayoutrecall;
    case OP_CB_NOTIFY:
         CB_NOTIFY4args            opcbnotify;
    case OP_CB_PUSH_DELEG:
         CB_PUSH_DELEG4args        opcbpush_deleg;
    case OP_CB_RECALL_ANY:
         CB_RECALL_ANY4args        opcbrecall_any;
    case OP_CB_RECALLABLE_OBJ_AVAIL:
         CB_RECALLABLE_OBJ_AVAIL4args opcbrecallable_obj_avail;
    case OP_CB_RECALL_SLOT:
         CB_RECALL_SLOT4args       opcbrecall_slot;
    case OP_CB_SEQUENCE:
         CB_SEQUENCE4args          opcbsequence;
    case OP_CB_WANTS_CANCELLED:
         CB_WANTS_CANCELLED4args   opcbwants_cancelled;
    case OP_CB_NOTIFY_LOCK:
         CB_NOTIFY_LOCK4args       opcbnotify_lock;
    case OP_CB_NOTIFY_DEVICEID:
         CB_NOTIFY_DEVICEID4args   opcbnotify_deviceid;
    case OP_CB_ILLEGAL:            void;
   };






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   struct CB_COMPOUND4args {
           utf8str_cs      tag;
           uint32_t        minorversion;
           uint32_t        callback_ident;
           nfs_cb_argop4   argarray<>;
   };

19.2.2.  RESULTS











































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   union nfs_cb_resop4 switch (unsigned resop) {
    case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
    case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;

    /* new NFSv4.1 operations */
    case OP_CB_LAYOUTRECALL:
                           CB_LAYOUTRECALL4res
                                           opcblayoutrecall;

    case OP_CB_NOTIFY:     CB_NOTIFY4res   opcbnotify;

    case OP_CB_PUSH_DELEG: CB_PUSH_DELEG4res
                                           opcbpush_deleg;

    case OP_CB_RECALL_ANY: CB_RECALL_ANY4res
                                           opcbrecall_any;

    case OP_CB_RECALLABLE_OBJ_AVAIL:
                           CB_RECALLABLE_OBJ_AVAIL4res
                                   opcbrecallable_obj_avail;

    case OP_CB_RECALL_SLOT:
                           CB_RECALL_SLOT4res
                                           opcbrecall_slot;

    case OP_CB_SEQUENCE:   CB_SEQUENCE4res opcbsequence;

    case OP_CB_WANTS_CANCELLED:
                           CB_WANTS_CANCELLED4res
                                   opcbwants_cancelled;

    case OP_CB_NOTIFY_LOCK:
                           CB_NOTIFY_LOCK4res
                                           opcbnotify_lock;

    case OP_CB_NOTIFY_DEVICEID:
                           CB_NOTIFY_DEVICEID4res
                                           opcbnotify_deviceid;

    /* Not new operation */
    case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
   };

   struct CB_COMPOUND4res {
           nfsstat4 status;
           utf8str_cs      tag;
           nfs_cb_resop4   resarray<>;
   };



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19.2.3.  DESCRIPTION

   The CB_COMPOUND procedure is used to combine one or more of the
   callback procedures into a single RPC request.  The main callback RPC
   program has two main procedures: CB_NULL and CB_COMPOUND.  All other
   operations use the CB_COMPOUND procedure as a wrapper.

   During the processing of the CB_COMPOUND procedure, the client may
   find that it does not have the available resources to execute any or
   all of the operations within the CB_COMPOUND sequence.  Refer to
   Section 2.10.6.4 for details.

   The minorversion field of the arguments MUST be the same as the
   minorversion of the COMPOUND procedure used to create the client ID
   and session.  For NFSv4.1, minorversion MUST be set to 1.

   Contained within the CB_COMPOUND results is a "status" field.  This
   status MUST be equal to the status of the last operation that was
   executed within the CB_COMPOUND procedure.  Therefore, if an
   operation incurred an error, then the "status" value will be the same
   error value as is being returned for the operation that failed.

   The "tag" field is handled the same way as that of the COMPOUND
   procedure (see Section 16.2.3).

   Illegal operation codes are handled in the same way as they are
   handled for the COMPOUND procedure.

19.2.4.  IMPLEMENTATION

   The CB_COMPOUND procedure is used to combine individual operations
   into a single RPC request.  The client interprets each of the
   operations in turn.  If an operation is executed by the client and
   the status of that operation is NFS4_OK, then the next operation in
   the CB_COMPOUND procedure is executed.  The client continues this
   process until there are no more operations to be executed or one of
   the operations has a status value other than NFS4_OK.

19.2.5.  ERRORS

   CB_COMPOUND will of course return every error that each operation on
   the backchannel can return (see Table 7).  However, if CB_COMPOUND
   returns zero operations, obviously the error returned by COMPOUND has
   nothing to do with an error returned by an operation.  The list of
   errors CB_COMPOUND will return if it processes zero operations
   includes:





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                         CB_COMPOUND error returns

   +------------------------------+------------------------------------+
   | Error                        | Notes                              |
   +------------------------------+------------------------------------+
   | NFS4ERR_BADCHAR              | The tag argument has a character   |
   |                              | the replier does not support.      |
   | NFS4ERR_BADXDR               |                                    |
   | NFS4ERR_DELAY                |                                    |
   | NFS4ERR_INVAL                | The tag argument is not in UTF-8   |
   |                              | encoding.                          |
   | NFS4ERR_MINOR_VERS_MISMATCH  |                                    |
   | NFS4ERR_SERVERFAULT          |                                    |
   | NFS4ERR_TOO_MANY_OPS         |                                    |
   | NFS4ERR_REP_TOO_BIG          |                                    |
   | NFS4ERR_REP_TOO_BIG_TO_CACHE |                                    |
   | NFS4ERR_REQ_TOO_BIG          |                                    |
   +------------------------------+------------------------------------+

                                 Table 15

20.  NFSv4.1 Callback Operations

20.1.  Operation 3: CB_GETATTR - Get Attributes

20.1.1.  ARGUMENT

   struct CB_GETATTR4args {
           nfs_fh4 fh;
           bitmap4 attr_request;
   };


20.1.2.  RESULT

   struct CB_GETATTR4resok {
           fattr4  obj_attributes;
   };

   union CB_GETATTR4res switch (nfsstat4 status) {
    case NFS4_OK:
            CB_GETATTR4resok       resok4;
    default:
            void;
   };






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20.1.3.  DESCRIPTION

   The CB_GETATTR operation is used by the server to obtain the current
   modified state of a file that has been OPEN_DELEGATE_WRITE delegated.
   The size and change attributes are the only ones guaranteed to be
   serviced by the client.  See Section 10.4.3 for a full description of
   how the client and server are to interact with the use of CB_GETATTR.

   If the filehandle specified is not one for which the client holds an
   OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error is
   returned.

20.1.4.  IMPLEMENTATION

   The client returns attrmask bits and the associated attribute values
   only for the change attribute, and attributes that it may change
   (time_modify, and size).

20.2.  Operation 4: CB_RECALL - Recall a Delegation

20.2.1.  ARGUMENT

   struct CB_RECALL4args {
           stateid4        stateid;
           bool            truncate;
           nfs_fh4         fh;
   };


20.2.2.  RESULT

   struct CB_RECALL4res {
           nfsstat4        status;
   };


20.2.3.  DESCRIPTION

   The CB_RECALL operation is used to begin the process of recalling a
   delegation and returning it to the server.

   The truncate flag is used to optimize recall for a file object that
   is a regular file and is about to be truncated to zero.  When it is
   TRUE, the client is freed of the obligation to propagate modified
   data for the file to the server, since this data is irrelevant.

   If the handle specified is not one for which the client holds a
   delegation, an NFS4ERR_BADHANDLE error is returned.



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   If the stateid specified is not one corresponding to an OPEN
   delegation for the file specified by the filehandle, an
   NFS4ERR_BAD_STATEID is returned.

20.2.4.  IMPLEMENTATION

   The client SHOULD reply to the callback immediately.  Replying does
   not complete the recall except when the value of the reply's status
   field is neither NFS4ERR_DELAY nor NFS4_OK.  The recall is not
   complete until the delegation is returned using a DELEGRETURN
   operation.

20.3.  Operation 5: CB_LAYOUTRECALL - Recall Layout from Client

20.3.1.  ARGUMENT

   /*
    * NFSv4.1 callback arguments and results
    */

   enum layoutrecall_type4 {
           LAYOUTRECALL4_FILE = LAYOUT4_RET_REC_FILE,
           LAYOUTRECALL4_FSID = LAYOUT4_RET_REC_FSID,
           LAYOUTRECALL4_ALL  = LAYOUT4_RET_REC_ALL
   };

   struct layoutrecall_file4 {
           nfs_fh4         lor_fh;
           offset4         lor_offset;
           length4         lor_length;
           stateid4        lor_stateid;
   };

   union layoutrecall4 switch(layoutrecall_type4 lor_recalltype) {
   case LAYOUTRECALL4_FILE:
           layoutrecall_file4 lor_layout;
   case LAYOUTRECALL4_FSID:
           fsid4              lor_fsid;
   case LAYOUTRECALL4_ALL:
           void;
   };

   struct CB_LAYOUTRECALL4args {
           layouttype4             clora_type;
           layoutiomode4           clora_iomode;
           bool                    clora_changed;
           layoutrecall4           clora_recall;
   };



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20.3.2.  RESULT

   struct CB_LAYOUTRECALL4res {
           nfsstat4        clorr_status;
   };


20.3.3.  DESCRIPTION

   The CB_LAYOUTRECALL operation is used by the server to recall layouts
   from the client; as a result, the client will begin the process of
   returning layouts via LAYOUTRETURN.  The CB_LAYOUTRECALL operation
   specifies one of three forms of recall processing with the value of
   layoutrecall_type4.  The recall is for one of the following: a
   specific layout of a specific file (LAYOUTRECALL4_FILE), an entire
   file system ID (LAYOUTRECALL4_FSID), or all file systems
   (LAYOUTRECALL4_ALL).

   The behavior of the operation varies based on the value of the
   layoutrecall_type4.  The value and behaviors are:

   LAYOUTRECALL4_FILE

      For a layout to match the recall request, the values of the
      following fields must match those of the layout: clora_type,
      clora_iomode, lor_fh, and the byte-range specified by lor_offset
      and lor_length.  The clora_iomode field may have a special value
      of LAYOUTIOMODE4_ANY.  The special value LAYOUTIOMODE4_ANY will
      match any iomode originally returned in a layout; therefore, it
      acts as a wild card.  The other special value used is for
      lor_length.  If lor_length has a value of NFS4_UINT64_MAX, the
      lor_length field means the maximum possible file size.  If a
      matching layout is found, it MUST be returned using the
      LAYOUTRETURN operation (see Section 18.44).  An example of the
      field's special value use is if clora_iomode is LAYOUTIOMODE4_ANY,
      lor_offset is zero, and lor_length is NFS4_UINT64_MAX, then the
      entire layout is to be returned.

      The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
      client does not hold layouts for the file or if the client does
      not have any overlapping layouts for the specification in the
      layout recall.

   LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL

      If LAYOUTRECALL4_FSID is specified, the fsid specifies the file
      system for which any outstanding layouts MUST be returned.  If
      LAYOUTRECALL4_ALL is specified, all outstanding layouts MUST be



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      returned.  In addition, LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL
      specify that all the storage device ID to storage device address
      mappings in the affected file system(s) are also recalled.  The
      respective LAYOUTRETURN with either LAYOUTRETURN4_FSID or
      LAYOUTRETURN4_ALL acknowledges to the server that the client
      invalidated the said device mappings.  See Section 12.5.5.2.1.5
      for considerations with "bulk" recall of layouts.

      The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
      client does not hold layouts and does not have valid deviceid
      mappings.

   In processing the layout recall request, the client also varies its
   behavior based on the value of the clora_changed field.  This field
   is used by the server to provide additional context for the reason
   why the layout is being recalled.  A FALSE value for clora_changed
   indicates that no change in the layout is expected and the client may
   write modified data to the storage devices involved; this must be
   done prior to returning the layout via LAYOUTRETURN.  A TRUE value
   for clora_changed indicates that the server is changing the layout.
   Examples of layout changes and reasons for a TRUE indication are the
   following: the metadata server is restriping the file or a permanent
   error has occurred on a storage device and the metadata server would
   like to provide a new layout for the file.  Therefore, a
   clora_changed value of TRUE indicates some level of change for the
   layout and the client SHOULD NOT write and commit modified data to
   the storage devices.  In this case, the client writes and commits
   data through the metadata server.

   See Section 12.5.3 for a description of how the lor_stateid field in
   the arguments is to be constructed.  Note that the "seqid" field of
   lor_stateid MUST NOT be zero.  See Sections 8.2, 12.5.3, and 12.5.5.2
   for a further discussion and requirements.

20.3.4.  IMPLEMENTATION

   The client's processing for CB_LAYOUTRECALL is similar to CB_RECALL
   (recall of file delegations) in that the client responds to the
   request before actually returning layouts via the LAYOUTRETURN
   operation.  While the client responds to the CB_LAYOUTRECALL
   immediately, the operation is not considered complete (i.e.,
   considered pending) until all affected layouts are returned to the
   server via the LAYOUTRETURN operation.

   Before returning the layout to the server via LAYOUTRETURN, the
   client should wait for the response from in-process or in-flight
   READ, WRITE, or COMMIT operations that use the recalled layout.




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   If the client is holding modified data that is affected by a recalled
   layout, the client has various options for writing the data to the
   server.  As always, the client may write the data through the
   metadata server.  In fact, the client may not have a choice other
   than writing to the metadata server when the clora_changed argument
   is TRUE and a new layout is unavailable from the server.  However,
   the client may be able to write the modified data to the storage
   device if the clora_changed argument is FALSE; this needs to be done
   before returning the layout via LAYOUTRETURN.  If the client were to
   obtain a new layout covering the modified data's byte-range, then
   writing to the storage devices is an available alternative.  Note
   that before obtaining a new layout, the client must first return the
   original layout.

   In the case of modified data being written while the layout is held,
   the client must use LAYOUTCOMMIT operations at the appropriate time;
   as required LAYOUTCOMMIT must be done before the LAYOUTRETURN.  If a
   large amount of modified data is outstanding, the client may send
   LAYOUTRETURNs for portions of the recalled layout; this allows the
   server to monitor the client's progress and adherence to the original
   recall request.  However, the last LAYOUTRETURN in a sequence of
   returns MUST specify the full range being recalled (see
   Section 12.5.5.1 for details).

   If a server needs to delete a device ID and there are layouts
   referring to the device ID, CB_LAYOUTRECALL MUST be invoked to cause
   the client to return all layouts referring to the device ID before
   the server can delete the device ID.  If the client does not return
   the affected layouts, the server MAY revoke the layouts.

20.4.  Operation 6: CB_NOTIFY - Notify Client of Directory Changes

20.4.1.  ARGUMENT

   /*
    * Directory notification types.
    */
   enum notify_type4 {
           NOTIFY4_CHANGE_CHILD_ATTRS = 0,
           NOTIFY4_CHANGE_DIR_ATTRS = 1,
           NOTIFY4_REMOVE_ENTRY = 2,
           NOTIFY4_ADD_ENTRY = 3,
           NOTIFY4_RENAME_ENTRY = 4,
           NOTIFY4_CHANGE_COOKIE_VERIFIER = 5
   };

   /* Changed entry information.  */
   struct notify_entry4 {



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           component4      ne_file;
           fattr4          ne_attrs;
   };

   /* Previous entry information */
   struct prev_entry4 {
           notify_entry4   pe_prev_entry;
           /* what READDIR returned for this entry */
           nfs_cookie4     pe_prev_entry_cookie;
   };

   struct notify_remove4 {
           notify_entry4   nrm_old_entry;
           nfs_cookie4     nrm_old_entry_cookie;
   };

   struct notify_add4 {
           /*
            * Information on object
            * possibly renamed over.
            */
           notify_remove4      nad_old_entry<1>;
           notify_entry4       nad_new_entry;
           /* what READDIR would have returned for this entry */
           nfs_cookie4         nad_new_entry_cookie<1>;
           prev_entry4         nad_prev_entry<1>;
           bool                nad_last_entry;
   };

   struct notify_attr4 {
           notify_entry4   na_changed_entry;
   };

   struct notify_rename4 {
           notify_remove4  nrn_old_entry;
           notify_add4     nrn_new_entry;
   };

   struct notify_verifier4 {
           verifier4       nv_old_cookieverf;
           verifier4       nv_new_cookieverf;
   };

   /*
    * Objects of type notify_<>4 and
    * notify_device_<>4 are encoded in this.
    */
   typedef opaque notifylist4<>;



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   struct notify4 {
           /* composed from notify_type4 or notify_deviceid_type4 */
           bitmap4         notify_mask;
           notifylist4     notify_vals;
   };

   struct CB_NOTIFY4args {
           stateid4    cna_stateid;
           nfs_fh4     cna_fh;
           notify4     cna_changes<>;
   };


20.4.2.  RESULT

   struct CB_NOTIFY4res {
           nfsstat4    cnr_status;
   };


20.4.3.  DESCRIPTION

   The CB_NOTIFY operation is used by the server to send notifications
   to clients about changes to delegated directories.  The registration
   of notifications for the directories occurs when the delegation is
   established using GET_DIR_DELEGATION.  These notifications are sent
   over the backchannel.  The notification is sent once the original
   request has been processed on the server.  The server will send an
   array of notifications for changes that might have occurred in the
   directory.  The notifications are sent as list of pairs of bitmaps
   and values.  See Section 3.3.7 for a description of how NFSv4.1
   bitmaps work.

   If the server has more notifications than can fit in the CB_COMPOUND
   request, it SHOULD send a sequence of serial CB_COMPOUND requests so
   that the client's view of the directory does not become confused.
   For example, if the server indicates that a file named "foo" is added
   and that the file "foo" is removed, the order in which the client
   receives these notifications needs to be the same as the order in
   which the corresponding operations occurred on the server.

   If the client holding the delegation makes any changes in the
   directory that cause files or sub-directories to be added or removed,
   the server will notify that client of the resulting change(s).  If
   the client holding the delegation is making attribute or cookie
   verifier changes only, the server does not need to send notifications
   to that client.  The server will send the following information for
   each operation:



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   NOTIFY4_ADD_ENTRY
      The server will send information about the new directory entry
      being created along with the cookie for that entry.  The entry
      information (data type notify_add4) includes the component name of
      the entry and attributes.  The server will send this type of entry
      when a file is actually being created, when an entry is being
      added to a directory as a result of a rename across directories
      (see below), and when a hard link is being created to an existing
      file.  If this entry is added to the end of the directory, the
      server will set the nad_last_entry flag to TRUE.  If the file is
      added such that there is at least one entry before it, the server
      will also return the previous entry information (nad_prev_entry, a
      variable-length array of up to one element.  If the array is of
      zero length, there is no previous entry), along with its cookie.
      This is to help clients find the right location in their file name
      caches and directory caches where this entry should be cached.  If
      the new entry's cookie is available, it will be in the
      nad_new_entry_cookie (another variable-length array of up to one
      element) field.  If the addition of the entry causes another entry
      to be deleted (which can only happen in the rename case)
      atomically with the addition, then information on this entry is
      reported in nad_old_entry.

   NOTIFY4_REMOVE_ENTRY
      The server will send information about the directory entry being
      deleted.  The server will also send the cookie value for the
      deleted entry so that clients can get to the cached information
      for this entry.

   NOTIFY4_RENAME_ENTRY
      The server will send information about both the old entry and the
      new entry.  This includes the name and attributes for each entry.
      In addition, if the rename causes the deletion of an entry (i.e.,
      the case of a file renamed over), then this is reported in
      nrn_new_new_entry.nad_old_entry.  This notification is only sent
      if both entries are in the same directory.  If the rename is
      across directories, the server will send a remove notification to
      one directory and an add notification to the other directory,
      assuming both have a directory delegation.

   NOTIFY4_CHANGE_CHILD_ATTRS/NOTIFY4_CHANGE_DIR_ATTRS
      The client will use the attribute mask to inform the server of
      attributes for which it wants to receive notifications.  This
      change notification can be requested for changes to the attributes
      of the directory as well as changes to any file's attributes in
      the directory by using two separate attribute masks.  The client
      cannot ask for change attribute notification for a specific file.
      One attribute mask covers all the files in the directory.  Upon



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      any attribute change, the server will send back the values of
      changed attributes.  Notifications might not make sense for some
      file system-wide attributes, and it is up to the server to decide
      which subset it wants to support.  The client can negotiate the
      frequency of attribute notifications by letting the server know
      how often it wants to be notified of an attribute change.  The
      server will return supported notification frequencies or an
      indication that no notification is permitted for directory or
      child attributes by setting the dir_notif_delay and
      dir_entry_notif_delay attributes, respectively.

   NOTIFY4_CHANGE_COOKIE_VERIFIER
      If the cookie verifier changes while a client is holding a
      delegation, the server will notify the client so that it can
      invalidate its cookies and re-send a READDIR to get the new set of
      cookies.

20.5.  Operation 7: CB_PUSH_DELEG - Offer Previously Requested
       Delegation to Client

20.5.1.  ARGUMENT

   struct CB_PUSH_DELEG4args {
           nfs_fh4          cpda_fh;
           open_delegation4 cpda_delegation;

   };


20.5.2.  RESULT

   struct CB_PUSH_DELEG4res {
           nfsstat4 cpdr_status;
   };


20.5.3.  DESCRIPTION

   CB_PUSH_DELEG is used by the server both to signal to the client that
   the delegation it wants (previously indicated via a want established
   from an OPEN or WANT_DELEGATION operation) is available and to
   simultaneously offer the delegation to the client.  The client has
   the choice of accepting the delegation by returning NFS4_OK to the
   server, delaying the decision to accept the offered delegation by
   returning NFS4ERR_DELAY, or permanently rejecting the offer of the
   delegation by returning NFS4ERR_REJECT_DELEG.  When a delegation is
   rejected in this fashion, the want previously established is




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   permanently deleted and the delegation is subject to acquisition by
   another client.

20.5.4.  IMPLEMENTATION

   If the client does return NFS4ERR_DELAY and there is a conflicting
   delegation request, the server MAY process it at the expense of the
   client that returned NFS4ERR_DELAY.  The client's want will not be
   cancelled, but MAY be processed behind other delegation requests or
   registered wants.

   When a client returns a status other than NFS4_OK, NFS4ERR_DELAY, or
   NFS4ERR_REJECT_DELAY, the want remains pending, although servers may
   decide to cancel the want by sending a CB_WANTS_CANCELLED.

20.6.  Operation 8: CB_RECALL_ANY - Keep Any N Recallable Objects

20.6.1.  ARGUMENT

   const RCA4_TYPE_MASK_RDATA_DLG          = 0;
   const RCA4_TYPE_MASK_WDATA_DLG          = 1;
   const RCA4_TYPE_MASK_DIR_DLG            = 2;
   const RCA4_TYPE_MASK_FILE_LAYOUT        = 3;
   const RCA4_TYPE_MASK_BLK_LAYOUT         = 4;
   const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN     = 8;
   const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX     = 9;
   const RCA4_TYPE_MASK_OTHER_LAYOUT_MIN   = 12;
   const RCA4_TYPE_MASK_OTHER_LAYOUT_MAX   = 15;

   struct  CB_RECALL_ANY4args      {
           uint32_t        craa_objects_to_keep;
           bitmap4         craa_type_mask;
   };


20.6.2.  RESULT

   struct CB_RECALL_ANY4res {
           nfsstat4        crar_status;
   };


20.6.3.  DESCRIPTION

   The server may decide that it cannot hold all of the state for
   recallable objects, such as delegations and layouts, without running
   out of resources.  In such a case, while not optimal, the server is
   free to recall individual objects to reduce the load.



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   Because the general purpose of such recallable objects as delegations
   is to eliminate client interaction with the server, the server cannot
   interpret lack of recent use as indicating that the object is no
   longer useful.  The absence of visible use is consistent with a
   delegation keeping potential operations from being sent to the
   server.  In the case of layouts, while it is true that the usefulness
   of a layout is indicated by the use of the layout when storage
   devices receive I/O requests, because there is no mandate that a
   storage device indicate to the metadata server any past or present
   use of a layout, the metadata server is not likely to know which
   layouts are good candidates to recall in response to low resources.

   In order to implement an effective reclaim scheme for such objects,
   the server's knowledge of available resources must be used to
   determine when objects must be recalled with the clients selecting
   the actual objects to be returned.

   Server implementations may differ in their resource allocation
   requirements.  For example, one server may share resources among all
   classes of recallable objects, whereas another may use separate
   resource pools for layouts and for delegations, or further separate
   resources by types of delegations.

   When a given resource pool is over-utilized, the server can send a
   CB_RECALL_ANY to clients holding recallable objects of the types
   involved, allowing it to keep a certain number of such objects and
   return any excess.  A mask specifies which types of objects are to be
   limited.  The client chooses, based on its own knowledge of current
   usefulness, which of the objects in that class should be returned.

   A number of bits are defined.  For some of these, ranges are defined
   and it is up to the definition of the storage protocol to specify how
   these are to be used.  There are ranges reserved for object-based
   storage protocols and for other experimental storage protocols.  An
   RFC defining such a storage protocol needs to specify how particular
   bits within its range are to be used.  For example, it may specify a
   mapping between attributes of the layout (read vs. write, size of
   area) and the bit to be used, or it may define a field in the layout
   where the associated bit position is made available by the server to
   the client.

   RCA4_TYPE_MASK_RDATA_DLG

      The client is to return OPEN_DELEGATE_READ delegations on non-
      directory file objects.

   RCA4_TYPE_MASK_WDATA_DLG




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      The client is to return OPEN_DELEGATE_WRITE delegations on regular
      file objects.

   RCA4_TYPE_MASK_DIR_DLG

      The client is to return directory delegations.

   RCA4_TYPE_MASK_FILE_LAYOUT

      The client is to return layouts of type LAYOUT4_NFSV4_1_FILES.

   RCA4_TYPE_MASK_BLK_LAYOUT

      See [41] for a description.

   RCA4_TYPE_MASK_OBJ_LAYOUT_MIN to RCA4_TYPE_MASK_OBJ_LAYOUT_MAX

      See [40] for a description.

   RCA4_TYPE_MASK_OTHER_LAYOUT_MIN to RCA4_TYPE_MASK_OTHER_LAYOUT_MAX

      This range is reserved for telling the client to recall layouts of
      experimental or site-specific layout types (see Section 3.3.13).

   When a bit is set in the type mask that corresponds to an undefined
   type of recallable object, NFS4ERR_INVAL MUST be returned.  When a
   bit is set that corresponds to a defined type of object but the
   client does not support an object of the type, NFS4ERR_INVAL MUST NOT
   be returned.  Future minor versions of NFSv4 may expand the set of
   valid type mask bits.

   CB_RECALL_ANY specifies a count of objects that the client may keep
   as opposed to a count that the client must return.  This is to avoid
   a potential race between a CB_RECALL_ANY that had a count of objects
   to free with a set of client-originated operations to return layouts
   or delegations.  As a result of the race, the client and server would
   have differing ideas as to how many objects to return.  Hence, the
   client could mistakenly free too many.

   If resource demands prompt it, the server may send another
   CB_RECALL_ANY with a lower count, even if it has not yet received an
   acknowledgment from the client for a previous CB_RECALL_ANY with the
   same type mask.  Although the possibility exists that these will be
   received by the client in an order different from the order in which
   they were sent, any such permutation of the callback stream is
   harmless.  It is the job of the client to bring down the size of the
   recallable object set in line with each CB_RECALL_ANY received, and
   until that obligation is met, it cannot be cancelled or modified by



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   any subsequent CB_RECALL_ANY for the same type mask.  Thus, if the
   server sends two CB_RECALL_ANYs, the effect will be the same as if
   the lower count was sent, whatever the order of recall receipt.  Note
   that this means that a server may not cancel the effect of a
   CB_RECALL_ANY by sending another recall with a higher count.  When a
   CB_RECALL_ANY is received and the count is already within the limit
   set or is above a limit that the client is working to get down to,
   that callback has no effect.

   Servers are generally free to deny recallable objects when
   insufficient resources are available.  Note that the effect of such a
   policy is implicitly to give precedence to existing objects relative
   to requested ones, with the result that resources might not be
   optimally used.  To prevent this, servers are well advised to make
   the point at which they start sending CB_RECALL_ANY callbacks
   somewhat below that at which they cease to give out new delegations
   and layouts.  This allows the client to purge its less-used objects
   whenever appropriate and so continue to have its subsequent requests
   given new resources freed up by object returns.

20.6.4.  IMPLEMENTATION

   The client can choose to return any type of object specified by the
   mask.  If a server wishes to limit the use of objects of a specific
   type, it should only specify that type in the mask it sends.  Should
   the client fail to return requested objects, it is up to the server
   to handle this situation, typically by sending specific recalls
   (i.e., sending CB_RECALL operations) to properly limit resource
   usage.  The server should give the client enough time to return
   objects before proceeding to specific recalls.  This time should not
   be less than the lease period.

20.7.  Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for
       Recallable Objects

20.7.1.  ARGUMENT

   typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;


20.7.2.  RESULT

   struct CB_RECALLABLE_OBJ_AVAIL4res {
           nfsstat4        croa_status;
   };






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20.7.3.  DESCRIPTION

   CB_RECALLABLE_OBJ_AVAIL is used by the server to signal the client
   that the server has resources to grant recallable objects that might
   previously have been denied by OPEN, WANT_DELEGATION, GET_DIR_DELEG,
   or LAYOUTGET.

   The argument craa_objects_to_keep means the total number of
   recallable objects of the types indicated in the argument type_mask
   that the server believes it can allow the client to have, including
   the number of such objects the client already has.  A client that
   tries to acquire more recallable objects than the server informs it
   can have runs the risk of having objects recalled.

   The server is not obligated to reserve the difference between the
   number of the objects the client currently has and the value of
   craa_objects_to_keep, nor does delaying the reply to
   CB_RECALLABLE_OBJ_AVAIL prevent the server from using the resources
   of the recallable objects for another purpose.  Indeed, if a client
   responds slowly to CB_RECALLABLE_OBJ_AVAIL, the server might
   interpret the client as having reduced capability to manage
   recallable objects, and so cancel or reduce any reservation it is
   maintaining on behalf of the client.  Thus, if the client desires to
   acquire more recallable objects, it needs to reply quickly to
   CB_RECALLABLE_OBJ_AVAIL, and then send the appropriate operations to
   acquire recallable objects.

20.8.  Operation 10: CB_RECALL_SLOT - Change Flow Control Limits

20.8.1.  ARGUMENT

   struct CB_RECALL_SLOT4args {
           slotid4       rsa_target_highest_slotid;
   };


20.8.2.  RESULT

   struct CB_RECALL_SLOT4res {
           nfsstat4   rsr_status;
   };


20.8.3.  DESCRIPTION

   The CB_RECALL_SLOT operation requests the client to return session
   slots, and if applicable, transport credits (e.g., RDMA credits for
   connections associated with the operations channel) of the session's



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   fore channel.  CB_RECALL_SLOT specifies rsa_target_highest_slotid,
   the value of the target highest slot ID the server wants for the
   session.  The client MUST then progress toward reducing the session's
   highest slot ID to the target value.

   If the session has only non-RDMA connections associated with its
   operations channel, then the client need only wait for all
   outstanding requests with a slot ID > rsa_target_highest_slotid to
   complete, then send a single COMPOUND consisting of a single SEQUENCE
   operation, with the sa_highestslot field set to
   rsa_target_highest_slotid.  If there are RDMA-based connections
   associated with operation channel, then the client needs to also send
   enough zero-length "RDMA Send" messages to take the total RDMA credit
   count to rsa_target_highest_slotid + 1 or below.

20.8.4.  IMPLEMENTATION

   If the client fails to reduce highest slot it has on the fore channel
   to what the server requests, the server can force the issue by
   asserting flow control on the receive side of all connections bound
   to the fore channel, and then finish servicing all outstanding
   requests that are in slots greater than rsa_target_highest_slotid.
   Once that is done, the server can then open the flow control, and any
   time the client sends a new request on a slot greater than
   rsa_target_highest_slotid, the server can return NFS4ERR_BADSLOT.

20.9.  Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing and
       Control

20.9.1.  ARGUMENT





















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   struct referring_call4 {
           sequenceid4     rc_sequenceid;
           slotid4         rc_slotid;
   };

   struct referring_call_list4 {
           sessionid4      rcl_sessionid;
           referring_call4 rcl_referring_calls<>;
   };

   struct CB_SEQUENCE4args {
           sessionid4           csa_sessionid;
           sequenceid4          csa_sequenceid;
           slotid4              csa_slotid;
           slotid4              csa_highest_slotid;
           bool                 csa_cachethis;
           referring_call_list4 csa_referring_call_lists<>;
   };


20.9.2.  RESULT

   struct CB_SEQUENCE4resok {
           sessionid4         csr_sessionid;
           sequenceid4        csr_sequenceid;
           slotid4            csr_slotid;
           slotid4            csr_highest_slotid;
           slotid4            csr_target_highest_slotid;
   };

   union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
   case NFS4_OK:
           CB_SEQUENCE4resok   csr_resok4;
   default:
           void;
   };


20.9.3.  DESCRIPTION

   The CB_SEQUENCE operation is used to manage operational accounting
   for the backchannel of the session on which a request is sent.  The
   contents include the session ID to which this request belongs, the
   slot ID and sequence ID used by the server to implement session
   request control and exactly once semantics, and exchanged slot ID
   maxima that are used to adjust the size of the reply cache.  In each
   CB_COMPOUND request, CB_SEQUENCE MUST appear once and MUST be the
   first operation.  The error NFS4ERR_SEQUENCE_POS MUST be returned



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   when CB_SEQUENCE is found in any position in a CB_COMPOUND beyond the
   first.  If any other operation is in the first position of
   CB_COMPOUND, NFS4ERR_OP_NOT_IN_SESSION MUST be returned.

   See Section 18.46.3 for a description of how slots are processed.

   If csa_cachethis is TRUE, then the server is requesting that the
   client cache the reply in the callback reply cache.  The client MUST
   cache the reply (see Section 2.10.6.1.3).

   The csa_referring_call_lists array is the list of COMPOUND requests,
   identified by session ID, slot ID, and sequence ID.  These are
   requests that the client previously sent to the server.  These
   previous requests created state that some operation(s) in the same
   CB_COMPOUND as the csa_referring_call_lists are identifying.  A
   session ID is included because leased state is tied to a client ID,
   and a client ID can have multiple sessions.  See Section 2.10.6.3.

   The value of the csa_sequenceid argument relative to the cached
   sequence ID on the slot falls into one of three cases.

   o  If the difference between csa_sequenceid and the client's cached
      sequence ID at the slot ID is two (2) or more, or if
      csa_sequenceid is less than the cached sequence ID (accounting for
      wraparound of the unsigned sequence ID value), then the client
      MUST return NFS4ERR_SEQ_MISORDERED.

   o  If csa_sequenceid and the cached sequence ID are the same, this is
      a retry, and the client returns the CB_COMPOUND request's cached
      reply.

   o  If csa_sequenceid is one greater (accounting for wraparound) than
      the cached sequence ID, then this is a new request, and the slot's
      sequence ID is incremented.  The operations subsequent to
      CB_SEQUENCE, if any, are processed.  If there are no other
      operations, the only other effects are to cache the CB_SEQUENCE
      reply in the slot, maintain the session's activity, and when the
      server receives the CB_SEQUENCE reply, renew the lease of state
      related to the client ID.

   If the server reuses a slot ID and sequence ID for a completely
   different request, the client MAY treat the request as if it is a
   retry of what it has already executed.  The client MAY however detect
   the server's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.

   If CB_SEQUENCE returns an error, then the state of the slot (sequence
   ID, cached reply) MUST NOT change.  See Section 2.10.6.1.3 for the




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   conditions when the error NFS4ERR_RETRY_UNCACHED_REP might be
   returned.

   The client returns two "highest_slotid" values: csr_highest_slotid
   and csr_target_highest_slotid.  The former is the highest slot ID the
   client will accept in a future CB_SEQUENCE operation, and SHOULD NOT
   be less than the value of csa_highest_slotid (but see
   Section 2.10.6.1 for an exception).  The latter is the highest slot
   ID the client would prefer the server use on a future CB_SEQUENCE
   operation.

20.10.  Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation
        Wants

20.10.1.  ARGUMENT

   struct CB_WANTS_CANCELLED4args {
           bool cwca_contended_wants_cancelled;
           bool cwca_resourced_wants_cancelled;
   };


20.10.2.  RESULT

   struct CB_WANTS_CANCELLED4res {
           nfsstat4        cwcr_status;
   };


20.10.3.  DESCRIPTION

   The CB_WANTS_CANCELLED operation is used to notify the client that
   some or all of the wants it registered for recallable delegations and
   layouts have been cancelled.

   If cwca_contended_wants_cancelled is TRUE, this indicates that the
   server will not be pushing to the client any delegations that become
   available after contention passes.

   If cwca_resourced_wants_cancelled is TRUE, this indicates that the
   server will not notify the client when there are resources on the
   server to grant delegations or layouts.

   After receiving a CB_WANTS_CANCELLED operation, the client is free to
   attempt to acquire the delegations or layouts it was waiting for, and
   possibly re-register wants.





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20.10.4.  IMPLEMENTATION

   When a client has an OPEN, WANT_DELEGATION, or GET_DIR_DELEGATION
   request outstanding, when a CB_WANTS_CANCELLED is sent, the server
   may need to make clear to the client whether a promise to signal
   delegation availability happened before the CB_WANTS_CANCELLED and is
   thus covered by it, or after the CB_WANTS_CANCELLED in which case it
   was not covered by it.  The server can make this distinction by
   putting the appropriate requests into the list of referring calls in
   the associated CB_SEQUENCE.

20.11.  Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible Lock
        Availability

20.11.1.  ARGUMENT

   struct CB_NOTIFY_LOCK4args {
       nfs_fh4     cnla_fh;
       lock_owner4 cnla_lock_owner;
   };


20.11.2.  RESULT

   struct CB_NOTIFY_LOCK4res {
           nfsstat4        cnlr_status;
   };


20.11.3.  DESCRIPTION

   The server can use this operation to indicate that a byte-range lock
   for the given file and lock-owner, previously requested by the client
   via an unsuccessful LOCK operation, might be available.

   This callback is meant to be used by servers to help reduce the
   latency of blocking locks in the case where they recognize that a
   client that has been polling for a blocking byte-range lock may now
   be able to acquire the lock.  If the server supports this callback
   for a given file, it MUST set the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
   when responding to successful opens for that file.  This does not
   commit the server to the use of CB_NOTIFY_LOCK, but the client may
   use this as a hint to decide how frequently to poll for locks derived
   from that open.

   If an OPEN operation results in an upgrade, in which the stateid
   returned has an "other" value matching that of a stateid already
   allocated, with a new "seqid" indicating a change in the lock being



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   represented, then the value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag
   when responding to that new OPEN controls handling from that point
   going forward.  When parallel OPENs are done on the same file and
   open-owner, the ordering of the "seqid" fields of the returned
   stateids (subject to wraparound) are to be used to select the
   controlling value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.

20.11.4.  IMPLEMENTATION

   The server MUST NOT grant the byte-range lock to the client unless
   and until it receives a LOCK operation from the client.  Similarly,
   the client receiving this callback cannot assume that it now has the
   lock or that a subsequent LOCK operation for the lock will be
   successful.

   The server is not required to implement this callback, and even if it
   does, it is not required to use it in any particular case.
   Therefore, the client must still rely on polling for blocking locks,
   as described in Section 9.6.

   Similarly, the client is not required to implement this callback, and
   even it does, is still free to ignore it.  Therefore, the server MUST
   NOT assume that the client will act based on the callback.

20.12.  Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device ID
        Changes

20.12.1.  ARGUMENT























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   /*
    * Device notification types.
    */
   enum notify_deviceid_type4 {
           NOTIFY_DEVICEID4_CHANGE = 1,
           NOTIFY_DEVICEID4_DELETE = 2
   };

   /* For NOTIFY4_DEVICEID4_DELETE */
   struct notify_deviceid_delete4 {
           layouttype4     ndd_layouttype;
           deviceid4       ndd_deviceid;
   };

   /* For NOTIFY4_DEVICEID4_CHANGE */
   struct notify_deviceid_change4 {
           layouttype4     ndc_layouttype;
           deviceid4       ndc_deviceid;
           bool            ndc_immediate;
   };

   struct CB_NOTIFY_DEVICEID4args {
           notify4 cnda_changes<>;
   };


20.12.2.  RESULT

   struct CB_NOTIFY_DEVICEID4res {
           nfsstat4        cndr_status;
   };


20.12.3.  DESCRIPTION

   The CB_NOTIFY_DEVICEID operation is used by the server to send
   notifications to clients about changes to pNFS device IDs.  The
   registration of device ID notifications is optional and is done via
   GETDEVICEINFO.  These notifications are sent over the backchannel
   once the original request has been processed on the server.  The
   server will send an array of notifications, cnda_changes, as a list
   of pairs of bitmaps and values.  See Section 3.3.7 for a description
   of how NFSv4.1 bitmaps work.

   As with CB_NOTIFY (Section 20.4.3), it is possible the server has
   more notifications than can fit in a CB_COMPOUND, thus requiring
   multiple CB_COMPOUNDs.  Unlike CB_NOTIFY, serialization is not an




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   issue because unlike directory entries, device IDs cannot be re-used
   after being deleted (Section 12.2.10).

   All device ID notifications contain a device ID and a layout type.
   The layout type is necessary because two different layout types can
   share the same device ID, and the common device ID can have
   completely different mappings for each layout type.

   The server will send the following notifications:

   NOTIFY_DEVICEID4_CHANGE
      A previously provided device-ID-to-device-address mapping has
      changed and the client uses GETDEVICEINFO to obtain the updated
      mapping.  The notification is encoded in a value of data type
      notify_deviceid_change4.  This data type also contains a boolean
      field, ndc_immediate, which if TRUE indicates that the change will
      be enforced immediately, and so the client might not be able to
      complete any pending I/O to the device ID.  If ndc_immediate is
      FALSE, then for an indefinite time, the client can complete
      pending I/O.  After pending I/O is complete, the client SHOULD get
      the new device-ID-to-device-address mappings before sending new I/
      O requests to the storage devices addressed by the device ID.

   NOTIFY4_DEVICEID_DELETE
      Deletes a device ID from the mappings.  This notification MUST NOT
      be sent if the client has a layout that refers to the device ID.
      In other words, if the server is sending a delete device ID
      notification, one of the following is true for layouts associated
      with the layout type:

      *  The client never had a layout referring to that device ID.

      *  The client has returned all layouts referring to that device
         ID.

      *  The server has revoked all layouts referring to that device ID.

      The notification is encoded in a value of data type
      notify_deviceid_delete4.  After a server deletes a device ID, it
      MUST NOT reuse that device ID for the same layout type until the
      client ID is deleted.

20.13.  Operation 10044: CB_ILLEGAL - Illegal Callback Operation








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20.13.1.  ARGUMENT

           void;

20.13.2.  RESULT

   /*
    * CB_ILLEGAL: Response for illegal operation numbers
    */
   struct CB_ILLEGAL4res {
           nfsstat4        status;
   };


20.13.3.  DESCRIPTION

   This operation is a placeholder for encoding a result to handle the
   case of the server sending an operation code within CB_COMPOUND that
   is not defined in the NFSv4.1 specification.  See Section 19.2.3 for
   more details.

   The status field of CB_ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.

20.13.4.  IMPLEMENTATION

   A server will probably not send an operation with code OP_CB_ILLEGAL,
   but if it does, the response will be CB_ILLEGAL4res just as it would
   be with any other invalid operation code.  Note that if the client
   gets an illegal operation code that is not OP_ILLEGAL, and if the
   client checks for legal operation codes during the XDR decode phase,
   then an instance of data type CB_ILLEGAL4res will not be returned.

21.  Security Considerations

   Historically, the authentication model of NFS was based on the entire
   machine being the NFS client, with the NFS server trusting the NFS
   client to authenticate the end-user.  The NFS server in turn shared
   its files only to specific clients, as identified by the client's
   source network address.  Given this model, the AUTH_SYS RPC security
   flavor simply identified the end-user using the client to the NFS
   server.  When processing NFS responses, the client ensured that the
   responses came from the same network address and port number to which
   the request was sent.  While such a model is easy to implement and
   simple to deploy and use, it is unsafe.  Thus, NFSv4.1
   implementations are REQUIRED to support a security model that uses
   end-to-end authentication, where an end-user on a client mutually
   authenticates (via cryptographic schemes that do not expose passwords
   or keys in the clear on the network) to a principal on an NFS server.



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   Consideration is also given to the integrity and privacy of NFS
   requests and responses.  The issues of end-to-end mutual
   authentication, integrity, and privacy are discussed in
   Section 2.2.1.1.1.  There are specific considerations when using
   Kerberos V5 as described in Section 2.2.1.1.1.2.1.1.

   Note that being REQUIRED to implement does not mean REQUIRED to use;
   AUTH_SYS can be used by NFSv4.1 clients and servers.  However,
   AUTH_SYS is merely an OPTIONAL security flavor in NFSv4.1, and so
   interoperability via AUTH_SYS is not assured.

   For reasons of reduced administration overhead, better performance,
   and/or reduction of CPU utilization, users of NFSv4.1 implementations
   might decline to use security mechanisms that enable integrity
   protection on each remote procedure call and response.  The use of
   mechanisms without integrity leaves the user vulnerable to a man-in-
   the-middle of the NFS client and server that modifies the RPC request
   and/or the response.  While implementations are free to provide the
   option to use weaker security mechanisms, there are three operations
   in particular that warrant the implementation overriding user
   choices.

   o  The first two such operations are SECINFO and SECINFO_NO_NAME.  It
      is RECOMMENDED that the client send both operations such that they
      are protected with a security flavor that has integrity
      protection, such as RPCSEC_GSS with either the
      rpc_gss_svc_integrity or rpc_gss_svc_privacy service.  Without
      integrity protection encapsulating SECINFO and SECINFO_NO_NAME and
      their results, a man-in-the-middle could modify results such that
      the client might select a weaker algorithm in the set allowed by
      the server, making the client and/or server vulnerable to further
      attacks.

   o  The third operation that SHOULD use integrity protection is any
      GETATTR for the fs_locations and fs_locations_info attributes, in
      order to mitigate the severity of a man-in-the-middle attack.  The
      attack has two steps.  First the attacker modifies the unprotected
      results of some operation to return NFS4ERR_MOVED.  Second, when
      the client follows up with a GETATTR for the fs_locations or
      fs_locations_info attributes, the attacker modifies the results to
      cause the client to migrate its traffic to a server controlled by
      the attacker.  With integrity protection, this attack is
      mitigated.

   Relative to previous NFS versions, NFSv4.1 has additional security
   considerations for pNFS (see Sections 12.9 and 13.12), locking and
   session state (see Section 2.10.8.3), and state recovery during grace
   period (see Section 8.4.2.1.1).  With respect to locking and session



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   state, if SP4_SSV state protection is being used, Section 2.10.10 has
   specific security considerations for the NFSv4.1 client and server.

22.  IANA Considerations

   This section uses terms that are defined in [55].

22.1.  Named Attribute Definitions

   IANA created a registry called the "NFSv4 Named Attribute Definitions
   Registry".

   The NFSv4.1 protocol supports the association of a file with zero or
   more named attributes.  The namespace identifiers for these
   attributes are defined as string names.  The protocol does not define
   the specific assignment of the namespace for these file attributes.
   The IANA registry promotes interoperability where common interests
   exist.  While application developers are allowed to define and use
   attributes as needed, they are encouraged to register the attributes
   with IANA.

   Such registered named attributes are presumed to apply to all minor
   versions of NFSv4, including those defined subsequently to the
   registration.  If the named attribute is intended to be limited to
   specific minor versions, this will be clearly stated in the
   registry's assignment.

   All assignments to the registry are made on a First Come First Served
   basis, per Section 4.1 of [55].  The policy for each assignment is
   Specification Required, per Section 4.1 of [55].

   Under the NFSv4.1 specification, the name of a named attribute can in
   theory be up to 2^32 - 1 bytes in length, but in practice NFSv4.1
   clients and servers will be unable to handle a string that long.
   IANA should reject any assignment request with a named attribute that
   exceeds 128 UTF-8 characters.  To give the IESG the flexibility to
   set up bases of assignment of Experimental Use and Standards Action,
   the prefixes of "EXPE" and "STDS" are Reserved.  The named attribute
   with a zero-length name is Reserved.

   The prefix "PRIV" is designated for Private Use.  A site that wants
   to make use of unregistered named attributes without risk of
   conflicting with an assignment in IANA's registry should use the
   prefix "PRIV" in all of its named attributes.

   Because some NFSv4.1 clients and servers have case-insensitive
   semantics, the fifteen additional lower case and mixed case
   permutations of each of "EXPE", "PRIV", and "STDS" are Reserved



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   (e.g., "expe", "expE", "exPe", etc. are Reserved).  Similarly, IANA
   must not allow two assignments that would conflict if both named
   attributes were converted to a common case.

   The registry of named attributes is a list of assignments, each
   containing three fields for each assignment.

   1.  A US-ASCII string name that is the actual name of the attribute.
       This name must be unique.  This string name can be 1 to 128 UTF-8
       characters long.

   2.  A reference to the specification of the named attribute.  The
       reference can consume up to 256 bytes (or more if IANA permits).

   3.  The point of contact of the registrant.  The point of contact can
       consume up to 256 bytes (or more if IANA permits).

22.1.1.  Initial Registry

   There is no initial registry.

22.1.2.  Updating Registrations

   The registrant is always permitted to update the point of contact
   field.  Any other change will require Expert Review or IESG Approval.

22.2.  Device ID Notifications

   IANA created a registry called the "NFSv4 Device ID Notifications
   Registry".

   The potential exists for new notification types to be added to the
   CB_NOTIFY_DEVICEID operation (see Section 20.12).  This can be done
   via changes to the operations that register notifications, or by
   adding new operations to NFSv4.  This requires a new minor version of
   NFSv4, and requires a Standards Track document from the IETF.
   Another way to add a notification is to specify a new layout type
   (see Section 22.4).

   Hence, all assignments to the registry are made on a Standards Action
   basis per Section 4.1 of [55], with Expert Review required.

   The registry is a list of assignments, each containing five fields
   per assignment.

   1.  The name of the notification type.  This name must have the
       prefix "NOTIFY_DEVICEID4_".  This name must be unique.




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   2.  The value of the notification.  IANA will assign this number, and
       the request from the registrant will use TBD1 instead of an
       actual value.  IANA MUST use a whole number that can be no higher
       than 2^32-1, and should be the next available value.  The value
       assigned must be unique.  A Designated Expert must be used to
       ensure that when the name of the notification type and its value
       are added to the NFSv4.1 notify_deviceid_type4 enumerated data
       type in the NFSv4.1 XDR description ([13]), the result continues
       to be a valid XDR description.

   3.  The Standards Track RFC(s) that describe the notification.  If
       the RFC(s) have not yet been published, the registrant will use
       RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.

   4.  How the RFC introduces the notification.  This is indicated by a
       single US-ASCII value.  If the value is N, it means a minor
       revision to the NFSv4 protocol.  If the value is L, it means a
       new pNFS layout type.  Other values can be used with IESG
       Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       notification.  While these are numeric values, IANA will not
       allocate and assign them; the author of the relevant RFCs with
       IESG Approval assigns these numbers.  Each time there is a new
       minor version of NFSv4 approved, a Designated Expert should
       review the registry to make recommended updates as needed.

22.2.1.  Initial Registry

   The initial registry is in Table 16.  Note that the next available
   value is zero.

   +-------------------------+-------+---------+-----+----------------+
   | Notification Name       | Value | RFC     | How | Minor Versions |
   +-------------------------+-------+---------+-----+----------------+
   | NOTIFY_DEVICEID4_CHANGE | 1     | RFC5661 | N   | 1              |
   | NOTIFY_DEVICEID4_DELETE | 2     | RFC5661 | N   | 1              |
   +-------------------------+-------+---------+-----+----------------+

           Table 16: Initial Device ID Notification Assignments

22.2.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.






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22.3.  Object Recall Types

   IANA created a registry called the "NFSv4 Recallable Object Types
   Registry".

   The potential exists for new object types to be added to the
   CB_RECALL_ANY operation (see Section 20.6).  This can be done via
   changes to the operations that add recallable types, or by adding new
   operations to NFSv4.  This requires a new minor version of NFSv4, and
   requires a Standards Track document from IETF.  Another way to add a
   new recallable object is to specify a new layout type (see
   Section 22.4).

   All assignments to the registry are made on a Standards Action basis
   per Section 4.1 of [55], with Expert Review required.

   Recallable object types are 32-bit unsigned numbers.  There are no
   Reserved values.  Values in the range 12 through 15, inclusive, are
   designated for Private Use.

   The registry is a list of assignments, each containing five fields
   per assignment.

   1.  The name of the recallable object type.  This name must have the
       prefix "RCA4_TYPE_MASK_".  The name must be unique.

   2.  The value of the recallable object type.  IANA will assign this
       number, and the request from the registrant will use TBD1 instead
       of an actual value.  IANA MUST use a whole number that can be no
       higher than 2^32-1, and should be the next available value.  The
       value must be unique.  A Designated Expert must be used to ensure
       that when the name of the recallable type and its value are added
       to the NFSv4 XDR description [13], the result continues to be a
       valid XDR description.

   3.  The Standards Track RFC(s) that describe the recallable object
       type.  If the RFC(s) have not yet been published, the registrant
       will use RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.

   4.  How the RFC introduces the recallable object type.  This is
       indicated by a single US-ASCII value.  If the value is N, it
       means a minor revision to the NFSv4 protocol.  If the value is L,
       it means a new pNFS layout type.  Other values can be used with
       IESG Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       recallable object type.  While these are numeric values, IANA
       will not allocate and assign them; the author of the relevant



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       RFCs with IESG Approval assigns these numbers.  Each time there
       is a new minor version of NFSv4 approved, a Designated Expert
       should review the registry to make recommended updates as needed.

22.3.1.  Initial Registry

   The initial registry is in Table 17.  Note that the next available
   value is five.

   +-------------------------------+-------+--------+-----+------------+
   | Recallable Object Type Name   | Value | RFC    | How | Minor      |
   |                               |       |        |     | Versions   |
   +-------------------------------+-------+--------+-----+------------+
   | RCA4_TYPE_MASK_RDATA_DLG      | 0     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_WDATA_DLG      | 1     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_DIR_DLG        | 2     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_FILE_LAYOUT    | 3     | RFC    | N   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_BLK_LAYOUT     | 4     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_OBJ_LAYOUT_MIN | 8     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   | RCA4_TYPE_MASK_OBJ_LAYOUT_MAX | 9     | RFC    | L   | 1          |
   |                               |       | 5661   |     |            |
   +-------------------------------+-------+--------+-----+------------+

           Table 17: Initial Recallable Object Type Assignments

22.3.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.

22.4.  Layout Types

   IANA created a registry called the "pNFS Layout Types Registry".

   All assignments to the registry are made on a Standards Action basis,
   with Expert Review required.

   Layout types are 32-bit numbers.  The value zero is Reserved.  Values
   in the range 0x80000000 to 0xFFFFFFFF inclusive are designated for
   Private Use.  IANA will assign numbers from the range 0x00000001 to
   0x7FFFFFFF inclusive.




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   The registry is a list of assignments, each containing five fields.

   1.  The name of the layout type.  This name must have the prefix
       "LAYOUT4_".  The name must be unique.

   2.  The value of the layout type.  IANA will assign this number, and
       the request from the registrant will use TBD1 instead of an
       actual value.  The value assigned must be unique.  A Designated
       Expert must be used to ensure that when the name of the layout
       type and its value are added to the NFSv4.1 layouttype4
       enumerated data type in the NFSv4.1 XDR description ([13]), the
       result continues to be a valid XDR description.

   3.  The Standards Track RFC(s) that describe the notification.  If
       the RFC(s) have not yet been published, the registrant will use
       RFCTBD2, RFCTBD3, etc. instead of an actual RFC number.
       Collectively, the RFC(s) must adhere to the guidelines listed in
       Section 22.4.3.

   4.  How the RFC introduces the layout type.  This is indicated by a
       single US-ASCII value.  If the value is N, it means a minor
       revision to the NFSv4 protocol.  If the value is L, it means a
       new pNFS layout type.  Other values can be used with IESG
       Approval.

   5.  The minor versions of NFSv4 that are allowed to use the
       notification.  While these are numeric values, IANA will not
       allocate and assign them; the author of the relevant RFCs with
       IESG Approval assigns these numbers.  Each time there is a new
       minor version of NFSv4 approved, a Designated Expert should
       review the registry to make recommended updates as needed.

22.4.1.  Initial Registry

   The initial registry is in Table 18.

    +-----------------------+-------+----------+-----+----------------+
    | Layout Type Name      | Value | RFC      | How | Minor Versions |
    +-----------------------+-------+----------+-----+----------------+
    | LAYOUT4_NFSV4_1_FILES | 0x1   | RFC 5661 | N   | 1              |
    | LAYOUT4_OSD2_OBJECTS  | 0x2   | RFC 5664 | L   | 1              |
    | LAYOUT4_BLOCK_VOLUME  | 0x3   | RFC 5663 | L   | 1              |
    +-----------------------+-------+----------+-----+----------------+

                 Table 18: Initial Layout Type Assignments






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22.4.2.  Updating Registrations

   The update of a registration will require IESG Approval on the advice
   of a Designated Expert.

22.4.3.  Guidelines for Writing Layout Type Specifications

   The author of a new pNFS layout specification must follow these steps
   to obtain acceptance of the layout type as a Standards Track RFC:

   1.  The author devises the new layout specification.

   2.  The new layout type specification MUST, at a minimum:

       *  Define the contents of the layout-type-specific fields of the
          following data types:

          +  the da_addr_body field of the device_addr4 data type;

          +  the loh_body field of the layouthint4 data type;

          +  the loc_body field of layout_content4 data type (which in
             turn is the lo_content field of the layout4 data type);

          +  the lou_body field of the layoutupdate4 data type;

       *  Describe or define the storage access protocol used to access
          the storage devices.

       *  Describe whether revocation of layouts is supported.

       *  At a minimum, describe the methods of recovery from:

          1.  Failure and restart for client, server, storage device.

          2.  Lease expiration from perspective of the active client,
              server, storage device.

          3.  Loss of layout state resulting in fencing of client access
              to storage devices (for an example, see Section 12.7.3).

       *  Include an IANA considerations section, which will in turn
          include:

          +  A request to IANA for a new layout type per Section 22.4.






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          +  A list of requests to IANA for any new recallable object
             types for CB_RECALL_ANY; each entry is to be presented in
             the form described in Section 22.3.

          +  A list of requests to IANA for any new notification values
             for CB_NOTIFY_DEVICEID; each entry is to be presented in
             the form described in Section 22.2.

       *  Include a security considerations section.  This section MUST
          explain how the NFSv4.1 authentication, authorization, and
          access-control models are preserved.  That is, if a metadata
          server would restrict a READ or WRITE operation, how would
          pNFS via the layout similarly restrict a corresponding input
          or output operation?

   3.  The author documents the new layout specification as an Internet-
       Draft.

   4.  The author submits the Internet-Draft for review through the IETF
       standards process as defined in "The Internet Standards Process--
       Revision 3" (BCP 9).  The new layout specification will be
       submitted for eventual publication as a Standards Track RFC.

   5.  The layout specification progresses through the IETF standards
       process.

22.5.  Path Variable Definitions

   This section deals with the IANA considerations associated with the
   variable substitution feature for location names as described in
   Section 11.10.3.  As described there, variables subject to
   substitution consist of a domain name and a specific name within that
   domain, with the two separated by a colon.  There are two sets of
   IANA considerations here:

   1.  The list of variable names.

   2.  For each variable name, the list of possible values.

   Thus, there will be one registry for the list of variable names, and
   possibly one registry for listing the values of each variable name.

22.5.1.  Path Variables Registry

   IANA created a registry called the "NFSv4 Path Variables Registry".






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22.5.1.1.  Path Variable Values

   Variable names are of the form "${", followed by a domain name,
   followed by a colon (":"), followed by a domain-specific portion of
   the variable name, followed by "}".  When the domain name is
   "ietf.org", all variables names must be registered with IANA on a
   Standards Action basis, with Expert Review required.  Path variables
   with registered domain names neither part of nor equal to ietf.org
   are assigned on a Hierarchical Allocation basis (delegating to the
   domain owner) and thus of no concern to IANA, unless the domain owner
   chooses to register a variable name from his domain.  If the domain
   owner chooses to do so, IANA will do so on a First Come First Serve
   basis.  To accommodate registrants who do not have their own domain,
   IANA will accept requests to register variables with the prefix
   "${FCFS.ietf.org:" on a First Come First Served basis.  Assignments
   on a First Come First Basis do not require Expert Review, unless the
   registrant also wants IANA to establish a registry for the values of
   the registered variable.

   The registry is a list of assignments, each containing three fields.

   1.  The name of the variable.  The name of this variable must start
       with a "${" followed by a registered domain name, followed by
       ":", or it must start with "${FCFS.ietf.org".  The name must be
       no more than 64 UTF-8 characters long.  The name must be unique.

   2.  For assignments made on Standards Action basis, the Standards
       Track RFC(s) that describe the variable.  If the RFC(s) have not
       yet been published, the registrant will use RFCTBD1, RFCTBD2,
       etc. instead of an actual RFC number.  Note that the RFCs do not
       have to be a part of an NFS minor version.  For assignments made
       on a First Come First Serve basis, an explanation (consuming no
       more than 1024 bytes, or more if IANA permits) of the purpose of
       the variable.  A reference to the explanation can be substituted.

   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).
       For assignments made on a Standards Action basis, the point of
       contact is always IESG.

22.5.1.1.1.  Initial Registry

   The initial registry is in Table 19.








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         +------------------------+----------+------------------+
         | Variable Name          | RFC      | Point of Contact |
         +------------------------+----------+------------------+
         | ${ietf.org:CPU_ARCH}   | RFC 5661 | IESG             |
         | ${ietf.org:OS_TYPE}    | RFC 5661 | IESG             |
         | ${ietf.org:OS_VERSION} | RFC 5661 | IESG             |
         +------------------------+----------+------------------+

                 Table 19: Initial List of Path Variables

   IANA has created registries for the values of the variable names
   ${ietf.org:CPU_ARCH} and ${ietf.org:OS_TYPE}. See Sections 22.5.2 and
   22.5.3.

   For the values of the variable ${ietf.org:OS_VERSION}, no registry is
   needed as the specifics of the values of the variable will vary with
   the value of ${ietf.org:OS_TYPE}. Thus, values for
   ${ietf.org:OS_VERSION} are on a Hierarchical Allocation basis and are
   of no concern to IANA.

22.5.1.1.2.  Updating Registrations

   The update of an assignment made on a Standards Action basis will
   require IESG Approval on the advice of a Designated Expert.

   The registrant can always update the point of contact of an
   assignment made on a First Come First Serve basis.  Any other update
   will require Expert Review.

22.5.2.  Values for the ${ietf.org:CPU_ARCH} Variable

   IANA created a registry called the "NFSv4 ${ietf.org:CPU_ARCH} Value
   Registry".

   Assignments to the registry are made on a First Come First Serve
   basis.  The zero-length value of ${ietf.org:CPU_ARCH} is Reserved.
   Values with a prefix of "PRIV" are designated for Private Use.

   The registry is a list of assignments, each containing three fields.

   1.  A value of the ${ietf.org:CPU_ARCH} variable.  The value must be
       1 to 32 UTF-8 characters long.  The value must be unique.

   2.  An explanation (consuming no more than 1024 bytes, or more if
       IANA permits) of what CPU architecture the value denotes.  A
       reference to the explanation can be substituted.





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   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).

22.5.2.1.  Initial Registry

   There is no initial registry.

22.5.2.2.  Updating Registrations

   The registrant is free to update the assignment, i.e., change the
   explanation and/or point-of-contact fields.

22.5.3.  Values for the ${ietf.org:OS_TYPE} Variable

   IANA created a registry called the "NFSv4 ${ietf.org:OS_TYPE} Value
   Registry".

   Assignments to the registry are made on a First Come First Serve
   basis.  The zero-length value of ${ietf.org:OS_TYPE} is Reserved.
   Values with a prefix of "PRIV" are designated for Private Use.

   The registry is a list of assignments, each containing three fields.

   1.  A value of the ${ietf.org:OS_TYPE} variable.  The value must be 1
       to 32 UTF-8 characters long.  The value must be unique.

   2.  An explanation (consuming no more than 1024 bytes, or more if
       IANA permits) of what CPU architecture the value denotes.  A
       reference to the explanation can be substituted.

   3.  The point of contact, including an email address.  The point of
       contact can consume up to 256 bytes (or more if IANA permits).

22.5.3.1.  Initial Registry

   There is no initial registry.

22.5.3.2.  Updating Registrations

   The registrant is free to update the assignment, i.e., change the
   explanation and/or point of contact fields.

23.  References








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23.1.  Normative References

   [1]        Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [2]        Eisler, M., Ed., "XDR: External Data Representation
              Standard", STD 67, RFC 4506, May 2006.

   [3]        Thurlow, R., "RPC: Remote Procedure Call Protocol
              Specification Version 2", RFC 5531, May 2009.

   [4]        Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, September 1997.

   [5]        Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
              Version 5 Generic Security Service Application Program
              Interface (GSS-API) Mechanism Version 2", RFC 4121, July
              2005.

   [6]        The Open Group, "Section 3.191 of Chapter 3 of Base
              Definitions of The Open Group Base Specifications Issue 6
              IEEE Std 1003.1, 2004 Edition, HTML Version
              (www.opengroup.org), ISBN 1931624232", 2004.

   [7]        Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [8]        Talpey, T. and B. Callaghan, "Remote Direct Memory Access
              Transport for Remote Procedure Call", RFC 5666, October
              2009.

   [9]        Talpey, T. and B. Callaghan, "Network File System (NFS)
              Direct Data Placement", RFC 5667, January 2010.

   [10]       Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, October 2007.

   [11]       Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104, February
              1997.

   [12]       Eisler, M., "RPCSEC_GSS Version 2", RFC 5403, February
              2009.







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   [13]       Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              External Data Representation Standard (XDR) Description",
              RFC 5662, January 2010.

   [14]       The Open Group, "Section 3.372 of Chapter 3 of Base
              Definitions of The Open Group Base Specifications Issue 6
              IEEE Std 1003.1, 2004 Edition, HTML Version
              (www.opengroup.org), ISBN 1931624232", 2004.

   [15]       Eisler, M., "IANA Considerations for Remote Procedure Call
              (RPC) Network Identifiers and Universal Address Formats",
              RFC 5665, January 2010.

   [16]       The Open Group, "Section 'read()' of System Interfaces of
              The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [17]       The Open Group, "Section 'readdir()' of System Interfaces
              of The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [18]       The Open Group, "Section 'write()' of System Interfaces of
              The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [19]       Hoffman, P. and M. Blanchet, "Preparation of
              Internationalized Strings ("stringprep")", RFC 3454,
              December 2002.

   [20]       The Open Group, "Section 'chmod()' of System Interfaces of
              The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [21]       International Organization for Standardization,
              "Information Technology - Universal Multiple-octet coded
              Character Set (UCS) - Part 1: Architecture and Basic
              Multilingual Plane", ISO Standard 10646-1, May 1993.

   [22]       Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, January 1998.






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RFC 5661                         NFSv4.1                    January 2010


   [23]       Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep
              Profile for Internationalized Domain Names (IDN)",
              RFC 3491, March 2003.

   [24]       The Open Group, "Section 'fcntl()' of System Interfaces of
              The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [25]       The Open Group, "Section 'fsync()' of System Interfaces of
              The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [26]       The Open Group, "Section 'getpwnam()' of System Interfaces
              of The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [27]       The Open Group, "Section 'unlink()' of System Interfaces
              of The Open Group Base Specifications Issue 6 IEEE Std
              1003.1, 2004 Edition, HTML Version (www.opengroup.org),
              ISBN 1931624232", 2004.

   [28]       Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [29]       National Institute of Standards and Technology,
              "Cryptographic Algorithm Object Registration", URL
              http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/
              algorithms.html, November 2007.

23.2.  Informative References

   [30]       Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "Network File System
              (NFS) version 4 Protocol", RFC 3530, April 2003.

   [31]       Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813, June 1995.

   [32]       Eisler, M., "LIPKEY - A Low Infrastructure Public Key
              Mechanism Using SPKM", RFC 2847, June 2000.





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   [33]       Eisler, M., "NFS Version 2 and Version 3 Security Issues
              and the NFS Protocol's Use of RPCSEC_GSS and Kerberos V5",
              RFC 2623, June 1999.

   [34]       Juszczak, C., "Improving the Performance and Correctness
              of an NFS Server", USENIX Conference Proceedings , June
              1990.

   [35]       Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
              by an On-line Database", RFC 3232, January 2002.

   [36]       Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
              RFC 1833, August 1995.

   [37]       Werme, R., "RPC XID Issues", USENIX Conference
              Proceedings , February 1996.

   [38]       Nowicki, B., "NFS: Network File System Protocol
              specification", RFC 1094, March 1989.

   [39]       Bhide, A., Elnozahy, E., and S. Morgan, "A Highly
              Available Network Server", USENIX Conference Proceedings ,
              January 1991.

   [40]       Halevy, B., Welch, B., and J. Zelenka, "Object-Based
              Parallel NFS (pNFS) Operations", RFC 5664, January 2010.

   [41]       Black, D., Glasgow, J., and S. Fridella, "Parallel NFS
              (pNFS) Block/Volume Layout", RFC 5663, January 2010.

   [42]       Callaghan, B., "WebNFS Client Specification", RFC 2054,
              October 1996.

   [43]       Callaghan, B., "WebNFS Server Specification", RFC 2055,
              October 1996.

   [44]       IESG, "IESG Processing of RFC Errata for the IETF Stream",
              July 2008.

   [45]       Shepler, S., "NFS Version 4 Design Considerations",
              RFC 2624, June 1999.

   [46]       The Open Group, "Protocols for Interworking: XNFS, Version
              3W, ISBN 1-85912-184-5", February 1998.

   [47]       Floyd, S. and V. Jacobson, "The Synchronization of
              Periodic Routing Messages", IEEE/ACM Transactions on
              Networking 2(2), pp. 122-136, April 1994.



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   [48]       Satran, J., Meth, K., Sapuntzakis, C., Chadalapaka, M.,
              and E. Zeidner, "Internet Small Computer Systems Interface
              (iSCSI)", RFC 3720, April 2004.

   [49]       Snively, R., "Fibre Channel Protocol for SCSI, 2nd Version
              (FCP-2)", ANSI/INCITS 350-2003, Oct 2003.

   [50]       Weber, R., "Object-Based Storage Device Commands (OSD)",
              ANSI/INCITS 400-2004, July 2004,
              <http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf>.

   [51]       Carns, P., Ligon III, W., Ross, R., and R. Thakur, "PVFS:
              A Parallel File System for Linux Clusters.", Proceedings
              of the 4th Annual Linux Showcase and Conference , 2000.

   [52]       The Open Group, "The Open Group Base Specifications Issue
              6, IEEE Std 1003.1, 2004 Edition", 2004.

   [53]       Callaghan, B., "NFS URL Scheme", RFC 2224, October 1997.

   [54]       Chiu, A., Eisler, M., and B. Callaghan, "Security
              Negotiation for WebNFS", RFC 2755, January 2000.

   [55]       Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

























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Appendix A.  Acknowledgments

   The initial text for the SECINFO extensions were edited by Mike
   Eisler with contributions from Peng Dai, Sergey Klyushin, and Carl
   Burnett.

   The initial text for the SESSIONS extensions were edited by Tom
   Talpey, Spencer Shepler, Jon Bauman with contributions from Charles
   Antonelli, Brent Callaghan, Mike Eisler, John Howard, Chet Juszczak,
   Trond Myklebust, Dave Noveck, John Scott, Mike Stolarchuk, and Mark
   Wittle.

   Initial text relating to multi-server namespace features, including
   the concept of referrals, were contributed by Dave Noveck, Carl
   Burnett, and Charles Fan with contributions from Ted Anderson, Neil
   Brown, and Jon Haswell.

   The initial text for the Directory Delegations support were
   contributed by Saadia Khan with input from Dave Noveck, Mike Eisler,
   Carl Burnett, Ted Anderson, and Tom Talpey.

   The initial text for the ACL explanations were contributed by Sam
   Falkner and Lisa Week.

   The pNFS work was inspired by the NASD and OSD work done by Garth
   Gibson.  Gary Grider has also been a champion of high-performance
   parallel I/O.  Garth Gibson and Peter Corbett started the pNFS effort
   with a problem statement document for the IETF that formed the basis
   for the pNFS work in NFSv4.1.

   The initial text for the parallel NFS support was edited by Brent
   Welch and Garth Goodson.  Additional authors for those documents were
   Benny Halevy, David Black, and Andy Adamson.  Additional input came
   from the informal group that contributed to the construction of the
   initial pNFS drafts; specific acknowledgment goes to Gary Grider,
   Peter Corbett, Dave Noveck, Peter Honeyman, and Stephen Fridella.

   Fredric Isaman found several errors in draft versions of the ONC RPC
   XDR description of the NFSv4.1 protocol.

   Audrey Van Belleghem provided, in numerous ways, essential co-
   ordination and management of the process of editing the specification
   documents.

   Richard Jernigan gave feedback on the file layout's striping pattern
   design.





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   Several formal inspection teams were formed to review various areas
   of the protocol.  All the inspections found significant errors and
   room for improvement.  NFSv4.1's inspection teams were:

   o  ACLs, with the following inspectors: Sam Falkner, Bruce Fields,
      Rahul Iyer, Saadia Khan, Dave Noveck, Lisa Week, Mario Wurzl, and
      Alan Yoder.

   o  Sessions, with the following inspectors: William Brown, Tom
      Doeppner, Robert Gordon, Benny Halevy, Fredric Isaman, Rick
      Macklem, Trond Myklebust, Dave Noveck, Karen Rochford, John Scott,
      and Peter Shah.

   o  Initial pNFS inspection, with the following inspectors: Andy
      Adamson, David Black, Mike Eisler, Marc Eshel, Sam Falkner, Garth
      Goodson, Benny Halevy, Rahul Iyer, Trond Myklebust, Spencer
      Shepler, and Lisa Week.

   o  Global namespace, with the following inspectors: Mike Eisler, Dan
      Ellard, Craig Everhart, Fredric Isaman, Trond Myklebust, Dave
      Noveck, Theresa Raj, Spencer Shepler, Renu Tewari, and Robert
      Thurlow.

   o  NFSv4.1 file layout type, with the following inspectors: Andy
      Adamson, Marc Eshel, Sam Falkner, Garth Goodson, Rahul Iyer, Trond
      Myklebust, and Lisa Week.

   o  NFSv4.1 locking and directory delegations, with the following
      inspectors: Mike Eisler, Pranoop Erasani, Robert Gordon, Saadia
      Khan, Eric Kustarz, Dave Noveck, Spencer Shepler, and Amy Weaver.

   o  EXCHANGE_ID and DESTROY_CLIENTID, with the following inspectors:
      Mike Eisler, Pranoop Erasani, Robert Gordon, Benny Halevy, Fredric
      Isaman, Saadia Khan, Ricardo Labiaga, Rick Macklem, Trond
      Myklebust, Spencer Shepler, and Brent Welch.

   o  Final pNFS inspection, with the following inspectors: Andy
      Adamson, Mike Eisler, Mark Eshel, Sam Falkner, Jason Glasgow,
      Garth Goodson, Robert Gordon, Benny Halevy, Dean Hildebrand, Rahul
      Iyer, Suchit Kaura, Trond Myklebust, Anatoly Pinchuk, Spencer
      Shepler, Renu Tewari, Lisa Week, and Brent Welch.

   A review team worked together to generate the tables of assignments
   of error sets to operations and make sure that each such assignment
   had two or more people validating it.  Participating in the process
   were Andy Adamson, Mike Eisler, Sam Falkner, Garth Goodson, Robert
   Gordon, Trond Myklebust, Dave Noveck, Spencer Shepler, Tom Talpey,
   Amy Weaver, and Lisa Week.



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   Jari Arkko, David Black, Scott Bradner, Lisa Dusseault, Lars Eggert,
   Chris Newman, and Tim Polk provided valuable review and guidance.

   Olga Kornievskaia found several errors in the SSV specification.

   Ricardo Labiaga found several places where the use of RPCSEC_GSS was
   underspecified.

   Those who provided miscellaneous comments include: Andy Adamson,
   Sunil Bhargo, Alex Burlyga, Pranoop Erasani, Bruce Fields, Vadim
   Finkelstein, Jason Goldschmidt, Vijay K.  Gurbani, Sergey Klyushin,
   Ricardo Labiaga, James Lentini, Anshul Madan, Daniel Muntz, Daniel
   Picken, Archana Ramani, Jim Rees, Mahesh Siddheshwar, Tom Talpey, and
   Peter Varga.

Authors' Addresses

   Spencer Shepler (editor)
   Storspeed, Inc.
   7808 Moonflower Drive
   Austin, TX  78750
   USA

   Phone: +1-512-402-5811 ext 8530
   EMail: shepler@xxxxxxxxxxxxx


   Mike Eisler (editor)
   NetApp
   5765 Chase Point Circle
   Colorado Springs, CO  80919
   USA

   Phone: +1-719-599-9026
   EMail: mike@xxxxxxxxxx
   URI:   http://www.eisler.com


   David Noveck (editor)
   NetApp
   1601 Trapelo Road, Suite 16
   Waltham, MA  02451
   USA

   Phone: +1-781-768-5347
   EMail: dnoveck@xxxxxxxxxx





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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>


<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc symrefs="no"?>
<?rfc sortrefs="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<?rfc rfcedstyle="yes" ?>

<rfc
    category="std"
    number="5661">
     

<front>
    <title abbrev="NFSv4.1">
    Network File System (NFS) Version 4 Minor Version 1 Protocol

    </title>

    <author fullname="Spencer Shepler" 
            initials="S." 
            surname="Shepler" role="editor">
        <organization>Storspeed, Inc.</organization>
        <address>
            <postal>
                <street>7808 Moonflower Drive</street>
                <city>Austin</city>
                <region>TX</region>
                <code>78750</code>
                <country>USA</country>
            </postal>
            <phone>+1-512-402-5811 ext 8530</phone>
            <email>shepler@xxxxxxxxxxxxx</email>
        </address>
    </author>
    <author fullname="Mike Eisler" 
            initials="M." 
            surname="Eisler" role="editor">
        <organization abbrev="NetApp">NetApp</organization>
        <address>
            <postal>
                <street>5765 Chase Point Circle</street>
                <city>Colorado Springs</city>
                <region>CO</region>
                <code>80919</code>
                <country>USA</country>
            </postal>
            <phone>+1-719-599-9026</phone>
            <email>mike@xxxxxxxxxx</email>
            <uri>http://www.eisler.com</uri>
        </address>
    </author>
    <author fullname="David Noveck" 
            initials="D." 
            surname="Noveck" role="editor">
        <organization abbrev="NetApp">NetApp</organization>
        <address>
            <postal>
                <street>1601 Trapelo Road, Suite 16</street>
                <city>Waltham</city>
                <region>MA</region>
                <code>02451</code>
                <country>USA</country>
            </postal>
            <phone>+1-781-768-5347</phone>
            <email>dnoveck@xxxxxxxxxx</email>
        </address>
    </author>

    <date year="2010" month="January"/>

    <area>Transport</area>
    <workgroup>NFSv4</workgroup>

    <abstract>
      <t>
      This document describes the Network File System (NFS) version 4 minor version 1,
      including features retained from the base protocol (NFS version 4 minor
      version 0, which is specified in RFC 3530) and protocol
      extensions made subsequently.  Major extensions introduced in
      NFS version 4 minor version 1 include Sessions, Directory
      Delegations, and parallel NFS (pNFS). NFS version 4 minor version 1
      has no dependencies on NFS version 4 minor version 0, and it
      is considered a separate protocol. Thus,
      this document neither updates nor obsoletes RFC 3530.
      NFS minor version 1 is deemed superior to NFS minor version 0
      with no loss of functionality, and its use is preferred over
      version 0. Both NFS minor versions 0 and 1 can be used
      simultaneously on the same network, between the same client and server.
      </t>
    </abstract>

</front>

<middle>

<section anchor="intro" title="Introduction" >
  <section anchor="intro_the_protocol" title="The NFS Version 4 Minor Version 1 Protocol">
    <t>
      The NFS version 4 minor version 1 (NFSv4.1) protocol
      is the second minor version of the NFS version 4
      (NFSv4) protocol. The first minor version, NFSv4.0, is
      described in <xref target="RFC3530" />.  It generally
      follows the guidelines for minor versioning that are
      listed in Section 10 of RFC 3530.  However, it
      diverges from guidelines 11 ("a client and server
      that support minor version X must support minor
      versions 0 through X-1") and 12 ("no new features may be
      introduced as mandatory in a minor version"). These
      divergences are due to the introduction of
      the sessions model for managing non-idempotent
      operations and the RECLAIM_COMPLETE operation.
      These two new features are infrastructural in
      nature and simplify implementation of existing and
      other new features.  Making them anything but REQUIRED
      would add undue complexity to protocol definition and
      implementation.  NFSv4.1 accordingly updates the
      <xref target="minor_versioning">minor versioning
      guidelines</xref>.

    </t>
    <t>
      As a minor version, NFSv4.1 is consistent with the overall
      goals for NFSv4, but extends the protocol so as to
      better meet those goals, based on experiences with NFSv4.0.
      In addition, NFSv4.1 has adopted some additional goals, which
      motivate some of the major extensions in NFSv4.1.
    </t>
  </section>
    <section title="Requirements Language">
<t>The key words &quot;MUST&quot;, &quot;MUST NOT&quot;,
&quot;REQUIRED&quot;, &quot;SHALL&quot;, &quot;SHALL NOT&quot;,
&quot;SHOULD&quot;, &quot;SHOULD NOT&quot;, &quot;RECOMMENDED&quot;,
&quot;MAY&quot;, and &quot;OPTIONAL&quot; in this document are to be
interpreted as described in <xref target="RFC2119">RFC 2119</xref>.
</t>

    </section>

  <section anchor="scope_of_doc" title="Scope of This Document">
  <t>

   This document describes the NFSv4.1 protocol. With
   respect to NFSv4.0, this document does not:

   <list style='symbols'>
   <t>
       describe the NFSv4.0 protocol, except where needed
       to contrast with NFSv4.1.

   </t> 

   <t>
       modify the specification of the NFSv4.0 protocol.

   </t>

   <t>
       clarify the NFSv4.0 protocol.

   </t>
   </list>
  </t>

  </section>
  <section anchor="version4_goals" title="NFSv4 Goals">
    <t>
      The NFSv4 protocol is a further revision of the NFS protocol
      defined already by NFSv3
      <xref target="RFC1813" />.  It retains
      the essential characteristics of previous versions: easy
      recovery; independence of transport protocols, operating systems, and
      file systems; simplicity; and good performance.  NFSv4 has the following goals:

      <list style='symbols'>
        <t>
          Improved access and good performance on the Internet
        <vspace blankLines='1' />
          The protocol is designed to transit firewalls easily, perform well
          where latency is high and bandwidth is low, and scale to very
          large numbers of clients per server.
        </t>
        <t>
          Strong security with negotiation built into the protocol
        <vspace blankLines='1' />
          The protocol builds on the work of the ONCRPC working group in
          supporting the RPCSEC_GSS protocol.  Additionally, the
        NFSv4.1 protocol provides a mechanism to allow clients and
        servers the ability to negotiate security and require clients and servers to
          support a minimal set of security schemes.
        </t>
        <t>
          Good cross-platform interoperability
        <vspace blankLines='1' />
          The protocol features a file system model that provides a useful,
          common set of features that does not unduly favor one file system
          or operating system over another.
        </t>
        <t>
          Designed for protocol extensions
        <vspace blankLines='1' />
          The protocol is designed to accept standard extensions within a
          framework that enables and encourages backward compatibility.
        </t>
      </list>
    </t>
  </section>
  <section anchor="minor_version1_goals" title="NFSv4.1 Goals">
    <t>
      NFSv4.1 has the following goals, within the framework 
      established by the overall NFSv4 goals.
      <list style="symbols">
        <t>
          To correct significant structural weaknesses and oversights 
          discovered in the base protocol.
        </t>
        <t>
          To add clarity and specificity to areas left
          unaddressed or not addressed in sufficient
          detail in the base protocol. However, as stated
          in <xref target="scope_of_doc" />, it is not
          a goal to clarify the NFSv4.0 protocol in the
          NFSv4.1 specification.

        </t>
        <t>
          To add specific features based on experience with the existing
          protocol and recent industry developments. 
        </t>
        <t>
          To provide protocol support to take advantage of clustered 
          server deployments including the ability to provide scalable
          parallel access to files distributed among multiple servers.
        </t>
      </list>
    </t>
  </section>
  <section anchor="intro_definitions" title="General Definitions">
    <t>
      The following definitions provide an appropriate context for the reader.
      <list style='hanging'>
        <t hangText="Byte:" anchor="byte">
          In this document, a byte is an octet, i.e., a datum
          exactly 8 bits in length.
        </t>
        <t hangText="Client:" anchor="client_def">
          The client is the entity that accesses the NFS server's
          resources.  The client may be an application that contains
          the logic to access the NFS server directly.  The client
          may also be the traditional operating system client that
	  provides remote file system services for a set of applications.
        <vspace blankLines='1' />
          A client is uniquely identified by a client owner.
        <vspace blankLines='1' />
          With reference to byte-range locking, the client is also the entity that
          maintains a set of locks on behalf of one or more
          applications.  This client is responsible for crash or
          failure recovery for those locks it manages.
        <vspace blankLines='1' />
          Note that multiple clients may share the same transport and
          connection and
          multiple clients may exist on the same network node.
        </t>
        <t hangText="Client ID:">
          The client ID is a 64-bit quantity used as a unique, short-hand reference to
          a client-supplied verifier and client owner.  The server is
          responsible for supplying the client ID.
        </t>
        <t hangText="Client Owner:">
          The client owner is a unique string, opaque to the server,
          that identifies a client. Multiple network connections and source
          network addresses originating from those connections may share
          a client owner. The server is expected to treat requests
          from connections with the same client owner as coming from
          the same client.
        </t>

        <t hangText="File System:">
          The file system is the collection of objects on a server (as
          identified by the major identifier of a server
          owner, which is defined later in this section)
          that share the same fsid attribute (see <xref
          target="attrdef_fsid"/>).

        </t>
        <t hangText="Lease:">
          A lease is an interval of time defined by the server for which the
          client is irrevocably granted locks.  At the end of a
          lease period, locks may be revoked if the lease has not
          been extended.  A lock must be revoked if a conflicting
          lock has been granted after the lease interval.
        <vspace blankLines='1' />
          A server grants a client a single lease for all state.
        </t>
        <t hangText="Lock:">
          The term "lock" is used to refer to byte-range (in UNIX environments,
          also known as record)
          locks, share reservations, delegations, or layouts unless
          specifically stated otherwise.
        </t>

        <t hangText="Secret State Verifier (SSV):">
          The SSV is a unique secret key shared between a client and
          server.  The SSV serves as the secret key for an internal (that
          is, internal to NFSv4.1) Generic Security Services (GSS)
          mechanism (the SSV GSS mechanism;
          see <xref target="ssv_mech"/>).  The SSV GSS mechanism uses the
          SSV to compute message integrity code (MIC) and Wrap tokens.
          See <xref target="protect_state_change"/> for more details on how NFSv4.1 uses
          the SSV and the SSV GSS mechanism.

        </t>

        <t hangText="Server:">
          The Server is the entity responsible for coordinating
          client access to a set of file systems and is identified by a server
          owner. A server can span multiple network addresses.
        </t>
        <t hangText="Server Owner:">
          The server owner identifies the server to the client.
          The server owner consists of a major identifier and a minor identifier.
          When the client has two connections each to a peer with the
          same major identifier, the client assumes that both peers are
          the same server (the server namespace is the
          same via each connection) and that
          lock state is sharable across both connections. When each peer
          has both the same major and minor identifiers, the client
          assumes that each connection might be associable with the same session.
        </t>
        <t hangText="Stable Storage:">
          Stable storage is storage from which data stored by
          an NFSv4.1 server can be recovered without data
          loss from multiple power failures (including cascading
          power failures, that is, several power failures in quick
          succession), operating system failures, and/or hardware
          failure of components other than the storage medium itself
          (such as disk, nonvolatile RAM, flash memory, etc.).
        <vspace blankLines='1' />
          Some examples of stable storage that are allowable for an
          NFS server include:
          <list style='numbers'>
             <t>
               Media commit of data; that is, the modified data has
               been successfully written to the disk media, for
               example, the disk platter.
             </t>
             <t>
               An immediate reply disk drive with battery-backed,
               on-drive intermediate storage or uninterruptible power
               system (UPS).
             </t>
             <t>
               Server commit of data with battery-backed intermediate
               storage and recovery software.
             </t>
             <t>
               Cache commit with uninterruptible power system (UPS) and
               recovery software.
             </t>
           </list>
        </t>
        <t hangText="Stateid:">
          A stateid is a 128-bit quantity returned by a server that uniquely
          defines the open and locking states provided by the server
          for a specific open-owner or lock-owner/open-owner pair
          for a specific file and type of lock.
        </t>
        <t hangText="Verifier:">
          A verifier is a 64-bit quantity generated by the client that the server
          can use to determine if the client has restarted and lost
           all previous lock state.        
        </t>
      </list>
    </t>
  </section>
  <section anchor="feature overview" 
           title="Overview of NFSv4.1 Features">
    <t>
      The major features of
      the NFSv4.1 protocol will be reviewed in brief.  This will be done
      to provide an appropriate context for both the reader who is familiar
      with the previous versions of the NFS protocol and the reader
      who is new to the NFS protocols.  For the reader new to the NFS protocols,
      there is still a set of fundamental knowledge that is expected.  
      The reader should be familiar with the External Data
      Representation (XDR) and Remote Procedure Call (RPC) protocols 
      as described in <xref target="RFC4506" /> and <xref target="RFC5531" />.
      A basic knowledge of file systems and distributed file systems is expected as well.
    </t>
    <t>
      In general, this specification of NFSv4.1 will
      not distinguish those features added in minor version
      1 from those present in the base protocol but
      will treat NFSv4.1 as a unified whole.  See <xref
      target="intro_differences" /> for a summary of
      the differences between NFSv4.0 and NFSv4.1.

    </t>
    <section anchor="rpc_and_security" title="RPC and Security">
      <t>
        As with previous versions of NFS, the External Data Representation
        (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFSv4.1 protocol are those defined in 
        <xref target="RFC4506" /> and <xref target="RFC5531" />.  To
        meet end-to-end security requirements, the RPCSEC_GSS framework
        <xref target="RFC2203" /> is used to extend the basic 
        RPC security.  With the
        use of RPCSEC_GSS, various mechanisms can be provided to offer
        authentication, integrity, and privacy to the NFSv4 protocol.
        Kerberos V5 is used as described in 
        <xref target="RFC4121" /> to provide one
        security framework.
        With the use of
        RPCSEC_GSS, other mechanisms may also be specified and used for NFSv4.1 security.
      </t>
      <t>
        To enable in-band security negotiation, the NFSv4.1 protocol
        has operations that provide the client a method of
        querying the server about its policies regarding which security
        mechanisms must be used for access to the server's file system
        resources.  With this, the client can securely match the security
        mechanism that meets the policies specified at both the client and
        server.
      </t>
      <t>
	NFSv4.1 introduces parallel access (see <xref
	target="parallel_access"/>), which is
	called pNFS.  

The security framework
	described in this section is
	significantly modified by the
	introduction of pNFS (see <xref
	target="security_considerations_pnfs"/>),
	because data access is sometimes not over
	RPC.  The level of significance varies
	with the storage protocol (see <xref
	target="storage_protocol"/>) and can be as low as zero
        impact (see <xref target="file_security_considerations"/>).

      </t>
    </section>
    <section anchor="protocol_structure" 
             title="Protocol Structure">
      <section anchor="core_protocol" 
               title="Core Protocol">
        <t>
          Unlike NFSv3, which used a series of ancillary 
          protocols (e.g., NLM, NSM (Network Status Monitor), MOUNT), within all minor versions
          of NFSv4 a single RPC protocol is used to make requests to 
          the server.  

Facilities that had been separate protocols, such
          as locking, are now integrated within a single unified
          protocol.
        </t>
      </section>
      <section anchor="parallel_access" 
               title="Parallel Access">
        <t>
          Minor version 1 supports high-performance data access to a
          clustered server implementation by enabling a separation of
          metadata access and data access, with the latter done to 
          multiple servers in parallel.
        </t>
        <t>
          Such parallel data access is controlled by recallable 
          objects known as "layouts", which are integrated into the
          protocol locking model.  Clients direct requests for
          data access to a set of data servers specified by the
          layout via a data
          storage protocol which may be NFSv4.1 or may be another
          protocol.
        </t>

        <t>
	  Because the protocols used for parallel
	  data access are not necessarily
	  RPC-based, the RPC-based security model
	  (<xref target="rpc_and_security"/>) is
	  obviously impacted (see <xref
	  target="security_considerations_pnfs"/>).
	  The degree of impact varies with the
	  storage protocol (see <xref
	  target="storage_protocol"/>) used for
	  data access, and can be as low as zero (see 
	  <xref target="file_security_considerations"/>).

        </t>
      </section>
    </section>
    <section anchor="file system_model" title="File System Model">
      <t>
        The general file system
        model used for the NFSv4.1 protocol 
        is the same as previous versions.  The server file system is 
        hierarchical with the regular files contained within being 
        treated as opaque byte
        streams.  In a slight departure, file and directory names are encoded
        with UTF-8 to deal with the basics of internationalization.
      </t>
      <t>
        The NFSv4.1 protocol does not require a separate 
        protocol to provide for the initial mapping between path 
        name and filehandle.  All file systems exported by a server
        are presented as a tree so that all file systems are reachable
        from a special per-server global root filehandle.  This
        allows LOOKUP operations to be used to perform functions
        previously provided by the MOUNT protocol.  The server
        provides any necessary pseudo file systems to bridge any
        gaps that arise due to unexported gaps between exported
        file systems.
      </t>
      <section anchor="intro_filehandles" title="Filehandles">
        <t>
          As in previous versions of the NFS protocol, opaque 
          filehandles are used to identify individual files
          and directories.  Lookup-type and create operations
          translate file and directory names to
          filehandles, which are then used to identify objects
          in subsequent operations.
        </t>
        <t>
          The NFSv4.1 protocol provides support for 
          persistent filehandles, guaranteed to be valid
          for the lifetime of the file system object designated.
          In addition, it provides support to servers to provide
          filehandles with more limited validity guarantees,
          called volatile filehandles. 
        </t>
      </section>
      <section anchor="intro_attributes" title="File Attributes">
        <t>
	  The NFSv4.1 protocol has a rich and extensible
	  file object attribute structure, which is divided
	  into REQUIRED, RECOMMENDED, and named attributes
	  (see <xref target="file_attributes"/>).

        </t>
        <t>
	  Several (but not all) of the REQUIRED attributes
	  are derived from the attributes of NFSv3 (see
	  the definition of the fattr3 data type in <xref
	  target="RFC1813"/>). An example of a REQUIRED
	  attribute is the file object's type (<xref
	  target="attrdef_type"/>) so that regular files
	  can be distinguished from directories (also known
	  as folders in some operating environments) and
	  other types of objects. REQUIRED attributes are
	  discussed in <xref
	  target="mandatory_attributes_intro"/>.

        </t>

        <t>
	  An example of three RECOMMENDED attributes are
	  acl, sacl, and dacl.  These attributes define an
	  Access Control List (ACL) on a file object
	  (<xref target="acl"/>).  An ACL provides
	  directory and file access control beyond the
	  model used in NFSv3.   The ACL definition allows
	  for specification of specific sets of permissions
	  for individual users and groups.  In addition,
	  ACL inheritance allows propagation of access
	  permissions and restrictions down a directory tree
	  as file system objects are created.  RECOMMENDED
	  attributes are discussed in <xref
	  target="recommended_attributes_intro"/>.


        </t>
        <t>
          A named attribute is an opaque byte stream that is associated 
          with a directory or file and referred to by a string name.  
          Named attributes are meant to be used by client applications 
          as a method to associate application-specific data with a 
          regular file or directory.  NFSv4.1 modifies named attributes
          relative to NFSv4.0 by tightening the allowed operations in
          order to prevent the development of non-interoperable
          implementations.  Named attributes are discussed in <xref target="named_attributes_intro" />.

        </t>
      </section>
      <section anchor="intro_ms_namespace" title="Multi-Server Namespace">
        <t>
          NFSv4.1 contains a number of features to allow
          implementation of namespaces that cross server boundaries
          and that allow and facilitate a non-disruptive transfer of 
          support for individual file systems between servers.  They 
          are all based upon attributes that allow one file system to
          specify alternate or new locations for that file system.   
        </t>
        <t>
          These attributes may be used together with the concept
          of absent file systems, which provide specifications
          for additional locations but no actual file system 
          content.  This allows a number of important facilities:
          <list style="symbols">
            <t>
              Location attributes may be used with absent file systems
              to implement referrals whereby one server may direct the
              client to a file system provided by another server.  This
              allows extensive multi-server namespaces to be constructed.
            </t>
            <t>
              Location attributes may be provided for present file systems
              to provide the locations of alternate file system instances
              or replicas to be used in the event that the current 
              file system instance becomes unavailable.
            </t>
            <t>
              Location attributes may be provided when a previously
              present file system becomes absent.  This allows 
              non-disruptive migration of file systems to alternate
              servers.
            </t>
          </list>
        </t>
      </section>
    </section>
    <section anchor="intro_locking" title="Locking Facilities">
      <t>
        As mentioned previously, NFSv4.1 is a single protocol that
        includes locking facilities.  These locking facilities 
        include support for many types of locks including a number
        of sorts of recallable locks.  Recallable locks such as
        delegations allow the client to be assured that certain 
        events will not occur so long as that lock is held.  When
        circumstances change, the lock is recalled 
        via a callback request.  The assurances provided by 
        delegations allow more extensive caching to be done safely
        when circumstances allow it.
      </t>
      <t>
	The types of locks are:
      </t>
      <t>
        <list style="symbols">
          <t>
            Share reservations as established by OPEN operations.
          </t>
          <t>
            Byte-range locks.
          </t>
          <t>
            File delegations, which are recallable locks that assure
            the holder that inconsistent opens and file changes cannot
            occur so long as the delegation is held.  
          </t>
          <t>
            Directory delegations, which are recallable locks
            that assure the holder that inconsistent directory 
            modifications cannot occur so long as the delegation 
            is held.
          </t>
          <t>
            Layouts, which are recallable objects that assure the
            holder that direct access to the file data may be 
            performed directly by the client and that no change
            to the data's location that is inconsistent with that access
            may be made so long as the layout is held.  
          </t>
        </list>
      </t>
      <t>
        All locks for a given client are tied together under a
        single client-wide lease.  All requests made on sessions
        associated with the client renew that lease.  When the client's
        lease
        is not promptly renewed, the client's locks are subject to revocation.
        In the event of server restart, clients have the
        opportunity to safely reclaim their locks within a special
        grace period.
      </t>
    </section>
  </section>
  <section anchor="intro_differences" title="Differences from NFSv4.0">
    <t>
      The following summarizes the major differences between minor version 
      1 and the base protocol:
      <list style="symbols">
        <t>
          Implementation of the sessions model (<xref target="Session"/>).
        </t>
        <t>
          Parallel access to data (<xref target="pnfs"/>).
        </t>
        <t>
          Addition of the RECLAIM_COMPLETE operation to better structure
          the lock reclamation process (<xref target="OP_RECLAIM_COMPLETE"/>).
        </t>

        <t>
         Enhanced delegation support as follows.

         <list style="symbols">
	 <t>
	   Delegations on directories and other
	   file types in addition to regular files (<xref
	   target="OP_GET_DIR_DELEGATION"/>, <xref
	   target="OP_WANT_DELEGATION"/>).

	 </t>
	 <t>
	   Operations to optimize acquisition of recalled
	   or denied delegations (<xref
	   target="OP_WANT_DELEGATION"/>, <xref
	   target="OP_CB_PUSH_DELEG"/>, <xref
	   target="OP_CB_RECALLABLE_OBJ_AVAIL"/>).

	 </t>

	 <t>
	   Notifications of changes to files and directories
	   (<xref target="OP_GET_DIR_DELEGATION"/>, <xref
	   target="OP_CB_NOTIFY"/>).

	 </t>

	 <t>
	   A method to allow a server to indicate that it is
	   recalling one or more delegations for resource
	   management reasons, and thus a method to allow
	   the client to pick which delegations to return
	   (<xref target="OP_CB_RECALL_ANY"/>).

        </t>

        </list>

        </t>

        <t>
	  Attributes can be set atomically
	  during exclusive file create via the OPEN operation
	  (see the new EXCLUSIVE4_1 creation method in
	  <xref target="OP_OPEN"/>).

        </t>
        <t>
	  Open files can be preserved if removed and the
	  hard link count ("hard link" is defined in
	  an <xref target="hardlink">Open Group</xref> standard) goes
	  to zero, thus obviating the
	  need for clients to rename deleted files to
	  partially hidden names -- colloquially called
	  "silly rename" (see the new
	  OPEN4_RESULT_PRESERVE_UNLINKED reply flag in
	  <xref target="OP_OPEN"/>).

        </t>
        <t>
	  Improved compatibility with Microsoft Windows for
	  Access Control Lists (<xref
	  target="attrdef_sacl"/>, <xref
	  target="attrdef_dacl"/>, <xref
	  target="auto_inherit"/>).

        </t>
        <t>
          Data retention (<xref target="retention"/>).

        </t>
        <t>
          Identification of the implementation of the NFS client
          and server (<xref target="OP_EXCHANGE_ID"/>).

        </t>

        <t>
	  Support for notification of the availability of
	  byte-range locks (see the new
	  OPEN4_RESULT_MAY_NOTIFY_LOCK reply flag in <xref
	  target="OP_OPEN"/> and see <xref
	  target="OP_CB_NOTIFY_LOCK"/>).

        </t>

        <t>
          In NFSv4.1, LIPKEY and SPKM-3 are not required security mechanisms
          <xref target="RFC2847"/>.
        </t>
         

      </list>
    </t>
  </section>
</section>


<section anchor="Core Infrastructure" title="Core Infrastructure">

 <section anchor="Introduction" title="Introduction">
 <t>
  NFSv4.1 relies on core infrastructure common to nearly
  every operation. This core infrastructure is described in the remainder
  of this section.
 </t>
 </section> <!-- Introduction -->

 <section anchor="RPC and XDR" title="RPC and XDR">
 <t>
  The NFSv4.1 protocol is a Remote Procedure Call (RPC)
  application that uses RPC version 2 and the corresponding eXternal
  Data Representation (XDR) as defined in
  <xref target="RFC5531"/> and
  <xref target="RFC4506"/>.
 </t>

  <section anchor="RPC-based Security" title="RPC-Based Security">
  <t>
   Previous NFS versions have been thought of as having a
   host-based authentication model, where the NFS server
   authenticates the NFS client, and trusts the client
   to authenticate all users.
   Actually, NFS has always depended on RPC for
   authentication. One of the first forms of RPC authentication,
   AUTH_SYS, had no strong authentication and
   required a host-based authentication
   approach. NFSv4.1 also depends on RPC for basic security
   services and mandates RPC support for a user-based
   authentication model. The user-based authentication
   model has user principals authenticated by a server, and
   in turn the server authenticated by user principals.
   RPC provides some basic security services that are used
   by NFSv4.1.
  </t>

   <section anchor="RPC Security Flavors" title="RPC Security Flavors">
    <t>
     As described in Section 7.2 ("Authentication") of <xref target="RFC5531"/>,
     RPC security is encapsulated in the RPC header, via a
     security or authentication flavor, and information
     specific to the specified security flavor.
     Every RPC header conveys information used to identify
     and authenticate a client and server. As discussed in
     <xref target="RPCSEC_GSS and Security Services" />,
     some security flavors provide additional security
     services.
    </t>
    <t>
     NFSv4.1 clients and servers MUST implement RPCSEC_GSS.
     (This requirement to implement is not a requirement to
     use.)  Other flavors, such as AUTH_NONE and
     AUTH_SYS, MAY be implemented as well.
    </t>

    <section anchor="RPCSEC_GSS and Security Services" title="RPCSEC_GSS and Security Services">
     <t>
      RPCSEC_GSS <xref target="RFC2203" /> uses the
      functionality of GSS-API <xref target="RFC2743"/>.  This allows for the
      use of various security mechanisms by the RPC layer
      without the additional implementation overhead of
      adding RPC security flavors.
     </t>

     <section anchor="Authentication, Integrity, Privacy" title="Identification, Authentication, Integrity, Privacy">
     <t>
      Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
      users on clients to servers, and servers to users. It can also
      perform integrity checking on the entire RPC message, including
      the RPC header, and on the arguments or results. Finally, privacy,
      usually via encryption, is a service available with RPCSEC_GSS.
      Privacy is performed on the arguments and results. Note that
      if privacy is selected, integrity, authentication, and identification
      are enabled.
      If privacy is not selected, but integrity is selected, authentication
      and identification are enabled. If integrity and privacy are not
      selected, but authentication is enabled,
      identification is enabled. RPCSEC_GSS does not provide identification as
      a separate service.
     </t>
     <t>
      Although GSS-API has an authentication service distinct from its
      privacy and integrity services, GSS-API's
      authentication service is not used for RPCSEC_GSS's authentication
      service. Instead, each RPC request and response header is
      integrity protected with the GSS-API integrity service, and
      this allows RPCSEC_GSS to offer per-RPC authentication and
      identity. See <xref target="RFC2203" /> for more information.
     </t>
     <t>
      NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and authentication
      service. NFSv4.1 servers MUST support RPCSEC_GSS's privacy service.
      NFSv4.1 clients SHOULD support  RPCSEC_GSS's privacy service.

     </t>
     </section> <!-- Identity, Authentication, Integrity, Privacy -->

     <section anchor="security_mechs" title="Security Mechanisms for NFSv4.1">
     <t>
      RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that
      provide security services. Therefore, NFSv4.1 clients and servers
      MUST support the Kerberos V5 security mechanism.
     </t>
     <t>
      The use of RPCSEC_GSS requires selection of mechanism,
      quality of protection (QOP), and service (authentication,
      integrity, privacy).  For the mandated security mechanisms,
      NFSv4.1 specifies that a QOP of zero is used, leaving it up 
      to the mechanism or the mechanism's configuration to map
      QOP zero to
      an appropriate level of protection.
      Each mandated mechanism specifies a minimum set of cryptographic
      algorithms for implementing integrity and privacy. NFSv4.1
      clients and servers MUST be implemented on operating environments
      that comply with the REQUIRED cryptographic algorithms
      of each REQUIRED mechanism.
     </t>

      <section anchor="kerberosv5" title="Kerberos V5">
      <t>
       The Kerberos V5 GSS-API mechanism as described in
       <xref target="RFC4121"/> MUST be implemented with
       the RPCSEC_GSS services as specified in the following
       table:
      </t>
      <t>
      <figure>
      <artwork>
   column descriptions:
   1 == number of pseudo flavor
   2 == name of pseudo flavor
   3 == mechanism's OID
   4 == RPCSEC_GSS service
   5 == NFSv4.1 clients MUST support
   6 == NFSv4.1 servers MUST support

   1      2        3                    4                     5   6
   ------------------------------------------------------------------
   390003 krb5     1.2.840.113554.1.2.2 rpc_gss_svc_none      yes yes
   390004 krb5i    1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
   390005 krb5p    1.2.840.113554.1.2.2 rpc_gss_svc_privacy    no yes
      </artwork>
      </figure>
      </t>
      <t>
       Note that the number and name of the pseudo flavor
       are presented here as a mapping aid to the implementor.
       Because the NFSv4.1 protocol includes a method to negotiate
       security and it understands the GSS-API mechanism, the pseudo flavor
       is not needed.  The pseudo flavor is needed for the NFSv3 since the security negotiation is done via
       the MOUNT protocol as described in <xref target="RFC2623"/>.
      </t>
      <t>
       At the time NFSv4.1 was specified, the Advanced Encryption
       Standard (AES) with HMAC-SHA1 was
       a REQUIRED algorithm set for Kerberos V5. In contrast, when
       NFSv4.0 was specified, weaker algorithm sets were REQUIRED for
       Kerberos V5, and were REQUIRED in the NFSv4.0 specification, because
       the Kerberos V5 specification at the time did not specify stronger
       algorithms.
       The NFSv4.1 specification does not specify REQUIRED algorithms
       for Kerberos V5, and instead, the implementor is expected
       to track the evolution of the Kerberos V5 standard if and when
       stronger algorithms are specified.
       
       
      </t>
        <section anchor="krb5_sec_consider"
 title="Security Considerations for Cryptographic Algorithms in Kerberos V5">
        <t>
          When deploying NFSv4.1, the strength of the security achieved depends
          on the existing Kerberos V5 infrastructure. The algorithms
          of Kerberos V5 are not directly exposed to or selectable by the
          client or server, so there is some due diligence required by
          the user of NFSv4.1 to ensure that security is acceptable 
          where needed.
        </t>
        </section>
        
      </section> <!-- Kerberos V5  -->

      </section> <!-- Security mechanisms for NFSv4.1  -->

     <section anchor="GSS Server Principal" title="GSS Server Principal">
     <t>
      Regardless of what security mechanism under RPCSEC_GSS
      is being used, the NFS server MUST identify itself
      in GSS-API via a GSS_C_NT_HOSTBASED_SERVICE name type.
      GSS_C_NT_HOSTBASED_SERVICE names are of the form:
     <figure>
     <artwork>
     service@hostname
     </artwork>
     </figure>
     </t>
     <t>
      For NFS, the "service" element is
     <figure>
     <artwork>
     nfs
     </artwork>
     </figure>
     </t>
     <t>
      Implementations of security mechanisms will convert
      nfs@hostname to various different forms.  For Kerberos
      V5, the following form is RECOMMENDED:
     <figure>
     <artwork>
     nfs/hostname
     </artwork>
     </figure>
     </t>
     </section> <!-- GSS Server Principal -->
    </section> <!-- RPCSEC_GSS and Security Services -->
   </section> <!-- RPC Security Flavors -->
  </section> <!-- RPC-based Security -->
 </section> <!-- RPC and XDR -->

 <section anchor="COMPOUND and CB_COMPOUND" title="COMPOUND and CB_COMPOUND">
 <t>
   A significant departure from the versions of the NFS
   protocol before NFSv4 is the introduction of the 
   COMPOUND procedure.  For the NFSv4 protocol, 
   in all minor versions, there are exactly two RPC procedures, 
   NULL and COMPOUND.  The COMPOUND procedure is defined 
   as a series of individual operations and these operations 
   perform the sorts of functions performed by traditional 
   NFS procedures.
 </t>
 <t>
   The operations combined within a COMPOUND
   request are evaluated in order by the server, without
   any atomicity guarantees.  A limited set of facilities
   exist to pass results from one operation to another.  Once an 
   operation returns a failing result, the evaluation ends 
   and the results of all
   evaluated operations are returned to the client.
 </t>
 <t>
   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, multi-component look up requests can
   be constructed by combining multiple LOOKUP operations.  Those
   can be further combined with operations such as GETATTR, READDIR,
   or OPEN plus READ to do more complicated sets of operation without
   incurring additional latency.
 </t>
 <t>
   NFSv4.1 also contains a considerable set of
   callback operations in which the server makes an RPC
   directed at the client.  Callback RPCs have a similar
   structure to that of the normal server requests.
   In all minor versions of the NFSv4 protocol,
   there are two callback RPC procedures:
   CB_NULL and CB_COMPOUND.  The CB_COMPOUND procedure is defined 
   in an analogous fashion to that of COMPOUND 
   with its own set of callback operations.
 </t>
 <t>
   The addition of new server and callback operations within the 
   COMPOUND and CB_COMPOUND request
   framework provides a means of extending the protocol in
   subsequent minor versions.
 </t>
 <t>
   Except for a small number of operations needed for session
   creation, server requests and callback requests are performed
   within the context of a session.  Sessions provide a client
   context for every request and support robust reply 
   protection for non-idempotent requests.
 </t>
 </section> <!-- COMPOUND and CB_COMPOUND -->

 <section anchor="Client Identifiers"
  title="Client Identifiers and Client Owners">
  <t>
    For each operation that obtains or depends on locking state, the 
    specific client needs to be identifiable by the server.

  </t>
  <t>
    Each distinct client instance is represented
    by a client ID.  A client ID is a 64-bit identifier
    representing a specific client at a given time.
    The client ID is changed whenever the client re-initializes,
    and may change when the server re-initializes.
    Client IDs are used to support lock identification
    and crash recovery.

  </t>
  <t>
    During steady state operation,
    the client ID associated with each operation
    is derived from the session (see <xref target="Session"
    />) on which the operation is sent. A session is associated with
    a client ID when the session is created. 
  </t>
  <t>
    Unlike NFSv4.0, the only NFSv4.1 operations possible before a
    client ID is established are those needed to
    establish the client ID.
  </t>
  <t>
    A sequence of an EXCHANGE_ID operation followed by a 
    CREATE_SESSION operation using that client ID 
    (eir_clientid as returned from EXCHANGE_ID)
    is required to establish and confirm the
    client ID on the server.  Establishment of identification by a
    new incarnation of the client also has the effect of immediately
    releasing any locking state that a previous incarnation of that 
    same client might have had on the server.  Such released state 
    would include all byte-range lock, share reservation, layout state, and -- where the server supports neither the CLAIM_DELEGATE_PREV nor CLAIM_DELEG_CUR_FH claim types -- all delegation state associated with the same client with the same
    identity. For discussion of delegation state recovery, see
    <xref target="delegation_recovery" />. For discussion of layout state
    recovery, see <xref target="pnfs_client_recovery" />.
  </t>
  <t>
    Releasing such state requires that the server be able to determine
    that one client instance is the successor of another.  Where this
    cannot be done, for any of a number of reasons, the locking state
    will remain for a time subject to lease expiration 
    (see <xref target="lease_renewal" />)
    and the new client will need to wait for
    such state to be removed, if it makes conflicting lock requests. 
  </t>
  <t>
    Client identification is encapsulated in the following client owner
    data type:
  </t>
  <t>
<figure>
 <artwork>
struct client_owner4 {
        verifier4       co_verifier;
        opaque          co_ownerid&lt;NFS4_OPAQUE_LIMIT>;
};
 </artwork>
</figure>
  </t>
  <t>
    The first field, co_verifier, is a client incarnation
    verifier.  The server will start the process of
    canceling the client's leased state if co_verifier
    is different than what the server has previously
    recorded for the identified client (as specified in
    the co_ownerid field).

  </t>
  <t>
    The second field, co_ownerid, is a variable length string that uniquely defines
    the client so that subsequent instances of the same client bear the
    same co_ownerid with a different verifier.
  </t>
  <t>
    There are several considerations for how the client
    generates the co_ownerid string:
    <list style='symbols'>
      <t>
        The string should be unique so that multiple clients
        do not present the same string. The consequences of
        two clients presenting the same string range from
        one client getting an error to one client having its
        leased state abruptly and unexpectedly cancelled.
      </t>
      <t> 
        The string should be selected so that subsequent incarnations
        (e.g., restarts) of the same client cause the client to present 
        the same string. The implementor 
        is cautioned from an approach that requires the string to 
        be recorded in a local file because this precludes the use
        of the implementation in an environment where there is no local
        disk and all file access is from an NFSv4.1 server.
      </t>
      <t>
        The string should be the same for each server network address that
        the client accesses.
        This way, if a server has multiple interfaces, the client
        can trunk traffic over multiple network paths
        as described in <xref target="Trunking" />.
        (Note: the precise opposite was advised in the NFSv4.0
        specification <xref target="RFC3530" />.) 
      </t>
      <t>
        The algorithm for generating the string should not
        assume that the client's network address will not
        change, unless the client implementation knows it
        is using statically assigned network addresses.
        This includes changes between client incarnations
        and even changes while the client is still running
        in its current incarnation.  Thus, with dynamic
        address assignment, if the
        client includes just the client's network address
        in the co_ownerid string, there is a real risk
        that after the
        client gives up the network address, another
        client, using a similar algorithm for generating
        the co_ownerid string, would generate a conflicting
        co_ownerid string.

      </t>
    </list>
  </t>
  <t>
    Given the above considerations, an example of a well-generated co_ownerid
    string is one that includes:
  </t>
  <t>
    <list style='symbols'>
      <t>
        If applicable, the client's statically assigned network address.
      </t>
      <t>
        Additional information that tends to be unique, such as one or more
        of:
        <list style='symbols'>
          <t>
            The client machine's serial number (for privacy reasons, it is best
            to perform some one-way function on the serial number).
          </t>
          <t>
            A Media Access Control (MAC) address (again, a one-way function should be performed).
          </t>
          <t>
            The timestamp of when the NFSv4.1 software was first installed
            on the client (though this is subject to the previously mentioned
            caution about using information that is stored in a file, because the
            file might only be accessible over NFSv4.1).
          </t>
          <t>
            A true random number. However, since this number ought to be the same
            between client incarnations, this shares the same problem as that of
            using the timestamp of the software installation.
          </t>
        </list>
      </t>
      <t>
        For a user-level NFSv4.1 client, it should contain additional
        information to distinguish the client from other user-level clients
        running on the same host, such as a process identifier or other unique
        sequence.
      </t>
    </list>
  </t>
  <t>
    The client ID is assigned by the server (the eir_clientid result from EXCHANGE_ID)
    and should be chosen so that it will not
    conflict with a client ID previously assigned by the
    server.  This applies across server restarts.
   </t>
   <t>
    In the event of a server restart, a client may find
    out that its current client ID is no longer valid when
    it receives an NFS4ERR_STALE_CLIENTID error.  The precise
    circumstances depend on the characteristics of the
    sessions involved, specifically whether the session is
    persistent (see <xref target="Persistence" />), but in
    each case the client will receive this error when it attempts
    to establish a new session with the existing client ID and
    receives the error NFS4ERR_STALE_CLIENTID, indicating that a new
    client ID needs to be obtained via EXCHANGE_ID and the new session
    established with that client ID.

  </t>
  <t>
    When a session is not persistent, the client will find out that
    it needs to create a new session as a result of getting an 
    NFS4ERR_BADSESSION, since the session in question was lost
    as part of a server restart.  When the existing client ID is 
    presented to a server as part of creating a session
    and that client ID is not recognized, as would happen after a server
    restart, the server will reject the request with the error
    NFS4ERR_STALE_CLIENTID.  
  </t>
  <t>
    In the case of the session being persistent, the
    client will re-establish communication using the
    existing session after the restart.  This session
    will be associated with the existing client ID but
    may only be used to retransmit operations that the
    client previously transmitted and did not see replies
    to. Replies to operations that the server previously performed
    will come from the reply cache; otherwise,
    NFS4ERR_DEADSESSION will be returned.
    Hence, such a session is referred to as "dead". In this situation,
    in order to perform new operations, the client needs to 
    establish a new session.  If an attempt is made to 
    establish this new session with the existing client ID,
    the server will reject the request with 
    NFS4ERR_STALE_CLIENTID.
  </t>
  <t>
    When NFS4ERR_STALE_CLIENTID is received in either of
    these situations, the client needs to obtain a
    new client ID by use of the EXCHANGE_ID operation, then 
    use that client ID as the basis of a new session, and
    then proceed to
    any other necessary recovery for the server restart case (see 
    <xref target="server_failure" />). 
  </t>
  <t>
    See the descriptions of EXCHANGE_ID 
    (<xref target="OP_EXCHANGE_ID" />) and CREATE_SESSION
    (<xref target="OP_CREATE_SESSION" />) for a complete
    specification of these operations.
  </t>
  <section title="Upgrade from NFSv4.0 to NFSv4.1" >
  <t>
    To facilitate upgrade from NFSv4.0 to NFSv4.1, a server
    may compare a value of data type client_owner4 in an EXCHANGE_ID with a
    value of data type nfs_client_id4 that was established using the SETCLIENTID operation of
    NFSv4.0. A server that does so will allow
    an upgraded client to avoid waiting
    until the lease (i.e., the lease established by the NFSv4.0 instance
    client) expires.
    This requires that the value of data type client_owner4 be constructed
    the same way as the value of data type nfs_client_id4.  If the latter's
    contents included the server's network address (per the
    recommendations of the NFSv4.0 specification <xref target="RFC3530" />), and
    the NFSv4.1 client does not wish to use a client
    ID that prevents trunking, it should send two
    EXCHANGE_ID operations.  The first EXCHANGE_ID will
    have a client_owner4 equal to the nfs_client_id4.
    This will clear the state created by the NFSv4.0
    client. The second EXCHANGE_ID will not have the
    server's network address. The state created for the
    second EXCHANGE_ID will not have to wait for lease
    expiration, because there will be no state to expire.

  </t>
  </section>

   <section title="Server Release of Client ID" >
   <t>
     NFSv4.1 introduces a new operation called 
     DESTROY_CLIENTID (<xref target="OP_DESTROY_CLIENTID" />), 
     which the client SHOULD use to destroy a client ID it
     no longer needs. This permits graceful, bilateral release of
     a client ID. The operation cannot be used if there are sessions
     associated with the client ID, or state with an unexpired lease.
   </t>
   <t>
     If the server determines that the client holds no associated state
     for its client ID (associated state includes unrevoked sessions,
     opens, locks, delegations, layouts, and wants), the server MAY
     choose to unilaterally release the client ID in order to
     conserve resources.

     If the client
     contacts the server after this release, the server
     MUST ensure that the client receives the appropriate error
     so that it will use the EXCHANGE_ID/CREATE_SESSION
     sequence to establish a new client ID.
     The server ought to be very hesitant to
     release a client ID since the resulting work on the
     client to recover from such an event will be the same
     burden as if the server had failed and restarted.
     Typically, a server would not release a client ID
     unless there had been no activity from that client
     for many minutes.  As long as there are sessions,
     opens, locks, delegations, layouts, or wants, the
     server MUST NOT release the client ID. See <xref
     target="loss_of_session" /> for discussion on
     releasing inactive sessions.

   </t>
   </section> <!-- Server Release of Client ID -->
   <section title="Resolving Client Owner Conflicts" anchor="cowner_conflicts">
   <t>
     When the server gets an EXCHANGE_ID for a client owner that
     currently has no state, or that has state but the lease has expired,
     the server MUST allow the
     EXCHANGE_ID and confirm the new client ID if followed by the
     appropriate CREATE_SESSION.
   </t>
   <t>
     When the server gets an EXCHANGE_ID for a 
     new incarnation of a client owner that
     currently has an old incarnation with state and an unexpired lease, the
     server is allowed to dispose of the state of the
     previous incarnation of the client owner if
     one of the following is true:

     <list style="symbols">
     <t>
       The principal that created the client ID for the client owner
       is the same as the principal that is sending the EXCHANGE_ID operation.
       Note that if the client ID was created with
       SP4_MACH_CRED state protection (<xref target="OP_EXCHANGE_ID" />),
       the principal MUST be based on RPCSEC_GSS authentication,
       the RPCSEC_GSS service used MUST be integrity or
       privacy, and the
       same GSS mechanism and principal
       MUST be used as that used when the client ID
       was created.
     </t>
     <t>
       The client ID was established with SP4_SSV
       protection (<xref target="OP_EXCHANGE_ID" />,

    <xref target="protect_state_change" />)

       and the client sends the EXCHANGE_ID with the
       security flavor set to RPCSEC_GSS using the GSS
       SSV mechanism (<xref target="ssv_mech" />).

     </t>
     <t>
       The client ID was established with SP4_SSV
       protection, and under the conditions described herein,
       the EXCHANGE_ID was sent with SP4_MACH_CRED state protection.
       Because the SSV might not persist
       across client and server restart, and because
       the first time a client sends EXCHANGE_ID to
       a server it does not have an SSV, the client
       MAY send the subsequent EXCHANGE_ID without
       an SSV RPCSEC_GSS handle.  Instead, as with
       SP4_MACH_CRED protection, the principal MUST be
       based on RPCSEC_GSS authentication, the RPCSEC_GSS
       service used MUST be integrity or privacy, and the
       same GSS mechanism and principal MUST be used as
       that used when the client ID was created.

     </t>
     </list>
     If none of the above situations apply, the server
     MUST return NFS4ERR_CLID_INUSE.

    </t>
    <t>
     If the server accepts the principal and co_ownerid
     as matching that which created the client ID, and
     the co_verifier in the EXCHANGE_ID differs from the
     co_verifier used when the client ID was created,
     then after the server receives a CREATE_SESSION that
     confirms the client ID, the server deletes state.

     If the co_verifier values are the same (e.g., the
     client either is updating properties of the client ID
     (<xref target="OP_EXCHANGE_ID" />) or
     is attempting trunking (<xref target="Trunking" />),
     the server MUST NOT delete state.

   </t>

   </section> <!-- Handling Client Owner Conflicts -->
 </section> <!-- Client Identifiers -->
 <section anchor="Server Owners" title="Server Owners">
 <t>
  The server owner is similar to a client owner
  (<xref target="Client Identifiers" />), but unlike the
  client owner, there is no shorthand server ID.
  The server owner is defined in the following data type:
  </t>
  <t>
<figure>
 <artwork>
struct server_owner4 {
 uint64_t       so_minor_id;
 opaque         so_major_id&lt;NFS4_OPAQUE_LIMIT>;
};
 </artwork>
</figure>
  </t>
  <t>
   The server owner is returned from
   EXCHANGE_ID. When the so_major_id fields are the same in
   two EXCHANGE_ID results, the connections that each EXCHANGE_ID
   were sent over can be assumed to address the same server
   (as defined in <xref target="intro_definitions" />). If
   the so_minor_id fields are also the same, then not only
   do both connections connect to the same server, but the
   session can be shared across both
   connections. The reader is cautioned that multiple
   servers may deliberately or accidentally claim to have
   the same so_major_id or so_major_id/so_minor_id; the
   reader should examine Sections <xref target="Trunking" format="counter" /> and
   <xref target="OP_EXCHANGE_ID" format="counter" /> in order to avoid
   acting on falsely matching server owner values.
  </t>
  <t>
   The considerations for generating a so_major_id are
   similar to that for generating a co_ownerid string (see
   <xref target="Client Identifiers" />). The consequences
   of two servers generating conflicting so_major_id values
   are less dire than they are for co_ownerid conflicts
   because the client can use RPCSEC_GSS to compare the
   authenticity of each server
   (see <xref target="Trunking" />).
  </t>
 </section> <!-- Server Owners -->

 <section anchor="Security Service Negotiation" title="Security Service Negotiation">
 <t>
    With the NFSv4.1 server potentially offering
    multiple security mechanisms, the client needs a method
    to determine or negotiate which mechanism is to be
    used for its communication with the server.  The NFS
    server may have multiple points within its file system
    namespace that are available for use by NFS clients.
    These points can be considered security policy boundaries,
    and, in some NFS implementations, are tied to NFS export points.
    In turn, the NFS server may be configured such that each
    of these security policy boundaries may have different or multiple
    security mechanisms in use.
 </t>
 <t>
    The security negotiation between client and server
    SHOULD be done with a secure channel to eliminate
    the possibility of a third party intercepting the
    negotiation sequence and forcing the client and server
    to choose a lower level of security than required or
    desired.  See 
    <xref target="securityconsider" /> for further discussion.
 </t>

  <section anchor="NFSv4 Security Tuples" title="NFSv4.1 Security Tuples">
  <t>
   An NFS server can assign one or more "security tuples" to each
   security policy boundary in its namespace. Each security tuple
   consists of a security flavor
   (see <xref target="RPC Security Flavors" />) and, if the flavor
   is RPCSEC_GSS, a GSS-API mechanism Object Identifier (OID), a GSS-API quality of
   protection, and an RPCSEC_GSS service. 
  </t>
  </section> <!-- NFSv4.1 Security Tuples -->

  <section anchor="SECINFO and SECINFO_NO_NAME" title="SECINFO and SECINFO_NO_NAME">
  <t>
   The SECINFO and SECINFO_NO_NAME operations allow the client to
   determine, on a per-filehandle basis, what security tuple is to be
   used for server access.  In general, the client will not have to
   use either operation except during initial communication with the
   server or when the client crosses security policy boundaries at the
   server.  However, the server's policies may also change at any time
   and force the client to negotiate a new security tuple.
  </t>
  <t>
   Where the use of different security tuples would affect the type of
   access that would be allowed if a request was sent over the same
   connection used for the SECINFO or SECINFO_NO_NAME operation
   (e.g., read-only vs. read-write) access, security tuples that allow
   greater access should be presented first.  Where the general level
   of access is the same and different security flavors limit the
   range of principals whose privileges are recognized (e.g., allowing
   or disallowing root access), flavors supporting the greatest range
   of principals should be listed first.
  </t>
  </section> <!-- SECINFO and SECINFO_NO_NAME -->

  <section anchor="Security Error" title="Security Error">
  <t>
   Based on the assumption that each NFSv4.1 client
   and server MUST support a minimum set of security (i.e.,
   Kerberos V5 under RPCSEC_GSS),
   the NFS client will initiate file access to the server
   with one of the minimal security tuples.  During
   communication with the server, the client may receive an
   NFS error of NFS4ERR_WRONGSEC.  This error allows the
   server to notify the client that the security tuple
   currently being used contravenes the server's
   security policy. The client is then responsible for
   determining (see <xref target="using_secinfo" />) what
   security tuples are available at the server and choosing
   one that is appropriate for the client.

  </t>

  <section anchor="using_secinfo" title="Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME">
  <t>
   This section explains the mechanics of NFSv4.1 security negotiation.
  </t>

  <section anchor="putfh_series" title="Put Filehandle Operations">

  <t>

   The term "put filehandle operation" refers to
   PUTROOTFH, PUTPUBFH, PUTFH, and RESTOREFH. Each of the subsections
   herein describes how the server handles a subseries of operations
   that starts with a put filehandle operation.
  </t>

   <section anchor="PUTFH + SAVEFH"
    title="Put Filehandle Operation + SAVEFH">
   <t>
    The client is saving a filehandle for a future
    RESTOREFH, LINK, or RENAME.  SAVEFH MUST NOT
    return NFS4ERR_WRONGSEC. To determine whether or not the put
    filehandle operation returns NFS4ERR_WRONGSEC,
    the server implementation pretends SAVEFH is not in
    the series of operations and examines which of the
    situations described in the other subsections of <xref
    target="putfh_series"/> apply.

   </t>
   </section> <!-- Put Filehandle Operation + SAVEFH -->
   <section anchor="PUTFH + PUTFH"
    title="Two or More Put Filehandle Operations">
   <t>
    For a series of N put filehandle operations, the server
    MUST NOT return NFS4ERR_WRONGSEC to the first N-1 put
    filehandle operations. 

The Nth put filehandle operation
    is handled as if it is the first in a subseries of
    operations.
    For example, if the
    server received a COMPOUND request with this series of
    operations -- PUTFH, PUTROOTFH, LOOKUP -- then the
    PUTFH operation is ignored for NFS4ERR_WRONGSEC purposes, and the
    PUTROOTFH, LOOKUP subseries is processed as according
    to <xref target="PUTFH + LOOKUP"/>.
   </t>
   </section> <!-- PUTFH + PUTFH -->
   <section anchor="PUTFH + LOOKUP"
    title="Put Filehandle Operation + LOOKUP (or OPEN of an Existing Name)">
   <t>
    This situation also applies to a put filehandle operation followed
    by a LOOKUP or an OPEN operation that specifies an existing component name.
   </t>
   <t>
    In this situation, the client is potentially crossing
    a security policy boundary, and the set of security tuples
    the parent directory supports may differ from those of
    the child.
    The server implementation may decide whether to impose
    any restrictions on security policy administration.
    There are at least three approaches (sec_policy_child is
    the tuple set of the child export, sec_policy_parent is
    that of the parent).
   </t>
   <t>
   <list style="format (%c)">
   <t>
    sec_policy_child &lt;= sec_policy_parent (&lt;= for subset).
    This means that the set of security tuples specified on the
    security policy of a child directory is always a subset
    of its parent directory.
   </t>
   <t>
    sec_policy_child ^ sec_policy_parent != {} (^ for intersection, {}
    for the empty set). This means that the set of security tuples specified
    on the security policy of a child directory always has a non-empty intersection
    with that of the parent.
   </t>
   <t>
    sec_policy_child ^ sec_policy_parent == {}. This means that the
    set of security tuples specified on the security policy of a child directory
    may not intersect with that of the parent. In other words, there
    are no restrictions on how the system administrator may
    set up these tuples.
   </t>
   </list>
   </t>
   <t>
    In order for a server to support approaches (b)
    (for the case when a client chooses a flavor that is
    not a member of sec_policy_parent) and (c), the put
    filehandle operation cannot return NFS4ERR_WRONGSEC
    when there is a security tuple mismatch.  Instead,
    it should be returned from the LOOKUP (or OPEN by
    existing component name) that follows.

   </t>
   <t>
    Since the above guideline does not contradict approach
    (a), it should be followed in general. Even if approach
    (a) is implemented, it is possible for the security
    tuple used to be acceptable for the target of LOOKUP
    but not for the filehandles used in the put filehandle operation. The 
    put filehandle operation
    could be a PUTROOTFH or PUTPUBFH, where the
    client cannot know the security tuples for the root
    or public filehandle. Or the security policy for the
    filehandle used by the put filehandle operation
    could have changed since the
    time the filehandle was obtained.
   </t>
   <t>
    Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC
    in response to the put filehandle operation
    if the operation
    is immediately followed by a LOOKUP or an OPEN by component name.
   </t>
   </section> <!-- PUTFH + LOOKUP -->

   <section anchor="PUTFH + LOOKUPP" title="Put Filehandle Operation + LOOKUPP">
   <t>
    Since SECINFO only works its way down, there is no way LOOKUPP can
    return NFS4ERR_WRONGSEC without SECINFO_NO_NAME. SECINFO_NO_NAME
    solves this issue via style
    SECINFO_STYLE4_PARENT, which works in the opposite direction as SECINFO.
    As with <xref target="PUTFH + LOOKUP" />, a put filehandle operation
    that is followed by a LOOKUPP
    MUST NOT return NFS4ERR_WRONGSEC.
    If the server does not support SECINFO_NO_NAME, the client's
    only recourse is to send the put filehandle operation,
    LOOKUPP, GETFH sequence
    of operations with every security tuple it supports.
   </t>
   <t>
    Regardless of whether SECINFO_NO_NAME is supported, an
    NFSv4.1 server  MUST NOT return NFS4ERR_WRONGSEC in
    response to a put filehandle operation if the
    operation is immediately followed by a LOOKUPP.
   </t>
   </section> <!-- PUTFH + LOOKUPP -->

   <section title="Put Filehandle Operation + SECINFO/SECINFO_NO_NAME"
    anchor="PUTFH+SECINFO">
   <t>
    A security-sensitive client is allowed to choose
    a strong security tuple when querying a server to
    determine a file object's permitted security tuples.
    The security tuple chosen by the client does not have
    to be included in the tuple list of the security policy
    of either the parent directory indicated in the put filehandle
    operation or the child file object indicated in SECINFO (or any parent directory
    indicated in SECINFO_NO_NAME). Of course, the server has to be
    configured for whatever security
    tuple the client selects; otherwise, the request will
    fail at the RPC layer with an appropriate authentication error.
   </t>
   <t>
    In theory, there is no connection between the security
    flavor used by SECINFO or SECINFO_NO_NAME and those
    supported by the security policy.  But in practice, the
    client may start looking for strong flavors from those
    supported by the security policy, followed by those in
    the REQUIRED set.
   </t>
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a
    put filehandle operation that
    is immediately followed by SECINFO or SECINFO_NO_NAME.
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or
    SECINFO_NO_NAME.
   </t>
   </section> <!-- PUTFH + SECINFO -->

   <section anchor="PUTFH + Nothing" title="Put Filehandle Operation + Nothing">
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.
   </t>
   </section> <!-- PUTFH + Nothing -->

   <section anchor="PUTFH+AnythingElse" title="Put Filehandle Operation + Anything Else">
   <t>
    "Anything Else" includes OPEN by filehandle.
   </t>
   <t>
    The security policy enforcement applies to the
    filehandle specified in the put filehandle operation. Therefore, the
    put filehandle operation MUST
    return NFS4ERR_WRONGSEC when there is a security tuple
    mismatch. This avoids the complexity of
    adding NFS4ERR_WRONGSEC as an allowable error to every
    other operation.
   </t>
   <t>
    A COMPOUND containing the series put filehandle
    operation + SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an
    efficient way for the client to recover from
    NFS4ERR_WRONGSEC.
   </t>
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to
    any operation other than a put filehandle operation,
    LOOKUP, LOOKUPP, and OPEN (by component name).
   </t>
   </section> <!-- PUTFH + Anything Else -->

   <section anchor="aftersecinfo" title="Operations after SECINFO and SECINFO_NO_NAME">
   <t>

     Suppose a client sends a COMPOUND procedure
     containing the series SEQUENCE, PUTFH,
     SECINFO_NONAME, READ, and suppose the security tuple
     used does not match that required for the target
     file. By rule (see <xref target="PUTFH+SECINFO"/>),
     neither PUTFH nor SECINFO_NO_NAME can
     return NFS4ERR_WRONGSEC. By rule (see <xref
     target="PUTFH+AnythingElse"/>), READ cannot return
     NFS4ERR_WRONGSEC. The issue is resolved by the fact
     that SECINFO and SECINFO_NO_NAME consume the current
     filehandle (note that this is a change from NFSv4.0). This leaves no current filehandle for
     READ to use, and READ returns NFS4ERR_NOFILEHANDLE.

   </t>

   </section> <!-- Operations after SECINFO and SECINFO_NO_NAME" -->


  </section>
  <section anchor="link_rename" title="LINK and RENAME" >
  <t>
   The LINK and RENAME operations use both the current
   and saved filehandles.
   Technically, the server MAY return NFS4ERR_WRONGSEC from
   LINK or RENAME
   if the security policy of the
   saved filehandle rejects the security flavor used in the
   COMPOUND request's credentials.  If the server does so,
   then if there is no intersection between the security
   policies of saved and current filehandles, this means that it
   will be impossible for the client to perform the intended
   LINK or RENAME operation.

  </t>
  <t>
   For example, suppose the client sends this COMPOUND
   request: SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH,
   RENAME "c" "d", where filehandles bFH and aFH refer
   to different directories.  Suppose no common security
   tuple exists between the security policies of aFH and
   bFH. If the client sends the request using credentials
   acceptable to bFH's security policy but not aFH's
   policy, then the PUTFH aFH operation will fail with
   NFS4ERR_WRONGSEC. After a SECINFO_NO_NAME request,
   the client sends SEQUENCE, PUTFH bFH, SAVEFH, PUTFH
   aFH, RENAME "c" "d", using credentials acceptable to
   aFH's security policy but not bFH's policy. The server
   returns NFS4ERR_WRONGSEC on the RENAME operation.

  </t>
  <t>
   To prevent a client from an endless sequence of a
   request containing LINK or RENAME, followed by a request
   containing SECINFO_NO_NAME or SECINFO, the server MUST detect
   when the security policies of the current and saved
   filehandles have no mutually acceptable security tuple,
   and MUST NOT return NFS4ERR_WRONGSEC from LINK or RENAME
   in that situation. Instead
   the server MUST do one of two things:
   <list style='symbols'>

   <t>
    The server can return NFS4ERR_XDEV.
   </t>

   <t>
    The server can 
    allow the security policy of the current filehandle to
    override that of the saved filehandle, and so return NFS4_OK.
   </t>

   </list>

  </t>
  </section>

  </section> <!-- Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME -->
 </section> <!-- Security Error -->
 </section> <!-- Security Service Negotiation -->

 <section anchor="minor_versioning" title="Minor Versioning">
 <t>
  To address the requirement of an NFS protocol that can evolve as the
  need arises, the NFSv4.1 protocol contains the rules and
  framework to allow for future minor changes or versioning.
 </t>
 <t>
  The base assumption with respect to minor versioning is that any
  future accepted minor version will be
  documented in one or more Standards Track RFCs.
  Minor version 0 of the NFSv4 protocol is represented by
  <xref target="RFC3530" />, and minor version 1 is represented by
  this RFC.
  The COMPOUND and CB_COMPOUND
  procedures support the encoding of the minor version
  being requested by the client.
 </t>
 <t>
  The following items represent the basic rules for the development of
  minor versions.  Note that a future minor version may modify
  or add to the following rules as part of the minor version definition.
 <list style='numbers'>
 <t>
  Procedures are not added or deleted.
  <vspace blankLines='1' />
  To maintain the general RPC model, NFSv4 minor versions will
  not add to or delete procedures from the NFS program.
 </t>

 <t>
  Minor versions may add operations to the COMPOUND and CB_COMPOUND
  procedures.
  <vspace blankLines='1' />
  The addition of operations to the COMPOUND and CB_COMPOUND procedures
  does not affect the RPC model.

  <list style='symbols'>
  <t>
  Minor versions may append attributes to the bitmap4 that represents
  sets of attributes and to the fattr4 that represents sets of attribute 
  values.
  <vspace blankLines='1' />
  This allows for the expansion of the attribute model to allow for
  future growth or adaptation.
  </t>

  <t>
  Minor version X must append any new attributes after the last
  documented attribute.
  <vspace blankLines='1' />
  Since attribute results are specified as an opaque array of
  per-attribute, XDR-encoded results, the complexity of adding new
  attributes in the midst of the current definitions would be too
  burdensome.
  </t>
  </list>
 </t>

 <t>
 Minor versions must not modify the structure of an existing
 operation's arguments or results.
 <vspace blankLines='1' />
 Again, the complexity of handling multiple structure definitions for a
 single operation is too burdensome.  New operations should be added
 instead of modifying existing structures for a minor version.
 <vspace blankLines='1' />
 This rule does not preclude the following adaptations in a minor version:
 <list style='symbols'>
 <t>
 adding bits to flag fields, such as new attributes to GETATTR's bitmap4
 data type, and providing corresponding variants of opaque arrays,
 such as a notify4 used together with such bitmaps
 </t>
 <t>
 adding bits to existing attributes like ACLs that have flag words
 </t>
 <t>
 extending enumerated types (including NFS4ERR_*) with new values
 </t>
 <t>
 adding cases to a switched union
 </t>
 </list>
 </t>

 <t>
 Minor versions must not modify the structure of existing attributes.
 </t>

 <t>
 Minor versions must not delete operations.
 <vspace blankLines='1' />
 This prevents the potential reuse of a particular operation "slot" in
 a future minor version.
 </t>

 <t>
 Minor versions must not delete attributes.
 </t>

 <t>
 Minor versions must not delete flag bits or enumeration values.
 </t>

 <t>
 Minor versions may declare an operation MUST NOT be implemented.
 <vspace blankLines='1' />
 Specifying that an operation MUST NOT be implemented is equivalent
 to obsoleting an operation.  For the client, it means that the
 operation MUST NOT be sent to the server.  For the server, an NFS
 error can be returned as opposed to "dropping" the request as an XDR
 decode error.  This approach allows for the obsolescence of an
 operation while maintaining its structure so that a future minor version can reintroduce the operation.
 <list style='numbers'>
 <t>
 Minor versions may declare that an attribute MUST NOT be implemented.
 </t>
 <t>
 Minor versions may declare that a flag bit or enumeration value MUST NOT
 be implemented.
 </t>
 </list>
 </t>

 <t>
 Minor versions may downgrade features from REQUIRED to RECOMMENDED,
 or RECOMMENDED to OPTIONAL.
 </t>

 <t>
 Minor versions may upgrade features from OPTIONAL to RECOMMENDED, or
 RECOMMENDED to REQUIRED.
 </t>

 <t>
 A client and server that support minor version X SHOULD support minor
 versions zero through X-1 as well.

 </t>

 <t>
 Except for infrastructural changes, a minor version must not
 introduce REQUIRED new features.
 <vspace blankLines='1' />
 This rule allows for the introduction of new functionality and forces
 the use of implementation experience before designating a feature as
 REQUIRED. On the other hand, some classes of features are
 infrastructural and have broad effects. Allowing infrastructural features
 to be RECOMMENDED or OPTIONAL complicates implementation of the minor version.
 </t>

 <t>
 A client MUST NOT attempt to use a stateid, filehandle, or similar
 returned object from the COMPOUND procedure with minor version X for
 another COMPOUND procedure with minor version Y, where X != Y.
 </t>
 </list>
 </t>
 </section> <!-- Minor Versioning -->

 <section anchor="Non-RPC-based Security Services" title="Non-RPC-Based Security Services">
 <t>
  As described in
  <xref target="Authentication, Integrity, Privacy" />,
  NFSv4.1 relies on RPC for identification,
  authentication, integrity, and privacy. NFSv4.1 itself
  provides or enables additional security services as described in the
  next several subsections.
 </t>

  <section anchor="Authorization" title="Authorization">
  <t>
   Authorization to access a file object via an NFSv4.1
   operation is ultimately determined by the NFSv4.1
   server. A client can predetermine its access to a file
   object via the OPEN (<xref target="OP_OPEN" />)
   and the ACCESS (<xref target="OP_ACCESS" />)
   operations.
  </t>
  <t>
   Principals with appropriate access rights can modify the
   authorization on a file object via the SETATTR
   (<xref target="OP_SETATTR" />) operation.  Attributes that affect
   access rights include mode, owner, owner_group, acl, dacl, and
   sacl. See <xref target="file_attributes" />.
   </t>
  </section> <!-- Authorization -->

  <section anchor="Auditing" title="Auditing">
  <t>
   NFSv4.1 provides auditing on a per-file object basis, via the acl
   and sacl attributes as described in <xref target="acl" />.  It is
   outside the scope of this specification to specify audit log
   formats or management policies.
  </t>
  </section> <!-- Auditing -->

  <section anchor="Intrusion Detection" title="Intrusion Detection">
  <t>
   NFSv4.1 provides alarm control on a per-file object basis, via the
   acl and sacl attributes as described in <xref target="acl" />.
   Alarms may serve as the basis for intrusion detection.  It is
   outside the scope of this specification to specify heuristics for
   detecting intrusion via alarms.
  </t>
  </section> <!-- Intrusion Detection -->
 </section> <!-- Non-RPC-based Security Services -->

 <section anchor="Transport Layers" title="Transport Layers">

  <section anchor="Required and Recommended Transport Attributes"
   title="REQUIRED and RECOMMENDED Properties of Transports">
  <t>
   NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-based transports with
   the following attributes: 
   <list style='symbols'>
   <t>
    The transport supports reliable delivery of data, which
    NFSv4.1 requires but neither NFSv4.1 nor RPC has facilities
    for ensuring  <xref target="Chet" />.
   </t>
   <t>
    The transport delivers data in the order it was sent.
    Ordered delivery simplifies detection of transmit
    errors, and simplifies the sending of arbitrary sized
    requests and responses via the record marking
    protocol <xref target="RFC5531" />.
   </t>
   </list>
  </t>
  <t>
   Where an NFSv4.1 implementation supports operation
   over the IP network protocol, any transport used between
   NFS and IP MUST be among the IETF-approved congestion
   control transport protocols.  At the time this document
   was written, the only two transports that had the above
   attributes were TCP and the Stream
   Control Transmission Protocol (SCTP).  To enhance the
   possibilities for interoperability, an NFSv4.1
   implementation MUST support operation over the TCP
   transport protocol.
  </t>
  <t>
   Even if NFSv4.1 is used over a non-IP network
   protocol, it is RECOMMENDED that the transport support
   congestion control.
  </t>
  <t>
   It is permissible for a connectionless transport to
   be used under NFSv4.1; however, reliable and in-order
   delivery of data combined with congestion control
   by the connectionless transport is
   REQUIRED.  As a consequence, UDP by itself MUST NOT be used
   as an NFSv4.1 transport. NFSv4.1 assumes that a client transport
   address and server transport address used to send data
   over a transport together constitute a connection,
   even if the underlying transport eschews the concept
   of a connection.

  </t>
  </section> <!-- Required and Recommended Transport Attributes -->

  <section anchor="Client and Server Transport Behavior" title="Client and Server Transport Behavior">
  <t>
   If a connection-oriented transport (e.g., TCP) is used,
   the client and server SHOULD use long-lived connections
   for at least three reasons:
   <list style='numbers'>
   <t>
    This will prevent the weakening of the transport's
    congestion control mechanisms via short-lived
    connections.
   </t>
   <t>
    This will improve performance for the WAN environment
    by eliminating the need for connection setup
    handshakes.
   </t>
   <t>
    The NFSv4.1 callback model differs from NFSv4.0, and
    requires the client and server to maintain a
    client-created backchannel (see <xref target="conn_chann_assoc" />) for the server to use.
   </t>
   </list>
  </t>
  <t>
   In order to reduce congestion, if a connection-oriented
   transport is used, and the request is not the NULL
   procedure:
   <list style='symbols'>
   <t>
    A requester MUST
    NOT retry a request unless the connection the request
    was sent over was lost before the reply was
    received.
   </t>
   <t>
    A replier MUST
    NOT silently drop a request, even if the request is a
    retry.  (The silent drop behavior of RPCSEC_GSS
    <xref target="RFC2203" /> does not apply
    because this behavior happens at the RPCSEC_GSS layer,
    a lower layer in the request processing.)  Instead, the
    replier SHOULD return an appropriate error (see
    <xref target="Slot Identifiers and Server Reply Cache" />),
    or it MAY disconnect the connection.
   </t>
   </list>
  </t>


  <t>

    When sending a reply, the replier MUST send the reply
    to the same full network address (e.g., if using an
    IP-based transport, the source port of the requester
    is part of the full network address) from which the requester
    sent the request. If using a connection-oriented
    transport, replies MUST be sent on the same connection from which
    the request was received.

  </t>

  <t>

    If a connection is dropped after the replier receives
    the request but before the replier sends the reply, the
    replier might have a pending reply.
    If a connection is established with the same
    source and destination full network address as the
    dropped connection, then the replier MUST NOT send
    the reply until the requester retries the request. The
    reason for this prohibition is that the requester MAY
    retry a request over a different connection (provided that connection
    is associated with the original request's session).

   </t>


  <t>
   When using RDMA transports, there are other reasons for not
   tolerating retries over the same connection:
   <list style='symbols'>
    <t>
     RDMA transports use "credits" to enforce flow control, where
     a credit is a right to a peer to transmit a message.
     If one peer were to retransmit a request (or reply), it would
     consume an additional credit.
     If the replier
     retransmitted a reply, it would certainly result in an RDMA
     connection loss, since the requester would typically only post a
     single receive buffer for each request.  If the requester
     retransmitted a request, the additional credit consumed on the
     server might lead to RDMA connection failure unless the client
     accounted for it and decreased its available credit, leading to
     wasted resources.
    </t>
    <t>
     RDMA credits present a new issue to the reply cache in
     NFSv4.1.  The reply cache may be used when a connection within a
     session is lost, such as after the client reconnects.  Credit
     information is a dynamic property of the RDMA connection, and stale
     values must not be replayed from the cache.  This implies that the
     reply cache contents must not be blindly used when replies are
     sent from it, and credit information appropriate to the channel
     must be refreshed by the RPC layer.
    </t>
   </list>
  </t>
  <t>
   In addition, as described in
   <xref target="Retry and Replay" />, while a session is active,
   the NFSv4.1 requester MUST NOT stop waiting for a reply.
  </t>
  </section> <!-- Client and Server Transport Behavior -->

  <section anchor="Ports" title="Ports">
  <t>
   Historically, NFSv3 servers have listened over
   TCP port 2049.  The registered port 2049 <xref target="RFC3232"/>
   for the NFS protocol should be the default configuration.  NFSv4.1
   clients SHOULD NOT use the RPC binding protocols as described in
   <xref target="RFC1833"/>.
  </t>
  </section> <!-- Ports -->

 </section> <!-- Transport Layers -->

 <section anchor="Session" title="Session">
  <t>
   NFSv4.1 clients and servers MUST support and MUST use the session
   feature as described in this section.

  </t>

  <section anchor="Motivation and Overview" title="Motivation and Overview">
  <t>
   Previous versions and minor versions of NFS have suffered from
   the following:
   <list style='symbols'>
   <t>
    Lack of support for Exactly Once Semantics (EOS). This includes
    lack of support for EOS through server failure and recovery.
   </t>
   <t>
    Limited callback support, including no support for sending callbacks
    through firewalls, and races between replies to normal requests
    and callbacks.
   </t>
   <t>
    Limited trunking over multiple network paths.
   </t>
   <t>
    Requiring machine credentials for fully secure operation.
   </t>
   </list>
   Through the introduction of a session, NFSv4.1 addresses the
   above shortfalls with practical solutions:
   <list style='symbols'>
   <t>
    EOS is enabled by a reply cache with a bounded size,
    making it feasible to keep the cache in persistent storage and enable
    EOS through server failure and recovery. One reason that
    previous revisions of NFS did not support EOS was
    because some EOS approaches often limited parallelism.
    As will be explained in
    <xref target="Exactly Once Semantics" />,
    NFSv4.1 supports both EOS and unlimited parallelism.
   </t>
   <t>
    The NFSv4.1 client (defined in <xref target="intro_definitions" />,
    <xref target="client_def"/>) creates transport
    connections and provides them to the server to use for sending
    callback requests, thus solving the firewall issue
    (<xref target="OP_BIND_CONN_TO_SESSION" />). Races between
    responses from client requests and callbacks caused by
    the requests are detected via the session's sequencing
    properties that are a consequence of EOS
    (<xref target="sessions_callback_races" />).
   </t>
   <t>
    The NFSv4.1 client can associate an arbitrary number of connections with
    the session, and thus provide trunking (<xref target="Trunking" />).
   </t>
   <t>
    The NFSv4.1 client and server produces a session key independent of client
    and server machine credentials which can be
    used to compute a digest for protecting critical session management operations
    (<xref target="protect_state_change" />).
   </t>
   <t>
    The NFSv4.1 client can also create secure RPCSEC_GSS contexts
    for use by the session's backchannel that do not require
    the server to authenticate to a client machine principal
    (<xref target="Backchannel RPC Security" />).
   </t>
   </list>
  </t>
  <t>
   A session is a dynamically created, long-lived server object
   created by a client and used over time from one or more transport
   connections.  Its function is to maintain the server's state
   relative to the connection(s) belonging to a client instance.  This
   state is entirely independent of the connection itself, and indeed
   the state exists whether or not the connection exists. A client may
   have one or more sessions associated with it so that
   client-associated state may be accessed using any of the sessions
   associated with that client's client ID, when connections are
   associated with those sessions. When no connections are associated
   with any of a client ID's sessions for an extended time, such
   objects as locks, opens, delegations, layouts, etc. are subject to
   expiration.  The session serves as an object representing a means
   of access by a client to the associated client state on the server,
   independent of the physical means of access to that state.
  </t>
  <t>
   A single client may create multiple sessions. A single session MUST
   NOT serve multiple clients.
  </t>
  </section> <!-- Motivation and Overview -->

  <section anchor="NFSv4 Integration" title="NFSv4 Integration">
  <t>
   Sessions are part of NFSv4.1 and not NFSv4.0. Normally, a major
   infrastructure change such as sessions would require a new major
   version number to an Open Network Computing (ONC) RPC program like
   NFS. However, because NFSv4 encapsulates its functionality in a single procedure, COMPOUND,
   and because COMPOUND can support an arbitrary number of
   operations, sessions have been added to NFSv4.1 with little difficulty. COMPOUND includes
   a minor version number field, and for NFSv4.1 this minor version
   is set to 1. When the NFSv4 server processes a COMPOUND with 
   the minor version set to 1, it expects a different set of
   operations than it does for NFSv4.0. NFSv4.1 defines the
   SEQUENCE operation, which is required for every
   COMPOUND that operates over an established session, with the
   exception of some session administration operations, such
   as DESTROY_SESSION (<xref target="OP_DESTROY_SESSION" />).
  </t>

   <section anchor="SEQUENCE and CB_SEQUENCE" title="SEQUENCE and CB_SEQUENCE">
    <t>
     In NFSv4.1, when the SEQUENCE operation is present, it MUST be
     the first operation in the COMPOUND procedure. The primary purpose
     of SEQUENCE is to carry the session identifier. The session identifier
     associates all other operations in the COMPOUND procedure with
     a particular session. SEQUENCE also contains required information
     for maintaining EOS (see <xref target="Exactly Once Semantics" />).
     Session-enabled NFSv4.1 COMPOUND requests thus have the form:
    </t>
    <figure>
    <artwork>
    +-----+--------------+-----------+------------+-----------+----
    | tag | minorversion | numops    |SEQUENCE op | op + args | ...
    |     |   (== 1)     | (limited) |  + args    |           |
    +-----+--------------+-----------+------------+-----------+----
    </artwork>
    </figure>

    <t>
    and the replies have the form:
    </t>

    <figure>
    <artwork>
    +------------+-----+--------+-------------------------------+--//
    |last status | tag | numres |status + SEQUENCE op + results |  //
    +------------+-----+--------+-------------------------------+--//
            //-----------------------+----
            // status + op + results | ...
            //-----------------------+----
    </artwork>
    </figure>
    <t>
     A CB_COMPOUND procedure request and reply has a similar form to
     COMPOUND, but
     instead of a SEQUENCE operation, there is a CB_SEQUENCE operation.
     CB_COMPOUND also has an additional field called "callback_ident", which
     is superfluous in NFSv4.1 and MUST be ignored by
     the client. CB_SEQUENCE has the same information
     as SEQUENCE, and also includes other information needed to resolve
     callback races
    (<xref target="sessions_callback_races" />).
    </t>
   </section> <!-- SEQUENCE and CB_SEQUENCE -->

   <section anchor="Client ID and Session Association" title="Client ID and Session Association">
   <t>
    Each client ID (<xref target="Client Identifiers" />) can have
    zero or more active sessions. A client ID and associated
    session are required to perform file access in 
    NFSv4.1. Each time a session is used (whether by a client sending
    a request to the server or the client replying to a callback
    request from the server), the state leased to its associated
    client ID is automatically renewed.

   </t>
   <t>
    State (which can consist of share reservations, locks, delegations,
    and layouts (<xref target="intro_locking" />)) is tied to
    the client ID. Client state is not tied to any individual session.
    Successive state changing operations from a given state
    owner MAY go over different sessions, provided the
    session is associated with the same client ID. A callback
    MAY arrive over a different session than that of the request
    that originally acquired the state pertaining to the
    callback. For example, if session A is used to
    acquire a delegation, a request to recall the
    delegation MAY arrive over session B if both sessions are
    associated with the same client ID. Sections
    <xref target="Session Callback Security" format="counter"/> and
    <xref target="Backchannel RPC Security" format="counter"/> discuss
    the security considerations around callbacks.
   </t>
    
   </section> <!-- Client ID and Session Association -->
  </section> <!-- NFSv4 Integration -->

  <section anchor="Channels" title="Channels">
  <t>
   A channel is not a connection. A channel represents the
   direction ONC RPC requests are sent.
  </t>
  <t>
   Each session has one or two channels: the fore channel and the backchannel.
   Because there are at most two channels per session, and because each
   channel has a distinct purpose, channels are not assigned
   identifiers.
  </t>
  <t>
   The fore channel is
   used for ordinary requests from the client to the server, and
   carries COMPOUND requests and responses.
   A session always has a fore channel.
  </t>
  <t>
   The backchannel is used for callback requests from server
   to client, and carries CB_COMPOUND requests and responses.
   Whether or not there is a backchannel is a decision made by the
   client; however, many features of NFSv4.1 require a backchannel.
   NFSv4.1 servers MUST support backchannels.
  </t>
  <t>
   Each session has resources for each channel,
   including separate reply caches (see
   <xref target="Slot Identifiers and Server Reply Cache" />).

   Note that even the backchannel requires a reply cache (or, at least,
   a slot table in order to detect retries) because
   some callback operations are nonidempotent.
  </t>

   <section anchor="conn_chann_assoc" title="Association of Connections, Channels, and Sessions"> 
   <t>
    Each channel is associated with zero or more transport
    connections (whether of the same transport protocol or different
    transport protocols).  A connection can be associated with
    one channel or both channels of a session; the client
    and server negotiate whether a connection will carry
    traffic for one channel or both channels via the
    CREATE_SESSION (<xref target="OP_CREATE_SESSION"
    />) and the BIND_CONN_TO_SESSION (<xref
    target="OP_BIND_CONN_TO_SESSION" />) operations. When a
    session is created via CREATE_SESSION, the connection
    that transported the CREATE_SESSION request is
    automatically associated with the fore channel, and
    optionally the backchannel. If the client specifies no
    state protection (<xref target="OP_EXCHANGE_ID" />)
    when the session is created, then when SEQUENCE is
    transmitted on a different connection, the connection
    is automatically associated with the fore channel of
    the session specified in the SEQUENCE operation.

   </t>
   <t>
    A connection's association with a session is
    not exclusive.  A connection associated with the channel(s)
    of one session may be simultaneously
    associated with the channel(s) of other sessions including
    sessions associated with other client IDs.

   </t>
   <t>
    It is permissible for connections of multiple transport
    types to be associated with the same channel. For
    example, both TCP and RDMA connections can be
    associated with the fore channel.  In the event an
    RDMA and non-RDMA connection are associated with the
    same channel, the maximum number of slots SHOULD be
    at least one more than the total number of RDMA credits
    (<xref target="Slot Identifiers and Server Reply Cache" />).
   This way, if all RDMA credits are used, the non-RDMA
   connection can have at least one outstanding request.
   If a server supports multiple transport types, it MUST
   allow a client to associate connections from each transport
   to a channel.

   </t>
   <t>
    It is permissible for a connection of one type of
    transport to be associated with the fore channel,
    and a connection of a different type to be associated
    with the backchannel.

   </t>
   </section>
  </section> <!-- Channels -->
  <section anchor="Server Scope" title="Server Scope">
    <t>
      Servers each specify a server scope value in the form
      of an opaque string eir_server_scope returned as part of
      the results of an EXCHANGE_ID operation.  The purpose of
      the server scope is to allow a group of servers to 
      indicate to clients that a set of servers sharing the 
      same server scope value has arranged to use compatible 
      values of otherwise opaque identifiers. Thus, the identifiers
      generated by one server of that set may be presented to
      another of that same scope.
    </t>
    <t>
      The use of such compatible values does not imply that
      a value generated by one server will always be accepted
      by another.  In most cases, it will not.  However, a
      server will not accept a value generated by another
      inadvertently.  When it does accept it, it will be because
      it is recognized as valid and carrying the same meaning  
      as on another server of the same scope.
    </t>
    <t>
      When servers are of the same server scope, this compatibility
      of values applies to the follow identifiers:
      <list style="symbols">
        <t>
          Filehandle values.  A filehandle value accepted by two 
          servers of the same server scope denotes the same object.
          A WRITE operation sent to one server is reflected immediately
          in a READ sent to the other, and locks obtained on one
          server conflict with those requested on the other. 
        </t>
        <t>
          Session ID values.  A session ID value accepted by two
          servers of the same server scope denotes the same session. 
        </t>
        <t>
          Client ID values.  A client ID value accepted as valid by
          two servers of the same server scope is associated with 
          two clients with the same client owner and verifier.
        </t>
        <t>
         State ID values.  A state ID value is recognized as valid
when the corresponding client ID is recognized as valid.

If the same stateid value is accepted as valid
          on two servers of the same scope and the client IDs on
          the two servers represent the same client owner and 
          verifier, then the two stateid values designate the
          same set of locks and are for the same file.
        </t>
        <t>
          Server owner values.  When the server scope values are 
          the same, server owner value may be validly compared.  
          In cases where the server scope values are different, server 
          owner values are treated as different even if they 
          contain all identical bytes.
        </t>
      </list>
    </t>
    <t>
      The coordination among servers required to provide such
      compatibility can be quite minimal, and limited to a simple
      partition of the ID space.  The recognition of common values
      requires additional implementation, but this can be tailored
      to the specific situations in which that recognition is 
      desired.
    </t>
    <t>
      Clients will have occasion to compare the server scope values
      of multiple servers under a number of circumstances, each of
      which will be discussed under the appropriate functional 
      section:
      <list style="symbols">
        <t>
          When server owner values received in response to 
          EXCHANGE_ID operations sent to multiple network
          addresses are compared for the purpose of determining
          the validity of various forms of trunking, as described
          in <xref target="Trunking" />. 
        </t>
        <t>
          When network or server reconfiguration causes the same
          network address to possibly be directed to different
          servers, with the necessity for the client to determine
          when lock reclaim should be attempted, as described
          in <xref target="reclaim_locks" />.
        </t>
        <t>
          When file system migration causes the transfer of
          responsibility for a file system between servers and
          the client needs to determine whether state has been
          transferred with the file system (as described in <xref
          target="transition_state"/>) or whether the
          client needs to reclaim state on a similar basis as in the
	  case of server restart, as described in <xref
	  target="server_failure"/>.

        </t>
      </list>
    </t>
    <t>
      When two replies from EXCHANGE_ID, each from two different
      server network addresses, have the same server scope, there
      are a number of ways a client can validate that the common
      server scope is due to two servers cooperating in a group.
      <list style="symbols">
        <t>
          If both EXCHANGE_ID requests were sent with RPCSEC_GSS
          authentication and the server principal is the same for 
          both targets, the equality of server scope is validated. 
          It is RECOMMENDED that two servers intending to share the
          same server scope also share the same principal name.
        </t>
        <t>
          The client may accept the appearance of the second
          server in the fs_locations or fs_locations_info attribute
          for a relevant file system.  For example, if there is
          a migration event for a particular file system
          or there are locks to be reclaimed on a particular file
          system, the attributes for that particular file system
          may be used.  The client sends the GETATTR request to 
          the first server for the fs_locations or 
          fs_locations_info attribute with RPCSEC_GSS 
          authentication.  It may need to do this in advance
          of the need to verify the common server scope.
          If the client successfully authenticates the reply 
          to GETATTR, and the GETATTR request and reply containing 
          the fs_locations or fs_locations_info attribute refers 
          to the second server, then the equality of server scope 
          is supported.  A client may choose to limit the use of
          this form of support to information relevant to the
          specific file system involved (e.g. a file system 
          being migrated).
        </t>
      </list>  
    </t>
  </section> <!-- Server Scope -->
  <section anchor="Trunking" title="Trunking">
    <t>
     Trunking is the use of multiple connections between a
     client and server in order to increase the speed of data
     transfer. NFSv4.1 supports two types of trunking:
     session trunking and client ID trunking. 
    </t>
    <t>
     NFSv4.1
     servers MUST support both forms of trunking within
     the context of a single server network address and
     MUST support both forms within the context of the
     set of network addresses used to access a single server.
     NFSv4.1 servers in a clustered configuration MAY allow
     network addresses for different servers to use client ID
     trunking.
    </t>
    <t> 
     Clients may use either form of trunking as long as they
     do not, when trunking between different server network 
     addresses, violate the servers' mandates as to the 
     kinds of trunking to be allowed (see below).  With regard 
     to callback channels, the client MUST allow the server to 
     choose among all callback channels valid for a given 
     client ID and MUST support trunking when the connections
     supporting the backchannel allow session or client ID 
     trunking to be used for callbacks.
    </t>
    <t>
     Session trunking is essentially the association of multiple
     connections, each with potentially different target and/or source
     network addresses, to the same session.  When the target network
     addresses (server addresses) of the two connections are the same, 
     the server MUST
     support such session trunking.  When the target network addresses
     are different, the server MAY indicate such support using the
     data returned by the EXCHANGE_ID operation (see below).
    </t>
    <t>
     Client ID trunking is the association of multiple
     sessions to the same client ID.  Servers MUST support client ID
     trunking for two target network addresses whenever they allow 
     session trunking for those same two network addresses.
     In addition, a server MAY, by presenting the same
     major server owner ID
     (<xref target="Server Owners" />) and server scope
     (<xref target="Server Scope" />), allow an additional 
     case of client ID trunking.  When two
     servers return the same major server owner and server
     scope, it means that the two servers are cooperating on
     locking state management, which is a prerequisite
     for client ID trunking.

    </t>
    <t>
     Distinguishing when the client is allowed to use session and
     client ID trunking requires understanding how the results of the
     EXCHANGE_ID (<xref target="OP_EXCHANGE_ID" />)
     operation identify a server.
     Suppose a client sends EXCHANGE_IDs over two different
     connections, each with a possibly different target
     network address, but each EXCHANGE_ID operation has the same
     value in the eia_clientowner field.  If the same
     NFSv4.1 server is listening over each connection,
     then each EXCHANGE_ID result MUST return the same
     values of eir_clientid, eir_server_owner.so_major_id,
     and eir_server_scope. The client can then treat each
     connection as referring to the same server (subject
     to verification; see
     <xref target="trust_but_verify" /> later in this section),
     and it can use each connection to trunk requests and
     replies.  

The client's choice is whether session trunking
     or client ID trunking applies.

    <list style="hanging">

    <t hangText="Session Trunking.">

     If the eia_clientowner argument is the same in
     two different EXCHANGE_ID requests, and
     the eir_clientid, eir_server_owner.so_major_id,
     eir_server_owner.so_minor_id, and eir_server_scope
     results match in both EXCHANGE_ID results, then
     the client is permitted to perform session trunking.
     If the client has no session mapping to the tuple of
     eir_clientid, eir_server_owner.so_major_id, eir_server_scope, and
     eir_server_owner.so_minor_id, then it creates
     the session via a CREATE_SESSION operation over one
     of the connections, which associates the connection
     to the session. If there is a session for the tuple,
     the client can send BIND_CONN_TO_SESSION to associate
     the connection to the session. 
      <vspace blankLines='1' />
     Of course, if the client
     does not desire to use session trunking, it is not 
     required to do so.  It can invoke
     CREATE_SESSION on the connection. This will result
     in client ID trunking as described below.  It can also
     decide to drop the connection if it does not choose to
     use trunking.
      <vspace blankLines='1' />

    </t>

    <t hangText="Client ID Trunking.">

     If the eia_clientowner argument is the same in
     two different EXCHANGE_ID requests, and
     the eir_clientid, eir_server_owner.so_major_id,
     and eir_server_scope
     results match in both EXCHANGE_ID results, then
     the client is permitted to perform client ID trunking
     (regardless of whether the eir_server_owner.so_minor_id results match).
     The client can associate
     each connection with different sessions, where
     each session is associated with the same server.

      <vspace blankLines='1' />

     The client completes the act of client ID trunking by invoking
     CREATE_SESSION on each connection, using the same
     client ID that was returned in eir_clientid. These
     invocations create two sessions and also associate
     each connection with its respective session.  The client 
     is free to decline to use client ID trunking by simply
     dropping the connection at this point.

      <vspace blankLines='1' />

     When doing client ID trunking, locking state
     is shared across sessions associated with that same
     client ID. This requires the server to coordinate
     state across sessions.

    </t>

    </list>

    </t>
    <t>
      The client should be prepared for the possibility
      that eir_server_owner values may be different on
      subsequent EXCHANGE_ID requests made to the same 
      network address, as a result of  various sorts of 
      reconfiguration events.  When this happens and the
      changes result in the invalidation of previously 
      valid forms of trunking, the client should cease 
      to use those forms, either by dropping connections 
      or by adding sessions.  For a discussion of lock 
      reclaim as it relates to such reconfiguration events,
      see <xref target="reclaim_locks" />. 
    </t>

    <section title="Verifying Claims of Matching Server Identity" anchor="trust_but_verify">
    <t>
     When two servers over two connections claim
     matching or partially matching eir_server_owner,
     eir_server_scope, and eir_clientid values, the client
     does not have to trust the servers' claims. The client
     may verify these claims before trunking traffic in
     the following ways:

    <list style='symbols'>

     <t>
      For session trunking,
      clients SHOULD
      reliably verify if connections between different
      network paths are in fact associated with the same NFSv4.1
      server and usable on the same session, and servers
      MUST allow clients to perform reliable verification.
      When a client ID is created, the client SHOULD specify that
      BIND_CONN_TO_SESSION is to be verified according to the
      SP4_SSV or SP4_MACH_CRED (<xref target="OP_EXCHANGE_ID" />)
      state protection options.  For SP4_SSV, reliable
      verification depends on a shared secret (the
      SSV) that is established via the SET_SSV (<xref
      target="OP_SET_SSV" />) operation. 

      <vspace blankLines='1' />

      When a new connection is associated with the
      session (via the BIND_CONN_TO_SESSION operation,
      see <xref target="OP_BIND_CONN_TO_SESSION" />), if
      the client specified SP4_SSV state protection for the
      BIND_CONN_TO_SESSION operation, the client MUST send
      the BIND_CONN_TO_SESSION with RPCSEC_GSS protection,
      using integrity or privacy, and an RPCSEC_GSS handle created
      with the GSS SSV mechanism (<xref
      target="ssv_mech" />).

      <vspace blankLines='1' />

      If the client mistakenly tries to associate a
      connection to a session of a wrong server, the
      server will either reject the attempt because
      it is not aware of the session identifier of the
      BIND_CONN_TO_SESSION arguments, or it will reject
      the attempt because the RPCSEC_GSS authentication
      fails.  Even if the server mistakenly or maliciously
      accepts the connection association attempt, the
      RPCSEC_GSS verifier it computes in the response
      will not be verified by the client, so the client will
      know it cannot use the connection for trunking the
      specified session.  <vspace blankLines='1' /> If the
      client specified SP4_MACH_CRED state protection, the
      BIND_CONN_TO_SESSION operation will use RPCSEC_GSS
      integrity or privacy, using the same credential that
      was used when the client ID was created. Mutual
      authentication via RPCSEC_GSS assures the client
      that the connection is associated with the correct
      session of the correct server.

      <vspace blankLines='1' />
     </t>
     <t>
      For client ID trunking, the client has at least two
      options for verifying that the same client ID
      obtained from two different EXCHANGE_ID operations
      came from the same server.  The first option is
      to use RPCSEC_GSS authentication when sending each
      EXCHANGE_ID operation. Each time an EXCHANGE_ID is sent with
      RPCSEC_GSS authentication, the client notes the
      principal name of the GSS target.  If the EXCHANGE_ID
      results indicate that client ID trunking is possible,
      and the GSS targets' principal names are the same,
      the servers are the same and client ID trunking is
      allowed.

      <vspace blankLines='1' />

      The second option for verification is to
      use SP4_SSV protection.  When the client sends
      EXCHANGE_ID, it specifies SP4_SSV protection. The
      first EXCHANGE_ID the client sends always has to
      be confirmed by a CREATE_SESSION call. The client
      then sends SET_SSV. Later, the client
      sends EXCHANGE_ID to a second destination
      network address different from the one the first 
      EXCHANGE_ID was sent to.
      The client checks that each EXCHANGE_ID reply has the
      same eir_clientid, eir_server_owner.so_major_id, and
      eir_server_scope. If so, the client verifies the
      claim by sending a CREATE_SESSION operation to the second
      destination address, protected with RPCSEC_GSS integrity
      using an RPCSEC_GSS handle returned by the second
      EXCHANGE_ID. If the server accepts the CREATE_SESSION
      request, and if the client verifies the RPCSEC_GSS
      verifier and integrity codes, then the client has
      proof the second server knows the SSV, and thus
      the two servers are cooperating for the purposes of
      specifying server scope and client ID trunking.

     </t>
    </list>
    </t>
    </section> <!-- Verifying Claims of Matching Server Identity -->
  </section> <!-- Trunking -->

  <section anchor="Exactly Once Semantics" title="Exactly Once Semantics">
  <t>
   Via the session, NFSv4.1 offers exactly once semantics (EOS)
   for requests sent over a channel. EOS is supported on both the
   fore channel and backchannel.
  </t>
  <t>
   Each COMPOUND or CB_COMPOUND request that is sent
   with a leading SEQUENCE or CB_SEQUENCE operation MUST
   be executed by the receiver exactly once. This requirement
   holds regardless of whether the request is sent with reply
   caching specified (see <xref target="optional_reply_caching" />).
   The requirement holds even if the requester is sending the
   request over a session created between a pNFS data client
   and pNFS data server. To understand the rationale for this requirement,
   divide the requests into three
   classifications:
   <list style='symbols'>
   <t>
    Non-idempotent requests.
   </t>
   <t>
    Idempotent modifying requests. 
   </t>
   <t>
    Idempotent non-modifying requests. 
   </t>
   </list>
    An example of a non-idempotent request is
    RENAME. Obviously, if a replier executes the
    same RENAME request twice, and the first execution succeeds,
    the re-execution will fail. If the replier returns the
    result from the re-execution, this result is incorrect.
    Therefore, EOS is required for non-idempotent requests.
   </t>
   <t>
    An example of an idempotent modifying request is
    a COMPOUND request containing a WRITE operation.
    Repeated execution of the same WRITE
    has the same effect as execution of that WRITE a single time.
    Nevertheless, enforcing EOS for WRITEs and other idempotent
    modifying requests is necessary
    to avoid data corruption.
   </t>
   <t>
    Suppose a client sends WRITE A to a
    noncompliant server that does not enforce EOS, and
    receives no response, perhaps due to a network
    partition.  The client reconnects to the server and
    re-sends WRITE A. Now, the server has
    outstanding two instances of A.  The
    server can be in a situation in which it executes and
    replies to the retry of A, while the first
    A is still waiting in the server's internal I/O system for some
    resource.  Upon receiving the
    reply to the second attempt of WRITE A,
    the client believes its WRITE is done so it is free
    to send WRITE B, which overlaps the byte-range of
    A.  When the original A is dispatched from the server's
    I/O system and
    executed (thus the second time A will have
    been written), then what has been
    written by B can be overwritten and thus corrupted.
   </t>
   <t>
    An example of an idempotent non-modifying request
    is a COMPOUND containing SEQUENCE, PUTFH, READLINK,
    and nothing else. The re-execution of such a
    request will not cause data corruption or
    produce an incorrect result. Nonetheless,
    to keep the implementation simple,
    the replier MUST enforce EOS for all requests, whether or not
    idempotent and non-modifying.
   </t>
   <t>
    Note that true and complete EOS is not possible unless the
    server persists the reply cache in stable storage, and unless the
    server is somehow implemented to never require a restart
    (indeed, if such a server exists, the distinction between a
    reply cache kept in stable storage versus one that is not is
    one without meaning). See <xref target="Persistence" /> for
    a discussion of persistence in the reply cache.
    Regardless, even if the server does not persist the reply cache,
    EOS improves robustness and correctness over previous versions
    of NFS because the legacy duplicate request/reply caches were
    based on the ONC RPC transaction identifier (XID). 
    <xref target="Slot Identifiers and Server Reply Cache" />
    explains the shortcomings of the XID as a basis for
   a reply cache and describes how NFSv4.1 sessions improve
   upon the XID.
   </t>

    <section anchor="Slot Identifiers and Server Reply Cache"
     title="Slot Identifiers and Reply Cache">
    <t>
     The RPC layer provides a transaction ID (XID), which,
     while required to be unique, is not
     convenient for tracking requests for two reasons.
     First, the XID is only
     meaningful to the requester; it cannot be interpreted
     by the replier except to test for equality with
     previously sent requests. When consulting an RPC-based
     duplicate request cache, the opaqueness of the XID requires
     a computationally expensive look up (often via a hash that
     includes XID and source address). NFSv4.1 requests use
     a non-opaque slot ID, which is an index into a slot table,
     which is far more efficient. Second, because RPC requests
     can be executed by the replier in any order, there is
     no bound on the number of requests that may be outstanding
     at any time. To achieve perfect EOS, using ONC RPC
     would require storing all replies in the reply cache.
     XIDs are 32 bits; storing over four billion (2^32) replies
     in the reply cache is not practical. In practice, previous versions
     of NFS have chosen to store a fixed number of replies in
     the cache, and to use a least recently used (LRU) approach to
     replacing cache entries with new entries when the cache
     is full. In NFSv4.1, the number of outstanding requests is
     bounded by the size of the slot table, and a sequence ID
     per slot is used to tell the replier when it is safe to
     delete a cached reply.
    </t>
    <t>
     In the NFSv4.1 reply cache, when the requester sends a new request,
     it selects a slot ID in the
     range 0..N, where N is the replier's current maximum slot ID
     granted to the requester on the session over which the request is to be
     sent. The value of N starts out as equal to
     ca_maxrequests - 1 (<xref target="OP_CREATE_SESSION" />), but
     can be adjusted by the response to SEQUENCE or CB_SEQUENCE as described
     later in this section.
     The slot ID must be unused by any of the requests that the
     requester has already active on the session.  "Unused" here means the
     requester has no outstanding request for that slot ID.
    </t>
    <t>
     A slot contains a sequence ID and the cached reply corresponding to
     the request sent with that sequence ID. The sequence ID is a
     32-bit unsigned value, and is therefore in the range 0..0xFFFFFFFF (2^32 - 1).
     The first time a slot is used, the requester MUST specify
     a sequence ID of one (<xref target="OP_CREATE_SESSION" />).
     Each time a slot is reused, the request MUST specify a sequence ID
     that is one greater than that of the previous request on the
     slot. If the previous sequence ID was 0xFFFFFFFF, then the next
     request for the slot MUST have the sequence ID set to zero (i.e.,
     (2^32 - 1) + 1 mod 2^32).
    </t>
    <t>
     The sequence ID accompanies the slot ID in each request. It is
     for the critical check at the replier: it used to efficiently
     determine whether a request using a certain
     slot ID is a retransmit or a new, never-before-seen request.  It is
     not feasible for the requester to assert that it is retransmitting to
     implement this, because for any given request the requester cannot
     know whether the replier has seen it unless the replier actually replies.  Of
     course, if the requester has seen the reply, the requester would
     not retransmit.
    </t>
    <t>
     The replier compares each received request's
     sequence ID with the last one previously received for that slot ID,
     to see if the new request is:
    </t>
    <t>
    <list style="symbols">
     <t>
      A new request, in which the sequence ID is one greater
      than that previously seen in the slot (accounting for sequence
      wraparound).  The replier proceeds to execute the new request,
      and the replier
      MUST increase the slot's sequence ID by one.
     </t>
     <t>
      A retransmitted request, in which the sequence ID is equal to
      that currently recorded in the slot. 
      If the original request has
      executed to completion, the replier returns the cached
      reply. See <xref target="Retry and Replay" /> for direction on how the replier
      deals with retries of requests that are still in progress.
     </t>
     <t>
      A misordered retry, in which the sequence ID
      is less than (accounting for sequence wraparound)
      that previously seen in the slot.  The
      replier MUST return NFS4ERR_SEQ_MISORDERED (as the
      result from SEQUENCE or CB_SEQUENCE).
     </t>
     <t>
      A misordered new request, in which the sequence ID
      is two or more than (accounting for sequence
      wraparound) that previously seen in the
      slot. Note that because the sequence ID MUST
      wrap around to zero once it reaches 0xFFFFFFFF, a
      misordered new request and a misordered retry
      cannot be distinguished. Thus, the replier MUST
      return NFS4ERR_SEQ_MISORDERED (as the result from
      SEQUENCE or CB_SEQUENCE).
     </t>
    </list>
    </t>
    <t>
     Unlike the XID, the slot ID is always within a specific
     range; this has two implications.  The first
     implication is that for a given session, the replier
     need only cache the results of a limited number of
     COMPOUND requests.
     The second implication derives
     from the first, which is that unlike XID-indexed reply
     caches (also known as duplicate request caches - DRCs),
     the slot ID-based reply cache cannot be overflowed.
     Through use of the sequence ID to identify
     retransmitted requests, the replier does not need to
     actually cache the request itself, reducing the
     storage requirements of the reply cache further.  These
     facilities make it practical to maintain all the
     required entries for an effective reply cache.

    </t>
    <t>
     The slot ID, sequence ID, and session ID therefore take over the traditional role
     of the XID and source network address in the replier's
     reply cache implementation.
     This approach is considerably
     more portable and completely robust -- it is not subject to the
     reassignment of ports as clients reconnect over IP
     networks.  In addition, the RPC XID is not used in the reply cache,
     enhancing robustness of the cache in the face of any rapid reuse of
     XIDs by the requester. While the replier does not care
     about the XID for the purposes of reply cache management
     (but the replier MUST return the same XID that was in the request),
     nonetheless there are considerations for the XID in NFSv4.1
     that are the same as all other previous versions of NFS.
     The RPC XID remains in each message and needs to be formulated
     in NFSv4.1 requests as in any other ONC RPC request. The reasons
     include:
    <list style="symbols">
    <t>
     The RPC layer retains its existing semantics and implementation.
    </t>
    <t>
     The requester and replier must be able to interoperate at the
     RPC layer, prior to the NFSv4.1 decoding of the SEQUENCE or CB_SEQUENCE
     operation.
    </t>
    <t>
     If an operation is being used that does not start with
     SEQUENCE or CB_SEQUENCE (e.g., BIND_CONN_TO_SESSION),
     then the RPC XID is needed for correct operation to
     match the reply to the request.

    </t>
    <t>
     The SEQUENCE or CB_SEQUENCE operation may generate an error.
     If so, the embedded slot ID, sequence ID, and session ID (if
     present) in the request will not be in the reply, and the
     requester has only the XID to match the reply to the request.
    </t>
    </list>
    </t>
    <t>
     Given that well-formulated XIDs continue to be required,
     this begs the question: why do SEQUENCE and CB_SEQUENCE replies
     have a session ID, slot ID, and sequence ID? Having the session ID
     in the reply means that the requester does not have to use the
     XID to look up
     the session ID, which would be necessary if the connection were
     associated with multiple sessions. Having the slot ID and sequence ID
     in the reply means that the requester does not have to use the XID to
     look up the slot ID and sequence ID.
     Furthermore, since the XID is only 32 bits, it is too small to
     guarantee the re-association of a reply with its request 
     <xref target="rpc_xid_issues" />; having
     session ID, slot ID, and sequence ID in the reply allows the
     client to validate that the reply in fact belongs to the matched request.
    </t>
    <t>
     The SEQUENCE (and CB_SEQUENCE) operation also carries
     a "highest_slotid" value, which carries additional
     requester slot usage information.  The requester MUST
     always indicate the slot ID representing the outstanding request with the
     highest-numbered slot
     value.
     The requester should in all cases provide the most
     conservative value possible, although it can be increased somewhat
     above the actual instantaneous usage to maintain some minimum or
     optimal level.  This provides a way for the requester to yield unused
     request slots back to the replier, which in turn can use the
     information to reallocate resources. 
    </t>
    <t>
     The replier
     responds with both a new target highest_slotid and an
     enforced highest_slotid, described as follows:
     <list style="symbols">
     <t>
      The target highest_slotid is
      an indication to the requester of the highest_slotid the replier
      wishes the requester to be using.  This permits the replier to withdraw
      (or add) resources from a requester that has been found to not be
      using them, in order to more fairly share resources among a varying
      level of demand from other requesters.  The requester must always comply
      with the replier's value updates, since they indicate newly
      established hard limits on the requester's access to session
      resources.  However, because of request pipelining, the requester may
      have active requests in flight reflecting prior values; therefore,
      the replier must not immediately require the requester to comply.
      <vspace blankLines='1' />
     </t>
     <t>
      The enforced highest_slotid indicates the highest slot ID
      the requester is permitted to use on a subsequent SEQUENCE or
      CB_SEQUENCE operation. The replier's enforced highest_slotid SHOULD
      be no less than the highest_slotid the requester indicated
      in the SEQUENCE or CB_SEQUENCE arguments.

      <vspace blankLines='1' />

      A requester can be intransigent with respect to lowering its
      highest_slotid argument to a Sequence operation, i.e. the requester
      continues to ignore the target highest_slotid in the response to
      a Sequence operation, and continues to set its highest_slotid
      argument to be higher than the target highest_slotid. This can
      be considered particularly egregious behavior when the replier
      knows there are no outstanding requests with slot IDs higher than
      its target highest_slotid.  When faced with such intransigence,
      the replier is free to take more forceful action, and MAY reply with
      a new enforced highest_slotid that is less than its previous
      enforced highest_slotid.  Thereafter, if the requester continues
      to send requests with a highest_slotid that is greater than
      the replier's new enforced highest_slotid, the server MAY return
      NFS4ERR_BAD_HIGH_SLOT, unless the slot ID in the request is greater
      than the new enforced highest_slotid and the request is a retry.

      <vspace blankLines='1' />

      The replier SHOULD retain the slots it wants to retire
      until
      the requester sends a request with a highest_slotid less than
      or equal to the replier's new enforced highest_slotid. 

      <vspace blankLines='1' />

      The requester can also be intransigent with
      respect to sending non-retry requests that have a slot ID that
      exceeds the replier's highest_slotid.
      Once the replier has forcibly lowered the enforced
      highest_slotid, the requester is only allowed to
      send retries on slots that exceed the replier's highest_slotid.
      If a request is received with a slot ID that is higher than
      the new enforced highest_slotid, and the sequence ID
      is one higher than what is in the slot's reply cache, then
      the server can both retire the slot and return NFS4ERR_BADSLOT
      (however, the server MUST NOT do one and not the other).
      The reason it is safe to retire the slot
      is because by using the next sequence ID, the requester
      is indicating it has received the previous reply for the
      slot.
      <vspace blankLines='1' />
    </t>
    <t>
     The requester SHOULD use the lowest available
     slot when sending a new request.  This way, the
     replier may be able to retire slot entries faster.
     However, where the replier is actively adjusting
     its granted highest_slotid,
     it will not be able
     to use only the receipt of the slot ID and highest_slotid
     in the request.  Neither the slot ID nor the
     highest_slotid used in a request may reflect the
     replier's current idea of the requester's session
     limit, because the request may have been sent from the
     requester before the update was received.  Therefore,
     in the downward adjustment case, the replier may have
     to retain a number of reply cache entries at least as
     large as the old value of maximum requests
     outstanding, until it can infer that the requester 
     has seen a reply containing the new granted highest_slotid.
     The replier can infer that the requester has seen such a 
     reply when it receives a new request with the same
     slot ID as the request replied to and the next higher 
     sequence ID.      
    </t>
    </list>
   </t>
     <section title="Caching of SEQUENCE and CB_SEQUENCE Replies" anchor="cacheseq">

     <t>
      When a SEQUENCE or CB_SEQUENCE operation is
      successfully executed, its reply MUST always be
      cached. Specifically, session ID, sequence ID,
      and slot ID MUST be cached in the reply cache.
      The reply from SEQUENCE also includes the highest
      slot ID, target highest slot ID, and status flags. Instead
      of caching these values, the server MAY
      re-compute the values from the current
      state of the fore channel, session, and/or client
      ID as appropriate.  Similarly, the reply from
      CB_SEQUENCE includes a highest slot ID and target
      highest slot ID. The client
      MAY re-compute the values from the
      current state of the session as appropriate.

     </t>

     <t>

       Regardless of whether or not a replier is re-computing highest slot ID,
       target slot ID, and status on replies to retries, the requester
       MUST NOT assume that the values are being re-computed whenever it
       receives a reply after a retry is sent, since it has no way
       of knowing whether the reply it has received was sent by the 
       replier in response to the retry or is a delayed response to
       the original request.  Therefore, it may be the case that 
       highest slot ID, target slot ID, or status bits may reflect
       the state of affairs when the request was first executed.  
       Although acting based on such delayed information is valid,
       it may cause the receiver of the reply to do unneeded work.  Requesters
       MAY choose to send additional requests to get the current 
       state of affairs or use the state of affairs reported by 
       subsequent requests, in preference to acting immediately
       on data that might be out of date.

     </t>

     </section>

     <section title="Errors from SEQUENCE and CB_SEQUENCE"
       anchor="err_sequence">
     <t>
      Any time SEQUENCE or CB_SEQUENCE returns an error, the
      sequence ID of the slot MUST NOT change. The replier MUST NOT
      modify the reply cache entry for the slot whenever an error
      is returned from SEQUENCE or CB_SEQUENCE.
     </t>
     </section> <!-- Errors from SEQUENCE and CB_SEQUENCE -->
     <section title="Optional Reply Caching"
      anchor="optional_reply_caching">
      <t>
       On a per-request basis, the requester can choose to
       direct the replier to cache the reply to all operations
       after the first operation (SEQUENCE or CB_SEQUENCE) via
       the sa_cachethis or csa_cachethis fields of the arguments
       to SEQUENCE or CB_SEQUENCE.
       The reason it would not direct the replier to cache
       the entire reply is that the request is composed of all
       idempotent operations <xref target="Chet" />.
       Caching the reply may offer little benefit. If
       the reply is too large (see

       <xref target="COMPOUND Sizing Issues" />),

       it may not be cacheable anyway. Even if the reply to
       idempotent request is small enough to cache, unnecessarily
       caching the reply slows down the server and increases
       RPC latency.
      </t>
      <t>
       Whether or not the requester requests the reply to be cached
       has no effect on the slot processing. If the
       results of SEQUENCE or CB_SEQUENCE are NFS4_OK, then
       the slot's sequence ID MUST be incremented by one.
       If a requester does not direct the replier to cache
       the reply, the replier MUST do one of following:
       <list style='symbols'>
       <t>
        The replier can cache the entire original reply.
        Even though sa_cachethis or csa_cachethis is FALSE,
        the replier is always free to cache. It may choose
        this approach in order to simplify implementation.
       </t>
       <t>
        The replier enters into its reply cache a reply consisting
        of the original results to the SEQUENCE or CB_SEQUENCE
        operation, and with the next operation in
        COMPOUND or CB_COMPOUND having the error NFS4ERR_RETRY_UNCACHED_REP.
        Thus, if the requester later retries the request, it will
        get NFS4ERR_RETRY_UNCACHED_REP.

        If a replier receives a retried Sequence operation where the reply
        to the COMPOUND or CB_COMPOUND was not cached, then the replier,

        <list style='symbols'>

        <t>
	  MAY return NFS4ERR_RETRY_UNCACHED_REP
	  in reply to a Sequence operation if the
	  Sequence operation is not the first
	  operation (granted, a requester that
	  does so is in violation of the NFSv4.1
	  protocol).

        </t>

        <t>
	  MUST NOT return
	  NFS4ERR_RETRY_UNCACHED_REP in reply to
	  a Sequence operation if the Sequence
	  operation is the first operation.

        </t>

        </list>

       </t>

       <t>
        If the second operation is an illegal operation, or an
        operation that was legal in a previous minor version of
        NFSv4 and MUST NOT
        be supported in the current minor version (e.g., SETCLIENTID), the
        replier MUST NOT ever return NFS4ERR_RETRY_UNCACHED_REP.
        Instead the replier MUST return NFS4ERR_OP_ILLEGAL or
        NFS4ERR_BADXDR or NFS4ERR_NOTSUPP as appropriate.
       </t>

       <t>
        If the second operation can result in another error status,
        the replier MAY return a status other than NFS4ERR_RETRY_UNCACHED_REP,
        provided the operation is not executed in such a way that the state
        of the replier is changed. Examples of such
        an error status include: NFS4ERR_NOTSUPP returned for an
        operation that is legal but not REQUIRED in the current 
        minor versions, and thus not supported by the replier;
        NFS4ERR_SEQUENCE_POS; and NFS4ERR_REQ_TOO_BIG.
       </t>

       </list>
      </t>
    
      <t>
	The discussion above assumes that the
	retried request matches the original
	one.  <xref target="false_retry"/>
	discusses what the replier might do, and
	MUST do when original and retried requests do not match.
        Since the replier may
	only cache a small amount of the
	information that would be required to
	determine whether this is a case of a
	false retry, the replier may send to the
	client any of the following responses:

	<list style='symbols'>

	<t>
         The cached reply to the original request (if the replier has cached
         it in its entirety and the users of the original request and retry match).
        </t>

	<t>
          A reply that consists only of the Sequence operation with the error
	  NFS4ERR_FALSE_RETRY.
        </t>

        <t>
	A reply consisting of the response to Sequence  with the status
	NFS4_OK, together with the second operation as it appeared in the retried
	request with an error of NFS4ERR_RETRY_UNCACHED_REP or other error as
	described above.
        </t>

	<t>
          A reply that consists of the response to Sequence with the status
	NFS4_OK, together with the second operation as it appeared in the original
	request with an error of NFS4ERR_RETRY_UNCACHED_REP or other error as
	described above.
        </t>
        </list>

      </t>

        <section anchor="false_retry" title="False Retry">
          <t>
	If a requester sent a Sequence operation
	with a slot ID and sequence ID that are
	in the reply cache but the replier
	detected that the retried request is not
	the same as the original request,
	including a retry that has different
	operations or different arguments in the
	operations from the original and a retry
	that uses a different principal in the
	RPC request's credential field that
	translates to a different user, then this
	is a false retry. When the replier
	detects a false retry, it is permitted 
	(but not always obligated) to return
	NFS4ERR_FALSE_RETRY in response to the
	Sequence operation when it detects a
	false retry.

          </t>
         
          <t>
	Translations of particularly privileged
	user values to other users due to the
	lack of appropriately secure credentials,
	as configured on the replier, should be
	applied before determining whether the
	users are the same or different. If the
	replier determines the users are
	different between the original request
	and a retry, then the replier MUST return
	NFS4ERR_FALSE_RETRY.

          </t>

          <t>
	If an operation of the retry is an
	illegal operation, or an operation that
	was legal in a previous minor version of
	NFSv4 and MUST NOT be supported in the 
	current minor version (e.g., SETCLIENTID),
	the replier MAY return
	NFS4ERR_FALSE_RETRY (and MUST do so if
	the users of the original request and
	retry differ). Otherwise, the replier MAY return
	NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
	NFS4ERR_NOTSUPP as appropriate.  Note
	that the handling is in contrast for how the
	replier deals with retries requests with
	no cached reply. The difference is due to
	NFS4ERR_FALSE_RETRY being a valid error
	for only Sequence operations, whereas
	NFS4ERR_RETRY_UNCACHED_REP is a valid
	error for all operations except illegal
	operations and operations that MUST NOT be
	supported in the current minor version of
	NFSv4.

          </t>
        </section>
        
     </section> <!-- Optional Reply Caching -->
    </section> <!-- Slot Identifiers and Server Reply Cache -->


    <section anchor="Retry and Replay" title="Retry and Replay of Reply">
    <t>
     A requester MUST NOT retry a request, unless
     the connection it used to send the request
     disconnects. The requester can then reconnect
     and re-send the request, or it can re-send the
     request over a different connection that is
     associated with the same session.
    </t>
    <t>
     If the requester is a server wanting to re-send a callback
     operation over the backchannel of a session, the requester
     of course cannot reconnect because only the client can
     associate connections with the backchannel. The
     server can re-send the request over another connection that
     is bound to the same session's backchannel. If there is no
     such connection, the server
     MUST indicate that the session has no backchannel by setting
     the SEQ4_STATUS_CB_PATH_DOWN_SESSION flag bit in the response
     to the next SEQUENCE operation from the client. The client MUST
     then associate a connection with the session (or destroy
     the session).
    </t>
    <t>
     Note that it is not fatal for a requester to retry
     without a disconnect between the request and retry.
     However, the retry does consume resources, especially
     with RDMA, where each request, retry or not, consumes
     a credit. Retries for no reason, especially retries
     sent shortly after the previous attempt, are a poor
     use of network bandwidth and defeat the purpose of a
     transport's inherent congestion control system.
    </t>
    <t>
     A requester MUST wait for a reply to a request before using
     the slot for another request. If it does not wait for
     a reply, then the requester does not know what
     sequence ID to use for the slot on its next request.
     For example, suppose a requester sends a request with sequence ID
     1, and does not wait for the response. The next time it uses
     the slot, it sends the new request with sequence ID 2.
     If the replier has not seen the request with sequence ID 1, then
     the replier is not expecting sequence ID 2, and rejects the
     requester's new request with NFS4ERR_SEQ_MISORDERED (as the
     result from SEQUENCE or CB_SEQUENCE).
    </t>
    <t>
     RDMA fabrics do not guarantee that the memory handles
     (Steering Tags) within each RPC/RDMA "chunk" <xref target="RPCRDMA" />
     are valid on a scope
     outside that of a single connection.  Therefore, handles used by
     the direct operations become invalid after connection loss.  The
     server must ensure that any RDMA operations that must be replayed
     from the reply cache use the newly provided handle(s) from the
     most recent request.
    </t>
    <t>
     A retry might be sent while the original request is still in
     progress on the replier. The replier SHOULD deal with the issue
     by returning NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE
     operation, but implementations MAY return NFS4ERR_MISORDERED.
     Since errors from SEQUENCE and CB_SEQUENCE are
     never recorded in the reply cache, this approach allows the
     results of the execution of the original request to be
     properly recorded in the reply cache (assuming that the requester
     specified the reply to be cached).
    </t>
 
 
     
    </section> <!-- Retry and Replay -->

    <section anchor="sessions_callback_races" title="Resolving Server Callback Races">
    <t>
     It is possible for server callbacks to arrive at the
     client before the reply from related fore channel
     operations. For example, a client may have been
     granted a delegation to a file it has opened, but the
     reply to the OPEN (informing the client of the
     granting of the delegation) may be delayed in the
     network. If a conflicting operation arrives at the
     server, it will recall the delegation using the
     backchannel, which may be on a different
     transport connection, perhaps even a different
     network, or even a different session associated with
     the same client ID.
    </t>
    <t>
     The presence of a session between the client and server
     alleviates this issue. When a session is in place,
     each client request is uniquely identified by its {
     session ID, slot ID, sequence ID } triple. By the rules under which
     slot entries (reply cache entries) are
     retired, the server has knowledge whether the client
     has "seen" each of the server's replies. The server
     can therefore provide sufficient information to the
     client to allow it to disambiguate between an
     erroneous or conflicting callback race
     condition.
    </t>
    <t>
     For each client operation that might result in some
     sort of server callback, the server SHOULD "remember"
     the { session ID, slot ID, sequence ID } triple of the client request
     until the slot ID retirement rules allow the server to
     determine that the client has, in fact, seen the
     server's reply. Until the time the { session ID, slot ID,
     sequence ID } request triple can be retired, any recalls
     of the associated object MUST carry an array of these
     referring identifiers (in the CB_SEQUENCE operation's
     arguments), for the benefit of the client.  After this
     time, it is not necessary for the server to provide
     this information in related callbacks, since it is
     certain that a race condition can no longer occur.
    </t>
    <t>
     The CB_SEQUENCE operation that begins each server
     callback carries a list of "referring" { session ID, slot ID,
     sequence ID } triples.  If the client finds the request
     corresponding to the referring session ID, slot ID, and sequence ID
     to be currently outstanding (i.e., the server's reply has
     not been seen by the client), it can determine that
     the callback has raced the reply, and act
     accordingly. If the client does not find the request
     corresponding to the referring triple to be outstanding (including
     the case of a session ID referring to a destroyed session),
     then there is no race with respect to this triple.
     The server SHOULD limit the referring triples
     to requests that refer to just those that apply to the objects 
     referred to in
     the CB_COMPOUND procedure.
    </t>
    <t>
     The client must not simply wait forever for the
     expected server reply to arrive before responding to the
     CB_COMPOUND that won the race,
     because it is possible
     that it will be delayed indefinitely. The client should
     assume the likely case that the reply will arrive within
     the average round-trip time for COMPOUND requests to the
     server, and wait that period of time. If
     that period of time
     expires, it can respond to the CB_COMPOUND with
     NFS4ERR_DELAY.
    </t>
    <t>
     There are other scenarios under which callbacks may race replies.
     Among them are pNFS layout recalls as described in
     <xref target="pnfs_operation_sequencing" />.
    </t>
    </section> <!-- Resolving server callback races with sessions -->
   <section anchor="COMPOUND Sizing Issues" title="COMPOUND and CB_COMPOUND Construction Issues">

   <t>
    Very large requests and replies may pose both buffer
    management issues (especially with RDMA) and reply
    cache issues. When the session is created
    (<xref target="OP_CREATE_SESSION" />), for each channel (fore and
    back), the client and server
    negotiate the maximum-sized request they will
    send or process (ca_maxrequestsize), the maximum-sized reply
    they will return or process (ca_maxresponsesize), and the 
    maximum-sized reply they will store in the reply cache
    (ca_maxresponsesize_cached).
   </t>
   <t>
    If a request exceeds ca_maxrequestsize, the reply will
    have the status NFS4ERR_REQ_TOO_BIG. A replier MAY
    return NFS4ERR_REQ_TOO_BIG as the status for the first operation
    (SEQUENCE or CB_SEQUENCE) in the request (which means that
    no operations in the request executed and that the
    state of the slot in the reply cache is unchanged), or it MAY
    opt to return it on a subsequent operation in the same
    COMPOUND or CB_COMPOUND request (which means that at least one
    operation did execute and that the state of the slot in the reply cache does
    change). The replier SHOULD set NFS4ERR_REQ_TOO_BIG on the
    operation that exceeds ca_maxrequestsize.
   </t>
   <t>
    If a reply exceeds ca_maxresponsesize, the reply will
    have the status NFS4ERR_REP_TOO_BIG. A replier MAY
    return NFS4ERR_REP_TOO_BIG as the status for the first operation
    (SEQUENCE or CB_SEQUENCE) in the request, or it MAY
    opt to return it on a subsequent operation (in the same
    COMPOUND or CB_COMPOUND reply). A replier MAY return NFS4ERR_REP_TOO_BIG
    in the reply to SEQUENCE or CB_SEQUENCE, even if the response
    would still exceed ca_maxresponsesize.
   </t>
   <t>
    If sa_cachethis or csa_cachethis is TRUE, then the
    replier MUST cache a reply except if an error is
    returned by the SEQUENCE or CB_SEQUENCE operation (see
    <xref target="err_sequence" />). If the reply exceeds
    ca_maxresponsesize_cached (and sa_cachethis or
    csa_cachethis is TRUE), then the server MUST return
    NFS4ERR_REP_TOO_BIG_TO_CACHE. Even if
    NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for
    that matter) is returned on an operation other than the
    first operation (SEQUENCE or CB_SEQUENCE), then
    the reply MUST be cached if sa_cachethis or
    csa_cachethis is TRUE.
    For example, if a COMPOUND has eleven
    operations, including SEQUENCE, the fifth operation is
    a RENAME, and the tenth operation is a READ for one
    million bytes, the server may return
    NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth operation.
    Since the server executed several operations, especially
    the non-idempotent RENAME, the client's request to
    cache the reply needs to be honored in order for the
    correct operation of exactly once semantics. If the
    client retries the request, the server will have cached
    a reply that contains results for ten of the eleven requested
    operations, with
    the tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.
   </t>
   <t>
    A client needs to take care that when sending
    operations that change the current filehandle (except for
    PUTFH, PUTPUBFH, PUTROOTFH, and RESTOREFH), it
    not exceed the maximum reply buffer before the GETFH
    operation. Otherwise, the client will have to retry
    the operation that changed the current filehandle, in order
    to obtain the desired filehandle.
    For the OPEN operation (see <xref target="OP_OPEN" />),
    retry is not always available as an option.
    The following guidelines for the handling of
    filehandle-changing operations are advised:
    <list style="symbols">
    <t>
     Within the same COMPOUND procedure, a client
     SHOULD send GETFH immediately after a current
     filehandle-changing operation. A client
     MUST send GETFH after a current filehandle-changing operation
     that is also non-idempotent (e.g., the OPEN operation), unless
     the operation is RESTOREFH. RESTOREFH is
     an exception, because even though it is
     non-idempotent, the filehandle RESTOREFH
     produced originated from an operation that
     is either idempotent (e.g., PUTFH, LOOKUP),
     or non-idempotent (e.g., OPEN, CREATE). If the
     origin is non-idempotent, then because the client
     MUST send GETFH after the origin operation, the
     client can recover if RESTOREFH returns an error.

    </t>
    <t>
     A server MAY return NFS4ERR_REP_TOO_BIG or
     NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE)
     on a filehandle-changing operation if the reply would
     be too large on the next operation.
    </t>
    <t>
     A server SHOULD return NFS4ERR_REP_TOO_BIG or
     NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE)
     on a filehandle-changing, non-idempotent operation if the reply would
     be too large on the next operation, especially if the operation
     is OPEN.
    </t>
    <t>
     A server MAY return NFS4ERR_UNSAFE_COMPOUND to a non-idempotent
     current filehandle-changing operation, if
     it looks at the next operation (in the same COMPOUND procedure)
     and finds it is
     not GETFH. The server SHOULD do this if it is unable to
     determine in advance whether the total response size
     would exceed ca_maxresponsesize_cached or ca_maxresponsesize.
    </t>
    </list>
   </t>
   </section> <!-- COMPOUND and CB_COMPOUND Construction Issues -->
   <section anchor="Persistence" title="Persistence">
   <t>
    Since the reply cache is bounded, it is practical for
    the reply cache to persist across server restarts.
    The replier MUST persist the following information
    if it agreed to persist the session (when the session
    was created; see <xref target="OP_CREATE_SESSION" />):

    <list style='symbols'>
    <t>
     The session ID.
    </t>
    <t>
     The slot table including the sequence ID and cached reply for
     each slot.
    </t>
    </list>
    The above are sufficient for a replier to provide EOS semantics
    for any requests that were sent and executed before the server
    restarted.
    If the replier is a client, then there is no need for
    it to persist any more information, unless the client will
    be persisting all other state across client restart, in which case,
    the server will never see any NFSv4.1-level protocol manifestation
    of a client restart.
    If the replier is a server, with just the
    slot table and session ID persisting,
    any requests the client retries after the server restart will 
    return the results that are cached in the reply cache, 
    and any new requests (i.e., the sequence ID is one greater than the
    slot's sequence ID) MUST be rejected with NFS4ERR_DEADSESSION
    (returned by SEQUENCE). Such a session is considered dead.
    A server MAY re-animate a session
    after a server restart so that the session will accept new
    requests as well as retries. To re-animate a session,
    the server needs to persist additional information
    through server restart:
    <list style='symbols'>
    <t>
     The client ID. This is a prerequisite to let the client
     create more sessions associated with the same client ID
     as the re-animated session.
    </t>
    <t>
     The client ID's sequence ID that is used for creating
     sessions (see Sections <xref target="OP_EXCHANGE_ID" format="counter" /> and
     <xref target="OP_CREATE_SESSION" format="counter" />). This is a
     prerequisite to let the client create more sessions.
    </t>
    <t>
     The principal that created the client ID. This
     allows the server to authenticate the client when
     it sends EXCHANGE_ID.
    </t>
    <t>
     The SSV, if SP4_SSV state protection was
     specified when the client ID was created (see <xref
     target="OP_EXCHANGE_ID" />). This lets the 
     client create new sessions, and associate connections
     with the new and existing sessions.
    </t>
    <t>
     The properties of the client ID as defined in
     <xref target="OP_EXCHANGE_ID" />.
    </t>
     

    </list>
   </t>
   <t>
    A persistent reply cache places certain demands on the server.
    The execution of the sequence of operations (starting with SEQUENCE)
    and placement of its results in the persistent cache MUST be atomic. If
    a client retries a sequence of operations that was previously
    executed on the server, the only acceptable outcomes are either
    the original cached reply or an indication that the client ID
    or session has been lost (indicating a catastrophic loss
    of the reply cache or a session that has been deleted because
    the client failed to use the session for an extended period
    of time).
   </t>
   <t>
    A server could fail and restart in the middle of a
    COMPOUND procedure that contains one or more non-idempotent
    or idempotent-but-modifying operations. This creates
    an even higher challenge for atomic execution and
    placement of results in the reply cache. One way
    to view the problem is as a single transaction consisting of
    each operation in the COMPOUND followed by storing
    the result in persistent storage, then finally a transaction
    commit. If there is a failure before the transaction
    is committed, then the server rolls back the transaction.
    If the server itself fails, then when it restarts, its
    recovery logic could roll back the transaction
    before starting the NFSv4.1 server.
   </t>
   <t>
    While the description of the
    implementation for atomic execution of the request
    and caching of the reply
    is beyond the scope of this document, an example implementation
    for NFSv2 <xref target="RFC1094"/> is described in <xref target="ha_nfs_ibm" />.
   </t>
   </section> <!-- Persistence -->
  </section> <!-- Exactly Once Semantics -->
  <section anchor="RDMA Considerations" title="RDMA Considerations">
  <t>
   A complete discussion of the operation of RPC-based
   protocols over RDMA transports is in <xref target="RPCRDMA" />. A
   discussion of the operation of NFSv4, including NFSv4.1,
   over RDMA is in <xref target="NFSDDP" />.  Where RDMA is considered,
   this specification assumes the use of such a layering;
   it addresses only the upper-layer issues relevant to
   making best use of RPC/RDMA.

  </t>
   <section anchor="RDMA Connection Resources" title="RDMA Connection Resources">
   <t>
    RDMA requires its consumers to register memory and post
    buffers of a specific size and number for receive
    operations.

   </t>
   <t>
    Registration of memory can be a relatively high-overhead operation,
    since it requires pinning of buffers, assignment of attributes
    (e.g., readable/writable), and initialization of hardware
    translation.  Preregistration is desirable to reduce overhead.
    These registrations are specific to hardware interfaces and even to
    RDMA connection endpoints; therefore, negotiation of their limits is
    desirable to manage resources effectively.
   </t>
   <t>
    Following basic registration, these buffers must be posted by
    the RPC layer to handle receives.  These buffers remain in use by
    the RPC/NFSv4.1 implementation; the size and number of them must be
    known to the remote peer in order to avoid RDMA errors that would
    cause a fatal error on the RDMA connection.
   </t>
   <t>
    NFSv4.1 manages slots as resources on a per-session
    basis (see <xref target="Session" />), while RDMA
    connections manage credits on a per-connection basis.
    This means that in order for a peer to send data over
    RDMA to a remote buffer, it has to have both an NFSv4.1
    slot and an RDMA credit.  If multiple RDMA connections
    are associated with a session, then if the total number
    of credits across all RDMA connections associated with
    the session is X, and the number of slots in the session
    is Y, then the maximum number of outstanding requests
    is the lesser of X and Y.

   </t>
   </section> <!-- RDMA Connection Resources -->
   <section anchor="Flow Control" title="Flow Control">
   <t>
    Previous versions of NFS do not provide flow control;
    instead, they rely on the windowing provided by
    transports like TCP to throttle requests.  This does
    not work with RDMA, which provides no operation flow
    control and will terminate a connection in error when
    limits are exceeded. 

    Limits such as maximum number of requests
    outstanding are therefore negotiated when a session
    is created (see the ca_maxrequests field in <xref
    target="OP_CREATE_SESSION" />).  These limits then
    provide the maxima within which each connection associated
    with the session's channel(s) must remain.
    RDMA connections are managed within these limits as
    described in Section 3.3 of <xref target="RPCRDMA" />; if there are multiple
    RDMA connections, then the maximum number of requests
    for a channel will be divided among the RDMA
    connections.  Put a different way, the onus is on the
    replier to ensure that the total number of RDMA credits
    across all connections associated with the replier's
    channel does exceed the channel's maximum number of
    outstanding requests.

   </t>
   <t>
    The limits may also be modified
    dynamically at the replier's choosing by manipulating
    certain parameters present in each NFSv4.1 reply. In
    addition, the CB_RECALL_SLOT callback operation (see
    <xref target="OP_CB_RECALL_SLOT" />) can be sent by
    a server to a client to return RDMA credits to the
    server, thereby lowering the maximum number of requests
    a client can have outstanding to the server.

   </t>
   </section> <!-- Flow Control -->

   <section anchor="Padding" title="Padding">
   <t>
        Header padding is requested by each peer at session initiation
        (see the ca_headerpadsize argument to CREATE_SESSION in
        <xref target="OP_CREATE_SESSION" />), and
        subsequently used by the RPC RDMA layer, as described in <xref target="RPCRDMA" />.
        Zero padding is permitted.
   </t>
   <t>
        Padding leverages the useful property
        that RDMA preserve alignment of data, even when they are
        placed into anonymous (untagged) buffers.  If requested, client
        inline writes will insert appropriate pad bytes within the request
        header to align the data payload on the specified boundary.  The
        client is encouraged to add sufficient padding (up to the
        negotiated size) so that
        the "data" field of the WRITE operation
        is aligned.
        Most servers can make good use of such padding,
        which allows them to chain receive buffers in such a way that any
        data carried by client requests will be placed into appropriate
        buffers at the server, ready for file system processing.  The
        receiver's RPC layer encounters no overhead from skipping over pad
        bytes, and the RDMA layer's high performance makes the insertion
        and transmission of padding on the sender a significant
        optimization.  In this way, the need for servers to perform RDMA
        Read to satisfy all but the largest client writes is obviated.  An
        added benefit is the reduction of message round trips on the network
        -- a potentially good trade, where latency is present.
   </t>
   <t>
        The value to choose for padding is subject to a number of criteria.
        A primary source of variable-length data in the RPC header is the
        authentication information, the form of which is client-determined,
        possibly in response to server specification.  The contents of
        COMPOUNDs, sizes of strings such as those passed to RENAME, etc.
        all go into the determination of a maximal NFSv4.1 request size and
        therefore minimal buffer size.  The client must select its offered
        value carefully, so as to avoid overburdening the server, and vice
        versa.  The benefit of an appropriate padding value is higher
        performance.
   </t>
   <figure>
   <artwork>
                 Sender gather:
     |RPC Request|Pad  bytes|Length| -> |User data...|
     \------+----------------------/      \
             \                             \
              \    Receiver scatter:        \-----------+- ...
         /-----+----------------\            \           \
         |RPC Request|Pad|Length|   ->  |FS buffer|->|FS buffer|->...
   </artwork>
   </figure>
   <t>
        In the above case, the server may recycle unused buffers to the
        next posted receive if unused by the actual received request, or
        may pass the now-complete buffers by reference for normal write
        processing.  For a server that can make use of it, this removes
        any need for data copies of incoming data, without resorting to
        complicated end-to-end buffer advertisement and management.  This
        includes most kernel-based and integrated server designs, among
        many others.  The client may perform similar optimizations, if
        desired.
   </t>
   </section> <!-- Padding -->
   <section anchor="dual" title="Dual RDMA and Non-RDMA Transports">
   <t>
    Some RDMA transports (e.g., <xref target="RDMAP">RFC 5040</xref>)
    permit a "streaming" (non-RDMA) phase,
    where ordinary traffic might flow before "stepping up"
    to RDMA mode, commencing RDMA traffic.  Some RDMA
    transports start connections always in RDMA mode.
    NFSv4.1 allows, but does not assume, a streaming phase
    before RDMA mode.  When a connection
    is associated with a session, the client and server negotiate whether the
    connection is used in RDMA or non-RDMA mode  (see Sections
    <xref target="OP_CREATE_SESSION" format="counter" /> and
    <xref target="OP_BIND_CONN_TO_SESSION" format="counter" />).
   </t>
   </section> <!-- RDMA Transports -->

  </section> <!-- RDMA Considerations -->

  <section anchor="Sessions Security" title="Session Security">
   <section anchor="Session Callback Security" title="Session Callback Security">
   <t>
    Via session/connection association, NFSv4.1 improves security over
    that provided by NFSv4.0 for the backchannel.  The
    connection is client-initiated (see
    <xref target="OP_BIND_CONN_TO_SESSION" />) and subject to the same
    firewall and routing checks as the fore channel.
    At the client's option (see <xref target="OP_EXCHANGE_ID" />),
    connection association is fully authenticated before being
    activated (see <xref target="OP_BIND_CONN_TO_SESSION" />).
    Traffic from the server over the
    backchannel is authenticated exactly as the client specifies
    (see <xref target="Backchannel RPC Security" />).
   </t>
   </section> <!-- Session Callback Security -->
    <section anchor="Backchannel RPC Security" title="Backchannel RPC Security">
    <t>
     When the NFSv4.1 client establishes the backchannel, it
     informs the  server of the security flavors and principals
     to use when sending requests. If the security flavor is
     RPCSEC_GSS, the client expresses the principal in the form
     of an established RPCSEC_GSS context.  The server is free
     to use any of the flavor/principal combinations the client
     offers, but it MUST NOT use unoffered combinations.

     This way, the client need not provide a target
     GSS principal for the backchannel as it did with
     NFSv4.0, nor does the server have to implement an
     RPCSEC_GSS initiator as it did with NFSv4.0 <xref
     target="RFC3530" />.

    </t>
    <t>
     The CREATE_SESSION (<xref target="OP_CREATE_SESSION" />)
     and BACKCHANNEL_CTL (<xref target="OP_BACKCHANNEL_CTL" />)
     operations allow the client to specify flavor/principal combinations.
    </t>
    <t>
     Also note that the SP4_SSV state protection mode 
     (see Sections <xref target="OP_EXCHANGE_ID" format="counter" /> and <xref
     target="protect_state_change" format="counter" />) has the side
     benefit of providing SSV-derived RPCSEC_GSS contexts (<xref target="ssv_mech" />).
    </t>
    </section> <!-- Backchannel RPC Security -->

   <section anchor="protect_state_change" title="Protection from Unauthorized State Changes">
   <t>
     As described to this point in the specification, the state model
     of NFSv4.1 is vulnerable to an attacker that
     sends a SEQUENCE operation with a forged session ID and with a slot ID that
     it expects the legitimate client to use next. When the legitimate client
     uses the slot ID with the same sequence number, the server
     returns the attacker's result from the reply cache, which
     disrupts the legitimate client and thus denies service to it.
     Similarly, an attacker could send a CREATE_SESSION with a forged
     client ID to create a new session associated with the client ID.
     The attacker could send requests using the new session that
     change locking state, such as LOCKU operations to release locks
     the legitimate client has acquired. Setting a security
     policy on the file that requires RPCSEC_GSS credentials when
     manipulating the file's state is one potential work around,
     but has the disadvantage of preventing a legitimate client from
     releasing state when RPCSEC_GSS is required to do so, but
     a GSS context cannot be obtained (possibly because the user
     has logged off the client).
   </t>
   <t>
     NFSv4.1 provides three options to a client for state protection,
     which are specified when a client creates
     a client ID via EXCHANGE_ID (<xref target="OP_EXCHANGE_ID" />).
   </t>
   <t>
     The first (SP4_NONE) is to simply waive state protection.
   </t>
   <t>
     The other two options (SP4_MACH_CRED and SP4_SSV)
     share several traits:
     <list style="symbols">
     <t>
      An RPCSEC_GSS-based credential is used to authenticate
      client ID and session maintenance operations,
      including creating and destroying a session,
      associating a connection with the session, and
      destroying the client ID.
     </t>
     <t>
      Because RPCSEC_GSS is used to authenticate
      client ID and session maintenance, the attacker cannot
      associate a rogue connection with a legitimate session, or
      associate a rogue session with a legitimate client ID in
      order to maliciously alter the client ID's lock state 
      via CLOSE, LOCKU, DELEGRETURN, LAYOUTRETURN, etc.
     </t>
     <t>
      In cases where the server's security policies on a
      portion of its namespace require RPCSEC_GSS authentication,
      a client may have to use an RPCSEC_GSS credential
      to remove per-file state (e.g., LOCKU, CLOSE, etc.).
      The server may require that the principal that removes
      the state match certain criteria (e.g.,
      the principal might have to be the same as the one
      that acquired the state). However, the client might
      not have an RPCSEC_GSS context for such a principal,
      and might not be able to create such a context (perhaps
      because the user has logged off). When the client
      establishes SP4_MACH_CRED or SP4_SSV protection,
      it can specify a list of operations that the server MUST
      allow using the machine credential (if SP4_MACH_CRED
      is used) or the SSV credential (if SP4_SSV is used).
     </t>
     </list>
   </t>
   <t>
     The SP4_MACH_CRED  state protection option uses a machine
     credential where the principal that
     creates the client ID MUST also be the principal
     that performs client ID and session maintenance 
    operations.
     The security of the machine credential state protection approach
     depends entirely on safe guarding the per-machine credential.
     Assuming a proper safeguard using the per-machine credential
     for operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
     DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker
     from associating a rogue connection with a session, or
     associating a rogue session with a client ID.
   </t>
   <t>
     There are at least three scenarios for the SP4_MACH_CRED
     option:
     <list style="numbers">
     <t>
      The system administrator configures a unique,
      permanent per-machine credential for one of the
      mandated GSS mechanisms (e.g., if Kerberos
      V5 is used, a "keytab" containing a principal derived from a
      client host name could be used).

     </t>
     <t>
      The client is used by a single user, and so the
      client ID and its sessions are used by just that
      user. If the user's credential expires, then session
      and client ID maintenance cannot occur, but since
      the client has a single user, only that user is
      inconvenienced.

     </t>
     <t>
      The physical client has multiple users, but the
      client implementation has a unique client ID for
      each user. This is effectively the same as the
      second scenario, but a disadvantage is that each
      user needs to be allocated at least one session each,
      so the approach suffers from lack of economy.

     </t>

     </list>
   </t>
   <t>
     The SP4_SSV protection option uses the SSV (<xref
     target="intro_definitions"/>), via RPCSEC_GSS and the SSV GSS
     mechanism (<xref target="ssv_mech" />), to protect state from attack.
     The SP4_SSV protection option is intended for the situation
     comprised of a client that has multiple active users and a system
     administrator who wants to avoid the burden of installing a permanent
     machine credential on each client.  The SSV is
     established and updated on the server via SET_SSV (see <xref
     target="OP_SET_SSV" />). To prevent eavesdropping,
     a client SHOULD send SET_SSV via RPCSEC_GSS with
     the privacy service.  Several aspects of the SSV
     make it intractable for an attacker to guess the SSV,
     and thus associate rogue connections with a session,
     and rogue sessions with a client ID:

    <list style="symbols">
    <t>
      The arguments to and results of SET_SSV include digests of the old and
      new SSV, respectively.
    </t>
    <t>
      Because the initial value of the SSV is zero,
      therefore known, the client that opts for SP4_SSV
      protection and opts to apply SP4_SSV protection to
      BIND_CONN_TO_SESSION and CREATE_SESSION MUST send
      at least one SET_SSV operation before the first
      BIND_CONN_TO_SESSION operation or before the second
      CREATE_SESSION operation on a client ID. If it does
      not, the SSV mechanism will not generate tokens
      (<xref target="ssv_mech" />).

      A client SHOULD send SET_SSV as soon as a session
      is created.

    </t>
    <t>
      A SET_SSV request does not replace the SSV with the argument to
      SET_SSV. Instead, the current SSV on the server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.
      Each time a new principal uses a client ID for the first
      time, the client
      SHOULD send a SET_SSV with that principal's RPCSEC_GSS
      credentials, with RPCSEC_GSS service set to RPC_GSS_SVC_PRIVACY.
    </t>
    </list>
   </t>
   <t>
     Here are the types of attacks that can be attempted by an attacker named
     Eve on a victim named Bob, and how SP4_SSV protection foils
     each attack:
     <list style="symbols">
     <t>
       Suppose Eve is the first user to log into a
       legitimate client.  Eve's use of an NFSv4.1
       file system will cause the legitimate client to
       create a client ID
       with SP4_SSV protection, specifying that the BIND_CONN_TO_SESSION
       operation MUST use the SSV credential. Eve's use of
       the file system also causes an SSV to be created.  The
       SET_SSV operation that creates the SSV will be protected by
       the RPCSEC_GSS context created by the legitimate
       client, which uses Eve's GSS principal and
       credentials. Eve can eavesdrop on the network while
       her RPCSEC_GSS context is created and the SET_SSV
       using her context is sent. Even if the legitimate
       client sends the SET_SSV with RPC_GSS_SVC_PRIVACY,
       because Eve knows her own credentials, she can
       decrypt the SSV.  Eve can compute an RPCSEC_GSS
       credential that BIND_CONN_TO_SESSION will accept,
       and so associate a new connection with the
       legitimate session. Eve can change the slot ID and
       sequence state of a legitimate session, and/or the
       SSV state, in such a way that when Bob accesses
       the server via the same legitimate client, the
       legitimate client will be unable to use the session.

       <vspace blankLines='1' />

       The client's only recourse is to create a new client
       ID for Bob to use, and establish a new SSV for the
       client ID.  The client will be unable to delete
       the old client ID, and will let the lease on the old
       client ID expire.

       <vspace blankLines='1' />

       Once the legitimate client establishes an SSV over
       the new session using Bob's RPCSEC_GSS context,
       Eve can use the new session via the legitimate
       client, but she cannot disrupt Bob.  Moreover,
       because the client SHOULD have modified the SSV
       due to Eve using the new session, Bob cannot get
       revenge on Eve by associating a rogue connection
       with the session. 

       <vspace blankLines='1' />

       The question is how did the legitimate client detect
       that Eve has hijacked the old session?  When the
       client detects that a new principal, Bob, wants to
       use the session, it SHOULD have sent a SET_SSV,
       which leads to the following sub-scenarios:

       <vspace blankLines='1' />

       <list style="symbols">
       <t>
         Let us suppose that from the rogue connection, Eve
         sent a SET_SSV with the same slot ID and sequence ID that
         the legitimate client later uses. The server will
         assume the SET_SSV sent with Bob's credentials is a retry,
         and return to the legitimate
         client the reply it sent Eve. However, unless Eve can
         correctly guess the SSV the legitimate client will use,
         the digest verification checks in the SET_SSV response
         will fail.  That is an indication to the client that the
         session has apparently been hijacked.
         <vspace blankLines='1' />
       </t>
       <t>
         Alternatively, Eve sent a SET_SSV with a different slot ID than
         the legitimate client uses for its SET_SSV. Then the digest
         verification of the SET_SSV sent with Bob's credentials fails
         on the server, and the error returned to the client makes it
         apparent that the session has been hijacked.
         <vspace blankLines='1' />
       </t>
       <t>
         Alternatively, Eve sent an operation other than SET_SSV,
         but with the same slot ID and sequence that the legitimate client
         uses for its SET_SSV. The server returns to the legitimate
         client the response it sent Eve. The client sees that the
         response is not at all what it expects. The client
         assumes either session hijacking or a server bug, and either way
         destroys the old session.
         <vspace blankLines='1' />
       </t>
       </list>
     </t>
     <t>
       Eve associates a rogue connection with the session
       as above, and then destroys the session. Again, Bob
       goes to use the server from the legitimate client,
       which sends a SET_SSV using Bob's credentials. The client receives an error
       that indicates that the session does not exist. When
       the client tries to create a new session, this
       will fail because the SSV it has does not match that which the
       server has, and now the client knows the session
       was hijacked. The legitimate client establishes a
       new client ID.

       <vspace blankLines='1' />

     </t>
     <t>
       If Eve creates a connection before the legitimate
       client establishes an SSV, because the initial
       value of the SSV is zero and therefore known,
       Eve can send a SET_SSV that will pass the digest
       verification check.  However, because the new
       connection has not been associated with the session,
       the SET_SSV is rejected for that reason.

       <vspace blankLines='1' />

     </t>
     </list>
     In summary, an attacker's disruption of state when
     SP4_SSV protection is in use is limited to the
     formative period of a client ID, its first session,
     and the establishment of the SSV. Once a non-malicious
     user uses the client ID, the client quickly detects
     any hijack and rectifies the situation. Once a
     non-malicious user successfully modifies the SSV,
     the attacker cannot use NFSv4.1 operations to disrupt
     the non-malicious user.

   </t>

   <t>
     Note that neither the SP4_MACH_CRED nor
     SP4_SSV protection approaches prevent hijacking
     of a transport connection that has previously been
     associated with a session. If the goal of a counter-threat
     strategy is to prevent connection hijacking, the use of IPsec is RECOMMENDED.
   </t>

   <t>
     If a connection hijack occurs, the hijacker could in
     theory change locking state and negatively impact the
     service to legitimate clients.  However, if the server
     is configured to require the use of RPCSEC_GSS with
     integrity or privacy on the affected file objects, and
     if EXCHGID4_FLAG_BIND_PRINC_STATEID capability (<xref
     target="OP_EXCHANGE_ID"/>) is in force, this will
     thwart unauthorized attempts to change locking state.
   </t>

   </section> <!-- Protection from Unauthorized State Changes -->
  </section> <!-- Sessions Security -->
  <section title="The Secret State Verifier (SSV) GSS Mechanism" anchor="ssv_mech">
  <t>
   The SSV provides the secret key for a GSS mechanism internal to NFSv4.1
   that NFSv4.1 uses for state protection. Contexts for this
   mechanism are not established via the RPCSEC_GSS
   protocol.  Instead, the contexts are automatically
   created when EXCHANGE_ID specifies
   SP4_SSV protection.  The only tokens
   defined are the PerMsgToken (emitted by GSS_GetMIC)
   and the SealedMessage token (emitted by GSS_Wrap).
  </t>
  <t>
   The mechanism OID for the SSV mechanism is
   iso.org.dod.internet.private.enterprise.Michael
   Eisler.nfs.ssv_mech (1.3.6.1.4.1.28882.1.1).  While the
   SSV mechanism does not define any initial context
   tokens, the OID can be used to let servers indicate
   that the SSV mechanism is acceptable whenever the
   client sends a SECINFO or SECINFO_NO_NAME operation
   (see

   <xref target="Security Service Negotiation" />).

  </t>

  <t>
   The SSV mechanism defines four subkeys derived from
   the SSV value. Each time SET_SSV is invoked, the subkeys
   are recalculated by the client and server. The
   calculation of each of the four subkeys depends on each
   of the four respective ssv_subkey4 enumerated values. The calculation
   uses the HMAC
   <xref target="RFC2104" /> algorithm, using the current SSV as the key, the one-way hash
   algorithm as negotiated by EXCHANGE_ID,
   and the input text as represented by the XDR encoded
   enumeration value for that subkey of data type ssv_subkey4.
   If the length of the output of the HMAC algorithm exceeds the length of
   key of the encryption algorithm (which is also negotiated by EXCHANGE_ID),
   then the subkey MUST be truncated from the HMAC output, i.e., if the
   subkey is of N bytes long, then the first N bytes of the HMAC output
   MUST be used for the subkey. The specification of EXCHANGE_ID
   states that the length of the output of the HMAC algorithm MUST NOT
   be less than the length of subkey needed for the encryption algorithm
   (see <xref target="OP_EXCHANGE_ID"/>).
  </t>
<figure>
 <artwork>

/* Input for computing subkeys */
enum ssv_subkey4 {
        SSV4_SUBKEY_MIC_I2T     = 1,
        SSV4_SUBKEY_MIC_T2I     = 2,
        SSV4_SUBKEY_SEAL_I2T    = 3,
        SSV4_SUBKEY_SEAL_T2I    = 4
};

 </artwork>
</figure>
  <t>
   The subkey derived from SSV4_SUBKEY_MIC_I2T
   is used for calculating message integrity codes (MICs)
   that originate from the NFSv4.1 client, whether as part
   of a request over the fore channel or a response
   over the backchannel. The subkey derived from
   SSV4_SUBKEY_MIC_T2I is used for MICs originating from the
   NFSv4.1 server. The subkey derived from SSV4_SUBKEY_SEAL_I2T
   is used for encryption text originating from the NFSv4.1
   client, and the subkey derived from SSV4_SUBKEY_SEAL_T2I
   is used for encryption text originating from the 
   NFSv4.1 server.
  </t>
  <t>
   The PerMsgToken description is based on an XDR definition:
  </t>
<figure>
 <artwork>

/* Input for computing smt_hmac */
struct ssv_mic_plain_tkn4 {
  uint32_t        smpt_ssv_seq;
  opaque          smpt_orig_plain&lt;>;
};

 </artwork>
</figure>
<figure>
 <artwork>

/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
  uint32_t        smt_ssv_seq;
  opaque          smt_hmac&lt;>;
};

 </artwork>
</figure>
  <t>

   The field smt_hmac is an HMAC calculated by using the
   subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I  as the key, the one-way hash algorithm
   as negotiated by EXCHANGE_ID, and the input text
   as represented by data of type ssv_mic_plain_tkn4.
   The field smpt_ssv_seq is the same as smt_ssv_seq.
   The field smpt_orig_plain is the "message" input passed
   to GSS_GetMIC() (see Section 2.3.1 of <xref target="RFC2743"/>).
   The caller of GSS_GetMIC() provides a pointer to a buffer
   containing the plain text. The SSV mechanism's entry point for
   GSS_GetMIC() encodes this into an opaque array, and the encoding
   will include an initial four-byte length, plus any necessary padding.
   Prepended to this will be the XDR encoded value of smpt_ssv_seq,
   thus making up an XDR encoding of a value of data type
   ssv_mic_plain_tkn4, which in turn is the input into the HMAC.
  </t>
  <t>
   The token emitted by GSS_GetMIC() is XDR encoded and
   of XDR data type ssv_mic_tkn4.  The field smt_ssv_seq
   comes from the SSV sequence number, which is equal to
   one after SET_SSV (<xref target="OP_SET_SSV" />)
   is called the first time on a client
   ID.
   Thereafter, the SSV sequence number is incremented on each SET_SSV.
   Thus, smt_ssv_seq represents the version of the SSV at
   the time GSS_GetMIC() was called.  As noted in <xref
   target="OP_EXCHANGE_ID" />, the client and server
   can maintain multiple concurrent versions of the SSV.
   This allows the SSV to be changed without serializing
   all RPC calls that use the SSV mechanism with SET_SSV
   operations.
   Once the HMAC is calculated, it is XDR encoded into
   smt_hmac, which will include an initial four-byte length,
   and any necessary padding. Prepended to this will be
   the XDR encoded value of smt_ssv_seq.

   </t>
  <t>
   The SealedMessage description is based on an XDR definition:
  </t>
<figure>
 <artwork>

/* Input for computing ssct_encr_data and ssct_hmac */
struct ssv_seal_plain_tkn4 {
  opaque          sspt_confounder&lt;>;
  uint32_t        sspt_ssv_seq;
  opaque          sspt_orig_plain&lt;>;
  opaque          sspt_pad&lt;>;
};

 </artwork>
</figure>
<figure>
 <artwork>

/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
  uint32_t      ssct_ssv_seq;
  opaque        ssct_iv&lt;>;
  opaque        ssct_encr_data&lt;>;
  opaque        ssct_hmac&lt;>;
};

 </artwork>
</figure>
  <t>
   The token emitted by GSS_Wrap() is XDR encoded and
   of XDR data type ssv_seal_cipher_tkn4.

  </t>

  <t>
   The ssct_ssv_seq field has the same meaning as smt_ssv_seq.

  </t>

  <t>
   The ssct_encr_data field is the result of encrypting a
   value of the XDR encoded data type ssv_seal_plain_tkn4.
   The encryption key is the subkey derived from SSV4_SUBKEY_SEAL_I2T
   or SSV4_SUBKEY_SEAL_T2I, and the encryption
   algorithm is that negotiated by EXCHANGE_ID.
  </t>

  <t>
   The ssct_iv field is the initialization vector (IV)
   for the encryption algorithm (if applicable) and is
   sent in clear text. The content and size of the IV MUST
   comply with the specification of the encryption algorithm.
   For example, the id-aes256-CBC algorithm MUST use
   a 16-byte initialization vector (IV), which MUST be
   unpredictable for each instance of a value of data type
   ssv_seal_plain_tkn4 that is encrypted with a particular
   SSV key.

  </t>
  <t>
   The ssct_hmac field is the result of computing an HMAC using the value
   of the XDR encoded data type ssv_seal_plain_tkn4 as the input
   text. The key is the subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I, and the one-way hash algorithm is that
   negotiated by EXCHANGE_ID.

  </t>
  <t>
   The sspt_confounder field is a random value.

  </t>
  <t>
   The sspt_ssv_seq field is the same as ssvt_ssv_seq.

  </t>
  <t>
   The field sspt_orig_plain field is the original plaintext
   and is the "input_message" input passed to
   GSS_Wrap() (see Section 2.3.3 of <xref target="RFC2743"/>).
   As with the handling of the plaintext by the SSV mechanism's
   GSS_GetMIC() entry point, the entry point for GSS_Wrap()
   expects a pointer to the plaintext, and will XDR encode
   an opaque array into sspt_orig_plain
   representing the plain text, along with
   the other fields of an instance of data type ssv_seal_plain_tkn4.

  </t>
  <t>
   The sspt_pad field is present to support encryption
   algorithms that require inputs to be in fixed-sized
   blocks.  The content of sspt_pad is zero filled
   except for the length.  Beware that the XDR encoding
   of ssv_seal_plain_tkn4 contains three variable-length
   arrays, and so each array consumes four bytes for an
   array length, and each array that follows the length
   is always padded to a multiple of four bytes per the
   XDR standard.

  </t>
  <t>
   For example, suppose the encryption algorithm uses 16-byte blocks, and
   the sspt_confounder is three bytes long, and
   the sspt_orig_plain field is 15 bytes long.

   The XDR encoding of sspt_confounder uses eight bytes
   (4 + 3 + 1 byte pad),

   the XDR encoding of sspt_ssv_seq uses four bytes,

   the XDR encoding of sspt_orig_plain uses 20 bytes
   (4 + 15 + 1 byte pad),

   and the smallest XDR encoding of the sspt_pad field
   is four bytes.

   This totals 36 bytes. The next multiple of 16 is 48;
   thus, the length field of sspt_pad needs to be set to
   12 bytes, or a total encoding of 16 bytes.

   The total number of XDR encoded bytes is thus 8 +
   4 + 20 + 16 = 48.

  </t>
  <t>
   GSS_Wrap() emits a token that is an XDR
   encoding of a value of data type ssv_seal_cipher_tkn4.

   Note that regardless of whether or not the caller of GSS_Wrap()
   requests confidentiality, the token always has
   confidentiality. This is because the SSV mechanism
   is for RPCSEC_GSS, and RPCSEC_GSS never produces
   GSS_wrap() tokens without confidentiality.

  </t>
  <t>
   There is one SSV per client ID.
   There is a single GSS context for
   a client ID / SSV pair.
   All SSV mechanism RPCSEC_GSS handles of a client ID / SSV pair
   share the same GSS context.
   SSV GSS contexts do not expire except when the SSV
   is destroyed (causes would include the client ID
   being destroyed or a server restart).
   Since one
   purpose of context expiration is to replace keys that
   have been in use for "too long", hence vulnerable to
   compromise by brute force or accident, the client can
   replace the SSV key by
   sending periodic SET_SSV operations, which is done by cycling through
   different users' RPCSEC_GSS credentials. This way, the SSV is
   replaced without destroying the SSV's GSS contexts.
  </t>
  <t>
   SSV RPCSEC_GSS handles can be expired or deleted by the server
   at any time, and the EXCHANGE_ID operation can be used to create
   more SSV RPCSEC_GSS handles. Expiration of SSV RPCSEC_GSS handles
   does not imply that the SSV or its GSS context has expired.
  </t>
  <t>
   The client MUST establish an SSV via SET_SSV before the
   SSV GSS context can be used to emit tokens from GSS_Wrap()
   and GSS_GetMIC(). If SET_SSV has not been successfully
   called, attempts to emit tokens MUST fail.

  </t>
  <t>
   The SSV mechanism does not support replay detection and sequencing
   in its tokens because RPCSEC_GSS does not use those features (See
   Section 5.2.2, "Context Creation Requests", in <xref target="RFC2203"
   />). However, <xref target="rpcsec_ssv_consider"/> discusses special
   considerations for the SSV mechanism when used with RPCSEC_GSS.

  </t>
  </section> <!-- The SSV GSS Mechanism -->

  <section anchor="rpcsec_ssv_consider" title="Security Considerations for RPCSEC_GSS When Using the SSV Mechanism">
  <t>
    When a client ID is created with SP4_SSV state protection (see <xref
    target="OP_EXCHANGE_ID"/>), the client is permitted to associate
    multiple RPCSEC_GSS handles with the single SSV GSS context
    (see <xref target="ssv_mech"/>). Because of the way RPCSEC_GSS
    (both version 1 and version 2, see <xref target="RFC2203"/> and
    <xref target="RFC5403"/>) calculate the verifier of the reply,
    special care must be taken by the implementation of the NFSv4.1
    client to prevent attacks by a man-in-the-middle.  The verifier
    of an RPCSEC_GSS reply is the output of GSS_GetMIC() applied to
    the input value of the seq_num field of the RPCSEC_GSS credential
    (data type rpc_gss_cred_ver_1_t) (see Section 5.3.3.2 of <xref
    target="RFC2203"/>). If multiple RPCSEC_GSS handles share the same
    GSS context, then if one handle is used to send a request with the
    same seq_num value as another handle, an attacker could block the
    reply, and replace it with the verifier used for the other handle.

  </t>

  <t>
   There are multiple ways to prevent the attack on the SSV RPCSEC_GSS
   verifier in the reply. The simplest is believed to be as follows.

   <list style='symbols'>

  <t>
   Each time one or more new SSV RPCSEC_GSS handles are created via
   EXCHANGE_ID, the client SHOULD send a SET_SSV operation to modify
   the SSV. By changing the SSV, the new handles will not result in the
   re-use of an SSV RPCSEC_GSS verifier in a reply.

  </t>
  
  <t>
   When a requester decides to use N SSV RPCSEC_GSS handles, it SHOULD
   assign a unique and non-overlapping range of seq_nums to each SSV
   RPCSEC_GSS handle. The size of each range SHOULD be equal to MAXSEQ
   / N (see Section 5 of <xref target="RFC2203"/> for the definition
   of MAXSEQ). When an SSV RPCSEC_GSS handle reaches its maximum, it
   SHOULD force the replier to destroy the handle by sending a NULL
   RPC request with seq_num set to MAXSEQ + 1 (see Section 5.3.3.3 of
   <xref target="RFC2203"/>).

  </t>

  <t>
   When the requester wants to increase or decrease N, it SHOULD force
   the replier to destroy all N handles by sending a NULL RPC request on
   each handle with seq_num set to MAXSEQ + 1. If the requester is the
   client, it SHOULD send a SET_SSV operation before using new handles.
   If the requester is the server, then the client SHOULD send a SET_SSV
   operation when it detects that the server has forced it to destroy a
   backchannel's SSV RPCSEC_GSS handle. By sending a SET_SSV operation,
   the SSV will change, and so the attacker will be unavailable to
   successfully replay a previous verifier in a reply to the requester.

  </t>

  </list>
  </t>

  <t>
    Note that if the replier carefully creates the SSV RPCSEC_GSS
    handles, the related risk of a man-in-the-middle splicing a forged
    SSV RPCSEC_GSS credential with a verifier for another handle does
    not exist. This is because the verifier in an RPCSEC_GSS request
    is computed from input that includes both the RPCSEC_GSS handle and
    seq_num (see Section 5.3.1 of <xref target="RFC2203"/>). Provided the
    replier takes care to avoid re-using the value of an RPCSEC_GSS
    handle that it creates, such as by including a generation number in the
    handle, the man-in-the-middle will not be able to successfully replay
    a previous verifier in the request to a replier.

  </t>

  </section>

  <section anchor="Session Mechanics - Steady State" title="Session Mechanics - Steady State">

   <section anchor="Obligations of the Server" title="Obligations of the Server">
   <t>
    The server has the primary obligation to monitor the
    state of backchannel resources that the client has
    created for the server (RPCSEC_GSS contexts and backchannel
    connections). If these resources vanish, the
    server takes action as specified in <xref target="Events Requiring Server Action" />.
   </t>
   </section> <!-- Obligations of the Server -->

   <section anchor="Obligations_of_the_Client" title="Obligations of the Client">
   <t>
   The client SHOULD honor the following obligations in order to
   utilize the session:
   <list style="symbols">
   <t>
     Keep a necessary session from going idle on the server. A client
     that requires a session but nonetheless is not
     sending operations risks having the session be destroyed
     by the server. This is because sessions consume
     resources, and resource limitations may force the
     server to cull an inactive session. A server MAY consider
     a session to be inactive if the client has not used
     the session before the session inactivity timer (<xref
     target="session_inactive"/>) has expired.

   </t>
   <t>
     Destroy the session when not needed. If a client has
     multiple sessions, one of which has no
     requests waiting for replies, and has been idle for
     some period of time, it SHOULD destroy the session.
   </t>
   <t>
     Maintain GSS contexts and RPCSEC_GSS handles
     for the backchannel. If the client
     requires the server to use the RPCSEC_GSS security
     flavor for callbacks, then it needs to be sure the
     RPCSEC_GSS handles and/or their GSS
     contexts that are handed to the server via BACKCHANNEL_CTL or
     CREATE_SESSION are unexpired.
   </t>
   <t>
     Preserve a connection for a backchannel. The server
     requires a backchannel in order to gracefully recall
     recallable state or notify the client of certain
     events. Note that if the connection is not being used
     for the fore channel, there is no way for the client to tell
     if the connection is still alive (e.g., the server
     restarted without sending a disconnect). The onus is
     on the server, not the client, to determine if the
     backchannel's connection is alive, and to indicate in
     the response to a SEQUENCE operation when the last
     connection associated with a session's backchannel
     has disconnected.

   </t>
   </list>
   </t>
   </section> <!-- Obligations of the Client -->

   <section anchor="Steps the Client Takes To Establish a Session" title="Steps the Client Takes to Establish a Session">
   <t>
     If the client does not have a client ID, the client
     sends EXCHANGE_ID to establish a client ID.  If it
     opts for SP4_MACH_CRED or SP4_SSV protection, in the
     spo_must_enforce list of operations, it SHOULD at
     minimum specify CREATE_SESSION, DESTROY_SESSION,
     BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID.
     If it opts for SP4_SSV protection, the client needs to
     ask for SSV-based RPCSEC_GSS handles.

   </t>
   <t>
     The client uses the client ID to send a
     CREATE_SESSION on a connection to the server.
     The results of CREATE_SESSION indicate whether or not the
     server will persist the session reply cache through
     a server that has restarted, and the client notes this
     for future reference.

   </t>
   <t>
     If the client specified SP4_SSV state protection
     when the client ID was created, then it SHOULD send
     SET_SSV in the first COMPOUND after the session is
     created. Each time a new principal goes to use the
     client ID, it SHOULD send a SET_SSV again.

   </t>
   <t>
     If the client wants to use delegations, layouts,
     directory notifications, or any other state that
     requires a backchannel, then it needs to add a connection
     to the backchannel if CREATE_SESSION did not already
     do so.  The client creates a connection, and calls
     BIND_CONN_TO_SESSION to associate the connection
     with the session and the session's backchannel. If
     CREATE_SESSION did not already do so, the client MUST
     tell the server what security is required in order
     for the client to accept callbacks. The client does
     this via BACKCHANNEL_CTL. If the client selected
     SP4_MACH_CRED or SP4_SSV protection when it called
     EXCHANGE_ID, then the client SHOULD specify that the
     backchannel use RPCSEC_GSS contexts for security.

   </t>
   <t>
     If the client wants to use additional
     connections for the backchannel, then it needs to call
     BIND_CONN_TO_SESSION on each connection it wants to
     use with the session. If the client wants to use
     additional connections for the fore channel, then
     it needs to call BIND_CONN_TO_SESSION if it specified
     SP4_SSV or SP4_MACH_CRED state protection when the
     client ID was created.

   </t>

   <t>
     At this point, the session has reached steady state.
   </t>
   </section> <!-- Steps the Client Takes To Establish a Session -->
  </section> <!-- Session Mechanics - Steady State -->

  <section anchor="session_inactive" title="Session Inactivity Timer" >
  <t>
   The server MAY maintain a session inactivity timer for
   each session.  If the session inactivity timer expires,
   then the server MAY destroy the session. To avoid losing
   a session due to inactivity, the client MUST renew
   the session inactivity timer. The length of session
   inactivity timer MUST NOT be less than the lease_time
   attribute (<xref target="attrdef_lease_time"/>).
   As with lease renewal (<xref target="lease_renewal"/>),
   when the server receives a SEQUENCE operation,
   it resets the session inactivity timer, and MUST NOT allow the
   timer to expire while the rest of the operations in the
   COMPOUND procedure's request are still executing. Once the
   last operation has finished, the server MUST set the session
   inactivity timer to expire no sooner than the sum of the
   current time and the value of the lease_time attribute.
  </t>

  </section>
  <section anchor="Session Mechanics - Recovery" title="Session Mechanics - Recovery">


   <section anchor="Events Requiring Client Action" title="Events Requiring Client Action">

   <t>
   The following events require client action to recover.
   </t>
   <section title="RPCSEC_GSS Context Loss by Callback Path">
   <t>
    If all RPCSEC_GSS handles
    granted by the client to the server for callback use have
    expired, the client MUST
    establish a new handle via BACKCHANNEL_CTL. The
    sr_status_flags field of the SEQUENCE results indicates when callback handles
    are nearly expired, or fully expired (see <xref target="OP_SEQUENCE_DESCRIPTION"/>).
   </t>
   </section> <!-- RPCSEC_GSS Context Loss by Callback Path -->
   <section title="Connection Loss">
   <t>
    If the client loses the last connection of the session
    and wants to retain the session, then it needs to
    create a new connection, and if, when the client
    ID was created, BIND_CONN_TO_SESSION was specified
    in the spo_must_enforce list, the client MUST use
    BIND_CONN_TO_SESSION to associate the connection with
    the session.

   </t>
   <t>
    If there was a request outstanding at the time
    of connection loss, then if the client wants to continue
    to use the session, it MUST retry the request, as
    described in
    <xref target="Retry and Replay" />. Note that it
    is not necessary to retry requests over a connection
    with the same source network address or the same
    destination network address as the lost connection. As
    long as the session ID, slot ID, and sequence ID in the
    retry match that of the original request, the server
    will recognize the request as a retry if it executed
    the request prior to disconnect.

   </t>
   <t>
    If the connection that was lost was the last one associated with
    the backchannel, and the client wants to retain the backchannel and/or
    prevent revocation of recallable state, the client needs to
    reconnect, and if it does, it
    MUST associate the connection to the session and backchannel via
    BIND_CONN_TO_SESSION.
    The server SHOULD indicate when it has no callback connection
    via the sr_status_flags result from SEQUENCE.
   </t>
   </section> <!-- Connection Disconnect -->
   <section title="Backchannel GSS Context Loss">
   <t>
    Via the sr_status_flags result of the SEQUENCE operation or
    other means, the client will learn if some or all of
    the RPCSEC_GSS contexts it assigned to the backchannel have
    been lost. If the client wants to retain the backchannel and/or
    not put recallable state subject to revocation,
    the client needs to use BACKCHANNEL_CTL to
    assign new contexts.
   </t>
   </section> <!-- Backchannel GSS Context Loss -->

    <section anchor="loss_of_session" title="Loss of Session">
    <t>
     The replier might lose a record of the session. Causes include:
     <list style="symbols">
      <t>
        Replier failure and restart.
      </t>
      <t>
        A catastrophe that causes the reply cache to be corrupted or
        lost on the media on which it was stored. This applies
        even if the replier indicated in the CREATE_SESSION results
        that it would persist the cache.
      </t>
      <t>
        The server purges the session of a client that has been
        inactive for a very extended period of time.
      </t>
      <t>
        As a result of configuration changes among a set of clustered
        servers, a network address previously connected to one 
        server becomes connected to a different server that has
        no knowledge of the session in question.  Such a configuration
        change will generally only happen when the original server
        ceases to function for a time.
      </t>
     </list>
     Loss of reply cache is equivalent to loss of session.
     The replier indicates loss of session to the requester
     by returning NFS4ERR_BADSESSION on the next operation
     that uses the session ID that refers to the lost
     session.
    </t>
    <t>
     After an event like a server restart, the client may have
     lost its connections. The client assumes for the moment
     that the session has not been lost. It reconnects, and
     if it specified connection association enforcement when
     the session was created, it 
     invokes BIND_CONN_TO_SESSION using the session ID. Otherwise,
     it invokes SEQUENCE. If
     BIND_CONN_TO_SESSION or SEQUENCE returns NFS4ERR_BADSESSION, the
     client knows the session is not available to it when communicating
     with that network address. If the connection survives
     session loss, then the next SEQUENCE operation the client
     sends over the connection will get back NFS4ERR_BADSESSION.
     The client again knows the session was lost.
    </t>
    <t>
     Here is one suggested algorithm for the client when it gets 
     NFS4ERR_BADSESSION.  It is not obligatory in that, if a 
     client does not want to take advantage of such features as 
     trunking, it may omit parts of it.  However, it is a useful
     example that draws attention to various possible recovery 
     issues:
     <list style="numbers">
       <t>
         If the client has other connections to
         other server network addresses
         associated with the same session, attempt
         a COMPOUND with a single operation, SEQUENCE,
         on each of the other connections.
       </t>
       <t>
         If the attempts succeed, the session is still alive,
         and this is a strong indicator that the server's
         network address has moved.
         The client might send an EXCHANGE_ID on the
         connection that returned NFS4ERR_BADSESSION
         to see if there are opportunities for client ID
         trunking (i.e., the same client ID and so_major are
         returned). The client might use DNS to see if
         the moved network address was replaced with another,
         so that the performance and availability benefits of
         session trunking can continue.
       </t>
       <t>
         If the SEQUENCE requests fail with NFS4ERR_BADSESSION,
         then the session no longer exists on any of the
         server network addresses for which the client has connections
         associated with that session ID. It is possible the
         session is still alive and available on other
         network addresses. The client sends an EXCHANGE_ID
         on all the connections to see if the server owner
         is still listening on those network addresses.
         If the same server owner is returned but a new
         client ID is returned, this is a strong
         indicator of a server restart. If both the same
         server owner and same client ID are
         returned, then this is a strong indication
         that the server did delete the session, and the
         client will need to send a CREATE_SESSION if it
         has no other sessions for that client ID.
         If a different server owner is returned,
         the client can use DNS to find
         other network addresses. If it does not, or if
         DNS does not find any other addresses for the server,
         then the client will be unable to provide NFSv4.1
         service, and fatal errors should be returned
         to processes that were using the server. If the
         client is using a "mount" paradigm, unmounting
         the server is advised.
       </t>
       <t>
         If the client knows of no other connections associated
         with the session ID and server network addresses that
         are, or have been, associated with the session ID,
         then the client can use DNS to find
         other network addresses. If it does not, or if
         DNS does not find any other addresses for the server,
         then the client will be unable to provide NFSv4.1
         service, and fatal errors should be returned
         to processes that were using the server. If the
         client is using a "mount" paradigm, unmounting
         the server is advised.
       </t>
     </list>
    </t>
    <t>
      If there is a reconfiguration event that results in the 
      same network address being assigned to servers where the 
      eir_server_scope value is different, it cannot be guaranteed
      that a session ID generated by the first will be recognized
      as invalid by the first.  Therefore, in managing server
      reconfigurations among servers with different server scope
      values, it is necessary to make sure that all clients have
      disconnected from the first server before effecting
      the reconfiguration.  Nonetheless, clients should not
      assume that servers will always adhere to this requirement;
      clients MUST be prepared to deal with unexpected
      effects of server reconfigurations.
      Even where a session ID is inappropriately 
      recognized as valid, it is likely either that the connection 
      will not be recognized as valid or that a sequence value
      for a slot will not be correct.  Therefore, when a client
      receives results indicating such unexpected errors, the use of
      EXCHANGE_ID to determine the current server configuration
      is RECOMMENDED.
    </t>
    <t>
      A variation on the above is that after a server's network 
      address moves, there is no NFSv4.1 server listening, e.g., no 
      listener on port 2049. In this example, one of the following occur: the NFSv4 server returns 
      NFS4ERR_MINOR_VERS_MISMATCH, the NFS server returns a 
      PROG_MISMATCH error, the RPC listener on 2049 returns 
      PROG_UNVAIL, or attempts to reconnect to the network address 
      timeout. These SHOULD be treated as equivalent to SEQUENCE 
      returning NFS4ERR_BADSESSION for these purposes.
    </t>
    <t>
     When the client detects session loss, it needs to call CREATE_SESSION
     to recover.  Any non-idempotent operations that were in progress
     might have been performed on the server at the time of
     session loss. The client has no general way to recover from this.
    </t>
    <t>
     Note that loss of session does not imply loss of byte-range lock, open, delegation,
     or layout state because locks, opens, delegations, and layouts
     are tied to the client ID and depend on the client ID, not the session.
     Nor does loss of byte-range lock, open, delegation,
     or layout state imply loss of session state, because the session depends
     on the client ID; loss of client ID however does imply loss of
     session, byte-range lock, open, delegation, and layout state.
     See <xref target="server_failure" />.
     A session can survive a server restart,
     but lock recovery may still be needed.
    </t>
    <t>
     It is possible that CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
     (e.g., the server restarts and does not preserve client ID
     state).
     If so, the client needs to call EXCHANGE_ID, followed by 
     CREATE_SESSION.
    </t>
    </section> <!-- Loss of Session -->
   </section> <!-- Events Requiring Client Action -->

   <section anchor="Events Requiring Server Action" title="Events Requiring Server Action">
   <t>
     The following events require server action to recover.
   </t>
    <section title="Client Crash and Restart">
    <t>
    As described in <xref target="OP_EXCHANGE_ID" />,
    a restarted client sends EXCHANGE_ID in such a way that it
    causes the server to delete any sessions it had.
    </t>
    </section> <!-- Client Crash and Restart -->
    <section title="Client Crash with No Restart" anchor="client_crash_no_restart">
    <t>
    If a client crashes and never comes back, it will never send
    EXCHANGE_ID with its old client owner. Thus, the server has session
    state that will never be used again. After an extended period of time,
    and if the server has resource constraints, it MAY destroy the old
    session as well as locking state.
    </t>
    </section> <!-- Client Crash with No Restart -->
    <section title="Extended Network Partition">
    <t>
     To the server, the extended network partition may be no
     different from a
     client crash with no
     restart (see
     <xref target="client_crash_no_restart" />).
     Unless the server can discern that there is
     a network partition, it is free to treat the
     situation as if the client has crashed permanently.
    </t>
    </section> <!-- "Extended Network Partition" -->
    <section title="Backchannel Connection Loss">
    <t>
     If there were callback requests outstanding at the time
     of a connection loss, then the server
     MUST retry the requests, as described in
     <xref target="Retry and Replay" />. Note that it
     is not necessary to retry requests over a connection
     with the same source network address or the same destination
     network address as the lost connection. As long as
     the session ID, slot ID, and sequence ID in the retry
     match that of the original request, the callback target will
     recognize the request as a retry even if it did see the request
     prior to disconnect.
    </t>
    <t>
     If the connection lost is the last one associated with the backchannel,
     then the server MUST indicate that in the sr_status_flags field of
     every SEQUENCE reply until the backchannel is re-established.
     There are two situations, each of which uses different
     status flags: no connectivity for the session's backchannel
     and no connectivity for any session backchannel of the client.
     See <xref target="OP_SEQUENCE" /> for a description of
     the appropriate flags in sr_status_flags.
    </t>
    </section> <!-- Backchannel Connection Loss -->
    <section title="GSS Context Loss">
    <t>
     The server SHOULD monitor when the number of RPCSEC_GSS
     handles assigned to the backchannel reaches one, and when that
     one handle is near expiry (i.e., between
     one and two periods of lease time), and
     indicate so in the sr_status_flags field of all SEQUENCE replies.
     The server MUST indicate when all of the
     backchannel's assigned RPCSEC_GSS handles
     have expired via the sr_status_flags field of all SEQUENCE replies.
    </t>
    </section> <!-- GSS Context Loss -->
   </section> <!-- Events Requiring Server Action -->
  </section> <!-- Session Mechanics - Recovery -->
  <section title="Parallel NFS and Sessions" anchor="pnfs_and_sessions">
  <t>
   A client and server can potentially be a non-pNFS implementation,
   a metadata server implementation, a data server implementation, or two or
   three types of implementations. The EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags
   (not mutually exclusive) are passed in the EXCHANGE_ID arguments
   and results to allow the client to indicate how it wants to use sessions created
   under the client ID, and to allow the server to indicate how it
   will allow the sessions to be used.
   See <xref target="pnfs_session_stuff" /> for pNFS sessions considerations.
  </t>
  </section> <!-- Parallel NFS and Sessions -->
 </section> <!-- Session -->
</section> <!-- Core Infrastructure -->
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Protocol Constants and Data Types">
  <t>
    The syntax and semantics to describe the data types of the NFSv4.1
    protocol are defined in the XDR <xref target="RFC4506">RFC 4506</xref> and RPC 
    <xref target="RFC5531">RFC 5531</xref> documents.  The next sections
    build upon the XDR data types to define constants, types, and structures
    specific to this protocol. The full list of XDR data types is in <xref target="RFC5662" />.
  </t>

  <section title="Basic Constants">
<figure>
 <artwork>
const NFS4_FHSIZE               = 128;
const NFS4_VERIFIER_SIZE        = 8;
const NFS4_OPAQUE_LIMIT         = 1024;
const NFS4_SESSIONID_SIZE       = 16;

const NFS4_INT64_MAX            = 0x7fffffffffffffff;
const NFS4_UINT64_MAX           = 0xffffffffffffffff;
const NFS4_INT32_MAX            = 0x7fffffff;
const NFS4_UINT32_MAX           = 0xffffffff;

const NFS4_MAXFILELEN           = 0xffffffffffffffff;
const NFS4_MAXFILEOFF           = 0xfffffffffffffffe;
 </artwork>
</figure>
  <t>
    Except where noted, all these constants are defined in bytes.
    <list style="symbols">
    <t>
       NFS4_FHSIZE is the maximum size of a filehandle.
    </t>
    <t>
       NFS4_VERIFIER_SIZE is the fixed size of a verifier.
    </t>
    <t>
       NFS4_OPAQUE_LIMIT is the maximum size of certain
       opaque information.
    </t>
    <t>
       NFS4_SESSIONID_SIZE is the fixed size of a session identifier.
    </t>
    <t>
       NFS4_INT64_MAX is the maximum value of a signed 64-bit integer.
    </t>
    <t>
       NFS4_UINT64_MAX is the maximum value of an unsigned 64-bit integer.
    </t>
    <t>
       NFS4_INT32_MAX is the maximum value of a signed 32-bit integer.
    </t>
    <t>
       NFS4_UINT32_MAX is the maximum value of an unsigned 32-bit integer.
    </t>
    <t>
       NFS4_MAXFILELEN is the maximum length of a regular file.
    </t>
    <t>
       NFS4_MAXFILEOFF is the maximum offset into a regular file.
    </t>
    </list>
  </t>
  </section>

  <section title="Basic Data Types">
      <t>
	These are the base NFSv4.1 data types.
      </t>
    <texttable anchor='basic_data_types'>

      <ttcol align='left'>Data Type</ttcol>
      <ttcol align='left'>Definition</ttcol>
	<c>int32_t</c>		<c>typedef int int32_t;</c>

	<c>uint32_t</c>		<c>typedef unsigned int uint32_t;</c>

	<c>int64_t</c>		<c>typedef hyper int64_t;</c>

	<c>uint64_t</c>		<c>typedef unsigned hyper uint64_t;</c>

	<c>attrlist4</c>		<c>typedef opaque attrlist4&lt;>;</c>
	<c/>	<c>Used for file/directory attributes.</c>

	<c>bitmap4</c>		<c>typedef uint32_t bitmap4&lt;>;</c>
	<c/>	<c>Used in attribute array encoding.</c>

	<c>changeid4</c>		<c>typedef uint64_t changeid4;</c>
	<c/>	<c>Used in the definition of change_info4.</c>

	<c>clientid4</c>		<c>typedef uint64_t clientid4;</c>
	<c/>	<c>Shorthand reference to client identification.</c>

	<c>count4</c>		<c>typedef uint32_t count4;</c>
	<c/>	<c>Various count parameters (READ, WRITE, COMMIT).</c>

	<c>length4</c>		<c>typedef uint64_t length4;</c>
	<c/>	<c>The length of a byte-range within a file.</c>

	<c>mode4</c>		<c>typedef uint32_t mode4;</c>
	<c/>	<c>Mode attribute data type.</c>

	<c>nfs_cookie4</c>		<c>typedef uint64_t nfs_cookie4;</c>
	<c/>	<c>Opaque cookie value for READDIR.</c>

	<c>nfs_fh4</c>		<c>typedef opaque nfs_fh4&lt;NFS4_FHSIZE>;</c>
	<c/>	<c>Filehandle definition.</c>

	<c>nfs_ftype4</c>		<c>enum nfs_ftype4;</c>
	<c/>	<c>Various defined file types.</c>

	<c>nfsstat4</c>		<c>enum nfsstat4;</c>
	<c/>	<c>Return value for operations.</c>

	<c>offset4</c>		<c>typedef uint64_t offset4;</c>
	<c/>	<c>Various offset designations (READ, WRITE, LOCK, COMMIT).</c>

	<c>qop4</c>		<c>typedef uint32_t qop4;</c>
	<c/>	<c>Quality of protection designation in SECINFO.</c>

	<c>sec_oid4</c>		<c>typedef opaque sec_oid4&lt;>;</c>
	<c/>	<c>Security Object Identifier. The sec_oid4 data type is not really opaque. Instead, it contains an ASN.1 OBJECT IDENTIFIER as used by GSS-API in the mech_type argument to GSS_Init_sec_context. See <xref target="RFC2743" /> for details.</c>

	<c>sequenceid4</c>		<c>typedef uint32_t sequenceid4;</c>
	<c/>	<c>Sequence number used for various session operations (EXCHANGE_ID, CREATE_SESSION, SEQUENCE, CB_SEQUENCE).</c>

	<c>seqid4</c>		<c>typedef uint32_t seqid4;</c>
	<c/>	<c>Sequence identifier used for locking.</c>

	<c>sessionid4</c>		<c>typedef opaque sessionid4[NFS4_SESSIONID_SIZE];</c>
	<c/>	<c>Session identifier.</c>

	<c>slotid4</c>		<c>typedef uint32_t slotid4;</c>
	<c/>	<c>Sequencing artifact for various session operations (SEQUENCE, CB_SEQUENCE).</c>

	<c>utf8string</c>		<c>typedef opaque utf8string&lt;>;</c>
	<c/>	<c>UTF-8 encoding for strings.</c>

	<c>utf8str_cis</c>		<c>typedef utf8string utf8str_cis;</c>
	<c/>	<c>Case-insensitive UTF-8 string.</c>

	<c>utf8str_cs</c>		<c>typedef utf8string utf8str_cs;</c>
	<c/>	<c>Case-sensitive UTF-8 string.</c>

	<c>utf8str_mixed</c>		<c>typedef utf8string utf8str_mixed;</c>
	<c/>	<c>UTF-8 strings with a case-sensitive prefix and a
	case-insensitive suffix.</c>

	<c>component4</c>		<c>typedef utf8str_cs component4;</c>
	<c/>	<c>Represents pathname components.</c>

	<c>linktext4</c>		<c>typedef utf8str_cs linktext4;</c>
	<c/>	<c>Symbolic link contents ("symbolic link" is defined in an <xref target="symlink">Open Group</xref> standard).</c>

	<c>pathname4</c>		<c>typedef component4 pathname4&lt;>;</c>
	<c/>	<c>Represents pathname for fs_locations.</c>

	<c>verifier4</c>		<c>typedef opaque verifier4[NFS4_VERIFIER_SIZE];</c>
	<c/>	<c>Verifier used for various operations (COMMIT, CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE) NFS4_VERIFIER_SIZE is defined as 8.</c>

      <postamble>End of Base Data Types</postamble>
    </texttable>
  </section>

  <!-- start here for the structured data types -->

  <section title="Structured Data Types">

    <section toc="exclude" anchor="nfstime4" title="nfstime4">
<figure>
 <artwork>
struct nfstime4 {
        int64_t         seconds;
        uint32_t        nseconds;
};
 </artwork>
</figure>
      <t>
	The nfstime4 data type gives the number of seconds and
	nanoseconds since midnight or zero hour January 1, 1970
	Coordinated Universal Time (UTC).  Values greater than zero
	for the seconds field denote dates after the zero hour January 1,
	1970.  Values less than zero for the seconds field denote
	dates before the zero hour January 1, 1970.  In both cases, the
	nseconds field is to be added to the seconds field for the
	final time representation.  For example, if the time to be
	represented is one-half second before zero hour January 1, 1970,
	the seconds field would have a value of negative one (-1) and
	the nseconds field would have a value of one-half second
	(500000000).  Values greater than 999,999,999 for nseconds are
	invalid.
      </t>
      <t>
	This data type is used to pass time and date information.  A
	server converts to and from its local representation of time
	when processing time values, preserving as much accuracy as
	possible. If the precision of timestamps stored for a
	file system object is less than defined, loss of precision can
	occur.  An adjunct time maintenance protocol is RECOMMENDED to
	reduce client and server time skew.
      </t>
    </section>

    <section toc="exclude" anchor="time_how4" title="time_how4">
<figure>
 <artwork>
enum time_how4 {
        SET_TO_SERVER_TIME4 = 0,
        SET_TO_CLIENT_TIME4 = 1
};
 </artwork>
</figure>
    </section>

    <section toc="exclude" anchor="settime4" title="settime4">
<figure>
 <artwork>
union settime4 switch (time_how4 set_it) {
 case SET_TO_CLIENT_TIME4:
         nfstime4       time;
 default:
         void;
};
 </artwork>
</figure>
      <t>
	The time_how4 and settime4 data types are used
	for setting timestamps in file object attributes.  If set_it is SET_TO_SERVER_TIME4, then the server
	uses its local representation of time for the time value.
      </t>
    </section>

    <section toc="exclude" anchor="specdata4" title="specdata4">
<figure>
 <artwork>
struct specdata4 {
 uint32_t specdata1; /* major device number */
 uint32_t specdata2; /* minor device number */
};
 </artwork>
</figure>
      <t>
	This data type represents the device numbers for the device file
	types NF4CHR and NF4BLK.
      </t>
    </section>

    <section toc="exclude" anchor="fsid4" title="fsid4">
<figure>
 <artwork>
struct fsid4 {
        uint64_t        major;
        uint64_t        minor;
};
 </artwork>
</figure>
    </section>

    <section toc="exclude" anchor="chg_policy4" title="change_policy4">
<figure>
 <artwork>
struct change_policy4 {
        uint64_t        cp_major;
        uint64_t        cp_minor;
};
 </artwork>
</figure>
      <t>
         The change_policy4 data type is used for the change_policy
         RECOMMENDED attribute.  It provides change sequencing indication
         analogous to the change attribute.  To enable the server to 
         present a value valid across server re-initialization without
         requiring persistent storage, two 64-bit quantities are used,
         allowing one to be a server instance ID and the second to be
         incremented non-persistently, within a given server instance.
      </t>
    </section>

    <section toc="exclude" anchor="fattr4" title="fattr4">
<figure>
 <artwork>
struct fattr4 {
        bitmap4         attrmask;
        attrlist4       attr_vals;
};
 </artwork>
</figure>
      <t>
	The fattr4 data type is used to represent file and directory attributes.
      </t>
      <t>
	The bitmap is a counted array of 32-bit integers used to contain bit
	values.  The position of the integer in the array that contains bit n
	can be computed from the expression (n / 32), and its bit within that
	integer is (n mod 32).
      </t>
      <t>
	<figure>
	  <artwork>
0            1       
+-----------+-----------+-----------+--
|  count    | 31  ..  0 | 63  .. 32 |  
+-----------+-----------+-----------+--
	  </artwork>
	</figure>
      </t>
    </section>

    <section toc="exclude" anchor="change_info4" title="change_info4">
<figure>
 <artwork>
struct change_info4 {
        bool            atomic;
        changeid4       before;
        changeid4       after;
};
 </artwork>
</figure>
      <t>
	This data type is used with the CREATE, LINK, OPEN, REMOVE, and RENAME
	operations to let the client know the value of the change attribute
	for the directory in which the target file system object resides.
      </t>
    </section>

    <section toc="exclude" anchor="netaddr4" title="netaddr4">
<figure>
 <artwork>
struct netaddr4 {
        /* see struct rpcb in RFC 1833 */
        string na_r_netid&lt;>; /* network id */
        string na_r_addr&lt;>;  /* universal address */
};
 </artwork>
</figure>
      <t>
	The netaddr4 data type is used to identify network transport endpoints.
	The r_netid and r_addr fields respectively contain a netid
        and uaddr. The netid and uaddr concepts are defined in
	<xref target="RFC5665"/>. The netid and uaddr formats for
        TCP over IPv4 and TCP over IPv6 are defined in <xref target="RFC5665"/>,
        specifically Tables 2 and 3 and Sections 5.2.3.3 and 5.2.3.4.
      </t>

    </section>

    <section toc="exclude" anchor="state_owner4" title="state_owner4">
<figure>
 <artwork>
struct state_owner4 {
        clientid4       clientid;
        opaque          owner&lt;NFS4_OPAQUE_LIMIT>;
};

typedef state_owner4 open_owner4;
typedef state_owner4 lock_owner4;
 </artwork>
</figure>
    <t>
     The state_owner4 data type is the base type for the 
     open_owner4 (<xref target="open_owner4" />) and
     lock_owner4 (<xref target="lock_owner4" />.
    </t>

     <section toc="exclude" anchor="open_owner4" title="open_owner4">
       <t>
	 This data type is used to identify the owner of OPEN state.
       </t>
     </section>

     <section toc="exclude" anchor="lock_owner4" title="lock_owner4">
       <t>
	 This structure is used to identify the owner of byte-range
         locking state.
       </t>
     </section>
    </section>

    <section toc="exclude" anchor="open_to_lock_owner4" 
	     title="open_to_lock_owner4">
<figure>
 <artwork>
struct open_to_lock_owner4 {
        seqid4          open_seqid;
        stateid4        open_stateid;
        seqid4          lock_seqid;
        lock_owner4     lock_owner;
};
 </artwork>
</figure>
      <t>
	This data type is used for the first LOCK operation done for
	an open_owner4.  It provides both the open_stateid and
	lock_owner, such that the transition is made from a valid
	open_stateid sequence to that of the new lock_stateid
	sequence.  Using this mechanism avoids the confirmation of the
	lock_owner/lock_seqid pair since it is tied to established
	state in the form of the open_stateid/open_seqid.
      </t>
    </section>

    <section toc="exclude" anchor="stateid4" title="stateid4">
<figure>
 <artwork>
struct stateid4 {
        uint32_t        seqid;
        opaque          other[12];
};
 </artwork>
</figure>
      <t>
	This data type is used for the various state sharing
	mechanisms between the client and server.  The client
	never modifies a value of data type stateid.
        The starting value of the
	"seqid" field is undefined.  The server is required to
	increment the "seqid" field by one at each transition
	of the stateid.  This is important since the client will
	inspect the seqid in OPEN stateids to determine the order of
	OPEN processing done by the server.
      </t>
    </section>

    <section toc="exclude" anchor="layouttype4" title="layouttype4">
<figure>
 <artwork>
enum layouttype4 {
        LAYOUT4_NFSV4_1_FILES   = 0x1,
        LAYOUT4_OSD2_OBJECTS    = 0x2,
        LAYOUT4_BLOCK_VOLUME    = 0x3
};
 </artwork>
</figure>

      <t>
	This data type indicates what type of layout is being used.
	The file server advertises the
	layout types it supports through the fs_layout_type file
	system attribute (<xref target="attrdef_fs_layout_type" />).
	A client asks for layouts of a particular type in LAYOUTGET,
	and processes those layouts in its layout-type-specific logic.
      </t>
      <t>
	The layouttype4 data type is 32 bits in length.  The range
	represented by the layout type is split into three parts.  Type
        0x0 is reserved. Types
	within the range 0x00000001-0x7FFFFFFF are globally unique and
	are assigned according to the description in <xref
	target="pnfsiana" />; they are maintained by IANA.  Types
	within the range 0x80000000-0xFFFFFFFF are site specific and
	for private use only.
      </t>
      <t>
	The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1
	file layout type, as defined in <xref target="file_layout_type" />, is to be used.  The LAYOUT4_OSD2_OBJECTS
	enumeration specifies that the object layout, as defined in
	<xref target="RFC5664" />, is to be used.  Similarly,
	the LAYOUT4_BLOCK_VOLUME enumeration specifies that the block/volume
	layout, as defined in <xref target="RFC5663" />, is to be
	used.
      </t>
    </section>

    <section toc="exclude" anchor="deviceid4" title="deviceid4">
<figure>
 <artwork>
const NFS4_DEVICEID4_SIZE = 16;

typedef opaque  deviceid4[NFS4_DEVICEID4_SIZE];
 </artwork>
</figure>
      <t>
	Layout information includes device IDs that
	specify a storage device through a compact handle.
	Addressing and type information is obtained
	with the GETDEVICEINFO operation.  Device IDs
	are not guaranteed to be valid across metadata
	server restarts.  A device ID is unique per client
	ID and layout type.  See <xref target="device_ids"
	/> for more details.

      </t>
    </section>
    <section toc="exclude" anchor="device_addr4"
	     title="device_addr4">
<figure>
 <artwork>
struct device_addr4 {
        layouttype4             da_layout_type;
        opaque                  da_addr_body&lt;>;
};
 </artwork>
</figure>
      <t>
        The device address is used to set up a communication channel
        with the storage device.  Different layout types will require
        different data types to define how they communicate
        with storage devices.  The opaque da_addr_body field is
        interpreted based on the specified da_layout_type field.
      </t>
      <t>
        This document defines the device address for the NFSv4.1 file
        layout (see <xref target="file_data_types" />), which
        identifies a storage device by network IP address and port
        number.  This is sufficient for the clients to communicate
        with the NFSv4.1 storage devices, and may be sufficient for
        other layout types as well.  Device types for object-based storage
        devices and block storage devices (e.g., Small Computer System
         Interface (SCSI) volume labels)
        are defined by their respective layout specifications.
      </t>
    </section>

    <section toc="exclude" anchor="layout_content4" title="layout_content4">
<figure>
 <artwork>
struct layout_content4 {
        layouttype4 loc_type;
        opaque      loc_body&lt;>;
};
 </artwork>
</figure>
      <t>
        The loc_body field is interpreted based on the layout type (loc_type). 
        This document defines the loc_body for the NFSv4.1
	file layout type; see <xref target="file_data_types"
	/> for its definition. 
      </t>
    </section>
    <section toc="exclude" anchor="layout4" title="layout4">
<figure>
 <artwork>
struct layout4 {
        offset4                 lo_offset;
        length4                 lo_length;
        layoutiomode4           lo_iomode;
        layout_content4         lo_content;
};
 </artwork>
</figure>
      <t>
	The layout4 data type defines a layout for a file.  The layout
	type specific data is opaque within lo_content.
        Since layouts are sub-dividable, the offset
	and length together with the file's filehandle, the client ID,
	iomode, and layout type identify the layout.
      </t>
    </section>

    <section toc="exclude" anchor="layoutupdate4"
	     title="layoutupdate4">
<figure>
 <artwork>
struct layoutupdate4 {
        layouttype4             lou_type;
        opaque                  lou_body&lt;>;
};
 </artwork>
</figure>
      <t>
	The layoutupdate4 data type is used by the client to return
	updated layout information to the metadata server via the
	LAYOUTCOMMIT (<xref target="OP_LAYOUTCOMMIT" />) operation.
	This data type provides a channel to pass
	layout type specific information (in field lou_body)
        back to the metadata server.
	For example, for the block/volume layout type, this could include the
	list of reserved blocks that were written.  The contents of
	the opaque lou_body argument are determined by the layout type.
	The NFSv4.1 file-based layout
	does not use this data type; if lou_type is LAYOUT4_NFSV4_1_FILES,
        the lou_body field MUST
	have a zero length.
      </t>
    </section>

    <section toc="exclude" anchor="layouthint4" title="layouthint4">
<figure>
 <artwork>
struct layouthint4 {
        layouttype4             loh_type;
        opaque                  loh_body&lt;>;
};
 </artwork>
</figure>
      <t>
	The layouthint4 data type is used by the client to pass in a
	hint about the type of layout it would like created for a particular
	file.  It is the data type specified by the layout_hint
	attribute described in <xref target="attrdef_layout_hint" />.
	The metadata server may ignore the hint
	or may selectively ignore fields within the hint.  This hint should
	be provided at create time as part of the initial attributes within
	OPEN.  The loh_body field is specific to the type of layout (loh_type).
        The NFSv4.1 file-based layout uses the nfsv4_1_file_layouthint4
	data type as defined in <xref target="file_data_types" />.
      </t>
    </section>


    <section toc="exclude" anchor="layoutiomode4"
	     title="layoutiomode4">
<figure>
 <artwork>
enum layoutiomode4 {
        LAYOUTIOMODE4_READ      = 1,
        LAYOUTIOMODE4_RW        = 2,
        LAYOUTIOMODE4_ANY       = 3
};
 </artwork>
</figure>
      <t>
	The iomode specifies whether the client intends to just read or both
        read and write the data represented by the
	layout.  While the LAYOUTIOMODE4_ANY iomode MUST NOT be used in
        the arguments to the LAYOUTGET operation, it MAY
	be used in the arguments to the LAYOUTRETURN and CB_LAYOUTRECALL
        operations.  The LAYOUTIOMODE4_ANY iomode
	specifies that layouts pertaining to both LAYOUTIOMODE4_READ
        and LAYOUTIOMODE4_RW iomodes are being returned or recalled,
        respectively.  The metadata server's use of the iomode may
        depend on the layout type being used.  The storage devices MAY
        validate I/O accesses against the iomode and reject invalid accesses.
      </t>
    </section>

    <section toc="exclude" anchor="nfs_impl_id4" title="nfs_impl_id4">
<figure>
 <artwork>
struct nfs_impl_id4 {
        utf8str_cis   nii_domain;
        utf8str_cs    nii_name;
        nfstime4      nii_date;
};
 </artwork>
</figure>
      <t>
	This data type is used to identify client and server
	implementation details.  The nii_domain field is the DNS domain
	name with which the implementor is associated.  The nii_name
	field is the product name of the implementation and is
	completely free form.  It is RECOMMENDED that the nii_name be
	used to distinguish machine architecture, machine platforms,
	revisions, versions, and patch levels.  The nii_date field is
	the timestamp of when the software instance was published or
	built.
      </t>
    </section>

    <section toc="exclude" anchor="threshold_item4" title="threshold_item4">
<figure>
 <artwork>
struct threshold_item4 {
        layouttype4     thi_layout_type;
        bitmap4         thi_hintset;
        opaque          thi_hintlist&lt;>;
};
 </artwork>
</figure>
      <t>
	This data type contains a list of hints specific to
	a layout type for helping the client determine when
	it should send I/O directly through the metadata
	server versus the storage devices.  The data type
	consists of the layout type (thi_layout_type),
	a bitmap (thi_hintset) describing the set of
	hints supported by the server (they may differ
	based on the layout type), and a list of hints
	(thi_hintlist) whose content is determined by
	the hintset bitmap.  See the mdsthreshold attribute
	for more details.

      </t>
      <t>
        The thi_hintset field is a bitmap of the following values:
      </t>
      <texttable>
        <ttcol align='left'>name</ttcol>
        <ttcol align='left'>#</ttcol>
        <ttcol align='left'>Data Type</ttcol>
        <ttcol align='left'>Description</ttcol>
  
        <c>threshold4_read_size</c><c>0</c><c>length4</c>
        <c>
           If a file's length is less than the value of threshold4_read_size,
           then it is RECOMMENDED that the client read from the file via the MDS and not
           a storage device.

        </c>
        <c>threshold4_write_size</c><c>1</c><c>length4</c>
        <c>
           If a file's length is less than the value of threshold4_write_size,
           then it is RECOMMENDED that the client write to the file via the MDS and not
           a storage device.
        </c>
        <c>threshold4_read_iosize</c><c>2</c><c>length4</c>
        <c>
          For read I/O sizes below this threshold, it is RECOMMENDED to
  	read data through the MDS.
        </c>
        <c>threshold4_write_iosize</c><c>3</c><c>length4</c>
        <c>
          For write I/O sizes below this threshold, it is RECOMMENDED to
  	write data through the MDS.
        </c>
      </texttable>      
    </section>

    <section toc="exclude" anchor="mdsthreshold4" title="mdsthreshold4">
<figure>
 <artwork>
struct mdsthreshold4 {
        threshold_item4 mth_hints&lt;>;
};
 </artwork>
</figure>
      <t>
        This data type holds an array of elements of data type
        threshold_item4,
	each of which is valid for a particular layout type.  An array
	is necessary because a server can support multiple layout types
	for a single file.
      </t>
    </section>

  </section>
</section>

<!-- End of Data Types -->

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="Filehandles" title="Filehandles">
  <t>
    The filehandle in the NFS protocol is a per-server unique identifier
    for a file system object.  The contents of the filehandle are opaque
    to the client.  Therefore, the server is responsible for translating
    the filehandle to an internal representation of the file system
    object.
  </t>
  <section title="Obtaining the First Filehandle">
    <t>
      The operations of the NFS protocol are defined in terms of one
      or more filehandles.  Therefore, the client needs a filehandle
      to initiate communication with the server.  With the NFSv3
      protocol (<xref target="RFC1813">RFC 1813</xref>), there
      exists an ancillary protocol to obtain this first filehandle.
      The MOUNT protocol, RPC program number 100005, provides the
      mechanism of translating a string-based file system pathname to
      a filehandle, which can then be used by the NFS protocols.
    </t>
    <t>
      The MOUNT protocol has deficiencies in the area of security and
      use via firewalls.  This is one reason that the use of the
      public filehandle was introduced in <xref
      target="RFC2054">RFC 2054</xref> and <xref
      target="RFC2055">RFC 2055</xref>.  With the use of the public
      filehandle in combination with the LOOKUP operation in the NFSv3
      protocol, it has been demonstrated that the
      MOUNT protocol is unnecessary for viable interaction between NFS
      client and server.
    </t>
    <t>
      Therefore, the NFSv4.1 protocol will not use an ancillary
      protocol for translation from string-based pathnames to a filehandle.
      Two special filehandles will be used as starting points for the NFS
      client.
    </t>
    <section title="Root Filehandle">
      <t>
        The first of the special filehandles is the ROOT filehandle.  The ROOT
        filehandle is the "conceptual" root of the file system namespace at
        the NFS server.  The client uses or starts with the ROOT filehandle
        by employing the PUTROOTFH operation.  The PUTROOTFH operation
        instructs the server to set the "current" filehandle to the ROOT of
        the server's file tree.  Once this PUTROOTFH operation is used, the
        client can then traverse the entirety of the server's file tree with
        the LOOKUP operation.  A complete discussion of the server namespace
        is in <xref target="single_server_namespace"/>.
      </t>
    </section>
    <section title="Public Filehandle">
      <t>
        The second special filehandle is the PUBLIC filehandle.  Unlike the
        ROOT filehandle, the PUBLIC filehandle may be bound or represent an
        arbitrary file system object at the server.  The server is responsible
        for this binding.  It may be that the PUBLIC filehandle and the ROOT
        filehandle refer to the same file system object.  However, it is up to
        the administrative software at the server and the policies of the
        server administrator to define the binding of the PUBLIC filehandle
        and server file system object.  The client may not make any
        assumptions about this binding. The client uses the PUBLIC filehandle
        via the PUTPUBFH operation.
      </t>
    </section>
  </section>
  <section title="Filehandle Types">
    <t>
      In the NFSv3 protocol, there was one type of filehandle
      with a single set of semantics.  This type of filehandle is termed
      "persistent" in NFSv4.1.  The semantics of a persistent
      filehandle remain the same as before.  A new type of filehandle
      introduced in NFSv4.1 is the "volatile" filehandle, which
      attempts to accommodate certain server environments.
    </t>
    <t>
      The volatile filehandle type was introduced to address server
      functionality or implementation issues that make correct
      implementation of a persistent filehandle infeasible.  Some server
      environments do not provide a file-system-level invariant that can be
      used to construct a persistent filehandle.  The underlying server
      file system may not provide the invariant or the server's file system
      programming interfaces may not provide access to the needed invariant.
      Volatile filehandles may ease the implementation of server
      functionality such as hierarchical storage management or file system
      reorganization or migration.  However, the volatile filehandle
      increases the implementation burden for the client.
    </t>
    <t>
      Since the client will need to handle persistent and volatile
      filehandles differently, a file attribute is defined that may be used
      by the client to determine the filehandle types being returned by the
      server.
    </t>
    <section title="General Properties of a Filehandle">
      <t>
        The filehandle contains all the information the
        server needs to distinguish an individual file.
        To the client, the filehandle is opaque. The
        client stores filehandles for use in a later
        request and can compare two filehandles from the
        same server for equality by doing a byte-by-byte
        comparison.  However, the client MUST NOT otherwise
        interpret the contents of filehandles.  If two
        filehandles from the same server are equal, they
        MUST refer to the same file.  Servers SHOULD try
        to maintain a one-to-one correspondence between
        filehandles and files, but this is not required.
        Clients MUST use filehandle comparisons only to
        improve performance, not for correct behavior.
        All clients need to be prepared for situations
        in which it cannot be determined whether two
        filehandles denote the same object and in such
        cases, avoid making invalid assumptions that might
        cause incorrect behavior.  Further discussion
        of filehandle and attribute comparison in the
        context of data caching is presented in <xref
        target="data_caching_and_file_identity"/>.

      </t>
      <t>
        As an example, in the case that two different pathnames when
        traversed at the server terminate at the same file system object, the
        server SHOULD return the same filehandle for each path.  This can
        occur if a hard link (see <xref target="hardlink"/>) is used
        to create two file names that refer to the same underlying
        file object and associated data.  For example, if paths /a/b/c
        and /a/d/c refer to the same file, the server SHOULD return
        the same filehandle for both pathnames' traversals.
      </t>
    </section>
    <section title="Persistent Filehandle">
      <t>
        A persistent filehandle is defined as having a fixed value for the
        lifetime of the file system object to which it refers.  Once the
        server creates the filehandle for a file system object, the server
        MUST accept the same filehandle for the object for the lifetime of the
        object.  If the server restarts, the NFS server MUST honor
        the same filehandle value as it did in the server's previous
        instantiation.  Similarly, if the file system is migrated, the new NFS
        server MUST honor the same filehandle as the old NFS server.
      </t>
      <t>
        The persistent filehandle will be become stale or invalid when the
        file system object is removed.  When the server is presented with a
        persistent filehandle that refers to a deleted object, it MUST return
        an error of NFS4ERR_STALE.  A filehandle may become stale when the
        file system containing the object is no longer available.  The file
        system may become unavailable if it exists on removable media and the
        media is no longer available at the server or the file system in whole
        has been destroyed or the file system has simply been removed from the
        server's namespace (i.e., unmounted in a UNIX environment).
      </t>
    </section>
    <section title="Volatile Filehandle">
      <t>
        A volatile filehandle does not share the same longevity
        characteristics of a persistent filehandle.  The server may
        determine that a volatile filehandle is no longer valid at many
        different points in time.  If the server can definitively determine
        that a volatile filehandle refers to an object that has been removed,
        the server should return NFS4ERR_STALE to the client (as is the case
        for persistent filehandles).  In all other cases where the server
        determines that a volatile filehandle can no longer be used, it should
        return an error of NFS4ERR_FHEXPIRED.
      </t>
      <t>
        The REQUIRED attribute "fh_expire_type" is used by the client to
        determine what type of filehandle the server is providing for a
        particular file system.  This attribute is a bitmask with the
        following values:
      </t>
      <t>
        <list style="hanging">
          <t hangText="FH4_PERSISTENT">
            The value of FH4_PERSISTENT is used to indicate a persistent
            filehandle, which is valid until the object is removed from the
            file system.  The server will not return NFS4ERR_FHEXPIRED for this
            filehandle.  FH4_PERSISTENT is defined as a value in which none of the
            bits specified below are set.
          </t>
          <t hangText="FH4_VOLATILE_ANY">
            The filehandle may expire at any time, except as specifically
            excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
          </t>
          <t hangText="FH4_NOEXPIRE_WITH_OPEN">
            May only be set when FH4_VOLATILE_ANY is set.  If this bit is set,
            then the meaning of FH4_VOLATILE_ANY is qualified to exclude any
            expiration of the filehandle when it is open.
          </t>
          <t hangText="FH4_VOL_MIGRATION">
	    The filehandle will expire as a result of a file system
	    transition (migration or replication), in those cases in
	    which the continuity of filehandle use is not specified by
	    handle class information
	    within the fs_locations_info attribute.  When this bit is
	    set, clients without access to fs_locations_info
	    information should assume that filehandles will expire on file
	    system transitions.
          </t>
          <t hangText="FH4_VOL_RENAME">
            The filehandle will expire during rename.  This includes a rename by
            the requesting client or a rename by any other client.  If FH4_VOL_ANY
            is set, FH4_VOL_RENAME is redundant.
          </t>
        </list>
      </t>
      <t>
        Servers that provide volatile filehandles that can expire 
        while open require special care as regards handling of RENAMEs
        and REMOVEs.  This situation can arise if FH4_VOL_MIGRATION or 
        FH4_VOL_RENAME is set, if FH4_VOLATILE_ANY is set and 
        FH4_NOEXPIRE_WITH_OPEN is not set, or if a non-read-only file system
        has a transition target in a different handle
         class.  In these cases, the server should deny a RENAME 
        or REMOVE that would affect an OPEN file of any of the
        components leading to the OPEN file.  In addition, the server 
        should deny all RENAME or REMOVE requests during the grace period,
        in order to make sure that reclaims of files where filehandles 
        may have expired do not do a reclaim for the wrong file.
      </t>
      <t>
        Volatile filehandles are especially suitable for implementation
        of the pseudo file systems used to bridge exports.  See 
        <xref target="pseudo_fs_volatility" /> for a discussion of this.
      </t>
    </section>
  </section>
  <section title="One Method of Constructing a Volatile Filehandle">
    <t>
      A volatile filehandle, while opaque to the client, could contain:
    </t>
    <figure>
      <artwork>
[volatile bit = 1 | server boot time | slot | generation number]
      </artwork>
    </figure>
    <t>
      <list style='symbols'>
        <t>
          slot is an index in the server volatile filehandle table
        </t>
        <t>
          generation number is the generation number for the table entry/slot
        </t>
      </list>
      When the client presents a volatile filehandle, the server makes the
      following checks, which assume that the check for the volatile bit has
      passed.  If the server boot time is less than the current server boot
      time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
      NFS4ERR_BADHANDLE.  If the generation number does not match, return
      NFS4ERR_FHEXPIRED.
    </t>
    <t>
      When the server restarts, the table is gone (it is volatile).
    </t>
    <t>
      If the volatile bit is 0, then it is a persistent filehandle with a
      different structure following it. 

    </t>
  </section>

  <section title="Client Recovery from Filehandle Expiration">
    <t>
      If possible, the client SHOULD recover from the receipt of an
      NFS4ERR_FHEXPIRED error.  The client must take on additional
      responsibility so that it may prepare itself to recover from the
      expiration of a volatile filehandle.  If the server returns persistent
      filehandles, the client does not need these additional steps.
    </t>
    <t>
      For volatile filehandles, most commonly the client will need to store
      the component names leading up to and including the file system object
      in question.  With these names, the client should be able to recover
      by finding a filehandle in the namespace that is still available or
      by starting at the root of the server's file system namespace.
    </t>
    <t>
      If the expired filehandle refers to an object that has been removed
      from the file system, obviously the client will not be able to recover
      from the expired filehandle.
    </t>
    <t>
      It is also possible that the expired filehandle refers to a file that
      has been renamed.  If the file was renamed by another client, again it
      is possible that the original client will not be able to recover.
      However, in the case that the client itself is renaming the file and
      the file is open, it is possible that the client may be able to
      recover.  The client can determine the new pathname based on the
      processing of the rename request.  The client can then regenerate the
      new filehandle based on the new pathname.  The client could also use
      the COMPOUND procedure to construct a series of operations
      like:
      <figure>
        <artwork>
          RENAME A B
          LOOKUP B
          GETFH
        </artwork>
      </figure>

      Note that the COMPOUND procedure does not provide atomicity.  This
      example only reduces the overhead of recovering from an expired
      filehandle.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="file_attributes" title="File Attributes">
  <t>
    To meet the requirements of extensibility and increased
    interoperability with non-UNIX platforms, attributes need to be handled
    in a flexible manner.  The NFSv3 fattr3 structure contains a
    fixed list of attributes that not all clients and servers are able to
    support or care about.  The fattr3 structure cannot be extended as
    new needs arise and it provides no way to indicate non-support.  With
    the NFSv4.1 protocol, the client is able to query what attributes
    the server supports and construct requests with only those supported
    attributes (or a subset thereof).
  </t>
  <t>
    To this end, attributes are divided into three groups: REQUIRED,
    RECOMMENDED, and named.  Both REQUIRED and RECOMMENDED attributes are
    supported in the NFSv4.1 protocol by a specific and well-defined
    encoding and are identified by number.  They are requested by setting
    a bit in the bit vector sent in the GETATTR request; the server
    response includes a bit vector to list what attributes were returned
    in the response.  New REQUIRED or RECOMMENDED attributes may be added
    to the NFSv4 protocol as part of a new minor version
    by publishing a
    Standards Track RFC that allocates a new attribute number value and
    defines the encoding for the attribute.  See
    <xref target="minor_versioning"/> for further
    discussion.
  </t>
  <t>
    Named attributes are accessed by the new OPENATTR operation, which
    accesses a hidden directory of attributes associated with a file
    system object.  OPENATTR takes a filehandle for the object and returns
    the filehandle for the attribute hierarchy.  The filehandle for the
    named attributes is a directory object accessible by LOOKUP or READDIR
    and contains files whose names represent the named attributes and
    whose data bytes are the value of the attribute.  For example:
  </t>
  <texttable>
    <ttcol align='left' />
    <ttcol align='left' />
    <ttcol align='left' />
    <c>LOOKUP</c><c>"foo"</c><c>; look up file</c>
    <c>GETATTR</c><c>attrbits</c><c />
    <c>OPENATTR</c><c /><c>; access foo's named attributes</c>
    <c>LOOKUP</c><c>"x11icon"</c><c>; look up specific attribute</c>
    <c>READ</c><c>0,4096</c><c>; read stream of bytes</c>
  </texttable>
  <t>
    Named attributes are intended for data needed by applications rather
    than by an NFS client implementation.  NFS implementors are strongly
    encouraged to define their new attributes as RECOMMENDED attributes by
    bringing them to the IETF Standards Track process.
  </t>
  <t>
    The set of attributes that are classified as REQUIRED is
    deliberately small since servers need to do whatever it takes to support
    them.  A server should support as many of the RECOMMENDED attributes
    as possible but, by their definition, the server is not required to
    support all of them.  Attributes are deemed REQUIRED if the data is
    both needed by a large number of clients and is not otherwise
    reasonably computable by the client when support is not provided on
    the server.
  </t>
  <t>
    Note that the hidden directory returned by OPENATTR is a convenience
    for protocol processing.  The client should not make any assumptions
    about the server's implementation of named attributes and whether
    or not the underlying file system at the server has a named
    attribute directory.  Therefore, operations such as SETATTR and
    GETATTR on the named attribute directory are undefined.
  </t>
  <section anchor="mandatory_attributes_intro" title="REQUIRED Attributes">
    <t>
      These MUST be supported by every NFSv4.1 client and server in
      order to ensure a minimum level of interoperability.  The server MUST
      store and return these attributes, and the client MUST be able to
      function with an attribute set limited to these attributes.  With just
      the REQUIRED attributes some client functionality may be impaired or
      limited in some ways.  A client may ask for any of these attributes to
      be returned by setting a bit in the GETATTR request, and the server
      MUST return their value.
    </t>
  </section>
  <section anchor="recommended_attributes_intro" title="RECOMMENDED Attributes">
    <t>
      These attributes are understood well enough to warrant support in the
      NFSv4.1 protocol.  However, they may not be supported on all
      clients and servers.  A client may ask for any of these attributes to
      be returned by setting a bit in the GETATTR request but must handle
      the case where the server does not return them.  A client MAY ask for
      the set of attributes the server supports and SHOULD NOT request
      attributes the server does not support.  A server should be tolerant
      of requests for unsupported attributes and simply not return them
      rather than considering the request an error.  It is expected that
      servers will support all attributes they comfortably can and only fail
      to support attributes that are difficult to support in their
      operating environments.  A server should provide attributes whenever
      they don't have to "tell lies" to the client.  For example, a file
      modification time should be either an accurate time or should not be
      supported by the server.  At times this will be difficult for
      clients, but a client is better positioned to decide whether and how to
      fabricate or construct an attribute or whether to do without the
      attribute.
    </t>
  </section>
  <section anchor="named_attributes_intro" title="Named Attributes">
    <t>
      These attributes are not supported by direct encoding in the NFSv4 
      protocol but are accessed by string names rather than
      numbers and correspond to an uninterpreted stream of bytes that are
      stored with the file system object.  The namespace for these
      attributes may be accessed by using the OPENATTR operation.  The
      OPENATTR operation returns a filehandle for a virtual "named attribute
      directory", and further perusal and modification of the namespace may 
      be done using operations that work on more typical directories.  In
      particular, READDIR may be used to get a list of such named attributes,
      and LOOKUP and OPEN may select a particular attribute.  Creation of
      a new named attribute may be the result of an OPEN specifying file
      creation.
    </t>
    <t>
      Once an OPEN is done, named attributes may be examined and changed 
      by normal READ and WRITE operations using the filehandles and stateids
      returned by OPEN.
    </t>
    <t>
      Named attributes and the named attribute directory may have 
      their own (non-named) attributes.  Each of these objects MUST have all 
      of the REQUIRED attributes and may have additional RECOMMENDED 
      attributes.  However, the set of attributes for named attributes 
      and the named attribute directory need not be, and
      typically will not be, as large as that for other objects in that 
      file system.
    </t>
    <t>
      Named attributes and the named attribute directory might be the
      target of delegations (in the case of the named attribute directory,
      these will be directory delegations).  However, since granting
      delegations is at the server's discretion, a server
      need not support delegations on named attributes or the named
      attribute directory.
    </t>
    <t>
      It is RECOMMENDED that servers support arbitrary named attributes.  A
      client should not depend on the ability to store any named attributes
      in the server's file system.  If a server does support named
      attributes, a client that is also able to handle them should be able
      to copy a file's data and metadata with complete transparency from
      one location to another; this would imply that names allowed for
      regular directory entries are valid for named attribute names as well.
    </t>
    <t>
      In NFSv4.1, the structure of named attribute directories is 
      restricted in a number of ways, in order to prevent the development
      of non-interoperable implementations in which some servers support
      a fully general hierarchical directory structure for named attributes
      while others support a limited but adequate structure for named attributes.
      In such an environment, clients or applications might come to
      depend on non-portable extensions.  The restrictions are:
      <list style="symbols">
        <t>
          CREATE is not allowed in a named attribute directory.  Thus, such
          objects as symbolic links and special files are not allowed to
          be named attributes.   Further, directories may not be created
          in a named attribute directory, so no hierarchical structure of
          named attributes for a single object is allowed.
        </t>
        <t>
          If OPENATTR is done on a named attribute directory or on
          a named attribute, the server MUST return NFS4ERR_WRONG_TYPE.
        </t>
        <t>
          Doing a RENAME of a named attribute to a different named 
          attribute directory or to an ordinary (i.e., non-named-attribute)
          directory is not allowed.
        </t>
        <t>
          Creating hard links between named attribute directories or 
          between named attribute directories and ordinary directories 
          is not allowed.
        </t>
      </list>
    </t>
    <t>
      Names of attributes will not be controlled by this document or other
      IETF Standards Track documents.  See
      <xref target="namedattributesiana"/>
      for further discussion.
    </t>
  </section>
  <section title="Classification of Attributes">
    <t>
      Each of the REQUIRED and RECOMMENDED attributes can be classified in
      one of three categories: per server (i.e., the value of the attribute will
      be the same for all file objects that share the same
      server owner; see <xref target="Server Owners"/> for a definition of server
      owner), per file system (i.e., the value of the attribute will
      be the same for some or all file objects that share the
      same <xref target="attrdef_fsid">fsid attribute</xref> and
      server owner), or per file system
      object.  Note that it is possible that some per file system attributes
      may vary within the file system, depending on the value of
      the <xref target="attrdef_homogeneous">"homogeneous"</xref>
      attribute. Note that the attributes time_access_set and
      time_modify_set are not listed in this section because they are
      write-only attributes corresponding to time_access and time_modify,
      and are used in a special instance of SETATTR.
      <list style='symbols'>
	<t>
	  The per-server attribute is:
	  <list style='empty'>
	    <t>
	      lease_time
	    </t>
	  </list>
	</t>
	<t>
	  The per-file system attributes are:
	  <list style='empty'>
	    <t>
	      supported_attrs, suppattr_exclcreat, fh_expire_type, link_support,
	      symlink_support, unique_handles, aclsupport,
	      cansettime, case_insensitive, case_preserving,
	      chown_restricted, files_avail, files_free,
	      files_total, fs_locations, homogeneous, maxfilesize,
	      maxname, maxread, maxwrite, no_trunc, space_avail,
	      space_free, space_total, time_delta,
              change_policy, fs_status,
	      fs_layout_type, fs_locations_info, fs_charset_cap
	    </t>
	  </list>
	</t>    
	<t>
	  The per-file system object attributes are:
	  <list style='empty'>
	    <t>
	      type, change, size, named_attr, fsid, rdattr_error,
	      filehandle, acl, archive, fileid, hidden, maxlink,
	      mimetype, mode, numlinks, owner, owner_group, rawdev,
	      space_used, system, time_access, time_backup,
	      time_create, time_metadata, time_modify,
	      mounted_on_fileid, dir_notif_delay, dirent_notif_delay,
              dacl, sacl,
	      layout_type, layout_hint, layout_blksize, layout_alignment,
              mdsthreshold, retention_get, retention_set, retentevt_get,
              retentevt_set, retention_hold, mode_set_masked
	    </t>
	  </list>
	</t>
      </list>
    </t>
    <t>
      For quota_avail_hard, quota_avail_soft, and quota_used, see their
      definitions below for the appropriate classification.
    </t>

  </section>

  <section anchor="rw_attr" 
	   title="Set-Only and Get-Only Attributes">
    <t>
     Some REQUIRED and RECOMMENDED attributes are set-only; i.e., they
     can be set via SETATTR but not retrieved via GETATTR. Similarly, some
     REQUIRED and RECOMMENDED attributes are get-only; i.e., they
     can be retrieved via GETATTR but not set via SETATTR. If a client attempts
     to set a get-only attribute or get a set-only attributes, the server
     MUST return NFS4ERR_INVAL.
   </t>

  </section>

  <section anchor="mandatory_attributes" 
	   title="REQUIRED Attributes - List and Definition References">
    <t>
     The list of REQUIRED attributes appears in <xref target="req_attr_table"/>.
     The meaning of the columns of the table are:
     <list style='symbols'>
     <t>Name: The name of the attribute.</t>
     <t>Id: The number assigned to the attribute. In
        the event of conflicts between the assigned number and <xref
        target="RFC5662"/>, the latter is
        likely authoritative, but should be resolved with Errata to
        this document and/or
        <xref target="RFC5662"/>. See <xref target="errata"/> for the Errata process.

</t>
     <t>Data Type: The XDR data type of the attribute.</t>
     <t>
        Acc: Access allowed to the attribute. R means
        read-only (GETATTR may retrieve, SETATTR may not
        set). W means write-only (SETATTR may set, GETATTR
        may not retrieve).  R W means read/write (GETATTR
        may retrieve, SETATTR may set).

     </t>
     <t>Defined in: The section of this specification that describes the
        attribute.</t>
     </list>
    </t>

    <texttable anchor="req_attr_table">
      <ttcol align='left' >Name</ttcol>
      <ttcol align='left' >Id</ttcol>
      <ttcol align='left' >Data Type</ttcol>
      <ttcol align='left' >Acc</ttcol>
      <ttcol align='left' >Defined in:</ttcol>

      <c>supported_attrs</c><c>0</c><c>bitmap4</c><c>R</c>
      <c>
	<xref target="attrdef_supp_attr" />
      </c>

      <c>type</c><c>1</c><c>nfs_ftype4</c><c>R</c>
      <c>
	<xref target="attrdef_type"  />
      </c>

      <c>fh_expire_type</c><c>2</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_fh_expire_type"  />
      </c>

      <c>change</c><c>3</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_change"  />
      </c>
      
      <c>size</c><c>4</c><c>uint64_t</c><c>R W</c>
      <c>
	<xref target="attrdef_size" />
      </c>

      <c>link_support</c><c>5</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_link_support" />
      </c>

      <c>symlink_support</c><c>6</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_symlink_support" />
      </c>

      <c>named_attr</c><c>7</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_named_attr" />
      </c>

      <c>fsid</c><c>8</c><c>fsid4</c><c>R</c>
      <c>
	<xref target="attrdef_fsid" />
      </c>

      <c>unique_handles</c><c>9</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_unique_handles" />
      </c>

      <c>lease_time</c><c>10</c><c>nfs_lease4</c><c>R</c>
      <c>
	<xref target="attrdef_lease_time" />
      </c>

      <c>rdattr_error</c><c>11</c><c>enum</c><c>R</c>
      <c>
	<xref target="attrdef_rdattr_error" />
      </c>

      <c>filehandle</c><c>19</c><c>nfs_fh4</c><c>R</c>
      <c>
	<xref target="attrdef_filehandle" />
      </c>

      <c>suppattr_exclcreat</c><c>75</c><c>bitmap4</c><c>R</c>
      <c>
	<xref target="attrdef_suppattr_exclcreat" />
      </c>

    </texttable>
  </section>
  <section anchor="recommended_attributes" 
	   title="RECOMMENDED Attributes - List and Definition References">
    <t>
     The RECOMMENDED attributes are defined in
     <xref target="rec_attr_tbl"/>.  The meanings
     of the column headers are the same as
     <xref target="req_attr_table"/>; see <xref
     target="mandatory_attributes" /> for the meanings.

    </t>
    <texttable anchor="rec_attr_tbl">
      <ttcol align='left' >Name</ttcol>
      <ttcol align='left' >Id</ttcol>
      <ttcol align='left' >Data Type</ttcol>
      <ttcol align='left' >Acc</ttcol>
      <ttcol align='left' >Defined in:</ttcol>

      <c>acl</c><c>12</c><c>nfsace4&lt;></c><c>R W</c>
      <c>
	<xref target="attrdef_acl" />
      </c>

      <c>aclsupport</c><c>13</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_aclsupport" />
      </c>

      <c>archive</c><c>14</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_archive" />
      </c>

      <c>cansettime</c><c>15</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_cansettime" />
      </c>

      <c>case_insensitive</c><c>16</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_case_insensitive" />
      </c>

      <c>case_preserving</c><c>17</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_case_preserving" />
      </c>

      <c>change_policy</c><c>60</c><c>chg_policy4</c><c>R</c>
      <c>
	<xref target="attrdef_change_policy" />
      </c>

      <c>chown_restricted</c><c>18</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_chown_restricted" />
      </c>

      <c>dacl</c><c>58</c><c>nfsacl41</c><c>R W</c>
      <c>
	<xref target="attrdef_dacl" />
      </c>

      <c>dir_notif_delay</c><c>56</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_dir_notif_delay" />
      </c>

      <c>dirent_notif_delay</c><c>57</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_dirent_notif_delay" />
      </c>

      <c>fileid</c><c>20</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_fileid" />
      </c>

      <c>files_avail</c><c>21</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_avail" />
      </c>

      <c>files_free</c><c>22</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_free" />
      </c>

      <c>files_total</c><c>23</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_total" />
      </c>

      <c>fs_charset_cap</c><c>76</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_fs_charset_cap" />
      </c>

      <c>fs_layout_type</c><c>62</c><c>layouttype4&lt;></c><c>R</c>
      <c>
	<xref target="attrdef_fs_layout_type" />
      </c>

      <c>fs_locations</c><c>24</c><c>fs_locations</c><c>R</c>
      <c>
	<xref target="attrdef_fs_locations" />
      </c>

      <c>fs_locations_info</c><c>67</c><c>*</c><c>R</c>
      <c>
	<xref target="attrdef_fs_locations_info" />
      </c>

      <c>fs_status</c><c>61</c><c>fs4_status</c><c>R</c>
      <c>
	<xref target="attrdef_fs_status" />
      </c>

      <c>hidden</c><c>25</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_hidden" />
      </c>

      <c>homogeneous</c><c>26</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_homogeneous" />
      </c>

      <c>layout_alignment</c><c>66</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_layout_alignment" />
      </c>

      <c>layout_blksize</c><c>65</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_layout_blksize" />
      </c>

      <c>layout_hint</c><c>63</c><c>layouthint4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_layout_hint" />
      </c>

      <c>layout_type</c><c>64</c><c>layouttype4&lt;></c><c>R</c>
      <c>
	<xref target="attrdef_layout_type" />
      </c>

      <c>maxfilesize</c><c>27</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxfilesize" />
      </c>

      <c>maxlink</c><c>28</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxlink" />
      </c>

      <c>maxname</c><c>29</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxname" />
      </c>

      <c>maxread</c><c>30</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxread" />
      </c>

      <c>maxwrite</c><c>31</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxwrite" />
      </c>

      <c>mdsthreshold</c><c>68</c><c>mdsthreshold4</c><c>R</c>
      <c>
	<xref target="attrdef_mdsthreshold" />
      </c>

      <c>mimetype</c><c>32</c><c>utf8str_cs</c><c>R W</c>
      <c>
	<xref target="attrdef_mimetype" />
      </c>

      <c>mode</c><c>33</c><c>mode4</c><c>R W</c>
      <c>
	<xref target="attrdef_mode" />
      </c>

      <c>mode_set_masked</c><c>74</c><c>mode_masked4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_mode_set_masked" />
      </c>

      <c>mounted_on_fileid</c><c>55</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_mounted_on_fileid" />
      </c>

      <c>no_trunc</c><c>34</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_no_trunc" />
      </c>

      <c>numlinks</c><c>35</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_numlinks" />
      </c>

      <c>owner</c>
      <c>36</c><c>utf8str_mixed</c><c>R W</c>
      <c>
	<xref target="attrdef_owner" />
      </c>

      <c>owner_group</c>
      <c>37</c><c>utf8str_mixed</c><c>R W</c>
      <c>
	<xref target="attrdef_owner_group" />
      </c>

      <c>quota_avail_hard</c>
      <c>38</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_avail_hard" />
      </c>

      <c>quota_avail_soft</c>
      <c>39</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_avail_soft" />
      </c>

      <c>quota_used</c>
      <c>40</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_used" />
      </c>

      <c>rawdev</c><c>41</c><c>specdata4</c><c>R</c>
      <c>
	<xref target="attrdef_rawdev" />
      </c>

      <c>retentevt_get</c><c>71</c><c>retention_get4</c><c>R</c>
      <c>
	<xref target="attrdef_retentevt_get" />
      </c>

      <c>retentevt_set</c><c>72</c><c>retention_set4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_retentevt_set" />
      </c>

      <c>retention_get</c><c>69</c><c>retention_get4</c><c>R</c>
      <c>
	<xref target="attrdef_retention_get" />
      </c>

      <c>retention_hold</c><c>73</c><c>uint64_t</c><c>R W</c>
      <c>
	<xref target="attrdef_retention_hold" />
      </c>

      <c>retention_set</c><c>70</c><c>retention_set4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_retention_set" />
      </c>

      <c>sacl</c><c>59</c><c>nfsacl41</c><c>R W</c>
      <c>
	<xref target="attrdef_sacl" />
      </c>

      <c>space_avail</c><c>42</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_avail" />
      </c>

      <c>space_free</c><c>43</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_free" />
      </c>

      <c>space_total</c><c>44</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_total" />
      </c>

      <c>space_used</c><c>45</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_used" />
      </c>

      <c>system</c><c>46</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_system" />
      </c>

      <c>time_access</c>
      <c>47</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_access" />
      </c>

      <c>time_access_set</c><c>48</c><c>settime4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_time_access_set" />
      </c>

      <c>time_backup</c><c>49</c><c>nfstime4</c><c>R W</c>
      <c>
	<xref target="attrdef_time_backup" />
      </c>

      <c>time_create</c><c>50</c><c>nfstime4</c><c>R W</c>
      <c>
	<xref target="attrdef_time_create" />
      </c>

      <c>time_delta</c><c>51</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_delta" />
      </c>

      <c>time_metadata</c><c>52</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_metadata" />
      </c>

      <c>time_modify</c><c>53</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_modify" />
      </c>

      <c>time_modify_set</c><c>54</c><c>settime4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_time_modify_set" />
      </c>

    </texttable>
    <t>* fs_locations_info4</t>
  </section>

  <section anchor="attribute_definitions" title="Attribute
						 Definitions">

   <section anchor="required_attr" title="Definitions of REQUIRED Attributes">

    <section toc="exclude" anchor="attrdef_supp_attr" 
	     title="Attribute 0: supported_attrs">
	<t>
	The bit vector that would retrieve all REQUIRED and
	RECOMMENDED attributes that are supported for this object.
	The scope of this attribute applies to all objects with a
	matching fsid.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_type" 
	     title="Attribute 1: type">
	<t>
	  Designates the type of an object in terms of one of a number
          of special constants:
          <list style="symbols">
            <t>
              NF4REG designates a regular file.
            </t>
            <t>
              NF4DIR designates a directory.
            </t>
            <t>
              NF4BLK designates a block device special file.
            </t>
            <t>
              NF4CHR designates a character device special file.
            </t>
            <t>
              NF4LNK designates a symbolic link.
            </t>
            <t>
              NF4SOCK designates a named socket special file.
            </t>
            <t>
              NF4FIFO designates a fifo special file.
            </t>
            <t>
              NF4ATTRDIR designates a named attribute directory.
            </t>
            <t>
              NF4NAMEDATTR designates a named attribute.
            </t>
          </list>
	</t>
	<t>
          Within the explanatory text and operation descriptions, the
          following phrases will be used with the meanings given below:
          <list style="symbols">
            <t>
              The phrase "is a directory" means that the object's
              type attribute is NF4DIR or NF4ATTRDIR.
            </t>
            <t>
              The phrase "is a special file" means that the object's type
              attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO. 
            </t>
            <t>
              The phrases "is an ordinary file" and
              "is a regular file" mean that the object's
              type attribute is NF4REG or NF4NAMEDATTR.
            </t>
          </list>
	</t>

    </section>

    <section toc="exclude" anchor="attrdef_fh_expire_type" 
	     title="Attribute 2: fh_expire_type">
	<t>
	  Server uses this to specify filehandle expiration behavior
	  to the client.  See <xref target="Filehandles"/> for additional
	  description.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_change" 
	     title="Attribute 3: change">
	<t>
	  A value created by the server that the client can use to
	  determine if file data, directory contents, or attributes of
	  the object have been modified.  The server may return the
	  object's time_metadata attribute for this attribute's value,
	  but only if the file system object cannot be updated more
	  frequently than the resolution of time_metadata.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_size" 
	     title="Attribute 4: size">
	<t>
	  The size of the object in bytes.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_link_support" 
	     title="Attribute 5: link_support">
	<t>
	  TRUE, if the object's file system supports hard links.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_symlink_support" 
	     title="Attribute 6: symlink_support">
	<t>
	  TRUE, if the object's file system supports symbolic links.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_named_attr" 
	     title="Attribute 7: named_attr">
	<t>
	  TRUE, if this object has named attributes. In other words,
	  object has a non-empty named attribute directory.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_fsid" 
	     title="Attribute 8: fsid">
	<t>
	  Unique file system identifier for the file system holding this
	  object.  The fsid attribute has major and minor components, each of
	  which are of data type uint64_t.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_unique_handles" 
	     title="Attribute 9: unique_handles">
	<t>
	  TRUE, if two distinct filehandles are guaranteed to refer to two
	  different file system objects.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_lease_time" 
	     title="Attribute 10: lease_time">
	<t>
	  Duration of the lease at server in seconds.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_rdattr_error" 
	     title="Attribute 11: rdattr_error">
	<t>
	  Error returned from an attempt to retrieve attributes during a READDIR operation.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_filehandle" 
	     title="Attribute 19: filehandle">
	<t>
	  The filehandle of this object (primarily for READDIR requests).
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_suppattr_exclcreat" 
	     title="Attribute 75: suppattr_exclcreat">
	<t>
	The bit vector that would set all REQUIRED and
	RECOMMENDED attributes that are supported by the EXCLUSIVE4_1
        method of file creation via the OPEN operation.
	The scope of this attribute applies to all objects with a
	matching fsid.
	</t>
    </section>

   </section>

   <section anchor="recommended_attr" title="Definitions of Uncategorized RECOMMENDED Attributes">
    <t>
     The definitions of most of the RECOMMENDED attributes follow. Collections
     that share a common category are defined in other sections.
    </t>

    <section toc="exclude" anchor="attrdef_archive"
	     title="Attribute 14: archive">
      <t>
	TRUE, if this file has been archived since the time of last
	modification (deprecated in favor of time_backup).
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_cansettime"
	     title="Attribute 15: cansettime">
      <t>
	TRUE, if the server is able to change the times for a
	file system object as specified in a SETATTR operation.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_case_insensitive"
	     title="Attribute 16: case_insensitive">
      <t>
	TRUE, if file name comparisons on this file system are case
	insensitive.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_case_preserving"
	     title="Attribute 17: case_preserving">
      <t>
	TRUE, if file name case on this file system is preserved.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_change_policy"
	     title="Attribute 60: change_policy">
      <t>
	A value created by the server that the client can use to
	determine if some server policy related to the current
        file system has been subject to change.  If the value 
        remains the same, then the client can be sure that the
        values of the attributes related to fs location
        and the fss_type field of the fs_status attribute have
        not changed.  On the other hand, a change in this value does
        necessarily imply a change in policy.  It is up to the client
        to interrogate the server to determine if some policy relevant to 
        it has changed.  See <xref target="chg_policy4" /> for 
        details.
      </t>
      <t>
        This attribute MUST change when the value returned by 
        the fs_locations or fs_locations_info attribute changes, when
        a file system goes from read-only to writable or vice versa,
        or when the allowable set of security flavors for the file system
        or any part thereof is changed.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_chown_restricted"
	     title="Attribute 18: chown_restricted">
      <t>
	If TRUE, the server will reject any request to change either
	the owner or the group associated with a file if the caller
	is not a privileged user (for example, "root" in UNIX
	operating environments or, in Windows 2000, the "Take
	Ownership" privilege).
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fileid"
	     title="Attribute 20: fileid">
      <t>
	A number uniquely identifying the file within the file system.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_avail"
	     title="Attribute 21: files_avail">
      <t>
	File slots available to this user on the file system
	containing this object -- this should be the smallest
	relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_free"
	     title="Attribute 22: files_free">
      <t>
	Free file slots on the file system containing this object --
	this should be the smallest relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_total"
	     title="Attribute 23: files_total">
      <t>
	Total file slots on the file system containing this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_charset_cap" 
	     title="Attribute 76: fs_charset_cap">
      <t>
        Character set capabilities for this file system. See
        <xref target="utf8_caps"/>.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_locations"
            title="Attribute 24: fs_locations">
       <t>
       Locations where this file system may be found.  If the server
       returns NFS4ERR_MOVED as an error, this attribute MUST be
       supported.
       See <xref target="fs_locations"/> for more details.
       </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_locations_info"
	     title="Attribute 67: fs_locations_info">
      <t>
	Full function file system location.
       See <xref target="fs_locations_info"/> for more details.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_status"
	     title="Attribute 61: fs_status">
      <t>
	Generic file system type information.
       See <xref target="fs_status"/> for more details.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_hidden"
	     title="Attribute 25: hidden">
      <t>
	TRUE, if the file is considered hidden with respect to 
	the Windows API.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_homogeneous"
	     title="Attribute 26: homogeneous">
      <t>
	TRUE, if this object's file system is homogeneous; i.e., all
	objects in the file system (all objects on the server with the
	same fsid) have common values for all per-file-system attributes.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxfilesize"
	     title="Attribute 27: maxfilesize">
      <t>
	Maximum supported file size for the file system of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxlink"
	     title="Attribute 28: maxlink">
      <t>
	Maximum number of links for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxname"
	     title="Attribute 29: maxname">
      <t>
	Maximum file name size supported for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxread"
	     title="Attribute 30: maxread">
      <t>
	Maximum amount of data the READ operation will return for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxwrite"
	     title="Attribute 31: maxwrite">
      <t>
	Maximum amount of data the WRITE operation will accept for this object.
	This
	attribute SHOULD be supported if the file is writable.  Lack
	of this attribute can lead to the client either wasting
	bandwidth or not receiving the best performance.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mimetype"
	     title="Attribute 32: mimetype">
      <t>
	MIME body type/subtype of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mounted_on_fileid"
	     title="Attribute 55: mounted_on_fileid">
      <t>
	Like fileid, but if the target filehandle is the root of a
	file system, this attribute represents the fileid of the
	underlying directory.
      </t>
      <t>
	UNIX-based operating environments connect a file system into
	the namespace by connecting (mounting) the file system onto
	the existing file object (the mount point, usually a
	directory) of an existing file system. When the mount point's
	parent directory is read via an API like readdir(), the return
	results are directory entries, each with a component name and
	a fileid. The fileid of the mount point's directory entry will
	be different from the fileid that the stat() system call
	returns. The stat() system call is returning the fileid of the
	root of the mounted file system, whereas readdir() is
	returning the fileid that stat() would have returned before any
	file systems were mounted on the mount point.
      </t>
      <t>
	Unlike NFSv3, NFSv4.1 allows a client's LOOKUP
	request to cross other file systems. The client detects the
	file system crossing whenever the filehandle argument of
	LOOKUP has an fsid attribute different from that of the
	filehandle returned by LOOKUP. A UNIX-based client will
	consider this a "mount point crossing".  UNIX has a legacy
	scheme for allowing a process to determine its current working
	directory. This relies on readdir() of a mount point's parent
	and stat() of the mount point returning fileids as previously
	described.  The mounted_on_fileid attribute corresponds to the
	fileid that readdir() would have returned as described
	previously.
      </t>
      <t>
	While the NFSv4.1 client could simply fabricate a fileid
	corresponding to what mounted_on_fileid provides (and if the
	server does not support mounted_on_fileid, the client has no
	choice), there is a risk that the client will generate a
	fileid that conflicts with one that is already assigned to
	another object in the file system. Instead, if the server can
	provide the mounted_on_fileid, the potential for client
	operational problems in this area is eliminated.
      </t>
      <t>
	If the server detects that there is no mounted point at the
	target file object, then the value for mounted_on_fileid that
	it returns is the same as that of the fileid attribute.
      </t>
      <t>
	The mounted_on_fileid attribute is RECOMMENDED, so the server
	SHOULD provide it if possible, and for a UNIX-based server,
	this is straightforward. Usually, mounted_on_fileid will be
	requested during a READDIR operation, in which case it is
	trivial (at least for UNIX-based servers) to return
	mounted_on_fileid since it is equal to the fileid of a
	directory entry returned by readdir().  If mounted_on_fileid
	is requested in a GETATTR operation, the server should obey an
	invariant that has it returning a value that is equal to the
	file object's entry in the object's parent directory,
	i.e., what readdir() would have returned.  Some operating
	environments allow a series of two or more file systems to be
	mounted onto a single mount point. In this case, for the
	server to obey the aforementioned invariant, it will need to
	find the base mount point, and not the intermediate mount
	points.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_no_trunc"
	     title="Attribute 34: no_trunc">
      <t>
	If this attribute is TRUE, then if the client uses a file
        name longer than name_max, an error will be
	returned instead of the name being truncated.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_numlinks"
	     title="Attribute 35: numlinks">
      <t>
	Number of hard links to this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_owner"
	     title="Attribute 36: owner">
      <t>
	The string name of the owner of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_owner_group"
	     title="Attribute 37: owner_group">
      <t>
	The string name of the group ownership of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_avail_hard"
	     title="Attribute 38: quota_avail_hard">
      <t anchor="quota_avail_hard">
	The value in bytes that represents the amount of additional
	disk space beyond the current allocation that can be allocated
	to this file or directory before further allocations will be
	refused.  It is understood that this space may be consumed by
	allocations to other files or directories.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_avail_soft"
	     title="Attribute 39: quota_avail_soft">
      <t anchor="quota_avail_soft">
	The value in bytes that represents the amount of additional
	disk space that can be allocated to this file or directory
	before the user may reasonably be warned.  It is understood
	that this space may be consumed by allocations to other files
	or directories though there is a rule as to which other files
	or directories.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_used"
	     title="Attribute 40: quota_used">
      <t anchor="quota_used">
	The value in bytes that represents the amount of disk
	space used by this file or directory and possibly a
	number of other similar files or directories, where the
	set of "similar" meets at least the criterion that
	allocating space to any file or directory in the set
	will reduce the "quota_avail_hard" of every other file
	or directory in the set.
	<vspace blankLines='1' />
	Note that there may be a number of distinct but
	overlapping sets of files or directories for which a
	quota_used value is maintained, e.g., "all files with a
	given owner", "all files with a given group owner", etc.
	The server is at liberty to choose any of those sets when
        providing the content of the quota_used attribute, but
	should do so in a repeatable way.  The rule may be
	configured per file system or may be "choose the set with
	the smallest quota".
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_rawdev"
	     title="Attribute 41: rawdev">
      <t>
	Raw device number of file of type NF4BLK or NF4CHR. The device
        number is split into major and minor numbers.
	If the file's type attribute is not NF4BLK or NF4CHR,
	the value returned SHOULD NOT be considered useful.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_avail"
	     title="Attribute 42: space_avail">
      <t>
	Disk space in bytes available to this user on the file system
	containing this object -- this should be the smallest
	relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_free"
	     title="Attribute 43: space_free">
      <t>
	Free disk space in bytes on the file system containing this
	object -- this should be the smallest relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_total"
	     title="Attribute 44: space_total">
      <t>
	Total disk space in bytes on the file system containing this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_used"
	     title="Attribute 45: space_used">
      <t>
	Number of file system bytes allocated to this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_system"
	     title="Attribute 46: system">
      <t>
	This attribute is TRUE if this file is a "system" file with
	respect to the Windows operating environment.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_access"
	     title="Attribute 47: time_access">
      <t>
	The time_access attribute represents the time of last access to
	the object by a READ operation sent to the server. The notion
	of what is an "access" depends on the server's operating environment
	and/or the server's file system semantics.  For example, for
	servers obeying Portable Operating System Interface (POSIX) semantics, time_access would be updated only
	by the READ and READDIR operations and not any of the operations
	that modify the content of the object <xref target="read_atime"/>,
	<xref target="readdir_atime"/>, <xref target="write_atime"/>. Of
	course, setting the corresponding time_access_set attribute is
	another way to modify the time_access attribute.

      </t>
      <t>
	Whenever the file object resides on a writable file system,
	the server should make its best efforts to record time_access into
	stable storage.  However, to mitigate the performance effects
	of doing so, and most especially whenever the server is
	satisfying the read of the object's content from its cache,
	the server MAY cache access time updates and lazily write them
	to stable storage.  It is also acceptable to give
	administrators of the server the option to disable time_access
	updates.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_access_set"
	     title="Attribute 48: time_access_set">
      <t>
	Sets the time of last access to the object.  SETATTR use only.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_backup"
	     title="Attribute 49: time_backup">
      <t>
	The time of last backup of the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_create"
	     title="Attribute 50: time_create">
      <t>
	The time of creation of the object. This attribute does not
	have any relation to the traditional UNIX file attribute
	"ctime" or "change time".
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_delta"
	     title="Attribute 51: time_delta">
      <t>
	Smallest useful server time granularity.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_metadata"
	     title="Attribute 52: time_metadata">
      <t>
	The time of last metadata modification of the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_modify"
	     title="Attribute 53: time_modify">
      <t>
	The time of last modification to the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_modify_set"
	     title="Attribute 54: time_modify_set">
      <t>
	Sets the time of last modification to the object.  SETATTR use only.
      </t>
    </section>

   </section>

  </section>

  <section anchor="owner_owner_group" 
	   title="Interpreting owner and owner_group">
    <t>
      The RECOMMENDED attributes "owner" and "owner_group" (and also
      users and groups within the "acl" attribute) are represented in
      terms of a UTF-8 string.  To avoid a representation that is tied
      to a particular underlying implementation at the client or
      server, the use of the UTF-8 string has been chosen.  Note that
      Section 6.1 of <xref target="RFC2624">RFC 2624</xref> provides
      additional rationale.  It is expected that the client and server
      will have their own local representation of owner and
      owner_group that is used for local storage or presentation to
      the end user.  Therefore, it is expected that when these
      attributes are transferred between the client and server,
      the local representation is translated to a syntax of the form
      "user@dns_domain".  This will allow for a client and server that
      do not use the same local representation the ability to
      translate to a common syntax that can be interpreted by both.
    </t>
    <t>
      Similarly, security principals may be represented in different
      ways by different security mechanisms.  Servers normally
      translate these representations into a common format,
      generally that used by local storage, to serve as a means of
      identifying the users corresponding to these security
      principals.  When these local identifiers are translated to
      the form of the owner attribute, associated with files created
      by such principals, they identify, in a common format, the
      users associated with each corresponding set of security
      principals.
    </t>
    <t>
      The translation used to interpret owner and group strings is
      not specified as part of the protocol.  This allows various
      solutions to be employed.  For example, a local translation
      table may be consulted that maps a numeric identifier to the
      user@dns_domain syntax.  A name service may also be used to
      accomplish the translation.  A server may provide a more
      general service, not limited by any particular translation
      (which would only translate a limited set of possible strings)
      by storing the owner and owner_group attributes in local
      storage without any translation or it may augment a
      translation method by storing the entire string for attributes
      for which no translation is available while using the local
      representation for those cases in which a translation is
      available.
    </t>
    <t>
      Servers that do not provide support for all possible values of
      the owner and owner_group attributes SHOULD return an error
      (NFS4ERR_BADOWNER) when a string is presented that has no
      translation, as the value to be set for a SETATTR of the
      owner, owner_group, or acl attributes.  When a server does
      accept an owner or owner_group value as valid on a SETATTR
      (and similarly for the owner and group strings in an acl), it
      is promising to return that same string when a corresponding
      GETATTR is done.  Configuration changes (including
      changes from the mapping of the string to the local representation)
      and ill-constructed
      name translations (those that contain aliasing) may make that
      promise impossible to honor.  Servers should make appropriate
      efforts to avoid a situation in which these attributes have
      their values changed when no real change to ownership has
      occurred.
    </t>
    <t>
      The "dns_domain" portion of the owner string is meant to be a
      DNS domain name, for example, user@xxxxxxxxxxx.  Servers should
      accept as valid a set of users for at least one domain.  A
      server may treat other domains as having no valid
      translations.  A more general service is provided when a
      server is capable of accepting users for multiple domains, or
      for all domains, subject to security constraints.
    </t>
    <t>
      In the case where there is no translation available to the
      client or server, the attribute value will be constructed
      without the "@".  Therefore, the absence of the @ from the
      owner or owner_group attribute signifies that no translation
      was available at the sender and that the receiver of the
      attribute should not use that string as a basis for
      translation into its own internal format.  Even though the
      attribute value cannot be translated, it may still be useful.
      In the case of a client, the attribute string may be used for
      local display of ownership.
    </t>
    <t>
      To provide a greater degree of compatibility with NFSv3,
      which identified users and groups by 32-bit unsigned user
      identifiers and group identifiers, owner and group strings that
      consist of decimal numeric values with no leading zeros can be
      given a special interpretation by clients and servers that
      choose to provide such support.  The receiver may treat such a
      user or group string as representing the same user as would be
      represented by an NFSv3 uid or gid having the corresponding
      numeric value.  A server is not obligated to accept such a
      string, but may return an NFS4ERR_BADOWNER instead.  To avoid
      this mechanism being used to subvert user and group translation,
      so that a client might pass all of the owners and groups in
      numeric form, a server SHOULD return an NFS4ERR_BADOWNER error
      when there is a valid translation for the user or owner
      designated in this way.  In that case, the client must use the
      appropriate name@domain string and not the special form for compatibility.
    </t>
    <t>
      The owner string "nobody" may be used to designate an
      anonymous user, which will be associated with a file created
      by a security principal that cannot be mapped through normal
      means to the owner attribute. Users and implementations
      of NFSv4.1 SHOULD NOT use "nobody" to designate a real user whose access is not anonymous.
    </t>
  </section>

  <section anchor="character_case_attributes" 
	   title="Character Case Attributes">
    <t>
      With respect to the case_insensitive and case_preserving
      attributes, each UCS-4 character (which UTF-8 encodes) can be
      mapped according to Appendix B.2 of 
      <xref target="RFC3454">RFC 3454</xref>.
      For general character handling and internationalization issues,
      see <xref target="internationalization"/>.
    </t>
  </section>

  <section title="Directory Notification Attributes" anchor="dir_not_attrs">
    <t>
      As described in <xref target="OP_GET_DIR_DELEGATION" />, the
      client can request a minimum delay for notifications of changes
      to attributes, but the server is free to ignore what the client
      requests. The client can determine in advance what notification
      delays the server will accept by sending a GETATTR operation for either or
      both of two directory notification attributes.  When the client
      calls the GET_DIR_DELEGATION operation and asks for attribute
      change notifications, it should request notification delays that
      are no less than the values in the server-provided attributes.
    </t>
    <section toc="exclude" anchor="attrdef_dir_notif_delay"
	     title="Attribute 56: dir_notif_delay">
      <t>
	The dir_notif_delay attribute is the minimum number of seconds
	the server will delay before notifying the client of a change
	to the directory's attributes.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_dirent_notif_delay"
	     title="Attribute 57: dirent_notif_delay">
      <t>
	The dirent_notif_delay attribute is the minimum number of seconds
	the server will delay before notifying the client of a change
	to a file object that has an entry in the directory.
      </t>
    </section>

  </section>

  <section anchor="pnfs_attr_full" title="pNFS Attribute Definitions">

    <section toc="exclude" anchor="attrdef_fs_layout_type"
	     title="Attribute 62: fs_layout_type">
      <t>
	The fs_layout_type attribute (see
	<xref target="layouttype4"/>) applies to a
	file system and indicates what layout types are supported by
	the file system.  When the client encounters a new fsid, the
	client SHOULD obtain the value for the fs_layout_type
	attribute associated with the new file system.  This attribute
	is used by the client to determine if the layout types
	supported by the server match any of the client's supported
	layout types.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_alignment"
	     title="Attribute 66: layout_alignment">
      <t>
	When a client holds layouts on files of a file system, the
        layout_alignment attribute indicates the preferred alignment
        for I/O to files on that file system.  Where possible, the
        client should send READ and WRITE operations with offsets
        that are whole multiples of the layout_alignment attribute.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_blksize"
	     title="Attribute 65: layout_blksize">
      <t>
	When a client holds layouts on files of a file system, the
	layout_blksize attribute indicates the preferred block size
	for I/O to files on that file system.  Where possible, the
	client should send READ operations with a count argument that
	is a whole multiple of layout_blksize, and WRITE operations
	with a data argument of size that is a whole multiple of
	layout_blksize.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_hint"
	     title="Attribute 63: layout_hint">
      <t>
	The layout_hint attribute (see
	<xref target="layouthint4"/>) may be set on
	newly created files to influence the metadata server's choice
	for the file's layout.  If possible, this attribute is one of
	those set in the initial attributes within the OPEN operation.
	The metadata server may choose to ignore this attribute.  The
	layout_hint attribute is a subset of the layout structure
	returned by LAYOUTGET.  For example, instead of specifying
	particular devices, this would be used to suggest the stripe
	width of a file.  The server implementation determines which
	fields within the layout will be used.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_type"
	     title="Attribute 64: layout_type">
      <t>
	This attribute lists the layout type(s) available for a file.
	The value returned by the server is for informational purposes
	only.  The client will use the LAYOUTGET operation to obtain
	the information needed in order to perform I/O, for example,
	the specific device information for the file and its layout.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mdsthreshold"
	     title="Attribute 68: mdsthreshold">
      <t>
	This attribute is a server-provided hint used to communicate
	to the client when it is more efficient to send READ and
	WRITE operations to the metadata server or the data server.
	The two types of thresholds described are file size thresholds
	and I/O size thresholds.  If a file's size is smaller than the
	file size threshold, data accesses SHOULD be sent to the
	metadata server.  If an I/O request has a length
        that is below the I/O size threshold,
	the I/O SHOULD be sent to the metadata server. 
	Each threshold type is specified separately for read and
	write.
      </t>
      <t>
	The server MAY provide both types of thresholds for a file.
	If both file size and I/O size are provided, the client SHOULD
	reach or exceed both thresholds before sending its read or write
	requests to the data server.  Alternatively, if only one of
	the specified thresholds is reached or exceeded, the I/O requests are
	sent to the metadata server.
      </t>
      <t>
	For each threshold type, a value of zero indicates no READ or WRITE
	should be sent to the metadata server, while a value of all ones
	indicates that all READs or WRITEs should be sent to the metadata
	server.
      </t>
      <t> 
	The attribute is available on a per-filehandle basis.  If the
	current filehandle refers to a non-pNFS file or directory, the
	metadata server should return an attribute that is
	representative of the filehandle's file system.  It is suggested
	that this attribute is queried as part of the OPEN operation.
	Due to dynamic system changes, the client should not assume that
	the attribute will remain constant for any specific time period;
	thus, it should be periodically refreshed.
      </t>
    </section>
  </section> <!-- "PNFS Attributes" -->

  <section anchor="retention" title="Retention Attributes">
    <t>
      Retention is a concept whereby a file object can be placed in an
      immutable, undeletable, unrenamable state for a fixed or
      infinite duration of time. Once in this "retained" state, the
      file cannot be moved out of the state until the duration of
      retention has been reached.
    </t>
    <t>
      When retention is enabled, retention MUST extend to the data of
      the file, and the name of file. The server MAY extend retention
      to any other property of the file, including any subset of
      REQUIRED, RECOMMENDED, and named attributes, with the
      exceptions noted in this section.
    </t>
    <t>
      Servers MAY support or not support retention on
      any file object type.
    </t>
    <t>
      The five retention attributes are explained in the next subsections.
    </t>

    <section toc="exclude" anchor="attrdef_retention_get"
	     title="Attribute 69: retention_get">
      <t>
      If retention is enabled for the associated file,
      this attribute's value represents the retention
      begin time of the file object.   This attribute's
      value is only readable with the GETATTR operation
      and MUST NOT be modified by the SETATTR operation
      (<xref target="rw_attr"/>).  The value of the
      attribute consists of:

<figure>
 <artwork>
const RET4_DURATION_INFINITE    = 0xffffffffffffffff;
struct retention_get4 {
        uint64_t        rg_duration;
        nfstime4        rg_begin_time&lt;1>;
};
 </artwork>
</figure>

      The field rg_duration is the duration in seconds indicating how
      long the file will be retained once retention is enabled. The
      field rg_begin_time is an array of up to one absolute time
      value. If the array is zero length, no beginning retention time
      has been established, and retention is not enabled.  
      If rg_duration is equal to RET4_DURATION_INFINITE, the file, once
      retention is enabled, will be retained for an infinite duration.
     </t>
     <t>
      If (as soon as) rg_duration is zero, then rg_begin_time will be
      of zero length, and again, retention is not (no longer) enabled.

     </t>
    </section>

    <section toc="exclude" anchor="attrdef_retention_set"
	     title="Attribute 70: retention_set">
      <t>
	This attribute is used to set the retention
	duration and optionally enable retention for
	the associated file object.  This attribute is
	only modifiable via the SETATTR operation and 
        MUST NOT be retrieved by the GETATTR operation
        (<xref target="rw_attr"/>). 
	This attribute corresponds to retention_get.
	The value of the attribute consists of:

<figure>
 <artwork>
struct retention_set4 {
        bool            rs_enable;
        uint64_t        rs_duration&lt;1>;
};
 </artwork>
</figure>

        If the client sets rs_enable to TRUE, then it is enabling
        retention on the file object with the begin time of retention
        starting from the server's current time and date. The
        duration of the retention can also be provided if the
        rs_duration array is of length one.  The duration is the time in
        seconds from the begin time of retention, and if set to
        RET4_DURATION_INFINITE, the file is to be retained forever. If
        retention is enabled, with no duration specified in either
        this SETATTR or a previous SETATTR, the duration defaults to
        zero seconds.  The server MAY restrict the enabling of
        retention or the duration of retention on the basis of the
        ACE4_WRITE_RETENTION ACL permission.  The enabling of
        retention MUST NOT prevent the enabling of event-based
        retention or the modification of the retention_hold
        attribute.
      </t>
      <t>
       The following rules apply to both the retention_set and
       retentevt_set attributes.

       <list style='symbols'>
       <t>
	 As long as retention is not enabled, the client
	 is permitted to decrease the duration.

       </t>
       <t>
	 The duration can always be set to an
	 equal or higher value, even if retention is
	 enabled. Note that once retention is enabled,
	 the actual duration (as returned by the
	 retention_get or retentevt_get attributes;
	 see <xref target="attrdef_retention_get"/>
	 or <xref target="attrdef_retentevt_get"/>)
	 is constantly counting down to zero (one unit
	 per second), unless the duration was set to
	 RET4_DURATION_INFINITE.  Thus, it will not be
	 possible for the client to precisely extend the
	 duration on a file that has retention enabled.

       </t>
       <t>
	 While retention is enabled, attempts to disable
	 retention or decrease the retention's duration
	 MUST fail with the error NFS4ERR_INVAL.

       </t>
   
       <t>
         If the principal attempting to change
         retention_set or retentevt_set does not have
         ACE4_WRITE_RETENTION permissions, the attempt
         MUST fail with NFS4ERR_ACCESS.

       </t>

       </list>
      </t>

    </section>

    <section toc="exclude" anchor="attrdef_retentevt_get"
	     title="Attribute 71: retentevt_get">
      <t>
	Gets the event-based retention duration, and if enabled, the
        event-based retention begin time of the file object.  This
        attribute is like retention_get, but refers to event-based
        retention.  The event that triggers event-based retention is
        not defined by the NFSv4.1 specification.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_retentevt_set"
	     title="Attribute 72: retentevt_set">
      <t>
	Sets the event-based retention duration, and optionally enables
	event-based retention on the file object.  This attribute
	corresponds to retentevt_get and is like retention_set, but
	refers to event-based retention.  When event-based retention
	is set, the file MUST be retained even if non-event-based
	retention has been set, and the duration of non-event-based
	retention has been reached. Conversely, when non-event-based
	retention has been set, the file MUST be retained even if
	event-based retention has been set, and the duration of
	event-based retention has been reached.  The server MAY
	restrict the enabling of event-based retention or the duration
	of event-based retention on the basis of the
	ACE4_WRITE_RETENTION ACL permission.  The enabling of
	event-based retention MUST NOT prevent the enabling of
	non-event-based retention or the modification of the
	retention_hold attribute.
     </t>
    </section>


    <section toc="exclude" anchor="attrdef_retention_hold"
	     title="Attribute 73: retention_hold">
      <t>
	Gets or sets administrative retention holds, one hold per bit
        position.
      </t>
      <t>
	This attribute allows one to 64 administrative holds, one hold
	per bit on the attribute. If retention_hold is not zero, then
	the file MUST NOT be deleted, renamed, or modified, even if
	the duration on enabled event or non-event-based retention has
	been reached.  The server MAY restrict the modification of
	retention_hold on the basis of the ACE4_WRITE_RETENTION_HOLD
	ACL permission.  The enabling of administration retention
	holds does not prevent the enabling of event-based or
	non-event-based retention.
      </t>
      <t>
	If the principal attempting to change retention_hold does
	not have ACE4_WRITE_RETENTION_HOLD permissions,
	the attempt MUST fail with NFS4ERR_ACCESS.
      </t>
    </section>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $  -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Access Control Attributes" anchor="acl">
    <t>
        Access Control Lists (ACLs) are file attributes that specify
        fine-grained access control. This section covers the
        &quot;acl&quot;, &quot;dacl&quot;, &quot;sacl&quot;,
        &quot;aclsupport&quot;, &quot;mode&quot;, and
        &quot;mode_set_masked&quot; file attributes and their
        interactions.  Note that file attributes may apply to any file
        system object.
    </t>
    
    <section title="Goals">
      <t>
        ACLs and modes represent two well-established models for
        specifying permissions. This section specifies requirements
        that attempt to meet the following goals:

        <list style="symbols">
          <t>
            If a server supports the mode attribute, it should provide
            reasonable semantics to clients that only set and retrieve
            the mode attribute.
          </t>
          <t>
            If a server supports ACL attributes, it should provide
            reasonable semantics to clients that only set and retrieve
            those attributes.
          </t>
          <t>
            On servers that support the mode attribute, if ACL
            attributes have never been set on an object, via
            inheritance or explicitly, the behavior should be
            traditional UNIX-like behavior.
          </t>
          <t>
            On servers that support the mode attribute, if the ACL
            attributes have been previously set on an object, either
            explicitly or via inheritance:
            <list>
              <t>
                Setting only the mode attribute should effectively
                control the traditional UNIX-like permissions of read,
                write, and execute on owner, owner_group, and other.
              </t>
              <t>
                Setting only the mode attribute should provide
                reasonable security. For example, setting a mode of
                000 should be enough to ensure that future OPEN operations for
                OPEN4_SHARE_ACCESS_READ or OPEN4_SHARE_ACCESS_WRITE by any principal fail, regardless of a
                previously existing or inherited ACL.
              </t>
            </list>
          </t>
          <t>
            NFSv4.1 may introduce different
            semantics relating to the mode and ACL attributes,
            but it does not render invalid any previously
            existing implementations. Additionally, this
            section provides clarifications based on previous
            implementations and discussions around them.
          </t>
          <t>
            On servers that support both the mode and the acl or
            dacl attributes, the server must keep the two consistent
            with each other.  The value of the mode attribute (with
            the exception of the three high-order bits described in
            <xref target="attrdef_mode" />) must be determined entirely
            by the value of the ACL, so that use of the mode is
            never required for anything other than setting the
            three high-order bits.  See <xref target="setattr" />
            for exact requirements.
          </t>
          <t>
            When a mode attribute is set on an object, the ACL
            attributes may need to be modified in order to not conflict
            with the new mode. In such cases, it is desirable that the
            ACL keep as much information as possible. This includes
            information about inheritance, AUDIT and ALARM ACEs, and
            permissions granted and denied that do not conflict with
            the new mode.
          </t>
        </list>
      </t>
    </section>
    
    <section title="File Attributes Discussion">
      <section anchor="attrdef_acl"
	       title="Attribute 12: acl">
        <t>
          The NFSv4.1 ACL attribute contains an array of Access
          Control Entries (ACEs) that are associated with the file
          system object.  Although the client can set and
          get the acl attribute, the server is responsible for using
          the ACL to perform access control. The client can use the
          OPEN or ACCESS operations to check access without modifying
          or reading data or metadata.
        </t>

        <t>
          The NFS ACE structure is defined as follows:
        </t>
<figure>
 <artwork>
typedef uint32_t        acetype4;
 </artwork>
</figure>
<figure>
 <artwork>
typedef uint32_t aceflag4;
 </artwork>
</figure>
<figure>
 <artwork>
typedef uint32_t        acemask4;
 </artwork>
</figure>
<figure>
 <artwork>
struct nfsace4 {
        acetype4        type;
        aceflag4        flag;
        acemask4        access_mask;
        utf8str_mixed   who;
};
 </artwork>
</figure>

        <t>
          To determine if a request succeeds, the server processes
          each nfsace4 entry in order.  Only ACEs that have a "who"
          that matches the requester are considered.  Each ACE is
          processed until all of the bits of the requester's access
          have been ALLOWED.  Once a bit (see below) has been ALLOWED
          by an ACCESS_ALLOWED_ACE, it is no longer considered in the
          processing of later ACEs.  If an ACCESS_DENIED_ACE is
          encountered where the requester's access still has unALLOWED
          bits in common with the "access_mask" of the ACE, the
          request is denied.  When the ACL is fully processed, if
          there are bits in the requester's mask that have not been
          ALLOWED or DENIED, access is denied.
        </t>
        <t>
          Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE
          types do not affect a requester's access, and instead are
          for triggering events as a result of a requester's access
          attempt.  Therefore, AUDIT and ALARM ACEs are processed only
          after processing ALLOW and DENY ACEs.
        </t>
        <t>
          The NFSv4.1 ACL model is quite rich. Some server
          platforms may provide access-control functionality that goes
          beyond the UNIX-style mode attribute, but that is not as
          rich as the NFS ACL model.  So that users can take advantage
          of this more limited functionality, the server may support
          the acl attributes by mapping between its ACL model and the
          NFSv4.1 ACL model.  Servers must ensure that the ACL
          they actually store or enforce is at least as strict as the
          NFSv4 ACL that was set.  It is tempting to accomplish this
          by rejecting any ACL that falls outside the small set that
          can be represented accurately.  However, such an approach
          can render ACLs unusable without special client-side
          knowledge of the server's mapping, which defeats the purpose
          of having a common NFSv4 ACL protocol.  Therefore, servers
          should accept every ACL that they can without compromising
          security.  To help accomplish this, servers may make a
          special exception, in the case of unsupported permission
          bits, to the rule that bits not ALLOWED or DENIED by an ACL
          must be denied.  For example, a UNIX-style server might
          choose to silently allow read attribute permissions even
          though an ACL does not explicitly allow those permissions.
          (An ACL that explicitly denies permission to read attributes
          should still be rejected.)
        </t>
        <t>
          The situation is complicated by the fact that a server may
          have multiple modules that enforce ACLs. For example, the
          enforcement for NFSv4.1 access may be different from,
          but not weaker than, the enforcement for local access, and
          both may be different from the enforcement for access
          through other protocols such as SMB (Server Message Block). So it may be useful for
          a server to accept an ACL even if not all of its modules are
          able to support it.
        </t>
        <t>
          The guiding principle with regard to NFSv4 access is
          that the server must not accept ACLs that appear to
          make access to the file more restrictive than it really is.
        </t>

        <section title="ACE Type">
          <t>
            The constants used for the type field (acetype4) are as
            follows:
          </t>

<figure>
 <artwork>
const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;
 </artwork>
</figure>
          <t>
            Only the ALLOWED and DENIED bits may be used in the
            dacl attribute, and only the AUDIT and ALARM bits may be
            used in the sacl attribute.  All four are permitted in the
            acl attribute.
          </t>
          <texttable>
            <ttcol>Value</ttcol>
            <ttcol>Abbreviation</ttcol>
            <ttcol>Description</ttcol>
            <c>ACE4_ACCESS_ALLOWED_ACE_TYPE</c>
            <c>ALLOW</c>
            <c>
              Explicitly grants the access defined in acemask4 to
              the file or directory.
            </c>
            <c>ACE4_ACCESS_DENIED_ACE_TYPE</c>
            <c>DENY</c>
            <c>
              Explicitly denies the access defined in acemask4 to
              the file or directory.
            </c>
            <c>ACE4_SYSTEM_AUDIT_ACE_TYPE</c>
            <c>AUDIT</c>
            <c>
              Log (in a system-dependent way) any access attempt to
              a file or directory that uses any of the access
              methods specified in acemask4.
            </c>
            <c>ACE4_SYSTEM_ALARM_ACE_TYPE</c>
            <c>ALARM</c>
            <c>
              Generate an alarm (in a system-dependent way) when any
              access attempt is made to a file or directory for the
              access methods specified in acemask4.
            </c>
          </texttable>
            <t>
              The &quot;Abbreviation&quot; column denotes how the
              types will be referred to throughout the rest of this
              section.
            </t>
        </section>
	<section anchor="attrdef_aclsupport"
	     title="Attribute 13: aclsupport">
          <t>
            A server need not support all of the above ACE types.
	    This attribute indicates which ACE types are supported for
	    the current file system.  The bitmask constants used to
	    represent the above definitions within the aclsupport
	    attribute are as follows:
          </t>

<figure>
 <artwork>
const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;
 </artwork>
</figure>
          <t>
            Servers that support either the ALLOW or DENY ACE type
            SHOULD support both ALLOW and DENY ACE types.
          </t>
          <t>
            Clients should not attempt to set an ACE unless the server
            claims support for that ACE type. If the server receives a
            request to set an ACE that it cannot store, it MUST reject
            the request with NFS4ERR_ATTRNOTSUPP. If the server
            receives a request to set an ACE that it can store but
            cannot enforce, the server SHOULD reject the request with
            NFS4ERR_ATTRNOTSUPP.
          </t>
          <t>
            Support for any of the ACL attributes is
            optional (albeit RECOMMENDED).
            However, a server that supports either of the new ACL
            attributes (dacl or sacl) MUST allow use of the new ACL
            attributes to access all of the ACE types that it
            supports.  In other words, if such a server supports ALLOW
            or DENY ACEs, then it MUST support the dacl attribute, and
            if it supports AUDIT or ALARM ACEs, then it MUST support
            the sacl attribute.
          </t>
        </section>
        <section anchor="acemask" title="ACE Access Mask">
          <t>
            The bitmask constants used for the access mask field
            are as follows:
          </t>

<figure>
 <artwork>
const ACE4_READ_DATA            = 0x00000001;
const ACE4_LIST_DIRECTORY       = 0x00000001;
const ACE4_WRITE_DATA           = 0x00000002;
const ACE4_ADD_FILE             = 0x00000002;
const ACE4_APPEND_DATA          = 0x00000004;
const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
const ACE4_READ_NAMED_ATTRS     = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
const ACE4_EXECUTE              = 0x00000020;
const ACE4_DELETE_CHILD         = 0x00000040;
const ACE4_READ_ATTRIBUTES      = 0x00000080;
const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
const ACE4_WRITE_RETENTION      = 0x00000200;
const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

const ACE4_DELETE               = 0x00010000;
const ACE4_READ_ACL             = 0x00020000;
const ACE4_WRITE_ACL            = 0x00040000;
const ACE4_WRITE_OWNER          = 0x00080000;
const ACE4_SYNCHRONIZE          = 0x00100000;
 </artwork>
</figure>
          <t>

	   Note that some masks have coincident values, for
	   example, ACE4_READ_DATA and ACE4_LIST_DIRECTORY.
	   The mask entries ACE4_LIST_DIRECTORY,
	   ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
	   intended to be used with directory objects,
	   while ACE4_READ_DATA, ACE4_WRITE_DATA, and
	   ACE4_APPEND_DATA are intended to be used with
	   non-directory objects.

          </t>
          <section title="Discussion of Mask Attributes">
	    <t>
	      <list style="hanging">
		<t hangText="ACE4_READ_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READ" />
			<t hangText="OPEN" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the data of the file.
		      <vspace blankLines='1' />
		      Servers SHOULD allow a user the ability to read the data
		      of the file when only the ACE4_EXECUTE access mask bit is
		      allowed.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_LIST_DIRECTORY">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READDIR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to list the contents of a directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="WRITE" />
			<t hangText="OPEN" />
			<t hangText="SETATTR of size" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify a file's data.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_ADD_FILE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="CREATE" />
			<t hangText="LINK" />
			<t hangText="OPEN" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to add a new file in a directory.
		      The CREATE operation is affected when nfs_ftype4
		      is NF4LNK, NF4BLK, NF4CHR, NF4SOCK, or
		      NF4FIFO. (NF4DIR is not listed because it is
		      covered by ACE4_ADD_SUBDIRECTORY.) OPEN is
		      affected when used to create a regular file.
		      LINK and RENAME are always affected.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_APPEND_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="WRITE" />
			<t hangText="OPEN" />
			<t hangText="SETATTR of size" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      The ability to modify a file's data, but only
		      starting at EOF.  This allows for the notion of
		      append-only files, by allowing ACE4_APPEND_DATA
		      and denying ACE4_WRITE_DATA to the same user or
		      group.  If a file has an ACL such as the one
		      described above and a WRITE request is made for
		      somewhere other than EOF, the server SHOULD
		      return NFS4ERR_ACCESS.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_ADD_SUBDIRECTORY">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="CREATE" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to create a subdirectory in a
		      directory.  The CREATE operation is affected
		      when nfs_ftype4 is NF4DIR.  The RENAME operation
		      is always affected.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_NAMED_ATTRS">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="OPENATTR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the named attributes of a
		      file or to look up the named attribute
		      directory.  OPENATTR is affected when it is not
		      used to create a named attribute directory.
		      This is when 1) createdir is TRUE, but a named
		      attribute directory already exists, or 2)
		      createdir is FALSE.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_NAMED_ATTRS">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="OPENATTR" />
			<t hangText="" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the named attributes of a
		      file or to create a named attribute directory.
		      OPENATTR is affected when it is used to create a
		      named attribute directory.  This is when
		      createdir is TRUE and no named attribute
		      directory exists.  The ability to check whether
		      or not a named attribute directory exists
		      depends on the ability to look it up; therefore,
		      users also need the ACE4_READ_NAMED_ATTRS
		      permission in order to create a named attribute
		      directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_EXECUTE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READ" />
			<t hangText="OPEN" />
			<t hangText="REMOVE" />
			<t hangText="RENAME" />
			<t hangText="LINK" />
			<t hangText="CREATE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to execute a file.
		      <vspace blankLines='1' />
		      Servers SHOULD allow a
		      user the ability to read the data of the file
		      when only the ACE4_EXECUTE access mask bit is
		      allowed.  This is because there is no way to
		      execute a file without reading the contents.
		      Though a server may treat ACE4_EXECUTE and
		      ACE4_READ_DATA bits identically when deciding to
		      permit a READ operation, it SHOULD still allow
		      the two bits to be set independently in ACLs,
		      and MUST distinguish between them when replying
		      to ACCESS operations.  In particular, servers
		      SHOULD NOT silently turn on one of the two bits
		      when the other is set, as that would make it
		      impossible for the client to correctly enforce
		      the distinction between read and execute
		      permissions.  
		      <vspace blankLines='1' />
		      As an example, following a SETATTR of the following ACL:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE:ALLOW
		      <vspace blankLines='1' />
		      A subsequent GETATTR of ACL for that file SHOULD return:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE:ALLOW
		      <vspace blankLines='1' />
		      Rather than:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_EXECUTE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="LOOKUP" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to traverse/search a directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_DELETE_CHILD">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="REMOVE" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to delete a file or directory within
		      a directory. 

		      See <xref
		      target="delete-delete_child"/>
		      for information on ACE4_DELETE and
		      ACE4_DELETE_CHILD interact.

		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_ATTRIBUTES">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="GETATTR of file system object attributes" />
			<t hangText="VERIFY" />
			<t hangText="NVERIFY" />
			<t hangText="READDIR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      The ability to read basic attributes (non-ACLs)
		      of a file.  On a UNIX system, basic attributes
		      can be thought of as the stat-level attributes.
		      Allowing this access mask bit would mean that the
		      entity can execute "ls -l" and stat.  If a
		      READDIR operation requests attributes, this mask
		      must be allowed for the READDIR to succeed.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_ATTRIBUTES">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of time_access_set, time_backup," />
			<t hangText="time_create, time_modify_set, mimetype, hidden, system" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to change the times associated with a
		      file or directory to an arbitrary value.  Also
		      permission to change the mimetype, hidden, and
		      system attributes.  A user having
		      ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be
		      allowed to set the times associated with a file
		      to the current server time.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_RETENTION">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of retention_set, retentevt_set." />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify the durations of event and
		      non-event-based retention. Also permission to
		      enable event and non-event-based retention. A
		      server MAY behave such that setting
		      ACE4_WRITE_ATTRIBUTES allows
		      ACE4_WRITE_RETENTION.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_RETENTION_HOLD">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of retention_hold." />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify the administration
		      retention holds.  A server MAY map
		      ACE4_WRITE_ATTRIBUTES to
		      ACE_WRITE_RETENTION_HOLD.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_DELETE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="REMOVE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />

		      Permission to delete the
		      file or directory. 

		      See <xref
		      target="delete-delete_child"/>
		      for information on ACE4_DELETE and
		      ACE4_DELETE_CHILD interact.

		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_ACL">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="GETATTR of acl, dacl, or sacl" />
			<t hangText="NVERIFY" />
			<t hangText="VERIFY" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the ACL.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_ACL">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of acl and mode" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the acl and mode attributes.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_OWNER">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of owner and owner_group" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the owner and owner_group
		      attributes.  On UNIX systems, this is the
		      ability to execute chown() and chgrp().
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_SYNCHRONIZE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="NONE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to use the file object as a
		      synchronization primitive for interprocess
		      communication. This permission is not enforced
		      or interpreted by the NFSv4.1 server on behalf of
		      the client.

		      <vspace blankLines='1' />

                      Typically, the ACE4_SYNCHRONIZE permission is
                      only meaningful on local file systems, i.e.,
                      file systems not accessed via NFSv4.1. The reason
                      that the permission bit exists is that some operating
                      environments, such as Windows, use ACE4_SYNCHRONIZE.

		      <vspace blankLines='1' />

                      For example, if a client copies a file that has
                      ACE4_SYNCHRONIZE set from a local file system to
                      an NFSv4.1 server, and then later copies the file
                      from the NFSv4.1 server to a local file system,
                      it is likely that if ACE4_SYNCHRONIZE was set
                      in the original file, the client will want it
                      set in the second copy.  The first copy will not
                      have the permission set unless the NFSv4.1 server
                      has the means to set the ACE4_SYNCHRONIZE bit. The
                      second copy will not have the permission set unless
                      the NFSv4.1 server has the means to retrieve the
                      ACE4_SYNCHRONIZE bit.

		    </t>
		  </list>
		</t>

	      </list>
	    </t>

            <t>
              Server implementations need not provide the granularity
              of control that is implied by this list of masks. For
              example, POSIX-based systems might not distinguish
              ACE4_APPEND_DATA (the ability to append to a file) from
              ACE4_WRITE_DATA (the ability to modify existing
              contents); both masks would be tied to a single "write"
              permission <xref target="chmod"/>. When such a server returns attributes to the
              client, it would show both ACE4_APPEND_DATA and
              ACE4_WRITE_DATA if and only if the write permission is
              enabled.
            </t>

            <t>
              If a server receives a SETATTR request that it cannot
              accurately implement, it should err in the direction of
              more restricted access, except in the previously
              discussed cases of execute and read. For example,
              suppose a server cannot distinguish overwriting data
              from appending new data, as described in the previous
              paragraph.  If a client submits an ALLOW ACE where
              ACE4_APPEND_DATA is set but ACE4_WRITE_DATA is not (or
              vice versa), the server should either turn off
              ACE4_APPEND_DATA or reject the request with
              NFS4ERR_ATTRNOTSUPP.
            </t>
          </section>

          <section anchor="delete-delete_child" title="ACE4_DELETE vs. ACE4_DELETE_CHILD">
            <t>
              Two access mask bits govern the ability to delete a
              directory entry: ACE4_DELETE on the object
              itself (the "target") and ACE4_DELETE_CHILD on
              the containing directory (the "parent").
            </t>

            <t>
              Many systems also take the "sticky bit" (MODE4_SVTX)
              on a directory to allow unlink only to a user that
              owns either the target or the parent; on some
              such systems the decision also depends on
              whether the target is writable.
            </t>

            <t>
              Servers SHOULD allow unlink if either ACE4_DELETE
              is permitted on the target, or ACE4_DELETE_CHILD is
              permitted on the parent.  (Note that this is
              true even if the parent or target explicitly
              denies one of these permissions.)
            </t>

            <t>
              If the ACLs in question neither explicitly ALLOW
              nor DENY either of the above, and if MODE4_SVTX is
              not set on the parent, then the server SHOULD allow
              the removal if and only if ACE4_ADD_FILE is permitted.
              In the case where MODE4_SVTX is set, the server
              may also require the remover to own either the parent
              or the target, or may require the target to be
              writable.
            </t>

            <t>
              This allows servers to support something close to
              traditional UNIX-like semantics, with ACE4_ADD_FILE
              taking the place of the write bit.
            </t>

          </section>
        </section>
        <section anchor="aceflag" title="ACE flag">
          <t>
            The bitmask constants used for the flag field are as
            follows:
<figure>
 <artwork>
const ACE4_FILE_INHERIT_ACE             = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
const ACE4_IDENTIFIER_GROUP             = 0x00000040;
const ACE4_INHERITED_ACE                = 0x00000080;
 </artwork>
</figure>

            A server need not support any of these flags. If the
            server supports flags that are similar to, but not
            exactly the same as, these flags, the implementation
            may define a mapping between the protocol-defined
            flags and the implementation-defined flags.
          </t>

          <t>
            For example, suppose a client tries to set an ACE with
            ACE4_FILE_INHERIT_ACE set but not
            ACE4_DIRECTORY_INHERIT_ACE. If the server does not
            support any form of ACL inheritance, the server should
            reject the request with NFS4ERR_ATTRNOTSUPP. If the
            server supports a single "inherit ACE" flag that
            applies to both files and directories, the server may
            reject the request (i.e., requiring the client to set
            both the file and directory inheritance flags). The
            server may also accept the request and silently turn
            on the ACE4_DIRECTORY_INHERIT_ACE flag.
          </t>
          <section title="Discussion of Flag Bits">


            <t>
              <list style="hanging">
                <t hangText="ACE4_FILE_INHERIT_ACE">
                  <vspace />
                  Any non-directory file in any
                  sub-directory will get this ACE
                  inherited.
                </t>

                <t hangText="ACE4_DIRECTORY_INHERIT_ACE">
                  <vspace />
                  Can be placed on a directory and indicates
                  that this ACE should be added to each new
                  directory created.
                  <vspace />
                  If this flag is set in an ACE in an ACL
                  attribute to be set on a non-directory
                  file system object, the operation
                  attempting to set the ACL SHOULD fail
                  with NFS4ERR_ATTRNOTSUPP.
                </t>



                <t hangText="ACE4_NO_PROPAGATE_INHERIT_ACE">
                  <vspace />
                  Can be placed on a directory.  This flag
                  tells the server that inheritance of this
                  ACE should stop at newly created child
                  directories.
                </t>

                <t hangText="ACE4_INHERIT_ONLY_ACE">
                  <vspace />
                  Can be placed on a directory but does not
                  apply to the directory; ALLOW and DENY ACEs
                  with this bit set do not affect access to
                  the directory, and AUDIT and ALARM ACEs
                  with this bit set do not trigger log or
                  alarm events.  Such ACEs only take effect
                  once they are applied (with this bit
                  cleared) to newly created files and
                  directories as specified by the
                  ACE4_FILE_INHERIT_ACE and ACE4_DIRECTORY_INHERIT_ACE
                  flags.
                  <vspace blankLines="1"/>
                  If this flag is present on an ACE, but
                  neither ACE4_DIRECTORY_INHERIT_ACE nor
                  ACE4_FILE_INHERIT_ACE is present, then
                  an operation attempting to set such an
                  attribute SHOULD fail with
                  NFS4ERR_ATTRNOTSUPP.
                </t>



                <t hangText="ACE4_SUCCESSFUL_ACCESS_ACE_FLAG">
                  <vspace />
                </t>
                <t hangText="ACE4_FAILED_ACCESS_ACE_FLAG">
                  <vspace />
                  The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
                  (SUCCESS) and ACE4_FAILED_ACCESS_ACE_FLAG
                  (FAILED) flag bits may be set only on
                  ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and
                  ACE4_SYSTEM_ALARM_ACE_TYPE (ALARM) ACE
                  types. If during the processing of the
                  file's ACL, the server encounters an AUDIT
                  or ALARM ACE that matches the principal
                  attempting the OPEN, the server notes that
                  fact, and the presence, if any, of the
                  SUCCESS and FAILED flags encountered in
                  the AUDIT or ALARM ACE. Once the server
                  completes the ACL processing, it then
                  notes if the operation succeeded or
                  failed. If the operation succeeded, and if
                  the SUCCESS flag was set for a matching
                  AUDIT or ALARM ACE, then the appropriate
                  AUDIT or ALARM event occurs. If the
                  operation failed, and if the FAILED flag
                  was set for the matching AUDIT or ALARM 
                  ACE, then the appropriate AUDIT or ALARM
                  event occurs.  Either or both of the
                  SUCCESS or FAILED can be set, but if
                  neither is set, the AUDIT or ALARM ACE is
                  not useful.
                </t>

                <t hangText="">
                  The previously described processing
                  applies to ACCESS operations even when
                  they return NFS4_OK.  For the purposes of
                  AUDIT and ALARM, we consider an ACCESS
                  operation to be a "failure" if it fails
                  to return a bit that was requested and
                  supported.
                </t>

                <t hangText="ACE4_IDENTIFIER_GROUP">
                  <vspace />
                  Indicates that the "who" refers to a GROUP
                  as defined under UNIX or a GROUP ACCOUNT
                  as defined under Windows. Clients and
                  servers MUST ignore the
                  ACE4_IDENTIFIER_GROUP flag on ACEs with a
                  who value equal to one of the special
                  identifiers outlined in
                  <xref target="acewho" />.
                </t>

                <t hangText="ACE4_INHERITED_ACE">
                  <vspace />
                  Indicates that this ACE is inherited from
                  a parent directory.  A server that supports
                  automatic inheritance will place
                  this flag on any ACEs inherited from the
                  parent directory when creating a new
                  object.  Client applications will use this
                  to perform automatic inheritance.
                  Clients and servers MUST clear this
                  bit in the acl attribute; it may only
                  be used in the dacl and sacl attributes.
                </t>
              </list>
            </t>
          </section>
        </section>
        <section title="ACE Who" anchor="acewho">
          <t>
            The &quot;who&quot; field of an ACE is an identifier that
            specifies the principal or principals to whom the ACE
            applies. It may refer to a user or a group, with the flag
            bit ACE4_IDENTIFIER_GROUP specifying which.
          </t>
          <t>
            There are several special identifiers that need to be
            understood universally, rather than in the context of a
            particular DNS domain. Some of these identifiers cannot be
            understood when an NFS client accesses the server, but
            have meaning when a local process accesses the file. The
            ability to display and modify these permissions is
            permitted over NFS, even if none of the access methods on
            the server understands the identifiers.
          </t>
          <texttable anchor="specialwho">
            <ttcol>Who</ttcol>
            <ttcol>Description</ttcol>
            <c>OWNER</c>
            <c>
              The owner of the file.
            </c>
            <c>GROUP</c>
            <c>
              The group associated with the file.
            </c>
            <c>EVERYONE</c>
            <c>
              The world, including the owner and owning group.
            </c>
            <c>INTERACTIVE</c>
            <c>
              Accessed from an interactive terminal.
            </c>
            <c>NETWORK</c>
            <c>
              Accessed via the network.
            </c>
            <c>DIALUP</c>
            <c>
              Accessed as a dialup user to the server.
            </c>
            <c>BATCH</c>
            <c>
              Accessed from a batch job.
            </c>
            <c>ANONYMOUS</c>
            <c>
              Accessed without any authentication.
            </c>
            <c>AUTHENTICATED</c>
            <c>
              Any authenticated user (opposite of
              ANONYMOUS).
            </c>
            <c>SERVICE</c>
            <c>
              Access from a system service.
            </c>
          </texttable>
          <t>
            To avoid conflict, these special identifiers are
            distinguished by an appended "@" and should appear in the
            form "xxxx@" (with no domain name after the "@"), for
            example, ANONYMOUS@.
          </t>
          <t>
            The ACE4_IDENTIFIER_GROUP flag MUST be ignored on
            entries with these special identifiers.  When encoding
            entries with these special identifiers, the
            ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.
          </t>

          <section title="Discussion of EVERYONE@">
            <t>
              It is important to note that "EVERYONE@" is not
              equivalent to the UNIX "other" entity. This is
              because, by definition, UNIX "other" does not include
              the owner or owning group of a file. "EVERYONE@" means
              literally everyone, including the owner or owning
              group.
            </t>
          </section>
        </section>
      </section>
      <section anchor="attrdef_dacl"
	       title="Attribute 58: dacl">
	<t>
          The dacl attribute is like the acl attribute,
          but dacl allows 
          just ALLOW and DENY ACEs.  The dacl
          attribute supports automatic inheritance (see
          <xref target="auto_inherit" />).
	</t>
      </section>

      <section anchor="attrdef_sacl"
	       title="Attribute 59: sacl">
	<t>
          The sacl attribute is like the acl attribute,
          but sacl allows
          just AUDIT and ALARM ACEs. The sacl
          attribute supports automatic inheritance (see
          <xref target="auto_inherit" />).
	</t>
      </section>

      <section anchor="attrdef_mode"
	       title="Attribute 33: mode">
        <t>
          The NFSv4.1 mode attribute is based on the UNIX mode
          bits. The following bits are defined:
        </t>

<figure>
 <artwork>
const MODE4_SUID = 0x800;  /* set user id on execution */
const MODE4_SGID = 0x400;  /* set group id on execution */
const MODE4_SVTX = 0x200;  /* save text even after use */
const MODE4_RUSR = 0x100;  /* read permission: owner */
const MODE4_WUSR = 0x080;  /* write permission: owner */
const MODE4_XUSR = 0x040;  /* execute permission: owner */
const MODE4_RGRP = 0x020;  /* read permission: group */
const MODE4_WGRP = 0x010;  /* write permission: group */
const MODE4_XGRP = 0x008;  /* execute permission: group */
const MODE4_ROTH = 0x004;  /* read permission: other */
const MODE4_WOTH = 0x002;  /* write permission: other */
const MODE4_XOTH = 0x001;  /* execute permission: other */
 </artwork>
</figure>

        <t>
          Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the
          principal identified in the owner attribute. Bits MODE4_RGRP,
          MODE4_WGRP, and MODE4_XGRP apply to principals identified in
          the owner_group attribute but who are not identified in the
          owner attribute. Bits MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH apply
          to any principal that does not match that in the owner
          attribute and does not have a group matching that of the
          owner_group attribute.
        </t>
        <t>
          Bits within a mode other than those specified above
          are not defined by this protocol. A server
          MUST NOT return bits other than those defined above in a
          GETATTR or READDIR operation, and it MUST return NFS4ERR_INVAL
          if bits other than those defined above are set in a SETATTR,
          CREATE, OPEN, VERIFY, or NVERIFY operation.
        </t>
      </section>
      <section anchor="attrdef_mode_set_masked"
	       title="Attribute 74: mode_set_masked">
        <t>
          The mode_set_masked attribute is a write-only attribute
          that allows individual bits in the mode attribute to be
          set or reset, without changing others.  It allows, for
          example, the bits MODE4_SUID, MODE4_SGID, and MODE4_SVTX
          to be modified while leaving unmodified any of the 
          nine low-order mode bits devoted to permissions.
        </t>
        <t>
          In such instances that the nine low-order bits are left
          unmodified, then neither the acl nor the dacl attribute
          should be automatically modified as discussed in 
	  <xref target="setattr" />.
        </t>
        <t>
          The mode_set_masked attribute consists of two words,
          each in the form of a mode4.  The first consists of the
          value to be applied to the current mode value and the
          second is a mask.  Only bits set to one in the mask word
          are changed (set or reset) in the file's mode.  All 
          other bits in the mode remain unchanged.  Bits in the
          first word that correspond to bits that are zero in
          the mask are ignored, except that undefined bits are
          checked for validity and can result in NFS4ERR_INVAL as
          described below.
        </t> 
        <t>
          The mode_set_masked attribute is only valid in a SETATTR
          operation.  If it is used in a CREATE or OPEN operation, the
          server MUST return NFS4ERR_INVAL.
        </t>
        <t>
          Bits not defined as valid in the mode attribute are not
          valid in either word of the mode_set_masked attribute.
          The server MUST return NFS4ERR_INVAL
          if any such bits are set to one in a SETATTR.  
If the mode and
          mode_set_masked attributes are both specified in the
          same SETATTR, the server MUST also return NFS4ERR_INVAL.
        </t>
      </section>

    </section>
    
    <section title="Common Methods">
      <t>
        The requirements in this section will be referred to in future
        sections, especially <xref target="aclreqs" />.
      </t>
      <section title="Interpreting an ACL" anchor="useacl">
        <section title="Server Considerations" anchor="serverinterp">
          <t> 
	    The server uses the algorithm described in
	    <xref target="attrdef_acl"/> to determine whether an ACL
	    allows access to an object.  However, the ACL might not be
	    the sole determiner of access.  For example:
            <list style="symbols">
              <t>
                In the case of a file system exported as read-only,
                the server may deny write access even though
                an object's ACL grants it.
              </t>

              <t>
                Server implementations MAY grant ACE4_WRITE_ACL
                and ACE4_READ_ACL permissions to prevent
                a situation from arising in which there is no valid
                way to ever modify the ACL.
              </t>

              <t>
                All servers will allow a user the ability to read
                the data of the file when only the execute
                permission is granted (i.e., if the ACL denies the
                user the ACE4_READ_DATA access and allows the user
                ACE4_EXECUTE, the server will allow the user to
                read the data of the file).
              </t>

              <t>
                Many servers have the notion of owner-override in
                which the owner of the object is allowed to
                override accesses that are denied by the ACL.
                This may be helpful, for example, to allow users
                continued access to open files on which the
                permissions have changed.
              </t>

              <t>
                Many servers have the notion of a
                &quot;superuser&quot; that has privileges beyond
                an ordinary user.  The superuser may be able
                to read or write data or metadata in ways that would
                not be permitted by the ACL.
              </t>

              <t>
                A retention attribute might also block access otherwise
                allowed by ACLs (see <xref target="retention"/>).
              </t>

            </list>
          </t>
        </section>

        <section title="Client Considerations" anchor="clientinterp">
          <t>
            Clients SHOULD NOT do their own access checks based on
            their interpretation of the ACL, but rather use the OPEN and
            ACCESS operations to do access checks. This allows the
            client to act on the results of having the server
            determine whether or not access should be granted based on
            its interpretation of the ACL.
          </t>

          <t>
            Clients must be aware of situations in which an object's
            ACL will define a certain access even though the server
            will not enforce it. In general, but especially in these
            situations, the client needs to do its part in the
            enforcement of access as defined by the ACL. To do this,
            the client MAY send the appropriate ACCESS operation
            prior to servicing the request of the user or application
            in order to determine whether the user or application
            should be granted the access requested. For examples in
            which the ACL may define accesses that the server doesn't
            enforce, see <xref target="serverinterp"/>.
          </t>
        </section>
      </section>

      <section title="Computing a Mode Attribute from an ACL"
               anchor="computemode">
        <t>
          The following method can be used to calculate the MODE4_R*,
          MODE4_W*, and MODE4_X* bits of a mode attribute, based upon
          an ACL.
        </t>

        <t>
          First, for each of the special identifiers OWNER@, GROUP@, and
          EVERYONE@, evaluate the ACL in order, considering only ALLOW
          and DENY ACEs for the identifier EVERYONE@ and for the
          identifier under consideration.  The result of the evaluation
          will be an NFSv4 ACL mask showing exactly which bits are
          permitted to that identifier.
        </t>

        <t>
          Then translate the calculated mask for OWNER@, GROUP@, and
          EVERYONE@ into mode bits for, respectively, the user, group,
          and other, as follows:

          <list style="numbers">
            <t>
              Set the read bit (MODE4_RUSR, MODE4_RGRP, or
              MODE4_ROTH) if and only if ACE4_READ_DATA is set in
              the corresponding mask.
            </t>

            <t>
              Set the write bit (MODE4_WUSR, MODE4_WGRP, or
              MODE4_WOTH) if and only if ACE4_WRITE_DATA and
              ACE4_APPEND_DATA are both set in the corresponding
              mask.
            </t>

            <t>
              Set the execute bit (MODE4_XUSR, MODE4_XGRP, or
              MODE4_XOTH), if and only if ACE4_EXECUTE is set in the
              corresponding mask.
            </t>
          </list>
        </t>
        <section title="Discussion">
          <t>
            Some server implementations also add bits permitted to
            named users and groups to the group bits (MODE4_RGRP,
            MODE4_WGRP, and MODE4_XGRP).
          </t>
          <t>
            Implementations are discouraged from doing this, because
            it has been found to cause confusion for users who see
            members of a file's group denied access that the mode
            bits appear to allow.  (The presence of DENY ACEs may also
            lead to such behavior, but DENY ACEs are expected to be
            more rarely used.)
          </t>
          <t>
            The same user confusion seen when fetching the mode also
            results if setting the mode does not effectively control
            permissions for the owner, group, and other users; this
            motivates some of the requirements that follow.
          </t>
        </section>
      </section>
    </section>
    
    <section title="Requirements" anchor="aclreqs">
      <t>
        The server that supports both mode and ACL must take care to
        synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with
        the ACEs that have respective who fields of "OWNER@", "GROUP@",
        and "EVERYONE@". This way, the client can see if semantically equivalent
        access permissions exist whether the client asks for the owner,
        owner_group, and mode attributes or for just the ACL.
      </t>
      <t>
        In this section, much is made of the methods in <xref
							   target="computemode" />. Many requirements refer to this section.
        But note that the methods have behaviors specified with
        &quot;SHOULD&quot;. This is intentional, to avoid invalidating
        existing implementations that compute the mode according to the
        withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
        actual permissions on owner, group, and other.
      </t>
      <section title="Setting the Mode and/or ACL Attributes"
               anchor="setattr">
        <t>
          In the case where a server supports the sacl or
          dacl attribute, in addition to the acl attribute,
          the server MUST fail a request to set the acl
          attribute simultaneously with a dacl or sacl
          attribute.  The error to be given is NFS4ERR_ATTRNOTSUPP.
        </t>
        <section title="Setting Mode and not ACL" anchor="setmode">
          <t>
            When any of the nine low-order mode bits
            are subject to change, either because the mode
            attribute was set or because the mode_set_masked
            attribute was set and the mask included one or more
            bits from the nine low-order mode bits,
            and no ACL attribute is explicitly
            set, the acl and dacl attributes must be modified
            in accordance with the updated value of those bits.
            This must happen
            even if the value of the low-order bits
            is the same after the mode is set as before.
          </t>
          <t>
            Note that any AUDIT or ALARM ACEs (hence any ACEs in the
            sacl attribute) are unaffected by changes to the mode.
          </t>
          <t>
            In cases in which the permissions bits are subject to
            change, the acl and dacl attributes
            MUST be modified such that the mode computed via the
            method in
            <xref target="computemode" />
            yields the low-order nine bits (MODE4_R*, MODE4_W*,
            MODE4_X*) of the mode attribute as modified by the
            attribute change.  The ACL attributes
            SHOULD also be modified such that:
            <list style="numbers">
              <t>
                If MODE4_RGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and EVERYONE@
                SHOULD NOT be granted ACE4_READ_DATA.
              </t>
              <t>
                If MODE4_WGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and
                EVERYONE@ SHOULD NOT be granted
                ACE4_WRITE_DATA or ACE4_APPEND_DATA.
              </t>
              <t>
                If MODE4_XGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and EVERYONE@
                SHOULD NOT be granted ACE4_EXECUTE.
              </t>
            </list>
            Access mask bits other than those listed above, appearing
            in ALLOW ACEs, MAY also be disabled.
          </t>
          <t>
            Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do
            not affect the permissions of the ACL itself, nor do ACEs
            of the type AUDIT and ALARM. As such, it is desirable to
            leave these ACEs unmodified when modifying the ACL
            attributes.
          </t>
          <t>
            Also note that the requirement may be met by
            discarding the acl and dacl, in favor of an ACL
            that represents the mode and only the mode. This is
            permitted, but it is preferable for a server to
            preserve as much of the ACL as possible without
            violating the above requirements. Discarding the
            ACL makes it effectively impossible for a file
            created with a mode attribute to inherit an ACL
            (see <xref target="aclcreate" />).
          </t>
        </section>
        <section title="Setting ACL and Not Mode"
                 anchor="settingacl">
          <t>
            When setting the acl or dacl and not setting the
            mode or mode_set_masked attributes, the permission
            bits of the mode need to be derived from the ACL.
            In this case, the ACL attribute SHOULD be set as
            given. The nine low-order bits of the mode
            attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be
            modified to match the result of the method in
	    <xref target="computemode" />. The three high-order bits
            of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX)
            SHOULD remain unchanged.
          </t>
        </section>
        <section title="Setting Both ACL and Mode" anchor="setboth">
          <t>
            When setting both the mode (includes use of either the
            mode attribute or the mode_set_masked attribute) 
            and the acl or dacl attributes in the
            same operation, the attributes MUST be applied in this
            order: mode (or mode_set_masked), then ACL.  The 
            mode-related attribute is set as given,
            then the ACL attribute is set as given, possibly changing
            the final mode, as described above in
            <xref target="settingacl" />.
          </t>
        </section>
      </section>
      <section title="Retrieving the Mode and/or ACL Attributes">
        <t>
          This section applies only to servers that support both the
          mode and ACL attributes.
        </t>
        <t>
          Some server implementations may have a concept of
          &quot;objects without ACLs&quot;, meaning that all permissions
          are granted and denied according to the mode attribute and
          that no ACL attribute is stored for that object. If an ACL
          attribute is requested of such a server, the server SHOULD
          return an ACL that does not conflict with the mode; that is to
          say, the ACL returned SHOULD represent the nine low-order bits
          of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
          described in <xref target="computemode" />.
        </t>
        <t>
          For other server implementations, the ACL attribute is always
          present for every object. Such servers SHOULD store at least
          the three high-order bits of the mode attribute (MODE4_SUID,
          MODE4_SGID, MODE4_SVTX). The server SHOULD return a mode
          attribute if one is requested, and the low-order nine bits of
          the mode (MODE4_R*, MODE4_W*, MODE4_X*) MUST match the result
          of applying the method in
          <xref target="computemode" /> to the ACL attribute.
        </t>
      </section>
      <section title="Creating New Objects" anchor="aclcreate">
        <t>
          If a server supports any ACL attributes, it may use the ACL
          attributes on the parent directory to compute an initial ACL
          attribute for a newly created object. This will be referred to
          as the inherited ACL within this section. The act of adding
          one or more ACEs to the inherited ACL that are based upon ACEs
          in the parent directory's ACL will be referred to as
          inheriting an ACE within this section.
        </t>
        <t>
          Implementors should standardize what the behavior of CREATE
          and OPEN must be depending on the presence or absence of the
          mode and ACL attributes.
          <list style="numbers">
            <t>If just the mode is given in the call:
              <vspace blankLines="1" /> In this case, inheritance
              SHOULD take place, but the mode MUST be applied to the
              inherited ACL as described in <xref target="setmode"
						  />, thereby modifying the ACL.

            </t>
            <t>If just the ACL is given in the call:
              <vspace blankLines="1" />
              In this case, inheritance SHOULD NOT take place, and
              the ACL as defined in the CREATE or OPEN will be set
              without modification, and the mode modified as in
              <xref target="settingacl" />.
		      
            </t>
            <t>If both mode and ACL are given in the call:
              <vspace blankLines="1" /> In this case, inheritance
              SHOULD NOT take place, and both attributes will be set
              as described in <xref target="setboth" />.
		      
            </t>
            <t>
              If neither mode nor ACL is given in the call:
              <vspace blankLines="1" />
              In the case where an object is being created without
              any initial attributes at all, e.g., an OPEN operation
              with an opentype4 of OPEN4_CREATE and a createmode4 of
              EXCLUSIVE4, inheritance SHOULD NOT take place (note that
              EXCLUSIVE4_1 is a better choice of createmode4, since it
              does permit initial attributes).
              Instead, the server SHOULD set permissions to deny all
              access to the newly created object. It is expected
              that the appropriate client will set the desired
              attributes in a subsequent SETATTR operation, and the
              server SHOULD allow that operation to succeed,
              regardless of what permissions the object is created
              with. For example, an empty ACL denies all
              permissions, but the server should allow the owner's
              SETATTR to succeed even though WRITE_ACL is implicitly
              denied.
              <vspace blankLines="1" />
              In other cases, inheritance SHOULD take place, and no
              modifications to the ACL will happen. The mode
              attribute, if supported, MUST be as computed in 
	      <xref target="computemode" />, with the MODE4_SUID,
              MODE4_SGID, and MODE4_SVTX bits clear.
              If no inheritable ACEs exist on the parent directory,
              the rules for creating acl, dacl, or sacl attributes
              are implementation defined.
              If either the dacl or sacl attribute is supported,
              then the ACL4_DEFAULTED flag SHOULD be set on the
              newly created attributes.
		      <vspace blankLines='1' />
            </t>
          </list>
        </t>
        <section title="The Inherited ACL" anchor="inheritreq">
          <t>
            If the object being created is not a directory, the
            inherited ACL SHOULD NOT inherit ACEs from the parent
            directory ACL unless the ACE4_FILE_INHERIT_FLAG is set.
          </t>
          <t>
            If the object being created is a directory, the inherited
            ACL should inherit all inheritable ACEs from the parent
            directory, that is, those that have the ACE4_FILE_INHERIT_ACE or
            ACE4_DIRECTORY_INHERIT_ACE flag set.  
If the inheritable
            ACE has ACE4_FILE_INHERIT_ACE set but
            ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on
            the newly created directory MUST have the
            ACE4_INHERIT_ONLY_ACE flag set to prevent the directory
            from being affected by ACEs meant for non-directories.
          </t>
          <t>
            When a new directory is created, the server MAY split
            any inherited ACE that is both inheritable and effective
            (in other words, that has neither ACE4_INHERIT_ONLY_ACE
            nor ACE4_NO_PROPAGATE_INHERIT_ACE set), into two ACEs,
            one with no inheritance flags and one with
            ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or
            sacl attribute, both of those ACEs SHOULD also have the
            ACE4_INHERITED_ACE flag set.)  This makes it simpler to
            modify the effective permissions on the directory
            without modifying the ACE that is to be inherited to the
            new directory's children.
          </t>
        </section>
        
        <section title="Automatic Inheritance" anchor="auto_inherit">
          <t>
            The acl attribute consists only of an array of ACEs, but
            the <xref target="attrdef_sacl">sacl</xref>
            and <xref target="attrdef_dacl">dacl</xref> attributes
            also include an additional flag field.

<figure>
 <artwork>
struct nfsacl41 {
        aclflag4        na41_flag;
        nfsace4         na41_aces&lt;>;
};
 </artwork>
</figure>

            The flag field
            applies to the entire sacl or dacl; three flag values are
            defined:

<figure>
 <artwork>
const ACL4_AUTO_INHERIT         = 0x00000001;
const ACL4_PROTECTED            = 0x00000002;
const ACL4_DEFAULTED            = 0x00000004;
 </artwork>
</figure>

            and all other bits must be cleared.  The
            ACE4_INHERITED_ACE flag may be set in the ACEs of the sacl
            or dacl (whereas it must always be cleared in the acl).
          </t>
          <t>
            Together these features allow a server to support automatic
            inheritance, which we now explain in more detail.
          </t>
          <t>
            Inheritable ACEs are normally inherited by child objects only
            at the time that the child objects are created; later
            modifications to inheritable ACEs do not result in
            modifications to inherited ACEs on descendants.
          </t>
          <t>
            However, the dacl and sacl provide an OPTIONAL mechanism
            that allows a client application to propagate changes to
            inheritable ACEs to an entire directory hierarchy.
          </t>
          <t>
            A server that supports this performs inheritance at object
            creation time in the normal way, and SHOULD  set the
            ACE4_INHERITED_ACE flag on any inherited ACEs as they are
            added to the new object.
          </t>
          <t>
            A client application such as an ACL editor may then propagate
            changes to inheritable ACEs on a directory by recursively
            traversing that directory's descendants and modifying each ACL
            encountered to remove any ACEs with the ACE4_INHERITED_ACE flag
            and to replace them by the new inheritable ACEs (also with the
            ACE4_INHERITED_ACE flag set).  It uses the existing ACE
            inheritance flags in the obvious way to decide which ACEs to
            propagate.  (Note that it may encounter further inheritable
            ACEs when descending the directory hierarchy and that those
            will also need to be taken into account when propagating
            inheritable ACEs to further descendants.)
          </t>
          <t>
            The reach of this propagation may be limited in two ways:
            first, automatic inheritance is not performed from any
            directory ACL that has the ACL4_AUTO_INHERIT flag
            cleared; and second, automatic inheritance stops wherever
            an ACL with the ACL4_PROTECTED flag is set, preventing
            modification of that ACL and also (if the ACL is set on
            a directory) of the ACL on any of the object's descendants.
          </t>
          <t>
            This propagation is performed independently for the sacl
            and the dacl attributes; thus, the ACL4_AUTO_INHERIT and
            ACL4_PROTECTED flags may be independently set for the sacl
            and the dacl, and propagation of one type of acl may continue
            down a hierarchy even where propagation of the other acl has
            stopped.
          </t>
          <t>
            New objects should be created with a dacl and a sacl that
            both have the ACL4_PROTECTED flag cleared and the
            ACL4_AUTO_INHERIT flag set to the same value as that on,
            respectively, the sacl or dacl of the parent object.
          </t>
          <t>
            Both the dacl and sacl attributes are RECOMMENDED, and a server
            may support one without supporting the other.
          </t>
          <t>
            A server that supports both the old acl attribute and
            one or both of the new dacl or sacl attributes must do so
            in such a way as to keep all three attributes consistent
            with each other.  Thus, the ACEs reported in the acl attribute
            should be the union of the ACEs reported in the dacl and
            sacl attributes, except that the ACE4_INHERITED_ACE flag must
            be cleared from the ACEs in the acl.  And of course a
            client that queries only the acl will be unable to determine
            the values of the sacl or dacl flag fields.
          </t>
          <t>
            When a client performs a SETATTR for the acl attribute,
            the server SHOULD set the ACL4_PROTECTED flag to true on
            both the sacl and the dacl.  By using the acl attribute,
            as opposed to the dacl or sacl attributes, the client signals
            that it may not understand automatic inheritance, and thus
            cannot be trusted to set an ACL for which automatic
            inheritance would make sense.
          </t>
          <t>
            When a client application queries an ACL, modifies it, and sets
            it again, it should leave any ACEs marked with
            ACE4_INHERITED_ACE unchanged, in their original order, at the
            end of the ACL.  If the application is unable to do this, it
            should set the ACL4_PROTECTED flag.  This behavior
            is not enforced by servers, but violations of this rule may
            lead to unexpected results when applications perform automatic
            inheritance.
          </t>
          <t>
            If a server also supports the mode attribute, it SHOULD set the
            mode in such a way that leaves inherited ACEs unchanged, in
            their original order, at the end of the ACL.  If it is unable
            to do so, it SHOULD set the ACL4_PROTECTED flag on the file's
            dacl.
          </t>
          <t>Finally, in the case where the request that creates a new file
            or directory does not also set permissions for that file or
            directory, and there are also no ACEs to inherit from the
            parent's directory, then the server's choice of ACL for the new
            object is implementation-dependent.  In this case, the server
            SHOULD set the ACL4_DEFAULTED flag on the ACL it chooses for
            the new object.  An application performing automatic
            inheritance takes the ACL4_DEFAULTED flag as a sign that the
            ACL should be completely replaced by one generated using the
            automatic inheritance rules.
          </t>
        </section>

      </section>
    </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="single_server_namespace" title="Single-Server Namespace">
  <t>
    This section describes the NFSv4 single-server namespace.
    Single-server namespaces may be presented directly to clients, 
    or they may be used as a basis to form larger multi-server 
    namespaces (e.g., site-wide or organization-wide) to be presented 
    to clients, as described in <xref target='multi_server_namespace' />.
  </t>
  <section anchor="server_exports" title="Server Exports">
    <t>
      On a UNIX server, the namespace describes all the files reachable by
      pathnames under the root directory or "/".  On a Windows server, the
      namespace constitutes all the files on disks named by mapped disk
      letters.  NFS server administrators rarely make the entire server's
      file system namespace available to NFS clients.  More often, portions
      of the namespace are made available via an "export" feature.  In
      previous versions of the NFS protocol, the root filehandle for each
      export is obtained through the MOUNT protocol; the client sent a
      string that identified the export name within the namespace and 
      the server returned the root filehandle 
      for that export.  The MOUNT protocol also provided an EXPORTS
      procedure that enumerated the server's exports.
    </t>
  </section>
  <section anchor="browsing_exports" title="Browsing Exports">
    <t>
      The NFSv4.1 protocol provides a root filehandle that clients can
      use to obtain filehandles for the exports of a particular server,
      via a series of LOOKUP operations within a COMPOUND, to traverse
      a path.  A common user experience is to use a graphical user interface
      (perhaps a file "Open" dialog window) to find a file via progressive
      browsing through a directory tree.  The client must be able to move
      from one export to another export via single-component, progressive
      LOOKUP operations.
    </t>
    <t>
      This style of browsing is not well supported by the NFSv3 protocol.  In NFSv3, the client expects all 
      LOOKUP operations to remain
      within a single server file system.  For example, the device attribute
      will not change.  This prevents a client from taking namespace paths
      that span exports.
    </t>
    <t>
      In the case of NFSv3, an automounter on the client
      can obtain a snapshot of the server's namespace
      using the EXPORTS procedure of the MOUNT protocol.
      If it understands the server's pathname syntax,
      it can create an image of the server's namespace
      on the client.  The parts of the namespace that
      are not exported by the server are filled in
      with directories that might be constructed similarly
      to an NFSv4.1 "pseudo file system" (see <xref
      target="server_pseudo_file_system" />) that
      allows the user to browse from one mounted file
      system to another.  There is a drawback to this
      representation of the server's namespace on the
      client: it is static.  If the server administrator
      adds a new export, the client will be unaware of it.

    </t>
  </section>
  <section anchor="server_pseudo_file_system" title="Server Pseudo File System">
    <t>
      NFSv4.1 servers avoid this namespace inconsistency by
      presenting all the exports for a given server within the
      framework of a single namespace for that server.
      An NFSv4.1 client uses LOOKUP and READDIR
      operations to browse seamlessly from one export to another.  
    </t>
    <t>
      Where there are portions of the server namespace that are not 
      exported, clients require some way of traversing those portions
      to reach actual exported file systems.  A technique that servers
      may use to provide for this is to bridge the unexported portion of 
      the namespace via a
      "pseudo file system" that provides a view of exported directories
      only.  A pseudo file system has a unique fsid and behaves like a
      normal, read-only file system.
    </t>
    <t>
      Based on the construction of the server's namespace, it is possible
      that multiple pseudo file systems may exist.  For example, 
    </t>
    <figure>
      <artwork>
        /a              pseudo file system
        /a/b            real file system
        /a/b/c          pseudo file system
        /a/b/c/d        real file system
      </artwork>
    </figure>
    <t>
      Each of the pseudo file systems is considered a separate entity and
      therefore MUST have its own fsid, unique among all the fsids for that
      server.
    </t>
  </section>
  <section title="Multiple Roots">
    <t>
      Certain operating environments are sometimes described as
      having "multiple roots".  In such environments, individual file 
      systems are commonly represented by disk or volume names.
      NFSv4 servers for these platforms can construct a pseudo file
      system above these root names so that disk letters or volume names are
      simply directory names in the pseudo root.
    </t>
  </section>
  <section title="Filehandle Volatility" anchor="pseudo_fs_volatility" >
    <t>
      The nature of the server's pseudo file system is that it is a logical
      representation of file system(s) available from the server.
      Therefore, the pseudo file system is most likely constructed
      dynamically when the server is first instantiated.  It is expected
      that the pseudo file system may not have an on-disk counterpart from
      which persistent filehandles could be constructed.  Even though it is
      preferable that the server provide persistent filehandles for the
      pseudo file system, the NFS client should expect that pseudo file
      system filehandles are volatile.  This can be confirmed by checking
      the associated "fh_expire_type" attribute for those filehandles in
      question.  If the filehandles are volatile, the NFS client must be
      prepared to recover a filehandle value (e.g., with a series of
      LOOKUP operations) when receiving an error of NFS4ERR_FHEXPIRED.
    </t>
    <t>
      Because it is quite likely that servers will implement pseudo
      file systems using volatile filehandles, clients need to be 
      prepared for them, rather than assuming that all filehandles
      will be persistent.
    </t>
  </section>
  <section title="Exported Root">
    <t>
      If the server's root file system is exported, one might conclude that
      a pseudo file system is unneeded.  This is not necessarily so.  Assume the
      following file systems on a server:
    </t>
    <figure>
      <artwork>
        /       fs1  (exported)
        /a      fs2  (not exported)
        /a/b    fs3  (exported)
      </artwork>
    </figure>
    <t>
      Because fs2 is not exported, fs3 cannot be reached with simple
      LOOKUPs.  The server must bridge the gap with a pseudo file system.
    </t>
  </section>
  <section title="Mount Point Crossing">
    <t>
      The server file system environment may be constructed in such a way
      that one file system contains a directory that is 'covered' or
      mounted upon by a second file system.  For example:
    </t>
    <figure>
      <artwork>
        /a/b            (file system 1)
        /a/b/c/d        (file system 2)
      </artwork>
    </figure>
    <t>
      The pseudo file system for this server may be constructed to look
      like:
    </t>
    <figure>
      <artwork>
        /               (place holder/not exported)
        /a/b            (file system 1)
        /a/b/c/d        (file system 2)
      </artwork>
    </figure>
    <t>
      It is the server's responsibility to present the pseudo file system
      that is complete to the client.  If the client sends a LOOKUP request
      for the path /a/b/c/d, the server's response is the filehandle of
      the root of the file system /a/b/c/d.  In previous versions of the 
      NFS protocol,
      the server would respond with the filehandle of directory
      /a/b/c/d within the file system /a/b.

    </t>
    <t>
      The NFS client will be able to determine if it crosses a server mount
      point by a change in the value of the "fsid" attribute.
    </t>
  </section>
  <section title="Security Policy and Namespace Presentation">
    <t>
      Because NFSv4 clients possess the ability to change the security
      mechanisms used, after determining what is allowed,
      by using SECINFO and SECINFO_NONAME, the server
      SHOULD NOT present a different view of the namespace based on
      the security mechanism being used by a client.  Instead, it 
      should present a consistent view and return NFS4ERR_WRONGSEC
      if an attempt is made to access data with an inappropriate
      security mechanism.
    </t>
    <t>
      If security considerations make it necessary to hide the existence
      of a particular file system, as opposed to all of the data within
      it, the server can apply the security policy of
      a shared resource in the server's namespace to components of the
      resource's ancestors. For example:
    </t>
    <figure>
      <artwork>
        /                           (place holder/not exported)
        /a/b                        (file system 1)
        /a/b/MySecretProject        (file system 2)

      </artwork>
    </figure>
    <t>
      The /a/b/MySecretProject directory is a real file system and 
      is the shared resource.
      Suppose the security policy for /a/b/MySecretProject is Kerberos 
      with integrity and it is desired to limit knowledge of the existence
      of this file system.  In this case, the
      server should apply the same security policy to /a/b.  This allows 
      for knowledge of the existence of a file system to be secured
      when desirable.
    </t>
    <t>
      For the case of the use of multiple, disjoint security mechanisms in
      the server's resources, applying that sort of policy would result
      in the higher-level file system not being accessible using any
      security flavor.
Therefore, that sort of configuration is not compatible
      with hiding the existence (as opposed to the contents) from clients
      using multiple disjoint sets of security flavors.
    </t>
    <t>
      In other circumstances, a desirable policy is for the security of a
      particular object in the
      server's namespace to include the union of all security mechanisms of
      all direct descendants.  A common and convenient practice, unless
      strong security requirements dictate otherwise, is to make the
      entire the pseudo file system accessible by all of the valid security 
      mechanisms.
    </t>
    <t>
      Where there is concern about the security of data on the network,
      clients should use strong security mechanisms to access the pseudo
      file system in order to prevent man-in-the-middle attacks.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="State Management" >
  <t>
    Integrating locking into the NFS protocol necessarily causes it to be
    stateful.  With the inclusion of such features as share reservations,
    file and directory delegations, recallable layouts, and support for 
    mandatory byte-range locking, the protocol becomes substantially more 
    dependent on proper management of state than the traditional
    combination of NFS and NLM (Network Lock Manager)
    <xref target="xnfs" />. These features include expanded
    locking facilities, which provide some measure of inter-client
    exclusion, but the state also offers
    features not readily providable using a stateless model.
    There are three components to
    making this state manageable:
    <list style='symbols'>
      <t>
        clear division between client and server
      </t>
      <t>
        ability to reliably detect inconsistency in state between client
        and server
      </t>
      <t>
        simple and robust recovery mechanisms
      </t>
    </list>
  </t>
  <t>
    In this model, the server owns the state information.  The client
    requests changes in locks and the server responds with the changes
    made.  Non-client-initiated changes in locking state are infrequent.
    The client receives prompt notification of such changes and can adjust
    its view of the locking state to reflect the server's changes. 
  </t>
  <t>
    Individual pieces of state created by the server and passed to the
    client at its request are represented by 128-bit stateids.  These
    stateids may represent a particular open file, a set of 
    byte-range locks held
    by a particular owner, or a recallable delegation of privileges 
    to access a file in particular ways or at a particular location.
  </t>
  <t>
    In all cases, there is a transition from the most general
    information that represents a client as a whole to the eventual 
    lightweight stateid used for most client and server
    locking interactions.  The details of this transition will vary
    with the type of object but it always starts with a client ID.
  </t>
  <section anchor="client_id" title="Client and Session ID" >
    <t>
      A client must establish a client ID (see <xref target="Client Identifiers" />) 
      and then one or more sessionids (see <xref target="Session" />) before
      performing any operations to open, byte-range lock, delegate, or obtain
      a layout for a file object.
      Each session ID is associated with a specific client ID, and thus 
      serves as a shorthand reference to an NFSv4.1 client.
     </t>
     <t>
       For some types of locking interactions, the client will represent
       some number of internal locking entities called "owners", which 
       normally correspond to processes internal to the client.  For 
       other types of locking-related objects, such as delegations and
       layouts, no such intermediate entities are provided for, and the 
       locking-related objects are considered to be transferred
       directly between the server and a unitary client.
      </t>
    </section> <!-- "Client and Session ID" -->
    <section anchor="stateid" title="Stateid Definition" >
      <t>
        When the server grants a lock of any type (including opens,
        byte-range locks, delegations, and layouts), it responds with a 
        unique stateid that represents a set of locks (often a single
        lock) for the same file, of the same type, and sharing the same
        ownership characteristics.  Thus, opens of the same file by
        different open-owners each have an identifying stateid.  Similarly,
        each set of byte-range locks on a file owned by a specific lock-owner
        has its own
        identifying stateid.  Delegations and layouts also have 
        associated stateids by which they may be referenced. 
        The stateid is used as a shorthand reference to a lock or set
        of locks, and given a stateid, the server can determine the associated
        state-owner or state-owners (in the case of an open-owner/lock-owner pair)
        and the associated filehandle.  When stateids are used, the current
        filehandle must be the one associated with that stateid.
      </t>
      <t>
        All stateids associated with a given client ID are associated with
        a common lease that represents the claim of those stateids 
        and the objects they represent to be maintained
        by the server.  See <xref target="lease_renewal" /> for a 
        discussion of the lease.   
      </t>
      <t>
        The server may assign stateids independently for different clients.
        A stateid with the same bit pattern for one client may designate
        an entirely different set of locks for a different client.  The
        stateid is always interpreted with respect to the client ID associated
        with the current session.  Stateids apply to all sessions associated
        with the given client ID, and the client may use a stateid obtained from
        one session on another session associated with the same client ID.
      </t>
      <section anchor="stateid_types" title="Stateid Types">
        <t>
          With the exception of special stateids (see <xref target="special_stateid"/>),
          each stateid
          represents locking objects of one of a set of types defined
          by the NFSv4.1 protocol.  Note that in all these cases, where
          we speak of guarantee, it is understood there are
          situations such as a client restart, or lock revocation,
          that allow the guarantee to be voided.
          <list style='symbols'>
            <t>
              Stateids may represent opens of files.
              <vspace blankLines="1" />
              Each stateid in this case represents the OPEN state for a
              given client ID/open-owner/filehandle triple.  Such
              stateids are subject to change (with consequent
              incrementing of the stateid's seqid) in response to OPENs that 
              result in upgrade and OPEN_DOWNGRADE operations. 
            </t>
            <t>
              Stateids may represent sets of byte-range locks.
              <vspace blankLines="1" />
              All locks held on a particular file by a particular owner and 
              gotten under the aegis of a particular open file
              are associated with a single stateid with the seqid
              being incremented whenever LOCK and LOCKU operations affect that 
              set of locks.
            </t>
            <t>
              Stateids may represent file delegations, which are 
              recallable guarantees by the server to the client
              that other clients will not reference or
              modify a particular file, until the delegation
              is returned.  In NFSv4.1, file delegations may be 
              obtained on both regular and non-regular files.
              <vspace blankLines="1" />
              A stateid represents a single delegation held by
              a client for a particular filehandle.
            </t>
            <t>
              Stateids may represent directory delegations, which
              are recallable guarantees by the server to the client
              that other clients will not modify the directory, 
              until the delegation is returned.
              <vspace blankLines="1" />
              A stateid represents a single delegation held by
              a client for a particular directory filehandle.
            </t>
            <t>
              Stateids may represent layouts, which are recallable
              guarantees by the server to the client that particular
              files may be accessed via an alternate data access 
              protocol at specific locations.  Such access is 
              limited to particular sets of byte-ranges and may
              proceed until those byte-ranges are reduced or the
              layout is returned.
              <vspace blankLines="1" />
              A stateid represents the set of all layouts held by a particular 
              client for a particular filehandle with a given 
              layout type.  The seqid is updated as the layouts
              of that set of byte-ranges change, via layout stateid changing operations such
              as LAYOUTGET and LAYOUTRETURN.
            </t>
          </list>
        </t>
      </section>
      <section anchor="stateid_structure" title="Stateid Structure">
        <t>
	  Stateids are divided into two fields, a 96-bit
	  "other" field identifying the specific set
	  of locks and a 32-bit "seqid" sequence value.
	  Except in the case of special stateids
          (see <xref target="special_stateid"/>), 
	  a particular value of the 
          "other" field denotes a 
          set of locks of the same type (for example, 
          byte-range locks, opens, delegations, or layouts),
          for a specific file or directory, and sharing
          the same ownership characteristics.  The seqid
          designates a specific instance of such a set of
          locks, and is incremented to indicate changes in
          such a set of locks, either by the addition or
          deletion of locks from the set, a change in the 
          byte-range they apply to, or an upgrade or downgrade
          in the type of one or more locks.
        </t>
        <t>  
          When such a set of locks is first created, the server returns a
          stateid with seqid value of one.  On subsequent
          operations that modify the set of locks, the server
          is required to increment the "seqid" field by one
          whenever it returns a stateid for the same 
          state-owner/file/type  combination and there is some
          change in the set of locks actually designated.
          In this case, the server will return a stateid with an "other" field
          the same as previously used for that 
          state-owner/file/type  combination, with an 
          incremented "seqid" field.
          This pattern continues until the seqid is incremented
          past NFS4_UINT32_MAX, and one
          (not zero) is the next seqid value. 
        </t>
        <t>
	  The purpose of the incrementing of the seqid
	  is to allow the server to
	  communicate to the client the order in which
	  operations that modified locking state associated
	  with a stateid have been processed and to make
          it possible for the client to send requests
          that are conditional on the set of locks not
          having changed since the stateid in question
          was returned.
        </t> 
        <t>
	  Except for layout stateids (<xref target="layout_stateid"/>),
          when a client sends a stateid to the server, it has two
          choices with regard to the seqid sent.  It may set the seqid
          to zero to indicate to the server that it wishes the most
          up-to-date seqid for that stateid's "other" field to be
          used.  This would be the common choice in the case of a
          stateid sent with a READ or WRITE operation.  It also may
          set a non-zero value, in which case the server checks if that
          seqid is the correct one.  In that case, the server is
          required to return NFS4ERR_OLD_STATEID if the seqid is lower
          than the most current value and NFS4ERR_BAD_STATEID if the
          seqid is greater than the most current value.  This would be
          the common choice in the case of stateids sent with a CLOSE
          or OPEN_DOWNGRADE.  Because OPENs may be sent in parallel
          for the same owner, a client might close a file without
          knowing that an OPEN upgrade had been done by the server,
          changing the lock in question.  If CLOSE were sent with a
          zero seqid, the OPEN upgrade would be cancelled before the
          client even received an indication that an upgrade had
          happened.
        </t>
        <t>
          When a stateid is sent by the server to the client as part of
          a callback operation, it is not subject to checking for
          a current seqid and returning NFS4ERR_OLD_STATEID.  This
          is because the client is not in a position to know the
          most up-to-date seqid and thus cannot verify it.  Unless
          specially noted, the seqid value for a stateid sent by the
          server to the client as part of a callback is required
          to be zero with NFS4ERR_BAD_STATEID returned if it is
          not.
        </t>
        <t>
          In making comparisons between seqids, both by the client
	  in determining the order of operations and by the server
	  in determining whether the NFS4ERR_OLD_STATEID is to be
          returned, the possibility of the seqid being swapped
	  around past the NFS4_UINT32_MAX value needs to be taken
	  into account.  When two seqid values are being compared,
  	  the total count of slots for all sessions associated 
	  with the current client is used to do this.  When one
	  seqid value is less than this total slot count and
	  another seqid value is greater than NFS4_UINT32_MAX
	  minus the total slot count, the former is to be treated
	  as lower than the latter, despite the fact that it is
	  numerically greater.
 	</t>
	  
      </section> <!-- "Stateid Structure" -->
      <section anchor="special_stateid" title="Special Stateids">
        <t>
          Stateid values whose "other" field is either all zeros or all
          ones are reserved.  They may not be assigned by the server but
          have special meanings defined by the protocol.  The particular
          meaning depends on whether the "other" field is all zeros or
          all ones and the specific value of the "seqid" field.
        </t>
        <t>
          The following combinations of "other" and "seqid" are defined
          in NFSv4.1:
          <list style='symbols'>
            <t>
              When "other" and "seqid" are both zero, the
              stateid is treated as a special anonymous
              stateid, which can be used in READ, WRITE,
              and SETATTR requests to indicate the absence
              of any OPEN state associated with the
              request.  When an anonymous stateid value is
              used and an existing open denies the form of
              access requested, then access will be denied
              to the request.  This stateid MUST NOT be
              used on operations to data servers (<xref
              target="ds_ops" />).
            </t>
            <t>
              When "other" and "seqid" are both all ones,
              the stateid is a special READ bypass stateid.
              When this value is used in WRITE or SETATTR,
              it is treated like the anonymous value.
              When used in READ, the server MAY grant
              access, even if access would normally be
              denied to READ operations.  This stateid MUST
              NOT be used on operations to data servers.
            </t>
            <t>
              When "other" is zero and "seqid" is one,
              the stateid represents the current stateid,
              which is whatever value is the last stateid
              returned by an operation within the COMPOUND.
              In the case of an OPEN, the stateid returned
              for the open file and not the delegation is
              used.  The stateid passed to the operation in
              place of the special value has its "seqid"
              value set to zero, except when the current 
              stateid is used by the operation CLOSE or
              OPEN_DOWNGRADE.  If there is no operation
              in the COMPOUND that has returned a stateid
              value, the server MUST return the error
	      NFS4ERR_BAD_STATEID. As illustrated  in <xref
	      target="csid_example4"/>, if the value of a
	      current stateid is a special stateid and the
	      stateid of an operation's arguments has
	      "other" set to zero and "seqid" set to one,
	      then the server MUST return the error
	      NFS4ERR_BAD_STATEID.

            </t>
            <t>
              When "other" is zero and "seqid" is NFS4_UINT32_MAX,
              the stateid represents a reserved stateid
              value defined to be invalid.  When this 
              stateid is used, the server MUST return the error
              NFS4ERR_BAD_STATEID.
            </t>
          </list>
        </t>
        <t>
          If a stateid value is used that has all zeros or all ones in the
          "other" field but does not match one of the cases above, the server
          MUST return the error NFS4ERR_BAD_STATEID.
        </t>
        <t>
          Special stateids, unlike other stateids, are not associated with
          individual client IDs or filehandles and can be used with all valid
          client IDs and filehandles.  In the case of a special 
          stateid designating the current stateid, the current stateid
          value substituted for the special stateid is associated with a
          particular client ID and filehandle, and so, if it is used
          where the current filehandle does not match that associated with the current
          stateid, the operation to which the stateid is passed will return
          NFS4ERR_BAD_STATEID.
        </t>
      </section> <!-- "Special Stateids" -->
      <section anchor="stateid_lifetime" title="Stateid Lifetime and Validation">
        <t>
          Stateids must remain valid until either a client restart or a 
          server restart or until the client returns all of the locks 
          associated with the stateid by means of an operation such as
          CLOSE or DELEGRETURN. 

          If the locks are lost due to revocation, as long
          as the client ID is valid, the stateid remains
          a valid designation of that revoked state until
          the client frees it by using FREE_STATEID.

          Stateids associated 
          with byte-range locks are an exception.  They remain valid even 
          if a LOCKU frees all remaining locks, so long as the open file 
          with which they are associated remains open, unless the client 
          frees the stateids via the FREE_STATEID operation.
        </t>
        <t>
          It should be noted that there are situations in which the
          client's locks become invalid, without the client requesting 
          they be returned.  These include lease expiration and a number
          of forms of lock revocation within the lease period.  It is 
          important to note that in these situations, the stateid remains 
          valid and the client can use it to determine the disposition of
          the associated lost locks. 
        </t>
        <t>
          An "other" value must never be reused for a different purpose
          (i.e., different filehandle, owner, or type of locks) within the
          context of a single client ID.  A server may retain the "other"
          value for the same purpose beyond the point where it may otherwise 
          be freed, but if it does so, it must maintain "seqid" continuity
          with previous values.
        </t>
        <t>
          One mechanism that may be used to satisfy the requirement that the 
          server recognize invalid and out-of-date stateids is for 
          the server to divide the "other" field of the stateid into two 
          fields.  
          <list style='symbols'>
            <t>
              an index into a table of locking-state structures.
            </t>
            <t>
              a generation number that is incremented on each allocation
              of a table entry for a particular use.
            </t>
          </list>
        </t>
        <t>
          And then store in each table entry,
          <list style='symbols'>
             <t>
               the client ID with which the stateid is associated.
             </t>
             <t>
               the current generation number for the (at most one)
               valid stateid sharing this index value.
             </t>
             <t>
               the filehandle of the file on which the locks are taken.
             </t>
             <t>
               an indication of the type of stateid (open, byte-range lock,
               file delegation, directory delegation, layout).
             </t>
             <t>
               the last "seqid" value returned corresponding to the current
               "other" value.
             </t>
             <t>
               an indication of the current status of the locks 
               associated with this stateid, in particular,
               whether these have been revoked and if so, for what reason.
             </t>
          </list>
        </t>
        <t>
          With this information, an incoming stateid can be validated and 
          the appropriate error returned when necessary.  Special and
          non-special stateids are handled separately. (See
          <xref target='special_stateid' /> for a discussion of special 
          stateids.) 
        </t>
        <t>
          Note that stateids are implicitly qualified by the current client
          ID, as derived from the client ID associated with the current 
          session.  Note, however, that the semantics of the session will
          prevent stateids associated with a previous client or server 
          instance from being analyzed by this procedure.
        </t>
        <t>
          If server restart has resulted in an invalid
          client ID or a session ID that is invalid, SEQUENCE will return
          an error and the operation that takes a stateid as an argument will never
          be processed.
        </t>
        <t>
          If there has been a server restart where there is a persistent
          session and all leased state has been lost, then the session
          in question will, although valid, be marked as dead, and any
          operation not satisfied by means of the reply cache will
          receive the error NFS4ERR_DEADSESSION, and thus not be 
          processed as indicated below.
        </t>
        <t>
          When a stateid is being tested and the "other" field is all
          zeros or all ones, a check that 
          the "other" and "seqid" fields match a defined combination for
          a special stateid is done and the results determined as follows:
          <list style='symbols'>        
            <t>
              If the "other" and "seqid" fields do not match a defined
              combination associated with a special stateid, the error
              NFS4ERR_BAD_STATEID is returned.
            </t>
            <t>
              If the special stateid is one designating the current 
              stateid and there is a current stateid, then the current
              stateid is substituted for the special stateid and the 
              checks appropriate to non-special stateids are performed.
            </t>
            <t>
              If the combination is valid in general but is not 
              appropriate to the context in which the stateid is used
              (e.g., an all-zero stateid is used when an OPEN stateid
              is required in a LOCK operation), the error
              NFS4ERR_BAD_STATEID is also returned.
            </t>
            <t>
              Otherwise, the check is completed and the special stateid 
              is accepted as valid.
            </t>
          </list>
        </t>
        <t>
          When a stateid is being tested, 
          and the "other" field is neither all zeros nor all ones, the  
          following procedure could be used to
          validate an incoming stateid and return an appropriate error,
          when necessary, assuming that the "other" field would be divided 
          into a table index and an entry generation.
          <list style='symbols'>
            <t>
              If the table index field is outside the range of the 
              associated table, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the selected table entry is of a different generation than
              that specified in the incoming stateid, return 
              NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the selected table entry does not match the current 
              filehandle, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the client ID in the table entry does not match the 
              client ID associated with the current session, 
              return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the stateid represents revoked state, then return 
              NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or 
              NFS4ERR_DELEG_REVOKED, as appropriate.
            </t>
            <t>
              If the stateid type is not valid for the context in which the
              stateid appears, return NFS4ERR_BAD_STATEID.
              Note that a stateid may be valid in general, as would be 
              reported by the TEST_STATEID operation, but be invalid for
              a particular operation, as, for example, when a stateid 
              that doesn't represent byte-range locks is passed to
              the non-from_open case of LOCK or to LOCKU, or when a stateid
              that does not represent an open is passed to CLOSE or
              OPEN_DOWNGRADE.  In such cases, the server MUST return
              NFS4ERR_BAD_STATEID. 
            </t>
            <t>
              If the "seqid" field is not zero and it is greater
              than the current sequence value corresponding to the 
              current "other" field, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the "seqid" field is not zero and it is less
              than the current sequence value corresponding to the 
              current "other" field, return NFS4ERR_OLD_STATEID.
            </t>
            <t>
              Otherwise, the stateid is valid and the table entry 
              should contain any additional information about the 
              type of stateid and information associated with that 
              particular type of stateid, such as the associated 
              set of locks, e.g., open-owner and 
              lock-owner information, as well as information on the 
              specific locks, e.g., open modes and byte-ranges.
            </t>
          </list>
        </t>
      </section> <!-- "Stateid Lifetime and Validation" -->
      <section anchor="stateid_use" title="Stateid Use for I/O Operations">
        <t>
          Clients performing I/O operations need to select an 
          appropriate stateid based on the
          locks (including opens and delegations) held by the client and 
          the various types of state-owners sending the I/O requests.
          SETATTR operations that change the file size are treated
          like I/O operations in this regard.
        </t>
        <t>
          The following rules, applied in order of decreasing priority, 
          govern the selection of the appropriate stateid.  In following 
          these rules, the client will only consider locks of which it
          has actually received notification by an appropriate operation
          response or callback.  Note that the
          rules are slightly different in the case of I/O to data servers
          when file layouts are being 
          used (see <xref target="global_stateid" />).
          <list style='symbols'>
            <t>
              If the client holds a delegation for the file in question, the
              delegation stateid SHOULD be used.
            </t>
            <t>
              Otherwise, if the entity corresponding to the lock-owner (e.g., a process)
              sending the I/O has a byte-range lock stateid for the associated open file,
              then the byte-range lock stateid for that lock-owner and open file SHOULD 
              be used.
            </t>
            <t>
              If there is no byte-range lock stateid, then the OPEN stateid for the open
              file in question SHOULD be used.
            </t>
            <t>
              Finally, if none of the above apply, then a special stateid 
              SHOULD be used.
            </t>
          </list> 
        </t> 
        <t>
          Ignoring these rules may result in situations in which the server
          does not have information necessary to properly process the request.
          For example, when mandatory byte-range locks are in effect, if the
          stateid does not indicate the proper lock-owner, via a lock stateid,
          a request might be avoidably rejected.
        </t>
        <t>
          The server however should not try to enforce these ordering rules 
          and should use whatever information is available to properly process 
          I/O requests. In particular, when a client has a delegation for a given file, it
          SHOULD take note of this fact in processing a request, even if it is
          sent with a special stateid.
        </t>  
      </section> <!-- "Stateid Use for I/O Operations" -->
      <section anchor="stateid_use_sa" title="Stateid Use for SETATTR Operations">
        <t>
          Because each operation is associated with a session ID and from that
          the clientid can be determined, operations do not need to 
          include a stateid for the server to be able to determine whether
          they should cause a delegation to be recalled or are to be 
          treated as done within the scope of the delegation.
        </t>
        <t>
          In the case of SETATTR operations, a stateid is present.  In cases
          other than those that set the file size, the client may send either
          a special stateid or, when a delegation is held for the file in 
          question, a delegation stateid.  While the server SHOULD validate
          the stateid and may use the stateid to optimize the determination
          as to whether a delegation is held, it SHOULD note the presence of
          a delegation even when a special stateid is sent, and MUST accept a
          valid delegation stateid when sent.
        </t>
      </section> <!-- "Stateid Use for SETATTR Operations" -->
    </section> <!-- "Stateid Definition" -->
  <section anchor="lease_renewal" title="Lease Renewal" >
    <t>
      Each client/server pair, as represented by a client ID, has a single
      lease.
      The purpose of the lease is to allow the client to indicate
      to the server, in a low-overhead way, that it is active, and 
      thus that the server is to retain the client's locks.  This arrangement 
      allows the server to remove stale locking-related objects
      that are held by a client that has crashed or is otherwise
      unreachable, once the relevant lease expires.  This in turn allows 
      other clients to obtain conflicting locks without being 
      delayed indefinitely by inactive or unreachable clients.  
      It is not a 
      mechanism for cache consistency and lease
      renewals may not be denied if the lease interval has not expired. 
    </t>
    <t>
      Since each session is associated with a specific
      client (identified by the client's client ID), any
      operation sent on that session is an indication
      that the associated client is reachable.  When a
      request is sent for a given session, successful
      execution of a SEQUENCE operation (or successful
      retrieval of the result of SEQUENCE from the reply
      cache) on an unexpired lease will result in the
      lease being implicitly renewed, for the standard
      renewal period (equal to the lease_time attribute).

    </t>
    <t>
      If the client ID's lease has not expired when the
      server receives a SEQUENCE operation, then the server
      MUST renew the lease.  If the client ID's lease has expired
      when the server receives a SEQUENCE operation, the
      server MAY renew the lease; this depends on whether
      any state was revoked as a result of the client's
      failure to renew the lease before expiration.

    </t>
    <t>
      Absent other activity that would renew the lease, a COMPOUND
      consisting of a single SEQUENCE operation will suffice.  The
      client should also take communication-related delays into
      account and take steps to ensure that the renewal messages
      actually reach the server in good time.  For example:
      <list style='symbols'>
        <t>
          When trunking is in effect, the client should 
          consider sending multiple requests on different
          connections, in order to ensure that renewal
          occurs, even in the event of blockage in the 
          path used for one of those connections.
        </t>
        <t>
	  Transport retransmission delays might become
	  so large as to approach or exceed the length
	  of the lease period.	This may be particularly
	  likely when the server is unresponsive due to
	  a restart; see <xref target="reclaim_locks"
	  />. If the client implementation is not careful,
	  transport retransmission delays can result in the
	  client failing to detect a server restart before
	  the grace period ends. The scenario is that the
	  client is using a transport with exponential
	  backoff, such that the maximum retransmission
	  timeout exceeds both the grace period and the
	  lease_time attribute. A network partition causes
	  the client's connection's retransmission interval
	  to back off, and even after the partition heals,
	  the next transport-level retransmission is sent
	  after the server has restarted and its grace
	  period ends.

              <vspace blankLines="1" />

          The client MUST either recover from the ensuing
          NFS4ERR_NO_GRACE errors or it MUST ensure that,
          despite transport-level retransmission intervals
          that exceed the lease_time, a SEQUENCE operation is sent
          that renews the lease before expiration. The client can achieve this
          by associating a new connection with the session,
          and sending a SEQUENCE operation on it. However, if
          the attempt to establish a new connection is delayed
          for some reason (e.g., exponential backoff of the connection
          establishment packets), the client will have to
          abort the connection establishment attempt before
          the lease expires, and attempt to reconnect.

        </t>
      </list>
    </t>
    <t>
      If the server renews the lease upon receiving
      a SEQUENCE operation, the server MUST NOT allow the lease
      to expire while the rest of the operations
      in the COMPOUND procedure's request are still
      executing. Once the last operation has finished, and
      the response to COMPOUND has been sent, the server
      MUST set the lease to expire no sooner than the
      sum of current time and the value of the lease_time attribute.

    </t>
    <t>
      A client ID's lease can expire when it has been
      at least the lease interval (lease_time) since the
      last lease-renewing SEQUENCE operation was sent
      on any of the client ID's sessions and there
      are no active COMPOUND operations on any such sessions.

    </t>
    <t>
      Because the SEQUENCE operation is the basic mechanism to renew
      a lease, and because it must be done at least once for each 
      lease period, it is the natural mechanism whereby the server 
      will inform the client of changes in the lease status that the
      client needs to be informed of.  The client should inspect the
      status flags (sr_status_flags) returned by sequence and take 
      the appropriate action (see 
      <xref target="OP_SEQUENCE_DESCRIPTION" /> for details).
      <list style="symbols">
        <t>
          The status bits SEQ4_STATUS_CB_PATH_DOWN and
          SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with
          the backchannel that the client may need to address
          in order to receive callback requests.
        </t>
        <t>
          The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
          SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicate
          problems with GSS contexts or RPCSEC_GSS handles
          for the backchannel that the
          client might have to address in order to allow callback requests 
          to be sent.
        </t>
        <t>
          The status bits SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
          SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED,
          SEQ4_STATUS_ADMIN_STATE_REVOKED, and 
          SEQ4_STATUS_RECALLABLE_STATE_REVOKED notify the 
          client of lock revocation events.  When these bits
          are set, the client should use TEST_STATEID to find
          what stateids have been revoked and use FREE_STATEID
          to acknowledge loss of the associated state.
        </t>
        <t>
          The status bit SEQ4_STATUS_LEASE_MOVE  
          indicates that 
          responsibility for lease renewal has been transferred to
          one or more new servers.
        </t>
        <t>
          The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED
	  indicates that due to server
	  restart the client must reclaim locking state. 
        </t>
        <t>
          The status bit SEQ4_STATUS_BACKCHANNEL_FAULT
          indicates that the server has encountered an unrecoverable fault
          with the backchannel (e.g., it has lost track of a 
          sequence ID for a slot in the backchannel).
        </t>
      </list>
    </t>
  </section> <!-- "Lease Renewal" -->
  <section title="Crash Recovery" anchor="lock_crash_recovery" >
    <t>
      A critical requirement in crash recovery is that both the client
      and the server know when the other has failed. Additionally, it
      is required that a client sees a consistent view of data across
      server restarts. All READ and WRITE operations that
      may have been queued within the client or network buffers must
      wait until the client has successfully recovered the locks
      protecting the READ and WRITE operations. Any that reach the
      server before the server can safely determine that the client
      has recovered enough locking state to be sure that such
      operations can be safely processed must be rejected.
      This will happen because either:
      <list style='symbols'>
        <t>
          The state presented is no longer valid since it is 
          associated with a now invalid client ID.  In this case, the
          client will receive either an NFS4ERR_BADSESSION or
          NFS4ERR_DEADSESSION error, and any attempt to attach a new
          session to that invalid client ID will result in an
          NFS4ERR_STALE_CLIENTID error.
        </t>
        <t>
          Subsequent recovery of locks may make execution of the 
          operation inappropriate (NFS4ERR_GRACE).
        </t>
      </list>
    </t>
    <section title="Client Failure and Recovery" >
      <t>
        In the event that a client fails, the server may release the 
        client's locks when the associated lease has expired.  Conflicting 
        locks from another client may only be granted after this lease 
        expiration.  As discussed in <xref target="lease_renewal" />, when
        a client has not failed and re-establishes its lease before expiration
        occurs, requests for conflicting locks will not be granted.
      </t>
      <t>
        To minimize client delay upon restart, lock requests are associated
        with an instance of the client by a client-supplied verifier.  This
        verifier is part of the client_owner4 sent in the initial 
        EXCHANGE_ID call made by the client.
        The server returns a client ID as a result of the EXCHANGE_ID
        operation.  The client then confirms the use of the client ID by
        establishing a session associated with that client ID  (see
        <xref target='OP_CREATE_SESSION_DESCRIPTION' /> for a
        description of how this is done).  All locks,
        including opens, byte-range locks, delegations, and layouts obtained
        by sessions using that client ID, are associated with that client ID.  
      </t>
      <t>
        Since the verifier will be changed by the client upon each
        initialization, the server can compare a new verifier to the verifier
        associated with currently held locks and determine that they do not
        match.  This signifies the client's new instantiation and subsequent
        loss (upon confirmation of the new client ID) of locking
        state.  As a result, the server is free to release all
        locks held that are associated with the old client ID that was
        derived from the old verifier.  At this point, conflicting locks from
        other clients, kept waiting while the lease had not yet expired, can
        be granted.  In addition, all stateids associated with the old client ID
        can also be freed, as they are no longer reference-able.
      </t>
      <t>
        Note that the verifier must have the same uniqueness properties as the
        verifier for the COMMIT operation.
      </t>
    </section> <!-- "Client Failure and Recovery" -->
    <section anchor="server_failure" title="Server Failure and Recovery" >
      <t>
        If the server loses locking state (usually as a result of a restart), it must allow clients time to discover this fact and
        re-establish the lost locking state.  The client must be able to
        re-establish the locking state without having the server deny valid
        requests because the server has granted conflicting access to another
        client.  Likewise, if there is a possibility that clients have not
        yet re-established their locking state for a file and that 
        such locking state might make it invalid to perform READ or 
        WRITE operations. For example, if mandatory locks are a possibility,
        the server must disallow READ and WRITE operations for that file.
      </t>
      <t>
        A client can determine that loss of locking
        state has occurred via several methods.
        <list style='numbers'>
        <t>
	When a SEQUENCE (most common) or other operation returns
	NFS4ERR_BADSESSION, this may mean that the session has
	been destroyed but the client ID is still valid.
	The client sends a CREATE_SESSION request with the
	client ID to re-establish the session. If
	CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
	the client must establish a new client ID (see
	<xref target="client_id" />) and re-establish its
	lock state with the new client ID, after the CREATE_SESSION
        operation succeeds (see <xref target="reclaim_locks" />).

        </t>
        <t>
        When a SEQUENCE (most common) or other operation on a
        persistent session returns NFS4ERR_DEADSESSION, this indicates
        that a session is no longer usable for new, i.e., not satisfied
        from the reply cache, operations.  Once all pending operations
        are determined to be either performed before the retry or not
        performed, the client sends a CREATE_SESSION request with the
	client ID to re-establish the session. If
	CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
	the client must establish a new client ID (see
	<xref target="client_id" />) and re-establish its
	lock state after the CREATE_SESSION, with the 
        new client ID, succeeds
        (<xref target="reclaim_locks" />).
        </t> 
        <t>
	When an operation, neither SEQUENCE nor preceded by SEQUENCE (for
	example, CREATE_SESSION, DESTROY_SESSION), returns
	NFS4ERR_STALE_CLIENTID, the client MUST establish
	a new client ID (<xref target="client_id" />) and
	re-establish its lock state (<xref
	target="reclaim_locks" />).
        </t>
        </list>
      </t>
      <section anchor="reclaim_locks" title="State Reclaim" >
      <t>
        When state information and the associated locks are lost
        as a result of a server restart, the protocol must provide
        a way to cause that state to be re-established.  The 
        approach used is to define, for most types of locking
        state (layouts are an exception), a request whose function 
        is to allow the client to 
        re-establish on the server a lock first obtained from a
        previous instance.  Generally, these requests are variants
        of the requests normally used to create locks of that type
        and are referred to as "reclaim-type" requests, and the process
        of re-establishing such locks is referred to as "reclaiming" 
        them.
      </t>
      <t anchor="read_write_grace">
        Because each client must have an opportunity to reclaim
        all of the locks that it has without the possibility that
        some other client will be granted a conflicting lock,
        a "grace period" is devoted
        to the reclaim process.  During this period, requests 
        creating client IDs and
        sessions are handled normally, but locking requests are
        subject to special restrictions.  Only 
        reclaim-type locking requests are allowed, unless the
        server can reliably determine (through state
        persistently maintained across restart instances) that
        granting any such lock cannot possibly conflict with a
        subsequent reclaim.  
        When a request is made to obtain
        a new lock (i.e., not a reclaim-type request) during the
        grace period and such a determination cannot be made,
        the server must return the error NFS4ERR_GRACE.
      </t> 
      <t>
        Once a session is established using the new client ID, the
        client will use reclaim-type locking requests (e.g., LOCK
        operations with reclaim set to TRUE and OPEN operations with a
        claim type of CLAIM_PREVIOUS;  see
        <xref target="open_br_reclaim" />) to re-establish its locking
        state.  Once this is done, or if there is no such locking
        state to reclaim, the client sends a global RECLAIM_COMPLETE
        operation, i.e., one with the rca_one_fs argument set to FALSE, to
        indicate that it has reclaimed all of the locking state that
        it will reclaim.  Once a client sends such a RECLAIM_COMPLETE
        operation, it may attempt non-reclaim locking operations,
        although it might get an NFS4ERR_GRACE status result from each such operation until
        the period of special handling is over.  
See <xref target="transition_state" /> for a discussion of the
        analogous handling lock reclamation in the case of file systems
        transitioning from server to server.
      </t>
      <t>
        During the grace period, the server must reject READ
        and WRITE operations 
        and non-reclaim locking requests (i.e., other LOCK
        and OPEN operations) with an error of NFS4ERR_GRACE,
        unless it can guarantee that these may be done 
        safely, as described below. 
      </t>
      <t>
        The grace period may last until all clients that are known to 
        possibly have had locks have done a global RECLAIM_COMPLETE operation, indicating
        that they have finished reclaiming the locks they held before
        the server restart.  This means that a client that has done a
        RECLAIM_COMPLETE must be prepared to receive an NFS4ERR_GRACE
        when attempting to acquire new locks.  
        In order for the server to know that all clients with possible prior
        lock state have done a RECLAIM_COMPLETE,
        the server must maintain in stable
        storage a list clients that may have such locks.  The server 
        may also terminate the grace period before all clients have
        done a global RECLAIM_COMPLETE.  The server SHOULD NOT terminate the
        grace period before a time equal to the lease period in order
        to give clients an opportunity to find out about the server 
        restart, as a result of sending requests on associated 
        sessions with a frequency governed by the lease time.  
        Note that when a client does not send such requests (or they
        are sent by the client but not received by the server),
        it is possible for the grace period to expire before the client
        finds out that the server restart has occurred.
      </t>
      <t>
        Some additional time in 
        order to allow a client to 
        establish a new client ID and session and to effect lock 
        reclaims may be added to the lease time.  Note that 
        analogous rules apply to
        file system-specific grace periods discussed in
        <xref target="transition_state" />.
      </t>
      <t>
        If the server can reliably determine that granting a non-reclaim
        request will not conflict with reclamation of locks by other 
        clients, the NFS4ERR_GRACE error does not have to be returned 
        even within the grace period, although NFS4ERR_GRACE must always
        be returned to clients attempting a non-reclaim lock request
        before doing their own global RECLAIM_COMPLETE.
        For the server to be able
        to service READ and WRITE operations during the grace period, it must
        again be able to guarantee that no possible conflict could arise
        between a potential reclaim locking request and the READ or WRITE
        operation.  If the server is unable to offer that guarantee, the
        NFS4ERR_GRACE error must be returned to the client.
      </t>
      <t>
        For a server to provide simple, valid handling during the grace
        period, the easiest method is to simply reject all non-reclaim locking
        requests and READ and WRITE operations by returning the NFS4ERR_GRACE
        error.  However, a server may keep information about granted locks in
        stable storage.  With this information, the server could determine if
        a locking, READ or WRITE operation can be safely processed.
      </t>
      <t>
        For example, if the server maintained on stable storage summary
        information on whether mandatory locks exist, either mandatory 
        byte-range locks, or share reservations specifying deny modes,
        many requests could be allowed during the grace period.  If it
        is known that no such share reservations exist, OPEN request that
        do not specify deny modes may be safely granted.  If, in addition,
        it is known that no mandatory byte-range locks exist, either 
        through information stored on stable storage or simply because
        the server does not support such locks, READ and WRITE operations
        may be safely processed during the grace period.
        Another important case is where it is known that no mandatory 
        byte-range locks exist, either because the server does not 
        provide support for them or because their absence is known
        from persistently recorded data.  In this case, READ and
        WRITE operations specifying stateids derived from reclaim-type
        operations may be validly processed during the grace period
        because of the fact that the valid reclaim ensures that no lock
        subsequently granted can prevent the I/O.  
      </t>
      <t>
        To reiterate, for a server that allows non-reclaim lock and I/O
        requests to be processed during the grace period, it MUST determine
        that no lock subsequently reclaimed will be rejected and that no lock
        subsequently reclaimed would have prevented any I/O operation
        processed during the grace period.
      </t>
      <t>
        Clients should be prepared for the return of NFS4ERR_GRACE errors for
        non-reclaim lock and I/O requests.  In this case, the client should
        employ a retry mechanism for the request.  A delay (on the order of
        several seconds) between retries should be used to avoid overwhelming
        the server.  Further discussion of the general issue is included in
        <xref target="Floyd" />.  The client must account for the server that
        can perform I/O and non-reclaim locking requests within the grace period
        as well as those that cannot do so.
      </t>
      <t>
        A reclaim-type locking request outside the server's grace period
        can only succeed if the server can guarantee that no conflicting
        lock or I/O request has been granted since restart.
      </t>
      <t>
        A server may, upon restart, establish a new value for the lease
        period.  Therefore, clients should, once a new client ID is
        established, refetch the lease_time attribute and use it as the basis
        for lease renewal for the lease associated with that server. However,
        the server must establish, for this restart event, a grace period at
        least as long as the lease period for the previous server
        instantiation. This allows the client state obtained during the
        previous server instance to be reliably re-established.
      </t>
      <t>
        The possibility exists that, because of server configuration 
        events, the client will be communicating with a server
        different than the one on which the locks were obtained, as
        shown by the combination of eir_server_scope and 
        eir_server_owner.  This leads to the issue of if and when
        the client should attempt to reclaim locks previously obtained
        on what is being reported as a different server.  The rules
        to resolve this question are as follows:
        <list style="symbols">
          <t>
            If the server scope is different, the client should not
            attempt to reclaim locks.  In this situation, no lock 
            reclaim is possible.  Any attempt to re-obtain the locks
            with non-reclaim operations is problematic since there is
            no guarantee that the existing filehandles will be recognized
            by the new server, or that if recognized, they denote the 
            same objects.  It is best to treat the locks as having been
            revoked by the reconfiguration event.
          </t>
          <t>
            If the server scope is the same, the client should attempt
            to reclaim locks, even if the eir_server_owner value is
            different.  In this situation, it is the responsibility
            of the server to return NFS4ERR_NO_GRACE if it cannot 
            provide correct support for lock reclaim operations, 
            including the prevention of edge conditions.
          </t>
        </list>
      </t>
      <t>
        The eir_server_owner field is not used in making this 
        determination.  Its function is to specify trunking
        possibilities for the client (see <xref target="Trunking" />)
        and not to control lock reclaim.
      </t>
        <section anchor="reclaim_security_considerations" title="Security Considerations for State Reclaim" >
        <t>
          During the grace period, a client can reclaim state that it believes or
          asserts it had before the server restarted. Unless the server
          maintained a complete record of all the state the client had,
          the server has little choice but to trust the client. (Of course,
          if the server maintained a complete record, then it would not
          have to force the client to reclaim state after server restart.)
          While the server has to trust the client to tell the truth, such
          trust does not have any negative consequences for security. The
          fundamental rule for the server when processing reclaim requests
          is that it MUST NOT grant the reclaim if an equivalent non-reclaim
          request would not be granted during steady state due to access
          control or access conflict issues. For example, an OPEN request
	  during a reclaim will be refused with NFS4ERR_ACCESS if the principal making
	  the request does not have access to open the file according to the
	  discretionary ACL (<xref target="attrdef_dacl"/>) on the file.

        </t>

        <t>
          Nonetheless, it is possible that a client operating in error or
          maliciously could, during reclaim, prevent another client from
          reclaiming access to state. For example, an attacker could
          send an OPEN reclaim operation with a deny mode that prevents
          another client from reclaiming the OPEN state it had before the
          server restarted.
          The attacker could perform the same denial of service during
          steady state prior to server restart, as long as the
          attacker had permissions. Given that the attack
          vectors are equivalent, the grace period does not offer any
          additional opportunity for denial of service, and any concerns
          about this attack vector, whether during grace or steady state,
          are addressed the same way: use RPCSEC_GSS for authentication
          and limit access to the file only to principals that the owner of
          the file trusts.

         </t>

         <t>
           Note that if prior to restart the server had client
           IDs with the  EXCHGID4_FLAG_BIND_PRINC_STATEID (<xref
           target="OP_EXCHANGE_ID"/>) capability set, then the server
           SHOULD record in stable storage the client owner and the
           principal that established the client ID via EXCHANGE_ID.
           If the server does not, then there is a risk a client will
           be unable to reclaim state if it does not have a credential
           for a principal that was originally authorized to
           establish the state.

         </t>

           
        </section> <!-- "Security Considerations for State Reclaim" -->
      </section> <!-- "State Reclaim" -->
    </section> <!-- "Server Failure and Recovery" -->
    <section anchor="network_partitions_and_recovery"
             title="Network Partitions and Recovery">
      <t>
        If the duration of a network partition is greater than the lease
        period provided by the server, the server will not have received a
        lease renewal from the client.  If this occurs, the server may free
        all locks held for the client or it may allow the lock state to
        remain for a considerable period, subject to the constraint that
        if a request for a conflicting lock is made, locks associated with
        an expired lease do not prevent such a conflicting lock from being
        granted but MUST be revoked as necessary so as to avoid interfering with
        such conflicting requests.
      </t>
      <t>
        If the server chooses to delay freeing of lock state until there 
        is a conflict, it may either free all of the client's locks once 
        there is a conflict or it may only revoke the minimum set of locks
        necessary to allow conflicting requests.  When it adopts the 
        finer-grained approach, it must revoke all locks associated with a
        given stateid, even if the conflict is with only a subset of locks.
      </t>
      <t>
        When the server chooses to free all of a client's lock state, either
        immediately upon lease expiration or as a result of the first
        attempt to obtain a conflicting a lock, the server may report the
        loss of lock state in a number of ways.
      </t>
      <t>
        The server may choose to invalidate the session and the associated
        client ID.  In this case, once the client can communicate
        with the server, it will receive an NFS4ERR_BADSESSION error.  Upon
        attempting to create a new session, it would get an 
        NFS4ERR_STALE_CLIENTID.  Upon creating the new client ID and new
        session, the client will attempt to reclaim locks. Normally, the
        server will not allow the client to reclaim locks, because the
        server will not be in its recovery grace period.
      </t>
      <t> 
        Another possibility is for the server to maintain the session and 
        client ID but for all stateids held by the
        client to become invalid or stale.  Once the client can reach
        the server after such a network partition, the status returned by
        the SEQUENCE operation will indicate a loss of locking state; i.e.,
        the flag SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED will be set in
        sr_status_flags. In
        addition, all I/O submitted by the
        client with the now invalid stateids will fail with the server
        returning the error NFS4ERR_EXPIRED.  Once the client learns of
        the loss of locking state, it 
        will suitably notify the applications that held the invalidated
        locks.  The client should then take action to free invalidated 
        stateids, either by establishing a new client ID using a new
        verifier or by doing a FREE_STATEID operation to release each
        of the invalidated stateids.
      </t>
      <t>
        When the server adopts a finer-grained approach to revocation
        of locks when a client's lease has expired, only a subset of stateids 
        will normally become invalid during a network partition.  
        When the client can communicate with the server after such a 
        network partition heals, the status returned by the SEQUENCE 
        operation will indicate a partial loss of locking state 
        (SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED).  
        In addition, operations, including I/O submitted by the
        client, with the now invalid stateids will fail with the server
        returning the error NFS4ERR_EXPIRED.  Once the client learns of
        the loss of locking state, it will use the TEST_STATEID operation 
        on all of its stateids to 
        determine which locks have been lost and then 
        suitably notify the applications that held the invalidated
        locks.  The client can then release the invalidated locking 
        state and acknowledge the revocation of the associated locks
        by doing a FREE_STATEID operation on each of the invalidated
        stateids.
      </t>
      <t>
        When a network partition is combined with a server restart, there are
        edge conditions that place requirements on the server in order to
        avoid silent data corruption following the server restart. Two of these
        edge conditions are known, and are discussed below.
      </t>
      <t>
        The first edge condition arises as a result of the scenarios such as
        the following:
        <list style='numbers'>
          <t>
            Client A acquires a lock.
          </t>
          <t>
            Client A and server experience mutual network partition, such that
            client A is unable to renew its lease.
          </t>
          <t>
            Client A's lease expires, and the server releases the lock.
          </t>
          <t>
            Client B acquires a lock that would have conflicted
            with that of client A.
          </t>
          <t>
            Client B releases its lock.
          </t>
          <t>
            Server restarts.
          </t>
          <t>
            Network partition between client A and server heals.
          </t>
          <t>
            Client A connects to a new server instance and finds out about 
            server restart.
          </t>
          <t>
            Client A reclaims its lock within the server's grace period.
          </t>
        </list>
      </t>
      <t>
        Thus, at the final step, the server has erroneously granted client A's
        lock reclaim. If client B modified the object the lock was protecting,
        client A will experience object corruption.
      </t>
      <t>
        The second known edge condition arises in situations such as the following:
        <list style="numbers">
          <t>
            Client A acquires one or more locks.
          </t>
          <t>
            Server restarts.
          </t>
          <t>
            Client A and server experience mutual network
            partition, such that client A is unable to reclaim
            all of its locks within the grace period.
          </t>
          <t>
            Server's reclaim grace period ends. Client A has either 
            no locks or an incomplete set of locks known to the server.
          </t>
          <t>
            Client B acquires a lock that would have conflicted
            with a lock of client A that was not reclaimed.
          </t>
          <t>
            Client B releases the lock.
          </t>
          <t>
            Server restarts a second time.
          </t>
          <t>
            Network partition between client A and server heals.
          </t>
          <t>
            Client A connects to new server instance and finds out about 
            server restart.
          </t>
          <t>
            Client A reclaims its lock within the server's
            grace period.
          </t>
        </list>
      </t>
      <t>
        As with the first edge condition, the final step of the scenario of
        the second edge condition has the server erroneously granting client
        A's lock reclaim.
      </t>
      <t>
        Solving the first and second edge conditions requires either that the server
        always assumes after it restarts that some edge condition 
        occurs, and thus returns NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
        record some information in stable storage.  The amount 
        of information the
        server records in stable storage is in inverse proportion to how harsh
        the server intends to be whenever edge conditions arise.
        The server
        that is completely tolerant of all edge conditions will record in
        stable storage every lock that is acquired, removing the lock record
        from stable storage only when the lock is released.
        For the two edge conditions discussed above, the harshest a
        server can be, and still support a grace period for reclaims, requires
        that the server record in stable storage some minimal
        information.  For example, a server implementation could, for each
        client, save in stable storage a record containing:
        <list style="symbols">
          <t>
            the co_ownerid field from the client_owner4 presented in the
            EXCHANGE_ID operation.
          </t>
          <t>
            a boolean that indicates if the client's lease expired
            or if there was administrative intervention (see
            <xref target="server_revocation" />) to revoke
            a byte-range lock, share reservation, or delegation and
            there has been no acknowledgment, via FREE_STATEID,
            of such revocation.
          </t>
          <t>
            a boolean that indicates whether the client may have locks
            that it believes to be reclaimable in situations in which the
            grace period was terminated, making the server's view of
            lock reclaimability suspect.  The server will set this for
            any client record in stable storage where the client has
            not done a suitable RECLAIM_COMPLETE (global or file
            system-specific depending on the target of the lock
            request) before it grants any new (i.e., not reclaimed)
            lock to any client.
          </t>
        </list>
      </t>
      <t>
        Assuming the above record keeping, for the first edge condition, after
        the server restarts, the record that client A's lease expired means
        that another client could have acquired a conflicting byte-range lock,
        share reservation, or delegation. Hence, the server must reject a
        reclaim from client A with the error NFS4ERR_NO_GRACE.
      </t>
      <t>
        For the second edge condition, after the server restarts for a second
        time, the indication that the client had not completed its
        reclaims at the time at which the grace period ended
        means that the server must reject a reclaim from client A
        with the error NFS4ERR_NO_GRACE.
      </t>
      <t>
        When either edge condition occurs, the client's attempt to reclaim
        locks will result in the error NFS4ERR_NO_GRACE.  When this is
        received, or after the client restarts with no lock state, the
        client will send a global RECLAIM_COMPLETE.  When 
        the RECLAIM_COMPLETE is received, the server and client are
        again in agreement regarding reclaimable locks and both booleans in persistent
        storage can be reset, to be set again only when there is a subsequent
        event that causes lock reclaim operations to be questionable.
      </t>
      <t>
        Regardless of the level and approach to record keeping, the server
        MUST implement one of the following strategies (which apply to
        reclaims of share reservations, byte-range locks, and delegations):
        <list style="numbers">
          <t>
            Reject all reclaims with NFS4ERR_NO_GRACE. This
            is extremely unforgiving, but necessary if the server does not
            record lock state in stable storage.
          </t>
          <t>
            Record sufficient state in stable storage such that
            all known edge conditions involving server restart,
            including the two noted in this section, are
            detected.  It is acceptable to erroneously recognize an edge condition 
            and not allow a reclaim, when, with sufficient knowledge, it
            would be allowed. The error the server would return in this
            case is NFS4ERR_NO_GRACE.  Note that it is not known if there are other
            edge conditions.
            <vspace blankLines='1' />
            In the event that, after a server restart, the server
            determines there is unrecoverable damage or
            corruption to the information in stable storage, then for
            all clients and/or locks that may be affected, the server MUST
            return NFS4ERR_NO_GRACE.
          </t>
        </list>
      </t>
      <t>
        A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
        outside the scope of this specification, since the strategies for such
        handling are very dependent on the client's operating environment.
        However, one potential approach is described below.
      </t>
      <t>
        When the client receives NFS4ERR_NO_GRACE, it could examine the change
        attribute of the objects  for which the client is trying to reclaim state,
        and use that to determine whether to re-establish the state via normal
        OPEN or LOCK operations. This is acceptable provided that the client's
        operating environment allows it.  In other words, the client
        implementor is advised to document for his users the behavior. The
        client could also inform the application that its byte-range lock or share
        reservations (whether or not they were delegated) have been lost, such
        as via a UNIX signal, a Graphical User Interface (GUI) pop-up window, etc. 
        See <xref target="data_caching_revocation" />
        for a discussion of what the client should do
        for dealing with unreclaimed delegations on client state.
      </t>
      <t>
        For further discussion of revocation of locks, see 
        <xref target="server_revocation" />.
      </t>
    </section> <!-- "Network Partitions and Recovery" -->
  </section> <!-- "Crash Recovery" -->
  <section anchor="server_revocation" title="Server Revocation of Locks" >
    <t>
      At any point, the server can revoke locks held by a client, and the
      client must be prepared for this event.  When the client detects that
      its locks have been or may have been revoked, the client is
      responsible for validating the state information between itself and
      the server.  Validating locking state for the client means that it
      must verify or reclaim state for each lock currently held.
    </t>
    <t>
      The first occasion of lock revocation is upon server
      restart.  Note that this includes situations
      in which sessions are persistent and locking state is
      lost.  In this class of instances, the client will
      receive an error (NFS4ERR_STALE_CLIENTID) on an 
      operation that takes client ID, usually as part of 
      recovery in response to a problem with the current 
      session), and the client will proceed
      with normal crash recovery as described in the <xref
      target="reclaim_locks" />.
    </t>
    <t>
      The second occasion of lock revocation is the inability to renew the lease
      before expiration, as discussed in  
      <xref target="network_partitions_and_recovery"  />. While this is 
      considered a rare or unusual event,
      the client must be prepared to recover.  The server is responsible
      for determining the precise consequences of the lease expiration, 
      informing the client of the scope of the lock revocation decided
      upon.  The client then uses the status information provided
      by the server in the SEQUENCE results (field sr_status_flags,
      see <xref target="OP_SEQUENCE_DESCRIPTION" />)
      to synchronize its locking state with that of the 
      server, in order to recover.
    </t>
    <t>
      The third occasion of lock revocation can occur as a result of
      revocation of locks within the lease period, either because of
      administrative intervention or because a recallable lock (a
      delegation or layout) was not returned within the lease period
      after having been recalled.  While these are
      considered rare events, they are possible, and the client must be
      prepared to deal with them.  When either of these events occurs,
      the client finds out about the situation through the status returned
      by the SEQUENCE operation.  Any use of stateids associated with 
      locks revoked during the lease period will receive the error 
      NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate.
    </t>
    <t>
      In all situations in which a subset of locking state may have been 
      revoked, which include all cases in which locking state is revoked
      within the lease period, it is up to the client to determine which
      locks have been revoked and which have not.  It does this by
      using the TEST_STATEID operation on the appropriate set of stateids.
      Once the set of revoked locks has been determined, the applications
      can be notified, and the invalidated stateids can be freed and
      lock revocation acknowledged by using FREE_STATEID.
    </t>
  </section> <!-- "Server Revocation of Locks" --> 
  <section title="Short and Long Leases" >
    <t>
      When determining the time period for the server lease, the usual lease
      tradeoffs apply.  A short lease is good for fast server recovery at a
      cost of increased operations to effect lease renewal (when there are
      no other operations during the period to effect lease renewal as a
      side effect).  A long lease is certainly kinder and gentler to
      servers trying to handle very large numbers of clients.  The number of extra requests 
      to effect lock renewal drops in inverse
      proportion to the lease time.  The disadvantages of a long lease
      include the possibility of slower recovery after certain failures.
      After server failure, a longer grace period may be required when
      some clients do not promptly reclaim their locks and do a 
      global RECLAIM_COMPLETE.  In the event of client failure,
      the longer period for a lease to expire will force conflicting
      requests to wait longer.
    </t>
    <t>
      A long lease is practical if the server can store lease state in
      stable storage.  Upon recovery, the server can reconstruct the
      lease state from its stable storage and continue operation with
      its clients.
    </t>
  </section> <!-- "Short and Long Leases" -->
  <section anchor="lease_propagation_delay" title="Clocks, Propagation Delay, and Calculating Lease Expiration" >
    <t>
      To avoid the need for synchronized clocks, lease times are granted by
      the server as a time delta.  However, there is a requirement that the
      client and server clocks do not drift excessively over the duration of
      the lease.  There is also the issue of propagation delay across the
      network, which could easily be several hundred milliseconds, as well as
      the possibility that requests will be lost and need to be
      retransmitted.
    </t>
    <t>
      To take propagation delay into account, the client should
      subtract it from lease times (e.g., if the client estimates the
      one-way propagation delay as 200 milliseconds, then it can
      assume that the lease is already 200 milliseconds old when it
      gets it).  In addition, it will take another 200 milliseconds to
      get a response back to the server.  So the client must send a
      lease renewal or write data back to the server at least 400
      milliseconds before the lease would expire. If the propagation delay
      varies over the life of the lease (e.g., the client is on a mobile
      host), the client will need to continuously subtract the increase
      in propagation delay from the lease times.
    </t>
    <t>
      The server's lease period configuration should take into account the
      network distance of the clients that will be accessing the server's
      resources.  It is expected that the lease period will take into
      account the network propagation delays and other network delay factors
      for the client population.  Since the protocol does not allow for an
      automatic method to determine an appropriate lease period, the
      server's administrator may have to tune the lease period.

    </t>
  </section> <!-- "Clocks, Propagation Delay, and Calculating Lease Expiration" -->
  <section title="Obsolete Locking Infrastructure from NFSv4.0" anchor="vestigial_locking" >
    <t>
      There are a number of operations and fields within existing 
      operations that no longer have a function in NFSv4.1.
      In one way or another, these changes are all due to
      the implementation of sessions that provide client context
      and exactly once semantics as a base feature of the protocol,
      separate from locking itself.
    </t>
    <t>
      The following NFSv4.0 operations MUST NOT be implemented in NFSv4.1.
      The server MUST return NFS4ERR_NOTSUPP if these operations are
      found in an NFSv4.1 COMPOUND.
      <list style='symbols'>
        <t>
          SETCLIENTID since its function has been replaced by
          EXCHANGE_ID.
        </t>
        <t>
          SETCLIENTID_CONFIRM since client ID confirmation now 
          happens by means of CREATE_SESSION.
        </t>
        <t>
          OPEN_CONFIRM because state-owner-based seqids
          have been replaced by the sequence ID in the
          SEQUENCE operation.
        </t>
        <t>
          RELEASE_LOCKOWNER because lock-owners with no associated
          locks do not have any sequence-related state and so can 
          be deleted by the server at will.
        </t>
        <t>
          RENEW because every SEQUENCE operation for a session causes
          lease renewal, making a separate operation superfluous.
        </t>
      </list>
    </t>
    <t>
      Also, there are a number of fields, present in existing operations,
      related to locking that have no use in minor version 1.  They 
      were used in minor version 0 to perform functions now provided 
      in a different
      fashion.
      <list style='symbols'>
        <t>
          Sequence ids used to sequence requests for a given state-owner
          and to provide retry protection, now provided
          via sessions.
        </t>
        <t>
          Client IDs used to identify the client associated with a given
          request.  Client identification is now available using the client ID
          associated with the current session, without needing an explicit
          client ID field. 
        </t>
      </list>
    </t>
    <t>
      Such vestigial fields in existing operations have no function in
      NFSv4.1 and are ignored by the server.  Note that client IDs in 
      operations new to NFSv4.1 (such as CREATE_SESSION and DESTROY_CLIENTID)
      are not ignored.
    </t>
  </section> <!-- "Vestigial Locking Infrastructure From V4.0" -->
</section> <!-- "State Management" -->
<!--  $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $       -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section title="File Locking and Share Reservations" anchor="file_locking">
  <t>
    To support Win32 share reservations, it is necessary to provide
    operations that atomically open or create files.  Having a
    separate share/unshare operation would not allow correct
    implementation of the Win32 OpenFile API.  In order to
    correctly implement share semantics, the previous NFS protocol
    mechanisms used when a file is opened or created (LOOKUP, CREATE,
    ACCESS) need to be replaced.  The NFSv4.1 protocol defines
    an OPEN operation that is capable of atomically looking up, creating,
    and locking a file on the server.

  </t>
  <section title="Opens and Byte-Range Locks" >
    <t>
      It is assumed that manipulating a byte-range lock is rare when 
      compared to READ
      and WRITE operations.  It is also assumed that server restarts and network
      partitions are relatively rare.  Therefore, it is important that the
      READ and WRITE operations have a lightweight mechanism to indicate if
      they possess a held lock.  A LOCK operation contains the 
      heavyweight information required to establish a byte-range lock and uniquely 
      define the owner of the lock.
    </t>
    <section anchor="state-owner" title="State-Owner Definition" >
      <t>
        When opening a file or requesting a byte-range lock, the 
        client must specify an identifier that represents the owner of
        the requested lock.  This identifier is in the form of a
        state-owner, represented in the protocol by a state_owner4, a 
        variable-length opaque array that, when concatenated with the
        current client ID, uniquely defines the owner of a lock managed
        by the client. This may be a thread ID, process ID, or other 
        unique value.  
      </t>
      <t>
        Owners of opens and owners of byte-range locks are separate 
        entities and remain separate even if the same opaque arrays
        are used to designate owners of each.  The protocol distinguishes
        between open-owners (represented by open_owner4 structures)
        and lock-owners (represented by lock_owner4 structures).
      </t>  
      <t>
        Each open is associated with a specific open-owner while each
        byte-range lock is associated with a lock-owner and an
        open-owner, the latter being the open-owner associated with the
        open file under which the LOCK operation was done.  Delegations
        and layouts, on the other hand, are not associated with a
        specific owner but are associated with the client as a whole
        (identified by a client ID).
      </t>
    </section> <!-- "State-owner Definition" -->
    <section title="Use of the Stateid and Locking" >
      <t>
        All READ, WRITE, and SETATTR operations contain a stateid.  For the
        purposes of this section, SETATTR operations that change the size
        attribute of a file are treated as if they are writing the area
        between the old and new sizes (i.e., the byte-range truncated or added to the
        file by means of the SETATTR), even where SETATTR is not explicitly
        mentioned in the text.  The stateid passed to one of these operations must
        be one that represents an open, a set of byte-range locks, or a 
        delegation, or it may be a special stateid representing anonymous
        access or the special bypass stateid.
      </t>
      <t>
        If the state-owner performs a READ or WRITE operation in a situation in which
        it has established a byte-range lock or share reservation 
        on the server (any OPEN constitutes a share reservation), the
        stateid (previously returned by the server) must be used to
        indicate what locks, including both byte-range
        locks and share reservations, are held by the state-owner.  If no state
        is established by the client, either a byte-range lock or a share reservation,
        a special stateid for anonymous state (zero as the value for "other" and "seqid") 
        is used.  (See <xref target='special_stateid' /> for a description of 
        'special' stateids in general.)
        Regardless of whether a stateid for anonymous state
        or a stateid returned by the server is used, if there is a
        conflicting share reservation or mandatory byte-range lock held on the
        file, the server MUST refuse to service the READ or WRITE operation.
      </t>
      <t>
        Share reservations are established by OPEN operations and by their
        nature are mandatory in that when the OPEN denies READ or WRITE
        operations, that denial results in such operations being rejected with
        error NFS4ERR_LOCKED.  Byte-range locks may be implemented by the server
        as either mandatory or advisory, or the choice of mandatory or
        advisory behavior may be determined by the server on the basis of the
        file being accessed (for example, some UNIX-based servers support a
        "mandatory lock bit" on the mode attribute such that if set, byte-range
        locks are required on the file before I/O is possible).  When byte-range
        locks are advisory, they only prevent the granting of conflicting lock
        requests and have no effect on READs or WRITEs.  Mandatory byte-range
        locks, however, prevent conflicting I/O operations.  When they are
        attempted, they are rejected with NFS4ERR_LOCKED.  When the client
        gets NFS4ERR_LOCKED on a file for which it knows it has the proper share
        reservation, it will need to send a LOCK operation on the byte-range of
        the file that includes the byte-range the I/O was to be performed on, with
        an appropriate locktype field of the LOCK operation's arguments (i.e., READ*_LT for a READ operation, WRITE*_LT
        for a WRITE operation).
      </t>
      <t>
        Note that for UNIX environments that support mandatory byte-range locking,
        the distinction between advisory and mandatory locking is subtle.  In
        fact, advisory and mandatory byte-range locks are exactly the same as
        far as the APIs and requirements on implementation. If the mandatory
        lock attribute is set on the file, the server checks to see if the
        lock-owner has an appropriate shared (READ_LT) or exclusive (WRITE_LT) byte-range
        lock on the byte-range it wishes to READ from or WRITE to. If there is no
        appropriate lock, the server checks if there is a conflicting lock
        (which can be done by attempting to acquire the conflicting lock on
        behalf of the lock-owner, and if successful, release the lock after
        the READ or WRITE operation is done), and if there is, the server returns
        NFS4ERR_LOCKED.
      </t>
      <t>
        For Windows environments, byte-range locks are always mandatory, so the
        server always checks for byte-range locks during I/O requests.
      </t>
      <t>
        Thus, the LOCK operation does not need to distinguish
        between advisory and mandatory byte-range locks. It is the
        server's processing of the READ and WRITE operations that introduces
        the distinction.
      </t>
      <t>
        Every stateid that is validly passed to READ, WRITE, or SETATTR,
        with the exception of special stateid values,
        defines an access mode for the file (i.e.,
        OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
        OPEN4_SHARE_ACCESS_BOTH).
        <list style='symbols'>
          <t>
            For stateids associated with opens, this is the mode defined by 
            the original OPEN that caused the 
            allocation of the OPEN stateid
            and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
            same open-owner/file pair.  
          </t>
          <t>
            For stateids returned by byte-range LOCK operations,
            the appropriate mode is the access mode for the OPEN 
            stateid associated with the lock set represented by the stateid.  
          </t>
          <t>
            For delegation stateids, the access mode is based on the type of delegation.
          </t>
        </list>
      </t>
      <t>
        When a READ, WRITE, or SETATTR (that specifies the
        size attribute) operation is done, the operation is subject to checking against
        the access mode to verify that the operation is appropriate given the
        stateid with which the operation is associated.
      </t>
      <t>
        In the case of WRITE-type operations (i.e., WRITEs and SETATTRs that
        set size), the server MUST verify that the access mode allows writing
        and MUST return an NFS4ERR_OPENMODE error if it does not.  In the case of
        READ, the server may perform the corresponding check on the access
        mode, or it may choose to allow READ on OPENs for OPEN4_SHARE_ACCESS_WRITE, to
        accommodate clients whose WRITE implementation may unavoidably do
        reads (e.g., due to buffer cache constraints).  However, even if READs
        are allowed in these circumstances, the server MUST still check for
        locks that conflict with the READ (e.g., another OPEN specified OPEN4_SHARE_DENY_READ or OPEN4_SHARE_DENY_BOTH).  Note that a server that does enforce the access mode check
        on READs need not explicitly check for conflicting share reservations
        since the existence of OPEN for OPEN4_SHARE_ACCESS_READ guarantees that no
        conflicting share reservation can exist.
      </t>
      <t>
        The READ bypass special stateid (all bits of "other" and "seqid" set
        to one)
        indicates a desire to bypass locking checks.  The server MAY 
        allow READ operations to bypass
        locking checks at the server, when this special stateid is used.
        However, WRITE operations with 
        this special stateid value MUST NOT bypass locking checks and are
        treated exactly the same as if a special stateid for anonymous state
        were used.
      </t>
      <t>
        A lock may not be granted while a READ or WRITE operation using one of
        the special stateids is being performed and the scope of the lock
        to be granted would conflict with the READ or WRITE operation.
        This can occur when:
        <list style='symbols'>
          <t>
            A mandatory byte-range lock is requested with a byte-range that
            conflicts with the byte-range of the READ or WRITE operation.  
            For the purposes of this paragraph, a conflict occurs when 
            a shared lock is requested and a WRITE operation is being 
            performed, or an exclusive lock is requested and either a 
            READ or a WRITE operation is being performed.
          </t>
          <t>
            A share reservation is requested that denies reading and/or
            writing and the corresponding operation is being performed.
          </t>
          <t>
            A delegation is to be granted and the delegation type would
            prevent the I/O operation, i.e., READ and WRITE conflict with
            an OPEN_DELEGATE_WRITE delegation and WRITE conflicts with an OPEN_DELEGATE_READ delegation.
          </t>
        </list>
      </t>
      <t>
        When a client holds a delegation, it needs to ensure
        that the stateid sent conveys the association of
        operation with the delegation, to avoid the delegation from 
        being avoidably recalled.  When the delegation stateid, 
        a stateid open associated with that delegation, or a stateid 
        representing byte-range locks derived from such an open is 
        used, the server knows that the READ, WRITE, or SETATTR
        does not conflict with the delegation but is sent under
        the aegis of the delegation.  Even though it is possible
        for the server to determine from the client ID (via
        the session ID) that the client does in fact have a 
        delegation, the server is not obliged to check this, so
        using a special stateid can result in avoidable recall
        of the delegation.
      </t>
    </section> <!-- "Use of the Stateid and Locking" -->
  </section> <!-- "Opens and Byte-Range Locks" -->
  <section title="Lock Ranges" >
    <t>
      The protocol allows a lock-owner to request a lock with a byte-range
      and then either upgrade, downgrade, or unlock a sub-range of 
      the initial lock, or a byte-range that 
      overlaps -- fully or partially -- either with that initial lock or a 
      combination of a set of existing locks for the same lock-owner.  It
      is expected that this will be an uncommon type of request.  In any
      case, servers or server file systems may not be able to support
      sub-range lock semantics.  In the event that a server receives a
      locking request that represents a sub-range of current locking state
      for the lock-owner, the server is allowed to return the error
      NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
      operations.  Therefore, the client should be prepared to receive this
      error and, if appropriate, report the error to the requesting
      application.
    </t>
    <t>
      The client is discouraged from combining multiple independent locking
      ranges that happen to be adjacent into a single request since the
      server may not support sub-range requests for reasons related to
      the recovery of byte-range locking state in the event of server failure.  As
      discussed in <xref target="server_failure" />, the
      server may employ certain optimizations during recovery that work
      effectively only when the client's behavior during lock recovery is
      similar to the client's locking behavior prior to server failure.
    </t>
  </section> <!-- "Lock Ranges" -->
  <section title="Upgrading and Downgrading Locks" >
    <t>
      If a client has a WRITE_LT lock on a byte-range, it can request an atomic
      downgrade of the lock to a READ_LT lock via the LOCK operation, by setting
      the type to READ_LT. If the server supports atomic downgrade, the
      request will succeed. If not, it will return NFS4ERR_LOCK_NOTSUPP. The
      client should be prepared to receive this error and, if appropriate,
      report the error to the requesting application.
    </t>
    <t>
      If a client has a READ_LT lock on a byte-range, it can request an atomic
      upgrade of the lock to a WRITE_LT lock via the LOCK operation by setting
      the type to WRITE_LT or WRITEW_LT.  If the server does not support
      atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
      can be achieved without an existing conflict, the request will
      succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
      NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the client
      sent the LOCK operation with the type set to WRITEW_LT and the server
      has detected a deadlock. The client should be prepared to receive such
      errors and, if appropriate, report the error to the requesting
      application.

    </t>
  </section> <!-- "Upgrading and Downgrading Locks" -->
  <section title="Stateid Seqid Values and Byte-Range Locks"
           anchor="byte_range_seqid" >
    <t>
      When a LOCK or LOCKU operation is performed,
      the stateid returned has the same "other" value as the argument's
      stateid, and a 
      "seqid" value that is incremented (relative to the argument's
      stateid) to reflect the occurrence
      of the LOCK or LOCKU operation.  The server MUST increment
      the value of the "seqid" field whenever there is any change
      to the locking status of any byte offset as described by 
      any of the locks covered by the stateid.  A change in locking
      status includes a change from locked to unlocked or the reverse or
      a change from being locked for READ_LT to being locked for WRITE_LT
      or the reverse. 
    </t>
    <t> 
      When there is no such change, as, for example, when a range
      already locked for WRITE_LT is locked again for WRITE_LT, the
      server MAY increment the "seqid" value.
    </t>
  </section> <!-- "Stateid Sequence Values and Byte-Range Locks" -->
  <section title="Issues with Multiple Open-Owners" 
           anchor="multiple_openowners" >
    <t>

      When the same file is opened by multiple open-owners,
      a client will have multiple OPEN stateids for that
      file, each associated with a different open-owner.
      In that case, there can be multiple LOCK and LOCKU
      requests for the same lock-owner sent using the
      different OPEN stateids, and so a situation may
      arise in which there are multiple stateids, each
      representing byte-range locks on the same file and
      held by the same lock-owner but each associated with
      a different open-owner.

    </t>
    <t>
      In such a situation, the locking status of each byte
      (i.e., whether it is locked, the READ_LT or WRITE_LT type of 
      the lock, and the lock-owner holding the lock) MUST 
      reflect the last LOCK or LOCKU operation done for the
      lock-owner in question, independent of the stateid through
      which the request was sent.
    </t>
    <t>
      When a byte is locked by the lock-owner in question, the
      open-owner to which that byte-range lock is assigned SHOULD be that 
      of the open-owner associated with the stateid through 
      which the last LOCK of that byte was done.  When there
      is a change in the open-owner associated with locks for
      the stateid through which a LOCK or LOCKU was done, the
      "seqid" field of the stateid MUST be incremented, even 
      if the locking, in terms of lock-owners has not changed.
      When there is a change to the set of locked bytes associated
      with a different stateid for the same lock-owner, i.e.,
      associated with a different open-owner, the "seqid" value
      for that stateid MUST NOT be incremented.
    </t>
  </section> <!-- "Issues with Multiple Open-Owners" -->
  <section title="Blocking Locks" anchor="blocking_locks" >
    <t>
      Some clients require the support of blocking locks.  While NFSv4.1 
      provides a callback when a previously unavailable lock becomes 
      available, this is an OPTIONAL feature and clients cannot 
      depend on its presence.  Clients need to be prepared to continually 
      poll for the lock.  This presents a fairness problem.  Two of
      the lock types, READW_LT and WRITEW_LT, are used to indicate to the
      server that the client is requesting a blocking lock.  When the
      callback is not used, the server should maintain an ordered
      list of pending blocking locks.  When the conflicting lock is
      released, the server may wait for the period of time equal to
      lease_time for the first waiting
      client to re-request the lock.  After the lease period expires, the
      next waiting client request is allowed the lock.  Clients are required
      to poll at an interval sufficiently small that it is likely to acquire
      the lock in a timely manner.  The server is not required to maintain a
      list of pending blocked locks as it is used to increase fairness and
      not correct operation.  Because of the unordered nature of crash
      recovery, storing of lock state to stable storage would be required to
      guarantee ordered granting of blocking locks.
    </t>
    <t>
      Servers may also note the lock types and delay returning denial of the
      request to allow extra time for a conflicting lock to be released,
      allowing a successful return.  In this way, clients can avoid the
      burden of needless frequent polling for blocking locks.  The server
      should take care in the length of delay in the event the client
      retransmits the request.
    </t>
    <t>
      If a server receives a blocking LOCK operation, denies it, and then
      later receives a nonblocking request for the same lock, which is
      also denied, then it should remove the lock in question from its list of
      pending blocking locks.  Clients should use such a nonblocking request
      to indicate to the server that this is the last time they intend to poll
      for the lock, as may happen when the process requesting the lock is
      interrupted.  This is a courtesy to the server, to prevent it from
      unnecessarily waiting a lease period before granting other LOCK operations.
      However, clients are not required to perform this courtesy, and servers
      must not depend on them doing so.  Also, clients must be prepared for
      the possibility that this final locking request will be accepted.
    </t>
    <t>
      When a server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK, that
      CB_NOTIFY_LOCK callbacks might be done for the current open file, the
      client should take notice of this, but, since this is a hint, cannot
      rely on a CB_NOTIFY_LOCK always being done.  A client may reasonably
      reduce the frequency with which it polls for a denied lock, since the
      greater latency that might occur is likely to be eliminated given a
      prompt callback, but it still needs to poll.  When it receives a 
      CB_NOTIFY_LOCK, it should promptly try to obtain the lock, but it
      should be aware that other clients may be polling and that the server is under
      no obligation to reserve the lock for that particular client.
    </t>
  </section> <!-- title="Blocking Locks" -->
  <section anchor="share_reserve" title="Share Reservations" >
    <t>
      A share reservation is a mechanism to control access to a file.  It is
      a separate and independent mechanism from byte-range locking.  When a
      client opens a file, it sends an OPEN operation to the server
      specifying the type of access required (READ, WRITE, or BOTH) and the
      type of access to deny others (OPEN4_SHARE_DENY_NONE,
      OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH).  If
      the OPEN fails, the client will fail the application's open request.
    </t>
    <t>
      Pseudo-code definition of the semantics:
    </t>
    <figure>
      <artwork>
        if (request.access == 0) {
          return (NFS4ERR_INVAL)
        } else {
          if ((request.access & file_state.deny)) ||
             (request.deny & file_state.access)) {
            return (NFS4ERR_SHARE_DENIED)
        }
        return (NFS4ERR_OK);
      </artwork>
    </figure>
    <t>
      When doing this checking of share reservations on OPEN, the current 
      file_state used in the algorithm includes bits that reflect all 
      current opens, including those for the open-owner making the 
      new OPEN request.
    </t>
    <t>
      The constants used for the OPEN and OPEN_DOWNGRADE operations for the
      access and deny fields are as follows:
    </t>
<figure>
 <artwork>
const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

const OPEN4_SHARE_DENY_NONE     = 0x00000000;
const OPEN4_SHARE_DENY_READ     = 0x00000001;
const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
const OPEN4_SHARE_DENY_BOTH     = 0x00000003;
 </artwork>
</figure>
  </section> <!-- "Share Reservations" -->
  <section title="OPEN/CLOSE Operations" >
    <t>
      To provide correct share semantics, a client MUST use the OPEN
      operation to obtain the initial filehandle and indicate the desired
      access and what access, if any, to deny.  Even if the client intends to
      use a special stateid for anonymous state or READ bypass, 
      it must still obtain the
      filehandle for the regular file with the OPEN operation so the
      appropriate share semantics can be applied.  Clients that do not
      have a deny mode built into their programming interfaces for opening
      a file should request a deny mode of
      OPEN4_SHARE_DENY_NONE.
    </t>
    <t>
      The OPEN operation with the CREATE flag also subsumes the CREATE
      operation for regular files as used in previous versions of the NFS
      protocol.  This allows a create with a share to be done atomically.
    </t>
    <t>
      The CLOSE operation removes all share reservations held by the
      open-owner on that file.  If byte-range locks are held, the client
      SHOULD release all locks before sending a CLOSE operation.  The server MAY free
      all outstanding locks on CLOSE, but some servers may not support the
      CLOSE of a file that still has byte-range locks held.  The server MUST
      return failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
      CLOSE.
    </t>
    <t>
      The LOOKUP operation will return a filehandle without establishing any
      lock state on the server.  Without a valid stateid, the server will
      assume that the client has the least access.  For example, if one
      client opened a file with OPEN4_SHARE_DENY_BOTH and another client
      accesses the file via a filehandle obtained through LOOKUP, the
      second client could only read the file using the special read
      bypass stateid. The second client could not WRITE the file
      at all because it would
      not have a valid stateid from OPEN and the special anonymous stateid would
      not be allowed access.
    </t>
  </section> <!-- "OPEN/CLOSE Operations" -->
  <section title="Open Upgrade and Downgrade" anchor="open_upgrade" >
    <t>
      When an OPEN is done for a file and the open-owner for which the OPEN
      is being done already has the file open, the result is to upgrade the
      open file status maintained on the server to include the access and
      deny bits specified by the new OPEN as well as those for the existing
      OPEN.  The result is that there is one open file, as far as the
      protocol is concerned, and it includes the union of the access and
      deny bits for all of the OPEN requests completed.  The OPEN 
      is represented by a single stateid whose "other" value matches
      that of the original open, and whose "seqid" value is incremented
      to reflect the occurrence of the upgrade.  The increment is required
      in cases in which the "upgrade" results in no change to the open mode (e.g., an OPEN
      is done for read when the existing open file is opened for 
      OPEN4_SHARE_ACCESS_BOTH).  Only a single CLOSE will be done to reset the
      effects of both OPENs.  The client may use the stateid returned
      by the OPEN effecting the upgrade or with a stateid sharing the
      same "other" field and a seqid of zero,
      although care needs to be taken as far as upgrades that happen 
      while the CLOSE is pending.  Note that the
      client, when sending the OPEN, may not know that the same file is in
      fact being opened.  The above only applies if both OPENs result in
      the OPENed object being designated by the same filehandle.
    </t>
    <t>
      When the server chooses to export multiple filehandles corresponding
      to the same file object and returns different filehandles on two
      different OPENs of the same file object, the server MUST NOT "OR"
      together the access and deny bits and coalesce the two open files.
      Instead, the server must maintain separate OPENs with separate
      stateids and will require separate CLOSEs to free them.
    </t>
    <t>
      When multiple open files on the client are merged into a single OPEN
      file object on the server, the close of one of the open files (on the
      client) may necessitate change of the access and deny status of the
      open file on the server.  This is because the union of the access and
      deny bits for the remaining opens may be smaller (i.e., a proper
      subset) than previously.  The OPEN_DOWNGRADE operation is used to make
      the necessary change and the client should use it to update the server
      so that share reservation requests by other clients are handled
      properly.  The stateid returned has the same "other" field as
      that passed to the server.  The "seqid" value in the returned 
      stateid MUST be incremented, even in situations in which there is
      no change to the access and deny bits for the file.
    </t>
  </section> <!-- "Open Upgrade and Downgrade" -->
  <section title="Parallel OPENs" anchor="parallel_opens">
    <t>
      Unlike the case of NFSv4.0, in which OPEN operations for the same 
      open-owner are inherently serialized because of the owner-based seqid,
      multiple OPENs for the same open-owner may be done in parallel.  When
      clients do this, they may encounter situations in which, because
      of the existence of hard links, two OPEN operations may turn out
      to open the same file, with a later OPEN performed being an upgrade of
      the first, with this fact only visible to the
      client once the operations complete.
    </t>    
    <t>
      In this situation, clients may determine the order in which the 
      OPENs were performed by examining the stateids returned by the OPENs.
      Stateids that share a common value of the "other" field can be
      recognized as having opened the same file, with the order of the 
      operations determinable from the order of the "seqid" fields, mod 
      any possible wraparound of the 32-bit field.
    </t>
    <t>
      When the possibility exists that the client will send multiple
      OPENs for the same open-owner in parallel, it may be the case that
      an open upgrade may happen without the client knowing beforehand
      that this could happen.  Because of this possibility, CLOSEs and
      OPEN_DOWNGRADEs should generally be sent with a non-zero seqid 
      in the stateid, to avoid the possibility that the status change
      associated with an open upgrade is not inadvertently lost.
    </t>
  </section> <!-- "Parallel OPENs" -->
  <section title="Reclaim of Open and Byte-Range Locks" anchor="open_br_reclaim">
    <t>
      Special forms of the LOCK and OPEN operations are provided when it
      is necessary to re-establish byte-range locks or opens after a 
      server failure.
      <list style='symbols'>
        <t>
          To reclaim existing opens, an OPEN operation is performed
          using a CLAIM_PREVIOUS.  Because the client, in this type 
          of situation, will have already opened the file and have
          the filehandle of the target file, this operation requires
          that the current filehandle be the target file, rather than
          a directory, and no file name is specified.
        </t>
        <t>
          To reclaim byte-range locks, a LOCK operation with the
          reclaim parameter set to true is used.
        </t>
      </list>
    </t>
    <t>
      Reclaims of opens associated with delegations are discussed in
      <xref target="delegation_recovery" />. 
    </t>
  </section>
</section> <!-- "File Locking and Share Reservations" -->
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Client-Side Caching" >
  <t>
    Client-side caching of data, of file attributes, and of file names is
    essential to providing good performance with the NFS protocol.
    Providing distributed cache coherence is a difficult problem, and
    previous versions of the NFS protocol have not attempted it.  Instead,
    several NFS client implementation techniques have been used to reduce
    the problems that a lack of coherence poses for users.  These
    techniques have not been clearly defined by earlier protocol
    specifications, and it is often unclear what is valid or invalid client
    behavior.
  </t>
  <t>
    The NFSv4.1 protocol uses many techniques similar to those that
    have been used in previous protocol versions.  The NFSv4.1
    protocol does not provide distributed cache coherence.  However, it
    defines a more limited set of caching guarantees to allow locks and
    share reservations to be used without destructive interference from
    client-side caching.
  </t>
  <t>
    In addition, the NFSv4.1 protocol introduces a delegation
    mechanism, which allows many decisions normally made by the server to
    be made locally by clients.  This mechanism provides efficient support
    of the common cases where sharing is infrequent or where sharing is
    read-only.
    
  </t>
  <section title="Performance Challenges for Client-Side Caching" >
    <t>
      Caching techniques used in previous versions of the NFS protocol have
      been successful in providing good performance.  However, several
      scalability challenges can arise when those techniques are used with
      very large numbers of clients.  This is particularly true when clients
      are geographically distributed, which classically increases the latency
      for cache revalidation requests.
    </t>
    <t>
      The previous versions of the NFS protocol repeat their file data cache
      validation requests at the time the file is opened.  This behavior can
      have serious performance drawbacks.  A common case is one in which a
      file is only accessed by a single client.  Therefore, sharing is
      infrequent.
    </t>
    <t>
      In this case, repeated references to the server to find that no
      conflicts exist are expensive.  A better option with regards to
      performance is to allow a client that repeatedly opens a file to do so
      without reference to the server.  This is done until potentially
      conflicting operations from another client actually occur.
    </t>
    <t>
      A similar situation arises in connection with byte-range locking.  Sending
      LOCK and LOCKU operations as well as the READ and
      WRITE operations necessary to make data caching consistent with the
      locking semantics (see <xref target="dc_file_locking" />)
      can severely limit performance.  When locking is used to provide
      protection against infrequent conflicts, a large penalty is incurred.
      This penalty may discourage the use of byte-range locking by applications.
    </t>
    <t>
      The NFSv4.1 protocol provides more aggressive caching strategies
      with the following design goals:
      <list style='symbols'>
        <t>
          Compatibility with a large range of server semantics.
        </t>
        <t>
          Providing the same caching benefits as previous versions of 
          the NFS protocol when unable to support the more aggressive model.
        </t>
        <t>
          Requirements for aggressive caching are organized so that a 
         large portion of the benefit can be obtained even when not 
         all of the requirements can be met.
        </t>
      </list>
    </t>
    <t>
      The appropriate requirements for the server are discussed in later
      sections in which specific forms of caching are covered (see 
      <xref target="open_delegation" />).
    </t>
  </section>
  <section title="Delegation and Callbacks" anchor="deleg_and_cb" >
    <t>
      Recallable delegation of server responsibilities for a file to a
      client improves performance by avoiding repeated requests to the
      server in the absence of inter-client conflict.  With the use of a
      "callback" RPC from server to client, a server recalls delegated
      responsibilities when another client engages in sharing of a delegated
      file.
    </t>
    <t>
      A delegation is passed from the server to the client, specifying the
      object of the delegation and the type of delegation.  There are
      different types of delegations, but each type contains a stateid to be
      used to represent the delegation when performing operations that
      depend on the delegation.  This stateid is similar to those associated
      with locks and share reservations but differs in that the stateid for
      a delegation is associated with a client ID and may be used on behalf
      of all the open-owners for the given client.  A delegation is made
      to the client as a whole and not to any specific process or thread of
      control within it.
    </t>
    <t>
      The backchannel is established by CREATE_SESSION and
      BIND_CONN_TO_SESSION, and the client is required
      to maintain it. Because the backchannel may be down, even
      temporarily,
      correct protocol operation does not depend on
      them.  Preliminary testing of backchannel functionality by means of a
      CB_COMPOUND procedure with a single operation, CB_SEQUENCE,
      can be used to check the continuity of the backchannel.  A
      server avoids delegating responsibilities until it has
      determined that the backchannel exists.  Because the granting of a
      delegation is always conditional upon the absence of conflicting
      access, clients MUST NOT assume that a delegation will be granted and
      they MUST always be prepared for OPENs, WANT_DELEGATIONs, and
      GET_DIR_DELEGATIONs to be processed without any
      delegations being granted.
    </t>
    <t>
      Unlike locks, an operation by a second client to a delegated file will
      cause the server to recall a delegation through a callback.  For
      individual operations, we will describe, under IMPLEMENTATION, when
      such operations are required to effect a recall.  A number of
      points should be noted, however.  
      <list style="symbols">
        <t>
          The server is free to recall a delegation
          whenever it feels it is desirable and may do so even if no 
          operations requiring recall are being done.  
        </t>
        <t>
          Operations done outside the NFSv4.1 protocol, due to, for 
          example, access by other protocols, or by local access, 
          also need to result in delegation recall when they make 
          analogous changes to file system data.  What is crucial 
          is if the change would invalidate the guarantees provided 
          by the delegation.  When this is possible, the
          delegation needs to be recalled and MUST be returned or
          revoked  before allowing the operation to proceed. 
        </t>
        <t>
          The semantics of the file system are crucial in defining
          when delegation recall is required.  If a particular change
          within a specific implementation causes change to a 
          file attribute, then delegation recall is required, whether
          that operation has been specifically listed as requiring
          delegation recall.  Again, what is critical is whether the
          guarantees provided by the delegation are being invalidated.
        </t>
      </list>
    </t>
    <t>
      Despite those caveats, the implementation sections for a number
      of operations describe situations in which delegation recall 
      would be required under some common circumstances:
      <list style="symbols">
        <t>
          For GETATTR, see <xref target="OP_GETATTR_IMPLEMENTATION" />.
        </t>
        <t>
          For OPEN, see <xref target="OP_OPEN_IMPLEMENTATION" />.
        </t>
        <t>
          For READ, see <xref target="OP_READ_IMPLEMENTATION" />.
        </t>
        <t>
          For REMOVE, see <xref target="OP_REMOVE_IMPLEMENTATION" />.
        </t>
        <t>
          For RENAME, see <xref target="OP_RENAME_IMPLEMENTATION" />.
        </t>
        <t>
          For SETATTR, see <xref target="OP_SETATTR_IMPLEMENTATION" />.
        </t>
        <t>
          For WRITE, see <xref target="OP_WRITE_IMPLEMENTATION" />.
        </t>
      </list>
    </t>
    <t>
      On recall, the client holding the delegation needs to flush modified
      state (such as modified data) to the server and return the
      delegation.  The conflicting request will not be acted on until
      the recall is complete.  The recall is considered complete when
      the client returns the delegation or the server times its wait
      for the delegation to be returned and revokes the delegation as
      a result of the timeout.  In the interim, the server will either
      delay responding to conflicting requests or respond to them with
      NFS4ERR_DELAY.  Following the resolution of the recall, the
      server has the information necessary to grant or deny the second
      client's request.
    </t>
    <t>
      At the time the client receives a delegation recall, it may have
      substantial state that needs to be flushed to the server.  Therefore,
      the server should allow sufficient time for the delegation to be
      returned since it may involve numerous RPCs to the server.  If the
      server is able to determine that the client is diligently flushing
      state to the server as a result of the recall, the server may extend
      the usual time allowed for a recall.  However, the time allowed for
      recall completion should not be unbounded.
    </t>
    <t>
      An example of this is when responsibility to mediate opens on a given
      file is delegated to a client (see <xref target="open_delegation" />).
      The server will not know what opens are in effect on the client.
      Without this knowledge, the server will be unable to determine if the
      access and deny states for the file allow any particular open until
      the delegation for the file has been returned.
    </t>
    <t>
      A client failure or a network partition can result in failure to
      respond to a recall callback. In this case, the server will revoke the
      delegation, which in turn will render useless any modified state still
      on the client.
    </t>
    <section title="Delegation Recovery" anchor="delegation_recovery" >
      <t>
        There are three situations that delegation recovery needs to deal with:
        <list style="symbols">
          <t>
            client restart
          </t>
          <t>
            server restart
          </t>
          <t>
            network partition (full or backchannel-only)
          </t>
        </list>
      </t>
      <t>
        In the event the client restarts, the failure to renew
        the lease will result in the revocation of byte-range locks and share
        reservations.  Delegations, however, may be treated a bit differently.
      </t>
      <t>
        There will be situations in which delegations will need to be
        re-established after a client restarts.  The reason for this
        is that the client may have file data stored locally and this data was
        associated with the previously held delegations.  The client will need
        to re-establish the appropriate file state on the server.
      </t>
      <t>
        To allow for this type of client recovery, the server MAY extend the
        period for delegation recovery beyond the typical lease expiration
        period.  This implies that requests from other clients that conflict
        with these delegations will need to wait.  Because the normal recall
        process may require significant time for the client to flush changed
        state to the server, other clients need be prepared for delays that
        occur because of a conflicting delegation.  This longer interval would
        increase the window for clients to restart and consult stable storage
        so that the delegations can be reclaimed.  For OPEN delegations, such
        delegations are reclaimed using OPEN with a claim type of
        CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH (see Sections
        <xref target="data_caching_revocation" format="counter" />
        and <xref target="OP_OPEN" format="counter" /> for discussion of OPEN delegation
        and the details of OPEN, respectively).
      </t>
      <t>
        A server MAY support claim types of CLAIM_DELEGATE_PREV and
        CLAIM_DELEG_PREV_FH, and if it
        does, it MUST NOT remove delegations upon a CREATE_SESSION that
        confirm a client ID created by EXCHANGE_ID.
        Instead, the server MUST, for a period of time no less than that of the value of
        the lease_time attribute, maintain the client's delegations to allow
        time for the client to send CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH requests. The server
        that supports CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH MUST support the DELEGPURGE
        operation.
      </t>
      <t>
        When the server restarts, delegations are reclaimed (using
        the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
        locks and share reservations.  However, there is a slight semantic
        difference.  In the normal case, if the server decides that a
        delegation should not be granted, it performs the requested action
        (e.g., OPEN) without granting any delegation.  For reclaim, the server
        grants the delegation but a special designation is applied so that the
        client treats the delegation as having been granted but recalled by
        the server.  Because of this, the client has the duty to write all
        modified state to the server and then return the delegation.  This
        process of handling delegation reclaim reconciles three principles of
        the NFSv4.1 protocol:
        <list style="symbols">
          <t>
            Upon reclaim, a client reporting resources assigned to it by an
            earlier server instance must be granted those resources.
          </t>
          <t>
            The server has unquestionable authority to determine whether
            delegations are to be granted and, once granted, whether they are to
            be continued.
          </t>
          <t>
            The use of callbacks should not be depended upon until the client has
            proven its ability to receive them.
          </t>
        </list>
      </t>
      <t>
        When a client needs to reclaim a delegation and there is no associated
        open, the client may use the CLAIM_PREVIOUS variant of the
        WANT_DELEGATION operation.  However, since the server is not required
        to support this operation, an alternative is to reclaim via a dummy OPEN 
        together with the delegation
        using an OPEN of type CLAIM_PREVIOUS.  The dummy open file can 
        be released using a CLOSE to re-establish the original state to be
        reclaimed, a delegation without an associated open.
      </t>
      <t>
        When a client has more than a single open associated with a delegation,
        state for those additional opens can be established using OPEN 
        operations of type CLAIM_DELEGATE_CUR.  When these are used to
        establish opens associated with reclaimed delegations, the 
        server MUST allow them when made within the grace period.
      </t>
      <t>       
        When a network partition occurs, delegations are subject to freeing by
        the server when the lease renewal period expires.  This is similar to
        the behavior for locks and share reservations.  For delegations,
        however, the server may extend the period in which conflicting
        requests are held off.  Eventually, the occurrence of a conflicting
        request from another client will cause revocation of the delegation.
        A loss of the backchannel (e.g., by later network configuration
        change) will have the same effect.  A recall request will fail and
        revocation of the delegation will result.
      </t>
      <t>
        A client normally finds out about revocation of a delegation when it
        uses a stateid associated with a delegation and receives one of the
        errors NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED.
        It also may find out about delegation revocation
        after a client restart when it attempts to reclaim a delegation and
        receives that same error.  Note that in the case of a revoked OPEN_DELEGATE_WRITE delegation, there are issues because data may have been modified
        by the client whose delegation is revoked and separately by other
        clients.  See <xref target="revocation_recovery_write" />
        for a discussion of such issues.  Note also that when
        delegations are revoked, information about the revoked delegation will
        be written by the server to stable storage (as described in
        <xref target="network_partitions_and_recovery" />).  This is done 
        to deal with the case in
        which a server restarts after revoking a delegation but before the
        client holding the revoked delegation is notified about the
        revocation.
      </t>
    </section>
  </section>
  <section title="Data Caching" >
    <t>
      When applications share access to a set of files, they need to be
      implemented so as to take account of the possibility of conflicting
      access by another application.  This is true whether the applications
      in question execute on different clients or reside on the same client.
    </t>
    <t>
      Share reservations and byte-range locks are the facilities the NFSv4.1 protocol 
      provides to allow applications to coordinate access by
      using  mutual exclusion facilities.  The NFSv4.1 protocol's
      data caching must be implemented such that it does not invalidate the
      assumptions on which those using these facilities depend.

    </t>
    <section title="Data Caching and OPENs" >
      <t>
        In order to avoid invalidating the sharing assumptions on which
        applications rely, NFSv4.1 clients should not provide cached
        data to applications or modify it on behalf of an application when it
        would not be valid to obtain or modify that same data via a READ or
        WRITE operation.
      </t>
      <t>
        Furthermore, in the absence of an OPEN delegation 
        (see <xref target="open_delegation" />),
        two additional rules apply.  Note that these rules are
        obeyed in practice by many NFSv3 clients.
        <list style='symbols'>
          <t>
            First, cached data present on a client must be revalidated after doing
            an OPEN. Revalidating means that the client fetches the change
            attribute from the server, compares it with the cached change
            attribute, and if different, declares the cached data (as well as the
            cached attributes) as invalid.  This is to ensure that the data for
            the OPENed file is still correctly reflected in the client's cache.
            This validation must be done at least when the client's OPEN operation
            includes a deny of OPEN4_SHARE_DENY_WRITE or
            OPEN4_SHARE_DENY_BOTH, thus terminating a period in which
            other
            clients may have had the opportunity to open the file with
            OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH
            access.  Clients may choose to do the revalidation more often (i.e., at
            OPENs specifying a deny mode of OPEN4_SHARE_DENY_NONE) to parallel the NFSv3 protocol's
            practice for the benefit of users assuming this degree of cache
            revalidation.
            <vspace blankLines='1' />

            Since the change attribute is updated for data and metadata
            modifications, some client implementors may be tempted to use the
            time_modify attribute and not the change attribute to validate cached data, so that
            metadata changes do not spuriously invalidate clean data.  The
            implementor is cautioned in  this approach. The change attribute is
            guaranteed to change for each update to the file, whereas time_modify
            is guaranteed to change only at the granularity of the time_delta
            attribute. Use by the client's data cache validation logic of
            time_modify and not change runs the risk of the client incorrectly
            marking stale data as valid. Thus, any cache validation approach
            by the client MUST include the use of the change attribute.
          </t>
          <t>
            Second, modified data must be flushed to the server before closing a
            file OPENed for OPEN4_SHARE_ACCESS_WRITE.  This is complementary to the first rule.  If
            the data is not flushed at CLOSE, the revalidation done
            after the client OPENs a file is unable to achieve its
            purpose.  The other aspect to flushing the data before
            close is that the data must be committed to stable
            storage, at the server, before the CLOSE operation is
            requested by the client.  In the case of a server restart and a CLOSEd
            file, it may not be possible to retransmit the data to be written to
            the file, hence, this requirement.
          </t>
        </list>
      </t>
    </section>
    <section title="Data Caching and File Locking" anchor="dc_file_locking">
      <t>
        For those applications that choose to use byte-range locking instead of
        share reservations to exclude inconsistent file access, there is an
        analogous set of constraints that apply to client-side data caching.
        These rules are effective only if the byte-range locking is used in a way
        that matches in an equivalent way the actual READ and WRITE operations
        executed.  This is as opposed to byte-range locking that is based on pure
        convention.  For example, it is possible to manipulate a two-megabyte
        file by dividing the file into two one-megabyte ranges and protecting
        access to the two byte-ranges by byte-range locks on bytes zero and one.  A WRITE_LT lock on
        byte zero of the file would represent the right to perform
        READ and WRITE operations on the first byte-range.  A WRITE_LT lock on
        byte one of the file would represent the right to perform READ and WRITE
        operations on the second byte-range.  As long as all applications
        manipulating the file obey this convention, they will work on a local
        file system.  However, they may not work with the NFSv4.1
        protocol unless clients refrain from data caching.
      </t>
      <t>
        The rules for data caching in the byte-range locking environment are:
        <list style='symbols'>
          <t>
            First, when a client obtains a byte-range lock for a particular byte-range, the
            data cache corresponding to that byte-range (if any cache data exists)
            must be revalidated.  If the change attribute indicates that the file
            may have been updated since the cached data was obtained, the client
            must flush or invalidate the cached data for the newly locked byte-range.
            A client might choose to invalidate all of the non-modified cached data
            that it has for the file, but the only requirement for correct
            operation is to invalidate all of the data in the newly locked byte-range.
          </t>
          <t>
            Second, before releasing a WRITE_LT lock for a byte-range, all modified data
            for that byte-range must be flushed to the server.  The modified data must
            also be written to stable storage.
          </t>
        </list>
      </t>
      <t>
        Note that flushing data to the server and the invalidation of cached
        data must reflect the actual byte-ranges locked or unlocked.  Rounding
        these up or down to reflect client cache block boundaries will cause
        problems if not carefully done.  For example, writing a modified block
        when only half of that block is within an area being unlocked may
        cause invalid modification to the byte-range outside the unlocked area.
        This, in turn, may be part of a byte-range locked by another client.
        Clients can avoid this situation by synchronously performing portions
        of WRITE operations that overlap that portion (initial or final) that
        is not a full block.  Similarly, invalidating a locked area that is
        not an integral number of full buffer blocks would require the client
        to read one or two partial blocks from the server if the revalidation
        procedure shows that the data that the client possesses may not be
        valid.
      </t>
      <t>
        The data that is written to the server as a prerequisite to the
        unlocking of a byte-range must be written, at the server, to stable
        storage.  The client may accomplish this either with synchronous
        writes or by following asynchronous writes with a COMMIT operation.
        This is required because retransmission of the modified data after a
        server restart might conflict with a lock held by another client.
      </t>
      <t>
        A client implementation may choose to accommodate applications that
        use byte-range locking in non-standard ways (e.g., using a byte-range lock as a
        global semaphore) by flushing to the server more data upon a LOCKU
        than is covered by the locked range.  This may include modified data
        within files other than the one for which the unlocks are being done.
        In such cases, the client must not interfere with applications whose
        READs and WRITEs are being done only within the bounds of byte-range locks
        that the application holds.  For example, an application locks a
        single byte of a file and proceeds to write that single byte.  A
        client that chose to handle a LOCKU by flushing all modified data to
        the server could validly write that single byte in response to an
        unrelated LOCKU operation.  However, it would not be valid to write the entire
        block in which that single written byte was located since it includes
        an area that is not locked and might be locked by another client.
        Client implementations can avoid this problem by dividing files with
        modified data into those for which all modifications are done to areas
        covered by an appropriate byte-range lock and those for which there are
        modifications not covered by a byte-range lock.  Any writes done for the
        former class of files must not include areas not locked and thus not
        modified on the client.

      </t>
    </section>
    <section title="Data Caching and Mandatory File Locking" >
      <t>
        Client-side data caching needs to respect mandatory byte-range locking when
        it is in effect.  The presence of mandatory byte-range locking for a given
        file is indicated when the client gets back NFS4ERR_LOCKED from a READ
        or WRITE operation on a file for which it has an appropriate share reservation.  When
        mandatory locking is in effect for a file, the client must check for
        an appropriate byte-range lock for data being read or written.  If a byte-range lock
        exists for the range being read or written, the client may satisfy the
        request using the client's validated cache.  If an appropriate
        byte-range lock is not held for the range of the read or write, the read or write
        request must not be satisfied by the client's cache and the request
        must be sent to the server for processing.  When a read or write
        request partially overlaps a locked byte-range, the request should be
        subdivided into multiple pieces with each byte-range (locked or not)
        treated appropriately.
        
      </t>
    </section>
    <section anchor="data_caching_and_file_identity"
     title="Data Caching and File Identity" >

      <t>
        When clients cache data, the file data needs to be organized according
        to the file system object to which the data belongs.  For NFSv3
        clients, the typical practice has been to assume for the purpose of
        caching that distinct filehandles represent distinct file system
        objects.  The client then has the choice to organize and maintain the
        data cache on this basis.
      </t>
      <t>
        In the NFSv4.1 protocol, there is now the possibility to have
        significant deviations from a "one filehandle per object" model
        because a filehandle may be constructed on the basis of the object's
        pathname.  Therefore, clients need a reliable method to determine if
        two filehandles designate the same file system object.  If clients
        were simply to assume that all distinct filehandles denote distinct
        objects and proceed to do data caching on this basis, caching
        inconsistencies would arise between the distinct client-side objects
        that mapped to the same server-side object.
      </t>
      <t>
        By providing a method to differentiate filehandles, the NFSv4.1
        protocol alleviates a potential functional regression in comparison
        with the NFSv3 protocol.  Without this method, caching
        inconsistencies within the same client could occur, and this has not
        been present in previous versions of the NFS protocol.  Note that it
        is possible to have such inconsistencies with applications executing
        on multiple clients, but that is not the issue being addressed here.
      </t>
      <t>
        For the purposes of data caching, the following steps allow an 
        NFSv4.1 client to determine whether two distinct filehandles denote
        the same server-side object:
        <list style="symbols">
          <t>
            If GETATTR directed to two filehandles returns different values of the
            fsid attribute, then the filehandles represent distinct objects.
          </t>
          <t>
            If GETATTR for any file with an fsid that matches the fsid of the two
            filehandles in question returns a unique_handles attribute with a
            value of TRUE, then the two objects are distinct.
          </t>
          <t>
            If GETATTR directed to the two filehandles does not return the fileid
            attribute for both of the handles, then it cannot be determined
            whether the two objects are the same.  Therefore,
            operations that depend on that knowledge (e.g.,
            client-side data caching) cannot be
            done reliably.  Note that if GETATTR does not return the fileid
	    attribute for both filehandles, it will return it for neither of
	    the filehandles, since the fsid for both filehandles is the same.
          </t>
          <t>
            If GETATTR directed to the two filehandles returns different values
            for the fileid attribute, then they are distinct objects.
          </t>
          <t>
            Otherwise, they are the same object.
          </t>
        </list>
      </t>
    </section>
  </section>
  <section title="Open Delegation" anchor="open_delegation" >
    <t>
      When a file is being OPENed, the server may delegate further handling
      of opens and closes for that file to the opening client.  Any such
      delegation is recallable since the circumstances that allowed for the
      delegation are subject to change.  In particular, if the server
      receives a conflicting OPEN from another client, the server must recall
      the delegation before deciding whether the OPEN from the other client
      may be granted.  Making a delegation is up to the server, and clients
      should not assume that any particular OPEN either will or will not
      result in an OPEN delegation.  The following is a typical set of
      conditions that servers might use in deciding whether an OPEN should be
      delegated:
      <list style="symbols">
        <t>
          The client must be able to respond to the
          server's callback requests.  If a backchannel
          has been established, the server will send
          a CB_COMPOUND request, containing a single
          operation, CB_SEQUENCE, for a test of backchannel
          availability.

        </t>
        <t>
          The client must have responded properly to previous recalls.
        </t>
        <t>
          There must be no current OPEN conflicting with the requested
          delegation.
        </t>
        <t>
          There should be no current delegation that conflicts with the 
          delegation being requested.
        </t>
        <t>
          The probability of future conflicting open requests should be 
          low based on the recent history of the file.
        </t>
        <t>
          The existence of any server-specific semantics of OPEN/CLOSE 
          that would make the required handling incompatible with the
          prescribed handling that the delegated client would apply 
          (see below).
        </t>
      </list>
      There are two types of OPEN delegations: OPEN_DELEGATE_READ and OPEN_DELEGATE_WRITE.  An OPEN_DELEGATE_READ
      delegation allows a client to handle, on its own, requests to open a
      file for reading that do not deny OPEN4_SHARE_ACCESS_READ access to others.  Multiple
      OPEN_DELEGATE_READ delegations may be outstanding simultaneously and do not
      conflict.  An OPEN_DELEGATE_WRITE delegation allows the client to handle, on its
      own, all opens.  Only OPEN_DELEGATE_WRITE delegation may exist for a given
      file at a given time, and it is inconsistent with any OPEN_DELEGATE_READ delegations.
    </t>
    <t>
      When a client has an OPEN_DELEGATE_READ delegation, it is assured that
      neither the contents, the attributes (with the exception of 
      time_access), nor the names of any
      links to the file will change without its knowledge, so long as the
      delegation is held.  When a client has an OPEN_DELEGATE_WRITE delegation, it
      may modify the file data locally since no other client will be 
      accessing the file's data.  The client holding an OPEN_DELEGATE_WRITE delegation 
      may only locally affect file attributes that are intimately 
      connected with the file data: size, change, time_access,
      time_metadata, and time_modify.
      All other attributes must be reflected on the server.
    </t>
    <t>
      When a client has an OPEN delegation, it does not need to send OPENs or
      CLOSEs to the server. Instead, the client may update the
      appropriate status internally. For an OPEN_DELEGATE_READ delegation, opens
      that cannot be handled locally (opens that are for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH or that
      deny OPEN4_SHARE_ACCESS_READ access) must be sent to the server.
    </t>
    <t>
      When an OPEN delegation is made, the reply to the OPEN contains an
      OPEN delegation structure that specifies the following:
      <list style="symbols">
        <t>
          the type of delegation (OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE).
        </t>
        <t>
          space limitation information to control flushing of data on close
          (OPEN_DELEGATE_WRITE delegation only;
          see <xref target="open_delegation_caching" />)
        </t>
        <t>
          an nfsace4 specifying read and write permissions
        </t>
        <t>
          a stateid to represent the delegation
        </t>
      </list>
      The delegation stateid is separate and distinct from the stateid for
      the OPEN proper.  The standard stateid, unlike the delegation stateid,
      is associated with a particular lock-owner and will continue to be
      valid after the delegation is recalled and the file remains open.
    </t>
    <t>
      When a request internal to the client is made to open a file and an OPEN
      delegation is in effect, it will be accepted or rejected solely on the
      basis of the following conditions.  Any requirement for other checks
      to be made by the delegate should result in the OPEN delegation being
      denied so that the checks can be made by the server itself.
      <list style="symbols">
        <t>
          The access and deny bits for the request and the file as
          described in <xref target="share_reserve" />.
        </t>
        <t>
          The read and write permissions as determined below.
        </t>
      </list>
      The nfsace4 passed with delegation can be used to avoid frequent
      ACCESS calls.  The permission check should be as follows:
      <list style="symbols">
        <t>
          If the nfsace4 indicates that the open may be done, then it should be
          granted without reference to the server.
        </t>
        <t>
          If the nfsace4 indicates that the open may not be done, then an ACCESS
          request must be sent to the server to obtain the definitive answer.
        </t>
      </list>
      The server may return an nfsace4 that is more restrictive than the
      actual ACL of the file.  This includes an nfsace4 that specifies
      denial of all access.  Note that some common practices such as mapping
      the traditional user "root" to the user "nobody" (see <xref target="owner_owner_group"/>) may make it incorrect
      to return the actual ACL of the file in the delegation response.
    </t>
    <t>
      The use of a delegation together with various other forms of caching
      creates the possibility that no server authentication and authorization
      will ever be
      performed for a given user since all of the user's requests might be
      satisfied locally.  Where the client is depending on the server for
      authentication and authorization, the client should be sure authentication and authorization occurs for
      each user by use of the ACCESS operation.  This should be the case
      even if an ACCESS operation would not be required otherwise.  As
      mentioned before, the server may enforce frequent authentication by
      returning an nfsace4 denying all access with every OPEN delegation.

    </t>
    <section title="Open Delegation and Data Caching" 
             anchor="open_delegation_caching" >
      <t>
        An OPEN delegation allows much of the message overhead associated with
        the opening and closing files to be eliminated.  An open when an OPEN
        delegation is in effect does not require that a validation
        message be sent to the server.  The continued endurance of the
        "OPEN_DELEGATE_READ delegation" provides a guarantee that no OPEN
        for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, and thus
        no write, has occurred.  Similarly, when closing a file opened
        for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH and if an OPEN_DELEGATE_WRITE delegation is in effect,
        the data written does not have to be written to the server until
        the OPEN delegation is recalled.  The continued endurance of
        the OPEN delegation provides a
        guarantee that no open, and thus no READ or WRITE, has been done by
        another client.
      </t>
      <t>
        For the purposes of OPEN delegation, READs and WRITEs done without an
        OPEN are treated as the functional equivalents of a corresponding type
        of OPEN.  Although a client SHOULD NOT use special stateids when 
        an open exists, delegation handling on the server can use the 
        client ID associated with the current session to determine if the
        operation has been done by the holder of the delegation (in which
        case, no recall is necessary) or by another client (in which case,
        the delegation must be recalled and I/O not proceed until the 
        delegation is recalled or revoked). 
      </t>
      <t>
        With delegations, a client is able to avoid writing data to the server
        when the CLOSE of a file is serviced.  The file close system call is
        the usual point at which the client is notified of a lack of stable
        storage for the modified file data generated by the application.  At
        the close, file data is written to the server and, through normal
        accounting, the server is able to determine if the available file system
        space for the data has been exceeded (i.e., the server returns
        NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting includes quotas.
        The introduction of delegations requires that an alternative method be
        in place for the same type of communication to occur between client
        and server.
      </t>
      <t>
        In the delegation response, the server provides either the limit of
        the size of the file or the number of modified blocks and associated
        block size.  The server must ensure that the client will be able to
        write modified data to the server of a size equal to that provided in the
        original delegation.  The server must make this assurance for all
        outstanding delegations.  Therefore, the server must be careful in its
        management of available space for new or modified data, taking into
        account available file system space and any applicable quotas.  The
        server can recall delegations as a result of managing the available
        file system space.  The client should abide by the server's state
        space limits for delegations.  If the client exceeds the stated limits
        for the delegation, the server's behavior is undefined.
      </t>
      <t>
        Based on server conditions, quotas, or available file system space, the
        server may grant OPEN_DELEGATE_WRITE delegations with very restrictive space
        limitations.  The limitations may be defined in a way that will always
        force modified data to be flushed to the server on close.
      </t>
      <t>
        With respect to authentication, flushing modified data to the server
        after a CLOSE has occurred may be problematic.  For example, the user
        of the application may have logged off the client, and unexpired
        authentication credentials may not be present.  In this case, the
        client may need to take special care to ensure that local unexpired
        credentials will in fact be available.  This may be accomplished by
        tracking the expiration time of credentials and flushing data well in
        advance of their expiration or by making private copies of credentials
        to assure their availability when needed.

      </t>
    </section>
    <section title="Open Delegation and File Locks" >
      <t>
        When a client holds an OPEN_DELEGATE_WRITE delegation, lock operations are
        performed locally.  This includes those required for mandatory byte-range
        locking.  This can be done since the delegation implies that there can
        be no conflicting locks.  Similarly, all of the revalidations that
        would normally be associated with obtaining locks and the flushing of
        data associated with the releasing of locks need not be done.
      </t>
      <t>
        When a client holds an OPEN_DELEGATE_READ delegation, lock operations are not
        performed locally.  All lock operations, including those requesting
        non-exclusive locks, are sent to the server for resolution. 

      </t>
    </section>
    <section anchor="handling_cb_getattr" title="Handling of CB_GETATTR" >
      <t>
        The server needs to employ special handling for a GETATTR where the
        target is a file that has an OPEN_DELEGATE_WRITE delegation in effect.  The
        reason for this is that the client holding the OPEN_DELEGATE_WRITE delegation may
        have modified the data, and the server needs to reflect this change to
        the second client that submitted the GETATTR.  Therefore, the client
        holding the OPEN_DELEGATE_WRITE delegation needs to be interrogated.  The server
        will use the CB_GETATTR operation.  The only attributes that the
        server can reliably query via CB_GETATTR are size and change.
      </t>
      <t>
        Since CB_GETATTR is being used to satisfy another client's GETATTR
        request, the server only needs to know if the client holding the
        delegation has a modified version of the file.  If the client's copy
        of the delegated file is not modified (data or size), the server can
        satisfy the second client's GETATTR request from the attributes stored
        locally at the server.  If the file is modified, the server only needs
        to know about this modified state.  If the server determines that the
        file is currently modified, it will respond to the second client's
        GETATTR as if the file had been modified locally at the server.
      </t>
      <t>
        Since the form of the change attribute is determined by the server and
        is opaque to the client, the client and server need to agree on a
        method of communicating the modified state of the file.  For the size
        attribute, the client will report its current view of the file size.
        For the change attribute, the handling is more involved.
      </t>
      <t>
        For the client, the following steps will be taken when receiving an
        OPEN_DELEGATE_WRITE delegation:
        <list style="symbols">
          <t>
            The value of the change attribute will be obtained from the server and
            cached.  Let this value be represented by c.  
          </t>
          <t>
            The client will create a value greater than c that will be used for
            communicating that modified data is held at the client.  Let this value be
            represented by d.
          </t>
          <t>
            When the client is queried via CB_GETATTR for the change attribute, it
            checks to see if it holds modified data.  If the file is modified, the
            value d is returned for the change attribute value.  If this file is
            not currently modified, the client returns the value c for the change
            attribute.
          </t>
        </list>
        For simplicity of implementation, the client MAY for each CB_GETATTR
        return the same value d.  This is true even if, between successive
        CB_GETATTR operations, the client again modifies the file's data or
        metadata in its cache.  The client can return the same value because
        the only requirement is that the client be able to indicate to the
        server that the client holds modified data.  Therefore, the value of d
        may always be c + 1.
      </t>
      <t>
        While the change attribute is opaque to the client in the sense that
        it has no idea what units of time, if any, the server is counting
        change with, it is not opaque in that the client has to treat it as an
        unsigned integer, and the server has to be able to see the results of
        the client's changes to that integer.  Therefore, the server MUST
        encode the change attribute in network order when sending it to the
        client.  The client MUST decode it from network order to its native
        order when receiving it, and the client MUST encode it in network order
        when sending it to the server.  For this reason, change is defined as
        an unsigned integer rather than an opaque array of bytes.
      </t>
      <t>
        For the server, the following steps will be taken when providing an
        OPEN_DELEGATE_WRITE delegation:
        <list style="symbols">
          <t>
            Upon providing an OPEN_DELEGATE_WRITE delegation, the server will cache a copy of the
            change attribute in the data structure it uses to record the
            delegation.  Let this value be represented by sc.
          </t>
          <t>
            When a second client sends a GETATTR operation on the same file to the
            server, the server obtains the change attribute from the first client.
            Let this value be cc.
          </t>
          <t>
            If the value cc is equal to sc, the file is not modified and the
            server returns the current values for change, time_metadata, and
            time_modify (for example) to the second client.
          </t>
          <t>
            If the value cc is NOT equal to sc, the file is currently modified at
            the first client and most likely will be modified at the server at a
            future time.  The server then uses its current time to construct
            attribute values for time_metadata and time_modify.  A new value of
            sc, which we will call nsc, is computed by the server, such that nsc
            >= sc + 1.  The server then returns the constructed time_metadata,
            time_modify, and nsc values to the requester.  The server replaces sc
            in the delegation record with nsc.  To prevent the possibility of
            time_modify, time_metadata, and change from appearing to go backward
            (which would happen if the client holding the delegation fails to
            write its modified data to the server before the delegation is revoked
            or returned), the server SHOULD update the file's metadata record with
            the constructed attribute values.  For reasons of reasonable
            performance, committing the constructed attribute values to stable
            storage is OPTIONAL.
          </t>
        </list>
      </t>
      <t>
        As discussed earlier in this section, the client MAY return the same
        cc value on subsequent CB_GETATTR calls, even if the file was modified
        in the client's cache yet again between successive CB_GETATTR calls.
        Therefore, the server must assume that the file has been modified yet
        again, and MUST take care to ensure that the new nsc it constructs and
        returns is greater than the previous nsc it returned.  An example
        implementation's delegation record would satisfy this mandate by
        including a boolean field (let us call it "modified") that is set to
        FALSE when the delegation is granted, and an sc value set at the time
        of grant to the change attribute value. The modified field would be
        set to TRUE the first time cc != sc, and would stay TRUE until the
        delegation is returned or revoked.  The processing for constructing
        nsc, time_modify, and time_metadata would use this pseudo code:
        <figure>
          <artwork>
    if (!modified) {
        do CB_GETATTR for change and size;

        if (cc != sc)
            modified = TRUE;
    } else {
        do CB_GETATTR for size;
    }

    if (modified) {
        sc = sc + 1;
        time_modify = time_metadata = current_time;
        update sc, time_modify, time_metadata into file's metadata;
    }

	    </artwork>
	  </figure>
	  This would return to the client (that sent GETATTR) the attributes
        it requested, but make sure size comes from what 
        CB_GETATTR returned. The server would not update the file's 
        metadata with the client's modified size.
      </t>
      <t>
        In the case that the file attribute size is different than the
        server's current value, the server treats this as a modification
        regardless of the value of the change attribute retrieved via
        CB_GETATTR and responds to the second client as in the last step.
      </t>
      <t>
        This methodology resolves issues of clock differences between client
        and server and other scenarios where the use of CB_GETATTR break down.
      </t>
      <t>
        It should be noted that the server is under no obligation to use
        CB_GETATTR, and therefore the server MAY simply recall the delegation
        to avoid its use.
      </t>
    </section>

    <section title="Recall of Open Delegation" >
      <t>
        The following events necessitate recall of an OPEN delegation:
        <list style="symbols">
          <t>
            potentially conflicting OPEN request (or a READ or WRITE operation
            done with a special stateid)
          </t>
          <t>
            SETATTR sent by another client
          </t>
          <t>
            REMOVE request for the file
          </t>
          <t>
            RENAME request for the file as either the source or target of the RENAME
          </t>
        </list>
        Whether a RENAME of a directory in the path leading to the file
        results in recall of an OPEN delegation depends on the semantics of
        the server's file system.  If that file system denies such RENAMEs when
        a file is open, the recall must be performed to determine whether the
        file in question is, in fact, open.
      </t>
      <t>
        In addition to the situations above, the server may choose to recall
        OPEN delegations at any time if resource constraints make it advisable
        to do so.  Clients should always be prepared for the possibility of
        recall.
      </t>
      <t>
        When a client receives a recall for an OPEN delegation, it needs
        to update state on the server before returning the delegation.
        These same updates must be done whenever a client chooses to
        return a delegation voluntarily.  The following items of state 
        need to be dealt with:
        <list style="symbols">
          <t>
            If the file associated with the delegation is no longer open and no
            previous CLOSE operation has been sent to the server, a CLOSE
            operation must be sent to the server.
          </t>
          <t>
            If a file has other open references at the client, then OPEN
            operations must be sent to the server.  The appropriate stateids will
            be provided by the server for subsequent use by the client since the
            delegation stateid will no longer be valid.  These OPEN requests are
            done with the claim type of CLAIM_DELEGATE_CUR.  This will allow the
            presentation of the delegation stateid so that the client can
            establish the appropriate rights to perform the OPEN.  (see
            <xref target="OP_OPEN" />, which describes the OPEN operation, 
            for details.)
          </t>
          <t>
            If there are granted byte-range locks, the corresponding LOCK operations
            need to be performed.  This applies to the OPEN_DELEGATE_WRITE delegation case
            only.
          </t>
          <t>
            For an OPEN_DELEGATE_WRITE delegation, if
            at the time of recall the file is not open for
            OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, all modified
            data for the file must be flushed to the
            server.  If the delegation had not existed, the client would have done
            this data flush before the CLOSE operation.
          </t>
          <t>
            For an OPEN_DELEGATE_WRITE delegation when a file is still open at the time of
            recall, any modified data for the file needs to be flushed to the
            server.
          </t>
          <t>
            With the OPEN_DELEGATE_WRITE delegation in place, it is possible that the file
            was truncated during the duration of the delegation.  For example, the
            truncation could have occurred as a result of an OPEN UNCHECKED with a
            size attribute value of zero.  Therefore, if a truncation of
            the file has occurred and this operation has not been propagated to
            the server, the truncation must occur before any modified data is
            written to the server.
          </t>
        </list>
        In the case of OPEN_DELEGATE_WRITE delegation, byte-range locking imposes some
        additional requirements.  To precisely maintain the associated
        invariant, it is required to flush any modified data in any byte-range for
        which a WRITE_LT lock was released while the OPEN_DELEGATE_WRITE delegation was in
        effect.  However, because the OPEN_DELEGATE_WRITE delegation implies no other
        locking by other clients, a simpler implementation is to flush all
        modified data for the file (as described just above) if any WRITE_LT lock
        has been released while the OPEN_DELEGATE_WRITE delegation was in effect.
      </t>
      <t>
        An implementation need not wait until delegation recall (or
        the decision to voluntarily return a delegation) to perform any of the above
        actions, if implementation considerations (e.g., resource availability
        constraints) make that desirable.  Generally, however, the fact that
        the actual OPEN state of the file may continue to change makes it not
        worthwhile to send information about opens and closes to the server,
        except as part of delegation return.  An exception is
        when the client has no more internal opens of the file. In this
        case, sending a CLOSE is useful because it
        reduces resource utilization on the client
        and server.


Regardless of the client's choices on scheduling these
        actions, all must be performed before the delegation is returned,
        including (when applicable) the close that corresponds to the OPEN
        that resulted in the delegation.  These actions can be performed
        either in previous requests or in previous operations in the same
        COMPOUND request.

      </t>
    </section>
    <section title="Clients That Fail to Honor Delegation Recalls" >
      <t>
        A client may fail to respond to a recall for various reasons, such as
        a failure of the backchannel from server to the client. The client
        may be unaware of a failure in the backchannel.  This lack of
        awareness could result in the client finding out long after the
        failure that its delegation has been revoked, and another client has
        modified the data for which the client had a delegation.  This is
        especially a problem for the client that held an OPEN_DELEGATE_WRITE delegation.
      </t>
      <t>
        Status bits returned by SEQUENCE operations help to provide an
        alternate way of informing the client of issues regarding the 
        status of the backchannel and of recalled delegations.  When the
        backchannel is not available, the server returns the status bit 
        SEQ4_STATUS_CB_PATH_DOWN on SEQUENCE operations.  The client can
        react by attempting to re-establish the backchannel and by 
        returning recallable objects if a backchannel cannot be successfully
        re-established. 
      </t>
      <t>
        Whether the backchannel is functioning or not, it may be that the
        recalled delegation is not returned.  Note that the client's lease
        might still be renewed, even though the recalled delegation is not
        returned.  In this situation, servers SHOULD revoke delegations that
        are not returned in a period of time equal to the lease period.  This
        period of time should allow the client time to note the 
        backchannel-down status and re-establish the backchannel.
      </t>
      <t>
        When delegations are revoked, the server will return with the
        SEQ4_STATUS_RECALLABLE_STATE_REVOKED status bit set on subsequent
        SEQUENCE operations.  The client should note this and then use 
        TEST_STATEID to find which delegations have been revoked.
      </t> 
    </section>
    <section title="Delegation Revocation" >
      <t>
        At the point a delegation is revoked, if there are associated opens 
        on the client, these opens may or may not be revoked.  If no 
        byte-range lock or open is granted that is inconsistent with the existing open,
        the stateid for the open may remain valid and be disconnected
        from the revoked delegation, just as would be the case if the 
        delegation were returned.
      </t>
      <t>
        For example, if an OPEN for OPEN4_SHARE_ACCESS_BOTH with a deny of OPEN4_SHARE_DENY_NONE is 
        associated with the delegation, granting of another such OPEN
        to a different client will revoke the delegation but need not
        revoke the OPEN, since the two OPENs are consistent with each other.
        On the other hand, if an OPEN denying write access is
        granted, then the existing OPEN must be revoked.
      </t>
      <t>
        When opens and/or locks are revoked,
        the applications holding these opens or locks need to be notified.
        This notification usually occurs by returning errors for READ/WRITE
        operations or when a close is attempted for the open file.
      </t>
      <t>
        If no opens exist for the file at the point the delegation is revoked,
        then notification of the revocation is unnecessary.  However, if there
        is modified data present at the client for the file, the user of the
        application should be notified.  Unfortunately, it may not be possible
        to notify the user since active applications may not be present at the
        client.  See <xref target="revocation_recovery_write" />
        for additional details.
      </t>
    </section>
    <section title="Delegations via WANT_DELEGATION"
             anchor="via_want_delegation" >
      <t>
        In addition to providing delegations as part of the reply 
        to OPEN operations, servers MAY provide delegations 
        separate from open, via the OPTIONAL WANT_DELEGATION operation.  This 
        allows delegations to be obtained in advance of an OPEN that 
        might benefit from them, for objects that are not a valid target
        of OPEN, or to deal with cases in which a 
        delegation has been recalled and the client wants to make 
        an attempt to re-establish it if the absence of use by other 
        clients allows that.
      </t>
      <t>
        The WANT_DELEGATION operation may be performed on any type of 
        file object other than a directory.
      </t>
      <t>
        When a delegation is obtained using WANT_DELEGATION, any open
        files for the same filehandle held by that client are to be
        treated as subordinate to the delegation, just as if they had
        been created using an OPEN of type CLAIM_DELEGATE_CUR.  They are
        otherwise unchanged as to seqid, access and deny modes, and the
        relationship with byte-range locks.  Similarly, because
        existing byte-range
        locks are subordinate to an open, those byte-range locks also become
        indirectly subordinate to that new delegation. 
      </t>
      <t>
        The WANT_DELEGATION operation provides for delivery of delegations
        via callbacks, when the delegations are not immediately available.
        When a requested delegation is available, it is delivered to the
        client via a CB_PUSH_DELEG operation.  When this happens, open files
        for the same filehandle become subordinate to the new delegation
        at the point at which the delegation is delivered, just as if they had
        been created using an OPEN of type CLAIM_DELEGATE_CUR.
        Similarly, this occurs for existing byte-range locks subordinate to an open.
      </t>
    </section>
  </section>
  <section title="Data Caching and Revocation" anchor="data_caching_revocation" >
    <t>
      When locks and delegations are revoked, the assumptions upon which
      successful caching depends are no longer guaranteed.  For any locks or
      share reservations that have been revoked, the corresponding state-owner
      needs to be notified.  This notification includes applications with a
      file open that has a corresponding delegation that has been revoked.
      Cached data associated with the revocation must be removed from the
      client.  In the case of modified data existing in the client's cache,
      that data must be removed from the client without being written to
      the server.  As mentioned, the assumptions made by the client are no
      longer valid at the point when a lock or delegation has been revoked.
      For example, another client may have been granted a conflicting byte-range lock
      after the revocation of the byte-range lock at the first client.  Therefore, the
      data within the lock range may have been modified by the other client.
      Obviously, the first client is unable to guarantee to the application
      what has occurred to the file in the case of revocation.
    </t>
    <t>
      Notification to a state-owner will in many cases consist of simply
      returning an error on the next and all subsequent READs/WRITEs to the
      open file or on the close.  Where the methods available to a client
      make such notification impossible because errors for certain
      operations may not be returned, more drastic action such as signals or
      process termination may be appropriate.  The justification here is
      that an invariant on which an application depends may be violated.
      Depending on how errors are typically treated for the client-operating
      environment, further levels of notification including logging, console
      messages, and GUI pop-ups may be appropriate.
    </t>
    <section title="Revocation Recovery for Write Open Delegation" 
             anchor="revocation_recovery_write" >
      <t>
        Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the special
        issue of modified data in the client cache while the file is not open.
        In this situation, any client that does not flush modified data to
        the server on each close must ensure that the user receives
        appropriate notification of the failure as a result of the revocation.
        Since such situations may require human action to correct problems,
        notification schemes in which the appropriate user or administrator is
        notified may be necessary.  Logging and console messages are typical
        examples.
      </t>
      <t>
        If there is modified data on the client, it must not be flushed
        normally to the server.  A client may attempt to provide a copy of the
        file data as modified during the delegation under a different name in
        the file system namespace to ease recovery.  Note that when the
        client can determine that the file has not been modified by any other
        client, or when the client has a complete cached copy of the file in
        question, such a saved copy of the client's view of the file may be of
        particular value for recovery.  In another case, recovery using a copy
        of the file based partially on the client's cached data and partially
        on the server's copy as modified by other clients will be anything but
        straightforward, so clients may avoid saving file contents in these
        situations or specially mark the results to warn users of possible
        problems.
      </t>
      <t>
        Saving of such modified data in delegation revocation situations
        may be limited to files of a certain size or might be used only when 
        sufficient disk space is available within the target file system.
        Such saving may also be restricted to situations when the client has
        sufficient buffering resources to keep the cached copy available
        until it is properly stored to the target file system. 
      </t>
    </section>
  </section>
  <section title="Attribute Caching" >
    <t>
      This section pertains to the caching of a file's attributes on a client
      when that client does not hold a delegation on the file.
    </t>

    <t>
      The attributes discussed in this section do not include named
      attributes.  Individual named attributes are analogous to files, and
      caching of the data for these needs to be handled just as data caching
      is for ordinary files.  Similarly, LOOKUP results from an OPENATTR
      directory (as well as the directory's contents) are to be cached on
      the same basis as any other pathnames.
    </t>
    <t>
      Clients may cache file attributes obtained from the server and use
      them to avoid subsequent GETATTR requests.  Such caching is write
      through in that modification to file attributes is always done by
      means of requests to the server and should not be done locally and
      should not be cached.  The exception to this are modifications to attributes that
      are intimately connected with data caching.  Therefore, extending a
      file by writing data to the local data cache is reflected immediately
      in the size as seen on the client without this change being
      immediately reflected on the server.  Normally, such changes are not
      propagated directly to the server, but when the modified data is
      flushed to the server, analogous attribute changes are made on the
      server.  When OPEN delegation is in effect, the modified attributes
      may be returned to the server in reaction to a CB_RECALL call.
    </t>
    <t>
      The result of local caching of attributes is that the attribute
      caches maintained on individual clients will not be coherent.  
      Changes made in one order on the server may be seen in a different
      order on one client and in a third order on another client.
    </t>
    <t>
      The typical file system application programming interfaces do not
      provide means to atomically modify or interrogate attributes for
      multiple files at the same time.  The following rules provide an
      environment where the potential incoherencies mentioned above can be
      reasonably managed.  These rules are derived from the practice of
      previous NFS protocols.
      <list style="symbols">
        <t>
          All attributes for a given file (per-fsid attributes excepted) are
          cached as a unit at the client so that no non-serializability can
          arise within the context of a single file.
        </t>
        <t>
          An upper time boundary is maintained on how long a client cache entry
          can be kept without being refreshed from the server.
        </t>
        <t>
          When operations are performed that change attributes at the server,
          the updated attribute set is requested as part of the containing RPC.
          This includes directory operations that update attributes indirectly.
          This is accomplished by following the modifying operation with a
          GETATTR operation and then using the results of the GETATTR to update
          the client's cached attributes.
        </t>
      </list>
      Note that if the full set of attributes to be cached is requested by
      READDIR, the results can be cached by the client on the same basis as
      attributes obtained via GETATTR.
    </t>
    <t>
      A client may validate its cached version of attributes for a file by
      fetching both the change and time_access attributes and assuming
      that if the change attribute has the same value as it did when the
      attributes were cached, then no attributes other than time_access have
      changed.  The reason why time_access is also fetched is because many
      servers operate in environments where the operation that updates
      change does not update time_access.  For example, POSIX file semantics
      do not update access time when a file is modified by the write system
      call <xref target="write_atime"/>.  Therefore, the client that wants a current time_access value
      should fetch it with change during the attribute cache validation
      processing and update its cached time_access.
    </t>
    <t>
      The client may maintain a cache of modified attributes for those
      attributes intimately connected with data of modified regular files
      (size, time_modify, and change). Other than those three attributes,
      the client MUST NOT maintain a cache of modified attributes. Instead,
      attribute changes are immediately sent to the server.
    </t>
    <t>
      In some operating environments, the equivalent to time_access is
      expected to be implicitly updated by each read of the content of the
      file object.  If an NFS client is caching the content of a file
      object, whether it is a regular file, directory, or symbolic link, the
      client SHOULD NOT update the time_access attribute (via SETATTR or a
      small READ or READDIR request) on the server with each read that is
      satisfied from cache.  The reason is that this can defeat the
      performance benefits of caching content, especially since an explicit
      SETATTR of time_access may alter the change attribute on the server.
      If the change attribute changes, clients that are caching the content
      will think the content has changed, and will re-read unmodified data
      from the server.  Nor is the client encouraged to maintain a modified
      version of time_access in its cache, since the client either would
      eventually have to write the access time to the server
      with bad performance effects or never update the
      server's time_access, thereby resulting in a situation where an
      application that caches access time between a close and open of
      the same file observes the access time oscillating between the past and
      present.  The time_access attribute always means the time of last
      access to a file by a read that was satisfied by the server. This way
      clients will tend to see only time_access changes that go forward in
      time.
      
    </t>
  </section>
  <section title="Data and Metadata Caching and Memory Mapped Files" >
    <t>
      Some operating environments include the capability for an application
      to map a file's content into the application's address space.  Each
      time the application accesses a memory location that corresponds to a
      block that has not been loaded into the address space, a page fault
      occurs and the file is read (or if the block does not exist in the
      file, the block is allocated and then instantiated in the
      application's address space).
    </t>
    <t>
      As long as each memory-mapped access to the file requires a page
      fault, the relevant attributes of the file that are used to detect
      access and modification (time_access, time_metadata, time_modify, and
      change) will be updated.  However, in many operating environments,
      when page faults are not required, these attributes will not be updated
      on reads or updates to the file via memory access (regardless of
      whether the file is local or is accessed remotely).  A client or
      server MAY fail to update attributes of a file that is being accessed
      via memory-mapped I/O.  This has several implications:
      <list style="symbols">
        <t>
          If there is an application on the server that has memory mapped a file
          that a client is also accessing, the client may not be able to get a
          consistent value of the change attribute to determine
          whether or not its cache is stale.  A server that knows that
          the file is memory-mapped could always pessimistically
          return updated values for change so as to force the
          application to always get the most up-to-date data
          and metadata for the file.  However, due to the negative performance
          implications of this, such behavior is OPTIONAL.
        </t>
        <t>
          If the memory-mapped file is not being modified on the server, and
          instead is just being read by an application via the memory-mapped
          interface, the client will not see an updated time_access attribute.
          However, in many operating environments, neither will any process
          running on the server. Thus, NFS clients are at no disadvantage with
          respect to local processes.
        </t>
        <t>
          If there is another client that is memory mapping the file, and if
          that client is holding an OPEN_DELEGATE_WRITE delegation, the same set of issues as
          discussed in the previous two bullet points apply.  So, when a server
          does a CB_GETATTR to a file that the client has modified in its cache,
          the reply from CB_GETATTR will not necessarily be accurate.  As
          discussed earlier, the client's obligation is to report that the file
          has been modified since the delegation was granted, not whether it has
          been modified again between successive CB_GETATTR calls, and the
          server MUST assume that any file the client has modified in cache has
          been modified again between successive CB_GETATTR calls.  Depending on
          the nature of the client's memory management system, this weak
          obligation may not be possible.  A client MAY return stale information
          in CB_GETATTR whenever the file is memory-mapped.
        </t>
        <t>
          The mixture of memory mapping and byte-range locking on the same file is
          problematic. Consider the following scenario, where a page size on
          each client is 8192 bytes.
          <list style="symbols">
            <t>
              Client A memory maps the first page (8192 bytes) of file X.
            </t>
            <t>
              Client B memory maps the first page (8192 bytes) of file X.
            </t>
            <t>
              Client A WRITE_LT locks the first 4096 bytes.
            </t>
            <t>
              Client B WRITE_LT locks the second 4096 bytes.
            </t>
            <t>
              Client A, via a STORE instruction, modifies part of its locked byte-range.
            </t>
            <t>
              Simultaneous to client A, client B executes a STORE on part of its
              locked byte-range.
            </t>
          </list>
        </t>
      </list>
    </t>
    <t>
      Here the challenge is for each client to resynchronize to get a
      correct view of the first page. In many operating environments, the
      virtual memory management systems on each client only know a page is
      modified, not that a subset of the page corresponding to the
      respective lock byte-ranges has been modified. So it is not possible for
      each client to do the right thing, which is to write to the
      server only that portion of the page that is locked.  For example, if
      client A simply writes out the page, and then client B writes out the
      page, client A's data is lost.
    </t>
    <t>
      Moreover, if mandatory locking is enabled on the file, then we have a
      different problem.  When clients A and B execute the STORE instructions,
      the resulting page faults require a byte-range lock on the entire page.
      Each client then tries to extend their locked range to the entire
      page, which results in a deadlock.  Communicating the NFS4ERR_DEADLOCK
      error to a STORE instruction is difficult at best.
    </t>
    <t>
      If a client is locking the entire memory-mapped file, there is no
      problem with advisory or mandatory byte-range locking, at least until the
      client unlocks a byte-range in the middle of the file.
    </t>
    <t>
      Given the above issues, the following are permitted:
      <list style="symbols">
        <t>
          Clients and servers MAY deny memory mapping a file for which they know there are
          byte-range locks.
        </t>
        <t>
          Clients and servers MAY deny a byte-range lock on a file they know is
          memory-mapped.
        </t>
        <t>
          A client MAY deny memory mapping a file that it knows requires
          mandatory locking for I/O.  If mandatory locking is enabled after the
          file is opened and mapped, the client MAY deny the application further
          access to its mapped file.
        </t>
      </list>
    </t>
  </section>
  <section title="Name and Directory Caching without Directory Delegations"
           anchor="without_dir_deleg">
    <t>
      The NFSv4.1 directory delegation facility
      (described in <xref target="dir_deleg" /> below) is OPTIONAL
      for servers to implement. Even where it is
      implemented, it may not always be functional because of resource
      availability issues or other constraints.  Thus, it is
      important to understand how name and directory caching are done
      in the absence of directory delegations. These topics are
      discussed in the next two subsections.
    </t>
    <section anchor="name_caching" title="Name Caching" >
      <t>
        The results of LOOKUP and READDIR operations may be cached to avoid
        the cost of subsequent LOOKUP operations.  Just as in the case of
        attribute caching, inconsistencies may arise among the various client
        caches.  To mitigate the effects of these inconsistencies and given
        the context of typical file system APIs, an upper time boundary is
        maintained for how long a client name cache entry can be kept without
        verifying that the entry has not been made invalid by a directory
        change operation performed by another client.
      </t>
      <t>
        When a client is not making changes to a directory for which there
        exist name cache entries, the client needs to periodically fetch
        attributes for that directory to ensure that it is not being modified.
        After determining that no modification has occurred, the expiration
        time for the associated name cache entries may be updated to be the
        current time plus the name cache staleness bound.
      </t>
      <t>
        When a client is making changes to a given directory, it needs to
        determine whether there have been changes made to the directory by
        other clients.  It does this by using the change attribute as reported
        before and after the directory operation in the associated
        change_info4 value returned for the operation.  The server is able to
        communicate to the client whether the change_info4 data is provided
        atomically with respect to the directory operation.  If the change
        values are provided atomically, the client has a basis for determining,
        given proper care, whether other clients are modifying the directory
        in question.
      </t>
      <t>
        The simplest way to enable the client to make this determination is
        for the client to serialize all changes made to a specific directory.
        When this is done, and the server provides before and after values of the 
        change attribute atomically, the client can simply compare the 
        after value of the change attribute from one operation on a 
        directory with the before value on the subsequent operation
        modifying that directory.  When these are equal, the client is
        assured that no other client is modifying the directory in question.
      </t>
      <t>
        When such serialization is not used, and there may be multiple 
        simultaneous outstanding operations modifying a single directory sent 
        from a single client, making this sort of determination can be more 
        complicated.  If two such operations
        complete in a different order than they were actually performed,
        that might give an appearance consistent with modification being 
        made by another client.  Where this appears to happen, the client
        needs to await the completion of all such modifications that were
        started previously, to see if the outstanding before and after
        change numbers can be sorted into a chain such that the before
        value of one change number matches the after value of a previous
        one, in a chain consistent with this client being the only one
        modifying the directory.
      </t>
      <t>
        In either of these cases, the client is able to determine whether
        the directory is being modified by another client.
        If the comparison indicates that the directory was updated by
        another client, the name cache associated with the modified directory
        is purged from the client.  If the comparison indicates no
        modification, the name cache can be updated on the client to reflect
        the directory operation and the associated timeout can be extended.  The
        post-operation change value needs to be saved as the basis for future
        change_info4 comparisons.
      </t>
      <t>
        As demonstrated by the scenario above, name caching requires that the
        client revalidate name cache data by inspecting the change attribute
        of a directory at the point when the name cache item was cached.  This
        requires that the server update the change attribute for directories
        when the contents of the corresponding directory is modified.  For a
        client to use the change_info4 information appropriately and
        correctly, the server must report the pre- and post-operation change
        attribute values atomically.  When the server is unable to report the
        before and after values atomically with respect to the directory
        operation, the server must indicate that fact in the change_info4
        return value.  When the information is not atomically reported, the
        client should not assume that other clients have not changed the
        directory.
      </t>
    </section>
    <section title="Directory Caching" >
      <t>
        The results of READDIR operations may be used to avoid subsequent
        READDIR operations.  Just as in the cases of attribute and name
        caching, inconsistencies may arise among the various client caches.  To
        mitigate the effects of these inconsistencies, and given the context of
        typical file system APIs, the following rules should be followed:
        <list style="symbols">
          <t>
            Cached READDIR information for a directory that is not obtained in a
            single READDIR operation must always be a consistent snapshot of
            directory contents.  This is determined by using a GETATTR before the
            first READDIR and after the last READDIR that contributes to the
            cache.
          </t>
          <t>
            An upper time boundary is maintained to indicate the length of time a
            directory cache entry is considered valid before the client must
            revalidate the cached information.
          </t>
        </list>
        The revalidation technique parallels that discussed in the case of
        name caching.  When the client is not changing the directory in
        question, checking the change attribute of the directory with GETATTR
        is adequate.  The lifetime of the cache entry can be extended at these
        checkpoints.  When a client is modifying the directory, the client
        needs to use the change_info4 data to determine whether there are
        other clients modifying the directory.  If it is determined that no
        other client modifications are occurring, the client may update its
        directory cache to reflect its own changes.
      </t>
      <t>
        As demonstrated previously, directory caching requires that the client
        revalidate directory cache data by inspecting the change attribute of
        a directory at the point when the directory was cached.  This requires
        that the server update the change attribute for directories when the
        contents of the corresponding directory is modified.  For a client to
        use the change_info4 information appropriately and correctly, the
        server must report the pre- and post-operation change attribute values
        atomically.  When the server is unable to report the before and after
        values atomically with respect to the directory operation, the server
        must indicate that fact in the change_info4 return value.  When the
        information is not atomically reported, the client should not assume
        that other clients have not changed the directory.
      </t>
    </section>
  </section>
  <section title="Directory Delegations" anchor="dir_deleg">
    <section title="Introduction to Directory Delegations">
      <t>
        Directory caching for the NFSv4.1 protocol, as previously
        described, is similar to file 
        caching in previous versions.  Clients typically cache 
        directory information for
        a duration determined by the client. At the end of a predefined
        timeout, the client will query the server to see if the directory has
        been updated. By caching attributes, clients reduce the number of
        GETATTR calls made to the server to validate attributes. Furthermore,
        frequently accessed files and directories, such as the current
        working directory, have their attributes cached on the client so that
        some NFS operations can be performed without having to make an RPC
        call. By caching name and inode information about most recently
        looked up entries in a Directory Name Lookup Cache (DNLC), clients do
        not need to send LOOKUP calls to the server every time these files
        are accessed.
      </t>
      <t>
        This caching approach works reasonably well at reducing network
        traffic in many environments. However, it does not address
        environments where there are numerous queries for files that do not
        exist. In these cases of "misses", the client sends requests to
        the server in order to provide reasonable application semantics and
        promptly detect the creation of new directory entries. Examples of
        high miss activity are compilation in software development
        environments. The current behavior of NFS limits its potential
        scalability and wide-area sharing effectiveness in these types of
        environments. Other distributed stateful file system architectures
        such as AFS and DFS have proven that adding state around directory
        contents can greatly reduce network traffic in high-miss
        environments.
      </t>
      <t>
        Delegation of directory contents is an OPTIONAL feature of NFSv4.1.
        Directory delegations provide similar traffic reduction
        benefits as with file delegations. By allowing clients to cache
        directory contents (in a read-only fashion) while being notified of
        changes, the client can avoid making frequent requests to interrogate
        the contents of slowly-changing directories, reducing network traffic
        and improving client performance.  It can also simplify the task of
        determining whether other clients are making changes to the directory
        when the client itself is making many changes to the directory and
        changes are not serialized.
      </t>
      <t>
        Directory delegations allow improved namespace cache consistency to be
        achieved through delegations and synchronous recalls, in the absence
        of notifications. In addition, if time-based consistency is
        sufficient, asynchronous notifications can provide performance
        benefits for the client, and possibly the server, under some common
        operating conditions such as slowly-changing and/or very large
        directories.
      </t>
    </section>
    <section title="Directory Delegation Design">
      <t>
        NFSv4.1 introduces the GET_DIR_DELEGATION 
        (<xref target="OP_GET_DIR_DELEGATION" />) operation to allow the 
        client to ask for a
        directory delegation. The delegation covers directory attributes and
        all entries in the directory. If either of these change, the
        delegation will be recalled synchronously. The operation causing the
        recall will have to wait before the recall is complete. Any changes
        to directory entry attributes will not cause the delegation to be
        recalled.
      </t>
      <t>
        In addition to asking for delegations, a client can also ask for
        notifications for certain events. These events include changes to
        the directory's attributes and/or its contents.  If a client asks for
        notification for a certain event, the server will notify the client
        when that event occurs. This will not result in the delegation being
        recalled for that client.  The notifications are asynchronous and
        provide a way of avoiding recalls in situations where a directory is
        changing enough that the pure recall model may not be effective while
        trying to allow the client to get substantial benefit. In the absence
        of notifications, once the delegation is recalled the client has to
        refresh its directory cache; this might not be very efficient for
        very large directories.
      </t>
      <t>
        The delegation is read-only and the client may not make changes to
        the directory other than by performing NFSv4.1 operations that modify
        the directory or the associated file attributes so that the server
        has knowledge of these changes. In order to keep the client's
        namespace synchronized with the server, the server will notify
        the delegation-holding client (assuming it has requested
        notifications) of the changes made as a result of that client's
        directory-modifying operations.  This is to avoid any need for
        that client to send subsequent GETATTR or READDIR operations
        to the server.  If a single client is holding the delegation
        and that client makes any changes to the directory (i.e., the
        changes are made via operations sent on a session
        associated with the client ID holding the delegation), the
        delegation will not be recalled. Multiple clients may hold a delegation
        on the same directory, but if any such client modifies the directory,
        the server MUST recall the delegation from the other clients,
        unless those clients have made provisions to be notified of that
        sort of modification.
      </t>
      <t>
        Delegations can be recalled by the server at any time.  Normally, the
        server will recall the delegation when the directory changes in a way
        that is not covered by the notification, or when the directory
        changes and notifications have not been requested.
        If another client removes the directory for
        which a delegation has been granted, the server will recall the
        delegation.
      </t>
    </section>
    <section title="Attributes in Support of Directory Notifications">
      <t>
       See <xref target="dir_not_attrs" /> for a description of the attributes
       associated with directory notifications.
      </t>
    </section>

    <section title="Directory Delegation Recall">
      <t>
        The server will recall the directory delegation by sending a callback
        to the client. It will use the same callback procedure as used for
        recalling file delegations. The server will recall the delegation
        when the directory changes in a way that is not covered by the
        notification. However, the server need not recall the delegation if
        attributes of an entry within the directory change.  
      </t>
      <t>
        If the
        server notices that handing out a delegation for a directory is
        causing too many notifications to be sent out, it may decide to
        not hand out delegations for that directory and/or recall those already
        granted.  If a client tries to remove the directory for which
        a delegation has been granted, the server will recall all associated delegations.
      </t>
      <t>
        The implementation sections for a number
        of operations describe situations in which notification or
        delegation recall would be required under some common circumstances.
        In this regard, a similar set of caveats to those listed
        in <xref target="deleg_and_cb" /> apply.
        <list style="symbols">
          <t>
            For CREATE, see <xref target="OP_CREATE_IMPLEMENTATION" />.
          </t>
          <t>
            For LINK, see <xref target="OP_LINK_IMPLEMENTATION" />.
          </t>
          <t>
            For OPEN, see <xref target="OP_OPEN_IMPLEMENTATION" />.
          </t>
          <t>
            For REMOVE, see <xref target="OP_REMOVE_IMPLEMENTATION" />.
          </t>
          <t>
            For RENAME, see <xref target="OP_RENAME_IMPLEMENTATION" />.
          </t>
          <t>
            For SETATTR, see <xref target="OP_SETATTR_IMPLEMENTATION" />.
          </t>
        </list>
      </t>
    </section>

    <section title="Directory Delegation Recovery">
      <t>
        Recovery from client or server restart for state on regular files
        has two main goals: avoiding the necessity of
        breaking application guarantees with respect to locked files and
        delivery of updates cached at the client.  Neither of these
        goals applies to directories protected by OPEN_DELEGATE_READ delegations and
        notifications. Thus, no provision is made for reclaiming
        directory delegations in the event of client or server restart.
        The client can simply establish a directory delegation in the
        same fashion as was done initially.
      </t>
    </section>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="multi_server_namespace" title="Multi-Server Namespace">
  <t>
    NFSv4.1 supports attributes that allow a namespace to extend
    beyond the boundaries of a single server.  It is RECOMMENDED
    that clients and servers support construction of such
    multi-server namespaces.  Use of such multi-server namespaces 
    is OPTIONAL, however, and for many purposes,
    single-server namespaces are perfectly acceptable.  Use of
    multi-server namespaces can provide many advantages, however, by
    separating a file system's logical position in a namespace from
    the (possibly changing) logistical and administrative
    considerations that result in particular file systems being
    located on particular servers.
  </t>
  <section anchor="location_attrs" title="Location Attributes">
    <t>
      NFSv4.1 contains RECOMMENDED attributes that allow file systems on
      one server to be associated with one or more instances of that
      file system on other servers.  These attributes specify such
      file system instances by specifying a server address
      target (either as a DNS name representing one or more IP
      addresses or as a literal IP address) together with the path 
      of that file system within the associated single-server namespace.
    </t>
    <t>
      The fs_locations_info RECOMMENDED attribute
      allows specification of one or more file system instance locations
      where the data corresponding to a given file
      system may be found.  This attribute provides to the client,
      in addition to
      information about file system instance locations,  
      significant information
      about the various file system instance choices (e.g., priority for 
      use, writability, currency, etc.).  It also includes information to
      help the client efficiently effect as seamless a transition
      as possible among multiple file system instances, when and if
      that should be necessary.
    </t>
    <t>
      The fs_locations RECOMMENDED
      attribute is inherited from NFSv4.0 and only allows specification 
      of the file system
      locations where the data corresponding to a given file
      system may be found.  Servers SHOULD make this attribute available
      whenever fs_locations_info is supported, but client use of 
      fs_locations_info is to be preferred.
    </t>
  </section>
  <section anchor="presence_or_absence" title="File System Presence or Absence">
    <t>
      A given location in an NFSv4.1 namespace (typically but not necessarily
      a multi-server namespace) can have a number of file system instance 
      locations
      associated with it (via the fs_locations or fs_locations_info
      attribute).  There may also be an actual current file system at 
      that location, accessible via normal namespace operations (e.g.,
      LOOKUP).  In this case, the file system is said to be 
      "present" at that position in the namespace, and clients will 
      typically use it, reserving use of additional locations 
      specified via the location-related attributes to situations in
      which the principal location is no longer available.
    </t>
    <t>
      When there is no actual file system at the namespace location
      in question, the file system is said to be "absent".  An absent
      file system contains no files or directories other than the
      root.  Any reference to it, except 
      to access a small set of attributes useful in determining
      alternate locations, will result in an error, NFS4ERR_MOVED.
      Note that if the server ever returns the error NFS4ERR_MOVED,
      it MUST support the fs_locations 
      attribute and SHOULD support the fs_locations_info and fs_status
      attributes.
    </t>
    <t>
      While the error name suggests that we have a case of a file system
      that once was present, and has only become absent later, this is 
      only one possibility.  A position in the namespace may be permanently
      absent with the set of file system(s) designated by the location 
      attributes being the only realization.  
      The name NFS4ERR_MOVED reflects an earlier,
      more limited conception of its function, but this error will be
      returned whenever the referenced file system is absent, whether it
      has moved or not.
    </t>
    <t>
      Except in the case of GETATTR-type operations (to be discussed 
      later), when the 
      current filehandle at the start of an operation is within an 
      absent file system, that operation is not performed and the error
      NFS4ERR_MOVED is returned, to indicate that the file system is
      absent on the current server.
    </t>
    <t>
      Because a GETFH cannot succeed if the current filehandle is
      within an absent file system, filehandles within an absent
      file system cannot be transferred to the client.  When a 
      client does have filehandles within an absent file system, it
      is the result of obtaining them when the file system was
      present, and having the file system become 
      absent subsequently.
    </t>
    <t>
      It should be noted that because the check for the current
      filehandle being within an absent file system happens at the
      start of every operation, operations that change the current
      filehandle so that it is within an absent file system will not
      result in an error.  This allows such combinations as 
      PUTFH-GETATTR and LOOKUP-GETATTR to be used to get attribute
      information, particularly location attribute information,
      as discussed below.
    </t>
    <t>
      The RECOMMENDED file system attribute fs_status 
      can be used to interrogate the present/absent status of a 
      given file system.
    </t>  
  </section>
  <section anchor="absent_fs_attributes" 
           title="Getting Attributes for an Absent File System">
    <t>
      When a file system is absent, most attributes are not available,
      but it is necessary to allow the client access to the small
      set of attributes that are available, and most particularly 
      those that give information about the correct current locations
      for this file system: fs_locations and fs_locations_info.
    </t>
    <section anchor="absent_getattr"
             title="GETATTR within an Absent File System">
      <t>
        As mentioned above, an exception is made for GETATTR in that
        attributes may be obtained for a filehandle within an absent
        file system.  This exception only applies if the attribute
        mask contains at least one attribute bit that indicates the
        client is interested in a result regarding an absent file
        system: fs_locations, fs_locations_info, or fs_status.
        If none of these attributes
        is requested, GETATTR will result in an NFS4ERR_MOVED error.
      </t>
      <t>
        When a GETATTR is done on an absent file system, the set of 
        supported attributes is very limited.  Many attributes, including
        those that are normally REQUIRED, will not be available on an
        absent file system.  In addition to the attributes mentioned
        above (fs_locations, fs_locations_info, fs_status), the following
        attributes SHOULD be available on absent file systems.  In the
        case of RECOMMENDED attributes, they should be available at
        least to the same degree that they are available on present file systems.
      </t>
      <t>
       <list style='hanging'>
        <t hangText="change_policy:">
          This attribute is useful for absent file systems
          and can be helpful in summarizing to the client when any
          of the location-related attributes change.
        </t>
        <t hangText="fsid:">
          This attribute should be provided so that the client
          can determine file system boundaries, including, in 
          particular, the boundary between present and absent file
          systems.  This value must be different from any other fsid
          on the current server and need have no particular relationship
          to fsids on any particular destination to which the client
          might be directed.
        </t>
        <t hangText="mounted_on_fileid:"> 
          For objects at the top of an absent
          file system, this attribute needs to be available.  Since
          the fileid is within the present parent file
          system, there should be no need to reference the absent file
          system to provide this information.
        </t>
       </list>
      </t>
      <t>
        Other attributes SHOULD NOT be made available for absent file
        systems, even when it is possible to provide them.  The server
        should not assume that more information is always better and
        should avoid gratuitously providing additional information.
      </t>
      <t>
        When a GETATTR operation includes a bit mask for one of the 
        attributes fs_locations, fs_locations_info, or fs_status, but
        where the bit mask includes attributes that are not supported,
        GETATTR will not return an error, but will return the mask
        of the actual attributes supported with the results.
      </t>
      <t>
        Handling of VERIFY/NVERIFY is similar to GETATTR in that if
        the attribute mask does not include fs_locations, fs_locations_info,
        or fs_status, the error NFS4ERR_MOVED will result.  It differs in
        that any appearance in the attribute mask of an attribute not 
        supported for an absent file system (and note that this will
        include some normally REQUIRED attributes) will also cause
        an NFS4ERR_MOVED result.
      </t>
    </section>
    <section anchor="absent_readdir"
             title="READDIR and Absent File Systems">
      <t>
        A READDIR performed when the current filehandle is within an
        absent file system will result in an NFS4ERR_MOVED error, 
        since, unlike the case of GETATTR, no such exception is
        made for READDIR.
      </t>
      <t>
        Attributes for an absent file system may be fetched via a
        READDIR for a directory in a present file system, when that
        directory contains the root directories of one or more absent
        file systems.  In this case, the handling is as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          If the attribute set requested includes one of the attributes
          fs_locations, fs_locations_info, or fs_status, then fetching of
          attributes proceeds normally and no NFS4ERR_MOVED indication
          is returned, even when the rdattr_error attribute is
          requested.
        </t>
        <t>
          If the attribute set requested does not include one of the 
          attributes
          fs_locations, fs_locations_info, or fs_status, then if the
          rdattr_error attribute is requested, each directory entry for
          the root of an absent file system will report 
          NFS4ERR_MOVED as the value of the rdattr_error attribute.
        </t>
        <t>
          If the attribute set requested does not include any of the 
          attributes fs_locations, fs_locations_info, fs_status, or
          rdattr_error, then the occurrence of the root of an absent
          file system within the directory will result in the
          READDIR failing with an NFS4ERR_MOVED error. 
        </t>
        <t>
          The unavailability of an attribute because of a file system's
          absence, even one that is ordinarily REQUIRED, does not result
          in any error indication.  The set of attributes returned for
          the root directory of the absent file system in that case is 
          simply restricted to those actually available.
        </t>
       </list>
      </t>
    </section>
  </section>
  <section anchor="location_uses" title="Uses of Location Information">
    <t>
      The location-bearing attributes (fs_locations and fs_locations_info),
      together with the possibility of absent file systems, provide
      a number of important facilities in providing reliable, manageable, 
      and scalable data access.
    </t>
    <t>
      When a file system is present, these attributes can provide  
      alternative locations, to be used to access the same data,
      in the event of server failures, communications problems, 
      or other difficulties that make continued access to the current
      file system impossible or otherwise impractical.
      Under some circumstances, multiple alternative locations
      may be used simultaneously to provide higher-performance 
      access to the file system in question.  
      Provision of
      such alternate locations is referred to as "replication"
      although there are cases in which replicated sets of data are
      not in fact present, and the replicas are instead different
      paths to the same data.  
    </t>
    <t>
      When a file system is present and becomes absent, clients can be
      given the opportunity to have continued access to their data,
      at an alternate location.  In this case, a continued attempt
      to use the data in the now-absent file system will result 
      in an NFS4ERR_MOVED error and, at that point, the successor 
      locations (typically only one although multiple choices are possible)
      can be fetched and used to continue access.  Transfer of the
      file system contents to the new location is referred to as 
      "migration", but it should be kept in mind that there are cases
      in which this term can be used, like "replication", when there 
      is no actual data migration per se.  
    </t>
    <t>
      Where a file system was not previously present, specification
      of file system location provides a means by which file systems
      located on one server can be associated with a namespace 
      defined by another server, thus allowing a general multi-server
      namespace facility.  A designation of such a location, in place
      of an absent file system, is called a "referral".
    </t>
    <t>
      Because client support for location-related attributes is 
      OPTIONAL, a server may (but is not required to) take action
      to hide migration and referral events from such clients, by
      acting as a proxy, for example.  The server can determine
      the presence of client support from the arguments of the 
      EXCHANGE_ID operation (see 
      <xref target="OP_EXCHANGE_ID_DESCRIPTION" />).
    </t>
    <section anchor="replication" title="File System Replication">
      <t>
        The fs_locations and fs_locations_info attributes provide
        alternative locations, to be used to access data in place
        of or in addition to 
        the current file system instance.  On first access to a
        file system, the client should obtain the value of the set
        of alternate locations by interrogating the fs_locations or
        fs_locations_info attribute, with the latter being preferred.
      </t>
      <t>
        In the event that server failures, communications problems, 
        or other difficulties make continued access to the current
        file system impossible or otherwise impractical, the client
        can use the alternate locations as a way to get continued 
        access to its data.  Depending on specific attributes of
        these alternate locations, as indicated within the
        fs_locations_info attribute, multiple locations may
        be used simultaneously, to provide higher performance 
        through the exploitation of multiple paths between client
        and target file system.  
      </t>
      <t>
        The alternate locations may be physical replicas of the
        (typically read-only) file system data, or they may
        reflect alternate paths to the same server or provide 
        for the use of various forms of server
        clustering in which multiple servers provide alternate 
        ways of accessing the same physical file system.  How these
        different modes of file system transition are represented 
        within the fs_locations and fs_locations_info attributes 
        and how the client deals with
        file system transition issues will be discussed in detail
        below.
      </t>
      <t>
        Multiple server addresses, whether they are derived from 
        a single entry with a DNS name representing a set of IP
        addresses or from multiple entries each with its own 
        server address, may correspond to the same actual
        server.  The fact that two addresses correspond to the
        same server is shown by a common so_major_id field
        within the eir_server_owner field returned by EXCHANGE_ID
        (see <xref target="OP_EXCHANGE_ID_DESCRIPTION" />).
        For a detailed discussion of how server address targets
        interact with the determination of server identity
        specified by the server owner field, see
        <xref target="loc_server_id" />.
      </t>
    </section>
    <section anchor="migration" title="File System Migration">
      <t>
        When a file system is present and becomes absent, clients can be
        given the opportunity to have continued access to their data,
        at an alternate location, as specified by the fs_locations or
        fs_locations_info attribute.  Typically, a client will be 
        accessing the file system in question, get an NFS4ERR_MOVED
        error, and then use the fs_locations or fs_locations_info
        attribute to determine the new location of the data.  When
        fs_locations_info is used, additional information will be
        available that will define the nature of the client's 
        handling of the transition to a new server.   
      </t>
      <t>
        Such migration can be helpful in providing 
        load balancing or general resource reallocation.  The protocol 
        does not specify how the file system will be moved between 
        servers.  It is anticipated that a number of different 
        server-to-server transfer mechanisms might be used with the
        choice left to the server implementor.  The NFSv4.1 protocol
        specifies the method used to communicate the migration
        event between client and server.
      </t>
      <t>
        The new location may be an alternate
        communication path to the same server or, in the case of
        various forms of server
        clustering, another server providing
        access to the same physical file system.  The client's 
        responsibilities in dealing with this transition depend on the
        specific nature of the new access path as well as how and whether data
        was in fact migrated.  These issues will be discussed in
        detail below.
      </t>
      <t>
        When multiple server addresses correspond to the same 
        actual server, as shown by a common value for the so_major_id field
        of the eir_server_owner field returned by EXCHANGE_ID, the location
        or locations may designate alternate server addresses in
        the form of specific server network addresses.  These can 
        be used to access
        the file system in question at those addresses
        and when it is no longer accessible at the original address. 
      </t>
      <t>
        Although a single successor location is typical, multiple 
        locations may be provided, together with information that
        allows priority among the choices to be indicated, via 
        information in the fs_locations_info attribute.  Where suitable,
        clustering mechanisms make it possible to provide multiple
        identical file systems or paths to them; this allows the client
        the opportunity to deal with any resource or communications
        issues that might limit data availability.
      </t>
      <t>
        When an alternate location is designated as the target for
        migration, it must designate the same data
        (with metadata being the same to the degree indicated by the
        fs_locations_info attribute).  Where file systems are writable,
        a change made on the original file system must be visible on
        all migration targets. Where a file system is not writable
        but represents a read-only copy (possibly periodically 
        updated) of
        a writable file system, similar requirements apply to the 
        propagation of updates.  Any change visible in the original
        file system must already be effected on all migration targets,
        to avoid any possibility that a client, in effecting a transition to 
        the migration target, will see any reversion in file system state.  
      </t>
    </section>
    <section anchor="referrals" title="Referrals">
      <t>
        Referrals provide a way of placing a file system in a location
        within the namespace
        essentially without respect to its physical location on a
        given server.  This allows a single server or a set of servers
        to present a multi-server namespace that encompasses file systems
        located on multiple servers.  Some likely uses of this include
        establishment of site-wide or organization-wide namespaces,
        or even knitting such together into a truly global namespace.
      </t>
      <t>
        Referrals occur when a client determines, upon first referencing
        a position in the current namespace, that it is part of a new 
        file system and that the file system is absent.  When this 
        occurs, typically by receiving the error NFS4ERR_MOVED, the
        actual location or locations of the file system can be 
        determined by fetching the fs_locations or fs_locations_info 
        attribute.
      </t>
      <t>
        The locations-related attribute may designate a single 
        file system location or multiple file system locations, to
        be selected based on the needs of the client.  The server,
        in the fs_locations_info attribute, may specify priorities to 
        be associated with various file system location choices.
        The server may assign different priorities to different
        locations as reported to individual clients, in order to
        adapt to client physical location or to effect load balancing.
        When both read-only and read-write file systems are present,
        some of the read-only locations might not be absolutely up-to-date
        (as they would have to be in the case of replication and
        migration).  Servers may also specify file system locations
        that include client-substituted variables so that different
        clients are referred to different file systems (with different
        data contents) based on client attributes such as CPU 
        architecture.
      </t>
      <t>
        When the fs_locations_info attribute indicates that there are
        multiple possible targets listed, the relationships among them
        may be important to the client in selecting which one to use.
        The same rules specified in <xref target="replication" />
        defining the appropriate standards for the data propagation
        apply to these multiple replicas as well.  For example, the
        client might prefer a writable target on a server that has additional writable
        replicas to which it subsequently might switch.  Note that,
        as distinguished from the case of replication, there is no
        need to deal with the case of propagation of updates made by
        the current client, since the current client has not accessed
        the file system in question.
      </t>
      <t>
        Use of multi-server namespaces is enabled by NFSv4.1 but is not
        required.  The use of multi-server namespaces and their scope
        will depend on the applications used and system administration
        preferences. 
      </t>
      <t>
        Multi-server namespaces can be established by a single 
        server providing a large set of referrals to all of the
        included file systems.  Alternatively, a single multi-server
        namespace may be administratively segmented with separate
        referral file systems (on separate servers) for each
        separately administered portion of the namespace. The
        top-level referral file system or any segment may use
        replicated referral file systems for higher availability.  
      </t>
      <t>
        Generally, multi-server namespaces are for the most part 
        uniform, in that the same data made available to one client
        at a given location in the namespace is made available to
        all clients at that location.  However, there are facilities
        provided that allow different clients to be directed to 
        different sets of data, so as to adapt to such client
        characteristics as CPU architecture.  
      </t>
    </section>
  </section>
  <section title="Location Entries and Server Identity"
           anchor="loc_server_id">
    <t>
      As mentioned above, a single location entry may have a server
      address target in the form of a DNS name that may represent 
      multiple IP addresses, while multiple location entries may have their 
      own server address targets that reference the same server.
      Whether two IP addresses designate the same server is
      indicated by the existence of a common so_major_id field
      within the eir_server_owner field returned by EXCHANGE_ID
      (see <xref target="OP_EXCHANGE_ID_DESCRIPTION" />), subject
      to further verification (for details see 
      <xref target="Trunking" />).
    </t>
    <t>
      When multiple addresses for the same server exist, the client 
      may assume that for each file system in the namespace of 
      a given server network address, there exist
      file systems at corresponding namespace locations for 
      each of the other server network addresses.
      It may do this even in the absence of 
      explicit listing in fs_locations and fs_locations_info.
      Such corresponding file system locations can be used as
      alternate locations, just as those explicitly specified via
      the fs_locations and fs_locations_info attributes.  Where
      these specific addresses are explicitly designated in the 
      fs_locations_info attribute, the conditions of use specified 
      in this attribute (e.g., priorities, specification of 
      simultaneous use) may limit the client's use of these 
      alternate locations. 
    </t>
    <t>
      If a single location entry designates multiple server IP
      addresses, the client cannot assume that these addresses
      are multiple paths to the same server.  In most cases, they 
      will be, but the client MUST verify that before acting on
      that assumption.  When two server addresses are designated
      by a single location entry and they correspond to different
      servers, this normally indicates some sort of misconfiguration,
      and so the client should avoid using such location entries
      when alternatives are available.  When they are not, 
      clients should pick one of IP addresses and use it,
      without using others that are not directed to the same 
      server.
    </t> 
  </section>
  <section title="Additional Client-Side Considerations">
    <t>
      When clients make use of servers that implement referrals,
      replication, and
      migration, care should be taken that a user who mounts a given
      file system that includes a referral or a relocated file system
      continues to see a coherent picture of that user-side file system
      despite the fact that it contains a number of server-side
      file systems that may be on different servers.
    </t>
    <t>
      One important issue is upward navigation from the root of a
      server-side file system to its parent (specified as ".." in UNIX),
      in the case in which it transitions to that file system as a
      result of referral, migration, or a transition as a result of
      replication.  When the client is at such a point, and it needs to ascend to
      the parent, it must go back to the parent as seen within the
      multi-server namespace rather than sending a LOOKUPP operation to the
      server, which would result in the parent within that server's
      single-server namespace.  In order to do this, the client
      needs to remember the filehandles that represent such
      file system roots and use these instead of sending a 
      LOOKUPP operation to the current server.  This will allow the client
      to present to applications a consistent namespace, where 
      upward navigation and downward navigation are consistent.
    </t>
    <t>
      Another issue concerns refresh of referral locations.  When
      referrals are used extensively, they may change as server
      configurations change.  It is expected that clients will cache
      information related to traversing referrals so that future
      client-side requests are resolved locally without server
      communication.
      This is usually rooted in client-side name look up caching. Clients
      should periodically purge this data for referral points in order to
      detect changes in location information.  When the change_policy
      attribute changes for directories that hold referral entries 
      or for the referral entries themselves, clients should consider 
      any associated
      cached referral information to be out of date.
    </t>
  </section>
  <section anchor="effecting_transitions" 
           title="Effecting File System Transitions">
    <t>
      Transitions between file system instances, whether due to
      switching between replicas upon server unavailability or 
      to server-initiated migration events, are best
      dealt with together.  This is so even though, for the server,
      pragmatic considerations will normally force different 
      implementation strategies for planned and unplanned transitions. 
      Even though the prototypical use cases
      of replication and migration contain distinctive sets of
      features, when all possibilities for these operations are
      considered, there is an underlying unity of these operations, 
      from the client's point of view, that makes treating
      them together desirable. 
    </t>
    <t>
      A number of methods are possible for servers to replicate data
      and to track client state in order to allow clients to transition
      between file system instances with a minimum of disruption.  Such
      methods vary between those that use inter-server clustering
      techniques to limit the changes seen by the client, to those that
      are less aggressive, use more standard methods of replicating
      data, and impose a greater burden on the client to adapt to 
      the transition.      
    </t>
    <t>
      The NFSv4.1 protocol does not impose choices on clients and
      servers with regard to that spectrum of transition methods.  In
      fact, there are many valid choices, depending on client and
      application requirements and their interaction with server 
      implementation choices.  The NFSv4.1 protocol does define the
      specific choices that can be made, how these choices are 
      communicated to the client, and how the client is to deal with
      any discontinuities.
    </t>
    <t>
      In the sections below, references will be made to various possible
      server implementation choices as a way of illustrating the transition
      scenarios that clients may deal with.  The intent here is not to
      define or limit server implementations but rather to illustrate
      the range of issues that clients may face.
    </t>
    <t>
      In the discussion below, references will be made to a file system
      having a particular property or to two file systems
      (typically the source and destination) belonging to a common
      class of any of several types.  Two file systems that belong to
      such a class share some important aspects of file system behavior
      that clients may depend upon when present, to easily effect a
      seamless transition between file system instances.  Conversely,
      where the file systems do not belong to such a common class, the
      client has to deal with various sorts of implementation 
      discontinuities that may cause performance or other issues in
      effecting a transition.
    </t> 
    <t>
      Where the fs_locations_info attribute is available, such file system
      classification data will be made directly available to the client
      (see <xref target='fs_locations_info' /> for details).  When only
      fs_locations is available, default assumptions with regard to
      such classifications have to be inferred
      (see <xref target='fs_locations' /> for details).
    </t>
    <t>
      In cases in which one server is expected to
      accept opaque values from the client that originated
      from another server, the servers SHOULD
      encode the "opaque" values in big-endian
      byte order.
      If this is done, servers acting as replicas or immigrating 
      file systems will
      be able to parse values like stateids, directory cookies,
      filehandles, etc., even if their native byte order is different from
      that of other servers cooperating in the replication and migration 
      of the
      file system.
    </t>
    <section anchor="transition_summary"
             title="File System Transitions and Simultaneous Access">
      <t>
        When a single file system may be accessed at multiple locations,
        either because of an indication of file system identity
        as reported by the fs_locations or fs_locations_info 
        attributes or because two file system instances have corresponding 
        locations on server addresses that connect to the same server
        (as indicated by a common so_major_id field in the eir_server_owner
        field returned by EXCHANGE_ID), the client
        will, depending on specific circumstances as discussed below,
        either:
      </t>
      <t>
       <list style='symbols'>
        <t>
          Access multiple instances simultaneously, each of which
          represents an alternate path to the same data and metadata. 
        </t>
        <t>
          Access one instance (or set of instances) and then
          transition to an alternative instance (or set of instances) 
          as a result of network issues, server unresponsiveness, or
          server-directed migration.  The transition may involve changes
          in filehandles, fileids, the change attribute, and/or locking
          state, depending on the attributes of the source and 
          destination file system instances, as specified in the
          fs_locations_info attribute. 
        </t>
       </list>
      </t>
      <t>
        Which of these choices is possible, and how a transition is 
        effected, is governed by equivalence classes of file system
        instances as reported by the fs_locations_info attribute,
        and for file system instances in the same location within
        a multi-homed single-server namespace, as indicated by the 
        value of the so_major_id field of the eir_server_owner field
        returned by EXCHANGE_ID.
      </t>
    </section>
    <section anchor="simultaneous_transparent" 
             title="Simultaneous Use and Transparent Transitions">
      <t>
        When two file system instances have the same location within
        their respective single-server namespaces and those two server 
        network addresses designate the same server (as indicated by
        the same value of the so_major_id field of the
        eir_server_owner field returned 
        in response to EXCHANGE_ID), those file system instances can 
        be treated as the same, and either used together simultaneously
        or serially with no transition activity required on the part of
        the client.  In this case, we refer to the transition as
        "transparent", and the client in transferring access from one
        to the other is acting as it would in the event that communication
        is interrupted, with a new connection and possibly a new session
        being established to continue access to the same file system.
      </t>
      <t>
        Whether simultaneous use of the two file system instances is
        valid is controlled by whether the 
        fs_locations_info attribute shows the two instances as having
        the same simultaneous-use class.
        See <xref target="fs_locations_server4" /> for information
        about the definition of the various use classes, including
        the simultaneous-use class.
      </t>
      <t>
        Note that for two such file systems,
        any information within the fs_locations_info
        attribute that indicates the need for special transition activity,
        i.e., the appearance of the two file system instances with different
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes, indicates a serious
        problem. The client, if it allows transition to the file system
        instance at all, must not treat this as a transparent transition.
        The server SHOULD NOT indicate that these instances
        belong to different 
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes, whether or not the two
        instances are shown belonging to the same 
        simultaneous-use class.
      </t>
      <t>
        Where these conditions do not apply, a non-transparent file
        system instance transition is required with the details 
        depending on the respective  
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes of the two 
        file system instances, and whether the two servers' addresses in
        question have the same eir_server_scope value as reported by
        EXCHANGE_ID.
      </t>
      <section anchor="simultaneous_use" 
               title="Simultaneous Use of File System Instances">
        <t>
          When the conditions in <xref target="simultaneous_transparent" />
          hold, 
          in either of the following two cases, the client may use the 
          two file system instances simultaneously.
         <list style='symbols'>
          <t>
            The fs_locations_info attribute does not contain separate
            per-network-address entries for file system instances at 
            the distinct network addresses.  This
            includes the case in which the fs_locations_info attribute is 
            unavailable.  In this case, the fact that the two server 
            addresses connect to the same server (as indicated by the
            two addresses sharing the same the so_major_id value 
            and subsequently confirmed as described in 
            <xref target="Trunking" />) justifies
            simultaneous use, and there is no fs_locations_info
            attribute information contradicting that.
          </t>
          <t>
            The fs_locations_info attribute indicates that two file system
            instances belong to the same simultaneous-use class.
          </t>
         </list>
        </t>
        <t>
          In this case, the client may use both file system instances 
          simultaneously, as representations of the same file system,
          whether that happens because the two network addresses connect to
          the same physical server or because different servers connect to 
          clustered file systems and export their data in common.  When
          simultaneous use is in effect, any change made to one file 
          system instance must be immediately reflected in the other
          file system instance(s).  Locks are treated as part of a
          common lease, associated with a common client ID.  Depending 
          on the details of the eir_server_owner returned by EXCHANGE_ID,
          the two server instances may be accessed by different sessions
          or a single session in common.
        </t>
      </section>
      <section anchor="transparent_transitions" 
               title="Transparent File System Transitions">
        <t>
          When the conditions in <xref target="simultaneous_use" /> hold
          and the fs_locations_info 
          attribute explicitly shows the file system instances for
          these distinct network addresses as belonging to different
          simultaneous-use classes,
          the file system instances should not be used by the client
          simultaneously.  Rather, they should be used serially with one being used
          unless and until communication difficulties, 
          lack of responsiveness,
          or an explicit migration event causes another file
          system instance (or set of file system instances sharing a
          common simultaneous-use class)
          to be used.
        </t>
        <t>
          When a change of file system instance is to be done, the
          client will use the same client ID already in effect.  If
          the client already has connections to the new server address, these
          will be used.  Otherwise, new connections to existing sessions
          or new sessions associated with the existing client ID 
          are established as indicated by the eir_server_owner returned by 
          EXCHANGE_ID.
        </t> 
        <t>
          In all such transparent transition cases, the following apply:
        </t>
        <t>
         <list style='symbols'>
          <t>
	    If filehandles are persistent, they stay the
	    same. If filehandles are volatile, they either
	    stay the same or expire, but the reason for
            expiration is not due to the file system transition.
          </t>
          <t>
            Fileid values do not change across the transition.
          </t>
          <t>
            The file system will have the same fsid in both the old and new
            locations.
          </t>
          <t>
            Change attribute values are consistent across the transition
            and do not have to be refetched.  When change attributes
            indicate that a cached object is still valid, it can remain
            cached.  
          </t>
          <t>
            Client and state identifiers retain their validity
            across the transition, except where their staleness is
            recognized and reported by the new server.  Except where 
            such staleness requires it, no lock reclamation is needed.
            Any such staleness is an indication that the server should
            be considered to have restarted and is reported as discussed
            in <xref target="server_failure" />.
          </t>
          <t>
            Write verifiers are presumed to retain their validity and
            can be used to compare with verifiers returned by COMMIT on
            the new server.
            If COMMIT on the new server returns an identical verifier,
            then it is expected that the new server has all of the data
            that was written unstably to the original server
            and has committed that data to stable storage as requested.

          </t>
          <t>
            Readdir cookies are presumed to retain their validity
            and can be presented to subsequent READDIR requests together
            with the readdir verifier with which they are associated.
            When the verifier is accepted as valid, the cookie will
            continue the READDIR operation so that the entire directory
            can be obtained by the client.
          </t>
         </list>
        </t>
      </section>
    </section>
    <section anchor="transition_handles"
             title="Filehandles and File System Transitions">
      <t>
        There are a number of ways in which filehandles can be handled
        across a file system transition.  These can be divided into 
        two broad classes depending upon whether the two file systems
        across which the transition happens share sufficient state to
        effect some sort of continuity of file system handling.
      </t>
      <t>
        When there is no such cooperation in filehandle assignment,
        the two file systems are reported as being in different 
        handle classes.  In this case,
        all filehandles are assumed to expire as part of the 
        file system transition.  Note that this behavior does not
        depend on the fh_expire_type attribute and supersedes the specification
        of the FH4_VOL_MIGRATION bit, which only affects behavior when
        fs_locations_info is not available.
      </t>
      <t>
        When there is cooperation in filehandle assignment,
        the two file systems are reported as being in the same
        handle classes.  In this case,
        persistent filehandles remain valid after the file system
        transition, while volatile filehandles (excluding those 
        that are only volatile due to the FH4_VOL_MIGRATION bit) are 
        subject to expiration on the target server.
      </t>
    </section>
    <section anchor="transition_fileid"
             title="Fileids and File System Transitions">
      <t>
        In NFSv4.0, the issue of continuity of fileids in the event
        of a file system transition was not addressed.  The general 
        expectation had been that in situations in
        which the two file system instances are created by a single vendor
        using some sort of file system image copy, fileids will be
        consistent across the transition, while in the analogous 
        multi-vendor transitions they will not.  This poses difficulties, 
        especially for the client without special knowledge  
        of the transition mechanisms adopted by the server.  Note
        that although fileid is not a REQUIRED attribute, many servers
        support fileids and many clients provide APIs that depend on fileids.
      </t>
      <t>
        It is important to note that while clients themselves may have no
        trouble with a fileid changing as a result of a file system
        transition event, applications do typically have access to the
        fileid (e.g., via stat).  The result is that an
        application may work perfectly well if there is no file system
        instance transition or if any such transition is among instances
        created by a single vendor, yet be unable to deal with the
        situation in which a multi-vendor transition occurs at the wrong
        time.
      </t>
      <t>
        Providing the same fileids in a multi-vendor (multiple server
        vendors) environment has generally been held to be quite difficult.
        While there is work to be done, it needs to be pointed out that
        this difficulty is partly self-imposed.  Servers have typically
        identified fileid with inode number, i.e. with a quantity used to
        find the file in question.  This identification poses special
        difficulties for migration of a file system between vendors
        where assigning
        the same index to a given file may not be possible.  Note here that
        a fileid is not required to be useful to find the file in
        question, only that it is unique within the given file system.  Servers
        prepared to accept a fileid as a single piece of metadata and store
        it apart from the value used to index the file information can
        relatively easily maintain a fileid value across a migration event,
        allowing a truly transparent migration event.
      </t>
      <t>
        In any case, where servers can provide continuity of fileids, they
        should, and the client should be able to find out that such
        continuity is available and take appropriate action.  Information
        about the continuity (or lack thereof) of fileids across a file
        system transition is represented by specifying whether the file systems 
        in question are of the same fileid class.
      </t>
      <t>
        Note that when consistent fileids do not exist across a 
        transition (either because there is no continuity of fileids
        or because fileid is not a supported attribute on one of 
        instances involved), and there are
        no reliable filehandles across a transition event (either because
        there is no filehandle continuity or because the filehandles are
        volatile), the client is in a position where it cannot verify
        that files it was accessing before the transition are the 
        same objects.  It is forced to assume that no object has been 
        renamed, and, unless there are guarantees that provide this
        (e.g., the file system is read-only), problems for applications
        may occur.  Therefore, use of such configurations should be 
        limited to situations where the problems that this may cause
        can be tolerated.
      </t>
    </section>
    <section anchor="transition_fsid"
             title="Fsids and File System Transitions">
      <t>
        Since fsids are generally only unique within a per-server basis,
        it is likely that they will change during a file system
        transition.  One exception is the case of transparent transitions,
        but in that case we have multiple network addresses that are
        defined as the same server (as specified by a common value of
        the so_major_id field of eir_server_owner).
        Clients should not make the fsids received
        from the server visible to applications since they may not be
        globally unique, and because they may change during a file
        system transition event.  Applications are best served if they
        are isolated from such transitions to the extent possible.
      </t>
      <t>
        Although normally a single source file system will transition
        to a single target file system, there is a provision for splitting
        a single source file system into multiple target file systems, by
        specifying the FSLI4F_MULTI_FS flag.
      </t>
      <section anchor="transition_fsid_split"
               title="File System Splitting">
        <t>
          When a file system transition is made and the fs_locations_info
          indicates that the file system in question may be split into 
          multiple file systems (via the FSLI4F_MULTI_FS flag), the client 
          SHOULD do GETATTRs to determine the fsid attribute on all known 
          objects within the file system undergoing transition to determine 
          the new file system boundaries.  
        </t>
        <t>
          Clients may maintain the fsids passed to existing applications 
          by mapping all of the fsids for the descendant file systems to 
          the common fsid used for the original file system.  
        </t> 
        <t>
          Splitting a file system may be done on a transition between
          file systems of the same fileid 
          class, since the fact that fileids are unique within the
          source file system ensure they will be unique in each of the
          target file systems.
        </t>
      </section>
    </section>
    <section anchor="transition_change"
             title= "The Change Attribute and File System Transitions">
      <t>
        Since the change attribute is defined as a server-specific one,
        change attributes fetched from one server are normally presumed to 
        be invalid on another server.  Such a presumption is troublesome
        since it would invalidate all cached change attributes, requiring
        refetching.  Even more disruptive, the absence of any assured
        continuity for the change attribute means that even if the same
        value is retrieved on refetch, no conclusions can be drawn as to whether
        the object in question has changed.  The identical change 
        attribute could be merely an artifact of a modified file with
        a different change attribute construction algorithm, with that
        new algorithm just happening to result in an identical change 
        value.
      </t>
      <t>
        When the two file systems have consistent change attribute formats,
        and this fact is communicated to the client by reporting 
        in the same change class, the 
        client may assume a continuity of change attribute construction
        and handle this situation just as it would be handled without
        any file system transition.
      </t>
    </section>
    <section anchor="transition_state"
             title="Lock State and File System Transitions">
      <t>
        In a file system transition, the client needs to handle cases
        in which the two servers have cooperated in state management
        and in which they have not.  Cooperation by two servers in
        state management requires coordination of client IDs.
        Before the client
        attempts to use a client ID associated with one
        server in a request to the server of the other file system,
        it must eliminate the possibility that
        two non-cooperating servers have assigned the same client ID
        by accident. The client needs to compare
        the eir_server_scope values returned by each server. If
        the scope values do not match, then the servers have not
        cooperated in state management. If the scope values match,
        then this indicates the servers have cooperated in assigning
        client IDs to the point that they will reject client IDs that
        refer to state they do not know about.  See 
        <xref target="Server Scope" /> for more information about
        the use of server scope.
      </t>
      <t>
        In the case of migration, the servers involved in the 
        migration of a file system SHOULD transfer all server state 
        from the original to the new server.  When this is done, 
        it must be done in a way that is transparent to the client.  
        With replication, such a degree of common state is 
        typically not the case.  Clients, however, should use 
        the information provided by the eir_server_scope 
        returned by EXCHANGE_ID (as modified by the validation 
        procedures described in <xref target="Server Scope" />)
        to determine whether such sharing may be in effect, rather
        than making assumptions based on the reason for the transition.
      </t>
      <t>
        This state transfer will reduce disruption to the client
        when a file system transition occurs.
        If the servers are successful in
        transferring all state, the client can attempt to establish
        sessions associated with the client ID used for the source
        file system instance.  If the server accepts that as a valid 
        client ID, then the client may use the existing stateids
        associated with that client ID for the old file system instance
        in connection with that same client ID in connection with
        the transitioned file system instance.  If the client in 
        question already had a client ID on the target system, it
        may interrogate the stateid values from the source system
        under that new client ID, with the assurance that if they
        are accepted as valid, then they represent validly transferred
        lock state for the source file system, which has been transferred to the
        target server.
      </t>
      <t>
        When the two servers belong to the same 
        server scope, it does not mean that when 
        dealing with the transition, the client will not have to reclaim
        state.  However, it does mean that the client may proceed using
        its current client ID when establishing communication with the 
        new server, and the new server will either recognize the
        client ID as valid or reject it, in which case locks must be
        reclaimed by the client.
      </t>
      <t>
        File systems cooperating in state management may actually
        share state or simply divide the identifier space so as to recognize
        (and reject as stale) each other's stateids and client IDs.
        Servers that do share state may not do so under all conditions
        or at all times.   If the server
        cannot be sure when accepting a client ID that it reflects the locks
        the client was given, the server must treat all associated state as 
        stale and report it as such to the client.
      </t>
      <t>
        When the two file system instances are on servers that do 
        not share a server scope value, the client must
        establish a new client ID on the destination, if it does not
        have one already, and reclaim locks if allowed by the server.  
        In this case, old stateids and client IDs should
        not be presented to the new server since there is no assurance
        that they will not conflict with IDs valid on that server.
        Note that in this case, lock reclaim may be attempted even
        when the servers involved in the transfer have different
        server scope values (see <xref target="reclaim_locks" />      
        for the contrary case of reclaim after server reboot).
        Servers with different server scope values may cooperate
        to allow reclaim for locks associated with the transfer of
        a file system even if they do not cooperate sufficiently 
        to share a server scope.
      </t>
      <t>
        In either case, when actual locks are not known to be maintained,
        the destination server may establish a grace period specific to
        the given file system, with non-reclaim locks being rejected for
        that file system, even though normal locks are being granted
        for other file systems.  Clients should not infer the absence of
        a grace period for file systems being transitioned to a server
        from responses to requests for other file systems. 
      </t>
      <t>
        In the case of lock reclamation for a given file system after
        a file system transition, edge conditions can arise similar to
        those for reclaim after server restart (although in the case of
        the planned state transfer associated with migration, these can
        be avoided by securely recording lock state as part of state 
        migration).  Unless the destination server can guarantee that
        locks will not be incorrectly granted, the destination server
        should not allow lock reclaims and should avoid establishing a grace
        period.  
      </t>
      <t>
        Once all locks have been reclaimed, or there were no locks to 
        reclaim, the client indicates that there are no more reclaims
        to be done for the file system in question by sending a 
        RECLAIM_COMPLETE operation with the rca_one_fs parameter set
        to true.  Once this has been done, non-reclaim locking operations
        may be done, and any subsequent request to do reclaims will
        be rejected with the error NFS4ERR_NO_GRACE. 
      </t>
      <t>
        Information about client identity may be propagated between
        servers in the form of client_owner4 and associated verifiers,
        under the assumption that the client presents the same values to
        all the servers with which it deals.  
      </t>
      <t>
        Servers are encouraged to provide facilities to allow locks
        to be reclaimed on the new server after a file system 
        transition.  Often, however, in cases in which the two
        servers do not share a server scope value,
        such facilities may not be available
        and the client should be prepared to re-obtain locks, even
        though it is possible that the client may have its LOCK
        or OPEN request denied due to a conflicting lock.
      </t>
      <t>
        The consequences of having no facilities available to 
        reclaim locks on the new server will depend on the type
        of environment.  In  
        some environments, such as the transition between read-only
        file systems, such denial of locks should not pose large 
        difficulties in practice.  When an attempt to
        re-establish a lock on a new server is denied, the client should
        treat the situation as if its original lock had been revoked.
        Note that when the lock is granted, the client cannot
        assume that no conflicting lock could have been granted in the
        interim.  Where change attribute continuity is present, the
        client may check the change attribute to check for unwanted
        file modifications.  Where even this is not available, and
        the file system is not read-only, a client may reasonably treat 
        all pending locks as having been revoked.
      </t>
      <section anchor="transferred_lease"
               title="Leases and File System Transitions">
        <t>
          In the case of lease renewal, the client may not be 
          submitting requests for a file system that has been transferred 
          to another server.  This can occur 
          because of the lease renewal mechanism.  The
          client renews the lease associated with all file systems 
          when submitting 
          a request on an associated session, regardless of the 
          specific file system being referenced.
        </t>
        <t>
          In order for the client to schedule renewal of its lease
          where there is locking state that may have been relocated 
          to the new server, the client 
          must find out about lease relocation before that lease
          expire.  To accomplish this, the SEQUENCE operation will
          return the status bit SEQ4_STATUS_LEASE_MOVED
          if responsibility for any of the renewed locking state 
          has been transferred to a new server.  This 
          will continue until the client receives an 
          NFS4ERR_MOVED error for each of the file systems for which
          there has been locking state relocation.
        </t>
        <t>
          When a client receives an SEQ4_STATUS_LEASE_MOVED indication from
          a server, for each file system of the server for which the client
          has locking state, the client should perform an operation.
          For simplicity, the client may choose to reference
          all file systems, but what is important
          is that it must reference all file systems for which there was
          locking state where that state has moved.  Once the client
          receives an NFS4ERR_MOVED error for each such file system,
          the server will clear the SEQ4_STATUS_LEASE_MOVED indication.
          The client can terminate the process of checking file systems
          once this indication is cleared (but only if the client
          has received a reply for all outstanding SEQUENCE requests
          on all sessions it has with the server), since there are no others
          for which locking state has moved.
        </t>
        <t>
          A client may use GETATTR of the fs_status 
          (or fs_locations_info) attribute on all of the file systems
          to get absence indications in a single (or a few) request(s),
          since absent file systems will not cause an error in this
          context.  However, it still must do an operation that 
          receives NFS4ERR_MOVED on each file system, in order to clear
          the SEQ4_STATUS_LEASE_MOVED indication.
        </t>
        <t>
          Once the set of file systems with transferred locking state
          has been determined, the client can follow the normal process 
          to obtain the new server information (through the 
          fs_locations and fs_locations_info attributes) and perform renewal
          of that lease on the new server, unless information in the
          fs_locations_info attribute shows that no state could have
          been transferred.  If the server has not 
          had state transferred to it transparently, the client 
          will receive NFS4ERR_STALE_CLIENTID 
          from the new server,
          as described above, and the client can then reclaim 
          locks 
          as is done in the event of server failure.
        </t>
      </section>
      <section anchor="transition_lease_time"
               title="Transitions and the Lease_time Attribute">
        <t>
          In order that the client may appropriately manage its lease
          in the case of a file system transition, the destination server must 
          establish proper values for the lease_time attribute.
        </t>
        <t>
          When state is transferred transparently, that state 
          should include the correct value of the lease_time 
          attribute.  The lease_time attribute on the destination 
          server must never be less than that on the source, since 
          this would result in premature expiration of a lease
          granted by the source server.  Upon transitions in which 
          state is transferred transparently, the client is under 
          no obligation to refetch the lease_time attribute and 
          may continue to use the value
          previously fetched (on the source server).
        </t>
        <t>
          If state has not been transferred transparently, either
          because the associated servers are shown as having different
          eir_server_scope strings or because the client ID 
          is rejected when presented to the new server,
          the client should fetch the value
          of lease_time on the new (i.e., destination) server, and 
          use it for subsequent locking requests.  However, the server 
          must respect a grace
          period of at least as long as the lease_time on the source 
          server, in order to ensure that clients have ample time to 
          reclaim their lock before potentially conflicting 
          non-reclaimed locks are granted.  
       </t>
     </section>
    </section>
    <section anchor="transition_verifier"
             title="Write Verifiers and File System Transitions">
      <t>
        In a file system transition, the two file systems may be
        clustered in the handling of unstably written data.  
        When this is the
        case, and the two file systems belong to the same
        write-verifier class, write
        verifiers returned
        from one system may be compared to those returned  by the 
        other and superfluous
        writes avoided.  
      </t>
      <t>
        When two file systems belong to different 
        write-verifier classes, any verifier
        generated by one must not be compared to one provided by the 
        other.  Instead, it should be treated as not equal even when
        the values are identical.
      </t>
    </section>
    <section anchor="transition_readdir"
             title="Readdir Cookies and Verifiers and File System Transitions">
      <t>
        In a file system transition, the two file systems may be
        consistent in their handling of READDIR cookies and verifiers.
        When this is the
        case, and the two file systems belong to the same
        readdir class, READDIR
        cookies and verifiers
        from one system may be recognized by the other and 
        READDIR operations started on one server may be validly
        continued on the other, simply by presenting the 
        cookie and verifier returned by a READDIR operation done
        on the first file system to the second.
      </t>
      <t>
        When two file systems belong to different 
        readdir classes, any READDIR
        cookie and verifier
        generated by one is not valid on the second, and must not
        be presented to that server by the client.  The client 
        should act as if the verifier was rejected.
      </t>
    </section>
    <section anchor="transition_data"
             title="File System Data and File System Transitions">
      <t>
        When multiple replicas exist and are used simultaneously or in
        succession by a client, applications using them will normally expect
        that they contain either the same data or data that is consistent with
        the normal sorts of changes that are made by other clients
        updating the data of the file system
        (with metadata being the same to the degree indicated by the
        fs_locations_info attribute).  However, when multiple file systems are 
        presented as replicas of one another, the precise relationship 
        between the data of one and the data of another is not, as a 
        general matter, specified by the NFSv4.1 protocol.  It is quite 
        possible to present as replicas file systems where the data of 
        those file systems is sufficiently different that some applications 
        have problems dealing with the transition between replicas.  The 
        namespace will typically be constructed so that applications can 
        choose an appropriate level of support, so that in one position in 
        the namespace a varied set of replicas will be listed, while in 
        another only those that are up-to-date may be considered replicas.  
        The protocol does define four special cases of the relationship among 
        replicas to be specified by the server and relied upon by clients:

        <list style='symbols'>
          <t>
            When multiple server addresses correspond to the same actual 
            server, as indicated by a common so_major_id field within 
            the eir_server_owner field returned by EXCHANGE_ID, the 
            client may depend on the fact 
            that changes to data, metadata, 
            or locks made on one file system are immediately reflected 
            on others.
          </t>
          <t>
            When multiple replicas exist and are used simultaneously
            by a client (see the FSLIB4_CLSIMUL definition within
            fs_locations_info), they must designate the same
            data. Where file systems are writable, a change made on
            one instance must be visible on all instances, immediately
            upon the earlier of the return of the modifying requester
            or the visibility of that change on any of the associated
            replicas.  This allows a client to use these replicas
            simultaneously without any special adaptation to the fact
            that there are multiple replicas.  In this case, locks
            (whether share reservations or byte-range locks) and delegations obtained on one
            replica are immediately reflected on all replicas, even
            though these locks will be managed under a set of client
            IDs.
          </t>
          <t>
            When one replica is designated as the successor instance to another
            existing instance after return NFS4ERR_MOVED (i.e., the case of 
            migration), the client may depend on the fact that all changes
            written to stable storage on the original instance
            are written to stable storage of the successor (uncommitted writes are dealt with in 
            <xref target="transition_verifier" />).
          </t>
          <t>
            Where a file system is not writable but represents a read-only 
            copy (possibly periodically updated) of a writable file system, 
            clients have similar requirements with regard to the propagation 
            of updates.  They may need a guarantee that any change visible on 
            the original file system instance must be immediately visible on 
            any replica before the client transitions access to that replica, 
            in order to 
            avoid any possibility that a client, in effecting a transition to a
            replica, will see any reversion in file system state.  The specific
            means of this guarantee varies based on the value of
            the fss_type field that is
            reported as part of the fs_status attribute (see 
            <xref target="fs_status" />).  Since these file systems are presumed 
            to be  
            unsuitable for simultaneous use, there is no specification of how 
            locking is handled; in general, locks obtained on one file
            system will be separate from those on others.  
            Since these are going to be read-only file systems, this is not 
            expected to pose an issue for clients or applications.
          </t>
        </list>
      </t>
    </section>
  </section>
  <section anchor="effecting_referrals" 
           title="Effecting File System Referrals">
    <t>
      Referrals are effected when an absent file system is encountered
      and one or more alternate locations are made available by the
      fs_locations or fs_locations_info attributes.  The client will
      typically get an NFS4ERR_MOVED error, fetch the appropriate 
      location information, and proceed to access the file system on
      a different server, even though it retains its logical position
      within the original namespace.  Referrals differ from migration
      events in that they happen only when the client has not 
      previously referenced the file system in question (so there
      is nothing to transition).  Referrals can only come into 
      effect when an absent file system is encountered at its
      root.
    </t>
    <t>
      The examples given in the sections below are somewhat artificial in
      that an actual client will not typically do a multi-component
      look up, but will have cached information regarding the upper levels
      of the name hierarchy.  However, these example are chosen to make
      the required behavior clear and easy to put within the scope of a
      small number of requests, without getting unduly into details of
      how specific clients might choose to cache things.
    </t>
    <section anchor="referrals_lookup" 
             title="Referral Example (LOOKUP)">
      <t>
        Let us suppose that the following COMPOUND is sent in an
        environment in which /this/is/the/path is absent from the
        target server.  This may be for a number of reasons.  It may 
        be that the file system has moved, or it may be that
        the target server is functioning mainly, or solely, to refer
        clients to the servers on which various file systems are located.
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          LOOKUP "path"
        </t>
        <t>
          GETFH
        </t>
        <t>
          GETATTR (fsid, fileid, size, time_modify)
        </t>
       </list>
      </t>
      <t>
        Under the given circumstances, the following will be the result.
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is now the root of 
          the pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK.  The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the 
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "path" --> NFS_OK.  The current fh is for 
          /this/is/the/path and is within a new, absent file system, but ...
          the client will never see the value of that fh.
        </t>
        <t>
          GETFH --> NFS4ERR_MOVED.
          Fails because current fh is in an absent file system at the start of
          the operation, and the specification makes no exception for GETFH.
        </t>
        <t>
          GETATTR (fsid, fileid, size, time_modify).
          Not executed because the failure of the GETFH stops processing
          of the COMPOUND.
        </t>
       </list>
      </t>
      <t>
        Given the failure of the GETFH, the client has the job of
        determining the root of the absent file system and where to find
        that file system, i.e., the server and path relative to that
        server's root fh.  Note that in this example, the client did
        not obtain filehandles and attribute information (e.g., fsid) for
        the intermediate directories, so that it would not be sure where
        the absent file system starts.  It could be the case, for example,
        that /this/is/the is the root of the moved file system and that
        the reason that the look up of "path" succeeded is that the
        file system was not absent on that operation but was moved between the last
        LOOKUP and the GETFH (since COMPOUND is not atomic).  Even if we
        had the fsids for all of the intermediate directories, we could
        have no way of knowing that /this/is/the/path was the root of a
        new file system, since we don't yet have its fsid.
      </t>
      <t>
        In order to get the necessary information, let us re-send the
        chain of LOOKUPs with GETFHs and GETATTRs to at least get the
        fsids so we can be sure where the appropriate file system boundaries are.
        The client could choose to get fs_locations_info 
        at the same time but in
        most cases the client will have a good guess as to where file system
        boundaries are (because of where NFS4ERR_MOVED was, and was not,
        received) making fetching of fs_locations_info unnecessary.
      </t>
      <t>
       <list style='hanging'>
        <t hangText='OP01:'>
          PUTROOTFH  --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is root of pseudo-fs.
        </t>
        <t hangText='OP02:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Just for completeness.  Normally, clients will know the fsid
          of the pseudo-fs as soon as they establish communication with
          a server.
        </t>
        <t hangText='OP03:'>
          LOOKUP "this" --> NFS_OK
        </t>
        <t hangText='OP04:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP05:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this and is within pseudo-fs.
        </t>
        <t hangText='OP06:'>
          LOOKUP "is" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is and is within pseudo-fs.
        </t>
        <t hangText='OP07:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP08:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is and is within pseudo-fs.
        </t>
        <t hangText='OP09:'>
          LOOKUP "the" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the and is within pseudo-fs.
        </t>
        <t hangText='OP10:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP11:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the and is within pseudo-fs.
        </t>
        <t hangText='OP12:'>
          LOOKUP "path" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the/path and is within a new,
          absent file system, but ...
        </t>
        <t hangText='- '>
          The client will never see the value of that fh.
        </t>
        <t hangText='OP13:'>
          GETATTR(fsid, fs_locations_info)  --> NFS_OK
        </t>
        <t hangText='- '>
          We are getting the fsid to know where the file system boundaries are.
          In this operation, the fsid will be different than that of the
          parent directory (which in turn was retrieved in OP10).
          Note that the fsid we are given will not necessarily be preserved at the new
          location.  That fsid might be different, and in fact the fsid
          we have for this file system might be a valid fsid of a different 
          file system on that new server.
        </t>
        <t hangText='- '>
          In this particular case, we are pretty sure anyway that what
          has moved is /this/is/the/path rather than /this/is/the
          since we have the fsid of the latter and it is that of the
          pseudo-fs, which presumably cannot move.  However, in other
          examples, we might not have this kind of information to rely
          on (e.g., /this/is/the might be a non-pseudo file system
          separate from /this/is/the/path), so we need to have
          other reliable source information on the boundary of the file system
          that is moved.  If, for example, the file system /this/is
          had moved, we would have a case of migration rather than
          referral, and once the boundaries of the migrated file system
          was clear we could fetch fs_locations_info.
        </t>
        <t hangText='- '>
          We are fetching fs_locations_info because the fact that we got an
          NFS4ERR_MOVED at this point means that it is most likely that
          this is a referral and we need the destination.  Even if it is
          the case that /this/is/the is a file system that has
          migrated, we will still need the location information for that
          file system.
        </t>
        <t hangText='OP14:'>
          GETFH --> NFS4ERR_MOVED
        </t>
        <t hangText='- '>
          Fails because current fh is in an absent file system at the start of
          the operation, and the specification makes no exception for GETFH.  Note
          that this means the server will never send the client a
          filehandle from within an absent file system.
        </t>
       </list>
      </t>
      <t>
        Given the above, the client knows where the root of the absent file
        system is (/this/is/the/path) by noting where the change of
        fsid occurred (between "the" and "path").  The
        fs_locations_info attribute also gives the client the 
        actual location of
        the absent file system, so that the referral can proceed.  The
        server gives the client the bare minimum of information about the
        absent file system so that there will be very little scope for
        problems of conflict between information sent by the referring
        server and information of the file system's home.  No filehandles
        and very few attributes are present on the referring server, and the
        client can treat those it receives as transient
        information with the function of enabling the referral.
      </t>
    </section>
    <section anchor="referrals_readdir" 
             title="Referral Example (READDIR)">
      <t>
        Another context in which a client may encounter referrals is when
        it does a READDIR on a directory in which some of the sub-directories
        are the roots of absent file systems.
      </t>
      <t>
        Suppose such a directory is read as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (fsid, size, time_modify, mounted_on_fileid)
        </t>
       </list>
      </t>
      <t>
        In this case, because rdattr_error is not requested, 
        fs_locations_info
        is not requested, and some of the attributes cannot be provided, the
        result will be an NFS4ERR_MOVED error on the READDIR, with the
        detailed results as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (fsid, size, time_modify, mounted_on_fileid) -->
          NFS4ERR_MOVED.  Note that the same error would have been 
          returned if /this/is/the had migrated, but it is returned because the
          directory contains the root of an absent file system.
        </t>
       </list>
      </t>
      <t>
        So now suppose that we re-send with rdattr_error:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
        </t>
       </list>
      </t>
      <t>
        The results will be:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
          --> NFS_OK.  The attributes for directory entry with the
          component named "path" will only contain
          rdattr_error
          with the value NFS4ERR_MOVED, together with an fsid
          value and a value for mounted_on_fileid.
        </t>
       </list>
      </t>
      <t>
        So suppose we do another READDIR to get fs_locations_info (although
        we could have used a GETATTR directly, as in
        <xref target="referrals_lookup" />).
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
          size, time_modify)
        </t>
       </list>
      </t>
      <t>
        The results would be:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
          size, time_modify) --> NFS_OK.  The attributes will be as shown below.
        </t>
       </list>
      </t>
      <t>
         The attributes for the directory entry with the
         component named "path" will only contain:
      </t>
      <t>
       <list style='symbols'>
        <t>
          rdattr_error (value: NFS_OK)
        </t>
        <t>
          fs_locations_info 
        </t>
        <t>
          mounted_on_fileid (value: unique fileid within referring file system)
        </t>
        <t>
          fsid (value: unique value within referring server)
        </t>
       </list>
      </t>
      <t>
        The attributes for entry "path" will not contain size or
        time_modify because these attributes are not available within an
        absent file system.
      </t>
    </section>
  </section>
  <section anchor="fs_locations" title="The Attribute fs_locations">
    <t>
      The fs_locations attribute is structured in the following way:
    </t>
<t>
<figure>
 <artwork>
struct fs_location4 {
        utf8str_cis     server&lt;>;
        pathname4       rootpath;
};
 </artwork>
</figure>
</t>
<t>
<figure>
 <artwork>
struct fs_locations4 {
        pathname4       fs_root;
        fs_location4    locations&lt;>;
};
 </artwork>
</figure>
</t>
    <t>
      The fs_location4 data type is used to represent the location of a
      file system by providing a server name and the path to the root 
      of the file system within that server's namespace.  
      When a set of servers have corresponding file systems at the
      same path within their namespaces, an array of server names may 
      be provided.  An
      entry in the server array is a UTF-8 string and represents one 
      of a
      traditional DNS host name, IPv4 address, IPv6 address, or a
      zero-length string.
      An IPv4 or IPv6 address is represented as a universal
      address (see <xref target="netaddr4"/> and <xref
      target="RFC5665"/>), minus the netid, and either with
      or without the trailing ".p1.p2" suffix that
      represents the port number. If the suffix is omitted,
      then the default port, 2049, SHOULD be assumed.

      A zero-length string SHOULD be used to indicate the current address 
      being used for the RPC call. It is not
      a requirement that all servers that share the same rootpath 
      be listed
      in one fs_location4 instance.  The array of server names is provided for
      convenience.  Servers that share the same rootpath may also be listed
      in separate fs_location4 entries in the fs_locations attribute.
    </t>
    <t>
     The fs_locations4 data type and fs_locations attribute contain an array of
     such locations.  Since the namespace of each server may be 
     constructed differently, the "fs_root" field is provided.  The 
     path represented
     by fs_root represents the location of the file system in the 
     current server's namespace, i.e., that of the
     server from which the fs_locations attribute was obtained.  The
     fs_root path is meant to aid the client by clearly referencing
     the root of the file system whose locations are being reported,
     no matter what object within the current file system the 
     current filehandle designates.  The fs_root is simply the
     pathname the client used to reach the object on the current server
     (i.e., the object to which the fs_locations attribute applies).
    </t>
    <t>
     When the fs_locations attribute
     is interrogated and there are no alternate file system locations,
     the server SHOULD return a zero-length array of fs_location4 
     structures, together with a valid fs_root. 
   </t>
   <t>
     As an example, suppose there is a replicated file system located 
     at two
     servers (servA and servB).  At servA, the file system is located at
     path /a/b/c.  At, servB the file system is located at path /x/y/z.
     If the client were to obtain the fs_locations value for the
     directory at /a/b/c/d, it might not necessarily know  
     that the file system's root is located in servA's namespace 
     at /a/b/c.  When the client switches to servB, it will need
     to determine that the directory it first referenced at servA is now
     represented by the path /x/y/z/d on servB.  To facilitate this, the
     fs_locations attribute provided by servA would have an fs_root value
     of /a/b/c and two entries in fs_locations.  One entry in fs_locations
     will be for itself (servA) and the other will be for servB with a
     path of /x/y/z.  With this information, the client is able to
     substitute /x/y/z for the /a/b/c at the beginning of its access
     path and construct /x/y/z/d to use for the new server.
   </t>
   <t>
     Note that there is no requirement that the number
     of components in each rootpath be the same; there
     is no relation between the number of components in
     rootpath or fs_root, and none of the components
     in a rootpath and fs_root have to be the same. In
     the above example, we could have had a third element
     in the locations array, with server equal to "servC"
     and rootpath equal to "/I/II", and a fourth element in
     locations with server equal to "servD" and rootpath
     equal to "/aleph/beth/gimel/daleth/he".

   </t>
   <t>
     The relationship between fs_root to a rootpath is
     that the client replaces the pathname indicated in
     fs_root for the current server for the substitute
     indicated in rootpath for the new server.

   </t>
   <t>
     For an example of a referred or migrated file
     system, suppose there is a file system located
     at serv1. At serv1, the file system is located at
     /az/buky/vedi/glagoli. The client finds that object
     at glagoli has migrated (or is a referral).  The
     client gets the fs_locations attribute, which contains
     an fs_root of /az/buky/vedi/glagoli, and one element
     in the locations array, with server equal to serv2,
     and rootpath equal to /izhitsa/fita. The client
     replaces /az/buky/vedi/glagoli with /izhitsa/fita,
     and uses the latter pathname on serv2.

   </t>

   <t>
     Thus, the server MUST return an fs_root that is equal
     to the path the client used to reach the object to which the
     fs_locations attribute applies. Otherwise, the
     client cannot determine the new path to use on the new server.

   </t>
   <t>
     Since the fs_locations attribute lacks information defining various 
     attributes of the various file system choices presented, it SHOULD
     only be interrogated and used when fs_locations_info is not available.
     When fs_locations is used, information about the 
     specific locations should be assumed based on the following rules.
   </t>
   <t>
     The following rules are general and apply irrespective of the
     context.
   </t>
   <t>
    <list style='symbols'>
     <t>
       All listed 
       file system instances should be considered as of the 
       same handle class, if and only if, the 
       current fh_expire_type attribute does not include the 
       FH4_VOL_MIGRATION
       bit.  Note that in the case of referral, filehandle issues do
       not apply since there can be no filehandles known within the 
       current file system, nor is there any access to the fh_expire_type
       attribute on the referring (absent) file system.
     </t> 
     <t>
       All listed file system instances should be considered as of the 
       same fileid class if and only if the 
       fh_expire_type attribute indicates persistent filehandles and 
       does not include the FH4_VOL_MIGRATION
       bit.  Note that in the case of referral, fileid issues do
       not apply since there can be no fileids known within the 
       referring (absent) file system, nor is there any access to 
       the fh_expire_type attribute.
     </t> 
     <t>
       All file system instances 
       servers should be considered as of different 
       change classes.
     </t> 
    </list>
   </t>
   <t>
     For other class assignments, handling of file system
     transitions depends on the reasons for the transition:
   </t>
   <t>
    <list style='symbols'>
     <t>
       When the transition is due to migration, that is, the client was
       directed to a new file system after receiving an NFS4ERR_MOVED error,
       the target should be
       treated as being of the same  
       write-verifier class as the source.
     </t>
     <t>
       When the transition is due to failover to another replica, 
       that is, the client selected another replica without
       receiving an NFS4ERR_MOVED error, the target should be
       treated as being of a different 
       write-verifier class from the source.
     </t>
    </list>
   </t>
   <t>
     The specific choices reflect typical implementation patterns for
     failover and controlled migration, respectively.  Since other 
     choices are possible and useful, this information is better
     obtained by using fs_locations_info.  When a server implementation
     needs to communicate other choices, it MUST support the 
     fs_locations_info attribute.
   </t>
   <t>
     See <xref target="securityconsider" /> for a
     discussion on the recommendations for the security
     flavor to be used by any GETATTR operation that
     requests the "fs_locations" attribute.

   </t>
  </section>
  <section anchor="fs_locations_info" 
           title="The Attribute fs_locations_info">
    <t>
      The fs_locations_info attribute is intended as a more functional
      replacement for fs_locations that will continue to exist and be
      supported.  Clients can use it to get a more complete set of 
      information about alternative file system locations.
      When the server does not support
      fs_locations_info, fs_locations can be used to get a subset of the
      information.  A server that supports fs_locations_info MUST support
      fs_locations as well.
    </t>
    <t>
      There is additional information present in
      fs_locations_info, that is not available in fs_locations:
    </t>
    <t>
     <list style='symbols'>
      <t>    
        Attribute continuity information. This information
        will allow a client to select a
        location that meets the transparency requirements of the
        applications accessing the data and to leverage
        optimizations due to the server guarantees of attribute
        continuity (e.g., if between multiple server locations the
        change attribute of a file of the file system is continuous,
        the client does not have to invalidate the file's cache if
        the change attribute is the same among all locations).
      </t>    
      <t>    
        File system identity information that indicates when multiple
        replicas, from the client's point of view, correspond to the
        same target file system, allowing them to be used
        interchangeably, without disruption, as multiple paths to the
        same thing.
      </t>    
      <t>    
        Information that will bear on the suitability of various
        replicas, depending on the use that the client intends.  For
        example, many applications need an absolutely up-to-date copy
        (e.g., those that write), while others may only need access to
        the most up-to-date copy reasonably available.
      </t>    
      <t>    
        Server-derived preference information for replicas, which can
        be used to implement load-balancing while giving the client
        the entire file system list to be used in case the primary fails.
      </t>    
     </list>
    </t>
    <t>
      The fs_locations_info attribute is structured similarly to the
      fs_locations attribute.  A top-level structure
      (fs_locations_info4) contains the entire attribute including the root
      pathname of the file system and an array of lower-level structures that
      define replicas that share a common rootpath on their respective
      servers.  The lower-level structure in turn
      (fs_locations_item4) contains a specific pathname and information on one
      or more individual server replicas.  For that last lowest-level,
      fs_locations_info has an fs_locations_server4
      structure that contains per-server-replica information in addition
      to the server name.  This per-server-replica information includes a
      nominally opaque array, fls_info, in which specific pieces of information
      are located at the specific indices listed below.
    </t>
    <t>
      The attribute will always contain at least a single fs_locations_server
      entry.  Typically, this will be an entry with the FS4LIGF_CUR_REQ
      flag set, although in the case of a referral there will be no
      entry with that flag set.
    </t>
    <t>
      It should be noted that fs_locations_info attributes returned by
      servers for various replicas may differ for various reasons.
      One server may know about a set of replicas that are not known to
      other servers.  Further, compatibility attributes may differ.
      Filehandles might be of the same class going from replica A to
      replica B but not going in the reverse direction.  This might happen 
      because the filehandles are the same, but
      replica B's server implementation might not have provision to note
      and report that equivalence.
    </t>
    <t>
      The fs_locations_info attribute consists of a root
      pathname (fli_fs_root, just like fs_root in the
      fs_locations attribute), together with an array of
      fs_location_item4 structures.  The fs_location_item4
      structures in turn consist of a root pathname
      (fli_rootpath) together with an array (fli_entries)
      of elements of data type fs_locations_server4,
      all defined as follows.

    </t>
<figure>
 <artwork>
/*
 * Defines an individual server replica
 */
struct  fs_locations_server4 {
        int32_t         fls_currency;
        opaque          fls_info&lt;>;
        utf8str_cis     fls_server;
};

/*
 * Byte indices of items within
 * fls_info: flag fields, class numbers,
 * bytes indicating ranks and orders.
 */
const FSLI4BX_GFLAGS            = 0;
const FSLI4BX_TFLAGS            = 1;

const FSLI4BX_CLSIMUL           = 2;
const FSLI4BX_CLHANDLE          = 3;
const FSLI4BX_CLFILEID          = 4;
const FSLI4BX_CLWRITEVER        = 5;
const FSLI4BX_CLCHANGE          = 6;
const FSLI4BX_CLREADDIR         = 7;

const FSLI4BX_READRANK          = 8;
const FSLI4BX_WRITERANK         = 9;
const FSLI4BX_READORDER         = 10;
const FSLI4BX_WRITEORDER        = 11;

/*
 * Bits defined within the general flag byte.
 */
const FSLI4GF_WRITABLE          = 0x01;
const FSLI4GF_CUR_REQ           = 0x02;
const FSLI4GF_ABSENT            = 0x04;
const FSLI4GF_GOING             = 0x08;
const FSLI4GF_SPLIT             = 0x10;

/*
 * Bits defined within the transport flag byte.
 */
const FSLI4TF_RDMA              = 0x01;

/*
 * Defines a set of replicas sharing
 * a common value of the rootpath
 * with in the corresponding
 * single-server namespaces.
 */
struct  fs_locations_item4 {
        fs_locations_server4    fli_entries&lt;>;
        pathname4               fli_rootpath;
};

/*
 * Defines the overall structure of
 * the fs_locations_info attribute.
 */
struct  fs_locations_info4 {
        uint32_t                fli_flags;
        int32_t                 fli_valid_for;
        pathname4               fli_fs_root;
        fs_locations_item4      fli_items&lt;>;
};

/*
 * Flag bits in fli_flags.
 */
const FSLI4IF_VAR_SUB           = 0x00000001;

typedef fs_locations_info4 fattr4_fs_locations_info;
 </artwork>
</figure>
    <t>
      As noted above, the fs_locations_info attribute, when supported, may
      be requested of absent file systems without causing NFS4ERR_MOVED to
      be returned.  It is generally expected that it will be available for
      both present and absent file systems even if only a single
      fs_locations_server4 entry is present, designating the current (present)
      file system, or two fs_locations_server4 entries designating the 
      previous location of an absent file system (the one just referenced) and its
      successor location.  Servers are strongly urged to support this
      attribute on all file systems if they support it on any file system.
    </t>
    <t>
      The data presented in the fs_locations_info attribute may be obtained
      by the server in any number of ways, including specification by
      the administrator or by current protocols for transferring data
      among replicas and protocols not yet developed.  NFSv4.1 only defines how this information is presented by the server to
      the client.
    </t>
    <section anchor="fs_locations_server4" 
             title="The fs_locations_server4 Structure">
      <t>
        The fs_locations_server4 structure consists of the following items:
      </t>
      <t>
       <list style='symbols'>
        <t>    
          An indication of how up-to-date the file system is (fls_currency) in
          seconds.  This value
          is relative to the master copy.  A negative
          value indicates that the server is unable to give any
          reasonably useful value here.  A value of zero indicates that the
          file system is the actual writable data or a reliably coherent
          and fully up-to-date copy.  Positive values indicate how 
          out-of-date this copy can normally be before it is considered for
          update.  Such a value is not a guarantee that such updates
          will always be performed on the required schedule but instead
          serves as a hint about how far the copy of the data would be
          expected to be behind the most up-to-date copy.
        </t>    
        <t>    
          A counted array of one-byte values (fls_info) containing
          information about the particular file system instance.  This
          data includes general flags, transport capability flags,
          file system equivalence class information, and selection
          priority information.  The encoding will be discussed below.  
        </t>    
        <t>    
          The server string (fls_server).  For the case of the
          replica currently
          being accessed (via GETATTR), a zero-length string MAY be used to
          indicate the current address being used for the RPC call.
          The fls_server field can also be an IPv4 or IPv6 address,
          formatted the same way as an IPv4 or IPv6 address in the "server"
          field of the fs_location4 data type (see <xref target="fs_locations"/>).
        </t>
       </list>
      </t>
      <t>
        Data within the fls_info array is in the form of 8-bit data items
        with constants giving the offsets within the array of various
        values describing this particular file system instance.  
        This style of
        definition was chosen, in preference to explicit XDR
        structure definitions for these values, for a number of
        reasons.
      </t>
      <t>
       <list style='symbols'>
        <t>
          The kinds of data in the fls_info array, representing flags, 
          file system classes, and priorities among sets of file systems
          representing the same data, are such that 8 bits provide
          a quite acceptable range of values.  Even where there might 
          be more than 256 such file system instances, having more than
          256 distinct classes or priorities is unlikely.
        </t>
        <t>
          Explicit definition of the various specific data items within
          XDR would limit expandability in that any extension within
          a subsequent minor version would require yet another attribute,
          leading to specification and implementation clumsiness.
        </t>
        <t>
          Such explicit definitions would also make it impossible to 
          propose Standards Track extensions apart from a full minor version.
        </t>
       </list>
      </t>
      <t>
        This encoding scheme can be adapted to the specification of
        multi-byte numeric values, even though none are currently
        defined.  If extensions are made via Standards Track RFCs,
        multi-byte quantities will be encoded as a range of bytes 
        with a range of indices, with the byte interpreted in big-endian
        byte order.  Further, any such index assignments are constrained
        so that the relevant quantities will not cross XDR word boundaries.
      </t>
      <t>
        The set of fls_info data is subject to expansion in a future minor 
        version, or in a Standards Track RFC, within the context of a single
        minor version.  The server SHOULD NOT send and the client MUST NOT
        use indices within the fls_info array that are not defined in 
        Standards Track RFCs.
      </t> 
      <t>
         The fls_info array contains:
      </t>
      <t>
       <list style='symbols'>
         <t>
           Two 8-bit flag fields, one devoted to general file-system
           characteristics and a second reserved for transport-related
           capabilities.
         </t>
         <t>
           Six 8-bit class values that define various file system
           equivalence classes as explained below.
         </t>
         <t>
           Four 8-bit priority values that govern file system selection
           as explained below.
         </t>
       </list>
      </t>
      <t>
        The general file system characteristics flag (at byte index
        FSLI4BX_GFLAGS) has the following
        bits defined within it:
      </t>
      <t>
       <list style='symbols'>
        <t>
          FSLI4GF_WRITABLE indicates that this file system target is writable,
          allowing it to be selected by clients that may need to write
          on this file system.  When the current file system instance
          is writable and is defined as of the same simultaneous use 
          class (as specified by the value at index FSLI4BX_CLSIMUL) 
          to which the client was previously writing, then it must
          incorporate within its data any committed
          write made on the source file system instance.  See
          <xref target="transition_verifier" />, which discusses
          the write-verifier class.  While there is no harm in not setting
          this flag for a file system that turns out to be writable,
          turning the flag on for a read-only file system can cause
          problems for clients that select a migration or replication
          target based on the flag and then find themselves unable to write.
        </t>
        <t>
          FSLI4GF_CUR_REQ indicates that this replica is the one on which
          the request is being made.  Only a single server entry may
          have this flag set and, in the case of a referral, no entry
          will have it.
        </t>
        <t>
          FSLI4GF_ABSENT indicates that this entry corresponds to an absent
          file system replica.  It can only be set if FSLI4GF_CUR_REQ is set.
          When both such bits are set, it indicates that a file system
          instance is not usable but that the information in the entry
          can be used to determine the sorts of continuity available
          when switching from this replica to other possible replicas.
          Since this bit can only be true if FSLI4GF_CUR_REQ is true, the
          value could be determined using the fs_status attribute, but
          the information is also made available here for the
          convenience of the client.  An entry with this bit, since it
          represents a true file system (albeit absent), does not appear
          in the event of a referral, but only when a file system has
          been accessed at this location and has subsequently been migrated.
        </t>
        <t>
          FSLI4GF_GOING indicates that a replica, while still available,
          should not be used further.  The client, if using it, should
          make an orderly transfer to another file system instance as
          expeditiously as possible.  It is expected that file systems
          going out of service will be announced as FSLI4GF_GOING some time
          before the actual loss of service. It is also expected that the fli_valid_for value
          will be sufficiently small to allow clients to detect and act
          on scheduled events, while large enough that the cost of the
          requests to fetch the fs_locations_info values will not be
          excessive.  Values on the order of ten minutes seem
          reasonable.

          <vspace blankLines='1' />
          When this flag is seen as part of a transition into a new
          file system, a client might choose to transfer immediately 
          to another replica, or it may reference the current file system
          and only transition when a migration event occurs.  Similarly,
          when this flag appears as a replica in the referral, clients
          would likely avoid being referred to this instance whenever
          there is another choice.
        </t>
        <t>
          FSLI4GF_SPLIT indicates that when a transition occurs from
          the current file system instance to this one, the replacement 
          may consist of multiple file systems.  In this case, the 
          client has to be prepared for the possibility that objects 
          on the same file system before migration will be on different ones 
          after.  Note that FSLI4GF_SPLIT is not incompatible with the
          file systems belonging to the same fileid
          class
          since, if one has a set of fileids that are unique within
          a file system, each subset assigned to a smaller file system after migration
          would not have any conflicts internal to that file system.
          <vspace blankLines='1' />
          A client, in the case of a split file system, will interrogate
          existing files with which it has continuing connection (it 
          is free to simply forget cached filehandles).  If the client
          remembers the directory filehandle associated with each open
          file, it may proceed upward using LOOKUPP to find the new file system
          boundaries.  Note that in the event of a referral, there will
          not be any such files and so these actions will not be performed.
	  Instead, a reference to a portion of the original
	  file system now split off into other file systems
	  will encounter an fsid change and possibly a
	  further referral.

          <vspace blankLines='1' />
          Once the client recognizes that one file system has been split 
          into two, it can prevent the disruption of running applications
          by presenting the two file systems as a single
          one until a convenient point to recognize the transition,
          such as a restart.  This would require a mapping
          from the server's fsids to fsids as seen by the client, but 
          this is already necessary for other reasons.  As noted 
          above, existing fileids within the two descendant file systems
          will not conflict.  Providing non-conflicting fileids for 
          newly created files on the split file systems
          is the responsibility of the server (or servers working in 
          concert).  The server can encode filehandles such
          that filehandles generated before the split event can be discerned
          from those generated after the split,
          allowing the server to determine when the need
          for emulating two file systems as one is over. 
          <vspace blankLines='1' />
          Although it is possible for this flag to be present in the
          event of referral, it would generally be of little interest
          to the client, since the client is not expected to have
          information regarding the current contents of the absent
          file system. 
        </t>
       </list>        
      </t>
      <t>
        The transport-flag field (at byte index FSLI4BX_TFLAGS) contains 
        the following bits related to the transport
        capabilities of the specific file system.
      </t>
      <t>
       <list style='symbols'>
        <t>
          FSLI4TF_RDMA indicates that this file system provides NFSv4.1
          file system access using an RDMA-capable transport.
        </t>
       </list>
      </t>
      <t>
        Attribute continuity and file system identity information are 
        expressed by defining equivalence relations on the sets of
        file systems presented to the client.  Each such relation
        is expressed as a set of file system equivalence classes.
        For each relation, a file system has an 8-bit class number.
        Two file systems belong to the same class if both have 
        identical non-zero class numbers.  Zero is treated as 
        non-matching.  Most often, 
        the relevant question for the client will be whether a
        given replica is identical to / continuous with the current one in a
        given respect, but the information should be available also as to
        whether two other replicas match in that respect as well.
      </t>
      <t>
        The following fields specify the file system's class numbers
        for the equivalence relations used in determining the nature of
        file system transitions.  See 
        <xref target='effecting_transitions' />  and its various subsections
        for details about how
        this information is to be used.  Servers may assign these values
        as they wish, so long as file system instances that share the 
        same value have the specified relationship to one another;
        conversely, file systems that have the specified relationship
        to one another share a common class value. As each instance
        entry is added, the relationships of this instance to previously
        entered instances can be consulted, and if one is found that
        bears the specified relationship, that entry's class value can
        be copied to the new entry.  When no such previous entry exists,
        a new value for that byte index (not previously used) can be 
        selected, most likely by incrementing the value of the last class
        value assigned for that index. 
      </t>
      <t>
       <list style='symbols'>
        <t>
          The field with byte index FSLI4BX_CLSIMUL defines the 
          simultaneous-use class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLHANDLE defines the handle
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLFILEID defines the fileid
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLWRITEVER defines the
          write-verifier class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLCHANGE defines the change
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLREADDIR defines the readdir
          class for the file system.
        </t>
       </list>
      </t>
      <t>     
        Server-specified preference information is also provided via
        8-bit values within the fls_info array.  The values provide a 
        rank and an order (see below) to be used with separate values
        specifiable for the cases of read-only and writable file 
        systems.  
        These values are compared
        for different file systems to establish the server-specified 
        preference, with lower values indicating "more preferred".
      </t>
      <t>
        Rank is used to express a strict server-imposed ordering on
        clients, with lower values indicating "more preferred".  Clients
        should attempt to use all replicas with a given rank before they
        use one with a higher rank.  Only if all of those file systems are
        unavailable should the client proceed to those of a higher rank.
        Because specifying a rank will override client preferences, servers
        should be conservative about using this mechanism, particularly
        when the environment is one in which client communication characteristics
        are neither tightly controlled nor visible to the server.
      </t>
      <t>
        Within a rank, the order value is used to specify the server's
        preference to guide the client's selection when the client's own
        preferences are not controlling, with lower values of order
        indicating "more preferred".  If replicas are approximately equal
        in all respects, clients should defer to the order specified by the
        server.  When clients look at server latency as part of their
        selection, they are free to use this criterion but it is suggested
        that when latency differences are not significant, the
        server-specified order should guide selection.

      </t>
      <t>
       <list style='symbols'>
        <t>
          The field at byte index FSLI4BX_READRANK gives the rank value to
          be used for read-only access. 
        </t>
        <t>
          The field at byte index FSLI4BX_READORDER gives the order value to
          be used for read-only access. 
        </t>
        <t>
          The field at byte index FSLI4BX_WRITERANK gives the rank value to
          be used for writable access. 
        </t>
        <t>
          The field at byte index FSLI4BX_WRITEORDER gives the order value to
          be used for writable access. 
        </t>
       </list>
      </t>
      <t>
        Depending on the potential need for write access by a given client,
        one of the pairs of rank and order values is used. 
        The read rank and order should only be used
        if the client knows that only reading will ever be done or if it is
        prepared to switch to a different replica in the event that any
        write access capability is required in the future.  
      </t>
    </section>
    <section anchor="fs_locations_info4" 
             title="The fs_locations_info4 Structure">
      <t>
        The fs_locations_info4 structure, encoding the fs_locations_info
        attribute, contains the following:
      </t>
      <t>
       <list style='symbols'>
        <t>
          The fli_flags field, which contains general flags that affect 
          the interpretation of this fs_locations_info4 structure and
          all fs_locations_item4 structures within it.  The only flag
          currently defined is FSLI4IF_VAR_SUB.  All bits in the
	  fli_flags field that are not defined should always be returned as zero.
        </t>
        <t>
          The fli_fs_root field, which contains the pathname of the root of
          the current file system on the current server, just as it does
          in the fs_locations4 structure.
        </t>
        <t>
          An array called fli_items of fs_locations4_item structures, which contain
          information about replicas of the current file system.  Where
          the current file system is actually present, or has been
          present, i.e., this is not a referral situation, one of the
          fs_locations_item4 structures will contain an fs_locations_server4 for
          the current server.  This structure will have FSLI4GF_ABSENT set
          if the current file system is absent, i.e., normal access to it
          will return NFS4ERR_MOVED.
        </t>
        <t>
          The fli_valid_for field specifies a time in seconds
          for which it is reasonable for a client to use the fs_locations_info attribute
          without refetch.  The fli_valid_for value does not provide a
          guarantee of validity since servers can unexpectedly go out of
          service or become inaccessible for any number of reasons.
          Clients are well-advised to refetch this information for an
          actively accessed file system at every fli_valid_for seconds.  This
          is particularly important when file system replicas may go out
          of service in a controlled way using the FSLI4GF_GOING flag to
          communicate an ongoing change.  The server should set
          fli_valid_for to a value that allows well-behaved clients to
          notice the FSLI4GF_GOING flag and make an orderly switch before
          the loss of service becomes effective.  If this value is zero,
          then no refetch interval is appropriate and the client need
          not refetch this data on any particular schedule.
          In the event of a transition to a new file system instance, a
          new value of the fs_locations_info attribute will be fetched at
          the destination.  It is to be expected that this may have a
          different fli_valid_for value, which the client should then use
          in the same fashion as the previous value.
        </t>
       </list>
      </t>
      <t>
        The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
        substitution is to be enabled.  See <xref target="fs_locations_item4" />
        for an explanation of variable substitution.
      </t>
    </section>
    <section anchor="fs_locations_item4" 
             title="The fs_locations_item4 Structure">
      <t>
        The fs_locations_item4 structure contains a pathname 
        (in the field fli_rootpath) that encodes
        the path of the target file system replicas on the set of 
        servers designated by the included fs_locations_server4 entries.
        The precise manner in which this target location
        is specified depends on the value of the FSLI4IF_VAR_SUB
        flag within the associated fs_locations_info4 structure. 
      </t>
      <t>
        If this flag is not set, then fli_rootpath simply designates
        the location of the target file system within each server's
        single-server namespace just as it does for the rootpath
        within the fs_location4 structure.  When this bit is set,
        however, component entries of a certain form are subject
        to client-specific variable substitution so as to allow
        a degree of namespace non-uniformity in order to accommodate
        the selection of client-specific file system targets to
        adapt to different client architectures or other
        characteristics.
      </t>
      <t>
        When such substitution is in effect, a variable beginning
        with the string "${" and ending with the string "}"
        and containing a colon is to be
        replaced by the client-specific value associated with
        that variable.  The string "unknown" should be used 
        by the client when it has no value for such a variable.
        The pathname resulting from such
        substitutions is used to designate the target file system,
        so that different clients may have different file systems,
        corresponding to that location in the multi-server namespace.
      </t>
      <t>
        As mentioned above, such substituted pathname variables
        contain a colon.  The part before the colon is to be a
        DNS domain name, and the part after is to be a case-insensitive
        alphanumeric string.
      </t>
      <t> 
        Where the domain is "ietf.org", only variable names defined
        in this document or subsequent Standards Track RFCs
        are subject to such substitution.  Organizations are
        free to use their domain names to create their own sets
        of client-specific variables, to be subject to such
        substitution.  In cases where such variables are intended
        to be used more broadly than a single organization, 
        publication of an Informational RFC defining such variables
        is RECOMMENDED. 
      </t>
      <t>
        The variable ${ietf.org:CPU_ARCH} is used to denote that the
        CPU architecture object files are compiled.  This specification
        does not limit the acceptable values (except that they must be
        valid UTF-8 strings), but such values as "x86", "x86_64", and "sparc"
        would be expected to be used in line with industry practice.
      </t>
      <t>
        The variable ${ietf.org:OS_TYPE} is used to denote the 
        operating system, and thus the kernel and library APIs,
        for which code might be compiled.  This specification does
        not limit the acceptable values (except that they must be
        valid UTF-8 strings), but such values as "linux" and "freebsd"
        would be expected to be used in line with industry practice.
      </t>
      <t>
        The variable ${ietf.org:OS_VERSION} is used to denote the 
        operating system version, and thus the specific details
        of versioned interfaces,
        for which code might be compiled.  This specification does
        not limit the acceptable values (except that they must be
        valid UTF-8 strings). However, combinations of numbers and 
        letters with interspersed dots would be expected to be used
        in line with industry practice, with the details of the 
        version format depending on the specific value of
        the variable ${ietf.org:OS_TYPE} with which
        it is used.
      </t>
      <t>
        Use of these variables could result in the direction of different
        clients to different file systems on the same server, as
        appropriate to particular clients.  In cases in which the
        target file systems are located on different servers, a single
        server could serve as a referral point so that each valid
        combination of variable values would designate a referral
        hosted on a single server, with the targets of those referrals on
        a number of different servers.
      </t>
      <t>
        Because namespace administration is affected by the values
        selected to substitute for various variables, clients should
        provide convenient means of determining what variable 
        substitutions a client will implement, as well as, where
        appropriate, providing means to control the substitutions to
        be used.  The exact means by which this will be done is 
        outside the scope of this specification.
      </t>
      <t>
        Although variable substitution is most suitable for use
        in the context of referrals, it may be used in the context
        of replication and migration.  If it is used in these contexts,
        the server must ensure that no matter what values the
        client presents for the substituted variables, the result 
        is always a valid successor file system instance to that
        from which a transition is occurring, i.e., that the data is
        identical or represents a later image of a writable file
        system. 
      </t>
      <t>
        Note that when fli_rootpath is a null pathname (that is, one
        with zero components), the file system designated is at the
        root of the specified server, whether or not the FSLI4IF_VAR_SUB
        flag within the associated fs_locations_info4 structure is 
        set. 
      </t>
    </section>
  </section>
  <section anchor="fs_status" title="The Attribute fs_status">
     <t>
       In an environment in which multiple copies of the same basic set of
       data are available, information regarding the particular source of
       such data and the relationships among different copies can be very
       helpful in providing consistent data to applications.
     </t>

<figure>
 <artwork>
enum fs4_status_type {
        STATUS4_FIXED = 1,
        STATUS4_UPDATED = 2,
        STATUS4_VERSIONED = 3,
        STATUS4_WRITABLE = 4,
        STATUS4_REFERRAL = 5
};

struct fs4_status {
        bool            fss_absent;
        fs4_status_type fss_type;
        utf8str_cs      fss_source;
        utf8str_cs      fss_current;
        int32_t         fss_age;
        nfstime4        fss_version;
};
 </artwork>
</figure>

    <t>
      The boolean fss_absent indicates whether the file system is 
      currently absent.  This value will be set if the file system was
      previously present and becomes absent, or if the file system has
      never been present and the type is STATUS4_REFERRAL.  When this
      boolean is set and the type is not STATUS4_REFERRAL, the 
      remaining information in the fs4_status reflects that last valid 
      when the file system was present.
    </t>
    <t>
      The fss_type field indicates the kind of file system image represented.
      This is of particular importance when using the version values to
      determine appropriate succession of file system images.  
      When fss_absent is set, and the file system was previously 
      present, the value of fss_type reflected is that when the file was last present. 
      Five values are distinguished:
    </t>
    <t>
     <list style='symbols'>
      <t>
        STATUS4_FIXED, which indicates a read-only image in the sense
        that it will never change.  The possibility is allowed that, as
        a result of migration or switch to a different image, changed
        data can be accessed, but within the confines of this instance,
        no change is allowed.  The client can use this fact to
        cache aggressively.
      </t>
      <t>
        STATUS4_VERSIONED, which indicates that the image, like the
        STATUS4_UPDATED case, is updated externally, but it provides
        a guarantee that the server will carefully update an
        associated version value so that the client can
        protect itself from a situation in which it reads
        data from one version of the file system and then later reads
        data from an earlier version of the same file system.  See
        below for a discussion of how this can be done.
      </t>
      <t>
        STATUS4_UPDATED, which indicates an image that cannot be
        updated by the user writing to it but that may be changed
        externally, typically because it is a periodically updated
        copy of another writable file system somewhere else.  In 
        this case, version information is not provided, and the 
        client does not have the responsibility of making sure 
        that this version only advances upon a file system instance
        transition.  In this case, it is the responsibility of the
        server to make sure that the data presented after a file
        system instance transition is a proper successor image and
        includes all changes seen by the client and any change made
        before all such changes.
      </t>
      <t>
        STATUS4_WRITABLE, which indicates that the file system is an
        actual writable one.  The client need not, of course, actually
        write to the file system, but once it does, it should not
        accept a transition to anything other than a writable instance
        of that same file system.
      </t>
      <t>
        STATUS4_REFERRAL, which indicates that the file system in
        question is absent and has never been present on this
        server.
      </t>
     </list>
    </t>
    <t>
      Note that in the STATUS4_UPDATED and STATUS4_VERSIONED cases, the
      server is responsible for the appropriate handling of locks that
      are inconsistent with external changes to delegations.
      If a server gives out delegations, they SHOULD be recalled
      before an inconsistent change is made to the data, and MUST
      be revoked if this is not possible.  Similarly, if an OPEN is
      inconsistent with data that is changed (the OPEN has
      OPEN4_SHARE_DENY_WRITE/OPEN4_SHARE_DENY_BOTH
      and the data is changed), that OPEN SHOULD be considered
      administratively revoked.
    </t>
    <t>
      The opaque strings fss_source and fss_current provide a way of presenting
      information about the source of the file system image being present.
      It is not intended that the client do anything with this information
      other than make it available to administrative tools.  It is
      intended that this information be helpful when researching possible
      problems with a file system image that might arise when it is
      unclear if the correct image is being accessed and, if not, how that
      image came to be made.  This kind of diagnostic information will be
      helpful, if, as seems likely, copies of file systems are made in
      many different ways (e.g., simple user-level copies, 
      file-system-level point-in-time copies, 
      clones of the underlying storage),
      under a variety of administrative arrangements.  In such
      environments, determining how a given set of data was constructed
      can be very helpful in resolving problems.
    </t>
    <t>
      The opaque string fss_source is used to indicate the source of a
      given file system with the expectation that tools capable of
      creating a file system image propagate this information, when
      possible.  It is understood that this may not always be possible
      since a user-level copy may be thought of as creating a new data
      set and the tools used may have no mechanism to propagate this
      data.  When a file system is initially created, it is desirable 
      to associate with it
      data regarding how the file system was created, where it was
      created, who created it, etc. Making this information available 
      in this attribute in a human-readable 
      string will be helpful for applications and 
      system administrators and will also serve to make it available when
      the original file system is used to make subsequent copies.
    </t>
    <t>
      The opaque string fss_current should provide whatever information is
      available about the source of the current copy.  Such
      information includes
      the tool creating it, any relevant parameters to that tool, the
      time at which the copy was done, the user making the change, the
      server on which the change was made, etc.  All information should be
      in a human-readable string.
    </t>
    <t>
      The field fss_age provides an indication of how out-of-date the file system 
      currently is with respect to its ultimate data source (in case of 
      cascading data updates).  This complements the fls_currency field of 
      fs_locations_server4 (see <xref target='fs_locations_info' />) in the 
      following way: the information in fls_currency
      gives a bound for how out of date the data in a file system might 
      typically get, while the value in fss_age gives a bound on how out-of-date that 
      data actually is.  Negative values imply that no information is 
      available.  A zero means that this data is known to be current.
      A positive value means that this data is known to be no older than 
      that number of seconds with respect to the ultimate data source.
      Using this value, the client may be able to decide that a data copy
      is too old, so that it may search for a newer version to use.
    </t>
    <t>
      The fss_version field provides a version identification, in the form of
      a time value, such that successive versions always have later time
      values.  When the fs_type is anything other than
      STATUS4_VERSIONED, the server may provide such a value, but there is
      no guarantee as to its validity and clients will not use it except
      to provide additional information to add to fss_source and fss_current.
    </t>
    <t>
      When fss_type is STATUS4_VERSIONED, servers SHOULD provide a value
      of fss_version that progresses monotonically whenever any new version
      of the data is established.  This allows the client, if reliable
      image progression is important to it, to fetch this attribute as
      part of each COMPOUND where data or metadata from the file system is
      used.
    </t>
    <t>
      When it is important to the client to make sure that only valid
      successor images are accepted, it must make sure that it does not
      read data or metadata from the file system without updating its
      sense of the current state of the image. This is to avoid the possibility
      that the fs_status that the client holds will be one for an
      earlier image, which would cause the client to accept a new file
      system instance that is later than that but still earlier than
      the updated data read by the client.
    </t>
    <t>
      In order to accept valid images reliably, the client must do a GETATTR of the fs_status
      attribute that follows any interrogation of data or metadata within the
      file system in question.  Often this is most conveniently done by
      appending such a GETATTR after all other operations that reference
      a given file system.  When errors occur between reading file system
      data and performing such a GETATTR, care must be exercised to make
      sure that the data in question is not used before obtaining the
      proper fs_status value.  In this connection, when an OPEN is done
      within such a versioned file system and the associated GETATTR of
      fs_status is not successfully completed, the open file in question
      must not be accessed until that fs_status is fetched.
    </t>
    <t>
      The procedure above will ensure that before using any data from the
      file system the client has in hand a newly-fetched current version
      of the file system image.  Multiple values for multiple requests in
      flight can be resolved by assembling them into the required partial
      order (and the elements should form a total order within the
      partial order) and
      using the last.  
The client may then, when switching among
      file system instances, decline to use an instance that does not have
      an fss_type of STATUS4_VERSIONED or whose fss_version field is earlier than the
      last one obtained from the predecessor file system instance.
    </t>
  </section>
</section>
<!-- $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $ -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Parallel NFS (pNFS)" anchor="pnfs">
<section title="Introduction" anchor="pnfs_intro">
<t>
  pNFS is an OPTIONAL feature within NFSv4.1; the pNFS feature
  set allows direct client access to the storage devices containing
  file data.  When file data for a single NFSv4 server is stored on
  multiple and/or higher-throughput storage devices (by comparison to
  the server's throughput capability), the result can be significantly
  better file access performance.  The relationship among multiple
  clients, a single server, and multiple storage devices for pNFS
  (server and clients have access to all storage devices) is shown in
  <xref target="fig_system"/>.
</t>
<figure anchor="fig_system">
<artwork><![CDATA[
    +-----------+
    |+-----------+                                 +-----------+
    ||+-----------+                                |           |
    |||           |        NFSv4.1 + pNFS          |           |
    +||  Clients  |<------------------------------>|   Server  |
     +|           |                                |           |
      +-----------+                                |           |
           |||                                     +-----------+
           |||                                           |
           |||                                           |
           ||| Storage        +-----------+              |
           ||| Protocol       |+-----------+             |
           ||+----------------||+-----------+  Control   |
           |+-----------------|||           |    Protocol|
           +------------------+||  Storage  |------------+
                               +|  Devices  |
                                +-----------+
]]></artwork>
</figure>
<t>
  In this model, the clients, server, and storage devices are
  responsible for managing file access.  This is in contrast to NFSv4
  without pNFS, where it is primarily the server's responsibility; some
  of this responsibility may be delegated to the client under strictly
  specified conditions. See <xref target="storage_protocol"/>
  for a discussion of the Storage Protocol. See <xref target="control_protocol"/> for a
  discussion of the Control Protocol. 
</t>
<t>
  pNFS takes the form of OPTIONAL operations that manage protocol
  objects called 'layouts' (<xref target="layout_types"/>) that
  contain a byte-range and storage location information.  The layout
  is managed in a similar fashion
  as NFSv4.1 data delegations.  For example, the layout is leased,
  recallable, and revocable.  However, layouts are distinct abstractions
  and are manipulated with new operations.  When a client holds a
  layout, it is granted the ability to directly access the byte-range
  at the storage location specified in the layout.

</t>
<t>
  There are interactions between layouts and other NFSv4.1
  abstractions such as data delegations and byte-range locking.
  Delegation issues are discussed in <xref
  target="recalling_layout"/>.  Byte-range locking issues are
  discussed in Sections <xref target="layout_iomode" format="counter" /> and <xref
  target="layout_semantics" format="counter" />.
</t>
</section>

<section title="pNFS Definitions">
<t>
  NFSv4.1's pNFS feature provides parallel data access to a
  file system that stripes its content across multiple
  storage servers.  The first instantiation of pNFS, as
  part of NFSv4.1, separates the file system protocol
  processing into two parts: metadata processing and data
  processing.  Data consist of the contents of regular
  files that are striped across storage servers. Data
  striping occurs in at least two ways:  on a file-by-file
  basis and, within sufficiently large files, on a
  block-by-block basis. In contrast, striped access to
  metadata by pNFS clients is not provided in NFSv4.1, even
  though the file system back end of a pNFS server might
  stripe metadata.  Metadata consist of everything else,
  including the contents of non-regular files (e.g.,
  directories); see <xref target="metadata"/>.  The
  metadata functionality is implemented by an NFSv4.1
  server that supports pNFS and the operations described in
  <xref target="nfsv41operations" />; such a server is
  called a metadata server (<xref target="mds"/>).

</t>
<t>
  The data functionality is implemented by one or more storage devices, each of which
  are accessed by the client via a storage protocol.  A subset (defined in <xref target="ds_ops"
  />) of NFSv4.1 is one such storage protocol.  New terms are
  introduced to the NFSv4.1 nomenclature and existing terms are
  clarified to allow for the description of the pNFS feature.

</t>

<section title="Metadata" anchor="metadata">
<t>
  Information about a file system object, such as its name, location
  within the namespace, owner, ACL, and other attributes.  Metadata may
  also include storage location information, and this will vary based
  on the underlying storage mechanism that is used.
</t>
</section>

<section title="Metadata Server" anchor="mds">
<t>
  An NFSv4.1 server that supports the pNFS feature.  A variety of
  architectural choices exist for the metadata server and its use of
  file system information held at the server.  Some servers may
  contain metadata only for file objects residing at the
  metadata server, while the file data resides on associated storage
  devices.  Other metadata servers may hold both metadata and a
  varying degree of file data.

</t>
</section>

<section title="pNFS Client">
<t>
  An NFSv4.1 client that supports pNFS operations and supports at
  least one storage protocol for performing I/O
  to storage devices.
</t>
</section>

<section title="Storage Device">
<t>
  A storage device stores a regular file's data, but leaves metadata
  management to the metadata server.  A storage device could be
  another NFSv4.1 server, an object-based storage device (OSD), 
a block
  device accessed over a System Area Network (SAN, e.g., either
  FiberChannel or iSCSI SAN), or some other entity.
</t>
</section>

<section anchor="storage_protocol" title="Storage Protocol">
<t>
  As noted in <xref
  target="fig_system"/>, 
  the storage protocol is the method used by the client to
  store and retrieve data directly from the storage devices.
  </t>
  <t>

  The NFSv4.1 pNFS feature has been structured to allow for a variety
  of storage protocols to be defined and used.

  One example storage protocol is NFSv4.1 itself (as documented in <xref
  target="file_layout_type"/>).  Other options for the storage protocol
  are described elsewhere and include:
  <list style="symbols">
    <t>
      Block/volume protocols such as Internet SCSI (iSCSI) <xref target="RFC3720"
      /> and FCP <xref target="FCP-2" />.  The block/volume
      protocol support can be independent of the addressing structure
      of the block/volume protocol used, allowing more than one
      protocol to access the same file data and enabling extensibility
      to other block/volume protocols. See
      <xref target="RFC5663"/> for a layout
      specification that
      allows pNFS to use block/volume storage protocols.
    </t>
    <t>
      Object protocols such as OSD over iSCSI or Fibre Channel <xref
      target="OSD-T10" />. See
      <xref target="RFC5664"/> for a layout specification
      that allows pNFS to use object storage protocols.
    </t>
  </list>
</t>
<t>
  It is possible that various storage protocols are available to
  both client and server and it may be possible that a client and
  server do not have a matching storage protocol available to them.
  Because of this, the pNFS server MUST support normal NFSv4.1 access
  to any file accessible by the pNFS feature; this will allow for
  continued interoperability between an NFSv4.1 client and server.
</t>
</section>

<section anchor="control_protocol" title="Control Protocol">
<t>
  As noted in <xref
  target="fig_system"/>, 
  the control protocol is used by the exported file system between the
  metadata server and storage devices.  Specification of such
  protocols is outside the scope of the NFSv4.1 protocol.  Such
  control protocols would be used to control activities such as the
  allocation and deallocation of storage, the management of state
  required by the storage devices to perform client access control,
  and, depending on the storage protocol, the enforcement of
  authentication and authorization so that restrictions that
  would be enforced by the metadata server are also enforced by
  the storage device.
</t>
<t>
  A particular control protocol is not REQUIRED by NFSv4.1 but
  requirements are placed on the control protocol for maintaining
  attributes like modify time, the change attribute, and the end-of-file
  (EOF) position. Note that if pNFS is layered over a clustered, parallel
  file system (e.g., <xref target="PVFS">PVFS</xref>), the mechanisms that
  enable clustering and parallelism in that file system can be considered
  the control protocol.

</t>
</section>

<section anchor="layout_types" title="Layout Types">
<t>
  A layout describes the mapping of a file's data to the storage
  devices that hold the data.  A layout is said to belong to a
  specific layout type (data type layouttype4, see <xref
  target="layouttype4" />).  The layout type allows for variants to
  handle different storage protocols, such as those associated with
  block/volume <xref target="RFC5663" />, object <xref
  target="RFC5664" />, and file (<xref target="file_layout_type"
  />) layout types.  A metadata server, along with its control
  protocol, MUST support at least one layout type.  A private
  sub-range of the layout type namespace is also defined. Values from
  the private layout type range MAY be used for internal testing or
  experimentation (see <xref target="layouttype4"/>).
</t>
<t>
  As an example,  the organization of the file layout type could be
  an array of tuples (e.g., device ID, filehandle), along with a
  definition of how the data is
  stored across the devices (e.g., striping). A block/volume layout
  might be an array of tuples that store &lt;device ID, block number,
  block count&gt; 
along with information about block size and the
  associated file offset of the block number.  An object layout might
  be an array of tuples &lt;device ID, object ID&gt; and an additional
  structure (i.e., the aggregation map) that defines how the logical
  byte sequence of the file data is serialized into the different
  objects.  Note that the actual layouts are typically more complex
  than these simple expository examples.
</t>
<t>
  Requests for pNFS-related operations will often specify a layout 
  type.  Examples of such operations are GETDEVICEINFO and LAYOUTGET.
  The response for these operations will include structures such
  as a device_addr4 or a layout4, each of which includes a layout type within
  it.  The layout type sent by the server MUST always be the same
  one requested by the client.  When a server sends a response that
  includes a different layout type, the client SHOULD ignore the
  response and behave as if the server had returned an error response.
</t>
</section>

<section title="Layout" anchor="layout">
<t>
  A layout defines how a file's data is organized on one or more
  storage devices.  There are many potential layout types; each of the
  layout types are differentiated by the storage protocol used to
  access data and by the aggregation scheme that lays out the file
  data on the underlying storage devices.  A layout is precisely
  identified by the tuple &lt;client ID, filehandle, layout
  type, iomode, range&gt;, where filehandle refers to the filehandle
  of the file on the metadata server.
</t>
<t>
  It is important to define when layouts overlap and/or conflict with
  each other.  For two layouts with overlapping byte-ranges to
  actually overlap each other, both layouts must be of the same layout
  type, correspond to the same filehandle, and have the same iomode.
  Layouts conflict when they overlap and differ in the content of the
  layout (i.e., the storage device/file mapping parameters differ).
  Note that differing iomodes do not lead to conflicting layouts.  It
  is permissible for layouts with different iomodes, pertaining to the
  same byte-range, to be held by the same client.  An example of this
  would be copy-on-write functionality for a block/volume layout type.
</t>

</section>
<section title="Layout Iomode" anchor="layout_iomode">
<t>
  The layout iomode (data type layoutiomode4, see <xref
  target="layoutiomode4" />) indicates to the metadata server the
  client's intent to perform either just READ operations
  or a mixture containing READ
  and WRITE operations. For certain layout
  types, it is useful for a client to specify this intent at the time it sends LAYOUTGET
  (<xref target="OP_LAYOUTGET" />).  For example, for
  block/volume-based protocols, block allocation could occur when a
  LAYOUTIOMODE4_RW iomode is specified.  A special LAYOUTIOMODE4_ANY iomode is defined
  and can only be used for LAYOUTRETURN and CB_LAYOUTRECALL, not for
  LAYOUTGET.  It specifies that layouts pertaining to both LAYOUTIOMODE4_READ and
  LAYOUTIOMODE4_RW iomodes are being returned or recalled, respectively.
</t>
<t>
  A storage device may validate I/O with regard to the iomode; this
  is dependent upon storage device implementation and layout type.
  Thus, if the client's layout iomode is inconsistent with the I/O
  being performed, the storage device may reject the client's I/O with
  an error indicating that a new layout with the correct iomode should be
  obtained via LAYOUTGET.  For example, if a client gets a layout with a LAYOUTIOMODE4_READ iomode and
  performs a WRITE to a storage device, the storage device is allowed
  to reject that WRITE.
</t>
<t>
  The use of the layout iomode does not conflict with OPEN share modes or byte-range LOCK operations;
  open share mode and byte-range lock conflicts are enforced as they are without the
  use of pNFS and are logically separate from the pNFS layout level.
  Open share modes and byte-range locks are the preferred method for
  restricting user access to data files.  For example, an OPEN of
  OPEN4_SHARE_ACCESS_WRITE does not conflict with a LAYOUTGET containing an iomode
  of LAYOUTIOMODE4_RW performed by another client.  Applications that depend
  on writing into the same file concurrently may use byte-range locking to
  serialize their accesses.
</t>
</section>

<section title="Device IDs" anchor="device_ids">
  <t>
    The device ID (data type deviceid4, see
    <xref target="deviceid4"/>) identifies a group of storage devices. The scope
    of a device ID is the pair &lt;client ID, layout type&gt;. In practice, a
    significant amount of information may be required to fully address
    a storage device.  Rather than embedding all such information in a
    layout, layouts embed device IDs.  The NFSv4.1 operation
    GETDEVICEINFO (<xref target="OP_GETDEVICEINFO" />) is used to
    retrieve the complete address information (including
    all device addresses for the device ID) regarding the storage
    device according to its layout type and device ID.  For example,
    the address of an NFSv4.1 data server or of an object-based storage
    device could be an IP address and port.  The address of a block
    storage device could be a volume label.
  </t>
  <t>
    Clients cannot expect the mapping between a device ID and
    its storage device address(es) to persist across metadata server restart.
    See <xref target="mds_recovery" /> for a description of how
    recovery works in that situation.
  </t>
  <t>
    A device ID lives as long as there is a layout
    referring to the device ID.  If there are no layouts
    referring to the device ID, the server is free to
    delete the device ID any time.
    Once a device ID is deleted by the server, the server MUST NOT
    reuse the device ID for the same layout type and client ID again.
    This requirement is feasible because the device ID is 16 bytes
    long, leaving sufficient room to store a generation number if the
    server's implementation requires most of the rest of the device ID's
    content to be reused. This requirement is necessary because
    otherwise the race conditions between asynchronous notification
    of device ID addition and deletion would be too difficult to
    sort out.

  </t>
  <t>
    Device ID to device address mappings are not leased,
    and can be changed at any time. (Note that while
    device ID to device address mappings are likely
    to change after the metadata server restarts, the
    server is not required to change the mappings.)
    A server has two
    choices for changing mappings.  It can recall all
    layouts referring to the device ID or it can use a
    notification mechanism.

  </t>
  <t>
    The NFSv4.1 protocol has no optimal way to recall
    all layouts that referred to a particular device ID
    (unless the server associates a single device ID with
    a single fsid or a single client ID; in which case,
    CB_LAYOUTRECALL has options for recalling all layouts
    associated with the fsid, client ID pair, or just the
    client ID).

  </t>
  <t>
    Via a notification mechanism
    (see <xref target="OP_CB_NOTIFY_DEVICEID" />),
    device ID to device address mappings can change over the duration
    of server operation without recalling or revoking the layouts that
    refer to device ID. The notification mechanism can also delete
    a device ID, but only if the client has no layouts referring
    to the device ID.
    A notification of a change to a device ID to device address
    mapping will immediately or eventually invalidate some or all of
    the device ID's mappings.
    The server MUST support notifications and the client must
    request them before they can be used.  For further information
    about the notification types <xref target="OP_CB_NOTIFY_DEVICEID" />.

  </t>
</section>

</section>

<section title="pNFS Operations" anchor="pnfs_ops">
<t>
  NFSv4.1 has several operations that are needed for
  pNFS servers, regardless of layout type or storage
  protocol. These operations are all sent to a metadata
  server and summarized here. While pNFS is an OPTIONAL
  feature, if pNFS is implemented, some operations
  are REQUIRED in order to comply with pNFS. See <xref
  target="operation_mandlist"/>.
</t>
<t>
 These are the fore channel pNFS operations:

 <list style='hanging'>
 <t hangText="GETDEVICEINFO">
  (<xref target="OP_GETDEVICEINFO" />), as noted previously
  (<xref target="device_ids" />), returns the mapping of device ID to
  storage device address.
 </t>

 <t hangText="GETDEVICELIST">
  (<xref target="OP_GETDEVICELIST" />)
  allows clients to fetch all device IDs
  for a specific file system.
 </t>
 <t hangText="LAYOUTGET">
  (<xref target="OP_LAYOUTGET" />) is used by a client to get
  a layout for a file.
 </t>
 <t hangText="LAYOUTCOMMIT">
  (<xref target="OP_LAYOUTCOMMIT" />) is used
  to inform the metadata server of the client's intent to commit data
  that has been written to the storage device (the storage device as
  originally indicated in the return value of LAYOUTGET).
 </t>
 <t hangText="LAYOUTRETURN">
  (<xref target="OP_LAYOUTRETURN" />) is used
  to return layouts for a file, a file system ID (FSID), or a client ID.
 </t>
 </list>
</t>
<t>

  These are the backchannel pNFS operations:

  <list style='hanging'>
  <t hangText="CB_LAYOUTRECALL">
   (<xref target="OP_CB_LAYOUTRECALL" />) recalls
   a layout, all layouts belonging to a file system, or all
   layouts belonging to a client ID.
 </t>
 <t hangText="CB_RECALL_ANY">
  (<xref target="OP_CB_RECALL_ANY" />)
  tells a client that it needs to return some number of recallable
  objects, including layouts, to the metadata server.
 </t>
 <t hangText="CB_RECALLABLE_OBJ_AVAIL">
  (<xref target="OP_CB_RECALLABLE_OBJ_AVAIL" />) tells a client
  that a recallable object that it was denied (in case of
  pNFS, a layout denied by LAYOUTGET) due to resource exhaustion
  is now available.
 </t>
 <t hangText="CB_NOTIFY_DEVICEID">
   (<xref target="OP_CB_NOTIFY_DEVICEID" />) notifies the client of
   changes to device IDs.
 </t>
 </list>
</t>

</section>
<section title="pNFS Attributes" anchor="pnfs_attr">
<t>
 A number of attributes specific to pNFS are listed and described in
 <xref target="pnfs_attr_full" />.
</t>
</section>

<section title="Layout Semantics">

<section title="Guarantees Provided by Layouts" anchor="layout_semantics">
<t>
  Layouts grant to the client the ability to access data located at
  a storage device with the appropriate storage protocol.  The client
  is guaranteed the layout will be recalled when one of two things
  occur: either a conflicting layout is requested or the state
  encapsulated by the layout becomes invalid (this can happen when
  an event directly or indirectly modifies the layout).  When a layout
  is recalled and returned by the client, the client continues with
  the ability to access file data with normal NFSv4.1 operations
  through the metadata server.  Only the ability to access the storage
  devices is affected.
</t>
<t>
  The requirement of NFSv4.1 that all user access rights MUST be
  obtained through the appropriate OPEN, LOCK, and ACCESS operations
  is not modified with the existence of layouts.  Layouts are provided
  to NFSv4.1 clients, and user access still follows the rules of the
  protocol as if they did not exist.  It is a requirement that for a
  client to access a storage device, a layout must be held by the
  client.  If a storage device receives an I/O request for a byte-range for
  which the client does not hold a layout, the storage device SHOULD
  reject that I/O request.  Note that the act of modifying a file for
  which a layout is held does not necessarily conflict with the
  holding of the layout that describes the file being modified.
  Therefore, it is the requirement of the storage protocol or layout
  type that determines the necessary behavior.  For example,
  block/volume layout types require that the layout's
  iomode agree with the type of I/O being performed.
</t>
<t>
  Depending upon the layout type and storage protocol in use, storage
  device access permissions may be granted by LAYOUTGET and may be
  encoded within the type-specific layout.  For an example of storage
  device access permissions, see an object-based protocol such as <xref
  target="OSD-T10" />.  If access permissions are encoded within the
  layout, the metadata server SHOULD recall the layout when those
  permissions become invalid for any reason -- for example, when a file
  becomes unwritable or inaccessible to a client.  Note, clients are
  still required to perform the appropriate
  OPEN, LOCK, and ACCESS operations as described above.  The degree to which it is
  possible for the client to circumvent these operations and
  the consequences of doing so must be clearly specified by the
  individual layout type specifications.  In addition, these
  specifications must be clear about the requirements and
  non-requirements for the checking performed by the server.
</t>
<t>
  In the presence of pNFS functionality, mandatory byte-range locks MUST
  behave as they would without pNFS.  Therefore, if mandatory file
  locks and layouts are provided simultaneously, the storage device
  MUST be able to enforce the mandatory byte-range locks.  For example, if
  one client obtains a mandatory byte-range lock and a second client accesses the
  storage device, the storage device MUST appropriately restrict I/O
  for the range of the mandatory byte-range lock.  If the storage
  device is incapable of providing this check in the presence of
  mandatory byte-range locks, then the metadata server MUST NOT grant
  layouts and mandatory byte-range locks simultaneously.
</t>
</section>

<section title="Getting a Layout" anchor="obtaining_layout">
<t>
  A client obtains a layout with the
  LAYOUTGET operation.  The metadata server
  will grant layouts of a particular type
  (e.g., block/volume, object, or file).
  The client selects an appropriate layout
  type that the server supports and the client
  is prepared to use.  The layout returned to
  the client might not exactly match the
  requested byte-range as described in <xref
  target="OP_LAYOUTGET_DESCRIPTION"/>.  As needed a client
  may send multiple LAYOUTGET operations; these might result
  in multiple overlapping, non-conflicting layouts (see
  <xref target="layout"/>).

</t>
<t>
  In order to get a layout, the client must first have opened the file
  via the OPEN operation. When a client has no layout on a file, it
  MUST present an open stateid, a delegation stateid, or
  a byte-range lock stateid in the loga_stateid argument. A successful
  LAYOUTGET result includes a layout stateid. The first successful
  LAYOUTGET processed by the server using a non-layout stateid as an
  argument MUST have the "seqid" field of the layout stateid in the
  response set to one. Thereafter, the client MUST use a layout
  stateid (see <xref target="layout_stateid" />) on future invocations
  of LAYOUTGET on the file, and the "seqid" MUST NOT be set to
  zero.  Once the layout has been retrieved, it can be held across
  multiple OPEN and CLOSE sequences.  Therefore, a client may hold a
  layout for a file that is not currently open by any user on the
  client.  This allows for the caching of layouts beyond CLOSE.
</t>
<t>
  The storage protocol used by the client to access the data on the
  storage device is determined by the layout's type.  The client is
  responsible for matching the layout type with an available method to
  interpret and use the layout.  The method for this layout type
  selection is outside the scope of the pNFS functionality.
</t>
<t>
  Although the metadata server is in control
  of the layout for a file, the pNFS client
  can provide hints to the server when a file
  is opened or created about the preferred
  layout type and aggregation schemes.
  pNFS introduces a layout_hint attribute (<xref
  target="attrdef_layout_hint" />) 
  that the client can set at file creation
  time to provide a hint to the server for new
  files. Setting this attribute separately,
  after the file has been created might make
  it difficult, or impossible, for the server
  implementation to comply.
</t>
<t>
  Because the EXCLUSIVE4 createmode4 does not allow the
  setting of attributes at file creation time, NFSv4.1
  introduces the EXCLUSIVE4_1 createmode4, which does
  allow attributes to be set at file creation time. In
  addition, if the session is created with persistent
  reply caches, EXCLUSIVE4_1 is neither necessary
  nor allowed. Instead, GUARDED4 both works better and is
  prescribed. <xref target="exclusive_create" /> in <xref
  target="OP_OPEN_DESCRIPTION" /> summarizes how a client
  is allowed to send an exclusive create.

</t>
</section>

<section title="Layout Stateid" anchor="layout_stateid">
<t>
  As with all other stateids, the layout stateid consists of a "seqid" and
  "other" field. Once a layout stateid is established, the "other" field
  will stay constant unless the stateid is revoked or the client
  returns all layouts on the file and the server disposes of the
  stateid.  The "seqid" field is initially set to one, and is never
  zero on any NFSv4.1 operation that uses layout stateids, whether it
  is a fore channel or backchannel operation. After the layout stateid
  is established, the server increments by one the value of the
  "seqid" in each subsequent LAYOUTGET and LAYOUTRETURN response, and
  in each CB_LAYOUTRECALL request.
</t>
<t>
  Given the design goal of pNFS to provide parallelism, the layout
  stateid differs from other stateid types in that the client is
  expected to send LAYOUTGET and LAYOUTRETURN operations in parallel.
  The "seqid" value is used by the client to properly sort responses
  to LAYOUTGET and LAYOUTRETURN.  The "seqid" is also used to prevent
  race conditions between LAYOUTGET and CB_LAYOUTRECALL.  Given that the
  processing rules differ from layout stateids and other stateid
  types, only the pNFS sections of this document should be considered
  to determine proper layout stateid handling.
</t>
<t>
  Once the client receives a layout stateid, it MUST use the correct
  "seqid" for subsequent LAYOUTGET or LAYOUTRETURN operations.  The
  correct "seqid" is defined as the highest "seqid" value from
  responses of fully processed LAYOUTGET or LAYOUTRETURN operations or
  arguments of a fully processed CB_LAYOUTRECALL operation.  Since the
  server is incrementing the "seqid" value on each layout operation,
  the client may determine the order of operation processing by
  inspecting the "seqid" value.  In the case of overlapping layout
  ranges, the ordering information will provide the client the
  knowledge of which layout ranges are held.  Note that overlapping
  layout ranges may occur because of the client's specific requests or
  because the server is allowed to expand the range of a requested
  layout and notify the client in the LAYOUTRETURN results. Additional
  layout stateid sequencing requirements are provided in
  <xref target="pnfs_operation_sequencing"/>.
</t>
<t>
  The client's receipt of a "seqid" is not sufficient for subsequent
  use.  The client must fully process the operations before the
  "seqid" can be used.  For LAYOUTGET results, if
  the client is not using the forgetful model
  (<xref target="recall_robustness"/>), it MUST first update its
  record of what ranges of the file's layout it has before using the
  seqid. For LAYOUTRETURN results, the client MUST delete the range
  from its record of what ranges of the file's layout it had before
  using the seqid. For CB_LAYOUTRECALL arguments, the client MUST send
  a response to the recall before using the seqid.
  The fundamental requirement in client
  processing is that the "seqid" is used to provide the order of
  processing.  LAYOUTGET results may be processed in parallel.
  LAYOUTRETURN results may be processed in parallel.  LAYOUTGET and
  LAYOUTRETURN responses may be processed in parallel as long as the
  ranges do not overlap.  CB_LAYOUTRECALL request processing MUST be
  processed in "seqid" order at all times. 
</t>
<t>
  Once a client has no more layouts on a file, the layout stateid is
  no longer valid and MUST NOT be used. Any attempt to use such a
  layout stateid will result in NFS4ERR_BAD_STATEID.
</t>

</section>

<section title="Committing a Layout" anchor="committing_layout">
<t>
  Allowing for varying storage protocol capabilities, the pNFS
  protocol does not require the metadata server and storage devices to
  have a consistent view of file attributes and data location
  mappings.  Data location mapping refers to aspects such as which offsets
  store data as opposed to storing holes (see <xref
  target="sparse_dense" /> for a discussion).  Related issues arise
  for storage protocols where a layout may hold provisionally
  allocated blocks where the allocation of those blocks does not
  survive a complete restart of both the client and server.  Because
  of this inconsistency, it is necessary to resynchronize the client
  with the metadata server and its storage devices and make any
  potential changes available to other clients.  This is accomplished
  by use of the LAYOUTCOMMIT operation.
</t>
<t>
  The LAYOUTCOMMIT operation is responsible for committing a modified
  layout to the metadata server.  The data should be written
  and committed to the appropriate storage devices before the
  LAYOUTCOMMIT occurs.  The
  scope of the LAYOUTCOMMIT operation depends on the storage protocol
  in use.  It is important to note that the level of
  synchronization is from the point of view of the client that sent
  the LAYOUTCOMMIT.  The updated state on the metadata server need
  only reflect the state as of the client's last operation previous to
  the LAYOUTCOMMIT.  The metadata server is not REQUIRED to maintain a global view
  that accounts for other clients' I/O that may have occurred within
  the same time frame.
</t>
<t>
  For block/volume-based layouts, LAYOUTCOMMIT may require
  updating the block list that comprises the file and committing this
  layout to stable storage.  For file-based layouts, synchronization of
  attributes between the metadata and storage devices, primarily the
  size attribute, is required.
</t>
<t>
  The control protocol is free to synchronize the attributes before
  it receives a LAYOUTCOMMIT; however, upon successful completion of a
  LAYOUTCOMMIT, state that exists on the metadata server that
  describes the file MUST be synchronized with the state that exists on the
  storage devices that comprise that file as of the client's
  last sent operation.  Thus, a client that queries the size of a file
  between a WRITE to a storage device and the LAYOUTCOMMIT might observe
  a size that does not reflect the actual data written.
</t>

<t>
  The client MUST have a layout in order to send a LAYOUTCOMMIT operation.
</t>

<section title="LAYOUTCOMMIT and change/time_modify">
<t>
  The change and time_modify attributes may be updated
  by the server when the LAYOUTCOMMIT operation is processed.  The
  reason for this is that some layout types do not support the update
  of these attributes when the storage devices process I/O operations.
  If a client has a layout with the LAYOUTIOMODE4_RW iomode on the file,
  the client MAY provide a suggested value to the server for
  time_modify within the arguments to LAYOUTCOMMIT.
  Based on the layout type, the provided value may or may not be used.
  The server should sanity-check the client-provided values
  before they are used.  For example, the server should ensure that
  time does not flow backwards.  The client always has the option to
  set time_modify through an explicit SETATTR operation.
</t>
<t>
  For some layout protocols, the storage device is able to notify the
  metadata server of the occurrence of an I/O; as a result, the
  change and time_modify attributes may be updated at
  the metadata server.  For a metadata server that is capable of
  monitoring updates to the change and time_modify
  attributes, LAYOUTCOMMIT processing is not required to update the
  change attribute.  In this case, the metadata server must ensure that
  no further update to the data has occurred since the last update of
  the attributes; file-based protocols may have enough information to
  make this determination or may update the change attribute upon each
  file modification.  This also applies for the time_modify
  attribute.  If the server implementation is able to
  determine that the file has not been modified since the last
  time_modify update, the server need not update time_modify at
  LAYOUTCOMMIT.  At LAYOUTCOMMIT completion, the updated attributes
  should be visible if that file was modified since the latest
  previous LAYOUTCOMMIT or LAYOUTGET.
</t>
</section>
<section title="LAYOUTCOMMIT and size" anchor="general_layoutcommit">
<t>
  The size of a file may be updated when the LAYOUTCOMMIT operation is
  used by the client.  One of the fields in the argument to
  LAYOUTCOMMIT is loca_last_write_offset; this field indicates the
  highest byte offset written but not yet committed with the
  LAYOUTCOMMIT operation.  The data type of loca_last_write_offset is
  newoffset4 and is switched on a boolean value, no_newoffset, that
  indicates if a previous write occurred or not.  If no_newoffset is
  FALSE, an offset is not given.  If the client has a layout with
  LAYOUTIOMODE4_RW iomode on the file, with a byte-range (denoted by the values of lo_offset and lo_length)
  that overlaps loca_last_write_offset, then the client MAY
  set no_newoffset to TRUE and provide an offset that will
  update the file size. Keep in mind that offset is not the same
  as length, though they are related. For example, a loca_last_write_offset
  value of zero means that one byte was written at offset zero, and so
  the length of the file is at least one byte.
</t>
<t>
  The metadata server may do one of the following:
    <list style="numbers">
    <t>
      Update the file's size using the last write offset provided by
      the client as either the true file size or as a hint of the file
      size.  If the metadata server has a method available, any new
      value for file size should be sanity-checked.  For example, the
      file must not be truncated if the client presents a last write
      offset less than the file's current size.
    </t>
    <t>
      Ignore the client-provided last write offset; the metadata
      server must have sufficient knowledge from other sources to
      determine the file's size.  For example, the metadata server
      queries the storage devices with the control protocol.
    </t>
    </list>
  </t>
<t>
  The method chosen to update the file's size will depend on the
  storage device's and/or the control protocol's capabilities.  For
  example, if the storage devices are block devices with no knowledge
  of file size, the metadata server must rely on the client to set the
  last write offset appropriately.
</t>
<t>
  The results of LAYOUTCOMMIT contain a new size value in the form of
  a newsize4 union data type.  If the file's size is set as a result
  of LAYOUTCOMMIT, the metadata server must reply with the new size;
  otherwise, the new size is not provided.
  If the file size is updated, the metadata server SHOULD update the
  storage devices such that the new file size is reflected when
  LAYOUTCOMMIT processing is complete.  For example, the client should
  be able to read up to the new file size.
</t>
<t> 
  The client can extend the length of a file
  or truncate a file by sending a SETATTR operation to the metadata server
  with the size attribute specified. If the size specified is larger than
  the current size of the file, the file is "zero extended", i.e., zeros are
  implicitly added between the file's previous EOF and the new EOF.
  (In many implementations, the zero-extended byte-range
  of the file consists of unallocated
  holes in the file.) When the client writes past EOF via WRITE,
  the SETATTR operation does not need to be used.

</t>
</section>
<section title="LAYOUTCOMMIT and layoutupdate" anchor="layoutcommit_update">
<t>
  The LAYOUTCOMMIT argument contains a loca_layoutupdate field (<xref
  target="OP_LAYOUTCOMMIT_ARGUMENT"/>) of data type layoutupdate4
  (<xref target="layoutupdate4"/>).  This argument is a
  layout-type-specific structure.  The structure can be used to pass
  arbitrary layout-type-specific information from the client to the
  metadata server at LAYOUTCOMMIT time.  For example, if using a
  block/volume layout, the client can indicate to the metadata server
  which reserved or allocated blocks the client used or did not use.
  The content of loca_layoutupdate (field lou_body) need not be the
  same layout-type-specific content returned by LAYOUTGET (<xref
  target="OP_LAYOUTGET_RESULT" />) in the loc_body field of the
  lo_content field of the logr_layout field.  
The content of
  loca_layoutupdate is defined by the layout type specification and is
  opaque to LAYOUTCOMMIT.
</t>
</section>
</section> <!-- Layout Semantics -->

<section title="Recalling a Layout" anchor="recalling_layout">
<t>
  Since a layout protects a client's access to a file via a direct
  client-storage-device path, a layout need only be recalled when it
  is semantically unable to serve this function.  Typically, this
  occurs when the layout no longer encapsulates the true location of
  the file over the byte-range it represents.  Any operation or
  action, such as server-driven restriping or load balancing, that
  changes the layout will result in a recall of the layout.  A layout
  is recalled by the CB_LAYOUTRECALL callback operation (see <xref
  target="OP_CB_LAYOUTRECALL" />) and returned with LAYOUTRETURN (see <xref
  target="OP_LAYOUTRETURN" />).  The CB_LAYOUTRECALL operation may
  recall a layout identified by a byte-range, all layouts
  associated with a file system ID (FSID), or all layouts associated with
  a client ID.
  <xref target="pnfs_operation_sequencing" /> discusses sequencing issues
  surrounding the getting, returning, and recalling of layouts.
</t>
<t>
  An iomode is also specified when recalling a layout.
  Generally, the iomode in the recall request must match the layout
  being returned; for example, a recall with an iomode of
  LAYOUTIOMODE4_RW should cause the client to only return
  LAYOUTIOMODE4_RW layouts and not LAYOUTIOMODE4_READ layouts.
  However, a special LAYOUTIOMODE4_ANY enumeration is
  defined to enable recalling a layout of any iomode; in other words,
  the client must return both LAYOUTIOMODE4_READ and LAYOUTIOMODE4_RW layouts.
</t>
<t>
  A REMOVE operation SHOULD cause the metadata server to recall the
  layout to prevent the client from accessing a non-existent file and
  to reclaim state stored on the client.  Since a REMOVE may be delayed
  until the last close of the file has occurred, the recall may also
  be delayed until this time.  After the last reference on the file
  has been released and the file has been removed, the client should
  no longer be able to perform I/O using the layout.  In the case of a
  file-based layout, the data server SHOULD return NFS4ERR_STALE in
  response to any operation on the removed file.
</t>
<t>
  Once a layout has been returned, the client MUST NOT send I/Os to
  the storage devices for the file, byte-range, and iomode
  represented by the returned layout. If a client does send an I/O to
  a storage device for which it does not hold a layout, the storage
  device SHOULD reject the I/O.
</t>
<t anchor="pnfs_and_delegations">
  Although pNFS does not alter the file data caching capabilities of
  clients, or their semantics, it recognizes that some clients may
  perform more aggressive write-behind caching to optimize the
  benefits provided by pNFS.  However, write-behind caching may
  negatively affect the latency in returning a layout in response to a
  CB_LAYOUTRECALL; this is similar to file delegations and the impact
  that file data caching has on DELEGRETURN.  Client implementations
  SHOULD limit the amount of unwritten data they have outstanding at
  any one time in order to prevent excessively long responses to
  CB_LAYOUTRECALL.  Once a layout is recalled, a server MUST wait one
  lease period before taking further action.  As soon as a lease
  period has passed, the server may choose to fence the client's access
  to the storage devices if the server perceives the client has taken
  too long to return a layout. However, just as in the case of data
  delegation and DELEGRETURN, the server may choose to wait, given that
  the client is showing forward progress on its way to returning the
  layout.  This forward progress can take the form of successful
  interaction with the storage devices or of sub-portions of the layout
  being returned by the client.  The server can also limit exposure to
  these problems by limiting the byte-ranges initially provided in
  the layouts and thus the amount of outstanding modified data.
</t>

<section title="Layout Recall Callback Robustness" anchor="recall_robustness">
<t>
  It has been assumed thus far that pNFS client
  state
  (layout ranges and iomode)
  for a file exactly matches that of the pNFS server for that file.
  This assumption
  leads to the implication that any callback results in a
  LAYOUTRETURN or set of LAYOUTRETURNs that exactly match the range in
  the callback, since both client and server agree about the state
  being maintained.  However, it can be useful if this assumption does
  not always hold.  For example:
</t>
<t>
<list style="symbols">
<t>
  If conflicts that require
  callbacks are very rare, and a server can use a multi-file callback
  to recover per-client resources (e.g., via an FSID recall or a
  multi-file recall within a single CB_COMPOUND), the result may be
  significantly less client-server pNFS traffic.
</t>
<t>
  It may be useful for servers to maintain information about
  what ranges are held by a client on a coarse-grained basis, leading
  to the server's layout ranges being beyond those actually held by
  the client.
  In the extreme, a server could manage conflicts on
  a per-file basis, only sending whole-file callbacks even though
  clients may request and be granted sub-file ranges.
</t>
<t>
  It may be useful for clients to "forget" details about
  what layouts and ranges the client actually has, leading
  to the server's layout ranges being beyond those that the
  client "thinks" it has. As long as the client does not
  assume it has layouts that are beyond what the server
  has granted, this is a safe practice.  When a client
  forgets what ranges and layouts it has, and it receives
  a CB_LAYOUTRECALL operation, the client MUST follow up
  with a LAYOUTRETURN for what the server recalled, or
  alternatively return the NFS4ERR_NOMATCHING_LAYOUT error
  if it has no layout to return in the recalled range.

</t>

<t>
  In order to avoid errors, it is vital that a client not assign
  itself layout permissions beyond what the server has granted, and
  that the server not forget layout permissions that have been granted.
  On the other hand, if a
  server believes that a client holds a layout that the client
  does not know about, it is useful for the client to cleanly indicate
  completion of the requested recall either by sending a LAYOUTRETURN
  operation for the entire requested range or by returning an
  NFS4ERR_NOMATCHING_LAYOUT error to the CB_LAYOUTRECALL.
</t>
</list>
</t>
<t>
  Thus, in light of the above, it is useful for a server to be able to
  send callbacks for layout ranges it has not granted to a client,
  and for a client to return ranges it does not hold.  A pNFS client
  MUST always return layouts that comprise the full range
  specified by the recall.  Note, the full recalled layout range need
  not be returned as part of a single operation, but may be returned
  in portions.  This allows the client to stage the flushing of dirty
  data and commits and returns of layouts.
Also, it indicates to the
  metadata server that the client is making progress.
</t>
<t>
  When a layout is returned, the client MUST NOT have any outstanding
  I/O requests to the storage devices involved in the layout.
  Rephrasing, the client MUST NOT return the layout while it has
  outstanding I/O requests to the storage device.
</t>
<t>
  Even with this requirement for the client, it is possible that I/O
  requests may be presented to a storage device no longer allowed to
  perform them.  Since the server has no strict control as to when the
  client will return the layout, the server may later decide to
  unilaterally revoke the client's access to the storage devices
  as provided by the layout.  In
  choosing to revoke access, the server must deal with the possibility
  of lingering I/O requests, i.e., I/O requests that are
  still in flight to
  storage devices identified by the revoked layout.

  All layout type specifications MUST define whether unilateral layout revocation by
  the metadata server is supported; if it is, the specification must
  also describe how lingering writes are processed.  For example,
  storage devices identified by the revoked layout could be fenced off
  from the client that held the layout.
</t>
<t>
  In order to ensure client/server convergence with regard to layout state,
  the final LAYOUTRETURN operation in a sequence of LAYOUTRETURN
  operations for a particular recall MUST specify the entire range
  being recalled, echoing the recalled layout type, iomode,
  recall/return type (FILE, FSID, or ALL), and byte-range, even if
  layouts pertaining to partial ranges were previously
  returned.  In addition, if the client holds no layouts that
  overlap the range being recalled, the client should return the
  NFS4ERR_NOMATCHING_LAYOUT error code to CB_LAYOUTRECALL.  This
  allows the server to update its view of the client's layout state.
</t>
</section>

<section title="Sequencing of Layout Operations" anchor="pnfs_operation_sequencing">
<t>
  As with other stateful operations, pNFS requires the correct
  sequencing of layout operations.  pNFS uses the "seqid" in the
  layout stateid to provide the correct sequencing between regular
  operations and callbacks.  It is the server's responsibility to
  avoid inconsistencies regarding the layouts provided and the
  client's responsibility to properly serialize its layout requests
  and layout returns.
</t>
<section title="Layout Recall and Return Sequencing">
<t>
  One critical issue with regard to layout operations sequencing
  concerns callbacks.  The protocol must defend against
  races between the reply to a LAYOUTGET or LAYOUTRETURN
  operation and a subsequent CB_LAYOUTRECALL.  A client
  MUST NOT process a CB_LAYOUTRECALL that implies one or
  more outstanding LAYOUTGET or LAYOUTRETURN operations to
  which the client has not yet received a reply. The client
  detects such a CB_LAYOUTRECALL by examining the "seqid"
  field of the recall's layout stateid. If the "seqid" 
  is not exactly one higher than what the client currently has recorded, and the
  client has at least one LAYOUTGET and/or LAYOUTRETURN operation
  outstanding, the client knows the server sent the CB_LAYOUTRECALL 
  after sending a response to an outstanding LAYOUTGET or LAYOUTRETURN.
  The client MUST wait before processing such a CB_LAYOUTRECALL
  until it processes all replies for outstanding LAYOUTGET and
  LAYOUTRETURN operations for the corresponding file
  with seqid less than the seqid given by CB_LAYOUTRECALL
  (lor_stateid; see <xref target="OP_CB_LAYOUTRECALL"/>.)
</t>
<t>
  In addition to the seqid-based mechanism,
  <xref target="sessions_callback_races"/>
  describes the sessions mechanism for allowing the
  client to detect callback race conditions and delay processing such a
  CB_LAYOUTRECALL. The server MAY reference conflicting operations
  in the CB_SEQUENCE that precedes the CB_LAYOUTRECALL.
  Because the server has already sent replies for these operations before
  sending the callback, the replies may race with the CB_LAYOUTRECALL.
  The client MUST wait for all the referenced calls to complete and update
  its view of the layout state before processing the CB_LAYOUTRECALL.
</t>

<section title="Get/Return Sequencing">
<t>
  The protocol allows the client to send concurrent
  LAYOUTGET and LAYOUTRETURN operations to the server. The
  protocol does not provide any means for the server to
  process the requests in the same order in which they
  were created. However, through the use of the "seqid"
  field in the layout stateid, the client can determine
  the order in which parallel outstanding operations were
  processed by the server. Thus, when a layout retrieved
  by an outstanding LAYOUTGET operation intersects with
  a layout returned by an outstanding LAYOUTRETURN on
  the same file, the order in which the two conflicting
  operations are processed determines the final state of
  the overlapping layout. The order is determined by
  the "seqid" returned in each operation: the operation with the
  higher seqid was executed later.

</t>
<t>
  It is permissible for the client to send multiple parallel
  LAYOUTGET operations for the same file or multiple parallel LAYOUTRETURN
  operations for the same file or a mix of both.
</t>
<t>
  It is permissible for the client to use the current stateid (see
  <xref target="current_stateid"/>) for LAYOUTGET operations, for
  example, when compounding LAYOUTGETs or compounding OPEN and
  LAYOUTGETs.  It is also permissible to use the current stateid when
  compounding LAYOUTRETURNs.
</t>
<t>
  It is permissible for the client to use the current stateid when
  combining LAYOUTRETURN and LAYOUTGET operations for the same file in
  the same COMPOUND request since the server MUST process these in
  order.  However, if a client does send such COMPOUND requests, it
  MUST NOT have more than one outstanding for the same file at the
  same time, and it MUST NOT have other LAYOUTGET or LAYOUTRETURN
  operations outstanding at the same time for that same file.
</t>
</section>

<section title="Client Considerations">
<t>
  Consider a pNFS client that has sent a LAYOUTGET, and before
  it receives the reply to LAYOUTGET, it receives
  a CB_LAYOUTRECALL for the same file with an overlapping range.  There are two
  possibilities, which the client can distinguish
  via the layout stateid in the recall.

  <list style="numbers">
  <t>
    The server processed the LAYOUTGET before sending the recall, so the
    LAYOUTGET must be waited for because it
    may be carrying layout information that will need to be returned to deal
    with the CB_LAYOUTRECALL.
  </t>
  <t>
    The
    server sent the callback before receiving the
    LAYOUTGET. The server will not respond to the LAYOUTGET
    until the CB_LAYOUTRECALL is processed.

  </t>
  </list>

  If these possibilities cannot be distinguished, a
  deadlock could result, as the client must wait for the
  LAYOUTGET response before processing the recall in the
  first case, but that response will not arrive until after
  the recall is processed in the second case. Note that
  in the first case, the "seqid" in the layout stateid
  of the recall is two greater than what the client has
  recorded; in the second case, the "seqid" is one greater than
  what the client has recorded.  This allows the client
  to disambiguate between the two cases. The client thus
  knows precisely which possibility applies.

</t>
<t>

  In case 1, the client knows it needs to wait for
  the LAYOUTGET response before processing the recall
  (or the client can return NFS4ERR_DELAY). 
</t>
<t>
  In case 2, the client will not wait for the LAYOUTGET
  response before processing the recall because waiting
  would cause deadlock.  Therefore, the action at the
  client will only require waiting in the case that the
  client has not yet seen the server's earlier responses
  to the LAYOUTGET operation(s).

</t>
<t>
  The recall process can be considered completed when
  the final LAYOUTRETURN operation for the recalled range is completed.
  The LAYOUTRETURN uses the layout stateid (with seqid) specified in
  CB_LAYOUTRECALL.  If the client uses multiple LAYOUTRETURNs in
  processing the recall, the first LAYOUTRETURN will use the layout
  stateid as specified in CB_LAYOUTRECALL.  Subsequent LAYOUTRETURNs
  will use the highest seqid as is the usual case.
</t>

</section>

<section title="Server Considerations" anchor="layout_server_consider">
<t>
  Consider a race from the metadata server's point of
  view.  The metadata server has sent a CB_LAYOUTRECALL and receives
  an overlapping LAYOUTGET for the same file before the
  LAYOUTRETURN(s) that respond to the CB_LAYOUTRECALL. There are
  three cases:

<list style="numbers">
<t>
  The client sent the LAYOUTGET before processing the CB_LAYOUTRECALL.
  The "seqid" in the layout stateid of the arguments of LAYOUTGET is one less 
  than the "seqid" in CB_LAYOUTRECALL. The server returns
  NFS4ERR_RECALLCONFLICT to the client, which indicates to the client
  that there is a pending recall.
</t>
<t>
  The client sent the LAYOUTGET after processing the
  CB_LAYOUTRECALL, but the LAYOUTGET arrived before the LAYOUTRETURN and
  the response to CB_LAYOUTRECALL that
  completed that processing.
  The "seqid" in the layout stateid
  of LAYOUTGET is equal to or greater than that of the "seqid" in
  CB_LAYOUTRECALL.
  The server has not received a response to the CB_LAYOUTRECALL,
  so it returns NFS4ERR_RECALLCONFLICT.
</t>
<t>
  The client sent the LAYOUTGET after processing the
  CB_LAYOUTRECALL; the server received the CB_LAYOUTRECALL
  response, but the LAYOUTGET arrived before the LAYOUTRETURN that
  completed that processing.
  The "seqid" in the layout stateid
  of LAYOUTGET is equal to that of the "seqid" in
  CB_LAYOUTRECALL.
  The server has received a response to the CB_LAYOUTRECALL,
  so it returns NFS4ERR_RETURNCONFLICT.
</t>
</list>
</t>

</section>

<section title="Wraparound and Validation of Seqid">
<t>
  The rules for layout stateid processing differ from other stateids
  in the protocol because the "seqid" value cannot be zero and the
  stateid's "seqid" value changes in a CB_LAYOUTRECALL operation.  The
  non-zero requirement combined with the inherent parallelism of
  layout operations means that a set of LAYOUTGET and LAYOUTRETURN
  operations may contain the same value for "seqid".
  The server uses a slightly modified version of the modulo arithmetic
  as described in 
  <xref target="Slot Identifiers and Server Reply Cache" /> 
  when incrementing the layout stateid's "seqid".  The difference
  is that zero is not a valid value for "seqid"; when the the value
  of a "seqid" is 0xFFFFFFFF, the next valid value will be 0x00000001.
  The modulo arithmetic is also used for the comparisons of
  "seqid" values in the processing of CB_LAYOUTRECALL events as
  described above in <xref target="layout_server_consider" />.
</t>
<t>
  Just as the server validates the "seqid" in the event of
  CB_LAYOUTRECALL usage, as described in
  <xref target="layout_server_consider" />, the server also validates
  the "seqid" value to ensure that it is within an appropriate range.
  This range represents the degree of parallelism the server supports
  for layout stateids.  If the client is sending multiple layout
  operations to the server in parallel, by definition, the "seqid"
  value in the supplied stateid will not be the current "seqid" as
  held by the server.  The range of parallelism spans from the highest
  or current "seqid" to a "seqid" value in the past.  To assist in the
  discussion, the server's current "seqid" value for a layout stateid
  is defined as SERVER_CURRENT_SEQID.  The lowest "seqid" value that
  is acceptable to the server is represented by PAST_SEQID.  And the
  value for the range of valid "seqid"s or range of parallelism is
  VALID_SEQID_RANGE.  Therefore, the following holds:
  VALID_SEQID_RANGE = SERVER_CURRENT_SEQID - PAST_SEQID.  In the
  following, all arithmetic is the modulo arithmetic as described
  above.
</t>
<t>
  The server MUST support a minimum VALID_SEQID_RANGE.  The minimum is
  defined as: VALID_SEQID_RANGE = summation over 1..N of
  (ca_maxoperations(i) - 1), where N is the number of session fore
  channels and ca_maxoperations(i) is the value of the ca_maxoperations returned from
  CREATE_SESSION of the i'th session.  The reason for "- 1" is to allow for the required
  SEQUENCE operation.  The server MAY support a VALID_SEQID_RANGE
  value larger than the minimum.  The maximum VALID_SEQID_RANGE is (2
  ^ 32 - 2) (accounting for zero not being a valid "seqid" value).
</t>
<t>
  If the server finds the "seqid" is zero, the NFS4ERR_BAD_STATEID
  error is returned to the client.  The server further validates the
  "seqid" to ensure it is within the range of parallelism,
  VALID_SEQID_RANGE.  If the "seqid" value is outside of that range,
  the error NFS4ERR_OLD_STATEID is returned to the client.  Upon
  receipt of NFS4ERR_OLD_STATEID, the client updates the stateid in
  the layout request based on processing of other layout requests and
  re-sends the operation to the server.
</t>
</section>  

<section title="Bulk Recall and Return" anchor="bulk_layouts">

<t>
 pNFS supports recalling and returning all layouts that
 are for files belonging to a particular fsid
 (LAYOUTRECALL4_FSID, LAYOUTRETURN4_FSID) or client ID
 (LAYOUTRECALL4_ALL, LAYOUTRETURN4_ALL).
 There are no "bulk" stateids, so detection of races
 via the seqid is not possible. 
 The server MUST NOT initiate bulk recall while another
 recall is in progress, or the corresponding LAYOUTRETURN
 is in progress or pending.
 In the event the server sends a bulk recall
 while the client has a pending or in-progress LAYOUTRETURN,
 CB_LAYOUTRECALL, or LAYOUTGET, the client returns
 NFS4ERR_DELAY. In the event the client sends a LAYOUTGET
 or LAYOUTRETURN while a bulk recall is in progress, the
 server returns NFS4ERR_RECALLCONFLICT.

 If the client sends a LAYOUTGET or LAYOUTRETURN after
 the server receives NFS4ERR_DELAY from a bulk recall,
 then to ensure forward progress, the server MAY return
 NFS4ERR_RECALLCONFLICT.

</t>
<t>
 Once a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL is sent,
 the server MUST NOT allow the client to use any layout
 stateid except for LAYOUTCOMMIT operations. Once the client receives
 a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL, it MUST NOT use
 any layout stateid except for LAYOUTCOMMIT operations.

 Once a LAYOUTRETURN of LAYOUTRETURN4_ALL is sent, all
 layout stateids granted to the client ID are freed.
 The client MUST NOT use the layout stateids again. It
 MUST use LAYOUTGET to obtain new layout stateids.

</t>
<t>
 Once a CB_LAYOUTRECALL of LAYOUTRECALL4_FSID is sent, the
 server MUST NOT allow the client to use any layout stateid
 that refers to a file with the specified fsid except for
 LAYOUTCOMMIT operations. Once the client receives a CB_LAYOUTRECALL
 of LAYOUTRECALL4_ALL, it MUST NOT use any layout stateid
 that refers to a file with the specified fsid except
 for LAYOUTCOMMIT operations.

 Once a LAYOUTRETURN of LAYOUTRETURN4_FSID is sent, all
 layout stateids granted to the referenced fsid are freed.
 The client MUST NOT use those freed layout stateids for files
 with the referenced fsid again. Subsequently, for any file with
 the referenced fsid, to use a layout, the client MUST first
 send a LAYOUTGET operation in order to
 obtain a new layout stateid for that file.

</t>
<t>
 If the server has sent a bulk CB_LAYOUTRECALL and
 receives a LAYOUTGET, or a LAYOUTRETURN with a stateid,
 the server MUST return NFS4ERR_RECALLCONFLICT. If the
 server has sent a bulk CB_LAYOUTRECALL and receives a
 LAYOUTRETURN with an lr_returntype that is not equal to
 the lor_recalltype of the CB_LAYOUTRECALL, the server
 MUST return NFS4ERR_RECALLCONFLICT.

</t>
</section>

</section>
</section>
</section>

<section title="Revoking Layouts" anchor="revoke_layout">
<t>

Parallel NFS permits servers to revoke layouts from clients
that fail to respond to recalls and/or fail to renew their
lease in time. Depending on the layout type,
the server might revoke the layout and might take certain actions
with respect to the client's I/O to data servers.

</t>
</section>
<section title="Metadata Server Write Propagation" anchor="async_writes">
<t>
  Asynchronous writes written through the metadata server may be
  propagated lazily to the storage devices.  For data written
  asynchronously through the metadata server, a client performing a
  read at the appropriate storage device is not guaranteed to see the
  newly written data until a COMMIT occurs at the metadata server.
  While the write is pending, reads to the storage device may give out
  either the old data, the new data, or a mixture of new and old.
  Upon completion of a synchronous WRITE or COMMIT (for asynchronously
  written data), the metadata server MUST ensure that storage devices
  give out the new data and that the data has been written to stable
  storage.  If the server implements its storage in any way such that
  it cannot obey these constraints, then it MUST recall the layouts to
  prevent reads being done that cannot be handled correctly.  Note
  that the layouts MUST be recalled prior to the server responding to
  the associated WRITE operations.
</t>
</section>

</section>

<section title="pNFS Mechanics">
<t>
  This section describes the operations flow taken by a pNFS client
  to a metadata server and storage device.
</t>
<t>
  When a pNFS client encounters a new FSID, it sends a GETATTR to the
  NFSv4.1 server for the fs_layout_type (<xref target="attrdef_fs_layout_type"
  />) attribute. If the attribute returns at least one layout type,
  and the layout types returned are among the set supported by
  the client, the client knows that pNFS is a possibility for the file
  system.  If, from the server that returned the new FSID, the client
  does not have a client ID that came from an EXCHANGE_ID result that
  returned EXCHGID4_FLAG_USE_PNFS_MDS, it MUST send an EXCHANGE_ID to
  the server with the EXCHGID4_FLAG_USE_PNFS_MDS bit set. If the
  server's response does not have EXCHGID4_FLAG_USE_PNFS_MDS, then
  contrary to what the fs_layout_type attribute said, the server does
  not support pNFS, and the client will not be able use pNFS to that
  server; in this case, the server MUST return NFS4ERR_NOTSUPP in
  response to any pNFS operation.
</t>
<t>
  The client then creates a session, requesting a persistent session, so
  that exclusive creates can be done with single round trip via the
  createmode4 of GUARDED4. If the session ends up not being persistent,
  the client will use EXCLUSIVE4_1 for exclusive creates.
</t>
<t>
  If a file is to be created on a pNFS-enabled file
  system, the client uses the OPEN operation.  With the
  normal set of attributes that may be provided upon OPEN
  used for creation, there is an OPTIONAL layout_hint
  attribute.  The client's use of layout_hint allows the
  client to express its preference for a layout type and its
  associated layout details. The use of a createmode4 of
  UNCHECKED4, GUARDED4, or EXCLUSIVE4_1 will allow the
  client to provide the layout_hint attribute at create
  time. The client MUST NOT use EXCLUSIVE4 (see <xref
  target="exclusive_create"/>).  The client is RECOMMENDED
  to combine a GETATTR operation after the OPEN within
  the same COMPOUND.  The GETATTR may then retrieve
  the layout_type attribute for the newly created file.
  The client will then know what layout type the server has
  chosen for the file and therefore what storage protocol
  the client must use.

</t>
<t>
  If the client wants to open an existing file, then it also includes
  a GETATTR to determine what layout type the file supports.
</t>
<t>
  The GETATTR in either the file creation or plain file open case can
  also include the layout_blksize and layout_alignment attributes so
  that the client can determine optimal offsets and lengths for I/O on
  the file.
</t>
<t>
  Assuming the client supports the layout type returned by GETATTR and
  it chooses to use pNFS for data access, it then sends LAYOUTGET
  using the filehandle and stateid returned by OPEN, specifying the range it wants
  to do I/O on. The response is a layout, which may be a subset of the
  range for which the client asked. It also includes device IDs and a
  description of how data is organized (or in the case of writing, how
  data is to be organized) across the devices.  The device IDs and
  data description are encoded in a format that is specific to the
  layout type, but the client is expected to understand.
</t>
<t>
  When the client wants to send an I/O, it determines to which device ID
  it needs to send the I/O command by examining the data
  description in the layout. It then sends a
  GETDEVICEINFO to find the device address(es) of the device ID.  The
  client then sends the I/O request to one of device ID's device addresses, using the
  storage protocol defined for the layout type.
  Note that if a client has multiple I/Os to send,
  these I/O requests may be done in parallel.
</t>
<t>
  If the I/O was a WRITE, then at some point
  the client may want to use LAYOUTCOMMIT to
  commit the modification time and the new size
  of the file (if it believes it extended the file size) to the
  metadata server and the modified data to the file system.
</t>
</section> 
<section title="Recovery" anchor="crash_recovery">
<t>
  Recovery is complicated by the distributed nature of the pNFS
  protocol.  In general, crash recovery for layouts is similar to
  crash recovery for delegations in the base NFSv4.1 protocol.  However,
  the client's ability to perform I/O without contacting the metadata
  server introduces subtleties that must be handled correctly if
  the possibility of file system corruption is to be avoided.
</t>
 <section title="Recovery from Client Restart" anchor="pnfs_client_recovery">
 <t>
   Client recovery for layouts is similar to client recovery for other
   lock and delegation state.  When a pNFS client restarts, it will lose
   all information about the layouts that it previously owned.  There
   are two methods by which the server can reclaim these resources and
   allow otherwise conflicting layouts to be provided to other
   clients.
 </t>
 <t>
   The first is through the expiry of the client's lease.  If the
   client recovery time is longer than the lease period, the client's
   lease will expire and the server will know that state may be
   released.  For layouts, the server may release the state immediately
   upon lease expiry or it may allow the layout to persist, awaiting
   possible lease revival, as long as no other layout conflicts.
 </t>
 <t>
   The second is through the client restarting in less time than it
   takes for the lease period to expire.  In such a case, the client
   will contact the server through the standard EXCHANGE_ID protocol.
   The server will find that the client's co_ownerid matches the
   co_ownerid of the previous client invocation, but that the verifier
   is different.  The server uses this as a signal to release all
   layout state associated with the client's previous invocation.  In
   this scenario, the data written by the client but not covered by a
   successful LAYOUTCOMMIT is in an undefined state; it may have been
   written or it may now be lost.  This is acceptable behavior and it
   is the client's responsibility to use LAYOUTCOMMIT to achieve the
   desired level of stability.
 </t>
 </section>

 <section title="Dealing with Lease Expiration on the Client"
   anchor="lease_expiration_client">
 <t anchor="pnfs_clnt_case1">
   If a client believes its lease has expired, it MUST NOT send I/O
   to the storage device until it has validated its lease. The client
   can send a SEQUENCE operation to the metadata server. If the
   SEQUENCE operation is successful, but sr_status_flag has
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
   SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST NOT use
   currently held layouts. The client has two
   choices to recover from the lease expiration. First, for all
   modified but uncommitted data, the client writes it to the metadata server
   using the FILE_SYNC4 flag for the WRITEs, or WRITE and
   COMMIT. Second, the client re-establishes a client ID and session with
   the server and obtains new layouts and device-ID-to-device-address
   mappings for the modified data ranges and then writes the data to the
   storage devices with the newly obtained layouts.
 </t>
 <t anchor="pnfs_clnt_case2">
   If sr_status_flags from the metadata server has
   SEQ4_STATUS_RESTART_RECLAIM_NEEDED set
   (or SEQUENCE returns NFS4ERR_BAD_SESSION and
   CREATE_SESSION returns NFS4ERR_STALE_CLIENTID), then the metadata
   server has restarted, and the client SHOULD recover using the
   methods described in <xref target="mds_recovery" />.
 </t>
 <t anchor="pnfs_clnt_case3">
   If sr_status_flags from the metadata server has
   SEQ4_STATUS_LEASE_MOVED set, then the client recovers by following
   the procedure described in <xref
   target="transferred_lease"/>. After that, the client may get an
   indication that the layout state was not moved with the file
   system.  The client recovers as in the other
   applicable situations discussed in the first two paragraphs of this section.
 </t>
 <t anchor="pnfs_clnt_case4">
   If sr_status_flags reports no loss of state, then the lease for the
   layouts that the client has are valid and
   renewed, and the client can once again send I/O requests to the
   storage devices.
 </t> 
 <t>
  While clients SHOULD NOT send I/Os to storage devices that may
  extend past the lease expiration time period, this is not always
  possible, for example, an extended network partition that starts
  after the I/O is sent and does not heal until the I/O request is
  received by the storage device.  Thus, the metadata server and/or
  storage devices are responsible for protecting themselves from I/Os
  that are both sent before the lease expires and arrive after the lease
  expires.  See <xref target="lease_expiration_mds" />.
 </t>
 </section>

 <section title="Dealing with Loss of Layout State on the Metadata Server"
   anchor="lease_expiration_mds">
 <t>
   This is a description of the case where all of the following are
   true: 
   <list style="symbols">
   <t>
     the metadata server has not restarted
   </t>
   <t>
     a pNFS client's
     layouts have been discarded (usually because the client's lease
     expired) and are invalid
   </t>
   <t>
     an I/O from the pNFS client arrives at the storage device
   </t>
   </list>
   The metadata server and its storage devices MUST solve this by
   fencing the client.  In other words, they MUST  solve this by
   preventing the execution of I/O operations from the client to the
   storage devices after layout
   state loss.  The details of how fencing is done are specific to the
   layout type.  The solution for NFSv4.1 file-based layouts is
   described in (<xref target="file_layout_revoke" />), and solutions for other
   layout types are in their respective external specification documents.
 </t>
 </section>

<section title="Recovery from Metadata Server Restart" anchor="mds_recovery">
   <t>
    The pNFS client will discover that the metadata server has
    restarted via the methods described in <xref
    target="server_failure" /> and discussed in a pNFS-specific
    context in <xref target="pnfs_clnt_case2" />, of <xref
    target="lease_expiration_client" />.  The client MUST stop using
    layouts and delete the device ID to device address mappings it
    previously received from the metadata server.  Having done that,
    if the client wrote data to the storage device without committing
    the layouts via LAYOUTCOMMIT, then the client has
    additional work to do in order to have the client, metadata server,
    and storage device(s) all synchronized on the state of the data.
    <list style='symbols'>
  <t>
    If the client has data still modified
    and unwritten in the client's memory, the client has only two choices.
    <list style='numbers'>
    <t>
     The client can obtain a layout via LAYOUTGET after the
     server's grace period and write the data to the storage devices.
    </t>
    <t>
     The client can WRITE that data through the metadata server using the
     WRITE (<xref target="OP_WRITE" />) operation, and then obtain
     layouts as desired.
    </t>
   </list> 
  </t>
  <t>
    If the client asynchronously wrote data to the storage device, but
    still has a copy of the data in its memory, then it has available
    to it the recovery options listed above in the previous bullet
    point.  If the metadata server is also in its grace period, the
    client has available to it the options below in the next bullet
    point.  
  </t>
  <t>
    The client does not have a copy of the data in its memory and the
    metadata server is still in its grace period.  The client cannot
    use LAYOUTGET (within or outside the grace period) to reclaim a
    layout because the contents of the response from LAYOUTGET
    may not match what it had previously.  The range might be
    different or the client might get the same range but the content of the
    layout might be different.  Even if the content of the layout
    appears to be the same, the device IDs may map to different
    device addresses, and even if the device addresses are the same,
    the device addresses could have been assigned to a different
    storage device.  The option of retrieving the data from the
    storage device and writing it to the metadata server per the
    recovery scenario described above is
    not available because, again, the mappings of range to device ID,
    device ID to device address, and device address to physical device are
    stale, and new mappings via new LAYOUTGET do not solve the problem.

    <vspace blankLines='1' />

    The only recovery option for this scenario is to send a
    LAYOUTCOMMIT in reclaim mode, which the metadata server will
    accept as long as it is in its grace period.  The use of
    LAYOUTCOMMIT in reclaim mode informs the metadata server that the
    layout has changed.  It is critical that the metadata server
    receive this information before its grace period ends, and thus
    before it starts allowing updates to the file system.

    <vspace blankLines='1' />

    To send LAYOUTCOMMIT in reclaim mode, the client sets the
    loca_reclaim field of the operation's arguments (<xref
    target="OP_LAYOUTCOMMIT_ARGUMENT"/>) to TRUE.  During the metadata
    server's recovery grace period (and only during the recovery grace
    period) the metadata server is prepared to accept LAYOUTCOMMIT
    requests with the loca_reclaim field set to TRUE.

    <vspace blankLines='1' />

    When loca_reclaim is TRUE, the client is attempting to commit
    changes to the layout that occurred prior to the restart
    of the metadata server.  The metadata server applies some
    consistency checks on the loca_layoutupdate field of the arguments
    to determine whether the client can commit the data written to the
    storage device to the file system.  The loca_layoutupdate field is of
    data type layoutupdate4 and contains layout-type-specific content
    (in the lou_body field of loca_layoutupdate).  The
    layout-type-specific information that loca_layoutupdate might have
    is discussed in <xref target="layoutcommit_update" />.  If the
    metadata server's consistency checks on loca_layoutupdate succeed,
    then the metadata server MUST commit the data (as described by the
    loca_offset, loca_length, and loca_layoutupdate fields of the
    arguments) that was written to the storage device.  If the metadata
    server's consistency checks on loca_layoutupdate fail, the
    metadata server rejects the LAYOUTCOMMIT operation and makes no
    changes to the file system.  However, any time LAYOUTCOMMIT with
    loca_reclaim TRUE fails, the pNFS client has lost all the data in
    the range defined by &lt;loca_offset, loca_length&gt;.  A client
    can defend against this risk by caching all data, whether written
    synchronously or asynchronously in its memory, and by not releasing the
    cached data until a successful LAYOUTCOMMIT.  This condition
    does not hold true for all layout types; for example, file-based
    storage devices need not suffer from this limitation.
  </t>
  <t>
    The client does not have a copy of the data in its memory and the
    metadata server is no longer in its grace period; i.e., the metadata
    server returns NFS4ERR_NO_GRACE. As with the scenario in the above
    bullet point, the failure of LAYOUTCOMMIT means the data
    in the range  &lt;loca_offset, loca_length&gt; lost. The
    defense against the risk is the same -- cache all written data
    on the client until a successful LAYOUTCOMMIT.
  </t>
  </list> 
  </t>
</section>
<section title="Operations during Metadata Server Grace Period"
  anchor="pnfs_grace_exception">
  <t>
    Some of the recovery scenarios thus far noted that some
    operations (namely, WRITE and LAYOUTGET) might be permitted during
    the metadata server's grace period. The metadata server may allow
    these operations during its grace period.  For LAYOUTGET, the
    metadata server must reliably determine that servicing such a
    request will not conflict with an impending LAYOUTCOMMIT reclaim
    request.  For WRITE, the metadata server
    must reliably determine that servicing the request
    will not conflict with an impending OPEN or with a LOCK where the
    file has mandatory byte-range locking enabled.
  </t>
  <t>
    As mentioned previously, for expediency, 
    the metadata server might reject some
    operations (namely, WRITE and LAYOUTGET) during its
    grace period, because the simplest correct approach
    is to reject all non-reclaim pNFS requests and WRITE operations by
    returning the NFS4ERR_GRACE error.  However, depending on the
    storage protocol (which is specific to the layout type) and
    metadata server implementation, the metadata server may be able to
    determine that a particular request is safe.  For example, a
    metadata server may save provisional allocation mappings for each
    file to stable storage, as well as information about potentially
    conflicting OPEN share modes and mandatory byte-range locks that might
    have been in effect at the time of restart, and the metadata
    server may use this information during the recovery grace period to determine that a
    WRITE request is safe.
  </t>
</section>

<section anchor="storage_device_recovery" title="Storage Device Recovery">
<t>
  Recovery from storage device restart is mostly dependent upon the layout type
  in use.  However, there are a few general techniques a client can
  use if it discovers a storage device has crashed while holding
  modified, uncommitted data that was asynchronously written.
  First and foremost, it
  is important to realize that the client is the only one that has the
  information necessary to recover non-committed data since
  it holds the modified data and probably nothing else does. Second,
  the best solution is for the client to err on the side of caution
  and attempt to rewrite the modified data through another path.
</t>
<t>
  The client SHOULD immediately WRITE the data to the metadata server,
  with the stable field in the WRITE4args set to FILE_SYNC4.  Once it
  does this, there is no need to wait for the original storage device.
</t>
</section>
</section>

<section title="Metadata and Storage Device Roles">
<t>
  If the same physical hardware is used to implement both a
  metadata server and storage device, then the same hardware
  entity is to be understood to be implementing two
  distinct roles and it is important that it be clearly
  understood on behalf of which role the hardware is
  executing at any given time.
</t>
<t>
  Two sub-cases can be distinguished.

  <list style="numbers">
  <t>
    The storage device uses NFSv4.1 as the storage protocol, i.e., the same
    physical hardware is used to implement both a metadata and data
    server. See <xref target="pnfs_session_stuff" />
    for a description of how multiple roles are handled.
  </t>

  <t>

    The storage device does not use NFSv4.1 as the storage protocol,
    and the same physical hardware is used to implement both a
    metadata and storage device. Whether distinct network addresses
    are used to access the metadata server and storage device is
    immaterial. This is because it is always clear to the pNFS client and
    server, from the upper-layer protocol being used (NFSv4.1 or
    non-NFSv4.1), to which role the request to the common server network
    address is directed.
  </t>
  </list>
</t>
</section>


<section title="Security Considerations for pNFS" anchor="security_considerations_pnfs">
<t>
  pNFS separates file system metadata and data and provides access to
  both.  There are pNFS-specific operations (listed in
  <xref target="pnfs_ops" />) that provide access to the metadata; all
  existing NFSv4.1 conventional (non-pNFS) security mechanisms and
  features apply to accessing the metadata.  The combination of
  components in a pNFS system (see <xref target="fig_system" />) is
  required to preserve the security properties of NFSv4.1 with respect
  to an entity that is accessing a storage device from a client, including
  security countermeasures to defend against threats for which NFSv4.1
  provides defenses in environments where these threats are
  considered significant.
</t>
<t>
  In some cases, the security countermeasures for connections
  to storage devices may take the form of physical isolation or a
  recommendation to avoid the use of pNFS in an environment.  For example, it
  may be impractical to provide confidentiality protection for some
  storage protocols to protect against eavesdropping.  In
  environments where eavesdropping on such protocols is of sufficient
  concern to require countermeasures, physical isolation of the
  communication channel (e.g., via direct connection from client(s)
  to storage device(s)) and/or a decision to forgo use of pNFS (e.g.,
  and fall back to conventional NFSv4.1) may be appropriate courses of action.
</t>
<t>
  Where communication with storage devices is subject to the same
  threats as client-to-metadata server communication, the protocols
  used for that communication need to provide security mechanisms as
  strong as or no weaker than those available via RPCSEC_GSS for
  NFSv4.1. Except for the storage protocol used for the LAYOUT4_NFSV4_1_FILES
  layout (see <xref target="file_layout_type"/>), i.e., except for NFSv4.1,
  it is beyond the scope of this document to specify the security mechanisms 
  for storage access protocols.
</t>
<t>
  pNFS implementations MUST NOT remove NFSv4.1's access controls.
  The combination of clients, storage devices, and the metadata server
  are responsible for ensuring that all client-to-storage-device file
  data access respects NFSv4.1's ACLs and file open modes.  This entails
  performing both of these checks on every access in the client, the
  storage device, or both (as applicable; when the storage device is
  an NFSv4.1 server, the storage device is ultimately responsible for
  controlling access as described in <xref target="state_propagation"/>).
  If a pNFS configuration performs these checks only in the client,
  the risk of a misbehaving client obtaining unauthorized access is
  an important consideration in determining when it is appropriate to
  use such a pNFS configuration.  Such layout types SHOULD NOT be used
  when client-only access checks do not provide sufficient assurance
  that NFSv4.1 access control is being applied correctly. (This
  is not a problem for the file layout type described in <xref
  target="file_layout_type"/> because the storage access protocol for
  LAYOUT4_NFSV4_1_FILES is NFSv4.1, and thus the security model for
  storage device access via LAYOUT4_NFSv4_1_FILES is the same as that
  of the metadata server.) For handling of access control specific to
  a layout, the reader should examine the layout specification, such as
  the <xref target="file_layout_type">NFSv4.1/file-based layout</xref>
  of this document, the <xref target="RFC5663">blocks
  layout</xref>, and <xref target="RFC5664">objects
  layout</xref>.

</t>
</section>

</section>
<!-- $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $ -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type" anchor="file_layout_type">
<t>
  This section describes the semantics and format of NFSv4.1 file-based
  layouts for pNFS.
  NFSv4.1 file-based layouts use the LAYOUT4_NFSV4_1_FILES layout type.
  The LAYOUT4_NFSV4_1_FILES type defines
  striping data across multiple NFSv4.1 data servers.
</t>
 <section title="Client ID and Session Considerations" anchor="pnfs_session_stuff">
 <t>
  Sessions are a REQUIRED feature of NFSv4.1, and this
  extends to both the metadata server and file-based (NFSv4.1-based)
  data servers.
 </t>
 <t>
  The role a server plays in pNFS is determined by the result it returns
  from EXCHANGE_ID.
  The roles are:
  <list style="symbols">
  <t>
   Metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result eir_flags).
  </t>

  <t>
   Data server (EXCHGID4_FLAG_USE_PNFS_DS).
  </t>

  <t>
   Non-metadata server (EXCHGID4_FLAG_USE_NON_PNFS). This is an NFSv4.1
   server that does not support operations (e.g.,
   LAYOUTGET) or attributes that pertain to pNFS.
  </t>
  </list>
  </t>
  <t>
   The client MAY request zero or more of 
   EXCHGID4_FLAG_USE_NON_PNFS, 
   EXCHGID4_FLAG_USE_PNFS_DS, or
   EXCHGID4_FLAG_USE_PNFS_MDS, even though some combinations
   (e.g., EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS) are
   contradictory. However, the server MUST only return the following
   acceptable combinations:
  </t>

  <texttable>

  <ttcol>Acceptable Results from EXCHANGE_ID</ttcol>

  <c>
   EXCHGID4_FLAG_USE_PNFS_MDS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_DS
  </c>

  <c>
   EXCHGID4_FLAG_USE_NON_PNFS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS
  </c>
  </texttable>
  <t>
  As the above table implies, a server can have one
  or two roles. A server can be both a metadata server
  and a data server, or it can be both a data server and
  non-metadata server.  In addition to returning two roles
  in the EXCHANGE_ID's results, and thus serving both roles
  via a common client ID, a server can serve two roles
  by returning a unique client ID and server owner for
  each role in each of two EXCHANGE_ID results, with each
  result indicating each role.

  </t>
  <t>

  In the case of a server with concurrent pNFS roles that
  are served by a common client ID, if the EXCHANGE_ID
  request from the client has zero or a combination of the
  bits set in eia_flags, the server result should set bits
  that represent the higher of the acceptable combination
  of the server roles, with a preference to match the roles
  requested by the client. Thus, if a client request has
  (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS
  | EXCHGID4_FLAG_USE_PNFS_DS) flags set, and the server
  is both a metadata server and a data server, serving
  both the roles by a common client ID, the server
  SHOULD return with (EXCHGID4_FLAG_USE_PNFS_MDS |
  EXCHGID4_FLAG_USE_PNFS_DS) set.

  </t>
  <t>

  In the case of a server that has multiple concurrent
  pNFS roles, each role served by a unique client ID,
  if the client specifies zero or a combination of roles
  in the request, the server results SHOULD return only
  one of the roles from the combination specified by the
  client request. If the role specified by the server
  result does not match the intended use by the client,
  the client should send the EXCHANGE_ID specifying just
  the interested pNFS role.

  </t>

  <t>
   If a pNFS metadata client gets a layout that refers it to an NFSv4.1
   data server, it needs a client ID on that data server. If it does not
   yet have a client ID from the server that had the EXCHGID4_FLAG_USE_PNFS_DS
   flag set in the EXCHANGE_ID results, then the client needs to
   send an EXCHANGE_ID to the data server, using
   the same co_ownerid as it sent to the metadata server, with the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the arguments.
   If the server's
   EXCHANGE_ID results have EXCHGID4_FLAG_USE_PNFS_DS set, then the
   client may use the client ID to create sessions that will
   exchange pNFS data operations.
   The client ID returned by the data server has no relationship with
   the client ID returned by a metadata server unless the client IDs
   are equal, and the server owners and server scopes of the data server
   and metadata server are equal.
  </t>
 <t>
   In NFSv4.1, the
   session ID in the SEQUENCE operation implies the
   client ID, which in turn might be used by the server to
   map the stateid to the right client/server pair.
   However, when a data server is presented with a READ or
   WRITE operation with a stateid, because the
   stateid is associated with a
   client ID on a metadata server, and because the session ID in
   the preceding SEQUENCE operation is tied to the
   client ID of the data server, the data server has no
   obvious way to determine the metadata server from the
   COMPOUND procedure, and thus has no way to validate the
   stateid. One RECOMMENDED approach is for pNFS servers to
   encode metadata server routing and/or identity
   information in the data server filehandles as returned
   in the layout.
  </t>
  <t>

   If metadata server routing and/or identity information is encoded
   in data server filehandles,
   when the metadata server identity or location
   changes, the data server filehandles it gave out will become
   invalid (stale), and so the metadata server MUST first
   recall the layouts.
   Invalidating a data server filehandle does not render
   the NFS client's data cache invalid. The client's cache should
   map a data server filehandle to a metadata server filehandle, and
   a metadata server filehandle to cached data.
  </t>

  <t>
   If a server is both a metadata server and a data server,
   the server might need to distinguish operations on
   files that are directed to the metadata server from
   those that are directed to the data server. It is
   RECOMMENDED that the values of the filehandles returned by
   the LAYOUTGET operation be different than the value
   of the filehandle returned by the OPEN of the same file.

  </t>
  <t>
   Another scenario is for the metadata server and the
   storage device to be distinct from one client's point of
   view, and the roles reversed from another client's point
   of view. For example, in the cluster file system model,
   a metadata server to one client might be a data server to
   another client. If NFSv4.1 is being used as the storage
   protocol, then pNFS servers need to encode the values
   of filehandles according to their specific roles.
  </t>
  <section anchor="dsonly" title="Sessions Considerations for Data Servers">
  <t>

   <xref target="Obligations_of_the_Client" /> states
   that a client has to keep its lease renewed in
   order to prevent a session from being deleted by
   the server. If the reply to EXCHANGE_ID has just the
   EXCHGID4_FLAG_USE_PNFS_DS role set, then (as noted in
   <xref target="ds_ops"/>) the client will not be able
   to determine the data server's lease_time attribute
   because GETATTR will not be permitted. Instead, the
   rule is that any time a client receives a layout
   referring it to a data server that returns just
   the EXCHGID4_FLAG_USE_PNFS_DS role, the client MAY
   assume that the lease_time attribute from the metadata
   server that returned the layout applies to the data
   server. Thus, the data server MUST be aware of the values
   of all lease_time attributes of all metadata servers for which it
   is providing I/O, and it MUST use the maximum of all such
   lease_time values as the lease interval for all client
   IDs and sessions established on it.

  </t>
  <t>

   For example, if one metadata server has a lease_time
   attribute of 20 seconds, and a second metadata
   server has a lease_time attribute of 10 seconds,
   then if both servers return layouts that refer to an
   EXCHGID4_FLAG_USE_PNFS_DS-only data server, the data
   server MUST renew a client's lease if the interval
   between two SEQUENCE operations on different COMPOUND
   requests is less than 20 seconds.

  </t>
 
  </section>

 </section>

 <section title="File Layout Definitions" anchor="file_layout_definitions">
 <t>
      The following definitions apply to the LAYOUT4_NFSV4_1_FILES
      layout type and may be applicable to other layout types.
      <list style='hanging'>
        <t hangText="Unit.">
         A unit is a fixed-size quantity of data written to a data server.
        </t>
        <t hangText="Pattern.">
         A pattern is a method of distributing one or more
         equal sized units across a set of data servers.
         A pattern is iterated one or more times.
        </t>
        <t hangText="Stripe.">
         A stripe is a set of data distributed
         across a set of data servers in a
         pattern before that pattern repeats.
        </t>
        <t hangText="Stripe Count.">
         A stripe count is the number of units in a pattern.
        </t>
        <t hangText="Stripe Width.">
         A stripe width is the size of a stripe in bytes.
         The stripe width = the stripe count * the size of the stripe unit.
        </t>
      </list>
      Hereafter, this document will refer to a unit that is a written
      in a pattern as a "stripe unit".
 </t>
 <t>
  A pattern may have more stripe units than data servers.
  If so, some data servers will have more than one stripe unit
  per stripe.  A data server that has multiple stripe
  units per stripe MAY store each unit in a different data file (and
  depending on the implementation, will possibly assign a unique data
  filehandle to each data file).
 </t>
 </section> <!--  "File Striping Definitions" "file_layout_definitions" -->

 <section title="File Layout Data Types" anchor="file_data_types">
 <t>
   The high level NFSv4.1 layout types are
   nfsv4_1_file_layouthint4,
   nfsv4_1_file_layout_ds_addr4,
   and nfsv4_1_file_layout4.
 </t>

  <t>
   The SETATTR operation supports a layout hint attribute
   (<xref target="attrdef_layout_hint" />).
   When the client sets a layout hint (data type layouthint4) with
   a layout type of LAYOUT4_NFSV4_1_FILES (the loh_type field),
   the loh_body field contains a value of data type
   nfsv4_1_file_layouthint4.
  </t>
<figure>
 <artwork>
const NFL4_UFLG_MASK            = 0x0000003F;
const NFL4_UFLG_DENSE           = 0x00000001;
const NFL4_UFLG_COMMIT_THRU_MDS = 0x00000002;
const NFL4_UFLG_STRIPE_UNIT_SIZE_MASK
                                = 0xFFFFFFC0;

typedef uint32_t nfl_util4;
 </artwork>
</figure>
<figure>
 <artwork>
enum filelayout_hint_care4 {
        NFLH4_CARE_DENSE        = NFL4_UFLG_DENSE,

        NFLH4_CARE_COMMIT_THRU_MDS
                                = NFL4_UFLG_COMMIT_THRU_MDS,

        NFLH4_CARE_STRIPE_UNIT_SIZE
                                = 0x00000040,

        NFLH4_CARE_STRIPE_COUNT = 0x00000080
};

/* Encoded in the loh_body field of data type layouthint4: */

struct nfsv4_1_file_layouthint4 {
        uint32_t        nflh_care;
        nfl_util4       nflh_util;
        count4          nflh_stripe_count;
};
 </artwork>
</figure>
 <t>
     The generic layout hint structure is described
     in <xref target="layouthint4" />.  The client uses the
     layout hint in the layout_hint (<xref
     target="attrdef_layout_hint" />) attribute to indicate the preferred type
     of layout to be used for a newly created file. The
     LAYOUT4_NFSV4_1_FILES layout-type-specific content for the
     layout hint is composed of three fields. The first field,
     nflh_care, is a set of flags indicating which values of the hint the
     client cares about. If the NFLH4_CARE_DENSE flag is set, then
     the client indicates in the second field, nflh_util,
     a preference for how the data
     file is packed (<xref target="sparse_dense" />), which is controlled
     by the value of the expression nflh_util & NFL4_UFLG_DENSE ("&" represents the bitwise AND operator). If the
     NFLH4_CARE_COMMIT_THRU_MDS flag is set, then the client indicates
     a preference for whether the client should send COMMIT operations
     to the metadata server or data server (<xref target="commit_thru_mds" />),
     which is controlled by the value of nflh_util & NFL4_UFLG_COMMIT_THRU_MDS.
     If the NFLH4_CARE_STRIPE_UNIT_SIZE flag is set, the client indicates
     its preferred stripe unit size, which is indicated in
     nflh_util &
     NFL4_UFLG_STRIPE_UNIT_SIZE_MASK (thus, the stripe
     unit size MUST be a multiple of 64 bytes). The minimum stripe unit
     size is 64 bytes.
     If the NFLH4_CARE_STRIPE_COUNT flag is set, the client indicates
     in the third field,
     nflh_stripe_count, the stripe count. The stripe count multiplied
     by the stripe unit size is the stripe width.
 </t>
 <t>
   When LAYOUTGET returns a LAYOUT4_NFSV4_1_FILES layout
   (indicated in the loc_type field of the lo_content field),
   the loc_body field of the lo_content field
   contains a value of data type nfsv4_1_file_layout4.
   Among other content, nfsv4_1_file_layout4 has a storage
   device ID (field nfl_deviceid) of data type
   deviceid4.
   The GETDEVICEINFO operation maps a device ID to
   a storage device address (type device_addr4). When GETDEVICEINFO
   returns a device address with a layout type of LAYOUT4_NFSV4_1_FILES
   (the da_layout_type field), the da_addr_body field contains
   a value of data type nfsv4_1_file_layout_ds_addr4.
  </t>
<figure>
 <artwork>

typedef netaddr4 multipath_list4&lt;>;

/*
 * Encoded in the da_addr_body field of
 * data type device_addr4:
 */
struct nfsv4_1_file_layout_ds_addr4 {
        uint32_t        nflda_stripe_indices&lt;>;
        multipath_list4 nflda_multipath_ds_list&lt;>;
};
 </artwork>
</figure>
 <t>
   The nfsv4_1_file_layout_ds_addr4 data type represents the
   device address. It is composed of two fields:
   <list style='numbers'>
   <t>
    nflda_multipath_ds_list: An array of lists of data servers, where
    each list can be one or more elements, and each element represents
    a data server address that may serve equally as the target of I/O operations (see
    <xref target="file_multipath" />).
    The length of this array might be different than the stripe count.
   </t>
   <t>
    nflda_stripe_indices: An array of indices used to index into
    nflda_multipath_ds_list. The value of each element of nflda_stripe_indices MUST
    be less than the number of elements in nflda_multipath_ds_list.
    Each element of nflda_multipath_ds_list SHOULD be referred to by one
    or more elements of nflda_stripe_indices.
    The number of elements in
    nflda_stripe_indices is always equal to the stripe count.
   </t>
   </list>
  </t>
<figure>
 <artwork>

/*
 * Encoded in the loc_body field of
 * data type layout_content4:
 */
struct nfsv4_1_file_layout4 {
         deviceid4      nfl_deviceid;
         nfl_util4      nfl_util;
         uint32_t       nfl_first_stripe_index;
         offset4        nfl_pattern_offset;
         nfs_fh4        nfl_fh_list&lt;>;
};
 </artwork>
</figure>
  <t>
   The nfsv4_1_file_layout4 data type represents the layout.
   It is composed of the following fields:
   <list style='numbers'>

   <t>
    nfl_deviceid: The device ID that maps to a value of type
    nfsv4_1_file_layout_ds_addr4.
   </t>

   <t>
    nfl_util: Like the nflh_util field of data type nfsv4_1_file_layouthint4,
    a compact representation of how the data on a file
    on each data server is packed, whether the client should send
    COMMIT operations to the metadata server or data server, and the
    stripe unit size. If a server returns two or
    more overlapping layouts, each stripe unit size in
    each overlapping layout MUST be the same.
   </t>

   <t>
    nfl_first_stripe_index: The index into the first element
    of the nflda_stripe_indices array to use.
   </t>

   <t>
     nfl_pattern_offset:
     This field is the logical offset into the file
     where the striping pattern starts. It is required for
     converting the client's logical I/O offset (e.g., the current
     offset in a POSIX file descriptor before the read() or write()
     system call is sent) into the stripe unit number (see
     <xref target="SUi"/>).

     <vspace blankLines='1' />

     If dense packing is used, then nfl_pattern_offset
     is also needed to convert the client's logical
     I/O offset to an offset on the file on the data
     server corresponding to the stripe unit number (see <xref
     target="sparse_dense"/>).

     <vspace blankLines='1' />

     Note that nfl_pattern_offset is not always the same as
     lo_offset. For example, via the LAYOUTGET operation,
     a client might request a layout starting at offset 1000 of a
     file that has its striping pattern start at offset zero.

     <vspace blankLines='1' />

   </t>

   <t>
    nfl_fh_list: An array of data server filehandles for each
    list of data servers in each element of the nflda_multipath_ds_list
    array. The number of elements in 
    nfl_fh_list depends on whether sparse or dense packing
    is being used.

    <list style='symbols'>
    <t>
     If sparse packing is being used, the number of elements in
     nfl_fh_list MUST be one of three values:

	     <list style="symbols">
	     <t>

	      Zero. This means that filehandles used
	      for each data server are the same as the
	      filehandle returned by the OPEN operation
	      from the metadata server.

	     </t>

	     <t>

	      One. This means that every data server uses
	      the same filehandle: what is specified in
	      nfl_fh_list[0].

	     </t>

	     <t>

	      The same number of elements in
	      nflda_multipath_ds_list. Thus, in this case,
	      when sending an I/O operation to any data server in
	      nflda_multipath_ds_list[X], the filehandle
	      in nfl_fh_list[X] MUST be used.

	     </t>

	     </list>

     See the discussion on sparse packing in <xref target="sparse_dense" />.
     <vspace blankLines='1' />
    </t>

    <t>

     If dense packing is being used, the number of elements
     in nfl_fh_list MUST be the same as the number
     of elements in nflda_stripe_indices. Thus,
     when sending an I/O operation to any data server in
     nflda_multipath_ds_list[nflda_stripe_indices[Y]],
     the filehandle in nfl_fh_list[Y] MUST be
     used. In addition, any time there exists i
     and j, (i != j), such that the intersection of
     nflda_multipath_ds_list[nflda_stripe_indices[i]]
     and nflda_multipath_ds_list[nflda_stripe_indices[j]]
     is not empty, then nfl_fh_list[i] MUST NOT equal
     nfl_fh_list[j]. In other words, when dense packing
     is being used, if a data server appears in two or more
     units of a striping pattern, each reference to
     the data server MUST use a different filehandle.

     <vspace blankLines='1' />

     Indeed, if there are multiple striping patterns,
     as indicated by the presence of multiple objects of
     data type layout4 (either returned in one or multiple
     LAYOUTGET operations), and a data server is the target
     of a unit of one pattern and another unit of another
     pattern, then each reference to each data server MUST
     use a different filehandle.

     <vspace blankLines='1' />

     See the discussion on dense packing in <xref target="sparse_dense" />.

    </t>
    </list>
   </t>
   </list>

   The details on the interpretation of the layout are in
   <xref target="file_layout_interpret" />.

  </t>

 </section> <!-- "File Layout Data Types" "file_data_types" -->
 <section title="Interpreting the File Layout"
  anchor="file_layout_interpret">

  <section title="Determining the Stripe Unit Number" anchor="SUi">

  <t>
   To find the stripe unit number that corresponds to the client's
   logical file offset, the pattern offset will also be used. The
   i'th stripe unit (SUi) is:

  <figure>
  <artwork><![CDATA[
    relative_offset = file_offset - nfl_pattern_offset;
    SUi = floor(relative_offset / stripe_unit_size);
  ]]></artwork>
  </figure>

  </t>

  </section>

  <section title="Interpreting the File Layout Using Sparse Packing">
 <t>
  When sparse packing is used, the algorithm for determining the filehandle and set
  of data-server network addresses to write stripe unit i
 (SUi) to is:
 </t>
  <figure>
  <artwork><![CDATA[

   stripe_count = number of elements in nflda_stripe_indices;

   j = (SUi + nfl_first_stripe_index) % stripe_count;

   idx = nflda_stripe_indices[j];

   fh_count = number of elements in nfl_fh_list;
   ds_count = number of elements in nflda_multipath_ds_list;

   switch (fh_count) {
     case ds_count:
       fh = nfl_fh_list[idx];
       break;

     case 1:
       fh = nfl_fh_list[0];
       break;

     case 0:
       fh = filehandle returned by OPEN;
       break;

     default:
       throw a fatal exception;
       break;
   }

   address_list = nflda_multipath_ds_list[idx];

  ]]></artwork>
  </figure>
 <t>
  The client would then select a data server from address_list, and
  send a READ or WRITE operation using the filehandle specified in fh.
 </t>
 <t>
     Consider the following example:
 </t>
 <t>
  Suppose we have a device address consisting of seven
  data servers, arranged in three equivalence (<xref
  target="file_multipath" />) classes:

  <list style='empty'>
  <t>
	  { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
 </t>
 <t>
  where A through G are network addresses.
 </t>
 <t>
  Then
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
	  i.e.,
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  <t>
	  nflda_multipath_ds_list[2] = { F, G }
  </t>
  </list>
 </t>
 <t>
  Suppose the striping index array is:
  <list style='empty'>
  <t>
	  nflda_stripe_indices<> = { 2, 0, 1, 0 }
  </t>
  </list>
 </t>
 <t>
  Now suppose the client gets a layout that has a device ID
  that maps to the above device address.  The initial index contains
  <list style='empty'>
  <t>
   nfl_first_stripe_index = 2,
  </t>
  </list>
 and the filehandle list is
  <list style='empty'>
  <t>
   nfl_fh_list = { 0x36, 0x87, 0x67 }.
  </t>
  </list>
 </t>
 <t>
  If the client wants to write to SU0, the
  set of valid { network address, filehandle } combinations
  for SUi are determined by:
  <list style='empty'>
  <t>
	  nfl_first_stripe_index = 2
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  idx = nflda_stripe_indices[(0 + 2) % 4]
   <list style='empty'>
   <t>
		  = nflda_stripe_indices[2]
   </t>
   <t>
		  = 1
   </t>
   </list>
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  </list>
  and
  <list style='empty'>
  <t>
	  nfl_fh_list[1] = { 0x87 }
  </t>
  </list>
 </t>
 <t>
  The client can thus write SU0 to { 0x87, { E } }.

 </t>
 <t>
  The destinations of the first 13 storage units are:
 </t>
 <texttable>

 <ttcol>SUi</ttcol> <ttcol>filehandle</ttcol> <ttcol>data servers</ttcol>

  <c>0</c>   <c>    87 </c><c>     E </c>
  <c>1</c><c>36</c><c>A,B,C,D</c>
  <c>2</c><c>67</c><c>F,G</c>
  <c>3</c><c>36 </c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>4</c><c>87</c><c>E</c>
  <c>5</c><c>36</c><c>A,B,C,D</c>
  <c>6</c><c>67</c><c>F,G</c>
  <c>7</c><c>36</c><c>A,B,C,D</c>

  <c/> <c/> <c/>
  <c>8</c><c>87</c><c>E</c>
  <c>9</c><c>36</c><c>A,B,C,D</c>
  <c>10</c><c>67</c><c>F,G</c>
  <c>11</c><c>36</c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>12</c><c>87</c><c>E</c>

 </texttable>
 </section>
  <section title="Interpreting the File Layout Using Dense Packing">
 <t>
  When dense packing is used, the algorithm for determining the filehandle and set
  of data server network addresses to write stripe unit i (SUi) to is:
 </t>
  <figure>
  <artwork><![CDATA[
   stripe_count = number of elements in nflda_stripe_indices;

   j = (SUi + nfl_first_stripe_index) % stripe_count;

   idx = nflda_stripe_indices[j];

   fh_count = number of elements in nfl_fh_list;
   ds_count = number of elements in nflda_multipath_ds_list;

   switch (fh_count) {
     case stripe_count:
       fh = nfl_fh_list[j];
       break;

     default:
       throw a fatal exception;
       break;
   }

   address_list = nflda_multipath_ds_list[idx];

  ]]></artwork>
  </figure>
 <t>
  The client would then select a data server from address_list, and
  send a READ or WRITE operation using the filehandle specified in fh.
 </t>
 <t>
     Consider the following example (which is the same
     as the sparse packing example, except for the
     filehandle list):
 </t>
 <t>
  Suppose we have a device address consisting of seven
  data servers, arranged in three equivalence (<xref
  target="file_multipath" />) classes:

  <list style='empty'>
  <t>
	  { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
 </t>
 <t>
  where A through G are network addresses.
 </t>
 <t>
  Then
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list<> = { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
	  i.e.,
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  <t>
	  nflda_multipath_ds_list[2] = { F, G }
  </t>
  </list>
 </t>
 <t>
  Suppose the striping index array is:
  <list style='empty'>
  <t>
	  nflda_stripe_indices<> = { 2, 0, 1, 0 }
  </t>
  </list>
 </t>
 <t>
  Now suppose the client gets a layout that has a device ID
  that maps to the above device address.  The initial index contains
  <list style='empty'>
  <t>
   nfl_first_stripe_index = 2,
  </t>
  </list>
 and
  <list style='empty'>
  <t>
   nfl_fh_list = { 0x67, 0x37, 0x87, 0x36 }.
  </t>
  </list>
 </t>
 <t>
  The interesting examples for dense packing are
  SU1 and SU3 because each stripe unit refers to the
  same data server list, yet each stripe unit MUST use a different filehandle.
  If the client wants to write to SU1, the
  set of valid { network address, filehandle } combinations
  for SUi are determined by:
  <list style='empty'>
  <t>
	  nfl_first_stripe_index = 2
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
          j = (1 + 2) % 4 = 3
   <list style='empty'>
   <t>
	  idx = nflda_stripe_indices[j]
   </t>
   <t>
		  = nflda_stripe_indices[3]
   </t>
   <t>
		  = 0
   </t>
   </list>
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  </list>
  and
  <list style='empty'>
  <t>
	  nfl_fh_list[3] = { 0x36 }
  </t>
  </list>
 </t>
 <t>
  The client can thus write SU1 to { 0x36, { A, B, C, D } }.

 </t>
 <t>
  For SU3, j = (3 + 2) % 4 = 1, and nflda_stripe_indices[1] = 0.
  Then nflda_multipath_ds_list[0] = { A, B, C, D }, and
  nfl_fh_list[1] = 0x37. The client can thus write SU3 to 
  { 0x37, { A, B, C, D } }.
 </t>
 <t>
  The destinations of the first 13 storage units are:
 </t>
 <texttable>

 <ttcol>SUi</ttcol> <ttcol>filehandle</ttcol> <ttcol>data servers</ttcol>

  <c>0</c>   <c>    87 </c><c>     E </c>
  <c>1</c><c>36</c><c>A,B,C,D</c>
  <c>2</c><c>67</c><c>F,G</c>
  <c>3</c><c>37 </c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>4</c><c>87</c><c>E</c>
  <c>5</c><c>36</c><c>A,B,C,D</c>
  <c>6</c><c>67</c><c>F,G</c>
  <c>7</c><c>37</c><c>A,B,C,D</c>

  <c/> <c/> <c/>
  <c>8</c><c>87</c><c>E</c>
  <c>9</c><c>36</c><c>A,B,C,D</c>
  <c>10</c><c>67</c><c>F,G</c>
  <c>11</c><c>37</c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>12</c><c>87</c><c>E</c>

 </texttable>
 </section>


 <section title="Sparse and Dense Stripe Unit Packing"
  anchor="sparse_dense">
 <t>
     The flag NFL4_UFLG_DENSE of the nfl_util4 data type (field nflh_util of the
     data type nfsv4_1_file_layouthint4 and field nfl_util of
     data type nfsv4_1_file_layout_ds_addr4) specifies how the data
     is packed within the
     data file on a data server.  It allows for two different data
     packings: sparse and dense.  The packing type determines the
     calculation that will be made to map the client-visible file offset
     to the offset within the data file located on the data server.
 </t>
 <t>
   If nfl_util & NFL4_UFLG_DENSE is zero, this means that
   sparse packing is being used. Hence, the logical offsets of the
   file as viewed by a client
   sending READs and WRITEs directly to the metadata server
   are the same offsets each data server uses when storing
   a stripe unit. The effect then, for striping patterns
   consisting of at least two stripe units, is for each
   data server file to be sparse or "holey". So for example,
   suppose there is a pattern with three stripe units, the stripe unit
   size is 4096 bytes, and there are three data servers in
   the pattern.  Then, the file in data server 1 will have
   stripe units 0, 3, 6, 9, ... filled; data server 2's
   file will have stripe units 1, 4, 7, 10, ... filled;
   and data server 3's file will have stripe units 2,
   5, 8, 11, ... filled. The unfilled stripe units of
   each file will be holes; hence, the files in each data
   server are sparse.

 </t>
 <t>
   If sparse packing is being used and a client attempts I/O to one of
   the holes, then an error MUST be
   returned by the data server. Using the above example, if data server 3 received a READ or WRITE operation for block 4, the data server
   would return NFS4ERR_PNFS_IO_HOLE. Thus,
   data servers need to understand the striping pattern in order
   to support sparse packing.
 </t>
 <t>
   If nfl_util & NFL4_UFLG_DENSE is one, this means that
   dense packing is being used, and the data server files have no holes.
   Dense packing might be selected because the data server does not
   (efficiently) support holey files or because the data server
   cannot recognize read-ahead unless there are no holes.
   If dense packing is indicated in the layout,
   the data files will be packed. Using the
   same striping pattern and stripe unit size that were used for
   the sparse packing example, the corresponding dense packing example would have
   all stripe units of all data files filled as follows:
   <list style='symbols'>

   <t>
   Logical stripe units 0, 3, 6, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 1.
   </t>

   <t>
   Logical stripe units 1, 4, 7, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 2.
   </t>

   <t>
   Logical stripe units 2, 5, 8, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 3.
   </t>
   </list>
 </t>
 <t>
   Because dense packing does not leave holes on the data servers,
   the pNFS client is allowed to write to any offset of any data file of
   any data server in the stripe. Thus, the data servers need not know
   the file's striping pattern.
 </t>
 <t>
   The calculation to determine the byte offset within the data file
   for dense data server layouts is:
 </t>
 <figure>
 <artwork><![CDATA[
   stripe_width = stripe_unit_size * N;
      where N = number of elements in nflda_stripe_indices.

   relative_offset = file_offset - nfl_pattern_offset;

   data_file_offset = floor(relative_offset / stripe_width)
      * stripe_unit_size
      + relative_offset % stripe_unit_size
 ]]></artwork>
 </figure>
 <t>
  If dense packing is being used, and a data server appears
  more than once in a striping pattern, then to distinguish
  one stripe unit from another, the data server MUST use a
  different filehandle. Let's suppose there are two data
  servers.  Logical stripe units 0, 3, 6 are served by
  data server 1; logical stripe units 1, 4, 7 are served
  by data server 2; and logical stripe units 2, 5, 8 are
  also served by data server 2.  Unless data server 2 has
  two filehandles (each referring to a different data
  file), then, for example, a write to logical stripe
  unit 1 overwrites the write to logical stripe unit 2
  because both logical stripe units are located in the
  same stripe unit (0) of data server 2.

 </t>

</section>
</section> <!--  "Interpreting the File Layout" anchor="file_layout_interpret" -->

<section title="Data Server Multipathing" anchor="file_multipath">
<t>
  The NFSv4.1 file layout supports multipathing to
  multiple data server addresses.
  Data-server-level multipathing is used for
  bandwidth scaling via trunking (<xref target="Trunking"
  />) and for higher availability of use in the case of
  a data-server failure.  Multipathing allows the client
  to switch to another data server address which may be that
  of another data server that is exporting the
  same data stripe unit, without having to contact the
  metadata server for a new layout.

</t>
<t>
  To support data server multipathing, each element of
  the nflda_multipath_ds_list contains an array of one
  more data server network addresses.  This array (data
  type multipath_list4) represents a list of data servers
  (each identified by a network address), with the possibility
  that some data servers will appear in the list multiple times.
</t>
<t>

  The client is free to use any of the network addresses
  as a destination to send data server requests. If some
  network addresses are less optimal paths to the data than
  others, then the MDS SHOULD NOT include those network
  addresses in an element of nflda_multipath_ds_list. If
  less optimal network addresses exist to provide failover, the 
  RECOMMENDED method to offer the addresses is
  to provide them in a replacement device-ID-to-device-address 
  mapping, or a replacement device ID. When
  a client finds that no data server in an element of
  nflda_multipath_ds_list responds, it SHOULD send a
  GETDEVICEINFO to attempt to replace the existing
  device-ID-to-device-address mappings. If the MDS detects
  that all data servers represented by an element of
  nflda_multipath_ds_list are unavailable, the MDS SHOULD
  send a CB_NOTIFY_DEVICEID (if the client has indicated
  it wants device ID notifications for changed device IDs)
  to change the device-ID-to-device-address mappings to
  the available data servers. If the device ID itself will
  be replaced, the MDS SHOULD recall all layouts with the
  device ID, and thus force the client to get new layouts
  and device ID mappings via LAYOUTGET and GETDEVICEINFO.
</t>
<t>
  Generally, if two network addresses appear in an element
  of nflda_multipath_ds_list, they will designate the same
  data server, and the two data server addresses will
  support the implementation of
  client ID or session trunking (the latter is RECOMMENDED)
  as defined in <xref target="Trunking"/>.  The two
  data server addresses will share the same server owner
  or major ID of the server owner.  It is not always necessary for the
  two data server addresses to designate the same server 
  with trunking being used.  For example,
  the data could be read-only, and the data consist of
  exact replicas.

</t>
</section>

<section title="Operations Sent to NFSv4.1 Data Servers" anchor="ds_ops">
 <t>
  Clients accessing data on an NFSv4.1 data server MUST send
  only the NULL procedure and COMPOUND procedures whose
  operations are taken only from two restricted
  subsets of the operations defined as valid NFSv4.1 
  operations.  Clients MUST use the filehandle specified
  by the layout when accessing data on NFSv4.1 data 
  servers. 
 </t>
 <t>
  The first of these operation subsets consists of management operations.
  This subset consists of the BACKCHANNEL_CTL, BIND_CONN_TO_SESSION, CREATE_SESSION,
  DESTROY_CLIENTID, DESTROY_SESSION, EXCHANGE_ID,
  SECINFO_NO_NAME, SET_SSV, and SEQUENCE operations.
  The client may use these operations in order to set
  up and maintain the appropriate client IDs,
  sessions, and security contexts involved in communication with the data
  server.  Henceforth, these will be referred to as
  data-server housekeeping operations.
 </t>
 <t>
  The second subset consists of COMMIT, READ, WRITE, and PUTFH.
  These operations MUST be used with a current filehandle specified by the 
  layout.  In the case of PUTFH, the new current filehandle MUST be
  one taken from the layout. Henceforth, these will be referred to as data-server
  I/O operations.  As described in <xref target="layout_semantics" />, 
  a client MUST NOT send an I/O to a data server for which it does not hold a
  valid layout; the data server MUST reject such an I/O.
 </t>
 <t>
  Unless the server has a concurrent non-data-server
  personality -- i.e., EXCHANGE_ID results returned 
  (EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_PNFS_MDS) 
  or (EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS) see
  <xref target="pnfs_session_stuff"/> -- any attempted use of
  operations against a data server other than those specified in the two 
  subsets above MUST return
  NFS4ERR_NOTSUPP to the client.
 </t>
 <t>
  When the server has concurrent data-server and 
  non-data-server personalities, each COMPOUND sent by the 
  client MUST be constructed
  so that it is appropriate to one of the two personalities, and it
  MUST NOT contain operations directed to a mix of those 
  personalities.  The server MUST enforce this.  To understand
  the constraints, operations within a COMPOUND are divided into
  the following three classes: 
  <list style='numbers'>
    <t>
      An operation that is ambiguous regarding its personality
      assignment.  This includes all of the data-server
      housekeeping operations.  Additionally, if the
      server has assigned filehandles so that the ones defined
      by the layout are the same as those used by the metadata 
      server, all operations using such filehandles are within this
      class, with the following exception. The exception is
      that if the operation uses a stateid that is incompatible with a
      data-server personality (e.g., a special stateid or the
      stateid has a non-zero "seqid" field, see
      <xref target="global_stateid"/>), the operation is in class 3,
      as described below. A COMPOUND containing
      multiple class 1 operations (and operations of no other
      class) MAY be sent to a server with multiple concurrent data server
      and non-data-server personalities.
    
    </t>
    <t>
      An operation that is unambiguously referable to the data-server
      personality.  This includes data-server I/O operations where the
      filehandle is one that can only be validly directed to the
      data-server personality.
    </t>
    <t>
      An operation that is unambiguously referable to the non-data-server
      personality.  This includes all COMPOUND operations that are
      neither data-server housekeeping nor data-server I/O 
      operations, plus data-server I/O operations where the 
      current fh (or the one to be made the current fh in the
      case of PUTFH) is only valid on the metadata
      server or where a stateid is used that is incompatible 
      with the data server, i.e., is a special stateid or has
      a non-zero seqid value.
    </t>
  </list>
 </t>
 <t>
  When a COMPOUND first executes an operation from class 3 above,
  it acts as a normal COMPOUND on any other server, and the 
  data-server personality ceases to be relevant. 
  There are no special restrictions on the 
  operations in the COMPOUND to limit them to those for
  a data server.  When a PUTFH is done, filehandles
  derived from the layout are not valid.  If their format
  is not normally acceptable, then NFS4ERR_BADHANDLE MUST
  result.  Similarly, current filehandles for other operations
  do not accept filehandles derived from layouts and are not 
  normally usable on the metadata server. Using these
  will result in NFS4ERR_STALE. 
 </t>
 <t>
  When a COMPOUND first executes an operation from class 2,
  which would be PUTFH where the filehandle
  is one from a layout, the COMPOUND henceforth is interpreted
  with respect to the data-server personality. 
  Operations outside the two classes discussed
  above MUST result in NFS4ERR_NOTSUPP.  Filehandles
  are validated using the rules of the data server,
  resulting in NFS4ERR_BADHANDLE and/or NFS4ERR_STALE
  even when they would not normally do so when addressed
  to the non-data-server personality.  Stateids must obey
  the rules of the data server in that any use of special
  stateids or stateids with non-zero seqid values must 
  result in NFS4ERR_BAD_STATEID.
 </t>	
 <t>
  Until the server first executes an operation from class 2
  or class 3, the client MUST NOT depend on the operation 
  being executed by either the data-server or the non-data-server
  personality.  The server MUST pick one personality consistently
  for a given COMPOUND, with the only possible transition being 
  a single one when the first operation from class 2 or class 3
  is executed.
 </t>
 <t>
  Because of the complexity induced by assigning filehandles so
  they can be used on both a data server and a metadata server, it
  is RECOMMENDED that where the same server can have both
  personalities, the server assign separate unique filehandles
  to both personalities. This makes it unambiguous for which server
  a given request is intended.
 </t>
<t>
  GETATTR and SETATTR MUST be directed to the metadata
  server. In the case of a SETATTR of the size attribute,
  the control protocol is responsible for propagating size
  updates/truncations to the data servers. In the case of
  extending WRITEs to the data servers, the new size must
  be visible on the metadata server once a LAYOUTCOMMIT
  has completed (see <xref target="general_layoutcommit"
  />). <xref target="component_file_size" /> describes the
  mechanism by which the client is to handle data-server
  files that do not reflect the metadata server's size.

</t>
</section>

<section title="COMMIT through Metadata Server" anchor="commit_thru_mds">
<t>
   The file layout provides two alternate means of providing for the 
   commit of data written through data servers.  The flag 
   NFL4_UFLG_COMMIT_THRU_MDS in the field nfl_util of the file layout
   (data type nfsv4_1_file_layout4)
   is an indication
   from the metadata server to the client of the REQUIRED way of
   performing COMMIT, either by sending the COMMIT to the data server
   or the metadata server.  These two methods of dealing with the issue 
   correspond to broad styles of implementation for a pNFS server
   supporting the file layout type.
   <list style="symbols">
     <t>
       When the flag is FALSE, COMMIT operations MUST to be sent
       to the data server to which the corresponding WRITE operations were 
       sent.  This approach
       is sometimes useful when file striping is implemented within the
       pNFS server (instead of the file system),
       with the individual data servers each implementing 
       their own file systems.
     </t>
     <t>
       When the flag is TRUE, COMMIT operations MUST be sent to the
       metadata server, rather than to the individual data servers.  
       This approach is sometimes useful when file striping
       is implemented within the clustered file system that is the backend
       to the pNFS server.  In such 
       an implementation, each COMMIT to each
       data server might result in repeated writes of metadata
       blocks to the 
       detriment of write performance.  Sending a single COMMIT 
       to the metadata server can be more efficient
       when there exists a clustered file 
       system capable of implementing such a coordinated COMMIT.
     <vspace blankLines='1' />
       If nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is TRUE,
       then in order to maintain the current NFSv4.1 commit and
       recovery model, the data servers MUST return a common
       writeverf verifier in all WRITE responses for a given file
       layout, and the metadata server's COMMIT implementation
       must return the same writeverf.  The value of the
       writeverf verifier MUST be changed at the metadata server
       or any data server that is referenced in the layout,
       whenever there is a server event that can possibly lead to
       loss of uncommitted data.  The scope of the verifier can
       be for a file or for the entire pNFS server.  It might be
       more difficult for the server to maintain the verifier
       at the file level, but the benefit is that only events
       that impact a given file will require recovery action.   
     </t>
   </list>
</t>
<t>
 Note that if the layout specified dense packing, then the
 offset used to a COMMIT to the MDS may differ than that of
 an offset used to a COMMIT to the data server.
</t>
<t>
 The single COMMIT to the metadata server will return a verifier, and
 the client should compare it to all the verifiers from the WRITEs and
 fail the COMMIT if there are any mismatched verifiers. If COMMIT to the
 metadata server fails, the client should re-send WRITEs for all the 
 modified data in the file. The client should treat modified data with 
 a mismatched verifier
 as a WRITE failure and try to recover by resending the WRITEs to the
 original data server or using another path to that data if the layout 
 has not been recalled.  Alternatively, the client can obtain
 a new layout or it could rewrite the data directly to the metadata server. If 
 nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is FALSE, sending
 a COMMIT to the metadata server might have no effect. If
 nfl_util & NFL4_UFLG_COMMIT_THRU_MDS is FALSE, a COMMIT
 sent to the metadata server should be used only to commit data that 
 was written to the metadata server.  See <xref target="storage_device_recovery" />
 for recovery options.
</t>
</section>

<section title="The Layout Iomode">
<t>
  The layout iomode need not be used by the metadata server when
  servicing NFSv4.1 file-based layouts, although in some circumstances
  it may be useful.  For example, if the server implementation
  supports reading from read-only replicas or mirrors, it would be
  useful for the server to return a layout enabling the client to do
  so.  As such, the client SHOULD set the iomode based on its intent
  to read or write the data.  The client may default to an iomode of
  LAYOUTIOMODE4_RW.  The iomode need not be checked by the
  data servers when clients perform I/O.  However, the data servers 
  SHOULD still validate that the client holds a valid layout
  and return an error if the client does not.
</t>
</section>

<section title="Metadata and Data Server State Coordination">

<section title="Global Stateid Requirements" anchor="global_stateid">
<t>
  When the client sends
  I/O to a data server, the stateid used MUST NOT be a layout stateid
  as returned by LAYOUTGET or sent by CB_LAYOUTRECALL. 
  Permitted stateids are based on one of the following:
  an OPEN stateid
  (the stateid field of data type OPEN4resok as returned by OPEN),
  a delegation stateid (the stateid field of data types open_read_delegation4
  and open_write_delegation4 as returned by OPEN or WANT_DELEGATION,
  or as sent by CB_PUSH_DELEG), or a stateid returned by the LOCK or LOCKU
  operations.  The stateid sent to the data server MUST be sent with
  the seqid set to zero, indicating the most current version of that
  stateid, rather than indicating a specific non-zero seqid value.  In
  no case is the use of special stateid values allowed.
</t>
<t>
  The stateid used for I/O MUST have the same
  effect and be subject to the same validation on a data server as it
  would if the I/O was being performed on the metadata server itself
  in the absence of pNFS. This has the implication that stateids are
  globally valid on both the metadata and data servers. This
  requires the metadata server to propagate changes in LOCK and OPEN
  state to the data servers, so that the data servers can
  validate I/O accesses. This is discussed further in <xref
  target="state_propagation" />.  Depending on when stateids are
  propagated, the existence of a valid stateid on the data server
  may act as proof of a valid layout.
</t>
        <t>
          Clients performing I/O operations need to select an appropriate 
          stateid based on the
          locks (including opens and delegations) held by the client and 
          the various types of state-owners sending the I/O requests.  The
          rules for doing so when referencing data servers are somewhat 
          different from those discussed in <xref target="stateid_use" />,
          which apply when accessing metadata servers.
        </t>
        <t>
          The following rules, applied in order of decreasing priority, govern 
          the selection of the appropriate stateid:
          <list style='symbols'>
            <t>
              If the client holds a delegation for the file in question, the
              delegation stateid should be used.
            </t>
            <t>
              Otherwise, there must be an OPEN stateid for the current 
              open-owner, and that 
              OPEN stateid for the open file in question is used, unless
              mandatory locking prevents that.  See below.
            </t>
            <t>
              If the data server had previously responded with NFS4ERR_LOCKED
              to use of the OPEN stateid, then the client should use the 
              byte-range lock stateid whenever one exists for that open file
              with the current lock-owner.
            </t>
            <t>
              Special stateids should never be used.  If they are used, the data
              server MUST reject the I/O with an NFS4ERR_BAD_STATEID error.
            </t>
          </list> 
        </t>   
</section>

<section title="Data Server State Propagation" anchor="state_propagation" >
<t>
  Since the metadata server, which handles byte-range lock and
  open-mode state changes as well as ACLs, might not be
  co-located with the data servers where I/O accesses
  are validated, the server implementation MUST take
  care of propagating changes of this state to the data
  servers. Once the propagation to the data servers is
  complete, the full effect of those changes MUST be in
  effect at the data servers. However, some state changes
  need not be propagated immediately, although all changes
  SHOULD be propagated promptly.  These state propagations
  have an impact on the design of the control protocol,
  even though the control protocol is outside of the scope
  of this specification.  Immediate propagation refers to
  the synchronous propagation of state from the metadata
  server to the data server(s); the propagation must be
  complete before returning to the client.

</t>

<section title="Lock State Propagation">
<t>
  If the pNFS server supports mandatory byte-range locking, any mandatory byte-range locks
  on a file MUST be made effective at the data servers before
  the request that establishes them returns to the caller. The
  effect MUST be the same as if the mandatory byte-range lock state were
  synchronously propagated to the data servers, even though the
  details of the control protocol may avoid actual transfer of the
  state under certain circumstances.  
</t>
<t>
  On the other hand, since 
  advisory byte-range lock state is not used for checking I/O accesses at 
  the data servers, there is no semantic reason for propagating 
  advisory byte-range lock state to the data servers.  
  Since updates to advisory locks neither confer nor remove
  privileges, these changes need not be propagated immediately, and
  may not need to be propagated promptly.  The updates to advisory
  locks need only be propagated when the data server needs to
  resolve a question about a stateid.  In fact, if byte-range locking
  is not mandatory (i.e., is advisory) the clients are advised to avoid
  using the byte-range lock-based stateids for I/O. The stateids returned by
  OPEN are sufficient and eliminate overhead for this kind of state
  propagation.
</t>
<t>
  If a client gets back an NFS4ERR_LOCKED error from a
  data server, this is an indication that mandatory byte-range
  locking is in force. The client recovers from this by
  getting a byte-range lock that covers the affected range
  and re-sends the I/O with the stateid of the byte-range lock.
</t>

</section>

<section title="Open and Deny Mode Validation">
<t>
  Open and deny mode validation MUST be performed against
  the open and deny mode(s) held by the data servers. When
  access is reduced or a deny mode made more restrictive
  (because of CLOSE or OPEN_DOWNGRADE), the data server MUST
  prevent any I/Os that would be denied if performed on the
  metadata server. When access is expanded,
  the data server MUST make sure that no requests are
  subsequently rejected because of
  open or deny issues that no longer apply, given the 
  previous relaxation.
</t>
</section>

<section title="File Attributes">
<t>
  Since the SETATTR operation has the ability to modify state that is
  visible on both the metadata and data servers (e.g., the size),
  care must be taken to ensure that the resultant state across the
  set of data servers is consistent, especially when truncating or
  growing the file.
</t>
<t>
  As described earlier, the LAYOUTCOMMIT operation is used to ensure
  that the metadata is synchronized with changes made to the data servers. For the NFSv4.1-based data storage protocol,
  it is necessary to re-synchronize
  state such as the size attribute, and the setting of mtime/change/atime.
  See <xref target="committing_layout" /> for a full
  description of the semantics regarding LAYOUTCOMMIT and
  attribute synchronization.  It should be noted that by
  using an NFSv4.1-based layout type, it is possible to
  synchronize this state before LAYOUTCOMMIT occurs.  For
  example, the control protocol can be used to query the
  attributes present on the data servers.
</t>
<t>
  Any changes to file attributes that control authorization or
  access as reflected by ACCESS calls or READs and WRITEs on the
  metadata server, MUST be propagated to the data servers for
  enforcement on READ and WRITE I/O calls.  If the changes made on the
  metadata server result in more restrictive access permissions for
  any user, those changes MUST be propagated to the data servers
  synchronously.
</t>
<t>
  The OPEN operation (<xref target="OP_OPEN_IMPLEMENTATION"
  />) does not impose any requirement that I/O operations
  on an open file have the same credentials as the OPEN
  itself (unless EXCHGID4_FLAG_BIND_PRINC_STATEID is
  set when EXCHANGE_ID creates the client ID), and so it
  requires the server's READ and WRITE operations to
  perform appropriate access checking.  Changes to ACLs
  also require new access checking by READ and WRITE on
  the server.  The propagation of access-right changes due
  to changes in ACLs may be asynchronous only if the server
  implementation is able to determine that the updated
  ACL is not more restrictive for any user specified in
  the old ACL. Due to the relative infrequency of ACL
  updates, it is suggested that all changes be propagated
  synchronously.

</t>
</section>
</section>
</section>

<section title="Data Server Component File Size"
         anchor="component_file_size">
<t>
  A potential problem exists when a component data file on a
  particular data server has grown past EOF; the problem exists for
  both dense and sparse layouts.  Imagine the following scenario: a
  client creates a new file (size == 0) and writes to byte 131072; the
  client then seeks to the beginning of the file and reads byte 100.
  The client should receive zeroes back as a result of the READ. However,
  if the striping pattern directs the client to send the READ to
  a data server other than the one that received the
  client's original WRITE, the data server servicing the READ may
  believe that the file's size is still 0 bytes. In that event, the
  data server's READ response will contain zero bytes and an
  indication of EOF.  The data server can only return zeroes if it knows that
  the file's size has been extended. This would require the immediate
  propagation of the file's size to all data servers, which is
  potentially very costly.  Therefore, the client that has
  initiated the extension of the file's size MUST be prepared to deal
  with these EOF conditions.
  When the offset in the arguments to READ
  is less than the client's view of the file size, if the READ response
  indicates EOF and/or contains fewer bytes than requested, the client
  will interpret such a response as a hole in the file, and the
  NFS client will substitute zeroes for the data.
</t>
<t>
  The NFSv4.1 protocol only provides close-to-open file data cache
  semantics; meaning that when the file is closed, all modified data is
  written to the server.  When a subsequent OPEN of the file is
  done, the change attribute is inspected for a difference from a
  cached value for the change attribute.  For the case above, this means
  that a LAYOUTCOMMIT will be done at close (along with the data
  WRITEs) and will update the file's size and change attribute.  Access
  from another client after that point will result in the appropriate
  size being returned.
</t>
</section>

<section title="Layout Revocation and Fencing" anchor="file_layout_revoke" >
<t>
  As described in <xref target="crash_recovery" />, the
  layout-type-specific storage protocol is responsible
  for handling the effects of I/Os that started before
  lease expiration and extend through lease expiration.
  The LAYOUT4_NFSV4_1_FILES layout type 
  can prevent all I/Os to data servers from
  being executed after lease expiration (this prevention is
  called "fencing"), without relying
  on a precise client lease timer and without requiring
  data servers to maintain lease timers. The
  LAYOUT4_NFSV4_1_FILES pNFS server has the flexibility to
  revoke individual layouts, and thus fence I/O on a per-file
  basis.
</t>
<t> 
  In addition to lease expiration,
  the reasons a layout can be revoked include: client fails to respond to
  a CB_LAYOUTRECALL,
  the
  metadata server restarts, or administrative intervention. Regardless
  of the reason, once a client's layout has been revoked, the pNFS
  server MUST prevent the client from sending I/O for the affected file
  from and to all data servers; in other words, it MUST fence the
  client from the affected file on the data servers.
</t>
<t> 
  Fencing works as follows. As described in <xref
  target="pnfs_session_stuff" />, in COMPOUND procedure
  requests to the data server, the data filehandle provided
  by the PUTFH operation and the stateid in the READ or
  WRITE operation are used to ensure that the client has
  a valid layout for the I/O being performed; if it does
  not, the I/O is rejected with NFS4ERR_PNFS_NO_LAYOUT.
  The server can simply check the stateid and, additionally,
  make the data filehandle stale if the layout specified
  a data filehandle that is different from the metadata server's
  filehandle for the file (see the nfl_fh_list description in
  <xref target="file_data_types" />).
</t>
<t>
  Before the metadata server takes any action to revoke
  layout state given out by a previous instance, it must make
  sure that all layout state from that previous instance are
  invalidated at the data servers. This has the following
  implications.
  <list style='symbols'>

  <t>
     The metadata server must not restripe a
     file until it has contacted all of the data servers
     to invalidate the layouts from the previous instance.
  </t>

  <t>
     The metadata server must not give out mandatory locks that conflict with
     layouts from the previous instance without either doing
     a specific layout invalidation (as it would have to do anyway)
     or doing a global data server invalidation.
  </t>
  </list>
</t>


</section>


<section title="Security Considerations for the File Layout Type" anchor="file_security_considerations">
<t>
  The NFSv4.1 file layout type MUST adhere to the security
  considerations outlined in <xref target="security_considerations_pnfs"
  />.  NFSv4.1 data servers MUST make all of the
  required access checks on each READ or WRITE I/O as determined by
  the NFSv4.1 protocol.
  If the metadata server would deny a READ or WRITE
  operation on a file due to its ACL, mode attribute, open
  access mode, open deny mode, mandatory byte-range lock state, or any other
  attributes and state, the data server MUST also deny the
  READ or WRITE operation.  This impacts the control
  protocol and the propagation of state from the metadata
  server to the data servers; see <xref
  target="state_propagation" /> for more details.

</t>
<t>
  The methods for authentication,
  integrity, and privacy for data servers based on the
  LAYOUT4_NFSV4_1_FILES layout type are the same as those used
  by metadata servers. Metadata and data servers
  use ONC RPC security flavors to
  authenticate, and SECINFO and SECINFO_NO_NAME
  to negotiate the security mechanism and services
  to be used. Thus, when using the LAYOUT4_NFSV4_1_FILES layout type,
  the impact on the RPC-based security
  model due to pNFS (as alluded to in Sections
  <xref target="rpc_and_security" format="counter"/>
  and <xref target="parallel_access" format="counter"/>) is zero.
</t>
<t>
  For a given file object, a metadata server
  MAY require different security parameters
  (secinfo4 value) than the data server.
  For a given file object with multiple data servers,
  the secinfo4 value SHOULD be the same across
  all data servers. If the secinfo4 values across a metadata server
  and its data servers differ for a specific file, the
  mapping of the principal to the server's internal user identifier
  MUST be the same in order for the access-control checks based on
  ACL, mode, open and deny mode, and mandatory locking to be
  consistent across on the pNFS server.
</t>
<t>
  If an NFSv4.1 implementation supports
  pNFS and supports NFSv4.1 file layouts, then the
  implementation MUST support the SECINFO_NO_NAME operation on both
  the metadata and data servers.
</t>

</section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="internationalization" title="Internationalization">
<t>
The primary issue in which NFSv4.1 needs to deal with
internationalization, or I18N, is with respect to file names and other
strings as used within the protocol.  The choice of string
representation must allow reasonable name/string access to clients
that use various languages.  The UTF-8 encoding of the UCS (Universal
Multiple-Octet Coded Character Set) as defined
by <xref target="ISO.10646-1.1993">ISO10646</xref> allows for this type
of access and follows the policy described in "IETF Policy on
Character Sets and Languages", <xref target="RFC2277">RFC 2277</xref>.
</t>
<t>
<xref target="RFC3454">RFC 3454</xref>, otherwise know as "stringprep", documents a
framework for using Unicode/UTF-8 in networking protocols so as "to
increase the likelihood that string input and string comparison work
in ways that make sense for typical users throughout the world". A
protocol must define a profile of stringprep "in order to fully
specify the processing options".  The remainder of this
section defines the NFSv4.1 stringprep profiles. Much of the terminology
used for the remainder of this section comes from stringprep.
</t>
<t>
There are three UTF-8 string types defined for NFSv4.1:
utf8str_cs, utf8str_cis, and utf8str_mixed.  Separate profiles are
defined for each. Each profile defines the following, as required by
stringprep:
<list style='symbols'>
<t>
The intended applicability of the profile.
</t>
<t>
The character repertoire that is the input and output to stringprep
(which is Unicode 3.2 for the referenced version of stringprep).
However, NFSv4.1 implementations are not limited to 3.2.
</t>
<t>
The mapping tables from stringprep used (as described in Section 3 of
stringprep).
</t>
<t>
Any additional mapping tables specific to the profile.
</t>
<t>
The Unicode normalization used, if any (as described in Section 4 of stringprep).
</t>
<t>
The tables from the stringprep listing of characters that are prohibited
as output (as described in Section 5 of stringprep).
</t>
<t>
The bidirectional string testing used, if any (as described in Section 6 of stringprep).
</t>
<t>
Any additional characters that are prohibited as output specific to
the profile.
</t>
</list>
</t>
<t>
Stringprep discusses Unicode characters, whereas NFSv4.1 renders
UTF-8 characters.  Since there is a one-to-one mapping from UTF-8 to
Unicode, when the remainder of this document refers to Unicode,
the reader should assume UTF-8.
</t>
<t>
Much of the text for the profiles comes from <xref target="RFC3491">RFC 3491</xref>.
</t>
<section title="Stringprep Profile for the utf8str_cs Type">
<t>
Every use of the utf8str_cs type definition in the NFSv4 protocol specification follows the profile named
nfs4_cs_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_cs_prep Profile">
<t>
The utf8str_cs type is a case-sensitive string of UTF-8 characters.
Its primary use in NFSv4.1 is for naming components and
pathnames.  Components and pathnames are stored on the server's
file system.  Two valid distinct UTF-8 strings might be the same after
processing via the utf8str_cs profile. If the strings are two names
inside a directory, the NFSv4.1 server will need to either:
<list style='symbols'>
<t>
disallow the creation of a second name if its post-processed form
collides with that of an existing name, or
</t>
<t>
allow the creation of the second name, but arrange so that after
post-processing, the second name is different than the post-processed
form of the first name.
</t>
</list>
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_cs_prep">
<t>
The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1.
However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cs_prep">
<t>
The nfs4_cs_prep profile specifies mapping using the
following tables from stringprep:
<list style='empty'>
<t>
Table B.1
</t>
</list>
</t>
<t>
Table B.2 is normally not part of the nfs4_cs_prep profile as it is
primarily for dealing with case-insensitive comparisons. However, if
the NFSv4.1 file server supports the case_insensitive file system
attribute, and if case_insensitive is TRUE, the NFSv4.1 server
MUST use Table B.2 (in addition to Table B1) when processing
utf8str_cs strings, and the NFSv4.1 client MUST assume Table B.2
(in addition to Table B.1) is being used.
</t>
<t>
If the case_preserving attribute is present and set to FALSE, then the
NFSv4.1 server MUST use Table B.2 to map case when processing
utf8str_cs strings. Whether the server maps from lower to upper case
or from upper to lower case is an implementation dependency.
</t>
</section>
<section toc="exclude" title="Normalization used by nfs4_cs_prep">
<t>
The nfs4_cs_prep profile does not specify a normalization form.  A
later revision of this specification may specify a particular
normalization form.  Therefore, the server and client can expect that
they may receive unnormalized characters within protocol requests and
responses.  If the operating environment requires normalization, then
the implementation must normalize utf8str_cs strings within the
protocol before presenting the information to an application (at the
client) or local file system (at the server).
</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_cs_prep">
<t>
The nfs4_cs_prep profile RECOMMENDS prohibiting the use of the
following tables from stringprep:
<list style='empty'>
<t>Table C.5</t>
<t>Table C.6</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_cs_prep">
<t>
The nfs4_cs_prep profile does not specify any checking of
bidirectional strings.
</t>
</section>
</section>
<section title="Stringprep Profile for the utf8str_cis Type">
<t>
Every use of the utf8str_cis type definition in the NFSv4.1
protocol specification follows the profile named nfs4_cis_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_cis_prep Profile">
<t>
The utf8str_cis type is a case-insensitive string of
UTF-8 characters.  Its primary use in NFSv4.1 is
for naming NFS servers.
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_cis_prep">
<t>
The nfs4_cis_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1. However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies mapping using the following tables from
stringprep:
<list style='empty'>
<t>Table B.1</t>
<t>Table B.2</t>
</list>
</t>
</section>
<section toc="exclude" title="Normalization Used by nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies using Unicode normalization form
KC, as described in stringprep.

</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies prohibiting using the following
tables from stringprep:
<list style='empty'>
<t>Table C.1.2</t>
<t>Table C.2.2</t>
<t>Table C.3</t>
<t>Table C.4</t>
<t>Table C.5</t>
<t>Table C.6</t>
<t>Table C.7</t>
<t>Table C.8</t>
<t>Table C.9</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies checking bidirectional strings as
described in stringprep's Section 6.
</t>
</section>
</section>
<section title="Stringprep Profile for the utf8str_mixed Type">
<t>
Every use of the utf8str_mixed type definition in the NFSv4.1
protocol specification follows the profile named nfs4_mixed_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_mixed_prep Profile">
<t>
The utf8str_mixed type is a string of UTF-8 characters, with a prefix
that is case sensitive, a separator equal to '@', and a suffix that is a
fully qualified domain name.  Its primary use in NFSv4.1 is for
naming principals identified in an Access Control Entry.
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1.
However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cis_prep">
<t>
For the prefix and the separator of a utf8str_mixed
string, the nfs4_mixed_prep profile specifies mapping
using the following table from stringprep:
<list style='empty'>
<t>Table B.1</t>
</list>
</t>
<t>
For the suffix of a utf8str_mixed string, the nfs4_mixed_prep
profile specifies mapping using the following tables from
stringprep:
<list style='empty'>
<t>Table B.1</t>
<t>Table B.2</t>
</list>
</t>
</section>
<section toc="exclude" title="Normalization Used by nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies using Unicode normalization form
KC, as described in stringprep.
</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies prohibiting using the
following tables from stringprep:
<list style='empty'>
<t>Table C.1.2</t>
<t>Table C.2.2</t>
<t>Table C.3</t>
<t>Table C.4</t>
<t>Table C.5</t>
<t>Table C.6</t>
<t>Table C.7</t>
<t>Table C.8</t>
<t>Table C.9</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies checking bidirectional strings
as described in stringprep's Section 6.
</t>
</section>
</section>
<section title="UTF-8 Capabilities" anchor="utf8_caps">
<figure>
 <artwork>
const FSCHARSET_CAP4_CONTAINS_NON_UTF8  = 0x1;
const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8   = 0x2;

typedef uint32_t        fs_charset_cap4;
 </artwork>
</figure>
<t>
Because some operating environments and file systems do
not enforce character set encodings, NFSv4.1 supports the
fs_charset_cap attribute (<xref target="attrdef_fs_charset_cap"/>)
that indicates to the client a file system's UTF-8 capabilities.
The attribute is an integer containing a pair of flags.
The first flag is FSCHARSET_CAP4_CONTAINS_NON_UTF8, which, if set
to one, tells the client that the file system contains non-UTF-8 characters,
and the server will not convert non-UTF characters to UTF-8 if the client
reads a symlink or directory, neither will operations with component
names or pathnames in the arguments convert the strings to UTF-8.
The second flag is FSCHARSET_CAP4_ALLOWS_ONLY_UTF8, which, if set to
one, indicates that the server will accept (and generate) only
UTF-8 characters on the file system. If 
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set to one, 
FSCHARSET_CAP4_CONTAINS_NON_UTF8 MUST be set to zero.
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 SHOULD always be set to one.
</t>
</section>
<section title="UTF-8 Related Errors" anchor="utf8_related_errors">
<t>
Where the client sends an invalid UTF-8 string, the server should
return NFS4ERR_INVAL (see <xref target="error_definitions"/>).
This includes cases in which inappropriate prefixes are detected and
where the count includes trailing bytes that do not constitute a full
UCS character.
</t>
<t>
    Where the client-supplied string is valid UTF-8 but contains
    characters that are not supported by the server as a value for that
    string (e.g., names containing characters outside of Unicode plane 0 on
    file systems that fail to support such characters despite their
    presence in the Unicode standard), the server should return
    NFS4ERR_BADCHAR.
</t>
<t>
Where a UTF-8 string is used as a file name, and the file system (while
supporting all of the characters within the name) does not allow that
particular name to be used, the server should return the error <xref
target="error_definitions">NFS4ERR_BADNAME</xref>.  This includes
situations in which the server file system imposes a normalization
constraint on name strings, but will also include such situations as
file system prohibitions of "."  and ".." as file names for certain
operations, and other such constraints.
</t>
</section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section title="Error Values">
  <t>
    NFS error numbers are assigned to failed operations within a 
    Compound (COMPOUND or CB_COMPOUND) request.  A Compound request 
    contains a number of NFS operations that have their results 
    encoded in sequence in a Compound reply.  The results of successful 
    operations will consist of an NFS4_OK status followed by the 
    encoded results of the operation.  If an NFS operation fails, an 
    error status will be entered in the reply and the Compound
    request will be terminated.
  </t>
  <section title="Error Definitions">
    <texttable anchor='error_definitions'>
      <preamble>
	Protocol Error Definitions
      </preamble>
      <ttcol align='left'>Error</ttcol>
      <ttcol align='left'>Number</ttcol>
      <ttcol align='left'>Description</ttcol>

      <c>NFS4_OK</c>
      <c>0</c>
      <c><xref target="err_OK" /></c>

      <c>NFS4ERR_ACCESS</c>
      <c>13</c>
      <c><xref target="err_ACCESS" /></c>

      <c>NFS4ERR_ATTRNOTSUPP</c>
      <c>10032</c>
      <c><xref target="err_ATTRNOTSUPP" /></c>

      <c>NFS4ERR_ADMIN_REVOKED</c>
      <c>10047</c>
      <c><xref target="err_ADMIN_REVOKED" /></c>

      <c>NFS4ERR_BACK_CHAN_BUSY</c>
      <c>10057</c>
      <c><xref target="err_BACK_CHAN_BUSY" /></c>

      <c>NFS4ERR_BADCHAR</c>
      <c>10040</c>
      <c><xref target="err_BADCHAR" /></c>

      <c>NFS4ERR_BADHANDLE</c>
      <c>10001</c>
      <c><xref target="err_BADHANDLE" /></c>

      <c>NFS4ERR_BADIOMODE</c>
      <c>10049</c>
      <c><xref target="err_BADIOMODE" /></c>

      <c>NFS4ERR_BADLAYOUT</c>
      <c>10050</c>
      <c><xref target="err_BADLAYOUT" /></c>

      <c>NFS4ERR_BADNAME</c>
      <c>10041</c>
      <c><xref target="err_BADNAME" /></c>

      <c>NFS4ERR_BADOWNER</c>
      <c>10039</c>
      <c><xref target="err_BADOWNER" /></c>

      <c>NFS4ERR_BADSESSION</c>
      <c>10052</c>
      <c><xref target="err_BADSESSION" /></c>

      <c>NFS4ERR_BADSLOT</c>
      <c>10053</c>
      <c><xref target="err_BADSLOT" /></c>

      <c>NFS4ERR_BADTYPE</c>
      <c>10007</c>
      <c><xref target="err_BADTYPE" /></c>

      <c>NFS4ERR_BADXDR</c>
      <c>10036</c>
      <c><xref target="err_BADXDR" /></c>

      <c>NFS4ERR_BAD_COOKIE</c>
      <c>10003</c>
      <c><xref target="err_BAD_COOKIE" /></c>

      <c>NFS4ERR_BAD_HIGH_SLOT</c>
      <c>10077</c>
      <c><xref target="err_BAD_HIGH_SLOT" /></c>

      <c>NFS4ERR_BAD_RANGE</c>
      <c>10042</c>
      <c><xref target="err_BAD_RANGE" /></c>

      <c>NFS4ERR_BAD_SEQID</c>
      <c>10026</c>
      <c><xref target="err_BAD_SEQID" /></c>

      <c>NFS4ERR_BAD_SESSION_DIGEST</c>
      <c>10051</c>
      <c><xref target="err_BAD_SESSION_DIGEST" /></c>

      <c>NFS4ERR_BAD_STATEID</c>
      <c>10025</c>
      <c><xref target="err_BAD_STATEID" /></c>

      <c>NFS4ERR_CB_PATH_DOWN</c>
      <c>10048</c>
      <c><xref target="err_CB_PATH_DOWN" /></c>

      <c>NFS4ERR_CLID_INUSE</c>
      <c>10017</c>
      <c><xref target="err_CLID_INUSE" /></c>

      <c>NFS4ERR_CLIENTID_BUSY</c>
      <c>10074</c>
      <c><xref target="err_CLIENTID_BUSY" /></c>

      <c>NFS4ERR_COMPLETE_ALREADY</c>
      <c>10054</c>
      <c><xref target="err_COMPLETE_ALREADY" /></c>

      <c>NFS4ERR_CONN_NOT_BOUND_TO_SESSION</c>
      <c>10055</c>
      <c><xref target="err_CONN_NOT_BOUND_TO_SESSION" /></c>

      <c>NFS4ERR_DEADLOCK</c>
      <c>10045</c>
      <c><xref target="err_DEADLOCK" /></c>

      <c>NFS4ERR_DEADSESSION</c>
      <c>10078</c>
      <c><xref target="err_DEADSESSION" /></c>

      <c>NFS4ERR_DELAY</c>
      <c>10008</c>
      <c><xref target="err_DELAY" /></c>

      <c>NFS4ERR_DELEG_ALREADY_WANTED</c>
      <c>10056</c>
      <c><xref target="err_DELEG_ALREADY_WANTED" /></c>

      <c>NFS4ERR_DELEG_REVOKED</c>
      <c>10087</c>
      <c><xref target="err_DELEG_REVOKED" /></c>

      <c>NFS4ERR_DENIED</c>
      <c>10010</c>
      <c><xref target="err_DENIED" /></c>

      <c>NFS4ERR_DIRDELEG_UNAVAIL</c>
      <c>10084</c>
      <c><xref target="err_DIRDELEG_UNAVAIL" /></c>

      <c>NFS4ERR_DQUOT</c>
      <c>69</c>
      <c><xref target="err_DQUOT" /></c>

      <c>NFS4ERR_ENCR_ALG_UNSUPP</c>
      <c>10079</c>
      <c><xref target="err_ENCR_ALG_UNSUPP" /></c>

      <c>NFS4ERR_EXIST</c>
      <c>17</c>
      <c><xref target="err_EXIST" /></c>

      <c>NFS4ERR_EXPIRED</c>
      <c>10011</c>
      <c><xref target="err_EXPIRED" /></c>

      <c>NFS4ERR_FBIG</c>
      <c>27</c>
      <c><xref target="err_FBIG" /></c>

      <c>NFS4ERR_FHEXPIRED</c>
      <c>10014</c>
      <c><xref target="err_FHEXPIRED" /></c>

      <c>NFS4ERR_FILE_OPEN</c>
      <c>10046</c>
      <c><xref target="err_FILE_OPEN" /></c>

      <c>NFS4ERR_GRACE</c>
      <c>10013</c>
      <c><xref target="err_GRACE" /></c>

      <c>NFS4ERR_HASH_ALG_UNSUPP</c>
      <c>10072</c>
      <c><xref target="err_HASH_ALG_UNSUPP" /></c>

      <c>NFS4ERR_INVAL</c>
      <c>22</c>
      <c><xref target="err_INVAL" /></c>

      <c>NFS4ERR_IO</c>
      <c>5</c>
      <c><xref target="err_IO" /></c>

      <c>NFS4ERR_ISDIR</c>
      <c>21</c>
      <c><xref target="err_ISDIR" /></c>

      <c>NFS4ERR_LAYOUTTRYLATER</c>
      <c>10058</c>
      <c><xref target="err_LAYOUTTRYLATER" /></c>

      <c>NFS4ERR_LAYOUTUNAVAILABLE</c>
      <c>10059</c>
      <c><xref target="err_LAYOUTUNAVAILABLE" /></c>

      <c>NFS4ERR_LEASE_MOVED</c>
      <c>10031</c>
      <c><xref target="err_LEASE_MOVED" /></c>

      <c>NFS4ERR_LOCKED</c>
      <c>10012</c>
      <c><xref target="err_LOCKED" /></c>

      <c>NFS4ERR_LOCKS_HELD</c>
      <c>10037</c>
      <c><xref target="err_LOCKS_HELD" /></c>

      <c>NFS4ERR_LOCK_NOTSUPP</c>
      <c>10043</c>
      <c><xref target="err_LOCK_NOTSUPP" /></c>

      <c>NFS4ERR_LOCK_RANGE</c>
      <c>10028</c>
      <c><xref target="err_LOCK_RANGE" /></c>

      <c>NFS4ERR_MINOR_VERS_MISMATCH</c>
      <c>10021</c>
      <c><xref target="err_MINOR_VERS_MISMATCH" /></c>

      <c>NFS4ERR_MLINK</c>
      <c>31</c>
      <c><xref target="err_MLINK" /></c>

      <c>NFS4ERR_MOVED</c>
      <c>10019</c>
      <c><xref target="err_MOVED" /></c>

      <c>NFS4ERR_NAMETOOLONG</c>
      <c>63</c>
      <c><xref target="err_NAMETOOLONG" /></c>

      <c>NFS4ERR_NOENT</c>
      <c>2</c>
      <c><xref target="err_NOENT" /></c>

      <c>NFS4ERR_NOFILEHANDLE</c>
      <c>10020</c>
      <c><xref target="err_NOFILEHANDLE" /></c>

      <c>NFS4ERR_NOMATCHING_LAYOUT</c>
      <c>10060</c>
      <c><xref target="err_NOMATCHING_LAYOUT" /></c>

      <c>NFS4ERR_NOSPC</c>
      <c>28</c>
      <c><xref target="err_NOSPC" /></c>

      <c>NFS4ERR_NOTDIR</c>
      <c>20</c>
      <c><xref target="err_NOTDIR" /></c>

      <c>NFS4ERR_NOTEMPTY</c>
      <c>66</c>
      <c><xref target="err_NOTEMPTY" /></c>

      <c>NFS4ERR_NOTSUPP</c>
      <c>10004</c>
      <c><xref target="err_NOTSUPP" /></c>

      <c>NFS4ERR_NOT_ONLY_OP</c>
      <c>10081</c>
      <c><xref target="err_NOT_ONLY_OP" /></c>

      <c>NFS4ERR_NOT_SAME</c>
      <c>10027</c>
      <c><xref target="err_NOT_SAME" /></c>

      <c>NFS4ERR_NO_GRACE</c>
      <c>10033</c>
      <c><xref target="err_NO_GRACE" /></c>

      <c>NFS4ERR_NXIO</c>
      <c>6</c>
      <c><xref target="err_NXIO" /></c>

      <c>NFS4ERR_OLD_STATEID</c>
      <c>10024</c>
      <c><xref target="err_OLD_STATEID" /></c>

      <c>NFS4ERR_OPENMODE</c>
      <c>10038</c>
      <c><xref target="err_OPENMODE" /></c>

      <c>NFS4ERR_OP_ILLEGAL</c>
      <c>10044</c>
      <c><xref target="err_OP_ILLEGAL" /></c>

      <c>NFS4ERR_OP_NOT_IN_SESSION</c>
      <c>10071</c>
      <c><xref target="err_OP_NOT_IN_SESSION" /></c>

      <c>NFS4ERR_PERM</c>
      <c>1</c>
      <c><xref target="err_PERM" /></c>

      <c>NFS4ERR_PNFS_IO_HOLE</c>
      <c>10075</c>
      <c><xref target="err_PNFS_IO_HOLE" /></c>

      <c>NFS4ERR_PNFS_NO_LAYOUT</c>
      <c>10080</c>
      <c><xref target="err_PNFS_NO_LAYOUT" /></c>

      <c>NFS4ERR_RECALLCONFLICT</c>
      <c>10061</c>
      <c><xref target="err_RECALLCONFLICT" /></c>

      <c>NFS4ERR_RECLAIM_BAD</c>
      <c>10034</c>
      <c><xref target="err_RECLAIM_BAD" /></c>

      <c>NFS4ERR_RECLAIM_CONFLICT</c>
      <c>10035</c>
      <c><xref target="err_RECLAIM_CONFLICT" /></c>

      <c>NFS4ERR_REJECT_DELEG</c>
      <c>10085</c>
      <c><xref target="err_REJECT_DELEG" /></c>

      <c>NFS4ERR_REP_TOO_BIG</c>
      <c>10066</c>
      <c><xref target="err_REP_TOO_BIG" /></c>

      <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c>
      <c>10067</c>
      <c><xref target="err_REP_TOO_BIG_TO_CACHE" /></c>

      <c>NFS4ERR_REQ_TOO_BIG</c>
      <c>10065</c>
      <c><xref target="err_REQ_TOO_BIG" /></c>

      <c>NFS4ERR_RESTOREFH</c>
      <c>10030</c>
      <c><xref target="err_RESTOREFH" /></c>

      <c>NFS4ERR_RETRY_UNCACHED_REP</c>
      <c>10068</c>
      <c><xref target="err_RETRY_UNCACHED_REP" /></c>

      <c>NFS4ERR_RETURNCONFLICT</c>
      <c>10086</c>
      <c><xref target="err_RETURNCONFLICT" /></c>

      <c>NFS4ERR_ROFS</c>
      <c>30</c>
      <c><xref target="err_ROFS" /></c>

      <c>NFS4ERR_SAME</c>
      <c>10009</c>
      <c><xref target="err_SAME" /></c>

      <c>NFS4ERR_SHARE_DENIED</c>
      <c>10015</c>
      <c><xref target="err_SHARE_DENIED" /></c>

      <c>NFS4ERR_SEQUENCE_POS</c>
      <c>10064</c>
      <c><xref target="err_SEQUENCE_POS" /></c>

      <c>NFS4ERR_SEQ_FALSE_RETRY</c>
      <c>10076</c>
      <c><xref target="err_SEQ_FALSE_RETRY" /></c>

      <c>NFS4ERR_SEQ_MISORDERED</c>
      <c>10063</c>
      <c><xref target="err_SEQ_MISORDERED" /></c>

      <c>NFS4ERR_SERVERFAULT</c>
      <c>10006</c>
      <c><xref target="err_SERVERFAULT" /></c>

      <c>NFS4ERR_STALE</c>
      <c>70</c>
      <c><xref target="err_STALE" /></c>

      <c>NFS4ERR_STALE_CLIENTID</c>
      <c>10022</c>
      <c><xref target="err_STALE_CLIENTID" /></c>

      <c>NFS4ERR_STALE_STATEID</c>
      <c>10023</c>
      <c><xref target="err_STALE_STATEID" /></c>

      <c>NFS4ERR_SYMLINK</c>
      <c>10029</c>
      <c><xref target="err_SYMLINK" /></c>

      <c>NFS4ERR_TOOSMALL</c>
      <c>10005</c>
      <c><xref target="err_TOOSMALL" /></c>

      <c>NFS4ERR_TOO_MANY_OPS</c>
      <c>10070</c>
      <c><xref target="err_TOO_MANY_OPS" /></c>

      <c>NFS4ERR_UNKNOWN_LAYOUTTYPE</c>
      <c>10062</c>
      <c><xref target="err_UNKNOWN_LAYOUTTYPE" /></c>

      <c>NFS4ERR_UNSAFE_COMPOUND</c>
      <c>10069</c>
      <c><xref target="err_UNSAFE_COMPOUND" /></c>
      
      <c>NFS4ERR_WRONGSEC</c>
      <c>10016</c>
      <c><xref target="err_WRONGSEC" /></c>

      <c>NFS4ERR_WRONG_CRED</c>
      <c>10082</c>
      <c><xref target="err_WRONG_CRED" /></c>

      <c>NFS4ERR_WRONG_TYPE</c>
      <c>10083</c>
      <c><xref target="err_WRONG_TYPE" /></c>

      <c>NFS4ERR_XDEV</c>
      <c>18</c>
      <c><xref target="err_XDEV" /></c>

    </texttable>
  <section title="General Errors" anchor="errors_gen">
    <t>
      This section deals with errors that are applicable to a broad
      set of different purposes.
    </t>
    <section title="NFS4ERR_BADXDR (Error Code 10036)" 
       	     anchor="err_BADXDR">
      <t>
        The arguments for this operation do not match those specified in
        the XDR definition.  This includes situations in which the
        request ends before all the arguments have been seen.  Note
        that this error applies when fixed enumerations (these include
        booleans) have a value within the input stream that is not
        valid for the enum.  A replier may pre-parse all operations for
        a Compound procedure before doing any operation execution 
        and return RPC-level XDR errors in that case.  
      </t>
    </section>
    <section title="NFS4ERR_BAD_COOKIE (Error Code 10003)" 
             anchor="err_BAD_COOKIE">
      <t>
        Used for operations that provide a set of information indexed by
        some quantity provided by the client or cookie sent by the
        server for an earlier invocation.  Where the value cannot 
        be used for its intended purpose, this error results. 
      </t>
    </section>
    <section title="NFS4ERR_DELAY (Error Code 10008)" 
             anchor="err_DELAY">
      <t>
        For any of a number of reasons, the replier could not 
        process this operation in what was deemed a reasonable
        time.  The client should wait and then try the request 
        with a new slot and sequence value.  
      </t>
      <t>
        Some examples of scenarios that might lead to this situation:
          <list style="symbols">
            <t>
              A server that supports hierarchical storage receives a 
              request to process a file that had been migrated. 
            </t>
            <t>
             An operation requires a delegation recall to proceed,
             and waiting for this delegation recall makes processing
             this request in a timely fashion impossible.
           </t>
         </list>
       </t>
       <t>
        In such cases, the error NFS4ERR_DELAY allows
        these preparatory operations to proceed without
        holding up client resources such as a session slot.
        After delaying for period of time, the client can
        then re-send the operation in question  (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).

      </t>
      <t>
        Note that without the ability to return NFS4ERR_DELAY and the
        client's willingness to re-send when receiving it, deadlock might
        result.  For example, if a recall is done, and if the delegation return or
        operations preparatory to delegation return are held up by
        other operations that need the delegation to be returned, 
        session slots might not be available.  The result could be
        deadlock.
      </t>
    </section>
    <section title="NFS4ERR_INVAL (Error Code 22)" 
             anchor="err_INVAL">
      <t>
        The arguments for this operation are not valid for some reason, even
        though they do match those specified in the XDR definition for
        the request.
      </t>
    </section>
    <section title="NFS4ERR_NOTSUPP (Error Code 10004)" 
             anchor="err_NOTSUPP">
      <t>
        Operation not supported, either because the operation is
        an OPTIONAL one and is not supported by this server or
        because the operation MUST NOT be implemented in 
        the current minor version.
      </t>
    </section>
    <section title="NFS4ERR_SERVERFAULT (Error Code 10006)" 
             anchor="err_SERVERFAULT">
      <t>
        An error occurred on the server that does not map to any of
        the specific legal NFSv4.1 protocol error values.  The client
        should translate this into an appropriate error.  UNIX clients
        may choose to translate this to EIO.

     </t>
    </section>
    <section title="NFS4ERR_TOOSMALL (Error Code 10005)" 
             anchor="err_TOOSMALL"> 
      <t>
        Used where an operation returns a variable amount of data,
        with a limit specified by the client.  Where the data 
        returned cannot be fit within the limit specified by the
        client, this error results.
      </t>
    </section>
  </section>

  <section title="Filehandle Errors" anchor="errors_fh">
    <t>
      These errors deal with the situation in which the current
      or saved filehandle, or the filehandle passed to PUTFH
      intended to become the current filehandle, is invalid
      in some way.  This includes situations in which the
      filehandle is a valid filehandle in general but is not 
      of the appropriate object type for the current operation.
    </t>
    <t>
      Where the error description indicates a problem with the
      current or saved filehandle, it is to be understood that 
      filehandles are only checked for the condition if they
      are implicit arguments of the operation in question.
    </t>
    <section title="NFS4ERR_BADHANDLE (Error Code 10001)" 
             anchor="err_BADHANDLE">
      <t>
        Illegal NFS filehandle for the current server.  The current
        file handle failed internal consistency checks.  Once accepted
        as valid (by PUTFH), no subsequent status change can cause the
        filehandle to generate this error.
      </t>
    </section> 
    <section title="NFS4ERR_FHEXPIRED (Error Code 10014)" 
             anchor="err_FHEXPIRED">
      <t>
        A current or saved filehandle that is an argument to the
        current operation is volatile and has expired at the server.
      </t>
    </section>
   <section title="NFS4ERR_ISDIR (Error Code 21)" 
             anchor="err_ISDIR">
      <t>
        The current or saved filehandle designates a directory 
        when the current operation does not allow a directory to 
        be accepted as the target of this operation.
      </t>
    </section>
    <section title="NFS4ERR_MOVED (Error Code 10019)" 
             anchor="err_MOVED">
      <t>
        The file system that contains the current filehandle object
        is not present at the server.  It may have been relocated or
        migrated to another server, or it may have never been present.
        The client may obtain the new file system location by obtaining 
        the "fs_locations" or "fs_locations_info" attribute for the 
        current filehandle.  For further discussion, refer to 
        <xref target="presence_or_absence" />.
      </t>
    </section>
    <section title="NFS4ERR_NOFILEHANDLE (Error Code 10020)" 
             anchor="err_NOFILEHANDLE">
      <t>
        The logical current or saved filehandle value is required by 
        the current operation and is not set.
        This may be a result of a malformed COMPOUND
        operation (i.e., no PUTFH or PUTROOTFH before an operation that
        requires the current filehandle be set).
      </t>
    </section>
    <section title="NFS4ERR_NOTDIR (Error Code 20)" 
             anchor="err_NOTDIR">
      <t>
        The current (or saved) filehandle designates an object that
        is not a directory for an operation in which a directory is
        required.
      </t>
    </section>
    <section title="NFS4ERR_STALE (Error Code 70)" 
             anchor="err_STALE">
      <t>
        The current or saved filehandle value designating an argument
        to the current operation is invalid. The file referred to by
        that filehandle no longer exists or access to it has been
        revoked.
      </t>
    </section>
    <section title="NFS4ERR_SYMLINK (Error Code 10029)" 
             anchor="err_SYMLINK">
      <t>
        The current filehandle designates a symbolic link when the 
        current operation does not allow a symbolic link as the 
        target.
      </t>
    </section>
    <section title="NFS4ERR_WRONG_TYPE (Error Code 10083)" 
             anchor="err_WRONG_TYPE">
      <t>
        The current (or saved) filehandle designates an object that
        is of an invalid type for the current operation, and there is no
        more specific error (such as NFS4ERR_ISDIR or NFS4ERR_SYMLINK)
        that applies.  Note that in NFSv4.0, such situations generally
        resulted in the less-specific error NFS4ERR_INVAL.
      </t>
    </section>
  </section>

  <section title="Compound Structure Errors" anchor="errors_comp">
    <t>
      This section deals with errors that relate to the overall structure
      of a Compound request (by which we mean to include both
      COMPOUND and CB_COMPOUND), rather than to particular operations. 
    </t>
    <t>
      There are a number of basic constraints on the operations that
      may appear in a Compound request.  Sessions add to these basic 
      constraints by requiring a Sequence operation (either SEQUENCE
      or CB_SEQUENCE) at the start of the Compound.
    </t>
    <section title="NFS_OK (Error code 0)"
             anchor="err_OK">
      <t>
        Indicates the operation completed successfully, in that all
        of the constituent operations completed without error.
      </t>
    </section>
    <section title="NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)"
             anchor="err_MINOR_VERS_MISMATCH">
      <t>
        The minor version specified is not one that the current listener
        supports.  This value is returned in the overall status for the
        Compound but is not associated with a specific operation since
        the results will specify a result count of zero.
      </t>
    </section>
    <section title="NFS4ERR_NOT_ONLY_OP (Error Code 10081)" 
             anchor="err_NOT_ONLY_OP">
      <t>
        Certain operations, which are allowed to be executed outside
        of a session, MUST be the only operation within a Compound
        whenever the Compound does not start with a Sequence
        operation. This error results when that constraint is not met.
      </t>
    </section>
    <section title="NFS4ERR_OP_ILLEGAL (Error Code 10044)" 
             anchor="err_OP_ILLEGAL">
      <t>
        The operation code is not a valid one for the current
        Compound procedure.  The opcode
        in the result stream matched with this error is the
        ILLEGAL value, although the value that appears in the
        request stream may be different.  Where an illegal 
        value appears and the replier pre-parses all operations for
        a Compound procedure before doing any operation execution, 
        an RPC-level XDR error may be returned.  
      </t>
    </section>
    <section title="NFS4ERR_OP_NOT_IN_SESSION (Error Code 10071)" 
             anchor="err_OP_NOT_IN_SESSION">
      <t>
        Most forward operations and all callback operations are only
        valid within the context of a session, so that the Compound
        request in question MUST begin with a Sequence operation.
        If an attempt is made to execute these operations outside 
        the context of session, this error results.
      </t>
    </section>
    <section title="NFS4ERR_REP_TOO_BIG (Error Code 10066)" 
             anchor="err_REP_TOO_BIG">
      <t>
        The reply to a Compound would exceed the 
        channel's negotiated maximum response size.
      </t>
    </section>
    <section title="NFS4ERR_REP_TOO_BIG_TO_CACHE (Error Code 10067)" 
             anchor="err_REP_TOO_BIG_TO_CACHE">
      <t>
        The reply to a Compound would exceed the 
        channel's negotiated maximum size for replies cached in the
        reply cache when the Sequence for the current request specifies
        that this request is to be cached.
      </t>
    </section>
    <section title="NFS4ERR_REQ_TOO_BIG (Error Code 10065)" 
             anchor="err_REQ_TOO_BIG">
      <t>
        The Compound request exceeds the 
        channel's negotiated maximum size for requests.
      </t>
    </section>
    <section title="NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)" 
             anchor="err_RETRY_UNCACHED_REP">
      <t>
        The requester has attempted a retry of a Compound
        that it previously requested not
        be placed in the reply cache.
      </t>
    </section>
    <section title="NFS4ERR_SEQUENCE_POS (Error Code 10064)" 
             anchor="err_SEQUENCE_POS">
      <t>
        A Sequence operation appeared in a 
        position other than the first operation of a 
        Compound request.
      </t>
    </section>
    <section title="NFS4ERR_TOO_MANY_OPS (Error Code 10070)" 
             anchor="err_TOO_MANY_OPS">
      <t>
        The Compound request has too many operations, exceeding the
        count negotiated when the session was created. 
      </t>
    </section>
    <section title="NFS4ERR_UNSAFE_COMPOUND (Error Code 10068)" 
             anchor="err_UNSAFE_COMPOUND">
      <t>
        The client has sent a COMPOUND request with an unsafe
        mix of operations -- specifically, with a non-idempotent
        operation that changes the current filehandle and that is not followed by a
        GETFH.
      </t>
    </section>
  </section>

  <section title="File System Errors" anchor="errors_fs">
    <t>
      These errors describe situations that occurred in the underlying
      file system implementation rather than in the protocol or any
      NFSv4.x feature.
    </t>
    <section title="NFS4ERR_BADTYPE (Error Code 10007)" 
             anchor="err_BADTYPE">
      <t>
        An attempt was made to create an object with an inappropriate
        type specified to CREATE.  This may be because the type 
        is undefined, because the type is not supported by the 
        server, or because the type is not intended to be created by CREATE
        (such as a regular file or named attribute, for 
        which OPEN is used to do the file creation).
      </t>
    </section>
    <section title="NFS4ERR_DQUOT (Error Code 19)" 
             anchor="err_DQUOT">
      <t>
        Resource (quota) hard limit exceeded. The user's resource
        limit on the server has been exceeded.
      </t>
    </section>
    <section title="NFS4ERR_EXIST (Error Code 17)" 
             anchor="err_EXIST">
      <t>
        A file of the specified target name (when creating, renaming,
        or linking) already exists.
      </t>
    </section>
    <section title="NFS4ERR_FBIG (Error Code 27)" 
             anchor="err_FBIG">
      <t>
        The file is too large. The operation would have caused the file to
        grow beyond the server's limit.
      </t>
    </section>
    <section title="NFS4ERR_FILE_OPEN (Error Code 10046)" 
             anchor="err_FILE_OPEN">
      <t>
        The operation is not allowed because a
        file involved in the operation is currently open.
        Servers may, but are not required to, disallow linking-to,
        removing, or renaming open files.
      </t>
    </section>
    <section title="NFS4ERR_IO (Error Code 5)" 
             anchor="err_IO">
      <t>
        Indicates that an I/O error occurred for which the file system
        was unable to provide recovery.
      </t>
    </section>
    <section title="NFS4ERR_MLINK (Error Code 31)" 
             anchor="err_MLINK">
      <t>
        The request would have caused the server's limit for the
        number of hard links a file may have to be exceeded.
      </t>
    </section>
    <section title="NFS4ERR_NOENT (Error Code 2)" 
             anchor="err_NOENT">
      <t>
         Indicates no such file or directory. The file or directory name
         specified does not exist.
      </t>
    </section>
    <section title="NFS4ERR_NOSPC (Error Code 28)" 
             anchor="err_NOSPC">
      <t>
        Indicates there is no space left on the device. The operation would have 
        caused the server's file system to exceed its limit.
      </t>
    </section>
    <section title="NFS4ERR_NOTEMPTY (Error Code 66)" 
             anchor="err_NOTEMPTY">
      <t>
         An attempt was made to remove a directory that was not
         empty.
      </t>
    </section>
    <section title="NFS4ERR_ROFS (Error Code 30)" 
             anchor="err_ROFS">
      <t>
         Indicates a read-only file system. A modifying operation was 
         attempted on a read-only file system.
      </t>
    </section>
    <section title="NFS4ERR_XDEV (Error Code 18)" 
             anchor="err_XDEV">
      <t>
        Indicates an attempt to do an operation, such as linking, that
        inappropriately crosses a boundary.  This may be due to such 
        boundaries as:
        <list style="symbols">
          <t>
            that between file systems (where the fsids are different).
          </t>
          <t>
            that between different named attribute directories or
            between a named attribute directory and an ordinary 
            directory.
          </t>
          <t>
            that between byte-ranges of a file system that the file system
            implementation treats as separate (for example, for space
            accounting purposes), and where cross-connection between
            the byte-ranges are not allowed.
          </t>
        </list>
      </t>
    </section>
  </section>

  <section title="State Management Errors" anchor="errors_state_mgt">
    <t>
      These errors indicate problems with the stateid (or one of
      the stateids) passed to a given operation.  
      This includes
      situations in which the stateid is invalid as well as
      situations in which the stateid is valid but designates 
      locking state that has been revoked.
Depending on the operation, the 
      stateid when valid may designate opens, byte-range locks,
      file or directory delegations, layouts, or device maps.
    </t>
    <section title="NFS4ERR_ADMIN_REVOKED (Error Code 10047)" 
             anchor="err_ADMIN_REVOKED">
      <t>
        A stateid designates locking state of any type that has
        been revoked due to administrative interaction, possibly
        while the lease is valid.
      </t>
    </section>
    <section title="NFS4ERR_BAD_STATEID (Error Code 10026)" 
             anchor="err_BAD_STATEID">
      <t>
        A stateid does not properly designate any valid 
        state.  See Sections <xref target="stateid_lifetime" format="counter" /> and 
        <xref target="special_stateid" format="counter" />
        for a discussion of how stateids are validated.
      </t>
    </section>
    <section title="NFS4ERR_DELEG_REVOKED (Error Code 10087)" 
             anchor="err_DELEG_REVOKED">
      <t>
	A stateid designates recallable locking state of
	any type (delegation or layout) that has been
	revoked due to the failure of the client to return
	the lock when it was recalled.

      </t>
    </section>
    <section title="NFS4ERR_EXPIRED (Error Code 10011)" 
             anchor="err_EXPIRED">
      <t>
        A stateid designates locking state of any type that has
        been revoked due to expiration of the client's lease,
        either immediately upon lease expiration, or following 
        a later request for a conflicting lock.
      </t>
    </section>
    <section title="NFS4ERR_OLD_STATEID (Error Code 10024)" 
             anchor="err_OLD_STATEID">
      <t>
        A stateid with a non-zero seqid value does match 
        the current seqid for the state designated by the
        user.
      </t>
    </section>
  </section>

  <section title="Security Errors" anchor="errors_sec">
    <t>
      These are the various permission-related errors in NFSv4.1.
    </t>
    <section title="NFS4ERR_ACCESS (Error Code 13)" 
             anchor="err_ACCESS">
      <t>
        Indicates permission denied. The caller does
        not have the correct permission to perform
        the requested operation. Contrast this with
        NFS4ERR_PERM (<xref target="err_PERM" />), which
        restricts itself to owner or privileged-user
        permission failures, and NFS4ERR_WRONG_CRED
        (<xref target="err_WRONG_CRED" />), which deals
        with appropriate permission to delete or modify
        transient objects based on the credentials of
        the user that created them.

      </t>
    </section>
    <section title="NFS4ERR_PERM (Error Code 1)" 
             anchor="err_PERM">
      <t>
        Indicates requester is not the owner. The operation was not 
        allowed because the caller is neither a privileged user 
        (root) nor the owner of the target of the operation.
      </t>
    </section>
    <section title="NFS4ERR_WRONGSEC (Error Code 10016)" 
             anchor="err_WRONGSEC">
      <t>
        Indicates that the security mechanism being used by the client 
        for the operation does not match the server's security policy.  
        The client should change the security mechanism being used and 
        re-send the operation (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).  SECINFO and SECINFO_NO_NAME can be used
        to determine the appropriate mechanism.
      </t>
    </section>
    <section title="NFS4ERR_WRONG_CRED (Error Code 10082)" 
             anchor="err_WRONG_CRED">
      <t>
        An operation that manipulates state was attempted by a principal
        that was not allowed to modify that piece of state.
      </t>
    </section>
  </section>

  <section title="Name Errors" anchor="errors_name">
    <t>
      Names in NFSv4 are UTF-8 strings.  When the strings are not
      valid UTF-8 or are of length zero, the error NFS4ERR_INVAL
      results.  Besides this, there are a number of other errors 
      to indicate specific problems with names.
    </t>
    <section title="NFS4ERR_BADCHAR (Error Code 10040)" 
             anchor="err_BADCHAR">
      <t>
        A UTF-8 string contains a character that is not supported 
        by the server in the context in which it being used.
      </t>
    </section>
    <section title="NFS4ERR_BADNAME (Error Code 10041)" 
             anchor="err_BADNAME">
      <t>
         A name string in a request consisted of valid UTF-8
         characters supported by the server, but the name is not 
         supported by the server as a valid name for the current operation.
         An example might be creating a file or directory named ".."
         on a server whose file system uses that name for links to
         parent directories.
      </t>
    </section>
    <section title="NFS4ERR_NAMETOOLONG (Error Code 63)" 
             anchor="err_NAMETOOLONG">
      <t>
         Returned when the filename in an operation exceeds the
         server's implementation limit.  
      </t>
    </section>
  </section>

  <section title="Locking Errors" anchor="errors_locking">
    <t>
      This section deals with errors related to locking, both as to
      share reservations and byte-range locking.  It does not deal
      with errors specific to the process of reclaiming locks.  Those
      are dealt with in <xref target="errors_reclaim"></xref>.
    </t>
    <section title="NFS4ERR_BAD_RANGE (Error Code 10042)" 
             anchor="err_BAD_RANGE">
      <t>
        The byte-range of a LOCK, LOCKT, or LOCKU operation is
        not allowed by the
        server.  For example, this error results when a server
        that only supports 32-bit ranges receives a range that
        cannot be handled by that server.  (See 
        <xref target="OP_LOCK_DESCRIPTION" />.)
      </t>
    </section>
    <section title="NFS4ERR_DEADLOCK (Error Code 10045)" 
             anchor="err_DEADLOCK">
      <t>
        The server has been able to determine a byte-range locking
        deadlock condition for a READW_LT or WRITEW_LT LOCK operation.
      </t>
    </section>
    <section title="NFS4ERR_DENIED (Error Code 10010)" 
             anchor="err_DENIED">
      <t>
        An attempt to lock a file is denied.  Since this may be a
        temporary condition, the client is encouraged to re-send the lock
        request (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send) until the lock is accepted.  See 
        <xref target="blocking_locks" /> for a discussion of the re-send.
      </t>
    </section>
    <section title="NFS4ERR_LOCKED (Error Code 10012)" 
             anchor="err_LOCKED">
      <t>
        A READ or WRITE operation was attempted on a file where there
        was a conflict between the I/O and an existing lock:
        <list style="symbols"> 
          <t>
            There is a share reservation inconsistent with the I/O
            being done.
          </t>
          <t>
            The range to be read or written intersects an existing
            mandatory byte-range lock.
          </t>
        </list>
      </t>
    </section>
    <section title="NFS4ERR_LOCKS_HELD (Error Code 10037)" 
             anchor="err_LOCKS_HELD">
      <t>
        An operation was prevented by the unexpected presence of locks.
      </t>
    </section>
    <section title="NFS4ERR_LOCK_NOTSUPP (Error Code 10043)" 
             anchor="err_LOCK_NOTSUPP">
      <t>
        A LOCK operation was attempted that would require the upgrade 
        or downgrade of a byte-range lock range already held by the owner, and the
        server does not support atomic upgrade or downgrade of locks.
      </t>
    </section>
    <section title="NFS4ERR_LOCK_RANGE (Error Code 10028)" 
             anchor="err_LOCK_RANGE">
      <t>
        A LOCK operation is operating on a range that overlaps in part a
        currently held byte-range lock for the current lock-owner and does not
        precisely match a single such byte-range lock where the server 
        does not support this type of request, and thus does not 
        implement POSIX locking semantics <xref target="fcntl"/>. See Sections
        <xref target="OP_LOCK_IMPLEMENTATION" format="counter" />,
        <xref target="OP_LOCKT_IMPLEMENTATION" format="counter" />, and
        <xref target="OP_LOCKU_IMPLEMENTATION" format="counter" /> for a discussion of
        how this applies to LOCK, LOCKT, and LOCKU respectively.
      </t>
    </section>
    <section title="NFS4ERR_OPENMODE (Error Code 10038)" 
             anchor="err_OPENMODE">
      <t>
        The client attempted a READ, WRITE, LOCK, or other operation
        not sanctioned by the stateid passed (e.g., writing to a file
        opened for read-only access).
      </t>
    </section>
    <section title="NFS4ERR_SHARE_DENIED (Error Code 10015)" 
             anchor="err_SHARE_DENIED">
      <t>
        An attempt to OPEN a file with a share reservation has failed
        because of a share conflict.
      </t>
    </section>
  </section>

  <section title="Reclaim Errors" anchor="errors_reclaim">
    <t>
      These errors relate to the process of reclaiming locks after a
      server restart.
    </t>
    <section title="NFS4ERR_COMPLETE_ALREADY (Error Code 10054)" 
             anchor="err_COMPLETE_ALREADY">
      <t>
        The client previously sent a successful RECLAIM_COMPLETE
        operation.  An additional RECLAIM_COMPLETE operation is not
        necessary and results in this error.
      </t>
    </section>
    <section title="NFS4ERR_GRACE (Error Code 10013)" 
             anchor="err_GRACE">
      <t>
        The server was in its recovery or grace period.
        The locking request was not a reclaim request and so
        could not be granted during that period.
      </t>
    </section>
    <section title="NFS4ERR_NO_GRACE (Error Code 10033)" 
             anchor="err_NO_GRACE">
      <t>
        A reclaim of client state was attempted in circumstances in 
        which the server cannot guarantee that conflicting state has 
        not been provided to another client.  This can occur because 
        the reclaim has been done outside of the grace period of the
        server, after the client has done a RECLAIM_COMPLETE operation,
        or because previous operations have created a situation in which
        the server is not able to determine that a reclaim-interfering
        edge condition does not exist.
      </t>
    </section>
    <section title="NFS4ERR_RECLAIM_BAD (Error Code 10034)" 
             anchor="err_RECLAIM_BAD">
      <t>

	The server has determined that a reclaim attempted by the client 
	is not valid, i.e. the lock specified as being reclaimed could
	not possibly have existed before the server restart.  A server 
	is not obliged to make this determination and will typically rely 
	on the client to only reclaim locks that the client was granted prior
        to restart.  However, 
	when a server does have reliable information to enable it make  
	this determination, this error indicates that the reclaim has 
	been rejected as invalid.  This is as opposed to the error
	NFS4ERR_RECLAIM_CONFLICT (see <xref target="err_RECLAIM_CONFLICT"/>)
        where the server can only determine that 
	there has been an invalid reclaim, but cannot determine
	which request is invalid.

      </t>
    </section>
    <section title="NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)" 
             anchor="err_RECLAIM_CONFLICT">
      <t>
        The reclaim attempted by the client has encountered a conflict
        and cannot be satisfied.  Potentially indicates a misbehaving
        client, although not necessarily the one receiving the error.
        The misbehavior might be on the part of the client that 
        established the lock with which this client conflicted.  See also
	<xref target="err_RECLAIM_BAD"/> for the related error,
	NFS4ERR_RECLAIM_BAD.

      </t>
    </section>
  </section>

  <section title="pNFS Errors" anchor="errors_pnfs">
    <t>
      This section deals with pNFS-related errors including those
      that are associated with using NFSv4.1 to communicate with a
      data server.
    </t>
    <section title="NFS4ERR_BADIOMODE (Error Code 10049)" 
             anchor="err_BADIOMODE">
      <t>
        An invalid or inappropriate layout iomode was specified.
        For example an inappropriate layout iomode, suppose
        a client's LAYOUTGET operation specified an iomode of
        LAYOUTIOMODE4_RW, and the server is neither able nor willing
        to let the client send write requests to data servers; the server
        can reply with NFS4ERR_BADIOMODE. The client would then 
        send another LAYOUTGET with an iomode of LAYOUTIOMODE4_READ.
      </t>
    </section>
    <section title="NFS4ERR_BADLAYOUT (Error Code 10050)" 
             anchor="err_BADLAYOUT">
      <t>
        The layout specified is invalid in some way.  For LAYOUTCOMMIT,
        this indicates that the specified layout is not held by the
        client or is not of mode LAYOUTIOMODE4_RW.  For LAYOUTGET, 
        it indicates that a layout matching the client's specification
        as to minimum length cannot be granted. 
      </t>
    </section>
    <section title="NFS4ERR_LAYOUTTRYLATER (Error Code 10058)" 
             anchor="err_LAYOUTTRYLATER">
      <t>
        Layouts are temporarily unavailable for the file.  The client 
        should re-send later (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).
      </t>
    </section>
    <section title="NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)" 
             anchor="err_LAYOUTUNAVAILABLE">
      <t>
        Returned when layouts are not available for the current file 
        system or the particular specified file.
      </t>
    </section>
    <section title="NFS4ERR_NOMATCHING_LAYOUT (Error Code 10060)" 
             anchor="err_NOMATCHING_LAYOUT">
      <t>
        Returned when layouts are recalled and the client has no layouts
        matching the specification of the layouts being recalled.
      </t>
    </section>
    <section title="NFS4ERR_PNFS_IO_HOLE (Error Code 10075)" 
             anchor="err_PNFS_IO_HOLE">
      <t>
        The pNFS client has attempted to read from or write to an
        illegal hole of a file of a data server that is using
        sparse packing. See <xref target="sparse_dense" />.
      </t>
    </section>
    <section title="NFS4ERR_PNFS_NO_LAYOUT (Error Code 10080)" 
             anchor="err_PNFS_NO_LAYOUT">
      <t>
        The pNFS client has attempted to read from or write to a file
        (using a request to a data server) without holding a valid 
        layout. This includes the case where the client had a layout,
        but the iomode does not allow a WRITE.
      </t>
    </section>
    <section title="NFS4ERR_RETURNCONFLICT (Error Code 10086)" 
             anchor="err_RETURNCONFLICT">
      <t>
        A layout
        is unavailable due to an attempt to perform the LAYOUTGET
        before a pending LAYOUTRETURN on the file has been received.
        See <xref target="layout_server_consider" />.

      </t>
    </section>
    <section title="NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)" 
             anchor="err_UNKNOWN_LAYOUTTYPE">
      <t>
        The client has specified a layout type that is not supported by 
        the server.
      </t>
    </section>
  </section>

  <section title="Session Use Errors" anchor="errors_sess_use">
    <t>
      This section deals with errors encountered when using sessions,
      that is, errors encountered when a request uses a Sequence
      (i.e., either SEQUENCE or CB_SEQUENCE) operation.
    </t>
    <section title="NFS4ERR_BADSESSION (Error Code 10052)" 
             anchor="err_BADSESSION">
      <t>
        The specified session ID is unknown to the server
        to which the operation is addressed.
      </t>
    </section>
    <section title="NFS4ERR_BADSLOT (Error Code 10053)" 
             anchor="err_BADSLOT">
      <t>
        The requester sent a Sequence operation
        that attempted to use a slot the replier
        does not have in its slot table. It is possible the
        slot may have been retired.
      </t>
    </section>
    <section title="NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)" 
             anchor="err_BAD_HIGH_SLOT">
      <t>
        The highest_slot argument in a Sequence operation
        exceeds the replier's enforced highest_slotid.
      </t>
    </section>
    <section title="NFS4ERR_CB_PATH_DOWN (Error Code 10048)" 
             anchor="err_CB_PATH_DOWN">
      <t>

        There is a problem contacting the client via
        the callback path. The function of this error has
        been mostly superseded by the use of
        status flags in the reply to the SEQUENCE
        operation (see <xref target="OP_SEQUENCE" />).

      </t>
    </section>
    <section title="NFS4ERR_DEADSESSION (Error Code 10078)" 
             anchor="err_DEADSESSION">
      <t>
        The specified session is a persistent session that is 
        dead and does not accept new
        requests or perform new operations on existing requests
        (in the case in which a request was partially executed
        before server restart).

      </t>
    </section>
    <section title="NFS4ERR_CONN_NOT_BOUND_TO_SESSION (Error Code 10055)" 
             anchor="err_CONN_NOT_BOUND_TO_SESSION">
      <t>
        A Sequence operation was sent on a connection that has not 
        been associated with the specified session,
        where the client specified that connection association
        was to be enforced with SP4_MACH_CRED or SP4_SSV state protection.
      </t>
    </section>
    <section title="NFS4ERR_SEQ_FALSE_RETRY (Error Code 10076)" 
             anchor="err_SEQ_FALSE_RETRY">
      <t>
        The requester sent a Sequence operation with a
        slot ID and sequence ID that are in the reply cache, but
        the replier has detected that the retried request
        is not the same as the original request. 
        See <xref target="false_retry"/>.
      </t>
    </section>
    <section title="NFS4ERR_SEQ_MISORDERED (Error Code 10063)" 
             anchor="err_SEQ_MISORDERED">
      <t>
        The requester sent a Sequence operation
        with an invalid sequence ID.
      </t>
    </section>
  </section>

  <section title="Session Management Errors" anchor="errors_sess_mgt">
    <t>
      This section deals with errors associated with requests used
      in session management.
    </t>
    <section title="NFS4ERR_BACK_CHAN_BUSY (Error Code 10057)" 
             anchor="err_BACK_CHAN_BUSY">
      <t>
         An attempt was made to destroy a session when the session 
         cannot be destroyed because the server has
         callback requests outstanding.
      </t>
    </section>
    <section title="NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)" 
             anchor="err_BAD_SESSION_DIGEST">
      <t>
        The digest used in a SET_SSV request is not valid.
      </t>
    </section>
  </section>

  <section title="Client Management Errors" anchor="errors_client_mgt">
    <t>
      This section deals with errors associated with requests used
      to create and manage client IDs.
    </t>
    <section title="NFS4ERR_CLIENTID_BUSY (Error Code 10074)" 
             anchor="err_CLIENTID_BUSY">
      <t>
        The DESTROY_CLIENTID operation has found there are
        sessions and/or unexpired state associated with the 
        client ID to be destroyed.
      </t>
    </section>
    <section title="NFS4ERR_CLID_INUSE (Error Code 10017)" 
             anchor="err_CLID_INUSE">
      <t>
        While processing an EXCHANGE_ID operation, the server was presented
        with a co_ownerid field that matches an existing client with
        valid leased state, but the principal sending the EXCHANGE_ID
        operation differs from the principal that established the existing
        client.
        This indicates a collision (most likely due to chance) between
        clients. The client should recover by changing the
        co_ownerid and re-sending EXCHANGE_ID (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).
      </t>
    </section>
    <section title="NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)" 
             anchor="err_ENCR_ALG_UNSUPP">
      <t>
        An EXCHANGE_ID was sent that specified state protection
        via SSV, and where the set of encryption algorithms presented
        by the client did not include any supported by the server.
      </t>
    </section>
    <section title="NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)" 
             anchor="err_HASH_ALG_UNSUPP">
      <t>
        An EXCHANGE_ID was sent that specified state protection
        via SSV, and where the set of hashing algorithms presented
        by the client did not include any supported by the server.
      </t>
    </section>
    <section title="NFS4ERR_STALE_CLIENTID (Error Code 10022)" 
             anchor="err_STALE_CLIENTID">
      <t>
        A client ID not recognized by the server was passed to an
        operation.  Note that unlike the case of NFSv4.0, client IDs
        are not passed explicitly to the server in ordinary locking
        operations and cannot result in this error.  Instead, when
        there is a server restart, it is first manifested through
        an error on the associated session, and the staleness of the
        client ID is detected when trying to associate a client ID
        with a new session.
      </t>
    </section>
  </section>

  <section title="Delegation Errors" anchor="errors_deleg">
    <t>
      This section deals with errors associated with requesting and
      returning delegations.
    </t>
    <section title="NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)" 
             anchor="err_DELEG_ALREADY_WANTED">
      <t>
        The client has requested a delegation when it had already 
        registered that it wants that same delegation.
      </t>
    </section>
    <section title="NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)" 
             anchor="err_DIRDELEG_UNAVAIL">
      <t>
        This error is returned when the server is unable or unwilling 
        to provide a requested directory delegation.
      </t>
    </section>
    <section title="NFS4ERR_RECALLCONFLICT (Error Code 10061)" 
             anchor="err_RECALLCONFLICT">
      <t>
        A recallable object (i.e., a layout or delegation)
        is unavailable due to a conflicting recall operation that is
        currently in progress for that object.
      </t>
    </section>
    <section title="NFS4ERR_REJECT_DELEG (Error Code 10085)" 
             anchor="err_REJECT_DELEG">
      <t>
        The callback operation invoked to deal with a new delegation has
        rejected it.
      </t>
    </section>
  </section>

  <section title="Attribute Handling Errors" anchor="errors_attr">
    <t>
      This section deals with errors specific to attribute handling
      within NFSv4.
    </t>
    <section title="NFS4ERR_ATTRNOTSUPP (Error Code 10032)" 
             anchor="err_ATTRNOTSUPP">
      <t>
        An attribute specified is not supported by the server.  This 
        error MUST NOT be returned by the GETATTR operation.
      </t>
    </section>
    <section title="NFS4ERR_BADOWNER (Error Code 10039)" 
             anchor="err_BADOWNER">
      <t>
        This error is returned when an owner or owner_group attribute value or the who 
        field of an ACE within an ACL attribute value cannot be
        translated to a local representation.
      </t>
    </section>
    <section title="NFS4ERR_NOT_SAME (Error Code 10027)" 
             anchor="err_NOT_SAME">
      <t>
        This error is returned by the VERIFY operation to signify
        that the attributes compared were not the same as those provided 
        in the client's request.
      </t>
    </section>
    <section title="NFS4ERR_SAME (Error Code 10009)" 
             anchor="err_SAME">
      <t>
        This error is returned by the NVERIFY operation to signify
        that the attributes compared were the same as those provided 
        in the client's request.
      </t>
    </section>
  </section>

  <section title="Obsoleted Errors" anchor="errors_obs">
    <t>
      These errors MUST NOT be generated by any NFSv4.1 operation.
      This can be for a number of reasons.
      <list style="symbols">
        <t>
          The function provided by the error has been superseded
          by one of the status bits returned by the SEQUENCE
          operation.
        </t>
        <t>
          The new session structure and associated change in
          locking have made the error unnecessary.
        </t>
        <t>
          There has been a restructuring of some errors for 
          NFSv4.1 that resulted in the elimination of certain errors.
        </t>
      </list>
    </t>
    <section title="NFS4ERR_BAD_SEQID (Error Code 10026)" 
             anchor="err_BAD_SEQID">
      <t>
        The sequence number (seqid) in a locking request is neither the 
        next expected number or the last number processed.  These
        seqids are ignored in NFSv4.1.
      </t>
    </section>
    <section title="NFS4ERR_LEASE_MOVED (Error Code 10031)" 
             anchor="err_LEASE_MOVED">
      <t>
        A lease being renewed is associated with a file system 
        that has been migrated to a new server. The error has
        been superseded by the SEQ4_STATUS_LEASE_MOVED status bit
        (see <xref target="OP_SEQUENCE" />).          
      </t>
    </section>
    <section title="NFS4ERR_NXIO (Error Code 5)" 
             anchor="err_NXIO">
      <t>
        I/O error. No such device or address. This error is
        for errors involving block and character device access,
        but because NFSv4.1 is not a device-access protocol, this
        error is not applicable.
      </t>
    </section>
    <section title="NFS4ERR_RESTOREFH (Error Code 10030)" 
             anchor="err_RESTOREFH">
      <t>
        The RESTOREFH operation does not have a saved filehandle
        (identified by SAVEFH) to operate upon. In NFSv4.1, this error has
        been superseded by NFS4ERR_NOFILEHANDLE.
      </t>
    </section>
    <section title="NFS4ERR_STALE_STATEID (Error Code 10023)" 
             anchor="err_STALE_STATEID">
      <t>
        A stateid generated by an earlier server instance was
        used. This error is moot in NFSv4.1 because all operations that
        take a stateid MUST be preceded by the SEQUENCE operation,
        and the earlier server instance is detected by the session
        infrastructure that supports SEQUENCE.
      </t>
    </section>
  </section>

  </section>

<!-- When adding new errors above, add them to the next section under -->
<!-- the appropriate operation; the next table for errors to -->
<!-- operations is automatically generated.  -->

<section title="Operations and Their Valid Errors">
  <t>
    This section contains a table that gives the valid error returns
    for each protocol operation.  The error code NFS4_OK (indicating 
    no error) is not listed but should be understood to be returnable
    by all operations with two important exceptions:
    <list style="symbols">
      <t>
        The operations that MUST NOT be implemented: 
        OPEN_CONFIRM, RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and
        SETCLIENTID_CONFIRM.
      </t>
      <t>
        The invalid operation: ILLEGAL.
      </t>
    </list>
  </t>
  <texttable anchor='op_error_returns'>
    <preamble> Valid Error Returns for Each Protocol
    Operation </preamble>

    <ttcol align='left'>Operation</ttcol>
    <ttcol align='left'>Errors</ttcol>
<!-- DO NOT MOVE THIS OR THE NEXT LINE - IT MUST BE AT THE START OF TABLE -->
<!-- STARTOFTHEERRORTABLE -->

    <c>ACCESS</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>BACKCHANNEL_CTL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>BIND_CONN_TO_SESSION</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_SESSION_DIGEST,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CLOSE</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_LOCKS_HELD,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>COMMIT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_ISDIR,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CREATE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADTYPE,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND
    </c>

    <c />
    <c />

    <c>CREATE_SESSION</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_CLID_INUSE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_NOSPC,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DELEGPURGE</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DELEGRETURN</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DESTROY_CLIENTID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_CLIENTID_BUSY,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DESTROY_SESSION</c>
    <c>
      NFS4ERR_BACK_CHAN_BUSY,
      NFS4ERR_BADSESSION,
      NFS4ERR_BADXDR,
      NFS4ERR_CB_PATH_DOWN,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>EXCHANGE_ID</c>
    <c>
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_CLID_INUSE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_ENCR_ALG_UNSUPP,
      NFS4ERR_HASH_ALG_UNSUPP,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_NOT_SAME,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>FREE_STATEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_LOCKS_HELD,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>GET_DIR_DELEGATION</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DIRDELEG_UNAVAIL,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>GETATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>GETDEVICEINFO</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE
    </c>

    <c />
    <c />

    <c>GETDEVICELIST</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_COOKIE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE
    </c>

    <c />
    <c />

    <c>GETFH</c>
    <c>
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_STALE
    </c>

    <c />
    <c />

    <c>ILLEGAL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_OP_ILLEGAL
    </c>

    <c />
    <c />

    <c>LAYOUTCOMMIT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADLAYOUT,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_ISDIR
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>LAYOUTGET</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADLAYOUT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_LAYOUTTRYLATER,
      NFS4ERR_LAYOUTUNAVAILABLE,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECALLCONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LAYOUTRETURN</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LINK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC,
      NFS4ERR_WRONG_TYPE,
      NFS4ERR_XDEV
    </c>

    <c />
    <c />

    <c>LOCK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADLOCK,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DENIED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCK_NOTSUPP,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LOCKT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DENIED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LOCKU</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>LOOKUP</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>LOOKUPP</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>NVERIFY</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SAME,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>OPEN</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_ALREADY_WANTED,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_SHARE_DENIED,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND,
      NFS4ERR_WRONGSEC,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>OPEN_CONFIRM</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>OPEN_DOWNGRADE</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>OPENATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>PUTFH</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_MOVED,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>PUTPUBFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>PUTROOTFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>READ</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PNFS_IO_HOLE,
      NFS4ERR_PNFS_NO_LAYOUT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
   </c>

    <c />
    <c />

    <c>READDIR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_COOKIE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>READLINK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>RECLAIM_COMPLETE</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_COMPLETE_ALREADY,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>RELEASE_LOCKOWNER</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>REMOVE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTEMPTY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>RENAME</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTEMPTY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC,
      NFS4ERR_XDEV
    </c>

    <c />
    <c />

    <c>RENEW</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>RESTOREFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>SAVEFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SECINFO</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SECINFO_NO_NAME</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SEQUENCE</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADSLOT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQUENCE_POS,
      NFS4ERR_SEQ_FALSE_RETRY,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SET_SSV</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_SESSION_DIGEST,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SETATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>SETCLIENTID</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>SETCLIENTID_CONFIRM</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>TEST_STATEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>VERIFY</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>WANT_DELEGATION</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_ALREADY_WANTED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECALLCONFLICT,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>WRITE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PNFS_IO_HOLE,
      NFS4ERR_PNFS_NO_LAYOUT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

<!-- ENDOFTHEERRORTABLE -->
<!-- DO NOT MOVE THIS OR THE ONE ABOVE LINE - IT MUST BE AT THE START OF TABLE -->
    
  </texttable>    
</section>

<!-- When adding new errors above, add them to the next section under -->
<!-- the appropriate operation; the next table for errors to -->
<!-- operations is automatically generated.  -->

<section title="Callback Operations and Their Valid Errors">
  <t>
    This section contains a table that gives the valid error returns
    for each callback operation.  The error code NFS4_OK (indicating 
    no error) is not listed but should be understood to be returnable
    by all callback operations with the exception of CB_ILLEGAL. 
  </t>
  <texttable anchor='cb_op_error_returns'>
    <preamble> Valid Error Returns for Each Protocol
    Callback Operation </preamble>

    <ttcol align='left'>Callback Operation</ttcol>
    <ttcol align='left'>Errors</ttcol>
<!-- DO NOT MOVE THIS OR THE NEXT LINE - IT MUST BE AT THE START OF TABLE -->
<!-- STARTOFTHEERRORTABLE -->

    <c>CB_GETATTR</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
    </c>

    <c />
    <c />

    <c>CB_ILLEGAL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_OP_ILLEGAL
    </c>

    <c />
    <c />

    <c>CB_LAYOUTRECALL</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOMATCHING_LAYOUT,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CB_NOTIFY</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_NOTIFY_DEVICEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />


    <c>CB_NOTIFY_LOCK</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_PUSH_DELEG</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REJECT_DELEG,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CB_RECALL</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALL_ANY</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALLABLE_OBJ_AVAIL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALL_SLOT</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_SEQUENCE</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADSLOT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DELAY,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQUENCE_POS,
      NFS4ERR_SEQ_FALSE_RETRY,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_WANTS_CANCELLED</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

<!-- ENDOFTHEERRORTABLE -->
<!-- DO NOT MOVE THIS OR THE ONE ABOVE LINE - IT MUST BE AT THE START OF TABLE -->
  </texttable>
</section>

<!-- INCLUDE THE AUTO GENERATED ERROR TO OP TABLE -->
<section title="Errors and the Operations That Use Them">
  <texttable anchor='error_op_returns'>
    <ttcol align='left'>Error</ttcol>
    <ttcol align='left'>Operations</ttcol>

    <c>NFS4ERR_ACCESS</c>
    <c>
	ACCESS,
	COMMIT,
	CREATE,
	GETATTR,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READDIR,
	READLINK,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ADMIN_REVOKED</c>
    <c>
	CLOSE,
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ATTRNOTSUPP</c>
    <c>
	CREATE,
	LAYOUTCOMMIT,
	NVERIFY,
	OPEN,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_BACK_CHAN_BUSY</c>
    <c>
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADCHAR</c>
    <c>
	CREATE,
	EXCHANGE_ID,
	LINK,
	LOOKUP,
	NVERIFY,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADHANDLE</c>
    <c>
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	PUTFH
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADIOMODE</c>
    <c>
	CB_LAYOUTRECALL,
	LAYOUTCOMMIT,
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADLAYOUT</c>
    <c>
	LAYOUTCOMMIT,
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADNAME</c>
    <c>
	CREATE,
	LINK,
	LOOKUP,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADOWNER</c>
    <c>
	CREATE,
	OPEN,
	SETATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADSESSION</c>
    <c>
	BIND_CONN_TO_SESSION,
	CB_SEQUENCE,
	DESTROY_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADSLOT</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADTYPE</c>
    <c>
	CREATE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADXDR</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_ILLEGAL,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	ILLEGAL,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_COOKIE</c>
    <c>
	GETDEVICELIST,
	READDIR
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_HIGH_SLOT</c>
    <c>
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_RANGE</c>
    <c>
	LOCK,
	LOCKT,
	LOCKU
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_SESSION_DIGEST</c>
    <c>
	BIND_CONN_TO_SESSION,
	SET_SSV
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_STATEID</c>
    <c>
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_LOCK,
	CB_RECALL,
	CLOSE,
	DELEGRETURN,
	FREE_STATEID,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_CB_PATH_DOWN</c>
    <c>
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_CLID_INUSE</c>
    <c>
	CREATE_SESSION,
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_CLIENTID_BUSY</c>
    <c>
	DESTROY_CLIENTID
    </c>
    <c />
    <c />

    <c>NFS4ERR_COMPLETE_ALREADY</c>
    <c>
	RECLAIM_COMPLETE
    </c>
    <c />
    <c />

    <c>NFS4ERR_CONN_NOT_BOUND_TO_SESSION</c>
    <c>
	CB_SEQUENCE,
	DESTROY_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DEADLOCK</c>
    <c>
	LOCK
    </c>
    <c />
    <c />

    <c>NFS4ERR_DEADSESSION</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELAY</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELEG_ALREADY_WANTED</c>
    <c>
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELEG_REVOKED</c>
    <c>
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	OPEN,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DENIED</c>
    <c>
	LOCK,
	LOCKT
    </c>
    <c />
    <c />

    <c>NFS4ERR_DIRDELEG_UNAVAIL</c>
    <c>
	GET_DIR_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_DQUOT</c>
    <c>
	CREATE,
	LAYOUTGET,
	LINK,
	OPEN,
	OPENATTR,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ENCR_ALG_UNSUPP</c>
    <c>
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_EXIST</c>
    <c>
	CREATE,
	LINK,
	OPEN,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_EXPIRED</c>
    <c>
	CLOSE,
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FBIG</c>
    <c>
	LAYOUTCOMMIT,
	OPEN,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FHEXPIRED</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FILE_OPEN</c>
    <c>
	LINK,
	REMOVE,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_GRACE</c>
    <c>
	GETATTR,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	NVERIFY,
	OPEN,
	READ,
	REMOVE,
	RENAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_HASH_ALG_UNSUPP</c>
    <c>
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_INVAL</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_PUSH_DELEG,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CREATE,
	CREATE_SESSION,
	DELEGRETURN,
	EXCHANGE_ID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	NVERIFY,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	SET_SSV,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_IO</c>
    <c>
	ACCESS,
	COMMIT,
	CREATE,
	GETATTR,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LINK,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READDIR,
	READLINK,
	REMOVE,
	RENAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ISDIR</c>
    <c>
	COMMIT,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	OPEN,
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_LAYOUTTRYLATER</c>
    <c>
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_LAYOUTUNAVAILABLE</c>
    <c>
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCKED</c>
    <c>
	LAYOUTGET,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCKS_HELD</c>
    <c>
	CLOSE,
	FREE_STATEID
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCK_NOTSUPP</c>
    <c>
	LOCK
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCK_RANGE</c>
    <c>
	LOCK,
	LOCKT,
	LOCKU
    </c>
    <c />
    <c />

    <c>NFS4ERR_MLINK</c>
    <c>
	CREATE,
	LINK,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_MOVED</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NAMETOOLONG</c>
    <c>
	CREATE,
	LINK,
	LOOKUP,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOENT</c>
    <c>
	BACKCHANNEL_CTL,
	CREATE_SESSION,
	EXCHANGE_ID,
	GETDEVICEINFO,
	LOOKUP,
	LOOKUPP,
	OPEN,
	OPENATTR,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOFILEHANDLE</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOMATCHING_LAYOUT</c>
    <c>
	CB_LAYOUTRECALL
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOSPC</c>
    <c>
	CREATE,
	CREATE_SESSION,
	LAYOUTGET,
	LINK,
	OPEN,
	OPENATTR,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTDIR</c>
    <c>
	CREATE,
	GET_DIR_DELEGATION,
	LINK,
	LOOKUP,
	LOOKUPP,
	OPEN,
	READDIR,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTEMPTY</c>
    <c>
	REMOVE,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTSUPP</c>
    <c>
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_WANTS_CANCELLED,
	DELEGPURGE,
	DELEGRETURN,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	OPENATTR,
	OPEN_CONFIRM,
	RELEASE_LOCKOWNER,
	RENEW,
	SECINFO_NO_NAME,
	SETCLIENTID,
	SETCLIENTID_CONFIRM,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOT_ONLY_OP</c>
    <c>
	BIND_CONN_TO_SESSION,
	CREATE_SESSION,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOT_SAME</c>
    <c>
	EXCHANGE_ID,
	GETDEVICELIST,
	READDIR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_NO_GRACE</c>
    <c>
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_OLD_STATEID</c>
    <c>
	CLOSE,
	DELEGRETURN,
	FREE_STATEID,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_OPENMODE</c>
    <c>
	LAYOUTGET,
	LOCK,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_OP_ILLEGAL</c>
    <c>
	CB_ILLEGAL,
	ILLEGAL
    </c>
    <c />
    <c />

    <c>NFS4ERR_OP_NOT_IN_SESSION</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGPURGE,
	DELEGRETURN,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_PERM</c>
    <c>
	CREATE,
	OPEN,
	SETATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_PNFS_IO_HOLE</c>
    <c>
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_PNFS_NO_LAYOUT</c>
    <c>
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECALLCONFLICT</c>
    <c>
	LAYOUTGET,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECLAIM_BAD</c>
    <c>
	LAYOUTCOMMIT,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECLAIM_CONFLICT</c>
    <c>
	LAYOUTCOMMIT,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_REJECT_DELEG</c>
    <c>
	CB_PUSH_DELEG
    </c>
    <c />
    <c />

    <c>NFS4ERR_REP_TOO_BIG</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_REQ_TOO_BIG</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_RETRY_UNCACHED_REP</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ROFS</c>
    <c>
	CREATE,
	LINK,
	LOCK,
	LOCKT,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	REMOVE,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SAME</c>
    <c>
	NVERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQUENCE_POS</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQ_FALSE_RETRY</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQ_MISORDERED</c>
    <c>
	CB_SEQUENCE,
	CREATE_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SERVERFAULT</c>
    <c>
	ACCESS,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SHARE_DENIED</c>
    <c>
	OPEN
    </c>
    <c />
    <c />

    <c>NFS4ERR_STALE</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_STALE_CLIENTID</c>
    <c>
	CREATE_SESSION,
	DESTROY_CLIENTID,
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_SYMLINK</c>
    <c>
	COMMIT,
	LAYOUTCOMMIT,
	LINK,
	LOCK,
	LOCKT,
	LOOKUP,
	LOOKUPP,
	OPEN,
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_TOOSMALL</c>
    <c>
	CREATE_SESSION,
	GETDEVICEINFO,
	LAYOUTGET,
	READDIR
    </c>
    <c />
    <c />

    <c>NFS4ERR_TOO_MANY_OPS</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_UNKNOWN_LAYOUTTYPE</c>
    <c>
	CB_LAYOUTRECALL,
	GETDEVICEINFO,
	GETDEVICELIST,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	NVERIFY,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_UNSAFE_COMPOUND</c>
    <c>
	CREATE,
	OPEN,
	OPENATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONGSEC</c>
    <c>
	LINK,
	LOOKUP,
	LOOKUPP,
	OPEN,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	RENAME,
	RESTOREFH
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONG_CRED</c>
    <c>
	CLOSE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	FREE_STATEID,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	LOCKT,
	LOCKU,
	OPEN_DOWNGRADE,
	RECLAIM_COMPLETE
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONG_TYPE</c>
    <c>
	CB_LAYOUTRECALL,
	CB_PUSH_DELEG,
	COMMIT,
	GETATTR,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READLINK,
	RECLAIM_COMPLETE,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_XDEV</c>
    <c>
	LINK,
	RENAME
    </c>
    <c />
    <c />

  </texttable>
</section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41procedures" title="NFSv4.1 Procedures">
<t>
 Both procedures, NULL and COMPOUND, MUST be implemented.
</t>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_NULL" title="Procedure 0: NULL - No Operation" >

  <section toc="exclude" anchor="PROC_NULL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_NULL_RESULTS" title="RESULTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="PROC_NULL_DESCRIPTION" title="DESCRIPTION">
    <t>
This is the standard NULL procedure with the standard void argument and
void response.
This procedure has no functionality associated with it.  Because of
this, it is sometimes used to measure the overhead of processing a
service request.  Therefore, the server SHOULD ensure that no
unnecessary work is done in servicing this procedure.
    </t>
  </section>
  <section toc="exclude" anchor="PROC_NULL_ERRORS" title="ERRORS">
    <t>
None.
	
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_COMPOUND" title="Procedure 1: COMPOUND - Compound Operations" >

  <section toc="exclude" anchor="OP_COMPOUND_ARGUMENTS" title="ARGUMENTS">

<figure>
 <artwork>
enum nfs_opnum4 {
 OP_ACCESS              = 3,
 OP_CLOSE               = 4,
 OP_COMMIT              = 5,
 OP_CREATE              = 6,
 OP_DELEGPURGE          = 7,
 OP_DELEGRETURN         = 8,
 OP_GETATTR             = 9,
 OP_GETFH               = 10,
 OP_LINK                = 11,
 OP_LOCK                = 12,
 OP_LOCKT               = 13,
 OP_LOCKU               = 14,
 OP_LOOKUP              = 15,
 OP_LOOKUPP             = 16,
 OP_NVERIFY             = 17,
 OP_OPEN                = 18,
 OP_OPENATTR            = 19,
 OP_OPEN_CONFIRM        = 20, /* Mandatory not-to-implement */
 OP_OPEN_DOWNGRADE      = 21,
 OP_PUTFH               = 22,
 OP_PUTPUBFH            = 23,
 OP_PUTROOTFH           = 24,
 OP_READ                = 25,
 OP_READDIR             = 26,
 OP_READLINK            = 27,
 OP_REMOVE              = 28,
 OP_RENAME              = 29,
 OP_RENEW               = 30, /* Mandatory not-to-implement */
 OP_RESTOREFH           = 31,
 OP_SAVEFH              = 32,
 OP_SECINFO             = 33,
 OP_SETATTR             = 34,
 OP_SETCLIENTID         = 35, /* Mandatory not-to-implement */
 OP_SETCLIENTID_CONFIRM = 36, /* Mandatory not-to-implement */
 OP_VERIFY              = 37,
 OP_WRITE               = 38,
 OP_RELEASE_LOCKOWNER   = 39, /* Mandatory not-to-implement */

/* new operations for NFSv4.1 */

 OP_BACKCHANNEL_CTL     = 40,
 OP_BIND_CONN_TO_SESSION = 41,
 OP_EXCHANGE_ID         = 42,
 OP_CREATE_SESSION      = 43,
 OP_DESTROY_SESSION     = 44,
 OP_FREE_STATEID        = 45,
 OP_GET_DIR_DELEGATION  = 46,
 OP_GETDEVICEINFO       = 47,
 OP_GETDEVICELIST       = 48,
 OP_LAYOUTCOMMIT        = 49,
 OP_LAYOUTGET           = 50,
 OP_LAYOUTRETURN        = 51,
 OP_SECINFO_NO_NAME     = 52,
 OP_SEQUENCE            = 53,
 OP_SET_SSV             = 54,
 OP_TEST_STATEID        = 55,
 OP_WANT_DELEGATION     = 56,
 OP_DESTROY_CLIENTID    = 57,
 OP_RECLAIM_COMPLETE    = 58,
 OP_ILLEGAL             = 10044
};
 </artwork>
</figure>
<figure>
 <artwork>
union nfs_argop4 switch (nfs_opnum4 argop) {
 case OP_ACCESS:        ACCESS4args opaccess;
 case OP_CLOSE:         CLOSE4args opclose;
 case OP_COMMIT:        COMMIT4args opcommit;
 case OP_CREATE:        CREATE4args opcreate;
 case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
 case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
 case OP_GETATTR:       GETATTR4args opgetattr;
 case OP_GETFH:         void;
 case OP_LINK:          LINK4args oplink;
 case OP_LOCK:          LOCK4args oplock;
 case OP_LOCKT:         LOCKT4args oplockt;
 case OP_LOCKU:         LOCKU4args oplocku;
 case OP_LOOKUP:        LOOKUP4args oplookup;
 case OP_LOOKUPP:       void;
 case OP_NVERIFY:       NVERIFY4args opnverify;
 case OP_OPEN:          OPEN4args opopen;
 case OP_OPENATTR:      OPENATTR4args opopenattr;

 /* Not for NFSv4.1 */
 case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;

 case OP_OPEN_DOWNGRADE:
                        OPEN_DOWNGRADE4args opopen_downgrade;

 case OP_PUTFH:         PUTFH4args opputfh;
 case OP_PUTPUBFH:      void;
 case OP_PUTROOTFH:     void;
 case OP_READ:          READ4args opread;
 case OP_READDIR:       READDIR4args opreaddir;
 case OP_READLINK:      void;
 case OP_REMOVE:        REMOVE4args opremove;
 case OP_RENAME:        RENAME4args oprename;

 /* Not for NFSv4.1 */
 case OP_RENEW:         RENEW4args oprenew;

 case OP_RESTOREFH:     void;
 case OP_SAVEFH:        void;
 case OP_SECINFO:       SECINFO4args opsecinfo;
 case OP_SETATTR:       SETATTR4args opsetattr;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
                                opsetclientid_confirm;
 case OP_VERIFY:        VERIFY4args opverify;
 case OP_WRITE:         WRITE4args opwrite;

 /* Not for NFSv4.1 */
 case OP_RELEASE_LOCKOWNER:
                        RELEASE_LOCKOWNER4args
                        oprelease_lockowner;

 /* Operations new to NFSv4.1 */
 case OP_BACKCHANNEL_CTL:
                        BACKCHANNEL_CTL4args opbackchannel_ctl;

 case OP_BIND_CONN_TO_SESSION:
                        BIND_CONN_TO_SESSION4args
                        opbind_conn_to_session;

 case OP_EXCHANGE_ID:   EXCHANGE_ID4args opexchange_id;

 case OP_CREATE_SESSION:
                        CREATE_SESSION4args opcreate_session;

 case OP_DESTROY_SESSION:
                        DESTROY_SESSION4args opdestroy_session;

 case OP_FREE_STATEID:  FREE_STATEID4args opfree_stateid;

 case OP_GET_DIR_DELEGATION:
                        GET_DIR_DELEGATION4args
                                opget_dir_delegation;

 case OP_GETDEVICEINFO: GETDEVICEINFO4args opgetdeviceinfo;
 case OP_GETDEVICELIST: GETDEVICELIST4args opgetdevicelist;
 case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4args oplayoutcommit;
 case OP_LAYOUTGET:     LAYOUTGET4args oplayoutget;
 case OP_LAYOUTRETURN:  LAYOUTRETURN4args oplayoutreturn;

 case OP_SECINFO_NO_NAME:
                        SECINFO_NO_NAME4args opsecinfo_no_name;

 case OP_SEQUENCE:      SEQUENCE4args opsequence;
 case OP_SET_SSV:       SET_SSV4args opset_ssv;
 case OP_TEST_STATEID:  TEST_STATEID4args optest_stateid;

 case OP_WANT_DELEGATION:
                        WANT_DELEGATION4args opwant_delegation;

 case OP_DESTROY_CLIENTID:
                        DESTROY_CLIENTID4args
                                opdestroy_clientid;

 case OP_RECLAIM_COMPLETE:
                        RECLAIM_COMPLETE4args
                                opreclaim_complete;

 /* Operations not new to NFSv4.1 */
 case OP_ILLEGAL:       void;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct COMPOUND4args {
        utf8str_cs      tag;
        uint32_t        minorversion;
        nfs_argop4      argarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="OP_COMPOUND_RESULTS" title="RESULTS">

<figure>
 <artwork>
union nfs_resop4 switch (nfs_opnum4 resop) {
 case OP_ACCESS:        ACCESS4res opaccess;
 case OP_CLOSE:         CLOSE4res opclose;
 case OP_COMMIT:        COMMIT4res opcommit;
 case OP_CREATE:        CREATE4res opcreate;
 case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
 case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;
 case OP_GETATTR:       GETATTR4res opgetattr;
 case OP_GETFH:         GETFH4res opgetfh;
 case OP_LINK:          LINK4res oplink;
 case OP_LOCK:          LOCK4res oplock;
 case OP_LOCKT:         LOCKT4res oplockt;
 case OP_LOCKU:         LOCKU4res oplocku;
 case OP_LOOKUP:        LOOKUP4res oplookup;
 case OP_LOOKUPP:       LOOKUPP4res oplookupp;
 case OP_NVERIFY:       NVERIFY4res opnverify;
 case OP_OPEN:          OPEN4res opopen;
 case OP_OPENATTR:      OPENATTR4res opopenattr;
 /* Not for NFSv4.1 */
 case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;

 case OP_OPEN_DOWNGRADE:
                        OPEN_DOWNGRADE4res
                                opopen_downgrade;

 case OP_PUTFH:         PUTFH4res opputfh;
 case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
 case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
 case OP_READ:          READ4res opread;
 case OP_READDIR:       READDIR4res opreaddir;
 case OP_READLINK:      READLINK4res opreadlink;
 case OP_REMOVE:        REMOVE4res opremove;
 case OP_RENAME:        RENAME4res oprename;
 /* Not for NFSv4.1 */
 case OP_RENEW:         RENEW4res oprenew;
 case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
 case OP_SAVEFH:        SAVEFH4res opsavefh;
 case OP_SECINFO:       SECINFO4res opsecinfo;
 case OP_SETATTR:       SETATTR4res opsetattr;
 /* Not for NFSv4.1 */
 case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID_CONFIRM:
                        SETCLIENTID_CONFIRM4res
                                opsetclientid_confirm;
 case OP_VERIFY:        VERIFY4res opverify;
 case OP_WRITE:         WRITE4res opwrite;

 /* Not for NFSv4.1 */
 case OP_RELEASE_LOCKOWNER:
                        RELEASE_LOCKOWNER4res
                                oprelease_lockowner;

 /* Operations new to NFSv4.1 */
 case OP_BACKCHANNEL_CTL:
                        BACKCHANNEL_CTL4res
                                opbackchannel_ctl;

 case OP_BIND_CONN_TO_SESSION:
                        BIND_CONN_TO_SESSION4res
                                 opbind_conn_to_session;

 case OP_EXCHANGE_ID:   EXCHANGE_ID4res opexchange_id;

 case OP_CREATE_SESSION:
                        CREATE_SESSION4res
                                opcreate_session;

 case OP_DESTROY_SESSION:
                        DESTROY_SESSION4res
                                opdestroy_session;

 case OP_FREE_STATEID:  FREE_STATEID4res
                                opfree_stateid;

 case OP_GET_DIR_DELEGATION:
                        GET_DIR_DELEGATION4res
                                opget_dir_delegation;

 case OP_GETDEVICEINFO: GETDEVICEINFO4res
                                opgetdeviceinfo;

 case OP_GETDEVICELIST: GETDEVICELIST4res
                                opgetdevicelist;

 case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4res oplayoutcommit;
 case OP_LAYOUTGET:     LAYOUTGET4res oplayoutget;
 case OP_LAYOUTRETURN:  LAYOUTRETURN4res oplayoutreturn;

 case OP_SECINFO_NO_NAME:
                        SECINFO_NO_NAME4res
                                opsecinfo_no_name;

 case OP_SEQUENCE:      SEQUENCE4res opsequence;
 case OP_SET_SSV:       SET_SSV4res opset_ssv;
 case OP_TEST_STATEID:  TEST_STATEID4res optest_stateid;

 case OP_WANT_DELEGATION:
                        WANT_DELEGATION4res
                                opwant_delegation;

 case OP_DESTROY_CLIENTID:
                        DESTROY_CLIENTID4res
                                opdestroy_clientid;

 case OP_RECLAIM_COMPLETE:
                        RECLAIM_COMPLETE4res
                                opreclaim_complete;

 /* Operations not new to NFSv4.1 */
 case OP_ILLEGAL:       ILLEGAL4res opillegal;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct COMPOUND4res {
        nfsstat4        status;
        utf8str_cs      tag;
        nfs_resop4      resarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="OP_COMPOUND_DESCRIPTION" title="DESCRIPTION">
    <t>
      The COMPOUND procedure is used to combine one or more NFSv4
      operations into a
      single RPC request.  The server interprets each of the operations in
      turn.  If an operation is executed by the server and the status of that
      operation is NFS4_OK, then the next operation in the COMPOUND
      procedure is executed.  The server continues this process until there
      are no more operations to be executed or until one of the operations has a
      status value other than NFS4_OK.
    </t>
    <t>
      In the processing of the COMPOUND procedure, the server may find that
      it does not have the available resources to execute any or all of the
      operations within the COMPOUND sequence. See
      <xref target="COMPOUND Sizing Issues" /> for a more detailed discussion.
    </t>
    <t>
      The server will generally choose between two methods of decoding the
      client's request.  The first would be the traditional one-pass XDR
      decode.  If there is an XDR decoding error in this case, the RPC XDR
      decode error would be returned.  The second method would be to make an
      initial pass to decode the basic COMPOUND request and then to XDR
      decode the individual operations; the most interesting is the decode
      of attributes.  In this case, the server may encounter an XDR decode
      error during the second pass.  If it does, the server would return
      the error NFS4ERR_BADXDR to signify the decode error.
    </t>
    <t>
      The COMPOUND arguments contain a "minorversion" field.  For NFSv4.1,
      the value for this field is 1.  If the server receives
      a COMPOUND procedure with a minorversion field value that it does not
      support, the server MUST return an error of
      NFS4ERR_MINOR_VERS_MISMATCH and a zero-length resultdata array.
    </t>
    <t>
      Contained within the COMPOUND results is a "status" field.  If the
      results array length is non-zero, this status must be equivalent to
      the status of the last operation that was executed within the COMPOUND
      procedure.  Therefore, if an operation incurred an error then the
      "status" value will be the same error value as is being returned for
      the operation that failed.
    </t>
    <t>
      Note that operations zero and one are not defined for the
      COMPOUND procedure.  Operation 2 is not defined and is reserved for
      future definition and use with minor versioning.  If the server
      receives an operation array that contains operation 2 and the
      minorversion field has a value of zero, an error of
      NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned to
      the client.  If an operation array contains an operation 2 and the
      minorversion field is non-zero and the server does not support the
      minor version, the server returns an error of
      NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
      NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
      errors.
    </t>
    <t>
      It is possible that the server receives a request that contains an
      operation that is less than the first legal operation (OP_ACCESS) or
      greater than the last legal operation (OP_RELEASE_LOCKOWNER).  In this
      case, the server's response will encode the opcode OP_ILLEGAL rather
      than the illegal opcode of the request. The status field in the
      ILLEGAL return results will be set to NFS4ERR_OP_ILLEGAL.  The COMPOUND
      procedure's return results will also be NFS4ERR_OP_ILLEGAL.
    </t>
    <t>
      The definition of the "tag" in the request is left to the implementor.
      It may be used to summarize the content of the Compound request for
      the benefit of packet-sniffers and engineers debugging
      implementations.  However, the value of "tag" in the response SHOULD
      be the same value as provided in the request.  This applies to the tag
      field of the CB_COMPOUND procedure as well.
    </t>
    <section toc="exclude" anchor="current_filehandle_stateid"
    title="Current Filehandle and Stateid">
    <t>
      The COMPOUND procedure offers a simple environment for the
      execution of the operations specified by the client.  The first
      two relate to the filehandle while the second two relate to the
      current stateid.
    </t>
    <section toc="exclude" anchor="current_filehandle" title="Current
    Filehandle">
    <t>
      The current and saved filehandles are used throughout
      the protocol.  Most operations implicitly use
      the current filehandle as an argument, and many set
      the current filehandle as part of the results.
      The combination of client-specified sequences
      of operations and current and saved filehandle
      arguments and results allows for greater protocol
      flexibility.  The best or easiest example of current
      filehandle usage is a sequence like the following:

    </t>
    <t>
      <figure anchor='curfh_example'>
      <artwork>
      PUTFH fh1              {fh1}
      LOOKUP "compA"         {fh2}
      GETATTR                {fh2}
      LOOKUP "compB"         {fh3}
      GETATTR                {fh3}
      LOOKUP "compC"         {fh4}
      GETATTR                {fh4}
      GETFH
      </artwork>
      </figure>
    </t>
    <t>
      In this example, the PUTFH (<xref target="OP_PUTFH"/>) operation explicitly sets the current
      filehandle value while the result of each LOOKUP operation sets
      the current filehandle value to the resultant file system
      object.  Also, the client is able to insert GETATTR operations
      using the current filehandle as an argument.
    </t>
    <t>
       The PUTROOTFH (<xref target="OP_PUTROOTFH"/>) and
       PUTPUBFH (<xref target="OP_PUTPUBFH"/>) operations also set the
       current filehandle. The above example would replace "PUTFH fh1" with
       PUTROOTFH or PUTPUBFH with no filehandle argument in order to 
       achieve the same effect (on the assumption that "compA" is directly
       below the root of the namespace).
    </t>
    <t>
      Along with the current filehandle, there is a saved filehandle.
      While the current filehandle is set as the result of
      operations like LOOKUP, the saved filehandle must be set
      directly with the use of the SAVEFH operation.  The SAVEFH
      operation copies the current filehandle value to the saved
      value.  The saved filehandle value is used in combination with
      the current filehandle value for the LINK and RENAME
      operations.  The RESTOREFH operation will copy the saved filehandle value to the current filehandle value; as a result, the
      saved filehandle value may be used a sort of "scratch" area for
      the client's series of operations.
    </t>
    </section>

    <section toc="exclude" anchor="current_stateid" title="Current Stateid">
    <t>
      With NFSv4.1, additions of a current stateid and a saved stateid
      have been made to the COMPOUND processing environment; this
      allows for the passing of stateids between operations.  There
      are no changes to the syntax of the protocol, only changes to
      the semantics of a few operations.
    </t>
    <t>
      A "current stateid" is the stateid that is associated
      with the current filehandle.  The current stateid
      may only be changed by an operation that modifies
      the current filehandle or returns a stateid.  If an
      operation returns a stateid, it MUST set the current
      stateid to the returned value. If an operation sets
      the current filehandle but does not return a stateid,
      the current stateid MUST be set to the all-zeros
      special stateid, i.e., (seqid, other) = (0, 0).
      If an operation uses a stateid as an argument but does
      not return a stateid, the current stateid MUST NOT be
      changed.
      For example, PUTFH, PUTROOTFH, and PUTPUBFH
      will change the current server state from {ocfh,
      (osid)} to {cfh, (0, 0)}, while LOCK will change the current
      state from {cfh, (osid} to {cfh, (nsid)}. Operations like
      LOOKUP that transform a current filehandle and
      component name into a new current filehandle will also
      change the current state to {0, 0}.  The SAVEFH
      and RESTOREFH operations will save and restore both
      the current filehandle and the current stateid as a set.

    </t>

    <t>
      The following example is the common case of a simple READ
      operation with a normal stateid showing that the PUTFH
      initializes the current stateid to (0, 0). The subsequent READ
      with stateid (sid1) leaves the current stateid unchanged.
    </t>
    <figure anchor='csid_example1'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    READ (sid1), 0, 1024      {fh1, (0, 0)} -> {fh1, (0, 0)}
    </artwork>
    </figure>

    <t>
      This next example performs an OPEN with the root
      filehandle and, as a result, generates stateid (sid1). The next
      operation specifies the READ with the argument stateid set such
      that (seqid, other) are equal to (1, 0),
      but the current stateid set by the previous operation is
      actually used when the operation is evaluated. This allows correct
      interaction with any existing, potentially conflicting,
      locks.
    </t>
    <figure anchor='csid_example2'>
    <artwork>
    PUTROOTFH                             - -> {fh1, (0, 0)}
    OPEN "compA"              {fh1, (0, 0)} -> {fh2, (sid1)}
    READ (1, 0), 0, 1024      {fh2, (sid1)} -> {fh2, (sid1)}
    CLOSE (1, 0)              {fh2, (sid1)} -> {fh2, (sid2)}
    </artwork>
    </figure>

    <t>
      This next example is similar to the second in how
      it passes the stateid sid2 generated by the LOCK
      operation to the next READ operation.  This allows
      the client to explicitly surround a single I/O
      operation with a lock and its appropriate stateid to
      guarantee correctness with other client locks. The
      example also shows how SAVEFH and RESTOREFH can
      save and later reuse a filehandle and stateid, passing them as the
      current filehandle and stateid to a READ operation.

    </t>
    <figure anchor='csid_example3'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    LOCK 0, 1024, (sid1)      {fh1, (sid1)} -> {fh1, (sid2)}
    READ (1, 0), 0, 1024      {fh1, (sid2)} -> {fh1, (sid2)}
    LOCKU 0, 1024, (1, 0)     {fh1, (sid2)} -> {fh1, (sid3)}
    SAVEFH                    {fh1, (sid3)} -> {fh1, (sid3)}

    PUTFH fh2                 {fh1, (sid3)} -> {fh2, (0, 0)}
    WRITE (1, 0), 0, 1024     {fh2, (0, 0)} -> {fh2, (0, 0)}

    RESTOREFH                 {fh2, (0, 0)} -> {fh1, (sid3)}
    READ (1, 0), 1024, 1024   {fh1, (sid3)} -> {fh1, (sid3)}
    </artwork>
    </figure>

    <t>
      The final example shows a disallowed use of
      the current stateid. The client is attempting
      to implicitly pass an anonymous special stateid, (0,0), to
      the READ operation. The server MUST return NFS4ERR_BAD_STATEID
      in the reply to the READ operation.

    </t>
    <figure anchor='csid_example4'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    READ (1, 0), 0, 1024      {fh1, (0, 0)} -> NFS4ERR_BAD_STATEID
    </artwork>
    </figure>

    </section>
    </section>
  </section>

  <section toc="exclude" anchor="OP_COMPOUND_ERRORS" title="ERRORS">
    <t>
     COMPOUND will of course return every error that each operation on
     the fore channel can return (see <xref target="op_error_returns"/>).
     However, if COMPOUND returns zero operations, obviously the error
     returned by COMPOUND has nothing to do with an error returned by
     an operation. The list of errors COMPOUND will return if it processes
     zero operations include:
    </t>
     <texttable anchor="compounderrs">
     <preamble>COMPOUND Error Returns</preamble>
     <ttcol align='left'>Error</ttcol>
     <ttcol align='left'>Notes</ttcol>

     <c>NFS4ERR_BADCHAR</c> <c>The tag argument has a character the replier
                               does not support. </c>

     <c>NFS4ERR_BADXDR</c> <c> </c>

     <c>NFS4ERR_DELAY</c> <c> </c>

     <c>NFS4ERR_INVAL</c> <c>The tag argument is not in UTF-8 encoding.</c>

     <c>NFS4ERR_MINOR_VERS_MISMATCH</c> <c> </c>

     <c>NFS4ERR_SERVERFAULT</c> <c> </c>

     <c>NFS4ERR_TOO_MANY_OPS</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c> <c> </c>

     <c>NFS4ERR_REQ_TOO_BIG</c> <c> </c>

     </texttable>
 
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<section anchor="operation_mandlist" 
	 title="Operations: REQUIRED, RECOMMENDED, or OPTIONAL">

  <t>
    The following tables summarize the operations of the NFSv4.1
    protocol and the corresponding designation of REQUIRED,
    RECOMMENDED, and OPTIONAL to implement or MUST NOT implement.  The
    designation of MUST NOT implement is reserved for those operations
    that were defined in NFSv4.0 and MUST NOT be implemented in NFSv4.1.
  </t>
  <t>
    For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation for
    operations sent by the client is for
    the server implementation.  The client is generally required to
    implement the operations needed for the operating environment for
    which it serves.  For example, a read-only NFSv4.1 client would
    have no need to implement the WRITE operation and is not required
    to do so.
  </t>
  <t>
    The REQUIRED or OPTIONAL designation for
    callback operations sent by the server is for both the client
    and server. Generally, the client has the option of
    creating the backchannel and sending the operations on the
    fore channel that will be a catalyst for the server sending
    callback operations. A partial
    exception is CB_RECALL_SLOT; the only way the client can
    avoid supporting this operation is by not creating a backchannel.
  </t>
  <t>
    Since this is a summary of the operations and their designation,
    there are subtleties that are not presented here.  Therefore, if
    there is a question of the requirements of implementation, the
    operation descriptions themselves must be consulted along with
    other relevant explanatory text within this specification.
  </t>
  <t>
    The abbreviations used in the second and third columns of the table
    are defined as follows.
    <list style="hanging">
      <t hangText="REQ">
	REQUIRED to implement
      </t>
      <t hangText="REC">
	RECOMMEND to implement
      </t>
      <t hangText="OPT">
	OPTIONAL to implement
      </t>
      <t hangText="MNI">
	MUST NOT implement
      </t>
    </list>
  </t>

  <t> For the NFSv4.1 features that are OPTIONAL, the operations that
    support those features are OPTIONAL, and the server would return
    NFS4ERR_NOTSUPP in response to the client's use of those
    operations.  If an OPTIONAL feature is supported, it is possible
    that a set of operations related to the feature become REQUIRED
    to implement.  The third column of the table designates the
    feature(s) and if the operation is REQUIRED or OPTIONAL in the
    presence of support for the feature.
  </t>
  <t>
    The OPTIONAL features identified and their abbreviations are as
    follows:
    <list style="hanging">
      <t hangText="pNFS">
	Parallel NFS
      </t>
      <t hangText="FDELG">
	File Delegations
      </t>
      <t hangText="DDELG">
	Directory Delegations
      </t>
    </list>
  </t>
    <texttable>

      <preamble> Operations </preamble>

      <ttcol align='left' >Operation</ttcol>
      <ttcol align='left' >REQ, REC, OPT, or MNI</ttcol>
      <ttcol align='left' >Feature (REQ, REC, or OPT)</ttcol>
      <ttcol align='left' >Definition</ttcol>

      <c> ACCESS </c> 
      <c>REQ</c> 
      <c></c> 
      <c> <xref target="OP_ACCESS" /> </c>

      <c> BACKCHANNEL_CTL </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_BACKCHANNEL_CTL" /> </c>

      <c> BIND_CONN_TO_SESSION</c> 
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_BIND_CONN_TO_SESSION" /> </c>

      <c> CLOSE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CLOSE" /> </c>

      <c> COMMIT </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_COMMIT" /> </c>

      <c> CREATE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CREATE" /> </c>

      <c> CREATE_SESSION </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CREATE_SESSION" /> </c>

      <c> DELEGPURGE </c>
      <c>OPT</c>
      <c>FDELG (REQ)</c>
      <c> <xref target="OP_DELEGPURGE" /> </c>

      <c> DELEGRETURN </c>
      <c>OPT</c>
      <c>FDELG, DDELG, pNFS (REQ)</c>
      <c> <xref target="OP_DELEGRETURN" /> </c>

      <c> DESTROY_CLIENTID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_DESTROY_CLIENTID" /> </c>

      <c> DESTROY_SESSION </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_DESTROY_SESSION" /> </c>

      <c> EXCHANGE_ID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_EXCHANGE_ID" /> </c>

      <c> FREE_STATEID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_FREE_STATEID" /> </c>

      <c> GETATTR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_GETATTR" /> </c>

      <c> GETDEVICEINFO </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_GETDEVICEINFO" /> </c>

      <c> GETDEVICELIST</c>
      <c>OPT</c>
      <c>pNFS (OPT)</c>
      <c> <xref target="OP_GETDEVICELIST" /> </c>

      <c> GETFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_GETFH" /> </c>

      <c> GET_DIR_DELEGATION </c>
      <c>OPT</c>
      <c>DDELG (REQ)</c>
      <c> <xref target="OP_GET_DIR_DELEGATION" /> </c>

      <c> LAYOUTCOMMIT </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTCOMMIT" /> </c>

      <c> LAYOUTGET </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTGET" /> </c>

      <c> LAYOUTRETURN </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTRETURN" /> </c>

      <c> LINK </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_LINK" /> </c>

      <c> LOCK </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCK" /> </c>

      <c> LOCKT </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCKT" /> </c>

      <c> LOCKU </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCKU" /> </c>

      <c> LOOKUP </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOOKUP" /> </c>

      <c> LOOKUPP </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOOKUPP" /> </c>

      <c> NVERIFY </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_NVERIFY" /> </c>

      <c> OPEN </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_OPEN" /> </c>

      <c> OPENATTR </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_OPENATTR" /> </c>

      <c> OPEN_CONFIRM </c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> OPEN_DOWNGRADE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_OPEN_DOWNGRADE" /> </c>

      <c> PUTFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTFH" /> </c>

      <c> PUTPUBFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTPUBFH" /> </c>

      <c> PUTROOTFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTROOTFH" /> </c>

      <c> READ </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_READ" /> </c>

      <c> READDIR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_READDIR" /> </c>

      <c> READLINK </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_READLINK" /> </c>

      <c> RECLAIM_COMPLETE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RECLAIM_COMPLETE" /> </c>

      <c> RELEASE_LOCKOWNER</c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> REMOVE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_REMOVE" /> </c>

      <c> RENAME </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RENAME" /> </c>

      <c> RENEW </c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> RESTOREFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RESTOREFH" /> </c>

      <c> SAVEFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SAVEFH" /> </c>

      <c> SECINFO </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SECINFO" /> </c>

      <c> SECINFO_NO_NAME </c>
      <c>REC</c>
      <c>pNFS file layout (REQ)</c>
      <c> <xref target="OP_SECINFO_NO_NAME" />,
          <xref target="file_security_considerations"/>
      </c>

      <c> SEQUENCE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SEQUENCE" /> </c>

      <c> SETATTR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SETATTR" /> </c>

      <c> SETCLIENTID</c> 
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> SETCLIENTID_CONFIRM</c> 
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> SET_SSV</c> 
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SET_SSV" /> </c>

      <c> TEST_STATEID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_TEST_STATEID" /> </c>

      <c> VERIFY </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_VERIFY" /> </c>

      <c> WANT_DELEGATION</c>
      <c>OPT</c>
      <c>FDELG (OPT)</c> 
      <c> <xref target="OP_WANT_DELEGATION" /> </c>

      <c> WRITE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_WRITE" /> </c>

    </texttable>




  <texttable>

      <preamble> Callback Operations </preamble>
      <ttcol align='left' >Operation</ttcol>
      <ttcol align='left' >REQ, REC, OPT, or MNI</ttcol>
      <ttcol align='left' >Feature (REQ, REC, or OPT)</ttcol>
      <ttcol align='left' >Definition</ttcol>

      <c> CB_GETATTR </c> 
      <c>OPT</c> 
      <c>FDELG (REQ)</c> 
      <c> <xref target="OP_CB_GETATTR" /> </c>

      <c> CB_LAYOUTRECALL </c> 
      <c>OPT</c> 
      <c>pNFS (REQ)</c> 
      <c> <xref target="OP_CB_LAYOUTRECALL" /> </c>

      <c> CB_NOTIFY </c> 
      <c>OPT</c> 
      <c>DDELG (REQ)</c> 
      <c> <xref target="OP_CB_NOTIFY" /> </c>

      <c> CB_NOTIFY_DEVICEID </c> 
      <c>OPT</c> 
      <c>pNFS (OPT)</c> 
      <c> <xref target="OP_CB_NOTIFY_DEVICEID" /> </c>

      <c> CB_NOTIFY_LOCK </c> 
      <c>OPT</c> 
      <c></c> 
      <c> <xref target="OP_CB_NOTIFY_LOCK" /> </c>

      <c> CB_PUSH_DELEG </c> 
      <c>OPT</c> 
      <c>FDELG (OPT)</c> 
      <c> <xref target="OP_CB_PUSH_DELEG" /> </c>

      <c> CB_RECALL </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALL" /> </c>

      <c> CB_RECALL_ANY </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALL_ANY" /> </c>

      <c> CB_RECALL_SLOT </c> 
      <c>REQ</c> 
      <c></c> 
      <c> <xref target="OP_CB_RECALL_SLOT" /> </c>

      <c> CB_RECALLABLE_OBJ_AVAIL </c> 
      <c>OPT</c> 
      <c>DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALLABLE_OBJ_AVAIL" /> </c>

      <c> CB_SEQUENCE </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_SEQUENCE" /> </c>

      <c> CB_WANTS_CANCELLED </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_WANTS_CANCELLED" /> </c>

    </texttable>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41operations" title="NFSv4.1 Operations">
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_ACCESS" title="Operation 3: ACCESS - Check Access Rights" >

  <section toc="exclude" anchor="OP_ACCESS_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>

const ACCESS4_READ      = 0x00000001;
const ACCESS4_LOOKUP    = 0x00000002;
const ACCESS4_MODIFY    = 0x00000004;
const ACCESS4_EXTEND    = 0x00000008;
const ACCESS4_DELETE    = 0x00000010;
const ACCESS4_EXECUTE   = 0x00000020;

struct ACCESS4args {
        /* CURRENT_FH: object */
        uint32_t        access;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_ACCESS_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct ACCESS4resok {
        uint32_t        supported;
        uint32_t        access;
};

union ACCESS4res switch (nfsstat4 status) {
 case NFS4_OK:
         ACCESS4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_ACCESS_DESCRIPTION" title="DESCRIPTION">
    <t>
ACCESS determines the access rights that a user, as identified by the
credentials in the RPC request, has with respect to the file system
object specified by the current filehandle.  The client encodes the
set of access rights that are to be checked in the bit mask "access".
The server checks the permissions encoded in the bit mask.  If a
status of NFS4_OK is returned, two bit masks are included in the
response.  The first, "supported", represents the access rights for
which the server can verify reliably.  The second, "access",
represents the access rights available to the user for the filehandle
provided.  On success, the current filehandle retains its value.
    </t>
    <t>
Note that the reply's supported and access fields MUST NOT
contain more values than originally set in the request's
access field.  For example, if the client sends an ACCESS
operation with just the ACCESS4_READ value set and the
server supports this value, the server MUST NOT set more
than ACCESS4_READ in the supported field even if it could
have reliably checked other values.

    </t>
    <t>
     The reply's access field MUST NOT contain more values than the
     supported field.
    </t>
    <t>
The results of this operation are necessarily advisory in nature.  A
return status of NFS4_OK and the appropriate bit set in the bit mask
do not imply that such access will be allowed to the file system
object in the future. This is because access rights can be revoked by
the server at any time.
    </t>
    <t>
The following access permissions may be requested:
<list style="hanging">
<t hangText="ACCESS4_READ">
Read data from file or read a directory.
</t>
<t hangText="ACCESS4_LOOKUP">
Look up a name in a directory (no meaning for non-directory objects).
</t>
<t hangText="ACCESS4_MODIFY">
Rewrite existing file data or modify existing directory entries.
</t>
<t hangText="ACCESS4_EXTEND">
Write new data or add directory entries.
</t>
<t hangText="ACCESS4_DELETE">
Delete an existing directory entry.
</t>
<t hangText="ACCESS4_EXECUTE">
Execute a regular file (no meaning for a directory).
</t>
</list>
On success, the current filehandle retains its value.
    </t>
   <t>
    ACCESS4_EXECUTE is a challenging semantic to implement because
    NFS provides remote file access, not remote
    execution. This leads to the following:
    <list style="symbols">
    <t>
     Whether or not a regular file is executable ought to be
     the responsibility of the NFS client and not the server. And yet
     the ACCESS operation is specified to seemingly require a server to
     own that responsibility.
    </t>
    <t>
     When a client executes a regular file, it has to
     read the file from the server. Strictly speaking,
     the server should not allow the client to read a file
     being executed unless the user has read permissions
     on the file. Requiring
     explicit read permissions on executable files in order to
     access them over NFS is not going to be acceptable to
     some users and storage administrators. Historically, NFS servers have allowed
     a user to READ a file if the user has execute access
     to the file.

    </t>
   </list>
  </t>
  <t>
   As a practical example, the UNIX specification <xref
   target="access_api"/> states that an implementation
   claiming conformance to UNIX may indicate in the
   access() programming interface's result that a
   privileged user has execute rights, even if no
   execute permission bits are set on the regular file's
   attributes. It is possible to claim conformance
   to the UNIX specification and instead not indicate
   execute rights in that situation, which is true for
   some operating environments. Suppose the operating
   environments of the client and server are implementing
   the access() semantics for privileged users differently,
   and the ACCESS operation implementations of the client
   and server follow their respective access() semantics.
   This can cause undesired behavior:

   <list style='symbols'>
   <t>
    Suppose the client's access() interface returns X_OK
    if the user is privileged and no execute permission
    bits are set on the regular file's attribute, and the
    server's access() interface does not return X_OK in
    that situation.  Then the client will be unable to
    execute files stored on the NFS server that could be
    executed if stored on a non-NFS file system.

   </t>
   <t>
    Suppose the client's access() interface does
    not return X_OK if the user is privileged, and no
    execute permission bits are set on the regular file's
    attribute, and the server's access() interface does
    return X_OK in that situation. Then:

    <list style='symbols'>
    <t>
     The client will be able to execute files stored on
     the NFS server that could be executed if stored on
     a non-NFS file system, unless the client's execution
     subsystem also checks for execute permission bits.

    </t>
    <t>
     Even if the execution subsystem is checking for
     execute permission bits, there are more potential
     issues.  For example, suppose the client is invoking access()
     to build a "path search table" of all executable
     files in the user's "search path", where the path
     is a list of directories each containing executable
     files. Suppose there are two files each in separate
     directories of the search path, such that files have
     the same component name.  In the first directory
     the file has no execute permission bits set,
     and in the second directory the file has execute
     bits set. The path search table will indicate that
     the first directory has the executable file, but
     the execute subsystem will fail to execute it. The
     command shell might fail to try the second file in
     the second directory. And even if it did, this is
     a potential performance issue. Clearly, the desired
     outcome for the client is for the path search table
     to not contain the first file.

    </t>
    </list>
   </t>
   </list>
  </t>
  <t>
   To deal with the problems described above, the "smart client,
   stupid server" principle is used. The client owns overall
   responsibility for determining execute access and
   relies on the server to parse the execution permissions
   within the file's mode, acl, and dacl attributes. The
   rules for the client and server follow:

   <list style='symbols'>
   <t>
    If the client is sending ACCESS in order to determine
    if the user can read the file, the client SHOULD
    set ACCESS4_READ in the request's access field.

   </t>
   <t>
    If the client's operating environment only grants
    execution to the user if the user has execute access
    according to the execute permissions in the mode,
    acl, and dacl attributes, then if the client wants
    to determine execute access, the client SHOULD send
    an ACCESS request with ACCESS4_EXECUTE bit set in the
    request's access field.

   </t>
   <t>
    If the client's operating environment grants execution
    to the user even if the user does not have execute
    access according to the execute permissions in the
    mode, acl, and dacl attributes, then if the client
    wants to determine execute access, it SHOULD send
    an ACCESS request with both the ACCESS4_EXECUTE and
    ACCESS4_READ bits set in the request's access field. This
    way, if any read or execute permission grants the user
    read or execute access (or if the server interprets
    the user as privileged), as indicated by the presence
    of ACCESS4_EXECUTE and/or ACCESS4_READ in the reply's
    access field, the client will be able to grant the
    user execute access to the file.

   </t>

   <t>
    If the server supports execute permission bits, or some other
    method for denoting executability (e.g., the suffix of the name
    of the file might indicate execute), it MUST check
    only execute permissions, not read permissions, when determining
    whether or not the reply will have ACCESS4_EXECUTE set in the access
    field.
    The server MUST NOT also examine read permission bits when
    determining whether or not the reply will have ACCESS4_EXECUTE
    set in the access field.  Even if the server's
    operating environment would grant execute access to the
    user (e.g., the user is privileged), the server MUST
    NOT reply with ACCESS4_EXECUTE set in reply's access
    field unless there is at least one execute permission
    bit set in the mode, acl, or dacl attributes. In the
    case of acl and dacl, the "one execute permission bit"
    MUST be an ACE4_EXECUTE bit set in an ALLOW ACE.

   </t>
   <t>
    If the server does not support execute permission
    bits or some other method for denoting executability, it MUST NOT set ACCESS4_EXECUTE in the
    reply's supported and access fields. If the client
    set ACCESS4_EXECUTE in the ACCESS request's access
    field, and ACCESS4_EXECUTE is not set in the reply's
    supported field, then the client will have to send
    an ACCESS request with the ACCESS4_READ bit set in
    the request's access field.

   </t>

   <t>
    If the server supports read permission bits, it MUST
    only check for read permissions in the mode, acl,
    and dacl attributes when it receives an ACCESS request
    with ACCESS4_READ set in the access field.  The server
    MUST NOT also examine execute permission bits when
    determining whether the reply will have ACCESS4_READ
    set in the access field or not.

   </t>

   </list>
   Note that if the ACCESS reply has ACCESS4_READ
   or ACCESS_EXECUTE set, then the user also has
   permissions to OPEN (<xref target="OP_OPEN"/>) or
   READ (<xref target="OP_READ"/>) the file. In other words, if
   the client sends an ACCESS request with the ACCESS4_READ
   and ACCESS_EXECUTE set in the access field (or two
   separate requests, one with ACCESS4_READ set and the
   other with ACCESS4_EXECUTE set), and the reply has
   just ACCESS4_EXECUTE set in the access field (or just
   one reply has ACCESS4_EXECUTE set), then the user has
   authorization to OPEN or READ the file.


  </t>
  </section>
  <section toc="exclude" anchor="OP_ACCESS_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
In general, it is not sufficient for the client to attempt to deduce
access permissions by inspecting the uid, gid, and mode fields in the
file attributes or by attempting to interpret the contents of the ACL
attribute.  This is because the server may perform uid or gid mapping
or enforce additional access-control restrictions.  It is also
possible that the server may not be in the same ID space as the
client.  In these cases (and perhaps others), the client cannot
reliably perform an access check with only current file attributes.
    </t>
    <t>
In the NFSv2 protocol, the only reliable way to determine
whether an operation was allowed was to try it and see if it succeeded
or failed.  Using the ACCESS operation in the NFSv4.1 protocol,
the client can ask the server to indicate whether or not one or more
classes of operations are permitted.  The ACCESS operation is provided
to allow clients to check before doing a series of operations that
will result in an access failure.  The OPEN operation provides a point
where the server can verify access to the file object and a method to
return that information to the client.  The ACCESS operation is still
useful for directory operations or for use in the case that the UNIX interface
access() is used on the client.
    </t>
    <t>
The information returned by the server in response to an ACCESS call
is not permanent.  It was correct at the exact time that the server
performed the checks, but not necessarily afterwards.  The server can
revoke access permission at any time.
    </t>
    <t>
The client should use the effective credentials of the user to build
the authentication information in the ACCESS request used to determine
access rights.  It is the effective user and group credentials that
are used in subsequent READ and WRITE operations.
    </t>
    <t>
Many implementations do not directly support the ACCESS4_DELETE
permission.  Operating systems like UNIX will ignore the ACCESS4_DELETE
bit if set on an access request on a non-directory object.  In these
systems, delete permission on a file is determined by the access
permissions on the directory in which the file resides, instead of
being determined by the permissions of the file itself.  Therefore,
the mask returned enumerating which access rights can be determined
will have the ACCESS4_DELETE value set to 0.  This indicates to the
client that the server was unable to check that particular access
right.  The ACCESS4_DELETE bit in the access mask returned will then be
ignored by the client.
    </t>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CLOSE" title="Operation 4: CLOSE - Close File" >

  <section toc="exclude" anchor="OP_CLOSE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct CLOSE4args {
        /* CURRENT_FH: object */
        seqid4          seqid;
        stateid4        open_stateid;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_CLOSE_RESULTS" title="RESULTS">
<figure>
 <artwork>
union CLOSE4res switch (nfsstat4 status) {
 case NFS4_OK:
         stateid4       open_stateid;
 default:
         void;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_CLOSE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CLOSE operation releases share reservations for the regular or
      named attribute file as specified by the current filehandle.  The
      share reservations and other state information released at the server
      as a result of this CLOSE are only those associated with the supplied
      stateid.  State associated with other OPENs is not affected.
    </t>
    <t>
      If byte-range locks are held, the client SHOULD release all locks before
      sending a CLOSE.  The server MAY free all outstanding locks on CLOSE,
      but some servers may not support the CLOSE of a file that still has
      byte-range locks held.  The server MUST return failure if any locks would
      exist after the CLOSE.
    </t>
    <t>
      The argument seqid MAY have any value, and the server MUST ignore seqid.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     The server MAY require that the combination of principal, security
     flavor, and, if applicable, GSS mechanism
     that sent the OPEN request also be the one to CLOSE
     the file. This might not be possible if credentials
     for the principal are no longer available. The server
     MAY allow the machine credential or SSV credential
     (see <xref target="OP_EXCHANGE_ID" />) to send CLOSE.

    </t>

  </section>
  <section toc="exclude" anchor="OP_CLOSE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Even though CLOSE returns a stateid, this stateid is not useful to the
      client and should be treated as deprecated.  CLOSE "shuts down" the
      state associated with all OPENs for the file by a single open-owner.
      As noted above, CLOSE will either release all file-locking state or
      return an error.  Therefore, the stateid returned by CLOSE is not
      useful for operations that follow.  To help find any uses of
      this stateid by clients, the server SHOULD return the invalid
      special stateid (the "other" value is zero and the "seqid" field
      is NFS4_UINT32_MAX, see <xref target="special_stateid"/>).
    </t>
    <t>
      A CLOSE operation may make delegations grantable
      where they were not previously.  Servers may choose to respond
      immediately if there are pending delegation want requests or may
      respond to the situation at a later time.
    </t>
  </section>
</section>

<section anchor="OP_COMMIT" title="Operation 5: COMMIT - Commit Cached Data" >

  <section toc="exclude" anchor="OP_COMMIT_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct COMMIT4args {
        /* CURRENT_FH: file */
        offset4         offset;
        count4          count;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_COMMIT_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct COMMIT4resok {
        verifier4       writeverf;
};

union COMMIT4res switch (nfsstat4 status) {
 case NFS4_OK:
         COMMIT4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_COMMIT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The COMMIT operation forces or flushes uncommitted, modified data to stable storage for the
      file specified by the current filehandle.  The flushed data is that
      which was previously written with one or more WRITE operations that had the
      "committed" field of their results field set to UNSTABLE4.

    </t>
    <t>
      The offset specifies the position within the file where the flush is
      to begin.  An offset value of zero means to flush data starting at
      the beginning of the file.  The count specifies the number of bytes of
      data to flush.  If the count is zero, a flush from the offset to the end
      of the file is done.
    </t>
    <t>
      The server returns a write verifier upon successful completion of the
      COMMIT.  The write verifier is used by the client to determine if the
      server has restarted between the initial WRITE operations and the
      COMMIT.  The client does this by comparing the write verifier returned
      from the initial WRITE operations and the verifier returned by the COMMIT
      operation.  The server must vary the value of the write verifier at
      each server event or instantiation that may lead to a loss of
      uncommitted data.  Most commonly this occurs when the server is
      restarted; however, other events at the server may result in
      uncommitted data loss as well.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_COMMIT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The COMMIT operation is similar in operation and semantics to the
      <xref target="fsync">POSIX fsync()</xref> system interface that synchronizes a file's state with the
      disk (file data and metadata is flushed to disk or stable
      storage). COMMIT performs the same operation for a client, flushing
      any unsynchronized data and metadata on the server to the server's
      disk or stable storage for the specified file.  Like fsync(), it may
      be that there is some modified data or no modified data to
      synchronize.  The data may have been synchronized by the server's
      normal periodic buffer synchronization activity.  COMMIT should return
      NFS4_OK, unless there has been an unexpected error.
    </t>
    <t>
      COMMIT differs from fsync() in that it is possible for the client to
      flush a range of the file (most likely triggered by a
      buffer-reclamation scheme on the client before the file has been
      completely written).
    </t>
    <t>
      The server implementation of COMMIT is reasonably simple.  If the
      server receives a full file COMMIT request, that is, starting at offset
      zero and count zero, it should do the equivalent of applying fsync() to
      the entire file.
      Otherwise, it should arrange to have the modified data in the range
      specified by offset and count to be flushed to stable storage.  In
      both cases, any metadata associated with the file must be flushed to
      stable storage before returning.  It is not an error for there to be
      nothing to flush on the server.  This means that the data and metadata
      that needed to be flushed have already been flushed or lost during the
      last server failure.
    </t>
    <t>
      The client implementation of COMMIT is a little more complex.  There
      are two reasons for wanting to commit a client buffer to stable
      storage.  The first is that the client wants to reuse a buffer.  In
      this case, the offset and count of the buffer are sent to the server
      in the COMMIT request.  The server then flushes any modified data based
      on the offset and count, and flushes any modified metadata associated with the
      file.  It then returns the status of the flush and the write verifier.
      The second reason for the client to generate a COMMIT is for a full
      file flush, such as may be done at close.  In this case, the client
      would gather all of the buffers for this file that contain uncommitted
      data, do the COMMIT operation with an offset of zero and count of zero, and
      then free all of those buffers.  Any other dirty buffers would be sent
      to the server in the normal fashion.
    </t>
    <t>
      After a buffer is written (via the WRITE operation)
      by the client with the "committed" field in the result of WRITE
      set to UNSTABLE4, the buffer must be considered as modified by
      the client
      until the buffer has either been flushed via a COMMIT operation or
      written via a WRITE operation with the "committed" field in the
      result set to FILE_SYNC4
      or DATA_SYNC4. This is done to prevent the buffer from being freed and
      reused before the data can be flushed to stable storage on the server.
    </t>
    <t>
      When a response is returned from either a WRITE or a COMMIT operation
      and it contains a write verifier that differs from that previously
      returned by the server, the client will need to retransmit all of the
      buffers containing uncommitted data to the server.  How this is
      to be done is up to the implementor.  If there is only one buffer of
      interest, then it should be sent in a WRITE request
      with the FILE_SYNC4 stable parameter.  If there is more than one
      buffer, it might be worthwhile retransmitting all of the buffers in
      WRITE operations with the stable parameter set to UNSTABLE4 and then
      retransmitting the COMMIT operation to flush all of the data on the
      server to stable storage. However, if the server repeatably
      returns from COMMIT a verifier that differs from that returned
      by WRITE, the only way to ensure progress is to retransmit all
      of the buffers with WRITE requests with the FILE_SYNC4 stable parameter.
    </t>
    <t>
      The above description applies to page-cache-based systems as well as
      buffer-cache-based systems.  In the former systems, the virtual memory
      system will need to be modified instead of the buffer cache.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CREATE" title="Operation 6: CREATE - Create a Non-Regular File Object" >

  <section toc="exclude" anchor="OP_CREATE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
union createtype4 switch (nfs_ftype4 type) {
 case NF4LNK:
         linktext4 linkdata;
 case NF4BLK:
 case NF4CHR:
         specdata4 devdata;
 case NF4SOCK:
 case NF4FIFO:
 case NF4DIR:
         void;
 default:
         void;  /* server should return NFS4ERR_BADTYPE */
};

struct CREATE4args {
        /* CURRENT_FH: directory for creation */
        createtype4     objtype;
        component4      objname;
        fattr4          createattrs;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CREATE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct CREATE4resok {
        change_info4    cinfo;
        bitmap4         attrset;        /* attributes set */
};

union CREATE4res switch (nfsstat4 status) {
 case NFS4_OK:
         /* new CURRENTFH: created object */
         CREATE4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CREATE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CREATE operation creates a file object other than an 
      ordinary file in a directory with a given name.
      The OPEN operation MUST be used to create a
      regular file or a named attribute.
    </t>
    <t>
      The current filehandle must be a directory: an object of type NF4DIR.  If the current
      filehandle is an attribute directory (type NF4ATTRDIR), the 
      error NFS4ERR_WRONG_TYPE is returned.  If the current file handle
      designates any other type of object, the error NFS4ERR_NOTDIR
      results.
    </t>
    <t>
      The objname specifies the name for the new object. 
      The objtype determines the type of object to be 
      created: directory, symlink, etc. If the object 
      type specified is that of an ordinary file, a 
      named attribute, or a named attribute directory, 
      the error NFS4ERR_BADTYPE results. 
    </t>
    <t>
      If an object of the same name already exists in the directory, the
      server will return the error NFS4ERR_EXIST.
    </t>
    <t>
      For the directory where the new file object was created, the server
      returns change_info4 information in cinfo.  With the atomic field of
      the change_info4 data type, the server will indicate if the before and
      after change attributes were obtained atomically with respect to the
      file object creation.
    </t>
    <t>
      If the objname has a length of zero, or if objname does not obey
      the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
    <t>
      The current filehandle is replaced by that of the new object.
    </t>
    <t>
      The createattrs specifies the initial set of attributes for the
      object.  The set of attributes may include any writable attribute
      valid for the object type. When the operation is successful, the
      server will return to the client an attribute mask signifying which
      attributes were successfully set for the object.
    </t>
    <t>
      If createattrs includes neither the owner attribute nor an ACL with an
      ACE for the owner, and if the server's file system both supports and
      requires an owner attribute (or an owner ACE), then the server MUST
      derive the owner (or the owner ACE). This would typically be from the
      principal indicated in the RPC credentials of the call, but the
      server's operating environment or file system semantics may dictate
      other methods of derivation. Similarly, if createattrs includes
      neither the group attribute nor a group ACE, and if the server's
      file system both supports and requires the notion of a group attribute
      (or group ACE), the server MUST derive the group attribute (or the
      corresponding owner ACE) for the file. This could be from the RPC
      call's credentials, such as the group principal if the credentials
      include it (such as with AUTH_SYS), from the group identifier
      associated with the principal in the credentials (e.g., POSIX
      systems have a <xref target="passwd">user database</xref> that has a group identifier for every
      user identifier), inherited from the directory in which the object is created,
      or whatever else the server's operating environment or file system
      semantics dictate. This applies to the OPEN operation too.
    </t>
    <t>
      Conversely, it is possible that the client will specify in createattrs an
      owner attribute, group attribute, or ACL that the principal indicated
      the RPC call's credentials does not have permissions to create files
      for. The error to be returned in this instance is NFS4ERR_PERM. This
      applies to the OPEN operation too.
    </t>
    <t>
      If the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the CREATE operation MUST NOT proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated
      as a result of this operation.
    </t>
    <t>
      If the capability FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set
      (<xref target="utf8_caps"/>),
      and a symbolic link is being created, then the content
      of the symbolic link MUST be in UTF-8 encoding.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CREATE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client desires to set attribute values after the create, a
      SETATTR operation can be added to the COMPOUND request so that the
      appropriate attributes will be set.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DELEGPURGE" title="Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery" >

  <section toc="exclude" anchor="OP_DELEGPURGE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct DELEGPURGE4args {
        clientid4       clientid;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGPURGE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct DELEGPURGE4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGPURGE_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation purges all of the delegations awaiting recovery for a given client.
      This is useful for clients that do not commit delegation information
      to stable storage to indicate that conflicting requests need not be
      delayed by the server awaiting recovery of delegation information.
    </t>
    <t>
      The client is NOT specified by the clientid field of
      the request.  The client SHOULD set the client field
      to zero, and the server MUST ignore the clientid
      field. Instead, the server MUST derive the client ID
      from the value of the session ID in the arguments of
      the SEQUENCE operation that precedes DELEGPURGE in
      the COMPOUND request.

    </t>
      
    <t>
      The DELEGPURGE operation should be used by clients that record delegation
      information on stable storage on the client.  In this case,
      after the client recovers all delegations it knows of,
      it should immediately send a DELEGPURGE operation.
      Doing so will notify the server that
      no additional delegations for the client will be recovered allowing it
      to free resources, and avoid delaying other clients which make requests
      that conflict with the unrecovered delegations.  The set of
      delegations known to the server and the client might be different.  The
      reason for this is that after sending a request that
      resulted in a delegation, the client might experience a failure
      before it both received the delegation and
      committed the delegation to the client's stable storage.
    </t>
    <t>
      The server MAY support DELEGPURGE, but if it does not, it MUST NOT
      support CLAIM_DELEGATE_PREV and MUST NOT support CLAIM_DELEG_PREV_FH.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DELEGRETURN" title="Operation 8: DELEGRETURN - Return Delegation" >

  <section toc="exclude" anchor="OP_DELEGRETURN_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct DELEGRETURN4args {
        /* CURRENT_FH: delegated object */
        stateid4        deleg_stateid;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGRETURN_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct DELEGRETURN4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGRETURN_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DELEGRETURN operation returns the delegation represented by
      the current filehandle and stateid. 
    </t>
    <t>
      Delegations may be returned voluntarily (i.e., before
      the server has recalled them) or when recalled.  In either case, the client must
      properly propagate state changed under the context of the delegation to
      the server before returning the delegation.
    </t>
    <t>
     The server MAY require that the principal, security
     flavor, and if applicable, the GSS mechanism, combination
     that acquired the delegation also be the one to send
     DELEGRETURN on the file. This might not be possible
     if credentials for the principal are no longer
     available. The server MAY allow the machine credential
     or SSV credential (see <xref target="OP_EXCHANGE_ID"
     />) to send DELEGRETURN.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETATTR" title="Operation 9: GETATTR - Get Attributes" >

  <section toc="exclude" anchor="OP_GETATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct GETATTR4args {
        /* CURRENT_FH: object */
        bitmap4         attr_request;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct GETATTR4resok {
        fattr4          obj_attributes;
};

union GETATTR4res switch (nfsstat4 status) {
 case NFS4_OK:
         GETATTR4resok  resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GETATTR operation will obtain attributes for the file system
      object specified by the current filehandle.  The client sets a bit in
      the bitmap argument for each attribute value that it would like the
      server to return.  The server returns an attribute bitmap that
      indicates the attribute values that it was able to return,
      which will include all attributes requested by the client that
      are attributes supported by the server for the target
      file system.  This bitmap is followed by the attribute values ordered 
      lowest attribute number first.
    </t>
    <t>
      The server MUST return a value for each attribute that the client
      requests if the attribute is supported by the server for the target
      file system.  If the server does not support a particular attribute 
      on the target file system, then it MUST NOT return the attribute value 
      and MUST NOT set the attribute bit in the result bitmap.  The server 
      MUST return an error if it supports an attribute on the target 
      but cannot obtain its value.  In that case, no attribute values will 
      be returned.
    </t>
    <t>
      File systems that are absent should be treated as having support for
      a very small set of attributes as described in 
      <xref target="absent_getattr"/>,
      even if previously, when the file system was present, more attributes
      were supported.
    </t>
    <t>
      All servers MUST support the REQUIRED attributes as specified in
      <xref target="mandatory_attributes"/>, for all file systems,
      with the exception of absent file systems.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Suppose there is an OPEN_DELEGATE_WRITE delegation held by another client for
the file
      in question and size and/or change are among the set of attributes being interrogated. The server has two choices.
      First, the server can obtain the actual
      current value of these attributes from the client holding the delegation
      by using the CB_GETATTR callback.  Second, the server, particularly when the
      delegated client is unresponsive, can recall the
      delegation in question.  The GETATTR MUST NOT proceed 
      until one of the following occurs:
      <list style="symbols">
        <t>
          The requested attribute values are returned in the response to
          CB_GETATTR.
        </t>
        <t>
          The OPEN_DELEGATE_WRITE delegation is returned.
        </t>
        <t>
          The OPEN_DELEGATE_WRITE delegation is revoked.
        </t>
      </list>
    </t>
    <t>
      Unless one of the above happens very quickly,
      one or more NFS4ERR_DELAY errors will be returned
      while a delegation is outstanding.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETFH" title="Operation 10: GETFH - Get Current Filehandle" >

  <section toc="exclude" anchor="OP_GETFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_GETFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct GETFH4resok {
        nfs_fh4         object;
};

union GETFH4res switch (nfsstat4 status) {
 case NFS4_OK:
        GETFH4resok     resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation returns the current filehandle value.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
      As described in <xref target="COMPOUND Sizing Issues"/>, GETFH
      is REQUIRED or RECOMMENDED to 
      immediately follow certain operations, and servers
      are free to reject such operations if
      the client fails to insert
      GETFH in the request as REQUIRED or RECOMMENDED.
      <xref target="open_getfh_issue"/> provides additional
      justification for why GETFH MUST follow OPEN.

    </t>
  </section>
  <section toc="exclude" anchor="OP_GETFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Operations that change the current filehandle like LOOKUP or CREATE do
      not automatically return the new filehandle as a result.  For
      instance, if a client needs to look up a directory entry and obtain its
      filehandle, then the following request is needed.
    </t>
    <t>
      <list style="empty">
	<t>
	  PUTFH  (directory filehandle)
	</t>
	<t>
	  LOOKUP (entry name)
	</t>
	<t>
	  GETFH
	</t>
      </list>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LINK" title="Operation 11: LINK - Create Link to a File" >

  <section toc="exclude" anchor="OP_LINK_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LINK4args {
        /* SAVED_FH: source object */
        /* CURRENT_FH: target directory */
        component4      newname;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LINK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LINK4resok {
        change_info4    cinfo;
};

union LINK4res switch (nfsstat4 status) {
 case NFS4_OK:
         LINK4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LINK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LINK operation creates an additional newname for the file
      represented by the saved filehandle, as set by the SAVEFH operation,
      in the directory represented by the current filehandle.  The existing
      file and the target directory must reside within the same file system
      on the server.  On success, the current filehandle will continue to be
      the target directory.  If an object exists in the target directory
      with the same name as newname, the server must return NFS4ERR_EXIST.
    </t>
    <t>
      For the target directory, the server returns change_info4 information
      in cinfo.  With the atomic field of the change_info4 data type, the
      server will indicate if the before and after change attributes were
      obtained atomically with respect to the link creation.
    </t>
    <t>
      If the newname has a length of zero, or if newname does not obey
      the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LINK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MAY impose restrictions on the LINK operation such that
      LINK may not be done when the file is open or when that open is done  
      by particular protocols, or with particular options or access modes.
      When LINK is rejected because of such restrictions, the error 
      NFS4ERR_FILE_OPEN is returned.
    </t>
    <t>
      If a server does implement such restrictions and those restrictions
      include cases of NFSv4 opens preventing successful execution of
      a link, the server needs to recall any delegations that could
      hide the existence of opens relevant to that decision.  The reason
      is that when a client holds a delegation, the server 
      might not have an accurate account of the opens for that client, since
      the client may execute OPENs and CLOSEs locally.  The LINK operation
      must be delayed only until a definitive result can be obtained.
      For example, suppose there are multiple delegations and one of them establishes
      an open whose presence would prevent the link. Given the server's 
      semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon
      as that delegation is returned without waiting for other delegations
      to be returned.  Similarly, if such opens are not associated with 
      delegations, NFS4ERR_FILE_OPEN can be returned immediately with no 
      delegation recall being done.
    </t>
    <t>
      If the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot be
      performed successfully until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, instead of a recall,
      NOTIFY4_ADD_ENTRY will be generated
      as a result of the LINK operation.
    </t>
    <t>
      If the current file system supports the numlinks attribute, and
      other clients have delegations to the file being linked, then those
      delegations MUST be recalled and the LINK operation MUST NOT proceed until
      all delegations are returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      Changes to any property of the "hard" linked files are reflected in
      all of the linked files.  When a link is made to a file, the
      attributes for the file should have a value for numlinks that is one
      greater than the value before the LINK operation.
    </t>
    <t>
      The statement "file and the target directory must reside within the
      same file system on the server" means that the fsid fields in the
      attributes for the objects are the same. If they reside on
      different file systems, the error NFS4ERR_XDEV is returned.  
      This error may be returned by some servers when there is an 
      internal partitioning of a file system that the LINK operation
      would violate.  
    </t>
    <t>
      On some
      servers, "." and ".." are illegal values for newname
      and the error NFS4ERR_BADNAME will be returned if they are specified.
    </t>
    <t>
      When the current filehandle designates a named attribute directory
      and the object to be linked (the saved filehandle) is not a named 
      attribute for the  same object, the error NFS4ERR_XDEV MUST be 
      returned.  When the saved filehandle designates a named attribute
      and the current filehandle is not the appropriate named attribute
      directory, the error NFS4ERR_XDEV MUST also be returned.  
    </t>
    <t>
      When the current filehandle designates a named attribute directory
      and the object to be linked (the saved filehandle) is a named
      attribute within that directory, the server may return 
      the error NFS4ERR_NOTSUPP.
    </t>
    <t>
      In the case that newname is already linked to the file represented by
      the saved filehandle, the server will return NFS4ERR_EXIST.
    </t>
    <t>
      Note that symbolic links are created with the CREATE operation.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCK" title="Operation 12: LOCK - Create Lock" >

  <section toc="exclude" anchor="OP_LOCK_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
/*
 * For LOCK, transition from open_stateid and lock_owner
 * to a lock stateid.
 */
struct open_to_lock_owner4 {
        seqid4          open_seqid;
        stateid4        open_stateid;
        seqid4          lock_seqid;
        lock_owner4     lock_owner;
};

/*
 * For LOCK, existing lock stateid continues to request new
 * file lock for the same lock_owner and open_stateid.
 */
struct exist_lock_owner4 {
        stateid4        lock_stateid;
        seqid4          lock_seqid;
};

union locker4 switch (bool new_lock_owner) {
 case TRUE:
        open_to_lock_owner4     open_owner;
 case FALSE:
        exist_lock_owner4       lock_owner;
};

/*
 * LOCK/LOCKT/LOCKU: Record lock management
 */
struct LOCK4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        bool            reclaim;
        offset4         offset;
        length4         length;
        locker4         locker;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOCK4denied {
        offset4         offset;
        length4         length;
        nfs_lock_type4  locktype;
        lock_owner4     owner;
};

struct LOCK4resok {
        stateid4        lock_stateid;
};

union LOCK4res switch (nfsstat4 status) {
 case NFS4_OK:
         LOCK4resok     resok4;
 case NFS4ERR_DENIED:
         LOCK4denied    denied;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCK operation requests a byte-range lock for the byte-range specified
      by the offset and length parameters, and lock type specified in
      the locktype parameter.  If this is a reclaim request, the
      reclaim parameter will be TRUE.
    </t>
    <t>
      Bytes in a file may be locked even if those bytes are not currently
      allocated to the file.  To lock the file from a specific offset
      through the end-of-file (no matter how long the file actually is) use
      a length field equal to NFS4_UINT64_MAX.
      The server MUST return NFS4ERR_INVAL under the following
      combinations of length and offset:

      <list style='symbols'>
      <t>
       Length is equal to zero.
      </t>
      <t>
       Length is not equal to NFS4_UINT64_MAX, and the sum of length
       and offset exceeds NFS4_UINT64_MAX.
      </t>
      </list>

    </t>
    <t>
      32-bit servers are servers that support locking for
      byte offsets that fit within 32 bits (i.e., less than
      or equal to NFS4_UINT32_MAX).  If the client specifies a
      range that overlaps one or more bytes beyond offset
      NFS4_UINT32_MAX but does not end at offset
      NFS4_UINT64_MAX, then such a 32-bit server MUST return the
      error NFS4ERR_BAD_RANGE.
    </t>
    <t>
      If the server returns NFS4ERR_DENIED, the
      owner, offset, and length
      of a conflicting lock are returned.
    </t>
    <t>
      The locker argument specifies the lock-owner that is associated with
      the LOCK operation.  The locker4 structure is a switched union that
      indicates whether the client has already created byte-range locking
      state associated with the current open file and lock-owner.  In the
      case in which it has, the argument is just a stateid representing
      the set of
      locks associated with that open file and lock-owner, together with
      a lock_seqid value that MAY be any value and MUST be ignored
      by the server.
      In the case where no byte-range locking state has been established, or the client
      does not have the stateid available, the argument contains the
      stateid of the open file with which this lock is to be associated,
      together with the lock-owner with which the lock is to be associated.
      The open_to_lock_owner case covers the very first lock done by a
      lock-owner for a given open file and offers a method to use the 
      established state of the open_stateid to transition to the use of 
      a lock stateid.
    </t>
    <t>
      The following fields of the locker parameter MAY be
      set to any value by the client and MUST be ignored
      by the server:

      <list style='symbols'>
      <t>
       The clientid field of the lock_owner
       field of the open_owner field
       (locker.open_owner.lock_owner.clientid). The
       reason the server MUST ignore the clientid field
       is that the server MUST derive the client ID from
       the session ID from the SEQUENCE operation of the
       COMPOUND request.

      </t>
      <t>
       The open_seqid and lock_seqid fields of the
       open_owner field (locker.open_owner.open_seqid and
       locker.open_owner.lock_seqid).

      </t>
      <t>
       The lock_seqid field of the lock_owner field
       (locker.lock_owner.lock_seqid).

      </t>
      </list>
    </t>

    <t>
      Note that the client ID appearing in a LOCK4denied
      structure is the actual client associated with the
      conflicting lock, whether this is the client ID
      associated with the current session or a different
      one. Thus, if the server returns NFS4ERR_DENIED,
      it MUST set the clientid field of the owner field of the
      denied field.
    </t>

    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server is unable to determine the exact offset and length of
      the conflicting byte-range lock, the same offset and length that were provided in
      the arguments should be returned in the denied results.
    </t>
    <t>
      LOCK operations are subject to permission checks and to checks against
      the access type of the associated file.  However, the specific right
      and modes required for various types of locks reflect the semantics of
      the server-exported file system, and are not specified by the protocol.
      For example, Windows 2000 allows a write lock of a file open for read access,
      while a POSIX-compliant system does not.
    </t>
    <t>
      When the client sends a LOCK operation that corresponds to a range that
      the lock-owner has locked already (with the same or different lock
      type), or to a sub-range of such a range, or to a byte-range that
      includes multiple locks already granted to that lock-owner, in whole or
      in part, and the server does not support such locking operations
      (i.e., does not support POSIX locking semantics), the server will
      return the error NFS4ERR_LOCK_RANGE.  In that case, the client may
      return an error, or it may emulate the required operations, using only
      LOCK for ranges that do not include any bytes already locked by that
      lock-owner and LOCKU of locks held by that lock-owner (specifying an
      exactly matching range and type).  Similarly, when the client sends a
      LOCK operation that amounts to upgrading (changing from a READ_LT lock to a
      WRITE_LT lock) or downgrading (changing from WRITE_LT lock to a READ_LT lock)
      an existing byte-range lock, and the server does not support such a lock,
      the server will return NFS4ERR_LOCK_NOTSUPP.  Such operations may not
      perfectly reflect the required semantics in the face of conflicting
      LOCK operations from other clients.
    </t>
    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, the client holding that 
      delegation is assured that there are no opens by other clients.
      Thus, there can be no conflicting LOCK operations from such clients.
      Therefore, the client may be handling locking requests locally, 
      without
      doing LOCK operations on the server.  If it does that, it must be
      prepared to update the lock status on the server, by sending 
      appropriate LOCK and LOCKU operations before returning
      the delegation.
    </t>
    <t>
      When one or more clients hold OPEN_DELEGATE_READ delegations, any LOCK operation
      where the server is implementing mandatory locking semantics MUST
      result in the recall of all such delegations.  The LOCK operation may
      not be granted until all such delegations are returned or revoked.
      Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCKT" title="Operation 13: LOCKT - Test for Lock" >

  <section toc="exclude" anchor="OP_LOCKT_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOCKT4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        offset4         offset;
        length4         length;
        lock_owner4     owner;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOCKT_RESULTS" title="RESULTS">
<figure>
 <artwork>
union LOCKT4res switch (nfsstat4 status) {
 case NFS4ERR_DENIED:
         LOCK4denied    denied;
 case NFS4_OK:
         void;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCKT operation tests the lock as specified in the arguments.  If
      a conflicting lock exists, the owner, offset, length, and type of the
      conflicting lock are returned.  
      The owner field in the results includes the client ID of the owner of 
      the conflicting lock, whether this is the client ID associated with the
      current session or a different client ID.
      If no lock is held, nothing other than
      NFS4_OK is returned.  Lock types READ_LT and READW_LT are processed in
      the same way in that a conflicting lock test is done without regard to
      blocking or non-blocking.  The same is true for WRITE_LT and WRITEW_LT.
    </t>
    <t>
      The ranges are specified as for LOCK.  The NFS4ERR_INVAL and 
      NFS4ERR_BAD_RANGE errors are returned under the same circumstances
      as for LOCK.
    </t>
    <t>
      The clientid field of the owner MAY be set to
      any value by the client and MUST be ignored by
      the server. The reason the server MUST ignore the
      clientid field is that the server MUST derive the
      client ID from the session ID from the SEQUENCE
      operation of the COMPOUND request.

    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCKT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server is unable to determine the exact offset
      and length of the conflicting lock, the same offset
      and length that were provided in the arguments should
      be returned in the denied results. 

    </t>

    <t>
      LOCKT uses a lock_owner4 rather a stateid4, as is used in
      LOCK to identify the owner.  This is because the client does not 
      have to open the file to test for the existence of a lock, so
      a stateid might not be available.  
    </t>
    <t>
      As noted in <xref target="OP_LOCK_IMPLEMENTATION"/>, some
      servers may return NFS4ERR_LOCK_RANGE to certain (otherwise
      non-conflicting) LOCK operations that overlap ranges already
      granted to the current lock-owner.
    </t>

    <t>
      The LOCKT operation's test for conflicting locks SHOULD exclude
      locks for the current lock-owner, and thus should return NFS4_OK in
      such cases.  Note that this means that a server might return
      NFS4_OK to a LOCKT request even though a LOCK operation for the
      same range and lock-owner would fail with NFS4ERR_LOCK_RANGE.
    </t>

    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose 
      (see <xref target="OP_LOCK_IMPLEMENTATION" />) to handle LOCK
      requests locally.  In such a case, LOCKT requests will similarly
      be handled locally. 
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCKU" title="Operation 14: LOCKU - Unlock File" >

  <section toc="exclude" anchor="OP_LOCKU_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOCKU4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        seqid4          seqid;
        stateid4        lock_stateid;
        offset4         offset;
        length4         length;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKU_RESULTS" title="RESULTS">
<figure>
 <artwork>
union LOCKU4res switch (nfsstat4 status) {
 case   NFS4_OK:
         stateid4       lock_stateid;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKU_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCKU operation unlocks the byte-range lock specified by the
      parameters. The client may set the locktype field to any value that is
      legal for the nfs_lock_type4 enumerated type, and the server MUST
      accept any legal value for locktype. Any legal value for locktype has
      no effect on the success or failure of the LOCKU operation.
    </t>
    <t>
      The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
      NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
      for LOCK.
    </t>
    <t>
      The seqid parameter MAY be any value and the server MUST ignore it.
    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     The server MAY require that the principal, security
     flavor, and if applicable, the GSS mechanism, combination
     that sent a LOCK operation also be the one to send
     LOCKU on the file. This might not be possible
     if credentials for the principal are no longer
     available. The server MAY allow the machine credential
     or SSV credential (see <xref target="OP_EXCHANGE_ID"
     />) to send LOCKU.

    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCKU_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the area to be unlocked does not correspond exactly to a lock
      actually held by the lock-owner, the server may return the error
      NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
      locked, where the area is a sub-range of the area locked, where it
      overlaps the area locked without matching exactly, or the area
      specified includes multiple locks held by the lock-owner.  In all of
      these cases, allowed by <xref target="fcntl">POSIX locking</xref> semantics, a client receiving
      this error should, if it desires support for such operations, simulate
      the operation using LOCKU on ranges corresponding to locks it actually
      holds, possibly followed by LOCK operations for the sub-ranges not being
      unlocked.
    </t>
    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose 
      (see <xref target="OP_LOCK_IMPLEMENTATION" />) to handle LOCK
      requests locally.  In such a case, LOCKU operations will similarly
      be handled locally. 
    </t>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOOKUP" title="Operation 15: LOOKUP - Lookup Filename" >

  <section toc="exclude" anchor="OP_LOOKUP_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOOKUP4args {
        /* CURRENT_FH: directory */
        component4      objname;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOOKUP_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOOKUP4res {
        /* New CURRENT_FH: object */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOOKUP_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOOKUP operation looks up or finds a file system object using the
      directory specified by the current filehandle.  LOOKUP evaluates the
      component and if the object exists, the current filehandle is replaced
      with the component's filehandle.
    </t>
    <t>
      If the component cannot be evaluated either because it does not exist
      or because the client does not have permission to evaluate the
      component, then an error will be returned and the current filehandle
      will be unchanged.
    </t>
    <t>
      If the component is a zero-length string or if any component does not
      obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOOKUP_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client wants to achieve the effect of a multi-component look up,
      it may construct a COMPOUND request such as (and obtain each
      filehandle):
	<figure>
	  <artwork>
      PUTFH  (directory filehandle)
      LOOKUP "pub"
      GETFH
      LOOKUP "foo"
      GETFH
      LOOKUP "bar"
      GETFH
	  </artwork>
	</figure>
      Unlike NFSv3, NFSv4.1 allows LOOKUP requests to cross mountpoints on the
      server.  The client can detect a mountpoint crossing by comparing the
      fsid attribute of the directory with the fsid attribute of the
      directory looked up.  If the fsids are different, then the new
      directory is a server mountpoint.  UNIX clients that detect a
      mountpoint crossing will need to mount the server's file system.  This
      needs to be done to maintain the file object identity checking
      mechanisms common to UNIX clients.
    </t>
    <t>
      Servers that limit NFS access to "shared" or "exported" file systems
      should provide a pseudo file system into which the exported file systems
      can be integrated, so that clients can browse the server's namespace.
      The clients view of a pseudo file system will be limited to paths that
      lead to exported file systems.
    </t>
    <t>
      Note: previous versions of the protocol assigned special semantics to
      the names "." and "..".  NFSv4.1 assigns no special semantics to
      these names.  The LOOKUPP operator must be used to look up a parent
      directory.
    </t>
    <t>
      Note that this operation does not follow symbolic links.  The client
      is responsible for all parsing of filenames including filenames that
      are modified by symbolic links encountered during the look up process.
    </t>
    <t>
      If the current filehandle supplied is not a directory but a symbolic
      link, the error NFS4ERR_SYMLINK is returned as the error.  For all
      other non-directory file types, the error NFS4ERR_NOTDIR is returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOOKUPP" title="Operation 16: LOOKUPP - Lookup Parent Directory" >

  <section toc="exclude" anchor="OP_LOOKUPP_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: object */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_LOOKUPP_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOOKUPP4res {
        /* new CURRENT_FH: parent directory */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LOOKUPP_DESCRIPTION" title="DESCRIPTION">
    <t>
      The current filehandle is assumed to refer to a regular
      directory or a named attribute directory.  LOOKUPP assigns the
      filehandle for its parent directory to be the current
      filehandle.  If there is no parent directory, an NFS4ERR_NOENT
      error must be returned.  Therefore, NFS4ERR_NOENT will be
      returned by the server when the current filehandle is at the
      root or top of the server's file tree.
    </t>
    <t>
      As is the case with LOOKUP, LOOKUPP will also cross mountpoints.
    </t>
    <t>
      If the current filehandle is not a directory or named attribute
      directory, the error NFS4ERR_NOTDIR is returned.
    </t>
    <t>
      If the requester's security flavor does not match that
      configured for the parent directory, then the server SHOULD
      return NFS4ERR_WRONGSEC (a future minor revision of NFSv4 may
      upgrade this to MUST) in the LOOKUPP response.  However, if the
      server does so, it MUST support the SECINFO_NO_NAME
      operation (<xref target="OP_SECINFO_NO_NAME"/>), so that the client can gracefully determine the
      correct security flavor.
    </t>
    <t>
      If the current filehandle is a named attribute directory that is
      associated with a file system object via OPENATTR (i.e., not a
      sub-directory of a named attribute directory), LOOKUPP SHOULD
      return the filehandle of the associated file system object.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOOKUPP_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      An issue to note is upward navigation from named attribute
      directories.  The named attribute directories are essentially
      detached from the namespace, and this property should be safely
      represented in the client operating environment.  LOOKUPP on a
      named attribute directory may return the filehandle of the
      associated file, and conveying this to applications might be
      unsafe as many applications expect the parent of an object to
      always be a directory.  Therefore, the client may want to hide
      the parent of named attribute directories (represented as ".."
      in UNIX) or represent the named attribute directory as its own
      parent (as is typically done for the file system root directory in
      UNIX).
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_NVERIFY" title="Operation 17: NVERIFY - Verify Difference in Attributes" >

  <section toc="exclude" anchor="OP_NVERIFY_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct NVERIFY4args {
        /* CURRENT_FH: object */
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_NVERIFY_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct NVERIFY4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_NVERIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to prefix a sequence of operations to be
      performed if one or more attributes have changed on some file system
      object.  If all the attributes match, then the error NFS4ERR_SAME MUST
      be returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_NVERIFY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is useful as a cache validation operator.  If the
      object to which the attributes belong has changed, then the following
      operations may obtain new data associated with that object, for
      instance, to check if a file has been changed and obtain new data if
      it has:
      <figure>
	<artwork>
      SEQUENCE
      PUTFH fh
      NVERIFY attrbits attrs
      READ 0 32767
	</artwork>
      </figure>
      Contrast this with NFSv3, which would first send a GETATTR in
      one request/reply round trip, and then if attributes indicated that
      the client's cache was stale, then send a READ in another request/reply
      round trip.
    </t>
    <t>
      In the case that a RECOMMENDED attribute is specified in the NVERIFY
      operation and the server does not support that attribute for the
      file system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
      client.
    </t>
    <t>
      When the attribute rdattr_error or any set-only attribute (e.g.,
      time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
      the client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section anchor="OP_OPEN" title="Operation 18: OPEN - Open a Regular File" >

  <section toc="exclude" anchor="OP_OPEN_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
/*
 * Various definitions for OPEN
 */
enum createmode4 {
        UNCHECKED4      = 0,
        GUARDED4        = 1,
        /* Deprecated in NFSv4.1. */
        EXCLUSIVE4      = 2,
        /*
         * New to NFSv4.1. If session is persistent,
         * GUARDED4 MUST be used. Otherwise, use
         * EXCLUSIVE4_1 instead of EXCLUSIVE4.
         */
        EXCLUSIVE4_1    = 3
};

struct creatverfattr {
         verifier4      cva_verf;
         fattr4         cva_attrs;
};

union createhow4 switch (createmode4 mode) {
 case UNCHECKED4:
 case GUARDED4:
         fattr4         createattrs;
 case EXCLUSIVE4:
         verifier4      createverf;
 case EXCLUSIVE4_1:
         creatverfattr  ch_createboth;
};

enum opentype4 {
        OPEN4_NOCREATE  = 0,
        OPEN4_CREATE    = 1
};

union openflag4 switch (opentype4 opentype) {
 case OPEN4_CREATE:
         createhow4     how;
 default:
         void;
};

/* Next definitions used for OPEN delegation */
enum limit_by4 {
        NFS_LIMIT_SIZE          = 1,
        NFS_LIMIT_BLOCKS        = 2
        /* others as needed */
};

struct nfs_modified_limit4 {
        uint32_t        num_blocks;
        uint32_t        bytes_per_block;
};

union nfs_space_limit4 switch (limit_by4 limitby) {
 /* limit specified as file size */
 case NFS_LIMIT_SIZE:
         uint64_t               filesize;
 /* limit specified by number of blocks */
 case NFS_LIMIT_BLOCKS:
         nfs_modified_limit4    mod_blocks;
} ;

/*
 * Share Access and Deny constants for open argument
 */
const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

const OPEN4_SHARE_DENY_NONE     = 0x00000000;
const OPEN4_SHARE_DENY_READ     = 0x00000001;
const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
const OPEN4_SHARE_DENY_BOTH     = 0x00000003;


/* new flags for share_access field of OPEN4args */
const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK        = 0xFF00;
const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE     = 0x0000;
const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x0100;
const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x0200;
const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0300;
const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x0400;
const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x0500;

const
 OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
 = 0x10000;

const
 OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
 = 0x20000;

enum open_delegation_type4 {
        OPEN_DELEGATE_NONE      = 0,
        OPEN_DELEGATE_READ      = 1,
        OPEN_DELEGATE_WRITE     = 2,
        OPEN_DELEGATE_NONE_EXT  = 3 /* new to v4.1 */
};

enum open_claim_type4 {
        /*
         * Not a reclaim.
         */
        CLAIM_NULL              = 0,

        CLAIM_PREVIOUS          = 1,
        CLAIM_DELEGATE_CUR      = 2,
        CLAIM_DELEGATE_PREV     = 3,

        /*
         * Not a reclaim.
         *
         * Like CLAIM_NULL, but object identified
         * by the current filehandle.
         */
        CLAIM_FH                = 4, /* new to v4.1 */

        /*
         * Like CLAIM_DELEGATE_CUR, but object identified
         * by current filehandle.
         */
        CLAIM_DELEG_CUR_FH      = 5, /* new to v4.1 */

        /*
         * Like CLAIM_DELEGATE_PREV, but object identified
         * by current filehandle.
         */
        CLAIM_DELEG_PREV_FH     = 6 /* new to v4.1 */
};

struct open_claim_delegate_cur4 {
        stateid4        delegate_stateid;
        component4      file;
};

union open_claim4 switch (open_claim_type4 claim) {
 /*
  * No special rights to file.
  * Ordinary OPEN of the specified file.
  */
 case CLAIM_NULL:
        /* CURRENT_FH: directory */
        component4      file;
 /*
  * Right to the file established by an
  * open previous to server reboot. File
  * identified by filehandle obtained at
  * that time rather than by name.
  */
 case CLAIM_PREVIOUS:
        /* CURRENT_FH: file being reclaimed */
        open_delegation_type4   delegate_type;

 /*
  * Right to file based on a delegation
  * granted by the server. File is
  * specified by name.
  */
 case CLAIM_DELEGATE_CUR:
        /* CURRENT_FH: directory */
        open_claim_delegate_cur4        delegate_cur_info;

 /*
  * Right to file based on a delegation
  * granted to a previous boot instance
  * of the client.  File is specified by name.
  */
 case CLAIM_DELEGATE_PREV:
         /* CURRENT_FH: directory */
        component4      file_delegate_prev;

 /*
  * Like CLAIM_NULL. No special rights
  * to file. Ordinary OPEN of the
  * specified file by current filehandle.
  */
 case CLAIM_FH: /* new to v4.1 */
        /* CURRENT_FH: regular file to open */
        void;

 /*
  * Like CLAIM_DELEGATE_PREV. Right to file based on a
  * delegation granted to a previous boot
  * instance of the client.  File is identified by
  * by filehandle.
  */
 case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
        /* CURRENT_FH: file being opened */
        void;

 /*
  * Like CLAIM_DELEGATE_CUR. Right to file based on
  * a delegation granted by the server.
  * File is identified by filehandle.
  */
 case CLAIM_DELEG_CUR_FH: /* new to v4.1 */
         /* CURRENT_FH: file being opened */
         stateid4       oc_delegate_stateid;

};

/*
 * OPEN: Open a file, potentially receiving an OPEN delegation
 */
struct OPEN4args {
        seqid4          seqid;
        uint32_t        share_access;
        uint32_t        share_deny;
        open_owner4     owner;
        openflag4       openhow;
        open_claim4     claim;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_OPEN_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct open_read_delegation4 {
 stateid4 stateid;    /* Stateid for delegation*/
 bool     recall;     /* Pre-recalled flag for
                         delegations obtained
                         by reclaim (CLAIM_PREVIOUS) */

 nfsace4 permissions; /* Defines users who don't
                         need an ACCESS call to
                         open for read */
};

struct open_write_delegation4 {
 stateid4 stateid;      /* Stateid for delegation */
 bool     recall;       /* Pre-recalled flag for
                           delegations obtained
                           by reclaim
                           (CLAIM_PREVIOUS) */

 nfs_space_limit4
           space_limit; /* Defines condition that
                           the client must check to
                           determine whether the
                           file needs to be flushed
                           to the server on close.  */

 nfsace4   permissions; /* Defines users who don't
                           need an ACCESS call as
                           part of a delegated
                           open. */
};


enum why_no_delegation4 { /* new to v4.1 */
        WND4_NOT_WANTED         = 0,
        WND4_CONTENTION         = 1,
        WND4_RESOURCE           = 2,
        WND4_NOT_SUPP_FTYPE     = 3,
        WND4_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
        WND4_NOT_SUPP_UPGRADE   = 5,
        WND4_NOT_SUPP_DOWNGRADE = 6,
        WND4_CANCELLED          = 7,
        WND4_IS_DIR             = 8
};

union open_none_delegation4 /* new to v4.1 */
switch (why_no_delegation4 ond_why) {
        case WND4_CONTENTION:
                bool ond_server_will_push_deleg;
        case WND4_RESOURCE:
                bool ond_server_will_signal_avail;
        default:
                void;
};

union open_delegation4
switch (open_delegation_type4 delegation_type) {
        case OPEN_DELEGATE_NONE:
                void;
        case OPEN_DELEGATE_READ:
                open_read_delegation4 read;
        case OPEN_DELEGATE_WRITE:
                open_write_delegation4 write;
        case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
                open_none_delegation4 od_whynone;
};

/*
 * Result flags
 */

/* Client must confirm open */
const OPEN4_RESULT_CONFIRM      = 0x00000002;
/* Type of file locking behavior at the server */
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
/* Server will preserve file if removed while open */
const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;

/*
 * Server may use CB_NOTIFY_LOCK on locks
 * derived from this open
 */
const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;

struct OPEN4resok {
 stateid4       stateid;      /* Stateid for open */
 change_info4   cinfo;        /* Directory Change Info */
 uint32_t       rflags;       /* Result flags */
 bitmap4        attrset;      /* attribute set for create*/
 open_delegation4 delegation; /* Info on any open
                                 delegation */
};

union OPEN4res switch (nfsstat4 status) {
 case NFS4_OK:
        /* New CURRENT_FH: opened file */
        OPEN4resok      resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DESCRIPTION" title="DESCRIPTION">
    <t>
      The OPEN operation opens a regular file in a
      directory with the provided name or filehandle.
      OPEN can also create a file if a name is provided,
      and the client specifies it wants to create a file.
      Specification of whether or not a file is to be created,
      and the method of creation is via the openhow
      parameter. The openhow parameter consists of
      a switched union (data type opengflag4), which
      switches on the value of opentype (OPEN4_NOCREATE
      or OPEN4_CREATE). If OPEN4_CREATE is specified,
      this leads to another switched union (data type
      createhow4) that supports four cases of creation
      methods: UNCHECKED4, GUARDED4, EXCLUSIVE4,
      or EXCLUSIVE4_1. If opentype is OPEN4_CREATE,
      then the claim field of the claim field
      MUST be one of CLAIM_NULL, CLAIM_DELEGATE_CUR, or
      CLAIM_DELEGATE_PREV, because these claim methods
      include a component of a file name.
    </t>
    <t>
      Upon success (which might entail creation of a new
      file), the current filehandle is replaced by that
      of the created or existing object.

    </t>
   
    <t>
      If the current filehandle is a named attribute
      directory, OPEN will then create or open a named
      attribute file.  Note that exclusive create
      of a named attribute is not supported.  If the
      createmode is EXCLUSIVE4 or EXCLUSIVE4_1 and the
      current filehandle is a named attribute directory,
      the server will return EINVAL.
    </t>

    <t>
      UNCHECKED4 means that the file should be created if a
      file of that name does not exist and encountering an
      existing regular file of that name is not an error.
      For this type of create, createattrs specifies the
      initial set of attributes for the file.  The set
      of attributes may include any writable attribute
      valid for regular files.  When an UNCHECKED4
      create encounters an existing file, the attributes
      specified by createattrs are not used, except that
      when createattrs specifies the size attribute
      with a size of zero, the existing file is truncated.

    </t>
    <t>
      If GUARDED4 is specified, the server checks for
      the presence of a duplicate object by name before
      performing the create.  If a duplicate exists,
      NFS4ERR_EXIST is returned.
      If the object does not exist, the request is
      performed as described for UNCHECKED4.

    </t>
    <t>
      For the UNCHECKED4 and GUARDED4 cases, where the
      operation is successful, the server will return
      to the client an attribute mask signifying which
      attributes were successfully set for the object.

    </t>

     <t>
      EXCLUSIVE4_1 and EXCLUSIVE4
      specify that the server is to follow exclusive
      creation semantics, using the verifier to ensure
      exclusive creation of the target.  The server should
      check for the presence of a duplicate object by name.
      If the object does not exist, the server creates
      the object and stores the verifier with the object.
      If the object does exist and the stored verifier
      matches the client provided verifier, the server
      uses the existing object as the newly created object.
      If the stored verifier does not match, then an error
      of NFS4ERR_EXIST is returned.
     </t>
     <t>
      If using EXCLUSIVE4, and if the server uses attributes to
      store the exclusive create verifier, the server will signify
      which attributes it used by setting the appropriate bits in
      the attribute mask that is returned in the results.
      Unlike UNCHECKED4, GUARDED4, and EXCLUSIVE4_1, EXCLUSIVE4 does
      not support the setting of attributes at file creation, and
      after a successful OPEN via EXCLUSIVE4, the client MUST
      send a SETATTR to set attributes to a known state.
     </t>
     <t>
      In NFSv4.1, EXCLUSIVE4 has been deprecated in favor
      of EXCLUSIVE4_1.
      Unlike EXCLUSIVE4, attributes may be provided
      in the EXCLUSIVE4_1 case, but because the server
      may use attributes of the target object to store
      the verifier, the set of allowable attributes
      may be fewer than the set of attributes SETATTR
      allows. The allowable attributes for EXCLUSIVE4_1
      are indicated in the suppattr_exclcreat (<xref
      target="attrdef_suppattr_exclcreat"/>) attribute. If the client
      attempts to set in cva_attrs an attribute that is not in
      suppattr_exclcreat, the server MUST return NFS4ERR_INVAL.
      The response field, attrset, indicates both which attributes
      the server set from cva_attrs and which attributes the
      server used to store the verifier. As described
      in <xref target="OP_OPEN_IMPLEMENTATION"/>, the client can compare
      cva_attrs.attrmask with attrset to determine which attributes
      were used to store the verifier.

     </t>
     <t>
      With the addition of persistent sessions and
      pNFS, under some conditions EXCLUSIVE4 MUST NOT
      be used by the client or supported by the server.
      The following table summarizes the appropriate and
      mandated exclusive create methods for implementations
      of NFSv4.1:

     </t>

      <texttable anchor='exclusive_create'>

      <preamble>
         Required methods for exclusive create
      </preamble>

      <ttcol>Persistent Reply Cache Enabled</ttcol>
      <ttcol>Server Supports pNFS</ttcol>
      <ttcol>Server REQUIRED</ttcol> <ttcol>Client Allowed</ttcol>

      <c>no</c> <c>no</c>
	<c>EXCLUSIVE4_1 and EXCLUSIVE4</c>
	<c>EXCLUSIVE4_1 (SHOULD) or EXCLUSIVE4 (SHOULD NOT)</c>

      <c>no</c> <c>yes</c>
	<c>EXCLUSIVE4_1</c>
	<c>EXCLUSIVE4_1</c>

      <c>yes</c> <c>no</c>
	<c>GUARDED4</c>
	<c>GUARDED4</c>

      <c>yes</c> <c>yes</c>
	<c>GUARDED4</c>
	<c>GUARDED4</c>

      </texttable>

    <t>
     If CREATE_SESSION4_FLAG_PERSIST is set in the results
     of CREATE_SESSION, the reply cache is persistent (see <xref target="OP_CREATE_SESSION"/>).
     If the EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the
     results from EXCHANGE_ID, the server is a pNFS server (see <xref target="OP_EXCHANGE_ID"/>).
     If the client attempts to use EXCLUSIVE4 on a persistent session,
     or a session derived from an
     EXCHGID4_FLAG_USE_PNFS_MDS client ID, the server MUST return
     NFS4ERR_INVAL.
    </t>

    <t>

     With persistent sessions, exclusive create semantics
     are fully achievable via GUARDED4, and so EXCLUSIVE4
     or EXCLUSIVE4_1 MUST NOT be used.  When pNFS is
     being used, the layout_hint attribute might
     not be supported after the file is created. Only the
     EXCLUSIVE4_1 and GUARDED methods of exclusive file
     creation allow the atomic setting of attributes.

    </t>

    <t>
      For the target directory, the server returns change_info4 information
      in cinfo.  With the atomic field of the change_info4 data type, the
      server will indicate if the before and after change attributes were
      obtained atomically with respect to the link creation.
    </t>
    <t>
      The OPEN operation provides for Windows share
      reservation capability with the use of the
      share_access and share_deny fields of the OPEN
      arguments.  The client specifies at OPEN the required
      share_access and share_deny modes.  For clients
      that do not directly support SHAREs (i.e., UNIX), the
      expected deny value is OPEN4_SHARE_DENY_NONE.  In the case that
      there is an existing SHARE reservation that conflicts
      with the OPEN request, the server returns the error
      NFS4ERR_SHARE_DENIED.  For additional discussion of
      SHARE semantics, see <xref target="share_reserve" />.

    </t>
    <t>
      For each OPEN, the client provides a value for
      the owner field of the OPEN argument.  The owner
      field is of data type open_owner4, and contains a
      field called clientid and a field called owner. The
      client can set the clientid field to any value and
      the server MUST ignore it.  Instead, the server MUST
      derive the client ID from the session ID of the
      SEQUENCE operation of the COMPOUND request.

    </t>
    <t>
      The "seqid" field of the request is not used in
      NFSv4.1, but it MAY be any value and the server MUST
      ignore it.

    </t>
    <t>
      In the case that the client is recovering state from a server failure,
      the claim field of the OPEN argument is used to signify that the
      request is meant to reclaim state previously held.
    </t>
    <t>
      The "claim" field of the OPEN argument is used to specify the file to
      be opened and the state information that the client claims to
      possess.  There are seven claim types as follows:
    </t>
    <texttable>
      <ttcol align='left'>open type</ttcol>
      <ttcol align='left'>description</ttcol>
      <c>
        CLAIM_NULL,
        CLAIM_FH
      </c>
      <c>
        For the client, this is a new OPEN request and there is no
        previous state associated with the file for the client. With
        CLAIM_NULL, the file is identified by the current filehandle
        and the specified component name. With CLAIM_FH (new to NFSv4.1),
        the file is identified by just the current filehandle.
      </c>
      <c>
        CLAIM_PREVIOUS
      </c>
      <c>
        The client is claiming basic OPEN state for a file that was held
        previous to a server restart.  Generally used when a server is
        returning persistent filehandles; the client may not have the file
        name to reclaim the OPEN.
      </c>
      <c>
        CLAIM_DELEGATE_CUR,
        CLAIM_DELEG_CUR_FH
      </c>
      <c>
        The client is claiming a delegation for OPEN
        as granted by the server.  Generally, this
        is done as part of recalling a delegation.
        With CLAIM_DELEGATE_CUR, the file is identified by
        the current filehandle and the specified component
        name. With CLAIM_DELEG_CUR_FH (new to NFSv4.1), the
        file is identified by just the current filehandle.

      </c>
      <c>
        CLAIM_DELEGATE_PREV,
        CLAIM_DELEG_PREV_FH
      </c>
      <c>
        The client is claiming a delegation granted to a
        previous client instance; used after the client
        restarts. The server MAY support CLAIM_DELEGATE_PREV
        and/or CLAIM_DELEG_PREV_FH (new to NFSv4.1). If it
        does support either claim type, CREATE_SESSION MUST
        NOT remove the client's delegation state, and the
        server MUST support the DELEGPURGE operation.

      </c>
    </texttable>

    <t>
      For OPEN requests that reach the server during
      the grace period, the server returns an error
      of NFS4ERR_GRACE.  The following claim types are
      exceptions:
      <list style='symbols'>
      
      <t>
       OPEN requests specifying the claim type CLAIM_PREVIOUS are devoted to 
       reclaiming opens after a server restart and are typically only  
       valid during the grace period.

      </t>

      <t>
       OPEN requests specifying the claim types CLAIM_DELEGATE_CUR and 
       CLAIM_DELEG_CUR_FH are valid both during and after the grace period.
       Since the granting of the delegation that they are subordinate
       to assures that there is no conflict with locks to be reclaimed
       by other clients, the server need not return NFS4ERR_GRACE when
       these are received during the grace period.

      </t>
      </list>

    </t>

    <t>
      For any OPEN request, the server may return an OPEN delegation, which
      allows further opens and closes to be handled locally on the client as
      described in <xref target="open_delegation"/>.  Note that delegation is 
      up to the server to decide.  The client should never assume that
      delegation will or will not be granted in a particular instance.  It
      should always be prepared for either case.  A partial exception is the
      reclaim (CLAIM_PREVIOUS) case, in which a delegation type is claimed.
      In this case, delegation will always be granted, although the server
      may specify an immediate recall in the delegation structure.
    </t>
    <t>
      The rflags returned by a successful OPEN allow the server to return
      information governing how the open file is to be handled.
      <list style="symbols">
      <t>
      OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned
      by an NFSv4.1 server.
      </t>
      <t>
      OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's byte-range locking
      behavior supports the complete set of POSIX locking techniques <xref target="fcntl"/>.  From
      this, the client can choose to manage byte-range locking state in a way to
      handle a mismatch of byte-range locking management.
      </t>
      <t>
      OPEN4_RESULT_PRESERVE_UNLINKED indicates that the server will
      preserve the open file if the client (or any other client)
      removes the file as long as it is open. Furthermore, the
      server promises to preserve the file through the
      grace period after server restart, thereby giving the client
      the opportunity to reclaim its open.
      </t>
      <t>
      OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
      CB_NOTIFY_LOCK callbacks for locks on this file.  This flag is a hint
      only, and may be safely ignored by the client.
      </t>
      </list>
    </t>
    <t>
      If the component is of zero length, NFS4ERR_INVAL will be returned.
      The component is also subject to the normal UTF-8, character support,
      and name checks.  See <xref target="utf8_related_errors" /> for
      further discussion.
    </t>
    <t>
      When an OPEN is done and the specified open-owner already has the
      resulting filehandle open, the result is to "OR" together the new
      share and deny status together with the existing status.  In this
      case, only a single CLOSE need be done, even though multiple OPENs
      were completed.  When such an OPEN is done, checking of share
      reservations for the new OPEN proceeds normally, with no exception for
      the existing OPEN held by the same open-owner.  In this case, the 
      stateid returned as an "other" field that matches that of the previous
      open while the "seqid" field is incremented to reflect the change
      status due to the new open.
    </t>
    <t>
      If the underlying file system at the server is only accessible in a
      read-only mode and the OPEN request has specified ACCESS_WRITE or
      ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a
      read-only file system.
    </t>
    <t>
      As with the CREATE operation, the server MUST derive
      the owner, owner ACE, group, or group ACE if any
      of the four attributes are required and supported
      by the server's file system.  For an OPEN with the
      EXCLUSIVE4 createmode, the server has no choice,
      since such OPEN calls do not include the createattrs
      field.  Conversely, if createattrs (UNCHECKED4 or
      GUARDED4) or cva_attrs (EXCLUSIVE4_1) is specified,
      and includes an owner, owner_group, or ACE that
      the principal in the RPC call's credentials does
      not have authorization to create files for, then
      the server may return NFS4ERR_PERM.

    </t>
    <t>
      In the case of an OPEN that specifies a size of zero (e.g., truncation)
      and the file has named attributes, the named attributes are left as
      is and are not removed.
    </t>

    <t>
      NFSv4.1 gives more precise control to clients over
      acquisition of delegations via the following new
      flags for the share_access field of OPEN4args:
      <list style="hanging">
      <t hangText="OPEN4_SHARE_ACCESS_WANT_READ_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_ANY_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_NO_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_CANCEL"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED"></t>
      </list>
    </t>
    <t>
      If (share_access & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is
      not zero, then the client will have specified one and only one of:
      <list style="hanging">
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_READ_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_ANY_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_NO_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_CANCEL"></t>
      </list>
      Otherwise, the client is neither indicating a desire nor a non-desire
      for a delegation, and the server MAY or MAY not return a delegation
      in the OPEN response.
    </t>
    <t>
      If the server supports the new _WANT_ flags and the
      client sends one or more of the new flags,
      then in the event the server does not return a
      delegation, it MUST return a delegation type of
      OPEN_DELEGATE_NONE_EXT.  The field ond_why in the reply
      indicates why
      no delegation was returned and will be one of:
      <list style="hanging">
      <t hangText="WND4_NOT_WANTED">
         The client specified OPEN4_SHARE_ACCESS_WANT_NO_DELEG.
      </t>
      <t hangText="WND4_CONTENTION">
         There is a conflicting delegation or open on the file.
      </t>
      <t hangText="WND4_RESOURCE">
         Resource limitations prevent the server from granting a
         delegation.
      </t>
      <t hangText="WND4_NOT_SUPP_FTYPE">
         The server does not support delegations on this file type.
      </t>
      <t hangText="WND4_WRITE_DELEG_NOT_SUPP_FTYPE">
         The server does not support OPEN_DELEGATE_WRITE delegations on this file
         type.
      </t>
      <t hangText="WND4_NOT_SUPP_UPGRADE">
         The server does not support atomic upgrade of an OPEN_DELEGATE_READ delegation to an OPEN_DELEGATE_WRITE delegation.
      </t>
      <t hangText="WND4_NOT_SUPP_DOWNGRADE">
         The server does not support atomic downgrade of an OPEN_DELEGATE_WRITE delegation to an OPEN_DELEGATE_READ delegation.
      </t>
      <t hangText="WND4_CANCELED">
         The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL and now
         any "want" for this file object is cancelled.
      </t>
      <t hangText="WND4_IS_DIR">
         The specified file object is a directory, and the operation
         is OPEN or WANT_DELEGATION, which do not support delegations
         on directories.
      </t>
      </list>
    </t>
    <t>
        OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
        OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
        OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the
        client wants an OPEN_DELEGATE_READ, OPEN_DELEGATE_WRITE, or any delegation regardless which
        of OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
        OPEN4_SHARE_ACCESS_BOTH is set. If the client has an OPEN_DELEGATE_READ delegation on a file and requests an OPEN_DELEGATE_WRITE delegation, then
        the client is requesting atomic upgrade of its OPEN_DELEGATE_READ delegation
        to an OPEN_DELEGATE_WRITE delegation. If the client has an OPEN_DELEGATE_WRITE delegation on
        a file and requests an OPEN_DELEGATE_READ delegation, then the client is
        requesting atomic downgrade to an OPEN_DELEGATE_READ delegation. A server MAY
        support atomic upgrade or downgrade. If it does, then the
	returned delegation_type of OPEN_DELEGATE_READ
        or OPEN_DELEGATE_WRITE that is different from the delegation
        type the client currently has, indicates successful upgrade
        or downgrade. If the server does not support atomic delegation upgrade or
        downgrade, then ond_why will be set to WND4_NOT_SUPP_UPGRADE or
        WND4_NOT_SUPP_DOWNGRADE.
     </t>
     <t>
        OPEN4_SHARE_ACCESS_WANT_NO_DELEG means that the client wants no
        delegation.
     </t>
     <t>
        OPEN4_SHARE_ACCESS_WANT_CANCEL means that the client wants no
        delegation and wants to cancel any previously registered
        "want" for a delegation.
     </t>
     <t>
        The client may set one or both of
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
        OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED.
        However, they will have no effect unless one of following is set:
        <list style="symbols">
              <t>OPEN4_SHARE_ACCESS_WANT_READ_DELEG</t>
              <t>OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG</t>
              <t>OPEN4_SHARE_ACCESS_WANT_ANY_DELEG</t>
         </list>
     </t>
     <t>
        If the client specifies
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it
        wishes to register a "want" for a delegation, in the event the
        OPEN results do not include a delegation.  If so and the
        server denies the delegation due to insufficient resources,
        the server MAY later inform the client, via the
        CB_RECALLABLE_OBJ_AVAIL operation, that the resource
        limitation condition has eased. The server will tell the
        client that it intends to send a future
        CB_RECALLABLE_OBJ_AVAIL operation by setting delegation_type
        in the results to OPEN_DELEGATE_NONE_EXT, ond_why
        to WND4_RESOURCE, and ond_server_will_signal_avail set to
        TRUE. If
        ond_server_will_signal_avail is set to TRUE, the server MUST
        later send a CB_RECALLABLE_OBJ_AVAIL operation.
     </t>
     <t>
        If the client specifies
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it
        wishes to register a "want" for a delegation, in the event the
        OPEN results do not include a delegation. If so and the server
        denies the delegation due to contention, the
        server MAY later inform the client, via the CB_PUSH_DELEG
        operation, that the contention condition
        has eased. The server will tell the client that it intends to
        send a future CB_PUSH_DELEG operation by setting
        delegation_type in the results to OPEN_DELEGATE_NONE_EXT,
        ond_why to WND4_CONTENTION, and
        ond_server_will_push_deleg to TRUE. If
        ond_server_will_push_deleg is TRUE, the server MUST later
        send a CB_PUSH_DELEG operation.
     </t>
     <t>
        If the client has previously registered a want for a
        delegation on a file, and then sends a request to register a
        want for a delegation on the same file, the server MUST return
        a new error: NFS4ERR_DELEG_ALREADY_WANTED. If the client
        wishes to register a different type of delegation want for the
        same file, it MUST cancel the existing delegation WANT.
     </t>
  </section>
  <section toc="exclude" anchor="OP_OPEN_IMPLEMENTATION" title="IMPLEMENTATION">
     <t>
      In absence of a persistent session, the client
      invokes exclusive create by setting the how parameter
      to EXCLUSIVE4 or EXCLUSIVE4_1.  In these cases, the
      client provides a verifier that can reasonably be
      expected to be unique.  A combination of a client
      identifier, perhaps the client network address,
      and a unique number generated by the client, perhaps
      the RPC transaction identifier, may be appropriate.
    </t>
    <t>
      If the object does not exist, the server creates the object and stores the
      verifier in stable storage. For file systems that do not provide a
      mechanism for the storage of arbitrary file attributes, the server may
      use one or more elements of the object's metadata to store the
      verifier. The verifier MUST be stored in stable storage to prevent
      erroneous failure on retransmission of the request. It is assumed that
      an exclusive create is being performed because exclusive semantics are
      critical to the application. Because of the expected usage, exclusive
      CREATE does not rely solely on the server's reply cache
      for storage of the verifier. A nonpersistent reply cache
      does not survive a crash and the session and reply cache
      may be deleted after a network partition that exceeds the
      lease time, thus opening failure windows. 
    </t>
    <t>
      An NFSv4.1 server SHOULD NOT store the verifier in
      any of the file's RECOMMENDED or REQUIRED attributes.
      If it does, the server SHOULD use time_modify_set or
      time_access_set to store the verifier.
      The server SHOULD NOT store the verifier in the
      following attributes:
<list style="empty">
	<t>acl (it is desirable for access control to
	be established at creation),</t>

	<t>dacl (ditto),</t>

	<t>mode (ditto),</t>

	<t>owner (ditto),</t>

	<t>owner_group (ditto),</t>

	<t>retentevt_set (it may be desired to
	establish retention at creation)</t>

	<t>retention_hold (ditto),</t>

	<t>retention_set (ditto),</t>

	<t>sacl (it is desirable for auditing control
	to be established at creation),</t>

	<t>size (on some servers, size may have a
	limited range of values),</t>

	<t>mode_set_masked (as with mode),
<list style="empty">
	<t>and</t>
</list>
</t>
	<t>time_creation (a meaningful file creation
	should be set when the file is created).</t>
</list>
     Another alternative for the server is to use a named attribute
     to store the verifier.
    </t>

    <t>
     Because the EXCLUSIVE4 create method does not specify
     initial attributes when processing an EXCLUSIVE4 create,
     the server

     <list style="symbols">
     <t>
       SHOULD set the
       owner of the file to that corresponding to the credential of
       request's RPC header.
     </t>

     <t>
      SHOULD NOT leave the file's access control to anyone
      but the owner of the file.
     </t>
     </list>

    </t>

    <t>
      If the server cannot support exclusive create
      semantics, possibly because of the requirement to
      commit the verifier to stable storage, it should fail
      the OPEN request with the error NFS4ERR_NOTSUPP.

    </t>
    <t>
      During an exclusive CREATE request, if the object
      already exists, the server reconstructs the object's
      verifier and compares it with the verifier in
      the request. If they match, the server treats the
      request as a success. The request is presumed to
      be a duplicate of an earlier, successful request
      for which the reply was lost and that the server
      duplicate request cache mechanism did not detect. If
      the verifiers do not match, the request is rejected
      with the status NFS4ERR_EXIST.

    </t>
    <t>
      After the client has performed a successful
      exclusive create, the attrset response indicates
      which attributes were used to store the verifier.
      If EXCLUSIVE4 was used, the attributes set in
      attrset were used for the verifier. If EXCLUSIVE4_1
      was used, the client determines the attributes
      used for the verifier by comparing attrset with
      cva_attrs.attrmask; any bits set in the former but
      not the latter identify the attributes used to store
      the verifier.  The client MUST immediately send a
      SETATTR to set attributes used to store the verifier.
      Until it does so, the attributes used to store the
      verifier cannot be relied upon.  The subsequent
      SETATTR MUST NOT occur in the same COMPOUND request
      as the OPEN.

    </t>
    <t>
      Unless a persistent session is used, use of the
      GUARDED4 attribute does not provide exactly once
      semantics.  In particular, if a reply is lost and
      the server does not detect the retransmission of the
      request, the operation can fail with NFS4ERR_EXIST,
      even though the create was performed successfully.
      The client would use this behavior in the case that
      the application has not requested an exclusive create
      but has asked to have the file truncated when the
      file is opened.  In the case of the client timing
      out and retransmitting the create request, the client
      can use GUARDED4 to prevent against a sequence like
      create, write, create (retransmitted) from occurring.

    </t>
    <t>
      For SHARE reservations, the value of the expression
      (share_access & ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) MUST be
      one of OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE,
      or OPEN4_SHARE_ACCESS_BOTH. If not, the server MUST
      return NFS4ERR_INVAL.  The value of share_deny MUST
      be one of OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ,
      OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH.  If not, the
      server MUST return NFS4ERR_INVAL.

    </t>
    <t>
      Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
      OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH), the client
      should check that the requester has the proper access rights
      to perform the specified operation.  This would generally be
      the results of applying the ACL access rules to the file for the
      current requester.  However, just as with the ACCESS operation, the
      client should not attempt to second-guess the server's decisions, as
      access rights may change and may be subject to server administrative
      controls outside the ACL framework.  If the requester's READ or
      WRITE operation is not authorized (depending on the share_access
      value), the server MUST return NFS4ERR_ACCESS.

    </t>

    <t>
      Note that if the client ID was not created
      with the EXCHGID4_FLAG_BIND_PRINC_STATEID capability set in
      the reply to EXCHANGE_ID, then the server MUST
      NOT impose any requirement that READs and WRITEs
      sent for an open file have the same credentials
      as the OPEN itself, and the server is REQUIRED to
      perform access checking on the READs and WRITEs
      themselves. Otherwise, if the reply to EXCHANGE_ID
      did have EXCHGID4_FLAG_BIND_PRINC_STATEID set,
      then with one exception, the credentials used in the OPEN request MUST
      match those used in the READs and WRITEs, and the
      stateids in the READs and WRITEs MUST match, or be
      derived from the stateid from the reply to OPEN.
      The exception is if SP4_SSV or SP4_MACH_CRED state
      protection is used, and the spo_must_allow
      result of EXCHANGE_ID includes the READ and/or WRITE
      operations. In that case, the machine or SSV
      credential will be allowed to send READ and/or WRITE.
      See <xref target="OP_EXCHANGE_ID"/>.

    </t>
    <t>
      If the component provided to OPEN is a symbolic link, the error
      NFS4ERR_SYMLINK will be returned to the client, while if it is
      a directory the error NFS4ERR_ISDIR will be returned.  
If the component is neither
      of those but not an ordinary file, the error NFS4ERR_WRONG_TYPE
      is returned.  If the current
      filehandle is not a directory, the error NFS4ERR_NOTDIR will be
      returned.
    </t>
    <t>
      The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows
      a client to avoid the common implementation practice of renaming
      an open file to ".nfs&lt;unique value>" after it removes the file.
      After the server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client
      sends a REMOVE operation that would reduce the file's link count to
      zero, the server SHOULD report a value
      of zero for the numlinks attribute on the file.
    </t>
    <t>
      If another client has a delegation of the file being opened that 
      conflicts with open being done (sometimes depending on the 
      share_access or share_deny value specified), 
      the delegation(s) MUST be recalled, and the 
      operation cannot proceed until each such delegation is returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
      In the case of an OPEN_DELEGATE_WRITE delegation, any open by a different client
      will conflict, while for an OPEN_DELEGATE_READ delegation, only opens with one 
      of the following characteristics will be considered conflicting:
      <list style="symbols">
        <t>
          The value of share_access includes the bit 
          OPEN4_SHARE_ACCESS_WRITE.
        </t>
        <t>
          The value of share_deny specifies OPEN4_SHARE_DENY_READ or
          OPEN4_SHARE_DENY_BOTH.

        </t>
        <t>
          OPEN4_CREATE is specified together with UNCHECKED4, the
          size attribute is specified as zero (for truncation), and
          an existing file is truncated.
        </t>
      </list>
    </t>
    <t>
      If OPEN4_CREATE is specified and the file does not exist and 
      the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      If OPEN4_CREATE is specified and the file does not exist and 
      the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated
      as a result of this operation.
    </t>
    <section toc="exclude" anchor="open_getfh_issue"
	title="Warning to Client Implementors">
    <t>
      OPEN resembles LOOKUP in that it generates a filehandle for the client
      to use.  Unlike LOOKUP though, OPEN creates server state on the
      filehandle.  In normal circumstances, the client can only release this
      state with a CLOSE operation.  CLOSE uses the current filehandle to
      determine which file to close.  Therefore, the client MUST follow every
      OPEN operation with a GETFH operation in the same COMPOUND procedure.
      This will supply the client with the filehandle such that CLOSE can be
      used appropriately.
    </t>
    <t>
      Simply waiting for the lease on the file to expire is insufficient
      because the server may maintain the state indefinitely as long as
      another client does not attempt to make a conflicting access to the
      same file.
    </t>
    <t>
      See also <xref target="COMPOUND Sizing Issues"/>.
    </t>
    </section>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_OPENATTR" title="Operation 19: OPENATTR - Open Named Attribute Directory" >

  <section toc="exclude" anchor="OP_OPENATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct OPENATTR4args {
        /* CURRENT_FH: object */
        bool    createdir;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPENATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct OPENATTR4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: named attribute
         *                   directory
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPENATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The OPENATTR operation is used to obtain the filehandle of the named
      attribute directory associated with the current filehandle.  The
      result of the OPENATTR will be a filehandle to an object of type
      NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
      be used to obtain filehandles for the various named attributes
      associated with the original file system object.  Filehandles returned
      within the named attribute directory will designate objects of
      type of NF4NAMEDATTR.
    </t>
    <t>
      The createdir argument allows the client to signify if a named
      attribute directory should be created as a result of the OPENATTR
      operation.  Some clients may use the OPENATTR operation with a value
      of FALSE for createdir to determine if any named attributes exist for
      the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
      createdir has a value of TRUE and no named attribute directory exists,
      one is created and its filehandle becomes the current filehandle.
      On the other hand, if createdir has a value of TRUE and the named
      attribute directory already exists, no error results and the filehandle
      of the existing directory becomes the current filehandle.  The 
      creation of a named attribute directory assumes
      that the server has implemented named attribute support in this
      fashion and is not required to do so by this definition.
    </t>
    <t>
      If the current file handle designates an object of type 
      NF4NAMEDATTR (a named attribute) or NF4ATTRDIR (a named attribute 
      directory), an error of NFS4ERR_WRONG_TYPE is returned to the
      client.  Named attributes or a named attribute directory MUST NOT 
      have their own named attributes.
    </t>
  </section>
  <section toc="exclude" anchor="OP_OPENATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server does not support named attributes for the current
      filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
      client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_OPEN_DOWNGRADE" title="Operation 21: OPEN_DOWNGRADE - Reduce Open File Access" >

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct OPEN_DOWNGRADE4args {
        /* CURRENT_FH: opened file */
        stateid4        open_stateid;
        seqid4          seqid;
        uint32_t        share_access;
        uint32_t        share_deny;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct OPEN_DOWNGRADE4resok {
        stateid4        open_stateid;
};

union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
 case NFS4_OK:
        OPEN_DOWNGRADE4resok    resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to adjust the access and deny states
      for a given open.  This is necessary when a given open-owner opens the
      same file multiple times with different access and deny
      values.  In this situation, a close of one of the opens may change the
      appropriate share_access and share_deny flags to remove bits
      associated with opens no longer in effect.
    </t>
    <t>
      Valid values for the expression (share_access &
      ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) are OPEN4_SHARE_ACCESS_READ,
      OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH. If the client
      specifies other values, the server MUST reply with NFS4ERR_INVAL.

    </t>

    <t>
      Valid values for the share_deny field are
      OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ,
      OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH. If
      the client specifies other values, the server MUST
      reply with NFS4ERR_INVAL.

    </t>
      
    <t>
      After checking for valid values of share_access and
      share_deny, the server replaces the current access
      and deny modes on the file with share_access and
      share_deny subject to the following constraints:
      <list style='symbols'>
      <t>
       The bits in share_access SHOULD equal the union of the share_access
       bits (not including OPEN4_SHARE_WANT_* bits)
       specified for some subset of the OPENs
       in effect for the current open-owner on the current
       file.
      </t>
 
      <t>
       The bits in share_deny SHOULD equal the union of the
       share_deny bits specified for some subset
       of the OPENs in effect for the current open-owner
       on the current file.

      </t>
      </list>

      If the above constraints are not respected,
      the server SHOULD return the error NFS4ERR_INVAL.
      Since share_access and share_deny bits should be
      subsets of those already granted, short of a defect
      in the client or server implementation, it is not
      possible for the OPEN_DOWNGRADE request to be denied
      because of conflicting share reservations.

    </t>

    <t>
      The seqid argument is not used in NFSv4.1, MAY be any value, and
      MUST be ignored by the server.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      An OPEN_DOWNGRADE operation may make OPEN_DELEGATE_READ delegations grantable
      where they were not previously.  Servers may choose to respond
      immediately if there are pending delegation want requests or may
      respond to the situation at a later time.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTFH" title="Operation 22: PUTFH - Set Current Filehandle" >

  <section toc="exclude" anchor="OP_PUTFH_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct PUTFH4args {
        nfs_fh4         object;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct PUTFH4res {
        /*
         * If status is NFS4_OK,
         *    new CURRENT_FH: argument to PUTFH
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle provided as an
      argument. It clears the current stateid.
    </t>
    <t>
      If the security mechanism used by the requester does not meet the
      requirements of the filehandle provided to this operation, the server
      MUST return NFS4ERR_WRONGSEC.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTPUBFH" title="Operation 23: PUTPUBFH - Set
  Public Filehandle" >

  <section toc="exclude" anchor="OP_PUTPUBFH_ARGUMENT" title="ARGUMENT">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_RESULT" title="RESULT">
<figure>
 <artwork>
struct PUTPUBFH4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: public fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle that
      represents the public filehandle of the server's namespace.
      This filehandle may be different from the "root" filehandle
      that may be associated with some other directory on the server.
    </t>
    <t>
      PUTPUBFH also clears the current stateid.
    </t>
    <t>
      The public filehandle represents the concepts embodied in <xref
      target="RFC2054">RFC 2054</xref>, <xref
      target="RFC2055">RFC 2055</xref>, and <xref
      target="RFC2224">RFC 2224</xref>.  The intent for NFSv4.1
      is that the public filehandle (represented by the PUTPUBFH
      operation) be used as a method of providing WebNFS server
      compatibility with NFSv3.
    </t>
    <t>
      The public filehandle and the root filehandle (represented by the
      PUTROOTFH operation) SHOULD be equivalent.  If the public and root
      filehandles are not equivalent, then the directory corresponding to the public filehandle MUST be a
      descendant of the directory corresponding to the root filehandle.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
    <t>
      With the NFSv3 public filehandle, the client is
      able to specify whether the pathname provided in the LOOKUP
      should be evaluated as either an absolute path relative to the
      server's root or relative to the public filehandle.  <xref
      target="RFC2224">RFC 2224</xref> contains further discussion of
      the functionality.  With NFSv4.1, that type of
      specification is not directly available in the LOOKUP operation.
      The reason for this is because the component separators needed
      to specify absolute vs. relative are not allowed in NFSv4.  Therefore, the client is responsible for constructing its
      request such that the use of either PUTROOTFH or PUTPUBFH
      signifies absolute or relative evaluation of an NFS URL,
      respectively.
    </t>
    <t>
      Note that there are warnings mentioned in <xref
      target="RFC2224">RFC 2224</xref> with respect to the use of
      absolute evaluation and the restrictions the server may place on
      that evaluation with respect to how much of its namespace has
      been made available.  These same warnings apply to NFSv4.1.  It is likely, therefore, that because of server
      implementation details, an NFSv3 absolute public
      filehandle look up may behave differently than an NFSv4.1
      absolute resolution.
    </t>
    <t>
      There is a form of security negotiation as described
      in <xref target="RFC2755">RFC 2755</xref> that uses
      the public filehandle and an overloading of the pathname.
      This method is not available with NFSv4.1 as
      filehandles are not overloaded with special
      meaning and therefore do not provide the same
      framework as NFSv3.  Clients should therefore use
      the security negotiation mechanisms described in
      <xref target="Security Service Negotiation" />.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTROOTFH" title="Operation 24: PUTROOTFH - Set Root Filehandle" >

  <section toc="exclude" anchor="OP_PUTROOTFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_PUTROOTFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct PUTROOTFH4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: root fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTROOTFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle that represents
      the root of the server's namespace.  From this filehandle, a LOOKUP
      operation can locate any other filehandle on the server. This
      filehandle may be different from the "public" filehandle that may be
      associated with some other directory on the server.
    </t>
    <t>
      PUTROOTFH also clears the current stateid.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTROOTFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READ" title="Operation 25: READ - Read from File" >

  <section toc="exclude" anchor="OP_READ_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct READ4args {
        /* CURRENT_FH: file */
        stateid4        stateid;
        offset4         offset;
        count4          count;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READ_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct READ4resok {
        bool            eof;
        opaque          data&lt;>;
};

union READ4res switch (nfsstat4 status) {
 case NFS4_OK:
         READ4resok     resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READ_DESCRIPTION" title="DESCRIPTION">
    <t>
      The READ operation reads data from the regular file identified by the
      current filehandle.
    </t>
    <t>
      The client provides an offset of where the READ is to start and a
      count of how many bytes are to be read.  An offset of zero means
      to read data starting at the beginning of the file.  If offset is
      greater than or equal to the size of the file, the status NFS4_OK is
      returned with a data length set to zero and eof is set to TRUE.
      The READ is subject to access permissions checking.
    </t>
    <t>
      If the client specifies a count value of zero, the READ succeeds
      and returns zero bytes of data again subject to access permissions
      checking.  The server may choose to return fewer bytes than specified
      by the client.  The client needs to check for this condition and
      handle the condition appropriately.
    </t>
    <t>
      Except when special stateids are used, the 
      stateid value for a READ request represents a value returned from
      a previous byte-range lock or share reservation request or the stateid
      associated with a delegation.  The stateid identifies the associated
      owners if any and is 
      used by the server to verify that the associated locks are still
      valid (e.g., have not been revoked).
    </t>
    <t>
      If the read ended at the end-of-file (formally, in a correctly formed
      READ operation, if offset + count is equal to the size of the file), or
      the READ operation extends beyond the size of the file (if offset +
      count is greater than the size of the file), eof is returned as TRUE;
      otherwise, it is FALSE.  A successful READ of an empty file will always
      return eof as TRUE.
    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      For a READ with a stateid value of all bits equal to zero, the server MAY allow
      the READ to be serviced subject to mandatory byte-range locks or the current
      share deny modes for the file.  For a READ with a stateid value of all
      bits equal to one, the server MAY allow READ operations to bypass locking checks
      at the server.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READ_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server returns a "short read" (i.e., fewer data than requested and eof is set to FALSE), the client should send another READ to get the
      remaining data.  A server may return less data than requested under
      several circumstances.  The file may have been truncated by another
      client or perhaps on the server itself, changing the file size from
      what the requesting client believes to be the case.  This would reduce
      the actual amount of data available to the client.  It is possible
      that the server reduce the transfer size and so return a short
      read result.  Server resource exhaustion may also occur in a
      short read.
    </t>
    <t>
      If mandatory byte-range locking is in effect for the file, and if the byte-range
      corresponding to the data to be read from the file is WRITE_LT locked by an
      owner not associated with the stateid, the server will return the
      NFS4ERR_LOCKED error.  The client should try to get the appropriate
      READ_LT via the LOCK operation before re-attempting the
      READ.  When the READ completes, the client should release the byte-range
      lock via LOCKU.
    </t>
    <t>
      If another client has an OPEN_DELEGATE_WRITE delegation for the file being read,
      the delegation must be recalled, and the 
      operation cannot proceed until that delegation is returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
      Normally, delegations will not be recalled as a result of a READ
      operation since the recall will occur as a result of an earlier
      OPEN.  However, since it is possible for a READ to be done with
      a special stateid, the server needs to check for this case even
      though the client should have done an OPEN previously.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READDIR" title="Operation 26: READDIR - Read Directory" >

  <section toc="exclude" anchor="OP_READDIR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct READDIR4args {
        /* CURRENT_FH: directory */
        nfs_cookie4     cookie;
        verifier4       cookieverf;
        count4          dircount;
        count4          maxcount;
        bitmap4         attr_request;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READDIR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct entry4 {
        nfs_cookie4     cookie;
        component4      name;
        fattr4          attrs;
        entry4          *nextentry;
};

struct dirlist4 {
        entry4          *entries;
        bool            eof;
};

struct READDIR4resok {
        verifier4       cookieverf;
        dirlist4        reply;
};


union READDIR4res switch (nfsstat4 status) {
 case NFS4_OK:
         READDIR4resok  resok4;
 default:
         void;
};


 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READDIR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The READDIR operation retrieves a variable number of entries from a
      file system directory and returns client-requested attributes for each
      entry along with information to allow the client to request additional
      directory entries in a subsequent READDIR.
    </t>
    <t>
      The arguments contain a cookie value that represents where the READDIR
      should start within the directory.  A value of zero for the cookie
      is used to start reading at the beginning of the directory.  For
      subsequent READDIR requests, the client specifies a cookie value that
      is provided by the server on a previous READDIR request.
    </t>
    <t>
      The request's cookieverf field should be set to 0
      zero) when the request's cookie field is zero
      (first read of the directory).  On subsequent requests, the
      cookieverf field must match the cookieverf returned
      by the READDIR in which the cookie was acquired.
      If the server determines that the cookieverf
      is no longer valid for the directory, the error
      NFS4ERR_NOT_SAME must be returned.

    </t>
    <t>
      The dircount field of the request is a hint of the maximum number
      of bytes of directory information that should be returned.  This value
      represents the total length of the names of the directory entries and the
      cookie value for these entries.  This length represents the XDR
      encoding of the data (names and cookies) and not the length in the
      native format of the server.
    </t>
    <t>
      The maxcount field of the request represents the maximum
      total size of all of the data being returned within
      the READDIR4resok structure and includes the XDR
      overhead.  The server MAY return less data.  If the
      server is unable to return a single directory entry
      within the maxcount limit, the error NFS4ERR_TOOSMALL
      MUST be returned to the client.

    </t>
    <t>
      Finally, the request's attr_request field represents
      the list of attributes to be returned for each
      directory entry supplied by the server.

    </t>
    <t>
      A successful reply consists of a list of
      directory entries.  Each of these entries contains the name of the
      directory entry, a cookie value for that entry, and the associated
      attributes as requested.  The "eof" flag has a value of TRUE if there
      are no more entries in the directory.
    </t>
    <t>
      The cookie value is only meaningful to the server and is used 
      as a cursor for the directory entry.  As mentioned, this cookie 
      is used by the client for subsequent READDIR operations so that it may
      continue reading a directory.  The cookie is similar in concept to a
      READ offset but MUST NOT be interpreted as such by the client.
      Ideally, the cookie value SHOULD NOT change if the directory is
      modified since the client may be caching these values.
    </t>
    <t>
      In some cases, the server may encounter an error while obtaining the
      attributes for a directory entry.  Instead of returning an error for
      the entire READDIR operation, the server can instead return the
      attribute rdattr_error (<xref target="attrdef_rdattr_error"/>).  With this, the server is able to
      communicate the failure to the client and not fail the entire
      operation in the instance of what might be a transient failure.
      Obviously, the client must request the fattr4_rdattr_error attribute
      for this method to work properly.  If the client does not request the
      attribute, the server has no choice but to return failure for the
      entire READDIR operation.
    </t>
    <t>
      For some file system environments, the directory entries "." and ".."
      have special meaning, and in other environments, they do not.  If the
      server supports these special entries within a directory, they SHOULD
      NOT be returned to the client as part of the READDIR response.  To
      enable some client environments, the cookie values of zero, 1, and 2 are
      to be considered reserved.  Note that the UNIX client will use these
      values when combining the server's response and local representations
      to enable a fully formed UNIX directory presentation to the
      application.
    </t>
    <t>
      For READDIR arguments, cookie values of one and two SHOULD NOT be used, and
      for READDIR results, cookie values of zero, one, and two SHOULD NOT be
      returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READDIR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server's file system directory representations
      can differ greatly.  A client's programming
      interfaces may also be bound to the local operating
      environment in a way that does not translate well
      into the NFS protocol.  Therefore, the use of the
      dircount and maxcount fields are provided to enable
      the client to provide hints to the server.  If the
      client is aggressive about attribute collection
      during a READDIR, the server has an idea of how to
      limit the encoded response.

    </t>
    <t>
      If dircount is zero, the server bounds the reply's
      size based on the request's maxcount field.

    </t>
    <t>
      The cookieverf may be used by the server to help manage cookie values
      that may become stale.  It should be a rare occurrence that a server is
      unable to continue properly reading a directory with the provided
      cookie/cookieverf pair.  The server SHOULD make every effort to avoid
      this condition since the application at the client might be unable to
      properly handle this type of failure.
    </t>
    <t>
      The use of the cookieverf will also protect the client from using
      READDIR cookie values that might be stale.  For example, if the file
      system has been migrated, the server might or might not be able to use the
      same cookie values to service READDIR as the previous server used.
      With the client providing the cookieverf, the server is able to
      provide the appropriate response to the client.  This prevents the
      case where the server accepts a cookie value but the underlying
      directory has changed and the response is invalid from the client's
      context of its previous READDIR.
    </t>
    <t>
      Since some servers will not be returning "." and ".." entries as has
      been done with previous versions of the NFS protocol, the client that
      requires these entries be present in READDIR responses must fabricate
      them.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READLINK" title="Operation 27: READLINK - Read Symbolic Link" >

  <section toc="exclude" anchor="OP_READLINK_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: symlink */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_READLINK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct READLINK4resok {
        linktext4       link;
};

union READLINK4res switch (nfsstat4 status) {
 case NFS4_OK:
         READLINK4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READLINK_DESCRIPTION" title="DESCRIPTION">
    <t>
      READLINK reads the data associated with a symbolic
      link.  Depending on the value of the UTF-8 capability
      attribute (<xref target="utf8_caps"/>), the data is encoded
      in UTF-8.
      Whether created by an NFS client or created locally
      on the server, the data in a symbolic link is not
      interpreted (except possibly to check for proper UTF-8
      encoding) when created, but is simply stored.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READLINK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A symbolic link is nominally a pointer to another file.  The data is
      not necessarily interpreted by the server, just stored in the file.
      It is possible for a client implementation to store a pathname that
      is not meaningful to the server operating system in a symbolic link.
      A READLINK operation returns the data to the client for
      interpretation. If different implementations want to share access to
      symbolic links, then they must agree on the interpretation of the data
      in the symbolic link.
    </t>
    <t>
      The READLINK operation is only allowed on objects of type NF4LNK.
      The server should return the error NFS4ERR_WRONG_TYPE if the 
      object is not of type NF4LNK.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_REMOVE" title="Operation 28: REMOVE - Remove File System Object" >

  <section toc="exclude" anchor="OP_REMOVE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct REMOVE4args {
        /* CURRENT_FH: directory */
        component4      target;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_REMOVE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct REMOVE4resok {
        change_info4    cinfo;
};

union REMOVE4res switch (nfsstat4 status) {
 case NFS4_OK:
         REMOVE4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_REMOVE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The REMOVE operation removes (deletes) a directory entry named by
      filename from the directory corresponding to the current filehandle.
      If the entry in the directory was the last reference to the
      corresponding file system object, the object may be destroyed.
      The directory may be either of type NF4DIR or NF4ATTRDIR.
    </t>
    <t>
      For the directory where the filename was removed, the server
      returns change_info4 information in cinfo.  With the atomic field of
      the change_info4 data type, the server will indicate if the before and
      after change attributes were obtained atomically with respect to the
      removal.
    </t>
    <t>
      If the target has a length of zero, or if
      the target does not obey the UTF-8 definition (and
      the server is enforcing UTF-8 encoding; see <xref
      target="utf8_caps"/>), the error NFS4ERR_INVAL will
      be returned.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_REMOVE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      NFSv3 required a different operator RMDIR for directory
      removal and REMOVE for non-directory removal. This allowed clients to
      skip checking the file type when being passed a non-directory delete
      system call (e.g., <xref target="unlink">unlink()</xref> in POSIX) to remove a directory, as well as
      the converse (e.g., a rmdir() on a non-directory) because they knew the
      server would check the file type.  NFSv4.1 REMOVE can be used to
      delete any directory entry independent of its file type. The
      implementor of an NFSv4.1 client's entry points from the
      unlink() and rmdir() system calls should first check the file type
      against the types the system call is allowed to remove before sending
      a REMOVE operation. Alternatively, the implementor can produce a COMPOUND call
      that includes a LOOKUP/VERIFY sequence of operations to verify the file type before
      a REMOVE operation in the same COMPOUND call.
    </t>
    <t>
      The concept of last reference is server
      specific. However, if the numlinks field in the
      previous attributes of the object had the value 1,
      the client should not rely on referring to the
      object via a filehandle. Likewise, the client
      should not rely on the resources (disk space,
      directory entry, and so on) formerly associated
      with the object becoming immediately available.
      Thus, if a client needs to be able to continue to
      access a file after using REMOVE to remove it, the
      client should take steps to make sure that the file
      will still be accessible.  While the traditional
      mechanism used is to RENAME the file from its old
      name to a new hidden name, the NFSv4.1 OPEN operation
      MAY return a result flag, OPEN4_RESULT_PRESERVE_UNLINKED,
      which indicates to the client that the file will be
      preserved if the file has an outstanding open (see <xref
      target="OP_OPEN"/>).

    </t>
    <t>
      If the server finds that the file is still open when the REMOVE
      arrives:
      <list style='symbols'>
        <t>
          The server SHOULD NOT delete the file's directory entry if the 
          file was opened with OPEN4_SHARE_DENY_WRITE or 
          OPEN4_SHARE_DENY_BOTH.
        </t>
        <t>
          If the file was not opened with OPEN4_SHARE_DENY_WRITE or
          OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's 
          directory entry.  However, until last CLOSE of the file, 
          the server MAY continue to allow access to the file via 
          its filehandle.
      </t>
      <t>
          The server MUST NOT delete the directory
          entry if the reply from OPEN had the flag
          OPEN4_RESULT_PRESERVE_UNLINKED set.

      </t>
          
      </list>
    </t>
    <t>
      The server MAY implement its own restrictions on removal
      of a file while it is open. The server might disallow
      such a REMOVE (or a removal that occurs
      as part of RENAME). The conditions that influence the restrictions
      on removal of a file while it is still open include:
      <list style='symbols'>
      <t>
        Whether certain access protocols (i.e., not just
        NFS) are holding the file open.

      </t>

      <t>
        Whether particular options, access modes, or policies on the
        server are enabled.
      </t>

      </list>
    </t>

    <t>
      If a file has an outstanding OPEN and this prevents the
      removal of the file's directory entry,
      the error NFS4ERR_FILE_OPEN is returned.

    </t>

    <t>
      Where the determination above cannot be made
      definitively because delegations are being held,
      they MUST be recalled to allow processing of the
      REMOVE to continue.  When a delegation is held,
      the server has no reliable  knowledge of the status of OPENs for
      that client, so unless
      there are files opened with the particular deny modes
      by clients without delegations, the determination
      cannot be made until delegations are recalled, and
      the operation cannot proceed until each sufficient
      delegation has been returned or revoked to allow
      the server to make a correct determination.
    </t>
    <t>
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while
      delegations remain outstanding.
    </t>

    <t>
      If the current filehandle designates a directory for
      which another client holds a directory delegation,
      then, unless the situation can be resolved by sending
      a notification, the directory delegation MUST be
      recalled, and the operation MUST NOT proceed until
      the delegation is returned or revoked.  Except where
      this happens very quickly, one or more NFS4ERR_DELAY
      errors will be returned to requests made while
      delegation remains outstanding.

    </t>
    <t>
      When the current filehandle designates a directory
      for which one or more directory delegations
      exist, then, when those delegations request
      such notifications, NOTIFY4_REMOVE_ENTRY will be
      generated as a result of this operation.
    </t>

    <t>
      Note that when a remove occurs as a result of a
      RENAME, NOTIFY4_REMOVE_ENTRY will only be generated
      if the removal happens as a separate operation.
      In the case in which the removal is integrated and
      atomic with RENAME, the notification of the removal
      is integrated with notification for the RENAME. See
      the discussion of the NOTIFY4_RENAME_ENTRY
      notification in <xref target="OP_CB_NOTIFY"/>.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RENAME" title="Operation 29: RENAME - Rename Directory Entry" >

  <section toc="exclude" anchor="OP_RENAME_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct RENAME4args {
        /* SAVED_FH: source directory */
        component4      oldname;
        /* CURRENT_FH: target directory */
        component4      newname;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RENAME_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RENAME4resok {
        change_info4    source_cinfo;
        change_info4    target_cinfo;
};

union RENAME4res switch (nfsstat4 status) {
 case NFS4_OK:
        RENAME4resok    resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RENAME_DESCRIPTION" title="DESCRIPTION">
    <t>
      The RENAME operation renames the object identified by oldname in the
      source directory corresponding to the saved filehandle, as set by the
      SAVEFH operation, to newname in the target directory corresponding to
      the current filehandle.  The operation is required to be atomic to the
      client.  Source and target directories MUST reside on the same
      file system on the server.  On success, the current filehandle will
      continue to be the target directory.
    </t>
    <t>
      If the target directory already contains an entry with the name
      newname, the source object MUST be compatible with the target: either
      both are non-directories or both are directories and the target MUST
      be empty.
      If compatible, the existing target is removed before the
      rename occurs or, preferably, the target is removed atomically as
      part of the rename.
      See <xref target="OP_REMOVE_IMPLEMENTATION" />
      for client and server actions whenever a target is removed.  
      Note however that when the removal is performed atomically with the
      rename, certain parts of the removal described there are integrated
      with the rename.  For example, notification of the removal will not
      be via a NOTIFY4_REMOVE_ENTRY but will be indicated as part of the
      NOTIFY4_ADD_ENTRY or NOTIFY4_RENAME_ENTRY generated by the rename.
    </t> 
    <t>
      If the source object and the target are not
      compatible or if the target is a directory but not empty, the server
      will return the error NFS4ERR_EXIST.
    </t>
    <t>
      If oldname and newname both refer to the same
      file (e.g., they might be hard links of each
      other), then unless the file is open (see <xref
      target="OP_RENAME_IMPLEMENTATION"/>), RENAME MUST
      perform no action and return NFS4_OK.

    </t>
    <t>
      For both directories involved in the RENAME, the server returns
      change_info4 information.  With the atomic field of the change_info4
      data type, the server will indicate if the before and after change
      attributes were obtained atomically with respect to the rename.
    </t>
    <t>
      If oldname refers to a named attribute and the saved and current
      filehandles refer to different file system objects, the server will
      return NFS4ERR_XDEV just as if the saved and current filehandles
      represented directories on different file systems.
    </t>
    <t>
      If oldname or newname has a length of zero, or if oldname or
      newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
      will be returned.
    </t>
  </section>

  <section toc="exclude" anchor="OP_RENAME_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MAY impose restrictions on the RENAME
      operation such that RENAME may not be done when the
      file being renamed is open or when that open is done
      by particular protocols, or with particular options
      or access modes.  Similar restrictions may be applied
      when a file exists with the target name and is open.
      When RENAME is rejected because of such restrictions,
      the error NFS4ERR_FILE_OPEN is returned.

    </t>
    <t>
      When oldname and rename refer to the same file and
      that file is open in a fashion such that RENAME
      would normally be rejected with NFS4ERR_FILE_OPEN
      if oldname and newname were different files, then
      RENAME SHOULD be rejected with NFS4ERR_FILE_OPEN.

    </t>
    <t>
      If a server does implement such restrictions and those restrictions
      include cases of NFSv4 opens preventing successful execution of
      a rename, the server needs to recall any delegations that could
      hide the existence of opens relevant to that decision.  This is 
      because when a client holds a delegation, the server
      might not have an accurate account of the opens for that client, since
      the client may execute OPENs and CLOSEs locally.  The RENAME operation
      need only be delayed until a definitive result can be obtained.  For
      example, if there are multiple delegations and one of them establishes
      an open whose presence would prevent the rename, given the server's 
      semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon
      as that delegation is returned without waiting for other delegations
      to be returned.  Similarly, if such opens are not associated with 
      delegations, NFS4ERR_FILE_OPEN can be returned immediately with no 
      delegation recall being done.
    </t>
    <t>
      If the current filehandle or the saved filehandle designates a 
      directory for which another client holds a directory delegation, 
      then, unless the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current and saved filehandles are the
      same and they designate a directory for which one
      or more directory delegations exist, then, when
      those delegations request such notifications,
      a notification of type NOTIFY4_RENAME_ENTRY
      will be generated as a result of this operation.
      When oldname and rename refer to the same file,
      no notification is generated (because, as <xref
      target="OP_RENAME_DESCRIPTION"/> states, the server
      MUST take no action).  When a file is removed
      because it has the same name as the target, if
      that removal is done atomically with the rename,
      a NOTIFY4_REMOVE_ENTRY notification will not be
      generated.  Instead, the deletion of the file will
      be reported as part of the NOTIFY4_RENAME_ENTRY
      notification.

    </t>
    <t>
      When the current and saved filehandles are not the same:
      <list style="symbols">
        <t>
          If the current filehandle designates a directory for which 
          one or more directory delegations exist, then, when those 
          delegations request such notifications, NOTIFY4_ADD_ENTRY 
          will be generated as a result of this operation.  When a file 
          is removed because it has the same name as the target, if that 
          removal is done atomically with the rename, a
          NOTIFY4_REMOVE_ENTRY notification will not be generated.  
          Instead, the deletion of the file will be reported as part 
          of the NOTIFY4_ADD_ENTRY notification.
        </t>
        <t>
          If the saved filehandle designates a directory for which 
          one or more directory delegations exist, then, when those 
          delegations request such notifications, NOTIFY4_REMOVE_ENTRY 
          will be generated as a result of this operation.
        </t>
      </list> 

    </t>    
    <t>
      If the object being renamed has file delegations
      held by clients other than the one doing the RENAME,
      the delegations MUST be recalled, and the 
      operation cannot proceed  
      until each such delegation is returned 
      or revoked.  Note that in the case of multiply linked files,
      the delegation recall requirement applies even if the 
      delegation was obtained through a different name than the
      one being renamed.  
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while the
      delegation(s) remains outstanding, although it might not do that if the
      delegations are returned quickly.
    </t>
    <t>
      The RENAME operation must be atomic to the client.  The statement
      "source and target directories MUST reside on the same file system 
      on the server"
      means that the fsid fields in the attributes for the
      directories are the same. If they reside on different file systems,
      the error NFS4ERR_XDEV is returned.
    </t>
    <t>
      Based on the value of the fh_expire_type attribute for the object, the
      filehandle may or may not expire on a RENAME.  However, server
      implementors are strongly encouraged to attempt to keep filehandles
      from expiring in this fashion.
    </t>
    <t>
      On some servers, the file names "." and ".." are illegal as either
      oldname or newname, and will result in the error NFS4ERR_BADNAME.
      In addition, on many servers the case of oldname or newname being
      an alias for the source directory will be checked for.  Such servers
      will return the error NFS4ERR_INVAL in these cases.
    </t>
    <t>
      If either of the source or target filehandles are not directories, the
      server will return NFS4ERR_NOTDIR.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RESTOREFH" title="Operation 31: RESTOREFH - Restore Saved Filehandle" >

  <section toc="exclude" anchor="OP_RESTOREFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* SAVED_FH: */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_RESTOREFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RESTOREFH4res {
        /*
         * If status is NFS4_OK,
         *     new CURRENT_FH: value of saved fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RESTOREFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      The RESTOREFH operation sets the current filehandle and stateid to the values in the
      saved filehandle and stateid.  If 
      there is no saved filehandle, then the server will
      return the error NFS4ERR_NOFILEHANDLE.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_RESTOREFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Operations like OPEN and LOOKUP use the current filehandle
      to represent a directory and replace it with a new filehandle.
      Assuming that the previous filehandle was saved with a SAVEFH operator,
      the previous filehandle can be restored as the current filehandle.
      This is commonly used to obtain post-operation attributes for
      the directory, e.g.,
      <figure>
	<artwork>
      PUTFH (directory filehandle)
      SAVEFH
      GETATTR attrbits     (pre-op dir attrs)
      CREATE optbits "foo" attrs
      GETATTR attrbits     (file attributes)
      RESTOREFH
      GETATTR attrbits     (post-op dir attrs)
	</artwork>
      </figure>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SAVEFH" title="Operation 32: SAVEFH - Save Current Filehandle" >

  <section toc="exclude" anchor="OP_SAVEFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: */
void;
      </artwork>
    </figure>
  </section>


  <section toc="exclude" anchor="OP_SAVEFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct SAVEFH4res {
        /*
         * If status is NFS4_OK,
         *    new SAVED_FH: value of current fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_SAVEFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SAVEFH operation saves the current filehandle and stateid.
      If a previous filehandle was saved, then
      it is no longer accessible.  The saved filehandle can be restored as
      the current filehandle with the RESTOREFH operator.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SAVEFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SECINFO" title="Operation 33: SECINFO - Obtain Available Security" >

  <section toc="exclude" anchor="OP_SECINFO_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct SECINFO4args {
        /* CURRENT_FH: directory */
        component4      name;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SECINFO_RESULTS" title="RESULTS">
<figure>
 <artwork>
/*
 * From RFC 2203
 */
enum rpc_gss_svc_t {
        RPC_GSS_SVC_NONE        = 1,
        RPC_GSS_SVC_INTEGRITY   = 2,
        RPC_GSS_SVC_PRIVACY     = 3
};

struct rpcsec_gss_info {
        sec_oid4        oid;
        qop4            qop;
        rpc_gss_svc_t   service;
};

/* RPCSEC_GSS has a value of '6' - See RFC 2203 */
union secinfo4 switch (uint32_t flavor) {
 case RPCSEC_GSS:
         rpcsec_gss_info        flavor_info;
 default:
         void;
};

typedef secinfo4 SECINFO4resok&lt;>;

union SECINFO4res switch (nfsstat4 status) {
 case NFS4_OK:
        /* CURRENTFH: consumed */
         SECINFO4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_SECINFO_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SECINFO operation is used by the client to obtain a list of
      valid RPC authentication flavors for a specific directory
      filehandle, file name pair.  SECINFO should apply the same
      access methodology used for LOOKUP when evaluating the name.
      Therefore, if the requester does not have the appropriate access
      to LOOKUP the name, then SECINFO MUST behave the same way and
      return NFS4ERR_ACCESS.
    </t>
    <t>
      The result will contain an array that represents the security
      mechanisms available, with an order corresponding to the
      server's preferences, the most preferred being first in the
      array. The client is free to pick whatever security mechanism it
      both desires and supports, or to pick in the server's preference
      order the first one it supports.  The array entries are
      represented by the secinfo4 structure.  The field 'flavor' will
      contain a value of AUTH_NONE, AUTH_SYS (as defined in <xref
      target="RFC5531">RFC 5531</xref>), or RPCSEC_GSS (as defined in
      <xref target="RFC2203">RFC 2203</xref>). The field flavor can
      also be any other security flavor registered with IANA.
    </t>
    <t>
      For the flavors AUTH_NONE and AUTH_SYS, no additional security
      information is returned.  The same is true of many (if not most)
      other security flavors, including AUTH_DH. For a return value of
      RPCSEC_GSS, a security triple is returned that contains the
      mechanism object identifier (OID, as defined in <xref
      target="RFC2743">RFC 2743</xref>), the quality of protection (as
      defined in <xref target="RFC2743">RFC 2743</xref>), and the
      service type (as defined in <xref
      target="RFC2203">RFC 2203</xref>).  It is possible for SECINFO to
      return multiple entries with flavor equal to RPCSEC_GSS with
      different security triple values.
    </t>
    <t>
      On success, the current filehandle is consumed (see
      <xref target="aftersecinfo" />), and if the
      next operation after SECINFO tries to use the current filehandle,
      that operation will fail with the status NFS4ERR_NOFILEHANDLE.
    </t>
    <t>
      If the name has a length of zero, or if the name does not obey
      the UTF-8 definition (assuming UTF-8 capabilities are enabled; see
      <xref target="utf8_caps"/>), the error NFS4ERR_INVAL will be returned.
    </t>
    <t>
      See <xref target="Security Service Negotiation"/>
      for additional information on the use of SECINFO.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_IMPLEMENTATION" title="IMPLEMENTATION">
        <t>
          The SECINFO operation is expected to be used by the NFS client
          when the error value of NFS4ERR_WRONGSEC is returned from
          another NFS operation.  This signifies to the client that the
          server&apos;s security policy is different from what the client is
          currently using.  At this point, the client is expected to
          obtain a list of possible security flavors and choose what best
          suits its policies.
        </t>
        <t>
          As mentioned, the server&apos;s security
          policies will determine when a client
          request receives NFS4ERR_WRONGSEC.  See <xref
          target="error_op_returns"/> for a list of operations
          that can return NFS4ERR_WRONGSEC. In addition,
          when READDIR returns attributes, the rdattr_error
          (<xref target="attrdef_rdattr_error" />)
          can contain NFS4ERR_WRONGSEC. Note that CREATE and
          REMOVE MUST NOT return NFS4ERR_WRONGSEC. The
          rationale for CREATE is that unless the
          target name exists, it cannot have a separate
          security policy from the parent directory,
          and the security policy of the parent was
          checked when its filehandle was injected into
          the COMPOUND request's operations stream (for
          similar reasons, an OPEN operation that creates
          the target MUST NOT return NFS4ERR_WRONGSEC). If
          the target name exists, while it might have a
          separate security policy, that is irrelevant
          because CREATE MUST return NFS4ERR_EXIST.
          The rationale for REMOVE is that while that
          target might have a separate security policy, the
          target is going to be removed, and so the
          security policy of the parent trumps that of the
          object being removed. RENAME and LINK MAY return
          NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error
          applies only to the saved filehandle (see <xref
          target="link_rename"/>). Any NFS4ERR_WRONGSEC
          error on the current filehandle used by LINK and
          RENAME MUST be returned by the PUTFH, PUTPUBFH,
          PUTROOTFH, or RESTOREFH operation that injected
          the current filehandle.

        </t>
        <t>
          With the exception of LINK and RENAME,
          the set of operations that can return NFS4ERR_WRONGSEC
          represents the point at which the client can inject a
          filehandle into the "current filehandle" at the server.  The
          filehandle is either provided by the client (PUTFH, PUTPUBFH,
          PUTROOTFH), generated as a result of a name-to-filehandle
          translation (LOOKUP and OPEN), or generated from the saved filehandle
          via RESTOREFH. As <xref target="PUTFH + SAVEFH"/> states,
          a put filehandle operation followed by SAVEFH MUST NOT
          return NFS4ERR_WRONGSEC. Thus, the RESTOREFH operation, under
          certain conditions (see <xref target="putfh_series"/>), is
          permitted to return NFS4ERR_WRONGSEC so that security policies
          can be honored.

        </t>

        <t>
          The READDIR operation will not directly return the
          NFS4ERR_WRONGSEC error.  However, if the READDIR request
          included a request for attributes, it is possible that the
          READDIR request&apos;s security triple did not match that of a
          directory entry.  If this is the case and the client has
          requested the rdattr_error attribute, the server will return the
          NFS4ERR_WRONGSEC error in rdattr_error for the entry.
        </t>

        <t>
          To resolve an error return of
          NFS4ERR_WRONGSEC, the client does the following:
        </t>

        <t>
          <list style="symbols">
            <t>
              For LOOKUP and OPEN, the client will use SECINFO with the
              same current filehandle and name as provided in the
              original LOOKUP or OPEN to enumerate the available security
              triples.

            </t>
            <t>
              For the rdattr_error, the client will use
              SECINFO with the same current filehandle
              as provided in the original READDIR. The
              name passed to SECINFO will be that of the
              directory entry (as returned from READDIR)
              that had the NFS4ERR_WRONGSEC error in the
              rdattr_error attribute.

            </t>
            <t>
              For PUTFH, PUTROOTFH, PUTPUBFH,
              RESTOREFH, LINK, and RENAME, the client will
              use SECINFO_NO_NAME { style =
              SECINFO_STYLE4_CURRENT_FH }. The client
              will prefix the SECINFO_NO_NAME operation
              with the appropriate PUTFH, PUTPUBFH,
              or PUTROOTFH operation that provides the
              filehandle originally provided by the PUTFH,
              PUTPUBFH, PUTROOTFH, or RESTOREFH operation.

              <vspace blankLines='1' />

              NOTE: In NFSv4.0, the client was required
              to use SECINFO, and had to reconstruct the
              parent of the original filehandle and the
              component name of the original filehandle. The
              introduction in NFSv4.1 of SECINFO_NO_NAME
              obviates the need for reconstruction.

            </t>
            <t>
              For LOOKUPP, the client will
              use SECINFO_NO_NAME { style =
              SECINFO_STYLE4_PARENT } and provide the
              filehandle that equals the filehandle
              originally provided to LOOKUPP.

            </t>           
          </list>
        </t>

        <t>
          See <xref target="securityconsider"/> for a discussion on
          the recommendations for the security flavor used by SECINFO and
          SECINFO_NO_NAME.
        </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SETATTR" title="Operation 34: SETATTR - Set Attributes" >

  <section toc="exclude" anchor="OP_SETATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct SETATTR4args {
        /* CURRENT_FH: target object */
        stateid4        stateid;
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SETATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct SETATTR4res {
        nfsstat4        status;
        bitmap4         attrsset;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SETATTR operation changes one or more of the attributes of a
      file system object.  The new attributes are specified with a bitmap and
      the attributes that follow the bitmap in bit order.
    </t>
    <t>
      The stateid argument for SETATTR is used to provide byte-range locking
      context that is necessary for SETATTR requests that set the size
      attribute.  Since setting the size attribute modifies the file's data,
      it has the same locking requirements as a corresponding WRITE.  Any
      SETATTR that sets the size attribute is incompatible with a share
      reservation that specifies OPEN4_SHARE_DENY_WRITE.  The area between the old
      end-of-file and the new end-of-file is considered to be modified just
      as would have been the case had the area in question been specified as
      the target of WRITE, for the purpose of checking conflicts with byte-range
      locks, for those cases in which a server is implementing mandatory
      byte-range locking behavior.  A valid stateid SHOULD always be specified.
      When the file size attribute is not set, the special stateid
      consisting of all bits equal to zero MAY be passed.
    </t>
    <t>
      On either success or failure of the operation, the server will return
      the attrsset bitmask to represent what (if any) attributes were
      successfully set.  The attrsset in the response is a subset of the
      attrmask field of the obj_attributes field in the argument.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the request specifies the owner attribute to be set, the server
      SHOULD allow the operation to succeed if the current owner of the
      object matches the value specified in the request.  Some servers may
      be implemented in a way as to prohibit the setting of the owner
      attribute unless the requester has privilege to do so.  If the server
      is lenient in this one case of matching owner values, the client
      implementation may be simplified in cases of creation of an object
      (e.g., an exclusive create via OPEN)
      followed by a SETATTR.
    </t>
    <t>
      The file size attribute is used to request changes
      to the size of a file. A value of zero causes the
      file to be truncated, a value less than the current
      size of the file causes data from new size to the
      end of the file to be discarded, and a size greater
      than the current size of the file causes logically
      zeroed data bytes to be added to the end of the
      file.  Servers are free to implement this using
      unallocated bytes (holes) or allocated data bytes
      set to zero. Clients should not make any assumptions
      regarding a server's implementation of this feature,
      beyond that the bytes in the affected byte-range returned by
      READ will be zeroed.  Servers MUST support extending
      the file size via SETATTR.

    </t>
    <t>
      SETATTR is not guaranteed to be atomic.  A failed SETATTR may partially
      change a file's attributes, hence the reason why the reply always
      includes the status and the list of attributes that were set.
    </t>
    <t>
      If the object whose attributes are being changed has a file delegation 
      that is held by a client other than the one doing the SETATTR,
      the delegation(s) must be recalled, and the 
      operation cannot proceed to actually change an attribute 
      until each such delegation is returned 
      or revoked.  
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while the
      delegation(s) remains outstanding, although it might not do that if the
      delegations are returned quickly.
    </t>
    <t>
      If the object whose attributes are being set is a directory
      and another client holds a directory delegation for that 
      directory, then if enabled, asynchronous notifications will be generated
      when the set of attributes changed has a non-null intersection 
      with the set of attributes for which notification is requested.
      Notifications of type NOTIFY4_CHANGE_DIR_ATTRS will be sent to 
      the appropriate client(s), but the SETATTR is not delayed by 
      waiting for these notifications to be sent.
    </t>
    <t>
      If the object whose attributes are being set is a member of
      the directory for which another client holds a directory delegation,
      then asynchronous notifications will be generated
      when the set of attributes changed has a non-null intersection 
      with the set of attributes for which notification is requested.
      Notifications of type NOTIFY4_CHANGE_CHILD_ATTRS will be sent to 
      the appropriate clients, but the SETATTR is not delayed by 
      waiting for these notifications to be sent.
    </t>
    <t>
      Changing the size of a file with SETATTR indirectly
      changes the time_modify and change attributes.
      A client must account for this as size changes can
      result in data deletion.

    </t>
    <t>
      The attributes time_access_set and time_modify_set are write-only
      attributes constructed as a switched union so the client can direct
      the server in setting the time values.  If the switched union
      specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
      be used for the operation.  If the switch union does not specify
      SET_TO_CLIENT_TIME4, the server is to use its current time for the
      SETATTR operation.
    </t>
    <t>
      If server and client times differ, programs that compare client time
      to file times can break. A time synchronization protocol should be used to
      limit client/server time skew.
    </t>
    <t>
      Use of a COMPOUND containing a VERIFY operation specifying only the
      change attribute, immediately followed by a SETATTR, provides a means
      whereby a client may specify a request that emulates the functionality
      of the SETATTR guard mechanism of NFSv3.  Since the function
      of the guard mechanism is to avoid changes to the file attributes
      based on stale information, delays between checking of the guard
      condition and the setting of the attributes have the potential to
      compromise this function, as would the corresponding delay in the 
      NFSv4 emulation.  Therefore, NFSv4.1 servers SHOULD take
      care to avoid such delays, to the degree possible, when executing such
      a request.
    </t>
    <t>
      If the server does not support an attribute as requested by the
      client, the server SHOULD return NFS4ERR_ATTRNOTSUPP.
    </t>
    <t>
      A mask of the attributes actually set is returned by SETATTR in all
      cases.  That mask MUST NOT include attribute bits not requested to be
      set by the client. 
If the attribute masks in the request and
      reply are equal, the status field in the reply MUST be NFS4_OK.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_VERIFY" title="Operation 37: VERIFY - Verify Same Attributes" >

  <section toc="exclude" anchor="OP_VERIFY_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct VERIFY4args {
        /* CURRENT_FH: object */
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_VERIFY_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct VERIFY4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_VERIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The VERIFY operation is used to verify that attributes have the value
      assumed by the client before proceeding with the following operations in
      the COMPOUND request.  If any of the attributes do not match, then the
      error NFS4ERR_NOT_SAME must be returned.  The current filehandle
      retains its value after successful completion of the operation.
    </t>
  </section>
  <section toc="exclude" anchor="OP_VERIFY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      One possible use of the VERIFY operation is the following series
      of operations. With this, the client is attempting to verify that the file
      being removed will match what the client expects to be removed.  This
      series can help prevent the unintended deletion of a file.
      <figure>
	<artwork>
      PUTFH (directory filehandle)
      LOOKUP (file name)
      VERIFY (filehandle == fh)
      PUTFH (directory filehandle)
      REMOVE (file name)
	</artwork>
      </figure>
      This series does not prevent a second client from removing and
      creating a new file in the middle of this sequence, but it does help
      avoid the unintended result.
    </t>
    <t>
      In the case that a RECOMMENDED attribute is specified in the VERIFY
      operation and the server does not support that attribute for the
      file system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
      client.
    </t>
    <t>
      When the attribute rdattr_error or any set-only attribute (e.g.,
      time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
      the client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_WRITE" title="Operation 38: WRITE - Write to File" >

  <section toc="exclude" anchor="OP_WRITE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
enum stable_how4 {
        UNSTABLE4       = 0,
        DATA_SYNC4      = 1,
        FILE_SYNC4      = 2
};

struct WRITE4args {
        /* CURRENT_FH: file */
        stateid4        stateid;
        offset4         offset;
        stable_how4     stable;
        opaque          data&lt;>;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_WRITE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct WRITE4resok {
        count4          count;
        stable_how4     committed;
        verifier4       writeverf;
};

union WRITE4res switch (nfsstat4 status) {
 case NFS4_OK:
         WRITE4resok    resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_WRITE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The WRITE operation is used to write data to a regular file.  The
      target file is specified by the current filehandle.  The offset
      specifies the offset where the data should be written.  An offset of zero
      specifies that the write should start at the beginning of the
      file.  The count, as encoded as part of the opaque data parameter,
      represents the number of bytes of data that are to be written.  If the
      count is zero, the WRITE will succeed and return a count of zero subject to permissions checking.  The server MAY
      write fewer bytes than requested by the client.
    </t>
    <t>
      The client specifies with the stable parameter the method
      of how the data is to be processed by the server.  If stable is
      FILE_SYNC4, the server MUST commit the data written plus all
      file system metadata to stable storage before returning results. This
      corresponds to the NFSv2 protocol semantics.  Any other
      behavior constitutes a protocol violation.  If stable is DATA_SYNC4,
      then the server MUST commit all of the data to stable storage and
      enough of the metadata to retrieve the data before returning.  The
      server implementor is free to implement DATA_SYNC4 in the same fashion
      as FILE_SYNC4, but with a possible performance drop.  If stable is
      UNSTABLE4, the server is free to commit any part of the data and the
      metadata to stable storage, including all or none, before returning a
      reply to the client. There is no guarantee whether or when any
      uncommitted data will subsequently be committed to stable storage. The
      only guarantees made by the server are that it will not destroy any
      data without changing the value of writeverf and that it will not commit
      the data and metadata at a level less than that requested by the
      client.
    </t>
    <t>
      Except when special stateids are used, the 
      stateid value for a WRITE request represents a value returned from
      a previous byte-range LOCK or OPEN request or the stateid
      associated with a delegation.  The stateid identifies the associated
      owners if any and is 
      used by the server to verify that the associated locks are still
      valid (e.g., have not been revoked).
    </t>
    <t>
      Upon successful completion, the following results are returned.  The
      count result is the number of bytes of data written to the file. The
      server may write fewer bytes than requested. If so, the actual number
      of bytes written starting at location, offset, is returned.
    </t>
    <t>
      The server also returns an indication of the level of commitment of
      the data and metadata via committed.
      Per <xref target="stable_committed"/>,
      <list style='symbols'>
      <t>
        The server MAY commit the data at a stronger level
        than requested.

      </t>

      <t>
        The server MUST commit the data at a level at
        least as high as that committed.

      </t>
      </list>

    </t>

    <texttable anchor="stable_committed">

    <preamble>
       Valid combinations of the fields stable in the request and committed in
       the reply.

    </preamble>

    <ttcol>stable</ttcol>

    <ttcol>committed</ttcol>

    <c>UNSTABLE4</c>   <c>FILE_SYNC4, DATA_SYNC4, UNSTABLE4</c>

    <c>DATA_SYNC4</c>  <c>FILE_SYNC4, DATA_SYNC4</c>

    <c>FILE_SYNC4</c>  <c>FILE_SYNC4</c>

    </texttable>
     
    <t>
      The final portion of the result is the field
      writeverf. This field is the write verifier and is a
      cookie that the client can use to determine whether
      a server has changed instance state (e.g., server
      restart) between a call to WRITE and a subsequent
      call to either WRITE or COMMIT.  This cookie MUST be
      unchanged during a single instance of the NFSv4.1
      server and MUST be unique between instances of the
      NFSv4.1 server. If the cookie changes, then the
      client MUST assume that any data written with an
      UNSTABLE4 value for committed and an old writeverf in the reply
      has been lost and will need to be recovered.

    </t>
    <t>
      If a client writes data to the server with the stable argument set to
      UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
      UNSTABLE4, the client will follow up some time in the future with a
      COMMIT operation to synchronize outstanding asynchronous data and
      metadata with the server's stable storage, barring client error. It is
      possible that due to client crash or other error that a subsequent
      COMMIT will not be received by the server.
    </t>
    <t>
      For a WRITE with a stateid value of all bits equal to zero, the server MAY allow
      the WRITE to be serviced subject to mandatory byte-range locks or the
      current share deny modes for the file.  For a WRITE with a stateid
      value of all bits equal to 1, the server MUST NOT allow the WRITE operation to
      bypass locking checks at the server and otherwise is
      treated as if a stateid of all bits equal to zero were used.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_WRITE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      It is possible for the server to write fewer bytes of data than
      requested by the client.  In this case, the server SHOULD NOT return
      an error unless no data was written at all.  If the server writes less
      than the number of bytes specified, the client will need to send another
      WRITE to write the remaining data.
    </t>
    <t>
      It is assumed that the act of writing data to
      a file will cause the time_modified and change
      attributes of the file to be updated.  However,
      these attributes SHOULD NOT be changed
      unless the contents of the file are changed.  Thus,
      a WRITE request with count set to zero SHOULD NOT cause
      the time_modified and change attributes of the file to be updated.

    </t>
    <t>
      Stable storage is persistent storage that survives:
    </t>
    <t>
      <list style="numbers">
	<t>
	  Repeated power failures.
	</t>
	<t>
	  Hardware failures (of any board, power supply, etc.).
	</t>
	<t>
	  Repeated software crashes and restarts.
	</t>
      </list>
    </t>
    <t>
      This definition does not address failure of the stable storage module
      itself.
    </t>
    <t>
      The verifier is defined to allow a client to detect
      different instances of an NFSv4.1 protocol server
      over which cached, uncommitted data may be lost. In
      the most likely case, the verifier allows the client
      to detect server restarts.  This information is
      required so that the client can safely determine
      whether the server could have lost cached data.
      If the server fails unexpectedly and the client has
      uncommitted data from previous WRITE requests (done
      with the stable argument set to UNSTABLE4 and in
      which the result committed was returned as UNSTABLE4
      as well), the server might not have flushed cached
      data to stable storage. The burden of recovery is
      on the client, and the client will need to retransmit
      the data to the server.

    </t>
    <t>
      A suggested verifier would be to use the time that
      the server was last started (if restarting the server
      results in lost buffers).

    </t>
    <t>
      The reply's committed field allows the client to do more
      effective caching.  If the server is committing all WRITE requests to
      stable storage, then it SHOULD return with committed set to FILE_SYNC4,
      regardless of the value of the stable field in the arguments. A server
      that uses an NVRAM accelerator may choose to implement this policy.
      The client can use this to increase the effectiveness of the cache by
      discarding cached data that has already been committed on the server.
    </t>
    <t>
      Some implementations may return NFS4ERR_NOSPC instead
      of NFS4ERR_DQUOT when a user's quota is exceeded.

    </t>
    <t>
      In the case that the current filehandle is of
      type NF4DIR, the server will return NFS4ERR_ISDIR.
      If the current file is a symbolic link, the error
      NFS4ERR_SYMLINK will be returned.  Otherwise, if the
      current filehandle does not designate an ordinary
      file, the server will return NFS4ERR_WRONG_TYPE.

    </t>
    <t>
      If mandatory byte-range locking is in effect for the file,
      and the corresponding byte-range of the data to
      be written to the file is READ_LT or WRITE_LT locked by
      an owner that is not associated with the stateid,
      the server MUST return NFS4ERR_LOCKED. If so,
      the client MUST check if the owner corresponding
      to the stateid used with the WRITE operation has a
      conflicting READ_LT lock that overlaps with the byte-range
      that was to be written. If the stateid's owner has
      no conflicting READ_LT lock, then the client SHOULD try
      to get the appropriate write byte-range lock via the
      LOCK operation before re-attempting the WRITE. When
      the WRITE completes, the client SHOULD release the
      byte-range lock via LOCKU.

    </t>
    <t>
      If the stateid's owner had a conflicting READ_LT lock, then the client
      has no choice but to return an error to the application that attempted
      the WRITE. The reason is that since the stateid's owner had a READ_LT
      lock, either the server attempted to temporarily effectively upgrade
      this READ_LT lock to a WRITE_LT lock or the server has no upgrade
      capability. If the server attempted to upgrade the READ_LT lock and
      failed, it is pointless for the client to re-attempt the upgrade via
      the LOCK operation, because there might be another client also trying
      to upgrade.  If two clients are blocked trying to upgrade the same lock,
      the clients deadlock.  If the server has no upgrade capability, then
      it is pointless to try a LOCK operation to upgrade.
    </t>
    <t>
      If one or more other clients have delegations for the file being 
      written, those delegations MUST be recalled, and the 
      operation cannot proceed until those delegations are returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
      Normally, delegations will not be recalled as a result of a WRITE
      operation since the recall will occur as a result of an earlier
      OPEN.  However, since it is possible for a WRITE to be done with
      a special stateid, the server needs to check for this case even
      though the client should have done an OPEN previously.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_BACKCHANNEL_CTL" title="Operation 40: BACKCHANNEL_CTL - Backchannel Control" >

  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
typedef opaque gsshandle4_t&lt;>;

struct gss_cb_handles4 {
        rpc_gss_svc_t           gcbp_service; /* RFC 2203 */
        gsshandle4_t            gcbp_handle_from_server;
        gsshandle4_t            gcbp_handle_from_client;
};

union callback_sec_parms4 switch (uint32_t cb_secflavor) {
case AUTH_NONE:
        void;
case AUTH_SYS:
        authsys_parms   cbsp_sys_cred; /* RFC 1831 */
case RPCSEC_GSS:
        gss_cb_handles4 cbsp_gss_handles;
};

struct BACKCHANNEL_CTL4args {
        uint32_t                bca_cb_program;
        callback_sec_parms4     bca_sec_parms&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_RESULT" title="RESULT">
<figure>
 <artwork>
struct BACKCHANNEL_CTL4res {
        nfsstat4                bcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The BACKCHANNEL_CTL operation replaces the
      backchannel's callback program number and adds
      (not replaces) RPCSEC_GSS handles for use by the
      backchannel.

    </t>
    <t>
      The arguments of the BACKCHANNEL_CTL call are
      a subset of the CREATE_SESSION parameters.
      In the arguments of BACKCHANNEL_CTL, the
      bca_cb_program field and bca_sec_parms fields
      correspond respectively to the csa_cb_program and
      csa_sec_parms fields of the arguments of CREATE_SESSION
      (<xref target="OP_CREATE_SESSION"/>).

    </t>
    <t>
      BACKCHANNEL_CTL MUST appear in a COMPOUND that starts
      with SEQUENCE.

    </t>
    <t>
      If the RPCSEC_GSS handle identified by 
      gcbp_handle_from_server does not exist on the server,
      the server MUST return NFS4ERR_NOENT.
    </t>

    <t>
       If an RPCSEC_GSS handle is using the SSV context (see <xref 
       target="ssv_mech"/>), then because each SSV RPCSEC_GSS 
       handle shares a common SSV GSS context, there are security
       considerations specific to this situation discussed in <xref
       target="rpcsec_ssv_consider"/>.
    </t>


  </section>
</section>

<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $       -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_BIND_CONN_TO_SESSION" title="Operation 41: BIND_CONN_TO_SESSION - Associate Connection with Session" >

  <section toc="exclude" 
           anchor="OP_BIND_CONN_TO_SESSION_ARGUMENT - Associate Connection with Session" 
           title="ARGUMENT">
<figure>
 <artwork>
enum channel_dir_from_client4 {
 CDFC4_FORE             = 0x1,
 CDFC4_BACK             = 0x2,
 CDFC4_FORE_OR_BOTH     = 0x3,
 CDFC4_BACK_OR_BOTH     = 0x7
};

struct BIND_CONN_TO_SESSION4args {
 sessionid4     bctsa_sessid;

 channel_dir_from_client4
                bctsa_dir;

 bool           bctsa_use_conn_in_rdma_mode;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
enum channel_dir_from_server4 {
 CDFS4_FORE     = 0x1,
 CDFS4_BACK     = 0x2,
 CDFS4_BOTH     = 0x3
};

struct BIND_CONN_TO_SESSION4resok {
 sessionid4     bctsr_sessid;

 channel_dir_from_server4
                bctsr_dir;

 bool           bctsr_use_conn_in_rdma_mode;
};

union BIND_CONN_TO_SESSION4res
 switch (nfsstat4 bctsr_status) {

 case NFS4_OK:
  BIND_CONN_TO_SESSION4resok
                bctsr_resok4;

 default:       void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      BIND_CONN_TO_SESSION is used to associate additional connections with a
      session. It MUST be used on the connection being associated with the session. It MUST
      be the only operation in the COMPOUND procedure.  If
      SP4_NONE (<xref target="OP_EXCHANGE_ID" />) state protection
      is used, any principal,
      security flavor, or RPCSEC_GSS context MAY be used to invoke the operation.
      If SP4_MACH_CRED is used, RPCSEC_GSS MUST be used with the
      integrity or privacy services, using the principal that
      created the client ID. If SP4_SSV is used, RPCSEC_GSS with
      the SSV GSS mechanism (<xref target="ssv_mech" />) and integrity or
      privacy MUST be used.
    </t>
    <t>
     If, when the client ID was created, the client opted for SP4_NONE
     state protection,
     the client is not required to use BIND_CONN_TO_SESSION to associate the
     connection with the session, unless
     the client wishes to associate the connection with the backchannel.
     When SP4_NONE protection is used, simply sending a COMPOUND
     request with a SEQUENCE operation is sufficient to associate the
     connection with the session specified in SEQUENCE.
    </t>
    <t>
      The field bctsa_dir indicates whether the client
      wants to associate the connection with the fore
      channel or the backchannel or both channels. The value
      CDFC4_FORE_OR_BOTH indicates that the client wants to
      associate the connection with both the fore channel and backchannel,
      but will accept the connection being associated to
      just the fore channel.  The value CDFC4_BACK_OR_BOTH
      indicates that the client wants to associate with both
      the fore channel and backchannel, but will accept the
      connection being associated with just the backchannel.
      The server replies in bctsr_dir which channel(s)
      the connection is associated with.
      If the client specified CDFC4_FORE, the server
      MUST return CDFS4_FORE. If the client specified
      CDFC4_BACK, the server MUST return CDFS4_BACK. If the
      client specified CDFC4_FORE_OR_BOTH, the server MUST return
      CDFS4_FORE or CDFS4_BOTH. If the client specified
      CDFC4_BACK_OR_BOTH, the server MUST return CDFS4_BACK
      or CDFS4_BOTH.

    </t>
    <t>
     See the CREATE_SESSION operation (<xref target="OP_CREATE_SESSION" />),
     and the description of the argument
     csa_use_conn_in_rdma_mode to understand
     bctsa_use_conn_in_rdma_mode, and the description of
     csr_use_conn_in_rdma_mode to understand bctsr_use_conn_in_rdma_mode.
    </t>
    <t>
     Invoking BIND_CONN_TO_SESSION on a connection already associated
     with the specified session has no effect, and the server MUST
     respond with NFS4_OK, unless the client is demanding changes
     to the set of channels the connection is associated with. If
     so, the server MUST return NFS4ERR_INVAL.
     
    </t>
 
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>      
      If a session's channel loses all connections, depending on
      the client ID's state protection and type of channel,
      the client might need to use
      BIND_CONN_TO_SESSION to associate a new connection. If the
      server restarted and does not keep the reply cache in stable
      storage, the server will not recognize the session ID.
      The client will ultimately have to invoke EXCHANGE_ID to
      create a new client ID and session.
    </t>
    <t>      
      Suppose SP4_SSV state protection is being used,
      and BIND_CONN_TO_SESSION is among the operations
      included in the spo_must_enforce set when the
      client ID was created (<xref target="OP_EXCHANGE_ID"/>).
      If so, there is an issue if SET_SSV is sent, no response
      is returned, and the last connection associated
      with the client ID drops.  The client, per
      the sessions model, MUST retry the SET_SSV. But
      it needs a new connection to do so, and MUST
      associate that connection with the session via a
      BIND_CONN_TO_SESSION authenticated with the SSV
      GSS mechanism. The problem is that the RPCSEC_GSS
      message integrity codes use a subkey derived from the SSV as the
      key and the
      SSV may have changed. While there are multiple
      recovery strategies, a single, general strategy
      is described here.
      <list style='symbols'>
      <t>
       The client reconnects.
      </t>
      <t>
       The client assumes that the SET_SSV was executed,
       and so sends BIND_CONN_TO_SESSION with the subkey (derived from
       the new SSV, i.e., what SET_SSV would have set the SSV to)
       used as the key for the RPCSEC_GSS credential message integrity codes.
      </t>
      <t>
       If the request succeeds, this means that the original attempted SET_SSV
       did execute successfully. The client re-sends the original
       SET_SSV, which the server will reply to via the
       reply cache.
      </t>
      <t>
       If the server returns an RPC authentication error,
       this means that the server's current SSV was not changed
       (and the SET_SSV was likely not executed).  The client then
       tries BIND_CONN_TO_SESSION with the subkey derived from the
       old SSV as the
       key for the RPCSEC_GSS message integrity codes.
      </t>
      <t>
       The attempted BIND_CONN_TO_SESSION with the old SSV
       should succeed. If so, the client re-sends the original
       SET_SSV. If the original SET_SSV was not executed, then the
       server executes it. If the original SET_SSV was executed but
       failed, the server will return the SET_SSV from the reply
       cache.
      </t>

     </list>

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_EXCHANGE_ID" title="Operation 42: EXCHANGE_ID - Instantiate Client ID" >
  <t>
      The EXCHANGE_ID exchanges long-hand client and server identifiers (owners),
      and creates a client ID.
  </t>

  <section toc="exclude" anchor="OP_EXCHANGE_ID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
const EXCHGID4_FLAG_SUPP_MOVED_REFER    = 0x00000001;
const EXCHGID4_FLAG_SUPP_MOVED_MIGR     = 0x00000002;

const EXCHGID4_FLAG_BIND_PRINC_STATEID  = 0x00000100;

const EXCHGID4_FLAG_USE_NON_PNFS        = 0x00010000;
const EXCHGID4_FLAG_USE_PNFS_MDS        = 0x00020000;
const EXCHGID4_FLAG_USE_PNFS_DS         = 0x00040000;

const EXCHGID4_FLAG_MASK_PNFS           = 0x00070000;

const EXCHGID4_FLAG_UPD_CONFIRMED_REC_A = 0x40000000;
const EXCHGID4_FLAG_CONFIRMED_R         = 0x80000000;

struct state_protect_ops4 {
        bitmap4 spo_must_enforce;
        bitmap4 spo_must_allow;
};

struct ssv_sp_parms4 {
        state_protect_ops4      ssp_ops;
        sec_oid4                ssp_hash_algs&lt;>;
        sec_oid4                ssp_encr_algs&lt;>;
        uint32_t                ssp_window;
        uint32_t                ssp_num_gss_handles;
};

enum state_protect_how4 {
        SP4_NONE = 0,
        SP4_MACH_CRED = 1,
        SP4_SSV = 2
};

union state_protect4_a switch(state_protect_how4 spa_how) {
        case SP4_NONE:
                void;
        case SP4_MACH_CRED:
                state_protect_ops4      spa_mach_ops;
        case SP4_SSV:
                ssv_sp_parms4           spa_ssv_parms;
};

struct EXCHANGE_ID4args {
        client_owner4           eia_clientowner;
        uint32_t                eia_flags;
        state_protect4_a        eia_state_protect;
        nfs_impl_id4            eia_client_impl_id&lt;1>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_RESULT" title="RESULT">
<figure>
 <artwork>
struct ssv_prot_info4 {
 state_protect_ops4     spi_ops;
 uint32_t               spi_hash_alg;
 uint32_t               spi_encr_alg;
 uint32_t               spi_ssv_len;
 uint32_t               spi_window;
 gsshandle4_t           spi_handles&lt;>;
};

union state_protect4_r switch(state_protect_how4 spr_how) {
 case SP4_NONE:
         void;
 case SP4_MACH_CRED:
         state_protect_ops4     spr_mach_ops;
 case SP4_SSV:
         ssv_prot_info4         spr_ssv_info;
};

struct EXCHANGE_ID4resok {
 clientid4        eir_clientid;
 sequenceid4      eir_sequenceid;
 uint32_t         eir_flags;
 state_protect4_r eir_state_protect;
 server_owner4    eir_server_owner;
 opaque           eir_server_scope&lt;NFS4_OPAQUE_LIMIT>;
 nfs_impl_id4     eir_server_impl_id&lt;1>;
};

union EXCHANGE_ID4res switch (nfsstat4 eir_status) {
case NFS4_OK:
 EXCHANGE_ID4resok      eir_resok4;

default:
 void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_DESCRIPTION" title="DESCRIPTION">
    <t>
     The client uses the EXCHANGE_ID operation to register
     a particular client owner with the server.  The client
     ID returned from this operation will be necessary
     for requests that create state on the server and
     will serve as a parent object to sessions created
     by the client.  In order to confirm the client ID
     it must first be used, along with the returned
     eir_sequenceid, as arguments to CREATE_SESSION.
     If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the result, eir_flags,
     then eir_sequenceid MUST be ignored, as it has no relevancy.
    </t>
    <t>
     EXCHANGE_ID MAY be sent in a COMPOUND procedure that starts with
     SEQUENCE. However, when a client communicates with a server
     for the first time, it will not have a session, so using
     SEQUENCE will not be possible.
     If EXCHANGE_ID is sent without a preceding SEQUENCE, then it
     MUST be the only operation in the COMPOUND procedure's request. If
     it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.
    </t>

    <t>
     The eia_clientowner field is composed of a co_verifier
     field and a co_ownerid string.  As noted in <xref
     target="Client Identifiers" />, the co_ownerid
     describes the client, and the co_verifier is
     the incarnation of the client. An EXCHANGE_ID
     sent with a new incarnation of the client will
     lead to the server removing lock state of the old
     incarnation. Whereas an EXCHANGE_ID sent with the
     current incarnation and co_ownerid will result in
     an error or an update of the client ID's properties,
     depending on the arguments to EXCHANGE_ID.
    </t>
    <t>
     A server MUST NOT use the same client ID for two different incarnations of
     an eir_clientowner.
    </t>
    <t>
     In addition to the client ID and sequence ID, the server
     returns a server owner (eir_server_owner) and
     server scope (eir_server_scope).  The former field is used for
     network trunking as described in <xref
     target="Trunking" />.  The latter field is used to
     allow clients to determine when client IDs sent by
     one server may be recognized by another in the event
     of file system migration (see <xref
     target="transition_state" />).
    </t>
    <t>
     The client ID returned by EXCHANGE_ID is only unique
     relative to the combination of eir_server_owner.so_major_id
     and eir_server_scope. Thus, if two servers return the
     same client ID, the onus is on the client to
     distinguish the client IDs on the basis of eir_server_owner.so_major_id
     and eir_server_scope. In the event two different servers
     claim matching server_owner.so_major_id and eir_server_scope,
     the client can use the verification techniques discussed
     in <xref target="Trunking" /> to determine if the servers
     are distinct. If they are distinct, then the client
     will need to note the destination network addresses
     of the connections used with each server, and use
     the network address as the final discriminator.
    </t>
    <t>
     The server, as defined by the unique identity expressed
     in the so_major_id of the server owner and the server scope,
     needs to track several properties of each client ID it
     hands out. The properties apply to the client ID and all
     sessions associated with the client ID.
     The properties are derived from the
     arguments and results of EXCHANGE_ID.
     The client ID properties include:
     <list style="symbols">
     <t>
      The capabilities expressed by the following bits, which
      come from the results of EXCHANGE_ID:
        <list>
        <t>EXCHGID4_FLAG_SUPP_MOVED_REFER</t>
	<t>EXCHGID4_FLAG_SUPP_MOVED_MIGR    </t>
	<t>EXCHGID4_FLAG_BIND_PRINC_STATEID        </t>
	<t>EXCHGID4_FLAG_USE_NON_PNFS     </t>
	<t>EXCHGID4_FLAG_USE_PNFS_MDS   </t>
	<t>EXCHGID4_FLAG_USE_PNFS_DS     </t>
        </list>
        These properties may be updated by subsequent
        EXCHANGE_ID requests on confirmed client IDs though the server MAY
        refuse to change them.
     </t>
     <t>
       The state protection method used, one of SP4_NONE,
       SP4_MACH_CRED, or SP4_SSV, as set by the spa_how
       field of the arguments to EXCHANGE_ID.  Once the
       client ID is confirmed, this property cannot be
       updated by subsequent EXCHANGE_ID requests.

     </t>
     <t>
       For SP4_MACH_CRED or SP4_SSV state protection:
       <list>
       <t>
	 The list of operations (spo_must_enforce) that MUST use the specified
	 state protection. This list comes
	 from the results of EXCHANGE_ID.

       </t>
       <t>
	 The list of operations (spo_must_allow) that MAY use the specified
	 state protection. This list comes
	 from the results of EXCHANGE_ID.

       </t>
       </list>
       Once the client ID is confirmed, these properties
       cannot be updated by subsequent EXCHANGE_ID
       requests.

     </t>
     <t>
      For SP4_SSV protection:
      <list>
   
      <t>
       The OID of the hash algorithm. This property is
       represented by one of the algorithms in the
       ssp_hash_algs field of the EXCHANGE_ID arguments.
       Once the client ID is confirmed, this property
       cannot be updated by subsequent EXCHANGE_ID
       requests.

      </t>
      <t>
       The OID of the encryption algorithm. This property
       is represented by one of the algorithms in the
       ssp_encr_algs field of the EXCHANGE_ID arguments.
       Once the client ID is confirmed, this property
       cannot be updated by subsequent EXCHANGE_ID
       requests.

      </t>

      <t>
       The length of the SSV. This property is
       represented by the spi_ssv_len field in the EXCHANGE_ID
       results.

       Once the client ID is confirmed,
       this property cannot be updated by 
       subsequent EXCHANGE_ID requests.

	 <vspace blankLines='1' />

       There are REQUIRED and RECOMMENDED relationships among the
       length of the key of the encryption algorithm ("key length"), the length of the
       output of hash algorithm ("hash length"), and the length of the SSV ("SSV length").
       <list style="symbols">
       <t>
        key length MUST be &lt;= hash length. This is because the keys used for
        the encryption algorithm are actually subkeys derived from the SSV,
        and the derivation is via the hash algorithm. The selection of an
        encryption algorithm with a key length that exceeded the length of
        the output of the hash algorithm would require padding, and thus
        weaken the use of the encryption algorithm.
       </t>
       <t>
        hash length SHOULD be &lt;= SSV length. This is because the
        SSV is a key used to derive subkeys via an HMAC, and
        it is recommended that the key used as input to an HMAC be
        at least as long as the length of the HMAC's hash algorithm's
        output (see Section 3 of <xref target="RFC2104">RFC2104</xref>).
       </t>

       <t>
        key length SHOULD be &lt;= SSV length. This is a transitive result of the
        above two invariants.
       </t>

       <t>
        key length SHOULD be >= hash length / 2. This is because the subkey
        derivation is via 
        an HMAC and it is recommended that if the HMAC has to be truncated,
        it should not be truncated to less than half the hash length
        (see Section 4 of <xref target="RFC2104">RFC2104</xref>).
       </t>
       </list>
      </t>

      <t>
       Number of concurrent versions of the SSV the client
       and server will support (<xref target="ssv_mech"
       />). This property is represented by spi_window
       in the EXCHANGE_ID results.  The property may be
       updated by subsequent EXCHANGE_ID requests.

      </t>
      </list>
    </t>
    <t>
     The client's implementation ID as represented by
     the eia_client_impl_id field of the arguments.
     The property may be updated by subsequent EXCHANGE_ID
     requests.
    </t>
    <t>
     The server's implementation ID as represented by
     the eir_server_impl_id field of the reply.
     The property may be updated by replies to subsequent EXCHANGE_ID
     requests.
    </t>
    </list>
    </t>

    <t>
      The eia_flags passed as part of the arguments and
      the eir_flags results allow the client and server
      to inform each other of their capabilities as well
      as indicate how the client ID will be used. Whether
      a bit is set or cleared on the arguments' flags
      does not force the server to set or clear the same
      bit on the results' side.  Bits not defined above
      cannot be set in the eia_flags field.  If they
      are, the server MUST reject the operation with
      NFS4ERR_INVAL.

    </t>
    <t>
      The EXCHGID4_FLAG_UPD_CONFIRMED_REC_A bit can only be set
      in eia_flags; it is always off in eir_flags.
      The EXCHGID4_FLAG_CONFIRMED_R bit can only be set in
      eir_flags; it is always off in eia_flags.  If the
      server recognizes the co_ownerid and co_verifier
      as mapping to a confirmed client ID, it sets
      EXCHGID4_FLAG_CONFIRMED_R in eir_flags.
      The EXCHGID4_FLAG_CONFIRMED_R flag allows a client
      to tell if the client ID it is trying to create
      already exists and is confirmed.

    </t>

    <t>
      If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set in eia_flags,
      this means that the client is attempting to update properties
      of an existing confirmed client ID (if the client wants to
      update properties of an unconfirmed client ID, it MUST NOT
      set EXCHGID4_FLAG_UPD_CONFIRMED_REC_A).
      If so, it is
      RECOMMENDED that the client send the update EXCHANGE_ID
      operation in the same COMPOUND as a SEQUENCE so that
      the EXCHANGE_ID is executed exactly once. Whether
      the client can update the properties of client ID
      depends on the state protection it selected when the
      client ID was created, and the principal and security
      flavor it uses when sending the EXCHANGE_ID request.
      The situations described in items

      <xref target="case_update" format="counter"/>,

      <xref target="case_update_noent" format="counter"/>,

      <xref target="case_update_exist" format="counter"/>,

      or

      <xref target="case_update_perm" format="counter"/>

      of the second numbered list of <xref
      target="OP_EXCHANGE_ID_IMPLEMENTATION" /> will apply.
      Note that if the operation succeeds
      and returns a client ID that is already
      confirmed, the server MUST set the
      EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.


    </t>

    <t>
      If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags,
      this means that the client is trying to establish a new
      client ID; it is
      attempting to trunk data communication to
      the server (<xref target="Trunking" />); or it
      is attempting to update properties of an unconfirmed
      client ID. The
      situations described in
      items
	<xref target="case_new_owner_id" format="counter"/>,
	<xref target="case_non_update" format="counter"/>,
	<xref target="case_client_collision" format="counter"/>,
	<xref target="case_retry" format="counter"/>, or
	<xref target="case_client_restart" format="counter"/>

      of the second numbered list of <xref
      target="OP_EXCHANGE_ID_IMPLEMENTATION" /> will apply.
      Note that if the operation succeeds
      and returns a client ID that was previously
      confirmed, the server MUST set the
      EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.

    </t>
    
    <t>
      When the EXCHGID4_FLAG_SUPP_MOVED_REFER flag bit
      is set, the client indicates that it is capable
      of dealing with an NFS4ERR_MOVED error as part of
      a referral sequence.  When this bit is not set, it
      is still legal for the server to perform a referral
      sequence.  However, a server may use the fact that
      the client is incapable of correctly responding
      to a referral, by avoiding it for that particular
      client.  It may, for instance, act as a proxy
      for that particular file system, at some cost in
      performance, although it is not obligated to do so.
      If the server will potentially perform a referral, it
      MUST set EXCHGID4_FLAG_SUPP_MOVED_REFER in eir_flags.

    </t>
    <t>
      When the EXCHGID4_FLAG_SUPP_MOVED_MIGR is set,
      the client indicates that it is capable of dealing
      with an NFS4ERR_MOVED error as part of a file system
      migration sequence.  When this bit is not set, it
      is still legal for the server to indicate that a
      file system has moved, when this in fact happens.
      However, a server may use the fact that the client
      is incapable of correctly responding to a migration
      in its scheduling of file systems to migrate so as to
      avoid migration of file systems being actively used.
      It may also hide actual migrations from clients
      unable to deal with them by acting as a proxy for a
      migrated file system for particular clients, at some
      cost in performance, although it is not obligated
      to do so.  If the server will potentially perform a
      migration, it MUST set EXCHGID4_FLAG_SUPP_MOVED_MIGR
      in eir_flags.

    </t>
    <t>
      When EXCHGID4_FLAG_BIND_PRINC_STATEID is set, the
      client indicates that it wants the server to bind the
      stateid to the principal. This means that when a
      principal creates a stateid, it has to be the one to
      use the stateid. If the server will perform binding,
      it will return EXCHGID4_FLAG_BIND_PRINC_STATEID. The
      server MAY return EXCHGID4_FLAG_BIND_PRINC_STATEID
      even if the client does not request it. If
      an update to the client ID changes the value
      of EXCHGID4_FLAG_BIND_PRINC_STATEID's client
      ID property, the effect applies only to new
      stateids. Existing stateids (and all stateids with
      the same "other" field) that were created with
      stateid to principal binding in force will continue
      to have binding in force.  Existing stateids (and all
      stateids with the same "other" field) that were created
      with stateid to principal not in force will continue
      to have binding not in force.

    </t>

    <t>
     The EXCHGID4_FLAG_USE_NON_PNFS,
     EXCHGID4_FLAG_USE_PNFS_MDS,  and
     EXCHGID4_FLAG_USE_PNFS_DS bits are described in <xref
     target="pnfs_session_stuff" /> and convey roles the
     client ID is to be used for in a pNFS environment.
     The server MUST set one of the acceptable combinations
     of these bits (roles) in eir_flags, as specified in <xref
     target="pnfs_session_stuff" />.
     Note that the same client owner/server owner pair can
     have multiple roles. Multiple roles can be associated
     with the same client ID or with different client
     IDs. Thus, if a client sends EXCHANGE_ID from the
     same client owner to the same server owner multiple
     times, but specifies different pNFS roles each time,
     the server might return different client IDs. Given
     that different pNFS roles might have different client
     IDs, the client may ask for different properties for
     each role/client ID.

    </t>

    <t>
     The spa_how field of the eia_state_protect field
     specifies how the client wants to protect its client,
     locking, and session states from unauthorized changes
     (<xref target="protect_state_change"/>):

     <list style="symbols">
     <t>
      SP4_NONE. The client does not request the NFSv4.1 server
      to enforce state protection. The NFSv4.1 server MUST NOT
      enforce state protection for the returned client ID.
     </t>
     <t>
      SP4_MACH_CRED.  If spa_how is SP4_MACH_CRED, then
      the client MUST send the EXCHANGE_ID request with RPCSEC_GSS
      as the security flavor, and with a service of
      RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY. If SP4_MACH_CRED
      is specified, then the
      client wants to use an RPCSEC_GSS-based machine
      credential to protect its state. The server MUST note
      the principal the EXCHANGE_ID operation was sent
      with, and the GSS mechanism used.  These notes
      collectively comprise the machine credential.

	 <vspace blankLines='1' />

      After the client ID is confirmed, as long as the lease associated with
      the client ID is unexpired, a subsequent EXCHANGE_ID
      operation that uses the same eia_clientowner.co_owner
      as the first EXCHANGE_ID MUST also use the same
      machine credential as the first EXCHANGE_ID. The
      server returns the same client ID for
      the subsequent EXCHANGE_ID as that returned from
      the first EXCHANGE_ID.

     </t>
     <t>
      SP4_SSV. If spa_how is SP4_SSV, then
      the client MUST send the EXCHANGE_ID request with RPCSEC_GSS
      as the security flavor, and with a service of
      RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY.
      If SP4_SSV is specified, then
      the client wants to use the SSV to protect its state.
      The server records the credential used in the request
      as the machine credential (as defined above) for
      the eia_clientowner.co_owner.
      The CREATE_SESSION operation that
      confirms the client ID MUST use the same machine
      credential.

     </t>
     </list>
     </t>
     <t>
     When a client specifies SP4_MACH_CRED or SP4_SSV,
     it also provides two lists of operations (each
     expressed as a bitmap).  The first list
     is spo_must_enforce and consists of those operations
     the client MUST send (subject to the server confirming the
     list of operations in the result of EXCHANGE_ID) with the
     machine credential (if SP4_MACH_CRED protection is
     specified) or the SSV-based credential (if SP4_SSV
     protection is used).  The client MUST send the
     operations with RPCSEC_GSS credentials that specify
     the RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY
     security service.  Typically, the first list of
     operations includes EXCHANGE_ID, CREATE_SESSION,
     DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION,
     and DESTROY_CLIENTID.  The client SHOULD NOT specify
     in this list any operations that require a filehandle
     because the server's access policies MAY conflict with
     the client's choice, and thus the client would then be
     unable to access a subset of the server's namespace.

     </t>
     <t>

     Note that if SP4_SSV protection is specified, and
     the client indicates that CREATE_SESSION must be
     protected with SP4_SSV, because the SSV cannot exist
     without a confirmed client ID, the first CREATE_SESSION
     MUST instead be sent using the machine credential,
     and the server MUST accept the machine credential.

     </t>
     <t>

     There is a corresponding result, also called spo_must_enforce,
     of the operations for which the server will require SP4_MACH_CRED or
     SP4_SSV protection. Normally, the server's result
     equals the client's argument, but the result MAY be different.
     If the client requests one or more operations in
     the set { EXCHANGE_ID, CREATE_SESSION,
     DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION,
     DESTROY_CLIENTID }, then the result spo_must_enforce
     MUST include the operations the client requested from that set.

     </t>
     <t>
     If spo_must_enforce in the results has BIND_CONN_TO_SESSION
     set, then connection binding enforcement is enabled, and
     the client MUST use the machine (if SP4_MACH_CRED protection is used)
     or SSV (if SP4_SSV protection is used) credential on calls
     to BIND_CONN_TO_SESSION.

     </t>
     <t>
     The second list is spo_must_allow and consists of those
     operations
     the client wants to have the option of sending with the machine credential or
     the SSV-based credential, even if the object the
     operations are performed on is not owned by the
     machine or SSV credential.

     </t>
     <t>

     The corresponding result, also called
     spo_must_allow, consists of the operations the server
     will allow the client to use SP4_SSV or SP4_MACH_CRED
     credentials with.
     Normally, the server's result
     equals the client's argument, but the result MAY be different.

     </t>
     <t>

     The purpose of spo_must_allow is to allow clients to
     solve the following conundrum. Suppose the client ID
     is confirmed with EXCHGID4_FLAG_BIND_PRINC_STATEID,
     and it calls OPEN with the RPCSEC_GSS credentials of
     a normal user. Now suppose the user's credentials expire,
     and cannot be renewed (e.g., a Kerberos ticket granting ticket
     expires, and the user has logged off and will not be
     acquiring a new ticket granting ticket). The client will be
     unable to send CLOSE without the user's credentials, which is to
     say the client has to either leave the state on the server
     or re-send EXCHANGE_ID with a new verifier to
     clear all state, that is, unless the client includes
     CLOSE on the list of operations in spo_must_allow and the
     server agrees.

     </t>
    <t>
     The SP4_SSV protection parameters also have:
     <list style="hanging">

     <t hangText="ssp_hash_algs:" />
     <t>
       This is the set of algorithms the client supports
       for the purpose of computing the digests needed for
       the internal SSV GSS mechanism and for the SET_SSV
       operation.  Each algorithm is specified as an object
       identifier (OID).  The REQUIRED algorithms for a
       server are id-sha1, id-sha224, id-sha256, id-sha384,
       and id-sha512 <xref target="RFC4055"/>.
       The algorithm the server selects among the
       set is indicated in spi_hash_alg, a field of
       spr_ssv_prot_info. The field spi_hash_alg is an
       index into the array ssp_hash_algs. 

       If the server
       does not support any of the offered algorithms,
       it returns NFS4ERR_HASH_ALG_UNSUPP.

       If ssp_hash_algs is empty, the server MUST return NFS4ERR_INVAL.

     </t>
     <t hangText="ssp_encr_algs:" />
     <t>
       This is the set of algorithms the client supports for the
       purpose of providing privacy protection for the internal
       SSV GSS mechanism.  Each algorithm is
       specified as an OID.
       The REQUIRED algorithm for a server is id-aes256-CBC.
       The RECOMMENDED algorithms are id-aes192-CBC and id-aes128-CBC
       <xref target="CSOR_AES" />. The selected algorithm is
       returned in spi_encr_alg, an index into ssp_encr_algs.

       If the server
       does not support any of the offered algorithms,
       it returns NFS4ERR_ENCR_ALG_UNSUPP.

       If ssp_encr_algs is empty, the server MUST return NFS4ERR_INVAL.

       Note that due to previously stated requirements and recommendations
       on the relationships between key length and hash length, some
       combinations of RECOMMENDED and REQUIRED encryption algorithm and
       hash algorithm either SHOULD NOT or MUST NOT be used.
       <xref target="algtbl"/> summarizes the illegal and discouraged
       combinations.

     </t>
     <t hangText="ssp_window:" />
     <t>
       This is the number of SSV versions the client wants
       the server to maintain (i.e., each successful call to SET_SSV
       produces a new version of the SSV). If ssp_window is zero, the
       server MUST return NFS4ERR_INVAL. The server responds
       with spi_window, which MUST NOT exceed ssp_window, and MUST 
       be at least one.
       Any requests on the backchannel or fore channel that
       are using a version of the SSV that is outside the window will fail with
       an ONC RPC authentication error, and the requester
       will have to retry them with the same slot ID and
       sequence ID.
     </t>

     <t hangText="ssp_num_gss_handles:" />
     <t>
       This is the number of RPCSEC_GSS handles the
       server should create that are based on the GSS
       SSV mechanism (<xref target="ssv_mech" />).
       It is not the total number of RPCSEC_GSS handles for
       the client ID. Indeed, subsequent calls to EXCHANGE_ID
       will add RPCSEC_GSS handles.
       The server responds with a list of handles in
       spi_handles. If the client asks for at least
       one handle and the server cannot create it,
       the server MUST return an error.  The handles in
       spi_handles are not available for use until the
       client ID is confirmed, which could be immediately
       if EXCHANGE_ID returns EXCHGID4_FLAG_CONFIRMED_R,
       or upon successful confirmation from CREATE_SESSION.
		 <vspace blankLines='1' />
       While a client ID can span all the connections
       that are connected to a server sharing the same
       eir_server_owner.so_major_id, the RPCSEC_GSS
       handles returned in spi_handles can only be used
       on connections connected to a server that returns
       the same the eir_server_owner.so_major_id and
       eir_server_owner.so_minor_id on each connection.
       It is permissible for the client to set
       ssp_num_gss_handles to zero; the client can
       create more handles with another EXCHANGE_ID call.
		 <vspace blankLines='1' />
       Because each SSV RPCSEC_GSS handle shares a common SSV GSS context,
       there are security considerations specific to this situation
       discussed in <xref target="rpcsec_ssv_consider"/>.
		 <vspace blankLines='1' />
       The seq_window (see Section 5.2.3.1 of <xref target="RFC2203">RFC2203</xref>)
       of each RPCSEC_GSS handle in spi_handle MUST be the same as the seq_window of
       the RPCSEC_GSS handle used for the credential of the RPC request
       that the EXCHANGE_ID request was sent with.

     </t>
      
     </list>
     
    </t>
      <texttable anchor='algtbl'>
	      <ttcol align='left'>Encryption Algorithm</ttcol>
	      <ttcol align='left'>MUST NOT be combined with</ttcol>
	      <ttcol align='left'>SHOULD NOT be combined with</ttcol>
	      <c>id-aes128-CBC</c> <c></c> <c>id-sha384, id-sha512</c>
	      <c>id-aes192-CBC</c> <c>id-sha1</c> <c>id-sha512</c>
	      <c>id-aes256-CBC</c> <c>id-sha1, id-sha224</c> <c></c>
      </texttable>

    <t>
      The arguments include an array of up to one
      element in length called eia_client_impl_id. If
      eia_client_impl_id is present, it contains the
      information identifying the implementation of the
      client. Similarly, the results include an array of up
      to one element in length called eir_server_impl_id
      that identifies the implementation of the server.
      Servers MUST accept a zero-length eia_client_impl_id
      array, and clients MUST accept a zero-length
      eir_server_impl_id array.
   
    </t>
    <t>
      An example use for implementation identifiers
      would be diagnostic software that extracts
      this information in an attempt to identify
      interoperability problems, performance workload
      behaviors, or general usage statistics.  Since the
      intent of having access to this information is for
      planning or general diagnosis only, the client and
      server MUST NOT interpret this implementation
      identity information in a way that affects
      interoperational behavior of the implementation.
      The reason is that if clients and servers did such
      a thing, they might use fewer capabilities of the
      protocol than the peer can support, or the client
      and server might refuse to interoperate.

    </t>
    <t>
      Because it is possible that some implementations will
      violate the protocol specification and interpret
      the identity information, implementations MUST
      allow the users of the NFSv4 client and server to
      set the contents of the sent nfs_impl_id structure
      to any value.

    </t>

  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A server's client record is a 5-tuple:
    </t>
    <t>
      <list style="numbers">
	<t>co_ownerid
	<list style="empty">
	  <t>The client identifier string, from the eia_clientowner
	  structure of the EXCHANGE_ID4args structure.</t>
	</list></t>

	<t>co_verifier:
	<list style="empty">
	  <t>A client-specific value used to indicate incarnations (where a client restart represents a new incarnation), from the
	  eia_clientowner structure of the EXCHANGE_ID4args
	  structure.</t>
	</list></t>

	<t>principal:
	<list style="empty">
	  <t>
           The principal that was defined in the RPC header's credential
           and/or verifier at the time the client record was
           established.
         </t>
	</list></t>

	<t>client ID:
	<list style="empty">
	  <t>The shorthand client identifier, generated by the server and
	  returned via the eir_clientid field in the EXCHANGE_ID4resok
	  structure.</t>
	</list></t>

	<t>confirmed:
	<list style="empty">
	  <t>A private field on the server indicating whether or not a
	  client record has been confirmed.  A client record is
	  confirmed if there has been a successful CREATE_SESSION
	  operation to confirm it.  Otherwise, it is unconfirmed.  An
	  unconfirmed record is established by an EXCHANGE_ID call.
	  Any unconfirmed record that is not confirmed within a lease
	  period SHOULD be removed.</t>
	</list></t>
	
      </list>
    </t>
    <!-- start new list -->
    <t>
      The following identifiers represent special values for the fields
      in the records.
      <list style="hanging">
	<t hangText="ownerid_arg:"/>
	<t>
	  The value of the eia_clientowner.co_ownerid subfield of the
	  EXCHANGE_ID4args structure of the current request.
	</t>
	<t hangText="verifier_arg:"/>
	<t>
	  The value of the eia_clientowner.co_verifier subfield of the
	  EXCHANGE_ID4args structure of the current request.
	</t>
	<t hangText="old_verifier_arg:"/>
	<t>
	  A value of the eia_clientowner.co_verifier field of a client record
	  received in a previous request; this is distinct from
	  verifier_arg.
	</t>
	<t hangText="principal_arg:"/>
	<t>
	  The value of the RPCSEC_GSS principal for the current request.
	</t>
	<t hangText="old_principal_arg:"/>
	<t>
	  A value of the principal of a client record as defined by the
          RPC header's credential or verifier of a previous request.
	  This is distinct from principal_arg.
	 
	</t>
	<t hangText="clientid_ret:"/>
	<t>
	  The value of the eir_clientid field the server will return in the
	  EXCHANGE_ID4resok structure for the current request.
	</t>
	<t hangText="old_clientid_ret:"/>
	<t>
	  The value of the eir_clientid field the server returned in the
	  EXCHANGE_ID4resok structure for a previous request.  This
	  is distinct from clientid_ret.
	</t>
	<t hangText="confirmed:"/>
	<t>
          The client ID has been confirmed.
	</t>
	<t hangText="unconfirmed:"/>
	<t>
          The client ID has not been confirmed.
	</t>
      </list>
    </t>
    <t>
      Since EXCHANGE_ID is a non-idempotent operation, we must
      consider the possibility that retries occur as a result of a
      client restart, network partition, malfunctioning router, etc.
      Retries are identified by the value of the eia_clientowner field of
      EXCHANGE_ID4args, and the method for dealing with them is
      outlined in the scenarios below.
    </t>
    <t>
      The scenarios are described in terms of the
      client record(s) a server has for a given
      co_ownerid. Note that if the client ID
      was created specifying SP4_SSV state protection and
      EXCHANGE_ID as the one of the operations in spo_must_allow,
      then the server MUST authorize EXCHANGE_IDs with the SSV
      principal in addition to the principal that created the
      client ID.
    </t>
    <t anchor="case_list">
      <list style="numbers">
	<t anchor="case_new_owner_id">New Owner ID
	<list style="empty">
	  <t>
	    If the server has no client records
	    with eia_clientowner.co_ownerid matching
	    ownerid_arg, and EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not
	    set in the EXCHANGE_ID, then a new shorthand
	    client ID (let us call it clientid_ret)
	    is generated, and the following unconfirmed
	    record is added to the server's state.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

	    Subsequently, the server returns clientid_ret.

		 <vspace blankLines='1' />

	  </t>
	</list>
		 <vspace blankLines='1' />
	</t>

	<t anchor="case_non_update">Non-Update on Existing Client ID
	<list style="empty">
	  <t>
	    If the server has the following confirmed record, and
            the request does not have
	    EXCHGID4_FLAG_UPD_CONFIRMED_REC_A set,
	    then the request is the result of a retried request due to a
	    faulty router or lost connection, or
            the client is trying to determine if it can perform
            trunking.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    Since the record has been confirmed, the client
	    must have received the server's reply from
	    the initial EXCHANGE_ID request. Since the
	    server has a confirmed record, and since
	    EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, with the
            possible exception of eir_server_owner.so_minor_id, the
	    server returns the same result it did when
	    the client ID's properties were last updated
	    (or if never updated, the result when the
	    client ID was created). The confirmed record
            is unchanged.
	  </t>
	</list>
	</t>

	<t anchor="case_client_collision">Client Collision
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and
	    if the server has the following confirmed
	    record, then this request is likely the result
	    of a chance collision between the values of
	    the eia_clientowner.co_ownerid subfield of
	    EXCHANGE_ID4args for two different clients.

	  </t>
	  <t>
      
	    { ownerid_arg, *, old_principal_arg, old_clientid_ret, confirmed }
	  </t>
	  <t>
            If there is currently no state associated with old_clientid_ret,
            or if there is state but the lease has expired, then
            this case is effectively equivalent to the
            New Owner ID case of <xref target="case_new_owner_id"/>.
            The confirmed record is deleted, the old_clientid_ret and its
            lock state are deleted, 
	    a new shorthand client ID
	    is generated, and the following unconfirmed
	    record is added to the server's state.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

	    Subsequently, the server returns clientid_ret.

		 <vspace blankLines='1' />
	  </t>
          <t>
            If old_clientid_ret has an unexpired lease with state, then
	    no state of old_clientid_ret is changed or deleted.
            The server returns NFS4ERR_CLID_INUSE
	    to indicate that the client should
	    retry with a different value for the
	    eia_clientowner.co_ownerid subfield of
	    EXCHANGE_ID4args. The client record is not changed.
	  </t>
	</list>
	</t>

	<t anchor="case_retry">Replacement of Unconfirmed Record
	<list style="empty">
	  <t>
            If the EXCHGID4_FLAG_UPD_CONFIRMED_REC_A flag is not set,
	    and the server has the following unconfirmed record, then
            the client is attempting EXCHANGE_ID again on an
            unconfirmed client ID, perhaps due to a retry, a client
            restart before client ID confirmation (i.e., 
            before CREATE_SESSION was called), or
            some other reason.

		 <vspace blankLines='1' />

	    { ownerid_arg, *, *, old_clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

            It is possible that
            the properties of old_clientid_ret are
            different than those specified in the current
            EXCHANGE_ID. Whether or not the properties are being updated,
            to eliminate ambiguity, the server
            deletes the unconfirmed record, generates a
            new client ID (clientid_ret), and establishes
            the following unconfirmed record:

		 <vspace blankLines='1' />

	    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }
		 <vspace blankLines='1' />
	  </t>
	</list>
	</t>

	<t anchor="case_client_restart">Client Restart
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and
	    if the server has the following confirmed client record, then
	    this request is likely from a previously confirmed client
	    that has restarted.
	  </t>
	  <t>
	    { ownerid_arg, old_verifier_arg, principal_arg, old_clientid_ret, confirmed }
	  </t>
	  <t>
	    Since the previous incarnation of the same
	    client will no longer be making requests,
	    once the new client ID is confirmed by
	    CREATE_SESSION, byte-range locks and share reservations
	    should be released immediately rather than
	    forcing the new incarnation to wait for
	    the lease time on the previous incarnation
	    to expire.	Furthermore, session state should
	    be removed since if the client had maintained
	    that information across restart, this request
	    would not have been sent.  If the server
	    supports neither the CLAIM_DELEGATE_PREV
            nor CLAIM_DELEG_PREV_FH
	    claim types, associated delegations should be
	    purged as well; otherwise, delegations are
	    retained and recovery proceeds according to
	    <xref target="delegation_recovery"/>.

	  </t>
	  <t>
	    After processing, clientid_ret is returned to the client and
	    this client record is added:
	  </t>
	  <t>
	    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }
		 <vspace blankLines='1' />
	  </t>
          <t>
	    The previously described confirmed record
	    continues to exist, and thus the same
	    ownerid_arg exists in both a confirmed and
	    unconfirmed state at the same time. The number
	    of states can collapse to one once the server
	    receives an applicable CREATE_SESSION or
	    EXCHANGE_ID.

            <list style='symbols'>

            <t>
	     If the server subsequently receives a successful
	     CREATE_SESSION that confirms clientid_ret,
	     then the server atomically destroys the
	     confirmed record and makes the unconfirmed
	     record confirmed as described in <xref
	     target="OP_CREATE_SESSION_IMPLEMENTATION" />.

            </t>

            <t>
	     If the server instead subsequently receives
	     an EXCHANGE_ID with the client owner equal
	     to ownerid_arg, one strategy is to simply
	     delete the unconfirmed record, and process the
	     EXCHANGE_ID as described in the entirety of
	     <xref target="OP_EXCHANGE_ID_IMPLEMENTATION"
	     />.

            </t>

	    </list>

          </t>
	</list>
	</t>

	<t anchor="case_update">Update
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an attempt at an update.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    Since the record has been confirmed, the client must have
	    received the server's reply from the initial EXCHANGE_ID
	    request. The server allows the update, and the client record
            is left intact.
	  </t>
	</list>
	</t>

	<t anchor="case_update_noent">Update but No Confirmed Record
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
            server has no confirmed record corresponding ownerid_arg,
            then the server returns NFS4ERR_NOENT and leaves any unconfirmed
            record intact.
          </t>
	</list>
	</t>

	<t anchor="case_update_exist">Update but Wrong Verifier
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an illegal attempt at an
	    update, perhaps because of a retry from a previous client
            incarnation.

		 <vspace blankLines='1' />

    { ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    The server returns NFS4ERR_NOT_SAME and leaves the client record
            intact.
          </t>
	</list>
	</t>

	<t anchor="case_update_perm">Update but Wrong Principal
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an illegal attempt at an
	    update by an unauthorized principal.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, old_principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    The server returns NFS4ERR_PERM and leaves the client record
            intact.
          </t>
	</list>
	</t>

      </list>
    </t>

  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $         -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CREATE_SESSION" title="Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID" >

  <section toc="exclude" anchor="OP_CREATE_SESSION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct channel_attrs4 {
        count4                  ca_headerpadsize;
        count4                  ca_maxrequestsize;
        count4                  ca_maxresponsesize;
        count4                  ca_maxresponsesize_cached;
        count4                  ca_maxoperations;
        count4                  ca_maxrequests;
        uint32_t                ca_rdma_ird&lt;1>;
};

const CREATE_SESSION4_FLAG_PERSIST              = 0x00000001;
const CREATE_SESSION4_FLAG_CONN_BACK_CHAN       = 0x00000002;
const CREATE_SESSION4_FLAG_CONN_RDMA            = 0x00000004;

struct CREATE_SESSION4args {
        clientid4               csa_clientid;
        sequenceid4             csa_sequence;

        uint32_t                csa_flags;

        channel_attrs4          csa_fore_chan_attrs;
        channel_attrs4          csa_back_chan_attrs;

        uint32_t                csa_cb_program;
        callback_sec_parms4     csa_sec_parms&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
struct CREATE_SESSION4resok {
        sessionid4              csr_sessionid;
        sequenceid4             csr_sequence;

        uint32_t                csr_flags;

        channel_attrs4          csr_fore_chan_attrs;
        channel_attrs4          csr_back_chan_attrs;
};

union CREATE_SESSION4res switch (nfsstat4 csr_status) {
case NFS4_OK:
        CREATE_SESSION4resok    csr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used by the client to create new session objects
      on the server.
    </t>
    <t>
      CREATE_SESSION can be sent with or without a preceding SEQUENCE
      operation in the same COMPOUND procedure.
      If CREATE_SESSION is sent with a preceding SEQUENCE 
      operation,
      any session created by CREATE_SESSION has no direct
      relation to the session specified in the SEQUENCE operation, although
      the two sessions might be associated with the same client ID.
      If CREATE_SESSION is sent without a preceding SEQUENCE, then it
      MUST be the only operation in the COMPOUND procedure's request. If
      it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.
    </t>
    <t>
     In addition to creating a session, CREATE_SESSION has the following
     effects:
      <list style="symbols">
      <t>
        The first session created with a new
        client ID serves to confirm the
        creation of that
        client's state on the server. The server returns the parameter
        values for the new session.
      </t>
      <t>
        The connection CREATE_SESSION that is sent over is associated with the
        session's fore channel.
      </t>
      </list>
     </t>
     <t>
      The arguments and results of CREATE_SESSION are described as follows:
      <list style="hanging">
        <t hangText="csa_clientid:"/>
        <t>
          This is the client ID with which the new session will be associated.
          The corresponding result is csr_sessionid, the session ID
          of the new session.
        </t>
        <t hangText="csa_sequence:"/>
        <t>
         Each client ID serializes CREATE_SESSION via a per-client ID
         sequence number (see
          <xref target="OP_CREATE_SESSION_IMPLEMENTATION" />).
         The corresponding result is csr_sequence, which MUST be equal to
         csa_sequence.
        </t>
      </list>
      </t>
      <t>
 
       In the next three arguments, the client offers a value
       that is to be a property of the session. Except where
       stated otherwise, it is RECOMMENDED that
       the server accept the value.
       If it is not acceptable, the server MAY use a different value.
       Regardless, the server MUST return the value the session will
       use (which will be either what the client offered, or what
       the server is insisting on) to the client.
      <list style="hanging">

        <t hangText="csa_flags:"/>
        <t>
          The csa_flags field contains a list of the following flag
          bits:
          <list style="hanging">
          <t hangText="CREATE_SESSION4_FLAG_PERSIST:"/>
          <t>
	    If CREATE_SESSION4_FLAG_PERSIST is set, the client
	    wants the server to provide a persistent reply cache.
	    For sessions in which only idempotent operations
	    will be used (e.g., a read-only session), clients
	    SHOULD NOT set CREATE_SESSION4_FLAG_PERSIST.  If
	    the server does not or cannot provide a persistent reply cache,
	    the server MUST NOT set CREATE_SESSION4_FLAG_PERSIST in
            the field csr_flags.

	    <vspace blankLines='1' />
 
            If the server is a pNFS metadata server, for
            reasons described in <xref target="obtaining_layout" />
            it SHOULD support CREATE_SESSION4_FLAG_PERSIST if it
            supports the layout_hint (<xref target="attrdef_layout_hint" />)
            attribute.

          </t>
	  <t hangText="CREATE_SESSION4_FLAG_CONN_BACK_CHAN:"/>
	  <t>
	     If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags,
	     the client is requesting that the connection over which the
	     CREATE_SESSION operation arrived be associated with the the session's
	     backchannel in addition to its fore channel.
	     If the server agrees, it
	     sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN
	     in the result field csr_flags. If
	     CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,
	     then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set
	     in csr_flags.

	  </t>
	  <t hangText="CREATE_SESSION4_FLAG_CONN_RDMA:"/>
	  <t>
	     If CREATE_SESSION4_FLAG_CONN_RDMA is set in csa_flags,
             and if the connection over which the CREATE_SESSION operation
             arrived
	     is currently in non-RDMA mode but
	     has the capability to operate in RDMA mode, then the client
	     is requesting that the server "step up" to RDMA mode
	     on the connection.
	     If the server agrees, it sets
             CREATE_SESSION4_FLAG_CONN_RDMA in the result
             field csr_flags. If CREATE_SESSION4_FLAG_CONN_RDMA is
	     not set in csa_flags, then CREATE_SESSION4_FLAG_CONN_RDMA MUST
             NOT be set in csr_flags.
	     Note that once the server agrees to step up, it and the client
	     MUST exchange all future traffic on the connection with RPC RDMA
	     framing and not Record Marking (<xref target="RPCRDMA" />).
	  </t>
          </list>
        </t>
        <t hangText="csa_fore_chan_attrs, csa_fore_chan_attrs:"/>
        <t>
          The csa_fore_chan_attrs and csa_back_chan_attrs
          fields apply to attributes of the
          fore channel (which conveys
          requests originating from the client to the server),
          and the backchannel (the channel that conveys
          callback requests originating from the
          server to the client), respectively. The results are in corresponding structures
          called csr_fore_chan_attrs and csr_back_chan_attrs.
          The results establish attributes for each channel, and
          on all subsequent use of each channel of the session.

          Each structure has the following fields:
          <list style="hanging">
	  <t hangText="ca_headerpadsize:"/>
	  <t>
	    The maximum amount of padding the requester is willing to apply
	    to ensure that write payloads are aligned on some boundary at
	    the replier.  For each channel, the server
            <list style="symbols">

            <t>
             will reply in ca_headerpadsize with
	     its preferred value,
	     or zero if padding is not in use, and
            </t>

            <t>
             MAY decrease this value but MUST NOT increase it.
            </t>
            </list>
	  </t>
          <t hangText="ca_maxrequestsize:"/>
          <t>
            The maximum size of a COMPOUND or CB_COMPOUND request that
            will be sent. This size represents the XDR encoded size of
            the request, including the RPC headers (including
            security flavor credentials and verifiers)
            but excludes any RPC transport framing headers.
            Imagine a request coming over a non-RDMA TCP/IP connection, and
            that it has a single Record Marking header preceding
            it. The maximum allowable
            count encoded in the header will be
            ca_maxrequestsize. If a requester sends
            a request that exceeds ca_maxrequestsize, the error
            NFS4ERR_REQ_TOO_BIG will be returned per the description in
            <xref target="COMPOUND Sizing Issues" />.

            For each channel,
            the server MAY decrease this value but MUST NOT increase it.

          </t>
          <t hangText="ca_maxresponsesize:"/>
          <t>
            The maximum size of a COMPOUND or CB_COMPOUND reply that
            the requester will
            accept from the replier including RPC headers (see
            the ca_maxrequestsize definition).

            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.

            However, if the client selects a value for
            ca_maxresponsesize such that a replier on a channel could
            never send a response, the server SHOULD return
            NFS4ERR_TOOSMALL in the CREATE_SESSION reply.
            After the session is created, if a requester sends a
            request for which the size of the reply would exceed
            this value, the replier will return NFS4ERR_REP_TOO_BIG,
            per the description in
            <xref target="COMPOUND Sizing Issues" />.
          </t>
          <t hangText="ca_maxresponsesize_cached:"/>
          <t>
            Like ca_maxresponsesize, but the maximum size of a reply
            that will be stored in the reply cache
            (<xref target="Slot Identifiers and Server Reply Cache" />).

            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.

            If, in the reply to CREATE_SESSION, the value of
            ca_maxresponsesize_cached of a channel is less than the value
            of ca_maxresponsesize of the same channel, then this is an
            indication to the requester that it needs to be selective
            about which replies it directs the replier to cache; for
            example, large replies from nonidempotent operations (e.g.,
            COMPOUND requests with a READ operation) should not be
            cached. The requester decides which replies to cache via an
            argument to the SEQUENCE (the sa_cachethis field, see <xref
            target="OP_SEQUENCE" />) or CB_SEQUENCE (the csa_cachethis
            field, see <xref target="OP_CB_SEQUENCE" />) operations.

            After the session is created, if a requester sends a
            request for which the size of the reply would exceed
            ca_maxresponsesize_cached, the replier will return
            NFS4ERR_REP_TOO_BIG_TO_CACHE, per the description in <xref
            target="COMPOUND Sizing Issues" />.

          </t>
          <t hangText="ca_maxoperations:"/>
          <t>
            The maximum number of operations the replier
            will accept in a COMPOUND or CB_COMPOUND.

            For the backchannel, the server MUST NOT change the value the
            client offers. For the fore channel, the server
            MAY change the requested value.

            After the session is created, if a requester sends a
            COMPOUND or CB_COMPOUND
            with more operations than ca_maxoperations,
            the replier MUST return NFS4ERR_TOO_MANY_OPS.

          </t>
          <t hangText="ca_maxrequests:"/>
          <t>
            The maximum number of concurrent COMPOUND or CB_COMPOUND
            requests the requester will send on the session.  Subsequent
            requests will each be assigned a slot identifier by the requester
            within the range zero to ca_maxrequests - 1 inclusive.

            For the backchannel, the server MUST NOT change the value the
            client offers. For the fore channel, the server
            MAY change the requested value.

          </t>
          <t hangText="ca_rdma_ird:"/>
          <t>
            This array has a maximum of one element. 
            If this array has one element, then the element contains the
            inbound RDMA read queue depth (IRD).
            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.
          </t>
          </list>
        </t>
        <t hangText="csa_cb_program"/>
        <t>
          This is the ONC RPC program number the server MUST use in
          any callbacks sent through the backchannel to the client.
          The server MUST specify an ONC RPC program number equal to
          csa_cb_program and an ONC RPC version number equal to 4 in
          callbacks sent to the client. If a CB_COMPOUND is
          sent to the client, the server MUST use a minor version
          number of 1.
          There is no corresponding result.
        </t>
        <t hangText="csa_sec_parms"/>
        <t>
          The field csa_sec_parms is an array of acceptable
          security credentials the server can use on
          the session's backchannel. Three security
          flavors are supported: AUTH_NONE, AUTH_SYS,
          and RPCSEC_GSS. If AUTH_NONE is specified for
          a credential, then this says the client is
          authorizing the server to use AUTH_NONE on
          all callbacks for the session.  If AUTH_SYS
          is specified, then the client is authorizing
          the server to use AUTH_SYS on all callbacks,
          using the credential specified cbsp_sys_cred. If
          RPCSEC_GSS is specified, then the server is
          allowed to use the RPCSEC_GSS context specified
          in cbsp_gss_parms as the RPCSEC_GSS context in
          the credential of the RPC header of callbacks
          to the client.

          There is no corresponding result.


	    <vspace blankLines='1' />
 
          The RPCSEC_GSS context for the backchannel is specified via
          a pair of values of data type
          gsshandle4_t. The data type gsshandle4_t represents an
          RPCSEC_GSS handle, and is
          precisely the same as the data type of the "handle" field of
          the rpc_gss_init_res data type defined in
          Section 5.2.3.1, "Context Creation Response -
          Successful Acceptance", of <xref target="RFC2203"
          />.

	    <vspace blankLines='1' />

          The first RPCSEC_GSS handle, gcbp_handle_from_server,
          is the fore handle the server returned to
          the client (either in the handle field of data type
          rpc_gss_init_res or as one of the elements of the spi_handles
          field returned in the reply to EXCHANGE_ID) when the RPCSEC_GSS context
          was created on the server.  The second handle,
          gcbp_handle_from_client, is the back handle to which the
          client will map the RPCSEC_GSS context. The
          server can immediately use the value of
          gcbp_handle_from_client in the RPCSEC_GSS credential
          in callback RPCs. That is, the value in
          gcbp_handle_from_client can be used as the
          value of the field "handle" in data type
          rpc_gss_cred_t (see Section 5, "Elements of
          the RPCSEC_GSS Security Protocol", of <xref
          target="RFC2203" />) in callback RPCs.
          The server MUST use the RPCSEC_GSS security service
          specified in gcbp_service, i.e., it MUST set the
          "service" field of the rpc_gss_cred_t data type in
          RPCSEC_GSS credential to the value of gcbp_service (see
          Section 5.3.1, "RPC Request Header", of <xref target="RFC2203" />).

	    <vspace blankLines='1' />

          If the RPCSEC_GSS handle identified by 
          gcbp_handle_from_server does not exist on the server,
          the server will return NFS4ERR_NOENT.

	    <vspace blankLines='1' />

          Within each element of csa_sec_parms, the fore and back RPCSEC_GSS contexts MUST 
          share the same GSS context
          and MUST have the same seq_window
          (see Section 5.2.3.1 of <xref target="RFC2203">RFC2203</xref>).
          The fore and back RPCSEC_GSS context state
          are independent of each other as far as the
          RPCSEC_GSS sequence number (see the seq_num
          field in the rpc_gss_cred_t data type of Sections
          5 and 5.3.1 of <xref target="RFC2203" />).
	    <vspace blankLines='1' />
       If an RPCSEC_GSS handle is using the SSV context (see <xref
       target="ssv_mech"/>), then because each SSV RPCSEC_GSS
       handle shares a common SSV GSS context, there are security
       considerations specific to this situation discussed in <xref
       target="rpcsec_ssv_consider"/>.
	    <vspace blankLines='1' />


        </t>
   </list>
   </t> 
   <t>
    Once the session is created, the first SEQUENCE or
    CB_SEQUENCE received on a slot MUST have a sequence
    ID equal to 1; if not, the replier MUST return
    NFS4ERR_SEQ_MISORDERED.

  </t>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      To describe a possible implementation, the same notation for client
      records introduced in the description of EXCHANGE_ID is used
      with the following addition:
      <list style="empty">
      <t>
        clientid_arg:
        The value of the csa_clientid field of the CREATE_SESSION4args
        structure of the current request.
      </t>
      </list>
    </t>     
      
    <t>
      Since CREATE_SESSION is a non-idempotent operation, we
      need to consider the possibility that retries may occur
      as a result of a client restart, network partition,
      malfunctioning router, etc.  For each client ID
      created by EXCHANGE_ID, the server maintains a
      separate reply cache (called the CREATE_SESSION reply cache)
      similar to the session reply
      cache used for SEQUENCE operations, with two
      distinctions.
      <list style="symbols">
      <t>
        First, this is a reply cache just for
        detecting and processing CREATE_SESSION requests for a
        given client ID.
      </t>
      <t>
        Second, the size of the client ID
        reply cache is of one slot (and as a result, the
        CREATE_SESSION request does not carry a slot number).
        This means that at most one CREATE_SESSION request for
        a given client ID can be outstanding.
      </t>
      </list>

      As previously stated, CREATE_SESSION can be sent with
      or without a preceding SEQUENCE operation. Even if a
      SEQUENCE precedes CREATE_SESSION, the server MUST
      maintain the CREATE_SESSION reply cache, which
      is separate from the reply cache for the session
      associated with a SEQUENCE. If CREATE_SESSION was
      originally sent by itself, the client MAY send
      a retry of the CREATE_SESSION operation within a
      COMPOUND preceded by a SEQUENCE. If CREATE_SESSION
      was originally sent in a COMPOUND that started with a
      SEQUENCE, then the client SHOULD send a retry in
      a COMPOUND that starts with a SEQUENCE that has the
      same session ID as the SEQUENCE of the original
      request. However, the client MAY send a retry in a
      COMPOUND that either has no preceding SEQUENCE, or
      has a preceding SEQUENCE that refers to a different
      session than the original CREATE_SESSION. This might
      be necessary if the client sends a CREATE_SESSION
      in a COMPOUND preceded by a SEQUENCE with session
      ID X, and session X no longer exists. Regardless, any
      retry of CREATE_SESSION, with or without a preceding
      SEQUENCE, MUST use the same value of csa_sequence
      as the original.

     </t>

     <t>

      After the client received a reply to an EXCHANGE_ID operation that contains
      a new, unconfirmed client ID,
      the server expects the client to follow
      with a CREATE_SESSION operation to confirm the client ID. The
      server expects value of csa_sequenceid in the arguments to
      that CREATE_SESSION to be
      to equal the value of the field eir_sequenceid that was returned in
      results of the EXCHANGE_ID that returned the unconfirmed
      client ID.
      Before the server replies to that EXCHANGE_ID operation,
      it initializes the client ID slot to be equal
      to eir_sequenceid - 1 (accounting for underflow),
      and records a contrived CREATE_SESSION result
      with a "cached" result of NFS4ERR_SEQ_MISORDERED.
      With the client ID slot thus initialized, the processing of the
      CREATE_SESSION operation is divided into four phases:

      <list style="numbers">
      <t>
        Client record look up. The server looks up the client ID
        in its client record table.
        If the server contains no records
        with client ID equal to clientid_arg, then most
        likely the client's state has been purged during a
        period of inactivity, possibly due to a loss of
        connectivity.  NFS4ERR_STALE_CLIENTID is returned,
        and no changes are made to any client records on
        the server. Otherwise, the server goes to phase 2.
      </t>
      <t>
        Sequence ID processing. If csa_sequenceid is equal to the
        sequence ID in the client ID's slot, then this is a replay 
        of the previous CREATE_SESSION request, and the server
        returns the cached result.
        If csa_sequenceid is not equal to the sequence ID in the slot,
        and is more than one greater (accounting for wraparound),
        then the server returns the error NFS4ERR_SEQ_MISORDERED,
        and does not change the slot.  If csa_sequenceid is
        equal to the slot's sequence ID + 1 (accounting for
        wraparound), then the slot's sequence ID is set to
        csa_sequenceid, and the CREATE_SESSION processing goes to
        the next phase. A subsequent new CREATE_SESSION call
        over the same client ID MUST
        use a csa_sequenceid that is one greater than the
        sequence ID in the slot.

      </t>
      <t>
        Client ID confirmation. If this would be the first session for the
        client ID, the CREATE_SESSION operation serves to confirm the
        client ID.
        Otherwise,
        the client ID confirmation phase is skipped and only
        the session creation phase occurs. 
        Any case in which there is more than one
        record with identical values for client ID represents
        a server implementation error.
        Operation in the
        potential valid cases is summarized as follows.
        <list style="symbols">
        <t>Successful Confirmation
        <list style="empty">
          <t>
            If the server has the following unconfirmed record, then this
            is the expected confirmation of an unconfirmed record.
          </t>
          <t>
            { ownerid, verifier, principal_arg, clientid_arg, unconfirmed }
          </t>
          <t>
            As noted in <xref target="OP_EXCHANGE_ID_IMPLEMENTATION" />,
            the server might also have the following confirmed record.
          </t>
          <t>
            { ownerid, old_verifier, principal_arg, old_clientid, confirmed }
          </t>
          <t>
            The server schedules the replacement of both records with:
          </t>
          <t>
            { ownerid, verifier, principal_arg, clientid_arg, confirmed }
          </t>
           <t>
            The processing of CREATE_SESSION continues on to session creation.
            Once the session is successfully created, the scheduled client
            record replacement is committed. If the session is not
            successfully created, then no changes are made to any client
            records on the server.
          </t>
        </list>
        </t>

        <t>Unsuccessful Confirmation
        <list style="empty">
          <t>
            If the server has the following record, then the client has
            changed principals after the previous EXCHANGE_ID request,
            or there has been a chance collision between shorthand client
            identifiers.
          </t>
          <t>
            { *, *, old_principal_arg, clientid_arg, * }
          </t>
          <t>
            Neither of these cases is permissible.  Processing stops and
            NFS4ERR_CLID_INUSE is returned to the client.  No changes are
            made to any client records on the server.
          </t>
        </list>
        </t>
      </list>
    </t>

    <t>
      Session creation.
      The server confirmed the client ID, either in this
      CREATE_SESSION operation, or a previous CREATE_SESSION
      operation.
      The server examines the remaining fields of the arguments.


	    <vspace blankLines='1' />

      The server creates the session by recording the
      parameter values used (including whether the
      CREATE_SESSION4_FLAG_PERSIST flag is set and has
      been accepted by the server) and allocating space
      for the session reply cache (if there is not enough
      space, the server returns NFS4ERR_NOSPC). For each slot in the
      reply cache, the server sets the sequence ID to zero,
      and records an entry containing a COMPOUND
      reply with zero operations and the error
      NFS4ERR_SEQ_MISORDERED. This way, if the first
      SEQUENCE request sent has a sequence ID equal to
      zero, the server can simply return what is in the
      reply cache: NFS4ERR_SEQ_MISORDERED.  The client
      initializes its reply cache for receiving callbacks
      in the same way, and similarly, the first CB_SEQUENCE
      operation on a slot after session creation MUST have
      a sequence ID of one.

	    <vspace blankLines='1' />

      If the session state is created successfully, the server associates
      the session with the client ID provided by the client. 

	    <vspace blankLines='1' />

       When a request that had CREATE_SESSION4_FLAG_CONN_RDMA set
       needs to be retried, the retry
       MUST be done on a new connection that is in non-RDMA mode.
       If properties of the new connection are different enough
       that the arguments to CREATE_SESSION need to change, then
       a non-retry MUST be sent. The server will eventually dispose
       of any session that was created on the original connection.
    </t>
   </list>
   </t>
   <t>
       On the backchannel, the client and server might wish to
       have many slots, in some cases perhaps more that the fore channel, in
       order to deal with the situations where the
       network link has high latency and is the primary
       bottleneck for response to recalls. If so, and if the
       client provides too few slots to the backchannel,
       the server might limit the number of recallable
       objects it gives to the client.
   </t>
   <t>
     Implementing RPCSEC_GSS callback support requires
     changes to both the client and server implementations of
     RPCSEC_GSS.  One possible set of changes includes:
     <list style="symbols">
     <t>
       Adding a data structure that wraps the GSS-API
       context with a reference count.
     </t>
     <t>        
       New functions to increment and decrement the reference
       count. If the reference count is decremented to zero,
       the wrapper data structure and the GSS-API context it
       refers to would be freed.
     </t>
     <t>        
       Change RPCSEC_GSS to create the wrapper data
       structure upon receiving GSS-API context from
       gss_accept_sec_context() and gss_init_sec_context().
       The reference count would be initialized to 1.
     </t>
     <t>        
       Adding a function to map an existing
       RPCSEC_GSS handle to a pointer to the wrapper data
       structure. The reference count would be incremented.
     </t>
     <t>        
       Adding a function to create a new RPCSEC_GSS
       handle from a pointer to the wrapper data structure.
       The reference count would be incremented.
     </t>
     <t>        
       Replacing calls from RPCSEC_GSS that free GSS-API
       contexts, with calls to decrement the reference count
       on the wrapper data structure.
     </t>
     </list>
   </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DESTROY_SESSION" title="Operation 44: DESTROY_SESSION - Destroy a Session" >

  <section toc="exclude" anchor="OP_DESTROY_SESSION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct DESTROY_SESSION4args {
        sessionid4      dsa_sessionid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
struct DESTROY_SESSION4res {
        nfsstat4        dsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DESTROY_SESSION operation closes the session and discards
      the session's reply cache, if any.
      Any remaining connections associated with the session are
      immediately disassociated. If the connection has no remaining
      associated sessions, the connection
      MAY be closed by the server.
      Locks, delegations, layouts, wants, and the lease, which are all
      tied to the client ID, are not affected by DESTROY_SESSION.
    </t>
    <t>
      DESTROY_SESSION MUST be invoked on a connection that
      is associated with the session being destroyed.
      In addition, if SP4_MACH_CRED state protection
      was specified when the client ID was created,
      the RPCSEC_GSS principal that created the session MUST be
      the one that destroys the session, using RPCSEC_GSS
      privacy or integrity. If SP4_SSV state protection was
      specified when the client ID was created, RPCSEC_GSS
      using the SSV mechanism (<xref target="ssv_mech" />)
      MUST be used, with integrity or privacy.

    </t>
    <t>
      If the COMPOUND request starts with SEQUENCE, and
      if the sessionids specified in SEQUENCE and DESTROY_SESSION
      are the same, then

      <list style="symbols">
      <t>
       DESTROY_SESSION MUST be the final operation in the COMPOUND
       request.

      </t>

      <t>
       It is advisable to avoid placing DESTROY_SESSION in a
       COMPOUND request with other state-modifying
       operations, because the DESTROY_SESSION will destroy
       the reply cache.

      </t>

      <t>
	Because the session and its reply cache are destroyed, a client that
	retries the request may receive an error in
	reply to the retry, even though the original request was
	successful.

      </t>

      </list>
    </t>

    <t>
      If the COMPOUND request starts with SEQUENCE, and
      if the sessionids specified in SEQUENCE and DESTROY_SESSION
      are different, then DESTROY_SESSION can appear in any position
      of the COMPOUND request (except for the first position). The
      two sessionids can belong to different client IDs. 
    </t>

    <t>
      If the COMPOUND request does not start with
      SEQUENCE, and if DESTROY_SESSION is not the
      sole operation, then server MUST return
      NFS4ERR_NOT_ONLY_OP.

    </t>

    <t>
     If there is a backchannel on the session and the
     server has outstanding CB_COMPOUND operations for the
     session which have not been replied to, then the server
     MAY refuse to destroy the session and return an error.
     If so, then
     in the event the backchannel is down, the server
     SHOULD return NFS4ERR_CB_PATH_DOWN to inform the
     client that the backchannel needs to be repaired before
     the server will allow the session to be destroyed.
     Otherwise, the error CB_BACK_CHAN_BUSY SHOULD be
     returned to indicate that there are CB_COMPOUNDs
     that need to be replied to.  The client SHOULD reply
     to all outstanding CB_COMPOUNDs before re-sending
     DESTROY_SESSION.

    </t>
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_FREE_STATEID" title="Operation 45: FREE_STATEID - Free Stateid with No Locks" >

  <section toc="exclude" anchor="OP_FREE_STATEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct FREE_STATEID4args {
        stateid4        fsa_stateid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_FREE_STATID_RESULT" title="RESULT">
<figure>
 <artwork>
struct FREE_STATEID4res {
        nfsstat4        fsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_FREE_STATEID4_DESCRIPTION" title="DESCRIPTION">
    <t>
      The FREE_STATEID operation is used to free a stateid that no longer
      has any associated locks (including opens, byte-range locks, delegations,
      and layouts).  This may be because of client LOCKU operations or because
      of server revocation.  If there are valid locks (of any kind) 
      associated with the stateid in question, the error NFS4ERR_LOCKS_HELD
      will be returned, and the associated stateid will not be freed.
    </t>
    <t>
      When a stateid is freed that had been associated with revoked locks,
      by sending the FREE_STATEID operation, the client acknowledges the loss of those
      locks.  This allows the server, once all such revoked state is 
      acknowledged,
      to allow that client again to reclaim locks, without encountering 
      the edge conditions discussed in <xref target="server_failure" />.
    </t>
    <t>
      Once a successful FREE_STATEID is done for a given stateid, any
      subsequent use of that stateid will result in an NFS4ERR_BAD_STATEID
      error.
    </t>
  </section>
</section>

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GET_DIR_DELEGATION" title="Operation 46: GET_DIR_DELEGATION - Get a Directory Delegation" >

  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>

typedef nfstime4 attr_notice4;

struct GET_DIR_DELEGATION4args {
        /* CURRENT_FH: delegated directory */
        bool            gdda_signal_deleg_avail;
        bitmap4         gdda_notification_types;
        attr_notice4    gdda_child_attr_delay;
        attr_notice4    gdda_dir_attr_delay;
        bitmap4         gdda_child_attributes;
        bitmap4         gdda_dir_attributes;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_RESULT" title="RESULT">
<figure>
 <artwork>
struct GET_DIR_DELEGATION4resok {
        verifier4       gddr_cookieverf;
        /* Stateid for get_dir_delegation */
        stateid4        gddr_stateid;
        /* Which notifications can the server support */
        bitmap4         gddr_notification;
        bitmap4         gddr_child_attributes;
        bitmap4         gddr_dir_attributes;
};

enum gddrnf4_status {
        GDD4_OK         = 0,
        GDD4_UNAVAIL    = 1
};

union GET_DIR_DELEGATION4res_non_fatal
 switch (gddrnf4_status gddrnf_status) {
 case GDD4_OK:
  GET_DIR_DELEGATION4resok      gddrnf_resok4;
 case GDD4_UNAVAIL:
  bool                          gddrnf_will_signal_deleg_avail;
};

union GET_DIR_DELEGATION4res
 switch (nfsstat4 gddr_status) {
 case NFS4_OK:
  GET_DIR_DELEGATION4res_non_fatal      gddr_res_non_fatal4;
 default:
  void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GET_DIR_DELEGATION operation is used by a client to request
      a directory delegation. The directory is represented by the
      current filehandle. The client also specifies whether it wants
      the server to notify it when the directory changes in certain
      ways by setting one or more bits in a bitmap. The server may
      refuse to grant the delegation. In that case, the server
      will return NFS4ERR_DIRDELEG_UNAVAIL. If the server decides to
      hand out the delegation, it will return a cookie verifier for
      that directory. If the cookie verifier changes when the client
      is holding the delegation, the delegation will be recalled
      unless the client has asked for notification for this event. 
    </t>
    <t>
      The server will also return a directory delegation stateid, 
      gddr_stateid, as a result of the
      GET_DIR_DELEGATION operation. This stateid will appear in
      callback messages related to the delegation, such as
      notifications and delegation recalls.  The client will use this
      stateid to return the delegation voluntarily or upon recall.  A
      delegation is returned by calling the DELEGRETURN operation.
    </t>
    <t>
      The server might not be able to support notifications of certain
      events. If the client asks for such notifications, the server
      MUST inform the client of its inability to do so as part of the
      GET_DIR_DELEGATION reply by not setting the appropriate bits in
      the supported notifications bitmask, gddr_notification, contained 
      in the reply.  The server MUST NOT add bits to gddr_notification
      that the client did not request.
    </t>
    <t>
      The GET_DIR_DELEGATION operation can be used for both normal and
      named attribute directories. 
    </t>
    <t>
      If client sets gdda_signal_deleg_avail to TRUE, then it is
      registering with the client a "want" for a directory
      delegation. If the delegation is not available, and the server 
      supports and will honor the "want",
      the results will have gddrnf_will_signal_deleg_avail set to TRUE
      and no error will be indicated on return.
      If so, the client should expect a future CB_RECALLABLE_OBJ_AVAIL
      operation to indicate that a directory delegation is available.
      If the server does not wish to honor the "want" or is not able
      to do so, it returns the error NFS4ERR_DIRDELEG_UNAVAIL.  If the
      delegation is immediately available, the server SHOULD return it with
      the response to the operation, rather than via a callback. 
    </t>

    <t>
      When a client makes a request for a
      directory delegation while it already holds
      a directory delegation for that directory
      (including the case where it has been
      recalled but not yet returned by the client
      or revoked by the server), the server MUST
      reply with the value of gddr_status set to
      NFS4_OK, the value of gddrnf_status set to
      GDD4_UNAVAIL, and the value of
      gddrnf_will_signal_deleg_avail set to
      FALSE.  The delegation the client held
      before the request remains intact, and its
      state is unchanged. The current stateid is
      not changed (see <xref
      target="current_stateid"/> for a description
      of the current stateid).

    </t>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Directory delegations provide the benefit of improving cache
      consistency of namespace information. This is done through
      synchronous callbacks. A server must support synchronous
      callbacks in order to support directory delegations. In addition
      to that, asynchronous notifications provide a way to reduce
      network traffic as well as improve client performance in certain
      conditions.
    </t>
    <t>
      Notifications are specified in terms of potential
      changes to the directory. A client can ask to be
      notified of events by setting one or more
      bits in gdda_notification_types.
      The client can ask for notifications on addition of entries
      to a directory (by setting the
      NOTIFY4_ADD_ENTRY in gdda_notification_types),
      notifications on entry removal
      (NOTIFY4_REMOVE_ENTRY), renames
      (NOTIFY4_RENAME_ENTRY), directory attribute
      changes (NOTIFY4_CHANGE_DIR_ATTRIBUTES),
      and cookie verifier changes
      (NOTIFY4_CHANGE_COOKIE_VERIFIER) by setting
      one or more corresponding bits in the
      gdda_notification_types field.
    </t>
    <t>
      The client can also ask for
      notifications of changes to
      attributes of directory entries
      (NOTIFY4_CHANGE_CHILD_ATTRIBUTES)
      in order to keep its attribute cache up to date. However, any
      changes made to child attributes do not cause the delegation to
      be recalled. If a client is interested in directory entry
      caching or negative name caching, it can set the
      gdda_notification_types appropriately to its particular need 
      and the server will notify it of
      all changes that would otherwise invalidate its name cache. The
      kind of notification a client asks for may depend on the
      directory size, its rate of change, and the applications being
      used to access that directory. The enumeration of the conditions under
      which a client might ask for a notification is out of the scope
      of this specification.
    </t>
    <t>
      For attribute notifications, the client
      will set bits in the gdda_dir_attributes
      bitmap to indicate which attributes
      it wants to be notified of. If the server does not support
      notifications for changes to a certain attribute, it SHOULD NOT
      set that attribute in the supported attribute bitmap
      specified in the reply (gddr_dir_attributes). The client will
      also set in the gdda_child_attributes bitmap the attributes
      of directory entries it wants to be notified of, and
      the server will indicate in gddr_child_attributes which
      attributes of directory entries it will notify the client of.
    </t>
    <t>
      The client will also let the server know if
      it wants to get the notification as soon as the attribute change
      occurs or after a certain delay by setting a delay factor;
      gdda_child_attr_delay is for attribute changes to directory entries and
      gdda_dir_attr_delay is for attribute changes to the directory. If this
      delay factor is set to zero, that indicates to the server that
      the client wants to be notified of any attribute changes as soon
      as they occur. If the delay factor is set to N seconds, the server will
      make a best-effort guarantee that attribute updates are
      synchronized within N seconds.
      If the client asks
      for a delay factor that the server does not support or that may
      cause significant resource consumption on the server by causing
      the server to send a lot of notifications, the server should not
      commit to sending out notifications for attributes and
      therefore must not set the appropriate bit in the
      gddr_child_attributes and gddr_dir_attributes bitmaps in the response.
    </t>
    <t>
      The client MUST use a security tuple (<xref
      target="NFSv4 Security Tuples"/>) that the
      directory or its applicable ancestor (<xref
      target="Security Service Negotiation"/>) is
      exported with. If not, the server MUST return
      NFS4ERR_WRONGSEC to the operation that both precedes
      GET_DIR_DELEGATION and sets the current filehandle
      (see <xref target="using_secinfo"/>).

    </t>
    <t>
      The directory delegation covers all the entries in the
      directory except the parent entry.  That means if a directory and
      its parent both hold directory delegations, any changes to the
      parent will not cause a notification to be sent for the child
      even though the child's parent entry points to the parent
      directory.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETDEVICEINFO" title="Operation 47: GETDEVICEINFO - Get Device Information" >

  <section toc="exclude" anchor="OP_GETDEVICEINFO_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct GETDEVICEINFO4args {
        deviceid4       gdia_device_id;
        layouttype4     gdia_layout_type;
        count4          gdia_maxcount;
        bitmap4         gdia_notify_types;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_RESULT" title="RESULT">
<figure>
 <artwork>
struct GETDEVICEINFO4resok {
        device_addr4    gdir_device_addr;
        bitmap4         gdir_notification;
};

union GETDEVICEINFO4res switch (nfsstat4 gdir_status) {
case NFS4_OK:
        GETDEVICEINFO4resok     gdir_resok4;
case NFS4ERR_TOOSMALL:
        count4                  gdir_mincount;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GETDEVICEINFO operation returns pNFS storage device address
      information for the specified device ID.
      The client identifies the device information to be returned by
      providing the gdia_device_id and gdia_layout_type that uniquely
      identify the device.  The client provides gdia_maxcount
      to limit the number of bytes for the result.  This maximum size
      represents all of the data being returned within the
      GETDEVICEINFO4resok structure and includes the XDR overhead.
      The server may return less data.  If the server is unable to
      return any information within the gdia_maxcount limit, the error
      NFS4ERR_TOOSMALL will be returned. However, if gdia_maxcount is
      zero, NFS4ERR_TOOSMALL MUST NOT be returned.
    </t>
    <t>
      The da_layout_type field of the gdir_device_addr returned 
      by the server MUST be equal to the gdia_layout_type specified
      by the client.  If it is not equal, the client SHOULD ignore
      the response as invalid and behave as if the server returned
      an error, even if the client does have support for the 
      layout type returned.
    </t> 
    <t>

      The client also provides a notification bitmap,
      gdia_notify_types, for the device ID mapping
      notification for which it is interested in receiving;
      the server must support device ID notifications
      for the notification request to have affect.
      The notification mask is composed in the same
      manner as the bitmap for file attributes (<xref
      target="fattr4" />).  The numbers of bit positions
      are listed in the notify_device_type4 enumeration type
      (<xref target="OP_CB_NOTIFY_DEVICEID" />). Only
      two enumerated values of notify_device_type4 currently
      apply to GETDEVICEINFO:
      NOTIFY_DEVICEID4_CHANGE
      and NOTIFY_DEVICEID4_DELETE (see <xref
      target="OP_CB_NOTIFY_DEVICEID" />).

    </t>
    <t>
      The notification bitmap applies only to the specified device ID.
      If a client sends a GETDEVICEINFO operation on a deviceID multiple times,
      the last notification bitmap is used by the server for
      subsequent notifications. If the bitmap is zero or empty,
      then the device ID's notifications are turned off.
    </t>
    <t>
     If the client wants to just update or turn off notifications,
     it MAY send a GETDEVICEINFO operation with gdia_maxcount set to zero.
     In that event, if the device ID is valid, the reply's da_addr_body
     field of the gdir_device_addr field will be of zero length.
    </t>
    <t>
      If an unknown device ID is given in gdia_device_id,
      the server returns NFS4ERR_NOENT.

      Otherwise, the device address
      information is returned in gdir_device_addr. 
      Finally, if the server supports
      notifications for device ID mappings, the gdir_notification
      result will contain a bitmap of which notifications
      it will actually send to the client (via CB_NOTIFY_DEVICEID,
      see <xref target="OP_CB_NOTIFY_DEVICEID" />).
    </t>
    <t>
      If NFS4ERR_TOOSMALL is returned, the results also contain
      gdir_mincount.  The value of gdir_mincount represents the
      minimum size necessary to obtain the device information.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
   Aside from updating or turning off notifications, another
   use case for gdia_maxcount being set to zero is to validate
   a device ID.
  </t>
  <t>
    The client SHOULD request a notification for changes or
    deletion of a device ID to device address mapping so
    that the server can allow the client gracefully use a
    new mapping, without having pending I/O fail abruptly,
    or force layouts using the device ID to be recalled
    or revoked.

  </t>

  <t>
    It is possible that GETDEVICEINFO (and
    GETDEVICELIST) will race with CB_NOTIFY_DEVICEID,
    i.e., CB_NOTIFY_DEVICEID arrives before the client
    gets and processes the response to GETDEVICEINFO or
    GETDEVICELIST.  The analysis of the race leverages the
    fact that the server MUST NOT delete a device ID that
    is referred to by a layout the client has.
    <list style="symbols">
    <t>
       CB_NOTIFY_DEVICEID deletes a device ID.
       If the client believes it has layouts that refer to the
       device ID, then it is possible that layouts referring to
       the deleted device ID have been revoked.
       The client should send a TEST_STATEID request using the
       stateid for each layout that might have been revoked. If
       TEST_STATEID indicates that any layouts have been revoked, the
       client must recover from layout revocation as described in
       <xref
       target="revoke_layout" />. If TEST_STATEID indicates that at least
       one layout has not been revoked, the client should send
       a GETDEVICEINFO operation on the supposedly deleted
       device ID to verify that the device ID
       has been deleted.

	    <vspace blankLines='1' />

       If GETDEVICEINFO indicates that the device ID
       does not exist, then the client assumes the server is faulty
       and recovers by sending an EXCHANGE_ID operation. If GETDEVICEINFO
       indicates that the device ID does exist, then while the server is
       faulty for sending an erroneous device ID deletion notification,
       the degree to which it is faulty does not require the client to
       create a new client ID.
   
	    <vspace blankLines='1' />

       If the client does not have layouts that refer to the
       device ID, no harm is done.
       The client should mark the device ID as deleted, and when
       GETDEVICEINFO or GETDEVICELIST results are
       received that indicate that the device ID has been
       in fact deleted, the device ID should be removed from the
       client's cache.

    </t>
    
    <t>
       CB_NOTIFY_DEVICEID indicates that a device ID's device
       addressing mappings have changed. The client should assume
       that the results from the in-progress GETDEVICEINFO
       will be stale for the device ID
       once received, and so it should send another GETDEVICEINFO
       on the device ID.
     
    </t>
   </list>
  </t> 

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETDEVICELIST" title="Operation 48: GETDEVICELIST - Get All Device Mappings for a File System" >

  <section toc="exclude" anchor="OP_GETDEVICELIST_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct GETDEVICELIST4args {
        /* CURRENT_FH: object belonging to the file system */
        layouttype4     gdla_layout_type;

        /* number of deviceIDs to return */
        count4          gdla_maxdevices;

        nfs_cookie4     gdla_cookie;
        verifier4       gdla_cookieverf;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_RESULT" title="RESULT">
<figure>
 <artwork>
struct GETDEVICELIST4resok {
        nfs_cookie4             gdlr_cookie;
        verifier4               gdlr_cookieverf;
        deviceid4               gdlr_deviceid_list&lt;>;
        bool                    gdlr_eof;
};

union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
case NFS4_OK:
        GETDEVICELIST4resok     gdlr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used by the client to enumerate all of the
      device IDs that a server's file system uses.
    </t>
    <t>
      The client provides a current filehandle of a file object that
      belongs to the file system (i.e., all file objects sharing the same
      fsid as that of the current filehandle) and the layout type
      in gdia_layout_type.  Since
      this operation might require multiple calls to enumerate all the
      device IDs (and is thus
      similar to the <xref target="OP_READDIR">
      READDIR</xref> operation), the client also provides gdia_cookie
      and gdia_cookieverf to specify the current cursor position in the
      list. When the client wants to read from the beginning of the
      file system's device mappings, it sets gdla_cookie to zero. The
      field gdla_cookieverf MUST be ignored by the server when
      gdla_cookie is zero.
      The client provides gdla_maxdevices to limit the number of device IDs
      in the result. If gdla_maxdevices is zero, the server MUST return
      NFS4ERR_INVAL.
      The server MAY return fewer device IDs.
    </t>
    
    <t>
      The successful response to the operation will contain the
      cookie, gdlr_cookie, and the cookie verifier, gdlr_cookieverf, to be
      used on the subsequent GETDEVICELIST.  A gdlr_eof value of TRUE
      signifies that there are no remaining entries in the server's
      device list.  Each element of gdlr_deviceid_list contains
      a device ID.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
      An example of the use of this operation is for pNFS
      clients and servers that use LAYOUT4_BLOCK_VOLUME
      layouts.  In these environments it may be helpful
      for a client to determine device accessibility upon
      first file system access.

  </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTCOMMIT" title="Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a Layout" >

  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
union newtime4 switch (bool nt_timechanged) {
case TRUE:
        nfstime4           nt_time;
case FALSE:
        void;
};

union newoffset4 switch (bool no_newoffset) {
case TRUE:
        offset4           no_offset;
case FALSE:
        void;
};

struct LAYOUTCOMMIT4args {
        /* CURRENT_FH: file */
        offset4                 loca_offset;
        length4                 loca_length;
        bool                    loca_reclaim;
        stateid4                loca_stateid;
        newoffset4              loca_last_write_offset;
        newtime4                loca_time_modify;
        layoutupdate4           loca_layoutupdate;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_RESULT" title="RESULT">
<figure>
 <artwork>
union newsize4 switch (bool ns_sizechanged) {
case TRUE:
        length4         ns_size;
case FALSE:
        void;
};

struct LAYOUTCOMMIT4resok {
        newsize4                locr_newsize;
};

union LAYOUTCOMMIT4res switch (nfsstat4 locr_status) {
case NFS4_OK:
        LAYOUTCOMMIT4resok      locr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LAYOUTCOMMIT operation commits changes in the layout represented by the current
      filehandle, client ID (derived from the session ID in the
      preceding SEQUENCE operation), byte-range, and stateid.  Since
      layouts are sub-dividable, a smaller portion of a layout,
      retrieved via LAYOUTGET, can be committed.  The byte-range being
      committed is specified through the byte-range (loca_offset and
      loca_length). This byte-range MUST overlap with one or more existing layouts
      previously granted via LAYOUTGET (<xref target="OP_LAYOUTGET"/>),
      each with an iomode of LAYOUTIOMODE4_RW.  In the
      case where the iomode of any held layout segment is not
      LAYOUTIOMODE4_RW, the server should return the error
      NFS4ERR_BAD_IOMODE.  For the case where the client
      does not hold matching layout segment(s) for the
      defined byte-range, the server should return the error
      NFS4ERR_BAD_LAYOUT.

    </t>
    <t>
      The LAYOUTCOMMIT operation indicates that the client has
      completed writes using a layout obtained by a previous
      LAYOUTGET.  The client may have only written a subset of the
      data range it previously requested.  LAYOUTCOMMIT allows it to
      commit or discard provisionally allocated space and to update
      the server with a new end-of-file.  The layout referenced by
      LAYOUTCOMMIT is still valid after the operation completes and
      can be continued to be referenced by the client ID, filehandle,
      byte-range, layout type, and stateid.
    </t>
    <t>
      If the loca_reclaim field is set to TRUE, this indicates that
      the client is attempting to commit changes to a layout after the
      restart of the metadata server during the metadata server's
      recovery grace period (see <xref target="mds_recovery"/>).  This type of request may be necessary
      when the client has uncommitted writes to provisionally
      allocated byte-ranges of a file that were sent to the storage
      devices before the restart of the metadata server.  In this case,
      the layout provided by the client MUST be a subset of a writable
      layout that the client held immediately before the restart of the
      metadata server. The value of the field loca_stateid MUST
      be a value that the metadata server returned before it restarted.
      The metadata server is free to accept or
      reject this request based on its own internal metadata
      consistency checks.  If the metadata server finds that the
      layout provided by the client does not pass its consistency
      checks, it MUST reject the request with the status
      NFS4ERR_RECLAIM_BAD.  The successful completion of the
      LAYOUTCOMMIT request with loca_reclaim set to TRUE does NOT
      provide the client with a layout for the file.  It simply
      commits the changes to the layout specified in the
      loca_layoutupdate field.  To obtain a layout for the file, the
      client must send a LAYOUTGET request to the server after the
      server's grace period has expired.  If the metadata server
      receives a LAYOUTCOMMIT request with loca_reclaim set to TRUE
      when the metadata server is not in its recovery grace period, it
      MUST reject the request with the status NFS4ERR_NO_GRACE.
    </t>
    <t>
      Setting the loca_reclaim field to TRUE is required if and only
      if the committed layout was acquired before the metadata server
      restart.  If the client is committing a layout that was acquired
      during the metadata server's grace period, it MUST set the
      "reclaim" field to FALSE.
    </t>
    <t>
      The loca_stateid is a layout stateid value as
      returned by previously successful layout operations
      (see <xref target="layout_stateid"/>).

    </t>
    <t>
      The loca_last_write_offset field specifies the offset of the
      last byte written by the client previous to the LAYOUTCOMMIT.
      Note that this value is never equal to the file's size (at most
      it is one byte less than the file's size) and MUST be less than
      or equal to NFS4_MAXFILEOFF.  Also, loca_last_write_offset MUST
      overlap the range described by loca_offset and loca_length.
      The metadata server
      may use this information to determine whether the file's size
      needs to be updated.  If the metadata server updates the file's
      size as the result of the LAYOUTCOMMIT operation, it must return
      the new size (locr_newsize.ns_size) as part of the results.
    </t>
    <t>
      The loca_time_modify field
      allows the client to suggest a modification time it would like the metadata
      server to set.  The metadata server may use the suggestion or
      it may use the time of the LAYOUTCOMMIT operation to set the modification
      time.  If the metadata server uses the client-provided
      modification time, it should ensure that time does not flow backwards.  If the
      client wants to force the metadata server to set an exact time,
      the client should use a SETATTR operation in a COMPOUND right
      after LAYOUTCOMMIT.  See <xref target="committing_layout" /> for
      more details.  If the client desires the resultant modification time,
      it should construct the COMPOUND so that a GETATTR
      follows the LAYOUTCOMMIT.
    </t>
    <t>
     The loca_layoutupdate argument to LAYOUTCOMMIT provides a mechanism
     for a client to provide layout-specific updates to the metadata
     server.  For example, the layout update can describe what byte-ranges
     of the original layout have been used and what byte-ranges can be
     deallocated.  There is no NFSv4.1 file layout-specific layoutupdate4
     structure.
    </t>
    <t>
      The layout information is more verbose for block devices than for
      objects and files because the latter two hide the details of block
      allocation behind their storage protocols.  At the minimum, the
      client needs to communicate changes to the end-of-file location back
      to the server, and, if desired, its view of the file's modification
      time.  For block/volume layouts, it needs to specify precisely
      which blocks have been used.
    </t>
    <t>
      If the layout identified in the arguments does not exist, the
      error NFS4ERR_BADLAYOUT is returned.  The layout being committed
      may also be rejected if it does not correspond to an existing
      layout with an iomode of LAYOUTIOMODE4_RW.
    </t>
    <t>
      On success, the current filehandle retains its value and the
      current stateid retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client MAY also use LAYOUTCOMMIT with the
      loca_reclaim field set to TRUE to convey hints to modified file
      attributes or to report layout-type specific information such as
      I/O errors for object-based storage layouts, as normally done
      during normal operation. Doing so may help the metadata server
      to recover files more efficiently after restart.  For example,
      some file system implementations may require expansive recovery
      of file system objects if the metadata server does not get a
      positive indication from all clients holding a LAYOUTIOMODE4_RW layout that
      they have successfully completed all their writes.  Sending a
      LAYOUTCOMMIT (if required) and then following with LAYOUTRETURN
      can provide such an indication and allow for graceful and
      efficient recovery.
    </t>
    <t>
      If loca_reclaim is TRUE, the metadata server is free to
      either examine or ignore the value in the field loca_stateid.
      The metadata server implementation might or might not
      encode in its layout
      stateid information that allows the metadate server to
      perform a consistency check on the LAYOUTCOMMIT request.
    </t>      
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTGET" title="Operation 50: LAYOUTGET - Get Layout Information" >

  <section toc="exclude" anchor="OP_LAYOUTGET_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct LAYOUTGET4args {
        /* CURRENT_FH: file */
        bool                    loga_signal_layout_avail;
        layouttype4             loga_layout_type;
        layoutiomode4           loga_iomode;
        offset4                 loga_offset;
        length4                 loga_length;
        length4                 loga_minlength;
        stateid4                loga_stateid;
        count4                  loga_maxcount;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_RESULT" title="RESULT">
<figure>
 <artwork>
struct LAYOUTGET4resok {
        bool               logr_return_on_close;
        stateid4           logr_stateid;
        layout4            logr_layout&lt;>;
};

union LAYOUTGET4res switch (nfsstat4 logr_status) {
case NFS4_OK:
        LAYOUTGET4resok     logr_resok4;
case NFS4ERR_LAYOUTTRYLATER:
        bool                logr_will_signal_layout_avail;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LAYOUTGET operation requests a layout from the metadata server for reading or
      writing the file given by the filehandle at the
      byte-range specified by offset and length.  Layouts are
      identified by the client ID (derived from the session ID in the
      preceding SEQUENCE operation), current filehandle, layout type
      (loga_layout_type), and the layout stateid (loga_stateid).  The
      use of the loga_iomode field depends upon the layout type, but should
      reflect the client's data access intent.
    </t>
    <t>
      If the metadata server is in a grace period, and does not
      persist layouts and device ID to device address mappings, then
      it MUST return NFS4ERR_GRACE (see <xref target="reclaim_locks"/>).
    </t>
     
    <t>
      The LAYOUTGET operation returns layout information
      for the specified byte-range: a layout.
      The client actually specifies two ranges, both starting
      at the offset in the loga_offset field. The first
      range is between loga_offset and loga_offset + loga_length - 1
      inclusive. This range indicates the desired range the client
      wants the layout to cover. The second range is between
      loga_offset and loga_offset + loga_minlength - 1 inclusive. This
      range indicates the required range the client needs the layout
      to cover. Thus, loga_minlength MUST be less than or equal to
      loga_length.
    </t>
      
    <t>
      When a length field is set to NFS4_UINT64_MAX,
      this indicates a desire (when loga_length is NFS4_UINT64_MAX)
      or requirement (when loga_minlength is NFS4_UINT64_MAX)
      to get a layout from loga_offset through the
      end-of-file, regardless of the file's length.
    </t>
    <t>
      The following rules govern the relationships among,
      and the minima of,
      loga_length, loga_minlength, and loga_offset.
      
      <list style='symbols'>
      <t>
       If loga_length is less than loga_minlength, the metadata server
       MUST return NFS4ERR_INVAL.

      </t>
      <t>
       If loga_minlength is zero, this is an indication
       to the metadata server that the client desires any layout
       at offset loga_offset or less that the metadata server has
       "readily available". Readily is subjective, and depends on
       the layout type and the pNFS server implementation. For example,
       some metadata servers might have to pre-allocate stable
       storage when they receive a request for a range of a
       file that goes beyond the file's current length.
       If loga_minlength is zero and
       loga_length is greater than zero, this tells the
       metadata server what range of the layout the client would
       prefer to have. If loga_length and loga_minlength
       are both zero, then the client is indicating that it desires
       a layout of any length with the ending offset of the range
       no less than the value specified loga_offset, and the starting offset at or
       below loga_offset. If the metadata server does not have
       a layout that is readily available, then it MUST return
       NFS4ERR_LAYOUTTRYLATER.
       
      </t>
      <t>
       If the sum of loga_offset and loga_minlength exceeds
       NFS4_UINT64_MAX, and loga_minlength is not NFS4_UINT64_MAX,
       the error NFS4ERR_INVAL MUST result.

      </t>
      <t>
       If the sum of loga_offset and loga_length exceeds
       NFS4_UINT64_MAX, and loga_length is not NFS4_UINT64_MAX,
       the error NFS4ERR_INVAL MUST result.

      </t>
      </list>

      After the metadata server has performed the above checks on loga_offset,
      loga_minlength, and loga_offset, the metadata server MUST return a
      layout according to the rules in <xref target="layout_hell"/>.
    </t>
    <texttable anchor='layout_hell'>

     <preamble>

      Acceptable layouts based on loga_minlength.
      Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
      a_minlen = loga_minlength.

     </preamble>

     <ttcol>Layout iomode of request</ttcol>
     <ttcol>Layout a_minlen of request</ttcol>
     <ttcol>Layout iomode of reply</ttcol>
     <ttcol>Layout offset of reply</ttcol>
     <ttcol>Layout length of reply</ttcol>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= file length - layout offset</c>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be u64m</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= MIN(file length, a_minlen + a_off) - layout offset</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= a_off - layout offset + a_minlen</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

     <c>_RW</c>
     <c>u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be u64m</c>

     <c>_RW</c>
     <c>> 0 and &lt; u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= a_off - layout offset + a_minlen</c>

     <c>_RW</c>
     <c>0</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

    </texttable>
    <t>
     If loga_minlength is not zero and the metadata server cannot return a layout according
     to the rules in <xref target="layout_hell"/>,
     then the metadata server MUST return the error
     NFS4ERR_BADLAYOUT.  If loga_minlength is zero and the metadata server
     cannot or will not return a layout according
     to the rules in <xref target="layout_hell"/>,
     then the metadata server MUST return the error
     NFS4ERR_LAYOUTTRYLATER.

     Assuming that loga_length is greater
     than loga_minlength or equal to zero, the metadata server SHOULD
     return a layout according to the rules in <xref
     target="layout_hell2"/>.
    </t>

    <texttable anchor='layout_hell2'>

     <preamble>

      Desired layouts based on loga_length.
      The rules of <xref target='layout_hell'/> MUST be applied first.
      Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
      a_len = loga_length.

     </preamble>

     <ttcol>Layout iomode of request</ttcol>
     <ttcol>Layout a_len of request</ttcol>
     <ttcol>Layout iomode of reply</ttcol>
     <ttcol>Layout offset of reply</ttcol>
     <ttcol>Layout length of reply</ttcol>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>

     <c>_RW</c>
     <c>u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_RW</c>
     <c>> 0 and &lt; u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_RW</c>
     <c>0</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>
    </texttable>

    <t>
      The loga_stateid field specifies a valid stateid.
      If a layout is not currently held by the client,
      the loga_stateid field represents a stateid
      reflecting the correspondingly valid open,
      byte-range lock, or delegation stateid.  Once a
      layout is held on the file by the client, the
      loga_stateid field MUST be a stateid as returned from
      a previous LAYOUTGET or LAYOUTRETURN operation or
      provided by a CB_LAYOUTRECALL operation (see <xref
      target="layout_stateid"/>).

    </t>
    <t>
      The loga_maxcount field specifies the maximum layout size (in bytes)
      that the client can handle.  If the size of the layout structure
      exceeds the size specified by maxcount, the metadata server will
      return the NFS4ERR_TOOSMALL error.

    </t>
    <t>
     The returned layout is expressed as an array,
     logr_layout, with each element of type layout4. If a
     file has a single striping pattern, then logr_layout
     SHOULD contain just one entry. Otherwise, if the
     requested range overlaps more than one striping
     pattern, logr_layout will contain the required number
     of entries. The elements of logr_layout MUST be sorted
     in ascending order of the value of the lo_offset field
     of each element. There MUST be no gaps or overlaps
     in the range between two successive elements of
     logr_layout. The lo_iomode field in each element of
     logr_layout MUST be the same.
    </t>

    <t>
      <xref target="layout_hell" />
      and
      <xref target="layout_hell2" />

      both refer to a returned layout iomode, offset, and length.
      Because the returned layout is encoded in the logr_layout array,
      more description is required.
     <list style='hanging'>

     <t hangText='iomode'/>
     <t>
       The value of the returned layout iomode listed in
       <xref target="layout_hell" />
       and
       <xref target="layout_hell2" />
       is equal to the value of the lo_iomode field in each
       element of logr_layout.

       As shown in <xref target="layout_hell" />
       and <xref target="layout_hell2" />,
       the metadata server MAY return a layout with an lo_iomode
       different from the requested iomode (field loga_iomode of the request).
       If it does so, it MUST
       ensure that the lo_iomode is more permissive than the
       loga_iomode requested.  For example, this behavior allows an
       implementation to upgrade LAYOUTIOMODE4_READ requests to LAYOUTIOMODE4_RW
       requests at its discretion, within the limits of the layout type
       specific protocol.  A lo_iomode of either LAYOUTIOMODE4_READ or
       LAYOUTIOMODE4_RW MUST be returned.

     </t>
    
     <t hangText='offset'/>
     <t>
       The value of the returned layout offset listed in
       <xref target="layout_hell" />
       and
       <xref target="layout_hell2" />
       is always equal to the lo_offset field of the first
       element logr_layout.

     </t>

     <t hangText='length'/>
     <t>
       When setting the value of the returned layout
       length, the situation is complicated by the
       possibility that the special layout length value
       NFS4_UINT64_MAX is involved.  For a logr_layout
       array of N elements, the lo_length field in the
       first N-1 elements MUST NOT be NFS4_UINT64_MAX. The
       lo_length field of the last element of logr_layout
       can be NFS4_UINT64_MAX under some conditions as
       described in the following list.

       <list style='symbols'>

       <t>
	If an applicable rule of <xref target="layout_hell"/>
	states that the metadata server MUST return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout MUST be NFS4_UINT64_MAX.

       </t>
       <t>
	If an applicable rule of <xref target="layout_hell"/>
	states that the metadata server MUST NOT return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout MUST NOT be NFS4_UINT64_MAX.

       </t>
       <t>
	If an applicable rule of <xref target="layout_hell2"/>
	states that the metadata server SHOULD return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout SHOULD be NFS4_UINT64_MAX.

       </t>
       <t>
	When the value of the returned layout length of
	<xref target="layout_hell" />
	and
	<xref target="layout_hell2" /> is not NFS4_UINT64_MAX, then
	the returned layout length is equal to the sum of the
	lo_length fields of each element of logr_layout.

       </t>

       </list style='symbols'>
       
     </t>
    </list>
    </t>

    <t>
      The logr_return_on_close result field is a directive to return
      the layout before closing the file.  When the metadata server sets this
      return value to TRUE, it MUST be prepared to recall the layout
      in the case in which the client fails to return the layout before close.
      For the metadata server that knows a layout must be returned before a
      close of the file, this return value can be used to communicate
      the desired behavior to the client and thus remove one extra
      step from the client's and metadata server's interaction.
    </t>
    <t>
      The logr_stateid stateid is returned to
      the client for use in subsequent layout related operations. See Sections
      <xref target="stateid" format="counter" />, <xref target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
    <t>
      The format of the returned layout (lo_content)
      is specific to the layout type.
      The value of the layout type (lo_content.loc_type) for each of
      the elements of the array of layouts returned by the metadata server
      (logr_layout) MUST be equal to the loga_layout_type specified
      by the client.  If it is not equal, the client SHOULD ignore
      the response as invalid and behave as if the metadata server returned
      an error, even if the client does have support for the
      layout type returned.
    </t>
    <t>
      If neither the requested file nor its
      containing file system support layouts, the metadata server MUST return
      NFS4ERR_LAYOUTUNAVAILABLE.  If the layout type is not supported,
      the metadata server MUST return NFS4ERR_UNKNOWN_LAYOUTTYPE.
      If layouts are supported but no layout matches the client
      provided layout identification, the metadata server MUST return
      NFS4ERR_BADLAYOUT.  If an invalid loga_iomode is specified, or a
      loga_iomode of LAYOUTIOMODE4_ANY is specified, the metadata server MUST
      return NFS4ERR_BADIOMODE.
    </t>
    <t>
      If the layout for the file is unavailable due to transient
      conditions, e.g., file sharing prohibits layouts, the metadata server MUST
      return NFS4ERR_LAYOUTTRYLATER.
    </t>
    <t>
      If the layout request is rejected due to an overlapping layout
      recall, the metadata server MUST return NFS4ERR_RECALLCONFLICT.  See <xref
      target="pnfs_operation_sequencing"/> for details.
    </t>
    <t>
      If the layout conflicts with a mandatory byte-range lock held on the
      file, and if the storage devices have no method of enforcing
      mandatory locks, other than through the restriction of layouts, the
      metadata server SHOULD return NFS4ERR_LOCKED.
    </t>
    <t>
      If client sets loga_signal_layout_avail to TRUE, then it is
      registering with the client a "want" for a layout in the event
      the layout cannot be obtained due to resource exhaustion.
      If the metadata server supports and will honor the "want",
      the results will have logr_will_signal_layout_avail
      set to TRUE.
      If so, the client should expect a CB_RECALLABLE_OBJ_AVAIL
      operation to indicate that a layout is available.
    </t>
    <t>
      On success, the current filehandle retains its value and the
      current stateid is updated to match the value as returned in the
      results.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Typically, LAYOUTGET will be called as part of a
      COMPOUND request after an OPEN operation and results
      in the client having location information for the
      file. This requires that loga_stateid be set to the
      special stateid that tells the metadata server to use the
      current stateid, which is set by OPEN (see <xref
      target="current_stateid"/>). A client may also hold
      a layout across multiple OPENs. The client specifies
      a layout type that limits what kind of layout the
      metadata server will return.  This prevents metadata servers from
      granting layouts that are unusable by the client.

    </t>
    <t>
      As indicated by <xref target="layout_hell" /> and
      <xref target="layout_hell2" />, the specification of
      LAYOUTGET allows a pNFS client and server considerable
      flexibility.

      A pNFS client can take several strategies for sending
      LAYOUTGET. Some examples are as follows.

      <list style='symbols'>
      <t>
       If LAYOUTGET is preceded by OPEN in the same
       COMPOUND request and the OPEN requests OPEN4_SHARE_ACCESS_READ access,
       the client might opt to request a _READ layout
       with loga_offset set to zero, loga_minlength set to
       zero, and loga_length set to NFS4_UINT64_MAX. If
       the file has space allocated to it, that space is
       striped over one or more storage devices, and there
       is either no conflicting layout or the concept of
       a conflicting layout does not apply to the pNFS
       server's layout type or implementation, then the
       metadata server might return a layout with a starting offset
       of zero, and a length equal to the length of the
       file, if not NFS4_UINT64_MAX. If the length of the
       file is not a multiple of the
       pNFS server's stripe
       width (see <xref target="file_layout_definitions"/>
       for a formal definition), the metadata server might round up
       the returned layout's length.

      </t>

      <t>
       If LAYOUTGET is preceded by OPEN in the same
       COMPOUND request, and the OPEN requests OPEN4_SHARE_ACCESS_WRITE access and does
       not truncate the file, the client might
       opt to request a _RW layout with loga_offset set
       to zero, loga_minlength set to zero, and loga_length
       set to the file's current length (if known), or
       NFS4_UINT64_MAX. As with the previous case, under
       some conditions the metadata server might return a layout
       that covers the entire length of the file or beyond.

      </t>
      <t>
       This strategy is as above, but the OPEN truncates the file. In this case,
       the client might anticipate it will be writing to the
       file from offset zero, and so loga_offset and loga_minlength
       are set to zero, and loga_length is set to the value of
       threshold4_write_iosize. The metadata server might return a layout
       from offset zero with a length at least as long as as
       threshold4_write_iosize.

      </t>
      <t>
       A process on the client invokes a request to read
       from offset 10000 for length 50000. The client
       is using buffered I/O, and has buffer sizes of
       4096 bytes. The client intends to map the request
       of the process into a series of READ requests
       starting at offset 8192. The end offset needs to be higher
       than 10000 + 50000 = 60000, and the next offset that is
       a multiple of 4096 is 61440. The difference between 61440 and
       that starting offset of the layout is 53248 (which is
       the product of 4096 and 15).
       The value
       of threshold4_read_iosize is less than 53248,
       so the client sends a LAYOUTGET request with
       loga_offset set to 8192, loga_minlength set to
       53248, and loga_length set to the file's length
       (if known) minus 8192 or NFS4_UINT64_MAX (if the
       file's length is not known). Since this LAYOUTGET
       request exceeds the metadata server's threshold, it grants
       the layout, possibly with an initial offset of
       zero, with an end offset of at least 8192 + 53248 -
       1 = 61439, but preferably a layout with an offset
       aligned on the stripe width and a length that is
       a multiple of the stripe width.

      </t>


      <t>
        This strategy is as above, but the client is not using buffered I/O, and
        instead all internal I/O requests are sent directly to
        the server. The LAYOUTGET request has loga_offset equal to
        10000 and loga_minlength set to 50000. The value of loga_length
        is set to the length of the file. The metadata server is free to
        return a layout that fully overlaps the requested range, with
        a starting offset and length aligned on the stripe width.
      </t>

      <t>
       Again, a process on the client invokes a request
       to read from offset 10000 for length 50000 (i.e.
       a range with a starting offset of 10000 and an ending
       offset of 69999), and
       buffered I/O is in use.  The client is expecting
       that the server might not be able to return the
       layout for the full I/O range.


       The client intends to map the request of the
       process into a series of thirteen READ requests starting at
       offset 8192, each with length 4096, with a total
       length of 53248 (which equals 13 * 4096), which
       fully contains the range that client's process wants to read.

       Because the value of threshold4_read_iosize is equal to
       4096, it is practical and reasonable for the client to
       use several LAYOUTGET operations to complete the series
       of READs.

       The client sends a LAYOUTGET request with
       loga_offset set to 8192, loga_minlength set to 4096,
       and loga_length set to 53248 or higher.  The server
       will grant a layout possibly with an initial offset
       of zero, with an end offset of at least 8192 + 4096 -
       1 = 12287, but preferably a layout with an offset
       aligned on the stripe width and a length that is a
       multiple of the stripe width.  This will allow the
       client to make forward progress, possibly
       sending more LAYOUTGET operations for the remainder
       of the range.

     </t>

      <t>
        An NFS client detects a sequential read pattern,
        and so sends a LAYOUTGET operation that goes well beyond any
        current or pending read requests to the server. The
        server might likewise detect this pattern, and
        grant the LAYOUTGET request. Once the client
        reads from an offset of the file that represents
        50% of the way through the range of the last layout
        it received, in order to avoid stalling I/O that would wait
        for a layout, the client sends more operations 
        from an offset of the file that represents 50%
        of the way through the last layout it received. The client
        continues to request layouts with byte-ranges that are
        well in advance of the byte-ranges of
        recent and/or read requests of processes running on the client.

      </t>
      <t>
        This strategy is as above, but the client fails to detect the
        pattern, but the server does. The next time the
        metadata server gets a LAYOUTGET, it returns a layout with
        a length that is well beyond loga_minlength.

      </t>

      <t>
        A client is using buffered I/O, and has a long
        queue of write-behinds to process and also detects
        a sequential write pattern. It sends a LAYOUTGET
        for a layout that spans the range of the queued
        write-behinds and well beyond, including ranges
        beyond the filer's current length.  The client
        continues to send LAYOUTGET operations once the write-behind
        queue reaches 50% of the maximum queue length.
   
      </t>

      </list>
    </t>

    <t>
      Once the client has obtained a layout referring to a
      particular device ID, the metadata server MUST NOT
      delete the device ID until the layout is returned
      or revoked.

    </t>
    <t>
      CB_NOTIFY_DEVICEID can race with LAYOUTGET. One race
      scenario is that LAYOUTGET returns a device ID for which the
      client does not have device address mappings,
      and the metadata server sends a CB_NOTIFY_DEVICEID
      to add the device ID to the client's awareness
      and meanwhile the client sends GETDEVICEINFO on
      the device ID.  This scenario is discussed in
      <xref target="OP_GETDEVICEINFO_IMPLEMENTATION"/>.
      Another scenario is that the CB_NOTIFY_DEVICEID
      is processed by the client before it processes
      the results from LAYOUTGET.  The client will send
      a GETDEVICEINFO on the device ID.  If the results
      from GETDEVICEINFO are received before the client
      gets results from LAYOUTGET, then there is no
      longer a race. If the results from LAYOUTGET are
      received before the results from GETDEVICEINFO, the
      client can either wait for results of GETDEVICEINFO
      or send another one to get possibly more up-to-date
      device address mappings for the device ID.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTRETURN" title="Operation 51: LAYOUTRETURN - Release Layout Information" >

  <section toc="exclude" anchor="OP_LAYOUTRETURN_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>

/* Constants used for LAYOUTRETURN and CB_LAYOUTRECALL */
const LAYOUT4_RET_REC_FILE      = 1;
const LAYOUT4_RET_REC_FSID      = 2;
const LAYOUT4_RET_REC_ALL       = 3;

enum layoutreturn_type4 {
        LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
        LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
        LAYOUTRETURN4_ALL  = LAYOUT4_RET_REC_ALL
};

struct layoutreturn_file4 {
        offset4         lrf_offset;
        length4         lrf_length;
        stateid4        lrf_stateid;
        /* layouttype4 specific data */
        opaque          lrf_body&lt;>;
};

union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
        case LAYOUTRETURN4_FILE:
                layoutreturn_file4      lr_layout;
        default:
                void;
};

 </artwork>
</figure>

<figure>
 <artwork>

struct LAYOUTRETURN4args {
        /* CURRENT_FH: file */
        bool                    lora_reclaim;
        layouttype4             lora_layout_type;
        layoutiomode4           lora_iomode;
        layoutreturn4           lora_layoutreturn;
};


 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_RESULT" title="RESULT">
<figure>
 <artwork>
union layoutreturn_stateid switch (bool lrs_present) {
case TRUE:
        stateid4                lrs_stateid;
case FALSE:
        void;
};

union LAYOUTRETURN4res switch (nfsstat4 lorr_status) {
case NFS4_OK:
        layoutreturn_stateid    lorr_stateid;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation returns from the client to the server
      one or more layouts represented by the client ID
      (derived from the session ID in the preceding SEQUENCE
      operation), lora_layout_type, and lora_iomode.
      When lr_returntype is LAYOUTRETURN4_FILE, the
      returned layout is further identified by the current
      filehandle, lrf_offset, lrf_length, and lrf_stateid.
      If the lrf_length field is NFS4_UINT64_MAX, all bytes
      of the layout, starting at lrf_offset, are returned.
      When lr_returntype is LAYOUTRETURN4_FSID, the
      current filehandle is used to identify the file
      system and all layouts matching the client ID,
      the fsid of the file system, lora_layout_type, and
      lora_iomode are returned.  When lr_returntype is
      LAYOUTRETURN4_ALL, all layouts matching the client
      ID, lora_layout_type, and lora_iomode are returned
      and the current filehandle is not used.  After this
      call, the client MUST NOT use the returned layout(s)
      and the associated storage protocol to access the
      file data.

    </t>
    <t>
      If the set of layouts designated in the case of 
      LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL is empty, then no error
      results.  In the case of LAYOUTRETURN4_FILE, the byte-range
      specified is returned even if it is a subdivision of a layout 
      previously obtained with LAYOUTGET, a combination of multiple
      layouts previously obtained with LAYOUTGET, or a combination
      including some layouts previously obtained with LAYOUTGET, 
      and one or more subdivisions of such layouts.  When the
      byte-range does not designate any bytes for which a layout
      is held for the specified file, client ID, layout type and
      mode, no error results.
        See <xref target="bulk_layouts" /> for considerations with
        "bulk" return of layouts.
    </t>
    <t>
      The layout being returned may be a subset
      or superset of a layout specified by CB_LAYOUTRECALL.  However,
      if it is a subset, the recall is not complete until the full
      recalled scope has been returned.  Recalled scope refers to the
      byte-range in the case of LAYOUTRETURN4_FILE, the use of
      LAYOUTRETURN4_FSID, or the use of LAYOUTRETURN4_ALL.  There must
      be a LAYOUTRETURN with a matching scope to complete the return
      even if all current layout ranges have been previously individually
      returned. 
    </t>
    <t>
      For all lr_returntype values, an iomode of LAYOUTIOMODE4_ANY
      specifies that all layouts that match the other arguments to
      LAYOUTRETURN (i.e., client ID, lora_layout_type, and one of
      current filehandle and range; fsid derived from current
      filehandle; or LAYOUTRETURN4_ALL) are being returned.
    </t>
    <t>
      In the case that lr_returntype is LAYOUTRETURN4_FILE, the
      lrf_stateid provided by the client is a layout stateid as
      returned from previous layout operations.  Note that the "seqid"
      field of lrf_stateid MUST NOT be zero.  See Sections
      <xref target="stateid" format="counter" />, <xref
target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
    <t>
      Return of a layout or all layouts does not invalidate the
      mapping of storage device ID to a storage device address. The
      mapping remains in effect until specifically changed or deleted via
      device ID notification callbacks.
      Of course if there are no remaining
      layouts that refer to a previously used device ID, the server is
      free to delete a device ID without a notification callback, which
      will be the case when notifications are not in effect.
      
    </t>
    <t>
      If the lora_reclaim field is set to TRUE, the
      client is attempting to return a layout that
      was acquired before the restart of the metadata
      server during the metadata server's grace period.
      When returning layouts that were acquired during
      the metadata server's grace period, the client MUST set the
      lora_reclaim field to FALSE.  The lora_reclaim field
      MUST be set to FALSE also when lr_layoutreturn is
      LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL. See <xref
      target="OP_LAYOUTCOMMIT">LAYOUTCOMMIT </xref> for
      more details.

    </t>
    <t>
      Layouts may be returned when recalled or voluntarily (i.e.,
      before the server has recalled them).  In either case, the client
      must properly propagate state changed under the context of the
      layout to the storage device(s) or to the metadata server before
      returning the layout.
    </t>
    <t>
      If the client returns the layout in response to a
      CB_LAYOUTRECALL where the lor_recalltype field of the
      clora_recall field was LAYOUTRECALL4_FILE, the client
      should use the lor_stateid value from CB_LAYOUTRECALL
      as the value for lrf_stateid. Otherwise, it should
      use logr_stateid (from a previous LAYOUTGET result)
      or lorr_stateid (from a previous LAYRETURN result).
      This is done to indicate the point in time (in terms
      of layout stateid transitions) when the recall was
      sent.  The client uses the precise lora_recallstateid
      value and MUST NOT set the stateid's seqid to
      zero; otherwise, NFS4ERR_BAD_STATEID MUST be
      returned. NFS4ERR_OLD_STATEID can be returned if
      the client is using an old seqid, and the server
      knows the client should not be using the old
      seqid. For example, the client uses the seqid on slot 1 of
      the session, receives the response with the new
      seqid, and uses the slot to send another request
      with the old seqid.

    </t>
    <t>
      If a client fails to return a layout
      in a timely manner, then the metadata server SHOULD use its
      control protocol with the storage devices to fence the client
      from accessing the data referenced by the layout.  See
      <xref target="recalling_layout" /> for more details.
    </t>
    <t>
      If the LAYOUTRETURN request sets the lora_reclaim field to TRUE after
      the metadata server's grace period, NFS4ERR_NO_GRACE is returned.
    </t>
    <t>
      If the LAYOUTRETURN request sets the lora_reclaim field to TRUE
      and lr_returntype is set to LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL,
      NFS4ERR_INVAL is returned.
    </t>
    <t>
      If the client sets the lr_returntype field to
      LAYOUTRETURN4_FILE, then the lrs_stateid field
      will represent the layout stateid as updated for
      this operation's processing; the current stateid
      will also be updated to match the returned value.
      If the last byte of any layout for the current
      file, client ID, and layout type is being returned
      and there are no remaining pending CB_LAYOUTRECALL
      operations for which a LAYOUTRETURN operation must be
      done, lrs_present MUST be FALSE, and no stateid
      will be returned. In addition, the COMPOUND request's current
      stateid will be set to the all-zeroes special stateid
      (see <xref target="current_stateid"/>).  The server
      MUST reject with NFS4ERR_BAD_STATEID any further
      use of the current stateid in that COMPOUND until
      the current stateid is re-established by a later
      stateid-returning operation.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     If the EXCHGID4_FLAG_BIND_PRINC_STATEID
     capability is set on the client ID (see <xref
     target="OP_EXCHANGE_ID"/>), the server will
     require that the principal, security flavor,
     and if applicable, the GSS mechanism, combination
     that acquired the layout also be the one to send
     LAYOUTRETURN. This might not be possible
     if credentials for the principal are no
     longer available. The server will allow the
     machine credential or SSV credential (see <xref
     target="OP_EXCHANGE_ID" />) to send LAYOUTRETURN
     if LAYOUTRETURN's operation code was set in the
     spo_must_allow result of EXCHANGE_ID.

    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
    The final LAYOUTRETURN operation in response to a CB_LAYOUTRECALL
    callback MUST be serialized with any outstanding, intersecting
    LAYOUTRETURN operations.  Note that it is possible that while a
    client is returning the layout for some recalled range, the server
    may recall a superset of that range (e.g., LAYOUTRECALL4_ALL); the final
    return operation for the latter must block until the former layout
    recall is done.
  </t>
  <t>
    Returning all layouts in a file system using LAYOUTRETURN4_FSID is
    typically done in response to a CB_LAYOUTRECALL for that file system
    as the final return operation. Similarly, LAYOUTRETURN4_ALL
    is used in response to a recall callback for all layouts.  It is
    possible that the client already returned some outstanding layouts
    via individual LAYOUTRETURN calls and the call for
    LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL marks the end of the
    LAYOUTRETURN sequence.  See <xref target="recall_robustness" />
    for more details.
  </t>
  <t>
    Once the client has returned all layouts referring to a particular
    device ID, the server MAY delete the device ID.
  </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object" anchor="OP_SECINFO_NO_NAME">

  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
enum secinfo_style4 {
        SECINFO_STYLE4_CURRENT_FH       = 0,
        SECINFO_STYLE4_PARENT           = 1
};

/* CURRENT_FH: object or child directory */
typedef secinfo_style4 SECINFO_NO_NAME4args;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_RESULT" title="RESULT">
<figure>
 <artwork>
/* CURRENTFH: consumed if status is NFS4_OK */
typedef SECINFO4res SECINFO_NO_NAME4res;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_DESCRIPTION" title="DESCRIPTION">
    <t>
      Like the SECINFO operation, SECINFO_NO_NAME is used by the
      client to obtain a list of valid RPC authentication flavors for
      a specific file object.  Unlike SECINFO, SECINFO_NO_NAME only
      works with objects that are accessed by filehandle.
    </t>
    <t>
      There are two styles of SECINFO_NO_NAME, as determined by the
      value of the secinfo_style4 enumeration. If SECINFO_STYLE4_CURRENT_FH is
      passed, then SECINFO_NO_NAME is querying for the required
      security for the current filehandle. If SECINFO_STYLE4_PARENT is passed, then
      SECINFO_NO_NAME is querying for the required security of the
      current filehandle's parent. If the style selected is SECINFO_STYLE4_PARENT,
      then SECINFO should apply the same access methodology used for
      LOOKUPP when evaluating the traversal to the parent directory.
      Therefore, if the requester does not have the appropriate access
      to LOOKUPP the parent, then SECINFO_NO_NAME must behave the same
      way and return NFS4ERR_ACCESS.
    </t>
    <t>
      If PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH returns
      NFS4ERR_WRONGSEC, then the client resolves the
      situation by sending a COMPOUND request that consists of
      PUTFH, PUTPUBFH, or PUTROOTFH immediately followed by
      SECINFO_NO_NAME, style SECINFO_STYLE4_CURRENT_FH.
      See <xref target="Security Service Negotiation" />
      for instructions on dealing with NFS4ERR_WRONGSEC error
      returns from PUTFH, PUTROOTFH, PUTPUBFH, or RESTOREFH.
    </t>
    <t>
      If SECINFO_STYLE4_PARENT is specified and there is no parent
      directory, SECINFO_NO_NAME MUST return NFS4ERR_NOENT.
    </t>
    <t>

      On success, the current filehandle is consumed
      (see <xref target="aftersecinfo" />), and if the
      next operation after SECINFO_NO_NAME tries to use
      the current filehandle, that operation will fail
      with the status NFS4ERR_NOFILEHANDLE.

    </t>
    <t>
      Everything else about SECINFO_NO_NAME is the same as SECINFO.
      See the discussion on SECINFO (<xref target="OP_SECINFO_DESCRIPTION"/>).
    </t>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      See the discussion on SECINFO (<xref target="OP_SECINFO_IMPLEMENTATION" />).
    </t>
  </section>
</section>

<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $   -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SEQUENCE" title="Operation 53: SEQUENCE - Supply Per-Procedure Sequencing and Control" >

  <section toc="exclude" anchor="OP_SEQUENCE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct SEQUENCE4args {
        sessionid4     sa_sessionid;
        sequenceid4    sa_sequenceid;
        slotid4        sa_slotid;
        slotid4        sa_highest_slotid;
        bool           sa_cachethis;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_RESULT" title="RESULT">
<figure>
 <artwork>
const SEQ4_STATUS_CB_PATH_DOWN                  = 0x00000001;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING      = 0x00000002;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED       = 0x00000004;
const SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED     = 0x00000008;
const SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED    = 0x00000010;
const SEQ4_STATUS_ADMIN_STATE_REVOKED           = 0x00000020;
const SEQ4_STATUS_RECALLABLE_STATE_REVOKED      = 0x00000040;
const SEQ4_STATUS_LEASE_MOVED                   = 0x00000080;
const SEQ4_STATUS_RESTART_RECLAIM_NEEDED        = 0x00000100;
const SEQ4_STATUS_CB_PATH_DOWN_SESSION          = 0x00000200;
const SEQ4_STATUS_BACKCHANNEL_FAULT             = 0x00000400;
const SEQ4_STATUS_DEVID_CHANGED                 = 0x00000800;
const SEQ4_STATUS_DEVID_DELETED                 = 0x00001000;

struct SEQUENCE4resok {
        sessionid4      sr_sessionid;
        sequenceid4     sr_sequenceid;
        slotid4         sr_slotid;
        slotid4         sr_highest_slotid;
        slotid4         sr_target_highest_slotid;
        uint32_t        sr_status_flags;
};

union SEQUENCE4res switch (nfsstat4 sr_status) {
case NFS4_OK:
        SEQUENCE4resok  sr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SEQUENCE operation is
      used by the server to implement session request control
      and the reply cache semantics.
    </t>
    <t>
      SEQUENCE MUST appear as the first operation of any COMPOUND
      in which it appears.  The error NFS4ERR_SEQUENCE_POS will be
      returned when it is found in any position in a COMPOUND
      beyond the first.  Operations other than SEQUENCE, BIND_CONN_TO_SESSION,
      EXCHANGE_ID, CREATE_SESSION, and DESTROY_SESSION,
      MUST NOT appear as the first operation in a
      COMPOUND.  Such operations MUST yield the error NFS4ERR_OP_NOT_IN_SESSION
      if they do appear at the start of a COMPOUND.
    </t>
    <t>
     If SEQUENCE is received on a connection not associated with the
     session via CREATE_SESSION or BIND_CONN_TO_SESSION, and
     connection association enforcement is enabled
     (see <xref target="OP_EXCHANGE_ID" />), then
     the server returns NFS4ERR_CONN_NOT_BOUND_TO_SESSION.
    </t>
    <t>
     The sa_sessionid argument identifies the session to which this
     request applies. The sr_sessionid result MUST equal
     sa_sessionid.
    </t>
    <t>
     The sa_slotid argument is the index in the reply cache
     for the request. The sa_sequenceid field is the sequence
     number of the request for the reply cache entry (slot).
     The sr_slotid result MUST equal sa_slotid. The sr_sequenceid
     result MUST equal sa_sequenceid.
    </t>
    <t>
     The sa_highest_slotid argument is the highest slot ID
     for which the client has a request outstanding; it could be
     equal to sa_slotid.
     The server returns two "highest_slotid" values: sr_highest_slotid
     and sr_target_highest_slotid. The former is the highest slot ID
     the server will accept in future SEQUENCE operation, and
     SHOULD NOT be less than the value of sa_highest_slotid
     (but see
     <xref target="Slot Identifiers and Server Reply Cache" />
     for an exception).
     The latter is the highest slot ID the server would prefer the
     client use on a future SEQUENCE operation.
    </t>
    <t>
     If sa_cachethis is TRUE, then the client is requesting that
     the server cache the entire
     reply in the server's reply cache; therefore, the server MUST
     cache the reply (see <xref target="optional_reply_caching" />).
     The server MAY cache the reply if sa_cachethis is FALSE.
     If the server does not cache the entire reply, it
     MUST still record that it executed the request at
     the specified slot and sequence ID.
    </t>
    <t>
      The response to the SEQUENCE operation contains a
      word of status flags (sr_status_flags) that can
      provide to the client information related to the
      status of the client's lock state and communications
      paths.  Note that any status bits relating to lock
      state MAY be reset when lock state is lost due to a
      server restart (even if the session is persistent across
      restarts; session persistence does not imply 
      lock state persistence)
      or the establishment of a new client
      instance.

      <list style='hanging'> 
        <t hangText="SEQ4_STATUS_CB_PATH_DOWN"><vspace />
          When set, indicates that the client has no
          operational backchannel path for any session
          associated with the client ID, making it
          necessary for the client to re-establish one.
          This bit
          remains set on all SEQUENCE responses on all sessions
          associated with the client ID
          until at least one backchannel is
          available on any session associated with the client ID.
          If the client fails to re-establish a 
          backchannel for the client ID, it is subject to
          having recallable state revoked.
        </t>
        <t hangText="SEQ4_STATUS_CB_PATH_DOWN_SESSION"><vspace />
          When set, indicates that the session has
          no operational backchannel. There are two reasons
          why SEQ4_STATUS_CB_PATH_DOWN_SESSION may be set and not
          SEQ4_STATUS_CB_PATH_DOWN. First is that a callback operation
          that applies specifically to the
          session (e.g., CB_RECALL_SLOT, see <xref
          target="OP_CB_RECALL_SLOT" />) needs to be sent.
          Second is that the server did send a callback operation,
          but the connection was lost before the reply. The
          server cannot be sure whether or not the client received the
          callback operation, and so, per rules on
          request retry, the server MUST retry the callback
          operation over the same session. The 
          SEQ4_STATUS_CB_PATH_DOWN_SESSION bit is the indication
          to the client that it needs to associate a connection
          to the session's backchannel.
          This bit remains set on all SEQUENCE responses of the
          session until a connection is associated with the
          session's a backchannel.
          If the client fails to re-establish a 
          backchannel for the session, it is subject to
          having recallable state revoked.

        </t>
        <t hangText="SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING"><vspace />
          When set, indicates that all GSS contexts or RPCSEC_GSS handles
          assigned to the session's backchannel will expire within a
          period equal to the lease time.  This bit remains set on all
          SEQUENCE replies until at least one of the following are true:

          <list style='symbols'>

          <t>
            All SSV RPCSEC_GSS handles on the session's backchannel
            have been destroyed and all non-SSV GSS contexts have expired.
          </t>
          <t>
            At least one more SSV RPCSEC_GSS handle has been added to
            the backchannel.
          </t>
          <t>
            The expiration time of at least one non-SSV GSS context
            of an RPCSEC_GSS handle
            is beyond the lease period from the current
            time (relative to the time of when a SEQUENCE
            response was sent)
          </t>

          </list>
        </t>
        <t hangText="SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED"><vspace />
          When set, indicates all non-SSV GSS contexts and all
          SSV RPCSEC_GSS handles assigned
          to the session's backchannel have expired or have been
          destroyed.
          This bit remains set on all SEQUENCE replies
          until at least one non-expired non-SSV GSS context for the
          session's backchannel has been established or at least one
          SSV RPCSEC_GSS handle has been assigned to the backchannel.
        </t>
        <t hangText="SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED"><vspace />
          When set, indicates that the lease has expired
          and as a result the server released all of the
          client's locking state.  This status bit remains
          set on all SEQUENCE replies until the loss of
          all such locks has been acknowledged by use of
          FREE_STATEID (see <xref target="OP_FREE_STATEID"
          />), or by establishing a new client instance by
          destroying all sessions (via DESTROY_SESSION),
          the client ID (via DESTROY_CLIENTID), and then
          invoking EXCHANGE_ID and CREATE_SESSION to
          establish a new client ID.

        </t>
        <t hangText="SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED"><vspace />
          When set, indicates that some subset of the client's locks 
          have been revoked due to expiration of the lease period 
          followed by another client's conflicting LOCK operation.
          This status bit remains set on all SEQUENCE replies
          until the loss of all
          such locks has been acknowledged by use of FREE_STATEID.
        </t>
        <t hangText="SEQ4_STATUS_ADMIN_STATE_REVOKED"><vspace />
          When set, indicates that one or more locks have been revoked 
          without expiration of the lease period, due to administrative 
          action.  This status bit remains set on all SEQUENCE replies
          until the loss of all
          such locks has been acknowledged by use of FREE_STATEID.
        </t>
        <t hangText="SEQ4_STATUS_RECALLABLE_STATE_REVOKED"><vspace />
	  When set, indicates that one or more recallable
	  objects have been revoked without expiration
	  of the lease period, due to the client's
	  failure to return them when recalled, which
	  may be a consequence of there being no working
	  backchannel and the client failing to re-establish
	  a backchannel per the SEQ4_STATUS_CB_PATH_DOWN,
	  SEQ4_STATUS_CB_PATH_DOWN_SESSION, or
	  SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED status flags.
	  This status bit remains set on all SEQUENCE
	  replies until the loss of all such locks has
	  been acknowledged by use of FREE_STATEID.

        </t>
        <t hangText="SEQ4_STATUS_LEASE_MOVED"><vspace /> 
	  When set, indicates that responsibility for lease renewal has
          been transferred to one or more new servers.  This condition
          will continue until the client receives an NFS4ERR_MOVED
          error and the server receives the subsequent GETATTR for the
          fs_locations or fs_locations_info attribute for an access to
          each file system for which a lease has been moved to a new
          server. See <xref target="transferred_lease" />.
        </t>
        <t hangText="SEQ4_STATUS_RESTART_RECLAIM_NEEDED"><vspace />
	  When set, indicates that due to server
	  restart, the client must reclaim locking state. 
	  Until the client sends a global RECLAIM_COMPLETE
	  (<xref target="OP_RECLAIM_COMPLETE" />), every
	  SEQUENCE operation will return
	  SEQ4_STATUS_RESTART_RECLAIM_NEEDED.
        </t>
        <t hangText="SEQ4_STATUS_BACKCHANNEL_FAULT"><vspace />
          The server has encountered an unrecoverable fault
          with the backchannel (e.g., it has lost track of the
          sequence ID for a slot in the backchannel). The
          client MUST stop sending more requests on the
          session's fore channel, wait for all outstanding requests to
          complete on the fore and back channel, and then
          destroy the session.
        </t>
	<t hangText="SEQ4_STATUS_DEVID_CHANGED"><vspace />
	  The client is using device ID notifications and the server
	  has changed a device ID mapping held by the client. This
	  flag will stay present until the client has obtained the new
	  mapping with GETDEVICEINFO.
	</t>
	<t hangText="SEQ4_STATUS_DEVID_DELETED"><vspace />
	  The client is using device ID notifications and the server
	  has deleted a device ID mapping held by the client.
          This flag will stay in effect until the client sends a GETDEVICEINFO
          on the device ID with a null value in the argument gdia_notify_types.
	</t>
      </list>
    </t>
    <t>
      The value of the sa_sequenceid argument relative to
      the cached sequence ID on the slot falls into one
      of three cases.
      <list style="symbols">
      <t>
       If the difference between sa_sequenceid and
       the server's cached sequence ID at the slot ID
       is two (2) or more,
       or if sa_sequenceid is less
       than the cached sequence ID (accounting
       for wraparound of the unsigned sequence ID value),
       then the server MUST return NFS4ERR_SEQ_MISORDERED.
      </t>
      <t>
       If sa_sequenceid and the cached sequence ID are
       the same, this is a retry, and the server replies
       with what is recorded in the reply
       cache.
The lease is possibly renewed as described below.

      </t>
      <t>
       If sa_sequenceid is one greater (accounting for
       wraparound) than the cached sequence ID, then
       this is a new request, and the slot's sequence
       ID is incremented.  The operations subsequent to
       SEQUENCE, if any, are processed. If there are no
       other operations, the only other effects are to
       cache the SEQUENCE reply in the slot, maintain the
       session's activity, and possibly renew the lease.

      </t>
      </list>
    </t>
    <t>
     If the client reuses a slot ID and sequence ID for
     a completely different request, the server MAY treat
     the request as if it is a retry of what it has already
     executed. The server MAY however detect the client's
     illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.

    </t>
    <t>
     If SEQUENCE returns an error, then the state of the
     slot (sequence ID, cached reply) MUST NOT change,
     and the associated lease MUST NOT be renewed.

    </t>
    <t>
     If SEQUENCE returns NFS4_OK, then the associated
     lease MUST be renewed (see <xref target="lease_renewal"/>),
     except if SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is
     returned in sr_status_flags.

    </t>

  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MUST maintain a mapping of session ID to client ID
      in order to validate any operations that follow SEQUENCE
      that take a stateid as an argument and/or result.
    </t>
    <t>
      If the client establishes a persistent session, then
      a SEQUENCE received after a server restart might encounter 
      requests performed and recorded in a persistent reply 
      cache before the server restart.  In this case, SEQUENCE
      will be processed successfully, while requests that
      were not previously performed and recorded are rejected with
      NFS4ERR_DEADSESSION.
   </t>
   <t>
      Depending on which of the operations within the COMPOUND were
      successfully
      performed before the server restart, these operations will
      also have replies sent from the server reply cache. 
      Note that when these operations establish locking state, it
      is locking state that applies to the previous server instance
      and to the previous client ID, even though the
      server restart, which logically happened after these 
      operations, eliminated that state.  In the
      case of a partially executed COMPOUND, processing may reach
      an operation not processed during the earlier server instance,
      making this operation a new one and not performable on the
      existing session.  In this case, NFS4ERR_DEADSESSION will be
      returned from that operation.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SET_SSV" 
         title="Operation 54: SET_SSV - Update SSV for a Client ID" >

  <section toc="exclude" anchor="OP_SET_SSV_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct ssa_digest_input4 {
        SEQUENCE4args sdi_seqargs;
};

struct SET_SSV4args {
        opaque          ssa_ssv&lt;>;
        opaque          ssa_digest&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_RESULT" title="RESULT">
<figure>
 <artwork>
struct ssr_digest_input4 {
        SEQUENCE4res sdi_seqres;
};

struct SET_SSV4resok {
        opaque          ssr_digest&lt;>;
};

union SET_SSV4res switch (nfsstat4 ssr_status) {
case NFS4_OK:
        SET_SSV4resok   ssr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to update the
      SSV for a client ID. Before SET_SSV is called the
      first time on a client ID, the SSV is zero.
      The SSV is the key used for the SSV GSS mechanism
      (<xref target="ssv_mech" /), and it is integral to
      protecting NFSv4.1's state model
      (<xref target="protect_state_changes" />)
    </t>
    <t>
      SET_SSV MUST be preceded by a
      SEQUENCE operation in the same COMPOUND.
      It MUST NOT be used if the client
      did not opt for SP4_SSV state protection when the
      client ID was created
      (see <xref target="OP_EXCHANGE_ID" />);
      the server returns NFS4ERR_INVAL in that case.
    </t>
    <t>
      The field ssa_digest is computed as the output of
      the HMAC (<xref target="RFC2104">RFC 2104</xref>) using the subkey derived
      from the SSV4_SUBKEY_MIC_I2T and current SSV
      as the key (see <xref target="ssv_mech" /> for a
      description of subkeys), and an XDR encoded value of data type ssa_digest_input4.
      The field sdi_seqargs is equal to the
      arguments of the SEQUENCE operation
      for the COMPOUND procedure that
      SET_SSV is within.
    </t>
    <t>
      The argument ssa_ssv
      is XORed with the current SSV to produce
      the new SSV. The argument ssa_ssv SHOULD be generated randomly.
    </t>
    <t>
      In the response, ssr_digest is the output of the HMAC using the
      subkey derived from SSV4_SUBKEY_MIC_T2I and new SSV as the key,
      and an XDR encoded value of data type ssr_digest_input4.  The
      field sdi_seqres is equal to the results of the SEQUENCE
      operation for the COMPOUND procedure that SET_SSV is within.
    </t>
    <t>
      As noted in <xref target="OP_EXCHANGE_ID" />, the client and
      server can maintain multiple concurrent versions of the SSV.
      The client and server each MUST maintain an internal
      SSV version number, which is set to one the first time
      SET_SSV executes on the server and the client
      receives the first SET_SSV reply. Each subsequent
      SET_SSV increases the internal SSV version number by one. The
      value of this version number corresponds to the smpt_ssv_seq,
      smt_ssv_seq, sspt_ssv_seq, and ssct_ssv_seq fields of the
      SSV GSS mechanism tokens (see <xref target="ssv_mech"/>).
    </t>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      When the server receives ssa_digest, it MUST verify the digest
      by computing the digest the same way the client did and
      comparing it with ssa_digest. If the server gets a different
      result, this is an error, NFS4ERR_BAD_SESSION_DIGEST.
      This error might be the result of another SET_SSV from the
      same client ID changing the SSV. If so, the client recovers
      by sending a SET_SSV operation again with a recomputed digest based on
      the subkey of the new SSV. If the transport connection is dropped after
      the SET_SSV request is sent, but before the 
      SET_SSV reply is received, then there are special considerations
      for recovery if the client has no more connections associated
      with sessions associated with the client ID of the SSV. See
      <xref target="OP_BIND_CONN_TO_SESSION_IMPLEMENTATION"/>.
    </t>
    <t>      
      Clients SHOULD NOT send an ssa_ssv that is equal to a previous
      ssa_ssv, nor equal to a previous or current SSV (including an ssa_ssv equal to zero
      since the SSV is initialized to zero when the client ID is created).
    </t>
    <t>      
      Clients SHOULD send SET_SSV with RPCSEC_GSS privacy. Servers
      MUST support RPCSEC_GSS with privacy for any COMPOUND that has {
      SEQUENCE, SET_SSV }.
    </t>
    <t>
      A client SHOULD NOT send SET_SSV with the SSV GSS
      mechanism's credential because the purpose of SET_SSV
      is to seed the SSV from non-SSV credentials. Instead,
      SET_SSV SHOULD be sent with the credential of
      a user that is accessing the client ID for the
      first time

      (<xref target="protect_state_change" />).

      However, if the client does send SET_SSV with SSV
      credentials, the digest protecting the arguments
      uses the value of the SSV before ssa_ssv is XORed in,
      and the digest protecting the results uses the value
      of the SSV after the ssa_ssv is XORed in.

    </t>
      
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_TEST_STATEID" title="Operation 55: TEST_STATEID - Test Stateids for Validity" >

  <section toc="exclude" anchor="OP_TEST_STATEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct TEST_STATEID4args {
        stateid4        ts_stateids&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID_RESULT" title="RESULT">
<figure>
 <artwork>
struct TEST_STATEID4resok {
        nfsstat4        tsr_status_codes&lt;>;
};

union TEST_STATEID4res switch (nfsstat4 tsr_status) {
    case NFS4_OK:
        TEST_STATEID4resok tsr_resok4;
    default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID4_DESCRIPTION" title="DESCRIPTION">
    <t>
      The TEST_STATEID operation is used to check the validity of 
      a set of stateids.  It can be used at any time, but the client
      should definitely use it when it 
      receives an indication that one or more of its stateids have been
      invalidated due to lock revocation.  This occurs when the SEQUENCE
      operation returns with one of the following sr_status_flags set:
      <list style='symbols'>
        <t>
          SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
        </t>
        <t>
          SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED
        </t>
        <t>
          SEQ4_STATUS_EXPIRED_RECALLABLE_STATE_REVOKED
        </t>
      </list>
    </t>
    <t>
      The client can use TEST_STATEID one or more times to test the
      validity of its stateids.  Each use of TEST_STATEID allows a large
      set of such stateids to be tested and avoids problems with earlier
      stateids in a COMPOUND request from interfering with the checking of
      subsequent stateids, as would happen if individual stateids were
      tested by a series of corresponding by operations in a COMPOUND
      request.

    </t>
    <t>
      For each stateid, the server returns the status code that 
      would be returned if that stateid were to be used in normal
      operation.  Returning such a status indication is not an
      error and does not cause COMPOUND processing to terminate.  Checks
      for the validity of the stateid proceed as they would for
      normal operations with a number of exceptions:
      <list style='symbols'>  
        <t>
          There is no check for the type of stateid object, as would be 
          the case for normal use of a stateid.
        </t>
        <t>
          There is no reference to the current filehandle.
        </t>
        <t>
          Special stateids are always considered invalid (they result
          in the error code NFS4ERR_BAD_STATEID).
        </t>
      </list> 
    </t>
    <t>
      All stateids are interpreted as being associated with the client
      for the current session.  Any possible association with a previous
      instance of the client (as stale stateids) is not considered.
    </t>
    <t>
      The valid status values in the returned status_code array 
      are NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID, 
      NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.
    </t>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      See Sections <xref target="stateid_structure" format="counter" /> and
<xref target="stateid_lifetime" format="counter" />
      for a discussion of stateid structure, lifetime, and validation.
    </t>
  </section>
</section>

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_WANT_DELEGATION" 
         title="Operation 56: WANT_DELEGATION - Request Delegation" >

  <section toc="exclude" anchor="OP_WANT_DELEGATION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
union deleg_claim4 switch (open_claim_type4 dc_claim) {
/*
 * No special rights to object. Ordinary delegation
 * request of the specified object. Object identified
 * by filehandle.
 */
case CLAIM_FH: /* new to v4.1 */
        /* CURRENT_FH: object being delegated */
        void;

/*
 * Right to file based on a delegation granted
 * to a previous boot instance of the client.
 * File is specified by filehandle.
 */
case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
        /* CURRENT_FH: object being delegated */
        void;

/*
 * Right to the file established by an open previous
 * to server reboot.  File identified by filehandle.
 * Used during server reclaim grace period.
 */
case CLAIM_PREVIOUS:
        /* CURRENT_FH: object being reclaimed */
        open_delegation_type4   dc_delegate_type;
};

struct WANT_DELEGATION4args {
        uint32_t        wda_want;
        deleg_claim4    wda_claim;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_RESULT" title="RESULT">
<figure>
 <artwork>
union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
case NFS4_OK:
        open_delegation4 wdr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_DESCRIPTION" title="DESCRIPTION">
    <t>
      Where this description mandates the return of a specific error
      code for a specific condition, and where multiple conditions
      apply, the server MAY return any of the mandated error codes.
    </t>
    <t>
      This operation allows a client to:
      <list style='symbols'>
      <t>
       Get a delegation on all types
       of files except directories.
      </t>
      <t>
       Register a "want" for a delegation for the
       specified file object, and be notified via a
       callback when the delegation is available. The
       server MAY support notifications of availability
       via callbacks. If the server does not support
       registration of wants, it MUST NOT return
       an error to indicate that, and instead MUST
       return with ond_why set to WND4_CONTENTION or
       WND4_RESOURCE and ond_server_will_push_deleg or
       ond_server_will_signal_avail set to FALSE.  When the
       server indicates that it will notify the client
       by means of a callback, it will either provide
       the delegation using a CB_PUSH_DELEG operation or
       cancel its promise by sending a CB_WANTS_CANCELLED
       operation.

      </t>
      <t>
       Cancel a want for a delegation. 
      </t>
      </list>
      </t>
    <t>
      The client SHOULD NOT set OPEN4_SHARE_ACCESS_READ and SHOULD NOT
      set OPEN4_SHARE_ACCESS_WRITE in wda_want. If it does, the server
      MUST ignore them.
    </t>
    <t>
      The meanings of the following flags in wda_want are the same as
      they are in OPEN, except as noted below.
      <list style="symbols">
        <t>
          OPEN4_SHARE_ACCESS_WANT_READ_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_NO_DELEG. Unlike the OPEN operation,
          this flag SHOULD NOT be set by the client in the arguments to
          WANT_DELEGATION, and MUST be ignored by the server.

        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_CANCEL
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
        </t>
      </list>
    </t>
    <t>
      The handling of the above flags in WANT_DELEGATION is the same
      as in OPEN.  Information about the delegation and/or the 
      promises the server is making regarding future callbacks are
      the same as those described in the open_delegation4 structure.
    </t>
    <t>
      The successful results of WANT_DELEGATION are of data type
      open_delegation4, which is the same data type as the "delegation"
      field in the results of the OPEN operation
      (see <xref target="OP_OPEN_DESCRIPTION" />).
      The server constructs wdr_resok4 the same way it constructs
      OPEN's "delegation" with one difference:
      WANT_DELEGATION MUST NOT return a delegation type of
      OPEN_DELEGATE_NONE.
    </t>
    <t> 
      If ((wda_want & OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) &
          ~OPEN4_SHARE_ACCESS_WANT_NO_DELEG) is zero,
      then the client is indicating no
      explicit desire or non-desire for a delegation and the server MUST return 
      NFS4ERR_INVAL.
    </t>
    <t>
       The client uses the 
          OPEN4_SHARE_ACCESS_WANT_CANCEL
       flag in the WANT_DELEGATION 
       operation to cancel a previously requested want for a delegation.
       Note that if the server is in the process of sending the
       delegation (via CB_PUSH_DELEG) at the time the client sends
       a cancellation of the want, the delegation might still be pushed
       to the client.
    </t>
    <t>
     If WANT_DELEGATION fails to return a delegation, and
     the server returns NFS4_OK, the server MUST set the
     delegation type to OPEN4_DELEGATE_NONE_EXT, and set
     od_whynone, as described in <xref target="OP_OPEN"
     />.  Write delegations are not available for
     file types that are not writable. This includes
     file objects of types NF4BLK, NF4CHR, NF4LNK,
     NF4SOCK, and NF4FIFO. If the client requests
     OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG without
     OPEN4_SHARE_ACCESS_WANT_READ_DELEG on an object with
     one of the aforementioned file types, the server must
     set wdr_resok4.od_whynone.ond_why to 
     WND4_WRITE_DELEG_NOT_SUPP_FTYPE.
    </t>  
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A request for a conflicting delegation is not normally intended to trigger 
      the recall of the existing delegation.  Servers may choose to treat
      some clients as having higher priority such that their wants will
      trigger recall of an existing delegation, although that is expected
      to be an unusual situation.
    </t>
    <t>
      Servers will generally recall delegations assigned by WANT_DELEGATION
      on the same basis as those assigned by OPEN.  CB_RECALL will generally
      be done only when other clients perform operations inconsistent with
      the delegation.  The normal response to aging of delegations is to use
      CB_RECALL_ANY, in order to give the client the opportunity to keep
      the delegations most useful from its point of view.
    </t>  

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DESTROY_CLIENTID" title="Operation 57: DESTROY_CLIENTID - Destroy a Client ID" >

  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct DESTROY_CLIENTID4args {
        clientid4       dca_clientid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_RESULT" title="RESULT">
<figure>
 <artwork>
struct DESTROY_CLIENTID4res {
        nfsstat4        dcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DESTROY_CLIENTID operation destroys the
      client ID.  If there are sessions (both idle and
      non-idle), opens, locks, delegations, layouts,
      and/or wants (<xref target="OP_WANT_DELEGATION" />)
      associated with the unexpired lease of the client
      ID, the server MUST return NFS4ERR_CLIENTID_BUSY.
      DESTROY_CLIENTID MAY be preceded with a SEQUENCE
      operation as long as the client ID derived from the
      session ID of SEQUENCE is not the same as the client
      ID to be destroyed. If the client IDs are the same,
      then the server MUST return NFS4ERR_CLIENTID_BUSY.

    </t>

    <t>
      If DESTROY_CLIENTID is not prefixed by SEQUENCE,
      it MUST be the only operation in the COMPOUND
      request (otherwise, the server MUST return
      NFS4ERR_NOT_ONLY_OP).  If the operation is sent
      without a SEQUENCE preceding it, a client that
      retransmits the request may receive an error in
      response, because the original request might have
      been successfully executed.

    </t>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      DESTROY_CLIENTID allows a server to immediately
      reclaim the resources consumed by an unused client
      ID, and also to forget that it ever generated the
      client ID. By forgetting that it ever generated the client
      ID, the server can safely reuse the client ID on a
      future EXCHANGE_ID operation.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RECLAIM_COMPLETE" title="Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished" >

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct RECLAIM_COMPLETE4args {
        /*
         * If rca_one_fs TRUE,
         *
         *    CURRENT_FH: object in
         *    file system reclaim is
         *    complete for.
         */
        bool            rca_one_fs;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RECLAIM_COMPLETE4res {
        nfsstat4        rcr_status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_DESCRIPTION" title="DESCRIPTION">
    <t>
      A RECLAIM_COMPLETE operation is used to indicate that the client
      has reclaimed all of the locking state that it will recover,
      when it is recovering state due to either a server restart or the
      transfer of a file system to another server.  There are two types
      of RECLAIM_COMPLETE operations:
      <list style="symbols">
        <t>
          When rca_one_fs is FALSE, a global RECLAIM_COMPLETE is being
          done.  This indicates that recovery of all
          locks that the client held on the previous server instance
          have been completed.
        </t>
        <t>
          When rca_one_fs is TRUE, a file system-specific RECLAIM_COMPLETE
          is being done.  This indicates that recovery of locks
          for a single fs (the one designated by the current filehandle)
          due to a file system transition have been completed.  Presence
          of a current filehandle is only required when rca_one_fs is set to TRUE. 
        </t>
      </list>
    </t>
    <t>
      Once a RECLAIM_COMPLETE is done, there can be no further
      reclaim operations for locks whose scope is defined as having
      completed recovery.  Once the client sends RECLAIM_COMPLETE, 
      the server will not allow the client to do
      subsequent reclaims of locking state for that scope 
      and, if these are attempted, will return NFS4ERR_NO_GRACE.
    </t>
    <t>
      Whenever a client establishes a new client ID and before it does
      the first non-reclaim operation that obtains a lock, it MUST send a
      RECLAIM_COMPLETE with rca_one_fs set to FALSE, even if there are no locks to 
      reclaim.  If non-reclaim
      locking operations are done before the RECLAIM_COMPLETE, an NFS4ERR_GRACE
      error will be returned.
    </t>
    <t>
      Similarly, when the client accesses a file system on a new
      server, before it sends the first non-reclaim operation that
      obtains a lock on this new server, it MUST send a RECLAIM_COMPLETE
      with rca_one_fs set to TRUE and current filehandle within that file system,
      even if there are no locks to reclaim.  If non-reclaim locking
      operations are done on that file system before the
      RECLAIM_COMPLETE, an NFS4ERR_GRACE error will be returned.
    </t>
    <t>
      Any locks not reclaimed at the point at which RECLAIM_COMPLETE
      is done become non-reclaimable.  The client MUST NOT attempt 
      to reclaim them, either during 
      the current server instance or in any subsequent
      server instance, or on another server to which responsibility
      for that file system is transferred.  If the client were to do so, 
      it would be
      violating the protocol by representing itself as owning locks
      that it does not own, and so has no right to reclaim.  See
      <xref target="network_partitions_and_recovery" /> for a 
      discussion of edge conditions related to lock reclaim.
    </t>
    <t>
      By sending a RECLAIM_COMPLETE, the client indicates readiness
      to proceed to do normal non-reclaim locking operations.  The client
      should be aware that such operations may temporarily result in 
      NFS4ERR_GRACE errors until the server is ready to terminate its
      grace period.
    </t>
  </section>
  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Servers will typically use the information as to when reclaim
      activity is complete to reduce the length of the grace period.
      When the server maintains in persistent storage
      a list of clients that might have had locks,
      it is in a position to use the fact that
      all such clients have done a RECLAIM_COMPLETE to terminate the
      grace period and begin normal operations (i.e., grant requests
      for new locks) sooner than it might otherwise.
    </t>
    <t>
      Latency can be minimized by doing a RECLAIM_COMPLETE as part of
      the COMPOUND request in which the last lock-reclaiming operation
      is done.  When there are no reclaims to be done, RECLAIM_COMPLETE
      should be done immediately in order to allow the grace period 
      to end as soon as possible.
    </t>
    <t>
      RECLAIM_COMPLETE should only be done once for each server instance
      or occasion of the transition of a file system.
      If it is done a second time, the error NFS4ERR_COMPLETE_ALREADY will 
      result.  Note that because of the session feature's retry protection,
      retries of COMPOUND
      requests containing RECLAIM_COMPLETE operation will not result 
      in this error.
    </t>
    <t>
      When a RECLAIM_COMPLETE is sent, the client effectively acknowledges
      any locks not yet reclaimed as lost.  This allows the server to
      re-enable the client to recover locks if
      the occurrence of edge conditions, as described in 
      <xref target="network_partitions_and_recovery" />, had caused the
      server to disable the client from recovering locks.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_ILLEGAL" title="Operation 10044: ILLEGAL - Illegal Operation" >

  <section toc="exclude" anchor="OP_ILLEGAL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_ILLEGAL_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct ILLEGAL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_ILLEGAL_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is a placeholder for encoding a result to handle the
      case of the client sending an operation code within COMPOUND that is
      not supported. See the COMPOUND procedure description for more
      details.
    </t>
    <t>
      The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
    </t>
  </section>
  <section toc="exclude" anchor="OP_ILLEGAL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A client will probably not send an operation with code OP_ILLEGAL but
      if it does, the response will be ILLEGAL4res just as it would be with
      any other invalid operation code. Note that if the server gets an
      illegal operation code that is not OP_ILLEGAL, and if the server
      checks for legal operation codes during the XDR decode phase, then the
      ILLEGAL4res would not be returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41callbackprocedures" title="NFSv4.1 Callback Procedures">
<t>
The procedures used for callbacks are defined in the following
sections.  In the interest of clarity, the terms "client" and "server"
refer to NFS clients and servers, despite the fact that for an
individual callback RPC, the sense of these terms would be precisely
the opposite.
</t>
<t>
 Both procedures, CB_NULL and CB_COMPOUND, MUST be implemented.
</t>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_CB_NULL" title="Procedure 0: CB_NULL - No Operation" >

  <section toc="exclude" anchor="PROC_CB_NULL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_RESULTS" title="RESULTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_DESCRIPTION" title="DESCRIPTION">
    <t>
      CB_NULL is the standard ONC RPC NULL procedure, with the standard void argument and void response.  Even though
      there is no direct functionality associated with this procedure, the
      server will use CB_NULL to confirm the existence of a path for RPCs
      from the server to client.
    </t>

  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_ERRORS" title="ERRORS">
    <t>
      None.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_CB_COMPOUND" title="Procedure 1: CB_COMPOUND - Compound Operations" >

  <section toc="exclude" anchor="PROC_CB_COMPOUND_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>

enum nfs_cb_opnum4 {
        OP_CB_GETATTR           = 3,
        OP_CB_RECALL            = 4,
/* Callback operations new to NFSv4.1 */
        OP_CB_LAYOUTRECALL      = 5,
        OP_CB_NOTIFY            = 6,
        OP_CB_PUSH_DELEG        = 7,
        OP_CB_RECALL_ANY        = 8,
        OP_CB_RECALLABLE_OBJ_AVAIL = 9,
        OP_CB_RECALL_SLOT       = 10,
        OP_CB_SEQUENCE          = 11,
        OP_CB_WANTS_CANCELLED   = 12,
        OP_CB_NOTIFY_LOCK       = 13,
        OP_CB_NOTIFY_DEVICEID   = 14,

        OP_CB_ILLEGAL           = 10044
};
 </artwork>
</figure>
<figure>
 <artwork>
union nfs_cb_argop4 switch (unsigned argop) {
 case OP_CB_GETATTR:
      CB_GETATTR4args           opcbgetattr;
 case OP_CB_RECALL:
      CB_RECALL4args            opcbrecall;
 case OP_CB_LAYOUTRECALL:
      CB_LAYOUTRECALL4args      opcblayoutrecall;
 case OP_CB_NOTIFY:
      CB_NOTIFY4args            opcbnotify;
 case OP_CB_PUSH_DELEG:
      CB_PUSH_DELEG4args        opcbpush_deleg;
 case OP_CB_RECALL_ANY:
      CB_RECALL_ANY4args        opcbrecall_any;
 case OP_CB_RECALLABLE_OBJ_AVAIL:
      CB_RECALLABLE_OBJ_AVAIL4args opcbrecallable_obj_avail;
 case OP_CB_RECALL_SLOT:
      CB_RECALL_SLOT4args       opcbrecall_slot;
 case OP_CB_SEQUENCE:
      CB_SEQUENCE4args          opcbsequence;
 case OP_CB_WANTS_CANCELLED:
      CB_WANTS_CANCELLED4args   opcbwants_cancelled;
 case OP_CB_NOTIFY_LOCK:
      CB_NOTIFY_LOCK4args       opcbnotify_lock;
 case OP_CB_NOTIFY_DEVICEID:
      CB_NOTIFY_DEVICEID4args   opcbnotify_deviceid;
 case OP_CB_ILLEGAL:            void;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct CB_COMPOUND4args {
        utf8str_cs      tag;
        uint32_t        minorversion;
        uint32_t        callback_ident;
        nfs_cb_argop4   argarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="PROC_CB_COMPOUND_RESULTS" title="RESULTS">
<figure>
 <artwork>
union nfs_cb_resop4 switch (unsigned resop) {
 case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
 case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;

 /* new NFSv4.1 operations */
 case OP_CB_LAYOUTRECALL:
                        CB_LAYOUTRECALL4res
                                        opcblayoutrecall;

 case OP_CB_NOTIFY:     CB_NOTIFY4res   opcbnotify;

 case OP_CB_PUSH_DELEG: CB_PUSH_DELEG4res
                                        opcbpush_deleg;

 case OP_CB_RECALL_ANY: CB_RECALL_ANY4res
                                        opcbrecall_any;

 case OP_CB_RECALLABLE_OBJ_AVAIL:
                        CB_RECALLABLE_OBJ_AVAIL4res
                                opcbrecallable_obj_avail;

 case OP_CB_RECALL_SLOT:
                        CB_RECALL_SLOT4res
                                        opcbrecall_slot;

 case OP_CB_SEQUENCE:   CB_SEQUENCE4res opcbsequence;

 case OP_CB_WANTS_CANCELLED:
                        CB_WANTS_CANCELLED4res
                                opcbwants_cancelled;

 case OP_CB_NOTIFY_LOCK:
                        CB_NOTIFY_LOCK4res
                                        opcbnotify_lock;

 case OP_CB_NOTIFY_DEVICEID:
                        CB_NOTIFY_DEVICEID4res
                                        opcbnotify_deviceid;

 /* Not new operation */
 case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct CB_COMPOUND4res {
        nfsstat4 status;
        utf8str_cs      tag;
        nfs_cb_resop4   resarray&lt;>;
};
 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CB_COMPOUND_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_COMPOUND procedure is used to combine one or more of the
      callback procedures into a single RPC request.  The main callback RPC
      program has two main procedures: CB_NULL and CB_COMPOUND.  All other
      operations use the CB_COMPOUND procedure as a wrapper.
    </t>
    <t>
      During the processing of the CB_COMPOUND procedure, the client may find
      that it does not have the available resources to execute any or all of
      the operations within the CB_COMPOUND sequence.
      Refer to <xref target="COMPOUND Sizing Issues" /> for details.
    </t>
    <t>
     The minorversion field of the arguments MUST be the same as the
     minorversion of the COMPOUND procedure used to create the client ID
     and session. For NFSv4.1, minorversion MUST be set to 1.
    </t>
    <t>
      Contained within the CB_COMPOUND results is a "status" field.  This
      status MUST be equal to the status of the last operation that was
      executed within the CB_COMPOUND procedure.  Therefore, if an operation
      incurred an error, then the "status" value will be the same error value
      as is being returned for the operation that failed.
    </t>
    <t>
      The "tag" field is handled the same way as that of the COMPOUND
      procedure (see <xref target="OP_COMPOUND_DESCRIPTION" />).
    </t>
    <t>
      Illegal operation codes are handled in the same way as they are
      handled for the COMPOUND procedure.
    </t>
  </section>
  <section toc="exclude" anchor="PROC_CB_COMPOUND_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The CB_COMPOUND procedure is used to combine individual operations
      into a single RPC request.  The client interprets each of the
      operations in turn.  If an operation is executed by the client and
      the status of that operation is NFS4_OK, then the next operation in
      the CB_COMPOUND procedure is executed.  The client continues this
      process until there are no more operations to be executed or one of
      the operations has a status value other than NFS4_OK.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_COMPOUND_ERRORS" title="ERRORS">
    <t>
     CB_COMPOUND will of course return every error that each operation on
     the backchannel can return (see <xref target="cb_op_error_returns"/>).
     However, if CB_COMPOUND returns zero operations, obviously the error
     returned by COMPOUND has nothing to do with an error returned by
     an operation. The list of errors CB_COMPOUND will return if it processes
     zero operations includes:
    </t>
     <texttable anchor="CB_compounderrs">
     <preamble>CB_COMPOUND error returns</preamble>
     <ttcol align='left'>Error</ttcol>
     <ttcol align='left'>Notes</ttcol>

     <c>NFS4ERR_BADCHAR</c> <c>The tag argument has a character the replier
                               does not support. </c>

     <c>NFS4ERR_BADXDR</c> <c> </c>

     <c>NFS4ERR_DELAY</c> <c> </c>

     <c>NFS4ERR_INVAL</c> <c>The tag argument is not in UTF-8 encoding.</c>

     <c>NFS4ERR_MINOR_VERS_MISMATCH</c> <c> </c>

     <c>NFS4ERR_SERVERFAULT</c> <c> </c>

     <c>NFS4ERR_TOO_MANY_OPS</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c> <c> </c>

     <c>NFS4ERR_REQ_TOO_BIG</c> <c> </c>

     </texttable>
 
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41cboperations" title="NFSv4.1 Callback Operations">
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_GETATTR" title="Operation 3: CB_GETATTR - Get Attributes" >

  <section toc="exclude" anchor="OP_CB_GETATTR_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_GETATTR4args {
        nfs_fh4 fh;
        bitmap4 attr_request;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_GETATTR4resok {
        fattr4  obj_attributes;
};

union CB_GETATTR4res switch (nfsstat4 status) {
 case NFS4_OK:
         CB_GETATTR4resok       resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
     The CB_GETATTR operation is used by the server to obtain the
     current modified state of a file that has been OPEN_DELEGATE_WRITE delegated.
     The size and change attributes are the only ones guaranteed to be
     serviced by the client.  See <xref
     target="handling_cb_getattr"/> for a full description
     of how the client and server are to interact with
     the use of CB_GETATTR.

    </t>
    <t>
     If the filehandle specified is not one for which the client holds an
     OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error is returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The client returns attrmask bits and the associated attribute
     values only for the change attribute, and attributes that it may
     change (time_modify, and size).
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL" title="Operation 4: CB_RECALL - Recall a Delegation" >

  <section toc="exclude" anchor="OP_CB_RECALL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_RECALL4args {
        stateid4        stateid;
        bool            truncate;
        nfs_fh4         fh;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_RECALL operation is used to begin the process of recalling
      a delegation and returning it to the server.
    </t>
    <t>      
      The truncate flag is used to optimize recall for a file object that
      is a regular file and is
      about to be truncated to zero.  When it is TRUE, the client is freed
      of the obligation to propagate modified data for the file to the
      server, since this data is irrelevant.
    </t>
    <t>      
      If the handle specified is not one for which the client holds a
      delegation, an NFS4ERR_BADHANDLE error is returned.
    </t>
    <t>      
      If the stateid specified is not one corresponding to an OPEN
      delegation for the file specified by the filehandle, an
      NFS4ERR_BAD_STATEID is returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The client SHOULD reply to the callback immediately.
     Replying does not complete the recall except when
     the value of the reply's status field is neither
     NFS4ERR_DELAY nor NFS4_OK.  The recall is not complete
     until the delegation is returned using a DELEGRETURN
     operation.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_LAYOUTRECALL" 
         title="Operation 5: CB_LAYOUTRECALL - Recall Layout from Client" >

  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * NFSv4.1 callback arguments and results
 */

enum layoutrecall_type4 {
        LAYOUTRECALL4_FILE = LAYOUT4_RET_REC_FILE,
        LAYOUTRECALL4_FSID = LAYOUT4_RET_REC_FSID,
        LAYOUTRECALL4_ALL  = LAYOUT4_RET_REC_ALL
};

struct layoutrecall_file4 {
        nfs_fh4         lor_fh;
        offset4         lor_offset;
        length4         lor_length;
        stateid4        lor_stateid;
};

union layoutrecall4 switch(layoutrecall_type4 lor_recalltype) {
case LAYOUTRECALL4_FILE:
        layoutrecall_file4 lor_layout;
case LAYOUTRECALL4_FSID:
        fsid4              lor_fsid;
case LAYOUTRECALL4_ALL:
        void;
};

struct CB_LAYOUTRECALL4args {
        layouttype4             clora_type;
        layoutiomode4           clora_iomode;
        bool                    clora_changed;
        layoutrecall4           clora_recall;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_LAYOUTRECALL4res {
        nfsstat4        clorr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_LAYOUTRECALL operation is used by the server to recall
      layouts from the client; as a result, the client will begin the
      process of returning layouts via LAYOUTRETURN.  The
      CB_LAYOUTRECALL operation specifies one of three forms of recall
      processing with the value of layoutrecall_type4.  The recall is
      for one of the following: a specific layout of a specific file
      (LAYOUTRECALL4_FILE), an entire file system ID
      (LAYOUTRECALL4_FSID), or all file systems (LAYOUTRECALL4_ALL).
    </t>
    <t>
      The behavior of the operation varies based on the value of the
      layoutrecall_type4.  The value and behaviors are:
      <list style="hanging">
      <t hangText="LAYOUTRECALL4_FILE"></t>
      <t>
        For a layout to match the recall request, the values of the following fields
        must match those of the layout: clora_type, clora_iomode,
        lor_fh, and the byte-range specified by lor_offset and
        lor_length.  The clora_iomode field may have a special value
        of LAYOUTIOMODE4_ANY.  The special value LAYOUTIOMODE4_ANY will match any
        iomode originally returned in a layout; therefore, it acts as a
        wild card.  The other special value used is for
        lor_length.  If lor_length has a value of NFS4_UINT64_MAX, the
        lor_length field means the maximum possible file size. If a
        matching layout is found, it MUST be returned using the
        LAYOUTRETURN operation (see <xref target="OP_LAYOUTRETURN" />).
        An example of the field's special value use is if clora_iomode
        is LAYOUTIOMODE4_ANY, lor_offset is zero, and lor_length is
        NFS4_UINT64_MAX, then the entire layout is to be returned.
      </t>
      <t>
        The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
        client does not hold layouts for the file or if the client
        does not have any overlapping layouts for the specification in
        the layout recall.
      </t>
      <t hangText="LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL"></t>
      <t>
        If LAYOUTRECALL4_FSID is specified, the fsid specifies the
        file system for which any outstanding layouts MUST be
        returned.  If LAYOUTRECALL4_ALL is specified, all outstanding
        layouts MUST be returned.  In addition, LAYOUTRECALL4_FSID and
        LAYOUTRECALL4_ALL specify that all the storage device ID to
        storage device address mappings in the affected file system(s)
        are also recalled. The respective LAYOUTRETURN with either
        LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL acknowledges to the
        server that the client invalidated the said device mappings.
        See <xref target="bulk_layouts" /> for considerations with
        "bulk" recall of layouts.
      </t>
      <t>
        The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
        client does not hold layouts and does not have valid deviceid
        mappings.
      </t>
    </list>
    </t>
    <t>
      In processing the layout recall request, the client also varies
      its behavior based on the value of the clora_changed field.  This
      field is used by the server to provide additional context for
      the reason why the layout is being recalled.  A FALSE value for
      clora_changed indicates that no change in the layout is expected
      and the client may write modified data to the storage devices
      involved; this must be done prior to returning the layout via
      LAYOUTRETURN.  A TRUE value for clora_changed indicates that the
      server is changing the layout.  Examples of layout changes and
      reasons for a TRUE indication are the following: the metadata server is restriping
      the file or a permanent error has occurred on a storage device
      and the metadata server would like to provide a new layout for
      the file.  Therefore, a clora_changed value of TRUE indicates
      some level of change for the layout and the client SHOULD NOT
      write and commit modified data to the storage devices.  In this
      case, the client writes and commits data through the metadata
      server.
    </t>
    <t>
      See <xref target="layout_stateid"/> for a description of how the
      lor_stateid field in the arguments is to be constructed. Note
      that the "seqid" field of lor_stateid MUST NOT be zero.  See Sections
      <xref target="stateid" format="counter" />, <xref
target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client's processing for CB_LAYOUTRECALL is similar to
      CB_RECALL (recall of file delegations) in that
      the client responds to
      the request before actually returning layouts via the
      LAYOUTRETURN operation.  While the client responds to the
      CB_LAYOUTRECALL immediately, the operation is not considered
      complete (i.e., considered pending) until all affected layouts are returned to the server
      via the LAYOUTRETURN operation.
    </t>
    <t>
      Before returning the layout to the server via LAYOUTRETURN, the
      client should wait for the response from in-process or in-flight
      READ, WRITE, or COMMIT operations that use the recalled layout.
    </t>
    <t>
      If the client is holding modified data that is affected by a
      recalled layout, the client has various options for writing the
      data to the server.  As always, the client may write the data
      through the metadata server.  In fact, the client may not have a
      choice other than writing to the metadata server when the
      clora_changed argument is TRUE and a new layout is unavailable
      from the server.  However, the client may be able to write the
      modified data to the storage device if the clora_changed
      argument is FALSE; this needs to be done before returning the
      layout via LAYOUTRETURN.  If the client were to obtain a new
      layout covering the modified data's byte-range, then writing to the
      storage devices is an available alternative.  Note that before
      obtaining a new layout, the client must first return the
      original layout.
    </t>
    <t>
      In the case of modified data being written while the layout is
      held, the client must use LAYOUTCOMMIT operations at the
      appropriate time; as required LAYOUTCOMMIT must be done before
      the LAYOUTRETURN.  If a large amount of modified data is
      outstanding, the client may send LAYOUTRETURNs for portions of
      the recalled layout; this allows the server to monitor the
      client's progress and adherence to the original recall request.
      However, the last LAYOUTRETURN in a sequence of returns MUST
      specify the full range being recalled (see <xref
      target="recall_robustness" /> for details).
    </t>
    <t>
      If a server needs to delete a device ID and there are layouts
      referring to the device ID, CB_LAYOUTRECALL MUST be invoked to
      cause the client to return all layouts referring to the device ID
      before the server can delete the device ID. If the client
      does not return the affected layouts, the server MAY revoke
      the layouts.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_NOTIFY" title="Operation 6: CB_NOTIFY - Notify Client of Directory Changes" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * Directory notification types.
 */
enum notify_type4 {
        NOTIFY4_CHANGE_CHILD_ATTRS = 0,
        NOTIFY4_CHANGE_DIR_ATTRS = 1,
        NOTIFY4_REMOVE_ENTRY = 2,
        NOTIFY4_ADD_ENTRY = 3,
        NOTIFY4_RENAME_ENTRY = 4,
        NOTIFY4_CHANGE_COOKIE_VERIFIER = 5
};

/* Changed entry information.  */
struct notify_entry4 {
        component4      ne_file;
        fattr4          ne_attrs;
};

/* Previous entry information */
struct prev_entry4 {
        notify_entry4   pe_prev_entry;
        /* what READDIR returned for this entry */
        nfs_cookie4     pe_prev_entry_cookie;
};

struct notify_remove4 {
        notify_entry4   nrm_old_entry;
        nfs_cookie4     nrm_old_entry_cookie;
};

struct notify_add4 {
        /*
         * Information on object
         * possibly renamed over.
         */
        notify_remove4      nad_old_entry&lt;1>;
        notify_entry4       nad_new_entry;
        /* what READDIR would have returned for this entry */
        nfs_cookie4         nad_new_entry_cookie&lt;1>;
        prev_entry4         nad_prev_entry&lt;1>;
        bool                nad_last_entry;
};

struct notify_attr4 {
        notify_entry4   na_changed_entry;
};

struct notify_rename4 {
        notify_remove4  nrn_old_entry;
        notify_add4     nrn_new_entry;
};

struct notify_verifier4 {
        verifier4       nv_old_cookieverf;
        verifier4       nv_new_cookieverf;
};

/*
 * Objects of type notify_&lt;>4 and
 * notify_device_&lt;>4 are encoded in this.
 */
typedef opaque notifylist4&lt;>;

struct notify4 {
        /* composed from notify_type4 or notify_deviceid_type4 */
        bitmap4         notify_mask;
        notifylist4     notify_vals;
};

struct CB_NOTIFY4args {
        stateid4    cna_stateid;
        nfs_fh4     cna_fh;
        notify4     cna_changes&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY4res {
        nfsstat4    cnr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_NOTIFY operation is used by the server to
      send notifications to clients about changes to
      delegated directories.
      The registration of notifications for the directories
      occurs when the delegation is established using
      GET_DIR_DELEGATION.
      These notifications are sent over the backchannel. The
      notification is sent once the original request has been
      processed on the server. The server will send an array of
      notifications for changes that might have occurred in the
      directory. The notifications are sent as list of pairs of
      bitmaps and values.
      See <xref target="fattr4" />
      for a description of how NFSv4.1 bitmaps work.

   </t>
   <t>
     If the server has more notifications than can fit in
     the CB_COMPOUND request, it SHOULD send a sequence of
     serial CB_COMPOUND requests so that the client's view
     of the directory does not become confused. For example, if the
     server indicates that a file named "foo" is added and that the
     file "foo" is removed, the order in which the client receives
     these notifications needs to be the same as the
     order in which the corresponding operations occurred on the server.

   </t>

   <t>

      If the client holding the delegation makes any
      changes in the directory that cause files or sub-directories to
      be added or removed, the server will
      notify that client of the resulting change(s). If the
      client holding the delegation is making attribute
      or cookie verifier changes only, the server does
      not need to send notifications to that client.
      The server will send the following information for
      each operation:

      <list style="hanging">
	<t hangText="NOTIFY4_ADD_ENTRY"><vspace /> 
	  The server will send
	  information about the new directory entry being created along with the
	  cookie for that entry.  The entry information (data type
	  notify_add4) includes the component name of the entry and
	  attributes.  The server will send this type of entry when a
	  file is actually being created, when an entry is being added
	  to a directory as a result of a rename across directories
	  (see below), and when a hard link is being created to an
	  existing file.  If this entry is added to the end of the
	  directory, the server will set the nad_last_entry flag to
	  TRUE. If the file is added such that there is at least one
	  entry before it, the server will also return the previous
	  entry information (nad_prev_entry, a variable-length array
	  of up to one element. If the array is of zero length, there
	  is no previous entry), along with its cookie.  This is to
	  help clients find the right location in their file name caches and
	  directory caches where this entry should be cached. If the
	  new entry's cookie is available, it will be in
	  the nad_new_entry_cookie (another variable-length array of up to
	  one element) field.  If the addition of the entry causes another 
          entry to be deleted (which can only happen in the rename
          case) atomically with the addition, then information on
          this entry is reported in nad_old_entry.
	</t>
	<t hangText="NOTIFY4_REMOVE_ENTRY"><vspace />
	  The server will send information about the directory entry
	  being deleted. The server will also send the cookie value
	  for the deleted entry so that clients can get to the cached
	  information for this entry.
	</t>
	<t hangText="NOTIFY4_RENAME_ENTRY"><vspace />
	  The server will send information about both
	  the old entry and the new entry. This includes the name and
	  attributes for each entry.  In addition, if the rename
          causes the deletion of an entry (i.e., the case of a file
          renamed over), then this is reported in 
          nrn_new_new_entry.nad_old_entry. 
          This notification is only sent if
	  both entries are in the same directory. If the rename is
	  across directories, the server will send a remove
	  notification to one directory and an add notification to the
	  other directory, assuming both have a directory delegation.
	</t>
	<t
	hangText="NOTIFY4_CHANGE_CHILD_ATTRS/NOTIFY4_CHANGE_DIR_ATTRS"><vspace
	/>

	  The client will use the attribute
	  mask to inform the server of attributes for which it wants to
	  receive notifications. This change notification can be
	  requested for changes to the attributes of the directory
	  as well as changes to any file's attributes in the directory by
	  using two separate attribute masks. The client cannot ask
	  for change attribute notification for a specific file. One attribute
	  mask covers all the files in the directory. Upon any
	  attribute change, the server will send back the values of
	  changed attributes. Notifications might not make sense for
	  some file system-wide attributes, and it is up to the server to
	  decide which subset it wants to support.  The client can
	  negotiate the frequency of attribute notifications by letting
	  the server know how often it wants to be notified of an
	  attribute change. The server will return supported
	  notification frequencies or an indication that no
	  notification is permitted for directory or child attributes
	  by setting the dir_notif_delay and
	  dir_entry_notif_delay attributes, respectively.
	</t>
	<t hangText="NOTIFY4_CHANGE_COOKIE_VERIFIER"><vspace />

	  If the cookie verifier changes while
	  a client is holding a delegation, the server will notify the
	  client so that it can invalidate its cookies and re-send a
	  READDIR to get the new set of cookies.
	</t>
      </list>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->


<section anchor="OP_CB_PUSH_DELEG" 
         title="Operation 7: CB_PUSH_DELEG - Offer Previously Requested Delegation to Client" >

  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_PUSH_DELEG4args {
        nfs_fh4          cpda_fh;
        open_delegation4 cpda_delegation;

};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_PUSH_DELEG4res {
        nfsstat4 cpdr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_DESCRIPTION" title="DESCRIPTION">
    <t>
	CB_PUSH_DELEG is used by the server both to signal to the
	client that the delegation it wants (previously indicated
        via a want established from an
        OPEN or WANT_DELEGATION operation) is available and to
	simultaneously offer the delegation to the client.  The client
	has the choice of accepting the delegation by returning
	NFS4_OK to the server, delaying the decision to accept the
	offered delegation by returning NFS4ERR_DELAY,
	or permanently rejecting the offer of the
	delegation by returning NFS4ERR_REJECT_DELEG.
        When a delegation is rejected in this fashion, the want
        previously established is permanently deleted and the delegation
        is subject to acquisition by another client.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
	If the client does return NFS4ERR_DELAY
	and there is a conflicting delegation request, the server MAY
	process it at the expense of the client that returned
	NFS4ERR_DELAY. The client's want will not be cancelled, but
	MAY be processed behind other delegation requests or registered
	wants.
    </t>
    <t>
        When a client returns a status other than NFS4_OK, NFS4ERR_DELAY,
        or NFS4ERR_REJECT_DELAY, the want remains pending, although 
        servers may decide to cancel the want by sending a CB_WANTS_CANCELLED.
      </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL_ANY" title="Operation 8: CB_RECALL_ANY - Keep Any N Recallable Objects" >

  <section toc="exclude" anchor="OP_CB_RECALL_ANY_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
const RCA4_TYPE_MASK_RDATA_DLG          = 0;
const RCA4_TYPE_MASK_WDATA_DLG          = 1;
const RCA4_TYPE_MASK_DIR_DLG            = 2;
const RCA4_TYPE_MASK_FILE_LAYOUT        = 3;
const RCA4_TYPE_MASK_BLK_LAYOUT         = 4;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN     = 8;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX     = 9;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MIN   = 12;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MAX   = 15;

struct  CB_RECALL_ANY4args      {
        uint32_t        craa_objects_to_keep;
        bitmap4         craa_type_mask;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL_ANY4res {
        nfsstat4        crar_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The server may decide that it cannot hold all of the state for
      recallable objects, such as delegations and layouts, without 
      running out of resources.  In such a case, while not optimal,
      the server is free to recall individual objects to reduce the load.
    </t>
    <t>
      Because the general purpose of such recallable objects as
      delegations is to eliminate client interaction with the server,
      the server cannot interpret lack of recent use as indicating
      that the object is no longer useful.  The absence of visible
      use is consistent with a delegation keeping potential operations
      from being sent to the server. In the case of layouts, while it
      is true that the usefulness of a layout
      is indicated by the use of the layout when storage devices receive
      I/O requests, because there is no mandate that a storage
      device indicate to the metadata server any past or
      present use of a layout, the metadata server is not likely to know
      which layouts are good candidates to recall in response to
      low resources.
    </t>
    <t>
      In order to implement an effective reclaim scheme for such 
      objects, the server's knowledge of available resources must be
      used to determine when objects must be recalled with the 
      clients selecting the actual objects to be returned.
    </t>
    <t>
      Server implementations may differ in their resource allocation
      requirements.  For example, one server may share resources among
      all classes of recallable objects, whereas another may use
      separate resource pools for layouts and for delegations, or
      further separate resources by types of delegations.
    </t>
    <t>
      When a given resource pool is over-utilized, the server can
      send a CB_RECALL_ANY to clients holding recallable objects of
      the types involved, allowing it to keep a certain number of
      such objects and return any excess.  A mask specifies which 
      types of objects are to be limited.  The client chooses, based
      on its own knowledge of current usefulness, which of the objects
      in that class should be returned.
    </t>
    <t>
      A number of bits are defined.  For some of these, ranges
      are defined and it is up to the definition of the storage 
      protocol to specify how these are to be used.  There are ranges 
      reserved for object-based storage 
      protocols and for other experimental storage 
      protocols.  An RFC defining such a storage protocol needs to
      specify how particular bits within its range are to be used.  
      For example, it may specify a mapping between attributes of 
      the layout (read vs. write, size of area) and the bit to be 
      used, or it may define a field in the layout where the associated
      bit position is made available by the server to the client.

      <list style='hanging'>
      <t hangText='RCA4_TYPE_MASK_RDATA_DLG'>
      </t>
      <t>
       The client is to return OPEN_DELEGATE_READ delegations on
       non-directory file objects.

      </t>

      <t hangText='RCA4_TYPE_MASK_WDATA_DLG'>
      </t>
      <t>
       The client is to return OPEN_DELEGATE_WRITE delegations on
       regular file objects.

      </t>

      <t hangText='RCA4_TYPE_MASK_DIR_DLG'>
      </t>
      <t>
       The client is to return directory delegations.

      </t>

      <t hangText='RCA4_TYPE_MASK_FILE_LAYOUT'>
      </t>
      <t>
       The client is to return layouts of type LAYOUT4_NFSV4_1_FILES.

      </t>
      <t hangText='RCA4_TYPE_MASK_BLK_LAYOUT'>
      </t>
      <t>
       See <xref target='RFC5663' /> for a description.

      </t>
      
      <t hangText='RCA4_TYPE_MASK_OBJ_LAYOUT_MIN to RCA4_TYPE_MASK_OBJ_LAYOUT_MAX'>
      </t>
      <t>
       See <xref target='RFC5664' /> for a description.

      </t>
      <t hangText='RCA4_TYPE_MASK_OTHER_LAYOUT_MIN to RCA4_TYPE_MASK_OTHER_LAYOUT_MAX'>
      </t>
      <t>
        This range is reserved for telling the client to recall
        layouts of experimental
        or site-specific layout types (see <xref
        target='layouttype4'/>).

      </t>
      </list>

    </t>
    <t>
      When a bit is set in the type mask that corresponds
      to an undefined type of recallable object,
      NFS4ERR_INVAL MUST be returned.  When a bit is set
      that corresponds to a defined type of object but
      the client does not support an object of the type,
      NFS4ERR_INVAL MUST NOT be returned.  Future minor
      versions of NFSv4 may expand the set of valid type
      mask bits.

    </t>
    <t>
      CB_RECALL_ANY specifies a count of objects that the client may
      keep as opposed to a count that the client must return.  This
      is to avoid a potential race between a CB_RECALL_ANY that had a 
      count of objects to free with a set of client-originated 
      operations to return layouts or delegations. As a result of the 
      race, the client and server would have differing ideas as to how
      many objects to return.  Hence, the client could mistakenly free 
      too many.
    </t>
    <t>
      If resource demands prompt it, the server may send another
      CB_RECALL_ANY with a lower count, even if it has not yet received
      an acknowledgment from the client for a previous CB_RECALL_ANY
      with the same type mask.  Although the possibility exists that
      these will be received by the client in an order different from
      the order in which they were sent, any such permutation of
      the callback stream is harmless.  It is the job of the client
      to bring down the size of the recallable object set in line
      with each CB_RECALL_ANY received, and until that obligation is
      met, it cannot be cancelled or modified by any subsequent 
      CB_RECALL_ANY for the same type mask.  Thus, if the server 
      sends two CB_RECALL_ANYs, the effect will be the same as 
      if the lower count was sent, whatever the order of recall
      receipt.  Note that this means that a server may not cancel
      the effect of a CB_RECALL_ANY by sending another recall with
      a higher count.  When a CB_RECALL_ANY is received and the
      count is already within the limit set or is above a limit 
      that the client is working to get down to, that callback has no
      effect. 
    </t>
    <t>
      Servers are generally free to deny recallable objects
      when insufficient resources are available.  Note that the 
      effect of such a policy is implicitly to give precedence to
      existing objects relative to requested ones, with the result
      that resources might not be optimally used.  To prevent this, 
      servers are well advised to make the point at which they start 
      sending CB_RECALL_ANY callbacks somewhat below that at which they
      cease to give out new delegations and layouts.  This allows the 
      client to purge its less-used objects whenever appropriate and
      so continue to have its subsequent requests given new resources
      freed up by object returns.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client can choose to return any type of object specified 
      by the mask.  If a server wishes to limit the use of objects of a
      specific type, it should only specify that type in the mask
      it sends.  Should the client fail to return requested objects, it is 
      up to the server to handle this situation, typically by sending
      specific recalls (i.e., sending CB_RECALL operations)
      to properly limit resource usage.  The server 
      should give the client enough time to return objects before 
      proceeding to specific recalls. This time should not be less
      than the lease period.
    </t>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $        -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALLABLE_OBJ_AVAIL" 
         title="Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for Recallable Objects" >

  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALLABLE_OBJ_AVAIL4res {
        nfsstat4        croa_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_DESCRIPTION" title="DESCRIPTION">
    <t>
        CB_RECALLABLE_OBJ_AVAIL is used by the server to signal the
        client that the server has resources to grant recallable
        objects that might previously have been denied by OPEN,
        WANT_DELEGATION, GET_DIR_DELEG, or LAYOUTGET.
    </t>
    <t>
        The argument craa_objects_to_keep means the total number of
        recallable objects of the types indicated in the argument
        type_mask that the server believes it can allow the client to
        have, including the number of such objects the client already
        has. A client that tries to acquire more recallable objects
        than the server informs it can have runs the risk of having
        objects recalled.
    </t>
    <t>
        The server is not obligated to reserve the
        difference between the number of the objects
        the client currently has and the value of
        craa_objects_to_keep, nor does delaying the reply
        to CB_RECALLABLE_OBJ_AVAIL prevent the server
        from using the resources of the recallable objects
        for another purpose. Indeed, if a client responds
        slowly to CB_RECALLABLE_OBJ_AVAIL, the server might
        interpret the client as having reduced capability
        to manage recallable objects, and so cancel
        or reduce any reservation it is maintaining on behalf
        of the client.
        Thus, if the client desires to acquire more
        recallable objects, it needs to reply quickly
        to CB_RECALLABLE_OBJ_AVAIL, and then send the
        appropriate operations to acquire recallable
        objects.
    </t>
  </section>


</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL_SLOT" title="Operation 10: CB_RECALL_SLOT - Change Flow Control Limits" >

  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_RECALL_SLOT4args {
        slotid4       rsa_target_highest_slotid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL_SLOT4res {
        nfsstat4   rsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_RECALL_SLOT operation requests the client to
      return session slots, and if applicable, transport
      credits (e.g., RDMA credits for connections associated with
      the operations channel) of the session's fore channel.
      CB_RECALL_SLOT specifies
      rsa_target_highest_slotid, the value of the target highest slot ID the server wants
      for the session. The client MUST then progress toward reducing
      the session's highest slot ID to the target value.
    </t>
    <t>
      If the session has only non-RDMA connections associated with its
      operations channel, then the client need only wait
      for all outstanding requests with a slot ID >
      rsa_target_highest_slotid to complete, then send
      a single COMPOUND consisting of a single SEQUENCE operation,
      with the sa_highestslot field set to rsa_target_highest_slotid.
      If there are RDMA-based connections associated with
      operation channel, then the client needs to also
      send enough zero-length "RDMA Send" messages to take the total
<!--  Please leave this use of "Send" capitalized in order to denote
      an artifact particular to RDMA-based communication. Thanks. -->
      RDMA credit count to rsa_target_highest_slotid + 1 or below.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client fails to reduce highest slot it has on the fore channel
      to what the server requests, the server can force the issue
      by asserting flow control on the receive side of
      all connections bound to the fore channel, and then
      finish servicing all outstanding requests that are
      in slots greater than rsa_target_highest_slotid. Once that
      is done, the server can then open the flow control, and any time
      the client sends a new request on a slot greater than
      rsa_target_highest_slotid, the server can return NFS4ERR_BADSLOT.
    </t>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $        -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_SEQUENCE" title="Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing and Control" >

  <section toc="exclude" anchor="OP_CB_SEQUENCE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct referring_call4 {
        sequenceid4     rc_sequenceid;
        slotid4         rc_slotid;
};

struct referring_call_list4 {
        sessionid4      rcl_sessionid;
        referring_call4 rcl_referring_calls&lt;>;
};

struct CB_SEQUENCE4args {
        sessionid4           csa_sessionid;
        sequenceid4          csa_sequenceid;
        slotid4              csa_slotid;
        slotid4              csa_highest_slotid;
        bool                 csa_cachethis;
        referring_call_list4 csa_referring_call_lists&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_SEQUENCE_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_SEQUENCE4resok {
        sessionid4         csr_sessionid;
        sequenceid4        csr_sequenceid;
        slotid4            csr_slotid;
        slotid4            csr_highest_slotid;
        slotid4            csr_target_highest_slotid;
};

union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
case NFS4_OK:
        CB_SEQUENCE4resok   csr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_SEQUENCE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_SEQUENCE operation is used to manage operational accounting
      for the backchannel of the session on which a request is
      sent.  The contents include the session ID to which this
      request belongs, the slot ID and sequence ID used by the server to
      implement session request control and exactly once
      semantics, and exchanged slot ID maxima that are used to adjust the
      size of the reply cache.  In each CB_COMPOUND request, CB_SEQUENCE
      MUST appear once and MUST be the first operation.  The error
      NFS4ERR_SEQUENCE_POS MUST be returned when CB_SEQUENCE is found in
      any position in a CB_COMPOUND beyond the first.  If any
      other operation is in the first position of CB_COMPOUND,
      NFS4ERR_OP_NOT_IN_SESSION MUST be returned.
    </t>
    <t>
      See <xref target="OP_SEQUENCE_DESCRIPTION"/> for a description of
      how slots are processed.
    </t>
    <t>
     If csa_cachethis is TRUE, then the server is requesting that
     the client cache the reply in the callback reply cache. The client MUST
     cache the reply (see <xref target="optional_reply_caching" />).
    </t>
    <t>
      The csa_referring_call_lists array is the list of COMPOUND
      requests, identified by session ID, slot ID, and sequence ID. These
      are requests that the client previously sent to the server.
      These previous requests created state that some operation(s)
      in the same CB_COMPOUND as the csa_referring_call_lists are
      identifying.
      A session ID is included because
      leased state is tied to a client ID, and a client ID can have
      multiple sessions. See
      <xref target="sessions_callback_races" />.
    </t>
    <t>
      The value of the csa_sequenceid argument relative to
      the cached sequence ID on the slot falls into one
      of three cases.
      <list style="symbols">
      <t>
       If the difference between csa_sequenceid and
       the client's cached sequence ID at the slot ID
       is two (2) or more,
       or if csa_sequenceid is less
       than the cached sequence ID (accounting
       for wraparound of the unsigned sequence ID value),
       then the client MUST return NFS4ERR_SEQ_MISORDERED.
      </t>
      <t>
       If csa_sequenceid and the cached sequence ID are the
       same, this is a retry, and the client returns the
       CB_COMPOUND request's cached reply.
      </t>
      <t>
       If csa_sequenceid is one greater (accounting for
       wraparound) than the cached sequence ID, then
       this is a new request, and the slot's sequence
       ID is incremented.  The operations subsequent to
       CB_SEQUENCE, if any, are processed. If there are no
       other operations, the only other effects are to
       cache the CB_SEQUENCE reply in the slot, maintain the
       session's activity, and when the server receives the
       CB_SEQUENCE reply, renew the lease of state
       related to the client ID.
      </t>
      </list>
    </t>
    <t>
     If the server reuses a slot ID and sequence ID for
     a completely different request, the client MAY
     treat the request as if it is a retry
     of what it has already executed. The client MAY however
     detect the server's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.
    </t>
    <t>
     If CB_SEQUENCE returns an error, then the state of the slot (sequence ID,
     cached reply) MUST NOT change.
     See <xref target="optional_reply_caching"/> for the conditions when the
     error NFS4ERR_RETRY_UNCACHED_REP might be returned.
    </t>
    <t>
     The client returns two "highest_slotid" values:
     csr_highest_slotid and csr_target_highest_slotid. The
     former is the highest slot ID the client will accept
     in a future CB_SEQUENCE operation, and SHOULD NOT be
     less than the value of csa_highest_slotid (but see
     <xref target="Slot Identifiers and Server Reply Cache"
     /> for an exception).  The latter is the highest slot
     ID the client would prefer the server use on a future
     CB_SEQUENCE operation.
    </t>
  </section>


</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_WANTS_CANCELLED" 
         title="Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation Wants " >

  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_WANTS_CANCELLED4args {
        bool cwca_contended_wants_cancelled;
        bool cwca_resourced_wants_cancelled;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_WANTS_CANCELLED4res {
        nfsstat4        cwcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_WANTS_CANCELLED operation is used to notify the client that
      some or all of the wants it registered for recallable delegations and layouts
      have been cancelled.
    </t>
    <t>
	If cwca_contended_wants_cancelled is TRUE, this indicates that
        the server will not be pushing to the client any delegations
        that become available after contention passes.
   </t>
    <t>
	If cwca_resourced_wants_cancelled is TRUE, this indicates that
        the server will not notify the client when there are resources
        on the server to grant delegations or layouts.
    </t>
    <t>
        After receiving a CB_WANTS_CANCELLED operation, the
        client is free to attempt to acquire the delegations or
        layouts it was waiting for, and possibly re-register wants.
    </t>


  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      When a client has an OPEN, WANT_DELEGATION, or GET_DIR_DELEGATION request 
      outstanding, when a CB_WANTS_CANCELLED is sent, the server may need to
      make clear to the client whether a promise to signal delegation availability
      happened before the CB_WANTS_CANCELLED and is thus covered by it, or after
      the CB_WANTS_CANCELLED in which case it was not covered by it.  The server
      can make this distinction by putting the appropriate requests into the
      list of referring calls in the associated CB_SEQUENCE.
    </t>
  </section>
</section>
<!-- Copyright (C) The Internet Society (2006) -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<section anchor="OP_CB_NOTIFY_LOCK" title="Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible Lock Availability" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_NOTIFY_LOCK4args {
    nfs_fh4     cnla_fh;
    lock_owner4 cnla_lock_owner;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY_LOCK4res {
        nfsstat4        cnlr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The server can use this operation to indicate that a byte-range lock for the given
      file and lock-owner, previously requested by the client via an unsuccessful
      LOCK operation, might be available.
    </t>
    <t>
      This callback is meant to be used by servers to help reduce the latency of
      blocking locks in the case where they recognize that a client that has
      been polling for a blocking byte-range lock may now be able to acquire the lock.
      If the server supports this callback for a given file, it MUST set the
      OPEN4_RESULT_MAY_NOTIFY_LOCK flag when responding to successful opens
      for that file.  This does not commit the server to the use of CB_NOTIFY_LOCK,
      but the client may use this as a hint to decide how frequently to poll
      for locks derived from that open.
    </t>
    <t>
      If an OPEN operation results in an upgrade, in which the stateid returned 
      has an "other" value matching that of a stateid already allocated, with a
      new "seqid" indicating a change in the lock being represented, then the
      value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag when responding to that new 
      OPEN controls handling from that point going forward.  When parallel OPENs
      are done on the same file and open-owner, the ordering of the "seqid" fields
      of the returned stateids (subject to wraparound) are to be used to select
      the controlling value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The server MUST NOT grant the byte-range lock to the client unless and until it
     receives a LOCK operation from the client.  Similarly, the client
     receiving this callback cannot assume that it now has the lock or that a
     subsequent LOCK operation for the lock will be successful.
    </t>
    <t>
     The server is not required to implement this callback, and even if it
     does, it is not required to use it in any particular case.  Therefore, the
     client must still rely on polling for blocking locks, as described in
     <xref target="blocking_locks"/>.
    </t>
    <t>
     Similarly, the client is not required to implement this callback, and even
     it does, is still free to ignore it.  Therefore, the server MUST NOT assume
     that the client will act based on the callback.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_NOTIFY_DEVICEID" title="Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device ID Changes" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * Device notification types.
 */
enum notify_deviceid_type4 {
        NOTIFY_DEVICEID4_CHANGE = 1,
        NOTIFY_DEVICEID4_DELETE = 2
};

/* For NOTIFY4_DEVICEID4_DELETE */
struct notify_deviceid_delete4 {
        layouttype4     ndd_layouttype;
        deviceid4       ndd_deviceid;
};

/* For NOTIFY4_DEVICEID4_CHANGE */
struct notify_deviceid_change4 {
        layouttype4     ndc_layouttype;
        deviceid4       ndc_deviceid;
        bool            ndc_immediate;
};

struct CB_NOTIFY_DEVICEID4args {
        notify4 cnda_changes&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY_DEVICEID4res {
        nfsstat4        cndr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_NOTIFY_DEVICEID operation is used by the
      server to send notifications to clients about
      changes to pNFS device IDs.  The registration of
      device ID notifications is optional and is done via
      GETDEVICEINFO.  These notifications are sent
      over the backchannel
      once the original request has been processed
      on the server. The server will send an array of
      notifications, cnda_changes, as a list of pairs of
      bitmaps and values.  See <xref target="fattr4" />
      for a description of how NFSv4.1 bitmaps work.

   </t>

   <t>
    As with CB_NOTIFY (<xref
    target="OP_CB_NOTIFY_DESCRIPTION"/>), it is
    possible the server has more notifications than
    can fit in a CB_COMPOUND, thus requiring multiple
    CB_COMPOUNDs. Unlike CB_NOTIFY, serialization is not
    an issue because unlike directory entries, device
    IDs cannot be re-used after being deleted (<xref
    target="device_ids" />).

   </t>

   <t>
    All device ID notifications contain a device ID and a
    layout type.  The layout type is necessary because two
    different layout types can share the same device ID,
    and the common device ID can have completely different
    mappings for each layout type.

   </t>

    <t>
     The server will send the following notifications:

      <list style="hanging">

	<t hangText="NOTIFY_DEVICEID4_CHANGE"><vspace />
	  A previously provided device-ID-to-device-address 
          mapping has changed and the client uses
	  GETDEVICEINFO to obtain the
	  updated mapping.

          The notification is encoded in a value of data
          type notify_deviceid_change4. This data type
          also contains a boolean field, ndc_immediate,
          which if TRUE indicates that the change will be
          enforced immediately, and so the client might not
          be able to complete any pending I/O to the device
          ID. If ndc_immediate is FALSE, then for an
          indefinite time, the client can complete pending
          I/O. After pending I/O is complete, the client
          SHOULD get the new device-ID-to-device-address
          mappings before sending new I/O requests to the
          storage devices addressed by the device ID.

	</t>

	<t hangText="NOTIFY4_DEVICEID_DELETE"><vspace />
	  Deletes a device ID from the mappings.  This
	  notification MUST NOT be sent if the client has
	  a layout that refers to the device ID. In other
	  words, if the server is sending a delete device ID
          notification, one of the following is true for layouts
	  associated with the layout type:

          <list style="symbols">

          <t>
           The client never had a layout referring to that device ID.
          </t>
          
          <t>
           The client has returned all layouts referring to that device ID.
          </t>

          <t>
           The server has revoked all layouts referring to that device ID.
          </t>

          </list>

	  The notification is encoded in a value of data
	  type notify_deviceid_delete4.

          After a server deletes a device ID, it MUST NOT
          reuse that device ID for the same layout type until the
          client ID is deleted.

	</t>
      </list>
    </t>
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_ILLEGAL" title="Operation 10044: CB_ILLEGAL - Illegal Callback Operation" >

  <section toc="exclude" anchor="OP_CB_ILLEGAL_ARGUMENT" title="ARGUMENT">
    <figure>
      <artwork>
        void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_RESULT" title="RESULT">
<figure>
 <artwork>
/*
 * CB_ILLEGAL: Response for illegal operation numbers
 */
struct CB_ILLEGAL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_DESCRIPTION" title="DESCRIPTION">
    <t>
     This operation is a placeholder for encoding a
     result to handle the case of the server sending
     an operation code within CB_COMPOUND that is not
     defined in the NFSv4.1 specification. See <xref
     target="OP_CB_COMPOUND_DESCRIPTION"/> for more details.

    </t>
    <t>
     The status field of CB_ILLEGAL4res MUST be set to
     NFS4ERR_OP_ILLEGAL.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     A server will probably not send an operation with code
     OP_CB_ILLEGAL, but if it does, the response will be CB_ILLEGAL4res
     just as it would be with any other invalid operation code. Note
     that if the client gets an illegal operation code that is not
     OP_ILLEGAL, and if the client checks for legal operation codes
     during the XDR decode phase, then an instance of
     data type CB_ILLEGAL4res will not be returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="securityconsider" title="Security Considerations">
<t>
   Historically, the authentication model of NFS
   was based on the entire machine being the NFS client, with the
   NFS server trusting the NFS client
   to authenticate the end-user.
   The NFS server in turn shared its files only to
   specific clients, as identified by the client's source
   network address.  Given this model, the AUTH_SYS
   RPC security flavor simply identified the end-user
   using the client to the NFS server.  When processing
   NFS responses, the client ensured that the responses
   came from the same network address and port number
   to which the request was sent.  While such a model is
   easy to implement and simple to deploy and use, it is
   unsafe.  Thus, NFSv4.1 
   implementations are REQUIRED to support a security model that uses
   end-to-end authentication, where an end-user on a client 
   mutually authenticates (via cryptographic schemes that
   do not expose passwords or keys in the clear on the
   network) to a principal on an NFS server.  Consideration
   is also given to the integrity and privacy of
   NFS requests and responses.  The issues of end-to-end
   mutual authentication, integrity, and privacy are
   discussed in <xref target="RPCSEC_GSS and Security Services" />. 
   There are specific considerations when using Kerberos V5 as described
   in <xref target="krb5_sec_consider"/>.
</t>
<t>
   Note that being REQUIRED to implement does not mean REQUIRED to
   use; AUTH_SYS can be used by NFSv4.1 clients and servers.
   However, AUTH_SYS is merely an OPTIONAL security flavor in NFSv4.1,
   and so interoperability via AUTH_SYS is not assured.

</t>
<t>
   For reasons of reduced administration overhead, better
   performance, and/or reduction of CPU utilization,
   users of NFSv4.1 implementations might decline to use
   security mechanisms that enable integrity protection
   on each remote procedure call and response. The
   use of mechanisms without integrity leaves the user
   vulnerable to a man-in-the-middle of the NFS
   client and server that modifies the RPC request and/or
   the response. While implementations are free to provide
   the option to use weaker security mechanisms, there
   are three operations in particular that warrant the
   implementation overriding user choices.
   <list style='symbols'>

<t>
   The first two such operations are SECINFO and
   SECINFO_NO_NAME.  It is RECOMMENDED that the client send
   both operations such that they are protected with a
   security flavor that has integrity protection, such
   as RPCSEC_GSS with either the rpc_gss_svc_integrity
   or rpc_gss_svc_privacy service. Without integrity
   protection encapsulating SECINFO and SECINFO_NO_NAME
   and their results, a man-in-the-middle could
   modify results such that the client might select a
   weaker algorithm in the set allowed by the server, making
   the client and/or server vulnerable to further attacks.

</t>
<t>
   The third operation that SHOULD use integrity protection
   is any GETATTR for the fs_locations and fs_locations_info attributes, in order to mitigate the severity of a man-in-the-middle attack. The attack has two
   steps.  First the attacker modifies the unprotected results of some
   operation to return NFS4ERR_MOVED. Second, when the client follows up
   with a GETATTR for the fs_locations or fs_locations_info attributes, the attacker modifies
   the results to cause the client to migrate its traffic to a server
   controlled by the attacker. With integrity protection, this attack is mitigated.

</t>
   </list>
</t>
<t>
  Relative to previous NFS versions, NFSv4.1 has additional security
  considerations for pNFS (see Sections <xref target="security_considerations_pnfs" format="counter" /> 
and <xref target="file_security_considerations" format="counter" />), locking
  and session state (see <xref target="protect_state_change"/>),
  and state recovery during grace period (see <xref
  target="reclaim_security_considerations"/>).
  With respect to locking and session state, if SP4_SSV state protection
  is being used, <xref target="rpcsec_ssv_consider"/> has specific security considerations for the NFSv4.1 client and server.

</t>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="ianaconsider" title="IANA Considerations">
<t>
This section uses terms that are defined in <xref target="RFC5226"/>.
</t>

 <section anchor="namedattributesiana" title="Named Attribute Definitions">
   <t>
     IANA created a registry called the "NFSv4 Named Attribute Definitions Registry".
   </t>
   <t>
     The NFSv4.1 protocol supports the association of a file with zero or
     more named attributes.  The namespace identifiers for these attributes
     are defined as string names.  The protocol does not define the
     specific assignment of the namespace for these file attributes.
     The IANA registry promotes interoperability where common interests exist.
     While application developers are allowed to define and use
     attributes as needed, they are encouraged to register the
     attributes with IANA. 
   </t>
   <t>
     Such registered named attributes are presumed to apply to all minor
     versions of NFSv4, including those defined subsequently to the 
     registration.  If the named attribute is intended to be 
     limited to specific minor versions, this will be clearly stated in
     the registry's assignment.
   </t>
   <t>
     All assignments to the registry are made on a First Come First Served basis,
     per Section 4.1 of <xref target="RFC5226"/>.

     The policy for each assignment is Specification Required, 
     per Section 4.1 of <xref target="RFC5226"/>.
   </t>
   <t>
     Under the NFSv4.1 specification, the name of a named
     attribute can in theory be up to 2^32 - 1 bytes in
     length, but in practice NFSv4.1 clients and servers
     will be unable to handle a string that long. IANA
     should reject any assignment request with a named
     attribute that exceeds 128 UTF-8 characters. To give the
     IESG the flexibility to set up bases of assignment of
     Experimental Use and Standards Action,
     the prefixes of "EXPE" and "STDS" are Reserved.
     The named attribute with a zero-length name is Reserved.
   </t>
   <t>
     The prefix "PRIV" is designated for Private Use.  A
     site that wants to make use of unregistered named
     attributes without risk of conflicting with an
     assignment in IANA's registry should use the prefix
     "PRIV" in all of its named attributes.

   </t>
   <t>
     Because some NFSv4.1 clients and servers have case-insensitive
     semantics, the fifteen additional lower case and mixed case
     permutations of each of "EXPE", "PRIV", and "STDS" are Reserved (e.g.,
     "expe", "expE", "exPe", etc. are Reserved).
     Similarly, IANA must not allow two assignments that would conflict
     if both named attributes were converted to a common case.
   </t>

   <t>
     The registry of named attributes is a list of assignments, each
     containing three fields for each assignment.

     <list style='numbers'>
	<t>
	  A US-ASCII string name that is the actual name of
	  the attribute. This name must be unique.  This
	  string name can be 1 to 128 UTF-8 characters
	  long.

	</t>

	<t>
	  A reference to the specification of the named attribute.
          The reference can consume up to 256 bytes (or more if IANA
          permits).
	</t>

	<t>
	  The point of contact of the registrant. The point
	  of contact can consume up to 256 bytes (or more if IANA
	  permits).

	</t>
     </list>
     </t>

  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>
  
  <section title="Updating Registrations">
  <t>
    The registrant is always permitted to update the point of contact
    field. Any other change will require Expert Review or IESG
    Approval.
  </t>
  </section>

 </section>

 <section anchor="notifyiana" title="Device ID Notifications">
   <t>
     IANA created a registry called the "NFSv4 Device ID
Notifications Registry".
   </t>

   <t>
      The potential exists for new notification types to be
      added to the CB_NOTIFY_DEVICEID operation (see <xref
      target="OP_CB_NOTIFY_DEVICEID" />). This can be done
      via changes to the operations that register
      notifications, or by adding new operations to NFSv4.
      This requires a new minor version of NFSv4, and
      requires a Standards Track document from the IETF.
      Another way to add a notification is to specify a new
      layout type (see <xref target="pnfsiana" />).

    </t>
   <t>
     Hence, all assignments to the registry are made on a Standards Action
     basis per Section 4.1 of <xref target="RFC5226"/>, with
     Expert Review required.
   </t>
   <t>
    The registry is a list of assignments, each containing
    five fields per assignment.

     <list style='numbers'>
        <t>
          The name of the notification type. This name must have the
          prefix "NOTIFY_DEVICEID4_". This name must be unique.
        </t>
        <t>
	  The value of the notification. IANA will assign
	  this number, and the request from the registrant
	  will use TBD1 instead of an actual value. IANA
	  MUST use a whole number that can be no higher
	  than 2^32-1, and should be the next available
	  value. The value assigned must be unique.
	  A Designated Expert must be used to
	  ensure that when the name of the notification
	  type and its value are added to the NFSv4.1
	  notify_deviceid_type4 enumerated data type in the
	  NFSv4.1 XDR description (<xref
	  target="RFC5662"/>), the result continues to
	  be a valid XDR description.

        </t>
        <t>
	  The Standards Track RFC(s) that describe the
	  notification. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
	  of an actual RFC number.

        </t>
        <t>
	  How the RFC introduces the notification. This is
	  indicated by a single US-ASCII value. If the
	  value is N, it means a minor revision to the
	  NFSv4 protocol. If the value is L, it means a new
	  pNFS layout type. Other values can be used with
	  IESG Approval.

        </t>
        <t>
	  The minor versions of NFSv4 that are allowed to
	  use the notification. While these are numeric
	  values, IANA will not allocate and assign them;
	  the author of the relevant RFCs with IESG
	  Approval assigns these numbers. Each time there is a
          new minor version of NFSv4 approved, a Designated
          Expert should review the registry to make recommended
          updates as needed.
          
        </t>
     </list>
   </t>

  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="devnotelist"/>. Note that the
    next available value is zero.
  </t>

  <texttable title="Initial Device ID Notification Assignments" anchor='devnotelist'>

	<ttcol>Notification Name</ttcol>
	<ttcol>Value</ttcol>
	<ttcol>RFC</ttcol>
	<ttcol>How</ttcol>
	<ttcol>Minor Versions</ttcol>

	<c>NOTIFY_DEVICEID4_CHANGE</c> <c>1</c> <c>RFC5661</c> <c>N</c> <c>1</c>

	<c>NOTIFY_DEVICEID4_DELETE</c> <c>2</c> <c>RFC5661</c> <c>N</c> <c>1</c>

  </texttable>
  
  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>
  </section>

 <section anchor="recalliana" title="Object Recall Types">

   <t>
     IANA created a registry called the "NFSv4 Recallable Object Types Registry".
   </t>
   <t>
      The potential exists for new object types to be added to the CB_RECALL_ANY operation (see
      <xref target="OP_CB_RECALL_ANY" />). This can be done via changes to
      the operations that add recallable types, or by adding new operations
      to NFSv4. This requires a new minor version of NFSv4, and requires
      a Standards Track document from IETF. Another way to
      add a new recallable object is to specify a new layout type (see <xref target="pnfsiana" />).
    </t>
   <t>
     All assignments to the registry are made on a Standards Action
     basis per Section 4.1 of <xref target="RFC5226"/>, with
     Expert Review required.
   </t>
   <t>
    Recallable object types are 32-bit unsigned numbers. There are no Reserved
    values. Values in the range 12 through 15, inclusive, are designated for Private
    Use.
   </t>

   <t>
    The registry is a list of assignments, each containing
    five fields per assignment.

     <list style='numbers'>
        <t>
          The name of the recallable object type. This name must have the
          prefix "RCA4_TYPE_MASK_". The name must be unique.
        </t>
        <t>
	  The value of the recallable object type. IANA
	  will assign this number, and the request from the
	  registrant will use TBD1 instead of an actual
	  value. IANA MUST use a whole number that can be
	  no higher than 2^32-1, and should be the next
	  available value. The value must be unique. A
	  Designated Expert must be used to ensure that
	  when the name of the recallable type and its
	  value are added to the NFSv4 XDR description
	  <xref target="RFC5662"/>,
	  the result continues to be a valid XDR
	  description.

        </t>
        <t>
	  The Standards Track RFC(s) that describe the
	  recallable object type. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
	  of an actual RFC number.

        </t>
        <t>
	  How the RFC introduces the recallable object type. This is
	  indicated by a single US-ASCII value. If the
	  value is N, it means a minor revision to the
	  NFSv4 protocol. If the value is L, it means a new
	  pNFS layout type. Other values can be used with
	  IESG Approval.

        </t>
        <t>
	  The minor versions of NFSv4 that are allowed to
	  use the recallable object type. While these
	  are numeric values, IANA will not allocate and
	  assign them; the author of the relevant RFCs with
	  IESG Approval assigns these numbers. Each time
	  there is a new minor version of NFSv4 approved, a
	  Designated Expert should review the registry to
	  make recommended updates as needed.

        </t>
     </list>
   </t>

  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="recalllist"/>. Note that
    the next available value is five.
  </t>

  <texttable title="Initial Recallable Object Type Assignments" anchor='recalllist'>

	<ttcol>Recallable Object Type Name</ttcol>
	<ttcol>Value</ttcol>
	<ttcol>RFC</ttcol>
	<ttcol>How</ttcol>
	<ttcol>Minor Versions</ttcol>

	<c>RCA4_TYPE_MASK_RDATA_DLG</c> <c>0</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_WDATA_DLG</c> <c>1</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_DIR_DLG</c> <c>2</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_FILE_LAYOUT</c> <c>3</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_BLK_LAYOUT</c> <c>4</c> <c>RFC 5661</c> <c>L</c> <c>1</c>

	<c>RCA4_TYPE_MASK_OBJ_LAYOUT_MIN</c> <c>8</c> <c>RFC 5661</c> <c>L</c> <c>1</c>
	<c>RCA4_TYPE_MASK_OBJ_LAYOUT_MAX</c> <c>9</c> <c>RFC 5661</c> <c>L</c> <c>1</c>

  </texttable>
  
  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>
  </section>
  
  <section anchor="pnfsiana" title="Layout Types">
    <t>
      IANA created a registry called the "pNFS Layout Types Registry".
    </t>
    <t>
      All assignments to the registry are made on a Standards Action basis,
      with Expert Review required.
    </t>
    <t>
      Layout types are 32-bit numbers. The value zero is Reserved.
      Values in the range 0x80000000 to 0xFFFFFFFF inclusive are designated for Private Use.
      IANA will assign numbers from the range
      0x00000001 to 0x7FFFFFFF inclusive.
    </t>
    <t>
      The registry is a list of assignments, each
      containing five fields.

      <list style='numbers'>
        <t>
          The name of the layout type. This name must have the
          prefix "LAYOUT4_". The name must be unique.
        </t>

	<t>
	  The value of the layout type. IANA will assign
          this number, and the request from the registrant
          will use TBD1 instead of an actual value. The value
          assigned must be unique.
          A Designated Expert must be used to ensure
          that when the name of the layout type and
	  its value are added to the NFSv4.1 layouttype4
	  enumerated data type in the NFSv4.1 XDR
	  description (<xref
	  target="RFC5662"/>),
	  the result continues to be a valid XDR
	  description.

        </t>

        <t>
          The Standards Track RFC(s) that describe the
          notification. If the RFC(s) have not yet been
          published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
          of an actual RFC number. Collectively, the RFC(s) must adhere to
          the guidelines listed in <xref target="layout_guidelines"/>.

        </t>

	 <t>
          How the RFC introduces the layout type. This is
          indicated by a single US-ASCII value. If the
          value is N, it means a minor revision to the
          NFSv4 protocol. If the value is L, it means a new
          pNFS layout type. Other values can be used with
          IESG Approval.

        </t>

        <t>
          The minor versions of NFSv4 that are allowed to
          use the notification. While these are numeric
          values, IANA will not allocate and assign them;
          the author of the relevant RFCs with IESG
          Approval assigns these numbers. Each time there is
          a new minor version of NFSv4 approved, a Designated
          Expert should review the registry to make recommended
          updates as needed.

        </t>
 
      </list>

    </t>
    
  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="layoutlist"/>.
  </t>

  <texttable title="Initial Layout Type Assignments" anchor='layoutlist'>

        <ttcol>Layout Type Name</ttcol>
        <ttcol>Value</ttcol>
        <ttcol>RFC</ttcol>
        <ttcol>How</ttcol>
        <ttcol>Minor Versions</ttcol>

        <c>LAYOUT4_NFSV4_1_FILES</c> <c>0x1</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

        <c>LAYOUT4_OSD2_OBJECTS</c> <c>0x2</c> <c>RFC 5664</c> <c>L</c> <c>1</c>
        <c>LAYOUT4_BLOCK_VOLUME</c> <c>0x3</c> <c>RFC 5663</c> <c>L</c> <c>1</c>
<!-- [rfced] The IANA site lists this document (RFC 5661) as the
reference for values 0x2 and 0x3, instead of RFCs 5664 and 5663,
respectively.  Does the IANA site need to be updated? 

     [Eisler]: The IANA site needs to be updated. -->
  </texttable>

  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>



    <section anchor="layout_guidelines" title="Guidelines for Writing Layout Type Specifications">
    <t>
      The author of a new pNFS layout specification must follow these
      steps to obtain acceptance of the layout type as a Standards Track RFC:
      <list style='numbers'>
	<t>
	  The author devises the new layout specification.
	</t>
	<t>
	  The new layout type specification MUST, at a minimum: 
	  <list style='symbols'>
	    <t>
	      Define the contents of the layout-type-specific fields of the
	      following data types:
	      <list style='symbols'>
		<t>
		  the da_addr_body field of the device_addr4
		  data type;
		</t>
		<t>
		  the loh_body field of the layouthint4
		  data type;
		</t>
		<t>
		  the loc_body field of layout_content4
		  data type (which in turn is the lo_content field of the
		  layout4 data type);
		</t>
		<t>
		  the lou_body field of the layoutupdate4
		  data type;
		</t>
	      </list>
	    </t>
	    <t>
	      Describe or define the storage access protocol used to access
	      the storage devices.
	    </t>
	    <t>
	      Describe whether revocation of layouts is supported.
	    </t>
	    <t>
	      At a minimum, describe the methods of recovery from:
	      <list style="numbers">
		<t> Failure and restart for client, server, storage device.
		</t>
		<t> Lease expiration from perspective of the active client,
		  server, storage device.
		</t>
		<t> Loss of layout state resulting in fencing of client
		  access to storage devices (for an example, see 
		  <xref target="lease_expiration_mds" />).
		</t>
	      </list>
	    </t>
	    <t>
	      Include an IANA considerations section, which will
	      in turn include:

              <list style="symbols">
	      <t>
		A request to IANA
		for a new layout type per <xref
		target="pnfsiana"/>.

	      </t>
	      <t>
		A list of requests to IANA for
		any new recallable object types for
		CB_RECALL_ANY; each entry is to be presented in the form described
		in <xref target="recalliana"/>.

	      </t>
	      <t>
		A list of requests to IANA for
		any new notification values for
		CB_NOTIFY_DEVICEID; each entry is to be presented in the form
		described in <xref target="notifyiana"/>.

	      </t>
              </list>

	    </t>
	    <t>
	      Include a security considerations section. This section MUST
              explain how the NFSv4.1 authentication, authorization, and
              access-control models are preserved. That is, if a metadata server
              would restrict a READ or WRITE operation, how would pNFS via
              the layout similarly restrict a corresponding input or
              output operation?
	    </t>

	  </list>
	</t>
	<t>
	  The author documents the new layout specification as an Internet-Draft.
	</t>
	<t>
	  The author submits the Internet-Draft for review through the
	  IETF standards process as defined in "The Internet Standards
	  Process--Revision 3" (BCP 9).

The new layout specification will be
	  submitted for eventual publication as a Standards Track RFC.
	</t>
	<t>
	  The layout specification progresses through the IETF standards
	  process.
	</t>
      </list>
    </t>
    </section>
  </section>

  <section anchor="path_var_iana" title="Path Variable Definitions">
   
    <t>
      This section deals with the IANA considerations associated with
      the variable substitution feature for location names as 
      described in <xref target="fs_locations_item4" />.  As
      described there, variables subject to substitution consist
      of a domain name and a specific name within that domain, with the
      two separated by a colon. There are two sets of IANA considerations
      here:
      <list style='numbers'>
        <t>
          The list of variable names.
        </t>

        <t>
          For each variable name, the list of possible values.
        </t>

      </list>
      Thus, there will be one registry for the list of variable names, and
      possibly one registry for listing the values of each variable name.
    </t>
  
    <section anchor="path_variables_iana" title="Path Variables Registry">
    <t>
     IANA created a registry called the "NFSv4 Path Variables Registry".
    </t>

 
    <section anchor="path_values_iana" title="Path Variable Values">
      <t>
       Variable names are of the form "${", followed by a
       domain name, followed by a colon (":"), followed by
       a domain-specific portion of the variable name,
       followed by "}". When the domain name is "ietf.org",
       all variables names must be registered with IANA on
       a Standards Action basis, with Expert Review
       required.  Path variables with registered domain
       names neither part of nor equal to ietf.org are
       assigned on a Hierarchical Allocation basis
       (delegating to the domain owner) and thus of no
       concern to IANA, unless the domain owner chooses to
       register a variable name from his domain. If the
       domain owner chooses to do so, IANA will do so on a
       First Come First Serve basis. To accommodate
       registrants who do not have their own domain, IANA
       will accept requests to register variables with the
       prefix "${FCFS.ietf.org:" on a First Come First
       Served basis. Assignments on a First Come First Basis
       do not require Expert Review, unless the registrant also
       wants IANA to establish a registry for the values of the
       registered variable.

      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  The name of the variable. The name of this
	  variable must start with a "${" followed by a
	  registered domain name, followed by ":", or it
	  must start with "${FCFS.ietf.org".  The name must
	  be no more than 64 UTF-8 characters long. The
	  name must be unique.

        </t>

        <t>
          For assignments made on Standards Action basis,
	  the Standards Track RFC(s) that describe the
	  variable. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD1,
	  RFCTBD2, etc. instead of an actual RFC number.
          Note that the RFCs do not have to be a part of an NFS minor version.
          For assignments made on a First Come First Serve basis, an explanation
          (consuming no more than 1024 bytes, or more if IANA permits)
          of the purpose of the variable. A reference to the explanation can
          be substituted.
          
        </t>
        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
          For assignments made on a Standards Action basis, the point of
          contact is always IESG.
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="varlist"/>.
  </t>

  <texttable title="Initial List of Path Variables" anchor='varlist'>

        <ttcol>Variable Name</ttcol>
        <ttcol>RFC</ttcol>
        <ttcol>Point of Contact</ttcol>

         <c>${ietf.org:CPU_ARCH}</c> <c>RFC 5661</c> <c>IESG</c>
         <c>${ietf.org:OS_TYPE}</c> <c>RFC 5661</c> <c>IESG</c>
         <c>${ietf.org:OS_VERSION}</c> <c>RFC 5661</c> <c>IESG</c>

  </texttable>

      <t>
	IANA has created registries for the values
	of the variable names ${ietf.org:CPU_ARCH} and
	${ietf.org:OS_TYPE}. See Sections <xref target="cpu_arch"
format="counter" />
	and <xref target="os_type" format="counter" />.
      </t>
      <t>
	For the values of the variable
	${ietf.org:OS_VERSION}, no registry is needed as
	the specifics of the values of the variable will
	vary with the value of ${ietf.org:OS_TYPE}. Thus,
	values for ${ietf.org:OS_VERSION} are on a
	Hierarchical Allocation basis and are of no concern
	to IANA.

      </t>
    </section>

      <section title="Updating Registrations">
      <t>
	The update of an assignment made on a Standards Action basis
        will require IESG Approval on the advice of a Designated Expert.
      </t>

      <t>
        The registrant can always update the point of contact of an assignment
        made on a First Come First Serve basis. Any other update will require
        Expert Review.
      </t>
       

      </section>
  </section>
  </section>
  <section title="Values for the ${ietf.org:CPU_ARCH} Variable" anchor="cpu_arch">
    <t>
     IANA created a registry called the "NFSv4 ${ietf.org:CPU_ARCH} Value Registry".
    </t>

 
      <t>
        Assignments to the registry are made on a First Come First Serve
        basis. The zero-length value of ${ietf.org:CPU_ARCH} is Reserved.
        Values with a prefix of "PRIV" are designated for Private Use.

      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  A value of the ${ietf.org:CPU_ARCH} variable. The value
	  must be 1 to 32 UTF-8 characters long. The value must be unique.
        </t>

        <t>
	  An explanation (consuming no more than 1024
	  bytes, or more if IANA permits) of what CPU
	  architecture the value denotes. A reference to
	  the explanation can be substituted.
        </t>

        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>

      <section title="Updating Registrations">
      <t>
        The registrant is free to update the assignment, i.e., change the
        explanation and/or point-of-contact fields.
      </t>
       

      </section>
  </section>
  <section title="Values for the ${ietf.org:OS_TYPE} Variable" anchor="os_type">
    <t>
     IANA created a registry called the "NFSv4 ${ietf.org:OS_TYPE} Value Registry".
    </t>

      <t>
        Assignments to the registry are made on a First Come First Serve
        basis. The zero-length value of ${ietf.org:OS_TYPE} is Reserved.
        Values with a prefix of "PRIV" are designated for Private Use.
      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  A value of the ${ietf.org:OS_TYPE} variable. The value
	  must be 1 to 32 UTF-8 characters long. The value must be unique.

        </t>

        <t>
	  An explanation (consuming no more than 1024
	  bytes, or more if IANA permits) of what CPU
	  architecture the value denotes. A reference to
	  the explanation can be substituted.
        </t>

        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>

      <section title="Updating Registrations">
      <t>
        The registrant is free to update the assignment, i.e., change the
        explanation and/or point of contact fields.
      </t>
       

      </section>

  </section>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->

</middle>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<back>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
  <references title="Normative References">

    <reference anchor="hardlink">
        <front>
	    <title>Section 3.191 of Chapter 3 of Base Definitions of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="symlink">
        <front>
	    <title>Section 3.372 of Chapter 3 of Base Definitions of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="write_atime">
        <front>
	    <title>Section 'write()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="read_atime">
        <front>
	    <title>Section 'read()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="readdir_atime">
        <front>
	    <title>Section 'readdir()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="fcntl">
        <front>
	    <title>Section 'fcntl()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="chmod">
        <front>
	    <title>Section 'chmod()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="fsync">
        <front>
	    <title>Section 'fsync()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="passwd">
        <front>
	    <title>Section 'getpwnam()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="unlink">
        <front>
	    <title>Section 'unlink()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="CSOR_AES">
      <front>
     <title>Cryptographic Algorithm Object Registration
     </title>
	<author>
	  <organization>National Institute of Standards and Technology
	  </organization>
	</author>
	<date month="November" year="2007" />
      </front>
      <seriesInfo name="URL" value="http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html"; />
    </reference>

    <reference anchor="ISO.10646-1.1993">
      <front>
     <title>Information Technology - Universal Multiple-octet coded
     Character Set (UCS) - Part 1: Architecture and Basic Multilingual
     Plane</title>
	<author>
	  <organization>International Organization for Standardization
	  </organization>
	</author>
	<date month="May" year="1993" />
      </front>

      <seriesInfo name="ISO" value="Standard 10646-1" />

    </reference>

<reference anchor='RFC5665'>
      <front>
	<title>
IANA Considerations for Remote Procedure Call (RPC) Network
Identifiers and Universal Address Formats
	</title>

	<author initials='M' surname='Eisler' fullname='Mike Eisler'>
	  <organization />
	</author>

	<date month='January' year='2010' />

	<abstract>
	  <t>
IANA Considerations for RPC Net Identifiers and Universal Address Formats.
	  </t>
	</abstract>

      </front>

      <seriesInfo name='RFC' value='5665' />
    </reference>

<reference anchor='RFC5662'>
<front>
<title>
Network File System (NFS) Version 4 Minor Version 1 External Data
Representation Standard (XDR) Description
</title>

<author initials='S' surname='Shepler' fullname='Spencer Shepler' role='editor'>
    <organization />
</author>

<author initials='M' surname='Eisler' fullname='Mike Eisler' role='editor'>
    <organization />
</author>

<author initials='D' surname='Noveck' fullname='David  Noveck' role='editor'>
    <organization />
</author>

<date month='January' year='2010' />

<abstract><t>This Internet-Draft provides the XDR description for NFSv4 minor version one.</t></abstract>

</front>

<seriesInfo name='RFC' value='5662' />
</reference>

    <reference anchor='RDMAP'>

      <front>
	<title abbrev='RDMAP - WIP'>A Remote Direct Memory Access Protocol
         Specification
	</title>
	<author initials='R.' surname='Recio'>
	  <organization>IBM Corporation</organization>
	</author>
	<author initials='B.' surname='Metzler'>
	  <organization>IBM Corporation</organization>
	</author>
	<author initials='P.' surname='Culley'>
	  <organization>Hewlett-Packard Company</organization>
	</author>
	<author initials='J.' surname='Hilland'>
	  <organization>Hewlett-Packard Company</organization>
	</author>
	<author initials='D.' surname='Garcia'>
	  <organization></organization>
	</author>
	<date year='2007' month='October' />
	<abstract>
	<t>
	This document defines a Remote Direct Memory Access Protocol 
	(RDMAP) that operates over the Direct Data Placement Protocol (DDP 
	protocol).  RDMAP provides read and write services directly to 
	applications and enables data to be transferred directly into 
	Upper Layer Protocol (ULP) buffers without intermediate data 
	copies. It also enables a kernel bypass implementation. 
	</t></abstract></front>

      <seriesInfo name='RFC' value='5040' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc5040.txt' />
    </reference>

    <reference anchor='RPCRDMA'>
      <front>
	<title>
Remote Direct Memory Access Transport for Remote Procedure Call
	</title>

	<author initials='T' surname='Talpey' fullname='Thomas Talpey'>
	  <organization />
	</author>

	<author initials='B' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization />
	</author>

	<date month='October' year='2009' />

	<abstract><t>A protocol is described providing Remote Direct
	Memory Access (RDMA) as a new transport for Remote Procedure
	Call (RPC).  The RDMA transport binding conveys the benefits
	of efficient, bulk data transport over high speed networks,
	while providing for minimal change to RPC applications and
	with no required revision of the application RPC protocol, or
	the RPC protocol itself.</t></abstract>

      </front>

      <seriesInfo name='RFC' value='5666' />
      <format type='TXT'
              target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-rpcrdma-09.txt' />
    </reference>

    <reference anchor='NFSDDP'>
      <front>
	<title>
Network File System (NFS) Direct Data Placement
	</title>

	<author initials='T' surname='Talpey' fullname='Thomas Talpey'>
	  <organization />
	</author>

	<author initials='B' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization />
	</author>

	<date month='January' year='2010' />

	<abstract>
	  <t>
	    This draft defines the bindings of the various Network
	    File System (NFS) versions to the Remote Direct Memory
	    Access (RDMA) operations supported by the RPC/RDMA
	    transport protocol.  It describes the use of direct data
	    placement by means of server-initiated RDMA operations
	    into client-supplied buffers for implementations of NFS
	    versions 2, 3, 4 and 4.1 over such an RDMA
	    transport.
	  </t>
	</abstract>

      </front>

      <seriesInfo name='RFC' value='5666' />
      <format type='TXT'
              target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-nfsdirect-08.txt' />
    </reference>

<!-- obsoleted by RFC 5531
    <reference anchor='RFC1831'>

      <front>
	<title abbrev='Remote Procedure Call Protocol Version 2'>RPC:
	Remote Procedure Call Protocol Specification Version 2</title>
	<author initials='R.' surname='Srinivasan' fullname='Raj Srinivasan'>
	  <organization>Sun Microsystems, Inc., ONC Technologies</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>M/S MTV-5-40</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043</code>
	    <country>US</country></postal>
	    <phone>+1 415 336 2478</phone>
	    <facsimile>+1 415 336 6015</facsimile>
	<email>raj@xxxxxxxxxxx</email></address></author>
	<date year='1995' month='August' />
	<abstract>
      <t>This document describes the ONC Remote Procedure Call (ONC
      RPC Version 2) protocol as it is currently deployed and
      accepted.  "ONC" stands for "Open Network
      Computing".</t></abstract></front>

      <seriesInfo name='RFC' value='1831' />
      <format type='TXT' octets='37798' target='ftp://ftp.isi.edu/in-notes/rfc1831.txt' />
    </reference> -->

<reference anchor='RFC5531'>

<front>
<title>
RPC: Remote Procedure Call Protocol Specification Version 2
</title>

<author initials='R.' surname='Thurlow' fullname='R. Thurlow'>
<organization />
</author>
<date year='2009' month='May' />
<abstract>
<t>This document describes the Open Network Computing (ONC) Remote
Procedure Call (RPC) version 2 protocol as it is currently deployed
and accepted.  This document obsoletes RFC 1831. [STANDARDS
TRACK]</t></abstract></front>

<seriesInfo name='RFC' value='5531' />
<format type='TXT' octets='161720'
target='ftp://ftp.isi.edu/in-notes/rfc5531.txt' />
</reference>

    <reference anchor='RFC4121'>
    
      <front>
        <title>The Kerberos Version 5 Generic Security Service Application Program Interface (GSS-API) Mechanism Version 2</title>

          <author initials='L.' surname='Zhu'>
		<organization>Microsoft</organization>
          </author>

          <author initials='K.' surname='Jaganathan'>
		<organization>Microsoft</organization>
          </author>

          <author initials='S.' surname='Hartman'>
		<organization>MIT</organization>
          </author>

        <date year='2005' month='July' />

        <abstract>
        <t>

	RFC 1964 is updated and incremental changes are proposed in
	response to recent developments such as the introduction of
	Kerberos crypto-system framework.  These changes support the
	inclusion of new crypto-systems, by defining new per-message
	tokens along with their encryption and checksum algorithms
	based on the crypto-system profiles.

	</t>
        </abstract>

      </front>
      <seriesInfo name='RFC' value='4121' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc4121.txt' />
    </reference>


    <reference anchor='RFC2119'>
      <front>
	<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
	<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
	  <organization>Harvard University</organization>
	  <address>
	    <postal>
	      <street>1350 Mass. Ave.</street>
	      <street>Cambridge</street>
	    <street>MA 02138</street></postal>
	    <phone>- +1 617 495 3864</phone>
	<email>sob@xxxxxxxxxxx</email></address></author>
	<date year='1997' month='March' />
      </front>
      <seriesInfo name='BCP' value='14' />
      <seriesInfo name='RFC' value='2119' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc2119.txt' />
    </reference>

	<reference anchor='RFC5403'>

	<front>
	<title>RPCSEC_GSS Version 2</title>
	<author initials='M.' surname='Eisler' fullname='M. Eisler'>
	<organization /></author>
	<date year='2009' month='February' />
	<abstract>
	<t>This document describes version 2 of the RPCSEC_GSS protocol.  Version 2 is the same as version 1 (specified in RFC 2203) except that support for channel bindings has been added.  RPCSEC_GSS allows remote procedure call (RPC) protocols to access the Generic Security Services Application Programming Interface (GSS-API). [STANDARDS TRACK]</t></abstract></front>

	<seriesInfo name='RFC' value='5403' />
	<format type='TXT' octets='30812' target='ftp://ftp.isi.edu/in-notes/rfc5403.txt' />
	</reference>

    <reference anchor='RFC2203'>
    
      <front>
      <title>RPCSEC_GSS Protocol Specification</title>

        <author initials='M.' surname='Eisler' fullname='Michael Eisler'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UCOS03</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (719) 599-9026</phone>
        <email>mre@xxxxxxxxxxx</email></address></author>
  
        <author initials='A.' surname='Chiu' fullname='Alex Chiu'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UMPK17-203</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (415) 786-6465</phone>
        <email>hacker@xxxxxxxxxxx</email></address></author>
  
        <author initials='L.' surname='Ling' fullname='Lin Ling'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UMPK17-201</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (415) 786-5084</phone>
        <email>lling@xxxxxxxxxxx</email></address></author>

      <date year='1997' month='September' />
      <area>Security</area>
      <keyword>generic security service</keyword>
      <keyword>remote procedure call</keyword>
      <keyword>security</keyword>
      <abstract>
      <t>
         This memo describes an ONC/RPC security flavor that allows RPC
         protocols to access the Generic Security Services Application
         Programming Interface (referred to henceforth as GSS-API).
      </t></abstract></front>
      
      <seriesInfo name='RFC' value='2203' />
      <format type='TXT' octets='50937' target='http://www.rfc-editor.org/rfc/rfc2203.txt' />
      <format type='HTML' octets='64234' target='http://xml.resource.org/public/rfc/html/rfc2203.html' />
      <format type='XML' octets='50069' target='http://xml.resource.org/public/rfc/xml/rfc2203.xml' />
    </reference>

    <reference anchor='RFC2277'>

      <front>
	<title abbrev='Charset Policy'>
	IETF Policy on Character Sets and Languages</title>
	<author initials='H.' surname='Alvestrand' 
		fullname='Harald Tveit Alvestrand'>
	  <organization>UNINETT</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 6883 Elgeseter</street>
	      <street>N-7002 TRONDHEIM</street>
	    <country>NORWAY</country></postal>
	    <phone>+47 73 59 70 94</phone>
	<email>Harald.T.Alvestrand@xxxxxxxxxx</email></address></author>
	<date year='1998' month='January' />
	<area>Applications</area>
	<keyword>Internet Engineering Task Force</keyword>
      <keyword>character encoding</keyword></front>

      <seriesInfo name='BCP' value='18' />
      <seriesInfo name='RFC' value='2277' />
      <format type='TXT' octets='16622' 
	      target='http://www.rfc-editor.org/rfc/rfc2277.txt' />
      <format type='HTML' octets='26556' 
	      target='http://xml.resource.org/public/rfc/html/rfc2277.html' />
      <format type='XML' octets='15544' 
	      target='http://xml.resource.org/public/rfc/xml/rfc2277.xml' />
    </reference>

    <reference anchor='RFC2104'>

      <front>
	<title abbrev='HMAC'>HMAC: Keyed-Hashing for Message Authentication</title>
	<author initials='H.' surname='Krawczyk' fullname='Hugo Krawczyk'>
	  <organization>IBM, T.J. Watson Research Center</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 704</street>
	      <city>Yorktown Heights</city>
	      <region>NY</region>
	      <code>10598</code>
	      <country>US</country></postal>
	    <email>hugo@xxxxxxxxxxxxxx</email></address></author>

	<author initials='M.' surname='Bellare' fullname='Mihir Bellare'>
	  <organization>University of California at San Diego, Dept of Computer Science and Engineering</organization>
	  <address>
	    <postal>
	      <street>9500 Gilman Drive</street>
	      <street>Mail Code 0114</street>
	      <city>La Jolla</city>
	      <region>CA</region>
	      <code>92093</code>
	      <country>US</country></postal>
	    <email>mihir@xxxxxxxxxxx</email></address></author>

	<author initials='R.' surname='Canetti' fullname='Ran Canetti'>
	  <organization>IBM T.J. Watson Research Center</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 704</street>
	      <city>Yorktown Heights</city>
	      <region>NY</region>
	      <code>10598</code>
	      <country>US</country></postal>
	    <email>canetti@xxxxxxxxxxxxxx</email></address></author>

	<date year='1997' month='February' />
	<abstract>
	  <t>This document describes HMAC, a mechanism for message
	  authentication using cryptographic hash functions. HMAC can
	  be used with any iterative cryptographic hash function,
	  e.g., MD5, SHA-1, in combination with a secret shared key.
	  The cryptographic strength of HMAC depends on the properties
	  of the underlying hash function.</t></abstract></front>

      <seriesInfo name='RFC' value='2104' />
      <format type='TXT' octets='22297' target='http://www.rfc-editor.org/rfc/rfc2104.txt' />
    </reference>

    <reference anchor='RFC2743'>

      <front>
	<title abbrev='GSS-API'>Generic Security Service Application
	Program Interface Version 2, Update 1</title>
	<author initials='J.' surname='Linn' fullname='John Linn'>
	  <organization>RSA Laboratories</organization>
	  <address>
	    <postal>
	      <street>20 Crosby Drive</street>
	      <city>Bedford</city>
	      <region>MA</region>
	      <code>01730</code>
	    <country>US</country></postal>
	    <phone>+1 781 687 7817</phone>
	<email>jlinn@xxxxxxxxxxxxxxx</email></address></author>
	<date year='2000' month='January' />
	<abstract>
	  <t>The Generic Security Service Application Program
	  Interface (GSS-API), Version 2, as defined in, provides
	  security services to callers in a generic fashion,
	  supportable with a range of underlying mechanisms and
	  technologies and hence allowing source-level portability of
	  applications to different environments. This specification
	  defines GSS-API services and primitives at a level
	  independent of underlying mechanism and programming language
	  environment, and is to be complemented by other, related
	  specifications:</t>
	  <t>documents defining specific parameter bindings for
	  particular language environments</t>
	  <t>documents defining token formats, protocols, and
	  procedures to be implemented in order to realize GSS-API
	  services atop particular security mechanisms</t> <t>This
	  memo obsoletesmaking specific, incremental changes in
	  response to implementation experience and liaison
	  requests. It is intended, therefore, that this memo or a
	  successor version thereto will become the basis for
	  subsequent progression of the GSS-API specification on the
	  standards track.</t></abstract></front>

      <seriesInfo name='RFC' value='2743' />
      <format type='TXT' octets='229418' 
	      target='http://www.rfc-editor.org/rfc/rfc2743.txt' />
    </reference>


    <reference anchor='RFC3454'>

      <front>
	<title>Preparation of Internationalized Strings ("stringprep")</title>
	<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
	  <organization /></author>
	<author initials='M.' surname='Blanchet' fullname='M. Blanchet'>
	  <organization /></author>
	<date year='2002' month='December' />
	<abstract>
	  <t>
	    &lt;p>This document describes a framework for preparing
	    Unicode text strings in order to increase the likelihood
	    that string input and string comparison work in ways that
	    make sense for typical users throughout the world. The
	    stringprep protocol is useful for protocol identifier
	    values, company and personal names, internationalized
	    domain names, and other text strings. This document does
	    not specify how protocols should prepare text
	    strings. Protocols must create profiles of stringprep in
	    order to fully specify the processing options. [STANDARDS
	    TRACK] &lt;/p>
          </t>
        </abstract>
      </front>

      <seriesInfo name='RFC' value='3454' />
      <format type='TXT' octets='138684' target='http://www.rfc-editor.org/rfc/rfc3454.txt' />
    </reference>

    <reference anchor='RFC3491'>

      <front>
	<title>Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)</title>
	<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
	  <organization /></author>
	<author initials='M.' surname='Blanchet' fullname='M. Blanchet'>
	  <organization /></author>
	<date year='2003' month='March' />
	<abstract>
	  <t>
	    &lt;p>This document describes how to prepare
	    internationalized domain name (IDN) labels in order to
	    increase the likelihood that name input and name
	    comparison work in ways that make sense for typical users
	    throughout the world. This profile of the stringprep
	    protocol is used as part of a suite of on-the-wire
	    protocols for internationalizing the Domain Name System
	    (DNS). [STANDARDS TRACK] &lt;/p>
          </t>
         </abstract>
        </front>

      <seriesInfo name='RFC' value='3491' />
      <format type='TXT' octets='10316' target='http://www.rfc-editor.org/rfc/rfc3491.txt' />
    </reference>

    <reference anchor='RFC4055'>

    <front>
    <title>
Additional Algorithms and Identifiers for RSA Cryptography for use in
the Internet X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile
</title>
    <author initials='J.' surname='Schaad' fullname='J. Schaad'>
    <organization /></author>
    <author initials='B.' surname='Kaliski' fullname='B. Kaliski'>
    <organization /></author>
    <author initials='R.' surname='Housley' fullname='R. Housley'>
    <organization /></author>
    <date year='2005' month='June' />
    <abstract>
    <t>&lt;p>This document supplements RFC 3279. It describes the
    conventions for using the RSA Probabilistic Signature Scheme
    (RSASSA-PSS) signature algorithm, the RSA Encryption Scheme -
    Optimal Asymmetric Encryption Padding (RSAES-OAEP) key transport
    algorithm and additional one-way hash functions with the
    Public-Key Cryptography Standards (PKCS) #1 version 1.5 signature
    algorithm in the Internet X.509 Public Key Infrastructure
    (PKI). Encoding formats, algorithm identifiers, and parameter
    formats are specified. [STANDARDS
    TRACK]&lt;/p>
    </t>
    </abstract>
    </front>

    <seriesInfo name='RFC' value='4055' />
    <format type='TXT' octets='57479' target='http://www.rfc-editor.org/rfc/rfc4055.txt' />
    </reference>

    <reference anchor='RFC4506'>

      <front>
      <title>XDR: External Data Representation Standard</title>
      <author initials='M.' surname='Eisler' fullname='M. Eisler' role='editor'>
      <organization /></author>
      <date year='2006' month='May' />
      <abstract>
      <t>&lt;p>This document describes the External Data
      Representation Standard (XDR) protocol as it is currently
      deployed and accepted. This document obsoletes RFC
      1832. [STANDARDS TRACK]&lt;/p></t></abstract></front>
      <seriesInfo name='STD' value='67' />
      <seriesInfo name='RFC' value='4506' />
      <format type='TXT' octets='55477' target='http://www.rfc-editor.org/rfc/rfc4506.txt' />
    </reference>

  </references>

  <references title="Informative References">

   <reference anchor='RFC5226'>

   <front>
   <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
   <author initials='T.' surname='Narten' fullname='T. Narten'>
   <organization /></author>
   <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
   <organization /></author>
   <date year='2008' month='May' />
   <abstract>
   <t>Many protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).&lt;/t>&lt;t> In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.&lt;/t>&lt;t> This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract></front>

   <seriesInfo name='BCP' value='26' />
   <seriesInfo name='RFC' value='5226' />
   <format type='TXT' octets='66160' target='http://www.rfc-editor.org/rfc/rfc5226.txt' />
   </reference>

<reference anchor='RFC1094'>

<front>
<title abbrev='NFS: Network File System'>NFS: Network File System Protocol specification</title>
<author initials='B.' surname='Nowicki' fullname='Bill Nowicki'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mail Stop 1-40</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>US</country></postal>
<phone>+1 415 336 7278</phone>
<email>nowicki@xxxxxxx</email></address></author>
<date year='1989' month='March' /></front>

<seriesInfo name='RFC' value='1094' />
<format type='TXT' octets='51454' target='http://www.rfc-editor.org/rfc/rfc1094.txt' />
</reference>

<reference anchor='RFC1813'>

<front>
<title abbrev='NFSv3 Protocol'>NFS Version 3 Protocol Specification</title>
<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mailstop UMTV05-44</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043-1100</code>
<country>US</country></postal>
<phone>+1 415 336 1051</phone>
<facsimile>+1 415 336 6015</facsimile>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>

<author initials='B.' surname='Pawlowski' fullname='Brian Pawlowski'>
<organization>NetApp</organization>
<address>
<postal>
<street>319 North Bernardo Ave.</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>US</country></postal>
<phone>+1 415 428 5136</phone>
<facsimile>+1 415 428 5151</facsimile>
<email>beepy@xxxxxxxxxx</email></address></author>

<author initials='P.' surname='Staubach' fullname='Peter Staubach'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mailstop UMTV05-44</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043-1100</code>
<country>US</country></postal>
<phone>+1 415 336 5615</phone>
<facsimile>+1 415 336 6015</facsimile>
<email>peter.staubach@xxxxxxxxxxx</email></address></author>

<date year='1995' month='June' />
<abstract>
<t>This paper describes the NFSv3 protocol.  This paper is provided so that people can write compatible implementations.</t></abstract></front>

<seriesInfo name='RFC' value='1813' />
<format type='TXT' octets='229793' target='http://www.rfc-editor.org/rfc/rfc1813.txt' />
</reference>

    <reference anchor='RFC1833'>

      <front>
	<title>Binding Protocols for ONC RPC Version 2</title>
	<author initials='R.' surname='Srinivasan' fullname='Raj Srinivasan'>
	  <organization>Sun Microsystems, Inc., ONC Technologies</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>M/S MTV-5-40</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043</code>
	    <country>US</country></postal>
	    <phone>+1 415 336 2478</phone>
	    <facsimile>+1 415 336 6015</facsimile>
	<email>raj@xxxxxxxxxxx</email></address></author>
	<date year='1995' month='August' />
	<abstract>
      <t>This document describes the binding protocols used in
      conjunction with the ONC Remote Procedure Call (ONC RPC Version
      2) protocols.</t></abstract></front>

      <seriesInfo name='RFC' value='1833' />
      <format type='TXT' octets='24449' target='http://www.rfc-editor.org/rfc/rfc1833.txt' />
    </reference>


<reference anchor='RFC5663'>
<front>
<title>
Parallel NFS (pNFS) Block/Volume Layout
</title>

<author initials='D' surname='Black' fullname='David Black'>
    <organization />
</author>

<author initials='J' surname='Glasgow' fullname='Jason Glasgow'>
    <organization />
</author>

<author initials='S' surname='Fridella' fullname='Stephen Fridella'>
    <organization />
</author>


<date month='January' year='2010' />

<abstract><t>Parallel NFS (pNFS) extends NFSv4 to allow clients to
directly access file data on the storage used by the NFSv4 server.
This ability to bypass the server for data access can increase both
performance and parallelism, but requires additional client
functionality for data access, some of which is dependent on the class
of storage used.  The main pNFS operations draft specifies
storage-class-independent extensions to NFS; this draft specifies the
additional extensions (primarily data structures) for use of pNFS with
block and volume based storage.</t></abstract> 

</front>

<seriesInfo name='RFC' value='5663' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-pnfs-block-11.txt' />
</reference>

    <reference anchor='RFC2054'>

      <front>
	<title>WebNFS Client Specification</title>
	<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization>Sun Microsystems, Inc.</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>Mailstop Mpk17-201</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043-1100</code>
	      <country>US</country></postal>
	    <phone>+1 415 786 5067</phone>
	    <facsimile>+1 415 786 5896</facsimile>
	    <email>brent.callaghan@xxxxxxxxxxx</email></address></author>
	<date year='1996' month='October' />
	<abstract>
	  <t>This document describes a lightweight binding mechanism that allows
	    NFS clients to obtain service from WebNFS-enabled servers with a
	    minimum of protocol overhead.  In removing this overhead, WebNFS
	    clients see benefits in faster response to requests, easy transit of
	    packet filter firewalls and TCP-based proxies, and better server
	    scalability.</t></abstract></front>

      <seriesInfo name='RFC' value='2054' />
      <format type='TXT' octets='36354' target='http://www.rfc-editor.org/rfc/rfc2054.txt' />
    </reference>

    <reference anchor='RFC2055'>

      <front>
	<title>WebNFS Server Specification</title>
	<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization>Sun Microsystems, Inc.</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>Mailstop Mpk17-201</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043-1100</code>
	      <country>US</country></postal>
	    <phone>+1 415 786 5067</phone>
	    <facsimile>+1 415 786 5896</facsimile>
	    <email>brent.callaghan@xxxxxxxxxxx</email></address></author>
	<date year='1996' month='October' />
	<abstract>
	  <t>This document describes the specifications for a server of WebNFS
	    clients.  WebNFS extends the semantics of the NFSv3
	    protocol to allow clients to obtain filehandles more easily, without
	    recourse to the portmap or MOUNT protocols.  In removing the need for
	    these protocols, WebNFS clients see benefits in faster response to
	    requests, easy transit of firewalls and better server scalability This
	    description is provided to facilitate compatible implementations of
	    WebNFS servers.</t></abstract></front>

      <seriesInfo name='RFC' value='2055' />
      <format type='TXT' octets='20498' target='http://www.rfc-editor.org/rfc/rfc2055.txt' />
    </reference>

    <reference anchor='RFC2623'>
    
      <front>
      <title abbrev='NFS Security, RPCSEC_GSS, and Kerberos V5'>
NFS Version 2 and Version 3 Security Issues and the NFS Protocol's Use
of RPCSEC_GSS and Kerberos V5
</title> 

        <author initials='M.' surname='Eisler' fullname='Mike Eisler'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>5565 Wilson Road</street>
        <city>Colorado Springs</city>
        <region>CO</region>
        <code>80919</code>
        <country>US</country></postal>
        <phone>+1 719 599 9026</phone>
        <email>mre@xxxxxxxxxxx</email></address></author>

      <date year='1999' month='June' />

      <abstract>

        <t>This memorandum clarifies various security issues involving
        the NFSv2 and NFSv3 protocols and then
        describes how the NFS protocol
        use the RPCSEC_GSS security flavor protocol and Kerberos V5.
        This memorandum is provided so that people can write compatible
        implementations.</t>
      </abstract>
      </front>
      
      <seriesInfo name='RFC' value='2623' />
      <format type='TXT' octets='42521' target='http://www.rfc-editor.org/rfc/rfc2623.txt' />
    </reference>

<reference anchor='RFC2224'>

<front>
<title>NFS URL Scheme</title>
<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>Mailstop Mpk17-201</street>
<street>901 San Antonio Road</street>
<street>Palo Alto</street>
<street>California 94303</street></postal>
<phone>1-415-786-5067</phone>
<facsimile>1-415-786-5896</facsimile>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>
<date year='1997' month='October' />
<area>Applications</area>
<keyword>NFS</keyword>
<keyword>network file system</keyword>
<keyword>uniform resource</keyword>
<abstract>
<t>
   A new URL scheme, &apos;nfs&apos; is defined.  It is used to refer to files and
   directories on NFS servers using the general URL syntax defined in
   RFC 1738, &quot;Uniform Resource Locators (URL)&quot;.
</t>
<t>
   This scheme uses the public filehandle and multi-component look up
   [RFC2054, RFC2055] to access server data with a minimum of protocol
   overhead.
</t>
<t>
   The NFS protocol provides access to shared file systems across
   networks.  It is designed to be machine, operating system, network
   architecture, and transport protocol independent.
</t></abstract></front>

<seriesInfo name='RFC' value='2224' />
<format type='TXT' octets='22726' target='http://www.rfc-editor.org/rfc/rfc2224.txt' />
<format type='HTML' octets='35259' target='http://xml.resource.org/public/rfc/html/rfc2224.html' />
<format type='XML' octets='24805' target='http://xml.resource.org/public/rfc/xml/rfc2224.xml' />
</reference>

<reference anchor='RFC2624'>

<front>
<title abbrev='NFSv4 Design Considerations'>NFS Version 4 Design Considerations</title>
<author initials='S.' surname='Shepler' fullname='Spencer Shepler'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>7808 Moonflower Drive</street>
<city>Austin</city>
<region>TX</region>
<code>78750</code>
<country>US</country></postal>
<phone>+1 512 349 9376</phone>
<email>spencer.shepler@xxxxxxxxxxx</email></address></author>
<date year='1999' month='June' />
<abstract>
<t>The main task of the NFSv4 working group is to create a
protocol definition for a distributed file system that focuses on the
following items: improved access and good performance on the Internet,
strong security with negotiation built into the protocol, better
cross-platform interoperability, and designed for protocol extensions.
NFSv4 will owe its general design to the previous versions of
NFS.  It is expected, however, that many features will be quite
different in NFSv4 than previous versions to facilitate the
goals of the working group and to address areas that NFSv2 and
NFSv3 have not.</t>
<t>This design considerations document is meant to present more detail
than the working group charter.  Specifically, it presents the areas
that the working group will investigate and consider while developing
a protocol specification for NFSv4.  Based on this
investigation the working group will decide the features of the new
protocol based on the cost and benefits within the specific feature
areas.</t></abstract> <note title='Key Words'>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC
2119.</t></note></front>

<seriesInfo name='RFC' value='2624' />
<format type='TXT' octets='52891' target='http://www.rfc-editor.org/rfc/rfc2624.txt' />
</reference>

<reference anchor='RFC2755'>

<front>
<title>Security Negotiation for WebNFS</title>
<author initials='A.' surname='Chiu' fullname='Alex Chiu'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 650 786 6465</phone>
<email>alex.chiu@xxxxxxxxxxx</email></address></author>

<author initials='M.' surname='Eisler' fullname='Mike Eisler'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 719 599 9026</phone>
<email>michael.eisler@xxxxxxxxxxx</email></address></author>

<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 650 786 5067</phone>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>

<date year='2000' month='January' />
<abstract>
<t>This document describes a protocol for a WebNFS clientto negotiate the desired security mechanism with a WebNFS serverbefore the WebNFS client falls back to the MOUNT v3 protocol. This document is provided so that people can write compatible implementations.</t></abstract></front>

<seriesInfo name='RFC' value='2755' />
<format type='TXT' octets='23493' target='http://www.rfc-editor.org/rfc/rfc2755.txt' />
</reference>

    <reference anchor='RFC3232'>
    
      <front>
        <title>Assigned Numbers: RFC 1700 is Replaced by an On-line Database</title>
        <author initials='J.' surname='Reynolds'
fullname='J. Reynolds' role='editor'>
        <organization /></author>
        <date year='2002' month='January' />
        <abstract>
          <t>&lt;p>This memo obsoletes RFC 1700 (STD 2) "Assigned
          Numbers", which contained an October 1994 snapshot of assigned
          Internet protocol parameters. This memo provides information
          for the Internet community. &lt;/p></t>
	</abstract></front>
    
      <seriesInfo name='RFC' value='3232' />
      <format type='TXT' octets='3849' target='http://www.rfc-editor.org/rfc/rfc3232.txt' />
    </reference>

    <reference anchor='RFC3530'>
      <front>
	<title>Network File System (NFS) version 4 Protocol</title>
	<author initials="S." surname="Shepler" fullname="S. Shepler">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="B." surname="Callaghan" fullname="B. Callaghan">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="D." surname="Robinson" fullname="D. Robinson">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="R." surname="Thurlow" fullname="R. Thurlow">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="C." surname="Beame" fullname="C. Beame">
	  <organization>Hummingbird, Ltd.</organization>
	</author>
	<author initials="M." surname="Eisler" fullname="M. Eisler">
	  <organization>NetApp</organization>
	</author>
	<author initials="D." surname="Noveck" fullname="D. Noveck">
	  <organization>NetApp</organization>
	</author>
	<date year="2003" month="April"/>
      </front>
      <seriesInfo name="RFC" value="3530"/>
      <format type="TXT" octets="600988" 
	      target="http://www.rfc-editor.org/rfc/rfc3530.txt"/>
    </reference>

    <reference anchor="RFC3720">
      <front>
	<title>Internet Small Computer Systems Interface (iSCSI)</title>
	<author initials="J." surname="Satran" fullname="J. Satran">
	  <organization/>
	</author>
	<author initials="K." surname="Meth" fullname="K. Meth">
	  <organization/>
	</author>
	<author initials="C." surname="Sapuntzakis" fullname="C. Sapuntzakis">
	  <organization/>
	</author>
	<author initials="M." surname="Chadalapaka" fullname="M. Chadalapaka">
	  <organization/>
	</author>
	<author initials="E." surname="Zeidner" fullname="E. Zeidner">
	  <organization/>
	</author>
	<date year="2004" month="April"/>
      </front>
      <seriesInfo name="RFC" value="3720"/>
      <format type="TXT" octets="578468" target="http://www.rfc-editor.org/rfc/rfc3720.txt"/>
    </reference>

    <reference anchor="FCP-2">
      <front>
	<title>Fibre Channel Protocol for SCSI, 2nd Version (FCP-2)</title>
	<author initials="R." surname="Snively" fullname="Robert Snively">
	  <organization>Brocade Communication Systems, Inc.</organization>
	</author>
	<date month="Oct" year="2003" />
      </front>
      <seriesInfo name="ANSI/INCITS" value="350-2003" />
    </reference>

    <reference anchor="Floyd">
        <front>
	    <title> The Synchronization of Periodic Routing Messages </title>

	    <author initials="S." surname="Floyd" >
	    <organization></organization>
            </author>
	    <author initials="V." surname="Jacobson">
	    <organization></organization>
            </author>
	    <date month="April" year="1994"/>
        </front>

        <seriesInfo name="IEEE/ACM Transactions on Networking" value="2(2), pp. 122-136" />

    </reference>

    <reference anchor='OSD-T10'
	       target='http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf'>
      <front>
	<title>Object-Based Storage Device Commands (OSD)</title>
	<author initials="R.O." surname="Weber" fullname="Ralph O. Weber">
	  <organization>ENDL Texas</organization>
	</author>
	<date month="July" year="2004"/>
      </front>
      <seriesInfo name="ANSI/INCITS" value="400-2004"/>
    </reference>


<reference anchor='RFC5664'>
<front>
<title>
Object-Based Parallel NFS (pNFS) Operations
</title>

<author initials='B' surname='Halevy' fullname='Benny Halevy'>
    <organization />
</author>

<author initials='B' surname='Welch' fullname='Brent Welch'>
    <organization />
</author>

<author initials='J' surname='Zelenka' fullname='Jim Zelenka'>
    <organization />
</author>

<date month='January' year='2010' />

<abstract><t>This Internet-Draft provides a description of the object-based pNFS extension for NFSv4.  This is a companion to the main pnfs specification in the NFSv4 Minor Version 1 Internet Draft, which is currently draft-ietf-nfsv4-minorversion1-23.</t></abstract>

</front>

<seriesInfo name='RFC' value='5664' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-pnfs-obj-12.txt' />
</reference>

    <reference anchor="Chet">
        <front>
	    <title>Improving the Performance
		    and Correctness of an NFS Server</title>

	    <author initials="C." surname="Juszczak" fullname="Chet Juszczak">
	      <organization>Digital Equipment Corporation</organization>
	    </author>
	    <date month="June" year="1990"/>
	    <abstract>
	    <t>
		Describes reply cache implementation that
		avoids work in the server by handling
		duplicate requests. More important, though
		listed as a side-effect, the reply cache
		aids in the avoidance of destructive non-
		idempotent operation re-application --
		improving correctness.

	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
      </reference>
    <reference anchor="ha_nfs_ibm">
        <front>
	    <title>A Highly Available Network Server</title>

	    <author initials="A." surname="Bhide" fullname="Anupam Bhide">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <author initials="E. N." surname="Elnozahy" fullname="Elmootazbellah N. Elnozahy">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <author initials="S. P." surname="Morgan" fullname="Stephen P. Morgan ">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <date month="January" year="1991"/>
	    <abstract>
	    <t>
	     This paper presents the design and implementation
	     of a Highly Available Network File Server
	     (HA-NFS). We separate the problem of network
	     file server reliability into three different subproblems:
	     server reliability, disk reliability, and network
	     reliability. HA-NFS offers a different solution
	     for each: dual-ported disks and impersonation
	     are used to provide server reliability, disk mirroring
	     can be used to provide disk reliability, and optional
	     network replication can be used to provide
	     network reliability. The implementation shows
	     that HA-NFS provides high availability without
	     the excessive resource overhead or the performance
	     degradation that characterize traditional replication
	     methods. Ongoing operations are not aborted
	     during fail-over and recovery is completely transparent
	     to applications. HA-NFS adheres to the
	     NFS protocol standard and can be used by existing
	     NFS clients without modification.
	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
      </reference>

    <reference anchor="rpc_xid_issues">
        <front>
	    <title>RPC XID Issues</title>

	    <author initials="R." surname="Werme" fullname="Ric Werme">
	      <organization>Digital Equipment Corporation</organization>
	    </author>
	    <date month="February" year="1996"/>
	    <abstract>
	    <t>
             The presentation provides implementation advice for
             ONC RPC transaction identifier (xid) generation.
	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
    </reference>

    <reference anchor="PVFS">
        <front>
            <title>PVFS: A Parallel File System for Linux Clusters.</title>

	    <author initials="P. H." surname="Carns">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>

	    </author>
	    <author initials="W. B." surname="Ligon III">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>
	    </author>

	    <author initials="R. B." surname="Ross">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>
	    </author>

	    <author initials="R." surname="Thakur">
            <organization>Mathematics and Computer Science Division,
            Argonne National Laboratory, Argonne, IL 60439</organization>
	    </author>

	    <date year="2000"/>
        </front>
        <seriesInfo name="Proceedings of the 4th Annual Linux Showcase and Conference" value=""/>

    </reference>

    <reference anchor="xnfs">
        <front>
	    <title> Protocols for Interworking: XNFS, Version 3W, ISBN 1-85912-184-5 </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date month="February" year="1998"/>
        </front>
      </reference>

    <reference anchor="access_api">
      <front>
     <title>The Open Group Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition
     </title>
	<author>
	  <organization>The Open Group
	  </organization>
	</author>
	<date year="2004" />
        <abstract>
          <t>
          The description of the access() function states: "If the process has appropriate privileges, an implementation may indicate success for X_OK even if none of the execute file permission bits are set." 
          </t>
        </abstract>

      </front>
    </reference>

    <reference anchor='RFC2847'>
    
      <front>
      <title>LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM</title>
        <author initials='M.' surname='Eisler' fullname='M. Eisler'>
        <organization /></author>
        <date year='2000' month='June' />

        <abstract>
          <t>&lt;p>This memorandum describes a method whereby one can
          use GSS-API (Generic Security Service Application Program
          Interface) to supply a secure channel between a client and
          server, authenticating the client with a password, and a
          server with a public key certificate. [STANDARDS TRACK]
          &lt;/p></t>
	</abstract>
      </front>
        
      <seriesInfo name='RFC' value='2847' />
      <format type='TXT' octets='50045' target='http://www.rfc-editor.org/rfc/rfc2847.txt' />
    </reference>

    <reference anchor="errata">
      <front>
     <title>IESG Processing of RFC Errata for the IETF Stream
     </title>
	<author>
	  <organization>IESG
	  </organization>
	</author>
	<date month="July" year="2008" />
      </front>
      <format type='TXT' target='http://www.ietf.org/IESG/STATEMENTS/iesg-statement-07-30-2008.txt' />
    </reference>
  </references>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
  <section title="Acknowledgments">
    <t>
      The initial text for the SECINFO extensions were edited by
      Mike Eisler with contributions from Peng Dai, Sergey Klyushin, and
      Carl Burnett.
    </t>
    <t>
      The initial text for the SESSIONS extensions were edited by
      Tom Talpey, Spencer Shepler, Jon Bauman with contributions from
      Charles Antonelli, Brent Callaghan, Mike Eisler, John Howard, Chet
      Juszczak, Trond Myklebust, Dave Noveck, John Scott, Mike
      Stolarchuk, and Mark Wittle.
    </t>
    <t>
      Initial text relating to multi-server namespace features, 
      including the concept of referrals, were contributed by 
      Dave Noveck, Carl Burnett, and Charles Fan with contributions
      from Ted Anderson, Neil Brown, and Jon Haswell. 
    </t>
    <t>
      The initial text for the Directory Delegations support were
      contributed by Saadia Khan with input from Dave Noveck, Mike
      Eisler, Carl Burnett, Ted Anderson, and Tom Talpey.
    </t>
    <t>
      The initial text for the ACL explanations were contributed by
      Sam Falkner and Lisa Week.
    </t>
    <t>
      The pNFS work was inspired by the NASD and OSD
      work done by Garth Gibson.  Gary Grider has also
      been a champion of high-performance parallel I/O.
      Garth Gibson and Peter Corbett started the pNFS
      effort with a problem statement document for the IETF
      that formed the basis for the pNFS work in NFSv4.1.

    </t>
    <t>
      The initial text for the parallel NFS support was edited by
      Brent Welch and Garth Goodson.  Additional authors for those
      documents were Benny Halevy, David Black, and Andy Adamson.
      Additional input came from the informal group that contributed
      to the construction of the initial pNFS drafts; specific
      acknowledgment goes to Gary Grider, Peter Corbett, Dave Noveck,
      Peter Honeyman, and Stephen Fridella.
    </t>
    <t>
      Fredric Isaman found several errors in draft versions of the
      ONC RPC XDR description of the NFSv4.1 protocol.
    </t>
    <t>
      Audrey Van Belleghem provided, in numerous ways, essential
      co-ordination and management of the process of editing the
      specification documents.
    </t>
    <t>
      Richard Jernigan gave feedback on the file layout's striping
      pattern design.
    </t>
    <t>
      Several formal inspection teams were formed to review various
      areas of the protocol. All the inspections found significant
      errors and room for improvement. NFSv4.1's inspection teams
      were:
      <list style="symbols">
      <t>

       ACLs, with the following inspectors:

	Sam Falkner,
	Bruce Fields,
	Rahul Iyer,
	Saadia Khan,
	Dave Noveck,
	Lisa Week,
	Mario Wurzl,

		and

	Alan Yoder.

      </t>
      <t>

       Sessions, with the following inspectors:

 	William Brown,
	Tom Doeppner,
	Robert Gordon,
	Benny Halevy,
	Fredric Isaman,
	Rick Macklem,
	Trond Myklebust,
	Dave Noveck,
	Karen Rochford,
	John Scott,

		and

	Peter Shah.

      </t>
      <t>

       Initial pNFS inspection, with the following inspectors:


        Andy Adamson,
        David Black,
        Mike Eisler,
        Marc Eshel,
        Sam Falkner,
        Garth Goodson,
        Benny Halevy,
        Rahul Iyer,
        Trond Myklebust,
        Spencer Shepler,

		and

        Lisa Week.

      </t>
      <t>

       Global namespace, with the following inspectors:


        Mike Eisler,
        Dan Ellard,
        Craig Everhart,
        Fredric Isaman,
        Trond Myklebust,
	Dave Noveck,
        Theresa Raj,
        Spencer Shepler,
        Renu Tewari,       

		and

        Robert Thurlow.

      </t>
      <t>

       NFSv4.1 file layout type, with the following inspectors:


	Andy Adamson,
	Marc Eshel,
	Sam Falkner,
	Garth Goodson,
	Rahul Iyer,
	Trond Myklebust,

		and

	Lisa Week.
      </t>

      <t>

       NFSv4.1 locking and directory delegations, with the following inspectors:


        Mike Eisler,
        Pranoop Erasani,
	Robert Gordon,
        Saadia Khan,
        Eric Kustarz, 
        Dave Noveck,
        Spencer Shepler,

		and

        Amy Weaver.
      </t>

      <t>
        
       EXCHANGE_ID and DESTROY_CLIENTID, with the following inspectors:

        Mike Eisler,
        Pranoop Erasani,
	Robert Gordon,
        Benny Halevy,
        Fredric Isaman,
        Saadia Khan,
	Ricardo Labiaga,
        Rick Macklem,
	Trond Myklebust,
        Spencer Shepler,

		and

        Brent Welch.

      </t>

      <t>

        Final pNFS inspection, with the following inspectors:

         Andy Adamson,
         Mike Eisler,
         Mark Eshel,
         Sam Falkner,
         Jason Glasgow,
         Garth Goodson,
         Robert Gordon,
         Benny Halevy,
         Dean Hildebrand,
         Rahul Iyer,
         Suchit Kaura,
         Trond Myklebust,
         Anatoly Pinchuk,
         Spencer Shepler,
         Renu Tewari,
         Lisa Week,

                and

         Brent Welch.

       </t>
    </list>
  </t>

  <t>

    A review team worked together to generate the tables of assignments of
    error sets to operations and make sure that each such assignment had
    two or more people validating it.  Participating in the process were

    Andy Adamson,
    Mike Eisler,
    Sam Falkner,
    Garth Goodson,
    Robert Gordon,
    Trond Myklebust,
    Dave Noveck,
    Spencer Shepler,
    Tom Talpey,
    Amy Weaver,
 
            and
 
    Lisa Week. 
  </t>
  <t>
    Jari Arkko, David Black, Scott Bradner, Lisa
    Dusseault, Lars Eggert, Chris Newman, and Tim
    Polk provided valuable review and guidance.

  </t>

  <t>
   Olga Kornievskaia found several errors in the SSV specification.
  </t>

  <t>
   Ricardo Labiaga found several places where the use of RPCSEC_GSS
   was underspecified.
  </t>

  <t>
   Those who provided miscellaneous comments include:

   Andy Adamson, Sunil Bhargo, Alex Burlyga, Pranoop Erasani,
   Bruce Fields, Vadim Finkelstein, Jason Goldschmidt, Vijay
   K. Gurbani, Sergey Klyushin, Ricardo Labiaga, James Lentini, Anshul
   Madan, Daniel Muntz, Daniel Picken, Archana Ramani, Jim Rees, Mahesh
   Siddheshwar, Tom Talpey, and Peter Varga.

  </t>

</section>

</back>

</rfc>

<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>


<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="2"?>
<?rfc symrefs="no"?>
<?rfc sortrefs="no" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<?rfc rfcedstyle="yes" ?>

<rfc
    category="std"
    number="5661">
     

<front>
    <title abbrev="NFSv4.1">
    Network File System (NFS) Version 4 Minor Version 1 Protocol

    </title>

    <author fullname="Spencer Shepler" 
            initials="S." 
            surname="Shepler" role="editor">
        <organization>Storspeed, Inc.</organization>
        <address>
            <postal>
                <street>7808 Moonflower Drive</street>
                <city>Austin</city>
                <region>TX</region>
                <code>78750</code>
                <country>USA</country>
            </postal>
            <phone>+1-512-402-5811 ext 8530</phone>
            <email>shepler@xxxxxxxxxxxxx</email>
        </address>
    </author>
    <author fullname="Mike Eisler" 
            initials="M." 
            surname="Eisler" role="editor">
        <organization abbrev="NetApp">NetApp</organization>
        <address>
            <postal>
                <street>5765 Chase Point Circle</street>
                <city>Colorado Springs</city>
                <region>CO</region>
                <code>80919</code>
                <country>USA</country>
            </postal>
            <phone>+1-719-599-9026</phone>
            <email>mike@xxxxxxxxxx</email>
            <uri>http://www.eisler.com</uri>
        </address>
    </author>
    <author fullname="David Noveck" 
            initials="D." 
            surname="Noveck" role="editor">
        <organization abbrev="NetApp">NetApp</organization>
        <address>
            <postal>
                <street>1601 Trapelo Road, Suite 16</street>
                <city>Waltham</city>
                <region>MA</region>
                <code>02451</code>
                <country>USA</country>
            </postal>
            <phone>+1-781-768-5347</phone>
            <email>dnoveck@xxxxxxxxxx</email>
        </address>
    </author>

    <date year="2010" month="January"/>

    <area>Transport</area>
    <workgroup>NFSv4</workgroup>

    <abstract>
      <t>
      This document describes the Network File System (NFS) version 4 minor version 1,
      including features retained from the base protocol (NFS version 4 minor
      version 0, which is specified in RFC 3530) and protocol
      extensions made subsequently.  Major extensions introduced in
      NFS version 4 minor version 1 include Sessions, Directory
      Delegations, and parallel NFS (pNFS). NFS version 4 minor version 1
      has no dependencies on NFS version 4 minor version 0, and it
      is considered a separate protocol. Thus,
      this document neither updates nor obsoletes RFC 3530.
      NFS minor version 1 is deemed superior to NFS minor version 0
      with no loss of functionality, and its use is preferred over
      version 0. Both NFS minor versions 0 and 1 can be used
      simultaneously on the same network, between the same client and server.
      </t>
    </abstract>

</front>

<middle>

<section anchor="intro" title="Introduction" >
  <section anchor="intro_the_protocol" title="The NFS Version 4 Minor Version 1 Protocol">
    <t>
      The NFS version 4 minor version 1 (NFSv4.1) protocol
      is the second minor version of the NFS version 4
      (NFSv4) protocol. The first minor version, NFSv4.0, is
      described in <xref target="RFC3530" />.  It generally
      follows the guidelines for minor versioning that are
      listed in Section 10 of RFC 3530.  However, it
      diverges from guidelines 11 ("a client and server
      that support minor version X must support minor
      versions 0 through X-1") and 12 ("no new features may be
      introduced as mandatory in a minor version"). These
      divergences are due to the introduction of
      the sessions model for managing non-idempotent
      operations and the RECLAIM_COMPLETE operation.
      These two new features are infrastructural in
      nature and simplify implementation of existing and
      other new features.  Making them anything but REQUIRED
      would add undue complexity to protocol definition and
      implementation.  NFSv4.1 accordingly updates the
      <xref target="minor_versioning">minor versioning
      guidelines</xref>.

    </t>
    <t>
      As a minor version, NFSv4.1 is consistent with the overall
      goals for NFSv4, but extends the protocol so as to
      better meet those goals, based on experiences with NFSv4.0.
      In addition, NFSv4.1 has adopted some additional goals, which
      motivate some of the major extensions in NFSv4.1.
    </t>
  </section>
    <section title="Requirements Language">
<t>The key words &quot;MUST&quot;, &quot;MUST NOT&quot;,
&quot;REQUIRED&quot;, &quot;SHALL&quot;, &quot;SHALL NOT&quot;,
&quot;SHOULD&quot;, &quot;SHOULD NOT&quot;, &quot;RECOMMENDED&quot;,
&quot;MAY&quot;, and &quot;OPTIONAL&quot; in this document are to be
interpreted as described in <xref target="RFC2119">RFC 2119</xref>.
</t>

    </section>

  <section anchor="scope_of_doc" title="Scope of This Document">
  <t>

   This document describes the NFSv4.1 protocol. With
   respect to NFSv4.0, this document does not:

   <list style='symbols'>
   <t>
       describe the NFSv4.0 protocol, except where needed
       to contrast with NFSv4.1.

   </t> 

   <t>
       modify the specification of the NFSv4.0 protocol.

   </t>

   <t>
       clarify the NFSv4.0 protocol.

   </t>
   </list>
  </t>

  </section>
  <section anchor="version4_goals" title="NFSv4 Goals">
    <t>
      The NFSv4 protocol is a further revision of the NFS protocol
      defined already by NFSv3
      <xref target="RFC1813" />.  It retains
      the essential characteristics of previous versions: easy
      recovery; independence of transport protocols, operating systems, and
      file systems; simplicity; and good performance.  NFSv4 has the following goals:

      <list style='symbols'>
        <t>
          Improved access and good performance on the Internet
        <vspace blankLines='1' />
          The protocol is designed to transit firewalls easily, perform well
          where latency is high and bandwidth is low, and scale to very
          large numbers of clients per server.
        </t>
        <t>
          Strong security with negotiation built into the protocol
        <vspace blankLines='1' />
          The protocol builds on the work of the ONCRPC working group in
          supporting the RPCSEC_GSS protocol.  Additionally, the
        NFSv4.1 protocol provides a mechanism to allow clients and
        servers the ability to negotiate security and require clients and servers to
          support a minimal set of security schemes.
        </t>
        <t>
          Good cross-platform interoperability
        <vspace blankLines='1' />
          The protocol features a file system model that provides a useful,
          common set of features that does not unduly favor one file system
          or operating system over another.
        </t>
        <t>
          Designed for protocol extensions
        <vspace blankLines='1' />
          The protocol is designed to accept standard extensions within a
          framework that enables and encourages backward compatibility.
        </t>
      </list>
    </t>
  </section>
  <section anchor="minor_version1_goals" title="NFSv4.1 Goals">
    <t>
      NFSv4.1 has the following goals, within the framework 
      established by the overall NFSv4 goals.
      <list style="symbols">
        <t>
          To correct significant structural weaknesses and oversights 
          discovered in the base protocol.
        </t>
        <t>
          To add clarity and specificity to areas left
          unaddressed or not addressed in sufficient
          detail in the base protocol. However, as stated
          in <xref target="scope_of_doc" />, it is not
          a goal to clarify the NFSv4.0 protocol in the
          NFSv4.1 specification.

        </t>
        <t>
          To add specific features based on experience with the existing
          protocol and recent industry developments. 
        </t>
        <t>
          To provide protocol support to take advantage of clustered 
          server deployments including the ability to provide scalable
          parallel access to files distributed among multiple servers.
        </t>
      </list>
    </t>
  </section>
  <section anchor="intro_definitions" title="General Definitions">
    <t>
      The following definitions provide an appropriate context for the reader.
      <list style='hanging'>
        <t hangText="Byte:" anchor="byte">
          In this document, a byte is an octet, i.e., a datum
          exactly 8 bits in length.
        </t>
        <t hangText="Client:" anchor="client_def">
          The client is the entity that accesses the NFS server's
          resources.  The client may be an application that contains
          the logic to access the NFS server directly.  The client
          may also be the traditional operating system client that
	  provides remote file system services for a set of applications.
        <vspace blankLines='1' />
          A client is uniquely identified by a client owner.
        <vspace blankLines='1' />
          With reference to byte-range locking, the client is also the entity that
          maintains a set of locks on behalf of one or more
          applications.  This client is responsible for crash or
          failure recovery for those locks it manages.
        <vspace blankLines='1' />
          Note that multiple clients may share the same transport and
          connection and
          multiple clients may exist on the same network node.
        </t>
        <t hangText="Client ID:">
          The client ID is a 64-bit quantity used as a unique, short-hand reference to
          a client-supplied verifier and client owner.  The server is
          responsible for supplying the client ID.
        </t>
        <t hangText="Client Owner:">
          The client owner is a unique string, opaque to the server,
          that identifies a client. Multiple network connections and source
          network addresses originating from those connections may share
          a client owner. The server is expected to treat requests
          from connections with the same client owner as coming from
          the same client.
        </t>

        <t hangText="File System:">
          The file system is the collection of objects on a server (as
          identified by the major identifier of a server
          owner, which is defined later in this section)
          that share the same fsid attribute (see <xref
          target="attrdef_fsid"/>).

        </t>
        <t hangText="Lease:">
          A lease is an interval of time defined by the server for which the
          client is irrevocably granted locks.  At the end of a
          lease period, locks may be revoked if the lease has not
          been extended.  A lock must be revoked if a conflicting
          lock has been granted after the lease interval.
        <vspace blankLines='1' />
          A server grants a client a single lease for all state.
        </t>
        <t hangText="Lock:">
          The term "lock" is used to refer to byte-range (in UNIX environments,
          also known as record)
          locks, share reservations, delegations, or layouts unless
          specifically stated otherwise.
        </t>

        <t hangText="Secret State Verifier (SSV):">
          The SSV is a unique secret key shared between a client and
          server.  The SSV serves as the secret key for an internal (that
          is, internal to NFSv4.1) Generic Security Services (GSS)
          mechanism (the SSV GSS mechanism;
          see <xref target="ssv_mech"/>).  The SSV GSS mechanism uses the
          SSV to compute message integrity code (MIC) and Wrap tokens.
          See <xref target="protect_state_change"/> for more details on how NFSv4.1 uses
          the SSV and the SSV GSS mechanism.

        </t>

        <t hangText="Server:">
          The Server is the entity responsible for coordinating
          client access to a set of file systems and is identified by a server
          owner. A server can span multiple network addresses.
        </t>
        <t hangText="Server Owner:">
          The server owner identifies the server to the client.
          The server owner consists of a major identifier and a minor identifier.
          When the client has two connections each to a peer with the
          same major identifier, the client assumes that both peers are
          the same server (the server namespace is the
          same via each connection) and that
          lock state is sharable across both connections. When each peer
          has both the same major and minor identifiers, the client
          assumes that each connection might be associable with the same session.
        </t>
        <t hangText="Stable Storage:">
          Stable storage is storage from which data stored by
          an NFSv4.1 server can be recovered without data
          loss from multiple power failures (including cascading
          power failures, that is, several power failures in quick
          succession), operating system failures, and/or hardware
          failure of components other than the storage medium itself
          (such as disk, nonvolatile RAM, flash memory, etc.).
        <vspace blankLines='1' />
          Some examples of stable storage that are allowable for an
          NFS server include:
          <list style='numbers'>
             <t>
               Media commit of data; that is, the modified data has
               been successfully written to the disk media, for
               example, the disk platter.
             </t>
             <t>
               An immediate reply disk drive with battery-backed,
               on-drive intermediate storage or uninterruptible power
               system (UPS).
             </t>
             <t>
               Server commit of data with battery-backed intermediate
               storage and recovery software.
             </t>
             <t>
               Cache commit with uninterruptible power system (UPS) and
               recovery software.
             </t>
           </list>
        </t>
        <t hangText="Stateid:">
          A stateid is a 128-bit quantity returned by a server that uniquely
          defines the open and locking states provided by the server
          for a specific open-owner or lock-owner/open-owner pair
          for a specific file and type of lock.
        </t>
        <t hangText="Verifier:">
          A verifier is a 64-bit quantity generated by the client that the server
          can use to determine if the client has restarted and lost
           all previous lock state.        
        </t>
      </list>
    </t>
  </section>
  <section anchor="feature-overview" 
           title="Overview of NFSv4.1 Features">
    <t>
      The major features of
      the NFSv4.1 protocol will be reviewed in brief.  This will be done
      to provide an appropriate context for both the reader who is familiar
      with the previous versions of the NFS protocol and the reader
      who is new to the NFS protocols.  For the reader new to the NFS protocols,
      there is still a set of fundamental knowledge that is expected.  
      The reader should be familiar with the External Data
      Representation (XDR) and Remote Procedure Call (RPC) protocols 
      as described in <xref target="RFC4506" /> and <xref target="RFC5531" />.
      A basic knowledge of file systems and distributed file systems is expected as well.
    </t>
    <t>
      In general, this specification of NFSv4.1 will
      not distinguish those features added in minor version
      1 from those present in the base protocol but
      will treat NFSv4.1 as a unified whole.  See <xref
      target="intro_differences" /> for a summary of
      the differences between NFSv4.0 and NFSv4.1.

    </t>
    <section anchor="rpc_and_security" title="RPC and Security">
      <t>
        As with previous versions of NFS, the External Data Representation
        (XDR) and Remote Procedure Call (RPC) mechanisms used for the NFSv4.1 protocol are those defined in 
        <xref target="RFC4506" /> and <xref target="RFC5531" />.  To
        meet end-to-end security requirements, the RPCSEC_GSS framework
        <xref target="RFC2203" /> is used to extend the basic 
        RPC security.  With the
        use of RPCSEC_GSS, various mechanisms can be provided to offer
        authentication, integrity, and privacy to the NFSv4 protocol.
        Kerberos V5 is used as described in 
        <xref target="RFC4121" /> to provide one
        security framework.
        With the use of
        RPCSEC_GSS, other mechanisms may also be specified and used for NFSv4.1 security.
      </t>
      <t>
        To enable in-band security negotiation, the NFSv4.1 protocol
        has operations that provide the client a method of
        querying the server about its policies regarding which security
        mechanisms must be used for access to the server's file system
        resources.  With this, the client can securely match the security
        mechanism that meets the policies specified at both the client and
        server.
      </t>
      <t>
	NFSv4.1 introduces parallel access (see <xref
	target="parallel_access"/>), which is
	called pNFS.  

The security framework
	described in this section is
	significantly modified by the
	introduction of pNFS (see <xref
	target="security_considerations_pnfs"/>),
	because data access is sometimes not over
	RPC.  The level of significance varies
	with the storage protocol (see <xref
	target="storage_protocol"/>) and can be as low as zero
        impact (see <xref target="file_security_considerations"/>).

      </t>
    </section>
    <section anchor="protocol_structure" 
             title="Protocol Structure">
      <section anchor="core_protocol" 
               title="Core Protocol">
        <t>
          Unlike NFSv3, which used a series of ancillary 
          protocols (e.g., NLM, NSM (Network Status Monitor), MOUNT), within all minor versions
          of NFSv4 a single RPC protocol is used to make requests to 
          the server.  

Facilities that had been separate protocols, such
          as locking, are now integrated within a single unified
          protocol.
        </t>
      </section>
      <section anchor="parallel_access" 
               title="Parallel Access">
        <t>
          Minor version 1 supports high-performance data access to a
          clustered server implementation by enabling a separation of
          metadata access and data access, with the latter done to 
          multiple servers in parallel.
        </t>
        <t>
          Such parallel data access is controlled by recallable 
          objects known as "layouts", which are integrated into the
          protocol locking model.  Clients direct requests for
          data access to a set of data servers specified by the
          layout via a data
          storage protocol which may be NFSv4.1 or may be another
          protocol.
        </t>

        <t>
	  Because the protocols used for parallel
	  data access are not necessarily
	  RPC-based, the RPC-based security model
	  (<xref target="rpc_and_security"/>) is
	  obviously impacted (see <xref
	  target="security_considerations_pnfs"/>).
	  The degree of impact varies with the
	  storage protocol (see <xref
	  target="storage_protocol"/>) used for
	  data access, and can be as low as zero (see 
	  <xref target="file_security_considerations"/>).

        </t>
      </section>
    </section>
    <section anchor="file_system_model" title="File System Model">
      <t>
        The general file system
        model used for the NFSv4.1 protocol 
        is the same as previous versions.  The server file system is 
        hierarchical with the regular files contained within being 
        treated as opaque byte
        streams.  In a slight departure, file and directory names are encoded
        with UTF-8 to deal with the basics of internationalization.
      </t>
      <t>
        The NFSv4.1 protocol does not require a separate 
        protocol to provide for the initial mapping between path 
        name and filehandle.  All file systems exported by a server
        are presented as a tree so that all file systems are reachable
        from a special per-server global root filehandle.  This
        allows LOOKUP operations to be used to perform functions
        previously provided by the MOUNT protocol.  The server
        provides any necessary pseudo file systems to bridge any
        gaps that arise due to unexported gaps between exported
        file systems.
      </t>
      <section anchor="intro_filehandles" title="Filehandles">
        <t>
          As in previous versions of the NFS protocol, opaque 
          filehandles are used to identify individual files
          and directories.  Lookup-type and create operations
          translate file and directory names to
          filehandles, which are then used to identify objects
          in subsequent operations.
        </t>
        <t>
          The NFSv4.1 protocol provides support for 
          persistent filehandles, guaranteed to be valid
          for the lifetime of the file system object designated.
          In addition, it provides support to servers to provide
          filehandles with more limited validity guarantees,
          called volatile filehandles. 
        </t>
      </section>
      <section anchor="intro_attributes" title="File Attributes">
        <t>
	  The NFSv4.1 protocol has a rich and extensible
	  file object attribute structure, which is divided
	  into REQUIRED, RECOMMENDED, and named attributes
	  (see <xref target="file_attributes"/>).

        </t>
        <t>
	  Several (but not all) of the REQUIRED attributes
	  are derived from the attributes of NFSv3 (see
	  the definition of the fattr3 data type in <xref
	  target="RFC1813"/>). An example of a REQUIRED
	  attribute is the file object's type (<xref
	  target="attrdef_type"/>) so that regular files
	  can be distinguished from directories (also known
	  as folders in some operating environments) and
	  other types of objects. REQUIRED attributes are
	  discussed in <xref
	  target="mandatory_attributes_intro"/>.

        </t>

        <t>
	  An example of three RECOMMENDED attributes are
	  acl, sacl, and dacl.  These attributes define an
	  Access Control List (ACL) on a file object
	  (<xref target="acl"/>).  An ACL provides
	  directory and file access control beyond the
	  model used in NFSv3.   The ACL definition allows
	  for specification of specific sets of permissions
	  for individual users and groups.  In addition,
	  ACL inheritance allows propagation of access
	  permissions and restrictions down a directory tree
	  as file system objects are created.  RECOMMENDED
	  attributes are discussed in <xref
	  target="recommended_attributes_intro"/>.


        </t>
        <t>
          A named attribute is an opaque byte stream that is associated 
          with a directory or file and referred to by a string name.  
          Named attributes are meant to be used by client applications 
          as a method to associate application-specific data with a 
          regular file or directory.  NFSv4.1 modifies named attributes
          relative to NFSv4.0 by tightening the allowed operations in
          order to prevent the development of non-interoperable
          implementations.  Named attributes are discussed in <xref target="named_attributes_intro" />.

        </t>
      </section>
      <section anchor="intro_ms_namespace" title="Multi-Server Namespace">
        <t>
          NFSv4.1 contains a number of features to allow
          implementation of namespaces that cross server boundaries
          and that allow and facilitate a non-disruptive transfer of 
          support for individual file systems between servers.  They 
          are all based upon attributes that allow one file system to
          specify alternate or new locations for that file system.   
        </t>
        <t>
          These attributes may be used together with the concept
          of absent file systems, which provide specifications
          for additional locations but no actual file system 
          content.  This allows a number of important facilities:
          <list style="symbols">
            <t>
              Location attributes may be used with absent file systems
              to implement referrals whereby one server may direct the
              client to a file system provided by another server.  This
              allows extensive multi-server namespaces to be constructed.
            </t>
            <t>
              Location attributes may be provided for present file systems
              to provide the locations of alternate file system instances
              or replicas to be used in the event that the current 
              file system instance becomes unavailable.
            </t>
            <t>
              Location attributes may be provided when a previously
              present file system becomes absent.  This allows 
              non-disruptive migration of file systems to alternate
              servers.
            </t>
          </list>
        </t>
      </section>
    </section>
    <section anchor="intro_locking" title="Locking Facilities">
      <t>
        As mentioned previously, NFSv4.1 is a single protocol that
        includes locking facilities.  These locking facilities 
        include support for many types of locks including a number
        of sorts of recallable locks.  Recallable locks such as
        delegations allow the client to be assured that certain 
        events will not occur so long as that lock is held.  When
        circumstances change, the lock is recalled 
        via a callback request.  The assurances provided by 
        delegations allow more extensive caching to be done safely
        when circumstances allow it.
      </t>
      <t>
	The types of locks are:
      </t>
      <t>
        <list style="symbols">
          <t>
            Share reservations as established by OPEN operations.
          </t>
          <t>
            Byte-range locks.
          </t>
          <t>
            File delegations, which are recallable locks that assure
            the holder that inconsistent opens and file changes cannot
            occur so long as the delegation is held.  
          </t>
          <t>
            Directory delegations, which are recallable locks
            that assure the holder that inconsistent directory 
            modifications cannot occur so long as the delegation 
            is held.
          </t>
          <t>
            Layouts, which are recallable objects that assure the
            holder that direct access to the file data may be 
            performed directly by the client and that no change
            to the data's location that is inconsistent with that access
            may be made so long as the layout is held.  
          </t>
        </list>
      </t>
      <t>
        All locks for a given client are tied together under a
        single client-wide lease.  All requests made on sessions
        associated with the client renew that lease.  When the client's
        lease
        is not promptly renewed, the client's locks are subject to revocation.
        In the event of server restart, clients have the
        opportunity to safely reclaim their locks within a special
        grace period.
      </t>
    </section>
  </section>
  <section anchor="intro_differences" title="Differences from NFSv4.0">
    <t>
      The following summarizes the major differences between minor version 
      1 and the base protocol:
      <list style="symbols">
        <t>
          Implementation of the sessions model (<xref target="Session"/>).
        </t>
        <t>
          Parallel access to data (<xref target="pnfs"/>).
        </t>
        <t>
          Addition of the RECLAIM_COMPLETE operation to better structure
          the lock reclamation process (<xref target="OP_RECLAIM_COMPLETE"/>).
        </t>

        <t>
         Enhanced delegation support as follows.

         <list style="symbols">
	 <t>
	   Delegations on directories and other
	   file types in addition to regular files (<xref
	   target="OP_GET_DIR_DELEGATION"/>, <xref
	   target="OP_WANT_DELEGATION"/>).

	 </t>
	 <t>
	   Operations to optimize acquisition of recalled
	   or denied delegations (<xref
	   target="OP_WANT_DELEGATION"/>, <xref
	   target="OP_CB_PUSH_DELEG"/>, <xref
	   target="OP_CB_RECALLABLE_OBJ_AVAIL"/>).

	 </t>

	 <t>
	   Notifications of changes to files and directories
	   (<xref target="OP_GET_DIR_DELEGATION"/>, <xref
	   target="OP_CB_NOTIFY"/>).

	 </t>

	 <t>
	   A method to allow a server to indicate that it is
	   recalling one or more delegations for resource
	   management reasons, and thus a method to allow
	   the client to pick which delegations to return
	   (<xref target="OP_CB_RECALL_ANY"/>).

        </t>

        </list>

        </t>

        <t>
	  Attributes can be set atomically
	  during exclusive file create via the OPEN operation
	  (see the new EXCLUSIVE4_1 creation method in
	  <xref target="OP_OPEN"/>).

        </t>
        <t>
	  Open files can be preserved if removed and the
	  hard link count ("hard link" is defined in
	  an <xref target="hardlink">Open Group</xref> standard) goes
	  to zero, thus obviating the
	  need for clients to rename deleted files to
	  partially hidden names -- colloquially called
	  "silly rename" (see the new
	  OPEN4_RESULT_PRESERVE_UNLINKED reply flag in
	  <xref target="OP_OPEN"/>).

        </t>
        <t>
	  Improved compatibility with Microsoft Windows for
	  Access Control Lists (<xref
	  target="attrdef_sacl"/>, <xref
	  target="attrdef_dacl"/>, <xref
	  target="auto_inherit"/>).

        </t>
        <t>
          Data retention (<xref target="retention"/>).

        </t>
        <t>
          Identification of the implementation of the NFS client
          and server (<xref target="OP_EXCHANGE_ID"/>).

        </t>

        <t>
	  Support for notification of the availability of
	  byte-range locks (see the new
	  OPEN4_RESULT_MAY_NOTIFY_LOCK reply flag in <xref
	  target="OP_OPEN"/> and see <xref
	  target="OP_CB_NOTIFY_LOCK"/>).

        </t>

        <t>
          In NFSv4.1, LIPKEY and SPKM-3 are not required security mechanisms
          <xref target="RFC2847"/>.
        </t>
         

      </list>
    </t>
  </section>
</section>


<section anchor="Core_Infrastructure" title="Core Infrastructure">

 <section anchor="Introduction" title="Introduction">
 <t>
  NFSv4.1 relies on core infrastructure common to nearly
  every operation. This core infrastructure is described in the remainder
  of this section.
 </t>
 </section> <!-- Introduction -->

 <section anchor="RPC_and_XDR" title="RPC and XDR">
 <t>
  The NFSv4.1 protocol is a Remote Procedure Call (RPC)
  application that uses RPC version 2 and the corresponding eXternal
  Data Representation (XDR) as defined in
  <xref target="RFC5531"/> and
  <xref target="RFC4506"/>.
 </t>

  <section anchor="RPC-based_Security" title="RPC-Based Security">
  <t>
   Previous NFS versions have been thought of as having a
   host-based authentication model, where the NFS server
   authenticates the NFS client, and trusts the client
   to authenticate all users.
   Actually, NFS has always depended on RPC for
   authentication. One of the first forms of RPC authentication,
   AUTH_SYS, had no strong authentication and
   required a host-based authentication
   approach. NFSv4.1 also depends on RPC for basic security
   services and mandates RPC support for a user-based
   authentication model. The user-based authentication
   model has user principals authenticated by a server, and
   in turn the server authenticated by user principals.
   RPC provides some basic security services that are used
   by NFSv4.1.
  </t>

   <section anchor="RPC_Security_Flavors" title="RPC Security Flavors">
    <t>
     As described in Section 7.2 ("Authentication") of <xref target="RFC5531"/>,
     RPC security is encapsulated in the RPC header, via a
     security or authentication flavor, and information
     specific to the specified security flavor.
     Every RPC header conveys information used to identify
     and authenticate a client and server. As discussed in
     <xref target="RPCSEC_GSS_and_Security_Services" />,
     some security flavors provide additional security
     services.
    </t>
    <t>
     NFSv4.1 clients and servers MUST implement RPCSEC_GSS.
     (This requirement to implement is not a requirement to
     use.)  Other flavors, such as AUTH_NONE and
     AUTH_SYS, MAY be implemented as well.
    </t>

    <section anchor="RPCSEC_GSS_and_Security_Services" title="RPCSEC_GSS and Security Services">
     <t>
      RPCSEC_GSS <xref target="RFC2203" /> uses the
      functionality of GSS-API <xref target="RFC2743"/>.  This allows for the
      use of various security mechanisms by the RPC layer
      without the additional implementation overhead of
      adding RPC security flavors.
     </t>

     <section anchor="Authentication_Integrity_Privacy" title="Identification, Authentication, Integrity, Privacy">
     <t>
      Via the GSS-API, RPCSEC_GSS can be used to identify and authenticate
      users on clients to servers, and servers to users. It can also
      perform integrity checking on the entire RPC message, including
      the RPC header, and on the arguments or results. Finally, privacy,
      usually via encryption, is a service available with RPCSEC_GSS.
      Privacy is performed on the arguments and results. Note that
      if privacy is selected, integrity, authentication, and identification
      are enabled.
      If privacy is not selected, but integrity is selected, authentication
      and identification are enabled. If integrity and privacy are not
      selected, but authentication is enabled,
      identification is enabled. RPCSEC_GSS does not provide identification as
      a separate service.
     </t>
     <t>
      Although GSS-API has an authentication service distinct from its
      privacy and integrity services, GSS-API's
      authentication service is not used for RPCSEC_GSS's authentication
      service. Instead, each RPC request and response header is
      integrity protected with the GSS-API integrity service, and
      this allows RPCSEC_GSS to offer per-RPC authentication and
      identity. See <xref target="RFC2203" /> for more information.
     </t>
     <t>
      NFSv4.1 client and servers MUST support RPCSEC_GSS's integrity and authentication
      service. NFSv4.1 servers MUST support RPCSEC_GSS's privacy service.
      NFSv4.1 clients SHOULD support  RPCSEC_GSS's privacy service.

     </t>
     </section> <!-- Identity, Authentication, Integrity, Privacy -->

     <section anchor="security_mechs" title="Security Mechanisms for NFSv4.1">
     <t>
      RPCSEC_GSS, via GSS-API, normalizes access to mechanisms that
      provide security services. Therefore, NFSv4.1 clients and servers
      MUST support the Kerberos V5 security mechanism.
     </t>
     <t>
      The use of RPCSEC_GSS requires selection of mechanism,
      quality of protection (QOP), and service (authentication,
      integrity, privacy).  For the mandated security mechanisms,
      NFSv4.1 specifies that a QOP of zero is used, leaving it up 
      to the mechanism or the mechanism's configuration to map
      QOP zero to
      an appropriate level of protection.
      Each mandated mechanism specifies a minimum set of cryptographic
      algorithms for implementing integrity and privacy. NFSv4.1
      clients and servers MUST be implemented on operating environments
      that comply with the REQUIRED cryptographic algorithms
      of each REQUIRED mechanism.
     </t>

      <section anchor="kerberosv5" title="Kerberos V5">
      <t>
       The Kerberos V5 GSS-API mechanism as described in
       <xref target="RFC4121"/> MUST be implemented with
       the RPCSEC_GSS services as specified in the following
       table:
      </t>
      <t>
      <figure>
      <artwork>
   column descriptions:
   1 == number of pseudo flavor
   2 == name of pseudo flavor
   3 == mechanism's OID
   4 == RPCSEC_GSS service
   5 == NFSv4.1 clients MUST support
   6 == NFSv4.1 servers MUST support

   1      2        3                    4                     5   6
   ------------------------------------------------------------------
   390003 krb5     1.2.840.113554.1.2.2 rpc_gss_svc_none      yes yes
   390004 krb5i    1.2.840.113554.1.2.2 rpc_gss_svc_integrity yes yes
   390005 krb5p    1.2.840.113554.1.2.2 rpc_gss_svc_privacy    no yes
      </artwork>
      </figure>
      </t>
      <t>
       Note that the number and name of the pseudo flavor
       are presented here as a mapping aid to the implementor.
       Because the NFSv4.1 protocol includes a method to negotiate
       security and it understands the GSS-API mechanism, the pseudo flavor
       is not needed.  The pseudo flavor is needed for the NFSv3 since the security negotiation is done via
       the MOUNT protocol as described in <xref target="RFC2623"/>.
      </t>
      <t>
       At the time NFSv4.1 was specified, the Advanced Encryption
       Standard (AES) with HMAC-SHA1 was
       a REQUIRED algorithm set for Kerberos V5. In contrast, when
       NFSv4.0 was specified, weaker algorithm sets were REQUIRED for
       Kerberos V5, and were REQUIRED in the NFSv4.0 specification, because
       the Kerberos V5 specification at the time did not specify stronger
       algorithms.
       The NFSv4.1 specification does not specify REQUIRED algorithms
       for Kerberos V5, and instead, the implementor is expected
       to track the evolution of the Kerberos V5 standard if and when
       stronger algorithms are specified.
       
       
      </t>
        <section anchor="krb5_sec_consider"
 title="Security Considerations for Cryptographic Algorithms in Kerberos V5">
        <t>
          When deploying NFSv4.1, the strength of the security achieved depends
          on the existing Kerberos V5 infrastructure. The algorithms
          of Kerberos V5 are not directly exposed to or selectable by the
          client or server, so there is some due diligence required by
          the user of NFSv4.1 to ensure that security is acceptable 
          where needed.
        </t>
        </section>
        
      </section> <!-- Kerberos V5  -->

      </section> <!-- Security mechanisms for NFSv4.1  -->

     <section anchor="GSS_Server_Principal" title="GSS Server Principal">
     <t>
      Regardless of what security mechanism under RPCSEC_GSS
      is being used, the NFS server MUST identify itself
      in GSS-API via a GSS_C_NT_HOSTBASED_SERVICE name type.
      GSS_C_NT_HOSTBASED_SERVICE names are of the form:
     <figure>
     <artwork>
     service@hostname
     </artwork>
     </figure>
     </t>
     <t>
      For NFS, the "service" element is
     <figure>
     <artwork>
     nfs
     </artwork>
     </figure>
     </t>
     <t>
      Implementations of security mechanisms will convert
      nfs@hostname to various different forms.  For Kerberos
      V5, the following form is RECOMMENDED:
     <figure>
     <artwork>
     nfs/hostname
     </artwork>
     </figure>
     </t>
     </section> <!-- GSS Server Principal -->
    </section> <!-- RPCSEC_GSS and Security Services -->
   </section> <!-- RPC Security Flavors -->
  </section> <!-- RPC-based Security -->
 </section> <!-- RPC and XDR -->

 <section anchor="COMPOUND_and_CB_COMPOUND" title="COMPOUND and CB_COMPOUND">
 <t>
   A significant departure from the versions of the NFS
   protocol before NFSv4 is the introduction of the 
   COMPOUND procedure.  For the NFSv4 protocol, 
   in all minor versions, there are exactly two RPC procedures, 
   NULL and COMPOUND.  The COMPOUND procedure is defined 
   as a series of individual operations and these operations 
   perform the sorts of functions performed by traditional 
   NFS procedures.
 </t>
 <t>
   The operations combined within a COMPOUND
   request are evaluated in order by the server, without
   any atomicity guarantees.  A limited set of facilities
   exist to pass results from one operation to another.  Once an 
   operation returns a failing result, the evaluation ends 
   and the results of all
   evaluated operations are returned to the client.
 </t>
 <t>
   With the use of the COMPOUND procedure, the client is able to build
   simple or complex requests.  These COMPOUND requests allow for a
   reduction in the number of RPCs needed for logical file system
   operations.  For example, multi-component look up requests can
   be constructed by combining multiple LOOKUP operations.  Those
   can be further combined with operations such as GETATTR, READDIR,
   or OPEN plus READ to do more complicated sets of operation without
   incurring additional latency.
 </t>
 <t>
   NFSv4.1 also contains a considerable set of
   callback operations in which the server makes an RPC
   directed at the client.  Callback RPCs have a similar
   structure to that of the normal server requests.
   In all minor versions of the NFSv4 protocol,
   there are two callback RPC procedures:
   CB_NULL and CB_COMPOUND.  The CB_COMPOUND procedure is defined 
   in an analogous fashion to that of COMPOUND 
   with its own set of callback operations.
 </t>
 <t>
   The addition of new server and callback operations within the 
   COMPOUND and CB_COMPOUND request
   framework provides a means of extending the protocol in
   subsequent minor versions.
 </t>
 <t>
   Except for a small number of operations needed for session
   creation, server requests and callback requests are performed
   within the context of a session.  Sessions provide a client
   context for every request and support robust reply 
   protection for non-idempotent requests.
 </t>
 </section> <!-- COMPOUND and CB_COMPOUND -->

 <section anchor="Client_Identifiers"
  title="Client Identifiers and Client Owners">
  <t>
    For each operation that obtains or depends on locking state, the 
    specific client needs to be identifiable by the server.

  </t>
  <t>
    Each distinct client instance is represented
    by a client ID.  A client ID is a 64-bit identifier
    representing a specific client at a given time.
    The client ID is changed whenever the client re-initializes,
    and may change when the server re-initializes.
    Client IDs are used to support lock identification
    and crash recovery.

  </t>
  <t>
    During steady state operation,
    the client ID associated with each operation
    is derived from the session (see <xref target="Session"
    />) on which the operation is sent. A session is associated with
    a client ID when the session is created. 
  </t>
  <t>
    Unlike NFSv4.0, the only NFSv4.1 operations possible before a
    client ID is established are those needed to
    establish the client ID.
  </t>
  <t>
    A sequence of an EXCHANGE_ID operation followed by a 
    CREATE_SESSION operation using that client ID 
    (eir_clientid as returned from EXCHANGE_ID)
    is required to establish and confirm the
    client ID on the server.  Establishment of identification by a
    new incarnation of the client also has the effect of immediately
    releasing any locking state that a previous incarnation of that 
    same client might have had on the server.  Such released state 
    would include all byte-range lock, share reservation, layout state, and -- where the server supports neither the CLAIM_DELEGATE_PREV nor CLAIM_DELEG_CUR_FH claim types -- all delegation state associated with the same client with the same
    identity. For discussion of delegation state recovery, see
    <xref target="delegation_recovery" />. For discussion of layout state
    recovery, see <xref target="pnfs_client_recovery" />.
  </t>
  <t>
    Releasing such state requires that the server be able to determine
    that one client instance is the successor of another.  Where this
    cannot be done, for any of a number of reasons, the locking state
    will remain for a time subject to lease expiration 
    (see <xref target="lease_renewal" />)
    and the new client will need to wait for
    such state to be removed, if it makes conflicting lock requests. 
  </t>
  <t>
    Client identification is encapsulated in the following client owner
    data type:
  </t>
  <t>
<figure>
 <artwork>
struct client_owner4 {
        verifier4       co_verifier;
        opaque          co_ownerid&lt;NFS4_OPAQUE_LIMIT>;
};
 </artwork>
</figure>
  </t>
  <t>
    The first field, co_verifier, is a client incarnation
    verifier.  The server will start the process of
    canceling the client's leased state if co_verifier
    is different than what the server has previously
    recorded for the identified client (as specified in
    the co_ownerid field).

  </t>
  <t>
    The second field, co_ownerid, is a variable length string that uniquely defines
    the client so that subsequent instances of the same client bear the
    same co_ownerid with a different verifier.
  </t>
  <t>
    There are several considerations for how the client
    generates the co_ownerid string:
    <list style='symbols'>
      <t>
        The string should be unique so that multiple clients
        do not present the same string. The consequences of
        two clients presenting the same string range from
        one client getting an error to one client having its
        leased state abruptly and unexpectedly cancelled.
      </t>
      <t> 
        The string should be selected so that subsequent incarnations
        (e.g., restarts) of the same client cause the client to present 
        the same string. The implementor 
        is cautioned from an approach that requires the string to 
        be recorded in a local file because this precludes the use
        of the implementation in an environment where there is no local
        disk and all file access is from an NFSv4.1 server.
      </t>
      <t>
        The string should be the same for each server network address that
        the client accesses.
        This way, if a server has multiple interfaces, the client
        can trunk traffic over multiple network paths
        as described in <xref target="Trunking" />.
        (Note: the precise opposite was advised in the NFSv4.0
        specification <xref target="RFC3530" />.) 
      </t>
      <t>
        The algorithm for generating the string should not
        assume that the client's network address will not
        change, unless the client implementation knows it
        is using statically assigned network addresses.
        This includes changes between client incarnations
        and even changes while the client is still running
        in its current incarnation.  Thus, with dynamic
        address assignment, if the
        client includes just the client's network address
        in the co_ownerid string, there is a real risk
        that after the
        client gives up the network address, another
        client, using a similar algorithm for generating
        the co_ownerid string, would generate a conflicting
        co_ownerid string.

      </t>
    </list>
  </t>
  <t>
    Given the above considerations, an example of a well-generated co_ownerid
    string is one that includes:
  </t>
  <t>
    <list style='symbols'>
      <t>
        If applicable, the client's statically assigned network address.
      </t>
      <t>
        Additional information that tends to be unique, such as one or more
        of:
        <list style='symbols'>
          <t>
            The client machine's serial number (for privacy reasons, it is best
            to perform some one-way function on the serial number).
          </t>
          <t>
            A Media Access Control (MAC) address (again, a one-way function should be performed).
          </t>
          <t>
            The timestamp of when the NFSv4.1 software was first installed
            on the client (though this is subject to the previously mentioned
            caution about using information that is stored in a file, because the
            file might only be accessible over NFSv4.1).
          </t>
          <t>
            A true random number. However, since this number ought to be the same
            between client incarnations, this shares the same problem as that of
            using the timestamp of the software installation.
          </t>
        </list>
      </t>
      <t>
        For a user-level NFSv4.1 client, it should contain additional
        information to distinguish the client from other user-level clients
        running on the same host, such as a process identifier or other unique
        sequence.
      </t>
    </list>
  </t>
  <t>
    The client ID is assigned by the server (the eir_clientid result from EXCHANGE_ID)
    and should be chosen so that it will not
    conflict with a client ID previously assigned by the
    server.  This applies across server restarts.
   </t>
   <t>
    In the event of a server restart, a client may find
    out that its current client ID is no longer valid when
    it receives an NFS4ERR_STALE_CLIENTID error.  The precise
    circumstances depend on the characteristics of the
    sessions involved, specifically whether the session is
    persistent (see <xref target="Persistence" />), but in
    each case the client will receive this error when it attempts
    to establish a new session with the existing client ID and
    receives the error NFS4ERR_STALE_CLIENTID, indicating that a new
    client ID needs to be obtained via EXCHANGE_ID and the new session
    established with that client ID.

  </t>
  <t>
    When a session is not persistent, the client will find out that
    it needs to create a new session as a result of getting an 
    NFS4ERR_BADSESSION, since the session in question was lost
    as part of a server restart.  When the existing client ID is 
    presented to a server as part of creating a session
    and that client ID is not recognized, as would happen after a server
    restart, the server will reject the request with the error
    NFS4ERR_STALE_CLIENTID.  
  </t>
  <t>
    In the case of the session being persistent, the
    client will re-establish communication using the
    existing session after the restart.  This session
    will be associated with the existing client ID but
    may only be used to retransmit operations that the
    client previously transmitted and did not see replies
    to. Replies to operations that the server previously performed
    will come from the reply cache; otherwise,
    NFS4ERR_DEADSESSION will be returned.
    Hence, such a session is referred to as "dead". In this situation,
    in order to perform new operations, the client needs to 
    establish a new session.  If an attempt is made to 
    establish this new session with the existing client ID,
    the server will reject the request with 
    NFS4ERR_STALE_CLIENTID.
  </t>
  <t>
    When NFS4ERR_STALE_CLIENTID is received in either of
    these situations, the client needs to obtain a
    new client ID by use of the EXCHANGE_ID operation, then 
    use that client ID as the basis of a new session, and
    then proceed to
    any other necessary recovery for the server restart case (see 
    <xref target="server_failure" />). 
  </t>
  <t>
    See the descriptions of EXCHANGE_ID 
    (<xref target="OP_EXCHANGE_ID" />) and CREATE_SESSION
    (<xref target="OP_CREATE_SESSION" />) for a complete
    specification of these operations.
  </t>
  <section title="Upgrade from NFSv4.0 to NFSv4.1" >
  <t>
    To facilitate upgrade from NFSv4.0 to NFSv4.1, a server
    may compare a value of data type client_owner4 in an EXCHANGE_ID with a
    value of data type nfs_client_id4 that was established using the SETCLIENTID operation of
    NFSv4.0. A server that does so will allow
    an upgraded client to avoid waiting
    until the lease (i.e., the lease established by the NFSv4.0 instance
    client) expires.
    This requires that the value of data type client_owner4 be constructed
    the same way as the value of data type nfs_client_id4.  If the latter's
    contents included the server's network address (per the
    recommendations of the NFSv4.0 specification <xref target="RFC3530" />), and
    the NFSv4.1 client does not wish to use a client
    ID that prevents trunking, it should send two
    EXCHANGE_ID operations.  The first EXCHANGE_ID will
    have a client_owner4 equal to the nfs_client_id4.
    This will clear the state created by the NFSv4.0
    client. The second EXCHANGE_ID will not have the
    server's network address. The state created for the
    second EXCHANGE_ID will not have to wait for lease
    expiration, because there will be no state to expire.

  </t>
  </section>

   <section title="Server Release of Client ID" >
   <t>
     NFSv4.1 introduces a new operation called 
     DESTROY_CLIENTID (<xref target="OP_DESTROY_CLIENTID" />), 
     which the client SHOULD use to destroy a client ID it
     no longer needs. This permits graceful, bilateral release of
     a client ID. The operation cannot be used if there are sessions
     associated with the client ID, or state with an unexpired lease.
   </t>
   <t>
     If the server determines that the client holds no associated state
     for its client ID (associated state includes unrevoked sessions,
     opens, locks, delegations, layouts, and wants), the server MAY
     choose to unilaterally release the client ID in order to
     conserve resources.

     If the client
     contacts the server after this release, the server
     MUST ensure that the client receives the appropriate error
     so that it will use the EXCHANGE_ID/CREATE_SESSION
     sequence to establish a new client ID.
     The server ought to be very hesitant to
     release a client ID since the resulting work on the
     client to recover from such an event will be the same
     burden as if the server had failed and restarted.
     Typically, a server would not release a client ID
     unless there had been no activity from that client
     for many minutes.  As long as there are sessions,
     opens, locks, delegations, layouts, or wants, the
     server MUST NOT release the client ID. See <xref
     target="loss_of_session" /> for discussion on
     releasing inactive sessions.

   </t>
   </section> <!-- Server Release of Client ID -->
   <section title="Resolving Client Owner Conflicts" anchor="cowner_conflicts">
   <t>
     When the server gets an EXCHANGE_ID for a client owner that
     currently has no state, or that has state but the lease has expired,
     the server MUST allow the
     EXCHANGE_ID and confirm the new client ID if followed by the
     appropriate CREATE_SESSION.
   </t>
   <t>
     When the server gets an EXCHANGE_ID for a 
     new incarnation of a client owner that
     currently has an old incarnation with state and an unexpired lease, the
     server is allowed to dispose of the state of the
     previous incarnation of the client owner if
     one of the following is true:

     <list style="symbols">
     <t>
       The principal that created the client ID for the client owner
       is the same as the principal that is sending the EXCHANGE_ID operation.
       Note that if the client ID was created with
       SP4_MACH_CRED state protection (<xref target="OP_EXCHANGE_ID" />),
       the principal MUST be based on RPCSEC_GSS authentication,
       the RPCSEC_GSS service used MUST be integrity or
       privacy, and the
       same GSS mechanism and principal
       MUST be used as that used when the client ID
       was created.
     </t>
     <t>
       The client ID was established with SP4_SSV
       protection (<xref target="OP_EXCHANGE_ID" />,

    <xref target="protect_state_change" />)

       and the client sends the EXCHANGE_ID with the
       security flavor set to RPCSEC_GSS using the GSS
       SSV mechanism (<xref target="ssv_mech" />).

     </t>
     <t>
       The client ID was established with SP4_SSV
       protection, and under the conditions described herein,
       the EXCHANGE_ID was sent with SP4_MACH_CRED state protection.
       Because the SSV might not persist
       across client and server restart, and because
       the first time a client sends EXCHANGE_ID to
       a server it does not have an SSV, the client
       MAY send the subsequent EXCHANGE_ID without
       an SSV RPCSEC_GSS handle.  Instead, as with
       SP4_MACH_CRED protection, the principal MUST be
       based on RPCSEC_GSS authentication, the RPCSEC_GSS
       service used MUST be integrity or privacy, and the
       same GSS mechanism and principal MUST be used as
       that used when the client ID was created.

     </t>
     </list>
     If none of the above situations apply, the server
     MUST return NFS4ERR_CLID_INUSE.

    </t>
    <t>
     If the server accepts the principal and co_ownerid
     as matching that which created the client ID, and
     the co_verifier in the EXCHANGE_ID differs from the
     co_verifier used when the client ID was created,
     then after the server receives a CREATE_SESSION that
     confirms the client ID, the server deletes state.

     If the co_verifier values are the same (e.g., the
     client either is updating properties of the client ID
     (<xref target="OP_EXCHANGE_ID" />) or
     is attempting trunking (<xref target="Trunking" />),
     the server MUST NOT delete state.

   </t>

   </section> <!-- Handling Client Owner Conflicts -->
 </section> <!-- Client Identifiers -->
 <section anchor="Server_Owners" title="Server Owners">
 <t>
  The server owner is similar to a client owner
  (<xref target="Client_Identifiers" />), but unlike the
  client owner, there is no shorthand server ID.
  The server owner is defined in the following data type:
  </t>
  <t>
<figure>
 <artwork>
struct server_owner4 {
 uint64_t       so_minor_id;
 opaque         so_major_id&lt;NFS4_OPAQUE_LIMIT>;
};
 </artwork>
</figure>
  </t>
  <t>
   The server owner is returned from
   EXCHANGE_ID. When the so_major_id fields are the same in
   two EXCHANGE_ID results, the connections that each EXCHANGE_ID
   were sent over can be assumed to address the same server
   (as defined in <xref target="intro_definitions" />). If
   the so_minor_id fields are also the same, then not only
   do both connections connect to the same server, but the
   session can be shared across both
   connections. The reader is cautioned that multiple
   servers may deliberately or accidentally claim to have
   the same so_major_id or so_major_id/so_minor_id; the
   reader should examine Sections <xref target="Trunking" format="counter" /> and
   <xref target="OP_EXCHANGE_ID" format="counter" /> in order to avoid
   acting on falsely matching server owner values.
  </t>
  <t>
   The considerations for generating a so_major_id are
   similar to that for generating a co_ownerid string (see
   <xref target="Client_Identifiers" />). The consequences
   of two servers generating conflicting so_major_id values
   are less dire than they are for co_ownerid conflicts
   because the client can use RPCSEC_GSS to compare the
   authenticity of each server
   (see <xref target="Trunking" />).
  </t>
 </section> <!-- Server Owners -->

 <section anchor="Security_Service_Negotiation" title="Security Service Negotiation">
 <t>
    With the NFSv4.1 server potentially offering
    multiple security mechanisms, the client needs a method
    to determine or negotiate which mechanism is to be
    used for its communication with the server.  The NFS
    server may have multiple points within its file system
    namespace that are available for use by NFS clients.
    These points can be considered security policy boundaries,
    and, in some NFS implementations, are tied to NFS export points.
    In turn, the NFS server may be configured such that each
    of these security policy boundaries may have different or multiple
    security mechanisms in use.
 </t>
 <t>
    The security negotiation between client and server
    SHOULD be done with a secure channel to eliminate
    the possibility of a third party intercepting the
    negotiation sequence and forcing the client and server
    to choose a lower level of security than required or
    desired.  See 
    <xref target="securityconsider" /> for further discussion.
 </t>

  <section anchor="NFSv4_Security_Tuples" title="NFSv4.1 Security Tuples">
  <t>
   An NFS server can assign one or more "security tuples" to each
   security policy boundary in its namespace. Each security tuple
   consists of a security flavor
   (see <xref target="RPC_Security_Flavors" />) and, if the flavor
   is RPCSEC_GSS, a GSS-API mechanism Object Identifier (OID), a GSS-API quality of
   protection, and an RPCSEC_GSS service. 
  </t>
  </section> <!-- NFSv4.1 Security Tuples -->

  <section anchor="SECINFO_and_SECINFO_NO_NAME" title="SECINFO and SECINFO_NO_NAME">
  <t>
   The SECINFO and SECINFO_NO_NAME operations allow the client to
   determine, on a per-filehandle basis, what security tuple is to be
   used for server access.  In general, the client will not have to
   use either operation except during initial communication with the
   server or when the client crosses security policy boundaries at the
   server.  However, the server's policies may also change at any time
   and force the client to negotiate a new security tuple.
  </t>
  <t>
   Where the use of different security tuples would affect the type of
   access that would be allowed if a request was sent over the same
   connection used for the SECINFO or SECINFO_NO_NAME operation
   (e.g., read-only vs. read-write) access, security tuples that allow
   greater access should be presented first.  Where the general level
   of access is the same and different security flavors limit the
   range of principals whose privileges are recognized (e.g., allowing
   or disallowing root access), flavors supporting the greatest range
   of principals should be listed first.
  </t>
  </section> <!-- SECINFO and SECINFO_NO_NAME -->

  <section anchor="Security_Error" title="Security Error">
  <t>
   Based on the assumption that each NFSv4.1 client
   and server MUST support a minimum set of security (i.e.,
   Kerberos V5 under RPCSEC_GSS),
   the NFS client will initiate file access to the server
   with one of the minimal security tuples.  During
   communication with the server, the client may receive an
   NFS error of NFS4ERR_WRONGSEC.  This error allows the
   server to notify the client that the security tuple
   currently being used contravenes the server's
   security policy. The client is then responsible for
   determining (see <xref target="using_secinfo" />) what
   security tuples are available at the server and choosing
   one that is appropriate for the client.

  </t>

  <section anchor="using_secinfo" title="Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME">
  <t>
   This section explains the mechanics of NFSv4.1 security negotiation.
  </t>

  <section anchor="putfh_series" title="Put Filehandle Operations">

  <t>

   The term "put filehandle operation" refers to
   PUTROOTFH, PUTPUBFH, PUTFH, and RESTOREFH. Each of the subsections
   herein describes how the server handles a subseries of operations
   that starts with a put filehandle operation.
  </t>

   <section anchor="PUTFHplusSAVEFH"
    title="Put Filehandle Operation + SAVEFH">
   <t>
    The client is saving a filehandle for a future
    RESTOREFH, LINK, or RENAME.  SAVEFH MUST NOT
    return NFS4ERR_WRONGSEC. To determine whether or not the put
    filehandle operation returns NFS4ERR_WRONGSEC,
    the server implementation pretends SAVEFH is not in
    the series of operations and examines which of the
    situations described in the other subsections of <xref
    target="putfh_series"/> apply.

   </t>
   </section> <!-- Put Filehandle Operation + SAVEFH -->
   <section anchor="PUTFHplusPUTFH"
    title="Two or More Put Filehandle Operations">
   <t>
    For a series of N put filehandle operations, the server
    MUST NOT return NFS4ERR_WRONGSEC to the first N-1 put
    filehandle operations. 

The Nth put filehandle operation
    is handled as if it is the first in a subseries of
    operations.
    For example, if the
    server received a COMPOUND request with this series of
    operations -- PUTFH, PUTROOTFH, LOOKUP -- then the
    PUTFH operation is ignored for NFS4ERR_WRONGSEC purposes, and the
    PUTROOTFH, LOOKUP subseries is processed as according
    to <xref target="PUTFHplusLOOKUP"/>.
   </t>
   </section> <!-- PUTFH + PUTFH -->
   <section anchor="PUTFHplusLOOKUP"
    title="Put Filehandle Operation + LOOKUP (or OPEN of an Existing Name)">
   <t>
    This situation also applies to a put filehandle operation followed
    by a LOOKUP or an OPEN operation that specifies an existing component name.
   </t>
   <t>
    In this situation, the client is potentially crossing
    a security policy boundary, and the set of security tuples
    the parent directory supports may differ from those of
    the child.
    The server implementation may decide whether to impose
    any restrictions on security policy administration.
    There are at least three approaches (sec_policy_child is
    the tuple set of the child export, sec_policy_parent is
    that of the parent).
   </t>
   <t>
   <list style="format (%c)">
   <t>
     sec_policy_child &lt;= sec_policy_parent (&lt;= for subset).  This
     means that the set of security tuples specified on the
     security policy of a child directory is always a subset
     of its parent directory.
   </t>
   <t>
    sec_policy_child ^ sec_policy_parent != {} (^ for intersection, {}
    for the empty set). This means that the set of security tuples specified
    on the security policy of a child directory always has a non-empty intersection
    with that of the parent.
   </t>
   <t>
    sec_policy_child ^ sec_policy_parent == {}.  This means that the
    set of security tuples specified on the security policy of a child directory
    may not intersect with that of the parent. In other words, there
    are no restrictions on how the system administrator may
    set up these tuples.
   </t>
   </list>
   </t>
   <t>
    In order for a server to support approaches (b)
    (for the case when a client chooses a flavor that is
    not a member of sec_policy_parent) and (c), the put
    filehandle operation cannot return NFS4ERR_WRONGSEC
    when there is a security tuple mismatch.  Instead,
    it should be returned from the LOOKUP (or OPEN by
    existing component name) that follows.

   </t>
   <t>
    Since the above guideline does not contradict approach
    (a), it should be followed in general. Even if approach
    (a) is implemented, it is possible for the security
    tuple used to be acceptable for the target of LOOKUP
    but not for the filehandles used in the put filehandle operation. The 
    put filehandle operation
    could be a PUTROOTFH or PUTPUBFH, where the
    client cannot know the security tuples for the root
    or public filehandle. Or the security policy for the
    filehandle used by the put filehandle operation
    could have changed since the
    time the filehandle was obtained.
   </t>
   <t>
    Therefore, an NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC
    in response to the put filehandle operation
    if the operation
    is immediately followed by a LOOKUP or an OPEN by component name.
   </t>
   </section> <!-- PUTFH + LOOKUP -->

   <section anchor="PUTFHplusLOOKUPP" title="Put Filehandle Operation + LOOKUPP">
   <t>
    Since SECINFO only works its way down, there is no way LOOKUPP can
    return NFS4ERR_WRONGSEC without SECINFO_NO_NAME. SECINFO_NO_NAME
    solves this issue via style
    SECINFO_STYLE4_PARENT, which works in the opposite direction as SECINFO.
    As with <xref target="PUTFHplusLOOKUP" />, a put filehandle operation
    that is followed by a LOOKUPP
    MUST NOT return NFS4ERR_WRONGSEC.
    If the server does not support SECINFO_NO_NAME, the client's
    only recourse is to send the put filehandle operation,
    LOOKUPP, GETFH sequence
    of operations with every security tuple it supports.
   </t>
   <t>
    Regardless of whether SECINFO_NO_NAME is supported, an
    NFSv4.1 server  MUST NOT return NFS4ERR_WRONGSEC in
    response to a put filehandle operation if the
    operation is immediately followed by a LOOKUPP.
   </t>
   </section> <!-- PUTFH + LOOKUPP -->

   <section title="Put Filehandle Operation + SECINFO/SECINFO_NO_NAME"
    anchor="PUTFHplusSECINFO">
   <t>
    A security-sensitive client is allowed to choose
    a strong security tuple when querying a server to
    determine a file object's permitted security tuples.
    The security tuple chosen by the client does not have
    to be included in the tuple list of the security policy
    of either the parent directory indicated in the put filehandle
    operation or the child file object indicated in SECINFO (or any parent directory
    indicated in SECINFO_NO_NAME). Of course, the server has to be
    configured for whatever security
    tuple the client selects; otherwise, the request will
    fail at the RPC layer with an appropriate authentication error.
   </t>
   <t>
    In theory, there is no connection between the security
    flavor used by SECINFO or SECINFO_NO_NAME and those
    supported by the security policy.  But in practice, the
    client may start looking for strong flavors from those
    supported by the security policy, followed by those in
    the REQUIRED set.
   </t>
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to a
    put filehandle operation that
    is immediately followed by SECINFO or SECINFO_NO_NAME.
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC from SECINFO or
    SECINFO_NO_NAME.
   </t>
   </section> <!-- PUTFH + SECINFO -->

   <section anchor="PUTFHplusNothing" title="Put Filehandle Operation + Nothing">
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC.
   </t>
   </section> <!-- PUTFH + Nothing -->

   <section anchor="PUTFHplusAnythingElse" title="Put Filehandle Operation + Anything Else">
   <t>
    "Anything Else" includes OPEN by filehandle.
   </t>
   <t>
    The security policy enforcement applies to the
    filehandle specified in the put filehandle operation. Therefore, the
    put filehandle operation MUST
    return NFS4ERR_WRONGSEC when there is a security tuple
    mismatch. This avoids the complexity of
    adding NFS4ERR_WRONGSEC as an allowable error to every
    other operation.
   </t>
   <t>
    A COMPOUND containing the series put filehandle
    operation + SECINFO_NO_NAME (style SECINFO_STYLE4_CURRENT_FH) is an
    efficient way for the client to recover from
    NFS4ERR_WRONGSEC.
   </t>
   <t>
    The NFSv4.1 server MUST NOT return NFS4ERR_WRONGSEC to
    any operation other than a put filehandle operation,
    LOOKUP, LOOKUPP, and OPEN (by component name).
   </t>
   </section> <!-- PUTFH + Anything Else -->

   <section anchor="aftersecinfo" title="Operations after SECINFO and SECINFO_NO_NAME">
   <t>

     Suppose a client sends a COMPOUND procedure
     containing the series SEQUENCE, PUTFH,
     SECINFO_NONAME, READ, and suppose the security tuple
     used does not match that required for the target
     file. By rule (see <xref target="PUTFHplusSECINFO"/>),
     neither PUTFH nor SECINFO_NO_NAME can
     return NFS4ERR_WRONGSEC. By rule (see <xref
     target="PUTFHplusAnythingElse"/>), READ cannot return
     NFS4ERR_WRONGSEC. The issue is resolved by the fact
     that SECINFO and SECINFO_NO_NAME consume the current
     filehandle (note that this is a change from NFSv4.0). This leaves no current filehandle for
     READ to use, and READ returns NFS4ERR_NOFILEHANDLE.

   </t>

   </section> <!-- Operations after SECINFO and SECINFO_NO_NAME" -->


  </section>
  <section anchor="link_rename" title="LINK and RENAME" >
  <t>
   The LINK and RENAME operations use both the current
   and saved filehandles.
   Technically, the server MAY return NFS4ERR_WRONGSEC from
   LINK or RENAME
   if the security policy of the
   saved filehandle rejects the security flavor used in the
   COMPOUND request's credentials.  If the server does so,
   then if there is no intersection between the security
   policies of saved and current filehandles, this means that it
   will be impossible for the client to perform the intended
   LINK or RENAME operation.

  </t>
  <t>
   For example, suppose the client sends this COMPOUND
   request: SEQUENCE, PUTFH bFH, SAVEFH, PUTFH aFH,
   RENAME "c" "d", where filehandles bFH and aFH refer
   to different directories.  Suppose no common security
   tuple exists between the security policies of aFH and
   bFH. If the client sends the request using credentials
   acceptable to bFH's security policy but not aFH's
   policy, then the PUTFH aFH operation will fail with
   NFS4ERR_WRONGSEC. After a SECINFO_NO_NAME request,
   the client sends SEQUENCE, PUTFH bFH, SAVEFH, PUTFH
   aFH, RENAME "c" "d", using credentials acceptable to
   aFH's security policy but not bFH's policy. The server
   returns NFS4ERR_WRONGSEC on the RENAME operation.

  </t>
  <t>
   To prevent a client from an endless sequence of a
   request containing LINK or RENAME, followed by a request
   containing SECINFO_NO_NAME or SECINFO, the server MUST detect
   when the security policies of the current and saved
   filehandles have no mutually acceptable security tuple,
   and MUST NOT return NFS4ERR_WRONGSEC from LINK or RENAME
   in that situation. Instead
   the server MUST do one of two things:
   <list style='symbols'>

   <t>
    The server can return NFS4ERR_XDEV.
   </t>

   <t>
    The server can 
    allow the security policy of the current filehandle to
    override that of the saved filehandle, and so return NFS4_OK.
   </t>

   </list>

  </t>
  </section>

  </section> <!-- Using NFS4ERR_WRONGSEC, SECINFO, and SECINFO_NO_NAME -->
 </section> <!-- Security Error -->
 </section> <!-- Security Service Negotiation -->

 <section anchor="minor_versioning" title="Minor Versioning">
 <t>
  To address the requirement of an NFS protocol that can evolve as the
  need arises, the NFSv4.1 protocol contains the rules and
  framework to allow for future minor changes or versioning.
 </t>
 <t>
  The base assumption with respect to minor versioning is that any
  future accepted minor version will be
  documented in one or more Standards Track RFCs.
  Minor version 0 of the NFSv4 protocol is represented by
  <xref target="RFC3530" />, and minor version 1 is represented by
  this RFC.
  The COMPOUND and CB_COMPOUND
  procedures support the encoding of the minor version
  being requested by the client.
 </t>
 <t>
  The following items represent the basic rules for the development of
  minor versions.  Note that a future minor version may modify
  or add to the following rules as part of the minor version definition.
 <list style='numbers'>
 <t>
  Procedures are not added or deleted.
  <vspace blankLines='1' />
  To maintain the general RPC model, NFSv4 minor versions will
  not add to or delete procedures from the NFS program.
 </t>

 <t>
  Minor versions may add operations to the COMPOUND and CB_COMPOUND
  procedures.
  <vspace blankLines='1' />
  The addition of operations to the COMPOUND and CB_COMPOUND procedures
  does not affect the RPC model.

  <list style='symbols'>
  <t>
  Minor versions may append attributes to the bitmap4 that represents
  sets of attributes and to the fattr4 that represents sets of attribute 
  values.
  <vspace blankLines='1' />
  This allows for the expansion of the attribute model to allow for
  future growth or adaptation.
  </t>

  <t>
  Minor version X must append any new attributes after the last
  documented attribute.
  <vspace blankLines='1' />
  Since attribute results are specified as an opaque array of
  per-attribute, XDR-encoded results, the complexity of adding new
  attributes in the midst of the current definitions would be too
  burdensome.
  </t>
  </list>
 </t>

 <t>
 Minor versions must not modify the structure of an existing
 operation's arguments or results.
 <vspace blankLines='1' />
 Again, the complexity of handling multiple structure definitions for a
 single operation is too burdensome.  New operations should be added
 instead of modifying existing structures for a minor version.
 <vspace blankLines='1' />
 This rule does not preclude the following adaptations in a minor version:
 <list style='symbols'>
 <t>
 adding bits to flag fields, such as new attributes to GETATTR's bitmap4
 data type, and providing corresponding variants of opaque arrays,
 such as a notify4 used together with such bitmaps
 </t>
 <t>
 adding bits to existing attributes like ACLs that have flag words
 </t>
 <t>
 extending enumerated types (including NFS4ERR_*) with new values
 </t>
 <t>
 adding cases to a switched union
 </t>
 </list>
 </t>

 <t>
 Minor versions must not modify the structure of existing attributes.
 </t>

 <t>
 Minor versions must not delete operations.
 <vspace blankLines='1' />
 This prevents the potential reuse of a particular operation "slot" in
 a future minor version.
 </t>

 <t>
 Minor versions must not delete attributes.
 </t>

 <t>
 Minor versions must not delete flag bits or enumeration values.
 </t>

 <t>
 Minor versions may declare an operation MUST NOT be implemented.
 <vspace blankLines='1' />
 Specifying that an operation MUST NOT be implemented is equivalent
 to obsoleting an operation.  For the client, it means that the
 operation MUST NOT be sent to the server.  For the server, an NFS
 error can be returned as opposed to "dropping" the request as an XDR
 decode error.  This approach allows for the obsolescence of an
 operation while maintaining its structure so that a future minor version can reintroduce the operation.
 <list style='numbers'>
 <t>
 Minor versions may declare that an attribute MUST NOT be implemented.
 </t>
 <t>
 Minor versions may declare that a flag bit or enumeration value MUST NOT
 be implemented.
 </t>
 </list>
 </t>

 <t>
 Minor versions may downgrade features from REQUIRED to RECOMMENDED,
 or RECOMMENDED to OPTIONAL.
 </t>

 <t>
 Minor versions may upgrade features from OPTIONAL to RECOMMENDED, or
 RECOMMENDED to REQUIRED.
 </t>

 <t>
 A client and server that support minor version X SHOULD support minor
 versions zero through X-1 as well.

 </t>

 <t>
 Except for infrastructural changes, a minor version must not
 introduce REQUIRED new features.
 <vspace blankLines='1' />
 This rule allows for the introduction of new functionality and forces
 the use of implementation experience before designating a feature as
 REQUIRED. On the other hand, some classes of features are
 infrastructural and have broad effects. Allowing infrastructural features
 to be RECOMMENDED or OPTIONAL complicates implementation of the minor version.
 </t>

 <t>
 A client MUST NOT attempt to use a stateid, filehandle, or similar
 returned object from the COMPOUND procedure with minor version X for
 another COMPOUND procedure with minor version Y, where X != Y.
 </t>
 </list>
 </t>
 </section> <!-- Minor Versioning -->

 <section anchor="Non-RPC-based_Security_Services" title="Non-RPC-Based Security Services">
 <t>
  As described in
  <xref target="Authentication_Integrity_Privacy" />,
  NFSv4.1 relies on RPC for identification,
  authentication, integrity, and privacy. NFSv4.1 itself
  provides or enables additional security services as described in the
  next several subsections.
 </t>

  <section anchor="Authorization" title="Authorization">
  <t>
   Authorization to access a file object via an NFSv4.1
   operation is ultimately determined by the NFSv4.1
   server. A client can predetermine its access to a file
   object via the OPEN (<xref target="OP_OPEN" />)
   and the ACCESS (<xref target="OP_ACCESS" />)
   operations.
  </t>
  <t>
   Principals with appropriate access rights can modify the
   authorization on a file object via the SETATTR
   (<xref target="OP_SETATTR" />) operation.  Attributes that affect
   access rights include mode, owner, owner_group, acl, dacl, and
   sacl. See <xref target="file_attributes" />.
   </t>
  </section> <!-- Authorization -->

  <section anchor="Auditing" title="Auditing">
  <t>
   NFSv4.1 provides auditing on a per-file object basis, via the acl
   and sacl attributes as described in <xref target="acl" />.  It is
   outside the scope of this specification to specify audit log
   formats or management policies.
  </t>
  </section> <!-- Auditing -->

  <section anchor="Intrusion_Detection" title="Intrusion Detection">
  <t>
   NFSv4.1 provides alarm control on a per-file object basis, via the
   acl and sacl attributes as described in <xref target="acl" />.
   Alarms may serve as the basis for intrusion detection.  It is
   outside the scope of this specification to specify heuristics for
   detecting intrusion via alarms.
  </t>
  </section> <!-- Intrusion Detection -->
 </section> <!-- Non-RPC-based Security Services -->

 <section anchor="Transport_Layers" title="Transport Layers">

  <section anchor="Required_and_Recommended_Transport_Attributes"
   title="REQUIRED and RECOMMENDED Properties of Transports">
  <t>
   NFSv4.1 works over Remote Direct Memory Access (RDMA) and non-RDMA-based transports with
   the following attributes: 
   <list style='symbols'>
   <t>
    The transport supports reliable delivery of data, which
    NFSv4.1 requires but neither NFSv4.1 nor RPC has facilities
    for ensuring  <xref target="Chet" />.
   </t>
   <t>
    The transport delivers data in the order it was sent.
    Ordered delivery simplifies detection of transmit
    errors, and simplifies the sending of arbitrary sized
    requests and responses via the record marking
    protocol <xref target="RFC5531" />.
   </t>
   </list>
  </t>
  <t>
   Where an NFSv4.1 implementation supports operation
   over the IP network protocol, any transport used between
   NFS and IP MUST be among the IETF-approved congestion
   control transport protocols.  At the time this document
   was written, the only two transports that had the above
   attributes were TCP and the Stream
   Control Transmission Protocol (SCTP).  To enhance the
   possibilities for interoperability, an NFSv4.1
   implementation MUST support operation over the TCP
   transport protocol.
  </t>
  <t>
   Even if NFSv4.1 is used over a non-IP network
   protocol, it is RECOMMENDED that the transport support
   congestion control.
  </t>
  <t>
   It is permissible for a connectionless transport to
   be used under NFSv4.1; however, reliable and in-order
   delivery of data combined with congestion control
   by the connectionless transport is
   REQUIRED.  As a consequence, UDP by itself MUST NOT be used
   as an NFSv4.1 transport. NFSv4.1 assumes that a client transport
   address and server transport address used to send data
   over a transport together constitute a connection,
   even if the underlying transport eschews the concept
   of a connection.

  </t>
  </section> <!-- Required and Recommended Transport Attributes -->

  <section anchor="Client_and_Server_Transport_Behavior" title="Client and Server Transport Behavior">
  <t>
   If a connection-oriented transport (e.g., TCP) is used,
   the client and server SHOULD use long-lived connections
   for at least three reasons:
   <list style='numbers'>
   <t>
    This will prevent the weakening of the transport's
    congestion control mechanisms via short-lived
    connections.
   </t>
   <t>
    This will improve performance for the WAN environment
    by eliminating the need for connection setup
    handshakes.
   </t>
   <t>
    The NFSv4.1 callback model differs from NFSv4.0, and
    requires the client and server to maintain a
    client-created backchannel (see <xref target="conn_chann_assoc" />) for the server to use.
   </t>
   </list>
  </t>
  <t>
   In order to reduce congestion, if a connection-oriented
   transport is used, and the request is not the NULL
   procedure:
   <list style='symbols'>
   <t>
    A requester MUST
    NOT retry a request unless the connection the request
    was sent over was lost before the reply was
    received.
   </t>
   <t>
    A replier MUST
    NOT silently drop a request, even if the request is a
    retry.  (The silent drop behavior of RPCSEC_GSS
    <xref target="RFC2203" /> does not apply
    because this behavior happens at the RPCSEC_GSS layer,
    a lower layer in the request processing.)  Instead, the
    replier SHOULD return an appropriate error (see
    <xref target="Slot_Identifiers_and_Server_Reply_Cache" />),
    or it MAY disconnect the connection.
   </t>
   </list>
  </t>


  <t>

    When sending a reply, the replier MUST send the reply
    to the same full network address (e.g., if using an
    IP-based transport, the source port of the requester
    is part of the full network address) from which the requester
    sent the request. If using a connection-oriented
    transport, replies MUST be sent on the same connection from which
    the request was received.

  </t>

  <t>

    If a connection is dropped after the replier receives
    the request but before the replier sends the reply, the
    replier might have a pending reply.
    If a connection is established with the same
    source and destination full network address as the
    dropped connection, then the replier MUST NOT send
    the reply until the requester retries the request. The
    reason for this prohibition is that the requester MAY
    retry a request over a different connection (provided that connection
    is associated with the original request's session).

   </t>


  <t>
   When using RDMA transports, there are other reasons for not
   tolerating retries over the same connection:
   <list style='symbols'>
    <t>
     RDMA transports use "credits" to enforce flow control, where
     a credit is a right to a peer to transmit a message.
     If one peer were to retransmit a request (or reply), it would
     consume an additional credit.
     If the replier
     retransmitted a reply, it would certainly result in an RDMA
     connection loss, since the requester would typically only post a
     single receive buffer for each request.  If the requester
     retransmitted a request, the additional credit consumed on the
     server might lead to RDMA connection failure unless the client
     accounted for it and decreased its available credit, leading to
     wasted resources.
    </t>
    <t>
     RDMA credits present a new issue to the reply cache in
     NFSv4.1.  The reply cache may be used when a connection within a
     session is lost, such as after the client reconnects.  Credit
     information is a dynamic property of the RDMA connection, and stale
     values must not be replayed from the cache.  This implies that the
     reply cache contents must not be blindly used when replies are
     sent from it, and credit information appropriate to the channel
     must be refreshed by the RPC layer.
    </t>
   </list>
  </t>
  <t>
   In addition, as described in
   <xref target="Retry_and_Replay" />, while a session is active,
   the NFSv4.1 requester MUST NOT stop waiting for a reply.
  </t>
  </section> <!-- Client and Server Transport Behavior -->

  <section anchor="Ports" title="Ports">
  <t>
   Historically, NFSv3 servers have listened over
   TCP port 2049.  The registered port 2049 <xref target="RFC3232"/>
   for the NFS protocol should be the default configuration.  NFSv4.1
   clients SHOULD NOT use the RPC binding protocols as described in
   <xref target="RFC1833"/>.
  </t>
  </section> <!-- Ports -->

 </section> <!-- Transport Layers -->

 <section anchor="Session" title="Session">
  <t>
   NFSv4.1 clients and servers MUST support and MUST use the session
   feature as described in this section.

  </t>

  <section anchor="Motivation_and_Overview" title="Motivation and Overview">
  <t>
   Previous versions and minor versions of NFS have suffered from
   the following:
   <list style='symbols'>
   <t>
    Lack of support for Exactly Once Semantics (EOS). This includes
    lack of support for EOS through server failure and recovery.
   </t>
   <t>
    Limited callback support, including no support for sending callbacks
    through firewalls, and races between replies to normal requests
    and callbacks.
   </t>
   <t>
    Limited trunking over multiple network paths.
   </t>
   <t>
    Requiring machine credentials for fully secure operation.
   </t>
   </list>
   Through the introduction of a session, NFSv4.1 addresses the
   above shortfalls with practical solutions:
   <list style='symbols'>
   <t>
    EOS is enabled by a reply cache with a bounded size,
    making it feasible to keep the cache in persistent storage and enable
    EOS through server failure and recovery. One reason that
    previous revisions of NFS did not support EOS was
    because some EOS approaches often limited parallelism.
    As will be explained in
    <xref target="Exactly_Once_Semantics" />,
    NFSv4.1 supports both EOS and unlimited parallelism.
   </t>
   <t>
    The NFSv4.1 client (defined in <xref target="intro_definitions" />,
    <xref target="client_def"/>) creates transport
    connections and provides them to the server to use for sending
    callback requests, thus solving the firewall issue
    (<xref target="OP_BIND_CONN_TO_SESSION" />). Races between
    responses from client requests and callbacks caused by
    the requests are detected via the session's sequencing
    properties that are a consequence of EOS
    (<xref target="sessions_callback_races" />).
   </t>
   <t>
    The NFSv4.1 client can associate an arbitrary number of connections with
    the session, and thus provide trunking (<xref target="Trunking" />).
   </t>
   <t>
    The NFSv4.1 client and server produces a session key independent of client
    and server machine credentials which can be
    used to compute a digest for protecting critical session management operations
    (<xref target="protect_state_change" />).
   </t>
   <t>
    The NFSv4.1 client can also create secure RPCSEC_GSS contexts
    for use by the session's backchannel that do not require
    the server to authenticate to a client machine principal
    (<xref target="Backchannel_RPC_Security" />).
   </t>
   </list>
  </t>
  <t>
   A session is a dynamically created, long-lived server object
   created by a client and used over time from one or more transport
   connections.  Its function is to maintain the server's state
   relative to the connection(s) belonging to a client instance.  This
   state is entirely independent of the connection itself, and indeed
   the state exists whether or not the connection exists. A client may
   have one or more sessions associated with it so that
   client-associated state may be accessed using any of the sessions
   associated with that client's client ID, when connections are
   associated with those sessions. When no connections are associated
   with any of a client ID's sessions for an extended time, such
   objects as locks, opens, delegations, layouts, etc. are subject to
   expiration.  The session serves as an object representing a means
   of access by a client to the associated client state on the server,
   independent of the physical means of access to that state.
  </t>
  <t>
   A single client may create multiple sessions. A single session MUST
   NOT serve multiple clients.
  </t>
  </section> <!-- Motivation and Overview -->

  <section anchor="NFSv4_Integration" title="NFSv4 Integration">
  <t>
   Sessions are part of NFSv4.1 and not NFSv4.0. Normally, a major
   infrastructure change such as sessions would require a new major
   version number to an Open Network Computing (ONC) RPC program like
   NFS. However, because NFSv4 encapsulates its functionality in a single procedure, COMPOUND,
   and because COMPOUND can support an arbitrary number of
   operations, sessions have been added to NFSv4.1 with little difficulty. COMPOUND includes
   a minor version number field, and for NFSv4.1 this minor version
   is set to 1. When the NFSv4 server processes a COMPOUND with 
   the minor version set to 1, it expects a different set of
   operations than it does for NFSv4.0. NFSv4.1 defines the
   SEQUENCE operation, which is required for every
   COMPOUND that operates over an established session, with the
   exception of some session administration operations, such
   as DESTROY_SESSION (<xref target="OP_DESTROY_SESSION" />).
  </t>

   <section anchor="SEQUENCE_and_CB_SEQUENCE" title="SEQUENCE and CB_SEQUENCE">
    <t>
     In NFSv4.1, when the SEQUENCE operation is present, it MUST be
     the first operation in the COMPOUND procedure. The primary purpose
     of SEQUENCE is to carry the session identifier. The session identifier
     associates all other operations in the COMPOUND procedure with
     a particular session. SEQUENCE also contains required information
     for maintaining EOS (see <xref target="Exactly_Once_Semantics" />).
     Session-enabled NFSv4.1 COMPOUND requests thus have the form:
    </t>
    <figure>
    <artwork>
    +-----+--------------+-----------+------------+-----------+----
    | tag | minorversion | numops    |SEQUENCE op | op + args | ...
    |     |   (== 1)     | (limited) |  + args    |           |
    +-----+--------------+-----------+------------+-----------+----
    </artwork>
    </figure>

    <t>
    and the replies have the form:
    </t>

    <figure>
    <artwork>
    +------------+-----+--------+-------------------------------+--//
    |last status | tag | numres |status + SEQUENCE op + results |  //
    +------------+-----+--------+-------------------------------+--//
            //-----------------------+----
            // status + op + results | ...
            //-----------------------+----
    </artwork>
    </figure>
    <t>
     A CB_COMPOUND procedure request and reply has a similar form to
     COMPOUND, but
     instead of a SEQUENCE operation, there is a CB_SEQUENCE operation.
     CB_COMPOUND also has an additional field called "callback_ident", which
     is superfluous in NFSv4.1 and MUST be ignored by
     the client. CB_SEQUENCE has the same information
     as SEQUENCE, and also includes other information needed to resolve
     callback races
    (<xref target="sessions_callback_races" />).
    </t>
   </section> <!-- SEQUENCE and CB_SEQUENCE -->

   <section anchor="Client_ID_and_Session_Association" title="Client ID and Session Association">
   <t>
    Each client ID (<xref target="Client_Identifiers" />) can have
    zero or more active sessions. A client ID and associated
    session are required to perform file access in 
    NFSv4.1. Each time a session is used (whether by a client sending
    a request to the server or the client replying to a callback
    request from the server), the state leased to its associated
    client ID is automatically renewed.

   </t>
   <t>
    State (which can consist of share reservations, locks, delegations,
    and layouts (<xref target="intro_locking" />)) is tied to
    the client ID. Client state is not tied to any individual session.
    Successive state changing operations from a given state
    owner MAY go over different sessions, provided the
    session is associated with the same client ID. A callback
    MAY arrive over a different session than that of the request
    that originally acquired the state pertaining to the
    callback. For example, if session A is used to
    acquire a delegation, a request to recall the
    delegation MAY arrive over session B if both sessions are
    associated with the same client ID. Sections
    <xref target="Session_Callback_Security" format="counter"/> and
    <xref target="Backchannel_RPC_Security" format="counter"/> discuss
    the security considerations around callbacks.
   </t>
    
   </section> <!-- Client ID and Session Association -->
  </section> <!-- NFSv4 Integration -->

  <section anchor="Channels" title="Channels">
  <t>
   A channel is not a connection. A channel represents the
   direction ONC RPC requests are sent.
  </t>
  <t>
   Each session has one or two channels: the fore channel and the backchannel.
   Because there are at most two channels per session, and because each
   channel has a distinct purpose, channels are not assigned
   identifiers.
  </t>
  <t>
   The fore channel is
   used for ordinary requests from the client to the server, and
   carries COMPOUND requests and responses.
   A session always has a fore channel.
  </t>
  <t>
   The backchannel is used for callback requests from server
   to client, and carries CB_COMPOUND requests and responses.
   Whether or not there is a backchannel is a decision made by the
   client; however, many features of NFSv4.1 require a backchannel.
   NFSv4.1 servers MUST support backchannels.
  </t>
  <t>
   Each session has resources for each channel,
   including separate reply caches (see
   <xref target="Slot_Identifiers_and_Server_Reply_Cache" />).

   Note that even the backchannel requires a reply cache (or, at least,
   a slot table in order to detect retries) because
   some callback operations are nonidempotent.
  </t>

   <section anchor="conn_chann_assoc" title="Association of Connections, Channels, and Sessions"> 
   <t>
    Each channel is associated with zero or more transport
    connections (whether of the same transport protocol or different
    transport protocols).  A connection can be associated with
    one channel or both channels of a session; the client
    and server negotiate whether a connection will carry
    traffic for one channel or both channels via the
    CREATE_SESSION (<xref target="OP_CREATE_SESSION"
    />) and the BIND_CONN_TO_SESSION (<xref
    target="OP_BIND_CONN_TO_SESSION" />) operations. When a
    session is created via CREATE_SESSION, the connection
    that transported the CREATE_SESSION request is
    automatically associated with the fore channel, and
    optionally the backchannel. If the client specifies no
    state protection (<xref target="OP_EXCHANGE_ID" />)
    when the session is created, then when SEQUENCE is
    transmitted on a different connection, the connection
    is automatically associated with the fore channel of
    the session specified in the SEQUENCE operation.

   </t>
   <t>
    A connection's association with a session is
    not exclusive.  A connection associated with the channel(s)
    of one session may be simultaneously
    associated with the channel(s) of other sessions including
    sessions associated with other client IDs.

   </t>
   <t>
    It is permissible for connections of multiple transport
    types to be associated with the same channel. For
    example, both TCP and RDMA connections can be
    associated with the fore channel.  In the event an
    RDMA and non-RDMA connection are associated with the
    same channel, the maximum number of slots SHOULD be
    at least one more than the total number of RDMA credits
    (<xref target="Slot_Identifiers_and_Server_Reply_Cache" />).
   This way, if all RDMA credits are used, the non-RDMA
   connection can have at least one outstanding request.
   If a server supports multiple transport types, it MUST
   allow a client to associate connections from each transport
   to a channel.

   </t>
   <t>
    It is permissible for a connection of one type of
    transport to be associated with the fore channel,
    and a connection of a different type to be associated
    with the backchannel.

   </t>
   </section>
  </section> <!-- Channels -->
  <section anchor="Server_Scope" title="Server Scope">
    <t>
      Servers each specify a server scope value in the form
      of an opaque string eir_server_scope returned as part of
      the results of an EXCHANGE_ID operation.  The purpose of
      the server scope is to allow a group of servers to 
      indicate to clients that a set of servers sharing the 
      same server scope value has arranged to use compatible 
      values of otherwise opaque identifiers. Thus, the identifiers
      generated by one server of that set may be presented to
      another of that same scope.
    </t>
    <t>
      The use of such compatible values does not imply that
      a value generated by one server will always be accepted
      by another.  In most cases, it will not.  However, a
      server will not accept a value generated by another
      inadvertently.  When it does accept it, it will be because
      it is recognized as valid and carrying the same meaning  
      as on another server of the same scope.
    </t>
    <t>
      When servers are of the same server scope, this compatibility
      of values applies to the follow identifiers:
      <list style="symbols">
        <t>
          Filehandle values.  A filehandle value accepted by two 
          servers of the same server scope denotes the same object.
          A WRITE operation sent to one server is reflected immediately
          in a READ sent to the other, and locks obtained on one
          server conflict with those requested on the other. 
        </t>
        <t>
          Session ID values.  A session ID value accepted by two
          servers of the same server scope denotes the same session. 
        </t>
        <t>
          Client ID values.  A client ID value accepted as valid by
          two servers of the same server scope is associated with 
          two clients with the same client owner and verifier.
        </t>
        <t>
         State ID values.  A state ID value is recognized as valid
when the corresponding client ID is recognized as valid.

If the same stateid value is accepted as valid
          on two servers of the same scope and the client IDs on
          the two servers represent the same client owner and 
          verifier, then the two stateid values designate the
          same set of locks and are for the same file.
        </t>
        <t>
          Server owner values.  When the server scope values are 
          the same, server owner value may be validly compared.  
          In cases where the server scope values are different, server 
          owner values are treated as different even if they 
          contain all identical bytes.
        </t>
      </list>
    </t>
    <t>
      The coordination among servers required to provide such
      compatibility can be quite minimal, and limited to a simple
      partition of the ID space.  The recognition of common values
      requires additional implementation, but this can be tailored
      to the specific situations in which that recognition is 
      desired.
    </t>
    <t>
      Clients will have occasion to compare the server scope values
      of multiple servers under a number of circumstances, each of
      which will be discussed under the appropriate functional 
      section:
      <list style="symbols">
        <t>
          When server owner values received in response to 
          EXCHANGE_ID operations sent to multiple network
          addresses are compared for the purpose of determining
          the validity of various forms of trunking, as described
          in <xref target="Trunking" />. 
        </t>
        <t>
          When network or server reconfiguration causes the same
          network address to possibly be directed to different
          servers, with the necessity for the client to determine
          when lock reclaim should be attempted, as described
          in <xref target="reclaim_locks" />.
        </t>
        <t>
          When file system migration causes the transfer of
          responsibility for a file system between servers and
          the client needs to determine whether state has been
          transferred with the file system (as described in <xref
          target="transition_state"/>) or whether the
          client needs to reclaim state on a similar basis as in the
	  case of server restart, as described in <xref
	  target="server_failure"/>.

        </t>
      </list>
    </t>
    <t>
      When two replies from EXCHANGE_ID, each from two different
      server network addresses, have the same server scope, there
      are a number of ways a client can validate that the common
      server scope is due to two servers cooperating in a group.
      <list style="symbols">
        <t>
          If both EXCHANGE_ID requests were sent with RPCSEC_GSS
          authentication and the server principal is the same for 
          both targets, the equality of server scope is validated. 
          It is RECOMMENDED that two servers intending to share the
          same server scope also share the same principal name.
        </t>
        <t>
          The client may accept the appearance of the second
          server in the fs_locations or fs_locations_info attribute
          for a relevant file system.  For example, if there is
          a migration event for a particular file system
          or there are locks to be reclaimed on a particular file
          system, the attributes for that particular file system
          may be used.  The client sends the GETATTR request to 
          the first server for the fs_locations or 
          fs_locations_info attribute with RPCSEC_GSS 
          authentication.  It may need to do this in advance
          of the need to verify the common server scope.
          If the client successfully authenticates the reply 
          to GETATTR, and the GETATTR request and reply containing 
          the fs_locations or fs_locations_info attribute refers 
          to the second server, then the equality of server scope 
          is supported.  A client may choose to limit the use of
          this form of support to information relevant to the
          specific file system involved (e.g. a file system 
          being migrated).
        </t>
      </list>  
    </t>
  </section> <!-- Server Scope -->
  <section anchor="Trunking" title="Trunking">
    <t>
     Trunking is the use of multiple connections between a
     client and server in order to increase the speed of data
     transfer. NFSv4.1 supports two types of trunking:
     session trunking and client ID trunking. 
    </t>
    <t>
     NFSv4.1
     servers MUST support both forms of trunking within
     the context of a single server network address and
     MUST support both forms within the context of the
     set of network addresses used to access a single server.
     NFSv4.1 servers in a clustered configuration MAY allow
     network addresses for different servers to use client ID
     trunking.
    </t>
    <t> 
     Clients may use either form of trunking as long as they
     do not, when trunking between different server network 
     addresses, violate the servers' mandates as to the 
     kinds of trunking to be allowed (see below).  With regard 
     to callback channels, the client MUST allow the server to 
     choose among all callback channels valid for a given 
     client ID and MUST support trunking when the connections
     supporting the backchannel allow session or client ID 
     trunking to be used for callbacks.
    </t>
    <t>
     Session trunking is essentially the association of multiple
     connections, each with potentially different target and/or source
     network addresses, to the same session.  When the target network
     addresses (server addresses) of the two connections are the same, 
     the server MUST
     support such session trunking.  When the target network addresses
     are different, the server MAY indicate such support using the
     data returned by the EXCHANGE_ID operation (see below).
    </t>
    <t>
     Client ID trunking is the association of multiple
     sessions to the same client ID.  Servers MUST support client ID
     trunking for two target network addresses whenever they allow 
     session trunking for those same two network addresses.
     In addition, a server MAY, by presenting the same
     major server owner ID
     (<xref target="Server_Owners" />) and server scope
     (<xref target="Server_Scope" />), allow an additional 
     case of client ID trunking.  When two
     servers return the same major server owner and server
     scope, it means that the two servers are cooperating on
     locking state management, which is a prerequisite
     for client ID trunking.

    </t>
    <t>
     Distinguishing when the client is allowed to use session and
     client ID trunking requires understanding how the results of the
     EXCHANGE_ID (<xref target="OP_EXCHANGE_ID" />)
     operation identify a server.
     Suppose a client sends EXCHANGE_IDs over two different
     connections, each with a possibly different target
     network address, but each EXCHANGE_ID operation has the same
     value in the eia_clientowner field.  If the same
     NFSv4.1 server is listening over each connection,
     then each EXCHANGE_ID result MUST return the same
     values of eir_clientid, eir_server_owner.so_major_id,
     and eir_server_scope. The client can then treat each
     connection as referring to the same server (subject
     to verification; see
     <xref target="trust_but_verify" /> later in this section),
     and it can use each connection to trunk requests and
     replies.  

The client's choice is whether session trunking
     or client ID trunking applies.

    <list style="hanging">

    <t hangText="Session Trunking.">

     If the eia_clientowner argument is the same in
     two different EXCHANGE_ID requests, and
     the eir_clientid, eir_server_owner.so_major_id,
     eir_server_owner.so_minor_id, and eir_server_scope
     results match in both EXCHANGE_ID results, then
     the client is permitted to perform session trunking.
     If the client has no session mapping to the tuple of
     eir_clientid, eir_server_owner.so_major_id, eir_server_scope, and
     eir_server_owner.so_minor_id, then it creates
     the session via a CREATE_SESSION operation over one
     of the connections, which associates the connection
     to the session. If there is a session for the tuple,
     the client can send BIND_CONN_TO_SESSION to associate
     the connection to the session. 
      <vspace blankLines='1' />
     Of course, if the client
     does not desire to use session trunking, it is not 
     required to do so.  It can invoke
     CREATE_SESSION on the connection. This will result
     in client ID trunking as described below.  It can also
     decide to drop the connection if it does not choose to
     use trunking.
      <vspace blankLines='1' />

    </t>

    <t hangText="Client ID Trunking.">

     If the eia_clientowner argument is the same in
     two different EXCHANGE_ID requests, and
     the eir_clientid, eir_server_owner.so_major_id,
     and eir_server_scope
     results match in both EXCHANGE_ID results, then
     the client is permitted to perform client ID trunking
     (regardless of whether the eir_server_owner.so_minor_id results match).
     The client can associate
     each connection with different sessions, where
     each session is associated with the same server.

      <vspace blankLines='1' />

     The client completes the act of client ID trunking by invoking
     CREATE_SESSION on each connection, using the same
     client ID that was returned in eir_clientid. These
     invocations create two sessions and also associate
     each connection with its respective session.  The client 
     is free to decline to use client ID trunking by simply
     dropping the connection at this point.

      <vspace blankLines='1' />

     When doing client ID trunking, locking state
     is shared across sessions associated with that same
     client ID. This requires the server to coordinate
     state across sessions.

    </t>

    </list>

    </t>
    <t>
      The client should be prepared for the possibility
      that eir_server_owner values may be different on
      subsequent EXCHANGE_ID requests made to the same 
      network address, as a result of  various sorts of 
      reconfiguration events.  When this happens and the
      changes result in the invalidation of previously 
      valid forms of trunking, the client should cease 
      to use those forms, either by dropping connections 
      or by adding sessions.  For a discussion of lock 
      reclaim as it relates to such reconfiguration events,
      see <xref target="reclaim_locks" />. 
    </t>

    <section title="Verifying Claims of Matching Server Identity" anchor="trust_but_verify">
    <t>
     When two servers over two connections claim
     matching or partially matching eir_server_owner,
     eir_server_scope, and eir_clientid values, the client
     does not have to trust the servers' claims. The client
     may verify these claims before trunking traffic in
     the following ways:

    <list style='symbols'>

     <t>
      For session trunking,
      clients SHOULD
      reliably verify if connections between different
      network paths are in fact associated with the same NFSv4.1
      server and usable on the same session, and servers
      MUST allow clients to perform reliable verification.
      When a client ID is created, the client SHOULD specify that
      BIND_CONN_TO_SESSION is to be verified according to the
      SP4_SSV or SP4_MACH_CRED (<xref target="OP_EXCHANGE_ID" />)
      state protection options.  For SP4_SSV, reliable
      verification depends on a shared secret (the
      SSV) that is established via the SET_SSV (<xref
      target="OP_SET_SSV" />) operation. 

      <vspace blankLines='1' />

      When a new connection is associated with the
      session (via the BIND_CONN_TO_SESSION operation,
      see <xref target="OP_BIND_CONN_TO_SESSION" />), if
      the client specified SP4_SSV state protection for the
      BIND_CONN_TO_SESSION operation, the client MUST send
      the BIND_CONN_TO_SESSION with RPCSEC_GSS protection,
      using integrity or privacy, and an RPCSEC_GSS handle created
      with the GSS SSV mechanism (<xref
      target="ssv_mech" />).

      <vspace blankLines='1' />

      If the client mistakenly tries to associate a
      connection to a session of a wrong server, the
      server will either reject the attempt because
      it is not aware of the session identifier of the
      BIND_CONN_TO_SESSION arguments, or it will reject
      the attempt because the RPCSEC_GSS authentication
      fails.  Even if the server mistakenly or maliciously
      accepts the connection association attempt, the
      RPCSEC_GSS verifier it computes in the response
      will not be verified by the client, so the client will
      know it cannot use the connection for trunking the
      specified session.  <vspace blankLines='1' /> If the
      client specified SP4_MACH_CRED state protection, the
      BIND_CONN_TO_SESSION operation will use RPCSEC_GSS
      integrity or privacy, using the same credential that
      was used when the client ID was created. Mutual
      authentication via RPCSEC_GSS assures the client
      that the connection is associated with the correct
      session of the correct server.

      <vspace blankLines='1' />
     </t>
     <t>
      For client ID trunking, the client has at least two
      options for verifying that the same client ID
      obtained from two different EXCHANGE_ID operations
      came from the same server.  The first option is
      to use RPCSEC_GSS authentication when sending each
      EXCHANGE_ID operation. Each time an EXCHANGE_ID is sent with
      RPCSEC_GSS authentication, the client notes the
      principal name of the GSS target.  If the EXCHANGE_ID
      results indicate that client ID trunking is possible,
      and the GSS targets' principal names are the same,
      the servers are the same and client ID trunking is
      allowed.

      <vspace blankLines='1' />

      The second option for verification is to
      use SP4_SSV protection.  When the client sends
      EXCHANGE_ID, it specifies SP4_SSV protection. The
      first EXCHANGE_ID the client sends always has to
      be confirmed by a CREATE_SESSION call. The client
      then sends SET_SSV. Later, the client
      sends EXCHANGE_ID to a second destination
      network address different from the one the first 
      EXCHANGE_ID was sent to.
      The client checks that each EXCHANGE_ID reply has the
      same eir_clientid, eir_server_owner.so_major_id, and
      eir_server_scope. If so, the client verifies the
      claim by sending a CREATE_SESSION operation to the second
      destination address, protected with RPCSEC_GSS integrity
      using an RPCSEC_GSS handle returned by the second
      EXCHANGE_ID. If the server accepts the CREATE_SESSION
      request, and if the client verifies the RPCSEC_GSS
      verifier and integrity codes, then the client has
      proof the second server knows the SSV, and thus
      the two servers are cooperating for the purposes of
      specifying server scope and client ID trunking.

     </t>
    </list>
    </t>
    </section> <!-- Verifying Claims of Matching Server Identity -->
  </section> <!-- Trunking -->

  <section anchor="Exactly_Once_Semantics" title="Exactly Once Semantics">
  <t>
   Via the session, NFSv4.1 offers exactly once semantics (EOS)
   for requests sent over a channel. EOS is supported on both the
   fore channel and backchannel.
  </t>
  <t>
   Each COMPOUND or CB_COMPOUND request that is sent
   with a leading SEQUENCE or CB_SEQUENCE operation MUST
   be executed by the receiver exactly once. This requirement
   holds regardless of whether the request is sent with reply
   caching specified (see <xref target="optional_reply_caching" />).
   The requirement holds even if the requester is sending the
   request over a session created between a pNFS data client
   and pNFS data server. To understand the rationale for this requirement,
   divide the requests into three
   classifications:
   <list style='symbols'>
   <t>
    Non-idempotent requests.
   </t>
   <t>
    Idempotent modifying requests. 
   </t>
   <t>
    Idempotent non-modifying requests. 
   </t>
   </list>
    An example of a non-idempotent request is
    RENAME. Obviously, if a replier executes the
    same RENAME request twice, and the first execution succeeds,
    the re-execution will fail. If the replier returns the
    result from the re-execution, this result is incorrect.
    Therefore, EOS is required for non-idempotent requests.
   </t>
   <t>
    An example of an idempotent modifying request is
    a COMPOUND request containing a WRITE operation.
    Repeated execution of the same WRITE
    has the same effect as execution of that WRITE a single time.
    Nevertheless, enforcing EOS for WRITEs and other idempotent
    modifying requests is necessary
    to avoid data corruption.
   </t>
   <t>
    Suppose a client sends WRITE A to a
    noncompliant server that does not enforce EOS, and
    receives no response, perhaps due to a network
    partition.  The client reconnects to the server and
    re-sends WRITE A. Now, the server has
    outstanding two instances of A.  The
    server can be in a situation in which it executes and
    replies to the retry of A, while the first
    A is still waiting in the server's internal I/O system for some
    resource.  Upon receiving the
    reply to the second attempt of WRITE A,
    the client believes its WRITE is done so it is free
    to send WRITE B, which overlaps the byte-range of
    A.  When the original A is dispatched from the server's
    I/O system and
    executed (thus the second time A will have
    been written), then what has been
    written by B can be overwritten and thus corrupted.
   </t>
   <t>
    An example of an idempotent non-modifying request
    is a COMPOUND containing SEQUENCE, PUTFH, READLINK,
    and nothing else. The re-execution of such a
    request will not cause data corruption or
    produce an incorrect result. Nonetheless,
    to keep the implementation simple,
    the replier MUST enforce EOS for all requests, whether or not
    idempotent and non-modifying.
   </t>
   <t>
    Note that true and complete EOS is not possible unless the
    server persists the reply cache in stable storage, and unless the
    server is somehow implemented to never require a restart
    (indeed, if such a server exists, the distinction between a
    reply cache kept in stable storage versus one that is not is
    one without meaning). See <xref target="Persistence" /> for
    a discussion of persistence in the reply cache.
    Regardless, even if the server does not persist the reply cache,
    EOS improves robustness and correctness over previous versions
    of NFS because the legacy duplicate request/reply caches were
    based on the ONC RPC transaction identifier (XID). 
    <xref target="Slot_Identifiers_and_Server_Reply_Cache" />
    explains the shortcomings of the XID as a basis for
   a reply cache and describes how NFSv4.1 sessions improve
   upon the XID.
   </t>

    <section anchor="Slot_Identifiers_and_Server_Reply_Cache"
     title="Slot Identifiers and Reply Cache">
    <t>
     The RPC layer provides a transaction ID (XID), which,
     while required to be unique, is not
     convenient for tracking requests for two reasons.
     First, the XID is only
     meaningful to the requester; it cannot be interpreted
     by the replier except to test for equality with
     previously sent requests. When consulting an RPC-based
     duplicate request cache, the opaqueness of the XID requires
     a computationally expensive look up (often via a hash that
     includes XID and source address). NFSv4.1 requests use
     a non-opaque slot ID, which is an index into a slot table,
     which is far more efficient. Second, because RPC requests
     can be executed by the replier in any order, there is
     no bound on the number of requests that may be outstanding
     at any time. To achieve perfect EOS, using ONC RPC
     would require storing all replies in the reply cache.
     XIDs are 32 bits; storing over four billion (2^32) replies
     in the reply cache is not practical. In practice, previous versions
     of NFS have chosen to store a fixed number of replies in
     the cache, and to use a least recently used (LRU) approach to
     replacing cache entries with new entries when the cache
     is full. In NFSv4.1, the number of outstanding requests is
     bounded by the size of the slot table, and a sequence ID
     per slot is used to tell the replier when it is safe to
     delete a cached reply.
    </t>
    <t>
     In the NFSv4.1 reply cache, when the requester sends a new request,
     it selects a slot ID in the
     range 0..N, where N is the replier's current maximum slot ID
     granted to the requester on the session over which the request is to be
     sent. The value of N starts out as equal to
     ca_maxrequests - 1 (<xref target="OP_CREATE_SESSION" />), but
     can be adjusted by the response to SEQUENCE or CB_SEQUENCE as described
     later in this section.
     The slot ID must be unused by any of the requests that the
     requester has already active on the session.  "Unused" here means the
     requester has no outstanding request for that slot ID.
    </t>
    <t>
     A slot contains a sequence ID and the cached reply corresponding to
     the request sent with that sequence ID. The sequence ID is a
     32-bit unsigned value, and is therefore in the range 0..0xFFFFFFFF (2^32 - 1).
     The first time a slot is used, the requester MUST specify
     a sequence ID of one (<xref target="OP_CREATE_SESSION" />).
     Each time a slot is reused, the request MUST specify a sequence ID
     that is one greater than that of the previous request on the
     slot. If the previous sequence ID was 0xFFFFFFFF, then the next
     request for the slot MUST have the sequence ID set to zero (i.e.,
     (2^32 - 1) + 1 mod 2^32).
    </t>
    <t>
     The sequence ID accompanies the slot ID in each request. It is
     for the critical check at the replier: it used to efficiently
     determine whether a request using a certain
     slot ID is a retransmit or a new, never-before-seen request.  It is
     not feasible for the requester to assert that it is retransmitting to
     implement this, because for any given request the requester cannot
     know whether the replier has seen it unless the replier actually replies.  Of
     course, if the requester has seen the reply, the requester would
     not retransmit.
    </t>
    <t>
     The replier compares each received request's
     sequence ID with the last one previously received for that slot ID,
     to see if the new request is:
    </t>
    <t>
    <list style="symbols">
     <t>
      A new request, in which the sequence ID is one greater
      than that previously seen in the slot (accounting for sequence
      wraparound).  The replier proceeds to execute the new request,
      and the replier
      MUST increase the slot's sequence ID by one.
     </t>
     <t>
      A retransmitted request, in which the sequence ID is equal to
      that currently recorded in the slot. 
      If the original request has
      executed to completion, the replier returns the cached
      reply. See <xref target="Retry_and_Replay" /> for direction on how the replier
      deals with retries of requests that are still in progress.
     </t>
     <t>
      A misordered retry, in which the sequence ID
      is less than (accounting for sequence wraparound)
      that previously seen in the slot.  The
      replier MUST return NFS4ERR_SEQ_MISORDERED (as the
      result from SEQUENCE or CB_SEQUENCE).
     </t>
     <t>
      A misordered new request, in which the sequence ID
      is two or more than (accounting for sequence
      wraparound) that previously seen in the
      slot. Note that because the sequence ID MUST
      wrap around to zero once it reaches 0xFFFFFFFF, a
      misordered new request and a misordered retry
      cannot be distinguished. Thus, the replier MUST
      return NFS4ERR_SEQ_MISORDERED (as the result from
      SEQUENCE or CB_SEQUENCE).
     </t>
    </list>
    </t>
    <t>
     Unlike the XID, the slot ID is always within a specific
     range; this has two implications.  The first
     implication is that for a given session, the replier
     need only cache the results of a limited number of
     COMPOUND requests.
     The second implication derives
     from the first, which is that unlike XID-indexed reply
     caches (also known as duplicate request caches - DRCs),
     the slot ID-based reply cache cannot be overflowed.
     Through use of the sequence ID to identify
     retransmitted requests, the replier does not need to
     actually cache the request itself, reducing the
     storage requirements of the reply cache further.  These
     facilities make it practical to maintain all the
     required entries for an effective reply cache.

    </t>
    <t>
     The slot ID, sequence ID, and session ID therefore take over the traditional role
     of the XID and source network address in the replier's
     reply cache implementation.
     This approach is considerably
     more portable and completely robust -- it is not subject to the
     reassignment of ports as clients reconnect over IP
     networks.  In addition, the RPC XID is not used in the reply cache,
     enhancing robustness of the cache in the face of any rapid reuse of
     XIDs by the requester. While the replier does not care
     about the XID for the purposes of reply cache management
     (but the replier MUST return the same XID that was in the request),
     nonetheless there are considerations for the XID in NFSv4.1
     that are the same as all other previous versions of NFS.
     The RPC XID remains in each message and needs to be formulated
     in NFSv4.1 requests as in any other ONC RPC request. The reasons
     include:
    <list style="symbols">
    <t>
     The RPC layer retains its existing semantics and implementation.
    </t>
    <t>
     The requester and replier must be able to interoperate at the
     RPC layer, prior to the NFSv4.1 decoding of the SEQUENCE or CB_SEQUENCE
     operation.
    </t>
    <t>
     If an operation is being used that does not start with
     SEQUENCE or CB_SEQUENCE (e.g., BIND_CONN_TO_SESSION),
     then the RPC XID is needed for correct operation to
     match the reply to the request.

    </t>
    <t>
     The SEQUENCE or CB_SEQUENCE operation may generate an error.
     If so, the embedded slot ID, sequence ID, and session ID (if
     present) in the request will not be in the reply, and the
     requester has only the XID to match the reply to the request.
    </t>
    </list>
    </t>
    <t>
     Given that well-formulated XIDs continue to be required,
     this begs the question: why do SEQUENCE and CB_SEQUENCE replies
     have a session ID, slot ID, and sequence ID? Having the session ID
     in the reply means that the requester does not have to use the
     XID to look up
     the session ID, which would be necessary if the connection were
     associated with multiple sessions. Having the slot ID and sequence ID
     in the reply means that the requester does not have to use the XID to
     look up the slot ID and sequence ID.
     Furthermore, since the XID is only 32 bits, it is too small to
     guarantee the re-association of a reply with its request 
     <xref target="rpc_xid_issues" />; having
     session ID, slot ID, and sequence ID in the reply allows the
     client to validate that the reply in fact belongs to the matched request.
    </t>
    <t>
     The SEQUENCE (and CB_SEQUENCE) operation also carries
     a "highest_slotid" value, which carries additional
     requester slot usage information.  The requester MUST
     always indicate the slot ID representing the outstanding request with the
     highest-numbered slot
     value.
     The requester should in all cases provide the most
     conservative value possible, although it can be increased somewhat
     above the actual instantaneous usage to maintain some minimum or
     optimal level.  This provides a way for the requester to yield unused
     request slots back to the replier, which in turn can use the
     information to reallocate resources. 
    </t>
    <t>
     The replier
     responds with both a new target highest_slotid and an
     enforced highest_slotid, described as follows:
     <list style="symbols">
     <t>
      The target highest_slotid is
      an indication to the requester of the highest_slotid the replier
      wishes the requester to be using.  This permits the replier to withdraw
      (or add) resources from a requester that has been found to not be
      using them, in order to more fairly share resources among a varying
      level of demand from other requesters.  The requester must always comply
      with the replier's value updates, since they indicate newly
      established hard limits on the requester's access to session
      resources.  However, because of request pipelining, the requester may
      have active requests in flight reflecting prior values; therefore,
      the replier must not immediately require the requester to comply.
      <vspace blankLines='1' />
     </t>
     <t>
      The enforced highest_slotid indicates the highest slot ID
      the requester is permitted to use on a subsequent SEQUENCE or
      CB_SEQUENCE operation. The replier's enforced highest_slotid SHOULD
      be no less than the highest_slotid the requester indicated
      in the SEQUENCE or CB_SEQUENCE arguments.

      <vspace blankLines='1' />

      A requester can be intransigent with respect to lowering its
      highest_slotid argument to a Sequence operation, i.e. the requester
      continues to ignore the target highest_slotid in the response to
      a Sequence operation, and continues to set its highest_slotid
      argument to be higher than the target highest_slotid. This can
      be considered particularly egregious behavior when the replier
      knows there are no outstanding requests with slot IDs higher than
      its target highest_slotid.  When faced with such intransigence,
      the replier is free to take more forceful action, and MAY reply with
      a new enforced highest_slotid that is less than its previous
      enforced highest_slotid.  Thereafter, if the requester continues
      to send requests with a highest_slotid that is greater than
      the replier's new enforced highest_slotid, the server MAY return
      NFS4ERR_BAD_HIGH_SLOT, unless the slot ID in the request is greater
      than the new enforced highest_slotid and the request is a retry.

      <vspace blankLines='1' />

      The replier SHOULD retain the slots it wants to retire
      until
      the requester sends a request with a highest_slotid less than
      or equal to the replier's new enforced highest_slotid. 

      <vspace blankLines='1' />

      The requester can also be intransigent with
      respect to sending non-retry requests that have a slot ID that
      exceeds the replier's highest_slotid.
      Once the replier has forcibly lowered the enforced
      highest_slotid, the requester is only allowed to
      send retries on slots that exceed the replier's highest_slotid.
      If a request is received with a slot ID that is higher than
      the new enforced highest_slotid, and the sequence ID
      is one higher than what is in the slot's reply cache, then
      the server can both retire the slot and return NFS4ERR_BADSLOT
      (however, the server MUST NOT do one and not the other).
      The reason it is safe to retire the slot
      is because by using the next sequence ID, the requester
      is indicating it has received the previous reply for the
      slot.
      <vspace blankLines='1' />
    </t>
    <t>
     The requester SHOULD use the lowest available
     slot when sending a new request.  This way, the
     replier may be able to retire slot entries faster.
     However, where the replier is actively adjusting
     its granted highest_slotid,
     it will not be able
     to use only the receipt of the slot ID and highest_slotid
     in the request.  Neither the slot ID nor the
     highest_slotid used in a request may reflect the
     replier's current idea of the requester's session
     limit, because the request may have been sent from the
     requester before the update was received.  Therefore,
     in the downward adjustment case, the replier may have
     to retain a number of reply cache entries at least as
     large as the old value of maximum requests
     outstanding, until it can infer that the requester 
     has seen a reply containing the new granted highest_slotid.
     The replier can infer that the requester has seen such a 
     reply when it receives a new request with the same
     slot ID as the request replied to and the next higher 
     sequence ID.      
    </t>
    </list>
   </t>
     <section title="Caching of SEQUENCE and CB_SEQUENCE Replies" anchor="cacheseq">

     <t>
      When a SEQUENCE or CB_SEQUENCE operation is
      successfully executed, its reply MUST always be
      cached. Specifically, session ID, sequence ID,
      and slot ID MUST be cached in the reply cache.
      The reply from SEQUENCE also includes the highest
      slot ID, target highest slot ID, and status flags. Instead
      of caching these values, the server MAY
      re-compute the values from the current
      state of the fore channel, session, and/or client
      ID as appropriate.  Similarly, the reply from
      CB_SEQUENCE includes a highest slot ID and target
      highest slot ID. The client
      MAY re-compute the values from the
      current state of the session as appropriate.

     </t>

     <t>

       Regardless of whether or not a replier is re-computing highest slot ID,
       target slot ID, and status on replies to retries, the requester
       MUST NOT assume that the values are being re-computed whenever it
       receives a reply after a retry is sent, since it has no way
       of knowing whether the reply it has received was sent by the 
       replier in response to the retry or is a delayed response to
       the original request.  Therefore, it may be the case that 
       highest slot ID, target slot ID, or status bits may reflect
       the state of affairs when the request was first executed.  
       Although acting based on such delayed information is valid,
       it may cause the receiver of the reply to do unneeded work.  Requesters
       MAY choose to send additional requests to get the current 
       state of affairs or use the state of affairs reported by 
       subsequent requests, in preference to acting immediately
       on data that might be out of date.

     </t>

     </section>

     <section title="Errors from SEQUENCE and CB_SEQUENCE"
       anchor="err_sequence">
     <t>
      Any time SEQUENCE or CB_SEQUENCE returns an error, the
      sequence ID of the slot MUST NOT change. The replier MUST NOT
      modify the reply cache entry for the slot whenever an error
      is returned from SEQUENCE or CB_SEQUENCE.
     </t>
     </section> <!-- Errors from SEQUENCE and CB_SEQUENCE -->
     <section title="Optional Reply Caching"
      anchor="optional_reply_caching">
      <t>
       On a per-request basis, the requester can choose to
       direct the replier to cache the reply to all operations
       after the first operation (SEQUENCE or CB_SEQUENCE) via
       the sa_cachethis or csa_cachethis fields of the arguments
       to SEQUENCE or CB_SEQUENCE.
       The reason it would not direct the replier to cache
       the entire reply is that the request is composed of all
       idempotent operations <xref target="Chet" />.
       Caching the reply may offer little benefit. If
       the reply is too large (see

       <xref target="COMPOUND_Sizing_Issues" />),

       it may not be cacheable anyway. Even if the reply to
       idempotent request is small enough to cache, unnecessarily
       caching the reply slows down the server and increases
       RPC latency.
      </t>
      <t>
       Whether or not the requester requests the reply to be cached
       has no effect on the slot processing. If the
       results of SEQUENCE or CB_SEQUENCE are NFS4_OK, then
       the slot's sequence ID MUST be incremented by one.
       If a requester does not direct the replier to cache
       the reply, the replier MUST do one of following:
       <list style='symbols'>
       <t>
        The replier can cache the entire original reply.
        Even though sa_cachethis or csa_cachethis is FALSE,
        the replier is always free to cache. It may choose
        this approach in order to simplify implementation.
       </t>
       <t>
        The replier enters into its reply cache a reply consisting
        of the original results to the SEQUENCE or CB_SEQUENCE
        operation, and with the next operation in
        COMPOUND or CB_COMPOUND having the error NFS4ERR_RETRY_UNCACHED_REP.
        Thus, if the requester later retries the request, it will
        get NFS4ERR_RETRY_UNCACHED_REP.

        If a replier receives a retried Sequence operation where the reply
        to the COMPOUND or CB_COMPOUND was not cached, then the replier,

        <list style='symbols'>

        <t>
	  MAY return NFS4ERR_RETRY_UNCACHED_REP
	  in reply to a Sequence operation if the
	  Sequence operation is not the first
	  operation (granted, a requester that
	  does so is in violation of the NFSv4.1
	  protocol).

        </t>

        <t>
	  MUST NOT return
	  NFS4ERR_RETRY_UNCACHED_REP in reply to
	  a Sequence operation if the Sequence
	  operation is the first operation.

        </t>

        </list>

       </t>

       <t>
        If the second operation is an illegal operation, or an
        operation that was legal in a previous minor version of
        NFSv4 and MUST NOT
        be supported in the current minor version (e.g., SETCLIENTID), the
        replier MUST NOT ever return NFS4ERR_RETRY_UNCACHED_REP.
        Instead the replier MUST return NFS4ERR_OP_ILLEGAL or
        NFS4ERR_BADXDR or NFS4ERR_NOTSUPP as appropriate.
       </t>

       <t>
        If the second operation can result in another error status,
        the replier MAY return a status other than NFS4ERR_RETRY_UNCACHED_REP,
        provided the operation is not executed in such a way that the state
        of the replier is changed. Examples of such
        an error status include: NFS4ERR_NOTSUPP returned for an
        operation that is legal but not REQUIRED in the current 
        minor versions, and thus not supported by the replier;
        NFS4ERR_SEQUENCE_POS; and NFS4ERR_REQ_TOO_BIG.
       </t>

       </list>
      </t>
    
      <t>
	The discussion above assumes that the
	retried request matches the original
	one.  <xref target="false_retry"/>
	discusses what the replier might do, and
	MUST do when original and retried requests do not match.
        Since the replier may
	only cache a small amount of the
	information that would be required to
	determine whether this is a case of a
	false retry, the replier may send to the
	client any of the following responses:

	<list style='symbols'>

	<t>
         The cached reply to the original request (if the replier has cached
         it in its entirety and the users of the original request and retry match).
        </t>

	<t>
          A reply that consists only of the Sequence operation with the error
	  NFS4ERR_FALSE_RETRY.
        </t>

        <t>
	A reply consisting of the response to Sequence  with the status
	NFS4_OK, together with the second operation as it appeared in the retried
	request with an error of NFS4ERR_RETRY_UNCACHED_REP or other error as
	described above.
        </t>

	<t>
          A reply that consists of the response to Sequence with the status
	NFS4_OK, together with the second operation as it appeared in the original
	request with an error of NFS4ERR_RETRY_UNCACHED_REP or other error as
	described above.
        </t>
        </list>

      </t>

        <section anchor="false_retry" title="False Retry">
          <t>
	If a requester sent a Sequence operation
	with a slot ID and sequence ID that are
	in the reply cache but the replier
	detected that the retried request is not
	the same as the original request,
	including a retry that has different
	operations or different arguments in the
	operations from the original and a retry
	that uses a different principal in the
	RPC request's credential field that
	translates to a different user, then this
	is a false retry. When the replier
	detects a false retry, it is permitted 
	(but not always obligated) to return
	NFS4ERR_FALSE_RETRY in response to the
	Sequence operation when it detects a
	false retry.

          </t>
         
          <t>
	Translations of particularly privileged
	user values to other users due to the
	lack of appropriately secure credentials,
	as configured on the replier, should be
	applied before determining whether the
	users are the same or different. If the
	replier determines the users are
	different between the original request
	and a retry, then the replier MUST return
	NFS4ERR_FALSE_RETRY.

          </t>

          <t>
	If an operation of the retry is an
	illegal operation, or an operation that
	was legal in a previous minor version of
	NFSv4 and MUST NOT be supported in the 
	current minor version (e.g., SETCLIENTID),
	the replier MAY return
	NFS4ERR_FALSE_RETRY (and MUST do so if
	the users of the original request and
	retry differ). Otherwise, the replier MAY return
	NFS4ERR_OP_ILLEGAL or NFS4ERR_BADXDR or
	NFS4ERR_NOTSUPP as appropriate.  Note
	that the handling is in contrast for how the
	replier deals with retries requests with
	no cached reply. The difference is due to
	NFS4ERR_FALSE_RETRY being a valid error
	for only Sequence operations, whereas
	NFS4ERR_RETRY_UNCACHED_REP is a valid
	error for all operations except illegal
	operations and operations that MUST NOT be
	supported in the current minor version of
	NFSv4.

          </t>
        </section>
        
     </section> <!-- Optional Reply Caching -->
    </section> <!-- Slot Identifiers and Server Reply Cache -->


    <section anchor="Retry_and_Replay" title="Retry and Replay of Reply">
    <t>
     A requester MUST NOT retry a request, unless
     the connection it used to send the request
     disconnects. The requester can then reconnect
     and re-send the request, or it can re-send the
     request over a different connection that is
     associated with the same session.
    </t>
    <t>
     If the requester is a server wanting to re-send a callback
     operation over the backchannel of a session, the requester
     of course cannot reconnect because only the client can
     associate connections with the backchannel. The
     server can re-send the request over another connection that
     is bound to the same session's backchannel. If there is no
     such connection, the server
     MUST indicate that the session has no backchannel by setting
     the SEQ4_STATUS_CB_PATH_DOWN_SESSION flag bit in the response
     to the next SEQUENCE operation from the client. The client MUST
     then associate a connection with the session (or destroy
     the session).
    </t>
    <t>
     Note that it is not fatal for a requester to retry
     without a disconnect between the request and retry.
     However, the retry does consume resources, especially
     with RDMA, where each request, retry or not, consumes
     a credit. Retries for no reason, especially retries
     sent shortly after the previous attempt, are a poor
     use of network bandwidth and defeat the purpose of a
     transport's inherent congestion control system.
    </t>
    <t>
     A requester MUST wait for a reply to a request before using
     the slot for another request. If it does not wait for
     a reply, then the requester does not know what
     sequence ID to use for the slot on its next request.
     For example, suppose a requester sends a request with sequence ID
     1, and does not wait for the response. The next time it uses
     the slot, it sends the new request with sequence ID 2.
     If the replier has not seen the request with sequence ID 1, then
     the replier is not expecting sequence ID 2, and rejects the
     requester's new request with NFS4ERR_SEQ_MISORDERED (as the
     result from SEQUENCE or CB_SEQUENCE).
    </t>
    <t>
     RDMA fabrics do not guarantee that the memory handles
     (Steering Tags) within each RPC/RDMA "chunk" <xref target="RPCRDMA" />
     are valid on a scope
     outside that of a single connection.  Therefore, handles used by
     the direct operations become invalid after connection loss.  The
     server must ensure that any RDMA operations that must be replayed
     from the reply cache use the newly provided handle(s) from the
     most recent request.
    </t>
    <t>
     A retry might be sent while the original request is still in
     progress on the replier. The replier SHOULD deal with the issue
     by returning NFS4ERR_DELAY as the reply to SEQUENCE or CB_SEQUENCE
     operation, but implementations MAY return NFS4ERR_MISORDERED.
     Since errors from SEQUENCE and CB_SEQUENCE are
     never recorded in the reply cache, this approach allows the
     results of the execution of the original request to be
     properly recorded in the reply cache (assuming that the requester
     specified the reply to be cached).
    </t>
 
 
     
    </section> <!-- Retry and Replay -->

    <section anchor="sessions_callback_races" title="Resolving Server Callback Races">
    <t>
     It is possible for server callbacks to arrive at the
     client before the reply from related fore channel
     operations. For example, a client may have been
     granted a delegation to a file it has opened, but the
     reply to the OPEN (informing the client of the
     granting of the delegation) may be delayed in the
     network. If a conflicting operation arrives at the
     server, it will recall the delegation using the
     backchannel, which may be on a different
     transport connection, perhaps even a different
     network, or even a different session associated with
     the same client ID.
    </t>
    <t>
     The presence of a session between the client and server
     alleviates this issue. When a session is in place,
     each client request is uniquely identified by its {
     session ID, slot ID, sequence ID } triple. By the rules under which
     slot entries (reply cache entries) are
     retired, the server has knowledge whether the client
     has "seen" each of the server's replies. The server
     can therefore provide sufficient information to the
     client to allow it to disambiguate between an
     erroneous or conflicting callback race
     condition.
    </t>
    <t>
     For each client operation that might result in some
     sort of server callback, the server SHOULD "remember"
     the { session ID, slot ID, sequence ID } triple of the client request
     until the slot ID retirement rules allow the server to
     determine that the client has, in fact, seen the
     server's reply. Until the time the { session ID, slot ID,
     sequence ID } request triple can be retired, any recalls
     of the associated object MUST carry an array of these
     referring identifiers (in the CB_SEQUENCE operation's
     arguments), for the benefit of the client.  After this
     time, it is not necessary for the server to provide
     this information in related callbacks, since it is
     certain that a race condition can no longer occur.
    </t>
    <t>
     The CB_SEQUENCE operation that begins each server
     callback carries a list of "referring" { session ID, slot ID,
     sequence ID } triples.  If the client finds the request
     corresponding to the referring session ID, slot ID, and sequence ID
     to be currently outstanding (i.e., the server's reply has
     not been seen by the client), it can determine that
     the callback has raced the reply, and act
     accordingly. If the client does not find the request
     corresponding to the referring triple to be outstanding (including
     the case of a session ID referring to a destroyed session),
     then there is no race with respect to this triple.
     The server SHOULD limit the referring triples
     to requests that refer to just those that apply to the objects 
     referred to in
     the CB_COMPOUND procedure.
    </t>
    <t>
     The client must not simply wait forever for the
     expected server reply to arrive before responding to the
     CB_COMPOUND that won the race,
     because it is possible
     that it will be delayed indefinitely. The client should
     assume the likely case that the reply will arrive within
     the average round-trip time for COMPOUND requests to the
     server, and wait that period of time. If
     that period of time
     expires, it can respond to the CB_COMPOUND with
     NFS4ERR_DELAY.  There are other scenarios under which callbacks
     may race replies.
     Among them are pNFS layout recalls as described in
     <xref target="pnfs_operation_sequencing" />.
    </t>
    </section> <!-- Resolving server callback races with sessions -->
   <section anchor="COMPOUND_Sizing_Issues" title="COMPOUND and CB_COMPOUND Construction Issues">

   <t>
    Very large requests and replies may pose both buffer
    management issues (especially with RDMA) and reply
    cache issues. When the session is created
    (<xref target="OP_CREATE_SESSION" />), for each channel (fore and
    back), the client and server
    negotiate the maximum-sized request they will
    send or process (ca_maxrequestsize), the maximum-sized reply
    they will return or process (ca_maxresponsesize), and the 
    maximum-sized reply they will store in the reply cache
    (ca_maxresponsesize_cached).
   </t>
   <t>
    If a request exceeds ca_maxrequestsize, the reply will
    have the status NFS4ERR_REQ_TOO_BIG. A replier MAY
    return NFS4ERR_REQ_TOO_BIG as the status for the first operation
    (SEQUENCE or CB_SEQUENCE) in the request (which means that
    no operations in the request executed and that the
    state of the slot in the reply cache is unchanged), or it MAY
    opt to return it on a subsequent operation in the same
    COMPOUND or CB_COMPOUND request (which means that at least one
    operation did execute and that the state of the slot in the reply cache does
    change). The replier SHOULD set NFS4ERR_REQ_TOO_BIG on the
    operation that exceeds ca_maxrequestsize.
   </t>
   <t>
    If a reply exceeds ca_maxresponsesize, the reply will
    have the status NFS4ERR_REP_TOO_BIG. A replier MAY
    return NFS4ERR_REP_TOO_BIG as the status for the first operation
    (SEQUENCE or CB_SEQUENCE) in the request, or it MAY
    opt to return it on a subsequent operation (in the same
    COMPOUND or CB_COMPOUND reply). A replier MAY return NFS4ERR_REP_TOO_BIG
    in the reply to SEQUENCE or CB_SEQUENCE, even if the response
    would still exceed ca_maxresponsesize.
   </t>
   <t>
    If sa_cachethis or csa_cachethis is TRUE, then the
    replier MUST cache a reply except if an error is
    returned by the SEQUENCE or CB_SEQUENCE operation (see
    <xref target="err_sequence" />). If the reply exceeds
    ca_maxresponsesize_cached (and sa_cachethis or
    csa_cachethis is TRUE), then the server MUST return
    NFS4ERR_REP_TOO_BIG_TO_CACHE. Even if
    NFS4ERR_REP_TOO_BIG_TO_CACHE (or any other error for
    that matter) is returned on an operation other than the
    first operation (SEQUENCE or CB_SEQUENCE), then
    the reply MUST be cached if sa_cachethis or
    csa_cachethis is TRUE.
    For example, if a COMPOUND has eleven
    operations, including SEQUENCE, the fifth operation is
    a RENAME, and the tenth operation is a READ for one
    million bytes, the server may return
    NFS4ERR_REP_TOO_BIG_TO_CACHE on the tenth operation.
    Since the server executed several operations, especially
    the non-idempotent RENAME, the client's request to
    cache the reply needs to be honored in order for the
    correct operation of exactly once semantics. If the
    client retries the request, the server will have cached
    a reply that contains results for ten of the eleven requested
    operations, with
    the tenth operation having a status of NFS4ERR_REP_TOO_BIG_TO_CACHE.
   </t>
   <t>
    A client needs to take care that when sending
    operations that change the current filehandle (except for
    PUTFH, PUTPUBFH, PUTROOTFH, and RESTOREFH), it
    not exceed the maximum reply buffer before the GETFH
    operation. Otherwise, the client will have to retry
    the operation that changed the current filehandle, in order
    to obtain the desired filehandle.
    For the OPEN operation (see <xref target="OP_OPEN" />),
    retry is not always available as an option.
    The following guidelines for the handling of
    filehandle-changing operations are advised:
    <list style="symbols">
    <t>
     Within the same COMPOUND procedure, a client
     SHOULD send GETFH immediately after a current
     filehandle-changing operation. A client
     MUST send GETFH after a current filehandle-changing operation
     that is also non-idempotent (e.g., the OPEN operation), unless
     the operation is RESTOREFH. RESTOREFH is
     an exception, because even though it is
     non-idempotent, the filehandle RESTOREFH
     produced originated from an operation that
     is either idempotent (e.g., PUTFH, LOOKUP),
     or non-idempotent (e.g., OPEN, CREATE). If the
     origin is non-idempotent, then because the client
     MUST send GETFH after the origin operation, the
     client can recover if RESTOREFH returns an error.

    </t>
    <t>
     A server MAY return NFS4ERR_REP_TOO_BIG or
     NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE)
     on a filehandle-changing operation if the reply would
     be too large on the next operation.
    </t>
    <t>
     A server SHOULD return NFS4ERR_REP_TOO_BIG or
     NFS4ERR_REP_TOO_BIG_TO_CACHE (if sa_cachethis is TRUE)
     on a filehandle-changing, non-idempotent operation if the reply would
     be too large on the next operation, especially if the operation
     is OPEN.
    </t>
    <t>
     A server MAY return NFS4ERR_UNSAFE_COMPOUND to a non-idempotent
     current filehandle-changing operation, if
     it looks at the next operation (in the same COMPOUND procedure)
     and finds it is
     not GETFH. The server SHOULD do this if it is unable to
     determine in advance whether the total response size
     would exceed ca_maxresponsesize_cached or ca_maxresponsesize.
    </t>
    </list>
   </t>
   </section> <!-- COMPOUND and CB_COMPOUND Construction Issues -->
   <section anchor="Persistence" title="Persistence">
   <t>
    Since the reply cache is bounded, it is practical for
    the reply cache to persist across server restarts.
    The replier MUST persist the following information
    if it agreed to persist the session (when the session
    was created; see <xref target="OP_CREATE_SESSION" />):

    <list style='symbols'>
    <t>
     The session ID.
    </t>
    <t>
     The slot table including the sequence ID and cached reply for
     each slot.
    </t>
    </list>
    The above are sufficient for a replier to provide EOS semantics
    for any requests that were sent and executed before the server
    restarted.
    If the replier is a client, then there is no need for
    it to persist any more information, unless the client will
    be persisting all other state across client restart, in which case,
    the server will never see any NFSv4.1-level protocol manifestation
    of a client restart.
    If the replier is a server, with just the
    slot table and session ID persisting,
    any requests the client retries after the server restart will 
    return the results that are cached in the reply cache, 
    and any new requests (i.e., the sequence ID is one greater than the
    slot's sequence ID) MUST be rejected with NFS4ERR_DEADSESSION
    (returned by SEQUENCE). Such a session is considered dead.
    A server MAY re-animate a session
    after a server restart so that the session will accept new
    requests as well as retries. To re-animate a session,
    the server needs to persist additional information
    through server restart:
    <list style='symbols'>
    <t>
     The client ID. This is a prerequisite to let the client
     create more sessions associated with the same client ID
     as the re-animated session.
    </t>
    <t>
     The client ID's sequence ID that is used for creating
     sessions (see Sections <xref target="OP_EXCHANGE_ID" format="counter" /> and
     <xref target="OP_CREATE_SESSION" format="counter" />). This is a
     prerequisite to let the client create more sessions.
    </t>
    <t>
     The principal that created the client ID. This
     allows the server to authenticate the client when
     it sends EXCHANGE_ID.
    </t>
    <t>
     The SSV, if SP4_SSV state protection was
     specified when the client ID was created (see <xref
     target="OP_EXCHANGE_ID" />). This lets the 
     client create new sessions, and associate connections
     with the new and existing sessions.
    </t>
    <t>
     The properties of the client ID as defined in
     <xref target="OP_EXCHANGE_ID" />.
    </t>
     

    </list>
   </t>
   <t>
    A persistent reply cache places certain demands on the server.
    The execution of the sequence of operations (starting with SEQUENCE)
    and placement of its results in the persistent cache MUST be atomic. If
    a client retries a sequence of operations that was previously
    executed on the server, the only acceptable outcomes are either
    the original cached reply or an indication that the client ID
    or session has been lost (indicating a catastrophic loss
    of the reply cache or a session that has been deleted because
    the client failed to use the session for an extended period
    of time).
   </t>
   <t>
    A server could fail and restart in the middle of a
    COMPOUND procedure that contains one or more non-idempotent
    or idempotent-but-modifying operations. This creates
    an even higher challenge for atomic execution and
    placement of results in the reply cache. One way
    to view the problem is as a single transaction consisting of
    each operation in the COMPOUND followed by storing
    the result in persistent storage, then finally a transaction
    commit. If there is a failure before the transaction
    is committed, then the server rolls back the transaction.
    If the server itself fails, then when it restarts, its
    recovery logic could roll back the transaction
    before starting the NFSv4.1 server.
   </t>
   <t>
    While the description of the
    implementation for atomic execution of the request
    and caching of the reply
    is beyond the scope of this document, an example implementation
    for NFSv2 <xref target="RFC1094"/> is described in <xref target="ha_nfs_ibm" />.
   </t>
   </section> <!-- Persistence -->
  </section> <!-- Exactly Once Semantics -->
  <section anchor="RDMA_Considerations" title="RDMA Considerations">
  <t>
   A complete discussion of the operation of RPC-based
   protocols over RDMA transports is in <xref target="RPCRDMA" />. A
   discussion of the operation of NFSv4, including NFSv4.1,
   over RDMA is in <xref target="NFSDDP" />.  Where RDMA is considered,
   this specification assumes the use of such a layering;
   it addresses only the upper-layer issues relevant to
   making best use of RPC/RDMA.

  </t>
   <section anchor="RDMA_Connection_Resources" title="RDMA Connection Resources">
   <t>
    RDMA requires its consumers to register memory and post
    buffers of a specific size and number for receive
    operations.

   </t>
   <t>
    Registration of memory can be a relatively high-overhead operation,
    since it requires pinning of buffers, assignment of attributes
    (e.g., readable/writable), and initialization of hardware
    translation.  Preregistration is desirable to reduce overhead.
    These registrations are specific to hardware interfaces and even to
    RDMA connection endpoints; therefore, negotiation of their limits is
    desirable to manage resources effectively.
   </t>
   <t>
    Following basic registration, these buffers must be posted by
    the RPC layer to handle receives.  These buffers remain in use by
    the RPC/NFSv4.1 implementation; the size and number of them must be
    known to the remote peer in order to avoid RDMA errors that would
    cause a fatal error on the RDMA connection.
   </t>
   <t>
    NFSv4.1 manages slots as resources on a per-session
    basis (see <xref target="Session" />), while RDMA
    connections manage credits on a per-connection basis.
    This means that in order for a peer to send data over
    RDMA to a remote buffer, it has to have both an NFSv4.1
    slot and an RDMA credit.  If multiple RDMA connections
    are associated with a session, then if the total number
    of credits across all RDMA connections associated with
    the session is X, and the number of slots in the session
    is Y, then the maximum number of outstanding requests
    is the lesser of X and Y.

   </t>
   </section> <!-- RDMA Connection Resources -->
   <section anchor="Flow_Control" title="Flow Control">
   <t>
    Previous versions of NFS do not provide flow control;
    instead, they rely on the windowing provided by
    transports like TCP to throttle requests.  This does
    not work with RDMA, which provides no operation flow
    control and will terminate a connection in error when
    limits are exceeded. 

    Limits such as maximum number of requests
    outstanding are therefore negotiated when a session
    is created (see the ca_maxrequests field in <xref
    target="OP_CREATE_SESSION" />).  These limits then
    provide the maxima within which each connection associated
    with the session's channel(s) must remain.
    RDMA connections are managed within these limits as
    described in Section 3.3 of <xref target="RPCRDMA" />; if there are multiple
    RDMA connections, then the maximum number of requests
    for a channel will be divided among the RDMA
    connections.  Put a different way, the onus is on the
    replier to ensure that the total number of RDMA credits
    across all connections associated with the replier's
    channel does exceed the channel's maximum number of
    outstanding requests.

   </t>
   <t>
    The limits may also be modified
    dynamically at the replier's choosing by manipulating
    certain parameters present in each NFSv4.1 reply. In
    addition, the CB_RECALL_SLOT callback operation (see
    <xref target="OP_CB_RECALL_SLOT" />) can be sent by
    a server to a client to return RDMA credits to the
    server, thereby lowering the maximum number of requests
    a client can have outstanding to the server.

   </t>
   </section> <!-- Flow Control -->

   <section anchor="Padding" title="Padding">
   <t>
        Header padding is requested by each peer at session initiation
        (see the ca_headerpadsize argument to CREATE_SESSION in
        <xref target="OP_CREATE_SESSION" />), and
        subsequently used by the RPC RDMA layer, as described in <xref target="RPCRDMA" />.
        Zero padding is permitted.
   </t>
   <t>
        Padding leverages the useful property
        that RDMA preserve alignment of data, even when they are
        placed into anonymous (untagged) buffers.  If requested, client
        inline writes will insert appropriate pad bytes within the request
        header to align the data payload on the specified boundary.  The
        client is encouraged to add sufficient padding (up to the
        negotiated size) so that
        the "data" field of the WRITE operation
        is aligned.
        Most servers can make good use of such padding,
        which allows them to chain receive buffers in such a way that any
        data carried by client requests will be placed into appropriate
        buffers at the server, ready for file system processing.  The
        receiver's RPC layer encounters no overhead from skipping over pad
        bytes, and the RDMA layer's high performance makes the insertion
        and transmission of padding on the sender a significant
        optimization.  In this way, the need for servers to perform RDMA
        Read to satisfy all but the largest client writes is obviated.  An
        added benefit is the reduction of message round trips on the network
        -- a potentially good trade, where latency is present.
   </t>
   <t>
        The value to choose for padding is subject to a number of criteria.
        A primary source of variable-length data in the RPC header is the
        authentication information, the form of which is client-determined,
        possibly in response to server specification.  The contents of
        COMPOUNDs, sizes of strings such as those passed to RENAME, etc. all
        go into the determination of a maximal NFSv4.1 request size and
        therefore minimal buffer size.  The client must select its offered
        value carefully, so as to avoid overburdening the server, and vice
        versa.  The benefit of an appropriate padding value is higher
        performance.
   </t>
   <figure>
   <artwork>
                 Sender gather:
     |RPC Request|Pad  bytes|Length| -> |User data...|
     \------+----------------------/      \
             \                             \
              \    Receiver scatter:        \-----------+- ...
         /-----+----------------\            \           \
         |RPC Request|Pad|Length|   ->  |FS buffer|->|FS buffer|->...
   </artwork>
   </figure>
   <t>
        In the above case, the server may recycle unused buffers to the
        next posted receive if unused by the actual received request, or
        may pass the now-complete buffers by reference for normal write
        processing.  For a server that can make use of it, this removes
        any need for data copies of incoming data, without resorting to
        complicated end-to-end buffer advertisement and management.  This
        includes most kernel-based and integrated server designs, among
        many others.  The client may perform similar optimizations, if
        desired.
   </t>
   </section> <!-- Padding -->
   <section anchor="dual" title="Dual RDMA and Non-RDMA Transports">
   <t>
    Some RDMA transports (e.g., <xref target="RDMAP">RFC 5040</xref>)
    permit a "streaming" (non-RDMA) phase,
    where ordinary traffic might flow before "stepping up"
    to RDMA mode, commencing RDMA traffic.  Some RDMA
    transports start connections always in RDMA mode.
    NFSv4.1 allows, but does not assume, a streaming phase
    before RDMA mode.  When a connection
    is associated with a session, the client and server negotiate whether the
    connection is used in RDMA or non-RDMA mode  (see Sections
    <xref target="OP_CREATE_SESSION" format="counter" /> and
    <xref target="OP_BIND_CONN_TO_SESSION" format="counter" />).
   </t>
   </section> <!-- RDMA Transports -->

  </section> <!-- RDMA Considerations -->

  <section anchor="Sessions_Security" title="Session Security">
   <section anchor="Session_Callback_Security" title="Session Callback Security">
   <t>
    Via session/connection association, NFSv4.1 improves security over
    that provided by NFSv4.0 for the backchannel.  The
    connection is client-initiated (see
    <xref target="OP_BIND_CONN_TO_SESSION" />) and subject to the same
    firewall and routing checks as the fore channel.
    At the client's option (see <xref target="OP_EXCHANGE_ID" />),
    connection association is fully authenticated before being
    activated (see <xref target="OP_BIND_CONN_TO_SESSION" />).
    Traffic from the server over the
    backchannel is authenticated exactly as the client specifies
    (see <xref target="Backchannel_RPC_Security" />).
   </t>
   </section> <!-- Session Callback Security -->
    <section anchor="Backchannel_RPC_Security" title="Backchannel RPC Security">
    <t>
     When the NFSv4.1 client establishes the backchannel, it
     informs the  server of the security flavors and principals
     to use when sending requests. If the security flavor is
     RPCSEC_GSS, the client expresses the principal in the form
     of an established RPCSEC_GSS context.  The server is free
     to use any of the flavor/principal combinations the client
     offers, but it MUST NOT use unoffered combinations.

     This way, the client need not provide a target
     GSS principal for the backchannel as it did with
     NFSv4.0, nor does the server have to implement an
     RPCSEC_GSS initiator as it did with NFSv4.0 <xref
     target="RFC3530" />.

    </t>
    <t>
     The CREATE_SESSION (<xref target="OP_CREATE_SESSION" />)
     and BACKCHANNEL_CTL (<xref target="OP_BACKCHANNEL_CTL" />)
     operations allow the client to specify flavor/principal combinations.
    </t>
    <t>
     Also note that the SP4_SSV state protection mode 
     (see Sections <xref target="OP_EXCHANGE_ID" format="counter" /> and <xref
     target="protect_state_change" format="counter" />) has the side
     benefit of providing SSV-derived RPCSEC_GSS contexts (<xref target="ssv_mech" />).
    </t>
    </section> <!-- Backchannel RPC Security -->

   <section anchor="protect_state_change" title="Protection from Unauthorized State Changes">
   <t>
     As described to this point in the specification, the state model
     of NFSv4.1 is vulnerable to an attacker that
     sends a SEQUENCE operation with a forged session ID and with a slot ID that
     it expects the legitimate client to use next. When the legitimate client
     uses the slot ID with the same sequence number, the server
     returns the attacker's result from the reply cache, which
     disrupts the legitimate client and thus denies service to it.
     Similarly, an attacker could send a CREATE_SESSION with a forged
     client ID to create a new session associated with the client ID.
     The attacker could send requests using the new session that
     change locking state, such as LOCKU operations to release locks
     the legitimate client has acquired. Setting a security
     policy on the file that requires RPCSEC_GSS credentials when
     manipulating the file's state is one potential work around,
     but has the disadvantage of preventing a legitimate client from
     releasing state when RPCSEC_GSS is required to do so, but
     a GSS context cannot be obtained (possibly because the user
     has logged off the client).
   </t>
   <t>
     NFSv4.1 provides three options to a client for state protection,
     which are specified when a client creates
     a client ID via EXCHANGE_ID (<xref target="OP_EXCHANGE_ID" />).
   </t>
   <t>
     The first (SP4_NONE) is to simply waive state protection.
   </t>
   <t>
     The other two options (SP4_MACH_CRED and SP4_SSV)
     share several traits:
     <list style="symbols">
     <t>
      An RPCSEC_GSS-based credential is used to authenticate
      client ID and session maintenance operations,
      including creating and destroying a session,
      associating a connection with the session, and
      destroying the client ID.
     </t>
     <t>
      Because RPCSEC_GSS is used to authenticate
      client ID and session maintenance, the attacker cannot
      associate a rogue connection with a legitimate session, or
      associate a rogue session with a legitimate client ID in
      order to maliciously alter the client ID's lock state 
      via CLOSE, LOCKU, DELEGRETURN, LAYOUTRETURN, etc.
     </t>
     <t>
      In cases where the server's security policies on a
      portion of its namespace require RPCSEC_GSS authentication,
      a client may have to use an RPCSEC_GSS credential
      to remove per-file state (e.g., LOCKU, CLOSE, etc.).
      The server may require that the principal that removes
      the state match certain criteria (e.g.,
      the principal might have to be the same as the one
      that acquired the state). However, the client might
      not have an RPCSEC_GSS context for such a principal,
      and might not be able to create such a context (perhaps
      because the user has logged off). When the client
      establishes SP4_MACH_CRED or SP4_SSV protection,
      it can specify a list of operations that the server MUST
      allow using the machine credential (if SP4_MACH_CRED
      is used) or the SSV credential (if SP4_SSV is used).
     </t>
     </list>
   </t>
   <t>
     The SP4_MACH_CRED  state protection option uses a machine
     credential where the principal that
     creates the client ID MUST also be the principal
     that performs client ID and session maintenance 
    operations.
     The security of the machine credential state protection approach
     depends entirely on safe guarding the per-machine credential.
     Assuming a proper safeguard using the per-machine credential
     for operations like CREATE_SESSION, BIND_CONN_TO_SESSION,
     DESTROY_SESSION, and DESTROY_CLIENTID will prevent an attacker
     from associating a rogue connection with a session, or
     associating a rogue session with a client ID.
   </t>
   <t>
     There are at least three scenarios for the SP4_MACH_CRED
     option:
     <list style="numbers">
     <t>
      The system administrator configures a unique,
      permanent per-machine credential for one of the
      mandated GSS mechanisms (e.g., if Kerberos
      V5 is used, a "keytab" containing a principal derived from a
      client host name could be used).

     </t>
     <t>
      The client is used by a single user, and so the
      client ID and its sessions are used by just that
      user. If the user's credential expires, then session
      and client ID maintenance cannot occur, but since
      the client has a single user, only that user is
      inconvenienced.

     </t>
     <t>
      The physical client has multiple users, but the
      client implementation has a unique client ID for
      each user. This is effectively the same as the
      second scenario, but a disadvantage is that each
      user needs to be allocated at least one session each,
      so the approach suffers from lack of economy.

     </t>

     </list>
   </t>
   <t>
     The SP4_SSV protection option uses the SSV (<xref
     target="intro_definitions"/>), via RPCSEC_GSS and the SSV GSS
     mechanism (<xref target="ssv_mech" />), to protect state from attack.
     The SP4_SSV protection option is intended for the situation
     comprised of a client that has multiple active users and a system
     administrator who wants to avoid the burden of installing a permanent
     machine credential on each client.  The SSV is
     established and updated on the server via SET_SSV (see <xref
     target="OP_SET_SSV" />). To prevent eavesdropping,
     a client SHOULD send SET_SSV via RPCSEC_GSS with
     the privacy service.  Several aspects of the SSV
     make it intractable for an attacker to guess the SSV,
     and thus associate rogue connections with a session,
     and rogue sessions with a client ID:

    <list style="symbols">
    <t>
      The arguments to and results of SET_SSV include digests of the old and
      new SSV, respectively.
    </t>
    <t>
      Because the initial value of the SSV is zero,
      therefore known, the client that opts for SP4_SSV
      protection and opts to apply SP4_SSV protection to
      BIND_CONN_TO_SESSION and CREATE_SESSION MUST send
      at least one SET_SSV operation before the first
      BIND_CONN_TO_SESSION operation or before the second
      CREATE_SESSION operation on a client ID. If it does
      not, the SSV mechanism will not generate tokens
      (<xref target="ssv_mech" />).

      A client SHOULD send SET_SSV as soon as a session
      is created.

    </t>
    <t>
      A SET_SSV request does not replace the SSV with the argument to
      SET_SSV. Instead, the current SSV on the server is logically
      exclusive ORed (XORed) with the argument to SET_SSV.
      Each time a new principal uses a client ID for the first
      time, the client
      SHOULD send a SET_SSV with that principal's RPCSEC_GSS
      credentials, with RPCSEC_GSS service set to RPC_GSS_SVC_PRIVACY.
    </t>
    </list>
   </t>
   <t>
     Here are the types of attacks that can be attempted by an attacker named
     Eve on a victim named Bob, and how SP4_SSV protection foils
     each attack:
     <list style="symbols">
     <t>
       Suppose Eve is the first user to log into a
       legitimate client.  Eve's use of an NFSv4.1
       file system will cause the legitimate client to
       create a client ID
       with SP4_SSV protection, specifying that the BIND_CONN_TO_SESSION
       operation MUST use the SSV credential. Eve's use of
       the file system also causes an SSV to be created.  The
       SET_SSV operation that creates the SSV will be protected by
       the RPCSEC_GSS context created by the legitimate
       client, which uses Eve's GSS principal and
       credentials. Eve can eavesdrop on the network while
       her RPCSEC_GSS context is created and the SET_SSV
       using her context is sent. Even if the legitimate
       client sends the SET_SSV with RPC_GSS_SVC_PRIVACY,
       because Eve knows her own credentials, she can
       decrypt the SSV.  Eve can compute an RPCSEC_GSS
       credential that BIND_CONN_TO_SESSION will accept,
       and so associate a new connection with the
       legitimate session. Eve can change the slot ID and
       sequence state of a legitimate session, and/or the
       SSV state, in such a way that when Bob accesses
       the server via the same legitimate client, the
       legitimate client will be unable to use the session.

       <vspace blankLines='1' />

       The client's only recourse is to create a new client
       ID for Bob to use, and establish a new SSV for the
       client ID.  The client will be unable to delete
       the old client ID, and will let the lease on the old
       client ID expire.

       <vspace blankLines='1' />

       Once the legitimate client establishes an SSV over
       the new session using Bob's RPCSEC_GSS context,
       Eve can use the new session via the legitimate
       client, but she cannot disrupt Bob.  Moreover,
       because the client SHOULD have modified the SSV
       due to Eve using the new session, Bob cannot get
       revenge on Eve by associating a rogue connection
       with the session. 

       <vspace blankLines='1' />

       The question is how did the legitimate client detect
       that Eve has hijacked the old session?  When the
       client detects that a new principal, Bob, wants to
       use the session, it SHOULD have sent a SET_SSV,
       which leads to the following sub-scenarios:

       <vspace blankLines='1' />

       <list style="symbols">
       <t>
         Let us suppose that from the rogue connection, Eve
         sent a SET_SSV with the same slot ID and sequence ID that
         the legitimate client later uses. The server will
         assume the SET_SSV sent with Bob's credentials is a retry,
         and return to the legitimate
         client the reply it sent Eve.  However, unless Eve can
         correctly guess the SSV the legitimate client will use,
         the digest verification checks in the SET_SSV response
         will fail.  That is an indication to the client that the
         session has apparently been hijacked.
         <vspace blankLines='1' />
       </t>
       <t>
         Alternatively, Eve sent a SET_SSV with a different slot ID than
         the legitimate client uses for its SET_SSV. Then the digest
         verification of the SET_SSV sent with Bob's credentials fails
         on the server, and the error returned to the client makes it
         apparent that the session has been hijacked.
         <vspace blankLines='1' />
       </t>
       <t>
         Alternatively, Eve sent an operation other than SET_SSV,
         but with the same slot ID and sequence that the legitimate client
         uses for its SET_SSV. The server returns to the legitimate
         client the response it sent Eve.  The client sees that the
         response is not at all what it expects. The client
         assumes either session hijacking or a server bug, and either way
         destroys the old session.
         <vspace blankLines='1' />
       </t>
       </list>
     </t>
     <t>
       Eve associates a rogue connection with the session
       as above, and then destroys the session. Again, Bob
       goes to use the server from the legitimate client,
       which sends a SET_SSV using Bob's credentials. The client receives an error
       that indicates that the session does not exist. When
       the client tries to create a new session, this
       will fail because the SSV it has does not match that which the
       server has, and now the client knows the session
       was hijacked. The legitimate client establishes a
       new client ID.

       <vspace blankLines='1' />

     </t>
     <t>
       If Eve creates a connection before the legitimate
       client establishes an SSV, because the initial
       value of the SSV is zero and therefore known,
       Eve can send a SET_SSV that will pass the digest
       verification check.  However, because the new
       connection has not been associated with the session,
       the SET_SSV is rejected for that reason.

       <vspace blankLines='1' />

     </t>
     </list>
     In summary, an attacker's disruption of state when
     SP4_SSV protection is in use is limited to the
     formative period of a client ID, its first session,
     and the establishment of the SSV. Once a non-malicious
     user uses the client ID, the client quickly detects
     any hijack and rectifies the situation. Once a
     non-malicious user successfully modifies the SSV,
     the attacker cannot use NFSv4.1 operations to disrupt
     the non-malicious user.

   </t>

   <t>
     Note that neither the SP4_MACH_CRED nor
     SP4_SSV protection approaches prevent hijacking
     of a transport connection that has previously been
     associated with a session. If the goal of a counter-threat
     strategy is to prevent connection hijacking, the use of IPsec is RECOMMENDED.
   </t>

   <t>
     If a connection hijack occurs, the hijacker could in
     theory change locking state and negatively impact the
     service to legitimate clients.  However, if the server
     is configured to require the use of RPCSEC_GSS with
     integrity or privacy on the affected file objects, and
     if EXCHGID4_FLAG_BIND_PRINC_STATEID capability (<xref
     target="OP_EXCHANGE_ID"/>) is in force, this will
     thwart unauthorized attempts to change locking state.
   </t>

   </section> <!-- Protection from Unauthorized State Changes -->
  </section> <!-- Sessions Security -->
  <section title="The Secret State Verifier (SSV) GSS Mechanism" anchor="ssv_mech">
  <t>
   The SSV provides the secret key for a GSS mechanism internal to NFSv4.1
   that NFSv4.1 uses for state protection. Contexts for this
   mechanism are not established via the RPCSEC_GSS
   protocol.  Instead, the contexts are automatically
   created when EXCHANGE_ID specifies
   SP4_SSV protection.  The only tokens
   defined are the PerMsgToken (emitted by GSS_GetMIC)
   and the SealedMessage token (emitted by GSS_Wrap).
  </t>
  <t>
   The mechanism OID for the SSV mechanism is
   iso.org.dod.internet.private.enterprise.Michael
   Eisler.nfs.ssv_mech (1.3.6.1.4.1.28882.1.1).  While the
   SSV mechanism does not define any initial context
   tokens, the OID can be used to let servers indicate
   that the SSV mechanism is acceptable whenever the
   client sends a SECINFO or SECINFO_NO_NAME operation
   (see

   <xref target="Security_Service_Negotiation" />).

  </t>

  <t>
   The SSV mechanism defines four subkeys derived from
   the SSV value. Each time SET_SSV is invoked, the subkeys
   are recalculated by the client and server. The
   calculation of each of the four subkeys depends on each
   of the four respective ssv_subkey4 enumerated values. The calculation
   uses the HMAC
   <xref target="RFC2104" /> algorithm, using the current SSV as the key, the one-way hash
   algorithm as negotiated by EXCHANGE_ID,
   and the input text as represented by the XDR encoded
   enumeration value for that subkey of data type ssv_subkey4.
   If the length of the output of the HMAC algorithm exceeds the length of
   key of the encryption algorithm (which is also negotiated by EXCHANGE_ID),
   then the subkey MUST be truncated from the HMAC output, i.e., if the
   subkey is of N bytes long, then the first N bytes of the HMAC output
   MUST be used for the subkey. The specification of EXCHANGE_ID
   states that the length of the output of the HMAC algorithm MUST NOT
   be less than the length of subkey needed for the encryption algorithm
   (see <xref target="OP_EXCHANGE_ID"/>).
  </t>
<figure>
 <artwork>

/* Input for computing subkeys */
enum ssv_subkey4 {
        SSV4_SUBKEY_MIC_I2T     = 1,
        SSV4_SUBKEY_MIC_T2I     = 2,
        SSV4_SUBKEY_SEAL_I2T    = 3,
        SSV4_SUBKEY_SEAL_T2I    = 4
};

 </artwork>
</figure>
  <t>
   The subkey derived from SSV4_SUBKEY_MIC_I2T
   is used for calculating message integrity codes (MICs)
   that originate from the NFSv4.1 client, whether as part
   of a request over the fore channel or a response
   over the backchannel. The subkey derived from
   SSV4_SUBKEY_MIC_T2I is used for MICs originating from the
   NFSv4.1 server. The subkey derived from SSV4_SUBKEY_SEAL_I2T
   is used for encryption text originating from the NFSv4.1
   client, and the subkey derived from SSV4_SUBKEY_SEAL_T2I
   is used for encryption text originating from the 
   NFSv4.1 server.
  </t>
  <t>
   The PerMsgToken description is based on an XDR definition:
  </t>
<figure>
 <artwork>

/* Input for computing smt_hmac */
struct ssv_mic_plain_tkn4 {
  uint32_t        smpt_ssv_seq;
  opaque          smpt_orig_plain&lt;>;
};

 </artwork>
</figure>
<figure>
 <artwork>

/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
  uint32_t        smt_ssv_seq;
  opaque          smt_hmac&lt;>;
};

 </artwork>
</figure>
  <t>

   The field smt_hmac is an HMAC calculated by using the
   subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I  as the key, the one-way hash algorithm
   as negotiated by EXCHANGE_ID, and the input text
   as represented by data of type ssv_mic_plain_tkn4.
   The field smpt_ssv_seq is the same as smt_ssv_seq.
   The field smpt_orig_plain is the "message" input passed
   to GSS_GetMIC() (see Section 2.3.1 of <xref target="RFC2743"/>).
   The caller of GSS_GetMIC() provides a pointer to a buffer
   containing the plain text. The SSV mechanism's entry point for
   GSS_GetMIC() encodes this into an opaque array, and the encoding
   will include an initial four-byte length, plus any necessary padding.
   Prepended to this will be the XDR encoded value of smpt_ssv_seq,
   thus making up an XDR encoding of a value of data type
   ssv_mic_plain_tkn4, which in turn is the input into the HMAC.
  </t>
  <t>
   The token emitted by GSS_GetMIC() is XDR encoded and
   of XDR data type ssv_mic_tkn4.  The field smt_ssv_seq
   comes from the SSV sequence number, which is equal to
   one after SET_SSV (<xref target="OP_SET_SSV" />)
   is called the first time on a client
   ID.
   Thereafter, the SSV sequence number is incremented on each SET_SSV.
   Thus, smt_ssv_seq represents the version of the SSV at
   the time GSS_GetMIC() was called.  As noted in <xref
   target="OP_EXCHANGE_ID" />, the client and server
   can maintain multiple concurrent versions of the SSV.
   This allows the SSV to be changed without serializing
   all RPC calls that use the SSV mechanism with SET_SSV
   operations.
   Once the HMAC is calculated, it is XDR encoded into
   smt_hmac, which will include an initial four-byte length,
   and any necessary padding. Prepended to this will be
   the XDR encoded value of smt_ssv_seq.

   </t>
  <t>
   The SealedMessage description is based on an XDR definition:
  </t>
<figure>
 <artwork>

/* Input for computing ssct_encr_data and ssct_hmac */
struct ssv_seal_plain_tkn4 {
  opaque          sspt_confounder&lt;>;
  uint32_t        sspt_ssv_seq;
  opaque          sspt_orig_plain&lt;>;
  opaque          sspt_pad&lt;>;
};

 </artwork>
</figure>
<figure>
 <artwork>

/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
  uint32_t      ssct_ssv_seq;
  opaque        ssct_iv&lt;>;
  opaque        ssct_encr_data&lt;>;
  opaque        ssct_hmac&lt;>;
};

 </artwork>
</figure>
  <t>
   The token emitted by GSS_Wrap() is XDR encoded and
   of XDR data type ssv_seal_cipher_tkn4.

  </t>

  <t>
   The ssct_ssv_seq field has the same meaning as smt_ssv_seq.

  </t>

  <t>
   The ssct_encr_data field is the result of encrypting a
   value of the XDR encoded data type ssv_seal_plain_tkn4.
   The encryption key is the subkey derived from SSV4_SUBKEY_SEAL_I2T
   or SSV4_SUBKEY_SEAL_T2I, and the encryption
   algorithm is that negotiated by EXCHANGE_ID.
  </t>

  <t>
   The ssct_iv field is the initialization vector (IV)
   for the encryption algorithm (if applicable) and is
   sent in clear text. The content and size of the IV MUST
   comply with the specification of the encryption algorithm.
   For example, the id-aes256-CBC algorithm MUST use
   a 16-byte initialization vector (IV), which MUST be
   unpredictable for each instance of a value of data type
   ssv_seal_plain_tkn4 that is encrypted with a particular
   SSV key.

  </t>
  <t>
   The ssct_hmac field is the result of computing an HMAC using the value
   of the XDR encoded data type ssv_seal_plain_tkn4 as the input
   text. The key is the subkey derived from SSV4_SUBKEY_MIC_I2T or
   SSV4_SUBKEY_MIC_T2I, and the one-way hash algorithm is that
   negotiated by EXCHANGE_ID.

  </t>
  <t>
   The sspt_confounder field is a random value.

  </t>
  <t>
   The sspt_ssv_seq field is the same as ssvt_ssv_seq.

  </t>
  <t>
   The field sspt_orig_plain field is the original plaintext
   and is the "input_message" input passed to
   GSS_Wrap() (see Section 2.3.3 of <xref target="RFC2743"/>).
   As with the handling of the plaintext by the SSV mechanism's
   GSS_GetMIC() entry point, the entry point for GSS_Wrap()
   expects a pointer to the plaintext, and will XDR encode
   an opaque array into sspt_orig_plain
   representing the plain text, along with
   the other fields of an instance of data type ssv_seal_plain_tkn4.

  </t>
  <t>
   The sspt_pad field is present to support encryption
   algorithms that require inputs to be in fixed-sized
   blocks.  The content of sspt_pad is zero filled
   except for the length.  Beware that the XDR encoding
   of ssv_seal_plain_tkn4 contains three variable-length
   arrays, and so each array consumes four bytes for an
   array length, and each array that follows the length
   is always padded to a multiple of four bytes per the
   XDR standard.

  </t>
  <t>
   For example, suppose the encryption algorithm uses 16-byte blocks, and
   the sspt_confounder is three bytes long, and
   the sspt_orig_plain field is 15 bytes long.

   The XDR encoding of sspt_confounder uses eight bytes
   (4 + 3 + 1 byte pad),

   the XDR encoding of sspt_ssv_seq uses four bytes,

   the XDR encoding of sspt_orig_plain uses 20 bytes
   (4 + 15 + 1 byte pad),

   and the smallest XDR encoding of the sspt_pad field
   is four bytes.

   This totals 36 bytes. The next multiple of 16 is 48;
   thus, the length field of sspt_pad needs to be set to
   12 bytes, or a total encoding of 16 bytes.

   The total number of XDR encoded bytes is thus 8 +
   4 + 20 + 16 = 48.

  </t>
  <t>
   GSS_Wrap() emits a token that is an XDR
   encoding of a value of data type ssv_seal_cipher_tkn4.

   Note that regardless of whether or not the caller of GSS_Wrap()
   requests confidentiality, the token always has
   confidentiality. This is because the SSV mechanism
   is for RPCSEC_GSS, and RPCSEC_GSS never produces
   GSS_wrap() tokens without confidentiality.

  </t>
  <t>
   There is one SSV per client ID.
   There is a single GSS context for
   a client ID / SSV pair.
   All SSV mechanism RPCSEC_GSS handles of a client ID / SSV pair
   share the same GSS context.
   SSV GSS contexts do not expire except when the SSV
   is destroyed (causes would include the client ID
   being destroyed or a server restart).
   Since one
   purpose of context expiration is to replace keys that
   have been in use for "too long", hence vulnerable to
   compromise by brute force or accident, the client can
   replace the SSV key by
   sending periodic SET_SSV operations, which is done by cycling through
   different users' RPCSEC_GSS credentials. This way, the SSV is
   replaced without destroying the SSV's GSS contexts.
  </t>
  <t>
   SSV RPCSEC_GSS handles can be expired or deleted by the server
   at any time, and the EXCHANGE_ID operation can be used to create
   more SSV RPCSEC_GSS handles. Expiration of SSV RPCSEC_GSS handles
   does not imply that the SSV or its GSS context has expired.
  </t>
  <t>
   The client MUST establish an SSV via SET_SSV before the
   SSV GSS context can be used to emit tokens from GSS_Wrap()
   and GSS_GetMIC(). If SET_SSV has not been successfully
   called, attempts to emit tokens MUST fail.

  </t>
  <t>
   The SSV mechanism does not support replay detection and sequencing
   in its tokens because RPCSEC_GSS does not use those features (See
   Section 5.2.2, "Context Creation Requests", in <xref target="RFC2203"
   />). However, <xref target="rpcsec_ssv_consider"/> discusses special
   considerations for the SSV mechanism when used with RPCSEC_GSS.

  </t>
  </section> <!-- The SSV GSS Mechanism -->

  <section anchor="rpcsec_ssv_consider" title="Security Considerations for RPCSEC_GSS When Using the SSV Mechanism">
  <t>
    When a client ID is created with SP4_SSV state protection (see <xref
    target="OP_EXCHANGE_ID"/>), the client is permitted to associate
    multiple RPCSEC_GSS handles with the single SSV GSS context
    (see <xref target="ssv_mech"/>). Because of the way RPCSEC_GSS
    (both version 1 and version 2, see <xref target="RFC2203"/> and
    <xref target="RFC5403"/>) calculate the verifier of the reply,
    special care must be taken by the implementation of the NFSv4.1
    client to prevent attacks by a man-in-the-middle.  The verifier
    of an RPCSEC_GSS reply is the output of GSS_GetMIC() applied to
    the input value of the seq_num field of the RPCSEC_GSS credential
    (data type rpc_gss_cred_ver_1_t) (see Section 5.3.3.2 of <xref
    target="RFC2203"/>). If multiple RPCSEC_GSS handles share the same
    GSS context, then if one handle is used to send a request with the
    same seq_num value as another handle, an attacker could block the
    reply, and replace it with the verifier used for the other handle.

  </t>

  <t>
   There are multiple ways to prevent the attack on the SSV RPCSEC_GSS
   verifier in the reply. The simplest is believed to be as follows.

   <list style='symbols'>

  <t>
   Each time one or more new SSV RPCSEC_GSS handles are created via
   EXCHANGE_ID, the client SHOULD send a SET_SSV operation to modify
   the SSV. By changing the SSV, the new handles will not result in the
   re-use of an SSV RPCSEC_GSS verifier in a reply.

  </t>
  
  <t>
   When a requester decides to use N SSV RPCSEC_GSS handles, it SHOULD
   assign a unique and non-overlapping range of seq_nums to each SSV
   RPCSEC_GSS handle. The size of each range SHOULD be equal to MAXSEQ
   / N (see Section 5 of <xref target="RFC2203"/> for the definition
   of MAXSEQ). When an SSV RPCSEC_GSS handle reaches its maximum, it
   SHOULD force the replier to destroy the handle by sending a NULL
   RPC request with seq_num set to MAXSEQ + 1 (see Section 5.3.3.3 of
   <xref target="RFC2203"/>).

  </t>

  <t>
   When the requester wants to increase or decrease N, it SHOULD force
   the replier to destroy all N handles by sending a NULL RPC request on
   each handle with seq_num set to MAXSEQ + 1. If the requester is the
   client, it SHOULD send a SET_SSV operation before using new handles.
   If the requester is the server, then the client SHOULD send a SET_SSV
   operation when it detects that the server has forced it to destroy a
   backchannel's SSV RPCSEC_GSS handle. By sending a SET_SSV operation,
   the SSV will change, and so the attacker will be unavailable to
   successfully replay a previous verifier in a reply to the requester.

  </t>

  </list>
  </t>

  <t>
    Note that if the replier carefully creates the SSV RPCSEC_GSS
    handles, the related risk of a man-in-the-middle splicing a forged
    SSV RPCSEC_GSS credential with a verifier for another handle does
    not exist. This is because the verifier in an RPCSEC_GSS request
    is computed from input that includes both the RPCSEC_GSS handle and
    seq_num (see Section 5.3.1 of <xref target="RFC2203"/>). Provided the
    replier takes care to avoid re-using the value of an RPCSEC_GSS
    handle that it creates, such as by including a generation number in the
    handle, the man-in-the-middle will not be able to successfully replay
    a previous verifier in the request to a replier.

  </t>

  </section>

  <section anchor="Session_Mechanics_Steady_State" title="Session Mechanics - Steady State">

   <section anchor="Obligations_of_the_Server" title="Obligations of the Server">
   <t>
    The server has the primary obligation to monitor the
    state of backchannel resources that the client has
    created for the server (RPCSEC_GSS contexts and backchannel
    connections). If these resources vanish, the
    server takes action as specified in <xref target="Events_Requiring_Server_Action" />.
   </t>
   </section> <!-- Obligations of the Server -->

   <section anchor="Obligations_of_the_Client" title="Obligations of the Client">
   <t>
   The client SHOULD honor the following obligations in order to
   utilize the session:
   <list style="symbols">
   <t>
     Keep a necessary session from going idle on the server. A client
     that requires a session but nonetheless is not
     sending operations risks having the session be destroyed
     by the server. This is because sessions consume
     resources, and resource limitations may force the
     server to cull an inactive session. A server MAY consider
     a session to be inactive if the client has not used
     the session before the session inactivity timer (<xref
     target="session_inactive"/>) has expired.

   </t>
   <t>
     Destroy the session when not needed. If a client has
     multiple sessions, one of which has no
     requests waiting for replies, and has been idle for
     some period of time, it SHOULD destroy the session.
   </t>
   <t>
     Maintain GSS contexts and RPCSEC_GSS handles
     for the backchannel. If the client
     requires the server to use the RPCSEC_GSS security
     flavor for callbacks, then it needs to be sure the
     RPCSEC_GSS handles and/or their GSS
     contexts that are handed to the server via BACKCHANNEL_CTL or
     CREATE_SESSION are unexpired.
   </t>
   <t>
     Preserve a connection for a backchannel. The server
     requires a backchannel in order to gracefully recall
     recallable state or notify the client of certain
     events. Note that if the connection is not being used
     for the fore channel, there is no way for the client to tell
     if the connection is still alive (e.g., the server
     restarted without sending a disconnect). The onus is
     on the server, not the client, to determine if the
     backchannel's connection is alive, and to indicate in
     the response to a SEQUENCE operation when the last
     connection associated with a session's backchannel
     has disconnected.

   </t>
   </list>
   </t>
   </section> <!-- Obligations of the Client -->

   <section anchor="Steps_the_Client_Takes_To_Establish_a_Session"
	    title="Steps the Client Takes to Establish a Session">
   <t>
     If the client does not have a client ID, the client
     sends EXCHANGE_ID to establish a client ID.  If it
     opts for SP4_MACH_CRED or SP4_SSV protection, in the
     spo_must_enforce list of operations, it SHOULD at
     minimum specify CREATE_SESSION, DESTROY_SESSION,
     BIND_CONN_TO_SESSION, BACKCHANNEL_CTL, and DESTROY_CLIENTID.
     If it opts for SP4_SSV protection, the client needs to
     ask for SSV-based RPCSEC_GSS handles.

   </t>
   <t>
     The client uses the client ID to send a
     CREATE_SESSION on a connection to the server.
     The results of CREATE_SESSION indicate whether or not the
     server will persist the session reply cache through
     a server that has restarted, and the client notes this
     for future reference.

   </t>
   <t>
     If the client specified SP4_SSV state protection
     when the client ID was created, then it SHOULD send
     SET_SSV in the first COMPOUND after the session is
     created. Each time a new principal goes to use the
     client ID, it SHOULD send a SET_SSV again.

   </t>
   <t>
     If the client wants to use delegations, layouts,
     directory notifications, or any other state that
     requires a backchannel, then it needs to add a connection
     to the backchannel if CREATE_SESSION did not already
     do so.  The client creates a connection, and calls
     BIND_CONN_TO_SESSION to associate the connection
     with the session and the session's backchannel. If
     CREATE_SESSION did not already do so, the client MUST
     tell the server what security is required in order
     for the client to accept callbacks. The client does
     this via BACKCHANNEL_CTL. If the client selected
     SP4_MACH_CRED or SP4_SSV protection when it called
     EXCHANGE_ID, then the client SHOULD specify that the
     backchannel use RPCSEC_GSS contexts for security.

   </t>
   <t>
     If the client wants to use additional
     connections for the backchannel, then it needs to call
     BIND_CONN_TO_SESSION on each connection it wants to
     use with the session. If the client wants to use
     additional connections for the fore channel, then
     it needs to call BIND_CONN_TO_SESSION if it specified
     SP4_SSV or SP4_MACH_CRED state protection when the
     client ID was created.

   </t>

   <t>
     At this point, the session has reached steady state.
   </t>
   </section> <!-- Steps the Client Takes To Establish a Session -->
  </section> <!-- Session Mechanics - Steady State -->

  <section anchor="session_inactive" title="Session Inactivity Timer" >
  <t>
   The server MAY maintain a session inactivity timer for
   each session.  If the session inactivity timer expires,
   then the server MAY destroy the session. To avoid losing
   a session due to inactivity, the client MUST renew
   the session inactivity timer. The length of session
   inactivity timer MUST NOT be less than the lease_time
   attribute (<xref target="attrdef_lease_time"/>).
   As with lease renewal (<xref target="lease_renewal"/>),
   when the server receives a SEQUENCE operation,
   it resets the session inactivity timer, and MUST NOT allow the
   timer to expire while the rest of the operations in the
   COMPOUND procedure's request are still executing. Once the
   last operation has finished, the server MUST set the session
   inactivity timer to expire no sooner than the sum of the
   current time and the value of the lease_time attribute.
  </t>

  </section>
  <section anchor="Session_Mechanics_Recovery" title="Session Mechanics - Recovery">


   <section anchor="Events_Requiring_Client_Action" title="Events Requiring Client Action">

   <t>
   The following events require client action to recover.
   </t>
   <section title="RPCSEC_GSS Context Loss by Callback Path">
   <t>
    If all RPCSEC_GSS handles
    granted by the client to the server for callback use have
    expired, the client MUST
    establish a new handle via BACKCHANNEL_CTL. The
    sr_status_flags field of the SEQUENCE results indicates when callback handles
    are nearly expired, or fully expired (see <xref target="OP_SEQUENCE_DESCRIPTION"/>).
   </t>
   </section> <!-- RPCSEC_GSS Context Loss by Callback_Path -->
   <section title="Connection Loss">
   <t>
    If the client loses the last connection of the session
    and wants to retain the session, then it needs to
    create a new connection, and if, when the client
    ID was created, BIND_CONN_TO_SESSION was specified
    in the spo_must_enforce list, the client MUST use
    BIND_CONN_TO_SESSION to associate the connection with
    the session.

   </t>
   <t>
    If there was a request outstanding at the time
    of connection loss, then if the client wants to continue
    to use the session, it MUST retry the request, as
    described in
    <xref target="Retry_and_Replay" />. Note that it
    is not necessary to retry requests over a connection
    with the same source network address or the same
    destination network address as the lost connection. As
    long as the session ID, slot ID, and sequence ID in the
    retry match that of the original request, the server
    will recognize the request as a retry if it executed
    the request prior to disconnect.

   </t>
   <t>
    If the connection that was lost was the last one associated with
    the backchannel, and the client wants to retain the backchannel and/or
    prevent revocation of recallable state, the client needs to
    reconnect, and if it does, it
    MUST associate the connection to the session and backchannel via
    BIND_CONN_TO_SESSION.
    The server SHOULD indicate when it has no callback connection
    via the sr_status_flags result from SEQUENCE.
   </t>
   </section> <!-- Connection Disconnect -->
   <section title="Backchannel GSS Context Loss">
   <t>
    Via the sr_status_flags result of the SEQUENCE operation or
    other means, the client will learn if some or all of
    the RPCSEC_GSS contexts it assigned to the backchannel have
    been lost. If the client wants to retain the backchannel and/or
    not put recallable state subject to revocation,
    the client needs to use BACKCHANNEL_CTL to
    assign new contexts.
   </t>
   </section> <!-- Backchannel GSS Context Loss -->

    <section anchor="loss_of_session" title="Loss of Session">
    <t>
     The replier might lose a record of the session. Causes include:
     <list style="symbols">
      <t>
        Replier failure and restart.
      </t>
      <t>
        A catastrophe that causes the reply cache to be corrupted or
        lost on the media on which it was stored. This applies
        even if the replier indicated in the CREATE_SESSION results
        that it would persist the cache.
      </t>
      <t>
        The server purges the session of a client that has been
        inactive for a very extended period of time.
      </t>
      <t>
        As a result of configuration changes among a set of clustered
        servers, a network address previously connected to one 
        server becomes connected to a different server that has
        no knowledge of the session in question.  Such a configuration
        change will generally only happen when the original server
        ceases to function for a time.
      </t>
     </list>
     Loss of reply cache is equivalent to loss of session.
     The replier indicates loss of session to the requester
     by returning NFS4ERR_BADSESSION on the next operation
     that uses the session ID that refers to the lost
     session.
    </t>
    <t>
     After an event like a server restart, the client may have
     lost its connections. The client assumes for the moment
     that the session has not been lost. It reconnects, and
     if it specified connection association enforcement when
     the session was created, it 
     invokes BIND_CONN_TO_SESSION using the session ID. Otherwise,
     it invokes SEQUENCE. If
     BIND_CONN_TO_SESSION or SEQUENCE returns NFS4ERR_BADSESSION, the
     client knows the session is not available to it when communicating
     with that network address. If the connection survives
     session loss, then the next SEQUENCE operation the client
     sends over the connection will get back NFS4ERR_BADSESSION.
     The client again knows the session was lost.
    </t>
    <t>
     Here is one suggested algorithm for the client when it gets 
     NFS4ERR_BADSESSION.  It is not obligatory in that, if a 
     client does not want to take advantage of such features as 
     trunking, it may omit parts of it.  However, it is a useful
     example that draws attention to various possible recovery 
     issues:
     <list style="numbers">
       <t>
         If the client has other connections to
         other server network addresses
         associated with the same session, attempt
         a COMPOUND with a single operation, SEQUENCE,
         on each of the other connections.
       </t>
       <t>
         If the attempts succeed, the session is still alive,
         and this is a strong indicator that the server's
         network address has moved.
         The client might send an EXCHANGE_ID on the
         connection that returned NFS4ERR_BADSESSION
         to see if there are opportunities for client ID
         trunking (i.e., the same client ID and so_major are
         returned). The client might use DNS to see if
         the moved network address was replaced with another,
         so that the performance and availability benefits of
         session trunking can continue.
       </t>
       <t>
         If the SEQUENCE requests fail with NFS4ERR_BADSESSION,
         then the session no longer exists on any of the
         server network addresses for which the client has connections
         associated with that session ID. It is possible the
         session is still alive and available on other
         network addresses. The client sends an EXCHANGE_ID
         on all the connections to see if the server owner
         is still listening on those network addresses.
         If the same server owner is returned but a new
         client ID is returned, this is a strong
         indicator of a server restart. If both the same
         server owner and same client ID are
         returned, then this is a strong indication
         that the server did delete the session, and the
         client will need to send a CREATE_SESSION if it
         has no other sessions for that client ID.
         If a different server owner is returned,
         the client can use DNS to find
         other network addresses. If it does not, or if
         DNS does not find any other addresses for the server,
         then the client will be unable to provide NFSv4.1
         service, and fatal errors should be returned
         to processes that were using the server. If the
         client is using a "mount" paradigm, unmounting
         the server is advised.
       </t>
       <t>
         If the client knows of no other connections associated
         with the session ID and server network addresses that
         are, or have been, associated with the session ID,
         then the client can use DNS to find
         other network addresses. If it does not, or if
         DNS does not find any other addresses for the server,
         then the client will be unable to provide NFSv4.1
         service, and fatal errors should be returned
         to processes that were using the server. If the
         client is using a "mount" paradigm, unmounting
         the server is advised.
       </t>
     </list>
    </t>
    <t>
      If there is a reconfiguration event that results in the 
      same network address being assigned to servers where the 
      eir_server_scope value is different, it cannot be guaranteed
      that a session ID generated by the first will be recognized
      as invalid by the first.  Therefore, in managing server
      reconfigurations among servers with different server scope
      values, it is necessary to make sure that all clients have
      disconnected from the first server before effecting
      the reconfiguration.  Nonetheless, clients should not
      assume that servers will always adhere to this requirement;
      clients MUST be prepared to deal with unexpected
      effects of server reconfigurations.
      Even where a session ID is inappropriately 
      recognized as valid, it is likely either that the connection 
      will not be recognized as valid or that a sequence value
      for a slot will not be correct.  Therefore, when a client
      receives results indicating such unexpected errors, the use of
      EXCHANGE_ID to determine the current server configuration
      is RECOMMENDED.
    </t>
    <t>
      A variation on the above is that after a server's network 
      address moves, there is no NFSv4.1 server listening, e.g., no 
      listener on port 2049. In this example, one of the following occur: the NFSv4 server returns 
      NFS4ERR_MINOR_VERS_MISMATCH, the NFS server returns a 
      PROG_MISMATCH error, the RPC listener on 2049 returns 
      PROG_UNVAIL, or attempts to reconnect to the network address 
      timeout. These SHOULD be treated as equivalent to SEQUENCE 
      returning NFS4ERR_BADSESSION for these purposes.
    </t>
    <t>
     When the client detects session loss, it needs to call CREATE_SESSION
     to recover.  Any non-idempotent operations that were in progress
     might have been performed on the server at the time of
     session loss. The client has no general way to recover from this.
    </t>
    <t>
     Note that loss of session does not imply loss of byte-range lock, open, delegation,
     or layout state because locks, opens, delegations, and layouts
     are tied to the client ID and depend on the client ID, not the session.
     Nor does loss of byte-range lock, open, delegation,
     or layout state imply loss of session state, because the session depends
     on the client ID; loss of client ID however does imply loss of
     session, byte-range lock, open, delegation, and layout state.
     See <xref target="server_failure" />.
     A session can survive a server restart,
     but lock recovery may still be needed.
    </t>
    <t>
     It is possible that CREATE_SESSION will fail with NFS4ERR_STALE_CLIENTID
     (e.g., the server restarts and does not preserve client ID
     state).
     If so, the client needs to call EXCHANGE_ID, followed by 
     CREATE_SESSION.
    </t>
    </section> <!-- Loss of Session -->
   </section> <!-- Events Requiring Client Action -->

   <section anchor="Events_Requiring_Server_Action" title="Events Requiring Server Action">
   <t>
     The following events require server action to recover.
   </t>
    <section title="Client Crash and Restart">
    <t>
    As described in <xref target="OP_EXCHANGE_ID" />,
    a restarted client sends EXCHANGE_ID in such a way that it
    causes the server to delete any sessions it had.
    </t>
    </section> <!-- Client Crash and Restart -->
    <section title="Client Crash with No Restart" anchor="client_crash_no_restart">
    <t>
    If a client crashes and never comes back, it will never send
    EXCHANGE_ID with its old client owner. Thus, the server has session
    state that will never be used again. After an extended period of time,
    and if the server has resource constraints, it MAY destroy the old
    session as well as locking state.
    </t>
    </section> <!-- Client Crash with No Restart -->
    <section title="Extended Network Partition">
    <t>
     To the server, the extended network partition may be no
     different from a
     client crash with no
     restart (see
     <xref target="client_crash_no_restart" />).
     Unless the server can discern that there is
     a network partition, it is free to treat the
     situation as if the client has crashed permanently.
    </t>
    </section> <!-- "Extended Network Partition" -->
    <section title="Backchannel Connection Loss">
    <t>
     If there were callback requests outstanding at the time
     of a connection loss, then the server
     MUST retry the requests, as described in
     <xref target="Retry_and_Replay" />. Note that it
     is not necessary to retry requests over a connection
     with the same source network address or the same destination
     network address as the lost connection. As long as
     the session ID, slot ID, and sequence ID in the retry
     match that of the original request, the callback target will
     recognize the request as a retry even if it did see the request
     prior to disconnect.
    </t>
    <t>
     If the connection lost is the last one associated with the backchannel,
     then the server MUST indicate that in the sr_status_flags field of
     every SEQUENCE reply until the backchannel is re-established.
     There are two situations, each of which uses different
     status flags: no connectivity for the session's backchannel
     and no connectivity for any session backchannel of the client.
     See <xref target="OP_SEQUENCE" /> for a description of
     the appropriate flags in sr_status_flags.
    </t>
    </section> <!-- Backchannel Connection Loss -->
    <section title="GSS Context Loss">
    <t>
     The server SHOULD monitor when the number of RPCSEC_GSS
     handles assigned to the backchannel reaches one, and when that
     one handle is near expiry (i.e., between
     one and two periods of lease time), and
     indicate so in the sr_status_flags field of all SEQUENCE replies.
     The server MUST indicate when all of the
     backchannel's assigned RPCSEC_GSS handles
     have expired via the sr_status_flags field of all SEQUENCE replies.
    </t>
    </section> <!-- GSS Context Loss -->
   </section> <!-- Events Requiring Server Action -->
  </section> <!-- Session Mechanics - Recovery -->
  <section title="Parallel NFS and Sessions" anchor="pnfs_and_sessions">
  <t>
   A client and server can potentially be a non-pNFS implementation,
   a metadata server implementation, a data server implementation, or two or
   three types of implementations. The EXCHGID4_FLAG_USE_NON_PNFS,
   EXCHGID4_FLAG_USE_PNFS_MDS, and EXCHGID4_FLAG_USE_PNFS_DS flags
   (not mutually exclusive) are passed in the EXCHANGE_ID arguments
   and results to allow the client to indicate how it wants to use sessions created
   under the client ID, and to allow the server to indicate how it
   will allow the sessions to be used.
   See <xref target="pnfs_session_stuff" /> for pNFS sessions considerations.
  </t>
  </section> <!-- Parallel NFS and Sessions -->
 </section> <!-- Session -->
</section> <!-- Core Infrastructure -->
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Protocol Constants and Data Types">
  <t>
    The syntax and semantics to describe the data types of the NFSv4.1
    protocol are defined in the XDR <xref target="RFC4506">RFC 4506</xref> and RPC 
    <xref target="RFC5531">RFC 5531</xref> documents.  The next sections
    build upon the XDR data types to define constants, types, and structures
    specific to this protocol. The full list of XDR data types is in <xref target="RFC5662" />.
  </t>

  <section title="Basic Constants">
<figure>
 <artwork>
const NFS4_FHSIZE               = 128;
const NFS4_VERIFIER_SIZE        = 8;
const NFS4_OPAQUE_LIMIT         = 1024;
const NFS4_SESSIONID_SIZE       = 16;

const NFS4_INT64_MAX            = 0x7fffffffffffffff;
const NFS4_UINT64_MAX           = 0xffffffffffffffff;
const NFS4_INT32_MAX            = 0x7fffffff;
const NFS4_UINT32_MAX           = 0xffffffff;

const NFS4_MAXFILELEN           = 0xffffffffffffffff;
const NFS4_MAXFILEOFF           = 0xfffffffffffffffe;
 </artwork>
</figure>
  <t>
    Except where noted, all these constants are defined in bytes.
    <list style="symbols">
    <t>
       NFS4_FHSIZE is the maximum size of a filehandle.
    </t>
    <t>
       NFS4_VERIFIER_SIZE is the fixed size of a verifier.
    </t>
    <t>
       NFS4_OPAQUE_LIMIT is the maximum size of certain
       opaque information.
    </t>
    <t>
       NFS4_SESSIONID_SIZE is the fixed size of a session identifier.
    </t>
    <t>
       NFS4_INT64_MAX is the maximum value of a signed 64-bit integer.
    </t>
    <t>
       NFS4_UINT64_MAX is the maximum value of an unsigned 64-bit integer.
    </t>
    <t>
       NFS4_INT32_MAX is the maximum value of a signed 32-bit integer.
    </t>
    <t>
       NFS4_UINT32_MAX is the maximum value of an unsigned 32-bit integer.
    </t>
    <t>
       NFS4_MAXFILELEN is the maximum length of a regular file.
    </t>
    <t>
       NFS4_MAXFILEOFF is the maximum offset into a regular file.
    </t>
    </list>
  </t>
  </section>

  <section title="Basic Data Types">
      <t>
	These are the base NFSv4.1 data types.
      </t>
    <texttable anchor='basic_data_types'>

      <ttcol align='left'>Data Type</ttcol>
      <ttcol align='left'>Definition</ttcol>
	<c>int32_t</c>		<c>typedef int int32_t;</c>

	<c>uint32_t</c>		<c>typedef unsigned int uint32_t;</c>

	<c>int64_t</c>		<c>typedef hyper int64_t;</c>

	<c>uint64_t</c>		<c>typedef unsigned hyper uint64_t;</c>

	<c>attrlist4</c>		<c>typedef opaque attrlist4&lt;>;</c>
	<c/>	<c>Used for file/directory attributes.</c>

	<c>bitmap4</c>		<c>typedef uint32_t bitmap4&lt;>;</c>
	<c/>	<c>Used in attribute array encoding.</c>

	<c>changeid4</c>		<c>typedef uint64_t changeid4;</c>
	<c/>	<c>Used in the definition of change_info4.</c>

	<c>clientid4</c>		<c>typedef uint64_t clientid4;</c>
	<c/>	<c>Shorthand reference to client identification.</c>

	<c>count4</c>		<c>typedef uint32_t count4;</c>
	<c/>	<c>Various count parameters (READ, WRITE, COMMIT).</c>

	<c>length4</c>		<c>typedef uint64_t length4;</c>
	<c/>	<c>The length of a byte-range within a file.</c>

	<c>mode4</c>		<c>typedef uint32_t mode4;</c>
	<c/>	<c>Mode attribute data type.</c>

	<c>nfs_cookie4</c>		<c>typedef uint64_t nfs_cookie4;</c>
	<c/>	<c>Opaque cookie value for READDIR.</c>

	<c>nfs_fh4</c>		<c>typedef opaque nfs_fh4&lt;NFS4_FHSIZE>;</c>
	<c/>	<c>Filehandle definition.</c>

	<c>nfs_ftype4</c>		<c>enum nfs_ftype4;</c>
	<c/>	<c>Various defined file types.</c>

	<c>nfsstat4</c>		<c>enum nfsstat4;</c>
	<c/>	<c>Return value for operations.</c>

	<c>offset4</c>		<c>typedef uint64_t offset4;</c>
	<c/>	<c>Various offset designations (READ, WRITE, LOCK, COMMIT).</c>

	<c>qop4</c>		<c>typedef uint32_t qop4;</c>
	<c/>	<c>Quality of protection designation in SECINFO.</c>

	<c>sec_oid4</c>		<c>typedef opaque sec_oid4&lt;>;</c>
	<c/>	<c>Security Object Identifier.  The sec_oid4 data type is not really opaque.  Instead, it contains an ASN.1 OBJECT IDENTIFIER as used by GSS-API in the mech_type argument to GSS_Init_sec_context. See <xref target="RFC2743" /> for details.</c>

	<c>sequenceid4</c>		<c>typedef uint32_t sequenceid4;</c>
	<c/>	<c>Sequence number used for various session operations (EXCHANGE_ID, CREATE_SESSION, SEQUENCE, CB_SEQUENCE).</c>

	<c>seqid4</c>		<c>typedef uint32_t seqid4;</c>
	<c/>	<c>Sequence identifier used for locking.</c>

	<c>sessionid4</c>		<c>typedef opaque sessionid4[NFS4_SESSIONID_SIZE];</c>
	<c/>	<c>Session identifier.</c>

	<c>slotid4</c>		<c>typedef uint32_t slotid4;</c>
	<c/>	<c>Sequencing artifact for various session operations (SEQUENCE, CB_SEQUENCE).</c>

	<c>utf8string</c>		<c>typedef opaque utf8string&lt;>;</c>
	<c/>	<c>UTF-8 encoding for strings.</c>

	<c>utf8str_cis</c>		<c>typedef utf8string utf8str_cis;</c>
	<c/>	<c>Case-insensitive UTF-8 string.</c>

	<c>utf8str_cs</c>		<c>typedef utf8string utf8str_cs;</c>
	<c/>	<c>Case-sensitive UTF-8 string.</c>

	<c>utf8str_mixed</c>		<c>typedef utf8string utf8str_mixed;</c>
	<c/>	<c>UTF-8 strings with a case-sensitive prefix and a
	case-insensitive suffix.</c>

	<c>component4</c>		<c>typedef utf8str_cs component4;</c>
	<c/>	<c>Represents pathname components.</c>

	<c>linktext4</c>		<c>typedef utf8str_cs linktext4;</c>
	<c/>	<c>Symbolic link contents ("symbolic link" is defined in an <xref target="symlink">Open Group</xref> standard).</c>

	<c>pathname4</c>		<c>typedef component4 pathname4&lt;>;</c>
	<c/>	<c>Represents pathname for fs_locations.</c>

	<c>verifier4</c>		<c>typedef opaque verifier4[NFS4_VERIFIER_SIZE];</c>
	<c/>	<c>Verifier used for various operations (COMMIT, CREATE, EXCHANGE_ID, OPEN, READDIR, WRITE) NFS4_VERIFIER_SIZE is defined as 8.</c>

      <postamble>End of Base Data Types</postamble>
    </texttable>
  </section>

  <!-- start here for the structured data types -->

  <section title="Structured Data Types">

    <section toc="exclude" anchor="nfstime4" title="nfstime4">
<figure>
 <artwork>
struct nfstime4 {
        int64_t         seconds;
        uint32_t        nseconds;
};
 </artwork>
</figure>
      <t>
	The nfstime4 data type gives the number of seconds and
	nanoseconds since midnight or zero hour January 1, 1970
	Coordinated Universal Time (UTC).  Values greater than zero
	for the seconds field denote dates after the zero hour January 1,
	1970.  Values less than zero for the seconds field denote
	dates before the zero hour January 1, 1970.  In both cases, the
	nseconds field is to be added to the seconds field for the
	final time representation.  For example, if the time to be
	represented is one-half second before zero hour January 1, 1970,
	the seconds field would have a value of negative one (-1) and
	the nseconds field would have a value of one-half second
	(500000000).  Values greater than 999,999,999 for nseconds are
	invalid.
      </t>
      <t>
	This data type is used to pass time and date information.  A
	server converts to and from its local representation of time
	when processing time values, preserving as much accuracy as
	possible. If the precision of timestamps stored for a
	file system object is less than defined, loss of precision can
	occur.  An adjunct time maintenance protocol is RECOMMENDED to
	reduce client and server time skew.
      </t>
    </section>

    <section toc="exclude" anchor="time_how4" title="time_how4">
<figure>
 <artwork>
enum time_how4 {
        SET_TO_SERVER_TIME4 = 0,
        SET_TO_CLIENT_TIME4 = 1
};
 </artwork>
</figure>
    </section>

    <section toc="exclude" anchor="settime4" title="settime4">
<figure>
 <artwork>
union settime4 switch (time_how4 set_it) {
 case SET_TO_CLIENT_TIME4:
         nfstime4       time;
 default:
         void;
};
 </artwork>
</figure>
      <t>
	The time_how4 and settime4 data types are used
	for setting timestamps in file object attributes.  If set_it is SET_TO_SERVER_TIME4, then the server
	uses its local representation of time for the time value.
      </t>
    </section>

    <section toc="exclude" anchor="specdata4" title="specdata4">
<figure>
 <artwork>
struct specdata4 {
 uint32_t specdata1; /* major device number */
 uint32_t specdata2; /* minor device number */
};
 </artwork>
</figure>
      <t>
	This data type represents the device numbers for the device file
	types NF4CHR and NF4BLK.
      </t>
    </section>

    <section toc="exclude" anchor="fsid4" title="fsid4">
<figure>
 <artwork>
struct fsid4 {
        uint64_t        major;
        uint64_t        minor;
};
 </artwork>
</figure>
    </section>

    <section toc="exclude" anchor="chg_policy4" title="change_policy4">
<figure>
 <artwork>
struct change_policy4 {
        uint64_t        cp_major;
        uint64_t        cp_minor;
};
 </artwork>
</figure>
      <t>
         The change_policy4 data type is used for the change_policy
         RECOMMENDED attribute.  It provides change sequencing indication
         analogous to the change attribute.  To enable the server to 
         present a value valid across server re-initialization without
         requiring persistent storage, two 64-bit quantities are used,
         allowing one to be a server instance ID and the second to be
         incremented non-persistently, within a given server instance.
      </t>
    </section>

    <section toc="exclude" anchor="fattr4" title="fattr4">
<figure>
 <artwork>
struct fattr4 {
        bitmap4         attrmask;
        attrlist4       attr_vals;
};
 </artwork>
</figure>
      <t>
	The fattr4 data type is used to represent file and directory attributes.
      </t>
      <t>
	The bitmap is a counted array of 32-bit integers used to contain bit
	values.  The position of the integer in the array that contains bit n
	can be computed from the expression (n / 32), and its bit within that
	integer is (n mod 32).
      </t>
      <t>
	<figure>
	  <artwork>
0            1       
+-----------+-----------+-----------+--
|  count    | 31  ..  0 | 63  .. 32 |  
+-----------+-----------+-----------+--
	  </artwork>
	</figure>
      </t>
    </section>

    <section toc="exclude" anchor="change_info4" title="change_info4">
<figure>
 <artwork>
struct change_info4 {
        bool            atomic;
        changeid4       before;
        changeid4       after;
};
 </artwork>
</figure>
      <t>
	This data type is used with the CREATE, LINK, OPEN, REMOVE, and RENAME
	operations to let the client know the value of the change attribute
	for the directory in which the target file system object resides.
      </t>
    </section>

    <section toc="exclude" anchor="netaddr4" title="netaddr4">
<figure>
 <artwork>
struct netaddr4 {
        /* see struct rpcb in RFC 1833 */
        string na_r_netid&lt;>; /* network id */
        string na_r_addr&lt;>;  /* universal address */
};
 </artwork>
</figure>
      <t>
	The netaddr4 data type is used to identify network transport endpoints.
	The r_netid and r_addr fields respectively contain a netid
        and uaddr. The netid and uaddr concepts are defined in
	<xref target="RFC5665"/>. The netid and uaddr formats for
        TCP over IPv4 and TCP over IPv6 are defined in <xref target="RFC5665"/>,
        specifically Tables 2 and 3 and Sections 5.2.3.3 and 5.2.3.4.
      </t>

    </section>

    <section toc="exclude" anchor="state_owner4" title="state_owner4">
<figure>
 <artwork>
struct state_owner4 {
        clientid4       clientid;
        opaque          owner&lt;NFS4_OPAQUE_LIMIT>;
};

typedef state_owner4 open_owner4;
typedef state_owner4 lock_owner4;
 </artwork>
</figure>
    <t>
     The state_owner4 data type is the base type for the 
     open_owner4 (<xref target="open_owner4" />) and
     lock_owner4 (<xref target="lock_owner4" />).
    </t>

     <section toc="exclude" anchor="open_owner4" title="open_owner4">
       <t>
	 This data type is used to identify the owner of OPEN state.
       </t>
     </section>

     <section toc="exclude" anchor="lock_owner4" title="lock_owner4">
       <t>
	 This structure is used to identify the owner of byte-range
         locking state.
       </t>
     </section>
    </section>

    <section toc="exclude" anchor="open_to_lock_owner4" 
	     title="open_to_lock_owner4">
<figure>
 <artwork>
struct open_to_lock_owner4 {
        seqid4          open_seqid;
        stateid4        open_stateid;
        seqid4          lock_seqid;
        lock_owner4     lock_owner;
};
 </artwork>
</figure>
      <t>
	This data type is used for the first LOCK operation done for
	an open_owner4.  It provides both the open_stateid and
	lock_owner, such that the transition is made from a valid
	open_stateid sequence to that of the new lock_stateid
	sequence.  Using this mechanism avoids the confirmation of the
	lock_owner/lock_seqid pair since it is tied to established
	state in the form of the open_stateid/open_seqid.
      </t>
    </section>

    <section toc="exclude" anchor="stateid4" title="stateid4">
<figure>
 <artwork>
struct stateid4 {
        uint32_t        seqid;
        opaque          other[12];
};
 </artwork>
</figure>
      <t>
	This data type is used for the various state sharing
	mechanisms between the client and server.  The client
	never modifies a value of data type stateid.
        The starting value of the
	"seqid" field is undefined.  The server is required to
	increment the "seqid" field by one at each transition
	of the stateid.  This is important since the client will
	inspect the seqid in OPEN stateids to determine the order of
	OPEN processing done by the server.
      </t>
    </section>

    <section toc="exclude" anchor="layouttype4" title="layouttype4">
<figure>
 <artwork>
enum layouttype4 {
        LAYOUT4_NFSV4_1_FILES   = 0x1,
        LAYOUT4_OSD2_OBJECTS    = 0x2,
        LAYOUT4_BLOCK_VOLUME    = 0x3
};
 </artwork>
</figure>

      <t>
	This data type indicates what type of layout is being used.
	The file server advertises the
	layout types it supports through the fs_layout_type file
	system attribute (<xref target="attrdef_fs_layout_type" />).
	A client asks for layouts of a particular type in LAYOUTGET,
	and processes those layouts in its layout-type-specific logic.
      </t>
      <t>
	The layouttype4 data type is 32 bits in length.  The range
	represented by the layout type is split into three parts.  Type
        0x0 is reserved. Types
	within the range 0x00000001-0x7FFFFFFF are globally unique and
	are assigned according to the description in <xref
	target="pnfsiana" />; they are maintained by IANA.  Types
	within the range 0x80000000-0xFFFFFFFF are site specific and
	for private use only.
      </t>
      <t>
	The LAYOUT4_NFSV4_1_FILES enumeration specifies that the NFSv4.1
	file layout type, as defined in <xref target="file_layout_type" />, is to be used.  The LAYOUT4_OSD2_OBJECTS
	enumeration specifies that the object layout, as defined in
	<xref target="RFC5664" />, is to be used.  Similarly,
	the LAYOUT4_BLOCK_VOLUME enumeration specifies that the block/volume
	layout, as defined in <xref target="RFC5663" />, is to be
	used.
      </t>
    </section>

    <section toc="exclude" anchor="deviceid4" title="deviceid4">
<figure>
 <artwork>
const NFS4_DEVICEID4_SIZE = 16;

typedef opaque  deviceid4[NFS4_DEVICEID4_SIZE];
 </artwork>
</figure>
      <t>
	Layout information includes device IDs that
	specify a storage device through a compact handle.
	Addressing and type information is obtained
	with the GETDEVICEINFO operation.  Device IDs
	are not guaranteed to be valid across metadata
	server restarts.  A device ID is unique per client
	ID and layout type.  See <xref target="device_ids"
	/> for more details.

      </t>
    </section>
    <section toc="exclude" anchor="device_addr4"
	     title="device_addr4">
<figure>
 <artwork>
struct device_addr4 {
        layouttype4             da_layout_type;
        opaque                  da_addr_body&lt;>;
};
 </artwork>
</figure>
      <t>
        The device address is used to set up a communication channel
        with the storage device.  Different layout types will require
        different data types to define how they communicate
        with storage devices.  The opaque da_addr_body field is
        interpreted based on the specified da_layout_type field.
      </t>
      <t>
        This document defines the device address for the NFSv4.1 file
        layout (see <xref target="file_data_types" />), which
        identifies a storage device by network IP address and port
        number.  This is sufficient for the clients to communicate
        with the NFSv4.1 storage devices, and may be sufficient for
        other layout types as well.  Device types for object-based storage
        devices and block storage devices (e.g., Small Computer System
         Interface (SCSI) volume labels)
        are defined by their respective layout specifications.
      </t>
    </section>

    <section toc="exclude" anchor="layout_content4" title="layout_content4">
<figure>
 <artwork>
struct layout_content4 {
        layouttype4 loc_type;
        opaque      loc_body&lt;>;
};
 </artwork>
</figure>
      <t>
        The loc_body field is interpreted based on the layout type (loc_type). 
        This document defines the loc_body for the NFSv4.1
	file layout type; see <xref target="file_data_types"
	/> for its definition. 
      </t>
    </section>
    <section toc="exclude" anchor="layout4" title="layout4">
<figure>
 <artwork>
struct layout4 {
        offset4                 lo_offset;
        length4                 lo_length;
        layoutiomode4           lo_iomode;
        layout_content4         lo_content;
};
 </artwork>
</figure>
      <t>
	The layout4 data type defines a layout for a file.  The layout
	type specific data is opaque within lo_content.
        Since layouts are sub-dividable, the offset
	and length together with the file's filehandle, the client ID,
	iomode, and layout type identify the layout.
      </t>
    </section>

    <section toc="exclude" anchor="layoutupdate4"
	     title="layoutupdate4">
<figure>
 <artwork>
struct layoutupdate4 {
        layouttype4             lou_type;
        opaque                  lou_body&lt;>;
};
 </artwork>
</figure>
      <t>
	The layoutupdate4 data type is used by the client to return
	updated layout information to the metadata server via the
	LAYOUTCOMMIT (<xref target="OP_LAYOUTCOMMIT" />) operation.
	This data type provides a channel to pass
	layout type specific information (in field lou_body)
        back to the metadata server.
	For example, for the block/volume layout type, this could include the
	list of reserved blocks that were written.  The contents of
	the opaque lou_body argument are determined by the layout type.
	The NFSv4.1 file-based layout
	does not use this data type; if lou_type is LAYOUT4_NFSV4_1_FILES,
        the lou_body field MUST
	have a zero length.
      </t>
    </section>

    <section toc="exclude" anchor="layouthint4" title="layouthint4">
<figure>
 <artwork>
struct layouthint4 {
        layouttype4             loh_type;
        opaque                  loh_body&lt;>;
};
 </artwork>
</figure>
      <t>
	The layouthint4 data type is used by the client to pass in a
	hint about the type of layout it would like created for a particular
	file.  It is the data type specified by the layout_hint
	attribute described in <xref target="attrdef_layout_hint" />.
	The metadata server may ignore the hint
	or may selectively ignore fields within the hint.  This hint should
	be provided at create time as part of the initial attributes within
	OPEN.  The loh_body field is specific to the type of layout (loh_type).
        The NFSv4.1 file-based layout uses the nfsv4_1_file_layouthint4
	data type as defined in <xref target="file_data_types" />.
      </t>
    </section>


    <section toc="exclude" anchor="layoutiomode4"
	     title="layoutiomode4">
<figure>
 <artwork>
enum layoutiomode4 {
        LAYOUTIOMODE4_READ      = 1,
        LAYOUTIOMODE4_RW        = 2,
        LAYOUTIOMODE4_ANY       = 3
};
 </artwork>
</figure>
      <t>
	The iomode specifies whether the client intends to just read or both
        read and write the data represented by the
	layout.  While the LAYOUTIOMODE4_ANY iomode MUST NOT be used in
        the arguments to the LAYOUTGET operation, it MAY
	be used in the arguments to the LAYOUTRETURN and CB_LAYOUTRECALL
        operations.  The LAYOUTIOMODE4_ANY iomode
	specifies that layouts pertaining to both LAYOUTIOMODE4_READ
        and LAYOUTIOMODE4_RW iomodes are being returned or recalled,
        respectively.  The metadata server's use of the iomode may
        depend on the layout type being used.  The storage devices MAY
        validate I/O accesses against the iomode and reject invalid accesses.
      </t>
    </section>

    <section toc="exclude" anchor="nfs_impl_id4" title="nfs_impl_id4">
<figure>
 <artwork>
struct nfs_impl_id4 {
        utf8str_cis   nii_domain;
        utf8str_cs    nii_name;
        nfstime4      nii_date;
};
 </artwork>
</figure>
      <t>
	This data type is used to identify client and server
	implementation details.  The nii_domain field is the DNS domain
	name with which the implementor is associated.  The nii_name
	field is the product name of the implementation and is
	completely free form.  It is RECOMMENDED that the nii_name be
	used to distinguish machine architecture, machine platforms,
	revisions, versions, and patch levels.  The nii_date field is
	the timestamp of when the software instance was published or
	built.
      </t>
    </section>

    <section toc="exclude" anchor="threshold_item4" title="threshold_item4">
<figure>
 <artwork>
struct threshold_item4 {
        layouttype4     thi_layout_type;
        bitmap4         thi_hintset;
        opaque          thi_hintlist&lt;>;
};
 </artwork>
</figure>
      <t>
	This data type contains a list of hints specific to
	a layout type for helping the client determine when
	it should send I/O directly through the metadata
	server versus the storage devices.  The data type
	consists of the layout type (thi_layout_type),
	a bitmap (thi_hintset) describing the set of
	hints supported by the server (they may differ
	based on the layout type), and a list of hints
	(thi_hintlist) whose content is determined by
	the hintset bitmap.  See the mdsthreshold attribute
	for more details.

      </t>
      <t>
        The thi_hintset field is a bitmap of the following values:
      </t>
      <texttable>
        <ttcol align='left'>name</ttcol>
        <ttcol align='left'>#</ttcol>
        <ttcol align='left'>Data Type</ttcol>
        <ttcol align='left'>Description</ttcol>
  
        <c>threshold4_read_size</c><c>0</c><c>length4</c>
        <c>
           If a file's length is less than the value of threshold4_read_size,
           then it is RECOMMENDED that the client read from the file via the MDS and not
           a storage device.

        </c>
        <c>threshold4_write_size</c><c>1</c><c>length4</c>
        <c>
           If a file's length is less than the value of threshold4_write_size,
           then it is RECOMMENDED that the client write to the file via the MDS and not
           a storage device.
        </c>
        <c>threshold4_read_iosize</c><c>2</c><c>length4</c>
        <c>
          For read I/O sizes below this threshold, it is RECOMMENDED to
  	read data through the MDS.
        </c>
        <c>threshold4_write_iosize</c><c>3</c><c>length4</c>
        <c>
          For write I/O sizes below this threshold, it is RECOMMENDED to
  	write data through the MDS.
        </c>
      </texttable>      
    </section>

    <section toc="exclude" anchor="mdsthreshold4" title="mdsthreshold4">
<figure>
 <artwork>
struct mdsthreshold4 {
        threshold_item4 mth_hints&lt;>;
};
 </artwork>
</figure>
      <t>
        This data type holds an array of elements of data type
        threshold_item4,
	each of which is valid for a particular layout type.  An array
	is necessary because a server can support multiple layout types
	for a single file.
      </t>
    </section>

  </section>
</section>

<!-- End of Data Types -->

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="Filehandles" title="Filehandles">
  <t>
    The filehandle in the NFS protocol is a per-server unique identifier
    for a file system object.  The contents of the filehandle are opaque
    to the client.  Therefore, the server is responsible for translating
    the filehandle to an internal representation of the file system
    object.
  </t>
  <section title="Obtaining the First Filehandle">
    <t>
      The operations of the NFS protocol are defined in terms of one
      or more filehandles.  Therefore, the client needs a filehandle
      to initiate communication with the server.  With the NFSv3
      protocol (<xref target="RFC1813">RFC 1813</xref>), there
      exists an ancillary protocol to obtain this first filehandle.
      The MOUNT protocol, RPC program number 100005, provides the
      mechanism of translating a string-based file system pathname to
      a filehandle, which can then be used by the NFS protocols.
    </t>
    <t>
      The MOUNT protocol has deficiencies in the area of security and
      use via firewalls.  This is one reason that the use of the
      public filehandle was introduced in <xref
      target="RFC2054">RFC 2054</xref> and <xref
      target="RFC2055">RFC 2055</xref>.  With the use of the public
      filehandle in combination with the LOOKUP operation in the NFSv3
      protocol, it has been demonstrated that the
      MOUNT protocol is unnecessary for viable interaction between NFS
      client and server.
    </t>
    <t>
      Therefore, the NFSv4.1 protocol will not use an ancillary
      protocol for translation from string-based pathnames to a filehandle.
      Two special filehandles will be used as starting points for the NFS
      client.
    </t>
    <section title="Root Filehandle">
      <t>
        The first of the special filehandles is the ROOT filehandle.  The ROOT
        filehandle is the "conceptual" root of the file system namespace at
        the NFS server.  The client uses or starts with the ROOT filehandle
        by employing the PUTROOTFH operation.  The PUTROOTFH operation
        instructs the server to set the "current" filehandle to the ROOT of
        the server's file tree.  Once this PUTROOTFH operation is used, the
        client can then traverse the entirety of the server's file tree with
        the LOOKUP operation.  A complete discussion of the server namespace
        is in <xref target="single_server_namespace"/>.
      </t>
    </section>
    <section title="Public Filehandle">
      <t>
        The second special filehandle is the PUBLIC filehandle.  Unlike the
        ROOT filehandle, the PUBLIC filehandle may be bound or represent an
        arbitrary file system object at the server.  The server is responsible
        for this binding.  It may be that the PUBLIC filehandle and the ROOT
        filehandle refer to the same file system object.  However, it is up to
        the administrative software at the server and the policies of the
        server administrator to define the binding of the PUBLIC filehandle
        and server file system object.  The client may not make any
        assumptions about this binding. The client uses the PUBLIC filehandle
        via the PUTPUBFH operation.
      </t>
    </section>
  </section>
  <section title="Filehandle Types">
    <t>
      In the NFSv3 protocol, there was one type of filehandle
      with a single set of semantics.  This type of filehandle is termed
      "persistent" in NFSv4.1.  The semantics of a persistent
      filehandle remain the same as before.  A new type of filehandle
      introduced in NFSv4.1 is the "volatile" filehandle, which
      attempts to accommodate certain server environments.
    </t>
    <t>
      The volatile filehandle type was introduced to address server
      functionality or implementation issues that make correct
      implementation of a persistent filehandle infeasible.  Some server
      environments do not provide a file-system-level invariant that can be
      used to construct a persistent filehandle.  The underlying server
      file system may not provide the invariant or the server's file system
      programming interfaces may not provide access to the needed invariant.
      Volatile filehandles may ease the implementation of server
      functionality such as hierarchical storage management or file system
      reorganization or migration.  However, the volatile filehandle
      increases the implementation burden for the client.
    </t>
    <t>
      Since the client will need to handle persistent and volatile
      filehandles differently, a file attribute is defined that may be used
      by the client to determine the filehandle types being returned by the
      server.
    </t>
    <section title="General Properties of a Filehandle">
      <t>
        The filehandle contains all the information the
        server needs to distinguish an individual file.
        To the client, the filehandle is opaque. The
        client stores filehandles for use in a later
        request and can compare two filehandles from the
        same server for equality by doing a byte-by-byte
        comparison.  However, the client MUST NOT otherwise
        interpret the contents of filehandles.  If two
        filehandles from the same server are equal, they
        MUST refer to the same file.  Servers SHOULD try
        to maintain a one-to-one correspondence between
        filehandles and files, but this is not required.
        Clients MUST use filehandle comparisons only to
        improve performance, not for correct behavior.
        All clients need to be prepared for situations
        in which it cannot be determined whether two
        filehandles denote the same object and in such
        cases, avoid making invalid assumptions that might
        cause incorrect behavior.  Further discussion
        of filehandle and attribute comparison in the
        context of data caching is presented in <xref
        target="data_caching_and_file_identity"/>.

      </t>
      <t>
        As an example, in the case that two different pathnames when
        traversed at the server terminate at the same file system object, the
        server SHOULD return the same filehandle for each path.  This can
        occur if a hard link (see <xref target="hardlink"/>) is used
        to create two file names that refer to the same underlying
        file object and associated data.  For example, if paths /a/b/c
        and /a/d/c refer to the same file, the server SHOULD return
        the same filehandle for both pathnames' traversals.
      </t>
    </section>
    <section title="Persistent Filehandle">
      <t>
        A persistent filehandle is defined as having a fixed value for the
        lifetime of the file system object to which it refers.  Once the
        server creates the filehandle for a file system object, the server
        MUST accept the same filehandle for the object for the lifetime of the
        object.  If the server restarts, the NFS server MUST honor
        the same filehandle value as it did in the server's previous
        instantiation.  Similarly, if the file system is migrated, the new NFS
        server MUST honor the same filehandle as the old NFS server.
      </t>
      <t>
        The persistent filehandle will be become stale or invalid when the
        file system object is removed.  When the server is presented with a
        persistent filehandle that refers to a deleted object, it MUST return
        an error of NFS4ERR_STALE.  A filehandle may become stale when the
        file system containing the object is no longer available.  The file
        system may become unavailable if it exists on removable media and the
        media is no longer available at the server or the file system in whole
        has been destroyed or the file system has simply been removed from the
        server's namespace (i.e., unmounted in a UNIX environment).
      </t>
    </section>
    <section title="Volatile Filehandle">
      <t>
        A volatile filehandle does not share the same longevity
        characteristics of a persistent filehandle.  The server may
        determine that a volatile filehandle is no longer valid at many
        different points in time.  If the server can definitively determine
        that a volatile filehandle refers to an object that has been removed,
        the server should return NFS4ERR_STALE to the client (as is the case
        for persistent filehandles).  In all other cases where the server
        determines that a volatile filehandle can no longer be used, it should
        return an error of NFS4ERR_FHEXPIRED.
      </t>
      <t>
        The REQUIRED attribute "fh_expire_type" is used by the client to
        determine what type of filehandle the server is providing for a
        particular file system.  This attribute is a bitmask with the
        following values:
      </t>
      <t>
        <list style="hanging">
          <t hangText="FH4_PERSISTENT">
            The value of FH4_PERSISTENT is used to indicate a persistent
            filehandle, which is valid until the object is removed from the
            file system.  The server will not return NFS4ERR_FHEXPIRED for this
            filehandle.  FH4_PERSISTENT is defined as a value in which none of the
            bits specified below are set.
          </t>
          <t hangText="FH4_VOLATILE_ANY">
            The filehandle may expire at any time, except as specifically
            excluded (i.e., FH4_NO_EXPIRE_WITH_OPEN).
          </t>
          <t hangText="FH4_NOEXPIRE_WITH_OPEN">
            May only be set when FH4_VOLATILE_ANY is set.  If this bit is set,
            then the meaning of FH4_VOLATILE_ANY is qualified to exclude any
            expiration of the filehandle when it is open.
          </t>
          <t hangText="FH4_VOL_MIGRATION">
	    The filehandle will expire as a result of a file system
	    transition (migration or replication), in those cases in
	    which the continuity of filehandle use is not specified by
	    handle class information
	    within the fs_locations_info attribute.  When this bit is
	    set, clients without access to fs_locations_info
	    information should assume that filehandles will expire on file
	    system transitions.
          </t>
          <t hangText="FH4_VOL_RENAME">
            The filehandle will expire during rename.  This includes a rename by
            the requesting client or a rename by any other client.  If FH4_VOL_ANY
            is set, FH4_VOL_RENAME is redundant.
          </t>
        </list>
      </t>
      <t>
        Servers that provide volatile filehandles that can expire 
        while open require special care as regards handling of RENAMEs
        and REMOVEs.  This situation can arise if FH4_VOL_MIGRATION or 
        FH4_VOL_RENAME is set, if FH4_VOLATILE_ANY is set and 
        FH4_NOEXPIRE_WITH_OPEN is not set, or if a non-read-only file system
        has a transition target in a different handle
         class.  In these cases, the server should deny a RENAME 
        or REMOVE that would affect an OPEN file of any of the
        components leading to the OPEN file.  In addition, the server 
        should deny all RENAME or REMOVE requests during the grace period,
        in order to make sure that reclaims of files where filehandles 
        may have expired do not do a reclaim for the wrong file.
      </t>
      <t>
        Volatile filehandles are especially suitable for implementation
        of the pseudo file systems used to bridge exports.  See 
        <xref target="pseudo_fs_volatility" /> for a discussion of this.
      </t>
    </section>
  </section>
  <section title="One Method of Constructing a Volatile Filehandle">
    <t>
      A volatile filehandle, while opaque to the client, could contain:
    </t>
    <figure>
      <artwork>
[volatile bit = 1 | server boot time | slot | generation number]
o  slot is an index in the server volatile filehandle table

	
o  generation number is the generation number for the table entry/
   slot 
      </artwork>
    </figure>
    <t>
      When the client presents a volatile filehandle, the server makes the
      following checks, which assume that the check for the volatile bit has
      passed.  If the server boot time is less than the current server boot
      time, return NFS4ERR_FHEXPIRED.  If slot is out of range, return
      NFS4ERR_BADHANDLE.  If the generation number does not match, return
      NFS4ERR_FHEXPIRED.
    </t>
    <t>
      When the server restarts, the table is gone (it is volatile).
    </t>
    <t>
      If the volatile bit is 0, then it is a persistent filehandle with a
      different structure following it. 

    </t>
  </section>

  <section title="Client Recovery from Filehandle Expiration">
    <t>
      If possible, the client SHOULD recover from the receipt of an
      NFS4ERR_FHEXPIRED error.  The client must take on additional
      responsibility so that it may prepare itself to recover from the
      expiration of a volatile filehandle.  If the server returns persistent
      filehandles, the client does not need these additional steps.
    </t>
    <t>
      For volatile filehandles, most commonly the client will need to store
      the component names leading up to and including the file system object
      in question.  With these names, the client should be able to recover
      by finding a filehandle in the namespace that is still available or
      by starting at the root of the server's file system namespace.
    </t>
    <t>
      If the expired filehandle refers to an object that has been removed
      from the file system, obviously the client will not be able to recover
      from the expired filehandle.
    </t>
    <t>
      It is also possible that the expired filehandle refers to a file that
      has been renamed.  If the file was renamed by another client, again it
      is possible that the original client will not be able to recover.
      However, in the case that the client itself is renaming the file and
      the file is open, it is possible that the client may be able to
      recover.  The client can determine the new pathname based on the
      processing of the rename request.  The client can then regenerate the
      new filehandle based on the new pathname.  The client could also use
      the COMPOUND procedure to construct a series of operations
      like:
      <figure>
        <artwork>
          RENAME A B
          LOOKUP B
          GETFH
        </artwork>
      </figure>

      Note that the COMPOUND procedure does not provide atomicity.  This
      example only reduces the overhead of recovering from an expired
      filehandle.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="file_attributes" title="File Attributes">
  <t>
    To meet the requirements of extensibility and increased
    interoperability with non-UNIX platforms, attributes need to be handled
    in a flexible manner.  The NFSv3 fattr3 structure contains a
    fixed list of attributes that not all clients and servers are able to
    support or care about.  The fattr3 structure cannot be extended as
    new needs arise and it provides no way to indicate non-support.  With
    the NFSv4.1 protocol, the client is able to query what attributes
    the server supports and construct requests with only those supported
    attributes (or a subset thereof).
  </t>
  <t>
    To this end, attributes are divided into three groups: REQUIRED,
    RECOMMENDED, and named.  Both REQUIRED and RECOMMENDED attributes are
    supported in the NFSv4.1 protocol by a specific and well-defined
    encoding and are identified by number.  They are requested by setting
    a bit in the bit vector sent in the GETATTR request; the server
    response includes a bit vector to list what attributes were returned
    in the response.  New REQUIRED or RECOMMENDED attributes may be added
    to the NFSv4 protocol as part of a new minor version
    by publishing a
    Standards Track RFC that allocates a new attribute number value and
    defines the encoding for the attribute.  See
    <xref target="minor_versioning"/> for further
    discussion.
  </t>
  <t>
    Named attributes are accessed by the new OPENATTR operation, which
    accesses a hidden directory of attributes associated with a file
    system object.  OPENATTR takes a filehandle for the object and returns
    the filehandle for the attribute hierarchy.  The filehandle for the
    named attributes is a directory object accessible by LOOKUP or READDIR
    and contains files whose names represent the named attributes and
    whose data bytes are the value of the attribute.  For example:
  </t>
  <texttable>
    <ttcol align='left' />
    <ttcol align='left' />
    <ttcol align='left' />
    <c>LOOKUP</c><c>"foo"</c><c>; look up file</c>
    <c>GETATTR</c><c>attrbits</c><c />
    <c>OPENATTR</c><c /><c>; access foo's named attributes</c>
    <c>LOOKUP</c><c>"x11icon"</c><c>; look up specific attribute</c>
    <c>READ</c><c>0,4096</c><c>; read stream of bytes</c>
  </texttable>
  <t>
    Named attributes are intended for data needed by applications rather
    than by an NFS client implementation.  NFS implementors are strongly
    encouraged to define their new attributes as RECOMMENDED attributes by
    bringing them to the IETF Standards Track process.
  </t>
  <t>
    The set of attributes that are classified as REQUIRED is
    deliberately small since servers need to do whatever it takes to support
    them.  A server should support as many of the RECOMMENDED attributes
    as possible but, by their definition, the server is not required to
    support all of them.  Attributes are deemed REQUIRED if the data is
    both needed by a large number of clients and is not otherwise
    reasonably computable by the client when support is not provided on
    the server.
  </t>
  <t>
    Note that the hidden directory returned by OPENATTR is a convenience
    for protocol processing.  The client should not make any assumptions
    about the server's implementation of named attributes and whether
    or not the underlying file system at the server has a named
    attribute directory.  Therefore, operations such as SETATTR and
    GETATTR on the named attribute directory are undefined.
  </t>
  <section anchor="mandatory_attributes_intro" title="REQUIRED Attributes">
    <t>
      These MUST be supported by every NFSv4.1 client and server in
      order to ensure a minimum level of interoperability.  The server MUST
      store and return these attributes, and the client MUST be able to
      function with an attribute set limited to these attributes.  With just
      the REQUIRED attributes some client functionality may be impaired or
      limited in some ways.  A client may ask for any of these attributes to
      be returned by setting a bit in the GETATTR request, and the server
      MUST return their value.
    </t>
  </section>
  <section anchor="recommended_attributes_intro" title="RECOMMENDED Attributes">
    <t>
      These attributes are understood well enough to warrant support in the
      NFSv4.1 protocol.  However, they may not be supported on all
      clients and servers.  A client may ask for any of these attributes to
      be returned by setting a bit in the GETATTR request but must handle
      the case where the server does not return them.  A client MAY ask for
      the set of attributes the server supports and SHOULD NOT request
      attributes the server does not support.  A server should be tolerant
      of requests for unsupported attributes and simply not return them
      rather than considering the request an error.  It is expected that
      servers will support all attributes they comfortably can and only fail
      to support attributes that are difficult to support in their
      operating environments.  A server should provide attributes whenever
      they don't have to "tell lies" to the client.  For example, a file
      modification time should be either an accurate time or should not be
      supported by the server.  At times this will be difficult for
      clients, but a client is better positioned to decide whether and how to
      fabricate or construct an attribute or whether to do without the
      attribute.
    </t>
  </section>
  <section anchor="named_attributes_intro" title="Named Attributes">
    <t>
      These attributes are not supported by direct encoding in the NFSv4 
      protocol but are accessed by string names rather than
      numbers and correspond to an uninterpreted stream of bytes that are
      stored with the file system object.  The namespace for these
      attributes may be accessed by using the OPENATTR operation.  The
      OPENATTR operation returns a filehandle for a virtual "named attribute
      directory", and further perusal and modification of the namespace may 
      be done using operations that work on more typical directories.  In
      particular, READDIR may be used to get a list of such named attributes,
      and LOOKUP and OPEN may select a particular attribute.  Creation of
      a new named attribute may be the result of an OPEN specifying file
      creation.
    </t>
    <t>
      Once an OPEN is done, named attributes may be examined and changed 
      by normal READ and WRITE operations using the filehandles and stateids
      returned by OPEN.
    </t>
    <t>
      Named attributes and the named attribute directory may have 
      their own (non-named) attributes.  Each of these objects MUST have all 
      of the REQUIRED attributes and may have additional RECOMMENDED 
      attributes.  However, the set of attributes for named attributes 
      and the named attribute directory need not be, and
      typically will not be, as large as that for other objects in that 
      file system.
    </t>
    <t>
      Named attributes and the named attribute directory might be the
      target of delegations (in the case of the named attribute directory,
      these will be directory delegations).  However, since granting
      delegations is at the server's discretion, a server
      need not support delegations on named attributes or the named
      attribute directory.
    </t>
    <t>
      It is RECOMMENDED that servers support arbitrary named attributes.  A
      client should not depend on the ability to store any named attributes
      in the server's file system.  If a server does support named
      attributes, a client that is also able to handle them should be able
      to copy a file's data and metadata with complete transparency from
      one location to another; this would imply that names allowed for
      regular directory entries are valid for named attribute names as well.
    </t>
    <t>
      In NFSv4.1, the structure of named attribute directories is 
      restricted in a number of ways, in order to prevent the development
      of non-interoperable implementations in which some servers support
      a fully general hierarchical directory structure for named attributes
      while others support a limited but adequate structure for named attributes.
      In such an environment, clients or applications might come to
      depend on non-portable extensions.  The restrictions are:
      <list style="symbols">
        <t>
          CREATE is not allowed in a named attribute directory.  Thus, such
          objects as symbolic links and special files are not allowed to
          be named attributes.   Further, directories may not be created
          in a named attribute directory, so no hierarchical structure of
          named attributes for a single object is allowed.
        </t>
        <t>
          If OPENATTR is done on a named attribute directory or on
          a named attribute, the server MUST return NFS4ERR_WRONG_TYPE.
        </t>
        <t>
          Doing a RENAME of a named attribute to a different named 
          attribute directory or to an ordinary (i.e., non-named-attribute)
          directory is not allowed.
        </t>
        <t>
          Creating hard links between named attribute directories or 
          between named attribute directories and ordinary directories 
          is not allowed.
        </t>
      </list>
    </t>
    <t>
      Names of attributes will not be controlled by this document or other
      IETF Standards Track documents.  See
      <xref target="namedattributesiana"/>
      for further discussion.
    </t>
  </section>
  <section title="Classification of Attributes">
    <t>
      Each of the REQUIRED and RECOMMENDED attributes can be classified in
      one of three categories: per server (i.e., the value of the attribute will
      be the same for all file objects that share the same
      server owner; see <xref target="Server_Owners"/> for a definition of server
      owner), per file system (i.e., the value of the attribute will
      be the same for some or all file objects that share the
      same <xref target="attrdef_fsid">fsid attribute</xref> and
      server owner), or per file system
      object.  Note that it is possible that some per file system attributes
      may vary within the file system, depending on the value of
      the <xref target="attrdef_homogeneous">"homogeneous"</xref>
      attribute. Note that the attributes time_access_set and
      time_modify_set are not listed in this section because they are
      write-only attributes corresponding to time_access and time_modify,
      and are used in a special instance of SETATTR.
      <list style='symbols'>
	<t>
	  The per-server attribute is:
	  <list style='empty'>
	    <t>
	      lease_time
	    </t>
	  </list>
	</t>
	<t>
	  The per-file system attributes are:
	  <list style='empty'>
	    <t>
	      supported_attrs, suppattr_exclcreat, fh_expire_type, link_support,
	      symlink_support, unique_handles, aclsupport,
	      cansettime, case_insensitive, case_preserving,
	      chown_restricted, files_avail, files_free,
	      files_total, fs_locations, homogeneous, maxfilesize,
	      maxname, maxread, maxwrite, no_trunc, space_avail,
	      space_free, space_total, time_delta,
              change_policy, fs_status,
	      fs_layout_type, fs_locations_info, fs_charset_cap
	    </t>
	  </list>
	</t>    
	<t>
	  The per-file system object attributes are:
	  <list style='empty'>
	    <t>
	      type, change, size, named_attr, fsid, rdattr_error,
	      filehandle, acl, archive, fileid, hidden, maxlink,
	      mimetype, mode, numlinks, owner, owner_group, rawdev,
	      space_used, system, time_access, time_backup,
	      time_create, time_metadata, time_modify,
	      mounted_on_fileid, dir_notif_delay, dirent_notif_delay,
              dacl, sacl,
	      layout_type, layout_hint, layout_blksize, layout_alignment,
              mdsthreshold, retention_get, retention_set, retentevt_get,
              retentevt_set, retention_hold, mode_set_masked
	    </t>
	  </list>
	</t>
      </list>
    </t>
    <t>
      For quota_avail_hard, quota_avail_soft, and quota_used, see their
      definitions below for the appropriate classification.
    </t>

  </section>

  <section anchor="rw_attr" 
	   title="Set-Only and Get-Only Attributes">
    <t>
     Some REQUIRED and RECOMMENDED attributes are set-only; i.e., they
     can be set via SETATTR but not retrieved via GETATTR. Similarly, some
     REQUIRED and RECOMMENDED attributes are get-only; i.e., they
     can be retrieved via GETATTR but not set via SETATTR. If a client attempts
     to set a get-only attribute or get a set-only attributes, the server
     MUST return NFS4ERR_INVAL.
   </t>

  </section>

  <section anchor="mandatory_attributes" 
	   title="REQUIRED Attributes - List and Definition References">
    <t>
     The list of REQUIRED attributes appears in <xref target="req_attr_table"/>.
     The meaning of the columns of the table are:
     <list style='symbols'>
     <t>Name: The name of the attribute.</t>
     <t>Id: The number assigned to the attribute. In
        the event of conflicts between the assigned number and <xref
        target="RFC5662"/>, the latter is
        likely authoritative, but should be resolved with Errata to
        this document and/or
        <xref target="RFC5662"/>. See <xref target="errata"/> for the Errata process.

</t>
     <t>Data Type: The XDR data type of the attribute.</t>
     <t>
        Acc: Access allowed to the attribute. R means
        read-only (GETATTR may retrieve, SETATTR may not
        set). W means write-only (SETATTR may set, GETATTR
        may not retrieve).  R W means read/write (GETATTR
        may retrieve, SETATTR may set).

     </t>
     <t>Defined in: The section of this specification that describes the
        attribute.</t>
     </list>
    </t>

    <texttable anchor="req_attr_table">
      <ttcol align='left' >Name</ttcol>
      <ttcol align='left' >Id</ttcol>
      <ttcol align='left' >Data Type</ttcol>
      <ttcol align='left' >Acc</ttcol>
      <ttcol align='left' >Defined in:</ttcol>

      <c>supported_attrs</c><c>0</c><c>bitmap4</c><c>R</c>
      <c>
	<xref target="attrdef_supp_attr" />
      </c>

      <c>type</c><c>1</c><c>nfs_ftype4</c><c>R</c>
      <c>
	<xref target="attrdef_type"  />
      </c>

      <c>fh_expire_type</c><c>2</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_fh_expire_type"  />
      </c>

      <c>change</c><c>3</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_change"  />
      </c>
      
      <c>size</c><c>4</c><c>uint64_t</c><c>R W</c>
      <c>
	<xref target="attrdef_size" />
      </c>

      <c>link_support</c><c>5</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_link_support" />
      </c>

      <c>symlink_support</c><c>6</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_symlink_support" />
      </c>

      <c>named_attr</c><c>7</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_named_attr" />
      </c>

      <c>fsid</c><c>8</c><c>fsid4</c><c>R</c>
      <c>
	<xref target="attrdef_fsid" />
      </c>

      <c>unique_handles</c><c>9</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_unique_handles" />
      </c>

      <c>lease_time</c><c>10</c><c>nfs_lease4</c><c>R</c>
      <c>
	<xref target="attrdef_lease_time" />
      </c>

      <c>rdattr_error</c><c>11</c><c>enum</c><c>R</c>
      <c>
	<xref target="attrdef_rdattr_error" />
      </c>

      <c>filehandle</c><c>19</c><c>nfs_fh4</c><c>R</c>
      <c>
	<xref target="attrdef_filehandle" />
      </c>

      <c>suppattr_exclcreat</c><c>75</c><c>bitmap4</c><c>R</c>
      <c>
	<xref target="attrdef_suppattr_exclcreat" />
      </c>

    </texttable>
  </section>
  <section anchor="recommended_attributes" 
	   title="RECOMMENDED Attributes - List and Definition References">
    <t>
     The RECOMMENDED attributes are defined in
     <xref target="rec_attr_tbl"/>.  The meanings
     of the column headers are the same as
     <xref target="req_attr_table"/>; see <xref
     target="mandatory_attributes" /> for the meanings.

    </t>
    <texttable anchor="rec_attr_tbl">
      <ttcol align='left' >Name</ttcol>
      <ttcol align='left' >Id</ttcol>
      <ttcol align='left' >Data Type</ttcol>
      <ttcol align='left' >Acc</ttcol>
      <ttcol align='left' >Defined in:</ttcol>

      <c>acl</c><c>12</c><c>nfsace4&lt;></c><c>R W</c>
      <c>
	<xref target="attrdef_acl" />
      </c>

      <c>aclsupport</c><c>13</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_aclsupport" />
      </c>

      <c>archive</c><c>14</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_archive" />
      </c>

      <c>cansettime</c><c>15</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_cansettime" />
      </c>

      <c>case_insensitive</c><c>16</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_case_insensitive" />
      </c>

      <c>case_preserving</c><c>17</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_case_preserving" />
      </c>

      <c>change_policy</c><c>60</c><c>chg_policy4</c><c>R</c>
      <c>
	<xref target="attrdef_change_policy" />
      </c>

      <c>chown_restricted</c><c>18</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_chown_restricted" />
      </c>

      <c>dacl</c><c>58</c><c>nfsacl41</c><c>R W</c>
      <c>
	<xref target="attrdef_dacl" />
      </c>

      <c>dir_notif_delay</c><c>56</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_dir_notif_delay" />
      </c>

      <c>dirent_notif_delay</c><c>57</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_dirent_notif_delay" />
      </c>

      <c>fileid</c><c>20</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_fileid" />
      </c>

      <c>files_avail</c><c>21</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_avail" />
      </c>

      <c>files_free</c><c>22</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_free" />
      </c>

      <c>files_total</c><c>23</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_files_total" />
      </c>

      <c>fs_charset_cap</c><c>76</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_fs_charset_cap" />
      </c>

      <c>fs_layout_type</c><c>62</c><c>layouttype4&lt;></c><c>R</c>
      <c>
	<xref target="attrdef_fs_layout_type" />
      </c>

      <c>fs_locations</c><c>24</c><c>fs_locations</c><c>R</c>
      <c>
	<xref target="attrdef_fs_locations" />
      </c>

      <c>fs_locations_info</c><c>67</c><c>*</c><c>R</c>
      <c>
	<xref target="attrdef_fs_locations_info" />
      </c>

      <c>fs_status</c><c>61</c><c>fs4_status</c><c>R</c>
      <c>
	<xref target="attrdef_fs_status" />
      </c>

      <c>hidden</c><c>25</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_hidden" />
      </c>

      <c>homogeneous</c><c>26</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_homogeneous" />
      </c>

      <c>layout_alignment</c><c>66</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_layout_alignment" />
      </c>

      <c>layout_blksize</c><c>65</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_layout_blksize" />
      </c>

      <c>layout_hint</c><c>63</c><c>layouthint4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_layout_hint" />
      </c>

      <c>layout_type</c><c>64</c><c>layouttype4&lt;></c><c>R</c>
      <c>
	<xref target="attrdef_layout_type" />
      </c>

      <c>maxfilesize</c><c>27</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxfilesize" />
      </c>

      <c>maxlink</c><c>28</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxlink" />
      </c>

      <c>maxname</c><c>29</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxname" />
      </c>

      <c>maxread</c><c>30</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxread" />
      </c>

      <c>maxwrite</c><c>31</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_maxwrite" />
      </c>

      <c>mdsthreshold</c><c>68</c><c>mdsthreshold4</c><c>R</c>
      <c>
	<xref target="attrdef_mdsthreshold" />
      </c>

      <c>mimetype</c><c>32</c><c>utf8str_cs</c><c>R W</c>
      <c>
	<xref target="attrdef_mimetype" />
      </c>

      <c>mode</c><c>33</c><c>mode4</c><c>R W</c>
      <c>
	<xref target="attrdef_mode" />
      </c>

      <c>mode_set_masked</c><c>74</c><c>mode_masked4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_mode_set_masked" />
      </c>

      <c>mounted_on_fileid</c><c>55</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_mounted_on_fileid" />
      </c>

      <c>no_trunc</c><c>34</c><c>bool</c><c>R</c>
      <c>
	<xref target="attrdef_no_trunc" />
      </c>

      <c>numlinks</c><c>35</c><c>uint32_t</c><c>R</c>
      <c>
	<xref target="attrdef_numlinks" />
      </c>

      <c>owner</c>
      <c>36</c><c>utf8str_mixed</c><c>R W</c>
      <c>
	<xref target="attrdef_owner" />
      </c>

      <c>owner_group</c>
      <c>37</c><c>utf8str_mixed</c><c>R W</c>
      <c>
	<xref target="attrdef_owner_group" />
      </c>

      <c>quota_avail_hard</c>
      <c>38</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_avail_hard" />
      </c>

      <c>quota_avail_soft</c>
      <c>39</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_avail_soft" />
      </c>

      <c>quota_used</c>
      <c>40</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_quota_used" />
      </c>

      <c>rawdev</c><c>41</c><c>specdata4</c><c>R</c>
      <c>
	<xref target="attrdef_rawdev" />
      </c>

      <c>retentevt_get</c><c>71</c><c>retention_get4</c><c>R</c>
      <c>
	<xref target="attrdef_retentevt_get" />
      </c>

      <c>retentevt_set</c><c>72</c><c>retention_set4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_retentevt_set" />
      </c>

      <c>retention_get</c><c>69</c><c>retention_get4</c><c>R</c>
      <c>
	<xref target="attrdef_retention_get" />
      </c>

      <c>retention_hold</c><c>73</c><c>uint64_t</c><c>R W</c>
      <c>
	<xref target="attrdef_retention_hold" />
      </c>

      <c>retention_set</c><c>70</c><c>retention_set4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_retention_set" />
      </c>

      <c>sacl</c><c>59</c><c>nfsacl41</c><c>R W</c>
      <c>
	<xref target="attrdef_sacl" />
      </c>

      <c>space_avail</c><c>42</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_avail" />
      </c>

      <c>space_free</c><c>43</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_free" />
      </c>

      <c>space_total</c><c>44</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_total" />
      </c>

      <c>space_used</c><c>45</c><c>uint64_t</c><c>R</c>
      <c>
	<xref target="attrdef_space_used" />
      </c>

      <c>system</c><c>46</c><c>bool</c><c>R W</c>
      <c>
	<xref target="attrdef_system" />
      </c>

      <c>time_access</c>
      <c>47</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_access" />
      </c>

      <c>time_access_set</c><c>48</c><c>settime4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_time_access_set" />
      </c>

      <c>time_backup</c><c>49</c><c>nfstime4</c><c>R W</c>
      <c>
	<xref target="attrdef_time_backup" />
      </c>

      <c>time_create</c><c>50</c><c>nfstime4</c><c>R W</c>
      <c>
	<xref target="attrdef_time_create" />
      </c>

      <c>time_delta</c><c>51</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_delta" />
      </c>

      <c>time_metadata</c><c>52</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_metadata" />
      </c>

      <c>time_modify</c><c>53</c><c>nfstime4</c><c>R</c>
      <c>
	<xref target="attrdef_time_modify" />
      </c>

      <c>time_modify_set</c><c>54</c><c>settime4</c><c>&nbsp;&nbsp;W</c>
      <c>
	<xref target="attrdef_time_modify_set" />
      </c>

    </texttable>
    <t>* fs_locations_info4</t>
  </section>

  <section anchor="attribute_definitions" title="Attribute
						 Definitions">

   <section anchor="required_attr" title="Definitions of REQUIRED Attributes">

    <section toc="exclude" anchor="attrdef_supp_attr" 
	     title="Attribute 0: supported_attrs">
	<t>
	The bit vector that would retrieve all REQUIRED and
	RECOMMENDED attributes that are supported for this object.
	The scope of this attribute applies to all objects with a
	matching fsid.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_type" 
	     title="Attribute 1: type">
	<t>
	  Designates the type of an object in terms of one of a number
          of special constants:
          <list style="symbols">
            <t>
              NF4REG designates a regular file.
            </t>
            <t>
              NF4DIR designates a directory.
            </t>
            <t>
              NF4BLK designates a block device special file.
            </t>
            <t>
              NF4CHR designates a character device special file.
            </t>
            <t>
              NF4LNK designates a symbolic link.
            </t>
            <t>
              NF4SOCK designates a named socket special file.
            </t>
            <t>
              NF4FIFO designates a fifo special file.
            </t>
            <t>
              NF4ATTRDIR designates a named attribute directory.
            </t>
            <t>
              NF4NAMEDATTR designates a named attribute.
            </t>
          </list>
	</t>
	<t>
          Within the explanatory text and operation descriptions, the
          following phrases will be used with the meanings given below:
          <list style="symbols">
            <t>
              The phrase "is a directory" means that the object's
              type attribute is NF4DIR or NF4ATTRDIR.
            </t>
            <t>
              The phrase "is a special file" means that the object's type
              attribute is NF4BLK, NF4CHR, NF4SOCK, or NF4FIFO. 
            </t>
            <t>
              The phrases "is an ordinary file" and
              "is a regular file" mean that the object's
              type attribute is NF4REG or NF4NAMEDATTR.
            </t>
          </list>
	</t>

    </section>

    <section toc="exclude" anchor="attrdef_fh_expire_type" 
	     title="Attribute 2: fh_expire_type">
	<t>
	  Server uses this to specify filehandle expiration behavior
	  to the client.  See <xref target="Filehandles"/> for additional
	  description.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_change" 
	     title="Attribute 3: change">
	<t>
	  A value created by the server that the client can use to
	  determine if file data, directory contents, or attributes of
	  the object have been modified.  The server may return the
	  object's time_metadata attribute for this attribute's value,
	  but only if the file system object cannot be updated more
	  frequently than the resolution of time_metadata.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_size" 
	     title="Attribute 4: size">
	<t>
	  The size of the object in bytes.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_link_support" 
	     title="Attribute 5: link_support">
	<t>
	  TRUE, if the object's file system supports hard links.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_symlink_support" 
	     title="Attribute 6: symlink_support">
	<t>
	  TRUE, if the object's file system supports symbolic links.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_named_attr" 
	     title="Attribute 7: named_attr">
	<t>
	  TRUE, if this object has named attributes. In other words,
	  object has a non-empty named attribute directory.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_fsid" 
	     title="Attribute 8: fsid">
	<t>
	  Unique file system identifier for the file system holding this
	  object.  The fsid attribute has major and minor components, each of
	  which are of data type uint64_t.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_unique_handles" 
	     title="Attribute 9: unique_handles">
	<t>
	  TRUE, if two distinct filehandles are guaranteed to refer to two
	  different file system objects.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_lease_time" 
	     title="Attribute 10: lease_time">
	<t>
	  Duration of the lease at server in seconds.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_rdattr_error" 
	     title="Attribute 11: rdattr_error">
	<t>
	  Error returned from an attempt to retrieve attributes during a READDIR operation.
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_filehandle" 
	     title="Attribute 19: filehandle">
	<t>
	  The filehandle of this object (primarily for READDIR requests).
	</t>
    </section>

    <section toc="exclude" anchor="attrdef_suppattr_exclcreat" 
	     title="Attribute 75: suppattr_exclcreat">
	<t>
	The bit vector that would set all REQUIRED and
	RECOMMENDED attributes that are supported by the EXCLUSIVE4_1
        method of file creation via the OPEN operation.
	The scope of this attribute applies to all objects with a
	matching fsid.
	</t>
    </section>

   </section>

   <section anchor="recommended_attr" title="Definitions of Uncategorized RECOMMENDED Attributes">
    <t>
     The definitions of most of the RECOMMENDED attributes follow. Collections
     that share a common category are defined in other sections.
    </t>

    <section toc="exclude" anchor="attrdef_archive"
	     title="Attribute 14: archive">
      <t>
	TRUE, if this file has been archived since the time of last
	modification (deprecated in favor of time_backup).
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_cansettime"
	     title="Attribute 15: cansettime">
      <t>
	TRUE, if the server is able to change the times for a
	file system object as specified in a SETATTR operation.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_case_insensitive"
	     title="Attribute 16: case_insensitive">
      <t>
	TRUE, if file name comparisons on this file system are case
	insensitive.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_case_preserving"
	     title="Attribute 17: case_preserving">
      <t>
	TRUE, if file name case on this file system is preserved.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_change_policy"
	     title="Attribute 60: change_policy">
      <t>
	A value created by the server that the client can use to
	determine if some server policy related to the current
        file system has been subject to change.  If the value 
        remains the same, then the client can be sure that the
        values of the attributes related to fs location
        and the fss_type field of the fs_status attribute have
        not changed.  On the other hand, a change in this value does
        necessarily imply a change in policy.  It is up to the client
        to interrogate the server to determine if some policy relevant to 
        it has changed.  See <xref target="chg_policy4" /> for 
        details.
      </t>
      <t>
        This attribute MUST change when the value returned by 
        the fs_locations or fs_locations_info attribute changes, when
        a file system goes from read-only to writable or vice versa,
        or when the allowable set of security flavors for the file system
        or any part thereof is changed.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_chown_restricted"
	     title="Attribute 18: chown_restricted">
      <t>
	If TRUE, the server will reject any request to change either
	the owner or the group associated with a file if the caller
	is not a privileged user (for example, "root" in UNIX
	operating environments or, in Windows 2000, the "Take
	Ownership" privilege).
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fileid"
	     title="Attribute 20: fileid">
      <t>
	A number uniquely identifying the file within the file system.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_avail"
	     title="Attribute 21: files_avail">
      <t>
	File slots available to this user on the file system
	containing this object -- this should be the smallest
	relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_free"
	     title="Attribute 22: files_free">
      <t>
	Free file slots on the file system containing this object --
	this should be the smallest relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_files_total"
	     title="Attribute 23: files_total">
      <t>
	Total file slots on the file system containing this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_charset_cap" 
	     title="Attribute 76: fs_charset_cap">
      <t>
        Character set capabilities for this file system. See
        <xref target="utf8_caps"/>.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_locations"
            title="Attribute 24: fs_locations">
       <t>
       Locations where this file system may be found.  If the server
       returns NFS4ERR_MOVED as an error, this attribute MUST be
       supported.
       See <xref target="fs_locations"/> for more details.
       </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_locations_info"
	     title="Attribute 67: fs_locations_info">
      <t>
	Full function file system location.
       See <xref target="fs_locations_info"/> for more details.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_fs_status"
	     title="Attribute 61: fs_status">
      <t>
	Generic file system type information.
       See <xref target="fs_status"/> for more details.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_hidden"
	     title="Attribute 25: hidden">
      <t>
	TRUE, if the file is considered hidden with respect to 
	the Windows API.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_homogeneous"
	     title="Attribute 26: homogeneous">
      <t>
	TRUE, if this object's file system is homogeneous; i.e., all
	objects in the file system (all objects on the server with the
	same fsid) have common values for all per-file-system attributes.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxfilesize"
	     title="Attribute 27: maxfilesize">
      <t>
	Maximum supported file size for the file system of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxlink"
	     title="Attribute 28: maxlink">
      <t>
	Maximum number of links for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxname"
	     title="Attribute 29: maxname">
      <t>
	Maximum file name size supported for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxread"
	     title="Attribute 30: maxread">
      <t>
	Maximum amount of data the READ operation will return for this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_maxwrite"
	     title="Attribute 31: maxwrite">
      <t>
	Maximum amount of data the WRITE operation will accept for this object.
	This
	attribute SHOULD be supported if the file is writable.  Lack
	of this attribute can lead to the client either wasting
	bandwidth or not receiving the best performance.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mimetype"
	     title="Attribute 32: mimetype">
      <t>
	MIME body type/subtype of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mounted_on_fileid"
	     title="Attribute 55: mounted_on_fileid">
      <t>
	Like fileid, but if the target filehandle is the root of a
	file system, this attribute represents the fileid of the
	underlying directory.
      </t>
      <t>
	UNIX-based operating environments connect a file system into
	the namespace by connecting (mounting) the file system onto
	the existing file object (the mount point, usually a
	directory) of an existing file system. When the mount point's
	parent directory is read via an API like readdir(), the return
	results are directory entries, each with a component name and
	a fileid. The fileid of the mount point's directory entry will
	be different from the fileid that the stat() system call
	returns. The stat() system call is returning the fileid of the
	root of the mounted file system, whereas readdir() is
	returning the fileid that stat() would have returned before any
	file systems were mounted on the mount point.
      </t>
      <t>
	Unlike NFSv3, NFSv4.1 allows a client's LOOKUP
	request to cross other file systems. The client detects the
	file system crossing whenever the filehandle argument of
	LOOKUP has an fsid attribute different from that of the
	filehandle returned by LOOKUP. A UNIX-based client will
	consider this a "mount point crossing".  UNIX has a legacy
	scheme for allowing a process to determine its current working
	directory. This relies on readdir() of a mount point's parent
	and stat() of the mount point returning fileids as previously
	described.  The mounted_on_fileid attribute corresponds to the
	fileid that readdir() would have returned as described
	previously.
      </t>
      <t>
	While the NFSv4.1 client could simply fabricate a fileid
	corresponding to what mounted_on_fileid provides (and if the
	server does not support mounted_on_fileid, the client has no
	choice), there is a risk that the client will generate a
	fileid that conflicts with one that is already assigned to
	another object in the file system. Instead, if the server can
	provide the mounted_on_fileid, the potential for client
	operational problems in this area is eliminated.
      </t>
      <t>
	If the server detects that there is no mounted point at the
	target file object, then the value for mounted_on_fileid that
	it returns is the same as that of the fileid attribute.
      </t>
      <t>
	The mounted_on_fileid attribute is RECOMMENDED, so the server
	SHOULD provide it if possible, and for a UNIX-based server,
	this is straightforward. Usually, mounted_on_fileid will be
	requested during a READDIR operation, in which case it is
	trivial (at least for UNIX-based servers) to return
	mounted_on_fileid since it is equal to the fileid of a
	directory entry returned by readdir().  If mounted_on_fileid
	is requested in a GETATTR operation, the server should obey an
	invariant that has it returning a value that is equal to the
	file object's entry in the object's parent directory,
	i.e., what readdir() would have returned.  Some operating
	environments allow a series of two or more file systems to be
	mounted onto a single mount point. In this case, for the
	server to obey the aforementioned invariant, it will need to
	find the base mount point, and not the intermediate mount
	points.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_no_trunc"
	     title="Attribute 34: no_trunc">
      <t>
	If this attribute is TRUE, then if the client uses a file
        name longer than name_max, an error will be
	returned instead of the name being truncated.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_numlinks"
	     title="Attribute 35: numlinks">
      <t>
	Number of hard links to this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_owner"
	     title="Attribute 36: owner">
      <t>
	The string name of the owner of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_owner_group"
	     title="Attribute 37: owner_group">
      <t>
	The string name of the group ownership of this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_avail_hard"
	     title="Attribute 38: quota_avail_hard">
      <t anchor="quota_avail_hard">
	The value in bytes that represents the amount of additional
	disk space beyond the current allocation that can be allocated
	to this file or directory before further allocations will be
	refused.  It is understood that this space may be consumed by
	allocations to other files or directories.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_avail_soft"
	     title="Attribute 39: quota_avail_soft">
      <t anchor="quota_avail_soft">
	The value in bytes that represents the amount of additional
	disk space that can be allocated to this file or directory
	before the user may reasonably be warned.  It is understood
	that this space may be consumed by allocations to other files
	or directories though there is a rule as to which other files
	or directories.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_quota_used"
	     title="Attribute 40: quota_used">
      <t anchor="quota_used">
	The value in bytes that represents the amount of disk
	space used by this file or directory and possibly a
	number of other similar files or directories, where the
	set of "similar" meets at least the criterion that
	allocating space to any file or directory in the set
	will reduce the "quota_avail_hard" of every other file
	or directory in the set.
	<vspace blankLines='1' />
	Note that there may be a number of distinct but
	overlapping sets of files or directories for which a
	quota_used value is maintained, e.g., "all files with a
	given owner", "all files with a given group owner", etc.
	The server is at liberty to choose any of those sets when
        providing the content of the quota_used attribute, but
	should do so in a repeatable way.  The rule may be
	configured per file system or may be "choose the set with
	the smallest quota".
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_rawdev"
	     title="Attribute 41: rawdev">
      <t>
	Raw device number of file of type NF4BLK or NF4CHR. The device
        number is split into major and minor numbers.
	If the file's type attribute is not NF4BLK or NF4CHR,
	the value returned SHOULD NOT be considered useful.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_avail"
	     title="Attribute 42: space_avail">
      <t>
	Disk space in bytes available to this user on the file system
	containing this object -- this should be the smallest
	relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_free"
	     title="Attribute 43: space_free">
      <t>
	Free disk space in bytes on the file system containing this
	object -- this should be the smallest relevant limit.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_total"
	     title="Attribute 44: space_total">
      <t>
	Total disk space in bytes on the file system containing this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_space_used"
	     title="Attribute 45: space_used">
      <t>
	Number of file system bytes allocated to this object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_system"
	     title="Attribute 46: system">
      <t>
	This attribute is TRUE if this file is a "system" file with
	respect to the Windows operating environment.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_access"
	     title="Attribute 47: time_access">
      <t>
	The time_access attribute represents the time of last access to
	the object by a READ operation sent to the server. The notion
	of what is an "access" depends on the server's operating environment
	and/or the server's file system semantics.  For example, for
	servers obeying Portable Operating System Interface (POSIX) semantics, time_access would be updated only
	by the READ and READDIR operations and not any of the operations
	that modify the content of the object <xref target="read_atime"/>,
	<xref target="readdir_atime"/>, <xref target="write_atime"/>. Of
	course, setting the corresponding time_access_set attribute is
	another way to modify the time_access attribute.

      </t>
      <t>
	Whenever the file object resides on a writable file system,
	the server should make its best efforts to record time_access into
	stable storage.  However, to mitigate the performance effects
	of doing so, and most especially whenever the server is
	satisfying the read of the object's content from its cache,
	the server MAY cache access time updates and lazily write them
	to stable storage.  It is also acceptable to give
	administrators of the server the option to disable time_access
	updates.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_access_set"
	     title="Attribute 48: time_access_set">
      <t>
	Sets the time of last access to the object.  SETATTR use only.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_backup"
	     title="Attribute 49: time_backup">
      <t>
	The time of last backup of the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_create"
	     title="Attribute 50: time_create">
      <t>
	The time of creation of the object. This attribute does not
	have any relation to the traditional UNIX file attribute
	"ctime" or "change time".
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_delta"
	     title="Attribute 51: time_delta">
      <t>
	Smallest useful server time granularity.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_metadata"
	     title="Attribute 52: time_metadata">
      <t>
	The time of last metadata modification of the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_modify"
	     title="Attribute 53: time_modify">
      <t>
	The time of last modification to the object.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_time_modify_set"
	     title="Attribute 54: time_modify_set">
      <t>
	Sets the time of last modification to the object.  SETATTR use only.
      </t>
    </section>

   </section>

  </section>

  <section anchor="owner_owner_group" 
	   title="Interpreting owner and owner_group">
    <t>
      The RECOMMENDED attributes "owner" and "owner_group" (and also
      users and groups within the "acl" attribute) are represented in
      terms of a UTF-8 string.  To avoid a representation that is tied
      to a particular underlying implementation at the client or
      server, the use of the UTF-8 string has been chosen.  Note that
      Section 6.1 of <xref target="RFC2624">RFC 2624</xref> provides
      additional rationale.  It is expected that the client and server
      will have their own local representation of owner and
      owner_group that is used for local storage or presentation to
      the end user.  Therefore, it is expected that when these
      attributes are transferred between the client and server,
      the local representation is translated to a syntax of the form
      "user@dns_domain".  This will allow for a client and server that
      do not use the same local representation the ability to
      translate to a common syntax that can be interpreted by both.
    </t>
    <t>
      Similarly, security principals may be represented in different
      ways by different security mechanisms.  Servers normally
      translate these representations into a common format,
      generally that used by local storage, to serve as a means of
      identifying the users corresponding to these security
      principals.  When these local identifiers are translated to
      the form of the owner attribute, associated with files created
      by such principals, they identify, in a common format, the
      users associated with each corresponding set of security
      principals.
    </t>
    <t>
      The translation used to interpret owner and group strings is
      not specified as part of the protocol.  This allows various
      solutions to be employed.  For example, a local translation
      table may be consulted that maps a numeric identifier to the
      user@dns_domain syntax.  A name service may also be used to
      accomplish the translation.  A server may provide a more
      general service, not limited by any particular translation
      (which would only translate a limited set of possible strings)
      by storing the owner and owner_group attributes in local
      storage without any translation or it may augment a
      translation method by storing the entire string for attributes
      for which no translation is available while using the local
      representation for those cases in which a translation is
      available.
    </t>
    <t>
      Servers that do not provide support for all possible values of
      the owner and owner_group attributes SHOULD return an error
      (NFS4ERR_BADOWNER) when a string is presented that has no
      translation, as the value to be set for a SETATTR of the
      owner, owner_group, or acl attributes.  When a server does
      accept an owner or owner_group value as valid on a SETATTR
      (and similarly for the owner and group strings in an acl), it
      is promising to return that same string when a corresponding
      GETATTR is done.  Configuration changes (including
      changes from the mapping of the string to the local representation)
      and ill-constructed
      name translations (those that contain aliasing) may make that
      promise impossible to honor.  Servers should make appropriate
      efforts to avoid a situation in which these attributes have
      their values changed when no real change to ownership has
      occurred.
    </t>
    <t>
      The "dns_domain" portion of the owner string is meant to be a
      DNS domain name, for example, user@xxxxxxxxxxx.  Servers should
      accept as valid a set of users for at least one domain.  A
      server may treat other domains as having no valid
      translations.  A more general service is provided when a
      server is capable of accepting users for multiple domains, or
      for all domains, subject to security constraints.
    </t>
    <t>
      In the case where there is no translation available to the
      client or server, the attribute value will be constructed
      without the "@".  Therefore, the absence of the @ from the
      owner or owner_group attribute signifies that no translation
      was available at the sender and that the receiver of the
      attribute should not use that string as a basis for
      translation into its own internal format.  Even though the
      attribute value cannot be translated, it may still be useful.
      In the case of a client, the attribute string may be used for
      local display of ownership.
    </t>
    <t>
      To provide a greater degree of compatibility with NFSv3,
      which identified users and groups by 32-bit unsigned user
      identifiers and group identifiers, owner and group strings that
      consist of decimal numeric values with no leading zeros can be
      given a special interpretation by clients and servers that
      choose to provide such support.  The receiver may treat such a
      user or group string as representing the same user as would be
      represented by an NFSv3 uid or gid having the corresponding
      numeric value.  A server is not obligated to accept such a
      string, but may return an NFS4ERR_BADOWNER instead.  To avoid
      this mechanism being used to subvert user and group translation,
      so that a client might pass all of the owners and groups in
      numeric form, a server SHOULD return an NFS4ERR_BADOWNER error
      when there is a valid translation for the user or owner
      designated in this way.  In that case, the client must use the
      appropriate name@domain string and not the special form for compatibility.
    </t>
    <t>
      The owner string "nobody" may be used to designate an
      anonymous user, which will be associated with a file created
      by a security principal that cannot be mapped through normal
      means to the owner attribute. Users and implementations
      of NFSv4.1 SHOULD NOT use "nobody" to designate a real user whose access is not anonymous.
    </t>
  </section>

  <section anchor="character_case_attributes" 
	   title="Character Case Attributes">
    <t>
      With respect to the case_insensitive and case_preserving
      attributes, each UCS-4 character (which UTF-8 encodes) can be
      mapped according to Appendix B.2 of 
      <xref target="RFC3454">RFC 3454</xref>.
      For general character handling and internationalization issues,
      see <xref target="internationalization"/>.
    </t>
  </section>

  <section title="Directory Notification Attributes" anchor="dir_not_attrs">
    <t>
      As described in <xref target="OP_GET_DIR_DELEGATION" />, the
      client can request a minimum delay for notifications of changes
      to attributes, but the server is free to ignore what the client
      requests. The client can determine in advance what notification
      delays the server will accept by sending a GETATTR operation for either or
      both of two directory notification attributes.  When the client
      calls the GET_DIR_DELEGATION operation and asks for attribute
      change notifications, it should request notification delays that
      are no less than the values in the server-provided attributes.
    </t>
    <section toc="exclude" anchor="attrdef_dir_notif_delay"
	     title="Attribute 56: dir_notif_delay">
      <t>
	The dir_notif_delay attribute is the minimum number of seconds
	the server will delay before notifying the client of a change
	to the directory's attributes.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_dirent_notif_delay"
	     title="Attribute 57: dirent_notif_delay">
      <t>
	The dirent_notif_delay attribute is the minimum number of seconds
	the server will delay before notifying the client of a change
	to a file object that has an entry in the directory.
      </t>
    </section>

  </section>

  <section anchor="pnfs_attr_full" title="pNFS Attribute Definitions">

    <section toc="exclude" anchor="attrdef_fs_layout_type"
	     title="Attribute 62: fs_layout_type">
      <t>
	The fs_layout_type attribute (see
	<xref target="layouttype4"/>) applies to a
	file system and indicates what layout types are supported by
	the file system.  When the client encounters a new fsid, the
	client SHOULD obtain the value for the fs_layout_type
	attribute associated with the new file system.  This attribute
	is used by the client to determine if the layout types
	supported by the server match any of the client's supported
	layout types.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_alignment"
	     title="Attribute 66: layout_alignment">
      <t>
	When a client holds layouts on files of a file system, the
        layout_alignment attribute indicates the preferred alignment
        for I/O to files on that file system.  Where possible, the
        client should send READ and WRITE operations with offsets
        that are whole multiples of the layout_alignment attribute.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_blksize"
	     title="Attribute 65: layout_blksize">
      <t>
	When a client holds layouts on files of a file system, the
	layout_blksize attribute indicates the preferred block size
	for I/O to files on that file system.  Where possible, the
	client should send READ operations with a count argument that
	is a whole multiple of layout_blksize, and WRITE operations
	with a data argument of size that is a whole multiple of
	layout_blksize.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_hint"
	     title="Attribute 63: layout_hint">
      <t>
	The layout_hint attribute (see
	<xref target="layouthint4"/>) may be set on
	newly created files to influence the metadata server's choice
	for the file's layout.  If possible, this attribute is one of
	those set in the initial attributes within the OPEN operation.
	The metadata server may choose to ignore this attribute.  The
	layout_hint attribute is a subset of the layout structure
	returned by LAYOUTGET.  For example, instead of specifying
	particular devices, this would be used to suggest the stripe
	width of a file.  The server implementation determines which
	fields within the layout will be used.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_layout_type"
	     title="Attribute 64: layout_type">
      <t>
	This attribute lists the layout type(s) available for a file.
	The value returned by the server is for informational purposes
	only.  The client will use the LAYOUTGET operation to obtain
	the information needed in order to perform I/O, for example,
	the specific device information for the file and its layout.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_mdsthreshold"
	     title="Attribute 68: mdsthreshold">
      <t>
	This attribute is a server-provided hint used to communicate
	to the client when it is more efficient to send READ and
	WRITE operations to the metadata server or the data server.
	The two types of thresholds described are file size thresholds
	and I/O size thresholds.  If a file's size is smaller than the
	file size threshold, data accesses SHOULD be sent to the
	metadata server.  If an I/O request has a length
        that is below the I/O size threshold,
	the I/O SHOULD be sent to the metadata server. 
	Each threshold type is specified separately for read and
	write.
      </t>
      <t>
	The server MAY provide both types of thresholds for a file.
	If both file size and I/O size are provided, the client SHOULD
	reach or exceed both thresholds before sending its read or write
	requests to the data server.  Alternatively, if only one of
	the specified thresholds is reached or exceeded, the I/O requests are
	sent to the metadata server.
      </t>
      <t>
	For each threshold type, a value of zero indicates no READ or WRITE
	should be sent to the metadata server, while a value of all ones
	indicates that all READs or WRITEs should be sent to the metadata
	server.
      </t>
      <t> 
	The attribute is available on a per-filehandle basis.  If the
	current filehandle refers to a non-pNFS file or directory, the
	metadata server should return an attribute that is
	representative of the filehandle's file system.  It is suggested
	that this attribute is queried as part of the OPEN operation.
	Due to dynamic system changes, the client should not assume that
	the attribute will remain constant for any specific time period;
	thus, it should be periodically refreshed.
      </t>
    </section>
  </section> <!-- "PNFS Attributes" -->

  <section anchor="retention" title="Retention Attributes">
    <t>
      Retention is a concept whereby a file object can be placed in an
      immutable, undeletable, unrenamable state for a fixed or
      infinite duration of time. Once in this "retained" state, the
      file cannot be moved out of the state until the duration of
      retention has been reached.
    </t>
    <t>
      When retention is enabled, retention MUST extend to the data of
      the file, and the name of file. The server MAY extend retention
      to any other property of the file, including any subset of
      REQUIRED, RECOMMENDED, and named attributes, with the
      exceptions noted in this section.
    </t>
    <t>
      Servers MAY support or not support retention on
      any file object type.
    </t>
    <t>
      The five retention attributes are explained in the next subsections.
    </t>

    <section toc="exclude" anchor="attrdef_retention_get"
	     title="Attribute 69: retention_get">
      <t>
      If retention is enabled for the associated file,
      this attribute's value represents the retention
      begin time of the file object.   This attribute's
      value is only readable with the GETATTR operation
      and MUST NOT be modified by the SETATTR operation
      (<xref target="rw_attr"/>).  The value of the
      attribute consists of:

<figure>
 <artwork>
const RET4_DURATION_INFINITE    = 0xffffffffffffffff;
struct retention_get4 {
        uint64_t        rg_duration;
        nfstime4        rg_begin_time&lt;1>;
};
 </artwork>
</figure>

      The field rg_duration is the duration in seconds indicating how
      long the file will be retained once retention is enabled. The
      field rg_begin_time is an array of up to one absolute time
      value. If the array is zero length, no beginning retention time
      has been established, and retention is not enabled.  
      If rg_duration is equal to RET4_DURATION_INFINITE, the file, once
      retention is enabled, will be retained for an infinite duration.
     </t>
     <t>
      If (as soon as) rg_duration is zero, then rg_begin_time will be
      of zero length, and again, retention is not (no longer) enabled.

     </t>
    </section>

    <section toc="exclude" anchor="attrdef_retention_set"
	     title="Attribute 70: retention_set">
      <t>
	This attribute is used to set the retention
	duration and optionally enable retention for
	the associated file object.  This attribute is
	only modifiable via the SETATTR operation and 
        MUST NOT be retrieved by the GETATTR operation
        (<xref target="rw_attr"/>). 
	This attribute corresponds to retention_get.
	The value of the attribute consists of:

<figure>
 <artwork>
struct retention_set4 {
        bool            rs_enable;
        uint64_t        rs_duration&lt;1>;
};
 </artwork>
</figure>

        If the client sets rs_enable to TRUE, then it is enabling
        retention on the file object with the begin time of retention
        starting from the server's current time and date. The
        duration of the retention can also be provided if the
        rs_duration array is of length one.  The duration is the time in
        seconds from the begin time of retention, and if set to
        RET4_DURATION_INFINITE, the file is to be retained forever. If
        retention is enabled, with no duration specified in either
        this SETATTR or a previous SETATTR, the duration defaults to
        zero seconds.  The server MAY restrict the enabling of
        retention or the duration of retention on the basis of the
        ACE4_WRITE_RETENTION ACL permission.  The enabling of
        retention MUST NOT prevent the enabling of event-based
        retention or the modification of the retention_hold
        attribute.
      </t>
      <t>
       The following rules apply to both the retention_set and
       retentevt_set attributes.

       <list style='symbols'>
       <t>
	 As long as retention is not enabled, the client
	 is permitted to decrease the duration.

       </t>
       <t>
	 The duration can always be set to an
	 equal or higher value, even if retention is
	 enabled. Note that once retention is enabled,
	 the actual duration (as returned by the
	 retention_get or retentevt_get attributes;
	 see <xref target="attrdef_retention_get"/>
	 or <xref target="attrdef_retentevt_get"/>)
	 is constantly counting down to zero (one unit
	 per second), unless the duration was set to
	 RET4_DURATION_INFINITE.  Thus, it will not be
	 possible for the client to precisely extend the
	 duration on a file that has retention enabled.

       </t>
       <t>
	 While retention is enabled, attempts to disable
	 retention or decrease the retention's duration
	 MUST fail with the error NFS4ERR_INVAL.

       </t>
   
       <t>
         If the principal attempting to change
         retention_set or retentevt_set does not have
         ACE4_WRITE_RETENTION permissions, the attempt
         MUST fail with NFS4ERR_ACCESS.

       </t>

       </list>
      </t>

    </section>

    <section toc="exclude" anchor="attrdef_retentevt_get"
	     title="Attribute 71: retentevt_get">
      <t>
	Gets the event-based retention duration, and if enabled, the
        event-based retention begin time of the file object.  This
        attribute is like retention_get, but refers to event-based
        retention.  The event that triggers event-based retention is
        not defined by the NFSv4.1 specification.
      </t>
    </section>

    <section toc="exclude" anchor="attrdef_retentevt_set"
	     title="Attribute 72: retentevt_set">
      <t>
	Sets the event-based retention duration, and optionally enables
	event-based retention on the file object.  This attribute
	corresponds to retentevt_get and is like retention_set, but
	refers to event-based retention.  When event-based retention
	is set, the file MUST be retained even if non-event-based
	retention has been set, and the duration of non-event-based
	retention has been reached. Conversely, when non-event-based
	retention has been set, the file MUST be retained even if
	event-based retention has been set, and the duration of
	event-based retention has been reached.  The server MAY
	restrict the enabling of event-based retention or the duration
	of event-based retention on the basis of the
	ACE4_WRITE_RETENTION ACL permission.  The enabling of
	event-based retention MUST NOT prevent the enabling of
	non-event-based retention or the modification of the
	retention_hold attribute.
     </t>
    </section>


    <section toc="exclude" anchor="attrdef_retention_hold"
	     title="Attribute 73: retention_hold">
      <t>
	Gets or sets administrative retention holds, one hold per bit
        position.
      </t>
      <t>
	This attribute allows one to 64 administrative holds, one hold
	per bit on the attribute. If retention_hold is not zero, then
	the file MUST NOT be deleted, renamed, or modified, even if
	the duration on enabled event or non-event-based retention has
	been reached.  The server MAY restrict the modification of
	retention_hold on the basis of the ACE4_WRITE_RETENTION_HOLD
	ACL permission.  The enabling of administration retention
	holds does not prevent the enabling of event-based or
	non-event-based retention.
      </t>
      <t>
	If the principal attempting to change retention_hold does
	not have ACE4_WRITE_RETENTION_HOLD permissions,
	the attempt MUST fail with NFS4ERR_ACCESS.
      </t>
    </section>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $  -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Access Control Attributes" anchor="acl">
    <t>
        Access Control Lists (ACLs) are file attributes that specify
        fine-grained access control. This section covers the
        &quot;acl&quot;, &quot;dacl&quot;, &quot;sacl&quot;,
        &quot;aclsupport&quot;, &quot;mode&quot;, and
        &quot;mode_set_masked&quot; file attributes and their
        interactions.  Note that file attributes may apply to any file
        system object.
    </t>
    
    <section title="Goals">
      <t>
        ACLs and modes represent two well-established models for
        specifying permissions. This section specifies requirements
        that attempt to meet the following goals:

        <list style="symbols">
          <t>
            If a server supports the mode attribute, it should provide
            reasonable semantics to clients that only set and retrieve
            the mode attribute.
          </t>
          <t>
            If a server supports ACL attributes, it should provide
            reasonable semantics to clients that only set and retrieve
            those attributes.
          </t>
          <t>
            On servers that support the mode attribute, if ACL
            attributes have never been set on an object, via
            inheritance or explicitly, the behavior should be
            traditional UNIX-like behavior.
          </t>
          <t>
            On servers that support the mode attribute, if the ACL
            attributes have been previously set on an object, either
            explicitly or via inheritance:
            <list>
              <t>
                Setting only the mode attribute should effectively
                control the traditional UNIX-like permissions of read,
                write, and execute on owner, owner_group, and other.
              </t>
              <t>
                Setting only the mode attribute should provide
                reasonable security. For example, setting a mode of
                000 should be enough to ensure that future OPEN operations for
                OPEN4_SHARE_ACCESS_READ or OPEN4_SHARE_ACCESS_WRITE by any principal fail, regardless of a
                previously existing or inherited ACL.
              </t>
            </list>
          </t>
          <t>
            NFSv4.1 may introduce different
            semantics relating to the mode and ACL attributes,
            but it does not render invalid any previously
            existing implementations. Additionally, this
            section provides clarifications based on previous
            implementations and discussions around them.
          </t>
          <t>
            On servers that support both the mode and the acl or
            dacl attributes, the server must keep the two consistent
            with each other.  The value of the mode attribute (with
            the exception of the three high-order bits described in
            <xref target="attrdef_mode" />) must be determined entirely
            by the value of the ACL, so that use of the mode is
            never required for anything other than setting the
            three high-order bits.  See <xref target="setattr" />
            for exact requirements.
          </t>
          <t>
            When a mode attribute is set on an object, the ACL
            attributes may need to be modified in order to not conflict
            with the new mode. In such cases, it is desirable that the
            ACL keep as much information as possible. This includes
            information about inheritance, AUDIT and ALARM ACEs, and
            permissions granted and denied that do not conflict with
            the new mode.
          </t>
        </list>
      </t>
    </section>
    
    <section title="File Attributes Discussion">
      <section anchor="attrdef_acl"
	       title="Attribute 12: acl">
        <t>
          The NFSv4.1 ACL attribute contains an array of Access
          Control Entries (ACEs) that are associated with the file
          system object.  Although the client can set and
          get the acl attribute, the server is responsible for using
          the ACL to perform access control. The client can use the
          OPEN or ACCESS operations to check access without modifying
          or reading data or metadata.
        </t>

        <t>
          The NFS ACE structure is defined as follows:
        </t>
<figure>
 <artwork>
typedef uint32_t        acetype4;
 </artwork>
</figure>
<figure>
 <artwork>
typedef uint32_t aceflag4;
 </artwork>
</figure>
<figure>
 <artwork>
typedef uint32_t        acemask4;
 </artwork>
</figure>
<figure>
 <artwork>
struct nfsace4 {
        acetype4        type;
        aceflag4        flag;
        acemask4        access_mask;
        utf8str_mixed   who;
};
 </artwork>
</figure>

        <t>
          To determine if a request succeeds, the server processes
          each nfsace4 entry in order.  Only ACEs that have a "who"
          that matches the requester are considered.  Each ACE is
          processed until all of the bits of the requester's access
          have been ALLOWED.  Once a bit (see below) has been ALLOWED
          by an ACCESS_ALLOWED_ACE, it is no longer considered in the
          processing of later ACEs.  If an ACCESS_DENIED_ACE is
          encountered where the requester's access still has unALLOWED
          bits in common with the "access_mask" of the ACE, the
          request is denied.  When the ACL is fully processed, if
          there are bits in the requester's mask that have not been
          ALLOWED or DENIED, access is denied.
        </t>
        <t>
          Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE
          types do not affect a requester's access, and instead are
          for triggering events as a result of a requester's access
          attempt.  Therefore, AUDIT and ALARM ACEs are processed only
          after processing ALLOW and DENY ACEs.
        </t>
        <t>
          The NFSv4.1 ACL model is quite rich. Some server
          platforms may provide access-control functionality that goes
          beyond the UNIX-style mode attribute, but that is not as
          rich as the NFS ACL model.  So that users can take advantage
          of this more limited functionality, the server may support
          the acl attributes by mapping between its ACL model and the
          NFSv4.1 ACL model.  Servers must ensure that the ACL
          they actually store or enforce is at least as strict as the
          NFSv4 ACL that was set.  It is tempting to accomplish this
          by rejecting any ACL that falls outside the small set that
          can be represented accurately.  However, such an approach
          can render ACLs unusable without special client-side
          knowledge of the server's mapping, which defeats the purpose
          of having a common NFSv4 ACL protocol.  Therefore, servers
          should accept every ACL that they can without compromising
          security.  To help accomplish this, servers may make a
          special exception, in the case of unsupported permission
          bits, to the rule that bits not ALLOWED or DENIED by an ACL
          must be denied.  For example, a UNIX-style server might
          choose to silently allow read attribute permissions even
          though an ACL does not explicitly allow those permissions.
          (An ACL that explicitly denies permission to read attributes
          should still be rejected.)
        </t>
        <t>
          The situation is complicated by the fact that a server may
          have multiple modules that enforce ACLs. For example, the
          enforcement for NFSv4.1 access may be different from,
          but not weaker than, the enforcement for local access, and
          both may be different from the enforcement for access
          through other protocols such as SMB (Server Message Block). So it may be useful for
          a server to accept an ACL even if not all of its modules are
          able to support it.
        </t>
        <t>
          The guiding principle with regard to NFSv4 access is
          that the server must not accept ACLs that appear to
          make access to the file more restrictive than it really is.
        </t>

        <section title="ACE Type">
          <t>
            The constants used for the type field (acetype4) are as
            follows:
          </t>

<figure>
 <artwork>
const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;
 </artwork>
</figure>
          <t>
            Only the ALLOWED and DENIED bits may be used in the
            dacl attribute, and only the AUDIT and ALARM bits may be
            used in the sacl attribute.  All four are permitted in the
            acl attribute.
          </t>
          <texttable>
            <ttcol>Value</ttcol>
            <ttcol>Abbreviation</ttcol>
            <ttcol>Description</ttcol>
            <c>ACE4_ACCESS_ALLOWED_ACE_TYPE</c>
            <c>ALLOW</c>
            <c>
              Explicitly grants the access defined in acemask4 to
              the file or directory.
            </c>
            <c>ACE4_ACCESS_DENIED_ACE_TYPE</c>
            <c>DENY</c>
            <c>
              Explicitly denies the access defined in acemask4 to
              the file or directory.
            </c>
            <c>ACE4_SYSTEM_AUDIT_ACE_TYPE</c>
            <c>AUDIT</c>
            <c>
              Log (in a system-dependent way) any access attempt to
              a file or directory that uses any of the access
              methods specified in acemask4.
            </c>
            <c>ACE4_SYSTEM_ALARM_ACE_TYPE</c>
            <c>ALARM</c>
            <c>
              Generate an alarm (in a system-dependent way) when any
              access attempt is made to a file or directory for the
              access methods specified in acemask4.
            </c>
          </texttable>
            <t>
              The &quot;Abbreviation&quot; column denotes how the
              types will be referred to throughout the rest of this
              section.
            </t>
        </section>
	<section anchor="attrdef_aclsupport"
	     title="Attribute 13: aclsupport">
          <t>
            A server need not support all of the above ACE types.
	    This attribute indicates which ACE types are supported for
	    the current file system.  The bitmask constants used to
	    represent the above definitions within the aclsupport
	    attribute are as follows:
          </t>

<figure>
 <artwork>
const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;
 </artwork>
</figure>
          <t>
            Servers that support either the ALLOW or DENY ACE type
            SHOULD support both ALLOW and DENY ACE types.
          </t>
          <t>
            Clients should not attempt to set an ACE unless the server
            claims support for that ACE type. If the server receives a
            request to set an ACE that it cannot store, it MUST reject
            the request with NFS4ERR_ATTRNOTSUPP. If the server
            receives a request to set an ACE that it can store but
            cannot enforce, the server SHOULD reject the request with
            NFS4ERR_ATTRNOTSUPP.
          </t>
          <t>
            Support for any of the ACL attributes is
            optional (albeit RECOMMENDED).
            However, a server that supports either of the new ACL
            attributes (dacl or sacl) MUST allow use of the new ACL
            attributes to access all of the ACE types that it
            supports.  In other words, if such a server supports ALLOW
            or DENY ACEs, then it MUST support the dacl attribute, and
            if it supports AUDIT or ALARM ACEs, then it MUST support
            the sacl attribute.
          </t>
        </section>
        <section anchor="acemask" title="ACE Access Mask">
          <t>
            The bitmask constants used for the access mask field
            are as follows:
          </t>

<figure>
 <artwork>
const ACE4_READ_DATA            = 0x00000001;
const ACE4_LIST_DIRECTORY       = 0x00000001;
const ACE4_WRITE_DATA           = 0x00000002;
const ACE4_ADD_FILE             = 0x00000002;
const ACE4_APPEND_DATA          = 0x00000004;
const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
const ACE4_READ_NAMED_ATTRS     = 0x00000008;
const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
const ACE4_EXECUTE              = 0x00000020;
const ACE4_DELETE_CHILD         = 0x00000040;
const ACE4_READ_ATTRIBUTES      = 0x00000080;
const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
const ACE4_WRITE_RETENTION      = 0x00000200;
const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

const ACE4_DELETE               = 0x00010000;
const ACE4_READ_ACL             = 0x00020000;
const ACE4_WRITE_ACL            = 0x00040000;
const ACE4_WRITE_OWNER          = 0x00080000;
const ACE4_SYNCHRONIZE          = 0x00100000;
 </artwork>
</figure>
          <t>

	   Note that some masks have coincident values, for
	   example, ACE4_READ_DATA and ACE4_LIST_DIRECTORY.
	   The mask entries ACE4_LIST_DIRECTORY,
	   ACE4_ADD_FILE, and ACE4_ADD_SUBDIRECTORY are
	   intended to be used with directory objects,
	   while ACE4_READ_DATA, ACE4_WRITE_DATA, and
	   ACE4_APPEND_DATA are intended to be used with
	   non-directory objects.

          </t>
          <section title="Discussion of Mask Attributes">
	    <t>
	      <list style="hanging">
		<t hangText="ACE4_READ_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READ" />
			<t hangText="OPEN" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the data of the file.
		      <vspace blankLines='1' />
		      Servers SHOULD allow a user the ability to read the data
		      of the file when only the ACE4_EXECUTE access mask bit is
		      allowed.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_LIST_DIRECTORY">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READDIR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to list the contents of a directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="WRITE" />
			<t hangText="OPEN" />
			<t hangText="SETATTR of size" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify a file's data.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_ADD_FILE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="CREATE" />
			<t hangText="LINK" />
			<t hangText="OPEN" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to add a new file in a directory.
		      The CREATE operation is affected when nfs_ftype4
		      is NF4LNK, NF4BLK, NF4CHR, NF4SOCK, or
		      NF4FIFO. (NF4DIR is not listed because it is
		      covered by ACE4_ADD_SUBDIRECTORY.) OPEN is
		      affected when used to create a regular file.
		      LINK and RENAME are always affected.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_APPEND_DATA">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="WRITE" />
			<t hangText="OPEN" />
			<t hangText="SETATTR of size" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      The ability to modify a file's data, but only
		      starting at EOF.  This allows for the notion of
		      append-only files, by allowing ACE4_APPEND_DATA
		      and denying ACE4_WRITE_DATA to the same user or
		      group.  If a file has an ACL such as the one
		      described above and a WRITE request is made for
		      somewhere other than EOF, the server SHOULD
		      return NFS4ERR_ACCESS.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_ADD_SUBDIRECTORY">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="CREATE" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to create a subdirectory in a
		      directory.  The CREATE operation is affected
		      when nfs_ftype4 is NF4DIR.  The RENAME operation
		      is always affected.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_NAMED_ATTRS">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="OPENATTR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the named attributes of a
		      file or to look up the named attribute
		      directory.  OPENATTR is affected when it is not
		      used to create a named attribute directory.
		      This is when 1) createdir is TRUE, but a named
		      attribute directory already exists, or 2)
		      createdir is FALSE.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_NAMED_ATTRS">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="OPENATTR" />
			<t hangText="" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the named attributes of a
		      file or to create a named attribute directory.
		      OPENATTR is affected when it is used to create a
		      named attribute directory.  This is when
		      createdir is TRUE and no named attribute
		      directory exists.  The ability to check whether
		      or not a named attribute directory exists
		      depends on the ability to look it up; therefore,
		      users also need the ACE4_READ_NAMED_ATTRS
		      permission in order to create a named attribute
		      directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_EXECUTE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="READ" />
			<t hangText="OPEN" />
			<t hangText="REMOVE" />
			<t hangText="RENAME" />
			<t hangText="LINK" />
			<t hangText="CREATE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to execute a file.
		      <vspace blankLines='1' />
		      Servers SHOULD allow a
		      user the ability to read the data of the file
		      when only the ACE4_EXECUTE access mask bit is
		      allowed.  This is because there is no way to
		      execute a file without reading the contents.
		      Though a server may treat ACE4_EXECUTE and
		      ACE4_READ_DATA bits identically when deciding to
		      permit a READ operation, it SHOULD still allow
		      the two bits to be set independently in ACLs,
		      and MUST distinguish between them when replying
		      to ACCESS operations.  In particular, servers
		      SHOULD NOT silently turn on one of the two bits
		      when the other is set, as that would make it
		      impossible for the client to correctly enforce
		      the distinction between read and execute
		      permissions.  
		      <vspace blankLines='1' />
		      As an example, following a SETATTR of the following ACL:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE:ALLOW
		      <vspace blankLines='1' />
		      A subsequent GETATTR of ACL for that file SHOULD return:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE:ALLOW
		      <vspace blankLines='1' />
		      Rather than:
		      <vspace blankLines='1' />
                      nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_EXECUTE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="LOOKUP" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to traverse/search a directory.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_DELETE_CHILD">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="REMOVE" />
			<t hangText="RENAME" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to delete a file or directory within
		      a directory. 

		      See <xref
		      target="delete-delete_child"/>
		      for information on ACE4_DELETE and
		      ACE4_DELETE_CHILD interact.

		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_ATTRIBUTES">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="GETATTR of file system object attributes" />
			<t hangText="VERIFY" />
			<t hangText="NVERIFY" />
			<t hangText="READDIR" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      The ability to read basic attributes (non-ACLs)
		      of a file.  On a UNIX system, basic attributes
		      can be thought of as the stat-level attributes.
		      Allowing this access mask bit would mean that the
		      entity can execute "ls -l" and stat.  If a
		      READDIR operation requests attributes, this mask
		      must be allowed for the READDIR to succeed.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_ATTRIBUTES">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of time_access_set, time_backup," />
			<t hangText="time_create, time_modify_set, mimetype, hidden, system" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to change the times associated with a
		      file or directory to an arbitrary value.  Also
		      permission to change the mimetype, hidden, and
		      system attributes.  A user having
		      ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be
		      allowed to set the times associated with a file
		      to the current server time.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_RETENTION">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of retention_set, retentevt_set." />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify the durations of event and
		      non-event-based retention. Also permission to
		      enable event and non-event-based retention. A
		      server MAY behave such that setting
		      ACE4_WRITE_ATTRIBUTES allows
		      ACE4_WRITE_RETENTION.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_RETENTION_HOLD">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of retention_hold." />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to modify the administration
		      retention holds.  A server MAY map
		      ACE4_WRITE_ATTRIBUTES to
		      ACE_WRITE_RETENTION_HOLD.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_DELETE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="REMOVE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />

		      Permission to delete the
		      file or directory. 

		      See <xref
		      target="delete-delete_child"/>
		      for information on ACE4_DELETE and
		      ACE4_DELETE_CHILD interact.

		    </t>
		  </list>
		</t>

		<t hangText="ACE4_READ_ACL">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="GETATTR of acl, dacl, or sacl" />
			<t hangText="NVERIFY" />
			<t hangText="VERIFY" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to read the ACL.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_ACL">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of acl and mode" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the acl and mode attributes.
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_WRITE_OWNER">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="SETATTR of owner and owner_group" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to write the owner and owner_group
		      attributes.  On UNIX systems, this is the
		      ability to execute chown() and chgrp().
		    </t>
		  </list>
		</t>

		<t hangText="ACE4_SYNCHRONIZE">
		  <list style="hanging">
		    <t hangText="Operation(s) affected:">
		      <list style="hanging">
			<t hangText="NONE" />
		      </list>
		    </t>
		    <t hangText="Discussion:">
		      <vspace blankLines='1' />
		      Permission to use the file object as a
		      synchronization primitive for interprocess
		      communication. This permission is not enforced
		      or interpreted by the NFSv4.1 server on behalf of
		      the client.

		      <vspace blankLines='1' />

                      Typically, the ACE4_SYNCHRONIZE permission is
                      only meaningful on local file systems, i.e.,
                      file systems not accessed via NFSv4.1. The reason
                      that the permission bit exists is that some operating
                      environments, such as Windows, use ACE4_SYNCHRONIZE.

		      <vspace blankLines='1' />

                      For example, if a client copies a file that has
                      ACE4_SYNCHRONIZE set from a local file system to
                      an NFSv4.1 server, and then later copies the file
                      from the NFSv4.1 server to a local file system,
                      it is likely that if ACE4_SYNCHRONIZE was set
                      in the original file, the client will want it
                      set in the second copy.  The first copy will not
                      have the permission set unless the NFSv4.1 server
                      has the means to set the ACE4_SYNCHRONIZE bit. The
                      second copy will not have the permission set unless
                      the NFSv4.1 server has the means to retrieve the
                      ACE4_SYNCHRONIZE bit.

		    </t>
		  </list>
		</t>

	      </list>
	    </t>

            <t>
              Server implementations need not provide the granularity
              of control that is implied by this list of masks. For
              example, POSIX-based systems might not distinguish
              ACE4_APPEND_DATA (the ability to append to a file) from
              ACE4_WRITE_DATA (the ability to modify existing
              contents); both masks would be tied to a single "write"
              permission <xref target="chmod"/>. When such a server returns attributes to the
              client, it would show both ACE4_APPEND_DATA and
              ACE4_WRITE_DATA if and only if the write permission is
              enabled.
            </t>

            <t>
              If a server receives a SETATTR request that it cannot
              accurately implement, it should err in the direction of
              more restricted access, except in the previously
              discussed cases of execute and read. For example,
              suppose a server cannot distinguish overwriting data
              from appending new data, as described in the previous
              paragraph.  If a client submits an ALLOW ACE where
              ACE4_APPEND_DATA is set but ACE4_WRITE_DATA is not (or
              vice versa), the server should either turn off
              ACE4_APPEND_DATA or reject the request with
              NFS4ERR_ATTRNOTSUPP.
            </t>
          </section>

          <section anchor="delete-delete_child" title="ACE4_DELETE vs. ACE4_DELETE_CHILD">
            <t>
              Two access mask bits govern the ability to delete a
              directory entry: ACE4_DELETE on the object
              itself (the "target") and ACE4_DELETE_CHILD on
              the containing directory (the "parent").
            </t>

            <t>
              Many systems also take the "sticky bit" (MODE4_SVTX)
              on a directory to allow unlink only to a user that
              owns either the target or the parent; on some
              such systems the decision also depends on
              whether the target is writable.
            </t>

            <t>
              Servers SHOULD allow unlink if either ACE4_DELETE
              is permitted on the target, or ACE4_DELETE_CHILD is
              permitted on the parent.  (Note that this is
              true even if the parent or target explicitly
              denies one of these permissions.)
            </t>

            <t>
              If the ACLs in question neither explicitly ALLOW
              nor DENY either of the above, and if MODE4_SVTX is
              not set on the parent, then the server SHOULD allow
              the removal if and only if ACE4_ADD_FILE is permitted.
              In the case where MODE4_SVTX is set, the server
              may also require the remover to own either the parent
              or the target, or may require the target to be
              writable.
            </t>

            <t>
              This allows servers to support something close to
              traditional UNIX-like semantics, with ACE4_ADD_FILE
              taking the place of the write bit.
            </t>

          </section>
        </section>
        <section anchor="aceflag" title="ACE flag">
          <t>
            The bitmask constants used for the flag field are as
            follows:
<figure>
 <artwork>
const ACE4_FILE_INHERIT_ACE             = 0x00000001;
const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
const ACE4_IDENTIFIER_GROUP             = 0x00000040;
const ACE4_INHERITED_ACE                = 0x00000080;
 </artwork>
</figure>

            A server need not support any of these flags. If the
            server supports flags that are similar to, but not
            exactly the same as, these flags, the implementation
            may define a mapping between the protocol-defined
            flags and the implementation-defined flags.
          </t>

          <t>
            For example, suppose a client tries to set an ACE with
            ACE4_FILE_INHERIT_ACE set but not
            ACE4_DIRECTORY_INHERIT_ACE. If the server does not
            support any form of ACL inheritance, the server should
            reject the request with NFS4ERR_ATTRNOTSUPP. If the
            server supports a single "inherit ACE" flag that
            applies to both files and directories, the server may
            reject the request (i.e., requiring the client to set
            both the file and directory inheritance flags). The
            server may also accept the request and silently turn
            on the ACE4_DIRECTORY_INHERIT_ACE flag.
          </t>
          <section title="Discussion of Flag Bits">


            <t>
              <list style="hanging">
                <t hangText="ACE4_FILE_INHERIT_ACE">
                  <vspace />
                  Any non-directory file in any
                  sub-directory will get this ACE
                  inherited.
                </t>

                <t hangText="ACE4_DIRECTORY_INHERIT_ACE">
                  <vspace />
                  Can be placed on a directory and indicates
                  that this ACE should be added to each new
                  directory created.
                  <vspace />
                  If this flag is set in an ACE in an ACL
                  attribute to be set on a non-directory
                  file system object, the operation
                  attempting to set the ACL SHOULD fail
                  with NFS4ERR_ATTRNOTSUPP.
                </t>



                <t hangText="ACE4_NO_PROPAGATE_INHERIT_ACE">
                  <vspace />
                  Can be placed on a directory.  This flag
                  tells the server that inheritance of this
                  ACE should stop at newly created child
                  directories.
                </t>

                <t hangText="ACE4_INHERIT_ONLY_ACE">
                  <vspace />
                  Can be placed on a directory but does not
                  apply to the directory; ALLOW and DENY ACEs
                  with this bit set do not affect access to
                  the directory, and AUDIT and ALARM ACEs
                  with this bit set do not trigger log or
                  alarm events.  Such ACEs only take effect
                  once they are applied (with this bit
                  cleared) to newly created files and
                  directories as specified by the
                  ACE4_FILE_INHERIT_ACE and ACE4_DIRECTORY_INHERIT_ACE
                  flags.
                  <vspace blankLines="1"/>
                  If this flag is present on an ACE, but
                  neither ACE4_DIRECTORY_INHERIT_ACE nor
                  ACE4_FILE_INHERIT_ACE is present, then
                  an operation attempting to set such an
                  attribute SHOULD fail with
                  NFS4ERR_ATTRNOTSUPP.
                </t>



                <t hangText="ACE4_SUCCESSFUL_ACCESS_ACE_FLAG">
                  <vspace />
                </t>
                <t hangText="ACE4_FAILED_ACCESS_ACE_FLAG">
                  <vspace />
                  The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG
                  (SUCCESS) and ACE4_FAILED_ACCESS_ACE_FLAG
                  (FAILED) flag bits may be set only on
                  ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and
                  ACE4_SYSTEM_ALARM_ACE_TYPE (ALARM) ACE
                  types. If during the processing of the
                  file's ACL, the server encounters an AUDIT
                  or ALARM ACE that matches the principal
                  attempting the OPEN, the server notes that
                  fact, and the presence, if any, of the
                  SUCCESS and FAILED flags encountered in
                  the AUDIT or ALARM ACE. Once the server
                  completes the ACL processing, it then
                  notes if the operation succeeded or
                  failed. If the operation succeeded, and if
                  the SUCCESS flag was set for a matching
                  AUDIT or ALARM ACE, then the appropriate
                  AUDIT or ALARM event occurs. If the
                  operation failed, and if the FAILED flag
                  was set for the matching AUDIT or ALARM 
                  ACE, then the appropriate AUDIT or ALARM
                  event occurs.  Either or both of the
                  SUCCESS or FAILED can be set, but if
                  neither is set, the AUDIT or ALARM ACE is
                  not useful.
                </t>

                <t hangText="">
                  The previously described processing
                  applies to ACCESS operations even when
                  they return NFS4_OK.  For the purposes of
                  AUDIT and ALARM, we consider an ACCESS
                  operation to be a "failure" if it fails
                  to return a bit that was requested and
                  supported.
                </t>

                <t hangText="ACE4_IDENTIFIER_GROUP">
                  <vspace />
                  Indicates that the "who" refers to a GROUP
                  as defined under UNIX or a GROUP ACCOUNT
                  as defined under Windows. Clients and
                  servers MUST ignore the
                  ACE4_IDENTIFIER_GROUP flag on ACEs with a
                  who value equal to one of the special
                  identifiers outlined in
                  <xref target="acewho" />.
                </t>

                <t hangText="ACE4_INHERITED_ACE">
                  <vspace />
                  Indicates that this ACE is inherited from
                  a parent directory.  A server that supports
                  automatic inheritance will place
                  this flag on any ACEs inherited from the
                  parent directory when creating a new
                  object.  Client applications will use this
                  to perform automatic inheritance.
                  Clients and servers MUST clear this
                  bit in the acl attribute; it may only
                  be used in the dacl and sacl attributes.
                </t>
              </list>
            </t>
          </section>
        </section>
        <section title="ACE Who" anchor="acewho">
          <t>
            The &quot;who&quot; field of an ACE is an identifier that
            specifies the principal or principals to whom the ACE
            applies. It may refer to a user or a group, with the flag
            bit ACE4_IDENTIFIER_GROUP specifying which.
          </t>
          <t>
            There are several special identifiers that need to be
            understood universally, rather than in the context of a
            particular DNS domain. Some of these identifiers cannot be
            understood when an NFS client accesses the server, but
            have meaning when a local process accesses the file. The
            ability to display and modify these permissions is
            permitted over NFS, even if none of the access methods on
            the server understands the identifiers.
          </t>
          <texttable anchor="specialwho">
            <ttcol>Who</ttcol>
            <ttcol>Description</ttcol>
            <c>OWNER</c>
            <c>
              The owner of the file.
            </c>
            <c>GROUP</c>
            <c>
              The group associated with the file.
            </c>
            <c>EVERYONE</c>
            <c>
              The world, including the owner and owning group.
            </c>
            <c>INTERACTIVE</c>
            <c>
              Accessed from an interactive terminal.
            </c>
            <c>NETWORK</c>
            <c>
              Accessed via the network.
            </c>
            <c>DIALUP</c>
            <c>
              Accessed as a dialup user to the server.
            </c>
            <c>BATCH</c>
            <c>
              Accessed from a batch job.
            </c>
            <c>ANONYMOUS</c>
            <c>
              Accessed without any authentication.
            </c>
            <c>AUTHENTICATED</c>
            <c>
              Any authenticated user (opposite of
              ANONYMOUS).
            </c>
            <c>SERVICE</c>
            <c>
              Access from a system service.
            </c>
          </texttable>
          <t>
            To avoid conflict, these special identifiers are
            distinguished by an appended "@" and should appear in the
            form "xxxx@" (with no domain name after the "@"), for
            example, ANONYMOUS@.
          </t>
          <t>
            The ACE4_IDENTIFIER_GROUP flag MUST be ignored on
            entries with these special identifiers.  When encoding
            entries with these special identifiers, the
            ACE4_IDENTIFIER_GROUP flag SHOULD be set to zero.
          </t>

          <section title="Discussion of EVERYONE@">
            <t>
              It is important to note that "EVERYONE@" is not
              equivalent to the UNIX "other" entity. This is
              because, by definition, UNIX "other" does not include
              the owner or owning group of a file. "EVERYONE@" means
              literally everyone, including the owner or owning
              group.
            </t>
          </section>
        </section>
      </section>
      <section anchor="attrdef_dacl"
	       title="Attribute 58: dacl">
	<t>
          The dacl attribute is like the acl attribute,
          but dacl allows 
          just ALLOW and DENY ACEs.  The dacl
          attribute supports automatic inheritance (see
          <xref target="auto_inherit" />).
	</t>
      </section>

      <section anchor="attrdef_sacl"
	       title="Attribute 59: sacl">
	<t>
          The sacl attribute is like the acl attribute,
          but sacl allows
          just AUDIT and ALARM ACEs. The sacl
          attribute supports automatic inheritance (see
          <xref target="auto_inherit" />).
	</t>
      </section>

      <section anchor="attrdef_mode"
	       title="Attribute 33: mode">
        <t>
          The NFSv4.1 mode attribute is based on the UNIX mode
          bits. The following bits are defined:
        </t>

<figure>
 <artwork>
const MODE4_SUID = 0x800;  /* set user id on execution */
const MODE4_SGID = 0x400;  /* set group id on execution */
const MODE4_SVTX = 0x200;  /* save text even after use */
const MODE4_RUSR = 0x100;  /* read permission: owner */
const MODE4_WUSR = 0x080;  /* write permission: owner */
const MODE4_XUSR = 0x040;  /* execute permission: owner */
const MODE4_RGRP = 0x020;  /* read permission: group */
const MODE4_WGRP = 0x010;  /* write permission: group */
const MODE4_XGRP = 0x008;  /* execute permission: group */
const MODE4_ROTH = 0x004;  /* read permission: other */
const MODE4_WOTH = 0x002;  /* write permission: other */
const MODE4_XOTH = 0x001;  /* execute permission: other */
 </artwork>
</figure>

        <t>
          Bits MODE4_RUSR, MODE4_WUSR, and MODE4_XUSR apply to the
          principal identified in the owner attribute. Bits MODE4_RGRP,
          MODE4_WGRP, and MODE4_XGRP apply to principals identified in
          the owner_group attribute but who are not identified in the
          owner attribute. Bits MODE4_ROTH, MODE4_WOTH, and MODE4_XOTH apply
          to any principal that does not match that in the owner
          attribute and does not have a group matching that of the
          owner_group attribute.
        </t>
        <t>
          Bits within a mode other than those specified above
          are not defined by this protocol. A server
          MUST NOT return bits other than those defined above in a
          GETATTR or READDIR operation, and it MUST return NFS4ERR_INVAL
          if bits other than those defined above are set in a SETATTR,
          CREATE, OPEN, VERIFY, or NVERIFY operation.
        </t>
      </section>
      <section anchor="attrdef_mode_set_masked"
	       title="Attribute 74: mode_set_masked">
        <t>
          The mode_set_masked attribute is a write-only attribute
          that allows individual bits in the mode attribute to be
          set or reset, without changing others.  It allows, for
          example, the bits MODE4_SUID, MODE4_SGID, and MODE4_SVTX
          to be modified while leaving unmodified any of the 
          nine low-order mode bits devoted to permissions.
        </t>
        <t>
          In such instances that the nine low-order bits are left
          unmodified, then neither the acl nor the dacl attribute
          should be automatically modified as discussed in 
	  <xref target="setattr" />.
        </t>
        <t>
          The mode_set_masked attribute consists of two words,
          each in the form of a mode4.  The first consists of the
          value to be applied to the current mode value and the
          second is a mask.  Only bits set to one in the mask word
          are changed (set or reset) in the file's mode.  All 
          other bits in the mode remain unchanged.  Bits in the
          first word that correspond to bits that are zero in
          the mask are ignored, except that undefined bits are
          checked for validity and can result in NFS4ERR_INVAL as
          described below.
        </t> 
        <t>
          The mode_set_masked attribute is only valid in a SETATTR
          operation.  If it is used in a CREATE or OPEN operation, the
          server MUST return NFS4ERR_INVAL.
        </t>
        <t>
          Bits not defined as valid in the mode attribute are not
          valid in either word of the mode_set_masked attribute.
          The server MUST return NFS4ERR_INVAL
          if any such bits are set to one in a SETATTR.  
If the mode and
          mode_set_masked attributes are both specified in the
          same SETATTR, the server MUST also return NFS4ERR_INVAL.
        </t>
      </section>

    </section>
    
    <section title="Common Methods">
      <t>
        The requirements in this section will be referred to in future
        sections, especially <xref target="aclreqs" />.
      </t>
      <section title="Interpreting an ACL" anchor="useacl">
        <section title="Server Considerations" anchor="serverinterp">
          <t> 
	    The server uses the algorithm described in
	    <xref target="attrdef_acl"/> to determine whether an ACL
	    allows access to an object.  However, the ACL might not be
	    the sole determiner of access.  For example:
            <list style="symbols">
              <t>
                In the case of a file system exported as read-only,
                the server may deny write access even though
                an object's ACL grants it.
              </t>

              <t>
                Server implementations MAY grant ACE4_WRITE_ACL
                and ACE4_READ_ACL permissions to prevent
                a situation from arising in which there is no valid
                way to ever modify the ACL.
              </t>

              <t>
                All servers will allow a user the ability to read
                the data of the file when only the execute
                permission is granted (i.e., if the ACL denies the
                user the ACE4_READ_DATA access and allows the user
                ACE4_EXECUTE, the server will allow the user to
                read the data of the file).
              </t>

              <t>
                Many servers have the notion of owner-override in
                which the owner of the object is allowed to
                override accesses that are denied by the ACL.
                This may be helpful, for example, to allow users
                continued access to open files on which the
                permissions have changed.
              </t>

              <t>
                Many servers have the notion of a
                &quot;superuser&quot; that has privileges beyond
                an ordinary user.  The superuser may be able
                to read or write data or metadata in ways that would
                not be permitted by the ACL.
              </t>

              <t>
                A retention attribute might also block access otherwise
                allowed by ACLs (see <xref target="retention"/>).
              </t>

            </list>
          </t>
        </section>

        <section title="Client Considerations" anchor="clientinterp">
          <t>
            Clients SHOULD NOT do their own access checks based on
            their interpretation of the ACL, but rather use the OPEN and
            ACCESS operations to do access checks. This allows the
            client to act on the results of having the server
            determine whether or not access should be granted based on
            its interpretation of the ACL.
          </t>

          <t>
            Clients must be aware of situations in which an object's
            ACL will define a certain access even though the server
            will not enforce it. In general, but especially in these
            situations, the client needs to do its part in the
            enforcement of access as defined by the ACL. To do this,
            the client MAY send the appropriate ACCESS operation
            prior to servicing the request of the user or application
            in order to determine whether the user or application
            should be granted the access requested. For examples in
            which the ACL may define accesses that the server doesn't
            enforce, see <xref target="serverinterp"/>.
          </t>
        </section>
      </section>

      <section title="Computing a Mode Attribute from an ACL"
               anchor="computemode">
        <t>
          The following method can be used to calculate the MODE4_R*,
          MODE4_W*, and MODE4_X* bits of a mode attribute, based upon
          an ACL.
        </t>

        <t>
          First, for each of the special identifiers OWNER@, GROUP@, and
          EVERYONE@, evaluate the ACL in order, considering only ALLOW
          and DENY ACEs for the identifier EVERYONE@ and for the
          identifier under consideration.  The result of the evaluation
          will be an NFSv4 ACL mask showing exactly which bits are
          permitted to that identifier.
        </t>

        <t>
          Then translate the calculated mask for OWNER@, GROUP@, and
          EVERYONE@ into mode bits for, respectively, the user, group,
          and other, as follows:

          <list style="numbers">
            <t>
              Set the read bit (MODE4_RUSR, MODE4_RGRP, or
              MODE4_ROTH) if and only if ACE4_READ_DATA is set in
              the corresponding mask.
            </t>

            <t>
              Set the write bit (MODE4_WUSR, MODE4_WGRP, or
              MODE4_WOTH) if and only if ACE4_WRITE_DATA and
              ACE4_APPEND_DATA are both set in the corresponding
              mask.
            </t>

            <t>
              Set the execute bit (MODE4_XUSR, MODE4_XGRP, or
              MODE4_XOTH), if and only if ACE4_EXECUTE is set in the
              corresponding mask.
            </t>
          </list>
        </t>
        <section title="Discussion">
          <t>
            Some server implementations also add bits permitted to
            named users and groups to the group bits (MODE4_RGRP,
            MODE4_WGRP, and MODE4_XGRP).
          </t>
          <t>
            Implementations are discouraged from doing this, because
            it has been found to cause confusion for users who see
            members of a file's group denied access that the mode
            bits appear to allow.  (The presence of DENY ACEs may also
            lead to such behavior, but DENY ACEs are expected to be
            more rarely used.)
          </t>
          <t>
            The same user confusion seen when fetching the mode also
            results if setting the mode does not effectively control
            permissions for the owner, group, and other users; this
            motivates some of the requirements that follow.
          </t>
        </section>
      </section>
    </section>
    
    <section title="Requirements" anchor="aclreqs">
      <t>
        The server that supports both mode and ACL must take care to
        synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with
        the ACEs that have respective who fields of "OWNER@", "GROUP@",
        and "EVERYONE@". This way, the client can see if semantically equivalent
        access permissions exist whether the client asks for the owner,
        owner_group, and mode attributes or for just the ACL.
      </t>
      <t>
        In this section, much is made of the methods in <xref
							   target="computemode" />. Many requirements refer to this section.
        But note that the methods have behaviors specified with
        &quot;SHOULD&quot;. This is intentional, to avoid invalidating
        existing implementations that compute the mode according to the
        withdrawn POSIX ACL draft (1003.1e draft 17), rather than by
        actual permissions on owner, group, and other.
      </t>
      <section title="Setting the Mode and/or ACL Attributes"
               anchor="setattr">
        <t>
          In the case where a server supports the sacl or
          dacl attribute, in addition to the acl attribute,
          the server MUST fail a request to set the acl
          attribute simultaneously with a dacl or sacl
          attribute.  The error to be given is NFS4ERR_ATTRNOTSUPP.
        </t>
        <section title="Setting Mode and not ACL" anchor="setmode">
          <t>
            When any of the nine low-order mode bits
            are subject to change, either because the mode
            attribute was set or because the mode_set_masked
            attribute was set and the mask included one or more
            bits from the nine low-order mode bits,
            and no ACL attribute is explicitly
            set, the acl and dacl attributes must be modified
            in accordance with the updated value of those bits.
            This must happen
            even if the value of the low-order bits
            is the same after the mode is set as before.
          </t>
          <t>
            Note that any AUDIT or ALARM ACEs (hence any ACEs in the
            sacl attribute) are unaffected by changes to the mode.
          </t>
          <t>
            In cases in which the permissions bits are subject to
            change, the acl and dacl attributes
            MUST be modified such that the mode computed via the
            method in
            <xref target="computemode" />
            yields the low-order nine bits (MODE4_R*, MODE4_W*,
            MODE4_X*) of the mode attribute as modified by the
            attribute change.  The ACL attributes
            SHOULD also be modified such that:
            <list style="numbers">
              <t>
                If MODE4_RGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and EVERYONE@
                SHOULD NOT be granted ACE4_READ_DATA.
              </t>
              <t>
                If MODE4_WGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and
                EVERYONE@ SHOULD NOT be granted
                ACE4_WRITE_DATA or ACE4_APPEND_DATA.
              </t>
              <t>
                If MODE4_XGRP is not set, entities explicitly
                listed in the ACL other than OWNER@ and EVERYONE@
                SHOULD NOT be granted ACE4_EXECUTE.
              </t>
            </list>
            Access mask bits other than those listed above, appearing
            in ALLOW ACEs, MAY also be disabled.
          </t>
          <t>
            Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do
            not affect the permissions of the ACL itself, nor do ACEs
            of the type AUDIT and ALARM. As such, it is desirable to
            leave these ACEs unmodified when modifying the ACL
            attributes.
          </t>
          <t>
            Also note that the requirement may be met by
            discarding the acl and dacl, in favor of an ACL
            that represents the mode and only the mode. This is
            permitted, but it is preferable for a server to
            preserve as much of the ACL as possible without
            violating the above requirements. Discarding the
            ACL makes it effectively impossible for a file
            created with a mode attribute to inherit an ACL
            (see <xref target="aclcreate" />).
          </t>
        </section>
        <section title="Setting ACL and Not Mode"
                 anchor="settingacl">
          <t>
            When setting the acl or dacl and not setting the
            mode or mode_set_masked attributes, the permission
            bits of the mode need to be derived from the ACL.
            In this case, the ACL attribute SHOULD be set as
            given. The nine low-order bits of the mode
            attribute (MODE4_R*, MODE4_W*, MODE4_X*) MUST be
            modified to match the result of the method in
	    <xref target="computemode" />. The three high-order bits
            of the mode (MODE4_SUID, MODE4_SGID, MODE4_SVTX)
            SHOULD remain unchanged.
          </t>
        </section>
        <section title="Setting Both ACL and Mode" anchor="setboth">
          <t>
            When setting both the mode (includes use of either the
            mode attribute or the mode_set_masked attribute) 
            and the acl or dacl attributes in the
            same operation, the attributes MUST be applied in this
            order: mode (or mode_set_masked), then ACL.  The 
            mode-related attribute is set as given,
            then the ACL attribute is set as given, possibly changing
            the final mode, as described above in
            <xref target="settingacl" />.
          </t>
        </section>
      </section>
      <section title="Retrieving the Mode and/or ACL Attributes">
        <t>
          This section applies only to servers that support both the
          mode and ACL attributes.
        </t>
        <t>
          Some server implementations may have a concept of
          &quot;objects without ACLs&quot;, meaning that all permissions
          are granted and denied according to the mode attribute and
          that no ACL attribute is stored for that object. If an ACL
          attribute is requested of such a server, the server SHOULD
          return an ACL that does not conflict with the mode; that is to
          say, the ACL returned SHOULD represent the nine low-order bits
          of the mode attribute (MODE4_R*, MODE4_W*, MODE4_X*) as
          described in <xref target="computemode" />.
        </t>
        <t>
          For other server implementations, the ACL attribute is always
          present for every object. Such servers SHOULD store at least
          the three high-order bits of the mode attribute (MODE4_SUID,
          MODE4_SGID, MODE4_SVTX). The server SHOULD return a mode
          attribute if one is requested, and the low-order nine bits of
          the mode (MODE4_R*, MODE4_W*, MODE4_X*) MUST match the result
          of applying the method in
          <xref target="computemode" /> to the ACL attribute.
        </t>
      </section>
      <section title="Creating New Objects" anchor="aclcreate">
        <t>
          If a server supports any ACL attributes, it may use the ACL
          attributes on the parent directory to compute an initial ACL
          attribute for a newly created object. This will be referred to
          as the inherited ACL within this section. The act of adding
          one or more ACEs to the inherited ACL that are based upon ACEs
          in the parent directory's ACL will be referred to as
          inheriting an ACE within this section.
        </t>
        <t>
          Implementors should standardize what the behavior of CREATE
          and OPEN must be depending on the presence or absence of the
          mode and ACL attributes.
          <list style="numbers">
            <t>If just the mode is given in the call:
              <vspace blankLines="1" /> In this case, inheritance
              SHOULD take place, but the mode MUST be applied to the
              inherited ACL as described in <xref target="setmode"
						  />, thereby modifying the ACL.

            </t>
            <t>If just the ACL is given in the call:
              <vspace blankLines="1" />
              In this case, inheritance SHOULD NOT take place, and
              the ACL as defined in the CREATE or OPEN will be set
              without modification, and the mode modified as in
              <xref target="settingacl" />.
		      
            </t>
            <t>If both mode and ACL are given in the call:
              <vspace blankLines="1" /> In this case, inheritance
              SHOULD NOT take place, and both attributes will be set
              as described in <xref target="setboth" />.
		      
            </t>
            <t>
              If neither mode nor ACL is given in the call:
              <vspace blankLines="1" />
              In the case where an object is being created without
              any initial attributes at all, e.g., an OPEN operation
              with an opentype4 of OPEN4_CREATE and a createmode4 of
              EXCLUSIVE4, inheritance SHOULD NOT take place (note that
              EXCLUSIVE4_1 is a better choice of createmode4, since it
              does permit initial attributes).
              Instead, the server SHOULD set permissions to deny all
              access to the newly created object. It is expected
              that the appropriate client will set the desired
              attributes in a subsequent SETATTR operation, and the
              server SHOULD allow that operation to succeed,
              regardless of what permissions the object is created
              with. For example, an empty ACL denies all
              permissions, but the server should allow the owner's
              SETATTR to succeed even though WRITE_ACL is implicitly
              denied.
              <vspace blankLines="1" />
              In other cases, inheritance SHOULD take place, and no
              modifications to the ACL will happen. The mode
              attribute, if supported, MUST be as computed in 
	      <xref target="computemode" />, with the MODE4_SUID,
              MODE4_SGID, and MODE4_SVTX bits clear.
              If no inheritable ACEs exist on the parent directory,
              the rules for creating acl, dacl, or sacl attributes
              are implementation defined.
              If either the dacl or sacl attribute is supported,
              then the ACL4_DEFAULTED flag SHOULD be set on the
              newly created attributes.
		      <vspace blankLines='1' />
            </t>
          </list>
        </t>
        <section title="The Inherited ACL" anchor="inheritreq">
          <t>
            If the object being created is not a directory, the
            inherited ACL SHOULD NOT inherit ACEs from the parent
            directory ACL unless the ACE4_FILE_INHERIT_FLAG is set.
          </t>
          <t>
            If the object being created is a directory, the inherited
            ACL should inherit all inheritable ACEs from the parent
            directory, that is, those that have the ACE4_FILE_INHERIT_ACE or
            ACE4_DIRECTORY_INHERIT_ACE flag set.  
If the inheritable
            ACE has ACE4_FILE_INHERIT_ACE set but
            ACE4_DIRECTORY_INHERIT_ACE is clear, the inherited ACE on
            the newly created directory MUST have the
            ACE4_INHERIT_ONLY_ACE flag set to prevent the directory
            from being affected by ACEs meant for non-directories.
          </t>
          <t>
            When a new directory is created, the server MAY split
            any inherited ACE that is both inheritable and effective
            (in other words, that has neither ACE4_INHERIT_ONLY_ACE
            nor ACE4_NO_PROPAGATE_INHERIT_ACE set), into two ACEs,
            one with no inheritance flags and one with
            ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or
            sacl attribute, both of those ACEs SHOULD also have the
            ACE4_INHERITED_ACE flag set.)  This makes it simpler to
            modify the effective permissions on the directory
            without modifying the ACE that is to be inherited to the
            new directory's children.
          </t>
        </section>
        
        <section title="Automatic Inheritance" anchor="auto_inherit">
          <t>
            The acl attribute consists only of an array of ACEs, but
            the <xref target="attrdef_sacl">sacl</xref>
            and <xref target="attrdef_dacl">dacl</xref> attributes
            also include an additional flag field.

<figure>
 <artwork>
struct nfsacl41 {
        aclflag4        na41_flag;
        nfsace4         na41_aces&lt;>;
};
 </artwork>
</figure>

            The flag field
            applies to the entire sacl or dacl; three flag values are
            defined:

<figure>
 <artwork>
const ACL4_AUTO_INHERIT         = 0x00000001;
const ACL4_PROTECTED            = 0x00000002;
const ACL4_DEFAULTED            = 0x00000004;
 </artwork>
</figure>

            and all other bits must be cleared.  The
            ACE4_INHERITED_ACE flag may be set in the ACEs of the sacl
            or dacl (whereas it must always be cleared in the acl).
          </t>
          <t>
            Together these features allow a server to support automatic
            inheritance, which we now explain in more detail.
          </t>
          <t>
            Inheritable ACEs are normally inherited by child objects only
            at the time that the child objects are created; later
            modifications to inheritable ACEs do not result in
            modifications to inherited ACEs on descendants.
          </t>
          <t>
            However, the dacl and sacl provide an OPTIONAL mechanism
            that allows a client application to propagate changes to
            inheritable ACEs to an entire directory hierarchy.
          </t>
          <t>
            A server that supports this performs inheritance at object
            creation time in the normal way, and SHOULD  set the
            ACE4_INHERITED_ACE flag on any inherited ACEs as they are
            added to the new object.
          </t>
          <t>
            A client application such as an ACL editor may then propagate
            changes to inheritable ACEs on a directory by recursively
            traversing that directory's descendants and modifying each ACL
            encountered to remove any ACEs with the ACE4_INHERITED_ACE flag
            and to replace them by the new inheritable ACEs (also with the
            ACE4_INHERITED_ACE flag set).  It uses the existing ACE
            inheritance flags in the obvious way to decide which ACEs to
            propagate.  (Note that it may encounter further inheritable
            ACEs when descending the directory hierarchy and that those
            will also need to be taken into account when propagating
            inheritable ACEs to further descendants.)
          </t>
          <t>
            The reach of this propagation may be limited in two ways:
            first, automatic inheritance is not performed from any
            directory ACL that has the ACL4_AUTO_INHERIT flag
            cleared; and second, automatic inheritance stops wherever
            an ACL with the ACL4_PROTECTED flag is set, preventing
            modification of that ACL and also (if the ACL is set on
            a directory) of the ACL on any of the object's descendants.
          </t>
          <t>
            This propagation is performed independently for the sacl
            and the dacl attributes; thus, the ACL4_AUTO_INHERIT and
            ACL4_PROTECTED flags may be independently set for the sacl
            and the dacl, and propagation of one type of acl may continue
            down a hierarchy even where propagation of the other acl has
            stopped.
          </t>
          <t>
            New objects should be created with a dacl and a sacl that
            both have the ACL4_PROTECTED flag cleared and the
            ACL4_AUTO_INHERIT flag set to the same value as that on,
            respectively, the sacl or dacl of the parent object.
          </t>
          <t>
            Both the dacl and sacl attributes are RECOMMENDED, and a server
            may support one without supporting the other.
          </t>
          <t>
            A server that supports both the old acl attribute and
            one or both of the new dacl or sacl attributes must do so
            in such a way as to keep all three attributes consistent
            with each other.  Thus, the ACEs reported in the acl attribute
            should be the union of the ACEs reported in the dacl and
            sacl attributes, except that the ACE4_INHERITED_ACE flag must
            be cleared from the ACEs in the acl.  And of course a
            client that queries only the acl will be unable to determine
            the values of the sacl or dacl flag fields.
          </t>
          <t>
            When a client performs a SETATTR for the acl attribute,
            the server SHOULD set the ACL4_PROTECTED flag to true on
            both the sacl and the dacl.  By using the acl attribute,
            as opposed to the dacl or sacl attributes, the client signals
            that it may not understand automatic inheritance, and thus
            cannot be trusted to set an ACL for which automatic
            inheritance would make sense.
          </t>
          <t>
            When a client application queries an ACL, modifies it, and sets
            it again, it should leave any ACEs marked with
            ACE4_INHERITED_ACE unchanged, in their original order, at the
            end of the ACL.  If the application is unable to do this, it
            should set the ACL4_PROTECTED flag.  This behavior
            is not enforced by servers, but violations of this rule may
            lead to unexpected results when applications perform automatic
            inheritance.
          </t>
          <t>
            If a server also supports the mode attribute, it SHOULD set the
            mode in such a way that leaves inherited ACEs unchanged, in
            their original order, at the end of the ACL.  If it is unable
            to do so, it SHOULD set the ACL4_PROTECTED flag on the file's
            dacl.
          </t>
          <t>Finally, in the case where the request that creates a new file
            or directory does not also set permissions for that file or
            directory, and there are also no ACEs to inherit from the
            parent's directory, then the server's choice of ACL for the new
            object is implementation-dependent.  In this case, the server
            SHOULD set the ACL4_DEFAULTED flag on the ACL it chooses for
            the new object.  An application performing automatic
            inheritance takes the ACL4_DEFAULTED flag as a sign that the
            ACL should be completely replaced by one generated using the
            automatic inheritance rules.
          </t>
        </section>

      </section>
    </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="single_server_namespace" title="Single-Server Namespace">
  <t>
    This section describes the NFSv4 single-server namespace.
    Single-server namespaces may be presented directly to clients, 
    or they may be used as a basis to form larger multi-server 
    namespaces (e.g., site-wide or organization-wide) to be presented 
    to clients, as described in <xref target='multi_server_namespace' />.
  </t>
  <section anchor="server_exports" title="Server Exports">
    <t>
      On a UNIX server, the namespace describes all the files reachable by
      pathnames under the root directory or "/".  On a Windows server, the
      namespace constitutes all the files on disks named by mapped disk
      letters.  NFS server administrators rarely make the entire server's
      file system namespace available to NFS clients.  More often, portions
      of the namespace are made available via an "export" feature.  In
      previous versions of the NFS protocol, the root filehandle for each
      export is obtained through the MOUNT protocol; the client sent a
      string that identified the export name within the namespace and 
      the server returned the root filehandle 
      for that export.  The MOUNT protocol also provided an EXPORTS
      procedure that enumerated the server's exports.
    </t>
  </section>
  <section anchor="browsing_exports" title="Browsing Exports">
    <t>
      The NFSv4.1 protocol provides a root filehandle that clients can
      use to obtain filehandles for the exports of a particular server,
      via a series of LOOKUP operations within a COMPOUND, to traverse
      a path.  A common user experience is to use a graphical user interface
      (perhaps a file "Open" dialog window) to find a file via progressive
      browsing through a directory tree.  The client must be able to move
      from one export to another export via single-component, progressive
      LOOKUP operations.
    </t>
    <t>
      This style of browsing is not well supported by the NFSv3 protocol.  In NFSv3, the client expects all 
      LOOKUP operations to remain
      within a single server file system.  For example, the device attribute
      will not change.  This prevents a client from taking namespace paths
      that span exports.
    </t>
    <t>
      In the case of NFSv3, an automounter on the client
      can obtain a snapshot of the server's namespace
      using the EXPORTS procedure of the MOUNT protocol.
      If it understands the server's pathname syntax,
      it can create an image of the server's namespace
      on the client.  The parts of the namespace that
      are not exported by the server are filled in
      with directories that might be constructed similarly
      to an NFSv4.1 "pseudo file system" (see <xref
      target="server_pseudo_file_system" />) that
      allows the user to browse from one mounted file
      system to another.  There is a drawback to this
      representation of the server's namespace on the
      client: it is static.  If the server administrator
      adds a new export, the client will be unaware of it.

    </t>
  </section>
  <section anchor="server_pseudo_file_system" title="Server Pseudo File System">
    <t>
      NFSv4.1 servers avoid this namespace inconsistency by
      presenting all the exports for a given server within the
      framework of a single namespace for that server.
      An NFSv4.1 client uses LOOKUP and READDIR
      operations to browse seamlessly from one export to another.  
    </t>
    <t>
      Where there are portions of the server namespace that are not 
      exported, clients require some way of traversing those portions
      to reach actual exported file systems.  A technique that servers
      may use to provide for this is to bridge the unexported portion of 
      the namespace via a
      "pseudo file system" that provides a view of exported directories
      only.  A pseudo file system has a unique fsid and behaves like a
      normal, read-only file system.
    </t>
    <t>
      Based on the construction of the server's namespace, it is possible
      that multiple pseudo file systems may exist.  For example, 
    </t>
    <figure>
      <artwork>
        /a              pseudo file system
        /a/b            real file system
        /a/b/c          pseudo file system
        /a/b/c/d        real file system
      </artwork>
    </figure>
    <t>
      Each of the pseudo file systems is considered a separate entity and
      therefore MUST have its own fsid, unique among all the fsids for that
      server.
    </t>
  </section>
  <section title="Multiple Roots">
    <t>
      Certain operating environments are sometimes described as
      having "multiple roots".  In such environments, individual file 
      systems are commonly represented by disk or volume names.
      NFSv4 servers for these platforms can construct a pseudo file
      system above these root names so that disk letters or volume names are
      simply directory names in the pseudo root.
    </t>
  </section>
  <section title="Filehandle Volatility" anchor="pseudo_fs_volatility" >
    <t>
      The nature of the server's pseudo file system is that it is a logical
      representation of file system(s) available from the server.
      Therefore, the pseudo file system is most likely constructed
      dynamically when the server is first instantiated.  It is expected
      that the pseudo file system may not have an on-disk counterpart from
      which persistent filehandles could be constructed.  Even though it is
      preferable that the server provide persistent filehandles for the
      pseudo file system, the NFS client should expect that pseudo file
      system filehandles are volatile.  This can be confirmed by checking
      the associated "fh_expire_type" attribute for those filehandles in
      question.  If the filehandles are volatile, the NFS client must be
      prepared to recover a filehandle value (e.g., with a series of
      LOOKUP operations) when receiving an error of NFS4ERR_FHEXPIRED.
    </t>
    <t>
      Because it is quite likely that servers will implement pseudo
      file systems using volatile filehandles, clients need to be 
      prepared for them, rather than assuming that all filehandles
      will be persistent.
    </t>
  </section>
  <section title="Exported Root">
    <t>
      If the server's root file system is exported, one might conclude that
      a pseudo file system is unneeded.  This is not necessarily so.  Assume the
      following file systems on a server:
    </t>
    <figure>
      <artwork>
        /       fs1  (exported)
        /a      fs2  (not exported)
        /a/b    fs3  (exported)
      </artwork>
    </figure>
    <t>
      Because fs2 is not exported, fs3 cannot be reached with simple
      LOOKUPs.  The server must bridge the gap with a pseudo file system.
    </t>
  </section>
  <section title="Mount Point Crossing">
    <t>
      The server file system environment may be constructed in such a way
      that one file system contains a directory that is 'covered' or
      mounted upon by a second file system.  For example:
    </t>
    <figure>
      <artwork>
        /a/b            (file system 1)
        /a/b/c/d        (file system 2)
      </artwork>
    </figure>
    <t>
      The pseudo file system for this server may be constructed to look
      like:
    </t>
    <figure>
      <artwork>
        /               (place holder/not exported)
        /a/b            (file system 1)
        /a/b/c/d        (file system 2)
      </artwork>
    </figure>
    <t>
      It is the server's responsibility to present the pseudo file system
      that is complete to the client.  If the client sends a LOOKUP request
      for the path /a/b/c/d, the server's response is the filehandle of
      the root of the file system /a/b/c/d.  In previous versions of the 
      NFS protocol,
      the server would respond with the filehandle of directory
      /a/b/c/d within the file system /a/b.

    </t>
    <t>
      The NFS client will be able to determine if it crosses a server mount
      point by a change in the value of the "fsid" attribute.
    </t>
  </section>
  <section title="Security Policy and Namespace Presentation">
    <t>
      Because NFSv4 clients possess the ability to change the security
      mechanisms used, after determining what is allowed,
      by using SECINFO and SECINFO_NONAME, the server
      SHOULD NOT present a different view of the namespace based on
      the security mechanism being used by a client.  Instead, it 
      should present a consistent view and return NFS4ERR_WRONGSEC
      if an attempt is made to access data with an inappropriate
      security mechanism.
    </t>
    <t>
      If security considerations make it necessary to hide the existence
      of a particular file system, as opposed to all of the data within
      it, the server can apply the security policy of
      a shared resource in the server's namespace to components of the
      resource's ancestors. For example:
    </t>
    <figure>
      <artwork>
        /                           (place holder/not exported)
        /a/b                        (file system 1)
        /a/b/MySecretProject        (file system 2)

      </artwork>
    </figure>
    <t>
      The /a/b/MySecretProject directory is a real file system and 
      is the shared resource.
      Suppose the security policy for /a/b/MySecretProject is Kerberos 
      with integrity and it is desired to limit knowledge of the existence
      of this file system.  In this case, the
      server should apply the same security policy to /a/b.  This allows 
      for knowledge of the existence of a file system to be secured
      when desirable.
    </t>
    <t>
      For the case of the use of multiple, disjoint security mechanisms in
      the server's resources, applying that sort of policy would result
      in the higher-level file system not being accessible using any
      security flavor.
Therefore, that sort of configuration is not compatible
      with hiding the existence (as opposed to the contents) from clients
      using multiple disjoint sets of security flavors.
    </t>
    <t>
      In other circumstances, a desirable policy is for the security of a
      particular object in the
      server's namespace to include the union of all security mechanisms of
      all direct descendants.  A common and convenient practice, unless
      strong security requirements dictate otherwise, is to make the
      entire the pseudo file system accessible by all of the valid security 
      mechanisms.
    </t>
    <t>
      Where there is concern about the security of data on the network,
      clients should use strong security mechanisms to access the pseudo
      file system in order to prevent man-in-the-middle attacks.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="State Management" >
  <t>
    Integrating locking into the NFS protocol necessarily causes it to be
    stateful.  With the inclusion of such features as share reservations,
    file and directory delegations, recallable layouts, and support for 
    mandatory byte-range locking, the protocol becomes substantially more 
    dependent on proper management of state than the traditional
    combination of NFS and NLM (Network Lock Manager)
    <xref target="xnfs" />. These features include expanded
    locking facilities, which provide some measure of inter-client
    exclusion, but the state also offers
    features not readily providable using a stateless model.
    There are three components to
    making this state manageable:
    <list style='symbols'>
      <t>
        clear division between client and server
      </t>
      <t>
        ability to reliably detect inconsistency in state between client
        and server
      </t>
      <t>
        simple and robust recovery mechanisms
      </t>
    </list>
  </t>
  <t>
    In this model, the server owns the state information.  The client
    requests changes in locks and the server responds with the changes
    made.  Non-client-initiated changes in locking state are infrequent.
    The client receives prompt notification of such changes and can adjust
    its view of the locking state to reflect the server's changes. 
  </t>
  <t>
    Individual pieces of state created by the server and passed to the
    client at its request are represented by 128-bit stateids.  These
    stateids may represent a particular open file, a set of 
    byte-range locks held
    by a particular owner, or a recallable delegation of privileges 
    to access a file in particular ways or at a particular location.
  </t>
  <t>
    In all cases, there is a transition from the most general
    information that represents a client as a whole to the eventual 
    lightweight stateid used for most client and server
    locking interactions.  The details of this transition will vary
    with the type of object but it always starts with a client ID.
  </t>
  <section anchor="client_id" title="Client and Session ID" >
    <t>
      A client must establish a client ID (see <xref target="Client_Identifiers" />) 
      and then one or more sessionids (see <xref target="Session" />) before
      performing any operations to open, byte-range lock, delegate, or obtain
      a layout for a file object.
      Each session ID is associated with a specific client ID, and thus 
      serves as a shorthand reference to an NFSv4.1 client.
     </t>
     <t>
       For some types of locking interactions, the client will represent
       some number of internal locking entities called "owners", which 
       normally correspond to processes internal to the client.  For 
       other types of locking-related objects, such as delegations and
       layouts, no such intermediate entities are provided for, and the 
       locking-related objects are considered to be transferred
       directly between the server and a unitary client.
      </t>
    </section> <!-- "Client and Session ID" -->
    <section anchor="stateid" title="Stateid Definition" >
      <t>
        When the server grants a lock of any type (including opens,
        byte-range locks, delegations, and layouts), it responds with a 
        unique stateid that represents a set of locks (often a single
        lock) for the same file, of the same type, and sharing the same
        ownership characteristics.  Thus, opens of the same file by
        different open-owners each have an identifying stateid.  Similarly,
        each set of byte-range locks on a file owned by a specific lock-owner
        has its own
        identifying stateid.  Delegations and layouts also have 
        associated stateids by which they may be referenced. 
        The stateid is used as a shorthand reference to a lock or set
        of locks, and given a stateid, the server can determine the associated
        state-owner or state-owners (in the case of an open-owner/lock-owner pair)
        and the associated filehandle.  When stateids are used, the current
        filehandle must be the one associated with that stateid.
      </t>
      <t>
        All stateids associated with a given client ID are associated with
        a common lease that represents the claim of those stateids 
        and the objects they represent to be maintained
        by the server.  See <xref target="lease_renewal" /> for a 
        discussion of the lease.   
      </t>
      <t>
        The server may assign stateids independently for different clients.
        A stateid with the same bit pattern for one client may designate
        an entirely different set of locks for a different client.  The
        stateid is always interpreted with respect to the client ID associated
        with the current session.  Stateids apply to all sessions associated
        with the given client ID, and the client may use a stateid obtained from
        one session on another session associated with the same client ID.
      </t>
      <section anchor="stateid_types" title="Stateid Types">
        <t>
          With the exception of special stateids (see <xref target="special_stateid"/>),
          each stateid
          represents locking objects of one of a set of types defined
          by the NFSv4.1 protocol.  Note that in all these cases, where
          we speak of guarantee, it is understood there are
          situations such as a client restart, or lock revocation,
          that allow the guarantee to be voided.
          <list style='symbols'>
            <t>
              Stateids may represent opens of files.
              <vspace blankLines="1" />
              Each stateid in this case represents the OPEN state for a
              given client ID/open-owner/filehandle triple.  Such
              stateids are subject to change (with consequent
              incrementing of the stateid's seqid) in response to OPENs that 
              result in upgrade and OPEN_DOWNGRADE operations. 
            </t>
            <t>
              Stateids may represent sets of byte-range locks.
              <vspace blankLines="1" />
              All locks held on a particular file by a particular owner and 
              gotten under the aegis of a particular open file
              are associated with a single stateid with the seqid
              being incremented whenever LOCK and LOCKU operations affect that 
              set of locks.
            </t>
            <t>
              Stateids may represent file delegations, which are 
              recallable guarantees by the server to the client
              that other clients will not reference or
              modify a particular file, until the delegation
              is returned.  In NFSv4.1, file delegations may be 
              obtained on both regular and non-regular files.
              <vspace blankLines="1" />
              A stateid represents a single delegation held by
              a client for a particular filehandle.
            </t>
            <t>
              Stateids may represent directory delegations, which
              are recallable guarantees by the server to the client
              that other clients will not modify the directory, 
              until the delegation is returned.
              <vspace blankLines="1" />
              A stateid represents a single delegation held by
              a client for a particular directory filehandle.
            </t>
            <t>
              Stateids may represent layouts, which are recallable
              guarantees by the server to the client that particular
              files may be accessed via an alternate data access 
              protocol at specific locations.  Such access is 
              limited to particular sets of byte-ranges and may
              proceed until those byte-ranges are reduced or the
              layout is returned.
              <vspace blankLines="1" />
              A stateid represents the set of all layouts held by a particular 
              client for a particular filehandle with a given 
              layout type.  The seqid is updated as the layouts
              of that set of byte-ranges change, via layout stateid changing operations such
              as LAYOUTGET and LAYOUTRETURN.
            </t>
          </list>
        </t>
      </section>
      <section anchor="stateid_structure" title="Stateid Structure">
        <t>
	  Stateids are divided into two fields, a 96-bit
	  "other" field identifying the specific set
	  of locks and a 32-bit "seqid" sequence value.
	  Except in the case of special stateids
          (see <xref target="special_stateid"/>), 
	  a particular value of the 
          "other" field denotes a 
          set of locks of the same type (for example, 
          byte-range locks, opens, delegations, or layouts),
          for a specific file or directory, and sharing
          the same ownership characteristics.  The seqid
          designates a specific instance of such a set of
          locks, and is incremented to indicate changes in
          such a set of locks, either by the addition or
          deletion of locks from the set, a change in the 
          byte-range they apply to, or an upgrade or downgrade
          in the type of one or more locks.
        </t>
        <t>  
          When such a set of locks is first created, the server returns a
          stateid with seqid value of one.  On subsequent
          operations that modify the set of locks, the server
          is required to increment the "seqid" field by one
          whenever it returns a stateid for the same 
          state-owner/file/type  combination and there is some
          change in the set of locks actually designated.
          In this case, the server will return a stateid with an "other" field
          the same as previously used for that 
          state-owner/file/type  combination, with an 
          incremented "seqid" field.
          This pattern continues until the seqid is incremented
          past NFS4_UINT32_MAX, and one
          (not zero) is the next seqid value. 
        </t>
        <t>
	  The purpose of the incrementing of the seqid
	  is to allow the server to
	  communicate to the client the order in which
	  operations that modified locking state associated
	  with a stateid have been processed and to make
          it possible for the client to send requests
          that are conditional on the set of locks not
          having changed since the stateid in question
          was returned.
        </t> 
        <t>
	  Except for layout stateids (<xref target="layout_stateid"/>),
          when a client sends a stateid to the server, it has two
          choices with regard to the seqid sent.  It may set the seqid
          to zero to indicate to the server that it wishes the most
          up-to-date seqid for that stateid's "other" field to be
          used.  This would be the common choice in the case of a
          stateid sent with a READ or WRITE operation.  It also may
          set a non-zero value, in which case the server checks if that
          seqid is the correct one.  In that case, the server is
          required to return NFS4ERR_OLD_STATEID if the seqid is lower
          than the most current value and NFS4ERR_BAD_STATEID if the
          seqid is greater than the most current value.  This would be
          the common choice in the case of stateids sent with a CLOSE
          or OPEN_DOWNGRADE.  Because OPENs may be sent in parallel
          for the same owner, a client might close a file without
          knowing that an OPEN upgrade had been done by the server,
          changing the lock in question.  If CLOSE were sent with a
          zero seqid, the OPEN upgrade would be cancelled before the
          client even received an indication that an upgrade had
          happened.
        </t>
        <t>
          When a stateid is sent by the server to the client as part of
          a callback operation, it is not subject to checking for
          a current seqid and returning NFS4ERR_OLD_STATEID.  This
          is because the client is not in a position to know the
          most up-to-date seqid and thus cannot verify it.  Unless
          specially noted, the seqid value for a stateid sent by the
          server to the client as part of a callback is required
          to be zero with NFS4ERR_BAD_STATEID returned if it is
          not.
        </t>
        <t>
          In making comparisons between seqids, both by the client
	  in determining the order of operations and by the server
	  in determining whether the NFS4ERR_OLD_STATEID is to be
          returned, the possibility of the seqid being swapped
	  around past the NFS4_UINT32_MAX value needs to be taken
	  into account.  When two seqid values are being compared,
  	  the total count of slots for all sessions associated 
	  with the current client is used to do this.  When one
	  seqid value is less than this total slot count and
	  another seqid value is greater than NFS4_UINT32_MAX
	  minus the total slot count, the former is to be treated
	  as lower than the latter, despite the fact that it is
	  numerically greater.
 	</t>
	  
      </section> <!-- "Stateid Structure" -->
      <section anchor="special_stateid" title="Special Stateids">
        <t>
          Stateid values whose "other" field is either all zeros or all
          ones are reserved.  They may not be assigned by the server but
          have special meanings defined by the protocol.  The particular
          meaning depends on whether the "other" field is all zeros or
          all ones and the specific value of the "seqid" field.
        </t>
        <t>
          The following combinations of "other" and "seqid" are defined
          in NFSv4.1:
          <list style='symbols'>
            <t>
              When "other" and "seqid" are both zero, the
              stateid is treated as a special anonymous
              stateid, which can be used in READ, WRITE,
              and SETATTR requests to indicate the absence
              of any OPEN state associated with the
              request.  When an anonymous stateid value is
              used and an existing open denies the form of
              access requested, then access will be denied
              to the request.  This stateid MUST NOT be
              used on operations to data servers (<xref
              target="ds_ops" />).
            </t>
            <t>
              When "other" and "seqid" are both all ones,
              the stateid is a special READ bypass stateid.
              When this value is used in WRITE or SETATTR,
              it is treated like the anonymous value.
              When used in READ, the server MAY grant
              access, even if access would normally be
              denied to READ operations.  This stateid MUST
              NOT be used on operations to data servers.
            </t>
            <t>
              When "other" is zero and "seqid" is one,
              the stateid represents the current stateid,
              which is whatever value is the last stateid
              returned by an operation within the COMPOUND.
              In the case of an OPEN, the stateid returned
              for the open file and not the delegation is
              used.  The stateid passed to the operation in
              place of the special value has its "seqid"
              value set to zero, except when the current 
              stateid is used by the operation CLOSE or
              OPEN_DOWNGRADE.  If there is no operation
              in the COMPOUND that has returned a stateid
              value, the server MUST return the error
	      NFS4ERR_BAD_STATEID. As illustrated  in <xref
	      target="csid_example4"/>, if the value of a
	      current stateid is a special stateid and the
	      stateid of an operation's arguments has
	      "other" set to zero and "seqid" set to one,
	      then the server MUST return the error
	      NFS4ERR_BAD_STATEID.

            </t>
            <t>
              When "other" is zero and "seqid" is NFS4_UINT32_MAX,
              the stateid represents a reserved stateid
              value defined to be invalid.  When this 
              stateid is used, the server MUST return the error
              NFS4ERR_BAD_STATEID.
            </t>
          </list>
        </t>
        <t>
          If a stateid value is used that has all zeros or all ones in the
          "other" field but does not match one of the cases above, the server
          MUST return the error NFS4ERR_BAD_STATEID.
        </t>
        <t>
          Special stateids, unlike other stateids, are not associated with
          individual client IDs or filehandles and can be used with all valid
          client IDs and filehandles.  In the case of a special 
          stateid designating the current stateid, the current stateid
          value substituted for the special stateid is associated with a
          particular client ID and filehandle, and so, if it is used
          where the current filehandle does not match that associated with the current
          stateid, the operation to which the stateid is passed will return
          NFS4ERR_BAD_STATEID.
        </t>
      </section> <!-- "Special Stateids" -->
      <section anchor="stateid_lifetime" title="Stateid Lifetime and Validation">
        <t>
          Stateids must remain valid until either a client restart or a 
          server restart or until the client returns all of the locks 
          associated with the stateid by means of an operation such as
          CLOSE or DELEGRETURN. 

          If the locks are lost due to revocation, as long
          as the client ID is valid, the stateid remains
          a valid designation of that revoked state until
          the client frees it by using FREE_STATEID.

          Stateids associated 
          with byte-range locks are an exception.  They remain valid even 
          if a LOCKU frees all remaining locks, so long as the open file 
          with which they are associated remains open, unless the client 
          frees the stateids via the FREE_STATEID operation.
        </t>
        <t>
          It should be noted that there are situations in which the
          client's locks become invalid, without the client requesting 
          they be returned.  These include lease expiration and a number
          of forms of lock revocation within the lease period.  It is 
          important to note that in these situations, the stateid remains 
          valid and the client can use it to determine the disposition of
          the associated lost locks. 
        </t>
        <t>
          An "other" value must never be reused for a different purpose
          (i.e., different filehandle, owner, or type of locks) within the
          context of a single client ID.  A server may retain the "other"
          value for the same purpose beyond the point where it may otherwise 
          be freed, but if it does so, it must maintain "seqid" continuity
          with previous values.
        </t>
        <t>
          One mechanism that may be used to satisfy the requirement that the 
          server recognize invalid and out-of-date stateids is for 
          the server to divide the "other" field of the stateid into two 
          fields.  
          <list style='symbols'>
            <t>
              an index into a table of locking-state structures.
            </t>
            <t>
              a generation number that is incremented on each allocation
              of a table entry for a particular use.
            </t>
          </list>
        </t>
        <t>
          And then store in each table entry,
          <list style='symbols'>
             <t>
               the client ID with which the stateid is associated.
             </t>
             <t>
               the current generation number for the (at most one)
               valid stateid sharing this index value.
             </t>
             <t>
               the filehandle of the file on which the locks are taken.
             </t>
             <t>
               an indication of the type of stateid (open, byte-range lock,
               file delegation, directory delegation, layout).
             </t>
             <t>
               the last "seqid" value returned corresponding to the current
               "other" value.
             </t>
             <t>
               an indication of the current status of the locks 
               associated with this stateid, in particular,
               whether these have been revoked and if so, for what reason.
             </t>
          </list>
        </t>
        <t>
          With this information, an incoming stateid can be validated and 
          the appropriate error returned when necessary.  Special and
          non-special stateids are handled separately. (See
          <xref target='special_stateid' /> for a discussion of special 
          stateids.) 
        </t>
        <t>
          Note that stateids are implicitly qualified by the current client
          ID, as derived from the client ID associated with the current 
          session.  Note, however, that the semantics of the session will
          prevent stateids associated with a previous client or server 
          instance from being analyzed by this procedure.
        </t>
        <t>
          If server restart has resulted in an invalid
          client ID or a session ID that is invalid, SEQUENCE will return
          an error and the operation that takes a stateid as an argument will never
          be processed.
        </t>
        <t>
          If there has been a server restart where there is a persistent
          session and all leased state has been lost, then the session
          in question will, although valid, be marked as dead, and any
          operation not satisfied by means of the reply cache will
          receive the error NFS4ERR_DEADSESSION, and thus not be 
          processed as indicated below.
        </t>
        <t>
          When a stateid is being tested and the "other" field is all
          zeros or all ones, a check that 
          the "other" and "seqid" fields match a defined combination for
          a special stateid is done and the results determined as follows:
          <list style='symbols'>        
            <t>
              If the "other" and "seqid" fields do not match a defined
              combination associated with a special stateid, the error
              NFS4ERR_BAD_STATEID is returned.
            </t>
            <t>
              If the special stateid is one designating the current 
              stateid and there is a current stateid, then the current
              stateid is substituted for the special stateid and the 
              checks appropriate to non-special stateids are performed.
            </t>
            <t>
              If the combination is valid in general but is not 
              appropriate to the context in which the stateid is used
              (e.g., an all-zero stateid is used when an OPEN stateid
              is required in a LOCK operation), the error
              NFS4ERR_BAD_STATEID is also returned.
            </t>
            <t>
              Otherwise, the check is completed and the special stateid 
              is accepted as valid.
            </t>
          </list>
        </t>
        <t>
          When a stateid is being tested, 
          and the "other" field is neither all zeros nor all ones, the  
          following procedure could be used to
          validate an incoming stateid and return an appropriate error,
          when necessary, assuming that the "other" field would be divided 
          into a table index and an entry generation.
          <list style='symbols'>
            <t>
              If the table index field is outside the range of the 
              associated table, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the selected table entry is of a different generation than
              that specified in the incoming stateid, return 
              NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the selected table entry does not match the current 
              filehandle, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the client ID in the table entry does not match the 
              client ID associated with the current session, 
              return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the stateid represents revoked state, then return 
              NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or 
              NFS4ERR_DELEG_REVOKED, as appropriate.
            </t>
            <t>
              If the stateid type is not valid for the context in which the
              stateid appears, return NFS4ERR_BAD_STATEID.
              Note that a stateid may be valid in general, as would be 
              reported by the TEST_STATEID operation, but be invalid for
              a particular operation, as, for example, when a stateid 
              that doesn't represent byte-range locks is passed to
              the non-from_open case of LOCK or to LOCKU, or when a stateid
              that does not represent an open is passed to CLOSE or
              OPEN_DOWNGRADE.  In such cases, the server MUST return
              NFS4ERR_BAD_STATEID. 
            </t>
            <t>
              If the "seqid" field is not zero and it is greater
              than the current sequence value corresponding to the 
              current "other" field, return NFS4ERR_BAD_STATEID.
            </t>
            <t>
              If the "seqid" field is not zero and it is less
              than the current sequence value corresponding to the 
              current "other" field, return NFS4ERR_OLD_STATEID.
            </t>
            <t>
              Otherwise, the stateid is valid and the table entry 
              should contain any additional information about the 
              type of stateid and information associated with that 
              particular type of stateid, such as the associated 
              set of locks, e.g., open-owner and 
              lock-owner information, as well as information on the 
              specific locks, e.g., open modes and byte-ranges.
            </t>
          </list>
        </t>
      </section> <!-- "Stateid Lifetime and Validation" -->
      <section anchor="stateid_use" title="Stateid Use for I/O Operations">
        <t>
          Clients performing I/O operations need to select an 
          appropriate stateid based on the
          locks (including opens and delegations) held by the client and 
          the various types of state-owners sending the I/O requests.
          SETATTR operations that change the file size are treated
          like I/O operations in this regard.
        </t>
        <t>
          The following rules, applied in order of decreasing priority, 
          govern the selection of the appropriate stateid.  In following 
          these rules, the client will only consider locks of which it
          has actually received notification by an appropriate operation
          response or callback.  Note that the
          rules are slightly different in the case of I/O to data servers
          when file layouts are being 
          used (see <xref target="global_stateid" />).
          <list style='symbols'>
            <t>
              If the client holds a delegation for the file in question, the
              delegation stateid SHOULD be used.
            </t>
            <t>
              Otherwise, if the entity corresponding to the lock-owner (e.g., a process)
              sending the I/O has a byte-range lock stateid for the associated open file,
              then the byte-range lock stateid for that lock-owner and open file SHOULD 
              be used.
            </t>
            <t>
              If there is no byte-range lock stateid, then the OPEN stateid for the open
              file in question SHOULD be used.
            </t>
            <t>
              Finally, if none of the above apply, then a special stateid 
              SHOULD be used.
            </t>
          </list> 
        </t> 
        <t>
          Ignoring these rules may result in situations in which the server
          does not have information necessary to properly process the request.
          For example, when mandatory byte-range locks are in effect, if the
          stateid does not indicate the proper lock-owner, via a lock stateid,
          a request might be avoidably rejected.
        </t>
        <t>
          The server however should not try to enforce these ordering rules 
          and should use whatever information is available to properly process 
          I/O requests. In particular, when a client has a delegation for a given file, it
          SHOULD take note of this fact in processing a request, even if it is
          sent with a special stateid.
        </t>  
      </section> <!-- "Stateid Use for I/O Operations" -->
      <section anchor="stateid_use_sa" title="Stateid Use for SETATTR Operations">
        <t>
          Because each operation is associated with a session ID and from that
          the clientid can be determined, operations do not need to 
          include a stateid for the server to be able to determine whether
          they should cause a delegation to be recalled or are to be 
          treated as done within the scope of the delegation.
        </t>
        <t>
          In the case of SETATTR operations, a stateid is present.  In cases
          other than those that set the file size, the client may send either
          a special stateid or, when a delegation is held for the file in 
          question, a delegation stateid.  While the server SHOULD validate
          the stateid and may use the stateid to optimize the determination
          as to whether a delegation is held, it SHOULD note the presence of
          a delegation even when a special stateid is sent, and MUST accept a
          valid delegation stateid when sent.
        </t>
      </section> <!-- "Stateid Use for SETATTR Operations" -->
    </section> <!-- "Stateid Definition" -->
  <section anchor="lease_renewal" title="Lease Renewal" >
    <t>
      Each client/server pair, as represented by a client ID, has a single
      lease.
      The purpose of the lease is to allow the client to indicate
      to the server, in a low-overhead way, that it is active, and 
      thus that the server is to retain the client's locks.  This arrangement 
      allows the server to remove stale locking-related objects
      that are held by a client that has crashed or is otherwise
      unreachable, once the relevant lease expires.  This in turn allows 
      other clients to obtain conflicting locks without being 
      delayed indefinitely by inactive or unreachable clients.  
      It is not a 
      mechanism for cache consistency and lease
      renewals may not be denied if the lease interval has not expired. 
    </t>
    <t>
      Since each session is associated with a specific
      client (identified by the client's client ID), any
      operation sent on that session is an indication
      that the associated client is reachable.  When a
      request is sent for a given session, successful
      execution of a SEQUENCE operation (or successful
      retrieval of the result of SEQUENCE from the reply
      cache) on an unexpired lease will result in the
      lease being implicitly renewed, for the standard
      renewal period (equal to the lease_time attribute).

    </t>
    <t>
      If the client ID's lease has not expired when the
      server receives a SEQUENCE operation, then the server
      MUST renew the lease.  If the client ID's lease has expired
      when the server receives a SEQUENCE operation, the
      server MAY renew the lease; this depends on whether
      any state was revoked as a result of the client's
      failure to renew the lease before expiration.

    </t>
    <t>
      Absent other activity that would renew the lease, a COMPOUND
      consisting of a single SEQUENCE operation will suffice.  The
      client should also take communication-related delays into
      account and take steps to ensure that the renewal messages
      actually reach the server in good time.  For example:
      <list style='symbols'>
        <t>
          When trunking is in effect, the client should 
          consider sending multiple requests on different
          connections, in order to ensure that renewal
          occurs, even in the event of blockage in the 
          path used for one of those connections.
        </t>
        <t>
	  Transport retransmission delays might become
	  so large as to approach or exceed the length
	  of the lease period.	This may be particularly
	  likely when the server is unresponsive due to
	  a restart; see <xref target="reclaim_locks"
	  />. If the client implementation is not careful,
	  transport retransmission delays can result in the
	  client failing to detect a server restart before
	  the grace period ends. The scenario is that the
	  client is using a transport with exponential
	  backoff, such that the maximum retransmission
	  timeout exceeds both the grace period and the
	  lease_time attribute. A network partition causes
	  the client's connection's retransmission interval
	  to back off, and even after the partition heals,
	  the next transport-level retransmission is sent
	  after the server has restarted and its grace
	  period ends.

              <vspace blankLines="1" />

          The client MUST either recover from the ensuing
          NFS4ERR_NO_GRACE errors or it MUST ensure that,
          despite transport-level retransmission intervals
          that exceed the lease_time, a SEQUENCE operation is sent
          that renews the lease before expiration. The client can achieve this
          by associating a new connection with the session,
          and sending a SEQUENCE operation on it. However, if
          the attempt to establish a new connection is delayed
          for some reason (e.g., exponential backoff of the connection
          establishment packets), the client will have to
          abort the connection establishment attempt before
          the lease expires, and attempt to reconnect.

        </t>
      </list>
    </t>
    <t>
      If the server renews the lease upon receiving
      a SEQUENCE operation, the server MUST NOT allow the lease
      to expire while the rest of the operations
      in the COMPOUND procedure's request are still
      executing. Once the last operation has finished, and
      the response to COMPOUND has been sent, the server
      MUST set the lease to expire no sooner than the
      sum of current time and the value of the lease_time attribute.

    </t>
    <t>
      A client ID's lease can expire when it has been
      at least the lease interval (lease_time) since the
      last lease-renewing SEQUENCE operation was sent
      on any of the client ID's sessions and there
      are no active COMPOUND operations on any such sessions.

    </t>
    <t>
      Because the SEQUENCE operation is the basic mechanism to renew
      a lease, and because it must be done at least once for each 
      lease period, it is the natural mechanism whereby the server 
      will inform the client of changes in the lease status that the
      client needs to be informed of.  The client should inspect the
      status flags (sr_status_flags) returned by sequence and take 
      the appropriate action (see 
      <xref target="OP_SEQUENCE_DESCRIPTION" /> for details).
      <list style="symbols">
        <t>
          The status bits SEQ4_STATUS_CB_PATH_DOWN and
          SEQ4_STATUS_CB_PATH_DOWN_SESSION indicate problems with
          the backchannel that the client may need to address
          in order to receive callback requests.
        </t>
        <t>
          The status bits SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING and
          SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED indicate
          problems with GSS contexts or RPCSEC_GSS handles
          for the backchannel that the
          client might have to address in order to allow callback requests 
          to be sent.
        </t>
        <t>
          The status bits SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
          SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED,
          SEQ4_STATUS_ADMIN_STATE_REVOKED, and 
          SEQ4_STATUS_RECALLABLE_STATE_REVOKED notify the 
          client of lock revocation events.  When these bits
          are set, the client should use TEST_STATEID to find
          what stateids have been revoked and use FREE_STATEID
          to acknowledge loss of the associated state.
        </t>
        <t>
          The status bit SEQ4_STATUS_LEASE_MOVE  
          indicates that 
          responsibility for lease renewal has been transferred to
          one or more new servers.
        </t>
        <t>
          The status bit SEQ4_STATUS_RESTART_RECLAIM_NEEDED
	  indicates that due to server
	  restart the client must reclaim locking state. 
        </t>
        <t>
          The status bit SEQ4_STATUS_BACKCHANNEL_FAULT
          indicates that the server has encountered an unrecoverable fault
          with the backchannel (e.g., it has lost track of a 
          sequence ID for a slot in the backchannel).
        </t>
      </list>
    </t>
  </section> <!-- "Lease Renewal" -->
  <section title="Crash Recovery" anchor="lock_crash_recovery" >
    <t>
      A critical requirement in crash recovery is that both the client
      and the server know when the other has failed. Additionally, it
      is required that a client sees a consistent view of data across
      server restarts. All READ and WRITE operations that
      may have been queued within the client or network buffers must
      wait until the client has successfully recovered the locks
      protecting the READ and WRITE operations. Any that reach the
      server before the server can safely determine that the client
      has recovered enough locking state to be sure that such
      operations can be safely processed must be rejected.
      This will happen because either:
      <list style='symbols'>
        <t>
          The state presented is no longer valid since it is 
          associated with a now invalid client ID.  In this case, the
          client will receive either an NFS4ERR_BADSESSION or
          NFS4ERR_DEADSESSION error, and any attempt to attach a new
          session to that invalid client ID will result in an
          NFS4ERR_STALE_CLIENTID error.
        </t>
        <t>
          Subsequent recovery of locks may make execution of the 
          operation inappropriate (NFS4ERR_GRACE).
        </t>
      </list>
    </t>
    <section title="Client Failure and Recovery" >
      <t>
        In the event that a client fails, the server may release the 
        client's locks when the associated lease has expired.  Conflicting 
        locks from another client may only be granted after this lease 
        expiration.  As discussed in <xref target="lease_renewal" />, when
        a client has not failed and re-establishes its lease before expiration
        occurs, requests for conflicting locks will not be granted.
      </t>
      <t>
        To minimize client delay upon restart, lock requests are associated
        with an instance of the client by a client-supplied verifier.  This
        verifier is part of the client_owner4 sent in the initial 
        EXCHANGE_ID call made by the client.
        The server returns a client ID as a result of the EXCHANGE_ID
        operation.  The client then confirms the use of the client ID by
        establishing a session associated with that client ID  (see
        <xref target='OP_CREATE_SESSION_DESCRIPTION' /> for a
        description of how this is done).  All locks,
        including opens, byte-range locks, delegations, and layouts obtained
        by sessions using that client ID, are associated with that client ID.  
      </t>
      <t>
        Since the verifier will be changed by the client upon each
        initialization, the server can compare a new verifier to the verifier
        associated with currently held locks and determine that they do not
        match.  This signifies the client's new instantiation and subsequent
        loss (upon confirmation of the new client ID) of locking
        state.  As a result, the server is free to release all
        locks held that are associated with the old client ID that was
        derived from the old verifier.  At this point, conflicting locks from
        other clients, kept waiting while the lease had not yet expired, can
        be granted.  In addition, all stateids associated with the old client ID
        can also be freed, as they are no longer reference-able.
      </t>
      <t>
        Note that the verifier must have the same uniqueness properties as the
        verifier for the COMMIT operation.
      </t>
    </section> <!-- "Client Failure and Recovery" -->
    <section anchor="server_failure" title="Server Failure and Recovery" >
      <t>
        If the server loses locking state (usually as a result of a restart), it must allow clients time to discover this fact and
        re-establish the lost locking state.  The client must be able to
        re-establish the locking state without having the server deny valid
        requests because the server has granted conflicting access to another
        client.  Likewise, if there is a possibility that clients have not
        yet re-established their locking state for a file and that 
        such locking state might make it invalid to perform READ or 
        WRITE operations. For example, if mandatory locks are a possibility,
        the server must disallow READ and WRITE operations for that file.
      </t>
      <t>
        A client can determine that loss of locking
        state has occurred via several methods.
        <list style='numbers'>
        <t>
	When a SEQUENCE (most common) or other operation returns
	NFS4ERR_BADSESSION, this may mean that the session has
	been destroyed but the client ID is still valid.
	The client sends a CREATE_SESSION request with the
	client ID to re-establish the session. If
	CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
	the client must establish a new client ID (see
	<xref target="client_id" />) and re-establish its
	lock state with the new client ID, after the CREATE_SESSION
        operation succeeds (see <xref target="reclaim_locks" />).

        </t>
        <t>
        When a SEQUENCE (most common) or other operation on a
        persistent session returns NFS4ERR_DEADSESSION, this indicates
        that a session is no longer usable for new, i.e., not satisfied
        from the reply cache, operations.  Once all pending operations
        are determined to be either performed before the retry or not
        performed, the client sends a CREATE_SESSION request with the
	client ID to re-establish the session. If
	CREATE_SESSION fails with NFS4ERR_STALE_CLIENTID,
	the client must establish a new client ID (see
	<xref target="client_id" />) and re-establish its
	lock state after the CREATE_SESSION, with the 
        new client ID, succeeds
        (<xref target="reclaim_locks" />).
        </t> 
        <t>
	When an operation, neither SEQUENCE nor preceded by SEQUENCE (for
	example, CREATE_SESSION, DESTROY_SESSION), returns
	NFS4ERR_STALE_CLIENTID, the client MUST establish
	a new client ID (<xref target="client_id" />) and
	re-establish its lock state (<xref
	target="reclaim_locks" />).
        </t>
        </list>
      </t>
      <section anchor="reclaim_locks" title="State Reclaim" >
      <t>
        When state information and the associated locks are lost
        as a result of a server restart, the protocol must provide
        a way to cause that state to be re-established.  The 
        approach used is to define, for most types of locking
        state (layouts are an exception), a request whose function 
        is to allow the client to 
        re-establish on the server a lock first obtained from a
        previous instance.  Generally, these requests are variants
        of the requests normally used to create locks of that type
        and are referred to as "reclaim-type" requests, and the process
        of re-establishing such locks is referred to as "reclaiming" 
        them.
      </t>
      <t anchor="read_write_grace">
        Because each client must have an opportunity to reclaim
        all of the locks that it has without the possibility that
        some other client will be granted a conflicting lock,
        a "grace period" is devoted
        to the reclaim process.  During this period, requests 
        creating client IDs and
        sessions are handled normally, but locking requests are
        subject to special restrictions.  Only 
        reclaim-type locking requests are allowed, unless the
        server can reliably determine (through state
        persistently maintained across restart instances) that
        granting any such lock cannot possibly conflict with a
        subsequent reclaim.  
        When a request is made to obtain
        a new lock (i.e., not a reclaim-type request) during the
        grace period and such a determination cannot be made,
        the server must return the error NFS4ERR_GRACE.
      </t> 
      <t>
        Once a session is established using the new client ID, the
        client will use reclaim-type locking requests (e.g., LOCK
        operations with reclaim set to TRUE and OPEN operations with a
        claim type of CLAIM_PREVIOUS;  see
        <xref target="open_br_reclaim" />) to re-establish its locking
        state.  Once this is done, or if there is no such locking
        state to reclaim, the client sends a global RECLAIM_COMPLETE
        operation, i.e., one with the rca_one_fs argument set to FALSE, to
        indicate that it has reclaimed all of the locking state that
        it will reclaim.  Once a client sends such a RECLAIM_COMPLETE
        operation, it may attempt non-reclaim locking operations,
        although it might get an NFS4ERR_GRACE status result from each such operation until
        the period of special handling is over.  
See <xref target="transition_state" /> for a discussion of the
        analogous handling lock reclamation in the case of file systems
        transitioning from server to server.
      </t>
      <t>
        During the grace period, the server must reject READ
        and WRITE operations 
        and non-reclaim locking requests (i.e., other LOCK
        and OPEN operations) with an error of NFS4ERR_GRACE,
        unless it can guarantee that these may be done 
        safely, as described below. 
      </t>
      <t>
        The grace period may last until all clients that are known to 
        possibly have had locks have done a global RECLAIM_COMPLETE operation, indicating
        that they have finished reclaiming the locks they held before
        the server restart.  This means that a client that has done a
        RECLAIM_COMPLETE must be prepared to receive an NFS4ERR_GRACE
        when attempting to acquire new locks.  
        In order for the server to know that all clients with possible prior
        lock state have done a RECLAIM_COMPLETE,
        the server must maintain in stable
        storage a list clients that may have such locks.  The server 
        may also terminate the grace period before all clients have
        done a global RECLAIM_COMPLETE.  The server SHOULD NOT terminate the
        grace period before a time equal to the lease period in order
        to give clients an opportunity to find out about the server 
        restart, as a result of sending requests on associated 
        sessions with a frequency governed by the lease time.  
        Note that when a client does not send such requests (or they
        are sent by the client but not received by the server),
        it is possible for the grace period to expire before the client
        finds out that the server restart has occurred.
      </t>
      <t>
        Some additional time in 
        order to allow a client to 
        establish a new client ID and session and to effect lock 
        reclaims may be added to the lease time.  Note that 
        analogous rules apply to
        file system-specific grace periods discussed in
        <xref target="transition_state" />.
      </t>
      <t>
        If the server can reliably determine that granting a non-reclaim
        request will not conflict with reclamation of locks by other 
        clients, the NFS4ERR_GRACE error does not have to be returned 
        even within the grace period, although NFS4ERR_GRACE must always
        be returned to clients attempting a non-reclaim lock request
        before doing their own global RECLAIM_COMPLETE.
        For the server to be able
        to service READ and WRITE operations during the grace period, it must
        again be able to guarantee that no possible conflict could arise
        between a potential reclaim locking request and the READ or WRITE
        operation.  If the server is unable to offer that guarantee, the
        NFS4ERR_GRACE error must be returned to the client.
      </t>
      <t>
        For a server to provide simple, valid handling during the grace
        period, the easiest method is to simply reject all non-reclaim locking
        requests and READ and WRITE operations by returning the NFS4ERR_GRACE
        error.  However, a server may keep information about granted locks in
        stable storage.  With this information, the server could determine if
        a locking, READ or WRITE operation can be safely processed.
      </t>
      <t>
        For example, if the server maintained on stable storage summary
        information on whether mandatory locks exist, either mandatory 
        byte-range locks, or share reservations specifying deny modes,
        many requests could be allowed during the grace period.  If it
        is known that no such share reservations exist, OPEN request that
        do not specify deny modes may be safely granted.  If, in addition,
        it is known that no mandatory byte-range locks exist, either 
        through information stored on stable storage or simply because
        the server does not support such locks, READ and WRITE operations
        may be safely processed during the grace period.
        Another important case is where it is known that no mandatory 
        byte-range locks exist, either because the server does not 
        provide support for them or because their absence is known
        from persistently recorded data.  In this case, READ and
        WRITE operations specifying stateids derived from reclaim-type
        operations may be validly processed during the grace period
        because of the fact that the valid reclaim ensures that no lock
        subsequently granted can prevent the I/O.  
      </t>
      <t>
        To reiterate, for a server that allows non-reclaim lock and I/O
        requests to be processed during the grace period, it MUST determine
        that no lock subsequently reclaimed will be rejected and that no lock
        subsequently reclaimed would have prevented any I/O operation
        processed during the grace period.
      </t>
      <t>
        Clients should be prepared for the return of NFS4ERR_GRACE errors for
        non-reclaim lock and I/O requests.  In this case, the client should
        employ a retry mechanism for the request.  A delay (on the order of
        several seconds) between retries should be used to avoid overwhelming
        the server.  Further discussion of the general issue is included in
        <xref target="Floyd" />.  The client must account for the server that
        can perform I/O and non-reclaim locking requests within the grace period
        as well as those that cannot do so.
      </t>
      <t>
        A reclaim-type locking request outside the server's grace period
        can only succeed if the server can guarantee that no conflicting
        lock or I/O request has been granted since restart.
      </t>
      <t>
        A server may, upon restart, establish a new value for the lease
        period.  Therefore, clients should, once a new client ID is
        established, refetch the lease_time attribute and use it as the basis
        for lease renewal for the lease associated with that server. However,
        the server must establish, for this restart event, a grace period at
        least as long as the lease period for the previous server
        instantiation. This allows the client state obtained during the
        previous server instance to be reliably re-established.
      </t>
      <t>
        The possibility exists that, because of server configuration 
        events, the client will be communicating with a server
        different than the one on which the locks were obtained, as
        shown by the combination of eir_server_scope and 
        eir_server_owner.  This leads to the issue of if and when
        the client should attempt to reclaim locks previously obtained
        on what is being reported as a different server.  The rules
        to resolve this question are as follows:
        <list style="symbols">
          <t>
            If the server scope is different, the client should not
            attempt to reclaim locks.  In this situation, no lock 
            reclaim is possible.  Any attempt to re-obtain the locks
            with non-reclaim operations is problematic since there is
            no guarantee that the existing filehandles will be recognized
            by the new server, or that if recognized, they denote the 
            same objects.  It is best to treat the locks as having been
            revoked by the reconfiguration event.
          </t>
          <t>
            If the server scope is the same, the client should attempt
            to reclaim locks, even if the eir_server_owner value is
            different.  In this situation, it is the responsibility
            of the server to return NFS4ERR_NO_GRACE if it cannot 
            provide correct support for lock reclaim operations, 
            including the prevention of edge conditions.
          </t>
        </list>
      </t>
      <t>
        The eir_server_owner field is not used in making this 
        determination.  Its function is to specify trunking
        possibilities for the client (see <xref target="Trunking" />)
        and not to control lock reclaim.
      </t>
        <section anchor="reclaim_security_considerations" title="Security Considerations for State Reclaim" >
        <t>
          During the grace period, a client can reclaim state that it believes or
          asserts it had before the server restarted. Unless the server
          maintained a complete record of all the state the client had,
          the server has little choice but to trust the client. (Of course,
          if the server maintained a complete record, then it would not
          have to force the client to reclaim state after server restart.)
          While the server has to trust the client to tell the truth, such
          trust does not have any negative consequences for security. The
          fundamental rule for the server when processing reclaim requests
          is that it MUST NOT grant the reclaim if an equivalent non-reclaim
          request would not be granted during steady state due to access
          control or access conflict issues. For example, an OPEN request
	  during a reclaim will be refused with NFS4ERR_ACCESS if the principal making
	  the request does not have access to open the file according to the
	  discretionary ACL (<xref target="attrdef_dacl"/>) on the file.

        </t>

        <t>
          Nonetheless, it is possible that a client operating in error or
          maliciously could, during reclaim, prevent another client from
          reclaiming access to state. For example, an attacker could
          send an OPEN reclaim operation with a deny mode that prevents
          another client from reclaiming the OPEN state it had before the
          server restarted.
          The attacker could perform the same denial of service during
          steady state prior to server restart, as long as the
          attacker had permissions. Given that the attack
          vectors are equivalent, the grace period does not offer any
          additional opportunity for denial of service, and any concerns
          about this attack vector, whether during grace or steady state,
          are addressed the same way: use RPCSEC_GSS for authentication
          and limit access to the file only to principals that the owner of
          the file trusts.

         </t>

         <t>
           Note that if prior to restart the server had client
           IDs with the  EXCHGID4_FLAG_BIND_PRINC_STATEID (<xref
           target="OP_EXCHANGE_ID"/>) capability set, then the server
           SHOULD record in stable storage the client owner and the
           principal that established the client ID via EXCHANGE_ID.
           If the server does not, then there is a risk a client will
           be unable to reclaim state if it does not have a credential
           for a principal that was originally authorized to
           establish the state.

         </t>

           
        </section> <!-- "Security Considerations for State Reclaim" -->
      </section> <!-- "State Reclaim" -->
    </section> <!-- "Server Failure and Recovery" -->
    <section anchor="network_partitions_and_recovery"
             title="Network Partitions and Recovery">
      <t>
        If the duration of a network partition is greater than the lease
        period provided by the server, the server will not have received a
        lease renewal from the client.  If this occurs, the server may free
        all locks held for the client or it may allow the lock state to
        remain for a considerable period, subject to the constraint that
        if a request for a conflicting lock is made, locks associated with
        an expired lease do not prevent such a conflicting lock from being
        granted but MUST be revoked as necessary so as to avoid interfering with
        such conflicting requests.
      </t>
      <t>
        If the server chooses to delay freeing of lock state until there 
        is a conflict, it may either free all of the client's locks once 
        there is a conflict or it may only revoke the minimum set of locks
        necessary to allow conflicting requests.  When it adopts the 
        finer-grained approach, it must revoke all locks associated with a
        given stateid, even if the conflict is with only a subset of locks.
      </t>
      <t>
        When the server chooses to free all of a client's lock state, either
        immediately upon lease expiration or as a result of the first
        attempt to obtain a conflicting a lock, the server may report the
        loss of lock state in a number of ways.
      </t>
      <t>
        The server may choose to invalidate the session and the associated
        client ID.  In this case, once the client can communicate
        with the server, it will receive an NFS4ERR_BADSESSION error.  Upon
        attempting to create a new session, it would get an 
        NFS4ERR_STALE_CLIENTID.  Upon creating the new client ID and new
        session, the client will attempt to reclaim locks. Normally, the
        server will not allow the client to reclaim locks, because the
        server will not be in its recovery grace period.
      </t>
      <t> 
        Another possibility is for the server to maintain the session and 
        client ID but for all stateids held by the
        client to become invalid or stale.  Once the client can reach
        the server after such a network partition, the status returned by
        the SEQUENCE operation will indicate a loss of locking state; i.e.,
        the flag SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED will be set in
        sr_status_flags. In
        addition, all I/O submitted by the
        client with the now invalid stateids will fail with the server
        returning the error NFS4ERR_EXPIRED.  Once the client learns of
        the loss of locking state, it 
        will suitably notify the applications that held the invalidated
        locks.  The client should then take action to free invalidated 
        stateids, either by establishing a new client ID using a new
        verifier or by doing a FREE_STATEID operation to release each
        of the invalidated stateids.
      </t>
      <t>
        When the server adopts a finer-grained approach to revocation
        of locks when a client's lease has expired, only a subset of stateids 
        will normally become invalid during a network partition.  
        When the client can communicate with the server after such a 
        network partition heals, the status returned by the SEQUENCE 
        operation will indicate a partial loss of locking state 
        (SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED).  
        In addition, operations, including I/O submitted by the
        client, with the now invalid stateids will fail with the server
        returning the error NFS4ERR_EXPIRED.  Once the client learns of
        the loss of locking state, it will use the TEST_STATEID operation 
        on all of its stateids to 
        determine which locks have been lost and then 
        suitably notify the applications that held the invalidated
        locks.  The client can then release the invalidated locking 
        state and acknowledge the revocation of the associated locks
        by doing a FREE_STATEID operation on each of the invalidated
        stateids.
      </t>
      <t>
        When a network partition is combined with a server restart, there are
        edge conditions that place requirements on the server in order to
        avoid silent data corruption following the server restart. Two of these
        edge conditions are known, and are discussed below.
      </t>
      <t>
        The first edge condition arises as a result of the scenarios such as
        the following:
        <list style='numbers'>
          <t>
            Client A acquires a lock.
          </t>
          <t>
            Client A and server experience mutual network partition, such that
            client A is unable to renew its lease.
          </t>
          <t>
            Client A's lease expires, and the server releases the lock.
          </t>
          <t>
            Client B acquires a lock that would have conflicted
            with that of client A.
          </t>
          <t>
            Client B releases its lock.
          </t>
          <t>
            Server restarts.
          </t>
          <t>
            Network partition between client A and server heals.
          </t>
          <t>
            Client A connects to a new server instance and finds out about 
            server restart.
          </t>
          <t>
            Client A reclaims its lock within the server's grace period.
          </t>
        </list>
      </t>
      <t>
        Thus, at the final step, the server has erroneously granted client A's
        lock reclaim. If client B modified the object the lock was protecting,
        client A will experience object corruption.
      </t>
      <t>
        The second known edge condition arises in situations such as the following:
        <list style="numbers">
          <t>
            Client A acquires one or more locks.
          </t>
          <t>
            Server restarts.
          </t>
          <t>
            Client A and server experience mutual network
            partition, such that client A is unable to reclaim
            all of its locks within the grace period.
          </t>
          <t>
            Server's reclaim grace period ends. Client A has either 
            no locks or an incomplete set of locks known to the server.
          </t>
          <t>
            Client B acquires a lock that would have conflicted
            with a lock of client A that was not reclaimed.
          </t>
          <t>
            Client B releases the lock.
          </t>
          <t>
            Server restarts a second time.
          </t>
          <t>
            Network partition between client A and server heals.
          </t>
          <t>
            Client A connects to new server instance and finds out about 
            server restart.
          </t>
          <t>
            Client A reclaims its lock within the server's
            grace period.
          </t>
        </list>
      </t>
      <t>
        As with the first edge condition, the final step of the scenario of
        the second edge condition has the server erroneously granting client
        A's lock reclaim.
      </t>
      <t>
        Solving the first and second edge conditions requires either that the server
        always assumes after it restarts that some edge condition 
        occurs, and thus returns NFS4ERR_NO_GRACE for all reclaim attempts, or that the server
        record some information in stable storage.  The amount 
        of information the
        server records in stable storage is in inverse proportion to how harsh
        the server intends to be whenever edge conditions arise.
        The server
        that is completely tolerant of all edge conditions will record in
        stable storage every lock that is acquired, removing the lock record
        from stable storage only when the lock is released.
        For the two edge conditions discussed above, the harshest a
        server can be, and still support a grace period for reclaims, requires
        that the server record in stable storage some minimal
        information.  For example, a server implementation could, for each
        client, save in stable storage a record containing:
        <list style="symbols">
          <t>
            the co_ownerid field from the client_owner4 presented in the
            EXCHANGE_ID operation.
          </t>
          <t>
            a boolean that indicates if the client's lease expired
            or if there was administrative intervention (see
            <xref target="server_revocation" />) to revoke
            a byte-range lock, share reservation, or delegation and
            there has been no acknowledgment, via FREE_STATEID,
            of such revocation.
          </t>
          <t>
            a boolean that indicates whether the client may have locks
            that it believes to be reclaimable in situations in which the
            grace period was terminated, making the server's view of
            lock reclaimability suspect.  The server will set this for
            any client record in stable storage where the client has
            not done a suitable RECLAIM_COMPLETE (global or file
            system-specific depending on the target of the lock
            request) before it grants any new (i.e., not reclaimed)
            lock to any client.
          </t>
        </list>
      </t>
      <t>
        Assuming the above record keeping, for the first edge condition, after
        the server restarts, the record that client A's lease expired means
        that another client could have acquired a conflicting byte-range lock,
        share reservation, or delegation. Hence, the server must reject a
        reclaim from client A with the error NFS4ERR_NO_GRACE.
      </t>
      <t>
        For the second edge condition, after the server restarts for a second
        time, the indication that the client had not completed its
        reclaims at the time at which the grace period ended
        means that the server must reject a reclaim from client A
        with the error NFS4ERR_NO_GRACE.
      </t>
      <t>
        When either edge condition occurs, the client's attempt to reclaim
        locks will result in the error NFS4ERR_NO_GRACE.  When this is
        received, or after the client restarts with no lock state, the
        client will send a global RECLAIM_COMPLETE.  When 
        the RECLAIM_COMPLETE is received, the server and client are
        again in agreement regarding reclaimable locks and both booleans in persistent
        storage can be reset, to be set again only when there is a subsequent
        event that causes lock reclaim operations to be questionable.
      </t>
      <t>
        Regardless of the level and approach to record keeping, the server
        MUST implement one of the following strategies (which apply to
        reclaims of share reservations, byte-range locks, and delegations):
        <list style="numbers">
          <t>
            Reject all reclaims with NFS4ERR_NO_GRACE. This
            is extremely unforgiving, but necessary if the server does not
            record lock state in stable storage.
          </t>
          <t>
            Record sufficient state in stable storage such that
            all known edge conditions involving server restart,
            including the two noted in this section, are
            detected.  It is acceptable to erroneously recognize an edge condition 
            and not allow a reclaim, when, with sufficient knowledge, it
            would be allowed. The error the server would return in this
            case is NFS4ERR_NO_GRACE.  Note that it is not known if there are other
            edge conditions.
            <vspace blankLines='1' />
            In the event that, after a server restart, the server
            determines there is unrecoverable damage or
            corruption to the information in stable storage, then for
            all clients and/or locks that may be affected, the server MUST
            return NFS4ERR_NO_GRACE.
          </t>
        </list>
      </t>
      <t>
        A mandate for the client's handling of the NFS4ERR_NO_GRACE error is
        outside the scope of this specification, since the strategies for such
        handling are very dependent on the client's operating environment.
        However, one potential approach is described below.
      </t>
      <t>
        When the client receives NFS4ERR_NO_GRACE, it could examine the change
        attribute of the objects  for which the client is trying to reclaim state,
        and use that to determine whether to re-establish the state via normal
        OPEN or LOCK operations. This is acceptable provided that the client's
        operating environment allows it.  In other words, the client
        implementor is advised to document for his users the behavior. The
        client could also inform the application that its byte-range lock or share
        reservations (whether or not they were delegated) have been lost, such
        as via a UNIX signal, a Graphical User Interface (GUI) pop-up window, etc. 
        See <xref target="data_caching_revocation" />
        for a discussion of what the client should do
        for dealing with unreclaimed delegations on client state.
      </t>
      <t>
        For further discussion of revocation of locks, see 
        <xref target="server_revocation" />.
      </t>
    </section> <!-- "Network Partitions and Recovery" -->
  </section> <!-- "Crash Recovery" -->
  <section anchor="server_revocation" title="Server Revocation of Locks" >
    <t>
      At any point, the server can revoke locks held by a client, and the
      client must be prepared for this event.  When the client detects that
      its locks have been or may have been revoked, the client is
      responsible for validating the state information between itself and
      the server.  Validating locking state for the client means that it
      must verify or reclaim state for each lock currently held.
    </t>
    <t>
      The first occasion of lock revocation is upon server
      restart.  Note that this includes situations
      in which sessions are persistent and locking state is
      lost.  In this class of instances, the client will
      receive an error (NFS4ERR_STALE_CLIENTID) on an 
      operation that takes client ID, usually as part of 
      recovery in response to a problem with the current 
      session), and the client will proceed
      with normal crash recovery as described in the <xref
      target="reclaim_locks" />.
    </t>
    <t>
      The second occasion of lock revocation is the inability to renew the lease
      before expiration, as discussed in  
      <xref target="network_partitions_and_recovery"  />. While this is 
      considered a rare or unusual event,
      the client must be prepared to recover.  The server is responsible
      for determining the precise consequences of the lease expiration, 
      informing the client of the scope of the lock revocation decided
      upon.  The client then uses the status information provided
      by the server in the SEQUENCE results (field sr_status_flags,
      see <xref target="OP_SEQUENCE_DESCRIPTION" />)
      to synchronize its locking state with that of the 
      server, in order to recover.
    </t>
    <t>
      The third occasion of lock revocation can occur as a result of
      revocation of locks within the lease period, either because of
      administrative intervention or because a recallable lock (a
      delegation or layout) was not returned within the lease period
      after having been recalled.  While these are
      considered rare events, they are possible, and the client must be
      prepared to deal with them.  When either of these events occurs,
      the client finds out about the situation through the status returned
      by the SEQUENCE operation.  Any use of stateids associated with 
      locks revoked during the lease period will receive the error 
      NFS4ERR_ADMIN_REVOKED or NFS4ERR_DELEG_REVOKED, as appropriate.
    </t>
    <t>
      In all situations in which a subset of locking state may have been 
      revoked, which include all cases in which locking state is revoked
      within the lease period, it is up to the client to determine which
      locks have been revoked and which have not.  It does this by
      using the TEST_STATEID operation on the appropriate set of stateids.
      Once the set of revoked locks has been determined, the applications
      can be notified, and the invalidated stateids can be freed and
      lock revocation acknowledged by using FREE_STATEID.
    </t>
  </section> <!-- "Server Revocation of Locks" --> 
  <section title="Short and Long Leases" >
    <t>
      When determining the time period for the server lease, the usual lease
      tradeoffs apply.  A short lease is good for fast server recovery at a
      cost of increased operations to effect lease renewal (when there are
      no other operations during the period to effect lease renewal as a
      side effect).  A long lease is certainly kinder and gentler to
      servers trying to handle very large numbers of clients.  The number of extra requests 
      to effect lock renewal drops in inverse
      proportion to the lease time.  The disadvantages of a long lease
      include the possibility of slower recovery after certain failures.
      After server failure, a longer grace period may be required when
      some clients do not promptly reclaim their locks and do a 
      global RECLAIM_COMPLETE.  In the event of client failure,
      the longer period for a lease to expire will force conflicting
      requests to wait longer.
    </t>
    <t>
      A long lease is practical if the server can store lease state in
      stable storage.  Upon recovery, the server can reconstruct the
      lease state from its stable storage and continue operation with
      its clients.
    </t>
  </section> <!-- "Short and Long Leases" -->
  <section anchor="lease_propagation_delay" title="Clocks, Propagation Delay, and Calculating Lease Expiration" >
    <t>
      To avoid the need for synchronized clocks, lease times are granted by
      the server as a time delta.  However, there is a requirement that the
      client and server clocks do not drift excessively over the duration of
      the lease.  There is also the issue of propagation delay across the
      network, which could easily be several hundred milliseconds, as well as
      the possibility that requests will be lost and need to be
      retransmitted.
    </t>
    <t>
      To take propagation delay into account, the client should
      subtract it from lease times (e.g., if the client estimates the
      one-way propagation delay as 200 milliseconds, then it can
      assume that the lease is already 200 milliseconds old when it
      gets it).  In addition, it will take another 200 milliseconds to
      get a response back to the server.  So the client must send a
      lease renewal or write data back to the server at least 400
      milliseconds before the lease would expire. If the propagation delay
      varies over the life of the lease (e.g., the client is on a mobile
      host), the client will need to continuously subtract the increase
      in propagation delay from the lease times.
    </t>
    <t>
      The server's lease period configuration should take into account the
      network distance of the clients that will be accessing the server's
      resources.  It is expected that the lease period will take into
      account the network propagation delays and other network delay factors
      for the client population.  Since the protocol does not allow for an
      automatic method to determine an appropriate lease period, the
      server's administrator may have to tune the lease period.

    </t>
  </section> <!-- "Clocks, Propagation Delay, and Calculating Lease Expiration" -->
  <section title="Obsolete Locking Infrastructure from NFSv4.0" anchor="vestigial_locking" >
    <t>
      There are a number of operations and fields within existing 
      operations that no longer have a function in NFSv4.1.
      In one way or another, these changes are all due to
      the implementation of sessions that provide client context
      and exactly once semantics as a base feature of the protocol,
      separate from locking itself.
    </t>
    <t>
      The following NFSv4.0 operations MUST NOT be implemented in NFSv4.1.
      The server MUST return NFS4ERR_NOTSUPP if these operations are
      found in an NFSv4.1 COMPOUND.
      <list style='symbols'>
        <t>
          SETCLIENTID since its function has been replaced by
          EXCHANGE_ID.
        </t>
        <t>
          SETCLIENTID_CONFIRM since client ID confirmation now 
          happens by means of CREATE_SESSION.
        </t>
        <t>
          OPEN_CONFIRM because state-owner-based seqids
          have been replaced by the sequence ID in the
          SEQUENCE operation.
        </t>
        <t>
          RELEASE_LOCKOWNER because lock-owners with no associated
          locks do not have any sequence-related state and so can 
          be deleted by the server at will.
        </t>
        <t>
          RENEW because every SEQUENCE operation for a session causes
          lease renewal, making a separate operation superfluous.
        </t>
      </list>
    </t>
    <t>
      Also, there are a number of fields, present in existing operations,
      related to locking that have no use in minor version 1.  They 
      were used in minor version 0 to perform functions now provided 
      in a different
      fashion.
      <list style='symbols'>
        <t>
          Sequence ids used to sequence requests for a given state-owner
          and to provide retry protection, now provided
          via sessions.
        </t>
        <t>
          Client IDs used to identify the client associated with a given
          request.  Client identification is now available using the client ID
          associated with the current session, without needing an explicit
          client ID field. 
        </t>
      </list>
    </t>
    <t>
      Such vestigial fields in existing operations have no function in
      NFSv4.1 and are ignored by the server.  Note that client IDs in 
      operations new to NFSv4.1 (such as CREATE_SESSION and DESTROY_CLIENTID)
      are not ignored.
    </t>
  </section> <!-- "Vestigial Locking Infrastructure From V4.0" -->
</section> <!-- "State Management" -->
<!--  $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $       -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section title="File Locking and Share Reservations" anchor="file_locking">
  <t>
    To support Win32 share reservations, it is necessary to provide
    operations that atomically open or create files.  Having a
    separate share/unshare operation would not allow correct
    implementation of the Win32 OpenFile API.  In order to
    correctly implement share semantics, the previous NFS protocol
    mechanisms used when a file is opened or created (LOOKUP, CREATE,
    ACCESS) need to be replaced.  The NFSv4.1 protocol defines
    an OPEN operation that is capable of atomically looking up, creating,
    and locking a file on the server.

  </t>
  <section title="Opens and Byte-Range Locks" >
    <t>
      It is assumed that manipulating a byte-range lock is rare when 
      compared to READ
      and WRITE operations.  It is also assumed that server restarts and network
      partitions are relatively rare.  Therefore, it is important that the
      READ and WRITE operations have a lightweight mechanism to indicate if
      they possess a held lock.  A LOCK operation contains the 
      heavyweight information required to establish a byte-range lock and uniquely 
      define the owner of the lock.
    </t>
    <section anchor="state-owner" title="State-Owner Definition" >
      <t>
        When opening a file or requesting a byte-range lock, the 
        client must specify an identifier that represents the owner of
        the requested lock.  This identifier is in the form of a
        state-owner, represented in the protocol by a state_owner4, a 
        variable-length opaque array that, when concatenated with the
        current client ID, uniquely defines the owner of a lock managed
        by the client. This may be a thread ID, process ID, or other 
        unique value.  
      </t>
      <t>
        Owners of opens and owners of byte-range locks are separate 
        entities and remain separate even if the same opaque arrays
        are used to designate owners of each.  The protocol distinguishes
        between open-owners (represented by open_owner4 structures)
        and lock-owners (represented by lock_owner4 structures).
      </t>  
      <t>
        Each open is associated with a specific open-owner while each
        byte-range lock is associated with a lock-owner and an
        open-owner, the latter being the open-owner associated with the
        open file under which the LOCK operation was done.  Delegations
        and layouts, on the other hand, are not associated with a
        specific owner but are associated with the client as a whole
        (identified by a client ID).
      </t>
    </section> <!-- "State-owner Definition" -->
    <section title="Use of the Stateid and Locking" >
      <t>
        All READ, WRITE, and SETATTR operations contain a stateid.  For the
        purposes of this section, SETATTR operations that change the size
        attribute of a file are treated as if they are writing the area
        between the old and new sizes (i.e., the byte-range truncated or added to the
        file by means of the SETATTR), even where SETATTR is not explicitly
        mentioned in the text.  The stateid passed to one of these operations must
        be one that represents an open, a set of byte-range locks, or a 
        delegation, or it may be a special stateid representing anonymous
        access or the special bypass stateid.
      </t>
      <t>
        If the state-owner performs a READ or WRITE operation in a situation in which
        it has established a byte-range lock or share reservation 
        on the server (any OPEN constitutes a share reservation), the
        stateid (previously returned by the server) must be used to
        indicate what locks, including both byte-range
        locks and share reservations, are held by the state-owner.  If no state
        is established by the client, either a byte-range lock or a share reservation,
        a special stateid for anonymous state (zero as the value for "other" and "seqid") 
        is used.  (See <xref target='special_stateid' /> for a description of 
        'special' stateids in general.)
        Regardless of whether a stateid for anonymous state
        or a stateid returned by the server is used, if there is a
        conflicting share reservation or mandatory byte-range lock held on the
        file, the server MUST refuse to service the READ or WRITE operation.
      </t>
      <t>
        Share reservations are established by OPEN operations and by their
        nature are mandatory in that when the OPEN denies READ or WRITE
        operations, that denial results in such operations being rejected with
        error NFS4ERR_LOCKED.  Byte-range locks may be implemented by the server
        as either mandatory or advisory, or the choice of mandatory or
        advisory behavior may be determined by the server on the basis of the
        file being accessed (for example, some UNIX-based servers support a
        "mandatory lock bit" on the mode attribute such that if set, byte-range
        locks are required on the file before I/O is possible).  When byte-range
        locks are advisory, they only prevent the granting of conflicting lock
        requests and have no effect on READs or WRITEs.  Mandatory byte-range
        locks, however, prevent conflicting I/O operations.  When they are
        attempted, they are rejected with NFS4ERR_LOCKED.  When the client
        gets NFS4ERR_LOCKED on a file for which it knows it has the proper share
        reservation, it will need to send a LOCK operation on the byte-range of
        the file that includes the byte-range the I/O was to be performed on, with
        an appropriate locktype field of the LOCK operation's arguments (i.e., READ*_LT for a READ operation, WRITE*_LT
        for a WRITE operation).
      </t>
      <t>
        Note that for UNIX environments that support mandatory byte-range locking,
        the distinction between advisory and mandatory locking is subtle.  In
        fact, advisory and mandatory byte-range locks are exactly the same as
        far as the APIs and requirements on implementation. If the mandatory
        lock attribute is set on the file, the server checks to see if the
        lock-owner has an appropriate shared (READ_LT) or exclusive (WRITE_LT) byte-range
        lock on the byte-range it wishes to READ from or WRITE to. If there is no
        appropriate lock, the server checks if there is a conflicting lock
        (which can be done by attempting to acquire the conflicting lock on
        behalf of the lock-owner, and if successful, release the lock after
        the READ or WRITE operation is done), and if there is, the server returns
        NFS4ERR_LOCKED.
      </t>
      <t>
        For Windows environments, byte-range locks are always mandatory, so the
        server always checks for byte-range locks during I/O requests.
      </t>
      <t>
        Thus, the LOCK operation does not need to distinguish
        between advisory and mandatory byte-range locks. It is the
        server's processing of the READ and WRITE operations that introduces
        the distinction.
      </t>
      <t>
        Every stateid that is validly passed to READ, WRITE, or SETATTR,
        with the exception of special stateid values,
        defines an access mode for the file (i.e.,
        OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
        OPEN4_SHARE_ACCESS_BOTH).
        <list style='symbols'>
          <t>
            For stateids associated with opens, this is the mode defined by 
            the original OPEN that caused the 
            allocation of the OPEN stateid
            and as modified by subsequent OPENs and OPEN_DOWNGRADEs for the
            same open-owner/file pair.  
          </t>
          <t>
            For stateids returned by byte-range LOCK operations,
            the appropriate mode is the access mode for the OPEN 
            stateid associated with the lock set represented by the stateid.  
          </t>
          <t>
            For delegation stateids, the access mode is based on the type of delegation.
          </t>
        </list>
      </t>
      <t>
        When a READ, WRITE, or SETATTR (that specifies the
        size attribute) operation is done, the operation is subject to checking against
        the access mode to verify that the operation is appropriate given the
        stateid with which the operation is associated.
      </t>
      <t>
        In the case of WRITE-type operations (i.e., WRITEs and SETATTRs that
        set size), the server MUST verify that the access mode allows writing
        and MUST return an NFS4ERR_OPENMODE error if it does not.  In the case of
        READ, the server may perform the corresponding check on the access
        mode, or it may choose to allow READ on OPENs for OPEN4_SHARE_ACCESS_WRITE, to
        accommodate clients whose WRITE implementation may unavoidably do
        reads (e.g., due to buffer cache constraints).  However, even if READs
        are allowed in these circumstances, the server MUST still check for
        locks that conflict with the READ (e.g., another OPEN specified OPEN4_SHARE_DENY_READ or OPEN4_SHARE_DENY_BOTH).  Note that a server that does enforce the access mode check
        on READs need not explicitly check for conflicting share reservations
        since the existence of OPEN for OPEN4_SHARE_ACCESS_READ guarantees that no
        conflicting share reservation can exist.
      </t>
      <t>
        The READ bypass special stateid (all bits of "other" and "seqid" set
        to one)
        indicates a desire to bypass locking checks.  The server MAY 
        allow READ operations to bypass
        locking checks at the server, when this special stateid is used.
        However, WRITE operations with 
        this special stateid value MUST NOT bypass locking checks and are
        treated exactly the same as if a special stateid for anonymous state
        were used.
      </t>
      <t>
        A lock may not be granted while a READ or WRITE operation using one of
        the special stateids is being performed and the scope of the lock
        to be granted would conflict with the READ or WRITE operation.
        This can occur when:
        <list style='symbols'>
          <t>
            A mandatory byte-range lock is requested with a byte-range that
            conflicts with the byte-range of the READ or WRITE operation.  
            For the purposes of this paragraph, a conflict occurs when 
            a shared lock is requested and a WRITE operation is being 
            performed, or an exclusive lock is requested and either a 
            READ or a WRITE operation is being performed.
          </t>
          <t>
            A share reservation is requested that denies reading and/or
            writing and the corresponding operation is being performed.
          </t>
          <t>
            A delegation is to be granted and the delegation type would
            prevent the I/O operation, i.e., READ and WRITE conflict with
            an OPEN_DELEGATE_WRITE delegation and WRITE conflicts with an OPEN_DELEGATE_READ delegation.
          </t>
        </list>
      </t>
      <t>
        When a client holds a delegation, it needs to ensure
        that the stateid sent conveys the association of
        operation with the delegation, to avoid the delegation from 
        being avoidably recalled.  When the delegation stateid, 
        a stateid open associated with that delegation, or a stateid 
        representing byte-range locks derived from such an open is 
        used, the server knows that the READ, WRITE, or SETATTR
        does not conflict with the delegation but is sent under
        the aegis of the delegation.  Even though it is possible
        for the server to determine from the client ID (via
        the session ID) that the client does in fact have a 
        delegation, the server is not obliged to check this, so
        using a special stateid can result in avoidable recall
        of the delegation.
      </t>
    </section> <!-- "Use of the Stateid and Locking" -->
  </section> <!-- "Opens and Byte-Range Locks" -->
  <section title="Lock Ranges" >
    <t>
      The protocol allows a lock-owner to request a lock with a byte-range
      and then either upgrade, downgrade, or unlock a sub-range of 
      the initial lock, or a byte-range that 
      overlaps -- fully or partially -- either with that initial lock or a 
      combination of a set of existing locks for the same lock-owner.  It
      is expected that this will be an uncommon type of request.  In any
      case, servers or server file systems may not be able to support
      sub-range lock semantics.  In the event that a server receives a
      locking request that represents a sub-range of current locking state
      for the lock-owner, the server is allowed to return the error
      NFS4ERR_LOCK_RANGE to signify that it does not support sub-range lock
      operations.  Therefore, the client should be prepared to receive this
      error and, if appropriate, report the error to the requesting
      application.
    </t>
    <t>
      The client is discouraged from combining multiple independent locking
      ranges that happen to be adjacent into a single request since the
      server may not support sub-range requests for reasons related to
      the recovery of byte-range locking state in the event of server failure.  As
      discussed in <xref target="server_failure" />, the
      server may employ certain optimizations during recovery that work
      effectively only when the client's behavior during lock recovery is
      similar to the client's locking behavior prior to server failure.
    </t>
  </section> <!-- "Lock Ranges" -->
  <section title="Upgrading and Downgrading Locks" >
    <t>
      If a client has a WRITE_LT lock on a byte-range, it can request an atomic
      downgrade of the lock to a READ_LT lock via the LOCK operation, by setting
      the type to READ_LT. If the server supports atomic downgrade, the
      request will succeed. If not, it will return NFS4ERR_LOCK_NOTSUPP. The
      client should be prepared to receive this error and, if appropriate,
      report the error to the requesting application.
    </t>
    <t>
      If a client has a READ_LT lock on a byte-range, it can request an atomic
      upgrade of the lock to a WRITE_LT lock via the LOCK operation by setting
      the type to WRITE_LT or WRITEW_LT.  If the server does not support
      atomic upgrade, it will return NFS4ERR_LOCK_NOTSUPP.  If the upgrade
      can be achieved without an existing conflict, the request will
      succeed.  Otherwise, the server will return either NFS4ERR_DENIED or
      NFS4ERR_DEADLOCK.  The error NFS4ERR_DEADLOCK is returned if the client
      sent the LOCK operation with the type set to WRITEW_LT and the server
      has detected a deadlock. The client should be prepared to receive such
      errors and, if appropriate, report the error to the requesting
      application.

    </t>
  </section> <!-- "Upgrading and Downgrading Locks" -->
  <section title="Stateid Seqid Values and Byte-Range Locks"
           anchor="byte_range_seqid" >
    <t>
      When a LOCK or LOCKU operation is performed,
      the stateid returned has the same "other" value as the argument's
      stateid, and a 
      "seqid" value that is incremented (relative to the argument's
      stateid) to reflect the occurrence
      of the LOCK or LOCKU operation.  The server MUST increment
      the value of the "seqid" field whenever there is any change
      to the locking status of any byte offset as described by 
      any of the locks covered by the stateid.  A change in locking
      status includes a change from locked to unlocked or the reverse or
      a change from being locked for READ_LT to being locked for WRITE_LT
      or the reverse. 
    </t>
    <t> 
      When there is no such change, as, for example, when a range
      already locked for WRITE_LT is locked again for WRITE_LT, the
      server MAY increment the "seqid" value.
    </t>
  </section> <!-- "Stateid Sequence Values and Byte-Range Locks" -->
  <section title="Issues with Multiple Open-Owners" 
           anchor="multiple_openowners" >
    <t>

      When the same file is opened by multiple open-owners,
      a client will have multiple OPEN stateids for that
      file, each associated with a different open-owner.
      In that case, there can be multiple LOCK and LOCKU
      requests for the same lock-owner sent using the
      different OPEN stateids, and so a situation may
      arise in which there are multiple stateids, each
      representing byte-range locks on the same file and
      held by the same lock-owner but each associated with
      a different open-owner.

    </t>
    <t>
      In such a situation, the locking status of each byte
      (i.e., whether it is locked, the READ_LT or WRITE_LT type of 
      the lock, and the lock-owner holding the lock) MUST 
      reflect the last LOCK or LOCKU operation done for the
      lock-owner in question, independent of the stateid through
      which the request was sent.
    </t>
    <t>
      When a byte is locked by the lock-owner in question, the
      open-owner to which that byte-range lock is assigned SHOULD be that 
      of the open-owner associated with the stateid through 
      which the last LOCK of that byte was done.  When there
      is a change in the open-owner associated with locks for
      the stateid through which a LOCK or LOCKU was done, the
      "seqid" field of the stateid MUST be incremented, even 
      if the locking, in terms of lock-owners has not changed.
      When there is a change to the set of locked bytes associated
      with a different stateid for the same lock-owner, i.e.,
      associated with a different open-owner, the "seqid" value
      for that stateid MUST NOT be incremented.
    </t>
  </section> <!-- "Issues with Multiple Open-Owners" -->
  <section title="Blocking Locks" anchor="blocking_locks" >
    <t>
      Some clients require the support of blocking locks.  While NFSv4.1 
      provides a callback when a previously unavailable lock becomes 
      available, this is an OPTIONAL feature and clients cannot 
      depend on its presence.  Clients need to be prepared to continually 
      poll for the lock.  This presents a fairness problem.  Two of
      the lock types, READW_LT and WRITEW_LT, are used to indicate to the
      server that the client is requesting a blocking lock.  When the
      callback is not used, the server should maintain an ordered
      list of pending blocking locks.  When the conflicting lock is
      released, the server may wait for the period of time equal to
      lease_time for the first waiting
      client to re-request the lock.  After the lease period expires, the
      next waiting client request is allowed the lock.  Clients are required
      to poll at an interval sufficiently small that it is likely to acquire
      the lock in a timely manner.  The server is not required to maintain a
      list of pending blocked locks as it is used to increase fairness and
      not correct operation.  Because of the unordered nature of crash
      recovery, storing of lock state to stable storage would be required to
      guarantee ordered granting of blocking locks.
    </t>
    <t>
      Servers may also note the lock types and delay returning denial of the
      request to allow extra time for a conflicting lock to be released,
      allowing a successful return.  In this way, clients can avoid the
      burden of needless frequent polling for blocking locks.  The server
      should take care in the length of delay in the event the client
      retransmits the request.
    </t>
    <t>
      If a server receives a blocking LOCK operation, denies it, and then
      later receives a nonblocking request for the same lock, which is
      also denied, then it should remove the lock in question from its list of
      pending blocking locks.  Clients should use such a nonblocking request
      to indicate to the server that this is the last time they intend to poll
      for the lock, as may happen when the process requesting the lock is
      interrupted.  This is a courtesy to the server, to prevent it from
      unnecessarily waiting a lease period before granting other LOCK operations.
      However, clients are not required to perform this courtesy, and servers
      must not depend on them doing so.  Also, clients must be prepared for
      the possibility that this final locking request will be accepted.
    </t>
    <t>
      When a server indicates, via the flag OPEN4_RESULT_MAY_NOTIFY_LOCK, that
      CB_NOTIFY_LOCK callbacks might be done for the current open file, the
      client should take notice of this, but, since this is a hint, cannot
      rely on a CB_NOTIFY_LOCK always being done.  A client may reasonably
      reduce the frequency with which it polls for a denied lock, since the
      greater latency that might occur is likely to be eliminated given a
      prompt callback, but it still needs to poll.  When it receives a 
      CB_NOTIFY_LOCK, it should promptly try to obtain the lock, but it
      should be aware that other clients may be polling and that the server is under
      no obligation to reserve the lock for that particular client.
    </t>
  </section> <!-- title="Blocking Locks" -->
  <section anchor="share_reserve" title="Share Reservations" >
    <t>
      A share reservation is a mechanism to control access to a file.  It is
      a separate and independent mechanism from byte-range locking.  When a
      client opens a file, it sends an OPEN operation to the server
      specifying the type of access required (READ, WRITE, or BOTH) and the
      type of access to deny others (OPEN4_SHARE_DENY_NONE,
      OPEN4_SHARE_DENY_READ, OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH).  If
      the OPEN fails, the client will fail the application's open request.
    </t>
    <t>
      Pseudo-code definition of the semantics:
    </t>
    <figure>
      <artwork>
        if (request.access == 0) {
          return (NFS4ERR_INVAL)
        } else {
          if ((request.access &amp; file_state.deny)) ||
             (request.deny &amp; file_state.access)) {
            return (NFS4ERR_SHARE_DENIED)
        }
        return (NFS4ERR_OK);
      </artwork>
    </figure>
    <t>
      When doing this checking of share reservations on OPEN, the current 
      file_state used in the algorithm includes bits that reflect all 
      current opens, including those for the open-owner making the 
      new OPEN request.
    </t>
    <t>
      The constants used for the OPEN and OPEN_DOWNGRADE operations for the
      access and deny fields are as follows:
    </t>
<figure>
 <artwork>
const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

const OPEN4_SHARE_DENY_NONE     = 0x00000000;
const OPEN4_SHARE_DENY_READ     = 0x00000001;
const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
const OPEN4_SHARE_DENY_BOTH     = 0x00000003;
 </artwork>
</figure>
  </section> <!-- "Share Reservations" -->
  <section title="OPEN/CLOSE Operations" >
    <t>
      To provide correct share semantics, a client MUST use the OPEN
      operation to obtain the initial filehandle and indicate the desired
      access and what access, if any, to deny.  Even if the client intends to
      use a special stateid for anonymous state or READ bypass, 
      it must still obtain the
      filehandle for the regular file with the OPEN operation so the
      appropriate share semantics can be applied.  Clients that do not
      have a deny mode built into their programming interfaces for opening
      a file should request a deny mode of
      OPEN4_SHARE_DENY_NONE.
    </t>
    <t>
      The OPEN operation with the CREATE flag also subsumes the CREATE
      operation for regular files as used in previous versions of the NFS
      protocol.  This allows a create with a share to be done atomically.
    </t>
    <t>
      The CLOSE operation removes all share reservations held by the
      open-owner on that file.  If byte-range locks are held, the client
      SHOULD release all locks before sending a CLOSE operation.  The server MAY free
      all outstanding locks on CLOSE, but some servers may not support the
      CLOSE of a file that still has byte-range locks held.  The server MUST
      return failure, NFS4ERR_LOCKS_HELD, if any locks would exist after the
      CLOSE.
    </t>
    <t>
      The LOOKUP operation will return a filehandle without establishing any
      lock state on the server.  Without a valid stateid, the server will
      assume that the client has the least access.  For example, if one
      client opened a file with OPEN4_SHARE_DENY_BOTH and another client
      accesses the file via a filehandle obtained through LOOKUP, the
      second client could only read the file using the special read
      bypass stateid. The second client could not WRITE the file
      at all because it would
      not have a valid stateid from OPEN and the special anonymous stateid would
      not be allowed access.
    </t>
  </section> <!-- "OPEN/CLOSE Operations" -->
  <section title="Open Upgrade and Downgrade" anchor="open_upgrade" >
    <t>
      When an OPEN is done for a file and the open-owner for which the OPEN
      is being done already has the file open, the result is to upgrade the
      open file status maintained on the server to include the access and
      deny bits specified by the new OPEN as well as those for the existing
      OPEN.  The result is that there is one open file, as far as the
      protocol is concerned, and it includes the union of the access and
      deny bits for all of the OPEN requests completed.  The OPEN 
      is represented by a single stateid whose "other" value matches
      that of the original open, and whose "seqid" value is incremented
      to reflect the occurrence of the upgrade.  The increment is required
      in cases in which the "upgrade" results in no change to the open mode (e.g., an OPEN
      is done for read when the existing open file is opened for 
      OPEN4_SHARE_ACCESS_BOTH).  Only a single CLOSE will be done to reset the
      effects of both OPENs.  The client may use the stateid returned
      by the OPEN effecting the upgrade or with a stateid sharing the
      same "other" field and a seqid of zero,
      although care needs to be taken as far as upgrades that happen 
      while the CLOSE is pending.  Note that the
      client, when sending the OPEN, may not know that the same file is in
      fact being opened.  The above only applies if both OPENs result in
      the OPENed object being designated by the same filehandle.
    </t>
    <t>
      When the server chooses to export multiple filehandles corresponding
      to the same file object and returns different filehandles on two
      different OPENs of the same file object, the server MUST NOT "OR"
      together the access and deny bits and coalesce the two open files.
      Instead, the server must maintain separate OPENs with separate
      stateids and will require separate CLOSEs to free them.
    </t>
    <t>
      When multiple open files on the client are merged into a single OPEN
      file object on the server, the close of one of the open files (on the
      client) may necessitate change of the access and deny status of the
      open file on the server.  This is because the union of the access and
      deny bits for the remaining opens may be smaller (i.e., a proper
      subset) than previously.  The OPEN_DOWNGRADE operation is used to make
      the necessary change and the client should use it to update the server
      so that share reservation requests by other clients are handled
      properly.  The stateid returned has the same "other" field as
      that passed to the server.  The "seqid" value in the returned 
      stateid MUST be incremented, even in situations in which there is
      no change to the access and deny bits for the file.
    </t>
  </section> <!-- "Open Upgrade and Downgrade" -->
  <section title="Parallel OPENs" anchor="parallel_opens">
    <t>
      Unlike the case of NFSv4.0, in which OPEN operations for the same 
      open-owner are inherently serialized because of the owner-based seqid,
      multiple OPENs for the same open-owner may be done in parallel.  When
      clients do this, they may encounter situations in which, because
      of the existence of hard links, two OPEN operations may turn out
      to open the same file, with a later OPEN performed being an upgrade of
      the first, with this fact only visible to the
      client once the operations complete.
    </t>    
    <t>
      In this situation, clients may determine the order in which the 
      OPENs were performed by examining the stateids returned by the OPENs.
      Stateids that share a common value of the "other" field can be
      recognized as having opened the same file, with the order of the 
      operations determinable from the order of the "seqid" fields, mod 
      any possible wraparound of the 32-bit field.
    </t>
    <t>
      When the possibility exists that the client will send multiple
      OPENs for the same open-owner in parallel, it may be the case that
      an open upgrade may happen without the client knowing beforehand
      that this could happen.  Because of this possibility, CLOSEs and
      OPEN_DOWNGRADEs should generally be sent with a non-zero seqid 
      in the stateid, to avoid the possibility that the status change
      associated with an open upgrade is not inadvertently lost.
    </t>
  </section> <!-- "Parallel OPENs" -->
  <section title="Reclaim of Open and Byte-Range Locks" anchor="open_br_reclaim">
    <t>
      Special forms of the LOCK and OPEN operations are provided when it
      is necessary to re-establish byte-range locks or opens after a 
      server failure.
      <list style='symbols'>
        <t>
          To reclaim existing opens, an OPEN operation is performed
          using a CLAIM_PREVIOUS.  Because the client, in this type 
          of situation, will have already opened the file and have
          the filehandle of the target file, this operation requires
          that the current filehandle be the target file, rather than
          a directory, and no file name is specified.
        </t>
        <t>
          To reclaim byte-range locks, a LOCK operation with the
          reclaim parameter set to true is used.
        </t>
      </list>
    </t>
    <t>
      Reclaims of opens associated with delegations are discussed in
      <xref target="delegation_recovery" />. 
    </t>
  </section>
</section> <!-- "File Locking and Share Reservations" -->
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Client-Side Caching" >
  <t>
    Client-side caching of data, of file attributes, and of file names is
    essential to providing good performance with the NFS protocol.
    Providing distributed cache coherence is a difficult problem, and
    previous versions of the NFS protocol have not attempted it.  Instead,
    several NFS client implementation techniques have been used to reduce
    the problems that a lack of coherence poses for users.  These
    techniques have not been clearly defined by earlier protocol
    specifications, and it is often unclear what is valid or invalid client
    behavior.
  </t>
  <t>
    The NFSv4.1 protocol uses many techniques similar to those that
    have been used in previous protocol versions.  The NFSv4.1
    protocol does not provide distributed cache coherence.  However, it
    defines a more limited set of caching guarantees to allow locks and
    share reservations to be used without destructive interference from
    client-side caching.
  </t>
  <t>
    In addition, the NFSv4.1 protocol introduces a delegation
    mechanism, which allows many decisions normally made by the server to
    be made locally by clients.  This mechanism provides efficient support
    of the common cases where sharing is infrequent or where sharing is
    read-only.
    
  </t>
  <section title="Performance Challenges for Client-Side Caching" >
    <t>
      Caching techniques used in previous versions of the NFS protocol have
      been successful in providing good performance.  However, several
      scalability challenges can arise when those techniques are used with
      very large numbers of clients.  This is particularly true when clients
      are geographically distributed, which classically increases the latency
      for cache revalidation requests.
    </t>
    <t>
      The previous versions of the NFS protocol repeat their file data cache
      validation requests at the time the file is opened.  This behavior can
      have serious performance drawbacks.  A common case is one in which a
      file is only accessed by a single client.  Therefore, sharing is
      infrequent.
    </t>
    <t>
      In this case, repeated references to the server to find that no
      conflicts exist are expensive.  A better option with regards to
      performance is to allow a client that repeatedly opens a file to do so
      without reference to the server.  This is done until potentially
      conflicting operations from another client actually occur.
    </t>
    <t>
      A similar situation arises in connection with byte-range locking.  Sending
      LOCK and LOCKU operations as well as the READ and
      WRITE operations necessary to make data caching consistent with the
      locking semantics (see <xref target="dc_file_locking" />)
      can severely limit performance.  When locking is used to provide
      protection against infrequent conflicts, a large penalty is incurred.
      This penalty may discourage the use of byte-range locking by applications.
    </t>
    <t>
      The NFSv4.1 protocol provides more aggressive caching strategies
      with the following design goals:
      <list style='symbols'>
        <t>
          Compatibility with a large range of server semantics.
        </t>
        <t>
          Providing the same caching benefits as previous versions of 
          the NFS protocol when unable to support the more aggressive model.
        </t>
        <t>
          Requirements for aggressive caching are organized so that a 
         large portion of the benefit can be obtained even when not 
         all of the requirements can be met.
        </t>
      </list>
    </t>
    <t>
      The appropriate requirements for the server are discussed in later
      sections in which specific forms of caching are covered (see 
      <xref target="open_delegation" />).
    </t>
  </section>
  <section title="Delegation and Callbacks" anchor="deleg_and_cb" >
    <t>
      Recallable delegation of server responsibilities for a file to a
      client improves performance by avoiding repeated requests to the
      server in the absence of inter-client conflict.  With the use of a
      "callback" RPC from server to client, a server recalls delegated
      responsibilities when another client engages in sharing of a delegated
      file.
    </t>
    <t>
      A delegation is passed from the server to the client, specifying the
      object of the delegation and the type of delegation.  There are
      different types of delegations, but each type contains a stateid to be
      used to represent the delegation when performing operations that
      depend on the delegation.  This stateid is similar to those associated
      with locks and share reservations but differs in that the stateid for
      a delegation is associated with a client ID and may be used on behalf
      of all the open-owners for the given client.  A delegation is made
      to the client as a whole and not to any specific process or thread of
      control within it.
    </t>
    <t>
      The backchannel is established by CREATE_SESSION and
      BIND_CONN_TO_SESSION, and the client is required
      to maintain it. Because the backchannel may be down, even
      temporarily,
      correct protocol operation does not depend on
      them.  Preliminary testing of backchannel functionality by means of a
      CB_COMPOUND procedure with a single operation, CB_SEQUENCE,
      can be used to check the continuity of the backchannel.  A
      server avoids delegating responsibilities until it has
      determined that the backchannel exists.  Because the granting of a
      delegation is always conditional upon the absence of conflicting
      access, clients MUST NOT assume that a delegation will be granted and
      they MUST always be prepared for OPENs, WANT_DELEGATIONs, and
      GET_DIR_DELEGATIONs to be processed without any
      delegations being granted.
    </t>
    <t>
      Unlike locks, an operation by a second client to a delegated file will
      cause the server to recall a delegation through a callback.  For
      individual operations, we will describe, under IMPLEMENTATION, when
      such operations are required to effect a recall.  A number of
      points should be noted, however.  
      <list style="symbols">
        <t>
          The server is free to recall a delegation
          whenever it feels it is desirable and may do so even if no 
          operations requiring recall are being done.  
        </t>
        <t>
          Operations done outside the NFSv4.1 protocol, due to, for 
          example, access by other protocols, or by local access, 
          also need to result in delegation recall when they make 
          analogous changes to file system data.  What is crucial 
          is if the change would invalidate the guarantees provided 
          by the delegation.  When this is possible, the
          delegation needs to be recalled and MUST be returned or
          revoked  before allowing the operation to proceed. 
        </t>
        <t>
          The semantics of the file system are crucial in defining
          when delegation recall is required.  If a particular change
          within a specific implementation causes change to a 
          file attribute, then delegation recall is required, whether
          that operation has been specifically listed as requiring
          delegation recall.  Again, what is critical is whether the
          guarantees provided by the delegation are being invalidated.
        </t>
      </list>
    </t>
    <t>
      Despite those caveats, the implementation sections for a number
      of operations describe situations in which delegation recall 
      would be required under some common circumstances:
      <list style="symbols">
        <t>
          For GETATTR, see <xref target="OP_GETATTR_IMPLEMENTATION" />.
        </t>
        <t>
          For OPEN, see <xref target="OP_OPEN_IMPLEMENTATION" />.
        </t>
        <t>
          For READ, see <xref target="OP_READ_IMPLEMENTATION" />.
        </t>
        <t>
          For REMOVE, see <xref target="OP_REMOVE_IMPLEMENTATION" />.
        </t>
        <t>
          For RENAME, see <xref target="OP_RENAME_IMPLEMENTATION" />.
        </t>
        <t>
          For SETATTR, see <xref target="OP_SETATTR_IMPLEMENTATION" />.
        </t>
        <t>
          For WRITE, see <xref target="OP_WRITE_IMPLEMENTATION" />.
        </t>
      </list>
    </t>
    <t>
      On recall, the client holding the delegation needs to flush modified
      state (such as modified data) to the server and return the
      delegation.  The conflicting request will not be acted on until
      the recall is complete.  The recall is considered complete when
      the client returns the delegation or the server times its wait
      for the delegation to be returned and revokes the delegation as
      a result of the timeout.  In the interim, the server will either
      delay responding to conflicting requests or respond to them with
      NFS4ERR_DELAY.  Following the resolution of the recall, the
      server has the information necessary to grant or deny the second
      client's request.
    </t>
    <t>
      At the time the client receives a delegation recall, it may have
      substantial state that needs to be flushed to the server.  Therefore,
      the server should allow sufficient time for the delegation to be
      returned since it may involve numerous RPCs to the server.  If the
      server is able to determine that the client is diligently flushing
      state to the server as a result of the recall, the server may extend
      the usual time allowed for a recall.  However, the time allowed for
      recall completion should not be unbounded.
    </t>
    <t>
      An example of this is when responsibility to mediate opens on a given
      file is delegated to a client (see <xref target="open_delegation" />).
      The server will not know what opens are in effect on the client.
      Without this knowledge, the server will be unable to determine if the
      access and deny states for the file allow any particular open until
      the delegation for the file has been returned.
    </t>
    <t>
      A client failure or a network partition can result in failure to
      respond to a recall callback. In this case, the server will revoke the
      delegation, which in turn will render useless any modified state still
      on the client.
    </t>
    <section title="Delegation Recovery" anchor="delegation_recovery" >
      <t>
        There are three situations that delegation recovery needs to deal with:
        <list style="symbols">
          <t>
            client restart
          </t>
          <t>
            server restart
          </t>
          <t>
            network partition (full or backchannel-only)
          </t>
        </list>
      </t>
      <t>
        In the event the client restarts, the failure to renew
        the lease will result in the revocation of byte-range locks and share
        reservations.  Delegations, however, may be treated a bit differently.
      </t>
      <t>
        There will be situations in which delegations will need to be
        re-established after a client restarts.  The reason for this
        is that the client may have file data stored locally and this data was
        associated with the previously held delegations.  The client will need
        to re-establish the appropriate file state on the server.
      </t>
      <t>
        To allow for this type of client recovery, the server MAY extend the
        period for delegation recovery beyond the typical lease expiration
        period.  This implies that requests from other clients that conflict
        with these delegations will need to wait.  Because the normal recall
        process may require significant time for the client to flush changed
        state to the server, other clients need be prepared for delays that
        occur because of a conflicting delegation.  This longer interval would
        increase the window for clients to restart and consult stable storage
        so that the delegations can be reclaimed.  For OPEN delegations, such
        delegations are reclaimed using OPEN with a claim type of
        CLAIM_DELEGATE_PREV or CLAIM_DELEG_PREV_FH (see Sections
        <xref target="data_caching_revocation" format="counter" />
        and <xref target="OP_OPEN" format="counter" /> for discussion of OPEN delegation
        and the details of OPEN, respectively).
      </t>
      <t>
        A server MAY support claim types of CLAIM_DELEGATE_PREV and
        CLAIM_DELEG_PREV_FH, and if it
        does, it MUST NOT remove delegations upon a CREATE_SESSION that
        confirm a client ID created by EXCHANGE_ID.
        Instead, the server MUST, for a period of time no less than that of the value of
        the lease_time attribute, maintain the client's delegations to allow
        time for the client to send CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH requests. The server
        that supports CLAIM_DELEGATE_PREV and/or CLAIM_DELEG_PREV_FH MUST support the DELEGPURGE
        operation.
      </t>
      <t>
        When the server restarts, delegations are reclaimed (using
        the OPEN operation with CLAIM_PREVIOUS) in a similar fashion to byte-range
        locks and share reservations.  However, there is a slight semantic
        difference.  In the normal case, if the server decides that a
        delegation should not be granted, it performs the requested action
        (e.g., OPEN) without granting any delegation.  For reclaim, the server
        grants the delegation but a special designation is applied so that the
        client treats the delegation as having been granted but recalled by
        the server.  Because of this, the client has the duty to write all
        modified state to the server and then return the delegation.  This
        process of handling delegation reclaim reconciles three principles of
        the NFSv4.1 protocol:
        <list style="symbols">
          <t>
            Upon reclaim, a client reporting resources assigned to it by an
            earlier server instance must be granted those resources.
          </t>
          <t>
            The server has unquestionable authority to determine whether
            delegations are to be granted and, once granted, whether they are to
            be continued.
          </t>
          <t>
            The use of callbacks should not be depended upon until the client has
            proven its ability to receive them.
          </t>
        </list>
      </t>
      <t>
        When a client needs to reclaim a delegation and there is no associated
        open, the client may use the CLAIM_PREVIOUS variant of the
        WANT_DELEGATION operation.  However, since the server is not required
        to support this operation, an alternative is to reclaim via a dummy OPEN 
        together with the delegation
        using an OPEN of type CLAIM_PREVIOUS.  The dummy open file can 
        be released using a CLOSE to re-establish the original state to be
        reclaimed, a delegation without an associated open.
      </t>
      <t>
        When a client has more than a single open associated with a delegation,
        state for those additional opens can be established using OPEN 
        operations of type CLAIM_DELEGATE_CUR.  When these are used to
        establish opens associated with reclaimed delegations, the 
        server MUST allow them when made within the grace period.
      </t>
      <t>       
        When a network partition occurs, delegations are subject to freeing by
        the server when the lease renewal period expires.  This is similar to
        the behavior for locks and share reservations.  For delegations,
        however, the server may extend the period in which conflicting
        requests are held off.  Eventually, the occurrence of a conflicting
        request from another client will cause revocation of the delegation.
        A loss of the backchannel (e.g., by later network configuration
        change) will have the same effect.  A recall request will fail and
        revocation of the delegation will result.
      </t>
      <t>
        A client normally finds out about revocation of a delegation when it
        uses a stateid associated with a delegation and receives one of the
        errors NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, or NFS4ERR_DELEG_REVOKED.
        It also may find out about delegation revocation
        after a client restart when it attempts to reclaim a delegation and
        receives that same error.  Note that in the case of a revoked OPEN_DELEGATE_WRITE delegation, there are issues because data may have been modified
        by the client whose delegation is revoked and separately by other
        clients.  See <xref target="revocation_recovery_write" />
        for a discussion of such issues.  Note also that when
        delegations are revoked, information about the revoked delegation will
        be written by the server to stable storage (as described in
        <xref target="network_partitions_and_recovery" />).  This is done 
        to deal with the case in
        which a server restarts after revoking a delegation but before the
        client holding the revoked delegation is notified about the
        revocation.
      </t>
    </section>
  </section>
  <section title="Data Caching" >
    <t>
      When applications share access to a set of files, they need to be
      implemented so as to take account of the possibility of conflicting
      access by another application.  This is true whether the applications
      in question execute on different clients or reside on the same client.
    </t>
    <t>
      Share reservations and byte-range locks are the facilities the NFSv4.1 protocol 
      provides to allow applications to coordinate access by
      using  mutual exclusion facilities.  The NFSv4.1 protocol's
      data caching must be implemented such that it does not invalidate the
      assumptions on which those using these facilities depend.

    </t>
    <section title="Data Caching and OPENs" >
      <t>
        In order to avoid invalidating the sharing assumptions on which
        applications rely, NFSv4.1 clients should not provide cached
        data to applications or modify it on behalf of an application when it
        would not be valid to obtain or modify that same data via a READ or
        WRITE operation.
      </t>
      <t>
        Furthermore, in the absence of an OPEN delegation 
        (see <xref target="open_delegation" />),
        two additional rules apply.  Note that these rules are
        obeyed in practice by many NFSv3 clients.
        <list style='symbols'>
          <t>
            First, cached data present on a client must be revalidated after doing
            an OPEN. Revalidating means that the client fetches the change
            attribute from the server, compares it with the cached change
            attribute, and if different, declares the cached data (as well as the
            cached attributes) as invalid.  This is to ensure that the data for
            the OPENed file is still correctly reflected in the client's cache.
            This validation must be done at least when the client's OPEN operation
            includes a deny of OPEN4_SHARE_DENY_WRITE or
            OPEN4_SHARE_DENY_BOTH, thus terminating a period in which
            other
            clients may have had the opportunity to open the file with
            OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH
            access.  Clients may choose to do the revalidation more often (i.e., at
            OPENs specifying a deny mode of OPEN4_SHARE_DENY_NONE) to parallel the NFSv3 protocol's
            practice for the benefit of users assuming this degree of cache
            revalidation.
            <vspace blankLines='1' />

            Since the change attribute is updated for data and metadata
            modifications, some client implementors may be tempted to use the
            time_modify attribute and not the change attribute to validate cached data, so that
            metadata changes do not spuriously invalidate clean data.  The
            implementor is cautioned in  this approach. The change attribute is
            guaranteed to change for each update to the file, whereas time_modify
            is guaranteed to change only at the granularity of the time_delta
            attribute. Use by the client's data cache validation logic of
            time_modify and not change runs the risk of the client incorrectly
            marking stale data as valid. Thus, any cache validation approach
            by the client MUST include the use of the change attribute.
          </t>
          <t>
            Second, modified data must be flushed to the server before closing a
            file OPENed for OPEN4_SHARE_ACCESS_WRITE.  This is complementary to the first rule.  If
            the data is not flushed at CLOSE, the revalidation done
            after the client OPENs a file is unable to achieve its
            purpose.  The other aspect to flushing the data before
            close is that the data must be committed to stable
            storage, at the server, before the CLOSE operation is
            requested by the client.  In the case of a server restart and a CLOSEd
            file, it may not be possible to retransmit the data to be written to
            the file, hence, this requirement.
          </t>
        </list>
      </t>
    </section>
    <section title="Data Caching and File Locking" anchor="dc_file_locking">
      <t>
        For those applications that choose to use byte-range locking instead of
        share reservations to exclude inconsistent file access, there is an
        analogous set of constraints that apply to client-side data caching.
        These rules are effective only if the byte-range locking is used in a way
        that matches in an equivalent way the actual READ and WRITE operations
        executed.  This is as opposed to byte-range locking that is based on pure
        convention.  For example, it is possible to manipulate a two-megabyte
        file by dividing the file into two one-megabyte ranges and protecting
        access to the two byte-ranges by byte-range locks on bytes zero and one.  A WRITE_LT lock on
        byte zero of the file would represent the right to perform
        READ and WRITE operations on the first byte-range.  A WRITE_LT lock on
        byte one of the file would represent the right to perform READ and WRITE
        operations on the second byte-range.  As long as all applications
        manipulating the file obey this convention, they will work on a local
        file system.  However, they may not work with the NFSv4.1
        protocol unless clients refrain from data caching.
      </t>
      <t>
        The rules for data caching in the byte-range locking environment are:
        <list style='symbols'>
          <t>
            First, when a client obtains a byte-range lock for a particular byte-range, the
            data cache corresponding to that byte-range (if any cache data exists)
            must be revalidated.  If the change attribute indicates that the file
            may have been updated since the cached data was obtained, the client
            must flush or invalidate the cached data for the newly locked byte-range.
            A client might choose to invalidate all of the non-modified cached data
            that it has for the file, but the only requirement for correct
            operation is to invalidate all of the data in the newly locked byte-range.
          </t>
          <t>
            Second, before releasing a WRITE_LT lock for a byte-range, all modified data
            for that byte-range must be flushed to the server.  The modified data must
            also be written to stable storage.
          </t>
        </list>
      </t>
      <t>
        Note that flushing data to the server and the invalidation of cached
        data must reflect the actual byte-ranges locked or unlocked.  Rounding
        these up or down to reflect client cache block boundaries will cause
        problems if not carefully done.  For example, writing a modified block
        when only half of that block is within an area being unlocked may
        cause invalid modification to the byte-range outside the unlocked area.
        This, in turn, may be part of a byte-range locked by another client.
        Clients can avoid this situation by synchronously performing portions
        of WRITE operations that overlap that portion (initial or final) that
        is not a full block.  Similarly, invalidating a locked area that is
        not an integral number of full buffer blocks would require the client
        to read one or two partial blocks from the server if the revalidation
        procedure shows that the data that the client possesses may not be
        valid.
      </t>
      <t>
        The data that is written to the server as a prerequisite to the
        unlocking of a byte-range must be written, at the server, to stable
        storage.  The client may accomplish this either with synchronous
        writes or by following asynchronous writes with a COMMIT operation.
        This is required because retransmission of the modified data after a
        server restart might conflict with a lock held by another client.
      </t>
      <t>
        A client implementation may choose to accommodate applications that
        use byte-range locking in non-standard ways (e.g., using a byte-range lock as a
        global semaphore) by flushing to the server more data upon a LOCKU
        than is covered by the locked range.  This may include modified data
        within files other than the one for which the unlocks are being done.
        In such cases, the client must not interfere with applications whose
        READs and WRITEs are being done only within the bounds of byte-range locks
        that the application holds.  For example, an application locks a
        single byte of a file and proceeds to write that single byte.  A
        client that chose to handle a LOCKU by flushing all modified data to
        the server could validly write that single byte in response to an
        unrelated LOCKU operation.  However, it would not be valid to write the entire
        block in which that single written byte was located since it includes
        an area that is not locked and might be locked by another client.
        Client implementations can avoid this problem by dividing files with
        modified data into those for which all modifications are done to areas
        covered by an appropriate byte-range lock and those for which there are
        modifications not covered by a byte-range lock.  Any writes done for the
        former class of files must not include areas not locked and thus not
        modified on the client.

      </t>
    </section>
    <section title="Data Caching and Mandatory File Locking" >
      <t>
        Client-side data caching needs to respect mandatory byte-range locking when
        it is in effect.  The presence of mandatory byte-range locking for a given
        file is indicated when the client gets back NFS4ERR_LOCKED from a READ
        or WRITE operation on a file for which it has an appropriate share reservation.  When
        mandatory locking is in effect for a file, the client must check for
        an appropriate byte-range lock for data being read or written.  If a byte-range lock
        exists for the range being read or written, the client may satisfy the
        request using the client's validated cache.  If an appropriate
        byte-range lock is not held for the range of the read or write, the read or write
        request must not be satisfied by the client's cache and the request
        must be sent to the server for processing.  When a read or write
        request partially overlaps a locked byte-range, the request should be
        subdivided into multiple pieces with each byte-range (locked or not)
        treated appropriately.
        
      </t>
    </section>
    <section anchor="data_caching_and_file_identity"
     title="Data Caching and File Identity" >

      <t>
        When clients cache data, the file data needs to be organized according
        to the file system object to which the data belongs.  For NFSv3
        clients, the typical practice has been to assume for the purpose of
        caching that distinct filehandles represent distinct file system
        objects.  The client then has the choice to organize and maintain the
        data cache on this basis.
      </t>
      <t>
        In the NFSv4.1 protocol, there is now the possibility to have
        significant deviations from a "one filehandle per object" model
        because a filehandle may be constructed on the basis of the object's
        pathname.  Therefore, clients need a reliable method to determine if
        two filehandles designate the same file system object.  If clients
        were simply to assume that all distinct filehandles denote distinct
        objects and proceed to do data caching on this basis, caching
        inconsistencies would arise between the distinct client-side objects
        that mapped to the same server-side object.
      </t>
      <t>
        By providing a method to differentiate filehandles, the NFSv4.1
        protocol alleviates a potential functional regression in comparison
        with the NFSv3 protocol.  Without this method, caching
        inconsistencies within the same client could occur, and this has not
        been present in previous versions of the NFS protocol.  Note that it
        is possible to have such inconsistencies with applications executing
        on multiple clients, but that is not the issue being addressed here.
      </t>
      <t>
        For the purposes of data caching, the following steps allow an 
        NFSv4.1 client to determine whether two distinct filehandles denote
        the same server-side object:
        <list style="symbols">
          <t>
            If GETATTR directed to two filehandles returns different values of the
            fsid attribute, then the filehandles represent distinct objects.
          </t>
          <t>
            If GETATTR for any file with an fsid that matches the fsid of the two
            filehandles in question returns a unique_handles attribute with a
            value of TRUE, then the two objects are distinct.
          </t>
          <t>
            If GETATTR directed to the two filehandles does not return the fileid
            attribute for both of the handles, then it cannot be determined
            whether the two objects are the same.  Therefore,
            operations that depend on that knowledge (e.g.,
            client-side data caching) cannot be
            done reliably.  Note that if GETATTR does not return the fileid
	    attribute for both filehandles, it will return it for neither of
	    the filehandles, since the fsid for both filehandles is the same.
          </t>
          <t>
            If GETATTR directed to the two filehandles returns different values
            for the fileid attribute, then they are distinct objects.
          </t>
          <t>
            Otherwise, they are the same object.
          </t>
        </list>
      </t>
    </section>
  </section>
  <section title="Open Delegation" anchor="open_delegation" >
    <t>
      When a file is being OPENed, the server may delegate further handling
      of opens and closes for that file to the opening client.  Any such
      delegation is recallable since the circumstances that allowed for the
      delegation are subject to change.  In particular, if the server
      receives a conflicting OPEN from another client, the server must recall
      the delegation before deciding whether the OPEN from the other client
      may be granted.  Making a delegation is up to the server, and clients
      should not assume that any particular OPEN either will or will not
      result in an OPEN delegation.  The following is a typical set of
      conditions that servers might use in deciding whether an OPEN should be
      delegated:
      <list style="symbols">
        <t>
          The client must be able to respond to the
          server's callback requests.  If a backchannel
          has been established, the server will send
          a CB_COMPOUND request, containing a single
          operation, CB_SEQUENCE, for a test of backchannel
          availability.

        </t>
        <t>
          The client must have responded properly to previous recalls.
        </t>
        <t>
          There must be no current OPEN conflicting with the requested
          delegation.
        </t>
        <t>
          There should be no current delegation that conflicts with the 
          delegation being requested.
        </t>
        <t>
          The probability of future conflicting open requests should be 
          low based on the recent history of the file.
        </t>
        <t>
          The existence of any server-specific semantics of OPEN/CLOSE 
          that would make the required handling incompatible with the
          prescribed handling that the delegated client would apply 
          (see below).
        </t>
      </list>
      There are two types of OPEN delegations: OPEN_DELEGATE_READ and OPEN_DELEGATE_WRITE.  An OPEN_DELEGATE_READ
      delegation allows a client to handle, on its own, requests to open a
      file for reading that do not deny OPEN4_SHARE_ACCESS_READ access to others.  Multiple
      OPEN_DELEGATE_READ delegations may be outstanding simultaneously and do not
      conflict.  An OPEN_DELEGATE_WRITE delegation allows the client to handle, on its
      own, all opens.  Only OPEN_DELEGATE_WRITE delegation may exist for a given
      file at a given time, and it is inconsistent with any OPEN_DELEGATE_READ delegations.
    </t>
    <t>
      When a client has an OPEN_DELEGATE_READ delegation, it is assured that
      neither the contents, the attributes (with the exception of 
      time_access), nor the names of any
      links to the file will change without its knowledge, so long as the
      delegation is held.  When a client has an OPEN_DELEGATE_WRITE delegation, it
      may modify the file data locally since no other client will be 
      accessing the file's data.  The client holding an OPEN_DELEGATE_WRITE delegation 
      may only locally affect file attributes that are intimately 
      connected with the file data: size, change, time_access,
      time_metadata, and time_modify.
      All other attributes must be reflected on the server.
    </t>
    <t>
      When a client has an OPEN delegation, it does not need to send OPENs or
      CLOSEs to the server. Instead, the client may update the
      appropriate status internally. For an OPEN_DELEGATE_READ delegation, opens
      that cannot be handled locally (opens that are for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH or that
      deny OPEN4_SHARE_ACCESS_READ access) must be sent to the server.
    </t>
    <t>
      When an OPEN delegation is made, the reply to the OPEN contains an
      OPEN delegation structure that specifies the following:
      <list style="symbols">
        <t>
          the type of delegation (OPEN_DELEGATE_READ or OPEN_DELEGATE_WRITE).
        </t>
        <t>
          space limitation information to control flushing of data on close
          (OPEN_DELEGATE_WRITE delegation only;
          see <xref target="open_delegation_caching" />)
        </t>
        <t>
          an nfsace4 specifying read and write permissions
        </t>
        <t>
          a stateid to represent the delegation
        </t>
      </list>
      The delegation stateid is separate and distinct from the stateid for
      the OPEN proper.  The standard stateid, unlike the delegation stateid,
      is associated with a particular lock-owner and will continue to be
      valid after the delegation is recalled and the file remains open.
    </t>
    <t>
      When a request internal to the client is made to open a file and an OPEN
      delegation is in effect, it will be accepted or rejected solely on the
      basis of the following conditions.  Any requirement for other checks
      to be made by the delegate should result in the OPEN delegation being
      denied so that the checks can be made by the server itself.
      <list style="symbols">
        <t>
          The access and deny bits for the request and the file as
          described in <xref target="share_reserve" />.
        </t>
        <t>
          The read and write permissions as determined below.
        </t>
      </list>
      The nfsace4 passed with delegation can be used to avoid frequent
      ACCESS calls.  The permission check should be as follows:
      <list style="symbols">
        <t>
          If the nfsace4 indicates that the open may be done, then it should be
          granted without reference to the server.
        </t>
        <t>
          If the nfsace4 indicates that the open may not be done, then an ACCESS
          request must be sent to the server to obtain the definitive answer.
        </t>
      </list>
      The server may return an nfsace4 that is more restrictive than the
      actual ACL of the file.  This includes an nfsace4 that specifies
      denial of all access.  Note that some common practices such as mapping
      the traditional user "root" to the user "nobody" (see <xref target="owner_owner_group"/>) may make it incorrect
      to return the actual ACL of the file in the delegation response.
    </t>
    <t>
      The use of a delegation together with various other forms of caching
      creates the possibility that no server authentication and authorization
      will ever be
      performed for a given user since all of the user's requests might be
      satisfied locally.  Where the client is depending on the server for
      authentication and authorization, the client should be sure authentication and authorization occurs for
      each user by use of the ACCESS operation.  This should be the case
      even if an ACCESS operation would not be required otherwise.  As
      mentioned before, the server may enforce frequent authentication by
      returning an nfsace4 denying all access with every OPEN delegation.

    </t>
    <section title="Open Delegation and Data Caching" 
             anchor="open_delegation_caching" >
      <t>
        An OPEN delegation allows much of the message overhead associated with
        the opening and closing files to be eliminated.  An open when an OPEN
        delegation is in effect does not require that a validation
        message be sent to the server.  The continued endurance of the
        "OPEN_DELEGATE_READ delegation" provides a guarantee that no OPEN
        for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, and thus
        no write, has occurred.  Similarly, when closing a file opened
        for OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH and if an OPEN_DELEGATE_WRITE delegation is in effect,
        the data written does not have to be written to the server until
        the OPEN delegation is recalled.  The continued endurance of
        the OPEN delegation provides a
        guarantee that no open, and thus no READ or WRITE, has been done by
        another client.
      </t>
      <t>
        For the purposes of OPEN delegation, READs and WRITEs done without an
        OPEN are treated as the functional equivalents of a corresponding type
        of OPEN.  Although a client SHOULD NOT use special stateids when 
        an open exists, delegation handling on the server can use the 
        client ID associated with the current session to determine if the
        operation has been done by the holder of the delegation (in which
        case, no recall is necessary) or by another client (in which case,
        the delegation must be recalled and I/O not proceed until the 
        delegation is recalled or revoked). 
      </t>
      <t>
        With delegations, a client is able to avoid writing data to the server
        when the CLOSE of a file is serviced.  The file close system call is
        the usual point at which the client is notified of a lack of stable
        storage for the modified file data generated by the application.  At
        the close, file data is written to the server and, through normal
        accounting, the server is able to determine if the available file system
        space for the data has been exceeded (i.e., the server returns
        NFS4ERR_NOSPC or NFS4ERR_DQUOT).  This accounting includes quotas.
        The introduction of delegations requires that an alternative method be
        in place for the same type of communication to occur between client
        and server.
      </t>
      <t>
        In the delegation response, the server provides either the limit of
        the size of the file or the number of modified blocks and associated
        block size.  The server must ensure that the client will be able to
        write modified data to the server of a size equal to that provided in the
        original delegation.  The server must make this assurance for all
        outstanding delegations.  Therefore, the server must be careful in its
        management of available space for new or modified data, taking into
        account available file system space and any applicable quotas.  The
        server can recall delegations as a result of managing the available
        file system space.  The client should abide by the server's state
        space limits for delegations.  If the client exceeds the stated limits
        for the delegation, the server's behavior is undefined.
      </t>
      <t>
        Based on server conditions, quotas, or available file system space, the
        server may grant OPEN_DELEGATE_WRITE delegations with very restrictive space
        limitations.  The limitations may be defined in a way that will always
        force modified data to be flushed to the server on close.
      </t>
      <t>
        With respect to authentication, flushing modified data to the server
        after a CLOSE has occurred may be problematic.  For example, the user
        of the application may have logged off the client, and unexpired
        authentication credentials may not be present.  In this case, the
        client may need to take special care to ensure that local unexpired
        credentials will in fact be available.  This may be accomplished by
        tracking the expiration time of credentials and flushing data well in
        advance of their expiration or by making private copies of credentials
        to assure their availability when needed.

      </t>
    </section>
    <section title="Open Delegation and File Locks" >
      <t>
        When a client holds an OPEN_DELEGATE_WRITE delegation, lock operations are
        performed locally.  This includes those required for mandatory byte-range
        locking.  This can be done since the delegation implies that there can
        be no conflicting locks.  Similarly, all of the revalidations that
        would normally be associated with obtaining locks and the flushing of
        data associated with the releasing of locks need not be done.
      </t>
      <t>
        When a client holds an OPEN_DELEGATE_READ delegation, lock operations are not
        performed locally.  All lock operations, including those requesting
        non-exclusive locks, are sent to the server for resolution. 

      </t>
    </section>
    <section anchor="handling_cb_getattr" title="Handling of CB_GETATTR" >
      <t>
        The server needs to employ special handling for a GETATTR where the
        target is a file that has an OPEN_DELEGATE_WRITE delegation in effect.  The
        reason for this is that the client holding the OPEN_DELEGATE_WRITE delegation may
        have modified the data, and the server needs to reflect this change to
        the second client that submitted the GETATTR.  Therefore, the client
        holding the OPEN_DELEGATE_WRITE delegation needs to be interrogated.  The server
        will use the CB_GETATTR operation.  The only attributes that the
        server can reliably query via CB_GETATTR are size and change.
      </t>
      <t>
        Since CB_GETATTR is being used to satisfy another client's GETATTR
        request, the server only needs to know if the client holding the
        delegation has a modified version of the file.  If the client's copy
        of the delegated file is not modified (data or size), the server can
        satisfy the second client's GETATTR request from the attributes stored
        locally at the server.  If the file is modified, the server only needs
        to know about this modified state.  If the server determines that the
        file is currently modified, it will respond to the second client's
        GETATTR as if the file had been modified locally at the server.
      </t>
      <t>
        Since the form of the change attribute is determined by the server and
        is opaque to the client, the client and server need to agree on a
        method of communicating the modified state of the file.  For the size
        attribute, the client will report its current view of the file size.
        For the change attribute, the handling is more involved.
      </t>
      <t>
        For the client, the following steps will be taken when receiving an
        OPEN_DELEGATE_WRITE delegation:
        <list style="symbols">
          <t>
            The value of the change attribute will be obtained from the server and
            cached.  Let this value be represented by c.  
          </t>
          <t>
            The client will create a value greater than c that will be used for
            communicating that modified data is held at the client.  Let this value be
            represented by d.
          </t>
          <t>
            When the client is queried via CB_GETATTR for the change attribute, it
            checks to see if it holds modified data.  If the file is modified, the
            value d is returned for the change attribute value.  If this file is
            not currently modified, the client returns the value c for the change
            attribute.
          </t>
        </list>
        For simplicity of implementation, the client MAY for each CB_GETATTR
        return the same value d.  This is true even if, between successive
        CB_GETATTR operations, the client again modifies the file's data or
        metadata in its cache.  The client can return the same value because
        the only requirement is that the client be able to indicate to the
        server that the client holds modified data.  Therefore, the value of d
        may always be c + 1.
      </t>
      <t>
        While the change attribute is opaque to the client in the sense that
        it has no idea what units of time, if any, the server is counting
        change with, it is not opaque in that the client has to treat it as an
        unsigned integer, and the server has to be able to see the results of
        the client's changes to that integer.  Therefore, the server MUST
        encode the change attribute in network order when sending it to the
        client.  The client MUST decode it from network order to its native
        order when receiving it, and the client MUST encode it in network order
        when sending it to the server.  For this reason, change is defined as
        an unsigned integer rather than an opaque array of bytes.
      </t>
      <t>
        For the server, the following steps will be taken when providing an
        OPEN_DELEGATE_WRITE delegation:
        <list style="symbols">
          <t>
            Upon providing an OPEN_DELEGATE_WRITE delegation, the server will cache a copy of the
            change attribute in the data structure it uses to record the
            delegation.  Let this value be represented by sc.
          </t>
          <t>
            When a second client sends a GETATTR operation on the same file to the
            server, the server obtains the change attribute from the first client.
            Let this value be cc.
          </t>
          <t>
            If the value cc is equal to sc, the file is not modified and the
            server returns the current values for change, time_metadata, and
            time_modify (for example) to the second client.
          </t>
          <t>
            If the value cc is NOT equal to sc, the file is currently modified at
            the first client and most likely will be modified at the server at a
            future time.  The server then uses its current time to construct
            attribute values for time_metadata and time_modify.  A new value of
            sc, which we will call nsc, is computed by the server, such that nsc
            >= sc + 1.  The server then returns the constructed time_metadata,
            time_modify, and nsc values to the requester.  The server replaces sc
            in the delegation record with nsc.  To prevent the possibility of
            time_modify, time_metadata, and change from appearing to go backward
            (which would happen if the client holding the delegation fails to
            write its modified data to the server before the delegation is revoked
            or returned), the server SHOULD update the file's metadata record with
            the constructed attribute values.  For reasons of reasonable
            performance, committing the constructed attribute values to stable
            storage is OPTIONAL.
          </t>
        </list>
      </t>
      <t>
        As discussed earlier in this section, the client MAY return the same
        cc value on subsequent CB_GETATTR calls, even if the file was modified
        in the client's cache yet again between successive CB_GETATTR calls.
        Therefore, the server must assume that the file has been modified yet
        again, and MUST take care to ensure that the new nsc it constructs and
        returns is greater than the previous nsc it returned.  An example
        implementation's delegation record would satisfy this mandate by
        including a boolean field (let us call it "modified") that is set to
        FALSE when the delegation is granted, and an sc value set at the time
        of grant to the change attribute value. The modified field would be
        set to TRUE the first time cc != sc, and would stay TRUE until the
        delegation is returned or revoked.  The processing for constructing
        nsc, time_modify, and time_metadata would use this pseudo code:
        <figure>
          <artwork>
    if (!modified) {
        do CB_GETATTR for change and size;

        if (cc != sc)
            modified = TRUE;
    } else {
        do CB_GETATTR for size;
    }

    if (modified) {
        sc = sc + 1;
        time_modify = time_metadata = current_time;
        update sc, time_modify, time_metadata into file's metadata;
    }

	    </artwork>
	  </figure>
	  This would return to the client (that sent GETATTR) the attributes
        it requested, but make sure size comes from what 
        CB_GETATTR returned. The server would not update the file's 
        metadata with the client's modified size.
      </t>
      <t>
        In the case that the file attribute size is different than the
        server's current value, the server treats this as a modification
        regardless of the value of the change attribute retrieved via
        CB_GETATTR and responds to the second client as in the last step.
      </t>
      <t>
        This methodology resolves issues of clock differences between client
        and server and other scenarios where the use of CB_GETATTR break down.
      </t>
      <t>
        It should be noted that the server is under no obligation to use
        CB_GETATTR, and therefore the server MAY simply recall the delegation
        to avoid its use.
      </t>
    </section>

    <section title="Recall of Open Delegation" >
      <t>
        The following events necessitate recall of an OPEN delegation:
        <list style="symbols">
          <t>
            potentially conflicting OPEN request (or a READ or WRITE operation
            done with a special stateid)
          </t>
          <t>
            SETATTR sent by another client
          </t>
          <t>
            REMOVE request for the file
          </t>
          <t>
            RENAME request for the file as either the source or target of the RENAME
          </t>
        </list>
        Whether a RENAME of a directory in the path leading to the file
        results in recall of an OPEN delegation depends on the semantics of
        the server's file system.  If that file system denies such RENAMEs when
        a file is open, the recall must be performed to determine whether the
        file in question is, in fact, open.
      </t>
      <t>
        In addition to the situations above, the server may choose to recall
        OPEN delegations at any time if resource constraints make it advisable
        to do so.  Clients should always be prepared for the possibility of
        recall.
      </t>
      <t>
        When a client receives a recall for an OPEN delegation, it needs
        to update state on the server before returning the delegation.
        These same updates must be done whenever a client chooses to
        return a delegation voluntarily.  The following items of state 
        need to be dealt with:
        <list style="symbols">
          <t>
            If the file associated with the delegation is no longer open and no
            previous CLOSE operation has been sent to the server, a CLOSE
            operation must be sent to the server.
          </t>
          <t>
            If a file has other open references at the client, then OPEN
            operations must be sent to the server.  The appropriate stateids will
            be provided by the server for subsequent use by the client since the
            delegation stateid will no longer be valid.  These OPEN requests are
            done with the claim type of CLAIM_DELEGATE_CUR.  This will allow the
            presentation of the delegation stateid so that the client can
            establish the appropriate rights to perform the OPEN.  (see
            <xref target="OP_OPEN" />, which describes the OPEN operation, 
            for details.)
          </t>
          <t>
            If there are granted byte-range locks, the corresponding LOCK operations
            need to be performed.  This applies to the OPEN_DELEGATE_WRITE delegation case
            only.
          </t>
          <t>
            For an OPEN_DELEGATE_WRITE delegation, if
            at the time of recall the file is not open for
            OPEN4_SHARE_ACCESS_WRITE/OPEN4_SHARE_ACCESS_BOTH, all modified
            data for the file must be flushed to the
            server.  If the delegation had not existed, the client would have done
            this data flush before the CLOSE operation.
          </t>
          <t>
            For an OPEN_DELEGATE_WRITE delegation when a file is still open at the time of
            recall, any modified data for the file needs to be flushed to the
            server.
          </t>
          <t>
            With the OPEN_DELEGATE_WRITE delegation in place, it is possible that the file
            was truncated during the duration of the delegation.  For example, the
            truncation could have occurred as a result of an OPEN UNCHECKED with a
            size attribute value of zero.  Therefore, if a truncation of
            the file has occurred and this operation has not been propagated to
            the server, the truncation must occur before any modified data is
            written to the server.
          </t>
        </list>
        In the case of OPEN_DELEGATE_WRITE delegation, byte-range locking imposes some
        additional requirements.  To precisely maintain the associated
        invariant, it is required to flush any modified data in any byte-range for
        which a WRITE_LT lock was released while the OPEN_DELEGATE_WRITE delegation was in
        effect.  However, because the OPEN_DELEGATE_WRITE delegation implies no other
        locking by other clients, a simpler implementation is to flush all
        modified data for the file (as described just above) if any WRITE_LT lock
        has been released while the OPEN_DELEGATE_WRITE delegation was in effect.
      </t>
      <t>
        An implementation need not wait until delegation recall (or
        the decision to voluntarily return a delegation) to perform any of the above
        actions, if implementation considerations (e.g., resource availability
        constraints) make that desirable.  Generally, however, the fact that
        the actual OPEN state of the file may continue to change makes it not
        worthwhile to send information about opens and closes to the server,
        except as part of delegation return.  An exception is
        when the client has no more internal opens of the file. In this
        case, sending a CLOSE is useful because it
        reduces resource utilization on the client
        and server.


Regardless of the client's choices on scheduling these
        actions, all must be performed before the delegation is returned,
        including (when applicable) the close that corresponds to the OPEN
        that resulted in the delegation.  These actions can be performed
        either in previous requests or in previous operations in the same
        COMPOUND request.

      </t>
    </section>
    <section title="Clients That Fail to Honor Delegation Recalls" >
      <t>
        A client may fail to respond to a recall for various reasons, such as
        a failure of the backchannel from server to the client. The client
        may be unaware of a failure in the backchannel.  This lack of
        awareness could result in the client finding out long after the
        failure that its delegation has been revoked, and another client has
        modified the data for which the client had a delegation.  This is
        especially a problem for the client that held an OPEN_DELEGATE_WRITE delegation.
      </t>
      <t>
        Status bits returned by SEQUENCE operations help to provide an
        alternate way of informing the client of issues regarding the 
        status of the backchannel and of recalled delegations.  When the
        backchannel is not available, the server returns the status bit 
        SEQ4_STATUS_CB_PATH_DOWN on SEQUENCE operations.  The client can
        react by attempting to re-establish the backchannel and by 
        returning recallable objects if a backchannel cannot be successfully
        re-established. 
      </t>
      <t>
        Whether the backchannel is functioning or not, it may be that the
        recalled delegation is not returned.  Note that the client's lease
        might still be renewed, even though the recalled delegation is not
        returned.  In this situation, servers SHOULD revoke delegations that
        are not returned in a period of time equal to the lease period.  This
        period of time should allow the client time to note the 
        backchannel-down status and re-establish the backchannel.
      </t>
      <t>
        When delegations are revoked, the server will return with the
        SEQ4_STATUS_RECALLABLE_STATE_REVOKED status bit set on subsequent
        SEQUENCE operations.  The client should note this and then use 
        TEST_STATEID to find which delegations have been revoked.
      </t> 
    </section>
    <section title="Delegation Revocation" >
      <t>
        At the point a delegation is revoked, if there are associated opens 
        on the client, these opens may or may not be revoked.  If no 
        byte-range lock or open is granted that is inconsistent with the existing open,
        the stateid for the open may remain valid and be disconnected
        from the revoked delegation, just as would be the case if the 
        delegation were returned.
      </t>
      <t>
        For example, if an OPEN for OPEN4_SHARE_ACCESS_BOTH with a deny of OPEN4_SHARE_DENY_NONE is 
        associated with the delegation, granting of another such OPEN
        to a different client will revoke the delegation but need not
        revoke the OPEN, since the two OPENs are consistent with each other.
        On the other hand, if an OPEN denying write access is
        granted, then the existing OPEN must be revoked.
      </t>
      <t>
        When opens and/or locks are revoked,
        the applications holding these opens or locks need to be notified.
        This notification usually occurs by returning errors for READ/WRITE
        operations or when a close is attempted for the open file.
      </t>
      <t>
        If no opens exist for the file at the point the delegation is revoked,
        then notification of the revocation is unnecessary.  However, if there
        is modified data present at the client for the file, the user of the
        application should be notified.  Unfortunately, it may not be possible
        to notify the user since active applications may not be present at the
        client.  See <xref target="revocation_recovery_write" />
        for additional details.
      </t>
    </section>
    <section title="Delegations via WANT_DELEGATION"
             anchor="via_want_delegation" >
      <t>
        In addition to providing delegations as part of the reply 
        to OPEN operations, servers MAY provide delegations 
        separate from open, via the OPTIONAL WANT_DELEGATION operation.  This 
        allows delegations to be obtained in advance of an OPEN that 
        might benefit from them, for objects that are not a valid target
        of OPEN, or to deal with cases in which a 
        delegation has been recalled and the client wants to make 
        an attempt to re-establish it if the absence of use by other 
        clients allows that.
      </t>
      <t>
        The WANT_DELEGATION operation may be performed on any type of 
        file object other than a directory.
      </t>
      <t>
        When a delegation is obtained using WANT_DELEGATION, any open
        files for the same filehandle held by that client are to be
        treated as subordinate to the delegation, just as if they had
        been created using an OPEN of type CLAIM_DELEGATE_CUR.  They are
        otherwise unchanged as to seqid, access and deny modes, and the
        relationship with byte-range locks.  Similarly, because
        existing byte-range
        locks are subordinate to an open, those byte-range locks also become
        indirectly subordinate to that new delegation. 
      </t>
      <t>
        The WANT_DELEGATION operation provides for delivery of delegations
        via callbacks, when the delegations are not immediately available.
        When a requested delegation is available, it is delivered to the
        client via a CB_PUSH_DELEG operation.  When this happens, open files
        for the same filehandle become subordinate to the new delegation
        at the point at which the delegation is delivered, just as if they had
        been created using an OPEN of type CLAIM_DELEGATE_CUR.
        Similarly, this occurs for existing byte-range locks subordinate to an open.
      </t>
    </section>
  </section>
  <section title="Data Caching and Revocation" anchor="data_caching_revocation" >
    <t>
      When locks and delegations are revoked, the assumptions upon which
      successful caching depends are no longer guaranteed.  For any locks or
      share reservations that have been revoked, the corresponding state-owner
      needs to be notified.  This notification includes applications with a
      file open that has a corresponding delegation that has been revoked.
      Cached data associated with the revocation must be removed from the
      client.  In the case of modified data existing in the client's cache,
      that data must be removed from the client without being written to
      the server.  As mentioned, the assumptions made by the client are no
      longer valid at the point when a lock or delegation has been revoked.
      For example, another client may have been granted a conflicting byte-range lock
      after the revocation of the byte-range lock at the first client.  Therefore, the
      data within the lock range may have been modified by the other client.
      Obviously, the first client is unable to guarantee to the application
      what has occurred to the file in the case of revocation.
    </t>
    <t>
      Notification to a state-owner will in many cases consist of simply
      returning an error on the next and all subsequent READs/WRITEs to the
      open file or on the close.  Where the methods available to a client
      make such notification impossible because errors for certain
      operations may not be returned, more drastic action such as signals or
      process termination may be appropriate.  The justification here is
      that an invariant on which an application depends may be violated.
      Depending on how errors are typically treated for the client-operating
      environment, further levels of notification including logging, console
      messages, and GUI pop-ups may be appropriate.
    </t>
    <section title="Revocation Recovery for Write Open Delegation" 
             anchor="revocation_recovery_write" >
      <t>
        Revocation recovery for an OPEN_DELEGATE_WRITE delegation poses the special
        issue of modified data in the client cache while the file is not open.
        In this situation, any client that does not flush modified data to
        the server on each close must ensure that the user receives
        appropriate notification of the failure as a result of the revocation.
        Since such situations may require human action to correct problems,
        notification schemes in which the appropriate user or administrator is
        notified may be necessary.  Logging and console messages are typical
        examples.
      </t>
      <t>
        If there is modified data on the client, it must not be flushed
        normally to the server.  A client may attempt to provide a copy of the
        file data as modified during the delegation under a different name in
        the file system namespace to ease recovery.  Note that when the
        client can determine that the file has not been modified by any other
        client, or when the client has a complete cached copy of the file in
        question, such a saved copy of the client's view of the file may be of
        particular value for recovery.  In another case, recovery using a copy
        of the file based partially on the client's cached data and partially
        on the server's copy as modified by other clients will be anything but
        straightforward, so clients may avoid saving file contents in these
        situations or specially mark the results to warn users of possible
        problems.
      </t>
      <t>
        Saving of such modified data in delegation revocation situations
        may be limited to files of a certain size or might be used only when 
        sufficient disk space is available within the target file system.
        Such saving may also be restricted to situations when the client has
        sufficient buffering resources to keep the cached copy available
        until it is properly stored to the target file system. 
      </t>
    </section>
  </section>
  <section title="Attribute Caching" >
    <t>
      This section pertains to the caching of a file's attributes on a client
      when that client does not hold a delegation on the file.
    </t>

    <t>
      The attributes discussed in this section do not include named
      attributes.  Individual named attributes are analogous to files, and
      caching of the data for these needs to be handled just as data caching
      is for ordinary files.  Similarly, LOOKUP results from an OPENATTR
      directory (as well as the directory's contents) are to be cached on
      the same basis as any other pathnames.
    </t>
    <t>
      Clients may cache file attributes obtained from the server and use
      them to avoid subsequent GETATTR requests.  Such caching is write
      through in that modification to file attributes is always done by
      means of requests to the server and should not be done locally and
      should not be cached.  The exception to this are modifications to attributes that
      are intimately connected with data caching.  Therefore, extending a
      file by writing data to the local data cache is reflected immediately
      in the size as seen on the client without this change being
      immediately reflected on the server.  Normally, such changes are not
      propagated directly to the server, but when the modified data is
      flushed to the server, analogous attribute changes are made on the
      server.  When OPEN delegation is in effect, the modified attributes
      may be returned to the server in reaction to a CB_RECALL call.
    </t>
    <t>
      The result of local caching of attributes is that the attribute
      caches maintained on individual clients will not be coherent.  
      Changes made in one order on the server may be seen in a different
      order on one client and in a third order on another client.
    </t>
    <t>
      The typical file system application programming interfaces do not
      provide means to atomically modify or interrogate attributes for
      multiple files at the same time.  The following rules provide an
      environment where the potential incoherencies mentioned above can be
      reasonably managed.  These rules are derived from the practice of
      previous NFS protocols.
      <list style="symbols">
        <t>
          All attributes for a given file (per-fsid attributes excepted) are
          cached as a unit at the client so that no non-serializability can
          arise within the context of a single file.
        </t>
        <t>
          An upper time boundary is maintained on how long a client cache entry
          can be kept without being refreshed from the server.
        </t>
        <t>
          When operations are performed that change attributes at the server,
          the updated attribute set is requested as part of the containing RPC.
          This includes directory operations that update attributes indirectly.
          This is accomplished by following the modifying operation with a
          GETATTR operation and then using the results of the GETATTR to update
          the client's cached attributes.
        </t>
      </list>
      Note that if the full set of attributes to be cached is requested by
      READDIR, the results can be cached by the client on the same basis as
      attributes obtained via GETATTR.
    </t>
    <t>
      A client may validate its cached version of attributes for a file by
      fetching both the change and time_access attributes and assuming
      that if the change attribute has the same value as it did when the
      attributes were cached, then no attributes other than time_access have
      changed.  The reason why time_access is also fetched is because many
      servers operate in environments where the operation that updates
      change does not update time_access.  For example, POSIX file semantics
      do not update access time when a file is modified by the write system
      call <xref target="write_atime"/>.  Therefore, the client that wants a current time_access value
      should fetch it with change during the attribute cache validation
      processing and update its cached time_access.
    </t>
    <t>
      The client may maintain a cache of modified attributes for those
      attributes intimately connected with data of modified regular files
      (size, time_modify, and change). Other than those three attributes,
      the client MUST NOT maintain a cache of modified attributes. Instead,
      attribute changes are immediately sent to the server.
    </t>
    <t>
      In some operating environments, the equivalent to time_access is
      expected to be implicitly updated by each read of the content of the
      file object.  If an NFS client is caching the content of a file
      object, whether it is a regular file, directory, or symbolic link, the
      client SHOULD NOT update the time_access attribute (via SETATTR or a
      small READ or READDIR request) on the server with each read that is
      satisfied from cache.  The reason is that this can defeat the
      performance benefits of caching content, especially since an explicit
      SETATTR of time_access may alter the change attribute on the server.
      If the change attribute changes, clients that are caching the content
      will think the content has changed, and will re-read unmodified data
      from the server.  Nor is the client encouraged to maintain a modified
      version of time_access in its cache, since the client either would
      eventually have to write the access time to the server
      with bad performance effects or never update the
      server's time_access, thereby resulting in a situation where an
      application that caches access time between a close and open of
      the same file observes the access time oscillating between the past and
      present.  The time_access attribute always means the time of last
      access to a file by a read that was satisfied by the server. This way
      clients will tend to see only time_access changes that go forward in
      time.
      
    </t>
  </section>
  <section title="Data and Metadata Caching and Memory Mapped Files" >
    <t>
      Some operating environments include the capability for an application
      to map a file's content into the application's address space.  Each
      time the application accesses a memory location that corresponds to a
      block that has not been loaded into the address space, a page fault
      occurs and the file is read (or if the block does not exist in the
      file, the block is allocated and then instantiated in the
      application's address space).
    </t>
    <t>
      As long as each memory-mapped access to the file requires a page
      fault, the relevant attributes of the file that are used to detect
      access and modification (time_access, time_metadata, time_modify, and
      change) will be updated.  However, in many operating environments,
      when page faults are not required, these attributes will not be updated
      on reads or updates to the file via memory access (regardless of
      whether the file is local or is accessed remotely).  A client or
      server MAY fail to update attributes of a file that is being accessed
      via memory-mapped I/O.  This has several implications:
      <list style="symbols">
        <t>
          If there is an application on the server that has memory mapped a file
          that a client is also accessing, the client may not be able to get a
          consistent value of the change attribute to determine
          whether or not its cache is stale.  A server that knows that
          the file is memory-mapped could always pessimistically
          return updated values for change so as to force the
          application to always get the most up-to-date data
          and metadata for the file.  However, due to the negative performance
          implications of this, such behavior is OPTIONAL.
        </t>
        <t>
          If the memory-mapped file is not being modified on the server, and
          instead is just being read by an application via the memory-mapped
          interface, the client will not see an updated time_access attribute.
          However, in many operating environments, neither will any process
          running on the server. Thus, NFS clients are at no disadvantage with
          respect to local processes.
        </t>
        <t>
          If there is another client that is memory mapping the file, and if
          that client is holding an OPEN_DELEGATE_WRITE delegation, the same set of issues as
          discussed in the previous two bullet points apply.  So, when a server
          does a CB_GETATTR to a file that the client has modified in its cache,
          the reply from CB_GETATTR will not necessarily be accurate.  As
          discussed earlier, the client's obligation is to report that the file
          has been modified since the delegation was granted, not whether it has
          been modified again between successive CB_GETATTR calls, and the
          server MUST assume that any file the client has modified in cache has
          been modified again between successive CB_GETATTR calls.  Depending on
          the nature of the client's memory management system, this weak
          obligation may not be possible.  A client MAY return stale information
          in CB_GETATTR whenever the file is memory-mapped.
        </t>
        <t>
          The mixture of memory mapping and byte-range locking on the same file is
          problematic. Consider the following scenario, where a page size on
          each client is 8192 bytes.
          <list style="symbols">
            <t>
              Client A memory maps the first page (8192 bytes) of file X.
            </t>
            <t>
              Client B memory maps the first page (8192 bytes) of file X.
            </t>
            <t>
              Client A WRITE_LT locks the first 4096 bytes.
            </t>
            <t>
              Client B WRITE_LT locks the second 4096 bytes.
            </t>
            <t>
              Client A, via a STORE instruction, modifies part of its locked byte-range.
            </t>
            <t>
              Simultaneous to client A, client B executes a STORE on part of its
              locked byte-range.
            </t>
          </list>
        </t>
      </list>
    </t>
    <t>
      Here the challenge is for each client to resynchronize to get a
      correct view of the first page. In many operating environments, the
      virtual memory management systems on each client only know a page is
      modified, not that a subset of the page corresponding to the
      respective lock byte-ranges has been modified. So it is not possible for
      each client to do the right thing, which is to write to the
      server only that portion of the page that is locked.  For example, if
      client A simply writes out the page, and then client B writes out the
      page, client A's data is lost.
    </t>
    <t>
      Moreover, if mandatory locking is enabled on the file, then we have a
      different problem.  When clients A and B execute the STORE instructions,
      the resulting page faults require a byte-range lock on the entire page.
      Each client then tries to extend their locked range to the entire
      page, which results in a deadlock.  Communicating the NFS4ERR_DEADLOCK
      error to a STORE instruction is difficult at best.
    </t>
    <t>
      If a client is locking the entire memory-mapped file, there is no
      problem with advisory or mandatory byte-range locking, at least until the
      client unlocks a byte-range in the middle of the file.
    </t>
    <t>
      Given the above issues, the following are permitted:
      <list style="symbols">
        <t>
          Clients and servers MAY deny memory mapping a file for which they know there are
          byte-range locks.
        </t>
        <t>
          Clients and servers MAY deny a byte-range lock on a file they know is
          memory-mapped.
        </t>
        <t>
          A client MAY deny memory mapping a file that it knows requires
          mandatory locking for I/O.  If mandatory locking is enabled after the
          file is opened and mapped, the client MAY deny the application further
          access to its mapped file.
        </t>
      </list>
    </t>
  </section>
  <section title="Name and Directory Caching without Directory Delegations"
           anchor="without_dir_deleg">
    <t>
      The NFSv4.1 directory delegation facility
      (described in <xref target="dir_deleg" /> below) is OPTIONAL
      for servers to implement. Even where it is
      implemented, it may not always be functional because of resource
      availability issues or other constraints.  Thus, it is
      important to understand how name and directory caching are done
      in the absence of directory delegations. These topics are
      discussed in the next two subsections.
    </t>
    <section anchor="name_caching" title="Name Caching" >
      <t>
        The results of LOOKUP and READDIR operations may be cached to avoid
        the cost of subsequent LOOKUP operations.  Just as in the case of
        attribute caching, inconsistencies may arise among the various client
        caches.  To mitigate the effects of these inconsistencies and given
        the context of typical file system APIs, an upper time boundary is
        maintained for how long a client name cache entry can be kept without
        verifying that the entry has not been made invalid by a directory
        change operation performed by another client.
      </t>
      <t>
        When a client is not making changes to a directory for which there
        exist name cache entries, the client needs to periodically fetch
        attributes for that directory to ensure that it is not being modified.
        After determining that no modification has occurred, the expiration
        time for the associated name cache entries may be updated to be the
        current time plus the name cache staleness bound.
      </t>
      <t>
        When a client is making changes to a given directory, it needs to
        determine whether there have been changes made to the directory by
        other clients.  It does this by using the change attribute as reported
        before and after the directory operation in the associated
        change_info4 value returned for the operation.  The server is able to
        communicate to the client whether the change_info4 data is provided
        atomically with respect to the directory operation.  If the change
        values are provided atomically, the client has a basis for determining,
        given proper care, whether other clients are modifying the directory
        in question.
      </t>
      <t>
        The simplest way to enable the client to make this determination is
        for the client to serialize all changes made to a specific directory.
        When this is done, and the server provides before and after values of the 
        change attribute atomically, the client can simply compare the 
        after value of the change attribute from one operation on a 
        directory with the before value on the subsequent operation
        modifying that directory.  When these are equal, the client is
        assured that no other client is modifying the directory in question.
      </t>
      <t>
        When such serialization is not used, and there may be multiple 
        simultaneous outstanding operations modifying a single directory sent 
        from a single client, making this sort of determination can be more 
        complicated.  If two such operations
        complete in a different order than they were actually performed,
        that might give an appearance consistent with modification being 
        made by another client.  Where this appears to happen, the client
        needs to await the completion of all such modifications that were
        started previously, to see if the outstanding before and after
        change numbers can be sorted into a chain such that the before
        value of one change number matches the after value of a previous
        one, in a chain consistent with this client being the only one
        modifying the directory.
      </t>
      <t>
        In either of these cases, the client is able to determine whether
        the directory is being modified by another client.
        If the comparison indicates that the directory was updated by
        another client, the name cache associated with the modified directory
        is purged from the client.  If the comparison indicates no
        modification, the name cache can be updated on the client to reflect
        the directory operation and the associated timeout can be extended.  The
        post-operation change value needs to be saved as the basis for future
        change_info4 comparisons.
      </t>
      <t>
        As demonstrated by the scenario above, name caching requires that the
        client revalidate name cache data by inspecting the change attribute
        of a directory at the point when the name cache item was cached.  This
        requires that the server update the change attribute for directories
        when the contents of the corresponding directory is modified.  For a
        client to use the change_info4 information appropriately and
        correctly, the server must report the pre- and post-operation change
        attribute values atomically.  When the server is unable to report the
        before and after values atomically with respect to the directory
        operation, the server must indicate that fact in the change_info4
        return value.  When the information is not atomically reported, the
        client should not assume that other clients have not changed the
        directory.
      </t>
    </section>
    <section title="Directory Caching" >
      <t>
        The results of READDIR operations may be used to avoid subsequent
        READDIR operations.  Just as in the cases of attribute and name
        caching, inconsistencies may arise among the various client caches.  To
        mitigate the effects of these inconsistencies, and given the context of
        typical file system APIs, the following rules should be followed:
        <list style="symbols">
          <t>
            Cached READDIR information for a directory that is not obtained in a
            single READDIR operation must always be a consistent snapshot of
            directory contents.  This is determined by using a GETATTR before the
            first READDIR and after the last READDIR that contributes to the
            cache.
          </t>
          <t>
            An upper time boundary is maintained to indicate the length of time a
            directory cache entry is considered valid before the client must
            revalidate the cached information.
          </t>
        </list>
        The revalidation technique parallels that discussed in the case of
        name caching.  When the client is not changing the directory in
        question, checking the change attribute of the directory with GETATTR
        is adequate.  The lifetime of the cache entry can be extended at these
        checkpoints.  When a client is modifying the directory, the client
        needs to use the change_info4 data to determine whether there are
        other clients modifying the directory.  If it is determined that no
        other client modifications are occurring, the client may update its
        directory cache to reflect its own changes.
      </t>
      <t>
        As demonstrated previously, directory caching requires that the client
        revalidate directory cache data by inspecting the change attribute of
        a directory at the point when the directory was cached.  This requires
        that the server update the change attribute for directories when the
        contents of the corresponding directory is modified.  For a client to
        use the change_info4 information appropriately and correctly, the
        server must report the pre- and post-operation change attribute values
        atomically.  When the server is unable to report the before and after
        values atomically with respect to the directory operation, the server
        must indicate that fact in the change_info4 return value.  When the
        information is not atomically reported, the client should not assume
        that other clients have not changed the directory.
      </t>
    </section>
  </section>
  <section title="Directory Delegations" anchor="dir_deleg">
    <section title="Introduction to Directory Delegations">
      <t>
        Directory caching for the NFSv4.1 protocol, as previously
        described, is similar to file 
        caching in previous versions.  Clients typically cache 
        directory information for
        a duration determined by the client. At the end of a predefined
        timeout, the client will query the server to see if the directory has
        been updated. By caching attributes, clients reduce the number of
        GETATTR calls made to the server to validate attributes. Furthermore,
        frequently accessed files and directories, such as the current
        working directory, have their attributes cached on the client so that
        some NFS operations can be performed without having to make an RPC
        call. By caching name and inode information about most recently
        looked up entries in a Directory Name Lookup Cache (DNLC), clients do
        not need to send LOOKUP calls to the server every time these files
        are accessed.
      </t>
      <t>
        This caching approach works reasonably well at reducing network
        traffic in many environments. However, it does not address
        environments where there are numerous queries for files that do not
        exist. In these cases of "misses", the client sends requests to
        the server in order to provide reasonable application semantics and
        promptly detect the creation of new directory entries. Examples of
        high miss activity are compilation in software development
        environments. The current behavior of NFS limits its potential
        scalability and wide-area sharing effectiveness in these types of
        environments. Other distributed stateful file system architectures
        such as AFS and DFS have proven that adding state around directory
        contents can greatly reduce network traffic in high-miss
        environments.
      </t>
      <t>
        Delegation of directory contents is an OPTIONAL feature of NFSv4.1.
        Directory delegations provide similar traffic reduction
        benefits as with file delegations. By allowing clients to cache
        directory contents (in a read-only fashion) while being notified of
        changes, the client can avoid making frequent requests to interrogate
        the contents of slowly-changing directories, reducing network traffic
        and improving client performance.  It can also simplify the task of
        determining whether other clients are making changes to the directory
        when the client itself is making many changes to the directory and
        changes are not serialized.
      </t>
      <t>
        Directory delegations allow improved namespace cache consistency to be
        achieved through delegations and synchronous recalls, in the absence
        of notifications. In addition, if time-based consistency is
        sufficient, asynchronous notifications can provide performance
        benefits for the client, and possibly the server, under some common
        operating conditions such as slowly-changing and/or very large
        directories.
      </t>
    </section>
    <section title="Directory Delegation Design">
      <t>
        NFSv4.1 introduces the GET_DIR_DELEGATION 
        (<xref target="OP_GET_DIR_DELEGATION" />) operation to allow the 
        client to ask for a
        directory delegation. The delegation covers directory attributes and
        all entries in the directory. If either of these change, the
        delegation will be recalled synchronously. The operation causing the
        recall will have to wait before the recall is complete. Any changes
        to directory entry attributes will not cause the delegation to be
        recalled.
      </t>
      <t>
        In addition to asking for delegations, a client can also ask for
        notifications for certain events. These events include changes to
        the directory's attributes and/or its contents.  If a client asks for
        notification for a certain event, the server will notify the client
        when that event occurs. This will not result in the delegation being
        recalled for that client.  The notifications are asynchronous and
        provide a way of avoiding recalls in situations where a directory is
        changing enough that the pure recall model may not be effective while
        trying to allow the client to get substantial benefit. In the absence
        of notifications, once the delegation is recalled the client has to
        refresh its directory cache; this might not be very efficient for
        very large directories.
      </t>
      <t>
        The delegation is read-only and the client may not make changes to
        the directory other than by performing NFSv4.1 operations that modify
        the directory or the associated file attributes so that the server
        has knowledge of these changes. In order to keep the client's
        namespace synchronized with the server, the server will notify
        the delegation-holding client (assuming it has requested
        notifications) of the changes made as a result of that client's
        directory-modifying operations.  This is to avoid any need for
        that client to send subsequent GETATTR or READDIR operations
        to the server.  If a single client is holding the delegation
        and that client makes any changes to the directory (i.e., the
        changes are made via operations sent on a session
        associated with the client ID holding the delegation), the
        delegation will not be recalled. Multiple clients may hold a delegation
        on the same directory, but if any such client modifies the directory,
        the server MUST recall the delegation from the other clients,
        unless those clients have made provisions to be notified of that
        sort of modification.
      </t>
      <t>
        Delegations can be recalled by the server at any time.  Normally, the
        server will recall the delegation when the directory changes in a way
        that is not covered by the notification, or when the directory
        changes and notifications have not been requested.
        If another client removes the directory for
        which a delegation has been granted, the server will recall the
        delegation.
      </t>
    </section>
    <section title="Attributes in Support of Directory Notifications">
      <t>
       See <xref target="dir_not_attrs" /> for a description of the attributes
       associated with directory notifications.
      </t>
    </section>

    <section title="Directory Delegation Recall">
      <t>
        The server will recall the directory delegation by sending a callback
        to the client. It will use the same callback procedure as used for
        recalling file delegations. The server will recall the delegation
        when the directory changes in a way that is not covered by the
        notification. However, the server need not recall the delegation if
        attributes of an entry within the directory change.  
      </t>
      <t>
        If the
        server notices that handing out a delegation for a directory is
        causing too many notifications to be sent out, it may decide to
        not hand out delegations for that directory and/or recall those already
        granted.  If a client tries to remove the directory for which
        a delegation has been granted, the server will recall all associated delegations.
      </t>
      <t>
        The implementation sections for a number
        of operations describe situations in which notification or
        delegation recall would be required under some common circumstances.
        In this regard, a similar set of caveats to those listed
        in <xref target="deleg_and_cb" /> apply.
        <list style="symbols">
          <t>
            For CREATE, see <xref target="OP_CREATE_IMPLEMENTATION" />.
          </t>
          <t>
            For LINK, see <xref target="OP_LINK_IMPLEMENTATION" />.
          </t>
          <t>
            For OPEN, see <xref target="OP_OPEN_IMPLEMENTATION" />.
          </t>
          <t>
            For REMOVE, see <xref target="OP_REMOVE_IMPLEMENTATION" />.
          </t>
          <t>
            For RENAME, see <xref target="OP_RENAME_IMPLEMENTATION" />.
          </t>
          <t>
            For SETATTR, see <xref target="OP_SETATTR_IMPLEMENTATION" />.
          </t>
        </list>
      </t>
    </section>

    <section title="Directory Delegation Recovery">
      <t>
        Recovery from client or server restart for state on regular files
        has two main goals: avoiding the necessity of
        breaking application guarantees with respect to locked files and
        delivery of updates cached at the client.  Neither of these
        goals applies to directories protected by OPEN_DELEGATE_READ delegations and
        notifications. Thus, no provision is made for reclaiming
        directory delegations in the event of client or server restart.
        The client can simply establish a directory delegation in the
        same fashion as was done initially.
      </t>
    </section>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="multi_server_namespace" title="Multi-Server Namespace">
  <t>
    NFSv4.1 supports attributes that allow a namespace to extend
    beyond the boundaries of a single server.  It is RECOMMENDED
    that clients and servers support construction of such
    multi-server namespaces.  Use of such multi-server namespaces 
    is OPTIONAL, however, and for many purposes,
    single-server namespaces are perfectly acceptable.  Use of
    multi-server namespaces can provide many advantages, however, by
    separating a file system's logical position in a namespace from
    the (possibly changing) logistical and administrative
    considerations that result in particular file systems being
    located on particular servers.
  </t>
  <section anchor="location_attrs" title="Location Attributes">
    <t>
      NFSv4.1 contains RECOMMENDED attributes that allow file systems on
      one server to be associated with one or more instances of that
      file system on other servers.  These attributes specify such
      file system instances by specifying a server address
      target (either as a DNS name representing one or more IP
      addresses or as a literal IP address) together with the path 
      of that file system within the associated single-server namespace.
    </t>
    <t>
      The fs_locations_info RECOMMENDED attribute
      allows specification of one or more file system instance locations
      where the data corresponding to a given file
      system may be found.  This attribute provides to the client,
      in addition to
      information about file system instance locations,  
      significant information
      about the various file system instance choices (e.g., priority for 
      use, writability, currency, etc.).  It also includes information to
      help the client efficiently effect as seamless a transition
      as possible among multiple file system instances, when and if
      that should be necessary.
    </t>
    <t>
      The fs_locations RECOMMENDED
      attribute is inherited from NFSv4.0 and only allows specification 
      of the file system
      locations where the data corresponding to a given file
      system may be found.  Servers SHOULD make this attribute available
      whenever fs_locations_info is supported, but client use of 
      fs_locations_info is to be preferred.
    </t>
  </section>
  <section anchor="presence_or_absence" title="File System Presence or Absence">
    <t>
      A given location in an NFSv4.1 namespace (typically but not necessarily
      a multi-server namespace) can have a number of file system instance 
      locations
      associated with it (via the fs_locations or fs_locations_info
      attribute).  There may also be an actual current file system at 
      that location, accessible via normal namespace operations (e.g.,
      LOOKUP).  In this case, the file system is said to be 
      "present" at that position in the namespace, and clients will 
      typically use it, reserving use of additional locations 
      specified via the location-related attributes to situations in
      which the principal location is no longer available.
    </t>
    <t>
      When there is no actual file system at the namespace location
      in question, the file system is said to be "absent".  An absent
      file system contains no files or directories other than the
      root.  Any reference to it, except 
      to access a small set of attributes useful in determining
      alternate locations, will result in an error, NFS4ERR_MOVED.
      Note that if the server ever returns the error NFS4ERR_MOVED,
      it MUST support the fs_locations 
      attribute and SHOULD support the fs_locations_info and fs_status
      attributes.
    </t>
    <t>
      While the error name suggests that we have a case of a file system
      that once was present, and has only become absent later, this is 
      only one possibility.  A position in the namespace may be permanently
      absent with the set of file system(s) designated by the location 
      attributes being the only realization.  
      The name NFS4ERR_MOVED reflects an earlier,
      more limited conception of its function, but this error will be
      returned whenever the referenced file system is absent, whether it
      has moved or not.
    </t>
    <t>
      Except in the case of GETATTR-type operations (to be discussed 
      later), when the 
      current filehandle at the start of an operation is within an 
      absent file system, that operation is not performed and the error
      NFS4ERR_MOVED is returned, to indicate that the file system is
      absent on the current server.
    </t>
    <t>
      Because a GETFH cannot succeed if the current filehandle is
      within an absent file system, filehandles within an absent
      file system cannot be transferred to the client.  When a 
      client does have filehandles within an absent file system, it
      is the result of obtaining them when the file system was
      present, and having the file system become 
      absent subsequently.
    </t>
    <t>
      It should be noted that because the check for the current
      filehandle being within an absent file system happens at the
      start of every operation, operations that change the current
      filehandle so that it is within an absent file system will not
      result in an error.  This allows such combinations as 
      PUTFH-GETATTR and LOOKUP-GETATTR to be used to get attribute
      information, particularly location attribute information,
      as discussed below.
    </t>
    <t>
      The RECOMMENDED file system attribute fs_status 
      can be used to interrogate the present/absent status of a 
      given file system.
    </t>  
  </section>
  <section anchor="absent_fs_attributes" 
           title="Getting Attributes for an Absent File System">
    <t>
      When a file system is absent, most attributes are not available,
      but it is necessary to allow the client access to the small
      set of attributes that are available, and most particularly 
      those that give information about the correct current locations
      for this file system: fs_locations and fs_locations_info.
    </t>
    <section anchor="absent_getattr"
             title="GETATTR within an Absent File System">
      <t>
        As mentioned above, an exception is made for GETATTR in that
        attributes may be obtained for a filehandle within an absent
        file system.  This exception only applies if the attribute
        mask contains at least one attribute bit that indicates the
        client is interested in a result regarding an absent file
        system: fs_locations, fs_locations_info, or fs_status.
        If none of these attributes
        is requested, GETATTR will result in an NFS4ERR_MOVED error.
      </t>
      <t>
        When a GETATTR is done on an absent file system, the set of 
        supported attributes is very limited.  Many attributes, including
        those that are normally REQUIRED, will not be available on an
        absent file system.  In addition to the attributes mentioned
        above (fs_locations, fs_locations_info, fs_status), the following
        attributes SHOULD be available on absent file systems.  In the
        case of RECOMMENDED attributes, they should be available at
        least to the same degree that they are available on present file systems.
      </t>
      <t>
       <list style='hanging'>
        <t hangText="change_policy:">
          This attribute is useful for absent file systems
          and can be helpful in summarizing to the client when any
          of the location-related attributes change.
        </t>
        <t hangText="fsid:">
          This attribute should be provided so that the client
          can determine file system boundaries, including, in 
          particular, the boundary between present and absent file
          systems.  This value must be different from any other fsid
          on the current server and need have no particular relationship
          to fsids on any particular destination to which the client
          might be directed.
        </t>
        <t hangText="mounted_on_fileid:"> 
          For objects at the top of an absent
          file system, this attribute needs to be available.  Since
          the fileid is within the present parent file
          system, there should be no need to reference the absent file
          system to provide this information.
        </t>
       </list>
      </t>
      <t>
        Other attributes SHOULD NOT be made available for absent file
        systems, even when it is possible to provide them.  The server
        should not assume that more information is always better and
        should avoid gratuitously providing additional information.
      </t>
      <t>
        When a GETATTR operation includes a bit mask for one of the 
        attributes fs_locations, fs_locations_info, or fs_status, but
        where the bit mask includes attributes that are not supported,
        GETATTR will not return an error, but will return the mask
        of the actual attributes supported with the results.
      </t>
      <t>
        Handling of VERIFY/NVERIFY is similar to GETATTR in that if
        the attribute mask does not include fs_locations, fs_locations_info,
        or fs_status, the error NFS4ERR_MOVED will result.  It differs in
        that any appearance in the attribute mask of an attribute not 
        supported for an absent file system (and note that this will
        include some normally REQUIRED attributes) will also cause
        an NFS4ERR_MOVED result.
      </t>
    </section>
    <section anchor="absent_readdir"
             title="READDIR and Absent File Systems">
      <t>
        A READDIR performed when the current filehandle is within an
        absent file system will result in an NFS4ERR_MOVED error, 
        since, unlike the case of GETATTR, no such exception is
        made for READDIR.
      </t>
      <t>
        Attributes for an absent file system may be fetched via a
        READDIR for a directory in a present file system, when that
        directory contains the root directories of one or more absent
        file systems.  In this case, the handling is as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          If the attribute set requested includes one of the attributes
          fs_locations, fs_locations_info, or fs_status, then fetching of
          attributes proceeds normally and no NFS4ERR_MOVED indication
          is returned, even when the rdattr_error attribute is
          requested.
        </t>
        <t>
          If the attribute set requested does not include one of the 
          attributes
          fs_locations, fs_locations_info, or fs_status, then if the
          rdattr_error attribute is requested, each directory entry for
          the root of an absent file system will report 
          NFS4ERR_MOVED as the value of the rdattr_error attribute.
        </t>
        <t>
          If the attribute set requested does not include any of the 
          attributes fs_locations, fs_locations_info, fs_status, or
          rdattr_error, then the occurrence of the root of an absent
          file system within the directory will result in the
          READDIR failing with an NFS4ERR_MOVED error. 
        </t>
        <t>
          The unavailability of an attribute because of a file system's
          absence, even one that is ordinarily REQUIRED, does not result
          in any error indication.  The set of attributes returned for
          the root directory of the absent file system in that case is 
          simply restricted to those actually available.
        </t>
       </list>
      </t>
    </section>
  </section>
  <section anchor="location_uses" title="Uses of Location Information">
    <t>
      The location-bearing attributes (fs_locations and fs_locations_info),
      together with the possibility of absent file systems, provide
      a number of important facilities in providing reliable, manageable, 
      and scalable data access.
    </t>
    <t>
      When a file system is present, these attributes can provide  
      alternative locations, to be used to access the same data,
      in the event of server failures, communications problems, 
      or other difficulties that make continued access to the current
      file system impossible or otherwise impractical.
      Under some circumstances, multiple alternative locations
      may be used simultaneously to provide higher-performance 
      access to the file system in question.  
      Provision of
      such alternate locations is referred to as "replication"
      although there are cases in which replicated sets of data are
      not in fact present, and the replicas are instead different
      paths to the same data.  
    </t>
    <t>
      When a file system is present and becomes absent, clients can be
      given the opportunity to have continued access to their data,
      at an alternate location.  In this case, a continued attempt
      to use the data in the now-absent file system will result 
      in an NFS4ERR_MOVED error and, at that point, the successor 
      locations (typically only one although multiple choices are possible)
      can be fetched and used to continue access.  Transfer of the
      file system contents to the new location is referred to as 
      "migration", but it should be kept in mind that there are cases
      in which this term can be used, like "replication", when there 
      is no actual data migration per se.  
    </t>
    <t>
      Where a file system was not previously present, specification
      of file system location provides a means by which file systems
      located on one server can be associated with a namespace 
      defined by another server, thus allowing a general multi-server
      namespace facility.  A designation of such a location, in place
      of an absent file system, is called a "referral".
    </t>
    <t>
      Because client support for location-related attributes is 
      OPTIONAL, a server may (but is not required to) take action
      to hide migration and referral events from such clients, by
      acting as a proxy, for example.  The server can determine
      the presence of client support from the arguments of the 
      EXCHANGE_ID operation (see 
      <xref target="OP_EXCHANGE_ID_DESCRIPTION" />).
    </t>
    <section anchor="replication" title="File System Replication">
      <t>
        The fs_locations and fs_locations_info attributes provide
        alternative locations, to be used to access data in place
        of or in addition to 
        the current file system instance.  On first access to a
        file system, the client should obtain the value of the set
        of alternate locations by interrogating the fs_locations or
        fs_locations_info attribute, with the latter being preferred.
      </t>
      <t>
        In the event that server failures, communications problems, 
        or other difficulties make continued access to the current
        file system impossible or otherwise impractical, the client
        can use the alternate locations as a way to get continued 
        access to its data.  Depending on specific attributes of
        these alternate locations, as indicated within the
        fs_locations_info attribute, multiple locations may
        be used simultaneously, to provide higher performance 
        through the exploitation of multiple paths between client
        and target file system.  
      </t>
      <t>
        The alternate locations may be physical replicas of the
        (typically read-only) file system data, or they may
        reflect alternate paths to the same server or provide 
        for the use of various forms of server
        clustering in which multiple servers provide alternate 
        ways of accessing the same physical file system.  How these
        different modes of file system transition are represented 
        within the fs_locations and fs_locations_info attributes 
        and how the client deals with
        file system transition issues will be discussed in detail
        below.
      </t>
      <t>
        Multiple server addresses, whether they are derived from 
        a single entry with a DNS name representing a set of IP
        addresses or from multiple entries each with its own 
        server address, may correspond to the same actual
        server.  The fact that two addresses correspond to the
        same server is shown by a common so_major_id field
        within the eir_server_owner field returned by EXCHANGE_ID
        (see <xref target="OP_EXCHANGE_ID_DESCRIPTION" />).
        For a detailed discussion of how server address targets
        interact with the determination of server identity
        specified by the server owner field, see
        <xref target="loc_server_id" />.
      </t>
    </section>
    <section anchor="migration" title="File System Migration">
      <t>
        When a file system is present and becomes absent, clients can be
        given the opportunity to have continued access to their data,
        at an alternate location, as specified by the fs_locations or
        fs_locations_info attribute.  Typically, a client will be 
        accessing the file system in question, get an NFS4ERR_MOVED
        error, and then use the fs_locations or fs_locations_info
        attribute to determine the new location of the data.  When
        fs_locations_info is used, additional information will be
        available that will define the nature of the client's 
        handling of the transition to a new server.   
      </t>
      <t>
        Such migration can be helpful in providing 
        load balancing or general resource reallocation.  The protocol 
        does not specify how the file system will be moved between 
        servers.  It is anticipated that a number of different 
        server-to-server transfer mechanisms might be used with the
        choice left to the server implementor.  The NFSv4.1 protocol
        specifies the method used to communicate the migration
        event between client and server.
      </t>
      <t>
        The new location may be an alternate
        communication path to the same server or, in the case of
        various forms of server
        clustering, another server providing
        access to the same physical file system.  The client's 
        responsibilities in dealing with this transition depend on the
        specific nature of the new access path as well as how and whether data
        was in fact migrated.  These issues will be discussed in
        detail below.
      </t>
      <t>
        When multiple server addresses correspond to the same 
        actual server, as shown by a common value for the so_major_id field
        of the eir_server_owner field returned by EXCHANGE_ID, the location
        or locations may designate alternate server addresses in
        the form of specific server network addresses.  These can 
        be used to access
        the file system in question at those addresses
        and when it is no longer accessible at the original address. 
      </t>
      <t>
        Although a single successor location is typical, multiple 
        locations may be provided, together with information that
        allows priority among the choices to be indicated, via 
        information in the fs_locations_info attribute.  Where suitable,
        clustering mechanisms make it possible to provide multiple
        identical file systems or paths to them; this allows the client
        the opportunity to deal with any resource or communications
        issues that might limit data availability.
      </t>
      <t>
        When an alternate location is designated as the target for
        migration, it must designate the same data
        (with metadata being the same to the degree indicated by the
        fs_locations_info attribute).  Where file systems are writable,
        a change made on the original file system must be visible on
        all migration targets. Where a file system is not writable
        but represents a read-only copy (possibly periodically 
        updated) of
        a writable file system, similar requirements apply to the 
        propagation of updates.  Any change visible in the original
        file system must already be effected on all migration targets,
        to avoid any possibility that a client, in effecting a transition to 
        the migration target, will see any reversion in file system state.  
      </t>
    </section>
    <section anchor="referrals" title="Referrals">
      <t>
        Referrals provide a way of placing a file system in a location
        within the namespace
        essentially without respect to its physical location on a
        given server.  This allows a single server or a set of servers
        to present a multi-server namespace that encompasses file systems
        located on multiple servers.  Some likely uses of this include
        establishment of site-wide or organization-wide namespaces,
        or even knitting such together into a truly global namespace.
      </t>
      <t>
        Referrals occur when a client determines, upon first referencing
        a position in the current namespace, that it is part of a new 
        file system and that the file system is absent.  When this 
        occurs, typically by receiving the error NFS4ERR_MOVED, the
        actual location or locations of the file system can be 
        determined by fetching the fs_locations or fs_locations_info 
        attribute.
      </t>
      <t>
        The locations-related attribute may designate a single 
        file system location or multiple file system locations, to
        be selected based on the needs of the client.  The server,
        in the fs_locations_info attribute, may specify priorities to 
        be associated with various file system location choices.
        The server may assign different priorities to different
        locations as reported to individual clients, in order to
        adapt to client physical location or to effect load balancing.
        When both read-only and read-write file systems are present,
        some of the read-only locations might not be absolutely up-to-date
        (as they would have to be in the case of replication and
        migration).  Servers may also specify file system locations
        that include client-substituted variables so that different
        clients are referred to different file systems (with different
        data contents) based on client attributes such as CPU 
        architecture.
      </t>
      <t>
        When the fs_locations_info attribute indicates that there are
        multiple possible targets listed, the relationships among them
        may be important to the client in selecting which one to use.
        The same rules specified in <xref target="replication" />
        defining the appropriate standards for the data propagation
        apply to these multiple replicas as well.  For example, the
        client might prefer a writable target on a server that has additional writable
        replicas to which it subsequently might switch.  Note that,
        as distinguished from the case of replication, there is no
        need to deal with the case of propagation of updates made by
        the current client, since the current client has not accessed
        the file system in question.
      </t>
      <t>
        Use of multi-server namespaces is enabled by NFSv4.1 but is not
        required.  The use of multi-server namespaces and their scope
        will depend on the applications used and system administration
        preferences. 
      </t>
      <t>
        Multi-server namespaces can be established by a single 
        server providing a large set of referrals to all of the
        included file systems.  Alternatively, a single multi-server
        namespace may be administratively segmented with separate
        referral file systems (on separate servers) for each
        separately administered portion of the namespace. The
        top-level referral file system or any segment may use
        replicated referral file systems for higher availability.  
      </t>
      <t>
        Generally, multi-server namespaces are for the most part 
        uniform, in that the same data made available to one client
        at a given location in the namespace is made available to
        all clients at that location.  However, there are facilities
        provided that allow different clients to be directed to 
        different sets of data, so as to adapt to such client
        characteristics as CPU architecture.  
      </t>
    </section>
  </section>
  <section title="Location Entries and Server Identity"
           anchor="loc_server_id">
    <t>
      As mentioned above, a single location entry may have a server
      address target in the form of a DNS name that may represent 
      multiple IP addresses, while multiple location entries may have their 
      own server address targets that reference the same server.
      Whether two IP addresses designate the same server is
      indicated by the existence of a common so_major_id field
      within the eir_server_owner field returned by EXCHANGE_ID
      (see <xref target="OP_EXCHANGE_ID_DESCRIPTION" />), subject
      to further verification (for details see 
      <xref target="Trunking" />).
    </t>
    <t>
      When multiple addresses for the same server exist, the client 
      may assume that for each file system in the namespace of 
      a given server network address, there exist
      file systems at corresponding namespace locations for 
      each of the other server network addresses.
      It may do this even in the absence of 
      explicit listing in fs_locations and fs_locations_info.
      Such corresponding file system locations can be used as
      alternate locations, just as those explicitly specified via
      the fs_locations and fs_locations_info attributes.  Where
      these specific addresses are explicitly designated in the 
      fs_locations_info attribute, the conditions of use specified 
      in this attribute (e.g., priorities, specification of 
      simultaneous use) may limit the client's use of these 
      alternate locations. 
    </t>
    <t>
      If a single location entry designates multiple server IP
      addresses, the client cannot assume that these addresses
      are multiple paths to the same server.  In most cases, they 
      will be, but the client MUST verify that before acting on
      that assumption.  When two server addresses are designated
      by a single location entry and they correspond to different
      servers, this normally indicates some sort of misconfiguration,
      and so the client should avoid using such location entries
      when alternatives are available.  When they are not, 
      clients should pick one of IP addresses and use it,
      without using others that are not directed to the same 
      server.
    </t> 
  </section>
  <section title="Additional Client-Side Considerations">
    <t>
      When clients make use of servers that implement referrals,
      replication, and
      migration, care should be taken that a user who mounts a given
      file system that includes a referral or a relocated file system
      continues to see a coherent picture of that user-side file system
      despite the fact that it contains a number of server-side
      file systems that may be on different servers.
    </t>
    <t>
      One important issue is upward navigation from the root of a
      server-side file system to its parent (specified as ".." in UNIX),
      in the case in which it transitions to that file system as a
      result of referral, migration, or a transition as a result of
      replication.  When the client is at such a point, and it needs to ascend to
      the parent, it must go back to the parent as seen within the
      multi-server namespace rather than sending a LOOKUPP operation to the
      server, which would result in the parent within that server's
      single-server namespace.  In order to do this, the client
      needs to remember the filehandles that represent such
      file system roots and use these instead of sending a 
      LOOKUPP operation to the current server.  This will allow the client
      to present to applications a consistent namespace, where 
      upward navigation and downward navigation are consistent.
    </t>
    <t>
      Another issue concerns refresh of referral locations.  When
      referrals are used extensively, they may change as server
      configurations change.  It is expected that clients will cache
      information related to traversing referrals so that future
      client-side requests are resolved locally without server
      communication.
      This is usually rooted in client-side name look up caching. Clients
      should periodically purge this data for referral points in order to
      detect changes in location information.  When the change_policy
      attribute changes for directories that hold referral entries 
      or for the referral entries themselves, clients should consider 
      any associated
      cached referral information to be out of date.
    </t>
  </section>
  <section anchor="effecting_transitions" 
           title="Effecting File System Transitions">
    <t>
      Transitions between file system instances, whether due to
      switching between replicas upon server unavailability or 
      to server-initiated migration events, are best
      dealt with together.  This is so even though, for the server,
      pragmatic considerations will normally force different 
      implementation strategies for planned and unplanned transitions. 
      Even though the prototypical use cases
      of replication and migration contain distinctive sets of
      features, when all possibilities for these operations are
      considered, there is an underlying unity of these operations, 
      from the client's point of view, that makes treating
      them together desirable. 
    </t>
    <t>
      A number of methods are possible for servers to replicate data
      and to track client state in order to allow clients to transition
      between file system instances with a minimum of disruption.  Such
      methods vary between those that use inter-server clustering
      techniques to limit the changes seen by the client, to those that
      are less aggressive, use more standard methods of replicating
      data, and impose a greater burden on the client to adapt to 
      the transition.      
    </t>
    <t>
      The NFSv4.1 protocol does not impose choices on clients and
      servers with regard to that spectrum of transition methods.  In
      fact, there are many valid choices, depending on client and
      application requirements and their interaction with server 
      implementation choices.  The NFSv4.1 protocol does define the
      specific choices that can be made, how these choices are 
      communicated to the client, and how the client is to deal with
      any discontinuities.
    </t>
    <t>
      In the sections below, references will be made to various possible
      server implementation choices as a way of illustrating the transition
      scenarios that clients may deal with.  The intent here is not to
      define or limit server implementations but rather to illustrate
      the range of issues that clients may face.
    </t>
    <t>
      In the discussion below, references will be made to a file system
      having a particular property or to two file systems
      (typically the source and destination) belonging to a common
      class of any of several types.  Two file systems that belong to
      such a class share some important aspects of file system behavior
      that clients may depend upon when present, to easily effect a
      seamless transition between file system instances.  Conversely,
      where the file systems do not belong to such a common class, the
      client has to deal with various sorts of implementation 
      discontinuities that may cause performance or other issues in
      effecting a transition.
    </t> 
    <t>
      Where the fs_locations_info attribute is available, such file system
      classification data will be made directly available to the client
      (see <xref target='fs_locations_info' /> for details).  When only
      fs_locations is available, default assumptions with regard to
      such classifications have to be inferred
      (see <xref target='fs_locations' /> for details).
    </t>
    <t>
      In cases in which one server is expected to
      accept opaque values from the client that originated
      from another server, the servers SHOULD
      encode the "opaque" values in big-endian
      byte order.
      If this is done, servers acting as replicas or immigrating 
      file systems will
      be able to parse values like stateids, directory cookies,
      filehandles, etc., even if their native byte order is different from
      that of other servers cooperating in the replication and migration 
      of the
      file system.
    </t>
    <section anchor="transition_summary"
             title="File System Transitions and Simultaneous Access">
      <t>
        When a single file system may be accessed at multiple locations,
        either because of an indication of file system identity
        as reported by the fs_locations or fs_locations_info 
        attributes or because two file system instances have corresponding 
        locations on server addresses that connect to the same server
        (as indicated by a common so_major_id field in the eir_server_owner
        field returned by EXCHANGE_ID), the client
        will, depending on specific circumstances as discussed below,
        either:
      </t>
      <t>
       <list style='symbols'>
        <t>
          Access multiple instances simultaneously, each of which
          represents an alternate path to the same data and metadata. 
        </t>
        <t>
          Access one instance (or set of instances) and then
          transition to an alternative instance (or set of instances) 
          as a result of network issues, server unresponsiveness, or
          server-directed migration.  The transition may involve changes
          in filehandles, fileids, the change attribute, and/or locking
          state, depending on the attributes of the source and 
          destination file system instances, as specified in the
          fs_locations_info attribute. 
        </t>
       </list>
      </t>
      <t>
        Which of these choices is possible, and how a transition is 
        effected, is governed by equivalence classes of file system
        instances as reported by the fs_locations_info attribute,
        and for file system instances in the same location within
        a multi-homed single-server namespace, as indicated by the 
        value of the so_major_id field of the eir_server_owner field
        returned by EXCHANGE_ID.
      </t>
    </section>
    <section anchor="simultaneous_transparent" 
             title="Simultaneous Use and Transparent Transitions">
      <t>
        When two file system instances have the same location within
        their respective single-server namespaces and those two server 
        network addresses designate the same server (as indicated by
        the same value of the so_major_id field of the
        eir_server_owner field returned 
        in response to EXCHANGE_ID), those file system instances can 
        be treated as the same, and either used together simultaneously
        or serially with no transition activity required on the part of
        the client.  In this case, we refer to the transition as
        "transparent", and the client in transferring access from one
        to the other is acting as it would in the event that communication
        is interrupted, with a new connection and possibly a new session
        being established to continue access to the same file system.
      </t>
      <t>
        Whether simultaneous use of the two file system instances is
        valid is controlled by whether the 
        fs_locations_info attribute shows the two instances as having
        the same simultaneous-use class.
        See <xref target="fs_locations_server4" /> for information
        about the definition of the various use classes, including
        the simultaneous-use class.
      </t>
      <t>
        Note that for two such file systems,
        any information within the fs_locations_info
        attribute that indicates the need for special transition activity,
        i.e., the appearance of the two file system instances with different
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes, indicates a serious
        problem. The client, if it allows transition to the file system
        instance at all, must not treat this as a transparent transition.
        The server SHOULD NOT indicate that these instances
        belong to different 
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes, whether or not the two
        instances are shown belonging to the same 
        simultaneous-use class.
      </t>
      <t>
        Where these conditions do not apply, a non-transparent file
        system instance transition is required with the details 
        depending on the respective  
        handle,
        fileid,
        write-verifier,
        change, and
        readdir classes of the two 
        file system instances, and whether the two servers' addresses in
        question have the same eir_server_scope value as reported by
        EXCHANGE_ID.
      </t>
      <section anchor="simultaneous_use" 
               title="Simultaneous Use of File System Instances">
        <t>
          When the conditions in <xref target="simultaneous_transparent" />
          hold, 
          in either of the following two cases, the client may use the 
          two file system instances simultaneously.
         <list style='symbols'>
          <t>
            The fs_locations_info attribute does not contain separate
            per-network-address entries for file system instances at 
            the distinct network addresses.  This
            includes the case in which the fs_locations_info attribute is 
            unavailable.  In this case, the fact that the two server 
            addresses connect to the same server (as indicated by the
            two addresses sharing the same the so_major_id value 
            and subsequently confirmed as described in 
            <xref target="Trunking" />) justifies
            simultaneous use, and there is no fs_locations_info
            attribute information contradicting that.
          </t>
          <t>
            The fs_locations_info attribute indicates that two file system
            instances belong to the same simultaneous-use class.
          </t>
         </list>
        </t>
        <t>
          In this case, the client may use both file system instances 
          simultaneously, as representations of the same file system,
          whether that happens because the two network addresses connect to
          the same physical server or because different servers connect to 
          clustered file systems and export their data in common.  When
          simultaneous use is in effect, any change made to one file 
          system instance must be immediately reflected in the other
          file system instance(s).  Locks are treated as part of a
          common lease, associated with a common client ID.  Depending 
          on the details of the eir_server_owner returned by EXCHANGE_ID,
          the two server instances may be accessed by different sessions
          or a single session in common.
        </t>
      </section>
      <section anchor="transparent_transitions" 
               title="Transparent File System Transitions">
        <t>
          When the conditions in <xref target="simultaneous_use" /> hold
          and the fs_locations_info 
          attribute explicitly shows the file system instances for
          these distinct network addresses as belonging to different
          simultaneous-use classes,
          the file system instances should not be used by the client
          simultaneously.  Rather, they should be used serially with one being used
          unless and until communication difficulties, 
          lack of responsiveness,
          or an explicit migration event causes another file
          system instance (or set of file system instances sharing a
          common simultaneous-use class)
          to be used.
        </t>
        <t>
          When a change of file system instance is to be done, the
          client will use the same client ID already in effect.  If
          the client already has connections to the new server address, these
          will be used.  Otherwise, new connections to existing sessions
          or new sessions associated with the existing client ID 
          are established as indicated by the eir_server_owner returned by 
          EXCHANGE_ID.
        </t> 
        <t>
          In all such transparent transition cases, the following apply:
        </t>
        <t>
         <list style='symbols'>
          <t>
	    If filehandles are persistent, they stay the
	    same. If filehandles are volatile, they either
	    stay the same or expire, but the reason for
            expiration is not due to the file system transition.
          </t>
          <t>
            Fileid values do not change across the transition.
          </t>
          <t>
            The file system will have the same fsid in both the old and new
            locations.
          </t>
          <t>
            Change attribute values are consistent across the transition
            and do not have to be refetched.  When change attributes
            indicate that a cached object is still valid, it can remain
            cached.  
          </t>
          <t>
            Client and state identifiers retain their validity
            across the transition, except where their staleness is
            recognized and reported by the new server.  Except where 
            such staleness requires it, no lock reclamation is needed.
            Any such staleness is an indication that the server should
            be considered to have restarted and is reported as discussed
            in <xref target="server_failure" />.
          </t>
          <t>
            Write verifiers are presumed to retain their validity and
            can be used to compare with verifiers returned by COMMIT on
            the new server.
            If COMMIT on the new server returns an identical verifier,
            then it is expected that the new server has all of the data
            that was written unstably to the original server
            and has committed that data to stable storage as requested.

          </t>
          <t>
            Readdir cookies are presumed to retain their validity
            and can be presented to subsequent READDIR requests together
            with the readdir verifier with which they are associated.
            When the verifier is accepted as valid, the cookie will
            continue the READDIR operation so that the entire directory
            can be obtained by the client.
          </t>
         </list>
        </t>
      </section>
    </section>
    <section anchor="transition_handles"
             title="Filehandles and File System Transitions">
      <t>
        There are a number of ways in which filehandles can be handled
        across a file system transition.  These can be divided into 
        two broad classes depending upon whether the two file systems
        across which the transition happens share sufficient state to
        effect some sort of continuity of file system handling.
      </t>
      <t>
        When there is no such cooperation in filehandle assignment,
        the two file systems are reported as being in different 
        handle classes.  In this case,
        all filehandles are assumed to expire as part of the 
        file system transition.  Note that this behavior does not
        depend on the fh_expire_type attribute and supersedes the specification
        of the FH4_VOL_MIGRATION bit, which only affects behavior when
        fs_locations_info is not available.
      </t>
      <t>
        When there is cooperation in filehandle assignment,
        the two file systems are reported as being in the same
        handle classes.  In this case,
        persistent filehandles remain valid after the file system
        transition, while volatile filehandles (excluding those 
        that are only volatile due to the FH4_VOL_MIGRATION bit) are 
        subject to expiration on the target server.
      </t>
    </section>
    <section anchor="transition_fileid"
             title="Fileids and File System Transitions">
      <t>
        In NFSv4.0, the issue of continuity of fileids in the event
        of a file system transition was not addressed.  The general 
        expectation had been that in situations in
        which the two file system instances are created by a single vendor
        using some sort of file system image copy, fileids will be
        consistent across the transition, while in the analogous 
        multi-vendor transitions they will not.  This poses difficulties, 
        especially for the client without special knowledge  
        of the transition mechanisms adopted by the server.  Note
        that although fileid is not a REQUIRED attribute, many servers
        support fileids and many clients provide APIs that depend on fileids.
      </t>
      <t>
        It is important to note that while clients themselves may have no
        trouble with a fileid changing as a result of a file system
        transition event, applications do typically have access to the
        fileid (e.g., via stat).  The result is that an
        application may work perfectly well if there is no file system
        instance transition or if any such transition is among instances
        created by a single vendor, yet be unable to deal with the
        situation in which a multi-vendor transition occurs at the wrong
        time.
      </t>
      <t>
        Providing the same fileids in a multi-vendor (multiple server
        vendors) environment has generally been held to be quite difficult.
        While there is work to be done, it needs to be pointed out that
        this difficulty is partly self-imposed.  Servers have typically
        identified fileid with inode number, i.e. with a quantity used to
        find the file in question.  This identification poses special
        difficulties for migration of a file system between vendors
        where assigning
        the same index to a given file may not be possible.  Note here that
        a fileid is not required to be useful to find the file in
        question, only that it is unique within the given file system.  Servers
        prepared to accept a fileid as a single piece of metadata and store
        it apart from the value used to index the file information can
        relatively easily maintain a fileid value across a migration event,
        allowing a truly transparent migration event.
      </t>
      <t>
        In any case, where servers can provide continuity of fileids, they
        should, and the client should be able to find out that such
        continuity is available and take appropriate action.  Information
        about the continuity (or lack thereof) of fileids across a file
        system transition is represented by specifying whether the file systems 
        in question are of the same fileid class.
      </t>
      <t>
        Note that when consistent fileids do not exist across a 
        transition (either because there is no continuity of fileids
        or because fileid is not a supported attribute on one of 
        instances involved), and there are
        no reliable filehandles across a transition event (either because
        there is no filehandle continuity or because the filehandles are
        volatile), the client is in a position where it cannot verify
        that files it was accessing before the transition are the 
        same objects.  It is forced to assume that no object has been 
        renamed, and, unless there are guarantees that provide this
        (e.g., the file system is read-only), problems for applications
        may occur.  Therefore, use of such configurations should be 
        limited to situations where the problems that this may cause
        can be tolerated.
      </t>
    </section>
    <section anchor="transition_fsid"
             title="Fsids and File System Transitions">
      <t>
        Since fsids are generally only unique within a per-server basis,
        it is likely that they will change during a file system
        transition.  One exception is the case of transparent transitions,
        but in that case we have multiple network addresses that are
        defined as the same server (as specified by a common value of
        the so_major_id field of eir_server_owner).
        Clients should not make the fsids received
        from the server visible to applications since they may not be
        globally unique, and because they may change during a file
        system transition event.  Applications are best served if they
        are isolated from such transitions to the extent possible.
      </t>
      <t>
        Although normally a single source file system will transition
        to a single target file system, there is a provision for splitting
        a single source file system into multiple target file systems, by
        specifying the FSLI4F_MULTI_FS flag.
      </t>
      <section anchor="transition_fsid_split"
               title="File System Splitting">
        <t>
          When a file system transition is made and the fs_locations_info
          indicates that the file system in question may be split into 
          multiple file systems (via the FSLI4F_MULTI_FS flag), the client 
          SHOULD do GETATTRs to determine the fsid attribute on all known 
          objects within the file system undergoing transition to determine 
          the new file system boundaries.  
        </t>
        <t>
          Clients may maintain the fsids passed to existing applications 
          by mapping all of the fsids for the descendant file systems to 
          the common fsid used for the original file system.  
        </t> 
        <t>
          Splitting a file system may be done on a transition between
          file systems of the same fileid 
          class, since the fact that fileids are unique within the
          source file system ensure they will be unique in each of the
          target file systems.
        </t>
      </section>
    </section>
    <section anchor="transition_change"
             title= "The Change Attribute and File System Transitions">
      <t>
        Since the change attribute is defined as a server-specific one,
        change attributes fetched from one server are normally presumed to 
        be invalid on another server.  Such a presumption is troublesome
        since it would invalidate all cached change attributes, requiring
        refetching.  Even more disruptive, the absence of any assured
        continuity for the change attribute means that even if the same
        value is retrieved on refetch, no conclusions can be drawn as to whether
        the object in question has changed.  The identical change 
        attribute could be merely an artifact of a modified file with
        a different change attribute construction algorithm, with that
        new algorithm just happening to result in an identical change 
        value.
      </t>
      <t>
        When the two file systems have consistent change attribute formats,
        and this fact is communicated to the client by reporting 
        in the same change class, the 
        client may assume a continuity of change attribute construction
        and handle this situation just as it would be handled without
        any file system transition.
      </t>
    </section>
    <section anchor="transition_state"
             title="Lock State and File System Transitions">
      <t>
        In a file system transition, the client needs to handle cases
        in which the two servers have cooperated in state management
        and in which they have not.  Cooperation by two servers in
        state management requires coordination of client IDs.
        Before the client
        attempts to use a client ID associated with one
        server in a request to the server of the other file system,
        it must eliminate the possibility that
        two non-cooperating servers have assigned the same client ID
        by accident. The client needs to compare
        the eir_server_scope values returned by each server. If
        the scope values do not match, then the servers have not
        cooperated in state management. If the scope values match,
        then this indicates the servers have cooperated in assigning
        client IDs to the point that they will reject client IDs that
        refer to state they do not know about.  See 
        <xref target="Server_Scope" /> for more information about
        the use of server scope.
      </t>
      <t>
        In the case of migration, the servers involved in the 
        migration of a file system SHOULD transfer all server state 
        from the original to the new server.  When this is done, 
        it must be done in a way that is transparent to the client.  
        With replication, such a degree of common state is 
        typically not the case.  Clients, however, should use 
        the information provided by the eir_server_scope 
        returned by EXCHANGE_ID (as modified by the validation 
        procedures described in <xref target="Server_Scope" />)
        to determine whether such sharing may be in effect, rather
        than making assumptions based on the reason for the transition.
      </t>
      <t>
        This state transfer will reduce disruption to the client
        when a file system transition occurs.
        If the servers are successful in
        transferring all state, the client can attempt to establish
        sessions associated with the client ID used for the source
        file system instance.  If the server accepts that as a valid 
        client ID, then the client may use the existing stateids
        associated with that client ID for the old file system instance
        in connection with that same client ID in connection with
        the transitioned file system instance.  If the client in 
        question already had a client ID on the target system, it
        may interrogate the stateid values from the source system
        under that new client ID, with the assurance that if they
        are accepted as valid, then they represent validly transferred
        lock state for the source file system, which has been transferred to the
        target server.
      </t>
      <t>
        When the two servers belong to the same 
        server scope, it does not mean that when 
        dealing with the transition, the client will not have to reclaim
        state.  However, it does mean that the client may proceed using
        its current client ID when establishing communication with the 
        new server, and the new server will either recognize the
        client ID as valid or reject it, in which case locks must be
        reclaimed by the client.
      </t>
      <t>
        File systems cooperating in state management may actually
        share state or simply divide the identifier space so as to recognize
        (and reject as stale) each other's stateids and client IDs.
        Servers that do share state may not do so under all conditions
        or at all times.   If the server
        cannot be sure when accepting a client ID that it reflects the locks
        the client was given, the server must treat all associated state as 
        stale and report it as such to the client.
      </t>
      <t>
        When the two file system instances are on servers that do 
        not share a server scope value, the client must
        establish a new client ID on the destination, if it does not
        have one already, and reclaim locks if allowed by the server.  
        In this case, old stateids and client IDs should
        not be presented to the new server since there is no assurance
        that they will not conflict with IDs valid on that server.
        Note that in this case, lock reclaim may be attempted even
        when the servers involved in the transfer have different
        server scope values (see <xref target="reclaim_locks" />      
        for the contrary case of reclaim after server reboot).
        Servers with different server scope values may cooperate
        to allow reclaim for locks associated with the transfer of
        a file system even if they do not cooperate sufficiently 
        to share a server scope.
      </t>
      <t>
        In either case, when actual locks are not known to be maintained,
        the destination server may establish a grace period specific to
        the given file system, with non-reclaim locks being rejected for
        that file system, even though normal locks are being granted
        for other file systems.  Clients should not infer the absence of
        a grace period for file systems being transitioned to a server
        from responses to requests for other file systems. 
      </t>
      <t>
        In the case of lock reclamation for a given file system after
        a file system transition, edge conditions can arise similar to
        those for reclaim after server restart (although in the case of
        the planned state transfer associated with migration, these can
        be avoided by securely recording lock state as part of state 
        migration).  Unless the destination server can guarantee that
        locks will not be incorrectly granted, the destination server
        should not allow lock reclaims and should avoid establishing a grace
        period.  
      </t>
      <t>
        Once all locks have been reclaimed, or there were no locks to 
        reclaim, the client indicates that there are no more reclaims
        to be done for the file system in question by sending a 
        RECLAIM_COMPLETE operation with the rca_one_fs parameter set
        to true.  Once this has been done, non-reclaim locking operations
        may be done, and any subsequent request to do reclaims will
        be rejected with the error NFS4ERR_NO_GRACE. 
      </t>
      <t>
        Information about client identity may be propagated between
        servers in the form of client_owner4 and associated verifiers,
        under the assumption that the client presents the same values to
        all the servers with which it deals.  
      </t>
      <t>
        Servers are encouraged to provide facilities to allow locks
        to be reclaimed on the new server after a file system 
        transition.  Often, however, in cases in which the two
        servers do not share a server scope value,
        such facilities may not be available
        and the client should be prepared to re-obtain locks, even
        though it is possible that the client may have its LOCK
        or OPEN request denied due to a conflicting lock.
      </t>
      <t>
        The consequences of having no facilities available to 
        reclaim locks on the new server will depend on the type
        of environment.  In  
        some environments, such as the transition between read-only
        file systems, such denial of locks should not pose large 
        difficulties in practice.  When an attempt to
        re-establish a lock on a new server is denied, the client should
        treat the situation as if its original lock had been revoked.
        Note that when the lock is granted, the client cannot
        assume that no conflicting lock could have been granted in the
        interim.  Where change attribute continuity is present, the
        client may check the change attribute to check for unwanted
        file modifications.  Where even this is not available, and
        the file system is not read-only, a client may reasonably treat 
        all pending locks as having been revoked.
      </t>
      <section anchor="transferred_lease"
               title="Leases and File System Transitions">
        <t>
          In the case of lease renewal, the client may not be 
          submitting requests for a file system that has been transferred 
          to another server.  This can occur 
          because of the lease renewal mechanism.  The
          client renews the lease associated with all file systems 
          when submitting 
          a request on an associated session, regardless of the 
          specific file system being referenced.
        </t>
        <t>
          In order for the client to schedule renewal of its lease
          where there is locking state that may have been relocated 
          to the new server, the client 
          must find out about lease relocation before that lease
          expire.  To accomplish this, the SEQUENCE operation will
          return the status bit SEQ4_STATUS_LEASE_MOVED
          if responsibility for any of the renewed locking state 
          has been transferred to a new server.  This 
          will continue until the client receives an 
          NFS4ERR_MOVED error for each of the file systems for which
          there has been locking state relocation.
        </t>
        <t>
          When a client receives an SEQ4_STATUS_LEASE_MOVED indication from
          a server, for each file system of the server for which the client
          has locking state, the client should perform an operation.
          For simplicity, the client may choose to reference
          all file systems, but what is important
          is that it must reference all file systems for which there was
          locking state where that state has moved.  Once the client
          receives an NFS4ERR_MOVED error for each such file system,
          the server will clear the SEQ4_STATUS_LEASE_MOVED indication.
          The client can terminate the process of checking file systems
          once this indication is cleared (but only if the client
          has received a reply for all outstanding SEQUENCE requests
          on all sessions it has with the server), since there are no others
          for which locking state has moved.
        </t>
        <t>
          A client may use GETATTR of the fs_status 
          (or fs_locations_info) attribute on all of the file systems
          to get absence indications in a single (or a few) request(s),
          since absent file systems will not cause an error in this
          context.  However, it still must do an operation that 
          receives NFS4ERR_MOVED on each file system, in order to clear
          the SEQ4_STATUS_LEASE_MOVED indication.
        </t>
        <t>
          Once the set of file systems with transferred locking state
          has been determined, the client can follow the normal process 
          to obtain the new server information (through the 
          fs_locations and fs_locations_info attributes) and perform renewal
          of that lease on the new server, unless information in the
          fs_locations_info attribute shows that no state could have
          been transferred.  If the server has not 
          had state transferred to it transparently, the client 
          will receive NFS4ERR_STALE_CLIENTID 
          from the new server,
          as described above, and the client can then reclaim 
          locks 
          as is done in the event of server failure.
        </t>
      </section>
      <section anchor="transition_lease_time"
               title="Transitions and the Lease_time Attribute">
        <t>
          In order that the client may appropriately manage its lease
          in the case of a file system transition, the destination server must 
          establish proper values for the lease_time attribute.
        </t>
        <t>
          When state is transferred transparently, that state 
          should include the correct value of the lease_time 
          attribute.  The lease_time attribute on the destination 
          server must never be less than that on the source, since 
          this would result in premature expiration of a lease
          granted by the source server.  Upon transitions in which 
          state is transferred transparently, the client is under 
          no obligation to refetch the lease_time attribute and 
          may continue to use the value
          previously fetched (on the source server).
        </t>
        <t>
          If state has not been transferred transparently, either
          because the associated servers are shown as having different
          eir_server_scope strings or because the client ID 
          is rejected when presented to the new server,
          the client should fetch the value
          of lease_time on the new (i.e., destination) server, and 
          use it for subsequent locking requests.  However, the server 
          must respect a grace
          period of at least as long as the lease_time on the source 
          server, in order to ensure that clients have ample time to 
          reclaim their lock before potentially conflicting 
          non-reclaimed locks are granted.  
       </t>
     </section>
    </section>
    <section anchor="transition_verifier"
             title="Write Verifiers and File System Transitions">
      <t>
        In a file system transition, the two file systems may be
        clustered in the handling of unstably written data.  
        When this is the
        case, and the two file systems belong to the same
        write-verifier class, write
        verifiers returned
        from one system may be compared to those returned  by the 
        other and superfluous
        writes avoided.  
      </t>
      <t>
        When two file systems belong to different 
        write-verifier classes, any verifier
        generated by one must not be compared to one provided by the 
        other.  Instead, it should be treated as not equal even when
        the values are identical.
      </t>
    </section>
    <section anchor="transition_readdir"
             title="Readdir Cookies and Verifiers and File System Transitions">
      <t>
        In a file system transition, the two file systems may be
        consistent in their handling of READDIR cookies and verifiers.
        When this is the
        case, and the two file systems belong to the same
        readdir class, READDIR
        cookies and verifiers
        from one system may be recognized by the other and 
        READDIR operations started on one server may be validly
        continued on the other, simply by presenting the 
        cookie and verifier returned by a READDIR operation done
        on the first file system to the second.
      </t>
      <t>
        When two file systems belong to different 
        readdir classes, any READDIR
        cookie and verifier
        generated by one is not valid on the second, and must not
        be presented to that server by the client.  The client 
        should act as if the verifier was rejected.
      </t>
    </section>
    <section anchor="transition_data"
             title="File System Data and File System Transitions">
      <t>
        When multiple replicas exist and are used simultaneously or in
        succession by a client, applications using them will normally expect
        that they contain either the same data or data that is consistent with
        the normal sorts of changes that are made by other clients
        updating the data of the file system
        (with metadata being the same to the degree indicated by the
        fs_locations_info attribute).  However, when multiple file systems are 
        presented as replicas of one another, the precise relationship 
        between the data of one and the data of another is not, as a 
        general matter, specified by the NFSv4.1 protocol.  It is quite 
        possible to present as replicas file systems where the data of 
        those file systems is sufficiently different that some applications 
        have problems dealing with the transition between replicas.  The 
        namespace will typically be constructed so that applications can 
        choose an appropriate level of support, so that in one position in 
        the namespace a varied set of replicas will be listed, while in 
        another only those that are up-to-date may be considered replicas.  
        The protocol does define four special cases of the relationship among 
        replicas to be specified by the server and relied upon by clients:

        <list style='symbols'>
          <t>
            When multiple server addresses correspond to the same actual 
            server, as indicated by a common so_major_id field within 
            the eir_server_owner field returned by EXCHANGE_ID, the 
            client may depend on the fact 
            that changes to data, metadata, 
            or locks made on one file system are immediately reflected 
            on others.
          </t>
          <t>
            When multiple replicas exist and are used simultaneously
            by a client (see the FSLIB4_CLSIMUL definition within
            fs_locations_info), they must designate the same
            data. Where file systems are writable, a change made on
            one instance must be visible on all instances, immediately
            upon the earlier of the return of the modifying requester
            or the visibility of that change on any of the associated
            replicas.  This allows a client to use these replicas
            simultaneously without any special adaptation to the fact
            that there are multiple replicas.  In this case, locks
            (whether share reservations or byte-range locks) and delegations obtained on one
            replica are immediately reflected on all replicas, even
            though these locks will be managed under a set of client
            IDs.
          </t>
          <t>
            When one replica is designated as the successor instance to another
            existing instance after return NFS4ERR_MOVED (i.e., the case of 
            migration), the client may depend on the fact that all changes
            written to stable storage on the original instance
            are written to stable storage of the successor (uncommitted writes are dealt with in 
            <xref target="transition_verifier" />).
          </t>
          <t>
            Where a file system is not writable but represents a read-only 
            copy (possibly periodically updated) of a writable file system, 
            clients have similar requirements with regard to the propagation 
            of updates.  They may need a guarantee that any change visible on 
            the original file system instance must be immediately visible on 
            any replica before the client transitions access to that replica, 
            in order to 
            avoid any possibility that a client, in effecting a transition to a
            replica, will see any reversion in file system state.  The specific
            means of this guarantee varies based on the value of
            the fss_type field that is
            reported as part of the fs_status attribute (see 
            <xref target="fs_status" />).  Since these file systems are presumed 
            to be  
            unsuitable for simultaneous use, there is no specification of how 
            locking is handled; in general, locks obtained on one file
            system will be separate from those on others.  
            Since these are going to be read-only file systems, this is not 
            expected to pose an issue for clients or applications.
          </t>
        </list>
      </t>
    </section>
  </section>
  <section anchor="effecting_referrals" 
           title="Effecting File System Referrals">
    <t>
      Referrals are effected when an absent file system is encountered
      and one or more alternate locations are made available by the
      fs_locations or fs_locations_info attributes.  The client will
      typically get an NFS4ERR_MOVED error, fetch the appropriate 
      location information, and proceed to access the file system on
      a different server, even though it retains its logical position
      within the original namespace.  Referrals differ from migration
      events in that they happen only when the client has not 
      previously referenced the file system in question (so there
      is nothing to transition).  Referrals can only come into 
      effect when an absent file system is encountered at its
      root.
    </t>
    <t>
      The examples given in the sections below are somewhat artificial in
      that an actual client will not typically do a multi-component
      look up, but will have cached information regarding the upper levels
      of the name hierarchy.  However, these example are chosen to make
      the required behavior clear and easy to put within the scope of a
      small number of requests, without getting unduly into details of
      how specific clients might choose to cache things.
    </t>
    <section anchor="referrals_lookup" 
             title="Referral Example (LOOKUP)">
      <t>
        Let us suppose that the following COMPOUND is sent in an
        environment in which /this/is/the/path is absent from the
        target server.  This may be for a number of reasons.  It may 
        be that the file system has moved, or it may be that
        the target server is functioning mainly, or solely, to refer
        clients to the servers on which various file systems are located.
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          LOOKUP "path"
        </t>
        <t>
          GETFH
        </t>
        <t>
          GETATTR (fsid, fileid, size, time_modify)
        </t>
       </list>
      </t>
      <t>
        Under the given circumstances, the following will be the result.
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is now the root of 
          the pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK.  The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the 
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "path" --> NFS_OK.  The current fh is for 
          /this/is/the/path and is within a new, absent file system,
	  but ... the client will never see the value of that fh.
        </t>
        <t>
          GETFH --> NFS4ERR_MOVED.
          Fails because current fh is in an absent file system at the start of
          the operation, and the specification makes no exception for GETFH.
        </t>
        <t>
          GETATTR (fsid, fileid, size, time_modify).
          Not executed because the failure of the GETFH stops processing
          of the COMPOUND.
        </t>
       </list>
      </t>
      <t>
        Given the failure of the GETFH, the client has the job of
        determining the root of the absent file system and where to find
        that file system, i.e., the server and path relative to that
        server's root fh.  Note that in this example, the client did
        not obtain filehandles and attribute information (e.g., fsid) for
        the intermediate directories, so that it would not be sure where
        the absent file system starts.  It could be the case, for example,
        that /this/is/the is the root of the moved file system and that
        the reason that the look up of "path" succeeded is that the
        file system was not absent on that operation but was moved between the last
        LOOKUP and the GETFH (since COMPOUND is not atomic).  Even if we
        had the fsids for all of the intermediate directories, we could
        have no way of knowing that /this/is/the/path was the root of a
        new file system, since we don't yet have its fsid.
      </t>
      <t>
        In order to get the necessary information, let us re-send the
        chain of LOOKUPs with GETFHs and GETATTRs to at least get the
        fsids so we can be sure where the appropriate file system boundaries are.
        The client could choose to get fs_locations_info 
        at the same time but in
        most cases the client will have a good guess as to where file system
        boundaries are (because of where NFS4ERR_MOVED was, and was not,
        received) making fetching of fs_locations_info unnecessary.
      </t>
      <t>
       <list style='hanging'>
        <t hangText='OP01:'>
          PUTROOTFH  --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is root of pseudo-fs.
        </t>
        <t hangText='OP02:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Just for completeness.  Normally, clients will know the fsid
          of the pseudo-fs as soon as they establish communication with
          a server.
        </t>
        <t hangText='OP03:'>
          LOOKUP "this" --> NFS_OK
        </t>
        <t hangText='OP04:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP05:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this and is within pseudo-fs.
        </t>
        <t hangText='OP06:'>
          LOOKUP "is" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is and is within pseudo-fs.
        </t>
        <t hangText='OP07:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP08:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is and is within pseudo-fs.
        </t>
        <t hangText='OP09:'>
          LOOKUP "the" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the and is within pseudo-fs.
        </t>
        <t hangText='OP10:'>
          GETATTR(fsid)  --> NFS_OK
        </t>
        <t hangText='- '>
          Get current fsid to see where file system boundaries are.  The fsid
          will be that for the pseudo-fs in this example, so no
          boundary.
        </t>
        <t hangText='OP11:'>
          GETFH --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the and is within pseudo-fs.
        </t>
        <t hangText='OP12:'>
          LOOKUP "path" --> NFS_OK
        </t>
        <t hangText='- '>
          Current fh is for /this/is/the/path and is within a new,
          absent file system, but ...
        </t>
        <t hangText='- '>
          The client will never see the value of that fh.
        </t>
        <t hangText='OP13:'>
          GETATTR(fsid, fs_locations_info)  --> NFS_OK
        </t>
        <t hangText='- '>
          We are getting the fsid to know where the file system boundaries are.
          In this operation, the fsid will be different than that of the
          parent directory (which in turn was retrieved in OP10).
          Note that the fsid we are given will not necessarily be preserved at the new
          location.  That fsid might be different, and in fact the fsid
          we have for this file system might be a valid fsid of a different 
          file system on that new server.
        </t>
        <t hangText='- '>
          In this particular case, we are pretty sure anyway that what
          has moved is /this/is/the/path rather than /this/is/the
          since we have the fsid of the latter and it is that of the
          pseudo-fs, which presumably cannot move.  However, in other
          examples, we might not have this kind of information to rely
          on (e.g., /this/is/the might be a non-pseudo file system
          separate from /this/is/the/path), so we need to have
          other reliable source information on the boundary of the file system
          that is moved.  If, for example, the file system /this/is
          had moved, we would have a case of migration rather than
          referral, and once the boundaries of the migrated file system
          was clear we could fetch fs_locations_info.
        </t>
        <t hangText='- '>
          We are fetching fs_locations_info because the fact that we got an
          NFS4ERR_MOVED at this point means that it is most likely that
          this is a referral and we need the destination.  Even if it is
          the case that /this/is/the is a file system that has
          migrated, we will still need the location information for that
          file system.
        </t>
        <t hangText='OP14:'>
          GETFH --> NFS4ERR_MOVED
        </t>
        <t hangText='- '>
          Fails because current fh is in an absent file system at the start of
          the operation, and the specification makes no exception for GETFH.  Note
          that this means the server will never send the client a
          filehandle from within an absent file system.
        </t>
       </list>
      </t>
      <t>
        Given the above, the client knows where the root of the absent file
        system is (/this/is/the/path) by noting where the change of
        fsid occurred (between "the" and "path").  The
        fs_locations_info attribute also gives the client the 
        actual location of
        the absent file system, so that the referral can proceed.  The
        server gives the client the bare minimum of information about the
        absent file system so that there will be very little scope for
        problems of conflict between information sent by the referring
        server and information of the file system's home.  No filehandles
        and very few attributes are present on the referring server, and the
        client can treat those it receives as transient
        information with the function of enabling the referral.
      </t>
    </section>
    <section anchor="referrals_readdir" 
             title="Referral Example (READDIR)">
      <t>
        Another context in which a client may encounter referrals is when
        it does a READDIR on a directory in which some of the sub-directories
        are the roots of absent file systems.
      </t>
      <t>
        Suppose such a directory is read as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (fsid, size, time_modify, mounted_on_fileid)
        </t>
       </list>
      </t>
      <t>
        In this case, because rdattr_error is not requested, 
        fs_locations_info
        is not requested, and some of the attributes cannot be provided, the
        result will be an NFS4ERR_MOVED error on the READDIR, with the
        detailed results as follows:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (fsid, size, time_modify, mounted_on_fileid) -->
          NFS4ERR_MOVED.  Note that the same error would have been 
          returned if /this/is/the had migrated, but it is returned because the
          directory contains the root of an absent file system.
        </t>
       </list>
      </t>
      <t>
        So now suppose that we re-send with rdattr_error:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
        </t>
       </list>
      </t>
      <t>
        The results will be:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (rdattr_error, fsid, size, time_modify, mounted_on_fileid)
          --> NFS_OK.  The attributes for directory entry with the
          component named "path" will only contain
          rdattr_error
          with the value NFS4ERR_MOVED, together with an fsid
          value and a value for mounted_on_fileid.
        </t>
       </list>
      </t>
      <t>
        So suppose we do another READDIR to get fs_locations_info (although
        we could have used a GETATTR directly, as in
        <xref target="referrals_lookup" />).
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH
        </t>
        <t>
          LOOKUP "this"
        </t>
        <t>
          LOOKUP "is"
        </t>
        <t>
          LOOKUP "the"
        </t>
        <t>
          READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
          size, time_modify)
        </t>
       </list>
      </t>
      <t>
        The results would be:
      </t>
      <t>
       <list style='symbols'>
        <t>
          PUTROOTFH  --> NFS_OK.  The current fh is at the root of the 
          pseudo-fs.
        </t>
        <t>
          LOOKUP "this" --> NFS_OK. The current fh is for /this and is 
          within the pseudo-fs.
        </t>
        <t>
          LOOKUP "is" --> NFS_OK.  The current fh is for /this/is
          and is within the pseudo-fs.
        </t>
        <t>
          LOOKUP "the" --> NFS_OK.  The current fh is for /this/is/the
          and is within the pseudo-fs.
        </t>
        <t>
          READDIR (rdattr_error, fs_locations_info, mounted_on_fileid, fsid,
          size, time_modify) --> NFS_OK.  The attributes will be as shown below.
        </t>
       </list>
      </t>
      <t>
         The attributes for the directory entry with the
         component named "path" will only contain:
      </t>
      <t>
       <list style='symbols'>
        <t>
          rdattr_error (value: NFS_OK)
        </t>
        <t>
          fs_locations_info 
        </t>
        <t>
          mounted_on_fileid (value: unique fileid within referring file system)
        </t>
        <t>
          fsid (value: unique value within referring server)
        </t>
       </list>
      </t>
      <t>
        The attributes for entry "path" will not contain size or
        time_modify because these attributes are not available within an
        absent file system.
      </t>
    </section>
  </section>
  <section anchor="fs_locations" title="The Attribute fs_locations">
    <t>
      The fs_locations attribute is structured in the following way:
    </t>
<t>
<figure>
 <artwork>
struct fs_location4 {
        utf8str_cis     server&lt;>;
        pathname4       rootpath;
};
 </artwork>
</figure>
</t>
<t>
<figure>
 <artwork>
struct fs_locations4 {
        pathname4       fs_root;
        fs_location4    locations&lt;>;
};
 </artwork>
</figure>
</t>
    <t>
      The fs_location4 data type is used to represent the location of a
      file system by providing a server name and the path to the root 
      of the file system within that server's namespace.  
      When a set of servers have corresponding file systems at the
      same path within their namespaces, an array of server names may 
      be provided.  An
      entry in the server array is a UTF-8 string and represents one 
      of a
      traditional DNS host name, IPv4 address, IPv6 address, or a
      zero-length string.
      An IPv4 or IPv6 address is represented as a universal
      address (see <xref target="netaddr4"/> and <xref
      target="RFC5665"/>), minus the netid, and either with
      or without the trailing ".p1.p2" suffix that
      represents the port number. If the suffix is omitted,
      then the default port, 2049, SHOULD be assumed.

      A zero-length string SHOULD be used to indicate the current address 
      being used for the RPC call. It is not
      a requirement that all servers that share the same rootpath 
      be listed
      in one fs_location4 instance.  The array of server names is provided for
      convenience.  Servers that share the same rootpath may also be listed
      in separate fs_location4 entries in the fs_locations attribute.
    </t>
    <t>
     The fs_locations4 data type and fs_locations attribute contain an array of
     such locations.  Since the namespace of each server may be 
     constructed differently, the "fs_root" field is provided.  The 
     path represented
     by fs_root represents the location of the file system in the 
     current server's namespace, i.e., that of the
     server from which the fs_locations attribute was obtained.  The
     fs_root path is meant to aid the client by clearly referencing
     the root of the file system whose locations are being reported,
     no matter what object within the current file system the 
     current filehandle designates.  The fs_root is simply the
     pathname the client used to reach the object on the current server
     (i.e., the object to which the fs_locations attribute applies).
    </t>
    <t>
     When the fs_locations attribute
     is interrogated and there are no alternate file system locations,
     the server SHOULD return a zero-length array of fs_location4 
     structures, together with a valid fs_root. 
   </t>
   <t>
     As an example, suppose there is a replicated file system located 
     at two
     servers (servA and servB).  At servA, the file system is located at
     path /a/b/c.  At, servB the file system is located at path /x/y/z.
     If the client were to obtain the fs_locations value for the
     directory at /a/b/c/d, it might not necessarily know  
     that the file system's root is located in servA's namespace 
     at /a/b/c.  When the client switches to servB, it will need
     to determine that the directory it first referenced at servA is now
     represented by the path /x/y/z/d on servB.  To facilitate this, the
     fs_locations attribute provided by servA would have an fs_root value
     of /a/b/c and two entries in fs_locations.  One entry in fs_locations
     will be for itself (servA) and the other will be for servB with a
     path of /x/y/z.  With this information, the client is able to
     substitute /x/y/z for the /a/b/c at the beginning of its access
     path and construct /x/y/z/d to use for the new server.
   </t>
   <t>
     Note that there is no requirement that the number
     of components in each rootpath be the same; there
     is no relation between the number of components in
     rootpath or fs_root, and none of the components
     in a rootpath and fs_root have to be the same. In
     the above example, we could have had a third element
     in the locations array, with server equal to "servC"
     and rootpath equal to "/I/II", and a fourth element in
     locations with server equal to "servD" and rootpath
     equal to "/aleph/beth/gimel/daleth/he".

   </t>
   <t>
     The relationship between fs_root to a rootpath is
     that the client replaces the pathname indicated in
     fs_root for the current server for the substitute
     indicated in rootpath for the new server.

   </t>
   <t>
     For an example of a referred or migrated file
     system, suppose there is a file system located
     at serv1. At serv1, the file system is located at 
     /az/buky/vedi/glagoli. The client finds that object
     at glagoli has migrated (or is a referral).  The
     client gets the fs_locations attribute, which contains
     an fs_root of /az/buky/vedi/glagoli, and one element
     in the locations array, with server equal to serv2,
     and rootpath equal to /izhitsa/fita. The client
     replaces /az/buky/vedi/glagoli with /izhitsa/fita,
     and uses the latter pathname on serv2.

   </t>

   <t>
     Thus, the server MUST return an fs_root that is equal
     to the path the client used to reach the object to which the
     fs_locations attribute applies. Otherwise, the
     client cannot determine the new path to use on the new server.

   </t>
   <t>
     Since the fs_locations attribute lacks information defining various 
     attributes of the various file system choices presented, it SHOULD
     only be interrogated and used when fs_locations_info is not available.
     When fs_locations is used, information about the 
     specific locations should be assumed based on the following rules.
   </t>
   <t>
     The following rules are general and apply irrespective of the
     context.
   </t>
   <t>
    <list style='symbols'>
     <t>
       All listed 
       file system instances should be considered as of the 
       same handle class, if and only if, the 
       current fh_expire_type attribute does not include the 
       FH4_VOL_MIGRATION
       bit.  Note that in the case of referral, filehandle issues do
       not apply since there can be no filehandles known within the 
       current file system, nor is there any access to the fh_expire_type
       attribute on the referring (absent) file system.
     </t> 
     <t>
       All listed file system instances should be considered as of the 
       same fileid class if and only if the 
       fh_expire_type attribute indicates persistent filehandles and 
       does not include the FH4_VOL_MIGRATION
       bit.  Note that in the case of referral, fileid issues do
       not apply since there can be no fileids known within the 
       referring (absent) file system, nor is there any access to 
       the fh_expire_type attribute.
     </t> 
     <t>
       All file system instances 
       servers should be considered as of different 
       change classes.
     </t> 
    </list>
   </t>
   <t>
     For other class assignments, handling of file system
     transitions depends on the reasons for the transition:
   </t>
   <t>
    <list style='symbols'>
     <t>
       When the transition is due to migration, that is, the client was
       directed to a new file system after receiving an NFS4ERR_MOVED error,
       the target should be
       treated as being of the same  
       write-verifier class as the source.
     </t>
     <t>
       When the transition is due to failover to another replica, 
       that is, the client selected another replica without
       receiving an NFS4ERR_MOVED error, the target should be
       treated as being of a different 
       write-verifier class from the source.
     </t>
    </list>
   </t>
   <t>
     The specific choices reflect typical implementation patterns for
     failover and controlled migration, respectively.  Since other 
     choices are possible and useful, this information is better
     obtained by using fs_locations_info.  When a server implementation
     needs to communicate other choices, it MUST support the 
     fs_locations_info attribute.
   </t>
   <t>
     See <xref target="securityconsider" /> for a
     discussion on the recommendations for the security
     flavor to be used by any GETATTR operation that
     requests the "fs_locations" attribute.

   </t>
  </section>
  <section anchor="fs_locations_info" 
           title="The Attribute fs_locations_info">
    <t>
      The fs_locations_info attribute is intended as a more functional
      replacement for fs_locations that will continue to exist and be
      supported.  Clients can use it to get a more complete set of 
      information about alternative file system locations.
      When the server does not support
      fs_locations_info, fs_locations can be used to get a subset of the
      information.  A server that supports fs_locations_info MUST support
      fs_locations as well.
    </t>
    <t>
      There is additional information present in
      fs_locations_info, that is not available in fs_locations:
    </t>
    <t>
     <list style='symbols'>
      <t>    
        Attribute continuity information. This information
        will allow a client to select a
        location that meets the transparency requirements of the
        applications accessing the data and to leverage
        optimizations due to the server guarantees of attribute
        continuity (e.g., if between multiple server locations the
        change attribute of a file of the file system is continuous,
        the client does not have to invalidate the file's cache if
        the change attribute is the same among all locations).
      </t>    
      <t>    
        File system identity information that indicates when multiple
        replicas, from the client's point of view, correspond to the
        same target file system, allowing them to be used
        interchangeably, without disruption, as multiple paths to the
        same thing.
      </t>    
      <t>    
        Information that will bear on the suitability of various
        replicas, depending on the use that the client intends.  For
        example, many applications need an absolutely up-to-date copy
        (e.g., those that write), while others may only need access to
        the most up-to-date copy reasonably available.
      </t>    
      <t>    
        Server-derived preference information for replicas, which can
        be used to implement load-balancing while giving the client
        the entire file system list to be used in case the primary fails.
      </t>    
     </list>
    </t>
    <t>
      The fs_locations_info attribute is structured similarly to the
      fs_locations attribute.  A top-level structure
      (fs_locations_info4) contains the entire attribute including the root
      pathname of the file system and an array of lower-level structures that
      define replicas that share a common rootpath on their respective
      servers.  The lower-level structure in turn
      (fs_locations_item4) contains a specific pathname and information on one
      or more individual server replicas.  For that last lowest-level,
      fs_locations_info has an fs_locations_server4
      structure that contains per-server-replica information in addition
      to the server name.  This per-server-replica information includes a
      nominally opaque array, fls_info, in which specific pieces of information
      are located at the specific indices listed below.
    </t>
    <t>
      The attribute will always contain at least a single fs_locations_server
      entry.  Typically, this will be an entry with the FS4LIGF_CUR_REQ
      flag set, although in the case of a referral there will be no
      entry with that flag set.
    </t>
    <t>
      It should be noted that fs_locations_info attributes returned by
      servers for various replicas may differ for various reasons.
      One server may know about a set of replicas that are not known to
      other servers.  Further, compatibility attributes may differ.
      Filehandles might be of the same class going from replica A to
      replica B but not going in the reverse direction.  This might happen 
      because the filehandles are the same, but
      replica B's server implementation might not have provision to note
      and report that equivalence.
    </t>
    <t>
      The fs_locations_info attribute consists of a root
      pathname (fli_fs_root, just like fs_root in the
      fs_locations attribute), together with an array of
      fs_location_item4 structures.  The fs_location_item4
      structures in turn consist of a root pathname
      (fli_rootpath) together with an array (fli_entries)
      of elements of data type fs_locations_server4,
      all defined as follows.

    </t>
<figure>
 <artwork>
/*
 * Defines an individual server replica
 */
struct  fs_locations_server4 {
        int32_t         fls_currency;
        opaque          fls_info&lt;>;
        utf8str_cis     fls_server;
};

/*
 * Byte indices of items within
 * fls_info: flag fields, class numbers,
 * bytes indicating ranks and orders.
 */
const FSLI4BX_GFLAGS            = 0;
const FSLI4BX_TFLAGS            = 1;

const FSLI4BX_CLSIMUL           = 2;
const FSLI4BX_CLHANDLE          = 3;
const FSLI4BX_CLFILEID          = 4;
const FSLI4BX_CLWRITEVER        = 5;
const FSLI4BX_CLCHANGE          = 6;
const FSLI4BX_CLREADDIR         = 7;

const FSLI4BX_READRANK          = 8;
const FSLI4BX_WRITERANK         = 9;
const FSLI4BX_READORDER         = 10;
const FSLI4BX_WRITEORDER        = 11;

/*
 * Bits defined within the general flag byte.
 */
const FSLI4GF_WRITABLE          = 0x01;
const FSLI4GF_CUR_REQ           = 0x02;
const FSLI4GF_ABSENT            = 0x04;
const FSLI4GF_GOING             = 0x08;
const FSLI4GF_SPLIT             = 0x10;

/*
 * Bits defined within the transport flag byte.
 */
const FSLI4TF_RDMA              = 0x01;

/*
 * Defines a set of replicas sharing
 * a common value of the rootpath
 * with in the corresponding
 * single-server namespaces.
 */
struct  fs_locations_item4 {
        fs_locations_server4    fli_entries&lt;>;
        pathname4               fli_rootpath;
};

/*
 * Defines the overall structure of
 * the fs_locations_info attribute.
 */
struct  fs_locations_info4 {
        uint32_t                fli_flags;
        int32_t                 fli_valid_for;
        pathname4               fli_fs_root;
        fs_locations_item4      fli_items&lt;>;
};

/*
 * Flag bits in fli_flags.
 */
const FSLI4IF_VAR_SUB           = 0x00000001;

typedef fs_locations_info4 fattr4_fs_locations_info;
 </artwork>
</figure>
    <t>
      As noted above, the fs_locations_info attribute, when supported, may
      be requested of absent file systems without causing NFS4ERR_MOVED to
      be returned.  It is generally expected that it will be available for
      both present and absent file systems even if only a single
      fs_locations_server4 entry is present, designating the current (present)
      file system, or two fs_locations_server4 entries designating the 
      previous location of an absent file system (the one just referenced) and its
      successor location.  Servers are strongly urged to support this
      attribute on all file systems if they support it on any file system.
    </t>
    <t>
      The data presented in the fs_locations_info attribute may be obtained
      by the server in any number of ways, including specification by
      the administrator or by current protocols for transferring data
      among replicas and protocols not yet developed.  NFSv4.1 only defines how this information is presented by the server to
      the client.
    </t>
    <section anchor="fs_locations_server4" 
             title="The fs_locations_server4 Structure">
      <t>
        The fs_locations_server4 structure consists of the following items:
      </t>
      <t>
       <list style='symbols'>
        <t>    
          An indication of how up-to-date the file system is (fls_currency) in
          seconds.  This value
          is relative to the master copy.  A negative
          value indicates that the server is unable to give any
          reasonably useful value here.  A value of zero indicates that the
          file system is the actual writable data or a reliably coherent
          and fully up-to-date copy.  Positive values indicate how 
          out-of-date this copy can normally be before it is considered for
          update.  Such a value is not a guarantee that such updates
          will always be performed on the required schedule but instead
          serves as a hint about how far the copy of the data would be
          expected to be behind the most up-to-date copy.
        </t>    
        <t>    
          A counted array of one-byte values (fls_info) containing
          information about the particular file system instance.  This
          data includes general flags, transport capability flags,
          file system equivalence class information, and selection
          priority information.  The encoding will be discussed below.  
        </t>    
        <t>    
          The server string (fls_server).  For the case of the
          replica currently
          being accessed (via GETATTR), a zero-length string MAY be used to
          indicate the current address being used for the RPC call.
          The fls_server field can also be an IPv4 or IPv6 address,
          formatted the same way as an IPv4 or IPv6 address in the "server"
          field of the fs_location4 data type (see <xref target="fs_locations"/>).
        </t>
       </list>
      </t>
      <t>
        Data within the fls_info array is in the form of 8-bit data items
        with constants giving the offsets within the array of various
        values describing this particular file system instance.  
        This style of
        definition was chosen, in preference to explicit XDR
        structure definitions for these values, for a number of
        reasons.
      </t>
      <t>
       <list style='symbols'>
        <t>
          The kinds of data in the fls_info array, representing flags, 
          file system classes, and priorities among sets of file systems
          representing the same data, are such that 8 bits provide
          a quite acceptable range of values.  Even where there might 
          be more than 256 such file system instances, having more than
          256 distinct classes or priorities is unlikely.
        </t>
        <t>
          Explicit definition of the various specific data items within
          XDR would limit expandability in that any extension within
          a subsequent minor version would require yet another attribute,
          leading to specification and implementation clumsiness.
        </t>
        <t>
          Such explicit definitions would also make it impossible to 
          propose Standards Track extensions apart from a full minor version.
        </t>
       </list>
      </t>
      <t>
        This encoding scheme can be adapted to the specification of
        multi-byte numeric values, even though none are currently
        defined.  If extensions are made via Standards Track RFCs,
        multi-byte quantities will be encoded as a range of bytes 
        with a range of indices, with the byte interpreted in big-endian
        byte order.  Further, any such index assignments are constrained
        so that the relevant quantities will not cross XDR word boundaries.
      </t>
      <t>
        The set of fls_info data is subject to expansion in a future minor 
        version, or in a Standards Track RFC, within the context of a single
        minor version.  The server SHOULD NOT send and the client MUST NOT
        use indices within the fls_info array that are not defined in 
        Standards Track RFCs.
      </t> 
      <t>
         The fls_info array contains:
      </t>
      <t>
       <list style='symbols'>
         <t>
           Two 8-bit flag fields, one devoted to general file-system
           characteristics and a second reserved for transport-related
           capabilities.
         </t>
         <t>
           Six 8-bit class values that define various file system
           equivalence classes as explained below.
         </t>
         <t>
           Four 8-bit priority values that govern file system selection
           as explained below.
         </t>
       </list>
      </t>
      <t>
        The general file system characteristics flag (at byte index
        FSLI4BX_GFLAGS) has the following
        bits defined within it:
      </t>
      <t>
       <list style='symbols'>
        <t>
          FSLI4GF_WRITABLE indicates that this file system target is writable,
          allowing it to be selected by clients that may need to write
          on this file system.  When the current file system instance
          is writable and is defined as of the same simultaneous use 
          class (as specified by the value at index FSLI4BX_CLSIMUL) 
          to which the client was previously writing, then it must
          incorporate within its data any committed
          write made on the source file system instance.  See
          <xref target="transition_verifier" />, which discusses
          the write-verifier class.  While there is no harm in not setting
          this flag for a file system that turns out to be writable,
          turning the flag on for a read-only file system can cause
          problems for clients that select a migration or replication
          target based on the flag and then find themselves unable to write.
        </t>
        <t>
          FSLI4GF_CUR_REQ indicates that this replica is the one on which
          the request is being made.  Only a single server entry may
          have this flag set and, in the case of a referral, no entry
          will have it.
        </t>
        <t>
          FSLI4GF_ABSENT indicates that this entry corresponds to an absent
          file system replica.  It can only be set if FSLI4GF_CUR_REQ is set.
          When both such bits are set, it indicates that a file system
          instance is not usable but that the information in the entry
          can be used to determine the sorts of continuity available
          when switching from this replica to other possible replicas.
          Since this bit can only be true if FSLI4GF_CUR_REQ is true, the
          value could be determined using the fs_status attribute, but
          the information is also made available here for the
          convenience of the client.  An entry with this bit, since it
          represents a true file system (albeit absent), does not appear
          in the event of a referral, but only when a file system has
          been accessed at this location and has subsequently been migrated.
        </t>
        <t>
          FSLI4GF_GOING indicates that a replica, while still available,
          should not be used further.  The client, if using it, should
          make an orderly transfer to another file system instance as
          expeditiously as possible.  It is expected that file systems
          going out of service will be announced as FSLI4GF_GOING some time
          before the actual loss of service. It is also expected that the fli_valid_for value
          will be sufficiently small to allow clients to detect and act
          on scheduled events, while large enough that the cost of the
          requests to fetch the fs_locations_info values will not be
          excessive.  Values on the order of ten minutes seem
          reasonable.

          <vspace blankLines='1' />
          When this flag is seen as part of a transition into a new
          file system, a client might choose to transfer immediately 
          to another replica, or it may reference the current file system
          and only transition when a migration event occurs.  Similarly,
          when this flag appears as a replica in the referral, clients
          would likely avoid being referred to this instance whenever
          there is another choice.
        </t>
        <t>
          FSLI4GF_SPLIT indicates that when a transition occurs from
          the current file system instance to this one, the replacement 
          may consist of multiple file systems.  In this case, the 
          client has to be prepared for the possibility that objects 
          on the same file system before migration will be on different ones 
          after.  Note that FSLI4GF_SPLIT is not incompatible with the
          file systems belonging to the same fileid
          class
          since, if one has a set of fileids that are unique within
          a file system, each subset assigned to a smaller file system after migration
          would not have any conflicts internal to that file system.
          <vspace blankLines='1' />
          A client, in the case of a split file system, will interrogate
          existing files with which it has continuing connection (it 
          is free to simply forget cached filehandles).  If the client
          remembers the directory filehandle associated with each open
          file, it may proceed upward using LOOKUPP to find the new file system
          boundaries.  Note that in the event of a referral, there will
          not be any such files and so these actions will not be performed.
	  Instead, a reference to a portion of the original
	  file system now split off into other file systems
	  will encounter an fsid change and possibly a
	  further referral.

          <vspace blankLines='1' />
          Once the client recognizes that one file system has been split 
          into two, it can prevent the disruption of running applications
          by presenting the two file systems as a single
          one until a convenient point to recognize the transition,
          such as a restart.  This would require a mapping
          from the server's fsids to fsids as seen by the client, but 
          this is already necessary for other reasons.  As noted 
          above, existing fileids within the two descendant file systems
          will not conflict.  Providing non-conflicting fileids for 
          newly created files on the split file systems
          is the responsibility of the server (or servers working in 
          concert).  The server can encode filehandles such
          that filehandles generated before the split event can be discerned
          from those generated after the split,
          allowing the server to determine when the need
          for emulating two file systems as one is over. 
          <vspace blankLines='1' />
          Although it is possible for this flag to be present in the
          event of referral, it would generally be of little interest
          to the client, since the client is not expected to have
          information regarding the current contents of the absent
          file system. 
        </t>
       </list>        
      </t>
      <t>
        The transport-flag field (at byte index FSLI4BX_TFLAGS) contains 
        the following bits related to the transport
        capabilities of the specific file system.
      </t>
      <t>
       <list style='symbols'>
        <t>
          FSLI4TF_RDMA indicates that this file system provides NFSv4.1
          file system access using an RDMA-capable transport.
        </t>
       </list>
      </t>
      <t>
        Attribute continuity and file system identity information are 
        expressed by defining equivalence relations on the sets of
        file systems presented to the client.  Each such relation
        is expressed as a set of file system equivalence classes.
        For each relation, a file system has an 8-bit class number.
        Two file systems belong to the same class if both have 
        identical non-zero class numbers.  Zero is treated as 
        non-matching.  Most often, 
        the relevant question for the client will be whether a
        given replica is identical to / continuous with the current one in a
        given respect, but the information should be available also as to
        whether two other replicas match in that respect as well.
      </t>
      <t>
        The following fields specify the file system's class numbers
        for the equivalence relations used in determining the nature of
        file system transitions.  See 
        <xref target='effecting_transitions' />  and its various subsections
        for details about how
        this information is to be used.  Servers may assign these values
        as they wish, so long as file system instances that share the 
        same value have the specified relationship to one another;
        conversely, file systems that have the specified relationship
        to one another share a common class value. As each instance
        entry is added, the relationships of this instance to previously
        entered instances can be consulted, and if one is found that
        bears the specified relationship, that entry's class value can
        be copied to the new entry.  When no such previous entry exists,
        a new value for that byte index (not previously used) can be 
        selected, most likely by incrementing the value of the last class
        value assigned for that index. 
      </t>
      <t>
       <list style='symbols'>
        <t>
          The field with byte index FSLI4BX_CLSIMUL defines the 
          simultaneous-use class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLHANDLE defines the handle
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLFILEID defines the fileid
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLWRITEVER defines the
          write-verifier class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLCHANGE defines the change
          class for the file system.
        </t>
        <t>
          The field with byte index FSLI4BX_CLREADDIR defines the readdir
          class for the file system.
        </t>
       </list>
      </t>
      <t>     
        Server-specified preference information is also provided via
        8-bit values within the fls_info array.  The values provide a 
        rank and an order (see below) to be used with separate values
        specifiable for the cases of read-only and writable file 
        systems.  
        These values are compared
        for different file systems to establish the server-specified 
        preference, with lower values indicating "more preferred".
      </t>
      <t>
        Rank is used to express a strict server-imposed ordering on
        clients, with lower values indicating "more preferred".  Clients
        should attempt to use all replicas with a given rank before they
        use one with a higher rank.  Only if all of those file systems are
        unavailable should the client proceed to those of a higher rank.
        Because specifying a rank will override client preferences, servers
        should be conservative about using this mechanism, particularly
        when the environment is one in which client communication characteristics
        are neither tightly controlled nor visible to the server.
      </t>
      <t>
        Within a rank, the order value is used to specify the server's
        preference to guide the client's selection when the client's own
        preferences are not controlling, with lower values of order
        indicating "more preferred".  If replicas are approximately equal
        in all respects, clients should defer to the order specified by the
        server.  When clients look at server latency as part of their
        selection, they are free to use this criterion but it is suggested
        that when latency differences are not significant, the
        server-specified order should guide selection.

      </t>
      <t>
       <list style='symbols'>
        <t>
          The field at byte index FSLI4BX_READRANK gives the rank value to
          be used for read-only access. 
        </t>
        <t>
          The field at byte index FSLI4BX_READORDER gives the order value to
          be used for read-only access. 
        </t>
        <t>
          The field at byte index FSLI4BX_WRITERANK gives the rank value to
          be used for writable access. 
        </t>
        <t>
          The field at byte index FSLI4BX_WRITEORDER gives the order value to
          be used for writable access. 
        </t>
       </list>
      </t>
      <t>
        Depending on the potential need for write access by a given client,
        one of the pairs of rank and order values is used. 
        The read rank and order should only be used
        if the client knows that only reading will ever be done or if it is
        prepared to switch to a different replica in the event that any
        write access capability is required in the future.  
      </t>
    </section>
    <section anchor="fs_locations_info4" 
             title="The fs_locations_info4 Structure">
      <t>
        The fs_locations_info4 structure, encoding the fs_locations_info
        attribute, contains the following:
      </t>
      <t>
       <list style='symbols'>
        <t>
          The fli_flags field, which contains general flags that affect 
          the interpretation of this fs_locations_info4 structure and
          all fs_locations_item4 structures within it.  The only flag
          currently defined is FSLI4IF_VAR_SUB.  All bits in the
	  fli_flags field that are not defined should always be returned as zero.
        </t>
        <t>
          The fli_fs_root field, which contains the pathname of the root of
          the current file system on the current server, just as it does
          in the fs_locations4 structure.
        </t>
        <t>
          An array called fli_items of fs_locations4_item structures, which contain
          information about replicas of the current file system.  Where
          the current file system is actually present, or has been
          present, i.e., this is not a referral situation, one of the
          fs_locations_item4 structures will contain an fs_locations_server4 for
          the current server.  This structure will have FSLI4GF_ABSENT set
          if the current file system is absent, i.e., normal access to it
          will return NFS4ERR_MOVED.
        </t>
        <t>
          The fli_valid_for field specifies a time in seconds
          for which it is reasonable for a client to use the fs_locations_info attribute
          without refetch.  The fli_valid_for value does not provide a
          guarantee of validity since servers can unexpectedly go out of
          service or become inaccessible for any number of reasons.
          Clients are well-advised to refetch this information for an
          actively accessed file system at every fli_valid_for seconds.  This
          is particularly important when file system replicas may go out
          of service in a controlled way using the FSLI4GF_GOING flag to
          communicate an ongoing change.  The server should set
          fli_valid_for to a value that allows well-behaved clients to
          notice the FSLI4GF_GOING flag and make an orderly switch before
          the loss of service becomes effective.  If this value is zero,
          then no refetch interval is appropriate and the client need
          not refetch this data on any particular schedule.
          In the event of a transition to a new file system instance, a
          new value of the fs_locations_info attribute will be fetched at
          the destination.  It is to be expected that this may have a
          different fli_valid_for value, which the client should then use
          in the same fashion as the previous value.
        </t>
       </list>
      </t>
      <t>
        The FSLI4IF_VAR_SUB flag within fli_flags controls whether variable
        substitution is to be enabled.  See <xref target="fs_locations_item4" />
        for an explanation of variable substitution.
      </t>
    </section>
    <section anchor="fs_locations_item4" 
             title="The fs_locations_item4 Structure">
      <t>
        The fs_locations_item4 structure contains a pathname 
        (in the field fli_rootpath) that encodes
        the path of the target file system replicas on the set of 
        servers designated by the included fs_locations_server4 entries.
        The precise manner in which this target location
        is specified depends on the value of the FSLI4IF_VAR_SUB
        flag within the associated fs_locations_info4 structure. 
      </t>
      <t>
        If this flag is not set, then fli_rootpath simply designates
        the location of the target file system within each server's
        single-server namespace just as it does for the rootpath
        within the fs_location4 structure.  When this bit is set,
        however, component entries of a certain form are subject
        to client-specific variable substitution so as to allow
        a degree of namespace non-uniformity in order to accommodate
        the selection of client-specific file system targets to
        adapt to different client architectures or other
        characteristics.
      </t>
      <t>
        When such substitution is in effect, a variable beginning
        with the string "${" and ending with the string "}"
        and containing a colon is to be
        replaced by the client-specific value associated with
        that variable.  The string "unknown" should be used 
        by the client when it has no value for such a variable.
        The pathname resulting from such
        substitutions is used to designate the target file system,
        so that different clients may have different file systems,
        corresponding to that location in the multi-server namespace.
      </t>
      <t>
        As mentioned above, such substituted pathname variables
        contain a colon.  The part before the colon is to be a
        DNS domain name, and the part after is to be a case-insensitive
        alphanumeric string.
      </t>
      <t> 
        Where the domain is "ietf.org", only variable names defined
        in this document or subsequent Standards Track RFCs
        are subject to such substitution.  Organizations are
        free to use their domain names to create their own sets
        of client-specific variables, to be subject to such
        substitution.  In cases where such variables are intended
        to be used more broadly than a single organization, 
        publication of an Informational RFC defining such variables
        is RECOMMENDED. 
      </t>
      <t>
        The variable ${ietf.org:CPU_ARCH} is used to denote that the
        CPU architecture object files are compiled.  This specification
        does not limit the acceptable values (except that they must be
        valid UTF-8 strings), but such values as "x86", "x86_64", and "sparc"
        would be expected to be used in line with industry practice.
      </t>
      <t>
        The variable ${ietf.org:OS_TYPE} is used to denote the 
        operating system, and thus the kernel and library APIs,
        for which code might be compiled.  This specification does
        not limit the acceptable values (except that they must be
        valid UTF-8 strings), but such values as "linux" and "freebsd"
        would be expected to be used in line with industry practice.
      </t>
      <t>
        The variable ${ietf.org:OS_VERSION} is used to denote the 
        operating system version, and thus the specific details
        of versioned interfaces,
        for which code might be compiled.  This specification does
        not limit the acceptable values (except that they must be
        valid UTF-8 strings). However, combinations of numbers and 
        letters with interspersed dots would be expected to be used
        in line with industry practice, with the details of the 
        version format depending on the specific value of
        the variable ${ietf.org:OS_TYPE} with which
        it is used.
      </t>
      <t>
        Use of these variables could result in the direction of different
        clients to different file systems on the same server, as
        appropriate to particular clients.  In cases in which the
        target file systems are located on different servers, a single
        server could serve as a referral point so that each valid
        combination of variable values would designate a referral
        hosted on a single server, with the targets of those referrals on
        a number of different servers.
      </t>
      <t>
        Because namespace administration is affected by the values
        selected to substitute for various variables, clients should
        provide convenient means of determining what variable 
        substitutions a client will implement, as well as, where
        appropriate, providing means to control the substitutions to
        be used.  The exact means by which this will be done is 
        outside the scope of this specification.
      </t>
      <t>
        Although variable substitution is most suitable for use
        in the context of referrals, it may be used in the context
        of replication and migration.  If it is used in these contexts,
        the server must ensure that no matter what values the
        client presents for the substituted variables, the result 
        is always a valid successor file system instance to that
        from which a transition is occurring, i.e., that the data is
        identical or represents a later image of a writable file
        system. 
      </t>
      <t>
        Note that when fli_rootpath is a null pathname (that is, one
        with zero components), the file system designated is at the
        root of the specified server, whether or not the FSLI4IF_VAR_SUB
        flag within the associated fs_locations_info4 structure is 
        set. 
      </t>
    </section>
  </section>
  <section anchor="fs_status" title="The Attribute fs_status">
     <t>
       In an environment in which multiple copies of the same basic set of
       data are available, information regarding the particular source of
       such data and the relationships among different copies can be very
       helpful in providing consistent data to applications.
     </t>

<figure>
 <artwork>
enum fs4_status_type {
        STATUS4_FIXED = 1,
        STATUS4_UPDATED = 2,
        STATUS4_VERSIONED = 3,
        STATUS4_WRITABLE = 4,
        STATUS4_REFERRAL = 5
};

struct fs4_status {
        bool            fss_absent;
        fs4_status_type fss_type;
        utf8str_cs      fss_source;
        utf8str_cs      fss_current;
        int32_t         fss_age;
        nfstime4        fss_version;
};
 </artwork>
</figure>

    <t>
      The boolean fss_absent indicates whether the file system is 
      currently absent.  This value will be set if the file system was
      previously present and becomes absent, or if the file system has
      never been present and the type is STATUS4_REFERRAL.  When this
      boolean is set and the type is not STATUS4_REFERRAL, the 
      remaining information in the fs4_status reflects that last valid 
      when the file system was present.
    </t>
    <t>
      The fss_type field indicates the kind of file system image represented.
      This is of particular importance when using the version values to
      determine appropriate succession of file system images.  
      When fss_absent is set, and the file system was previously 
      present, the value of fss_type reflected is that when the file was last present. 
      Five values are distinguished:
    </t>
    <t>
     <list style='symbols'>
      <t>
        STATUS4_FIXED, which indicates a read-only image in the sense
        that it will never change.  The possibility is allowed that, as
        a result of migration or switch to a different image, changed
        data can be accessed, but within the confines of this instance,
        no change is allowed.  The client can use this fact to
        cache aggressively.
      </t>
      <t>
        STATUS4_VERSIONED, which indicates that the image, like the
        STATUS4_UPDATED case, is updated externally, but it provides
        a guarantee that the server will carefully update an
        associated version value so that the client can
        protect itself from a situation in which it reads
        data from one version of the file system and then later reads
        data from an earlier version of the same file system.  See
        below for a discussion of how this can be done.
      </t>
      <t>
        STATUS4_UPDATED, which indicates an image that cannot be
        updated by the user writing to it but that may be changed
        externally, typically because it is a periodically updated
        copy of another writable file system somewhere else.  In 
        this case, version information is not provided, and the 
        client does not have the responsibility of making sure 
        that this version only advances upon a file system instance
        transition.  In this case, it is the responsibility of the
        server to make sure that the data presented after a file
        system instance transition is a proper successor image and
        includes all changes seen by the client and any change made
        before all such changes.
      </t>
      <t>
        STATUS4_WRITABLE, which indicates that the file system is an
        actual writable one.  The client need not, of course, actually
        write to the file system, but once it does, it should not
        accept a transition to anything other than a writable instance
        of that same file system.
      </t>
      <t>
        STATUS4_REFERRAL, which indicates that the file system in
        question is absent and has never been present on this
        server.
      </t>
     </list>
    </t>
    <t>
      Note that in the STATUS4_UPDATED and STATUS4_VERSIONED cases, the
      server is responsible for the appropriate handling of locks that
      are inconsistent with external changes to delegations.
      If a server gives out delegations, they SHOULD be recalled
      before an inconsistent change is made to the data, and MUST
      be revoked if this is not possible.  Similarly, if an OPEN is
      inconsistent with data that is changed (the OPEN has
      OPEN4_SHARE_DENY_WRITE/OPEN4_SHARE_DENY_BOTH
      and the data is changed), that OPEN SHOULD be considered
      administratively revoked.
    </t>
    <t>
      The opaque strings fss_source and fss_current provide a way of presenting
      information about the source of the file system image being present.
      It is not intended that the client do anything with this information
      other than make it available to administrative tools.  It is
      intended that this information be helpful when researching possible
      problems with a file system image that might arise when it is
      unclear if the correct image is being accessed and, if not, how that
      image came to be made.  This kind of diagnostic information will be
      helpful, if, as seems likely, copies of file systems are made in
      many different ways (e.g., simple user-level copies, 
      file-system-level point-in-time copies, 
      clones of the underlying storage),
      under a variety of administrative arrangements.  In such
      environments, determining how a given set of data was constructed
      can be very helpful in resolving problems.
    </t>
    <t>
      The opaque string fss_source is used to indicate the source of a
      given file system with the expectation that tools capable of
      creating a file system image propagate this information, when
      possible.  It is understood that this may not always be possible
      since a user-level copy may be thought of as creating a new data
      set and the tools used may have no mechanism to propagate this
      data.  When a file system is initially created, it is desirable 
      to associate with it
      data regarding how the file system was created, where it was
      created, who created it, etc. Making this information available 
      in this attribute in a human-readable 
      string will be helpful for applications and 
      system administrators and will also serve to make it available when
      the original file system is used to make subsequent copies.
    </t>
    <t>
      The opaque string fss_current should provide whatever information is
      available about the source of the current copy.  Such
      information includes
      the tool creating it, any relevant parameters to that tool, the
      time at which the copy was done, the user making the change, the
      server on which the change was made, etc.  All information should be
      in a human-readable string.
    </t>
    <t>
      The field fss_age provides an indication of how out-of-date the file system 
      currently is with respect to its ultimate data source (in case of 
      cascading data updates).  This complements the fls_currency field of 
      fs_locations_server4 (see <xref target='fs_locations_info' />) in the 
      following way: the information in fls_currency
      gives a bound for how out of date the data in a file system might 
      typically get, while the value in fss_age gives a bound on how out-of-date that 
      data actually is.  Negative values imply that no information is 
      available.  A zero means that this data is known to be current.
      A positive value means that this data is known to be no older than 
      that number of seconds with respect to the ultimate data source.
      Using this value, the client may be able to decide that a data copy
      is too old, so that it may search for a newer version to use.
    </t>
    <t>
      The fss_version field provides a version identification, in the form of
      a time value, such that successive versions always have later time
      values.  When the fs_type is anything other than
      STATUS4_VERSIONED, the server may provide such a value, but there is
      no guarantee as to its validity and clients will not use it except
      to provide additional information to add to fss_source and fss_current.
    </t>
    <t>
      When fss_type is STATUS4_VERSIONED, servers SHOULD provide a value
      of fss_version that progresses monotonically whenever any new version
      of the data is established.  This allows the client, if reliable
      image progression is important to it, to fetch this attribute as
      part of each COMPOUND where data or metadata from the file system is
      used.
    </t>
    <t>
      When it is important to the client to make sure that only valid
      successor images are accepted, it must make sure that it does not
      read data or metadata from the file system without updating its
      sense of the current state of the image. This is to avoid the possibility
      that the fs_status that the client holds will be one for an
      earlier image, which would cause the client to accept a new file
      system instance that is later than that but still earlier than
      the updated data read by the client.
    </t>
    <t>
      In order to accept valid images reliably, the client must do a GETATTR of the fs_status
      attribute that follows any interrogation of data or metadata within the
      file system in question.  Often this is most conveniently done by
      appending such a GETATTR after all other operations that reference
      a given file system.  When errors occur between reading file system
      data and performing such a GETATTR, care must be exercised to make
      sure that the data in question is not used before obtaining the
      proper fs_status value.  In this connection, when an OPEN is done
      within such a versioned file system and the associated GETATTR of
      fs_status is not successfully completed, the open file in question
      must not be accessed until that fs_status is fetched.
    </t>
    <t>
      The procedure above will ensure that before using any data from the
      file system the client has in hand a newly-fetched current version
      of the file system image.  Multiple values for multiple requests in
      flight can be resolved by assembling them into the required partial
      order (and the elements should form a total order within the
      partial order) and
      using the last.  
The client may then, when switching among
      file system instances, decline to use an instance that does not have
      an fss_type of STATUS4_VERSIONED or whose fss_version field is earlier than the
      last one obtained from the predecessor file system instance.
    </t>
  </section>
</section>
<!-- $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $ -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Parallel NFS (pNFS)" anchor="pnfs">
<section title="Introduction" anchor="pnfs_intro">
<t>
  pNFS is an OPTIONAL feature within NFSv4.1; the pNFS feature
  set allows direct client access to the storage devices containing
  file data.  When file data for a single NFSv4 server is stored on
  multiple and/or higher-throughput storage devices (by comparison to
  the server's throughput capability), the result can be significantly
  better file access performance.  The relationship among multiple
  clients, a single server, and multiple storage devices for pNFS
  (server and clients have access to all storage devices) is shown in
  <xref target="fig_system"/>.
</t>
<figure anchor="fig_system">
<artwork><![CDATA[
    +-----------+
    |+-----------+                                 +-----------+
    ||+-----------+                                |           |
    |||           |        NFSv4.1 + pNFS          |           |
    +||  Clients  |<------------------------------>|   Server  |
     +|           |                                |           |
      +-----------+                                |           |
           |||                                     +-----------+
           |||                                           |
           |||                                           |
           ||| Storage        +-----------+              |
           ||| Protocol       |+-----------+             |
           ||+----------------||+-----------+  Control   |
           |+-----------------|||           |    Protocol|
           +------------------+||  Storage  |------------+
                               +|  Devices  |
                                +-----------+
]]></artwork>
</figure>
<t>
  In this model, the clients, server, and storage devices are
  responsible for managing file access.  This is in contrast to NFSv4
  without pNFS, where it is primarily the server's responsibility; some
  of this responsibility may be delegated to the client under strictly
  specified conditions. See <xref target="storage_protocol"/>
  for a discussion of the Storage Protocol. See <xref target="control_protocol"/> for a
  discussion of the Control Protocol. 
</t>
<t>
  pNFS takes the form of OPTIONAL operations that manage protocol
  objects called 'layouts' (<xref target="layout_types"/>) that
  contain a byte-range and storage location information.  The layout
  is managed in a similar fashion
  as NFSv4.1 data delegations.  For example, the layout is leased,
  recallable, and revocable.  However, layouts are distinct abstractions
  and are manipulated with new operations.  When a client holds a
  layout, it is granted the ability to directly access the byte-range
  at the storage location specified in the layout.

</t>
<t>
  There are interactions between layouts and other NFSv4.1
  abstractions such as data delegations and byte-range locking.
  Delegation issues are discussed in <xref
  target="recalling_layout"/>.  Byte-range locking issues are
  discussed in Sections <xref target="layout_iomode" format="counter" /> and <xref
  target="layout_semantics" format="counter" />.
</t>
</section>

<section title="pNFS Definitions">
<t>
  NFSv4.1's pNFS feature provides parallel data access to a
  file system that stripes its content across multiple
  storage servers.  The first instantiation of pNFS, as
  part of NFSv4.1, separates the file system protocol
  processing into two parts: metadata processing and data
  processing.  Data consist of the contents of regular
  files that are striped across storage servers. Data
  striping occurs in at least two ways:  on a file-by-file
  basis and, within sufficiently large files, on a
  block-by-block basis. In contrast, striped access to
  metadata by pNFS clients is not provided in NFSv4.1, even
  though the file system back end of a pNFS server might
  stripe metadata.  Metadata consist of everything else,
  including the contents of non-regular files (e.g.,
  directories); see <xref target="metadata"/>.  The
  metadata functionality is implemented by an NFSv4.1
  server that supports pNFS and the operations described in
  <xref target="nfsv41operations" />; such a server is
  called a metadata server (<xref target="mds"/>).

</t>
<t>
  The data functionality is implemented by one or more storage devices, each of which
  are accessed by the client via a storage protocol.  A subset (defined in <xref target="ds_ops"
  />) of NFSv4.1 is one such storage protocol.  New terms are
  introduced to the NFSv4.1 nomenclature and existing terms are
  clarified to allow for the description of the pNFS feature.

</t>

<section title="Metadata" anchor="metadata">
<t>
  Information about a file system object, such as its name, location
  within the namespace, owner, ACL, and other attributes.  Metadata may
  also include storage location information, and this will vary based
  on the underlying storage mechanism that is used.
</t>
</section>

<section title="Metadata Server" anchor="mds">
<t>
  An NFSv4.1 server that supports the pNFS feature.  A variety of
  architectural choices exist for the metadata server and its use of
  file system information held at the server.  Some servers may
  contain metadata only for file objects residing at the
  metadata server, while the file data resides on associated storage
  devices.  Other metadata servers may hold both metadata and a
  varying degree of file data.

</t>
</section>

<section title="pNFS Client">
<t>
  An NFSv4.1 client that supports pNFS operations and supports at
  least one storage protocol for performing I/O
  to storage devices.
</t>
</section>

<section title="Storage Device">
<t>
  A storage device stores a regular file's data, but leaves metadata
  management to the metadata server.  A storage device could be
  another NFSv4.1 server, an object-based storage device (OSD), 
a block
  device accessed over a System Area Network (SAN, e.g., either
  FiberChannel or iSCSI SAN), or some other entity.
</t>
</section>

<section anchor="storage_protocol" title="Storage Protocol">
<t>
  As noted in <xref
  target="fig_system"/>, 
  the storage protocol is the method used by the client to
  store and retrieve data directly from the storage devices.
  </t>
  <t>

  The NFSv4.1 pNFS feature has been structured to allow for a variety
  of storage protocols to be defined and used.

  One example storage protocol is NFSv4.1 itself (as documented in <xref
  target="file_layout_type"/>).  Other options for the storage protocol
  are described elsewhere and include:
  <list style="symbols">
    <t>
      Block/volume protocols such as Internet SCSI (iSCSI) <xref target="RFC3720"
      /> and FCP <xref target="FCP-2" />.  The block/volume
      protocol support can be independent of the addressing structure
      of the block/volume protocol used, allowing more than one
      protocol to access the same file data and enabling extensibility
      to other block/volume protocols. See
      <xref target="RFC5663"/> for a layout
      specification that
      allows pNFS to use block/volume storage protocols.
    </t>
    <t>
      Object protocols such as OSD over iSCSI or Fibre Channel <xref
      target="OSD-T10" />. See
      <xref target="RFC5664"/> for a layout specification
      that allows pNFS to use object storage protocols.
    </t>
  </list>
</t>
<t>
  It is possible that various storage protocols are available to
  both client and server and it may be possible that a client and
  server do not have a matching storage protocol available to them.
  Because of this, the pNFS server MUST support normal NFSv4.1 access
  to any file accessible by the pNFS feature; this will allow for
  continued interoperability between an NFSv4.1 client and server.
</t>
</section>

<section anchor="control_protocol" title="Control Protocol">
<t>
  As noted in <xref
  target="fig_system"/>, 
  the control protocol is used by the exported file system between the
  metadata server and storage devices.  Specification of such
  protocols is outside the scope of the NFSv4.1 protocol.  Such
  control protocols would be used to control activities such as the
  allocation and deallocation of storage, the management of state
  required by the storage devices to perform client access control,
  and, depending on the storage protocol, the enforcement of
  authentication and authorization so that restrictions that
  would be enforced by the metadata server are also enforced by
  the storage device.
</t>
<t>
  A particular control protocol is not REQUIRED by NFSv4.1 but
  requirements are placed on the control protocol for maintaining
  attributes like modify time, the change attribute, and the end-of-file
  (EOF) position. Note that if pNFS is layered over a clustered, parallel
  file system (e.g., <xref target="PVFS">PVFS</xref>), the mechanisms that
  enable clustering and parallelism in that file system can be considered
  the control protocol.

</t>
</section>

<section anchor="layout_types" title="Layout Types">
<t>
  A layout describes the mapping of a file's data to the storage
  devices that hold the data.  A layout is said to belong to a
  specific layout type (data type layouttype4, see <xref
  target="layouttype4" />).  The layout type allows for variants to
  handle different storage protocols, such as those associated with
  block/volume <xref target="RFC5663" />, object <xref
  target="RFC5664" />, and file (<xref target="file_layout_type"
  />) layout types.  A metadata server, along with its control
  protocol, MUST support at least one layout type.  A private
  sub-range of the layout type namespace is also defined. Values from
  the private layout type range MAY be used for internal testing or
  experimentation (see <xref target="layouttype4"/>).
</t>
<t>
  As an example,  the organization of the file layout type could be
  an array of tuples (e.g., device ID, filehandle), along with a
  definition of how the data is
  stored across the devices (e.g., striping). A block/volume layout
  might be an array of tuples that store &lt;device ID, block number,
  block count&gt; 
along with information about block size and the
  associated file offset of the block number.  An object layout might
  be an array of tuples &lt;device ID, object ID&gt; and an additional
  structure (i.e., the aggregation map) that defines how the logical
  byte sequence of the file data is serialized into the different
  objects.  Note that the actual layouts are typically more complex
  than these simple expository examples.
</t>
<t>
  Requests for pNFS-related operations will often specify a layout 
  type.  Examples of such operations are GETDEVICEINFO and LAYOUTGET.
  The response for these operations will include structures such
  as a device_addr4 or a layout4, each of which includes a layout type within
  it.  The layout type sent by the server MUST always be the same
  one requested by the client.  When a server sends a response that
  includes a different layout type, the client SHOULD ignore the
  response and behave as if the server had returned an error response.
</t>
</section>

<section title="Layout" anchor="layout">
<t>
  A layout defines how a file's data is organized on one or more
  storage devices.  There are many potential layout types; each of the
  layout types are differentiated by the storage protocol used to
  access data and by the aggregation scheme that lays out the file
  data on the underlying storage devices.  A layout is precisely
  identified by the tuple &lt;client ID, filehandle, layout
  type, iomode, range&gt;, where filehandle refers to the filehandle
  of the file on the metadata server.
</t>
<t>
  It is important to define when layouts overlap and/or conflict with
  each other.  For two layouts with overlapping byte-ranges to
  actually overlap each other, both layouts must be of the same layout
  type, correspond to the same filehandle, and have the same iomode.
  Layouts conflict when they overlap and differ in the content of the
  layout (i.e., the storage device/file mapping parameters differ).
  Note that differing iomodes do not lead to conflicting layouts.  It
  is permissible for layouts with different iomodes, pertaining to the
  same byte-range, to be held by the same client.  An example of this
  would be copy-on-write functionality for a block/volume layout type.
</t>

</section>
<section title="Layout Iomode" anchor="layout_iomode">
<t>
  The layout iomode (data type layoutiomode4, see <xref
  target="layoutiomode4" />) indicates to the metadata server the
  client's intent to perform either just READ operations
  or a mixture containing READ
  and WRITE operations. For certain layout
  types, it is useful for a client to specify this intent at the time it sends LAYOUTGET
  (<xref target="OP_LAYOUTGET" />).  For example, for
  block/volume-based protocols, block allocation could occur when a
  LAYOUTIOMODE4_RW iomode is specified.  A special LAYOUTIOMODE4_ANY iomode is defined
  and can only be used for LAYOUTRETURN and CB_LAYOUTRECALL, not for
  LAYOUTGET.  It specifies that layouts pertaining to both LAYOUTIOMODE4_READ and
  LAYOUTIOMODE4_RW iomodes are being returned or recalled, respectively.
</t>
<t>
  A storage device may validate I/O with regard to the iomode; this
  is dependent upon storage device implementation and layout type.
  Thus, if the client's layout iomode is inconsistent with the I/O
  being performed, the storage device may reject the client's I/O with
  an error indicating that a new layout with the correct iomode should be
  obtained via LAYOUTGET.  For example, if a client gets a layout with a LAYOUTIOMODE4_READ iomode and
  performs a WRITE to a storage device, the storage device is allowed
  to reject that WRITE.
</t>
<t>
  The use of the layout iomode does not conflict with OPEN share modes or byte-range LOCK operations;
  open share mode and byte-range lock conflicts are enforced as they are without the
  use of pNFS and are logically separate from the pNFS layout level.
  Open share modes and byte-range locks are the preferred method for
  restricting user access to data files.  For example, an OPEN of
  OPEN4_SHARE_ACCESS_WRITE does not conflict with a LAYOUTGET containing an iomode
  of LAYOUTIOMODE4_RW performed by another client.  Applications that depend
  on writing into the same file concurrently may use byte-range locking to
  serialize their accesses.
</t>
</section>

<section title="Device IDs" anchor="device_ids">
  <t>
    The device ID (data type deviceid4, see
    <xref target="deviceid4"/>) identifies a group of storage devices. The scope
    of a device ID is the pair &lt;client ID, layout type&gt;. In practice, a
    significant amount of information may be required to fully address
    a storage device.  Rather than embedding all such information in a
    layout, layouts embed device IDs.  The NFSv4.1 operation
    GETDEVICEINFO (<xref target="OP_GETDEVICEINFO" />) is used to
    retrieve the complete address information (including
    all device addresses for the device ID) regarding the storage
    device according to its layout type and device ID.  For example,
    the address of an NFSv4.1 data server or of an object-based storage
    device could be an IP address and port.  The address of a block
    storage device could be a volume label.
  </t>
  <t>
    Clients cannot expect the mapping between a device ID and
    its storage device address(es) to persist across metadata server restart.
    See <xref target="mds_recovery" /> for a description of how
    recovery works in that situation.
  </t>
  <t>
    A device ID lives as long as there is a layout
    referring to the device ID.  If there are no layouts
    referring to the device ID, the server is free to
    delete the device ID any time.
    Once a device ID is deleted by the server, the server MUST NOT
    reuse the device ID for the same layout type and client ID again.
    This requirement is feasible because the device ID is 16 bytes
    long, leaving sufficient room to store a generation number if the
    server's implementation requires most of the rest of the device ID's
    content to be reused. This requirement is necessary because
    otherwise the race conditions between asynchronous notification
    of device ID addition and deletion would be too difficult to
    sort out.

  </t>
  <t>
    Device ID to device address mappings are not leased,
    and can be changed at any time. (Note that while
    device ID to device address mappings are likely
    to change after the metadata server restarts, the
    server is not required to change the mappings.)
    A server has two
    choices for changing mappings.  It can recall all
    layouts referring to the device ID or it can use a
    notification mechanism.

  </t>
  <t>
    The NFSv4.1 protocol has no optimal way to recall
    all layouts that referred to a particular device ID
    (unless the server associates a single device ID with
    a single fsid or a single client ID; in which case,
    CB_LAYOUTRECALL has options for recalling all layouts
    associated with the fsid, client ID pair, or just the
    client ID).

  </t>
  <t>
    Via a notification mechanism
    (see <xref target="OP_CB_NOTIFY_DEVICEID" />),
    device ID to device address mappings can change over the duration
    of server operation without recalling or revoking the layouts that
    refer to device ID. The notification mechanism can also delete
    a device ID, but only if the client has no layouts referring
    to the device ID.
    A notification of a change to a device ID to device address
    mapping will immediately or eventually invalidate some or all of
    the device ID's mappings.
    The server MUST support notifications and the client must
    request them before they can be used.  For further information
    about the notification types <xref target="OP_CB_NOTIFY_DEVICEID" />.

  </t>
</section>

</section>

<section title="pNFS Operations" anchor="pnfs_ops">
<t>
  NFSv4.1 has several operations that are needed for
  pNFS servers, regardless of layout type or storage
  protocol. These operations are all sent to a metadata
  server and summarized here. While pNFS is an OPTIONAL
  feature, if pNFS is implemented, some operations
  are REQUIRED in order to comply with pNFS. See <xref
  target="operation_mandlist"/>.
</t>
<t>
 These are the fore channel pNFS operations:

 <list style='hanging'>
 <t hangText="GETDEVICEINFO">
  (<xref target="OP_GETDEVICEINFO" />), as noted previously
  (<xref target="device_ids" />), returns the mapping of device ID to
  storage device address.
 </t>

 <t hangText="GETDEVICELIST">
  (<xref target="OP_GETDEVICELIST" />)
  allows clients to fetch all device IDs
  for a specific file system.
 </t>
 <t hangText="LAYOUTGET">
  (<xref target="OP_LAYOUTGET" />) is used by a client to get
  a layout for a file.
 </t>
 <t hangText="LAYOUTCOMMIT">
  (<xref target="OP_LAYOUTCOMMIT" />) is used
  to inform the metadata server of the client's intent to commit data
  that has been written to the storage device (the storage device as
  originally indicated in the return value of LAYOUTGET).
 </t>
 <t hangText="LAYOUTRETURN">
  (<xref target="OP_LAYOUTRETURN" />) is used
  to return layouts for a file, a file system ID (FSID), or a client ID.
 </t>
 </list>
</t>
<t>

  These are the backchannel pNFS operations:

  <list style='hanging'>
  <t hangText="CB_LAYOUTRECALL">
   (<xref target="OP_CB_LAYOUTRECALL" />) recalls
   a layout, all layouts belonging to a file system, or all
   layouts belonging to a client ID.
 </t>
 <t hangText="CB_RECALL_ANY">
  (<xref target="OP_CB_RECALL_ANY" />)
  tells a client that it needs to return some number of recallable
  objects, including layouts, to the metadata server.
 </t>
 <t hangText="CB_RECALLABLE_OBJ_AVAIL">
  (<xref target="OP_CB_RECALLABLE_OBJ_AVAIL" />) tells a client
  that a recallable object that it was denied (in case of
  pNFS, a layout denied by LAYOUTGET) due to resource exhaustion
  is now available.
 </t>
 <t hangText="CB_NOTIFY_DEVICEID">
   (<xref target="OP_CB_NOTIFY_DEVICEID" />) notifies the client of
   changes to device IDs.
 </t>
 </list>
</t>

</section>
<section title="pNFS Attributes" anchor="pnfs_attr">
<t>
 A number of attributes specific to pNFS are listed and described in
 <xref target="pnfs_attr_full" />.
</t>
</section>

<section title="Layout Semantics">

<section title="Guarantees Provided by Layouts" anchor="layout_semantics">
<t>
  Layouts grant to the client the ability to access data located at
  a storage device with the appropriate storage protocol.  The client
  is guaranteed the layout will be recalled when one of two things
  occur: either a conflicting layout is requested or the state
  encapsulated by the layout becomes invalid (this can happen when
  an event directly or indirectly modifies the layout).  When a layout
  is recalled and returned by the client, the client continues with
  the ability to access file data with normal NFSv4.1 operations
  through the metadata server.  Only the ability to access the storage
  devices is affected.
</t>
<t>
  The requirement of NFSv4.1 that all user access rights MUST be
  obtained through the appropriate OPEN, LOCK, and ACCESS operations
  is not modified with the existence of layouts.  Layouts are provided
  to NFSv4.1 clients, and user access still follows the rules of the
  protocol as if they did not exist.  It is a requirement that for a
  client to access a storage device, a layout must be held by the
  client.  If a storage device receives an I/O request for a byte-range for
  which the client does not hold a layout, the storage device SHOULD
  reject that I/O request.  Note that the act of modifying a file for
  which a layout is held does not necessarily conflict with the
  holding of the layout that describes the file being modified.
  Therefore, it is the requirement of the storage protocol or layout
  type that determines the necessary behavior.  For example,
  block/volume layout types require that the layout's
  iomode agree with the type of I/O being performed.
</t>
<t>
  Depending upon the layout type and storage protocol in use, storage
  device access permissions may be granted by LAYOUTGET and may be
  encoded within the type-specific layout.  For an example of storage
  device access permissions, see an object-based protocol such as <xref
  target="OSD-T10" />.  If access permissions are encoded within the
  layout, the metadata server SHOULD recall the layout when those
  permissions become invalid for any reason -- for example, when a file
  becomes unwritable or inaccessible to a client.  Note, clients are
  still required to perform the appropriate
  OPEN, LOCK, and ACCESS operations as described above.  The degree to which it is
  possible for the client to circumvent these operations and
  the consequences of doing so must be clearly specified by the
  individual layout type specifications.  In addition, these
  specifications must be clear about the requirements and
  non-requirements for the checking performed by the server.
</t>
<t>
  In the presence of pNFS functionality, mandatory byte-range locks MUST
  behave as they would without pNFS.  Therefore, if mandatory file
  locks and layouts are provided simultaneously, the storage device
  MUST be able to enforce the mandatory byte-range locks.  For example, if
  one client obtains a mandatory byte-range lock and a second client accesses the
  storage device, the storage device MUST appropriately restrict I/O
  for the range of the mandatory byte-range lock.  If the storage
  device is incapable of providing this check in the presence of
  mandatory byte-range locks, then the metadata server MUST NOT grant
  layouts and mandatory byte-range locks simultaneously.
</t>
</section>

<section title="Getting a Layout" anchor="obtaining_layout">
<t>
  A client obtains a layout with the
  LAYOUTGET operation.  The metadata server
  will grant layouts of a particular type
  (e.g., block/volume, object, or file).
  The client selects an appropriate layout
  type that the server supports and the client
  is prepared to use.  The layout returned to
  the client might not exactly match the
  requested byte-range as described in <xref
  target="OP_LAYOUTGET_DESCRIPTION"/>.  As needed a client
  may send multiple LAYOUTGET operations; these might result
  in multiple overlapping, non-conflicting layouts (see
  <xref target="layout"/>).

</t>
<t>
  In order to get a layout, the client must first have opened the file
  via the OPEN operation. When a client has no layout on a file, it
  MUST present an open stateid, a delegation stateid, or
  a byte-range lock stateid in the loga_stateid argument. A successful
  LAYOUTGET result includes a layout stateid. The first successful
  LAYOUTGET processed by the server using a non-layout stateid as an
  argument MUST have the "seqid" field of the layout stateid in the
  response set to one. Thereafter, the client MUST use a layout
  stateid (see <xref target="layout_stateid" />) on future invocations
  of LAYOUTGET on the file, and the "seqid" MUST NOT be set to
  zero.  Once the layout has been retrieved, it can be held across
  multiple OPEN and CLOSE sequences.  Therefore, a client may hold a
  layout for a file that is not currently open by any user on the
  client.  This allows for the caching of layouts beyond CLOSE.
</t>
<t>
  The storage protocol used by the client to access the data on the
  storage device is determined by the layout's type.  The client is
  responsible for matching the layout type with an available method to
  interpret and use the layout.  The method for this layout type
  selection is outside the scope of the pNFS functionality.
</t>
<t>
  Although the metadata server is in control
  of the layout for a file, the pNFS client
  can provide hints to the server when a file
  is opened or created about the preferred
  layout type and aggregation schemes.
  pNFS introduces a layout_hint attribute (<xref
  target="attrdef_layout_hint" />) 
  that the client can set at file creation
  time to provide a hint to the server for new
  files. Setting this attribute separately,
  after the file has been created might make
  it difficult, or impossible, for the server
  implementation to comply.
</t>
<t>
  Because the EXCLUSIVE4 createmode4 does not allow the
  setting of attributes at file creation time, NFSv4.1
  introduces the EXCLUSIVE4_1 createmode4, which does
  allow attributes to be set at file creation time. In
  addition, if the session is created with persistent
  reply caches, EXCLUSIVE4_1 is neither necessary
  nor allowed. Instead, GUARDED4 both works better and is
  prescribed. <xref target="exclusive_create" /> in <xref
  target="OP_OPEN_DESCRIPTION" /> summarizes how a client
  is allowed to send an exclusive create.

</t>
</section>

<section title="Layout Stateid" anchor="layout_stateid">
<t>
  As with all other stateids, the layout stateid consists of a "seqid" and
  "other" field. Once a layout stateid is established, the "other" field
  will stay constant unless the stateid is revoked or the client
  returns all layouts on the file and the server disposes of the
  stateid.  The "seqid" field is initially set to one, and is never
  zero on any NFSv4.1 operation that uses layout stateids, whether it
  is a fore channel or backchannel operation. After the layout stateid
  is established, the server increments by one the value of the
  "seqid" in each subsequent LAYOUTGET and LAYOUTRETURN response, and
  in each CB_LAYOUTRECALL request.
</t>
<t>
  Given the design goal of pNFS to provide parallelism, the layout
  stateid differs from other stateid types in that the client is
  expected to send LAYOUTGET and LAYOUTRETURN operations in parallel.
  The "seqid" value is used by the client to properly sort responses
  to LAYOUTGET and LAYOUTRETURN.  The "seqid" is also used to prevent
  race conditions between LAYOUTGET and CB_LAYOUTRECALL.  Given that the
  processing rules differ from layout stateids and other stateid
  types, only the pNFS sections of this document should be considered
  to determine proper layout stateid handling.
</t>
<t>
  Once the client receives a layout stateid, it MUST use the correct
  "seqid" for subsequent LAYOUTGET or LAYOUTRETURN operations.  The
  correct "seqid" is defined as the highest "seqid" value from
  responses of fully processed LAYOUTGET or LAYOUTRETURN operations or
  arguments of a fully processed CB_LAYOUTRECALL operation.  Since the
  server is incrementing the "seqid" value on each layout operation,
  the client may determine the order of operation processing by
  inspecting the "seqid" value.  In the case of overlapping layout
  ranges, the ordering information will provide the client the
  knowledge of which layout ranges are held.  Note that overlapping
  layout ranges may occur because of the client's specific requests or
  because the server is allowed to expand the range of a requested
  layout and notify the client in the LAYOUTRETURN results. Additional
  layout stateid sequencing requirements are provided in
  <xref target="pnfs_operation_sequencing"/>.
</t>
<t>
  The client's receipt of a "seqid" is not sufficient for subsequent
  use.  The client must fully process the operations before the
  "seqid" can be used.  For LAYOUTGET results, if
  the client is not using the forgetful model
  (<xref target="recall_robustness"/>), it MUST first update its
  record of what ranges of the file's layout it has before using the
  seqid. For LAYOUTRETURN results, the client MUST delete the range
  from its record of what ranges of the file's layout it had before
  using the seqid. For CB_LAYOUTRECALL arguments, the client MUST send
  a response to the recall before using the seqid.
  The fundamental requirement in client
  processing is that the "seqid" is used to provide the order of
  processing.  LAYOUTGET results may be processed in parallel.
  LAYOUTRETURN results may be processed in parallel.  LAYOUTGET and
  LAYOUTRETURN responses may be processed in parallel as long as the
  ranges do not overlap.  CB_LAYOUTRECALL request processing MUST be
  processed in "seqid" order at all times. 
</t>
<t>
  Once a client has no more layouts on a file, the layout stateid is
  no longer valid and MUST NOT be used. Any attempt to use such a
  layout stateid will result in NFS4ERR_BAD_STATEID.
</t>

</section>

<section title="Committing a Layout" anchor="committing_layout">
<t>
  Allowing for varying storage protocol capabilities, the pNFS
  protocol does not require the metadata server and storage devices to
  have a consistent view of file attributes and data location
  mappings.  Data location mapping refers to aspects such as which offsets
  store data as opposed to storing holes (see <xref
  target="sparse_dense" /> for a discussion).  Related issues arise
  for storage protocols where a layout may hold provisionally
  allocated blocks where the allocation of those blocks does not
  survive a complete restart of both the client and server.  Because
  of this inconsistency, it is necessary to resynchronize the client
  with the metadata server and its storage devices and make any
  potential changes available to other clients.  This is accomplished
  by use of the LAYOUTCOMMIT operation.
</t>
<t>
  The LAYOUTCOMMIT operation is responsible for committing a modified
  layout to the metadata server.  The data should be written
  and committed to the appropriate storage devices before the
  LAYOUTCOMMIT occurs.  The
  scope of the LAYOUTCOMMIT operation depends on the storage protocol
  in use.  It is important to note that the level of
  synchronization is from the point of view of the client that sent
  the LAYOUTCOMMIT.  The updated state on the metadata server need
  only reflect the state as of the client's last operation previous to
  the LAYOUTCOMMIT.  The metadata server is not REQUIRED to maintain a global view
  that accounts for other clients' I/O that may have occurred within
  the same time frame.
</t>
<t>
  For block/volume-based layouts, LAYOUTCOMMIT may require
  updating the block list that comprises the file and committing this
  layout to stable storage.  For file-based layouts, synchronization of
  attributes between the metadata and storage devices, primarily the
  size attribute, is required.
</t>
<t>
  The control protocol is free to synchronize the attributes before
  it receives a LAYOUTCOMMIT; however, upon successful completion of a
  LAYOUTCOMMIT, state that exists on the metadata server that
  describes the file MUST be synchronized with the state that exists on the
  storage devices that comprise that file as of the client's
  last sent operation.  Thus, a client that queries the size of a file
  between a WRITE to a storage device and the LAYOUTCOMMIT might observe
  a size that does not reflect the actual data written.
</t>

<t>
  The client MUST have a layout in order to send a LAYOUTCOMMIT operation.
</t>

<section title="LAYOUTCOMMIT and change/time_modify">
<t>
  The change and time_modify attributes may be updated
  by the server when the LAYOUTCOMMIT operation is processed.  The
  reason for this is that some layout types do not support the update
  of these attributes when the storage devices process I/O operations.
  If a client has a layout with the LAYOUTIOMODE4_RW iomode on the file,
  the client MAY provide a suggested value to the server for
  time_modify within the arguments to LAYOUTCOMMIT.
  Based on the layout type, the provided value may or may not be used.
  The server should sanity-check the client-provided values
  before they are used.  For example, the server should ensure that
  time does not flow backwards.  The client always has the option to
  set time_modify through an explicit SETATTR operation.
</t>
<t>
  For some layout protocols, the storage device is able to notify the
  metadata server of the occurrence of an I/O; as a result, the
  change and time_modify attributes may be updated at
  the metadata server.  For a metadata server that is capable of
  monitoring updates to the change and time_modify
  attributes, LAYOUTCOMMIT processing is not required to update the
  change attribute.  In this case, the metadata server must ensure that
  no further update to the data has occurred since the last update of
  the attributes; file-based protocols may have enough information to
  make this determination or may update the change attribute upon each
  file modification.  This also applies for the time_modify
  attribute.  If the server implementation is able to
  determine that the file has not been modified since the last
  time_modify update, the server need not update time_modify at
  LAYOUTCOMMIT.  At LAYOUTCOMMIT completion, the updated attributes
  should be visible if that file was modified since the latest
  previous LAYOUTCOMMIT or LAYOUTGET.
</t>
</section>
<section title="LAYOUTCOMMIT and size" anchor="general_layoutcommit">
<t>
  The size of a file may be updated when the LAYOUTCOMMIT operation is
  used by the client.  One of the fields in the argument to
  LAYOUTCOMMIT is loca_last_write_offset; this field indicates the
  highest byte offset written but not yet committed with the
  LAYOUTCOMMIT operation.  The data type of loca_last_write_offset is
  newoffset4 and is switched on a boolean value, no_newoffset, that
  indicates if a previous write occurred or not.  If no_newoffset is
  FALSE, an offset is not given.  If the client has a layout with
  LAYOUTIOMODE4_RW iomode on the file, with a byte-range (denoted by the values of lo_offset and lo_length)
  that overlaps loca_last_write_offset, then the client MAY
  set no_newoffset to TRUE and provide an offset that will
  update the file size. Keep in mind that offset is not the same
  as length, though they are related. For example, a loca_last_write_offset
  value of zero means that one byte was written at offset zero, and so
  the length of the file is at least one byte.
</t>
<t>
  The metadata server may do one of the following:
    <list style="numbers">
    <t>
      Update the file's size using the last write offset provided by
      the client as either the true file size or as a hint of the file
      size.  If the metadata server has a method available, any new
      value for file size should be sanity-checked.  For example, the
      file must not be truncated if the client presents a last write
      offset less than the file's current size.
    </t>
    <t>
      Ignore the client-provided last write offset; the metadata
      server must have sufficient knowledge from other sources to
      determine the file's size.  For example, the metadata server
      queries the storage devices with the control protocol.
    </t>
    </list>
  </t>
<t>
  The method chosen to update the file's size will depend on the
  storage device's and/or the control protocol's capabilities.  For
  example, if the storage devices are block devices with no knowledge
  of file size, the metadata server must rely on the client to set the
  last write offset appropriately.
</t>
<t>
  The results of LAYOUTCOMMIT contain a new size value in the form of
  a newsize4 union data type.  If the file's size is set as a result
  of LAYOUTCOMMIT, the metadata server must reply with the new size;
  otherwise, the new size is not provided.
  If the file size is updated, the metadata server SHOULD update the
  storage devices such that the new file size is reflected when
  LAYOUTCOMMIT processing is complete.  For example, the client should
  be able to read up to the new file size.
</t>
<t> 
  The client can extend the length of a file
  or truncate a file by sending a SETATTR operation to the metadata server
  with the size attribute specified. If the size specified is larger than
  the current size of the file, the file is "zero extended", i.e., zeros are
  implicitly added between the file's previous EOF and the new EOF.
  (In many implementations, the zero-extended byte-range
  of the file consists of unallocated
  holes in the file.) When the client writes past EOF via WRITE,
  the SETATTR operation does not need to be used.

</t>
</section>
<section title="LAYOUTCOMMIT and layoutupdate" anchor="layoutcommit_update">
<t>
  The LAYOUTCOMMIT argument contains a loca_layoutupdate field (<xref
  target="OP_LAYOUTCOMMIT_ARGUMENT"/>) of data type layoutupdate4
  (<xref target="layoutupdate4"/>).  This argument is a
  layout-type-specific structure.  The structure can be used to pass
  arbitrary layout-type-specific information from the client to the
  metadata server at LAYOUTCOMMIT time.  For example, if using a
  block/volume layout, the client can indicate to the metadata server
  which reserved or allocated blocks the client used or did not use.
  The content of loca_layoutupdate (field lou_body) need not be the
  same layout-type-specific content returned by LAYOUTGET (<xref
  target="OP_LAYOUTGET_RESULT" />) in the loc_body field of the
  lo_content field of the logr_layout field.  
The content of
  loca_layoutupdate is defined by the layout type specification and is
  opaque to LAYOUTCOMMIT.
</t>
</section>
</section> <!-- Layout Semantics -->

<section title="Recalling a Layout" anchor="recalling_layout">
<t>
  Since a layout protects a client's access to a file via a direct
  client-storage-device path, a layout need only be recalled when it
  is semantically unable to serve this function.  Typically, this
  occurs when the layout no longer encapsulates the true location of
  the file over the byte-range it represents.  Any operation or
  action, such as server-driven restriping or load balancing, that
  changes the layout will result in a recall of the layout.  A layout
  is recalled by the CB_LAYOUTRECALL callback operation (see <xref
  target="OP_CB_LAYOUTRECALL" />) and returned with LAYOUTRETURN (see <xref
  target="OP_LAYOUTRETURN" />).  The CB_LAYOUTRECALL operation may
  recall a layout identified by a byte-range, all layouts
  associated with a file system ID (FSID), or all layouts associated with
  a client ID.
  <xref target="pnfs_operation_sequencing" /> discusses sequencing issues
  surrounding the getting, returning, and recalling of layouts.
</t>
<t>
  An iomode is also specified when recalling a layout.
  Generally, the iomode in the recall request must match the layout
  being returned; for example, a recall with an iomode of
  LAYOUTIOMODE4_RW should cause the client to only return
  LAYOUTIOMODE4_RW layouts and not LAYOUTIOMODE4_READ layouts.
  However, a special LAYOUTIOMODE4_ANY enumeration is
  defined to enable recalling a layout of any iomode; in other words,
  the client must return both LAYOUTIOMODE4_READ and LAYOUTIOMODE4_RW layouts.
</t>
<t>
  A REMOVE operation SHOULD cause the metadata server to recall the
  layout to prevent the client from accessing a non-existent file and
  to reclaim state stored on the client.  Since a REMOVE may be delayed
  until the last close of the file has occurred, the recall may also
  be delayed until this time.  After the last reference on the file
  has been released and the file has been removed, the client should
  no longer be able to perform I/O using the layout.  In the case of a
  file-based layout, the data server SHOULD return NFS4ERR_STALE in
  response to any operation on the removed file.
</t>
<t>
  Once a layout has been returned, the client MUST NOT send I/Os to
  the storage devices for the file, byte-range, and iomode
  represented by the returned layout. If a client does send an I/O to
  a storage device for which it does not hold a layout, the storage
  device SHOULD reject the I/O.
</t>
<t anchor="pnfs_and_delegations">
  Although pNFS does not alter the file data caching capabilities of
  clients, or their semantics, it recognizes that some clients may
  perform more aggressive write-behind caching to optimize the
  benefits provided by pNFS.  However, write-behind caching may
  negatively affect the latency in returning a layout in response to a
  CB_LAYOUTRECALL; this is similar to file delegations and the impact
  that file data caching has on DELEGRETURN.  Client implementations
  SHOULD limit the amount of unwritten data they have outstanding at
  any one time in order to prevent excessively long responses to
  CB_LAYOUTRECALL.  Once a layout is recalled, a server MUST wait one
  lease period before taking further action.  As soon as a lease
  period has passed, the server may choose to fence the client's access
  to the storage devices if the server perceives the client has taken
  too long to return a layout. However, just as in the case of data
  delegation and DELEGRETURN, the server may choose to wait, given that
  the client is showing forward progress on its way to returning the
  layout.  This forward progress can take the form of successful
  interaction with the storage devices or of sub-portions of the layout
  being returned by the client.  The server can also limit exposure to
  these problems by limiting the byte-ranges initially provided in
  the layouts and thus the amount of outstanding modified data.
</t>

<section title="Layout Recall Callback Robustness" anchor="recall_robustness">
<t>
  It has been assumed thus far that pNFS client
  state
  (layout ranges and iomode)
  for a file exactly matches that of the pNFS server for that file.
  This assumption
  leads to the implication that any callback results in a
  LAYOUTRETURN or set of LAYOUTRETURNs that exactly match the range in
  the callback, since both client and server agree about the state
  being maintained.  However, it can be useful if this assumption does
  not always hold.  For example:
</t>
<t>
<list style="symbols">
<t>
  If conflicts that require
  callbacks are very rare, and a server can use a multi-file callback
  to recover per-client resources (e.g., via an FSID recall or a
  multi-file recall within a single CB_COMPOUND), the result may be
  significantly less client-server pNFS traffic.
</t>
<t>
  It may be useful for servers to maintain information about
  what ranges are held by a client on a coarse-grained basis, leading
  to the server's layout ranges being beyond those actually held by
  the client.
  In the extreme, a server could manage conflicts on
  a per-file basis, only sending whole-file callbacks even though
  clients may request and be granted sub-file ranges.
</t>
<t>
  It may be useful for clients to "forget" details about
  what layouts and ranges the client actually has, leading
  to the server's layout ranges being beyond those that the
  client "thinks" it has. As long as the client does not
  assume it has layouts that are beyond what the server
  has granted, this is a safe practice.  When a client
  forgets what ranges and layouts it has, and it receives
  a CB_LAYOUTRECALL operation, the client MUST follow up
  with a LAYOUTRETURN for what the server recalled, or
  alternatively return the NFS4ERR_NOMATCHING_LAYOUT error
  if it has no layout to return in the recalled range.

</t>

<t>
  In order to avoid errors, it is vital that a client not assign
  itself layout permissions beyond what the server has granted, and
  that the server not forget layout permissions that have been granted.
  On the other hand, if a
  server believes that a client holds a layout that the client
  does not know about, it is useful for the client to cleanly indicate
  completion of the requested recall either by sending a LAYOUTRETURN
  operation for the entire requested range or by returning an
  NFS4ERR_NOMATCHING_LAYOUT error to the CB_LAYOUTRECALL.
</t>
</list>
</t>
<t>
  Thus, in light of the above, it is useful for a server to be able to
  send callbacks for layout ranges it has not granted to a client,
  and for a client to return ranges it does not hold.  A pNFS client
  MUST always return layouts that comprise the full range
  specified by the recall.  Note, the full recalled layout range need
  not be returned as part of a single operation, but may be returned
  in portions.  This allows the client to stage the flushing of dirty
  data and commits and returns of layouts.
Also, it indicates to the
  metadata server that the client is making progress.
</t>
<t>
  When a layout is returned, the client MUST NOT have any outstanding
  I/O requests to the storage devices involved in the layout.
  Rephrasing, the client MUST NOT return the layout while it has
  outstanding I/O requests to the storage device.
</t>
<t>
  Even with this requirement for the client, it is possible that I/O
  requests may be presented to a storage device no longer allowed to
  perform them.  Since the server has no strict control as to when the
  client will return the layout, the server may later decide to
  unilaterally revoke the client's access to the storage devices
  as provided by the layout.  In
  choosing to revoke access, the server must deal with the possibility
  of lingering I/O requests, i.e., I/O requests that are
  still in flight to
  storage devices identified by the revoked layout.

  All layout type specifications MUST define whether unilateral layout revocation by
  the metadata server is supported; if it is, the specification must
  also describe how lingering writes are processed.  For example,
  storage devices identified by the revoked layout could be fenced off
  from the client that held the layout.
</t>
<t>
  In order to ensure client/server convergence with regard to layout state,
  the final LAYOUTRETURN operation in a sequence of LAYOUTRETURN
  operations for a particular recall MUST specify the entire range
  being recalled, echoing the recalled layout type, iomode,
  recall/return type (FILE, FSID, or ALL), and byte-range, even if
  layouts pertaining to partial ranges were previously
  returned.  In addition, if the client holds no layouts that
  overlap the range being recalled, the client should return the
  NFS4ERR_NOMATCHING_LAYOUT error code to CB_LAYOUTRECALL.  This
  allows the server to update its view of the client's layout state.
</t>
</section>

<section title="Sequencing of Layout Operations" anchor="pnfs_operation_sequencing">
<t>
  As with other stateful operations, pNFS requires the correct
  sequencing of layout operations. pNFS uses the "seqid" in the
  layout stateid to provide the correct sequencing between regular
  operations and callbacks.  It is the server's responsibility to
  avoid inconsistencies regarding the layouts provided and the
  client's responsibility to properly serialize its layout requests
  and layout returns.
</t>
<section title="Layout Recall and Return Sequencing">
<t>
  One critical issue with regard to layout operations sequencing
  concerns callbacks.  The protocol must defend against
  races between the reply to a LAYOUTGET or LAYOUTRETURN
  operation and a subsequent CB_LAYOUTRECALL.  A client
  MUST NOT process a CB_LAYOUTRECALL that implies one or
  more outstanding LAYOUTGET or LAYOUTRETURN operations to
  which the client has not yet received a reply. The client
  detects such a CB_LAYOUTRECALL by examining the "seqid"
  field of the recall's layout stateid. If the "seqid" 
  is not exactly one higher than what the client currently has recorded, and the
  client has at least one LAYOUTGET and/or LAYOUTRETURN operation
  outstanding, the client knows the server sent the CB_LAYOUTRECALL 
  after sending a response to an outstanding LAYOUTGET or LAYOUTRETURN.
  The client MUST wait before processing such a CB_LAYOUTRECALL
  until it processes all replies for outstanding LAYOUTGET and
  LAYOUTRETURN operations for the corresponding file
  with seqid less than the seqid given by CB_LAYOUTRECALL
  (lor_stateid; see <xref target="OP_CB_LAYOUTRECALL"/>.)
</t>
<t>
  In addition to the seqid-based mechanism,
  <xref target="sessions_callback_races"/>
  describes the sessions mechanism for allowing the
  client to detect callback race conditions and delay processing such a
  CB_LAYOUTRECALL. The server MAY reference conflicting operations
  in the CB_SEQUENCE that precedes the CB_LAYOUTRECALL.
  Because the server has already sent replies for these operations before
  sending the callback, the replies may race with the CB_LAYOUTRECALL.
  The client MUST wait for all the referenced calls to complete and update
  its view of the layout state before processing the CB_LAYOUTRECALL.
</t>

<section title="Get/Return Sequencing">
<t>
  The protocol allows the client to send concurrent
  LAYOUTGET and LAYOUTRETURN operations to the server. The
  protocol does not provide any means for the server to
  process the requests in the same order in which they
  were created. However, through the use of the "seqid"
  field in the layout stateid, the client can determine
  the order in which parallel outstanding operations were
  processed by the server. Thus, when a layout retrieved
  by an outstanding LAYOUTGET operation intersects with
  a layout returned by an outstanding LAYOUTRETURN on
  the same file, the order in which the two conflicting
  operations are processed determines the final state of
  the overlapping layout. The order is determined by
  the "seqid" returned in each operation: the operation with the
  higher seqid was executed later.

</t>
<t>
  It is permissible for the client to send multiple parallel
  LAYOUTGET operations for the same file or multiple parallel LAYOUTRETURN
  operations for the same file or a mix of both.
</t>
<t>
  It is permissible for the client to use the current stateid (see
  <xref target="current_stateid"/>) for LAYOUTGET operations, for
  example, when compounding LAYOUTGETs or compounding OPEN and
  LAYOUTGETs.  It is also permissible to use the current stateid when
  compounding LAYOUTRETURNs.
</t>
<t>
  It is permissible for the client to use the current stateid when
  combining LAYOUTRETURN and LAYOUTGET operations for the same file in
  the same COMPOUND request since the server MUST process these in
  order.  However, if a client does send such COMPOUND requests, it
  MUST NOT have more than one outstanding for the same file at the
  same time, and it MUST NOT have other LAYOUTGET or LAYOUTRETURN
  operations outstanding at the same time for that same file.
</t>
</section>

<section title="Client Considerations">
<t>
  Consider a pNFS client that has sent a LAYOUTGET, and before
  it receives the reply to LAYOUTGET, it receives
  a CB_LAYOUTRECALL for the same file with an overlapping range.  There are two
  possibilities, which the client can distinguish
  via the layout stateid in the recall.

  <list style="numbers">
  <t>
    The server processed the LAYOUTGET before sending the recall, so the
    LAYOUTGET must be waited for because it
    may be carrying layout information that will need to be returned to deal
    with the CB_LAYOUTRECALL.
  </t>
  <t>
    The
    server sent the callback before receiving the
    LAYOUTGET. The server will not respond to the LAYOUTGET
    until the CB_LAYOUTRECALL is processed.

  </t>
  </list>

  If these possibilities cannot be distinguished, a
  deadlock could result, as the client must wait for the
  LAYOUTGET response before processing the recall in the
  first case, but that response will not arrive until after
  the recall is processed in the second case. Note that
  in the first case, the "seqid" in the layout stateid
  of the recall is two greater than what the client has
  recorded; in the second case, the "seqid" is one greater than
  what the client has recorded.  This allows the client
  to disambiguate between the two cases. The client thus
  knows precisely which possibility applies.

</t>
<t>

  In case 1, the client knows it needs to wait for
  the LAYOUTGET response before processing the recall
  (or the client can return NFS4ERR_DELAY). 
</t>
<t>
  In case 2, the client will not wait for the LAYOUTGET
  response before processing the recall because waiting
  would cause deadlock.  Therefore, the action at the
  client will only require waiting in the case that the
  client has not yet seen the server's earlier responses
  to the LAYOUTGET operation(s).

</t>
<t>
  The recall process can be considered completed when
  the final LAYOUTRETURN operation for the recalled range is completed.
  The LAYOUTRETURN uses the layout stateid (with seqid) specified in
  CB_LAYOUTRECALL.  If the client uses multiple LAYOUTRETURNs in
  processing the recall, the first LAYOUTRETURN will use the layout
  stateid as specified in CB_LAYOUTRECALL.  Subsequent LAYOUTRETURNs
  will use the highest seqid as is the usual case.
</t>

</section>

<section title="Server Considerations" anchor="layout_server_consider">
<t>
  Consider a race from the metadata server's point of
  view.  The metadata server has sent a CB_LAYOUTRECALL and receives
  an overlapping LAYOUTGET for the same file before the
  LAYOUTRETURN(s) that respond to the CB_LAYOUTRECALL. There are
  three cases:

<list style="numbers">
<t>
  The client sent the LAYOUTGET before processing the CB_LAYOUTRECALL.
  The "seqid" in the layout stateid of the arguments of LAYOUTGET is one less 
  than the "seqid" in CB_LAYOUTRECALL. The server returns
  NFS4ERR_RECALLCONFLICT to the client, which indicates to the client
  that there is a pending recall.
</t>
<t>
  The client sent the LAYOUTGET after processing the
  CB_LAYOUTRECALL, but the LAYOUTGET arrived before the LAYOUTRETURN and
  the response to CB_LAYOUTRECALL that
  completed that processing.
  The "seqid" in the layout stateid
  of LAYOUTGET is equal to or greater than that of the "seqid" in
  CB_LAYOUTRECALL.
  The server has not received a response to the CB_LAYOUTRECALL,
  so it returns NFS4ERR_RECALLCONFLICT.
</t>
<t>
  The client sent the LAYOUTGET after processing the
  CB_LAYOUTRECALL; the server received the CB_LAYOUTRECALL
  response, but the LAYOUTGET arrived before the LAYOUTRETURN that
  completed that processing.
  The "seqid" in the layout stateid
  of LAYOUTGET is equal to that of the "seqid" in
  CB_LAYOUTRECALL.
  The server has received a response to the CB_LAYOUTRECALL,
  so it returns NFS4ERR_RETURNCONFLICT.
</t>
</list>
</t>

</section>

<section title="Wraparound and Validation of Seqid">
<t>
  The rules for layout stateid processing differ from other stateids
  in the protocol because the "seqid" value cannot be zero and the
  stateid's "seqid" value changes in a CB_LAYOUTRECALL operation.  The
  non-zero requirement combined with the inherent parallelism of
  layout operations means that a set of LAYOUTGET and LAYOUTRETURN
  operations may contain the same value for "seqid".
  The server uses a slightly modified version of the modulo arithmetic
  as described in 
  <xref target="Slot_Identifiers_and_Server_Reply_Cache" /> 
  when incrementing the layout stateid's "seqid".  The difference
  is that zero is not a valid value for "seqid"; when the value
  of a "seqid" is 0xFFFFFFFF, the next valid value will be 0x00000001.
  The modulo arithmetic is also used for the comparisons of
  "seqid" values in the processing of CB_LAYOUTRECALL events as
  described above in <xref target="layout_server_consider" />.
</t>
<t>
  Just as the server validates the "seqid" in the event of
  CB_LAYOUTRECALL usage, as described in
  <xref target="layout_server_consider" />, the server also validates
  the "seqid" value to ensure that it is within an appropriate range.
  This range represents the degree of parallelism the server supports
  for layout stateids.  If the client is sending multiple layout
  operations to the server in parallel, by definition, the "seqid"
  value in the supplied stateid will not be the current "seqid" as
  held by the server.  The range of parallelism spans from the highest
  or current "seqid" to a "seqid" value in the past.  To assist in the
  discussion, the server's current "seqid" value for a layout stateid
  is defined as SERVER_CURRENT_SEQID.  The lowest "seqid" value that
  is acceptable to the server is represented by PAST_SEQID.  And the
  value for the range of valid "seqid"s or range of parallelism is
  VALID_SEQID_RANGE.  Therefore, the following holds:
  VALID_SEQID_RANGE = SERVER_CURRENT_SEQID - PAST_SEQID.  In the
  following, all arithmetic is the modulo arithmetic as described
  above.
</t>
<t>
  The server MUST support a minimum VALID_SEQID_RANGE.  The minimum is
  defined as: VALID_SEQID_RANGE = summation over 1..N of
  (ca_maxoperations(i) - 1), where N is the number of session fore
  channels and ca_maxoperations(i) is the value of the ca_maxoperations returned from
  CREATE_SESSION of the i'th session.  The reason for "- 1" is to allow for the required
  SEQUENCE operation.  The server MAY support a VALID_SEQID_RANGE
  value larger than the minimum.  The maximum VALID_SEQID_RANGE is (2
  ^ 32 - 2) (accounting for zero not being a valid "seqid" value).
</t>
<t>
  If the server finds the "seqid" is zero, the NFS4ERR_BAD_STATEID
  error is returned to the client.  The server further validates the
  "seqid" to ensure it is within the range of parallelism,
  VALID_SEQID_RANGE.  If the "seqid" value is outside of that range,
  the error NFS4ERR_OLD_STATEID is returned to the client.  Upon
  receipt of NFS4ERR_OLD_STATEID, the client updates the stateid in
  the layout request based on processing of other layout requests and
  re-sends the operation to the server.
</t>
</section>  

<section title="Bulk Recall and Return" anchor="bulk_layouts">

<t>
 pNFS supports recalling and returning all layouts that
 are for files belonging to a particular fsid
 (LAYOUTRECALL4_FSID, LAYOUTRETURN4_FSID) or client ID
 (LAYOUTRECALL4_ALL, LAYOUTRETURN4_ALL).
 There are no "bulk" stateids, so detection of races
 via the seqid is not possible. 
 The server MUST NOT initiate bulk recall while another
 recall is in progress, or the corresponding LAYOUTRETURN
 is in progress or pending.
 In the event the server sends a bulk recall
 while the client has a pending or in-progress LAYOUTRETURN,
 CB_LAYOUTRECALL, or LAYOUTGET, the client returns
 NFS4ERR_DELAY. In the event the client sends a LAYOUTGET
 or LAYOUTRETURN while a bulk recall is in progress, the
 server returns NFS4ERR_RECALLCONFLICT.

 If the client sends a LAYOUTGET or LAYOUTRETURN after
 the server receives NFS4ERR_DELAY from a bulk recall,
 then to ensure forward progress, the server MAY return
 NFS4ERR_RECALLCONFLICT.

</t>
<t>
 Once a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL is sent,
 the server MUST NOT allow the client to use any layout
 stateid except for LAYOUTCOMMIT operations. Once the client receives
 a CB_LAYOUTRECALL of LAYOUTRECALL4_ALL, it MUST NOT use
 any layout stateid except for LAYOUTCOMMIT operations.

 Once a LAYOUTRETURN of LAYOUTRETURN4_ALL is sent, all
 layout stateids granted to the client ID are freed.
 The client MUST NOT use the layout stateids again. It
 MUST use LAYOUTGET to obtain new layout stateids.

</t>
<t>
 Once a CB_LAYOUTRECALL of LAYOUTRECALL4_FSID is sent, the
 server MUST NOT allow the client to use any layout stateid
 that refers to a file with the specified fsid except for
 LAYOUTCOMMIT operations. Once the client receives a CB_LAYOUTRECALL
 of LAYOUTRECALL4_ALL, it MUST NOT use any layout stateid
 that refers to a file with the specified fsid except
 for LAYOUTCOMMIT operations.

 Once a LAYOUTRETURN of LAYOUTRETURN4_FSID is sent, all
 layout stateids granted to the referenced fsid are freed.
 The client MUST NOT use those freed layout stateids for files
 with the referenced fsid again. Subsequently, for any file with
 the referenced fsid, to use a layout, the client MUST first
 send a LAYOUTGET operation in order to
 obtain a new layout stateid for that file.

</t>
<t>
 If the server has sent a bulk CB_LAYOUTRECALL and
 receives a LAYOUTGET, or a LAYOUTRETURN with a stateid,
 the server MUST return NFS4ERR_RECALLCONFLICT. If the
 server has sent a bulk CB_LAYOUTRECALL and receives a
 LAYOUTRETURN with an lr_returntype that is not equal to
 the lor_recalltype of the CB_LAYOUTRECALL, the server
 MUST return NFS4ERR_RECALLCONFLICT.

</t>
</section>

</section>
</section>
</section>

<section title="Revoking Layouts" anchor="revoke_layout">
<t>

Parallel NFS permits servers to revoke layouts from clients
that fail to respond to recalls and/or fail to renew their
lease in time. Depending on the layout type,
the server might revoke the layout and might take certain actions
with respect to the client's I/O to data servers.

</t>
</section>
<section title="Metadata Server Write Propagation" anchor="async_writes">
<t>
  Asynchronous writes written through the metadata server may be
  propagated lazily to the storage devices.  For data written
  asynchronously through the metadata server, a client performing a
  read at the appropriate storage device is not guaranteed to see the
  newly written data until a COMMIT occurs at the metadata server.
  While the write is pending, reads to the storage device may give out
  either the old data, the new data, or a mixture of new and old.
  Upon completion of a synchronous WRITE or COMMIT (for asynchronously
  written data), the metadata server MUST ensure that storage devices
  give out the new data and that the data has been written to stable
  storage.  If the server implements its storage in any way such that
  it cannot obey these constraints, then it MUST recall the layouts to
  prevent reads being done that cannot be handled correctly.  Note
  that the layouts MUST be recalled prior to the server responding to
  the associated WRITE operations.
</t>
</section>

</section>

<section title="pNFS Mechanics">
<t>
  This section describes the operations flow taken by a pNFS client
  to a metadata server and storage device.
</t>
<t>
  When a pNFS client encounters a new FSID, it sends a GETATTR to the
  NFSv4.1 server for the fs_layout_type (<xref target="attrdef_fs_layout_type"
  />) attribute. If the attribute returns at least one layout type,
  and the layout types returned are among the set supported by
  the client, the client knows that pNFS is a possibility for the file
  system.  If, from the server that returned the new FSID, the client
  does not have a client ID that came from an EXCHANGE_ID result that
  returned EXCHGID4_FLAG_USE_PNFS_MDS, it MUST send an EXCHANGE_ID to
  the server with the EXCHGID4_FLAG_USE_PNFS_MDS bit set. If the
  server's response does not have EXCHGID4_FLAG_USE_PNFS_MDS, then
  contrary to what the fs_layout_type attribute said, the server does
  not support pNFS, and the client will not be able use pNFS to that
  server; in this case, the server MUST return NFS4ERR_NOTSUPP in
  response to any pNFS operation.
</t>
<t>
  The client then creates a session, requesting a persistent session, so
  that exclusive creates can be done with single round trip via the
  createmode4 of GUARDED4. If the session ends up not being persistent,
  the client will use EXCLUSIVE4_1 for exclusive creates.
</t>
<t>
  If a file is to be created on a pNFS-enabled file
  system, the client uses the OPEN operation.  With the
  normal set of attributes that may be provided upon OPEN
  used for creation, there is an OPTIONAL layout_hint
  attribute.  The client's use of layout_hint allows the
  client to express its preference for a layout type and its
  associated layout details. The use of a createmode4 of
  UNCHECKED4, GUARDED4, or EXCLUSIVE4_1 will allow the
  client to provide the layout_hint attribute at create
  time. The client MUST NOT use EXCLUSIVE4 (see <xref
  target="exclusive_create"/>).  The client is RECOMMENDED
  to combine a GETATTR operation after the OPEN within
  the same COMPOUND.  The GETATTR may then retrieve
  the layout_type attribute for the newly created file.
  The client will then know what layout type the server has
  chosen for the file and therefore what storage protocol
  the client must use.

</t>
<t>
  If the client wants to open an existing file, then it also includes
  a GETATTR to determine what layout type the file supports.
</t>
<t>
  The GETATTR in either the file creation or plain file open case can
  also include the layout_blksize and layout_alignment attributes so
  that the client can determine optimal offsets and lengths for I/O on
  the file.
</t>
<t>
  Assuming the client supports the layout type returned by GETATTR and
  it chooses to use pNFS for data access, it then sends LAYOUTGET
  using the filehandle and stateid returned by OPEN, specifying the range it wants
  to do I/O on. The response is a layout, which may be a subset of the
  range for which the client asked. It also includes device IDs and a
  description of how data is organized (or in the case of writing, how
  data is to be organized) across the devices.  The device IDs and
  data description are encoded in a format that is specific to the
  layout type, but the client is expected to understand.
</t>
<t>
  When the client wants to send an I/O, it determines to which device ID
  it needs to send the I/O command by examining the data
  description in the layout. It then sends a
  GETDEVICEINFO to find the device address(es) of the device ID.  The
  client then sends the I/O request to one of device ID's device addresses, using the
  storage protocol defined for the layout type.
  Note that if a client has multiple I/Os to send,
  these I/O requests may be done in parallel.
</t>
<t>
  If the I/O was a WRITE, then at some point
  the client may want to use LAYOUTCOMMIT to
  commit the modification time and the new size
  of the file (if it believes it extended the file size) to the
  metadata server and the modified data to the file system.
</t>
</section> 
<section title="Recovery" anchor="crash_recovery">
<t>
  Recovery is complicated by the distributed nature of the pNFS
  protocol.  In general, crash recovery for layouts is similar to
  crash recovery for delegations in the base NFSv4.1 protocol.  However,
  the client's ability to perform I/O without contacting the metadata
  server introduces subtleties that must be handled correctly if
  the possibility of file system corruption is to be avoided.
</t>
 <section title="Recovery from Client Restart" anchor="pnfs_client_recovery">
 <t>
   Client recovery for layouts is similar to client recovery for other
   lock and delegation state.  When a pNFS client restarts, it will lose
   all information about the layouts that it previously owned.  There
   are two methods by which the server can reclaim these resources and
   allow otherwise conflicting layouts to be provided to other
   clients.
 </t>
 <t>
   The first is through the expiry of the client's lease.  If the
   client recovery time is longer than the lease period, the client's
   lease will expire and the server will know that state may be
   released.  For layouts, the server may release the state immediately
   upon lease expiry or it may allow the layout to persist, awaiting
   possible lease revival, as long as no other layout conflicts.
 </t>
 <t>
   The second is through the client restarting in less time than it
   takes for the lease period to expire.  In such a case, the client
   will contact the server through the standard EXCHANGE_ID protocol.
   The server will find that the client's co_ownerid matches the
   co_ownerid of the previous client invocation, but that the verifier
   is different.  The server uses this as a signal to release all
   layout state associated with the client's previous invocation.  In
   this scenario, the data written by the client but not covered by a
   successful LAYOUTCOMMIT is in an undefined state; it may have been
   written or it may now be lost.  This is acceptable behavior and it
   is the client's responsibility to use LAYOUTCOMMIT to achieve the
   desired level of stability.
 </t>
 </section>

 <section title="Dealing with Lease Expiration on the Client"
   anchor="lease_expiration_client">
 <t anchor="pnfs_clnt_case1">
   If a client believes its lease has expired, it MUST NOT send I/O
   to the storage device until it has validated its lease. The client
   can send a SEQUENCE operation to the metadata server. If the
   SEQUENCE operation is successful, but sr_status_flag has
   SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED,
   SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED, or
   SEQ4_STATUS_ADMIN_STATE_REVOKED set, the client MUST NOT use
   currently held layouts. The client has two
   choices to recover from the lease expiration. First, for all
   modified but uncommitted data, the client writes it to the metadata server
   using the FILE_SYNC4 flag for the WRITEs, or WRITE and
   COMMIT. Second, the client re-establishes a client ID and session with
   the server and obtains new layouts and device-ID-to-device-address
   mappings for the modified data ranges and then writes the data to the
   storage devices with the newly obtained layouts.
 </t>
 <t anchor="pnfs_clnt_case2">
   If sr_status_flags from the metadata server has
   SEQ4_STATUS_RESTART_RECLAIM_NEEDED set
   (or SEQUENCE returns NFS4ERR_BAD_SESSION and
   CREATE_SESSION returns NFS4ERR_STALE_CLIENTID), then the metadata
   server has restarted, and the client SHOULD recover using the
   methods described in <xref target="mds_recovery" />.
 </t>
 <t anchor="pnfs_clnt_case3">
   If sr_status_flags from the metadata server has
   SEQ4_STATUS_LEASE_MOVED set, then the client recovers by following
   the procedure described in <xref
   target="transferred_lease"/>. After that, the client may get an
   indication that the layout state was not moved with the file
   system.  The client recovers as in the other
   applicable situations discussed in the first two paragraphs of this section.
 </t>
 <t anchor="pnfs_clnt_case4">
   If sr_status_flags reports no loss of state, then the lease for the
   layouts that the client has are valid and
   renewed, and the client can once again send I/O requests to the
   storage devices.
 </t> 
 <t>
  While clients SHOULD NOT send I/Os to storage devices that may
  extend past the lease expiration time period, this is not always
  possible, for example, an extended network partition that starts
  after the I/O is sent and does not heal until the I/O request is
  received by the storage device.  Thus, the metadata server and/or
  storage devices are responsible for protecting themselves from I/Os
  that are both sent before the lease expires and arrive after the lease
  expires.  See <xref target="lease_expiration_mds" />.
 </t>
 </section>

 <section title="Dealing with Loss of Layout State on the Metadata Server"
   anchor="lease_expiration_mds">
 <t>
   This is a description of the case where all of the following are
   true: 
   <list style="symbols">
   <t>
     the metadata server has not restarted
   </t>
   <t>
     a pNFS client's
     layouts have been discarded (usually because the client's lease
     expired) and are invalid
   </t>
   <t>
     an I/O from the pNFS client arrives at the storage device
   </t>
   </list>
   The metadata server and its storage devices MUST solve this by
   fencing the client.  In other words, they MUST  solve this by
   preventing the execution of I/O operations from the client to the
   storage devices after layout
   state loss.  The details of how fencing is done are specific to the
   layout type.  The solution for NFSv4.1 file-based layouts is
   described in (<xref target="file_layout_revoke" />), and solutions for other
   layout types are in their respective external specification documents.
 </t>
 </section>

<section title="Recovery from Metadata Server Restart" anchor="mds_recovery">
   <t>
    The pNFS client will discover that the metadata server has
    restarted via the methods described in <xref
    target="server_failure" /> and discussed in a pNFS-specific
    context in <xref target="pnfs_clnt_case2" />.  The client MUST stop using
    layouts and delete the device ID to device address mappings it
    previously received from the metadata server.  Having done that,
    if the client wrote data to the storage device without committing
    the layouts via LAYOUTCOMMIT, then the client has
    additional work to do in order to have the client, metadata server,
    and storage device(s) all synchronized on the state of the data.
    <list style='symbols'>
  <t>
    If the client has data still modified
    and unwritten in the client's memory, the client has only two choices.
    <list style='numbers'>
    <t>
     The client can obtain a layout via LAYOUTGET after the
     server's grace period and write the data to the storage devices.
    </t>
    <t>
     The client can WRITE that data through the metadata server using the
     WRITE (<xref target="OP_WRITE" />) operation, and then obtain
     layouts as desired.
    </t>
   </list> 
  </t>
  <t>
    If the client asynchronously wrote data to the storage device, but
    still has a copy of the data in its memory, then it has available
    to it the recovery options listed above in the previous bullet
    point.  If the metadata server is also in its grace period, the
    client has available to it the options below in the next bullet
    point.  
  </t>
  <t>
    The client does not have a copy of the data in its memory and the
    metadata server is still in its grace period.  The client cannot
    use LAYOUTGET (within or outside the grace period) to reclaim a
    layout because the contents of the response from LAYOUTGET
    may not match what it had previously.  The range might be
    different or the client might get the same range but the content of the
    layout might be different.  Even if the content of the layout
    appears to be the same, the device IDs may map to different
    device addresses, and even if the device addresses are the same,
    the device addresses could have been assigned to a different
    storage device.  The option of retrieving the data from the
    storage device and writing it to the metadata server per the
    recovery scenario described above is
    not available because, again, the mappings of range to device ID,
    device ID to device address, and device address to physical device are
    stale, and new mappings via new LAYOUTGET do not solve the problem.

    <vspace blankLines='1' />

    The only recovery option for this scenario is to send a
    LAYOUTCOMMIT in reclaim mode, which the metadata server will
    accept as long as it is in its grace period.  The use of
    LAYOUTCOMMIT in reclaim mode informs the metadata server that the
    layout has changed.  It is critical that the metadata server
    receive this information before its grace period ends, and thus
    before it starts allowing updates to the file system.

    <vspace blankLines='1' />

    To send LAYOUTCOMMIT in reclaim mode, the client sets the
    loca_reclaim field of the operation's arguments (<xref
    target="OP_LAYOUTCOMMIT_ARGUMENT"/>) to TRUE.  During the metadata
    server's recovery grace period (and only during the recovery grace
    period) the metadata server is prepared to accept LAYOUTCOMMIT
    requests with the loca_reclaim field set to TRUE.

    <vspace blankLines='1' />

    When loca_reclaim is TRUE, the client is attempting to commit
    changes to the layout that occurred prior to the restart
    of the metadata server.  The metadata server applies some
    consistency checks on the loca_layoutupdate field of the arguments
    to determine whether the client can commit the data written to the
    storage device to the file system.  The loca_layoutupdate field is of
    data type layoutupdate4 and contains layout-type-specific content
    (in the lou_body field of loca_layoutupdate).  The
    layout-type-specific information that loca_layoutupdate might have
    is discussed in <xref target="layoutcommit_update" />.  If the
    metadata server's consistency checks on loca_layoutupdate succeed,
    then the metadata server MUST commit the data (as described by the
    loca_offset, loca_length, and loca_layoutupdate fields of the
    arguments) that was written to the storage device.  If the metadata
    server's consistency checks on loca_layoutupdate fail, the
    metadata server rejects the LAYOUTCOMMIT operation and makes no
    changes to the file system.  However, any time LAYOUTCOMMIT with
    loca_reclaim TRUE fails, the pNFS client has lost all the data in
    the range defined by &lt;loca_offset, loca_length&gt;.  A client
    can defend against this risk by caching all data, whether written
    synchronously or asynchronously in its memory, and by not releasing the
    cached data until a successful LAYOUTCOMMIT.  This condition
    does not hold true for all layout types; for example, file-based
    storage devices need not suffer from this limitation.
  </t>
  <t>
    The client does not have a copy of the data in its memory and the
    metadata server is no longer in its grace period; i.e., the metadata
    server returns NFS4ERR_NO_GRACE. As with the scenario in the above
    bullet point, the failure of LAYOUTCOMMIT means the data
    in the range  &lt;loca_offset, loca_length&gt; lost. The
    defense against the risk is the same -- cache all written data
    on the client until a successful LAYOUTCOMMIT.
  </t>
  </list> 
  </t>
</section>
<section title="Operations during Metadata Server Grace Period"
  anchor="pnfs_grace_exception">
  <t>
    Some of the recovery scenarios thus far noted that some
    operations (namely, WRITE and LAYOUTGET) might be permitted during
    the metadata server's grace period. The metadata server may allow
    these operations during its grace period.  For LAYOUTGET, the
    metadata server must reliably determine that servicing such a
    request will not conflict with an impending LAYOUTCOMMIT reclaim
    request.  For WRITE, the metadata server
    must reliably determine that servicing the request
    will not conflict with an impending OPEN or with a LOCK where the
    file has mandatory byte-range locking enabled.
  </t>
  <t>
    As mentioned previously, for expediency, 
    the metadata server might reject some
    operations (namely, WRITE and LAYOUTGET) during its
    grace period, because the simplest correct approach
    is to reject all non-reclaim pNFS requests and WRITE operations by
    returning the NFS4ERR_GRACE error.  However, depending on the
    storage protocol (which is specific to the layout type) and
    metadata server implementation, the metadata server may be able to
    determine that a particular request is safe.  For example, a
    metadata server may save provisional allocation mappings for each
    file to stable storage, as well as information about potentially
    conflicting OPEN share modes and mandatory byte-range locks that might
    have been in effect at the time of restart, and the metadata
    server may use this information during the recovery grace period to determine that a
    WRITE request is safe.
  </t>
</section>

<section anchor="storage_device_recovery" title="Storage Device Recovery">
<t>
  Recovery from storage device restart is mostly dependent upon the layout type
  in use.  However, there are a few general techniques a client can
  use if it discovers a storage device has crashed while holding
  modified, uncommitted data that was asynchronously written.
  First and foremost, it
  is important to realize that the client is the only one that has the
  information necessary to recover non-committed data since
  it holds the modified data and probably nothing else does. Second,
  the best solution is for the client to err on the side of caution
  and attempt to rewrite the modified data through another path.
</t>
<t>
  The client SHOULD immediately WRITE the data to the metadata server,
  with the stable field in the WRITE4args set to FILE_SYNC4.  Once it
  does this, there is no need to wait for the original storage device.
</t>
</section>
</section>

<section title="Metadata and Storage Device Roles">
<t>
  If the same physical hardware is used to implement both a
  metadata server and storage device, then the same hardware
  entity is to be understood to be implementing two
  distinct roles and it is important that it be clearly
  understood on behalf of which role the hardware is
  executing at any given time.
</t>
<t>
  Two sub-cases can be distinguished.

  <list style="numbers">
  <t>
    The storage device uses NFSv4.1 as the storage protocol, i.e., the same
    physical hardware is used to implement both a metadata and data
    server. See <xref target="pnfs_session_stuff" />
    for a description of how multiple roles are handled.
  </t>

  <t>

    The storage device does not use NFSv4.1 as the storage protocol,
    and the same physical hardware is used to implement both a
    metadata and storage device. Whether distinct network addresses
    are used to access the metadata server and storage device is
    immaterial. This is because it is always clear to the pNFS client and
    server, from the upper-layer protocol being used (NFSv4.1 or
    non-NFSv4.1), to which role the request to the common server network
    address is directed.
  </t>
  </list>
</t>
</section>


<section title="Security Considerations for pNFS" anchor="security_considerations_pnfs">
<t>
  pNFS separates file system metadata and data and provides access to
  both.  There are pNFS-specific operations (listed in
  <xref target="pnfs_ops" />) that provide access to the metadata; all
  existing NFSv4.1 conventional (non-pNFS) security mechanisms and
  features apply to accessing the metadata.  The combination of
  components in a pNFS system (see <xref target="fig_system" />) is
  required to preserve the security properties of NFSv4.1 with respect
  to an entity that is accessing a storage device from a client, including
  security countermeasures to defend against threats for which NFSv4.1
  provides defenses in environments where these threats are
  considered significant.
</t>
<t>
  In some cases, the security countermeasures for connections
  to storage devices may take the form of physical isolation or a
  recommendation to avoid the use of pNFS in an environment.  For example, it
  may be impractical to provide confidentiality protection for some
  storage protocols to protect against eavesdropping.  In
  environments where eavesdropping on such protocols is of sufficient
  concern to require countermeasures, physical isolation of the
  communication channel (e.g., via direct connection from client(s)
  to storage device(s)) and/or a decision to forgo use of pNFS (e.g.,
  and fall back to conventional NFSv4.1) may be appropriate courses of action.
</t>
<t>
  Where communication with storage devices is subject to the same
  threats as client-to-metadata server communication, the protocols
  used for that communication need to provide security mechanisms as
  strong as or no weaker than those available via RPCSEC_GSS for
  NFSv4.1. Except for the storage protocol used for the LAYOUT4_NFSV4_1_FILES
  layout (see <xref target="file_layout_type"/>), i.e., except for NFSv4.1,
  it is beyond the scope of this document to specify the security mechanisms 
  for storage access protocols.
</t>
<t>
  pNFS implementations MUST NOT remove NFSv4.1's access controls.
  The combination of clients, storage devices, and the metadata server
  are responsible for ensuring that all client-to-storage-device file
  data access respects NFSv4.1's ACLs and file open modes.  This entails
  performing both of these checks on every access in the client, the
  storage device, or both (as applicable; when the storage device is
  an NFSv4.1 server, the storage device is ultimately responsible for
  controlling access as described in <xref target="state_propagation"/>).
  If a pNFS configuration performs these checks only in the client,
  the risk of a misbehaving client obtaining unauthorized access is
  an important consideration in determining when it is appropriate to
  use such a pNFS configuration.  Such layout types SHOULD NOT be used
  when client-only access checks do not provide sufficient assurance
  that NFSv4.1 access control is being applied correctly. (This
  is not a problem for the file layout type described in <xref
  target="file_layout_type"/> because the storage access protocol for
  LAYOUT4_NFSV4_1_FILES is NFSv4.1, and thus the security model for
  storage device access via LAYOUT4_NFSv4_1_FILES is the same as that
  of the metadata server.) For handling of access control specific to
  a layout, the reader should examine the layout specification, such as
  the <xref target="file_layout_type">NFSv4.1/file-based layout</xref>
  of this document, the <xref target="RFC5663">blocks
  layout</xref>, and <xref target="RFC5664">objects
  layout</xref>.

</t>
</section>

</section>
<!-- $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $ -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="NFSv4.1 as a Storage Protocol in pNFS: the File Layout Type" anchor="file_layout_type">
<t>
  This section describes the semantics and format of NFSv4.1 file-based
  layouts for pNFS.
  NFSv4.1 file-based layouts use the LAYOUT4_NFSV4_1_FILES layout type.
  The LAYOUT4_NFSV4_1_FILES type defines
  striping data across multiple NFSv4.1 data servers.
</t>
 <section title="Client ID and Session Considerations" anchor="pnfs_session_stuff">
 <t>
  Sessions are a REQUIRED feature of NFSv4.1, and this
  extends to both the metadata server and file-based (NFSv4.1-based)
  data servers.
 </t>
 <t>
  The role a server plays in pNFS is determined by the result it returns
  from EXCHANGE_ID.
  The roles are:
  <list style="symbols">
  <t>
   Metadata server (EXCHGID4_FLAG_USE_PNFS_MDS is set in the result eir_flags).
  </t>

  <t>
   Data server (EXCHGID4_FLAG_USE_PNFS_DS).
  </t>

  <t>
   Non-metadata server (EXCHGID4_FLAG_USE_NON_PNFS). This is an NFSv4.1
   server that does not support operations (e.g.,
   LAYOUTGET) or attributes that pertain to pNFS.
  </t>
  </list>
  </t>
  <t>
   The client MAY request zero or more of 
   EXCHGID4_FLAG_USE_NON_PNFS, 
   EXCHGID4_FLAG_USE_PNFS_DS, or
   EXCHGID4_FLAG_USE_PNFS_MDS, even though some combinations
   (e.g., EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS) are
   contradictory. However, the server MUST only return the following
   acceptable combinations:
  </t>

  <texttable>

  <ttcol>Acceptable Results from EXCHANGE_ID</ttcol>

  <c>
   EXCHGID4_FLAG_USE_PNFS_MDS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_MDS | EXCHGID4_FLAG_USE_PNFS_DS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_DS
  </c>

  <c>
   EXCHGID4_FLAG_USE_NON_PNFS
  </c>

  <c>
   EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS
  </c>
  </texttable>
  <t>
  As the above table implies, a server can have one
  or two roles. A server can be both a metadata server
  and a data server, or it can be both a data server and
  non-metadata server.  In addition to returning two roles
  in the EXCHANGE_ID's results, and thus serving both roles
  via a common client ID, a server can serve two roles
  by returning a unique client ID and server owner for
  each role in each of two EXCHANGE_ID results, with each
  result indicating each role.

  </t>
  <t>

  In the case of a server with concurrent pNFS roles that
  are served by a common client ID, if the EXCHANGE_ID
  request from the client has zero or a combination of the
  bits set in eia_flags, the server result should set bits
  that represent the higher of the acceptable combination
  of the server roles, with a preference to match the roles
  requested by the client. Thus, if a client request has
  (EXCHGID4_FLAG_USE_NON_PNFS | EXCHGID4_FLAG_USE_PNFS_MDS
  | EXCHGID4_FLAG_USE_PNFS_DS) flags set, and the server
  is both a metadata server and a data server, serving
  both the roles by a common client ID, the server
  SHOULD return with (EXCHGID4_FLAG_USE_PNFS_MDS |
  EXCHGID4_FLAG_USE_PNFS_DS) set.

  </t>
  <t>

  In the case of a server that has multiple concurrent
  pNFS roles, each role served by a unique client ID,
  if the client specifies zero or a combination of roles
  in the request, the server results SHOULD return only
  one of the roles from the combination specified by the
  client request. If the role specified by the server
  result does not match the intended use by the client,
  the client should send the EXCHANGE_ID specifying just
  the interested pNFS role.

  </t>

  <t>
   If a pNFS metadata client gets a layout that refers it to an NFSv4.1
   data server, it needs a client ID on that data server. If it does not
   yet have a client ID from the server that had the EXCHGID4_FLAG_USE_PNFS_DS
   flag set in the EXCHANGE_ID results, then the client needs to
   send an EXCHANGE_ID to the data server, using
   the same co_ownerid as it sent to the metadata server, with the
   EXCHGID4_FLAG_USE_PNFS_DS flag set in the arguments.
   If the server's
   EXCHANGE_ID results have EXCHGID4_FLAG_USE_PNFS_DS set, then the
   client may use the client ID to create sessions that will
   exchange pNFS data operations.
   The client ID returned by the data server has no relationship with
   the client ID returned by a metadata server unless the client IDs
   are equal, and the server owners and server scopes of the data server
   and metadata server are equal.
  </t>
 <t>
   In NFSv4.1, the
   session ID in the SEQUENCE operation implies the
   client ID, which in turn might be used by the server to
   map the stateid to the right client/server pair.
   However, when a data server is presented with a READ or
   WRITE operation with a stateid, because the
   stateid is associated with a
   client ID on a metadata server, and because the session ID in
   the preceding SEQUENCE operation is tied to the
   client ID of the data server, the data server has no
   obvious way to determine the metadata server from the
   COMPOUND procedure, and thus has no way to validate the
   stateid. One RECOMMENDED approach is for pNFS servers to
   encode metadata server routing and/or identity
   information in the data server filehandles as returned
   in the layout.
  </t>
  <t>

   If metadata server routing and/or identity information is encoded
   in data server filehandles,
   when the metadata server identity or location
   changes, the data server filehandles it gave out will become
   invalid (stale), and so the metadata server MUST first
   recall the layouts.
   Invalidating a data server filehandle does not render
   the NFS client's data cache invalid. The client's cache should
   map a data server filehandle to a metadata server filehandle, and
   a metadata server filehandle to cached data.
  </t>

  <t>
   If a server is both a metadata server and a data server,
   the server might need to distinguish operations on
   files that are directed to the metadata server from
   those that are directed to the data server. It is
   RECOMMENDED that the values of the filehandles returned by
   the LAYOUTGET operation be different than the value
   of the filehandle returned by the OPEN of the same file.

  </t>
  <t>
   Another scenario is for the metadata server and the
   storage device to be distinct from one client's point of
   view, and the roles reversed from another client's point
   of view. For example, in the cluster file system model,
   a metadata server to one client might be a data server to
   another client. If NFSv4.1 is being used as the storage
   protocol, then pNFS servers need to encode the values
   of filehandles according to their specific roles.
  </t>
  <section anchor="dsonly" title="Sessions Considerations for Data Servers">
  <t>

   <xref target="Obligations_of_the_Client" /> states
   that a client has to keep its lease renewed in
   order to prevent a session from being deleted by
   the server. If the reply to EXCHANGE_ID has just the
   EXCHGID4_FLAG_USE_PNFS_DS role set, then (as noted in
   <xref target="ds_ops"/>) the client will not be able
   to determine the data server's lease_time attribute
   because GETATTR will not be permitted. Instead, the
   rule is that any time a client receives a layout
   referring it to a data server that returns just
   the EXCHGID4_FLAG_USE_PNFS_DS role, the client MAY
   assume that the lease_time attribute from the metadata
   server that returned the layout applies to the data
   server. Thus, the data server MUST be aware of the values
   of all lease_time attributes of all metadata servers for which it
   is providing I/O, and it MUST use the maximum of all such
   lease_time values as the lease interval for all client
   IDs and sessions established on it.

  </t>
  <t>

   For example, if one metadata server has a lease_time
   attribute of 20 seconds, and a second metadata
   server has a lease_time attribute of 10 seconds,
   then if both servers return layouts that refer to an
   EXCHGID4_FLAG_USE_PNFS_DS-only data server, the data
   server MUST renew a client's lease if the interval
   between two SEQUENCE operations on different COMPOUND
   requests is less than 20 seconds.

  </t>
 
  </section>

 </section>

 <section title="File Layout Definitions" anchor="file_layout_definitions">
 <t>
      The following definitions apply to the LAYOUT4_NFSV4_1_FILES
      layout type and may be applicable to other layout types.
      <list style='hanging'>
        <t hangText="Unit.">
         A unit is a fixed-size quantity of data written to a data server.
        </t>
        <t hangText="Pattern.">
         A pattern is a method of distributing one or more
         equal sized units across a set of data servers.
         A pattern is iterated one or more times.
        </t>
        <t hangText="Stripe.">
         A stripe is a set of data distributed
         across a set of data servers in a
         pattern before that pattern repeats.
        </t>
        <t hangText="Stripe Count.">
         A stripe count is the number of units in a pattern.
        </t>
        <t hangText="Stripe Width.">
         A stripe width is the size of a stripe in bytes.
         The stripe width = the stripe count * the size of the stripe unit.
        </t>
      </list>
      Hereafter, this document will refer to a unit that is a written
      in a pattern as a "stripe unit".
 </t>
 <t>
  A pattern may have more stripe units than data servers.
  If so, some data servers will have more than one stripe unit
  per stripe.  A data server that has multiple stripe
  units per stripe MAY store each unit in a different data file (and
  depending on the implementation, will possibly assign a unique data
  filehandle to each data file).
 </t>
 </section> <!--  "File Striping Definitions" "file_layout_definitions" -->

 <section title="File Layout Data Types" anchor="file_data_types">
 <t>
   The high level NFSv4.1 layout types are
   nfsv4_1_file_layouthint4,
   nfsv4_1_file_layout_ds_addr4,
   and nfsv4_1_file_layout4.
 </t>

  <t>
   The SETATTR operation supports a layout hint attribute
   (<xref target="attrdef_layout_hint" />).
   When the client sets a layout hint (data type layouthint4) with
   a layout type of LAYOUT4_NFSV4_1_FILES (the loh_type field),
   the loh_body field contains a value of data type
   nfsv4_1_file_layouthint4.
  </t>
<figure>
 <artwork>
const NFL4_UFLG_MASK            = 0x0000003F;
const NFL4_UFLG_DENSE           = 0x00000001;
const NFL4_UFLG_COMMIT_THRU_MDS = 0x00000002;
const NFL4_UFLG_STRIPE_UNIT_SIZE_MASK
                                = 0xFFFFFFC0;

typedef uint32_t nfl_util4;
 </artwork>
</figure>
<figure>
 <artwork>
enum filelayout_hint_care4 {
        NFLH4_CARE_DENSE        = NFL4_UFLG_DENSE,

        NFLH4_CARE_COMMIT_THRU_MDS
                                = NFL4_UFLG_COMMIT_THRU_MDS,

        NFLH4_CARE_STRIPE_UNIT_SIZE
                                = 0x00000040,

        NFLH4_CARE_STRIPE_COUNT = 0x00000080
};

/* Encoded in the loh_body field of data type layouthint4: */

struct nfsv4_1_file_layouthint4 {
        uint32_t        nflh_care;
        nfl_util4       nflh_util;
        count4          nflh_stripe_count;
};
 </artwork>
</figure>
 <t>
     The generic layout hint structure is described
     in <xref target="layouthint4" />.  The client uses the
     layout hint in the layout_hint (<xref
     target="attrdef_layout_hint" />) attribute to indicate the preferred type
     of layout to be used for a newly created file. The
     LAYOUT4_NFSV4_1_FILES layout-type-specific content for the
     layout hint is composed of three fields. The first field,
     nflh_care, is a set of flags indicating which values of the hint the
     client cares about. If the NFLH4_CARE_DENSE flag is set, then
     the client indicates in the second field, nflh_util,
     a preference for how the data
     file is packed (<xref target="sparse_dense" />), which is controlled
     by the value of the expression nflh_util &amp; NFL4_UFLG_DENSE ("&amp;" represents the bitwise AND operator). If the
     NFLH4_CARE_COMMIT_THRU_MDS flag is set, then the client indicates
     a preference for whether the client should send COMMIT operations
     to the metadata server or data server (<xref target="commit_thru_mds" />),
     which is controlled by the value of nflh_util &amp; NFL4_UFLG_COMMIT_THRU_MDS.
     If the NFLH4_CARE_STRIPE_UNIT_SIZE flag is set, the client indicates
     its preferred stripe unit size, which is indicated in
     nflh_util &amp;
     NFL4_UFLG_STRIPE_UNIT_SIZE_MASK (thus, the stripe
     unit size MUST be a multiple of 64 bytes). The minimum stripe unit
     size is 64 bytes.
     If the NFLH4_CARE_STRIPE_COUNT flag is set, the client indicates
     in the third field,
     nflh_stripe_count, the stripe count. The stripe count multiplied
     by the stripe unit size is the stripe width.
 </t>
 <t>
   When LAYOUTGET returns a LAYOUT4_NFSV4_1_FILES layout
   (indicated in the loc_type field of the lo_content field),
   the loc_body field of the lo_content field
   contains a value of data type nfsv4_1_file_layout4.
   Among other content, nfsv4_1_file_layout4 has a storage
   device ID (field nfl_deviceid) of data type
   deviceid4.
   The GETDEVICEINFO operation maps a device ID to
   a storage device address (type device_addr4). When GETDEVICEINFO
   returns a device address with a layout type of LAYOUT4_NFSV4_1_FILES
   (the da_layout_type field), the da_addr_body field contains
   a value of data type nfsv4_1_file_layout_ds_addr4.
  </t>
<figure>
 <artwork>

typedef netaddr4 multipath_list4&lt;>;

/*
 * Encoded in the da_addr_body field of
 * data type device_addr4:
 */
struct nfsv4_1_file_layout_ds_addr4 {
        uint32_t        nflda_stripe_indices&lt;>;
        multipath_list4 nflda_multipath_ds_list&lt;>;
};
 </artwork>
</figure>
 <t>
   The nfsv4_1_file_layout_ds_addr4 data type represents the
   device address. It is composed of two fields:
   <list style='numbers'>
   <t>
    nflda_multipath_ds_list: An array of lists of data servers, where
    each list can be one or more elements, and each element represents
    a data server address that may serve equally as the target of I/O operations (see
    <xref target="file_multipath" />).
    The length of this array might be different than the stripe count.
   </t>
   <t>
    nflda_stripe_indices: An array of indices used to index into
    nflda_multipath_ds_list. The value of each element of nflda_stripe_indices MUST
    be less than the number of elements in nflda_multipath_ds_list.
    Each element of nflda_multipath_ds_list SHOULD be referred to by one
    or more elements of nflda_stripe_indices.
    The number of elements in
    nflda_stripe_indices is always equal to the stripe count.
   </t>
   </list>
  </t>
<figure>
 <artwork>

/*
 * Encoded in the loc_body field of
 * data type layout_content4:
 */
struct nfsv4_1_file_layout4 {
         deviceid4      nfl_deviceid;
         nfl_util4      nfl_util;
         uint32_t       nfl_first_stripe_index;
         offset4        nfl_pattern_offset;
         nfs_fh4        nfl_fh_list&lt;>;
};
 </artwork>
</figure>
  <t>
   The nfsv4_1_file_layout4 data type represents the layout.
   It is composed of the following fields:
   <list style='numbers'>

   <t>
    nfl_deviceid: The device ID that maps to a value of type
    nfsv4_1_file_layout_ds_addr4.
   </t>

   <t>
    nfl_util: Like the nflh_util field of data type nfsv4_1_file_layouthint4,
    a compact representation of how the data on a file
    on each data server is packed, whether the client should send
    COMMIT operations to the metadata server or data server, and the
    stripe unit size. If a server returns two or
    more overlapping layouts, each stripe unit size in
    each overlapping layout MUST be the same.
   </t>

   <t>
    nfl_first_stripe_index: The index into the first element
    of the nflda_stripe_indices array to use.
   </t>

   <t>
     nfl_pattern_offset:
     This field is the logical offset into the file
     where the striping pattern starts. It is required for
     converting the client's logical I/O offset (e.g., the current
     offset in a POSIX file descriptor before the read() or write()
     system call is sent) into the stripe unit number (see
     <xref target="SUi"/>).

     <vspace blankLines='1' />

     If dense packing is used, then nfl_pattern_offset
     is also needed to convert the client's logical
     I/O offset to an offset on the file on the data
     server corresponding to the stripe unit number (see <xref
     target="sparse_dense"/>).

     <vspace blankLines='1' />

     Note that nfl_pattern_offset is not always the same as
     lo_offset. For example, via the LAYOUTGET operation,
     a client might request a layout starting at offset 1000 of a
     file that has its striping pattern start at offset zero.

     <vspace blankLines='1' />

   </t>

   <t>
    nfl_fh_list: An array of data server filehandles for each
    list of data servers in each element of the nflda_multipath_ds_list
    array. The number of elements in 
    nfl_fh_list depends on whether sparse or dense packing
    is being used.

    <list style='symbols'>
    <t>
     If sparse packing is being used, the number of elements in
     nfl_fh_list MUST be one of three values:

	     <list style="symbols">
	     <t>

	      Zero. This means that filehandles used
	      for each data server are the same as the
	      filehandle returned by the OPEN operation
	      from the metadata server.

	     </t>

	     <t>

	      One.  This means that every data server uses
	      the same filehandle: what is specified in
	      nfl_fh_list[0].

	     </t>

	     <t>

	      The same number of elements in
	      nflda_multipath_ds_list. Thus, in this case,
	      when sending an I/O operation to any data server in
	      nflda_multipath_ds_list[X], the filehandle
	      in nfl_fh_list[X] MUST be used.

	     </t>

	     </list>

     See the discussion on sparse packing in <xref target="sparse_dense" />.
     <vspace blankLines='1' />
    </t>

    <t>

     If dense packing is being used, the number of elements
     in nfl_fh_list MUST be the same as the number
     of elements in nflda_stripe_indices. Thus,
     when sending an I/O operation to any data server in
     nflda_multipath_ds_list[nflda_stripe_indices[Y]],
     the filehandle in nfl_fh_list[Y] MUST be
     used. In addition, any time there exists i
     and j, (i != j), such that the intersection of
     nflda_multipath_ds_list[nflda_stripe_indices[i]]
     and nflda_multipath_ds_list[nflda_stripe_indices[j]]
     is not empty, then nfl_fh_list[i] MUST NOT equal
     nfl_fh_list[j]. In other words, when dense packing
     is being used, if a data server appears in two or more
     units of a striping pattern, each reference to
     the data server MUST use a different filehandle.

     <vspace blankLines='1' />

     Indeed, if there are multiple striping patterns,
     as indicated by the presence of multiple objects of
     data type layout4 (either returned in one or multiple
     LAYOUTGET operations), and a data server is the target
     of a unit of one pattern and another unit of another
     pattern, then each reference to each data server MUST
     use a different filehandle.

     <vspace blankLines='1' />

     See the discussion on dense packing in <xref target="sparse_dense" />.

    </t>
    </list>
   </t>
   </list>

   The details on the interpretation of the layout are in
   <xref target="file_layout_interpret" />.

  </t>

 </section> <!-- "File Layout Data Types" "file_data_types" -->
 <section title="Interpreting the File Layout"
  anchor="file_layout_interpret">

  <section title="Determining the Stripe Unit Number" anchor="SUi">

  <t>
   To find the stripe unit number that corresponds to the client's
   logical file offset, the pattern offset will also be used. The
   i'th stripe unit (SUi) is:

  <figure>
  <artwork><![CDATA[
    relative_offset = file_offset - nfl_pattern_offset;
    SUi = floor(relative_offset / stripe_unit_size);
  ]]></artwork>
  </figure>

  </t>

  </section>

  <section title="Interpreting the File Layout Using Sparse Packing">
 <t>
  When sparse packing is used, the algorithm for determining the filehandle and set
  of data-server network addresses to write stripe unit i
 (SUi) to is:
 </t>
  <figure>
  <artwork><![CDATA[

   stripe_count = number of elements in nflda_stripe_indices;

   j = (SUi + nfl_first_stripe_index) % stripe_count;

   idx = nflda_stripe_indices[j];

   fh_count = number of elements in nfl_fh_list;
   ds_count = number of elements in nflda_multipath_ds_list;

   switch (fh_count) {
     case ds_count:
       fh = nfl_fh_list[idx];
       break;

     case 1:
       fh = nfl_fh_list[0];
       break;

     case 0:
       fh = filehandle returned by OPEN;
       break;

     default:
       throw a fatal exception;
       break;
   }

   address_list = nflda_multipath_ds_list[idx];

  ]]></artwork>
  </figure>
 <t>
  The client would then select a data server from address_list, and
  send a READ or WRITE operation using the filehandle specified in fh.
 </t>
 <t>
     Consider the following example:
 </t>
 <t>
  Suppose we have a device address consisting of seven
  data servers, arranged in three equivalence (<xref
  target="file_multipath" />) classes:

  <list style='empty'>
  <t>
	  { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
 </t>
 <t>
  where A through G are network addresses.
 </t>
 <t>
  Then
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list&lt;&gt; = { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
	  i.e.,
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  <t>
	  nflda_multipath_ds_list[2] = { F, G }
  </t>
  </list>
 </t>
 <t>
  Suppose the striping index array is:
  <list style='empty'>
  <t>
	  nflda_stripe_indices&lt;&gt; = { 2, 0, 1, 0 }
  </t>
  </list>
 </t>
 <t>
  Now suppose the client gets a layout that has a device ID
  that maps to the above device address.  The initial index contains
  <list style='empty'>
  <t>
   nfl_first_stripe_index = 2,
  </t>
  </list>
 and the filehandle list is
  <list style='empty'>
  <t>
   nfl_fh_list = { 0x36, 0x87, 0x67 }.
  </t>
  </list>
 </t>
 <t>
  If the client wants to write to SU0, the
  set of valid { network address, filehandle } combinations
  for SUi are determined by:
  <list style='empty'>
  <t>
	  nfl_first_stripe_index = 2
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  idx = nflda_stripe_indices[(0 + 2) % 4]
   <list style='empty'>
   <t>
		  = nflda_stripe_indices[2]
   </t>
   <t>
		  = 1
   </t>
   </list>
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  </list>
  and
  <list style='empty'>
  <t>
	  nfl_fh_list[1] = { 0x87 }
  </t>
  </list>
 </t>
 <t>
  The client can thus write SU0 to { 0x87, { E } }.

 </t>
 <t>
  The destinations of the first 13 storage units are:
 </t>
 <texttable>

 <ttcol>SUi</ttcol> <ttcol>filehandle</ttcol> <ttcol>data servers</ttcol>

  <c>0</c>   <c>    87 </c><c>     E </c>
  <c>1</c><c>36</c><c>A,B,C,D</c>
  <c>2</c><c>67</c><c>F,G</c>
  <c>3</c><c>36 </c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>4</c><c>87</c><c>E</c>
  <c>5</c><c>36</c><c>A,B,C,D</c>
  <c>6</c><c>67</c><c>F,G</c>
  <c>7</c><c>36</c><c>A,B,C,D</c>

  <c/> <c/> <c/>
  <c>8</c><c>87</c><c>E</c>
  <c>9</c><c>36</c><c>A,B,C,D</c>
  <c>10</c><c>67</c><c>F,G</c>
  <c>11</c><c>36</c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>12</c><c>87</c><c>E</c>

 </texttable>
 </section>
  <section title="Interpreting the File Layout Using Dense Packing">
 <t>
  When dense packing is used, the algorithm for determining the filehandle and set
  of data server network addresses to write stripe unit i (SUi) to is:
 </t>
  <figure>
  <artwork><![CDATA[
   stripe_count = number of elements in nflda_stripe_indices;

   j = (SUi + nfl_first_stripe_index) % stripe_count;

   idx = nflda_stripe_indices[j];

   fh_count = number of elements in nfl_fh_list;
   ds_count = number of elements in nflda_multipath_ds_list;

   switch (fh_count) {
     case stripe_count:
       fh = nfl_fh_list[j];
       break;

     default:
       throw a fatal exception;
       break;
   }

   address_list = nflda_multipath_ds_list[idx];

  ]]></artwork>
  </figure>
 <t>
  The client would then select a data server from address_list, and
  send a READ or WRITE operation using the filehandle specified in fh.
 </t>
 <t>
     Consider the following example (which is the same
     as the sparse packing example, except for the
     filehandle list):
 </t>
 <t>
  Suppose we have a device address consisting of seven
  data servers, arranged in three equivalence (<xref
  target="file_multipath" />) classes:

  <list style='empty'>
  <t>
	  { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
 </t>
 <t>
  where A through G are network addresses.
 </t>
 <t>
  Then
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list&lt;&gt; = { A, B, C, D }, { E }, { F, G }
  </t>
  </list>
	  i.e.,
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  <t>
	  nflda_multipath_ds_list[1] = { E }
  </t>
  <t>
	  nflda_multipath_ds_list[2] = { F, G }
  </t>
  </list>
 </t>
 <t>
  Suppose the striping index array is:
  <list style='empty'>
  <t>
	  nflda_stripe_indices&lt;&gt; = { 2, 0, 1, 0 }
  </t>
  </list>
 </t>
 <t>
  Now suppose the client gets a layout that has a device ID
  that maps to the above device address.  The initial index contains
  <list style='empty'>
  <t>
   nfl_first_stripe_index = 2,
  </t>
  </list>
 and
  <list style='empty'>
  <t>
   nfl_fh_list = { 0x67, 0x37, 0x87, 0x36 }.
  </t>
  </list>
 </t>
 <t>
  The interesting examples for dense packing are
  SU1 and SU3 because each stripe unit refers to the
  same data server list, yet each stripe unit MUST use a different filehandle.
  If the client wants to write to SU1, the
  set of valid { network address, filehandle } combinations
  for SUi are determined by:
  <list style='empty'>
  <t>
	  nfl_first_stripe_index = 2
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
          j = (1 + 2) % 4 = 3
   <list style='empty'>
   <t>
	  idx = nflda_stripe_indices[j]
   </t>
   <t>
		  = nflda_stripe_indices[3]
   </t>
   <t>
		  = 0
   </t>
   </list>
  </t>
  </list>
 </t>
 <t>
  So
  <list style='empty'>
  <t>
	  nflda_multipath_ds_list[0] = { A, B, C, D }
  </t>
  </list>
  and
  <list style='empty'>
  <t>
	  nfl_fh_list[3] = { 0x36 }
  </t>
  </list>
 </t>
 <t>
  The client can thus write SU1 to { 0x36, { A, B, C, D } }.

 </t>
 <t>
  For SU3, j = (3 + 2) % 4 = 1, and nflda_stripe_indices[1] = 0.
  Then nflda_multipath_ds_list[0] = { A, B, C, D }, and
  nfl_fh_list[1] = 0x37. The client can thus write SU3 to 
  { 0x37, { A, B, C, D } }.
 </t>
 <t>
  The destinations of the first 13 storage units are:
 </t>
 <texttable>

 <ttcol>SUi</ttcol> <ttcol>filehandle</ttcol> <ttcol>data servers</ttcol>

  <c>0</c>   <c>    87 </c><c>     E </c>
  <c>1</c><c>36</c><c>A,B,C,D</c>
  <c>2</c><c>67</c><c>F,G</c>
  <c>3</c><c>37 </c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>4</c><c>87</c><c>E</c>
  <c>5</c><c>36</c><c>A,B,C,D</c>
  <c>6</c><c>67</c><c>F,G</c>
  <c>7</c><c>37</c><c>A,B,C,D</c>

  <c/> <c/> <c/>
  <c>8</c><c>87</c><c>E</c>
  <c>9</c><c>36</c><c>A,B,C,D</c>
  <c>10</c><c>67</c><c>F,G</c>
  <c>11</c><c>37</c><c>A,B,C,D</c>

  <c/> <c/> <c/>

  <c>12</c><c>87</c><c>E</c>

 </texttable>
 </section>


 <section title="Sparse and Dense Stripe Unit Packing"
  anchor="sparse_dense">
 <t>
     The flag NFL4_UFLG_DENSE of the nfl_util4 data type (field nflh_util of the
     data type nfsv4_1_file_layouthint4 and field nfl_util of
     data type nfsv4_1_file_layout_ds_addr4) specifies how the data
     is packed within the
     data file on a data server.  It allows for two different data
     packings: sparse and dense.  The packing type determines the
     calculation that will be made to map the client-visible file offset
     to the offset within the data file located on the data server.
 </t>
 <t>
   If nfl_util &amp; NFL4_UFLG_DENSE is zero, this means that
   sparse packing is being used. Hence, the logical offsets of the
   file as viewed by a client
   sending READs and WRITEs directly to the metadata server
   are the same offsets each data server uses when storing
   a stripe unit. The effect then, for striping patterns
   consisting of at least two stripe units, is for each
   data server file to be sparse or "holey". So for example,
   suppose there is a pattern with three stripe units, the stripe unit
   size is 4096 bytes, and there are three data servers in
   the pattern.  Then, the file in data server 1 will have
   stripe units 0, 3, 6, 9, ... filled; data server 2's
   file will have stripe units 1, 4, 7, 10, ... filled;
   and data server 3's file will have stripe units 2,
   5, 8, 11, ... filled. The unfilled stripe units of
   each file will be holes; hence, the files in each data
   server are sparse.

 </t>
 <t>
   If sparse packing is being used and a client attempts I/O to one of
   the holes, then an error MUST be
   returned by the data server. Using the above example, if data server 3 received a READ or WRITE operation for block 4, the data server
   would return NFS4ERR_PNFS_IO_HOLE. Thus,
   data servers need to understand the striping pattern in order
   to support sparse packing.
 </t>
 <t>
   If nfl_util &amp; NFL4_UFLG_DENSE is one, this means that
   dense packing is being used, and the data server files have no holes.
   Dense packing might be selected because the data server does not
   (efficiently) support holey files or because the data server
   cannot recognize read-ahead unless there are no holes.
   If dense packing is indicated in the layout,
   the data files will be packed. Using the
   same striping pattern and stripe unit size that were used for
   the sparse packing example, the corresponding dense packing example would have
   all stripe units of all data files filled as follows:
   <list style='symbols'>

   <t>
   Logical stripe units 0, 3, 6, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 1.
   </t>

   <t>
   Logical stripe units 1, 4, 7, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 2.
   </t>

   <t>
   Logical stripe units 2, 5, 8, ... of the file would live on
   stripe units 0, 1, 2, ... of the file of data server 3.
   </t>
   </list>
 </t>
 <t>
   Because dense packing does not leave holes on the data servers,
   the pNFS client is allowed to write to any offset of any data file of
   any data server in the stripe. Thus, the data servers need not know
   the file's striping pattern.
 </t>
 <t>
   The calculation to determine the byte offset within the data file
   for dense data server layouts is:
 </t>
 <figure>
 <artwork><![CDATA[
   stripe_width = stripe_unit_size * N;
      where N = number of elements in nflda_stripe_indices.

   relative_offset = file_offset - nfl_pattern_offset;

   data_file_offset = floor(relative_offset / stripe_width)
      * stripe_unit_size
      + relative_offset % stripe_unit_size
 ]]></artwork>
 </figure>
 <t>
  If dense packing is being used, and a data server appears
  more than once in a striping pattern, then to distinguish
  one stripe unit from another, the data server MUST use a
  different filehandle. Let's suppose there are two data
  servers.  Logical stripe units 0, 3, 6 are served by
  data server 1; logical stripe units 1, 4, 7 are served
  by data server 2; and logical stripe units 2, 5, 8 are
  also served by data server 2.  Unless data server 2 has
  two filehandles (each referring to a different data
  file), then, for example, a write to logical stripe
  unit 1 overwrites the write to logical stripe unit 2
  because both logical stripe units are located in the
  same stripe unit (0) of data server 2.

 </t>

</section>
</section> <!--  "Interpreting the File Layout" anchor="file_layout_interpret" -->

<section title="Data Server Multipathing" anchor="file_multipath">
<t>
  The NFSv4.1 file layout supports multipathing to
  multiple data server addresses.
  Data-server-level multipathing is used for
  bandwidth scaling via trunking (<xref target="Trunking"
  />) and for higher availability of use in the case of
  a data-server failure.  Multipathing allows the client
  to switch to another data server address which may be that
  of another data server that is exporting the
  same data stripe unit, without having to contact the
  metadata server for a new layout.

</t>
<t>
  To support data server multipathing, each element of
  the nflda_multipath_ds_list contains an array of one
  more data server network addresses.  This array (data
  type multipath_list4) represents a list of data servers
  (each identified by a network address), with the possibility
  that some data servers will appear in the list multiple times.
</t>
<t>

  The client is free to use any of the network addresses
  as a destination to send data server requests. If some
  network addresses are less optimal paths to the data than
  others, then the MDS SHOULD NOT include those network
  addresses in an element of nflda_multipath_ds_list. If
  less optimal network addresses exist to provide failover, the 
  RECOMMENDED method to offer the addresses is
  to provide them in a replacement device-ID-to-device-address 
  mapping, or a replacement device ID. When
  a client finds that no data server in an element of
  nflda_multipath_ds_list responds, it SHOULD send a
  GETDEVICEINFO to attempt to replace the existing
  device-ID-to-device-address mappings. If the MDS detects
  that all data servers represented by an element of
  nflda_multipath_ds_list are unavailable, the MDS SHOULD
  send a CB_NOTIFY_DEVICEID (if the client has indicated
  it wants device ID notifications for changed device IDs)
  to change the device-ID-to-device-address mappings to
  the available data servers. If the device ID itself will
  be replaced, the MDS SHOULD recall all layouts with the
  device ID, and thus force the client to get new layouts
  and device ID mappings via LAYOUTGET and GETDEVICEINFO.
</t>
<t>
  Generally, if two network addresses appear in an element
  of nflda_multipath_ds_list, they will designate the same
  data server, and the two data server addresses will
  support the implementation of
  client ID or session trunking (the latter is RECOMMENDED)
  as defined in <xref target="Trunking"/>.  The two
  data server addresses will share the same server owner
  or major ID of the server owner.  It is not always necessary for the
  two data server addresses to designate the same server 
  with trunking being used.  For example,
  the data could be read-only, and the data consist of
  exact replicas.

</t>
</section>

<section title="Operations Sent to NFSv4.1 Data Servers" anchor="ds_ops">
 <t>
  Clients accessing data on an NFSv4.1 data server MUST send
  only the NULL procedure and COMPOUND procedures whose
  operations are taken only from two restricted
  subsets of the operations defined as valid NFSv4.1 
  operations.  Clients MUST use the filehandle specified
  by the layout when accessing data on NFSv4.1 data 
  servers. 
 </t>
 <t>
  The first of these operation subsets consists of management operations.
  This subset consists of the BACKCHANNEL_CTL, BIND_CONN_TO_SESSION, CREATE_SESSION,
  DESTROY_CLIENTID, DESTROY_SESSION, EXCHANGE_ID,
  SECINFO_NO_NAME, SET_SSV, and SEQUENCE operations.
  The client may use these operations in order to set
  up and maintain the appropriate client IDs,
  sessions, and security contexts involved in communication with the data
  server.  Henceforth, these will be referred to as
  data-server housekeeping operations.
 </t>
 <t>
  The second subset consists of COMMIT, READ, WRITE, and PUTFH.
  These operations MUST be used with a current filehandle specified by the 
  layout.  In the case of PUTFH, the new current filehandle MUST be
  one taken from the layout. Henceforth, these will be referred to as data-server
  I/O operations.  As described in <xref target="layout_semantics" />, 
  a client MUST NOT send an I/O to a data server for which it does not hold a
  valid layout; the data server MUST reject such an I/O.
 </t>
 <t>
  Unless the server has a concurrent non-data-server
  personality -- i.e., EXCHANGE_ID results returned 
  (EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_PNFS_MDS) 
  or (EXCHGID4_FLAG_USE_PNFS_DS | EXCHGID4_FLAG_USE_NON_PNFS) see
  <xref target="pnfs_session_stuff"/> -- any attempted use of
  operations against a data server other than those specified in the two 
  subsets above MUST return
  NFS4ERR_NOTSUPP to the client.
 </t>
 <t>
  When the server has concurrent data-server and 
  non-data-server personalities, each COMPOUND sent by the 
  client MUST be constructed
  so that it is appropriate to one of the two personalities, and it
  MUST NOT contain operations directed to a mix of those 
  personalities.  The server MUST enforce this.  To understand
  the constraints, operations within a COMPOUND are divided into
  the following three classes: 
  <list style='numbers'>
    <t>
      An operation that is ambiguous regarding its personality
      assignment.  This includes all of the data-server
      housekeeping operations.  Additionally, if the
      server has assigned filehandles so that the ones defined
      by the layout are the same as those used by the metadata 
      server, all operations using such filehandles are within this
      class, with the following exception. The exception is
      that if the operation uses a stateid that is incompatible with a
      data-server personality (e.g., a special stateid or the
      stateid has a non-zero "seqid" field, see
      <xref target="global_stateid"/>), the operation is in class 3,
      as described below. A COMPOUND containing
      multiple class 1 operations (and operations of no other
      class) MAY be sent to a server with multiple concurrent data server
      and non-data-server personalities.
    
    </t>
    <t>
      An operation that is unambiguously referable to the data-server
      personality.  This includes data-server I/O operations where the
      filehandle is one that can only be validly directed to the
      data-server personality.
    </t>
    <t>
      An operation that is unambiguously referable to the non-data-server
      personality.  This includes all COMPOUND operations that are
      neither data-server housekeeping nor data-server I/O 
      operations, plus data-server I/O operations where the 
      current fh (or the one to be made the current fh in the
      case of PUTFH) is only valid on the metadata
      server or where a stateid is used that is incompatible 
      with the data server, i.e., is a special stateid or has
      a non-zero seqid value.
    </t>
  </list>
 </t>
 <t>
  When a COMPOUND first executes an operation from class 3 above,
  it acts as a normal COMPOUND on any other server, and the 
  data-server personality ceases to be relevant. 
  There are no special restrictions on the 
  operations in the COMPOUND to limit them to those for
  a data server.  When a PUTFH is done, filehandles
  derived from the layout are not valid.  If their format
  is not normally acceptable, then NFS4ERR_BADHANDLE MUST
  result.  Similarly, current filehandles for other operations
  do not accept filehandles derived from layouts and are not 
  normally usable on the metadata server. Using these
  will result in NFS4ERR_STALE. 
 </t>
 <t>
  When a COMPOUND first executes an operation from class 2,
  which would be PUTFH where the filehandle
  is one from a layout, the COMPOUND henceforth is interpreted
  with respect to the data-server personality. 
  Operations outside the two classes discussed
  above MUST result in NFS4ERR_NOTSUPP.  Filehandles
  are validated using the rules of the data server,
  resulting in NFS4ERR_BADHANDLE and/or NFS4ERR_STALE
  even when they would not normally do so when addressed
  to the non-data-server personality.  Stateids must obey
  the rules of the data server in that any use of special
  stateids or stateids with non-zero seqid values must 
  result in NFS4ERR_BAD_STATEID.
 </t>	
 <t>
  Until the server first executes an operation from class 2
  or class 3, the client MUST NOT depend on the operation 
  being executed by either the data-server or the non-data-server
  personality.  The server MUST pick one personality consistently
  for a given COMPOUND, with the only possible transition being 
  a single one when the first operation from class 2 or class 3
  is executed.
 </t>
 <t>
  Because of the complexity induced by assigning filehandles so
  they can be used on both a data server and a metadata server, it
  is RECOMMENDED that where the same server can have both
  personalities, the server assign separate unique filehandles
  to both personalities. This makes it unambiguous for which server
  a given request is intended.
 </t>
<t>
  GETATTR and SETATTR MUST be directed to the metadata
  server. In the case of a SETATTR of the size attribute,
  the control protocol is responsible for propagating size
  updates/truncations to the data servers. In the case of
  extending WRITEs to the data servers, the new size must
  be visible on the metadata server once a LAYOUTCOMMIT
  has completed (see <xref target="general_layoutcommit"
  />). <xref target="component_file_size" /> describes the
  mechanism by which the client is to handle data-server
  files that do not reflect the metadata server's size.

</t>
</section>

<section title="COMMIT through Metadata Server" anchor="commit_thru_mds">
<t>
   The file layout provides two alternate means of providing for the 
   commit of data written through data servers.  The flag 
   NFL4_UFLG_COMMIT_THRU_MDS in the field nfl_util of the file layout
   (data type nfsv4_1_file_layout4)
   is an indication
   from the metadata server to the client of the REQUIRED way of
   performing COMMIT, either by sending the COMMIT to the data server
   or the metadata server.  These two methods of dealing with the issue 
   correspond to broad styles of implementation for a pNFS server
   supporting the file layout type.
   <list style="symbols">
     <t>
       When the flag is FALSE, COMMIT operations MUST to be sent
       to the data server to which the corresponding WRITE operations were 
       sent.  This approach
       is sometimes useful when file striping is implemented within the
       pNFS server (instead of the file system),
       with the individual data servers each implementing 
       their own file systems.
     </t>
     <t>
       When the flag is TRUE, COMMIT operations MUST be sent to the
       metadata server, rather than to the individual data servers.  
       This approach is sometimes useful when file striping
       is implemented within the clustered file system that is the backend
       to the pNFS server.  In such 
       an implementation, each COMMIT to each
       data server might result in repeated writes of metadata
       blocks to the 
       detriment of write performance.  Sending a single COMMIT 
       to the metadata server can be more efficient
       when there exists a clustered file 
       system capable of implementing such a coordinated COMMIT.
     <vspace blankLines='1' />
       If nfl_util &amp; NFL4_UFLG_COMMIT_THRU_MDS is TRUE,
       then in order to maintain the current NFSv4.1 commit and
       recovery model, the data servers MUST return a common
       writeverf verifier in all WRITE responses for a given file
       layout, and the metadata server's COMMIT implementation
       must return the same writeverf.  The value of the
       writeverf verifier MUST be changed at the metadata server
       or any data server that is referenced in the layout,
       whenever there is a server event that can possibly lead to
       loss of uncommitted data.  The scope of the verifier can
       be for a file or for the entire pNFS server.  It might be
       more difficult for the server to maintain the verifier
       at the file level, but the benefit is that only events
       that impact a given file will require recovery action.   
     </t>
   </list>
</t>
<t>
 Note that if the layout specified dense packing, then the
 offset used to a COMMIT to the MDS may differ than that of
 an offset used to a COMMIT to the data server.
</t>
<t>
 The single COMMIT to the metadata server will return a verifier, and
 the client should compare it to all the verifiers from the WRITEs and
 fail the COMMIT if there are any mismatched verifiers. If COMMIT to the
 metadata server fails, the client should re-send WRITEs for all the 
 modified data in the file. The client should treat modified data with 
 a mismatched verifier
 as a WRITE failure and try to recover by resending the WRITEs to the
 original data server or using another path to that data if the layout 
 has not been recalled.  Alternatively, the client can obtain
 a new layout or it could rewrite the data directly to the metadata server. If 
 nfl_util &amp; NFL4_UFLG_COMMIT_THRU_MDS is FALSE, sending
 a COMMIT to the metadata server might have no effect. If
 nfl_util &amp; NFL4_UFLG_COMMIT_THRU_MDS is FALSE, a COMMIT
 sent to the metadata server should be used only to commit data that 
 was written to the metadata server.  See <xref target="storage_device_recovery" />
 for recovery options.
</t>
</section>

<section title="The Layout Iomode">
<t>
  The layout iomode need not be used by the metadata server when
  servicing NFSv4.1 file-based layouts, although in some circumstances
  it may be useful.  For example, if the server implementation
  supports reading from read-only replicas or mirrors, it would be
  useful for the server to return a layout enabling the client to do
  so.  As such, the client SHOULD set the iomode based on its intent
  to read or write the data.  The client may default to an iomode of
  LAYOUTIOMODE4_RW.  The iomode need not be checked by the
  data servers when clients perform I/O.  However, the data servers 
  SHOULD still validate that the client holds a valid layout
  and return an error if the client does not.
</t>
</section>

<section title="Metadata and Data Server State Coordination">

<section title="Global Stateid Requirements" anchor="global_stateid">
<t>
  When the client sends
  I/O to a data server, the stateid used MUST NOT be a layout stateid
  as returned by LAYOUTGET or sent by CB_LAYOUTRECALL. 
  Permitted stateids are based on one of the following:
  an OPEN stateid
  (the stateid field of data type OPEN4resok as returned by OPEN),
  a delegation stateid (the stateid field of data types open_read_delegation4
  and open_write_delegation4 as returned by OPEN or WANT_DELEGATION,
  or as sent by CB_PUSH_DELEG), or a stateid returned by the LOCK or LOCKU
  operations.  The stateid sent to the data server MUST be sent with
  the seqid set to zero, indicating the most current version of that
  stateid, rather than indicating a specific non-zero seqid value.  In
  no case is the use of special stateid values allowed.
</t>
<t>
  The stateid used for I/O MUST have the same
  effect and be subject to the same validation on a data server as it
  would if the I/O was being performed on the metadata server itself
  in the absence of pNFS. This has the implication that stateids are
  globally valid on both the metadata and data servers. This
  requires the metadata server to propagate changes in LOCK and OPEN
  state to the data servers, so that the data servers can
  validate I/O accesses. This is discussed further in <xref
  target="state_propagation" />.  Depending on when stateids are
  propagated, the existence of a valid stateid on the data server
  may act as proof of a valid layout.
</t>
        <t>
          Clients performing I/O operations need to select an appropriate 
          stateid based on the
          locks (including opens and delegations) held by the client and 
          the various types of state-owners sending the I/O requests.  The
          rules for doing so when referencing data servers are somewhat 
          different from those discussed in <xref target="stateid_use" />,
          which apply when accessing metadata servers.
        </t>
        <t>
          The following rules, applied in order of decreasing priority, govern 
          the selection of the appropriate stateid:
          <list style='symbols'>
            <t>
              If the client holds a delegation for the file in question, the
              delegation stateid should be used.
            </t>
            <t>
              Otherwise, there must be an OPEN stateid for the current 
              open-owner, and that 
              OPEN stateid for the open file in question is used, unless
              mandatory locking prevents that.  See below.
            </t>
            <t>
              If the data server had previously responded with NFS4ERR_LOCKED
              to use of the OPEN stateid, then the client should use the 
              byte-range lock stateid whenever one exists for that open file
              with the current lock-owner.
            </t>
            <t>
              Special stateids should never be used.  If they are used, the data
              server MUST reject the I/O with an NFS4ERR_BAD_STATEID error.
            </t>
          </list> 
        </t>   
</section>

<section title="Data Server State Propagation" anchor="state_propagation" >
<t>
  Since the metadata server, which handles byte-range lock and
  open-mode state changes as well as ACLs, might not be
  co-located with the data servers where I/O accesses
  are validated, the server implementation MUST take
  care of propagating changes of this state to the data
  servers. Once the propagation to the data servers is
  complete, the full effect of those changes MUST be in
  effect at the data servers. However, some state changes
  need not be propagated immediately, although all changes
  SHOULD be propagated promptly.  These state propagations
  have an impact on the design of the control protocol,
  even though the control protocol is outside of the scope
  of this specification.  Immediate propagation refers to
  the synchronous propagation of state from the metadata
  server to the data server(s); the propagation must be
  complete before returning to the client.

</t>

<section title="Lock State Propagation">
<t>
  If the pNFS server supports mandatory byte-range locking, any mandatory byte-range locks
  on a file MUST be made effective at the data servers before
  the request that establishes them returns to the caller. The
  effect MUST be the same as if the mandatory byte-range lock state were
  synchronously propagated to the data servers, even though the
  details of the control protocol may avoid actual transfer of the
  state under certain circumstances.  
</t>
<t>
  On the other hand, since 
  advisory byte-range lock state is not used for checking I/O accesses at 
  the data servers, there is no semantic reason for propagating 
  advisory byte-range lock state to the data servers.  
  Since updates to advisory locks neither confer nor remove
  privileges, these changes need not be propagated immediately, and
  may not need to be propagated promptly.  The updates to advisory
  locks need only be propagated when the data server needs to
  resolve a question about a stateid.  In fact, if byte-range locking
  is not mandatory (i.e., is advisory) the clients are advised to avoid
  using the byte-range lock-based stateids for I/O. The stateids returned by
  OPEN are sufficient and eliminate overhead for this kind of state
  propagation.
</t>
<t>
  If a client gets back an NFS4ERR_LOCKED error from a
  data server, this is an indication that mandatory byte-range
  locking is in force. The client recovers from this by
  getting a byte-range lock that covers the affected range
  and re-sends the I/O with the stateid of the byte-range lock.
</t>

</section>

<section title="Open and Deny Mode Validation">
<t>
  Open and deny mode validation MUST be performed against
  the open and deny mode(s) held by the data servers. When
  access is reduced or a deny mode made more restrictive
  (because of CLOSE or OPEN_DOWNGRADE), the data server MUST
  prevent any I/Os that would be denied if performed on the
  metadata server. When access is expanded,
  the data server MUST make sure that no requests are
  subsequently rejected because of
  open or deny issues that no longer apply, given the 
  previous relaxation.
</t>
</section>

<section title="File Attributes">
<t>
  Since the SETATTR operation has the ability to modify state that is
  visible on both the metadata and data servers (e.g., the size),
  care must be taken to ensure that the resultant state across the
  set of data servers is consistent, especially when truncating or
  growing the file.
</t>
<t>
  As described earlier, the LAYOUTCOMMIT operation is used to ensure
  that the metadata is synchronized with changes made to the data servers. For the NFSv4.1-based data storage protocol,
  it is necessary to re-synchronize
  state such as the size attribute, and the setting of mtime/change/atime.
  See <xref target="committing_layout" /> for a full
  description of the semantics regarding LAYOUTCOMMIT and
  attribute synchronization.  It should be noted that by
  using an NFSv4.1-based layout type, it is possible to
  synchronize this state before LAYOUTCOMMIT occurs.  For
  example, the control protocol can be used to query the
  attributes present on the data servers.
</t>
<t>
  Any changes to file attributes that control authorization or
  access as reflected by ACCESS calls or READs and WRITEs on the
  metadata server, MUST be propagated to the data servers for
  enforcement on READ and WRITE I/O calls.  If the changes made on the
  metadata server result in more restrictive access permissions for
  any user, those changes MUST be propagated to the data servers
  synchronously.
</t>
<t>
  The OPEN operation (<xref target="OP_OPEN_IMPLEMENTATION"
  />) does not impose any requirement that I/O operations
  on an open file have the same credentials as the OPEN
  itself (unless EXCHGID4_FLAG_BIND_PRINC_STATEID is
  set when EXCHANGE_ID creates the client ID), and so it
  requires the server's READ and WRITE operations to
  perform appropriate access checking.  Changes to ACLs
  also require new access checking by READ and WRITE on
  the server.  The propagation of access-right changes due
  to changes in ACLs may be asynchronous only if the server
  implementation is able to determine that the updated
  ACL is not more restrictive for any user specified in
  the old ACL. Due to the relative infrequency of ACL
  updates, it is suggested that all changes be propagated
  synchronously.

</t>
</section>
</section>
</section>

<section title="Data Server Component File Size"
         anchor="component_file_size">
<t>
  A potential problem exists when a component data file on a
  particular data server has grown past EOF; the problem exists for
  both dense and sparse layouts.  Imagine the following scenario: a
  client creates a new file (size == 0) and writes to byte 131072; the
  client then seeks to the beginning of the file and reads byte 100.
  The client should receive zeroes back as a result of the READ. However,
  if the striping pattern directs the client to send the READ to
  a data server other than the one that received the
  client's original WRITE, the data server servicing the READ may
  believe that the file's size is still 0 bytes. In that event, the
  data server's READ response will contain zero bytes and an
  indication of EOF.  The data server can only return zeroes if it knows that
  the file's size has been extended. This would require the immediate
  propagation of the file's size to all data servers, which is
  potentially very costly.  Therefore, the client that has
  initiated the extension of the file's size MUST be prepared to deal
  with these EOF conditions.
  When the offset in the arguments to READ
  is less than the client's view of the file size, if the READ response
  indicates EOF and/or contains fewer bytes than requested, the client
  will interpret such a response as a hole in the file, and the
  NFS client will substitute zeroes for the data.
</t>
<t>
  The NFSv4.1 protocol only provides close-to-open file data cache
  semantics; meaning that when the file is closed, all modified data is
  written to the server.  When a subsequent OPEN of the file is
  done, the change attribute is inspected for a difference from a
  cached value for the change attribute.  For the case above, this means
  that a LAYOUTCOMMIT will be done at close (along with the data
  WRITEs) and will update the file's size and change attribute.  Access
  from another client after that point will result in the appropriate
  size being returned.
</t>
</section>

<section title="Layout Revocation and Fencing" anchor="file_layout_revoke" >
<t>
  As described in <xref target="crash_recovery" />, the
  layout-type-specific storage protocol is responsible
  for handling the effects of I/Os that started before
  lease expiration and extend through lease expiration.
  The LAYOUT4_NFSV4_1_FILES layout type 
  can prevent all I/Os to data servers from
  being executed after lease expiration (this prevention is
  called "fencing"), without relying
  on a precise client lease timer and without requiring
  data servers to maintain lease timers. The
  LAYOUT4_NFSV4_1_FILES pNFS server has the flexibility to
  revoke individual layouts, and thus fence I/O on a per-file
  basis.
</t>
<t> 
  In addition to lease expiration,
  the reasons a layout can be revoked include: client fails to respond to
  a CB_LAYOUTRECALL,
  the
  metadata server restarts, or administrative intervention. Regardless
  of the reason, once a client's layout has been revoked, the pNFS
  server MUST prevent the client from sending I/O for the affected file
  from and to all data servers; in other words, it MUST fence the
  client from the affected file on the data servers.
</t>
<t> 
  Fencing works as follows. As described in <xref
  target="pnfs_session_stuff" />, in COMPOUND procedure
  requests to the data server, the data filehandle provided
  by the PUTFH operation and the stateid in the READ or
  WRITE operation are used to ensure that the client has
  a valid layout for the I/O being performed; if it does
  not, the I/O is rejected with NFS4ERR_PNFS_NO_LAYOUT.
  The server can simply check the stateid and, additionally,
  make the data filehandle stale if the layout specified
  a data filehandle that is different from the metadata server's
  filehandle for the file (see the nfl_fh_list description in
  <xref target="file_data_types" />).
</t>
<t>
  Before the metadata server takes any action to revoke
  layout state given out by a previous instance, it must make
  sure that all layout state from that previous instance are
  invalidated at the data servers. This has the following
  implications.
  <list style='symbols'>

  <t>
     The metadata server must not restripe a
     file until it has contacted all of the data servers
     to invalidate the layouts from the previous instance.
  </t>

  <t>
     The metadata server must not give out mandatory locks that conflict with
     layouts from the previous instance without either doing
     a specific layout invalidation (as it would have to do anyway)
     or doing a global data server invalidation.
  </t>
  </list>
</t>


</section>


<section title="Security Considerations for the File Layout Type" anchor="file_security_considerations">
<t>
  The NFSv4.1 file layout type MUST adhere to the security
  considerations outlined in <xref target="security_considerations_pnfs"
  />.  NFSv4.1 data servers MUST make all of the
  required access checks on each READ or WRITE I/O as determined by
  the NFSv4.1 protocol.
  If the metadata server would deny a READ or WRITE
  operation on a file due to its ACL, mode attribute, open
  access mode, open deny mode, mandatory byte-range lock state, or any other
  attributes and state, the data server MUST also deny the
  READ or WRITE operation.  This impacts the control
  protocol and the propagation of state from the metadata
  server to the data servers; see <xref
  target="state_propagation" /> for more details.

</t>
<t>
  The methods for authentication,
  integrity, and privacy for data servers based on the
  LAYOUT4_NFSV4_1_FILES layout type are the same as those used
  by metadata servers. Metadata and data servers
  use ONC RPC security flavors to
  authenticate, and SECINFO and SECINFO_NO_NAME
  to negotiate the security mechanism and services
  to be used. Thus, when using the LAYOUT4_NFSV4_1_FILES layout type,
  the impact on the RPC-based security
  model due to pNFS (as alluded to in Sections
  <xref target="rpc_and_security" format="counter"/>
  and <xref target="parallel_access" format="counter"/>) is zero.
</t>
<t>
  For a given file object, a metadata server
  MAY require different security parameters
  (secinfo4 value) than the data server.
  For a given file object with multiple data servers,
  the secinfo4 value SHOULD be the same across
  all data servers. If the secinfo4 values across a metadata server
  and its data servers differ for a specific file, the
  mapping of the principal to the server's internal user identifier
  MUST be the same in order for the access-control checks based on
  ACL, mode, open and deny mode, and mandatory locking to be
  consistent across on the pNFS server.
</t>
<t>
  If an NFSv4.1 implementation supports
  pNFS and supports NFSv4.1 file layouts, then the
  implementation MUST support the SECINFO_NO_NAME operation on both
  the metadata and data servers.
</t>

</section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="internationalization" title="Internationalization">
<t>
The primary issue in which NFSv4.1 needs to deal with
internationalization, or I18N, is with respect to file names and other
strings as used within the protocol.  The choice of string
representation must allow reasonable name/string access to clients
that use various languages.  The UTF-8 encoding of the UCS (Universal
Multiple-Octet Coded Character Set) as defined
by <xref target="ISO.10646-1.1993">ISO10646</xref> allows for this type
of access and follows the policy described in "IETF Policy on
Character Sets and Languages", <xref target="RFC2277">RFC 2277</xref>.
</t>
<t>
<xref target="RFC3454">RFC 3454</xref>, otherwise know as "stringprep", documents a
framework for using Unicode/UTF-8 in networking protocols so as "to
increase the likelihood that string input and string comparison work
in ways that make sense for typical users throughout the world". A
protocol must define a profile of stringprep "in order to fully
specify the processing options".  The remainder of this
section defines the NFSv4.1 stringprep profiles. Much of the terminology
used for the remainder of this section comes from stringprep.
</t>
<t>
There are three UTF-8 string types defined for NFSv4.1:
utf8str_cs, utf8str_cis, and utf8str_mixed.  Separate profiles are
defined for each. Each profile defines the following, as required by
stringprep:
<list style='symbols'>
<t>
The intended applicability of the profile.
</t>
<t>
The character repertoire that is the input and output to stringprep
(which is Unicode 3.2 for the referenced version of stringprep).
However, NFSv4.1 implementations are not limited to 3.2.
</t>
<t>
The mapping tables from stringprep used (as described in Section 3 of
stringprep).
</t>
<t>
Any additional mapping tables specific to the profile.
</t>
<t>
The Unicode normalization used, if any (as described in Section 4 of stringprep).
</t>
<t>
The tables from the stringprep listing of characters that are prohibited
as output (as described in Section 5 of stringprep).
</t>
<t>
The bidirectional string testing used, if any (as described in Section 6 of stringprep).
</t>
<t>
Any additional characters that are prohibited as output specific to
the profile.
</t>
</list>
</t>
<t>
Stringprep discusses Unicode characters, whereas NFSv4.1 renders
UTF-8 characters.  Since there is a one-to-one mapping from UTF-8 to
Unicode, when the remainder of this document refers to Unicode,
the reader should assume UTF-8.
</t>
<t>
Much of the text for the profiles comes from <xref target="RFC3491">RFC 3491</xref>.
</t>
<section title="Stringprep Profile for the utf8str_cs Type">
<t>
Every use of the utf8str_cs type definition in the NFSv4 protocol specification follows the profile named
nfs4_cs_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_cs_prep Profile">
<t>
The utf8str_cs type is a case-sensitive string of UTF-8 characters.
Its primary use in NFSv4.1 is for naming components and
pathnames.  Components and pathnames are stored on the server's
file system.  Two valid distinct UTF-8 strings might be the same after
processing via the utf8str_cs profile. If the strings are two names
inside a directory, the NFSv4.1 server will need to either:
<list style='symbols'>
<t>
disallow the creation of a second name if its post-processed form
collides with that of an existing name, or
</t>
<t>
allow the creation of the second name, but arrange so that after
post-processing, the second name is different than the post-processed
form of the first name.
</t>
</list>
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_cs_prep">
<t>
The nfs4_cs_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1.
However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cs_prep">
<t>
The nfs4_cs_prep profile specifies mapping using the
following tables from stringprep:
<list style='empty'>
<t>
Table B.1
</t>
</list>
</t>
<t>
Table B.2 is normally not part of the nfs4_cs_prep profile as it is
primarily for dealing with case-insensitive comparisons. However, if
the NFSv4.1 file server supports the case_insensitive file system
attribute, and if case_insensitive is TRUE, the NFSv4.1 server
MUST use Table B.2 (in addition to Table B1) when processing
utf8str_cs strings, and the NFSv4.1 client MUST assume Table B.2
(in addition to Table B.1) is being used.
</t>
<t>
If the case_preserving attribute is present and set to FALSE, then the
NFSv4.1 server MUST use Table B.2 to map case when processing
utf8str_cs strings. Whether the server maps from lower to upper case
or from upper to lower case is an implementation dependency.
</t>
</section>
<section toc="exclude" title="Normalization used by nfs4_cs_prep">
<t>
The nfs4_cs_prep profile does not specify a normalization form.  A
later revision of this specification may specify a particular
normalization form.  Therefore, the server and client can expect that
they may receive unnormalized characters within protocol requests and
responses.  If the operating environment requires normalization, then
the implementation must normalize utf8str_cs strings within the
protocol before presenting the information to an application (at the
client) or local file system (at the server).
</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_cs_prep">
<t>
The nfs4_cs_prep profile RECOMMENDS prohibiting the use of the
following tables from stringprep:
<list style='empty'>
<t>Table C.5</t>
<t>Table C.6</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_cs_prep">
<t>
The nfs4_cs_prep profile does not specify any checking of
bidirectional strings.
</t>
</section>
</section>
<section title="Stringprep Profile for the utf8str_cis Type">
<t>
Every use of the utf8str_cis type definition in the NFSv4.1
protocol specification follows the profile named nfs4_cis_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_cis_prep Profile">
<t>
The utf8str_cis type is a case-insensitive string of
UTF-8 characters.  Its primary use in NFSv4.1 is
for naming NFS servers.
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_cis_prep">
<t>
The nfs4_cis_prep profile uses Unicode 3.2, as defined in stringprep's
Appendix A.1. However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies mapping using the following tables from
stringprep:
<list style='empty'>
<t>Table B.1</t>
<t>Table B.2</t>
</list>
</t>
</section>
<section toc="exclude" title="Normalization Used by nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies using Unicode normalization form
KC, as described in stringprep.

</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies prohibiting using the following
tables from stringprep:
<list style='empty'>
<t>Table C.1.2</t>
<t>Table C.2.2</t>
<t>Table C.3</t>
<t>Table C.4</t>
<t>Table C.5</t>
<t>Table C.6</t>
<t>Table C.7</t>
<t>Table C.8</t>
<t>Table C.9</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_cis_prep">
<t>
The nfs4_cis_prep profile specifies checking bidirectional strings as
described in stringprep's Section 6.
</t>
</section>
</section>
<section title="Stringprep Profile for the utf8str_mixed Type">
<t>
Every use of the utf8str_mixed type definition in the NFSv4.1
protocol specification follows the profile named nfs4_mixed_prep.
</t>
<section toc="exclude" title="Intended Applicability of the nfs4_mixed_prep Profile">
<t>
The utf8str_mixed type is a string of UTF-8 characters, with a prefix
that is case sensitive, a separator equal to '@', and a suffix that is a
fully qualified domain name.  Its primary use in NFSv4.1 is for
naming principals identified in an Access Control Entry.
</t>
</section>
<section toc="exclude" title="Character Repertoire of nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile uses Unicode 3.2, as defined in
stringprep's Appendix A.1.
However, NFSv4.1 implementations are not limited to 3.2.
</t>
</section>
<section toc="exclude" title="Mapping Used by nfs4_cis_prep">
<t>
For the prefix and the separator of a utf8str_mixed
string, the nfs4_mixed_prep profile specifies mapping
using the following table from stringprep:
<list style='empty'>
<t>Table B.1</t>
</list>
</t>
<t>
For the suffix of a utf8str_mixed string, the nfs4_mixed_prep
profile specifies mapping using the following tables from
stringprep:
<list style='empty'>
<t>Table B.1</t>
<t>Table B.2</t>
</list>
</t>
</section>
<section toc="exclude" title="Normalization Used by nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies using Unicode normalization form
KC, as described in stringprep.
</t>
</section>
<section toc="exclude" title="Prohibited Output for nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies prohibiting using the
following tables from stringprep:
<list style='empty'>
<t>Table C.1.2</t>
<t>Table C.2.2</t>
<t>Table C.3</t>
<t>Table C.4</t>
<t>Table C.5</t>
<t>Table C.6</t>
<t>Table C.7</t>
<t>Table C.8</t>
<t>Table C.9</t>
</list>
</t>
</section>
<section toc="exclude" title="Bidirectional Output for nfs4_mixed_prep">
<t>
The nfs4_mixed_prep profile specifies checking bidirectional strings
as described in stringprep's Section 6.
</t>
</section>
</section>
<section title="UTF-8 Capabilities" anchor="utf8_caps">
<figure>
 <artwork>
const FSCHARSET_CAP4_CONTAINS_NON_UTF8  = 0x1;
const FSCHARSET_CAP4_ALLOWS_ONLY_UTF8   = 0x2;

typedef uint32_t        fs_charset_cap4;
 </artwork>
</figure>
<t>
Because some operating environments and file systems do
not enforce character set encodings, NFSv4.1 supports the
fs_charset_cap attribute (<xref target="attrdef_fs_charset_cap"/>)
that indicates to the client a file system's UTF-8 capabilities.
The attribute is an integer containing a pair of flags.
The first flag is FSCHARSET_CAP4_CONTAINS_NON_UTF8, which, if set
to one, tells the client that the file system contains non-UTF-8 characters,
and the server will not convert non-UTF characters to UTF-8 if the client
reads a symlink or directory, neither will operations with component
names or pathnames in the arguments convert the strings to UTF-8.
The second flag is FSCHARSET_CAP4_ALLOWS_ONLY_UTF8, which, if set to
one, indicates that the server will accept (and generate) only
UTF-8 characters on the file system. If 
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set to one, 
FSCHARSET_CAP4_CONTAINS_NON_UTF8 MUST be set to zero.
FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 SHOULD always be set to one.
</t>
</section>
<section title="UTF-8 Related Errors" anchor="utf8_related_errors">
<t>
Where the client sends an invalid UTF-8 string, the server should
return NFS4ERR_INVAL (see <xref target="error_definitions"/>).
This includes cases in which inappropriate prefixes are detected and
where the count includes trailing bytes that do not constitute a full
UCS character.
</t>
<t>
    Where the client-supplied string is valid UTF-8 but contains
    characters that are not supported by the server as a value for that
    string (e.g., names containing characters outside of Unicode plane 0 on
    file systems that fail to support such characters despite their
    presence in the Unicode standard), the server should return
    NFS4ERR_BADCHAR.
</t>
<t>
Where a UTF-8 string is used as a file name, and the file system (while
supporting all of the characters within the name) does not allow that
particular name to be used, the server should return the error <xref
target="error_definitions">NFS4ERR_BADNAME</xref>.  This includes
situations in which the server file system imposes a normalization
constraint on name strings, but will also include such situations as
file system prohibitions of "."  and ".." as file names for certain
operations, and other such constraints.
</t>
</section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section title="Error Values">
  <t>
    NFS error numbers are assigned to failed operations within a 
    Compound (COMPOUND or CB_COMPOUND) request.  A Compound request 
    contains a number of NFS operations that have their results 
    encoded in sequence in a Compound reply.  The results of successful 
    operations will consist of an NFS4_OK status followed by the 
    encoded results of the operation.  If an NFS operation fails, an 
    error status will be entered in the reply and the Compound
    request will be terminated.
  </t>
  <section title="Error Definitions">
    <texttable anchor='error_definitions'>
      <preamble>
	Protocol Error Definitions
      </preamble>
      <ttcol align='left'>Error</ttcol>
      <ttcol align='left'>Number</ttcol>
      <ttcol align='left'>Description</ttcol>

      <c>NFS4_OK</c>
      <c>0</c>
      <c><xref target="err_OK" /></c>

      <c>NFS4ERR_ACCESS</c>
      <c>13</c>
      <c><xref target="err_ACCESS" /></c>

      <c>NFS4ERR_ATTRNOTSUPP</c>
      <c>10032</c>
      <c><xref target="err_ATTRNOTSUPP" /></c>

      <c>NFS4ERR_ADMIN_REVOKED</c>
      <c>10047</c>
      <c><xref target="err_ADMIN_REVOKED" /></c>

      <c>NFS4ERR_BACK_CHAN_BUSY</c>
      <c>10057</c>
      <c><xref target="err_BACK_CHAN_BUSY" /></c>

      <c>NFS4ERR_BADCHAR</c>
      <c>10040</c>
      <c><xref target="err_BADCHAR" /></c>

      <c>NFS4ERR_BADHANDLE</c>
      <c>10001</c>
      <c><xref target="err_BADHANDLE" /></c>

      <c>NFS4ERR_BADIOMODE</c>
      <c>10049</c>
      <c><xref target="err_BADIOMODE" /></c>

      <c>NFS4ERR_BADLAYOUT</c>
      <c>10050</c>
      <c><xref target="err_BADLAYOUT" /></c>

      <c>NFS4ERR_BADNAME</c>
      <c>10041</c>
      <c><xref target="err_BADNAME" /></c>

      <c>NFS4ERR_BADOWNER</c>
      <c>10039</c>
      <c><xref target="err_BADOWNER" /></c>

      <c>NFS4ERR_BADSESSION</c>
      <c>10052</c>
      <c><xref target="err_BADSESSION" /></c>

      <c>NFS4ERR_BADSLOT</c>
      <c>10053</c>
      <c><xref target="err_BADSLOT" /></c>

      <c>NFS4ERR_BADTYPE</c>
      <c>10007</c>
      <c><xref target="err_BADTYPE" /></c>

      <c>NFS4ERR_BADXDR</c>
      <c>10036</c>
      <c><xref target="err_BADXDR" /></c>

      <c>NFS4ERR_BAD_COOKIE</c>
      <c>10003</c>
      <c><xref target="err_BAD_COOKIE" /></c>

      <c>NFS4ERR_BAD_HIGH_SLOT</c>
      <c>10077</c>
      <c><xref target="err_BAD_HIGH_SLOT" /></c>

      <c>NFS4ERR_BAD_RANGE</c>
      <c>10042</c>
      <c><xref target="err_BAD_RANGE" /></c>

      <c>NFS4ERR_BAD_SEQID</c>
      <c>10026</c>
      <c><xref target="err_BAD_SEQID" /></c>

      <c>NFS4ERR_BAD_SESSION_DIGEST</c>
      <c>10051</c>
      <c><xref target="err_BAD_SESSION_DIGEST" /></c>

      <c>NFS4ERR_BAD_STATEID</c>
      <c>10025</c>
      <c><xref target="err_BAD_STATEID" /></c>

      <c>NFS4ERR_CB_PATH_DOWN</c>
      <c>10048</c>
      <c><xref target="err_CB_PATH_DOWN" /></c>

      <c>NFS4ERR_CLID_INUSE</c>
      <c>10017</c>
      <c><xref target="err_CLID_INUSE" /></c>

      <c>NFS4ERR_CLIENTID_BUSY</c>
      <c>10074</c>
      <c><xref target="err_CLIENTID_BUSY" /></c>

      <c>NFS4ERR_COMPLETE_ALREADY</c>
      <c>10054</c>
      <c><xref target="err_COMPLETE_ALREADY" /></c>

      <c>NFS4ERR_CONN_NOT_BOUND_TO_SESSION</c>
      <c>10055</c>
      <c><xref target="err_CONN_NOT_BOUND_TO_SESSION" /></c>

      <c>NFS4ERR_DEADLOCK</c>
      <c>10045</c>
      <c><xref target="err_DEADLOCK" /></c>

      <c>NFS4ERR_DEADSESSION</c>
      <c>10078</c>
      <c><xref target="err_DEADSESSION" /></c>

      <c>NFS4ERR_DELAY</c>
      <c>10008</c>
      <c><xref target="err_DELAY" /></c>

      <c>NFS4ERR_DELEG_ALREADY_WANTED</c>
      <c>10056</c>
      <c><xref target="err_DELEG_ALREADY_WANTED" /></c>

      <c>NFS4ERR_DELEG_REVOKED</c>
      <c>10087</c>
      <c><xref target="err_DELEG_REVOKED" /></c>

      <c>NFS4ERR_DENIED</c>
      <c>10010</c>
      <c><xref target="err_DENIED" /></c>

      <c>NFS4ERR_DIRDELEG_UNAVAIL</c>
      <c>10084</c>
      <c><xref target="err_DIRDELEG_UNAVAIL" /></c>

      <c>NFS4ERR_DQUOT</c>
      <c>69</c>
      <c><xref target="err_DQUOT" /></c>

      <c>NFS4ERR_ENCR_ALG_UNSUPP</c>
      <c>10079</c>
      <c><xref target="err_ENCR_ALG_UNSUPP" /></c>

      <c>NFS4ERR_EXIST</c>
      <c>17</c>
      <c><xref target="err_EXIST" /></c>

      <c>NFS4ERR_EXPIRED</c>
      <c>10011</c>
      <c><xref target="err_EXPIRED" /></c>

      <c>NFS4ERR_FBIG</c>
      <c>27</c>
      <c><xref target="err_FBIG" /></c>

      <c>NFS4ERR_FHEXPIRED</c>
      <c>10014</c>
      <c><xref target="err_FHEXPIRED" /></c>

      <c>NFS4ERR_FILE_OPEN</c>
      <c>10046</c>
      <c><xref target="err_FILE_OPEN" /></c>

      <c>NFS4ERR_GRACE</c>
      <c>10013</c>
      <c><xref target="err_GRACE" /></c>

      <c>NFS4ERR_HASH_ALG_UNSUPP</c>
      <c>10072</c>
      <c><xref target="err_HASH_ALG_UNSUPP" /></c>

      <c>NFS4ERR_INVAL</c>
      <c>22</c>
      <c><xref target="err_INVAL" /></c>

      <c>NFS4ERR_IO</c>
      <c>5</c>
      <c><xref target="err_IO" /></c>

      <c>NFS4ERR_ISDIR</c>
      <c>21</c>
      <c><xref target="err_ISDIR" /></c>

      <c>NFS4ERR_LAYOUTTRYLATER</c>
      <c>10058</c>
      <c><xref target="err_LAYOUTTRYLATER" /></c>

      <c>NFS4ERR_LAYOUTUNAVAILABLE</c>
      <c>10059</c>
      <c><xref target="err_LAYOUTUNAVAILABLE" /></c>

      <c>NFS4ERR_LEASE_MOVED</c>
      <c>10031</c>
      <c><xref target="err_LEASE_MOVED" /></c>

      <c>NFS4ERR_LOCKED</c>
      <c>10012</c>
      <c><xref target="err_LOCKED" /></c>

      <c>NFS4ERR_LOCKS_HELD</c>
      <c>10037</c>
      <c><xref target="err_LOCKS_HELD" /></c>

      <c>NFS4ERR_LOCK_NOTSUPP</c>
      <c>10043</c>
      <c><xref target="err_LOCK_NOTSUPP" /></c>

      <c>NFS4ERR_LOCK_RANGE</c>
      <c>10028</c>
      <c><xref target="err_LOCK_RANGE" /></c>

      <c>NFS4ERR_MINOR_VERS_MISMATCH</c>
      <c>10021</c>
      <c><xref target="err_MINOR_VERS_MISMATCH" /></c>

      <c>NFS4ERR_MLINK</c>
      <c>31</c>
      <c><xref target="err_MLINK" /></c>

      <c>NFS4ERR_MOVED</c>
      <c>10019</c>
      <c><xref target="err_MOVED" /></c>

      <c>NFS4ERR_NAMETOOLONG</c>
      <c>63</c>
      <c><xref target="err_NAMETOOLONG" /></c>

      <c>NFS4ERR_NOENT</c>
      <c>2</c>
      <c><xref target="err_NOENT" /></c>

      <c>NFS4ERR_NOFILEHANDLE</c>
      <c>10020</c>
      <c><xref target="err_NOFILEHANDLE" /></c>

      <c>NFS4ERR_NOMATCHING_LAYOUT</c>
      <c>10060</c>
      <c><xref target="err_NOMATCHING_LAYOUT" /></c>

      <c>NFS4ERR_NOSPC</c>
      <c>28</c>
      <c><xref target="err_NOSPC" /></c>

      <c>NFS4ERR_NOTDIR</c>
      <c>20</c>
      <c><xref target="err_NOTDIR" /></c>

      <c>NFS4ERR_NOTEMPTY</c>
      <c>66</c>
      <c><xref target="err_NOTEMPTY" /></c>

      <c>NFS4ERR_NOTSUPP</c>
      <c>10004</c>
      <c><xref target="err_NOTSUPP" /></c>

      <c>NFS4ERR_NOT_ONLY_OP</c>
      <c>10081</c>
      <c><xref target="err_NOT_ONLY_OP" /></c>

      <c>NFS4ERR_NOT_SAME</c>
      <c>10027</c>
      <c><xref target="err_NOT_SAME" /></c>

      <c>NFS4ERR_NO_GRACE</c>
      <c>10033</c>
      <c><xref target="err_NO_GRACE" /></c>

      <c>NFS4ERR_NXIO</c>
      <c>6</c>
      <c><xref target="err_NXIO" /></c>

      <c>NFS4ERR_OLD_STATEID</c>
      <c>10024</c>
      <c><xref target="err_OLD_STATEID" /></c>

      <c>NFS4ERR_OPENMODE</c>
      <c>10038</c>
      <c><xref target="err_OPENMODE" /></c>

      <c>NFS4ERR_OP_ILLEGAL</c>
      <c>10044</c>
      <c><xref target="err_OP_ILLEGAL" /></c>

      <c>NFS4ERR_OP_NOT_IN_SESSION</c>
      <c>10071</c>
      <c><xref target="err_OP_NOT_IN_SESSION" /></c>

      <c>NFS4ERR_PERM</c>
      <c>1</c>
      <c><xref target="err_PERM" /></c>

      <c>NFS4ERR_PNFS_IO_HOLE</c>
      <c>10075</c>
      <c><xref target="err_PNFS_IO_HOLE" /></c>

      <c>NFS4ERR_PNFS_NO_LAYOUT</c>
      <c>10080</c>
      <c><xref target="err_PNFS_NO_LAYOUT" /></c>

      <c>NFS4ERR_RECALLCONFLICT</c>
      <c>10061</c>
      <c><xref target="err_RECALLCONFLICT" /></c>

      <c>NFS4ERR_RECLAIM_BAD</c>
      <c>10034</c>
      <c><xref target="err_RECLAIM_BAD" /></c>

      <c>NFS4ERR_RECLAIM_CONFLICT</c>
      <c>10035</c>
      <c><xref target="err_RECLAIM_CONFLICT" /></c>

      <c>NFS4ERR_REJECT_DELEG</c>
      <c>10085</c>
      <c><xref target="err_REJECT_DELEG" /></c>

      <c>NFS4ERR_REP_TOO_BIG</c>
      <c>10066</c>
      <c><xref target="err_REP_TOO_BIG" /></c>

      <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c>
      <c>10067</c>
      <c><xref target="err_REP_TOO_BIG_TO_CACHE" /></c>

      <c>NFS4ERR_REQ_TOO_BIG</c>
      <c>10065</c>
      <c><xref target="err_REQ_TOO_BIG" /></c>

      <c>NFS4ERR_RESTOREFH</c>
      <c>10030</c>
      <c><xref target="err_RESTOREFH" /></c>

      <c>NFS4ERR_RETRY_UNCACHED_REP</c>
      <c>10068</c>
      <c><xref target="err_RETRY_UNCACHED_REP" /></c>

      <c>NFS4ERR_RETURNCONFLICT</c>
      <c>10086</c>
      <c><xref target="err_RETURNCONFLICT" /></c>

      <c>NFS4ERR_ROFS</c>
      <c>30</c>
      <c><xref target="err_ROFS" /></c>

      <c>NFS4ERR_SAME</c>
      <c>10009</c>
      <c><xref target="err_SAME" /></c>

      <c>NFS4ERR_SHARE_DENIED</c>
      <c>10015</c>
      <c><xref target="err_SHARE_DENIED" /></c>

      <c>NFS4ERR_SEQUENCE_POS</c>
      <c>10064</c>
      <c><xref target="err_SEQUENCE_POS" /></c>

      <c>NFS4ERR_SEQ_FALSE_RETRY</c>
      <c>10076</c>
      <c><xref target="err_SEQ_FALSE_RETRY" /></c>

      <c>NFS4ERR_SEQ_MISORDERED</c>
      <c>10063</c>
      <c><xref target="err_SEQ_MISORDERED" /></c>

      <c>NFS4ERR_SERVERFAULT</c>
      <c>10006</c>
      <c><xref target="err_SERVERFAULT" /></c>

      <c>NFS4ERR_STALE</c>
      <c>70</c>
      <c><xref target="err_STALE" /></c>

      <c>NFS4ERR_STALE_CLIENTID</c>
      <c>10022</c>
      <c><xref target="err_STALE_CLIENTID" /></c>

      <c>NFS4ERR_STALE_STATEID</c>
      <c>10023</c>
      <c><xref target="err_STALE_STATEID" /></c>

      <c>NFS4ERR_SYMLINK</c>
      <c>10029</c>
      <c><xref target="err_SYMLINK" /></c>

      <c>NFS4ERR_TOOSMALL</c>
      <c>10005</c>
      <c><xref target="err_TOOSMALL" /></c>

      <c>NFS4ERR_TOO_MANY_OPS</c>
      <c>10070</c>
      <c><xref target="err_TOO_MANY_OPS" /></c>

      <c>NFS4ERR_UNKNOWN_LAYOUTTYPE</c>
      <c>10062</c>
      <c><xref target="err_UNKNOWN_LAYOUTTYPE" /></c>

      <c>NFS4ERR_UNSAFE_COMPOUND</c>
      <c>10069</c>
      <c><xref target="err_UNSAFE_COMPOUND" /></c>
      
      <c>NFS4ERR_WRONGSEC</c>
      <c>10016</c>
      <c><xref target="err_WRONGSEC" /></c>

      <c>NFS4ERR_WRONG_CRED</c>
      <c>10082</c>
      <c><xref target="err_WRONG_CRED" /></c>

      <c>NFS4ERR_WRONG_TYPE</c>
      <c>10083</c>
      <c><xref target="err_WRONG_TYPE" /></c>

      <c>NFS4ERR_XDEV</c>
      <c>18</c>
      <c><xref target="err_XDEV" /></c>

    </texttable>
  <section title="General Errors" anchor="errors_gen">
    <t>
      This section deals with errors that are applicable to a broad
      set of different purposes.
    </t>
    <section title="NFS4ERR_BADXDR (Error Code 10036)" 
       	     anchor="err_BADXDR">
      <t>
        The arguments for this operation do not match those specified in
        the XDR definition.  This includes situations in which the
        request ends before all the arguments have been seen.  Note
        that this error applies when fixed enumerations (these include
        booleans) have a value within the input stream that is not
        valid for the enum.  A replier may pre-parse all operations for
        a Compound procedure before doing any operation execution 
        and return RPC-level XDR errors in that case.  
      </t>
    </section>
    <section title="NFS4ERR_BAD_COOKIE (Error Code 10003)" 
             anchor="err_BAD_COOKIE">
      <t>
        Used for operations that provide a set of information indexed by
        some quantity provided by the client or cookie sent by the
        server for an earlier invocation.  Where the value cannot 
        be used for its intended purpose, this error results. 
      </t>
    </section>
    <section title="NFS4ERR_DELAY (Error Code 10008)" 
             anchor="err_DELAY">
      <t>
        For any of a number of reasons, the replier could not 
        process this operation in what was deemed a reasonable
        time.  The client should wait and then try the request 
        with a new slot and sequence value.  
      </t>
      <t>
        Some examples of scenarios that might lead to this situation:
          <list style="symbols">
            <t>
              A server that supports hierarchical storage receives a 
              request to process a file that had been migrated. 
            </t>
            <t>
             An operation requires a delegation recall to proceed,
             and waiting for this delegation recall makes processing
             this request in a timely fashion impossible.
           </t>
         </list>
       </t>
       <t>
        In such cases, the error NFS4ERR_DELAY allows
        these preparatory operations to proceed without
        holding up client resources such as a session slot.
        After delaying for period of time, the client can
        then re-send the operation in question  (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).

      </t>
      <t>
        Note that without the ability to return NFS4ERR_DELAY and the
        client's willingness to re-send when receiving it, deadlock might
        result.  For example, if a recall is done, and if the delegation return or
        operations preparatory to delegation return are held up by
        other operations that need the delegation to be returned, 
        session slots might not be available.  The result could be
        deadlock.
      </t>
    </section>
    <section title="NFS4ERR_INVAL (Error Code 22)" 
             anchor="err_INVAL">
      <t>
        The arguments for this operation are not valid for some reason, even
        though they do match those specified in the XDR definition for
        the request.
      </t>
    </section>
    <section title="NFS4ERR_NOTSUPP (Error Code 10004)" 
             anchor="err_NOTSUPP">
      <t>
        Operation not supported, either because the operation is
        an OPTIONAL one and is not supported by this server or
        because the operation MUST NOT be implemented in 
        the current minor version.
      </t>
    </section>
    <section title="NFS4ERR_SERVERFAULT (Error Code 10006)" 
             anchor="err_SERVERFAULT">
      <t>
        An error occurred on the server that does not map to any of
        the specific legal NFSv4.1 protocol error values.  The client
        should translate this into an appropriate error.  UNIX clients
        may choose to translate this to EIO.

     </t>
    </section>
    <section title="NFS4ERR_TOOSMALL (Error Code 10005)" 
             anchor="err_TOOSMALL"> 
      <t>
        Used where an operation returns a variable amount of data,
        with a limit specified by the client.  Where the data 
        returned cannot be fit within the limit specified by the
        client, this error results.
      </t>
    </section>
  </section>

  <section title="Filehandle Errors" anchor="errors_fh">
    <t>
      These errors deal with the situation in which the current
      or saved filehandle, or the filehandle passed to PUTFH
      intended to become the current filehandle, is invalid
      in some way.  This includes situations in which the
      filehandle is a valid filehandle in general but is not 
      of the appropriate object type for the current operation.
    </t>
    <t>
      Where the error description indicates a problem with the
      current or saved filehandle, it is to be understood that 
      filehandles are only checked for the condition if they
      are implicit arguments of the operation in question.
    </t>
    <section title="NFS4ERR_BADHANDLE (Error Code 10001)" 
             anchor="err_BADHANDLE">
      <t>
        Illegal NFS filehandle for the current server.  The current
        file handle failed internal consistency checks.  Once accepted
        as valid (by PUTFH), no subsequent status change can cause the
        filehandle to generate this error.
      </t>
    </section> 
    <section title="NFS4ERR_FHEXPIRED (Error Code 10014)" 
             anchor="err_FHEXPIRED">
      <t>
        A current or saved filehandle that is an argument to the
        current operation is volatile and has expired at the server.
      </t>
    </section>
   <section title="NFS4ERR_ISDIR (Error Code 21)" 
             anchor="err_ISDIR">
      <t>
        The current or saved filehandle designates a directory 
        when the current operation does not allow a directory to 
        be accepted as the target of this operation.
      </t>
    </section>
    <section title="NFS4ERR_MOVED (Error Code 10019)" 
             anchor="err_MOVED">
      <t>
        The file system that contains the current filehandle object
        is not present at the server.  It may have been relocated or
        migrated to another server, or it may have never been present.
        The client may obtain the new file system location by obtaining 
        the "fs_locations" or "fs_locations_info" attribute for the 
        current filehandle.  For further discussion, refer to 
        <xref target="presence_or_absence" />.
      </t>
    </section>
    <section title="NFS4ERR_NOFILEHANDLE (Error Code 10020)" 
             anchor="err_NOFILEHANDLE">
      <t>
        The logical current or saved filehandle value is required by 
        the current operation and is not set.
        This may be a result of a malformed COMPOUND
        operation (i.e., no PUTFH or PUTROOTFH before an operation that
        requires the current filehandle be set).
      </t>
    </section>
    <section title="NFS4ERR_NOTDIR (Error Code 20)" 
             anchor="err_NOTDIR">
      <t>
        The current (or saved) filehandle designates an object that
        is not a directory for an operation in which a directory is
        required.
      </t>
    </section>
    <section title="NFS4ERR_STALE (Error Code 70)" 
             anchor="err_STALE">
      <t>
        The current or saved filehandle value designating an argument
        to the current operation is invalid. The file referred to by
        that filehandle no longer exists or access to it has been
        revoked.
      </t>
    </section>
    <section title="NFS4ERR_SYMLINK (Error Code 10029)" 
             anchor="err_SYMLINK">
      <t>
        The current filehandle designates a symbolic link when the 
        current operation does not allow a symbolic link as the 
        target.
      </t>
    </section>
    <section title="NFS4ERR_WRONG_TYPE (Error Code 10083)" 
             anchor="err_WRONG_TYPE">
      <t>
        The current (or saved) filehandle designates an object that
        is of an invalid type for the current operation, and there is no
        more specific error (such as NFS4ERR_ISDIR or NFS4ERR_SYMLINK)
        that applies.  Note that in NFSv4.0, such situations generally
        resulted in the less-specific error NFS4ERR_INVAL.
      </t>
    </section>
  </section>

  <section title="Compound Structure Errors" anchor="errors_comp">
    <t>
      This section deals with errors that relate to the overall structure
      of a Compound request (by which we mean to include both
      COMPOUND and CB_COMPOUND), rather than to particular operations. 
    </t>
    <t>
      There are a number of basic constraints on the operations that
      may appear in a Compound request.  Sessions add to these basic 
      constraints by requiring a Sequence operation (either SEQUENCE
      or CB_SEQUENCE) at the start of the Compound.
    </t>
    <section title="NFS_OK (Error code 0)"
             anchor="err_OK">
      <t>
        Indicates the operation completed successfully, in that all
        of the constituent operations completed without error.
      </t>
    </section>
    <section title="NFS4ERR_MINOR_VERS_MISMATCH (Error code 10021)"
             anchor="err_MINOR_VERS_MISMATCH">
      <t>
        The minor version specified is not one that the current listener
        supports.  This value is returned in the overall status for the
        Compound but is not associated with a specific operation since
        the results will specify a result count of zero.
      </t>
    </section>
    <section title="NFS4ERR_NOT_ONLY_OP (Error Code 10081)" 
             anchor="err_NOT_ONLY_OP">
      <t>
        Certain operations, which are allowed to be executed outside
        of a session, MUST be the only operation within a Compound
        whenever the Compound does not start with a Sequence
        operation. This error results when that constraint is not met.
      </t>
    </section>
    <section title="NFS4ERR_OP_ILLEGAL (Error Code 10044)" 
             anchor="err_OP_ILLEGAL">
      <t>
        The operation code is not a valid one for the current
        Compound procedure.  The opcode
        in the result stream matched with this error is the
        ILLEGAL value, although the value that appears in the
        request stream may be different.  Where an illegal 
        value appears and the replier pre-parses all operations for
        a Compound procedure before doing any operation execution, 
        an RPC-level XDR error may be returned.  
      </t>
    </section>
    <section title="NFS4ERR_OP_NOT_IN_SESSION (Error Code 10071)" 
             anchor="err_OP_NOT_IN_SESSION">
      <t>
        Most forward operations and all callback operations are only
        valid within the context of a session, so that the Compound
        request in question MUST begin with a Sequence operation.
        If an attempt is made to execute these operations outside 
        the context of session, this error results.
      </t>
    </section>
    <section title="NFS4ERR_REP_TOO_BIG (Error Code 10066)" 
             anchor="err_REP_TOO_BIG">
      <t>
        The reply to a Compound would exceed the 
        channel's negotiated maximum response size.
      </t>
    </section>
    <section title="NFS4ERR_REP_TOO_BIG_TO_CACHE (Error Code 10067)" 
             anchor="err_REP_TOO_BIG_TO_CACHE">
      <t>
        The reply to a Compound would exceed the 
        channel's negotiated maximum size for replies cached in the
        reply cache when the Sequence for the current request specifies
        that this request is to be cached.
      </t>
    </section>
    <section title="NFS4ERR_REQ_TOO_BIG (Error Code 10065)" 
             anchor="err_REQ_TOO_BIG">
      <t>
        The Compound request exceeds the 
        channel's negotiated maximum size for requests.
      </t>
    </section>
    <section title="NFS4ERR_RETRY_UNCACHED_REP (Error Code 10068)" 
             anchor="err_RETRY_UNCACHED_REP">
      <t>
        The requester has attempted a retry of a Compound
        that it previously requested not
        be placed in the reply cache.
      </t>
    </section>
    <section title="NFS4ERR_SEQUENCE_POS (Error Code 10064)" 
             anchor="err_SEQUENCE_POS">
      <t>
        A Sequence operation appeared in a 
        position other than the first operation of a 
        Compound request.
      </t>
    </section>
    <section title="NFS4ERR_TOO_MANY_OPS (Error Code 10070)" 
             anchor="err_TOO_MANY_OPS">
      <t>
        The Compound request has too many operations, exceeding the
        count negotiated when the session was created. 
      </t>
    </section>
    <section title="NFS4ERR_UNSAFE_COMPOUND (Error Code 10068)" 
             anchor="err_UNSAFE_COMPOUND">
      <t>
        The client has sent a COMPOUND request with an unsafe
        mix of operations -- specifically, with a non-idempotent
        operation that changes the current filehandle and that is not followed by a
        GETFH.
      </t>
    </section>
  </section>

  <section title="File System Errors" anchor="errors_fs">
    <t>
      These errors describe situations that occurred in the underlying
      file system implementation rather than in the protocol or any
      NFSv4.x feature.
    </t>
    <section title="NFS4ERR_BADTYPE (Error Code 10007)" 
             anchor="err_BADTYPE">
      <t>
        An attempt was made to create an object with an inappropriate
        type specified to CREATE.  This may be because the type 
        is undefined, because the type is not supported by the 
        server, or because the type is not intended to be created by CREATE
        (such as a regular file or named attribute, for 
        which OPEN is used to do the file creation).
      </t>
    </section>
    <section title="NFS4ERR_DQUOT (Error Code 19)" 
             anchor="err_DQUOT">
      <t>
        Resource (quota) hard limit exceeded. The user's resource
        limit on the server has been exceeded.
      </t>
    </section>
    <section title="NFS4ERR_EXIST (Error Code 17)" 
             anchor="err_EXIST">
      <t>
        A file of the specified target name (when creating, renaming,
        or linking) already exists.
      </t>
    </section>
    <section title="NFS4ERR_FBIG (Error Code 27)" 
             anchor="err_FBIG">
      <t>
        The file is too large. The operation would have caused the file to
        grow beyond the server's limit.
      </t>
    </section>
    <section title="NFS4ERR_FILE_OPEN (Error Code 10046)" 
             anchor="err_FILE_OPEN">
      <t>
        The operation is not allowed because a
        file involved in the operation is currently open.
        Servers may, but are not required to, disallow linking-to,
        removing, or renaming open files.
      </t>
    </section>
    <section title="NFS4ERR_IO (Error Code 5)" 
             anchor="err_IO">
      <t>
        Indicates that an I/O error occurred for which the file system
        was unable to provide recovery.
      </t>
    </section>
    <section title="NFS4ERR_MLINK (Error Code 31)" 
             anchor="err_MLINK">
      <t>
        The request would have caused the server's limit for the
        number of hard links a file may have to be exceeded.
      </t>
    </section>
    <section title="NFS4ERR_NOENT (Error Code 2)" 
             anchor="err_NOENT">
      <t>
         Indicates no such file or directory. The file or directory name
         specified does not exist.
      </t>
    </section>
    <section title="NFS4ERR_NOSPC (Error Code 28)" 
             anchor="err_NOSPC">
      <t>
        Indicates there is no space left on the device. The operation would have 
        caused the server's file system to exceed its limit.
      </t>
    </section>
    <section title="NFS4ERR_NOTEMPTY (Error Code 66)" 
             anchor="err_NOTEMPTY">
      <t>
         An attempt was made to remove a directory that was not
         empty.
      </t>
    </section>
    <section title="NFS4ERR_ROFS (Error Code 30)" 
             anchor="err_ROFS">
      <t>
         Indicates a read-only file system. A modifying operation was 
         attempted on a read-only file system.
      </t>
    </section>
    <section title="NFS4ERR_XDEV (Error Code 18)" 
             anchor="err_XDEV">
      <t>
        Indicates an attempt to do an operation, such as linking, that
        inappropriately crosses a boundary.  This may be due to such 
        boundaries as:
        <list style="symbols">
          <t>
            that between file systems (where the fsids are different).
          </t>
          <t>
            that between different named attribute directories or
            between a named attribute directory and an ordinary 
            directory.
          </t>
          <t>
            that between byte-ranges of a file system that the file system
            implementation treats as separate (for example, for space
            accounting purposes), and where cross-connection between
            the byte-ranges are not allowed.
          </t>
        </list>
      </t>
    </section>
  </section>

  <section title="State Management Errors" anchor="errors_state_mgt">
    <t>
      These errors indicate problems with the stateid (or one of
      the stateids) passed to a given operation.  
      This includes
      situations in which the stateid is invalid as well as
      situations in which the stateid is valid but designates 
      locking state that has been revoked.
Depending on the operation, the 
      stateid when valid may designate opens, byte-range locks,
      file or directory delegations, layouts, or device maps.
    </t>
    <section title="NFS4ERR_ADMIN_REVOKED (Error Code 10047)" 
             anchor="err_ADMIN_REVOKED">
      <t>
        A stateid designates locking state of any type that has
        been revoked due to administrative interaction, possibly
        while the lease is valid.
      </t>
    </section>
    <section title="NFS4ERR_BAD_STATEID (Error Code 10026)" 
             anchor="err_BAD_STATEID">
      <t>
        A stateid does not properly designate any valid 
        state.  See Sections <xref target="stateid_lifetime" format="counter" /> and 
        <xref target="special_stateid" format="counter" />
        for a discussion of how stateids are validated.
      </t>
    </section>
    <section title="NFS4ERR_DELEG_REVOKED (Error Code 10087)" 
             anchor="err_DELEG_REVOKED">
      <t>
	A stateid designates recallable locking state of
	any type (delegation or layout) that has been
	revoked due to the failure of the client to return
	the lock when it was recalled.

      </t>
    </section>
    <section title="NFS4ERR_EXPIRED (Error Code 10011)" 
             anchor="err_EXPIRED">
      <t>
        A stateid designates locking state of any type that has
        been revoked due to expiration of the client's lease,
        either immediately upon lease expiration, or following 
        a later request for a conflicting lock.
      </t>
    </section>
    <section title="NFS4ERR_OLD_STATEID (Error Code 10024)" 
             anchor="err_OLD_STATEID">
      <t>
        A stateid with a non-zero seqid value does match 
        the current seqid for the state designated by the
        user.
      </t>
    </section>
  </section>

  <section title="Security Errors" anchor="errors_sec">
    <t>
      These are the various permission-related errors in NFSv4.1.
    </t>
    <section title="NFS4ERR_ACCESS (Error Code 13)" 
             anchor="err_ACCESS">
      <t>
        Indicates permission denied. The caller does
        not have the correct permission to perform
        the requested operation. Contrast this with
        NFS4ERR_PERM (<xref target="err_PERM" />), which
        restricts itself to owner or privileged-user
        permission failures, and NFS4ERR_WRONG_CRED
        (<xref target="err_WRONG_CRED" />), which deals
        with appropriate permission to delete or modify
        transient objects based on the credentials of
        the user that created them.

      </t>
    </section>
    <section title="NFS4ERR_PERM (Error Code 1)" 
             anchor="err_PERM">
      <t>
        Indicates requester is not the owner. The operation was not 
        allowed because the caller is neither a privileged user 
        (root) nor the owner of the target of the operation.
      </t>
    </section>
    <section title="NFS4ERR_WRONGSEC (Error Code 10016)" 
             anchor="err_WRONGSEC">
      <t>
        Indicates that the security mechanism being used by the client 
        for the operation does not match the server's security policy.  
        The client should change the security mechanism being used and 
        re-send the operation (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).  SECINFO and SECINFO_NO_NAME can be used
        to determine the appropriate mechanism.
      </t>
    </section>
    <section title="NFS4ERR_WRONG_CRED (Error Code 10082)" 
             anchor="err_WRONG_CRED">
      <t>
        An operation that manipulates state was attempted by a principal
        that was not allowed to modify that piece of state.
      </t>
    </section>
  </section>

  <section title="Name Errors" anchor="errors_name">
    <t>
      Names in NFSv4 are UTF-8 strings.  When the strings are not
      valid UTF-8 or are of length zero, the error NFS4ERR_INVAL
      results.  Besides this, there are a number of other errors 
      to indicate specific problems with names.
    </t>
    <section title="NFS4ERR_BADCHAR (Error Code 10040)" 
             anchor="err_BADCHAR">
      <t>
        A UTF-8 string contains a character that is not supported 
        by the server in the context in which it being used.
      </t>
    </section>
    <section title="NFS4ERR_BADNAME (Error Code 10041)" 
             anchor="err_BADNAME">
      <t>
         A name string in a request consisted of valid UTF-8
         characters supported by the server, but the name is not 
         supported by the server as a valid name for the current operation.
         An example might be creating a file or directory named ".."
         on a server whose file system uses that name for links to
         parent directories.
      </t>
    </section>
    <section title="NFS4ERR_NAMETOOLONG (Error Code 63)" 
             anchor="err_NAMETOOLONG">
      <t>
         Returned when the filename in an operation exceeds the
         server's implementation limit.  
      </t>
    </section>
  </section>

  <section title="Locking Errors" anchor="errors_locking">
    <t>
      This section deals with errors related to locking, both as to
      share reservations and byte-range locking.  It does not deal
      with errors specific to the process of reclaiming locks.  Those
      are dealt with in <xref target="errors_reclaim"></xref>.
    </t>
    <section title="NFS4ERR_BAD_RANGE (Error Code 10042)" 
             anchor="err_BAD_RANGE">
      <t>
        The byte-range of a LOCK, LOCKT, or LOCKU operation is
        not allowed by the
        server.  For example, this error results when a server
        that only supports 32-bit ranges receives a range that
        cannot be handled by that server.  (See 
        <xref target="OP_LOCK_DESCRIPTION" />.)
      </t>
    </section>
    <section title="NFS4ERR_DEADLOCK (Error Code 10045)" 
             anchor="err_DEADLOCK">
      <t>
        The server has been able to determine a byte-range locking
        deadlock condition for a READW_LT or WRITEW_LT LOCK operation.
      </t>
    </section>
    <section title="NFS4ERR_DENIED (Error Code 10010)" 
             anchor="err_DENIED">
      <t>
        An attempt to lock a file is denied.  Since this may be a
        temporary condition, the client is encouraged to re-send the lock
        request (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send) until the lock is accepted.  See 
        <xref target="blocking_locks" /> for a discussion of the re-send.
      </t>
    </section>
    <section title="NFS4ERR_LOCKED (Error Code 10012)" 
             anchor="err_LOCKED">
      <t>
        A READ or WRITE operation was attempted on a file where there
        was a conflict between the I/O and an existing lock:
        <list style="symbols"> 
          <t>
            There is a share reservation inconsistent with the I/O
            being done.
          </t>
          <t>
            The range to be read or written intersects an existing
            mandatory byte-range lock.
          </t>
        </list>
      </t>
    </section>
    <section title="NFS4ERR_LOCKS_HELD (Error Code 10037)" 
             anchor="err_LOCKS_HELD">
      <t>
        An operation was prevented by the unexpected presence of locks.
      </t>
    </section>
    <section title="NFS4ERR_LOCK_NOTSUPP (Error Code 10043)" 
             anchor="err_LOCK_NOTSUPP">
      <t>
        A LOCK operation was attempted that would require the upgrade 
        or downgrade of a byte-range lock range already held by the owner, and the
        server does not support atomic upgrade or downgrade of locks.
      </t>
    </section>
    <section title="NFS4ERR_LOCK_RANGE (Error Code 10028)" 
             anchor="err_LOCK_RANGE">
      <t>
        A LOCK operation is operating on a range that overlaps in part a
        currently held byte-range lock for the current lock-owner and does not
        precisely match a single such byte-range lock where the server 
        does not support this type of request, and thus does not 
        implement POSIX locking semantics <xref target="fcntl"/>. See Sections
        <xref target="OP_LOCK_IMPLEMENTATION" format="counter" />,
        <xref target="OP_LOCKT_IMPLEMENTATION" format="counter" />, and
        <xref target="OP_LOCKU_IMPLEMENTATION" format="counter" /> for a discussion of
        how this applies to LOCK, LOCKT, and LOCKU respectively.
      </t>
    </section>
    <section title="NFS4ERR_OPENMODE (Error Code 10038)" 
             anchor="err_OPENMODE">
      <t>
        The client attempted a READ, WRITE, LOCK, or other operation
        not sanctioned by the stateid passed (e.g., writing to a file
        opened for read-only access).
      </t>
    </section>
    <section title="NFS4ERR_SHARE_DENIED (Error Code 10015)" 
             anchor="err_SHARE_DENIED">
      <t>
        An attempt to OPEN a file with a share reservation has failed
        because of a share conflict.
      </t>
    </section>
  </section>

  <section title="Reclaim Errors" anchor="errors_reclaim">
    <t>
      These errors relate to the process of reclaiming locks after a
      server restart.
    </t>
    <section title="NFS4ERR_COMPLETE_ALREADY (Error Code 10054)" 
             anchor="err_COMPLETE_ALREADY">
      <t>
        The client previously sent a successful RECLAIM_COMPLETE
        operation.  An additional RECLAIM_COMPLETE operation is not
        necessary and results in this error.
      </t>
    </section>
    <section title="NFS4ERR_GRACE (Error Code 10013)" 
             anchor="err_GRACE">
      <t>
        The server was in its recovery or grace period.
        The locking request was not a reclaim request and so
        could not be granted during that period.
      </t>
    </section>
    <section title="NFS4ERR_NO_GRACE (Error Code 10033)" 
             anchor="err_NO_GRACE">
      <t>
        A reclaim of client state was attempted in circumstances in 
        which the server cannot guarantee that conflicting state has 
        not been provided to another client.  This can occur because 
        the reclaim has been done outside of the grace period of the
        server, after the client has done a RECLAIM_COMPLETE operation,
        or because previous operations have created a situation in which
        the server is not able to determine that a reclaim-interfering
        edge condition does not exist.
      </t>
    </section>
    <section title="NFS4ERR_RECLAIM_BAD (Error Code 10034)" 
             anchor="err_RECLAIM_BAD">
      <t>

	The server has determined that a reclaim attempted by the client 
	is not valid, i.e. the lock specified as being reclaimed could
	not possibly have existed before the server restart.  A server 
	is not obliged to make this determination and will typically rely 
	on the client to only reclaim locks that the client was granted prior
        to restart.  However, 
	when a server does have reliable information to enable it make  
	this determination, this error indicates that the reclaim has 
	been rejected as invalid.  This is as opposed to the error
	NFS4ERR_RECLAIM_CONFLICT (see <xref target="err_RECLAIM_CONFLICT"/>)
        where the server can only determine that 
	there has been an invalid reclaim, but cannot determine
	which request is invalid.

      </t>
    </section>
    <section title="NFS4ERR_RECLAIM_CONFLICT (Error Code 10035)" 
             anchor="err_RECLAIM_CONFLICT">
      <t>
        The reclaim attempted by the client has encountered a conflict
        and cannot be satisfied.  Potentially indicates a misbehaving
        client, although not necessarily the one receiving the error.
        The misbehavior might be on the part of the client that 
        established the lock with which this client conflicted.  See also
	<xref target="err_RECLAIM_BAD"/> for the related error,
	NFS4ERR_RECLAIM_BAD.

      </t>
    </section>
  </section>

  <section title="pNFS Errors" anchor="errors_pnfs">
    <t>
      This section deals with pNFS-related errors including those
      that are associated with using NFSv4.1 to communicate with a
      data server.
    </t>
    <section title="NFS4ERR_BADIOMODE (Error Code 10049)" 
             anchor="err_BADIOMODE">
      <t>
        An invalid or inappropriate layout iomode was specified.
        For example an inappropriate layout iomode, suppose
        a client's LAYOUTGET operation specified an iomode of
        LAYOUTIOMODE4_RW, and the server is neither able nor willing
        to let the client send write requests to data servers; the server
        can reply with NFS4ERR_BADIOMODE. The client would then 
        send another LAYOUTGET with an iomode of LAYOUTIOMODE4_READ.
      </t>
    </section>
    <section title="NFS4ERR_BADLAYOUT (Error Code 10050)" 
             anchor="err_BADLAYOUT">
      <t>
        The layout specified is invalid in some way.  For LAYOUTCOMMIT,
        this indicates that the specified layout is not held by the
        client or is not of mode LAYOUTIOMODE4_RW.  For LAYOUTGET, 
        it indicates that a layout matching the client's specification
        as to minimum length cannot be granted. 
      </t>
    </section>
    <section title="NFS4ERR_LAYOUTTRYLATER (Error Code 10058)" 
             anchor="err_LAYOUTTRYLATER">
      <t>
        Layouts are temporarily unavailable for the file.  The client 
        should re-send later (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).
      </t>
    </section>
    <section title="NFS4ERR_LAYOUTUNAVAILABLE (Error Code 10059)" 
             anchor="err_LAYOUTUNAVAILABLE">
      <t>
        Returned when layouts are not available for the current file 
        system or the particular specified file.
      </t>
    </section>
    <section title="NFS4ERR_NOMATCHING_LAYOUT (Error Code 10060)" 
             anchor="err_NOMATCHING_LAYOUT">
      <t>
        Returned when layouts are recalled and the client has no layouts
        matching the specification of the layouts being recalled.
      </t>
    </section>
    <section title="NFS4ERR_PNFS_IO_HOLE (Error Code 10075)" 
             anchor="err_PNFS_IO_HOLE">
      <t>
        The pNFS client has attempted to read from or write to an
        illegal hole of a file of a data server that is using
        sparse packing. See <xref target="sparse_dense" />.
      </t>
    </section>
    <section title="NFS4ERR_PNFS_NO_LAYOUT (Error Code 10080)" 
             anchor="err_PNFS_NO_LAYOUT">
      <t>
        The pNFS client has attempted to read from or write to a file
        (using a request to a data server) without holding a valid 
        layout. This includes the case where the client had a layout,
        but the iomode does not allow a WRITE.
      </t>
    </section>
    <section title="NFS4ERR_RETURNCONFLICT (Error Code 10086)" 
             anchor="err_RETURNCONFLICT">
      <t>
        A layout
        is unavailable due to an attempt to perform the LAYOUTGET
        before a pending LAYOUTRETURN on the file has been received.
        See <xref target="layout_server_consider" />.

      </t>
    </section>
    <section title="NFS4ERR_UNKNOWN_LAYOUTTYPE (Error Code 10062)" 
             anchor="err_UNKNOWN_LAYOUTTYPE">
      <t>
        The client has specified a layout type that is not supported by 
        the server.
      </t>
    </section>
  </section>

  <section title="Session Use Errors" anchor="errors_sess_use">
    <t>
      This section deals with errors encountered when using sessions,
      that is, errors encountered when a request uses a Sequence
      (i.e., either SEQUENCE or CB_SEQUENCE) operation.
    </t>
    <section title="NFS4ERR_BADSESSION (Error Code 10052)" 
             anchor="err_BADSESSION">
      <t>
        The specified session ID is unknown to the server
        to which the operation is addressed.
      </t>
    </section>
    <section title="NFS4ERR_BADSLOT (Error Code 10053)" 
             anchor="err_BADSLOT">
      <t>
        The requester sent a Sequence operation
        that attempted to use a slot the replier
        does not have in its slot table. It is possible the
        slot may have been retired.
      </t>
    </section>
    <section title="NFS4ERR_BAD_HIGH_SLOT (Error Code 10077)" 
             anchor="err_BAD_HIGH_SLOT">
      <t>
        The highest_slot argument in a Sequence operation
        exceeds the replier's enforced highest_slotid.
      </t>
    </section>
    <section title="NFS4ERR_CB_PATH_DOWN (Error Code 10048)" 
             anchor="err_CB_PATH_DOWN">
      <t>

        There is a problem contacting the client via
        the callback path. The function of this error has
        been mostly superseded by the use of
        status flags in the reply to the SEQUENCE
        operation (see <xref target="OP_SEQUENCE" />).

      </t>
    </section>
    <section title="NFS4ERR_DEADSESSION (Error Code 10078)" 
             anchor="err_DEADSESSION">
      <t>
        The specified session is a persistent session that is 
        dead and does not accept new
        requests or perform new operations on existing requests
        (in the case in which a request was partially executed
        before server restart).

      </t>
    </section>
    <section title="NFS4ERR_CONN_NOT_BOUND_TO_SESSION (Error Code 10055)" 
             anchor="err_CONN_NOT_BOUND_TO_SESSION">
      <t>
        A Sequence operation was sent on a connection that has not 
        been associated with the specified session,
        where the client specified that connection association
        was to be enforced with SP4_MACH_CRED or SP4_SSV state protection.
      </t>
    </section>
    <section title="NFS4ERR_SEQ_FALSE_RETRY (Error Code 10076)" 
             anchor="err_SEQ_FALSE_RETRY">
      <t>
        The requester sent a Sequence operation with a
        slot ID and sequence ID that are in the reply cache, but
        the replier has detected that the retried request
        is not the same as the original request. 
        See <xref target="false_retry"/>.
      </t>
    </section>
    <section title="NFS4ERR_SEQ_MISORDERED (Error Code 10063)" 
             anchor="err_SEQ_MISORDERED">
      <t>
        The requester sent a Sequence operation
        with an invalid sequence ID.
      </t>
    </section>
  </section>

  <section title="Session Management Errors" anchor="errors_sess_mgt">
    <t>
      This section deals with errors associated with requests used
      in session management.
    </t>
    <section title="NFS4ERR_BACK_CHAN_BUSY (Error Code 10057)" 
             anchor="err_BACK_CHAN_BUSY">
      <t>
         An attempt was made to destroy a session when the session 
         cannot be destroyed because the server has
         callback requests outstanding.
      </t>
    </section>
    <section title="NFS4ERR_BAD_SESSION_DIGEST (Error Code 10051)" 
             anchor="err_BAD_SESSION_DIGEST">
      <t>
        The digest used in a SET_SSV request is not valid.
      </t>
    </section>
  </section>

  <section title="Client Management Errors" anchor="errors_client_mgt">
    <t>
      This section deals with errors associated with requests used
      to create and manage client IDs.
    </t>
    <section title="NFS4ERR_CLIENTID_BUSY (Error Code 10074)" 
             anchor="err_CLIENTID_BUSY">
      <t>
        The DESTROY_CLIENTID operation has found there are
        sessions and/or unexpired state associated with the 
        client ID to be destroyed.
      </t>
    </section>
    <section title="NFS4ERR_CLID_INUSE (Error Code 10017)" 
             anchor="err_CLID_INUSE">
      <t>
        While processing an EXCHANGE_ID operation, the server was presented
        with a co_ownerid field that matches an existing client with
        valid leased state, but the principal sending the EXCHANGE_ID
        operation differs from the principal that established the existing
        client.
        This indicates a collision (most likely due to chance) between
        clients. The client should recover by changing the
        co_ownerid and re-sending EXCHANGE_ID (but not with the same slot ID and
        sequence ID; one or both MUST be different on the re-send).
      </t>
    </section>
    <section title="NFS4ERR_ENCR_ALG_UNSUPP (Error Code 10079)" 
             anchor="err_ENCR_ALG_UNSUPP">
      <t>
        An EXCHANGE_ID was sent that specified state protection
        via SSV, and where the set of encryption algorithms presented
        by the client did not include any supported by the server.
      </t>
    </section>
    <section title="NFS4ERR_HASH_ALG_UNSUPP (Error Code 10072)" 
             anchor="err_HASH_ALG_UNSUPP">
      <t>
        An EXCHANGE_ID was sent that specified state protection
        via SSV, and where the set of hashing algorithms presented
        by the client did not include any supported by the server.
      </t>
    </section>
    <section title="NFS4ERR_STALE_CLIENTID (Error Code 10022)" 
             anchor="err_STALE_CLIENTID">
      <t>
        A client ID not recognized by the server was passed to an
        operation.  Note that unlike the case of NFSv4.0, client IDs
        are not passed explicitly to the server in ordinary locking
        operations and cannot result in this error.  Instead, when
        there is a server restart, it is first manifested through
        an error on the associated session, and the staleness of the
        client ID is detected when trying to associate a client ID
        with a new session.
      </t>
    </section>
  </section>

  <section title="Delegation Errors" anchor="errors_deleg">
    <t>
      This section deals with errors associated with requesting and
      returning delegations.
    </t>
    <section title="NFS4ERR_DELEG_ALREADY_WANTED (Error Code 10056)" 
             anchor="err_DELEG_ALREADY_WANTED">
      <t>
        The client has requested a delegation when it had already 
        registered that it wants that same delegation.
      </t>
    </section>
    <section title="NFS4ERR_DIRDELEG_UNAVAIL (Error Code 10084)" 
             anchor="err_DIRDELEG_UNAVAIL">
      <t>
        This error is returned when the server is unable or unwilling 
        to provide a requested directory delegation.
      </t>
    </section>
    <section title="NFS4ERR_RECALLCONFLICT (Error Code 10061)" 
             anchor="err_RECALLCONFLICT">
      <t>
        A recallable object (i.e., a layout or delegation)
        is unavailable due to a conflicting recall operation that is
        currently in progress for that object.
      </t>
    </section>
    <section title="NFS4ERR_REJECT_DELEG (Error Code 10085)" 
             anchor="err_REJECT_DELEG">
      <t>
        The callback operation invoked to deal with a new delegation has
        rejected it.
      </t>
    </section>
  </section>

  <section title="Attribute Handling Errors" anchor="errors_attr">
    <t>
      This section deals with errors specific to attribute handling
      within NFSv4.
    </t>
    <section title="NFS4ERR_ATTRNOTSUPP (Error Code 10032)" 
             anchor="err_ATTRNOTSUPP">
      <t>
        An attribute specified is not supported by the server.  This 
        error MUST NOT be returned by the GETATTR operation.
      </t>
    </section>
    <section title="NFS4ERR_BADOWNER (Error Code 10039)" 
             anchor="err_BADOWNER">
      <t>
        This error is returned when an owner or owner_group attribute value or the who 
        field of an ACE within an ACL attribute value cannot be
        translated to a local representation.
      </t>
    </section>
    <section title="NFS4ERR_NOT_SAME (Error Code 10027)" 
             anchor="err_NOT_SAME">
      <t>
        This error is returned by the VERIFY operation to signify
        that the attributes compared were not the same as those provided 
        in the client's request.
      </t>
    </section>
    <section title="NFS4ERR_SAME (Error Code 10009)" 
             anchor="err_SAME">
      <t>
        This error is returned by the NVERIFY operation to signify
        that the attributes compared were the same as those provided 
        in the client's request.
      </t>
    </section>
  </section>

  <section title="Obsoleted Errors" anchor="errors_obs">
    <t>
      These errors MUST NOT be generated by any NFSv4.1 operation.
      This can be for a number of reasons.
      <list style="symbols">
        <t>
          The function provided by the error has been superseded
          by one of the status bits returned by the SEQUENCE
          operation.
        </t>
        <t>
          The new session structure and associated change in
          locking have made the error unnecessary.
        </t>
        <t>
          There has been a restructuring of some errors for 
          NFSv4.1 that resulted in the elimination of certain errors.
        </t>
      </list>
    </t>
    <section title="NFS4ERR_BAD_SEQID (Error Code 10026)" 
             anchor="err_BAD_SEQID">
      <t>
        The sequence number (seqid) in a locking request is neither the 
        next expected number or the last number processed.  These
        seqids are ignored in NFSv4.1.
      </t>
    </section>
    <section title="NFS4ERR_LEASE_MOVED (Error Code 10031)" 
             anchor="err_LEASE_MOVED">
      <t>
        A lease being renewed is associated with a file system 
        that has been migrated to a new server. The error has
        been superseded by the SEQ4_STATUS_LEASE_MOVED status bit
        (see <xref target="OP_SEQUENCE" />).          
      </t>
    </section>
    <section title="NFS4ERR_NXIO (Error Code 5)" 
             anchor="err_NXIO">
      <t>
        I/O error. No such device or address. This error is
        for errors involving block and character device access,
        but because NFSv4.1 is not a device-access protocol, this
        error is not applicable.
      </t>
    </section>
    <section title="NFS4ERR_RESTOREFH (Error Code 10030)" 
             anchor="err_RESTOREFH">
      <t>
        The RESTOREFH operation does not have a saved filehandle
        (identified by SAVEFH) to operate upon. In NFSv4.1, this error has
        been superseded by NFS4ERR_NOFILEHANDLE.
      </t>
    </section>
    <section title="NFS4ERR_STALE_STATEID (Error Code 10023)" 
             anchor="err_STALE_STATEID">
      <t>
        A stateid generated by an earlier server instance was
        used. This error is moot in NFSv4.1 because all operations that
        take a stateid MUST be preceded by the SEQUENCE operation,
        and the earlier server instance is detected by the session
        infrastructure that supports SEQUENCE.
      </t>
    </section>
  </section>

  </section>

<!-- When adding new errors above, add them to the next section under -->
<!-- the appropriate operation; the next table for errors to -->
<!-- operations is automatically generated.  -->

<section title="Operations and Their Valid Errors">
  <t>
    This section contains a table that gives the valid error returns
    for each protocol operation.  The error code NFS4_OK (indicating 
    no error) is not listed but should be understood to be returnable
    by all operations with two important exceptions:
    <list style="symbols">
      <t>
        The operations that MUST NOT be implemented: 
        OPEN_CONFIRM, RELEASE_LOCKOWNER, RENEW, SETCLIENTID, and
        SETCLIENTID_CONFIRM.
      </t>
      <t>
        The invalid operation: ILLEGAL.
      </t>
    </list>
  </t>
  <texttable anchor='op_error_returns'>
    <preamble> Valid Error Returns for Each Protocol
    Operation </preamble>

    <ttcol align='left'>Operation</ttcol>
    <ttcol align='left'>Errors</ttcol>
<!-- DO NOT MOVE THIS OR THE NEXT LINE - IT MUST BE AT THE START OF TABLE -->
<!-- STARTOFTHEERRORTABLE -->

    <c>ACCESS</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>BACKCHANNEL_CTL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>BIND_CONN_TO_SESSION</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_SESSION_DIGEST,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CLOSE</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_LOCKS_HELD,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>COMMIT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_ISDIR,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CREATE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADTYPE,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND
    </c>

    <c />
    <c />

    <c>CREATE_SESSION</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_CLID_INUSE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_NOSPC,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DELEGPURGE</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DELEGRETURN</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DESTROY_CLIENTID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_CLIENTID_BUSY,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>DESTROY_SESSION</c>
    <c>
      NFS4ERR_BACK_CHAN_BUSY,
      NFS4ERR_BADSESSION,
      NFS4ERR_BADXDR,
      NFS4ERR_CB_PATH_DOWN,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE_CLIENTID,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>EXCHANGE_ID</c>
    <c>
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_CLID_INUSE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_ENCR_ALG_UNSUPP,
      NFS4ERR_HASH_ALG_UNSUPP,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOT_ONLY_OP,
      NFS4ERR_NOT_SAME,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>FREE_STATEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_LOCKS_HELD,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>GET_DIR_DELEGATION</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DIRDELEG_UNAVAIL,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>GETATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>GETDEVICEINFO</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOENT,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE
    </c>

    <c />
    <c />

    <c>GETDEVICELIST</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_COOKIE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE
    </c>

    <c />
    <c />

    <c>GETFH</c>
    <c>
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_STALE
    </c>

    <c />
    <c />

    <c>ILLEGAL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_OP_ILLEGAL
    </c>

    <c />
    <c />

    <c>LAYOUTCOMMIT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADLAYOUT,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_ISDIR
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>LAYOUTGET</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADLAYOUT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_LAYOUTTRYLATER,
      NFS4ERR_LAYOUTUNAVAILABLE,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECALLCONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LAYOUTRETURN</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LINK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC,
      NFS4ERR_WRONG_TYPE,
      NFS4ERR_XDEV
    </c>

    <c />
    <c />

    <c>LOCK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADLOCK,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DENIED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCK_NOTSUPP,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LOCKT</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DENIED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>LOCKU</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_RANGE,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_LOCK_RANGE,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>LOOKUP</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>LOOKUPP</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>NVERIFY</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SAME,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>OPEN</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_ALREADY_WANTED,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_SHARE_DENIED,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND,
      NFS4ERR_WRONGSEC,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>OPEN_CONFIRM</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>OPEN_DOWNGRADE</c>
    <c>
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED
    </c>

    <c />
    <c />

    <c>OPENATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNSAFE_COMPOUND,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>PUTFH</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_MOVED,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>PUTPUBFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>PUTROOTFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>READ</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_EXPIRED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_ISDIR,
      NFS4ERR_IO,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PNFS_IO_HOLE,
      NFS4ERR_PNFS_NO_LAYOUT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
   </c>

    <c />
    <c />

    <c>READDIR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_COOKIE,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOOSMALL,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>READLINK</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>RECLAIM_COMPLETE</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_COMPLETE_ALREADY,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_CRED,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>RELEASE_LOCKOWNER</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>REMOVE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTEMPTY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>RENAME</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DQUOT,
      NFS4ERR_EXIST,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_FILE_OPEN,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MLINK,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTEMPTY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC,
      NFS4ERR_XDEV
    </c>

    <c />
    <c />

    <c>RENEW</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>RESTOREFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONGSEC
    </c>

    <c />
    <c />

    <c>SAVEFH</c>
    <c>
      NFS4ERR_DEADSESSION,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SECINFO</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADNAME,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NAMETOOLONG,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SECINFO_NO_NAME</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_INVAL,
      NFS4ERR_MOVED,
      NFS4ERR_NOENT,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTDIR,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SEQUENCE</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADSLOT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQUENCE_POS,
      NFS4ERR_SEQ_FALSE_RETRY,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SET_SSV</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_SESSION_DIGEST,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>SETATTR</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADOWNER,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PERM,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>SETCLIENTID</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>SETCLIENTID_CONFIRM</c>
    <c>
      NFS4ERR_NOTSUPP
    </c>

    <c />
    <c />

    <c>TEST_STATEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>VERIFY</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ATTRNOTSUPP,
      NFS4ERR_BADCHAR,
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOT_SAME,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>WANT_DELEGATION</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_ALREADY_WANTED,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOTSUPP,
      NFS4ERR_NO_GRACE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_RECALLCONFLICT,
      NFS4ERR_RECLAIM_BAD,
      NFS4ERR_RECLAIM_CONFLICT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>WRITE</c>
    <c>
      NFS4ERR_ACCESS,
      NFS4ERR_ADMIN_REVOKED,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DEADSESSION,
      NFS4ERR_DELAY,
      NFS4ERR_DELEG_REVOKED,
      NFS4ERR_DQUOT,
      NFS4ERR_EXPIRED,
      NFS4ERR_FBIG,
      NFS4ERR_FHEXPIRED,
      NFS4ERR_GRACE,
      NFS4ERR_INVAL,
      NFS4ERR_IO,
      NFS4ERR_ISDIR,
      NFS4ERR_LOCKED,
      NFS4ERR_MOVED,
      NFS4ERR_NOFILEHANDLE,
      NFS4ERR_NOSPC,
      NFS4ERR_OLD_STATEID,
      NFS4ERR_OPENMODE,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_PNFS_IO_HOLE,
      NFS4ERR_PNFS_NO_LAYOUT,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_ROFS,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_STALE,
      NFS4ERR_SYMLINK,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

<!-- ENDOFTHEERRORTABLE -->
<!-- DO NOT MOVE THIS OR THE ONE ABOVE LINE - IT MUST BE AT THE START OF TABLE -->
    
  </texttable>    
</section>

<!-- When adding new errors above, add them to the next section under -->
<!-- the appropriate operation; the next table for errors to -->
<!-- operations is automatically generated.  -->

<section title="Callback Operations and Their Valid Errors">
  <t>
    This section contains a table that gives the valid error returns
    for each callback operation.  The error code NFS4_OK (indicating 
    no error) is not listed but should be understood to be returnable
    by all callback operations with the exception of CB_ILLEGAL. 
  </t>
  <texttable anchor='cb_op_error_returns'>
    <preamble> Valid Error Returns for Each Protocol
    Callback Operation </preamble>

    <ttcol align='left'>Callback Operation</ttcol>
    <ttcol align='left'>Errors</ttcol>
<!-- DO NOT MOVE THIS OR THE NEXT LINE - IT MUST BE AT THE START OF TABLE -->
<!-- STARTOFTHEERRORTABLE -->

    <c>CB_GETATTR</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
    </c>

    <c />
    <c />

    <c>CB_ILLEGAL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_OP_ILLEGAL
    </c>

    <c />
    <c />

    <c>CB_LAYOUTRECALL</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADIOMODE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOMATCHING_LAYOUT,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_UNKNOWN_LAYOUTTYPE,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CB_NOTIFY</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_NOTIFY_DEVICEID</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />


    <c>CB_NOTIFY_LOCK</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_PUSH_DELEG</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REJECT_DELEG,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS,
      NFS4ERR_WRONG_TYPE
    </c>

    <c />
    <c />

    <c>CB_RECALL</c>
    <c>
      NFS4ERR_BADHANDLE,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_STATEID,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALL_ANY</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALLABLE_OBJ_AVAIL</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_INVAL,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_RECALL_SLOT</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_DELAY,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_SEQUENCE</c>
    <c>
      NFS4ERR_BADSESSION,
      NFS4ERR_BADSLOT,
      NFS4ERR_BADXDR,
      NFS4ERR_BAD_HIGH_SLOT,
      NFS4ERR_CONN_NOT_BOUND_TO_SESSION,
      NFS4ERR_DELAY,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SEQUENCE_POS,
      NFS4ERR_SEQ_FALSE_RETRY,
      NFS4ERR_SEQ_MISORDERED,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

    <c>CB_WANTS_CANCELLED</c>
    <c>
      NFS4ERR_BADXDR,
      NFS4ERR_DELAY,
      NFS4ERR_NOTSUPP,
      NFS4ERR_OP_NOT_IN_SESSION,
      NFS4ERR_REP_TOO_BIG,
      NFS4ERR_REP_TOO_BIG_TO_CACHE,
      NFS4ERR_REQ_TOO_BIG,
      NFS4ERR_RETRY_UNCACHED_REP,
      NFS4ERR_SERVERFAULT,
      NFS4ERR_TOO_MANY_OPS
    </c>

    <c />
    <c />

<!-- ENDOFTHEERRORTABLE -->
<!-- DO NOT MOVE THIS OR THE ONE ABOVE LINE - IT MUST BE AT THE START OF TABLE -->
  </texttable>
</section>

<!-- INCLUDE THE AUTO GENERATED ERROR TO OP TABLE -->
<section title="Errors and the Operations That Use Them">
  <texttable anchor='error_op_returns'>
    <ttcol align='left'>Error</ttcol>
    <ttcol align='left'>Operations</ttcol>

    <c>NFS4ERR_ACCESS</c>
    <c>
	ACCESS,
	COMMIT,
	CREATE,
	GETATTR,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READDIR,
	READLINK,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ADMIN_REVOKED</c>
    <c>
	CLOSE,
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ATTRNOTSUPP</c>
    <c>
	CREATE,
	LAYOUTCOMMIT,
	NVERIFY,
	OPEN,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_BACK_CHAN_BUSY</c>
    <c>
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADCHAR</c>
    <c>
	CREATE,
	EXCHANGE_ID,
	LINK,
	LOOKUP,
	NVERIFY,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADHANDLE</c>
    <c>
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	PUTFH
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADIOMODE</c>
    <c>
	CB_LAYOUTRECALL,
	LAYOUTCOMMIT,
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADLAYOUT</c>
    <c>
	LAYOUTCOMMIT,
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADNAME</c>
    <c>
	CREATE,
	LINK,
	LOOKUP,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADOWNER</c>
    <c>
	CREATE,
	OPEN,
	SETATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADSESSION</c>
    <c>
	BIND_CONN_TO_SESSION,
	CB_SEQUENCE,
	DESTROY_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADSLOT</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADTYPE</c>
    <c>
	CREATE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BADXDR</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_ILLEGAL,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	ILLEGAL,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_COOKIE</c>
    <c>
	GETDEVICELIST,
	READDIR
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_HIGH_SLOT</c>
    <c>
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_RANGE</c>
    <c>
	LOCK,
	LOCKT,
	LOCKU
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_SESSION_DIGEST</c>
    <c>
	BIND_CONN_TO_SESSION,
	SET_SSV
    </c>
    <c />
    <c />

    <c>NFS4ERR_BAD_STATEID</c>
    <c>
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_LOCK,
	CB_RECALL,
	CLOSE,
	DELEGRETURN,
	FREE_STATEID,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_CB_PATH_DOWN</c>
    <c>
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_CLID_INUSE</c>
    <c>
	CREATE_SESSION,
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_CLIENTID_BUSY</c>
    <c>
	DESTROY_CLIENTID
    </c>
    <c />
    <c />

    <c>NFS4ERR_COMPLETE_ALREADY</c>
    <c>
	RECLAIM_COMPLETE
    </c>
    <c />
    <c />

    <c>NFS4ERR_CONN_NOT_BOUND_TO_SESSION</c>
    <c>
	CB_SEQUENCE,
	DESTROY_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DEADLOCK</c>
    <c>
	LOCK
    </c>
    <c />
    <c />

    <c>NFS4ERR_DEADSESSION</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELAY</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELEG_ALREADY_WANTED</c>
    <c>
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_DELEG_REVOKED</c>
    <c>
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	OPEN,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_DENIED</c>
    <c>
	LOCK,
	LOCKT
    </c>
    <c />
    <c />

    <c>NFS4ERR_DIRDELEG_UNAVAIL</c>
    <c>
	GET_DIR_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_DQUOT</c>
    <c>
	CREATE,
	LAYOUTGET,
	LINK,
	OPEN,
	OPENATTR,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ENCR_ALG_UNSUPP</c>
    <c>
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_EXIST</c>
    <c>
	CREATE,
	LINK,
	OPEN,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_EXPIRED</c>
    <c>
	CLOSE,
	DELEGRETURN,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FBIG</c>
    <c>
	LAYOUTCOMMIT,
	OPEN,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FHEXPIRED</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_FILE_OPEN</c>
    <c>
	LINK,
	REMOVE,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_GRACE</c>
    <c>
	GETATTR,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	NVERIFY,
	OPEN,
	READ,
	REMOVE,
	RENAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_HASH_ALG_UNSUPP</c>
    <c>
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_INVAL</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_PUSH_DELEG,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CREATE,
	CREATE_SESSION,
	DELEGRETURN,
	EXCHANGE_ID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	NVERIFY,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	SET_SSV,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_IO</c>
    <c>
	ACCESS,
	COMMIT,
	CREATE,
	GETATTR,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LINK,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READDIR,
	READLINK,
	REMOVE,
	RENAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ISDIR</c>
    <c>
	COMMIT,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	OPEN,
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_LAYOUTTRYLATER</c>
    <c>
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_LAYOUTUNAVAILABLE</c>
    <c>
	LAYOUTGET
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCKED</c>
    <c>
	LAYOUTGET,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCKS_HELD</c>
    <c>
	CLOSE,
	FREE_STATEID
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCK_NOTSUPP</c>
    <c>
	LOCK
    </c>
    <c />
    <c />

    <c>NFS4ERR_LOCK_RANGE</c>
    <c>
	LOCK,
	LOCKT,
	LOCKU
    </c>
    <c />
    <c />

    <c>NFS4ERR_MLINK</c>
    <c>
	CREATE,
	LINK,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_MOVED</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NAMETOOLONG</c>
    <c>
	CREATE,
	LINK,
	LOOKUP,
	OPEN,
	REMOVE,
	RENAME,
	SECINFO
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOENT</c>
    <c>
	BACKCHANNEL_CTL,
	CREATE_SESSION,
	EXCHANGE_ID,
	GETDEVICEINFO,
	LOOKUP,
	LOOKUPP,
	OPEN,
	OPENATTR,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOFILEHANDLE</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOMATCHING_LAYOUT</c>
    <c>
	CB_LAYOUTRECALL
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOSPC</c>
    <c>
	CREATE,
	CREATE_SESSION,
	LAYOUTGET,
	LINK,
	OPEN,
	OPENATTR,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTDIR</c>
    <c>
	CREATE,
	GET_DIR_DELEGATION,
	LINK,
	LOOKUP,
	LOOKUPP,
	OPEN,
	READDIR,
	REMOVE,
	RENAME,
	SECINFO,
	SECINFO_NO_NAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTEMPTY</c>
    <c>
	REMOVE,
	RENAME
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOTSUPP</c>
    <c>
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_WANTS_CANCELLED,
	DELEGPURGE,
	DELEGRETURN,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	OPENATTR,
	OPEN_CONFIRM,
	RELEASE_LOCKOWNER,
	RENEW,
	SECINFO_NO_NAME,
	SETCLIENTID,
	SETCLIENTID_CONFIRM,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOT_ONLY_OP</c>
    <c>
	BIND_CONN_TO_SESSION,
	CREATE_SESSION,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID
    </c>
    <c />
    <c />

    <c>NFS4ERR_NOT_SAME</c>
    <c>
	EXCHANGE_ID,
	GETDEVICELIST,
	READDIR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_NO_GRACE</c>
    <c>
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_OLD_STATEID</c>
    <c>
	CLOSE,
	DELEGRETURN,
	FREE_STATEID,
	LAYOUTGET,
	LAYOUTRETURN,
	LOCK,
	LOCKU,
	OPEN,
	OPEN_DOWNGRADE,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_OPENMODE</c>
    <c>
	LAYOUTGET,
	LOCK,
	READ,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_OP_ILLEGAL</c>
    <c>
	CB_ILLEGAL,
	ILLEGAL
    </c>
    <c />
    <c />

    <c>NFS4ERR_OP_NOT_IN_SESSION</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGPURGE,
	DELEGRETURN,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_PERM</c>
    <c>
	CREATE,
	OPEN,
	SETATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_PNFS_IO_HOLE</c>
    <c>
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_PNFS_NO_LAYOUT</c>
    <c>
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECALLCONFLICT</c>
    <c>
	LAYOUTGET,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECLAIM_BAD</c>
    <c>
	LAYOUTCOMMIT,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_RECLAIM_CONFLICT</c>
    <c>
	LAYOUTCOMMIT,
	LOCK,
	OPEN,
	WANT_DELEGATION
    </c>
    <c />
    <c />

    <c>NFS4ERR_REJECT_DELEG</c>
    <c>
	CB_PUSH_DELEG
    </c>
    <c />
    <c />

    <c>NFS4ERR_REP_TOO_BIG</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_REQ_TOO_BIG</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_RETRY_UNCACHED_REP</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_ROFS</c>
    <c>
	CREATE,
	LINK,
	LOCK,
	LOCKT,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	REMOVE,
	RENAME,
	SETATTR,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SAME</c>
    <c>
	NVERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQUENCE_POS</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQ_FALSE_RETRY</c>
    <c>
	CB_SEQUENCE,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SEQ_MISORDERED</c>
    <c>
	CB_SEQUENCE,
	CREATE_SESSION,
	SEQUENCE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SERVERFAULT</c>
    <c>
	ACCESS,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_SHARE_DENIED</c>
    <c>
	OPEN
    </c>
    <c />
    <c />

    <c>NFS4ERR_STALE</c>
    <c>
	ACCESS,
	CLOSE,
	COMMIT,
	CREATE,
	DELEGRETURN,
	GETATTR,
	GETFH,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_STALE_CLIENTID</c>
    <c>
	CREATE_SESSION,
	DESTROY_CLIENTID,
	DESTROY_SESSION
    </c>
    <c />
    <c />

    <c>NFS4ERR_SYMLINK</c>
    <c>
	COMMIT,
	LAYOUTCOMMIT,
	LINK,
	LOCK,
	LOCKT,
	LOOKUP,
	LOOKUPP,
	OPEN,
	READ,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_TOOSMALL</c>
    <c>
	CREATE_SESSION,
	GETDEVICEINFO,
	LAYOUTGET,
	READDIR
    </c>
    <c />
    <c />

    <c>NFS4ERR_TOO_MANY_OPS</c>
    <c>
	ACCESS,
	BACKCHANNEL_CTL,
	BIND_CONN_TO_SESSION,
	CB_GETATTR,
	CB_LAYOUTRECALL,
	CB_NOTIFY,
	CB_NOTIFY_DEVICEID,
	CB_NOTIFY_LOCK,
	CB_PUSH_DELEG,
	CB_RECALL,
	CB_RECALLABLE_OBJ_AVAIL,
	CB_RECALL_ANY,
	CB_RECALL_SLOT,
	CB_SEQUENCE,
	CB_WANTS_CANCELLED,
	CLOSE,
	COMMIT,
	CREATE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	EXCHANGE_ID,
	FREE_STATEID,
	GETATTR,
	GETDEVICEINFO,
	GETDEVICELIST,
	GET_DIR_DELEGATION,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	LOCKU,
	LOOKUP,
	LOOKUPP,
	NVERIFY,
	OPEN,
	OPENATTR,
	OPEN_DOWNGRADE,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	READ,
	READDIR,
	READLINK,
	RECLAIM_COMPLETE,
	REMOVE,
	RENAME,
	RESTOREFH,
	SAVEFH,
	SECINFO,
	SECINFO_NO_NAME,
	SEQUENCE,
	SETATTR,
	SET_SSV,
	TEST_STATEID,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_UNKNOWN_LAYOUTTYPE</c>
    <c>
	CB_LAYOUTRECALL,
	GETDEVICEINFO,
	GETDEVICELIST,
	LAYOUTCOMMIT,
	LAYOUTGET,
	LAYOUTRETURN,
	NVERIFY,
	SETATTR,
	VERIFY
    </c>
    <c />
    <c />

    <c>NFS4ERR_UNSAFE_COMPOUND</c>
    <c>
	CREATE,
	OPEN,
	OPENATTR
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONGSEC</c>
    <c>
	LINK,
	LOOKUP,
	LOOKUPP,
	OPEN,
	PUTFH,
	PUTPUBFH,
	PUTROOTFH,
	RENAME,
	RESTOREFH
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONG_CRED</c>
    <c>
	CLOSE,
	CREATE_SESSION,
	DELEGPURGE,
	DELEGRETURN,
	DESTROY_CLIENTID,
	DESTROY_SESSION,
	FREE_STATEID,
	LAYOUTCOMMIT,
	LAYOUTRETURN,
	LOCK,
	LOCKT,
	LOCKU,
	OPEN_DOWNGRADE,
	RECLAIM_COMPLETE
    </c>
    <c />
    <c />

    <c>NFS4ERR_WRONG_TYPE</c>
    <c>
	CB_LAYOUTRECALL,
	CB_PUSH_DELEG,
	COMMIT,
	GETATTR,
	LAYOUTGET,
	LAYOUTRETURN,
	LINK,
	LOCK,
	LOCKT,
	NVERIFY,
	OPEN,
	OPENATTR,
	READ,
	READLINK,
	RECLAIM_COMPLETE,
	SETATTR,
	VERIFY,
	WANT_DELEGATION,
	WRITE
    </c>
    <c />
    <c />

    <c>NFS4ERR_XDEV</c>
    <c>
	LINK,
	RENAME
    </c>
    <c />
    <c />

  </texttable>
</section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41procedures" title="NFSv4.1 Procedures">
<t>
 Both procedures, NULL and COMPOUND, MUST be implemented.
</t>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_NULL" title="Procedure 0: NULL - No Operation" >

  <section toc="exclude" anchor="PROC_NULL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_NULL_RESULTS" title="RESULTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="PROC_NULL_DESCRIPTION" title="DESCRIPTION">
    <t>
This is the standard NULL procedure with the standard void argument and
void response.
This procedure has no functionality associated with it.  Because of
this, it is sometimes used to measure the overhead of processing a
service request.  Therefore, the server SHOULD ensure that no
unnecessary work is done in servicing this procedure.
    </t>
  </section>
  <section toc="exclude" anchor="PROC_NULL_ERRORS" title="ERRORS">
    <t>
None.
	
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_COMPOUND" title="Procedure 1: COMPOUND - Compound Operations" >

  <section toc="exclude" anchor="OP_COMPOUND_ARGUMENTS" title="ARGUMENTS">

<figure>
 <artwork>
enum nfs_opnum4 {
 OP_ACCESS              = 3,
 OP_CLOSE               = 4,
 OP_COMMIT              = 5,
 OP_CREATE              = 6,
 OP_DELEGPURGE          = 7,
 OP_DELEGRETURN         = 8,
 OP_GETATTR             = 9,
 OP_GETFH               = 10,
 OP_LINK                = 11,
 OP_LOCK                = 12,
 OP_LOCKT               = 13,
 OP_LOCKU               = 14,
 OP_LOOKUP              = 15,
 OP_LOOKUPP             = 16,
 OP_NVERIFY             = 17,
 OP_OPEN                = 18,
 OP_OPENATTR            = 19,
 OP_OPEN_CONFIRM        = 20, /* Mandatory not-to-implement */
 OP_OPEN_DOWNGRADE      = 21,
 OP_PUTFH               = 22,
 OP_PUTPUBFH            = 23,
 OP_PUTROOTFH           = 24,
 OP_READ                = 25,
 OP_READDIR             = 26,
 OP_READLINK            = 27,
 OP_REMOVE              = 28,
 OP_RENAME              = 29,
 OP_RENEW               = 30, /* Mandatory not-to-implement */
 OP_RESTOREFH           = 31,
 OP_SAVEFH              = 32,
 OP_SECINFO             = 33,
 OP_SETATTR             = 34,
 OP_SETCLIENTID         = 35, /* Mandatory not-to-implement */
 OP_SETCLIENTID_CONFIRM = 36, /* Mandatory not-to-implement */
 OP_VERIFY              = 37,
 OP_WRITE               = 38,
 OP_RELEASE_LOCKOWNER   = 39, /* Mandatory not-to-implement */

/* new operations for NFSv4.1 */

 OP_BACKCHANNEL_CTL     = 40,
 OP_BIND_CONN_TO_SESSION = 41,
 OP_EXCHANGE_ID         = 42,
 OP_CREATE_SESSION      = 43,
 OP_DESTROY_SESSION     = 44,
 OP_FREE_STATEID        = 45,
 OP_GET_DIR_DELEGATION  = 46,
 OP_GETDEVICEINFO       = 47,
 OP_GETDEVICELIST       = 48,
 OP_LAYOUTCOMMIT        = 49,
 OP_LAYOUTGET           = 50,
 OP_LAYOUTRETURN        = 51,
 OP_SECINFO_NO_NAME     = 52,
 OP_SEQUENCE            = 53,
 OP_SET_SSV             = 54,
 OP_TEST_STATEID        = 55,
 OP_WANT_DELEGATION     = 56,
 OP_DESTROY_CLIENTID    = 57,
 OP_RECLAIM_COMPLETE    = 58,
 OP_ILLEGAL             = 10044
};
 </artwork>
</figure>
<figure>
 <artwork>
union nfs_argop4 switch (nfs_opnum4 argop) {
 case OP_ACCESS:        ACCESS4args opaccess;
 case OP_CLOSE:         CLOSE4args opclose;
 case OP_COMMIT:        COMMIT4args opcommit;
 case OP_CREATE:        CREATE4args opcreate;
 case OP_DELEGPURGE:    DELEGPURGE4args opdelegpurge;
 case OP_DELEGRETURN:   DELEGRETURN4args opdelegreturn;
 case OP_GETATTR:       GETATTR4args opgetattr;
 case OP_GETFH:         void;
 case OP_LINK:          LINK4args oplink;
 case OP_LOCK:          LOCK4args oplock;
 case OP_LOCKT:         LOCKT4args oplockt;
 case OP_LOCKU:         LOCKU4args oplocku;
 case OP_LOOKUP:        LOOKUP4args oplookup;
 case OP_LOOKUPP:       void;
 case OP_NVERIFY:       NVERIFY4args opnverify;
 case OP_OPEN:          OPEN4args opopen;
 case OP_OPENATTR:      OPENATTR4args opopenattr;

 /* Not for NFSv4.1 */
 case OP_OPEN_CONFIRM:  OPEN_CONFIRM4args opopen_confirm;

 case OP_OPEN_DOWNGRADE:
                        OPEN_DOWNGRADE4args opopen_downgrade;

 case OP_PUTFH:         PUTFH4args opputfh;
 case OP_PUTPUBFH:      void;
 case OP_PUTROOTFH:     void;
 case OP_READ:          READ4args opread;
 case OP_READDIR:       READDIR4args opreaddir;
 case OP_READLINK:      void;
 case OP_REMOVE:        REMOVE4args opremove;
 case OP_RENAME:        RENAME4args oprename;

 /* Not for NFSv4.1 */
 case OP_RENEW:         RENEW4args oprenew;

 case OP_RESTOREFH:     void;
 case OP_SAVEFH:        void;
 case OP_SECINFO:       SECINFO4args opsecinfo;
 case OP_SETATTR:       SETATTR4args opsetattr;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID: SETCLIENTID4args opsetclientid;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID_CONFIRM: SETCLIENTID_CONFIRM4args
                                opsetclientid_confirm;
 case OP_VERIFY:        VERIFY4args opverify;
 case OP_WRITE:         WRITE4args opwrite;

 /* Not for NFSv4.1 */
 case OP_RELEASE_LOCKOWNER:
                        RELEASE_LOCKOWNER4args
                        oprelease_lockowner;

 /* Operations new to NFSv4.1 */
 case OP_BACKCHANNEL_CTL:
                        BACKCHANNEL_CTL4args opbackchannel_ctl;

 case OP_BIND_CONN_TO_SESSION:
                        BIND_CONN_TO_SESSION4args
                        opbind_conn_to_session;

 case OP_EXCHANGE_ID:   EXCHANGE_ID4args opexchange_id;

 case OP_CREATE_SESSION:
                        CREATE_SESSION4args opcreate_session;

 case OP_DESTROY_SESSION:
                        DESTROY_SESSION4args opdestroy_session;

 case OP_FREE_STATEID:  FREE_STATEID4args opfree_stateid;

 case OP_GET_DIR_DELEGATION:
                        GET_DIR_DELEGATION4args
                                opget_dir_delegation;

 case OP_GETDEVICEINFO: GETDEVICEINFO4args opgetdeviceinfo;
 case OP_GETDEVICELIST: GETDEVICELIST4args opgetdevicelist;
 case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4args oplayoutcommit;
 case OP_LAYOUTGET:     LAYOUTGET4args oplayoutget;
 case OP_LAYOUTRETURN:  LAYOUTRETURN4args oplayoutreturn;

 case OP_SECINFO_NO_NAME:
                        SECINFO_NO_NAME4args opsecinfo_no_name;

 case OP_SEQUENCE:      SEQUENCE4args opsequence;
 case OP_SET_SSV:       SET_SSV4args opset_ssv;
 case OP_TEST_STATEID:  TEST_STATEID4args optest_stateid;

 case OP_WANT_DELEGATION:
                        WANT_DELEGATION4args opwant_delegation;

 case OP_DESTROY_CLIENTID:
                        DESTROY_CLIENTID4args
                                opdestroy_clientid;

 case OP_RECLAIM_COMPLETE:
                        RECLAIM_COMPLETE4args
                                opreclaim_complete;

 /* Operations not new to NFSv4.1 */
 case OP_ILLEGAL:       void;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct COMPOUND4args {
        utf8str_cs      tag;
        uint32_t        minorversion;
        nfs_argop4      argarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="OP_COMPOUND_RESULTS" title="RESULTS">

<figure>
 <artwork>
union nfs_resop4 switch (nfs_opnum4 resop) {
 case OP_ACCESS:        ACCESS4res opaccess;
 case OP_CLOSE:         CLOSE4res opclose;
 case OP_COMMIT:        COMMIT4res opcommit;
 case OP_CREATE:        CREATE4res opcreate;
 case OP_DELEGPURGE:    DELEGPURGE4res opdelegpurge;
 case OP_DELEGRETURN:   DELEGRETURN4res opdelegreturn;
 case OP_GETATTR:       GETATTR4res opgetattr;
 case OP_GETFH:         GETFH4res opgetfh;
 case OP_LINK:          LINK4res oplink;
 case OP_LOCK:          LOCK4res oplock;
 case OP_LOCKT:         LOCKT4res oplockt;
 case OP_LOCKU:         LOCKU4res oplocku;
 case OP_LOOKUP:        LOOKUP4res oplookup;
 case OP_LOOKUPP:       LOOKUPP4res oplookupp;
 case OP_NVERIFY:       NVERIFY4res opnverify;
 case OP_OPEN:          OPEN4res opopen;
 case OP_OPENATTR:      OPENATTR4res opopenattr;
 /* Not for NFSv4.1 */
 case OP_OPEN_CONFIRM:  OPEN_CONFIRM4res opopen_confirm;

 case OP_OPEN_DOWNGRADE:
                        OPEN_DOWNGRADE4res
                                opopen_downgrade;

 case OP_PUTFH:         PUTFH4res opputfh;
 case OP_PUTPUBFH:      PUTPUBFH4res opputpubfh;
 case OP_PUTROOTFH:     PUTROOTFH4res opputrootfh;
 case OP_READ:          READ4res opread;
 case OP_READDIR:       READDIR4res opreaddir;
 case OP_READLINK:      READLINK4res opreadlink;
 case OP_REMOVE:        REMOVE4res opremove;
 case OP_RENAME:        RENAME4res oprename;
 /* Not for NFSv4.1 */
 case OP_RENEW:         RENEW4res oprenew;
 case OP_RESTOREFH:     RESTOREFH4res oprestorefh;
 case OP_SAVEFH:        SAVEFH4res opsavefh;
 case OP_SECINFO:       SECINFO4res opsecinfo;
 case OP_SETATTR:       SETATTR4res opsetattr;
 /* Not for NFSv4.1 */
 case OP_SETCLIENTID: SETCLIENTID4res opsetclientid;

 /* Not for NFSv4.1 */
 case OP_SETCLIENTID_CONFIRM:
                        SETCLIENTID_CONFIRM4res
                                opsetclientid_confirm;
 case OP_VERIFY:        VERIFY4res opverify;
 case OP_WRITE:         WRITE4res opwrite;

 /* Not for NFSv4.1 */
 case OP_RELEASE_LOCKOWNER:
                        RELEASE_LOCKOWNER4res
                                oprelease_lockowner;

 /* Operations new to NFSv4.1 */
 case OP_BACKCHANNEL_CTL:
                        BACKCHANNEL_CTL4res
                                opbackchannel_ctl;

 case OP_BIND_CONN_TO_SESSION:
                        BIND_CONN_TO_SESSION4res
                                 opbind_conn_to_session;

 case OP_EXCHANGE_ID:   EXCHANGE_ID4res opexchange_id;

 case OP_CREATE_SESSION:
                        CREATE_SESSION4res
                                opcreate_session;

 case OP_DESTROY_SESSION:
                        DESTROY_SESSION4res
                                opdestroy_session;

 case OP_FREE_STATEID:  FREE_STATEID4res
                                opfree_stateid;

 case OP_GET_DIR_DELEGATION:
                        GET_DIR_DELEGATION4res
                                opget_dir_delegation;

 case OP_GETDEVICEINFO: GETDEVICEINFO4res
                                opgetdeviceinfo;

 case OP_GETDEVICELIST: GETDEVICELIST4res
                                opgetdevicelist;

 case OP_LAYOUTCOMMIT:  LAYOUTCOMMIT4res oplayoutcommit;
 case OP_LAYOUTGET:     LAYOUTGET4res oplayoutget;
 case OP_LAYOUTRETURN:  LAYOUTRETURN4res oplayoutreturn;

 case OP_SECINFO_NO_NAME:
                        SECINFO_NO_NAME4res
                                opsecinfo_no_name;

 case OP_SEQUENCE:      SEQUENCE4res opsequence;
 case OP_SET_SSV:       SET_SSV4res opset_ssv;
 case OP_TEST_STATEID:  TEST_STATEID4res optest_stateid;

 case OP_WANT_DELEGATION:
                        WANT_DELEGATION4res
                                opwant_delegation;

 case OP_DESTROY_CLIENTID:
                        DESTROY_CLIENTID4res
                                opdestroy_clientid;

 case OP_RECLAIM_COMPLETE:
                        RECLAIM_COMPLETE4res
                                opreclaim_complete;

 /* Operations not new to NFSv4.1 */
 case OP_ILLEGAL:       ILLEGAL4res opillegal;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct COMPOUND4res {
        nfsstat4        status;
        utf8str_cs      tag;
        nfs_resop4      resarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="OP_COMPOUND_DESCRIPTION" title="DESCRIPTION">
    <t>
      The COMPOUND procedure is used to combine one or more NFSv4
      operations into a
      single RPC request.  The server interprets each of the operations in
      turn.  If an operation is executed by the server and the status of that
      operation is NFS4_OK, then the next operation in the COMPOUND
      procedure is executed.  The server continues this process until there
      are no more operations to be executed or until one of the operations has a
      status value other than NFS4_OK.
    </t>
    <t>
      In the processing of the COMPOUND procedure, the server may find that
      it does not have the available resources to execute any or all of the
      operations within the COMPOUND sequence. See
      <xref target="COMPOUND_Sizing_Issues" /> for a more detailed discussion.
    </t>
    <t>
      The server will generally choose between two methods of decoding the
      client's request.  The first would be the traditional one-pass XDR
      decode.  If there is an XDR decoding error in this case, the RPC XDR
      decode error would be returned.  The second method would be to make an
      initial pass to decode the basic COMPOUND request and then to XDR
      decode the individual operations; the most interesting is the decode
      of attributes.  In this case, the server may encounter an XDR decode
      error during the second pass.  If it does, the server would return
      the error NFS4ERR_BADXDR to signify the decode error.
    </t>
    <t>
      The COMPOUND arguments contain a "minorversion" field.  For NFSv4.1,
      the value for this field is 1.  If the server receives
      a COMPOUND procedure with a minorversion field value that it does not
      support, the server MUST return an error of
      NFS4ERR_MINOR_VERS_MISMATCH and a zero-length resultdata array.
    </t>
    <t>
      Contained within the COMPOUND results is a "status" field.  If the
      results array length is non-zero, this status must be equivalent to
      the status of the last operation that was executed within the COMPOUND
      procedure.  Therefore, if an operation incurred an error then the
      "status" value will be the same error value as is being returned for
      the operation that failed.
    </t>
    <t>
      Note that operations zero and one are not defined for the
      COMPOUND procedure.  Operation 2 is not defined and is reserved for
      future definition and use with minor versioning.  If the server
      receives an operation array that contains operation 2 and the
      minorversion field has a value of zero, an error of
      NFS4ERR_OP_ILLEGAL, as described in the next paragraph, is returned to
      the client.  If an operation array contains an operation 2 and the
      minorversion field is non-zero and the server does not support the
      minor version, the server returns an error of
      NFS4ERR_MINOR_VERS_MISMATCH.  Therefore, the
      NFS4ERR_MINOR_VERS_MISMATCH error takes precedence over all other
      errors.
    </t>
    <t>
      It is possible that the server receives a request that contains an
      operation that is less than the first legal operation (OP_ACCESS) or
      greater than the last legal operation (OP_RELEASE_LOCKOWNER).  In this
      case, the server's response will encode the opcode OP_ILLEGAL rather
      than the illegal opcode of the request. The status field in the
      ILLEGAL return results will be set to NFS4ERR_OP_ILLEGAL.  The COMPOUND
      procedure's return results will also be NFS4ERR_OP_ILLEGAL.
    </t>
    <t>
      The definition of the "tag" in the request is left to the implementor.
      It may be used to summarize the content of the Compound request for
      the benefit of packet-sniffers and engineers debugging
      implementations.  However, the value of "tag" in the response SHOULD
      be the same value as provided in the request.  This applies to the tag
      field of the CB_COMPOUND procedure as well.
    </t>
    <section toc="exclude" anchor="current_filehandle_stateid"
    title="Current Filehandle and Stateid">
    <t>
      The COMPOUND procedure offers a simple environment for the
      execution of the operations specified by the client.  The first
      two relate to the filehandle while the second two relate to the
      current stateid.
    </t>
    <section toc="exclude" anchor="current_filehandle" title="Current
    Filehandle">
    <t>
      The current and saved filehandles are used throughout
      the protocol.  Most operations implicitly use
      the current filehandle as an argument, and many set
      the current filehandle as part of the results.
      The combination of client-specified sequences
      of operations and current and saved filehandle
      arguments and results allows for greater protocol
      flexibility.  The best or easiest example of current
      filehandle usage is a sequence like the following:

    </t>
    <t>
      <figure anchor='curfh_example'>
      <artwork>
      PUTFH fh1              {fh1}
      LOOKUP "compA"         {fh2}
      GETATTR                {fh2}
      LOOKUP "compB"         {fh3}
      GETATTR                {fh3}
      LOOKUP "compC"         {fh4}
      GETATTR                {fh4}
      GETFH
      </artwork>
      </figure>
    </t>
    <t>
      In this example, the PUTFH (<xref target="OP_PUTFH"/>) operation explicitly sets the current
      filehandle value while the result of each LOOKUP operation sets
      the current filehandle value to the resultant file system
      object.  Also, the client is able to insert GETATTR operations
      using the current filehandle as an argument.
    </t>
    <t>
       The PUTROOTFH (<xref target="OP_PUTROOTFH"/>) and
       PUTPUBFH (<xref target="OP_PUTPUBFH"/>) operations also set the
       current filehandle. The above example would replace "PUTFH fh1" with
       PUTROOTFH or PUTPUBFH with no filehandle argument in order to 
       achieve the same effect (on the assumption that "compA" is directly
       below the root of the namespace).
    </t>
    <t>
      Along with the current filehandle, there is a saved filehandle.
      While the current filehandle is set as the result of
      operations like LOOKUP, the saved filehandle must be set
      directly with the use of the SAVEFH operation.  The SAVEFH
      operation copies the current filehandle value to the saved
      value.  The saved filehandle value is used in combination with
      the current filehandle value for the LINK and RENAME
      operations.  The RESTOREFH operation will copy the saved filehandle value to the current filehandle value; as a result, the
      saved filehandle value may be used a sort of "scratch" area for
      the client's series of operations.
    </t>
    </section>

    <section toc="exclude" anchor="current_stateid" title="Current Stateid">
    <t>
      With NFSv4.1, additions of a current stateid and a saved stateid
      have been made to the COMPOUND processing environment; this
      allows for the passing of stateids between operations.  There
      are no changes to the syntax of the protocol, only changes to
      the semantics of a few operations.
    </t>
    <t>
      A "current stateid" is the stateid that is associated
      with the current filehandle.  The current stateid
      may only be changed by an operation that modifies
      the current filehandle or returns a stateid.  If an
      operation returns a stateid, it MUST set the current
      stateid to the returned value. If an operation sets
      the current filehandle but does not return a stateid,
      the current stateid MUST be set to the all-zeros
      special stateid, i.e., (seqid, other) = (0, 0).
      If an operation uses a stateid as an argument but does
      not return a stateid, the current stateid MUST NOT be
      changed.
      For example, PUTFH, PUTROOTFH, and PUTPUBFH
      will change the current server state from {ocfh,
      (osid)} to {cfh, (0, 0)}, while LOCK will change the current
      state from {cfh, (osid} to {cfh, (nsid)}.  Operations like
      LOOKUP that transform a current filehandle and
      component name into a new current filehandle will also
      change the current state to {0, 0}.  The SAVEFH
      and RESTOREFH operations will save and restore both
      the current filehandle and the current stateid as a set.

    </t>

    <t>
      The following example is the common case of a simple READ
      operation with a normal stateid showing that the PUTFH
      initializes the current stateid to (0, 0). The subsequent READ
      with stateid (sid1) leaves the current stateid unchanged.
    </t>
    <figure anchor='csid_example1'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    READ (sid1), 0, 1024      {fh1, (0, 0)} -> {fh1, (0, 0)}
    </artwork>
    </figure>

    <t>
      This next example performs an OPEN with the root
      filehandle and, as a result, generates stateid (sid1). The next
      operation specifies the READ with the argument stateid set such
      that (seqid, other) are equal to (1, 0),
      but the current stateid set by the previous operation is
      actually used when the operation is evaluated. This allows correct
      interaction with any existing, potentially conflicting,
      locks.
    </t>
    <figure anchor='csid_example2'>
    <artwork>
    PUTROOTFH                             - -> {fh1, (0, 0)}
    OPEN "compA"              {fh1, (0, 0)} -> {fh2, (sid1)}
    READ (1, 0), 0, 1024      {fh2, (sid1)} -> {fh2, (sid1)}
    CLOSE (1, 0)              {fh2, (sid1)} -> {fh2, (sid2)}
    </artwork>
    </figure>

    <t>
      This next example is similar to the second in how
      it passes the stateid sid2 generated by the LOCK
      operation to the next READ operation.  This allows
      the client to explicitly surround a single I/O
      operation with a lock and its appropriate stateid to
      guarantee correctness with other client locks. The
      example also shows how SAVEFH and RESTOREFH can
      save and later reuse a filehandle and stateid, passing them as the
      current filehandle and stateid to a READ operation.

    </t>
    <figure anchor='csid_example3'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    LOCK 0, 1024, (sid1)      {fh1, (sid1)} -> {fh1, (sid2)}
    READ (1, 0), 0, 1024      {fh1, (sid2)} -> {fh1, (sid2)}
    LOCKU 0, 1024, (1, 0)     {fh1, (sid2)} -> {fh1, (sid3)}
    SAVEFH                    {fh1, (sid3)} -> {fh1, (sid3)}

    PUTFH fh2                 {fh1, (sid3)} -> {fh2, (0, 0)}
    WRITE (1, 0), 0, 1024     {fh2, (0, 0)} -> {fh2, (0, 0)}

    RESTOREFH                 {fh2, (0, 0)} -> {fh1, (sid3)}
    READ (1, 0), 1024, 1024   {fh1, (sid3)} -> {fh1, (sid3)}
    </artwork>
    </figure>

    <t>
      The final example shows a disallowed use of
      the current stateid. The client is attempting
      to implicitly pass an anonymous special stateid, (0,0), to
      the READ operation. The server MUST return NFS4ERR_BAD_STATEID
      in the reply to the READ operation.

    </t>
    <figure anchor='csid_example4'>
    <artwork>
    PUTFH fh1                             - -> {fh1, (0, 0)}
    READ (1, 0), 0, 1024      {fh1, (0, 0)} -> NFS4ERR_BAD_STATEID
    </artwork>
    </figure>

    </section>
    </section>
  </section>

  <section toc="exclude" anchor="OP_COMPOUND_ERRORS" title="ERRORS">
    <t>
     COMPOUND will of course return every error that each operation on
     the fore channel can return (see <xref target="op_error_returns"/>).
     However, if COMPOUND returns zero operations, obviously the error
     returned by COMPOUND has nothing to do with an error returned by
     an operation. The list of errors COMPOUND will return if it processes
     zero operations include:
    </t>
     <texttable anchor="compounderrs">
     <preamble>COMPOUND Error Returns</preamble>
     <ttcol align='left'>Error</ttcol>
     <ttcol align='left'>Notes</ttcol>

     <c>NFS4ERR_BADCHAR</c> <c>The tag argument has a character the replier
                               does not support. </c>

     <c>NFS4ERR_BADXDR</c> <c> </c>

     <c>NFS4ERR_DELAY</c> <c> </c>

     <c>NFS4ERR_INVAL</c> <c>The tag argument is not in UTF-8 encoding.</c>

     <c>NFS4ERR_MINOR_VERS_MISMATCH</c> <c> </c>

     <c>NFS4ERR_SERVERFAULT</c> <c> </c>

     <c>NFS4ERR_TOO_MANY_OPS</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c> <c> </c>

     <c>NFS4ERR_REQ_TOO_BIG</c> <c> </c>

     </texttable>
 
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<section anchor="operation_mandlist" 
	 title="Operations: REQUIRED, RECOMMENDED, or OPTIONAL">

  <t>
    The following tables summarize the operations of the NFSv4.1
    protocol and the corresponding designation of REQUIRED,
    RECOMMENDED, and OPTIONAL to implement or MUST NOT implement.  The
    designation of MUST NOT implement is reserved for those operations
    that were defined in NFSv4.0 and MUST NOT be implemented in NFSv4.1.
  </t>
  <t>
    For the most part, the REQUIRED, RECOMMENDED, or OPTIONAL designation for
    operations sent by the client is for
    the server implementation.  The client is generally required to
    implement the operations needed for the operating environment for
    which it serves.  For example, a read-only NFSv4.1 client would
    have no need to implement the WRITE operation and is not required
    to do so.
  </t>
  <t>
    The REQUIRED or OPTIONAL designation for
    callback operations sent by the server is for both the client
    and server. Generally, the client has the option of
    creating the backchannel and sending the operations on the
    fore channel that will be a catalyst for the server sending
    callback operations. A partial
    exception is CB_RECALL_SLOT; the only way the client can
    avoid supporting this operation is by not creating a backchannel.
  </t>
  <t>
    Since this is a summary of the operations and their designation,
    there are subtleties that are not presented here.  Therefore, if
    there is a question of the requirements of implementation, the
    operation descriptions themselves must be consulted along with
    other relevant explanatory text within this specification.
  </t>
  <t>
    The abbreviations used in the second and third columns of the table
    are defined as follows.
    <list style="hanging">
      <t hangText="REQ">
	REQUIRED to implement
      </t>
      <t hangText="REC">
	RECOMMEND to implement
      </t>
      <t hangText="OPT">
	OPTIONAL to implement
      </t>
      <t hangText="MNI">
	MUST NOT implement
      </t>
    </list>
  </t>

  <t> For the NFSv4.1 features that are OPTIONAL, the operations that
    support those features are OPTIONAL, and the server would return
    NFS4ERR_NOTSUPP in response to the client's use of those
    operations.  If an OPTIONAL feature is supported, it is possible
    that a set of operations related to the feature become REQUIRED
    to implement.  The third column of the table designates the
    feature(s) and if the operation is REQUIRED or OPTIONAL in the
    presence of support for the feature.
  </t>
  <t>
    The OPTIONAL features identified and their abbreviations are as
    follows:
    <list style="hanging">
      <t hangText="pNFS">
	Parallel NFS
      </t>
      <t hangText="FDELG">
	File Delegations
      </t>
      <t hangText="DDELG">
	Directory Delegations
      </t>
    </list>
  </t>
    <texttable>

      <preamble> Operations </preamble>

      <ttcol align='left' >Operation</ttcol>
      <ttcol align='left' >REQ, REC, OPT, or MNI</ttcol>
      <ttcol align='left' >Feature (REQ, REC, or OPT)</ttcol>
      <ttcol align='left' >Definition</ttcol>

      <c> ACCESS </c> 
      <c>REQ</c> 
      <c></c> 
      <c> <xref target="OP_ACCESS" /> </c>

      <c> BACKCHANNEL_CTL </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_BACKCHANNEL_CTL" /> </c>

      <c> BIND_CONN_TO_SESSION</c> 
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_BIND_CONN_TO_SESSION" /> </c>

      <c> CLOSE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CLOSE" /> </c>

      <c> COMMIT </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_COMMIT" /> </c>

      <c> CREATE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CREATE" /> </c>

      <c> CREATE_SESSION </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_CREATE_SESSION" /> </c>

      <c> DELEGPURGE </c>
      <c>OPT</c>
      <c>FDELG (REQ)</c>
      <c> <xref target="OP_DELEGPURGE" /> </c>

      <c> DELEGRETURN </c>
      <c>OPT</c>
      <c>FDELG, DDELG, pNFS (REQ)</c>
      <c> <xref target="OP_DELEGRETURN" /> </c>

      <c> DESTROY_CLIENTID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_DESTROY_CLIENTID" /> </c>

      <c> DESTROY_SESSION </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_DESTROY_SESSION" /> </c>

      <c> EXCHANGE_ID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_EXCHANGE_ID" /> </c>

      <c> FREE_STATEID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_FREE_STATEID" /> </c>

      <c> GETATTR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_GETATTR" /> </c>

      <c> GETDEVICEINFO </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_GETDEVICEINFO" /> </c>

      <c> GETDEVICELIST</c>
      <c>OPT</c>
      <c>pNFS (OPT)</c>
      <c> <xref target="OP_GETDEVICELIST" /> </c>

      <c> GETFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_GETFH" /> </c>

      <c> GET_DIR_DELEGATION </c>
      <c>OPT</c>
      <c>DDELG (REQ)</c>
      <c> <xref target="OP_GET_DIR_DELEGATION" /> </c>

      <c> LAYOUTCOMMIT </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTCOMMIT" /> </c>

      <c> LAYOUTGET </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTGET" /> </c>

      <c> LAYOUTRETURN </c>
      <c>OPT</c>
      <c>pNFS (REQ)</c>
      <c> <xref target="OP_LAYOUTRETURN" /> </c>

      <c> LINK </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_LINK" /> </c>

      <c> LOCK </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCK" /> </c>

      <c> LOCKT </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCKT" /> </c>

      <c> LOCKU </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOCKU" /> </c>

      <c> LOOKUP </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOOKUP" /> </c>

      <c> LOOKUPP </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_LOOKUPP" /> </c>

      <c> NVERIFY </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_NVERIFY" /> </c>

      <c> OPEN </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_OPEN" /> </c>

      <c> OPENATTR </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_OPENATTR" /> </c>

      <c> OPEN_CONFIRM </c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> OPEN_DOWNGRADE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_OPEN_DOWNGRADE" /> </c>

      <c> PUTFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTFH" /> </c>

      <c> PUTPUBFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTPUBFH" /> </c>

      <c> PUTROOTFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_PUTROOTFH" /> </c>

      <c> READ </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_READ" /> </c>

      <c> READDIR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_READDIR" /> </c>

      <c> READLINK </c>
      <c>OPT</c>
      <c></c>
      <c> <xref target="OP_READLINK" /> </c>

      <c> RECLAIM_COMPLETE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RECLAIM_COMPLETE" /> </c>

      <c> RELEASE_LOCKOWNER</c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> REMOVE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_REMOVE" /> </c>

      <c> RENAME </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RENAME" /> </c>

      <c> RENEW </c>
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> RESTOREFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_RESTOREFH" /> </c>

      <c> SAVEFH </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SAVEFH" /> </c>

      <c> SECINFO </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SECINFO" /> </c>

      <c> SECINFO_NO_NAME </c>
      <c>REC</c>
      <c>pNFS file layout (REQ)</c>
      <c> <xref target="OP_SECINFO_NO_NAME" />,
          <xref target="file_security_considerations"/>
      </c>

      <c> SEQUENCE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SEQUENCE" /> </c>

      <c> SETATTR </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SETATTR" /> </c>

      <c> SETCLIENTID</c> 
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> SETCLIENTID_CONFIRM</c> 
      <c>MNI</c>
      <c></c>
      <c> N/A </c>

      <c> SET_SSV</c> 
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_SET_SSV" /> </c>

      <c> TEST_STATEID </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_TEST_STATEID" /> </c>

      <c> VERIFY </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_VERIFY" /> </c>

      <c> WANT_DELEGATION</c>
      <c>OPT</c>
      <c>FDELG (OPT)</c> 
      <c> <xref target="OP_WANT_DELEGATION" /> </c>

      <c> WRITE </c>
      <c>REQ</c>
      <c></c>
      <c> <xref target="OP_WRITE" /> </c>

    </texttable>




  <texttable>

      <preamble> Callback Operations </preamble>
      <ttcol align='left' >Operation</ttcol>
      <ttcol align='left' >REQ, REC, OPT, or MNI</ttcol>
      <ttcol align='left' >Feature (REQ, REC, or OPT)</ttcol>
      <ttcol align='left' >Definition</ttcol>

      <c> CB_GETATTR </c> 
      <c>OPT</c> 
      <c>FDELG (REQ)</c> 
      <c> <xref target="OP_CB_GETATTR" /> </c>

      <c> CB_LAYOUTRECALL </c> 
      <c>OPT</c> 
      <c>pNFS (REQ)</c> 
      <c> <xref target="OP_CB_LAYOUTRECALL" /> </c>

      <c> CB_NOTIFY </c> 
      <c>OPT</c> 
      <c>DDELG (REQ)</c> 
      <c> <xref target="OP_CB_NOTIFY" /> </c>

      <c> CB_NOTIFY_DEVICEID </c> 
      <c>OPT</c> 
      <c>pNFS (OPT)</c> 
      <c> <xref target="OP_CB_NOTIFY_DEVICEID" /> </c>

      <c> CB_NOTIFY_LOCK </c> 
      <c>OPT</c> 
      <c></c> 
      <c> <xref target="OP_CB_NOTIFY_LOCK" /> </c>

      <c> CB_PUSH_DELEG </c> 
      <c>OPT</c> 
      <c>FDELG (OPT)</c> 
      <c> <xref target="OP_CB_PUSH_DELEG" /> </c>

      <c> CB_RECALL </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALL" /> </c>

      <c> CB_RECALL_ANY </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALL_ANY" /> </c>

      <c> CB_RECALL_SLOT </c> 
      <c>REQ</c> 
      <c></c> 
      <c> <xref target="OP_CB_RECALL_SLOT" /> </c>

      <c> CB_RECALLABLE_OBJ_AVAIL </c> 
      <c>OPT</c> 
      <c>DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_RECALLABLE_OBJ_AVAIL" /> </c>

      <c> CB_SEQUENCE </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_SEQUENCE" /> </c>

      <c> CB_WANTS_CANCELLED </c> 
      <c>OPT</c> 
      <c>FDELG, DDELG, pNFS (REQ)</c> 
      <c> <xref target="OP_CB_WANTS_CANCELLED" /> </c>

    </texttable>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41operations" title="NFSv4.1 Operations">
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_ACCESS" title="Operation 3: ACCESS - Check Access Rights" >

  <section toc="exclude" anchor="OP_ACCESS_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>

const ACCESS4_READ      = 0x00000001;
const ACCESS4_LOOKUP    = 0x00000002;
const ACCESS4_MODIFY    = 0x00000004;
const ACCESS4_EXTEND    = 0x00000008;
const ACCESS4_DELETE    = 0x00000010;
const ACCESS4_EXECUTE   = 0x00000020;

struct ACCESS4args {
        /* CURRENT_FH: object */
        uint32_t        access;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_ACCESS_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct ACCESS4resok {
        uint32_t        supported;
        uint32_t        access;
};

union ACCESS4res switch (nfsstat4 status) {
 case NFS4_OK:
         ACCESS4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_ACCESS_DESCRIPTION" title="DESCRIPTION">
    <t>
ACCESS determines the access rights that a user, as identified by the
credentials in the RPC request, has with respect to the file system
object specified by the current filehandle.  The client encodes the
set of access rights that are to be checked in the bit mask "access".
The server checks the permissions encoded in the bit mask.  If a
status of NFS4_OK is returned, two bit masks are included in the
response.  The first, "supported", represents the access rights for
which the server can verify reliably.  The second, "access",
represents the access rights available to the user for the filehandle
provided.  On success, the current filehandle retains its value.
    </t>
    <t>
Note that the reply's supported and access fields MUST NOT
contain more values than originally set in the request's
access field.  For example, if the client sends an ACCESS
operation with just the ACCESS4_READ value set and the
server supports this value, the server MUST NOT set more
than ACCESS4_READ in the supported field even if it could
have reliably checked other values.

    </t>
    <t>
     The reply's access field MUST NOT contain more values than the
     supported field.
    </t>
    <t>
The results of this operation are necessarily advisory in nature.  A
return status of NFS4_OK and the appropriate bit set in the bit mask
do not imply that such access will be allowed to the file system
object in the future. This is because access rights can be revoked by
the server at any time.
    </t>
    <t>
The following access permissions may be requested:
<list style="hanging">
<t hangText="ACCESS4_READ">
Read data from file or read a directory.
</t>
<t hangText="ACCESS4_LOOKUP">
Look up a name in a directory (no meaning for non-directory objects).
</t>
<t hangText="ACCESS4_MODIFY">
Rewrite existing file data or modify existing directory entries.
</t>
<t hangText="ACCESS4_EXTEND">
Write new data or add directory entries.
</t>
<t hangText="ACCESS4_DELETE">
Delete an existing directory entry.
</t>
<t hangText="ACCESS4_EXECUTE">
Execute a regular file (no meaning for a directory).
</t>
</list>
On success, the current filehandle retains its value.
    </t>
   <t>
    ACCESS4_EXECUTE is a challenging semantic to implement because
    NFS provides remote file access, not remote
    execution. This leads to the following:
    <list style="symbols">
    <t>
     Whether or not a regular file is executable ought to be
     the responsibility of the NFS client and not the server. And yet
     the ACCESS operation is specified to seemingly require a server to
     own that responsibility.
    </t>
    <t>
     When a client executes a regular file, it has to
     read the file from the server. Strictly speaking,
     the server should not allow the client to read a file
     being executed unless the user has read permissions
     on the file. Requiring
     explicit read permissions on executable files in order to
     access them over NFS is not going to be acceptable to
     some users and storage administrators. Historically, NFS servers have allowed
     a user to READ a file if the user has execute access
     to the file.

    </t>
   </list>
  </t>
  <t>
   As a practical example, the UNIX specification <xref
   target="access_api"/> states that an implementation
   claiming conformance to UNIX may indicate in the
   access() programming interface's result that a
   privileged user has execute rights, even if no
   execute permission bits are set on the regular file's
   attributes. It is possible to claim conformance
   to the UNIX specification and instead not indicate
   execute rights in that situation, which is true for
   some operating environments. Suppose the operating
   environments of the client and server are implementing
   the access() semantics for privileged users differently,
   and the ACCESS operation implementations of the client
   and server follow their respective access() semantics.
   This can cause undesired behavior:

   <list style='symbols'>
   <t>
    Suppose the client's access() interface returns X_OK
    if the user is privileged and no execute permission
    bits are set on the regular file's attribute, and the
    server's access() interface does not return X_OK in
    that situation.  Then the client will be unable to
    execute files stored on the NFS server that could be
    executed if stored on a non-NFS file system.

   </t>
   <t>
    Suppose the client's access() interface does
    not return X_OK if the user is privileged, and no
    execute permission bits are set on the regular file's
    attribute, and the server's access() interface does
    return X_OK in that situation. Then:

    <list style='symbols'>
    <t>
     The client will be able to execute files stored on
     the NFS server that could be executed if stored on
     a non-NFS file system, unless the client's execution
     subsystem also checks for execute permission bits.

    </t>
    <t>
     Even if the execution subsystem is checking for
     execute permission bits, there are more potential
     issues.  For example, suppose the client is invoking access()
     to build a "path search table" of all executable
     files in the user's "search path", where the path
     is a list of directories each containing executable
     files. Suppose there are two files each in separate
     directories of the search path, such that files have
     the same component name.  In the first directory
     the file has no execute permission bits set,
     and in the second directory the file has execute
     bits set. The path search table will indicate that
     the first directory has the executable file, but
     the execute subsystem will fail to execute it. The
     command shell might fail to try the second file in
     the second directory. And even if it did, this is
     a potential performance issue. Clearly, the desired
     outcome for the client is for the path search table
     to not contain the first file.

    </t>
    </list>
   </t>
   </list>
  </t>
  <t>
   To deal with the problems described above, the "smart client,
   stupid server" principle is used. The client owns overall
   responsibility for determining execute access and
   relies on the server to parse the execution permissions
   within the file's mode, acl, and dacl attributes. The
   rules for the client and server follow:

   <list style='symbols'>
   <t>
    If the client is sending ACCESS in order to determine
    if the user can read the file, the client SHOULD
    set ACCESS4_READ in the request's access field.

   </t>
   <t>
    If the client's operating environment only grants
    execution to the user if the user has execute access
    according to the execute permissions in the mode,
    acl, and dacl attributes, then if the client wants
    to determine execute access, the client SHOULD send
    an ACCESS request with ACCESS4_EXECUTE bit set in the
    request's access field.

   </t>
   <t>
    If the client's operating environment grants execution
    to the user even if the user does not have execute
    access according to the execute permissions in the
    mode, acl, and dacl attributes, then if the client
    wants to determine execute access, it SHOULD send
    an ACCESS request with both the ACCESS4_EXECUTE and
    ACCESS4_READ bits set in the request's access field. This
    way, if any read or execute permission grants the user
    read or execute access (or if the server interprets
    the user as privileged), as indicated by the presence
    of ACCESS4_EXECUTE and/or ACCESS4_READ in the reply's
    access field, the client will be able to grant the
    user execute access to the file.

   </t>

   <t>
    If the server supports execute permission bits, or some other
    method for denoting executability (e.g., the suffix of the name
    of the file might indicate execute), it MUST check
    only execute permissions, not read permissions, when determining
    whether or not the reply will have ACCESS4_EXECUTE set in the access
    field.
    The server MUST NOT also examine read permission bits when
    determining whether or not the reply will have ACCESS4_EXECUTE
    set in the access field.  Even if the server's
    operating environment would grant execute access to the
    user (e.g., the user is privileged), the server MUST
    NOT reply with ACCESS4_EXECUTE set in reply's access
    field unless there is at least one execute permission
    bit set in the mode, acl, or dacl attributes. In the
    case of acl and dacl, the "one execute permission bit"
    MUST be an ACE4_EXECUTE bit set in an ALLOW ACE.

   </t>
   <t>
    If the server does not support execute permission
    bits or some other method for denoting executability, it MUST NOT set ACCESS4_EXECUTE in the
    reply's supported and access fields. If the client
    set ACCESS4_EXECUTE in the ACCESS request's access
    field, and ACCESS4_EXECUTE is not set in the reply's
    supported field, then the client will have to send
    an ACCESS request with the ACCESS4_READ bit set in
    the request's access field.

   </t>

   <t>
    If the server supports read permission bits, it MUST
    only check for read permissions in the mode, acl,
    and dacl attributes when it receives an ACCESS request
    with ACCESS4_READ set in the access field.  The server
    MUST NOT also examine execute permission bits when
    determining whether the reply will have ACCESS4_READ
    set in the access field or not.

   </t>

   </list>
   Note that if the ACCESS reply has ACCESS4_READ
   or ACCESS_EXECUTE set, then the user also has
   permissions to OPEN (<xref target="OP_OPEN"/>) or
   READ (<xref target="OP_READ"/>) the file. In other words, if
   the client sends an ACCESS request with the ACCESS4_READ
   and ACCESS_EXECUTE set in the access field (or two
   separate requests, one with ACCESS4_READ set and the
   other with ACCESS4_EXECUTE set), and the reply has
   just ACCESS4_EXECUTE set in the access field (or just
   one reply has ACCESS4_EXECUTE set), then the user has
   authorization to OPEN or READ the file.


  </t>
  </section>
  <section toc="exclude" anchor="OP_ACCESS_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
In general, it is not sufficient for the client to attempt to deduce
access permissions by inspecting the uid, gid, and mode fields in the
file attributes or by attempting to interpret the contents of the ACL
attribute.  This is because the server may perform uid or gid mapping
or enforce additional access-control restrictions.  It is also
possible that the server may not be in the same ID space as the
client.  In these cases (and perhaps others), the client cannot
reliably perform an access check with only current file attributes.
    </t>
    <t>
In the NFSv2 protocol, the only reliable way to determine
whether an operation was allowed was to try it and see if it succeeded
or failed.  Using the ACCESS operation in the NFSv4.1 protocol,
the client can ask the server to indicate whether or not one or more
classes of operations are permitted.  The ACCESS operation is provided
to allow clients to check before doing a series of operations that
will result in an access failure.  The OPEN operation provides a point
where the server can verify access to the file object and a method to
return that information to the client.  The ACCESS operation is still
useful for directory operations or for use in the case that the UNIX interface
access() is used on the client.
    </t>
    <t>
The information returned by the server in response to an ACCESS call
is not permanent.  It was correct at the exact time that the server
performed the checks, but not necessarily afterwards.  The server can
revoke access permission at any time.
    </t>
    <t>
The client should use the effective credentials of the user to build
the authentication information in the ACCESS request used to determine
access rights.  It is the effective user and group credentials that
are used in subsequent READ and WRITE operations.
    </t>
    <t>
Many implementations do not directly support the ACCESS4_DELETE
permission.  Operating systems like UNIX will ignore the ACCESS4_DELETE
bit if set on an access request on a non-directory object.  In these
systems, delete permission on a file is determined by the access
permissions on the directory in which the file resides, instead of
being determined by the permissions of the file itself.  Therefore,
the mask returned enumerating which access rights can be determined
will have the ACCESS4_DELETE value set to 0.  This indicates to the
client that the server was unable to check that particular access
right.  The ACCESS4_DELETE bit in the access mask returned will then be
ignored by the client.
    </t>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CLOSE" title="Operation 4: CLOSE - Close File" >

  <section toc="exclude" anchor="OP_CLOSE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct CLOSE4args {
        /* CURRENT_FH: object */
        seqid4          seqid;
        stateid4        open_stateid;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_CLOSE_RESULTS" title="RESULTS">
<figure>
 <artwork>
union CLOSE4res switch (nfsstat4 status) {
 case NFS4_OK:
         stateid4       open_stateid;
 default:
         void;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_CLOSE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CLOSE operation releases share reservations for the regular or
      named attribute file as specified by the current filehandle.  The
      share reservations and other state information released at the server
      as a result of this CLOSE are only those associated with the supplied
      stateid.  State associated with other OPENs is not affected.
    </t>
    <t>
      If byte-range locks are held, the client SHOULD release all locks before
      sending a CLOSE.  The server MAY free all outstanding locks on CLOSE,
      but some servers may not support the CLOSE of a file that still has
      byte-range locks held.  The server MUST return failure if any locks would
      exist after the CLOSE.
    </t>
    <t>
      The argument seqid MAY have any value, and the server MUST ignore seqid.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     The server MAY require that the combination of principal, security
     flavor, and, if applicable, GSS mechanism
     that sent the OPEN request also be the one to CLOSE
     the file. This might not be possible if credentials
     for the principal are no longer available. The server
     MAY allow the machine credential or SSV credential
     (see <xref target="OP_EXCHANGE_ID" />) to send CLOSE.

    </t>

  </section>
  <section toc="exclude" anchor="OP_CLOSE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Even though CLOSE returns a stateid, this stateid is not useful to the
      client and should be treated as deprecated.  CLOSE "shuts down" the
      state associated with all OPENs for the file by a single open-owner.
      As noted above, CLOSE will either release all file-locking state or
      return an error.  Therefore, the stateid returned by CLOSE is not
      useful for operations that follow.  To help find any uses of
      this stateid by clients, the server SHOULD return the invalid
      special stateid (the "other" value is zero and the "seqid" field
      is NFS4_UINT32_MAX, see <xref target="special_stateid"/>).
    </t>
    <t>
      A CLOSE operation may make delegations grantable
      where they were not previously.  Servers may choose to respond
      immediately if there are pending delegation want requests or may
      respond to the situation at a later time.
    </t>
  </section>
</section>

<section anchor="OP_COMMIT" title="Operation 5: COMMIT - Commit Cached Data" >

  <section toc="exclude" anchor="OP_COMMIT_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct COMMIT4args {
        /* CURRENT_FH: file */
        offset4         offset;
        count4          count;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_COMMIT_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct COMMIT4resok {
        verifier4       writeverf;
};

union COMMIT4res switch (nfsstat4 status) {
 case NFS4_OK:
         COMMIT4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_COMMIT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The COMMIT operation forces or flushes uncommitted, modified data to stable storage for the
      file specified by the current filehandle.  The flushed data is that
      which was previously written with one or more WRITE operations that had the
      "committed" field of their results field set to UNSTABLE4.

    </t>
    <t>
      The offset specifies the position within the file where the flush is
      to begin.  An offset value of zero means to flush data starting at
      the beginning of the file.  The count specifies the number of bytes of
      data to flush.  If the count is zero, a flush from the offset to the end
      of the file is done.
    </t>
    <t>
      The server returns a write verifier upon successful completion of the
      COMMIT.  The write verifier is used by the client to determine if the
      server has restarted between the initial WRITE operations and the
      COMMIT.  The client does this by comparing the write verifier returned
      from the initial WRITE operations and the verifier returned by the COMMIT
      operation.  The server must vary the value of the write verifier at
      each server event or instantiation that may lead to a loss of
      uncommitted data.  Most commonly this occurs when the server is
      restarted; however, other events at the server may result in
      uncommitted data loss as well.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_COMMIT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The COMMIT operation is similar in operation and semantics to the
      <xref target="fsync">POSIX fsync()</xref> system interface that synchronizes a file's state with the
      disk (file data and metadata is flushed to disk or stable
      storage). COMMIT performs the same operation for a client, flushing
      any unsynchronized data and metadata on the server to the server's
      disk or stable storage for the specified file.  Like fsync(), it may
      be that there is some modified data or no modified data to
      synchronize.  The data may have been synchronized by the server's
      normal periodic buffer synchronization activity.  COMMIT should return
      NFS4_OK, unless there has been an unexpected error.
    </t>
    <t>
      COMMIT differs from fsync() in that it is possible for the client to
      flush a range of the file (most likely triggered by a
      buffer-reclamation scheme on the client before the file has been
      completely written).
    </t>
    <t>
      The server implementation of COMMIT is reasonably simple.  If the
      server receives a full file COMMIT request, that is, starting at offset
      zero and count zero, it should do the equivalent of applying fsync() to
      the entire file.
      Otherwise, it should arrange to have the modified data in the range
      specified by offset and count to be flushed to stable storage.  In
      both cases, any metadata associated with the file must be flushed to
      stable storage before returning.  It is not an error for there to be
      nothing to flush on the server.  This means that the data and metadata
      that needed to be flushed have already been flushed or lost during the
      last server failure.
    </t>
    <t>
      The client implementation of COMMIT is a little more complex.  There
      are two reasons for wanting to commit a client buffer to stable
      storage.  The first is that the client wants to reuse a buffer.  In
      this case, the offset and count of the buffer are sent to the server
      in the COMMIT request.  The server then flushes any modified data based
      on the offset and count, and flushes any modified metadata associated with the
      file.  It then returns the status of the flush and the write verifier.
      The second reason for the client to generate a COMMIT is for a full
      file flush, such as may be done at close.  In this case, the client
      would gather all of the buffers for this file that contain uncommitted
      data, do the COMMIT operation with an offset of zero and count of zero, and
      then free all of those buffers.  Any other dirty buffers would be sent
      to the server in the normal fashion.
    </t>
    <t>
      After a buffer is written (via the WRITE operation)
      by the client with the "committed" field in the result of WRITE
      set to UNSTABLE4, the buffer must be considered as modified by
      the client
      until the buffer has either been flushed via a COMMIT operation or
      written via a WRITE operation with the "committed" field in the
      result set to FILE_SYNC4
      or DATA_SYNC4. This is done to prevent the buffer from being freed and
      reused before the data can be flushed to stable storage on the server.
    </t>
    <t>
      When a response is returned from either a WRITE or a COMMIT operation
      and it contains a write verifier that differs from that previously
      returned by the server, the client will need to retransmit all of the
      buffers containing uncommitted data to the server.  How this is
      to be done is up to the implementor.  If there is only one buffer of
      interest, then it should be sent in a WRITE request
      with the FILE_SYNC4 stable parameter.  If there is more than one
      buffer, it might be worthwhile retransmitting all of the buffers in
      WRITE operations with the stable parameter set to UNSTABLE4 and then
      retransmitting the COMMIT operation to flush all of the data on the
      server to stable storage. However, if the server repeatably
      returns from COMMIT a verifier that differs from that returned
      by WRITE, the only way to ensure progress is to retransmit all
      of the buffers with WRITE requests with the FILE_SYNC4 stable parameter.
    </t>
    <t>
      The above description applies to page-cache-based systems as well as
      buffer-cache-based systems.  In the former systems, the virtual memory
      system will need to be modified instead of the buffer cache.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CREATE" title="Operation 6: CREATE - Create a Non-Regular File Object" >

  <section toc="exclude" anchor="OP_CREATE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
union createtype4 switch (nfs_ftype4 type) {
 case NF4LNK:
         linktext4 linkdata;
 case NF4BLK:
 case NF4CHR:
         specdata4 devdata;
 case NF4SOCK:
 case NF4FIFO:
 case NF4DIR:
         void;
 default:
         void;  /* server should return NFS4ERR_BADTYPE */
};

struct CREATE4args {
        /* CURRENT_FH: directory for creation */
        createtype4     objtype;
        component4      objname;
        fattr4          createattrs;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CREATE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct CREATE4resok {
        change_info4    cinfo;
        bitmap4         attrset;        /* attributes set */
};

union CREATE4res switch (nfsstat4 status) {
 case NFS4_OK:
         /* new CURRENTFH: created object */
         CREATE4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CREATE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CREATE operation creates a file object other than an 
      ordinary file in a directory with a given name.
      The OPEN operation MUST be used to create a
      regular file or a named attribute.
    </t>
    <t>
      The current filehandle must be a directory: an object of type NF4DIR.  If the current
      filehandle is an attribute directory (type NF4ATTRDIR), the 
      error NFS4ERR_WRONG_TYPE is returned.  If the current file handle
      designates any other type of object, the error NFS4ERR_NOTDIR
      results.
    </t>
    <t>
      The objname specifies the name for the new object. 
      The objtype determines the type of object to be 
      created: directory, symlink, etc. If the object 
      type specified is that of an ordinary file, a 
      named attribute, or a named attribute directory, 
      the error NFS4ERR_BADTYPE results. 
    </t>
    <t>
      If an object of the same name already exists in the directory, the
      server will return the error NFS4ERR_EXIST.
    </t>
    <t>
      For the directory where the new file object was created, the server
      returns change_info4 information in cinfo.  With the atomic field of
      the change_info4 data type, the server will indicate if the before and
      after change attributes were obtained atomically with respect to the
      file object creation.
    </t>
    <t>
      If the objname has a length of zero, or if objname does not obey
      the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
    <t>
      The current filehandle is replaced by that of the new object.
    </t>
    <t>
      The createattrs specifies the initial set of attributes for the
      object.  The set of attributes may include any writable attribute
      valid for the object type. When the operation is successful, the
      server will return to the client an attribute mask signifying which
      attributes were successfully set for the object.
    </t>
    <t>
      If createattrs includes neither the owner attribute nor an ACL with an
      ACE for the owner, and if the server's file system both supports and
      requires an owner attribute (or an owner ACE), then the server MUST
      derive the owner (or the owner ACE). This would typically be from the
      principal indicated in the RPC credentials of the call, but the
      server's operating environment or file system semantics may dictate
      other methods of derivation. Similarly, if createattrs includes
      neither the group attribute nor a group ACE, and if the server's
      file system both supports and requires the notion of a group attribute
      (or group ACE), the server MUST derive the group attribute (or the
      corresponding owner ACE) for the file. This could be from the RPC
      call's credentials, such as the group principal if the credentials
      include it (such as with AUTH_SYS), from the group identifier
      associated with the principal in the credentials (e.g., POSIX
      systems have a <xref target="passwd">user database</xref> that has a group identifier for every
      user identifier), inherited from the directory in which the object is created,
      or whatever else the server's operating environment or file system
      semantics dictate. This applies to the OPEN operation too.
    </t>
    <t>
      Conversely, it is possible that the client will specify in createattrs an
      owner attribute, group attribute, or ACL that the principal indicated
      the RPC call's credentials does not have permissions to create files
      for. The error to be returned in this instance is NFS4ERR_PERM. This
      applies to the OPEN operation too.
    </t>
    <t>
      If the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the CREATE operation MUST NOT proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated
      as a result of this operation.
    </t>
    <t>
      If the capability FSCHARSET_CAP4_ALLOWS_ONLY_UTF8 is set
      (<xref target="utf8_caps"/>),
      and a symbolic link is being created, then the content
      of the symbolic link MUST be in UTF-8 encoding.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CREATE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client desires to set attribute values after the create, a
      SETATTR operation can be added to the COMPOUND request so that the
      appropriate attributes will be set.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DELEGPURGE" title="Operation 7: DELEGPURGE - Purge Delegations Awaiting Recovery" >

  <section toc="exclude" anchor="OP_DELEGPURGE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct DELEGPURGE4args {
        clientid4       clientid;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGPURGE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct DELEGPURGE4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGPURGE_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation purges all of the delegations awaiting recovery for a given client.
      This is useful for clients that do not commit delegation information
      to stable storage to indicate that conflicting requests need not be
      delayed by the server awaiting recovery of delegation information.
    </t>
    <t>
      The client is NOT specified by the clientid field of
      the request.  The client SHOULD set the client field
      to zero, and the server MUST ignore the clientid
      field. Instead, the server MUST derive the client ID
      from the value of the session ID in the arguments of
      the SEQUENCE operation that precedes DELEGPURGE in
      the COMPOUND request.

    </t>
      
    <t>
      The DELEGPURGE operation should be used by clients that record delegation
      information on stable storage on the client.  In this case,
      after the client recovers all delegations it knows of,
      it should immediately send a DELEGPURGE operation.
      Doing so will notify the server that
      no additional delegations for the client will be recovered allowing it
      to free resources, and avoid delaying other clients which make requests
      that conflict with the unrecovered delegations.  The set of
      delegations known to the server and the client might be different.  The
      reason for this is that after sending a request that
      resulted in a delegation, the client might experience a failure
      before it both received the delegation and
      committed the delegation to the client's stable storage.
    </t>
    <t>
      The server MAY support DELEGPURGE, but if it does not, it MUST NOT
      support CLAIM_DELEGATE_PREV and MUST NOT support CLAIM_DELEG_PREV_FH.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DELEGRETURN" title="Operation 8: DELEGRETURN - Return Delegation" >

  <section toc="exclude" anchor="OP_DELEGRETURN_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct DELEGRETURN4args {
        /* CURRENT_FH: delegated object */
        stateid4        deleg_stateid;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGRETURN_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct DELEGRETURN4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_DELEGRETURN_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DELEGRETURN operation returns the delegation represented by
      the current filehandle and stateid. 
    </t>
    <t>
      Delegations may be returned voluntarily (i.e., before
      the server has recalled them) or when recalled.  In either case, the client must
      properly propagate state changed under the context of the delegation to
      the server before returning the delegation.
    </t>
    <t>
     The server MAY require that the principal, security
     flavor, and if applicable, the GSS mechanism, combination
     that acquired the delegation also be the one to send
     DELEGRETURN on the file. This might not be possible
     if credentials for the principal are no longer
     available. The server MAY allow the machine credential
     or SSV credential (see <xref target="OP_EXCHANGE_ID"
     />) to send DELEGRETURN.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETATTR" title="Operation 9: GETATTR - Get Attributes" >

  <section toc="exclude" anchor="OP_GETATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct GETATTR4args {
        /* CURRENT_FH: object */
        bitmap4         attr_request;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct GETATTR4resok {
        fattr4          obj_attributes;
};

union GETATTR4res switch (nfsstat4 status) {
 case NFS4_OK:
         GETATTR4resok  resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GETATTR operation will obtain attributes for the file system
      object specified by the current filehandle.  The client sets a bit in
      the bitmap argument for each attribute value that it would like the
      server to return.  The server returns an attribute bitmap that
      indicates the attribute values that it was able to return,
      which will include all attributes requested by the client that
      are attributes supported by the server for the target
      file system.  This bitmap is followed by the attribute values ordered 
      lowest attribute number first.
    </t>
    <t>
      The server MUST return a value for each attribute that the client
      requests if the attribute is supported by the server for the target
      file system.  If the server does not support a particular attribute 
      on the target file system, then it MUST NOT return the attribute value 
      and MUST NOT set the attribute bit in the result bitmap.  The server 
      MUST return an error if it supports an attribute on the target 
      but cannot obtain its value.  In that case, no attribute values will 
      be returned.
    </t>
    <t>
      File systems that are absent should be treated as having support for
      a very small set of attributes as described in 
      <xref target="absent_getattr"/>,
      even if previously, when the file system was present, more attributes
      were supported.
    </t>
    <t>
      All servers MUST support the REQUIRED attributes as specified in
      <xref target="mandatory_attributes"/>, for all file systems,
      with the exception of absent file systems.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Suppose there is an OPEN_DELEGATE_WRITE delegation held by another client for
the file
      in question and size and/or change are among the set of attributes being interrogated. The server has two choices.
      First, the server can obtain the actual
      current value of these attributes from the client holding the delegation
      by using the CB_GETATTR callback.  Second, the server, particularly when the
      delegated client is unresponsive, can recall the
      delegation in question.  The GETATTR MUST NOT proceed 
      until one of the following occurs:
      <list style="symbols">
        <t>
          The requested attribute values are returned in the response to
          CB_GETATTR.
        </t>
        <t>
          The OPEN_DELEGATE_WRITE delegation is returned.
        </t>
        <t>
          The OPEN_DELEGATE_WRITE delegation is revoked.
        </t>
      </list>
    </t>
    <t>
      Unless one of the above happens very quickly,
      one or more NFS4ERR_DELAY errors will be returned
      while a delegation is outstanding.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETFH" title="Operation 10: GETFH - Get Current Filehandle" >

  <section toc="exclude" anchor="OP_GETFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_GETFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct GETFH4resok {
        nfs_fh4         object;
};

union GETFH4res switch (nfsstat4 status) {
 case NFS4_OK:
        GETFH4resok     resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_GETFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation returns the current filehandle value.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
      As described in <xref target="COMPOUND_Sizing_Issues"/>, GETFH
      is REQUIRED or RECOMMENDED to 
      immediately follow certain operations, and servers
      are free to reject such operations if
      the client fails to insert
      GETFH in the request as REQUIRED or RECOMMENDED.
      <xref target="open_getfh_issue"/> provides additional
      justification for why GETFH MUST follow OPEN.

    </t>
  </section>
  <section toc="exclude" anchor="OP_GETFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Operations that change the current filehandle like LOOKUP or CREATE do
      not automatically return the new filehandle as a result.  For
      instance, if a client needs to look up a directory entry and obtain its
      filehandle, then the following request is needed.
    </t>
    <t>
      <list style="empty">
	<t>
	  PUTFH  (directory filehandle)
	</t>
	<t>
	  LOOKUP (entry name)
	</t>
	<t>
	  GETFH
	</t>
      </list>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LINK" title="Operation 11: LINK - Create Link to a File" >

  <section toc="exclude" anchor="OP_LINK_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LINK4args {
        /* SAVED_FH: source object */
        /* CURRENT_FH: target directory */
        component4      newname;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LINK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LINK4resok {
        change_info4    cinfo;
};

union LINK4res switch (nfsstat4 status) {
 case NFS4_OK:
         LINK4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LINK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LINK operation creates an additional newname for the file
      represented by the saved filehandle, as set by the SAVEFH operation,
      in the directory represented by the current filehandle.  The existing
      file and the target directory must reside within the same file system
      on the server.  On success, the current filehandle will continue to be
      the target directory.  If an object exists in the target directory
      with the same name as newname, the server must return NFS4ERR_EXIST.
    </t>
    <t>
      For the target directory, the server returns change_info4 information
      in cinfo.  With the atomic field of the change_info4 data type, the
      server will indicate if the before and after change attributes were
      obtained atomically with respect to the link creation.
    </t>
    <t>
      If the newname has a length of zero, or if newname does not obey
      the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LINK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MAY impose restrictions on the LINK operation such that
      LINK may not be done when the file is open or when that open is done  
      by particular protocols, or with particular options or access modes.
      When LINK is rejected because of such restrictions, the error 
      NFS4ERR_FILE_OPEN is returned.
    </t>
    <t>
      If a server does implement such restrictions and those restrictions
      include cases of NFSv4 opens preventing successful execution of
      a link, the server needs to recall any delegations that could
      hide the existence of opens relevant to that decision.  The reason
      is that when a client holds a delegation, the server 
      might not have an accurate account of the opens for that client, since
      the client may execute OPENs and CLOSEs locally.  The LINK operation
      must be delayed only until a definitive result can be obtained.
      For example, suppose there are multiple delegations and one of them establishes
      an open whose presence would prevent the link. Given the server's 
      semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon
      as that delegation is returned without waiting for other delegations
      to be returned.  Similarly, if such opens are not associated with 
      delegations, NFS4ERR_FILE_OPEN can be returned immediately with no 
      delegation recall being done.
    </t>
    <t>
      If the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot be
      performed successfully until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, instead of a recall,
      NOTIFY4_ADD_ENTRY will be generated
      as a result of the LINK operation.
    </t>
    <t>
      If the current file system supports the numlinks attribute, and
      other clients have delegations to the file being linked, then those
      delegations MUST be recalled and the LINK operation MUST NOT proceed until
      all delegations are returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      Changes to any property of the "hard" linked files are reflected in
      all of the linked files.  When a link is made to a file, the
      attributes for the file should have a value for numlinks that is one
      greater than the value before the LINK operation.
    </t>
    <t>
      The statement "file and the target directory must reside within the
      same file system on the server" means that the fsid fields in the
      attributes for the objects are the same. If they reside on
      different file systems, the error NFS4ERR_XDEV is returned.  
      This error may be returned by some servers when there is an 
      internal partitioning of a file system that the LINK operation
      would violate.  
    </t>
    <t>
      On some
      servers, "." and ".." are illegal values for newname
      and the error NFS4ERR_BADNAME will be returned if they are specified.
    </t>
    <t>
      When the current filehandle designates a named attribute directory
      and the object to be linked (the saved filehandle) is not a named 
      attribute for the  same object, the error NFS4ERR_XDEV MUST be 
      returned.  When the saved filehandle designates a named attribute
      and the current filehandle is not the appropriate named attribute
      directory, the error NFS4ERR_XDEV MUST also be returned.  
    </t>
    <t>
      When the current filehandle designates a named attribute directory
      and the object to be linked (the saved filehandle) is a named
      attribute within that directory, the server may return 
      the error NFS4ERR_NOTSUPP.
    </t>
    <t>
      In the case that newname is already linked to the file represented by
      the saved filehandle, the server will return NFS4ERR_EXIST.
    </t>
    <t>
      Note that symbolic links are created with the CREATE operation.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCK" title="Operation 12: LOCK - Create Lock" >

  <section toc="exclude" anchor="OP_LOCK_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
/*
 * For LOCK, transition from open_stateid and lock_owner
 * to a lock stateid.
 */
struct open_to_lock_owner4 {
        seqid4          open_seqid;
        stateid4        open_stateid;
        seqid4          lock_seqid;
        lock_owner4     lock_owner;
};

/*
 * For LOCK, existing lock stateid continues to request new
 * file lock for the same lock_owner and open_stateid.
 */
struct exist_lock_owner4 {
        stateid4        lock_stateid;
        seqid4          lock_seqid;
};

union locker4 switch (bool new_lock_owner) {
 case TRUE:
        open_to_lock_owner4     open_owner;
 case FALSE:
        exist_lock_owner4       lock_owner;
};

/*
 * LOCK/LOCKT/LOCKU: Record lock management
 */
struct LOCK4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        bool            reclaim;
        offset4         offset;
        length4         length;
        locker4         locker;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOCK4denied {
        offset4         offset;
        length4         length;
        nfs_lock_type4  locktype;
        lock_owner4     owner;
};

struct LOCK4resok {
        stateid4        lock_stateid;
};

union LOCK4res switch (nfsstat4 status) {
 case NFS4_OK:
         LOCK4resok     resok4;
 case NFS4ERR_DENIED:
         LOCK4denied    denied;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCK operation requests a byte-range lock for the byte-range specified
      by the offset and length parameters, and lock type specified in
      the locktype parameter.  If this is a reclaim request, the
      reclaim parameter will be TRUE.
    </t>
    <t>
      Bytes in a file may be locked even if those bytes are not currently
      allocated to the file.  To lock the file from a specific offset
      through the end-of-file (no matter how long the file actually is) use
      a length field equal to NFS4_UINT64_MAX.
      The server MUST return NFS4ERR_INVAL under the following
      combinations of length and offset:

      <list style='symbols'>
      <t>
       Length is equal to zero.
      </t>
      <t>
       Length is not equal to NFS4_UINT64_MAX, and the sum of length
       and offset exceeds NFS4_UINT64_MAX.
      </t>
      </list>

    </t>
    <t>
      32-bit servers are servers that support locking for
      byte offsets that fit within 32 bits (i.e., less than
      or equal to NFS4_UINT32_MAX).  If the client specifies a
      range that overlaps one or more bytes beyond offset
      NFS4_UINT32_MAX but does not end at offset
      NFS4_UINT64_MAX, then such a 32-bit server MUST return the
      error NFS4ERR_BAD_RANGE.
    </t>
    <t>
      If the server returns NFS4ERR_DENIED, the
      owner, offset, and length
      of a conflicting lock are returned.
    </t>
    <t>
      The locker argument specifies the lock-owner that is associated with
      the LOCK operation.  The locker4 structure is a switched union that
      indicates whether the client has already created byte-range locking
      state associated with the current open file and lock-owner.  In the
      case in which it has, the argument is just a stateid representing
      the set of
      locks associated with that open file and lock-owner, together with
      a lock_seqid value that MAY be any value and MUST be ignored
      by the server.
      In the case where no byte-range locking state has been established, or the client
      does not have the stateid available, the argument contains the
      stateid of the open file with which this lock is to be associated,
      together with the lock-owner with which the lock is to be associated.
      The open_to_lock_owner case covers the very first lock done by a
      lock-owner for a given open file and offers a method to use the 
      established state of the open_stateid to transition to the use of 
      a lock stateid.
    </t>
    <t>
      The following fields of the locker parameter MAY be
      set to any value by the client and MUST be ignored
      by the server:

      <list style='symbols'>
      <t>
       The clientid field of the lock_owner
       field of the open_owner field
       (locker.open_owner.lock_owner.clientid). The
       reason the server MUST ignore the clientid field
       is that the server MUST derive the client ID from
       the session ID from the SEQUENCE operation of the
       COMPOUND request.

      </t>
      <t>
       The open_seqid and lock_seqid fields of the
       open_owner field (locker.open_owner.open_seqid and
       locker.open_owner.lock_seqid).

      </t>
      <t>
       The lock_seqid field of the lock_owner field
       (locker.lock_owner.lock_seqid).

      </t>
      </list>
    </t>

    <t>
      Note that the client ID appearing in a LOCK4denied
      structure is the actual client associated with the
      conflicting lock, whether this is the client ID
      associated with the current session or a different
      one. Thus, if the server returns NFS4ERR_DENIED,
      it MUST set the clientid field of the owner field of the
      denied field.
    </t>

    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server is unable to determine the exact offset and length of
      the conflicting byte-range lock, the same offset and length that were provided in
      the arguments should be returned in the denied results.
    </t>
    <t>
      LOCK operations are subject to permission checks and to checks against
      the access type of the associated file.  However, the specific right
      and modes required for various types of locks reflect the semantics of
      the server-exported file system, and are not specified by the protocol.
      For example, Windows 2000 allows a write lock of a file open for read access,
      while a POSIX-compliant system does not.
    </t>
    <t>
      When the client sends a LOCK operation that corresponds to a range that
      the lock-owner has locked already (with the same or different lock
      type), or to a sub-range of such a range, or to a byte-range that
      includes multiple locks already granted to that lock-owner, in whole or
      in part, and the server does not support such locking operations
      (i.e., does not support POSIX locking semantics), the server will
      return the error NFS4ERR_LOCK_RANGE.  In that case, the client may
      return an error, or it may emulate the required operations, using only
      LOCK for ranges that do not include any bytes already locked by that
      lock-owner and LOCKU of locks held by that lock-owner (specifying an
      exactly matching range and type).  Similarly, when the client sends a
      LOCK operation that amounts to upgrading (changing from a READ_LT lock to a
      WRITE_LT lock) or downgrading (changing from WRITE_LT lock to a READ_LT lock)
      an existing byte-range lock, and the server does not support such a lock,
      the server will return NFS4ERR_LOCK_NOTSUPP.  Such operations may not
      perfectly reflect the required semantics in the face of conflicting
      LOCK operations from other clients.
    </t>
    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, the client holding that 
      delegation is assured that there are no opens by other clients.
      Thus, there can be no conflicting LOCK operations from such clients.
      Therefore, the client may be handling locking requests locally, 
      without
      doing LOCK operations on the server.  If it does that, it must be
      prepared to update the lock status on the server, by sending 
      appropriate LOCK and LOCKU operations before returning
      the delegation.
    </t>
    <t>
      When one or more clients hold OPEN_DELEGATE_READ delegations, any LOCK operation
      where the server is implementing mandatory locking semantics MUST
      result in the recall of all such delegations.  The LOCK operation may
      not be granted until all such delegations are returned or revoked.
      Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCKT" title="Operation 13: LOCKT - Test for Lock" >

  <section toc="exclude" anchor="OP_LOCKT_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOCKT4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        offset4         offset;
        length4         length;
        lock_owner4     owner;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOCKT_RESULTS" title="RESULTS">
<figure>
 <artwork>
union LOCKT4res switch (nfsstat4 status) {
 case NFS4ERR_DENIED:
         LOCK4denied    denied;
 case NFS4_OK:
         void;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCKT operation tests the lock as specified in the arguments.  If
      a conflicting lock exists, the owner, offset, length, and type of the
      conflicting lock are returned.  
      The owner field in the results includes the client ID of the owner of 
      the conflicting lock, whether this is the client ID associated with the
      current session or a different client ID.
      If no lock is held, nothing other than
      NFS4_OK is returned.  Lock types READ_LT and READW_LT are processed in
      the same way in that a conflicting lock test is done without regard to
      blocking or non-blocking.  The same is true for WRITE_LT and WRITEW_LT.
    </t>
    <t>
      The ranges are specified as for LOCK.  The NFS4ERR_INVAL and 
      NFS4ERR_BAD_RANGE errors are returned under the same circumstances
      as for LOCK.
    </t>
    <t>
      The clientid field of the owner MAY be set to
      any value by the client and MUST be ignored by
      the server. The reason the server MUST ignore the
      clientid field is that the server MUST derive the
      client ID from the session ID from the SEQUENCE
      operation of the COMPOUND request.

    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCKT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server is unable to determine the exact offset
      and length of the conflicting lock, the same offset
      and length that were provided in the arguments should
      be returned in the denied results. 

    </t>

    <t>
      LOCKT uses a lock_owner4 rather a stateid4, as is used in
      LOCK to identify the owner.  This is because the client does not 
      have to open the file to test for the existence of a lock, so
      a stateid might not be available.  
    </t>
    <t>
      As noted in <xref target="OP_LOCK_IMPLEMENTATION"/>, some
      servers may return NFS4ERR_LOCK_RANGE to certain (otherwise
      non-conflicting) LOCK operations that overlap ranges already
      granted to the current lock-owner.
    </t>

    <t>
      The LOCKT operation's test for conflicting locks SHOULD exclude
      locks for the current lock-owner, and thus should return NFS4_OK in
      such cases.  Note that this means that a server might return
      NFS4_OK to a LOCKT request even though a LOCK operation for the
      same range and lock-owner would fail with NFS4ERR_LOCK_RANGE.
    </t>

    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose 
      (see <xref target="OP_LOCK_IMPLEMENTATION" />) to handle LOCK
      requests locally.  In such a case, LOCKT requests will similarly
      be handled locally. 
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOCKU" title="Operation 14: LOCKU - Unlock File" >

  <section toc="exclude" anchor="OP_LOCKU_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOCKU4args {
        /* CURRENT_FH: file */
        nfs_lock_type4  locktype;
        seqid4          seqid;
        stateid4        lock_stateid;
        offset4         offset;
        length4         length;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKU_RESULTS" title="RESULTS">
<figure>
 <artwork>
union LOCKU4res switch (nfsstat4 status) {
 case   NFS4_OK:
         stateid4       lock_stateid;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_LOCKU_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOCKU operation unlocks the byte-range lock specified by the
      parameters. The client may set the locktype field to any value that is
      legal for the nfs_lock_type4 enumerated type, and the server MUST
      accept any legal value for locktype. Any legal value for locktype has
      no effect on the success or failure of the LOCKU operation.
    </t>
    <t>
      The ranges are specified as for LOCK.  The NFS4ERR_INVAL and
      NFS4ERR_BAD_RANGE errors are returned under the same circumstances as
      for LOCK.
    </t>
    <t>
      The seqid parameter MAY be any value and the server MUST ignore it.
    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     The server MAY require that the principal, security
     flavor, and if applicable, the GSS mechanism, combination
     that sent a LOCK operation also be the one to send
     LOCKU on the file. This might not be possible
     if credentials for the principal are no longer
     available. The server MAY allow the machine credential
     or SSV credential (see <xref target="OP_EXCHANGE_ID"
     />) to send LOCKU.

    </t>
  </section>
  <section toc="exclude" anchor="OP_LOCKU_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the area to be unlocked does not correspond exactly to a lock
      actually held by the lock-owner, the server may return the error
      NFS4ERR_LOCK_RANGE.  This includes the case in which the area is not
      locked, where the area is a sub-range of the area locked, where it
      overlaps the area locked without matching exactly, or the area
      specified includes multiple locks held by the lock-owner.  In all of
      these cases, allowed by <xref target="fcntl">POSIX locking</xref> semantics, a client receiving
      this error should, if it desires support for such operations, simulate
      the operation using LOCKU on ranges corresponding to locks it actually
      holds, possibly followed by LOCK operations for the sub-ranges not being
      unlocked.
    </t>
    <t>
      When a client holds an OPEN_DELEGATE_WRITE delegation, it may choose 
      (see <xref target="OP_LOCK_IMPLEMENTATION" />) to handle LOCK
      requests locally.  In such a case, LOCKU operations will similarly
      be handled locally. 
    </t>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOOKUP" title="Operation 15: LOOKUP - Lookup Filename" >

  <section toc="exclude" anchor="OP_LOOKUP_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct LOOKUP4args {
        /* CURRENT_FH: directory */
        component4      objname;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOOKUP_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOOKUP4res {
        /* New CURRENT_FH: object */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_LOOKUP_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LOOKUP operation looks up or finds a file system object using the
      directory specified by the current filehandle.  LOOKUP evaluates the
      component and if the object exists, the current filehandle is replaced
      with the component's filehandle.
    </t>
    <t>
      If the component cannot be evaluated either because it does not exist
      or because the client does not have permission to evaluate the
      component, then an error will be returned and the current filehandle
      will be unchanged.
    </t>
    <t>
      If the component is a zero-length string or if any component does not
      obey the UTF-8 definition, the error NFS4ERR_INVAL will be returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOOKUP_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client wants to achieve the effect of a multi-component look up,
      it may construct a COMPOUND request such as (and obtain each
      filehandle):
	<figure>
	  <artwork>
      PUTFH  (directory filehandle)
      LOOKUP "pub"
      GETFH
      LOOKUP "foo"
      GETFH
      LOOKUP "bar"
      GETFH
	  </artwork>
	</figure>
      Unlike NFSv3, NFSv4.1 allows LOOKUP requests to cross mountpoints on the
      server.  The client can detect a mountpoint crossing by comparing the
      fsid attribute of the directory with the fsid attribute of the
      directory looked up.  If the fsids are different, then the new
      directory is a server mountpoint.  UNIX clients that detect a
      mountpoint crossing will need to mount the server's file system.  This
      needs to be done to maintain the file object identity checking
      mechanisms common to UNIX clients.
    </t>
    <t>
      Servers that limit NFS access to "shared" or "exported" file systems
      should provide a pseudo file system into which the exported file systems
      can be integrated, so that clients can browse the server's namespace.
      The clients view of a pseudo file system will be limited to paths that
      lead to exported file systems.
    </t>
    <t>
      Note: previous versions of the protocol assigned special semantics to
      the names "." and "..".  NFSv4.1 assigns no special semantics to
      these names.  The LOOKUPP operator must be used to look up a parent
      directory.
    </t>
    <t>
      Note that this operation does not follow symbolic links.  The client
      is responsible for all parsing of filenames including filenames that
      are modified by symbolic links encountered during the look up process.
    </t>
    <t>
      If the current filehandle supplied is not a directory but a symbolic
      link, the error NFS4ERR_SYMLINK is returned as the error.  For all
      other non-directory file types, the error NFS4ERR_NOTDIR is returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LOOKUPP" title="Operation 16: LOOKUPP - Lookup Parent Directory" >

  <section toc="exclude" anchor="OP_LOOKUPP_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: object */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_LOOKUPP_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct LOOKUPP4res {
        /* new CURRENT_FH: parent directory */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LOOKUPP_DESCRIPTION" title="DESCRIPTION">
    <t>
      The current filehandle is assumed to refer to a regular
      directory or a named attribute directory.  LOOKUPP assigns the
      filehandle for its parent directory to be the current
      filehandle.  If there is no parent directory, an NFS4ERR_NOENT
      error must be returned.  Therefore, NFS4ERR_NOENT will be
      returned by the server when the current filehandle is at the
      root or top of the server's file tree.
    </t>
    <t>
      As is the case with LOOKUP, LOOKUPP will also cross mountpoints.
    </t>
    <t>
      If the current filehandle is not a directory or named attribute
      directory, the error NFS4ERR_NOTDIR is returned.
    </t>
    <t>
      If the requester's security flavor does not match that
      configured for the parent directory, then the server SHOULD
      return NFS4ERR_WRONGSEC (a future minor revision of NFSv4 may
      upgrade this to MUST) in the LOOKUPP response.  However, if the
      server does so, it MUST support the SECINFO_NO_NAME
      operation (<xref target="OP_SECINFO_NO_NAME"/>), so that the client can gracefully determine the
      correct security flavor.
    </t>
    <t>
      If the current filehandle is a named attribute directory that is
      associated with a file system object via OPENATTR (i.e., not a
      sub-directory of a named attribute directory), LOOKUPP SHOULD
      return the filehandle of the associated file system object.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LOOKUPP_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      An issue to note is upward navigation from named attribute
      directories.  The named attribute directories are essentially
      detached from the namespace, and this property should be safely
      represented in the client operating environment.  LOOKUPP on a
      named attribute directory may return the filehandle of the
      associated file, and conveying this to applications might be
      unsafe as many applications expect the parent of an object to
      always be a directory.  Therefore, the client may want to hide
      the parent of named attribute directories (represented as ".."
      in UNIX) or represent the named attribute directory as its own
      parent (as is typically done for the file system root directory in
      UNIX).
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_NVERIFY" title="Operation 17: NVERIFY - Verify Difference in Attributes" >

  <section toc="exclude" anchor="OP_NVERIFY_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct NVERIFY4args {
        /* CURRENT_FH: object */
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_NVERIFY_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct NVERIFY4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_NVERIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to prefix a sequence of operations to be
      performed if one or more attributes have changed on some file system
      object.  If all the attributes match, then the error NFS4ERR_SAME MUST
      be returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_NVERIFY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is useful as a cache validation operator.  If the
      object to which the attributes belong has changed, then the following
      operations may obtain new data associated with that object, for
      instance, to check if a file has been changed and obtain new data if
      it has:
      <figure>
	<artwork>
      SEQUENCE
      PUTFH fh
      NVERIFY attrbits attrs
      READ 0 32767
	</artwork>
      </figure>
      Contrast this with NFSv3, which would first send a GETATTR in
      one request/reply round trip, and then if attributes indicated that
      the client's cache was stale, then send a READ in another request/reply
      round trip.
    </t>
    <t>
      In the case that a RECOMMENDED attribute is specified in the NVERIFY
      operation and the server does not support that attribute for the
      file system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
      client.
    </t>
    <t>
      When the attribute rdattr_error or any set-only attribute (e.g.,
      time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
      the client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->

<section anchor="OP_OPEN" title="Operation 18: OPEN - Open a Regular File" >

  <section toc="exclude" anchor="OP_OPEN_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
/*
 * Various definitions for OPEN
 */
enum createmode4 {
        UNCHECKED4      = 0,
        GUARDED4        = 1,
        /* Deprecated in NFSv4.1. */
        EXCLUSIVE4      = 2,
        /*
         * New to NFSv4.1. If session is persistent,
         * GUARDED4 MUST be used.  Otherwise, use
         * EXCLUSIVE4_1 instead of EXCLUSIVE4.
         */
        EXCLUSIVE4_1    = 3
};

struct creatverfattr {
         verifier4      cva_verf;
         fattr4         cva_attrs;
};

union createhow4 switch (createmode4 mode) {
 case UNCHECKED4:
 case GUARDED4:
         fattr4         createattrs;
 case EXCLUSIVE4:
         verifier4      createverf;
 case EXCLUSIVE4_1:
         creatverfattr  ch_createboth;
};

enum opentype4 {
        OPEN4_NOCREATE  = 0,
        OPEN4_CREATE    = 1
};

union openflag4 switch (opentype4 opentype) {
 case OPEN4_CREATE:
         createhow4     how;
 default:
         void;
};

/* Next definitions used for OPEN delegation */
enum limit_by4 {
        NFS_LIMIT_SIZE          = 1,
        NFS_LIMIT_BLOCKS        = 2
        /* others as needed */
};

struct nfs_modified_limit4 {
        uint32_t        num_blocks;
        uint32_t        bytes_per_block;
};

union nfs_space_limit4 switch (limit_by4 limitby) {
 /* limit specified as file size */
 case NFS_LIMIT_SIZE:
         uint64_t               filesize;
 /* limit specified by number of blocks */
 case NFS_LIMIT_BLOCKS:
         nfs_modified_limit4    mod_blocks;
} ;

/*
 * Share Access and Deny constants for open argument
 */
const OPEN4_SHARE_ACCESS_READ   = 0x00000001;
const OPEN4_SHARE_ACCESS_WRITE  = 0x00000002;
const OPEN4_SHARE_ACCESS_BOTH   = 0x00000003;

const OPEN4_SHARE_DENY_NONE     = 0x00000000;
const OPEN4_SHARE_DENY_READ     = 0x00000001;
const OPEN4_SHARE_DENY_WRITE    = 0x00000002;
const OPEN4_SHARE_DENY_BOTH     = 0x00000003;


/* new flags for share_access field of OPEN4args */
const OPEN4_SHARE_ACCESS_WANT_DELEG_MASK        = 0xFF00;
const OPEN4_SHARE_ACCESS_WANT_NO_PREFERENCE     = 0x0000;
const OPEN4_SHARE_ACCESS_WANT_READ_DELEG        = 0x0100;
const OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG       = 0x0200;
const OPEN4_SHARE_ACCESS_WANT_ANY_DELEG         = 0x0300;
const OPEN4_SHARE_ACCESS_WANT_NO_DELEG          = 0x0400;
const OPEN4_SHARE_ACCESS_WANT_CANCEL            = 0x0500;

const
 OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
 = 0x10000;

const
 OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
 = 0x20000;

enum open_delegation_type4 {
        OPEN_DELEGATE_NONE      = 0,
        OPEN_DELEGATE_READ      = 1,
        OPEN_DELEGATE_WRITE     = 2,
        OPEN_DELEGATE_NONE_EXT  = 3 /* new to v4.1 */
};

enum open_claim_type4 {
        /*
         * Not a reclaim.
         */
        CLAIM_NULL              = 0,

        CLAIM_PREVIOUS          = 1,
        CLAIM_DELEGATE_CUR      = 2,
        CLAIM_DELEGATE_PREV     = 3,

        /*
         * Not a reclaim.
         *
         * Like CLAIM_NULL, but object identified
         * by the current filehandle.
         */
        CLAIM_FH                = 4, /* new to v4.1 */

        /*
         * Like CLAIM_DELEGATE_CUR, but object identified
         * by current filehandle.
         */
        CLAIM_DELEG_CUR_FH      = 5, /* new to v4.1 */

        /*
         * Like CLAIM_DELEGATE_PREV, but object identified
         * by current filehandle.
         */
        CLAIM_DELEG_PREV_FH     = 6 /* new to v4.1 */
};

struct open_claim_delegate_cur4 {
        stateid4        delegate_stateid;
        component4      file;
};

union open_claim4 switch (open_claim_type4 claim) {
 /*
  * No special rights to file.
  * Ordinary OPEN of the specified file.
  */
 case CLAIM_NULL:
        /* CURRENT_FH: directory */
        component4      file;
 /*
  * Right to the file established by an
  * open previous to server reboot.  File
  * identified by filehandle obtained at
  * that time rather than by name.
  */
 case CLAIM_PREVIOUS:
        /* CURRENT_FH: file being reclaimed */
        open_delegation_type4   delegate_type;

 /*
  * Right to file based on a delegation
  * granted by the server.  File is
  * specified by name.
  */
 case CLAIM_DELEGATE_CUR:
        /* CURRENT_FH: directory */
        open_claim_delegate_cur4        delegate_cur_info;

 /*
  * Right to file based on a delegation
  * granted to a previous boot instance
  * of the client.  File is specified by name.
  */
 case CLAIM_DELEGATE_PREV:
         /* CURRENT_FH: directory */
        component4      file_delegate_prev;

 /*
  * Like CLAIM_NULL.  No special rights
  * to file.  Ordinary OPEN of the
  * specified file by current filehandle.
  */
 case CLAIM_FH: /* new to v4.1 */
        /* CURRENT_FH: regular file to open */
        void;

 /*
  * Like CLAIM_DELEGATE_PREV.  Right to file based on a
  * delegation granted to a previous boot
  * instance of the client.  File is identified by
  * by filehandle.
  */
 case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
        /* CURRENT_FH: file being opened */
        void;

 /*
  * Like CLAIM_DELEGATE_CUR.  Right to file based on
  * a delegation granted by the server.
  * File is identified by filehandle.
  */
 case CLAIM_DELEG_CUR_FH: /* new to v4.1 */
         /* CURRENT_FH: file being opened */
         stateid4       oc_delegate_stateid;

};

/*
 * OPEN: Open a file, potentially receiving an OPEN delegation
 */
struct OPEN4args {
        seqid4          seqid;
        uint32_t        share_access;
        uint32_t        share_deny;
        open_owner4     owner;
        openflag4       openhow;
        open_claim4     claim;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_OPEN_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct open_read_delegation4 {
 stateid4 stateid;    /* Stateid for delegation*/
 bool     recall;     /* Pre-recalled flag for
                         delegations obtained
                         by reclaim (CLAIM_PREVIOUS) */

 nfsace4 permissions; /* Defines users who don't
                         need an ACCESS call to
                         open for read */
};

struct open_write_delegation4 {
 stateid4 stateid;      /* Stateid for delegation */
 bool     recall;       /* Pre-recalled flag for
                           delegations obtained
                           by reclaim
                           (CLAIM_PREVIOUS) */

 nfs_space_limit4
           space_limit; /* Defines condition that
                           the client must check to
                           determine whether the
                           file needs to be flushed
                           to the server on close.  */

 nfsace4   permissions; /* Defines users who don't
                           need an ACCESS call as
                           part of a delegated
                           open. */
};


enum why_no_delegation4 { /* new to v4.1 */
        WND4_NOT_WANTED         = 0,
        WND4_CONTENTION         = 1,
        WND4_RESOURCE           = 2,
        WND4_NOT_SUPP_FTYPE     = 3,
        WND4_WRITE_DELEG_NOT_SUPP_FTYPE = 4,
        WND4_NOT_SUPP_UPGRADE   = 5,
        WND4_NOT_SUPP_DOWNGRADE = 6,
        WND4_CANCELLED          = 7,
        WND4_IS_DIR             = 8
};

union open_none_delegation4 /* new to v4.1 */
switch (why_no_delegation4 ond_why) {
        case WND4_CONTENTION:
                bool ond_server_will_push_deleg;
        case WND4_RESOURCE:
                bool ond_server_will_signal_avail;
        default:
                void;
};

union open_delegation4
switch (open_delegation_type4 delegation_type) {
        case OPEN_DELEGATE_NONE:
                void;
        case OPEN_DELEGATE_READ:
                open_read_delegation4 read;
        case OPEN_DELEGATE_WRITE:
                open_write_delegation4 write;
        case OPEN_DELEGATE_NONE_EXT: /* new to v4.1 */
                open_none_delegation4 od_whynone;
};

/*
 * Result flags
 */

/* Client must confirm open */
const OPEN4_RESULT_CONFIRM      = 0x00000002;
/* Type of file locking behavior at the server */
const OPEN4_RESULT_LOCKTYPE_POSIX = 0x00000004;
/* Server will preserve file if removed while open */
const OPEN4_RESULT_PRESERVE_UNLINKED = 0x00000008;

/*
 * Server may use CB_NOTIFY_LOCK on locks
 * derived from this open
 */
const OPEN4_RESULT_MAY_NOTIFY_LOCK = 0x00000020;

struct OPEN4resok {
 stateid4       stateid;      /* Stateid for open */
 change_info4   cinfo;        /* Directory Change Info */
 uint32_t       rflags;       /* Result flags */
 bitmap4        attrset;      /* attribute set for create*/
 open_delegation4 delegation; /* Info on any open
                                 delegation */
};

union OPEN4res switch (nfsstat4 status) {
 case NFS4_OK:
        /* New CURRENT_FH: opened file */
        OPEN4resok      resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DESCRIPTION" title="DESCRIPTION">
    <t>
      The OPEN operation opens a regular file in a
      directory with the provided name or filehandle.
      OPEN can also create a file if a name is provided,
      and the client specifies it wants to create a file.
      Specification of whether or not a file is to be created,
      and the method of creation is via the openhow
      parameter. The openhow parameter consists of
      a switched union (data type opengflag4), which
      switches on the value of opentype (OPEN4_NOCREATE
      or OPEN4_CREATE). If OPEN4_CREATE is specified,
      this leads to another switched union (data type
      createhow4) that supports four cases of creation
      methods: UNCHECKED4, GUARDED4, EXCLUSIVE4,
      or EXCLUSIVE4_1. If opentype is OPEN4_CREATE,
      then the claim field of the claim field
      MUST be one of CLAIM_NULL, CLAIM_DELEGATE_CUR, or
      CLAIM_DELEGATE_PREV, because these claim methods
      include a component of a file name.
    </t>
    <t>
      Upon success (which might entail creation of a new
      file), the current filehandle is replaced by that
      of the created or existing object.

    </t>
   
    <t>
      If the current filehandle is a named attribute
      directory, OPEN will then create or open a named
      attribute file.  Note that exclusive create
      of a named attribute is not supported.  If the
      createmode is EXCLUSIVE4 or EXCLUSIVE4_1 and the
      current filehandle is a named attribute directory,
      the server will return EINVAL.
    </t>

    <t>
      UNCHECKED4 means that the file should be created if a
      file of that name does not exist and encountering an
      existing regular file of that name is not an error.
      For this type of create, createattrs specifies the
      initial set of attributes for the file.  The set
      of attributes may include any writable attribute
      valid for regular files.  When an UNCHECKED4
      create encounters an existing file, the attributes
      specified by createattrs are not used, except that
      when createattrs specifies the size attribute
      with a size of zero, the existing file is truncated.

    </t>
    <t>
      If GUARDED4 is specified, the server checks for
      the presence of a duplicate object by name before
      performing the create.  If a duplicate exists,
      NFS4ERR_EXIST is returned.
      If the object does not exist, the request is
      performed as described for UNCHECKED4.

    </t>
    <t>
      For the UNCHECKED4 and GUARDED4 cases, where the
      operation is successful, the server will return
      to the client an attribute mask signifying which
      attributes were successfully set for the object.

    </t>

     <t>
      EXCLUSIVE4_1 and EXCLUSIVE4
      specify that the server is to follow exclusive
      creation semantics, using the verifier to ensure
      exclusive creation of the target.  The server should
      check for the presence of a duplicate object by name.
      If the object does not exist, the server creates
      the object and stores the verifier with the object.
      If the object does exist and the stored verifier
      matches the client provided verifier, the server
      uses the existing object as the newly created object.
      If the stored verifier does not match, then an error
      of NFS4ERR_EXIST is returned.
     </t>
     <t>
      If using EXCLUSIVE4, and if the server uses attributes to
      store the exclusive create verifier, the server will signify
      which attributes it used by setting the appropriate bits in
      the attribute mask that is returned in the results.
      Unlike UNCHECKED4, GUARDED4, and EXCLUSIVE4_1, EXCLUSIVE4 does
      not support the setting of attributes at file creation, and
      after a successful OPEN via EXCLUSIVE4, the client MUST
      send a SETATTR to set attributes to a known state.
     </t>
     <t>
      In NFSv4.1, EXCLUSIVE4 has been deprecated in favor
      of EXCLUSIVE4_1.
      Unlike EXCLUSIVE4, attributes may be provided
      in the EXCLUSIVE4_1 case, but because the server
      may use attributes of the target object to store
      the verifier, the set of allowable attributes
      may be fewer than the set of attributes SETATTR
      allows. The allowable attributes for EXCLUSIVE4_1
      are indicated in the suppattr_exclcreat (<xref
      target="attrdef_suppattr_exclcreat"/>) attribute. If the client
      attempts to set in cva_attrs an attribute that is not in
      suppattr_exclcreat, the server MUST return NFS4ERR_INVAL.
      The response field, attrset, indicates both which attributes
      the server set from cva_attrs and which attributes the
      server used to store the verifier. As described
      in <xref target="OP_OPEN_IMPLEMENTATION"/>, the client can compare
      cva_attrs.attrmask with attrset to determine which attributes
      were used to store the verifier.

     </t>
     <t>
      With the addition of persistent sessions and
      pNFS, under some conditions EXCLUSIVE4 MUST NOT
      be used by the client or supported by the server.
      The following table summarizes the appropriate and
      mandated exclusive create methods for implementations
      of NFSv4.1:

     </t>

      <texttable anchor='exclusive_create'>

      <preamble>
         Required methods for exclusive create
      </preamble>

      <ttcol>Persistent Reply Cache Enabled</ttcol>
      <ttcol>Server Supports pNFS</ttcol>
      <ttcol>Server REQUIRED</ttcol> <ttcol>Client Allowed</ttcol>

      <c>no</c> <c>no</c>
	<c>EXCLUSIVE4_1 and EXCLUSIVE4</c>
	<c>EXCLUSIVE4_1 (SHOULD) or EXCLUSIVE4 (SHOULD NOT)</c>

      <c>no</c> <c>yes</c>
	<c>EXCLUSIVE4_1</c>
	<c>EXCLUSIVE4_1</c>

      <c>yes</c> <c>no</c>
	<c>GUARDED4</c>
	<c>GUARDED4</c>

      <c>yes</c> <c>yes</c>
	<c>GUARDED4</c>
	<c>GUARDED4</c>

      </texttable>

    <t>
     If CREATE_SESSION4_FLAG_PERSIST is set in the results
     of CREATE_SESSION, the reply cache is persistent (see <xref target="OP_CREATE_SESSION"/>).
     If the EXCHGID4_FLAG_USE_PNFS_MDS flag is set in the
     results from EXCHANGE_ID, the server is a pNFS server (see <xref target="OP_EXCHANGE_ID"/>).
     If the client attempts to use EXCLUSIVE4 on a persistent session,
     or a session derived from an
     EXCHGID4_FLAG_USE_PNFS_MDS client ID, the server MUST return
     NFS4ERR_INVAL.
    </t>

    <t>

     With persistent sessions, exclusive create semantics
     are fully achievable via GUARDED4, and so EXCLUSIVE4
     or EXCLUSIVE4_1 MUST NOT be used.  When pNFS is
     being used, the layout_hint attribute might
     not be supported after the file is created. Only the
     EXCLUSIVE4_1 and GUARDED methods of exclusive file
     creation allow the atomic setting of attributes.

    </t>

    <t>
      For the target directory, the server returns change_info4 information
      in cinfo.  With the atomic field of the change_info4 data type, the
      server will indicate if the before and after change attributes were
      obtained atomically with respect to the link creation.
    </t>
    <t>
      The OPEN operation provides for Windows share
      reservation capability with the use of the
      share_access and share_deny fields of the OPEN
      arguments.  The client specifies at OPEN the required
      share_access and share_deny modes.  For clients
      that do not directly support SHAREs (i.e., UNIX), the
      expected deny value is OPEN4_SHARE_DENY_NONE.  In the case that
      there is an existing SHARE reservation that conflicts
      with the OPEN request, the server returns the error
      NFS4ERR_SHARE_DENIED.  For additional discussion of
      SHARE semantics, see <xref target="share_reserve" />.

    </t>
    <t>
      For each OPEN, the client provides a value for
      the owner field of the OPEN argument.  The owner
      field is of data type open_owner4, and contains a
      field called clientid and a field called owner. The
      client can set the clientid field to any value and
      the server MUST ignore it.  Instead, the server MUST
      derive the client ID from the session ID of the
      SEQUENCE operation of the COMPOUND request.

    </t>
    <t>
      The "seqid" field of the request is not used in
      NFSv4.1, but it MAY be any value and the server MUST
      ignore it.

    </t>
    <t>
      In the case that the client is recovering state from a server failure,
      the claim field of the OPEN argument is used to signify that the
      request is meant to reclaim state previously held.
    </t>
    <t>
      The "claim" field of the OPEN argument is used to specify the file to
      be opened and the state information that the client claims to
      possess.  There are seven claim types as follows:
    </t>
    <texttable>
      <ttcol align='left'>open type</ttcol>
      <ttcol align='left'>description</ttcol>
      <c>
        CLAIM_NULL,
        CLAIM_FH
      </c>
      <c>
        For the client, this is a new OPEN request and there is no
        previous state associated with the file for the client.  With
        CLAIM_NULL, the file is identified by the current filehandle
        and the specified component name.  With CLAIM_FH (new to NFSv4.1),
        the file is identified by just the current filehandle.
      </c>
      <c>
        CLAIM_PREVIOUS
      </c>
      <c>
        The client is claiming basic OPEN state for a file that was held
        previous to a server restart.  Generally used when a server is
        returning persistent filehandles; the client may not have the file
        name to reclaim the OPEN.
      </c>
      <c>
        CLAIM_DELEGATE_CUR,
        CLAIM_DELEG_CUR_FH
      </c>
      <c>
        The client is claiming a delegation for OPEN
        as granted by the server.  Generally, this
        is done as part of recalling a delegation.  With
        CLAIM_DELEGATE_CUR, the file is identified by
        the current filehandle and the specified component
        name.  With CLAIM_DELEG_CUR_FH (new to NFSv4.1), the
        file is identified by just the current filehandle.

      </c>
      <c>
        CLAIM_DELEGATE_PREV,
        CLAIM_DELEG_PREV_FH
      </c>
      <c>
        The client is claiming a delegation granted to a
        previous client instance; used after the client
        restarts. The server MAY support CLAIM_DELEGATE_PREV
        and/or CLAIM_DELEG_PREV_FH (new to NFSv4.1).  If it
        does support either claim type, CREATE_SESSION MUST
        NOT remove the client's delegation state, and the
        server MUST support the DELEGPURGE operation.

      </c>
    </texttable>

    <t>
      For OPEN requests that reach the server during
      the grace period, the server returns an error
      of NFS4ERR_GRACE.  The following claim types are
      exceptions:
      <list style='symbols'>
      
      <t>
       OPEN requests specifying the claim type CLAIM_PREVIOUS are devoted to 
       reclaiming opens after a server restart and are typically only  
       valid during the grace period.

      </t>

      <t>
       OPEN requests specifying the claim types CLAIM_DELEGATE_CUR and 
       CLAIM_DELEG_CUR_FH are valid both during and after the grace period.
       Since the granting of the delegation that they are subordinate
       to assures that there is no conflict with locks to be reclaimed
       by other clients, the server need not return NFS4ERR_GRACE when
       these are received during the grace period.

      </t>
      </list>

    </t>

    <t>
      For any OPEN request, the server may return an OPEN delegation, which
      allows further opens and closes to be handled locally on the client as
      described in <xref target="open_delegation"/>.  Note that delegation is 
      up to the server to decide.  The client should never assume that
      delegation will or will not be granted in a particular instance.  It
      should always be prepared for either case.  A partial exception is the
      reclaim (CLAIM_PREVIOUS) case, in which a delegation type is claimed.
      In this case, delegation will always be granted, although the server
      may specify an immediate recall in the delegation structure.
    </t>
    <t>
      The rflags returned by a successful OPEN allow the server to return
      information governing how the open file is to be handled.
      <list style="symbols">
      <t>
      OPEN4_RESULT_CONFIRM is deprecated and MUST NOT be returned
      by an NFSv4.1 server.
      </t>
      <t>
      OPEN4_RESULT_LOCKTYPE_POSIX indicates that the server's byte-range locking
      behavior supports the complete set of POSIX locking techniques <xref target="fcntl"/>.  From
      this, the client can choose to manage byte-range locking state in a way to
      handle a mismatch of byte-range locking management.
      </t>
      <t>
      OPEN4_RESULT_PRESERVE_UNLINKED indicates that the server will
      preserve the open file if the client (or any other client)
      removes the file as long as it is open. Furthermore, the
      server promises to preserve the file through the
      grace period after server restart, thereby giving the client
      the opportunity to reclaim its open.
      </t>
      <t>
      OPEN4_RESULT_MAY_NOTIFY_LOCK indicates that the server may attempt
      CB_NOTIFY_LOCK callbacks for locks on this file.  This flag is a hint
      only, and may be safely ignored by the client.
      </t>
      </list>
    </t>
    <t>
      If the component is of zero length, NFS4ERR_INVAL will be returned.
      The component is also subject to the normal UTF-8, character support,
      and name checks.  See <xref target="utf8_related_errors" /> for
      further discussion.
    </t>
    <t>
      When an OPEN is done and the specified open-owner already has the
      resulting filehandle open, the result is to "OR" together the new
      share and deny status together with the existing status.  In this
      case, only a single CLOSE need be done, even though multiple OPENs
      were completed.  When such an OPEN is done, checking of share
      reservations for the new OPEN proceeds normally, with no exception for
      the existing OPEN held by the same open-owner.  In this case, the 
      stateid returned as an "other" field that matches that of the previous
      open while the "seqid" field is incremented to reflect the change
      status due to the new open.
    </t>
    <t>
      If the underlying file system at the server is only accessible in a
      read-only mode and the OPEN request has specified ACCESS_WRITE or
      ACCESS_BOTH, the server will return NFS4ERR_ROFS to indicate a
      read-only file system.
    </t>
    <t>
      As with the CREATE operation, the server MUST derive
      the owner, owner ACE, group, or group ACE if any
      of the four attributes are required and supported
      by the server's file system.  For an OPEN with the
      EXCLUSIVE4 createmode, the server has no choice,
      since such OPEN calls do not include the createattrs
      field.  Conversely, if createattrs (UNCHECKED4 or
      GUARDED4) or cva_attrs (EXCLUSIVE4_1) is specified,
      and includes an owner, owner_group, or ACE that
      the principal in the RPC call's credentials does
      not have authorization to create files for, then
      the server may return NFS4ERR_PERM.

    </t>
    <t>
      In the case of an OPEN that specifies a size of zero (e.g., truncation)
      and the file has named attributes, the named attributes are left as
      is and are not removed.
    </t>

    <t>
      NFSv4.1 gives more precise control to clients over
      acquisition of delegations via the following new
      flags for the share_access field of OPEN4args:
      <list style="hanging">
      <t hangText="OPEN4_SHARE_ACCESS_WANT_READ_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_ANY_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_NO_DELEG"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_CANCEL"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL"></t>
      <t hangText="OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED"></t>
      </list>
    </t>
    <t>
      If (share_access &amp; OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) is
      not zero, then the client will have specified one and only one of:
      <list style="hanging">
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_READ_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_ANY_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_NO_DELEG"></t>
	      <t hangText="OPEN4_SHARE_ACCESS_WANT_CANCEL"></t>
      </list>
      Otherwise, the client is neither indicating a desire nor a non-desire
      for a delegation, and the server MAY or MAY not return a delegation
      in the OPEN response.
    </t>
    <t>
      If the server supports the new _WANT_ flags and the
      client sends one or more of the new flags,
      then in the event the server does not return a
      delegation, it MUST return a delegation type of
      OPEN_DELEGATE_NONE_EXT.  The field ond_why in the reply
      indicates why
      no delegation was returned and will be one of:
      <list style="hanging">
      <t hangText="WND4_NOT_WANTED">
         The client specified OPEN4_SHARE_ACCESS_WANT_NO_DELEG.
      </t>
      <t hangText="WND4_CONTENTION">
         There is a conflicting delegation or open on the file.
      </t>
      <t hangText="WND4_RESOURCE">
         Resource limitations prevent the server from granting a
         delegation.
      </t>
      <t hangText="WND4_NOT_SUPP_FTYPE">
         The server does not support delegations on this file type.
      </t>
      <t hangText="WND4_WRITE_DELEG_NOT_SUPP_FTYPE">
         The server does not support OPEN_DELEGATE_WRITE delegations on this file
         type.
      </t>
      <t hangText="WND4_NOT_SUPP_UPGRADE">
         The server does not support atomic upgrade of an OPEN_DELEGATE_READ delegation to an OPEN_DELEGATE_WRITE delegation.
      </t>
      <t hangText="WND4_NOT_SUPP_DOWNGRADE">
         The server does not support atomic downgrade of an OPEN_DELEGATE_WRITE delegation to an OPEN_DELEGATE_READ delegation.
      </t>
      <t hangText="WND4_CANCELED">
         The client specified OPEN4_SHARE_ACCESS_WANT_CANCEL and now
         any "want" for this file object is cancelled.
      </t>
      <t hangText="WND4_IS_DIR">
         The specified file object is a directory, and the operation
         is OPEN or WANT_DELEGATION, which do not support delegations
         on directories.
      </t>
      </list>
    </t>
    <t>
        OPEN4_SHARE_ACCESS_WANT_READ_DELEG,
        OPEN_SHARE_ACCESS_WANT_WRITE_DELEG, or
        OPEN_SHARE_ACCESS_WANT_ANY_DELEG mean, respectively, the
        client wants an OPEN_DELEGATE_READ, OPEN_DELEGATE_WRITE, or any delegation regardless which
        of OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE, or
        OPEN4_SHARE_ACCESS_BOTH is set. If the client has an OPEN_DELEGATE_READ delegation on a file and requests an OPEN_DELEGATE_WRITE delegation, then
        the client is requesting atomic upgrade of its OPEN_DELEGATE_READ delegation
        to an OPEN_DELEGATE_WRITE delegation. If the client has an OPEN_DELEGATE_WRITE delegation on
        a file and requests an OPEN_DELEGATE_READ delegation, then the client is
        requesting atomic downgrade to an OPEN_DELEGATE_READ delegation. A server MAY
        support atomic upgrade or downgrade. If it does, then the
	returned delegation_type of OPEN_DELEGATE_READ
        or OPEN_DELEGATE_WRITE that is different from the delegation
        type the client currently has, indicates successful upgrade
        or downgrade. If the server does not support atomic delegation upgrade or
        downgrade, then ond_why will be set to WND4_NOT_SUPP_UPGRADE or
        WND4_NOT_SUPP_DOWNGRADE.
     </t>
     <t>
        OPEN4_SHARE_ACCESS_WANT_NO_DELEG means that the client wants no
        delegation.
     </t>
     <t>
        OPEN4_SHARE_ACCESS_WANT_CANCEL means that the client wants no
        delegation and wants to cancel any previously registered
        "want" for a delegation.
     </t>
     <t>
        The client may set one or both of
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL and
        OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED.
        However, they will have no effect unless one of following is set:
        <list style="symbols">
              <t>OPEN4_SHARE_ACCESS_WANT_READ_DELEG</t>
              <t>OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG</t>
              <t>OPEN4_SHARE_ACCESS_WANT_ANY_DELEG</t>
         </list>
     </t>
     <t>
        If the client specifies
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL, then it
        wishes to register a "want" for a delegation, in the event the
        OPEN results do not include a delegation.  If so and the
        server denies the delegation due to insufficient resources,
        the server MAY later inform the client, via the
        CB_RECALLABLE_OBJ_AVAIL operation, that the resource
        limitation condition has eased. The server will tell the
        client that it intends to send a future
        CB_RECALLABLE_OBJ_AVAIL operation by setting delegation_type
        in the results to OPEN_DELEGATE_NONE_EXT, ond_why
        to WND4_RESOURCE, and ond_server_will_signal_avail set to
        TRUE. If
        ond_server_will_signal_avail is set to TRUE, the server MUST
        later send a CB_RECALLABLE_OBJ_AVAIL operation.
     </t>
     <t>
        If the client specifies
        OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_UNCONTENDED, then it
        wishes to register a "want" for a delegation, in the event the
        OPEN results do not include a delegation. If so and the server
        denies the delegation due to contention, the
        server MAY later inform the client, via the CB_PUSH_DELEG
        operation, that the contention condition
        has eased. The server will tell the client that it intends to
        send a future CB_PUSH_DELEG operation by setting
        delegation_type in the results to OPEN_DELEGATE_NONE_EXT,
        ond_why to WND4_CONTENTION, and
        ond_server_will_push_deleg to TRUE. If
        ond_server_will_push_deleg is TRUE, the server MUST later
        send a CB_PUSH_DELEG operation.
     </t>
     <t>
        If the client has previously registered a want for a
        delegation on a file, and then sends a request to register a
        want for a delegation on the same file, the server MUST return
        a new error: NFS4ERR_DELEG_ALREADY_WANTED. If the client
        wishes to register a different type of delegation want for the
        same file, it MUST cancel the existing delegation WANT.
     </t>
  </section>
  <section toc="exclude" anchor="OP_OPEN_IMPLEMENTATION" title="IMPLEMENTATION">
     <t>
      In absence of a persistent session, the client
      invokes exclusive create by setting the how parameter
      to EXCLUSIVE4 or EXCLUSIVE4_1.  In these cases, the
      client provides a verifier that can reasonably be
      expected to be unique.  A combination of a client
      identifier, perhaps the client network address,
      and a unique number generated by the client, perhaps
      the RPC transaction identifier, may be appropriate.
    </t>
    <t>
      If the object does not exist, the server creates the object and stores the
      verifier in stable storage. For file systems that do not provide a
      mechanism for the storage of arbitrary file attributes, the server may
      use one or more elements of the object's metadata to store the
      verifier. The verifier MUST be stored in stable storage to prevent
      erroneous failure on retransmission of the request. It is assumed that
      an exclusive create is being performed because exclusive semantics are
      critical to the application. Because of the expected usage, exclusive
      CREATE does not rely solely on the server's reply cache
      for storage of the verifier. A nonpersistent reply cache
      does not survive a crash and the session and reply cache
      may be deleted after a network partition that exceeds the
      lease time, thus opening failure windows. 
    </t>
    <t>
      An NFSv4.1 server SHOULD NOT store the verifier in
      any of the file's RECOMMENDED or REQUIRED attributes.
      If it does, the server SHOULD use time_modify_set or
      time_access_set to store the verifier.
      The server SHOULD NOT store the verifier in the
      following attributes:
<list style="empty">
	<t>acl (it is desirable for access control to
	be established at creation),</t>

	<t>dacl (ditto),</t>

	<t>mode (ditto),</t>

	<t>owner (ditto),</t>

	<t>owner_group (ditto),</t>

	<t>retentevt_set (it may be desired to
	establish retention at creation)</t>

	<t>retention_hold (ditto),</t>

	<t>retention_set (ditto),</t>

	<t>sacl (it is desirable for auditing control
	to be established at creation),</t>

	<t>size (on some servers, size may have a
	limited range of values),</t>

	<t>mode_set_masked (as with mode),
<list style="empty">
	<t>and</t>
</list>
</t>
	<t>time_creation (a meaningful file creation
	should be set when the file is created).</t>
</list>
     Another alternative for the server is to use a named attribute
     to store the verifier.
    </t>

    <t>
     Because the EXCLUSIVE4 create method does not specify
     initial attributes when processing an EXCLUSIVE4 create,
     the server

     <list style="symbols">
     <t>
       SHOULD set the
       owner of the file to that corresponding to the credential of
       request's RPC header.
     </t>

     <t>
      SHOULD NOT leave the file's access control to anyone
      but the owner of the file.
     </t>
     </list>

    </t>

    <t>
      If the server cannot support exclusive create
      semantics, possibly because of the requirement to
      commit the verifier to stable storage, it should fail
      the OPEN request with the error NFS4ERR_NOTSUPP.

    </t>
    <t>
      During an exclusive CREATE request, if the object
      already exists, the server reconstructs the object's
      verifier and compares it with the verifier in
      the request. If they match, the server treats the
      request as a success. The request is presumed to
      be a duplicate of an earlier, successful request
      for which the reply was lost and that the server
      duplicate request cache mechanism did not detect. If
      the verifiers do not match, the request is rejected
      with the status NFS4ERR_EXIST.

    </t>
    <t>
      After the client has performed a successful
      exclusive create, the attrset response indicates
      which attributes were used to store the verifier.
      If EXCLUSIVE4 was used, the attributes set in
      attrset were used for the verifier. If EXCLUSIVE4_1
      was used, the client determines the attributes
      used for the verifier by comparing attrset with
      cva_attrs.attrmask; any bits set in the former but
      not the latter identify the attributes used to store
      the verifier.  The client MUST immediately send a
      SETATTR to set attributes used to store the verifier.
      Until it does so, the attributes used to store the
      verifier cannot be relied upon.  The subsequent
      SETATTR MUST NOT occur in the same COMPOUND request
      as the OPEN.

    </t>
    <t>
      Unless a persistent session is used, use of the
      GUARDED4 attribute does not provide exactly once
      semantics.  In particular, if a reply is lost and
      the server does not detect the retransmission of the
      request, the operation can fail with NFS4ERR_EXIST,
      even though the create was performed successfully.
      The client would use this behavior in the case that
      the application has not requested an exclusive create
      but has asked to have the file truncated when the
      file is opened.  In the case of the client timing
      out and retransmitting the create request, the client
      can use GUARDED4 to prevent against a sequence like
      create, write, create (retransmitted) from occurring.

    </t>
    <t>
      For SHARE reservations, the value of the expression
      (share_access &amp; ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) MUST be
      one of OPEN4_SHARE_ACCESS_READ, OPEN4_SHARE_ACCESS_WRITE,
      or OPEN4_SHARE_ACCESS_BOTH. If not, the server MUST
      return NFS4ERR_INVAL.  The value of share_deny MUST
      be one of OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ,
      OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH.  If not, the
      server MUST return NFS4ERR_INVAL.

    </t>
    <t>
      Based on the share_access value (OPEN4_SHARE_ACCESS_READ,
      OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH), the client
      should check that the requester has the proper access rights
      to perform the specified operation.  This would generally be
      the results of applying the ACL access rules to the file for the
      current requester.  However, just as with the ACCESS operation, the
      client should not attempt to second-guess the server's decisions, as
      access rights may change and may be subject to server administrative
      controls outside the ACL framework.  If the requester's READ or
      WRITE operation is not authorized (depending on the share_access
      value), the server MUST return NFS4ERR_ACCESS.

    </t>

    <t>
      Note that if the client ID was not created
      with the EXCHGID4_FLAG_BIND_PRINC_STATEID capability set in
      the reply to EXCHANGE_ID, then the server MUST
      NOT impose any requirement that READs and WRITEs
      sent for an open file have the same credentials
      as the OPEN itself, and the server is REQUIRED to
      perform access checking on the READs and WRITEs
      themselves. Otherwise, if the reply to EXCHANGE_ID
      did have EXCHGID4_FLAG_BIND_PRINC_STATEID set,
      then with one exception, the credentials used in the OPEN request MUST
      match those used in the READs and WRITEs, and the
      stateids in the READs and WRITEs MUST match, or be
      derived from the stateid from the reply to OPEN.
      The exception is if SP4_SSV or SP4_MACH_CRED state
      protection is used, and the spo_must_allow
      result of EXCHANGE_ID includes the READ and/or WRITE
      operations. In that case, the machine or SSV
      credential will be allowed to send READ and/or WRITE.
      See <xref target="OP_EXCHANGE_ID"/>.

    </t>
    <t>
      If the component provided to OPEN is a symbolic link, the error
      NFS4ERR_SYMLINK will be returned to the client, while if it is
      a directory the error NFS4ERR_ISDIR will be returned.  
If the component is neither
      of those but not an ordinary file, the error NFS4ERR_WRONG_TYPE
      is returned.  If the current
      filehandle is not a directory, the error NFS4ERR_NOTDIR will be
      returned.
    </t>
    <t>
      The use of the OPEN4_RESULT_PRESERVE_UNLINKED result flag allows
      a client to avoid the common implementation practice of renaming
      an open file to ".nfs&lt;unique value>" after it removes the file.
      After the server returns OPEN4_RESULT_PRESERVE_UNLINKED, if a client
      sends a REMOVE operation that would reduce the file's link count to
      zero, the server SHOULD report a value
      of zero for the numlinks attribute on the file.
    </t>
    <t>
      If another client has a delegation of the file being opened that 
      conflicts with open being done (sometimes depending on the 
      share_access or share_deny value specified), 
      the delegation(s) MUST be recalled, and the 
      operation cannot proceed until each such delegation is returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
      In the case of an OPEN_DELEGATE_WRITE delegation, any open by a different client
      will conflict, while for an OPEN_DELEGATE_READ delegation, only opens with one 
      of the following characteristics will be considered conflicting:
      <list style="symbols">
        <t>
          The value of share_access includes the bit 
          OPEN4_SHARE_ACCESS_WRITE.
        </t>
        <t>
          The value of share_deny specifies OPEN4_SHARE_DENY_READ or
          OPEN4_SHARE_DENY_BOTH.

        </t>
        <t>
          OPEN4_CREATE is specified together with UNCHECKED4, the
          size attribute is specified as zero (for truncation), and
          an existing file is truncated.
        </t>
      </list>
    </t>
    <t>
      If OPEN4_CREATE is specified and the file does not exist and 
      the current filehandle designates a directory for which another
      client holds a directory delegation, then, unless the delegation 
      is such that the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      If OPEN4_CREATE is specified and the file does not exist and 
      the current filehandle designates a directory for which 
      one or more directory delegations exist, then, when those delegations
      request such notifications, NOTIFY4_ADD_ENTRY will be generated
      as a result of this operation.
    </t>
    <section toc="exclude" anchor="open_getfh_issue"
	title="Warning to Client Implementors">
    <t>
      OPEN resembles LOOKUP in that it generates a filehandle for the client
      to use.  Unlike LOOKUP though, OPEN creates server state on the
      filehandle.  In normal circumstances, the client can only release this
      state with a CLOSE operation.  CLOSE uses the current filehandle to
      determine which file to close.  Therefore, the client MUST follow every
      OPEN operation with a GETFH operation in the same COMPOUND procedure.
      This will supply the client with the filehandle such that CLOSE can be
      used appropriately.
    </t>
    <t>
      Simply waiting for the lease on the file to expire is insufficient
      because the server may maintain the state indefinitely as long as
      another client does not attempt to make a conflicting access to the
      same file.
    </t>
    <t>
      See also <xref target="COMPOUND_Sizing_Issues"/>.
    </t>
    </section>

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_OPENATTR" title="Operation 19: OPENATTR - Open Named Attribute Directory" >

  <section toc="exclude" anchor="OP_OPENATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct OPENATTR4args {
        /* CURRENT_FH: object */
        bool    createdir;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPENATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct OPENATTR4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: named attribute
         *                   directory
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPENATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The OPENATTR operation is used to obtain the filehandle of the named
      attribute directory associated with the current filehandle.  The
      result of the OPENATTR will be a filehandle to an object of type
      NF4ATTRDIR.  From this filehandle, READDIR and LOOKUP operations can
      be used to obtain filehandles for the various named attributes
      associated with the original file system object.  Filehandles returned
      within the named attribute directory will designate objects of
      type of NF4NAMEDATTR.
    </t>
    <t>
      The createdir argument allows the client to signify if a named
      attribute directory should be created as a result of the OPENATTR
      operation.  Some clients may use the OPENATTR operation with a value
      of FALSE for createdir to determine if any named attributes exist for
      the object.  If none exist, then NFS4ERR_NOENT will be returned.  If
      createdir has a value of TRUE and no named attribute directory exists,
      one is created and its filehandle becomes the current filehandle.
      On the other hand, if createdir has a value of TRUE and the named
      attribute directory already exists, no error results and the filehandle
      of the existing directory becomes the current filehandle.  The 
      creation of a named attribute directory assumes
      that the server has implemented named attribute support in this
      fashion and is not required to do so by this definition.
    </t>
    <t>
      If the current file handle designates an object of type 
      NF4NAMEDATTR (a named attribute) or NF4ATTRDIR (a named attribute 
      directory), an error of NFS4ERR_WRONG_TYPE is returned to the
      client.  Named attributes or a named attribute directory MUST NOT 
      have their own named attributes.
    </t>
  </section>
  <section toc="exclude" anchor="OP_OPENATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server does not support named attributes for the current
      filehandle, an error of NFS4ERR_NOTSUPP will be returned to the
      client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_OPEN_DOWNGRADE" title="Operation 21: OPEN_DOWNGRADE - Reduce Open File Access" >

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct OPEN_DOWNGRADE4args {
        /* CURRENT_FH: opened file */
        stateid4        open_stateid;
        seqid4          seqid;
        uint32_t        share_access;
        uint32_t        share_deny;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct OPEN_DOWNGRADE4resok {
        stateid4        open_stateid;
};

union OPEN_DOWNGRADE4res switch(nfsstat4 status) {
 case NFS4_OK:
        OPEN_DOWNGRADE4resok    resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to adjust the access and deny states
      for a given open.  This is necessary when a given open-owner opens the
      same file multiple times with different access and deny
      values.  In this situation, a close of one of the opens may change the
      appropriate share_access and share_deny flags to remove bits
      associated with opens no longer in effect.
    </t>
    <t>
      Valid values for the expression (share_access &amp;
      ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) are OPEN4_SHARE_ACCESS_READ,
      OPEN4_SHARE_ACCESS_WRITE, or OPEN4_SHARE_ACCESS_BOTH. If the client
      specifies other values, the server MUST reply with NFS4ERR_INVAL.

    </t>

    <t>
      Valid values for the share_deny field are
      OPEN4_SHARE_DENY_NONE, OPEN4_SHARE_DENY_READ,
      OPEN4_SHARE_DENY_WRITE, or OPEN4_SHARE_DENY_BOTH. If
      the client specifies other values, the server MUST
      reply with NFS4ERR_INVAL.

    </t>
      
    <t>
      After checking for valid values of share_access and
      share_deny, the server replaces the current access
      and deny modes on the file with share_access and
      share_deny subject to the following constraints:
      <list style='symbols'>
      <t>
       The bits in share_access SHOULD equal the union of the share_access
       bits (not including OPEN4_SHARE_WANT_* bits)
       specified for some subset of the OPENs
       in effect for the current open-owner on the current
       file.
      </t>
 
      <t>
       The bits in share_deny SHOULD equal the union of the
       share_deny bits specified for some subset
       of the OPENs in effect for the current open-owner
       on the current file.

      </t>
      </list>

      If the above constraints are not respected,
      the server SHOULD return the error NFS4ERR_INVAL.
      Since share_access and share_deny bits should be
      subsets of those already granted, short of a defect
      in the client or server implementation, it is not
      possible for the OPEN_DOWNGRADE request to be denied
      because of conflicting share reservations.

    </t>

    <t>
      The seqid argument is not used in NFSv4.1, MAY be any value, and
      MUST be ignored by the server.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_OPEN_DOWNGRADE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      An OPEN_DOWNGRADE operation may make OPEN_DELEGATE_READ delegations grantable
      where they were not previously.  Servers may choose to respond
      immediately if there are pending delegation want requests or may
      respond to the situation at a later time.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTFH" title="Operation 22: PUTFH - Set Current Filehandle" >

  <section toc="exclude" anchor="OP_PUTFH_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct PUTFH4args {
        nfs_fh4         object;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct PUTFH4res {
        /*
         * If status is NFS4_OK,
         *    new CURRENT_FH: argument to PUTFH
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle provided as an
      argument. It clears the current stateid.
    </t>
    <t>
      If the security mechanism used by the requester does not meet the
      requirements of the filehandle provided to this operation, the server
      MUST return NFS4ERR_WRONGSEC.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTPUBFH" title="Operation 23: PUTPUBFH - Set
  Public Filehandle" >

  <section toc="exclude" anchor="OP_PUTPUBFH_ARGUMENT" title="ARGUMENT">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_RESULT" title="RESULT">
<figure>
 <artwork>
struct PUTPUBFH4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: public fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle that
      represents the public filehandle of the server's namespace.
      This filehandle may be different from the "root" filehandle
      that may be associated with some other directory on the server.
    </t>
    <t>
      PUTPUBFH also clears the current stateid.
    </t>
    <t>
      The public filehandle represents the concepts embodied in <xref
      target="RFC2054">RFC 2054</xref>, <xref
      target="RFC2055">RFC 2055</xref>, and <xref
      target="RFC2224">RFC 2224</xref>.  The intent for NFSv4.1
      is that the public filehandle (represented by the PUTPUBFH
      operation) be used as a method of providing WebNFS server
      compatibility with NFSv3.
    </t>
    <t>
      The public filehandle and the root filehandle (represented by the
      PUTROOTFH operation) SHOULD be equivalent.  If the public and root
      filehandles are not equivalent, then the directory corresponding to the public filehandle MUST be a
      descendant of the directory corresponding to the root filehandle.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTPUBFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
    <t>
      With the NFSv3 public filehandle, the client is
      able to specify whether the pathname provided in the LOOKUP
      should be evaluated as either an absolute path relative to the
      server's root or relative to the public filehandle.  <xref
      target="RFC2224">RFC 2224</xref> contains further discussion of
      the functionality.  With NFSv4.1, that type of
      specification is not directly available in the LOOKUP operation.
      The reason for this is because the component separators needed
      to specify absolute vs. relative are not allowed in NFSv4.  Therefore, the client is responsible for constructing its
      request such that the use of either PUTROOTFH or PUTPUBFH
      signifies absolute or relative evaluation of an NFS URL,
      respectively.
    </t>
    <t>
      Note that there are warnings mentioned in <xref
      target="RFC2224">RFC 2224</xref> with respect to the use of
      absolute evaluation and the restrictions the server may place on
      that evaluation with respect to how much of its namespace has
      been made available.  These same warnings apply to NFSv4.1.  It is likely, therefore, that because of server
      implementation details, an NFSv3 absolute public
      filehandle look up may behave differently than an NFSv4.1
      absolute resolution.
    </t>
    <t>
      There is a form of security negotiation as described
      in <xref target="RFC2755">RFC 2755</xref> that uses
      the public filehandle and an overloading of the pathname.
      This method is not available with NFSv4.1 as
      filehandles are not overloaded with special
      meaning and therefore do not provide the same
      framework as NFSv3.  Clients should therefore use
      the security negotiation mechanisms described in
      <xref target="Security_Service_Negotiation" />.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_PUTROOTFH" title="Operation 24: PUTROOTFH - Set Root Filehandle" >

  <section toc="exclude" anchor="OP_PUTROOTFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_PUTROOTFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct PUTROOTFH4res {
        /*
         * If status is NFS4_OK,
         *   new CURRENT_FH: root fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_PUTROOTFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation replaces the current filehandle with the filehandle that represents
      the root of the server's namespace.  From this filehandle, a LOOKUP
      operation can locate any other filehandle on the server. This
      filehandle may be different from the "public" filehandle that may be
      associated with some other directory on the server.
    </t>
    <t>
      PUTROOTFH also clears the current stateid.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_PUTROOTFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      This operation is used
      in an NFS request to set the context for file accessing operations that
      follow in the same COMPOUND request.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READ" title="Operation 25: READ - Read from File" >

  <section toc="exclude" anchor="OP_READ_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct READ4args {
        /* CURRENT_FH: file */
        stateid4        stateid;
        offset4         offset;
        count4          count;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READ_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct READ4resok {
        bool            eof;
        opaque          data&lt;>;
};

union READ4res switch (nfsstat4 status) {
 case NFS4_OK:
         READ4resok     resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READ_DESCRIPTION" title="DESCRIPTION">
    <t>
      The READ operation reads data from the regular file identified by the
      current filehandle.
    </t>
    <t>
      The client provides an offset of where the READ is to start and a
      count of how many bytes are to be read.  An offset of zero means
      to read data starting at the beginning of the file.  If offset is
      greater than or equal to the size of the file, the status NFS4_OK is
      returned with a data length set to zero and eof is set to TRUE.
      The READ is subject to access permissions checking.
    </t>
    <t>
      If the client specifies a count value of zero, the READ succeeds
      and returns zero bytes of data again subject to access permissions
      checking.  The server may choose to return fewer bytes than specified
      by the client.  The client needs to check for this condition and
      handle the condition appropriately.
    </t>
    <t>
      Except when special stateids are used, the 
      stateid value for a READ request represents a value returned from
      a previous byte-range lock or share reservation request or the stateid
      associated with a delegation.  The stateid identifies the associated
      owners if any and is 
      used by the server to verify that the associated locks are still
      valid (e.g., have not been revoked).
    </t>
    <t>
      If the read ended at the end-of-file (formally, in a correctly formed
      READ operation, if offset + count is equal to the size of the file), or
      the READ operation extends beyond the size of the file (if offset +
      count is greater than the size of the file), eof is returned as TRUE;
      otherwise, it is FALSE.  A successful READ of an empty file will always
      return eof as TRUE.
    </t>
    <t>
      If the current filehandle is not an ordinary file, an error will be
      returned to the client.  In the case that the current filehandle 
      represents an object of type NF4DIR, NFS4ERR_ISDIR is returned.   
      If the current filehandle designates a symbolic link, 
      NFS4ERR_SYMLINK is returned.  In all other cases, 
      NFS4ERR_WRONG_TYPE is returned.
    </t>
    <t>
      For a READ with a stateid value of all bits equal to zero, the server MAY allow
      the READ to be serviced subject to mandatory byte-range locks or the current
      share deny modes for the file.  For a READ with a stateid value of all
      bits equal to one, the server MAY allow READ operations to bypass locking checks
      at the server.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READ_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the server returns a "short read" (i.e., fewer data than requested and eof is set to FALSE), the client should send another READ to get the
      remaining data.  A server may return less data than requested under
      several circumstances.  The file may have been truncated by another
      client or perhaps on the server itself, changing the file size from
      what the requesting client believes to be the case.  This would reduce
      the actual amount of data available to the client.  It is possible
      that the server reduce the transfer size and so return a short
      read result.  Server resource exhaustion may also occur in a
      short read.
    </t>
    <t>
      If mandatory byte-range locking is in effect for the file, and if the byte-range
      corresponding to the data to be read from the file is WRITE_LT locked by an
      owner not associated with the stateid, the server will return the
      NFS4ERR_LOCKED error.  The client should try to get the appropriate
      READ_LT via the LOCK operation before re-attempting the
      READ.  When the READ completes, the client should release the byte-range
      lock via LOCKU.
    </t>
    <t>
      If another client has an OPEN_DELEGATE_WRITE delegation for the file being read,
      the delegation must be recalled, and the 
      operation cannot proceed until that delegation is returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
      Normally, delegations will not be recalled as a result of a READ
      operation since the recall will occur as a result of an earlier
      OPEN.  However, since it is possible for a READ to be done with
      a special stateid, the server needs to check for this case even
      though the client should have done an OPEN previously.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READDIR" title="Operation 26: READDIR - Read Directory" >

  <section toc="exclude" anchor="OP_READDIR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct READDIR4args {
        /* CURRENT_FH: directory */
        nfs_cookie4     cookie;
        verifier4       cookieverf;
        count4          dircount;
        count4          maxcount;
        bitmap4         attr_request;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READDIR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct entry4 {
        nfs_cookie4     cookie;
        component4      name;
        fattr4          attrs;
        entry4          *nextentry;
};

struct dirlist4 {
        entry4          *entries;
        bool            eof;
};

struct READDIR4resok {
        verifier4       cookieverf;
        dirlist4        reply;
};


union READDIR4res switch (nfsstat4 status) {
 case NFS4_OK:
         READDIR4resok  resok4;
 default:
         void;
};


 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READDIR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The READDIR operation retrieves a variable number of entries from a
      file system directory and returns client-requested attributes for each
      entry along with information to allow the client to request additional
      directory entries in a subsequent READDIR.
    </t>
    <t>
      The arguments contain a cookie value that represents where the READDIR
      should start within the directory.  A value of zero for the cookie
      is used to start reading at the beginning of the directory.  For
      subsequent READDIR requests, the client specifies a cookie value that
      is provided by the server on a previous READDIR request.
    </t>
    <t>
      The request's cookieverf field should be set to 0
      zero) when the request's cookie field is zero
      (first read of the directory).  On subsequent requests, the
      cookieverf field must match the cookieverf returned
      by the READDIR in which the cookie was acquired.
      If the server determines that the cookieverf
      is no longer valid for the directory, the error
      NFS4ERR_NOT_SAME must be returned.

    </t>
    <t>
      The dircount field of the request is a hint of the maximum number
      of bytes of directory information that should be returned.  This value
      represents the total length of the names of the directory entries and the
      cookie value for these entries.  This length represents the XDR
      encoding of the data (names and cookies) and not the length in the
      native format of the server.
    </t>
    <t>
      The maxcount field of the request represents the maximum
      total size of all of the data being returned within
      the READDIR4resok structure and includes the XDR
      overhead.  The server MAY return less data.  If the
      server is unable to return a single directory entry
      within the maxcount limit, the error NFS4ERR_TOOSMALL
      MUST be returned to the client.

    </t>
    <t>
      Finally, the request's attr_request field represents
      the list of attributes to be returned for each
      directory entry supplied by the server.

    </t>
    <t>
      A successful reply consists of a list of
      directory entries.  Each of these entries contains the name of the
      directory entry, a cookie value for that entry, and the associated
      attributes as requested.  The "eof" flag has a value of TRUE if there
      are no more entries in the directory.
    </t>
    <t>
      The cookie value is only meaningful to the server and is used 
      as a cursor for the directory entry.  As mentioned, this cookie 
      is used by the client for subsequent READDIR operations so that it may
      continue reading a directory.  The cookie is similar in concept to a
      READ offset but MUST NOT be interpreted as such by the client.
      Ideally, the cookie value SHOULD NOT change if the directory is
      modified since the client may be caching these values.
    </t>
    <t>
      In some cases, the server may encounter an error while obtaining the
      attributes for a directory entry.  Instead of returning an error for
      the entire READDIR operation, the server can instead return the
      attribute rdattr_error (<xref target="attrdef_rdattr_error"/>).  With this, the server is able to
      communicate the failure to the client and not fail the entire
      operation in the instance of what might be a transient failure.
      Obviously, the client must request the fattr4_rdattr_error attribute
      for this method to work properly.  If the client does not request the
      attribute, the server has no choice but to return failure for the
      entire READDIR operation.
    </t>
    <t>
      For some file system environments, the directory entries "." and ".."
      have special meaning, and in other environments, they do not.  If the
      server supports these special entries within a directory, they SHOULD
      NOT be returned to the client as part of the READDIR response.  To
      enable some client environments, the cookie values of zero, 1, and 2 are
      to be considered reserved.  Note that the UNIX client will use these
      values when combining the server's response and local representations
      to enable a fully formed UNIX directory presentation to the
      application.
    </t>
    <t>
      For READDIR arguments, cookie values of one and two SHOULD NOT be used, and
      for READDIR results, cookie values of zero, one, and two SHOULD NOT be
      returned.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READDIR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server's file system directory representations
      can differ greatly.  A client's programming
      interfaces may also be bound to the local operating
      environment in a way that does not translate well
      into the NFS protocol.  Therefore, the use of the
      dircount and maxcount fields are provided to enable
      the client to provide hints to the server.  If the
      client is aggressive about attribute collection
      during a READDIR, the server has an idea of how to
      limit the encoded response.

    </t>
    <t>
      If dircount is zero, the server bounds the reply's
      size based on the request's maxcount field.

    </t>
    <t>
      The cookieverf may be used by the server to help manage cookie values
      that may become stale.  It should be a rare occurrence that a server is
      unable to continue properly reading a directory with the provided
      cookie/cookieverf pair.  The server SHOULD make every effort to avoid
      this condition since the application at the client might be unable to
      properly handle this type of failure.
    </t>
    <t>
      The use of the cookieverf will also protect the client from using
      READDIR cookie values that might be stale.  For example, if the file
      system has been migrated, the server might or might not be able to use the
      same cookie values to service READDIR as the previous server used.
      With the client providing the cookieverf, the server is able to
      provide the appropriate response to the client.  This prevents the
      case where the server accepts a cookie value but the underlying
      directory has changed and the response is invalid from the client's
      context of its previous READDIR.
    </t>
    <t>
      Since some servers will not be returning "." and ".." entries as has
      been done with previous versions of the NFS protocol, the client that
      requires these entries be present in READDIR responses must fabricate
      them.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_READLINK" title="Operation 27: READLINK - Read Symbolic Link" >

  <section toc="exclude" anchor="OP_READLINK_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: symlink */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_READLINK_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct READLINK4resok {
        linktext4       link;
};

union READLINK4res switch (nfsstat4 status) {
 case NFS4_OK:
         READLINK4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_READLINK_DESCRIPTION" title="DESCRIPTION">
    <t>
      READLINK reads the data associated with a symbolic
      link.  Depending on the value of the UTF-8 capability
      attribute (<xref target="utf8_caps"/>), the data is encoded
      in UTF-8.
      Whether created by an NFS client or created locally
      on the server, the data in a symbolic link is not
      interpreted (except possibly to check for proper UTF-8
      encoding) when created, but is simply stored.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_READLINK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A symbolic link is nominally a pointer to another file.  The data is
      not necessarily interpreted by the server, just stored in the file.
      It is possible for a client implementation to store a pathname that
      is not meaningful to the server operating system in a symbolic link.
      A READLINK operation returns the data to the client for
      interpretation. If different implementations want to share access to
      symbolic links, then they must agree on the interpretation of the data
      in the symbolic link.
    </t>
    <t>
      The READLINK operation is only allowed on objects of type NF4LNK.
      The server should return the error NFS4ERR_WRONG_TYPE if the 
      object is not of type NF4LNK.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_REMOVE" title="Operation 28: REMOVE - Remove File System Object" >

  <section toc="exclude" anchor="OP_REMOVE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct REMOVE4args {
        /* CURRENT_FH: directory */
        component4      target;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_REMOVE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct REMOVE4resok {
        change_info4    cinfo;
};

union REMOVE4res switch (nfsstat4 status) {
 case NFS4_OK:
         REMOVE4resok   resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_REMOVE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The REMOVE operation removes (deletes) a directory entry named by
      filename from the directory corresponding to the current filehandle.
      If the entry in the directory was the last reference to the
      corresponding file system object, the object may be destroyed.
      The directory may be either of type NF4DIR or NF4ATTRDIR.
    </t>
    <t>
      For the directory where the filename was removed, the server
      returns change_info4 information in cinfo.  With the atomic field of
      the change_info4 data type, the server will indicate if the before and
      after change attributes were obtained atomically with respect to the
      removal.
    </t>
    <t>
      If the target has a length of zero, or if
      the target does not obey the UTF-8 definition (and
      the server is enforcing UTF-8 encoding; see <xref
      target="utf8_caps"/>), the error NFS4ERR_INVAL will
      be returned.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_REMOVE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      NFSv3 required a different operator RMDIR for directory
      removal and REMOVE for non-directory removal. This allowed clients to
      skip checking the file type when being passed a non-directory delete
      system call (e.g., <xref target="unlink">unlink()</xref> in POSIX) to remove a directory, as well as
      the converse (e.g., a rmdir() on a non-directory) because they knew the
      server would check the file type.  NFSv4.1 REMOVE can be used to
      delete any directory entry independent of its file type. The
      implementor of an NFSv4.1 client's entry points from the
      unlink() and rmdir() system calls should first check the file type
      against the types the system call is allowed to remove before sending
      a REMOVE operation. Alternatively, the implementor can produce a COMPOUND call
      that includes a LOOKUP/VERIFY sequence of operations to verify the file type before
      a REMOVE operation in the same COMPOUND call.
    </t>
    <t>
      The concept of last reference is server
      specific. However, if the numlinks field in the
      previous attributes of the object had the value 1,
      the client should not rely on referring to the
      object via a filehandle. Likewise, the client
      should not rely on the resources (disk space,
      directory entry, and so on) formerly associated
      with the object becoming immediately available.
      Thus, if a client needs to be able to continue to
      access a file after using REMOVE to remove it, the
      client should take steps to make sure that the file
      will still be accessible.  While the traditional
      mechanism used is to RENAME the file from its old
      name to a new hidden name, the NFSv4.1 OPEN operation
      MAY return a result flag, OPEN4_RESULT_PRESERVE_UNLINKED,
      which indicates to the client that the file will be
      preserved if the file has an outstanding open (see <xref
      target="OP_OPEN"/>).

    </t>
    <t>
      If the server finds that the file is still open when the REMOVE
      arrives:
      <list style='symbols'>
        <t>
          The server SHOULD NOT delete the file's directory entry if the 
          file was opened with OPEN4_SHARE_DENY_WRITE or 
          OPEN4_SHARE_DENY_BOTH.
        </t>
        <t>
          If the file was not opened with OPEN4_SHARE_DENY_WRITE or
          OPEN4_SHARE_DENY_BOTH, the server SHOULD delete the file's 
          directory entry.  However, until last CLOSE of the file, 
          the server MAY continue to allow access to the file via 
          its filehandle.
      </t>
      <t>
          The server MUST NOT delete the directory
          entry if the reply from OPEN had the flag
          OPEN4_RESULT_PRESERVE_UNLINKED set.

      </t>
          
      </list>
    </t>
    <t>
      The server MAY implement its own restrictions on removal
      of a file while it is open. The server might disallow
      such a REMOVE (or a removal that occurs
      as part of RENAME). The conditions that influence the restrictions
      on removal of a file while it is still open include:
      <list style='symbols'>
      <t>
        Whether certain access protocols (i.e., not just
        NFS) are holding the file open.

      </t>

      <t>
        Whether particular options, access modes, or policies on the
        server are enabled.
      </t>

      </list>
    </t>

    <t>
      If a file has an outstanding OPEN and this prevents the
      removal of the file's directory entry,
      the error NFS4ERR_FILE_OPEN is returned.

    </t>

    <t>
      Where the determination above cannot be made
      definitively because delegations are being held,
      they MUST be recalled to allow processing of the
      REMOVE to continue.  When a delegation is held,
      the server has no reliable  knowledge of the status of OPENs for
      that client, so unless
      there are files opened with the particular deny modes
      by clients without delegations, the determination
      cannot be made until delegations are recalled, and
      the operation cannot proceed until each sufficient
      delegation has been returned or revoked to allow
      the server to make a correct determination.
    </t>
    <t>
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while
      delegations remain outstanding.
    </t>

    <t>
      If the current filehandle designates a directory for
      which another client holds a directory delegation,
      then, unless the situation can be resolved by sending
      a notification, the directory delegation MUST be
      recalled, and the operation MUST NOT proceed until
      the delegation is returned or revoked.  Except where
      this happens very quickly, one or more NFS4ERR_DELAY
      errors will be returned to requests made while
      delegation remains outstanding.

    </t>
    <t>
      When the current filehandle designates a directory
      for which one or more directory delegations
      exist, then, when those delegations request
      such notifications, NOTIFY4_REMOVE_ENTRY will be
      generated as a result of this operation.
    </t>

    <t>
      Note that when a remove occurs as a result of a
      RENAME, NOTIFY4_REMOVE_ENTRY will only be generated
      if the removal happens as a separate operation.
      In the case in which the removal is integrated and
      atomic with RENAME, the notification of the removal
      is integrated with notification for the RENAME. See
      the discussion of the NOTIFY4_RENAME_ENTRY
      notification in <xref target="OP_CB_NOTIFY"/>.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RENAME" title="Operation 29: RENAME - Rename Directory Entry" >

  <section toc="exclude" anchor="OP_RENAME_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct RENAME4args {
        /* SAVED_FH: source directory */
        component4      oldname;
        /* CURRENT_FH: target directory */
        component4      newname;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RENAME_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RENAME4resok {
        change_info4    source_cinfo;
        change_info4    target_cinfo;
};

union RENAME4res switch (nfsstat4 status) {
 case NFS4_OK:
        RENAME4resok    resok4;
 default:
        void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RENAME_DESCRIPTION" title="DESCRIPTION">
    <t>
      The RENAME operation renames the object identified by oldname in the
      source directory corresponding to the saved filehandle, as set by the
      SAVEFH operation, to newname in the target directory corresponding to
      the current filehandle.  The operation is required to be atomic to the
      client.  Source and target directories MUST reside on the same
      file system on the server.  On success, the current filehandle will
      continue to be the target directory.
    </t>
    <t>
      If the target directory already contains an entry with the name
      newname, the source object MUST be compatible with the target: either
      both are non-directories or both are directories and the target MUST
      be empty.
      If compatible, the existing target is removed before the
      rename occurs or, preferably, the target is removed atomically as
      part of the rename.
      See <xref target="OP_REMOVE_IMPLEMENTATION" />
      for client and server actions whenever a target is removed.  
      Note however that when the removal is performed atomically with the
      rename, certain parts of the removal described there are integrated
      with the rename.  For example, notification of the removal will not
      be via a NOTIFY4_REMOVE_ENTRY but will be indicated as part of the
      NOTIFY4_ADD_ENTRY or NOTIFY4_RENAME_ENTRY generated by the rename.
    </t> 
    <t>
      If the source object and the target are not
      compatible or if the target is a directory but not empty, the server
      will return the error NFS4ERR_EXIST.
    </t>
    <t>
      If oldname and newname both refer to the same
      file (e.g., they might be hard links of each
      other), then unless the file is open (see <xref
      target="OP_RENAME_IMPLEMENTATION"/>), RENAME MUST
      perform no action and return NFS4_OK.

    </t>
    <t>
      For both directories involved in the RENAME, the server returns
      change_info4 information.  With the atomic field of the change_info4
      data type, the server will indicate if the before and after change
      attributes were obtained atomically with respect to the rename.
    </t>
    <t>
      If oldname refers to a named attribute and the saved and current
      filehandles refer to different file system objects, the server will
      return NFS4ERR_XDEV just as if the saved and current filehandles
      represented directories on different file systems.
    </t>
    <t>
      If oldname or newname has a length of zero, or if oldname or
      newname does not obey the UTF-8 definition, the error NFS4ERR_INVAL
      will be returned.
    </t>
  </section>

  <section toc="exclude" anchor="OP_RENAME_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MAY impose restrictions on the RENAME
      operation such that RENAME may not be done when the
      file being renamed is open or when that open is done
      by particular protocols, or with particular options
      or access modes.  Similar restrictions may be applied
      when a file exists with the target name and is open.
      When RENAME is rejected because of such restrictions,
      the error NFS4ERR_FILE_OPEN is returned.

    </t>
    <t>
      When oldname and rename refer to the same file and
      that file is open in a fashion such that RENAME
      would normally be rejected with NFS4ERR_FILE_OPEN
      if oldname and newname were different files, then
      RENAME SHOULD be rejected with NFS4ERR_FILE_OPEN.

    </t>
    <t>
      If a server does implement such restrictions and those restrictions
      include cases of NFSv4 opens preventing successful execution of
      a rename, the server needs to recall any delegations that could
      hide the existence of opens relevant to that decision.  This is 
      because when a client holds a delegation, the server
      might not have an accurate account of the opens for that client, since
      the client may execute OPENs and CLOSEs locally.  The RENAME operation
      need only be delayed until a definitive result can be obtained.  For
      example, if there are multiple delegations and one of them establishes
      an open whose presence would prevent the rename, given the server's 
      semantics, NFS4ERR_FILE_OPEN may be returned to the caller as soon
      as that delegation is returned without waiting for other delegations
      to be returned.  Similarly, if such opens are not associated with 
      delegations, NFS4ERR_FILE_OPEN can be returned immediately with no 
      delegation recall being done.
    </t>
    <t>
      If the current filehandle or the saved filehandle designates a 
      directory for which another client holds a directory delegation, 
      then, unless the situation can be resolved by sending a notification,
      the delegation MUST be recalled, and the operation cannot proceed
      until the delegation is returned or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while delegation remains outstanding.
    </t>
    <t>
      When the current and saved filehandles are the
      same and they designate a directory for which one
      or more directory delegations exist, then, when
      those delegations request such notifications,
      a notification of type NOTIFY4_RENAME_ENTRY
      will be generated as a result of this operation.
      When oldname and rename refer to the same file,
      no notification is generated (because, as <xref
      target="OP_RENAME_DESCRIPTION"/> states, the server
      MUST take no action).  When a file is removed
      because it has the same name as the target, if
      that removal is done atomically with the rename,
      a NOTIFY4_REMOVE_ENTRY notification will not be
      generated.  Instead, the deletion of the file will
      be reported as part of the NOTIFY4_RENAME_ENTRY
      notification.

    </t>
    <t>
      When the current and saved filehandles are not the same:
      <list style="symbols">
        <t>
          If the current filehandle designates a directory for which 
          one or more directory delegations exist, then, when those 
          delegations request such notifications, NOTIFY4_ADD_ENTRY 
          will be generated as a result of this operation.  When a file 
          is removed because it has the same name as the target, if that 
          removal is done atomically with the rename, a
          NOTIFY4_REMOVE_ENTRY notification will not be generated.  
          Instead, the deletion of the file will be reported as part 
          of the NOTIFY4_ADD_ENTRY notification.
        </t>
        <t>
          If the saved filehandle designates a directory for which 
          one or more directory delegations exist, then, when those 
          delegations request such notifications, NOTIFY4_REMOVE_ENTRY 
          will be generated as a result of this operation.
        </t>
      </list> 

    </t>    
    <t>
      If the object being renamed has file delegations
      held by clients other than the one doing the RENAME,
      the delegations MUST be recalled, and the 
      operation cannot proceed  
      until each such delegation is returned 
      or revoked.  Note that in the case of multiply linked files,
      the delegation recall requirement applies even if the 
      delegation was obtained through a different name than the
      one being renamed.  
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while the
      delegation(s) remains outstanding, although it might not do that if the
      delegations are returned quickly.
    </t>
    <t>
      The RENAME operation must be atomic to the client.  The statement
      "source and target directories MUST reside on the same file system 
      on the server"
      means that the fsid fields in the attributes for the
      directories are the same. If they reside on different file systems,
      the error NFS4ERR_XDEV is returned.
    </t>
    <t>
      Based on the value of the fh_expire_type attribute for the object, the
      filehandle may or may not expire on a RENAME.  However, server
      implementors are strongly encouraged to attempt to keep filehandles
      from expiring in this fashion.
    </t>
    <t>
      On some servers, the file names "." and ".." are illegal as either
      oldname or newname, and will result in the error NFS4ERR_BADNAME.
      In addition, on many servers the case of oldname or newname being
      an alias for the source directory will be checked for.  Such servers
      will return the error NFS4ERR_INVAL in these cases.
    </t>
    <t>
      If either of the source or target filehandles are not directories, the
      server will return NFS4ERR_NOTDIR.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RESTOREFH" title="Operation 31: RESTOREFH - Restore Saved Filehandle" >

  <section toc="exclude" anchor="OP_RESTOREFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* SAVED_FH: */
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_RESTOREFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RESTOREFH4res {
        /*
         * If status is NFS4_OK,
         *     new CURRENT_FH: value of saved fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RESTOREFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      The RESTOREFH operation sets the current filehandle and stateid to the values in the
      saved filehandle and stateid.  If 
      there is no saved filehandle, then the server will
      return the error NFS4ERR_NOFILEHANDLE.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_RESTOREFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Operations like OPEN and LOOKUP use the current filehandle
      to represent a directory and replace it with a new filehandle.
      Assuming that the previous filehandle was saved with a SAVEFH operator,
      the previous filehandle can be restored as the current filehandle.
      This is commonly used to obtain post-operation attributes for
      the directory, e.g.,
      <figure>
	<artwork>
      PUTFH (directory filehandle)
      SAVEFH
      GETATTR attrbits     (pre-op dir attrs)
      CREATE optbits "foo" attrs
      GETATTR attrbits     (file attributes)
      RESTOREFH
      GETATTR attrbits     (post-op dir attrs)
	</artwork>
      </figure>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SAVEFH" title="Operation 32: SAVEFH - Save Current Filehandle" >

  <section toc="exclude" anchor="OP_SAVEFH_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
/* CURRENT_FH: */
void;
      </artwork>
    </figure>
  </section>


  <section toc="exclude" anchor="OP_SAVEFH_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct SAVEFH4res {
        /*
         * If status is NFS4_OK,
         *    new SAVED_FH: value of current fh
         */
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_SAVEFH_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SAVEFH operation saves the current filehandle and stateid.
      If a previous filehandle was saved, then
      it is no longer accessible.  The saved filehandle can be restored as
      the current filehandle with the RESTOREFH operator.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
      See <xref target="current_filehandle"/> for more details on the
      current filehandle.
    </t>
    <t>
      See <xref target="current_stateid"/> for more details on the current
      stateid.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SAVEFH_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SECINFO" title="Operation 33: SECINFO - Obtain Available Security" >

  <section toc="exclude" anchor="OP_SECINFO_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct SECINFO4args {
        /* CURRENT_FH: directory */
        component4      name;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SECINFO_RESULTS" title="RESULTS">
<figure>
 <artwork>
/*
 * From RFC 2203
 */
enum rpc_gss_svc_t {
        RPC_GSS_SVC_NONE        = 1,
        RPC_GSS_SVC_INTEGRITY   = 2,
        RPC_GSS_SVC_PRIVACY     = 3
};

struct rpcsec_gss_info {
        sec_oid4        oid;
        qop4            qop;
        rpc_gss_svc_t   service;
};

/* RPCSEC_GSS has a value of '6' - See RFC 2203 */
union secinfo4 switch (uint32_t flavor) {
 case RPCSEC_GSS:
         rpcsec_gss_info        flavor_info;
 default:
         void;
};

typedef secinfo4 SECINFO4resok&lt;>;

union SECINFO4res switch (nfsstat4 status) {
 case NFS4_OK:
        /* CURRENTFH: consumed */
         SECINFO4resok resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>


  <section toc="exclude" anchor="OP_SECINFO_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SECINFO operation is used by the client to obtain a list of
      valid RPC authentication flavors for a specific directory
      filehandle, file name pair.  SECINFO should apply the same
      access methodology used for LOOKUP when evaluating the name.
      Therefore, if the requester does not have the appropriate access
      to LOOKUP the name, then SECINFO MUST behave the same way and
      return NFS4ERR_ACCESS.
    </t>
    <t>
      The result will contain an array that represents the security
      mechanisms available, with an order corresponding to the
      server's preferences, the most preferred being first in the
      array. The client is free to pick whatever security mechanism it
      both desires and supports, or to pick in the server's preference
      order the first one it supports.  The array entries are
      represented by the secinfo4 structure.  The field 'flavor' will
      contain a value of AUTH_NONE, AUTH_SYS (as defined in <xref
      target="RFC5531">RFC 5531</xref>), or RPCSEC_GSS (as defined in
      <xref target="RFC2203">RFC 2203</xref>). The field flavor can
      also be any other security flavor registered with IANA.
    </t>
    <t>
      For the flavors AUTH_NONE and AUTH_SYS, no additional security
      information is returned.  The same is true of many (if not most)
      other security flavors, including AUTH_DH. For a return value of
      RPCSEC_GSS, a security triple is returned that contains the
      mechanism object identifier (OID, as defined in <xref
      target="RFC2743">RFC 2743</xref>), the quality of protection (as
      defined in <xref target="RFC2743">RFC 2743</xref>), and the
      service type (as defined in <xref
      target="RFC2203">RFC 2203</xref>).  It is possible for SECINFO to
      return multiple entries with flavor equal to RPCSEC_GSS with
      different security triple values.
    </t>
    <t>
      On success, the current filehandle is consumed (see
      <xref target="aftersecinfo" />), and if the
      next operation after SECINFO tries to use the current filehandle,
      that operation will fail with the status NFS4ERR_NOFILEHANDLE.
    </t>
    <t>
      If the name has a length of zero, or if the name does not obey
      the UTF-8 definition (assuming UTF-8 capabilities are enabled; see
      <xref target="utf8_caps"/>), the error NFS4ERR_INVAL will be returned.
    </t>
    <t>
      See <xref target="Security_Service_Negotiation"/>
      for additional information on the use of SECINFO.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_IMPLEMENTATION" title="IMPLEMENTATION">
        <t>
          The SECINFO operation is expected to be used by the NFS client
          when the error value of NFS4ERR_WRONGSEC is returned from
          another NFS operation.  This signifies to the client that the
          server&apos;s security policy is different from what the client is
          currently using.  At this point, the client is expected to
          obtain a list of possible security flavors and choose what best
          suits its policies.
        </t>
        <t>
          As mentioned, the server&apos;s security
          policies will determine when a client
          request receives NFS4ERR_WRONGSEC.  See <xref
          target="error_op_returns"/> for a list of operations
          that can return NFS4ERR_WRONGSEC. In addition,
          when READDIR returns attributes, the rdattr_error
          (<xref target="attrdef_rdattr_error" />)
          can contain NFS4ERR_WRONGSEC. Note that CREATE and
          REMOVE MUST NOT return NFS4ERR_WRONGSEC. The
          rationale for CREATE is that unless the
          target name exists, it cannot have a separate
          security policy from the parent directory,
          and the security policy of the parent was
          checked when its filehandle was injected into
          the COMPOUND request's operations stream (for
          similar reasons, an OPEN operation that creates
          the target MUST NOT return NFS4ERR_WRONGSEC). If
          the target name exists, while it might have a
          separate security policy, that is irrelevant
          because CREATE MUST return NFS4ERR_EXIST.
          The rationale for REMOVE is that while that
          target might have a separate security policy, the
          target is going to be removed, and so the
          security policy of the parent trumps that of the
          object being removed. RENAME and LINK MAY return
          NFS4ERR_WRONGSEC, but the NFS4ERR_WRONGSEC error
          applies only to the saved filehandle (see <xref
          target="link_rename"/>). Any NFS4ERR_WRONGSEC
          error on the current filehandle used by LINK and
          RENAME MUST be returned by the PUTFH, PUTPUBFH,
          PUTROOTFH, or RESTOREFH operation that injected
          the current filehandle.

        </t>
        <t>
          With the exception of LINK and RENAME,
          the set of operations that can return NFS4ERR_WRONGSEC
          represents the point at which the client can inject a
          filehandle into the "current filehandle" at the server.  The
          filehandle is either provided by the client (PUTFH, PUTPUBFH,
          PUTROOTFH), generated as a result of a name-to-filehandle
          translation (LOOKUP and OPEN), or generated from the saved filehandle
          via RESTOREFH. As <xref target="PUTFHplusSAVEFH"/> states,
          a put filehandle operation followed by SAVEFH MUST NOT
          return NFS4ERR_WRONGSEC. Thus, the RESTOREFH operation, under
          certain conditions (see <xref target="putfh_series"/>), is
          permitted to return NFS4ERR_WRONGSEC so that security policies
          can be honored.

        </t>

        <t>
          The READDIR operation will not directly return the
          NFS4ERR_WRONGSEC error.  However, if the READDIR request
          included a request for attributes, it is possible that the
          READDIR request&apos;s security triple did not match that of a
          directory entry.  If this is the case and the client has
          requested the rdattr_error attribute, the server will return the
          NFS4ERR_WRONGSEC error in rdattr_error for the entry.
        </t>

        <t>
          To resolve an error return of
          NFS4ERR_WRONGSEC, the client does the following:
        </t>

        <t>
          <list style="symbols">
            <t>
              For LOOKUP and OPEN, the client will use SECINFO with the
              same current filehandle and name as provided in the
              original LOOKUP or OPEN to enumerate the available security
              triples.

            </t>
            <t>
              For the rdattr_error, the client will use
              SECINFO with the same current filehandle
              as provided in the original READDIR. The
              name passed to SECINFO will be that of the
              directory entry (as returned from READDIR)
              that had the NFS4ERR_WRONGSEC error in the
              rdattr_error attribute.

            </t>
            <t>
              For PUTFH, PUTROOTFH, PUTPUBFH,
              RESTOREFH, LINK, and RENAME, the client will
              use SECINFO_NO_NAME { style =
              SECINFO_STYLE4_CURRENT_FH }.  The client
              will prefix the SECINFO_NO_NAME operation
              with the appropriate PUTFH, PUTPUBFH,
              or PUTROOTFH operation that provides the
              filehandle originally provided by the PUTFH,
              PUTPUBFH, PUTROOTFH, or RESTOREFH operation.

              <vspace blankLines='1' />

              NOTE: In NFSv4.0, the client was required
              to use SECINFO, and had to reconstruct the
              parent of the original filehandle and the
              component name of the original filehandle. The
              introduction in NFSv4.1 of SECINFO_NO_NAME
              obviates the need for reconstruction.

            </t>
            <t>
              For LOOKUPP, the client will
              use SECINFO_NO_NAME { style =
              SECINFO_STYLE4_PARENT } and provide the
              filehandle that equals the filehandle
              originally provided to LOOKUPP.

            </t>           
          </list>
        </t>

        <t>
          See <xref target="securityconsider"/> for a discussion on
          the recommendations for the security flavor used by SECINFO and
          SECINFO_NO_NAME.
        </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SETATTR" title="Operation 34: SETATTR - Set Attributes" >

  <section toc="exclude" anchor="OP_SETATTR_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct SETATTR4args {
        /* CURRENT_FH: target object */
        stateid4        stateid;
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SETATTR_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct SETATTR4res {
        nfsstat4        status;
        bitmap4         attrsset;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_SETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SETATTR operation changes one or more of the attributes of a
      file system object.  The new attributes are specified with a bitmap and
      the attributes that follow the bitmap in bit order.
    </t>
    <t>
      The stateid argument for SETATTR is used to provide byte-range locking
      context that is necessary for SETATTR requests that set the size
      attribute.  Since setting the size attribute modifies the file's data,
      it has the same locking requirements as a corresponding WRITE.  Any
      SETATTR that sets the size attribute is incompatible with a share
      reservation that specifies OPEN4_SHARE_DENY_WRITE.  The area between the old
      end-of-file and the new end-of-file is considered to be modified just
      as would have been the case had the area in question been specified as
      the target of WRITE, for the purpose of checking conflicts with byte-range
      locks, for those cases in which a server is implementing mandatory
      byte-range locking behavior.  A valid stateid SHOULD always be specified.
      When the file size attribute is not set, the special stateid
      consisting of all bits equal to zero MAY be passed.
    </t>
    <t>
      On either success or failure of the operation, the server will return
      the attrsset bitmask to represent what (if any) attributes were
      successfully set.  The attrsset in the response is a subset of the
      attrmask field of the obj_attributes field in the argument.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_SETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the request specifies the owner attribute to be set, the server
      SHOULD allow the operation to succeed if the current owner of the
      object matches the value specified in the request.  Some servers may
      be implemented in a way as to prohibit the setting of the owner
      attribute unless the requester has privilege to do so.  If the server
      is lenient in this one case of matching owner values, the client
      implementation may be simplified in cases of creation of an object
      (e.g., an exclusive create via OPEN)
      followed by a SETATTR.
    </t>
    <t>
      The file size attribute is used to request changes
      to the size of a file. A value of zero causes the
      file to be truncated, a value less than the current
      size of the file causes data from new size to the
      end of the file to be discarded, and a size greater
      than the current size of the file causes logically
      zeroed data bytes to be added to the end of the
      file.  Servers are free to implement this using
      unallocated bytes (holes) or allocated data bytes
      set to zero. Clients should not make any assumptions
      regarding a server's implementation of this feature,
      beyond that the bytes in the affected byte-range returned by
      READ will be zeroed.  Servers MUST support extending
      the file size via SETATTR.

    </t>
    <t>
      SETATTR is not guaranteed to be atomic.  A failed SETATTR may partially
      change a file's attributes, hence the reason why the reply always
      includes the status and the list of attributes that were set.
    </t>
    <t>
      If the object whose attributes are being changed has a file delegation 
      that is held by a client other than the one doing the SETATTR,
      the delegation(s) must be recalled, and the 
      operation cannot proceed to actually change an attribute 
      until each such delegation is returned 
      or revoked.  
      In all cases in which delegations are recalled, the server
      is likely to return one or more NFS4ERR_DELAY errors while the
      delegation(s) remains outstanding, although it might not do that if the
      delegations are returned quickly.
    </t>
    <t>
      If the object whose attributes are being set is a directory
      and another client holds a directory delegation for that 
      directory, then if enabled, asynchronous notifications will be generated
      when the set of attributes changed has a non-null intersection 
      with the set of attributes for which notification is requested.
      Notifications of type NOTIFY4_CHANGE_DIR_ATTRS will be sent to 
      the appropriate client(s), but the SETATTR is not delayed by 
      waiting for these notifications to be sent.
    </t>
    <t>
      If the object whose attributes are being set is a member of
      the directory for which another client holds a directory delegation,
      then asynchronous notifications will be generated
      when the set of attributes changed has a non-null intersection 
      with the set of attributes for which notification is requested.
      Notifications of type NOTIFY4_CHANGE_CHILD_ATTRS will be sent to 
      the appropriate clients, but the SETATTR is not delayed by 
      waiting for these notifications to be sent.
    </t>
    <t>
      Changing the size of a file with SETATTR indirectly
      changes the time_modify and change attributes.
      A client must account for this as size changes can
      result in data deletion.

    </t>
    <t>
      The attributes time_access_set and time_modify_set are write-only
      attributes constructed as a switched union so the client can direct
      the server in setting the time values.  If the switched union
      specifies SET_TO_CLIENT_TIME4, the client has provided an nfstime4 to
      be used for the operation.  If the switch union does not specify
      SET_TO_CLIENT_TIME4, the server is to use its current time for the
      SETATTR operation.
    </t>
    <t>
      If server and client times differ, programs that compare client time
      to file times can break. A time synchronization protocol should be used to
      limit client/server time skew.
    </t>
    <t>
      Use of a COMPOUND containing a VERIFY operation specifying only the
      change attribute, immediately followed by a SETATTR, provides a means
      whereby a client may specify a request that emulates the functionality
      of the SETATTR guard mechanism of NFSv3.  Since the function
      of the guard mechanism is to avoid changes to the file attributes
      based on stale information, delays between checking of the guard
      condition and the setting of the attributes have the potential to
      compromise this function, as would the corresponding delay in the 
      NFSv4 emulation.  Therefore, NFSv4.1 servers SHOULD take
      care to avoid such delays, to the degree possible, when executing such
      a request.
    </t>
    <t>
      If the server does not support an attribute as requested by the
      client, the server SHOULD return NFS4ERR_ATTRNOTSUPP.
    </t>
    <t>
      A mask of the attributes actually set is returned by SETATTR in all
      cases.  That mask MUST NOT include attribute bits not requested to be
      set by the client. 
If the attribute masks in the request and
      reply are equal, the status field in the reply MUST be NFS4_OK.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_VERIFY" title="Operation 37: VERIFY - Verify Same Attributes" >

  <section toc="exclude" anchor="OP_VERIFY_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
struct VERIFY4args {
        /* CURRENT_FH: object */
        fattr4          obj_attributes;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_VERIFY_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct VERIFY4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_VERIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The VERIFY operation is used to verify that attributes have the value
      assumed by the client before proceeding with the following operations in
      the COMPOUND request.  If any of the attributes do not match, then the
      error NFS4ERR_NOT_SAME must be returned.  The current filehandle
      retains its value after successful completion of the operation.
    </t>
  </section>
  <section toc="exclude" anchor="OP_VERIFY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      One possible use of the VERIFY operation is the following series
      of operations. With this, the client is attempting to verify that the file
      being removed will match what the client expects to be removed.  This
      series can help prevent the unintended deletion of a file.
      <figure>
	<artwork>
      PUTFH (directory filehandle)
      LOOKUP (file name)
      VERIFY (filehandle == fh)
      PUTFH (directory filehandle)
      REMOVE (file name)
	</artwork>
      </figure>
      This series does not prevent a second client from removing and
      creating a new file in the middle of this sequence, but it does help
      avoid the unintended result.
    </t>
    <t>
      In the case that a RECOMMENDED attribute is specified in the VERIFY
      operation and the server does not support that attribute for the
      file system object, the error NFS4ERR_ATTRNOTSUPP is returned to the
      client.
    </t>
    <t>
      When the attribute rdattr_error or any set-only attribute (e.g.,
      time_modify_set) is specified, the error NFS4ERR_INVAL is returned to
      the client.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_WRITE" title="Operation 38: WRITE - Write to File" >

  <section toc="exclude" anchor="OP_WRITE_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>
enum stable_how4 {
        UNSTABLE4       = 0,
        DATA_SYNC4      = 1,
        FILE_SYNC4      = 2
};

struct WRITE4args {
        /* CURRENT_FH: file */
        stateid4        stateid;
        offset4         offset;
        stable_how4     stable;
        opaque          data&lt;>;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_WRITE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct WRITE4resok {
        count4          count;
        stable_how4     committed;
        verifier4       writeverf;
};

union WRITE4res switch (nfsstat4 status) {
 case NFS4_OK:
         WRITE4resok    resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_WRITE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The WRITE operation is used to write data to a regular file.  The
      target file is specified by the current filehandle.  The offset
      specifies the offset where the data should be written.  An offset of zero
      specifies that the write should start at the beginning of the
      file.  The count, as encoded as part of the opaque data parameter,
      represents the number of bytes of data that are to be written.  If the
      count is zero, the WRITE will succeed and return a count of zero subject to permissions checking.  The server MAY
      write fewer bytes than requested by the client.
    </t>
    <t>
      The client specifies with the stable parameter the method
      of how the data is to be processed by the server.  If stable is
      FILE_SYNC4, the server MUST commit the data written plus all
      file system metadata to stable storage before returning results. This
      corresponds to the NFSv2 protocol semantics.  Any other
      behavior constitutes a protocol violation.  If stable is DATA_SYNC4,
      then the server MUST commit all of the data to stable storage and
      enough of the metadata to retrieve the data before returning.  The
      server implementor is free to implement DATA_SYNC4 in the same fashion
      as FILE_SYNC4, but with a possible performance drop.  If stable is
      UNSTABLE4, the server is free to commit any part of the data and the
      metadata to stable storage, including all or none, before returning a
      reply to the client. There is no guarantee whether or when any
      uncommitted data will subsequently be committed to stable storage. The
      only guarantees made by the server are that it will not destroy any
      data without changing the value of writeverf and that it will not commit
      the data and metadata at a level less than that requested by the
      client.
    </t>
    <t>
      Except when special stateids are used, the 
      stateid value for a WRITE request represents a value returned from
      a previous byte-range LOCK or OPEN request or the stateid
      associated with a delegation.  The stateid identifies the associated
      owners if any and is 
      used by the server to verify that the associated locks are still
      valid (e.g., have not been revoked).
    </t>
    <t>
      Upon successful completion, the following results are returned.  The
      count result is the number of bytes of data written to the file. The
      server may write fewer bytes than requested. If so, the actual number
      of bytes written starting at location, offset, is returned.
    </t>
    <t>
      The server also returns an indication of the level of commitment of
      the data and metadata via committed.
      Per <xref target="stable_committed"/>,
      <list style='symbols'>
      <t>
        The server MAY commit the data at a stronger level
        than requested.

      </t>

      <t>
        The server MUST commit the data at a level at
        least as high as that committed.

      </t>
      </list>

    </t>

    <texttable anchor="stable_committed">

    <preamble>
       Valid combinations of the fields stable in the request and committed in
       the reply.

    </preamble>

    <ttcol>stable</ttcol>

    <ttcol>committed</ttcol>

    <c>UNSTABLE4</c>   <c>FILE_SYNC4, DATA_SYNC4, UNSTABLE4</c>

    <c>DATA_SYNC4</c>  <c>FILE_SYNC4, DATA_SYNC4</c>

    <c>FILE_SYNC4</c>  <c>FILE_SYNC4</c>

    </texttable>
     
    <t>
      The final portion of the result is the field
      writeverf. This field is the write verifier and is a
      cookie that the client can use to determine whether
      a server has changed instance state (e.g., server
      restart) between a call to WRITE and a subsequent
      call to either WRITE or COMMIT.  This cookie MUST be
      unchanged during a single instance of the NFSv4.1
      server and MUST be unique between instances of the
      NFSv4.1 server. If the cookie changes, then the
      client MUST assume that any data written with an
      UNSTABLE4 value for committed and an old writeverf in the reply
      has been lost and will need to be recovered.

    </t>
    <t>
      If a client writes data to the server with the stable argument set to
      UNSTABLE4 and the reply yields a committed response of DATA_SYNC4 or
      UNSTABLE4, the client will follow up some time in the future with a
      COMMIT operation to synchronize outstanding asynchronous data and
      metadata with the server's stable storage, barring client error. It is
      possible that due to client crash or other error that a subsequent
      COMMIT will not be received by the server.
    </t>
    <t>
      For a WRITE with a stateid value of all bits equal to zero, the server MAY allow
      the WRITE to be serviced subject to mandatory byte-range locks or the
      current share deny modes for the file.  For a WRITE with a stateid
      value of all bits equal to 1, the server MUST NOT allow the WRITE operation to
      bypass locking checks at the server and otherwise is
      treated as if a stateid of all bits equal to zero were used.
    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_WRITE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      It is possible for the server to write fewer bytes of data than
      requested by the client.  In this case, the server SHOULD NOT return
      an error unless no data was written at all.  If the server writes less
      than the number of bytes specified, the client will need to send another
      WRITE to write the remaining data.
    </t>
    <t>
      It is assumed that the act of writing data to
      a file will cause the time_modified and change
      attributes of the file to be updated.  However,
      these attributes SHOULD NOT be changed
      unless the contents of the file are changed.  Thus,
      a WRITE request with count set to zero SHOULD NOT cause
      the time_modified and change attributes of the file to be updated.

    </t>
    <t>
      Stable storage is persistent storage that survives:
    </t>
    <t>
      <list style="numbers">
	<t>
	  Repeated power failures.
	</t>
	<t>
	  Hardware failures (of any board, power supply, etc.).
	</t>
	<t>
	  Repeated software crashes and restarts.
	</t>
      </list>
    </t>
    <t>
      This definition does not address failure of the stable storage module
      itself.
    </t>
    <t>
      The verifier is defined to allow a client to detect
      different instances of an NFSv4.1 protocol server
      over which cached, uncommitted data may be lost. In
      the most likely case, the verifier allows the client
      to detect server restarts.  This information is
      required so that the client can safely determine
      whether the server could have lost cached data.
      If the server fails unexpectedly and the client has
      uncommitted data from previous WRITE requests (done
      with the stable argument set to UNSTABLE4 and in
      which the result committed was returned as UNSTABLE4
      as well), the server might not have flushed cached
      data to stable storage. The burden of recovery is
      on the client, and the client will need to retransmit
      the data to the server.

    </t>
    <t>
      A suggested verifier would be to use the time that
      the server was last started (if restarting the server
      results in lost buffers).

    </t>
    <t>
      The reply's committed field allows the client to do more
      effective caching.  If the server is committing all WRITE requests to
      stable storage, then it SHOULD return with committed set to FILE_SYNC4,
      regardless of the value of the stable field in the arguments. A server
      that uses an NVRAM accelerator may choose to implement this policy.
      The client can use this to increase the effectiveness of the cache by
      discarding cached data that has already been committed on the server.
    </t>
    <t>
      Some implementations may return NFS4ERR_NOSPC instead
      of NFS4ERR_DQUOT when a user's quota is exceeded.

    </t>
    <t>
      In the case that the current filehandle is of
      type NF4DIR, the server will return NFS4ERR_ISDIR.
      If the current file is a symbolic link, the error
      NFS4ERR_SYMLINK will be returned.  Otherwise, if the
      current filehandle does not designate an ordinary
      file, the server will return NFS4ERR_WRONG_TYPE.

    </t>
    <t>
      If mandatory byte-range locking is in effect for the file,
      and the corresponding byte-range of the data to
      be written to the file is READ_LT or WRITE_LT locked by
      an owner that is not associated with the stateid,
      the server MUST return NFS4ERR_LOCKED. If so,
      the client MUST check if the owner corresponding
      to the stateid used with the WRITE operation has a
      conflicting READ_LT lock that overlaps with the byte-range
      that was to be written. If the stateid's owner has
      no conflicting READ_LT lock, then the client SHOULD try
      to get the appropriate write byte-range lock via the
      LOCK operation before re-attempting the WRITE. When
      the WRITE completes, the client SHOULD release the
      byte-range lock via LOCKU.

    </t>
    <t>
      If the stateid's owner had a conflicting READ_LT lock, then the client
      has no choice but to return an error to the application that attempted
      the WRITE. The reason is that since the stateid's owner had a READ_LT
      lock, either the server attempted to temporarily effectively upgrade
      this READ_LT lock to a WRITE_LT lock or the server has no upgrade
      capability. If the server attempted to upgrade the READ_LT lock and
      failed, it is pointless for the client to re-attempt the upgrade via
      the LOCK operation, because there might be another client also trying
      to upgrade.  If two clients are blocked trying to upgrade the same lock,
      the clients deadlock.  If the server has no upgrade capability, then
      it is pointless to try a LOCK operation to upgrade.
    </t>
    <t>
      If one or more other clients have delegations for the file being 
      written, those delegations MUST be recalled, and the 
      operation cannot proceed until those delegations are returned 
      or revoked.  Except where this
      happens very quickly, one or more NFS4ERR_DELAY errors will be
      returned to requests made while the delegation remains outstanding.
      Normally, delegations will not be recalled as a result of a WRITE
      operation since the recall will occur as a result of an earlier
      OPEN.  However, since it is possible for a WRITE to be done with
      a special stateid, the server needs to check for this case even
      though the client should have done an OPEN previously.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_BACKCHANNEL_CTL" title="Operation 40: BACKCHANNEL_CTL - Backchannel Control" >

  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
typedef opaque gsshandle4_t&lt;>;

struct gss_cb_handles4 {
        rpc_gss_svc_t           gcbp_service; /* RFC 2203 */
        gsshandle4_t            gcbp_handle_from_server;
        gsshandle4_t            gcbp_handle_from_client;
};

union callback_sec_parms4 switch (uint32_t cb_secflavor) {
case AUTH_NONE:
        void;
case AUTH_SYS:
        authsys_parms   cbsp_sys_cred; /* RFC 1831 */
case RPCSEC_GSS:
        gss_cb_handles4 cbsp_gss_handles;
};

struct BACKCHANNEL_CTL4args {
        uint32_t                bca_cb_program;
        callback_sec_parms4     bca_sec_parms&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_RESULT" title="RESULT">
<figure>
 <artwork>
struct BACKCHANNEL_CTL4res {
        nfsstat4                bcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BACKCHANNEL_CTL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The BACKCHANNEL_CTL operation replaces the
      backchannel's callback program number and adds
      (not replaces) RPCSEC_GSS handles for use by the
      backchannel.

    </t>
    <t>
      The arguments of the BACKCHANNEL_CTL call are
      a subset of the CREATE_SESSION parameters.
      In the arguments of BACKCHANNEL_CTL, the
      bca_cb_program field and bca_sec_parms fields
      correspond respectively to the csa_cb_program and
      csa_sec_parms fields of the arguments of CREATE_SESSION
      (<xref target="OP_CREATE_SESSION"/>).

    </t>
    <t>
      BACKCHANNEL_CTL MUST appear in a COMPOUND that starts
      with SEQUENCE.

    </t>
    <t>
      If the RPCSEC_GSS handle identified by 
      gcbp_handle_from_server does not exist on the server,
      the server MUST return NFS4ERR_NOENT.
    </t>

    <t>
       If an RPCSEC_GSS handle is using the SSV context (see <xref 
       target="ssv_mech"/>), then because each SSV RPCSEC_GSS 
       handle shares a common SSV GSS context, there are security
       considerations specific to this situation discussed in <xref
       target="rpcsec_ssv_consider"/>.
    </t>


  </section>
</section>

<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $       -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_BIND_CONN_TO_SESSION" title="Operation 41: BIND_CONN_TO_SESSION - Associate Connection with Session" >

  <section toc="exclude" 
           anchor="OP_BIND_CONN_TO_SESSION_ARGUMENT" 
           title="ARGUMENT">
<figure>
 <artwork>
enum channel_dir_from_client4 {
 CDFC4_FORE             = 0x1,
 CDFC4_BACK             = 0x2,
 CDFC4_FORE_OR_BOTH     = 0x3,
 CDFC4_BACK_OR_BOTH     = 0x7
};

struct BIND_CONN_TO_SESSION4args {
 sessionid4     bctsa_sessid;

 channel_dir_from_client4
                bctsa_dir;

 bool           bctsa_use_conn_in_rdma_mode;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
enum channel_dir_from_server4 {
 CDFS4_FORE     = 0x1,
 CDFS4_BACK     = 0x2,
 CDFS4_BOTH     = 0x3
};

struct BIND_CONN_TO_SESSION4resok {
 sessionid4     bctsr_sessid;

 channel_dir_from_server4
                bctsr_dir;

 bool           bctsr_use_conn_in_rdma_mode;
};

union BIND_CONN_TO_SESSION4res
 switch (nfsstat4 bctsr_status) {

 case NFS4_OK:
  BIND_CONN_TO_SESSION4resok
                bctsr_resok4;

 default:       void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      BIND_CONN_TO_SESSION is used to associate additional connections with a
      session. It MUST be used on the connection being associated with the session. It MUST
      be the only operation in the COMPOUND procedure.  If
      SP4_NONE (<xref target="OP_EXCHANGE_ID" />) state protection
      is used, any principal,
      security flavor, or RPCSEC_GSS context MAY be used to invoke the operation.
      If SP4_MACH_CRED is used, RPCSEC_GSS MUST be used with the
      integrity or privacy services, using the principal that
      created the client ID. If SP4_SSV is used, RPCSEC_GSS with
      the SSV GSS mechanism (<xref target="ssv_mech" />) and integrity or
      privacy MUST be used.
    </t>
    <t>
     If, when the client ID was created, the client opted for SP4_NONE
     state protection,
     the client is not required to use BIND_CONN_TO_SESSION to associate the
     connection with the session, unless
     the client wishes to associate the connection with the backchannel.
     When SP4_NONE protection is used, simply sending a COMPOUND
     request with a SEQUENCE operation is sufficient to associate the
     connection with the session specified in SEQUENCE.
    </t>
    <t>
      The field bctsa_dir indicates whether the client
      wants to associate the connection with the fore
      channel or the backchannel or both channels. The value
      CDFC4_FORE_OR_BOTH indicates that the client wants to
      associate the connection with both the fore channel and backchannel,
      but will accept the connection being associated to
      just the fore channel.  The value CDFC4_BACK_OR_BOTH
      indicates that the client wants to associate with both
      the fore channel and backchannel, but will accept the
      connection being associated with just the backchannel.
      The server replies in bctsr_dir which channel(s)
      the connection is associated with.
      If the client specified CDFC4_FORE, the server
      MUST return CDFS4_FORE. If the client specified
      CDFC4_BACK, the server MUST return CDFS4_BACK. If the
      client specified CDFC4_FORE_OR_BOTH, the server MUST return
      CDFS4_FORE or CDFS4_BOTH. If the client specified
      CDFC4_BACK_OR_BOTH, the server MUST return CDFS4_BACK
      or CDFS4_BOTH.

    </t>
    <t>
     See the CREATE_SESSION operation (<xref target="OP_CREATE_SESSION" />),
     and the description of the argument
     csa_use_conn_in_rdma_mode to understand
     bctsa_use_conn_in_rdma_mode, and the description of
     csr_use_conn_in_rdma_mode to understand bctsr_use_conn_in_rdma_mode.
    </t>
    <t>
     Invoking BIND_CONN_TO_SESSION on a connection already associated
     with the specified session has no effect, and the server MUST
     respond with NFS4_OK, unless the client is demanding changes
     to the set of channels the connection is associated with. If
     so, the server MUST return NFS4ERR_INVAL.
     
    </t>
 
  </section>
  <section toc="exclude" anchor="OP_BIND_CONN_TO_SESSION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>      
      If a session's channel loses all connections, depending on
      the client ID's state protection and type of channel,
      the client might need to use
      BIND_CONN_TO_SESSION to associate a new connection. If the
      server restarted and does not keep the reply cache in stable
      storage, the server will not recognize the session ID.
      The client will ultimately have to invoke EXCHANGE_ID to
      create a new client ID and session.
    </t>
    <t>      
      Suppose SP4_SSV state protection is being used,
      and BIND_CONN_TO_SESSION is among the operations
      included in the spo_must_enforce set when the
      client ID was created (<xref target="OP_EXCHANGE_ID"/>).
      If so, there is an issue if SET_SSV is sent, no response
      is returned, and the last connection associated
      with the client ID drops.  The client, per
      the sessions model, MUST retry the SET_SSV. But
      it needs a new connection to do so, and MUST
      associate that connection with the session via a
      BIND_CONN_TO_SESSION authenticated with the SSV
      GSS mechanism. The problem is that the RPCSEC_GSS
      message integrity codes use a subkey derived from the SSV as the
      key and the
      SSV may have changed. While there are multiple
      recovery strategies, a single, general strategy
      is described here.
      <list style='symbols'>
      <t>
       The client reconnects.
      </t>
      <t>
       The client assumes that the SET_SSV was executed,
       and so sends BIND_CONN_TO_SESSION with the subkey (derived from
       the new SSV, i.e., what SET_SSV would have set the SSV to)
       used as the key for the RPCSEC_GSS credential message integrity codes.
      </t>
      <t>
       If the request succeeds, this means that the original attempted SET_SSV
       did execute successfully. The client re-sends the original
       SET_SSV, which the server will reply to via the
       reply cache.
      </t>
      <t>
       If the server returns an RPC authentication error,
       this means that the server's current SSV was not changed
       (and the SET_SSV was likely not executed).  The client then
       tries BIND_CONN_TO_SESSION with the subkey derived from the
       old SSV as the
       key for the RPCSEC_GSS message integrity codes.
      </t>
      <t>
       The attempted BIND_CONN_TO_SESSION with the old SSV
       should succeed. If so, the client re-sends the original
       SET_SSV. If the original SET_SSV was not executed, then the
       server executes it. If the original SET_SSV was executed but
       failed, the server will return the SET_SSV from the reply
       cache.
      </t>

     </list>

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_EXCHANGE_ID" title="Operation 42: EXCHANGE_ID - Instantiate Client ID" >
  <t>
      The EXCHANGE_ID exchanges long-hand client and server identifiers (owners),
      and creates a client ID.
  </t>

  <section toc="exclude" anchor="OP_EXCHANGE_ID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
const EXCHGID4_FLAG_SUPP_MOVED_REFER    = 0x00000001;
const EXCHGID4_FLAG_SUPP_MOVED_MIGR     = 0x00000002;

const EXCHGID4_FLAG_BIND_PRINC_STATEID  = 0x00000100;

const EXCHGID4_FLAG_USE_NON_PNFS        = 0x00010000;
const EXCHGID4_FLAG_USE_PNFS_MDS        = 0x00020000;
const EXCHGID4_FLAG_USE_PNFS_DS         = 0x00040000;

const EXCHGID4_FLAG_MASK_PNFS           = 0x00070000;

const EXCHGID4_FLAG_UPD_CONFIRMED_REC_A = 0x40000000;
const EXCHGID4_FLAG_CONFIRMED_R         = 0x80000000;

struct state_protect_ops4 {
        bitmap4 spo_must_enforce;
        bitmap4 spo_must_allow;
};

struct ssv_sp_parms4 {
        state_protect_ops4      ssp_ops;
        sec_oid4                ssp_hash_algs&lt;>;
        sec_oid4                ssp_encr_algs&lt;>;
        uint32_t                ssp_window;
        uint32_t                ssp_num_gss_handles;
};

enum state_protect_how4 {
        SP4_NONE = 0,
        SP4_MACH_CRED = 1,
        SP4_SSV = 2
};

union state_protect4_a switch(state_protect_how4 spa_how) {
        case SP4_NONE:
                void;
        case SP4_MACH_CRED:
                state_protect_ops4      spa_mach_ops;
        case SP4_SSV:
                ssv_sp_parms4           spa_ssv_parms;
};

struct EXCHANGE_ID4args {
        client_owner4           eia_clientowner;
        uint32_t                eia_flags;
        state_protect4_a        eia_state_protect;
        nfs_impl_id4            eia_client_impl_id&lt;1>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_RESULT" title="RESULT">
<figure>
 <artwork>
struct ssv_prot_info4 {
 state_protect_ops4     spi_ops;
 uint32_t               spi_hash_alg;
 uint32_t               spi_encr_alg;
 uint32_t               spi_ssv_len;
 uint32_t               spi_window;
 gsshandle4_t           spi_handles&lt;>;
};

union state_protect4_r switch(state_protect_how4 spr_how) {
 case SP4_NONE:
         void;
 case SP4_MACH_CRED:
         state_protect_ops4     spr_mach_ops;
 case SP4_SSV:
         ssv_prot_info4         spr_ssv_info;
};

struct EXCHANGE_ID4resok {
 clientid4        eir_clientid;
 sequenceid4      eir_sequenceid;
 uint32_t         eir_flags;
 state_protect4_r eir_state_protect;
 server_owner4    eir_server_owner;
 opaque           eir_server_scope&lt;NFS4_OPAQUE_LIMIT>;
 nfs_impl_id4     eir_server_impl_id&lt;1>;
};

union EXCHANGE_ID4res switch (nfsstat4 eir_status) {
case NFS4_OK:
 EXCHANGE_ID4resok      eir_resok4;

default:
 void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_DESCRIPTION" title="DESCRIPTION">
    <t>
     The client uses the EXCHANGE_ID operation to register
     a particular client owner with the server.  The client
     ID returned from this operation will be necessary
     for requests that create state on the server and
     will serve as a parent object to sessions created
     by the client.  In order to confirm the client ID
     it must first be used, along with the returned
     eir_sequenceid, as arguments to CREATE_SESSION.
     If the flag EXCHGID4_FLAG_CONFIRMED_R is set in the result, eir_flags,
     then eir_sequenceid MUST be ignored, as it has no relevancy.
    </t>
    <t>
     EXCHANGE_ID MAY be sent in a COMPOUND procedure that starts with
     SEQUENCE. However, when a client communicates with a server
     for the first time, it will not have a session, so using
     SEQUENCE will not be possible.
     If EXCHANGE_ID is sent without a preceding SEQUENCE, then it
     MUST be the only operation in the COMPOUND procedure's request. If
     it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.
    </t>

    <t>
     The eia_clientowner field is composed of a co_verifier
     field and a co_ownerid string.  As noted in <xref
     target="Client_Identifiers" />, the co_ownerid
     describes the client, and the co_verifier is
     the incarnation of the client. An EXCHANGE_ID
     sent with a new incarnation of the client will
     lead to the server removing lock state of the old
     incarnation. Whereas an EXCHANGE_ID sent with the
     current incarnation and co_ownerid will result in
     an error or an update of the client ID's properties,
     depending on the arguments to EXCHANGE_ID.
    </t>
    <t>
     A server MUST NOT use the same client ID for two different incarnations of
     an eir_clientowner.
    </t>
    <t>
     In addition to the client ID and sequence ID, the server
     returns a server owner (eir_server_owner) and
     server scope (eir_server_scope).  The former field is used for
     network trunking as described in <xref
     target="Trunking" />.  The latter field is used to
     allow clients to determine when client IDs sent by
     one server may be recognized by another in the event
     of file system migration (see <xref
     target="transition_state" />).
    </t>
    <t>
     The client ID returned by EXCHANGE_ID is only unique
     relative to the combination of eir_server_owner.so_major_id
     and eir_server_scope. Thus, if two servers return the
     same client ID, the onus is on the client to
     distinguish the client IDs on the basis of eir_server_owner.so_major_id
     and eir_server_scope. In the event two different servers
     claim matching server_owner.so_major_id and eir_server_scope,
     the client can use the verification techniques discussed
     in <xref target="Trunking" /> to determine if the servers
     are distinct. If they are distinct, then the client
     will need to note the destination network addresses
     of the connections used with each server, and use
     the network address as the final discriminator.
    </t>
    <t>
     The server, as defined by the unique identity expressed
     in the so_major_id of the server owner and the server scope,
     needs to track several properties of each client ID it
     hands out. The properties apply to the client ID and all
     sessions associated with the client ID.
     The properties are derived from the
     arguments and results of EXCHANGE_ID.
     The client ID properties include:
     <list style="symbols">
     <t>
      The capabilities expressed by the following bits, which
      come from the results of EXCHANGE_ID:
        <list>
        <t>EXCHGID4_FLAG_SUPP_MOVED_REFER</t>
	<t>EXCHGID4_FLAG_SUPP_MOVED_MIGR    </t>
	<t>EXCHGID4_FLAG_BIND_PRINC_STATEID        </t>
	<t>EXCHGID4_FLAG_USE_NON_PNFS     </t>
	<t>EXCHGID4_FLAG_USE_PNFS_MDS   </t>
	<t>EXCHGID4_FLAG_USE_PNFS_DS     </t>
        </list>
        These properties may be updated by subsequent
        EXCHANGE_ID requests on confirmed client IDs though the server MAY
        refuse to change them.
     </t>
     <t>
       The state protection method used, one of SP4_NONE,
       SP4_MACH_CRED, or SP4_SSV, as set by the spa_how
       field of the arguments to EXCHANGE_ID.  Once the
       client ID is confirmed, this property cannot be
       updated by subsequent EXCHANGE_ID requests.

     </t>
     <t>
       For SP4_MACH_CRED or SP4_SSV state protection:
       <list>
       <t>
	 The list of operations (spo_must_enforce) that MUST use the specified
	 state protection. This list comes
	 from the results of EXCHANGE_ID.

       </t>
       <t>
	 The list of operations (spo_must_allow) that MAY use the specified
	 state protection. This list comes
	 from the results of EXCHANGE_ID.

       </t>
       </list>
       Once the client ID is confirmed, these properties
       cannot be updated by subsequent EXCHANGE_ID
       requests.

     </t>
     <t>
      For SP4_SSV protection:
      <list>
   
      <t>
       The OID of the hash algorithm. This property is
       represented by one of the algorithms in the
       ssp_hash_algs field of the EXCHANGE_ID arguments.
       Once the client ID is confirmed, this property
       cannot be updated by subsequent EXCHANGE_ID
       requests.

      </t>
      <t>
       The OID of the encryption algorithm. This property
       is represented by one of the algorithms in the
       ssp_encr_algs field of the EXCHANGE_ID arguments.
       Once the client ID is confirmed, this property
       cannot be updated by subsequent EXCHANGE_ID
       requests.

      </t>

      <t>
       The length of the SSV. This property is
       represented by the spi_ssv_len field in the EXCHANGE_ID
       results.

       Once the client ID is confirmed,
       this property cannot be updated by 
       subsequent EXCHANGE_ID requests.

	 <vspace blankLines='1' />

       There are REQUIRED and RECOMMENDED relationships among the
       length of the key of the encryption algorithm ("key length"), the length of the
       output of hash algorithm ("hash length"), and the length of the SSV ("SSV length").
       <list style="symbols">
       <t>
        key length MUST be &lt;= hash length. This is because the keys used for
        the encryption algorithm are actually subkeys derived from the SSV,
        and the derivation is via the hash algorithm. The selection of an
        encryption algorithm with a key length that exceeded the length of
        the output of the hash algorithm would require padding, and thus
        weaken the use of the encryption algorithm.
       </t>
       <t>
        hash length SHOULD be &lt;= SSV length. This is because the
        SSV is a key used to derive subkeys via an HMAC, and
        it is recommended that the key used as input to an HMAC be
        at least as long as the length of the HMAC's hash algorithm's
        output (see Section 3 of <xref target="RFC2104">RFC2104</xref>).
       </t>

       <t>
        key length SHOULD be &lt;= SSV length. This is a transitive result of the
        above two invariants.
       </t>

       <t>
        key length SHOULD be >= hash length / 2. This is because the subkey
        derivation is via 
        an HMAC and it is recommended that if the HMAC has to be truncated,
        it should not be truncated to less than half the hash length
        (see Section 4 of <xref target="RFC2104">RFC2104</xref>).
       </t>
       </list>
      </t>

      <t>
       Number of concurrent versions of the SSV the client
       and server will support (<xref target="ssv_mech"
       />). This property is represented by spi_window
       in the EXCHANGE_ID results.  The property may be
       updated by subsequent EXCHANGE_ID requests.

      </t>
      </list>
    </t>
    <t>
     The client's implementation ID as represented by
     the eia_client_impl_id field of the arguments.
     The property may be updated by subsequent EXCHANGE_ID
     requests.
    </t>
    <t>
     The server's implementation ID as represented by
     the eir_server_impl_id field of the reply.
     The property may be updated by replies to subsequent EXCHANGE_ID
     requests.
    </t>
    </list>
    </t>

    <t>
      The eia_flags passed as part of the arguments and
      the eir_flags results allow the client and server
      to inform each other of their capabilities as well
      as indicate how the client ID will be used. Whether
      a bit is set or cleared on the arguments' flags
      does not force the server to set or clear the same
      bit on the results' side.  Bits not defined above
      cannot be set in the eia_flags field.  If they
      are, the server MUST reject the operation with
      NFS4ERR_INVAL.

    </t>
    <t>
      The EXCHGID4_FLAG_UPD_CONFIRMED_REC_A bit can only be set
      in eia_flags; it is always off in eir_flags.
      The EXCHGID4_FLAG_CONFIRMED_R bit can only be set in
      eir_flags; it is always off in eia_flags.  If the
      server recognizes the co_ownerid and co_verifier
      as mapping to a confirmed client ID, it sets
      EXCHGID4_FLAG_CONFIRMED_R in eir_flags.
      The EXCHGID4_FLAG_CONFIRMED_R flag allows a client
      to tell if the client ID it is trying to create
      already exists and is confirmed.

    </t>

    <t>
      If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set in eia_flags,
      this means that the client is attempting to update properties
      of an existing confirmed client ID (if the client wants to
      update properties of an unconfirmed client ID, it MUST NOT
      set EXCHGID4_FLAG_UPD_CONFIRMED_REC_A).
      If so, it is
      RECOMMENDED that the client send the update EXCHANGE_ID
      operation in the same COMPOUND as a SEQUENCE so that
      the EXCHANGE_ID is executed exactly once. Whether
      the client can update the properties of client ID
      depends on the state protection it selected when the
      client ID was created, and the principal and security
      flavor it uses when sending the EXCHANGE_ID request.
      The situations described in items

      <xref target="case_update" format="counter"/>,

      <xref target="case_update_noent" format="counter"/>,

      <xref target="case_update_exist" format="counter"/>,

      or

      <xref target="case_update_perm" format="counter"/>

      of the second numbered list of <xref
      target="OP_EXCHANGE_ID_IMPLEMENTATION" /> will apply.
      Note that if the operation succeeds
      and returns a client ID that is already
      confirmed, the server MUST set the
      EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.


    </t>

    <t>
      If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set in eia_flags,
      this means that the client is trying to establish a new
      client ID; it is
      attempting to trunk data communication to
      the server (<xref target="Trunking" />); or it
      is attempting to update properties of an unconfirmed
      client ID. The
      situations described in
      items
	<xref target="case_new_owner_id" format="counter"/>,
	<xref target="case_non_update" format="counter"/>,
	<xref target="case_client_collision" format="counter"/>,
	<xref target="case_retry" format="counter"/>, or
	<xref target="case_client_restart" format="counter"/>

      of the second numbered list of <xref
      target="OP_EXCHANGE_ID_IMPLEMENTATION" /> will apply.
      Note that if the operation succeeds
      and returns a client ID that was previously
      confirmed, the server MUST set the
      EXCHGID4_FLAG_CONFIRMED_R bit in eir_flags.

    </t>
    
    <t>
      When the EXCHGID4_FLAG_SUPP_MOVED_REFER flag bit
      is set, the client indicates that it is capable
      of dealing with an NFS4ERR_MOVED error as part of
      a referral sequence.  When this bit is not set, it
      is still legal for the server to perform a referral
      sequence.  However, a server may use the fact that
      the client is incapable of correctly responding
      to a referral, by avoiding it for that particular
      client.  It may, for instance, act as a proxy
      for that particular file system, at some cost in
      performance, although it is not obligated to do so.
      If the server will potentially perform a referral, it
      MUST set EXCHGID4_FLAG_SUPP_MOVED_REFER in eir_flags.

    </t>
    <t>
      When the EXCHGID4_FLAG_SUPP_MOVED_MIGR is set,
      the client indicates that it is capable of dealing
      with an NFS4ERR_MOVED error as part of a file system
      migration sequence.  When this bit is not set, it
      is still legal for the server to indicate that a
      file system has moved, when this in fact happens.
      However, a server may use the fact that the client
      is incapable of correctly responding to a migration
      in its scheduling of file systems to migrate so as to
      avoid migration of file systems being actively used.
      It may also hide actual migrations from clients
      unable to deal with them by acting as a proxy for a
      migrated file system for particular clients, at some
      cost in performance, although it is not obligated
      to do so.  If the server will potentially perform a
      migration, it MUST set EXCHGID4_FLAG_SUPP_MOVED_MIGR
      in eir_flags.

    </t>
    <t>
      When EXCHGID4_FLAG_BIND_PRINC_STATEID is set, the
      client indicates that it wants the server to bind the
      stateid to the principal. This means that when a
      principal creates a stateid, it has to be the one to
      use the stateid. If the server will perform binding,
      it will return EXCHGID4_FLAG_BIND_PRINC_STATEID. The
      server MAY return EXCHGID4_FLAG_BIND_PRINC_STATEID
      even if the client does not request it. If
      an update to the client ID changes the value
      of EXCHGID4_FLAG_BIND_PRINC_STATEID's client
      ID property, the effect applies only to new
      stateids. Existing stateids (and all stateids with
      the same "other" field) that were created with
      stateid to principal binding in force will continue
      to have binding in force.  Existing stateids (and all
      stateids with the same "other" field) that were created
      with stateid to principal not in force will continue
      to have binding not in force.

    </t>

    <t>
     The EXCHGID4_FLAG_USE_NON_PNFS,
     EXCHGID4_FLAG_USE_PNFS_MDS,  and
     EXCHGID4_FLAG_USE_PNFS_DS bits are described in <xref
     target="pnfs_session_stuff" /> and convey roles the
     client ID is to be used for in a pNFS environment.
     The server MUST set one of the acceptable combinations
     of these bits (roles) in eir_flags, as specified in <xref
     target="pnfs_session_stuff" />.
     Note that the same client owner/server owner pair can
     have multiple roles. Multiple roles can be associated
     with the same client ID or with different client
     IDs. Thus, if a client sends EXCHANGE_ID from the
     same client owner to the same server owner multiple
     times, but specifies different pNFS roles each time,
     the server might return different client IDs. Given
     that different pNFS roles might have different client
     IDs, the client may ask for different properties for
     each role/client ID.

    </t>

    <t>
     The spa_how field of the eia_state_protect field
     specifies how the client wants to protect its client,
     locking, and session states from unauthorized changes
     (<xref target="protect_state_change"/>):

     <list style="symbols">
     <t>
      SP4_NONE. The client does not request the NFSv4.1 server
      to enforce state protection. The NFSv4.1 server MUST NOT
      enforce state protection for the returned client ID.
     </t>
     <t>
      SP4_MACH_CRED.  If spa_how is SP4_MACH_CRED, then
      the client MUST send the EXCHANGE_ID request with RPCSEC_GSS
      as the security flavor, and with a service of
      RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY. If SP4_MACH_CRED
      is specified, then the
      client wants to use an RPCSEC_GSS-based machine
      credential to protect its state. The server MUST note
      the principal the EXCHANGE_ID operation was sent
      with, and the GSS mechanism used.  These notes
      collectively comprise the machine credential.

	 <vspace blankLines='1' />

      After the client ID is confirmed, as long as the lease associated with
      the client ID is unexpired, a subsequent EXCHANGE_ID
      operation that uses the same eia_clientowner.co_owner
      as the first EXCHANGE_ID MUST also use the same
      machine credential as the first EXCHANGE_ID. The
      server returns the same client ID for
      the subsequent EXCHANGE_ID as that returned from
      the first EXCHANGE_ID.

     </t>
     <t>
      SP4_SSV. If spa_how is SP4_SSV, then
      the client MUST send the EXCHANGE_ID request with RPCSEC_GSS
      as the security flavor, and with a service of
      RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY.
      If SP4_SSV is specified, then
      the client wants to use the SSV to protect its state.
      The server records the credential used in the request
      as the machine credential (as defined above) for
      the eia_clientowner.co_owner.
      The CREATE_SESSION operation that
      confirms the client ID MUST use the same machine
      credential.

     </t>
     </list>
     </t>
     <t>
     When a client specifies SP4_MACH_CRED or SP4_SSV,
     it also provides two lists of operations (each
     expressed as a bitmap).  The first list
     is spo_must_enforce and consists of those operations
     the client MUST send (subject to the server confirming the
     list of operations in the result of EXCHANGE_ID) with the
     machine credential (if SP4_MACH_CRED protection is
     specified) or the SSV-based credential (if SP4_SSV
     protection is used).  The client MUST send the
     operations with RPCSEC_GSS credentials that specify
     the RPC_GSS_SVC_INTEGRITY or RPC_GSS_SVC_PRIVACY
     security service.  Typically, the first list of
     operations includes EXCHANGE_ID, CREATE_SESSION,
     DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION,
     and DESTROY_CLIENTID.  The client SHOULD NOT specify
     in this list any operations that require a filehandle
     because the server's access policies MAY conflict with
     the client's choice, and thus the client would then be
     unable to access a subset of the server's namespace.

     </t>
     <t>

     Note that if SP4_SSV protection is specified, and
     the client indicates that CREATE_SESSION must be
     protected with SP4_SSV, because the SSV cannot exist
     without a confirmed client ID, the first CREATE_SESSION
     MUST instead be sent using the machine credential,
     and the server MUST accept the machine credential.

     </t>
     <t>

     There is a corresponding result, also called spo_must_enforce,
     of the operations for which the server will require SP4_MACH_CRED or
     SP4_SSV protection. Normally, the server's result
     equals the client's argument, but the result MAY be different.
     If the client requests one or more operations in
     the set { EXCHANGE_ID, CREATE_SESSION,
     DELEGPURGE, DESTROY_SESSION, BIND_CONN_TO_SESSION,
     DESTROY_CLIENTID }, then the result spo_must_enforce
     MUST include the operations the client requested from that set.

     </t>
     <t>
     If spo_must_enforce in the results has BIND_CONN_TO_SESSION
     set, then connection binding enforcement is enabled, and
     the client MUST use the machine (if SP4_MACH_CRED protection is used)
     or SSV (if SP4_SSV protection is used) credential on calls
     to BIND_CONN_TO_SESSION.

     </t>
     <t>
     The second list is spo_must_allow and consists of those
     operations
     the client wants to have the option of sending with the machine credential or
     the SSV-based credential, even if the object the
     operations are performed on is not owned by the
     machine or SSV credential.

     </t>
     <t>

     The corresponding result, also called
     spo_must_allow, consists of the operations the server
     will allow the client to use SP4_SSV or SP4_MACH_CRED
     credentials with.
     Normally, the server's result
     equals the client's argument, but the result MAY be different.

     </t>
     <t>

     The purpose of spo_must_allow is to allow clients to
     solve the following conundrum. Suppose the client ID
     is confirmed with EXCHGID4_FLAG_BIND_PRINC_STATEID,
     and it calls OPEN with the RPCSEC_GSS credentials of
     a normal user. Now suppose the user's credentials expire,
     and cannot be renewed (e.g., a Kerberos ticket granting ticket
     expires, and the user has logged off and will not be
     acquiring a new ticket granting ticket). The client will be
     unable to send CLOSE without the user's credentials, which is to
     say the client has to either leave the state on the server
     or re-send EXCHANGE_ID with a new verifier to
     clear all state, that is, unless the client includes
     CLOSE on the list of operations in spo_must_allow and the
     server agrees.

     </t>
    <t>
     The SP4_SSV protection parameters also have:
     <list style="hanging">

     <t hangText="ssp_hash_algs:" />
     <t>
       This is the set of algorithms the client supports
       for the purpose of computing the digests needed for
       the internal SSV GSS mechanism and for the SET_SSV
       operation.  Each algorithm is specified as an object
       identifier (OID).  The REQUIRED algorithms for a
       server are id-sha1, id-sha224, id-sha256, id-sha384,
       and id-sha512 <xref target="RFC4055"/>.
       The algorithm the server selects among the
       set is indicated in spi_hash_alg, a field of
       spr_ssv_prot_info. The field spi_hash_alg is an
       index into the array ssp_hash_algs. 

       If the server
       does not support any of the offered algorithms,
       it returns NFS4ERR_HASH_ALG_UNSUPP.

       If ssp_hash_algs is empty, the server MUST return NFS4ERR_INVAL.

     </t>
     <t hangText="ssp_encr_algs:" />
     <t>
       This is the set of algorithms the client supports for the
       purpose of providing privacy protection for the internal
       SSV GSS mechanism.  Each algorithm is
       specified as an OID.
       The REQUIRED algorithm for a server is id-aes256-CBC.
       The RECOMMENDED algorithms are id-aes192-CBC and id-aes128-CBC
       <xref target="CSOR_AES" />. The selected algorithm is
       returned in spi_encr_alg, an index into ssp_encr_algs.

       If the server
       does not support any of the offered algorithms,
       it returns NFS4ERR_ENCR_ALG_UNSUPP.

       If ssp_encr_algs is empty, the server MUST return NFS4ERR_INVAL.

       Note that due to previously stated requirements and recommendations
       on the relationships between key length and hash length, some
       combinations of RECOMMENDED and REQUIRED encryption algorithm and
       hash algorithm either SHOULD NOT or MUST NOT be used.
       <xref target="algtbl"/> summarizes the illegal and discouraged
       combinations.

     </t>
     <t hangText="ssp_window:" />
     <t>
       This is the number of SSV versions the client wants
       the server to maintain (i.e., each successful call to SET_SSV
       produces a new version of the SSV). If ssp_window is zero, the
       server MUST return NFS4ERR_INVAL. The server responds
       with spi_window, which MUST NOT exceed ssp_window, and MUST 
       be at least one.
       Any requests on the backchannel or fore channel that
       are using a version of the SSV that is outside the window will fail with
       an ONC RPC authentication error, and the requester
       will have to retry them with the same slot ID and
       sequence ID.
     </t>

     <t hangText="ssp_num_gss_handles:" />
     <t>
       This is the number of RPCSEC_GSS handles the
       server should create that are based on the GSS
       SSV mechanism (<xref target="ssv_mech" />).
       It is not the total number of RPCSEC_GSS handles for
       the client ID. Indeed, subsequent calls to EXCHANGE_ID
       will add RPCSEC_GSS handles.
       The server responds with a list of handles in
       spi_handles. If the client asks for at least
       one handle and the server cannot create it,
       the server MUST return an error.  The handles in
       spi_handles are not available for use until the
       client ID is confirmed, which could be immediately
       if EXCHANGE_ID returns EXCHGID4_FLAG_CONFIRMED_R,
       or upon successful confirmation from CREATE_SESSION.
		 <vspace blankLines='1' />
       While a client ID can span all the connections
       that are connected to a server sharing the same
       eir_server_owner.so_major_id, the RPCSEC_GSS
       handles returned in spi_handles can only be used
       on connections connected to a server that returns
       the same the eir_server_owner.so_major_id and
       eir_server_owner.so_minor_id on each connection.
       It is permissible for the client to set
       ssp_num_gss_handles to zero; the client can
       create more handles with another EXCHANGE_ID call.
		 <vspace blankLines='1' />
       Because each SSV RPCSEC_GSS handle shares a common SSV GSS context,
       there are security considerations specific to this situation
       discussed in <xref target="rpcsec_ssv_consider"/>.
		 <vspace blankLines='1' />
       The seq_window (see Section 5.2.3.1 of <xref target="RFC2203">RFC2203</xref>)
       of each RPCSEC_GSS handle in spi_handle MUST be the same as the seq_window of
       the RPCSEC_GSS handle used for the credential of the RPC request
       that the EXCHANGE_ID request was sent with.

     </t>
      
     </list>
     
    </t>
      <texttable anchor='algtbl'>
	      <ttcol align='left'>Encryption Algorithm</ttcol>
	      <ttcol align='left'>MUST NOT be combined with</ttcol>
	      <ttcol align='left'>SHOULD NOT be combined with</ttcol>
	      <c>id-aes128-CBC</c> <c></c> <c>id-sha384, id-sha512</c>
	      <c>id-aes192-CBC</c> <c>id-sha1</c> <c>id-sha512</c>
	      <c>id-aes256-CBC</c> <c>id-sha1, id-sha224</c> <c></c>
      </texttable>

    <t>
      The arguments include an array of up to one
      element in length called eia_client_impl_id. If
      eia_client_impl_id is present, it contains the
      information identifying the implementation of the
      client. Similarly, the results include an array of up
      to one element in length called eir_server_impl_id
      that identifies the implementation of the server.
      Servers MUST accept a zero-length eia_client_impl_id
      array, and clients MUST accept a zero-length
      eir_server_impl_id array.
   
    </t>
    <t>
      An example use for implementation identifiers
      would be diagnostic software that extracts
      this information in an attempt to identify
      interoperability problems, performance workload
      behaviors, or general usage statistics.  Since the
      intent of having access to this information is for
      planning or general diagnosis only, the client and
      server MUST NOT interpret this implementation
      identity information in a way that affects
      interoperational behavior of the implementation.
      The reason is that if clients and servers did such
      a thing, they might use fewer capabilities of the
      protocol than the peer can support, or the client
      and server might refuse to interoperate.

    </t>
    <t>
      Because it is possible that some implementations will
      violate the protocol specification and interpret
      the identity information, implementations MUST
      allow the users of the NFSv4 client and server to
      set the contents of the sent nfs_impl_id structure
      to any value.

    </t>

  </section>
  <section toc="exclude" anchor="OP_EXCHANGE_ID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A server's client record is a 5-tuple:
    </t>
    <t>
      <list style="numbers">
	<t>co_ownerid
	<list style="empty">
	  <t>The client identifier string, from the eia_clientowner
	  structure of the EXCHANGE_ID4args structure.</t>
	</list></t>

	<t>co_verifier:
	<list style="empty">
	  <t>A client-specific value used to indicate incarnations (where a client restart represents a new incarnation), from the
	  eia_clientowner structure of the EXCHANGE_ID4args
	  structure.</t>
	</list></t>

	<t>principal:
	<list style="empty">
	  <t>
           The principal that was defined in the RPC header's credential
           and/or verifier at the time the client record was
           established.
         </t>
	</list></t>

	<t>client ID:
	<list style="empty">
	  <t>The shorthand client identifier, generated by the server and
	  returned via the eir_clientid field in the EXCHANGE_ID4resok
	  structure.</t>
	</list></t>

	<t>confirmed:
	<list style="empty">
	  <t>A private field on the server indicating whether or not a
	  client record has been confirmed.  A client record is
	  confirmed if there has been a successful CREATE_SESSION
	  operation to confirm it.  Otherwise, it is unconfirmed.  An
	  unconfirmed record is established by an EXCHANGE_ID call.
	  Any unconfirmed record that is not confirmed within a lease
	  period SHOULD be removed.</t>
	</list></t>
	
      </list>
    </t>
    <!-- start new list -->
    <t>
      The following identifiers represent special values for the fields
      in the records.
      <list style="hanging">
	<t hangText="ownerid_arg:"/>
	<t>
	  The value of the eia_clientowner.co_ownerid subfield of the
	  EXCHANGE_ID4args structure of the current request.
	</t>
	<t hangText="verifier_arg:"/>
	<t>
	  The value of the eia_clientowner.co_verifier subfield of the
	  EXCHANGE_ID4args structure of the current request.
	</t>
	<t hangText="old_verifier_arg:"/>
	<t>
	  A value of the eia_clientowner.co_verifier field of a client record
	  received in a previous request; this is distinct from
	  verifier_arg.
	</t>
	<t hangText="principal_arg:"/>
	<t>
	  The value of the RPCSEC_GSS principal for the current request.
	</t>
	<t hangText="old_principal_arg:"/>
	<t>
	  A value of the principal of a client record as defined by the
          RPC header's credential or verifier of a previous request.
	  This is distinct from principal_arg.
	 
	</t>
	<t hangText="clientid_ret:"/>
	<t>
	  The value of the eir_clientid field the server will return in the
	  EXCHANGE_ID4resok structure for the current request.
	</t>
	<t hangText="old_clientid_ret:"/>
	<t>
	  The value of the eir_clientid field the server returned in the
	  EXCHANGE_ID4resok structure for a previous request.  This
	  is distinct from clientid_ret.
	</t>
	<t hangText="confirmed:"/>
	<t>
          The client ID has been confirmed.
	</t>
	<t hangText="unconfirmed:"/>
	<t>
          The client ID has not been confirmed.
	</t>
      </list>
    </t>
    <t>
      Since EXCHANGE_ID is a non-idempotent operation, we must
      consider the possibility that retries occur as a result of a
      client restart, network partition, malfunctioning router, etc.
      Retries are identified by the value of the eia_clientowner field of
      EXCHANGE_ID4args, and the method for dealing with them is
      outlined in the scenarios below.
    </t>
    <t>
      The scenarios are described in terms of the
      client record(s) a server has for a given
      co_ownerid. Note that if the client ID
      was created specifying SP4_SSV state protection and
      EXCHANGE_ID as the one of the operations in spo_must_allow,
      then the server MUST authorize EXCHANGE_IDs with the SSV
      principal in addition to the principal that created the
      client ID.
    </t>
    <t anchor="case_list">
      <list style="numbers">
	<t anchor="case_new_owner_id">New Owner ID
	<list style="empty">
	  <t>
	    If the server has no client records
	    with eia_clientowner.co_ownerid matching
	    ownerid_arg, and EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not
	    set in the EXCHANGE_ID, then a new shorthand
	    client ID (let us call it clientid_ret)
	    is generated, and the following unconfirmed
	    record is added to the server's state.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

	    Subsequently, the server returns clientid_ret.

		 <vspace blankLines='1' />

	  </t>
	</list>
		 <vspace blankLines='1' />
	</t>

	<t anchor="case_non_update">Non-Update on Existing Client ID
	<list style="empty">
	  <t>
	    If the server has the following confirmed record, and
            the request does not have
	    EXCHGID4_FLAG_UPD_CONFIRMED_REC_A set,
	    then the request is the result of a retried request due to a
	    faulty router or lost connection, or
            the client is trying to determine if it can perform
            trunking.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    Since the record has been confirmed, the client
	    must have received the server's reply from
	    the initial EXCHANGE_ID request. Since the
	    server has a confirmed record, and since
	    EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, with the
            possible exception of eir_server_owner.so_minor_id, the
	    server returns the same result it did when
	    the client ID's properties were last updated
	    (or if never updated, the result when the
	    client ID was created). The confirmed record
            is unchanged.
	  </t>
	</list>
	</t>

	<t anchor="case_client_collision">Client Collision
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and
	    if the server has the following confirmed
	    record, then this request is likely the result
	    of a chance collision between the values of
	    the eia_clientowner.co_ownerid subfield of
	    EXCHANGE_ID4args for two different clients.

	  </t>
	  <t>
      
	    { ownerid_arg, *, old_principal_arg, old_clientid_ret, confirmed }
	  </t>
	  <t>
            If there is currently no state associated with old_clientid_ret,
            or if there is state but the lease has expired, then
            this case is effectively equivalent to the
            New Owner ID case of <xref target="case_new_owner_id"/>.
            The confirmed record is deleted, the old_clientid_ret and its
            lock state are deleted, 
	    a new shorthand client ID
	    is generated, and the following unconfirmed
	    record is added to the server's state.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

	    Subsequently, the server returns clientid_ret.

		 <vspace blankLines='1' />
	  </t>
          <t>
            If old_clientid_ret has an unexpired lease with state, then
	    no state of old_clientid_ret is changed or deleted.
            The server returns NFS4ERR_CLID_INUSE
	    to indicate that the client should
	    retry with a different value for the
	    eia_clientowner.co_ownerid subfield of
	    EXCHANGE_ID4args. The client record is not changed.
	  </t>
	</list>
	</t>

	<t anchor="case_retry">Replacement of Unconfirmed Record
	<list style="empty">
	  <t>
            If the EXCHGID4_FLAG_UPD_CONFIRMED_REC_A flag is not set,
	    and the server has the following unconfirmed record, then
            the client is attempting EXCHANGE_ID again on an
            unconfirmed client ID, perhaps due to a retry, a client
            restart before client ID confirmation (i.e., 
            before CREATE_SESSION was called), or
            some other reason.

		 <vspace blankLines='1' />

	    { ownerid_arg, *, *, old_clientid_ret, unconfirmed }

		 <vspace blankLines='1' />

            It is possible that
            the properties of old_clientid_ret are
            different than those specified in the current
            EXCHANGE_ID. Whether or not the properties are being updated,
            to eliminate ambiguity, the server
            deletes the unconfirmed record, generates a
            new client ID (clientid_ret), and establishes
            the following unconfirmed record:

		 <vspace blankLines='1' />

	    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }
		 <vspace blankLines='1' />
	  </t>
	</list>
	</t>

	<t anchor="case_client_restart">Client Restart
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is not set, and
	    if the server has the following confirmed client record, then
	    this request is likely from a previously confirmed client
	    that has restarted.
	  </t>
	  <t>
	    { ownerid_arg, old_verifier_arg, principal_arg, old_clientid_ret, confirmed }
	  </t>
	  <t>
	    Since the previous incarnation of the same
	    client will no longer be making requests,
	    once the new client ID is confirmed by
	    CREATE_SESSION, byte-range locks and share reservations
	    should be released immediately rather than
	    forcing the new incarnation to wait for
	    the lease time on the previous incarnation
	    to expire.	Furthermore, session state should
	    be removed since if the client had maintained
	    that information across restart, this request
	    would not have been sent.  If the server
	    supports neither the CLAIM_DELEGATE_PREV
            nor CLAIM_DELEG_PREV_FH
	    claim types, associated delegations should be
	    purged as well; otherwise, delegations are
	    retained and recovery proceeds according to
	    <xref target="delegation_recovery"/>.

	  </t>
	  <t>
	    After processing, clientid_ret is returned to the client and
	    this client record is added:
	  </t>
	  <t>
	    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, unconfirmed }
		 <vspace blankLines='1' />
	  </t>
          <t>
	    The previously described confirmed record
	    continues to exist, and thus the same
	    ownerid_arg exists in both a confirmed and
	    unconfirmed state at the same time. The number
	    of states can collapse to one once the server
	    receives an applicable CREATE_SESSION or
	    EXCHANGE_ID.

            <list style='symbols'>

            <t>
	     If the server subsequently receives a successful
	     CREATE_SESSION that confirms clientid_ret,
	     then the server atomically destroys the
	     confirmed record and makes the unconfirmed
	     record confirmed as described in <xref
	     target="OP_CREATE_SESSION_IMPLEMENTATION" />.

            </t>

            <t>
	     If the server instead subsequently receives
	     an EXCHANGE_ID with the client owner equal
	     to ownerid_arg, one strategy is to simply
	     delete the unconfirmed record, and process the
	     EXCHANGE_ID as described in the entirety of
	     <xref target="OP_EXCHANGE_ID_IMPLEMENTATION"
	     />.

            </t>

	    </list>

          </t>
	</list>
	</t>

	<t anchor="case_update">Update
	<list style="empty">
	  <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an attempt at an update.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    Since the record has been confirmed, the client must have
	    received the server's reply from the initial EXCHANGE_ID
	    request. The server allows the update, and the client record
            is left intact.
	  </t>
	</list>
	</t>

	<t anchor="case_update_noent">Update but No Confirmed Record
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
            server has no confirmed record corresponding ownerid_arg,
            then the server returns NFS4ERR_NOENT and leaves any unconfirmed
            record intact.
          </t>
	</list>
	</t>

	<t anchor="case_update_exist">Update but Wrong Verifier
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an illegal attempt at an
	    update, perhaps because of a retry from a previous client
            incarnation.

		 <vspace blankLines='1' />

    { ownerid_arg, old_verifier_arg, *, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    The server returns NFS4ERR_NOT_SAME and leaves the client record
            intact.
          </t>
	</list>
	</t>

	<t anchor="case_update_perm">Update but Wrong Principal
	<list style="empty">
          <t>
	    If EXCHGID4_FLAG_UPD_CONFIRMED_REC_A is set, and the
	    server has the following confirmed record,
	    then this request is an illegal attempt at an
	    update by an unauthorized principal.

		 <vspace blankLines='1' />

    { ownerid_arg, verifier_arg, old_principal_arg, clientid_ret, confirmed }

		 <vspace blankLines='1' />

	    The server returns NFS4ERR_PERM and leaves the client record
            intact.
          </t>
	</list>
	</t>

      </list>
    </t>

  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $         -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CREATE_SESSION" title="Operation 43: CREATE_SESSION - Create New Session and Confirm Client ID" >

  <section toc="exclude" anchor="OP_CREATE_SESSION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct channel_attrs4 {
        count4                  ca_headerpadsize;
        count4                  ca_maxrequestsize;
        count4                  ca_maxresponsesize;
        count4                  ca_maxresponsesize_cached;
        count4                  ca_maxoperations;
        count4                  ca_maxrequests;
        uint32_t                ca_rdma_ird&lt;1>;
};

const CREATE_SESSION4_FLAG_PERSIST              = 0x00000001;
const CREATE_SESSION4_FLAG_CONN_BACK_CHAN       = 0x00000002;
const CREATE_SESSION4_FLAG_CONN_RDMA            = 0x00000004;

struct CREATE_SESSION4args {
        clientid4               csa_clientid;
        sequenceid4             csa_sequence;

        uint32_t                csa_flags;

        channel_attrs4          csa_fore_chan_attrs;
        channel_attrs4          csa_back_chan_attrs;

        uint32_t                csa_cb_program;
        callback_sec_parms4     csa_sec_parms&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
struct CREATE_SESSION4resok {
        sessionid4              csr_sessionid;
        sequenceid4             csr_sequence;

        uint32_t                csr_flags;

        channel_attrs4          csr_fore_chan_attrs;
        channel_attrs4          csr_back_chan_attrs;
};

union CREATE_SESSION4res switch (nfsstat4 csr_status) {
case NFS4_OK:
        CREATE_SESSION4resok    csr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used by the client to create new session objects
      on the server.
    </t>
    <t>
      CREATE_SESSION can be sent with or without a preceding SEQUENCE
      operation in the same COMPOUND procedure.
      If CREATE_SESSION is sent with a preceding SEQUENCE 
      operation,
      any session created by CREATE_SESSION has no direct
      relation to the session specified in the SEQUENCE operation, although
      the two sessions might be associated with the same client ID.
      If CREATE_SESSION is sent without a preceding SEQUENCE, then it
      MUST be the only operation in the COMPOUND procedure's request. If
      it is not, the server MUST return NFS4ERR_NOT_ONLY_OP.
    </t>
    <t>
     In addition to creating a session, CREATE_SESSION has the following
     effects:
      <list style="symbols">
      <t>
        The first session created with a new
        client ID serves to confirm the
        creation of that
        client's state on the server. The server returns the parameter
        values for the new session.
      </t>
      <t>
        The connection CREATE_SESSION that is sent over is associated with the
        session's fore channel.
      </t>
      </list>
     </t>
     <t>
      The arguments and results of CREATE_SESSION are described as follows:
      <list style="hanging">
        <t hangText="csa_clientid:"/>
        <t>
          This is the client ID with which the new session will be associated.
          The corresponding result is csr_sessionid, the session ID
          of the new session.
        </t>
        <t hangText="csa_sequence:"/>
        <t>
         Each client ID serializes CREATE_SESSION via a per-client ID
         sequence number (see
          <xref target="OP_CREATE_SESSION_IMPLEMENTATION" />).
         The corresponding result is csr_sequence, which MUST be equal to
         csa_sequence.
        </t>
      </list>
      </t>
      <t>
 
       In the next three arguments, the client offers a value
       that is to be a property of the session. Except where
       stated otherwise, it is RECOMMENDED that
       the server accept the value.
       If it is not acceptable, the server MAY use a different value.
       Regardless, the server MUST return the value the session will
       use (which will be either what the client offered, or what
       the server is insisting on) to the client.
      <list style="hanging">

        <t hangText="csa_flags:"/>
        <t>
          The csa_flags field contains a list of the following flag
          bits:
          <list style="hanging">
          <t hangText="CREATE_SESSION4_FLAG_PERSIST:"/>
          <t>
	    If CREATE_SESSION4_FLAG_PERSIST is set, the client
	    wants the server to provide a persistent reply cache.
	    For sessions in which only idempotent operations
	    will be used (e.g., a read-only session), clients
	    SHOULD NOT set CREATE_SESSION4_FLAG_PERSIST.  If
	    the server does not or cannot provide a persistent reply cache,
	    the server MUST NOT set CREATE_SESSION4_FLAG_PERSIST in
            the field csr_flags.

	    <vspace blankLines='1' />
 
            If the server is a pNFS metadata server, for
            reasons described in <xref target="obtaining_layout" />
            it SHOULD support CREATE_SESSION4_FLAG_PERSIST if it
            supports the layout_hint (<xref target="attrdef_layout_hint" />)
            attribute.

          </t>
	  <t hangText="CREATE_SESSION4_FLAG_CONN_BACK_CHAN:"/>
	  <t>
	     If CREATE_SESSION4_FLAG_CONN_BACK_CHAN is set in csa_flags,
	     the client is requesting that the connection over which the
	     CREATE_SESSION operation arrived be associated with the session's
	     backchannel in addition to its fore channel.
	     If the server agrees, it
	     sets CREATE_SESSION4_FLAG_CONN_BACK_CHAN
	     in the result field csr_flags. If
	     CREATE_SESSION4_FLAG_CONN_BACK_CHAN is not set in csa_flags,
	     then CREATE_SESSION4_FLAG_CONN_BACK_CHAN MUST NOT be set
	     in csr_flags.

	  </t>
	  <t hangText="CREATE_SESSION4_FLAG_CONN_RDMA:"/>
	  <t>
	     If CREATE_SESSION4_FLAG_CONN_RDMA is set in csa_flags,
             and if the connection over which the CREATE_SESSION operation
             arrived
	     is currently in non-RDMA mode but
	     has the capability to operate in RDMA mode, then the client
	     is requesting that the server "step up" to RDMA mode
	     on the connection.
	     If the server agrees, it sets
             CREATE_SESSION4_FLAG_CONN_RDMA in the result
             field csr_flags. If CREATE_SESSION4_FLAG_CONN_RDMA is
	     not set in csa_flags, then CREATE_SESSION4_FLAG_CONN_RDMA MUST
             NOT be set in csr_flags.
	     Note that once the server agrees to step up, it and the client
	     MUST exchange all future traffic on the connection with RPC RDMA
	     framing and not Record Marking (<xref target="RPCRDMA" />).
	  </t>
          </list>
        </t>
        <t hangText="csa_fore_chan_attrs, csa_fore_chan_attrs:"/>
        <t>
          The csa_fore_chan_attrs and csa_back_chan_attrs
          fields apply to attributes of the
          fore channel (which conveys
          requests originating from the client to the server),
          and the backchannel (the channel that conveys
          callback requests originating from the
          server to the client), respectively. The results are in corresponding structures
          called csr_fore_chan_attrs and csr_back_chan_attrs.
          The results establish attributes for each channel, and
          on all subsequent use of each channel of the session.

          Each structure has the following fields:
          <list style="hanging">
	  <t hangText="ca_headerpadsize:"/>
	  <t>
	    The maximum amount of padding the requester is willing to apply
	    to ensure that write payloads are aligned on some boundary at
	    the replier.  For each channel, the server
            <list style="symbols">

            <t>
             will reply in ca_headerpadsize with
	     its preferred value,
	     or zero if padding is not in use, and
            </t>

            <t>
             MAY decrease this value but MUST NOT increase it.
            </t>
            </list>
	  </t>
          <t hangText="ca_maxrequestsize:"/>
          <t>
            The maximum size of a COMPOUND or CB_COMPOUND request that
            will be sent. This size represents the XDR encoded size of
            the request, including the RPC headers (including
            security flavor credentials and verifiers)
            but excludes any RPC transport framing headers.
            Imagine a request coming over a non-RDMA TCP/IP connection, and
            that it has a single Record Marking header preceding
            it. The maximum allowable
            count encoded in the header will be
            ca_maxrequestsize. If a requester sends
            a request that exceeds ca_maxrequestsize, the error
            NFS4ERR_REQ_TOO_BIG will be returned per the description in
            <xref target="COMPOUND_Sizing_Issues" />.

            For each channel,
            the server MAY decrease this value but MUST NOT increase it.

          </t>
          <t hangText="ca_maxresponsesize:"/>
          <t>
            The maximum size of a COMPOUND or CB_COMPOUND reply that
            the requester will
            accept from the replier including RPC headers (see
            the ca_maxrequestsize definition).

            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.

            However, if the client selects a value for
            ca_maxresponsesize such that a replier on a channel could
            never send a response, the server SHOULD return
            NFS4ERR_TOOSMALL in the CREATE_SESSION reply.
            After the session is created, if a requester sends a
            request for which the size of the reply would exceed
            this value, the replier will return NFS4ERR_REP_TOO_BIG,
            per the description in
            <xref target="COMPOUND_Sizing_Issues" />.
          </t>
          <t hangText="ca_maxresponsesize_cached:"/>
          <t>
            Like ca_maxresponsesize, but the maximum size of a reply
            that will be stored in the reply cache
            (<xref target="Slot_Identifiers_and_Server_Reply_Cache" />).

            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.

            If, in the reply to CREATE_SESSION, the value of
            ca_maxresponsesize_cached of a channel is less than the value
            of ca_maxresponsesize of the same channel, then this is an
            indication to the requester that it needs to be selective
            about which replies it directs the replier to cache; for
            example, large replies from nonidempotent operations (e.g.,
            COMPOUND requests with a READ operation) should not be
            cached. The requester decides which replies to cache via an
            argument to the SEQUENCE (the sa_cachethis field, see <xref
            target="OP_SEQUENCE" />) or CB_SEQUENCE (the csa_cachethis
            field, see <xref target="OP_CB_SEQUENCE" />) operations.

            After the session is created, if a requester sends a
            request for which the size of the reply would exceed
            ca_maxresponsesize_cached, the replier will return
            NFS4ERR_REP_TOO_BIG_TO_CACHE, per the description in <xref
            target="COMPOUND_Sizing_Issues" />.

          </t>
          <t hangText="ca_maxoperations:"/>
          <t>
            The maximum number of operations the replier
            will accept in a COMPOUND or CB_COMPOUND.

            For the backchannel, the server MUST NOT change the value the
            client offers. For the fore channel, the server
            MAY change the requested value.

            After the session is created, if a requester sends a
            COMPOUND or CB_COMPOUND
            with more operations than ca_maxoperations,
            the replier MUST return NFS4ERR_TOO_MANY_OPS.

          </t>
          <t hangText="ca_maxrequests:"/>
          <t>
            The maximum number of concurrent COMPOUND or CB_COMPOUND
            requests the requester will send on the session.  Subsequent
            requests will each be assigned a slot identifier by the requester
            within the range zero to ca_maxrequests - 1 inclusive.

            For the backchannel, the server MUST NOT change the value the
            client offers. For the fore channel, the server
            MAY change the requested value.

          </t>
          <t hangText="ca_rdma_ird:"/>
          <t>
            This array has a maximum of one element. 
            If this array has one element, then the element contains the
            inbound RDMA read queue depth (IRD).
            For each channel, the server MAY decrease this value, but MUST
            NOT increase it.
          </t>
          </list>
        </t>
        <t hangText="csa_cb_program"/>
        <t>
          This is the ONC RPC program number the server MUST use in
          any callbacks sent through the backchannel to the client.
          The server MUST specify an ONC RPC program number equal to
          csa_cb_program and an ONC RPC version number equal to 4 in
          callbacks sent to the client. If a CB_COMPOUND is
          sent to the client, the server MUST use a minor version
          number of 1.
          There is no corresponding result.
        </t>
        <t hangText="csa_sec_parms"/>
        <t>
          The field csa_sec_parms is an array of acceptable
          security credentials the server can use on
          the session's backchannel. Three security
          flavors are supported: AUTH_NONE, AUTH_SYS,
          and RPCSEC_GSS. If AUTH_NONE is specified for
          a credential, then this says the client is
          authorizing the server to use AUTH_NONE on
          all callbacks for the session.  If AUTH_SYS
          is specified, then the client is authorizing
          the server to use AUTH_SYS on all callbacks,
          using the credential specified cbsp_sys_cred. If
          RPCSEC_GSS is specified, then the server is
          allowed to use the RPCSEC_GSS context specified
          in cbsp_gss_parms as the RPCSEC_GSS context in
          the credential of the RPC header of callbacks
          to the client.

          There is no corresponding result.


	    <vspace blankLines='1' />
 
          The RPCSEC_GSS context for the backchannel is specified via
          a pair of values of data type
          gsshandle4_t. The data type gsshandle4_t represents an
          RPCSEC_GSS handle, and is
          precisely the same as the data type of the "handle" field of
          the rpc_gss_init_res data type defined in
          Section 5.2.3.1, "Context Creation Response -
          Successful Acceptance", of <xref target="RFC2203"
          />.

	    <vspace blankLines='1' />

          The first RPCSEC_GSS handle, gcbp_handle_from_server,
          is the fore handle the server returned to
          the client (either in the handle field of data type
          rpc_gss_init_res or as one of the elements of the spi_handles
          field returned in the reply to EXCHANGE_ID) when the RPCSEC_GSS context
          was created on the server.  The second handle,
          gcbp_handle_from_client, is the back handle to which the
          client will map the RPCSEC_GSS context. The
          server can immediately use the value of
          gcbp_handle_from_client in the RPCSEC_GSS credential
          in callback RPCs. That is, the value in
          gcbp_handle_from_client can be used as the
          value of the field "handle" in data type
          rpc_gss_cred_t (see Section 5, "Elements of
          the RPCSEC_GSS Security Protocol", of <xref
          target="RFC2203" />) in callback RPCs.
          The server MUST use the RPCSEC_GSS security service
          specified in gcbp_service, i.e., it MUST set the
          "service" field of the rpc_gss_cred_t data type in
          RPCSEC_GSS credential to the value of gcbp_service (see
          Section 5.3.1, "RPC Request Header", of <xref target="RFC2203" />).

	    <vspace blankLines='1' />

          If the RPCSEC_GSS handle identified by 
          gcbp_handle_from_server does not exist on the server,
          the server will return NFS4ERR_NOENT.

	    <vspace blankLines='1' />

          Within each element of csa_sec_parms, the fore and back RPCSEC_GSS contexts MUST 
          share the same GSS context
          and MUST have the same seq_window
          (see Section 5.2.3.1 of <xref target="RFC2203">RFC2203</xref>).
          The fore and back RPCSEC_GSS context state
          are independent of each other as far as the
          RPCSEC_GSS sequence number (see the seq_num
          field in the rpc_gss_cred_t data type of Sections
          5 and 5.3.1 of <xref target="RFC2203" />).
	    <vspace blankLines='1' />
       If an RPCSEC_GSS handle is using the SSV context (see <xref
       target="ssv_mech"/>), then because each SSV RPCSEC_GSS
       handle shares a common SSV GSS context, there are security
       considerations specific to this situation discussed in <xref
       target="rpcsec_ssv_consider"/>.
	    <vspace blankLines='1' />


        </t>
   </list>
   </t> 
   <t>
    Once the session is created, the first SEQUENCE or
    CB_SEQUENCE received on a slot MUST have a sequence
    ID equal to 1; if not, the replier MUST return
    NFS4ERR_SEQ_MISORDERED.

  </t>
  </section>
  <section toc="exclude" anchor="OP_CREATE_SESSION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      To describe a possible implementation, the same notation for client
      records introduced in the description of EXCHANGE_ID is used
      with the following addition:
      <list style="empty">
      <t>
        clientid_arg:
        The value of the csa_clientid field of the CREATE_SESSION4args
        structure of the current request.
      </t>
      </list>
    </t>     
      
    <t>
      Since CREATE_SESSION is a non-idempotent operation, we
      need to consider the possibility that retries may occur
      as a result of a client restart, network partition,
      malfunctioning router, etc.  For each client ID
      created by EXCHANGE_ID, the server maintains a
      separate reply cache (called the CREATE_SESSION reply cache)
      similar to the session reply
      cache used for SEQUENCE operations, with two
      distinctions.
      <list style="symbols">
      <t>
        First, this is a reply cache just for
        detecting and processing CREATE_SESSION requests for a
        given client ID.
      </t>
      <t>
        Second, the size of the client ID
        reply cache is of one slot (and as a result, the
        CREATE_SESSION request does not carry a slot number).
        This means that at most one CREATE_SESSION request for
        a given client ID can be outstanding.
      </t>
      </list>

      As previously stated, CREATE_SESSION can be sent with
      or without a preceding SEQUENCE operation. Even if a
      SEQUENCE precedes CREATE_SESSION, the server MUST
      maintain the CREATE_SESSION reply cache, which
      is separate from the reply cache for the session
      associated with a SEQUENCE. If CREATE_SESSION was
      originally sent by itself, the client MAY send
      a retry of the CREATE_SESSION operation within a
      COMPOUND preceded by a SEQUENCE. If CREATE_SESSION
      was originally sent in a COMPOUND that started with a
      SEQUENCE, then the client SHOULD send a retry in
      a COMPOUND that starts with a SEQUENCE that has the
      same session ID as the SEQUENCE of the original
      request. However, the client MAY send a retry in a
      COMPOUND that either has no preceding SEQUENCE, or
      has a preceding SEQUENCE that refers to a different
      session than the original CREATE_SESSION. This might
      be necessary if the client sends a CREATE_SESSION
      in a COMPOUND preceded by a SEQUENCE with session
      ID X, and session X no longer exists. Regardless, any
      retry of CREATE_SESSION, with or without a preceding
      SEQUENCE, MUST use the same value of csa_sequence
      as the original.

     </t>

     <t>

      After the client received a reply to an EXCHANGE_ID operation that contains
      a new, unconfirmed client ID,
      the server expects the client to follow
      with a CREATE_SESSION operation to confirm the client ID. The
      server expects value of csa_sequenceid in the arguments to
      that CREATE_SESSION to be
      to equal the value of the field eir_sequenceid that was returned in
      results of the EXCHANGE_ID that returned the unconfirmed
      client ID.
      Before the server replies to that EXCHANGE_ID operation,
      it initializes the client ID slot to be equal
      to eir_sequenceid - 1 (accounting for underflow),
      and records a contrived CREATE_SESSION result
      with a "cached" result of NFS4ERR_SEQ_MISORDERED.
      With the client ID slot thus initialized, the processing of the
      CREATE_SESSION operation is divided into four phases:

      <list style="numbers">
      <t>
        Client record look up. The server looks up the client ID
        in its client record table.
        If the server contains no records
        with client ID equal to clientid_arg, then most
        likely the client's state has been purged during a
        period of inactivity, possibly due to a loss of
        connectivity.  NFS4ERR_STALE_CLIENTID is returned,
        and no changes are made to any client records on
        the server. Otherwise, the server goes to phase 2.
      </t>
      <t>
        Sequence ID processing. If csa_sequenceid is equal to the
        sequence ID in the client ID's slot, then this is a replay 
        of the previous CREATE_SESSION request, and the server
        returns the cached result.
        If csa_sequenceid is not equal to the sequence ID in the slot,
        and is more than one greater (accounting for wraparound),
        then the server returns the error NFS4ERR_SEQ_MISORDERED,
        and does not change the slot.  If csa_sequenceid is
        equal to the slot's sequence ID + 1 (accounting for
        wraparound), then the slot's sequence ID is set to
        csa_sequenceid, and the CREATE_SESSION processing goes to
        the next phase. A subsequent new CREATE_SESSION call
        over the same client ID MUST
        use a csa_sequenceid that is one greater than the
        sequence ID in the slot.

      </t>
      <t>
        Client ID confirmation. If this would be the first session for the
        client ID, the CREATE_SESSION operation serves to confirm the
        client ID.
        Otherwise,
        the client ID confirmation phase is skipped and only
        the session creation phase occurs. 
        Any case in which there is more than one
        record with identical values for client ID represents
        a server implementation error.
        Operation in the
        potential valid cases is summarized as follows.
        <list style="symbols">
        <t>Successful Confirmation
        <list style="empty">
          <t>
            If the server has the following unconfirmed record, then this
            is the expected confirmation of an unconfirmed record.
          </t>
          <t>
            { ownerid, verifier, principal_arg, clientid_arg, unconfirmed }
          </t>
          <t>
            As noted in <xref target="OP_EXCHANGE_ID_IMPLEMENTATION" />,
            the server might also have the following confirmed record.
          </t>
          <t>
            { ownerid, old_verifier, principal_arg, old_clientid, confirmed }
          </t>
          <t>
            The server schedules the replacement of both records with:
          </t>
          <t>
            { ownerid, verifier, principal_arg, clientid_arg, confirmed }
          </t>
           <t>
            The processing of CREATE_SESSION continues on to session creation.
            Once the session is successfully created, the scheduled client
            record replacement is committed. If the session is not
            successfully created, then no changes are made to any client
            records on the server.
          </t>
        </list>
        </t>

        <t>Unsuccessful Confirmation
        <list style="empty">
          <t>
            If the server has the following record, then the client has
            changed principals after the previous EXCHANGE_ID request,
            or there has been a chance collision between shorthand client
            identifiers.
          </t>
          <t>
            { *, *, old_principal_arg, clientid_arg, * }
          </t>
          <t>
            Neither of these cases is permissible.  Processing stops and
            NFS4ERR_CLID_INUSE is returned to the client.  No changes are
            made to any client records on the server.
          </t>
        </list>
        </t>
      </list>
    </t>

    <t>
      Session creation.
      The server confirmed the client ID, either in this
      CREATE_SESSION operation, or a previous CREATE_SESSION
      operation.
      The server examines the remaining fields of the arguments.


	    <vspace blankLines='1' />

      The server creates the session by recording the
      parameter values used (including whether the
      CREATE_SESSION4_FLAG_PERSIST flag is set and has
      been accepted by the server) and allocating space
      for the session reply cache (if there is not enough
      space, the server returns NFS4ERR_NOSPC). For each slot in the
      reply cache, the server sets the sequence ID to zero,
      and records an entry containing a COMPOUND
      reply with zero operations and the error
      NFS4ERR_SEQ_MISORDERED. This way, if the first
      SEQUENCE request sent has a sequence ID equal to
      zero, the server can simply return what is in the
      reply cache: NFS4ERR_SEQ_MISORDERED.  The client
      initializes its reply cache for receiving callbacks
      in the same way, and similarly, the first CB_SEQUENCE
      operation on a slot after session creation MUST have
      a sequence ID of one.

	    <vspace blankLines='1' />

      If the session state is created successfully, the server associates
      the session with the client ID provided by the client. 

	    <vspace blankLines='1' />

       When a request that had CREATE_SESSION4_FLAG_CONN_RDMA set
       needs to be retried, the retry
       MUST be done on a new connection that is in non-RDMA mode.
       If properties of the new connection are different enough
       that the arguments to CREATE_SESSION need to change, then
       a non-retry MUST be sent. The server will eventually dispose
       of any session that was created on the original connection.
    </t>
   </list>
   </t>
   <t>
       On the backchannel, the client and server might wish to
       have many slots, in some cases perhaps more that the fore channel, in
       order to deal with the situations where the
       network link has high latency and is the primary
       bottleneck for response to recalls. If so, and if the
       client provides too few slots to the backchannel,
       the server might limit the number of recallable
       objects it gives to the client.
   </t>
   <t>
     Implementing RPCSEC_GSS callback support requires
     changes to both the client and server implementations of
     RPCSEC_GSS.  One possible set of changes includes:
     <list style="symbols">
     <t>
       Adding a data structure that wraps the GSS-API
       context with a reference count.
     </t>
     <t>        
       New functions to increment and decrement the reference
       count. If the reference count is decremented to zero,
       the wrapper data structure and the GSS-API context it
       refers to would be freed.
     </t>
     <t>        
       Change RPCSEC_GSS to create the wrapper data
       structure upon receiving GSS-API context from
       gss_accept_sec_context() and gss_init_sec_context().
       The reference count would be initialized to 1.
     </t>
     <t>        
       Adding a function to map an existing
       RPCSEC_GSS handle to a pointer to the wrapper data
       structure. The reference count would be incremented.
     </t>
     <t>        
       Adding a function to create a new RPCSEC_GSS
       handle from a pointer to the wrapper data structure.
       The reference count would be incremented.
     </t>
     <t>        
       Replacing calls from RPCSEC_GSS that free GSS-API
       contexts, with calls to decrement the reference count
       on the wrapper data structure.
     </t>
     </list>
   </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DESTROY_SESSION" title="Operation 44: DESTROY_SESSION - Destroy a Session" >

  <section toc="exclude" anchor="OP_DESTROY_SESSION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct DESTROY_SESSION4args {
        sessionid4      dsa_sessionid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_SESSION_RESULT" title="RESULT">
<figure>
 <artwork>
struct DESTROY_SESSION4res {
        nfsstat4        dsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_SESSION_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DESTROY_SESSION operation closes the session and discards
      the session's reply cache, if any.
      Any remaining connections associated with the session are
      immediately disassociated. If the connection has no remaining
      associated sessions, the connection
      MAY be closed by the server.
      Locks, delegations, layouts, wants, and the lease, which are all
      tied to the client ID, are not affected by DESTROY_SESSION.
    </t>
    <t>
      DESTROY_SESSION MUST be invoked on a connection that
      is associated with the session being destroyed.
      In addition, if SP4_MACH_CRED state protection
      was specified when the client ID was created,
      the RPCSEC_GSS principal that created the session MUST be
      the one that destroys the session, using RPCSEC_GSS
      privacy or integrity. If SP4_SSV state protection was
      specified when the client ID was created, RPCSEC_GSS
      using the SSV mechanism (<xref target="ssv_mech" />)
      MUST be used, with integrity or privacy.

    </t>
    <t>
      If the COMPOUND request starts with SEQUENCE, and
      if the sessionids specified in SEQUENCE and DESTROY_SESSION
      are the same, then

      <list style="symbols">
      <t>
       DESTROY_SESSION MUST be the final operation in the COMPOUND
       request.

      </t>

      <t>
       It is advisable to avoid placing DESTROY_SESSION in a
       COMPOUND request with other state-modifying
       operations, because the DESTROY_SESSION will destroy
       the reply cache.

      </t>

      <t>
	Because the session and its reply cache are destroyed, a client that
	retries the request may receive an error in
	reply to the retry, even though the original request was
	successful.

      </t>

      </list>
    </t>

    <t>
      If the COMPOUND request starts with SEQUENCE, and
      if the sessionids specified in SEQUENCE and DESTROY_SESSION
      are different, then DESTROY_SESSION can appear in any position
      of the COMPOUND request (except for the first position). The
      two sessionids can belong to different client IDs. 
    </t>

    <t>
      If the COMPOUND request does not start with
      SEQUENCE, and if DESTROY_SESSION is not the
      sole operation, then server MUST return
      NFS4ERR_NOT_ONLY_OP.

    </t>

    <t>
     If there is a backchannel on the session and the
     server has outstanding CB_COMPOUND operations for the
     session which have not been replied to, then the server
     MAY refuse to destroy the session and return an error.
     If so, then
     in the event the backchannel is down, the server
     SHOULD return NFS4ERR_CB_PATH_DOWN to inform the
     client that the backchannel needs to be repaired before
     the server will allow the session to be destroyed.
     Otherwise, the error CB_BACK_CHAN_BUSY SHOULD be
     returned to indicate that there are CB_COMPOUNDs
     that need to be replied to.  The client SHOULD reply
     to all outstanding CB_COMPOUNDs before re-sending
     DESTROY_SESSION.

    </t>
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_FREE_STATEID" title="Operation 45: FREE_STATEID - Free Stateid with No Locks" >

  <section toc="exclude" anchor="OP_FREE_STATEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct FREE_STATEID4args {
        stateid4        fsa_stateid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_FREE_STATID_RESULT" title="RESULT">
<figure>
 <artwork>
struct FREE_STATEID4res {
        nfsstat4        fsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_FREE_STATEID4_DESCRIPTION" title="DESCRIPTION">
    <t>
      The FREE_STATEID operation is used to free a stateid that no longer
      has any associated locks (including opens, byte-range locks, delegations,
      and layouts).  This may be because of client LOCKU operations or because
      of server revocation.  If there are valid locks (of any kind) 
      associated with the stateid in question, the error NFS4ERR_LOCKS_HELD
      will be returned, and the associated stateid will not be freed.
    </t>
    <t>
      When a stateid is freed that had been associated with revoked locks,
      by sending the FREE_STATEID operation, the client acknowledges the loss of those
      locks.  This allows the server, once all such revoked state is 
      acknowledged,
      to allow that client again to reclaim locks, without encountering 
      the edge conditions discussed in <xref target="server_failure" />.
    </t>
    <t>
      Once a successful FREE_STATEID is done for a given stateid, any
      subsequent use of that stateid will result in an NFS4ERR_BAD_STATEID
      error.
    </t>
  </section>
</section>

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GET_DIR_DELEGATION" title="Operation 46: GET_DIR_DELEGATION - Get a Directory Delegation" >

  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>

typedef nfstime4 attr_notice4;

struct GET_DIR_DELEGATION4args {
        /* CURRENT_FH: delegated directory */
        bool            gdda_signal_deleg_avail;
        bitmap4         gdda_notification_types;
        attr_notice4    gdda_child_attr_delay;
        attr_notice4    gdda_dir_attr_delay;
        bitmap4         gdda_child_attributes;
        bitmap4         gdda_dir_attributes;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_RESULT" title="RESULT">
<figure>
 <artwork>
struct GET_DIR_DELEGATION4resok {
        verifier4       gddr_cookieverf;
        /* Stateid for get_dir_delegation */
        stateid4        gddr_stateid;
        /* Which notifications can the server support */
        bitmap4         gddr_notification;
        bitmap4         gddr_child_attributes;
        bitmap4         gddr_dir_attributes;
};

enum gddrnf4_status {
        GDD4_OK         = 0,
        GDD4_UNAVAIL    = 1
};

union GET_DIR_DELEGATION4res_non_fatal
 switch (gddrnf4_status gddrnf_status) {
 case GDD4_OK:
  GET_DIR_DELEGATION4resok      gddrnf_resok4;
 case GDD4_UNAVAIL:
  bool                          gddrnf_will_signal_deleg_avail;
};

union GET_DIR_DELEGATION4res
 switch (nfsstat4 gddr_status) {
 case NFS4_OK:
  GET_DIR_DELEGATION4res_non_fatal      gddr_res_non_fatal4;
 default:
  void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GET_DIR_DELEGATION operation is used by a client to request
      a directory delegation. The directory is represented by the
      current filehandle. The client also specifies whether it wants
      the server to notify it when the directory changes in certain
      ways by setting one or more bits in a bitmap. The server may
      refuse to grant the delegation. In that case, the server
      will return NFS4ERR_DIRDELEG_UNAVAIL. If the server decides to
      hand out the delegation, it will return a cookie verifier for
      that directory. If the cookie verifier changes when the client
      is holding the delegation, the delegation will be recalled
      unless the client has asked for notification for this event. 
    </t>
    <t>
      The server will also return a directory delegation stateid, 
      gddr_stateid, as a result of the
      GET_DIR_DELEGATION operation. This stateid will appear in
      callback messages related to the delegation, such as
      notifications and delegation recalls.  The client will use this
      stateid to return the delegation voluntarily or upon recall.  A
      delegation is returned by calling the DELEGRETURN operation.
    </t>
    <t>
      The server might not be able to support notifications of certain
      events. If the client asks for such notifications, the server
      MUST inform the client of its inability to do so as part of the
      GET_DIR_DELEGATION reply by not setting the appropriate bits in
      the supported notifications bitmask, gddr_notification, contained 
      in the reply.  The server MUST NOT add bits to gddr_notification
      that the client did not request.
    </t>
    <t>
      The GET_DIR_DELEGATION operation can be used for both normal and
      named attribute directories. 
    </t>
    <t>
      If client sets gdda_signal_deleg_avail to TRUE, then it is
      registering with the client a "want" for a directory
      delegation. If the delegation is not available, and the server 
      supports and will honor the "want",
      the results will have gddrnf_will_signal_deleg_avail set to TRUE
      and no error will be indicated on return.
      If so, the client should expect a future CB_RECALLABLE_OBJ_AVAIL
      operation to indicate that a directory delegation is available.
      If the server does not wish to honor the "want" or is not able
      to do so, it returns the error NFS4ERR_DIRDELEG_UNAVAIL.  If the
      delegation is immediately available, the server SHOULD return it with
      the response to the operation, rather than via a callback. 
    </t>

    <t>
      When a client makes a request for a
      directory delegation while it already holds
      a directory delegation for that directory
      (including the case where it has been
      recalled but not yet returned by the client
      or revoked by the server), the server MUST
      reply with the value of gddr_status set to
      NFS4_OK, the value of gddrnf_status set to
      GDD4_UNAVAIL, and the value of
      gddrnf_will_signal_deleg_avail set to
      FALSE.  The delegation the client held
      before the request remains intact, and its
      state is unchanged. The current stateid is
      not changed (see <xref
      target="current_stateid"/> for a description
      of the current stateid).

    </t>
  </section>
  <section toc="exclude" anchor="OP_GET_DIR_DELEGATION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Directory delegations provide the benefit of improving cache
      consistency of namespace information. This is done through
      synchronous callbacks. A server must support synchronous
      callbacks in order to support directory delegations. In addition
      to that, asynchronous notifications provide a way to reduce
      network traffic as well as improve client performance in certain
      conditions.
    </t>
    <t>
      Notifications are specified in terms of potential
      changes to the directory. A client can ask to be
      notified of events by setting one or more
      bits in gdda_notification_types.
      The client can ask for notifications on addition of entries
      to a directory (by setting the
      NOTIFY4_ADD_ENTRY in gdda_notification_types),
      notifications on entry removal
      (NOTIFY4_REMOVE_ENTRY), renames
      (NOTIFY4_RENAME_ENTRY), directory attribute
      changes (NOTIFY4_CHANGE_DIR_ATTRIBUTES),
      and cookie verifier changes
      (NOTIFY4_CHANGE_COOKIE_VERIFIER) by setting
      one or more corresponding bits in the
      gdda_notification_types field.
    </t>
    <t>
      The client can also ask for
      notifications of changes to
      attributes of directory entries
      (NOTIFY4_CHANGE_CHILD_ATTRIBUTES)
      in order to keep its attribute cache up to date. However, any
      changes made to child attributes do not cause the delegation to
      be recalled. If a client is interested in directory entry
      caching or negative name caching, it can set the
      gdda_notification_types appropriately to its particular need 
      and the server will notify it of
      all changes that would otherwise invalidate its name cache. The
      kind of notification a client asks for may depend on the
      directory size, its rate of change, and the applications being
      used to access that directory. The enumeration of the conditions under
      which a client might ask for a notification is out of the scope
      of this specification.
    </t>
    <t>
      For attribute notifications, the client
      will set bits in the gdda_dir_attributes
      bitmap to indicate which attributes
      it wants to be notified of. If the server does not support
      notifications for changes to a certain attribute, it SHOULD NOT
      set that attribute in the supported attribute bitmap
      specified in the reply (gddr_dir_attributes). The client will
      also set in the gdda_child_attributes bitmap the attributes
      of directory entries it wants to be notified of, and
      the server will indicate in gddr_child_attributes which
      attributes of directory entries it will notify the client of.
    </t>
    <t>
      The client will also let the server know if
      it wants to get the notification as soon as the attribute change
      occurs or after a certain delay by setting a delay factor;
      gdda_child_attr_delay is for attribute changes to directory entries and
      gdda_dir_attr_delay is for attribute changes to the directory. If this
      delay factor is set to zero, that indicates to the server that
      the client wants to be notified of any attribute changes as soon
      as they occur. If the delay factor is set to N seconds, the server will
      make a best-effort guarantee that attribute updates are
      synchronized within N seconds.
      If the client asks
      for a delay factor that the server does not support or that may
      cause significant resource consumption on the server by causing
      the server to send a lot of notifications, the server should not
      commit to sending out notifications for attributes and
      therefore must not set the appropriate bit in the
      gddr_child_attributes and gddr_dir_attributes bitmaps in the response.
    </t>
    <t>
      The client MUST use a security tuple (<xref
      target="NFSv4_Security_Tuples"/>) that the
      directory or its applicable ancestor (<xref
      target="Security_Service_Negotiation"/>) is
      exported with. If not, the server MUST return
      NFS4ERR_WRONGSEC to the operation that both precedes
      GET_DIR_DELEGATION and sets the current filehandle
      (see <xref target="using_secinfo"/>).

    </t>
    <t>
      The directory delegation covers all the entries in the
      directory except the parent entry.  That means if a directory and
      its parent both hold directory delegations, any changes to the
      parent will not cause a notification to be sent for the child
      even though the child's parent entry points to the parent
      directory.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETDEVICEINFO" title="Operation 47: GETDEVICEINFO - Get Device Information" >

  <section toc="exclude" anchor="OP_GETDEVICEINFO_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct GETDEVICEINFO4args {
        deviceid4       gdia_device_id;
        layouttype4     gdia_layout_type;
        count4          gdia_maxcount;
        bitmap4         gdia_notify_types;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_RESULT" title="RESULT">
<figure>
 <artwork>
struct GETDEVICEINFO4resok {
        device_addr4    gdir_device_addr;
        bitmap4         gdir_notification;
};

union GETDEVICEINFO4res switch (nfsstat4 gdir_status) {
case NFS4_OK:
        GETDEVICEINFO4resok     gdir_resok4;
case NFS4ERR_TOOSMALL:
        count4                  gdir_mincount;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_DESCRIPTION" title="DESCRIPTION">
    <t>
      The GETDEVICEINFO operation returns pNFS storage device address
      information for the specified device ID.
      The client identifies the device information to be returned by
      providing the gdia_device_id and gdia_layout_type that uniquely
      identify the device.  The client provides gdia_maxcount
      to limit the number of bytes for the result.  This maximum size
      represents all of the data being returned within the
      GETDEVICEINFO4resok structure and includes the XDR overhead.
      The server may return less data.  If the server is unable to
      return any information within the gdia_maxcount limit, the error
      NFS4ERR_TOOSMALL will be returned. However, if gdia_maxcount is
      zero, NFS4ERR_TOOSMALL MUST NOT be returned.
    </t>
    <t>
      The da_layout_type field of the gdir_device_addr returned 
      by the server MUST be equal to the gdia_layout_type specified
      by the client.  If it is not equal, the client SHOULD ignore
      the response as invalid and behave as if the server returned
      an error, even if the client does have support for the 
      layout type returned.
    </t> 
    <t>

      The client also provides a notification bitmap,
      gdia_notify_types, for the device ID mapping
      notification for which it is interested in receiving;
      the server must support device ID notifications
      for the notification request to have affect.
      The notification mask is composed in the same
      manner as the bitmap for file attributes (<xref
      target="fattr4" />).  The numbers of bit positions
      are listed in the notify_device_type4 enumeration type
      (<xref target="OP_CB_NOTIFY_DEVICEID" />). Only
      two enumerated values of notify_device_type4 currently
      apply to GETDEVICEINFO:
      NOTIFY_DEVICEID4_CHANGE
      and NOTIFY_DEVICEID4_DELETE (see <xref
      target="OP_CB_NOTIFY_DEVICEID" />).

    </t>
    <t>
      The notification bitmap applies only to the specified device ID.
      If a client sends a GETDEVICEINFO operation on a deviceID multiple times,
      the last notification bitmap is used by the server for
      subsequent notifications. If the bitmap is zero or empty,
      then the device ID's notifications are turned off.
    </t>
    <t>
     If the client wants to just update or turn off notifications,
     it MAY send a GETDEVICEINFO operation with gdia_maxcount set to zero.
     In that event, if the device ID is valid, the reply's da_addr_body
     field of the gdir_device_addr field will be of zero length.
    </t>
    <t>
      If an unknown device ID is given in gdia_device_id,
      the server returns NFS4ERR_NOENT.

      Otherwise, the device address
      information is returned in gdir_device_addr. 
      Finally, if the server supports
      notifications for device ID mappings, the gdir_notification
      result will contain a bitmap of which notifications
      it will actually send to the client (via CB_NOTIFY_DEVICEID,
      see <xref target="OP_CB_NOTIFY_DEVICEID" />).
    </t>
    <t>
      If NFS4ERR_TOOSMALL is returned, the results also contain
      gdir_mincount.  The value of gdir_mincount represents the
      minimum size necessary to obtain the device information.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICEINFO_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
   Aside from updating or turning off notifications, another
   use case for gdia_maxcount being set to zero is to validate
   a device ID.
  </t>
  <t>
    The client SHOULD request a notification for changes or
    deletion of a device ID to device address mapping so
    that the server can allow the client gracefully use a
    new mapping, without having pending I/O fail abruptly,
    or force layouts using the device ID to be recalled
    or revoked.

  </t>

  <t>
    It is possible that GETDEVICEINFO (and
    GETDEVICELIST) will race with CB_NOTIFY_DEVICEID,
    i.e., CB_NOTIFY_DEVICEID arrives before the client
    gets and processes the response to GETDEVICEINFO or
    GETDEVICELIST.  The analysis of the race leverages the
    fact that the server MUST NOT delete a device ID that
    is referred to by a layout the client has.
    <list style="symbols">
    <t>
       CB_NOTIFY_DEVICEID deletes a device ID.
       If the client believes it has layouts that refer to the
       device ID, then it is possible that layouts referring to
       the deleted device ID have been revoked.
       The client should send a TEST_STATEID request using the
       stateid for each layout that might have been revoked. If
       TEST_STATEID indicates that any layouts have been revoked, the
       client must recover from layout revocation as described in
       <xref
       target="revoke_layout" />. If TEST_STATEID indicates that at least
       one layout has not been revoked, the client should send
       a GETDEVICEINFO operation on the supposedly deleted
       device ID to verify that the device ID
       has been deleted.

	    <vspace blankLines='1' />

       If GETDEVICEINFO indicates that the device ID
       does not exist, then the client assumes the server is faulty
       and recovers by sending an EXCHANGE_ID operation. If GETDEVICEINFO
       indicates that the device ID does exist, then while the server is
       faulty for sending an erroneous device ID deletion notification,
       the degree to which it is faulty does not require the client to
       create a new client ID.
   
	    <vspace blankLines='1' />

       If the client does not have layouts that refer to the
       device ID, no harm is done.
       The client should mark the device ID as deleted, and when
       GETDEVICEINFO or GETDEVICELIST results are
       received that indicate that the device ID has been
       in fact deleted, the device ID should be removed from the
       client's cache.

    </t>
    
    <t>
       CB_NOTIFY_DEVICEID indicates that a device ID's device
       addressing mappings have changed. The client should assume
       that the results from the in-progress GETDEVICEINFO
       will be stale for the device ID
       once received, and so it should send another GETDEVICEINFO
       on the device ID.
     
    </t>
   </list>
  </t> 

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_GETDEVICELIST" title="Operation 48: GETDEVICELIST - Get All Device Mappings for a File System" >

  <section toc="exclude" anchor="OP_GETDEVICELIST_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct GETDEVICELIST4args {
        /* CURRENT_FH: object belonging to the file system */
        layouttype4     gdla_layout_type;

        /* number of deviceIDs to return */
        count4          gdla_maxdevices;

        nfs_cookie4     gdla_cookie;
        verifier4       gdla_cookieverf;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_RESULT" title="RESULT">
<figure>
 <artwork>
struct GETDEVICELIST4resok {
        nfs_cookie4             gdlr_cookie;
        verifier4               gdlr_cookieverf;
        deviceid4               gdlr_deviceid_list&lt;>;
        bool                    gdlr_eof;
};

union GETDEVICELIST4res switch (nfsstat4 gdlr_status) {
case NFS4_OK:
        GETDEVICELIST4resok     gdlr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used by the client to enumerate all of the
      device IDs that a server's file system uses.
    </t>
    <t>
      The client provides a current filehandle of a file object that
      belongs to the file system (i.e., all file objects sharing the same
      fsid as that of the current filehandle) and the layout type
      in gdia_layout_type.  Since
      this operation might require multiple calls to enumerate all the
      device IDs (and is thus
      similar to the <xref target="OP_READDIR">
      READDIR</xref> operation), the client also provides gdia_cookie
      and gdia_cookieverf to specify the current cursor position in the
      list. When the client wants to read from the beginning of the
      file system's device mappings, it sets gdla_cookie to zero. The
      field gdla_cookieverf MUST be ignored by the server when
      gdla_cookie is zero.
      The client provides gdla_maxdevices to limit the number of device IDs
      in the result. If gdla_maxdevices is zero, the server MUST return
      NFS4ERR_INVAL.
      The server MAY return fewer device IDs.
    </t>
    
    <t>
      The successful response to the operation will contain the
      cookie, gdlr_cookie, and the cookie verifier, gdlr_cookieverf, to be
      used on the subsequent GETDEVICELIST.  A gdlr_eof value of TRUE
      signifies that there are no remaining entries in the server's
      device list.  Each element of gdlr_deviceid_list contains
      a device ID.
    </t>
  </section>
  <section toc="exclude" anchor="OP_GETDEVICELIST_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
      An example of the use of this operation is for pNFS
      clients and servers that use LAYOUT4_BLOCK_VOLUME
      layouts.  In these environments it may be helpful
      for a client to determine device accessibility upon
      first file system access.

  </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTCOMMIT" title="Operation 49: LAYOUTCOMMIT - Commit Writes Made Using a Layout" >

  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
union newtime4 switch (bool nt_timechanged) {
case TRUE:
        nfstime4           nt_time;
case FALSE:
        void;
};

union newoffset4 switch (bool no_newoffset) {
case TRUE:
        offset4           no_offset;
case FALSE:
        void;
};

struct LAYOUTCOMMIT4args {
        /* CURRENT_FH: file */
        offset4                 loca_offset;
        length4                 loca_length;
        bool                    loca_reclaim;
        stateid4                loca_stateid;
        newoffset4              loca_last_write_offset;
        newtime4                loca_time_modify;
        layoutupdate4           loca_layoutupdate;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_RESULT" title="RESULT">
<figure>
 <artwork>
union newsize4 switch (bool ns_sizechanged) {
case TRUE:
        length4         ns_size;
case FALSE:
        void;
};

struct LAYOUTCOMMIT4resok {
        newsize4                locr_newsize;
};

union LAYOUTCOMMIT4res switch (nfsstat4 locr_status) {
case NFS4_OK:
        LAYOUTCOMMIT4resok      locr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LAYOUTCOMMIT operation commits changes in the layout represented by the current
      filehandle, client ID (derived from the session ID in the
      preceding SEQUENCE operation), byte-range, and stateid.  Since
      layouts are sub-dividable, a smaller portion of a layout,
      retrieved via LAYOUTGET, can be committed.  The byte-range being
      committed is specified through the byte-range (loca_offset and
      loca_length). This byte-range MUST overlap with one or more existing layouts
      previously granted via LAYOUTGET (<xref target="OP_LAYOUTGET"/>),
      each with an iomode of LAYOUTIOMODE4_RW.  In the
      case where the iomode of any held layout segment is not
      LAYOUTIOMODE4_RW, the server should return the error
      NFS4ERR_BAD_IOMODE.  For the case where the client
      does not hold matching layout segment(s) for the
      defined byte-range, the server should return the error
      NFS4ERR_BAD_LAYOUT.

    </t>
    <t>
      The LAYOUTCOMMIT operation indicates that the client has
      completed writes using a layout obtained by a previous
      LAYOUTGET.  The client may have only written a subset of the
      data range it previously requested.  LAYOUTCOMMIT allows it to
      commit or discard provisionally allocated space and to update
      the server with a new end-of-file.  The layout referenced by
      LAYOUTCOMMIT is still valid after the operation completes and
      can be continued to be referenced by the client ID, filehandle,
      byte-range, layout type, and stateid.
    </t>
    <t>
      If the loca_reclaim field is set to TRUE, this indicates that
      the client is attempting to commit changes to a layout after the
      restart of the metadata server during the metadata server's
      recovery grace period (see <xref target="mds_recovery"/>).  This type of request may be necessary
      when the client has uncommitted writes to provisionally
      allocated byte-ranges of a file that were sent to the storage
      devices before the restart of the metadata server.  In this case,
      the layout provided by the client MUST be a subset of a writable
      layout that the client held immediately before the restart of the
      metadata server. The value of the field loca_stateid MUST
      be a value that the metadata server returned before it restarted.
      The metadata server is free to accept or
      reject this request based on its own internal metadata
      consistency checks.  If the metadata server finds that the
      layout provided by the client does not pass its consistency
      checks, it MUST reject the request with the status
      NFS4ERR_RECLAIM_BAD.  The successful completion of the
      LAYOUTCOMMIT request with loca_reclaim set to TRUE does NOT
      provide the client with a layout for the file.  It simply
      commits the changes to the layout specified in the
      loca_layoutupdate field.  To obtain a layout for the file, the
      client must send a LAYOUTGET request to the server after the
      server's grace period has expired.  If the metadata server
      receives a LAYOUTCOMMIT request with loca_reclaim set to TRUE
      when the metadata server is not in its recovery grace period, it
      MUST reject the request with the status NFS4ERR_NO_GRACE.
    </t>
    <t>
      Setting the loca_reclaim field to TRUE is required if and only
      if the committed layout was acquired before the metadata server
      restart.  If the client is committing a layout that was acquired
      during the metadata server's grace period, it MUST set the
      "reclaim" field to FALSE.
    </t>
    <t>
      The loca_stateid is a layout stateid value as
      returned by previously successful layout operations
      (see <xref target="layout_stateid"/>).

    </t>
    <t>
      The loca_last_write_offset field specifies the offset of the
      last byte written by the client previous to the LAYOUTCOMMIT.
      Note that this value is never equal to the file's size (at most
      it is one byte less than the file's size) and MUST be less than
      or equal to NFS4_MAXFILEOFF.  Also, loca_last_write_offset MUST
      overlap the range described by loca_offset and loca_length.
      The metadata server
      may use this information to determine whether the file's size
      needs to be updated.  If the metadata server updates the file's
      size as the result of the LAYOUTCOMMIT operation, it must return
      the new size (locr_newsize.ns_size) as part of the results.
    </t>
    <t>
      The loca_time_modify field
      allows the client to suggest a modification time it would like the metadata
      server to set.  The metadata server may use the suggestion or
      it may use the time of the LAYOUTCOMMIT operation to set the modification
      time.  If the metadata server uses the client-provided
      modification time, it should ensure that time does not flow backwards.  If the
      client wants to force the metadata server to set an exact time,
      the client should use a SETATTR operation in a COMPOUND right
      after LAYOUTCOMMIT.  See <xref target="committing_layout" /> for
      more details.  If the client desires the resultant modification time,
      it should construct the COMPOUND so that a GETATTR
      follows the LAYOUTCOMMIT.
    </t>
    <t>
     The loca_layoutupdate argument to LAYOUTCOMMIT provides a mechanism
     for a client to provide layout-specific updates to the metadata
     server.  For example, the layout update can describe what byte-ranges
     of the original layout have been used and what byte-ranges can be
     deallocated.  There is no NFSv4.1 file layout-specific layoutupdate4
     structure.
    </t>
    <t>
      The layout information is more verbose for block devices than for
      objects and files because the latter two hide the details of block
      allocation behind their storage protocols.  At the minimum, the
      client needs to communicate changes to the end-of-file location back
      to the server, and, if desired, its view of the file's modification
      time.  For block/volume layouts, it needs to specify precisely
      which blocks have been used.
    </t>
    <t>
      If the layout identified in the arguments does not exist, the
      error NFS4ERR_BADLAYOUT is returned.  The layout being committed
      may also be rejected if it does not correspond to an existing
      layout with an iomode of LAYOUTIOMODE4_RW.
    </t>
    <t>
      On success, the current filehandle retains its value and the
      current stateid retains its value.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTCOMMIT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client MAY also use LAYOUTCOMMIT with the
      loca_reclaim field set to TRUE to convey hints to modified file
      attributes or to report layout-type specific information such as
      I/O errors for object-based storage layouts, as normally done
      during normal operation. Doing so may help the metadata server
      to recover files more efficiently after restart.  For example,
      some file system implementations may require expansive recovery
      of file system objects if the metadata server does not get a
      positive indication from all clients holding a LAYOUTIOMODE4_RW layout that
      they have successfully completed all their writes.  Sending a
      LAYOUTCOMMIT (if required) and then following with LAYOUTRETURN
      can provide such an indication and allow for graceful and
      efficient recovery.
    </t>
    <t>
      If loca_reclaim is TRUE, the metadata server is free to
      either examine or ignore the value in the field loca_stateid.
      The metadata server implementation might or might not
      encode in its layout
      stateid information that allows the metadate server to
      perform a consistency check on the LAYOUTCOMMIT request.
    </t>      
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTGET" title="Operation 50: LAYOUTGET - Get Layout Information" >

  <section toc="exclude" anchor="OP_LAYOUTGET_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct LAYOUTGET4args {
        /* CURRENT_FH: file */
        bool                    loga_signal_layout_avail;
        layouttype4             loga_layout_type;
        layoutiomode4           loga_iomode;
        offset4                 loga_offset;
        length4                 loga_length;
        length4                 loga_minlength;
        stateid4                loga_stateid;
        count4                  loga_maxcount;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_RESULT" title="RESULT">
<figure>
 <artwork>
struct LAYOUTGET4resok {
        bool               logr_return_on_close;
        stateid4           logr_stateid;
        layout4            logr_layout&lt;>;
};

union LAYOUTGET4res switch (nfsstat4 logr_status) {
case NFS4_OK:
        LAYOUTGET4resok     logr_resok4;
case NFS4ERR_LAYOUTTRYLATER:
        bool                logr_will_signal_layout_avail;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_DESCRIPTION" title="DESCRIPTION">
    <t>
      The LAYOUTGET operation requests a layout from the metadata server for reading or
      writing the file given by the filehandle at the
      byte-range specified by offset and length.  Layouts are
      identified by the client ID (derived from the session ID in the
      preceding SEQUENCE operation), current filehandle, layout type
      (loga_layout_type), and the layout stateid (loga_stateid).  The
      use of the loga_iomode field depends upon the layout type, but should
      reflect the client's data access intent.
    </t>
    <t>
      If the metadata server is in a grace period, and does not
      persist layouts and device ID to device address mappings, then
      it MUST return NFS4ERR_GRACE (see <xref target="reclaim_locks"/>).
    </t>
     
    <t>
      The LAYOUTGET operation returns layout information
      for the specified byte-range: a layout.
      The client actually specifies two ranges, both starting
      at the offset in the loga_offset field. The first
      range is between loga_offset and loga_offset + loga_length - 1
      inclusive. This range indicates the desired range the client
      wants the layout to cover. The second range is between
      loga_offset and loga_offset + loga_minlength - 1 inclusive. This
      range indicates the required range the client needs the layout
      to cover. Thus, loga_minlength MUST be less than or equal to
      loga_length.
    </t>
      
    <t>
      When a length field is set to NFS4_UINT64_MAX,
      this indicates a desire (when loga_length is NFS4_UINT64_MAX)
      or requirement (when loga_minlength is NFS4_UINT64_MAX)
      to get a layout from loga_offset through the
      end-of-file, regardless of the file's length.
    </t>
    <t>
      The following rules govern the relationships among,
      and the minima of,
      loga_length, loga_minlength, and loga_offset.
      
      <list style='symbols'>
      <t>
       If loga_length is less than loga_minlength, the metadata server
       MUST return NFS4ERR_INVAL.

      </t>
      <t>
       If loga_minlength is zero, this is an indication
       to the metadata server that the client desires any layout
       at offset loga_offset or less that the metadata server has
       "readily available". Readily is subjective, and depends on
       the layout type and the pNFS server implementation. For example,
       some metadata servers might have to pre-allocate stable
       storage when they receive a request for a range of a
       file that goes beyond the file's current length.
       If loga_minlength is zero and
       loga_length is greater than zero, this tells the
       metadata server what range of the layout the client would
       prefer to have. If loga_length and loga_minlength
       are both zero, then the client is indicating that it desires
       a layout of any length with the ending offset of the range
       no less than the value specified loga_offset, and the starting offset at or
       below loga_offset. If the metadata server does not have
       a layout that is readily available, then it MUST return
       NFS4ERR_LAYOUTTRYLATER.
       
      </t>
      <t>
       If the sum of loga_offset and loga_minlength exceeds
       NFS4_UINT64_MAX, and loga_minlength is not NFS4_UINT64_MAX,
       the error NFS4ERR_INVAL MUST result.

      </t>
      <t>
       If the sum of loga_offset and loga_length exceeds
       NFS4_UINT64_MAX, and loga_length is not NFS4_UINT64_MAX,
       the error NFS4ERR_INVAL MUST result.

      </t>
      </list>

      After the metadata server has performed the above checks on loga_offset,
      loga_minlength, and loga_offset, the metadata server MUST return a
      layout according to the rules in <xref target="layout_hell"/>.
    </t>
    <texttable anchor='layout_hell'>

     <preamble>

      Acceptable layouts based on loga_minlength.
      Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
      a_minlen = loga_minlength.

     </preamble>

     <ttcol>Layout iomode of request</ttcol>
     <ttcol>Layout a_minlen of request</ttcol>
     <ttcol>Layout iomode of reply</ttcol>
     <ttcol>Layout offset of reply</ttcol>
     <ttcol>Layout length of reply</ttcol>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= file length - layout offset</c>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be u64m</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= MIN(file length, a_minlen + a_off) - layout offset</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= a_off - layout offset + a_minlen</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

     <c>_RW</c>
     <c>u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be u64m</c>

     <c>_RW</c>
     <c>> 0 and &lt; u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be >= a_off - layout offset + a_minlen</c>

     <c>_RW</c>
     <c>0</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>MUST be > 0</c>

    </texttable>
    <t>
     If loga_minlength is not zero and the metadata server cannot return a layout according
     to the rules in <xref target="layout_hell"/>,
     then the metadata server MUST return the error
     NFS4ERR_BADLAYOUT.  If loga_minlength is zero and the metadata server
     cannot or will not return a layout according
     to the rules in <xref target="layout_hell"/>,
     then the metadata server MUST return the error
     NFS4ERR_LAYOUTTRYLATER.

     Assuming that loga_length is greater
     than loga_minlength or equal to zero, the metadata server SHOULD
     return a layout according to the rules in <xref
     target="layout_hell2"/>.
    </t>

    <texttable anchor='layout_hell2'>

     <preamble>

      Desired layouts based on loga_length.
      The rules of <xref target='layout_hell'/> MUST be applied first.
      Note: u64m = NFS4_UINT64_MAX; a_off = loga_offset;
      a_len = loga_length.

     </preamble>

     <ttcol>Layout iomode of request</ttcol>
     <ttcol>Layout a_len of request</ttcol>
     <ttcol>Layout iomode of reply</ttcol>
     <ttcol>Layout offset of reply</ttcol>
     <ttcol>Layout length of reply</ttcol>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_READ</c>
     <c>u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_READ</c>
     <c>> 0 and &lt; u64m</c>
     <c>MAY be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>

     <c>_READ</c>
     <c>0</c>
     <c>MAY be _READ</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>

     <c>_RW</c>
     <c>u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be u64m</c>

     <c>_RW</c>
     <c>> 0 and &lt; u64m</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be >= a_off - layout offset + a_len</c>

     <c>_RW</c>
     <c>0</c>
     <c>MUST be _RW</c>
     <c>MUST be &lt;= a_off</c>
     <c>SHOULD be > a_off - layout offset</c>
    </texttable>

    <t>
      The loga_stateid field specifies a valid stateid.
      If a layout is not currently held by the client,
      the loga_stateid field represents a stateid
      reflecting the correspondingly valid open,
      byte-range lock, or delegation stateid.  Once a
      layout is held on the file by the client, the
      loga_stateid field MUST be a stateid as returned from
      a previous LAYOUTGET or LAYOUTRETURN operation or
      provided by a CB_LAYOUTRECALL operation (see <xref
      target="layout_stateid"/>).

    </t>
    <t>
      The loga_maxcount field specifies the maximum layout size (in bytes)
      that the client can handle.  If the size of the layout structure
      exceeds the size specified by maxcount, the metadata server will
      return the NFS4ERR_TOOSMALL error.

    </t>
    <t>
     The returned layout is expressed as an array,
     logr_layout, with each element of type layout4. If a
     file has a single striping pattern, then logr_layout
     SHOULD contain just one entry. Otherwise, if the
     requested range overlaps more than one striping
     pattern, logr_layout will contain the required number
     of entries. The elements of logr_layout MUST be sorted
     in ascending order of the value of the lo_offset field
     of each element. There MUST be no gaps or overlaps
     in the range between two successive elements of
     logr_layout. The lo_iomode field in each element of
     logr_layout MUST be the same.
    </t>

    <t>
      <xref target="layout_hell" />
      and
      <xref target="layout_hell2" />

      both refer to a returned layout iomode, offset, and length.
      Because the returned layout is encoded in the logr_layout array,
      more description is required.
     <list style='hanging'>

     <t hangText='iomode'/>
     <t>
       The value of the returned layout iomode listed in
       <xref target="layout_hell" />
       and
       <xref target="layout_hell2" />
       is equal to the value of the lo_iomode field in each
       element of logr_layout.

       As shown in <xref target="layout_hell" />
       and <xref target="layout_hell2" />,
       the metadata server MAY return a layout with an lo_iomode
       different from the requested iomode (field loga_iomode of the request).
       If it does so, it MUST
       ensure that the lo_iomode is more permissive than the
       loga_iomode requested.  For example, this behavior allows an
       implementation to upgrade LAYOUTIOMODE4_READ requests to LAYOUTIOMODE4_RW
       requests at its discretion, within the limits of the layout type
       specific protocol.  A lo_iomode of either LAYOUTIOMODE4_READ or
       LAYOUTIOMODE4_RW MUST be returned.

     </t>
    
     <t hangText='offset'/>
     <t>
       The value of the returned layout offset listed in
       <xref target="layout_hell" />
       and
       <xref target="layout_hell2" />
       is always equal to the lo_offset field of the first
       element logr_layout.

     </t>

     <t hangText='length'/>
     <t>
       When setting the value of the returned layout
       length, the situation is complicated by the
       possibility that the special layout length value
       NFS4_UINT64_MAX is involved.  For a logr_layout
       array of N elements, the lo_length field in the
       first N-1 elements MUST NOT be NFS4_UINT64_MAX. The
       lo_length field of the last element of logr_layout
       can be NFS4_UINT64_MAX under some conditions as
       described in the following list.

       <list style='symbols'>

       <t>
	If an applicable rule of <xref target="layout_hell"/>
	states that the metadata server MUST return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout MUST be NFS4_UINT64_MAX.

       </t>
       <t>
	If an applicable rule of <xref target="layout_hell"/>
	states that the metadata server MUST NOT return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout MUST NOT be NFS4_UINT64_MAX.

       </t>
       <t>
	If an applicable rule of <xref target="layout_hell2"/>
	states that the metadata server SHOULD return a layout of length
	NFS4_UINT64_MAX, then the lo_length field of the last
	element of logr_layout SHOULD be NFS4_UINT64_MAX.

       </t>
       <t>
	When the value of the returned layout length of
	<xref target="layout_hell" />
	and
	<xref target="layout_hell2" /> is not NFS4_UINT64_MAX, then
	the returned layout length is equal to the sum of the
	lo_length fields of each element of logr_layout.

       </t>

       </list>
       
     </t>
    </list>
    </t>

    <t>
      The logr_return_on_close result field is a directive to return
      the layout before closing the file.  When the metadata server sets this
      return value to TRUE, it MUST be prepared to recall the layout
      in the case in which the client fails to return the layout before close.
      For the metadata server that knows a layout must be returned before a
      close of the file, this return value can be used to communicate
      the desired behavior to the client and thus remove one extra
      step from the client's and metadata server's interaction.
    </t>
    <t>
      The logr_stateid stateid is returned to
      the client for use in subsequent layout related operations. See Sections
      <xref target="stateid" format="counter" />, <xref target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
    <t>
      The format of the returned layout (lo_content)
      is specific to the layout type.
      The value of the layout type (lo_content.loc_type) for each of
      the elements of the array of layouts returned by the metadata server
      (logr_layout) MUST be equal to the loga_layout_type specified
      by the client.  If it is not equal, the client SHOULD ignore
      the response as invalid and behave as if the metadata server returned
      an error, even if the client does have support for the
      layout type returned.
    </t>
    <t>
      If neither the requested file nor its
      containing file system support layouts, the metadata server MUST return
      NFS4ERR_LAYOUTUNAVAILABLE.  If the layout type is not supported,
      the metadata server MUST return NFS4ERR_UNKNOWN_LAYOUTTYPE.
      If layouts are supported but no layout matches the client
      provided layout identification, the metadata server MUST return
      NFS4ERR_BADLAYOUT.  If an invalid loga_iomode is specified, or a
      loga_iomode of LAYOUTIOMODE4_ANY is specified, the metadata server MUST
      return NFS4ERR_BADIOMODE.
    </t>
    <t>
      If the layout for the file is unavailable due to transient
      conditions, e.g., file sharing prohibits layouts, the metadata server MUST
      return NFS4ERR_LAYOUTTRYLATER.
    </t>
    <t>
      If the layout request is rejected due to an overlapping layout
      recall, the metadata server MUST return NFS4ERR_RECALLCONFLICT.  See <xref
      target="pnfs_operation_sequencing"/> for details.
    </t>
    <t>
      If the layout conflicts with a mandatory byte-range lock held on the
      file, and if the storage devices have no method of enforcing
      mandatory locks, other than through the restriction of layouts, the
      metadata server SHOULD return NFS4ERR_LOCKED.
    </t>
    <t>
      If client sets loga_signal_layout_avail to TRUE, then it is
      registering with the client a "want" for a layout in the event
      the layout cannot be obtained due to resource exhaustion.
      If the metadata server supports and will honor the "want",
      the results will have logr_will_signal_layout_avail
      set to TRUE.
      If so, the client should expect a CB_RECALLABLE_OBJ_AVAIL
      operation to indicate that a layout is available.
    </t>
    <t>
      On success, the current filehandle retains its value and the
      current stateid is updated to match the value as returned in the
      results.
    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTGET_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Typically, LAYOUTGET will be called as part of a
      COMPOUND request after an OPEN operation and results
      in the client having location information for the
      file. This requires that loga_stateid be set to the
      special stateid that tells the metadata server to use the
      current stateid, which is set by OPEN (see <xref
      target="current_stateid"/>). A client may also hold
      a layout across multiple OPENs. The client specifies
      a layout type that limits what kind of layout the
      metadata server will return.  This prevents metadata servers from
      granting layouts that are unusable by the client.

    </t>
    <t>
      As indicated by <xref target="layout_hell" /> and
      <xref target="layout_hell2" />, the specification of
      LAYOUTGET allows a pNFS client and server considerable
      flexibility.

      A pNFS client can take several strategies for sending
      LAYOUTGET. Some examples are as follows.

      <list style='symbols'>
      <t>
       If LAYOUTGET is preceded by OPEN in the same
       COMPOUND request and the OPEN requests OPEN4_SHARE_ACCESS_READ access,
       the client might opt to request a _READ layout
       with loga_offset set to zero, loga_minlength set to
       zero, and loga_length set to NFS4_UINT64_MAX. If
       the file has space allocated to it, that space is
       striped over one or more storage devices, and there
       is either no conflicting layout or the concept of
       a conflicting layout does not apply to the pNFS
       server's layout type or implementation, then the
       metadata server might return a layout with a starting offset
       of zero, and a length equal to the length of the
       file, if not NFS4_UINT64_MAX. If the length of the
       file is not a multiple of the
       pNFS server's stripe
       width (see <xref target="file_layout_definitions"/>
       for a formal definition), the metadata server might round up
       the returned layout's length.

      </t>

      <t>
       If LAYOUTGET is preceded by OPEN in the same
       COMPOUND request, and the OPEN requests OPEN4_SHARE_ACCESS_WRITE access and does
       not truncate the file, the client might
       opt to request a _RW layout with loga_offset set
       to zero, loga_minlength set to zero, and loga_length
       set to the file's current length (if known), or
       NFS4_UINT64_MAX. As with the previous case, under
       some conditions the metadata server might return a layout
       that covers the entire length of the file or beyond.

      </t>
      <t>
       This strategy is as above, but the OPEN truncates the file. In this case,
       the client might anticipate it will be writing to the
       file from offset zero, and so loga_offset and loga_minlength
       are set to zero, and loga_length is set to the value of
       threshold4_write_iosize. The metadata server might return a layout
       from offset zero with a length at least as long as 
       threshold4_write_iosize.

      </t>
      <t>
       A process on the client invokes a request to read
       from offset 10000 for length 50000. The client
       is using buffered I/O, and has buffer sizes of
       4096 bytes. The client intends to map the request
       of the process into a series of READ requests
       starting at offset 8192. The end offset needs to be higher
       than 10000 + 50000 = 60000, and the next offset that is
       a multiple of 4096 is 61440. The difference between 61440 and
       that starting offset of the layout is 53248 (which is
       the product of 4096 and 15).
       The value
       of threshold4_read_iosize is less than 53248,
       so the client sends a LAYOUTGET request with
       loga_offset set to 8192, loga_minlength set to
       53248, and loga_length set to the file's length
       (if known) minus 8192 or NFS4_UINT64_MAX (if the
       file's length is not known). Since this LAYOUTGET
       request exceeds the metadata server's threshold, it grants
       the layout, possibly with an initial offset of
       zero, with an end offset of at least 8192 + 53248 -
       1 = 61439, but preferably a layout with an offset
       aligned on the stripe width and a length that is
       a multiple of the stripe width.

      </t>


      <t>
        This strategy is as above, but the client is not using buffered I/O, and
        instead all internal I/O requests are sent directly to
        the server. The LAYOUTGET request has loga_offset equal to
        10000 and loga_minlength set to 50000. The value of loga_length
        is set to the length of the file. The metadata server is free to
        return a layout that fully overlaps the requested range, with
        a starting offset and length aligned on the stripe width.
      </t>

      <t>
       Again, a process on the client invokes a request
       to read from offset 10000 for length 50000 (i.e. a
       range with a starting offset of 10000 and an ending
       offset of 69999), and
       buffered I/O is in use.  The client is expecting
       that the server might not be able to return the
       layout for the full I/O range.


       The client intends to map the request of the
       process into a series of thirteen READ requests starting at
       offset 8192, each with length 4096, with a total
       length of 53248 (which equals 13 * 4096), which
       fully contains the range that client's process wants to read.

       Because the value of threshold4_read_iosize is equal to
       4096, it is practical and reasonable for the client to
       use several LAYOUTGET operations to complete the series
       of READs.

       The client sends a LAYOUTGET request with
       loga_offset set to 8192, loga_minlength set to 4096,
       and loga_length set to 53248 or higher.  The server
       will grant a layout possibly with an initial offset
       of zero, with an end offset of at least 8192 + 4096 -
       1 = 12287, but preferably a layout with an offset
       aligned on the stripe width and a length that is a
       multiple of the stripe width.  This will allow the
       client to make forward progress, possibly
       sending more LAYOUTGET operations for the remainder
       of the range.

     </t>

      <t>
        An NFS client detects a sequential read pattern,
        and so sends a LAYOUTGET operation that goes well beyond any
        current or pending read requests to the server. The
        server might likewise detect this pattern, and
        grant the LAYOUTGET request. Once the client
        reads from an offset of the file that represents
        50% of the way through the range of the last layout
        it received, in order to avoid stalling I/O that would wait
        for a layout, the client sends more operations 
        from an offset of the file that represents 50%
        of the way through the last layout it received. The client
        continues to request layouts with byte-ranges that are
        well in advance of the byte-ranges of
        recent and/or read requests of processes running on the client.

      </t>
      <t>
        This strategy is as above, but the client fails to detect the
        pattern, but the server does. The next time the
        metadata server gets a LAYOUTGET, it returns a layout with
        a length that is well beyond loga_minlength.

      </t>

      <t>
        A client is using buffered I/O, and has a long
        queue of write-behinds to process and also detects
        a sequential write pattern. It sends a LAYOUTGET
        for a layout that spans the range of the queued
        write-behinds and well beyond, including ranges
        beyond the filer's current length.  The client
        continues to send LAYOUTGET operations once the write-behind
        queue reaches 50% of the maximum queue length.
   
      </t>

      </list>
    </t>

    <t>
      Once the client has obtained a layout referring to a
      particular device ID, the metadata server MUST NOT
      delete the device ID until the layout is returned
      or revoked.

    </t>
    <t>
      CB_NOTIFY_DEVICEID can race with LAYOUTGET. One race
      scenario is that LAYOUTGET returns a device ID for which the
      client does not have device address mappings,
      and the metadata server sends a CB_NOTIFY_DEVICEID
      to add the device ID to the client's awareness
      and meanwhile the client sends GETDEVICEINFO on
      the device ID.  This scenario is discussed in
      <xref target="OP_GETDEVICEINFO_IMPLEMENTATION"/>.
      Another scenario is that the CB_NOTIFY_DEVICEID
      is processed by the client before it processes
      the results from LAYOUTGET.  The client will send
      a GETDEVICEINFO on the device ID.  If the results
      from GETDEVICEINFO are received before the client
      gets results from LAYOUTGET, then there is no
      longer a race. If the results from LAYOUTGET are
      received before the results from GETDEVICEINFO, the
      client can either wait for results of GETDEVICEINFO
      or send another one to get possibly more up-to-date
      device address mappings for the device ID.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_LAYOUTRETURN" title="Operation 51: LAYOUTRETURN - Release Layout Information" >

  <section toc="exclude" anchor="OP_LAYOUTRETURN_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>

/* Constants used for LAYOUTRETURN and CB_LAYOUTRECALL */
const LAYOUT4_RET_REC_FILE      = 1;
const LAYOUT4_RET_REC_FSID      = 2;
const LAYOUT4_RET_REC_ALL       = 3;

enum layoutreturn_type4 {
        LAYOUTRETURN4_FILE = LAYOUT4_RET_REC_FILE,
        LAYOUTRETURN4_FSID = LAYOUT4_RET_REC_FSID,
        LAYOUTRETURN4_ALL  = LAYOUT4_RET_REC_ALL
};

struct layoutreturn_file4 {
        offset4         lrf_offset;
        length4         lrf_length;
        stateid4        lrf_stateid;
        /* layouttype4 specific data */
        opaque          lrf_body&lt;>;
};

union layoutreturn4 switch(layoutreturn_type4 lr_returntype) {
        case LAYOUTRETURN4_FILE:
                layoutreturn_file4      lr_layout;
        default:
                void;
};

 </artwork>
</figure>

<figure>
 <artwork>

struct LAYOUTRETURN4args {
        /* CURRENT_FH: file */
        bool                    lora_reclaim;
        layouttype4             lora_layout_type;
        layoutiomode4           lora_iomode;
        layoutreturn4           lora_layoutreturn;
};


 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_RESULT" title="RESULT">
<figure>
 <artwork>
union layoutreturn_stateid switch (bool lrs_present) {
case TRUE:
        stateid4                lrs_stateid;
case FALSE:
        void;
};

union LAYOUTRETURN4res switch (nfsstat4 lorr_status) {
case NFS4_OK:
        layoutreturn_stateid    lorr_stateid;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation returns from the client to the server
      one or more layouts represented by the client ID
      (derived from the session ID in the preceding SEQUENCE
      operation), lora_layout_type, and lora_iomode.
      When lr_returntype is LAYOUTRETURN4_FILE, the
      returned layout is further identified by the current
      filehandle, lrf_offset, lrf_length, and lrf_stateid.
      If the lrf_length field is NFS4_UINT64_MAX, all bytes
      of the layout, starting at lrf_offset, are returned.
      When lr_returntype is LAYOUTRETURN4_FSID, the
      current filehandle is used to identify the file
      system and all layouts matching the client ID,
      the fsid of the file system, lora_layout_type, and
      lora_iomode are returned.  When lr_returntype is
      LAYOUTRETURN4_ALL, all layouts matching the client
      ID, lora_layout_type, and lora_iomode are returned
      and the current filehandle is not used.  After this
      call, the client MUST NOT use the returned layout(s)
      and the associated storage protocol to access the
      file data.

    </t>
    <t>
      If the set of layouts designated in the case of 
      LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL is empty, then no error
      results.  In the case of LAYOUTRETURN4_FILE, the byte-range
      specified is returned even if it is a subdivision of a layout 
      previously obtained with LAYOUTGET, a combination of multiple
      layouts previously obtained with LAYOUTGET, or a combination
      including some layouts previously obtained with LAYOUTGET, 
      and one or more subdivisions of such layouts.  When the
      byte-range does not designate any bytes for which a layout
      is held for the specified file, client ID, layout type and
      mode, no error results.
        See <xref target="bulk_layouts" /> for considerations with
        "bulk" return of layouts.
    </t>
    <t>
      The layout being returned may be a subset
      or superset of a layout specified by CB_LAYOUTRECALL.  However,
      if it is a subset, the recall is not complete until the full
      recalled scope has been returned.  Recalled scope refers to the
      byte-range in the case of LAYOUTRETURN4_FILE, the use of
      LAYOUTRETURN4_FSID, or the use of LAYOUTRETURN4_ALL.  There must
      be a LAYOUTRETURN with a matching scope to complete the return
      even if all current layout ranges have been previously individually
      returned. 
    </t>
    <t>
      For all lr_returntype values, an iomode of LAYOUTIOMODE4_ANY
      specifies that all layouts that match the other arguments to
      LAYOUTRETURN (i.e., client ID, lora_layout_type, and one of
      current filehandle and range; fsid derived from current
      filehandle; or LAYOUTRETURN4_ALL) are being returned.
    </t>
    <t>
      In the case that lr_returntype is LAYOUTRETURN4_FILE, the
      lrf_stateid provided by the client is a layout stateid as
      returned from previous layout operations.  Note that the "seqid"
      field of lrf_stateid MUST NOT be zero.  See Sections
      <xref target="stateid" format="counter" />, <xref
target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
    <t>
      Return of a layout or all layouts does not invalidate the
      mapping of storage device ID to a storage device address. The
      mapping remains in effect until specifically changed or deleted via
      device ID notification callbacks.
      Of course if there are no remaining
      layouts that refer to a previously used device ID, the server is
      free to delete a device ID without a notification callback, which
      will be the case when notifications are not in effect.
      
    </t>
    <t>
      If the lora_reclaim field is set to TRUE, the
      client is attempting to return a layout that
      was acquired before the restart of the metadata
      server during the metadata server's grace period.
      When returning layouts that were acquired during
      the metadata server's grace period, the client MUST set the
      lora_reclaim field to FALSE.  The lora_reclaim field
      MUST be set to FALSE also when lr_layoutreturn is
      LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL. See <xref
      target="OP_LAYOUTCOMMIT">LAYOUTCOMMIT </xref> for
      more details.

    </t>
    <t>
      Layouts may be returned when recalled or voluntarily (i.e.,
      before the server has recalled them).  In either case, the client
      must properly propagate state changed under the context of the
      layout to the storage device(s) or to the metadata server before
      returning the layout.
    </t>
    <t>
      If the client returns the layout in response to a
      CB_LAYOUTRECALL where the lor_recalltype field of the
      clora_recall field was LAYOUTRECALL4_FILE, the client
      should use the lor_stateid value from CB_LAYOUTRECALL
      as the value for lrf_stateid. Otherwise, it should
      use logr_stateid (from a previous LAYOUTGET result)
      or lorr_stateid (from a previous LAYRETURN result).
      This is done to indicate the point in time (in terms
      of layout stateid transitions) when the recall was
      sent.  The client uses the precise lora_recallstateid
      value and MUST NOT set the stateid's seqid to
      zero; otherwise, NFS4ERR_BAD_STATEID MUST be
      returned. NFS4ERR_OLD_STATEID can be returned if
      the client is using an old seqid, and the server
      knows the client should not be using the old
      seqid. For example, the client uses the seqid on slot 1 of
      the session, receives the response with the new
      seqid, and uses the slot to send another request
      with the old seqid.

    </t>
    <t>
      If a client fails to return a layout
      in a timely manner, then the metadata server SHOULD use its
      control protocol with the storage devices to fence the client
      from accessing the data referenced by the layout.  See
      <xref target="recalling_layout" /> for more details.
    </t>
    <t>
      If the LAYOUTRETURN request sets the lora_reclaim field to TRUE after
      the metadata server's grace period, NFS4ERR_NO_GRACE is returned.
    </t>
    <t>
      If the LAYOUTRETURN request sets the lora_reclaim field to TRUE
      and lr_returntype is set to LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL,
      NFS4ERR_INVAL is returned.
    </t>
    <t>
      If the client sets the lr_returntype field to
      LAYOUTRETURN4_FILE, then the lrs_stateid field
      will represent the layout stateid as updated for
      this operation's processing; the current stateid
      will also be updated to match the returned value.
      If the last byte of any layout for the current
      file, client ID, and layout type is being returned
      and there are no remaining pending CB_LAYOUTRECALL
      operations for which a LAYOUTRETURN operation must be
      done, lrs_present MUST be FALSE, and no stateid
      will be returned. In addition, the COMPOUND request's current
      stateid will be set to the all-zeroes special stateid
      (see <xref target="current_stateid"/>).  The server
      MUST reject with NFS4ERR_BAD_STATEID any further
      use of the current stateid in that COMPOUND until
      the current stateid is re-established by a later
      stateid-returning operation.

    </t>
    <t>
      On success, the current filehandle retains its value.
    </t>
    <t>
     If the EXCHGID4_FLAG_BIND_PRINC_STATEID
     capability is set on the client ID (see <xref
     target="OP_EXCHANGE_ID"/>), the server will
     require that the principal, security flavor,
     and if applicable, the GSS mechanism, combination
     that acquired the layout also be the one to send
     LAYOUTRETURN. This might not be possible
     if credentials for the principal are no
     longer available. The server will allow the
     machine credential or SSV credential (see <xref
     target="OP_EXCHANGE_ID" />) to send LAYOUTRETURN
     if LAYOUTRETURN's operation code was set in the
     spo_must_allow result of EXCHANGE_ID.

    </t>
  </section>
  <section toc="exclude" anchor="OP_LAYOUTRETURN_IMPLEMENTATION" title="IMPLEMENTATION">
  <t>
    The final LAYOUTRETURN operation in response to a CB_LAYOUTRECALL
    callback MUST be serialized with any outstanding, intersecting
    LAYOUTRETURN operations.  Note that it is possible that while a
    client is returning the layout for some recalled range, the server
    may recall a superset of that range (e.g., LAYOUTRECALL4_ALL); the final
    return operation for the latter must block until the former layout
    recall is done.
  </t>
  <t>
    Returning all layouts in a file system using LAYOUTRETURN4_FSID is
    typically done in response to a CB_LAYOUTRECALL for that file system
    as the final return operation. Similarly, LAYOUTRETURN4_ALL
    is used in response to a recall callback for all layouts.  It is
    possible that the client already returned some outstanding layouts
    via individual LAYOUTRETURN calls and the call for
    LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL marks the end of the
    LAYOUTRETURN sequence.  See <xref target="recall_robustness" />
    for more details.
  </t>
  <t>
    Once the client has returned all layouts referring to a particular
    device ID, the server MAY delete the device ID.
  </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section title="Operation 52: SECINFO_NO_NAME - Get Security on Unnamed Object" anchor="OP_SECINFO_NO_NAME">

  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
enum secinfo_style4 {
        SECINFO_STYLE4_CURRENT_FH       = 0,
        SECINFO_STYLE4_PARENT           = 1
};

/* CURRENT_FH: object or child directory */
typedef secinfo_style4 SECINFO_NO_NAME4args;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_RESULT" title="RESULT">
<figure>
 <artwork>
/* CURRENTFH: consumed if status is NFS4_OK */
typedef SECINFO4res SECINFO_NO_NAME4res;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_DESCRIPTION" title="DESCRIPTION">
    <t>
      Like the SECINFO operation, SECINFO_NO_NAME is used by the
      client to obtain a list of valid RPC authentication flavors for
      a specific file object.  Unlike SECINFO, SECINFO_NO_NAME only
      works with objects that are accessed by filehandle.
    </t>
    <t>
      There are two styles of SECINFO_NO_NAME, as determined by the
      value of the secinfo_style4 enumeration. If SECINFO_STYLE4_CURRENT_FH is
      passed, then SECINFO_NO_NAME is querying for the required
      security for the current filehandle. If SECINFO_STYLE4_PARENT is passed, then
      SECINFO_NO_NAME is querying for the required security of the
      current filehandle's parent. If the style selected is SECINFO_STYLE4_PARENT,
      then SECINFO should apply the same access methodology used for
      LOOKUPP when evaluating the traversal to the parent directory.
      Therefore, if the requester does not have the appropriate access
      to LOOKUPP the parent, then SECINFO_NO_NAME must behave the same
      way and return NFS4ERR_ACCESS.
    </t>
    <t>
      If PUTFH, PUTPUBFH, PUTROOTFH, or RESTOREFH returns
      NFS4ERR_WRONGSEC, then the client resolves the
      situation by sending a COMPOUND request that consists of
      PUTFH, PUTPUBFH, or PUTROOTFH immediately followed by
      SECINFO_NO_NAME, style SECINFO_STYLE4_CURRENT_FH.
      See <xref target="Security_Service_Negotiation" />
      for instructions on dealing with NFS4ERR_WRONGSEC error
      returns from PUTFH, PUTROOTFH, PUTPUBFH, or RESTOREFH.
    </t>
    <t>
      If SECINFO_STYLE4_PARENT is specified and there is no parent
      directory, SECINFO_NO_NAME MUST return NFS4ERR_NOENT.
    </t>
    <t>

      On success, the current filehandle is consumed
      (see <xref target="aftersecinfo" />), and if the
      next operation after SECINFO_NO_NAME tries to use
      the current filehandle, that operation will fail
      with the status NFS4ERR_NOFILEHANDLE.

    </t>
    <t>
      Everything else about SECINFO_NO_NAME is the same as SECINFO.
      See the discussion on SECINFO (<xref target="OP_SECINFO_DESCRIPTION"/>).
    </t>
  </section>
  <section toc="exclude" anchor="OP_SECINFO_NO_NAME_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      See the discussion on SECINFO (<xref target="OP_SECINFO_IMPLEMENTATION" />).
    </t>
  </section>
</section>

<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $   -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SEQUENCE" title="Operation 53: SEQUENCE - Supply Per-Procedure Sequencing and Control" >

  <section toc="exclude" anchor="OP_SEQUENCE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct SEQUENCE4args {
        sessionid4     sa_sessionid;
        sequenceid4    sa_sequenceid;
        slotid4        sa_slotid;
        slotid4        sa_highest_slotid;
        bool           sa_cachethis;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_RESULT" title="RESULT">
<figure>
 <artwork>
const SEQ4_STATUS_CB_PATH_DOWN                  = 0x00000001;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING      = 0x00000002;
const SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED       = 0x00000004;
const SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED     = 0x00000008;
const SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED    = 0x00000010;
const SEQ4_STATUS_ADMIN_STATE_REVOKED           = 0x00000020;
const SEQ4_STATUS_RECALLABLE_STATE_REVOKED      = 0x00000040;
const SEQ4_STATUS_LEASE_MOVED                   = 0x00000080;
const SEQ4_STATUS_RESTART_RECLAIM_NEEDED        = 0x00000100;
const SEQ4_STATUS_CB_PATH_DOWN_SESSION          = 0x00000200;
const SEQ4_STATUS_BACKCHANNEL_FAULT             = 0x00000400;
const SEQ4_STATUS_DEVID_CHANGED                 = 0x00000800;
const SEQ4_STATUS_DEVID_DELETED                 = 0x00001000;

struct SEQUENCE4resok {
        sessionid4      sr_sessionid;
        sequenceid4     sr_sequenceid;
        slotid4         sr_slotid;
        slotid4         sr_highest_slotid;
        slotid4         sr_target_highest_slotid;
        uint32_t        sr_status_flags;
};

union SEQUENCE4res switch (nfsstat4 sr_status) {
case NFS4_OK:
        SEQUENCE4resok  sr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The SEQUENCE operation is
      used by the server to implement session request control
      and the reply cache semantics.
    </t>
    <t>
      SEQUENCE MUST appear as the first operation of any COMPOUND
      in which it appears.  The error NFS4ERR_SEQUENCE_POS will be
      returned when it is found in any position in a COMPOUND
      beyond the first.  Operations other than SEQUENCE, BIND_CONN_TO_SESSION,
      EXCHANGE_ID, CREATE_SESSION, and DESTROY_SESSION,
      MUST NOT appear as the first operation in a
      COMPOUND.  Such operations MUST yield the error NFS4ERR_OP_NOT_IN_SESSION
      if they do appear at the start of a COMPOUND.
    </t>
    <t>
     If SEQUENCE is received on a connection not associated with the
     session via CREATE_SESSION or BIND_CONN_TO_SESSION, and
     connection association enforcement is enabled
     (see <xref target="OP_EXCHANGE_ID" />), then
     the server returns NFS4ERR_CONN_NOT_BOUND_TO_SESSION.
    </t>
    <t>
     The sa_sessionid argument identifies the session to which this
     request applies. The sr_sessionid result MUST equal
     sa_sessionid.
    </t>
    <t>
     The sa_slotid argument is the index in the reply cache
     for the request. The sa_sequenceid field is the sequence
     number of the request for the reply cache entry (slot).
     The sr_slotid result MUST equal sa_slotid. The sr_sequenceid
     result MUST equal sa_sequenceid.
    </t>
    <t>
     The sa_highest_slotid argument is the highest slot ID
     for which the client has a request outstanding; it could be
     equal to sa_slotid.
     The server returns two "highest_slotid" values: sr_highest_slotid
     and sr_target_highest_slotid. The former is the highest slot ID
     the server will accept in future SEQUENCE operation, and
     SHOULD NOT be less than the value of sa_highest_slotid
     (but see
     <xref target="Slot_Identifiers_and_Server_Reply_Cache" />
     for an exception).
     The latter is the highest slot ID the server would prefer the
     client use on a future SEQUENCE operation.
    </t>
    <t>
     If sa_cachethis is TRUE, then the client is requesting that
     the server cache the entire
     reply in the server's reply cache; therefore, the server MUST
     cache the reply (see <xref target="optional_reply_caching" />).
     The server MAY cache the reply if sa_cachethis is FALSE.
     If the server does not cache the entire reply, it
     MUST still record that it executed the request at
     the specified slot and sequence ID.
    </t>
    <t>
      The response to the SEQUENCE operation contains a
      word of status flags (sr_status_flags) that can
      provide to the client information related to the
      status of the client's lock state and communications
      paths.  Note that any status bits relating to lock
      state MAY be reset when lock state is lost due to a
      server restart (even if the session is persistent across
      restarts; session persistence does not imply 
      lock state persistence)
      or the establishment of a new client
      instance.

      <list style='hanging'> 
        <t hangText="SEQ4_STATUS_CB_PATH_DOWN"><vspace />
          When set, indicates that the client has no
          operational backchannel path for any session
          associated with the client ID, making it
          necessary for the client to re-establish one.
          This bit
          remains set on all SEQUENCE responses on all sessions
          associated with the client ID
          until at least one backchannel is
          available on any session associated with the client ID.
          If the client fails to re-establish a 
          backchannel for the client ID, it is subject to
          having recallable state revoked.
        </t>
        <t hangText="SEQ4_STATUS_CB_PATH_DOWN_SESSION"><vspace />
          When set, indicates that the session has
          no operational backchannel. There are two reasons
          why SEQ4_STATUS_CB_PATH_DOWN_SESSION may be set and not
          SEQ4_STATUS_CB_PATH_DOWN. First is that a callback operation
          that applies specifically to the
          session (e.g., CB_RECALL_SLOT, see <xref
          target="OP_CB_RECALL_SLOT" />) needs to be sent.
          Second is that the server did send a callback operation,
          but the connection was lost before the reply. The
          server cannot be sure whether or not the client received the
          callback operation, and so, per rules on
          request retry, the server MUST retry the callback
          operation over the same session. The 
          SEQ4_STATUS_CB_PATH_DOWN_SESSION bit is the indication
          to the client that it needs to associate a connection
          to the session's backchannel.
          This bit remains set on all SEQUENCE responses of the
          session until a connection is associated with the
          session's a backchannel.
          If the client fails to re-establish a 
          backchannel for the session, it is subject to
          having recallable state revoked.

        </t>
        <t hangText="SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRING"><vspace />
          When set, indicates that all GSS contexts or RPCSEC_GSS handles
          assigned to the session's backchannel will expire within a
          period equal to the lease time.  This bit remains set on all
          SEQUENCE replies until at least one of the following are true:

          <list style='symbols'>

          <t>
            All SSV RPCSEC_GSS handles on the session's backchannel
            have been destroyed and all non-SSV GSS contexts have expired.
          </t>
          <t>
            At least one more SSV RPCSEC_GSS handle has been added to
            the backchannel.
          </t>
          <t>
            The expiration time of at least one non-SSV GSS context
            of an RPCSEC_GSS handle
            is beyond the lease period from the current
            time (relative to the time of when a SEQUENCE
            response was sent)
          </t>

          </list>
        </t>
        <t hangText="SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED"><vspace />
          When set, indicates all non-SSV GSS contexts and all
          SSV RPCSEC_GSS handles assigned
          to the session's backchannel have expired or have been
          destroyed.
          This bit remains set on all SEQUENCE replies
          until at least one non-expired non-SSV GSS context for the
          session's backchannel has been established or at least one
          SSV RPCSEC_GSS handle has been assigned to the backchannel.
        </t>
        <t hangText="SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED"><vspace />
          When set, indicates that the lease has expired
          and as a result the server released all of the
          client's locking state.  This status bit remains
          set on all SEQUENCE replies until the loss of
          all such locks has been acknowledged by use of
          FREE_STATEID (see <xref target="OP_FREE_STATEID"
          />), or by establishing a new client instance by
          destroying all sessions (via DESTROY_SESSION),
          the client ID (via DESTROY_CLIENTID), and then
          invoking EXCHANGE_ID and CREATE_SESSION to
          establish a new client ID.

        </t>
        <t hangText="SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED"><vspace />
          When set, indicates that some subset of the client's locks 
          have been revoked due to expiration of the lease period 
          followed by another client's conflicting LOCK operation.
          This status bit remains set on all SEQUENCE replies
          until the loss of all
          such locks has been acknowledged by use of FREE_STATEID.
        </t>
        <t hangText="SEQ4_STATUS_ADMIN_STATE_REVOKED"><vspace />
          When set, indicates that one or more locks have been revoked 
          without expiration of the lease period, due to administrative 
          action.  This status bit remains set on all SEQUENCE replies
          until the loss of all
          such locks has been acknowledged by use of FREE_STATEID.
        </t>
        <t hangText="SEQ4_STATUS_RECALLABLE_STATE_REVOKED"><vspace />
	  When set, indicates that one or more recallable
	  objects have been revoked without expiration
	  of the lease period, due to the client's
	  failure to return them when recalled, which
	  may be a consequence of there being no working
	  backchannel and the client failing to re-establish
	  a backchannel per the SEQ4_STATUS_CB_PATH_DOWN,
	  SEQ4_STATUS_CB_PATH_DOWN_SESSION, or
	  SEQ4_STATUS_CB_GSS_CONTEXTS_EXPIRED status flags.
	  This status bit remains set on all SEQUENCE
	  replies until the loss of all such locks has
	  been acknowledged by use of FREE_STATEID.

        </t>
        <t hangText="SEQ4_STATUS_LEASE_MOVED"><vspace /> 
	  When set, indicates that responsibility for lease renewal has
          been transferred to one or more new servers.  This condition
          will continue until the client receives an NFS4ERR_MOVED
          error and the server receives the subsequent GETATTR for the
          fs_locations or fs_locations_info attribute for an access to
          each file system for which a lease has been moved to a new
          server. See <xref target="transferred_lease" />.
        </t>
        <t hangText="SEQ4_STATUS_RESTART_RECLAIM_NEEDED"><vspace />
	  When set, indicates that due to server
	  restart, the client must reclaim locking state. 
	  Until the client sends a global RECLAIM_COMPLETE
	  (<xref target="OP_RECLAIM_COMPLETE" />), every
	  SEQUENCE operation will return
	  SEQ4_STATUS_RESTART_RECLAIM_NEEDED.
        </t>
        <t hangText="SEQ4_STATUS_BACKCHANNEL_FAULT"><vspace />
          The server has encountered an unrecoverable fault
          with the backchannel (e.g., it has lost track of the
          sequence ID for a slot in the backchannel). The
          client MUST stop sending more requests on the
          session's fore channel, wait for all outstanding requests to
          complete on the fore and back channel, and then
          destroy the session.
        </t>
	<t hangText="SEQ4_STATUS_DEVID_CHANGED"><vspace />
	  The client is using device ID notifications and the server
	  has changed a device ID mapping held by the client. This
	  flag will stay present until the client has obtained the new
	  mapping with GETDEVICEINFO.
	</t>
	<t hangText="SEQ4_STATUS_DEVID_DELETED"><vspace />
	  The client is using device ID notifications and the server
	  has deleted a device ID mapping held by the client.
          This flag will stay in effect until the client sends a GETDEVICEINFO
          on the device ID with a null value in the argument gdia_notify_types.
	</t>
      </list>
    </t>
    <t>
      The value of the sa_sequenceid argument relative to
      the cached sequence ID on the slot falls into one
      of three cases.
      <list style="symbols">
      <t>
       If the difference between sa_sequenceid and
       the server's cached sequence ID at the slot ID
       is two (2) or more,
       or if sa_sequenceid is less
       than the cached sequence ID (accounting
       for wraparound of the unsigned sequence ID value),
       then the server MUST return NFS4ERR_SEQ_MISORDERED.
      </t>
      <t>
       If sa_sequenceid and the cached sequence ID are
       the same, this is a retry, and the server replies
       with what is recorded in the reply
       cache.
The lease is possibly renewed as described below.

      </t>
      <t>
       If sa_sequenceid is one greater (accounting for
       wraparound) than the cached sequence ID, then
       this is a new request, and the slot's sequence
       ID is incremented.  The operations subsequent to
       SEQUENCE, if any, are processed. If there are no
       other operations, the only other effects are to
       cache the SEQUENCE reply in the slot, maintain the
       session's activity, and possibly renew the lease.

      </t>
      </list>
    </t>
    <t>
     If the client reuses a slot ID and sequence ID for
     a completely different request, the server MAY treat
     the request as if it is a retry of what it has already
     executed. The server MAY however detect the client's
     illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.

    </t>
    <t>
     If SEQUENCE returns an error, then the state of the
     slot (sequence ID, cached reply) MUST NOT change,
     and the associated lease MUST NOT be renewed.

    </t>
    <t>
     If SEQUENCE returns NFS4_OK, then the associated
     lease MUST be renewed (see <xref target="lease_renewal"/>),
     except if SEQ4_STATUS_EXPIRED_ALL_STATE_REVOKED is
     returned in sr_status_flags.

    </t>

  </section>
  <section toc="exclude" anchor="OP_SEQUENCE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The server MUST maintain a mapping of session ID to client ID
      in order to validate any operations that follow SEQUENCE
      that take a stateid as an argument and/or result.
    </t>
    <t>
      If the client establishes a persistent session, then
      a SEQUENCE received after a server restart might encounter 
      requests performed and recorded in a persistent reply 
      cache before the server restart.  In this case, SEQUENCE
      will be processed successfully, while requests that
      were not previously performed and recorded are rejected with
      NFS4ERR_DEADSESSION.
   </t>
   <t>
      Depending on which of the operations within the COMPOUND were
      successfully
      performed before the server restart, these operations will
      also have replies sent from the server reply cache. 
      Note that when these operations establish locking state, it
      is locking state that applies to the previous server instance
      and to the previous client ID, even though the
      server restart, which logically happened after these 
      operations, eliminated that state.  In the
      case of a partially executed COMPOUND, processing may reach
      an operation not processed during the earlier server instance,
      making this operation a new one and not performable on the
      existing session.  In this case, NFS4ERR_DEADSESSION will be
      returned from that operation.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_SET_SSV" 
         title="Operation 54: SET_SSV - Update SSV for a Client ID" >

  <section toc="exclude" anchor="OP_SET_SSV_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct ssa_digest_input4 {
        SEQUENCE4args sdi_seqargs;
};

struct SET_SSV4args {
        opaque          ssa_ssv&lt;>;
        opaque          ssa_digest&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_RESULT" title="RESULT">
<figure>
 <artwork>
struct ssr_digest_input4 {
        SEQUENCE4res sdi_seqres;
};

struct SET_SSV4resok {
        opaque          ssr_digest&lt;>;
};

union SET_SSV4res switch (nfsstat4 ssr_status) {
case NFS4_OK:
        SET_SSV4resok   ssr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is used to update the
      SSV for a client ID. Before SET_SSV is called the
      first time on a client ID, the SSV is zero.
      The SSV is the key used for the SSV GSS mechanism
      (<xref target="ssv_mech" />)
    </t>
    <t>
      SET_SSV MUST be preceded by a
      SEQUENCE operation in the same COMPOUND.
      It MUST NOT be used if the client
      did not opt for SP4_SSV state protection when the
      client ID was created
      (see <xref target="OP_EXCHANGE_ID" />);
      the server returns NFS4ERR_INVAL in that case.
    </t>
    <t>
      The field ssa_digest is computed as the output of
      the HMAC (<xref target="RFC2104">RFC 2104</xref>) using the subkey derived
      from the SSV4_SUBKEY_MIC_I2T and current SSV
      as the key (see <xref target="ssv_mech" /> for a
      description of subkeys), and an XDR encoded value of data type ssa_digest_input4.
      The field sdi_seqargs is equal to the
      arguments of the SEQUENCE operation
      for the COMPOUND procedure that
      SET_SSV is within.
    </t>
    <t>
      The argument ssa_ssv
      is XORed with the current SSV to produce
      the new SSV. The argument ssa_ssv SHOULD be generated randomly.
    </t>
    <t>
      In the response, ssr_digest is the output of the HMAC using the
      subkey derived from SSV4_SUBKEY_MIC_T2I and new SSV as the key,
      and an XDR encoded value of data type ssr_digest_input4.  The
      field sdi_seqres is equal to the results of the SEQUENCE
      operation for the COMPOUND procedure that SET_SSV is within.
    </t>
    <t>
      As noted in <xref target="OP_EXCHANGE_ID" />, the client and
      server can maintain multiple concurrent versions of the SSV.
      The client and server each MUST maintain an internal
      SSV version number, which is set to one the first time
      SET_SSV executes on the server and the client
      receives the first SET_SSV reply. Each subsequent
      SET_SSV increases the internal SSV version number by one. The
      value of this version number corresponds to the smpt_ssv_seq,
      smt_ssv_seq, sspt_ssv_seq, and ssct_ssv_seq fields of the
      SSV GSS mechanism tokens (see <xref target="ssv_mech"/>).
    </t>
  </section>
  <section toc="exclude" anchor="OP_SET_SSV_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      When the server receives ssa_digest, it MUST verify the digest
      by computing the digest the same way the client did and
      comparing it with ssa_digest. If the server gets a different
      result, this is an error, NFS4ERR_BAD_SESSION_DIGEST.
      This error might be the result of another SET_SSV from the
      same client ID changing the SSV. If so, the client recovers
      by sending a SET_SSV operation again with a recomputed digest based on
      the subkey of the new SSV. If the transport connection is dropped after
      the SET_SSV request is sent, but before the 
      SET_SSV reply is received, then there are special considerations
      for recovery if the client has no more connections associated
      with sessions associated with the client ID of the SSV. See
      <xref target="OP_BIND_CONN_TO_SESSION_IMPLEMENTATION"/>.
    </t>
    <t>      
      Clients SHOULD NOT send an ssa_ssv that is equal to a previous
      ssa_ssv, nor equal to a previous or current SSV (including an ssa_ssv equal to zero
      since the SSV is initialized to zero when the client ID is created).
    </t>
    <t>      
      Clients SHOULD send SET_SSV with RPCSEC_GSS privacy. Servers
      MUST support RPCSEC_GSS with privacy for any COMPOUND that has {
      SEQUENCE, SET_SSV }.
    </t>
    <t>
      A client SHOULD NOT send SET_SSV with the SSV GSS
      mechanism's credential because the purpose of SET_SSV
      is to seed the SSV from non-SSV credentials. Instead,
      SET_SSV SHOULD be sent with the credential of
      a user that is accessing the client ID for the
      first time

      (<xref target="protect_state_change" />).

      However, if the client does send SET_SSV with SSV
      credentials, the digest protecting the arguments
      uses the value of the SSV before ssa_ssv is XORed in,
      and the digest protecting the results uses the value
      of the SSV after the ssa_ssv is XORed in.

    </t>
      
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_TEST_STATEID" title="Operation 55: TEST_STATEID - Test Stateids for Validity" >

  <section toc="exclude" anchor="OP_TEST_STATEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct TEST_STATEID4args {
        stateid4        ts_stateids&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID_RESULT" title="RESULT">
<figure>
 <artwork>
struct TEST_STATEID4resok {
        nfsstat4        tsr_status_codes&lt;>;
};

union TEST_STATEID4res switch (nfsstat4 tsr_status) {
    case NFS4_OK:
        TEST_STATEID4resok tsr_resok4;
    default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID4_DESCRIPTION" title="DESCRIPTION">
    <t>
      The TEST_STATEID operation is used to check the validity of 
      a set of stateids.  It can be used at any time, but the client
      should definitely use it when it 
      receives an indication that one or more of its stateids have been
      invalidated due to lock revocation.  This occurs when the SEQUENCE
      operation returns with one of the following sr_status_flags set:
      <list style='symbols'>
        <t>
          SEQ4_STATUS_EXPIRED_SOME_STATE_REVOKED
        </t>
        <t>
          SEQ4_STATUS_EXPIRED_ADMIN_STATE_REVOKED
        </t>
        <t>
          SEQ4_STATUS_EXPIRED_RECALLABLE_STATE_REVOKED
        </t>
      </list>
    </t>
    <t>
      The client can use TEST_STATEID one or more times to test the
      validity of its stateids.  Each use of TEST_STATEID allows a large
      set of such stateids to be tested and avoids problems with earlier
      stateids in a COMPOUND request from interfering with the checking of
      subsequent stateids, as would happen if individual stateids were
      tested by a series of corresponding by operations in a COMPOUND
      request.

    </t>
    <t>
      For each stateid, the server returns the status code that 
      would be returned if that stateid were to be used in normal
      operation.  Returning such a status indication is not an
      error and does not cause COMPOUND processing to terminate.  Checks
      for the validity of the stateid proceed as they would for
      normal operations with a number of exceptions:
      <list style='symbols'>  
        <t>
          There is no check for the type of stateid object, as would be 
          the case for normal use of a stateid.
        </t>
        <t>
          There is no reference to the current filehandle.
        </t>
        <t>
          Special stateids are always considered invalid (they result
          in the error code NFS4ERR_BAD_STATEID).
        </t>
      </list> 
    </t>
    <t>
      All stateids are interpreted as being associated with the client
      for the current session.  Any possible association with a previous
      instance of the client (as stale stateids) is not considered.
    </t>
    <t>
      The valid status values in the returned status_code array 
      are NFS4ERR_OK, NFS4ERR_BAD_STATEID, NFS4ERR_OLD_STATEID, 
      NFS4ERR_EXPIRED, NFS4ERR_ADMIN_REVOKED, and NFS4ERR_DELEG_REVOKED.
    </t>
  </section>
  <section toc="exclude" anchor="OP_TEST_STATEID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      See Sections <xref target="stateid_structure" format="counter" /> and
<xref target="stateid_lifetime" format="counter" />
      for a discussion of stateid structure, lifetime, and validation.
    </t>
  </section>
</section>

<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_WANT_DELEGATION" 
         title="Operation 56: WANT_DELEGATION - Request Delegation" >

  <section toc="exclude" anchor="OP_WANT_DELEGATION_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
union deleg_claim4 switch (open_claim_type4 dc_claim) {
/*
 * No special rights to object.  Ordinary delegation
 * request of the specified object.  Object identified
 * by filehandle.
 */
case CLAIM_FH: /* new to v4.1 */
        /* CURRENT_FH: object being delegated */
        void;

/*
 * Right to file based on a delegation granted
 * to a previous boot instance of the client.
 * File is specified by filehandle.
 */
case CLAIM_DELEG_PREV_FH: /* new to v4.1 */
        /* CURRENT_FH: object being delegated */
        void;

/*
 * Right to the file established by an open previous
 * to server reboot.  File identified by filehandle.
 * Used during server reclaim grace period.
 */
case CLAIM_PREVIOUS:
        /* CURRENT_FH: object being reclaimed */
        open_delegation_type4   dc_delegate_type;
};

struct WANT_DELEGATION4args {
        uint32_t        wda_want;
        deleg_claim4    wda_claim;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_RESULT" title="RESULT">
<figure>
 <artwork>
union WANT_DELEGATION4res switch (nfsstat4 wdr_status) {
case NFS4_OK:
        open_delegation4 wdr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_DESCRIPTION" title="DESCRIPTION">
    <t>
      Where this description mandates the return of a specific error
      code for a specific condition, and where multiple conditions
      apply, the server MAY return any of the mandated error codes.
    </t>
    <t>
      This operation allows a client to:
      <list style='symbols'>
      <t>
       Get a delegation on all types
       of files except directories.
      </t>
      <t>
       Register a "want" for a delegation for the
       specified file object, and be notified via a
       callback when the delegation is available. The
       server MAY support notifications of availability
       via callbacks. If the server does not support
       registration of wants, it MUST NOT return
       an error to indicate that, and instead MUST
       return with ond_why set to WND4_CONTENTION or
       WND4_RESOURCE and ond_server_will_push_deleg or
       ond_server_will_signal_avail set to FALSE.  When the
       server indicates that it will notify the client
       by means of a callback, it will either provide
       the delegation using a CB_PUSH_DELEG operation or
       cancel its promise by sending a CB_WANTS_CANCELLED
       operation.

      </t>
      <t>
       Cancel a want for a delegation. 
      </t>
      </list>
      </t>
    <t>
      The client SHOULD NOT set OPEN4_SHARE_ACCESS_READ and SHOULD NOT
      set OPEN4_SHARE_ACCESS_WRITE in wda_want. If it does, the server
      MUST ignore them.
    </t>
    <t>
      The meanings of the following flags in wda_want are the same as
      they are in OPEN, except as noted below.
      <list style="symbols">
        <t>
          OPEN4_SHARE_ACCESS_WANT_READ_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_ANY_DELEG
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_NO_DELEG. Unlike the OPEN operation,
          this flag SHOULD NOT be set by the client in the arguments to
          WANT_DELEGATION, and MUST be ignored by the server.

        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_CANCEL
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_SIGNAL_DELEG_WHEN_RESRC_AVAIL
        </t>
        <t>
          OPEN4_SHARE_ACCESS_WANT_PUSH_DELEG_WHEN_UNCONTENDED
        </t>
      </list>
    </t>
    <t>
      The handling of the above flags in WANT_DELEGATION is the same
      as in OPEN.  Information about the delegation and/or the 
      promises the server is making regarding future callbacks are
      the same as those described in the open_delegation4 structure.
    </t>
    <t>
      The successful results of WANT_DELEGATION are of data type
      open_delegation4, which is the same data type as the "delegation"
      field in the results of the OPEN operation
      (see <xref target="OP_OPEN_DESCRIPTION" />).
      The server constructs wdr_resok4 the same way it constructs
      OPEN's "delegation" with one difference:
      WANT_DELEGATION MUST NOT return a delegation type of
      OPEN_DELEGATE_NONE.
    </t>
    <t> 
      If ((wda_want &amp; OPEN4_SHARE_ACCESS_WANT_DELEG_MASK) &amp;
          ~OPEN4_SHARE_ACCESS_WANT_NO_DELEG) is zero,
      then the client is indicating no
      explicit desire or non-desire for a delegation and the server MUST return 
      NFS4ERR_INVAL.
    </t>
    <t>
       The client uses the 
          OPEN4_SHARE_ACCESS_WANT_CANCEL
       flag in the WANT_DELEGATION 
       operation to cancel a previously requested want for a delegation.
       Note that if the server is in the process of sending the
       delegation (via CB_PUSH_DELEG) at the time the client sends
       a cancellation of the want, the delegation might still be pushed
       to the client.
    </t>
    <t>
     If WANT_DELEGATION fails to return a delegation, and
     the server returns NFS4_OK, the server MUST set the
     delegation type to OPEN4_DELEGATE_NONE_EXT, and set
     od_whynone, as described in <xref target="OP_OPEN"
     />.  Write delegations are not available for
     file types that are not writable. This includes
     file objects of types NF4BLK, NF4CHR, NF4LNK,
     NF4SOCK, and NF4FIFO. If the client requests
     OPEN4_SHARE_ACCESS_WANT_WRITE_DELEG without
     OPEN4_SHARE_ACCESS_WANT_READ_DELEG on an object with
     one of the aforementioned file types, the server must
     set wdr_resok4.od_whynone.ond_why to 
     WND4_WRITE_DELEG_NOT_SUPP_FTYPE.
    </t>  
  </section>
  <section toc="exclude" anchor="OP_WANT_DELEGATION_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A request for a conflicting delegation is not normally intended to trigger 
      the recall of the existing delegation.  Servers may choose to treat
      some clients as having higher priority such that their wants will
      trigger recall of an existing delegation, although that is expected
      to be an unusual situation.
    </t>
    <t>
      Servers will generally recall delegations assigned by WANT_DELEGATION
      on the same basis as those assigned by OPEN.  CB_RECALL will generally
      be done only when other clients perform operations inconsistent with
      the delegation.  The normal response to aging of delegations is to use
      CB_RECALL_ANY, in order to give the client the opportunity to keep
      the delegations most useful from its point of view.
    </t>  

  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_DESTROY_CLIENTID" title="Operation 57: DESTROY_CLIENTID - Destroy a Client ID" >

  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct DESTROY_CLIENTID4args {
        clientid4       dca_clientid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_RESULT" title="RESULT">
<figure>
 <artwork>
struct DESTROY_CLIENTID4res {
        nfsstat4        dcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_DESCRIPTION" title="DESCRIPTION">
    <t>
      The DESTROY_CLIENTID operation destroys the
      client ID.  If there are sessions (both idle and
      non-idle), opens, locks, delegations, layouts,
      and/or wants (<xref target="OP_WANT_DELEGATION" />)
      associated with the unexpired lease of the client
      ID, the server MUST return NFS4ERR_CLIENTID_BUSY.
      DESTROY_CLIENTID MAY be preceded with a SEQUENCE
      operation as long as the client ID derived from the
      session ID of SEQUENCE is not the same as the client
      ID to be destroyed. If the client IDs are the same,
      then the server MUST return NFS4ERR_CLIENTID_BUSY.

    </t>

    <t>
      If DESTROY_CLIENTID is not prefixed by SEQUENCE,
      it MUST be the only operation in the COMPOUND
      request (otherwise, the server MUST return
      NFS4ERR_NOT_ONLY_OP).  If the operation is sent
      without a SEQUENCE preceding it, a client that
      retransmits the request may receive an error in
      response, because the original request might have
      been successfully executed.

    </t>
  </section>
  <section toc="exclude" anchor="OP_DESTROY_CLIENTID_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      DESTROY_CLIENTID allows a server to immediately
      reclaim the resources consumed by an unused client
      ID, and also to forget that it ever generated the
      client ID. By forgetting that it ever generated the client
      ID, the server can safely reuse the client ID on a
      future EXCHANGE_ID operation.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_RECLAIM_COMPLETE" title="Operation 58: RECLAIM_COMPLETE - Indicates Reclaims Finished" >

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct RECLAIM_COMPLETE4args {
        /*
         * If rca_one_fs TRUE,
         *
         *    CURRENT_FH: object in
         *    file system reclaim is
         *    complete for.
         */
        bool            rca_one_fs;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct RECLAIM_COMPLETE4res {
        nfsstat4        rcr_status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_DESCRIPTION" title="DESCRIPTION">
    <t>
      A RECLAIM_COMPLETE operation is used to indicate that the client
      has reclaimed all of the locking state that it will recover,
      when it is recovering state due to either a server restart or the
      transfer of a file system to another server.  There are two types
      of RECLAIM_COMPLETE operations:
      <list style="symbols">
        <t>
          When rca_one_fs is FALSE, a global RECLAIM_COMPLETE is being
          done.  This indicates that recovery of all
          locks that the client held on the previous server instance
          have been completed.
        </t>
        <t>
          When rca_one_fs is TRUE, a file system-specific RECLAIM_COMPLETE
          is being done.  This indicates that recovery of locks
          for a single fs (the one designated by the current filehandle)
          due to a file system transition have been completed.  Presence
          of a current filehandle is only required when rca_one_fs is set to TRUE. 
        </t>
      </list>
    </t>
    <t>
      Once a RECLAIM_COMPLETE is done, there can be no further
      reclaim operations for locks whose scope is defined as having
      completed recovery.  Once the client sends RECLAIM_COMPLETE, 
      the server will not allow the client to do
      subsequent reclaims of locking state for that scope 
      and, if these are attempted, will return NFS4ERR_NO_GRACE.
    </t>
    <t>
      Whenever a client establishes a new client ID and before it does
      the first non-reclaim operation that obtains a lock, it MUST send a
      RECLAIM_COMPLETE with rca_one_fs set to FALSE, even if there are no locks to 
      reclaim.  If non-reclaim
      locking operations are done before the RECLAIM_COMPLETE, an NFS4ERR_GRACE
      error will be returned.
    </t>
    <t>
      Similarly, when the client accesses a file system on a new
      server, before it sends the first non-reclaim operation that
      obtains a lock on this new server, it MUST send a RECLAIM_COMPLETE
      with rca_one_fs set to TRUE and current filehandle within that file system,
      even if there are no locks to reclaim.  If non-reclaim locking
      operations are done on that file system before the
      RECLAIM_COMPLETE, an NFS4ERR_GRACE error will be returned.
    </t>
    <t>
      Any locks not reclaimed at the point at which RECLAIM_COMPLETE
      is done become non-reclaimable.  The client MUST NOT attempt 
      to reclaim them, either during 
      the current server instance or in any subsequent
      server instance, or on another server to which responsibility
      for that file system is transferred.  If the client were to do so, 
      it would be
      violating the protocol by representing itself as owning locks
      that it does not own, and so has no right to reclaim.  See
      <xref target="network_partitions_and_recovery" /> for a 
      discussion of edge conditions related to lock reclaim.
    </t>
    <t>
      By sending a RECLAIM_COMPLETE, the client indicates readiness
      to proceed to do normal non-reclaim locking operations.  The client
      should be aware that such operations may temporarily result in 
      NFS4ERR_GRACE errors until the server is ready to terminate its
      grace period.
    </t>
  </section>
  <section toc="exclude" anchor="OP_RECLAIM_COMPLETE_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      Servers will typically use the information as to when reclaim
      activity is complete to reduce the length of the grace period.
      When the server maintains in persistent storage
      a list of clients that might have had locks,
      it is in a position to use the fact that
      all such clients have done a RECLAIM_COMPLETE to terminate the
      grace period and begin normal operations (i.e., grant requests
      for new locks) sooner than it might otherwise.
    </t>
    <t>
      Latency can be minimized by doing a RECLAIM_COMPLETE as part of
      the COMPOUND request in which the last lock-reclaiming operation
      is done.  When there are no reclaims to be done, RECLAIM_COMPLETE
      should be done immediately in order to allow the grace period 
      to end as soon as possible.
    </t>
    <t>
      RECLAIM_COMPLETE should only be done once for each server instance
      or occasion of the transition of a file system.
      If it is done a second time, the error NFS4ERR_COMPLETE_ALREADY will 
      result.  Note that because of the session feature's retry protection,
      retries of COMPOUND
      requests containing RECLAIM_COMPLETE operation will not result 
      in this error.
    </t>
    <t>
      When a RECLAIM_COMPLETE is sent, the client effectively acknowledges
      any locks not yet reclaimed as lost.  This allows the server to
      re-enable the client to recover locks if
      the occurrence of edge conditions, as described in 
      <xref target="network_partitions_and_recovery" />, had caused the
      server to disable the client from recovering locks.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_ILLEGAL" title="Operation 10044: ILLEGAL - Illegal Operation" >

  <section toc="exclude" anchor="OP_ILLEGAL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="OP_ILLEGAL_RESULTS" title="RESULTS">
<figure>
 <artwork>
struct ILLEGAL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_ILLEGAL_DESCRIPTION" title="DESCRIPTION">
    <t>
      This operation is a placeholder for encoding a result to handle the
      case of the client sending an operation code within COMPOUND that is
      not supported. See the COMPOUND procedure description for more
      details.
    </t>
    <t>
      The status field of ILLEGAL4res MUST be set to NFS4ERR_OP_ILLEGAL.
    </t>
  </section>
  <section toc="exclude" anchor="OP_ILLEGAL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      A client will probably not send an operation with code OP_ILLEGAL but
      if it does, the response will be ILLEGAL4res just as it would be with
      any other invalid operation code. Note that if the server gets an
      illegal operation code that is not OP_ILLEGAL, and if the server
      checks for legal operation codes during the XDR decode phase, then the
      ILLEGAL4res would not be returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41callbackprocedures" title="NFSv4.1 Callback Procedures">
<t>
The procedures used for callbacks are defined in the following
sections.  In the interest of clarity, the terms "client" and "server"
refer to NFS clients and servers, despite the fact that for an
individual callback RPC, the sense of these terms would be precisely
the opposite.
</t>
<t>
 Both procedures, CB_NULL and CB_COMPOUND, MUST be implemented.
</t>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_CB_NULL" title="Procedure 0: CB_NULL - No Operation" >

  <section toc="exclude" anchor="PROC_CB_NULL_ARGUMENTS" title="ARGUMENTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_RESULTS" title="RESULTS">
    <figure>
      <artwork>
void;
      </artwork>
    </figure>
  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_DESCRIPTION" title="DESCRIPTION">
    <t>
      CB_NULL is the standard ONC RPC NULL procedure, with the standard void argument and void response.  Even though
      there is no direct functionality associated with this procedure, the
      server will use CB_NULL to confirm the existence of a path for RPCs
      from the server to client.
    </t>

  </section>

  <section toc="exclude" anchor="PROC_CB_NULL_ERRORS" title="ERRORS">
    <t>
      None.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="PROC_CB_COMPOUND" title="Procedure 1: CB_COMPOUND - Compound Operations" >

  <section toc="exclude" anchor="PROC_CB_COMPOUND_ARGUMENTS" title="ARGUMENTS">
<figure>
 <artwork>

enum nfs_cb_opnum4 {
        OP_CB_GETATTR           = 3,
        OP_CB_RECALL            = 4,
/* Callback operations new to NFSv4.1 */
        OP_CB_LAYOUTRECALL      = 5,
        OP_CB_NOTIFY            = 6,
        OP_CB_PUSH_DELEG        = 7,
        OP_CB_RECALL_ANY        = 8,
        OP_CB_RECALLABLE_OBJ_AVAIL = 9,
        OP_CB_RECALL_SLOT       = 10,
        OP_CB_SEQUENCE          = 11,
        OP_CB_WANTS_CANCELLED   = 12,
        OP_CB_NOTIFY_LOCK       = 13,
        OP_CB_NOTIFY_DEVICEID   = 14,

        OP_CB_ILLEGAL           = 10044
};
 </artwork>
</figure>
<figure>
 <artwork>
union nfs_cb_argop4 switch (unsigned argop) {
 case OP_CB_GETATTR:
      CB_GETATTR4args           opcbgetattr;
 case OP_CB_RECALL:
      CB_RECALL4args            opcbrecall;
 case OP_CB_LAYOUTRECALL:
      CB_LAYOUTRECALL4args      opcblayoutrecall;
 case OP_CB_NOTIFY:
      CB_NOTIFY4args            opcbnotify;
 case OP_CB_PUSH_DELEG:
      CB_PUSH_DELEG4args        opcbpush_deleg;
 case OP_CB_RECALL_ANY:
      CB_RECALL_ANY4args        opcbrecall_any;
 case OP_CB_RECALLABLE_OBJ_AVAIL:
      CB_RECALLABLE_OBJ_AVAIL4args opcbrecallable_obj_avail;
 case OP_CB_RECALL_SLOT:
      CB_RECALL_SLOT4args       opcbrecall_slot;
 case OP_CB_SEQUENCE:
      CB_SEQUENCE4args          opcbsequence;
 case OP_CB_WANTS_CANCELLED:
      CB_WANTS_CANCELLED4args   opcbwants_cancelled;
 case OP_CB_NOTIFY_LOCK:
      CB_NOTIFY_LOCK4args       opcbnotify_lock;
 case OP_CB_NOTIFY_DEVICEID:
      CB_NOTIFY_DEVICEID4args   opcbnotify_deviceid;
 case OP_CB_ILLEGAL:            void;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct CB_COMPOUND4args {
        utf8str_cs      tag;
        uint32_t        minorversion;
        uint32_t        callback_ident;
        nfs_cb_argop4   argarray&lt;>;
};
 </artwork>
</figure>

  </section>

  <section toc="exclude" anchor="PROC_CB_COMPOUND_RESULTS" title="RESULTS">
<figure>
 <artwork>
union nfs_cb_resop4 switch (unsigned resop) {
 case OP_CB_GETATTR:    CB_GETATTR4res  opcbgetattr;
 case OP_CB_RECALL:     CB_RECALL4res   opcbrecall;

 /* new NFSv4.1 operations */
 case OP_CB_LAYOUTRECALL:
                        CB_LAYOUTRECALL4res
                                        opcblayoutrecall;

 case OP_CB_NOTIFY:     CB_NOTIFY4res   opcbnotify;

 case OP_CB_PUSH_DELEG: CB_PUSH_DELEG4res
                                        opcbpush_deleg;

 case OP_CB_RECALL_ANY: CB_RECALL_ANY4res
                                        opcbrecall_any;

 case OP_CB_RECALLABLE_OBJ_AVAIL:
                        CB_RECALLABLE_OBJ_AVAIL4res
                                opcbrecallable_obj_avail;

 case OP_CB_RECALL_SLOT:
                        CB_RECALL_SLOT4res
                                        opcbrecall_slot;

 case OP_CB_SEQUENCE:   CB_SEQUENCE4res opcbsequence;

 case OP_CB_WANTS_CANCELLED:
                        CB_WANTS_CANCELLED4res
                                opcbwants_cancelled;

 case OP_CB_NOTIFY_LOCK:
                        CB_NOTIFY_LOCK4res
                                        opcbnotify_lock;

 case OP_CB_NOTIFY_DEVICEID:
                        CB_NOTIFY_DEVICEID4res
                                        opcbnotify_deviceid;

 /* Not new operation */
 case OP_CB_ILLEGAL:    CB_ILLEGAL4res  opcbillegal;
};
 </artwork>
</figure>
<figure>
 <artwork>
struct CB_COMPOUND4res {
        nfsstat4 status;
        utf8str_cs      tag;
        nfs_cb_resop4   resarray&lt;>;
};
 </artwork>
</figure>
  </section>

  <section toc="exclude" anchor="OP_CB_COMPOUND_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_COMPOUND procedure is used to combine one or more of the
      callback procedures into a single RPC request.  The main callback RPC
      program has two main procedures: CB_NULL and CB_COMPOUND.  All other
      operations use the CB_COMPOUND procedure as a wrapper.
    </t>
    <t>
      During the processing of the CB_COMPOUND procedure, the client may find
      that it does not have the available resources to execute any or all of
      the operations within the CB_COMPOUND sequence.
      Refer to <xref target="COMPOUND_Sizing_Issues" /> for details.
    </t>
    <t>
     The minorversion field of the arguments MUST be the same as the
     minorversion of the COMPOUND procedure used to create the client ID
     and session. For NFSv4.1, minorversion MUST be set to 1.
    </t>
    <t>
      Contained within the CB_COMPOUND results is a "status" field.  This
      status MUST be equal to the status of the last operation that was
      executed within the CB_COMPOUND procedure.  Therefore, if an operation
      incurred an error, then the "status" value will be the same error value
      as is being returned for the operation that failed.
    </t>
    <t>
      The "tag" field is handled the same way as that of the COMPOUND
      procedure (see <xref target="OP_COMPOUND_DESCRIPTION" />).
    </t>
    <t>
      Illegal operation codes are handled in the same way as they are
      handled for the COMPOUND procedure.
    </t>
  </section>
  <section toc="exclude" anchor="PROC_CB_COMPOUND_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The CB_COMPOUND procedure is used to combine individual operations
      into a single RPC request.  The client interprets each of the
      operations in turn.  If an operation is executed by the client and
      the status of that operation is NFS4_OK, then the next operation in
      the CB_COMPOUND procedure is executed.  The client continues this
      process until there are no more operations to be executed or one of
      the operations has a status value other than NFS4_OK.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_COMPOUND_ERRORS" title="ERRORS">
    <t>
     CB_COMPOUND will of course return every error that each operation on
     the backchannel can return (see <xref target="cb_op_error_returns"/>).
     However, if CB_COMPOUND returns zero operations, obviously the error
     returned by COMPOUND has nothing to do with an error returned by
     an operation. The list of errors CB_COMPOUND will return if it processes
     zero operations includes:
    </t>
     <texttable anchor="CB_compounderrs">
     <preamble>CB_COMPOUND error returns</preamble>
     <ttcol align='left'>Error</ttcol>
     <ttcol align='left'>Notes</ttcol>

     <c>NFS4ERR_BADCHAR</c> <c>The tag argument has a character the replier
                               does not support. </c>

     <c>NFS4ERR_BADXDR</c> <c> </c>

     <c>NFS4ERR_DELAY</c> <c> </c>

     <c>NFS4ERR_INVAL</c> <c>The tag argument is not in UTF-8 encoding.</c>

     <c>NFS4ERR_MINOR_VERS_MISMATCH</c> <c> </c>

     <c>NFS4ERR_SERVERFAULT</c> <c> </c>

     <c>NFS4ERR_TOO_MANY_OPS</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG</c> <c> </c>

     <c>NFS4ERR_REP_TOO_BIG_TO_CACHE</c> <c> </c>

     <c>NFS4ERR_REQ_TOO_BIG</c> <c> </c>

     </texttable>
 
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="nfsv41cboperations" title="NFSv4.1 Callback Operations">
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_GETATTR" title="Operation 3: CB_GETATTR - Get Attributes" >

  <section toc="exclude" anchor="OP_CB_GETATTR_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_GETATTR4args {
        nfs_fh4 fh;
        bitmap4 attr_request;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_GETATTR4resok {
        fattr4  obj_attributes;
};

union CB_GETATTR4res switch (nfsstat4 status) {
 case NFS4_OK:
         CB_GETATTR4resok       resok4;
 default:
         void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_DESCRIPTION" title="DESCRIPTION">
    <t>
     The CB_GETATTR operation is used by the server to obtain the
     current modified state of a file that has been OPEN_DELEGATE_WRITE delegated.
     The size and change attributes are the only ones guaranteed to be
     serviced by the client.  See <xref
     target="handling_cb_getattr"/> for a full description
     of how the client and server are to interact with
     the use of CB_GETATTR.

    </t>
    <t>
     If the filehandle specified is not one for which the client holds an
     OPEN_DELEGATE_WRITE delegation, an NFS4ERR_BADHANDLE error is returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_GETATTR_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The client returns attrmask bits and the associated attribute
     values only for the change attribute, and attributes that it may
     change (time_modify, and size).
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL" title="Operation 4: CB_RECALL - Recall a Delegation" >

  <section toc="exclude" anchor="OP_CB_RECALL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_RECALL4args {
        stateid4        stateid;
        bool            truncate;
        nfs_fh4         fh;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_RECALL operation is used to begin the process of recalling
      a delegation and returning it to the server.
    </t>
    <t>      
      The truncate flag is used to optimize recall for a file object that
      is a regular file and is
      about to be truncated to zero.  When it is TRUE, the client is freed
      of the obligation to propagate modified data for the file to the
      server, since this data is irrelevant.
    </t>
    <t>      
      If the handle specified is not one for which the client holds a
      delegation, an NFS4ERR_BADHANDLE error is returned.
    </t>
    <t>      
      If the stateid specified is not one corresponding to an OPEN
      delegation for the file specified by the filehandle, an
      NFS4ERR_BAD_STATEID is returned.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The client SHOULD reply to the callback immediately.
     Replying does not complete the recall except when
     the value of the reply's status field is neither
     NFS4ERR_DELAY nor NFS4_OK.  The recall is not complete
     until the delegation is returned using a DELEGRETURN
     operation.

    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_LAYOUTRECALL" 
         title="Operation 5: CB_LAYOUTRECALL - Recall Layout from Client" >

  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * NFSv4.1 callback arguments and results
 */

enum layoutrecall_type4 {
        LAYOUTRECALL4_FILE = LAYOUT4_RET_REC_FILE,
        LAYOUTRECALL4_FSID = LAYOUT4_RET_REC_FSID,
        LAYOUTRECALL4_ALL  = LAYOUT4_RET_REC_ALL
};

struct layoutrecall_file4 {
        nfs_fh4         lor_fh;
        offset4         lor_offset;
        length4         lor_length;
        stateid4        lor_stateid;
};

union layoutrecall4 switch(layoutrecall_type4 lor_recalltype) {
case LAYOUTRECALL4_FILE:
        layoutrecall_file4 lor_layout;
case LAYOUTRECALL4_FSID:
        fsid4              lor_fsid;
case LAYOUTRECALL4_ALL:
        void;
};

struct CB_LAYOUTRECALL4args {
        layouttype4             clora_type;
        layoutiomode4           clora_iomode;
        bool                    clora_changed;
        layoutrecall4           clora_recall;
};
 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_LAYOUTRECALL4res {
        nfsstat4        clorr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_LAYOUTRECALL operation is used by the server to recall
      layouts from the client; as a result, the client will begin the
      process of returning layouts via LAYOUTRETURN.  The
      CB_LAYOUTRECALL operation specifies one of three forms of recall
      processing with the value of layoutrecall_type4.  The recall is
      for one of the following: a specific layout of a specific file
      (LAYOUTRECALL4_FILE), an entire file system ID
      (LAYOUTRECALL4_FSID), or all file systems (LAYOUTRECALL4_ALL).
    </t>
    <t>
      The behavior of the operation varies based on the value of the
      layoutrecall_type4.  The value and behaviors are:
      <list style="hanging">
      <t hangText="LAYOUTRECALL4_FILE"></t>
      <t>
        For a layout to match the recall request, the values of the following fields
        must match those of the layout: clora_type, clora_iomode,
        lor_fh, and the byte-range specified by lor_offset and
        lor_length.  The clora_iomode field may have a special value
        of LAYOUTIOMODE4_ANY.  The special value LAYOUTIOMODE4_ANY will match any
        iomode originally returned in a layout; therefore, it acts as a
        wild card.  The other special value used is for
        lor_length.  If lor_length has a value of NFS4_UINT64_MAX, the
        lor_length field means the maximum possible file size. If a
        matching layout is found, it MUST be returned using the
        LAYOUTRETURN operation (see <xref target="OP_LAYOUTRETURN" />).
        An example of the field's special value use is if clora_iomode
        is LAYOUTIOMODE4_ANY, lor_offset is zero, and lor_length is
        NFS4_UINT64_MAX, then the entire layout is to be returned.
      </t>
      <t>
        The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
        client does not hold layouts for the file or if the client
        does not have any overlapping layouts for the specification in
        the layout recall.
      </t>
      <t hangText="LAYOUTRECALL4_FSID and LAYOUTRECALL4_ALL"></t>
      <t>
        If LAYOUTRECALL4_FSID is specified, the fsid specifies the
        file system for which any outstanding layouts MUST be
        returned.  If LAYOUTRECALL4_ALL is specified, all outstanding
        layouts MUST be returned.  In addition, LAYOUTRECALL4_FSID and
        LAYOUTRECALL4_ALL specify that all the storage device ID to
        storage device address mappings in the affected file system(s)
        are also recalled. The respective LAYOUTRETURN with either
        LAYOUTRETURN4_FSID or LAYOUTRETURN4_ALL acknowledges to the
        server that the client invalidated the said device mappings.
        See <xref target="bulk_layouts" /> for considerations with
        "bulk" recall of layouts.
      </t>
      <t>
        The NFS4ERR_NOMATCHING_LAYOUT error is only returned when the
        client does not hold layouts and does not have valid deviceid
        mappings.
      </t>
    </list>
    </t>
    <t>
      In processing the layout recall request, the client also varies
      its behavior based on the value of the clora_changed field.  This
      field is used by the server to provide additional context for
      the reason why the layout is being recalled.  A FALSE value for
      clora_changed indicates that no change in the layout is expected
      and the client may write modified data to the storage devices
      involved; this must be done prior to returning the layout via
      LAYOUTRETURN.  A TRUE value for clora_changed indicates that the
      server is changing the layout.  Examples of layout changes and
      reasons for a TRUE indication are the following: the metadata server is restriping
      the file or a permanent error has occurred on a storage device
      and the metadata server would like to provide a new layout for
      the file.  Therefore, a clora_changed value of TRUE indicates
      some level of change for the layout and the client SHOULD NOT
      write and commit modified data to the storage devices.  In this
      case, the client writes and commits data through the metadata
      server.
    </t>
    <t>
      See <xref target="layout_stateid"/> for a description of how the
      lor_stateid field in the arguments is to be constructed. Note
      that the "seqid" field of lor_stateid MUST NOT be zero.  See Sections
      <xref target="stateid" format="counter" />, <xref
target="layout_stateid" format="counter" />, and
      <xref target="pnfs_operation_sequencing" format="counter" /> for a further
      discussion and requirements.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_LAYOUTRECALL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client's processing for CB_LAYOUTRECALL is similar to
      CB_RECALL (recall of file delegations) in that
      the client responds to
      the request before actually returning layouts via the
      LAYOUTRETURN operation.  While the client responds to the
      CB_LAYOUTRECALL immediately, the operation is not considered
      complete (i.e., considered pending) until all affected layouts are returned to the server
      via the LAYOUTRETURN operation.
    </t>
    <t>
      Before returning the layout to the server via LAYOUTRETURN, the
      client should wait for the response from in-process or in-flight
      READ, WRITE, or COMMIT operations that use the recalled layout.
    </t>
    <t>
      If the client is holding modified data that is affected by a
      recalled layout, the client has various options for writing the
      data to the server.  As always, the client may write the data
      through the metadata server.  In fact, the client may not have a
      choice other than writing to the metadata server when the
      clora_changed argument is TRUE and a new layout is unavailable
      from the server.  However, the client may be able to write the
      modified data to the storage device if the clora_changed
      argument is FALSE; this needs to be done before returning the
      layout via LAYOUTRETURN.  If the client were to obtain a new
      layout covering the modified data's byte-range, then writing to the
      storage devices is an available alternative.  Note that before
      obtaining a new layout, the client must first return the
      original layout.
    </t>
    <t>
      In the case of modified data being written while the layout is
      held, the client must use LAYOUTCOMMIT operations at the
      appropriate time; as required LAYOUTCOMMIT must be done before
      the LAYOUTRETURN.  If a large amount of modified data is
      outstanding, the client may send LAYOUTRETURNs for portions of
      the recalled layout; this allows the server to monitor the
      client's progress and adherence to the original recall request.
      However, the last LAYOUTRETURN in a sequence of returns MUST
      specify the full range being recalled (see <xref
      target="recall_robustness" /> for details).
    </t>
    <t>
      If a server needs to delete a device ID and there are layouts
      referring to the device ID, CB_LAYOUTRECALL MUST be invoked to
      cause the client to return all layouts referring to the device ID
      before the server can delete the device ID. If the client
      does not return the affected layouts, the server MAY revoke
      the layouts.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_NOTIFY" title="Operation 6: CB_NOTIFY - Notify Client of Directory Changes" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * Directory notification types.
 */
enum notify_type4 {
        NOTIFY4_CHANGE_CHILD_ATTRS = 0,
        NOTIFY4_CHANGE_DIR_ATTRS = 1,
        NOTIFY4_REMOVE_ENTRY = 2,
        NOTIFY4_ADD_ENTRY = 3,
        NOTIFY4_RENAME_ENTRY = 4,
        NOTIFY4_CHANGE_COOKIE_VERIFIER = 5
};

/* Changed entry information.  */
struct notify_entry4 {
        component4      ne_file;
        fattr4          ne_attrs;
};

/* Previous entry information */
struct prev_entry4 {
        notify_entry4   pe_prev_entry;
        /* what READDIR returned for this entry */
        nfs_cookie4     pe_prev_entry_cookie;
};

struct notify_remove4 {
        notify_entry4   nrm_old_entry;
        nfs_cookie4     nrm_old_entry_cookie;
};

struct notify_add4 {
        /*
         * Information on object
         * possibly renamed over.
         */
        notify_remove4      nad_old_entry&lt;1>;
        notify_entry4       nad_new_entry;
        /* what READDIR would have returned for this entry */
        nfs_cookie4         nad_new_entry_cookie&lt;1>;
        prev_entry4         nad_prev_entry&lt;1>;
        bool                nad_last_entry;
};

struct notify_attr4 {
        notify_entry4   na_changed_entry;
};

struct notify_rename4 {
        notify_remove4  nrn_old_entry;
        notify_add4     nrn_new_entry;
};

struct notify_verifier4 {
        verifier4       nv_old_cookieverf;
        verifier4       nv_new_cookieverf;
};

/*
 * Objects of type notify_&lt;>4 and
 * notify_device_&lt;>4 are encoded in this.
 */
typedef opaque notifylist4&lt;>;

struct notify4 {
        /* composed from notify_type4 or notify_deviceid_type4 */
        bitmap4         notify_mask;
        notifylist4     notify_vals;
};

struct CB_NOTIFY4args {
        stateid4    cna_stateid;
        nfs_fh4     cna_fh;
        notify4     cna_changes&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY4res {
        nfsstat4    cnr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_NOTIFY operation is used by the server to
      send notifications to clients about changes to
      delegated directories.
      The registration of notifications for the directories
      occurs when the delegation is established using
      GET_DIR_DELEGATION.
      These notifications are sent over the backchannel. The
      notification is sent once the original request has been
      processed on the server. The server will send an array of
      notifications for changes that might have occurred in the
      directory. The notifications are sent as list of pairs of
      bitmaps and values.
      See <xref target="fattr4" />
      for a description of how NFSv4.1 bitmaps work.

   </t>
   <t>
     If the server has more notifications than can fit in
     the CB_COMPOUND request, it SHOULD send a sequence of
     serial CB_COMPOUND requests so that the client's view
     of the directory does not become confused. For example, if the
     server indicates that a file named "foo" is added and that the
     file "foo" is removed, the order in which the client receives
     these notifications needs to be the same as the
     order in which the corresponding operations occurred on the server.

   </t>

   <t>

      If the client holding the delegation makes any
      changes in the directory that cause files or sub-directories to
      be added or removed, the server will
      notify that client of the resulting change(s). If the
      client holding the delegation is making attribute
      or cookie verifier changes only, the server does
      not need to send notifications to that client.
      The server will send the following information for
      each operation:

      <list style="hanging">
	<t hangText="NOTIFY4_ADD_ENTRY"><vspace /> 
	  The server will send
	  information about the new directory entry being created along with the
	  cookie for that entry.  The entry information (data type
	  notify_add4) includes the component name of the entry and
	  attributes.  The server will send this type of entry when a
	  file is actually being created, when an entry is being added
	  to a directory as a result of a rename across directories
	  (see below), and when a hard link is being created to an
	  existing file.  If this entry is added to the end of the
	  directory, the server will set the nad_last_entry flag to
	  TRUE. If the file is added such that there is at least one
	  entry before it, the server will also return the previous
	  entry information (nad_prev_entry, a variable-length array
	  of up to one element. If the array is of zero length, there
	  is no previous entry), along with its cookie.  This is to
	  help clients find the right location in their file name caches and
	  directory caches where this entry should be cached. If the
	  new entry's cookie is available, it will be in
	  the nad_new_entry_cookie (another variable-length array of up to
	  one element) field.  If the addition of the entry causes another 
          entry to be deleted (which can only happen in the rename
          case) atomically with the addition, then information on
          this entry is reported in nad_old_entry.
	</t>
	<t hangText="NOTIFY4_REMOVE_ENTRY"><vspace />
	  The server will send information about the directory entry
	  being deleted. The server will also send the cookie value
	  for the deleted entry so that clients can get to the cached
	  information for this entry.
	</t>
	<t hangText="NOTIFY4_RENAME_ENTRY"><vspace />
	  The server will send information about both
	  the old entry and the new entry. This includes the name and
	  attributes for each entry.  In addition, if the rename
          causes the deletion of an entry (i.e., the case of a file
          renamed over), then this is reported in 
          nrn_new_new_entry.nad_old_entry. 
          This notification is only sent if
	  both entries are in the same directory. If the rename is
	  across directories, the server will send a remove
	  notification to one directory and an add notification to the
	  other directory, assuming both have a directory delegation.
	</t>
	<t
	hangText="NOTIFY4_CHANGE_CHILD_ATTRS/NOTIFY4_CHANGE_DIR_ATTRS"><vspace
	/>

	  The client will use the attribute
	  mask to inform the server of attributes for which it wants to
	  receive notifications. This change notification can be
	  requested for changes to the attributes of the directory
	  as well as changes to any file's attributes in the directory by
	  using two separate attribute masks. The client cannot ask
	  for change attribute notification for a specific file. One attribute
	  mask covers all the files in the directory. Upon any
	  attribute change, the server will send back the values of
	  changed attributes. Notifications might not make sense for
	  some file system-wide attributes, and it is up to the server to
	  decide which subset it wants to support.  The client can
	  negotiate the frequency of attribute notifications by letting
	  the server know how often it wants to be notified of an
	  attribute change. The server will return supported
	  notification frequencies or an indication that no
	  notification is permitted for directory or child attributes
	  by setting the dir_notif_delay and
	  dir_entry_notif_delay attributes, respectively.
	</t>
	<t hangText="NOTIFY4_CHANGE_COOKIE_VERIFIER"><vspace />

	  If the cookie verifier changes while
	  a client is holding a delegation, the server will notify the
	  client so that it can invalidate its cookies and re-send a
	  READDIR to get the new set of cookies.
	</t>
      </list>
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->


<section anchor="OP_CB_PUSH_DELEG" 
         title="Operation 7: CB_PUSH_DELEG - Offer Previously Requested Delegation to Client" >

  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_PUSH_DELEG4args {
        nfs_fh4          cpda_fh;
        open_delegation4 cpda_delegation;

};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_PUSH_DELEG4res {
        nfsstat4 cpdr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_DESCRIPTION" title="DESCRIPTION">
    <t>
	CB_PUSH_DELEG is used by the server both to signal to the
	client that the delegation it wants (previously indicated
        via a want established from an
        OPEN or WANT_DELEGATION operation) is available and to
	simultaneously offer the delegation to the client.  The client
	has the choice of accepting the delegation by returning
	NFS4_OK to the server, delaying the decision to accept the
	offered delegation by returning NFS4ERR_DELAY,
	or permanently rejecting the offer of the
	delegation by returning NFS4ERR_REJECT_DELEG.
        When a delegation is rejected in this fashion, the want
        previously established is permanently deleted and the delegation
        is subject to acquisition by another client.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_PUSH_DELEG_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
	If the client does return NFS4ERR_DELAY
	and there is a conflicting delegation request, the server MAY
	process it at the expense of the client that returned
	NFS4ERR_DELAY. The client's want will not be cancelled, but
	MAY be processed behind other delegation requests or registered
	wants.
    </t>
    <t>
        When a client returns a status other than NFS4_OK, NFS4ERR_DELAY,
        or NFS4ERR_REJECT_DELAY, the want remains pending, although 
        servers may decide to cancel the want by sending a CB_WANTS_CANCELLED.
      </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL_ANY" title="Operation 8: CB_RECALL_ANY - Keep Any N Recallable Objects" >

  <section toc="exclude" anchor="OP_CB_RECALL_ANY_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
const RCA4_TYPE_MASK_RDATA_DLG          = 0;
const RCA4_TYPE_MASK_WDATA_DLG          = 1;
const RCA4_TYPE_MASK_DIR_DLG            = 2;
const RCA4_TYPE_MASK_FILE_LAYOUT        = 3;
const RCA4_TYPE_MASK_BLK_LAYOUT         = 4;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MIN     = 8;
const RCA4_TYPE_MASK_OBJ_LAYOUT_MAX     = 9;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MIN   = 12;
const RCA4_TYPE_MASK_OTHER_LAYOUT_MAX   = 15;

struct  CB_RECALL_ANY4args      {
        uint32_t        craa_objects_to_keep;
        bitmap4         craa_type_mask;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL_ANY4res {
        nfsstat4        crar_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_DESCRIPTION" title="DESCRIPTION">
    <t>
      The server may decide that it cannot hold all of the state for
      recallable objects, such as delegations and layouts, without 
      running out of resources.  In such a case, while not optimal,
      the server is free to recall individual objects to reduce the load.
    </t>
    <t>
      Because the general purpose of such recallable objects as
      delegations is to eliminate client interaction with the server,
      the server cannot interpret lack of recent use as indicating
      that the object is no longer useful.  The absence of visible
      use is consistent with a delegation keeping potential operations
      from being sent to the server. In the case of layouts, while it
      is true that the usefulness of a layout
      is indicated by the use of the layout when storage devices receive
      I/O requests, because there is no mandate that a storage
      device indicate to the metadata server any past or
      present use of a layout, the metadata server is not likely to know
      which layouts are good candidates to recall in response to
      low resources.
    </t>
    <t>
      In order to implement an effective reclaim scheme for such 
      objects, the server's knowledge of available resources must be
      used to determine when objects must be recalled with the 
      clients selecting the actual objects to be returned.
    </t>
    <t>
      Server implementations may differ in their resource allocation
      requirements.  For example, one server may share resources among
      all classes of recallable objects, whereas another may use
      separate resource pools for layouts and for delegations, or
      further separate resources by types of delegations.
    </t>
    <t>
      When a given resource pool is over-utilized, the server can
      send a CB_RECALL_ANY to clients holding recallable objects of
      the types involved, allowing it to keep a certain number of
      such objects and return any excess.  A mask specifies which 
      types of objects are to be limited.  The client chooses, based
      on its own knowledge of current usefulness, which of the objects
      in that class should be returned.
    </t>
    <t>
      A number of bits are defined.  For some of these, ranges
      are defined and it is up to the definition of the storage 
      protocol to specify how these are to be used.  There are ranges 
      reserved for object-based storage 
      protocols and for other experimental storage 
      protocols.  An RFC defining such a storage protocol needs to
      specify how particular bits within its range are to be used.  
      For example, it may specify a mapping between attributes of 
      the layout (read vs. write, size of area) and the bit to be 
      used, or it may define a field in the layout where the associated
      bit position is made available by the server to the client.

      <list style='hanging'>
      <t hangText='RCA4_TYPE_MASK_RDATA_DLG'>
      </t>
      <t>
       The client is to return OPEN_DELEGATE_READ delegations on
       non-directory file objects.

      </t>

      <t hangText='RCA4_TYPE_MASK_WDATA_DLG'>
      </t>
      <t>
       The client is to return OPEN_DELEGATE_WRITE delegations on
       regular file objects.

      </t>

      <t hangText='RCA4_TYPE_MASK_DIR_DLG'>
      </t>
      <t>
       The client is to return directory delegations.

      </t>

      <t hangText='RCA4_TYPE_MASK_FILE_LAYOUT'>
      </t>
      <t>
       The client is to return layouts of type LAYOUT4_NFSV4_1_FILES.

      </t>
      <t hangText='RCA4_TYPE_MASK_BLK_LAYOUT'>
      </t>
      <t>
       See <xref target='RFC5663' /> for a description.

      </t>
      
      <t hangText='RCA4_TYPE_MASK_OBJ_LAYOUT_MIN to RCA4_TYPE_MASK_OBJ_LAYOUT_MAX'>
      </t>
      <t>
       See <xref target='RFC5664' /> for a description.

      </t>
      <t hangText='RCA4_TYPE_MASK_OTHER_LAYOUT_MIN to RCA4_TYPE_MASK_OTHER_LAYOUT_MAX'>
      </t>
      <t>
        This range is reserved for telling the client to recall
        layouts of experimental
        or site-specific layout types (see <xref
        target='layouttype4'/>).

      </t>
      </list>

    </t>
    <t>
      When a bit is set in the type mask that corresponds
      to an undefined type of recallable object,
      NFS4ERR_INVAL MUST be returned.  When a bit is set
      that corresponds to a defined type of object but
      the client does not support an object of the type,
      NFS4ERR_INVAL MUST NOT be returned.  Future minor
      versions of NFSv4 may expand the set of valid type
      mask bits.

    </t>
    <t>
      CB_RECALL_ANY specifies a count of objects that the client may
      keep as opposed to a count that the client must return.  This
      is to avoid a potential race between a CB_RECALL_ANY that had a 
      count of objects to free with a set of client-originated 
      operations to return layouts or delegations. As a result of the 
      race, the client and server would have differing ideas as to how
      many objects to return.  Hence, the client could mistakenly free 
      too many.
    </t>
    <t>
      If resource demands prompt it, the server may send another
      CB_RECALL_ANY with a lower count, even if it has not yet received
      an acknowledgment from the client for a previous CB_RECALL_ANY
      with the same type mask.  Although the possibility exists that
      these will be received by the client in an order different from
      the order in which they were sent, any such permutation of
      the callback stream is harmless.  It is the job of the client
      to bring down the size of the recallable object set in line
      with each CB_RECALL_ANY received, and until that obligation is
      met, it cannot be cancelled or modified by any subsequent 
      CB_RECALL_ANY for the same type mask.  Thus, if the server 
      sends two CB_RECALL_ANYs, the effect will be the same as 
      if the lower count was sent, whatever the order of recall
      receipt.  Note that this means that a server may not cancel
      the effect of a CB_RECALL_ANY by sending another recall with
      a higher count.  When a CB_RECALL_ANY is received and the
      count is already within the limit set or is above a limit 
      that the client is working to get down to, that callback has no
      effect. 
    </t>
    <t>
      Servers are generally free to deny recallable objects
      when insufficient resources are available.  Note that the 
      effect of such a policy is implicitly to give precedence to
      existing objects relative to requested ones, with the result
      that resources might not be optimally used.  To prevent this, 
      servers are well advised to make the point at which they start 
      sending CB_RECALL_ANY callbacks somewhat below that at which they
      cease to give out new delegations and layouts.  This allows the 
      client to purge its less-used objects whenever appropriate and
      so continue to have its subsequent requests given new resources
      freed up by object returns.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_ANY_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      The client can choose to return any type of object specified 
      by the mask.  If a server wishes to limit the use of objects of a
      specific type, it should only specify that type in the mask
      it sends.  Should the client fail to return requested objects, it is 
      up to the server to handle this situation, typically by sending
      specific recalls (i.e., sending CB_RECALL operations)
      to properly limit resource usage.  The server 
      should give the client enough time to return objects before 
      proceeding to specific recalls. This time should not be less
      than the lease period.
    </t>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $        -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALLABLE_OBJ_AVAIL" 
         title="Operation 9: CB_RECALLABLE_OBJ_AVAIL - Signal Resources for Recallable Objects" >

  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
typedef CB_RECALL_ANY4args CB_RECALLABLE_OBJ_AVAIL4args;

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALLABLE_OBJ_AVAIL4res {
        nfsstat4        croa_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALLABLE_OBJ_AVAIL_DESCRIPTION" title="DESCRIPTION">
    <t>
        CB_RECALLABLE_OBJ_AVAIL is used by the server to signal the
        client that the server has resources to grant recallable
        objects that might previously have been denied by OPEN,
        WANT_DELEGATION, GET_DIR_DELEG, or LAYOUTGET.
    </t>
    <t>
        The argument craa_objects_to_keep means the total number of
        recallable objects of the types indicated in the argument
        type_mask that the server believes it can allow the client to
        have, including the number of such objects the client already
        has. A client that tries to acquire more recallable objects
        than the server informs it can have runs the risk of having
        objects recalled.
    </t>
    <t>
        The server is not obligated to reserve the
        difference between the number of the objects
        the client currently has and the value of
        craa_objects_to_keep, nor does delaying the reply
        to CB_RECALLABLE_OBJ_AVAIL prevent the server
        from using the resources of the recallable objects
        for another purpose. Indeed, if a client responds
        slowly to CB_RECALLABLE_OBJ_AVAIL, the server might
        interpret the client as having reduced capability
        to manage recallable objects, and so cancel
        or reduce any reservation it is maintaining on behalf
        of the client.
        Thus, if the client desires to acquire more
        recallable objects, it needs to reply quickly
        to CB_RECALLABLE_OBJ_AVAIL, and then send the
        appropriate operations to acquire recallable
        objects.
    </t>
  </section>


</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_RECALL_SLOT" title="Operation 10: CB_RECALL_SLOT - Change Flow Control Limits" >

  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_RECALL_SLOT4args {
        slotid4       rsa_target_highest_slotid;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_RECALL_SLOT4res {
        nfsstat4   rsr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_RECALL_SLOT operation requests the client to
      return session slots, and if applicable, transport
      credits (e.g., RDMA credits for connections associated with
      the operations channel) of the session's fore channel.
      CB_RECALL_SLOT specifies
      rsa_target_highest_slotid, the value of the target highest slot ID the server wants
      for the session. The client MUST then progress toward reducing
      the session's highest slot ID to the target value.
    </t>
    <t>
      If the session has only non-RDMA connections associated with its
      operations channel, then the client need only wait
      for all outstanding requests with a slot ID >
      rsa_target_highest_slotid to complete, then send
      a single COMPOUND consisting of a single SEQUENCE operation,
      with the sa_highestslot field set to rsa_target_highest_slotid.
      If there are RDMA-based connections associated with
      operation channel, then the client needs to also
      send enough zero-length "RDMA Send" messages to take the total
<!--  Please leave this use of "Send" capitalized in order to denote
      an artifact particular to RDMA-based communication. Thanks. -->
      RDMA credit count to rsa_target_highest_slotid + 1 or below.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_RECALL_SLOT_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      If the client fails to reduce highest slot it has on the fore channel
      to what the server requests, the server can force the issue
      by asserting flow control on the receive side of
      all connections bound to the fore channel, and then
      finish servicing all outstanding requests that are
      in slots greater than rsa_target_highest_slotid. Once that
      is done, the server can then open the flow control, and any time
      the client sends a new request on a slot greater than
      rsa_target_highest_slotid, the server can return NFS4ERR_BADSLOT.
    </t>
  </section>
</section>
<!--    $Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $        -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_SEQUENCE" title="Operation 11: CB_SEQUENCE - Supply Backchannel Sequencing and Control" >

  <section toc="exclude" anchor="OP_CB_SEQUENCE_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct referring_call4 {
        sequenceid4     rc_sequenceid;
        slotid4         rc_slotid;
};

struct referring_call_list4 {
        sessionid4      rcl_sessionid;
        referring_call4 rcl_referring_calls&lt;>;
};

struct CB_SEQUENCE4args {
        sessionid4           csa_sessionid;
        sequenceid4          csa_sequenceid;
        slotid4              csa_slotid;
        slotid4              csa_highest_slotid;
        bool                 csa_cachethis;
        referring_call_list4 csa_referring_call_lists&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_SEQUENCE_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_SEQUENCE4resok {
        sessionid4         csr_sessionid;
        sequenceid4        csr_sequenceid;
        slotid4            csr_slotid;
        slotid4            csr_highest_slotid;
        slotid4            csr_target_highest_slotid;
};

union CB_SEQUENCE4res switch (nfsstat4 csr_status) {
case NFS4_OK:
        CB_SEQUENCE4resok   csr_resok4;
default:
        void;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_SEQUENCE_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_SEQUENCE operation is used to manage operational accounting
      for the backchannel of the session on which a request is
      sent.  The contents include the session ID to which this
      request belongs, the slot ID and sequence ID used by the server to
      implement session request control and exactly once
      semantics, and exchanged slot ID maxima that are used to adjust the
      size of the reply cache.  In each CB_COMPOUND request, CB_SEQUENCE
      MUST appear once and MUST be the first operation.  The error
      NFS4ERR_SEQUENCE_POS MUST be returned when CB_SEQUENCE is found in
      any position in a CB_COMPOUND beyond the first.  If any
      other operation is in the first position of CB_COMPOUND,
      NFS4ERR_OP_NOT_IN_SESSION MUST be returned.
    </t>
    <t>
      See <xref target="OP_SEQUENCE_DESCRIPTION"/> for a description of
      how slots are processed.
    </t>
    <t>
     If csa_cachethis is TRUE, then the server is requesting that
     the client cache the reply in the callback reply cache. The client MUST
     cache the reply (see <xref target="optional_reply_caching" />).
    </t>
    <t>
      The csa_referring_call_lists array is the list of COMPOUND
      requests, identified by session ID, slot ID, and sequence ID. These
      are requests that the client previously sent to the server.
      These previous requests created state that some operation(s)
      in the same CB_COMPOUND as the csa_referring_call_lists are
      identifying.
      A session ID is included because
      leased state is tied to a client ID, and a client ID can have
      multiple sessions. See
      <xref target="sessions_callback_races" />.
    </t>
    <t>
      The value of the csa_sequenceid argument relative to
      the cached sequence ID on the slot falls into one
      of three cases.
      <list style="symbols">
      <t>
       If the difference between csa_sequenceid and
       the client's cached sequence ID at the slot ID
       is two (2) or more,
       or if csa_sequenceid is less
       than the cached sequence ID (accounting
       for wraparound of the unsigned sequence ID value),
       then the client MUST return NFS4ERR_SEQ_MISORDERED.
      </t>
      <t>
       If csa_sequenceid and the cached sequence ID are the
       same, this is a retry, and the client returns the
       CB_COMPOUND request's cached reply.
      </t>
      <t>
       If csa_sequenceid is one greater (accounting for
       wraparound) than the cached sequence ID, then
       this is a new request, and the slot's sequence
       ID is incremented.  The operations subsequent to
       CB_SEQUENCE, if any, are processed. If there are no
       other operations, the only other effects are to
       cache the CB_SEQUENCE reply in the slot, maintain the
       session's activity, and when the server receives the
       CB_SEQUENCE reply, renew the lease of state
       related to the client ID.
      </t>
      </list>
    </t>
    <t>
     If the server reuses a slot ID and sequence ID for
     a completely different request, the client MAY
     treat the request as if it is a retry
     of what it has already executed. The client MAY however
     detect the server's illegal reuse and return NFS4ERR_SEQ_FALSE_RETRY.
    </t>
    <t>
     If CB_SEQUENCE returns an error, then the state of the slot (sequence ID,
     cached reply) MUST NOT change.
     See <xref target="optional_reply_caching"/> for the conditions when the
     error NFS4ERR_RETRY_UNCACHED_REP might be returned.
    </t>
    <t>
     The client returns two "highest_slotid" values:
     csr_highest_slotid and csr_target_highest_slotid. The
     former is the highest slot ID the client will accept
     in a future CB_SEQUENCE operation, and SHOULD NOT be
     less than the value of csa_highest_slotid (but see
     <xref target="Slot_Identifiers_and_Server_Reply_Cache"
     /> for an exception).  The latter is the highest slot
     ID the client would prefer the server use on a future
     CB_SEQUENCE operation.
    </t>
  </section>


</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_WANTS_CANCELLED" 
         title="Operation 12: CB_WANTS_CANCELLED - Cancel Pending Delegation Wants " >

  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_WANTS_CANCELLED4args {
        bool cwca_contended_wants_cancelled;
        bool cwca_resourced_wants_cancelled;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_WANTS_CANCELLED4res {
        nfsstat4        cwcr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_WANTS_CANCELLED operation is used to notify the client that
      some or all of the wants it registered for recallable delegations and layouts
      have been cancelled.
    </t>
    <t>
	If cwca_contended_wants_cancelled is TRUE, this indicates that
        the server will not be pushing to the client any delegations
        that become available after contention passes.
   </t>
    <t>
	If cwca_resourced_wants_cancelled is TRUE, this indicates that
        the server will not notify the client when there are resources
        on the server to grant delegations or layouts.
    </t>
    <t>
        After receiving a CB_WANTS_CANCELLED operation, the
        client is free to attempt to acquire the delegations or
        layouts it was waiting for, and possibly re-register wants.
    </t>


  </section>
  <section toc="exclude" anchor="OP_CB_WANTS_CANCELLED_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
      When a client has an OPEN, WANT_DELEGATION, or GET_DIR_DELEGATION request 
      outstanding, when a CB_WANTS_CANCELLED is sent, the server may need to
      make clear to the client whether a promise to signal delegation availability
      happened before the CB_WANTS_CANCELLED and is thus covered by it, or after
      the CB_WANTS_CANCELLED in which case it was not covered by it.  The server
      can make this distinction by putting the appropriate requests into the
      list of referring calls in the associated CB_SEQUENCE.
    </t>
  </section>
</section>
<!-- Copyright (C) The Internet Society (2006) -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<section anchor="OP_CB_NOTIFY_LOCK" title="Operation 13: CB_NOTIFY_LOCK - Notify Client of Possible Lock Availability" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
struct CB_NOTIFY_LOCK4args {
    nfs_fh4     cnla_fh;
    lock_owner4 cnla_lock_owner;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY_LOCK4res {
        nfsstat4        cnlr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_DESCRIPTION" title="DESCRIPTION">
    <t>
      The server can use this operation to indicate that a byte-range lock for the given
      file and lock-owner, previously requested by the client via an unsuccessful
      LOCK operation, might be available.
    </t>
    <t>
      This callback is meant to be used by servers to help reduce the latency of
      blocking locks in the case where they recognize that a client that has
      been polling for a blocking byte-range lock may now be able to acquire the lock.
      If the server supports this callback for a given file, it MUST set the
      OPEN4_RESULT_MAY_NOTIFY_LOCK flag when responding to successful opens
      for that file.  This does not commit the server to the use of CB_NOTIFY_LOCK,
      but the client may use this as a hint to decide how frequently to poll
      for locks derived from that open.
    </t>
    <t>
      If an OPEN operation results in an upgrade, in which the stateid returned 
      has an "other" value matching that of a stateid already allocated, with a
      new "seqid" indicating a change in the lock being represented, then the
      value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag when responding to that new 
      OPEN controls handling from that point going forward.  When parallel OPENs
      are done on the same file and open-owner, the ordering of the "seqid" fields
      of the returned stateids (subject to wraparound) are to be used to select
      the controlling value of the OPEN4_RESULT_MAY_NOTIFY_LOCK flag.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_LOCK_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     The server MUST NOT grant the byte-range lock to the client unless and until it
     receives a LOCK operation from the client.  Similarly, the client
     receiving this callback cannot assume that it now has the lock or that a
     subsequent LOCK operation for the lock will be successful.
    </t>
    <t>
     The server is not required to implement this callback, and even if it
     does, it is not required to use it in any particular case.  Therefore, the
     client must still rely on polling for blocking locks, as described in
     <xref target="blocking_locks"/>.
    </t>
    <t>
     Similarly, the client is not required to implement this callback, and even
     it does, is still free to ignore it.  Therefore, the server MUST NOT assume
     that the client will act based on the callback.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_NOTIFY_DEVICEID" title="Operation 14: CB_NOTIFY_DEVICEID - Notify Client of Device ID Changes" >

  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_ARGUMENT" title="ARGUMENT">
<figure>
 <artwork>
/*
 * Device notification types.
 */
enum notify_deviceid_type4 {
        NOTIFY_DEVICEID4_CHANGE = 1,
        NOTIFY_DEVICEID4_DELETE = 2
};

/* For NOTIFY4_DEVICEID4_DELETE */
struct notify_deviceid_delete4 {
        layouttype4     ndd_layouttype;
        deviceid4       ndd_deviceid;
};

/* For NOTIFY4_DEVICEID4_CHANGE */
struct notify_deviceid_change4 {
        layouttype4     ndc_layouttype;
        deviceid4       ndc_deviceid;
        bool            ndc_immediate;
};

struct CB_NOTIFY_DEVICEID4args {
        notify4 cnda_changes&lt;>;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_RESULT" title="RESULT">
<figure>
 <artwork>
struct CB_NOTIFY_DEVICEID4res {
        nfsstat4        cndr_status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_NOTIFY_DEVICEID_DESCRIPTION" title="DESCRIPTION">
    <t>
      The CB_NOTIFY_DEVICEID operation is used by the
      server to send notifications to clients about
      changes to pNFS device IDs.  The registration of
      device ID notifications is optional and is done via
      GETDEVICEINFO.  These notifications are sent
      over the backchannel
      once the original request has been processed
      on the server. The server will send an array of
      notifications, cnda_changes, as a list of pairs of
      bitmaps and values.  See <xref target="fattr4" />
      for a description of how NFSv4.1 bitmaps work.

   </t>

   <t>
    As with CB_NOTIFY (<xref
    target="OP_CB_NOTIFY_DESCRIPTION"/>), it is
    possible the server has more notifications than
    can fit in a CB_COMPOUND, thus requiring multiple
    CB_COMPOUNDs. Unlike CB_NOTIFY, serialization is not
    an issue because unlike directory entries, device
    IDs cannot be re-used after being deleted (<xref
    target="device_ids" />).

   </t>

   <t>
    All device ID notifications contain a device ID and a
    layout type.  The layout type is necessary because two
    different layout types can share the same device ID,
    and the common device ID can have completely different
    mappings for each layout type.

   </t>

    <t>
     The server will send the following notifications:

      <list style="hanging">

	<t hangText="NOTIFY_DEVICEID4_CHANGE"><vspace />
	  A previously provided device-ID-to-device-address 
          mapping has changed and the client uses
	  GETDEVICEINFO to obtain the
	  updated mapping.

          The notification is encoded in a value of data
          type notify_deviceid_change4. This data type
          also contains a boolean field, ndc_immediate,
          which if TRUE indicates that the change will be
          enforced immediately, and so the client might not
          be able to complete any pending I/O to the device
          ID. If ndc_immediate is FALSE, then for an
          indefinite time, the client can complete pending
          I/O. After pending I/O is complete, the client
          SHOULD get the new device-ID-to-device-address
          mappings before sending new I/O requests to the
          storage devices addressed by the device ID.

	</t>

	<t hangText="NOTIFY4_DEVICEID_DELETE"><vspace />
	  Deletes a device ID from the mappings.  This
	  notification MUST NOT be sent if the client has
	  a layout that refers to the device ID. In other
	  words, if the server is sending a delete device ID
          notification, one of the following is true for layouts
	  associated with the layout type:

          <list style="symbols">

          <t>
           The client never had a layout referring to that device ID.
          </t>
          
          <t>
           The client has returned all layouts referring to that device ID.
          </t>

          <t>
           The server has revoked all layouts referring to that device ID.
          </t>

          </list>

	  The notification is encoded in a value of data
	  type notify_deviceid_delete4.

          After a server deletes a device ID, it MUST NOT
          reuse that device ID for the same layout type until the
          client ID is deleted.

	</t>
      </list>
    </t>
  </section>

</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="OP_CB_ILLEGAL" title="Operation 10044: CB_ILLEGAL - Illegal Callback Operation" >

  <section toc="exclude" anchor="OP_CB_ILLEGAL_ARGUMENT" title="ARGUMENT">
    <figure>
      <artwork>
        void;
      </artwork>
    </figure>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_RESULT" title="RESULT">
<figure>
 <artwork>
/*
 * CB_ILLEGAL: Response for illegal operation numbers
 */
struct CB_ILLEGAL4res {
        nfsstat4        status;
};

 </artwork>
</figure>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_DESCRIPTION" title="DESCRIPTION">
    <t>
     This operation is a placeholder for encoding a
     result to handle the case of the server sending
     an operation code within CB_COMPOUND that is not
     defined in the NFSv4.1 specification. See <xref
     target="OP_CB_COMPOUND_DESCRIPTION"/> for more details.

    </t>
    <t>
     The status field of CB_ILLEGAL4res MUST be set to
     NFS4ERR_OP_ILLEGAL.
    </t>
  </section>
  <section toc="exclude" anchor="OP_CB_ILLEGAL_IMPLEMENTATION" title="IMPLEMENTATION">
    <t>
     A server will probably not send an operation with code
     OP_CB_ILLEGAL, but if it does, the response will be CB_ILLEGAL4res
     just as it would be with any other invalid operation code. Note
     that if the client gets an illegal operation code that is not
     OP_ILLEGAL, and if the client checks for legal operation codes
     during the XDR decode phase, then an instance of
     data type CB_ILLEGAL4res will not be returned.
    </t>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="securityconsider" title="Security Considerations">
<t>
   Historically, the authentication model of NFS
   was based on the entire machine being the NFS client, with the
   NFS server trusting the NFS client
   to authenticate the end-user.
   The NFS server in turn shared its files only to
   specific clients, as identified by the client's source
   network address.  Given this model, the AUTH_SYS
   RPC security flavor simply identified the end-user
   using the client to the NFS server.  When processing
   NFS responses, the client ensured that the responses
   came from the same network address and port number
   to which the request was sent.  While such a model is
   easy to implement and simple to deploy and use, it is
   unsafe.  Thus, NFSv4.1 
   implementations are REQUIRED to support a security model that uses
   end-to-end authentication, where an end-user on a client 
   mutually authenticates (via cryptographic schemes that
   do not expose passwords or keys in the clear on the
   network) to a principal on an NFS server.  Consideration
   is also given to the integrity and privacy of
   NFS requests and responses.  The issues of end-to-end
   mutual authentication, integrity, and privacy are
   discussed in <xref target="RPCSEC_GSS_and_Security_Services" />. 
   There are specific considerations when using Kerberos V5 as described
   in <xref target="krb5_sec_consider"/>.
</t>
<t>
   Note that being REQUIRED to implement does not mean REQUIRED to
   use; AUTH_SYS can be used by NFSv4.1 clients and servers.
   However, AUTH_SYS is merely an OPTIONAL security flavor in NFSv4.1,
   and so interoperability via AUTH_SYS is not assured.

</t>
<t>
   For reasons of reduced administration overhead, better
   performance, and/or reduction of CPU utilization,
   users of NFSv4.1 implementations might decline to use
   security mechanisms that enable integrity protection
   on each remote procedure call and response. The
   use of mechanisms without integrity leaves the user
   vulnerable to a man-in-the-middle of the NFS
   client and server that modifies the RPC request and/or
   the response. While implementations are free to provide
   the option to use weaker security mechanisms, there
   are three operations in particular that warrant the
   implementation overriding user choices.
   <list style='symbols'>

<t>
   The first two such operations are SECINFO and
   SECINFO_NO_NAME.  It is RECOMMENDED that the client send
   both operations such that they are protected with a
   security flavor that has integrity protection, such
   as RPCSEC_GSS with either the rpc_gss_svc_integrity
   or rpc_gss_svc_privacy service. Without integrity
   protection encapsulating SECINFO and SECINFO_NO_NAME
   and their results, a man-in-the-middle could
   modify results such that the client might select a
   weaker algorithm in the set allowed by the server, making
   the client and/or server vulnerable to further attacks.

</t>
<t>
   The third operation that SHOULD use integrity protection
   is any GETATTR for the fs_locations and fs_locations_info attributes, in order to mitigate the severity of a man-in-the-middle attack. The attack has two
   steps.  First the attacker modifies the unprotected results of some
   operation to return NFS4ERR_MOVED. Second, when the client follows up
   with a GETATTR for the fs_locations or fs_locations_info attributes, the attacker modifies
   the results to cause the client to migrate its traffic to a server
   controlled by the attacker. With integrity protection, this attack is mitigated.

</t>
   </list>
</t>
<t>
  Relative to previous NFS versions, NFSv4.1 has additional security
  considerations for pNFS (see Sections <xref target="security_considerations_pnfs" format="counter" /> 
and <xref target="file_security_considerations" format="counter" />), locking
  and session state (see <xref target="protect_state_change"/>),
  and state recovery during grace period (see <xref
  target="reclaim_security_considerations"/>).
  With respect to locking and session state, if SP4_SSV state protection
  is being used, <xref target="rpcsec_ssv_consider"/> has specific security considerations for the NFSv4.1 client and server.

</t>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
<section anchor="ianaconsider" title="IANA Considerations">
<t>
This section uses terms that are defined in <xref target="RFC5226"/>.
</t>

 <section anchor="namedattributesiana" title="Named Attribute Definitions">
   <t>
     IANA created a registry called the "NFSv4 Named Attribute Definitions Registry".
   </t>
   <t>
     The NFSv4.1 protocol supports the association of a file with zero or
     more named attributes.  The namespace identifiers for these attributes
     are defined as string names.  The protocol does not define the
     specific assignment of the namespace for these file attributes.
     The IANA registry promotes interoperability where common interests exist.
     While application developers are allowed to define and use
     attributes as needed, they are encouraged to register the
     attributes with IANA. 
   </t>
   <t>
     Such registered named attributes are presumed to apply to all minor
     versions of NFSv4, including those defined subsequently to the 
     registration.  If the named attribute is intended to be 
     limited to specific minor versions, this will be clearly stated in
     the registry's assignment.
   </t>
   <t>
     All assignments to the registry are made on a First Come First Served basis,
     per Section 4.1 of <xref target="RFC5226"/>.

     The policy for each assignment is Specification Required, 
     per Section 4.1 of <xref target="RFC5226"/>.
   </t>
   <t>
     Under the NFSv4.1 specification, the name of a named
     attribute can in theory be up to 2^32 - 1 bytes in
     length, but in practice NFSv4.1 clients and servers
     will be unable to handle a string that long. IANA
     should reject any assignment request with a named
     attribute that exceeds 128 UTF-8 characters. To give the
     IESG the flexibility to set up bases of assignment of
     Experimental Use and Standards Action,
     the prefixes of "EXPE" and "STDS" are Reserved.
     The named attribute with a zero-length name is Reserved.
   </t>
   <t>
     The prefix "PRIV" is designated for Private Use.  A
     site that wants to make use of unregistered named
     attributes without risk of conflicting with an
     assignment in IANA's registry should use the prefix
     "PRIV" in all of its named attributes.

   </t>
   <t>
     Because some NFSv4.1 clients and servers have case-insensitive
     semantics, the fifteen additional lower case and mixed case
     permutations of each of "EXPE", "PRIV", and "STDS" are Reserved (e.g.,
     "expe", "expE", "exPe", etc. are Reserved).
     Similarly, IANA must not allow two assignments that would conflict
     if both named attributes were converted to a common case.
   </t>

   <t>
     The registry of named attributes is a list of assignments, each
     containing three fields for each assignment.

     <list style='numbers'>
	<t>
	  A US-ASCII string name that is the actual name of
	  the attribute. This name must be unique.  This
	  string name can be 1 to 128 UTF-8 characters
	  long.

	</t>

	<t>
	  A reference to the specification of the named attribute.
          The reference can consume up to 256 bytes (or more if IANA
          permits).
	</t>

	<t>
	  The point of contact of the registrant. The point
	  of contact can consume up to 256 bytes (or more if IANA
	  permits).

	</t>
     </list>
     </t>

  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>
  
  <section title="Updating Registrations">
  <t>
    The registrant is always permitted to update the point of contact
    field. Any other change will require Expert Review or IESG
    Approval.
  </t>
  </section>

 </section>

 <section anchor="notifyiana" title="Device ID Notifications">
   <t>
     IANA created a registry called the "NFSv4 Device ID
Notifications Registry".
   </t>

   <t>
      The potential exists for new notification types to be
      added to the CB_NOTIFY_DEVICEID operation (see <xref
      target="OP_CB_NOTIFY_DEVICEID" />). This can be done
      via changes to the operations that register
      notifications, or by adding new operations to NFSv4.
      This requires a new minor version of NFSv4, and
      requires a Standards Track document from the IETF.
      Another way to add a notification is to specify a new
      layout type (see <xref target="pnfsiana" />).

    </t>
   <t>
     Hence, all assignments to the registry are made on a Standards Action
     basis per Section 4.1 of <xref target="RFC5226"/>, with
     Expert Review required.
   </t>
   <t>
    The registry is a list of assignments, each containing
    five fields per assignment.

     <list style='numbers'>
        <t>
          The name of the notification type. This name must have the
          prefix "NOTIFY_DEVICEID4_". This name must be unique.
        </t>
        <t>
	  The value of the notification. IANA will assign
	  this number, and the request from the registrant
	  will use TBD1 instead of an actual value. IANA
	  MUST use a whole number that can be no higher
	  than 2^32-1, and should be the next available
	  value. The value assigned must be unique.
	  A Designated Expert must be used to
	  ensure that when the name of the notification
	  type and its value are added to the NFSv4.1
	  notify_deviceid_type4 enumerated data type in the
	  NFSv4.1 XDR description (<xref
	  target="RFC5662"/>), the result continues to
	  be a valid XDR description.

        </t>
        <t>
	  The Standards Track RFC(s) that describe the
	  notification. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
	  of an actual RFC number.

        </t>
        <t>
	  How the RFC introduces the notification. This is
	  indicated by a single US-ASCII value. If the
	  value is N, it means a minor revision to the
	  NFSv4 protocol. If the value is L, it means a new
	  pNFS layout type. Other values can be used with
	  IESG Approval.

        </t>
        <t>
	  The minor versions of NFSv4 that are allowed to
	  use the notification. While these are numeric
	  values, IANA will not allocate and assign them;
	  the author of the relevant RFCs with IESG
	  Approval assigns these numbers. Each time there is a
          new minor version of NFSv4 approved, a Designated
          Expert should review the registry to make recommended
          updates as needed.
          
        </t>
     </list>
   </t>

  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="devnotelist"/>. Note that the
    next available value is zero.
  </t>

  <texttable title="Initial Device ID Notification Assignments" anchor='devnotelist'>

	<ttcol>Notification Name</ttcol>
	<ttcol>Value</ttcol>
	<ttcol>RFC</ttcol>
	<ttcol>How</ttcol>
	<ttcol>Minor Versions</ttcol>

	<c>NOTIFY_DEVICEID4_CHANGE</c> <c>1</c> <c>RFC5661</c> <c>N</c> <c>1</c>

	<c>NOTIFY_DEVICEID4_DELETE</c> <c>2</c> <c>RFC5661</c> <c>N</c> <c>1</c>

  </texttable>
  
  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>
  </section>

 <section anchor="recalliana" title="Object Recall Types">

   <t>
     IANA created a registry called the "NFSv4 Recallable Object Types Registry".
   </t>
   <t>
      The potential exists for new object types to be added to the CB_RECALL_ANY operation (see
      <xref target="OP_CB_RECALL_ANY" />). This can be done via changes to
      the operations that add recallable types, or by adding new operations
      to NFSv4. This requires a new minor version of NFSv4, and requires
      a Standards Track document from IETF. Another way to
      add a new recallable object is to specify a new layout type (see <xref target="pnfsiana" />).
    </t>
   <t>
     All assignments to the registry are made on a Standards Action
     basis per Section 4.1 of <xref target="RFC5226"/>, with
     Expert Review required.
   </t>
   <t>
    Recallable object types are 32-bit unsigned numbers. There are no Reserved
    values. Values in the range 12 through 15, inclusive, are designated for Private
    Use.
   </t>

   <t>
    The registry is a list of assignments, each containing
    five fields per assignment.

     <list style='numbers'>
        <t>
          The name of the recallable object type. This name must have the
          prefix "RCA4_TYPE_MASK_". The name must be unique.
        </t>
        <t>
	  The value of the recallable object type. IANA
	  will assign this number, and the request from the
	  registrant will use TBD1 instead of an actual
	  value. IANA MUST use a whole number that can be
	  no higher than 2^32-1, and should be the next
	  available value. The value must be unique. A
	  Designated Expert must be used to ensure that
	  when the name of the recallable type and its
	  value are added to the NFSv4 XDR description
	  <xref target="RFC5662"/>,
	  the result continues to be a valid XDR
	  description.

        </t>
        <t>
	  The Standards Track RFC(s) that describe the
	  recallable object type. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
	  of an actual RFC number.

        </t>
        <t>
	  How the RFC introduces the recallable object type. This is
	  indicated by a single US-ASCII value. If the
	  value is N, it means a minor revision to the
	  NFSv4 protocol. If the value is L, it means a new
	  pNFS layout type. Other values can be used with
	  IESG Approval.

        </t>
        <t>
	  The minor versions of NFSv4 that are allowed to
	  use the recallable object type. While these
	  are numeric values, IANA will not allocate and
	  assign them; the author of the relevant RFCs with
	  IESG Approval assigns these numbers. Each time
	  there is a new minor version of NFSv4 approved, a
	  Designated Expert should review the registry to
	  make recommended updates as needed.

        </t>
     </list>
   </t>

  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="recalllist"/>. Note that
    the next available value is five.
  </t>

  <texttable title="Initial Recallable Object Type Assignments" anchor='recalllist'>

	<ttcol>Recallable Object Type Name</ttcol>
	<ttcol>Value</ttcol>
	<ttcol>RFC</ttcol>
	<ttcol>How</ttcol>
	<ttcol>Minor Versions</ttcol>

	<c>RCA4_TYPE_MASK_RDATA_DLG</c> <c>0</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_WDATA_DLG</c> <c>1</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_DIR_DLG</c> <c>2</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_FILE_LAYOUT</c> <c>3</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

	<c>RCA4_TYPE_MASK_BLK_LAYOUT</c> <c>4</c> <c>RFC 5661</c> <c>L</c> <c>1</c>

	<c>RCA4_TYPE_MASK_OBJ_LAYOUT_MIN</c> <c>8</c> <c>RFC 5661</c> <c>L</c> <c>1</c>
	<c>RCA4_TYPE_MASK_OBJ_LAYOUT_MAX</c> <c>9</c> <c>RFC 5661</c> <c>L</c> <c>1</c>

  </texttable>
  
  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>
  </section>
  
  <section anchor="pnfsiana" title="Layout Types">
    <t>
      IANA created a registry called the "pNFS Layout Types Registry".
    </t>
    <t>
      All assignments to the registry are made on a Standards Action basis,
      with Expert Review required.
    </t>
    <t>
      Layout types are 32-bit numbers. The value zero is Reserved.
      Values in the range 0x80000000 to 0xFFFFFFFF inclusive are designated for Private Use.
      IANA will assign numbers from the range
      0x00000001 to 0x7FFFFFFF inclusive.
    </t>
    <t>
      The registry is a list of assignments, each
      containing five fields.

      <list style='numbers'>
        <t>
          The name of the layout type. This name must have the
          prefix "LAYOUT4_". The name must be unique.
        </t>

	<t>
	  The value of the layout type. IANA will assign
          this number, and the request from the registrant
          will use TBD1 instead of an actual value. The value
          assigned must be unique.
          A Designated Expert must be used to ensure
          that when the name of the layout type and
	  its value are added to the NFSv4.1 layouttype4
	  enumerated data type in the NFSv4.1 XDR
	  description (<xref
	  target="RFC5662"/>),
	  the result continues to be a valid XDR
	  description.

        </t>

        <t>
          The Standards Track RFC(s) that describe the
          notification. If the RFC(s) have not yet been
          published, the registrant will use RFCTBD2, RFCTBD3, etc. instead
          of an actual RFC number. Collectively, the RFC(s) must adhere to
          the guidelines listed in <xref target="layout_guidelines"/>.

        </t>

	 <t>
          How the RFC introduces the layout type. This is
          indicated by a single US-ASCII value. If the
          value is N, it means a minor revision to the
          NFSv4 protocol. If the value is L, it means a new
          pNFS layout type. Other values can be used with
          IESG Approval.

        </t>

        <t>
          The minor versions of NFSv4 that are allowed to
          use the notification. While these are numeric
          values, IANA will not allocate and assign them;
          the author of the relevant RFCs with IESG
          Approval assigns these numbers. Each time there is
          a new minor version of NFSv4 approved, a Designated
          Expert should review the registry to make recommended
          updates as needed.

        </t>
 
      </list>

    </t>
    
  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="layoutlist"/>.
  </t>

  <texttable title="Initial Layout Type Assignments" anchor='layoutlist'>

        <ttcol>Layout Type Name</ttcol>
        <ttcol>Value</ttcol>
        <ttcol>RFC</ttcol>
        <ttcol>How</ttcol>
        <ttcol>Minor Versions</ttcol>

        <c>LAYOUT4_NFSV4_1_FILES</c> <c>0x1</c> <c>RFC 5661</c> <c>N</c> <c>1</c>

        <c>LAYOUT4_OSD2_OBJECTS</c> <c>0x2</c> <c>RFC 5664</c> <c>L</c> <c>1</c>
        <c>LAYOUT4_BLOCK_VOLUME</c> <c>0x3</c> <c>RFC 5663</c> <c>L</c> <c>1</c>
<!-- [rfced] The IANA site lists this document (RFC 5661) as the
reference for values 0x2 and 0x3, instead of RFCs 5664 and 5663,
respectively.  Does the IANA site need to be updated? 

     [Eisler]: The IANA site needs to be updated. -->
  </texttable>

  </section>

  <section title="Updating Registrations">
  <t>
    The update of a registration will require IESG
    Approval on the advice of a Designated Expert.
  </t>

  </section>



    <section anchor="layout_guidelines" title="Guidelines for Writing Layout Type Specifications">
    <t>
      The author of a new pNFS layout specification must follow these
      steps to obtain acceptance of the layout type as a Standards Track RFC:
      <list style='numbers'>
	<t>
	  The author devises the new layout specification.
	</t>
	<t>
	  The new layout type specification MUST, at a minimum: 
	  <list style='symbols'>
	    <t>
	      Define the contents of the layout-type-specific fields of the
	      following data types:
	      <list style='symbols'>
		<t>
		  the da_addr_body field of the device_addr4
		  data type;
		</t>
		<t>
		  the loh_body field of the layouthint4
		  data type;
		</t>
		<t>
		  the loc_body field of layout_content4
		  data type (which in turn is the lo_content field of the
		  layout4 data type);
		</t>
		<t>
		  the lou_body field of the layoutupdate4
		  data type;
		</t>
	      </list>
	    </t>
	    <t>
	      Describe or define the storage access protocol used to access
	      the storage devices.
	    </t>
	    <t>
	      Describe whether revocation of layouts is supported.
	    </t>
	    <t>
	      At a minimum, describe the methods of recovery from:
	      <list style="numbers">
		<t> Failure and restart for client, server, storage device.
		</t>
		<t> Lease expiration from perspective of the active client,
		  server, storage device.
		</t>
		<t> Loss of layout state resulting in fencing of client
		  access to storage devices (for an example, see 
		  <xref target="lease_expiration_mds" />).
		</t>
	      </list>
	    </t>
	    <t>
	      Include an IANA considerations section, which will
	      in turn include:

              <list style="symbols">
	      <t>
		A request to IANA
		for a new layout type per <xref
		target="pnfsiana"/>.

	      </t>
	      <t>
		A list of requests to IANA for
		any new recallable object types for
		CB_RECALL_ANY; each entry is to be presented in the form described
		in <xref target="recalliana"/>.

	      </t>
	      <t>
		A list of requests to IANA for
		any new notification values for
		CB_NOTIFY_DEVICEID; each entry is to be presented in the form
		described in <xref target="notifyiana"/>.

	      </t>
              </list>

	    </t>
	    <t>
	      Include a security considerations section. This section MUST
              explain how the NFSv4.1 authentication, authorization, and
              access-control models are preserved. That is, if a metadata server
              would restrict a READ or WRITE operation, how would pNFS via
              the layout similarly restrict a corresponding input or
              output operation?
	    </t>

	  </list>
	</t>
	<t>
	  The author documents the new layout specification as an Internet-Draft.
	</t>
	<t>
	  The author submits the Internet-Draft for review through the
	  IETF standards process as defined in "The Internet Standards
	  Process--Revision 3" (BCP 9).

The new layout specification will be
	  submitted for eventual publication as a Standards Track RFC.
	</t>
	<t>
	  The layout specification progresses through the IETF standards
	  process.
	</t>
      </list>
    </t>
    </section>
  </section>

  <section anchor="path_var_iana" title="Path Variable Definitions">
   
    <t>
      This section deals with the IANA considerations associated with
      the variable substitution feature for location names as 
      described in <xref target="fs_locations_item4" />.  As
      described there, variables subject to substitution consist
      of a domain name and a specific name within that domain, with the
      two separated by a colon. There are two sets of IANA considerations
      here:
      <list style='numbers'>
        <t>
          The list of variable names.
        </t>

        <t>
          For each variable name, the list of possible values.
        </t>

      </list>
      Thus, there will be one registry for the list of variable names, and
      possibly one registry for listing the values of each variable name.
    </t>
  
    <section anchor="path_variables_iana" title="Path Variables Registry">
    <t>
     IANA created a registry called the "NFSv4 Path Variables Registry".
    </t>

 
    <section anchor="path_values_iana" title="Path Variable Values">
      <t>
       Variable names are of the form "${", followed by a
       domain name, followed by a colon (":"), followed by
       a domain-specific portion of the variable name,
       followed by "}". When the domain name is "ietf.org",
       all variables names must be registered with IANA on
       a Standards Action basis, with Expert Review
       required.  Path variables with registered domain
       names neither part of nor equal to ietf.org are
       assigned on a Hierarchical Allocation basis
       (delegating to the domain owner) and thus of no
       concern to IANA, unless the domain owner chooses to
       register a variable name from his domain. If the
       domain owner chooses to do so, IANA will do so on a
       First Come First Serve basis. To accommodate
       registrants who do not have their own domain, IANA
       will accept requests to register variables with the
       prefix "${FCFS.ietf.org:" on a First Come First
       Served basis. Assignments on a First Come First Basis
       do not require Expert Review, unless the registrant also
       wants IANA to establish a registry for the values of the
       registered variable.

      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  The name of the variable. The name of this
	  variable must start with a "${" followed by a
	  registered domain name, followed by ":", or it
	  must start with "${FCFS.ietf.org".  The name must
	  be no more than 64 UTF-8 characters long. The
	  name must be unique.

        </t>

        <t>
          For assignments made on Standards Action basis,
	  the Standards Track RFC(s) that describe the
	  variable. If the RFC(s) have not yet been
	  published, the registrant will use RFCTBD1,
	  RFCTBD2, etc. instead of an actual RFC number.
          Note that the RFCs do not have to be a part of an NFS minor version.
          For assignments made on a First Come First Serve basis, an explanation
          (consuming no more than 1024 bytes, or more if IANA permits)
          of the purpose of the variable. A reference to the explanation can
          be substituted.
          
        </t>
        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
          For assignments made on a Standards Action basis, the point of
          contact is always IESG.
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   The initial registry is in <xref target="varlist"/>.
  </t>

  <texttable title="Initial List of Path Variables" anchor='varlist'>

        <ttcol>Variable Name</ttcol>
        <ttcol>RFC</ttcol>
        <ttcol>Point of Contact</ttcol>

         <c>${ietf.org:CPU_ARCH}</c> <c>RFC 5661</c> <c>IESG</c>
         <c>${ietf.org:OS_TYPE}</c> <c>RFC 5661</c> <c>IESG</c>
         <c>${ietf.org:OS_VERSION}</c> <c>RFC 5661</c> <c>IESG</c>

  </texttable>

      <t>
	IANA has created registries for the values
	of the variable names ${ietf.org:CPU_ARCH} and
	${ietf.org:OS_TYPE}. See Sections <xref target="cpu_arch"
format="counter" />
	and <xref target="os_type" format="counter" />.
      </t>
      <t>
	For the values of the variable
	${ietf.org:OS_VERSION}, no registry is needed as
	the specifics of the values of the variable will
	vary with the value of ${ietf.org:OS_TYPE}. Thus,
	values for ${ietf.org:OS_VERSION} are on a
	Hierarchical Allocation basis and are of no concern
	to IANA.

      </t>
    </section>

      <section title="Updating Registrations">
      <t>
	The update of an assignment made on a Standards Action basis
        will require IESG Approval on the advice of a Designated Expert.
      </t>

      <t>
        The registrant can always update the point of contact of an assignment
        made on a First Come First Serve basis. Any other update will require
        Expert Review.
      </t>
       

      </section>
  </section>
  </section>
  <section title="Values for the ${ietf.org:CPU_ARCH} Variable" anchor="cpu_arch">
    <t>
     IANA created a registry called the "NFSv4 ${ietf.org:CPU_ARCH} Value Registry".
    </t>

 
      <t>
        Assignments to the registry are made on a First Come First Serve
        basis. The zero-length value of ${ietf.org:CPU_ARCH} is Reserved.
        Values with a prefix of "PRIV" are designated for Private Use.

      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  A value of the ${ietf.org:CPU_ARCH} variable. The value
	  must be 1 to 32 UTF-8 characters long. The value must be unique.
        </t>

        <t>
	  An explanation (consuming no more than 1024
	  bytes, or more if IANA permits) of what CPU
	  architecture the value denotes. A reference to
	  the explanation can be substituted.
        </t>

        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>

      <section title="Updating Registrations">
      <t>
        The registrant is free to update the assignment, i.e., change the
        explanation and/or point-of-contact fields.
      </t>
       

      </section>
  </section>
  <section title="Values for the ${ietf.org:OS_TYPE} Variable" anchor="os_type">
    <t>
     IANA created a registry called the "NFSv4 ${ietf.org:OS_TYPE} Value Registry".
    </t>

      <t>
        Assignments to the registry are made on a First Come First Serve
        basis. The zero-length value of ${ietf.org:OS_TYPE} is Reserved.
        Values with a prefix of "PRIV" are designated for Private Use.
      </t>
      
      <t>
      The registry is a list of assignments, each
      containing three fields.

      <list style='numbers'>
        <t>
	  A value of the ${ietf.org:OS_TYPE} variable. The value
	  must be 1 to 32 UTF-8 characters long. The value must be unique.

        </t>

        <t>
	  An explanation (consuming no more than 1024
	  bytes, or more if IANA permits) of what CPU
	  architecture the value denotes. A reference to
	  the explanation can be substituted.
        </t>

        <t>
          The point of contact, including an email address. The point of
          contact can consume up to 256 bytes (or more if IANA permits).
        </t>

      </list>
      </t>

        
  <section title="Initial Registry">
  <t>
   There is no initial registry.
  </t>
  </section>

      <section title="Updating Registrations">
      <t>
        The registrant is free to update the assignment, i.e., change the
        explanation and/or point of contact fields.
      </t>
       

      </section>

  </section>
  </section>
</section>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->

</middle>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007) -->
<!-- Copyright (C) The Internet Society (2006) -->
<back>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
  <references title="Normative References">

    <reference anchor='RFC2119'>
      <front>
	<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
	<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
	  <organization>Harvard University</organization>
	  <address>
	    <postal>
	      <street>1350 Mass. Ave.</street>
	      <street>Cambridge</street>
	    <street>MA 02138</street></postal>
	    <phone>- +1 617 495 3864</phone>
	<email>sob@xxxxxxxxxxx</email></address></author>
	<date year='1997' month='March' />
      </front>
      <seriesInfo name='BCP' value='14' />
      <seriesInfo name='RFC' value='2119' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc2119.txt' />
    </reference>

    <reference anchor='RFC4506'>

      <front>
      <title>XDR: External Data Representation Standard</title>
      <author initials='M.' surname='Eisler' fullname='M. Eisler' role='editor'>
      <organization /></author>
      <date year='2006' month='May' />
      <abstract>
      <t>&lt;p>This document describes the External Data
      Representation Standard (XDR) protocol as it is currently
      deployed and accepted. This document obsoletes RFC
      1832. [STANDARDS TRACK]&lt;/p></t></abstract></front>
      <seriesInfo name='STD' value='67' />
      <seriesInfo name='RFC' value='4506' />
      <format type='TXT' octets='55477' target='http://www.rfc-editor.org/rfc/rfc4506.txt' />
    </reference>

<reference anchor='RFC5531'>

<front>
<title>
RPC: Remote Procedure Call Protocol Specification Version 2
</title>

<author initials='R.' surname='Thurlow' fullname='R. Thurlow'>
<organization />
</author>
<date year='2009' month='May' />
<abstract>
<t>This document describes the Open Network Computing (ONC) Remote
Procedure Call (RPC) version 2 protocol as it is currently deployed
and accepted.  This document obsoletes RFC 1831. [STANDARDS
TRACK]</t></abstract></front>

<seriesInfo name='RFC' value='5531' />
<format type='TXT' octets='161720'
target='ftp://ftp.isi.edu/in-notes/rfc5531.txt' />
</reference>
    <reference anchor='RFC2203'>
    
      <front>
      <title>RPCSEC_GSS Protocol Specification</title>

        <author initials='M.' surname='Eisler' fullname='Michael Eisler'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UCOS03</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (719) 599-9026</phone>
        <email>mre@xxxxxxxxxxx</email></address></author>
  
        <author initials='A.' surname='Chiu' fullname='Alex Chiu'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UMPK17-203</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (415) 786-6465</phone>
        <email>hacker@xxxxxxxxxxx</email></address></author>
  
        <author initials='L.' surname='Ling' fullname='Lin Ling'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>M/S UMPK17-201</street>
        <street>2550 Garcia Avenue</street>
        <street>Mountain View</street>
        <street>CA 94043</street></postal>
        <phone>+1 (415) 786-5084</phone>
        <email>lling@xxxxxxxxxxx</email></address></author>

      <date year='1997' month='September' />
      <area>Security</area>
      <keyword>generic security service</keyword>
      <keyword>remote procedure call</keyword>
      <keyword>security</keyword>
      <abstract>
      <t>
         This memo describes an ONC/RPC security flavor that allows RPC
         protocols to access the Generic Security Services Application
         Programming Interface (referred to henceforth as GSS-API).
      </t></abstract></front>
      
      <seriesInfo name='RFC' value='2203' />
      <format type='TXT' octets='50937' target='http://www.rfc-editor.org/rfc/rfc2203.txt' />
      <format type='HTML' octets='64234' target='http://xml.resource.org/public/rfc/html/rfc2203.html' />
      <format type='XML' octets='50069' target='http://xml.resource.org/public/rfc/xml/rfc2203.xml' />
    </reference>

    <reference anchor='RFC4121'>
    
      <front>
        <title>The Kerberos Version 5 Generic Security Service Application Program Interface (GSS-API) Mechanism Version 2</title>

          <author initials='L.' surname='Zhu'>
		<organization>Microsoft</organization>
          </author>

          <author initials='K.' surname='Jaganathan'>
		<organization>Microsoft</organization>
          </author>

          <author initials='S.' surname='Hartman'>
		<organization>MIT</organization>
          </author>

        <date year='2005' month='July' />

        <abstract>
        <t>

	RFC 1964 is updated and incremental changes are proposed in
	response to recent developments such as the introduction of
	Kerberos crypto-system framework.  These changes support the
	inclusion of new crypto-systems, by defining new per-message
	tokens along with their encryption and checksum algorithms
	based on the crypto-system profiles.

	</t>
        </abstract>

      </front>
      <seriesInfo name='RFC' value='4121' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc4121.txt' />
    </reference>


    <reference anchor="hardlink">
        <front>
	    <title>Section 3.191 of Chapter 3 of Base Definitions of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor='RFC2743'>

      <front>
	<title abbrev='GSS-API'>Generic Security Service Application
	Program Interface Version 2, Update 1</title>
	<author initials='J.' surname='Linn' fullname='John Linn'>
	  <organization>RSA Laboratories</organization>
	  <address>
	    <postal>
	      <street>20 Crosby Drive</street>
	      <city>Bedford</city>
	      <region>MA</region>
	      <code>01730</code>
	    <country>US</country></postal>
	    <phone>+1 781 687 7817</phone>
	<email>jlinn@xxxxxxxxxxxxxxx</email></address></author>
	<date year='2000' month='January' />
	<abstract>
	  <t>The Generic Security Service Application Program
	  Interface (GSS-API), Version 2, as defined in, provides
	  security services to callers in a generic fashion,
	  supportable with a range of underlying mechanisms and
	  technologies and hence allowing source-level portability of
	  applications to different environments. This specification
	  defines GSS-API services and primitives at a level
	  independent of underlying mechanism and programming language
	  environment, and is to be complemented by other, related
	  specifications:</t>
	  <t>documents defining specific parameter bindings for
	  particular language environments</t>
	  <t>documents defining token formats, protocols, and
	  procedures to be implemented in order to realize GSS-API
	  services atop particular security mechanisms</t> <t>This
	  memo obsoletesmaking specific, incremental changes in
	  response to implementation experience and liaison
	  requests. It is intended, therefore, that this memo or a
	  successor version thereto will become the basis for
	  subsequent progression of the GSS-API specification on the
	  standards track.</t></abstract></front>

      <seriesInfo name='RFC' value='2743' />
      <format type='TXT' octets='229418' 
	      target='http://www.rfc-editor.org/rfc/rfc2743.txt' />
    </reference>

    <reference anchor='RPCRDMA'>
      <front>
	<title>
Remote Direct Memory Access Transport for Remote Procedure Call
	</title>

	<author initials='T' surname='Talpey' fullname='Thomas Talpey'>
	  <organization />
	</author>

	<author initials='B' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization />
	</author>

	<date month='October' year='2009' />

	<abstract><t>A protocol is described providing Remote Direct
	Memory Access (RDMA) as a new transport for Remote Procedure
	Call (RPC).  The RDMA transport binding conveys the benefits
	of efficient, bulk data transport over high speed networks,
	while providing for minimal change to RPC applications and
	with no required revision of the application RPC protocol, or
	the RPC protocol itself.</t></abstract>

      </front>

      <seriesInfo name='RFC' value='5666' />
      <format type='TXT'
              target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-rpcrdma-09.txt' />
    </reference>

    <reference anchor='NFSDDP'>
      <front>
	<title>
Network File System (NFS) Direct Data Placement
	</title>

	<author initials='T' surname='Talpey' fullname='Thomas Talpey'>
	  <organization />
	</author>

	<author initials='B' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization />
	</author>

	<date month='January' year='2010' />

	<abstract>
	  <t>
	    This draft defines the bindings of the various Network
	    File System (NFS) versions to the Remote Direct Memory
	    Access (RDMA) operations supported by the RPC/RDMA
	    transport protocol.  It describes the use of direct data
	    placement by means of server-initiated RDMA operations
	    into client-supplied buffers for implementations of NFS
	    versions 2, 3, 4 and 4.1 over such an RDMA
	    transport.
	  </t>
	</abstract>

      </front>

      <seriesInfo name='RFC' value='5667' />
      <format type='TXT'
              target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-nfsdirect-08.txt' />
    </reference>

    <reference anchor='RDMAP'>

      <front>
	<title abbrev='RDMAP - WIP'>A Remote Direct Memory Access Protocol
         Specification
	</title>
	<author initials='R.' surname='Recio'>
	  <organization>IBM Corporation</organization>
	</author>
	<author initials='B.' surname='Metzler'>
	  <organization>IBM Corporation</organization>
	</author>
	<author initials='P.' surname='Culley'>
	  <organization>Hewlett-Packard Company</organization>
	</author>
	<author initials='J.' surname='Hilland'>
	  <organization>Hewlett-Packard Company</organization>
	</author>
	<author initials='D.' surname='Garcia'>
	  <organization></organization>
	</author>
	<date year='2007' month='October' />
	<abstract>
	<t>
	This document defines a Remote Direct Memory Access Protocol 
	(RDMAP) that operates over the Direct Data Placement Protocol (DDP 
	protocol).  RDMAP provides read and write services directly to 
	applications and enables data to be transferred directly into 
	Upper Layer Protocol (ULP) buffers without intermediate data 
	copies. It also enables a kernel bypass implementation. 
	</t></abstract></front>

      <seriesInfo name='RFC' value='5040' />
      <format type='TXT' target='http://www.rfc-editor.org/rfc/rfc5040.txt' />
    </reference>

    <reference anchor='RFC2104'>

      <front>
	<title abbrev='HMAC'>HMAC: Keyed-Hashing for Message Authentication</title>
	<author initials='H.' surname='Krawczyk' fullname='Hugo Krawczyk'>
	  <organization>IBM, T.J. Watson Research Center</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 704</street>
	      <city>Yorktown Heights</city>
	      <region>NY</region>
	      <code>10598</code>
	      <country>US</country></postal>
	    <email>hugo@xxxxxxxxxxxxxx</email></address></author>

	<author initials='M.' surname='Bellare' fullname='Mihir Bellare'>
	  <organization>University of California at San Diego, Dept of Computer Science and Engineering</organization>
	  <address>
	    <postal>
	      <street>9500 Gilman Drive</street>
	      <street>Mail Code 0114</street>
	      <city>La Jolla</city>
	      <region>CA</region>
	      <code>92093</code>
	      <country>US</country></postal>
	    <email>mihir@xxxxxxxxxxx</email></address></author>

	<author initials='R.' surname='Canetti' fullname='Ran Canetti'>
	  <organization>IBM T.J. Watson Research Center</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 704</street>
	      <city>Yorktown Heights</city>
	      <region>NY</region>
	      <code>10598</code>
	      <country>US</country></postal>
	    <email>canetti@xxxxxxxxxxxxxx</email></address></author>

	<date year='1997' month='February' />
	<abstract>
	  <t>This document describes HMAC, a mechanism for message
	  authentication using cryptographic hash functions. HMAC can
	  be used with any iterative cryptographic hash function,
	  e.g., MD5, SHA-1, in combination with a secret shared key.
	  The cryptographic strength of HMAC depends on the properties
	  of the underlying hash function.</t></abstract></front>

      <seriesInfo name='RFC' value='2104' />
      <format type='TXT' octets='22297' target='http://www.rfc-editor.org/rfc/rfc2104.txt' />
    </reference>

	<reference anchor='RFC5403'>

	<front>
	<title>RPCSEC_GSS Version 2</title>
	<author initials='M.' surname='Eisler' fullname='M. Eisler'>
	<organization /></author>
	<date year='2009' month='February' />
	<abstract>
	<t>This document describes version 2 of the RPCSEC_GSS protocol.  Version 2 is the same as version 1 (specified in RFC 2203) except that support for channel bindings has been added.  RPCSEC_GSS allows remote procedure call (RPC) protocols to access the Generic Security Services Application Programming Interface (GSS-API). [STANDARDS TRACK]</t></abstract></front>

	<seriesInfo name='RFC' value='5403' />
	<format type='TXT' octets='30812' target='ftp://ftp.isi.edu/in-notes/rfc5403.txt' />
	</reference>

<reference anchor='RFC5662'>
<front>
<title>
Network File System (NFS) Version 4 Minor Version 1 External Data
Representation Standard (XDR) Description
</title>

<author initials='S' surname='Shepler' fullname='Spencer Shepler' role='editor'>
    <organization />
</author>

<author initials='M' surname='Eisler' fullname='Mike Eisler' role='editor'>
    <organization />
</author>

<author initials='D' surname='Noveck' fullname='David  Noveck' role='editor'>
    <organization />
</author>

<date month='January' year='2010' />

<abstract><t>This Internet-Draft provides the XDR description for NFSv4 minor version one.</t></abstract>

</front>

<seriesInfo name='RFC' value='5662' />
</reference>


    
    <reference anchor="symlink">
        <front>
	    <title>Section 3.372 of Chapter 3 of Base Definitions of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

<reference anchor='RFC5665'>
      <front>
	<title>
IANA Considerations for Remote Procedure Call (RPC) Network
Identifiers and Universal Address Formats
	</title>

	<author initials='M' surname='Eisler' fullname='Mike Eisler'>
	  <organization />
	</author>

	<date month='January' year='2010' />

	<abstract>
	  <t>
IANA Considerations for RPC Net Identifiers and Universal Address Formats.
	  </t>
	</abstract>

      </front>

      <seriesInfo name='RFC' value='5665' />
    </reference>

    <reference anchor="read_atime">
        <front>
	    <title>Section 'read()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="readdir_atime">
        <front>
	    <title>Section 'readdir()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>
    <reference anchor="write_atime">
        <front>
	    <title>Section 'write()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor='RFC3454'>

      <front>
	<title>Preparation of Internationalized Strings ("stringprep")</title>
	<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
	  <organization /></author>
	<author initials='M.' surname='Blanchet' fullname='M. Blanchet'>
	  <organization /></author>
	<date year='2002' month='December' />
	<abstract>
	  <t>
	    &lt;p>This document describes a framework for preparing
	    Unicode text strings in order to increase the likelihood
	    that string input and string comparison work in ways that
	    make sense for typical users throughout the world. The
	    stringprep protocol is useful for protocol identifier
	    values, company and personal names, internationalized
	    domain names, and other text strings. This document does
	    not specify how protocols should prepare text
	    strings. Protocols must create profiles of stringprep in
	    order to fully specify the processing options. [STANDARDS
	    TRACK] &lt;/p>
          </t>
        </abstract>
      </front>

      <seriesInfo name='RFC' value='3454' />
      <format type='TXT' octets='138684' target='http://www.rfc-editor.org/rfc/rfc3454.txt' />
    </reference>

    <reference anchor="chmod">
        <front>
	    <title>Section 'chmod()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>
    <reference anchor="ISO.10646-1.1993">
      <front>
     <title>Information Technology - Universal Multiple-octet coded
     Character Set (UCS) - Part 1: Architecture and Basic Multilingual
     Plane</title>
	<author>
	  <organization>International Organization for Standardization
	  </organization>
	</author>
	<date month="May" year="1993" />
      </front>

      <seriesInfo name="ISO" value="Standard 10646-1" />

    </reference>
    <reference anchor='RFC2277'>

      <front>
	<title abbrev='Charset Policy'>
	IETF Policy on Character Sets and Languages</title>
	<author initials='H.' surname='Alvestrand' 
		fullname='Harald Tveit Alvestrand'>
	  <organization>UNINETT</organization>
	  <address>
	    <postal>
	      <street>P.O.Box 6883 Elgeseter</street>
	      <street>N-7002 TRONDHEIM</street>
	    <country>NORWAY</country></postal>
	    <phone>+47 73 59 70 94</phone>
	<email>Harald.T.Alvestrand@xxxxxxxxxx</email></address></author>
	<date year='1998' month='January' />
	<area>Applications</area>
	<keyword>Internet Engineering Task Force</keyword>
      <keyword>character encoding</keyword></front>

      <seriesInfo name='BCP' value='18' />
      <seriesInfo name='RFC' value='2277' />
      <format type='TXT' octets='16622' 
	      target='http://www.rfc-editor.org/rfc/rfc2277.txt' />
      <format type='HTML' octets='26556' 
	      target='http://xml.resource.org/public/rfc/html/rfc2277.html' />
      <format type='XML' octets='15544' 
	      target='http://xml.resource.org/public/rfc/xml/rfc2277.xml' />
    </reference>

    <reference anchor='RFC3491'>

      <front>
	<title>Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)</title>
	<author initials='P.' surname='Hoffman' fullname='P. Hoffman'>
	  <organization /></author>
	<author initials='M.' surname='Blanchet' fullname='M. Blanchet'>
	  <organization /></author>
	<date year='2003' month='March' />
	<abstract>
	  <t>
	    &lt;p>This document describes how to prepare
	    internationalized domain name (IDN) labels in order to
	    increase the likelihood that name input and name
	    comparison work in ways that make sense for typical users
	    throughout the world. This profile of the stringprep
	    protocol is used as part of a suite of on-the-wire
	    protocols for internationalizing the Domain Name System
	    (DNS). [STANDARDS TRACK] &lt;/p>
          </t>
         </abstract>
        </front>

      <seriesInfo name='RFC' value='3491' />
      <format type='TXT' octets='10316' target='http://www.rfc-editor.org/rfc/rfc3491.txt' />
    </reference>

    <reference anchor="fcntl">
        <front>
	    <title>Section 'fcntl()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>


    <reference anchor="fsync">
        <front>
	    <title>Section 'fsync()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="passwd">
        <front>
	    <title>Section 'getpwnam()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>

    <reference anchor="unlink">
        <front>
	    <title>Section 'unlink()' of System Interfaces of
	    The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition, HTML Version (www.opengroup.org), ISBN
1931624232  </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date year="2004"/>
        </front>
    </reference>


<!-- obsoleted by RFC 5531
    <reference anchor='RFC1831'>

      <front>
	<title abbrev='Remote Procedure Call Protocol Version 2'>RPC:
	Remote Procedure Call Protocol Specification Version 2</title>
	<author initials='R.' surname='Srinivasan' fullname='Raj Srinivasan'>
	  <organization>Sun Microsystems, Inc., ONC Technologies</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>M/S MTV-5-40</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043</code>
	    <country>US</country></postal>
	    <phone>+1 415 336 2478</phone>
	    <facsimile>+1 415 336 6015</facsimile>
	<email>raj@xxxxxxxxxxx</email></address></author>
	<date year='1995' month='August' />
	<abstract>
      <t>This document describes the ONC Remote Procedure Call (ONC
      RPC Version 2) protocol as it is currently deployed and
      accepted.  "ONC" stands for "Open Network
      Computing".</t></abstract></front>

      <seriesInfo name='RFC' value='1831' />
      <format type='TXT' octets='37798' target='ftp://ftp.isi.edu/in-notes/rfc1831.txt' />
    </reference> -->



    <reference anchor='RFC4055'>

    <front>
    <title>
Additional Algorithms and Identifiers for RSA Cryptography for use in
the Internet X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile
</title>
    <author initials='J.' surname='Schaad' fullname='J. Schaad'>
    <organization /></author>
    <author initials='B.' surname='Kaliski' fullname='B. Kaliski'>
    <organization /></author>
    <author initials='R.' surname='Housley' fullname='R. Housley'>
    <organization /></author>
    <date year='2005' month='June' />
    <abstract>
    <t>&lt;p>This document supplements RFC 3279. It describes the
    conventions for using the RSA Probabilistic Signature Scheme
    (RSASSA-PSS) signature algorithm, the RSA Encryption Scheme -
    Optimal Asymmetric Encryption Padding (RSAES-OAEP) key transport
    algorithm and additional one-way hash functions with the
    Public-Key Cryptography Standards (PKCS) #1 version 1.5 signature
    algorithm in the Internet X.509 Public Key Infrastructure
    (PKI). Encoding formats, algorithm identifiers, and parameter
    formats are specified. [STANDARDS
    TRACK]&lt;/p>
    </t>
    </abstract>
    </front>

    <seriesInfo name='RFC' value='4055' />
    <format type='TXT' octets='57479' target='http://www.rfc-editor.org/rfc/rfc4055.txt' />
    </reference>
    <reference anchor="CSOR_AES">
      <front>
     <title>Cryptographic Algorithm Object Registration
     </title>
	<author>
	  <organization>National Institute of Standards and Technology
	  </organization>
	</author>
	<date month="November" year="2007" />
      </front>
      <seriesInfo name="URL" value="http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html"; />
    </reference>



  </references>

  <references title="Informative References">
    <reference anchor='RFC3530'>
      <front>
	<title>Network File System (NFS) version 4 Protocol</title>
	<author initials="S." surname="Shepler" fullname="S. Shepler">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="B." surname="Callaghan" fullname="B. Callaghan">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="D." surname="Robinson" fullname="D. Robinson">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="R." surname="Thurlow" fullname="R. Thurlow">
	  <organization>Sun Microsystems, Inc.</organization>
	</author>
	<author initials="C." surname="Beame" fullname="C. Beame">
	  <organization>Hummingbird, Ltd.</organization>
	</author>
	<author initials="M." surname="Eisler" fullname="M. Eisler">
	  <organization>NetApp</organization>
	</author>
	<author initials="D." surname="Noveck" fullname="D. Noveck">
	  <organization>NetApp</organization>
	</author>
	<date year="2003" month="April"/>
      </front>
      <seriesInfo name="RFC" value="3530"/>
      <format type="TXT" octets="600988" 
	      target="http://www.rfc-editor.org/rfc/rfc3530.txt"/>
    </reference>

<reference anchor='RFC1813'>

<front>
<title abbrev='NFSv3 Protocol'>NFS Version 3 Protocol Specification</title>
<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mailstop UMTV05-44</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043-1100</code>
<country>US</country></postal>
<phone>+1 415 336 1051</phone>
<facsimile>+1 415 336 6015</facsimile>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>

<author initials='B.' surname='Pawlowski' fullname='Brian Pawlowski'>
<organization>NetApp</organization>
<address>
<postal>
<street>319 North Bernardo Ave.</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>US</country></postal>
<phone>+1 415 428 5136</phone>
<facsimile>+1 415 428 5151</facsimile>
<email>beepy@xxxxxxxxxx</email></address></author>

<author initials='P.' surname='Staubach' fullname='Peter Staubach'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mailstop UMTV05-44</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043-1100</code>
<country>US</country></postal>
<phone>+1 415 336 5615</phone>
<facsimile>+1 415 336 6015</facsimile>
<email>peter.staubach@xxxxxxxxxxx</email></address></author>

<date year='1995' month='June' />
<abstract>
<t>This paper describes the NFSv3 protocol.  This paper is provided so that people can write compatible implementations.</t></abstract></front>

<seriesInfo name='RFC' value='1813' />
<format type='TXT' octets='229793' target='http://www.rfc-editor.org/rfc/rfc1813.txt' />
</reference>

    <reference anchor='RFC2847'>
    
      <front>
      <title>LIPKEY - A Low Infrastructure Public Key Mechanism Using SPKM</title>
        <author initials='M.' surname='Eisler' fullname='M. Eisler'>
        <organization /></author>
        <date year='2000' month='June' />

        <abstract>
          <t>&lt;p>This memorandum describes a method whereby one can
          use GSS-API (Generic Security Service Application Program
          Interface) to supply a secure channel between a client and
          server, authenticating the client with a password, and a
          server with a public key certificate. [STANDARDS TRACK]
          &lt;/p></t>
	</abstract>
      </front>
        
      <seriesInfo name='RFC' value='2847' />
      <format type='TXT' octets='50045' target='http://www.rfc-editor.org/rfc/rfc2847.txt' />
    </reference>

    <reference anchor='RFC2623'>
    
      <front>
      <title abbrev='NFS Security, RPCSEC_GSS, and Kerberos V5'>
NFS Version 2 and Version 3 Security Issues and the NFS Protocol's Use
of RPCSEC_GSS and Kerberos V5
</title> 

        <author initials='M.' surname='Eisler' fullname='Mike Eisler'>
        <organization>Sun Microsystems, Inc.</organization>
        <address>
        <postal>
        <street>5565 Wilson Road</street>
        <city>Colorado Springs</city>
        <region>CO</region>
        <code>80919</code>
        <country>US</country></postal>
        <phone>+1 719 599 9026</phone>
        <email>mre@xxxxxxxxxxx</email></address></author>

      <date year='1999' month='June' />

      <abstract>

        <t>This memorandum clarifies various security issues involving
        the NFSv2 and NFSv3 protocols and then
        describes how the NFS protocol
        use the RPCSEC_GSS security flavor protocol and Kerberos V5.
        This memorandum is provided so that people can write compatible
        implementations.</t>
      </abstract>
      </front>
      
      <seriesInfo name='RFC' value='2623' />
      <format type='TXT' octets='42521' target='http://www.rfc-editor.org/rfc/rfc2623.txt' />
    </reference>

        <reference anchor="Chet">
        <front>
	    <title>Improving the Performance
		    and Correctness of an NFS Server</title>

	    <author initials="C." surname="Juszczak" fullname="Chet Juszczak">
	      <organization>Digital Equipment Corporation</organization>
	    </author>
	    <date month="June" year="1990"/>
	    <abstract>
	    <t>
		Describes reply cache implementation that
		avoids work in the server by handling
		duplicate requests. More important, though
		listed as a side-effect, the reply cache
		aids in the avoidance of destructive non-
		idempotent operation re-application --
		improving correctness.

	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
      </reference>

    <reference anchor='RFC3232'>
    
      <front>
        <title>Assigned Numbers: RFC 1700 is Replaced by an On-line Database</title>
        <author initials='J.' surname='Reynolds'
fullname='J. Reynolds' role='editor'>
        <organization /></author>
        <date year='2002' month='January' />
        <abstract>
          <t>&lt;p>This memo obsoletes RFC 1700 (STD 2) "Assigned
          Numbers", which contained an October 1994 snapshot of assigned
          Internet protocol parameters. This memo provides information
          for the Internet community. &lt;/p></t>
	</abstract></front>
    
      <seriesInfo name='RFC' value='3232' />
      <format type='TXT' octets='3849' target='http://www.rfc-editor.org/rfc/rfc3232.txt' />
    </reference>

    <reference anchor='RFC1833'>

      <front>
	<title>Binding Protocols for ONC RPC Version 2</title>
	<author initials='R.' surname='Srinivasan' fullname='Raj Srinivasan'>
	  <organization>Sun Microsystems, Inc., ONC Technologies</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>M/S MTV-5-40</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043</code>
	    <country>US</country></postal>
	    <phone>+1 415 336 2478</phone>
	    <facsimile>+1 415 336 6015</facsimile>
	<email>raj@xxxxxxxxxxx</email></address></author>
	<date year='1995' month='August' />
	<abstract>
      <t>This document describes the binding protocols used in
      conjunction with the ONC Remote Procedure Call (ONC RPC Version
      2) protocols.</t></abstract></front>

      <seriesInfo name='RFC' value='1833' />
      <format type='TXT' octets='24449' target='http://www.rfc-editor.org/rfc/rfc1833.txt' />
    </reference>
    <reference anchor="rpc_xid_issues">
        <front>
	    <title>RPC XID Issues</title>

	    <author initials="R." surname="Werme" fullname="Ric Werme">
	      <organization>Digital Equipment Corporation</organization>
	    </author>
	    <date month="February" year="1996"/>
	    <abstract>
	    <t>
             The presentation provides implementation advice for
             ONC RPC transaction identifier (xid) generation.
	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
    </reference>

<reference anchor='RFC1094'>

<front>
<title abbrev='NFS: Network File System'>NFS: Network File System Protocol specification</title>
<author initials='B.' surname='Nowicki' fullname='Bill Nowicki'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>2550 Garcia Avenue</street>
<street>Mail Stop 1-40</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>US</country></postal>
<phone>+1 415 336 7278</phone>
<email>nowicki@xxxxxxx</email></address></author>
<date year='1989' month='March' /></front>

<seriesInfo name='RFC' value='1094' />
<format type='TXT' octets='51454' target='http://www.rfc-editor.org/rfc/rfc1094.txt' />
</reference>

    <reference anchor="ha_nfs_ibm">
        <front>
	    <title>A Highly Available Network Server</title>

	    <author initials="A." surname="Bhide" fullname="Anupam Bhide">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <author initials="E. N." surname="Elnozahy" fullname="Elmootazbellah N. Elnozahy">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <author initials="S. P." surname="Morgan" fullname="Stephen P. Morgan ">
	      <organization>IBM T.J. Watson Research Center</organization>
	    </author>
	    <date month="January" year="1991"/>
	    <abstract>
	    <t>
	     This paper presents the design and implementation
	     of a Highly Available Network File Server
	     (HA-NFS). We separate the problem of network
	     file server reliability into three different subproblems:
	     server reliability, disk reliability, and network
	     reliability. HA-NFS offers a different solution
	     for each: dual-ported disks and impersonation
	     are used to provide server reliability, disk mirroring
	     can be used to provide disk reliability, and optional
	     network replication can be used to provide
	     network reliability. The implementation shows
	     that HA-NFS provides high availability without
	     the excessive resource overhead or the performance
	     degradation that characterize traditional replication
	     methods. Ongoing operations are not aborted
	     during fail-over and recovery is completely transparent
	     to applications. HA-NFS adheres to the
	     NFS protocol standard and can be used by existing
	     NFS clients without modification.
	    </t>
	    </abstract>
        </front>
        <seriesInfo name="USENIX Conference Proceedings" value="" />
      </reference>

<reference anchor='RFC5664'>
<front>
<title>
Object-Based Parallel NFS (pNFS) Operations
</title>

<author initials='B' surname='Halevy' fullname='Benny Halevy'>
    <organization />
</author>

<author initials='B' surname='Welch' fullname='Brent Welch'>
    <organization />
</author>

<author initials='J' surname='Zelenka' fullname='Jim Zelenka'>
    <organization />
</author>

<date month='January' year='2010' />

<abstract><t>This Internet-Draft provides a description of the object-based pNFS extension for NFSv4.  This is a companion to the main pnfs specification in the NFSv4 Minor Version 1 Internet Draft, which is currently draft-ietf-nfsv4-minorversion1-23.</t></abstract>

</front>

<seriesInfo name='RFC' value='5664' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-pnfs-obj-12.txt' />
</reference>

<reference anchor='RFC5663'>
<front>
<title>
Parallel NFS (pNFS) Block/Volume Layout
</title>

<author initials='D' surname='Black' fullname='David Black'>
    <organization />
</author>

<author initials='J' surname='Glasgow' fullname='Jason Glasgow'>
    <organization />
</author>

<author initials='S' surname='Fridella' fullname='Stephen Fridella'>
    <organization />
</author>


<date month='January' year='2010' />

<abstract><t>Parallel NFS (pNFS) extends NFSv4 to allow clients to
directly access file data on the storage used by the NFSv4 server.
This ability to bypass the server for data access can increase both
performance and parallelism, but requires additional client
functionality for data access, some of which is dependent on the class
of storage used.  The main pNFS operations draft specifies
storage-class-independent extensions to NFS; this draft specifies the
additional extensions (primarily data structures) for use of pNFS with
block and volume based storage.</t></abstract> 

</front>

<seriesInfo name='RFC' value='5663' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-nfsv4-pnfs-block-11.txt' />
</reference>

    <reference anchor='RFC2054'>

      <front>
	<title>WebNFS Client Specification</title>
	<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization>Sun Microsystems, Inc.</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>Mailstop Mpk17-201</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043-1100</code>
	      <country>US</country></postal>
	    <phone>+1 415 786 5067</phone>
	    <facsimile>+1 415 786 5896</facsimile>
	    <email>brent.callaghan@xxxxxxxxxxx</email></address></author>
	<date year='1996' month='October' />
	<abstract>
	  <t>This document describes a lightweight binding mechanism that allows
	    NFS clients to obtain service from WebNFS-enabled servers with a
	    minimum of protocol overhead.  In removing this overhead, WebNFS
	    clients see benefits in faster response to requests, easy transit of
	    packet filter firewalls and TCP-based proxies, and better server
	    scalability.</t></abstract></front>

      <seriesInfo name='RFC' value='2054' />
      <format type='TXT' octets='36354' target='http://www.rfc-editor.org/rfc/rfc2054.txt' />
    </reference>

    <reference anchor='RFC2055'>

      <front>
	<title>WebNFS Server Specification</title>
	<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
	  <organization>Sun Microsystems, Inc.</organization>
	  <address>
	    <postal>
	      <street>2550 Garcia Avenue</street>
	      <street>Mailstop Mpk17-201</street>
	      <city>Mountain View</city>
	      <region>CA</region>
	      <code>94043-1100</code>
	      <country>US</country></postal>
	    <phone>+1 415 786 5067</phone>
	    <facsimile>+1 415 786 5896</facsimile>
	    <email>brent.callaghan@xxxxxxxxxxx</email></address></author>
	<date year='1996' month='October' />
	<abstract>
	  <t>This document describes the specifications for a server of WebNFS
	    clients.  WebNFS extends the semantics of the NFSv3
	    protocol to allow clients to obtain filehandles more easily, without
	    recourse to the portmap or MOUNT protocols.  In removing the need for
	    these protocols, WebNFS clients see benefits in faster response to
	    requests, easy transit of firewalls and better server scalability This
	    description is provided to facilitate compatible implementations of
	    WebNFS servers.</t></abstract></front>

      <seriesInfo name='RFC' value='2055' />
      <format type='TXT' octets='20498' target='http://www.rfc-editor.org/rfc/rfc2055.txt' />
    </reference>

    <reference anchor="errata">
      <front>
     <title>IESG Processing of RFC Errata for the IETF Stream
     </title>
	<author>
	  <organization>IESG
	  </organization>
	</author>
	<date month="July" year="2008" />
      </front>
      <format type='TXT' target='http://www.ietf.org/IESG/STATEMENTS/iesg-statement-07-30-2008.txt' />
    </reference>
    
<reference anchor='RFC2624'>

<front>
<title abbrev='NFSv4 Design Considerations'>NFS Version 4 Design Considerations</title>
<author initials='S.' surname='Shepler' fullname='Spencer Shepler'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>7808 Moonflower Drive</street>
<city>Austin</city>
<region>TX</region>
<code>78750</code>
<country>US</country></postal>
<phone>+1 512 349 9376</phone>
<email>spencer.shepler@xxxxxxxxxxx</email></address></author>
<date year='1999' month='June' />
<abstract>
<t>The main task of the NFSv4 working group is to create a
protocol definition for a distributed file system that focuses on the
following items: improved access and good performance on the Internet,
strong security with negotiation built into the protocol, better
cross-platform interoperability, and designed for protocol extensions.
NFSv4 will owe its general design to the previous versions of
NFS.  It is expected, however, that many features will be quite
different in NFSv4 than previous versions to facilitate the
goals of the working group and to address areas that NFSv2 and
NFSv3 have not.</t>
<t>This design considerations document is meant to present more detail
than the working group charter.  Specifically, it presents the areas
that the working group will investigate and consider while developing
a protocol specification for NFSv4.  Based on this
investigation the working group will decide the features of the new
protocol based on the cost and benefits within the specific feature
areas.</t></abstract> <note title='Key Words'>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC
2119.</t></note></front>

<seriesInfo name='RFC' value='2624' />
<format type='TXT' octets='52891' target='http://www.rfc-editor.org/rfc/rfc2624.txt' />
</reference>

    <reference anchor="xnfs">
        <front>
	    <title> Protocols for Interworking: XNFS, Version 3W, ISBN 1-85912-184-5 </title>

	    <author>
	      <organization>The Open Group </organization>
	    </author>
	    <date month="February" year="1998"/>
        </front>
      </reference>

    <reference anchor="Floyd">
        <front>
	    <title> The Synchronization of Periodic Routing Messages </title>

	    <author initials="S." surname="Floyd" >
	    <organization></organization>
            </author>
	    <author initials="V." surname="Jacobson">
	    <organization></organization>
            </author>
	    <date month="April" year="1994"/>
        </front>

        <seriesInfo name="IEEE/ACM Transactions on Networking" value="2(2), pp. 122-136" />

    </reference>

    <reference anchor="RFC3720">
      <front>
	<title>Internet Small Computer Systems Interface (iSCSI)</title>
	<author initials="J." surname="Satran" fullname="J. Satran">
	  <organization/>
	</author>
	<author initials="K." surname="Meth" fullname="K. Meth">
	  <organization/>
	</author>
	<author initials="C." surname="Sapuntzakis" fullname="C. Sapuntzakis">
	  <organization/>
	</author>
	<author initials="M." surname="Chadalapaka" fullname="M. Chadalapaka">
	  <organization/>
	</author>
	<author initials="E." surname="Zeidner" fullname="E. Zeidner">
	  <organization/>
	</author>
	<date year="2004" month="April"/>
      </front>
      <seriesInfo name="RFC" value="3720"/>
      <format type="TXT" octets="578468" target="http://www.rfc-editor.org/rfc/rfc3720.txt"/>
    </reference>
    
    <reference anchor="FCP-2">
      <front>
	<title>Fibre Channel Protocol for SCSI, 2nd Version (FCP-2)</title>
	<author initials="R." surname="Snively" fullname="Robert Snively">
	  <organization>Brocade Communication Systems, Inc.</organization>
	</author>
	<date month="Oct" year="2003" />
      </front>
      <seriesInfo name="ANSI/INCITS" value="350-2003" />
    </reference>

    <reference anchor='OSD-T10'
	       target='http://www.t10.org/ftp/t10/drafts/osd/osd-r10.pdf'>
      <front>
	<title>Object-Based Storage Device Commands (OSD)</title>
	<author initials="R.O." surname="Weber" fullname="Ralph O. Weber">
	  <organization>ENDL Texas</organization>
	</author>
	<date month="July" year="2004"/>
      </front>
      <seriesInfo name="ANSI/INCITS" value="400-2004"/>
    </reference>

    <reference anchor="PVFS">
        <front>
            <title>PVFS: A Parallel File System for Linux Clusters.</title>

	    <author initials="P. H." surname="Carns">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>

	    </author>
	    <author initials="W. B." surname="Ligon III">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>
	    </author>

	    <author initials="R. B." surname="Ross">
            <organization> Parallel Architecture Research Laboratory,
            Clemson University, Clemson, SC 29634 </organization>
	    </author>

	    <author initials="R." surname="Thakur">
            <organization>Mathematics and Computer Science Division,
            Argonne National Laboratory, Argonne, IL 60439</organization>
	    </author>

	    <date year="2000"/>
        </front>
        <seriesInfo name="Proceedings of the 4th Annual Linux Showcase and Conference" value=""/>

    </reference>

    <reference anchor="access_api">
      <front>
     <title>The Open Group Base Specifications Issue 6, IEEE Std 1003.1, 2004 Edition
     </title>
	<author>
	  <organization>The Open Group
	  </organization>
	</author>
	<date year="2004" />
        <abstract>
          <t>
          The description of the access() function states: "If the process has appropriate privileges, an implementation may indicate success for X_OK even if none of the execute file permission bits are set." 
          </t>
        </abstract>

      </front>
    </reference>



<reference anchor='RFC2224'>



<front>
<title>NFS URL Scheme</title>
<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>Mailstop Mpk17-201</street>
<street>901 San Antonio Road</street>
<street>Palo Alto</street>
<street>California 94303</street></postal>
<phone>1-415-786-5067</phone>
<facsimile>1-415-786-5896</facsimile>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>
<date year='1997' month='October' />
<area>Applications</area>
<keyword>NFS</keyword>
<keyword>network file system</keyword>
<keyword>uniform resource</keyword>
<abstract>
<t>
   A new URL scheme, &apos;nfs&apos; is defined.  It is used to refer to files and
   directories on NFS servers using the general URL syntax defined in
   RFC 1738, &quot;Uniform Resource Locators (URL)&quot;.
</t>
<t>
   This scheme uses the public filehandle and multi-component look up
   [RFC2054, RFC2055] to access server data with a minimum of protocol
   overhead.
</t>
<t>
   The NFS protocol provides access to shared file systems across
   networks.  It is designed to be machine, operating system, network
   architecture, and transport protocol independent.
</t></abstract></front>

<seriesInfo name='RFC' value='2224' />
<format type='TXT' octets='22726' target='http://www.rfc-editor.org/rfc/rfc2224.txt' />
<format type='HTML' octets='35259' target='http://xml.resource.org/public/rfc/html/rfc2224.html' />
<format type='XML' octets='24805' target='http://xml.resource.org/public/rfc/xml/rfc2224.xml' />
</reference>
<reference anchor='RFC2755'>

<front>
<title>Security Negotiation for WebNFS</title>
<author initials='A.' surname='Chiu' fullname='Alex Chiu'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 650 786 6465</phone>
<email>alex.chiu@xxxxxxxxxxx</email></address></author>

<author initials='M.' surname='Eisler' fullname='Mike Eisler'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 719 599 9026</phone>
<email>michael.eisler@xxxxxxxxxxx</email></address></author>

<author initials='B.' surname='Callaghan' fullname='Brent Callaghan'>
<organization>Sun Microsystems, Inc.</organization>
<address>
<postal>
<street>901 San Antonio Road</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>US</country></postal>
<phone>+1 650 786 5067</phone>
<email>brent.callaghan@xxxxxxxxxxx</email></address></author>

<date year='2000' month='January' />
<abstract>
<t>This document describes a protocol for a WebNFS clientto negotiate the desired security mechanism with a WebNFS serverbefore the WebNFS client falls back to the MOUNT v3 protocol. This document is provided so that people can write compatible implementations.</t></abstract></front>

<seriesInfo name='RFC' value='2755' />
<format type='TXT' octets='23493' target='http://www.rfc-editor.org/rfc/rfc2755.txt' />
</reference>

   <reference anchor='RFC5226'>

   <front>
   <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
   <author initials='T.' surname='Narten' fullname='T. Narten'>
   <organization /></author>
   <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
   <organization /></author>
   <date year='2008' month='May' />
   <abstract>
   <t>Many protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).&lt;/t>&lt;t> In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.&lt;/t>&lt;t> This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract></front>

   <seriesInfo name='BCP' value='26' />
   <seriesInfo name='RFC' value='5226' />
   <format type='TXT' octets='66160' target='http://www.rfc-editor.org/rfc/rfc5226.txt' />
   </reference>



  </references>
<!-- 	$Id: 2009-12-20-TO-rfc5661.xml,v 1.2 2009/12/21 05:59:32 shepler.mre Exp $	 -->
<!-- Copyright (C) The IETF Trust (2007-2008) -->
<!-- Copyright (C) The Internet Society (2006) -->
  <section title="Acknowledgments">
    <t>
      The initial text for the SECINFO extensions were edited by
      Mike Eisler with contributions from Peng Dai, Sergey Klyushin, and
      Carl Burnett.
    </t>
    <t>
      The initial text for the SESSIONS extensions were edited by
      Tom Talpey, Spencer Shepler, Jon Bauman with contributions from
      Charles Antonelli, Brent Callaghan, Mike Eisler, John Howard, Chet
      Juszczak, Trond Myklebust, Dave Noveck, John Scott, Mike
      Stolarchuk, and Mark Wittle.
    </t>
    <t>
      Initial text relating to multi-server namespace features, 
      including the concept of referrals, were contributed by 
      Dave Noveck, Carl Burnett, and Charles Fan with contributions
      from Ted Anderson, Neil Brown, and Jon Haswell. 
    </t>
    <t>
      The initial text for the Directory Delegations support were
      contributed by Saadia Khan with input from Dave Noveck, Mike
      Eisler, Carl Burnett, Ted Anderson, and Tom Talpey.
    </t>
    <t>
      The initial text for the ACL explanations were contributed by
      Sam Falkner and Lisa Week.
    </t>
    <t>
      The pNFS work was inspired by the NASD and OSD
      work done by Garth Gibson.  Gary Grider has also
      been a champion of high-performance parallel I/O.
      Garth Gibson and Peter Corbett started the pNFS
      effort with a problem statement document for the IETF
      that formed the basis for the pNFS work in NFSv4.1.

    </t>
    <t>
      The initial text for the parallel NFS support was edited by
      Brent Welch and Garth Goodson.  Additional authors for those
      documents were Benny Halevy, David Black, and Andy Adamson.
      Additional input came from the informal group that contributed
      to the construction of the initial pNFS drafts; specific
      acknowledgment goes to Gary Grider, Peter Corbett, Dave Noveck,
      Peter Honeyman, and Stephen Fridella.
    </t>
    <t>
      Fredric Isaman found several errors in draft versions of the
      ONC RPC XDR description of the NFSv4.1 protocol.
    </t>
    <t>
      Audrey Van Belleghem provided, in numerous ways, essential
      co-ordination and management of the process of editing the
      specification documents.
    </t>
    <t>
      Richard Jernigan gave feedback on the file layout's striping
      pattern design.
    </t>
    <t>
      Several formal inspection teams were formed to review various
      areas of the protocol. All the inspections found significant
      errors and room for improvement. NFSv4.1's inspection teams
      were:
      <list style="symbols">
      <t>

       ACLs, with the following inspectors:

	Sam Falkner,
	Bruce Fields,
	Rahul Iyer,
	Saadia Khan,
	Dave Noveck,
	Lisa Week,
	Mario Wurzl,

		and

	Alan Yoder.

      </t>
      <t>

       Sessions, with the following inspectors:

 	William Brown,
	Tom Doeppner,
	Robert Gordon,
	Benny Halevy,
	Fredric Isaman,
	Rick Macklem,
	Trond Myklebust,
	Dave Noveck,
	Karen Rochford,
	John Scott,

		and

	Peter Shah.

      </t>
      <t>

       Initial pNFS inspection, with the following inspectors:


        Andy Adamson,
        David Black,
        Mike Eisler,
        Marc Eshel,
        Sam Falkner,
        Garth Goodson,
        Benny Halevy,
        Rahul Iyer,
        Trond Myklebust,
        Spencer Shepler,

		and

        Lisa Week.

      </t>
      <t>

       Global namespace, with the following inspectors:


        Mike Eisler,
        Dan Ellard,
        Craig Everhart,
        Fredric Isaman,
        Trond Myklebust,
	Dave Noveck,
        Theresa Raj,
        Spencer Shepler,
        Renu Tewari,       

		and

        Robert Thurlow.

      </t>
      <t>

       NFSv4.1 file layout type, with the following inspectors:


	Andy Adamson,
	Marc Eshel,
	Sam Falkner,
	Garth Goodson,
	Rahul Iyer,
	Trond Myklebust,

		and

	Lisa Week.
      </t>

      <t>

       NFSv4.1 locking and directory delegations, with the following inspectors:


        Mike Eisler,
        Pranoop Erasani,
	Robert Gordon,
        Saadia Khan,
        Eric Kustarz, 
        Dave Noveck,
        Spencer Shepler,

		and

        Amy Weaver.
      </t>

      <t>
        
       EXCHANGE_ID and DESTROY_CLIENTID, with the following inspectors:

        Mike Eisler,
        Pranoop Erasani,
	Robert Gordon,
        Benny Halevy,
        Fredric Isaman,
        Saadia Khan,
	Ricardo Labiaga,
        Rick Macklem,
	Trond Myklebust,
        Spencer Shepler,

		and

        Brent Welch.

      </t>

      <t>

        Final pNFS inspection, with the following inspectors:

         Andy Adamson,
         Mike Eisler,
         Mark Eshel,
         Sam Falkner,
         Jason Glasgow,
         Garth Goodson,
         Robert Gordon,
         Benny Halevy,
         Dean Hildebrand,
         Rahul Iyer,
         Suchit Kaura,
         Trond Myklebust,
         Anatoly Pinchuk,
         Spencer Shepler,
         Renu Tewari,
         Lisa Week,

                and

         Brent Welch.

       </t>
    </list>
  </t>

  <t>

    A review team worked together to generate the tables of assignments of
    error sets to operations and make sure that each such assignment had
    two or more people validating it.  Participating in the process were

    Andy Adamson,
    Mike Eisler,
    Sam Falkner,
    Garth Goodson,
    Robert Gordon,
    Trond Myklebust,
    Dave Noveck,
    Spencer Shepler,
    Tom Talpey,
    Amy Weaver,
 
            and
 
    Lisa Week. 
  </t>
  <t>
    Jari Arkko, David Black, Scott Bradner, Lisa
    Dusseault, Lars Eggert, Chris Newman, and Tim
    Polk provided valuable review and guidance.

  </t>

  <t>
   Olga Kornievskaia found several errors in the SSV specification.
  </t>

  <t>
   Ricardo Labiaga found several places where the use of RPCSEC_GSS
   was underspecified.
  </t>

  <t>
   Those who provided miscellaneous comments include:

   Andy Adamson, Sunil Bhargo, Alex Burlyga, Pranoop Erasani,
   Bruce Fields, Vadim Finkelstein, Jason Goldschmidt, Vijay
   K. Gurbani, Sergey Klyushin, Ricardo Labiaga, James Lentini, Anshul
   Madan, Daniel Muntz, Daniel Picken, Archana Ramani, Jim Rees, Mahesh
   Siddheshwar, Tom Talpey, and Peter Varga.

  </t>

</section>

</back>

</rfc>


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