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 thev1 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 matchrfc5661. 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
Shepler, et al. Standards Track [Page 1]
RFC 5661 NFSv4.1 January 2010
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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| 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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RFC 5661 NFSv4.1 January 2010
| 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 |
Shepler, et al. Standards Track [Page 361]
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 |
Shepler, et al. Standards Track [Page 362]
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 |
Shepler, et al. Standards Track [Page 371]
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.
Shepler, et al. Standards Track [Page 372]
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 |
Shepler, et al. Standards Track [Page 373]
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 |
Shepler, et al. Standards Track [Page 374]
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 |
Shepler, et al. Standards Track [Page 379]
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 |
Shepler, et al. Standards Track [Page 390]
RFC 5661 NFSv4.1 January 2010
| 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.
Shepler, et al. Standards Track [Page 391]
RFC 5661 NFSv4.1 January 2010
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 */
Shepler, et al. Standards Track [Page 392]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 606]
RFC 5661 NFSv4.1 January 2010
+-----------------------+-------+----------+-----+----------------+
| 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.
Shepler, et al. Standards Track [Page 607]
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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,
Shepler, et al. Standards Track [Page 612]
RFC 5661 NFSv4.1 January 2010
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
Shepler, et al. Standards Track [Page 613]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 614]
RFC 5661 NFSv4.1 January 2010
[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.
Shepler, et al. Standards Track [Page 615]
RFC 5661 NFSv4.1 January 2010
[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.
Shepler, et al. Standards Track [Page 616]
RFC 5661 NFSv4.1 January 2010
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,
Shepler, et al. Standards Track [Page 617]
RFC 5661 NFSv4.1 January 2010
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
Shepler, et al. Standards Track [Page 618]
RFC 5661 NFSv4.1 January 2010
David Noveck (editor)
NetApp
1601 Trapelo Road, Suite 16
Waltham, MA 02451
USA
Phone: +1-781-768-5347
EMail: dnoveck@xxxxxxxxxx
Shepler, et al. Standards Track [Page 619]
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
Shepler, et al. Standards Track [Page 1]
RFC 5661 NFSv4.1 January 2010
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, |
Shepler, et al. Standards Track [Page 359]
RFC 5661 NFSv4.1 January 2010
| | 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, |
Shepler, et al. Standards Track [Page 360]
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, |
Shepler, et al. Standards Track [Page 361]
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, |
Shepler, et al. Standards Track [Page 362]
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, |
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| | 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]
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| | 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]
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| | 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, |
Shepler, et al. Standards Track [Page 372]
RFC 5661 NFSv4.1 January 2010
| | 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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RFC 5661 NFSv4.1 January 2010
| | 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, |
Shepler, et al. Standards Track [Page 374]
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, |
Shepler, et al. Standards Track [Page 375]
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, |
Shepler, et al. Standards Track [Page 376]
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 |
| | |
Shepler, et al. Standards Track [Page 377]
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.
Shepler, et al. Standards Track [Page 400]
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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
Shepler, et al. Standards Track [Page 608]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 609]
RFC 5661 NFSv4.1 January 2010
+ 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".
Shepler, et al. Standards Track [Page 610]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 611]
RFC 5661 NFSv4.1 January 2010
+------------------------+----------+------------------+
| 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.
Shepler, et al. Standards Track [Page 612]
RFC 5661 NFSv4.1 January 2010
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
Shepler, et al. Standards Track [Page 613]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 614]
RFC 5661 NFSv4.1 January 2010
[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.
Shepler, et al. Standards Track [Page 615]
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.
Shepler, et al. Standards Track [Page 616]
RFC 5661 NFSv4.1 January 2010
[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.
Shepler, et al. Standards Track [Page 617]
RFC 5661 NFSv4.1 January 2010
[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.
Shepler, et al. Standards Track [Page 618]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 619]
RFC 5661 NFSv4.1 January 2010
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.
Shepler, et al. Standards Track [Page 620]
RFC 5661 NFSv4.1 January 2010
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
Shepler, et al. Standards Track [Page 621]
<?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 "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" 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<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<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 <= 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.
</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<>;
};
</artwork>
</figure>
<figure>
<artwork>
/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
uint32_t smt_ssv_seq;
opaque smt_hmac<>;
};
</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<>;
uint32_t sspt_ssv_seq;
opaque sspt_orig_plain<>;
opaque sspt_pad<>;
};
</artwork>
</figure>
<figure>
<artwork>
/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
uint32_t ssct_ssv_seq;
opaque ssct_iv<>;
opaque ssct_encr_data<>;
opaque ssct_hmac<>;
};
</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<>;</c>
<c/> <c>Used for file/directory attributes.</c>
<c>bitmap4</c> <c>typedef uint32_t bitmap4<>;</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<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<>;</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<>;</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<>;</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<>; /* network id */
string na_r_addr<>; /* 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<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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<></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<></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> W</c>
<c>
<xref target="attrdef_layout_hint" />
</c>
<c>layout_type</c><c>64</c><c>layouttype4<></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> 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> 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> 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> 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> 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<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<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
"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.
</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 "Abbreviation" 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 "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.
</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
"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.
</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
"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.
</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
"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 <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<>;
};
</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<>;
pathname4 rootpath;
};
</artwork>
</figure>
</t>
<t>
<figure>
<artwork>
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
</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<>;
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<>;
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;
</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 <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.
</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 <client ID, filehandle, layout
type, iomode, range>, 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 <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 (<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 <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.
</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 <loca_offset, loca_length> 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<>;
/*
* 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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<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<>;
};
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<>;
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'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'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'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<>;
};
</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<>;
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<>;
};
</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<>;
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>;
};
</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<>;
};
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;
};
</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 <= 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 <= 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 <= 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<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<>;
};
</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<>;
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<>;
};
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 <= 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 <= a_off</c>
<c>MUST be u64m</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _READ</c>
<c>MUST be <= a_off</c>
<c>MUST be >= MIN(file length, a_minlen + a_off) - layout offset</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= 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 <= a_off</c>
<c>MUST be > 0</c>
<c>_READ</c>
<c>0</c>
<c>MAY be _RW</c>
<c>MUST be <= a_off</c>
<c>MUST be > 0</c>
<c>_RW</c>
<c>u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= a_off</c>
<c>MUST be u64m</c>
<c>_RW</c>
<c>> 0 and < u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= 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 <= 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 <= a_off</c>
<c>SHOULD be u64m</c>
<c>_READ</c>
<c>u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= a_off</c>
<c>SHOULD be u64m</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _READ</c>
<c>MUST be <= a_off</c>
<c>SHOULD be >= a_off - layout offset + a_len</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= 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 <= 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 <= 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 <= a_off</c>
<c>SHOULD be u64m</c>
<c>_RW</c>
<c>> 0 and < u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= 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 <= 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<>;
};
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<>;
opaque ssa_digest<>;
};
</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<>;
};
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<>;
};
</artwork>
</figure>
</section>
<section toc="exclude" anchor="OP_TEST_STATEID_RESULT" title="RESULT">
<figure>
<artwork>
struct TEST_STATEID4resok {
nfsstat4 tsr_status_codes<>;
};
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<>;
};
</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<>;
};
</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<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<>;
};
</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<>;
};
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<>;
};
</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<>;
};
</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>
<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] </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>
<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] </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><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]</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><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]</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).</t><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.</t><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, 'nfs' is defined. It is used to refer to files and
directories on NFS servers using the general URL syntax defined in
RFC 1738, "Uniform Resource Locators (URL)".
</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><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. </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><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]
</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 "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" 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<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<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 <= 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.
</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<>;
};
</artwork>
</figure>
<figure>
<artwork>
/* SSV GSS PerMsgToken token */
struct ssv_mic_tkn4 {
uint32_t smt_ssv_seq;
opaque smt_hmac<>;
};
</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<>;
uint32_t sspt_ssv_seq;
opaque sspt_orig_plain<>;
opaque sspt_pad<>;
};
</artwork>
</figure>
<figure>
<artwork>
/* SSV GSS SealedMessage token */
struct ssv_seal_cipher_tkn4 {
uint32_t ssct_ssv_seq;
opaque ssct_iv<>;
opaque ssct_encr_data<>;
opaque ssct_hmac<>;
};
</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<>;</c>
<c/> <c>Used for file/directory attributes.</c>
<c>bitmap4</c> <c>typedef uint32_t bitmap4<>;</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<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<>;</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<>;</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<>;</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<>; /* network id */
string na_r_addr<>; /* 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<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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<></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<></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> W</c>
<c>
<xref target="attrdef_layout_hint" />
</c>
<c>layout_type</c><c>64</c><c>layouttype4<></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> 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> 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> 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> 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> 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<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<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
"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.
</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 "Abbreviation" 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 "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.
</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
"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.
</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
"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.
</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
"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 <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<>;
};
</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<>;
pathname4 rootpath;
};
</artwork>
</figure>
</t>
<t>
<figure>
<artwork>
struct fs_locations4 {
pathname4 fs_root;
fs_location4 locations<>;
};
</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<>;
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<>;
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;
</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 <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.
</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 <client ID, filehandle, layout
type, iomode, range>, 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 <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 (<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 <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.
</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 <loca_offset, loca_length> 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<>;
/*
* 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<>;
};
</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<>;
};
</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<>;
};
</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<>;
};
</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<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<>;
};
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<>;
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'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'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'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<>;
};
</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<>;
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<>;
};
</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<>;
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>;
};
</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<>;
};
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;
};
</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 <= 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 <= 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 <= 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<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<>;
};
</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<>;
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<>;
};
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 <= 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 <= a_off</c>
<c>MUST be u64m</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _READ</c>
<c>MUST be <= a_off</c>
<c>MUST be >= MIN(file length, a_minlen + a_off) - layout offset</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= 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 <= a_off</c>
<c>MUST be > 0</c>
<c>_READ</c>
<c>0</c>
<c>MAY be _RW</c>
<c>MUST be <= a_off</c>
<c>MUST be > 0</c>
<c>_RW</c>
<c>u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= a_off</c>
<c>MUST be u64m</c>
<c>_RW</c>
<c>> 0 and < u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= 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 <= 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 <= a_off</c>
<c>SHOULD be u64m</c>
<c>_READ</c>
<c>u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= a_off</c>
<c>SHOULD be u64m</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _READ</c>
<c>MUST be <= a_off</c>
<c>SHOULD be >= a_off - layout offset + a_len</c>
<c>_READ</c>
<c>> 0 and < u64m</c>
<c>MAY be _RW</c>
<c>MUST be <= 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 <= 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 <= 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 <= a_off</c>
<c>SHOULD be u64m</c>
<c>_RW</c>
<c>> 0 and < u64m</c>
<c>MUST be _RW</c>
<c>MUST be <= 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 <= 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<>;
};
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<>;
opaque ssa_digest<>;
};
</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<>;
};
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<>;
};
</artwork>
</figure>
</section>
<section toc="exclude" anchor="OP_TEST_STATEID_RESULT" title="RESULT">
<figure>
<artwork>
struct TEST_STATEID4resok {
nfsstat4 tsr_status_codes<>;
};
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<>;
};
</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<>;
};
</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<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<>;
};
</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<>;
};
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<>;
};
</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<>;
};
</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><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]</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>
<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] </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>
<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] </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><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]</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><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]
</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><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. </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, 'nfs' is defined. It is used to refer to files and
directories on NFS servers using the general URL syntax defined in
RFC 1738, "Uniform Resource Locators (URL)".
</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).</t><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.</t><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>
