On Jan 18, 2008, at 11:55 AM, Peter Staubach wrote:
Chuck Lever wrote:
Hi Peter-
On Jan 18, 2008, at 10:35 AM, Peter Staubach wrote:
Hi.
Here is a patch set which modifies the system to enhance the
ESTALE error handling for system calls which take pathnames
as arguments.
The VFS already handles ESTALE.
If a pathname resolution encounters an ESTALE at any point, the
resolution is restarted exactly once, and an additional flag is
passed to the file system during each lookup that forces each
component in the path to be revalidated on the server. This has
no possibility of causing an infinite loop.
Is there some part of this logic that is no longer working?
The VFS does not fully handle ESTALE. An ESTALE error can occur
during the second pathname resolution attempt.
If an ESTALE occurs during the second resolution attempt, we should
give up. When I addressed this issue two years ago, the two-try
logic was the only acceptable solution because there's no way to
guarantee the pathname resolution will ever finish unless we put a
hard limit on it.
There are lots of
reasons, some of which are the 1 second resolution from some file
systems on the server
Which is a server bug, AFAICS. It's simply impossible to close all
the windows that result from sloppy file time stamps without
completely disabling client-side caching. The NFS protocol relies on
file time stamps to manage cache coherence. If the server is lying
about time stamps, there's no way the client can cache coherently.
and the window in between the revalidation
and the actual use of the file handle associated with each
dentry/inode pair.
A use case or two would be useful to explore (on linux-nfs or linux-
fsdevel, rather than lkml).
Also, there was no support for ESTALE errors which occur during
subsequent operations to the pathname resolution process. For
example, during a mkdir(2) operation, the ESTALE can occur from
the over the wire MKDIR operation after the LOOKUP operations
have all succeeded.
If the final operation fails after a pathname resolution, then it's a
real error. Is there a fixed and valid recovery script for the
client in this case that will allow the mkdir to proceed?
Admittedly, the NFS client could recover more cleanly from some of
these problems, but given the architecture of the Linux VFS, it will
be difficult to address some of the corner cases.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
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