Re: [PATCH RFC] vfs: make fstatat retry on ESTALE errors from getattr call

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On 04/15/2012 09:27 PM, J. Bruce Fields wrote:
On Sun, Apr 15, 2012 at 09:03:23PM +0200, Bernd Schubert wrote:
On 04/13/2012 05:42 PM, Jeff Layton wrote:
(note: please don't trim the CC list!)

Indefinitely does make some sense (as Peter articulated in his original
set). It's possible you could race several times in a row, or a server
misconfiguration or something has happened and you have a transient
error that will eventually recover. His assertion was that any limit on
the number of retries is by definition wrong. For NFS, a fatal signal
ought to interrupt things as well, so retrying indefinitely has some
appeal there.

OTOH, we do have to contend with filesystems that might return ESTALE
persistently for other reasons and that might not respond to signals.
Miklos pointed out that some FUSE fs' do this in his review of Peter's
set.

As a purely defensive coding measure, limiting the number of retries to
something finite makes sense. If we're going to do that though, I'd
probably recommend that we set the number of retries be something
higher just so that this is more resilient in the face of multiple
races. Those other fs' might "spin" a bit in that case but it is an
error condition and IMO resiliency trumps performance -- at least in
  this case.

I am definitely voting against an infinite number of retries. I'm
working on FhGFS, which supports distributed meta data servers. So when
a file is moved around between directories, its file handle, which
contains the meta-data target id might become invalid.  As NFSv3 is
stateless we cannot inform the client about that and must return ESTALE
then.

Note we're not talking about retrying the operation that returned ESTALE
with the same filehandle--probably any server would return ESTALE again
in that case.

We're talking about re-looking up the path (in the case where we're
implementing a system call that takes a path as an argument), and then
retrying the operation with the newly looked-up filehandle.


Oh, sorry my mistake. Somehow I missed that it is really _only_ about path lookups and not already opened files.

Thanks,
Bernd
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