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

[Bernd Schubert]

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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