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List:       linux-nfs
Subject:    Re: [PATCH 1/2] NFSv4: Servers should only check SETATTR stateid open mode on size change
From:       "J. Bruce Fields" <bfields () fieldses ! org>
Date:       2013-04-29 19:16:54
Message-ID: 20130429191654.GQ17268 () fieldses ! org
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On Mon, Apr 29, 2013 at 07:09:41PM +0000, Myklebust, Trond wrote:
> On Mon, 2013-04-29 at 14:41 -0400, J. Bruce Fields wrote:
> > On Mon, Apr 29, 2013 at 06:33:02PM +0000, Myklebust, Trond wrote:
> > > On Mon, 2013-04-29 at 14:29 -0400, J. Bruce Fields wrote:
> > > > On Mon, Apr 29, 2013 at 06:27:07PM +0000, Myklebust, Trond wrote:
> > > > > On Mon, 2013-04-29 at 14:21 -0400, J. Bruce Fields wrote:
> > > > > > On Mon, Apr 29, 2013 at 06:15:52PM +0000, Myklebust, Trond wrote:
> > > > > > > On Mon, 2013-04-29 at 11:15 -0400, Trond Myklebust wrote:
> > > > > > > > The NFSv4 and NFSv4.1 specs are both clear that the server should only check
> > > > > > > > stateid open mode if a SETATTR specifies the size attribute. If the
> > > > > > > > open mode is not one that allows writing, then it returns NFS4ERR_OPENMODE.
> > > > > > > > 
> > > > > > > > In the case where the SETATTR is not changing the size, the client will
> > > > > > > > still pass it the delegation stateid to ensure that the server does not
> > > > > > > > recall that delegation. In that case, the server should _ignore_ the
> > > > > > > > delegation open mode, and simply apply standard permission checks.
> > > > > > > 
> > > > > > > Bruce, what does the Linux server do when we send it a delegation
> > > > > > > stateid as part of a SETATTR that just changes the mode or acl (no size
> > > > > > > change)? Will it recall the delegation? How about the delegations held
> > > > > > > by other clients?
> > > > > > 
> > > > > > Yes, it breaks all delegations on any setattr.
> > > > > 
> > > > > Do you plan to change that?
> > > > 
> > > > I'd take patches.
> > > 
> > > Have the NFSv4 delegation patches been merged yet, and do they hand out
> > > delegations on file creation?
> > 
> > The vfs support patches haven't been merged, but nfsd still continues to
> > give out read delegations on any confirmed read-open of a file that
> > hasn't had a recent delegation conflict.  (They're just not consistent
> > w.r.t local metadata operations....)
> 
> The problem is that without those there seems to be no VFS level
> functionality that allows you to say "break the leases for all processes
> except this one".

There isn't any *with* those patches, either.  I agree that it would be
nice to allow a client issuing a write or setattr to continue to hold
its read delegation, if it's the only holder of a delegation.  But my
understanding is that a server isn't required to do that.  So I'm taking
this one step at a time and ignoring that problem for now.

--b.
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