From: "Myklebust, Trond" <Trond.Myklebust@netapp.com>
To: Christoph Hellwig <hch@infradead.org>
CC: Bruce Fields <bfields@fieldses.org>,
        "Schumaker, Bryan" <Bryan.Schumaker@netapp.com>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 3/4] NFSD: Add WRITE_PLUS support for hole punches
Date: Sat, 2 Nov 2013 15:02:29 +0000
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On Nov 2, 2013, at 10:51, Christoph Hellwig <hch@infradead.org> wrote:

> On Sat, Nov 02, 2013 at 10:44:31AM -0400, J. Bruce Fields wrote:
>> On Sat, Nov 02, 2013 at 06:54:09AM -0700, Christoph Hellwig wrote:
>>> On Tue, Oct 29, 2013 at 09:06:49AM -0400, J. Bruce Fields wrote:
>>>> What I meant was--why are we doing a sync at all, instead of returning
>>>> NFS_UNSTABLE and making the client commit?
>>> 
>>> Did NFSv4.2 introduce a concept of unstable metadata operations?
>> 
>> No, but I think WRITE_PLUS does have a stable/unstable bit so I think we
>> could choose not to do the sync if that'd make sense.
> 
> Both operations are idempotent, so supporting it shouldn't be a major
> obstactle.  But suddenly having some metadata operations that can be
> unstable seems like a major wart in the spec.

COMMIT has always had a metadata part to it, though. It guarantees stability of the ctime/mime and change attributes in addition to the file size and data.

IOW: it really is more akin to fsync() than to fdatasync().

Cheers
  Trond