Re: [PATCH 2/2] nfs: update time staps on truncate

[Christoph Hellwig <hch@lst.de>]

On Sun, Sep 07, 2014 at 12:41:28PM -0400, Trond Myklebust wrote:
> I'm still confused as to why we need this change to the client. In
> RFC5661, Section 18.30.4 there is wording to the effect that:
> 
>    Changing the size of a file with SETATTR indirectly changes the
>    time_modify and change attributes.  A client must account for this as
>    size changes can result in data deletion.
> 
> There is similar wording in RFC3530 and even in RFC1813 (see section
> 3.3.2). Without this sort of guarantee by the server, you could, for
> instance, get into nasty situations where the file changes, but the
> NFSv3 client doesn't detect it.
> 
> So basically, I interpret the spec is saying that we should be able to
> rely on the server figuring this out all by itself. I agree that we
> have the special corner case of ftruncate(), but the VFS is still
> setting the ATTR_CTIME|ATTR_MTIME flags for us in that case, right?

Yes.  Looks like the problem is on the server side indeed.  nfsd_setattr
adds a non-conditional ATTR_CTIME for all calls, but never adds ATTR_MTIME
for ATTR_SIZE requests.  I'll send a server patch instead.

[patch 1 in the series still seems worthwhile for the client, though]