Re: [PATCH] NFS server does not update mtime on setattr request

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Tue, 2006-06-06 at 14:05 -0400, Peter Staubach wrote:

> On the NFS client side, there was an optimization added which attempted
> to avoid an over the wire call if the size of the file was not going to
> change.  This would be great, except for the side effect of the mtime
> on the file needing to change anyway.  The solution is just to issue the
> over the wire call anyway, which, as a side effect, updates the mtime and
> ctime fields.

Vetoed!

The current code gets it quite right: if someone calls open(O_TRUNC),
then may_open() calls do_truncate() with the ATTR_MTIME|ATTR_CTIME flags
set. That will cause the client to do the right thing _regardless_ of
the size optimisation.

> On the NFS server side, there was a change to the routine, inode_setattr(),
> which now relies upon the caller to set the ATTR_MTIME and ATTR_CTIME
> flags in ia_valid in addition to the ATTR_SIZE.  Previously, this routine
> would force these bits on if the size of the file was not changing.  Now,
> this routine relies upon the caller to specify all of the fields which need
> to be updated.

Also wrong.

This change causes the server to do entirely the wrong thing for
truncate()/ftruncate() calls: in the SuSv3 spec, a call that fails to
change the file length is supposed to leave the file entirely unchanged:
that includes mtime/ctime as well as suid/sgid bits.

Cheers,
  Trond