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

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

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