Re: [PATCH] xfs: reinstate the old i_version counter as STATX_CHANGE_COOKIE

[Darrick J. Wong]

On Wed, Oct 11, 2023 at 09:09:38AM -0400, Jeff Layton wrote:
> On Fri, 2023-09-29 at 14:43 -0400, Jeff Layton wrote:
> > The handling of STATX_CHANGE_COOKIE was moved into generic_fillattr in
> > commit 0d72b92883c6 (fs: pass the request_mask to generic_fillattr), but
> > we didn't account for the fact that xfs doesn't call generic_fillattr at
> > all.
> > 
> > Make XFS report its i_version as the STATX_CHANGE_COOKIE.
> > 
> > Fixes: 0d72b92883c6 (fs: pass the request_mask to generic_fillattr)
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> > I had hoped to fix this in a better way with the multigrain patches, but
> > it's taking longer than expected (if it even pans out at this point).
> > 
> > Until then, make sure we use XFS's i_version as the STATX_CHANGE_COOKIE,
> > even if it's bumped due to atime updates. Too many invalidations is
> > preferable to not enough.
> > ---
> >  fs/xfs/xfs_iops.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> > index 1c1e6171209d..2b3b05c28e9e 100644
> > --- a/fs/xfs/xfs_iops.c
> > +++ b/fs/xfs/xfs_iops.c
> > @@ -584,6 +584,11 @@ xfs_vn_getattr(
> >  		}
> >  	}
> >  
> > +	if ((request_mask & STATX_CHANGE_COOKIE) && IS_I_VERSION(inode)) {
> > +		stat->change_cookie = inode_query_iversion(inode);
> > +		stat->result_mask |= STATX_CHANGE_COOKIE;
> > +	}
> > +
> >  	/*
> >  	 * Note: If you add another clause to set an attribute flag, please
> >  	 * update attributes_mask below.
> > 
> > ---
> > base-commit: df964ce9ef9fea10cf131bf6bad8658fde7956f6
> > change-id: 20230929-xfs-iversion-819fa2c18591
> > 
> > Best regards,
> 
> Ping?
> 
> This patch is needed in v6.6 to prevent a regression when serving XFS
> via NFSD. I'd prefer this go in via the xfs tree, but let me know if
> you need me to get this merged this via a different one.

Oh!   Right, this is needed because the "hide a state in the high bit of
tv_nsec" stuff got reverted in -rc3, correct?  So now nfsd needs some
way to know that something changed in the file, and better to have too
many client invalidations than not enough?  And I guess bumping
i_version will keep nfsd sane for now?

If the answers are [yes, yes, yes] then:
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>

--D

> Thanks,
> -- 
> Jeff Layton <jlayton@xxxxxxxxxx>