Re: [PATCH v4 09/11] fs: handle delegated timestamps in setattr_copy_mgtime

[Christian Brauner]

On Thu, Sep 05, 2024 at 01:46:14PM GMT, Jeff Layton wrote:
> On Thu, 2024-09-05 at 11:44 -0400, Chuck Lever wrote:
> > On Thu, Sep 05, 2024 at 08:41:53AM -0400, Jeff Layton wrote:
> > > When updating the ctime on an inode for a SETATTR with a multigrain
> > > filesystem, we usually want to take the latest time we can get for the
> > > ctime. The exception to this rule is when there is a nfsd write
> > > delegation and the server is proxying timestamps from the client.
> > > 
> > > When nfsd gets a CB_GETATTR response, we want to update the timestamp
> > > value in the inode to the values that the client is tracking. The client
> > > doesn't send a ctime value (since that's always determined by the
> > > exported filesystem), but it can send a mtime value. In the case where
> > > it does, then we may need to update the ctime to a value commensurate
> > > with that instead of the current time.
> > > 
> > > If ATTR_DELEG is set, then use ia_ctime value instead of setting the
> > > timestamp to the current time.
> > > 
> > > With the addition of delegated timestamps we can also receive a request
> > > to update only the atime, but we may not need to set the ctime. Trust
> > > the ATTR_CTIME flag in the update and only update the ctime when it's
> > > set.
> > > 
> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > > ---
> > >  fs/attr.c          | 28 +++++++++++++--------
> > >  fs/inode.c         | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  include/linux/fs.h |  2 ++
> > >  3 files changed, 94 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/fs/attr.c b/fs/attr.c
> > > index 3bcbc45708a3..392eb62aa609 100644
> > > --- a/fs/attr.c
> > > +++ b/fs/attr.c
> > > @@ -286,16 +286,20 @@ static void setattr_copy_mgtime(struct inode *inode, const struct iattr *attr)
> > >  	unsigned int ia_valid = attr->ia_valid;
> > >  	struct timespec64 now;
> > >  
> > > -	/*
> > > -	 * If the ctime isn't being updated then nothing else should be
> > > -	 * either.
> > > -	 */
> > > -	if (!(ia_valid & ATTR_CTIME)) {
> > > -		WARN_ON_ONCE(ia_valid & (ATTR_ATIME|ATTR_MTIME));
> > > -		return;
> > > +	if (ia_valid & ATTR_CTIME) {
> > > +		/*
> > > +		 * In the case of an update for a write delegation, we must respect
> > > +		 * the value in ia_ctime and not use the current time.
> > > +		 */
> > > +		if (ia_valid & ATTR_DELEG)
> > > +			now = inode_set_ctime_deleg(inode, attr->ia_ctime);
> > > +		else
> > > +			now = inode_set_ctime_current(inode);
> > > +	} else {
> > > +		/* If ATTR_CTIME isn't set, then ATTR_MTIME shouldn't be either. */
> > > +		WARN_ON_ONCE(ia_valid & ATTR_MTIME);
> > >  	}
> > >  
> > > -	now = inode_set_ctime_current(inode);
> > >  	if (ia_valid & ATTR_ATIME_SET)
> > >  		inode_set_atime_to_ts(inode, attr->ia_atime);
> > >  	else if (ia_valid & ATTR_ATIME)
> > > @@ -354,8 +358,12 @@ void setattr_copy(struct mnt_idmap *idmap, struct inode *inode,
> > >  		inode_set_atime_to_ts(inode, attr->ia_atime);
> > >  	if (ia_valid & ATTR_MTIME)
> > >  		inode_set_mtime_to_ts(inode, attr->ia_mtime);
> > > -	if (ia_valid & ATTR_CTIME)
> > > -		inode_set_ctime_to_ts(inode, attr->ia_ctime);
> > > +	if (ia_valid & ATTR_CTIME) {
> > > +		if (ia_valid & ATTR_DELEG)
> > > +			inode_set_ctime_deleg(inode, attr->ia_ctime);
> > > +		else
> > > +			inode_set_ctime_to_ts(inode, attr->ia_ctime);
> > > +	}
> > >  }
> > >  EXPORT_SYMBOL(setattr_copy);
> > >  
> > 
> > This patch fails to apply cleanly to my copy of nfsd-next:
> > 
> >   error: `git apply --index`: error: patch failed: fs/attr.c:286
> >   error: fs/attr.c: patch does not apply
> > 
> > Before I try jiggling this to get it to apply, is there anything
> > I should know? I worry about a potential merge conflict here,
> > hopefully it will be no more complicated than that.
> > 
> > 
> 
> This is based on a combo of your nfsd-next branch and Christian's
> vfs.mgtime branch. This patch in particular depends on the multigrain
> patches in his tree.
> 
> I think we can just drop this patch from the series in your tree, and
> I'll get Christian to pick it up in his tree. The ctime setting will be
> a bit racy without it but everything should still work.
> 
> Sound ok? Christian, are you OK with picking this up in vfs.mgtime?

Yep, of course. Already picked it up.