Re: [PATCH] nfsd: special case truncates some more

["J. Bruce Fields" <bfields@redhat.com>]

On Tue, Feb 21, 2017 at 10:07:51AM -0500, Chuck Lever wrote:
> 
> > On Feb 20, 2017, at 1:21 AM, Christoph Hellwig <hch@lst.de> wrote:
> > 
> > Both the NFS protocols and the Linux VFS use a setattr operation with a
> > bitmap of attributs to set to set various file attributes including the
> > file size and the uid/gid.
> > 
> > The Linux syscalls never mixes size updates with unrelated updates like
> > the uid/gid, and some file systems like XFS and GFS2 rely on the fact
> > that truncates might not update random other attributes, and many other
> > file systems handle the case but do not update the different attributes
> > in the same transaction.  NFSD on the other hand passes the attributes
> > it gets on the wire more or less directly through to the VFS, leading to
> > updates the file systems don't expect.  XFS at least has an assert on
> > the allowed attributes, which caught an unusual NFS client setting the
> > size and group at the same time.
> > 
> > To handle this issue properly this splits the notify_change call in
> > nfsd_setattr into two separate ones.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Cc: stable@kernel.org
> 
> Tested-by: Chuck Lever <chuck.lever@oracle.com>

Thanks.--b.