Re: [PATCH] nfsd: Fix error return values for nfsd4_clone_file_range()

[Trond Myklebust <trondmy@gmail.com>]

On Thu, 2019-01-24 at 19:46 -0500, J. Bruce Fields wrote:
> On Mon, Jan 21, 2019 at 03:58:38PM -0500, Trond Myklebust wrote:
> > If the parameter 'count' is non-zero, nfsd4_clone_file_range() will
> > currently clobber all errors returned by vfs_clone_file_range() and
> > replace them with EINVAL.
> 
> Oops, thanks for the fix.  I'm still a little confused, though:
> 
> > Fixes: 42ec3d4c0218 ("vfs: make remap_file_range functions take
> > and...")
> > Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> > Cc: stable@vger.kernel.org # v4.20+
> > ---
> >  fs/nfsd/vfs.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > index 9824e32b2f23..7dc98e14655d 100644
> > --- a/fs/nfsd/vfs.c
> > +++ b/fs/nfsd/vfs.c
> > @@ -557,9 +557,11 @@ __be32 nfsd4_clone_file_range(struct file
> > *src, u64 src_pos, struct file *dst,
> >  	loff_t cloned;
> >  
> >  	cloned = vfs_clone_file_range(src, src_pos, dst, dst_pos,
> > count, 0);
> > +	if (cloned < 0)
> > +		return nfserrno(cloned);
> >  	if (count && cloned != count)
> > -		cloned = -EINVAL;
> > -	return nfserrno(cloned < 0 ? cloned : 0);
> > +		return nfserrno(-EINVAL);
> > +	return 0;
> 
> I still don't understand the cloned != count case.  I thought clone
> was
> supposed to be all-or-nothing and atomic, can it really return a
> short
> copy?  And how is that inval, shouldn't that be serverfault?

That, quite frankly, seems like more of a question for Darrick, not me.
I haven't changed that part of the code.

The main thing I care about is being able to correctly report
EOPNOTSUPP errors for the vast majority of filesystems that don't
support clone() or dedup().

Cheers
  Trond