[PATCH] knfsd: ignore ref_fh when crossing a mountpoint

nfsd tries to return to a client the same sort of filehandle as was used by
the client.  This removes some filehandle aliasing issues and means that a
server upgrade followed by a downgrade will not confused clients not restarted
during that time.

However when crossing a mountpoint, the filehandle used for one filesystem
doesn't provide any useful information on what sort of filehandle should be
used on the other, and can provide misleading information.  So if the
reference filehandle is on a different filesystem to the one being generated,
ignore it.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>