Use the VFS xattr handler infrastructure and get rid of similar code in
the filesystem. For implementing shmem_xattr_handler_set, we need a
version of simple_xattr_set which removes the attribute when value is
NULL. Use this to implement kernfs_iop_removexattr as well.
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Reviewed-by: James Morris <james.l.morris@oracle.com> Cc: Hugh Dickins <hughd@google.com> Cc: linux-mm@kvack.org Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>