These helpers are required to support idmapped mounts in CephFS.

Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>