commit 4eb4517c upstream.

- replace an ad-hoc array with a struct
- rename to calc_signature() for consistency
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>