libceph: calculate placement based on the internal data types

Instead of using the old ceph_object_layout struct, update our internal
ceph_calc_object_layout method to use the ceph_pg type.  This allows us to
pass the full 32-bit precision of the pgid.seed to the callers.  It also
allows some callers to avoid reaching into the request structures for the
struct ceph_object_layout fields.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>

include/linux/ceph/osd_client.h

@@ -82,6 +82,7 @@ struct ceph_osd_request {
 
 	char              r_oid[MAX_OBJ_NAME_SIZE];          /* object name */
 	int               r_oid_len;
+	u64               r_snapid;
 	unsigned long     r_stamp;            /* send OR check time */
 
 	struct ceph_file_layout r_file_layout;