libceph: start using oloc abstraction

Instead of relying on pool fields in ceph_file_layout (for mapping) and
ceph_pg (for enconding), start using ceph_object_locator (oloc)
abstraction.  Note that userspace oloc currently consists of pool, key,
nspace and hash fields, while this one contains only a pool.  This is
OK, because at this point we only send (i.e. encode) olocs and never
have to receive (i.e. decode) them.

This makes keeping a copy of ceph_file_layout in every osd request
unnecessary, so ceph_osd_request::r_file_layout field is nuked.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

include/linux/ceph/osd_client.h

@@ -159,12 +159,13 @@ struct ceph_osd_request {
 	struct inode *r_inode;         	      /* for use by callbacks */
 	void *r_priv;			      /* ditto */
 
+	struct ceph_object_locator r_oloc;
+
 	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;
 	struct ceph_snap_context *r_snapc;    /* snap context for writes */
 };