rbd: only reset capacity when pointing to head

Snapshots cannot be resized, and the new capacity of head should not
be reflected by the snapshot.
Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Reviewed-by: Alex Elder <elder@inktank.com>
(cherry picked from commit 474ef7ce)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/block/rbd.c

@@ -1721,7 +1721,12 @@ static int __rbd_update_snaps(struct rbd_device *rbd_dev)
 		return ret;
 
 	/* resized? */
-	set_capacity(rbd_dev->disk, h.image_size / SECTOR_SIZE);
+	if (rbd_dev->snap_id == CEPH_NOSNAP) {
+		sector_t size = (sector_t) h.image_size / SECTOR_SIZE;
+
+		dout("setting size to %llu sectors", (unsigned long long) size);
+		set_capacity(rbd_dev->disk, size);
+	}
 
 	down_write(&rbd_dev->header_rwsem);