rbd: handle online resize of underlying rbd image

If we get a notification that the image header has changed, check for
a change in the image size.

Signed-off-by: Sage Weil <sage@newdream.net>

drivers/block/rbd.c

@@ -1664,6 +1664,9 @@ static int __rbd_update_snaps(struct rbd_device *rbd_dev)
 	if (ret < 0)
 		return ret;
 
+	/* resized? */
+	set_capacity(rbd_dev->disk, h.image_size / 512ULL);
+
 	down_write(&rbd_dev->header.snap_rwsem);
 
 	snap_seq = rbd_dev->header.snapc->seq;