rbd: track object rather than osd request for watch

Switch to keeping track of the object request pointer rather than
the osd request used to watch the rbd image header object.

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -272,7 +272,7 @@ struct rbd_device {
 	struct ceph_file_layout	layout;
 
 	struct ceph_osd_event   *watch_event;
-	struct ceph_osd_request *watch_request;
+	struct rbd_obj_request	*watch_request;
 
 	struct rbd_spec		*parent_spec;
 	u64			parent_overlap;
@@ -1719,11 +1719,11 @@ static int rbd_dev_header_watch_sync(struct rbd_device *rbd_dev, int start)
 		goto out_cancel;
 
 	if (start) {
-		rbd_dev->watch_request = obj_request->osd_req;
-		ceph_osdc_set_request_linger(osdc, rbd_dev->watch_request);
+		ceph_osdc_set_request_linger(osdc, obj_request->osd_req);
+		rbd_dev->watch_request = obj_request;
 	} else {
 		ceph_osdc_unregister_linger_request(osdc,
-						rbd_dev->watch_request);
+					rbd_dev->watch_request->osd_req);
 		rbd_dev->watch_request = NULL;
 	}
 	ret = rbd_obj_request_submit(osdc, obj_request);