rbd: don't retry setting up header watch

When an rbd image is initially mapped a watch event is registered so
we can do something if the header object changes.

The code that does this currently loops if initiating the watch
request results in an ERANGE error.  The osds will never return
ERANGE, so there's no reason to do this loop, so get rid of it.

This resolves:
    http://tracker.newdream.net/issues/3860

Note that the problem this loop was intended to solve is a race
between collecting image header information and setting up the watch
on the header object.  The real fix for that problem is described
here:
    http://tracker.newdream.net/issues/3871

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

drivers/block/rbd.c

@@ -1474,6 +1474,9 @@ static int rbd_req_sync_watch(struct rbd_device *rbd_dev, int start)
 	struct ceph_osd_req_op *op;
 	int ret = 0;
 
+	rbd_assert(start ^ !!rbd_dev->watch_event);
+	rbd_assert(start ^ !!rbd_dev->watch_request);
+
 	if (start) {
 		struct ceph_osd_client *osdc;
 
@@ -1482,8 +1485,6 @@ static int rbd_req_sync_watch(struct rbd_device *rbd_dev, int start)
 						&rbd_dev->watch_event);
 		if (ret < 0)
 			return ret;
-	} else {
-		rbd_assert(rbd_dev->watch_request != NULL);
 	}
 
 	op = rbd_osd_req_op_create(CEPH_OSD_OP_WATCH,
@@ -3023,22 +3024,6 @@ static void rbd_bus_del_dev(struct rbd_device *rbd_dev)
 	device_unregister(&rbd_dev->dev);
 }
 
-static int rbd_init_watch_dev(struct rbd_device *rbd_dev)
-{
-	int ret, rc;
-
-	do {
-		ret = rbd_req_sync_watch(rbd_dev, 1);
-		if (ret == -ERANGE) {
-			rc = rbd_dev_refresh(rbd_dev, NULL);
-			if (rc < 0)
-				return rc;
-		}
-	} while (ret == -ERANGE);
-
-	return ret;
-}
-
 static atomic64_t rbd_dev_id_max = ATOMIC64_INIT(0);
 
 /*
@@ -3584,7 +3569,7 @@ static int rbd_dev_probe_finish(struct rbd_device *rbd_dev)
 	if (ret)
 		goto err_out_bus;
 
-	ret = rbd_init_watch_dev(rbd_dev);
+	ret = rbd_req_sync_watch(rbd_dev, 1);
 	if (ret)
 		goto err_out_bus;