rbd: don't register snapshots in bus_add_dev()

When rbd_bus_add_dev() is called (one spot--in rbd_add()), the rbd
image header has not even been read yet.  This means that the list
of snapshots will be empty at the time of the call.  As a result,
there is no need for the code that calls rbd_register_snap_dev()
for each entry in that list--so get rid of it.

Once the header has been read (just after returning), a call will
be made to rbd_dev_snap_devs_update(), which will then find every
snapshot in the context to be new and will therefore call
rbd_register_snap_dev() via __rbd_add_snap_dev() accomplishing
the same thing.
Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

drivers/block/rbd.c

@@ -2244,29 +2244,21 @@ static int rbd_dev_snap_devs_update(struct rbd_device *rbd_dev)
 
 static int rbd_bus_add_dev(struct rbd_device *rbd_dev)
 {
-	int ret;
 	struct device *dev;
-	struct rbd_snap *snap;
+	int ret;
 
 	mutex_lock_nested(&ctl_mutex, SINGLE_DEPTH_NESTING);
-	dev = &rbd_dev->dev;
 
+	dev = &rbd_dev->dev;
 	dev->bus = &rbd_bus_type;
 	dev->type = &rbd_device_type;
 	dev->parent = &rbd_root_dev;
 	dev->release = rbd_dev_release;
 	dev_set_name(dev, "%d", rbd_dev->dev_id);
 	ret = device_register(dev);
-	if (ret < 0)
-		goto out;
 
-	list_for_each_entry(snap, &rbd_dev->snaps, node) {
-		ret = rbd_register_snap_dev(snap, &rbd_dev->dev);
-		if (ret < 0)
-			break;
-	}
-out:
 	mutex_unlock(&ctl_mutex);
+
 	return ret;
 }