rbd: allow null image name

We will know the image id for format 2 parent images, but won't
initially know its image name.  Avoid making the query for an image
id in rbd_dev_image_id() if it's already known.

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

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 8d26c0f..a852133 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -3068,6 +3068,14 @@ static int rbd_dev_image_id(struct rbd_device *rbd_dev)
        void *p;
 
        /*
+        * When probing a parent image, the image id is already
+        * known (and the image name likely is not).  There's no
+        * need to fetch the image id again in this case.
+        */
+       if (rbd_dev->spec->image_id)
+               return 0;
+
+       /*
         * First, see if the format 2 image id file exists, and if
         * so, get the image's persistent id from it.
         */