rbd: pass a max-depth to getCloneDepth()

The `getCloneDepth()` function does not need to traverse the whole chain
of parents when a certain max-limit is configured. The traversing can be
aborted once the hard-limit is reached. This makes the procedure a
little more efficient, as unnecessary traversing is prevented.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/rbd/nodeserver.go

@@ -595,7 +595,7 @@ func flattenImageBeforeMapping(
 		if err != nil {
 			return err
 		}
-		depth, err = volOptions.getCloneDepth()
+		depth, err = volOptions.getCloneDepth(rbdHardMaxCloneDepth + 1)
 		if err != nil {
 			return err
 		}

internal/rbd/rbd_util.go

@@ -707,11 +707,13 @@ func (ri *rbdImage) trashRemoveImage(ctx context.Context) error {
 }
 
 // getCloneDepth walks the parents of the image and returns the number of
-// images in the chain.
+// images in the chain. The `max` argument to the function is used to specify a
+// limit of the depth to check. When `max` depth is reached, no further
+// traversing of the depth is required.
 //
 // This function re-uses the ioctx of the image to open all images in the
 // chain. There is no need to open new ioctx's for every image.
-func (ri *rbdImage) getCloneDepth() (uint, error) {
+func (ri *rbdImage) getCloneDepth(max uint) (uint, error) {
 	var (
 		depth uint
 		info  *librbd.ParentInfo
@@ -741,6 +743,13 @@ func (ri *rbdImage) getCloneDepth() (uint, error) {
 		// if there is a parent, count it to the depth
 		depth++
 
+		// if max (usually hard-limit) is reached, further traversing
+		// parents is not needed, some action (flattening) will be
+		// triggered regardless of deeper depth
+		if depth == max {
+			break
+		}
+
 		// open the parent image, so that the for-loop can continue
 		// with checking for the parent of the parent
 		image, err = librbd.OpenImageById(ri.ioctx, info.Image.ImageID, info.Snap.SnapName)
@@ -830,7 +839,7 @@ func (ri *rbdImage) flattenRbdImage(
 
 	// skip clone depth check if request is for force flatten
 	if !forceFlatten {
-		depth, err = ri.getCloneDepth()
+		depth, err = ri.getCloneDepth(hardlimit)
 		if err != nil {
 			return err
 		}