rbd: discard flattening error if the image doesnt have parent

if the image is created without flattening image-feature
the image will get few image-features by default, deep-flatten
is one of them. if the image doesnot have any parent
the rbd image flattening will fail, This commit discards
error message if the image doesnt have any parent.

Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>

internal/rbd/rbd_util.go

@@ -458,6 +458,11 @@ func (rv *rbdVolume) flattenRbdImage(ctx context.Context, cr *util.Credentials,
 		supported, err := addRbdManagerTask(ctx, rv, args)
 		if supported {
 			if err != nil {
+				// discard flattening error if the image doesnot have any parent
+				rbdFlattenNoParent := fmt.Sprintf("Image %s/%s does not have a parent", rv.Pool, rv.RbdImageName)
+				if strings.Contains(err.Error(), rbdFlattenNoParent) {
+					return nil
+				}
 				klog.Errorf(util.Log(ctx, "failed to add task flatten for %s : %v"), rv, err)
 				return err
 			}
@@ -472,12 +477,8 @@ func (rv *rbdVolume) flattenRbdImage(ctx context.Context, cr *util.Credentials,
 				if err != nil {
 					return err
 				}
-				rbdImage, err := rv.open()
+				err := rv.flatten()
 				if err != nil {
-					return err
-				}
-				defer rbdImage.Close()
-				if err = rbdImage.Flatten(); err != nil {
 					klog.Errorf(util.Log(ctx, "rbd failed to flatten image %s %s: %v"), rv.Pool, rv.RbdImageName, err)
 					return err
 				}
@@ -487,6 +488,45 @@ func (rv *rbdVolume) flattenRbdImage(ctx context.Context, cr *util.Credentials,
 	return nil
 }
 
+func (rv *rbdVolume) getParentName() (string, error) {
+	rbdImage, err := rv.open()
+	if err != nil {
+		return "", err
+	}
+	defer rbdImage.Close()
+
+	parentPool := make([]byte, 128)
+	parentName := make([]byte, 128)
+	parentSnapname := make([]byte, 128)
+
+	err = rbdImage.GetParentInfo(parentPool, parentName, parentSnapname)
+	if err != nil {
+		return "", err
+	}
+	return string(parentName), nil
+}
+
+func (rv *rbdVolume) flatten() error {
+	rbdImage, err := rv.open()
+	if err != nil {
+		return err
+	}
+	defer rbdImage.Close()
+
+	err = rbdImage.Flatten()
+	if err != nil {
+		// rbd image flatten will fail if the rbd image does not have a parent
+		parent, pErr := rv.getParentName()
+		if pErr != nil {
+			return util.JoinErrors(err, pErr)
+		}
+		if parent == "" {
+			return nil
+		}
+	}
+	return nil
+}
+
 func (rv *rbdVolume) hasFeature(feature uint64) bool {
 	return (uint64(rv.imageFeatureSet) & feature) == feature
 }