rbd: create 1MiB size dummy image

we added a workaround for rbd scheduling by creating
a dummy image in ceph#2656. with the fix we are creating
a dummy image of the size of the first actual rbd
image which is sent in EnableVolumeReplication request
if the actual rbd image size is 1TiB we are creating
a dummy image of 1TiB which is not good. even though
its a thin provisioned rbd images this is causing
issue for the transfer of the snapshot during
the mirroring operation.

This commit recreates the rbd image with 1MiB size
which is the smaller supported size in rbd.

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

internal/rbd/replicationcontrollerserver.go

@@ -300,23 +300,44 @@ func getOperationName(poolName string, optName operation) string {
 // createDummyImage creates a dummy image as a workaround for the rbd
 // scheduling problem.
 func createDummyImage(ctx context.Context, rbdVol *rbdVolume) error {
+	var err error
+	var imgName string
 	optName := getOperationName(rbdVol.Pool, dummyImageCreated)
 	if _, ok := operationLock.Load(optName); !ok {
 		// create a dummy image
-		imgName, err := getDummyImageName(rbdVol.conn)
+		imgName, err = getDummyImageName(rbdVol.conn)
 		if err != nil {
 			return err
 		}
 		dummyVol := *rbdVol
 		dummyVol.RbdImageName = imgName
+		// create 1MiB dummy image. 1MiB=1048576 bytes
+		dummyVol.VolSize = 1048576
 		err = createImage(ctx, &dummyVol, dummyVol.conn.Creds)
-		if err != nil && !strings.Contains(err.Error(), "File exists") {
-			return err
+		if err != nil {
+			if strings.Contains(err.Error(), "File exists") {
+				err = repairDummyImage(ctx, &dummyVol)
+			}
 		}
+	}
+
+	if err == nil {
 		operationLock.Store(optName, true)
 	}
 
-	return nil
+	return err
+}
+
+// repairDummyImage deletes and recreates the dummy image.
+func repairDummyImage(ctx context.Context, dummyVol *rbdVolume) error {
+	// deleting and recreating the dummy image will not impact anything as its
+	// a workaround to fix the scheduling problem.
+	err := deleteImage(ctx, dummyVol, dummyVol.conn.Creds)
+	if err != nil {
+		return err
+	}
+
+	return createImage(ctx, dummyVol, dummyVol.conn.Creds)
 }
 
 // tickleMirroringOnDummyImage disables and reenables mirroring on the dummy image, and sets a