add rbd-nbd mounter in storage class

Signed-off-by: Huamin Chen <hchen@redhat.com>

examples/rbd/storageclass.yaml

@@ -25,4 +25,6 @@ parameters:
     # Ceph users for operating RBD
     adminid: admin
     userid: kubernetes
+    # uncomment the following to use rbd-nbd as mounter on supported nodes
+    #mounter: rbd-nbd
 reclaimPolicy: Delete

pkg/rbd/rbd_attach.go

@@ -35,7 +35,7 @@ const (
 
 var (
 	hostRootFS = "/"
-	useNBD     = false
+	hasNBD     = false
 )
 
 func init() {
@@ -43,7 +43,7 @@ func init() {
 	if len(host) > 0 {
 		hostRootFS = host
 	}
-	useNBD = checkRbdNbdTools()
+	hasNBD = checkRbdNbdTools()
 }
 
 func getDevFromImageAndPool(pool, image string) (string, bool) {
@@ -226,12 +226,15 @@ func attachRBDImage(volOptions *rbdVolume, userId string, credentials map[string
 	image := volOptions.VolName
 	imagePath := fmt.Sprintf("%s/%s", volOptions.Pool, image)
 
+	useNBD := false
 	cmdName := "rbd"
 	moduleName := "rbd"
-	if useNBD {
+	if volOptions.Mounter == "rbd-nbd" && hasNBD {
+		useNBD = true
 		cmdName = "rbd-nbd"
 		moduleName = "nbd"
 	}
+
 	devicePath, found := waitForPath(volOptions.Pool, image, 1, useNBD)
 	if !found {
 		attachdetachMutex.LockKey(string(imagePath))
@@ -258,7 +261,7 @@ func attachRBDImage(volOptions *rbdVolume, userId string, credentials map[string
 		if err == wait.ErrWaitTimeout {
 			return "", fmt.Errorf("rbd image %s is still being used", imagePath)
 		}
-		// return error if any other errors were encountered during wating for the image to becme avialble
+		// return error if any other errors were encountered during wating for the image to become available
 		if err != nil {
 			return "", err
 		}

pkg/rbd/rbd_util.go

@@ -42,6 +42,7 @@ const (
 	rbdImageWatcherInitDelay = 1 * time.Second
 	rbdImageWatcherFactor    = 1.4
 	rbdImageWatcherSteps     = 10
+	rbdDefaultMounter        = "rbd"
 )
 
 type rbdVolume struct {
@@ -54,6 +55,7 @@ type rbdVolume struct {
 	VolSize       int64  `json:"volSize"`
 	AdminId       string `json:"adminId"`
 	UserId        string `json:"userId"`
+	Mounter       string `json:"mounter"`
 }
 
 type rbdSnapshot struct {
@@ -226,6 +228,10 @@ func getRBDVolumeOptions(volOptions map[string]string) (*rbdVolume, error) {
 	if !ok {
 		rbdVol.UserId = rbdDefaultUserId
 	}
+	rbdVol.Mounter, ok = volOptions["mounter"]
+	if !ok {
+		rbdVol.Mounter = rbdDefaultMounter
+	}
 	return rbdVol, nil
 }