Merge pull request kubernetes#36686 from rkouj/check-gluster-fs-binaries

Automatic merge from submit-queue

Implement CanMount() for gfsMounter for linux

**What this PR does / why we need it**:
To implement CanMount() check for glusterfs. If mount binaries are not present on the underlying node, the mount will not proceed and return an error message stating so.

Related to issue : kubernetes#36098


Related to similar change for NFS : 
kubernetes#36280

**Release note**:
`Check binaries for GlusterFS on the underlying node before doing mount`





Sample output from testing in GCE/GCI:

rkouj@rkouj0:~/go/src/k8s.io/kubernetes$ kubectl describe pods
Name:		glusterfs
Namespace:	default
Node:		e2e-test-rkouj-minion-group-kjq3/10.240.0.3
Start Time:	Fri, 11 Nov 2016 17:22:04 -0800
Labels:		<none>
Status:		Pending
IP:		
Controllers:	<none>
Containers:
  glusterfs:
    Container ID:	
    Image:		gcr.io/google_containers/busybox
    Image ID:		
    Port:		
    QoS Tier:
      cpu:	Burstable
      memory:	BestEffort
    Requests:
      cpu:		100m
    State:		Waiting
      Reason:		ContainerCreating
    Ready:		False
    Restart Count:	0
    Environment Variables:
Conditions:
  Type		Status
  Initialized 	True 
  Ready 	False 
  PodScheduled 	True 
Volumes:
  glusterfs:
    Type:		Glusterfs (a Glusterfs mount on the host that shares a pod's lifetime)
    EndpointsName:	glusterfs-cluster
    Path:		kube_vol
    ReadOnly:		true
  default-token-2zcao:
    Type:	Secret (a volume populated by a Secret)
    SecretName:	default-token-2zcao
Events:
  FirstSeen	LastSeen	Count	From						SubobjectPath	Type		Reason		Message
  ---------	--------	-----	----						-------------	--------	------		-------
  8s		8s		1	{default-scheduler }						Normal		Scheduled	Successfully assigned glusterfs to e2e-test-rkouj-minion-group-kjq3
  7s		4s		4	{kubelet e2e-test-rkouj-minion-group-kjq3}			Warning		FailedMount	Unable to mount volume kubernetes.io/glusterfs/6bb04587-a876-11e6-a712-42010af00002-glusterfs (spec.Name: glusterfs) on pod glusterfs (UID: 6bb04587-a876-11e6-a712-42010af00002). Verify that your node machine has the required components before attempting to mount this volume type. Required binary /sbin/mount.glusterfs is missing

Author: Kubernetes Submit Queue

pkg/volume/glusterfs/glusterfs.go

@@ -35,6 +35,7 @@ import (
 	"k8s.io/kubernetes/pkg/util/strings"
 	"k8s.io/kubernetes/pkg/volume"
 	volutil "k8s.io/kubernetes/pkg/volume/util"
+	"runtime"
 )
 
 // This is the primary entrypoint for volume plugins.
@@ -55,17 +56,18 @@ var _ volume.Provisioner = &glusterfsVolumeProvisioner{}
 var _ volume.Deleter = &glusterfsVolumeDeleter{}
 
 const (
-	glusterfsPluginName       = "kubernetes.io/glusterfs"
-	volPrefix                 = "vol_"
-	dynamicEpSvcPrefix        = "glusterfs-dynamic-"
-	replicaCount              = 3
-	durabilityType            = "replicate"
-	secretKeyName             = "key" // key name used in secret
-	annGlusterURL             = "glusterfs.kubernetes.io/url"
-	annGlusterSecretName      = "glusterfs.kubernetes.io/secretname"
-	annGlusterSecretNamespace = "glusterfs.kubernetes.io/secretnamespace"
-	annGlusterUserKey         = "glusterfs.kubernetes.io/userkey"
-	annGlusterUser            = "glusterfs.kubernetes.io/userid"
+	glusterfsPluginName         = "kubernetes.io/glusterfs"
+	volPrefix                   = "vol_"
+	dynamicEpSvcPrefix          = "glusterfs-dynamic-"
+	replicaCount                = 3
+	durabilityType              = "replicate"
+	secretKeyName               = "key" // key name used in secret
+	annGlusterURL               = "glusterfs.kubernetes.io/url"
+	annGlusterSecretName        = "glusterfs.kubernetes.io/secretname"
+	annGlusterSecretNamespace   = "glusterfs.kubernetes.io/secretnamespace"
+	annGlusterUserKey           = "glusterfs.kubernetes.io/userkey"
+	annGlusterUser              = "glusterfs.kubernetes.io/userid"
+	gciGlusterMountBinariesPath = "/sbin/mount.glusterfs"
 )
 
 func (plugin *glusterfsPlugin) Init(host volume.VolumeHost) error {
@@ -211,6 +213,13 @@ func (b *glusterfsMounter) GetAttributes() volume.Attributes {
 // to mount the volume are available on the underlying node.
 // If not, it returns an error
 func (b *glusterfsMounter) CanMount() error {
+	exe := exec.New()
+	switch runtime.GOOS {
+	case "linux":
+		if _, err := exe.Command("/bin/ls", gciGlusterMountBinariesPath).CombinedOutput(); err != nil {
+			return fmt.Errorf("Required binary %s is missing", gciGlusterMountBinariesPath)
+		}
+	}
 	return nil
 }