Merge pull request #61914 from ianchakeres/mount-unsupported-err

Automatic merge from submit-queue (batch tested with PRs 62324, 61459, 62475, 62476, 61914). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Return error in mount_unsupported for unsupported platforms

**What this PR does / why we need it**:

Presently, `util/mount_unsupported.go` does not return any errors. For unsupported platforms, this hides failures. This PR returns errors, thereby properly informing users attempting to run on an unsupported platform.

**Which issue(s) this PR fixes** :
Fixes https://github.com/kubernetes/kubernetes/issues/61919

**Special notes for your reviewer**:

There are a few methods that simply call through to other methods. I did not return errors from those methods.

I've also updated an error check and message in `volume/fc/fc_test.go`, since it was ignoring an error on unsupported platforms.

**Release note**:
```release-note
NONE
```

pkg/util/mount/mount_unsupported.go

@@ -21,12 +21,16 @@ package mount
 import (
 	"errors"
 	"os"
+
+	"github.com/golang/glog"
 )
 
 type Mounter struct {
 	mounterPath string
 }
 
+var unsupportedErr = errors.New("util/mount on this platform is not supported")
+
 // New returns a mount.Interface for the current system.
 // It provides options to override the default mounter behavior.
 // mounterPath allows using an alternative to `/bin/mount` for mounting.
@@ -37,21 +41,21 @@ func New(mounterPath string) Interface {
 }
 
 func (mounter *Mounter) Mount(source string, target string, fstype string, options []string) error {
-	return nil
+	return unsupportedErr
 }
 
 func (mounter *Mounter) Unmount(target string) error {
-	return nil
+	return unsupportedErr
 }
 
 // GetMountRefs finds all other references to the device referenced
 // by mountPath; returns a list of paths.
 func GetMountRefs(mounter Interface, mountPath string) ([]string, error) {
-	return []string{}, nil
+	return []string{}, unsupportedErr
 }
 
 func (mounter *Mounter) List() ([]MountPoint, error) {
-	return []MountPoint{}, nil
+	return []MountPoint{}, unsupportedErr
 }
 
 func (mounter *Mounter) IsMountPointMatch(mp MountPoint, dir string) bool {
@@ -63,27 +67,27 @@ func (mounter *Mounter) IsNotMountPoint(dir string) (bool, error) {
 }
 
 func (mounter *Mounter) IsLikelyNotMountPoint(file string) (bool, error) {
-	return true, nil
+	return true, unsupportedErr
 }
 
 func (mounter *Mounter) GetDeviceNameFromMount(mountPath, pluginDir string) (string, error) {
-	return "", nil
+	return "", unsupportedErr
 }
 
 func getDeviceNameFromMount(mounter Interface, mountPath, pluginDir string) (string, error) {
-	return "", nil
+	return "", unsupportedErr
 }
 
 func (mounter *Mounter) DeviceOpened(pathname string) (bool, error) {
-	return false, nil
+	return false, unsupportedErr
 }
 
 func (mounter *Mounter) PathIsDevice(pathname string) (bool, error) {
-	return true, nil
+	return true, unsupportedErr
 }
 
 func (mounter *Mounter) MakeRShared(path string) error {
-	return nil
+	return unsupportedErr
 }
 
 func (mounter *SafeFormatAndMount) formatAndMount(source string, target string, fstype string, options []string) error {
@@ -91,33 +95,34 @@ func (mounter *SafeFormatAndMount) formatAndMount(source string, target string,
 }
 
 func (mounter *SafeFormatAndMount) diskLooksUnformatted(disk string) (bool, error) {
-	return true, nil
+	return true, unsupportedErr
 }
 
 func (mounter *Mounter) GetFileType(pathname string) (FileType, error) {
-	return FileType("fake"), errors.New("not implemented")
+	return FileType("fake"), unsupportedErr
 }
 
 func (mounter *Mounter) MakeDir(pathname string) error {
-	return nil
+	return unsupportedErr
 }
 
 func (mounter *Mounter) MakeFile(pathname string) error {
-	return nil
+	return unsupportedErr
 }
 
 func (mounter *Mounter) ExistsPath(pathname string) bool {
+	glog.Errorf("%s", unsupportedErr)
 	return true
 }
 
 func (mounter *Mounter) PrepareSafeSubpath(subPath Subpath) (newHostPath string, cleanupAction func(), err error) {
-	return subPath.Path, nil, nil
+	return subPath.Path, nil, unsupportedErr
 }
 
 func (mounter *Mounter) CleanSubPaths(podDir string, volumeName string) error {
-	return nil
+	return unsupportedErr
 }
 
 func (mounter *Mounter) SafeMakeDir(pathname string, base string, perm os.FileMode) error {
-	return nil
+	return unsupportedErr
 }

pkg/volume/fc/fc_test.go

@@ -441,7 +441,10 @@ func Test_ConstructVolumeSpec(t *testing.T) {
 		"/var/lib/kubelet/pods/some-pod/volumes/kubernetes.io~fc/fc-in-pod2",
 	}
 	for _, path := range mountPaths {
-		refs, _ := mount.GetMountRefs(fm, path)
+		refs, err := mount.GetMountRefs(fm, path)
+		if err != nil {
+			t.Errorf("couldn't get mountrefs. err: %v", err)
+		}
 		var globalPDPath string
 		for _, ref := range refs {
 			if strings.Contains(ref, "kubernetes.io/fc") {