Add SupportsMetrics() for Block-mode volumes

Volumes that are provisioned with `VolumeMode: Block` often have a
MetrucsProvider interface declared in their type. However, the
MetricsProvider should implement a GetMetrics() function. In the cases
where the storage drivers do not implement GetMetrics(), a panic can
occur.

Usual type-assertions are not sufficient in this case. All assertions
assume the interface is present. There is no straight forward way to
verify that a valid GetMetrics() function is provided.

By adding SupportsMetrics(), storage driver implementations require
careful reviewing for metrics support.

pkg/kubelet/kubelet_volumes_test.go

@@ -567,6 +567,10 @@ func (f *stubBlockVolume) UnmapPodDevice() error {
 	return nil
 }
 
+func (f *stubBlockVolume) SupportsMetrics() bool {
+	return false
+}
+
 func (f *stubBlockVolume) GetMetrics() (*volume.Metrics, error) {
 	return nil, nil
 }

pkg/kubelet/server/stats/volume_stat_calculator.go

@@ -112,7 +112,12 @@ func (s *volumeStatCalculator) calcAndStoreStats() {
 		for name, v := range blockVolumes {
 			// Only add the blockVolume if it implements the MetricsProvider interface
 			if _, ok := v.(volume.MetricsProvider); ok {
-				metricVolumes[name] = v
+				// Some drivers inherit the MetricsProvider interface from Filesystem
+				// mode volumes, but do not implement it for Block mode. Checking
+				// SupportsMetrics() will prevent panics in that case.
+				if v.SupportsMetrics() {
+					metricVolumes[name] = v
+				}
 			}
 		}
 	}

pkg/kubelet/server/stats/volume_stat_calculator_test.go

@@ -246,6 +246,8 @@ func (v *fakeBlockVolume) GetGlobalMapPath(*volume.Spec) (string, error) { retur
 
 func (v *fakeBlockVolume) GetPodDeviceMapPath() (string, string) { return "", "" }
 
+func (v *fakeBlockVolume) SupportsMetrics() bool { return true }
+
 func (v *fakeBlockVolume) GetMetrics() (*volume.Metrics, error) {
 	return expectedBlockMetrics(), nil
 }

pkg/volume/awsebs/aws_ebs_block.go

@@ -165,3 +165,9 @@ func (ebs *awsElasticBlockStore) GetPodDeviceMapPath() (string, string) {
 	name := awsElasticBlockStorePluginName
 	return ebs.plugin.host.GetPodVolumeDeviceDir(ebs.podUID, utilstrings.EscapeQualifiedName(name)), ebs.volName
 }
+
+// SupportsMetrics returns true for awsElasticBlockStore as it initializes the
+// MetricsProvider.
+func (ebs *awsElasticBlockStore) SupportsMetrics() bool {
+	return true
+}

pkg/volume/azuredd/azure_dd_block.go

@@ -129,6 +129,7 @@ func (plugin *azureDataDiskPlugin) newUnmapperInternal(volName string, podUID ty
 
 type azureDataDiskUnmapper struct {
 	*dataDisk
+	volume.MetricsNil
 }
 
 var _ volume.BlockVolumeUnmapper = &azureDataDiskUnmapper{}
@@ -157,3 +158,9 @@ func (disk *dataDisk) GetPodDeviceMapPath() (string, string) {
 	name := azureDataDiskPluginName
 	return disk.plugin.host.GetPodVolumeDeviceDir(disk.podUID, utilstrings.EscapeQualifiedName(name)), disk.volumeName
 }
+
+// SupportsMetrics returns true for azureDataDiskMapper as it initializes the
+// MetricsProvider.
+func (addm *azureDataDiskMapper) SupportsMetrics() bool {
+	return true
+}

pkg/volume/cinder/cinder_block.go

@@ -140,6 +140,7 @@ func (plugin *cinderPlugin) newUnmapperInternal(volName string, podUID types.UID
 
 type cinderPluginUnmapper struct {
 	*cinderVolume
+	volume.MetricsNil
 }
 
 var _ volume.BlockVolumeUnmapper = &cinderPluginUnmapper{}
@@ -168,3 +169,9 @@ func (cd *cinderVolume) GetPodDeviceMapPath() (string, string) {
 	name := cinderVolumePluginName
 	return cd.plugin.host.GetPodVolumeDeviceDir(cd.podUID, utilstrings.EscapeQualifiedName(name)), cd.volName
 }
+
+// SupportsMetrics returns true for cinderVolumeMapper as it initializes the
+// MetricsProvider.
+func (cvm *cinderVolumeMapper) SupportsMetrics() bool {
+	return true
+}

pkg/volume/csi/csi_block.go

@@ -115,6 +115,12 @@ func (m *csiBlockMapper) GetStagingPath() string {
 	return filepath.Join(m.plugin.host.GetVolumeDevicePluginDir(CSIPluginName), "staging", m.specName)
 }
 
+// SupportsMetrics returns true for csiBlockMapper as it initializes the
+// MetricsProvider.
+func (m *csiBlockMapper) SupportsMetrics() bool {
+	return true
+}
+
 // getPublishDir returns path to a directory, where the volume is published to each pod.
 // Example: plugins/kubernetes.io/csi/volumeDevices/publish/{specName}
 func (m *csiBlockMapper) getPublishDir() string {

pkg/volume/gcepd/gce_pd_block.go

@@ -174,3 +174,9 @@ func (pd *gcePersistentDisk) GetPodDeviceMapPath() (string, string) {
 	name := gcePersistentDiskPluginName
 	return pd.plugin.host.GetPodVolumeDeviceDir(pd.podUID, utilstrings.EscapeQualifiedName(name)), pd.volName
 }
+
+// SupportsMetrics returns true for gcePersistentDisk as it initializes the
+// MetricsProvider.
+func (pd *gcePersistentDisk) SupportsMetrics() bool {
+	return true
+}

pkg/volume/iscsi/iscsi.go

@@ -393,6 +393,13 @@ type iscsiDiskUnmapper struct {
 	*iscsiDisk
 	exec       utilexec.Interface
 	deviceUtil ioutil.DeviceUtil
+	volume.MetricsNil
+}
+
+// SupportsMetrics returns true for SupportsMetrics as it initializes the
+// MetricsProvider.
+func (idm *iscsiDiskMapper) SupportsMetrics() bool {
+	return true
 }
 
 var _ volume.BlockVolumeUnmapper = &iscsiDiskUnmapper{}

pkg/volume/local/local.go

@@ -633,9 +633,16 @@ func (m *localVolumeMapper) GetStagingPath() string {
 	return ""
 }
 
+// SupportsMetrics returns true for SupportsMetrics as it initializes the
+// MetricsProvider.
+func (m *localVolumeMapper) SupportsMetrics() bool {
+	return true
+}
+
 // localVolumeUnmapper implements the BlockVolumeUnmapper interface for local volumes.
 type localVolumeUnmapper struct {
 	*localVolume
+	volume.MetricsNil
 }
 
 var _ volume.BlockVolumeUnmapper = &localVolumeUnmapper{}

pkg/volume/metrics_nil.go

@@ -23,6 +23,11 @@ var _ MetricsProvider = &MetricsNil{}
 // metrics.
 type MetricsNil struct{}
 
+// SupportsMetrics returns false for the MetricsNil type.
+func (*MetricsNil) SupportsMetrics() bool {
+	return false
+}
+
 // GetMetrics returns an empty Metrics and an error.
 // See MetricsProvider.GetMetrics
 func (*MetricsNil) GetMetrics() (*Metrics, error) {

pkg/volume/metrics_nil_test.go

@@ -20,6 +20,14 @@ import (
 	"testing"
 )
 
+func TestMetricsNilSupportsMetrics(t *testing.T) {
+	metrics := &MetricsNil{}
+	supported := metrics.SupportsMetrics()
+	if supported {
+		t.Error("Expected no support for metrics")
+	}
+}
+
 func TestMetricsNilGetCapacity(t *testing.T) {
 	metrics := &MetricsNil{}
 	actual, err := metrics.GetMetrics()

pkg/volume/rbd/rbd.go

@@ -938,6 +938,12 @@ func (rbd *rbd) rbdPodDeviceMapPath() (string, string) {
 	return rbd.plugin.host.GetPodVolumeDeviceDir(rbd.podUID, utilstrings.EscapeQualifiedName(name)), rbd.volName
 }
 
+// SupportsMetrics returns true for rbdDiskMapper as it initializes the
+// MetricsProvider.
+func (rdm *rbdDiskMapper) SupportsMetrics() bool {
+	return true
+}
+
 type rbdDiskUnmapper struct {
 	*rbdDiskMapper
 }

pkg/volume/volume.go

@@ -49,6 +49,10 @@ type BlockVolume interface {
 	// ex. pods/{podUid}/{DefaultKubeletVolumeDevicesDirName}/{escapeQualifiedPluginName}/, {volumeName}
 	GetPodDeviceMapPath() (string, string)
 
+	// SupportsMetrics should return true if the MetricsProvider is
+	// initialized
+	SupportsMetrics() bool
+
 	// MetricsProvider embeds methods for exposing metrics (e.g.
 	// used, available space).
 	MetricsProvider

pkg/volume/vsphere_volume/vsphere_volume_block.go

@@ -144,6 +144,7 @@ var _ volume.BlockVolumeUnmapper = &vsphereBlockVolumeUnmapper{}
 
 type vsphereBlockVolumeUnmapper struct {
 	*vsphereVolume
+	volume.MetricsNil
 }
 
 // GetGlobalMapPath returns global map path and error
@@ -159,3 +160,9 @@ func (v *vsphereVolume) GetGlobalMapPath(spec *volume.Spec) (string, error) {
 func (v *vsphereVolume) GetPodDeviceMapPath() (string, string) {
 	return v.plugin.host.GetPodVolumeDeviceDir(v.podUID, utilstrings.EscapeQualifiedName(vsphereVolumePluginName)), v.volName
 }
+
+// SupportsMetrics returns true for vsphereBlockVolumeMapper as it initializes the
+// MetricsProvider.
+func (vbvm *vsphereBlockVolumeMapper) SupportsMetrics() bool {
+	return true
+}