Volume Metrics Interface and base implementation.

- Add volume.MetricsProvider function to Volume interface.
- Add volume.MetricsDu for providing metrics via executing "du".
- Add volulme.MetricsNil for unsupported Volumes.

pkg/volume/host_path/host_path_test.go

@@ -18,6 +18,7 @@ package host_path
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
 	"testing"
 
@@ -92,7 +93,7 @@ func TestDeleter(t *testing.T) {
 	defer os.RemoveAll(tempPath)
 	err := os.MkdirAll(tempPath, 0750)
 	if err != nil {
-		t.Fatal("Failed to create tmp directory for deleter: %v", err)
+		t.Fatalf("Failed to create tmp directory for deleter: %v", err)
 	}
 
 	plugMgr := volume.VolumePluginMgr{}
@@ -272,3 +273,45 @@ func TestPersistentClaimReadOnlyFlag(t *testing.T) {
 		t.Errorf("Expected true for builder.IsReadOnly")
 	}
 }
+
+// TestMetrics tests that MetricProvider methods return sane values.
+func TestMetrics(t *testing.T) {
+	// Create an empty temp directory for the volume
+	tmpDir, err := ioutil.TempDir(os.TempDir(), "host_path_test")
+	if err != nil {
+		t.Fatalf("Can't make a tmp dir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	plugMgr := volume.VolumePluginMgr{}
+	plugMgr.InitPlugins(ProbeVolumePlugins(volume.VolumeConfig{}), volume.NewFakeVolumeHost(tmpDir, nil, nil))
+
+	plug, err := plugMgr.FindPluginByName("kubernetes.io/host-path")
+	if err != nil {
+		t.Errorf("Can't find the plugin by name")
+	}
+	spec := &api.Volume{
+		Name:         "vol1",
+		VolumeSource: api.VolumeSource{HostPath: &api.HostPathVolumeSource{Path: tmpDir}},
+	}
+	pod := &api.Pod{ObjectMeta: api.ObjectMeta{UID: types.UID("poduid")}}
+	builder, err := plug.NewBuilder(volume.NewSpecFromVolume(spec), pod, volume.VolumeOptions{})
+	if err != nil {
+		t.Errorf("Failed to make a new Builder: %v", err)
+	}
+
+	// TODO(pwittroc): Move this into a reusable testing utility
+	metrics, err := builder.GetMetrics()
+	if err != nil {
+		t.Errorf("Unexpected error when calling GetMetrics %v", err)
+	}
+	if metrics.Used.Value() != 4096 {
+		t.Errorf("Expected Used %d to be 4096", metrics.Used)
+	}
+	if metrics.Capacity.Value() <= 0 {
+		t.Errorf("Expected Capacity to be greater than 0")
+	}
+	if metrics.Available.Value() <= 0 {
+		t.Errorf("Expected Available to be greater than 0")
+	}
+}