Track image storage usage for docker containers

add image fs info to summary stats API.
Adding node e2e test for image stats.

Signed-off-by: Vishnu kannan <vishnuk@google.com>

pkg/kubelet/container/runtime.go

@@ -46,6 +46,12 @@ type ImageSpec struct {
 	Image string
 }
 
+// ImageStats contains statistics about all the images currently available.
+type ImageStats struct {
+	// Total amount of storage consumed by existing images.
+	TotalStorageBytes uint64
+}
+
 // Runtime interface defines the interfaces that should be implemented
 // by a container runtime.
 // Thread safety is required from implementations of this interface.
@@ -86,6 +92,8 @@ type Runtime interface {
 	ListImages() ([]Image, error)
 	// Removes the specified image.
 	RemoveImage(image ImageSpec) error
+	// Returns Image statistics.
+	ImageStats() (*ImageStats, error)
 	// TODO(vmarmol): Unify pod and containerID args.
 	// GetContainerLogs returns logs of a specific container. By
 	// default, it returns a snapshot of the container log. Set 'follow' to true to

pkg/kubelet/container/testing/fake_runtime.go

@@ -353,3 +353,11 @@ func (f *FakeRuntime) GarbageCollect(gcPolicy ContainerGCPolicy) error {
 	f.CalledFunctions = append(f.CalledFunctions, "GarbageCollect")
 	return f.Err
 }
+
+func (f *FakeRuntime) ImageStats() (*ImageStats, error) {
+	f.Lock()
+	defer f.Unlock()
+
+	f.CalledFunctions = append(f.CalledFunctions, "ImageStats")
+	return nil, f.Err
+}

pkg/kubelet/container/testing/runtime_mock.go

@@ -137,3 +137,8 @@ func (r *Mock) GarbageCollect(gcPolicy ContainerGCPolicy) error {
 	args := r.Called(gcPolicy)
 	return args.Error(0)
 }
+
+func (r *Mock) ImageStats() (*ImageStats, error) {
+	args := r.Called()
+	return args.Get(0).(*ImageStats), args.Error(1)
+}