Add versioning to docker image format. IMPORTANT: the format versioning is pegged to docker's versioning, so changes to the format MUST trigger an increment in version number.

graph.go

@@ -85,9 +85,10 @@ func (graph *Graph) Get(name string) (*Image, error) {
 // Create creates a new image and registers it in the graph.
 func (graph *Graph) Create(layerData Archive, container *Container, comment string) (*Image, error) {
 	img := &Image{
-		Id:      GenerateId(),
-		Comment: comment,
-		Created: time.Now(),
+		Id:            GenerateId(),
+		Comment:       comment,
+		Created:       time.Now(),
+		DockerVersion: VERSION,
 	}
 	if container != nil {
 		img.Parent = container.Image

graph_test.go

@@ -45,6 +45,9 @@ func TestGraphCreate(t *testing.T) {
 	if image.Comment != "Testing" {
 		t.Fatalf("Wrong comment: should be '%s', not '%s'", "Testing", image.Comment)
 	}
+	if image.DockerVersion != VERSION {
+		t.Fatalf("Wrong docker_version: should be '%s', not '%s'", VERSION, image.DockerVersion)
+	}
 	if images, err := graph.All(); err != nil {
 		t.Fatal(err)
 	} else if l := len(images); l != 1 {

image.go

@@ -20,6 +20,7 @@ type Image struct {
 	Created         time.Time `json:"created"`
 	Container       string    `json:"container,omitempty"`
 	ContainerConfig Config    `json:"container_config,omitempty"`
+	DockerVersion   string    `json:"docker_version,omitempty"`
 	graph           *Graph
 }