@@ -111,7 +111,7 @@ func (fi *HashedFileInfo) SetHash(h string) {

 type Backend interface {

 	// TODO: use digest reference instead of name

-	// LookupImage looks up a Docker image referenced by `name`.

+	// GetImage looks up a Docker image referenced by `name`.

 	GetImage(name string) (*image.Image, error)

 	// Pull tells Docker to pull image referenced by `name`.

 	Pull(name string) (*image.Image, error)

@@ -142,12 +142,11 @@ type Backend interface {

 	// TODO: use copyBackend api

 	BuilderCopy(containerID string, destPath string, src FileInfo, decompress bool) error

-	// Retain retains an image avoiding it to be removed or overwritten until a corresponding Release() call.

 	// TODO: remove

-	Retain(sessionID, imgID string)

-	// Release releases a list of images that were retained for the time of a build.

-	// TODO: remove

-	Release(sessionID string, activeImages []string)

+	// Mount mounts the root filesystem for the container.

+	Mount(containerID string) error

+	// Unmount unmounts the root filesystem for the container.

+	Unmount(containerID string) error

 }

 // ImageCache abstracts an image cache store.

@@ -95,8 +95,7 @@ type Builder struct {

 	allowedBuildArgs map[string]bool // list of build-time args that are allowed for expansion/substitution and passing to commands in 'run'.

 	// TODO: remove once docker.Commit can receive a tag

-	id           string

-	activeImages []string

+	id string

 }

 // NewBuilder creates a new Dockerfile builder from an optional dockerfile and a Config.

@@ -145,11 +144,6 @@ func NewBuilder(config *Config, docker builder.Backend, context builder.Context,

 // * NOT tag the image, that is responsibility of the caller.

 //

 func (b *Builder) Build() (string, error) {

-	// TODO: remove once b.docker.Commit can take a tag parameter.

-	defer func() {

-		b.docker.Release(b.id, b.activeImages)

-	}()

-

 	// If Dockerfile was not parsed yet, extract it from the Context

 	if b.dockerfile == nil {

 		if err := b.readDockerfile(); err != nil {

@@ -399,6 +399,9 @@ func run(b *Builder, args []string, attributes map[string]bool, original string)

 		return err

 	}

+	b.docker.Mount(cID)

+	defer b.docker.Unmount(cID)

+

 	if err := b.run(cID); err != nil {

 		return err

 	}

@@ -66,6 +66,10 @@ func (b *Builder) commit(id string, autoCmd *stringutils.StrSlice, comment strin

 		if err != nil {

 			return err

 		}

+		if err := b.docker.Mount(id); err != nil {

+			return err

+		}

+		defer b.docker.Unmount(id)

 	}

 	// Note: Actually copy the struct

@@ -83,8 +87,6 @@ func (b *Builder) commit(id string, autoCmd *stringutils.StrSlice, comment strin

 	if err != nil {

 		return err

 	}

-	b.docker.Retain(b.id, imageID)

-	b.activeImages = append(b.activeImages, imageID)

 	b.image = imageID

 	return nil

 }

@@ -191,6 +193,10 @@ func (b *Builder) runContextCommand(args []string, allowRemote bool, allowLocalD

 	if err != nil {

 		return err

 	}

+	if err := b.docker.Mount(container.ID); err != nil {

+		return err

+	}

+	defer b.docker.Unmount(container.ID)

 	b.tmpContainers[container.ID] = struct{}{}

 	comment := fmt.Sprintf("%s %s in %s", cmdName, origPaths, dest)

@@ -471,10 +477,6 @@ func (b *Builder) probeCache() (bool, error) {

 	logrus.Debugf("[BUILDER] Use cached version: %s", b.runConfig.Cmd)

 	b.image = string(cache)

-	// TODO: remove once Commit can take a tag parameter.

-	b.docker.Retain(b.id, b.image)

-	b.activeImages = append(b.activeImages, b.image)

-

 	return true, nil

 }

@@ -176,6 +176,25 @@ func (d Docker) BuilderCopy(cID string, destPath string, src builder.FileInfo, d

 	return fixPermissions(srcPath, destPath, rootUID, rootGID, destExists)

 }

+// Mount mounts the root filesystem for the container.

+func (d Docker) Mount(cID string) error {

+	c, err := d.Daemon.GetContainer(cID)

+	if err != nil {

+		return err

+	}

+	return d.Daemon.Mount(c)

+}

+

+// Unmount unmounts the root filesystem for the container.

+func (d Docker) Unmount(cID string) error {

+	c, err := d.Daemon.GetContainer(cID)

+	if err != nil {

+		return err

+	}

+	d.Daemon.Unmount(c)

+	return nil

+}

+

 // GetCachedImage returns a reference to a cached image whose parent equals `parent`

 // and runconfig equals `cfg`. A cache miss is expected to return an empty ID and a nil error.

 func (d Docker) GetCachedImage(imgID string, cfg *runconfig.Config) (string, error) {