@@ -145,7 +145,7 @@ func (daemon *Daemon) exportContainerRw(container *container.Container) (archive

 	}

 	return ioutils.NewReadCloserWrapper(archive, func() error {

 			archive.Close()

-			return daemon.layerStore.Unmount(container.ID)

+			return container.RWLayer.Unmount()

 		}),

 		nil

 }

@@ -98,7 +98,7 @@ func (daemon *Daemon) populateCommand(c *container.Container, env []string) erro

 		}

 	}

-	m, err := daemon.layerStore.Metadata(c.ID)

+	m, err := c.RWLayer.Metadata()

 	if err != nil {

 		return derr.ErrorCodeGetLayerMetadata.WithArgs(err)

 	}

@@ -7,6 +7,7 @@ import (

 	"github.com/docker/docker/container"

 	derr "github.com/docker/docker/errors"

 	"github.com/docker/docker/image"

+	"github.com/docker/docker/layer"

 	"github.com/docker/docker/pkg/idtools"

 	"github.com/docker/docker/pkg/stringid"

 	"github.com/docker/docker/volume"

@@ -95,6 +96,11 @@ func (daemon *Daemon) create(params types.ContainerCreateConfig) (*container.Con

 		}

 	}()

+	// Set RWLayer for container after mount labels have been set

+	if err := daemon.setRWLayer(container); err != nil {

+		return nil, err

+	}

+

 	if err := daemon.createContainerPlatformSpecificSettings(container, params.Config, params.HostConfig, img); err != nil {

 		return nil, err

 	}

@@ -126,6 +132,24 @@ func (daemon *Daemon) generateSecurityOpt(ipcMode containertypes.IpcMode, pidMod

 	return nil, nil

 }

+func (daemon *Daemon) setRWLayer(container *container.Container) error {

+	var layerID layer.ChainID

+	if container.ImageID != "" {

+		img, err := daemon.imageStore.Get(container.ImageID)

+		if err != nil {

+			return err

+		}

+		layerID = img.RootFS.ChainID()

+	}

+	rwLayer, err := daemon.layerStore.CreateRWLayer(container.ID, layerID, container.MountLabel, daemon.setupInitLayer)

+	if err != nil {

+		return err

+	}

+	container.RWLayer = rwLayer

+

+	return nil

+}

+

 // VolumeCreate creates a volume with the specified name, driver, and opts

 // This is called directly from the remote API

 func (daemon *Daemon) VolumeCreate(name, driverName string, opts map[string]string) (*types.Volume, error) {

@@ -323,6 +323,13 @@ func (daemon *Daemon) restore() error {

 			continue

 		}

+		rwlayer, err := daemon.layerStore.GetRWLayer(container.ID)

+		if err != nil {

+			logrus.Errorf("Failed to load container mount %v: %v", id, err)

+			continue

+		}

+		container.RWLayer = rwlayer

+

 		// Ignore the container if it does not support the current driver being used by the graph

 		if (container.Driver == "" && currentDriver == "aufs") || container.Driver == currentDriver {

 			logrus.Debugf("Loaded container %v", container.ID)

@@ -961,19 +968,7 @@ func (daemon *Daemon) Shutdown() error {

 // Mount sets container.BaseFS

 // (is it not set coming in? why is it unset?)

 func (daemon *Daemon) Mount(container *container.Container) error {

-	var layerID layer.ChainID

-	if container.ImageID != "" {

-		img, err := daemon.imageStore.Get(container.ImageID)

-		if err != nil {

-			return err

-		}

-		layerID = img.RootFS.ChainID()

-	}

-	rwlayer, err := daemon.layerStore.Mount(container.ID, layerID, container.GetMountLabel(), daemon.setupInitLayer)

-	if err != nil {

-		return err

-	}

-	dir, err := rwlayer.Path()

+	dir, err := container.RWLayer.Mount(container.GetMountLabel())

 	if err != nil {

 		return err

 	}

@@ -990,13 +985,12 @@ func (daemon *Daemon) Mount(container *container.Container) error {

 		}

 	}

 	container.BaseFS = dir // TODO: combine these fields

-	container.RWLayer = rwlayer

 	return nil

 }

 // Unmount unsets the container base filesystem

 func (daemon *Daemon) Unmount(container *container.Container) {

-	if err := daemon.layerStore.Unmount(container.ID); err != nil {

+	if err := container.RWLayer.Unmount(); err != nil {

 		logrus.Errorf("Error unmounting container %s: %s", container.ID, err)

 	}

 }

@@ -1029,7 +1023,7 @@ func (daemon *Daemon) unsubscribeToContainerStats(c *container.Container, ch cha

 }

 func (daemon *Daemon) changes(container *container.Container) ([]archive.Change, error) {

-	return daemon.layerStore.Changes(container.ID)

+	return container.RWLayer.Changes()

 }

 // TagImage creates a tag in the repository reponame, pointing to the image named

@@ -130,7 +130,7 @@ func (daemon *Daemon) cleanupContainer(container *container.Container, forceRemo

 		return derr.ErrorCodeRmFS.WithArgs(container.ID, err)

 	}

-	metadata, err := daemon.layerStore.DeleteMount(container.ID)

+	metadata, err := daemon.layerStore.ReleaseRWLayer(container.RWLayer)

 	layer.LogReleaseMetadata(metadata)

 	if err != nil && err != layer.ErrMountDoesNotExist {

 		return derr.ErrorCodeRmDriverFS.WithArgs(daemon.driver, container.ID, err)

@@ -163,7 +163,7 @@ func (daemon *Daemon) getInspectData(container *container.Container, size bool)

 	contJSONBase.GraphDriver.Name = container.Driver

-	graphDriverData, err := daemon.layerStore.Metadata(container.ID)

+	graphDriverData, err := container.RWLayer.Metadata()

 	if err != nil {

 		return nil, err

 	}

@@ -12,7 +12,6 @@ import (

 	"github.com/docker/distribution/digest"

 	"github.com/docker/docker/image"

 	"github.com/docker/docker/layer"

-	"github.com/docker/docker/pkg/archive"

 	"github.com/docker/docker/pkg/progress"

 	"golang.org/x/net/context"

 )

@@ -115,25 +114,18 @@ func (ls *mockLayerStore) Get(chainID layer.ChainID) (layer.Layer, error) {

 func (ls *mockLayerStore) Release(l layer.Layer) ([]layer.Metadata, error) {

 	return []layer.Metadata{}, nil

 }

-

-func (ls *mockLayerStore) Mount(id string, parent layer.ChainID, label string, init layer.MountInit) (layer.RWLayer, error) {

+func (ls *mockLayerStore) CreateRWLayer(string, layer.ChainID, string, layer.MountInit) (layer.RWLayer, error) {

 	return nil, errors.New("not implemented")

 }

-func (ls *mockLayerStore) Unmount(id string) error {

-	return errors.New("not implemented")

-}

-

-func (ls *mockLayerStore) DeleteMount(id string) ([]layer.Metadata, error) {

+func (ls *mockLayerStore) GetRWLayer(string) (layer.RWLayer, error) {

 	return nil, errors.New("not implemented")

-}

-func (ls *mockLayerStore) Changes(id string) ([]archive.Change, error) {

-	return nil, errors.New("not implemented")

 }

-func (ls *mockLayerStore) Metadata(id string) (map[string]string, error) {

+func (ls *mockLayerStore) ReleaseRWLayer(layer.RWLayer) ([]layer.Metadata, error) {

 	return nil, errors.New("not implemented")

+

 }

 type mockDownloadDescriptor struct {

@@ -31,6 +31,11 @@ var (

 	// attempted on a mount layer which does not exist.

 	ErrMountDoesNotExist = errors.New("mount does not exist")

+	// ErrMountNameConflict is used when a mount is attempted

+	// to be created but there is already a mount with the name

+	// used for creation.

+	ErrMountNameConflict = errors.New("mount already exists with name")

+

 	// ErrActiveMount is used when an operation on a

 	// mount is attempted but the layer is still

 	// mounted and the operation cannot be performed.

@@ -103,18 +108,33 @@ type Layer interface {

 type RWLayer interface {

 	TarStreamer

-	// Path returns the filesystem path to the writable

-	// layer.

-	Path() (string, error)

+	// Name of mounted layer

+	Name() string

 	// Parent returns the layer which the writable

 	// layer was created from.

 	Parent() Layer

+	// Mount mounts the RWLayer and returns the filesystem path

+	// the to the writable layer.

+	Mount(mountLabel string) (string, error)

+

+	// Unmount unmounts the RWLayer. This should be called

+	// for every mount. If there are multiple mount calls

+	// this operation will only decrement the internal mount counter.

+	Unmount() error

+

 	// Size represents the size of the writable layer

 	// as calculated by the total size of the files

 	// changed in the mutable layer.

 	Size() (int64, error)

+

+	// Changes returns the set of changes for the mutable layer

+	// from the base layer.

+	Changes() ([]archive.Change, error)

+

+	// Metadata returns the low level metadata for the mutable layer

+	Metadata() (map[string]string, error)

 }

 // Metadata holds information about a

@@ -147,11 +167,9 @@ type Store interface {

 	Get(ChainID) (Layer, error)

 	Release(Layer) ([]Metadata, error)

-	Mount(id string, parent ChainID, label string, init MountInit) (RWLayer, error)

-	Unmount(id string) error

-	DeleteMount(id string) ([]Metadata, error)

-	Changes(id string) ([]archive.Change, error)

-	Metadata(id string) (map[string]string, error)

+	CreateRWLayer(id string, parent ChainID, mountLabel string, initFunc MountInit) (RWLayer, error)

+	GetRWLayer(id string) (RWLayer, error)

+	ReleaseRWLayer(RWLayer) ([]Metadata, error)

 }

 // MetadataTransaction represents functions for setting layer metadata

@@ -5,7 +5,6 @@ import (

 	"fmt"

 	"io"

 	"io/ioutil"

-	"runtime"

 	"sync"

 	"github.com/Sirupsen/logrus"

@@ -144,6 +143,7 @@ func (ls *layerStore) loadMount(mount string) error {

 		mountID:    mountID,

 		initID:     initID,

 		layerStore: ls,

+		references: map[RWLayer]*referencedRWLayer{},

 	}

 	if parent != "" {

@@ -382,78 +382,15 @@ func (ls *layerStore) Release(l Layer) ([]Metadata, error) {

 	return ls.releaseLayer(layer)

 }

-func (ls *layerStore) mount(m *mountedLayer, mountLabel string) error {

-	dir, err := ls.driver.Get(m.mountID, mountLabel)

-	if err != nil {

-		return err

-	}

-	m.path = dir

-	m.activityCount++

-

-	return nil

-}

-

-func (ls *layerStore) saveMount(mount *mountedLayer) error {

-	if err := ls.store.SetMountID(mount.name, mount.mountID); err != nil {

-		return err

-	}

-

-	if mount.initID != "" {

-		if err := ls.store.SetInitID(mount.name, mount.initID); err != nil {

-			return err

-		}

-	}

-

-	if mount.parent != nil {

-		if err := ls.store.SetMountParent(mount.name, mount.parent.chainID); err != nil {

-			return err

-		}

-	}

-

-	ls.mounts[mount.name] = mount

-

-	return nil

-}

-

-func (ls *layerStore) initMount(graphID, parent, mountLabel string, initFunc MountInit) (string, error) {

-	// Use "<graph-id>-init" to maintain compatibility with graph drivers

-	// which are expecting this layer with this special name. If all

-	// graph drivers can be updated to not rely on knowing about this layer

-	// then the initID should be randomly generated.

-	initID := fmt.Sprintf("%s-init", graphID)

-

-	if err := ls.driver.Create(initID, parent, mountLabel); err != nil {

-		return "", err

-	}

-	p, err := ls.driver.Get(initID, "")

-	if err != nil {

-		return "", err

-	}

-

-	if err := initFunc(p); err != nil {

-		ls.driver.Put(initID)

-		return "", err

-	}

-

-	if err := ls.driver.Put(initID); err != nil {

-		return "", err

-	}

-

-	return initID, nil

-}

-

-func (ls *layerStore) Mount(name string, parent ChainID, mountLabel string, initFunc MountInit) (l RWLayer, err error) {

+func (ls *layerStore) CreateRWLayer(name string, parent ChainID, mountLabel string, initFunc MountInit) (RWLayer, error) {

 	ls.mountL.Lock()

 	defer ls.mountL.Unlock()

 	m, ok := ls.mounts[name]

 	if ok {

-		// Check if has path

-		if err := ls.mount(m, mountLabel); err != nil {

-			return nil, err

-		}

-		return m, nil

+		return nil, ErrMountNameConflict

 	}

+	var err error

 	var pid string

 	var p *roLayer

 	if string(parent) != "" {

@@ -473,17 +410,12 @@ func (ls *layerStore) Mount(name string, parent ChainID, mountLabel string, init

 		}()

 	}

-	mountID := name

-	if runtime.GOOS != "windows" {

-		// windows has issues if container ID doesn't match mount ID

-		mountID = stringid.GenerateRandomID()

-	}

-

 	m = &mountedLayer{

 		name:       name,

 		parent:     p,

-		mountID:    mountID,

+		mountID:    ls.mountID(name),

 		layerStore: ls,

+		references: map[RWLayer]*referencedRWLayer{},

 	}

 	if initFunc != nil {

@@ -502,44 +434,35 @@ func (ls *layerStore) Mount(name string, parent ChainID, mountLabel string, init

 		return nil, err

 	}

-	if err = ls.mount(m, mountLabel); err != nil {

-		return nil, err

-	}

-

-	return m, nil

+	return m.getReference(), nil

 }

-func (ls *layerStore) Unmount(name string) error {

+func (ls *layerStore) GetRWLayer(id string) (RWLayer, error) {

 	ls.mountL.Lock()

 	defer ls.mountL.Unlock()

-

-	m := ls.mounts[name]

-	if m == nil {

-		return ErrMountDoesNotExist

-	}

-

-	m.activityCount--

-

-	if err := ls.driver.Put(m.mountID); err != nil {

-		return err

+	mount, ok := ls.mounts[id]

+	if !ok {

+		return nil, ErrMountDoesNotExist

 	}

-	return nil

+	return mount.getReference(), nil

 }

-func (ls *layerStore) DeleteMount(name string) ([]Metadata, error) {

+func (ls *layerStore) ReleaseRWLayer(l RWLayer) ([]Metadata, error) {

 	ls.mountL.Lock()

 	defer ls.mountL.Unlock()

-

-	m := ls.mounts[name]

-	if m == nil {

-		return nil, ErrMountDoesNotExist

+	m, ok := ls.mounts[l.Name()]

+	if !ok {

+		return []Metadata{}, nil

 	}

-	if m.activityCount > 0 {

-		return nil, ErrActiveMount

+

+	if err := m.deleteReference(l); err != nil {

+		return nil, err

 	}

-	delete(ls.mounts, name)

+	if m.hasReferences() {

+		return []Metadata{}, nil

+	}

 	if err := ls.driver.Remove(m.mountID); err != nil {

 		logrus.Errorf("Error removing mounted layer %s: %s", m.name, err)

@@ -558,6 +481,8 @@ func (ls *layerStore) DeleteMount(name string) ([]Metadata, error) {

 		return nil, err

 	}

+	delete(ls.mounts, m.Name())

+

 	ls.layerL.Lock()

 	defer ls.layerL.Unlock()

 	if m.parent != nil {

@@ -567,18 +492,53 @@ func (ls *layerStore) DeleteMount(name string) ([]Metadata, error) {

 	return []Metadata{}, nil

 }

-func (ls *layerStore) Changes(name string) ([]archive.Change, error) {

-	ls.mountL.Lock()

-	m := ls.mounts[name]

-	ls.mountL.Unlock()

-	if m == nil {

-		return nil, ErrMountDoesNotExist

+func (ls *layerStore) saveMount(mount *mountedLayer) error {

+	if err := ls.store.SetMountID(mount.name, mount.mountID); err != nil {

+		return err

 	}

-	pid := m.initID

-	if pid == "" && m.parent != nil {

-		pid = m.parent.cacheID

+

+	if mount.initID != "" {

+		if err := ls.store.SetInitID(mount.name, mount.initID); err != nil {

+			return err

+		}

 	}

-	return ls.driver.Changes(m.mountID, pid)

+

+	if mount.parent != nil {

+		if err := ls.store.SetMountParent(mount.name, mount.parent.chainID); err != nil {

+			return err

+		}

+	}

+

+	ls.mounts[mount.name] = mount

+

+	return nil

+}

+

+func (ls *layerStore) initMount(graphID, parent, mountLabel string, initFunc MountInit) (string, error) {

+	// Use "<graph-id>-init" to maintain compatibility with graph drivers

+	// which are expecting this layer with this special name. If all

+	// graph drivers can be updated to not rely on knowing about this layer

+	// then the initID should be randomly generated.

+	initID := fmt.Sprintf("%s-init", graphID)

+

+	if err := ls.driver.Create(initID, parent, mountLabel); err != nil {

+		return "", err

+	}

+	p, err := ls.driver.Get(initID, "")

+	if err != nil {

+		return "", err

+	}

+

+	if err := initFunc(p); err != nil {

+		ls.driver.Put(initID)

+		return "", err

+	}

+

+	if err := ls.driver.Put(initID); err != nil {

+		return "", err

+	}

+

+	return initID, nil

 }

 func (ls *layerStore) assembleTar(graphID string, metadata io.ReadCloser, size *int64) (io.ReadCloser, error) {

@@ -621,17 +581,6 @@ func (ls *layerStore) assembleTar(graphID string, metadata io.ReadCloser, size *

 	return pR, nil

 }

-// Metadata returns the low level metadata from the mount with the given name

-func (ls *layerStore) Metadata(name string) (map[string]string, error) {

-	ls.mountL.Lock()

-	m := ls.mounts[name]

-	ls.mountL.Unlock()

-	if m == nil {

-		return nil, ErrMountDoesNotExist

-	}

-	return ls.driver.GetMetadata(m.mountID)

-}

-

 type naiveDiffPathDriver struct {

 	graphdriver.Driver

 }

@@ -82,12 +82,12 @@ type layerInit func(root string) error

 func createLayer(ls Store, parent ChainID, layerFunc layerInit) (Layer, error) {

 	containerID := stringid.GenerateRandomID()

-	mount, err := ls.Mount(containerID, parent, "", nil)

+	mount, err := ls.CreateRWLayer(containerID, parent, "", nil)

 	if err != nil {

 		return nil, err

 	}

-	path, err := mount.Path()

+	path, err := mount.Mount("")

 	if err != nil {

 		return nil, err

 	}

@@ -107,11 +107,11 @@ func createLayer(ls Store, parent ChainID, layerFunc layerInit) (Layer, error) {

 		return nil, err

 	}

-	if err := ls.Unmount(containerID); err != nil {

+	if err := mount.Unmount(); err != nil {

 		return nil, err

 	}

-	if _, err := ls.DeleteMount(containerID); err != nil {

+	if _, err := ls.ReleaseRWLayer(mount); err != nil {

 		return nil, err

 	}

@@ -171,6 +171,13 @@ func getCachedLayer(l Layer) *roLayer {

 	return l.(*roLayer)

 }

+func getMountLayer(l RWLayer) *mountedLayer {

+	if rl, ok := l.(*referencedRWLayer); ok {

+		return rl.mountedLayer

+	}

+	return l.(*mountedLayer)

+}

+

 func createMetadata(layers ...Layer) []Metadata {

 	metadata := make([]Metadata, len(layers))

 	for i := range layers {

@@ -270,12 +277,12 @@ func TestMountAndRegister(t *testing.T) {

 	size, _ := layer.Size()

 	t.Logf("Layer size: %d", size)

-	mount2, err := ls.Mount("new-test-mount", layer.ChainID(), "", nil)

+	mount2, err := ls.CreateRWLayer("new-test-mount", layer.ChainID(), "", nil)

 	if err != nil {

 		t.Fatal(err)

 	}

-	path2, err := mount2.Path()

+	path2, err := mount2.Mount("")

 	if err != nil {

 		t.Fatal(err)

 	}

@@ -289,11 +296,11 @@ func TestMountAndRegister(t *testing.T) {

 		t.Fatalf("Wrong file data, expected %q, got %q", expected, string(b))

 	}

-	if err := ls.Unmount("new-test-mount"); err != nil {

+	if err := mount2.Unmount(); err != nil {

 		t.Fatal(err)

 	}

-	if _, err := ls.DeleteMount("new-test-mount"); err != nil {

+	if _, err := ls.ReleaseRWLayer(mount2); err != nil {

 		t.Fatal(err)

 	}

 }

@@ -370,12 +377,12 @@ func TestStoreRestore(t *testing.T) {

 		t.Fatal(err)

 	}

-	m, err := ls.Mount("some-mount_name", layer3.ChainID(), "", nil)

+	m, err := ls.CreateRWLayer("some-mount_name", layer3.ChainID(), "", nil)

 	if err != nil {

 		t.Fatal(err)

 	}

-	path, err := m.Path()

+	path, err := m.Mount("")

 	if err != nil {

 		t.Fatal(err)

 	}

@@ -383,11 +390,14 @@ func TestStoreRestore(t *testing.T) {

 	if err := ioutil.WriteFile(filepath.Join(path, "testfile.txt"), []byte("nothing here"), 0644); err != nil {

 		t.Fatal(err)

 	}

+	assertActivityCount(t, m, 1)

-	if err := ls.Unmount("some-mount_name"); err != nil {

+	if err := m.Unmount(); err != nil {

 		t.Fatal(err)

 	}

+	assertActivityCount(t, m, 0)

+

 	ls2, err := NewStore(ls.(*layerStore).store, ls.(*layerStore).driver)

 	if err != nil {

 		t.Fatal(err)

@@ -400,18 +410,39 @@ func TestStoreRestore(t *testing.T) {

 	assertLayerEqual(t, layer3b, layer3)

-	// Mount again with same name, should already be loaded

-	m2, err := ls2.Mount("some-mount_name", layer3b.ChainID(), "", nil)

-	if err != nil {

+	// Create again with same name, should return error

+	if _, err := ls2.CreateRWLayer("some-mount_name", layer3b.ChainID(), "", nil); err == nil {

+		t.Fatal("Expected error creating mount with same name")

+	} else if err != ErrMountNameConflict {

 		t.Fatal(err)

 	}

-	path2, err := m2.Path()

+	m2, err := ls2.GetRWLayer("some-mount_name")

 	if err != nil {

 		t.Fatal(err)

 	}

-	b, err := ioutil.ReadFile(filepath.Join(path2, "testfile.txt"))

+	if mountPath, err := m2.Mount(""); err != nil {

+		t.Fatal(err)

+	} else if path != mountPath {

+		t.Fatalf("Unexpected path %s, expected %s", mountPath, path)

+	}

+

+	assertActivityCount(t, m2, 1)

+

+	if mountPath, err := m2.Mount(""); err != nil {

+		t.Fatal(err)

+	} else if path != mountPath {

+		t.Fatalf("Unexpected path %s, expected %s", mountPath, path)

+	}

+	assertActivityCount(t, m2, 2)

+	if err := m2.Unmount(); err != nil {

+		t.Fatal(err)

+	}

+

+	assertActivityCount(t, m2, 1)

+

+	b, err := ioutil.ReadFile(filepath.Join(path, "testfile.txt"))

 	if err != nil {

 		t.Fatal(err)

 	}

@@ -419,11 +450,19 @@ func TestStoreRestore(t *testing.T) {

 		t.Fatalf("Unexpected content %q, expected %q", string(b), expected)

 	}

-	if err := ls2.Unmount("some-mount_name"); err != nil {

+	if err := m2.Unmount(); err != nil {

+		t.Fatal(err)

+	}

+

+	assertActivityCount(t, m2, 0)

+

+	if metadata, err := ls2.ReleaseRWLayer(m2); err != nil {

 		t.Fatal(err)

+	} else if len(metadata) != 0 {

+		t.Fatalf("Unexpectedly deleted layers: %#v", metadata)

 	}

-	if metadata, err := ls2.DeleteMount("some-mount_name"); err != nil {

+	if metadata, err := ls2.ReleaseRWLayer(m2); err != nil {

 		t.Fatal(err)

 	} else if len(metadata) != 0 {

 		t.Fatalf("Unexpectedly deleted layers: %#v", metadata)

@@ -627,6 +666,13 @@ func assertReferences(t *testing.T, references ...Layer) {

 	}

 }

+func assertActivityCount(t *testing.T, l RWLayer, expected int) {

+	rl := l.(*referencedRWLayer)

+	if rl.activityCount != expected {

+		t.Fatalf("Unexpected activity count %d, expected %d", rl.activityCount, expected)

+	}

+}

+

 func TestRegisterExistingLayer(t *testing.T) {

 	ls, cleanup := newTestStore(t)

 	defer cleanup()

new file mode 100644

@@ -0,0 +1,9 @@

+// +build linux freebsd darwin

+

+package layer

+

+import "github.com/docker/docker/pkg/stringid"

+

+func (ls *layerStore) mountID(name string) string {

+	return stringid.GenerateRandomID()

+}

@@ -89,3 +89,8 @@ func (ls *layerStore) RegisterDiffID(graphID string, size int64) (Layer, error)

 	return layer.getReference(), nil

 }

+

+func (ls *layerStore) mountID(name string) string {

+	// windows has issues if container ID doesn't match mount ID

+	return name

+}

@@ -14,30 +14,33 @@ import (

 	"github.com/vbatts/tar-split/tar/storage"

 )

-func (ls *layerStore) MountByGraphID(name string, graphID string, parent ChainID) (l RWLayer, err error) {

+// CreateRWLayerByGraphID creates a RWLayer in the layer store using

+// the provided name with the given graphID. To get the RWLayer

+// after migration the layer may be retrieved by the given name.

+func (ls *layerStore) CreateRWLayerByGraphID(name string, graphID string, parent ChainID) (err error) {

 	ls.mountL.Lock()

 	defer ls.mountL.Unlock()

 	m, ok := ls.mounts[name]

 	if ok {

 		if m.parent.chainID != parent {

-			return nil, errors.New("name conflict, mismatched parent")

+			return errors.New("name conflict, mismatched parent")

 		}

 		if m.mountID != graphID {

-			return nil, errors.New("mount already exists")

+			return errors.New("mount already exists")

 		}

-		return m, nil

+		return nil

 	}

 	if !ls.driver.Exists(graphID) {

-		return nil, errors.New("graph ID does not exist")

+		return errors.New("graph ID does not exist")

 	}

 	var p *roLayer

 	if string(parent) != "" {

 		p = ls.get(parent)

 		if p == nil {

-			return nil, ErrLayerDoesNotExist

+			return ErrLayerDoesNotExist

 		}

 		// Release parent chain if error

@@ -57,6 +60,7 @@ func (ls *layerStore) MountByGraphID(name string, graphID string, parent ChainID

 		parent:     p,

 		mountID:    graphID,

 		layerStore: ls,

+		references: map[RWLayer]*referencedRWLayer{},

 	}

 	// Check for existing init layer

@@ -66,15 +70,10 @@ func (ls *layerStore) MountByGraphID(name string, graphID string, parent ChainID

 	}

 	if err = ls.saveMount(m); err != nil {

-		return nil, err

-	}

-

-	// TODO: provide a mount label

-	if err = ls.mount(m, ""); err != nil {

-		return nil, err

+		return err

 	}

-	return m, nil

+	return nil

 }

 func (ls *layerStore) migrateLayer(tx MetadataTransaction, tarDataFile string, layer *roLayer) error {

@@ -303,12 +303,20 @@ func TestMountMigration(t *testing.T) {

 		t.Fatal(err)

 	}

-	rwLayer1, err := ls.(*layerStore).MountByGraphID("migration-mount", containerID, layer1.ChainID())

+	if err := ls.(*layerStore).CreateRWLayerByGraphID("migration-mount", containerID, layer1.ChainID()); err != nil {

+		t.Fatal(err)

+	}

+

+	rwLayer1, err := ls.GetRWLayer("migration-mount")

 	if err != nil {

 		t.Fatal(err)

 	}

-	changes, err := ls.Changes("migration-mount")

+	if _, err := rwLayer1.Mount(""); err != nil {

+		t.Fatal(err)

+	}

+

+	changes, err := rwLayer1.Changes()

 	if err != nil {

 		t.Fatal(err)

 	}

@@ -341,39 +349,63 @@ func TestMountMigration(t *testing.T) {

 		Kind: archive.ChangeAdd,

 	})

-	if expectedCount := 1; rwLayer1.(*mountedLayer).activityCount != expectedCount {

-		t.Fatalf("Wrong activity count %d, expected %d", rwLayer1.(*mountedLayer).activityCount, expectedCount)

+	assertActivityCount(t, rwLayer1, 1)

+

+	if _, err := ls.CreateRWLayer("migration-mount", layer1.ChainID(), "", nil); err == nil {

+		t.Fatal("Expected error creating mount with same name")

+	} else if err != ErrMountNameConflict {

+		t.Fatal(err)

 	}

-	rwLayer2, err := ls.Mount("migration-mount", layer1.ChainID(), "", nil)

+	rwLayer2, err := ls.GetRWLayer("migration-mount")

 	if err != nil {

 		t.Fatal(err)

 	}

-	if rwLayer1 != rwLayer2 {

-		t.Fatalf("Wrong rwlayer %v, expected %v", rwLayer2, rwLayer1)

+	if getMountLayer(rwLayer1) != getMountLayer(rwLayer2) {

+		t.Fatal("Expected same layer from get with same name as from migrate")

+	}

+

+	if _, err := rwLayer2.Mount(""); err != nil {

+		t.Fatal(err)

 	}

-	if expectedCount := 2; rwLayer2.(*mountedLayer).activityCount != expectedCount {

-		t.Fatalf("Wrong activity count %d, expected %d", rwLayer2.(*mountedLayer).activityCount, expectedCount)

+	assertActivityCount(t, rwLayer2, 1)

+	assertActivityCount(t, rwLayer1, 1)

+

+	if _, err := rwLayer2.Mount(""); err != nil {

+		t.Fatal(err)

 	}

+	assertActivityCount(t, rwLayer2, 2)

+	assertActivityCount(t, rwLayer1, 1)

+

 	if metadata, err := ls.Release(layer1); err != nil {

 		t.Fatal(err)

 	} else if len(metadata) > 0 {

 		t.Fatalf("Expected no layers to be deleted, deleted %#v", metadata)

 	}

-	if err := ls.Unmount("migration-mount"); err != nil {

+	if err := rwLayer1.Unmount(); err != nil {

+		t.Fatal(err)

+	}

+	assertActivityCount(t, rwLayer2, 2)

+	assertActivityCount(t, rwLayer1, 0)

+

+	if _, err := ls.ReleaseRWLayer(rwLayer1); err != nil {

+		t.Fatal(err)

+	}

+

+	if err := rwLayer2.Unmount(); err != nil {

 		t.Fatal(err)

 	}

-	if _, err := ls.DeleteMount("migration-mount"); err == nil {

+	if _, err := ls.ReleaseRWLayer(rwLayer2); err == nil {

 		t.Fatal("Expected error deleting active mount")

 	}

-	if err := ls.Unmount("migration-mount"); err != nil {

+	if err := rwLayer2.Unmount(); err != nil {