func (daemon *Daemon) createRootfs(container *Container) error {
	// Step 1: create the container directory.
	// This doubles as a barrier to avoid race conditions.
	rootUID, rootGID, err := idtools.GetRootUIDGID(daemon.uidMaps, daemon.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAs(container.root, 0700, rootUID, rootGID); err != nil {
		return err
	}
	initID := fmt.Sprintf("%s-init", container.ID)
	if err := daemon.driver.Create(initID, container.ImageID); err != nil {
		return err
	}
	initPath, err := daemon.driver.Get(initID, "")
	if err != nil {
		return err
	}

	if err := setupInitLayer(initPath, rootUID, rootGID); err != nil {
		daemon.driver.Put(initID)
		return err
	}

	// We want to unmount init layer before we take snapshot of it
	// for the actual container.
	daemon.driver.Put(initID)

	if err := daemon.driver.Create(container.ID, initID); err != nil {
		return err
	}
	return nil
}

// Get returns the mountpoint for the given id after creating the target directories if necessary.
func (d *Driver) Get(id, mountLabel string) (string, error) {
	mountpoint := d.mountPath(id)
	filesystem := d.zfsPath(id)
	options := label.FormatMountLabel("", mountLabel)
	logrus.Debugf(`[zfs] mount("%s", "%s", "%s")`, filesystem, mountpoint, options)

	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return "", err
	}
	// Create the target directories if they don't exist
	if err := idtools.MkdirAllAs(mountpoint, 0755, rootUID, rootGID); err != nil {
		return "", err
	}

	if err := mount.Mount(filesystem, mountpoint, "zfs", options); err != nil {
		return "", fmt.Errorf("error creating zfs mount of %s to %s: %v", filesystem, mountpoint, err)
	}
	// this could be our first mount after creation of the filesystem, and the root dir may still have root
	// permissions instead of the remapped root uid:gid (if user namespaces are enabled):
	if err := os.Chown(mountpoint, rootUID, rootGID); err != nil {
		return "", fmt.Errorf("error modifying zfs mountpoint (%s) directory ownership: %v", mountpoint, err)
	}

	return mountpoint, nil
}

// Create prepares the filesystem for the VFS driver and copies the directory for the given id under the parent.
func (d *Driver) Create(id, parent, mountLabel string) error {
	dir := d.dir(id)
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAllAs(filepath.Dir(dir), 0700, rootUID, rootGID); err != nil {
		return err
	}
	if err := idtools.MkdirAs(dir, 0755, rootUID, rootGID); err != nil {
		return err
	}
	opts := []string{"level:s0"}
	if _, mountLabel, err := label.InitLabels(opts); err == nil {
		label.SetFileLabel(dir, mountLabel)
	}
	if parent == "" {
		return nil
	}
	parentDir, err := d.Get(parent, "")
	if err != nil {
		return fmt.Errorf("%s: %s", parent, err)
	}
	if err := chrootarchive.CopyWithTar(parentDir, dir); err != nil {
		return err
	}
	return nil
}

// Init returns a new BTRFS driver.
// An error is returned if BTRFS is not supported.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}

	if fsMagic != graphdriver.FsMagicBtrfs {
		return nil, graphdriver.ErrPrerequisites
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	driver := &Driver{
		home:    home,
		uidMaps: uidMaps,
		gidMaps: gidMaps,
	}

	return graphdriver.NewNaiveDiffDriver(driver, uidMaps, gidMaps), nil
}

// Create the filesystem with given id.
func (d *Driver) Create(id, parent, mountLabel string) error {
	subvolumes := path.Join(d.home, "subvolumes")
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAllAs(subvolumes, 0700, rootUID, rootGID); err != nil {
		return err
	}
	if parent == "" {
		if err := subvolCreate(subvolumes, id); err != nil {
			return err
		}
	} else {
		parentDir, err := d.Get(parent, "")
		if err != nil {
			return err
		}
		if err := subvolSnapshot(parentDir, subvolumes, id); err != nil {
			return err
		}
	}

	// if we have a remapped root (user namespaces enabled), change the created snapshot
	// dir ownership to match
	if rootUID != 0 || rootGID != 0 {
		if err := os.Chown(path.Join(subvolumes, id), rootUID, rootGID); err != nil {
			return err
		}
	}

	return label.Relabel(path.Join(subvolumes, id), mountLabel, false)
}

// Init returns a new AUFS driver.
// An error is returned if AUFS is not supported.
func Init(root string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	// Try to load the aufs kernel module
	if err := supportsAufs(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	fsMagic, err := graphdriver.GetFSMagic(root)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	for _, magic := range incompatibleFsMagic {
		if fsMagic == magic {
			return nil, graphdriver.ErrIncompatibleFS
		}
	}

	paths := []string{
		"mnt",
		"diff",
		"layers",
	}

	a := &Driver{
		root:      root,
		uidMaps:   uidMaps,
		gidMaps:   gidMaps,
		pathCache: make(map[string]string),
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the root aufs driver dir and return
	// if it already exists
	// If not populate the dir structure
	if err := idtools.MkdirAllAs(root, 0700, rootUID, rootGID); err != nil {
		if os.IsExist(err) {
			return a, nil
		}
		return nil, err
	}

	if err := mountpk.MakePrivate(root); err != nil {
		return nil, err
	}

	// Populate the dir structure
	for _, p := range paths {
		if err := idtools.MkdirAllAs(path.Join(root, p), 0700, rootUID, rootGID); err != nil {
			return nil, err
		}
	}
	return a, nil
}

// Create prepares the filesystem for the VFS driver and copies the directory for the given id under the parent.
func (d *Driver) Create(id, parent, mountLabel string, storageOpt map[string]string) error {
	if len(storageOpt) != 0 {
		return fmt.Errorf("--storage-opt is not supported for vfs")
	}

	dir := d.dir(id)
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAllAs(filepath.Dir(dir), 0700, rootUID, rootGID); err != nil {
		return err
	}
	if err := idtools.MkdirAs(dir, 0755, rootUID, rootGID); err != nil {
		return err
	}
	opts := []string{"level:s0"}
	if _, mountLabel, err := label.InitLabels(opts); err == nil {
		label.SetFileLabel(dir, mountLabel)
	}
	if parent == "" {
		return nil
	}
	parentDir, err := d.Get(parent, "")
	if err != nil {
		return fmt.Errorf("%s: %s", parent, err)
	}
	if err := CopyWithTar(parentDir, dir); err != nil {
		return err
	}
	return nil
}

// CreateDaemonRoot creates the root for the daemon
func CreateDaemonRoot(config *Config) error {
	// get the canonical path to the Docker root directory
	var realRoot string
	if _, err := os.Stat(config.Root); err != nil && os.IsNotExist(err) {
		realRoot = config.Root
	} else {
		realRoot, err = fileutils.ReadSymlinkedDirectory(config.Root)
		if err != nil {
			return fmt.Errorf("Unable to get the full path to root (%s): %s", config.Root, err)
		}
	}

	uidMaps, gidMaps, err := setupRemappedRoot(config)
	if err != nil {
		return err
	}
	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return err
	}

	if err := setupDaemonRoot(config, realRoot, rootUID, rootGID); err != nil {
		return err
	}

	return nil
}

// NewGraph instantiates a new graph at the given root path in the filesystem.
// `root` will be created if it doesn't exist.
func NewGraph(root string, driver graphdriver.Driver, uidMaps, gidMaps []idtools.IDMap) (*Graph, error) {
	abspath, err := filepath.Abs(root)
	if err != nil {
		return nil, err
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the root directory if it doesn't exists
	if err := idtools.MkdirAllAs(root, 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	graph := &Graph{
		root:       abspath,
		idIndex:    truncindex.NewTruncIndex([]string{}),
		driver:     driver,
		retained:   &retainedLayers{layerHolders: make(map[string]map[string]struct{})},
		uidMaps:    uidMaps,
		gidMaps:    gidMaps,
		parentRefs: make(map[string]int),
	}

	// Windows does not currently support tarsplit functionality.
	if runtime.GOOS == "windows" {
		graph.tarSplitDisabled = true
	}

	if err := graph.restore(); err != nil {
		return nil, err
	}
	return graph, nil
}

// Init returns a new BTRFS driver.
// An error is returned if BTRFS is not supported.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	rootdir := path.Dir(home)

	var buf syscall.Statfs_t
	if err := syscall.Statfs(rootdir, &buf); err != nil {
		return nil, err
	}

	if graphdriver.FsMagic(buf.Type) != graphdriver.FsMagicBtrfs {
		return nil, graphdriver.ErrPrerequisites
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	driver := &Driver{
		home:    home,
		uidMaps: uidMaps,
		gidMaps: gidMaps,
	}

	return graphdriver.NewNaiveDiffDriver(driver, uidMaps, gidMaps), nil
}

// Create the filesystem with given id.
func (d *Driver) Create(id, parent, mountLabel string) error {
	subvolumes := path.Join(d.home, "subvolumes")
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAllAs(subvolumes, 0700, rootUID, rootGID); err != nil {
		return err
	}
	if parent == "" {
		if err := subvolCreate(subvolumes, id); err != nil {
			return err
		}
	} else {
		parentDir, err := d.Get(parent, "")
		if err != nil {
			return err
		}
		if err := subvolSnapshot(parentDir, subvolumes, id); err != nil {
			return err
		}
	}

	return label.Relabel(path.Join(subvolumes, id), mountLabel, false)
}

// Init returns the a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If a overlay filesystem is not supported over a existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	opts, err := parseOptions(options)
	if err != nil {
		return nil, err
	}

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	// require kernel 4.0.0 to ensure multiple lower dirs are supported
	v, err := kernel.GetKernelVersion()
	if err != nil {
		return nil, err
	}
	if kernel.CompareKernelVersion(*v, kernel.VersionInfo{Kernel: 4, Major: 0, Minor: 0}) < 0 {
		if !opts.overrideKernelCheck {
			return nil, graphdriver.ErrNotSupported
		}
		logrus.Warnf("Using pre-4.0.0 kernel for overlay2, mount failures may require kernel update")
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	// check if they are running over btrfs, aufs, zfs, overlay, or ecryptfs
	switch fsMagic {
	case graphdriver.FsMagicBtrfs, graphdriver.FsMagicAufs, graphdriver.FsMagicZfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicEcryptfs:
		logrus.Errorf("'overlay2' is not supported over %s", backingFs)
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(path.Join(home, linkDir), 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	d := &Driver{
		home:    home,
		uidMaps: uidMaps,
		gidMaps: gidMaps,
		ctr:     graphdriver.NewRefCounter(graphdriver.NewFsChecker(graphdriver.FsMagicOverlay)),
	}

	return d, nil
}

// Create the filesystem with given id.
func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
	subvolumes := path.Join(d.home, "subvolumes")
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return err
	}
	if err := idtools.MkdirAllAs(subvolumes, 0700, rootUID, rootGID); err != nil {
		return err
	}
	if parent == "" {
		if err := subvolCreate(subvolumes, id); err != nil {
			return err
		}
	} else {
		parentDir := d.subvolumesDirID(parent)
		st, err := os.Stat(parentDir)
		if err != nil {
			return err
		}
		if !st.IsDir() {
			return fmt.Errorf("%s: not a directory", parentDir)
		}
		if err := subvolSnapshot(parentDir, subvolumes, id); err != nil {
			return err
		}
	}

	var storageOpt map[string]string
	if opts != nil {
		storageOpt = opts.StorageOpt
	}

	if _, ok := storageOpt["size"]; ok {
		driver := &Driver{}
		if err := d.parseStorageOpt(storageOpt, driver); err != nil {
			return err
		}
		if err := d.setStorageSize(path.Join(subvolumes, id), driver); err != nil {
			return err
		}
	}

	// if we have a remapped root (user namespaces enabled), change the created snapshot
	// dir ownership to match
	if rootUID != 0 || rootGID != 0 {
		if err := os.Chown(path.Join(subvolumes, id), rootUID, rootGID); err != nil {
			return err
		}
	}

	mountLabel := ""
	if opts != nil {
		mountLabel = opts.MountLabel
	}

	return label.Relabel(path.Join(subvolumes, id), mountLabel, false)
}

// Get creates and mounts the required file system for the given id and returns the mount path.
func (d *Driver) Get(id string, mountLabel string) (string, error) {
	// Protect the d.active from concurrent access
	d.Lock()
	defer d.Unlock()

	mount := d.active[id]
	if mount != nil {
		mount.count++
		return mount.path, nil
	}

	mount = &ActiveMount{count: 1}

	dir := d.dir(id)
	if _, err := os.Stat(dir); err != nil {
		return "", err
	}

	// If id has a root, just return it
	rootDir := path.Join(dir, "root")
	if _, err := os.Stat(rootDir); err == nil {
		mount.path = rootDir
		d.active[id] = mount
		return mount.path, nil
	}

	lowerID, err := ioutil.ReadFile(path.Join(dir, "lower-id"))
	if err != nil {
		return "", err
	}
	lowerDir := path.Join(d.dir(string(lowerID)), "root")
	upperDir := path.Join(dir, "upper")
	workDir := path.Join(dir, "work")
	mergedDir := path.Join(dir, "merged")

	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, upperDir, workDir)
	if err := syscall.Mount("overlay", mergedDir, "overlay", 0, label.FormatMountLabel(opts, mountLabel)); err != nil {
		return "", fmt.Errorf("error creating overlay mount to %s: %v", mergedDir, err)
	}
	// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a
	// user namespace requires this to move a directory from lower to upper.
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return "", err
	}

	if err := os.Chown(path.Join(workDir, "work"), rootUID, rootGID); err != nil {
		return "", err
	}
	mount.path = mergedDir
	mount.mounted = true
	d.active[id] = mount

	return mount.path, nil
}

// Get creates and mounts the required file system for the given id and returns the mount path.
func (d *Driver) Get(id string, mountLabel string) (string, error) {
	dir := d.dir(id)
	if _, err := os.Stat(dir); err != nil {
		return "", err
	}

	// If id has a root, just return it
	rootDir := path.Join(dir, "root")
	if _, err := os.Stat(rootDir); err == nil {
		d.pathCacheLock.Lock()
		d.pathCache[id] = rootDir
		d.pathCacheLock.Unlock()
		return rootDir, nil
	}

	lowerID, err := ioutil.ReadFile(path.Join(dir, "lower-id"))
	if err != nil {
		return "", err
	}
	lowerDir := path.Join(d.dir(string(lowerID)), "root")
	upperDir := path.Join(dir, "upper")
	workDir := path.Join(dir, "work")
	mergedDir := path.Join(dir, "merged")

	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, upperDir, workDir)

	// if it's mounted already, just return
	mounted, err := d.mounted(mergedDir)
	if err != nil {
		return "", err
	}
	if mounted {
		return mergedDir, nil
	}

	if err := syscall.Mount("overlay", mergedDir, "overlay", 0, label.FormatMountLabel(opts, mountLabel)); err != nil {
		return "", fmt.Errorf("error creating overlay mount to %s: %v", mergedDir, err)
	}
	// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a
	// user namespace requires this to move a directory from lower to upper.
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return "", err
	}

	if err := os.Chown(path.Join(workDir, "work"), rootUID, rootGID); err != nil {
		return "", err
	}

	d.pathCacheLock.Lock()
	d.pathCache[id] = mergedDir
	d.pathCacheLock.Unlock()

	return mergedDir, nil
}

// mktemp creates a temporary sub-directory inside the graph's filesystem.
func (graph *Graph) mktemp() (string, error) {
	dir := filepath.Join(graph.root, "_tmp", stringid.GenerateNonCryptoID())
	rootUID, rootGID, err := idtools.GetRootUIDGID(graph.uidMaps, graph.gidMaps)
	if err != nil {
		return "", err
	}
	if err := idtools.MkdirAllAs(dir, 0700, rootUID, rootGID); err != nil {
		return "", err
	}
	return dir, nil
}

// Init returns the NaiveDiffDriver, a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If a overlay filesystem is not supported over a existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	// check if they are running over btrfs, aufs, zfs or overlay
	switch fsMagic {
	case graphdriver.FsMagicBtrfs:
		logrus.Error("'overlay' is not supported over btrfs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicAufs:
		logrus.Error("'overlay' is not supported over aufs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicZfs:
		logrus.Error("'overlay' is not supported over zfs.")
		return nil, graphdriver.ErrIncompatibleFS
	case graphdriver.FsMagicOverlay:
		logrus.Error("'overlay' is not supported over overlay.")
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	d := &Driver{
		home:      home,
		pathCache: make(map[string]string),
		uidMaps:   uidMaps,
		gidMaps:   gidMaps,
		ctr:       graphdriver.NewRefCounter(),
	}

	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil
}

// Get creates and mounts the required file system for the given id and returns the mount path.
func (d *Driver) Get(id string, mountLabel string) (s string, err error) {
	dir := d.dir(id)
	if _, err := os.Stat(dir); err != nil {
		return "", err
	}

	diffDir := path.Join(dir, "diff")
	lowers, err := ioutil.ReadFile(path.Join(dir, lowerFile))
	if err != nil {
		// If no lower, just return diff directory
		if os.IsNotExist(err) {
			return diffDir, nil
		}
		return "", err
	}

	mergedDir := path.Join(dir, "merged")
	if count := d.ctr.Increment(mergedDir); count > 1 {
		return mergedDir, nil
	}
	defer func() {
		if err != nil {
			if c := d.ctr.Decrement(mergedDir); c <= 0 {
				syscall.Unmount(mergedDir, 0)
			}
		}
	}()

	workDir := path.Join(dir, "work")
	opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", string(lowers), path.Join(id, "diff"), path.Join(id, "work"))
	mountLabel = label.FormatMountLabel(opts, mountLabel)
	if len(mountLabel) > syscall.Getpagesize() {
		return "", fmt.Errorf("cannot mount layer, mount label too large %d", len(mountLabel))
	}

	if err := mountFrom(d.home, "overlay", path.Join(id, "merged"), "overlay", mountLabel); err != nil {
		return "", fmt.Errorf("error creating overlay mount to %s: %v", mergedDir, err)
	}

	// chown "workdir/work" to the remapped root UID/GID. Overlay fs inside a
	// user namespace requires this to move a directory from lower to upper.
	rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps)
	if err != nil {
		return "", err
	}

	if err := os.Chown(path.Join(workDir, "work"), rootUID, rootGID); err != nil {
		return "", err
	}

	return mergedDir, nil
}

// Init returns the NaiveDiffDriver, a native diff driver for overlay filesystem.
// If overlay filesystem is not supported on the host, graphdriver.ErrNotSupported is returned as error.
// If an overlay filesystem is not supported over an existing filesystem then error graphdriver.ErrIncompatibleFS is returned.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {

	if err := supportsOverlay(); err != nil {
		return nil, graphdriver.ErrNotSupported
	}

	fsMagic, err := graphdriver.GetFSMagic(home)
	if err != nil {
		return nil, err
	}
	if fsName, ok := graphdriver.FsNames[fsMagic]; ok {
		backingFs = fsName
	}

	switch fsMagic {
	case graphdriver.FsMagicAufs, graphdriver.FsMagicBtrfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs, graphdriver.FsMagicEcryptfs:
		logrus.Errorf("'overlay' is not supported over %s", backingFs)
		return nil, graphdriver.ErrIncompatibleFS
	}

	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	// Create the driver home dir
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil && !os.IsExist(err) {
		return nil, err
	}

	if err := mount.MakePrivate(home); err != nil {
		return nil, err
	}

	supportsDType, err := fsutils.SupportsDType(home)
	if err != nil {
		return nil, err
	}
	if !supportsDType {
		// not a fatal error until v1.16 (#27443)
		logrus.Warn(overlayutils.ErrDTypeNotSupported("overlay", backingFs))
	}

	d := &Driver{
		home:          home,
		uidMaps:       uidMaps,
		gidMaps:       gidMaps,
		ctr:           graphdriver.NewRefCounter(graphdriver.NewFsChecker(graphdriver.FsMagicOverlay)),
		supportsDType: supportsDType,
	}

	return NaiveDiffDriverWithApply(d, uidMaps, gidMaps), nil
}

// Init returns a new VFS driver.
// This sets the home directory for the driver and returns NaiveDiffDriver.
func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (graphdriver.Driver, error) {
	d := &Driver{
		home:    home,
		uidMaps: uidMaps,
		gidMaps: gidMaps,
	}
	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
	if err != nil {
		return nil, err
	}
	if err := idtools.MkdirAllAs(home, 0700, rootUID, rootGID); err != nil {
		return nil, err
	}
	return graphdriver.NewNaiveDiffDriver(d, uidMaps, gidMaps), nil
}