From 23e5c94cfb26eb72c097892712d3dbaa93ee9bc0 Mon Sep 17 00:00:00 2001 From: Derek McGowan Date: Mon, 16 May 2016 17:02:51 -0700 Subject: [PATCH] Add separate overlay2 driver Adds a new overlay driver which uses multiple lower directories to create the union fs. Additionally it uses symlinks and relative mount paths to allow a depth of 128 and stay within the mount page size limit. Diffs and done directly over a single directory allowing diffs to be done efficiently and without the need fo the naive diff driver. Signed-off-by: Derek McGowan (github: dmcgowan) --- daemon/graphdriver/overlay2/mount.go | 91 ++++ daemon/graphdriver/overlay2/overlay.go | 476 ++++++++++++++++++ daemon/graphdriver/overlay2/overlay_test.go | 106 ++++ .../overlay2/overlay_unsupported.go | 3 + daemon/graphdriver/overlay2/randomid.go | 80 +++ .../graphdriver/register/register_overlay.go | 1 + 6 files changed, 757 insertions(+) create mode 100644 daemon/graphdriver/overlay2/mount.go create mode 100644 daemon/graphdriver/overlay2/overlay.go create mode 100644 daemon/graphdriver/overlay2/overlay_test.go create mode 100644 daemon/graphdriver/overlay2/overlay_unsupported.go create mode 100644 daemon/graphdriver/overlay2/randomid.go diff --git a/daemon/graphdriver/overlay2/mount.go b/daemon/graphdriver/overlay2/mount.go new file mode 100644 index 0000000000..493960a5eb --- /dev/null +++ b/daemon/graphdriver/overlay2/mount.go @@ -0,0 +1,91 @@ +// +build linux + +package overlay2 + +import ( + "bytes" + "encoding/json" + "flag" + "fmt" + "os" + "runtime" + "syscall" + + "github.com/docker/docker/pkg/reexec" +) + +func init() { + reexec.Register("docker-mountfrom", mountFromMain) +} + +func fatal(err error) { + fmt.Fprint(os.Stderr, err) + os.Exit(1) +} + +type mountOptions struct { + Device string + Target string + Type string + Label string + Flag uint32 +} + +func mountFrom(dir, device, target, mType, label string) error { + + r, w, err := os.Pipe() + if err != nil { + return fmt.Errorf("mountfrom pipe failure: %v", err) + } + + options := &mountOptions{ + Device: device, + Target: target, + Type: mType, + Flag: 0, + Label: label, + } + + cmd := reexec.Command("docker-mountfrom", dir) + cmd.Stdin = r + + output := bytes.NewBuffer(nil) + cmd.Stdout = output + cmd.Stderr = output + + if err := cmd.Start(); err != nil { + return fmt.Errorf("mountfrom error on re-exec cmd: %v", err) + } + //write the options to the pipe for the untar exec to read + if err := json.NewEncoder(w).Encode(options); err != nil { + return fmt.Errorf("mountfrom json encode to pipe failed: %v", err) + } + w.Close() + + if err := cmd.Wait(); err != nil { + return fmt.Errorf("mountfrom re-exec error: %v: output: %s", err, output) + } + return nil +} + +// mountfromMain is the entry-point for docker-mountfrom on re-exec. +func mountFromMain() { + runtime.LockOSThread() + flag.Parse() + + var options *mountOptions + + if err := json.NewDecoder(os.Stdin).Decode(&options); err != nil { + fatal(err) + } + + if err := os.Chdir(flag.Arg(0)); err != nil { + fatal(err) + } + + if err := syscall.Mount(options.Device, options.Target, options.Type, uintptr(options.Flag), options.Label); err != nil { + fatal(err) + } + + os.Exit(0) +} diff --git a/daemon/graphdriver/overlay2/overlay.go b/daemon/graphdriver/overlay2/overlay.go new file mode 100644 index 0000000000..603a8ff8ec --- /dev/null +++ b/daemon/graphdriver/overlay2/overlay.go @@ -0,0 +1,476 @@ +// +build linux + +package overlay2 + +import ( + "bufio" + "errors" + "fmt" + "io/ioutil" + "os" + "os/exec" + "path" + "strings" + "syscall" + + "github.com/Sirupsen/logrus" + + "github.com/docker/docker/daemon/graphdriver" + "github.com/docker/docker/pkg/archive" + "github.com/docker/docker/pkg/chrootarchive" + "github.com/docker/docker/pkg/directory" + "github.com/docker/docker/pkg/idtools" + "github.com/docker/docker/pkg/mount" + "github.com/docker/docker/pkg/parsers/kernel" + + "github.com/opencontainers/runc/libcontainer/label" +) + +var ( + // untar defines the untar method + untar = chrootarchive.UntarUncompressed +) + +// This backend uses the overlay union filesystem for containers +// with diff directories for each layer. + +// This version of the overlay driver requires at least kernel +// 4.0.0 in order to support mounting multiple diff directories. + +// Each container/image has at least a "diff" directory and "link" file. +// If there is also a "lower" file when there are diff layers +// below as well as "merged" and "work" directories. The "diff" directory +// has the upper layer of the overlay and is used to capture any +// changes to the layer. The "lower" file contains all the lower layer +// mounts separated by ":" and ordered from uppermost to lowermost +// layers. The overlay itself is mounted in the "merged" directory, +// and the "work" dir is needed for overlay to work. + +// The "link" file for each layer contains a unique string for the layer. +// Under the "l" directory at the root there will be a symbolic link +// with that unique string pointing the "diff" directory for the layer. +// The symbolic links are used to reference lower layers in the "lower" +// file and on mount. The links are used to shorten the total length +// of a layer reference without requiring changes to the layer identifier +// or root directory. Mounts are always done relative to root and +// referencing the symbolic links in order to ensure the number of +// lower directories can fit in a single page for making the mount +// syscall. A hard upper limit of 128 lower layers is enforced to ensure +// that mounts do not fail due to length. + +const ( + driverName = "overlay2" + linkDir = "l" + lowerFile = "lower" + maxDepth = 128 + + // idLength represents the number of random characters + // which can be used to create the unique link identifer + // for every layer. If this value is too long then the + // page size limit for the mount command may be exceeded. + // The idLength should be selected such that following equation + // is true (512 is a buffer for label metadata). + // ((idLength + len(linkDir) + 1) * maxDepth) <= (pageSize - 512) + idLength = 26 +) + +// Driver contains information about the home directory and the list of active mounts that are created using this driver. +type Driver struct { + home string + uidMaps []idtools.IDMap + gidMaps []idtools.IDMap + ctr *graphdriver.RefCounter +} + +var backingFs = "" + +func init() { + graphdriver.Register(driverName, Init) +} + +// 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) { + + 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 { + 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(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 +} + +func supportsOverlay() error { + // We can try to modprobe overlay first before looking at + // proc/filesystems for when overlay is supported + exec.Command("modprobe", "overlay").Run() + + f, err := os.Open("/proc/filesystems") + if err != nil { + return err + } + defer f.Close() + + s := bufio.NewScanner(f) + for s.Scan() { + if s.Text() == "nodev\toverlay" { + return nil + } + } + logrus.Error("'overlay' not found as a supported filesystem on this host. Please ensure kernel is new enough and has overlay support loaded.") + return graphdriver.ErrNotSupported +} + +func (d *Driver) String() string { + return driverName +} + +// Status returns current driver information in a two dimensional string array. +// Output contains "Backing Filesystem" used in this implementation. +func (d *Driver) Status() [][2]string { + return [][2]string{ + {"Backing Filesystem", backingFs}, + } +} + +// GetMetadata returns meta data about the overlay driver such as +// LowerDir, UpperDir, WorkDir and MergeDir used to store data. +func (d *Driver) GetMetadata(id string) (map[string]string, error) { + dir := d.dir(id) + if _, err := os.Stat(dir); err != nil { + return nil, err + } + + metadata := map[string]string{ + "WorkDir": path.Join(dir, "work"), + "MergedDir": path.Join(dir, "merged"), + "UpperDir": path.Join(dir, "diff"), + } + + lowerDirs, err := d.getLowerDirs(id) + if err != nil { + return nil, err + } + if len(lowerDirs) > 0 { + metadata["LowerDir"] = strings.Join(lowerDirs, ":") + } + + return metadata, nil +} + +// Cleanup any state created by overlay which should be cleaned when daemon +// is being shutdown. For now, we just have to unmount the bind mounted +// we had created. +func (d *Driver) Cleanup() error { + return mount.Unmount(d.home) +} + +// CreateReadWrite creates a layer that is writable for use as a container +// file system. +func (d *Driver) CreateReadWrite(id, parent, mountLabel string, storageOpt map[string]string) error { + return d.Create(id, parent, mountLabel, storageOpt) +} + +// Create is used to create the upper, lower, and merge directories required for overlay fs for a given id. +// The parent filesystem is used to configure these directories for the overlay. +func (d *Driver) Create(id, parent, mountLabel string, storageOpt map[string]string) (retErr error) { + + if len(storageOpt) != 0 { + return fmt.Errorf("--storage-opt is not supported for overlay") + } + + dir := d.dir(id) + + rootUID, rootGID, err := idtools.GetRootUIDGID(d.uidMaps, d.gidMaps) + if err != nil { + return err + } + if err := idtools.MkdirAllAs(path.Dir(dir), 0700, rootUID, rootGID); err != nil { + return err + } + if err := idtools.MkdirAs(dir, 0700, rootUID, rootGID); err != nil { + return err + } + + defer func() { + // Clean up on failure + if retErr != nil { + os.RemoveAll(dir) + } + }() + + if err := idtools.MkdirAs(path.Join(dir, "diff"), 0755, rootUID, rootGID); err != nil { + return err + } + + lid := generateID(idLength) + if err := os.Symlink(path.Join("..", id, "diff"), path.Join(d.home, linkDir, lid)); err != nil { + return err + } + + // Write link id to link file + if err := ioutil.WriteFile(path.Join(dir, "link"), []byte(lid), 0644); err != nil { + return err + } + + // if no parent directory, done + if parent == "" { + return nil + } + + if err := idtools.MkdirAs(path.Join(dir, "work"), 0700, rootUID, rootGID); err != nil { + return err + } + if err := idtools.MkdirAs(path.Join(dir, "merged"), 0700, rootUID, rootGID); err != nil { + return err + } + + lower, err := d.getLower(parent) + if err != nil { + return err + } + if lower != "" { + if err := ioutil.WriteFile(path.Join(dir, lowerFile), []byte(lower), 0666); err != nil { + return err + } + } + + return nil +} + +func (d *Driver) getLower(parent string) (string, error) { + parentDir := d.dir(parent) + + // Ensure parent exists + if _, err := os.Lstat(parentDir); err != nil { + return "", err + } + + // Read Parent link fileA + parentLink, err := ioutil.ReadFile(path.Join(parentDir, "link")) + if err != nil { + return "", err + } + lowers := []string{path.Join(linkDir, string(parentLink))} + + parentLower, err := ioutil.ReadFile(path.Join(parentDir, lowerFile)) + if err == nil { + parentLowers := strings.Split(string(parentLower), ":") + lowers = append(lowers, parentLowers...) + } + if len(lowers) > maxDepth { + return "", errors.New("max depth exceeded") + } + return strings.Join(lowers, ":"), nil +} + +func (d *Driver) dir(id string) string { + return path.Join(d.home, id) +} + +func (d *Driver) getLowerDirs(id string) ([]string, error) { + var lowersArray []string + lowers, err := ioutil.ReadFile(path.Join(d.dir(id), lowerFile)) + if err == nil { + for _, s := range strings.Split(string(lowers), ":") { + lp, err := os.Readlink(path.Join(d.home, s)) + if err != nil { + return nil, err + } + lowersArray = append(lowersArray, path.Clean(path.Join(d.home, "link", lp))) + } + } else if !os.IsNotExist(err) { + return nil, err + } + return lowersArray, nil +} + +// Remove cleans the directories that are created for this id. +func (d *Driver) Remove(id string) error { + if err := os.RemoveAll(d.dir(id)); err != nil && !os.IsNotExist(err) { + return err + } + return 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 +} + +// Put unmounts the mount path created for the give id. +func (d *Driver) Put(id string) error { + mountpoint := path.Join(d.dir(id), "merged") + if count := d.ctr.Decrement(mountpoint); count > 0 { + return nil + } + if err := syscall.Unmount(mountpoint, 0); err != nil { + logrus.Debugf("Failed to unmount %s overlay: %v", id, err) + } + return nil +} + +// Exists checks to see if the id is already mounted. +func (d *Driver) Exists(id string) bool { + _, err := os.Stat(d.dir(id)) + return err == nil +} + +// ApplyDiff applies the new layer into a root +func (d *Driver) ApplyDiff(id string, parent string, diff archive.Reader) (size int64, err error) { + applyDir := d.getDiffPath(id) + + logrus.Debugf("Applying tar in %s", applyDir) + // Overlay doesn't need the parent id to apply the diff + if err := untar(diff, applyDir, &archive.TarOptions{ + UIDMaps: d.uidMaps, + GIDMaps: d.gidMaps, + WhiteoutFormat: archive.OverlayWhiteoutFormat, + }); err != nil { + return 0, err + } + + return d.DiffSize(id, parent) +} + +func (d *Driver) getDiffPath(id string) string { + dir := d.dir(id) + + return path.Join(dir, "diff") +} + +// DiffSize calculates the changes between the specified id +// and its parent and returns the size in bytes of the changes +// relative to its base filesystem directory. +func (d *Driver) DiffSize(id, parent string) (size int64, err error) { + return directory.Size(d.getDiffPath(id)) +} + +// Diff produces an archive of the changes between the specified +// layer and its parent layer which may be "". +func (d *Driver) Diff(id, parent string) (archive.Archive, error) { + diffPath := d.getDiffPath(id) + logrus.Debugf("Tar with options on %s", diffPath) + return archive.TarWithOptions(diffPath, &archive.TarOptions{ + Compression: archive.Uncompressed, + UIDMaps: d.uidMaps, + GIDMaps: d.gidMaps, + WhiteoutFormat: archive.OverlayWhiteoutFormat, + }) +} + +// Changes produces a list of changes between the specified layer +// and its parent layer. If parent is "", then all changes will be ADD changes. +func (d *Driver) Changes(id, parent string) ([]archive.Change, error) { + // Overlay doesn't have snapshots, so we need to get changes from all parent + // layers. + diffPath := d.getDiffPath(id) + layers, err := d.getLowerDirs(id) + if err != nil { + return nil, err + } + + return archive.OverlayChanges(layers, diffPath) +} diff --git a/daemon/graphdriver/overlay2/overlay_test.go b/daemon/graphdriver/overlay2/overlay_test.go new file mode 100644 index 0000000000..ae4b785dcb --- /dev/null +++ b/daemon/graphdriver/overlay2/overlay_test.go @@ -0,0 +1,106 @@ +// +build linux + +package overlay2 + +import ( + "os" + "syscall" + "testing" + + "github.com/docker/docker/daemon/graphdriver" + "github.com/docker/docker/daemon/graphdriver/graphtest" + "github.com/docker/docker/pkg/archive" + "github.com/docker/docker/pkg/reexec" +) + +func init() { + // Do not sure chroot to speed run time and allow archive + // errors or hangs to be debugged directly from the test process. + untar = archive.UntarUncompressed + graphdriver.ApplyUncompressedLayer = archive.ApplyUncompressedLayer + + reexec.Init() +} + +func cdMountFrom(dir, device, target, mType, label string) error { + wd, err := os.Getwd() + if err != nil { + return err + } + os.Chdir(dir) + defer os.Chdir(wd) + + return syscall.Mount(device, target, mType, 0, label) +} + +// This avoids creating a new driver for each test if all tests are run +// Make sure to put new tests between TestOverlaySetup and TestOverlayTeardown +func TestOverlaySetup(t *testing.T) { + graphtest.GetDriver(t, driverName) +} + +func TestOverlayCreateEmpty(t *testing.T) { + graphtest.DriverTestCreateEmpty(t, driverName) +} + +func TestOverlayCreateBase(t *testing.T) { + graphtest.DriverTestCreateBase(t, driverName) +} + +func TestOverlayCreateSnap(t *testing.T) { + graphtest.DriverTestCreateSnap(t, driverName) +} + +func TestOverlay128LayerRead(t *testing.T) { + graphtest.DriverTestDeepLayerRead(t, 128, driverName) +} + +func TestOverlayDiffApply10Files(t *testing.T) { + graphtest.DriverTestDiffApply(t, 10, driverName) +} + +func TestOverlayChanges(t *testing.T) { + graphtest.DriverTestChanges(t, driverName) +} + +func TestOverlayTeardown(t *testing.T) { + graphtest.PutDriver(t) +} + +// Benchmarks should always setup new driver + +func BenchmarkExists(b *testing.B) { + graphtest.DriverBenchExists(b, driverName) +} + +func BenchmarkGetEmpty(b *testing.B) { + graphtest.DriverBenchGetEmpty(b, driverName) +} + +func BenchmarkDiffBase(b *testing.B) { + graphtest.DriverBenchDiffBase(b, driverName) +} + +func BenchmarkDiffSmallUpper(b *testing.B) { + graphtest.DriverBenchDiffN(b, 10, 10, driverName) +} + +func BenchmarkDiff10KFileUpper(b *testing.B) { + graphtest.DriverBenchDiffN(b, 10, 10000, driverName) +} + +func BenchmarkDiff10KFilesBottom(b *testing.B) { + graphtest.DriverBenchDiffN(b, 10000, 10, driverName) +} + +func BenchmarkDiffApply100(b *testing.B) { + graphtest.DriverBenchDiffApplyN(b, 100, driverName) +} + +func BenchmarkDiff20Layers(b *testing.B) { + graphtest.DriverBenchDeepLayerDiff(b, 20, driverName) +} + +func BenchmarkRead20Layers(b *testing.B) { + graphtest.DriverBenchDeepLayerRead(b, 20, driverName) +} diff --git a/daemon/graphdriver/overlay2/overlay_unsupported.go b/daemon/graphdriver/overlay2/overlay_unsupported.go new file mode 100644 index 0000000000..e5ac4ca8c6 --- /dev/null +++ b/daemon/graphdriver/overlay2/overlay_unsupported.go @@ -0,0 +1,3 @@ +// +build !linux + +package overlay2 diff --git a/daemon/graphdriver/overlay2/randomid.go b/daemon/graphdriver/overlay2/randomid.go new file mode 100644 index 0000000000..af5cb659d5 --- /dev/null +++ b/daemon/graphdriver/overlay2/randomid.go @@ -0,0 +1,80 @@ +// +build linux + +package overlay2 + +import ( + "crypto/rand" + "encoding/base32" + "fmt" + "io" + "os" + "syscall" + "time" + + "github.com/Sirupsen/logrus" +) + +// generateID creates a new random string identifier with the given length +func generateID(l int) string { + const ( + // ensures we backoff for less than 450ms total. Use the following to + // select new value, in units of 10ms: + // n*(n+1)/2 = d -> n^2 + n - 2d -> n = (sqrt(8d + 1) - 1)/2 + maxretries = 9 + backoff = time.Millisecond * 10 + ) + + var ( + totalBackoff time.Duration + count int + retries int + size = (l*5 + 7) / 8 + u = make([]byte, size) + ) + // TODO: Include time component, counter component, random component + + for { + // This should never block but the read may fail. Because of this, + // we just try to read the random number generator until we get + // something. This is a very rare condition but may happen. + b := time.Duration(retries) * backoff + time.Sleep(b) + totalBackoff += b + + n, err := io.ReadFull(rand.Reader, u[count:]) + if err != nil { + if retryOnError(err) && retries < maxretries { + count += n + retries++ + logrus.Errorf("error generating version 4 uuid, retrying: %v", err) + continue + } + + // Any other errors represent a system problem. What did someone + // do to /dev/urandom? + panic(fmt.Errorf("error reading random number generator, retried for %v: %v", totalBackoff.String(), err)) + } + + break + } + + s := base32.StdEncoding.EncodeToString(u) + + return s[:l] +} + +// retryOnError tries to detect whether or not retrying would be fruitful. +func retryOnError(err error) bool { + switch err := err.(type) { + case *os.PathError: + return retryOnError(err.Err) // unpack the target error + case syscall.Errno: + if err == syscall.EPERM { + // EPERM represents an entropy pool exhaustion, a condition under + // which we backoff and retry. + return true + } + } + + return false +} diff --git a/daemon/graphdriver/register/register_overlay.go b/daemon/graphdriver/register/register_overlay.go index 3a9526420f..9ba849cedc 100644 --- a/daemon/graphdriver/register/register_overlay.go +++ b/daemon/graphdriver/register/register_overlay.go @@ -5,4 +5,5 @@ package register import ( // register the overlay graphdriver _ "github.com/docker/docker/daemon/graphdriver/overlay" + _ "github.com/docker/docker/daemon/graphdriver/overlay2" )