daemon/graphdriver/fuse-overlayfs/fuseoverlayfs.go
//go:build linux
package fuseoverlayfs // import "github.com/docker/docker/daemon/graphdriver/fuse-overlayfs"
import (
"bytes"
"context"
"fmt"
"io"
"os"
"os/exec"
"path"
"path/filepath"
"strings"
"github.com/containerd/log"
"github.com/docker/docker/daemon/graphdriver"
"github.com/docker/docker/daemon/graphdriver/overlayutils"
"github.com/docker/docker/daemon/internal/fstype"
"github.com/docker/docker/daemon/internal/mountref"
"github.com/docker/docker/internal/containerfs"
"github.com/docker/docker/internal/directory"
"github.com/docker/docker/pkg/archive"
"github.com/docker/docker/pkg/chrootarchive"
"github.com/docker/docker/pkg/idtools"
"github.com/docker/docker/pkg/parsers/kernel"
"github.com/moby/locker"
"github.com/moby/sys/mount"
"github.com/moby/sys/userns"
"github.com/opencontainers/selinux/go-selinux/label"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
)
// untar defines the untar method
var untar = chrootarchive.UntarUncompressed
const (
driverName = "fuse-overlayfs"
binary = "fuse-overlayfs"
linkDir = "l"
diffDirName = "diff"
workDirName = "work"
mergedDirName = "merged"
lowerFile = "lower"
maxDepth = 128
// idLength represents the number of random characters
// which can be used to create the unique link identifier
// 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
idMap idtools.IdentityMapping
ctr *mountref.Counter
naiveDiff graphdriver.DiffDriver
locker *locker.Locker
}
var logger = log.G(context.TODO()).WithField("storage-driver", driverName)
func init() {
graphdriver.Register(driverName, Init)
}
// Init returns the naive diff driver for fuse-overlayfs.
// If fuse-overlayfs is not supported on the host, the error
// graphdriver.ErrNotSupported is returned.
func Init(home string, options []string, idMap idtools.IdentityMapping) (graphdriver.Driver, error) {
if _, err := exec.LookPath(binary); err != nil {
logger.Error(err)
return nil, graphdriver.ErrNotSupported
}
if !kernel.CheckKernelVersion(4, 18, 0) {
return nil, graphdriver.ErrNotSupported
}
currentID := idtools.CurrentIdentity()
dirID := idtools.Identity{
UID: currentID.UID,
GID: idMap.RootPair().GID,
}
if err := idtools.MkdirAllAndChown(home, 0o710, dirID); err != nil {
return nil, err
}
if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0o700, currentID); err != nil {
return nil, err
}
d := &Driver{
home: home,
idMap: idMap,
ctr: mountref.NewCounter(isMounted),
locker: locker.New(),
}
d.naiveDiff = graphdriver.NewNaiveDiffDriver(d, idMap)
return d, nil
}
// isMounted checks whether the given path is a [fstype.FsMagicFUSE] mount.
func isMounted(path string) bool {
fsType, _ := fstype.GetFSMagic(path)
return fsType == fstype.FsMagicFUSE
}
func (d *Driver) String() string {
return driverName
}
// Status returns current driver information in a two dimensional string array.
func (d *Driver) Status() [][2]string {
return [][2]string{}
}
// GetMetadata returns metadata about the overlay driver such as the 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, workDirName),
"MergedDir": path.Join(dir, mergedDirName),
"UpperDir": path.Join(dir, diffDirName),
}
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.RecursiveUnmount(d.home)
}
// CreateReadWrite creates a layer that is writable for use as a container
// file system.
func (d *Driver) CreateReadWrite(id, parent string, opts *graphdriver.CreateOpts) error {
if opts != nil && len(opts.StorageOpt) != 0 {
return fmt.Errorf("--storage-opt is not supported")
}
return d.create(id, parent, opts)
}
// 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 string, opts *graphdriver.CreateOpts) (retErr error) {
if opts != nil && len(opts.StorageOpt) != 0 {
return fmt.Errorf("--storage-opt is not supported")
}
return d.create(id, parent, opts)
}
func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr error) {
dir := d.dir(id)
root := d.idMap.RootPair()
if err := idtools.MkdirAllAndChown(path.Dir(dir), 0o710, root); err != nil {
return err
}
if err := idtools.MkdirAndChown(dir, 0o710, root); err != nil {
return err
}
defer func() {
// Clean up on failure
if retErr != nil {
os.RemoveAll(dir)
}
}()
if opts != nil && len(opts.StorageOpt) > 0 {
return fmt.Errorf("--storage-opt is not supported")
}
if err := idtools.MkdirAndChown(path.Join(dir, diffDirName), 0o755, root); err != nil {
return err
}
lid := overlayutils.GenerateID(idLength, logger)
if err := os.Symlink(path.Join("..", id, diffDirName), path.Join(d.home, linkDir, lid)); err != nil {
return err
}
// Write link id to link file
if err := os.WriteFile(path.Join(dir, "link"), []byte(lid), 0o644); err != nil {
return err
}
// if no parent directory, done
if parent == "" {
return nil
}
if err := idtools.MkdirAndChown(path.Join(dir, workDirName), 0o710, root); err != nil {
return err
}
if err := os.WriteFile(path.Join(d.dir(parent), "committed"), []byte{}, 0o600); err != nil {
return err
}
lower, err := d.getLower(parent)
if err != nil {
return err
}
if lower != "" {
if err := os.WriteFile(path.Join(dir, lowerFile), []byte(lower), 0o666); 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 := os.ReadFile(path.Join(parentDir, "link"))
if err != nil {
return "", err
}
lowers := []string{path.Join(linkDir, string(parentLink))}
parentLower, err := os.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 := os.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, linkDir, 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 id == "" {
return fmt.Errorf("refusing to remove the directories: id is empty")
}
d.locker.Lock(id)
defer d.locker.Unlock(id)
dir := d.dir(id)
lid, err := os.ReadFile(path.Join(dir, "link"))
if err == nil {
if len(lid) == 0 {
logger.Errorf("refusing to remove empty link for layer %v", id)
} else if err := os.RemoveAll(path.Join(d.home, linkDir, string(lid))); err != nil {
logger.Debugf("Failed to remove link: %v", err)
}
}
if err := containerfs.EnsureRemoveAll(dir); 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, mountLabel string) (_ string, retErr error) {
d.locker.Lock(id)
defer d.locker.Unlock(id)
dir := d.dir(id)
if _, err := os.Stat(dir); err != nil {
return "", err
}
diffDir := path.Join(dir, diffDirName)
lowers, err := os.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, mergedDirName)
if count := d.ctr.Increment(mergedDir); count > 1 {
return mergedDir, nil
}
defer func() {
if retErr != nil {
if c := d.ctr.Decrement(mergedDir); c <= 0 {
if unmounted := fusermountU(mergedDir); !unmounted {
if mntErr := unix.Unmount(mergedDir, 0); mntErr != nil {
logger.Errorf("error unmounting %v: %v", mergedDir, mntErr)
}
}
// Cleanup the created merged directory; see the comment in Put's rmdir
if rmErr := unix.Rmdir(mergedDir); rmErr != nil && !os.IsNotExist(rmErr) {
logger.Debugf("Failed to remove %s: %v: %v", id, rmErr, err)
}
}
}
}()
workDir := path.Join(dir, workDirName)
splitLowers := strings.Split(string(lowers), ":")
absLowers := make([]string, len(splitLowers))
for i, s := range splitLowers {
absLowers[i] = path.Join(d.home, s)
}
var readonly bool
if _, err := os.Stat(path.Join(dir, "committed")); err == nil {
readonly = true
} else if !os.IsNotExist(err) {
return "", err
}
var opts string
if readonly {
opts = "lowerdir=" + diffDir + ":" + strings.Join(absLowers, ":")
} else {
opts = "lowerdir=" + strings.Join(absLowers, ":") + ",upperdir=" + diffDir + ",workdir=" + workDir
}
mountData := label.FormatMountLabel(opts, mountLabel)
mountTarget := mergedDir
if err := idtools.MkdirAndChown(mergedDir, 0o700, d.idMap.RootPair()); err != nil {
return "", err
}
mountProgram := exec.Command(binary, "-o", mountData, mountTarget)
mountProgram.Dir = d.home
var b bytes.Buffer
mountProgram.Stderr = &b
if err = mountProgram.Run(); err != nil {
output := b.String()
if output == "" {
output = "<stderr empty>"
}
return "", errors.Wrapf(err, "using mount program %s: %s", binary, output)
}
return mergedDir, nil
}
// Put unmounts the mount path created for the give id.
// It also removes the 'merged' directory to force the kernel to unmount the
// overlay mount in other namespaces.
func (d *Driver) Put(id string) error {
d.locker.Lock(id)
defer d.locker.Unlock(id)
dir := d.dir(id)
_, err := os.ReadFile(path.Join(dir, lowerFile))
if err != nil {
// If no lower, no mount happened and just return directly
if os.IsNotExist(err) {
return nil
}
return err
}
mountpoint := path.Join(dir, mergedDirName)
if count := d.ctr.Decrement(mountpoint); count > 0 {
return nil
}
if unmounted := fusermountU(mountpoint); !unmounted {
if err := unix.Unmount(mountpoint, unix.MNT_DETACH); err != nil {
logger.Debugf("Failed to unmount %s overlay: %s - %v", id, mountpoint, err)
}
}
// Remove the mountpoint here. Removing the mountpoint (in newer kernels)
// will cause all other instances of this mount in other mount namespaces
// to be unmounted. This is necessary to avoid cases where an overlay mount
// that is present in another namespace will cause subsequent mounts
// operations to fail with ebusy. We ignore any errors here because this may
// fail on older kernels which don't have
// torvalds/linux@8ed936b5671bfb33d89bc60bdcc7cf0470ba52fe applied.
if err := unix.Rmdir(mountpoint); err != nil && !os.IsNotExist(err) {
logger.Debugf("Failed to remove %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
}
// isParent determines whether the given parent is the direct parent of the
// given layer id
func (d *Driver) isParent(id, parent string) bool {
lowers, err := d.getLowerDirs(id)
if err != nil {
return false
}
if parent == "" && len(lowers) > 0 {
return false
}
parentDir := d.dir(parent)
var ld string
if len(lowers) > 0 {
ld = filepath.Dir(lowers[0])
}
if ld == "" && parent == "" {
return true
}
return ld == parentDir
}
// ApplyDiff applies the new layer into a root
func (d *Driver) ApplyDiff(id string, parent string, diff io.Reader) (size int64, err error) {
if !d.isParent(id, parent) {
return d.naiveDiff.ApplyDiff(id, parent, diff)
}
applyDir := d.getDiffPath(id)
logger.Debugf("Applying tar in %s", applyDir)
// Overlay doesn't need the parent id to apply the diff
if err := untar(diff, applyDir, &archive.TarOptions{
IDMap: d.idMap,
// Use AUFS whiteout format: https://github.com/containers/storage/blob/39a8d5ed9843844eafb5d2ba6e6a7510e0126f40/drivers/overlay/overlay.go#L1084-L1089
WhiteoutFormat: archive.AUFSWhiteoutFormat,
InUserNS: userns.RunningInUserNS(),
}); err != nil {
return 0, err
}
return directory.Size(context.TODO(), applyDir)
}
func (d *Driver) getDiffPath(id string) string {
dir := d.dir(id)
return path.Join(dir, diffDirName)
}
// 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 d.naiveDiff.DiffSize(id, parent)
}
// 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) (io.ReadCloser, error) {
return d.naiveDiff.Diff(id, parent)
}
// 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) {
return d.naiveDiff.Changes(id, parent)
}
// fusermountU is from https://github.com/containers/storage/blob/39a8d5ed9843844eafb5d2ba6e6a7510e0126f40/drivers/overlay/overlay.go#L1016-L1040
func fusermountU(mountpoint string) (unmounted bool) {
// Attempt to unmount the FUSE mount using either fusermount or fusermount3.
// If they fail, fallback to unix.Unmount
for _, v := range []string{"fusermount3", "fusermount"} {
err := exec.Command(v, "-u", mountpoint).Run()
if err != nil && !os.IsNotExist(err) {
log.G(context.TODO()).Debugf("Error unmounting %s with %s - %v", mountpoint, v, err)
}
if err == nil {
unmounted = true
break
}
}
// If fusermount|fusermount3 failed to unmount the FUSE file system, make sure all
// pending changes are propagated to the file system
if !unmounted {
fd, err := unix.Open(mountpoint, unix.O_DIRECTORY, 0)
if err == nil {
if err := unix.Syncfs(fd); err != nil {
log.G(context.TODO()).Debugf("Error Syncfs(%s) - %v", mountpoint, err)
}
unix.Close(fd)
}
}
return
}