Implement overlay fs snapshot driver
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
This commit is contained in:
Michael Crosby
parent
2bee4ac5cd
commit
0808a5c485
65
mount.go
65
mount.go
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@ -4,6 +4,7 @@ import (
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"os"
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"os/exec"
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"strings"
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"syscall"
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)
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// Mount is the lingua franca of the containerkit. A mount represents a
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@ -48,3 +49,67 @@ func MountAll(mounts ...Mount) error {
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return nil
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}
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func MountFS(mounts []Mount, target string) error {
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for _, m := range mounts {
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flags, data := parseMountOptions(m.Options)
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if err := syscall.Mount(m.Source, target, m.Type, uintptr(flags), data); err != nil {
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return err
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}
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}
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return nil
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}
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// parseMountOptions takes fstab style mount options and parses them for
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// use with a standard mount() syscall
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func parseMountOptions(options []string) (int, string) {
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var (
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flag int
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data []string
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)
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flags := map[string]struct {
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clear bool
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flag int
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}{
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"async": {true, syscall.MS_SYNCHRONOUS},
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"atime": {true, syscall.MS_NOATIME},
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"bind": {false, syscall.MS_BIND},
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"defaults": {false, 0},
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"dev": {true, syscall.MS_NODEV},
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"diratime": {true, syscall.MS_NODIRATIME},
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"dirsync": {false, syscall.MS_DIRSYNC},
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"exec": {true, syscall.MS_NOEXEC},
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"mand": {false, syscall.MS_MANDLOCK},
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"noatime": {false, syscall.MS_NOATIME},
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"nodev": {false, syscall.MS_NODEV},
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"nodiratime": {false, syscall.MS_NODIRATIME},
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"noexec": {false, syscall.MS_NOEXEC},
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"nomand": {true, syscall.MS_MANDLOCK},
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"norelatime": {true, syscall.MS_RELATIME},
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"nostrictatime": {true, syscall.MS_STRICTATIME},
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"nosuid": {false, syscall.MS_NOSUID},
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"rbind": {false, syscall.MS_BIND | syscall.MS_REC},
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"relatime": {false, syscall.MS_RELATIME},
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"remount": {false, syscall.MS_REMOUNT},
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"ro": {false, syscall.MS_RDONLY},
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"rw": {true, syscall.MS_RDONLY},
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"strictatime": {false, syscall.MS_STRICTATIME},
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"suid": {true, syscall.MS_NOSUID},
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"sync": {false, syscall.MS_SYNCHRONOUS},
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}
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for _, o := range options {
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// If the option does not exist in the flags table or the flag
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// is not supported on the platform,
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// then it is a data value for a specific fs type
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if f, exists := flags[o]; exists && f.flag != 0 {
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if f.clear {
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flag &= ^f.flag
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} else {
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flag |= f.flag
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}
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} else {
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data = append(data, o)
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}
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}
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return flag, strings.Join(data, ",")
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}
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@ -0,0 +1,157 @@
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package snapshot
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import (
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"crypto/md5"
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"encoding/hex"
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"fmt"
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"os"
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"path/filepath"
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"strings"
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"github.com/docker/containerd"
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)
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func NewOverlayfs(root string) (*Overlayfs, error) {
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if err := os.MkdirAll(root, 0700); err != nil {
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return nil, err
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}
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for _, p := range []string{
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"snapshots",
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"active",
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} {
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if err := os.MkdirAll(filepath.Join(root, p), 0700); err != nil {
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return nil, err
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}
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}
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return &Overlayfs{
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root: root,
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}, nil
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}
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type Overlayfs struct {
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root string
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}
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func (o *Overlayfs) Prepare(key string, parentName string) ([]containerd.Mount, error) {
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if err := validKey(key); err != nil {
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return nil, err
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}
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active, err := o.newActiveDir(key)
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if err != nil {
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return nil, err
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}
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if parentName != "" {
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if err := active.setParent(parentName); err != nil {
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return nil, err
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}
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}
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return active.mounts()
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}
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func (o *Overlayfs) Commit(key string, name string) error {
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active := o.getActive(key)
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return active.commit(name)
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}
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func (o *Overlayfs) newActiveDir(key string) (*activeDir, error) {
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var (
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hash = hash(key)
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path = filepath.Join(o.root, "active", hash)
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)
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a := &activeDir{
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path: path,
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snapshotsDir: filepath.Join(o.root, "snapshots"),
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}
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for _, p := range []string{
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"work",
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"fs",
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} {
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if err := os.MkdirAll(filepath.Join(path, p), 0700); err != nil {
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a.delete()
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return nil, err
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}
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}
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return a, nil
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}
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func (o *Overlayfs) getActive(key string) *activeDir {
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return &activeDir{
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path: filepath.Join(o.root, "active", hash(key)),
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snapshotsDir: filepath.Join(o.root, "snapshots"),
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}
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}
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func validKey(key string) error {
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_, err := filepath.Abs(key)
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return err
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}
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func hash(k string) string {
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h := md5.New()
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h.Write([]byte(k))
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return hex.EncodeToString(h.Sum(nil))
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}
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type activeDir struct {
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snapshotsDir string
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path string
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}
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func (a *activeDir) delete() error {
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return os.RemoveAll(a.path)
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}
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func (a *activeDir) setParent(name string) error {
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return os.Symlink(filepath.Join(a.snapshotsDir, name), filepath.Join(a.path, "parent"))
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}
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func (a *activeDir) commit(name string) error {
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if err := os.RemoveAll(filepath.Join(a.path, "work")); err != nil {
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return err
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}
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return os.Rename(a.path, filepath.Join(a.snapshotsDir, name))
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}
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func (a *activeDir) mounts() ([]containerd.Mount, error) {
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var (
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parentLink = filepath.Join(a.path, "parent")
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parents []string
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)
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for {
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snapshot, err := os.Readlink(parentLink)
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if err != nil {
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if os.IsNotExist(err) {
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break
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}
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return nil, err
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}
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parents = append(parents, filepath.Join(snapshot, "fs"))
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parentLink = filepath.Join(snapshot, "parent")
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}
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if len(parents) == 0 {
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// if we only have one layer/no parents then just return a bind mount as overlay
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// will not work
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return []containerd.Mount{
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{
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Source: filepath.Join(a.path, "fs"),
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Type: "bind",
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Options: []string{
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"rw",
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"rbind",
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},
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},
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}, nil
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}
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options := []string{
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fmt.Sprintf("workdir=%s", filepath.Join(a.path, "work")),
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fmt.Sprintf("upperdir=%s", filepath.Join(a.path, "fs")),
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fmt.Sprintf("lowerdir=%s", strings.Join(parents, ":")),
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}
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return []containerd.Mount{
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{
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Type: "overlay",
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Source: "overlay",
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Options: options,
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},
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}, nil
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}
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@ -0,0 +1,180 @@
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package snapshot
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import (
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"io/ioutil"
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"os"
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"path/filepath"
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"syscall"
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"testing"
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"github.com/docker/containerd"
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)
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func TestOverlayfs(t *testing.T) {
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root, err := ioutil.TempDir("", "overlay")
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if err != nil {
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t.Fatal(err)
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}
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defer os.RemoveAll(root)
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o, err := NewOverlayfs(root)
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if err != nil {
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t.Error(err)
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return
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}
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mounts, err := o.Prepare("/tmp/test", "")
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if err != nil {
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t.Error(err)
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return
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}
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if len(mounts) != 1 {
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t.Errorf("should only have 1 mount but received %d", len(mounts))
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}
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m := mounts[0]
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if m.Type != "bind" {
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t.Errorf("mount type should be bind but received %q", m.Type)
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}
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expected := filepath.Join(root, "active", hash("/tmp/test"), "fs")
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if m.Source != expected {
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t.Errorf("expected source %q but received %q", expected, m.Source)
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}
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if m.Options[0] != "rw" {
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t.Errorf("expected mount option rw but received %q", m.Options[0])
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}
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if m.Options[1] != "rbind" {
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t.Errorf("expected mount option rbind but received %q", m.Options[1])
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}
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}
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func TestOverlayfsCommit(t *testing.T) {
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root, err := ioutil.TempDir("", "overlay")
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if err != nil {
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t.Fatal(err)
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}
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defer os.RemoveAll(root)
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o, err := NewOverlayfs(root)
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if err != nil {
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t.Error(err)
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return
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}
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key := "/tmp/test"
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mounts, err := o.Prepare(key, "")
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if err != nil {
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t.Error(err)
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return
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}
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m := mounts[0]
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if err := ioutil.WriteFile(filepath.Join(m.Source, "foo"), []byte("hi"), 0660); err != nil {
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t.Error(err)
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return
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}
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if err := o.Commit(key, "base"); err != nil {
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t.Error(err)
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return
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}
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}
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func TestOverlayfsOverlayMount(t *testing.T) {
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root, err := ioutil.TempDir("", "overlay")
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if err != nil {
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t.Fatal(err)
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}
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defer os.RemoveAll(root)
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o, err := NewOverlayfs(root)
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if err != nil {
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t.Error(err)
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return
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}
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key := "/tmp/test"
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mounts, err := o.Prepare(key, "")
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if err != nil {
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t.Error(err)
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return
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}
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if err := o.Commit(key, "base"); err != nil {
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t.Error(err)
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return
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}
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if mounts, err = o.Prepare("/tmp/layer2", "base"); err != nil {
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t.Error(err)
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return
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}
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if len(mounts) != 1 {
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t.Errorf("should only have 1 mount but received %d", len(mounts))
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}
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m := mounts[0]
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if m.Type != "overlay" {
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t.Errorf("mount type should be overlay but received %q", m.Type)
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}
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if m.Source != "overlay" {
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t.Errorf("expected source %q but received %q", "overlay", m.Source)
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}
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var (
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hash = hash("/tmp/layer2")
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work = "workdir=" + filepath.Join(root, "active", hash, "work")
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upper = "upperdir=" + filepath.Join(root, "active", hash, "fs")
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lower = "lowerdir=" + filepath.Join(root, "snapshots", "base", "fs")
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)
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for i, v := range []string{
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work,
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upper,
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lower,
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} {
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if m.Options[i] != v {
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t.Errorf("expected %q but received %q", v, m.Options[i])
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}
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}
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}
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func TestOverlayfsOverlayRead(t *testing.T) {
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if os.Getuid() != 0 {
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t.Skip("not running as root")
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}
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root, err := ioutil.TempDir("", "overlay")
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if err != nil {
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t.Fatal(err)
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}
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defer os.RemoveAll(root)
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o, err := NewOverlayfs(root)
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if err != nil {
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t.Error(err)
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return
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}
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key := "/tmp/test"
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mounts, err := o.Prepare(key, "")
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if err != nil {
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t.Error(err)
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return
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}
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m := mounts[0]
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if err := ioutil.WriteFile(filepath.Join(m.Source, "foo"), []byte("hi"), 0660); err != nil {
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t.Error(err)
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return
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}
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if err := o.Commit(key, "base"); err != nil {
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t.Error(err)
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return
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}
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if mounts, err = o.Prepare("/tmp/layer2", "base"); err != nil {
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t.Error(err)
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return
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}
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dest := filepath.Join(root, "dest")
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if err := os.Mkdir(dest, 0700); err != nil {
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t.Error(err)
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return
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}
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if err := containerd.MountFS(mounts, dest); err != nil {
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t.Error(err)
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return
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}
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defer syscall.Unmount(dest, 0)
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data, err := ioutil.ReadFile(filepath.Join(dest, "foo"))
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if err != nil {
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t.Error(err)
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return
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}
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if e := string(data); e != "hi" {
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t.Errorf("expected file contents hi but got %q", e)
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return
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}
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}
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Reference in New Issue