docker-cli/components/engine/graphdriver/aufs/aufs.go

/*

aufs driver directory structure

.
├── layers // Metadata of layers
│   ├── 1
│   ├── 2
│   └── 3
├── diffs  // Content of the layer
│   ├── 1  // Contains layers that need to be mounted for the id
│   ├── 2
│   └── 3
└── mnt    // Mount points for the rw layers to be mounted
    ├── 1
    ├── 2
    └── 3

*/

package aufs

import (
	"bufio"
	"fmt"
	"github.com/dotcloud/docker/archive"
	"github.com/dotcloud/docker/graphdriver"
	"github.com/dotcloud/docker/utils"
	"log"
	"os"
	"os/exec"
	"path"
	"strings"
)

func init() {
	graphdriver.Register("aufs", Init)
}

type Driver struct {
	root string
}

// New returns a new AUFS driver.
// An error is returned if AUFS is not supported.
func Init(root string) (graphdriver.Driver, error) {
	// Try to load the aufs kernel module
	if err := supportsAufs(); err != nil {
		return nil, err
	}
	paths := []string{
		"mnt",
		"diff",
		"layers",
	}

	// Create the root aufs driver dir and return
	// if it already exists
	// If not populate the dir structure
	if err := os.MkdirAll(root, 0755); err != nil {
		if os.IsExist(err) {
			return &Driver{root}, nil
		}
		return nil, err
	}

	for _, p := range paths {
		if err := os.MkdirAll(path.Join(root, p), 0755); err != nil {
			return nil, err
		}
	}
	return &Driver{root}, nil
}

// Return a nil error if the kernel supports aufs
// We cannot modprobe because inside dind modprobe fails
// to run
func supportsAufs() error {
	// We can try to modprobe aufs first before looking at
	// proc/filesystems for when aufs is supported
	exec.Command("modprobe", "aufs").Run()

	f, err := os.Open("/proc/filesystems")
	if err != nil {
		return err
	}
	defer f.Close()

	s := bufio.NewScanner(f)
	for s.Scan() {
		if strings.Contains(s.Text(), "aufs") {
			return nil
		}
	}
	return fmt.Errorf("AUFS was not found in /proc/filesystems")
}

func (a Driver) rootPath() string {
	return a.root
}

func (Driver) String() string {
	return "aufs"
}

func (a Driver) Status() [][2]string {
	ids, _ := loadIds(path.Join(a.rootPath(), "layers"))
	return [][2]string{
		{"Root Dir", a.rootPath()},
		{"Dirs", fmt.Sprintf("%d", len(ids))},
	}
}

// Exists returns true if the given id is registered with
// this driver
func (a Driver) Exists(id string) bool {
	if _, err := os.Lstat(path.Join(a.rootPath(), "layers", id)); err != nil {
		return false
	}
	return true
}

// Three folders are created for each id
// mnt, layers, and diff
func (a *Driver) Create(id, parent string) error {
	if err := a.createDirsFor(id); err != nil {
		return err
	}
	// Write the layers metadata
	f, err := os.Create(path.Join(a.rootPath(), "layers", id))
	if err != nil {
		return err
	}
	defer f.Close()

	if parent != "" {
		ids, err := getParentIds(a.rootPath(), parent)
		if err != nil {
			return err
		}

		if _, err := fmt.Fprintln(f, parent); err != nil {
			return err
		}
		for _, i := range ids {
			if _, err := fmt.Fprintln(f, i); err != nil {
				return err
			}
		}
	}
	return nil
}

func (a *Driver) createDirsFor(id string) error {
	paths := []string{
		"mnt",
		"diff",
	}

	for _, p := range paths {
		if err := os.MkdirAll(path.Join(a.rootPath(), p, id), 0755); err != nil {
			return err
		}
	}
	return nil
}

// Unmount and remove the dir information
func (a *Driver) Remove(id string) error {
	// Make sure the dir is umounted first
	if err := a.unmount(id); err != nil {
		return err
	}
	tmpDirs := []string{
		"mnt",
		"diff",
	}

	// Remove the dirs atomically
	for _, p := range tmpDirs {
		// We need to use a temp dir in the same dir as the driver so Rename
		// does not fall back to the slow copy if /tmp and the driver dir
		// are on different devices
		tmp := path.Join(a.rootPath(), "tmp", p, id)
		if err := os.MkdirAll(tmp, 0755); err != nil {
			return err
		}
		realPath := path.Join(a.rootPath(), p, id)
		if err := os.Rename(realPath, tmp); err != nil && !os.IsNotExist(err) {
			return err
		}
		defer os.RemoveAll(tmp)
	}

	// Remove the layers file for the id
	if err := os.Remove(path.Join(a.rootPath(), "layers", id)); err != nil && !os.IsNotExist(err) {
		return err
	}
	return nil
}

// Return the rootfs path for the id
// This will mount the dir at it's given path
func (a *Driver) Get(id string) (string, error) {
	ids, err := getParentIds(a.rootPath(), id)
	if err != nil {
		if !os.IsNotExist(err) {
			return "", err
		}
		ids = []string{}
	}

	// If a dir does not have a parent ( no layers )do not try to mount
	// just return the diff path to the data
	out := path.Join(a.rootPath(), "diff", id)
	if len(ids) > 0 {
		out = path.Join(a.rootPath(), "mnt", id)
		if err := a.mount(id); err != nil {
			return "", err
		}
	}
	return out, nil
}

// Returns an archive of the contents for the id
func (a *Driver) Diff(id string) (archive.Archive, error) {
	return archive.TarFilter(path.Join(a.rootPath(), "diff", id), &archive.TarOptions{
		Recursive:   true,
		Compression: archive.Uncompressed,
	})
}

func (a *Driver) ApplyDiff(id string, diff archive.Archive) error {
	return archive.Untar(diff, path.Join(a.rootPath(), "diff", id), nil)
}

// Returns the size of the contents for the id
func (a *Driver) DiffSize(id string) (int64, error) {
	return utils.TreeSize(path.Join(a.rootPath(), "diff", id))
}

func (a *Driver) Changes(id string) ([]archive.Change, error) {
	layers, err := a.getParentLayerPaths(id)
	if err != nil {
		return nil, err
	}
	return archive.Changes(layers, path.Join(a.rootPath(), "diff", id))
}

func (a *Driver) getParentLayerPaths(id string) ([]string, error) {
	parentIds, err := getParentIds(a.rootPath(), id)
	if err != nil {
		return nil, err
	}
	if len(parentIds) == 0 {
		return nil, fmt.Errorf("Dir %s does not have any parent layers", id)
	}
	layers := make([]string, len(parentIds))

	// Get the diff paths for all the parent ids
	for i, p := range parentIds {
		layers[i] = path.Join(a.rootPath(), "diff", p)
	}
	return layers, nil
}

func (a *Driver) mount(id string) error {
	// If the id is mounted or we get an error return
	if mounted, err := a.mounted(id); err != nil || mounted {
		return err
	}

	var (
		target = path.Join(a.rootPath(), "mnt", id)
		rw     = path.Join(a.rootPath(), "diff", id)
	)

	layers, err := a.getParentLayerPaths(id)
	if err != nil {
		return err
	}

	if err := a.aufsMount(layers, rw, target); err != nil {
		return err
	}
	return nil
}

func (a *Driver) unmount(id string) error {
	if mounted, err := a.mounted(id); err != nil || !mounted {
		return err
	}
	target := path.Join(a.rootPath(), "mnt", id)
	return Unmount(target)
}

func (a *Driver) mounted(id string) (bool, error) {
	target := path.Join(a.rootPath(), "mnt", id)
	return Mounted(target)
}

// During cleanup aufs needs to unmount all mountpoints
func (a *Driver) Cleanup() error {
	ids, err := loadIds(path.Join(a.rootPath(), "layers"))
	if err != nil {
		return err
	}
	for _, id := range ids {
		if err := a.unmount(id); err != nil {
			utils.Errorf("Unmounting %s: %s", utils.TruncateID(id), err)
		}
	}
	return nil
}

func (a *Driver) aufsMount(ro []string, rw, target string) error {
	rwBranch := fmt.Sprintf("%v=rw", rw)
	roBranches := ""
	for _, layer := range ro {
		roBranches += fmt.Sprintf("%v=ro+wh:", layer)
	}
	branches := fmt.Sprintf("br:%v:%v,xino=/dev/shm/aufs.xino", rwBranch, roBranches)

	//if error, try to load aufs kernel module
	if err := mount("none", target, "aufs", 0, branches); err != nil {
		log.Printf("Kernel does not support AUFS, trying to load the AUFS module with modprobe...")
		if err := exec.Command("modprobe", "aufs").Run(); err != nil {
			return fmt.Errorf("Unable to load the AUFS module")
		}
		log.Printf("...module loaded.")
		if err := mount("none", target, "aufs", 0, branches); err != nil {
			return fmt.Errorf("Unable to mount using aufs %s", err)
		}
	}
	return nil
}