aufs-driver.go

package driver

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"syscall"
)

type AufsDriver struct {
	OverlaysDir string
}

func (driver *AufsDriver) CreateVolume(path string) error {
	layerDir := driver.layerDir(path)

	err := os.MkdirAll(layerDir, 0755)
	if err != nil {
		return err
	}

	err = os.Mkdir(path, 0755)
	if err != nil {
		return err
	}

	return syscall.Mount(layerDir, path, "", syscall.MS_BIND, "")
}

func (driver *AufsDriver) DestroyVolume(path string) error {
	err := syscall.Unmount(path, 0)
	if err != nil {
		return err
	}

	err = os.RemoveAll(driver.layerDir(path))
	if err != nil {
		return err
	}

	return os.RemoveAll(path)
}

func (driver *AufsDriver) CreateCopyOnWriteLayer(path string, parent string) error {
	ancestry, err := driver.ancestry(parent)
	if err != nil {
		return err
	}

	childDir := driver.layerDir(path)

	err = os.MkdirAll(childDir, 0755)
	if err != nil {
		return err
	}

	err = os.MkdirAll(path, 0755)
	if err != nil {
		return err
	}

	layers := []string{fmt.Sprintf("br:%s=rw", childDir)}

	for _, lower := range ancestry {
		layers = append(layers, fmt.Sprintf("%s=ro+wh", lower))
	}

	opts := []string{
		strings.Join(layers, ":"),
		"dio",
		"xino=/dev/shm/aufs.xino",
		"dirperm1",
	}

	return syscall.Mount("aufs", path, "aufs", 0, strings.Join(opts, ","))
}

func (driver *AufsDriver) GetVolumeSizeInBytes(path string) (int64, error) {
	stdout := &bytes.Buffer{}
	cmd := exec.Command("du", "-s", driver.layerDir(path))
	cmd.Stdout = stdout

	err := cmd.Run()
	if err != nil {
		return 0, err
	}

	var size int64
	_, err = fmt.Sscanf(stdout.String(), "%d", &size)
	if err != nil {
		return 0, err
	}

	return size, nil
}

func (driver *AufsDriver) layerDir(path string) string {
	return filepath.Join(driver.OverlaysDir, driver.pathId(path))
}

func (driver *AufsDriver) ancestry(path string) ([]string, error) {
	ancestry := []string{}

	currentPath := path
	for {
		ancestry = append(ancestry, driver.layerDir(currentPath))

		parentVolume, err := os.Readlink(filepath.Join(filepath.Dir(currentPath), "parent"))
		if err != nil {
			if _, ok := err.(*os.PathError); ok {
				break
			}

			return nil, err
		}

		currentPath = filepath.Join(parentVolume, "volume")
	}

	return ancestry, nil
}

func (driver *AufsDriver) pathId(path string) string {
	return filepath.Base(filepath.Dir(path))
}