Allow to downgrade local volumes from > 1.7 to 1.6.

Signed-off-by: David Calavera <david.calavera@gmail.com>

volume/local/local.go

@@ -6,29 +6,46 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 
 	"github.com/docker/docker/volume"
 )
 
-func New(rootDirectory string) (*Root, error) {
+// VolumeDataPathName is the name of the directory where the volume data is stored.
+// It uses a very distintive name to avoid colissions migrating data between
+// Docker versions.
+const (
+	VolumeDataPathName = "_data"
+	volumesPathName    = "volumes"
+)
+
+var oldVfsDir = filepath.Join("vfs", "dir")
+
+func New(scope string) (*Root, error) {
+	rootDirectory := filepath.Join(scope, volumesPathName)
+
 	if err := os.MkdirAll(rootDirectory, 0700); err != nil {
 		return nil, err
 	}
+
 	r := &Root{
+		scope:   scope,
 		path:    rootDirectory,
 		volumes: make(map[string]*Volume),
 	}
+
 	dirs, err := ioutil.ReadDir(rootDirectory)
 	if err != nil {
 		return nil, err
 	}
+
 	for _, d := range dirs {
 		name := filepath.Base(d.Name())
 		r.volumes[name] = &Volume{
 			driverName: r.Name(),
 			name:       name,
-			path:       filepath.Join(rootDirectory, name),
+			path:       r.DataPath(name),
 		}
 	}
 	return r, nil
@@ -36,10 +53,15 @@ func New(rootDirectory string) (*Root, error) {
 
 type Root struct {
 	m       sync.Mutex
+	scope   string
 	path    string
 	volumes map[string]*Volume
 }
 
+func (r *Root) DataPath(volumeName string) string {
+	return filepath.Join(r.path, volumeName, VolumeDataPathName)
+}
+
 func (r *Root) Name() string {
 	return "local"
 }
@@ -47,12 +69,13 @@ func (r *Root) Name() string {
 func (r *Root) Create(name string) (volume.Volume, error) {
 	r.m.Lock()
 	defer r.m.Unlock()
+
 	v, exists := r.volumes[name]
 	if !exists {
-		path := filepath.Join(r.path, name)
-		if err := os.Mkdir(path, 0755); err != nil {
+		path := r.DataPath(name)
+		if err := os.MkdirAll(path, 0755); err != nil {
 			if os.IsExist(err) {
-				return nil, fmt.Errorf("volume already exists under %s", path)
+				return nil, fmt.Errorf("volume already exists under %s", filepath.Dir(path))
 			}
 			return nil, err
 		}
@@ -76,12 +99,40 @@ func (r *Root) Remove(v volume.Volume) error {
 	}
 	lv.release()
 	if lv.usedCount == 0 {
+		realPath, err := filepath.EvalSymlinks(lv.path)
+		if err != nil {
+			return err
+		}
+		if !r.scopedPath(realPath) {
+			return fmt.Errorf("Unable to remove a directory of out the Docker root: %s", realPath)
+		}
+
+		if err := os.RemoveAll(realPath); err != nil {
+			return err
+		}
+
 		delete(r.volumes, lv.name)
-		return os.RemoveAll(lv.path)
+		return os.RemoveAll(filepath.Dir(lv.path))
 	}
 	return nil
 }
 
+// scopedPath verifies that the path where the volume is located
+// is under Docker's root and the valid local paths.
+func (r *Root) scopedPath(realPath string) bool {
+	// Volumes path for Docker version >= 1.7
+	if strings.HasPrefix(realPath, filepath.Join(r.scope, volumesPathName)) {
+		return true
+	}
+
+	// Volumes path for Docker version < 1.7
+	if strings.HasPrefix(realPath, filepath.Join(r.scope, oldVfsDir)) {
+		return true
+	}
+
+	return false
+}
+
 type Volume struct {
 	m         sync.Mutex
 	usedCount int