@@ -26,11 +26,11 @@ import (

 	"github.com/dotcloud/docker/archive"

 	"github.com/dotcloud/docker/graphdriver"

 	"github.com/dotcloud/docker/utils"

-	"log"

 	"os"

 	"os/exec"

 	"path"

 	"strings"

+	"syscall"

 )

 func init() {

@@ -313,24 +313,44 @@ func (a *Driver) Cleanup() error {

 	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)

+func (a *Driver) aufsMount(ro []string, rw, target string) (err error) {

+	defer func() {

+		if err != nil {

+			Unmount(target)

+		}

+	}()

-	//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")

+	if err = a.tryMount(ro, rw, target); err != nil {

+		if err = a.mountRw(rw, target); err != nil {

+			return

 		}

-		log.Printf("...module loaded.")

-		if err := mount("none", target, "aufs", 0, branches); err != nil {

-			return fmt.Errorf("Unable to mount using aufs %s", err)

+

+		for _, layer := range ro {

+			branch := fmt.Sprintf("append:%s=ro+wh", layer)

+			if err = mount("none", target, "aufs", syscall.MS_REMOUNT, branch); err != nil {

+				return

+			}

 		}

 	}

-	return nil

+	return

+}

+

+// Try to mount using the aufs fast path, if this fails then

+// append ro layers.

+func (a *Driver) tryMount(ro []string, rw, target string) (err error) {

+	var (

+		rwBranch   = fmt.Sprintf("%s=rw", rw)

+		roBranches = fmt.Sprintf("%s=ro+wh:", strings.Join(ro, "=ro+wh:"))

+	)

+	return mount("none", target, "aufs", 0, fmt.Sprintf("br:%v:%v,xino=/dev/shm/aufs.xino", rwBranch, roBranches))

+}

+

+func (a *Driver) mountRw(rw, target string) error {

+	return mount("none", target, "aufs", 0, fmt.Sprintf("br:%s,xino=/dev/shm/aufs.xino", rw))

+}

+

+func rollbackMount(target string, err error) {

+	if err != nil {

+		Unmount(target)

+	}

 }

@@ -1,7 +1,11 @@

 package aufs

 import (

+	"crypto/sha256"

+	"encoding/hex"

+	"fmt"

 	"github.com/dotcloud/docker/archive"

+	"io/ioutil"

 	"os"

 	"path"

 	"testing"

@@ -621,3 +625,70 @@ func TestApplyDiff(t *testing.T) {

 		t.Fatal(err)

 	}

 }

+

+func hash(c string) string {

+	h := sha256.New()

+	fmt.Fprint(h, c)

+	return hex.EncodeToString(h.Sum(nil))

+}

+

+func TestMountMoreThan42Layers(t *testing.T) {

+	d := newDriver(t)

+	defer os.RemoveAll(tmp)

+	defer d.Cleanup()

+	var last string

+	var expected int

+

+	for i := 1; i < 127; i++ {

+		expected++

+		var (

+			parent  = fmt.Sprintf("%d", i-1)

+			current = fmt.Sprintf("%d", i)

+		)

+

+		if parent == "0" {

+			parent = ""

+		} else {

+			parent = hash(parent)

+		}

+		current = hash(current)

+

+		if err := d.Create(current, parent); err != nil {

+			t.Logf("Current layer %d", i)

+			t.Fatal(err)

+		}

+		point, err := d.Get(current)

+		if err != nil {

+			t.Logf("Current layer %d", i)

+			t.Fatal(err)

+		}

+		f, err := os.Create(path.Join(point, current))

+		if err != nil {

+			t.Logf("Current layer %d", i)

+			t.Fatal(err)

+		}

+		f.Close()

+

+		if i%10 == 0 {

+			if err := os.Remove(path.Join(point, parent)); err != nil {

+				t.Logf("Current layer %d", i)

+				t.Fatal(err)

+			}

+			expected--

+		}

+		last = current

+	}

+

+	// Perform the actual mount for the top most image

+	point, err := d.Get(last)

+	if err != nil {

+		t.Fatal(err)

+	}

+	files, err := ioutil.ReadDir(point)

+	if err != nil {

+		t.Fatal(err)

+	}

+	if len(files) != expected {

+		t.Fatalf("Expected %d got %d", expected, len(files))

+	}

+}

@@ -2,6 +2,6 @@ package aufs

 import "syscall"

-func mount(source string, target string, fstype string, flags uintptr, data string) (err error) {

+func mount(source string, target string, fstype string, flags uintptr, data string) error {

 	return syscall.Mount(source, target, fstype, flags, data)

 }

@@ -24,8 +24,10 @@ import (

 	"time"

 )

-// Set the max depth to the aufs restriction

-const MaxImageDepth = 42

+// Set the max depth to the aufs default that most

+// kernels are compiled with

+// For more information see: http://sourceforge.net/p/aufs/aufs3-standalone/ci/aufs3.12/tree/config.mk

+const MaxImageDepth = 127

 var defaultDns = []string{"8.8.8.8", "8.8.4.4"}