@@ -8,6 +8,7 @@ import (

 	"os"

 	"os/exec"

 	"path"

+	"syscall"

 	"testing"

 	"time"

@@ -63,6 +64,50 @@ func TestCmdStreamGood(t *testing.T) {

 	}

 }

+func TestTarFiles(t *testing.T) {

+	// try without hardlinks

+	if err := checkNoChanges(1000, false); err != nil {

+		t.Fatal(err)

+	}

+	// try with hardlinks

+	if err := checkNoChanges(1000, true); err != nil {

+		t.Fatal(err)

+	}

+}

+

+func checkNoChanges(fileNum int, hardlinks bool) error {

+	srcDir, err := ioutil.TempDir("", "docker-test-srcDir")

+	if err != nil {

+		return err

+	}

+	defer os.RemoveAll(srcDir)

+

+	destDir, err := ioutil.TempDir("", "docker-test-destDir")

+	if err != nil {

+		return err

+	}

+	defer os.RemoveAll(destDir)

+

+	_, err = prepareUntarSourceDirectory(fileNum, srcDir, hardlinks)

+	if err != nil {

+		return err

+	}

+

+	err = TarUntar(srcDir, destDir)

+	if err != nil {

+		return err

+	}

+

+	changes, err := ChangesDirs(destDir, srcDir)

+	if err != nil {

+		return err

+	}

+	if len(changes) > 0 {

+		return fmt.Errorf("with %d files and %v hardlinks: expected 0 changes, got %d", fileNum, hardlinks, len(changes))

+	}

+	return nil

+}

+

 func tarUntar(t *testing.T, origin string, options *TarOptions) ([]Change, error) {

 	archive, err := TarWithOptions(origin, options)

 	if err != nil {

@@ -204,13 +249,42 @@ func TestUntarUstarGnuConflict(t *testing.T) {

 	}

 }

-func prepareUntarSourceDirectory(numberOfFiles int, targetPath string) (int, error) {

+func getNlink(path string) (uint64, error) {

+	stat, err := os.Stat(path)

+	if err != nil {

+		return 0, err

+	}

+	statT, ok := stat.Sys().(*syscall.Stat_t)

+	if !ok {

+		return 0, fmt.Errorf("expected type *syscall.Stat_t, got %t", stat.Sys())

+	}

+	return statT.Nlink, nil

+}

+

+func getInode(path string) (uint64, error) {

+	stat, err := os.Stat(path)

+	if err != nil {

+		return 0, err

+	}

+	statT, ok := stat.Sys().(*syscall.Stat_t)

+	if !ok {

+		return 0, fmt.Errorf("expected type *syscall.Stat_t, got %t", stat.Sys())

+	}

+	return statT.Ino, nil

+}

+

+func prepareUntarSourceDirectory(numberOfFiles int, targetPath string, makeLinks bool) (int, error) {

 	fileData := []byte("fooo")

 	for n := 0; n < numberOfFiles; n++ {

 		fileName := fmt.Sprintf("file-%d", n)

 		if err := ioutil.WriteFile(path.Join(targetPath, fileName), fileData, 0700); err != nil {

 			return 0, err

 		}

+		if makeLinks {

+			if err := os.Link(path.Join(targetPath, fileName), path.Join(targetPath, fileName+"-link")); err != nil {

+				return 0, err

+			}

+		}

 	}

 	totalSize := numberOfFiles * len(fileData)

 	return totalSize, nil

@@ -226,14 +300,43 @@ func BenchmarkTarUntar(b *testing.B) {

 		b.Fatal(err)

 	}

 	target := path.Join(tempDir, "dest")

-	n, err := prepareUntarSourceDirectory(100, origin)

+	n, err := prepareUntarSourceDirectory(100, origin, false)

 	if err != nil {

 		b.Fatal(err)

 	}

+	defer os.RemoveAll(origin)

+	defer os.RemoveAll(tempDir)

+

 	b.ResetTimer()

 	b.SetBytes(int64(n))

+	for n := 0; n < b.N; n++ {

+		err := TarUntar(origin, target)

+		if err != nil {

+			b.Fatal(err)

+		}

+		os.RemoveAll(target)

+	}

+}

+

+func BenchmarkTarUntarWithLinks(b *testing.B) {

+	origin, err := ioutil.TempDir("", "docker-test-untar-origin")

+	if err != nil {

+		b.Fatal(err)

+	}

+	tempDir, err := ioutil.TempDir("", "docker-test-untar-destination")

+	if err != nil {

+		b.Fatal(err)

+	}

+	target := path.Join(tempDir, "dest")

+	n, err := prepareUntarSourceDirectory(100, origin, true)

+	if err != nil {

+		b.Fatal(err)

+	}

 	defer os.RemoveAll(origin)

 	defer os.RemoveAll(tempDir)

+

+	b.ResetTimer()

+	b.SetBytes(int64(n))

 	for n := 0; n < b.N; n++ {

 		err := TarUntar(origin, target)

 		if err != nil {