@@ -322,7 +322,7 @@ func (a *Driver) Diff(id, parent string) (archive.Archive, error) {

 	// AUFS doesn't need the parent layer to produce a diff.

 	return archive.TarWithOptions(path.Join(a.rootPath(), "diff", id), &archive.TarOptions{

 		Compression:     archive.Uncompressed,

-		ExcludePatterns: []string{".wh..wh.*", "!.wh..wh..opq"},

+		ExcludePatterns: []string{archive.WhiteoutMetaPrefix + "*", "!" + archive.WhiteoutOpaqueDir},

 	})

 }

@@ -102,7 +102,7 @@ func Changes(layers []string, rw string) ([]Change, error) {

 		}

 		// Skip AUFS metadata

-		if matched, err := filepath.Match(string(os.PathSeparator)+".wh..wh.*", path); err != nil || matched {

+		if matched, err := filepath.Match(string(os.PathSeparator)+WhiteoutMetaPrefix+"*", path); err != nil || matched {

 			return err

 		}

@@ -113,8 +113,8 @@ func Changes(layers []string, rw string) ([]Change, error) {

 		// Find out what kind of modification happened

 		file := filepath.Base(path)

 		// If there is a whiteout, then the file was removed

-		if strings.HasPrefix(file, ".wh.") {

-			originalFile := file[len(".wh."):]

+		if strings.HasPrefix(file, WhiteoutPrefix) {

+			originalFile := file[len(WhiteoutPrefix):]

 			change.Path = filepath.Join(filepath.Dir(path), originalFile)

 			change.Kind = ChangeDelete

 		} else {

@@ -362,7 +362,7 @@ func ExportChanges(dir string, changes []Change) (Archive, error) {

 			if change.Kind == ChangeDelete {

 				whiteOutDir := filepath.Dir(change.Path)

 				whiteOutBase := filepath.Base(change.Path)

-				whiteOut := filepath.Join(whiteOutDir, ".wh."+whiteOutBase)

+				whiteOut := filepath.Join(whiteOutDir, WhiteoutPrefix+whiteOutBase)

 				timestamp := time.Now()

 				hdr := &tar.Header{

 					Name:       whiteOut[1:],

@@ -83,11 +83,11 @@ func UnpackLayer(dest string, layer Reader) (size int64, err error) {

 		}

 		// Skip AUFS metadata dirs

-		if strings.HasPrefix(hdr.Name, ".wh..wh.") {

+		if strings.HasPrefix(hdr.Name, WhiteoutMetaPrefix) {

 			// Regular files inside /.wh..wh.plnk can be used as hardlink targets

 			// We don't want this directory, but we need the files in them so that

 			// such hardlinks can be resolved.

-			if strings.HasPrefix(hdr.Name, ".wh..wh.plnk") && hdr.Typeflag == tar.TypeReg {

+			if strings.HasPrefix(hdr.Name, WhiteoutLinkDir) && hdr.Typeflag == tar.TypeReg {

 				basename := filepath.Base(hdr.Name)

 				aufsHardlinks[basename] = hdr

 				if aufsTempdir == "" {

@@ -101,7 +101,7 @@ func UnpackLayer(dest string, layer Reader) (size int64, err error) {

 				}

 			}

-			if hdr.Name != ".wh..wh..opq" {

+			if hdr.Name != WhiteoutOpaqueDir {

 				continue

 			}

 		}

@@ -117,10 +117,9 @@ func UnpackLayer(dest string, layer Reader) (size int64, err error) {

 		}

 		base := filepath.Base(path)

-		if strings.HasPrefix(base, ".wh.") {

-			originalBase := base[len(".wh."):]

+		if strings.HasPrefix(base, WhiteoutPrefix) {

 			dir := filepath.Dir(path)

-			if originalBase == ".wh..opq" {

+			if base == WhiteoutOpaqueDir {

 				fi, err := os.Lstat(dir)

 				if err != nil && !os.IsNotExist(err) {

 					return 0, err

@@ -132,6 +131,7 @@ func UnpackLayer(dest string, layer Reader) (size int64, err error) {

 					return 0, err

 				}

 			} else {

+				originalBase := base[len(WhiteoutPrefix):]

 				originalPath := filepath.Join(dir, originalBase)

 				if err := os.RemoveAll(originalPath); err != nil {

 					return 0, err

@@ -156,7 +156,7 @@ func UnpackLayer(dest string, layer Reader) (size int64, err error) {

 			// Hard links into /.wh..wh.plnk don't work, as we don't extract that directory, so

 			// we manually retarget these into the temporary files we extracted them into

-			if hdr.Typeflag == tar.TypeLink && strings.HasPrefix(filepath.Clean(hdr.Linkname), ".wh..wh.plnk") {

+			if hdr.Typeflag == tar.TypeLink && strings.HasPrefix(filepath.Clean(hdr.Linkname), WhiteoutLinkDir) {

 				linkBasename := filepath.Base(hdr.Linkname)

 				srcHdr = aufsHardlinks[linkBasename]

 				if srcHdr == nil {

new file mode 100644

@@ -0,0 +1,23 @@

+package archive

+

+// Whiteouts are files with a special meaning for the layered filesystem.

+// Docker uses AUFS whiteout files inside exported archives. In other

+// filesystems these files are generated/handled on tar creation/extraction.

+

+// WhiteoutPrefix prefix means file is a whiteout. If this is followed by a

+// filename this means that file has been removed from the base layer.

+const WhiteoutPrefix = ".wh."

+

+// WhiteoutMetaPrefix prefix means whiteout has a special meaning and is not

+// for remoing an actaul file. Normally these files are excluded from exported

+// archives.

+const WhiteoutMetaPrefix = WhiteoutPrefix + WhiteoutPrefix

+

+// WhiteoutLinkDir is a directory AUFS uses for storing hardlink links to other

+// layers. Normally these should not go into exported archives and all changed

+// hardlinks should be copied to the top layer.

+const WhiteoutLinkDir = WhiteoutMetaPrefix + "plnk"

+

+// WhiteoutOpaqueDir file means directory has been made opaque - meaning

+// readdir calls to this directory do not follow to lower layers.

+const WhiteoutOpaqueDir = WhiteoutMetaPrefix + ".opq"