Refactor to optimize storage driver ApplyDiff()

To avoid an expensive call to archive.ChangesDirs() which walks two directory
trees and compares every entry, archive.ApplyLayer() has been extended to
also return the size of the layer changes.

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

archive/diff.go

@@ -15,7 +15,7 @@ import (
 	"github.com/docker/docker/pkg/system"
 )
 
-func UnpackLayer(dest string, layer ArchiveReader) error {
+func UnpackLayer(dest string, layer ArchiveReader) (size int64, err error) {
 	tr := tar.NewReader(layer)
 	trBuf := pools.BufioReader32KPool.Get(tr)
 	defer pools.BufioReader32KPool.Put(trBuf)
@@ -33,9 +33,11 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 			break
 		}
 		if err != nil {
-			return err
+			return 0, err
 		}
 
+		size += hdr.Size
+
 		// Normalize name, for safety and for a simple is-root check
 		hdr.Name = filepath.Clean(hdr.Name)
 
@@ -48,7 +50,7 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 			if _, err := os.Lstat(parentPath); err != nil && os.IsNotExist(err) {
 				err = os.MkdirAll(parentPath, 0600)
 				if err != nil {
-					return err
+					return 0, err
 				}
 			}
 		}
@@ -63,12 +65,12 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 				aufsHardlinks[basename] = hdr
 				if aufsTempdir == "" {
 					if aufsTempdir, err = ioutil.TempDir("", "dockerplnk"); err != nil {
-						return err
+						return 0, err
 					}
 					defer os.RemoveAll(aufsTempdir)
 				}
 				if err := createTarFile(filepath.Join(aufsTempdir, basename), dest, hdr, tr, true); err != nil {
-					return err
+					return 0, err
 				}
 			}
 			continue
@@ -77,10 +79,10 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 		path := filepath.Join(dest, hdr.Name)
 		rel, err := filepath.Rel(dest, path)
 		if err != nil {
-			return err
+			return 0, err
 		}
 		if strings.HasPrefix(rel, "..") {
-			return breakoutError(fmt.Errorf("%q is outside of %q", hdr.Name, dest))
+			return 0, breakoutError(fmt.Errorf("%q is outside of %q", hdr.Name, dest))
 		}
 		base := filepath.Base(path)
 
@@ -88,7 +90,7 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 			originalBase := base[len(".wh."):]
 			originalPath := filepath.Join(filepath.Dir(path), originalBase)
 			if err := os.RemoveAll(originalPath); err != nil {
-				return err
+				return 0, err
 			}
 		} else {
 			// If path exits we almost always just want to remove and replace it.
@@ -98,7 +100,7 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 			if fi, err := os.Lstat(path); err == nil {
 				if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
 					if err := os.RemoveAll(path); err != nil {
-						return err
+						return 0, err
 					}
 				}
 			}
@@ -113,18 +115,18 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 				linkBasename := filepath.Base(hdr.Linkname)
 				srcHdr = aufsHardlinks[linkBasename]
 				if srcHdr == nil {
-					return fmt.Errorf("Invalid aufs hardlink")
+					return 0, fmt.Errorf("Invalid aufs hardlink")
 				}
 				tmpFile, err := os.Open(filepath.Join(aufsTempdir, linkBasename))
 				if err != nil {
-					return err
+					return 0, err
 				}
 				defer tmpFile.Close()
 				srcData = tmpFile
 			}
 
 			if err := createTarFile(path, dest, srcHdr, srcData, true); err != nil {
-				return err
+				return 0, err
 			}
 
 			// Directory mtimes must be handled at the end to avoid further
@@ -139,27 +141,29 @@ func UnpackLayer(dest string, layer ArchiveReader) error {
 		path := filepath.Join(dest, hdr.Name)
 		ts := []syscall.Timespec{timeToTimespec(hdr.AccessTime), timeToTimespec(hdr.ModTime)}
 		if err := syscall.UtimesNano(path, ts); err != nil {
-			return err
+			return 0, err
 		}
 	}
-	return nil
+
+	return size, nil
 }
 
 // ApplyLayer parses a diff in the standard layer format from `layer`, and
-// applies it to the directory `dest`.
-func ApplyLayer(dest string, layer ArchiveReader) error {
+// applies it to the directory `dest`. Returns the size in bytes of the
+// contents of the layer.
+func ApplyLayer(dest string, layer ArchiveReader) (int64, error) {
 	dest = filepath.Clean(dest)
 
 	// We need to be able to set any perms
 	oldmask, err := system.Umask(0)
 	if err != nil {
-		return err
+		return 0, err
 	}
 	defer system.Umask(oldmask) // ignore err, ErrNotSupportedPlatform
 
 	layer, err = DecompressStream(layer)
 	if err != nil {
-		return err
+		return 0, err
 	}
 	return UnpackLayer(dest, layer)
 }