Add direct unpack support for overlay and aufs

Signed-off-by: Lantao Liu <lantaol@google.com>

archive/tar.go

@@ -19,9 +19,7 @@ package archive
 import (
 	"archive/tar"
 	"context"
-	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -91,11 +89,6 @@ const (
 	// archives.
 	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.
-	whiteoutLinkDir = whiteoutMetaPrefix + "plnk"
-
 	// whiteoutOpaqueDir file means directory has been made opaque - meaning
 	// readdir calls to this directory do not follow to lower layers.
 	whiteoutOpaqueDir = whiteoutMetaPrefix + ".opq"
@@ -130,10 +123,6 @@ func applyNaive(ctx context.Context, root string, tr *tar.Reader, options ApplyO
 		// Used for handling opaque directory markers which
 		// may occur out of order
 		unpackedPaths = make(map[string]struct{})
-
-		// Used for aufs plink directory
-		aufsTempdir   = ""
-		aufsHardlinks = make(map[string]*tar.Header)
 	)
 
 	// Iterate through the files in the archive.
@@ -201,40 +190,15 @@ func applyNaive(ctx context.Context, root string, tr *tar.Reader, options ApplyO
 			}
 		}
 
-		// Skip AUFS metadata dirs
-		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, whiteoutLinkDir) && hdr.Typeflag == tar.TypeReg {
-				basename := filepath.Base(hdr.Name)
-				aufsHardlinks[basename] = hdr
-				if aufsTempdir == "" {
-					if aufsTempdir, err = ioutil.TempDir(os.Getenv("XDG_RUNTIME_DIR"), "dockerplnk"); err != nil {
-						return 0, err
-					}
-					defer os.RemoveAll(aufsTempdir)
-				}
-				p, err := fs.RootPath(aufsTempdir, basename)
-				if err != nil {
-					return 0, err
-				}
-				if err := createTarFile(ctx, p, root, hdr, tr); err != nil {
-					return 0, err
-				}
-			}
-
-			if hdr.Name != whiteoutOpaqueDir {
-				continue
-			}
-		}
-
-		if strings.HasPrefix(base, whiteoutPrefix) {
+		// Naive whiteout convert function which handles whiteout files by
+		// removing the target files.
+		convertWhiteout := func(hdr *tar.Header, path string) (bool, error) {
+			base := filepath.Base(path)
 			dir := filepath.Dir(path)
 			if base == whiteoutOpaqueDir {
 				_, err := os.Lstat(dir)
 				if err != nil {
-					return 0, err
+					return false, err
 				}
 				err = filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
 					if err != nil {
@@ -252,26 +216,29 @@ func applyNaive(ctx context.Context, root string, tr *tar.Reader, options ApplyO
 					}
 					return nil
 				})
-				if err != nil {
-					return 0, err
-				}
-				continue
+				return false, err
 			}
 
-			originalBase := base[len(whiteoutPrefix):]
-			originalPath := filepath.Join(dir, originalBase)
+			if strings.HasPrefix(base, whiteoutPrefix) {
+				originalBase := base[len(whiteoutPrefix):]
+				originalPath := filepath.Join(dir, originalBase)
 
-			// Ensure originalPath is under dir
-			if dir[len(dir)-1] != filepath.Separator {
-				dir += string(filepath.Separator)
-			}
-			if !strings.HasPrefix(originalPath, dir) {
-				return 0, errors.Wrapf(errInvalidArchive, "invalid whiteout name: %v", base)
+				return false, os.RemoveAll(originalPath)
 			}
 
-			if err := os.RemoveAll(originalPath); err != nil {
-				return 0, err
-			}
+			return true, nil
+		}
+		if options.ConvertWhiteout != nil {
+			convertWhiteout = options.ConvertWhiteout
+		}
+		if err := validateWhiteout(path); err != nil {
+			return 0, err
+		}
+		writeFile, err := convertWhiteout(hdr, path)
+		if err != nil {
+			return 0, errors.Wrapf(err, "failed to convert whiteout file %q", hdr.Name)
+		}
+		if !writeFile {
 			continue
 		}
 		// If path exits we almost always just want to remove and replace it.
@@ -289,26 +256,6 @@ func applyNaive(ctx context.Context, root string, tr *tar.Reader, options ApplyO
 		srcData := io.Reader(tr)
 		srcHdr := hdr
 
-		// 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), whiteoutLinkDir) {
-			linkBasename := filepath.Base(hdr.Linkname)
-			srcHdr = aufsHardlinks[linkBasename]
-			if srcHdr == nil {
-				return 0, fmt.Errorf("invalid aufs hardlink")
-			}
-			p, err := fs.RootPath(aufsTempdir, linkBasename)
-			if err != nil {
-				return 0, err
-			}
-			tmpFile, err := os.Open(p)
-			if err != nil {
-				return 0, err
-			}
-			defer tmpFile.Close()
-			srcData = tmpFile
-		}
-
 		if err := createTarFile(ctx, path, root, srcHdr, srcData); err != nil {
 			return 0, err
 		}
@@ -684,3 +631,26 @@ func hardlinkRootPath(root, linkname string) (string, error) {
 	}
 	return targetPath, nil
 }
+
+func validateWhiteout(path string) error {
+	base := filepath.Base(path)
+	dir := filepath.Dir(path)
+
+	if base == whiteoutOpaqueDir {
+		return nil
+	}
+
+	if strings.HasPrefix(base, whiteoutPrefix) {
+		originalBase := base[len(whiteoutPrefix):]
+		originalPath := filepath.Join(dir, originalBase)
+
+		// Ensure originalPath is under dir
+		if dir[len(dir)-1] != filepath.Separator {
+			dir += string(filepath.Separator)
+		}
+		if !strings.HasPrefix(originalPath, dir) {
+			return errors.Wrapf(errInvalidArchive, "invalid whiteout name: %v", base)
+		}
+	}
+	return nil
+}