func (s *saveSession) saveImage(id image.ID) (map[layer.DiffID]distribution.Descriptor, error) {
	img, err := s.is.Get(id)
	if err != nil {
		return nil, err
	}

	if len(img.RootFS.DiffIDs) == 0 {
		return nil, fmt.Errorf("empty export - not implemented")
	}

	var parent digest.Digest
	var layers []string
	var foreignSrcs map[layer.DiffID]distribution.Descriptor
	for i := range img.RootFS.DiffIDs {
		v1Img := image.V1Image{
			Created: img.Created,
		}
		if i == len(img.RootFS.DiffIDs)-1 {
			v1Img = img.V1Image
		}
		rootFS := *img.RootFS
		rootFS.DiffIDs = rootFS.DiffIDs[:i+1]
		v1ID, err := v1.CreateID(v1Img, rootFS.ChainID(), parent)
		if err != nil {
			return nil, err
		}

		v1Img.ID = v1ID.Hex()
		if parent != "" {
			v1Img.Parent = parent.Hex()
		}

		src, err := s.saveLayer(rootFS.ChainID(), v1Img, img.Created)
		if err != nil {
			return nil, err
		}
		layers = append(layers, v1Img.ID)
		parent = v1ID
		if src.Digest != "" {
			if foreignSrcs == nil {
				foreignSrcs = make(map[layer.DiffID]distribution.Descriptor)
			}
			foreignSrcs[img.RootFS.DiffIDs[i]] = src
		}
	}

	configFile := filepath.Join(s.outDir, id.Digest().Hex()+".json")
	if err := ioutil.WriteFile(configFile, img.RawJSON(), 0644); err != nil {
		return nil, err
	}
	if err := system.Chtimes(configFile, img.Created, img.Created); err != nil {
		return nil, err
	}

	s.images[id].layers = layers
	return foreignSrcs, nil
}

func (s *saveSession) saveLayer(id layer.ChainID, legacyImg image.V1Image, createdTime time.Time) error {
	if _, exists := s.savedLayers[legacyImg.ID]; exists {
		return nil
	}

	outDir := filepath.Join(s.outDir, legacyImg.ID)
	if err := os.Mkdir(outDir, 0755); err != nil {
		return err
	}

	// todo: why is this version file here?
	if err := ioutil.WriteFile(filepath.Join(outDir, legacyVersionFileName), []byte("1.0"), 0644); err != nil {
		return err
	}

	imageConfig, err := json.Marshal(legacyImg)
	if err != nil {
		return err
	}

	if err := ioutil.WriteFile(filepath.Join(outDir, legacyConfigFileName), imageConfig, 0644); err != nil {
		return err
	}

	// serialize filesystem
	tarFile, err := os.Create(filepath.Join(outDir, legacyLayerFileName))
	if err != nil {
		return err
	}
	defer tarFile.Close()

	l, err := s.ls.Get(id)
	if err != nil {
		return err
	}
	defer layer.ReleaseAndLog(s.ls, l)

	arch, err := l.TarStream()
	if err != nil {
		return err
	}
	defer arch.Close()

	if _, err := io.Copy(tarFile, arch); err != nil {
		return err
	}

	for _, fname := range []string{"", legacyVersionFileName, legacyConfigFileName, legacyLayerFileName} {
		// todo: maybe save layer created timestamp?
		if err := system.Chtimes(filepath.Join(outDir, fname), createdTime, createdTime); err != nil {
			return err
		}
	}

	s.savedLayers[legacyImg.ID] = struct{}{}
	return nil
}

func createSampleDir(t *testing.T, root string) {
	files := []FileData{
		{Regular, "file1", "file1\n", 0600},
		{Regular, "file2", "file2\n", 0666},
		{Regular, "file3", "file3\n", 0404},
		{Regular, "file4", "file4\n", 0600},
		{Regular, "file5", "file5\n", 0600},
		{Regular, "file6", "file6\n", 0600},
		{Regular, "file7", "file7\n", 0600},
		{Dir, "dir1", "", 0740},
		{Regular, "dir1/file1-1", "file1-1\n", 01444},
		{Regular, "dir1/file1-2", "file1-2\n", 0666},
		{Dir, "dir2", "", 0700},
		{Regular, "dir2/file2-1", "file2-1\n", 0666},
		{Regular, "dir2/file2-2", "file2-2\n", 0666},
		{Dir, "dir3", "", 0700},
		{Regular, "dir3/file3-1", "file3-1\n", 0666},
		{Regular, "dir3/file3-2", "file3-2\n", 0666},
		{Dir, "dir4", "", 0700},
		{Regular, "dir4/file3-1", "file4-1\n", 0666},
		{Regular, "dir4/file3-2", "file4-2\n", 0666},
		{Symlink, "symlink1", "target1", 0666},
		{Symlink, "symlink2", "target2", 0666},
		{Symlink, "symlink3", root + "/file1", 0666},
		{Symlink, "symlink4", root + "/symlink3", 0666},
		{Symlink, "dirSymlink", root + "/dir1", 0740},
	}

	now := time.Now()
	for _, info := range files {
		p := path.Join(root, info.path)
		if info.filetype == Dir {
			if err := os.MkdirAll(p, info.permissions); err != nil {
				t.Fatal(err)
			}
		} else if info.filetype == Regular {
			if err := ioutil.WriteFile(p, []byte(info.contents), info.permissions); err != nil {
				t.Fatal(err)
			}
		} else if info.filetype == Symlink {
			if err := os.Symlink(info.contents, p); err != nil {
				t.Fatal(err)
			}
		}

		if info.filetype != Symlink {
			// Set a consistent ctime, atime for all files and dirs
			if err := system.Chtimes(p, now, now); err != nil {
				t.Fatal(err)
			}
		}
	}
}

func (s *saveSession) saveImage(id image.ID) error {
	img, err := s.is.Get(id)
	if err != nil {
		return err
	}

	if len(img.RootFS.DiffIDs) == 0 {
		return fmt.Errorf("empty export - not implemented")
	}

	var parent digest.Digest
	var layers []string
	for i := range img.RootFS.DiffIDs {
		v1Img := image.V1Image{}
		if i == len(img.RootFS.DiffIDs)-1 {
			v1Img = img.V1Image
		}
		rootFS := *img.RootFS
		rootFS.DiffIDs = rootFS.DiffIDs[:i+1]
		v1ID, err := v1.CreateID(v1Img, rootFS.ChainID(), parent)
		if err != nil {
			return err
		}

		v1Img.ID = v1ID.Hex()
		if parent != "" {
			v1Img.Parent = parent.Hex()
		}

		if err := s.saveLayer(rootFS.ChainID(), v1Img, img.Created); err != nil {
			return err
		}
		layers = append(layers, v1Img.ID)
		parent = v1ID
	}

	configFile := filepath.Join(s.outDir, digest.Digest(id).Hex()+".json")
	if err := ioutil.WriteFile(configFile, img.RawJSON(), 0644); err != nil {
		return err
	}
	if err := system.Chtimes(configFile, img.Created, img.Created); err != nil {
		return err
	}

	s.images[id].layers = layers
	return nil
}

func (s *saveSession) saveLayer(id layer.ChainID, legacyImg image.V1Image, createdTime time.Time) (distribution.Descriptor, error) {
	if _, exists := s.savedLayers[legacyImg.ID]; exists {
		return distribution.Descriptor{}, nil
	}

	outDir := filepath.Join(s.outDir, legacyImg.ID)
	if err := os.Mkdir(outDir, 0755); err != nil {
		return distribution.Descriptor{}, err
	}

	// todo: why is this version file here?
	if err := ioutil.WriteFile(filepath.Join(outDir, legacyVersionFileName), []byte("1.0"), 0644); err != nil {
		return distribution.Descriptor{}, err
	}

	imageConfig, err := json.Marshal(legacyImg)
	if err != nil {
		return distribution.Descriptor{}, err
	}

	if err := ioutil.WriteFile(filepath.Join(outDir, legacyConfigFileName), imageConfig, 0644); err != nil {
		return distribution.Descriptor{}, err
	}

	// serialize filesystem
	layerPath := filepath.Join(outDir, legacyLayerFileName)
	l, err := s.ls.Get(id)
	if err != nil {
		return distribution.Descriptor{}, err
	}
	defer layer.ReleaseAndLog(s.ls, l)

	if oldPath, exists := s.diffIDPaths[l.DiffID()]; exists {
		relPath, err := filepath.Rel(outDir, oldPath)
		if err != nil {
			return distribution.Descriptor{}, err
		}
		os.Symlink(relPath, layerPath)
	} else {

		tarFile, err := os.Create(layerPath)
		if err != nil {
			return distribution.Descriptor{}, err
		}
		defer tarFile.Close()

		arch, err := l.TarStream()
		if err != nil {
			return distribution.Descriptor{}, err
		}
		defer arch.Close()

		if _, err := io.Copy(tarFile, arch); err != nil {
			return distribution.Descriptor{}, err
		}

		for _, fname := range []string{"", legacyVersionFileName, legacyConfigFileName, legacyLayerFileName} {
			// todo: maybe save layer created timestamp?
			if err := system.Chtimes(filepath.Join(outDir, fname), createdTime, createdTime); err != nil {
				return distribution.Descriptor{}, err
			}
		}

		s.diffIDPaths[l.DiffID()] = layerPath
	}
	s.savedLayers[legacyImg.ID] = struct{}{}

	var src distribution.Descriptor
	if fs, ok := l.(distribution.Describable); ok {
		src = fs.Descriptor()
	}
	return src, nil
}

func (s *saveSession) save(outStream io.Writer) error {
	s.savedLayers = make(map[string]struct{})
	s.diffIDPaths = make(map[layer.DiffID]string)

	// get image json
	tempDir, err := ioutil.TempDir("", "docker-export-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(tempDir)

	s.outDir = tempDir
	reposLegacy := make(map[string]map[string]string)

	var manifest []manifestItem
	var parentLinks []parentLink

	for id, imageDescr := range s.images {
		foreignSrcs, err := s.saveImage(id)
		if err != nil {
			return err
		}

		var repoTags []string
		var layers []string

		for _, ref := range imageDescr.refs {
			if _, ok := reposLegacy[ref.Name()]; !ok {
				reposLegacy[ref.Name()] = make(map[string]string)
			}
			reposLegacy[ref.Name()][ref.Tag()] = imageDescr.layers[len(imageDescr.layers)-1]
			repoTags = append(repoTags, ref.String())
		}

		for _, l := range imageDescr.layers {
			layers = append(layers, filepath.Join(l, legacyLayerFileName))
		}

		manifest = append(manifest, manifestItem{
			Config:       digest.Digest(id).Hex() + ".json",
			RepoTags:     repoTags,
			Layers:       layers,
			LayerSources: foreignSrcs,
		})

		parentID, _ := s.is.GetParent(id)
		parentLinks = append(parentLinks, parentLink{id, parentID})
		s.tarexporter.loggerImgEvent.LogImageEvent(id.String(), id.String(), "save")
	}

	for i, p := range validatedParentLinks(parentLinks) {
		if p.parentID != "" {
			manifest[i].Parent = p.parentID
		}
	}

	if len(reposLegacy) > 0 {
		reposFile := filepath.Join(tempDir, legacyRepositoriesFileName)
		f, err := os.OpenFile(reposFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
		if err != nil {
			f.Close()
			return err
		}
		if err := json.NewEncoder(f).Encode(reposLegacy); err != nil {
			return err
		}
		if err := f.Close(); err != nil {
			return err
		}
		if err := system.Chtimes(reposFile, time.Unix(0, 0), time.Unix(0, 0)); err != nil {
			return err
		}
	}

	manifestFileName := filepath.Join(tempDir, manifestFileName)
	f, err := os.OpenFile(manifestFileName, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		f.Close()
		return err
	}
	if err := json.NewEncoder(f).Encode(manifest); err != nil {
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	if err := system.Chtimes(manifestFileName, time.Unix(0, 0), time.Unix(0, 0)); err != nil {
		return err
	}

	fs, err := archive.Tar(tempDir, archive.Uncompressed)
	if err != nil {
		return err
	}
	defer fs.Close()

	if _, err := io.Copy(outStream, fs); err != nil {
		return err
	}
	return nil
//.........这里部分代码省略.........

func (b *Builder) download(srcURL string) (fi builder.FileInfo, err error) {
	// get filename from URL
	u, err := url.Parse(srcURL)
	if err != nil {
		return
	}
	path := filepath.FromSlash(u.Path) // Ensure in platform semantics
	if strings.HasSuffix(path, string(os.PathSeparator)) {
		path = path[:len(path)-1]
	}
	parts := strings.Split(path, string(os.PathSeparator))
	filename := parts[len(parts)-1]
	if filename == "" {
		err = fmt.Errorf("cannot determine filename from url: %s", u)
		return
	}

	// Initiate the download
	resp, err := httputils.Download(srcURL)
	if err != nil {
		return
	}

	// Prepare file in a tmp dir
	tmpDir, err := ioutils.TempDir("", "docker-remote")
	if err != nil {
		return
	}
	defer func() {
		if err != nil {
			os.RemoveAll(tmpDir)
		}
	}()
	tmpFileName := filepath.Join(tmpDir, filename)
	tmpFile, err := os.OpenFile(tmpFileName, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
	if err != nil {
		return
	}

	stdoutFormatter := b.Stdout.(*streamformatter.StdoutFormatter)
	progressOutput := stdoutFormatter.StreamFormatter.NewProgressOutput(stdoutFormatter.Writer, true)
	progressReader := progress.NewProgressReader(resp.Body, progressOutput, resp.ContentLength, "", "Downloading")
	// Download and dump result to tmp file
	if _, err = io.Copy(tmpFile, progressReader); err != nil {
		tmpFile.Close()
		return
	}
	fmt.Fprintln(b.Stdout)
	// ignoring error because the file was already opened successfully
	tmpFileSt, err := tmpFile.Stat()
	if err != nil {
		return
	}
	tmpFile.Close()

	// Set the mtime to the Last-Modified header value if present
	// Otherwise just remove atime and mtime
	mTime := time.Time{}

	lastMod := resp.Header.Get("Last-Modified")
	if lastMod != "" {
		// If we can't parse it then just let it default to 'zero'
		// otherwise use the parsed time value
		if parsedMTime, err := http.ParseTime(lastMod); err == nil {
			mTime = parsedMTime
		}
	}

	if err = system.Chtimes(tmpFileName, mTime, mTime); err != nil {
		return
	}

	// Calc the checksum, even if we're using the cache
	r, err := archive.Tar(tmpFileName, archive.Uncompressed)
	if err != nil {
		return
	}
	tarSum, err := tarsum.NewTarSum(r, true, tarsum.Version1)
	if err != nil {
		return
	}
	if _, err = io.Copy(ioutil.Discard, tarSum); err != nil {
		return
	}
	hash := tarSum.Sum(nil)
	r.Close()
	return &builder.HashedFileInfo{FileInfo: builder.PathFileInfo{FileInfo: tmpFileSt, FilePath: tmpFileName}, FileHash: hash}, nil
}

//.........这里部分代码省略.........
			parent := filepath.Dir(hdr.Name)
			parentPath := filepath.Join(dest, parent)
			if _, err := os.Lstat(parentPath); err != nil && os.IsNotExist(err) {
				err = idtools.MkdirAllNewAs(parentPath, 0777, remappedRootUID, remappedRootGID)
				if err != nil {
					return err
				}
			}
		}

		path := filepath.Join(dest, hdr.Name)
		rel, err := filepath.Rel(dest, path)
		if err != nil {
			return err
		}
		if strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
			return breakoutError(fmt.Errorf("%q is outside of %q", hdr.Name, dest))
		}

		// If path exits we almost always just want to remove and replace it
		// The only exception is when it is a directory *and* the file from
		// the layer is also a directory. Then we want to merge them (i.e.
		// just apply the metadata from the layer).
		if fi, err := os.Lstat(path); err == nil {
			if options.NoOverwriteDirNonDir && fi.IsDir() && hdr.Typeflag != tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing directory with a non-directory from the archive.
				return fmt.Errorf("cannot overwrite directory %q with non-directory %q", path, dest)
			}

			if options.NoOverwriteDirNonDir && !fi.IsDir() && hdr.Typeflag == tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing non-directory with a directory from the archive.
				return fmt.Errorf("cannot overwrite non-directory %q with directory %q", path, dest)
			}

			if fi.IsDir() && hdr.Name == "." {
				continue
			}

			if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
				if err := os.RemoveAll(path); err != nil {
					return err
				}
			}
		}
		trBuf.Reset(tr)

		// if the options contain a uid & gid maps, convert header uid/gid
		// entries using the maps such that lchown sets the proper mapped
		// uid/gid after writing the file. We only perform this mapping if
		// the file isn't already owned by the remapped root UID or GID, as
		// that specific uid/gid has no mapping from container -> host, and
		// those files already have the proper ownership for inside the
		// container.
		if hdr.Uid != remappedRootUID {
			xUID, err := idtools.ToHost(hdr.Uid, options.UIDMaps)
			if err != nil {
				return err
			}
			hdr.Uid = xUID
		}
		if hdr.Gid != remappedRootGID {
			xGID, err := idtools.ToHost(hdr.Gid, options.GIDMaps)
			if err != nil {
				return err
			}
			hdr.Gid = xGID
		}

		if whiteoutConverter != nil {
			writeFile, err := whiteoutConverter.ConvertRead(hdr, path)
			if err != nil {
				return err
			}
			if !writeFile {
				continue
			}
		}

		if err := createTarFile(path, dest, hdr, trBuf, !options.NoLchown, options.ChownOpts, options.InUserNS); err != nil {
			return err
		}

		// Directory mtimes must be handled at the end to avoid further
		// file creation in them to modify the directory mtime
		if hdr.Typeflag == tar.TypeDir {
			dirs = append(dirs, hdr)
		}
	}

	for _, hdr := range dirs {
		path := filepath.Join(dest, hdr.Name)

		if err := system.Chtimes(path, hdr.AccessTime, hdr.ModTime); err != nil {
			return err
		}
	}
	return nil
}

//.........这里部分代码省略.........
		// Handle this is an OS-specific way
		if err := handleTarTypeBlockCharFifo(hdr, path); err != nil {
			return err
		}

	case tar.TypeLink:
		targetPath := filepath.Join(extractDir, hdr.Linkname)
		// check for hardlink breakout
		if !strings.HasPrefix(targetPath, extractDir) {
			return breakoutError(fmt.Errorf("invalid hardlink %q -> %q", targetPath, hdr.Linkname))
		}
		if err := os.Link(targetPath, path); err != nil {
			return err
		}

	case tar.TypeSymlink:
		// 	path 				-> hdr.Linkname = targetPath
		// e.g. /extractDir/path/to/symlink 	-> ../2/file	= /extractDir/path/2/file
		targetPath := filepath.Join(filepath.Dir(path), hdr.Linkname)

		// the reason we don't need to check symlinks in the path (with FollowSymlinkInScope) is because
		// that symlink would first have to be created, which would be caught earlier, at this very check:
		if !strings.HasPrefix(targetPath, extractDir) {
			return breakoutError(fmt.Errorf("invalid symlink %q -> %q", path, hdr.Linkname))
		}
		if err := os.Symlink(hdr.Linkname, path); err != nil {
			return err
		}

	case tar.TypeXGlobalHeader:
		logrus.Debug("PAX Global Extended Headers found and ignored")
		return nil

	default:
		return fmt.Errorf("Unhandled tar header type %d\n", hdr.Typeflag)
	}

	// Lchown is not supported on Windows.
	if Lchown && runtime.GOOS != "windows" {
		if chownOpts == nil {
			chownOpts = &TarChownOptions{UID: hdr.Uid, GID: hdr.Gid}
		}
		if err := os.Lchown(path, chownOpts.UID, chownOpts.GID); err != nil {
			return err
		}
	}

	var errors []string
	for key, value := range hdr.Xattrs {
		if err := system.Lsetxattr(path, key, []byte(value), 0); err != nil {
			if err == syscall.ENOTSUP {
				// We ignore errors here because not all graphdrivers support
				// xattrs *cough* old versions of AUFS *cough*. However only
				// ENOTSUP should be emitted in that case, otherwise we still
				// bail.
				errors = append(errors, err.Error())
				continue
			}
			return err
		}

	}

	if len(errors) > 0 {
		logrus.WithFields(logrus.Fields{
			"errors": errors,
		}).Warn("ignored xattrs in archive: underlying filesystem doesn't support them")
	}

	// There is no LChmod, so ignore mode for symlink. Also, this
	// must happen after chown, as that can modify the file mode
	if err := handleLChmod(hdr, path, hdrInfo); err != nil {
		return err
	}

	aTime := hdr.AccessTime
	if aTime.Before(hdr.ModTime) {
		// Last access time should never be before last modified time.
		aTime = hdr.ModTime
	}

	// system.Chtimes doesn't support a NOFOLLOW flag atm
	if hdr.Typeflag == tar.TypeLink {
		if fi, err := os.Lstat(hdr.Linkname); err == nil && (fi.Mode()&os.ModeSymlink == 0) {
			if err := system.Chtimes(path, aTime, hdr.ModTime); err != nil {
				return err
			}
		}
	} else if hdr.Typeflag != tar.TypeSymlink {
		if err := system.Chtimes(path, aTime, hdr.ModTime); err != nil {
			return err
		}
	} else {
		ts := []syscall.Timespec{timeToTimespec(aTime), timeToTimespec(hdr.ModTime)}
		if err := system.LUtimesNano(path, ts); err != nil && err != system.ErrNotSupportedPlatform {
			return err
		}
	}
	return nil
}

//.........这里部分代码省略.........
						if os.IsNotExist(err) {
							err = nil // parent was deleted
						}
						return err
					}
					if path == dir {
						return nil
					}
					if _, exists := unpackedPaths[path]; !exists {
						err := os.RemoveAll(path)
						return err
					}
					return nil
				})
				if err != nil {
					return 0, err
				}
			} else {
				originalBase := base[len(WhiteoutPrefix):]
				originalPath := filepath.Join(dir, originalBase)
				if err := os.RemoveAll(originalPath); err != nil {
					return 0, err
				}
			}
		} else {
			// If path exits we almost always just want to remove and replace it.
			// The only exception is when it is a directory *and* the file from
			// the layer is also a directory. Then we want to merge them (i.e.
			// just apply the metadata from the layer).
			if fi, err := os.Lstat(path); err == nil {
				if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
					if err := os.RemoveAll(path); err != nil {
						return 0, err
					}
				}
			}

			trBuf.Reset(tr)
			srcData := io.Reader(trBuf)
			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")
				}
				tmpFile, err := os.Open(filepath.Join(aufsTempdir, linkBasename))
				if err != nil {
					return 0, err
				}
				defer tmpFile.Close()
				srcData = tmpFile
			}

			// if the options contain a uid & gid maps, convert header uid/gid
			// entries using the maps such that lchown sets the proper mapped
			// uid/gid after writing the file. We only perform this mapping if
			// the file isn't already owned by the remapped root UID or GID, as
			// that specific uid/gid has no mapping from container -> host, and
			// those files already have the proper ownership for inside the
			// container.
			if srcHdr.Uid != remappedRootUID {
				xUID, err := idtools.ToHost(srcHdr.Uid, options.UIDMaps)
				if err != nil {
					return 0, err
				}
				srcHdr.Uid = xUID
			}
			if srcHdr.Gid != remappedRootGID {
				xGID, err := idtools.ToHost(srcHdr.Gid, options.GIDMaps)
				if err != nil {
					return 0, err
				}
				srcHdr.Gid = xGID
			}
			if err := createTarFile(path, dest, srcHdr, srcData, true, nil); err != nil {
				return 0, err
			}

			// Directory mtimes must be handled at the end to avoid further
			// file creation in them to modify the directory mtime
			if hdr.Typeflag == tar.TypeDir {
				dirs = append(dirs, hdr)
			}
			unpackedPaths[path] = struct{}{}
		}
	}

	for _, hdr := range dirs {
		path := filepath.Join(dest, hdr.Name)
		if err := system.Chtimes(path, hdr.AccessTime, hdr.ModTime); err != nil {
			return 0, err
		}
	}

	return size, nil
}

//.........这里部分代码省略.........
		stat, ok := f.Sys().(*syscall.Stat_t)
		if !ok {
			return fmt.Errorf("Unable to get raw syscall.Stat_t data for %s", srcPath)
		}

		isHardlink := false

		switch f.Mode() & os.ModeType {
		case 0: // Regular file
			if flags&copyHardlink != 0 {
				isHardlink = true
				if err := os.Link(srcPath, dstPath); err != nil {
					return err
				}
			} else {
				if err := copyRegular(srcPath, dstPath, f.Mode()); err != nil {
					return err
				}
			}

		case os.ModeDir:
			if err := os.Mkdir(dstPath, f.Mode()); err != nil && !os.IsExist(err) {
				return err
			}

		case os.ModeSymlink:
			link, err := os.Readlink(srcPath)
			if err != nil {
				return err
			}

			if err := os.Symlink(link, dstPath); err != nil {
				return err
			}

		case os.ModeNamedPipe:
			fallthrough
		case os.ModeSocket:
			if err := syscall.Mkfifo(dstPath, stat.Mode); err != nil {
				return err
			}

		case os.ModeDevice:
			if err := syscall.Mknod(dstPath, stat.Mode, int(stat.Rdev)); err != nil {
				return err
			}

		default:
			return fmt.Errorf("Unknown file type for %s\n", srcPath)
		}

		// Everything below is copying metadata from src to dst. All this metadata
		// already shares an inode for hardlinks.
		if isHardlink {
			return nil
		}

		if err := os.Lchown(dstPath, int(stat.Uid), int(stat.Gid)); err != nil {
			return err
		}

		if err := copyXattr(srcPath, dstPath, "security.capability"); err != nil {
			return err
		}

		// We need to copy this attribute if it appears in an overlay upper layer, as
		// this function is used to copy those. It is set by overlay if a directory
		// is removed and then re-created and should not inherit anything from the
		// same dir in the lower dir.
		if err := copyXattr(srcPath, dstPath, "trusted.overlay.opaque"); err != nil {
			return err
		}

		isSymlink := f.Mode()&os.ModeSymlink != 0

		// There is no LChmod, so ignore mode for symlink. Also, this
		// must happen after chown, as that can modify the file mode
		if !isSymlink {
			if err := os.Chmod(dstPath, f.Mode()); err != nil {
				return err
			}
		}

		// system.Chtimes doesn't support a NOFOLLOW flag atm
		if !isSymlink {
			aTime := time.Unix(int64(stat.Atim.Sec), int64(stat.Atim.Nsec))
			mTime := time.Unix(int64(stat.Mtim.Sec), int64(stat.Mtim.Nsec))
			if err := system.Chtimes(dstPath, aTime, mTime); err != nil {
				return err
			}
		} else {
			ts := []syscall.Timespec{stat.Atim, stat.Mtim}
			if err := system.LUtimesNano(dstPath, ts); err != nil {
				return err
			}
		}
		return nil
	})
	return err
}

func calcCopyInfo(b *builder, cmdName string, cInfos *[]*copyInfo, origPath string, destPath string, allowRemote bool, allowDecompression bool, allowWildcards bool) error {

	// Work in daemon-specific OS filepath semantics. However, we save
	// the the origPath passed in here, as it might also be a URL which
	// we need to check for in this function.
	passedInOrigPath := origPath
	origPath = filepath.FromSlash(origPath)
	destPath = filepath.FromSlash(destPath)

	if origPath != "" && origPath[0] == os.PathSeparator && len(origPath) > 1 {
		origPath = origPath[1:]
	}
	origPath = strings.TrimPrefix(origPath, "."+string(os.PathSeparator))

	// Twiddle the destPath when its a relative path - meaning, make it
	// relative to the WORKINGDIR
	if !system.IsAbs(destPath) {
		hasSlash := strings.HasSuffix(destPath, string(os.PathSeparator))
		destPath = filepath.Join(string(os.PathSeparator), filepath.FromSlash(b.Config.WorkingDir), destPath)

		// Make sure we preserve any trailing slash
		if hasSlash {
			destPath += string(os.PathSeparator)
		}
	}

	// In the remote/URL case, download it and gen its hashcode
	if urlutil.IsURL(passedInOrigPath) {

		// As it's a URL, we go back to processing on what was passed in
		// to this function
		origPath = passedInOrigPath

		if !allowRemote {
			return fmt.Errorf("Source can't be a URL for %s", cmdName)
		}

		ci := copyInfo{}
		ci.origPath = origPath
		ci.hash = origPath // default to this but can change
		ci.destPath = destPath
		ci.decompress = false
		*cInfos = append(*cInfos, &ci)

		// Initiate the download
		resp, err := httputils.Download(ci.origPath)
		if err != nil {
			return err
		}

		// Create a tmp dir
		tmpDirName, err := getTempDir(b.contextPath, "docker-remote")
		if err != nil {
			return err
		}
		ci.tmpDir = tmpDirName

		// Create a tmp file within our tmp dir
		tmpFileName := filepath.Join(tmpDirName, "tmp")
		tmpFile, err := os.OpenFile(tmpFileName, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
		if err != nil {
			return err
		}

		// Download and dump result to tmp file
		if _, err := io.Copy(tmpFile, progressreader.New(progressreader.Config{
			In:        resp.Body,
			Out:       b.OutOld,
			Formatter: b.StreamFormatter,
			Size:      resp.ContentLength,
			NewLines:  true,
			ID:        "",
			Action:    "Downloading",
		})); err != nil {
			tmpFile.Close()
			return err
		}
		fmt.Fprintf(b.OutStream, "\n")
		tmpFile.Close()

		// Set the mtime to the Last-Modified header value if present
		// Otherwise just remove atime and mtime
		mTime := time.Time{}

		lastMod := resp.Header.Get("Last-Modified")
		if lastMod != "" {
			// If we can't parse it then just let it default to 'zero'
			// otherwise use the parsed time value
			if parsedMTime, err := http.ParseTime(lastMod); err == nil {
				mTime = parsedMTime
			}
		}

		if err := system.Chtimes(tmpFileName, time.Time{}, mTime); err != nil {
			return err
		}

		ci.origPath = filepath.Join(filepath.Base(tmpDirName), filepath.Base(tmpFileName))

		// If the destination is a directory, figure out the filename.
//.........这里部分代码省略.........

// Unpack unpacks the decompressedArchive to dest with options.
func Unpack(decompressedArchive io.Reader, dest string, options *TarOptions) error {
	tr := tar.NewReader(decompressedArchive)
	trBuf := pools.BufioReader32KPool.Get(nil)
	defer pools.BufioReader32KPool.Put(trBuf)

	var dirs []*tar.Header

	// Iterate through the files in the archive.
loop:
	for {
		hdr, err := tr.Next()
		if err == io.EOF {
			// end of tar archive
			break
		}
		if err != nil {
			return err
		}

		// Normalize name, for safety and for a simple is-root check
		// This keeps "../" as-is, but normalizes "/../" to "/". Or Windows:
		// This keeps "..\" as-is, but normalizes "\..\" to "\".
		hdr.Name = filepath.Clean(hdr.Name)

		for _, exclude := range options.ExcludePatterns {
			if strings.HasPrefix(hdr.Name, exclude) {
				continue loop
			}
		}

		// After calling filepath.Clean(hdr.Name) above, hdr.Name will now be in
		// the filepath format for the OS on which the daemon is running. Hence
		// the check for a slash-suffix MUST be done in an OS-agnostic way.
		if !strings.HasSuffix(hdr.Name, string(os.PathSeparator)) {
			// Not the root directory, ensure that the parent directory exists
			parent := filepath.Dir(hdr.Name)
			parentPath := filepath.Join(dest, parent)
			if _, err := os.Lstat(parentPath); err != nil && os.IsNotExist(err) {
				err = system.MkdirAll(parentPath, 0777)
				if err != nil {
					return err
				}
			}
		}

		path := filepath.Join(dest, hdr.Name)
		rel, err := filepath.Rel(dest, path)
		if err != nil {
			return err
		}
		if strings.HasPrefix(rel, ".."+string(os.PathSeparator)) {
			return breakoutError(fmt.Errorf("%q is outside of %q", hdr.Name, dest))
		}

		// If path exits we almost always just want to remove and replace it
		// The only exception is when it is a directory *and* the file from
		// the layer is also a directory. Then we want to merge them (i.e.
		// just apply the metadata from the layer).
		if fi, err := os.Lstat(path); err == nil {
			if options.NoOverwriteDirNonDir && fi.IsDir() && hdr.Typeflag != tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing directory with a non-directory from the archive.
				return fmt.Errorf("cannot overwrite directory %q with non-directory %q", path, dest)
			}

			if options.NoOverwriteDirNonDir && !fi.IsDir() && hdr.Typeflag == tar.TypeDir {
				// If NoOverwriteDirNonDir is true then we cannot replace
				// an existing non-directory with a directory from the archive.
				return fmt.Errorf("cannot overwrite non-directory %q with directory %q", path, dest)
			}

			if fi.IsDir() && hdr.Name == "." {
				continue
			}

			if !(fi.IsDir() && hdr.Typeflag == tar.TypeDir) {
				if err := os.RemoveAll(path); err != nil {
					return err
				}
			}
		}
		trBuf.Reset(tr)

		if err := createTarFile(path, dest, hdr, trBuf, !options.NoLchown, options.ChownOpts); err != nil {
			return err
		}

		// Directory mtimes must be handled at the end to avoid further
		// file creation in them to modify the directory mtime
		if hdr.Typeflag == tar.TypeDir {
			dirs = append(dirs, hdr)
		}
	}

	for _, hdr := range dirs {
		path := filepath.Join(dest, hdr.Name)

		if err := system.Chtimes(path, hdr.AccessTime, hdr.ModTime); err != nil {
			return err
//.........这里部分代码省略.........

func (s *saveSession) save(outStream io.Writer) error {
	s.savedLayers = make(map[string]struct{})

	// get image json
	tempDir, err := ioutil.TempDir("", "docker-export-")
	if err != nil {
		return err
	}
	defer os.RemoveAll(tempDir)

	s.outDir = tempDir
	reposLegacy := make(map[string]map[string]string)

	var manifest []manifestItem

	for id, imageDescr := range s.images {
		if err = s.saveImage(id); err != nil {
			return err
		}

		var repoTags []string
		var layers []string

		for _, ref := range imageDescr.refs {
			if _, ok := reposLegacy[ref.Name()]; !ok {
				reposLegacy[ref.Name()] = make(map[string]string)
			}
			reposLegacy[ref.Name()][ref.Tag()] = imageDescr.layers[len(imageDescr.layers)-1]
			repoTags = append(repoTags, ref.String())
		}

		for _, l := range imageDescr.layers {
			layers = append(layers, filepath.Join(l, legacyLayerFileName))
		}

		manifest = append(manifest, manifestItem{
			Config:   digest.Digest(id).Hex() + ".json",
			RepoTags: repoTags,
			Layers:   layers,
		})
	}

	if len(reposLegacy) > 0 {
		reposFile := filepath.Join(tempDir, legacyRepositoriesFileName)
		f, err := os.OpenFile(reposFile, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
		if err != nil {
			f.Close()
			return err
		}
		if err := json.NewEncoder(f).Encode(reposLegacy); err != nil {
			return err
		}
		if err := f.Close(); err != nil {
			return err
		}
		if err := system.Chtimes(reposFile, time.Unix(0, 0), time.Unix(0, 0)); err != nil {
			return err
		}
	}

	manifestFileName := filepath.Join(tempDir, manifestFileName)
	f, err := os.OpenFile(manifestFileName, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
	if err != nil {
		f.Close()
		return err
	}
	if err := json.NewEncoder(f).Encode(manifest); err != nil {
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	if err := system.Chtimes(manifestFileName, time.Unix(0, 0), time.Unix(0, 0)); err != nil {
		return err
	}

	fs, err := archive.Tar(tempDir, archive.Uncompressed)
	if err != nil {
		return err
	}
	defer fs.Close()

	if _, err := io.Copy(outStream, fs); err != nil {
		return err
	}
	return nil
}

func mutateSampleDir(t *testing.T, root string) {
	// Remove a regular file
	if err := os.RemoveAll(path.Join(root, "file1")); err != nil {
		t.Fatal(err)
	}

	// Remove a directory
	if err := os.RemoveAll(path.Join(root, "dir1")); err != nil {
		t.Fatal(err)
	}

	// Remove a symlink
	if err := os.RemoveAll(path.Join(root, "symlink1")); err != nil {
		t.Fatal(err)
	}

	// Rewrite a file
	if err := ioutil.WriteFile(path.Join(root, "file2"), []byte("fileNN\n"), 0777); err != nil {
		t.Fatal(err)
	}

	// Replace a file
	if err := os.RemoveAll(path.Join(root, "file3")); err != nil {
		t.Fatal(err)
	}
	if err := ioutil.WriteFile(path.Join(root, "file3"), []byte("fileMM\n"), 0404); err != nil {
		t.Fatal(err)
	}

	// Touch file
	if err := system.Chtimes(path.Join(root, "file4"), time.Now().Add(time.Second), time.Now().Add(time.Second)); err != nil {
		t.Fatal(err)
	}

	// Replace file with dir
	if err := os.RemoveAll(path.Join(root, "file5")); err != nil {
		t.Fatal(err)
	}
	if err := os.MkdirAll(path.Join(root, "file5"), 0666); err != nil {
		t.Fatal(err)
	}

	// Create new file
	if err := ioutil.WriteFile(path.Join(root, "filenew"), []byte("filenew\n"), 0777); err != nil {
		t.Fatal(err)
	}

	// Create new dir
	if err := os.MkdirAll(path.Join(root, "dirnew"), 0766); err != nil {
		t.Fatal(err)
	}

	// Create a new symlink
	if err := os.Symlink("targetnew", path.Join(root, "symlinknew")); err != nil {
		t.Fatal(err)
	}

	// Change a symlink
	if err := os.RemoveAll(path.Join(root, "symlink2")); err != nil {
		t.Fatal(err)
	}
	if err := os.Symlink("target2change", path.Join(root, "symlink2")); err != nil {
		t.Fatal(err)
	}

	// Replace dir with file
	if err := os.RemoveAll(path.Join(root, "dir2")); err != nil {
		t.Fatal(err)
	}
	if err := ioutil.WriteFile(path.Join(root, "dir2"), []byte("dir2\n"), 0777); err != nil {
		t.Fatal(err)
	}

	// Touch dir
	if err := system.Chtimes(path.Join(root, "dir3"), time.Now().Add(time.Second), time.Now().Add(time.Second)); err != nil {
		t.Fatal(err)
	}
}