func writeSquashedImage(outputFile *os.File, renderedACI acirenderer.RenderedACI, aciProvider acirenderer.ACIProvider, manifests []schema.ImageManifest) error {
	gw := gzip.NewWriter(outputFile)
	defer gw.Close()
	outputWriter := tar.NewWriter(gw)
	defer outputWriter.Close()

	for _, aciFile := range renderedACI {
		rs, err := aciProvider.ReadStream(aciFile.Key)
		if err != nil {
			return err
		}
		defer rs.Close()

		squashWalker := func(t *tarball.TarFile) error {
			cleanName := filepath.Clean(t.Name())

			if _, ok := aciFile.FileMap[cleanName]; ok {
				// we generate and add the squashed manifest later
				if cleanName == "manifest" {
					return nil
				}
				if err := outputWriter.WriteHeader(t.Header); err != nil {
					return fmt.Errorf("error writing header: %v", err)
				}
				if _, err := io.Copy(outputWriter, t.TarStream); err != nil {
					return fmt.Errorf("error copying file into the tar out: %v", err)
				}
			}
			return nil
		}

		tr := tar.NewReader(rs)
		if err := tarball.Walk(*tr, squashWalker); err != nil {
			return err
		}
	}

	if err := common.WriteRootfsDir(outputWriter); err != nil {
		return err
	}

	finalManifest := mergeManifests(manifests)

	if err := common.WriteManifest(outputWriter, finalManifest); err != nil {
		return err
	}

	return nil
}

// Given a RenderedACI, it will extract, under the provided directory, the
// needed files from the right source ACI.
// The manifest will be extracted from the upper ACI.
// No file overwriting is done as it should usually be called
// providing an empty directory.
func renderImage(renderedACI acirenderer.RenderedACI, dir string, ap acirenderer.ACIProvider, uidRange *user.UidRange) error {
	for _, ra := range renderedACI {
		rs, err := ap.ReadStream(ra.Key)
		if err != nil {
			return err
		}

		// Overwrite is not needed. If a file needs to be overwritten then the renderedACI builder has a bug
		if err := ptar.ExtractTar(rs, dir, false, uidRange, ra.FileMap); err != nil {
			rs.Close()
			return errwrap.Wrap(errors.New("error extracting ACI"), err)
		}
		rs.Close()
	}

	return nil
}

func writeSquashedImage(outputFile *os.File, renderedACI acirenderer.RenderedACI, aciProvider acirenderer.ACIProvider, manifests []schema.ImageManifest, compression common.Compression) error {
	var tarWriterTarget io.WriteCloser = outputFile

	switch compression {
	case common.NoCompression:
	case common.GzipCompression:
		tarWriterTarget = gzip.NewWriter(outputFile)
		defer tarWriterTarget.Close()
	default:
		return fmt.Errorf("unexpected compression enum value: %d", compression)
	}

	outputWriter := tar.NewWriter(tarWriterTarget)
	defer outputWriter.Close()

	finalManifest := mergeManifests(manifests)

	if err := internal.WriteManifest(outputWriter, finalManifest); err != nil {
		return err
	}

	if err := internal.WriteRootfsDir(outputWriter); err != nil {
		return err
	}

	type hardLinkEntry struct {
		firstLinkCleanName string
		firstLinkHeader    tar.Header
		keepOriginal       bool
		walked             bool
	}
	// map aciFileKey -> cleanTarget -> hardLinkEntry
	hardLinks := make(map[string]map[string]hardLinkEntry)

	// first pass: read all the entries and build the hardLinks map in memory
	// but don't write on disk
	for _, aciFile := range renderedACI {
		rs, err := aciProvider.ReadStream(aciFile.Key)
		if err != nil {
			return err
		}
		defer rs.Close()

		hardLinks[aciFile.Key] = map[string]hardLinkEntry{}

		squashWalker := func(t *tarball.TarFile) error {
			cleanName := filepath.Clean(t.Name())
			// the rootfs and the squashed manifest are added separately
			if cleanName == "manifest" || cleanName == "rootfs" {
				return nil
			}
			_, keep := aciFile.FileMap[cleanName]
			if keep && t.Header.Typeflag == tar.TypeLink {
				cleanTarget := filepath.Clean(t.Linkname())
				if _, ok := hardLinks[aciFile.Key][cleanTarget]; !ok {
					_, keepOriginal := aciFile.FileMap[cleanTarget]
					hardLinks[aciFile.Key][cleanTarget] = hardLinkEntry{cleanName, *t.Header, keepOriginal, false}
				}
			}
			return nil
		}

		tr := tar.NewReader(rs)
		if err := tarball.Walk(*tr, squashWalker); err != nil {
			return err
		}
	}

	// second pass: write on disk
	for _, aciFile := range renderedACI {
		rs, err := aciProvider.ReadStream(aciFile.Key)
		if err != nil {
			return err
		}
		defer rs.Close()

		squashWalker := func(t *tarball.TarFile) error {
			cleanName := filepath.Clean(t.Name())
			// the rootfs and the squashed manifest are added separately
			if cleanName == "manifest" || cleanName == "rootfs" {
				return nil
			}
			_, keep := aciFile.FileMap[cleanName]

			if link, ok := hardLinks[aciFile.Key][cleanName]; ok {
				if keep != link.keepOriginal {
					return fmt.Errorf("logic error: should we keep file %q?", cleanName)
				}
				if keep {
					if err := outputWriter.WriteHeader(t.Header); err != nil {
						return fmt.Errorf("error writing header: %v", err)
					}
					if _, err := io.Copy(outputWriter, t.TarStream); err != nil {
						return fmt.Errorf("error copying file into the tar out: %v", err)
					}
				} else {
					// The current file does not remain but there is a hard link pointing to
					// it. Write the current file but with the filename of the first hard link
					// pointing to it. That first hard link will not be written later, see
					// variable "alreadyWritten".
//.........这里部分代码省略.........