func getContextRoot(srcPath string) (string, error) {
	cr, err := filepath.Abs(srcPath)
	if err != nil {
		return "", err
	}
	return longpath.AddPrefix(cr), nil
}

// applyLayerHandler parses a diff in the standard layer format from `layer`, and
// applies it to the directory `dest`. Returns the size in bytes of the
// contents of the layer.
func applyLayerHandler(dest string, layer archive.Reader, decompress bool) (size int64, err error) {
	dest = filepath.Clean(dest)

	// Ensure it is a Windows-style volume path
	dest = longpath.AddPrefix(dest)

	if decompress {
		decompressed, err := archive.DecompressStream(layer)
		if err != nil {
			return 0, err
		}
		defer decompressed.Close()

		layer = decompressed
	}

	tmpDir, err := ioutil.TempDir(os.Getenv("temp"), "temp-docker-extract")
	if err != nil {
		return 0, fmt.Errorf("ApplyLayer failed to create temp-docker-extract under %s. %s", dest, err)
	}

	s, err := archive.UnpackLayer(dest, layer)
	os.RemoveAll(tmpDir)
	if err != nil {
		return 0, fmt.Errorf("ApplyLayer %s failed UnpackLayer to %s", err, dest)
	}

	return s, nil
}

// TempDir is the equivalent of ioutil.TempDir, except that the result is in Windows longpath format.
func TempDir(dir, prefix string) (string, error) {
	tempDir, err := ioutil.TempDir(dir, prefix)
	if err != nil {
		return "", err
	}
	return longpath.AddPrefix(tempDir), nil
}

func invokeUnpack(decompressedArchive io.ReadCloser,
	dest string,
	options *archive.TarOptions) error {
	// Windows is different to Linux here because Windows does not support
	// chroot. Hence there is no point sandboxing a chrooted process to
	// do the unpack. We call inline instead within the daemon process.
	return archive.Unpack(decompressedArchive, longpath.AddPrefix(dest), options)
}

func (fg *fileGetCloserWithBackupPrivileges) Get(filename string) (io.ReadCloser, error) {
	var f *os.File
	// Open the file while holding the Windows backup privilege. This ensures that the
	// file can be opened even if the caller does not actually have access to it according
	// to the security descriptor.
	err := winio.RunWithPrivilege(winio.SeBackupPrivilege, func() error {
		path := longpath.AddPrefix(filepath.Join(fg.path, filename))
		p, err := syscall.UTF16FromString(path)
		if err != nil {
			return err
		}
		h, err := syscall.CreateFile(&p[0], syscall.GENERIC_READ, syscall.FILE_SHARE_READ, nil, syscall.OPEN_EXISTING, syscall.FILE_FLAG_BACKUP_SEMANTICS, 0)
		if err != nil {
			return &os.PathError{Op: "open", Path: path, Err: err}
		}
		f = os.NewFile(uintptr(h), path)
		return nil
	})
	return f, err
}

// Size walks a directory tree and returns its total size in bytes.
func Size(dir string) (size int64, err error) {
	fixedPath, err := filepath.Abs(dir)
	if err != nil {
		return
	}
	fixedPath = longpath.AddPrefix(fixedPath)
	err = filepath.Walk(dir, func(d string, fileInfo os.FileInfo, e error) error {
		// Ignore directory sizes
		if fileInfo == nil {
			return nil
		}

		s := fileInfo.Size()
		if fileInfo.IsDir() || s == 0 {
			return nil
		}

		size += s

		return nil
	})
	return
}

// fixVolumePathPrefix does platform specific processing to ensure that if
// the path being passed in is not in a volume path format, convert it to one.
func fixVolumePathPrefix(srcPath string) string {
	return longpath.AddPrefix(srcPath)
}