code: func (f *File) ReadDir() ([]Dir, error) {
  	var dirs []Dir
  	err := f.walkDir(func(name []byte, ino uint32) bool {
  		dirs = append(dirs, Dir{string(name), ino})
  		return true
  	})
  	return dirs, err
  }
docs: // ReadDir returns all the directory entries in f.