pkg os, func Lstat(string) (FileInfo, error)
pkg os, func Mkdir(string, FileMode) error
pkg os, func MkdirAll(string, FileMode) error
pkg os, func OpenFile(string, int, FileMode) (*File, error)
pkg os, func SameFile(FileInfo, FileInfo) bool
pkg os, func Stat(string) (FileInfo, error)
pkg os, method (*File) Chmod(FileMode) error
pkg os, method (*File) Readdir(int) ([]FileInfo, error)
pkg os, method (*File) Stat() (FileInfo, error)

		s.RUnlock()
		return diskID, nil
	}
	s.RUnlock()

	fi, err := s.checkFormatJSON()
	if err != nil {
		return "", err
	}

	if xioutil.SameFile(fi, fileInfo) && diskID != "" {
		s.Lock()
		// If the file has not changed, just return the cached diskID information.
		s.formatLastCheck = time.Now()
		s.Unlock()
		return diskID, nil
	}