code: func FSReadLock(f *os.File) error {
  	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_SH); err != nil {
  		return trace.ConvertSystemError(err)
  	}
  	return nil
  }
docs: // FSReadLock grabs Flock-style filesystem lock on an open file
  // in read (shared) mode