code: func SetCapacity(file *os.File) error {
  	if err := ioctlLoopSetCapacity(file.Fd(), 0); err != nil {
  		logrus.Errorf("Error loopbackSetCapacity: %s", err)
  		return ErrSetCapacity
  	}
  	return nil
  }
docs: // SetCapacity reloads the size for the loopback device.