code: func (n *Mounter) DeviceOpened(pathname string) (bool, error) {
  	return mount.ExclusiveOpenFailsOnDevice(pathname)
  }
docs: // DeviceOpened checks if block device in use by calling Open with O_EXCL flag.
  // Returns true if open returns errno EBUSY, and false if errno is nil.
  // Returns an error if errno is any error other than EBUSY.
  // Returns with error if pathname is not a device.