code: func Mount(cfg *MountCfg) error {
  	err := syscall.Mount("overlay", cfg.Dest, "overlay", 0, cfg.Opts())
  	if err != nil {
  		const text = "error mounting overlay with options '%s' and dest '%s'"
  		return errwrap.Wrap(fmt.Errorf(text, cfg.Opts(), cfg.Dest), err)
  	}
  
  	return nil
  }
docs: // Mount mounts the upper and lower directories to the destination directory.
  // The MountCfg struct supplies information required to build the mount system
  // call.