poll

  int wait_for_incoming_packet = 0; /* 1:block, 0:non blocking */

  rv = pfring_recv(ring, &b, 0, &h, wait_for_incoming_packet);
  if (rv < 0)
    return -1;

  if (rv == 0)
    {
      pfd.fd = pfring_get_selectable_fd(ring);
      pfd.events = POLLIN;
      pfd.revents = 0;

      rc = poll(&pfd, 1, ACK_FROM_NV_TIMEOUT);

      if (rc > 0) {
	rv = pfring_recv(ring, &b, 0, &h, wait_for_incoming_packet);

	/* pfring_recv() ritorna success */
	if (rv == 1) {
	  if (b[42] != chunk_nr) {
	    printf("-3\n");
	    return -3;	/* non era ACK */
	  }
	  else
	    return 0;		/* OK - ACK ricevuto */
	}
      }

      if (rc == 0)		/* timeout */
	{
	  printf("-2\n");
	  return -2;
	}

      if (rc < 0) {
	printf("-1\n");
	return -1;		/* errore ritornato da pfring_recv() */
      }
    }