tcp_output.c

qemu虚拟机代码

 	}
 
 	/*
	 * Send a timestamp and echo-reply if this is a SYN and our side 
	 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
	 * and our peer have sent timestamps in our SYN's.
 	 */
/* 	if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 *	     (flags & TH_RST) == 0 &&
 *	    ((flags & (TH_SYN|TH_ACK)) == TH_SYN ||
 *	     (tp->t_flags & TF_RCVD_TSTMP))) {
 *		u_int32_t *lp = (u_int32_t *)(opt + optlen);
 *
 *		/ * Form timestamp option as shown in appendix A of RFC 1323. *  /
 *		*lp++ = htonl(TCPOPT_TSTAMP_HDR);
 *		*lp++ = htonl(tcp_now);
 *		*lp   = htonl(tp->ts_recent);
 *		optlen += TCPOLEN_TSTAMP_APPA;
 *	}
 */
 	hdrlen += optlen;
 
	/*
	 * Adjust data length if insertion of options will
	 * bump the packet length beyond the t_maxseg length.
	 */
	 if (len > tp->t_maxseg - optlen) {
		len = tp->t_maxseg - optlen;
		sendalot = 1;
	 }

	/*
	 * Grab a header mbuf, attaching a copy of data to
	 * be transmitted, and initialize the header from
	 * the template for sends on this connection.
	 */
	if (len) {
		if (tp->t_force && len == 1)
			tcpstat.tcps_sndprobe++;
		else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
			tcpstat.tcps_sndrexmitpack++;
			tcpstat.tcps_sndrexmitbyte += len;
		} else {
			tcpstat.tcps_sndpack++;
			tcpstat.tcps_sndbyte += len;
		}

		m = m_get();
		if (m == NULL) {
/*			error = ENOBUFS; */
			error = 1;
			goto out;
		}
		m->m_data += if_maxlinkhdr;
		m->m_len = hdrlen;
		
		/* 
		 * This will always succeed, since we make sure our mbufs
		 * are big enough to hold one MSS packet + header + ... etc.
		 */
/*		if (len <= MHLEN - hdrlen - max_linkhdr) { */

			sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
			m->m_len += len;

/*		} else {
 *			m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
 *			if (m->m_next == 0)
 *				len = 0;
 *		}
 */
		/*
		 * If we're sending everything we've got, set PUSH.
		 * (This will keep happy those implementations which only
		 * give data to the user when a buffer fills or
		 * a PUSH comes in.)
		 */
		if (off + len == so->so_snd.sb_cc)
			flags |= TH_PUSH;
	} else {
		if (tp->t_flags & TF_ACKNOW)
			tcpstat.tcps_sndacks++;
		else if (flags & (TH_SYN|TH_FIN|TH_RST))
			tcpstat.tcps_sndctrl++;
		else if (SEQ_GT(tp->snd_up, tp->snd_una))
			tcpstat.tcps_sndurg++;
		else
			tcpstat.tcps_sndwinup++;

		m = m_get();
		if (m == NULL) {
/*			error = ENOBUFS; */
			error = 1;
			goto out;
		}
		m->m_data += if_maxlinkhdr;
		m->m_len = hdrlen;
	}

	ti = mtod(m, struct tcpiphdr *);
	
	memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));

	/*
	 * Fill in fields, remembering maximum advertised
	 * window for use in delaying messages about window sizes.
	 * If resending a FIN, be sure not to use a new sequence number.
	 */
	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 
	    tp->snd_nxt == tp->snd_max)
		tp->snd_nxt--;
	/*
	 * If we are doing retransmissions, then snd_nxt will
	 * not reflect the first unsent octet.  For ACK only
	 * packets, we do not want the sequence number of the
	 * retransmitted packet, we want the sequence number
	 * of the next unsent octet.  So, if there is no data
	 * (and no SYN or FIN), use snd_max instead of snd_nxt
	 * when filling in ti_seq.  But if we are in persist
	 * state, snd_max might reflect one byte beyond the
	 * right edge of the window, so use snd_nxt in that
	 * case, since we know we aren't doing a retransmission.
	 * (retransmit and persist are mutually exclusive...)
	 */
	if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])
		ti->ti_seq = htonl(tp->snd_nxt);
	else
		ti->ti_seq = htonl(tp->snd_max);
	ti->ti_ack = htonl(tp->rcv_nxt);
	if (optlen) {
		memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
		ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
	}
	ti->ti_flags = flags;
	/*
	 * Calculate receive window.  Don't shrink window,
	 * but avoid silly window syndrome.
	 */
	if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
		win = 0;
	if (win > (long)TCP_MAXWIN << tp->rcv_scale)
		win = (long)TCP_MAXWIN << tp->rcv_scale;
	if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
		win = (long)(tp->rcv_adv - tp->rcv_nxt);
	ti->ti_win = htons((u_int16_t) (win>>tp->rcv_scale));
	
	if (SEQ_GT(tp->snd_up, tp->snd_una)) {
		ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq)));
#ifdef notdef		
	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
		ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt));
#endif
		ti->ti_flags |= TH_URG;
	} else
		/*
		 * If no urgent pointer to send, then we pull
		 * the urgent pointer to the left edge of the send window
		 * so that it doesn't drift into the send window on sequence
		 * number wraparound.
		 */
		tp->snd_up = tp->snd_una;		/* drag it along */

	/*
	 * Put TCP length in extended header, and then
	 * checksum extended header and data.
	 */
	if (len + optlen)
		ti->ti_len = htons((u_int16_t)(sizeof (struct tcphdr) +
		    optlen + len));
	ti->ti_sum = cksum(m, (int)(hdrlen + len));

	/*
	 * In transmit state, time the transmission and arrange for
	 * the retransmit.  In persist state, just set snd_max.
	 */
	if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
		tcp_seq startseq = tp->snd_nxt;

		/*
		 * Advance snd_nxt over sequence space of this segment.
		 */
		if (flags & (TH_SYN|TH_FIN)) {
			if (flags & TH_SYN)
				tp->snd_nxt++;
			if (flags & TH_FIN) {
				tp->snd_nxt++;
				tp->t_flags |= TF_SENTFIN;
			}
		}
		tp->snd_nxt += len;
		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
			tp->snd_max = tp->snd_nxt;
			/*
			 * Time this transmission if not a retransmission and
			 * not currently timing anything.
			 */
			if (tp->t_rtt == 0) {
				tp->t_rtt = 1;
				tp->t_rtseq = startseq;
				tcpstat.tcps_segstimed++;
			}
		}

		/*
		 * Set retransmit timer if not currently set,
		 * and not doing an ack or a keep-alive probe.
		 * Initial value for retransmit timer is smoothed
		 * round-trip time + 2 * round-trip time variance.
		 * Initialize shift counter which is used for backoff
		 * of retransmit time.
		 */
		if (tp->t_timer[TCPT_REXMT] == 0 &&
		    tp->snd_nxt != tp->snd_una) {
			tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
			if (tp->t_timer[TCPT_PERSIST]) {
				tp->t_timer[TCPT_PERSIST] = 0;
				tp->t_rxtshift = 0;
			}
		}
	} else
		if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
			tp->snd_max = tp->snd_nxt + len;

	/*
	 * Fill in IP length and desired time to live and
	 * send to IP level.  There should be a better way
	 * to handle ttl and tos; we could keep them in
	 * the template, but need a way to checksum without them.
	 */
	m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
	
    {
	    
	((struct ip *)ti)->ip_len = m->m_len;

	((struct ip *)ti)->ip_ttl = ip_defttl;
	((struct ip *)ti)->ip_tos = so->so_iptos;
	    
/* #if BSD >= 43 */
	/* Don't do IP options... */
/*	error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
 *	    so->so_options & SO_DONTROUTE, 0);
 */
	error = ip_output(so, m);

/* #else
 *	error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route, 
 *	    so->so_options & SO_DONTROUTE);
 * #endif
 */
    }
	if (error) {
out:
/*		if (error == ENOBUFS) {
 *			tcp_quench(tp->t_inpcb, 0);
 *			return (0);
 *		}
 */
/*		if ((error == EHOSTUNREACH || error == ENETDOWN)
 *		    && TCPS_HAVERCVDSYN(tp->t_state)) {
 *			tp->t_softerror = error;
 *			return (0);
 *		}
 */
		return (error);
	}
	tcpstat.tcps_sndtotal++;

	/*
	 * Data sent (as far as we can tell).
	 * If this advertises a larger window than any other segment,
	 * then remember the size of the advertised window.
	 * Any pending ACK has now been sent.
	 */
	if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
		tp->rcv_adv = tp->rcv_nxt + win;
	tp->last_ack_sent = tp->rcv_nxt;
	tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
	if (sendalot)
		goto again;

	return (0);
}

void
tcp_setpersist(tp)
	register struct tcpcb *tp;
{
    int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;

/*	if (tp->t_timer[TCPT_REXMT])
 *		panic("tcp_output REXMT");
 */
	/*
	 * Start/restart persistence timer.
	 */
	TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
	    t * tcp_backoff[tp->t_rxtshift],
	    TCPTV_PERSMIN, TCPTV_PERSMAX);
	if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
		tp->t_rxtshift++;
}