big footnotes, too.

[unix-history] / usr / src / sys / netinet / tcp_output.c

/*	tcp_output.c	4.32	82/03/12	*/

#include "../h/param.h"
#include "../h/systm.h"
#include "../h/mbuf.h"
#include "../h/protosw.h"
#include "../h/socket.h"
#include "../h/socketvar.h"
#include "../net/in.h"
#include "../net/in_pcb.h"
#include "../net/in_systm.h"
#include "../net/ip.h"
#include "../net/ip_var.h"
#include "../net/tcp.h"
#define	TCPOUTFLAGS
#include "../net/tcp_fsm.h"
#include "../net/tcp_seq.h"
#include "../net/tcp_timer.h"
#include "../net/tcp_var.h"
#include "../net/tcpip.h"
#include "../net/tcp_debug.h"
#include "../errno.h"

char *tcpstates[]; /* XXX */

/*
 * Initial options: indicate max segment length 1/2 of space
 * allocated for receive; if TCPTRUEOOB is defined, indicate
 * willingness to do true out-of-band.
 */
#ifndef TCPTRUEOOB
u_char	tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, };
#else
u_char	tcp_initopt[6] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, TCPOPT_WILLOOB, 2 };
#endif

/*
 * Tcp output routine: figure out what should be sent and send it.
 */
tcp_output(tp)
	register struct tcpcb *tp;
{
	register struct socket *so = tp->t_inpcb->inp_socket;
	register int len;
	struct mbuf *m0;
	int off, flags, win;
	register struct mbuf *m;
	register struct tcpiphdr *ti;
	u_char *opt;
	unsigned optlen = 0;

COUNT(TCP_OUTPUT);

	/*
	 * Determine length of data that can be transmitted,
	 * and flags that will be used.
	 * If there is some data or critical controls (SYN, RST)
	 * to send, then transmit; otherwise, investigate further.
	 */
	off = tp->snd_nxt - tp->snd_una;
	len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off;
	if (len < 0)
		return (0);			/* past FIN */
	if (len > tp->t_maxseg)
		len = tp->t_maxseg;
	flags = tcp_outflags[tp->t_state];
	if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc)
		flags &= ~TH_FIN;
	if (len || (flags & (TH_SYN|TH_RST|TH_FIN)))
		goto send;

	/*
	 * Send if we owe peer an ACK.
	 */
	if (tp->t_flags&TF_ACKNOW)
		goto send;

#ifdef TCPTRUEOOB
	/*
	 * Send if an out of band data or ack should be transmitted.
	 */
	if (tp->t_oobflags&(TCPOOB_OWEACK|TCPOOB_NEEDACK)))
		goto send;
#endif

	/*
	 * Calculate available window in i, and also amount
	 * of window known to peer (as advertised window less
	 * next expected input.)  If this is 35% or more of the
	 * maximum possible window, then want to send a segment to peer.
	 */
	win = sbspace(&so->so_rcv);
	if (win > 0 &&
	    ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35))
		goto send;

	/*
	 * No reason to send a segment, just return.
	 */
	return (0);

send:
	/*
	 * Grab a header mbuf, attaching a copy of data to
	 * be transmitted, and initialize the header from
	 * the template for sends on this connection.
	 */
	MGET(m, 0);
	if (m == 0)
		return (0);
	m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
	m->m_len = sizeof (struct tcpiphdr);
	if (len) {
		m->m_next = m_copy(so->so_snd.sb_mb, off, len);
		if (m->m_next == 0)
			len = 0;
	}
	ti = mtod(m, struct tcpiphdr *);
	if (tp->t_template == 0)
		panic("tcp_output");
	bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr));

	/*
	 * Fill in fields, remembering maximum advertised
	 * window for use in delaying messages about window sizes.
	 */
	ti->ti_seq = tp->snd_nxt;
	ti->ti_ack = tp->rcv_nxt;
#if vax
	ti->ti_seq = htonl(ti->ti_seq);
	ti->ti_ack = htonl(ti->ti_ack);
#endif
	/*
	 * Before ESTABLISHED, force sending of initial options
	 * unless TCP set to not do any options.
	 */
	if (tp->t_state < TCPS_ESTABLISHED) {
		if (tp->t_flags&TF_NOOPT)
			goto noopt;
		opt = tcp_initopt;
		optlen = sizeof (tcp_initopt);
		*(u_short *)(opt + 2) = so->so_rcv.sb_hiwat / 2;
#if vax
		*(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2));
#endif
	} else {
		if (tp->t_tcpopt == 0)
			goto noopt;
		opt = mtod(tp->t_tcpopt, u_char *);
		optlen = tp->t_tcpopt->m_len;
	}
#ifndef TCPTRUEOOB
	if (opt)
#else
	if (opt || (tp->t_oobflags&(TCPOOB_OWEACK|TCPOOB_NEEDACK)))
#endif
	{
		m0 = m->m_next;
		m->m_next = m_get(M_DONTWAIT);
		if (m->m_next == 0) {
			(void) m_free(m);
			m_freem(m0);
			return (0);
		}
		m->m_next->m_next = m0;
		m0 = m->m_next;
		m0->m_off = MMINOFF;
		m0->m_len = optlen;
		bcopy(opt, mtod(m0, caddr_t), optlen);
		opt = (u_char *)(mtod(m0, caddr_t) + optlen);
#ifdef TCPTRUEOOB
		if (tp->t_oobflags&TCPOOB_OWEACK) {
printf("tp %x send OOBACK for %x\n", tp->t_iobseq);
			*opt++ = TCPOPT_OOBACK;
			*opt++ = 3;
			*opt++ = tp->t_iobseq;
			m0->m_len += 3;
			tp->t_oobflags &= ~TCPOOB_OWEACK;
			/* sender should rexmt oob to force ack repeat */
		}
		if (tp->t_oobflags&TCPOOB_NEEDACK) {
printf("tp %x send OOBDATA seq %x data %x\n", tp->t_oobseq, tp->t_oobc);
			*opt++ = TCPOPT_OOBDATA;
			*opt++ = 8;
			*opt++ = tp->t_oobseq;
			*opt++ = tp->t_oobc;
			*(tcp_seq *)opt = tp->t_oobmark - tp->snd_nxt;
#ifdef vax
			*(tcp_seq *)opt = htonl((unsigned)*(tcp_seq *)opt);
#endif
			m0->m_len += 8;
			TCPT_RANGESET(tp->t_timer[TCPT_OOBREXMT],
			    tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
		}
#endif
		while (m0->m_len & 0x3) {
			*opt++ = TCPOPT_EOL;
			m0->m_len++;
		}
		optlen = m0->m_len;
		ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
	}
noopt:
	ti->ti_flags = flags;
	win = sbspace(&so->so_rcv);
	if (win > 0)
		ti->ti_win = htons((u_short)win);
	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
		ti->ti_urp = tp->snd_up - tp->snd_nxt;
#if vax
		ti->ti_urp = htons(ti->ti_urp);
#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 */
	/* PUSH */

	/*
	 * Put TCP length in extended header, and then
	 * checksum extended header and data.
	 */
	if (len + optlen) {
		ti->ti_len = sizeof (struct tcphdr) + optlen + len;
#if vax
		ti->ti_len = htons((u_short)ti->ti_len);
#endif
	}
	ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + optlen + len);

	/*
	 * Advance snd_nxt over sequence space of this segment
	 */
	if (flags & (TH_SYN|TH_FIN))
		tp->snd_nxt++;
	tp->snd_nxt += len;

	/*
	 * If this transmission closes the window,
	 * start persistance timer at 2 round trip times
	 * but at least TCPTV_PERSMIN ticks.
	 */
	if (TCPS_HAVERCVDSYN(tp->t_state) &&
	    SEQ_GEQ(tp->snd_nxt, tp->snd_una+tp->snd_wnd) &&
	    tp->t_timer[TCPT_PERSIST] == 0)
		TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
		    2 * tp->t_srtt, TCPTV_PERSMIN, TCPTV_MAX);

	/*
	 * Time this transmission if not a retransmission and
	 * not currently timing anything.
	 */
	if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) {
		tp->t_rtt = 1;
		tp->t_rtseq = tp->snd_nxt - len;
	}

	/*
	 * Set retransmit timer if not currently set.
	 * Initial value for retransmit timer to tcp_beta*tp->t_srtt.
	 * Initialize shift counter which is used for exponential
	 * backoff of retransmit time.
	 */
	if (tp->t_timer[TCPT_REXMT] == 0 && tp->snd_nxt != tp->snd_una) {
		TCPT_RANGESET(tp->t_timer[TCPT_REXMT],
		    tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX);
		tp->t_rtt = 0;
		tp->t_rxtshift = 0;
	}

	/*
	 * Trace.
	 */
	if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)
		tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0);

	/*
	 * Fill in IP length and desired time to live and
	 * send to IP level.
	 */
	((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len;
	((struct ip *)ti)->ip_ttl = TCP_TTL;
	if (ip_output(m, tp->t_ipopt) == 0)
		return (0);

	/*
	 * 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.
	 * Drop send for purpose of ACK requirements.
	 */
	if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
		tp->rcv_adv = tp->rcv_nxt + win;
	tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
	if (SEQ_GT(tp->snd_nxt, tp->snd_max))
		tp->snd_max = tp->snd_nxt;
	return (1);
}