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

/*      tcp_output.c    4.29    82/01/17        */

#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;
       register struct mbuf *m;
       register struct tcpiphdr *ti;
       int win, force;
       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;                 /* 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(0);
               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++ = 4;
                       *opt++ = tp->t_oobseq;
                       *opt++ = tp->t_oobc;
                       m0->m_len += 4;
                       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);
}