revert between 56095 -> 55830 in arch

[AROS.git] / workbench / network / stacks / AROSTCP / bsdsocket / netinet / tcp_input.c

/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 * Copyright (c) 2006 Pavel Fedin
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      From: @(#)tcp_input.c   8.5 (Berkeley) 4/10/94
 *      $Id$
 */

#ifndef TUBA_INCLUDE
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/errno.h>
#include <sys/queue.h>

#include <net/route.h>
#include <net/if.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcpip.h>
#ifdef TCPDEBUG
#include <netinet/tcp_debug.h>
struct  tcpiphdr tcp_saveti;
#endif

int     tcprexmtthresh = 3;
#if defined(__AROS__)
int     tcp_iss;
int     tcp_ccgen;
#else
tcp_seq tcp_iss;
tcp_cc  tcp_ccgen;
#endif
struct  tcpstat tcpstat;
u_long  tcp_now;
struct inpcbhead tcb;
struct inpcbinfo tcbinfo;

#endif /* TUBA_INCLUDE */

#include <kern/uipc_socket2_protos.h>
//#include <netinet/tcp_subr_protos.h>

/*
 * Insert segment ti into reassembly queue of tcp with
 * control block tp.  Return TH_FIN if reassembly now includes
 * a segment with FIN.  The macro form does the common case inline
 * (segment is the next to be received on an established connection,
 * and the queue is empty), avoiding linkage into and removal
 * from the queue and repetition of various conversions.
 * Set DELACK for segments received in order, but ack immediately
 * when segments are out of order (so fast retransmit can work).
 */
#define TCP_REASS(tp, ti, m, so, flags) { \
    if ((ti)->ti_seq == (tp)->rcv_nxt && \
        (tp)->t_segq == NULL && \
        (tp)->t_state == TCPS_ESTABLISHED) { \
        if (ti->ti_flags & TH_PUSH) \
                        tp->t_flags |= TF_ACKNOW; \
                else \
                        tp->t_flags |= TF_DELACK; \
        (tp)->rcv_nxt += (ti)->ti_len; \
        flags = (ti)->ti_flags & TH_FIN; \
        tcpstat.tcps_rcvpack++;\
        tcpstat.tcps_rcvbyte += (ti)->ti_len;\
        sbappend(&(so)->so_rcv, (m)); \
        sorwakeup(so); \
    } else { \
        (flags) = tcp_reass((tp), (ti), (m)); \
        tp->t_flags |= TF_ACKNOW; \
    } \
}

int
tcp_reass(tp, ti, m)
        struct tcpcb *tp;
        struct tcpiphdr *ti;
        struct mbuf *m;
{
        struct mbuf *q;
        struct mbuf *p;
        struct mbuf *nq;
        struct socket *so = tp->t_inpcb->inp_socket;
        int flags;

#define GETTCP(m)       ((struct tcpiphdr *)m->m_pkthdr.header)

        /*
         * Call with ti==0 after become established to
         * force pre-ESTABLISHED data up to user socket.
         */
        if (ti == 0)
                goto present;

        m->m_pkthdr.header = (caddr_t)ti;

        /*
         * Find a segment which begins after this one does.
         */
        for (q = tp->t_segq, p = NULL; q; p = q, q = q->m_nextpkt)
                if (SEQ_GT(GETTCP(q)->ti_seq, ti->ti_seq))
                        break;

        /*
         * If there is a preceding segment, it may provide some of
         * our data already.  If so, drop the data from the incoming
         * segment.  If it provides all of our data, drop us.
         */
        if (p != NULL) {
                register int i;
                /* conversion to int (in i) handles seq wraparound */
                i = GETTCP(p)->ti_seq + GETTCP(p)->ti_len - ti->ti_seq;
                if (i > 0) {
                        if (i >= ti->ti_len) {
                                tcpstat.tcps_rcvduppack++;
                                tcpstat.tcps_rcvdupbyte += ti->ti_len;
                                m_freem(m);
                                /*
                                 * Try to present any queued data
                                 * at the left window edge to the user.
                                 * This is needed after the 3-WHS
                                 * completes.
                                 */
                                goto present;   /* ??? */
                        }
                        m_adj(m, i);
                        ti->ti_len -= i;
                        ti->ti_seq += i;
                }
        }
        tcpstat.tcps_rcvoopack++;
        tcpstat.tcps_rcvoobyte += ti->ti_len;

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        while (q) {
                register int i = (ti->ti_seq + ti->ti_len) - GETTCP(q)->ti_seq;
                if (i <= 0)
                        break;
                if (i < GETTCP(q)->ti_len) {
                        GETTCP(q)->ti_seq += i;
                        GETTCP(q)->ti_len -= i;
                        m_adj(q, i);
                        break;
                }

                nq = q->m_nextpkt;
                if (p)
                        p->m_nextpkt = nq;
                else
                        tp->t_segq = nq;
                m_freem(q);
                q = nq;
        }

        if (p == NULL) {
                m->m_nextpkt = tp->t_segq;
                tp->t_segq = m;
        } else {
                m->m_nextpkt = p->m_nextpkt;
                p->m_nextpkt = m;
        }

present:
        /*
         * Present data to user, advancing rcv_nxt through
         * completed sequence space.
         */
        if (!TCPS_HAVEESTABLISHED(tp->t_state))
                return (0);
        q = tp->t_segq;
        if (!q || GETTCP(q)->ti_seq != tp->rcv_nxt)
                return (0);
        do {
                tp->rcv_nxt += GETTCP(q)->ti_len;
                flags = GETTCP(q)->ti_flags & TH_FIN;
                nq = q->m_nextpkt;
                tp->t_segq = nq;
                q->m_nextpkt = NULL;
                if (so->so_state & SS_CANTRCVMORE)
                        m_freem(q);
                else
                        sbappend(&so->so_rcv, q);
                q = nq;
        } while (q && GETTCP(q)->ti_seq == tp->rcv_nxt);
        sorwakeup(so);
        return (flags);

#undef GETTCP
}

/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
void tcp_input(void *arg, ...)
{
        register struct mbuf *m = arg;
        int iphlen;
        register struct tcpiphdr *ti;
        register struct inpcb *inp;
        caddr_t optp = NULL;
        int optlen = 0;
        int len, tlen, off;
        register struct tcpcb *tp = 0;
        register int tiflags;
        struct socket *so = 0;
        int todrop, acked, ourfinisacked, needoutput = 0;
        struct in_addr laddr;
        int dropsocket = 0;
        int iss = 0;
        u_long tiwin;
        struct tcpopt to;               /* options in this segment */
        struct rmxp_tao *taop;          /* pointer to our TAO cache entry */
        struct rmxp_tao tao_noncached;  /* in case there's no cached entry */
#ifdef TCPDEBUG
        short ostate = 0;
#endif
        va_list va;

        va_start(va, arg);
        iphlen = va_arg(va, int);
        va_end(va);


        bzero((char *)&to, sizeof(to));

        tcpstat.tcps_rcvtotal++;
        /*
         * Get IP and TCP header together in first mbuf.
         * Note: IP leaves IP header in first mbuf.
         */
        ti = mtod(m, struct tcpiphdr *);
        if (iphlen > sizeof (struct ip))
                ip_stripoptions(m, (struct mbuf *)0);
        if (m->m_len < sizeof (struct tcpiphdr)) {
                if ((m = m_pullup(m, sizeof (struct tcpiphdr))) == 0) {
                        tcpstat.tcps_rcvshort++;
                        return;
                }
                ti = mtod(m, struct tcpiphdr *);
        }

        /*
         * Checksum extended TCP header and data.
         */
        tlen = ((struct ip *)ti)->ip_len;
        len = sizeof (struct ip) + tlen;
        bzero(ti->ti_x1, sizeof(ti->ti_x1));
        ti->ti_len = (u_short)tlen;
        HTONS(ti->ti_len);
        ti->ti_sum = in_cksum(m, len);
        if (ti->ti_sum) {
                tcpstat.tcps_rcvbadsum++;
                goto drop;
        }

        /*
         * Check that TCP offset makes sense,
         * pull out TCP options and adjust length.              XXX
         */
        off = ti->ti_off << 2;
        if (off < sizeof (struct tcphdr) || off > tlen) {
                tcpstat.tcps_rcvbadoff++;
                goto drop;
        }
        tlen -= off;
        ti->ti_len = tlen;
        if (off > sizeof (struct tcphdr)) {
                if (m->m_len < sizeof(struct ip) + off) {
                        if ((m = m_pullup(m, sizeof (struct ip) + off)) == 0) {
                                tcpstat.tcps_rcvshort++;
                                return;
                        }
                        ti = mtod(m, struct tcpiphdr *);
                }
                optlen = off - sizeof (struct tcphdr);
                optp = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
                /*
                 * Do quick retrieval of timestamp options ("options
                 * prediction?").  If timestamp is the only option and it's
                 * formatted as recommended in RFC 1323 appendix A, we
                 * quickly get the values now and not bother calling
                 * tcp_dooptions(), etc.
                 */
                if ((optlen == TCPOLEN_TSTAMP_APPA ||
                     (optlen > TCPOLEN_TSTAMP_APPA &&
                        optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
                     *(u_long *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
                     (ti->ti_flags & TH_SYN) == 0) {
                        to.to_flag |= TOF_TS;
                        to.to_tsval = ntohl(*(u_long *)(optp + 4));
                        to.to_tsecr = ntohl(*(u_long *)(optp + 8));
                        optp = NULL;    /* we've parsed the options */
                }
        }
        tiflags = ti->ti_flags;

        /*
         * Convert TCP protocol specific fields to host format.
         */
        NTOHL(ti->ti_seq);
        NTOHL(ti->ti_ack);
        NTOHS(ti->ti_win);
        NTOHS(ti->ti_urp);

        /*
         * Drop TCP, IP headers and TCP options.
         */
        m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
        m->m_len  -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);

        /*
         * Locate pcb for segment.
         */
findpcb:
        /*
         * First look for an exact match.
         */
        inp = in_pcblookuphash(&tcbinfo, ti->ti_src, ti->ti_sport,
            ti->ti_dst, ti->ti_dport);
        /*
         * ...and if that fails, do a wildcard search.
         */
        if (inp == NULL) {
                inp = in_pcblookup(&tcb, ti->ti_src, ti->ti_sport,
                    ti->ti_dst, ti->ti_dport, INPLOOKUP_WILDCARD);
        }

        /*
         * If the state is CLOSED (i.e., TCB does not exist) then
         * all data in the incoming segment is discarded.
         * If the TCB exists but is in CLOSED state, it is embryonic,
         * but should either do a listen or a connect soon.
         */
        if (inp == NULL)
                goto dropwithreset;
        tp = intotcpcb(inp);
        if (tp == 0)
                goto dropwithreset;
        if (tp->t_state == TCPS_CLOSED)
                goto drop;

        /* Unscale the window into a 32-bit value. */
        if ((tiflags & TH_SYN) == 0)
                tiwin = ti->ti_win << tp->snd_scale;
        else
                tiwin = ti->ti_win;

        so = inp->inp_socket;
        if (so->so_options & (SO_DEBUG|SO_ACCEPTCONN)) {
#ifdef TCPDEBUG
                if (so->so_options & SO_DEBUG) {
                        ostate = tp->t_state;
                        tcp_saveti = *ti;
                }
#endif
                if (so->so_options & SO_ACCEPTCONN) {
                        register struct tcpcb *tp0 = tp;
                        /*
                         * call to access control.. (AmiTCP/IP extra)
                         */
                        if (controlaccess(ti->ti_src, ti->ti_dport) == 0)
                                goto dropwithreset;
                        so = sonewconn(so, 0);
                        if (so == 0)
                                goto drop;
                        /*
                         * This is ugly, but ....
                         *
                         * Mark socket as temporary until we're
                         * committed to keeping it.  The code at
                         * ``drop'' and ``dropwithreset'' check the
                         * flag dropsocket to see if the temporary
                         * socket created here should be discarded.
                         * We mark the socket as discardable until
                         * we're committed to it below in TCPS_LISTEN.
                         */
                        dropsocket++;
                        inp = (struct inpcb *)so->so_pcb;
                        inp->inp_laddr = ti->ti_dst;
                        inp->inp_lport = ti->ti_dport;
                        in_pcbrehash(inp);
#if BSD>=43
                        inp->inp_options = ip_srcroute();
#endif
                        tp = intotcpcb(inp);
                        tp->t_state = TCPS_LISTEN;
                        tp->t_flags |= tp0->t_flags & (TF_NOPUSH|TF_NOOPT);

                        /* Compute proper scaling value from buffer space */
                        while (tp->request_r_scale < TCP_MAX_WINSHIFT &&
                           TCP_MAXWIN << tp->request_r_scale < so->so_rcv.sb_hiwat)
                                tp->request_r_scale++;
                }
        }

        /*
         * Segment received on connection.
         * Reset idle time and keep-alive timer.
         */
        tp->t_idle = 0;
        tp->t_timer[TCPT_KEEP] = tcp_keepidle;

        /*
         * Process options if not in LISTEN state,
         * else do it below (after getting remote address).
         */
        if (optp && tp->t_state != TCPS_LISTEN)
                tcp_dooptions(tp, optp, optlen, ti,
                        &to);

        /*
         * Header prediction: check for the two common cases
         * of a uni-directional data xfer.  If the packet has
         * no control flags, is in-sequence, the window didn't
         * change and we're not retransmitting, it's a
         * candidate.  If the length is zero and the ack moved
         * forward, we're the sender side of the xfer.  Just
         * free the data acked & wake any higher level process
         * that was blocked waiting for space.  If the length
         * is non-zero and the ack didn't move, we're the
         * receiver side.  If we're getting packets in-order
         * (the reassembly queue is empty), add the data to
         * the socket buffer and note that we need a delayed ack.
         * Make sure that the hidden state-flags are also off.
         * Since we check for TCPS_ESTABLISHED above, it can only
         * be TH_NEEDSYN.
         */
        if (tp->t_state == TCPS_ESTABLISHED &&
            (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
            ((tp->t_flags & (TF_NEEDSYN|TF_NEEDFIN)) == 0) &&
            ((to.to_flag & TOF_TS) == 0 ||
             TSTMP_GEQ(to.to_tsval, tp->ts_recent)) &&
            /*
             * Using the CC option is compulsory if once started:
             *   the segment is OK if no T/TCP was negotiated or
             *   if the segment has a CC option equal to CCrecv
             */
            ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) != (TF_REQ_CC|TF_RCVD_CC) ||
             (to.to_flag & TOF_CC) != 0 && to.to_cc == tp->cc_recv) &&
            ti->ti_seq == tp->rcv_nxt &&
            tiwin && tiwin == tp->snd_wnd &&
            tp->snd_nxt == tp->snd_max) {

                /*
                 * If last ACK falls within this segment's sequence numbers,
                 * record the timestamp.
                 * NOTE that the test is modified according to the latest
                 * proposal of the tcplw@cray.com list (Braden 1993/04/26).
                 */
                if ((to.to_flag & TOF_TS) != 0 &&
                   SEQ_LEQ(ti->ti_seq, tp->last_ack_sent)) {
                        tp->ts_recent_age = tcp_now;
                        tp->ts_recent = to.to_tsval;
                }

                if (ti->ti_len == 0) {
                        if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
                            SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
                            tp->snd_cwnd >= tp->snd_wnd) {
                                /*
                                 * this is a pure ack for outstanding data.
                                 */
                                ++tcpstat.tcps_predack;
                                if ((to.to_flag & TOF_TS) != 0)
                                        tcp_xmit_timer(tp,
                                            tcp_now - to.to_tsecr + 1);
                                else if (tp->t_rtt &&
                                            SEQ_GT(ti->ti_ack, tp->t_rtseq))
                                        tcp_xmit_timer(tp, tp->t_rtt);
                                acked = ti->ti_ack - tp->snd_una;
                                tcpstat.tcps_rcvackpack++;
                                tcpstat.tcps_rcvackbyte += acked;
                                sbdrop(&so->so_snd, acked);
                                tp->snd_una = ti->ti_ack;
                                m_freem(m);

                                /*
                                 * If all outstanding data are acked, stop
                                 * retransmit timer, otherwise restart timer
                                 * using current (possibly backed-off) value.
                                 * If process is waiting for space,
                                 * wakeup/selwakeup/signal.  If data
                                 * are ready to send, let tcp_output
                                 * decide between more output or persist.
                                 */
                                if (tp->snd_una == tp->snd_max)
                                        tp->t_timer[TCPT_REXMT] = 0;
                                else if (tp->t_timer[TCPT_PERSIST] == 0)
                                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

                                if (so->so_snd.sb_flags & SB_NOTIFY)
                                        sowwakeup(so);
                                if (so->so_snd.sb_cc)
                                        (void) tcp_output(tp);
                                return;
                        }
                } else if (ti->ti_ack == tp->snd_una &&
                        tp->t_segq == NULL &&
                    ti->ti_len <= sbspace(&so->so_rcv)) {
                        /*
                         * this is a pure, in-sequence data packet
                         * with nothing on the reassembly queue and
                         * we have enough buffer space to take it.
                         */
                        ++tcpstat.tcps_preddat;
                        tp->rcv_nxt += ti->ti_len;
                        tcpstat.tcps_rcvpack++;
                        tcpstat.tcps_rcvbyte += ti->ti_len;
                        /*
                         * Add data to socket buffer.
                         */
                        sbappend(&so->so_rcv, m);
                        sorwakeup(so);
#ifdef TCP_ACK_HACK
                        /*
                         * If this is a short packet, then ACK now - with Nagel
                         *      congestion avoidance sender won't send more until
                         *      he gets an ACK.
                         */
                        if (tiflags & TH_PUSH) {
                                tp->t_flags |= TF_ACKNOW;
                                tcp_output(tp);
                        } else {
                                tp->t_flags |= TF_DELACK;
                        }
#else
                        tp->t_flags |= TF_DELACK;
#endif
                        return;
                }
        }

        /*
         * Calculate amount of space in receive window,
         * and then do TCP input processing.
         * Receive window is amount of space in rcv queue,
         * but not less than advertised window.
         */
        { int win;

        win = sbspace(&so->so_rcv);
        if (win < 0)
                win = 0;
        tp->rcv_wnd = MAX(win, (int)(tp->rcv_adv - tp->rcv_nxt));
        }

        switch (tp->t_state) {

        /*
         * If the state is LISTEN then ignore segment if it contains an RST.
         * If the segment contains an ACK then it is bad and send a RST.
         * If it does not contain a SYN then it is not interesting; drop it.
         * Don't bother responding if the destination was a broadcast.
         * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
         * tp->iss, and send a segment:
         *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
         * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
         * Fill in remote peer address fields if not previously specified.
         * Enter SYN_RECEIVED state, and process any other fields of this
         * segment in this state.
         */
        case TCPS_LISTEN: {
                struct mbuf *am;
                register struct sockaddr_in *sin;

                if (tiflags & TH_RST)
                        goto drop;
                if (tiflags & TH_ACK)
                        goto dropwithreset;
                if ((tiflags & TH_SYN) == 0)
                        goto drop;
                /*
                 * RFC1122 4.2.3.10, p. 104: discard bcast/mcast SYN
                 * in_broadcast() should never return true on a received
                 * packet with M_BCAST not set.
                 */
                if (m->m_flags & (M_BCAST|M_MCAST) ||
                    IN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
                        goto drop;
                am = m_get(M_DONTWAIT, MT_SONAME);      /* XXX */
                if (am == NULL)
                        goto drop;
                am->m_len = sizeof (struct sockaddr_in);
                sin = mtod(am, struct sockaddr_in *);
                sin->sin_family = AF_INET;
                sin->sin_len = sizeof(*sin);
                sin->sin_addr = ti->ti_src;
                sin->sin_port = ti->ti_sport;
                bzero((caddr_t)sin->sin_zero, sizeof(sin->sin_zero));
                laddr = inp->inp_laddr;
                if (inp->inp_laddr.s_addr == INADDR_ANY)
                        inp->inp_laddr = ti->ti_dst;
                if (in_pcbconnect(inp, am)) {
                        inp->inp_laddr = laddr;
                        (void) m_free(am);
                        goto drop;
                }
                (void) m_free(am);
                tp->t_template = tcp_template(tp);
                if (tp->t_template == 0) {
                        tp = tcp_drop(tp, ENOBUFS);
                        dropsocket = 0;         /* socket is already gone */
                        goto drop;
                }
                if ((taop = tcp_gettaocache(inp)) == NULL) {
                        taop = &tao_noncached;
                        bzero(taop, sizeof(*taop));
                }
                if (optp)
                        tcp_dooptions(tp, optp, optlen, ti,
                                &to);
                if (iss)
                        tp->iss = iss;
                else
                        tp->iss = tcp_iss;
                tcp_iss += TCP_ISSINCR/2;
                tp->irs = ti->ti_seq;
                tcp_sendseqinit(tp);
                tcp_rcvseqinit(tp);
                /*
                 * Initialization of the tcpcb for transaction;
                 *   set SND.WND = SEG.WND,
                 *   initialize CCsend and CCrecv.
                 */
                tp->snd_wnd = tiwin;    /* initial send-window */
                tp->cc_send = CC_INC(tcp_ccgen);
                tp->cc_recv = to.to_cc;
                /*
                 * Perform TAO test on incoming CC (SEG.CC) option, if any.
                 * - compare SEG.CC against cached CC from the same host,
                 *      if any.
                 * - if SEG.CC > chached value, SYN must be new and is accepted
                 *      immediately: save new CC in the cache, mark the socket
                 *      connected, enter ESTABLISHED state, turn on flag to
                 *      send a SYN in the next segment.
                 *      A virtual advertised window is set in rcv_adv to
                 *      initialize SWS prevention.  Then enter normal segment
                 *      processing: drop SYN, process data and FIN.
                 * - otherwise do a normal 3-way handshake.
                 */
                if ((to.to_flag & TOF_CC) != 0) {
                    if (taop->tao_cc != 0 && CC_GT(to.to_cc, taop->tao_cc)) {
                        taop->tao_cc = to.to_cc;
                        tp->t_state = TCPS_ESTABLISHED;

                        /*
                         * If there is a FIN, or if there is data and the
                         * connection is local, then delay SYN,ACK(SYN) in
                         * the hope of piggy-backing it on a response
                         * segment.  Otherwise must send ACK now in case
                         * the other side is slow starting.
                         */
                        if ((tiflags & TH_FIN) || (ti->ti_len != 0 &&
                            in_localaddr(inp->inp_faddr)))
                                tp->t_flags |= (TF_DELACK | TF_NEEDSYN);
                        else
                                tp->t_flags |= (TF_ACKNOW | TF_NEEDSYN);
                        tp->rcv_adv += tp->rcv_wnd;
                        tcpstat.tcps_connects++;
                        soisconnected(so);
                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
                        dropsocket = 0;         /* committed to socket */
                        tcpstat.tcps_accepts++;
                        goto trimthenstep6;
                    }
                /* else do standard 3-way handshake */
                } else {
                    /*
                     * No CC option, but maybe CC.NEW:
                     *   invalidate cached value.
                     */
                     taop->tao_cc = 0;
                }
                /*
                 * TAO test failed or there was no CC option,
                 *    do a standard 3-way handshake.
                 */
                tp->t_flags |= TF_ACKNOW;
                tp->t_state = TCPS_SYN_RECEIVED;
                tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
                dropsocket = 0;         /* committed to socket */
                tcpstat.tcps_accepts++;
                goto trimthenstep6;
                }

        /*
         * If the state is SYN_SENT:
         *      if seg contains an ACK, but not for our SYN, drop the input.
         *      if seg contains a RST, then drop the connection.
         *      if seg does not contain SYN, then drop it.
         * Otherwise this is an acceptable SYN segment
         *      initialize tp->rcv_nxt and tp->irs
         *      if seg contains ack then advance tp->snd_una
         *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
         *      arrange for segment to be acked (eventually)
         *      continue processing rest of data/controls, beginning with URG
         */
        case TCPS_SYN_SENT:
                if ((taop = tcp_gettaocache(inp)) == NULL) {
                        taop = &tao_noncached;
                        bzero(taop, sizeof(*taop));
                }

                if ((tiflags & TH_ACK) &&
                    (SEQ_LEQ(ti->ti_ack, tp->iss) ||
                     SEQ_GT(ti->ti_ack, tp->snd_max))) {
                        /*
                         * If we have a cached CCsent for the remote host,
                         * hence we haven't just crashed and restarted,
                         * do not send a RST.  This may be a retransmission
                         * from the other side after our earlier ACK was lost.
                         * Our new SYN, when it arrives, will serve as the
                         * needed ACK.
                         */
                        if (taop->tao_ccsent != 0)
                                goto drop;
                        else
                                goto dropwithreset;
                }
                if (tiflags & TH_RST) {
                        if (tiflags & TH_ACK)
                                tp = tcp_drop(tp, ECONNREFUSED);
                        goto drop;
                }
                if ((tiflags & TH_SYN) == 0)
                        goto drop;
                tp->snd_wnd = ti->ti_win;       /* initial send window */
                tp->cc_recv = to.to_cc;         /* foreign CC */

                tp->irs = ti->ti_seq;
                tcp_rcvseqinit(tp);
                if (tiflags & TH_ACK && SEQ_GT(ti->ti_ack, tp->iss)) {
                        tcpstat.tcps_connects++;
                        soisconnected(so);
                        /* Do window scaling on this connection? */
                        if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
                                (TF_RCVD_SCALE|TF_REQ_SCALE)) {
                                tp->snd_scale = tp->requested_s_scale;
                                tp->rcv_scale = tp->request_r_scale;
                        }
                        /*
                         * Our SYN was acked.  If segment contains CC.ECHO
                         * option, check it to make sure this segment really
                         * matches our SYN.  If not, just drop it as old
                         * duplicate, but send an RST if we're still playing
                         * by the old rules.
                         */
                        if ((to.to_flag & TOF_CCECHO) &&
                            tp->cc_send != to.to_ccecho) {
                                if (taop->tao_ccsent != 0)
                                        goto drop;
                                else
                                        goto dropwithreset;
                        }
                        /* Segment is acceptable, update cache if undefined. */
                        if (taop->tao_ccsent == 0)
                                taop->tao_ccsent = to.to_ccecho;

                        tp->rcv_adv += tp->rcv_wnd;
                        tp->snd_una++;          /* SYN is acked */
                        /*
                         * If there's data, delay ACK; if there's also a FIN
                         * ACKNOW will be turned on later.
                         */
                        if (ti->ti_len != 0)
                                tp->t_flags |= TF_DELACK;
                        else
                                tp->t_flags |= TF_ACKNOW;
                        /*
                         * Received <SYN,ACK> in SYN_SENT[*] state.
                         * Transitions:
                         *      SYN_SENT  --> ESTABLISHED
                         *      SYN_SENT* --> FIN_WAIT_1
                         */
                        if (tp->t_flags & TF_NEEDFIN) {
                                tp->t_state = TCPS_FIN_WAIT_1;
                                tp->t_flags &= ~TF_NEEDFIN;
                                tiflags &= ~TH_SYN;
                        } else
                                tp->t_state = TCPS_ESTABLISHED;

                } else {
                /*
                 *  Received initial SYN in SYN-SENT[*] state => simul-
                 *  taneous open.  If segment contains CC option and there is
                 *  a cached CC, apply TAO test; if it succeeds, connection is
                 *  half-synchronized.  Otherwise, do 3-way handshake:
                 *        SYN-SENT -> SYN-RECEIVED
                 *        SYN-SENT* -> SYN-RECEIVED*
                 *  If there was no CC option, clear cached CC value.
                 */
                        tp->t_flags |= TF_ACKNOW;
                        tp->t_timer[TCPT_REXMT] = 0;
                        if (to.to_flag & TOF_CC) {
                                if (taop->tao_cc != 0 &&
                                    CC_GT(to.to_cc, taop->tao_cc)) {
                                        /*
                                         * update cache and make transition:
                                         *        SYN-SENT -> ESTABLISHED*
                                         *        SYN-SENT* -> FIN-WAIT-1*
                                         */
                                        taop->tao_cc = to.to_cc;
                                        if (tp->t_flags & TF_NEEDFIN) {
                                                tp->t_state = TCPS_FIN_WAIT_1;
                                                tp->t_flags &= ~TF_NEEDFIN;
                                        } else
                                                tp->t_state = TCPS_ESTABLISHED;
                                        tp->t_flags |= TF_NEEDSYN;
                                } else
                                        tp->t_state = TCPS_SYN_RECEIVED;
                        } else {
                                /* CC.NEW or no option => invalidate cache */
                                taop->tao_cc = 0;
                                tp->t_state = TCPS_SYN_RECEIVED;
                        }
                }

trimthenstep6:
                /*
                 * Advance ti->ti_seq to correspond to first data byte.
                 * If data, trim to stay within window,
                 * dropping FIN if necessary.
                 */
                ti->ti_seq++;
                if (ti->ti_len > tp->rcv_wnd) {
                        todrop = ti->ti_len - tp->rcv_wnd;
                        m_adj(m, -todrop);
                        ti->ti_len = tp->rcv_wnd;
                        tiflags &= ~TH_FIN;
                        tcpstat.tcps_rcvpackafterwin++;
                        tcpstat.tcps_rcvbyteafterwin += todrop;
                }
                tp->snd_wl1 = ti->ti_seq - 1;
                tp->rcv_up = ti->ti_seq;
                /*
                 *  Client side of transaction: already sent SYN and data.
                 *  If the remote host used T/TCP to validate the SYN,
                 *  our data will be ACK'd; if so, enter normal data segment
                 *  processing in the middle of step 5, ack processing.
                 *  Otherwise, goto step 6.
                 */
                if (tiflags & TH_ACK)
                        goto process_ACK;
                goto step6;
        /*
         * If the state is LAST_ACK or CLOSING or TIME_WAIT:
         *      if segment contains a SYN and CC [not CC.NEW] option:
         *              if state == TIME_WAIT and connection duration > MSL,
         *                  drop packet and send RST;
         *
         *              if SEG.CC > CCrecv then is new SYN, and can implicitly
         *                  ack the FIN (and data) in retransmission queue.
         *                  Complete close and delete TCPCB.  Then reprocess
         *                  segment, hoping to find new TCPCB in LISTEN state;
         *
         *              else must be old SYN; drop it.
         *      else do normal processing.
         */
        case TCPS_LAST_ACK:
        case TCPS_CLOSING:
        case TCPS_TIME_WAIT:
                if ((tiflags & TH_SYN) &&
                    (to.to_flag & TOF_CC) && tp->cc_recv != 0) {
                        if (tp->t_state == TCPS_TIME_WAIT &&
                                        tp->t_duration > TCPTV_MSL)
                                goto dropwithreset;
                        if (CC_GT(to.to_cc, tp->cc_recv)) {
                                tp = tcp_close(tp);
                                goto findpcb;
                        }
                        else
                                goto drop;
                }
                break;  /* continue normal processing */
        }

        /*
         * States other than LISTEN or SYN_SENT.
         * First check timestamp, if present.
         * Then check the connection count, if present.
         * Then check that at least some bytes of segment are within
         * receive window.  If segment begins before rcv_nxt,
         * drop leading data (and SYN); if nothing left, just ack.
         *
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than ts_recent, drop it.
         */
        if ((to.to_flag & TOF_TS) != 0 && (tiflags & TH_RST) == 0 &&
            tp->ts_recent && TSTMP_LT(to.to_tsval, tp->ts_recent)) {

                /* Check to see if ts_recent is over 24 days old.  */
                if ((int)(tcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
                        /*
                         * Invalidate ts_recent.  If this segment updates
                         * ts_recent, the age will be reset later and ts_recent
                         * will get a valid value.  If it does not, setting
                         * ts_recent to zero will at least satisfy the
                         * requirement that zero be placed in the timestamp
                         * echo reply when ts_recent isn't valid.  The
                         * age isn't reset until we get a valid ts_recent
                         * because we don't want out-of-order segments to be
                         * dropped when ts_recent is old.
                         */
                        tp->ts_recent = 0;
                } else {
                        tcpstat.tcps_rcvduppack++;
                        tcpstat.tcps_rcvdupbyte += ti->ti_len;
                        tcpstat.tcps_pawsdrop++;
                        goto dropafterack;
                }
        }

        /*
         * T/TCP mechanism
         *   If T/TCP was negotiated and the segment doesn't have CC,
         *   or if it's CC is wrong then drop the segment.
         *   RST segments do not have to comply with this.
         */
        if ((tp->t_flags & (TF_REQ_CC|TF_RCVD_CC)) == (TF_REQ_CC|TF_RCVD_CC) &&
            ((to.to_flag & TOF_CC) == 0 || tp->cc_recv != to.to_cc) &&
            (tiflags & TH_RST) == 0)
                goto dropafterack;

        todrop = tp->rcv_nxt - ti->ti_seq;
        if (todrop > 0) {
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        ti->ti_seq++;
                        if (ti->ti_urp > 1)
                                ti->ti_urp--;
                        else
                                tiflags &= ~TH_URG;
                        todrop--;
                }
                /*
                 * Following if statement from Stevens, vol. 2, p. 960.
                 */
                if (todrop > ti->ti_len
                    || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
                        /*
                         * Any valid FIN must be to the left of the window.
                         * At this point the FIN must be a duplicate or out
                         * of sequence; drop it.
                         */
                        tiflags &= ~TH_FIN;

                        /*
                         * Send an ACK to resynchronize and drop any data.
                         * But keep on processing for RST or ACK.
                         */
                        tp->t_flags |= TF_ACKNOW;
                        todrop = ti->ti_len;
                        tcpstat.tcps_rcvduppack++;
                        tcpstat.tcps_rcvdupbyte += todrop;
                } else {
                        tcpstat.tcps_rcvpartduppack++;
                        tcpstat.tcps_rcvpartdupbyte += todrop;
                }
                m_adj(m, todrop);
                ti->ti_seq += todrop;
                ti->ti_len -= todrop;
                if (ti->ti_urp > todrop)
                        ti->ti_urp -= todrop;
                else {
                        tiflags &= ~TH_URG;
                        ti->ti_urp = 0;
                }
        }

        /*
         * If new data are received on a connection after the
         * user processes are gone, then RST the other end.
         */
        if ((so->so_state & SS_NOFDREF) &&
            tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
                tp = tcp_close(tp);
                tcpstat.tcps_rcvafterclose++;
                goto dropwithreset;
        }

        /*
         * If segment ends after window, drop trailing data
         * (and PUSH and FIN); if nothing left, just ACK.
         */
        todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
        if (todrop > 0) {
                tcpstat.tcps_rcvpackafterwin++;
                if (todrop >= ti->ti_len) {
                        tcpstat.tcps_rcvbyteafterwin += ti->ti_len;
                        /*
                         * If a new connection request is received
                         * while in TIME_WAIT, drop the old connection
                         * and start over if the sequence numbers
                         * are above the previous ones.
                         */
                        if (tiflags & TH_SYN &&
                            tp->t_state == TCPS_TIME_WAIT &&
                            SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
                                iss = tp->rcv_nxt + TCP_ISSINCR;
                                tp = tcp_close(tp);
                                goto findpcb;
                        }
                        /*
                         * If window is closed can only take segments at
                         * window edge, and have to drop data and PUSH from
                         * incoming segments.  Continue processing, but
                         * remember to ack.  Otherwise, drop segment
                         * and ack.
                         */
                        if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
                                tp->t_flags |= TF_ACKNOW;
                                tcpstat.tcps_rcvwinprobe++;
                        } else
                                goto dropafterack;
                } else
                        tcpstat.tcps_rcvbyteafterwin += todrop;
                m_adj(m, -todrop);
                ti->ti_len -= todrop;
                tiflags &= ~(TH_PUSH|TH_FIN);
        }

        /*
         * If last ACK falls within this segment's sequence numbers,
         * record its timestamp.
         * NOTE that the test is modified according to the latest
         * proposal of the tcplw@cray.com list (Braden 1993/04/26).
         */
        if ((to.to_flag & TOF_TS) != 0 &&
            SEQ_LEQ(ti->ti_seq, tp->last_ack_sent)) {
                tp->ts_recent_age = tcp_now;
                tp->ts_recent = to.to_tsval;
        }

        /*
         * If the RST bit is set examine the state:
         *    SYN_RECEIVED STATE:
         *      If passive open, return to LISTEN state.
         *      If active open, inform user that connection was refused.
         *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
         *      Inform user that connection was reset, and close tcb.
         *    CLOSING, LAST_ACK, TIME_WAIT STATES
         *      Close the tcb.
         */
        if (tiflags&TH_RST) switch (tp->t_state) {

        case TCPS_SYN_RECEIVED:
                so->so_error = ECONNREFUSED;
                goto close;

        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSE_WAIT:
                so->so_error = ECONNRESET;
        close:
                tp->t_state = TCPS_CLOSED;
                tcpstat.tcps_drops++;
                tp = tcp_close(tp);
                goto drop;

        case TCPS_CLOSING:
        case TCPS_LAST_ACK:
        case TCPS_TIME_WAIT:
                tp = tcp_close(tp);
                goto drop;
        }

        /*
         * If a SYN is in the window, then this is an
         * error and we send an RST and drop the connection.
         */
        if (tiflags & TH_SYN) {
                tp = tcp_drop(tp, ECONNRESET);
                goto dropwithreset;
        }

        /*
         * If the ACK bit is off:  if in SYN-RECEIVED state or SENDSYN
         * flag is on (half-synchronized state), then queue data for
         * later processing; else drop segment and return.
         */
        if ((tiflags & TH_ACK) == 0) {
                if (tp->t_state == TCPS_SYN_RECEIVED ||
                    (tp->t_flags & TF_NEEDSYN))
                        goto step6;
                else
                        goto drop;
        }

        /*
         * Ack processing.
         */
        switch (tp->t_state) {

        /*
         * In SYN_RECEIVED state if the ack ACKs our SYN then enter
         * ESTABLISHED state and continue processing, otherwise
         * send an RST.
         */
        case TCPS_SYN_RECEIVED:
                if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
                    SEQ_GT(ti->ti_ack, tp->snd_max))
                        goto dropwithreset;

                tcpstat.tcps_connects++;
                soisconnected(so);
                /* Do window scaling? */
                if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
                        (TF_RCVD_SCALE|TF_REQ_SCALE)) {
                        tp->snd_scale = tp->requested_s_scale;
                        tp->rcv_scale = tp->request_r_scale;
                }
                /*
                 * Upon successful completion of 3-way handshake,
                 * update cache.CC if it was undefined, pass any queued
                 * data to the user, and advance state appropriately.
                 */
                if ((taop = tcp_gettaocache(inp)) != NULL &&
                    taop->tao_cc == 0)
                        taop->tao_cc = tp->cc_recv;

                /*
                 * Make transitions:
                 *      SYN-RECEIVED  -> ESTABLISHED
                 *      SYN-RECEIVED* -> FIN-WAIT-1
                 */
                if (tp->t_flags & TF_NEEDFIN) {
                        tp->t_state = TCPS_FIN_WAIT_1;
                        tp->t_flags &= ~TF_NEEDFIN;
                } else
                        tp->t_state = TCPS_ESTABLISHED;
                /*
                 * If segment contains data or ACK, will call tcp_reass()
                 * later; if not, do so now to pass queued data to user.
                 */
                if (ti->ti_len == 0 && (tiflags & TH_FIN) == 0)
                        (void) tcp_reass(tp, (struct tcpiphdr *)0,
                            (struct mbuf *)0);
                tp->snd_wl1 = ti->ti_seq - 1;
                /* fall into ... */

        /*
         * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
         * ACKs.  If the ack is in the range
         *      tp->snd_una < ti->ti_ack <= tp->snd_max
         * then advance tp->snd_una to ti->ti_ack and drop
         * data from the retransmission queue.  If this ACK reflects
         * more up to date window information we update our window information.
         */
        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSE_WAIT:
        case TCPS_CLOSING:
        case TCPS_LAST_ACK:
        case TCPS_TIME_WAIT:

                if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
                        if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
                                tcpstat.tcps_rcvdupack++;
                                /*
                                 * If we have outstanding data (other than
                                 * a window probe), this is a completely
                                 * duplicate ack (ie, window info didn't
                                 * change), the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshhold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 * Kludge snd_nxt & the congestion
                                 * window so we send only this one
                                 * packet.
                                 *
                                 * We know we're losing at the current
                                 * window size so do congestion avoidance
                                 * (set ssthresh to half the current window
                                 * and pull our congestion window back to
                                 * the new ssthresh).
                                 *
                                 * Dup acks mean that packets have left the
                                 * network (they're now cached at the receiver)
                                 * so bump cwnd by the amount in the receiver
                                 * to keep a constant cwnd packets in the
                                 * network.
                                 */
                                if (tp->t_timer[TCPT_REXMT] == 0 ||
                                    ti->ti_ack != tp->snd_una)
                                        tp->t_dupacks = 0;
                                else if (++tp->t_dupacks == tcprexmtthresh) {
                                        tcp_seq onxt = tp->snd_nxt;
                                        u_int win =
                                            MIN(tp->snd_wnd, tp->snd_cwnd) / 2 /
                                                tp->t_maxseg;

                                        if (win < 2)
                                                win = 2;
                                        tp->snd_ssthresh = win * tp->t_maxseg;
                                        tp->t_timer[TCPT_REXMT] = 0;
                                        tp->t_rtt = 0;
                                        tp->snd_nxt = ti->ti_ack;
                                        tp->snd_cwnd = tp->t_maxseg;
                                        (void) tcp_output(tp);
                                        tp->snd_cwnd = tp->snd_ssthresh +
                                               tp->t_maxseg * tp->t_dupacks;
                                        if (SEQ_GT(onxt, tp->snd_nxt))
                                                tp->snd_nxt = onxt;
                                        goto drop;
                                } else if (tp->t_dupacks > tcprexmtthresh) {
                                        tp->snd_cwnd += tp->t_maxseg;
                                        (void) tcp_output(tp);
                                        goto drop;
                                }
                        } else
                                tp->t_dupacks = 0;
                        break;
                }
                /*
                 * If the congestion window was inflated to account
                 * for the other side's cached packets, retract it.
                 */
                if (tp->t_dupacks > tcprexmtthresh &&
                    tp->snd_cwnd > tp->snd_ssthresh)
                        tp->snd_cwnd = tp->snd_ssthresh;
                tp->t_dupacks = 0;
                if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
                        tcpstat.tcps_rcvacktoomuch++;
                        goto dropafterack;
                }
                /*
                 *  If we reach this point, ACK is not a duplicate,
                 *     i.e., it ACKs something we sent.
                 */
                if (tp->t_flags & TF_NEEDSYN) {
                        /*
                         *   T/TCP: Connection was half-synchronized, and our
                         *   SYN has been ACK'd (so connection is now fully
                         *   synchronized).  Go to non-starred state and
                         *   increment snd_una for ACK of SYN.
                         */
                        tp->t_flags &= ~TF_NEEDSYN;
                        tp->snd_una++;
                }

process_ACK:
                acked = ti->ti_ack - tp->snd_una;
                tcpstat.tcps_rcvackpack++;
                tcpstat.tcps_rcvackbyte += acked;

                /*
                 * If we have a timestamp reply, update smoothed
                 * round trip time.  If no timestamp is present but
                 * transmit timer is running and timed sequence
                 * number was acked, update smoothed round trip time.
                 * Since we now have an rtt measurement, cancel the
                 * timer backoff (cf., Phil Karn's retransmit alg.).
                 * Recompute the initial retransmit timer.
                 */
                if (to.to_flag & TOF_TS)
                        tcp_xmit_timer(tp, tcp_now - to.to_tsecr + 1);
                else if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
                        tcp_xmit_timer(tp,tp->t_rtt);

                /*
                 * If all outstanding data is acked, stop retransmit
                 * timer and remember to restart (more output or persist).
                 * If there is more data to be acked, restart retransmit
                 * timer, using current (possibly backed-off) value.
                 */
                if (ti->ti_ack == tp->snd_max) {
                        tp->t_timer[TCPT_REXMT] = 0;
                        needoutput = 1;
                } else if (tp->t_timer[TCPT_PERSIST] == 0)
                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

                /*
                 * If no data (only SYN) was ACK'd,
                 *    skip rest of ACK processing.
                 */
                if (acked == 0)
                        goto step6;

                /*
                 * When new data is acked, open the congestion window.
                 * If the window gives us less than ssthresh packets
                 * in flight, open exponentially (maxseg per packet).
                 * Otherwise open linearly: maxseg per window
                 * (maxseg^2 / cwnd per packet).
                 */
                {
                register u_int cw = tp->snd_cwnd;
                register u_int incr = tp->t_maxseg;

                if (cw > tp->snd_ssthresh)
                        incr = incr * incr / cw;
                tp->snd_cwnd = MIN(cw + incr, TCP_MAXWIN<<tp->snd_scale);
                }
                if (acked > so->so_snd.sb_cc) {
                        tp->snd_wnd -= so->so_snd.sb_cc;
                        sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
                        ourfinisacked = 1;
                } else {
                        sbdrop(&so->so_snd, acked);
                        tp->snd_wnd -= acked;
                        ourfinisacked = 0;
                }
                if (so->so_snd.sb_flags & SB_NOTIFY)
                        sowwakeup(so);
                tp->snd_una = ti->ti_ack;
                if (SEQ_LT(tp->snd_nxt, tp->snd_una))
                        tp->snd_nxt = tp->snd_una;

                switch (tp->t_state) {

                /*
                 * In FIN_WAIT_1 STATE in addition to the processing
                 * for the ESTABLISHED state if our FIN is now acknowledged
                 * then enter FIN_WAIT_2.
                 */
                case TCPS_FIN_WAIT_1:
                        if (ourfinisacked) {
                                /*
                                 * If we can't receive any more
                                 * data, then closing user can proceed.
                                 * Starting the timer is contrary to the
                                 * specification, but if we don't get a FIN
                                 * we'll hang forever.
                                 */
                                if (so->so_state & SS_CANTRCVMORE) {
                                        soisdisconnected(so);
                                        tp->t_timer[TCPT_2MSL] = tcp_maxidle;
                                }
                                tp->t_state = TCPS_FIN_WAIT_2;
                        }
                        break;

                /*
                 * In CLOSING STATE in addition to the processing for
                 * the ESTABLISHED state if the ACK acknowledges our FIN
                 * then enter the TIME-WAIT state, otherwise ignore
                 * the segment.
                 */
                case TCPS_CLOSING:
                        if (ourfinisacked) {
                                tp->t_state = TCPS_TIME_WAIT;
                                tcp_canceltimers(tp);
                                /* Shorten TIME_WAIT [RFC-1644, p.28] */
                                if (tp->cc_recv != 0 &&
                                    tp->t_duration < TCPTV_MSL)
                                        tp->t_timer[TCPT_2MSL] =
                                            tp->t_rxtcur * TCPTV_TWTRUNC;
                                else
                                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                                soisdisconnected(so);
                        }
                        break;

                /*
                 * In LAST_ACK, we may still be waiting for data to drain
                 * and/or to be acked, as well as for the ack of our FIN.
                 * If our FIN is now acknowledged, delete the TCB,
                 * enter the closed state and return.
                 */
                case TCPS_LAST_ACK:
                        if (ourfinisacked) {
                                tp = tcp_close(tp);
                                goto drop;
                        }
                        break;

                /*
                 * In TIME_WAIT state the only thing that should arrive
                 * is a retransmission of the remote FIN.  Acknowledge
                 * it and restart the finack timer.
                 */
                case TCPS_TIME_WAIT:
                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        goto dropafterack;
                }
        }

step6:
        /*
         * Update window information.
         * Don't look at window if no ACK: TAC's send garbage on first SYN.
         */
        if ((tiflags & TH_ACK) &&
            (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
            (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
             (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
                /* keep track of pure window updates */
                if (ti->ti_len == 0 &&
                    tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd)
                        tcpstat.tcps_rcvwinupd++;
                tp->snd_wnd = tiwin;
                tp->snd_wl1 = ti->ti_seq;
                tp->snd_wl2 = ti->ti_ack;
                if (tp->snd_wnd > tp->max_sndwnd)
                        tp->max_sndwnd = tp->snd_wnd;
                needoutput = 1;
        }

        /*
         * Process segments with URG.
         */
        if ((tiflags & TH_URG) && ti->ti_urp &&
            TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                /*
                 * This is a kludge, but if we receive and accept
                 * random urgent pointers, we'll crash in
                 * soreceive.  It's hard to imagine someone
                 * actually wanting to send this much urgent data.
                 */
                if (ti->ti_urp + so->so_rcv.sb_cc > sb_max) {
                        ti->ti_urp = 0;                 /* XXX */
                        tiflags &= ~TH_URG;             /* XXX */
                        goto dodata;                    /* XXX */
                }
                /*
                 * If this segment advances the known urgent pointer,
                 * then mark the data stream.  This should not happen
                 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
                 * a FIN has been received from the remote side.
                 * In these states we ignore the URG.
                 *
                 * According to RFC961 (Assigned Protocols),
                 * the urgent pointer points to the last octet
                 * of urgent data.  We continue, however,
                 * to consider it to indicate the first octet
                 * of data past the urgent section as the original
                 * spec states (in one of two places).
                 */
                if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
                        tp->rcv_up = ti->ti_seq + ti->ti_urp;
                        so->so_oobmark = so->so_rcv.sb_cc +
                            (tp->rcv_up - tp->rcv_nxt) - 1;
                        if (so->so_oobmark == 0)
                                so->so_state |= SS_RCVATMARK;
                        sohasoutofband(so);
                        tp->t_oobflags &= ~(TCPOOB_HAVEDATA | TCPOOB_HADDATA);
                }
                /*
                 * Remove out of band data so doesn't get presented to user.
                 * This can happen independent of advancing the URG pointer,
                 * but if two URG's are pending at once, some out-of-band
                 * data may creep in... ick.
                 */
                if (ti->ti_urp <= (u_long)ti->ti_len
#ifdef SO_OOBINLINE
                     && (so->so_options & SO_OOBINLINE) == 0
#endif
                     )
                        tcp_pulloutofband(so, ti, m);
        } else
                /*
                 * If no out of band data is expected,
                 * pull receive urgent pointer along
                 * with the receive window.
                 */
                if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
                        tp->rcv_up = tp->rcv_nxt;
dodata:                                                 /* XXX */

        /*
         * Process the segment text, merging it into the TCP sequencing queue,
         * and arranging for acknowledgment of receipt if necessary.
         * This process logically involves adjusting tp->rcv_wnd as data
         * is presented to the user (this happens in tcp_usrreq.c,
         * case PRU_RCVD).  If a FIN has already been received on this
         * connection then we just ignore the text.
         */
        if ((ti->ti_len || (tiflags&TH_FIN)) &&
            TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                TCP_REASS(tp, ti, m, so, tiflags);
                /*
                 * Note the amount of data that peer has sent into
                 * our window, in order to estimate the sender's
                 * buffer size.
                 */
                len = so->so_rcv.sb_hiwat - (tp->rcv_adv - tp->rcv_nxt);
        } else {
                m_freem(m);
                tiflags &= ~TH_FIN;
        }

        /*
         * If FIN is received ACK the FIN and let the user know
         * that the connection is closing.
         */
        if (tiflags & TH_FIN) {
                if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                        socantrcvmore(so);
                        /*
                         *  If connection is half-synchronized
                         *  (ie SEND_SYN flag on) then delay ACK,
                         *  so it may be piggybacked when SYN is sent.
                         *  Otherwise, since we received a FIN then no
                         *  more input can be expected, send ACK now.
                         */
                        if (tp->t_flags & TF_NEEDSYN)
                                tp->t_flags |= TF_DELACK;
                        else
                                tp->t_flags |= TF_ACKNOW;
                        tp->rcv_nxt++;
                }
                switch (tp->t_state) {

                /*
                 * In SYN_RECEIVED and ESTABLISHED STATES
                 * enter the CLOSE_WAIT state.
                 */
                case TCPS_SYN_RECEIVED:
                case TCPS_ESTABLISHED:
                        tp->t_state = TCPS_CLOSE_WAIT;
                        break;

                /*
                 * If still in FIN_WAIT_1 STATE FIN has not been acked so
                 * enter the CLOSING state.
                 */
                case TCPS_FIN_WAIT_1:
                        tp->t_state = TCPS_CLOSING;
                        break;

                /*
                 * In FIN_WAIT_2 state enter the TIME_WAIT state,
                 * starting the time-wait timer, turning off the other
                 * standard timers.
                 */
                case TCPS_FIN_WAIT_2:
                        tp->t_state = TCPS_TIME_WAIT;
                        tcp_canceltimers(tp);
                        /* Shorten TIME_WAIT [RFC-1644, p.28] */
                        if (tp->cc_recv != 0 &&
                            tp->t_duration < TCPTV_MSL) {
                                tp->t_timer[TCPT_2MSL] =
                                    tp->t_rxtcur * TCPTV_TWTRUNC;
                                /* For transaction client, force ACK now. */
                                tp->t_flags |= TF_ACKNOW;
                        }
                        else
                                tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        soisdisconnected(so);
                        break;

                /*
                 * In TIME_WAIT state restart the 2 MSL time_wait timer.
                 */
                case TCPS_TIME_WAIT:
                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        break;
                }
        }
#ifdef TCPDEBUG
        if (so->so_options & SO_DEBUG)
                tcp_trace(TA_INPUT, ostate, tp, &tcp_saveti, 0);
#endif

        /*
         * Return any desired output.
         */
        if (needoutput || (tp->t_flags & TF_ACKNOW))
                (void) tcp_output(tp);
        return;

dropafterack:
        /*
         * Generate an ACK dropping incoming segment if it occupies
         * sequence space, where the ACK reflects our state.
         */
        if (tiflags & TH_RST)
                goto drop;
#ifdef TCPDEBUG
        if (so->so_options & SO_DEBUG)
                tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
        m_freem(m);
        tp->t_flags |= TF_ACKNOW;
        (void) tcp_output(tp);
        return;

dropwithreset:
        /*
         * Generate a RST, dropping incoming segment.
         * Make ACK acceptable to originator of segment.
         * Don't bother to respond if destination was broadcast/multicast.
         */
        if ((tiflags & TH_RST) || m->m_flags & (M_BCAST|M_MCAST) ||
            IN_MULTICAST(ntohl(ti->ti_dst.s_addr)))
                goto drop;
#ifdef TCPDEBUG
        if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
        if (tiflags & TH_ACK)
                tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
        else {
                if (tiflags & TH_SYN)
                        ti->ti_len++;
                tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
                    TH_RST|TH_ACK);
        }
        /* destroy temporarily created socket */
        if (dropsocket)
                (void) soabort(so);
        return;

drop:
        /*
         * Drop space held by incoming segment and return.
         */
#ifdef TCPDEBUG
        if (tp == 0 || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
                tcp_trace(TA_DROP, ostate, tp, &tcp_saveti, 0);
#endif
        m_freem(m);
        /* destroy temporarily created socket */
        if (dropsocket)
                (void) soabort(so);
        return;
#ifndef TUBA_INCLUDE
}

void
tcp_dooptions(tp, cp, cnt, ti, to)
        struct tcpcb *tp;
        u_char *cp;
        int cnt;
        struct tcpiphdr *ti;
        struct tcpopt *to;
{
        u_short mss = 0;
        int opt, optlen;

        for (; cnt > 0; cnt -= optlen, cp += optlen) {
                opt = cp[0];
                if (opt == TCPOPT_EOL)
                        break;
                if (opt == TCPOPT_NOP)
                        optlen = 1;
                else {
                        optlen = cp[1];
                        if (optlen <= 0)
                                break;
                }
                switch (opt) {

                default:
                        continue;

                case TCPOPT_MAXSEG:
                        if (optlen != TCPOLEN_MAXSEG)
                                continue;
                        if (!(ti->ti_flags & TH_SYN))
                                continue;
                        bcopy((char *) cp + 2, (char *) &mss, sizeof(mss));
                        NTOHS(mss);
                        break;

                case TCPOPT_WINDOW:
                        if (optlen != TCPOLEN_WINDOW)
                                continue;
                        if (!(ti->ti_flags & TH_SYN))
                                continue;
                        tp->t_flags |= TF_RCVD_SCALE;
                        tp->requested_s_scale = MIN(cp[2], TCP_MAX_WINSHIFT);
                        break;

                case TCPOPT_TIMESTAMP:
                        if (optlen != TCPOLEN_TIMESTAMP)
                                continue;
                        to->to_flag |= TOF_TS;
                        bcopy((char *)cp + 2,
                            (char *)&to->to_tsval, sizeof(to->to_tsval));
                        NTOHL(to->to_tsval);
                        bcopy((char *)cp + 6,
                            (char *)&to->to_tsecr, sizeof(to->to_tsecr));
                        NTOHL(to->to_tsecr);

                        /*
                         * A timestamp received in a SYN makes
                         * it ok to send timestamp requests and replies.
                         */
                        if (ti->ti_flags & TH_SYN) {
                                tp->t_flags |= TF_RCVD_TSTMP;
                                tp->ts_recent = to->to_tsval;
                                tp->ts_recent_age = tcp_now;
                        }
                        break;
                case TCPOPT_CC:
                        if (optlen != TCPOLEN_CC)
                                continue;
                        to->to_flag |= TOF_CC;
                        bcopy((char *)cp + 2,
                            (char *)&to->to_cc, sizeof(to->to_cc));
                        NTOHL(to->to_cc);
                        /*
                         * A CC or CC.new option received in a SYN makes
                         * it ok to send CC in subsequent segments.
                         */
                        if (ti->ti_flags & TH_SYN)
                                tp->t_flags |= TF_RCVD_CC;
                        break;
                case TCPOPT_CCNEW:
                        if (optlen != TCPOLEN_CC)
                                continue;
                        if (!(ti->ti_flags & TH_SYN))
                                continue;
                        to->to_flag |= TOF_CCNEW;
                        bcopy((char *)cp + 2,
                            (char *)&to->to_cc, sizeof(to->to_cc));
                        NTOHL(to->to_cc);
                        /*
                         * A CC or CC.new option received in a SYN makes
                         * it ok to send CC in subsequent segments.
                         */
                        tp->t_flags |= TF_RCVD_CC;
                        break;
                case TCPOPT_CCECHO:
                        if (optlen != TCPOLEN_CC)
                                continue;
                        if (!(ti->ti_flags & TH_SYN))
                                continue;
                        to->to_flag |= TOF_CCECHO;
                        bcopy((char *)cp + 2,
                            (char *)&to->to_ccecho, sizeof(to->to_ccecho));
                        NTOHL(to->to_ccecho);
                        break;
                }
        }
        if (ti->ti_flags & TH_SYN)
                tcp_mss(tp, mss);       /* sets t_maxseg */
}

/*
 * Pull out of band byte out of a segment so
 * it doesn't appear in the user's data queue.
 * It is still reflected in the segment length for
 * sequencing purposes.
 */
void
tcp_pulloutofband(so, ti, m)
        struct socket *so;
        struct tcpiphdr *ti;
        register struct mbuf *m;
{
        int cnt = ti->ti_urp - 1;

        while (cnt >= 0) {
                if (m->m_len > cnt) {
                        char *cp = mtod(m, caddr_t) + cnt;
                        struct tcpcb *tp = sototcpcb(so);

                        tp->t_iobc = *cp;
                        tp->t_oobflags |= TCPOOB_HAVEDATA;
                        bcopy(cp+1, cp, (unsigned)(m->m_len - cnt - 1));
                        m->m_len--;
                        return;
                }
                cnt -= m->m_len;
                m = m->m_next;
                if (m == 0)
                        break;
        }
        panic("tcp_pulloutofband");
}

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 */
void
tcp_xmit_timer(tp, rtt)
        register struct tcpcb *tp;
        short rtt;
{
        register short delta;

        tcpstat.tcps_rttupdated++;
        if (tp->t_srtt != 0) {
                /*
                 * srtt is stored as fixed point with 3 bits after the
                 * binary point (i.e., scaled by 8).  The following magic
                 * is equivalent to the smoothing algorithm in rfc793 with
                 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
                 * point).  Adjust rtt to origin 0.
                 */
                delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
                if ((tp->t_srtt += delta) <= 0)
                        tp->t_srtt = 1;
                /*
                 * We accumulate a smoothed rtt variance (actually, a
                 * smoothed mean difference), then set the retransmit
                 * timer to smoothed rtt + 4 times the smoothed variance.
                 * rttvar is stored as fixed point with 2 bits after the
                 * binary point (scaled by 4).  The following is
                 * equivalent to rfc793 smoothing with an alpha of .75
                 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
                 * rfc793's wired-in beta.
                 */
                if (delta < 0)
                        delta = -delta;
                delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
                if ((tp->t_rttvar += delta) <= 0)
                        tp->t_rttvar = 1;
        } else {
                /*
                 * No rtt measurement yet - use the unsmoothed rtt.
                 * Set the variance to half the rtt (so our first
                 * retransmit happens at 3*rtt).
                 */
                tp->t_srtt = rtt << TCP_RTT_SHIFT;
                tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
        }
        tp->t_rtt = 0;
        tp->t_rxtshift = 0;

        /*
         * the retransmit should happen at rtt + 4 * rttvar.
         * Because of the way we do the smoothing, srtt and rttvar
         * will each average +1/2 tick of bias.  When we compute
         * the retransmit timer, we want 1/2 tick of rounding and
         * 1 extra tick because of +-1/2 tick uncertainty in the
         * firing of the timer.  The bias will give us exactly the
         * 1.5 tick we need.  But, because the bias is
         * statistical, we have to test that we don't drop below
         * the minimum feasible timer (which is 2 ticks).
         */
        TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
            tp->t_rttmin, TCPTV_REXMTMAX);

        /*
         * We received an ack for a packet that wasn't retransmitted;
         * it is probably safe to discard any error indications we've
         * received recently.  This isn't quite right, but close enough
         * for now (a route might have failed after we sent a segment,
         * and the return path might not be symmetrical).
         */
        tp->t_softerror = 0;
}

/*
 * Determine a reasonable value for maxseg size.
 * If the route is known, check route for mtu.
 * If none, use an mss that can be handled on the outgoing
 * interface without forcing IP to fragment; if bigger than
 * an mbuf cluster (mbconf.mclbytes), round down to nearest multiple of mbconf.mclbytes
 * to utilize large mbufs.  If no route is found, route has no mtu,
 * or the destination isn't local, use a default, hopefully conservative
 * size (usually 512 or the default IP max size, but no more than the mtu
 * of the interface), as we can't discover anything about intervening
 * gateways or networks.  We also initialize the congestion/slow start
 * window to be a single segment if the destination isn't local.
 * While looking at the routing entry, we also initialize other path-dependent
 * parameters from pre-set or cached values in the routing entry.
 *
 * Also take into account the space needed for options that we
 * send regularly.  Make maxseg shorter by that amount to assure
 * that we can send maxseg amount of data even when the options
 * are present.  Store the upper limit of the length of options plus
 * data in maxopd.
 *
 * NOTE that this routine is only called when we process an incoming
 * segment, for outgoing segments only tcp_mssopt is called.
 *
 * In case of T/TCP, we call this routine during implicit connection
 * setup as well (offer = -1), to initialize maxseg from the cached
 * MSS of our peer.
 */
void
tcp_mss(tp, offer)
        struct tcpcb *tp;
        int offer;
{
        register struct rtentry *rt;
        struct ifnet *ifp;
        register int rtt, mss;
        u_long bufsize;
        struct inpcb *inp;
        struct socket *so;
        struct rmxp_tao *taop;
        int origoffer = offer;

        inp = tp->t_inpcb;
        if ((rt = tcp_rtlookup(inp)) == NULL) {
                tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
                return;
        }
        ifp = rt->rt_ifp;
        so = inp->inp_socket;

        taop = rmx_taop(rt->rt_rmx);
        /*
         * Offer == -1 means that we didn't receive SYN yet,
         * use cached value in that case;
         */
        if (offer == -1)
                offer = taop->tao_mssopt;
        /*
         * Offer == 0 means that there was no MSS on the SYN segment,
         * in this case we use tcp_mssdflt.
         */
        if (offer == 0)
                offer = tcp_mssdflt;
        else
                /*
                 * Sanity check: make sure that maxopd will be large
                 * enough to allow some data on segments even is the
                 * all the option space is used (40bytes).  Otherwise
                 * funny things may happen in tcp_output.
                 */
                offer = MAX(offer, 64);
        taop->tao_mssopt = offer;

#ifdef RTV_MTU  /* if route characteristics exist ... */
        /*
         * While we're here, check if there's an initial rtt
         * or rttvar.  Convert from the route-table units
         * to scaled multiples of the slow timeout timer.
         */
        if (tp->t_srtt == 0 && (rtt = rt->rt_rmx.rmx_rtt)) {
                /*
                 * XXX the lock bit for RTT indicates that the value
                 * is also a minimum value; this is subject to time.
                 */
                if (rt->rt_rmx.rmx_locks & RTV_RTT)
                        tp->t_rttmin = rtt / (RTM_RTTUNIT / PR_SLOWHZ);
                tp->t_srtt = rtt / (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTT_SCALE));
                if (rt->rt_rmx.rmx_rttvar)
                        tp->t_rttvar = rt->rt_rmx.rmx_rttvar /
                            (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTTVAR_SCALE));
                else
                        /* default variation is +- 1 rtt */
                        tp->t_rttvar =
                            tp->t_srtt * TCP_RTTVAR_SCALE / TCP_RTT_SCALE;
                TCPT_RANGESET(tp->t_rxtcur,
                    ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1,
                    tp->t_rttmin, TCPTV_REXMTMAX);
        }
        /*
         * if there's an mtu associated with the route, use it
         */
        if (rt->rt_rmx.rmx_mtu)
                mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);
        else
#endif /* RTV_MTU */
        {
                mss = ifp->if_mtu - sizeof(struct tcpiphdr);
                if (!in_localaddr(inp->inp_faddr))
                        mss = MIN(mss, tcp_mssdflt);
        }
        mss = MIN(mss, offer);
        /*
         * maxopd stores the maximum length of data AND options
         * in a segment; maxseg is the amount of data in a normal
         * segment.  We need to store this value (maxopd) apart
         * from maxseg, because now every segment carries options
         * and thus we normally have somewhat less data in segments.
         */
        tp->t_maxopd = mss;

        /*
         * In case of T/TCP, origoffer==-1 indicates, that no segments
         * were received yet.  In this case we just guess, otherwise
         * we do the same as before T/TCP.
         */
        if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
            (origoffer == -1 ||
             (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP))
                mss -= TCPOLEN_TSTAMP_APPA;
        if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
            (origoffer == -1 ||
             (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC))
                mss -= TCPOLEN_CC_APPA;

        if ((mbconf.mclbytes & (mbconf.mclbytes - 1)) == 0) {
                if (mss > mbconf.mclbytes)
                        mss &= ~(mbconf.mclbytes-1);
        } else {
                if (mss > mbconf.mclbytes)
                       /*
                        * DO NOT REMOVE THIS! A side effect is rounding.
                        * Read the function description for more info
                        */
                        mss = mss / mbconf.mclbytes * mbconf.mclbytes;
        }
        /*
         * If there's a pipesize, change the socket buffer
         * to that size.  Make the socket buffers an integral
         * number of mss units; if the mss is larger than
         * the socket buffer, decrease the mss.
         */
#ifdef RTV_SPIPE
        if ((bufsize = rt->rt_rmx.rmx_sendpipe) == 0)
#endif
                bufsize = so->so_snd.sb_hiwat;
        if (bufsize < mss)
                mss = bufsize;
        else {
                bufsize = roundup(bufsize, mss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void)sbreserve(&so->so_snd, bufsize);
        }
        tp->t_maxseg = mss;

#ifdef RTV_RPIPE
        if ((bufsize = rt->rt_rmx.rmx_recvpipe) == 0)
#endif
                bufsize = so->so_rcv.sb_hiwat;
        if (bufsize > mss) {
                bufsize = roundup(bufsize, mss);
                if (bufsize > sb_max)
                        bufsize = sb_max;
                (void)sbreserve(&so->so_rcv, bufsize);
        }
        /*
         * Don't force slow-start on local network.
         */
        if (!in_localaddr(inp->inp_faddr))
                tp->snd_cwnd = mss;

#ifdef RTV_SSTHRESH
        if (rt->rt_rmx.rmx_ssthresh) {
                /*
                 * There's some sort of gateway or interface
                 * buffer limit on the path.  Use this to set
                 * the slow start threshhold, but set the
                 * threshold to no less than 2*mss.
                 */
                tp->snd_ssthresh = MAX(2 * mss, rt->rt_rmx.rmx_ssthresh);
        }
#endif
}

/*
 * Determine the MSS option to send on an outgoing SYN.
 */
int
tcp_mssopt(tp)
        struct tcpcb *tp;
{
        struct rtentry *rt;

        rt = tcp_rtlookup(tp->t_inpcb);
        if (rt == NULL)
                return tcp_mssdflt;

        /*
         * if there's an mtu associated with the route, use it
         */
        if (rt->rt_rmx.rmx_mtu)
                return rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);

        return rt->rt_ifp->if_mtu - sizeof(struct tcpiphdr);
}
#endif /* TUBA_INCLUDE */