qemu/slirp/tcp_input.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  *
  29  *      @(#)tcp_input.c 8.5 (Berkeley) 4/10/94
  30  * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp
  31  */
  32
  33 /*
  34  * Changes and additions relating to SLiRP
  35  * Copyright (c) 1995 Danny Gasparovski.
  36  *
  37  * Please read the file COPYRIGHT for the
  38  * terms and conditions of the copyright.
  39  */
  40
  41 #include <slirp.h>
  42 #include "ip_icmp.h"
  43
  44 #define TCPREXMTTHRESH 3
  45
  46 #define TCP_PAWS_IDLE   (24 * 24 * 60 * 60 * PR_SLOWHZ)
  47
  48 /* for modulo comparisons of timestamps */
  49 #define TSTMP_LT(a,b)   ((int)((a)-(b)) < 0)
  50 #define TSTMP_GEQ(a,b)  ((int)((a)-(b)) >= 0)
  51
  52 /*
  53  * Insert segment ti into reassembly queue of tcp with
  54  * control block tp.  Return TH_FIN if reassembly now includes
  55  * a segment with FIN.  The macro form does the common case inline
  56  * (segment is the next to be received on an established connection,
  57  * and the queue is empty), avoiding linkage into and removal
  58  * from the queue and repetition of various conversions.
  59  * Set DELACK for segments received in order, but ack immediately
  60  * when segments are out of order (so fast retransmit can work).
  61  */
  62 #ifdef TCP_ACK_HACK
  63 #define TCP_REASS(tp, ti, m, so, flags) {\
  64        if ((ti)->ti_seq == (tp)->rcv_nxt && \
  65            tcpfrag_list_empty(tp) && \
  66            (tp)->t_state == TCPS_ESTABLISHED) {\
  67                if (ti->ti_flags & TH_PUSH) \
  68                        tp->t_flags |= TF_ACKNOW; \
  69                else \
  70                        tp->t_flags |= TF_DELACK; \
  71                (tp)->rcv_nxt += (ti)->ti_len; \
  72                flags = (ti)->ti_flags & TH_FIN; \
  73                if (so->so_emu) { \
  74                        if (tcp_emu((so),(m))) sbappend((so), (m)); \
  75                } else \
  76                        sbappend((so), (m)); \
  77         } else {\
  78                (flags) = tcp_reass((tp), (ti), (m)); \
  79                tp->t_flags |= TF_ACKNOW; \
  80        } \
  81 }
  82 #else
  83 #define TCP_REASS(tp, ti, m, so, flags) { \
  84         if ((ti)->ti_seq == (tp)->rcv_nxt && \
  85         tcpfrag_list_empty(tp) && \
  86             (tp)->t_state == TCPS_ESTABLISHED) { \
  87                 tp->t_flags |= TF_DELACK; \
  88                 (tp)->rcv_nxt += (ti)->ti_len; \
  89                 flags = (ti)->ti_flags & TH_FIN; \
  90                 if (so->so_emu) { \
  91                         if (tcp_emu((so),(m))) sbappend(so, (m)); \
  92                 } else \
  93                         sbappend((so), (m)); \
  94         } else { \
  95                 (flags) = tcp_reass((tp), (ti), (m)); \
  96                 tp->t_flags |= TF_ACKNOW; \
  97         } \
  98 }
  99 #endif
 100 static void tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt,
 101                           struct tcpiphdr *ti);
 102 static void tcp_xmit_timer(register struct tcpcb *tp, int rtt);
 103
 104 static int
 105 tcp_reass(register struct tcpcb *tp, register struct tcpiphdr *ti,
 106           struct mbuf *m)
 107 {
 108         register struct tcpiphdr *q;
 109         struct socket *so = tp->t_socket;
 110         int flags;
 111
 112         /*
 113          * Call with ti==NULL after become established to
 114          * force pre-ESTABLISHED data up to user socket.
 115          */
 116         if (ti == NULL)
 117                 goto present;
 118
 119         /*
 120          * Find a segment which begins after this one does.
 121          */
 122         for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp);
 123             q = tcpiphdr_next(q))
 124                 if (SEQ_GT(q->ti_seq, ti->ti_seq))
 125                         break;
 126
 127         /*
 128          * If there is a preceding segment, it may provide some of
 129          * our data already.  If so, drop the data from the incoming
 130          * segment.  If it provides all of our data, drop us.
 131          */
 132         if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) {
 133                 register int i;
 134                 q = tcpiphdr_prev(q);
 135                 /* conversion to int (in i) handles seq wraparound */
 136                 i = q->ti_seq + q->ti_len - ti->ti_seq;
 137                 if (i > 0) {
 138                         if (i >= ti->ti_len) {
 139                                 m_free(m);
 140                                 /*
 141                                  * Try to present any queued data
 142                                  * at the left window edge to the user.
 143                                  * This is needed after the 3-WHS
 144                                  * completes.
 145                                  */
 146                                 goto present;   /* ??? */
 147                         }
 148                         m_adj(m, i);
 149                         ti->ti_len -= i;
 150                         ti->ti_seq += i;
 151                 }
 152                 q = tcpiphdr_next(q);
 153         }
 154         ti->ti_mbuf = m;
 155
 156         /*
 157          * While we overlap succeeding segments trim them or,
 158          * if they are completely covered, dequeue them.
 159          */
 160         while (!tcpfrag_list_end(q, tp)) {
 161                 register int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
 162                 if (i <= 0)
 163                         break;
 164                 if (i < q->ti_len) {
 165                         q->ti_seq += i;
 166                         q->ti_len -= i;
 167                         m_adj(q->ti_mbuf, i);
 168                         break;
 169                 }
 170                 q = tcpiphdr_next(q);
 171                 m = tcpiphdr_prev(q)->ti_mbuf;
 172                 remque(tcpiphdr2qlink(tcpiphdr_prev(q)));
 173                 m_free(m);
 174         }
 175
 176         /*
 177          * Stick new segment in its place.
 178          */
 179         insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q)));
 180
 181 present:
 182         /*
 183          * Present data to user, advancing rcv_nxt through
 184          * completed sequence space.
 185          */
 186         if (!TCPS_HAVEESTABLISHED(tp->t_state))
 187                 return (0);
 188         ti = tcpfrag_list_first(tp);
 189         if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt)
 190                 return (0);
 191         if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
 192                 return (0);
 193         do {
 194                 tp->rcv_nxt += ti->ti_len;
 195                 flags = ti->ti_flags & TH_FIN;
 196                 remque(tcpiphdr2qlink(ti));
 197                 m = ti->ti_mbuf;
 198                 ti = tcpiphdr_next(ti);
 199                 if (so->so_state & SS_FCANTSENDMORE)
 200                         m_free(m);
 201                 else {
 202                         if (so->so_emu) {
 203                                 if (tcp_emu(so,m)) sbappend(so, m);
 204                         } else
 205                                 sbappend(so, m);
 206                 }
 207         } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
 208         return (flags);
 209 }
 210
 211 /*
 212  * TCP input routine, follows pages 65-76 of the
 213  * protocol specification dated September, 1981 very closely.
 214  */
 215 void
 216 tcp_input(struct mbuf *m, int iphlen, struct socket *inso)
 217 {
 218         struct ip save_ip, *ip;
 219         register struct tcpiphdr *ti;
 220         caddr_t optp = NULL;
 221         int optlen = 0;
 222         int len, tlen, off;
 223         register struct tcpcb *tp = NULL;
 224         register int tiflags;
 225         struct socket *so = NULL;
 226         int todrop, acked, ourfinisacked, needoutput = 0;
 227         int iss = 0;
 228         u_long tiwin;
 229         int ret;
 230     struct ex_list *ex_ptr;
 231     Slirp *slirp;
 232
 233         DEBUG_CALL("tcp_input");
 234         DEBUG_ARGS((dfd, " m = %8lx  iphlen = %2d  inso = %lx\n",
 235                     (long )m, iphlen, (long )inso ));
 236
 237         /*
 238          * If called with m == 0, then we're continuing the connect
 239          */
 240         if (m == NULL) {
 241                 so = inso;
 242                 slirp = so->slirp;
 243
 244                 /* Re-set a few variables */
 245                 tp = sototcpcb(so);
 246                 m = so->so_m;
 247                 so->so_m = NULL;
 248                 ti = so->so_ti;
 249                 tiwin = ti->ti_win;
 250                 tiflags = ti->ti_flags;
 251
 252                 goto cont_conn;
 253         }
 254         slirp = m->slirp;
 255
 256         /*
 257          * Get IP and TCP header together in first mbuf.
 258          * Note: IP leaves IP header in first mbuf.
 259          */
 260         ti = mtod(m, struct tcpiphdr *);
 261         if (iphlen > sizeof(struct ip )) {
 262           ip_stripoptions(m, (struct mbuf *)0);
 263           iphlen=sizeof(struct ip );
 264         }
 265         /* XXX Check if too short */
 266
 267
 268         /*
 269          * Save a copy of the IP header in case we want restore it
 270          * for sending an ICMP error message in response.
 271          */
 272         ip=mtod(m, struct ip *);
 273         save_ip = *ip;
 274         save_ip.ip_len+= iphlen;
 275
 276         /*
 277          * Checksum extended TCP header and data.
 278          */
 279         tlen = ((struct ip *)ti)->ip_len;
 280         tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = NULL;
 281         memset(&ti->ti_i.ih_mbuf, 0 , sizeof(struct mbuf_ptr));
 282         ti->ti_x1 = 0;
 283         ti->ti_len = htons((uint16_t)tlen);
 284         len = sizeof(struct ip ) + tlen;
 285         if(cksum(m, len)) {
 286           goto drop;
 287         }
 288
 289         /*
 290          * Check that TCP offset makes sense,
 291          * pull out TCP options and adjust length.              XXX
 292          */
 293         off = ti->ti_off << 2;
 294         if (off < sizeof (struct tcphdr) || off > tlen) {
 295           goto drop;
 296         }
 297         tlen -= off;
 298         ti->ti_len = tlen;
 299         if (off > sizeof (struct tcphdr)) {
 300           optlen = off - sizeof (struct tcphdr);
 301           optp = mtod(m, caddr_t) + sizeof (struct tcpiphdr);
 302         }
 303         tiflags = ti->ti_flags;
 304
 305         /*
 306          * Convert TCP protocol specific fields to host format.
 307          */
 308         NTOHL(ti->ti_seq);
 309         NTOHL(ti->ti_ack);
 310         NTOHS(ti->ti_win);
 311         NTOHS(ti->ti_urp);
 312
 313         /*
 314          * Drop TCP, IP headers and TCP options.
 315          */
 316         m->m_data += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 317         m->m_len  -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 318
 319         /*
 320          * Locate pcb for segment.
 321          */
 322 findso:
 323         so = slirp->tcp_last_so;
 324         if (so->so_fport != ti->ti_dport ||
 325             so->so_lport != ti->ti_sport ||
 326             so->so_laddr.s_addr != ti->ti_src.s_addr ||
 327             so->so_faddr.s_addr != ti->ti_dst.s_addr) {
 328                 so = solookup(&slirp->tcb, ti->ti_src, ti->ti_sport,
 329                                ti->ti_dst, ti->ti_dport);
 330                 if (so)
 331                         slirp->tcp_last_so = so;
 332         }
 333
 334         /*
 335          * If the state is CLOSED (i.e., TCB does not exist) then
 336          * all data in the incoming segment is discarded.
 337          * If the TCB exists but is in CLOSED state, it is embryonic,
 338          * but should either do a listen or a connect soon.
 339          *
 340          * state == CLOSED means we've done socreate() but haven't
 341          * attached it to a protocol yet...
 342          *
 343          * XXX If a TCB does not exist, and the TH_SYN flag is
 344          * the only flag set, then create a session, mark it
 345          * as if it was LISTENING, and continue...
 346          */
 347         if (so == NULL) {
 348           if (slirp->restricted) {
 349             /* Any hostfwds will have an existing socket, so we only get here
 350              * for non-hostfwd connections. These should be dropped, unless it
 351              * happens to be a guestfwd.
 352              */
 353             for (ex_ptr = slirp->exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
 354                 if (ex_ptr->ex_fport == ti->ti_dport &&
 355                     ti->ti_dst.s_addr == ex_ptr->ex_addr.s_addr) {
 356                     break;
 357                 }
 358             }
 359             if (!ex_ptr) {
 360                 goto dropwithreset;
 361             }
 362           }
 363
 364           if ((tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) != TH_SYN)
 365             goto dropwithreset;
 366
 367           if ((so = socreate(slirp)) == NULL)
 368             goto dropwithreset;
 369           if (tcp_attach(so) < 0) {
 370             free(so); /* Not sofree (if it failed, it's not insqued) */
 371             goto dropwithreset;
 372           }
 373
 374           sbreserve(&so->so_snd, TCP_SNDSPACE);
 375           sbreserve(&so->so_rcv, TCP_RCVSPACE);
 376
 377           so->so_laddr = ti->ti_src;
 378           so->so_lport = ti->ti_sport;
 379           so->so_faddr = ti->ti_dst;
 380           so->so_fport = ti->ti_dport;
 381
 382           if ((so->so_iptos = tcp_tos(so)) == 0)
 383             so->so_iptos = ((struct ip *)ti)->ip_tos;
 384
 385           tp = sototcpcb(so);
 386           tp->t_state = TCPS_LISTEN;
 387         }
 388
 389         /*
 390          * If this is a still-connecting socket, this probably
 391          * a retransmit of the SYN.  Whether it's a retransmit SYN
 392          * or something else, we nuke it.
 393          */
 394         if (so->so_state & SS_ISFCONNECTING)
 395                 goto drop;
 396
 397         tp = sototcpcb(so);
 398
 399         /* XXX Should never fail */
 400         if (tp == NULL)
 401                 goto dropwithreset;
 402         if (tp->t_state == TCPS_CLOSED)
 403                 goto drop;
 404
 405         tiwin = ti->ti_win;
 406
 407         /*
 408          * Segment received on connection.
 409          * Reset idle time and keep-alive timer.
 410          */
 411         tp->t_idle = 0;
 412         if (SO_OPTIONS)
 413            tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
 414         else
 415            tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
 416
 417         /*
 418          * Process options if not in LISTEN state,
 419          * else do it below (after getting remote address).
 420          */
 421         if (optp && tp->t_state != TCPS_LISTEN)
 422                 tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 423
 424         /*
 425          * Header prediction: check for the two common cases
 426          * of a uni-directional data xfer.  If the packet has
 427          * no control flags, is in-sequence, the window didn't
 428          * change and we're not retransmitting, it's a
 429          * candidate.  If the length is zero and the ack moved
 430          * forward, we're the sender side of the xfer.  Just
 431          * free the data acked & wake any higher level process
 432          * that was blocked waiting for space.  If the length
 433          * is non-zero and the ack didn't move, we're the
 434          * receiver side.  If we're getting packets in-order
 435          * (the reassembly queue is empty), add the data to
 436          * the socket buffer and note that we need a delayed ack.
 437          *
 438          * XXX Some of these tests are not needed
 439          * eg: the tiwin == tp->snd_wnd prevents many more
 440          * predictions.. with no *real* advantage..
 441          */
 442         if (tp->t_state == TCPS_ESTABLISHED &&
 443             (tiflags & (TH_SYN|TH_FIN|TH_RST|TH_URG|TH_ACK)) == TH_ACK &&
 444             ti->ti_seq == tp->rcv_nxt &&
 445             tiwin && tiwin == tp->snd_wnd &&
 446             tp->snd_nxt == tp->snd_max) {
 447                 if (ti->ti_len == 0) {
 448                         if (SEQ_GT(ti->ti_ack, tp->snd_una) &&
 449                             SEQ_LEQ(ti->ti_ack, tp->snd_max) &&
 450                             tp->snd_cwnd >= tp->snd_wnd) {
 451                                 /*
 452                                  * this is a pure ack for outstanding data.
 453                                  */
 454                                 if (tp->t_rtt &&
 455                                     SEQ_GT(ti->ti_ack, tp->t_rtseq))
 456                                         tcp_xmit_timer(tp, tp->t_rtt);
 457                                 acked = ti->ti_ack - tp->snd_una;
 458                                 sbdrop(&so->so_snd, acked);
 459                                 tp->snd_una = ti->ti_ack;
 460                                 m_free(m);
 461
 462                                 /*
 463                                  * If all outstanding data are acked, stop
 464                                  * retransmit timer, otherwise restart timer
 465                                  * using current (possibly backed-off) value.
 466                                  * If process is waiting for space,
 467                                  * wakeup/selwakeup/signal.  If data
 468                                  * are ready to send, let tcp_output
 469                                  * decide between more output or persist.
 470                                  */
 471                                 if (tp->snd_una == tp->snd_max)
 472                                         tp->t_timer[TCPT_REXMT] = 0;
 473                                 else if (tp->t_timer[TCPT_PERSIST] == 0)
 474                                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
 475
 476                                 /*
 477                                  * This is called because sowwakeup might have
 478                                  * put data into so_snd.  Since we don't so sowwakeup,
 479                                  * we don't need this.. XXX???
 480                                  */
 481                                 if (so->so_snd.sb_cc)
 482                                         (void) tcp_output(tp);
 483
 484                                 return;
 485                         }
 486                 } else if (ti->ti_ack == tp->snd_una &&
 487                     tcpfrag_list_empty(tp) &&
 488                     ti->ti_len <= sbspace(&so->so_rcv)) {
 489                         /*
 490                          * this is a pure, in-sequence data packet
 491                          * with nothing on the reassembly queue and
 492                          * we have enough buffer space to take it.
 493                          */
 494                         tp->rcv_nxt += ti->ti_len;
 495                         /*
 496                          * Add data to socket buffer.
 497                          */
 498                         if (so->so_emu) {
 499                                 if (tcp_emu(so,m)) sbappend(so, m);
 500                         } else
 501                                 sbappend(so, m);
 502
 503                         /*
 504                          * If this is a short packet, then ACK now - with Nagel
 505                          *      congestion avoidance sender won't send more until
 506                          *      he gets an ACK.
 507                          *
 508                          * It is better to not delay acks at all to maximize
 509                          * TCP throughput.  See RFC 2581.
 510                          */
 511                         tp->t_flags |= TF_ACKNOW;
 512                         tcp_output(tp);
 513                         return;
 514                 }
 515         } /* header prediction */
 516         /*
 517          * Calculate amount of space in receive window,
 518          * and then do TCP input processing.
 519          * Receive window is amount of space in rcv queue,
 520          * but not less than advertised window.
 521          */
 522         { int win;
 523           win = sbspace(&so->so_rcv);
 524           if (win < 0)
 525             win = 0;
 526           tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
 527         }
 528
 529         switch (tp->t_state) {
 530
 531         /*
 532          * If the state is LISTEN then ignore segment if it contains an RST.
 533          * If the segment contains an ACK then it is bad and send a RST.
 534          * If it does not contain a SYN then it is not interesting; drop it.
 535          * Don't bother responding if the destination was a broadcast.
 536          * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
 537          * tp->iss, and send a segment:
 538          *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
 539          * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
 540          * Fill in remote peer address fields if not previously specified.
 541          * Enter SYN_RECEIVED state, and process any other fields of this
 542          * segment in this state.
 543          */
 544         case TCPS_LISTEN: {
 545
 546           if (tiflags & TH_RST)
 547             goto drop;
 548           if (tiflags & TH_ACK)
 549             goto dropwithreset;
 550           if ((tiflags & TH_SYN) == 0)
 551             goto drop;
 552
 553           /*
 554            * This has way too many gotos...
 555            * But a bit of spaghetti code never hurt anybody :)
 556            */
 557
 558           /*
 559            * If this is destined for the control address, then flag to
 560            * tcp_ctl once connected, otherwise connect
 561            */
 562           if ((so->so_faddr.s_addr & slirp->vnetwork_mask.s_addr) ==
 563               slirp->vnetwork_addr.s_addr) {
 564             if (so->so_faddr.s_addr != slirp->vhost_addr.s_addr &&
 565                 so->so_faddr.s_addr != slirp->vnameserver_addr.s_addr) {
 566                 /* May be an add exec */
 567                 for (ex_ptr = slirp->exec_list; ex_ptr;
 568                      ex_ptr = ex_ptr->ex_next) {
 569                   if(ex_ptr->ex_fport == so->so_fport &&
 570                      so->so_faddr.s_addr == ex_ptr->ex_addr.s_addr) {
 571                     so->so_state |= SS_CTL;
 572                     break;
 573                   }
 574                 }
 575                 if (so->so_state & SS_CTL) {
 576                     goto cont_input;
 577                 }
 578             }
 579             /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
 580           }
 581
 582           if (so->so_emu & EMU_NOCONNECT) {
 583             so->so_emu &= ~EMU_NOCONNECT;
 584             goto cont_input;
 585           }
 586
 587           if((tcp_fconnect(so) == -1) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
 588             u_char code=ICMP_UNREACH_NET;
 589             DEBUG_MISC((dfd, " tcp fconnect errno = %d-%s\n",
 590                         errno,strerror(errno)));
 591             if(errno == ECONNREFUSED) {
 592               /* ACK the SYN, send RST to refuse the connection */
 593               tcp_respond(tp, ti, m, ti->ti_seq+1, (tcp_seq)0,
 594                           TH_RST|TH_ACK);
 595             } else {
 596               if(errno == EHOSTUNREACH) code=ICMP_UNREACH_HOST;
 597               HTONL(ti->ti_seq);             /* restore tcp header */
 598               HTONL(ti->ti_ack);
 599               HTONS(ti->ti_win);
 600               HTONS(ti->ti_urp);
 601               m->m_data -= sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 602               m->m_len  += sizeof(struct tcpiphdr)+off-sizeof(struct tcphdr);
 603               *ip=save_ip;
 604               icmp_error(m, ICMP_UNREACH,code, 0,strerror(errno));
 605             }
 606             tcp_close(tp);
 607             m_free(m);
 608           } else {
 609             /*
 610              * Haven't connected yet, save the current mbuf
 611              * and ti, and return
 612              * XXX Some OS's don't tell us whether the connect()
 613              * succeeded or not.  So we must time it out.
 614              */
 615             so->so_m = m;
 616             so->so_ti = ti;
 617             tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 618             tp->t_state = TCPS_SYN_RECEIVED;
 619             tcp_template(tp);
 620           }
 621           return;
 622
 623         cont_conn:
 624           /* m==NULL
 625            * Check if the connect succeeded
 626            */
 627           if (so->so_state & SS_NOFDREF) {
 628             tp = tcp_close(tp);
 629             goto dropwithreset;
 630           }
 631         cont_input:
 632           tcp_template(tp);
 633
 634           if (optp)
 635             tcp_dooptions(tp, (u_char *)optp, optlen, ti);
 636
 637           if (iss)
 638             tp->iss = iss;
 639           else
 640             tp->iss = slirp->tcp_iss;
 641           slirp->tcp_iss += TCP_ISSINCR/2;
 642           tp->irs = ti->ti_seq;
 643           tcp_sendseqinit(tp);
 644           tcp_rcvseqinit(tp);
 645           tp->t_flags |= TF_ACKNOW;
 646           tp->t_state = TCPS_SYN_RECEIVED;
 647           tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
 648           goto trimthenstep6;
 649         } /* case TCPS_LISTEN */
 650
 651         /*
 652          * If the state is SYN_SENT:
 653          *      if seg contains an ACK, but not for our SYN, drop the input.
 654          *      if seg contains a RST, then drop the connection.
 655          *      if seg does not contain SYN, then drop it.
 656          * Otherwise this is an acceptable SYN segment
 657          *      initialize tp->rcv_nxt and tp->irs
 658          *      if seg contains ack then advance tp->snd_una
 659          *      if SYN has been acked change to ESTABLISHED else SYN_RCVD state
 660          *      arrange for segment to be acked (eventually)
 661          *      continue processing rest of data/controls, beginning with URG
 662          */
 663         case TCPS_SYN_SENT:
 664                 if ((tiflags & TH_ACK) &&
 665                     (SEQ_LEQ(ti->ti_ack, tp->iss) ||
 666                      SEQ_GT(ti->ti_ack, tp->snd_max)))
 667                         goto dropwithreset;
 668
 669                 if (tiflags & TH_RST) {
 670                         if (tiflags & TH_ACK) {
 671                                 tcp_drop(tp, 0); /* XXX Check t_softerror! */
 672                         }
 673                         goto drop;
 674                 }
 675
 676                 if ((tiflags & TH_SYN) == 0)
 677                         goto drop;
 678                 if (tiflags & TH_ACK) {
 679                         tp->snd_una = ti->ti_ack;
 680                         if (SEQ_LT(tp->snd_nxt, tp->snd_una))
 681                                 tp->snd_nxt = tp->snd_una;
 682                 }
 683
 684                 tp->t_timer[TCPT_REXMT] = 0;
 685                 tp->irs = ti->ti_seq;
 686                 tcp_rcvseqinit(tp);
 687                 tp->t_flags |= TF_ACKNOW;
 688                 if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
 689                         soisfconnected(so);
 690                         tp->t_state = TCPS_ESTABLISHED;
 691
 692                         (void) tcp_reass(tp, (struct tcpiphdr *)0,
 693                                 (struct mbuf *)0);
 694                         /*
 695                          * if we didn't have to retransmit the SYN,
 696                          * use its rtt as our initial srtt & rtt var.
 697                          */
 698                         if (tp->t_rtt)
 699                                 tcp_xmit_timer(tp, tp->t_rtt);
 700                 } else
 701                         tp->t_state = TCPS_SYN_RECEIVED;
 702
 703 trimthenstep6:
 704                 /*
 705                  * Advance ti->ti_seq to correspond to first data byte.
 706                  * If data, trim to stay within window,
 707                  * dropping FIN if necessary.
 708                  */
 709                 ti->ti_seq++;
 710                 if (ti->ti_len > tp->rcv_wnd) {
 711                         todrop = ti->ti_len - tp->rcv_wnd;
 712                         m_adj(m, -todrop);
 713                         ti->ti_len = tp->rcv_wnd;
 714                         tiflags &= ~TH_FIN;
 715                 }
 716                 tp->snd_wl1 = ti->ti_seq - 1;
 717                 tp->rcv_up = ti->ti_seq;
 718                 goto step6;
 719         } /* switch tp->t_state */
 720         /*
 721          * States other than LISTEN or SYN_SENT.
 722          * Check that at least some bytes of segment are within
 723          * receive window.  If segment begins before rcv_nxt,
 724          * drop leading data (and SYN); if nothing left, just ack.
 725          */
 726         todrop = tp->rcv_nxt - ti->ti_seq;
 727         if (todrop > 0) {
 728                 if (tiflags & TH_SYN) {
 729                         tiflags &= ~TH_SYN;
 730                         ti->ti_seq++;
 731                         if (ti->ti_urp > 1)
 732                                 ti->ti_urp--;
 733                         else
 734                                 tiflags &= ~TH_URG;
 735                         todrop--;
 736                 }
 737                 /*
 738                  * Following if statement from Stevens, vol. 2, p. 960.
 739                  */
 740                 if (todrop > ti->ti_len
 741                     || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
 742                         /*
 743                          * Any valid FIN must be to the left of the window.
 744                          * At this point the FIN must be a duplicate or out
 745                          * of sequence; drop it.
 746                          */
 747                         tiflags &= ~TH_FIN;
 748
 749                         /*
 750                          * Send an ACK to resynchronize and drop any data.
 751                          * But keep on processing for RST or ACK.
 752                          */
 753                         tp->t_flags |= TF_ACKNOW;
 754                         todrop = ti->ti_len;
 755                 }
 756                 m_adj(m, todrop);
 757                 ti->ti_seq += todrop;
 758                 ti->ti_len -= todrop;
 759                 if (ti->ti_urp > todrop)
 760                         ti->ti_urp -= todrop;
 761                 else {
 762                         tiflags &= ~TH_URG;
 763                         ti->ti_urp = 0;
 764                 }
 765         }
 766         /*
 767          * If new data are received on a connection after the
 768          * user processes are gone, then RST the other end.
 769          */
 770         if ((so->so_state & SS_NOFDREF) &&
 771             tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
 772                 tp = tcp_close(tp);
 773                 goto dropwithreset;
 774         }
 775
 776         /*
 777          * If segment ends after window, drop trailing data
 778          * (and PUSH and FIN); if nothing left, just ACK.
 779          */
 780         todrop = (ti->ti_seq+ti->ti_len) - (tp->rcv_nxt+tp->rcv_wnd);
 781         if (todrop > 0) {
 782                 if (todrop >= ti->ti_len) {
 783                         /*
 784                          * If a new connection request is received
 785                          * while in TIME_WAIT, drop the old connection
 786                          * and start over if the sequence numbers
 787                          * are above the previous ones.
 788                          */
 789                         if (tiflags & TH_SYN &&
 790                             tp->t_state == TCPS_TIME_WAIT &&
 791                             SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
 792                                 iss = tp->rcv_nxt + TCP_ISSINCR;
 793                                 tp = tcp_close(tp);
 794                                 goto findso;
 795                         }
 796                         /*
 797                          * If window is closed can only take segments at
 798                          * window edge, and have to drop data and PUSH from
 799                          * incoming segments.  Continue processing, but
 800                          * remember to ack.  Otherwise, drop segment
 801                          * and ack.
 802                          */
 803                         if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
 804                                 tp->t_flags |= TF_ACKNOW;
 805                         } else {
 806                                 goto dropafterack;
 807                         }
 808                 }
 809                 m_adj(m, -todrop);
 810                 ti->ti_len -= todrop;
 811                 tiflags &= ~(TH_PUSH|TH_FIN);
 812         }
 813
 814         /*
 815          * If the RST bit is set examine the state:
 816          *    SYN_RECEIVED STATE:
 817          *      If passive open, return to LISTEN state.
 818          *      If active open, inform user that connection was refused.
 819          *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
 820          *      Inform user that connection was reset, and close tcb.
 821          *    CLOSING, LAST_ACK, TIME_WAIT STATES
 822          *      Close the tcb.
 823          */
 824         if (tiflags&TH_RST) switch (tp->t_state) {
 825
 826         case TCPS_SYN_RECEIVED:
 827         case TCPS_ESTABLISHED:
 828         case TCPS_FIN_WAIT_1:
 829         case TCPS_FIN_WAIT_2:
 830         case TCPS_CLOSE_WAIT:
 831                 tp->t_state = TCPS_CLOSED;
 832                 tcp_close(tp);
 833                 goto drop;
 834
 835         case TCPS_CLOSING:
 836         case TCPS_LAST_ACK:
 837         case TCPS_TIME_WAIT:
 838                 tcp_close(tp);
 839                 goto drop;
 840         }
 841
 842         /*
 843          * If a SYN is in the window, then this is an
 844          * error and we send an RST and drop the connection.
 845          */
 846         if (tiflags & TH_SYN) {
 847                 tp = tcp_drop(tp,0);
 848                 goto dropwithreset;
 849         }
 850
 851         /*
 852          * If the ACK bit is off we drop the segment and return.
 853          */
 854         if ((tiflags & TH_ACK) == 0) goto drop;
 855
 856         /*
 857          * Ack processing.
 858          */
 859         switch (tp->t_state) {
 860         /*
 861          * In SYN_RECEIVED state if the ack ACKs our SYN then enter
 862          * ESTABLISHED state and continue processing, otherwise
 863          * send an RST.  una<=ack<=max
 864          */
 865         case TCPS_SYN_RECEIVED:
 866
 867                 if (SEQ_GT(tp->snd_una, ti->ti_ack) ||
 868                     SEQ_GT(ti->ti_ack, tp->snd_max))
 869                         goto dropwithreset;
 870                 tp->t_state = TCPS_ESTABLISHED;
 871                 /*
 872                  * The sent SYN is ack'ed with our sequence number +1
 873                  * The first data byte already in the buffer will get
 874                  * lost if no correction is made.  This is only needed for
 875                  * SS_CTL since the buffer is empty otherwise.
 876                  * tp->snd_una++; or:
 877                  */
 878                 tp->snd_una=ti->ti_ack;
 879                 if (so->so_state & SS_CTL) {
 880                   /* So tcp_ctl reports the right state */
 881                   ret = tcp_ctl(so);
 882                   if (ret == 1) {
 883                     soisfconnected(so);
 884                     so->so_state &= ~SS_CTL;   /* success XXX */
 885                   } else if (ret == 2) {
 886                     so->so_state &= SS_PERSISTENT_MASK;
 887                     so->so_state |= SS_NOFDREF; /* CTL_CMD */
 888                   } else {
 889                     needoutput = 1;
 890                     tp->t_state = TCPS_FIN_WAIT_1;
 891                   }
 892                 } else {
 893                   soisfconnected(so);
 894                 }
 895
 896                 (void) tcp_reass(tp, (struct tcpiphdr *)0, (struct mbuf *)0);
 897                 tp->snd_wl1 = ti->ti_seq - 1;
 898                 /* Avoid ack processing; snd_una==ti_ack  =>  dup ack */
 899                 goto synrx_to_est;
 900                 /* fall into ... */
 901
 902         /*
 903          * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
 904          * ACKs.  If the ack is in the range
 905          *      tp->snd_una < ti->ti_ack <= tp->snd_max
 906          * then advance tp->snd_una to ti->ti_ack and drop
 907          * data from the retransmission queue.  If this ACK reflects
 908          * more up to date window information we update our window information.
 909          */
 910         case TCPS_ESTABLISHED:
 911         case TCPS_FIN_WAIT_1:
 912         case TCPS_FIN_WAIT_2:
 913         case TCPS_CLOSE_WAIT:
 914         case TCPS_CLOSING:
 915         case TCPS_LAST_ACK:
 916         case TCPS_TIME_WAIT:
 917
 918                 if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
 919                         if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
 920                           DEBUG_MISC((dfd, " dup ack  m = %lx  so = %lx\n",
 921                                       (long )m, (long )so));
 922                                 /*
 923                                  * If we have outstanding data (other than
 924                                  * a window probe), this is a completely
 925                                  * duplicate ack (ie, window info didn't
 926                                  * change), the ack is the biggest we've
 927                                  * seen and we've seen exactly our rexmt
 928                                  * threshold of them, assume a packet
 929                                  * has been dropped and retransmit it.
 930                                  * Kludge snd_nxt & the congestion
 931                                  * window so we send only this one
 932                                  * packet.
 933                                  *
 934                                  * We know we're losing at the current
 935                                  * window size so do congestion avoidance
 936                                  * (set ssthresh to half the current window
 937                                  * and pull our congestion window back to
 938                                  * the new ssthresh).
 939                                  *
 940                                  * Dup acks mean that packets have left the
 941                                  * network (they're now cached at the receiver)
 942                                  * so bump cwnd by the amount in the receiver
 943                                  * to keep a constant cwnd packets in the
 944                                  * network.
 945                                  */
 946                                 if (tp->t_timer[TCPT_REXMT] == 0 ||
 947                                     ti->ti_ack != tp->snd_una)
 948                                         tp->t_dupacks = 0;
 949                                 else if (++tp->t_dupacks == TCPREXMTTHRESH) {
 950                                         tcp_seq onxt = tp->snd_nxt;
 951                                         u_int win =
 952                                             min(tp->snd_wnd, tp->snd_cwnd) / 2 /
 953                                                 tp->t_maxseg;
 954
 955                                         if (win < 2)
 956                                                 win = 2;
 957                                         tp->snd_ssthresh = win * tp->t_maxseg;
 958                                         tp->t_timer[TCPT_REXMT] = 0;
 959                                         tp->t_rtt = 0;
 960                                         tp->snd_nxt = ti->ti_ack;
 961                                         tp->snd_cwnd = tp->t_maxseg;
 962                                         (void) tcp_output(tp);
 963                                         tp->snd_cwnd = tp->snd_ssthresh +
 964                                                tp->t_maxseg * tp->t_dupacks;
 965                                         if (SEQ_GT(onxt, tp->snd_nxt))
 966                                                 tp->snd_nxt = onxt;
 967                                         goto drop;
 968                                 } else if (tp->t_dupacks > TCPREXMTTHRESH) {
 969                                         tp->snd_cwnd += tp->t_maxseg;
 970                                         (void) tcp_output(tp);
 971                                         goto drop;
 972                                 }
 973                         } else
 974                                 tp->t_dupacks = 0;
 975                         break;
 976                 }
 977         synrx_to_est:
 978                 /*
 979                  * If the congestion window was inflated to account
 980                  * for the other side's cached packets, retract it.
 981                  */
 982                 if (tp->t_dupacks > TCPREXMTTHRESH &&
 983                     tp->snd_cwnd > tp->snd_ssthresh)
 984                         tp->snd_cwnd = tp->snd_ssthresh;
 985                 tp->t_dupacks = 0;
 986                 if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
 987                         goto dropafterack;
 988                 }
 989                 acked = ti->ti_ack - tp->snd_una;
 990
 991                 /*
 992                  * If transmit timer is running and timed sequence
 993                  * number was acked, update smoothed round trip time.
 994                  * Since we now have an rtt measurement, cancel the
 995                  * timer backoff (cf., Phil Karn's retransmit alg.).
 996                  * Recompute the initial retransmit timer.
 997                  */
 998                 if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
 999                         tcp_xmit_timer(tp,tp->t_rtt);
1000
1001                 /*
1002                  * If all outstanding data is acked, stop retransmit
1003                  * timer and remember to restart (more output or persist).
1004                  * If there is more data to be acked, restart retransmit
1005                  * timer, using current (possibly backed-off) value.
1006                  */
1007                 if (ti->ti_ack == tp->snd_max) {
1008                         tp->t_timer[TCPT_REXMT] = 0;
1009                         needoutput = 1;
1010                 } else if (tp->t_timer[TCPT_PERSIST] == 0)
1011                         tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
1012                 /*
1013                  * When new data is acked, open the congestion window.
1014                  * If the window gives us less than ssthresh packets
1015                  * in flight, open exponentially (maxseg per packet).
1016                  * Otherwise open linearly: maxseg per window
1017                  * (maxseg^2 / cwnd per packet).
1018                  */
1019                 {
1020                   register u_int cw = tp->snd_cwnd;
1021                   register u_int incr = tp->t_maxseg;
1022
1023                   if (cw > tp->snd_ssthresh)
1024                     incr = incr * incr / cw;
1025                   tp->snd_cwnd = min(cw + incr, TCP_MAXWIN<<tp->snd_scale);
1026                 }
1027                 if (acked > so->so_snd.sb_cc) {
1028                         tp->snd_wnd -= so->so_snd.sb_cc;
1029                         sbdrop(&so->so_snd, (int )so->so_snd.sb_cc);
1030                         ourfinisacked = 1;
1031                 } else {
1032                         sbdrop(&so->so_snd, acked);
1033                         tp->snd_wnd -= acked;
1034                         ourfinisacked = 0;
1035                 }
1036                 tp->snd_una = ti->ti_ack;
1037                 if (SEQ_LT(tp->snd_nxt, tp->snd_una))
1038                         tp->snd_nxt = tp->snd_una;
1039
1040                 switch (tp->t_state) {
1041
1042                 /*
1043                  * In FIN_WAIT_1 STATE in addition to the processing
1044                  * for the ESTABLISHED state if our FIN is now acknowledged
1045                  * then enter FIN_WAIT_2.
1046                  */
1047                 case TCPS_FIN_WAIT_1:
1048                         if (ourfinisacked) {
1049                                 /*
1050                                  * If we can't receive any more
1051                                  * data, then closing user can proceed.
1052                                  * Starting the timer is contrary to the
1053                                  * specification, but if we don't get a FIN
1054                                  * we'll hang forever.
1055                                  */
1056                                 if (so->so_state & SS_FCANTRCVMORE) {
1057                                         tp->t_timer[TCPT_2MSL] = TCP_MAXIDLE;
1058                                 }
1059                                 tp->t_state = TCPS_FIN_WAIT_2;
1060                         }
1061                         break;
1062
1063                 /*
1064                  * In CLOSING STATE in addition to the processing for
1065                  * the ESTABLISHED state if the ACK acknowledges our FIN
1066                  * then enter the TIME-WAIT state, otherwise ignore
1067                  * the segment.
1068                  */
1069                 case TCPS_CLOSING:
1070                         if (ourfinisacked) {
1071                                 tp->t_state = TCPS_TIME_WAIT;
1072                                 tcp_canceltimers(tp);
1073                                 tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1074                         }
1075                         break;
1076
1077                 /*
1078                  * In LAST_ACK, we may still be waiting for data to drain
1079                  * and/or to be acked, as well as for the ack of our FIN.
1080                  * If our FIN is now acknowledged, delete the TCB,
1081                  * enter the closed state and return.
1082                  */
1083                 case TCPS_LAST_ACK:
1084                         if (ourfinisacked) {
1085                                 tcp_close(tp);
1086                                 goto drop;
1087                         }
1088                         break;
1089
1090                 /*
1091                  * In TIME_WAIT state the only thing that should arrive
1092                  * is a retransmission of the remote FIN.  Acknowledge
1093                  * it and restart the finack timer.
1094                  */
1095                 case TCPS_TIME_WAIT:
1096                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1097                         goto dropafterack;
1098                 }
1099         } /* switch(tp->t_state) */
1100
1101 step6:
1102         /*
1103          * Update window information.
1104          * Don't look at window if no ACK: TAC's send garbage on first SYN.
1105          */
1106         if ((tiflags & TH_ACK) &&
1107             (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
1108             (tp->snd_wl1 == ti->ti_seq && (SEQ_LT(tp->snd_wl2, ti->ti_ack) ||
1109             (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
1110                 tp->snd_wnd = tiwin;
1111                 tp->snd_wl1 = ti->ti_seq;
1112                 tp->snd_wl2 = ti->ti_ack;
1113                 if (tp->snd_wnd > tp->max_sndwnd)
1114                         tp->max_sndwnd = tp->snd_wnd;
1115                 needoutput = 1;
1116         }
1117
1118         /*
1119          * Process segments with URG.
1120          */
1121         if ((tiflags & TH_URG) && ti->ti_urp &&
1122             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1123                 /*
1124                  * This is a kludge, but if we receive and accept
1125                  * random urgent pointers, we'll crash in
1126                  * soreceive.  It's hard to imagine someone
1127                  * actually wanting to send this much urgent data.
1128                  */
1129                 if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) {
1130                         ti->ti_urp = 0;
1131                         tiflags &= ~TH_URG;
1132                         goto dodata;
1133                 }
1134                 /*
1135                  * If this segment advances the known urgent pointer,
1136                  * then mark the data stream.  This should not happen
1137                  * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
1138                  * a FIN has been received from the remote side.
1139                  * In these states we ignore the URG.
1140                  *
1141                  * According to RFC961 (Assigned Protocols),
1142                  * the urgent pointer points to the last octet
1143                  * of urgent data.  We continue, however,
1144                  * to consider it to indicate the first octet
1145                  * of data past the urgent section as the original
1146                  * spec states (in one of two places).
1147                  */
1148                 if (SEQ_GT(ti->ti_seq+ti->ti_urp, tp->rcv_up)) {
1149                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1150                         so->so_urgc =  so->so_rcv.sb_cc +
1151                                 (tp->rcv_up - tp->rcv_nxt); /* -1; */
1152                         tp->rcv_up = ti->ti_seq + ti->ti_urp;
1153
1154                 }
1155         } else
1156                 /*
1157                  * If no out of band data is expected,
1158                  * pull receive urgent pointer along
1159                  * with the receive window.
1160                  */
1161                 if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
1162                         tp->rcv_up = tp->rcv_nxt;
1163 dodata:
1164
1165         /*
1166          * If this is a small packet, then ACK now - with Nagel
1167          *      congestion avoidance sender won't send more until
1168          *      he gets an ACK.
1169          */
1170         if (ti->ti_len && (unsigned)ti->ti_len <= 5 &&
1171             ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
1172                 tp->t_flags |= TF_ACKNOW;
1173         }
1174
1175         /*
1176          * Process the segment text, merging it into the TCP sequencing queue,
1177          * and arranging for acknowledgment of receipt if necessary.
1178          * This process logically involves adjusting tp->rcv_wnd as data
1179          * is presented to the user (this happens in tcp_usrreq.c,
1180          * case PRU_RCVD).  If a FIN has already been received on this
1181          * connection then we just ignore the text.
1182          */
1183         if ((ti->ti_len || (tiflags&TH_FIN)) &&
1184             TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1185                 TCP_REASS(tp, ti, m, so, tiflags);
1186         } else {
1187                 m_free(m);
1188                 tiflags &= ~TH_FIN;
1189         }
1190
1191         /*
1192          * If FIN is received ACK the FIN and let the user know
1193          * that the connection is closing.
1194          */
1195         if (tiflags & TH_FIN) {
1196                 if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
1197                         /*
1198                          * If we receive a FIN we can't send more data,
1199                          * set it SS_FDRAIN
1200                          * Shutdown the socket if there is no rx data in the
1201                          * buffer.
1202                          * soread() is called on completion of shutdown() and
1203                          * will got to TCPS_LAST_ACK, and use tcp_output()
1204                          * to send the FIN.
1205                          */
1206                         sofwdrain(so);
1207
1208                         tp->t_flags |= TF_ACKNOW;
1209                         tp->rcv_nxt++;
1210                 }
1211                 switch (tp->t_state) {
1212
1213                 /*
1214                  * In SYN_RECEIVED and ESTABLISHED STATES
1215                  * enter the CLOSE_WAIT state.
1216                  */
1217                 case TCPS_SYN_RECEIVED:
1218                 case TCPS_ESTABLISHED:
1219                   if(so->so_emu == EMU_CTL)        /* no shutdown on socket */
1220                     tp->t_state = TCPS_LAST_ACK;
1221                   else
1222                     tp->t_state = TCPS_CLOSE_WAIT;
1223                   break;
1224
1225                 /*
1226                  * If still in FIN_WAIT_1 STATE FIN has not been acked so
1227                  * enter the CLOSING state.
1228                  */
1229                 case TCPS_FIN_WAIT_1:
1230                         tp->t_state = TCPS_CLOSING;
1231                         break;
1232
1233                 /*
1234                  * In FIN_WAIT_2 state enter the TIME_WAIT state,
1235                  * starting the time-wait timer, turning off the other
1236                  * standard timers.
1237                  */
1238                 case TCPS_FIN_WAIT_2:
1239                         tp->t_state = TCPS_TIME_WAIT;
1240                         tcp_canceltimers(tp);
1241                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1242                         break;
1243
1244                 /*
1245                  * In TIME_WAIT state restart the 2 MSL time_wait timer.
1246                  */
1247                 case TCPS_TIME_WAIT:
1248                         tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
1249                         break;
1250                 }
1251         }
1252
1253         /*
1254          * Return any desired output.
1255          */
1256         if (needoutput || (tp->t_flags & TF_ACKNOW)) {
1257                 (void) tcp_output(tp);
1258         }
1259         return;
1260
1261 dropafterack:
1262         /*
1263          * Generate an ACK dropping incoming segment if it occupies
1264          * sequence space, where the ACK reflects our state.
1265          */
1266         if (tiflags & TH_RST)
1267                 goto drop;
1268         m_free(m);
1269         tp->t_flags |= TF_ACKNOW;
1270         (void) tcp_output(tp);
1271         return;
1272
1273 dropwithreset:
1274         /* reuses m if m!=NULL, m_free() unnecessary */
1275         if (tiflags & TH_ACK)
1276                 tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
1277         else {
1278                 if (tiflags & TH_SYN) ti->ti_len++;
1279                 tcp_respond(tp, ti, m, ti->ti_seq+ti->ti_len, (tcp_seq)0,
1280                     TH_RST|TH_ACK);
1281         }
1282
1283         return;
1284
1285 drop:
1286         /*
1287          * Drop space held by incoming segment and return.
1288          */
1289         m_free(m);
1290 }
1291
1292 static void
1293 tcp_dooptions(struct tcpcb *tp, u_char *cp, int cnt, struct tcpiphdr *ti)
1294 {
1295         uint16_t mss;
1296         int opt, optlen;
1297
1298         DEBUG_CALL("tcp_dooptions");
1299         DEBUG_ARGS((dfd, " tp = %lx  cnt=%i\n", (long)tp, cnt));
1300
1301         for (; cnt > 0; cnt -= optlen, cp += optlen) {
1302                 opt = cp[0];
1303                 if (opt == TCPOPT_EOL)
1304                         break;
1305                 if (opt == TCPOPT_NOP)
1306                         optlen = 1;
1307                 else {
1308                         optlen = cp[1];
1309                         if (optlen <= 0)
1310                                 break;
1311                 }
1312                 switch (opt) {
1313
1314                 default:
1315                         continue;
1316
1317                 case TCPOPT_MAXSEG:
1318                         if (optlen != TCPOLEN_MAXSEG)
1319                                 continue;
1320                         if (!(ti->ti_flags & TH_SYN))
1321                                 continue;
1322                         memcpy((char *) &mss, (char *) cp + 2, sizeof(mss));
1323                         NTOHS(mss);
1324                         (void) tcp_mss(tp, mss);        /* sets t_maxseg */
1325                         break;
1326                 }
1327         }
1328 }
1329
1330
1331 /*
1332  * Pull out of band byte out of a segment so
1333  * it doesn't appear in the user's data queue.
1334  * It is still reflected in the segment length for
1335  * sequencing purposes.
1336  */
1337
1338 #ifdef notdef
1339
1340 void
1341 tcp_pulloutofband(so, ti, m)
1342         struct socket *so;
1343         struct tcpiphdr *ti;
1344         register struct mbuf *m;
1345 {
1346         int cnt = ti->ti_urp - 1;
1347
1348         while (cnt >= 0) {
1349                 if (m->m_len > cnt) {
1350                         char *cp = mtod(m, caddr_t) + cnt;
1351                         struct tcpcb *tp = sototcpcb(so);
1352
1353                         tp->t_iobc = *cp;
1354                         tp->t_oobflags |= TCPOOB_HAVEDATA;
1355                         memcpy(sp, cp+1, (unsigned)(m->m_len - cnt - 1));
1356                         m->m_len--;
1357                         return;
1358                 }
1359                 cnt -= m->m_len;
1360                 m = m->m_next; /* XXX WRONG! Fix it! */
1361                 if (m == 0)
1362                         break;
1363         }
1364         panic("tcp_pulloutofband");
1365 }
1366
1367 #endif /* notdef */
1368
1369 /*
1370  * Collect new round-trip time estimate
1371  * and update averages and current timeout.
1372  */
1373
1374 static void
1375 tcp_xmit_timer(register struct tcpcb *tp, int rtt)
1376 {
1377         register short delta;
1378
1379         DEBUG_CALL("tcp_xmit_timer");
1380         DEBUG_ARG("tp = %lx", (long)tp);
1381         DEBUG_ARG("rtt = %d", rtt);
1382
1383         if (tp->t_srtt != 0) {
1384                 /*
1385                  * srtt is stored as fixed point with 3 bits after the
1386                  * binary point (i.e., scaled by 8).  The following magic
1387                  * is equivalent to the smoothing algorithm in rfc793 with
1388                  * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
1389                  * point).  Adjust rtt to origin 0.
1390                  */
1391                 delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
1392                 if ((tp->t_srtt += delta) <= 0)
1393                         tp->t_srtt = 1;
1394                 /*
1395                  * We accumulate a smoothed rtt variance (actually, a
1396                  * smoothed mean difference), then set the retransmit
1397                  * timer to smoothed rtt + 4 times the smoothed variance.
1398                  * rttvar is stored as fixed point with 2 bits after the
1399                  * binary point (scaled by 4).  The following is
1400                  * equivalent to rfc793 smoothing with an alpha of .75
1401                  * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
1402                  * rfc793's wired-in beta.
1403                  */
1404                 if (delta < 0)
1405                         delta = -delta;
1406                 delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
1407                 if ((tp->t_rttvar += delta) <= 0)
1408                         tp->t_rttvar = 1;
1409         } else {
1410                 /*
1411                  * No rtt measurement yet - use the unsmoothed rtt.
1412                  * Set the variance to half the rtt (so our first
1413                  * retransmit happens at 3*rtt).
1414                  */
1415                 tp->t_srtt = rtt << TCP_RTT_SHIFT;
1416                 tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
1417         }
1418         tp->t_rtt = 0;
1419         tp->t_rxtshift = 0;
1420
1421         /*
1422          * the retransmit should happen at rtt + 4 * rttvar.
1423          * Because of the way we do the smoothing, srtt and rttvar
1424          * will each average +1/2 tick of bias.  When we compute
1425          * the retransmit timer, we want 1/2 tick of rounding and
1426          * 1 extra tick because of +-1/2 tick uncertainty in the
1427          * firing of the timer.  The bias will give us exactly the
1428          * 1.5 tick we need.  But, because the bias is
1429          * statistical, we have to test that we don't drop below
1430          * the minimum feasible timer (which is 2 ticks).
1431          */
1432         TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp),
1433             (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
1434
1435         /*
1436          * We received an ack for a packet that wasn't retransmitted;
1437          * it is probably safe to discard any error indications we've
1438          * received recently.  This isn't quite right, but close enough
1439          * for now (a route might have failed after we sent a segment,
1440          * and the return path might not be symmetrical).
1441          */
1442         tp->t_softerror = 0;
1443 }
1444
1445 /*
1446  * Determine a reasonable value for maxseg size.
1447  * If the route is known, check route for mtu.
1448  * If none, use an mss that can be handled on the outgoing
1449  * interface without forcing IP to fragment; if bigger than
1450  * an mbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
1451  * to utilize large mbufs.  If no route is found, route has no mtu,
1452  * or the destination isn't local, use a default, hopefully conservative
1453  * size (usually 512 or the default IP max size, but no more than the mtu
1454  * of the interface), as we can't discover anything about intervening
1455  * gateways or networks.  We also initialize the congestion/slow start
1456  * window to be a single segment if the destination isn't local.
1457  * While looking at the routing entry, we also initialize other path-dependent
1458  * parameters from pre-set or cached values in the routing entry.
1459  */
1460
1461 int
1462 tcp_mss(struct tcpcb *tp, u_int offer)
1463 {
1464         struct socket *so = tp->t_socket;
1465         int mss;
1466
1467         DEBUG_CALL("tcp_mss");
1468         DEBUG_ARG("tp = %lx", (long)tp);
1469         DEBUG_ARG("offer = %d", offer);
1470
1471         mss = min(IF_MTU, IF_MRU) - sizeof(struct tcpiphdr);
1472         if (offer)
1473                 mss = min(mss, offer);
1474         mss = max(mss, 32);
1475         if (mss < tp->t_maxseg || offer != 0)
1476            tp->t_maxseg = mss;
1477
1478         tp->snd_cwnd = mss;
1479
1480         sbreserve(&so->so_snd, TCP_SNDSPACE + ((TCP_SNDSPACE % mss) ?
1481                                                (mss - (TCP_SNDSPACE % mss)) :
1482                                                0));
1483         sbreserve(&so->so_rcv, TCP_RCVSPACE + ((TCP_RCVSPACE % mss) ?
1484                                                (mss - (TCP_RCVSPACE % mss)) :
1485                                                0));
1486
1487         DEBUG_MISC((dfd, " returning mss = %d\n", mss));
1488
1489         return mss;
1490 }