reactos/lib/drivers/oskittcp/oskittcp/tcp_subr.c

   1 /*
   2  * Copyright (c) 1982, 1986, 1988, 1990, 1993
   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. All advertising materials mentioning features or use of this software
  14  *    must display the following acknowledgement:
  15  *      This product includes software developed by the University of
  16  *      California, Berkeley and its contributors.
  17  * 4. Neither the name of the University nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  *
  33  *      @(#)tcp_subr.c  8.1 (Berkeley) 6/10/93
  34  */
  35
  36 #include <sys/param.h>
  37 #include <sys/proc.h>
  38 #include <sys/systm.h>
  39 #include <sys/kernel.h>
  40 #include <sys/malloc.h>
  41 #include <sys/mbuf.h>
  42 #include <sys/socket.h>
  43 #include <sys/socketvar.h>
  44 #include <sys/protosw.h>
  45 #include <sys/errno.h>
  46 #include <sys/queue.h>
  47
  48 #include <net/route.h>
  49 #include <net/if.h>
  50
  51 #include <netinet/in.h>
  52 #include <netinet/in_systm.h>
  53 #include <netinet/ip.h>
  54 #include <netinet/in_pcb.h>
  55 #include <netinet/in_var.h>
  56 #include <netinet/ip_var.h>
  57 #include <netinet/ip_icmp.h>
  58 #include <netinet/tcp.h>
  59 #include <netinet/tcp_fsm.h>
  60 #include <netinet/tcp_seq.h>
  61 #include <netinet/tcp_timer.h>
  62 #include <netinet/tcp_var.h>
  63 #include <netinet/tcpip.h>
  64 #ifdef TCPDEBUG
  65 #include <netinet/tcp_debug.h>
  66 #endif
  67 #include <oskittcp.h>
  68
  69 /* patchable/settable parameters for tcp */
  70 int     tcp_mssdflt = TCP_MSS;
  71 int     tcp_rttdflt = TCPTV_SRTTDFLT / PR_SLOWHZ;
  72 int     tcp_do_rfc1323 = 1;
  73 int     tcp_do_rfc1644 = 1;
  74 static  void tcp_cleartaocache(void);
  75
  76 /*
  77  * Target size of TCP PCB hash table. Will be rounded down to a prime
  78  * number.
  79  */
  80 #ifndef TCBHASHSIZE
  81 #define TCBHASHSIZE     128
  82 #endif
  83
  84 /*
  85  * Tcp initialization
  86  */
  87 void
  88 tcp_init()
  89 {
  90
  91         tcp_iss = boottime.tv_sec;              /* wrong */
  92         tcp_ccgen = 1;
  93         tcp_cleartaocache();
  94         LIST_INIT(&tcb);
  95         tcbinfo.listhead = &tcb;
  96         tcbinfo.hashbase = phashinit(TCBHASHSIZE, M_PCB, &tcbinfo.hashsize);
  97         if (max_protohdr < sizeof(struct tcpiphdr))
  98                 max_protohdr = sizeof(struct tcpiphdr);
  99         if (max_linkhdr + sizeof(struct tcpiphdr) > MHLEN)
 100                 panic("tcp_init");
 101 }
 102
 103 /*
 104  * Create template to be used to send tcp packets on a connection.
 105  * Call after host entry created, allocates an mbuf and fills
 106  * in a skeletal tcp/ip header, minimizing the amount of work
 107  * necessary when the connection is used.
 108  */
 109 struct tcpiphdr *
 110 tcp_template(tp)
 111         struct tcpcb *tp;
 112 {
 113         register struct inpcb *inp = tp->t_inpcb;
 114         register struct mbuf *m;
 115         register struct tcpiphdr *n;
 116
 117         if ((n = tp->t_template) == 0) {
 118                 m = m_get(M_DONTWAIT, MT_HEADER);
 119                 OS_DbgPrint(OSK_MID_TRACE,("tp->t_template = %x\n", m));
 120                 if (m == NULL)
 121                         return (0);
 122                 m->m_len = sizeof (struct tcpiphdr);
 123                 n = mtod(m, struct tcpiphdr *);
 124         }
 125         n->ti_next = n->ti_prev = 0;
 126         n->ti_x1 = 0;
 127         n->ti_pr = IPPROTO_TCP;
 128         n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
 129         n->ti_src = inp->inp_laddr;
 130         OS_DbgPrint(OSK_MID_TRACE,("INP_LADDR = %x\n", n->ti_src));
 131         n->ti_dst = inp->inp_faddr;
 132         n->ti_sport = inp->inp_lport;
 133         n->ti_dport = inp->inp_fport;
 134         n->ti_seq = 0;
 135         n->ti_ack = 0;
 136         n->ti_x2 = 0;
 137         n->ti_off = 5;
 138         n->ti_flags = 0;
 139         n->ti_win = 0;
 140         n->ti_sum = 0;
 141         n->ti_urp = 0;
 142         return (n);
 143 }
 144
 145 /*
 146  * Send a single message to the TCP at address specified by
 147  * the given TCP/IP header.  If m == 0, then we make a copy
 148  * of the tcpiphdr at ti and send directly to the addressed host.
 149  * This is used to force keep alive messages out using the TCP
 150  * template for a connection tp->t_template.  If flags are given
 151  * then we send a message back to the TCP which originated the
 152  * segment ti, and discard the mbuf containing it and any other
 153  * attached mbufs.
 154  *
 155  * In any case the ack and sequence number of the transmitted
 156  * segment are as specified by the parameters.
 157  */
 158 void
 159 tcp_respond(tp, ti, m, ack, seq, flags)
 160         struct tcpcb *tp;
 161         register struct tcpiphdr *ti;
 162         register struct mbuf *m;
 163         tcp_seq ack, seq;
 164         int flags;
 165 {
 166         struct mbuf *n;
 167         register int tlen;
 168         int win = 0;
 169         struct route *ro = 0;
 170
 171         if (tp) {
 172                 win = sbspace(&tp->t_inpcb->inp_socket->so_rcv);
 173                 ro = &tp->t_inpcb->inp_route;
 174         }
 175         if (m == 0) {
 176                 m = m_gethdr(M_DONTWAIT, MT_HEADER);
 177                 if (m == NULL)
 178                         return;
 179 #ifdef TCP_COMPAT_42
 180                 tlen = 1;
 181 #else
 182                 tlen = 0;
 183 #endif
 184                 m->m_data += max_linkhdr;
 185                 *mtod(m, struct tcpiphdr *) = *ti;
 186                 ti = mtod(m, struct tcpiphdr *);
 187                 flags = TH_ACK;
 188         } else {
 189                 m_freem(m->m_next);
 190                 m->m_next = 0;
 191                 m->m_data = (caddr_t)ti;
 192                 m->m_len = sizeof (struct tcpiphdr);
 193                 tlen = 0;
 194 #define xchg(a,b,type) { type t; t=a; a=b; b=t; }
 195                 xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, u_long);
 196                 xchg(ti->ti_dport, ti->ti_sport, u_short);
 197 #undef xchg
 198         }
 199         ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + tlen));
 200         tlen += sizeof (struct tcpiphdr);
 201         m->m_len = tlen;
 202         m->m_pkthdr.len = tlen;
 203         m->m_pkthdr.rcvif = (struct ifnet *) 0;
 204         ti->ti_next = ti->ti_prev = 0;
 205         ti->ti_x1 = 0;
 206         ti->ti_seq = htonl(seq);
 207         ti->ti_ack = htonl(ack);
 208         ti->ti_x2 = 0;
 209         ti->ti_off = sizeof (struct tcphdr) >> 2;
 210         ti->ti_flags = flags;
 211         if (tp)
 212                 ti->ti_win = htons((u_short) (win >> tp->rcv_scale));
 213         else
 214                 ti->ti_win = htons((u_short)win);
 215         ti->ti_urp = 0;
 216         ti->ti_sum = 0;
 217         ti->ti_sum = in_cksum(m, tlen);
 218         ((struct ip *)ti)->ip_len = tlen;
 219         ((struct ip *)ti)->ip_ttl = ip_defttl;
 220 #ifdef TCPDEBUG
 221         if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG))
 222                 tcp_trace(TA_OUTPUT, 0, tp, ti, 0);
 223 #endif
 224         (void) ip_output(m, NULL, ro, 0, NULL);
 225 #ifdef __REACTOS__
 226         /* We allocated m, so we are responsible for freeing it. If the mbuf
 227            contains a pointer to an external datablock, we (or rather, m_copy)
 228            didn't allocate it but pointed it to the data to send. So we have
 229            to cheat a little bit and keep M_FREE from freeing the external
 230            data block */
 231         while (NULL != m) {
 232             m->m_flags &= ~M_EXT;
 233             MFREE(m, n);
 234             m = n;
 235         }
 236 #endif
 237 }
 238
 239 /*
 240  * Create a new TCP control block, making an
 241  * empty reassembly queue and hooking it to the argument
 242  * protocol control block.
 243  */
 244 struct tcpcb *
 245 tcp_newtcpcb(inp)
 246         struct inpcb *inp;
 247 {
 248         register struct tcpcb *tp;
 249
 250         tp = malloc(sizeof(*tp), M_PCB, M_NOWAIT);
 251         if (tp == NULL)
 252                 return ((struct tcpcb *)0);
 253         bzero((char *) tp, sizeof(struct tcpcb));
 254         tp->seg_next = tp->seg_prev = (struct tcpiphdr *)tp;
 255         tp->t_maxseg = tp->t_maxopd = tcp_mssdflt;
 256
 257         if (tcp_do_rfc1323)
 258                 tp->t_flags = (TF_REQ_SCALE|TF_REQ_TSTMP);
 259         if (tcp_do_rfc1644)
 260                 tp->t_flags |= TF_REQ_CC;
 261         tp->t_inpcb = inp;
 262         /*
 263          * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
 264          * rtt estimate.  Set rttvar so that srtt + 2 * rttvar gives
 265          * reasonable initial retransmit time.
 266          */
 267         tp->t_srtt = TCPTV_SRTTBASE;
 268         tp->t_rttvar = tcp_rttdflt * PR_SLOWHZ << 2;
 269         tp->t_rttmin = TCPTV_MIN;
 270         TCPT_RANGESET(tp->t_rxtcur,
 271             ((TCPTV_SRTTBASE >> 2) + (TCPTV_SRTTDFLT << 2)) >> 1,
 272             TCPTV_MIN, TCPTV_REXMTMAX);
 273         tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 274         tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
 275         inp->inp_ip.ip_ttl = ip_defttl;
 276         inp->inp_ppcb = (caddr_t)tp;
 277         return (tp);
 278 }
 279
 280 /*
 281  * Drop a TCP connection, reporting
 282  * the specified error.  If connection is synchronized,
 283  * then send a RST to peer.
 284  */
 285 struct tcpcb *
 286 tcp_drop(tp, errno)
 287         register struct tcpcb *tp;
 288         int errno;
 289 {
 290         struct socket *so = tp->t_inpcb->inp_socket;
 291
 292         if (TCPS_HAVERCVDSYN(tp->t_state)) {
 293                 tp->t_state = TCPS_CLOSED;
 294                 (void) tcp_output(tp);
 295                 tcpstat.tcps_drops++;
 296         } else
 297                 tcpstat.tcps_conndrops++;
 298         if (errno == ETIMEDOUT && tp->t_softerror)
 299                 errno = tp->t_softerror;
 300         so->so_error = errno;
 301         return (tcp_close(tp));
 302 }
 303
 304 /*
 305  * Close a TCP control block:
 306  *      discard all space held by the tcp
 307  *      discard internet protocol block
 308  *      wake up any sleepers
 309  */
 310 struct tcpcb *
 311 tcp_close(tp)
 312         register struct tcpcb *tp;
 313 {
 314         register struct tcpiphdr *t;
 315         struct inpcb *inp = tp->t_inpcb;
 316         struct socket *so = inp->inp_socket;
 317         register struct mbuf *m;
 318 #ifdef RTV_RTT
 319         register struct rtentry *rt;
 320
 321         /*
 322          * If we got enough samples through the srtt filter,
 323          * save the rtt and rttvar in the routing entry.
 324          * 'Enough' is arbitrarily defined as the 16 samples.
 325          * 16 samples is enough for the srtt filter to converge
 326          * to within 5% of the correct value; fewer samples and
 327          * we could save a very bogus rtt.
 328          *
 329          * Don't update the default route's characteristics and don't
 330          * update anything that the user "locked".
 331          */
 332         if (tp->t_rttupdated >= 16 &&
 333             (rt = inp->inp_route.ro_rt) &&
 334             ((struct sockaddr_in *)rt_key(rt))->sin_addr.s_addr != INADDR_ANY) {
 335                 register u_long i = 0;
 336
 337                 if ((rt->rt_rmx.rmx_locks & RTV_RTT) == 0) {
 338                         i = tp->t_srtt *
 339                             (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTT_SCALE));
 340                         if (rt->rt_rmx.rmx_rtt && i)
 341                                 /*
 342                                  * filter this update to half the old & half
 343                                  * the new values, converting scale.
 344                                  * See route.h and tcp_var.h for a
 345                                  * description of the scaling constants.
 346                                  */
 347                                 rt->rt_rmx.rmx_rtt =
 348                                     (rt->rt_rmx.rmx_rtt + i) / 2;
 349                         else
 350                                 rt->rt_rmx.rmx_rtt = i;
 351                         tcpstat.tcps_cachedrtt++;
 352                 }
 353                 if ((rt->rt_rmx.rmx_locks & RTV_RTTVAR) == 0) {
 354                         i = tp->t_rttvar *
 355                             (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTTVAR_SCALE));
 356                         if (rt->rt_rmx.rmx_rttvar && i)
 357                                 rt->rt_rmx.rmx_rttvar =
 358                                     (rt->rt_rmx.rmx_rttvar + i) / 2;
 359                         else
 360                                 rt->rt_rmx.rmx_rttvar = i;
 361                         tcpstat.tcps_cachedrttvar++;
 362                 }
 363                 /*
 364                  * update the pipelimit (ssthresh) if it has been updated
 365                  * already or if a pipesize was specified & the threshhold
 366                  * got below half the pipesize.  I.e., wait for bad news
 367                  * before we start updating, then update on both good
 368                  * and bad news.
 369                  */
 370                 if (((rt->rt_rmx.rmx_locks & RTV_SSTHRESH) == 0 &&
 371                     ((i = tp->snd_ssthresh) != 0) && rt->rt_rmx.rmx_ssthresh) ||
 372                     i < (rt->rt_rmx.rmx_sendpipe / 2)) {
 373                         /*
 374                          * convert the limit from user data bytes to
 375                          * packets then to packet data bytes.
 376                          */
 377                         i = (i + tp->t_maxseg / 2) / tp->t_maxseg;
 378                         if (i < 2)
 379                                 i = 2;
 380                         i *= (u_long)(tp->t_maxseg + sizeof (struct tcpiphdr));
 381                         if (rt->rt_rmx.rmx_ssthresh)
 382                                 rt->rt_rmx.rmx_ssthresh =
 383                                     (rt->rt_rmx.rmx_ssthresh + i) / 2;
 384                         else
 385                                 rt->rt_rmx.rmx_ssthresh = i;
 386                         tcpstat.tcps_cachedssthresh++;
 387                 }
 388         }
 389 #endif /* RTV_RTT */
 390         /* free the reassembly queue, if any */
 391         t = tp->seg_next;
 392         while (t != (struct tcpiphdr *)tp) {
 393                 t = (struct tcpiphdr *)t->ti_next;
 394                 m = REASS_MBUF((struct tcpiphdr *)t->ti_prev);
 395                 remque(t->ti_prev);
 396                 m_freem(m);
 397         }
 398         if (tp->t_template)
 399                 (void) m_free(dtom(tp->t_template));
 400         free(tp, M_PCB);
 401         inp->inp_ppcb = 0;
 402         soisdisconnected(so);
 403         in_pcbdetach(inp);
 404         tcpstat.tcps_closed++;
 405         return ((struct tcpcb *)0);
 406 }
 407
 408 void
 409 tcp_drain()
 410 {
 411
 412 }
 413
 414 /*
 415  * Notify a tcp user of an asynchronous error;
 416  * store error as soft error, but wake up user
 417  * (for now, won't do anything until can select for soft error).
 418  */
 419 void
 420 tcp_notify(inp, error)
 421         struct inpcb *inp;
 422         int error;
 423 {
 424         register struct tcpcb *tp = (struct tcpcb *)inp->inp_ppcb;
 425         register struct socket *so = inp->inp_socket;
 426
 427         /*
 428          * Ignore some errors if we are hooked up.
 429          * If connection hasn't completed, has retransmitted several times,
 430          * and receives a second error, give up now.  This is better
 431          * than waiting a long time to establish a connection that
 432          * can never complete.
 433          */
 434         if (tp->t_state == TCPS_ESTABLISHED &&
 435              (error == EHOSTUNREACH || error == ENETUNREACH ||
 436               error == EHOSTDOWN)) {
 437                 return;
 438         } else if (tp->t_state < TCPS_ESTABLISHED && tp->t_rxtshift > 3 &&
 439             tp->t_softerror)
 440                 so->so_error = error;
 441         else
 442                 tp->t_softerror = error;
 443         wakeup( so, (caddr_t) &so->so_timeo);
 444         sorwakeup(so);
 445         sowwakeup(so);
 446 }
 447
 448 void
 449 tcp_ctlinput(cmd, sa, ip)
 450         int cmd;
 451         struct sockaddr *sa;
 452         register struct ip *ip;
 453 {
 454         register struct tcphdr *th;
 455         void (*notify) __P((struct inpcb *, int)) = tcp_notify;
 456
 457         if (cmd == PRC_QUENCH)
 458                 notify = tcp_quench;
 459 #if 1
 460         else if (cmd == PRC_MSGSIZE)
 461                 notify = tcp_mtudisc;
 462 #endif
 463         else if (!PRC_IS_REDIRECT(cmd) &&
 464                  ((unsigned)cmd > PRC_NCMDS || inetctlerrmap[cmd] == 0))
 465                 return;
 466         if (ip) {
 467                 th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
 468                 in_pcbnotify(&tcb, sa, th->th_dport, ip->ip_src, th->th_sport,
 469                         cmd, notify);
 470         } else
 471                 in_pcbnotify(&tcb, sa, 0, zeroin_addr, 0, cmd, notify);
 472 }
 473
 474 /*
 475  * When a source quench is received, close congestion window
 476  * to one segment.  We will gradually open it again as we proceed.
 477  */
 478 void
 479 tcp_quench(inp, errno)
 480         struct inpcb *inp;
 481         int errno;
 482 {
 483         struct tcpcb *tp = intotcpcb(inp);
 484
 485         if (tp)
 486                 tp->snd_cwnd = tp->t_maxseg;
 487 }
 488
 489 #if 1
 490 /*
 491  * When `need fragmentation' ICMP is received, update our idea of the MSS
 492  * based on the new value in the route.  Also nudge TCP to send something,
 493  * since we know the packet we just sent was dropped.
 494  * This duplicates some code in the tcp_mss() function in tcp_input.c.
 495  */
 496 void
 497 tcp_mtudisc(inp, errno)
 498         struct inpcb *inp;
 499         int errno;
 500 {
 501         struct tcpcb *tp = intotcpcb(inp);
 502         struct rtentry *rt;
 503         struct rmxp_tao *taop;
 504         struct socket *so = inp->inp_socket;
 505         int offered;
 506         int mss;
 507
 508         if (tp) {
 509                 rt = tcp_rtlookup(inp);
 510                 if (!rt || !rt->rt_rmx.rmx_mtu) {
 511                         tp->t_maxopd = tp->t_maxseg = tcp_mssdflt;
 512                         return;
 513                 }
 514                 taop = rmx_taop(rt->rt_rmx);
 515                 offered = taop->tao_mssopt;
 516                 mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr);
 517                 if (offered)
 518                         mss = min(mss, offered);
 519                 /*
 520                  * XXX - The above conditional probably violates the TCP
 521                  * spec.  The problem is that, since we don't know the
 522                  * other end's MSS, we are supposed to use a conservative
 523                  * default.  But, if we do that, then MTU discovery will
 524                  * never actually take place, because the conservative
 525                  * default is much less than the MTUs typically seen
 526                  * on the Internet today.  For the moment, we'll sweep
 527                  * this under the carpet.
 528                  *
 529                  * The conservative default might not actually be a problem
 530                  * if the only case this occurs is when sending an initial
 531                  * SYN with options and data to a host we've never talked
 532                  * to before.  Then, they will reply with an MSS value which
 533                  * will get recorded and the new parameters should get
 534                  * recomputed.  For Further Study.
 535                  */
 536                 if (tp->t_maxopd <= mss)
 537                         return;
 538                 tp->t_maxopd = mss;
 539
 540                 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
 541                     (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP)
 542                         mss -= TCPOLEN_TSTAMP_APPA;
 543                 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
 544                     (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC)
 545                         mss -= TCPOLEN_CC_APPA;
 546 #if     (MCLBYTES & (MCLBYTES - 1)) == 0
 547                 if (mss > MCLBYTES)
 548                         mss &= ~(MCLBYTES-1);
 549 #else
 550                 if (mss > MCLBYTES)
 551                         mss = mss / MCLBYTES * MCLBYTES;
 552 #endif
 553                 if (so->so_snd.sb_hiwat < mss)
 554                         mss = so->so_snd.sb_hiwat;
 555
 556                 tp->t_maxseg = mss;
 557
 558                 tcpstat.tcps_mturesent++;
 559                 tp->t_rtt = 0;
 560                 tp->snd_nxt = tp->snd_una;
 561                 tcp_output(tp);
 562         }
 563 }
 564 #endif
 565
 566 /*
 567  * Look-up the routing entry to the peer of this inpcb.  If no route
 568  * is found and it cannot be allocated the return NULL.  This routine
 569  * is called by TCP routines that access the rmx structure and by tcp_mss
 570  * to get the interface MTU.
 571  */
 572 struct rtentry *
 573 tcp_rtlookup(inp)
 574         struct inpcb *inp;
 575 {
 576         struct route *ro;
 577         struct rtentry *rt;
 578
 579         ro = &inp->inp_route;
 580         rt = ro->ro_rt;
 581         if (rt == NULL || !(rt->rt_flags & RTF_UP)) {
 582                 /* No route yet, so try to acquire one */
 583                 if (inp->inp_faddr.s_addr != INADDR_ANY) {
 584                         ro->ro_dst.sa_family = AF_INET;
 585                         ro->ro_dst.sa_len = sizeof(ro->ro_dst);
 586                         ((struct sockaddr_in *) &ro->ro_dst)->sin_addr =
 587                                 inp->inp_faddr;
 588                         rtalloc(ro);
 589                         rt = ro->ro_rt;
 590                 }
 591         }
 592         return rt;
 593 }
 594
 595 /*
 596  * Return a pointer to the cached information about the remote host.
 597  * The cached information is stored in the protocol specific part of
 598  * the route metrics.
 599  */
 600 struct rmxp_tao *
 601 tcp_gettaocache(inp)
 602         struct inpcb *inp;
 603 {
 604         struct rtentry *rt = tcp_rtlookup(inp);
 605
 606         /* Make sure this is a host route and is up. */
 607         if (rt == NULL ||
 608             (rt->rt_flags & (RTF_UP|RTF_HOST)) != (RTF_UP|RTF_HOST))
 609                 return NULL;
 610
 611         return rmx_taop(rt->rt_rmx);
 612 }
 613
 614 /*
 615  * Clear all the TAO cache entries, called from tcp_init.
 616  *
 617  * XXX
 618  * This routine is just an empty one, because we assume that the routing
 619  * routing tables are initialized at the same time when TCP, so there is
 620  * nothing in the cache left over.
 621  */
 622 static void
 623 tcp_cleartaocache(void)
 624 { }