tcp_timewait.c revision 14754
1/* 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 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 8.2 (Berkeley) 5/24/95 34 * $Id: tcp_subr.c,v 1.26 1996/03/11 15:13:33 davidg Exp $ 35 */ 36 37#include <sys/param.h> 38#include <sys/queue.h> 39#include <sys/proc.h> 40#include <sys/systm.h> 41#include <sys/kernel.h> 42#include <sys/sysctl.h> 43#include <sys/malloc.h> 44#include <sys/mbuf.h> 45#include <sys/socket.h> 46#include <sys/socketvar.h> 47#include <sys/protosw.h> 48#include <sys/errno.h> 49 50#include <net/route.h> 51#include <net/if.h> 52 53#include <netinet/in.h> 54#include <netinet/in_systm.h> 55#include <netinet/ip.h> 56#include <netinet/in_pcb.h> 57#include <netinet/in_var.h> 58#include <netinet/ip_var.h> 59#include <netinet/ip_icmp.h> 60#include <netinet/tcp.h> 61#include <netinet/tcp_fsm.h> 62#include <netinet/tcp_seq.h> 63#include <netinet/tcp_timer.h> 64#include <netinet/tcp_var.h> 65#include <netinet/tcpip.h> 66#ifdef TCPDEBUG 67#include <netinet/tcp_debug.h> 68#endif 69 70int tcp_mssdflt = TCP_MSS; 71SYSCTL_INT(_net_inet_tcp, TCPCTL_MSSDFLT, mssdflt, 72 CTLFLAG_RW, &tcp_mssdflt , 0, ""); 73 74static int tcp_rttdflt = TCPTV_SRTTDFLT / PR_SLOWHZ; 75SYSCTL_INT(_net_inet_tcp, TCPCTL_RTTDFLT, rttdflt, 76 CTLFLAG_RW, &tcp_rttdflt , 0, ""); 77 78static int tcp_do_rfc1323 = 1; 79SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1323, rfc1323, 80 CTLFLAG_RW, &tcp_do_rfc1323 , 0, ""); 81 82static int tcp_do_rfc1644 = 1; 83SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1644, rfc1644, 84 CTLFLAG_RW, &tcp_do_rfc1644 , 0, ""); 85 86static void tcp_cleartaocache(void); 87static void tcp_notify __P((struct inpcb *, int)); 88 89/* 90 * Target size of TCP PCB hash table. Will be rounded down to a prime 91 * number. 92 */ 93#ifndef TCBHASHSIZE 94#define TCBHASHSIZE 128 95#endif 96 97/* 98 * Tcp initialization 99 */ 100void 101tcp_init() 102{ 103 104 tcp_iss = random(); /* wrong, but better than a constant */ 105 tcp_ccgen = 1; 106 tcp_cleartaocache(); 107 LIST_INIT(&tcb); 108 tcbinfo.listhead = &tcb; 109 tcbinfo.hashbase = phashinit(TCBHASHSIZE, M_PCB, &tcbinfo.hashsize); 110 if (max_protohdr < sizeof(struct tcpiphdr)) 111 max_protohdr = sizeof(struct tcpiphdr); 112 if (max_linkhdr + sizeof(struct tcpiphdr) > MHLEN) 113 panic("tcp_init"); 114} 115 116/* 117 * Create template to be used to send tcp packets on a connection. 118 * Call after host entry created, allocates an mbuf and fills 119 * in a skeletal tcp/ip header, minimizing the amount of work 120 * necessary when the connection is used. 121 */ 122struct tcpiphdr * 123tcp_template(tp) 124 struct tcpcb *tp; 125{ 126 register struct inpcb *inp = tp->t_inpcb; 127 register struct mbuf *m; 128 register struct tcpiphdr *n; 129 130 if ((n = tp->t_template) == 0) { 131 m = m_get(M_DONTWAIT, MT_HEADER); 132 if (m == NULL) 133 return (0); 134 m->m_len = sizeof (struct tcpiphdr); 135 n = mtod(m, struct tcpiphdr *); 136 } 137 n->ti_next = n->ti_prev = 0; 138 n->ti_x1 = 0; 139 n->ti_pr = IPPROTO_TCP; 140 n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip)); 141 n->ti_src = inp->inp_laddr; 142 n->ti_dst = inp->inp_faddr; 143 n->ti_sport = inp->inp_lport; 144 n->ti_dport = inp->inp_fport; 145 n->ti_seq = 0; 146 n->ti_ack = 0; 147 n->ti_x2 = 0; 148 n->ti_off = 5; 149 n->ti_flags = 0; 150 n->ti_win = 0; 151 n->ti_sum = 0; 152 n->ti_urp = 0; 153 return (n); 154} 155 156/* 157 * Send a single message to the TCP at address specified by 158 * the given TCP/IP header. If m == 0, then we make a copy 159 * of the tcpiphdr at ti and send directly to the addressed host. 160 * This is used to force keep alive messages out using the TCP 161 * template for a connection tp->t_template. If flags are given 162 * then we send a message back to the TCP which originated the 163 * segment ti, and discard the mbuf containing it and any other 164 * attached mbufs. 165 * 166 * In any case the ack and sequence number of the transmitted 167 * segment are as specified by the parameters. 168 */ 169void 170tcp_respond(tp, ti, m, ack, seq, flags) 171 struct tcpcb *tp; 172 register struct tcpiphdr *ti; 173 register struct mbuf *m; 174 tcp_seq ack, seq; 175 int flags; 176{ 177 register int tlen; 178 int win = 0; 179 struct route *ro = 0; 180 struct route sro; 181 182 if (tp) { 183 win = sbspace(&tp->t_inpcb->inp_socket->so_rcv); 184 ro = &tp->t_inpcb->inp_route; 185 } else { 186 ro = &sro; 187 bzero(ro, sizeof *ro); 188 } 189 if (m == 0) { 190 m = m_gethdr(M_DONTWAIT, MT_HEADER); 191 if (m == NULL) 192 return; 193#ifdef TCP_COMPAT_42 194 tlen = 1; 195#else 196 tlen = 0; 197#endif 198 m->m_data += max_linkhdr; 199 *mtod(m, struct tcpiphdr *) = *ti; 200 ti = mtod(m, struct tcpiphdr *); 201 flags = TH_ACK; 202 } else { 203 m_freem(m->m_next); 204 m->m_next = 0; 205 m->m_data = (caddr_t)ti; 206 m->m_len = sizeof (struct tcpiphdr); 207 tlen = 0; 208#define xchg(a,b,type) { type t; t=a; a=b; b=t; } 209 xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, u_long); 210 xchg(ti->ti_dport, ti->ti_sport, u_short); 211#undef xchg 212 } 213 ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + tlen)); 214 tlen += sizeof (struct tcpiphdr); 215 m->m_len = tlen; 216 m->m_pkthdr.len = tlen; 217 m->m_pkthdr.rcvif = (struct ifnet *) 0; 218 ti->ti_next = ti->ti_prev = 0; 219 ti->ti_x1 = 0; 220 ti->ti_seq = htonl(seq); 221 ti->ti_ack = htonl(ack); 222 ti->ti_x2 = 0; 223 ti->ti_off = sizeof (struct tcphdr) >> 2; 224 ti->ti_flags = flags; 225 if (tp) 226 ti->ti_win = htons((u_short) (win >> tp->rcv_scale)); 227 else 228 ti->ti_win = htons((u_short)win); 229 ti->ti_urp = 0; 230 ti->ti_sum = 0; 231 ti->ti_sum = in_cksum(m, tlen); 232 ((struct ip *)ti)->ip_len = tlen; 233 ((struct ip *)ti)->ip_ttl = ip_defttl; 234#ifdef TCPDEBUG 235 if (tp == NULL || (tp->t_inpcb->inp_socket->so_options & SO_DEBUG)) 236 tcp_trace(TA_OUTPUT, 0, tp, ti, 0); 237#endif 238 (void) ip_output(m, NULL, ro, 0, NULL); 239 if (ro == &sro) { 240 RTFREE(ro->ro_rt); 241 } 242} 243 244/* 245 * Create a new TCP control block, making an 246 * empty reassembly queue and hooking it to the argument 247 * protocol control block. 248 */ 249struct tcpcb * 250tcp_newtcpcb(inp) 251 struct inpcb *inp; 252{ 253 register struct tcpcb *tp; 254 255 tp = malloc(sizeof(*tp), M_PCB, M_NOWAIT); 256 if (tp == NULL) 257 return ((struct tcpcb *)0); 258 bzero((char *) tp, sizeof(struct tcpcb)); 259 tp->seg_next = tp->seg_prev = (struct tcpiphdr *)tp; 260 tp->t_maxseg = tp->t_maxopd = tcp_mssdflt; 261 262 if (tcp_do_rfc1323) 263 tp->t_flags = (TF_REQ_SCALE|TF_REQ_TSTMP); 264 if (tcp_do_rfc1644) 265 tp->t_flags |= TF_REQ_CC; 266 tp->t_inpcb = inp; 267 /* 268 * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no 269 * rtt estimate. Set rttvar so that srtt + 2 * rttvar gives 270 * reasonable initial retransmit time. 271 */ 272 tp->t_srtt = TCPTV_SRTTBASE; 273 tp->t_rttvar = tcp_rttdflt * PR_SLOWHZ << 2; 274 tp->t_rttmin = TCPTV_MIN; 275 TCPT_RANGESET(tp->t_rxtcur, 276 ((TCPTV_SRTTBASE >> 2) + (TCPTV_SRTTDFLT << 2)) >> 1, 277 TCPTV_MIN, TCPTV_REXMTMAX); 278 tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT; 279 tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT; 280 inp->inp_ip.ip_ttl = ip_defttl; 281 inp->inp_ppcb = (caddr_t)tp; 282 return (tp); 283} 284 285/* 286 * Drop a TCP connection, reporting 287 * the specified error. If connection is synchronized, 288 * then send a RST to peer. 289 */ 290struct tcpcb * 291tcp_drop(tp, errno) 292 register struct tcpcb *tp; 293 int errno; 294{ 295 struct socket *so = tp->t_inpcb->inp_socket; 296 297 if (TCPS_HAVERCVDSYN(tp->t_state)) { 298 tp->t_state = TCPS_CLOSED; 299 (void) tcp_output(tp); 300 tcpstat.tcps_drops++; 301 } else 302 tcpstat.tcps_conndrops++; 303 if (errno == ETIMEDOUT && tp->t_softerror) 304 errno = tp->t_softerror; 305 so->so_error = errno; 306 return (tcp_close(tp)); 307} 308 309/* 310 * Close a TCP control block: 311 * discard all space held by the tcp 312 * discard internet protocol block 313 * wake up any sleepers 314 */ 315struct tcpcb * 316tcp_close(tp) 317 register struct tcpcb *tp; 318{ 319 register struct tcpiphdr *t; 320 struct inpcb *inp = tp->t_inpcb; 321 struct socket *so = inp->inp_socket; 322 register struct mbuf *m; 323#ifdef RTV_RTT 324 register struct rtentry *rt; 325 326 /* 327 * If we got enough samples through the srtt filter, 328 * save the rtt and rttvar in the routing entry. 329 * 'Enough' is arbitrarily defined as the 16 samples. 330 * 16 samples is enough for the srtt filter to converge 331 * to within 5% of the correct value; fewer samples and 332 * we could save a very bogus rtt. 333 * 334 * Don't update the default route's characteristics and don't 335 * update anything that the user "locked". 336 */ 337 if (tp->t_rttupdated >= 16 && 338 (rt = inp->inp_route.ro_rt) && 339 ((struct sockaddr_in *)rt_key(rt))->sin_addr.s_addr != INADDR_ANY) { 340 register u_long i = 0; 341 342 if ((rt->rt_rmx.rmx_locks & RTV_RTT) == 0) { 343 i = tp->t_srtt * 344 (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTT_SCALE)); 345 if (rt->rt_rmx.rmx_rtt && i) 346 /* 347 * filter this update to half the old & half 348 * the new values, converting scale. 349 * See route.h and tcp_var.h for a 350 * description of the scaling constants. 351 */ 352 rt->rt_rmx.rmx_rtt = 353 (rt->rt_rmx.rmx_rtt + i) / 2; 354 else 355 rt->rt_rmx.rmx_rtt = i; 356 tcpstat.tcps_cachedrtt++; 357 } 358 if ((rt->rt_rmx.rmx_locks & RTV_RTTVAR) == 0) { 359 i = tp->t_rttvar * 360 (RTM_RTTUNIT / (PR_SLOWHZ * TCP_RTTVAR_SCALE)); 361 if (rt->rt_rmx.rmx_rttvar && i) 362 rt->rt_rmx.rmx_rttvar = 363 (rt->rt_rmx.rmx_rttvar + i) / 2; 364 else 365 rt->rt_rmx.rmx_rttvar = i; 366 tcpstat.tcps_cachedrttvar++; 367 } 368 /* 369 * update the pipelimit (ssthresh) if it has been updated 370 * already or if a pipesize was specified & the threshhold 371 * got below half the pipesize. I.e., wait for bad news 372 * before we start updating, then update on both good 373 * and bad news. 374 */ 375 if (((rt->rt_rmx.rmx_locks & RTV_SSTHRESH) == 0 && 376 ((i = tp->snd_ssthresh) != 0) && rt->rt_rmx.rmx_ssthresh) || 377 i < (rt->rt_rmx.rmx_sendpipe / 2)) { 378 /* 379 * convert the limit from user data bytes to 380 * packets then to packet data bytes. 381 */ 382 i = (i + tp->t_maxseg / 2) / tp->t_maxseg; 383 if (i < 2) 384 i = 2; 385 i *= (u_long)(tp->t_maxseg + sizeof (struct tcpiphdr)); 386 if (rt->rt_rmx.rmx_ssthresh) 387 rt->rt_rmx.rmx_ssthresh = 388 (rt->rt_rmx.rmx_ssthresh + i) / 2; 389 else 390 rt->rt_rmx.rmx_ssthresh = i; 391 tcpstat.tcps_cachedssthresh++; 392 } 393 } 394#endif /* RTV_RTT */ 395 /* free the reassembly queue, if any */ 396 t = tp->seg_next; 397 while (t != (struct tcpiphdr *)tp) { 398 t = (struct tcpiphdr *)t->ti_next; 399 m = REASS_MBUF((struct tcpiphdr *)t->ti_prev); 400 remque(t->ti_prev); 401 m_freem(m); 402 } 403 if (tp->t_template) 404 (void) m_free(dtom(tp->t_template)); 405 free(tp, M_PCB); 406 inp->inp_ppcb = 0; 407 soisdisconnected(so); 408 in_pcbdetach(inp); 409 tcpstat.tcps_closed++; 410 return ((struct tcpcb *)0); 411} 412 413void 414tcp_drain() 415{ 416 417} 418 419/* 420 * Notify a tcp user of an asynchronous error; 421 * store error as soft error, but wake up user 422 * (for now, won't do anything until can select for soft error). 423 */ 424static void 425tcp_notify(inp, error) 426 struct inpcb *inp; 427 int error; 428{ 429 register struct tcpcb *tp = (struct tcpcb *)inp->inp_ppcb; 430 register struct socket *so = inp->inp_socket; 431 432 /* 433 * Ignore some errors if we are hooked up. 434 * If connection hasn't completed, has retransmitted several times, 435 * and receives a second error, give up now. This is better 436 * than waiting a long time to establish a connection that 437 * can never complete. 438 */ 439 if (tp->t_state == TCPS_ESTABLISHED && 440 (error == EHOSTUNREACH || error == ENETUNREACH || 441 error == EHOSTDOWN)) { 442 return; 443 } else if (tp->t_state < TCPS_ESTABLISHED && tp->t_rxtshift > 3 && 444 tp->t_softerror) 445 so->so_error = error; 446 else 447 tp->t_softerror = error; 448 wakeup((caddr_t) &so->so_timeo); 449 sorwakeup(so); 450 sowwakeup(so); 451} 452 453void 454tcp_ctlinput(cmd, sa, vip) 455 int cmd; 456 struct sockaddr *sa; 457 void *vip; 458{ 459 register struct ip *ip = vip; 460 register struct tcphdr *th; 461 void (*notify) __P((struct inpcb *, int)) = tcp_notify; 462 463 if (cmd == PRC_QUENCH) 464 notify = tcp_quench; 465#if 1 466 else if (cmd == PRC_MSGSIZE) 467 notify = tcp_mtudisc; 468#endif 469 else if (!PRC_IS_REDIRECT(cmd) && 470 ((unsigned)cmd > PRC_NCMDS || inetctlerrmap[cmd] == 0)) 471 return; 472 if (ip) { 473 th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2)); 474 in_pcbnotify(&tcb, sa, th->th_dport, ip->ip_src, th->th_sport, 475 cmd, notify); 476 } else 477 in_pcbnotify(&tcb, sa, 0, zeroin_addr, 0, cmd, notify); 478} 479 480/* 481 * When a source quench is received, close congestion window 482 * to one segment. We will gradually open it again as we proceed. 483 */ 484void 485tcp_quench(inp, errno) 486 struct inpcb *inp; 487 int errno; 488{ 489 struct tcpcb *tp = intotcpcb(inp); 490 491 if (tp) 492 tp->snd_cwnd = tp->t_maxseg; 493} 494 495#if 1 496/* 497 * When `need fragmentation' ICMP is received, update our idea of the MSS 498 * based on the new value in the route. Also nudge TCP to send something, 499 * since we know the packet we just sent was dropped. 500 * This duplicates some code in the tcp_mss() function in tcp_input.c. 501 */ 502void 503tcp_mtudisc(inp, errno) 504 struct inpcb *inp; 505 int errno; 506{ 507 struct tcpcb *tp = intotcpcb(inp); 508 struct rtentry *rt; 509 struct rmxp_tao *taop; 510 struct socket *so = inp->inp_socket; 511 int offered; 512 int mss; 513 514 if (tp) { 515 rt = tcp_rtlookup(inp); 516 if (!rt || !rt->rt_rmx.rmx_mtu) { 517 tp->t_maxopd = tp->t_maxseg = tcp_mssdflt; 518 return; 519 } 520 taop = rmx_taop(rt->rt_rmx); 521 offered = taop->tao_mssopt; 522 mss = rt->rt_rmx.rmx_mtu - sizeof(struct tcpiphdr); 523 if (offered) 524 mss = min(mss, offered); 525 /* 526 * XXX - The above conditional probably violates the TCP 527 * spec. The problem is that, since we don't know the 528 * other end's MSS, we are supposed to use a conservative 529 * default. But, if we do that, then MTU discovery will 530 * never actually take place, because the conservative 531 * default is much less than the MTUs typically seen 532 * on the Internet today. For the moment, we'll sweep 533 * this under the carpet. 534 * 535 * The conservative default might not actually be a problem 536 * if the only case this occurs is when sending an initial 537 * SYN with options and data to a host we've never talked 538 * to before. Then, they will reply with an MSS value which 539 * will get recorded and the new parameters should get 540 * recomputed. For Further Study. 541 */ 542 if (tp->t_maxopd <= mss) 543 return; 544 tp->t_maxopd = mss; 545 546 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 547 (tp->t_flags & TF_RCVD_TSTMP) == TF_RCVD_TSTMP) 548 mss -= TCPOLEN_TSTAMP_APPA; 549 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC && 550 (tp->t_flags & TF_RCVD_CC) == TF_RCVD_CC) 551 mss -= TCPOLEN_CC_APPA; 552#if (MCLBYTES & (MCLBYTES - 1)) == 0 553 if (mss > MCLBYTES) 554 mss &= ~(MCLBYTES-1); 555#else 556 if (mss > MCLBYTES) 557 mss = mss / MCLBYTES * MCLBYTES; 558#endif 559 if (so->so_snd.sb_hiwat < mss) 560 mss = so->so_snd.sb_hiwat; 561 562 tp->t_maxseg = mss; 563 564 tcpstat.tcps_mturesent++; 565 tp->t_rtt = 0; 566 tp->snd_nxt = tp->snd_una; 567 tcp_output(tp); 568 } 569} 570#endif 571 572/* 573 * Look-up the routing entry to the peer of this inpcb. If no route 574 * is found and it cannot be allocated the return NULL. This routine 575 * is called by TCP routines that access the rmx structure and by tcp_mss 576 * to get the interface MTU. 577 */ 578struct rtentry * 579tcp_rtlookup(inp) 580 struct inpcb *inp; 581{ 582 struct route *ro; 583 struct rtentry *rt; 584 585 ro = &inp->inp_route; 586 rt = ro->ro_rt; 587 if (rt == NULL || !(rt->rt_flags & RTF_UP)) { 588 /* No route yet, so try to acquire one */ 589 if (inp->inp_faddr.s_addr != INADDR_ANY) { 590 ro->ro_dst.sa_family = AF_INET; 591 ro->ro_dst.sa_len = sizeof(ro->ro_dst); 592 ((struct sockaddr_in *) &ro->ro_dst)->sin_addr = 593 inp->inp_faddr; 594 rtalloc(ro); 595 rt = ro->ro_rt; 596 } 597 } 598 return rt; 599} 600 601/* 602 * Return a pointer to the cached information about the remote host. 603 * The cached information is stored in the protocol specific part of 604 * the route metrics. 605 */ 606struct rmxp_tao * 607tcp_gettaocache(inp) 608 struct inpcb *inp; 609{ 610 struct rtentry *rt = tcp_rtlookup(inp); 611 612 /* Make sure this is a host route and is up. */ 613 if (rt == NULL || 614 (rt->rt_flags & (RTF_UP|RTF_HOST)) != (RTF_UP|RTF_HOST)) 615 return NULL; 616 617 return rmx_taop(rt->rt_rmx); 618} 619 620/* 621 * Clear all the TAO cache entries, called from tcp_init. 622 * 623 * XXX 624 * This routine is just an empty one, because we assume that the routing 625 * routing tables are initialized at the same time when TCP, so there is 626 * nothing in the cache left over. 627 */ 628static void 629tcp_cleartaocache(void) 630{ } 631