1 /* 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)tcp_output.c 8.4 (Berkeley) 05/24/95 8 */ 9 10 #include <sys/param.h> 11 #include <sys/systm.h> 12 #include <sys/malloc.h> 13 #include <sys/mbuf.h> 14 #include <sys/protosw.h> 15 #include <sys/socket.h> 16 #include <sys/socketvar.h> 17 #include <sys/errno.h> 18 19 #include <net/route.h> 20 21 #include <netinet/in.h> 22 #include <netinet/in_systm.h> 23 #include <netinet/ip.h> 24 #include <netinet/in_pcb.h> 25 #include <netinet/ip_var.h> 26 #include <netinet/tcp.h> 27 #define TCPOUTFLAGS 28 #include <netinet/tcp_fsm.h> 29 #include <netinet/tcp_seq.h> 30 #include <netinet/tcp_timer.h> 31 #include <netinet/tcp_var.h> 32 #include <netinet/tcpip.h> 33 #include <netinet/tcp_debug.h> 34 35 #ifdef notyet 36 extern struct mbuf *m_copypack(); 37 #endif 38 39 40 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */ 41 42 /* 43 * Tcp output routine: figure out what should be sent and send it. 44 */ 45 int 46 tcp_output(tp) 47 register struct tcpcb *tp; 48 { 49 register struct socket *so = tp->t_inpcb->inp_socket; 50 register long len, win; 51 int off, flags, error; 52 register struct mbuf *m; 53 register struct tcpiphdr *ti; 54 u_char opt[MAX_TCPOPTLEN]; 55 unsigned optlen, hdrlen; 56 int idle, sendalot; 57 58 /* 59 * Determine length of data that should be transmitted, 60 * and flags that will be used. 61 * If there is some data or critical controls (SYN, RST) 62 * to send, then transmit; otherwise, investigate further. 63 */ 64 idle = (tp->snd_max == tp->snd_una); 65 if (idle && tp->t_idle >= tp->t_rxtcur) 66 /* 67 * We have been idle for "a while" and no acks are 68 * expected to clock out any data we send -- 69 * slow start to get ack "clock" running again. 70 */ 71 tp->snd_cwnd = tp->t_maxseg; 72 again: 73 sendalot = 0; 74 off = tp->snd_nxt - tp->snd_una; 75 win = min(tp->snd_wnd, tp->snd_cwnd); 76 77 flags = tcp_outflags[tp->t_state]; 78 /* 79 * If in persist timeout with window of 0, send 1 byte. 80 * Otherwise, if window is small but nonzero 81 * and timer expired, we will send what we can 82 * and go to transmit state. 83 */ 84 if (tp->t_force) { 85 if (win == 0) { 86 /* 87 * If we still have some data to send, then 88 * clear the FIN bit. Usually this would 89 * happen below when it realizes that we 90 * aren't sending all the data. However, 91 * if we have exactly 1 byte of unset data, 92 * then it won't clear the FIN bit below, 93 * and if we are in persist state, we wind 94 * up sending the packet without recording 95 * that we sent the FIN bit. 96 * 97 * We can't just blindly clear the FIN bit, 98 * because if we don't have any more data 99 * to send then the probe will be the FIN 100 * itself. 101 */ 102 if (off < so->so_snd.sb_cc) 103 flags &= ~TH_FIN; 104 win = 1; 105 } else { 106 tp->t_timer[TCPT_PERSIST] = 0; 107 tp->t_rxtshift = 0; 108 } 109 } 110 111 len = min(so->so_snd.sb_cc, win) - off; 112 113 if (len < 0) { 114 /* 115 * If FIN has been sent but not acked, 116 * but we haven't been called to retransmit, 117 * len will be -1. Otherwise, window shrank 118 * after we sent into it. If window shrank to 0, 119 * cancel pending retransmit and pull snd_nxt 120 * back to (closed) window. We will enter persist 121 * state below. If the window didn't close completely, 122 * just wait for an ACK. 123 */ 124 len = 0; 125 if (win == 0) { 126 tp->t_timer[TCPT_REXMT] = 0; 127 tp->snd_nxt = tp->snd_una; 128 } 129 } 130 if (len > tp->t_maxseg) { 131 len = tp->t_maxseg; 132 sendalot = 1; 133 } 134 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 135 flags &= ~TH_FIN; 136 137 win = sbspace(&so->so_rcv); 138 139 /* 140 * Sender silly window avoidance. If connection is idle 141 * and can send all data, a maximum segment, 142 * at least a maximum default-size segment do it, 143 * or are forced, do it; otherwise don't bother. 144 * If peer's buffer is tiny, then send 145 * when window is at least half open. 146 * If retransmitting (possibly after persist timer forced us 147 * to send into a small window), then must resend. 148 */ 149 if (len) { 150 if (len == tp->t_maxseg) 151 goto send; 152 if ((idle || tp->t_flags & TF_NODELAY) && 153 len + off >= so->so_snd.sb_cc) 154 goto send; 155 if (tp->t_force) 156 goto send; 157 if (len >= tp->max_sndwnd / 2) 158 goto send; 159 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 160 goto send; 161 } 162 163 /* 164 * Compare available window to amount of window 165 * known to peer (as advertised window less 166 * next expected input). If the difference is at least two 167 * max size segments, or at least 50% of the maximum possible 168 * window, then want to send a window update to peer. 169 */ 170 if (win > 0) { 171 /* 172 * "adv" is the amount we can increase the window, 173 * taking into account that we are limited by 174 * TCP_MAXWIN << tp->rcv_scale. 175 */ 176 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) - 177 (tp->rcv_adv - tp->rcv_nxt); 178 179 if (adv >= (long) (2 * tp->t_maxseg)) 180 goto send; 181 if (2 * adv >= (long) so->so_rcv.sb_hiwat) 182 goto send; 183 } 184 185 /* 186 * Send if we owe peer an ACK. 187 */ 188 if (tp->t_flags & TF_ACKNOW) 189 goto send; 190 if (flags & (TH_SYN|TH_RST)) 191 goto send; 192 if (SEQ_GT(tp->snd_up, tp->snd_una)) 193 goto send; 194 /* 195 * If our state indicates that FIN should be sent 196 * and we have not yet done so, or we're retransmitting the FIN, 197 * then we need to send. 198 */ 199 if (flags & TH_FIN && 200 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 201 goto send; 202 203 /* 204 * TCP window updates are not reliable, rather a polling protocol 205 * using ``persist'' packets is used to insure receipt of window 206 * updates. The three ``states'' for the output side are: 207 * idle not doing retransmits or persists 208 * persisting to move a small or zero window 209 * (re)transmitting and thereby not persisting 210 * 211 * tp->t_timer[TCPT_PERSIST] 212 * is set when we are in persist state. 213 * tp->t_force 214 * is set when we are called to send a persist packet. 215 * tp->t_timer[TCPT_REXMT] 216 * is set when we are retransmitting 217 * The output side is idle when both timers are zero. 218 * 219 * If send window is too small, there is data to transmit, and no 220 * retransmit or persist is pending, then go to persist state. 221 * If nothing happens soon, send when timer expires: 222 * if window is nonzero, transmit what we can, 223 * otherwise force out a byte. 224 */ 225 if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 && 226 tp->t_timer[TCPT_PERSIST] == 0) { 227 tp->t_rxtshift = 0; 228 tcp_setpersist(tp); 229 } 230 231 /* 232 * No reason to send a segment, just return. 233 */ 234 return (0); 235 236 send: 237 /* 238 * Before ESTABLISHED, force sending of initial options 239 * unless TCP set not to do any options. 240 * NOTE: we assume that the IP/TCP header plus TCP options 241 * always fit in a single mbuf, leaving room for a maximum 242 * link header, i.e. 243 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN 244 */ 245 optlen = 0; 246 hdrlen = sizeof (struct tcpiphdr); 247 if (flags & TH_SYN) { 248 tp->snd_nxt = tp->iss; 249 if ((tp->t_flags & TF_NOOPT) == 0) { 250 u_short mss; 251 252 opt[0] = TCPOPT_MAXSEG; 253 opt[1] = 4; 254 mss = htons((u_short) tcp_mss(tp, 0)); 255 bcopy((caddr_t)&mss, (caddr_t)(opt + 2), sizeof(mss)); 256 optlen = 4; 257 258 if ((tp->t_flags & TF_REQ_SCALE) && 259 ((flags & TH_ACK) == 0 || 260 (tp->t_flags & TF_RCVD_SCALE))) { 261 *((u_long *) (opt + optlen)) = htonl( 262 TCPOPT_NOP << 24 | 263 TCPOPT_WINDOW << 16 | 264 TCPOLEN_WINDOW << 8 | 265 tp->request_r_scale); 266 optlen += 4; 267 } 268 } 269 } 270 271 /* 272 * Send a timestamp and echo-reply if this is a SYN and our side 273 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side 274 * and our peer have sent timestamps in our SYN's. 275 */ 276 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP && 277 (flags & TH_RST) == 0 && 278 ((flags & (TH_SYN|TH_ACK)) == TH_SYN || 279 (tp->t_flags & TF_RCVD_TSTMP))) { 280 u_long *lp = (u_long *)(opt + optlen); 281 282 /* Form timestamp option as shown in appendix A of RFC 1323. */ 283 *lp++ = htonl(TCPOPT_TSTAMP_HDR); 284 *lp++ = htonl(tcp_now); 285 *lp = htonl(tp->ts_recent); 286 optlen += TCPOLEN_TSTAMP_APPA; 287 } 288 289 hdrlen += optlen; 290 291 /* 292 * Adjust data length if insertion of options will 293 * bump the packet length beyond the t_maxseg length. 294 */ 295 if (len > tp->t_maxseg - optlen) { 296 len = tp->t_maxseg - optlen; 297 sendalot = 1; 298 flags &= ~TH_FIN; 299 } 300 301 302 #ifdef DIAGNOSTIC 303 if (max_linkhdr + hdrlen > MHLEN) 304 panic("tcphdr too big"); 305 #endif 306 307 /* 308 * Grab a header mbuf, attaching a copy of data to 309 * be transmitted, and initialize the header from 310 * the template for sends on this connection. 311 */ 312 if (len) { 313 if (tp->t_force && len == 1) 314 tcpstat.tcps_sndprobe++; 315 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 316 tcpstat.tcps_sndrexmitpack++; 317 tcpstat.tcps_sndrexmitbyte += len; 318 } else { 319 tcpstat.tcps_sndpack++; 320 tcpstat.tcps_sndbyte += len; 321 } 322 #ifdef notyet 323 if ((m = m_copypack(so->so_snd.sb_mb, off, 324 (int)len, max_linkhdr + hdrlen)) == 0) { 325 error = ENOBUFS; 326 goto out; 327 } 328 /* 329 * m_copypack left space for our hdr; use it. 330 */ 331 m->m_len += hdrlen; 332 m->m_data -= hdrlen; 333 #else 334 MGETHDR(m, M_DONTWAIT, MT_HEADER); 335 if (m == NULL) { 336 error = ENOBUFS; 337 goto out; 338 } 339 m->m_data += max_linkhdr; 340 m->m_len = hdrlen; 341 if (len <= MHLEN - hdrlen - max_linkhdr) { 342 m_copydata(so->so_snd.sb_mb, off, (int) len, 343 mtod(m, caddr_t) + hdrlen); 344 m->m_len += len; 345 } else { 346 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len); 347 if (m->m_next == 0) { 348 (void) m_free(m); 349 error = ENOBUFS; 350 goto out; 351 } 352 } 353 #endif 354 /* 355 * If we're sending everything we've got, set PUSH. 356 * (This will keep happy those implementations which only 357 * give data to the user when a buffer fills or 358 * a PUSH comes in.) 359 */ 360 if (off + len == so->so_snd.sb_cc) 361 flags |= TH_PUSH; 362 } else { 363 if (tp->t_flags & TF_ACKNOW) 364 tcpstat.tcps_sndacks++; 365 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 366 tcpstat.tcps_sndctrl++; 367 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 368 tcpstat.tcps_sndurg++; 369 else 370 tcpstat.tcps_sndwinup++; 371 372 MGETHDR(m, M_DONTWAIT, MT_HEADER); 373 if (m == NULL) { 374 error = ENOBUFS; 375 goto out; 376 } 377 m->m_data += max_linkhdr; 378 m->m_len = hdrlen; 379 } 380 m->m_pkthdr.rcvif = (struct ifnet *)0; 381 ti = mtod(m, struct tcpiphdr *); 382 if (tp->t_template == 0) 383 panic("tcp_output"); 384 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 385 386 /* 387 * Fill in fields, remembering maximum advertised 388 * window for use in delaying messages about window sizes. 389 * If resending a FIN, be sure not to use a new sequence number. 390 */ 391 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 392 tp->snd_nxt == tp->snd_max) 393 tp->snd_nxt--; 394 /* 395 * If we are doing retransmissions, then snd_nxt will 396 * not reflect the first unsent octet. For ACK only 397 * packets, we do not want the sequence number of the 398 * retransmitted packet, we want the sequence number 399 * of the next unsent octet. So, if there is no data 400 * (and no SYN or FIN), use snd_max instead of snd_nxt 401 * when filling in ti_seq. But if we are in persist 402 * state, snd_max might reflect one byte beyond the 403 * right edge of the window, so use snd_nxt in that 404 * case, since we know we aren't doing a retransmission. 405 * (retransmit and persist are mutually exclusive...) 406 */ 407 if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST]) 408 ti->ti_seq = htonl(tp->snd_nxt); 409 else 410 ti->ti_seq = htonl(tp->snd_max); 411 ti->ti_ack = htonl(tp->rcv_nxt); 412 if (optlen) { 413 bcopy((caddr_t)opt, (caddr_t)(ti + 1), optlen); 414 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 415 } 416 ti->ti_flags = flags; 417 /* 418 * Calculate receive window. Don't shrink window, 419 * but avoid silly window syndrome. 420 */ 421 if (win < (long)(so->so_rcv.sb_hiwat / 4) && win < (long)tp->t_maxseg) 422 win = 0; 423 if (win > (long)TCP_MAXWIN << tp->rcv_scale) 424 win = (long)TCP_MAXWIN << tp->rcv_scale; 425 if (win < (long)(tp->rcv_adv - tp->rcv_nxt)) 426 win = (long)(tp->rcv_adv - tp->rcv_nxt); 427 ti->ti_win = htons((u_short) (win>>tp->rcv_scale)); 428 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 429 ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 430 ti->ti_flags |= TH_URG; 431 } else 432 /* 433 * If no urgent pointer to send, then we pull 434 * the urgent pointer to the left edge of the send window 435 * so that it doesn't drift into the send window on sequence 436 * number wraparound. 437 */ 438 tp->snd_up = tp->snd_una; /* drag it along */ 439 440 /* 441 * Put TCP length in extended header, and then 442 * checksum extended header and data. 443 */ 444 if (len + optlen) 445 ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + 446 optlen + len)); 447 ti->ti_sum = in_cksum(m, (int)(hdrlen + len)); 448 449 /* 450 * In transmit state, time the transmission and arrange for 451 * the retransmit. In persist state, just set snd_max. 452 */ 453 if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) { 454 tcp_seq startseq = tp->snd_nxt; 455 456 /* 457 * Advance snd_nxt over sequence space of this segment. 458 */ 459 if (flags & (TH_SYN|TH_FIN)) { 460 if (flags & TH_SYN) 461 tp->snd_nxt++; 462 if (flags & TH_FIN) { 463 tp->snd_nxt++; 464 tp->t_flags |= TF_SENTFIN; 465 } 466 } 467 tp->snd_nxt += len; 468 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 469 tp->snd_max = tp->snd_nxt; 470 /* 471 * Time this transmission if not a retransmission and 472 * not currently timing anything. 473 */ 474 if (tp->t_rtt == 0) { 475 tp->t_rtt = 1; 476 tp->t_rtseq = startseq; 477 tcpstat.tcps_segstimed++; 478 } 479 } 480 481 /* 482 * Set retransmit timer if not currently set, 483 * and not doing an ack or a keep-alive probe. 484 * Initial value for retransmit timer is smoothed 485 * round-trip time + 2 * round-trip time variance. 486 * Initialize shift counter which is used for backoff 487 * of retransmit time. 488 */ 489 if (tp->t_timer[TCPT_REXMT] == 0 && 490 tp->snd_nxt != tp->snd_una) { 491 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 492 if (tp->t_timer[TCPT_PERSIST]) { 493 tp->t_timer[TCPT_PERSIST] = 0; 494 tp->t_rxtshift = 0; 495 } 496 } 497 } else 498 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 499 tp->snd_max = tp->snd_nxt + len; 500 501 /* 502 * Trace. 503 */ 504 if (so->so_options & SO_DEBUG) 505 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 506 507 /* 508 * Fill in IP length and desired time to live and 509 * send to IP level. There should be a better way 510 * to handle ttl and tos; we could keep them in 511 * the template, but need a way to checksum without them. 512 */ 513 m->m_pkthdr.len = hdrlen + len; 514 #ifdef TUBA 515 if (tp->t_tuba_pcb) 516 error = tuba_output(m, tp); 517 else 518 #endif 519 { 520 ((struct ip *)ti)->ip_len = m->m_pkthdr.len; 521 ((struct ip *)ti)->ip_ttl = tp->t_inpcb->inp_ip.ip_ttl; /* XXX */ 522 ((struct ip *)ti)->ip_tos = tp->t_inpcb->inp_ip.ip_tos; /* XXX */ 523 #if BSD >= 43 524 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 525 so->so_options & SO_DONTROUTE, 0); 526 #else 527 error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route, 528 so->so_options & SO_DONTROUTE); 529 #endif 530 } 531 if (error) { 532 out: 533 if (error == ENOBUFS) { 534 tcp_quench(tp->t_inpcb, 0); 535 return (0); 536 } 537 if ((error == EHOSTUNREACH || error == ENETDOWN) 538 && TCPS_HAVERCVDSYN(tp->t_state)) { 539 tp->t_softerror = error; 540 return (0); 541 } 542 return (error); 543 } 544 tcpstat.tcps_sndtotal++; 545 546 /* 547 * Data sent (as far as we can tell). 548 * If this advertises a larger window than any other segment, 549 * then remember the size of the advertised window. 550 * Any pending ACK has now been sent. 551 */ 552 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 553 tp->rcv_adv = tp->rcv_nxt + win; 554 tp->last_ack_sent = tp->rcv_nxt; 555 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 556 if (sendalot) 557 goto again; 558 return (0); 559 } 560 561 void 562 tcp_setpersist(tp) 563 register struct tcpcb *tp; 564 { 565 register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 566 567 if (tp->t_timer[TCPT_REXMT]) 568 panic("tcp_output REXMT"); 569 /* 570 * Start/restart persistance timer. 571 */ 572 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 573 t * tcp_backoff[tp->t_rxtshift], 574 TCPTV_PERSMIN, TCPTV_PERSMAX); 575 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 576 tp->t_rxtshift++; 577 } 578