1 /* 2 * Copyright (c) 1982, 1986 Regents of the University of California. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms are permitted 6 * provided that this notice is preserved and that due credit is given 7 * to the University of California at Berkeley. The name of the University 8 * may not be used to endorse or promote products derived from this 9 * software without specific prior written permission. This software 10 * is provided ``as is'' without express or implied warranty. 11 * 12 * @(#)tcp_output.c 7.13 (Berkeley) 02/07/88 13 */ 14 15 #include "param.h" 16 #include "systm.h" 17 #include "mbuf.h" 18 #include "protosw.h" 19 #include "socket.h" 20 #include "socketvar.h" 21 #include "errno.h" 22 23 #include "../net/route.h" 24 25 #include "in.h" 26 #include "in_pcb.h" 27 #include "in_systm.h" 28 #include "ip.h" 29 #include "ip_var.h" 30 #include "tcp.h" 31 #define TCPOUTFLAGS 32 #include "tcp_fsm.h" 33 #include "tcp_seq.h" 34 #include "tcp_timer.h" 35 #include "tcp_var.h" 36 #include "tcpip.h" 37 #include "tcp_debug.h" 38 39 /* 40 * Initial options. 41 */ 42 u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, }; 43 44 /* 45 * Tcp output routine: figure out what should be sent and send it. 46 */ 47 tcp_output(tp) 48 register struct tcpcb *tp; 49 { 50 register struct socket *so = tp->t_inpcb->inp_socket; 51 register int len, win; 52 struct mbuf *m0; 53 int off, flags, error; 54 register struct mbuf *m; 55 register struct tcpiphdr *ti; 56 u_char *opt; 57 unsigned optlen = 0; 58 int idle, sendalot; 59 60 /* 61 * Determine length of data that should be transmitted, 62 * and flags that will be used. 63 * If there is some data or critical controls (SYN, RST) 64 * to send, then transmit; otherwise, investigate further. 65 */ 66 idle = (tp->snd_max == tp->snd_una); 67 again: 68 sendalot = 0; 69 off = tp->snd_nxt - tp->snd_una; 70 win = MIN(tp->snd_wnd, tp->snd_cwnd); 71 72 /* 73 * If in persist timeout with window of 0, send 1 byte. 74 * Otherwise, if window is small but nonzero 75 * and timer expired, we will send what we can 76 * and go to transmit state. 77 */ 78 if (tp->t_force) { 79 if (win == 0) 80 win = 1; 81 else { 82 tp->t_timer[TCPT_PERSIST] = 0; 83 tp->t_rxtshift = 0; 84 } 85 } 86 87 len = MIN(so->so_snd.sb_cc, win) - off; 88 flags = tcp_outflags[tp->t_state]; 89 90 if (len < 0) { 91 /* 92 * If FIN has been sent but not acked, 93 * but we haven't been called to retransmit, 94 * len will be -1. Otherwise, window shrank 95 * after we sent into it. If window shrank to 0, 96 * cancel pending retransmit and pull snd_nxt 97 * back to (closed) window. We will enter persist 98 * state below. If the window didn't close completely, 99 * just wait for an ACK. 100 */ 101 len = 0; 102 if (win == 0) { 103 tp->t_timer[TCPT_REXMT] = 0; 104 tp->snd_nxt = tp->snd_una; 105 } 106 } 107 if (len > tp->t_maxseg) { 108 len = tp->t_maxseg; 109 sendalot = 1; 110 } 111 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 112 flags &= ~TH_FIN; 113 win = sbspace(&so->so_rcv); 114 115 116 /* 117 * If our state indicates that FIN should be sent 118 * and we have not yet done so, or we're retransmitting the FIN, 119 * then we need to send. 120 */ 121 if (flags & TH_FIN && 122 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 123 goto send; 124 /* 125 * Send if we owe peer an ACK. 126 */ 127 if (tp->t_flags & TF_ACKNOW) 128 goto send; 129 if (flags & (TH_SYN|TH_RST)) 130 goto send; 131 if (SEQ_GT(tp->snd_up, tp->snd_una)) 132 goto send; 133 134 /* 135 * Sender silly window avoidance. If connection is idle 136 * and can send all data, a maximum segment, 137 * at least a maximum default-size segment do it, 138 * or are forced, do it; otherwise don't bother. 139 * If peer's buffer is tiny, then send 140 * when window is at least half open. 141 * If retransmitting (possibly after persist timer forced us 142 * to send into a small window), then must resend. 143 */ 144 if (len) { 145 if (len == tp->t_maxseg) 146 goto send; 147 if ((idle || tp->t_flags & TF_NODELAY) && 148 len + off >= so->so_snd.sb_cc) 149 goto send; 150 if (tp->t_force) 151 goto send; 152 if (len >= tp->max_sndwnd / 2) 153 goto send; 154 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 155 goto send; 156 } 157 158 /* 159 * Compare available window to amount of window 160 * known to peer (as advertised window less 161 * next expected input). If the difference is at least two 162 * max size segments or at least 35% of the maximum possible 163 * window, then want to send a window update to peer. 164 */ 165 if (win > 0) { 166 int adv = win - (tp->rcv_adv - tp->rcv_nxt); 167 168 if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg) 169 goto send; 170 if (100 * adv / so->so_rcv.sb_hiwat >= 35) 171 goto send; 172 } 173 174 /* 175 * TCP window updates are not reliable, rather a polling protocol 176 * using ``persist'' packets is used to insure receipt of window 177 * updates. The three ``states'' for the output side are: 178 * idle not doing retransmits or persists 179 * persisting to move a small or zero window 180 * (re)transmitting and thereby not persisting 181 * 182 * tp->t_timer[TCPT_PERSIST] 183 * is set when we are in persist state. 184 * tp->t_force 185 * is set when we are called to send a persist packet. 186 * tp->t_timer[TCPT_REXMT] 187 * is set when we are retransmitting 188 * The output side is idle when both timers are zero. 189 * 190 * If send window is too small, there is data to transmit, and no 191 * retransmit or persist is pending, then go to persist state. 192 * If nothing happens soon, send when timer expires: 193 * if window is nonzero, transmit what we can, 194 * otherwise force out a byte. 195 */ 196 if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 && 197 tp->t_timer[TCPT_PERSIST] == 0) { 198 tp->t_rxtshift = 0; 199 tcp_setpersist(tp); 200 } 201 202 /* 203 * No reason to send a segment, just return. 204 */ 205 return (0); 206 207 send: 208 /* 209 * Grab a header mbuf, attaching a copy of data to 210 * be transmitted, and initialize the header from 211 * the template for sends on this connection. 212 */ 213 MGET(m, M_DONTWAIT, MT_HEADER); 214 if (m == NULL) 215 return (ENOBUFS); 216 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 217 m->m_len = sizeof (struct tcpiphdr); 218 if (len) { 219 if (tp->t_force && len == 1) 220 tcpstat.tcps_sndprobe++; 221 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 222 tcpstat.tcps_sndrexmitpack++; 223 tcpstat.tcps_sndrexmitbyte += len; 224 } else { 225 tcpstat.tcps_sndpack++; 226 tcpstat.tcps_sndbyte += len; 227 } 228 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 229 if (m->m_next == 0) 230 len = 0; 231 } else if (tp->t_flags & TF_ACKNOW) 232 tcpstat.tcps_sndacks++; 233 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 234 tcpstat.tcps_sndctrl++; 235 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 236 tcpstat.tcps_sndurg++; 237 else 238 tcpstat.tcps_sndwinup++; 239 240 ti = mtod(m, struct tcpiphdr *); 241 if (tp->t_template == 0) 242 panic("tcp_output"); 243 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 244 245 /* 246 * Fill in fields, remembering maximum advertised 247 * window for use in delaying messages about window sizes. 248 * If resending a FIN, be sure not to use a new sequence number. 249 */ 250 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 251 tp->snd_nxt == tp->snd_max) 252 tp->snd_nxt--; 253 ti->ti_seq = htonl(tp->snd_nxt); 254 ti->ti_ack = htonl(tp->rcv_nxt); 255 /* 256 * Before ESTABLISHED, force sending of initial options 257 * unless TCP set to not do any options. 258 */ 259 opt = NULL; 260 if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) { 261 u_short mss; 262 263 mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp)); 264 if (mss > IP_MSS - sizeof(struct tcpiphdr)) { 265 opt = tcp_initopt; 266 optlen = sizeof (tcp_initopt); 267 *(u_short *)(opt + 2) = htons(mss); 268 } 269 } 270 if (opt) { 271 m0 = m->m_next; 272 m->m_next = m_get(M_DONTWAIT, MT_DATA); 273 if (m->m_next == 0) { 274 (void) m_free(m); 275 m_freem(m0); 276 return (ENOBUFS); 277 } 278 m->m_next->m_next = m0; 279 m0 = m->m_next; 280 m0->m_len = optlen; 281 bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen); 282 opt = (u_char *)(mtod(m0, caddr_t) + optlen); 283 while (m0->m_len & 0x3) { 284 *opt++ = TCPOPT_EOL; 285 m0->m_len++; 286 } 287 optlen = m0->m_len; 288 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 289 } 290 ti->ti_flags = flags; 291 /* 292 * Calculate receive window. Don't shrink window, 293 * but avoid silly window syndrome. 294 */ 295 if (win < so->so_rcv.sb_hiwat / 4 && win < tp->t_maxseg) 296 win = 0; 297 if (win < (int)(tp->rcv_adv - tp->rcv_nxt)) 298 win = (int)(tp->rcv_adv - tp->rcv_nxt); 299 ti->ti_win = htons((u_short)win); 300 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 301 ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 302 ti->ti_flags |= TH_URG; 303 } else 304 /* 305 * If no urgent pointer to send, then we pull 306 * the urgent pointer to the left edge of the send window 307 * so that it doesn't drift into the send window on sequence 308 * number wraparound. 309 */ 310 tp->snd_up = tp->snd_una; /* drag it along */ 311 /* 312 * If anything to send and we can send it all, set PUSH. 313 * (This will keep happy those implementations which only 314 * give data to the user when a buffer fills or a PUSH comes in.) 315 */ 316 if (len && off+len == so->so_snd.sb_cc) 317 ti->ti_flags |= TH_PUSH; 318 319 /* 320 * Put TCP length in extended header, and then 321 * checksum extended header and data. 322 */ 323 if (len + optlen) 324 ti->ti_len = htons((u_short)(sizeof(struct tcphdr) + 325 optlen + len)); 326 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len); 327 328 /* 329 * In transmit state, time the transmission and arrange for 330 * the retransmit. In persist state, just set snd_max. 331 */ 332 if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) { 333 tcp_seq startseq = tp->snd_nxt; 334 335 /* 336 * Advance snd_nxt over sequence space of this segment. 337 */ 338 if (flags & TH_SYN) 339 tp->snd_nxt++; 340 if (flags & TH_FIN) { 341 tp->snd_nxt++; 342 tp->t_flags |= TF_SENTFIN; 343 } 344 tp->snd_nxt += len; 345 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 346 tp->snd_max = tp->snd_nxt; 347 /* 348 * Time this transmission if not a retransmission and 349 * not currently timing anything. 350 */ 351 if (tp->t_rtt == 0) { 352 tp->t_rtt = 1; 353 tp->t_rtseq = startseq; 354 tcpstat.tcps_segstimed++; 355 } 356 } 357 358 /* 359 * Set retransmit timer if not currently set, 360 * and not doing an ack or a keep-alive probe. 361 * Initial value for retransmit timer is smoothed 362 * round-trip time + 2 * round-trip time variance. 363 * Initialize shift counter which is used for backoff 364 * of retransmit time. 365 */ 366 if (tp->t_timer[TCPT_REXMT] == 0 && 367 tp->snd_nxt != tp->snd_una) { 368 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 369 if (tp->t_timer[TCPT_PERSIST]) { 370 tp->t_timer[TCPT_PERSIST] = 0; 371 tp->t_rxtshift = 0; 372 } 373 } 374 } else 375 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 376 tp->snd_max = tp->snd_nxt + len; 377 378 /* 379 * Trace. 380 */ 381 if (so->so_options & SO_DEBUG) 382 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 383 384 /* 385 * Fill in IP length and desired time to live and 386 * send to IP level. 387 */ 388 ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len; 389 ((struct ip *)ti)->ip_ttl = TCP_TTL; 390 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 391 so->so_options & SO_DONTROUTE); 392 if (error) { 393 if (error == ENOBUFS) { 394 tcp_quench(tp->t_inpcb); 395 return (0); 396 } 397 return (error); 398 } 399 tcpstat.tcps_sndtotal++; 400 401 /* 402 * Data sent (as far as we can tell). 403 * If this advertises a larger window than any other segment, 404 * then remember the size of the advertised window. 405 * Any pending ACK has now been sent. 406 */ 407 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 408 tp->rcv_adv = tp->rcv_nxt + win; 409 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 410 if (sendalot) 411 goto again; 412 return (0); 413 } 414 415 tcp_setpersist(tp) 416 register struct tcpcb *tp; 417 { 418 register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 419 420 if (tp->t_timer[TCPT_REXMT]) 421 panic("tcp_output REXMT"); 422 /* 423 * Start/restart persistance timer. 424 */ 425 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 426 t * tcp_backoff[tp->t_rxtshift], 427 TCPTV_PERSMIN, TCPTV_PERSMAX); 428 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 429 tp->t_rxtshift++; 430 } 431