1 /* 2 * Copyright (c) 1982, 1986 Regents of the University of California. 3 * All rights reserved. The Berkeley software License Agreement 4 * specifies the terms and conditions for redistribution. 5 * 6 * @(#)tcp_output.c 7.11 (Berkeley) 12/07/87 7 */ 8 9 #include "param.h" 10 #include "systm.h" 11 #include "mbuf.h" 12 #include "protosw.h" 13 #include "socket.h" 14 #include "socketvar.h" 15 #include "errno.h" 16 17 #include "../net/route.h" 18 19 #include "in.h" 20 #include "in_pcb.h" 21 #include "in_systm.h" 22 #include "ip.h" 23 #include "ip_var.h" 24 #include "tcp.h" 25 #define TCPOUTFLAGS 26 #include "tcp_fsm.h" 27 #include "tcp_seq.h" 28 #include "tcp_timer.h" 29 #include "tcp_var.h" 30 #include "tcpip.h" 31 #include "tcp_debug.h" 32 33 /* 34 * Initial options. 35 */ 36 u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, }; 37 38 /* 39 * Tcp output routine: figure out what should be sent and send it. 40 */ 41 tcp_output(tp) 42 register struct tcpcb *tp; 43 { 44 register struct socket *so = tp->t_inpcb->inp_socket; 45 register int len, win; 46 struct mbuf *m0; 47 int off, flags, error; 48 register struct mbuf *m; 49 register struct tcpiphdr *ti; 50 u_char *opt; 51 unsigned optlen = 0; 52 int idle, sendalot; 53 54 /* 55 * Determine length of data that should be transmitted, 56 * and flags that will be used. 57 * If there is some data or critical controls (SYN, RST) 58 * to send, then transmit; otherwise, investigate further. 59 */ 60 idle = (tp->snd_max == tp->snd_una); 61 again: 62 sendalot = 0; 63 off = tp->snd_nxt - tp->snd_una; 64 win = MIN(tp->snd_wnd, tp->snd_cwnd); 65 66 /* 67 * If in persist timeout with window of 0, send 1 byte. 68 * Otherwise, if window is small but nonzero 69 * and timer expired, we will send what we can 70 * and go to transmit state. 71 */ 72 if (tp->t_force) { 73 if (win == 0) 74 win = 1; 75 else { 76 tp->t_timer[TCPT_PERSIST] = 0; 77 tp->t_rxtshift = 0; 78 } 79 } 80 81 len = MIN(so->so_snd.sb_cc, win) - off; 82 flags = tcp_outflags[tp->t_state]; 83 84 if (len < 0) { 85 /* 86 * If FIN has been sent but not acked, 87 * but we haven't been called to retransmit, 88 * len will be -1. Otherwise, window shrank 89 * after we sent into it. If window shrank to 0, 90 * cancel pending retransmit and pull snd_nxt 91 * back to (closed) window. We will enter persist 92 * state below. If the window didn't close completely, 93 * just wait for an ACK. 94 */ 95 len = 0; 96 if (win == 0) { 97 tp->t_timer[TCPT_REXMT] = 0; 98 tp->snd_nxt = tp->snd_una; 99 } 100 } 101 if (len > tp->t_maxseg) { 102 len = tp->t_maxseg; 103 sendalot = 1; 104 } 105 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc)) 106 flags &= ~TH_FIN; 107 win = sbspace(&so->so_rcv); 108 109 110 /* 111 * If our state indicates that FIN should be sent 112 * and we have not yet done so, or we're retransmitting the FIN, 113 * then we need to send. 114 */ 115 if (flags & TH_FIN && 116 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una)) 117 goto send; 118 /* 119 * Send if we owe peer an ACK. 120 */ 121 if (tp->t_flags & TF_ACKNOW) 122 goto send; 123 if (flags & (TH_SYN|TH_RST)) 124 goto send; 125 if (SEQ_GT(tp->snd_up, tp->snd_una)) 126 goto send; 127 128 /* 129 * Sender silly window avoidance. If connection is idle 130 * and can send all data, a maximum segment, 131 * at least a maximum default-size segment do it, 132 * or are forced, do it; otherwise don't bother. 133 * If peer's buffer is tiny, then send 134 * when window is at least half open. 135 * If retransmitting (possibly after persist timer forced us 136 * to send into a small window), then must resend. 137 */ 138 if (len) { 139 if (len == tp->t_maxseg) 140 goto send; 141 if ((idle || tp->t_flags & TF_NODELAY) && 142 len + off >= so->so_snd.sb_cc) 143 goto send; 144 if (tp->t_force) 145 goto send; 146 if (len >= tp->max_sndwnd / 2) 147 goto send; 148 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) 149 goto send; 150 } 151 152 /* 153 * Compare available window to amount of window 154 * known to peer (as advertised window less 155 * next expected input). If the difference is at least two 156 * max size segments or at least 35% of the maximum possible 157 * window, then want to send a window update to peer. 158 */ 159 if (win > 0) { 160 int adv = win - (tp->rcv_adv - tp->rcv_nxt); 161 162 if (so->so_rcv.sb_cc == 0 && adv >= 2 * tp->t_maxseg) 163 goto send; 164 if (100 * adv / so->so_rcv.sb_hiwat >= 35) 165 goto send; 166 } 167 168 /* 169 * TCP window updates are not reliable, rather a polling protocol 170 * using ``persist'' packets is used to insure receipt of window 171 * updates. The three ``states'' for the output side are: 172 * idle not doing retransmits or persists 173 * persisting to move a small or zero window 174 * (re)transmitting and thereby not persisting 175 * 176 * tp->t_timer[TCPT_PERSIST] 177 * is set when we are in persist state. 178 * tp->t_force 179 * is set when we are called to send a persist packet. 180 * tp->t_timer[TCPT_REXMT] 181 * is set when we are retransmitting 182 * The output side is idle when both timers are zero. 183 * 184 * If send window is too small, there is data to transmit, and no 185 * retransmit or persist is pending, then go to persist state. 186 * If nothing happens soon, send when timer expires: 187 * if window is nonzero, transmit what we can, 188 * otherwise force out a byte. 189 */ 190 if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 && 191 tp->t_timer[TCPT_PERSIST] == 0) { 192 tp->t_rxtshift = 0; 193 tcp_setpersist(tp); 194 } 195 196 /* 197 * No reason to send a segment, just return. 198 */ 199 return (0); 200 201 send: 202 /* 203 * Grab a header mbuf, attaching a copy of data to 204 * be transmitted, and initialize the header from 205 * the template for sends on this connection. 206 */ 207 MGET(m, M_DONTWAIT, MT_HEADER); 208 if (m == NULL) 209 return (ENOBUFS); 210 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 211 m->m_len = sizeof (struct tcpiphdr); 212 if (len) { 213 if (tp->t_force && len == 1) 214 tcpstat.tcps_sndprobe++; 215 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) { 216 tcpstat.tcps_sndrexmitpack++; 217 tcpstat.tcps_sndrexmitbyte += len; 218 } else { 219 tcpstat.tcps_sndpack++; 220 tcpstat.tcps_sndbyte += len; 221 } 222 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 223 if (m->m_next == 0) 224 len = 0; 225 } else if (tp->t_flags & TF_ACKNOW) 226 tcpstat.tcps_sndacks++; 227 else if (flags & (TH_SYN|TH_FIN|TH_RST)) 228 tcpstat.tcps_sndctrl++; 229 else if (SEQ_GT(tp->snd_up, tp->snd_una)) 230 tcpstat.tcps_sndurg++; 231 else 232 tcpstat.tcps_sndwinup++; 233 234 ti = mtod(m, struct tcpiphdr *); 235 if (tp->t_template == 0) 236 panic("tcp_output"); 237 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 238 239 /* 240 * Fill in fields, remembering maximum advertised 241 * window for use in delaying messages about window sizes. 242 * If resending a FIN, be sure not to use a new sequence number. 243 */ 244 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN && 245 tp->snd_nxt == tp->snd_max) 246 tp->snd_nxt--; 247 ti->ti_seq = htonl(tp->snd_nxt); 248 ti->ti_ack = htonl(tp->rcv_nxt); 249 /* 250 * Before ESTABLISHED, force sending of initial options 251 * unless TCP set to not do any options. 252 */ 253 opt = NULL; 254 if (flags & TH_SYN && (tp->t_flags & TF_NOOPT) == 0) { 255 u_short mss; 256 257 mss = MIN(so->so_rcv.sb_hiwat / 2, tcp_mss(tp)); 258 if (mss > IP_MSS - sizeof(struct tcpiphdr)) { 259 opt = tcp_initopt; 260 optlen = sizeof (tcp_initopt); 261 *(u_short *)(opt + 2) = htons(mss); 262 } 263 } 264 if (opt) { 265 m0 = m->m_next; 266 m->m_next = m_get(M_DONTWAIT, MT_DATA); 267 if (m->m_next == 0) { 268 (void) m_free(m); 269 m_freem(m0); 270 return (ENOBUFS); 271 } 272 m->m_next->m_next = m0; 273 m0 = m->m_next; 274 m0->m_len = optlen; 275 bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen); 276 opt = (u_char *)(mtod(m0, caddr_t) + optlen); 277 while (m0->m_len & 0x3) { 278 *opt++ = TCPOPT_EOL; 279 m0->m_len++; 280 } 281 optlen = m0->m_len; 282 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 283 } 284 ti->ti_flags = flags; 285 /* 286 * Calculate receive window. Don't shrink window, 287 * but avoid silly window syndrome. 288 */ 289 if (win < so->so_rcv.sb_hiwat / 4 && win < tp->t_maxseg) 290 win = 0; 291 if (win < (int)(tp->rcv_adv - tp->rcv_nxt)) 292 win = (int)(tp->rcv_adv - tp->rcv_nxt); 293 ti->ti_win = htons((u_short)win); 294 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 295 ti->ti_urp = htons((u_short)(tp->snd_up - tp->snd_nxt)); 296 ti->ti_flags |= TH_URG; 297 } else 298 /* 299 * If no urgent pointer to send, then we pull 300 * the urgent pointer to the left edge of the send window 301 * so that it doesn't drift into the send window on sequence 302 * number wraparound. 303 */ 304 tp->snd_up = tp->snd_una; /* drag it along */ 305 /* 306 * If anything to send and we can send it all, set PUSH. 307 * (This will keep happy those implementations which only 308 * give data to the user when a buffer fills or a PUSH comes in.) 309 */ 310 if (len && off+len == so->so_snd.sb_cc) 311 ti->ti_flags |= TH_PUSH; 312 313 /* 314 * Put TCP length in extended header, and then 315 * checksum extended header and data. 316 */ 317 if (len + optlen) 318 ti->ti_len = htons((u_short)(sizeof(struct tcphdr) + 319 optlen + len)); 320 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len); 321 322 /* 323 * In transmit state, time the transmission and arrange for 324 * the retransmit. In persist state, just set snd_max. 325 */ 326 if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) { 327 tcp_seq startseq = tp->snd_nxt; 328 329 /* 330 * Advance snd_nxt over sequence space of this segment. 331 */ 332 if (flags & TH_SYN) 333 tp->snd_nxt++; 334 if (flags & TH_FIN) { 335 tp->snd_nxt++; 336 tp->t_flags |= TF_SENTFIN; 337 } 338 tp->snd_nxt += len; 339 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) { 340 tp->snd_max = tp->snd_nxt; 341 /* 342 * Time this transmission if not a retransmission and 343 * not currently timing anything. 344 */ 345 if (tp->t_rtt == 0) { 346 tp->t_rtt = 1; 347 tp->t_rtseq = startseq; 348 tcpstat.tcps_segstimed++; 349 } 350 } 351 352 /* 353 * Set retransmit timer if not currently set, 354 * and not doing an ack or a keep-alive probe. 355 * Initial value for retransmit timer is smoothed 356 * round-trip time + 2 * round-trip time variance. 357 * Initialize shift counter which is used for backoff 358 * of retransmit time. 359 */ 360 if (tp->t_timer[TCPT_REXMT] == 0 && 361 tp->snd_nxt != tp->snd_una) { 362 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 363 if (tp->t_timer[TCPT_PERSIST]) { 364 tp->t_timer[TCPT_PERSIST] = 0; 365 tp->t_rxtshift = 0; 366 } 367 } 368 } else 369 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max)) 370 tp->snd_max = tp->snd_nxt + len; 371 372 /* 373 * Trace. 374 */ 375 if (so->so_options & SO_DEBUG) 376 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 377 378 /* 379 * Fill in IP length and desired time to live and 380 * send to IP level. 381 */ 382 ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len; 383 ((struct ip *)ti)->ip_ttl = TCP_TTL; 384 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route, 385 so->so_options & SO_DONTROUTE); 386 if (error) 387 return (error); 388 tcpstat.tcps_sndtotal++; 389 390 /* 391 * Data sent (as far as we can tell). 392 * If this advertises a larger window than any other segment, 393 * then remember the size of the advertised window. 394 * Any pending ACK has now been sent. 395 */ 396 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 397 tp->rcv_adv = tp->rcv_nxt + win; 398 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 399 if (sendalot) 400 goto again; 401 return (0); 402 } 403 404 tcp_setpersist(tp) 405 register struct tcpcb *tp; 406 { 407 register t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 408 409 if (tp->t_timer[TCPT_REXMT]) 410 panic("tcp_output REXMT"); 411 /* 412 * Start/restart persistance timer. 413 */ 414 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 415 t * tcp_backoff[tp->t_rxtshift], 416 TCPTV_PERSMIN, TCPTV_PERSMAX); 417 if (tp->t_rxtshift < TCP_MAXRXTSHIFT) 418 tp->t_rxtshift++; 419 } 420