1 /* tcp_output.c 4.39 82/06/08 */ 2 3 #include "../h/param.h" 4 #include "../h/systm.h" 5 #include "../h/mbuf.h" 6 #include "../h/protosw.h" 7 #include "../h/socket.h" 8 #include "../h/socketvar.h" 9 #include "../net/in.h" 10 #include "../net/route.h" 11 #include "../net/in_pcb.h" 12 #include "../net/in_systm.h" 13 #include "../net/ip.h" 14 #include "../net/ip_var.h" 15 #include "../net/tcp.h" 16 #define TCPOUTFLAGS 17 #include "../net/tcp_fsm.h" 18 #include "../net/tcp_seq.h" 19 #include "../net/tcp_timer.h" 20 #include "../net/tcp_var.h" 21 #include "../net/tcpip.h" 22 #include "../net/tcp_debug.h" 23 #include <errno.h> 24 25 char *tcpstates[]; /* XXX */ 26 27 /* 28 * Initial options: indicate max segment length 1/2 of space 29 * allocated for receive; if TCPTRUEOOB is defined, indicate 30 * willingness to do true out-of-band. 31 */ 32 #ifndef TCPTRUEOOB 33 u_char tcp_initopt[4] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, }; 34 #else 35 u_char tcp_initopt[6] = { TCPOPT_MAXSEG, 4, 0x0, 0x0, TCPOPT_WILLOOB, 2 }; 36 #endif 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; 46 struct mbuf *m0; 47 int off, flags, win, error; 48 register struct mbuf *m; 49 register struct tcpiphdr *ti; 50 u_char *opt; 51 unsigned optlen = 0; 52 int sendalot; 53 54 COUNT(TCP_OUTPUT); 55 56 /* 57 * Determine length of data that should be transmitted, 58 * and flags that will be used. 59 * If there is some data or critical controls (SYN, RST) 60 * to send, then transmit; otherwise, investigate further. 61 */ 62 again: 63 sendalot = 0; 64 off = tp->snd_nxt - tp->snd_una; 65 len = MIN(so->so_snd.sb_cc, tp->snd_wnd+tp->t_force) - off; 66 if (len < 0) 67 return (0); /* ??? */ /* past FIN */ 68 if (len > tp->t_maxseg) { 69 len = tp->t_maxseg; 70 sendalot = 1; 71 } 72 73 flags = tcp_outflags[tp->t_state]; 74 if (tp->snd_nxt + len < tp->snd_una + so->so_snd.sb_cc) 75 flags &= ~TH_FIN; 76 if (flags & (TH_SYN|TH_RST|TH_FIN)) 77 goto send; 78 if (SEQ_GT(tp->snd_up, tp->snd_una)) 79 goto send; 80 81 /* 82 * Sender silly window avoidance. If can send all data, 83 * a maximum segment, at least 1/4 of window do it, 84 * or are forced, do it; otherwise don't bother. 85 */ 86 if (len) { 87 if (len == tp->t_maxseg || off+len >= so->so_snd.sb_cc) 88 goto send; 89 if (len * 4 >= tp->snd_wnd) /* a lot */ 90 goto send; 91 if (tp->t_force) 92 goto send; 93 } 94 95 /* 96 * Send if we owe peer an ACK. 97 */ 98 if (tp->t_flags&TF_ACKNOW) 99 goto send; 100 101 #ifdef TCPTRUEOOB 102 /* 103 * Send if an out of band data or ack should be transmitted. 104 */ 105 if (tp->t_oobflags&(TCPOOB_OWEACK|TCPOOB_NEEDACK))) 106 goto send; 107 #endif 108 109 /* 110 * Calculate available window in i, and also amount 111 * of window known to peer (as advertised window less 112 * next expected input.) If this is 35% or more of the 113 * maximum possible window, then want to send a segment to peer. 114 */ 115 win = sbspace(&so->so_rcv); 116 if (win > 0 && 117 ((100*(win-(tp->rcv_adv-tp->rcv_nxt))/so->so_rcv.sb_hiwat) >= 35)) 118 goto send; 119 120 /* 121 * TCP window updates are not reliable, rather a polling protocol 122 * using ``persist'' packets is used to insure receipt of window 123 * updates. The three ``states'' for the output side are: 124 * idle not doing retransmits or persists 125 * persisting to move a zero window 126 * (re)transmitting and thereby not persisting 127 * 128 * tp->t_timer[TCPT_PERSIST] 129 * is set when we are in persist state. 130 * tp->t_force 131 * is set when we are called to send a persist packet. 132 * tp->t_timer[TCPT_REXMT] 133 * is set when we are retransmitting 134 * The output side is idle when both timers are zero. 135 * 136 * If send window is closed, there is data to transmit, and no 137 * retransmit or persist is pending, then go to persist state, 138 * arranging to force out a byte to get more current window information 139 * if nothing happens soon. 140 */ 141 if (tp->snd_wnd == 0 && so->so_snd.sb_cc && 142 tp->t_timer[TCPT_REXMT] == 0 && tp->t_timer[TCPT_PERSIST] == 0) { 143 tp->t_rxtshift = 0; 144 tcp_setpersist(tp); 145 } 146 147 /* 148 * No reason to send a segment, just return. 149 */ 150 return (0); 151 152 send: 153 /* 154 * Grab a header mbuf, attaching a copy of data to 155 * be transmitted, and initialize the header from 156 * the template for sends on this connection. 157 */ 158 MGET(m, 0); 159 if (m == 0) 160 return (ENOBUFS); 161 m->m_off = MMAXOFF - sizeof (struct tcpiphdr); 162 m->m_len = sizeof (struct tcpiphdr); 163 if (len) { 164 m->m_next = m_copy(so->so_snd.sb_mb, off, len); 165 if (m->m_next == 0) 166 len = 0; 167 } 168 ti = mtod(m, struct tcpiphdr *); 169 if (tp->t_template == 0) 170 panic("tcp_output"); 171 bcopy((caddr_t)tp->t_template, (caddr_t)ti, sizeof (struct tcpiphdr)); 172 173 /* 174 * Fill in fields, remembering maximum advertised 175 * window for use in delaying messages about window sizes. 176 */ 177 ti->ti_seq = tp->snd_nxt; 178 ti->ti_ack = tp->rcv_nxt; 179 #if vax 180 ti->ti_seq = htonl(ti->ti_seq); 181 ti->ti_ack = htonl(ti->ti_ack); 182 #endif 183 /* 184 * Before ESTABLISHED, force sending of initial options 185 * unless TCP set to not do any options. 186 */ 187 if (tp->t_state < TCPS_ESTABLISHED) { 188 if (tp->t_flags&TF_NOOPT) 189 goto noopt; 190 opt = tcp_initopt; 191 optlen = sizeof (tcp_initopt); 192 *(u_short *)(opt + 2) = so->so_rcv.sb_hiwat / 2; 193 #if vax 194 *(u_short *)(opt + 2) = htons(*(u_short *)(opt + 2)); 195 #endif 196 } else { 197 if (tp->t_tcpopt == 0) 198 goto noopt; 199 opt = mtod(tp->t_tcpopt, u_char *); 200 optlen = tp->t_tcpopt->m_len; 201 } 202 #ifndef TCPTRUEOOB 203 if (opt) 204 #else 205 if (opt || (tp->t_oobflags&(TCPOOB_OWEACK|TCPOOB_NEEDACK))) 206 #endif 207 { 208 m0 = m->m_next; 209 m->m_next = m_get(M_DONTWAIT); 210 if (m->m_next == 0) { 211 (void) m_free(m); 212 m_freem(m0); 213 return (ENOBUFS); 214 } 215 m->m_next->m_next = m0; 216 m0 = m->m_next; 217 m0->m_off = MMINOFF; 218 m0->m_len = optlen; 219 bcopy((caddr_t)opt, mtod(m0, caddr_t), optlen); 220 opt = (u_char *)(mtod(m0, caddr_t) + optlen); 221 #ifdef TCPTRUEOOB 222 if (tp->t_oobflags&TCPOOB_OWEACK) { 223 printf("tp %x send OOBACK for %x\n", tp->t_iobseq); 224 *opt++ = TCPOPT_OOBACK; 225 *opt++ = 3; 226 *opt++ = tp->t_iobseq; 227 m0->m_len += 3; 228 tp->t_oobflags &= ~TCPOOB_OWEACK; 229 /* sender should rexmt oob to force ack repeat */ 230 } 231 if (tp->t_oobflags&TCPOOB_NEEDACK) { 232 printf("tp %x send OOBDATA seq %x data %x\n", tp->t_oobseq, tp->t_oobc); 233 *opt++ = TCPOPT_OOBDATA; 234 *opt++ = 8; 235 *opt++ = tp->t_oobseq; 236 *opt++ = tp->t_oobc; 237 *(tcp_seq *)opt = tp->t_oobmark - tp->snd_nxt; 238 #ifdef vax 239 *(tcp_seq *)opt = htonl((unsigned)*(tcp_seq *)opt); 240 #endif 241 m0->m_len += 8; 242 TCPT_RANGESET(tp->t_timer[TCPT_OOBREXMT], 243 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 244 } 245 #endif 246 while (m0->m_len & 0x3) { 247 *opt++ = TCPOPT_EOL; 248 m0->m_len++; 249 } 250 optlen = m0->m_len; 251 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2; 252 } 253 noopt: 254 ti->ti_flags = flags; 255 win = sbspace(&so->so_rcv); 256 if (win < so->so_rcv.sb_hiwat / 4) /* avoid silly window */ 257 win = 0; 258 if (win > 0) 259 #if vax 260 ti->ti_win = htons((u_short)win); 261 #else 262 ti->ti_win = win; 263 #endif 264 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) { 265 ti->ti_urp = tp->snd_up - tp->snd_nxt; 266 #if vax 267 ti->ti_urp = htons(ti->ti_urp); 268 #endif 269 ti->ti_flags |= TH_URG; 270 } else 271 /* 272 * If no urgent pointer to send, then we pull 273 * the urgent pointer to the left edge of the send window 274 * so that it doesn't drift into the send window on sequence 275 * number wraparound. 276 */ 277 tp->snd_up = tp->snd_una; /* drag it along */ 278 /* PUSH */ 279 280 /* 281 * Put TCP length in extended header, and then 282 * checksum extended header and data. 283 */ 284 if (len + optlen) { 285 ti->ti_len = sizeof (struct tcphdr) + optlen + len; 286 #if vax 287 ti->ti_len = htons((u_short)ti->ti_len); 288 #endif 289 } 290 ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + (int)optlen + len); 291 292 /* 293 * In transmit state, time the transmission and arrange for 294 * the retransmit. In persist state, reset persist time for 295 * next persist. 296 */ 297 if (tp->t_force == 0) { 298 /* 299 * Advance snd_nxt over sequence space of this segment 300 */ 301 if (flags & (TH_SYN|TH_FIN)) 302 tp->snd_nxt++; 303 tp->snd_nxt += len; 304 305 /* 306 * Time this transmission if not a retransmission and 307 * not currently timing anything. 308 */ 309 if (SEQ_GT(tp->snd_nxt, tp->snd_max) && tp->t_rtt == 0) { 310 tp->t_rtt = 1; 311 tp->t_rtseq = tp->snd_nxt - len; 312 } 313 314 /* 315 * Set retransmit timer if not currently set. 316 * Initial value for retransmit timer to tcp_beta*tp->t_srtt. 317 * Initialize shift counter which is used for exponential 318 * backoff of retransmit time. 319 */ 320 if (tp->t_timer[TCPT_REXMT] == 0 && 321 tp->snd_nxt != tp->snd_una) { 322 TCPT_RANGESET(tp->t_timer[TCPT_REXMT], 323 tcp_beta * tp->t_srtt, TCPTV_MIN, TCPTV_MAX); 324 tp->t_rtt = 0; 325 tp->t_rxtshift = 0; 326 } 327 tp->t_timer[TCPT_PERSIST] = 0; 328 } else 329 tcp_setpersist(tp); 330 331 /* 332 * Trace. 333 */ 334 if (tp->t_inpcb->inp_socket->so_options & SO_DEBUG) 335 tcp_trace(TA_OUTPUT, tp->t_state, tp, ti, 0); 336 337 /* 338 * Fill in IP length and desired time to live and 339 * send to IP level. 340 */ 341 ((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + optlen + len; 342 ((struct ip *)ti)->ip_ttl = TCP_TTL; 343 if (error = ip_output(m, tp->t_ipopt, &tp->t_inpcb->inp_route, 0)) 344 return (error); 345 346 /* 347 * Data sent (as far as we can tell). 348 * If this advertises a larger window than any other segment, 349 * then remember the size of the advertised window. 350 * Drop send for purpose of ACK requirements. 351 */ 352 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv)) 353 tp->rcv_adv = tp->rcv_nxt + win; 354 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK); 355 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) 356 tp->snd_max = tp->snd_nxt; 357 if (sendalot && tp->t_force == 0) 358 goto again; 359 return (0); 360 } 361 362 tcp_setpersist(tp) 363 register struct tcpcb *tp; 364 { 365 366 if (tp->t_timer[TCPT_REXMT]) 367 panic("tcp_output REXMT"); 368 /* 369 * Start/restart persistance timer. 370 */ 371 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST], 372 ((int)(tcp_beta * tp->t_srtt)) << tp->t_rxtshift, 373 TCPTV_PERSMIN, TCPTV_MAX); 374 tp->t_rxtshift++; 375 if (tp->t_rxtshift >= TCP_MAXRXTSHIFT) 376 tp->t_rxtshift = 0; 377 } 378