1 /* 2 * Copyright (c) 1982, 1986, 1988, 1990, 1993 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. Neither the name of the University nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93 30 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp 31 */ 32 33 #include <slirp.h> 34 35 #ifdef LOG_ENABLED 36 struct tcpstat tcpstat; /* tcp statistics */ 37 #endif 38 39 u_int32_t tcp_now; /* for RFC 1323 timestamps */ 40 41 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer); 42 43 /* 44 * Fast timeout routine for processing delayed acks 45 */ 46 void 47 tcp_fasttimo(void) 48 { 49 register struct socket *so; 50 register struct tcpcb *tp; 51 52 DEBUG_CALL("tcp_fasttimo"); 53 54 so = tcb.so_next; 55 if (so) 56 for (; so != &tcb; so = so->so_next) 57 if ((tp = (struct tcpcb *)so->so_tcpcb) && 58 (tp->t_flags & TF_DELACK)) { 59 tp->t_flags &= ~TF_DELACK; 60 tp->t_flags |= TF_ACKNOW; 61 STAT(tcpstat.tcps_delack++); 62 (void) tcp_output(tp); 63 } 64 } 65 66 /* 67 * Tcp protocol timeout routine called every 500 ms. 68 * Updates the timers in all active tcb's and 69 * causes finite state machine actions if timers expire. 70 */ 71 void 72 tcp_slowtimo(void) 73 { 74 register struct socket *ip, *ipnxt; 75 register struct tcpcb *tp; 76 register int i; 77 78 DEBUG_CALL("tcp_slowtimo"); 79 80 /* 81 * Search through tcb's and update active timers. 82 */ 83 ip = tcb.so_next; 84 if (ip == 0) 85 return; 86 for (; ip != &tcb; ip = ipnxt) { 87 ipnxt = ip->so_next; 88 tp = sototcpcb(ip); 89 if (tp == 0) 90 continue; 91 for (i = 0; i < TCPT_NTIMERS; i++) { 92 if (tp->t_timer[i] && --tp->t_timer[i] == 0) { 93 tcp_timers(tp,i); 94 if (ipnxt->so_prev != ip) 95 goto tpgone; 96 } 97 } 98 tp->t_idle++; 99 if (tp->t_rtt) 100 tp->t_rtt++; 101 tpgone: 102 ; 103 } 104 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */ 105 #ifdef TCP_COMPAT_42 106 if ((int)tcp_iss < 0) 107 tcp_iss = 0; /* XXX */ 108 #endif 109 tcp_now++; /* for timestamps */ 110 } 111 112 /* 113 * Cancel all timers for TCP tp. 114 */ 115 void 116 tcp_canceltimers(struct tcpcb *tp) 117 { 118 register int i; 119 120 for (i = 0; i < TCPT_NTIMERS; i++) 121 tp->t_timer[i] = 0; 122 } 123 124 const int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 125 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 126 127 /* 128 * TCP timer processing. 129 */ 130 static struct tcpcb * 131 tcp_timers(register struct tcpcb *tp, int timer) 132 { 133 register int rexmt; 134 135 DEBUG_CALL("tcp_timers"); 136 137 switch (timer) { 138 139 /* 140 * 2 MSL timeout in shutdown went off. If we're closed but 141 * still waiting for peer to close and connection has been idle 142 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 143 * control block. Otherwise, check again in a bit. 144 */ 145 case TCPT_2MSL: 146 if (tp->t_state != TCPS_TIME_WAIT && 147 tp->t_idle <= TCP_MAXIDLE) 148 tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL; 149 else 150 tp = tcp_close(tp); 151 break; 152 153 /* 154 * Retransmission timer went off. Message has not 155 * been acked within retransmit interval. Back off 156 * to a longer retransmit interval and retransmit one segment. 157 */ 158 case TCPT_REXMT: 159 160 /* 161 * XXXXX If a packet has timed out, then remove all the queued 162 * packets for that session. 163 */ 164 165 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 166 /* 167 * This is a hack to suit our terminal server here at the uni of canberra 168 * since they have trouble with zeroes... It usually lets them through 169 * unharmed, but under some conditions, it'll eat the zeros. If we 170 * keep retransmitting it, it'll keep eating the zeroes, so we keep 171 * retransmitting, and eventually the connection dies... 172 * (this only happens on incoming data) 173 * 174 * So, if we were gonna drop the connection from too many retransmits, 175 * don't... instead halve the t_maxseg, which might break up the NULLs and 176 * let them through 177 * 178 * *sigh* 179 */ 180 181 tp->t_maxseg >>= 1; 182 if (tp->t_maxseg < 32) { 183 /* 184 * We tried our best, now the connection must die! 185 */ 186 tp->t_rxtshift = TCP_MAXRXTSHIFT; 187 STAT(tcpstat.tcps_timeoutdrop++); 188 tp = tcp_drop(tp, tp->t_softerror); 189 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */ 190 return (tp); /* XXX */ 191 } 192 193 /* 194 * Set rxtshift to 6, which is still at the maximum 195 * backoff time 196 */ 197 tp->t_rxtshift = 6; 198 } 199 STAT(tcpstat.tcps_rexmttimeo++); 200 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 201 TCPT_RANGESET(tp->t_rxtcur, rexmt, 202 (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */ 203 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 204 /* 205 * If losing, let the lower level know and try for 206 * a better route. Also, if we backed off this far, 207 * our srtt estimate is probably bogus. Clobber it 208 * so we'll take the next rtt measurement as our srtt; 209 * move the current srtt into rttvar to keep the current 210 * retransmit times until then. 211 */ 212 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 213 /* in_losing(tp->t_inpcb); */ 214 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 215 tp->t_srtt = 0; 216 } 217 tp->snd_nxt = tp->snd_una; 218 /* 219 * If timing a segment in this window, stop the timer. 220 */ 221 tp->t_rtt = 0; 222 /* 223 * Close the congestion window down to one segment 224 * (we'll open it by one segment for each ack we get). 225 * Since we probably have a window's worth of unacked 226 * data accumulated, this "slow start" keeps us from 227 * dumping all that data as back-to-back packets (which 228 * might overwhelm an intermediate gateway). 229 * 230 * There are two phases to the opening: Initially we 231 * open by one mss on each ack. This makes the window 232 * size increase exponentially with time. If the 233 * window is larger than the path can handle, this 234 * exponential growth results in dropped packet(s) 235 * almost immediately. To get more time between 236 * drops but still "push" the network to take advantage 237 * of improving conditions, we switch from exponential 238 * to linear window opening at some threshold size. 239 * For a threshold, we use half the current window 240 * size, truncated to a multiple of the mss. 241 * 242 * (the minimum cwnd that will give us exponential 243 * growth is 2 mss. We don't allow the threshold 244 * to go below this.) 245 */ 246 { 247 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 248 if (win < 2) 249 win = 2; 250 tp->snd_cwnd = tp->t_maxseg; 251 tp->snd_ssthresh = win * tp->t_maxseg; 252 tp->t_dupacks = 0; 253 } 254 (void) tcp_output(tp); 255 break; 256 257 /* 258 * Persistence timer into zero window. 259 * Force a byte to be output, if possible. 260 */ 261 case TCPT_PERSIST: 262 STAT(tcpstat.tcps_persisttimeo++); 263 tcp_setpersist(tp); 264 tp->t_force = 1; 265 (void) tcp_output(tp); 266 tp->t_force = 0; 267 break; 268 269 /* 270 * Keep-alive timer went off; send something 271 * or drop connection if idle for too long. 272 */ 273 case TCPT_KEEP: 274 STAT(tcpstat.tcps_keeptimeo++); 275 if (tp->t_state < TCPS_ESTABLISHED) 276 goto dropit; 277 278 /* if (tp->t_socket->so_options & SO_KEEPALIVE && */ 279 if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) { 280 if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE) 281 goto dropit; 282 /* 283 * Send a packet designed to force a response 284 * if the peer is up and reachable: 285 * either an ACK if the connection is still alive, 286 * or an RST if the peer has closed the connection 287 * due to timeout or reboot. 288 * Using sequence number tp->snd_una-1 289 * causes the transmitted zero-length segment 290 * to lie outside the receive window; 291 * by the protocol spec, this requires the 292 * correspondent TCP to respond. 293 */ 294 STAT(tcpstat.tcps_keepprobe++); 295 #ifdef TCP_COMPAT_42 296 /* 297 * The keepalive packet must have nonzero length 298 * to get a 4.2 host to respond. 299 */ 300 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL, 301 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 302 #else 303 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL, 304 tp->rcv_nxt, tp->snd_una - 1, 0); 305 #endif 306 tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL; 307 } else 308 tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE; 309 break; 310 311 dropit: 312 STAT(tcpstat.tcps_keepdrops++); 313 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */ 314 break; 315 } 316 317 return (tp); 318 } 319
