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_timer.c 7.12 (Berkeley) 03/16/88 13 */ 14 15 #include "param.h" 16 #include "systm.h" 17 #include "mbuf.h" 18 #include "socket.h" 19 #include "socketvar.h" 20 #include "protosw.h" 21 #include "errno.h" 22 23 #include "../net/if.h" 24 #include "../net/route.h" 25 26 #include "in.h" 27 #include "in_pcb.h" 28 #include "in_systm.h" 29 #include "ip.h" 30 #include "ip_var.h" 31 #include "tcp.h" 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 38 int tcpnodelack = 0; 39 int tcp_keepidle = TCPTV_KEEP_IDLE; 40 int tcp_keepintvl = TCPTV_KEEPINTVL; 41 int tcp_maxidle; 42 /* 43 * Fast timeout routine for processing delayed acks 44 */ 45 tcp_fasttimo() 46 { 47 register struct inpcb *inp; 48 register struct tcpcb *tp; 49 int s = splnet(); 50 51 inp = tcb.inp_next; 52 if (inp) 53 for (; inp != &tcb; inp = inp->inp_next) 54 if ((tp = (struct tcpcb *)inp->inp_ppcb) && 55 (tp->t_flags & TF_DELACK)) { 56 tp->t_flags &= ~TF_DELACK; 57 tp->t_flags |= TF_ACKNOW; 58 tcpstat.tcps_delack++; 59 (void) tcp_output(tp); 60 } 61 splx(s); 62 } 63 64 /* 65 * Tcp protocol timeout routine called every 500 ms. 66 * Updates the timers in all active tcb's and 67 * causes finite state machine actions if timers expire. 68 */ 69 tcp_slowtimo() 70 { 71 register struct inpcb *ip, *ipnxt; 72 register struct tcpcb *tp; 73 int s = splnet(); 74 register int i; 75 76 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl; 77 /* 78 * Search through tcb's and update active timers. 79 */ 80 ip = tcb.inp_next; 81 if (ip == 0) { 82 splx(s); 83 return; 84 } 85 for (; ip != &tcb; ip = ipnxt) { 86 ipnxt = ip->inp_next; 87 tp = intotcpcb(ip); 88 if (tp == 0) 89 continue; 90 for (i = 0; i < TCPT_NTIMERS; i++) { 91 if (tp->t_timer[i] && --tp->t_timer[i] == 0) { 92 (void) tcp_usrreq(tp->t_inpcb->inp_socket, 93 PRU_SLOWTIMO, (struct mbuf *)0, 94 (struct mbuf *)i, (struct mbuf *)0); 95 if (ipnxt->inp_prev != ip) 96 goto tpgone; 97 } 98 } 99 tp->t_idle++; 100 if (tp->t_rtt) 101 tp->t_rtt++; 102 tpgone: 103 ; 104 } 105 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */ 106 #ifdef TCP_COMPAT_42 107 if ((int)tcp_iss < 0) 108 tcp_iss = 0; /* XXX */ 109 #endif 110 splx(s); 111 } 112 113 /* 114 * Cancel all timers for TCP tp. 115 */ 116 tcp_canceltimers(tp) 117 struct tcpcb *tp; 118 { 119 register int i; 120 121 for (i = 0; i < TCPT_NTIMERS; i++) 122 tp->t_timer[i] = 0; 123 } 124 125 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 126 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 127 128 /* 129 * TCP timer processing. 130 */ 131 struct tcpcb * 132 tcp_timers(tp, timer) 133 register struct tcpcb *tp; 134 int timer; 135 { 136 register int rexmt; 137 138 switch (timer) { 139 140 /* 141 * 2 MSL timeout in shutdown went off. If we're closed but 142 * still waiting for peer to close and connection has been idle 143 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 144 * control block. Otherwise, check again in a bit. 145 */ 146 case TCPT_2MSL: 147 if (tp->t_state != TCPS_TIME_WAIT && 148 tp->t_idle <= tcp_maxidle) 149 tp->t_timer[TCPT_2MSL] = tcp_keepintvl; 150 else 151 tp = tcp_close(tp); 152 break; 153 154 /* 155 * Retransmission timer went off. Message has not 156 * been acked within retransmit interval. Back off 157 * to a longer retransmit interval and retransmit one segment. 158 */ 159 case TCPT_REXMT: 160 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 161 tp->t_rxtshift = TCP_MAXRXTSHIFT; 162 tcpstat.tcps_timeoutdrop++; 163 tp = tcp_drop(tp, ETIMEDOUT); 164 break; 165 } 166 tcpstat.tcps_rexmttimeo++; 167 rexmt = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 168 rexmt *= tcp_backoff[tp->t_rxtshift]; 169 TCPT_RANGESET(tp->t_rxtcur, rexmt, TCPTV_MIN, TCPTV_REXMTMAX); 170 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 171 /* 172 * If losing, let the lower level know and try for 173 * a better route. Also, if we backed off this far, 174 * our srtt estimate is probably bogus. Clobber it 175 * so we'll take the next rtt measurement as our srtt; 176 * move the current srtt into rttvar to keep the current 177 * retransmit times until then. 178 */ 179 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 180 in_losing(tp->t_inpcb); 181 tp->t_rttvar += (tp->t_srtt >> 2); 182 tp->t_srtt = 0; 183 } 184 tp->snd_nxt = tp->snd_una; 185 /* 186 * If timing a segment in this window, stop the timer. 187 */ 188 tp->t_rtt = 0; 189 /* 190 * Close the congestion window down to one segment 191 * (we'll open it by one segment for each ack we get). 192 * Since we probably have a window's worth of unacked 193 * data accumulated, this "slow start" keeps us from 194 * dumping all that data as back-to-back packets (which 195 * might overwhelm an intermediate gateway). 196 * 197 * There are two phases to the opening: Initially we 198 * open by one mss on each ack. This makes the window 199 * size increase exponentially with time. If the 200 * window is larger than the path can handle, this 201 * exponential growth results in dropped packet(s) 202 * almost immediately. To get more time between 203 * drops but still "push" the network to take advantage 204 * of improving conditions, we switch from exponential 205 * to linear window opening at some threshhold size. 206 * For a threshhold, we use half the current window 207 * size, truncated to a multiple of the mss. 208 * 209 * (the minimum cwnd that will give us exponential 210 * growth is 2 mss. We don't allow the threshhold 211 * to go below this.) 212 */ 213 { 214 u_int win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 215 if (win < 2) 216 win = 2; 217 tp->snd_cwnd = tp->t_maxseg; 218 tp->snd_ssthresh = win * tp->t_maxseg; 219 } 220 (void) tcp_output(tp); 221 break; 222 223 /* 224 * Persistance timer into zero window. 225 * Force a byte to be output, if possible. 226 */ 227 case TCPT_PERSIST: 228 tcpstat.tcps_persisttimeo++; 229 tcp_setpersist(tp); 230 tp->t_force = 1; 231 (void) tcp_output(tp); 232 tp->t_force = 0; 233 break; 234 235 /* 236 * Keep-alive timer went off; send something 237 * or drop connection if idle for too long. 238 */ 239 case TCPT_KEEP: 240 tcpstat.tcps_keeptimeo++; 241 if (tp->t_state < TCPS_ESTABLISHED) 242 goto dropit; 243 if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE && 244 tp->t_state <= TCPS_CLOSE_WAIT) { 245 if (tp->t_idle >= tcp_keepidle + tcp_maxidle) 246 goto dropit; 247 /* 248 * Send a packet designed to force a response 249 * if the peer is up and reachable: 250 * either an ACK if the connection is still alive, 251 * or an RST if the peer has closed the connection 252 * due to timeout or reboot. 253 * Using sequence number tp->snd_una-1 254 * causes the transmitted zero-length segment 255 * to lie outside the receive window; 256 * by the protocol spec, this requires the 257 * correspondent TCP to respond. 258 */ 259 tcpstat.tcps_keepprobe++; 260 #ifdef TCP_COMPAT_42 261 /* 262 * The keepalive packet must have nonzero length 263 * to get a 4.2 host to respond. 264 */ 265 tcp_respond(tp, tp->t_template, 266 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 267 #else 268 tcp_respond(tp, tp->t_template, 269 tp->rcv_nxt, tp->snd_una - 1, 0); 270 #endif 271 tp->t_timer[TCPT_KEEP] = tcp_keepintvl; 272 } else 273 tp->t_timer[TCPT_KEEP] = tcp_keepidle; 274 break; 275 dropit: 276 tcpstat.tcps_keepdrops++; 277 tp = tcp_drop(tp, ETIMEDOUT); 278 break; 279 } 280 return (tp); 281 } 282