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 7.13 (Berkeley) 05/14/88 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 tcp_keepidle = TCPTV_KEEP_IDLE; 39 int tcp_keepintvl = TCPTV_KEEPINTVL; 40 int tcp_maxidle; 41 /* 42 * Fast timeout routine for processing delayed acks 43 */ 44 tcp_fasttimo() 45 { 46 register struct inpcb *inp; 47 register struct tcpcb *tp; 48 int s = splnet(); 49 50 inp = tcb.inp_next; 51 if (inp) 52 for (; inp != &tcb; inp = inp->inp_next) 53 if ((tp = (struct tcpcb *)inp->inp_ppcb) && 54 (tp->t_flags & TF_DELACK)) { 55 tp->t_flags &= ~TF_DELACK; 56 tp->t_flags |= TF_ACKNOW; 57 tcpstat.tcps_delack++; 58 (void) tcp_output(tp); 59 } 60 splx(s); 61 } 62 63 /* 64 * Tcp protocol timeout routine called every 500 ms. 65 * Updates the timers in all active tcb's and 66 * causes finite state machine actions if timers expire. 67 */ 68 tcp_slowtimo() 69 { 70 register struct inpcb *ip, *ipnxt; 71 register struct tcpcb *tp; 72 int s = splnet(); 73 register int i; 74 75 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl; 76 /* 77 * Search through tcb's and update active timers. 78 */ 79 ip = tcb.inp_next; 80 if (ip == 0) { 81 splx(s); 82 return; 83 } 84 for (; ip != &tcb; ip = ipnxt) { 85 ipnxt = ip->inp_next; 86 tp = intotcpcb(ip); 87 if (tp == 0) 88 continue; 89 for (i = 0; i < TCPT_NTIMERS; i++) { 90 if (tp->t_timer[i] && --tp->t_timer[i] == 0) { 91 (void) tcp_usrreq(tp->t_inpcb->inp_socket, 92 PRU_SLOWTIMO, (struct mbuf *)0, 93 (struct mbuf *)i, (struct mbuf *)0); 94 if (ipnxt->inp_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 splx(s); 110 } 111 112 /* 113 * Cancel all timers for TCP tp. 114 */ 115 tcp_canceltimers(tp) 116 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 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 struct tcpcb * 131 tcp_timers(tp, timer) 132 register struct tcpcb *tp; 133 int timer; 134 { 135 register int rexmt; 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] = tcp_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 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 160 tp->t_rxtshift = TCP_MAXRXTSHIFT; 161 tcpstat.tcps_timeoutdrop++; 162 tp = tcp_drop(tp, ETIMEDOUT); 163 break; 164 } 165 tcpstat.tcps_rexmttimeo++; 166 rexmt = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 167 rexmt *= tcp_backoff[tp->t_rxtshift]; 168 TCPT_RANGESET(tp->t_rxtcur, rexmt, TCPTV_MIN, TCPTV_REXMTMAX); 169 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 170 /* 171 * If losing, let the lower level know and try for 172 * a better route. Also, if we backed off this far, 173 * our srtt estimate is probably bogus. Clobber it 174 * so we'll take the next rtt measurement as our srtt; 175 * move the current srtt into rttvar to keep the current 176 * retransmit times until then. 177 */ 178 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 179 in_losing(tp->t_inpcb); 180 tp->t_rttvar += (tp->t_srtt >> 2); 181 tp->t_srtt = 0; 182 } 183 tp->snd_nxt = tp->snd_una; 184 /* 185 * If timing a segment in this window, stop the timer. 186 */ 187 tp->t_rtt = 0; 188 /* 189 * Close the congestion window down to one segment 190 * (we'll open it by one segment for each ack we get). 191 * Since we probably have a window's worth of unacked 192 * data accumulated, this "slow start" keeps us from 193 * dumping all that data as back-to-back packets (which 194 * might overwhelm an intermediate gateway). 195 * 196 * There are two phases to the opening: Initially we 197 * open by one mss on each ack. This makes the window 198 * size increase exponentially with time. If the 199 * window is larger than the path can handle, this 200 * exponential growth results in dropped packet(s) 201 * almost immediately. To get more time between 202 * drops but still "push" the network to take advantage 203 * of improving conditions, we switch from exponential 204 * to linear window opening at some threshhold size. 205 * For a threshhold, we use half the current window 206 * size, truncated to a multiple of the mss. 207 * 208 * (the minimum cwnd that will give us exponential 209 * growth is 2 mss. We don't allow the threshhold 210 * to go below this.) 211 */ 212 { 213 u_int win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 214 if (win < 2) 215 win = 2; 216 tp->snd_cwnd = tp->t_maxseg; 217 tp->snd_ssthresh = win * tp->t_maxseg; 218 } 219 (void) tcp_output(tp); 220 break; 221 222 /* 223 * Persistance timer into zero window. 224 * Force a byte to be output, if possible. 225 */ 226 case TCPT_PERSIST: 227 tcpstat.tcps_persisttimeo++; 228 tcp_setpersist(tp); 229 tp->t_force = 1; 230 (void) tcp_output(tp); 231 tp->t_force = 0; 232 break; 233 234 /* 235 * Keep-alive timer went off; send something 236 * or drop connection if idle for too long. 237 */ 238 case TCPT_KEEP: 239 tcpstat.tcps_keeptimeo++; 240 if (tp->t_state < TCPS_ESTABLISHED) 241 goto dropit; 242 if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE && 243 tp->t_state <= TCPS_CLOSE_WAIT) { 244 if (tp->t_idle >= tcp_keepidle + tcp_maxidle) 245 goto dropit; 246 /* 247 * Send a packet designed to force a response 248 * if the peer is up and reachable: 249 * either an ACK if the connection is still alive, 250 * or an RST if the peer has closed the connection 251 * due to timeout or reboot. 252 * Using sequence number tp->snd_una-1 253 * causes the transmitted zero-length segment 254 * to lie outside the receive window; 255 * by the protocol spec, this requires the 256 * correspondent TCP to respond. 257 */ 258 tcpstat.tcps_keepprobe++; 259 #ifdef TCP_COMPAT_42 260 /* 261 * The keepalive packet must have nonzero length 262 * to get a 4.2 host to respond. 263 */ 264 tcp_respond(tp, tp->t_template, 265 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 266 #else 267 tcp_respond(tp, tp->t_template, 268 tp->rcv_nxt, tp->snd_una - 1, 0); 269 #endif 270 tp->t_timer[TCPT_KEEP] = tcp_keepintvl; 271 } else 272 tp->t_timer[TCPT_KEEP] = tcp_keepidle; 273 break; 274 dropit: 275 tcpstat.tcps_keepdrops++; 276 tp = tcp_drop(tp, ETIMEDOUT); 277 break; 278 } 279 return (tp); 280 } 281