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 7.11 (Berkeley) 12/07/87 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 /* 40 * Fast timeout routine for processing delayed acks 41 */ 42 tcp_fasttimo() 43 { 44 register struct inpcb *inp; 45 register struct tcpcb *tp; 46 int s = splnet(); 47 48 inp = tcb.inp_next; 49 if (inp) 50 for (; inp != &tcb; inp = inp->inp_next) 51 if ((tp = (struct tcpcb *)inp->inp_ppcb) && 52 (tp->t_flags & TF_DELACK)) { 53 tp->t_flags &= ~TF_DELACK; 54 tp->t_flags |= TF_ACKNOW; 55 tcpstat.tcps_delack++; 56 (void) tcp_output(tp); 57 } 58 splx(s); 59 } 60 61 /* 62 * Tcp protocol timeout routine called every 500 ms. 63 * Updates the timers in all active tcb's and 64 * causes finite state machine actions if timers expire. 65 */ 66 tcp_slowtimo() 67 { 68 register struct inpcb *ip, *ipnxt; 69 register struct tcpcb *tp; 70 int s = splnet(); 71 register int i; 72 73 /* 74 * Search through tcb's and update active timers. 75 */ 76 ip = tcb.inp_next; 77 if (ip == 0) { 78 splx(s); 79 return; 80 } 81 for (; ip != &tcb; ip = ipnxt) { 82 ipnxt = ip->inp_next; 83 tp = intotcpcb(ip); 84 if (tp == 0) 85 continue; 86 for (i = 0; i < TCPT_NTIMERS; i++) { 87 if (tp->t_timer[i] && --tp->t_timer[i] == 0) { 88 (void) tcp_usrreq(tp->t_inpcb->inp_socket, 89 PRU_SLOWTIMO, (struct mbuf *)0, 90 (struct mbuf *)i, (struct mbuf *)0); 91 if (ipnxt->inp_prev != ip) 92 goto tpgone; 93 } 94 } 95 tp->t_idle++; 96 if (tp->t_rtt) 97 tp->t_rtt++; 98 tpgone: 99 ; 100 } 101 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */ 102 #ifdef TCP_COMPAT_42 103 if ((int)tcp_iss < 0) 104 tcp_iss = 0; /* XXX */ 105 #endif 106 splx(s); 107 } 108 109 /* 110 * Cancel all timers for TCP tp. 111 */ 112 tcp_canceltimers(tp) 113 struct tcpcb *tp; 114 { 115 register int i; 116 117 for (i = 0; i < TCPT_NTIMERS; i++) 118 tp->t_timer[i] = 0; 119 } 120 121 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 122 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 123 124 /* 125 * TCP timer processing. 126 */ 127 struct tcpcb * 128 tcp_timers(tp, timer) 129 register struct tcpcb *tp; 130 int timer; 131 { 132 register int rexmt; 133 134 switch (timer) { 135 136 /* 137 * 2 MSL timeout in shutdown went off. If we're closed but 138 * still waiting for peer to close and connection has been idle 139 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 140 * control block. Otherwise, check again in a bit. 141 */ 142 case TCPT_2MSL: 143 if (tp->t_state != TCPS_TIME_WAIT && 144 tp->t_idle <= TCPTV_MAXIDLE) 145 tp->t_timer[TCPT_2MSL] = TCPTV_KEEP; 146 else 147 tp = tcp_close(tp); 148 break; 149 150 /* 151 * Retransmission timer went off. Message has not 152 * been acked within retransmit interval. Back off 153 * to a longer retransmit interval and retransmit one segment. 154 */ 155 case TCPT_REXMT: 156 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 157 tp->t_rxtshift = TCP_MAXRXTSHIFT; 158 tcpstat.tcps_timeoutdrop++; 159 tp = tcp_drop(tp, ETIMEDOUT); 160 break; 161 } 162 tcpstat.tcps_rexmttimeo++; 163 rexmt = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1; 164 rexmt *= tcp_backoff[tp->t_rxtshift]; 165 TCPT_RANGESET(tp->t_rxtcur, rexmt, TCPTV_MIN, TCPTV_REXMTMAX); 166 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 167 /* 168 * If losing, let the lower level know and try for 169 * a better route. Also, if we backed off this far, 170 * our srtt estimate is probably bogus. Clobber it 171 * so we'll take the next rtt measurement as our srtt; 172 * move the current srtt into rttvar to keep the current 173 * retransmit times until then. 174 */ 175 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 176 in_losing(tp->t_inpcb); 177 tp->t_rttvar += (tp->t_srtt >> 2); 178 tp->t_srtt = 0; 179 } 180 tp->snd_nxt = tp->snd_una; 181 /* 182 * If timing a segment in this window, stop the timer. 183 */ 184 tp->t_rtt = 0; 185 /* 186 * Close the congestion window down to one segment 187 * (we'll open it by one segment for each ack we get). 188 * Since we probably have a window's worth of unacked 189 * data accumulated, this "slow start" keeps us from 190 * dumping all that data as back-to-back packets (which 191 * might overwhelm an intermediate gateway). 192 * 193 * There are two phases to the opening: Initially we 194 * open by one mss on each ack. This makes the window 195 * size increase exponentially with time. If the 196 * window is larger than the path can handle, this 197 * exponential growth results in dropped packet(s) 198 * almost immediately. To get more time between 199 * drops but still "push" the network to take advantage 200 * of improving conditions, we switch from exponential 201 * to linear window opening at some threshhold size. 202 * For a threshhold, we use half the current window 203 * size, truncated to a multiple of the mss. 204 * 205 * (the minimum cwnd that will give us exponential 206 * growth is 2 mss. We don't allow the threshhold 207 * to go below this.) 208 */ 209 { 210 u_int win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 211 if (win < 2) 212 win = 2; 213 tp->snd_cwnd = tp->t_maxseg; 214 tp->snd_ssthresh = win * tp->t_maxseg; 215 } 216 (void) tcp_output(tp); 217 break; 218 219 /* 220 * Persistance timer into zero window. 221 * Force a byte to be output, if possible. 222 */ 223 case TCPT_PERSIST: 224 tcpstat.tcps_persisttimeo++; 225 tcp_setpersist(tp); 226 tp->t_force = 1; 227 (void) tcp_output(tp); 228 tp->t_force = 0; 229 break; 230 231 /* 232 * Keep-alive timer went off; send something 233 * or drop connection if idle for too long. 234 */ 235 case TCPT_KEEP: 236 tcpstat.tcps_keeptimeo++; 237 if (tp->t_state < TCPS_ESTABLISHED) 238 goto dropit; 239 if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE && 240 tp->t_state <= TCPS_CLOSE_WAIT) { 241 if (tp->t_idle >= TCPTV_MAXIDLE) 242 goto dropit; 243 /* 244 * Send a packet designed to force a response 245 * if the peer is up and reachable: 246 * either an ACK if the connection is still alive, 247 * or an RST if the peer has closed the connection 248 * due to timeout or reboot. 249 * Using sequence number tp->snd_una-1 250 * causes the transmitted zero-length segment 251 * to lie outside the receive window; 252 * by the protocol spec, this requires the 253 * correspondent TCP to respond. 254 */ 255 tcpstat.tcps_keepprobe++; 256 #ifdef TCP_COMPAT_42 257 /* 258 * The keepalive packet must have nonzero length 259 * to get a 4.2 host to respond. 260 */ 261 tcp_respond(tp, tp->t_template, 262 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 263 #else 264 tcp_respond(tp, tp->t_template, 265 tp->rcv_nxt, tp->snd_una - 1, 0); 266 #endif 267 } 268 tp->t_timer[TCPT_KEEP] = TCPTV_KEEP; 269 break; 270 dropit: 271 tcpstat.tcps_keepdrops++; 272 tp = tcp_drop(tp, ETIMEDOUT); 273 break; 274 } 275 return (tp); 276 } 277