1 /* 2 * Copyright (c) 1982, 1986, 1988, 1990 Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 * 7 * @(#)tcp_timer.c 7.18 (Berkeley) 06/28/90 8 */ 9 10 #include "param.h" 11 #include "systm.h" 12 #include "malloc.h" 13 #include "mbuf.h" 14 #include "socket.h" 15 #include "socketvar.h" 16 #include "protosw.h" 17 #include "errno.h" 18 19 #include "../net/if.h" 20 #include "../net/route.h" 21 22 #include "in.h" 23 #include "in_systm.h" 24 #include "ip.h" 25 #include "in_pcb.h" 26 #include "ip_var.h" 27 #include "tcp.h" 28 #include "tcp_fsm.h" 29 #include "tcp_seq.h" 30 #include "tcp_timer.h" 31 #include "tcp_var.h" 32 #include "tcpip.h" 33 34 int tcp_keepidle = TCPTV_KEEP_IDLE; 35 int tcp_keepintvl = TCPTV_KEEPINTVL; 36 int tcp_maxidle; 37 /* 38 * Fast timeout routine for processing delayed acks 39 */ 40 tcp_fasttimo() 41 { 42 register struct inpcb *inp; 43 register struct tcpcb *tp; 44 int s = splnet(); 45 46 inp = tcb.inp_next; 47 if (inp) 48 for (; inp != &tcb; inp = inp->inp_next) 49 if ((tp = (struct tcpcb *)inp->inp_ppcb) && 50 (tp->t_flags & TF_DELACK)) { 51 tp->t_flags &= ~TF_DELACK; 52 tp->t_flags |= TF_ACKNOW; 53 tcpstat.tcps_delack++; 54 (void) tcp_output(tp); 55 } 56 splx(s); 57 } 58 59 /* 60 * Tcp protocol timeout routine called every 500 ms. 61 * Updates the timers in all active tcb's and 62 * causes finite state machine actions if timers expire. 63 */ 64 tcp_slowtimo() 65 { 66 register struct inpcb *ip, *ipnxt; 67 register struct tcpcb *tp; 68 int s = splnet(); 69 register int i; 70 71 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl; 72 /* 73 * Search through tcb's and update active timers. 74 */ 75 ip = tcb.inp_next; 76 if (ip == 0) { 77 splx(s); 78 return; 79 } 80 for (; ip != &tcb; ip = ipnxt) { 81 ipnxt = ip->inp_next; 82 tp = intotcpcb(ip); 83 if (tp == 0) 84 continue; 85 for (i = 0; i < TCPT_NTIMERS; i++) { 86 if (tp->t_timer[i] && --tp->t_timer[i] == 0) { 87 (void) tcp_usrreq(tp->t_inpcb->inp_socket, 88 PRU_SLOWTIMO, (struct mbuf *)0, 89 (struct mbuf *)i, (struct mbuf *)0); 90 if (ipnxt->inp_prev != ip) 91 goto tpgone; 92 } 93 } 94 tp->t_idle++; 95 if (tp->t_rtt) 96 tp->t_rtt++; 97 tpgone: 98 ; 99 } 100 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */ 101 #ifdef TCP_COMPAT_42 102 if ((int)tcp_iss < 0) 103 tcp_iss = 0; /* XXX */ 104 #endif 105 splx(s); 106 } 107 108 /* 109 * Cancel all timers for TCP tp. 110 */ 111 tcp_canceltimers(tp) 112 struct tcpcb *tp; 113 { 114 register int i; 115 116 for (i = 0; i < TCPT_NTIMERS; i++) 117 tp->t_timer[i] = 0; 118 } 119 120 int tcp_backoff[TCP_MAXRXTSHIFT + 1] = 121 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 }; 122 123 /* 124 * TCP timer processing. 125 */ 126 struct tcpcb * 127 tcp_timers(tp, timer) 128 register struct tcpcb *tp; 129 int timer; 130 { 131 register int rexmt; 132 133 switch (timer) { 134 135 /* 136 * 2 MSL timeout in shutdown went off. If we're closed but 137 * still waiting for peer to close and connection has been idle 138 * too long, or if 2MSL time is up from TIME_WAIT, delete connection 139 * control block. Otherwise, check again in a bit. 140 */ 141 case TCPT_2MSL: 142 if (tp->t_state != TCPS_TIME_WAIT && 143 tp->t_idle <= tcp_maxidle) 144 tp->t_timer[TCPT_2MSL] = tcp_keepintvl; 145 else 146 tp = tcp_close(tp); 147 break; 148 149 /* 150 * Retransmission timer went off. Message has not 151 * been acked within retransmit interval. Back off 152 * to a longer retransmit interval and retransmit one segment. 153 */ 154 case TCPT_REXMT: 155 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) { 156 tp->t_rxtshift = TCP_MAXRXTSHIFT; 157 tcpstat.tcps_timeoutdrop++; 158 tp = tcp_drop(tp, tp->t_softerror ? 159 tp->t_softerror : ETIMEDOUT); 160 break; 161 } 162 tcpstat.tcps_rexmttimeo++; 163 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 164 TCPT_RANGESET(tp->t_rxtcur, rexmt, 165 tp->t_rttmin, 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 >> TCP_RTT_SHIFT); 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 tp->t_dupacks = 0; 216 } 217 (void) tcp_output(tp); 218 break; 219 220 /* 221 * Persistance timer into zero window. 222 * Force a byte to be output, if possible. 223 */ 224 case TCPT_PERSIST: 225 tcpstat.tcps_persisttimeo++; 226 tcp_setpersist(tp); 227 tp->t_force = 1; 228 (void) tcp_output(tp); 229 tp->t_force = 0; 230 break; 231 232 /* 233 * Keep-alive timer went off; send something 234 * or drop connection if idle for too long. 235 */ 236 case TCPT_KEEP: 237 tcpstat.tcps_keeptimeo++; 238 if (tp->t_state < TCPS_ESTABLISHED) 239 goto dropit; 240 if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE && 241 tp->t_state <= TCPS_CLOSE_WAIT) { 242 if (tp->t_idle >= tcp_keepidle + tcp_maxidle) 243 goto dropit; 244 /* 245 * Send a packet designed to force a response 246 * if the peer is up and reachable: 247 * either an ACK if the connection is still alive, 248 * or an RST if the peer has closed the connection 249 * due to timeout or reboot. 250 * Using sequence number tp->snd_una-1 251 * causes the transmitted zero-length segment 252 * to lie outside the receive window; 253 * by the protocol spec, this requires the 254 * correspondent TCP to respond. 255 */ 256 tcpstat.tcps_keepprobe++; 257 #ifdef TCP_COMPAT_42 258 /* 259 * The keepalive packet must have nonzero length 260 * to get a 4.2 host to respond. 261 */ 262 tcp_respond(tp, tp->t_template, (struct mbuf *)NULL, 263 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 264 #else 265 tcp_respond(tp, tp->t_template, (struct mbuf *)NULL, 266 tp->rcv_nxt, tp->snd_una - 1, 0); 267 #endif 268 tp->t_timer[TCPT_KEEP] = tcp_keepintvl; 269 } else 270 tp->t_timer[TCPT_KEEP] = tcp_keepidle; 271 break; 272 dropit: 273 tcpstat.tcps_keepdrops++; 274 tp = tcp_drop(tp, ETIMEDOUT); 275 break; 276 } 277 return (tp); 278 } 279