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 7.20 (Berkeley) 01/08/93 8 */ 9 10 #include <sys/param.h> 11 #include <sys/systm.h> 12 #include <sys/malloc.h> 13 #include <sys/mbuf.h> 14 #include <sys/socket.h> 15 #include <sys/socketvar.h> 16 #include <sys/protosw.h> 17 #include <sys/errno.h> 18 19 #include <net/if.h> 20 #include <net/route.h> 21 22 #include <netinet/in.h> 23 #include <netinet/in_systm.h> 24 #include <netinet/ip.h> 25 #include <netinet/in_pcb.h> 26 #include <netinet/ip_var.h> 27 #include <netinet/tcp.h> 28 #include <netinet/tcp_fsm.h> 29 #include <netinet/tcp_seq.h> 30 #include <netinet/tcp_timer.h> 31 #include <netinet/tcp_var.h> 32 #include <netinet/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 tcp_now++; /* for timestamps */ 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 <= tcp_maxidle) 145 tp->t_timer[TCPT_2MSL] = tcp_keepintvl; 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, tp->t_softerror ? 160 tp->t_softerror : ETIMEDOUT); 161 break; 162 } 163 tcpstat.tcps_rexmttimeo++; 164 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift]; 165 TCPT_RANGESET(tp->t_rxtcur, rexmt, 166 tp->t_rttmin, TCPTV_REXMTMAX); 167 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur; 168 /* 169 * If losing, let the lower level know and try for 170 * a better route. Also, if we backed off this far, 171 * our srtt estimate is probably bogus. Clobber it 172 * so we'll take the next rtt measurement as our srtt; 173 * move the current srtt into rttvar to keep the current 174 * retransmit times until then. 175 */ 176 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) { 177 in_losing(tp->t_inpcb); 178 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT); 179 tp->t_srtt = 0; 180 } 181 tp->snd_nxt = tp->snd_una; 182 /* 183 * If timing a segment in this window, stop the timer. 184 */ 185 tp->t_rtt = 0; 186 /* 187 * Close the congestion window down to one segment 188 * (we'll open it by one segment for each ack we get). 189 * Since we probably have a window's worth of unacked 190 * data accumulated, this "slow start" keeps us from 191 * dumping all that data as back-to-back packets (which 192 * might overwhelm an intermediate gateway). 193 * 194 * There are two phases to the opening: Initially we 195 * open by one mss on each ack. This makes the window 196 * size increase exponentially with time. If the 197 * window is larger than the path can handle, this 198 * exponential growth results in dropped packet(s) 199 * almost immediately. To get more time between 200 * drops but still "push" the network to take advantage 201 * of improving conditions, we switch from exponential 202 * to linear window opening at some threshhold size. 203 * For a threshhold, we use half the current window 204 * size, truncated to a multiple of the mss. 205 * 206 * (the minimum cwnd that will give us exponential 207 * growth is 2 mss. We don't allow the threshhold 208 * to go below this.) 209 */ 210 { 211 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg; 212 if (win < 2) 213 win = 2; 214 tp->snd_cwnd = tp->t_maxseg; 215 tp->snd_ssthresh = win * tp->t_maxseg; 216 tp->t_dupacks = 0; 217 } 218 (void) tcp_output(tp); 219 break; 220 221 /* 222 * Persistance timer into zero window. 223 * Force a byte to be output, if possible. 224 */ 225 case TCPT_PERSIST: 226 tcpstat.tcps_persisttimeo++; 227 tcp_setpersist(tp); 228 tp->t_force = 1; 229 (void) tcp_output(tp); 230 tp->t_force = 0; 231 break; 232 233 /* 234 * Keep-alive timer went off; send something 235 * or drop connection if idle for too long. 236 */ 237 case TCPT_KEEP: 238 tcpstat.tcps_keeptimeo++; 239 if (tp->t_state < TCPS_ESTABLISHED) 240 goto dropit; 241 if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE && 242 tp->t_state <= TCPS_CLOSE_WAIT) { 243 if (tp->t_idle >= tcp_keepidle + tcp_maxidle) 244 goto dropit; 245 /* 246 * Send a packet designed to force a response 247 * if the peer is up and reachable: 248 * either an ACK if the connection is still alive, 249 * or an RST if the peer has closed the connection 250 * due to timeout or reboot. 251 * Using sequence number tp->snd_una-1 252 * causes the transmitted zero-length segment 253 * to lie outside the receive window; 254 * by the protocol spec, this requires the 255 * correspondent TCP to respond. 256 */ 257 tcpstat.tcps_keepprobe++; 258 #ifdef TCP_COMPAT_42 259 /* 260 * The keepalive packet must have nonzero length 261 * to get a 4.2 host to respond. 262 */ 263 tcp_respond(tp, tp->t_template, (struct mbuf *)NULL, 264 tp->rcv_nxt - 1, tp->snd_una - 1, 0); 265 #else 266 tcp_respond(tp, tp->t_template, (struct mbuf *)NULL, 267 tp->rcv_nxt, tp->snd_una - 1, 0); 268 #endif 269 tp->t_timer[TCPT_KEEP] = tcp_keepintvl; 270 } else 271 tp->t_timer[TCPT_KEEP] = tcp_keepidle; 272 break; 273 dropit: 274 tcpstat.tcps_keepdrops++; 275 tp = tcp_drop(tp, ETIMEDOUT); 276 break; 277 } 278 return (tp); 279 } 280