1 /*
2 * Copyright (c) 1982, 1986, 1988, 1990, 1993
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 *
29 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
30 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
31 */
32
33 #include <slirp.h>
34
35 #ifdef LOG_ENABLED
36 struct tcpstat tcpstat; /* tcp statistics */
37 #endif
38
39 u_int32_t tcp_now; /* for RFC 1323 timestamps */
40
41 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
42
43 /*
44 * Fast timeout routine for processing delayed acks
45 */
46 void
tcp_fasttimo(void)47 tcp_fasttimo(void)
48 {
49 register struct socket *so;
50 register struct tcpcb *tp;
51
52 DEBUG_CALL("tcp_fasttimo");
53
54 so = tcb.so_next;
55 if (so)
56 for (; so != &tcb; so = so->so_next)
57 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
58 (tp->t_flags & TF_DELACK)) {
59 tp->t_flags &= ~TF_DELACK;
60 tp->t_flags |= TF_ACKNOW;
61 STAT(tcpstat.tcps_delack++);
62 (void) tcp_output(tp);
63 }
64 }
65
66 /*
67 * Tcp protocol timeout routine called every 500 ms.
68 * Updates the timers in all active tcb's and
69 * causes finite state machine actions if timers expire.
70 */
71 void
tcp_slowtimo(void)72 tcp_slowtimo(void)
73 {
74 register struct socket *ip, *ipnxt;
75 register struct tcpcb *tp;
76 register int i;
77
78 DEBUG_CALL("tcp_slowtimo");
79
80 /*
81 * Search through tcb's and update active timers.
82 */
83 ip = tcb.so_next;
84 if (ip == 0)
85 return;
86 for (; ip != &tcb; ip = ipnxt) {
87 ipnxt = ip->so_next;
88 tp = sototcpcb(ip);
89 if (tp == 0)
90 continue;
91 for (i = 0; i < TCPT_NTIMERS; i++) {
92 if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
93 tcp_timers(tp,i);
94 if (ipnxt->so_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 tcp_now++; /* for timestamps */
110 }
111
112 /*
113 * Cancel all timers for TCP tp.
114 */
115 void
tcp_canceltimers(struct tcpcb * tp)116 tcp_canceltimers(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 const 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 static struct tcpcb *
tcp_timers(register struct tcpcb * tp,int timer)131 tcp_timers(register struct tcpcb *tp, int timer)
132 {
133 register int rexmt;
134
135 DEBUG_CALL("tcp_timers");
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] = TCPTV_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
160 /*
161 * XXXXX If a packet has timed out, then remove all the queued
162 * packets for that session.
163 */
164
165 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
166 /*
167 * This is a hack to suit our terminal server here at the uni of canberra
168 * since they have trouble with zeroes... It usually lets them through
169 * unharmed, but under some conditions, it'll eat the zeros. If we
170 * keep retransmitting it, it'll keep eating the zeroes, so we keep
171 * retransmitting, and eventually the connection dies...
172 * (this only happens on incoming data)
173 *
174 * So, if we were gonna drop the connection from too many retransmits,
175 * don't... instead halve the t_maxseg, which might break up the NULLs and
176 * let them through
177 *
178 * *sigh*
179 */
180
181 tp->t_maxseg >>= 1;
182 if (tp->t_maxseg < 32) {
183 /*
184 * We tried our best, now the connection must die!
185 */
186 tp->t_rxtshift = TCP_MAXRXTSHIFT;
187 STAT(tcpstat.tcps_timeoutdrop++);
188 tp = tcp_drop(tp, tp->t_softerror);
189 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
190 return (tp); /* XXX */
191 }
192
193 /*
194 * Set rxtshift to 6, which is still at the maximum
195 * backoff time
196 */
197 tp->t_rxtshift = 6;
198 }
199 STAT(tcpstat.tcps_rexmttimeo++);
200 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
201 TCPT_RANGESET(tp->t_rxtcur, rexmt,
202 (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
203 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
204 /*
205 * If losing, let the lower level know and try for
206 * a better route. Also, if we backed off this far,
207 * our srtt estimate is probably bogus. Clobber it
208 * so we'll take the next rtt measurement as our srtt;
209 * move the current srtt into rttvar to keep the current
210 * retransmit times until then.
211 */
212 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
213 /* in_losing(tp->t_inpcb); */
214 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
215 tp->t_srtt = 0;
216 }
217 tp->snd_nxt = tp->snd_una;
218 /*
219 * If timing a segment in this window, stop the timer.
220 */
221 tp->t_rtt = 0;
222 /*
223 * Close the congestion window down to one segment
224 * (we'll open it by one segment for each ack we get).
225 * Since we probably have a window's worth of unacked
226 * data accumulated, this "slow start" keeps us from
227 * dumping all that data as back-to-back packets (which
228 * might overwhelm an intermediate gateway).
229 *
230 * There are two phases to the opening: Initially we
231 * open by one mss on each ack. This makes the window
232 * size increase exponentially with time. If the
233 * window is larger than the path can handle, this
234 * exponential growth results in dropped packet(s)
235 * almost immediately. To get more time between
236 * drops but still "push" the network to take advantage
237 * of improving conditions, we switch from exponential
238 * to linear window opening at some threshold size.
239 * For a threshold, we use half the current window
240 * size, truncated to a multiple of the mss.
241 *
242 * (the minimum cwnd that will give us exponential
243 * growth is 2 mss. We don't allow the threshold
244 * to go below this.)
245 */
246 {
247 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
248 if (win < 2)
249 win = 2;
250 tp->snd_cwnd = tp->t_maxseg;
251 tp->snd_ssthresh = win * tp->t_maxseg;
252 tp->t_dupacks = 0;
253 }
254 (void) tcp_output(tp);
255 break;
256
257 /*
258 * Persistence timer into zero window.
259 * Force a byte to be output, if possible.
260 */
261 case TCPT_PERSIST:
262 STAT(tcpstat.tcps_persisttimeo++);
263 tcp_setpersist(tp);
264 tp->t_force = 1;
265 (void) tcp_output(tp);
266 tp->t_force = 0;
267 break;
268
269 /*
270 * Keep-alive timer went off; send something
271 * or drop connection if idle for too long.
272 */
273 case TCPT_KEEP:
274 STAT(tcpstat.tcps_keeptimeo++);
275 if (tp->t_state < TCPS_ESTABLISHED)
276 goto dropit;
277
278 /* if (tp->t_socket->so_options & SO_KEEPALIVE && */
279 if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
280 if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
281 goto dropit;
282 /*
283 * Send a packet designed to force a response
284 * if the peer is up and reachable:
285 * either an ACK if the connection is still alive,
286 * or an RST if the peer has closed the connection
287 * due to timeout or reboot.
288 * Using sequence number tp->snd_una-1
289 * causes the transmitted zero-length segment
290 * to lie outside the receive window;
291 * by the protocol spec, this requires the
292 * correspondent TCP to respond.
293 */
294 STAT(tcpstat.tcps_keepprobe++);
295 #ifdef TCP_COMPAT_42
296 /*
297 * The keepalive packet must have nonzero length
298 * to get a 4.2 host to respond.
299 */
300 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
301 tp->rcv_nxt - 1, tp->snd_una - 1, 0);
302 #else
303 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
304 tp->rcv_nxt, tp->snd_una - 1, 0);
305 #endif
306 tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
307 } else
308 tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
309 break;
310
311 dropit:
312 STAT(tcpstat.tcps_keepdrops++);
313 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
314 break;
315 }
316
317 return (tp);
318 }
319