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. All advertising materials mentioning features or use of this software
14 * must display the following acknowledgement:
15 * This product includes software developed by the University of
16 * California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
34 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
35 */
36
37 #include <slirp.h>
38
39 int tcp_keepidle = TCPTV_KEEP_IDLE;
40 int tcp_keepintvl = TCPTV_KEEPINTVL;
41 int tcp_maxidle;
42 int so_options = DO_KEEPALIVE;
43
44 struct tcpstat tcpstat; /* tcp statistics */
45 u_int32_t tcp_now; /* for RFC 1323 timestamps */
46
47 /*
48 * Fast timeout routine for processing delayed acks
49 */
50 void
tcp_fasttimo()51 tcp_fasttimo()
52 {
53 register struct socket *so;
54 register struct tcpcb *tp;
55
56 DEBUG_CALL("tcp_fasttimo");
57
58 so = tcb.so_next;
59 if (so)
60 for (; so != &tcb; so = so->so_next)
61 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
62 (tp->t_flags & TF_DELACK)) {
63 tp->t_flags &= ~TF_DELACK;
64 tp->t_flags |= TF_ACKNOW;
65 tcpstat.tcps_delack++;
66 (void) tcp_output(tp);
67 }
68 }
69
70 /*
71 * Tcp protocol timeout routine called every 500 ms.
72 * Updates the timers in all active tcb's and
73 * causes finite state machine actions if timers expire.
74 */
75 void
tcp_slowtimo()76 tcp_slowtimo()
77 {
78 register struct socket *ip, *ipnxt;
79 register struct tcpcb *tp;
80 register int i;
81
82 DEBUG_CALL("tcp_slowtimo");
83
84 tcp_maxidle = TCPTV_KEEPCNT * tcp_keepintvl;
85 /*
86 * Search through tcb's and update active timers.
87 */
88 ip = tcb.so_next;
89 if (ip == 0)
90 return;
91 for (; ip != &tcb; ip = ipnxt) {
92 ipnxt = ip->so_next;
93 tp = sototcpcb(ip);
94 if (tp == 0)
95 continue;
96 for (i = 0; i < TCPT_NTIMERS; i++) {
97 if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
98 tcp_timers(tp,i);
99 if (ipnxt->so_prev != ip)
100 goto tpgone;
101 }
102 }
103 tp->t_idle++;
104 if (tp->t_rtt)
105 tp->t_rtt++;
106 tpgone:
107 ;
108 }
109 tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */
110 #ifdef TCP_COMPAT_42
111 if ((int)tcp_iss < 0)
112 tcp_iss = 0; /* XXX */
113 #endif
114 tcp_now++; /* for timestamps */
115 }
116
117 /*
118 * Cancel all timers for TCP tp.
119 */
120 void
tcp_canceltimers(tp)121 tcp_canceltimers(tp)
122 struct tcpcb *tp;
123 {
124 register int i;
125
126 for (i = 0; i < TCPT_NTIMERS; i++)
127 tp->t_timer[i] = 0;
128 }
129
130 int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
131 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
132
133 /*
134 * TCP timer processing.
135 */
136 struct tcpcb *
tcp_timers(tp,timer)137 tcp_timers(tp, timer)
138 register struct tcpcb *tp;
139 int timer;
140 {
141 register int rexmt;
142
143 DEBUG_CALL("tcp_timers");
144
145 switch (timer) {
146
147 /*
148 * 2 MSL timeout in shutdown went off. If we're closed but
149 * still waiting for peer to close and connection has been idle
150 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
151 * control block. Otherwise, check again in a bit.
152 */
153 case TCPT_2MSL:
154 if (tp->t_state != TCPS_TIME_WAIT &&
155 tp->t_idle <= tcp_maxidle)
156 tp->t_timer[TCPT_2MSL] = tcp_keepintvl;
157 else
158 tp = tcp_close(tp);
159 break;
160
161 /*
162 * Retransmission timer went off. Message has not
163 * been acked within retransmit interval. Back off
164 * to a longer retransmit interval and retransmit one segment.
165 */
166 case TCPT_REXMT:
167
168 /*
169 * XXXXX If a packet has timed out, then remove all the queued
170 * packets for that session.
171 */
172
173 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
174 /*
175 * This is a hack to suit our terminal server here at the uni of canberra
176 * since they have trouble with zeroes... It usually lets them through
177 * unharmed, but under some conditions, it'll eat the zeros. If we
178 * keep retransmitting it, it'll keep eating the zeroes, so we keep
179 * retransmitting, and eventually the connection dies...
180 * (this only happens on incoming data)
181 *
182 * So, if we were gonna drop the connection from too many retransmits,
183 * don't... instead halve the t_maxseg, which might break up the NULLs and
184 * let them through
185 *
186 * *sigh*
187 */
188
189 tp->t_maxseg >>= 1;
190 if (tp->t_maxseg < 32) {
191 /*
192 * We tried our best, now the connection must die!
193 */
194 tp->t_rxtshift = TCP_MAXRXTSHIFT;
195 tcpstat.tcps_timeoutdrop++;
196 tp = tcp_drop(tp, tp->t_softerror);
197 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
198 return (tp); /* XXX */
199 }
200
201 /*
202 * Set rxtshift to 6, which is still at the maximum
203 * backoff time
204 */
205 tp->t_rxtshift = 6;
206 }
207 tcpstat.tcps_rexmttimeo++;
208 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
209 TCPT_RANGESET(tp->t_rxtcur, rexmt,
210 (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
211 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
212 /*
213 * If losing, let the lower level know and try for
214 * a better route. Also, if we backed off this far,
215 * our srtt estimate is probably bogus. Clobber it
216 * so we'll take the next rtt measurement as our srtt;
217 * move the current srtt into rttvar to keep the current
218 * retransmit times until then.
219 */
220 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
221 /* in_losing(tp->t_inpcb); */
222 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
223 tp->t_srtt = 0;
224 }
225 tp->snd_nxt = tp->snd_una;
226 /*
227 * If timing a segment in this window, stop the timer.
228 */
229 tp->t_rtt = 0;
230 /*
231 * Close the congestion window down to one segment
232 * (we'll open it by one segment for each ack we get).
233 * Since we probably have a window's worth of unacked
234 * data accumulated, this "slow start" keeps us from
235 * dumping all that data as back-to-back packets (which
236 * might overwhelm an intermediate gateway).
237 *
238 * There are two phases to the opening: Initially we
239 * open by one mss on each ack. This makes the window
240 * size increase exponentially with time. If the
241 * window is larger than the path can handle, this
242 * exponential growth results in dropped packet(s)
243 * almost immediately. To get more time between
244 * drops but still "push" the network to take advantage
245 * of improving conditions, we switch from exponential
246 * to linear window opening at some threshold size.
247 * For a threshold, we use half the current window
248 * size, truncated to a multiple of the mss.
249 *
250 * (the minimum cwnd that will give us exponential
251 * growth is 2 mss. We don't allow the threshold
252 * to go below this.)
253 */
254 {
255 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
256 if (win < 2)
257 win = 2;
258 tp->snd_cwnd = tp->t_maxseg;
259 tp->snd_ssthresh = win * tp->t_maxseg;
260 tp->t_dupacks = 0;
261 }
262 (void) tcp_output(tp);
263 break;
264
265 /*
266 * Persistence timer into zero window.
267 * Force a byte to be output, if possible.
268 */
269 case TCPT_PERSIST:
270 tcpstat.tcps_persisttimeo++;
271 tcp_setpersist(tp);
272 tp->t_force = 1;
273 (void) tcp_output(tp);
274 tp->t_force = 0;
275 break;
276
277 /*
278 * Keep-alive timer went off; send something
279 * or drop connection if idle for too long.
280 */
281 case TCPT_KEEP:
282 tcpstat.tcps_keeptimeo++;
283 if (tp->t_state < TCPS_ESTABLISHED)
284 goto dropit;
285
286 /* if (tp->t_socket->so_options & SO_KEEPALIVE && */
287 if ((so_options) && tp->t_state <= TCPS_CLOSE_WAIT) {
288 if (tp->t_idle >= tcp_keepidle + tcp_maxidle)
289 goto dropit;
290 /*
291 * Send a packet designed to force a response
292 * if the peer is up and reachable:
293 * either an ACK if the connection is still alive,
294 * or an RST if the peer has closed the connection
295 * due to timeout or reboot.
296 * Using sequence number tp->snd_una-1
297 * causes the transmitted zero-length segment
298 * to lie outside the receive window;
299 * by the protocol spec, this requires the
300 * correspondent TCP to respond.
301 */
302 tcpstat.tcps_keepprobe++;
303 #ifdef TCP_COMPAT_42
304 /*
305 * The keepalive packet must have nonzero length
306 * to get a 4.2 host to respond.
307 */
308 tcp_respond(tp, &tp->t_template, (MBuf )NULL,
309 tp->rcv_nxt - 1, tp->snd_una - 1, 0);
310 #else
311 tcp_respond(tp, &tp->t_template, (MBuf )NULL,
312 tp->rcv_nxt, tp->snd_una - 1, 0);
313 #endif
314 tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
315 } else
316 tp->t_timer[TCPT_KEEP] = tcp_keepidle;
317 break;
318
319 dropit:
320 tcpstat.tcps_keepdrops++;
321 tp = tcp_drop(tp, 0); /* ETIMEDOUT); */
322 break;
323 }
324
325 return (tp);
326 }
327