1 /* SPDX-License-Identifier: BSD-3-Clause */
2 /*
3 * Copyright (c) 1982, 1986, 1988, 1990, 1993
4 * The Regents of the University of California. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 * may be used to endorse or promote products derived from this software
16 * without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 *
30 * @(#)tcp_timer.c 8.1 (Berkeley) 6/10/93
31 * tcp_timer.c,v 1.2 1994/08/02 07:49:10 davidg Exp
32 */
33
34 #include "slirp.h"
35
36 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
37
38 /*
39 * Fast timeout routine for processing delayed acks
40 */
tcp_fasttimo(Slirp * slirp)41 void tcp_fasttimo(Slirp *slirp)
42 {
43 register struct socket *so;
44 register struct tcpcb *tp;
45
46 DEBUG_CALL("tcp_fasttimo");
47
48 so = slirp->tcb.so_next;
49 if (so)
50 for (; so != &slirp->tcb; so = so->so_next)
51 if ((tp = (struct tcpcb *)so->so_tcpcb) &&
52 (tp->t_flags & TF_DELACK)) {
53 tp->t_flags &= ~TF_DELACK;
54 tp->t_flags |= TF_ACKNOW;
55 tcp_output(tp);
56 }
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 */
tcp_slowtimo(Slirp * slirp)64 void tcp_slowtimo(Slirp *slirp)
65 {
66 register struct socket *ip, *ipnxt;
67 register struct tcpcb *tp;
68 register int i;
69
70 DEBUG_CALL("tcp_slowtimo");
71
72 /*
73 * Search through tcb's and update active timers.
74 */
75 ip = slirp->tcb.so_next;
76 if (ip == NULL) {
77 return;
78 }
79 for (; ip != &slirp->tcb; ip = ipnxt) {
80 ipnxt = ip->so_next;
81 tp = sototcpcb(ip);
82 if (tp == NULL) {
83 continue;
84 }
85 for (i = 0; i < TCPT_NTIMERS; i++) {
86 if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
87 tcp_timers(tp, i);
88 if (ipnxt->so_prev != ip)
89 goto tpgone;
90 }
91 }
92 tp->t_idle++;
93 if (tp->t_rtt)
94 tp->t_rtt++;
95 tpgone:;
96 }
97 slirp->tcp_iss += TCP_ISSINCR / PR_SLOWHZ; /* increment iss */
98 slirp->tcp_now++; /* for timestamps */
99 }
100
101 /*
102 * Cancel all timers for TCP tp.
103 */
tcp_canceltimers(struct tcpcb * tp)104 void tcp_canceltimers(struct tcpcb *tp)
105 {
106 register int i;
107
108 for (i = 0; i < TCPT_NTIMERS; i++)
109 tp->t_timer[i] = 0;
110 }
111
112 const int tcp_backoff[TCP_MAXRXTSHIFT + 1] = { 1, 2, 4, 8, 16, 32, 64,
113 64, 64, 64, 64, 64, 64 };
114
115 /*
116 * TCP timer processing.
117 */
tcp_timers(register struct tcpcb * tp,int timer)118 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer)
119 {
120 register int rexmt;
121
122 DEBUG_CALL("tcp_timers");
123
124 switch (timer) {
125 /*
126 * 2 MSL timeout in shutdown went off. If we're closed but
127 * still waiting for peer to close and connection has been idle
128 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
129 * control block. Otherwise, check again in a bit.
130 */
131 case TCPT_2MSL:
132 if (tp->t_state != TCPS_TIME_WAIT && tp->t_idle <= TCP_MAXIDLE)
133 tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
134 else
135 tp = tcp_close(tp);
136 break;
137
138 /*
139 * Retransmission timer went off. Message has not
140 * been acked within retransmit interval. Back off
141 * to a longer retransmit interval and retransmit one segment.
142 */
143 case TCPT_REXMT:
144
145 /*
146 * XXXXX If a packet has timed out, then remove all the queued
147 * packets for that session.
148 */
149
150 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
151 /*
152 * This is a hack to suit our terminal server here at the uni of
153 * canberra since they have trouble with zeroes... It usually lets
154 * them through unharmed, but under some conditions, it'll eat the
155 * zeros. If we keep retransmitting it, it'll keep eating the
156 * zeroes, so we keep retransmitting, and eventually the connection
157 * dies... (this only happens on incoming data)
158 *
159 * So, if we were gonna drop the connection from too many
160 * retransmits, don't... instead halve the t_maxseg, which might
161 * break up the NULLs and let them through
162 *
163 * *sigh*
164 */
165
166 tp->t_maxseg >>= 1;
167 if (tp->t_maxseg < 32) {
168 /*
169 * We tried our best, now the connection must die!
170 */
171 tp->t_rxtshift = TCP_MAXRXTSHIFT;
172 tp = tcp_drop(tp, tp->t_softerror);
173 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
174 return (tp); /* XXX */
175 }
176
177 /*
178 * Set rxtshift to 6, which is still at the maximum
179 * backoff time
180 */
181 tp->t_rxtshift = 6;
182 }
183 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
184 TCPT_RANGESET(tp->t_rxtcur, rexmt, (short)tp->t_rttmin,
185 TCPTV_REXMTMAX); /* XXX */
186 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
187 /*
188 * If losing, let the lower level know and try for
189 * a better route. Also, if we backed off this far,
190 * our srtt estimate is probably bogus. Clobber it
191 * so we'll take the next rtt measurement as our srtt;
192 * move the current srtt into rttvar to keep the current
193 * retransmit times until then.
194 */
195 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
196 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
197 tp->t_srtt = 0;
198 }
199 tp->snd_nxt = tp->snd_una;
200 /*
201 * If timing a segment in this window, stop the timer.
202 */
203 tp->t_rtt = 0;
204 /*
205 * Close the congestion window down to one segment
206 * (we'll open it by one segment for each ack we get).
207 * Since we probably have a window's worth of unacked
208 * data accumulated, this "slow start" keeps us from
209 * dumping all that data as back-to-back packets (which
210 * might overwhelm an intermediate gateway).
211 *
212 * There are two phases to the opening: Initially we
213 * open by one mss on each ack. This makes the window
214 * size increase exponentially with time. If the
215 * window is larger than the path can handle, this
216 * exponential growth results in dropped packet(s)
217 * almost immediately. To get more time between
218 * drops but still "push" the network to take advantage
219 * of improving conditions, we switch from exponential
220 * to linear window opening at some threshold size.
221 * For a threshold, we use half the current window
222 * size, truncated to a multiple of the mss.
223 *
224 * (the minimum cwnd that will give us exponential
225 * growth is 2 mss. We don't allow the threshold
226 * to go below this.)
227 */
228 {
229 unsigned win = MIN(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
230 if (win < 2)
231 win = 2;
232 tp->snd_cwnd = tp->t_maxseg;
233 tp->snd_ssthresh = win * tp->t_maxseg;
234 tp->t_dupacks = 0;
235 }
236 tcp_output(tp);
237 break;
238
239 /*
240 * Persistence timer into zero window.
241 * Force a byte to be output, if possible.
242 */
243 case TCPT_PERSIST:
244 tcp_setpersist(tp);
245 tp->t_force = 1;
246 tcp_output(tp);
247 tp->t_force = 0;
248 break;
249
250 /*
251 * Keep-alive timer went off; send something
252 * or drop connection if idle for too long.
253 */
254 case TCPT_KEEP:
255 if (tp->t_state < TCPS_ESTABLISHED)
256 goto dropit;
257
258 if (slirp_do_keepalive && tp->t_state <= TCPS_CLOSE_WAIT) {
259 if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
260 goto dropit;
261 /*
262 * Send a packet designed to force a response
263 * if the peer is up and reachable:
264 * either an ACK if the connection is still alive,
265 * or an RST if the peer has closed the connection
266 * due to timeout or reboot.
267 * Using sequence number tp->snd_una-1
268 * causes the transmitted zero-length segment
269 * to lie outside the receive window;
270 * by the protocol spec, this requires the
271 * correspondent TCP to respond.
272 */
273 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL, tp->rcv_nxt,
274 tp->snd_una - 1, 0, tp->t_socket->so_ffamily);
275 tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
276 } else
277 tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
278 break;
279
280 dropit:
281 tp = tcp_drop(tp, 0);
282 break;
283 }
284
285 return (tp);
286 }
287