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 | */ |
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 | (void)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 | */ |
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 | */ |
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 | */ |
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 | (void)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 | (void)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 | |