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68396ea @rmustacc Initial commit of d32e8d0b8d9e0ef7cf7ab2e74548982972789dfc from qemu-kvm
rmustacc authored Jun 24, 2011
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 static struct tcpcb *tcp_timers(register struct tcpcb *tp, int timer);
36
37 /*
38 * Fast timeout routine for processing delayed acks
39 */
40 void
41 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
65 tcp_slowtimo(Slirp *slirp)
66 {
67 register struct socket *ip, *ipnxt;
68 register struct tcpcb *tp;
69 register int i;
70
71 DEBUG_CALL("tcp_slowtimo");
72
73 /*
74 * Search through tcb's and update active timers.
75 */
76 ip = slirp->tcb.so_next;
77 if (ip == NULL) {
78 return;
79 }
80 for (; ip != &slirp->tcb; ip = ipnxt) {
81 ipnxt = ip->so_next;
82 tp = sototcpcb(ip);
83 if (tp == NULL) {
84 continue;
85 }
86 for (i = 0; i < TCPT_NTIMERS; i++) {
87 if (tp->t_timer[i] && --tp->t_timer[i] == 0) {
88 tcp_timers(tp,i);
89 if (ipnxt->so_prev != ip)
90 goto tpgone;
91 }
92 }
93 tp->t_idle++;
94 if (tp->t_rtt)
95 tp->t_rtt++;
96 tpgone:
97 ;
98 }
99 slirp->tcp_iss += TCP_ISSINCR/PR_SLOWHZ; /* increment iss */
100 slirp->tcp_now++; /* for timestamps */
101 }
102
103 /*
104 * Cancel all timers for TCP tp.
105 */
106 void
107 tcp_canceltimers(struct tcpcb *tp)
108 {
109 register int i;
110
111 for (i = 0; i < TCPT_NTIMERS; i++)
112 tp->t_timer[i] = 0;
113 }
114
115 const int tcp_backoff[TCP_MAXRXTSHIFT + 1] =
116 { 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
117
118 /*
119 * TCP timer processing.
120 */
121 static struct tcpcb *
122 tcp_timers(register struct tcpcb *tp, int timer)
123 {
124 register int rexmt;
125
126 DEBUG_CALL("tcp_timers");
127
128 switch (timer) {
129
130 /*
131 * 2 MSL timeout in shutdown went off. If we're closed but
132 * still waiting for peer to close and connection has been idle
133 * too long, or if 2MSL time is up from TIME_WAIT, delete connection
134 * control block. Otherwise, check again in a bit.
135 */
136 case TCPT_2MSL:
137 if (tp->t_state != TCPS_TIME_WAIT &&
138 tp->t_idle <= TCP_MAXIDLE)
139 tp->t_timer[TCPT_2MSL] = TCPTV_KEEPINTVL;
140 else
141 tp = tcp_close(tp);
142 break;
143
144 /*
145 * Retransmission timer went off. Message has not
146 * been acked within retransmit interval. Back off
147 * to a longer retransmit interval and retransmit one segment.
148 */
149 case TCPT_REXMT:
150
151 /*
152 * XXXXX If a packet has timed out, then remove all the queued
153 * packets for that session.
154 */
155
156 if (++tp->t_rxtshift > TCP_MAXRXTSHIFT) {
157 /*
158 * This is a hack to suit our terminal server here at the uni of canberra
159 * since they have trouble with zeroes... It usually lets them through
160 * unharmed, but under some conditions, it'll eat the zeros. If we
161 * keep retransmitting it, it'll keep eating the zeroes, so we keep
162 * retransmitting, and eventually the connection dies...
163 * (this only happens on incoming data)
164 *
165 * So, if we were gonna drop the connection from too many retransmits,
166 * don't... instead halve the t_maxseg, which might break up the NULLs and
167 * let them through
168 *
169 * *sigh*
170 */
171
172 tp->t_maxseg >>= 1;
173 if (tp->t_maxseg < 32) {
174 /*
175 * We tried our best, now the connection must die!
176 */
177 tp->t_rxtshift = TCP_MAXRXTSHIFT;
178 tp = tcp_drop(tp, tp->t_softerror);
179 /* tp->t_softerror : ETIMEDOUT); */ /* XXX */
180 return (tp); /* XXX */
181 }
182
183 /*
184 * Set rxtshift to 6, which is still at the maximum
185 * backoff time
186 */
187 tp->t_rxtshift = 6;
188 }
189 rexmt = TCP_REXMTVAL(tp) * tcp_backoff[tp->t_rxtshift];
190 TCPT_RANGESET(tp->t_rxtcur, rexmt,
191 (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */
192 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
193 /*
194 * If losing, let the lower level know and try for
195 * a better route. Also, if we backed off this far,
196 * our srtt estimate is probably bogus. Clobber it
197 * so we'll take the next rtt measurement as our srtt;
198 * move the current srtt into rttvar to keep the current
199 * retransmit times until then.
200 */
201 if (tp->t_rxtshift > TCP_MAXRXTSHIFT / 4) {
202 tp->t_rttvar += (tp->t_srtt >> TCP_RTT_SHIFT);
203 tp->t_srtt = 0;
204 }
205 tp->snd_nxt = tp->snd_una;
206 /*
207 * If timing a segment in this window, stop the timer.
208 */
209 tp->t_rtt = 0;
210 /*
211 * Close the congestion window down to one segment
212 * (we'll open it by one segment for each ack we get).
213 * Since we probably have a window's worth of unacked
214 * data accumulated, this "slow start" keeps us from
215 * dumping all that data as back-to-back packets (which
216 * might overwhelm an intermediate gateway).
217 *
218 * There are two phases to the opening: Initially we
219 * open by one mss on each ack. This makes the window
220 * size increase exponentially with time. If the
221 * window is larger than the path can handle, this
222 * exponential growth results in dropped packet(s)
223 * almost immediately. To get more time between
224 * drops but still "push" the network to take advantage
225 * of improving conditions, we switch from exponential
226 * to linear window opening at some threshold size.
227 * For a threshold, we use half the current window
228 * size, truncated to a multiple of the mss.
229 *
230 * (the minimum cwnd that will give us exponential
231 * growth is 2 mss. We don't allow the threshold
232 * to go below this.)
233 */
234 {
235 u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;
236 if (win < 2)
237 win = 2;
238 tp->snd_cwnd = tp->t_maxseg;
239 tp->snd_ssthresh = win * tp->t_maxseg;
240 tp->t_dupacks = 0;
241 }
242 (void) tcp_output(tp);
243 break;
244
245 /*
246 * Persistence timer into zero window.
247 * Force a byte to be output, if possible.
248 */
249 case TCPT_PERSIST:
250 tcp_setpersist(tp);
251 tp->t_force = 1;
252 (void) tcp_output(tp);
253 tp->t_force = 0;
254 break;
255
256 /*
257 * Keep-alive timer went off; send something
258 * or drop connection if idle for too long.
259 */
260 case TCPT_KEEP:
261 if (tp->t_state < TCPS_ESTABLISHED)
262 goto dropit;
263
264 if ((SO_OPTIONS) && tp->t_state <= TCPS_CLOSE_WAIT) {
265 if (tp->t_idle >= TCPTV_KEEP_IDLE + TCP_MAXIDLE)
266 goto dropit;
267 /*
268 * Send a packet designed to force a response
269 * if the peer is up and reachable:
270 * either an ACK if the connection is still alive,
271 * or an RST if the peer has closed the connection
272 * due to timeout or reboot.
273 * Using sequence number tp->snd_una-1
274 * causes the transmitted zero-length segment
275 * to lie outside the receive window;
276 * by the protocol spec, this requires the
277 * correspondent TCP to respond.
278 */
279 tcp_respond(tp, &tp->t_template, (struct mbuf *)NULL,
280 tp->rcv_nxt, tp->snd_una - 1, 0);
281 tp->t_timer[TCPT_KEEP] = TCPTV_KEEPINTVL;
282 } else
283 tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_IDLE;
284 break;
285
286 dropit:
287 tp = tcp_drop(tp, 0);
288 break;
289 }
290
291 return (tp);
292 }
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