linux-user: stack_base is now mandatory on all targets
[qemu.git] / slirp / tcp_output.c
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_output.c 8.3 (Berkeley) 12/30/93
30 * tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp
31 */
32
33 /*
34 * Changes and additions relating to SLiRP
35 * Copyright (c) 1995 Danny Gasparovski.
36 *
37 * Please read the file COPYRIGHT for the
38 * terms and conditions of the copyright.
39 */
40
41 #include <slirp.h>
42
43 static const u_char tcp_outflags[TCP_NSTATES] = {
44 TH_RST|TH_ACK, 0, TH_SYN, TH_SYN|TH_ACK,
45 TH_ACK, TH_ACK, TH_FIN|TH_ACK, TH_FIN|TH_ACK,
46 TH_FIN|TH_ACK, TH_ACK, TH_ACK,
47 };
48
49
50 #define MAX_TCPOPTLEN 32 /* max # bytes that go in options */
51
52 /*
53 * Tcp output routine: figure out what should be sent and send it.
54 */
55 int
56 tcp_output(struct tcpcb *tp)
57 {
58 register struct socket *so = tp->t_socket;
59 register long len, win;
60 int off, flags, error;
61 register struct mbuf *m;
62 register struct tcpiphdr *ti;
63 u_char opt[MAX_TCPOPTLEN];
64 unsigned optlen, hdrlen;
65 int idle, sendalot;
66
67 DEBUG_CALL("tcp_output");
68 DEBUG_ARG("tp = %lx", (long )tp);
69
70 /*
71 * Determine length of data that should be transmitted,
72 * and flags that will be used.
73 * If there is some data or critical controls (SYN, RST)
74 * to send, then transmit; otherwise, investigate further.
75 */
76 idle = (tp->snd_max == tp->snd_una);
77 if (idle && tp->t_idle >= tp->t_rxtcur)
78 /*
79 * We have been idle for "a while" and no acks are
80 * expected to clock out any data we send --
81 * slow start to get ack "clock" running again.
82 */
83 tp->snd_cwnd = tp->t_maxseg;
84 again:
85 sendalot = 0;
86 off = tp->snd_nxt - tp->snd_una;
87 win = min(tp->snd_wnd, tp->snd_cwnd);
88
89 flags = tcp_outflags[tp->t_state];
90
91 DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
92
93 /*
94 * If in persist timeout with window of 0, send 1 byte.
95 * Otherwise, if window is small but nonzero
96 * and timer expired, we will send what we can
97 * and go to transmit state.
98 */
99 if (tp->t_force) {
100 if (win == 0) {
101 /*
102 * If we still have some data to send, then
103 * clear the FIN bit. Usually this would
104 * happen below when it realizes that we
105 * aren't sending all the data. However,
106 * if we have exactly 1 byte of unset data,
107 * then it won't clear the FIN bit below,
108 * and if we are in persist state, we wind
109 * up sending the packet without recording
110 * that we sent the FIN bit.
111 *
112 * We can't just blindly clear the FIN bit,
113 * because if we don't have any more data
114 * to send then the probe will be the FIN
115 * itself.
116 */
117 if (off < so->so_snd.sb_cc)
118 flags &= ~TH_FIN;
119 win = 1;
120 } else {
121 tp->t_timer[TCPT_PERSIST] = 0;
122 tp->t_rxtshift = 0;
123 }
124 }
125
126 len = min(so->so_snd.sb_cc, win) - off;
127
128 if (len < 0) {
129 /*
130 * If FIN has been sent but not acked,
131 * but we haven't been called to retransmit,
132 * len will be -1. Otherwise, window shrank
133 * after we sent into it. If window shrank to 0,
134 * cancel pending retransmit and pull snd_nxt
135 * back to (closed) window. We will enter persist
136 * state below. If the window didn't close completely,
137 * just wait for an ACK.
138 */
139 len = 0;
140 if (win == 0) {
141 tp->t_timer[TCPT_REXMT] = 0;
142 tp->snd_nxt = tp->snd_una;
143 }
144 }
145
146 if (len > tp->t_maxseg) {
147 len = tp->t_maxseg;
148 sendalot = 1;
149 }
150 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
151 flags &= ~TH_FIN;
152
153 win = sbspace(&so->so_rcv);
154
155 /*
156 * Sender silly window avoidance. If connection is idle
157 * and can send all data, a maximum segment,
158 * at least a maximum default-size segment do it,
159 * or are forced, do it; otherwise don't bother.
160 * If peer's buffer is tiny, then send
161 * when window is at least half open.
162 * If retransmitting (possibly after persist timer forced us
163 * to send into a small window), then must resend.
164 */
165 if (len) {
166 if (len == tp->t_maxseg)
167 goto send;
168 if ((1 || idle || tp->t_flags & TF_NODELAY) &&
169 len + off >= so->so_snd.sb_cc)
170 goto send;
171 if (tp->t_force)
172 goto send;
173 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
174 goto send;
175 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
176 goto send;
177 }
178
179 /*
180 * Compare available window to amount of window
181 * known to peer (as advertised window less
182 * next expected input). If the difference is at least two
183 * max size segments, or at least 50% of the maximum possible
184 * window, then want to send a window update to peer.
185 */
186 if (win > 0) {
187 /*
188 * "adv" is the amount we can increase the window,
189 * taking into account that we are limited by
190 * TCP_MAXWIN << tp->rcv_scale.
191 */
192 long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
193 (tp->rcv_adv - tp->rcv_nxt);
194
195 if (adv >= (long) (2 * tp->t_maxseg))
196 goto send;
197 if (2 * adv >= (long) so->so_rcv.sb_datalen)
198 goto send;
199 }
200
201 /*
202 * Send if we owe peer an ACK.
203 */
204 if (tp->t_flags & TF_ACKNOW)
205 goto send;
206 if (flags & (TH_SYN|TH_RST))
207 goto send;
208 if (SEQ_GT(tp->snd_up, tp->snd_una))
209 goto send;
210 /*
211 * If our state indicates that FIN should be sent
212 * and we have not yet done so, or we're retransmitting the FIN,
213 * then we need to send.
214 */
215 if (flags & TH_FIN &&
216 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
217 goto send;
218
219 /*
220 * TCP window updates are not reliable, rather a polling protocol
221 * using ``persist'' packets is used to insure receipt of window
222 * updates. The three ``states'' for the output side are:
223 * idle not doing retransmits or persists
224 * persisting to move a small or zero window
225 * (re)transmitting and thereby not persisting
226 *
227 * tp->t_timer[TCPT_PERSIST]
228 * is set when we are in persist state.
229 * tp->t_force
230 * is set when we are called to send a persist packet.
231 * tp->t_timer[TCPT_REXMT]
232 * is set when we are retransmitting
233 * The output side is idle when both timers are zero.
234 *
235 * If send window is too small, there is data to transmit, and no
236 * retransmit or persist is pending, then go to persist state.
237 * If nothing happens soon, send when timer expires:
238 * if window is nonzero, transmit what we can,
239 * otherwise force out a byte.
240 */
241 if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
242 tp->t_timer[TCPT_PERSIST] == 0) {
243 tp->t_rxtshift = 0;
244 tcp_setpersist(tp);
245 }
246
247 /*
248 * No reason to send a segment, just return.
249 */
250 return (0);
251
252 send:
253 /*
254 * Before ESTABLISHED, force sending of initial options
255 * unless TCP set not to do any options.
256 * NOTE: we assume that the IP/TCP header plus TCP options
257 * always fit in a single mbuf, leaving room for a maximum
258 * link header, i.e.
259 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
260 */
261 optlen = 0;
262 hdrlen = sizeof (struct tcpiphdr);
263 if (flags & TH_SYN) {
264 tp->snd_nxt = tp->iss;
265 if ((tp->t_flags & TF_NOOPT) == 0) {
266 uint16_t mss;
267
268 opt[0] = TCPOPT_MAXSEG;
269 opt[1] = 4;
270 mss = htons((uint16_t) tcp_mss(tp, 0));
271 memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
272 optlen = 4;
273 }
274 }
275
276 hdrlen += optlen;
277
278 /*
279 * Adjust data length if insertion of options will
280 * bump the packet length beyond the t_maxseg length.
281 */
282 if (len > tp->t_maxseg - optlen) {
283 len = tp->t_maxseg - optlen;
284 sendalot = 1;
285 }
286
287 /*
288 * Grab a header mbuf, attaching a copy of data to
289 * be transmitted, and initialize the header from
290 * the template for sends on this connection.
291 */
292 if (len) {
293 m = m_get(so->slirp);
294 if (m == NULL) {
295 error = 1;
296 goto out;
297 }
298 m->m_data += IF_MAXLINKHDR;
299 m->m_len = hdrlen;
300
301 sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
302 m->m_len += len;
303
304 /*
305 * If we're sending everything we've got, set PUSH.
306 * (This will keep happy those implementations which only
307 * give data to the user when a buffer fills or
308 * a PUSH comes in.)
309 */
310 if (off + len == so->so_snd.sb_cc)
311 flags |= TH_PUSH;
312 } else {
313 m = m_get(so->slirp);
314 if (m == NULL) {
315 error = 1;
316 goto out;
317 }
318 m->m_data += IF_MAXLINKHDR;
319 m->m_len = hdrlen;
320 }
321
322 ti = mtod(m, struct tcpiphdr *);
323
324 memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));
325
326 /*
327 * Fill in fields, remembering maximum advertised
328 * window for use in delaying messages about window sizes.
329 * If resending a FIN, be sure not to use a new sequence number.
330 */
331 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
332 tp->snd_nxt == tp->snd_max)
333 tp->snd_nxt--;
334 /*
335 * If we are doing retransmissions, then snd_nxt will
336 * not reflect the first unsent octet. For ACK only
337 * packets, we do not want the sequence number of the
338 * retransmitted packet, we want the sequence number
339 * of the next unsent octet. So, if there is no data
340 * (and no SYN or FIN), use snd_max instead of snd_nxt
341 * when filling in ti_seq. But if we are in persist
342 * state, snd_max might reflect one byte beyond the
343 * right edge of the window, so use snd_nxt in that
344 * case, since we know we aren't doing a retransmission.
345 * (retransmit and persist are mutually exclusive...)
346 */
347 if (len || (flags & (TH_SYN|TH_FIN)) || tp->t_timer[TCPT_PERSIST])
348 ti->ti_seq = htonl(tp->snd_nxt);
349 else
350 ti->ti_seq = htonl(tp->snd_max);
351 ti->ti_ack = htonl(tp->rcv_nxt);
352 if (optlen) {
353 memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
354 ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
355 }
356 ti->ti_flags = flags;
357 /*
358 * Calculate receive window. Don't shrink window,
359 * but avoid silly window syndrome.
360 */
361 if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
362 win = 0;
363 if (win > (long)TCP_MAXWIN << tp->rcv_scale)
364 win = (long)TCP_MAXWIN << tp->rcv_scale;
365 if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
366 win = (long)(tp->rcv_adv - tp->rcv_nxt);
367 ti->ti_win = htons((uint16_t) (win>>tp->rcv_scale));
368
369 if (SEQ_GT(tp->snd_up, tp->snd_una)) {
370 ti->ti_urp = htons((uint16_t)(tp->snd_up - ntohl(ti->ti_seq)));
371 ti->ti_flags |= TH_URG;
372 } else
373 /*
374 * If no urgent pointer to send, then we pull
375 * the urgent pointer to the left edge of the send window
376 * so that it doesn't drift into the send window on sequence
377 * number wraparound.
378 */
379 tp->snd_up = tp->snd_una; /* drag it along */
380
381 /*
382 * Put TCP length in extended header, and then
383 * checksum extended header and data.
384 */
385 if (len + optlen)
386 ti->ti_len = htons((uint16_t)(sizeof (struct tcphdr) +
387 optlen + len));
388 ti->ti_sum = cksum(m, (int)(hdrlen + len));
389
390 /*
391 * In transmit state, time the transmission and arrange for
392 * the retransmit. In persist state, just set snd_max.
393 */
394 if (tp->t_force == 0 || tp->t_timer[TCPT_PERSIST] == 0) {
395 tcp_seq startseq = tp->snd_nxt;
396
397 /*
398 * Advance snd_nxt over sequence space of this segment.
399 */
400 if (flags & (TH_SYN|TH_FIN)) {
401 if (flags & TH_SYN)
402 tp->snd_nxt++;
403 if (flags & TH_FIN) {
404 tp->snd_nxt++;
405 tp->t_flags |= TF_SENTFIN;
406 }
407 }
408 tp->snd_nxt += len;
409 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
410 tp->snd_max = tp->snd_nxt;
411 /*
412 * Time this transmission if not a retransmission and
413 * not currently timing anything.
414 */
415 if (tp->t_rtt == 0) {
416 tp->t_rtt = 1;
417 tp->t_rtseq = startseq;
418 }
419 }
420
421 /*
422 * Set retransmit timer if not currently set,
423 * and not doing an ack or a keep-alive probe.
424 * Initial value for retransmit timer is smoothed
425 * round-trip time + 2 * round-trip time variance.
426 * Initialize shift counter which is used for backoff
427 * of retransmit time.
428 */
429 if (tp->t_timer[TCPT_REXMT] == 0 &&
430 tp->snd_nxt != tp->snd_una) {
431 tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
432 if (tp->t_timer[TCPT_PERSIST]) {
433 tp->t_timer[TCPT_PERSIST] = 0;
434 tp->t_rxtshift = 0;
435 }
436 }
437 } else
438 if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
439 tp->snd_max = tp->snd_nxt + len;
440
441 /*
442 * Fill in IP length and desired time to live and
443 * send to IP level. There should be a better way
444 * to handle ttl and tos; we could keep them in
445 * the template, but need a way to checksum without them.
446 */
447 m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
448
449 {
450
451 ((struct ip *)ti)->ip_len = m->m_len;
452
453 ((struct ip *)ti)->ip_ttl = IPDEFTTL;
454 ((struct ip *)ti)->ip_tos = so->so_iptos;
455
456 error = ip_output(so, m);
457 }
458 if (error) {
459 out:
460 return (error);
461 }
462
463 /*
464 * Data sent (as far as we can tell).
465 * If this advertises a larger window than any other segment,
466 * then remember the size of the advertised window.
467 * Any pending ACK has now been sent.
468 */
469 if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
470 tp->rcv_adv = tp->rcv_nxt + win;
471 tp->last_ack_sent = tp->rcv_nxt;
472 tp->t_flags &= ~(TF_ACKNOW|TF_DELACK);
473 if (sendalot)
474 goto again;
475
476 return (0);
477 }
478
479 void
480 tcp_setpersist(struct tcpcb *tp)
481 {
482 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
483
484 /*
485 * Start/restart persistence timer.
486 */
487 TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
488 t * tcp_backoff[tp->t_rxtshift],
489 TCPTV_PERSMIN, TCPTV_PERSMAX);
490 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
491 tp->t_rxtshift++;
492 }