tcp_output.c@ 14470

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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_output.c 8.3 (Berkeley) 12/30/93
34	* tcp_output.c,v 1.3 1994/09/15 10:36:55 davidg Exp
35	*/
36
37	/*
38	* Changes and additions relating to SLiRP
39	* Copyright (c) 1995 Danny Gasparovski.
40	*
41	* Please read the file COPYRIGHT for the
42	* terms and conditions of the copyright.
43	*/
44
45	#include <slirp.h>
46
47	/*
48	* Since this is only used in "stats socket", we give meaning
49	* names instead of the REAL names
50	*/
51	const char * const tcpstates[] = {
52	/* "CLOSED", "LISTEN", "SYN_SENT", "SYN_RCVD", */
53	"REDIRECT", "LISTEN", "SYN_SENT", "SYN_RCVD",
54	"ESTABLISHED", "CLOSE_WAIT", "FIN_WAIT_1", "CLOSING",
55	"LAST_ACK", "FIN_WAIT_2", "TIME_WAIT",
56	};
57
58	static const u_char tcp_outflags[TCP_NSTATES] = {
59	TH_RST\|TH_ACK, 0, TH_SYN, TH_SYN\|TH_ACK,
60	TH_ACK, TH_ACK, TH_FIN\|TH_ACK, TH_FIN\|TH_ACK,
61	TH_FIN\|TH_ACK, TH_ACK, TH_ACK,
62	};
63
64
65	#define MAX_TCPOPTLEN 32 /* max # bytes that go in options */
66
67	/*
68	* Tcp output routine: figure out what should be sent and send it.
69	*/
70	int
71	tcp_output(PNATState pData, register struct tcpcb *tp)
72	{
73	register struct socket *so = tp->t_socket;
74	register long len, win;
75	int off, flags, error;
76	register struct mbuf *m;
77	register struct tcpiphdr *ti;
78	u_char opt[MAX_TCPOPTLEN];
79	unsigned optlen, hdrlen;
80	int idle, sendalot;
81
82	DEBUG_CALL("tcp_output");
83	DEBUG_ARG("tp = %lx", (long )tp);
84
85	/*
86	* Determine length of data that should be transmitted,
87	* and flags that will be used.
88	* If there is some data or critical controls (SYN, RST)
89	* to send, then transmit; otherwise, investigate further.
90	*/
91	idle = (tp->snd_max == tp->snd_una);
92	if (idle && tp->t_idle >= tp->t_rxtcur)
93	/*
94	* We have been idle for "a while" and no acks are
95	* expected to clock out any data we send --
96	* slow start to get ack "clock" running again.
97	*/
98	tp->snd_cwnd = tp->t_maxseg;
99	again:
100	sendalot = 0;
101	off = tp->snd_nxt - tp->snd_una;
102	win = min(tp->snd_wnd, tp->snd_cwnd);
103
104	flags = tcp_outflags[tp->t_state];
105
106	DEBUG_MISC((dfd, " --- tcp_output flags = 0x%x\n",flags));
107
108	/*
109	* If in persist timeout with window of 0, send 1 byte.
110	* Otherwise, if window is small but nonzero
111	* and timer expired, we will send what we can
112	* and go to transmit state.
113	*/
114	if (tp->t_force) {
115	if (win == 0) {
116	/*
117	* If we still have some data to send, then
118	* clear the FIN bit. Usually this would
119	* happen below when it realizes that we
120	* aren't sending all the data. However,
121	* if we have exactly 1 byte of unset data,
122	* then it won't clear the FIN bit below,
123	* and if we are in persist state, we wind
124	* up sending the packet without recording
125	* that we sent the FIN bit.
126	*
127	* We can't just blindly clear the FIN bit,
128	* because if we don't have any more data
129	* to send then the probe will be the FIN
130	* itself.
131	*/
132	if (off < so->so_snd.sb_cc)
133	flags &= ~TH_FIN;
134	win = 1;
135	} else {
136	tp->t_timer[TCPT_PERSIST] = 0;
137	tp->t_rxtshift = 0;
138	}
139	}
140
141	len = min(so->so_snd.sb_cc, win) - off;
142
143	if (len < 0) {
144	/*
145	* If FIN has been sent but not acked,
146	* but we haven't been called to retransmit,
147	* len will be -1. Otherwise, window shrank
148	* after we sent into it. If window shrank to 0,
149	* cancel pending retransmit and pull snd_nxt
150	* back to (closed) window. We will enter persist
151	* state below. If the window didn't close completely,
152	* just wait for an ACK.
153	*/
154	len = 0;
155	if (win == 0) {
156	tp->t_timer[TCPT_REXMT] = 0;
157	tp->snd_nxt = tp->snd_una;
158	}
159	}
160
161	if (len > tp->t_maxseg) {
162	len = tp->t_maxseg;
163	sendalot = 1;
164	}
165	if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
166	flags &= ~TH_FIN;
167
168	win = sbspace(&so->so_rcv);
169
170	/*
171	* Sender silly window avoidance. If connection is idle
172	* and can send all data, a maximum segment,
173	* at least a maximum default-size segment do it,
174	* or are forced, do it; otherwise don't bother.
175	* If peer's buffer is tiny, then send
176	* when window is at least half open.
177	* If retransmitting (possibly after persist timer forced us
178	* to send into a small window), then must resend.
179	*/
180	if (len) {
181	if (len == tp->t_maxseg)
182	goto send;
183	if ((1 \|\| idle \|\| tp->t_flags & TF_NODELAY) &&
184	len + off >= so->so_snd.sb_cc)
185	goto send;
186	if (tp->t_force)
187	goto send;
188	if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
189	goto send;
190	if (SEQ_LT(tp->snd_nxt, tp->snd_max))
191	goto send;
192	}
193
194	/*
195	* Compare available window to amount of window
196	* known to peer (as advertised window less
197	* next expected input). If the difference is at least two
198	* max size segments, or at least 50% of the maximum possible
199	* window, then want to send a window update to peer.
200	*/
201	if (win > 0) {
202	/*
203	* "adv" is the amount we can increase the window,
204	* taking into account that we are limited by
205	* TCP_MAXWIN << tp->rcv_scale.
206	*/
207	long adv = min(win, (long)TCP_MAXWIN << tp->rcv_scale) -
208	(tp->rcv_adv - tp->rcv_nxt);
209
210	if (adv >= (long) (2 * tp->t_maxseg))
211	goto send;
212	if (2 * adv >= (long) so->so_rcv.sb_datalen)
213	goto send;
214	}
215
216	/*
217	* Send if we owe peer an ACK.
218	*/
219	if (tp->t_flags & TF_ACKNOW)
220	goto send;
221	if (flags & (TH_SYN\|TH_RST))
222	goto send;
223	if (SEQ_GT(tp->snd_up, tp->snd_una))
224	goto send;
225	/*
226	* If our state indicates that FIN should be sent
227	* and we have not yet done so, or we're retransmitting the FIN,
228	* then we need to send.
229	*/
230	if (flags & TH_FIN &&
231	((tp->t_flags & TF_SENTFIN) == 0 \|\| tp->snd_nxt == tp->snd_una))
232	goto send;
233
234	/*
235	* TCP window updates are not reliable, rather a polling protocol
236	* using ``persist'' packets is used to insure receipt of window
237	* updates. The three ``states'' for the output side are:
238	* idle not doing retransmits or persists
239	* persisting to move a small or zero window
240	* (re)transmitting and thereby not persisting
241	*
242	* tp->t_timer[TCPT_PERSIST]
243	* is set when we are in persist state.
244	* tp->t_force
245	* is set when we are called to send a persist packet.
246	* tp->t_timer[TCPT_REXMT]
247	* is set when we are retransmitting
248	* The output side is idle when both timers are zero.
249	*
250	* If send window is too small, there is data to transmit, and no
251	* retransmit or persist is pending, then go to persist state.
252	* If nothing happens soon, send when timer expires:
253	* if window is nonzero, transmit what we can,
254	* otherwise force out a byte.
255	*/
256	if (so->so_snd.sb_cc && tp->t_timer[TCPT_REXMT] == 0 &&
257	tp->t_timer[TCPT_PERSIST] == 0) {
258	tp->t_rxtshift = 0;
259	tcp_setpersist(tp);
260	}
261
262	/*
263	* No reason to send a segment, just return.
264	*/
265	tcpstat.tcps_didnuttin++;
266
267	return (0);
268
269	send:
270	/*
271	* Before ESTABLISHED, force sending of initial options
272	* unless TCP set not to do any options.
273	* NOTE: we assume that the IP/TCP header plus TCP options
274	* always fit in a single mbuf, leaving room for a maximum
275	* link header, i.e.
276	* max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MHLEN
277	*/
278	optlen = 0;
279	hdrlen = sizeof (struct tcpiphdr);
280	if (flags & TH_SYN) {
281	tp->snd_nxt = tp->iss;
282	if ((tp->t_flags & TF_NOOPT) == 0) {
283	u_int16_t mss;
284
285	opt[0] = TCPOPT_MAXSEG;
286	opt[1] = 4;
287	mss = htons((u_int16_t) tcp_mss(pData, tp, 0));
288	memcpy((caddr_t)(opt + 2), (caddr_t)&mss, sizeof(mss));
289	optlen = 4;
290
291	/* if ((tp->t_flags & TF_REQ_SCALE) &&
292	* ((flags & TH_ACK) == 0 \|\|
293	* (tp->t_flags & TF_RCVD_SCALE))) {
294	* ((u_int32_t ) (opt + optlen)) = htonl(
295	* TCPOPT_NOP << 24 \|
296	* TCPOPT_WINDOW << 16 \|
297	* TCPOLEN_WINDOW << 8 \|
298	* tp->request_r_scale);
299	* optlen += 4;
300	* }
301	*/
302	}
303	}
304
305	/*
306	* Send a timestamp and echo-reply if this is a SYN and our side
307	* wants to use timestamps (TF_REQ_TSTMP is set) or both our side
308	* and our peer have sent timestamps in our SYN's.
309	*/
310	/* if ((tp->t_flags & (TF_REQ_TSTMP\|TF_NOOPT)) == TF_REQ_TSTMP &&
311	* (flags & TH_RST) == 0 &&
312	* ((flags & (TH_SYN\|TH_ACK)) == TH_SYN \|\|
313	* (tp->t_flags & TF_RCVD_TSTMP))) {
314	* u_int32_t lp = (u_int32_t )(opt + optlen);
315	*
316	* / * Form timestamp option as shown in appendix A of RFC 1323. * /
317	* *lp++ = htonl(TCPOPT_TSTAMP_HDR);
318	* *lp++ = htonl(tcp_now);
319	* *lp = htonl(tp->ts_recent);
320	* optlen += TCPOLEN_TSTAMP_APPA;
321	* }
322	*/
323	hdrlen += optlen;
324
325	/*
326	* Adjust data length if insertion of options will
327	* bump the packet length beyond the t_maxseg length.
328	*/
329	if (len > tp->t_maxseg - optlen) {
330	len = tp->t_maxseg - optlen;
331	sendalot = 1;
332	}
333
334	/*
335	* Grab a header mbuf, attaching a copy of data to
336	* be transmitted, and initialize the header from
337	* the template for sends on this connection.
338	*/
339	if (len) {
340	if (tp->t_force && len == 1)
341	tcpstat.tcps_sndprobe++;
342	else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
343	tcpstat.tcps_sndrexmitpack++;
344	tcpstat.tcps_sndrexmitbyte += len;
345	} else {
346	tcpstat.tcps_sndpack++;
347	tcpstat.tcps_sndbyte += len;
348	}
349
350	m = m_get(pData);
351	if (m == NULL) {
352	/* error = ENOBUFS; */
353	error = 1;
354	goto out;
355	}
356	m->m_data += if_maxlinkhdr;
357	m->m_len = hdrlen;
358
359	/*
360	* This will always succeed, since we make sure our mbufs
361	* are big enough to hold one MSS packet + header + ... etc.
362	*/
363	/* if (len <= MHLEN - hdrlen - max_linkhdr) { */
364
365	sbcopy(&so->so_snd, off, (int) len, mtod(m, caddr_t) + hdrlen);
366	m->m_len += len;
367
368	/* } else {
369	* m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
370	* if (m->m_next == 0)
371	* len = 0;
372	* }
373	*/
374	/*
375	* If we're sending everything we've got, set PUSH.
376	* (This will keep happy those implementations which only
377	* give data to the user when a buffer fills or
378	* a PUSH comes in.)
379	*/
380	if (off + len == so->so_snd.sb_cc)
381	flags \|= TH_PUSH;
382	} else {
383	if (tp->t_flags & TF_ACKNOW)
384	tcpstat.tcps_sndacks++;
385	else if (flags & (TH_SYN\|TH_FIN\|TH_RST))
386	tcpstat.tcps_sndctrl++;
387	else if (SEQ_GT(tp->snd_up, tp->snd_una))
388	tcpstat.tcps_sndurg++;
389	else
390	tcpstat.tcps_sndwinup++;
391
392	m = m_get(pData);
393	if (m == NULL) {
394	/* error = ENOBUFS; */
395	error = 1;
396	goto out;
397	}
398	m->m_data += if_maxlinkhdr;
399	m->m_len = hdrlen;
400	}
401
402	ti = mtod(m, struct tcpiphdr *);
403
404	memcpy((caddr_t)ti, &tp->t_template, sizeof (struct tcpiphdr));
405
406	/*
407	* Fill in fields, remembering maximum advertised
408	* window for use in delaying messages about window sizes.
409	* If resending a FIN, be sure not to use a new sequence number.
410	*/
411	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
412	tp->snd_nxt == tp->snd_max)
413	tp->snd_nxt--;
414	/*
415	* If we are doing retransmissions, then snd_nxt will
416	* not reflect the first unsent octet. For ACK only
417	* packets, we do not want the sequence number of the
418	* retransmitted packet, we want the sequence number
419	* of the next unsent octet. So, if there is no data
420	* (and no SYN or FIN), use snd_max instead of snd_nxt
421	* when filling in ti_seq. But if we are in persist
422	* state, snd_max might reflect one byte beyond the
423	* right edge of the window, so use snd_nxt in that
424	* case, since we know we aren't doing a retransmission.
425	* (retransmit and persist are mutually exclusive...)
426	*/
427	if (len \|\| (flags & (TH_SYN\|TH_FIN)) \|\| tp->t_timer[TCPT_PERSIST])
428	ti->ti_seq = htonl(tp->snd_nxt);
429	else
430	ti->ti_seq = htonl(tp->snd_max);
431	ti->ti_ack = htonl(tp->rcv_nxt);
432	if (optlen) {
433	memcpy((caddr_t)(ti + 1), (caddr_t)opt, optlen);
434	ti->ti_off = (sizeof (struct tcphdr) + optlen) >> 2;
435	}
436	ti->ti_flags = flags;
437	/*
438	* Calculate receive window. Don't shrink window,
439	* but avoid silly window syndrome.
440	*/
441	if (win < (long)(so->so_rcv.sb_datalen / 4) && win < (long)tp->t_maxseg)
442	win = 0;
443	if (win > (long)TCP_MAXWIN << tp->rcv_scale)
444	win = (long)TCP_MAXWIN << tp->rcv_scale;
445	if (win < (long)(tp->rcv_adv - tp->rcv_nxt))
446	win = (long)(tp->rcv_adv - tp->rcv_nxt);
447	ti->ti_win = htons((u_int16_t) (win>>tp->rcv_scale));
448
449	if (SEQ_GT(tp->snd_up, tp->snd_una)) {
450	ti->ti_urp = htons((u_int16_t)(tp->snd_up - ntohl(ti->ti_seq)));
451	#ifdef notdef
452	if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
453	ti->ti_urp = htons((u_int16_t)(tp->snd_up - tp->snd_nxt));
454	#endif
455	ti->ti_flags \|= TH_URG;
456	} else
457	/*
458	* If no urgent pointer to send, then we pull
459	* the urgent pointer to the left edge of the send window
460	* so that it doesn't drift into the send window on sequence
461	* number wraparound.
462	*/
463	tp->snd_up = tp->snd_una; /* drag it along */
464
465	/*
466	* Put TCP length in extended header, and then
467	* checksum extended header and data.
468	*/
469	if (len + optlen)
470	ti->ti_len = htons((u_int16_t)(sizeof (struct tcphdr) +
471	optlen + len));
472	ti->ti_sum = cksum(m, (int)(hdrlen + len));
473
474	/*
475	* In transmit state, time the transmission and arrange for
476	* the retransmit. In persist state, just set snd_max.
477	*/
478	if (tp->t_force == 0 \|\| tp->t_timer[TCPT_PERSIST] == 0) {
479	tcp_seq startseq = tp->snd_nxt;
480
481	/*
482	* Advance snd_nxt over sequence space of this segment.
483	*/
484	if (flags & (TH_SYN\|TH_FIN)) {
485	if (flags & TH_SYN)
486	tp->snd_nxt++;
487	if (flags & TH_FIN) {
488	tp->snd_nxt++;
489	tp->t_flags \|= TF_SENTFIN;
490	}
491	}
492	tp->snd_nxt += len;
493	if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
494	tp->snd_max = tp->snd_nxt;
495	/*
496	* Time this transmission if not a retransmission and
497	* not currently timing anything.
498	*/
499	if (tp->t_rtt == 0) {
500	tp->t_rtt = 1;
501	tp->t_rtseq = startseq;
502	tcpstat.tcps_segstimed++;
503	}
504	}
505
506	/*
507	* Set retransmit timer if not currently set,
508	* and not doing an ack or a keep-alive probe.
509	* Initial value for retransmit timer is smoothed
510	* round-trip time + 2 * round-trip time variance.
511	* Initialize shift counter which is used for backoff
512	* of retransmit time.
513	*/
514	if (tp->t_timer[TCPT_REXMT] == 0 &&
515	tp->snd_nxt != tp->snd_una) {
516	tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
517	if (tp->t_timer[TCPT_PERSIST]) {
518	tp->t_timer[TCPT_PERSIST] = 0;
519	tp->t_rxtshift = 0;
520	}
521	}
522	} else
523	if (SEQ_GT(tp->snd_nxt + len, tp->snd_max))
524	tp->snd_max = tp->snd_nxt + len;
525
526	/*
527	* Fill in IP length and desired time to live and
528	* send to IP level. There should be a better way
529	* to handle ttl and tos; we could keep them in
530	* the template, but need a way to checksum without them.
531	*/
532	m->m_len = hdrlen + len; /* XXX Needed? m_len should be correct */
533
534	{
535
536	((struct ip *)ti)->ip_len = m->m_len;
537
538	((struct ip *)ti)->ip_ttl = ip_defttl;
539	((struct ip *)ti)->ip_tos = so->so_iptos;
540
541	/* #if BSD >= 43 */
542	/* Don't do IP options... */
543	/* error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
544	* so->so_options & SO_DONTROUTE, 0);
545	*/
546	error = ip_output(pData, so, m);
547
548	/* #else
549	* error = ip_output(m, (struct mbuf *)0, &tp->t_inpcb->inp_route,
550	* so->so_options & SO_DONTROUTE);
551	* #endif
552	*/
553	}
554	if (error) {
555	out:
556	/* if (error == ENOBUFS) {
557	* tcp_quench(tp->t_inpcb, 0);
558	* return (0);
559	* }
560	*/
561	/* if ((error == EHOSTUNREACH \|\| error == ENETDOWN)
562	* && TCPS_HAVERCVDSYN(tp->t_state)) {
563	* tp->t_softerror = error;
564	* return (0);
565	* }
566	*/
567	return (error);
568	}
569	tcpstat.tcps_sndtotal++;
570
571	/*
572	* Data sent (as far as we can tell).
573	* If this advertises a larger window than any other segment,
574	* then remember the size of the advertised window.
575	* Any pending ACK has now been sent.
576	*/
577	if (win > 0 && SEQ_GT(tp->rcv_nxt+win, tp->rcv_adv))
578	tp->rcv_adv = tp->rcv_nxt + win;
579	tp->last_ack_sent = tp->rcv_nxt;
580	tp->t_flags &= ~(TF_ACKNOW\|TF_DELACK);
581	if (sendalot)
582	goto again;
583
584	return (0);
585	}
586
587	void
588	tcp_setpersist(tp)
589	register struct tcpcb *tp;
590	{
591	int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
592
593	/* if (tp->t_timer[TCPT_REXMT])
594	* panic("tcp_output REXMT");
595	*/
596	/*
597	* Start/restart persistence timer.
598	*/
599	TCPT_RANGESET(tp->t_timer[TCPT_PERSIST],
600	t * tcp_backoff[tp->t_rxtshift],
601	TCPTV_PERSMIN, TCPTV_PERSMAX);
602	if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
603	tp->t_rxtshift++;
604	}

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