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tcp_output.c
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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. 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: u_int16_t mss;
267:
268: opt[0] = TCPOPT_MAXSEG;
269: opt[1] = 4;
270: mss = htons((u_int16_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((u_int16_t) (win>>tp->rcv_scale));
368:
369: if (SEQ_GT(tp->snd_up, tp->snd_una)) {
370: ti->ti_urp = htons((u_int16_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((u_int16_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: }
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