2 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
3 * Copyright (c) 2004 The DragonFly Project. All rights reserved.
5 * This code is derived from software contributed to The DragonFly Project
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of The DragonFly Project nor the names of its
17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
24 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
37 * License terms: all terms for the DragonFly license above plus the following:
39 * 4. All advertising materials mentioning features or use of this software
40 * must display the following acknowledgement:
42 * This product includes software developed by Jeffrey M. Hsu
43 * for the DragonFly Project.
45 * This requirement may be waived with permission from Jeffrey Hsu.
46 * This requirement will sunset and may be removed on July 8 2005,
47 * after which the standard DragonFly license (as shown above) will
52 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
53 * The Regents of the University of California. All rights reserved.
55 * Redistribution and use in source and binary forms, with or without
56 * modification, are permitted provided that the following conditions
58 * 1. Redistributions of source code must retain the above copyright
59 * notice, this list of conditions and the following disclaimer.
60 * 2. Redistributions in binary form must reproduce the above copyright
61 * notice, this list of conditions and the following disclaimer in the
62 * documentation and/or other materials provided with the distribution.
63 * 3. All advertising materials mentioning features or use of this software
64 * must display the following acknowledgement:
65 * This product includes software developed by the University of
66 * California, Berkeley and its contributors.
67 * 4. Neither the name of the University nor the names of its contributors
68 * may be used to endorse or promote products derived from this software
69 * without specific prior written permission.
71 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
72 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
73 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
74 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
75 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
76 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
77 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
78 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
79 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
80 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
83 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
84 * $FreeBSD: src/sys/netinet/tcp_output.c,v 1.39.2.20 2003/01/29 22:45:36 hsu Exp $
85 * $DragonFly: src/sys/netinet/tcp_output.c,v 1.31 2006/04/14 21:18:24 dillon Exp $
88 #include "opt_inet6.h"
89 #include "opt_ipsec.h"
90 #include "opt_tcpdebug.h"
92 #include <sys/param.h>
93 #include <sys/systm.h>
94 #include <sys/kernel.h>
95 #include <sys/sysctl.h>
97 #include <sys/domain.h>
98 #include <sys/protosw.h>
99 #include <sys/socket.h>
100 #include <sys/socketvar.h>
101 #include <sys/in_cksum.h>
102 #include <sys/thread.h>
103 #include <sys/globaldata.h>
105 #include <net/route.h>
107 #include <netinet/in.h>
108 #include <netinet/in_systm.h>
109 #include <netinet/ip.h>
110 #include <netinet/in_pcb.h>
111 #include <netinet/ip_var.h>
112 #include <netinet6/in6_pcb.h>
113 #include <netinet/ip6.h>
114 #include <netinet6/ip6_var.h>
115 #include <netinet/tcp.h>
117 #include <netinet/tcp_fsm.h>
118 #include <netinet/tcp_seq.h>
119 #include <netinet/tcp_timer.h>
120 #include <netinet/tcp_var.h>
121 #include <netinet/tcpip.h>
123 #include <netinet/tcp_debug.h>
127 #include <netinet6/ipsec.h>
131 #include <netproto/ipsec/ipsec.h>
133 #endif /*FAST_IPSEC*/
136 extern struct mbuf *m_copypack();
139 int path_mtu_discovery = 0;
140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
141 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
143 static int avoid_pure_win_update = 1;
144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, avoid_pure_win_update, CTLFLAG_RW,
145 &avoid_pure_win_update, 1, "Avoid pure window updates when possible");
148 * Tcp output routine: figure out what should be sent and send it.
151 tcp_output(struct tcpcb *tp)
153 struct inpcb * const inp = tp->t_inpcb;
154 struct socket *so = inp->inp_socket;
155 long len, recvwin, sendwin;
157 int off, flags, error;
159 struct ip *ip = NULL;
160 struct ipovly *ipov = NULL;
162 u_char opt[TCP_MAXOLEN];
163 unsigned int ipoptlen, optlen, hdrlen;
166 struct ip6_hdr *ip6 = NULL;
168 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
170 const boolean_t isipv6 = FALSE;
172 struct rmxp_tao *taop;
175 * Determine length of data that should be transmitted,
176 * and flags that will be used.
177 * If there is some data or critical controls (SYN, RST)
178 * to send, then transmit; otherwise, investigate further.
182 * If we have been idle for a while, the send congestion window
183 * could be no longer representative of the current state of the link.
184 * So unless we are expecting more acks to come in, slow-start from
185 * scratch to re-determine the send congestion window.
187 if (tp->snd_max == tp->snd_una &&
188 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
189 if (tcp_do_rfc3390) {
191 min(4 * tp->t_maxseg, max(2 * tp->t_maxseg, 4380));
193 tp->snd_cwnd = min(tp->snd_cwnd, initial_cwnd);
195 tp->snd_cwnd = tp->t_maxseg;
201 * Calculate whether the transmit stream was previously idle
202 * and adjust TF_LASTIDLE for the next time.
204 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
205 if (idle && (tp->t_flags & TF_MORETOCOME))
206 tp->t_flags |= TF_LASTIDLE;
208 tp->t_flags &= ~TF_LASTIDLE;
210 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
211 !IN_FASTRECOVERY(tp))
212 nsacked = tcp_sack_bytes_below(&tp->scb, tp->snd_nxt);
215 /* Make use of SACK information when slow-starting after a RTO. */
216 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
217 !IN_FASTRECOVERY(tp)) {
218 tcp_seq old_snd_nxt = tp->snd_nxt;
220 tcp_sack_skip_sacked(&tp->scb, &tp->snd_nxt);
221 nsacked += tp->snd_nxt - old_snd_nxt;
225 off = tp->snd_nxt - tp->snd_una;
226 sendwin = min(tp->snd_wnd, tp->snd_cwnd + nsacked);
227 sendwin = min(sendwin, tp->snd_bwnd);
229 flags = tcp_outflags[tp->t_state];
231 * Get standard flags, and add SYN or FIN if requested by 'hidden'
234 if (tp->t_flags & TF_NEEDFIN)
236 if (tp->t_flags & TF_NEEDSYN)
240 * If in persist timeout with window of 0, send 1 byte.
241 * Otherwise, if window is small but nonzero
242 * and timer expired, we will send what we can
243 * and go to transmit state.
245 if (tp->t_flags & TF_FORCE) {
248 * If we still have some data to send, then
249 * clear the FIN bit. Usually this would
250 * happen below when it realizes that we
251 * aren't sending all the data. However,
252 * if we have exactly 1 byte of unsent data,
253 * then it won't clear the FIN bit below,
254 * and if we are in persist state, we wind
255 * up sending the packet without recording
256 * that we sent the FIN bit.
258 * We can't just blindly clear the FIN bit,
259 * because if we don't have any more data
260 * to send then the probe will be the FIN
263 if (off < so->so_snd.sb_cc)
267 callout_stop(tp->tt_persist);
273 * If snd_nxt == snd_max and we have transmitted a FIN, the
274 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
275 * a negative length. This can also occur when TCP opens up
276 * its congestion window while receiving additional duplicate
277 * acks after fast-retransmit because TCP will reset snd_nxt
278 * to snd_max after the fast-retransmit.
280 * In the normal retransmit-FIN-only case, however, snd_nxt will
281 * be set to snd_una, the offset will be 0, and the length may
284 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
287 * Lop off SYN bit if it has already been sent. However, if this
288 * is SYN-SENT state and if segment contains data and if we don't
289 * know that foreign host supports TAO, suppress sending segment.
291 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
294 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
295 ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL ||
296 taop->tao_ccsent == 0))
301 * Be careful not to send data and/or FIN on SYN segments
302 * in cases when no CC option will be sent.
303 * This measure is needed to prevent interoperability problems
304 * with not fully conformant TCP implementations.
306 if ((flags & TH_SYN) &&
307 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
308 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
315 * If FIN has been sent but not acked,
316 * but we haven't been called to retransmit,
317 * len will be < 0. Otherwise, window shrank
318 * after we sent into it. If window shrank to 0,
319 * cancel pending retransmit, pull snd_nxt back
320 * to (closed) window, and set the persist timer
321 * if it isn't already going. If the window didn't
322 * close completely, just wait for an ACK.
326 callout_stop(tp->tt_rexmt);
328 tp->snd_nxt = tp->snd_una;
329 if (!callout_active(tp->tt_persist))
335 * len will be >= 0 after this point. Truncate to the maximum
336 * segment length and ensure that FIN is removed if the length
337 * no longer contains the last data byte.
339 if (len > tp->t_maxseg) {
343 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
346 recvwin = sbspace(&so->so_rcv);
349 * Sender silly window avoidance. We transmit under the following
350 * conditions when len is non-zero:
352 * - We have a full segment
353 * - This is the last buffer in a write()/send() and we are
354 * either idle or running NODELAY
355 * - we've timed out (e.g. persist timer)
356 * - we have more then 1/2 the maximum send window's worth of
357 * data (receiver may be limiting the window size)
358 * - we need to retransmit
361 if (len == tp->t_maxseg)
364 * NOTE! on localhost connections an 'ack' from the remote
365 * end may occur synchronously with the output and cause
366 * us to flush a buffer queued with moretocome. XXX
368 * note: the len + off check is almost certainly unnecessary.
370 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
371 (idle || (tp->t_flags & TF_NODELAY)) &&
372 len + off >= so->so_snd.sb_cc &&
373 !(tp->t_flags & TF_NOPUSH)) {
376 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
378 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
380 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
385 * Compare available window to amount of window
386 * known to peer (as advertised window less
387 * next expected input). If the difference is at least two
388 * max size segments, or at least 50% of the maximum possible
389 * window, then want to send a window update to peer.
393 * "adv" is the amount we can increase the window,
394 * taking into account that we are limited by
395 * TCP_MAXWIN << tp->rcv_scale.
397 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
398 (tp->rcv_adv - tp->rcv_nxt);
401 * This ack case typically occurs when the user has drained
402 * the TCP socket buffer sufficiently to warrent an ack
403 * containing a 'pure window update'... that is, an ack that
404 * ONLY updates the tcp window.
406 * It is unclear why we would need to do a pure window update
407 * past 2 segments if we are going to do one at 1/2 the high
408 * water mark anyway, especially since under normal conditions
409 * the user program will drain the socket buffer quickly.
410 * The 2-segment pure window update will often add a large
411 * number of extra, unnecessary acks to the stream.
413 * avoid_pure_win_update now defaults to 1.
415 if (avoid_pure_win_update == 0) {
416 if (adv >= (long) (2 * tp->t_maxseg))
419 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
424 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
425 * is also a catch-all for the retransmit timer timeout case.
427 if (tp->t_flags & TF_ACKNOW)
429 if ((flags & TH_RST) ||
430 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
432 if (SEQ_GT(tp->snd_up, tp->snd_una))
435 * If our state indicates that FIN should be sent
436 * and we have not yet done so, then we need to send.
438 if (flags & TH_FIN &&
439 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
443 * TCP window updates are not reliable, rather a polling protocol
444 * using ``persist'' packets is used to insure receipt of window
445 * updates. The three ``states'' for the output side are:
446 * idle not doing retransmits or persists
447 * persisting to move a small or zero window
448 * (re)transmitting and thereby not persisting
450 * callout_active(tp->tt_persist)
451 * is true when we are in persist state.
452 * The TF_FORCE flag in tp->t_flags
453 * is set when we are called to send a persist packet.
454 * callout_active(tp->tt_rexmt)
455 * is set when we are retransmitting
456 * The output side is idle when both timers are zero.
458 * If send window is too small, there is data to transmit, and no
459 * retransmit or persist is pending, then go to persist state.
460 * If nothing happens soon, send when timer expires:
461 * if window is nonzero, transmit what we can,
462 * otherwise force out a byte.
464 if (so->so_snd.sb_cc > 0 &&
465 !callout_active(tp->tt_rexmt) && !callout_active(tp->tt_persist)) {
471 * No reason to send a segment, just return.
477 * Before ESTABLISHED, force sending of initial options
478 * unless TCP set not to do any options.
479 * NOTE: we assume that the IP/TCP header plus TCP options
480 * always fit in a single mbuf, leaving room for a maximum
482 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
486 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
488 hdrlen = sizeof(struct tcpiphdr);
489 if (flags & TH_SYN) {
490 tp->snd_nxt = tp->iss;
491 if (!(tp->t_flags & TF_NOOPT)) {
494 opt[0] = TCPOPT_MAXSEG;
495 opt[1] = TCPOLEN_MAXSEG;
496 mss = htons((u_short) tcp_mssopt(tp));
497 memcpy(opt + 2, &mss, sizeof mss);
498 optlen = TCPOLEN_MAXSEG;
500 if ((tp->t_flags & TF_REQ_SCALE) &&
501 (!(flags & TH_ACK) ||
502 (tp->t_flags & TF_RCVD_SCALE))) {
503 *((u_int32_t *)(opt + optlen)) = htonl(
505 TCPOPT_WINDOW << 16 |
506 TCPOLEN_WINDOW << 8 |
507 tp->request_r_scale);
511 if ((tcp_do_sack && !(flags & TH_ACK)) ||
512 tp->t_flags & TF_SACK_PERMITTED) {
513 uint32_t *lp = (uint32_t *)(opt + optlen);
515 *lp = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
516 optlen += TCPOLEN_SACK_PERMITTED_ALIGNED;
522 * Send a timestamp and echo-reply if this is a SYN and our side
523 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
524 * and our peer have sent timestamps in our SYN's.
526 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
528 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
529 u_int32_t *lp = (u_int32_t *)(opt + optlen);
531 /* Form timestamp option as shown in appendix A of RFC 1323. */
532 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
533 *lp++ = htonl(ticks);
534 *lp = htonl(tp->ts_recent);
535 optlen += TCPOLEN_TSTAMP_APPA;
539 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
540 * options are allowed (!TF_NOOPT) and it's not a RST.
542 if ((tp->t_flags & (TF_REQ_CC | TF_NOOPT)) == TF_REQ_CC &&
544 switch (flags & (TH_SYN | TH_ACK)) {
546 * This is a normal ACK, send CC if we received CC before
550 if (!(tp->t_flags & TF_RCVD_CC))
555 * We can only get here in T/TCP's SYN_SENT* state, when
556 * we're a sending a non-SYN segment without waiting for
557 * the ACK of our SYN. A check above assures that we only
558 * do this if our peer understands T/TCP.
561 opt[optlen++] = TCPOPT_NOP;
562 opt[optlen++] = TCPOPT_NOP;
563 opt[optlen++] = TCPOPT_CC;
564 opt[optlen++] = TCPOLEN_CC;
565 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
570 * This is our initial SYN, check whether we have to use
574 opt[optlen++] = TCPOPT_NOP;
575 opt[optlen++] = TCPOPT_NOP;
576 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
577 TCPOPT_CCNEW : TCPOPT_CC;
578 opt[optlen++] = TCPOLEN_CC;
579 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
584 * This is a SYN,ACK; send CC and CC.echo if we received
587 case (TH_SYN | TH_ACK):
588 if (tp->t_flags & TF_RCVD_CC) {
589 opt[optlen++] = TCPOPT_NOP;
590 opt[optlen++] = TCPOPT_NOP;
591 opt[optlen++] = TCPOPT_CC;
592 opt[optlen++] = TCPOLEN_CC;
593 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
595 opt[optlen++] = TCPOPT_NOP;
596 opt[optlen++] = TCPOPT_NOP;
597 opt[optlen++] = TCPOPT_CCECHO;
598 opt[optlen++] = TCPOLEN_CC;
599 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_recv);
607 * If this is a SACK connection and we have a block to report,
608 * fill in the SACK blocks in the TCP options.
610 if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
612 (!LIST_EMPTY(&tp->t_segq) ||
613 tp->reportblk.rblk_start != tp->reportblk.rblk_end))
614 tcp_sack_fill_report(tp, opt, &optlen);
616 KASSERT(optlen <= TCP_MAXOLEN, ("too many TCP options"));
620 ipoptlen = ip6_optlen(inp);
622 if (inp->inp_options) {
623 ipoptlen = inp->inp_options->m_len -
624 offsetof(struct ipoption, ipopt_list);
630 ipoptlen += ipsec_hdrsiz_tcp(tp);
634 * Adjust data length if insertion of options will bump the packet
635 * length beyond the t_maxopd length. Clear FIN to prevent premature
636 * closure since there is still more data to send after this (now
639 * If just the options do not fit we are in a no-win situation and
640 * we treat it as an unreachable host.
642 if (len + optlen + ipoptlen > tp->t_maxopd) {
643 if (tp->t_maxopd <= optlen + ipoptlen) {
644 static time_t last_optlen_report;
646 if (last_optlen_report != time_second) {
647 last_optlen_report = time_second;
648 printf("tcpcb %p: MSS (%d) too small to hold options!\n", tp, tp->t_maxopd);
650 error = EHOSTUNREACH;
654 len = tp->t_maxopd - optlen - ipoptlen;
660 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
662 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
666 * Grab a header mbuf, attaching a copy of data to
667 * be transmitted, and initialize the header from
668 * the template for sends on this connection.
671 if ((tp->t_flags & TF_FORCE) && len == 1)
672 tcpstat.tcps_sndprobe++;
673 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
674 if (tp->snd_nxt == tp->snd_una)
675 tp->snd_max_rexmt = tp->snd_max;
676 tcpstat.tcps_sndrexmitpack++;
677 tcpstat.tcps_sndrexmitbyte += len;
679 tcpstat.tcps_sndpack++;
680 tcpstat.tcps_sndbyte += len;
683 if ((m = m_copypack(so->so_snd.sb_mb, off, (int)len,
684 max_linkhdr + hdrlen)) == NULL) {
689 * m_copypack left space for our hdr; use it.
695 m = m_gethdr(MB_DONTWAIT, MT_HEADER);
697 m = m_getl(hdrlen + max_linkhdr, MB_DONTWAIT, MT_HEADER,
704 m->m_data += max_linkhdr;
706 if (len <= MHLEN - hdrlen - max_linkhdr) {
707 m_copydata(so->so_snd.sb_mb, off, (int) len,
708 mtod(m, caddr_t) + hdrlen);
711 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
712 if (m->m_next == NULL) {
720 * If we're sending everything we've got, set PUSH.
721 * (This will keep happy those implementations which only
722 * give data to the user when a buffer fills or
725 if (off + len == so->so_snd.sb_cc)
728 if (tp->t_flags & TF_ACKNOW)
729 tcpstat.tcps_sndacks++;
730 else if (flags & (TH_SYN | TH_FIN | TH_RST))
731 tcpstat.tcps_sndctrl++;
732 else if (SEQ_GT(tp->snd_up, tp->snd_una))
733 tcpstat.tcps_sndurg++;
735 tcpstat.tcps_sndwinup++;
737 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
743 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
746 m->m_data += max_linkhdr;
749 m->m_pkthdr.rcvif = (struct ifnet *)0;
751 ip6 = mtod(m, struct ip6_hdr *);
752 th = (struct tcphdr *)(ip6 + 1);
753 tcp_fillheaders(tp, ip6, th);
755 ip = mtod(m, struct ip *);
756 ipov = (struct ipovly *)ip;
757 th = (struct tcphdr *)(ip + 1);
758 /* this picks up the pseudo header (w/o the length) */
759 tcp_fillheaders(tp, ip, th);
763 * Fill in fields, remembering maximum advertised
764 * window for use in delaying messages about window sizes.
765 * If resending a FIN, be sure not to use a new sequence number.
767 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
768 tp->snd_nxt == tp->snd_max)
771 * If we are doing retransmissions, then snd_nxt will
772 * not reflect the first unsent octet. For ACK only
773 * packets, we do not want the sequence number of the
774 * retransmitted packet, we want the sequence number
775 * of the next unsent octet. So, if there is no data
776 * (and no SYN or FIN), use snd_max instead of snd_nxt
777 * when filling in ti_seq. But if we are in persist
778 * state, snd_max might reflect one byte beyond the
779 * right edge of the window, so use snd_nxt in that
780 * case, since we know we aren't doing a retransmission.
781 * (retransmit and persist are mutually exclusive...)
783 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
784 th->th_seq = htonl(tp->snd_nxt);
786 th->th_seq = htonl(tp->snd_max);
787 th->th_ack = htonl(tp->rcv_nxt);
789 bcopy(opt, th + 1, optlen);
790 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
792 th->th_flags = flags;
794 * Calculate receive window. Don't shrink window,
795 * but avoid silly window syndrome.
797 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
798 recvwin < (long)tp->t_maxseg)
800 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
801 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
802 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
803 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
804 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
807 * Adjust the RXWIN0SENT flag - indicate that we have advertised
808 * a 0 window. This may cause the remote transmitter to stall. This
809 * flag tells soreceive() to disable delayed acknowledgements when
810 * draining the buffer. This can occur if the receiver is attempting
811 * to read more data then can be buffered prior to transmitting on
815 tp->t_flags |= TF_RXWIN0SENT;
817 tp->t_flags &= ~TF_RXWIN0SENT;
819 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
820 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
821 th->th_flags |= TH_URG;
824 * If no urgent pointer to send, then we pull
825 * the urgent pointer to the left edge of the send window
826 * so that it doesn't drift into the send window on sequence
829 tp->snd_up = tp->snd_una; /* drag it along */
833 * Put TCP length in extended header, and then
834 * checksum extended header and data.
836 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
839 * ip6_plen is not need to be filled now, and will be filled
842 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
843 sizeof(struct tcphdr) + optlen + len);
845 m->m_pkthdr.csum_flags = CSUM_TCP;
846 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
848 th->th_sum = in_addword(th->th_sum,
849 htons((u_short)(optlen + len)));
851 /* IP version must be set here for ipv4/ipv6 checking later */
852 KASSERT(ip->ip_v == IPVERSION,
853 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
857 * In transmit state, time the transmission and arrange for
858 * the retransmit. In persist state, just set snd_max.
860 if (!(tp->t_flags & TF_FORCE) || !callout_active(tp->tt_persist)) {
861 tcp_seq startseq = tp->snd_nxt;
864 * Advance snd_nxt over sequence space of this segment.
866 if (flags & (TH_SYN | TH_FIN)) {
869 if (flags & TH_FIN) {
871 tp->t_flags |= TF_SENTFIN;
875 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
876 tp->snd_max = tp->snd_nxt;
878 * Time this transmission if not a retransmission and
879 * not currently timing anything.
881 if (tp->t_rtttime == 0) {
882 tp->t_rtttime = ticks;
883 tp->t_rtseq = startseq;
884 tcpstat.tcps_segstimed++;
889 * Set retransmit timer if not currently set,
890 * and not doing a pure ack or a keep-alive probe.
891 * Initial value for retransmit timer is smoothed
892 * round-trip time + 2 * round-trip time variance.
893 * Initialize shift counter which is used for backoff
894 * of retransmit time.
896 if (!callout_active(tp->tt_rexmt) &&
897 tp->snd_nxt != tp->snd_una) {
898 if (callout_active(tp->tt_persist)) {
899 callout_stop(tp->tt_persist);
902 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
903 tcp_timer_rexmt, tp);
907 * Persist case, update snd_max but since we are in
908 * persist mode (no window) we do not update snd_nxt.
913 if (flags & TH_FIN) {
915 tp->t_flags |= TF_SENTFIN;
917 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
918 tp->snd_max = tp->snd_nxt + xlen;
925 if (so->so_options & SO_DEBUG)
926 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
930 * Fill in IP length and desired time to live and
931 * send to IP level. There should be a better way
932 * to handle ttl and tos; we could keep them in
933 * the template, but need a way to checksum without them.
936 * m->m_pkthdr.len should have been set before cksum calcuration,
937 * because in6_cksum() need it.
941 * we separately set hoplimit for every segment, since the
942 * user might want to change the value via setsockopt.
943 * Also, desired default hop limit might be changed via
944 * Neighbor Discovery.
946 ip6->ip6_hlim = in6_selecthlim(inp,
947 (inp->in6p_route.ro_rt ?
948 inp->in6p_route.ro_rt->rt_ifp : NULL));
950 /* TODO: IPv6 IP6TOS_ECT bit on */
951 error = ip6_output(m, inp->in6p_outputopts, &inp->in6p_route,
952 (so->so_options & SO_DONTROUTE), NULL, NULL,
956 ip->ip_len = m->m_pkthdr.len;
958 if (INP_CHECK_SOCKAF(so, AF_INET6))
959 ip->ip_ttl = in6_selecthlim(inp,
960 (inp->in6p_route.ro_rt ?
961 inp->in6p_route.ro_rt->rt_ifp : NULL));
964 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
966 ip->ip_tos = inp->inp_ip_tos; /* XXX */
968 * See if we should do MTU discovery.
969 * We do it only if the following are true:
970 * 1) we have a valid route to the destination
971 * 2) the MTU is not locked (if it is,
972 * then discovery has been disabled)
974 if (path_mtu_discovery &&
975 (rt = inp->inp_route.ro_rt) && (rt->rt_flags & RTF_UP) &&
976 !(rt->rt_rmx.rmx_locks & RTV_MTU))
979 error = ip_output(m, inp->inp_options, &inp->inp_route,
980 (so->so_options & SO_DONTROUTE), NULL, inp);
985 * We know that the packet was lost, so back out the
986 * sequence number advance, if any.
988 if (!(tp->t_flags & TF_FORCE) ||
989 !callout_active(tp->tt_persist)) {
991 * No need to check for TH_FIN here because
992 * the TF_SENTFIN flag handles that case.
994 if (!(flags & TH_SYN))
999 if (error == ENOBUFS) {
1001 * If we can't send, make sure there is something
1002 * to get us going again later. Persist state
1003 * is not necessarily right, but it is close enough.
1005 if (!callout_active(tp->tt_rexmt) &&
1006 !callout_active(tp->tt_persist)) {
1013 if (error == EMSGSIZE) {
1015 * ip_output() will have already fixed the route
1016 * for us. tcp_mtudisc() will, as its last action,
1017 * initiate retransmission, so it is important to
1020 tcp_mtudisc(inp, 0);
1023 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
1024 TCPS_HAVERCVDSYN(tp->t_state)) {
1025 tp->t_softerror = error;
1030 tcpstat.tcps_sndtotal++;
1033 * Data sent (as far as we can tell).
1034 * If this advertises a larger window than any other segment,
1035 * then remember the size of the advertised window.
1036 * Any pending ACK has now been sent.
1038 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
1039 tp->rcv_adv = tp->rcv_nxt + recvwin;
1040 tp->last_ack_sent = tp->rcv_nxt;
1041 tp->t_flags &= ~TF_ACKNOW;
1042 if (tcp_delack_enabled)
1043 callout_stop(tp->tt_delack);
1050 tcp_setpersist(struct tcpcb *tp)
1052 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1055 if (callout_active(tp->tt_rexmt))
1056 panic("tcp_setpersist: retransmit pending");
1058 * Start/restart persistance timer.
1060 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN,
1062 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
1063 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)