2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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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
33 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
34 * $FreeBSD: src/sys/netinet/tcp_output.c,v 1.39.2.20 2003/01/29 22:45:36 hsu Exp $
35 * $DragonFly: src/sys/netinet/tcp_output.c,v 1.10 2004/03/08 00:36:30 hsu Exp $
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_tcpdebug.h"
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/kernel.h>
45 #include <sys/sysctl.h>
47 #include <sys/domain.h>
48 #include <sys/protosw.h>
49 #include <sys/socket.h>
50 #include <sys/socketvar.h>
51 #include <sys/in_cksum.h>
53 #include <net/route.h>
55 #include <netinet/in.h>
56 #include <netinet/in_systm.h>
57 #include <netinet/ip.h>
58 #include <netinet/in_pcb.h>
59 #include <netinet/ip_var.h>
60 #include <netinet6/in6_pcb.h>
61 #include <netinet/ip6.h>
62 #include <netinet6/ip6_var.h>
63 #include <netinet/tcp.h>
65 #include <netinet/tcp_fsm.h>
66 #include <netinet/tcp_seq.h>
67 #include <netinet/tcp_timer.h>
68 #include <netinet/tcp_var.h>
69 #include <netinet/tcpip.h>
71 #include <netinet/tcp_debug.h>
75 #include <netinet6/ipsec.h>
79 #include <netipsec/ipsec.h>
84 extern struct mbuf *m_copypack();
87 int path_mtu_discovery = 1;
88 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
89 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
92 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
93 &ss_fltsz, 1, "Slow start flight size");
95 int ss_fltsz_local = 4;
96 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
97 &ss_fltsz_local, 1, "Slow start flight size for local networks");
99 int tcp_do_newreno = 1;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
101 0, "Enable NewReno Algorithms");
104 * Tcp output routine: figure out what should be sent and send it.
110 struct inpcb * const inp = tp->t_inpcb;
111 struct socket *so = inp->inp_socket;
112 long len, recvwin, sendwin;
113 int off, flags, error;
115 struct ip *ip = NULL;
116 struct ipovly *ipov = NULL;
118 u_char opt[TCP_MAXOLEN];
119 unsigned ipoptlen, optlen, hdrlen;
121 struct ip6_hdr *ip6 = NULL;
123 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
125 const boolean_t isipv6 = FALSE;
127 struct rmxp_tao *taop;
130 * Determine length of data that should be transmitted,
131 * and flags that will be used.
132 * If there is some data or critical controls (SYN, RST)
133 * to send, then transmit; otherwise, investigate further.
135 if ((tp->snd_max == tp->snd_una) &&
136 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
138 * We have been idle for "a while" and no acks are
139 * expected to clock out any data we send --
140 * slow start to get ack "clock" running again.
142 * Set the slow-start flight size depending on whether
143 * this is a local network or not.
145 if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
146 (!isipv6 && in_localaddr(inp->inp_faddr)))
147 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
149 tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
151 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
152 if (idle && (tp->t_flags & TF_MORETOCOME))
153 tp->t_flags |= TF_LASTIDLE;
155 tp->t_flags &= ~TF_LASTIDLE;
159 off = tp->snd_nxt - tp->snd_una;
160 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
161 sendwin = min(sendwin, tp->snd_bwnd);
163 flags = tcp_outflags[tp->t_state];
165 * Get standard flags, and add SYN or FIN if requested by 'hidden'
168 if (tp->t_flags & TF_NEEDFIN)
170 if (tp->t_flags & TF_NEEDSYN)
174 * If in persist timeout with window of 0, send 1 byte.
175 * Otherwise, if window is small but nonzero
176 * and timer expired, we will send what we can
177 * and go to transmit state.
182 * If we still have some data to send, then
183 * clear the FIN bit. Usually this would
184 * happen below when it realizes that we
185 * aren't sending all the data. However,
186 * if we have exactly 1 byte of unsent data,
187 * then it won't clear the FIN bit below,
188 * and if we are in persist state, we wind
189 * up sending the packet without recording
190 * that we sent the FIN bit.
192 * We can't just blindly clear the FIN bit,
193 * because if we don't have any more data
194 * to send then the probe will be the FIN
197 if (off < so->so_snd.sb_cc)
201 callout_stop(tp->tt_persist);
207 * If snd_nxt == snd_max and we have transmitted a FIN, the
208 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
209 * a negative length. This can also occur when TCP opens up
210 * its congestion window while receiving additional duplicate
211 * acks after fast-retransmit because TCP will reset snd_nxt
212 * to snd_max after the fast-retransmit.
214 * In the normal retransmit-FIN-only case, however, snd_nxt will
215 * be set to snd_una, the offset will be 0, and the length may
218 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
221 * Lop off SYN bit if it has already been sent. However, if this
222 * is SYN-SENT state and if segment contains data and if we don't
223 * know that foreign host supports TAO, suppress sending segment.
225 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
228 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
229 ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL ||
230 taop->tao_ccsent == 0))
235 * Be careful not to send data and/or FIN on SYN segments
236 * in cases when no CC option will be sent.
237 * This measure is needed to prevent interoperability problems
238 * with not fully conformant TCP implementations.
240 if ((flags & TH_SYN) &&
241 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
242 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
249 * If FIN has been sent but not acked,
250 * but we haven't been called to retransmit,
251 * len will be < 0. Otherwise, window shrank
252 * after we sent into it. If window shrank to 0,
253 * cancel pending retransmit, pull snd_nxt back
254 * to (closed) window, and set the persist timer
255 * if it isn't already going. If the window didn't
256 * close completely, just wait for an ACK.
260 callout_stop(tp->tt_rexmt);
262 tp->snd_nxt = tp->snd_una;
263 if (!callout_active(tp->tt_persist))
269 * len will be >= 0 after this point. Truncate to the maximum
270 * segment length and ensure that FIN is removed if the length
271 * no longer contains the last data byte.
273 if (len > tp->t_maxseg) {
277 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
280 recvwin = sbspace(&so->so_rcv);
283 * Sender silly window avoidance. We transmit under the following
284 * conditions when len is non-zero:
286 * - We have a full segment
287 * - This is the last buffer in a write()/send() and we are
288 * either idle or running NODELAY
289 * - we've timed out (e.g. persist timer)
290 * - we have more then 1/2 the maximum send window's worth of
291 * data (receiver may be limited the window size)
292 * - we need to retransmit
295 if (len == tp->t_maxseg)
298 * NOTE! on localhost connections an 'ack' from the remote
299 * end may occur synchronously with the output and cause
300 * us to flush a buffer queued with moretocome. XXX
302 * note: the len + off check is almost certainly unnecessary.
304 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
305 (idle || (tp->t_flags & TF_NODELAY)) &&
306 len + off >= so->so_snd.sb_cc &&
307 !(tp->t_flags & TF_NOPUSH)) {
310 if (tp->t_force) /* typ. timeout case */
312 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
314 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
319 * Compare available window to amount of window
320 * known to peer (as advertised window less
321 * next expected input). If the difference is at least two
322 * max size segments, or at least 50% of the maximum possible
323 * window, then want to send a window update to peer.
327 * "adv" is the amount we can increase the window,
328 * taking into account that we are limited by
329 * TCP_MAXWIN << tp->rcv_scale.
331 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
332 (tp->rcv_adv - tp->rcv_nxt);
334 if (adv >= (long) (2 * tp->t_maxseg))
336 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
341 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
342 * is also a catch-all for the retransmit timer timeout case.
344 if (tp->t_flags & TF_ACKNOW)
346 if ((flags & TH_RST) ||
347 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
349 if (SEQ_GT(tp->snd_up, tp->snd_una))
352 * If our state indicates that FIN should be sent
353 * and we have not yet done so, then we need to send.
355 if (flags & TH_FIN &&
356 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
360 * TCP window updates are not reliable, rather a polling protocol
361 * using ``persist'' packets is used to insure receipt of window
362 * updates. The three ``states'' for the output side are:
363 * idle not doing retransmits or persists
364 * persisting to move a small or zero window
365 * (re)transmitting and thereby not persisting
367 * callout_active(tp->tt_persist)
368 * is true when we are in persist state.
370 * is set when we are called to send a persist packet.
371 * callout_active(tp->tt_rexmt)
372 * is set when we are retransmitting
373 * The output side is idle when both timers are zero.
375 * If send window is too small, there is data to transmit, and no
376 * retransmit or persist is pending, then go to persist state.
377 * If nothing happens soon, send when timer expires:
378 * if window is nonzero, transmit what we can,
379 * otherwise force out a byte.
381 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
382 !callout_active(tp->tt_persist)) {
388 * No reason to send a segment, just return.
394 * Before ESTABLISHED, force sending of initial options
395 * unless TCP set not to do any options.
396 * NOTE: we assume that the IP/TCP header plus TCP options
397 * always fit in a single mbuf, leaving room for a maximum
399 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
403 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
405 hdrlen = sizeof(struct tcpiphdr);
406 if (flags & TH_SYN) {
407 tp->snd_nxt = tp->iss;
408 if (!(tp->t_flags & TF_NOOPT)) {
411 opt[0] = TCPOPT_MAXSEG;
412 opt[1] = TCPOLEN_MAXSEG;
413 mss = htons((u_short) tcp_mssopt(tp));
414 (void)memcpy(opt + 2, &mss, sizeof(mss));
415 optlen = TCPOLEN_MAXSEG;
417 if ((tp->t_flags & TF_REQ_SCALE) &&
418 (!(flags & TH_ACK) ||
419 (tp->t_flags & TF_RCVD_SCALE))) {
420 *((u_int32_t *)(opt + optlen)) = htonl(
422 TCPOPT_WINDOW << 16 |
423 TCPOLEN_WINDOW << 8 |
424 tp->request_r_scale);
431 * Send a timestamp and echo-reply if this is a SYN and our side
432 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
433 * and our peer have sent timestamps in our SYN's.
435 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
437 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
438 u_int32_t *lp = (u_int32_t *)(opt + optlen);
440 /* Form timestamp option as shown in appendix A of RFC 1323. */
441 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
442 *lp++ = htonl(ticks);
443 *lp = htonl(tp->ts_recent);
444 optlen += TCPOLEN_TSTAMP_APPA;
448 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
449 * options are allowed (!TF_NOOPT) and it's not a RST.
451 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
453 switch (flags & (TH_SYN|TH_ACK)) {
455 * This is a normal ACK, send CC if we received CC before
459 if (!(tp->t_flags & TF_RCVD_CC))
464 * We can only get here in T/TCP's SYN_SENT* state, when
465 * we're a sending a non-SYN segment without waiting for
466 * the ACK of our SYN. A check above assures that we only
467 * do this if our peer understands T/TCP.
470 opt[optlen++] = TCPOPT_NOP;
471 opt[optlen++] = TCPOPT_NOP;
472 opt[optlen++] = TCPOPT_CC;
473 opt[optlen++] = TCPOLEN_CC;
474 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
480 * This is our initial SYN, check whether we have to use
484 opt[optlen++] = TCPOPT_NOP;
485 opt[optlen++] = TCPOPT_NOP;
486 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
487 TCPOPT_CCNEW : TCPOPT_CC;
488 opt[optlen++] = TCPOLEN_CC;
489 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
494 * This is a SYN,ACK; send CC and CC.echo if we received
497 case (TH_SYN|TH_ACK):
498 if (tp->t_flags & TF_RCVD_CC) {
499 opt[optlen++] = TCPOPT_NOP;
500 opt[optlen++] = TCPOPT_NOP;
501 opt[optlen++] = TCPOPT_CC;
502 opt[optlen++] = TCPOLEN_CC;
503 *(u_int32_t *)&opt[optlen] =
506 opt[optlen++] = TCPOPT_NOP;
507 opt[optlen++] = TCPOPT_NOP;
508 opt[optlen++] = TCPOPT_CCECHO;
509 opt[optlen++] = TCPOLEN_CC;
510 *(u_int32_t *)&opt[optlen] =
521 ipoptlen = ip6_optlen(inp);
523 if (inp->inp_options) {
524 ipoptlen = inp->inp_options->m_len -
525 offsetof(struct ipoption, ipopt_list);
531 ipoptlen += ipsec_hdrsiz_tcp(tp);
535 * Adjust data length if insertion of options will
536 * bump the packet length beyond the t_maxopd length.
537 * Clear the FIN bit because we cut off the tail of
540 if (len + optlen + ipoptlen > tp->t_maxopd) {
542 * If there is still more to send, don't close the connection.
545 len = tp->t_maxopd - optlen - ipoptlen;
550 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
552 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
556 * Grab a header mbuf, attaching a copy of data to
557 * be transmitted, and initialize the header from
558 * the template for sends on this connection.
561 if (tp->t_force && len == 1)
562 tcpstat.tcps_sndprobe++;
563 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
564 tcpstat.tcps_sndrexmitpack++;
565 tcpstat.tcps_sndrexmitbyte += len;
567 tcpstat.tcps_sndpack++;
568 tcpstat.tcps_sndbyte += len;
571 if ((m = m_copypack(so->so_snd.sb_mb, off,
572 (int)len, max_linkhdr + hdrlen)) == 0) {
577 * m_copypack left space for our hdr; use it.
582 MGETHDR(m, M_DONTWAIT, MT_HEADER);
588 if (MHLEN < hdrlen + max_linkhdr) {
589 MCLGET(m, M_DONTWAIT);
590 if (!(m->m_flags & M_EXT)) {
597 m->m_data += max_linkhdr;
599 if (len <= MHLEN - hdrlen - max_linkhdr) {
600 m_copydata(so->so_snd.sb_mb, off, (int) len,
601 mtod(m, caddr_t) + hdrlen);
604 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
605 if (m->m_next == 0) {
613 * If we're sending everything we've got, set PUSH.
614 * (This will keep happy those implementations which only
615 * give data to the user when a buffer fills or
618 if (off + len == so->so_snd.sb_cc)
621 if (tp->t_flags & TF_ACKNOW)
622 tcpstat.tcps_sndacks++;
623 else if (flags & (TH_SYN|TH_FIN|TH_RST))
624 tcpstat.tcps_sndctrl++;
625 else if (SEQ_GT(tp->snd_up, tp->snd_una))
626 tcpstat.tcps_sndurg++;
628 tcpstat.tcps_sndwinup++;
630 MGETHDR(m, M_DONTWAIT, MT_HEADER);
636 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
639 m->m_data += max_linkhdr;
642 m->m_pkthdr.rcvif = (struct ifnet *)0;
644 ip6 = mtod(m, struct ip6_hdr *);
645 th = (struct tcphdr *)(ip6 + 1);
646 tcp_fillheaders(tp, ip6, th);
648 ip = mtod(m, struct ip *);
649 ipov = (struct ipovly *)ip;
650 th = (struct tcphdr *)(ip + 1);
651 /* this picks up the pseudo header (w/o the length) */
652 tcp_fillheaders(tp, ip, th);
656 * Fill in fields, remembering maximum advertised
657 * window for use in delaying messages about window sizes.
658 * If resending a FIN, be sure not to use a new sequence number.
660 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
661 tp->snd_nxt == tp->snd_max)
664 * If we are doing retransmissions, then snd_nxt will
665 * not reflect the first unsent octet. For ACK only
666 * packets, we do not want the sequence number of the
667 * retransmitted packet, we want the sequence number
668 * of the next unsent octet. So, if there is no data
669 * (and no SYN or FIN), use snd_max instead of snd_nxt
670 * when filling in ti_seq. But if we are in persist
671 * state, snd_max might reflect one byte beyond the
672 * right edge of the window, so use snd_nxt in that
673 * case, since we know we aren't doing a retransmission.
674 * (retransmit and persist are mutually exclusive...)
676 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
677 th->th_seq = htonl(tp->snd_nxt);
679 th->th_seq = htonl(tp->snd_max);
680 th->th_ack = htonl(tp->rcv_nxt);
682 bcopy(opt, th + 1, optlen);
683 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
685 th->th_flags = flags;
687 * Calculate receive window. Don't shrink window,
688 * but avoid silly window syndrome.
690 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
691 recvwin < (long)tp->t_maxseg)
693 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
694 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
695 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
696 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
697 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
700 * Adjust the RXWIN0SENT flag - indicate that we have advertised
701 * a 0 window. This may cause the remote transmitter to stall. This
702 * flag tells soreceive() to disable delayed acknowledgements when
703 * draining the buffer. This can occur if the receiver is attempting
704 * to read more data then can be buffered prior to transmitting on
708 tp->t_flags |= TF_RXWIN0SENT;
710 tp->t_flags &= ~TF_RXWIN0SENT;
712 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
713 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
714 th->th_flags |= TH_URG;
717 * If no urgent pointer to send, then we pull
718 * the urgent pointer to the left edge of the send window
719 * so that it doesn't drift into the send window on sequence
722 tp->snd_up = tp->snd_una; /* drag it along */
726 * Put TCP length in extended header, and then
727 * checksum extended header and data.
729 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
732 * ip6_plen is not need to be filled now, and will be filled
735 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
736 sizeof(struct tcphdr) + optlen + len);
738 m->m_pkthdr.csum_flags = CSUM_TCP;
739 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
741 th->th_sum = in_addword(th->th_sum,
742 htons((u_short)(optlen + len)));
744 /* IP version must be set here for ipv4/ipv6 checking later */
745 KASSERT(ip->ip_v == IPVERSION,
746 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
750 * In transmit state, time the transmission and arrange for
751 * the retransmit. In persist state, just set snd_max.
753 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
754 tcp_seq startseq = tp->snd_nxt;
757 * Advance snd_nxt over sequence space of this segment.
759 if (flags & (TH_SYN|TH_FIN)) {
762 if (flags & TH_FIN) {
764 tp->t_flags |= TF_SENTFIN;
768 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
769 tp->snd_max = tp->snd_nxt;
771 * Time this transmission if not a retransmission and
772 * not currently timing anything.
774 if (tp->t_rtttime == 0) {
775 tp->t_rtttime = ticks;
776 tp->t_rtseq = startseq;
777 tcpstat.tcps_segstimed++;
782 * Set retransmit timer if not currently set,
783 * and not doing a pure ack or a keep-alive probe.
784 * Initial value for retransmit timer is smoothed
785 * round-trip time + 2 * round-trip time variance.
786 * Initialize shift counter which is used for backoff
787 * of retransmit time.
789 if (!callout_active(tp->tt_rexmt) &&
790 tp->snd_nxt != tp->snd_una) {
791 if (callout_active(tp->tt_persist)) {
792 callout_stop(tp->tt_persist);
795 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
796 tcp_timer_rexmt, tp);
800 * Persist case, update snd_max but since we are in
801 * persist mode (no window) we do not update snd_nxt.
806 if (flags & TH_FIN) {
808 tp->t_flags |= TF_SENTFIN;
810 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
811 tp->snd_max = tp->snd_nxt + xlen;
818 if (so->so_options & SO_DEBUG)
819 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
823 * Fill in IP length and desired time to live and
824 * send to IP level. There should be a better way
825 * to handle ttl and tos; we could keep them in
826 * the template, but need a way to checksum without them.
829 * m->m_pkthdr.len should have been set before cksum calcuration,
830 * because in6_cksum() need it.
834 * we separately set hoplimit for every segment, since the
835 * user might want to change the value via setsockopt.
836 * Also, desired default hop limit might be changed via
837 * Neighbor Discovery.
839 ip6->ip6_hlim = in6_selecthlim(inp,
840 (inp->in6p_route.ro_rt ?
841 inp->in6p_route.ro_rt->rt_ifp : NULL));
843 /* TODO: IPv6 IP6TOS_ECT bit on */
844 error = ip6_output(m, inp->in6p_outputopts, &inp->in6p_route,
845 (so->so_options & SO_DONTROUTE), NULL, NULL, inp);
848 ip->ip_len = m->m_pkthdr.len;
850 if (INP_CHECK_SOCKAF(so, AF_INET6))
851 ip->ip_ttl = in6_selecthlim(inp,
852 (inp->in6p_route.ro_rt ?
853 inp->in6p_route.ro_rt->rt_ifp : NULL));
856 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
858 ip->ip_tos = inp->inp_ip_tos; /* XXX */
860 * See if we should do MTU discovery.
861 * We do it only if the following are true:
862 * 1) we have a valid route to the destination
863 * 2) the MTU is not locked (if it is,
864 * then discovery has been disabled)
866 if (path_mtu_discovery &&
867 (rt = inp->inp_route.ro_rt) && (rt->rt_flags & RTF_UP) &&
868 !(rt->rt_rmx.rmx_locks & RTV_MTU))
871 error = ip_output(m, inp->inp_options, &inp->inp_route,
872 (so->so_options & SO_DONTROUTE), NULL, inp);
877 * We know that the packet was lost, so back out the
878 * sequence number advance, if any.
880 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
882 * No need to check for TH_FIN here because
883 * the TF_SENTFIN flag handles that case.
885 if (!(flags & TH_SYN))
890 if (error == ENOBUFS) {
892 * If we can't send, make sure there is something
893 * to get us going again later. Persist state
894 * is not necessarily right, but it is close enough.
896 if (!callout_active(tp->tt_rexmt) &&
897 !callout_active(tp->tt_persist)) {
904 if (error == EMSGSIZE) {
906 * ip_output() will have already fixed the route
907 * for us. tcp_mtudisc() will, as its last action,
908 * initiate retransmission, so it is important to
914 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
915 TCPS_HAVERCVDSYN(tp->t_state)) {
916 tp->t_softerror = error;
921 tcpstat.tcps_sndtotal++;
924 * Data sent (as far as we can tell).
925 * If this advertises a larger window than any other segment,
926 * then remember the size of the advertised window.
927 * Any pending ACK has now been sent.
929 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
930 tp->rcv_adv = tp->rcv_nxt + recvwin;
931 tp->last_ack_sent = tp->rcv_nxt;
932 tp->t_flags &= ~TF_ACKNOW;
933 if (tcp_delack_enabled)
934 callout_stop(tp->tt_delack);
944 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
947 if (callout_active(tp->tt_rexmt))
948 panic("tcp_setpersist: retransmit pending");
950 * Start/restart persistance timer.
952 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
953 TCPTV_PERSMIN, TCPTV_PERSMAX);
954 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
955 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)