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
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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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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 1.11 2004/04/07 17:01:25 dillon 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>
52 #include <sys/thread.h>
53 #include <sys/globaldata.h>
55 #include <net/route.h>
57 #include <netinet/in.h>
58 #include <netinet/in_systm.h>
59 #include <netinet/ip.h>
60 #include <netinet/in_pcb.h>
61 #include <netinet/ip_var.h>
62 #include <netinet6/in6_pcb.h>
63 #include <netinet/ip6.h>
64 #include <netinet6/ip6_var.h>
65 #include <netinet/tcp.h>
67 #include <netinet/tcp_fsm.h>
68 #include <netinet/tcp_seq.h>
69 #include <netinet/tcp_timer.h>
70 #include <netinet/tcp_var.h>
71 #include <netinet/tcpip.h>
73 #include <netinet/tcp_debug.h>
77 #include <netinet6/ipsec.h>
81 #include <netipsec/ipsec.h>
86 extern struct mbuf *m_copypack();
89 int path_mtu_discovery = 1;
90 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
91 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
94 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
95 &ss_fltsz, 1, "Slow start flight size");
97 int ss_fltsz_local = 4;
98 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
99 &ss_fltsz_local, 1, "Slow start flight size for local networks");
101 int tcp_do_newreno = 1;
102 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
103 0, "Enable NewReno Algorithms");
106 * Tcp output routine: figure out what should be sent and send it.
112 struct inpcb * const inp = tp->t_inpcb;
113 struct socket *so = inp->inp_socket;
114 long len, recvwin, sendwin;
115 int off, flags, error;
117 struct ip *ip = NULL;
118 struct ipovly *ipov = NULL;
120 u_char opt[TCP_MAXOLEN];
121 unsigned ipoptlen, optlen, hdrlen;
123 struct ip6_hdr *ip6 = NULL;
125 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
127 const boolean_t isipv6 = FALSE;
129 struct rmxp_tao *taop;
132 * Determine length of data that should be transmitted,
133 * and flags that will be used.
134 * If there is some data or critical controls (SYN, RST)
135 * to send, then transmit; otherwise, investigate further.
137 if ((tp->snd_max == tp->snd_una) &&
138 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
140 * We have been idle for "a while" and no acks are
141 * expected to clock out any data we send --
142 * slow start to get ack "clock" running again.
144 * Set the slow-start flight size depending on whether
145 * this is a local network or not.
147 if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
148 (!isipv6 && in_localaddr(inp->inp_faddr)))
149 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
151 tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
153 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
154 if (idle && (tp->t_flags & TF_MORETOCOME))
155 tp->t_flags |= TF_LASTIDLE;
157 tp->t_flags &= ~TF_LASTIDLE;
161 off = tp->snd_nxt - tp->snd_una;
162 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
163 sendwin = min(sendwin, tp->snd_bwnd);
165 flags = tcp_outflags[tp->t_state];
167 * Get standard flags, and add SYN or FIN if requested by 'hidden'
170 if (tp->t_flags & TF_NEEDFIN)
172 if (tp->t_flags & TF_NEEDSYN)
176 * If in persist timeout with window of 0, send 1 byte.
177 * Otherwise, if window is small but nonzero
178 * and timer expired, we will send what we can
179 * and go to transmit state.
184 * If we still have some data to send, then
185 * clear the FIN bit. Usually this would
186 * happen below when it realizes that we
187 * aren't sending all the data. However,
188 * if we have exactly 1 byte of unsent data,
189 * then it won't clear the FIN bit below,
190 * and if we are in persist state, we wind
191 * up sending the packet without recording
192 * that we sent the FIN bit.
194 * We can't just blindly clear the FIN bit,
195 * because if we don't have any more data
196 * to send then the probe will be the FIN
199 if (off < so->so_snd.sb_cc)
203 callout_stop(tp->tt_persist);
209 * If snd_nxt == snd_max and we have transmitted a FIN, the
210 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
211 * a negative length. This can also occur when TCP opens up
212 * its congestion window while receiving additional duplicate
213 * acks after fast-retransmit because TCP will reset snd_nxt
214 * to snd_max after the fast-retransmit.
216 * In the normal retransmit-FIN-only case, however, snd_nxt will
217 * be set to snd_una, the offset will be 0, and the length may
220 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
223 * Lop off SYN bit if it has already been sent. However, if this
224 * is SYN-SENT state and if segment contains data and if we don't
225 * know that foreign host supports TAO, suppress sending segment.
227 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
230 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
231 ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL ||
232 taop->tao_ccsent == 0))
237 * Be careful not to send data and/or FIN on SYN segments
238 * in cases when no CC option will be sent.
239 * This measure is needed to prevent interoperability problems
240 * with not fully conformant TCP implementations.
242 if ((flags & TH_SYN) &&
243 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
244 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
251 * If FIN has been sent but not acked,
252 * but we haven't been called to retransmit,
253 * len will be < 0. Otherwise, window shrank
254 * after we sent into it. If window shrank to 0,
255 * cancel pending retransmit, pull snd_nxt back
256 * to (closed) window, and set the persist timer
257 * if it isn't already going. If the window didn't
258 * close completely, just wait for an ACK.
262 callout_stop(tp->tt_rexmt);
264 tp->snd_nxt = tp->snd_una;
265 if (!callout_active(tp->tt_persist))
271 * len will be >= 0 after this point. Truncate to the maximum
272 * segment length and ensure that FIN is removed if the length
273 * no longer contains the last data byte.
275 if (len > tp->t_maxseg) {
279 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
282 recvwin = sbspace(&so->so_rcv);
285 * Sender silly window avoidance. We transmit under the following
286 * conditions when len is non-zero:
288 * - We have a full segment
289 * - This is the last buffer in a write()/send() and we are
290 * either idle or running NODELAY
291 * - we've timed out (e.g. persist timer)
292 * - we have more then 1/2 the maximum send window's worth of
293 * data (receiver may be limited the window size)
294 * - we need to retransmit
297 if (len == tp->t_maxseg)
300 * NOTE! on localhost connections an 'ack' from the remote
301 * end may occur synchronously with the output and cause
302 * us to flush a buffer queued with moretocome. XXX
304 * note: the len + off check is almost certainly unnecessary.
306 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
307 (idle || (tp->t_flags & TF_NODELAY)) &&
308 len + off >= so->so_snd.sb_cc &&
309 !(tp->t_flags & TF_NOPUSH)) {
312 if (tp->t_force) /* typ. timeout case */
314 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
316 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
321 * Compare available window to amount of window
322 * known to peer (as advertised window less
323 * next expected input). If the difference is at least two
324 * max size segments, or at least 50% of the maximum possible
325 * window, then want to send a window update to peer.
329 * "adv" is the amount we can increase the window,
330 * taking into account that we are limited by
331 * TCP_MAXWIN << tp->rcv_scale.
333 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
334 (tp->rcv_adv - tp->rcv_nxt);
336 if (adv >= (long) (2 * tp->t_maxseg))
338 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
343 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
344 * is also a catch-all for the retransmit timer timeout case.
346 if (tp->t_flags & TF_ACKNOW)
348 if ((flags & TH_RST) ||
349 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
351 if (SEQ_GT(tp->snd_up, tp->snd_una))
354 * If our state indicates that FIN should be sent
355 * and we have not yet done so, then we need to send.
357 if (flags & TH_FIN &&
358 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
362 * TCP window updates are not reliable, rather a polling protocol
363 * using ``persist'' packets is used to insure receipt of window
364 * updates. The three ``states'' for the output side are:
365 * idle not doing retransmits or persists
366 * persisting to move a small or zero window
367 * (re)transmitting and thereby not persisting
369 * callout_active(tp->tt_persist)
370 * is true when we are in persist state.
372 * is set when we are called to send a persist packet.
373 * callout_active(tp->tt_rexmt)
374 * is set when we are retransmitting
375 * The output side is idle when both timers are zero.
377 * If send window is too small, there is data to transmit, and no
378 * retransmit or persist is pending, then go to persist state.
379 * If nothing happens soon, send when timer expires:
380 * if window is nonzero, transmit what we can,
381 * otherwise force out a byte.
383 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
384 !callout_active(tp->tt_persist)) {
390 * No reason to send a segment, just return.
396 * Before ESTABLISHED, force sending of initial options
397 * unless TCP set not to do any options.
398 * NOTE: we assume that the IP/TCP header plus TCP options
399 * always fit in a single mbuf, leaving room for a maximum
401 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
405 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
407 hdrlen = sizeof(struct tcpiphdr);
408 if (flags & TH_SYN) {
409 tp->snd_nxt = tp->iss;
410 if (!(tp->t_flags & TF_NOOPT)) {
413 opt[0] = TCPOPT_MAXSEG;
414 opt[1] = TCPOLEN_MAXSEG;
415 mss = htons((u_short) tcp_mssopt(tp));
416 (void)memcpy(opt + 2, &mss, sizeof(mss));
417 optlen = TCPOLEN_MAXSEG;
419 if ((tp->t_flags & TF_REQ_SCALE) &&
420 (!(flags & TH_ACK) ||
421 (tp->t_flags & TF_RCVD_SCALE))) {
422 *((u_int32_t *)(opt + optlen)) = htonl(
424 TCPOPT_WINDOW << 16 |
425 TCPOLEN_WINDOW << 8 |
426 tp->request_r_scale);
433 * Send a timestamp and echo-reply if this is a SYN and our side
434 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
435 * and our peer have sent timestamps in our SYN's.
437 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
439 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
440 u_int32_t *lp = (u_int32_t *)(opt + optlen);
442 /* Form timestamp option as shown in appendix A of RFC 1323. */
443 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
444 *lp++ = htonl(ticks);
445 *lp = htonl(tp->ts_recent);
446 optlen += TCPOLEN_TSTAMP_APPA;
450 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
451 * options are allowed (!TF_NOOPT) and it's not a RST.
453 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
455 switch (flags & (TH_SYN|TH_ACK)) {
457 * This is a normal ACK, send CC if we received CC before
461 if (!(tp->t_flags & TF_RCVD_CC))
466 * We can only get here in T/TCP's SYN_SENT* state, when
467 * we're a sending a non-SYN segment without waiting for
468 * the ACK of our SYN. A check above assures that we only
469 * do this if our peer understands T/TCP.
472 opt[optlen++] = TCPOPT_NOP;
473 opt[optlen++] = TCPOPT_NOP;
474 opt[optlen++] = TCPOPT_CC;
475 opt[optlen++] = TCPOLEN_CC;
476 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
482 * This is our initial SYN, check whether we have to use
486 opt[optlen++] = TCPOPT_NOP;
487 opt[optlen++] = TCPOPT_NOP;
488 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
489 TCPOPT_CCNEW : TCPOPT_CC;
490 opt[optlen++] = TCPOLEN_CC;
491 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
496 * This is a SYN,ACK; send CC and CC.echo if we received
499 case (TH_SYN|TH_ACK):
500 if (tp->t_flags & TF_RCVD_CC) {
501 opt[optlen++] = TCPOPT_NOP;
502 opt[optlen++] = TCPOPT_NOP;
503 opt[optlen++] = TCPOPT_CC;
504 opt[optlen++] = TCPOLEN_CC;
505 *(u_int32_t *)&opt[optlen] =
508 opt[optlen++] = TCPOPT_NOP;
509 opt[optlen++] = TCPOPT_NOP;
510 opt[optlen++] = TCPOPT_CCECHO;
511 opt[optlen++] = TCPOLEN_CC;
512 *(u_int32_t *)&opt[optlen] =
523 ipoptlen = ip6_optlen(inp);
525 if (inp->inp_options) {
526 ipoptlen = inp->inp_options->m_len -
527 offsetof(struct ipoption, ipopt_list);
533 ipoptlen += ipsec_hdrsiz_tcp(tp);
537 * Adjust data length if insertion of options will
538 * bump the packet length beyond the t_maxopd length.
539 * Clear the FIN bit because we cut off the tail of
542 if (len + optlen + ipoptlen > tp->t_maxopd) {
544 * If there is still more to send, don't close the connection.
547 len = tp->t_maxopd - optlen - ipoptlen;
552 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
554 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
558 * Grab a header mbuf, attaching a copy of data to
559 * be transmitted, and initialize the header from
560 * the template for sends on this connection.
563 if (tp->t_force && len == 1)
564 tcpstat.tcps_sndprobe++;
565 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
566 tcpstat.tcps_sndrexmitpack++;
567 tcpstat.tcps_sndrexmitbyte += len;
569 tcpstat.tcps_sndpack++;
570 tcpstat.tcps_sndbyte += len;
573 if ((m = m_copypack(so->so_snd.sb_mb, off,
574 (int)len, max_linkhdr + hdrlen)) == 0) {
579 * m_copypack left space for our hdr; use it.
584 MGETHDR(m, M_DONTWAIT, MT_HEADER);
590 if (MHLEN < hdrlen + max_linkhdr) {
591 MCLGET(m, M_DONTWAIT);
592 if (!(m->m_flags & M_EXT)) {
599 m->m_data += max_linkhdr;
601 if (len <= MHLEN - hdrlen - max_linkhdr) {
602 m_copydata(so->so_snd.sb_mb, off, (int) len,
603 mtod(m, caddr_t) + hdrlen);
606 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
607 if (m->m_next == 0) {
615 * If we're sending everything we've got, set PUSH.
616 * (This will keep happy those implementations which only
617 * give data to the user when a buffer fills or
620 if (off + len == so->so_snd.sb_cc)
623 if (tp->t_flags & TF_ACKNOW)
624 tcpstat.tcps_sndacks++;
625 else if (flags & (TH_SYN|TH_FIN|TH_RST))
626 tcpstat.tcps_sndctrl++;
627 else if (SEQ_GT(tp->snd_up, tp->snd_una))
628 tcpstat.tcps_sndurg++;
630 tcpstat.tcps_sndwinup++;
632 MGETHDR(m, M_DONTWAIT, MT_HEADER);
638 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
641 m->m_data += max_linkhdr;
644 m->m_pkthdr.rcvif = (struct ifnet *)0;
646 ip6 = mtod(m, struct ip6_hdr *);
647 th = (struct tcphdr *)(ip6 + 1);
648 tcp_fillheaders(tp, ip6, th);
650 ip = mtod(m, struct ip *);
651 ipov = (struct ipovly *)ip;
652 th = (struct tcphdr *)(ip + 1);
653 /* this picks up the pseudo header (w/o the length) */
654 tcp_fillheaders(tp, ip, th);
658 * Fill in fields, remembering maximum advertised
659 * window for use in delaying messages about window sizes.
660 * If resending a FIN, be sure not to use a new sequence number.
662 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
663 tp->snd_nxt == tp->snd_max)
666 * If we are doing retransmissions, then snd_nxt will
667 * not reflect the first unsent octet. For ACK only
668 * packets, we do not want the sequence number of the
669 * retransmitted packet, we want the sequence number
670 * of the next unsent octet. So, if there is no data
671 * (and no SYN or FIN), use snd_max instead of snd_nxt
672 * when filling in ti_seq. But if we are in persist
673 * state, snd_max might reflect one byte beyond the
674 * right edge of the window, so use snd_nxt in that
675 * case, since we know we aren't doing a retransmission.
676 * (retransmit and persist are mutually exclusive...)
678 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
679 th->th_seq = htonl(tp->snd_nxt);
681 th->th_seq = htonl(tp->snd_max);
682 th->th_ack = htonl(tp->rcv_nxt);
684 bcopy(opt, th + 1, optlen);
685 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
687 th->th_flags = flags;
689 * Calculate receive window. Don't shrink window,
690 * but avoid silly window syndrome.
692 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
693 recvwin < (long)tp->t_maxseg)
695 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
696 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
697 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
698 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
699 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
702 * Adjust the RXWIN0SENT flag - indicate that we have advertised
703 * a 0 window. This may cause the remote transmitter to stall. This
704 * flag tells soreceive() to disable delayed acknowledgements when
705 * draining the buffer. This can occur if the receiver is attempting
706 * to read more data then can be buffered prior to transmitting on
710 tp->t_flags |= TF_RXWIN0SENT;
712 tp->t_flags &= ~TF_RXWIN0SENT;
714 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
715 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
716 th->th_flags |= TH_URG;
719 * If no urgent pointer to send, then we pull
720 * the urgent pointer to the left edge of the send window
721 * so that it doesn't drift into the send window on sequence
724 tp->snd_up = tp->snd_una; /* drag it along */
728 * Put TCP length in extended header, and then
729 * checksum extended header and data.
731 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
734 * ip6_plen is not need to be filled now, and will be filled
737 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
738 sizeof(struct tcphdr) + optlen + len);
740 m->m_pkthdr.csum_flags = CSUM_TCP;
741 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
743 th->th_sum = in_addword(th->th_sum,
744 htons((u_short)(optlen + len)));
746 /* IP version must be set here for ipv4/ipv6 checking later */
747 KASSERT(ip->ip_v == IPVERSION,
748 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
752 * In transmit state, time the transmission and arrange for
753 * the retransmit. In persist state, just set snd_max.
755 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
756 tcp_seq startseq = tp->snd_nxt;
759 * Advance snd_nxt over sequence space of this segment.
761 if (flags & (TH_SYN|TH_FIN)) {
764 if (flags & TH_FIN) {
766 tp->t_flags |= TF_SENTFIN;
770 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
771 tp->snd_max = tp->snd_nxt;
773 * Time this transmission if not a retransmission and
774 * not currently timing anything.
776 if (tp->t_rtttime == 0) {
777 tp->t_rtttime = ticks;
778 tp->t_rtseq = startseq;
779 tcpstat.tcps_segstimed++;
784 * Set retransmit timer if not currently set,
785 * and not doing a pure ack or a keep-alive probe.
786 * Initial value for retransmit timer is smoothed
787 * round-trip time + 2 * round-trip time variance.
788 * Initialize shift counter which is used for backoff
789 * of retransmit time.
791 if (!callout_active(tp->tt_rexmt) &&
792 tp->snd_nxt != tp->snd_una) {
793 if (callout_active(tp->tt_persist)) {
794 callout_stop(tp->tt_persist);
797 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
798 tcp_timer_rexmt, tp);
802 * Persist case, update snd_max but since we are in
803 * persist mode (no window) we do not update snd_nxt.
808 if (flags & TH_FIN) {
810 tp->t_flags |= TF_SENTFIN;
812 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
813 tp->snd_max = tp->snd_nxt + xlen;
820 if (so->so_options & SO_DEBUG)
821 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
825 * Fill in IP length and desired time to live and
826 * send to IP level. There should be a better way
827 * to handle ttl and tos; we could keep them in
828 * the template, but need a way to checksum without them.
831 * m->m_pkthdr.len should have been set before cksum calcuration,
832 * because in6_cksum() need it.
836 * we separately set hoplimit for every segment, since the
837 * user might want to change the value via setsockopt.
838 * Also, desired default hop limit might be changed via
839 * Neighbor Discovery.
841 ip6->ip6_hlim = in6_selecthlim(inp,
842 (inp->in6p_route.ro_rt ?
843 inp->in6p_route.ro_rt->rt_ifp : NULL));
845 /* TODO: IPv6 IP6TOS_ECT bit on */
846 error = ip6_output(m, inp->in6p_outputopts, &inp->in6p_route,
847 (so->so_options & SO_DONTROUTE), NULL, NULL, inp);
850 ip->ip_len = m->m_pkthdr.len;
852 if (INP_CHECK_SOCKAF(so, AF_INET6))
853 ip->ip_ttl = in6_selecthlim(inp,
854 (inp->in6p_route.ro_rt ?
855 inp->in6p_route.ro_rt->rt_ifp : NULL));
858 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
860 ip->ip_tos = inp->inp_ip_tos; /* XXX */
862 * See if we should do MTU discovery.
863 * We do it only if the following are true:
864 * 1) we have a valid route to the destination
865 * 2) the MTU is not locked (if it is,
866 * then discovery has been disabled)
868 if (path_mtu_discovery &&
869 (rt = inp->inp_route.ro_rt) && (rt->rt_flags & RTF_UP) &&
870 !(rt->rt_rmx.rmx_locks & RTV_MTU))
873 error = ip_output(m, inp->inp_options, &inp->inp_route,
874 (so->so_options & SO_DONTROUTE), NULL, inp);
879 * We know that the packet was lost, so back out the
880 * sequence number advance, if any.
882 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
884 * No need to check for TH_FIN here because
885 * the TF_SENTFIN flag handles that case.
887 if (!(flags & TH_SYN))
892 if (error == ENOBUFS) {
894 * If we can't send, make sure there is something
895 * to get us going again later. Persist state
896 * is not necessarily right, but it is close enough.
898 if (!callout_active(tp->tt_rexmt) &&
899 !callout_active(tp->tt_persist)) {
906 if (error == EMSGSIZE) {
908 * ip_output() will have already fixed the route
909 * for us. tcp_mtudisc() will, as its last action,
910 * initiate retransmission, so it is important to
916 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
917 TCPS_HAVERCVDSYN(tp->t_state)) {
918 tp->t_softerror = error;
923 tcpstat.tcps_sndtotal++;
926 * Data sent (as far as we can tell).
927 * If this advertises a larger window than any other segment,
928 * then remember the size of the advertised window.
929 * Any pending ACK has now been sent.
931 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
932 tp->rcv_adv = tp->rcv_nxt + recvwin;
933 tp->last_ack_sent = tp->rcv_nxt;
934 tp->t_flags &= ~TF_ACKNOW;
935 if (tcp_delack_enabled)
936 callout_stop(tp->tt_delack);
946 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
949 if (callout_active(tp->tt_rexmt))
950 panic("tcp_setpersist: retransmit pending");
952 * Start/restart persistance timer.
954 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
955 TCPTV_PERSMIN, TCPTV_PERSMAX);
956 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
957 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)