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
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9 * notice, this list of conditions and the following disclaimer.
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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
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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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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 1.7 2003/09/18 18:32:55 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>
52 #include <net/route.h>
54 #include <netinet/in.h>
55 #include <netinet/in_systm.h>
56 #include <netinet/ip.h>
57 #include <netinet/in_pcb.h>
58 #include <netinet/ip_var.h>
60 #include <netinet6/in6_pcb.h>
61 #include <netinet/ip6.h>
62 #include <netinet6/ip6_var.h>
64 #include <netinet/tcp.h>
66 #include <netinet/tcp_fsm.h>
67 #include <netinet/tcp_seq.h>
68 #include <netinet/tcp_timer.h>
69 #include <netinet/tcp_var.h>
70 #include <netinet/tcpip.h>
72 #include <netinet/tcp_debug.h>
76 #include <netinet6/ipsec.h>
80 #include <netipsec/ipsec.h>
84 #include <machine/in_cksum.h>
87 extern struct mbuf *m_copypack();
90 int path_mtu_discovery = 1;
91 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
92 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
95 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
96 &ss_fltsz, 1, "Slow start flight size");
98 int ss_fltsz_local = 4;
99 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
100 &ss_fltsz_local, 1, "Slow start flight size for local networks");
102 int tcp_do_newreno = 1;
103 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
104 0, "Enable NewReno Algorithms");
107 * Tcp output routine: figure out what should be sent and send it.
113 struct socket *so = tp->t_inpcb->inp_socket;
114 long len, recvwin, sendwin;
115 int off, flags, error;
117 struct ip *ip = NULL;
118 struct ipovly *ipov = NULL;
120 struct ip6_hdr *ip6 = NULL;
123 u_char opt[TCP_MAXOLEN];
124 unsigned ipoptlen, optlen, hdrlen;
127 int maxburst = TCP_MAXBURST;
129 struct rmxp_tao *taop;
135 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
139 * Determine length of data that should be transmitted,
140 * and flags that will be used.
141 * If there is some data or critical controls (SYN, RST)
142 * to send, then transmit; otherwise, investigate further.
144 if ((tp->snd_max == tp->snd_una) &&
145 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
147 * We have been idle for "a while" and no acks are
148 * expected to clock out any data we send --
149 * slow start to get ack "clock" running again.
151 * Set the slow-start flight size depending on whether
152 * this is a local network or not.
156 (isipv6 && in6_localaddr(&tp->t_inpcb->in6p_faddr)) ||
159 in_localaddr(tp->t_inpcb->inp_faddr)
164 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
166 tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
168 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
169 if (idle && (tp->t_flags & TF_MORETOCOME))
170 tp->t_flags |= TF_LASTIDLE;
172 tp->t_flags &= ~TF_LASTIDLE;
175 off = tp->snd_nxt - tp->snd_una;
176 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
177 sendwin = min(sendwin, tp->snd_bwnd);
179 flags = tcp_outflags[tp->t_state];
181 * Get standard flags, and add SYN or FIN if requested by 'hidden'
184 if (tp->t_flags & TF_NEEDFIN)
186 if (tp->t_flags & TF_NEEDSYN)
190 * If in persist timeout with window of 0, send 1 byte.
191 * Otherwise, if window is small but nonzero
192 * and timer expired, we will send what we can
193 * and go to transmit state.
198 * If we still have some data to send, then
199 * clear the FIN bit. Usually this would
200 * happen below when it realizes that we
201 * aren't sending all the data. However,
202 * if we have exactly 1 byte of unsent data,
203 * then it won't clear the FIN bit below,
204 * and if we are in persist state, we wind
205 * up sending the packet without recording
206 * that we sent the FIN bit.
208 * We can't just blindly clear the FIN bit,
209 * because if we don't have any more data
210 * to send then the probe will be the FIN
213 if (off < so->so_snd.sb_cc)
217 callout_stop(tp->tt_persist);
223 * If snd_nxt == snd_max and we have transmitted a FIN, the
224 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
225 * a negative length. This can also occur when TCP opens up
226 * its congestion window while receiving additional duplicate
227 * acks after fast-retransmit because TCP will reset snd_nxt
228 * to snd_max after the fast-retransmit.
230 * In the normal retransmit-FIN-only case, however, snd_nxt will
231 * be set to snd_una, the offset will be 0, and the length may
234 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
236 taop = tcp_gettaocache(&tp->t_inpcb->inp_inc);
239 * Lop off SYN bit if it has already been sent. However, if this
240 * is SYN-SENT state and if segment contains data and if we don't
241 * know that foreign host supports TAO, suppress sending segment.
243 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
246 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
247 (taop == NULL || taop->tao_ccsent == 0))
252 * Be careful not to send data and/or FIN on SYN segments
253 * in cases when no CC option will be sent.
254 * This measure is needed to prevent interoperability problems
255 * with not fully conformant TCP implementations.
257 if ((flags & TH_SYN) &&
258 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
259 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
266 * If FIN has been sent but not acked,
267 * but we haven't been called to retransmit,
268 * len will be < 0. Otherwise, window shrank
269 * after we sent into it. If window shrank to 0,
270 * cancel pending retransmit, pull snd_nxt back
271 * to (closed) window, and set the persist timer
272 * if it isn't already going. If the window didn't
273 * close completely, just wait for an ACK.
277 callout_stop(tp->tt_rexmt);
279 tp->snd_nxt = tp->snd_una;
280 if (!callout_active(tp->tt_persist))
286 * len will be >= 0 after this point. Truncate to the maximum
287 * segment length and ensure that FIN is removed if the length
288 * no longer contains the last data byte.
290 if (len > tp->t_maxseg) {
294 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
297 recvwin = sbspace(&so->so_rcv);
300 * Sender silly window avoidance. We transmit under the following
301 * conditions when len is non-zero:
303 * - We have a full segment
304 * - This is the last buffer in a write()/send() and we are
305 * either idle or running NODELAY
306 * - we've timed out (e.g. persist timer)
307 * - we have more then 1/2 the maximum send window's worth of
308 * data (receiver may be limited the window size)
309 * - we need to retransmit
312 if (len == tp->t_maxseg)
315 * NOTE! on localhost connections an 'ack' from the remote
316 * end may occur synchronously with the output and cause
317 * us to flush a buffer queued with moretocome. XXX
319 * note: the len + off check is almost certainly unnecessary.
321 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
322 (idle || (tp->t_flags & TF_NODELAY)) &&
323 len + off >= so->so_snd.sb_cc &&
324 (tp->t_flags & TF_NOPUSH) == 0) {
327 if (tp->t_force) /* typ. timeout case */
329 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
331 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
336 * Compare available window to amount of window
337 * known to peer (as advertised window less
338 * next expected input). If the difference is at least two
339 * max size segments, or at least 50% of the maximum possible
340 * window, then want to send a window update to peer.
344 * "adv" is the amount we can increase the window,
345 * taking into account that we are limited by
346 * TCP_MAXWIN << tp->rcv_scale.
348 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
349 (tp->rcv_adv - tp->rcv_nxt);
351 if (adv >= (long) (2 * tp->t_maxseg))
353 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
358 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
359 * is also a catch-all for the retransmit timer timeout case.
361 if (tp->t_flags & TF_ACKNOW)
363 if ((flags & TH_RST) ||
364 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
366 if (SEQ_GT(tp->snd_up, tp->snd_una))
369 * If our state indicates that FIN should be sent
370 * and we have not yet done so, then we need to send.
372 if (flags & TH_FIN &&
373 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
377 * TCP window updates are not reliable, rather a polling protocol
378 * using ``persist'' packets is used to insure receipt of window
379 * updates. The three ``states'' for the output side are:
380 * idle not doing retransmits or persists
381 * persisting to move a small or zero window
382 * (re)transmitting and thereby not persisting
384 * callout_active(tp->tt_persist)
385 * is true when we are in persist state.
387 * is set when we are called to send a persist packet.
388 * callout_active(tp->tt_rexmt)
389 * is set when we are retransmitting
390 * The output side is idle when both timers are zero.
392 * If send window is too small, there is data to transmit, and no
393 * retransmit or persist is pending, then go to persist state.
394 * If nothing happens soon, send when timer expires:
395 * if window is nonzero, transmit what we can,
396 * otherwise force out a byte.
398 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
399 !callout_active(tp->tt_persist)) {
405 * No reason to send a segment, just return.
411 * Before ESTABLISHED, force sending of initial options
412 * unless TCP set not to do any options.
413 * NOTE: we assume that the IP/TCP header plus TCP options
414 * always fit in a single mbuf, leaving room for a maximum
416 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
421 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
424 hdrlen = sizeof (struct tcpiphdr);
425 if (flags & TH_SYN) {
426 tp->snd_nxt = tp->iss;
427 if ((tp->t_flags & TF_NOOPT) == 0) {
430 opt[0] = TCPOPT_MAXSEG;
431 opt[1] = TCPOLEN_MAXSEG;
432 mss = htons((u_short) tcp_mssopt(tp));
433 (void)memcpy(opt + 2, &mss, sizeof(mss));
434 optlen = TCPOLEN_MAXSEG;
436 if ((tp->t_flags & TF_REQ_SCALE) &&
437 ((flags & TH_ACK) == 0 ||
438 (tp->t_flags & TF_RCVD_SCALE))) {
439 *((u_int32_t *)(opt + optlen)) = htonl(
441 TCPOPT_WINDOW << 16 |
442 TCPOLEN_WINDOW << 8 |
443 tp->request_r_scale);
450 * Send a timestamp and echo-reply if this is a SYN and our side
451 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
452 * and our peer have sent timestamps in our SYN's.
454 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
455 (flags & TH_RST) == 0 &&
456 ((flags & TH_ACK) == 0 ||
457 (tp->t_flags & TF_RCVD_TSTMP))) {
458 u_int32_t *lp = (u_int32_t *)(opt + optlen);
460 /* Form timestamp option as shown in appendix A of RFC 1323. */
461 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
462 *lp++ = htonl(ticks);
463 *lp = htonl(tp->ts_recent);
464 optlen += TCPOLEN_TSTAMP_APPA;
468 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
469 * options are allowed (!TF_NOOPT) and it's not a RST.
471 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
472 (flags & TH_RST) == 0) {
473 switch (flags & (TH_SYN|TH_ACK)) {
475 * This is a normal ACK, send CC if we received CC before
479 if (!(tp->t_flags & TF_RCVD_CC))
484 * We can only get here in T/TCP's SYN_SENT* state, when
485 * we're a sending a non-SYN segment without waiting for
486 * the ACK of our SYN. A check above assures that we only
487 * do this if our peer understands T/TCP.
490 opt[optlen++] = TCPOPT_NOP;
491 opt[optlen++] = TCPOPT_NOP;
492 opt[optlen++] = TCPOPT_CC;
493 opt[optlen++] = TCPOLEN_CC;
494 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
500 * This is our initial SYN, check whether we have to use
504 opt[optlen++] = TCPOPT_NOP;
505 opt[optlen++] = TCPOPT_NOP;
506 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
507 TCPOPT_CCNEW : TCPOPT_CC;
508 opt[optlen++] = TCPOLEN_CC;
509 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
514 * This is a SYN,ACK; send CC and CC.echo if we received
517 case (TH_SYN|TH_ACK):
518 if (tp->t_flags & TF_RCVD_CC) {
519 opt[optlen++] = TCPOPT_NOP;
520 opt[optlen++] = TCPOPT_NOP;
521 opt[optlen++] = TCPOPT_CC;
522 opt[optlen++] = TCPOLEN_CC;
523 *(u_int32_t *)&opt[optlen] =
526 opt[optlen++] = TCPOPT_NOP;
527 opt[optlen++] = TCPOPT_NOP;
528 opt[optlen++] = TCPOPT_CCECHO;
529 opt[optlen++] = TCPOLEN_CC;
530 *(u_int32_t *)&opt[optlen] =
542 ipoptlen = ip6_optlen(tp->t_inpcb);
546 if (tp->t_inpcb->inp_options) {
547 ipoptlen = tp->t_inpcb->inp_options->m_len -
548 offsetof(struct ipoption, ipopt_list);
554 ipoptlen += ipsec_hdrsiz_tcp(tp);
558 * Adjust data length if insertion of options will
559 * bump the packet length beyond the t_maxopd length.
560 * Clear the FIN bit because we cut off the tail of
563 if (len + optlen + ipoptlen > tp->t_maxopd) {
565 * If there is still more to send, don't close the connection.
568 len = tp->t_maxopd - optlen - ipoptlen;
572 /*#ifdef DIAGNOSTIC*/
574 if (max_linkhdr + hdrlen > MCLBYTES)
575 panic("tcphdr too big");
577 if (max_linkhdr + hdrlen > MHLEN)
578 panic("tcphdr too big");
583 * Grab a header mbuf, attaching a copy of data to
584 * be transmitted, and initialize the header from
585 * the template for sends on this connection.
588 if (tp->t_force && len == 1)
589 tcpstat.tcps_sndprobe++;
590 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
591 tcpstat.tcps_sndrexmitpack++;
592 tcpstat.tcps_sndrexmitbyte += len;
594 tcpstat.tcps_sndpack++;
595 tcpstat.tcps_sndbyte += len;
598 if ((m = m_copypack(so->so_snd.sb_mb, off,
599 (int)len, max_linkhdr + hdrlen)) == 0) {
604 * m_copypack left space for our hdr; use it.
609 MGETHDR(m, M_DONTWAIT, MT_HEADER);
615 if (MHLEN < hdrlen + max_linkhdr) {
616 MCLGET(m, M_DONTWAIT);
617 if ((m->m_flags & M_EXT) == 0) {
624 m->m_data += max_linkhdr;
626 if (len <= MHLEN - hdrlen - max_linkhdr) {
627 m_copydata(so->so_snd.sb_mb, off, (int) len,
628 mtod(m, caddr_t) + hdrlen);
631 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
632 if (m->m_next == 0) {
640 * If we're sending everything we've got, set PUSH.
641 * (This will keep happy those implementations which only
642 * give data to the user when a buffer fills or
645 if (off + len == so->so_snd.sb_cc)
648 if (tp->t_flags & TF_ACKNOW)
649 tcpstat.tcps_sndacks++;
650 else if (flags & (TH_SYN|TH_FIN|TH_RST))
651 tcpstat.tcps_sndctrl++;
652 else if (SEQ_GT(tp->snd_up, tp->snd_una))
653 tcpstat.tcps_sndurg++;
655 tcpstat.tcps_sndwinup++;
657 MGETHDR(m, M_DONTWAIT, MT_HEADER);
663 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
668 m->m_data += max_linkhdr;
671 m->m_pkthdr.rcvif = (struct ifnet *)0;
674 ip6 = mtod(m, struct ip6_hdr *);
675 th = (struct tcphdr *)(ip6 + 1);
676 tcp_fillheaders(tp, ip6, th);
680 ip = mtod(m, struct ip *);
681 ipov = (struct ipovly *)ip;
682 th = (struct tcphdr *)(ip + 1);
683 /* this picks up the pseudo header (w/o the length) */
684 tcp_fillheaders(tp, ip, th);
688 * Fill in fields, remembering maximum advertised
689 * window for use in delaying messages about window sizes.
690 * If resending a FIN, be sure not to use a new sequence number.
692 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
693 tp->snd_nxt == tp->snd_max)
696 * If we are doing retransmissions, then snd_nxt will
697 * not reflect the first unsent octet. For ACK only
698 * packets, we do not want the sequence number of the
699 * retransmitted packet, we want the sequence number
700 * of the next unsent octet. So, if there is no data
701 * (and no SYN or FIN), use snd_max instead of snd_nxt
702 * when filling in ti_seq. But if we are in persist
703 * state, snd_max might reflect one byte beyond the
704 * right edge of the window, so use snd_nxt in that
705 * case, since we know we aren't doing a retransmission.
706 * (retransmit and persist are mutually exclusive...)
708 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
709 th->th_seq = htonl(tp->snd_nxt);
711 th->th_seq = htonl(tp->snd_max);
712 th->th_ack = htonl(tp->rcv_nxt);
714 bcopy(opt, th + 1, optlen);
715 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
717 th->th_flags = flags;
719 * Calculate receive window. Don't shrink window,
720 * but avoid silly window syndrome.
722 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
723 recvwin < (long)tp->t_maxseg)
725 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
726 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
727 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
728 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
729 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
732 * Adjust the RXWIN0SENT flag - indicate that we have advertised
733 * a 0 window. This may cause the remote transmitter to stall. This
734 * flag tells soreceive() to disable delayed acknowledgements when
735 * draining the buffer. This can occur if the receiver is attempting
736 * to read more data then can be buffered prior to transmitting on
740 tp->t_flags |= TF_RXWIN0SENT;
742 tp->t_flags &= ~TF_RXWIN0SENT;
744 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
745 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
746 th->th_flags |= TH_URG;
749 * If no urgent pointer to send, then we pull
750 * the urgent pointer to the left edge of the send window
751 * so that it doesn't drift into the send window on sequence
754 tp->snd_up = tp->snd_una; /* drag it along */
757 * Put TCP length in extended header, and then
758 * checksum extended header and data.
760 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
764 * ip6_plen is not need to be filled now, and will be filled
767 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
768 sizeof(struct tcphdr) + optlen + len);
772 m->m_pkthdr.csum_flags = CSUM_TCP;
773 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
775 th->th_sum = in_addword(th->th_sum,
776 htons((u_short)(optlen + len)));
778 /* IP version must be set here for ipv4/ipv6 checking later */
779 KASSERT(ip->ip_v == IPVERSION,
780 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
784 * In transmit state, time the transmission and arrange for
785 * the retransmit. In persist state, just set snd_max.
787 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
788 tcp_seq startseq = tp->snd_nxt;
791 * Advance snd_nxt over sequence space of this segment.
793 if (flags & (TH_SYN|TH_FIN)) {
796 if (flags & TH_FIN) {
798 tp->t_flags |= TF_SENTFIN;
802 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
803 tp->snd_max = tp->snd_nxt;
805 * Time this transmission if not a retransmission and
806 * not currently timing anything.
808 if (tp->t_rtttime == 0) {
809 tp->t_rtttime = ticks;
810 tp->t_rtseq = startseq;
811 tcpstat.tcps_segstimed++;
816 * Set retransmit timer if not currently set,
817 * and not doing a pure ack or a keep-alive probe.
818 * Initial value for retransmit timer is smoothed
819 * round-trip time + 2 * round-trip time variance.
820 * Initialize shift counter which is used for backoff
821 * of retransmit time.
823 if (!callout_active(tp->tt_rexmt) &&
824 tp->snd_nxt != tp->snd_una) {
825 if (callout_active(tp->tt_persist)) {
826 callout_stop(tp->tt_persist);
829 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
830 tcp_timer_rexmt, tp);
834 * Persist case, update snd_max but since we are in
835 * persist mode (no window) we do not update snd_nxt.
840 if (flags & TH_FIN) {
842 tp->t_flags |= TF_SENTFIN;
844 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
845 tp->snd_max = tp->snd_nxt + xlen;
852 if (so->so_options & SO_DEBUG)
853 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
857 * Fill in IP length and desired time to live and
858 * send to IP level. There should be a better way
859 * to handle ttl and tos; we could keep them in
860 * the template, but need a way to checksum without them.
863 * m->m_pkthdr.len should have been set before cksum calcuration,
864 * because in6_cksum() need it.
869 * we separately set hoplimit for every segment, since the
870 * user might want to change the value via setsockopt.
871 * Also, desired default hop limit might be changed via
872 * Neighbor Discovery.
874 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb,
875 tp->t_inpcb->in6p_route.ro_rt ?
876 tp->t_inpcb->in6p_route.ro_rt->rt_ifp
879 /* TODO: IPv6 IP6TOS_ECT bit on */
880 error = ip6_output(m,
881 tp->t_inpcb->in6p_outputopts,
882 &tp->t_inpcb->in6p_route,
883 (so->so_options & SO_DONTROUTE), NULL, NULL,
889 ip->ip_len = m->m_pkthdr.len;
891 if (INP_CHECK_SOCKAF(so, AF_INET6))
892 ip->ip_ttl = in6_selecthlim(tp->t_inpcb,
893 tp->t_inpcb->in6p_route.ro_rt ?
894 tp->t_inpcb->in6p_route.ro_rt->rt_ifp
898 ip->ip_ttl = tp->t_inpcb->inp_ip_ttl; /* XXX */
899 ip->ip_tos = tp->t_inpcb->inp_ip_tos; /* XXX */
901 * See if we should do MTU discovery. We do it only if the following
903 * 1) we have a valid route to the destination
904 * 2) the MTU is not locked (if it is, then discovery has been
907 if (path_mtu_discovery && (rt = tp->t_inpcb->inp_route.ro_rt) &&
908 (rt->rt_flags & RTF_UP) && !(rt->rt_rmx.rmx_locks & RTV_MTU))
910 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
911 (so->so_options & SO_DONTROUTE), 0, tp->t_inpcb);
916 * We know that the packet was lost, so back out the
917 * sequence number advance, if any.
919 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
921 * No need to check for TH_FIN here because
922 * the TF_SENTFIN flag handles that case.
924 if ((flags & TH_SYN) == 0)
929 if (error == ENOBUFS) {
931 * If we can't send, make sure there is something
932 * to get us going again later. Persist state
933 * is not necessarily right, but it is close enough.
935 if (!callout_active(tp->tt_rexmt) &&
936 !callout_active(tp->tt_persist)) {
940 tcp_quench(tp->t_inpcb, 0);
943 if (error == EMSGSIZE) {
945 * ip_output() will have already fixed the route
946 * for us. tcp_mtudisc() will, as its last action,
947 * initiate retransmission, so it is important to
950 tcp_mtudisc(tp->t_inpcb, 0);
953 if ((error == EHOSTUNREACH || error == ENETDOWN)
954 && TCPS_HAVERCVDSYN(tp->t_state)) {
955 tp->t_softerror = error;
960 tcpstat.tcps_sndtotal++;
963 * Data sent (as far as we can tell).
964 * If this advertises a larger window than any other segment,
965 * then remember the size of the advertised window.
966 * Any pending ACK has now been sent.
968 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
969 tp->rcv_adv = tp->rcv_nxt + recvwin;
970 tp->last_ack_sent = tp->rcv_nxt;
971 tp->t_flags &= ~TF_ACKNOW;
972 if (tcp_delack_enabled)
973 callout_stop(tp->tt_delack);
976 * This completely breaks TCP if newreno is turned on. What happens
977 * is that if delayed-acks are turned on on the receiver, this code
978 * on the transmitter effectively destroys the TCP window, forcing
979 * it to four packets (1.5Kx4 = 6K window).
981 if (sendalot && (!tcp_do_newreno || --maxburst))
993 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
996 if (callout_active(tp->tt_rexmt))
997 panic("tcp_setpersist: retransmit pending");
999 * Start/restart persistance timer.
1001 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1002 TCPTV_PERSMIN, TCPTV_PERSMAX);
1003 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
1004 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)