2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
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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.
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13 * 4. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
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17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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29 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
34 #include "opt_inet6.h"
35 #include "opt_ipsec.h"
37 #include "opt_tcpdebug.h"
38 #include "opt_tcp_sack.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/domain.h>
43 #include <sys/kernel.h>
47 #include <sys/mutex.h>
48 #include <sys/protosw.h>
49 #include <sys/socket.h>
50 #include <sys/socketvar.h>
51 #include <sys/sysctl.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>
61 #include <netinet6/in6_pcb.h>
62 #include <netinet/ip6.h>
63 #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>
85 #include <machine/in_cksum.h>
88 extern struct mbuf *m_copypack();
91 int path_mtu_discovery = 1;
92 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
93 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
96 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
97 &ss_fltsz, 1, "Slow start flight size");
99 int ss_fltsz_local = 4;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
101 &ss_fltsz_local, 1, "Slow start flight size for local networks");
103 int tcp_do_newreno = 1;
104 SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
105 0, "Enable NewReno Algorithms");
108 * Tcp output routine: figure out what should be sent and send it.
111 tcp_output(struct tcpcb *tp)
113 struct socket *so = tp->t_inpcb->inp_socket;
114 long len, recwin, sendwin;
115 int off, flags, error;
120 struct ip *ip = NULL;
121 struct ipovly *ipov = NULL;
123 u_char opt[TCP_MAXOLEN];
124 unsigned ipoptlen, optlen, hdrlen;
130 int maxburst = TCP_MAXBURST;
133 struct ip6_hdr *ip6 = NULL;
136 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
139 INP_LOCK_ASSERT(tp->t_inpcb);
142 * Determine length of data that should be transmitted,
143 * and flags that will be used.
144 * If there is some data or critical controls (SYN, RST)
145 * to send, then transmit; otherwise, investigate further.
147 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
148 if (idle && (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
150 * We have been idle for "a while" and no acks are
151 * expected to clock out any data we send --
152 * slow start to get ack "clock" running again.
154 * Set the slow-start flight size depending on whether
155 * this is a local network or not.
160 if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
164 if (in_localaddr(tp->t_inpcb->inp_faddr))
166 tp->snd_cwnd = tp->t_maxseg * ss;
168 tp->t_flags &= ~TF_LASTIDLE;
170 if (tp->t_flags & TF_MORETOCOME) {
171 tp->t_flags |= TF_LASTIDLE;
177 * If we've recently taken a timeout, snd_max will be greater than
178 * snd_nxt. There may be SACK information that allows us to avoid
179 * resending already delivered data. Adjust snd_nxt accordingly.
181 if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max))
184 off = tp->snd_nxt - tp->snd_una;
185 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
186 sendwin = min(sendwin, tp->snd_bwnd);
188 flags = tcp_outflags[tp->t_state];
190 * Send any SACK-generated retransmissions. If we're explicitly trying
191 * to send out new data (when sendalot is 1), bypass this function.
192 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
193 * we're replacing a (future) new transmission with a retransmission
194 * now, and we previously incremented snd_cwnd in tcp_input().
197 * Still in sack recovery , reset rxmit flag to zero.
203 if (tp->sack_enable && IN_FASTRECOVERY(tp) &&
204 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
207 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
210 /* Do not retransmit SACK segments beyond snd_recover */
211 if (SEQ_GT(p->end, tp->snd_recover)) {
213 * (At least) part of sack hole extends beyond
214 * snd_recover. Check to see if we can rexmit data
217 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
219 * Can't rexmit any more data for this hole.
220 * That data will be rexmitted in the next
221 * sack recovery episode, when snd_recover
222 * moves past p->rxmit.
225 goto after_sack_rexmit;
227 /* Can rexmit part of the current hole */
228 len = ((long)ulmin(cwin,
229 tp->snd_recover - p->rxmit));
231 len = ((long)ulmin(cwin, p->end - p->rxmit));
232 off = p->rxmit - tp->snd_una;
233 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
238 tcpstat.tcps_sack_rexmits++;
239 tcpstat.tcps_sack_rexmit_bytes +=
240 min(len, tp->t_maxseg);
245 * Get standard flags, and add SYN or FIN if requested by 'hidden'
248 if (tp->t_flags & TF_NEEDFIN)
250 if (tp->t_flags & TF_NEEDSYN)
253 SOCKBUF_LOCK(&so->so_snd);
255 * If in persist timeout with window of 0, send 1 byte.
256 * Otherwise, if window is small but nonzero
257 * and timer expired, we will send what we can
258 * and go to transmit state.
263 * If we still have some data to send, then
264 * clear the FIN bit. Usually this would
265 * happen below when it realizes that we
266 * aren't sending all the data. However,
267 * if we have exactly 1 byte of unsent data,
268 * then it won't clear the FIN bit below,
269 * and if we are in persist state, we wind
270 * up sending the packet without recording
271 * that we sent the FIN bit.
273 * We can't just blindly clear the FIN bit,
274 * because if we don't have any more data
275 * to send then the probe will be the FIN
278 if (off < so->so_snd.sb_cc)
282 callout_stop(tp->tt_persist);
288 * If snd_nxt == snd_max and we have transmitted a FIN, the
289 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
290 * a negative length. This can also occur when TCP opens up
291 * its congestion window while receiving additional duplicate
292 * acks after fast-retransmit because TCP will reset snd_nxt
293 * to snd_max after the fast-retransmit.
295 * In the normal retransmit-FIN-only case, however, snd_nxt will
296 * be set to snd_una, the offset will be 0, and the length may
299 * If sack_rxmit is true we are retransmitting from the scoreboard
300 * in which case len is already set.
302 if (sack_rxmit == 0) {
303 if (sack_bytes_rxmt == 0)
304 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
309 * We are inside of a SACK recovery episode and are
310 * sending new data, having retransmitted all the
311 * data possible in the scoreboard.
313 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd)
316 * Don't remove this (len > 0) check !
317 * We explicitly check for len > 0 here (although it
318 * isn't really necessary), to work around a gcc
319 * optimization issue - to force gcc to compute
320 * len above. Without this check, the computation
321 * of len is bungled by the optimizer.
324 cwin = tp->snd_cwnd -
325 (tp->snd_nxt - tp->sack_newdata) -
329 len = lmin(len, cwin);
335 * Lop off SYN bit if it has already been sent. However, if this
336 * is SYN-SENT state and if segment contains data and if we don't
337 * know that foreign host supports TAO, suppress sending segment.
339 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
345 * Be careful not to send data and/or FIN on SYN segments.
346 * This measure is needed to prevent interoperability problems
347 * with not fully conformant TCP implementations.
349 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
356 * If FIN has been sent but not acked,
357 * but we haven't been called to retransmit,
358 * len will be < 0. Otherwise, window shrank
359 * after we sent into it. If window shrank to 0,
360 * cancel pending retransmit, pull snd_nxt back
361 * to (closed) window, and set the persist timer
362 * if it isn't already going. If the window didn't
363 * close completely, just wait for an ACK.
367 callout_stop(tp->tt_rexmt);
369 tp->snd_nxt = tp->snd_una;
370 if (!callout_active(tp->tt_persist))
376 * len will be >= 0 after this point. Truncate to the maximum
377 * segment length and ensure that FIN is removed if the length
378 * no longer contains the last data byte.
380 if (len > tp->t_maxseg) {
385 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
388 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
392 recwin = sbspace(&so->so_rcv);
395 * Sender silly window avoidance. We transmit under the following
396 * conditions when len is non-zero:
398 * - We have a full segment
399 * - This is the last buffer in a write()/send() and we are
400 * either idle or running NODELAY
401 * - we've timed out (e.g. persist timer)
402 * - we have more then 1/2 the maximum send window's worth of
403 * data (receiver may be limited the window size)
404 * - we need to retransmit
407 if (len == tp->t_maxseg)
410 * NOTE! on localhost connections an 'ack' from the remote
411 * end may occur synchronously with the output and cause
412 * us to flush a buffer queued with moretocome. XXX
414 * note: the len + off check is almost certainly unnecessary.
416 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
417 (idle || (tp->t_flags & TF_NODELAY)) &&
418 len + off >= so->so_snd.sb_cc &&
419 (tp->t_flags & TF_NOPUSH) == 0) {
422 if (tp->t_force) /* typ. timeout case */
424 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
426 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
433 * Compare available window to amount of window
434 * known to peer (as advertised window less
435 * next expected input). If the difference is at least two
436 * max size segments, or at least 50% of the maximum possible
437 * window, then want to send a window update to peer.
438 * Skip this if the connection is in T/TCP half-open state.
440 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN)) {
442 * "adv" is the amount we can increase the window,
443 * taking into account that we are limited by
444 * TCP_MAXWIN << tp->rcv_scale.
446 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
447 (tp->rcv_adv - tp->rcv_nxt);
449 if (adv >= (long) (2 * tp->t_maxseg))
451 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
456 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
457 * is also a catch-all for the retransmit timer timeout case.
459 if (tp->t_flags & TF_ACKNOW)
461 if ((flags & TH_RST) ||
462 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
464 if (SEQ_GT(tp->snd_up, tp->snd_una))
467 * If our state indicates that FIN should be sent
468 * and we have not yet done so, then we need to send.
470 if (flags & TH_FIN &&
471 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
474 * In SACK, it is possible for tcp_output to fail to send a segment
475 * after the retransmission timer has been turned off. Make sure
476 * that the retransmission timer is set.
478 if (tp->sack_enable && SEQ_GT(tp->snd_max, tp->snd_una) &&
479 !callout_active(tp->tt_rexmt) &&
480 !callout_active(tp->tt_persist)) {
481 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
482 tcp_timer_rexmt, tp);
486 * TCP window updates are not reliable, rather a polling protocol
487 * using ``persist'' packets is used to insure receipt of window
488 * updates. The three ``states'' for the output side are:
489 * idle not doing retransmits or persists
490 * persisting to move a small or zero window
491 * (re)transmitting and thereby not persisting
493 * callout_active(tp->tt_persist)
494 * is true when we are in persist state.
496 * is set when we are called to send a persist packet.
497 * callout_active(tp->tt_rexmt)
498 * is set when we are retransmitting
499 * The output side is idle when both timers are zero.
501 * If send window is too small, there is data to transmit, and no
502 * retransmit or persist is pending, then go to persist state.
503 * If nothing happens soon, send when timer expires:
504 * if window is nonzero, transmit what we can,
505 * otherwise force out a byte.
507 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
508 !callout_active(tp->tt_persist)) {
514 * No reason to send a segment, just return.
517 SOCKBUF_UNLOCK(&so->so_snd);
521 SOCKBUF_LOCK_ASSERT(&so->so_snd);
523 * Before ESTABLISHED, force sending of initial options
524 * unless TCP set not to do any options.
525 * NOTE: we assume that the IP/TCP header plus TCP options
526 * always fit in a single mbuf, leaving room for a maximum
528 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
533 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
536 hdrlen = sizeof (struct tcpiphdr);
537 if (flags & TH_SYN) {
538 tp->snd_nxt = tp->iss;
539 if ((tp->t_flags & TF_NOOPT) == 0) {
542 opt[0] = TCPOPT_MAXSEG;
543 opt[1] = TCPOLEN_MAXSEG;
544 mss = htons((u_short) tcp_mssopt(&tp->t_inpcb->inp_inc));
545 (void)memcpy(opt + 2, &mss, sizeof(mss));
546 optlen = TCPOLEN_MAXSEG;
548 if ((tp->t_flags & TF_REQ_SCALE) &&
549 ((flags & TH_ACK) == 0 ||
550 (tp->t_flags & TF_RCVD_SCALE))) {
551 *((u_int32_t *)(opt + optlen)) = htonl(
553 TCPOPT_WINDOW << 16 |
554 TCPOLEN_WINDOW << 8 |
555 tp->request_r_scale);
562 * Send a timestamp and echo-reply if this is a SYN and our side
563 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
564 * and our peer have sent timestamps in our SYN's.
566 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
567 (flags & TH_RST) == 0 &&
568 ((flags & TH_ACK) == 0 ||
569 (tp->t_flags & TF_RCVD_TSTMP))) {
570 u_int32_t *lp = (u_int32_t *)(opt + optlen);
572 /* Form timestamp option as shown in appendix A of RFC 1323. */
573 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
574 *lp++ = htonl(ticks);
575 *lp = htonl(tp->ts_recent);
576 optlen += TCPOLEN_TSTAMP_APPA;
583 if (tp->t_flags & TF_SIGNATURE) {
587 /* Initialize TCP-MD5 option (RFC2385) */
588 bp = (u_char *)opt + optlen;
589 *bp++ = TCPOPT_SIGNATURE;
590 *bp++ = TCPOLEN_SIGNATURE;
592 for (i = 0; i < TCP_SIGLEN; i++)
594 optlen += TCPOLEN_SIGNATURE;
596 #endif /* TCP_SIGNATURE */
598 if (tp->sack_enable && ((tp->t_flags & TF_NOOPT) == 0)) {
600 * Tack on the SACK permitted option *last*.
601 * And do padding of options after tacking this on.
602 * This is because of MSS, TS, WinScale and Signatures are
603 * all present, we have just 2 bytes left for the SACK
604 * permitted option, which is just enough.
607 * If this is the first SYN of connection (not a SYN
608 * ACK), include SACK permitted option. If this is a
609 * SYN ACK, include SACK permitted option if peer has
610 * already done so. This is only for active connect,
611 * since the syncache takes care of the passive connect.
613 if ((flags & TH_SYN) &&
614 (!(flags & TH_ACK) || (tp->t_flags & TF_SACK_PERMIT))) {
616 bp = (u_char *)opt + optlen;
618 *bp++ = TCPOPT_SACK_PERMITTED;
619 *bp++ = TCPOLEN_SACK_PERMITTED;
620 optlen += TCPOLEN_SACK_PERMITTED;
624 * Send SACKs if necessary. This should be the last
625 * option processed. Only as many SACKs are sent as
626 * are permitted by the maximum options size.
628 * In general, SACK blocks consume 8*n+2 bytes.
629 * So a full size SACK blocks option is 34 bytes
630 * (to generate 4 SACK blocks). At a minimum,
631 * we need 10 bytes (to generate 1 SACK block).
632 * If TCP Timestamps (12 bytes) and TCP Signatures
633 * (18 bytes) are both present, we'll just have
634 * 10 bytes for SACK options 40 - (12 + 18).
636 if (TCPS_HAVEESTABLISHED(tp->t_state) &&
637 (tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks > 0 &&
638 MAX_TCPOPTLEN - optlen - 2 >= TCPOLEN_SACK) {
639 int nsack, sackoptlen, padlen;
640 u_char *bp = (u_char *)opt + optlen;
643 nsack = (MAX_TCPOPTLEN - optlen - 2) / TCPOLEN_SACK;
644 nsack = min(nsack, tp->rcv_numsacks);
645 sackoptlen = (2 + nsack * TCPOLEN_SACK);
648 * First we need to pad options so that the
649 * SACK blocks can start at a 4-byte boundary
650 * (sack option and length are at a 2 byte offset).
652 padlen = (MAX_TCPOPTLEN - optlen - sackoptlen) % 4;
657 tcpstat.tcps_sack_send_blocks++;
660 lp = (u_int32_t *)bp;
661 for (i = 0; i < nsack; i++) {
662 struct sackblk sack = tp->sackblks[i];
663 *lp++ = htonl(sack.start);
664 *lp++ = htonl(sack.end);
666 optlen += sackoptlen;
670 /* Pad TCP options to a 4 byte boundary */
671 if (optlen < MAX_TCPOPTLEN && (optlen % sizeof(u_int32_t))) {
672 int pad = sizeof(u_int32_t) - (optlen % sizeof(u_int32_t));
673 u_char *bp = (u_char *)opt + optlen;
686 ipoptlen = ip6_optlen(tp->t_inpcb);
689 if (tp->t_inpcb->inp_options)
690 ipoptlen = tp->t_inpcb->inp_options->m_len -
691 offsetof(struct ipoption, ipopt_list);
695 ipoptlen += ipsec_hdrsiz_tcp(tp);
699 * Adjust data length if insertion of options will
700 * bump the packet length beyond the t_maxopd length.
701 * Clear the FIN bit because we cut off the tail of
704 if (len + optlen + ipoptlen > tp->t_maxopd) {
706 * If there is still more to send, don't close the connection.
709 len = tp->t_maxopd - optlen - ipoptlen;
713 /*#ifdef DIAGNOSTIC*/
715 if (max_linkhdr + hdrlen > MCLBYTES)
717 if (max_linkhdr + hdrlen > MHLEN)
719 panic("tcphdr too big");
723 * Grab a header mbuf, attaching a copy of data to
724 * be transmitted, and initialize the header from
725 * the template for sends on this connection.
728 if (tp->t_force && len == 1)
729 tcpstat.tcps_sndprobe++;
730 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
731 tcpstat.tcps_sndrexmitpack++;
732 tcpstat.tcps_sndrexmitbyte += len;
734 tcpstat.tcps_sndpack++;
735 tcpstat.tcps_sndbyte += len;
738 if ((m = m_copypack(so->so_snd.sb_mb, off,
739 (int)len, max_linkhdr + hdrlen)) == 0) {
740 SOCKBUF_UNLOCK(&so->so_snd);
745 * m_copypack left space for our hdr; use it.
750 MGETHDR(m, M_DONTWAIT, MT_HEADER);
752 SOCKBUF_UNLOCK(&so->so_snd);
757 if (MHLEN < hdrlen + max_linkhdr) {
758 MCLGET(m, M_DONTWAIT);
759 if ((m->m_flags & M_EXT) == 0) {
760 SOCKBUF_UNLOCK(&so->so_snd);
767 m->m_data += max_linkhdr;
769 if (len <= MHLEN - hdrlen - max_linkhdr) {
770 m_copydata(so->so_snd.sb_mb, off, (int) len,
771 mtod(m, caddr_t) + hdrlen);
774 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
775 if (m->m_next == 0) {
776 SOCKBUF_UNLOCK(&so->so_snd);
784 * If we're sending everything we've got, set PUSH.
785 * (This will keep happy those implementations which only
786 * give data to the user when a buffer fills or
789 if (off + len == so->so_snd.sb_cc)
791 SOCKBUF_UNLOCK(&so->so_snd);
793 SOCKBUF_UNLOCK(&so->so_snd);
794 if (tp->t_flags & TF_ACKNOW)
795 tcpstat.tcps_sndacks++;
796 else if (flags & (TH_SYN|TH_FIN|TH_RST))
797 tcpstat.tcps_sndctrl++;
798 else if (SEQ_GT(tp->snd_up, tp->snd_una))
799 tcpstat.tcps_sndurg++;
801 tcpstat.tcps_sndwinup++;
803 MGETHDR(m, M_DONTWAIT, MT_HEADER);
809 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
814 m->m_data += max_linkhdr;
817 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
818 m->m_pkthdr.rcvif = (struct ifnet *)0;
820 mac_create_mbuf_from_inpcb(tp->t_inpcb, m);
824 ip6 = mtod(m, struct ip6_hdr *);
825 th = (struct tcphdr *)(ip6 + 1);
826 tcpip_fillheaders(tp->t_inpcb, ip6, th);
830 ip = mtod(m, struct ip *);
831 ipov = (struct ipovly *)ip;
832 th = (struct tcphdr *)(ip + 1);
833 tcpip_fillheaders(tp->t_inpcb, ip, th);
837 * Fill in fields, remembering maximum advertised
838 * window for use in delaying messages about window sizes.
839 * If resending a FIN, be sure not to use a new sequence number.
841 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
842 tp->snd_nxt == tp->snd_max)
845 * If we are doing retransmissions, then snd_nxt will
846 * not reflect the first unsent octet. For ACK only
847 * packets, we do not want the sequence number of the
848 * retransmitted packet, we want the sequence number
849 * of the next unsent octet. So, if there is no data
850 * (and no SYN or FIN), use snd_max instead of snd_nxt
851 * when filling in ti_seq. But if we are in persist
852 * state, snd_max might reflect one byte beyond the
853 * right edge of the window, so use snd_nxt in that
854 * case, since we know we aren't doing a retransmission.
855 * (retransmit and persist are mutually exclusive...)
857 if (sack_rxmit == 0) {
858 if (len || (flags & (TH_SYN|TH_FIN))
859 || callout_active(tp->tt_persist))
860 th->th_seq = htonl(tp->snd_nxt);
862 th->th_seq = htonl(tp->snd_max);
864 th->th_seq = htonl(p->rxmit);
867 th->th_ack = htonl(tp->rcv_nxt);
869 bcopy(opt, th + 1, optlen);
870 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
872 th->th_flags = flags;
874 * Calculate receive window. Don't shrink window,
875 * but avoid silly window syndrome.
877 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
878 recwin < (long)tp->t_maxseg)
880 if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
881 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
882 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
883 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
884 th->th_win = htons((u_short) (recwin >> tp->rcv_scale));
888 * Adjust the RXWIN0SENT flag - indicate that we have advertised
889 * a 0 window. This may cause the remote transmitter to stall. This
890 * flag tells soreceive() to disable delayed acknowledgements when
891 * draining the buffer. This can occur if the receiver is attempting
892 * to read more data then can be buffered prior to transmitting on
896 tp->t_flags |= TF_RXWIN0SENT;
898 tp->t_flags &= ~TF_RXWIN0SENT;
899 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
900 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
901 th->th_flags |= TH_URG;
904 * If no urgent pointer to send, then we pull
905 * the urgent pointer to the left edge of the send window
906 * so that it doesn't drift into the send window on sequence
909 tp->snd_up = tp->snd_una; /* drag it along */
915 if (tp->t_flags & TF_SIGNATURE)
916 tcp_signature_compute(m, sizeof(struct ip), len, optlen,
917 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
921 * Put TCP length in extended header, and then
922 * checksum extended header and data.
924 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
928 * ip6_plen is not need to be filled now, and will be filled
931 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
932 sizeof(struct tcphdr) + optlen + len);
936 m->m_pkthdr.csum_flags = CSUM_TCP;
937 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
938 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
939 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
941 /* IP version must be set here for ipv4/ipv6 checking later */
942 KASSERT(ip->ip_v == IPVERSION,
943 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
947 * In transmit state, time the transmission and arrange for
948 * the retransmit. In persist state, just set snd_max.
950 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
951 tcp_seq startseq = tp->snd_nxt;
954 * Advance snd_nxt over sequence space of this segment.
956 if (flags & (TH_SYN|TH_FIN)) {
959 if (flags & TH_FIN) {
961 tp->t_flags |= TF_SENTFIN;
967 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
968 tp->snd_max = tp->snd_nxt;
970 * Time this transmission if not a retransmission and
971 * not currently timing anything.
973 if (tp->t_rtttime == 0) {
974 tp->t_rtttime = ticks;
975 tp->t_rtseq = startseq;
976 tcpstat.tcps_segstimed++;
981 * Set retransmit timer if not currently set,
982 * and not doing a pure ack or a keep-alive probe.
983 * Initial value for retransmit timer is smoothed
984 * round-trip time + 2 * round-trip time variance.
985 * Initialize shift counter which is used for backoff
986 * of retransmit time.
989 if (!callout_active(tp->tt_rexmt) &&
990 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
991 (tp->snd_nxt != tp->snd_una))) {
992 if (callout_active(tp->tt_persist)) {
993 callout_stop(tp->tt_persist);
996 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
997 tcp_timer_rexmt, tp);
1001 * Persist case, update snd_max but since we are in
1002 * persist mode (no window) we do not update snd_nxt.
1007 if (flags & TH_FIN) {
1009 tp->t_flags |= TF_SENTFIN;
1011 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1012 tp->snd_max = tp->snd_nxt + len;
1019 if (so->so_options & SO_DEBUG) {
1025 save = ipov->ih_len;
1026 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1028 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1032 ipov->ih_len = save;
1037 * Fill in IP length and desired time to live and
1038 * send to IP level. There should be a better way
1039 * to handle ttl and tos; we could keep them in
1040 * the template, but need a way to checksum without them.
1043 * m->m_pkthdr.len should have been set before cksum calcuration,
1044 * because in6_cksum() need it.
1049 * we separately set hoplimit for every segment, since the
1050 * user might want to change the value via setsockopt.
1051 * Also, desired default hop limit might be changed via
1052 * Neighbor Discovery.
1054 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1056 /* TODO: IPv6 IP6TOS_ECT bit on */
1057 error = ip6_output(m,
1058 tp->t_inpcb->in6p_outputopts, NULL,
1059 ((so->so_options & SO_DONTROUTE) ?
1060 IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb);
1064 ip->ip_len = m->m_pkthdr.len;
1066 if (INP_CHECK_SOCKAF(so, AF_INET6))
1067 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1070 * If we do path MTU discovery, then we set DF on every packet.
1071 * This might not be the best thing to do according to RFC3390
1072 * Section 2. However the tcp hostcache migitates the problem
1073 * so it affects only the first tcp connection with a host.
1075 if (path_mtu_discovery)
1076 ip->ip_off |= IP_DF;
1078 error = ip_output(m, tp->t_inpcb->inp_options, NULL,
1079 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1085 * We know that the packet was lost, so back out the
1086 * sequence number advance, if any.
1088 if (tp->t_force == 0 || !callout_active(tp->tt_persist)) {
1090 * No need to check for TH_FIN here because
1091 * the TF_SENTFIN flag handles that case.
1093 if ((flags & TH_SYN) == 0) {
1102 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1103 if (error == ENOBUFS) {
1104 if (!callout_active(tp->tt_rexmt) &&
1105 !callout_active(tp->tt_persist))
1106 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
1107 tcp_timer_rexmt, tp);
1108 tp->snd_cwnd = tp->t_maxseg;
1111 if (error == EMSGSIZE) {
1113 * ip_output() will have already fixed the route
1114 * for us. tcp_mtudisc() will, as its last action,
1115 * initiate retransmission, so it is important to
1118 tcp_mtudisc(tp->t_inpcb, 0);
1121 if ((error == EHOSTUNREACH || error == ENETDOWN)
1122 && TCPS_HAVERCVDSYN(tp->t_state)) {
1123 tp->t_softerror = error;
1128 tcpstat.tcps_sndtotal++;
1131 * Data sent (as far as we can tell).
1132 * If this advertises a larger window than any other segment,
1133 * then remember the size of the advertised window.
1134 * Any pending ACK has now been sent.
1136 if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1137 tp->rcv_adv = tp->rcv_nxt + recwin;
1138 tp->last_ack_sent = tp->rcv_nxt;
1139 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1140 if (callout_active(tp->tt_delack))
1141 callout_stop(tp->tt_delack);
1144 * This completely breaks TCP if newreno is turned on. What happens
1145 * is that if delayed-acks are turned on on the receiver, this code
1146 * on the transmitter effectively destroys the TCP window, forcing
1147 * it to four packets (1.5Kx4 = 6K window).
1149 if (sendalot && (!tcp_do_newreno || --maxburst))
1159 register struct tcpcb *tp;
1161 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1164 if (callout_active(tp->tt_rexmt))
1165 panic("tcp_setpersist: retransmit pending");
1167 * Start/restart persistance timer.
1169 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1170 TCPTV_PERSMIN, TCPTV_PERSMAX);
1171 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
1172 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)