2 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
3 * Copyright (c) 2004 The DragonFly Project. All rights reserved.
5 * This code is derived from software contributed to The DragonFly Project
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of The DragonFly Project nor the names of its
17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
24 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
37 * License terms: all terms for the DragonFly license above plus the following:
39 * 4. All advertising materials mentioning features or use of this software
40 * must display the following acknowledgement:
42 * This product includes software developed by Jeffrey M. Hsu
43 * for the DragonFly Project.
45 * This requirement may be waived with permission from Jeffrey Hsu.
46 * This requirement will sunset and may be removed on July 8 2005,
47 * after which the standard DragonFly license (as shown above) will
52 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
53 * The Regents of the University of California. All rights reserved.
55 * Redistribution and use in source and binary forms, with or without
56 * modification, are permitted provided that the following conditions
58 * 1. Redistributions of source code must retain the above copyright
59 * notice, this list of conditions and the following disclaimer.
60 * 2. Redistributions in binary form must reproduce the above copyright
61 * notice, this list of conditions and the following disclaimer in the
62 * documentation and/or other materials provided with the distribution.
63 * 3. All advertising materials mentioning features or use of this software
64 * must display the following acknowledgement:
65 * This product includes software developed by the University of
66 * California, Berkeley and its contributors.
67 * 4. Neither the name of the University nor the names of its contributors
68 * may be used to endorse or promote products derived from this software
69 * without specific prior written permission.
71 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
72 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
73 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
74 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
75 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
76 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
77 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
78 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
79 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
80 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
83 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
84 * $FreeBSD: src/sys/netinet/tcp_output.c,v 1.39.2.20 2003/01/29 22:45:36 hsu Exp $
85 * $DragonFly: src/sys/netinet/tcp_output.c,v 1.18 2004/08/08 06:33:24 hsu Exp $
88 #include "opt_inet6.h"
89 #include "opt_ipsec.h"
90 #include "opt_tcpdebug.h"
92 #include <sys/param.h>
93 #include <sys/systm.h>
94 #include <sys/kernel.h>
95 #include <sys/sysctl.h>
97 #include <sys/domain.h>
98 #include <sys/protosw.h>
99 #include <sys/socket.h>
100 #include <sys/socketvar.h>
101 #include <sys/in_cksum.h>
102 #include <sys/thread.h>
103 #include <sys/globaldata.h>
105 #include <net/route.h>
107 #include <netinet/in.h>
108 #include <netinet/in_systm.h>
109 #include <netinet/ip.h>
110 #include <netinet/in_pcb.h>
111 #include <netinet/ip_var.h>
112 #include <netinet6/in6_pcb.h>
113 #include <netinet/ip6.h>
114 #include <netinet6/ip6_var.h>
115 #include <netinet/tcp.h>
117 #include <netinet/tcp_fsm.h>
118 #include <netinet/tcp_seq.h>
119 #include <netinet/tcp_timer.h>
120 #include <netinet/tcp_var.h>
121 #include <netinet/tcpip.h>
123 #include <netinet/tcp_debug.h>
127 #include <netinet6/ipsec.h>
131 #include <netipsec/ipsec.h>
133 #endif /*FAST_IPSEC*/
136 extern struct mbuf *m_copypack();
139 int path_mtu_discovery = 1;
140 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
141 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
144 SYSCTL_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
145 &ss_fltsz, 1, "Slow start flight size");
147 int ss_fltsz_local = 4;
148 SYSCTL_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize, CTLFLAG_RW,
149 &ss_fltsz_local, 1, "Slow start flight size for local networks");
151 static int avoid_pure_win_update = 1;
152 SYSCTL_INT(_net_inet_tcp, OID_AUTO, avoid_pure_win_update, CTLFLAG_RW,
153 &avoid_pure_win_update, 1, "Avoid pure window updates when possible");
156 * Tcp output routine: figure out what should be sent and send it.
162 struct inpcb * const inp = tp->t_inpcb;
163 struct socket *so = inp->inp_socket;
164 long len, recvwin, sendwin;
165 int off, flags, error;
167 struct ip *ip = NULL;
168 struct ipovly *ipov = NULL;
170 u_char opt[TCP_MAXOLEN];
171 unsigned ipoptlen, optlen, hdrlen;
174 struct ip6_hdr *ip6 = NULL;
176 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
178 const boolean_t isipv6 = FALSE;
180 struct rmxp_tao *taop;
183 * Determine length of data that should be transmitted,
184 * and flags that will be used.
185 * If there is some data or critical controls (SYN, RST)
186 * to send, then transmit; otherwise, investigate further.
188 if ((tp->snd_max == tp->snd_una) &&
189 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
191 * We have been idle for "a while" and no acks are
192 * expected to clock out any data we send --
193 * slow start to get ack "clock" running again.
195 * Set the slow-start flight size depending on whether
196 * this is a local network or not.
198 if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
199 (!isipv6 && in_localaddr(inp->inp_faddr)))
200 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
202 tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
204 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
205 if (idle && (tp->t_flags & TF_MORETOCOME))
206 tp->t_flags |= TF_LASTIDLE;
208 tp->t_flags &= ~TF_LASTIDLE;
212 off = tp->snd_nxt - tp->snd_una;
213 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
214 sendwin = min(sendwin, tp->snd_bwnd);
216 flags = tcp_outflags[tp->t_state];
218 * Get standard flags, and add SYN or FIN if requested by 'hidden'
221 if (tp->t_flags & TF_NEEDFIN)
223 if (tp->t_flags & TF_NEEDSYN)
227 * If in persist timeout with window of 0, send 1 byte.
228 * Otherwise, if window is small but nonzero
229 * and timer expired, we will send what we can
230 * and go to transmit state.
232 if (tp->t_flags & TF_FORCE) {
235 * If we still have some data to send, then
236 * clear the FIN bit. Usually this would
237 * happen below when it realizes that we
238 * aren't sending all the data. However,
239 * if we have exactly 1 byte of unsent data,
240 * then it won't clear the FIN bit below,
241 * and if we are in persist state, we wind
242 * up sending the packet without recording
243 * that we sent the FIN bit.
245 * We can't just blindly clear the FIN bit,
246 * because if we don't have any more data
247 * to send then the probe will be the FIN
250 if (off < so->so_snd.sb_cc)
254 callout_stop(tp->tt_persist);
260 * If snd_nxt == snd_max and we have transmitted a FIN, the
261 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
262 * a negative length. This can also occur when TCP opens up
263 * its congestion window while receiving additional duplicate
264 * acks after fast-retransmit because TCP will reset snd_nxt
265 * to snd_max after the fast-retransmit.
267 * In the normal retransmit-FIN-only case, however, snd_nxt will
268 * be set to snd_una, the offset will be 0, and the length may
271 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
274 * Lop off SYN bit if it has already been sent. However, if this
275 * is SYN-SENT state and if segment contains data and if we don't
276 * know that foreign host supports TAO, suppress sending segment.
278 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
281 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
282 ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL ||
283 taop->tao_ccsent == 0))
288 * Be careful not to send data and/or FIN on SYN segments
289 * in cases when no CC option will be sent.
290 * This measure is needed to prevent interoperability problems
291 * with not fully conformant TCP implementations.
293 if ((flags & TH_SYN) &&
294 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
295 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
302 * If FIN has been sent but not acked,
303 * but we haven't been called to retransmit,
304 * len will be < 0. Otherwise, window shrank
305 * after we sent into it. If window shrank to 0,
306 * cancel pending retransmit, pull snd_nxt back
307 * to (closed) window, and set the persist timer
308 * if it isn't already going. If the window didn't
309 * close completely, just wait for an ACK.
313 callout_stop(tp->tt_rexmt);
315 tp->snd_nxt = tp->snd_una;
316 if (!callout_active(tp->tt_persist))
322 * len will be >= 0 after this point. Truncate to the maximum
323 * segment length and ensure that FIN is removed if the length
324 * no longer contains the last data byte.
326 if (len > tp->t_maxseg) {
330 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
333 recvwin = sbspace(&so->so_rcv);
336 * Sender silly window avoidance. We transmit under the following
337 * conditions when len is non-zero:
339 * - We have a full segment
340 * - This is the last buffer in a write()/send() and we are
341 * either idle or running NODELAY
342 * - we've timed out (e.g. persist timer)
343 * - we have more then 1/2 the maximum send window's worth of
344 * data (receiver may be limited the window size)
345 * - we need to retransmit
348 if (len == tp->t_maxseg)
351 * NOTE! on localhost connections an 'ack' from the remote
352 * end may occur synchronously with the output and cause
353 * us to flush a buffer queued with moretocome. XXX
355 * note: the len + off check is almost certainly unnecessary.
357 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
358 (idle || (tp->t_flags & TF_NODELAY)) &&
359 len + off >= so->so_snd.sb_cc &&
360 !(tp->t_flags & TF_NOPUSH)) {
363 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
365 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
367 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
372 * Compare available window to amount of window
373 * known to peer (as advertised window less
374 * next expected input). If the difference is at least two
375 * max size segments, or at least 50% of the maximum possible
376 * window, then want to send a window update to peer.
380 * "adv" is the amount we can increase the window,
381 * taking into account that we are limited by
382 * TCP_MAXWIN << tp->rcv_scale.
384 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
385 (tp->rcv_adv - tp->rcv_nxt);
388 * This ack case typically occurs when the user has drained
389 * the TCP socket buffer sufficiently to warrent an ack
390 * containing a 'pure window update'... that is, an ack that
391 * ONLY updates the tcp window.
393 * It is unclear why we would need to do a pure window update
394 * past 2 segments if we are going to do one at 1/2 the high
395 * water mark anyway, especially since under normal conditions
396 * the user program will drain the socket buffer quickly.
397 * The 2-segment pure window update will often add a large
398 * number of extra, unnecessary acks to the stream.
400 * avoid_pure_win_update now defaults to 1.
402 if (avoid_pure_win_update == 0) {
403 if (adv >= (long) (2 * tp->t_maxseg))
406 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
411 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
412 * is also a catch-all for the retransmit timer timeout case.
414 if (tp->t_flags & TF_ACKNOW)
416 if ((flags & TH_RST) ||
417 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
419 if (SEQ_GT(tp->snd_up, tp->snd_una))
422 * If our state indicates that FIN should be sent
423 * and we have not yet done so, then we need to send.
425 if (flags & TH_FIN &&
426 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
430 * TCP window updates are not reliable, rather a polling protocol
431 * using ``persist'' packets is used to insure receipt of window
432 * updates. The three ``states'' for the output side are:
433 * idle not doing retransmits or persists
434 * persisting to move a small or zero window
435 * (re)transmitting and thereby not persisting
437 * callout_active(tp->tt_persist)
438 * is true when we are in persist state.
439 * The TF_FORCE flag in tp->t_flags
440 * is set when we are called to send a persist packet.
441 * callout_active(tp->tt_rexmt)
442 * is set when we are retransmitting
443 * The output side is idle when both timers are zero.
445 * If send window is too small, there is data to transmit, and no
446 * retransmit or persist is pending, then go to persist state.
447 * If nothing happens soon, send when timer expires:
448 * if window is nonzero, transmit what we can,
449 * otherwise force out a byte.
451 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
452 !callout_active(tp->tt_persist)) {
458 * No reason to send a segment, just return.
464 * Before ESTABLISHED, force sending of initial options
465 * unless TCP set not to do any options.
466 * NOTE: we assume that the IP/TCP header plus TCP options
467 * always fit in a single mbuf, leaving room for a maximum
469 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
473 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
475 hdrlen = sizeof(struct tcpiphdr);
476 if (flags & TH_SYN) {
477 tp->snd_nxt = tp->iss;
478 if (!(tp->t_flags & TF_NOOPT)) {
481 opt[0] = TCPOPT_MAXSEG;
482 opt[1] = TCPOLEN_MAXSEG;
483 mss = htons((u_short) tcp_mssopt(tp));
484 (void)memcpy(opt + 2, &mss, sizeof(mss));
485 optlen = TCPOLEN_MAXSEG;
487 if ((tp->t_flags & TF_REQ_SCALE) &&
488 (!(flags & TH_ACK) ||
489 (tp->t_flags & TF_RCVD_SCALE))) {
490 *((u_int32_t *)(opt + optlen)) = htonl(
492 TCPOPT_WINDOW << 16 |
493 TCPOLEN_WINDOW << 8 |
494 tp->request_r_scale);
501 * Send a timestamp and echo-reply if this is a SYN and our side
502 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
503 * and our peer have sent timestamps in our SYN's.
505 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
507 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
508 u_int32_t *lp = (u_int32_t *)(opt + optlen);
510 /* Form timestamp option as shown in appendix A of RFC 1323. */
511 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
512 *lp++ = htonl(ticks);
513 *lp = htonl(tp->ts_recent);
514 optlen += TCPOLEN_TSTAMP_APPA;
518 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
519 * options are allowed (!TF_NOOPT) and it's not a RST.
521 if ((tp->t_flags & (TF_REQ_CC | TF_NOOPT)) == TF_REQ_CC &&
523 switch (flags & (TH_SYN | TH_ACK)) {
525 * This is a normal ACK, send CC if we received CC before
529 if (!(tp->t_flags & TF_RCVD_CC))
534 * We can only get here in T/TCP's SYN_SENT* state, when
535 * we're a sending a non-SYN segment without waiting for
536 * the ACK of our SYN. A check above assures that we only
537 * do this if our peer understands T/TCP.
540 opt[optlen++] = TCPOPT_NOP;
541 opt[optlen++] = TCPOPT_NOP;
542 opt[optlen++] = TCPOPT_CC;
543 opt[optlen++] = TCPOLEN_CC;
544 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
549 * This is our initial SYN, check whether we have to use
553 opt[optlen++] = TCPOPT_NOP;
554 opt[optlen++] = TCPOPT_NOP;
555 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
556 TCPOPT_CCNEW : TCPOPT_CC;
557 opt[optlen++] = TCPOLEN_CC;
558 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
563 * This is a SYN,ACK; send CC and CC.echo if we received
566 case (TH_SYN | TH_ACK):
567 if (tp->t_flags & TF_RCVD_CC) {
568 opt[optlen++] = TCPOPT_NOP;
569 opt[optlen++] = TCPOPT_NOP;
570 opt[optlen++] = TCPOPT_CC;
571 opt[optlen++] = TCPOLEN_CC;
572 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
574 opt[optlen++] = TCPOPT_NOP;
575 opt[optlen++] = TCPOPT_NOP;
576 opt[optlen++] = TCPOPT_CCECHO;
577 opt[optlen++] = TCPOLEN_CC;
578 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_recv);
588 ipoptlen = ip6_optlen(inp);
590 if (inp->inp_options) {
591 ipoptlen = inp->inp_options->m_len -
592 offsetof(struct ipoption, ipopt_list);
598 ipoptlen += ipsec_hdrsiz_tcp(tp);
602 * Adjust data length if insertion of options will
603 * bump the packet length beyond the t_maxopd length.
604 * Clear the FIN bit because we cut off the tail of
607 if (len + optlen + ipoptlen > tp->t_maxopd) {
609 * If there is still more to send, don't close the connection.
612 len = tp->t_maxopd - optlen - ipoptlen;
617 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
619 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
623 * Grab a header mbuf, attaching a copy of data to
624 * be transmitted, and initialize the header from
625 * the template for sends on this connection.
628 if ((tp->t_flags & TF_FORCE) && len == 1)
629 tcpstat.tcps_sndprobe++;
630 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
631 tcpstat.tcps_sndrexmitpack++;
632 tcpstat.tcps_sndrexmitbyte += len;
634 tcpstat.tcps_sndpack++;
635 tcpstat.tcps_sndbyte += len;
638 if ((m = m_copypack(so->so_snd.sb_mb, off, (int)len,
639 max_linkhdr + hdrlen)) == NULL) {
644 * m_copypack left space for our hdr; use it.
649 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
655 if (MHLEN < hdrlen + max_linkhdr) {
656 MCLGET(m, MB_DONTWAIT);
657 if (!(m->m_flags & M_EXT)) {
664 m->m_data += max_linkhdr;
666 if (len <= MHLEN - hdrlen - max_linkhdr) {
667 m_copydata(so->so_snd.sb_mb, off, (int) len,
668 mtod(m, caddr_t) + hdrlen);
671 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
672 if (m->m_next == NULL) {
680 * If we're sending everything we've got, set PUSH.
681 * (This will keep happy those implementations which only
682 * give data to the user when a buffer fills or
685 if (off + len == so->so_snd.sb_cc)
688 if (tp->t_flags & TF_ACKNOW)
689 tcpstat.tcps_sndacks++;
690 else if (flags & (TH_SYN | TH_FIN | TH_RST))
691 tcpstat.tcps_sndctrl++;
692 else if (SEQ_GT(tp->snd_up, tp->snd_una))
693 tcpstat.tcps_sndurg++;
695 tcpstat.tcps_sndwinup++;
697 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
703 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
706 m->m_data += max_linkhdr;
709 m->m_pkthdr.rcvif = (struct ifnet *)0;
711 ip6 = mtod(m, struct ip6_hdr *);
712 th = (struct tcphdr *)(ip6 + 1);
713 tcp_fillheaders(tp, ip6, th);
715 ip = mtod(m, struct ip *);
716 ipov = (struct ipovly *)ip;
717 th = (struct tcphdr *)(ip + 1);
718 /* this picks up the pseudo header (w/o the length) */
719 tcp_fillheaders(tp, ip, th);
723 * Fill in fields, remembering maximum advertised
724 * window for use in delaying messages about window sizes.
725 * If resending a FIN, be sure not to use a new sequence number.
727 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
728 tp->snd_nxt == tp->snd_max)
731 * If we are doing retransmissions, then snd_nxt will
732 * not reflect the first unsent octet. For ACK only
733 * packets, we do not want the sequence number of the
734 * retransmitted packet, we want the sequence number
735 * of the next unsent octet. So, if there is no data
736 * (and no SYN or FIN), use snd_max instead of snd_nxt
737 * when filling in ti_seq. But if we are in persist
738 * state, snd_max might reflect one byte beyond the
739 * right edge of the window, so use snd_nxt in that
740 * case, since we know we aren't doing a retransmission.
741 * (retransmit and persist are mutually exclusive...)
743 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
744 th->th_seq = htonl(tp->snd_nxt);
746 th->th_seq = htonl(tp->snd_max);
747 th->th_ack = htonl(tp->rcv_nxt);
749 bcopy(opt, th + 1, optlen);
750 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
752 th->th_flags = flags;
754 * Calculate receive window. Don't shrink window,
755 * but avoid silly window syndrome.
757 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
758 recvwin < (long)tp->t_maxseg)
760 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
761 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
762 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
763 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
764 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
767 * Adjust the RXWIN0SENT flag - indicate that we have advertised
768 * a 0 window. This may cause the remote transmitter to stall. This
769 * flag tells soreceive() to disable delayed acknowledgements when
770 * draining the buffer. This can occur if the receiver is attempting
771 * to read more data then can be buffered prior to transmitting on
775 tp->t_flags |= TF_RXWIN0SENT;
777 tp->t_flags &= ~TF_RXWIN0SENT;
779 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
780 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
781 th->th_flags |= TH_URG;
784 * If no urgent pointer to send, then we pull
785 * the urgent pointer to the left edge of the send window
786 * so that it doesn't drift into the send window on sequence
789 tp->snd_up = tp->snd_una; /* drag it along */
793 * Put TCP length in extended header, and then
794 * checksum extended header and data.
796 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
799 * ip6_plen is not need to be filled now, and will be filled
802 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
803 sizeof(struct tcphdr) + optlen + len);
805 m->m_pkthdr.csum_flags = CSUM_TCP;
806 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
808 th->th_sum = in_addword(th->th_sum,
809 htons((u_short)(optlen + len)));
811 /* IP version must be set here for ipv4/ipv6 checking later */
812 KASSERT(ip->ip_v == IPVERSION,
813 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
817 * In transmit state, time the transmission and arrange for
818 * the retransmit. In persist state, just set snd_max.
820 if (!(tp->t_flags & TF_FORCE) || !callout_active(tp->tt_persist)) {
821 tcp_seq startseq = tp->snd_nxt;
824 * Advance snd_nxt over sequence space of this segment.
826 if (flags & (TH_SYN | TH_FIN)) {
829 if (flags & TH_FIN) {
831 tp->t_flags |= TF_SENTFIN;
835 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
836 tp->snd_max = tp->snd_nxt;
838 * Time this transmission if not a retransmission and
839 * not currently timing anything.
841 if (tp->t_rtttime == 0) {
842 tp->t_rtttime = ticks;
843 tp->t_rtseq = startseq;
844 tcpstat.tcps_segstimed++;
849 * Set retransmit timer if not currently set,
850 * and not doing a pure ack or a keep-alive probe.
851 * Initial value for retransmit timer is smoothed
852 * round-trip time + 2 * round-trip time variance.
853 * Initialize shift counter which is used for backoff
854 * of retransmit time.
856 if (!callout_active(tp->tt_rexmt) &&
857 tp->snd_nxt != tp->snd_una) {
858 if (callout_active(tp->tt_persist)) {
859 callout_stop(tp->tt_persist);
862 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
863 tcp_timer_rexmt, tp);
867 * Persist case, update snd_max but since we are in
868 * persist mode (no window) we do not update snd_nxt.
873 if (flags & TH_FIN) {
875 tp->t_flags |= TF_SENTFIN;
877 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
878 tp->snd_max = tp->snd_nxt + xlen;
885 if (so->so_options & SO_DEBUG)
886 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
890 * Fill in IP length and desired time to live and
891 * send to IP level. There should be a better way
892 * to handle ttl and tos; we could keep them in
893 * the template, but need a way to checksum without them.
896 * m->m_pkthdr.len should have been set before cksum calcuration,
897 * because in6_cksum() need it.
901 * we separately set hoplimit for every segment, since the
902 * user might want to change the value via setsockopt.
903 * Also, desired default hop limit might be changed via
904 * Neighbor Discovery.
906 ip6->ip6_hlim = in6_selecthlim(inp,
907 (inp->in6p_route.ro_rt ?
908 inp->in6p_route.ro_rt->rt_ifp : NULL));
910 /* TODO: IPv6 IP6TOS_ECT bit on */
911 error = ip6_output(m, inp->in6p_outputopts, &inp->in6p_route,
912 (so->so_options & SO_DONTROUTE), NULL, NULL, inp);
915 ip->ip_len = m->m_pkthdr.len;
917 if (INP_CHECK_SOCKAF(so, AF_INET6))
918 ip->ip_ttl = in6_selecthlim(inp,
919 (inp->in6p_route.ro_rt ?
920 inp->in6p_route.ro_rt->rt_ifp : NULL));
923 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
925 ip->ip_tos = inp->inp_ip_tos; /* XXX */
927 * See if we should do MTU discovery.
928 * We do it only if the following are true:
929 * 1) we have a valid route to the destination
930 * 2) the MTU is not locked (if it is,
931 * then discovery has been disabled)
933 if (path_mtu_discovery &&
934 (rt = inp->inp_route.ro_rt) && (rt->rt_flags & RTF_UP) &&
935 !(rt->rt_rmx.rmx_locks & RTV_MTU))
938 error = ip_output(m, inp->inp_options, &inp->inp_route,
939 (so->so_options & SO_DONTROUTE), NULL, inp);
944 * We know that the packet was lost, so back out the
945 * sequence number advance, if any.
947 if (!(tp->t_flags & TF_FORCE) ||
948 !callout_active(tp->tt_persist)) {
950 * No need to check for TH_FIN here because
951 * the TF_SENTFIN flag handles that case.
953 if (!(flags & TH_SYN))
958 if (error == ENOBUFS) {
960 * If we can't send, make sure there is something
961 * to get us going again later. Persist state
962 * is not necessarily right, but it is close enough.
964 if (!callout_active(tp->tt_rexmt) &&
965 !callout_active(tp->tt_persist)) {
972 if (error == EMSGSIZE) {
974 * ip_output() will have already fixed the route
975 * for us. tcp_mtudisc() will, as its last action,
976 * initiate retransmission, so it is important to
982 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
983 TCPS_HAVERCVDSYN(tp->t_state)) {
984 tp->t_softerror = error;
989 tcpstat.tcps_sndtotal++;
992 * Data sent (as far as we can tell).
993 * If this advertises a larger window than any other segment,
994 * then remember the size of the advertised window.
995 * Any pending ACK has now been sent.
997 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
998 tp->rcv_adv = tp->rcv_nxt + recvwin;
999 tp->last_ack_sent = tp->rcv_nxt;
1000 tp->t_flags &= ~TF_ACKNOW;
1001 if (tcp_delack_enabled)
1002 callout_stop(tp->tt_delack);
1012 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1015 if (callout_active(tp->tt_rexmt))
1016 panic("tcp_setpersist: retransmit pending");
1018 * Start/restart persistance timer.
1020 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1021 TCPTV_PERSMIN, TCPTV_PERSMAX);
1022 callout_reset(tp->tt_persist, tt, tcp_timer_persist, tp);
1023 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)