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 1.16 2004/07/17 20:31:31 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");
152 * Tcp output routine: figure out what should be sent and send it.
158 struct inpcb * const inp = tp->t_inpcb;
159 struct socket *so = inp->inp_socket;
160 long len, recvwin, sendwin;
161 int off, flags, error;
163 struct ip *ip = NULL;
164 struct ipovly *ipov = NULL;
166 u_char opt[TCP_MAXOLEN];
167 unsigned ipoptlen, optlen, hdrlen;
169 struct ip6_hdr *ip6 = NULL;
171 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
173 const boolean_t isipv6 = FALSE;
175 struct rmxp_tao *taop;
178 * Determine length of data that should be transmitted,
179 * and flags that will be used.
180 * If there is some data or critical controls (SYN, RST)
181 * to send, then transmit; otherwise, investigate further.
183 if ((tp->snd_max == tp->snd_una) &&
184 (ticks - tp->t_rcvtime) >= tp->t_rxtcur) {
186 * We have been idle for "a while" and no acks are
187 * expected to clock out any data we send --
188 * slow start to get ack "clock" running again.
190 * Set the slow-start flight size depending on whether
191 * this is a local network or not.
193 if ((isipv6 && in6_localaddr(&inp->in6p_faddr)) ||
194 (!isipv6 && in_localaddr(inp->inp_faddr)))
195 tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
197 tp->snd_cwnd = tp->t_maxseg * ss_fltsz;
199 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
200 if (idle && (tp->t_flags & TF_MORETOCOME))
201 tp->t_flags |= TF_LASTIDLE;
203 tp->t_flags &= ~TF_LASTIDLE;
207 off = tp->snd_nxt - tp->snd_una;
208 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
209 sendwin = min(sendwin, tp->snd_bwnd);
211 flags = tcp_outflags[tp->t_state];
213 * Get standard flags, and add SYN or FIN if requested by 'hidden'
216 if (tp->t_flags & TF_NEEDFIN)
218 if (tp->t_flags & TF_NEEDSYN)
222 * If in persist timeout with window of 0, send 1 byte.
223 * Otherwise, if window is small but nonzero
224 * and timer expired, we will send what we can
225 * and go to transmit state.
227 if (tp->t_flags & TF_FORCE) {
230 * If we still have some data to send, then
231 * clear the FIN bit. Usually this would
232 * happen below when it realizes that we
233 * aren't sending all the data. However,
234 * if we have exactly 1 byte of unsent data,
235 * then it won't clear the FIN bit below,
236 * and if we are in persist state, we wind
237 * up sending the packet without recording
238 * that we sent the FIN bit.
240 * We can't just blindly clear the FIN bit,
241 * because if we don't have any more data
242 * to send then the probe will be the FIN
245 if (off < so->so_snd.sb_cc)
249 callout_stop(tp->tt_persist);
255 * If snd_nxt == snd_max and we have transmitted a FIN, the
256 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
257 * a negative length. This can also occur when TCP opens up
258 * its congestion window while receiving additional duplicate
259 * acks after fast-retransmit because TCP will reset snd_nxt
260 * to snd_max after the fast-retransmit.
262 * In the normal retransmit-FIN-only case, however, snd_nxt will
263 * be set to snd_una, the offset will be 0, and the length may
266 len = (long)ulmin(so->so_snd.sb_cc, sendwin) - off;
269 * Lop off SYN bit if it has already been sent. However, if this
270 * is SYN-SENT state and if segment contains data and if we don't
271 * know that foreign host supports TAO, suppress sending segment.
273 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
276 if (len > 0 && tp->t_state == TCPS_SYN_SENT &&
277 ((taop = tcp_gettaocache(&inp->inp_inc)) == NULL ||
278 taop->tao_ccsent == 0))
283 * Be careful not to send data and/or FIN on SYN segments
284 * in cases when no CC option will be sent.
285 * This measure is needed to prevent interoperability problems
286 * with not fully conformant TCP implementations.
288 if ((flags & TH_SYN) &&
289 ((tp->t_flags & TF_NOOPT) || !(tp->t_flags & TF_REQ_CC) ||
290 ((flags & TH_ACK) && !(tp->t_flags & TF_RCVD_CC)))) {
297 * If FIN has been sent but not acked,
298 * but we haven't been called to retransmit,
299 * len will be < 0. Otherwise, window shrank
300 * after we sent into it. If window shrank to 0,
301 * cancel pending retransmit, pull snd_nxt back
302 * to (closed) window, and set the persist timer
303 * if it isn't already going. If the window didn't
304 * close completely, just wait for an ACK.
308 callout_stop(tp->tt_rexmt);
310 tp->snd_nxt = tp->snd_una;
311 if (!callout_active(tp->tt_persist))
317 * len will be >= 0 after this point. Truncate to the maximum
318 * segment length and ensure that FIN is removed if the length
319 * no longer contains the last data byte.
321 if (len > tp->t_maxseg) {
325 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
328 recvwin = sbspace(&so->so_rcv);
331 * Sender silly window avoidance. We transmit under the following
332 * conditions when len is non-zero:
334 * - We have a full segment
335 * - This is the last buffer in a write()/send() and we are
336 * either idle or running NODELAY
337 * - we've timed out (e.g. persist timer)
338 * - we have more then 1/2 the maximum send window's worth of
339 * data (receiver may be limited the window size)
340 * - we need to retransmit
343 if (len == tp->t_maxseg)
346 * NOTE! on localhost connections an 'ack' from the remote
347 * end may occur synchronously with the output and cause
348 * us to flush a buffer queued with moretocome. XXX
350 * note: the len + off check is almost certainly unnecessary.
352 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
353 (idle || (tp->t_flags & TF_NODELAY)) &&
354 len + off >= so->so_snd.sb_cc &&
355 !(tp->t_flags & TF_NOPUSH)) {
358 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
360 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
362 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
367 * Compare available window to amount of window
368 * known to peer (as advertised window less
369 * next expected input). If the difference is at least two
370 * max size segments, or at least 50% of the maximum possible
371 * window, then want to send a window update to peer.
375 * "adv" is the amount we can increase the window,
376 * taking into account that we are limited by
377 * TCP_MAXWIN << tp->rcv_scale.
379 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
380 (tp->rcv_adv - tp->rcv_nxt);
382 if (adv >= (long) (2 * tp->t_maxseg))
384 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
389 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
390 * is also a catch-all for the retransmit timer timeout case.
392 if (tp->t_flags & TF_ACKNOW)
394 if ((flags & TH_RST) ||
395 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
397 if (SEQ_GT(tp->snd_up, tp->snd_una))
400 * If our state indicates that FIN should be sent
401 * and we have not yet done so, then we need to send.
403 if (flags & TH_FIN &&
404 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
408 * TCP window updates are not reliable, rather a polling protocol
409 * using ``persist'' packets is used to insure receipt of window
410 * updates. The three ``states'' for the output side are:
411 * idle not doing retransmits or persists
412 * persisting to move a small or zero window
413 * (re)transmitting and thereby not persisting
415 * callout_active(tp->tt_persist)
416 * is true when we are in persist state.
417 * The TF_FORCE flag in tp->t_flags
418 * is set when we are called to send a persist packet.
419 * callout_active(tp->tt_rexmt)
420 * is set when we are retransmitting
421 * The output side is idle when both timers are zero.
423 * If send window is too small, there is data to transmit, and no
424 * retransmit or persist is pending, then go to persist state.
425 * If nothing happens soon, send when timer expires:
426 * if window is nonzero, transmit what we can,
427 * otherwise force out a byte.
429 if (so->so_snd.sb_cc && !callout_active(tp->tt_rexmt) &&
430 !callout_active(tp->tt_persist)) {
436 * No reason to send a segment, just return.
442 * Before ESTABLISHED, force sending of initial options
443 * unless TCP set not to do any options.
444 * NOTE: we assume that the IP/TCP header plus TCP options
445 * always fit in a single mbuf, leaving room for a maximum
447 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
451 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
453 hdrlen = sizeof(struct tcpiphdr);
454 if (flags & TH_SYN) {
455 tp->snd_nxt = tp->iss;
456 if (!(tp->t_flags & TF_NOOPT)) {
459 opt[0] = TCPOPT_MAXSEG;
460 opt[1] = TCPOLEN_MAXSEG;
461 mss = htons((u_short) tcp_mssopt(tp));
462 (void)memcpy(opt + 2, &mss, sizeof(mss));
463 optlen = TCPOLEN_MAXSEG;
465 if ((tp->t_flags & TF_REQ_SCALE) &&
466 (!(flags & TH_ACK) ||
467 (tp->t_flags & TF_RCVD_SCALE))) {
468 *((u_int32_t *)(opt + optlen)) = htonl(
470 TCPOPT_WINDOW << 16 |
471 TCPOLEN_WINDOW << 8 |
472 tp->request_r_scale);
479 * Send a timestamp and echo-reply if this is a SYN and our side
480 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
481 * and our peer have sent timestamps in our SYN's.
483 if ((tp->t_flags & (TF_REQ_TSTMP|TF_NOOPT)) == TF_REQ_TSTMP &&
485 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
486 u_int32_t *lp = (u_int32_t *)(opt + optlen);
488 /* Form timestamp option as shown in appendix A of RFC 1323. */
489 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
490 *lp++ = htonl(ticks);
491 *lp = htonl(tp->ts_recent);
492 optlen += TCPOLEN_TSTAMP_APPA;
496 * Send `CC-family' options if our side wants to use them (TF_REQ_CC),
497 * options are allowed (!TF_NOOPT) and it's not a RST.
499 if ((tp->t_flags & (TF_REQ_CC|TF_NOOPT)) == TF_REQ_CC &&
501 switch (flags & (TH_SYN|TH_ACK)) {
503 * This is a normal ACK, send CC if we received CC before
507 if (!(tp->t_flags & TF_RCVD_CC))
512 * We can only get here in T/TCP's SYN_SENT* state, when
513 * we're a sending a non-SYN segment without waiting for
514 * the ACK of our SYN. A check above assures that we only
515 * do this if our peer understands T/TCP.
518 opt[optlen++] = TCPOPT_NOP;
519 opt[optlen++] = TCPOPT_NOP;
520 opt[optlen++] = TCPOPT_CC;
521 opt[optlen++] = TCPOLEN_CC;
522 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
528 * This is our initial SYN, check whether we have to use
532 opt[optlen++] = TCPOPT_NOP;
533 opt[optlen++] = TCPOPT_NOP;
534 opt[optlen++] = tp->t_flags & TF_SENDCCNEW ?
535 TCPOPT_CCNEW : TCPOPT_CC;
536 opt[optlen++] = TCPOLEN_CC;
537 *(u_int32_t *)&opt[optlen] = htonl(tp->cc_send);
542 * This is a SYN,ACK; send CC and CC.echo if we received
545 case (TH_SYN|TH_ACK):
546 if (tp->t_flags & TF_RCVD_CC) {
547 opt[optlen++] = TCPOPT_NOP;
548 opt[optlen++] = TCPOPT_NOP;
549 opt[optlen++] = TCPOPT_CC;
550 opt[optlen++] = TCPOLEN_CC;
551 *(u_int32_t *)&opt[optlen] =
554 opt[optlen++] = TCPOPT_NOP;
555 opt[optlen++] = TCPOPT_NOP;
556 opt[optlen++] = TCPOPT_CCECHO;
557 opt[optlen++] = TCPOLEN_CC;
558 *(u_int32_t *)&opt[optlen] =
569 ipoptlen = ip6_optlen(inp);
571 if (inp->inp_options) {
572 ipoptlen = inp->inp_options->m_len -
573 offsetof(struct ipoption, ipopt_list);
579 ipoptlen += ipsec_hdrsiz_tcp(tp);
583 * Adjust data length if insertion of options will
584 * bump the packet length beyond the t_maxopd length.
585 * Clear the FIN bit because we cut off the tail of
588 if (len + optlen + ipoptlen > tp->t_maxopd) {
590 * If there is still more to send, don't close the connection.
593 len = tp->t_maxopd - optlen - ipoptlen;
598 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
600 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
604 * Grab a header mbuf, attaching a copy of data to
605 * be transmitted, and initialize the header from
606 * the template for sends on this connection.
609 if ((tp->t_flags & TF_FORCE) && len == 1)
610 tcpstat.tcps_sndprobe++;
611 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
612 tcpstat.tcps_sndrexmitpack++;
613 tcpstat.tcps_sndrexmitbyte += len;
615 tcpstat.tcps_sndpack++;
616 tcpstat.tcps_sndbyte += len;
619 if ((m = m_copypack(so->so_snd.sb_mb, off,
620 (int)len, max_linkhdr + hdrlen)) == 0) {
625 * m_copypack left space for our hdr; use it.
630 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
636 if (MHLEN < hdrlen + max_linkhdr) {
637 MCLGET(m, MB_DONTWAIT);
638 if (!(m->m_flags & M_EXT)) {
645 m->m_data += max_linkhdr;
647 if (len <= MHLEN - hdrlen - max_linkhdr) {
648 m_copydata(so->so_snd.sb_mb, off, (int) len,
649 mtod(m, caddr_t) + hdrlen);
652 m->m_next = m_copy(so->so_snd.sb_mb, off, (int) len);
653 if (m->m_next == 0) {
661 * If we're sending everything we've got, set PUSH.
662 * (This will keep happy those implementations which only
663 * give data to the user when a buffer fills or
666 if (off + len == so->so_snd.sb_cc)
669 if (tp->t_flags & TF_ACKNOW)
670 tcpstat.tcps_sndacks++;
671 else if (flags & (TH_SYN|TH_FIN|TH_RST))
672 tcpstat.tcps_sndctrl++;
673 else if (SEQ_GT(tp->snd_up, tp->snd_una))
674 tcpstat.tcps_sndurg++;
676 tcpstat.tcps_sndwinup++;
678 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
684 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
687 m->m_data += max_linkhdr;
690 m->m_pkthdr.rcvif = (struct ifnet *)0;
692 ip6 = mtod(m, struct ip6_hdr *);
693 th = (struct tcphdr *)(ip6 + 1);
694 tcp_fillheaders(tp, ip6, th);
696 ip = mtod(m, struct ip *);
697 ipov = (struct ipovly *)ip;
698 th = (struct tcphdr *)(ip + 1);
699 /* this picks up the pseudo header (w/o the length) */
700 tcp_fillheaders(tp, ip, th);
704 * Fill in fields, remembering maximum advertised
705 * window for use in delaying messages about window sizes.
706 * If resending a FIN, be sure not to use a new sequence number.
708 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
709 tp->snd_nxt == tp->snd_max)
712 * If we are doing retransmissions, then snd_nxt will
713 * not reflect the first unsent octet. For ACK only
714 * packets, we do not want the sequence number of the
715 * retransmitted packet, we want the sequence number
716 * of the next unsent octet. So, if there is no data
717 * (and no SYN or FIN), use snd_max instead of snd_nxt
718 * when filling in ti_seq. But if we are in persist
719 * state, snd_max might reflect one byte beyond the
720 * right edge of the window, so use snd_nxt in that
721 * case, since we know we aren't doing a retransmission.
722 * (retransmit and persist are mutually exclusive...)
724 if (len || (flags & (TH_SYN|TH_FIN)) || callout_active(tp->tt_persist))
725 th->th_seq = htonl(tp->snd_nxt);
727 th->th_seq = htonl(tp->snd_max);
728 th->th_ack = htonl(tp->rcv_nxt);
730 bcopy(opt, th + 1, optlen);
731 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
733 th->th_flags = flags;
735 * Calculate receive window. Don't shrink window,
736 * but avoid silly window syndrome.
738 if (recvwin < (long)(so->so_rcv.sb_hiwat / 4) &&
739 recvwin < (long)tp->t_maxseg)
741 if (recvwin < (long)(tp->rcv_adv - tp->rcv_nxt))
742 recvwin = (long)(tp->rcv_adv - tp->rcv_nxt);
743 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
744 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
745 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
748 * Adjust the RXWIN0SENT flag - indicate that we have advertised
749 * a 0 window. This may cause the remote transmitter to stall. This
750 * flag tells soreceive() to disable delayed acknowledgements when
751 * draining the buffer. This can occur if the receiver is attempting
752 * to read more data then can be buffered prior to transmitting on
756 tp->t_flags |= TF_RXWIN0SENT;
758 tp->t_flags &= ~TF_RXWIN0SENT;
760 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
761 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
762 th->th_flags |= TH_URG;
765 * If no urgent pointer to send, then we pull
766 * the urgent pointer to the left edge of the send window
767 * so that it doesn't drift into the send window on sequence
770 tp->snd_up = tp->snd_una; /* drag it along */
774 * Put TCP length in extended header, and then
775 * checksum extended header and data.
777 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
780 * ip6_plen is not need to be filled now, and will be filled
783 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
784 sizeof(struct tcphdr) + optlen + len);
786 m->m_pkthdr.csum_flags = CSUM_TCP;
787 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
789 th->th_sum = in_addword(th->th_sum,
790 htons((u_short)(optlen + len)));
792 /* IP version must be set here for ipv4/ipv6 checking later */
793 KASSERT(ip->ip_v == IPVERSION,
794 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
798 * In transmit state, time the transmission and arrange for
799 * the retransmit. In persist state, just set snd_max.
801 if (!(tp->t_flags & TF_FORCE) || !callout_active(tp->tt_persist)) {
802 tcp_seq startseq = tp->snd_nxt;
805 * Advance snd_nxt over sequence space of this segment.
807 if (flags & (TH_SYN|TH_FIN)) {
810 if (flags & TH_FIN) {
812 tp->t_flags |= TF_SENTFIN;
816 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
817 tp->snd_max = tp->snd_nxt;
819 * Time this transmission if not a retransmission and
820 * not currently timing anything.
822 if (tp->t_rtttime == 0) {
823 tp->t_rtttime = ticks;
824 tp->t_rtseq = startseq;
825 tcpstat.tcps_segstimed++;
830 * Set retransmit timer if not currently set,
831 * and not doing a pure ack or a keep-alive probe.
832 * Initial value for retransmit timer is smoothed
833 * round-trip time + 2 * round-trip time variance.
834 * Initialize shift counter which is used for backoff
835 * of retransmit time.
837 if (!callout_active(tp->tt_rexmt) &&
838 tp->snd_nxt != tp->snd_una) {
839 if (callout_active(tp->tt_persist)) {
840 callout_stop(tp->tt_persist);
843 callout_reset(tp->tt_rexmt, tp->t_rxtcur,
844 tcp_timer_rexmt, tp);
848 * Persist case, update snd_max but since we are in
849 * persist mode (no window) we do not update snd_nxt.
854 if (flags & TH_FIN) {
856 tp->t_flags |= TF_SENTFIN;
858 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
859 tp->snd_max = tp->snd_nxt + xlen;
866 if (so->so_options & SO_DEBUG)
867 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
871 * Fill in IP length and desired time to live and
872 * send to IP level. There should be a better way
873 * to handle ttl and tos; we could keep them in
874 * the template, but need a way to checksum without them.
877 * m->m_pkthdr.len should have been set before cksum calcuration,
878 * because in6_cksum() need it.
882 * we separately set hoplimit for every segment, since the
883 * user might want to change the value via setsockopt.
884 * Also, desired default hop limit might be changed via
885 * Neighbor Discovery.
887 ip6->ip6_hlim = in6_selecthlim(inp,
888 (inp->in6p_route.ro_rt ?
889 inp->in6p_route.ro_rt->rt_ifp : NULL));
891 /* TODO: IPv6 IP6TOS_ECT bit on */
892 error = ip6_output(m, inp->in6p_outputopts, &inp->in6p_route,
893 (so->so_options & SO_DONTROUTE), NULL, NULL, inp);
896 ip->ip_len = m->m_pkthdr.len;
898 if (INP_CHECK_SOCKAF(so, AF_INET6))
899 ip->ip_ttl = in6_selecthlim(inp,
900 (inp->in6p_route.ro_rt ?
901 inp->in6p_route.ro_rt->rt_ifp : NULL));
904 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
906 ip->ip_tos = inp->inp_ip_tos; /* XXX */
908 * See if we should do MTU discovery.
909 * We do it only if the following are true:
910 * 1) we have a valid route to the destination
911 * 2) the MTU is not locked (if it is,
912 * then discovery has been disabled)
914 if (path_mtu_discovery &&
915 (rt = inp->inp_route.ro_rt) && (rt->rt_flags & RTF_UP) &&
916 !(rt->rt_rmx.rmx_locks & RTV_MTU))
919 error = ip_output(m, inp->inp_options, &inp->inp_route,
920 (so->so_options & SO_DONTROUTE), NULL, inp);
925 * We know that the packet was lost, so back out the
926 * sequence number advance, if any.
928 if (!(tp->t_flags & TF_FORCE) ||
929 !callout_active(tp->tt_persist)) {
931 * No need to check for TH_FIN here because
932 * the TF_SENTFIN flag handles that case.
934 if (!(flags & TH_SYN))
939 if (error == ENOBUFS) {
941 * If we can't send, make sure there is something
942 * to get us going again later. Persist state
943 * is not necessarily right, but it is close enough.
945 if (!callout_active(tp->tt_rexmt) &&
946 !callout_active(tp->tt_persist)) {
953 if (error == EMSGSIZE) {
955 * ip_output() will have already fixed the route
956 * for us. tcp_mtudisc() will, as its last action,
957 * initiate retransmission, so it is important to
963 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
964 TCPS_HAVERCVDSYN(tp->t_state)) {
965 tp->t_softerror = error;
970 tcpstat.tcps_sndtotal++;
973 * Data sent (as far as we can tell).
974 * If this advertises a larger window than any other segment,
975 * then remember the size of the advertised window.
976 * Any pending ACK has now been sent.
978 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv))
979 tp->rcv_adv = tp->rcv_nxt + recvwin;
980 tp->last_ack_sent = tp->rcv_nxt;
981 tp->t_flags &= ~TF_ACKNOW;
982 if (tcp_delack_enabled)
983 callout_stop(tp->tt_delack);
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)