2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
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
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38 #include "opt_tcpdebug.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/domain.h>
43 #include <sys/kernel.h>
46 #include <sys/mutex.h>
47 #include <sys/protosw.h>
48 #include <sys/socket.h>
49 #include <sys/socketvar.h>
50 #include <sys/sysctl.h>
53 #include <net/route.h>
56 #include <netinet/in.h>
57 #include <netinet/in_systm.h>
58 #include <netinet/ip.h>
59 #include <netinet/in_pcb.h>
60 #include <netinet/ip_var.h>
61 #include <netinet/ip_options.h>
63 #include <netinet6/in6_pcb.h>
64 #include <netinet/ip6.h>
65 #include <netinet6/ip6_var.h>
67 #include <netinet/tcp.h>
69 #include <netinet/tcp_fsm.h>
70 #include <netinet/tcp_seq.h>
71 #include <netinet/tcp_timer.h>
72 #include <netinet/tcp_var.h>
73 #include <netinet/tcpip.h>
75 #include <netinet/tcp_debug.h>
79 #include <netipsec/ipsec.h>
82 #include <machine/in_cksum.h>
84 #include <security/mac/mac_framework.h>
87 extern struct mbuf *m_copypack();
90 VNET_DEFINE(int, path_mtu_discovery);
91 VNET_DEFINE(int, ss_fltsz);
92 VNET_DEFINE(int, ss_fltsz_local);
93 VNET_DEFINE(int, tcp_do_newreno);
94 VNET_DEFINE(int, tcp_do_tso);
95 VNET_DEFINE(int, tcp_do_autosndbuf);
96 VNET_DEFINE(int, tcp_autosndbuf_inc);
97 VNET_DEFINE(int, tcp_autosndbuf_max);
99 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
100 &VNET_NAME(path_mtu_discovery), 1,
101 "Enable Path MTU Discovery");
103 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
104 &VNET_NAME(ss_fltsz), 1,
105 "Slow start flight size");
107 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize,
108 CTLFLAG_RW, &VNET_NAME(ss_fltsz_local), 1,
109 "Slow start flight size for local networks");
111 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW,
112 &VNET_NAME(tcp_do_newreno), 0,
113 "Enable NewReno Algorithms");
115 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
116 &VNET_NAME(tcp_do_tso), 0,
117 "Enable TCP Segmentation Offload");
119 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
120 &VNET_NAME(tcp_do_autosndbuf), 0,
121 "Enable automatic send buffer sizing");
123 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
124 &VNET_NAME(tcp_autosndbuf_inc), 0,
125 "Incrementor step size of automatic send buffer");
127 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
128 &VNET_NAME(tcp_autosndbuf_max), 0,
129 "Max size of automatic send buffer");
133 * Tcp output routine: figure out what should be sent and send it.
136 tcp_output(struct tcpcb *tp)
138 struct socket *so = tp->t_inpcb->inp_socket;
139 long len, recwin, sendwin;
140 int off, flags, error;
142 struct ip *ip = NULL;
143 struct ipovly *ipov = NULL;
145 u_char opt[TCP_MAXOLEN];
146 unsigned ipoptlen, optlen, hdrlen;
148 unsigned ipsec_optlen = 0;
151 int sack_rxmit, sack_bytes_rxmt;
156 int maxburst = TCP_MAXBURST;
159 struct ip6_hdr *ip6 = NULL;
162 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
165 INP_WLOCK_ASSERT(tp->t_inpcb);
168 * Determine length of data that should be transmitted,
169 * and flags that will be used.
170 * If there is some data or critical controls (SYN, RST)
171 * to send, then transmit; otherwise, investigate further.
173 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
174 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur) {
176 * We have been idle for "a while" and no acks are
177 * expected to clock out any data we send --
178 * slow start to get ack "clock" running again.
180 * Set the slow-start flight size depending on whether
181 * this is a local network or not.
186 if (in6_localaddr(&tp->t_inpcb->in6p_faddr))
187 ss = V_ss_fltsz_local;
190 if (in_localaddr(tp->t_inpcb->inp_faddr))
191 ss = V_ss_fltsz_local;
192 tp->snd_cwnd = tp->t_maxseg * ss;
194 tp->t_flags &= ~TF_LASTIDLE;
196 if (tp->t_flags & TF_MORETOCOME) {
197 tp->t_flags |= TF_LASTIDLE;
203 * If we've recently taken a timeout, snd_max will be greater than
204 * snd_nxt. There may be SACK information that allows us to avoid
205 * resending already delivered data. Adjust snd_nxt accordingly.
207 if ((tp->t_flags & TF_SACK_PERMIT) &&
208 SEQ_LT(tp->snd_nxt, tp->snd_max))
211 off = tp->snd_nxt - tp->snd_una;
212 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
213 sendwin = min(sendwin, tp->snd_bwnd);
215 flags = tcp_outflags[tp->t_state];
217 * Send any SACK-generated retransmissions. If we're explicitly trying
218 * to send out new data (when sendalot is 1), bypass this function.
219 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
220 * we're replacing a (future) new transmission with a retransmission
221 * now, and we previously incremented snd_cwnd in tcp_input().
224 * Still in sack recovery , reset rxmit flag to zero.
230 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp) &&
231 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
234 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
237 /* Do not retransmit SACK segments beyond snd_recover */
238 if (SEQ_GT(p->end, tp->snd_recover)) {
240 * (At least) part of sack hole extends beyond
241 * snd_recover. Check to see if we can rexmit data
244 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
246 * Can't rexmit any more data for this hole.
247 * That data will be rexmitted in the next
248 * sack recovery episode, when snd_recover
249 * moves past p->rxmit.
252 goto after_sack_rexmit;
254 /* Can rexmit part of the current hole */
255 len = ((long)ulmin(cwin,
256 tp->snd_recover - p->rxmit));
258 len = ((long)ulmin(cwin, p->end - p->rxmit));
259 off = p->rxmit - tp->snd_una;
260 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
265 TCPSTAT_INC(tcps_sack_rexmits);
266 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
267 min(len, tp->t_maxseg));
272 * Get standard flags, and add SYN or FIN if requested by 'hidden'
275 if (tp->t_flags & TF_NEEDFIN)
277 if (tp->t_flags & TF_NEEDSYN)
280 SOCKBUF_LOCK(&so->so_snd);
282 * If in persist timeout with window of 0, send 1 byte.
283 * Otherwise, if window is small but nonzero
284 * and timer expired, we will send what we can
285 * and go to transmit state.
287 if (tp->t_flags & TF_FORCEDATA) {
290 * If we still have some data to send, then
291 * clear the FIN bit. Usually this would
292 * happen below when it realizes that we
293 * aren't sending all the data. However,
294 * if we have exactly 1 byte of unsent data,
295 * then it won't clear the FIN bit below,
296 * and if we are in persist state, we wind
297 * up sending the packet without recording
298 * that we sent the FIN bit.
300 * We can't just blindly clear the FIN bit,
301 * because if we don't have any more data
302 * to send then the probe will be the FIN
305 if (off < so->so_snd.sb_cc)
309 tcp_timer_activate(tp, TT_PERSIST, 0);
315 * If snd_nxt == snd_max and we have transmitted a FIN, the
316 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
317 * a negative length. This can also occur when TCP opens up
318 * its congestion window while receiving additional duplicate
319 * acks after fast-retransmit because TCP will reset snd_nxt
320 * to snd_max after the fast-retransmit.
322 * In the normal retransmit-FIN-only case, however, snd_nxt will
323 * be set to snd_una, the offset will be 0, and the length may
326 * If sack_rxmit is true we are retransmitting from the scoreboard
327 * in which case len is already set.
329 if (sack_rxmit == 0) {
330 if (sack_bytes_rxmt == 0)
331 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
336 * We are inside of a SACK recovery episode and are
337 * sending new data, having retransmitted all the
338 * data possible in the scoreboard.
340 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd)
343 * Don't remove this (len > 0) check !
344 * We explicitly check for len > 0 here (although it
345 * isn't really necessary), to work around a gcc
346 * optimization issue - to force gcc to compute
347 * len above. Without this check, the computation
348 * of len is bungled by the optimizer.
351 cwin = tp->snd_cwnd -
352 (tp->snd_nxt - tp->sack_newdata) -
356 len = lmin(len, cwin);
362 * Lop off SYN bit if it has already been sent. However, if this
363 * is SYN-SENT state and if segment contains data and if we don't
364 * know that foreign host supports TAO, suppress sending segment.
366 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
367 if (tp->t_state != TCPS_SYN_RECEIVED)
373 * Be careful not to send data and/or FIN on SYN segments.
374 * This measure is needed to prevent interoperability problems
375 * with not fully conformant TCP implementations.
377 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
384 * If FIN has been sent but not acked,
385 * but we haven't been called to retransmit,
386 * len will be < 0. Otherwise, window shrank
387 * after we sent into it. If window shrank to 0,
388 * cancel pending retransmit, pull snd_nxt back
389 * to (closed) window, and set the persist timer
390 * if it isn't already going. If the window didn't
391 * close completely, just wait for an ACK.
395 tcp_timer_activate(tp, TT_REXMT, 0);
397 tp->snd_nxt = tp->snd_una;
398 if (!tcp_timer_active(tp, TT_PERSIST))
403 /* len will be >= 0 after this point. */
404 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
407 * Automatic sizing of send socket buffer. Often the send buffer
408 * size is not optimally adjusted to the actual network conditions
409 * at hand (delay bandwidth product). Setting the buffer size too
410 * small limits throughput on links with high bandwidth and high
411 * delay (eg. trans-continental/oceanic links). Setting the
412 * buffer size too big consumes too much real kernel memory,
413 * especially with many connections on busy servers.
415 * The criteria to step up the send buffer one notch are:
416 * 1. receive window of remote host is larger than send buffer
417 * (with a fudge factor of 5/4th);
418 * 2. send buffer is filled to 7/8th with data (so we actually
419 * have data to make use of it);
420 * 3. send buffer fill has not hit maximal automatic size;
421 * 4. our send window (slow start and cogestion controlled) is
422 * larger than sent but unacknowledged data in send buffer.
424 * The remote host receive window scaling factor may limit the
425 * growing of the send buffer before it reaches its allowed
428 * It scales directly with slow start or congestion window
429 * and does at most one step per received ACK. This fast
430 * scaling has the drawback of growing the send buffer beyond
431 * what is strictly necessary to make full use of a given
432 * delay*bandwith product. However testing has shown this not
433 * to be much of an problem. At worst we are trading wasting
434 * of available bandwith (the non-use of it) for wasting some
435 * socket buffer memory.
437 * TODO: Shrink send buffer during idle periods together
438 * with congestion window. Requires another timer. Has to
439 * wait for upcoming tcp timer rewrite.
441 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
442 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
443 so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
444 so->so_snd.sb_cc < V_tcp_autosndbuf_max &&
445 sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
446 if (!sbreserve_locked(&so->so_snd,
447 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
448 V_tcp_autosndbuf_max), so, curthread))
449 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
454 * Truncate to the maximum segment length or enable TCP Segmentation
455 * Offloading (if supported by hardware) and ensure that FIN is removed
456 * if the length no longer contains the last data byte.
458 * TSO may only be used if we are in a pure bulk sending state. The
459 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
460 * IP options prevent using TSO. With TSO the TCP header is the same
461 * (except for the sequence number) for all generated packets. This
462 * makes it impossible to transmit any options which vary per generated
465 * The length of TSO bursts is limited to TCP_MAXWIN. That limit and
466 * removal of FIN (if not already catched here) are handled later after
467 * the exact length of the TCP options are known.
471 * Pre-calculate here as we save another lookup into the darknesses
472 * of IPsec that way and can actually decide if TSO is ok.
474 ipsec_optlen = ipsec_hdrsiz_tcp(tp);
476 if (len > tp->t_maxseg) {
477 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso &&
478 ((tp->t_flags & TF_SIGNATURE) == 0) &&
479 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
480 tp->t_inpcb->inp_options == NULL &&
481 tp->t_inpcb->in6p_options == NULL
494 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
497 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
501 recwin = sbspace(&so->so_rcv);
504 * Sender silly window avoidance. We transmit under the following
505 * conditions when len is non-zero:
507 * - We have a full segment (or more with TSO)
508 * - This is the last buffer in a write()/send() and we are
509 * either idle or running NODELAY
510 * - we've timed out (e.g. persist timer)
511 * - we have more then 1/2 the maximum send window's worth of
512 * data (receiver may be limited the window size)
513 * - we need to retransmit
516 if (len >= tp->t_maxseg)
519 * NOTE! on localhost connections an 'ack' from the remote
520 * end may occur synchronously with the output and cause
521 * us to flush a buffer queued with moretocome. XXX
523 * note: the len + off check is almost certainly unnecessary.
525 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
526 (idle || (tp->t_flags & TF_NODELAY)) &&
527 len + off >= so->so_snd.sb_cc &&
528 (tp->t_flags & TF_NOPUSH) == 0) {
531 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
533 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
535 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
542 * Compare available window to amount of window
543 * known to peer (as advertised window less
544 * next expected input). If the difference is at least two
545 * max size segments, or at least 50% of the maximum possible
546 * window, then want to send a window update to peer.
547 * Skip this if the connection is in T/TCP half-open state.
548 * Don't send pure window updates when the peer has closed
549 * the connection and won't ever send more data.
551 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
552 !TCPS_HAVERCVDFIN(tp->t_state)) {
554 * "adv" is the amount we can increase the window,
555 * taking into account that we are limited by
556 * TCP_MAXWIN << tp->rcv_scale.
558 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
559 (tp->rcv_adv - tp->rcv_nxt);
561 if (adv >= (long) (2 * tp->t_maxseg))
563 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
568 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
569 * is also a catch-all for the retransmit timer timeout case.
571 if (tp->t_flags & TF_ACKNOW)
573 if ((flags & TH_RST) ||
574 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
576 if (SEQ_GT(tp->snd_up, tp->snd_una))
579 * If our state indicates that FIN should be sent
580 * and we have not yet done so, then we need to send.
582 if (flags & TH_FIN &&
583 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
586 * In SACK, it is possible for tcp_output to fail to send a segment
587 * after the retransmission timer has been turned off. Make sure
588 * that the retransmission timer is set.
590 if ((tp->t_flags & TF_SACK_PERMIT) &&
591 SEQ_GT(tp->snd_max, tp->snd_una) &&
592 !tcp_timer_active(tp, TT_REXMT) &&
593 !tcp_timer_active(tp, TT_PERSIST)) {
594 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
598 * TCP window updates are not reliable, rather a polling protocol
599 * using ``persist'' packets is used to insure receipt of window
600 * updates. The three ``states'' for the output side are:
601 * idle not doing retransmits or persists
602 * persisting to move a small or zero window
603 * (re)transmitting and thereby not persisting
605 * tcp_timer_active(tp, TT_PERSIST)
606 * is true when we are in persist state.
607 * (tp->t_flags & TF_FORCEDATA)
608 * is set when we are called to send a persist packet.
609 * tcp_timer_active(tp, TT_REXMT)
610 * is set when we are retransmitting
611 * The output side is idle when both timers are zero.
613 * If send window is too small, there is data to transmit, and no
614 * retransmit or persist is pending, then go to persist state.
615 * If nothing happens soon, send when timer expires:
616 * if window is nonzero, transmit what we can,
617 * otherwise force out a byte.
619 if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) &&
620 !tcp_timer_active(tp, TT_PERSIST)) {
626 * No reason to send a segment, just return.
629 SOCKBUF_UNLOCK(&so->so_snd);
633 SOCKBUF_LOCK_ASSERT(&so->so_snd);
635 * Before ESTABLISHED, force sending of initial options
636 * unless TCP set not to do any options.
637 * NOTE: we assume that the IP/TCP header plus TCP options
638 * always fit in a single mbuf, leaving room for a maximum
640 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
645 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
648 hdrlen = sizeof (struct tcpiphdr);
651 * Compute options for segment.
652 * We only have to care about SYN and established connection
653 * segments. Options for SYN-ACK segments are handled in TCP
656 if ((tp->t_flags & TF_NOOPT) == 0) {
658 /* Maximum segment size. */
659 if (flags & TH_SYN) {
660 tp->snd_nxt = tp->iss;
661 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
662 to.to_flags |= TOF_MSS;
664 /* Window scaling. */
665 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
666 to.to_wscale = tp->request_r_scale;
667 to.to_flags |= TOF_SCALE;
670 if ((tp->t_flags & TF_RCVD_TSTMP) ||
671 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
672 to.to_tsval = ticks + tp->ts_offset;
673 to.to_tsecr = tp->ts_recent;
674 to.to_flags |= TOF_TS;
675 /* Set receive buffer autosizing timestamp. */
676 if (tp->rfbuf_ts == 0 &&
677 (so->so_rcv.sb_flags & SB_AUTOSIZE))
678 tp->rfbuf_ts = ticks;
680 /* Selective ACK's. */
681 if (tp->t_flags & TF_SACK_PERMIT) {
683 to.to_flags |= TOF_SACKPERM;
684 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
685 (tp->t_flags & TF_SACK_PERMIT) &&
686 tp->rcv_numsacks > 0) {
687 to.to_flags |= TOF_SACK;
688 to.to_nsacks = tp->rcv_numsacks;
689 to.to_sacks = (u_char *)tp->sackblks;
693 /* TCP-MD5 (RFC2385). */
694 if (tp->t_flags & TF_SIGNATURE)
695 to.to_flags |= TOF_SIGNATURE;
696 #endif /* TCP_SIGNATURE */
698 /* Processing the options. */
699 hdrlen += optlen = tcp_addoptions(&to, opt);
704 ipoptlen = ip6_optlen(tp->t_inpcb);
707 if (tp->t_inpcb->inp_options)
708 ipoptlen = tp->t_inpcb->inp_options->m_len -
709 offsetof(struct ipoption, ipopt_list);
713 ipoptlen += ipsec_optlen;
717 * Adjust data length if insertion of options will
718 * bump the packet length beyond the t_maxopd length.
719 * Clear the FIN bit because we cut off the tail of
722 * When doing TSO limit a burst to TCP_MAXWIN minus the
723 * IP, TCP and Options length to keep ip->ip_len from
724 * overflowing. Prevent the last segment from being
725 * fractional thus making them all equal sized and set
726 * the flag to continue sending. TSO is disabled when
727 * IP options or IPSEC are present.
729 if (len + optlen + ipoptlen > tp->t_maxopd) {
732 if (len > TCP_MAXWIN - hdrlen - optlen) {
733 len = TCP_MAXWIN - hdrlen - optlen;
734 len = len - (len % (tp->t_maxopd - optlen));
736 } else if (tp->t_flags & TF_NEEDFIN)
739 len = tp->t_maxopd - optlen - ipoptlen;
744 /*#ifdef DIAGNOSTIC*/
746 if (max_linkhdr + hdrlen > MCLBYTES)
748 if (max_linkhdr + hdrlen > MHLEN)
750 panic("tcphdr too big");
754 * This KASSERT is here to catch edge cases at a well defined place.
755 * Before, those had triggered (random) panic conditions further down.
757 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
760 * Grab a header mbuf, attaching a copy of data to
761 * be transmitted, and initialize the header from
762 * the template for sends on this connection.
768 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
769 TCPSTAT_INC(tcps_sndprobe);
770 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
771 TCPSTAT_INC(tcps_sndrexmitpack);
772 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
774 TCPSTAT_INC(tcps_sndpack);
775 TCPSTAT_ADD(tcps_sndbyte, len);
778 if ((m = m_copypack(so->so_snd.sb_mb, off,
779 (int)len, max_linkhdr + hdrlen)) == 0) {
780 SOCKBUF_UNLOCK(&so->so_snd);
785 * m_copypack left space for our hdr; use it.
790 MGETHDR(m, M_DONTWAIT, MT_DATA);
792 SOCKBUF_UNLOCK(&so->so_snd);
797 if (MHLEN < hdrlen + max_linkhdr) {
798 MCLGET(m, M_DONTWAIT);
799 if ((m->m_flags & M_EXT) == 0) {
800 SOCKBUF_UNLOCK(&so->so_snd);
807 m->m_data += max_linkhdr;
811 * Start the m_copy functions from the closest mbuf
812 * to the offset in the socket buffer chain.
814 mb = sbsndptr(&so->so_snd, off, len, &moff);
816 if (len <= MHLEN - hdrlen - max_linkhdr) {
817 m_copydata(mb, moff, (int)len,
818 mtod(m, caddr_t) + hdrlen);
821 m->m_next = m_copy(mb, moff, (int)len);
822 if (m->m_next == NULL) {
823 SOCKBUF_UNLOCK(&so->so_snd);
831 * If we're sending everything we've got, set PUSH.
832 * (This will keep happy those implementations which only
833 * give data to the user when a buffer fills or
836 if (off + len == so->so_snd.sb_cc)
838 SOCKBUF_UNLOCK(&so->so_snd);
840 SOCKBUF_UNLOCK(&so->so_snd);
841 if (tp->t_flags & TF_ACKNOW)
842 TCPSTAT_INC(tcps_sndacks);
843 else if (flags & (TH_SYN|TH_FIN|TH_RST))
844 TCPSTAT_INC(tcps_sndctrl);
845 else if (SEQ_GT(tp->snd_up, tp->snd_una))
846 TCPSTAT_INC(tcps_sndurg);
848 TCPSTAT_INC(tcps_sndwinup);
850 MGETHDR(m, M_DONTWAIT, MT_DATA);
856 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
861 m->m_data += max_linkhdr;
864 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
865 m->m_pkthdr.rcvif = (struct ifnet *)0;
867 mac_inpcb_create_mbuf(tp->t_inpcb, m);
871 ip6 = mtod(m, struct ip6_hdr *);
872 th = (struct tcphdr *)(ip6 + 1);
873 tcpip_fillheaders(tp->t_inpcb, ip6, th);
877 ip = mtod(m, struct ip *);
878 ipov = (struct ipovly *)ip;
879 th = (struct tcphdr *)(ip + 1);
880 tcpip_fillheaders(tp->t_inpcb, ip, th);
884 * Fill in fields, remembering maximum advertised
885 * window for use in delaying messages about window sizes.
886 * If resending a FIN, be sure not to use a new sequence number.
888 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
889 tp->snd_nxt == tp->snd_max)
892 * If we are starting a connection, send ECN setup
893 * SYN packet. If we are on a retransmit, we may
894 * resend those bits a number of times as per
897 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
898 if (tp->t_rxtshift >= 1) {
899 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
900 flags |= TH_ECE|TH_CWR;
902 flags |= TH_ECE|TH_CWR;
905 if (tp->t_state == TCPS_ESTABLISHED &&
906 (tp->t_flags & TF_ECN_PERMIT)) {
908 * If the peer has ECN, mark data packets with
909 * ECN capable transmission (ECT).
910 * Ignore pure ack packets, retransmissions and window probes.
912 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
913 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
916 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
919 ip->ip_tos |= IPTOS_ECN_ECT0;
920 TCPSTAT_INC(tcps_ecn_ect0);
924 * Reply with proper ECN notifications.
926 if (tp->t_flags & TF_ECN_SND_CWR) {
928 tp->t_flags &= ~TF_ECN_SND_CWR;
930 if (tp->t_flags & TF_ECN_SND_ECE)
935 * If we are doing retransmissions, then snd_nxt will
936 * not reflect the first unsent octet. For ACK only
937 * packets, we do not want the sequence number of the
938 * retransmitted packet, we want the sequence number
939 * of the next unsent octet. So, if there is no data
940 * (and no SYN or FIN), use snd_max instead of snd_nxt
941 * when filling in ti_seq. But if we are in persist
942 * state, snd_max might reflect one byte beyond the
943 * right edge of the window, so use snd_nxt in that
944 * case, since we know we aren't doing a retransmission.
945 * (retransmit and persist are mutually exclusive...)
947 if (sack_rxmit == 0) {
948 if (len || (flags & (TH_SYN|TH_FIN)) ||
949 tcp_timer_active(tp, TT_PERSIST))
950 th->th_seq = htonl(tp->snd_nxt);
952 th->th_seq = htonl(tp->snd_max);
954 th->th_seq = htonl(p->rxmit);
956 tp->sackhint.sack_bytes_rexmit += len;
958 th->th_ack = htonl(tp->rcv_nxt);
960 bcopy(opt, th + 1, optlen);
961 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
963 th->th_flags = flags;
965 * Calculate receive window. Don't shrink window,
966 * but avoid silly window syndrome.
968 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
969 recwin < (long)tp->t_maxseg)
971 if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
972 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
973 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
974 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
977 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
978 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
979 * case is handled in syncache.
982 th->th_win = htons((u_short)
983 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
985 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
988 * Adjust the RXWIN0SENT flag - indicate that we have advertised
989 * a 0 window. This may cause the remote transmitter to stall. This
990 * flag tells soreceive() to disable delayed acknowledgements when
991 * draining the buffer. This can occur if the receiver is attempting
992 * to read more data than can be buffered prior to transmitting on
996 tp->t_flags |= TF_RXWIN0SENT;
998 tp->t_flags &= ~TF_RXWIN0SENT;
999 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1000 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1001 th->th_flags |= TH_URG;
1004 * If no urgent pointer to send, then we pull
1005 * the urgent pointer to the left edge of the send window
1006 * so that it doesn't drift into the send window on sequence
1007 * number wraparound.
1009 tp->snd_up = tp->snd_una; /* drag it along */
1011 #ifdef TCP_SIGNATURE
1012 if (tp->t_flags & TF_SIGNATURE) {
1013 int sigoff = to.to_signature - opt;
1014 tcp_signature_compute(m, 0, len, optlen,
1015 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1020 * Put TCP length in extended header, and then
1021 * checksum extended header and data.
1023 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1027 * ip6_plen is not need to be filled now, and will be filled
1030 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
1031 sizeof(struct tcphdr) + optlen + len);
1035 m->m_pkthdr.csum_flags = CSUM_TCP;
1036 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1037 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1038 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1040 /* IP version must be set here for ipv4/ipv6 checking later */
1041 KASSERT(ip->ip_v == IPVERSION,
1042 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1046 * Enable TSO and specify the size of the segments.
1047 * The TCP pseudo header checksum is always provided.
1048 * XXX: Fixme: This is currently not the case for IPv6.
1051 m->m_pkthdr.csum_flags = CSUM_TSO;
1052 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
1056 * In transmit state, time the transmission and arrange for
1057 * the retransmit. In persist state, just set snd_max.
1059 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1060 !tcp_timer_active(tp, TT_PERSIST)) {
1061 tcp_seq startseq = tp->snd_nxt;
1064 * Advance snd_nxt over sequence space of this segment.
1066 if (flags & (TH_SYN|TH_FIN)) {
1069 if (flags & TH_FIN) {
1071 tp->t_flags |= TF_SENTFIN;
1077 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1078 tp->snd_max = tp->snd_nxt;
1080 * Time this transmission if not a retransmission and
1081 * not currently timing anything.
1083 if (tp->t_rtttime == 0) {
1084 tp->t_rtttime = ticks;
1085 tp->t_rtseq = startseq;
1086 TCPSTAT_INC(tcps_segstimed);
1091 * Set retransmit timer if not currently set,
1092 * and not doing a pure ack or a keep-alive probe.
1093 * Initial value for retransmit timer is smoothed
1094 * round-trip time + 2 * round-trip time variance.
1095 * Initialize shift counter which is used for backoff
1096 * of retransmit time.
1099 if (!tcp_timer_active(tp, TT_REXMT) &&
1100 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1101 (tp->snd_nxt != tp->snd_una))) {
1102 if (tcp_timer_active(tp, TT_PERSIST)) {
1103 tcp_timer_activate(tp, TT_PERSIST, 0);
1106 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1110 * Persist case, update snd_max but since we are in
1111 * persist mode (no window) we do not update snd_nxt.
1116 if (flags & TH_FIN) {
1118 tp->t_flags |= TF_SENTFIN;
1120 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1121 tp->snd_max = tp->snd_nxt + len;
1128 if (so->so_options & SO_DEBUG) {
1134 save = ipov->ih_len;
1135 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1137 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1141 ipov->ih_len = save;
1146 * Fill in IP length and desired time to live and
1147 * send to IP level. There should be a better way
1148 * to handle ttl and tos; we could keep them in
1149 * the template, but need a way to checksum without them.
1152 * m->m_pkthdr.len should have been set before cksum calcuration,
1153 * because in6_cksum() need it.
1158 * we separately set hoplimit for every segment, since the
1159 * user might want to change the value via setsockopt.
1160 * Also, desired default hop limit might be changed via
1161 * Neighbor Discovery.
1163 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1165 /* TODO: IPv6 IP6TOS_ECT bit on */
1166 error = ip6_output(m,
1167 tp->t_inpcb->in6p_outputopts, NULL,
1168 ((so->so_options & SO_DONTROUTE) ?
1169 IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb);
1173 ip->ip_len = m->m_pkthdr.len;
1175 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1176 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1179 * If we do path MTU discovery, then we set DF on every packet.
1180 * This might not be the best thing to do according to RFC3390
1181 * Section 2. However the tcp hostcache migitates the problem
1182 * so it affects only the first tcp connection with a host.
1184 if (V_path_mtu_discovery)
1185 ip->ip_off |= IP_DF;
1187 error = ip_output(m, tp->t_inpcb->inp_options, NULL,
1188 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1194 * We know that the packet was lost, so back out the
1195 * sequence number advance, if any.
1197 * If the error is EPERM the packet got blocked by the
1198 * local firewall. Normally we should terminate the
1199 * connection but the blocking may have been spurious
1200 * due to a firewall reconfiguration cycle. So we treat
1201 * it like a packet loss and let the retransmit timer and
1202 * timeouts do their work over time.
1203 * XXX: It is a POLA question whether calling tcp_drop right
1204 * away would be the really correct behavior instead.
1206 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1207 !tcp_timer_active(tp, TT_PERSIST)) &&
1208 ((flags & TH_SYN) == 0) &&
1212 tp->sackhint.sack_bytes_rexmit -= len;
1213 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1214 ("sackhint bytes rtx >= 0"));
1219 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1222 tp->t_softerror = error;
1225 if (!tcp_timer_active(tp, TT_REXMT) &&
1226 !tcp_timer_active(tp, TT_PERSIST))
1227 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1228 tp->snd_cwnd = tp->t_maxseg;
1232 * For some reason the interface we used initially
1233 * to send segments changed to another or lowered
1236 * tcp_mtudisc() will find out the new MTU and as
1237 * its last action, initiate retransmission, so it
1238 * is important to not do so here.
1240 * If TSO was active we either got an interface
1241 * without TSO capabilits or TSO was turned off.
1242 * Disable it for this connection as too and
1243 * immediatly retry with MSS sized segments generated
1247 tp->t_flags &= ~TF_TSO;
1248 tcp_mtudisc(tp->t_inpcb, 0);
1254 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1255 tp->t_softerror = error;
1263 TCPSTAT_INC(tcps_sndtotal);
1266 * Data sent (as far as we can tell).
1267 * If this advertises a larger window than any other segment,
1268 * then remember the size of the advertised window.
1269 * Any pending ACK has now been sent.
1271 if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1272 tp->rcv_adv = tp->rcv_nxt + recwin;
1273 tp->last_ack_sent = tp->rcv_nxt;
1274 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1275 if (tcp_timer_active(tp, TT_DELACK))
1276 tcp_timer_activate(tp, TT_DELACK, 0);
1279 * This completely breaks TCP if newreno is turned on. What happens
1280 * is that if delayed-acks are turned on on the receiver, this code
1281 * on the transmitter effectively destroys the TCP window, forcing
1282 * it to four packets (1.5Kx4 = 6K window).
1284 if (sendalot && (!V_tcp_do_newreno || --maxburst))
1293 tcp_setpersist(struct tcpcb *tp)
1295 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1298 if (tcp_timer_active(tp, TT_REXMT))
1299 panic("tcp_setpersist: retransmit pending");
1301 * Start/restart persistance timer.
1303 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1304 TCPTV_PERSMIN, TCPTV_PERSMAX);
1305 tcp_timer_activate(tp, TT_PERSIST, tt);
1306 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1311 * Insert TCP options according to the supplied parameters to the place
1312 * optp in a consistent way. Can handle unaligned destinations.
1314 * The order of the option processing is crucial for optimal packing and
1315 * alignment for the scarce option space.
1317 * The optimal order for a SYN/SYN-ACK segment is:
1318 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1319 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1321 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1322 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1323 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1324 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1325 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1328 tcp_addoptions(struct tcpopt *to, u_char *optp)
1330 u_int mask, optlen = 0;
1332 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1333 if ((to->to_flags & mask) != mask)
1335 if (optlen == TCP_MAXOLEN)
1337 switch (to->to_flags & mask) {
1339 while (optlen % 4) {
1340 optlen += TCPOLEN_NOP;
1341 *optp++ = TCPOPT_NOP;
1343 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1345 optlen += TCPOLEN_MAXSEG;
1346 *optp++ = TCPOPT_MAXSEG;
1347 *optp++ = TCPOLEN_MAXSEG;
1348 to->to_mss = htons(to->to_mss);
1349 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1350 optp += sizeof(to->to_mss);
1353 while (!optlen || optlen % 2 != 1) {
1354 optlen += TCPOLEN_NOP;
1355 *optp++ = TCPOPT_NOP;
1357 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1359 optlen += TCPOLEN_WINDOW;
1360 *optp++ = TCPOPT_WINDOW;
1361 *optp++ = TCPOLEN_WINDOW;
1362 *optp++ = to->to_wscale;
1365 while (optlen % 2) {
1366 optlen += TCPOLEN_NOP;
1367 *optp++ = TCPOPT_NOP;
1369 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1371 optlen += TCPOLEN_SACK_PERMITTED;
1372 *optp++ = TCPOPT_SACK_PERMITTED;
1373 *optp++ = TCPOLEN_SACK_PERMITTED;
1376 while (!optlen || optlen % 4 != 2) {
1377 optlen += TCPOLEN_NOP;
1378 *optp++ = TCPOPT_NOP;
1380 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1382 optlen += TCPOLEN_TIMESTAMP;
1383 *optp++ = TCPOPT_TIMESTAMP;
1384 *optp++ = TCPOLEN_TIMESTAMP;
1385 to->to_tsval = htonl(to->to_tsval);
1386 to->to_tsecr = htonl(to->to_tsecr);
1387 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1388 optp += sizeof(to->to_tsval);
1389 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1390 optp += sizeof(to->to_tsecr);
1394 int siglen = TCPOLEN_SIGNATURE - 2;
1396 while (!optlen || optlen % 4 != 2) {
1397 optlen += TCPOLEN_NOP;
1398 *optp++ = TCPOPT_NOP;
1400 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
1402 optlen += TCPOLEN_SIGNATURE;
1403 *optp++ = TCPOPT_SIGNATURE;
1404 *optp++ = TCPOLEN_SIGNATURE;
1405 to->to_signature = optp;
1413 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1416 while (!optlen || optlen % 4 != 2) {
1417 optlen += TCPOLEN_NOP;
1418 *optp++ = TCPOPT_NOP;
1420 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1422 optlen += TCPOLEN_SACKHDR;
1423 *optp++ = TCPOPT_SACK;
1424 sackblks = min(to->to_nsacks,
1425 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1426 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1427 while (sackblks--) {
1428 sack_seq = htonl(sack->start);
1429 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1430 optp += sizeof(sack_seq);
1431 sack_seq = htonl(sack->end);
1432 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1433 optp += sizeof(sack_seq);
1434 optlen += TCPOLEN_SACK;
1437 TCPSTAT_INC(tcps_sack_send_blocks);
1441 panic("%s: unknown TCP option type", __func__);
1446 /* Terminate and pad TCP options to a 4 byte boundary. */
1448 optlen += TCPOLEN_EOL;
1449 *optp++ = TCPOPT_EOL;
1452 * According to RFC 793 (STD0007):
1453 * "The content of the header beyond the End-of-Option option
1454 * must be header padding (i.e., zero)."
1455 * and later: "The padding is composed of zeros."
1457 while (optlen % 4) {
1458 optlen += TCPOLEN_PAD;
1459 *optp++ = TCPOPT_PAD;
1462 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));