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)
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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_kdtrace.h"
39 #include "opt_tcpdebug.h"
41 #include <sys/param.h>
42 #include <sys/systm.h>
43 #include <sys/domain.h>
44 #include <sys/hhook.h>
45 #include <sys/kernel.h>
48 #include <sys/mutex.h>
49 #include <sys/protosw.h>
51 #include <sys/socket.h>
52 #include <sys/socketvar.h>
53 #include <sys/sysctl.h>
56 #include <net/route.h>
59 #include <netinet/cc.h>
60 #include <netinet/in.h>
61 #include <netinet/in_kdtrace.h>
62 #include <netinet/in_systm.h>
63 #include <netinet/ip.h>
64 #include <netinet/in_pcb.h>
65 #include <netinet/ip_var.h>
66 #include <netinet/ip_options.h>
68 #include <netinet6/in6_pcb.h>
69 #include <netinet/ip6.h>
70 #include <netinet6/ip6_var.h>
73 #include <netinet/tcp_fastopen.h>
76 #include <netinet/tcp_fsm.h>
77 #include <netinet/tcp_seq.h>
78 #include <netinet/tcp_timer.h>
79 #include <netinet/tcp_var.h>
80 #include <netinet/tcpip.h>
82 #include <netinet/tcp_debug.h>
85 #include <netinet/tcp_offload.h>
89 #include <netipsec/ipsec.h>
92 #include <machine/in_cksum.h>
94 #include <security/mac/mac_framework.h>
96 VNET_DEFINE(int, path_mtu_discovery) = 1;
97 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
98 &VNET_NAME(path_mtu_discovery), 1,
99 "Enable Path MTU Discovery");
101 VNET_DEFINE(int, tcp_do_tso) = 1;
102 #define V_tcp_do_tso VNET(tcp_do_tso)
103 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
104 &VNET_NAME(tcp_do_tso), 0,
105 "Enable TCP Segmentation Offload");
107 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
108 #define V_tcp_sendspace VNET(tcp_sendspace)
109 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_RW,
110 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
112 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
113 #define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)
114 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
115 &VNET_NAME(tcp_do_autosndbuf), 0,
116 "Enable automatic send buffer sizing");
118 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
119 #define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
120 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
121 &VNET_NAME(tcp_autosndbuf_inc), 0,
122 "Incrementor step size of automatic send buffer");
124 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
125 #define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
126 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
127 &VNET_NAME(tcp_autosndbuf_max), 0,
128 "Max size of automatic send buffer");
131 * Make sure that either retransmit or persist timer is set for SYN, FIN and
134 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
135 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
136 tcp_timer_active((tp), TT_REXMT) || \
137 tcp_timer_active((tp), TT_PERSIST), \
138 ("neither rexmt nor persist timer is set"))
140 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
141 struct tcphdr *th, struct tcpopt *to,
143 static void inline cc_after_idle(struct tcpcb *tp);
146 * Wrapper for the TCP established output helper hook.
149 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
150 struct tcpopt *to, long len, int tso)
152 struct tcp_hhook_data hhook_data;
154 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
158 hhook_data.len = len;
159 hhook_data.tso = tso;
161 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
167 * CC wrapper hook functions
170 cc_after_idle(struct tcpcb *tp)
172 INP_WLOCK_ASSERT(tp->t_inpcb);
174 if (CC_ALGO(tp)->after_idle != NULL)
175 CC_ALGO(tp)->after_idle(tp->ccv);
179 * Tcp output routine: figure out what should be sent and send it.
182 tcp_output(struct tcpcb *tp)
184 struct socket *so = tp->t_inpcb->inp_socket;
185 long len, recwin, sendwin;
186 int off, flags, error = 0; /* Keep compiler happy */
188 struct ip *ip = NULL;
189 struct ipovly *ipov = NULL;
191 u_char opt[TCP_MAXOLEN];
192 unsigned ipoptlen, optlen, hdrlen;
194 unsigned ipsec_optlen = 0;
197 int sack_rxmit, sack_bytes_rxmt;
202 int maxburst = TCP_MAXBURST;
205 struct ip6_hdr *ip6 = NULL;
208 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
211 INP_WLOCK_ASSERT(tp->t_inpcb);
214 if (tp->t_flags & TF_TOE)
215 return (tcp_offload_output(tp));
220 * For TFO connections in SYN_RECEIVED, only allow the initial
221 * SYN|ACK and those sent by the retransmit timer.
223 if ((tp->t_flags & TF_FASTOPEN) &&
224 (tp->t_state == TCPS_SYN_RECEIVED) &&
225 SEQ_GT(tp->snd_max, tp->snd_una) && /* inital SYN|ACK sent */
226 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */
230 * Determine length of data that should be transmitted,
231 * and flags that will be used.
232 * If there is some data or critical controls (SYN, RST)
233 * to send, then transmit; otherwise, investigate further.
235 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
236 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
238 tp->t_flags &= ~TF_LASTIDLE;
240 if (tp->t_flags & TF_MORETOCOME) {
241 tp->t_flags |= TF_LASTIDLE;
247 * If we've recently taken a timeout, snd_max will be greater than
248 * snd_nxt. There may be SACK information that allows us to avoid
249 * resending already delivered data. Adjust snd_nxt accordingly.
251 if ((tp->t_flags & TF_SACK_PERMIT) &&
252 SEQ_LT(tp->snd_nxt, tp->snd_max))
257 off = tp->snd_nxt - tp->snd_una;
258 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
260 flags = tcp_outflags[tp->t_state];
262 * Send any SACK-generated retransmissions. If we're explicitly trying
263 * to send out new data (when sendalot is 1), bypass this function.
264 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
265 * we're replacing a (future) new transmission with a retransmission
266 * now, and we previously incremented snd_cwnd in tcp_input().
269 * Still in sack recovery , reset rxmit flag to zero.
275 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
276 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
279 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
282 /* Do not retransmit SACK segments beyond snd_recover */
283 if (SEQ_GT(p->end, tp->snd_recover)) {
285 * (At least) part of sack hole extends beyond
286 * snd_recover. Check to see if we can rexmit data
289 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
291 * Can't rexmit any more data for this hole.
292 * That data will be rexmitted in the next
293 * sack recovery episode, when snd_recover
294 * moves past p->rxmit.
297 goto after_sack_rexmit;
299 /* Can rexmit part of the current hole */
300 len = ((long)ulmin(cwin,
301 tp->snd_recover - p->rxmit));
303 len = ((long)ulmin(cwin, p->end - p->rxmit));
304 off = p->rxmit - tp->snd_una;
305 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
310 TCPSTAT_INC(tcps_sack_rexmits);
311 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
312 min(len, tp->t_maxseg));
317 * Get standard flags, and add SYN or FIN if requested by 'hidden'
320 if (tp->t_flags & TF_NEEDFIN)
322 if (tp->t_flags & TF_NEEDSYN)
325 SOCKBUF_LOCK(&so->so_snd);
327 * If in persist timeout with window of 0, send 1 byte.
328 * Otherwise, if window is small but nonzero
329 * and timer expired, we will send what we can
330 * and go to transmit state.
332 if (tp->t_flags & TF_FORCEDATA) {
335 * If we still have some data to send, then
336 * clear the FIN bit. Usually this would
337 * happen below when it realizes that we
338 * aren't sending all the data. However,
339 * if we have exactly 1 byte of unsent data,
340 * then it won't clear the FIN bit below,
341 * and if we are in persist state, we wind
342 * up sending the packet without recording
343 * that we sent the FIN bit.
345 * We can't just blindly clear the FIN bit,
346 * because if we don't have any more data
347 * to send then the probe will be the FIN
350 if (off < so->so_snd.sb_cc)
354 tcp_timer_activate(tp, TT_PERSIST, 0);
360 * If snd_nxt == snd_max and we have transmitted a FIN, the
361 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
362 * a negative length. This can also occur when TCP opens up
363 * its congestion window while receiving additional duplicate
364 * acks after fast-retransmit because TCP will reset snd_nxt
365 * to snd_max after the fast-retransmit.
367 * In the normal retransmit-FIN-only case, however, snd_nxt will
368 * be set to snd_una, the offset will be 0, and the length may
371 * If sack_rxmit is true we are retransmitting from the scoreboard
372 * in which case len is already set.
374 if (sack_rxmit == 0) {
375 if (sack_bytes_rxmt == 0)
376 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
381 * We are inside of a SACK recovery episode and are
382 * sending new data, having retransmitted all the
383 * data possible in the scoreboard.
385 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd)
388 * Don't remove this (len > 0) check !
389 * We explicitly check for len > 0 here (although it
390 * isn't really necessary), to work around a gcc
391 * optimization issue - to force gcc to compute
392 * len above. Without this check, the computation
393 * of len is bungled by the optimizer.
396 cwin = tp->snd_cwnd -
397 (tp->snd_nxt - tp->sack_newdata) -
401 len = lmin(len, cwin);
407 * Lop off SYN bit if it has already been sent. However, if this
408 * is SYN-SENT state and if segment contains data and if we don't
409 * know that foreign host supports TAO, suppress sending segment.
411 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
412 if (tp->t_state != TCPS_SYN_RECEIVED)
416 * When sending additional segments following a TFO SYN|ACK,
417 * do not include the SYN bit.
419 if ((tp->t_flags & TF_FASTOPEN) &&
420 (tp->t_state == TCPS_SYN_RECEIVED))
427 * Be careful not to send data and/or FIN on SYN segments.
428 * This measure is needed to prevent interoperability problems
429 * with not fully conformant TCP implementations.
431 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
438 * When retransmitting SYN|ACK on a passively-created TFO socket,
439 * don't include data, as the presence of data may have caused the
440 * original SYN|ACK to have been dropped by a middlebox.
442 if ((tp->t_flags & TF_FASTOPEN) &&
443 (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) ||
449 * If FIN has been sent but not acked,
450 * but we haven't been called to retransmit,
451 * len will be < 0. Otherwise, window shrank
452 * after we sent into it. If window shrank to 0,
453 * cancel pending retransmit, pull snd_nxt back
454 * to (closed) window, and set the persist timer
455 * if it isn't already going. If the window didn't
456 * close completely, just wait for an ACK.
458 * We also do a general check here to ensure that
459 * we will set the persist timer when we have data
460 * to send, but a 0-byte window. This makes sure
461 * the persist timer is set even if the packet
462 * hits one of the "goto send" lines below.
465 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
466 (off < (int) so->so_snd.sb_cc)) {
467 tcp_timer_activate(tp, TT_REXMT, 0);
469 tp->snd_nxt = tp->snd_una;
470 if (!tcp_timer_active(tp, TT_PERSIST))
475 /* len will be >= 0 after this point. */
476 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
479 * Automatic sizing of send socket buffer. Often the send buffer
480 * size is not optimally adjusted to the actual network conditions
481 * at hand (delay bandwidth product). Setting the buffer size too
482 * small limits throughput on links with high bandwidth and high
483 * delay (eg. trans-continental/oceanic links). Setting the
484 * buffer size too big consumes too much real kernel memory,
485 * especially with many connections on busy servers.
487 * The criteria to step up the send buffer one notch are:
488 * 1. receive window of remote host is larger than send buffer
489 * (with a fudge factor of 5/4th);
490 * 2. send buffer is filled to 7/8th with data (so we actually
491 * have data to make use of it);
492 * 3. send buffer fill has not hit maximal automatic size;
493 * 4. our send window (slow start and cogestion controlled) is
494 * larger than sent but unacknowledged data in send buffer.
496 * The remote host receive window scaling factor may limit the
497 * growing of the send buffer before it reaches its allowed
500 * It scales directly with slow start or congestion window
501 * and does at most one step per received ACK. This fast
502 * scaling has the drawback of growing the send buffer beyond
503 * what is strictly necessary to make full use of a given
504 * delay*bandwith product. However testing has shown this not
505 * to be much of an problem. At worst we are trading wasting
506 * of available bandwith (the non-use of it) for wasting some
507 * socket buffer memory.
509 * TODO: Shrink send buffer during idle periods together
510 * with congestion window. Requires another timer. Has to
511 * wait for upcoming tcp timer rewrite.
513 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
514 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
515 so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
516 so->so_snd.sb_cc < V_tcp_autosndbuf_max &&
517 sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
518 if (!sbreserve_locked(&so->so_snd,
519 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
520 V_tcp_autosndbuf_max), so, curthread))
521 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
526 * Decide if we can use TCP Segmentation Offloading (if supported by
529 * TSO may only be used if we are in a pure bulk sending state. The
530 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
531 * IP options prevent using TSO. With TSO the TCP header is the same
532 * (except for the sequence number) for all generated packets. This
533 * makes it impossible to transmit any options which vary per generated
538 * Pre-calculate here as we save another lookup into the darknesses
539 * of IPsec that way and can actually decide if TSO is ok.
541 ipsec_optlen = ipsec_hdrsiz_tcp(tp);
543 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
544 ((tp->t_flags & TF_SIGNATURE) == 0) &&
545 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
549 tp->t_inpcb->inp_options == NULL &&
550 tp->t_inpcb->in6p_options == NULL)
554 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
557 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
561 recwin = sbspace(&so->so_rcv);
564 * Sender silly window avoidance. We transmit under the following
565 * conditions when len is non-zero:
567 * - We have a full segment (or more with TSO)
568 * - This is the last buffer in a write()/send() and we are
569 * either idle or running NODELAY
570 * - we've timed out (e.g. persist timer)
571 * - we have more then 1/2 the maximum send window's worth of
572 * data (receiver may be limited the window size)
573 * - we need to retransmit
576 if (len >= tp->t_maxseg)
579 * NOTE! on localhost connections an 'ack' from the remote
580 * end may occur synchronously with the output and cause
581 * us to flush a buffer queued with moretocome. XXX
583 * note: the len + off check is almost certainly unnecessary.
585 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
586 (idle || (tp->t_flags & TF_NODELAY)) &&
587 len + off >= so->so_snd.sb_cc &&
588 (tp->t_flags & TF_NOPUSH) == 0) {
591 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
593 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
595 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
602 * Sending of standalone window updates.
604 * Window updates are important when we close our window due to a
605 * full socket buffer and are opening it again after the application
606 * reads data from it. Once the window has opened again and the
607 * remote end starts to send again the ACK clock takes over and
608 * provides the most current window information.
610 * We must avoid the silly window syndrome whereas every read
611 * from the receive buffer, no matter how small, causes a window
612 * update to be sent. We also should avoid sending a flurry of
613 * window updates when the socket buffer had queued a lot of data
614 * and the application is doing small reads.
616 * Prevent a flurry of pointless window updates by only sending
617 * an update when we can increase the advertized window by more
618 * than 1/4th of the socket buffer capacity. When the buffer is
619 * getting full or is very small be more aggressive and send an
620 * update whenever we can increase by two mss sized segments.
621 * In all other situations the ACK's to new incoming data will
622 * carry further window increases.
624 * Don't send an independent window update if a delayed
625 * ACK is pending (it will get piggy-backed on it) or the
626 * remote side already has done a half-close and won't send
627 * more data. Skip this if the connection is in T/TCP
630 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
631 !(tp->t_flags & TF_DELACK) &&
632 !TCPS_HAVERCVDFIN(tp->t_state)) {
634 * "adv" is the amount we could increase the window,
635 * taking into account that we are limited by
636 * TCP_MAXWIN << tp->rcv_scale.
641 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
642 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
643 oldwin = (tp->rcv_adv - tp->rcv_nxt);
649 * If the new window size ends up being the same as the old
650 * size when it is scaled, then don't force a window update.
652 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
655 if (adv >= (long)(2 * tp->t_maxseg) &&
656 (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
657 recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
658 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
664 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
665 * is also a catch-all for the retransmit timer timeout case.
667 if (tp->t_flags & TF_ACKNOW)
669 if ((flags & TH_RST) ||
670 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
672 if (SEQ_GT(tp->snd_up, tp->snd_una))
675 * If our state indicates that FIN should be sent
676 * and we have not yet done so, then we need to send.
678 if (flags & TH_FIN &&
679 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
682 * In SACK, it is possible for tcp_output to fail to send a segment
683 * after the retransmission timer has been turned off. Make sure
684 * that the retransmission timer is set.
686 if ((tp->t_flags & TF_SACK_PERMIT) &&
687 SEQ_GT(tp->snd_max, tp->snd_una) &&
688 !tcp_timer_active(tp, TT_REXMT) &&
689 !tcp_timer_active(tp, TT_PERSIST)) {
690 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
694 * TCP window updates are not reliable, rather a polling protocol
695 * using ``persist'' packets is used to insure receipt of window
696 * updates. The three ``states'' for the output side are:
697 * idle not doing retransmits or persists
698 * persisting to move a small or zero window
699 * (re)transmitting and thereby not persisting
701 * tcp_timer_active(tp, TT_PERSIST)
702 * is true when we are in persist state.
703 * (tp->t_flags & TF_FORCEDATA)
704 * is set when we are called to send a persist packet.
705 * tcp_timer_active(tp, TT_REXMT)
706 * is set when we are retransmitting
707 * The output side is idle when both timers are zero.
709 * If send window is too small, there is data to transmit, and no
710 * retransmit or persist is pending, then go to persist state.
711 * If nothing happens soon, send when timer expires:
712 * if window is nonzero, transmit what we can,
713 * otherwise force out a byte.
715 if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) &&
716 !tcp_timer_active(tp, TT_PERSIST)) {
722 * No reason to send a segment, just return.
725 SOCKBUF_UNLOCK(&so->so_snd);
729 SOCKBUF_LOCK_ASSERT(&so->so_snd);
731 if (len >= tp->t_maxseg)
732 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
734 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
737 * Before ESTABLISHED, force sending of initial options
738 * unless TCP set not to do any options.
739 * NOTE: we assume that the IP/TCP header plus TCP options
740 * always fit in a single mbuf, leaving room for a maximum
742 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
747 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
750 hdrlen = sizeof (struct tcpiphdr);
753 * Compute options for segment.
754 * We only have to care about SYN and established connection
755 * segments. Options for SYN-ACK segments are handled in TCP
759 if ((tp->t_flags & TF_NOOPT) == 0) {
760 /* Maximum segment size. */
761 if (flags & TH_SYN) {
762 tp->snd_nxt = tp->iss;
763 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
764 to.to_flags |= TOF_MSS;
767 * Only include the TFO option on the first
768 * transmission of the SYN|ACK on a
769 * passively-created TFO socket, as the presence of
770 * the TFO option may have caused the original
771 * SYN|ACK to have been dropped by a middlebox.
773 if ((tp->t_flags & TF_FASTOPEN) &&
774 (tp->t_state == TCPS_SYN_RECEIVED) &&
775 (tp->t_rxtshift == 0)) {
776 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
777 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie;
778 to.to_flags |= TOF_FASTOPEN;
782 /* Window scaling. */
783 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
784 to.to_wscale = tp->request_r_scale;
785 to.to_flags |= TOF_SCALE;
788 if ((tp->t_flags & TF_RCVD_TSTMP) ||
789 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
790 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
791 to.to_tsecr = tp->ts_recent;
792 to.to_flags |= TOF_TS;
793 /* Set receive buffer autosizing timestamp. */
794 if (tp->rfbuf_ts == 0 &&
795 (so->so_rcv.sb_flags & SB_AUTOSIZE))
796 tp->rfbuf_ts = tcp_ts_getticks();
798 /* Selective ACK's. */
799 if (tp->t_flags & TF_SACK_PERMIT) {
801 to.to_flags |= TOF_SACKPERM;
802 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
803 (tp->t_flags & TF_SACK_PERMIT) &&
804 tp->rcv_numsacks > 0) {
805 to.to_flags |= TOF_SACK;
806 to.to_nsacks = tp->rcv_numsacks;
807 to.to_sacks = (u_char *)tp->sackblks;
811 /* TCP-MD5 (RFC2385). */
812 if (tp->t_flags & TF_SIGNATURE)
813 to.to_flags |= TOF_SIGNATURE;
814 #endif /* TCP_SIGNATURE */
816 /* Processing the options. */
817 hdrlen += optlen = tcp_addoptions(&to, opt);
822 ipoptlen = ip6_optlen(tp->t_inpcb);
825 if (tp->t_inpcb->inp_options)
826 ipoptlen = tp->t_inpcb->inp_options->m_len -
827 offsetof(struct ipoption, ipopt_list);
831 ipoptlen += ipsec_optlen;
835 * Adjust data length if insertion of options will
836 * bump the packet length beyond the t_maxopd length.
837 * Clear the FIN bit because we cut off the tail of
840 if (len + optlen + ipoptlen > tp->t_maxopd) {
845 u_int if_hw_tsomaxsegcount;
846 u_int if_hw_tsomaxsegsize;
851 /* extract TSO information */
852 if_hw_tsomax = tp->t_tsomax;
853 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
854 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
857 * Limit a TSO burst to prevent it from
858 * overflowing or exceeding the maximum length
859 * allowed by the network interface:
861 KASSERT(ipoptlen == 0,
862 ("%s: TSO can't do IP options", __func__));
865 * Check if we should limit by maximum payload
868 if (if_hw_tsomax != 0) {
869 /* compute maximum TSO length */
870 max_len = (if_hw_tsomax - hdrlen -
874 } else if (len > max_len) {
881 * Check if we should limit by maximum segment
884 if (if_hw_tsomaxsegcount != 0 &&
885 if_hw_tsomaxsegsize != 0) {
887 * Subtract one segment for the LINK
888 * and TCP/IP headers mbuf that will
889 * be prepended to this mbuf chain
890 * after the code in this section
891 * limits the number of mbufs in the
892 * chain to if_hw_tsomaxsegcount.
894 if_hw_tsomaxsegcount -= 1;
896 mb = sbsndmbuf(&so->so_snd, off, &moff);
898 while (mb != NULL && max_len < len) {
903 * Get length of mbuf fragment
904 * and how many hardware frags,
905 * rounded up, it would use:
907 mlen = (mb->m_len - moff);
908 frags = howmany(mlen,
909 if_hw_tsomaxsegsize);
911 /* Handle special case: Zero Length Mbuf */
916 * Check if the fragment limit
917 * will be reached or exceeded:
919 if (frags >= if_hw_tsomaxsegcount) {
921 if_hw_tsomaxsegcount *
922 if_hw_tsomaxsegsize);
926 if_hw_tsomaxsegcount -= frags;
932 } else if (len > max_len) {
939 * Prevent the last segment from being
940 * fractional unless the send sockbuf can be
943 max_len = (tp->t_maxopd - optlen);
944 if ((off + len) < so->so_snd.sb_cc) {
945 moff = len % max_len;
953 * In case there are too many small fragments
956 if (len <= max_len) {
963 * Send the FIN in a separate segment
964 * after the bulk sending is done.
965 * We don't trust the TSO implementations
966 * to clear the FIN flag on all but the
969 if (tp->t_flags & TF_NEEDFIN)
973 len = tp->t_maxopd - optlen - ipoptlen;
979 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
980 ("%s: len > IP_MAXPACKET", __func__));
982 /*#ifdef DIAGNOSTIC*/
984 if (max_linkhdr + hdrlen > MCLBYTES)
986 if (max_linkhdr + hdrlen > MHLEN)
988 panic("tcphdr too big");
992 * This KASSERT is here to catch edge cases at a well defined place.
993 * Before, those had triggered (random) panic conditions further down.
995 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
998 * Grab a header mbuf, attaching a copy of data to
999 * be transmitted, and initialize the header from
1000 * the template for sends on this connection.
1006 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1007 TCPSTAT_INC(tcps_sndprobe);
1008 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1009 tp->t_sndrexmitpack++;
1010 TCPSTAT_INC(tcps_sndrexmitpack);
1011 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1013 TCPSTAT_INC(tcps_sndpack);
1014 TCPSTAT_ADD(tcps_sndbyte, len);
1017 if (MHLEN < hdrlen + max_linkhdr)
1018 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1021 m = m_gethdr(M_NOWAIT, MT_DATA);
1024 SOCKBUF_UNLOCK(&so->so_snd);
1030 m->m_data += max_linkhdr;
1034 * Start the m_copy functions from the closest mbuf
1035 * to the offset in the socket buffer chain.
1037 mb = sbsndptr(&so->so_snd, off, len, &moff);
1039 if (len <= MHLEN - hdrlen - max_linkhdr) {
1040 m_copydata(mb, moff, (int)len,
1041 mtod(m, caddr_t) + hdrlen);
1044 m->m_next = m_copy(mb, moff, (int)len);
1045 if (m->m_next == NULL) {
1046 SOCKBUF_UNLOCK(&so->so_snd);
1055 * If we're sending everything we've got, set PUSH.
1056 * (This will keep happy those implementations which only
1057 * give data to the user when a buffer fills or
1060 if ((off + len == so->so_snd.sb_cc) && !(flags & TH_SYN))
1062 SOCKBUF_UNLOCK(&so->so_snd);
1064 SOCKBUF_UNLOCK(&so->so_snd);
1065 if (tp->t_flags & TF_ACKNOW)
1066 TCPSTAT_INC(tcps_sndacks);
1067 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1068 TCPSTAT_INC(tcps_sndctrl);
1069 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1070 TCPSTAT_INC(tcps_sndurg);
1072 TCPSTAT_INC(tcps_sndwinup);
1074 m = m_gethdr(M_NOWAIT, MT_DATA);
1081 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1083 MH_ALIGN(m, hdrlen);
1086 m->m_data += max_linkhdr;
1089 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1090 m->m_pkthdr.rcvif = (struct ifnet *)0;
1092 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1096 ip6 = mtod(m, struct ip6_hdr *);
1097 th = (struct tcphdr *)(ip6 + 1);
1098 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1102 ip = mtod(m, struct ip *);
1103 ipov = (struct ipovly *)ip;
1104 th = (struct tcphdr *)(ip + 1);
1105 tcpip_fillheaders(tp->t_inpcb, ip, th);
1109 * Fill in fields, remembering maximum advertised
1110 * window for use in delaying messages about window sizes.
1111 * If resending a FIN, be sure not to use a new sequence number.
1113 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1114 tp->snd_nxt == tp->snd_max)
1117 * If we are starting a connection, send ECN setup
1118 * SYN packet. If we are on a retransmit, we may
1119 * resend those bits a number of times as per
1122 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1123 if (tp->t_rxtshift >= 1) {
1124 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1125 flags |= TH_ECE|TH_CWR;
1127 flags |= TH_ECE|TH_CWR;
1130 if (tp->t_state == TCPS_ESTABLISHED &&
1131 (tp->t_flags & TF_ECN_PERMIT)) {
1133 * If the peer has ECN, mark data packets with
1134 * ECN capable transmission (ECT).
1135 * Ignore pure ack packets, retransmissions and window probes.
1137 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1138 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1141 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1144 ip->ip_tos |= IPTOS_ECN_ECT0;
1145 TCPSTAT_INC(tcps_ecn_ect0);
1149 * Reply with proper ECN notifications.
1151 if (tp->t_flags & TF_ECN_SND_CWR) {
1153 tp->t_flags &= ~TF_ECN_SND_CWR;
1155 if (tp->t_flags & TF_ECN_SND_ECE)
1160 * If we are doing retransmissions, then snd_nxt will
1161 * not reflect the first unsent octet. For ACK only
1162 * packets, we do not want the sequence number of the
1163 * retransmitted packet, we want the sequence number
1164 * of the next unsent octet. So, if there is no data
1165 * (and no SYN or FIN), use snd_max instead of snd_nxt
1166 * when filling in ti_seq. But if we are in persist
1167 * state, snd_max might reflect one byte beyond the
1168 * right edge of the window, so use snd_nxt in that
1169 * case, since we know we aren't doing a retransmission.
1170 * (retransmit and persist are mutually exclusive...)
1172 if (sack_rxmit == 0) {
1173 if (len || (flags & (TH_SYN|TH_FIN)) ||
1174 tcp_timer_active(tp, TT_PERSIST))
1175 th->th_seq = htonl(tp->snd_nxt);
1177 th->th_seq = htonl(tp->snd_max);
1179 th->th_seq = htonl(p->rxmit);
1181 tp->sackhint.sack_bytes_rexmit += len;
1183 th->th_ack = htonl(tp->rcv_nxt);
1185 bcopy(opt, th + 1, optlen);
1186 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1188 th->th_flags = flags;
1190 * Calculate receive window. Don't shrink window,
1191 * but avoid silly window syndrome.
1193 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1194 recwin < (long)tp->t_maxseg)
1196 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1197 recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1198 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1199 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1200 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1203 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1204 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1205 * case is handled in syncache.
1208 th->th_win = htons((u_short)
1209 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1211 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1214 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1215 * a 0 window. This may cause the remote transmitter to stall. This
1216 * flag tells soreceive() to disable delayed acknowledgements when
1217 * draining the buffer. This can occur if the receiver is attempting
1218 * to read more data than can be buffered prior to transmitting on
1221 if (th->th_win == 0) {
1223 tp->t_flags |= TF_RXWIN0SENT;
1225 tp->t_flags &= ~TF_RXWIN0SENT;
1226 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1227 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1228 th->th_flags |= TH_URG;
1231 * If no urgent pointer to send, then we pull
1232 * the urgent pointer to the left edge of the send window
1233 * so that it doesn't drift into the send window on sequence
1234 * number wraparound.
1236 tp->snd_up = tp->snd_una; /* drag it along */
1238 #ifdef TCP_SIGNATURE
1239 if (to.to_flags & TOF_SIGNATURE) {
1240 int sigoff = to.to_signature - opt;
1241 tcp_signature_compute(m, 0, len, optlen,
1242 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1247 * Put TCP length in extended header, and then
1248 * checksum extended header and data.
1250 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1251 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1255 * ip6_plen is not need to be filled now, and will be filled
1258 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1259 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1260 optlen + len, IPPROTO_TCP, 0);
1263 #if defined(INET6) && defined(INET)
1268 m->m_pkthdr.csum_flags = CSUM_TCP;
1269 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1270 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1272 /* IP version must be set here for ipv4/ipv6 checking later */
1273 KASSERT(ip->ip_v == IPVERSION,
1274 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1279 * Enable TSO and specify the size of the segments.
1280 * The TCP pseudo header checksum is always provided.
1281 * XXX: Fixme: This is currently not the case for IPv6.
1284 KASSERT(len > tp->t_maxopd - optlen,
1285 ("%s: len <= tso_segsz", __func__));
1286 m->m_pkthdr.csum_flags |= CSUM_TSO;
1287 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
1291 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1292 ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
1293 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1295 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1296 ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
1297 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1300 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1301 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1307 if (so->so_options & SO_DEBUG) {
1313 save = ipov->ih_len;
1314 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1316 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1320 ipov->ih_len = save;
1322 #endif /* TCPDEBUG */
1325 * Fill in IP length and desired time to live and
1326 * send to IP level. There should be a better way
1327 * to handle ttl and tos; we could keep them in
1328 * the template, but need a way to checksum without them.
1331 * m->m_pkthdr.len should have been set before cksum calcuration,
1332 * because in6_cksum() need it.
1336 struct route_in6 ro;
1338 bzero(&ro, sizeof(ro));
1340 * we separately set hoplimit for every segment, since the
1341 * user might want to change the value via setsockopt.
1342 * Also, desired default hop limit might be changed via
1343 * Neighbor Discovery.
1345 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1348 * Set the packet size here for the benefit of DTrace probes.
1349 * ip6_output() will set it properly; it's supposed to include
1350 * the option header lengths as well.
1352 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1354 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss)
1355 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1357 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1359 if (tp->t_state == TCPS_SYN_SENT)
1360 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1362 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1364 /* TODO: IPv6 IP6TOS_ECT bit on */
1365 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
1366 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1367 NULL, NULL, tp->t_inpcb);
1369 if (error == EMSGSIZE && ro.ro_rt != NULL)
1370 mtu = ro.ro_rt->rt_mtu;
1374 #if defined(INET) && defined(INET6)
1381 bzero(&ro, sizeof(ro));
1382 ip->ip_len = htons(m->m_pkthdr.len);
1384 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1385 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1388 * If we do path MTU discovery, then we set DF on every packet.
1389 * This might not be the best thing to do according to RFC3390
1390 * Section 2. However the tcp hostcache migitates the problem
1391 * so it affects only the first tcp connection with a host.
1393 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1395 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) {
1396 ip->ip_off |= htons(IP_DF);
1397 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1399 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1402 if (tp->t_state == TCPS_SYN_SENT)
1403 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1405 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1407 error = ip_output(m, tp->t_inpcb->inp_options, &ro,
1408 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1411 if (error == EMSGSIZE && ro.ro_rt != NULL)
1412 mtu = ro.ro_rt->rt_mtu;
1419 * In transmit state, time the transmission and arrange for
1420 * the retransmit. In persist state, just set snd_max.
1422 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1423 !tcp_timer_active(tp, TT_PERSIST)) {
1424 tcp_seq startseq = tp->snd_nxt;
1427 * Advance snd_nxt over sequence space of this segment.
1429 if (flags & (TH_SYN|TH_FIN)) {
1432 if (flags & TH_FIN) {
1434 tp->t_flags |= TF_SENTFIN;
1440 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1441 tp->snd_max = tp->snd_nxt;
1443 * Time this transmission if not a retransmission and
1444 * not currently timing anything.
1446 if (tp->t_rtttime == 0) {
1447 tp->t_rtttime = ticks;
1448 tp->t_rtseq = startseq;
1449 TCPSTAT_INC(tcps_segstimed);
1454 * Set retransmit timer if not currently set,
1455 * and not doing a pure ack or a keep-alive probe.
1456 * Initial value for retransmit timer is smoothed
1457 * round-trip time + 2 * round-trip time variance.
1458 * Initialize shift counter which is used for backoff
1459 * of retransmit time.
1462 if (!tcp_timer_active(tp, TT_REXMT) &&
1463 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1464 (tp->snd_nxt != tp->snd_una))) {
1465 if (tcp_timer_active(tp, TT_PERSIST)) {
1466 tcp_timer_activate(tp, TT_PERSIST, 0);
1469 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1470 } else if (len == 0 && so->so_snd.sb_cc &&
1471 !tcp_timer_active(tp, TT_REXMT) &&
1472 !tcp_timer_active(tp, TT_PERSIST)) {
1474 * Avoid a situation where we do not set persist timer
1475 * after a zero window condition. For example:
1476 * 1) A -> B: packet with enough data to fill the window
1477 * 2) B -> A: ACK for #1 + new data (0 window
1479 * 3) A -> B: ACK for #2, 0 len packet
1481 * In this case, A will not activate the persist timer,
1482 * because it chose to send a packet. Unless tcp_output
1483 * is called for some other reason (delayed ack timer,
1484 * another input packet from B, socket syscall), A will
1485 * not send zero window probes.
1487 * So, if you send a 0-length packet, but there is data
1488 * in the socket buffer, and neither the rexmt or
1489 * persist timer is already set, then activate the
1497 * Persist case, update snd_max but since we are in
1498 * persist mode (no window) we do not update snd_nxt.
1503 if (flags & TH_FIN) {
1505 tp->t_flags |= TF_SENTFIN;
1507 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1508 tp->snd_max = tp->snd_nxt + len;
1514 * We know that the packet was lost, so back out the
1515 * sequence number advance, if any.
1517 * If the error is EPERM the packet got blocked by the
1518 * local firewall. Normally we should terminate the
1519 * connection but the blocking may have been spurious
1520 * due to a firewall reconfiguration cycle. So we treat
1521 * it like a packet loss and let the retransmit timer and
1522 * timeouts do their work over time.
1523 * XXX: It is a POLA question whether calling tcp_drop right
1524 * away would be the really correct behavior instead.
1526 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1527 !tcp_timer_active(tp, TT_PERSIST)) &&
1528 ((flags & TH_SYN) == 0) &&
1532 tp->sackhint.sack_bytes_rexmit -= len;
1533 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1534 ("sackhint bytes rtx >= 0"));
1538 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1541 tp->t_softerror = error;
1544 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1545 tp->snd_cwnd = tp->t_maxseg;
1549 * For some reason the interface we used initially
1550 * to send segments changed to another or lowered
1552 * If TSO was active we either got an interface
1553 * without TSO capabilits or TSO was turned off.
1554 * If we obtained mtu from ip_output() then update
1558 tp->t_flags &= ~TF_TSO;
1560 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1568 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1569 tp->t_softerror = error;
1577 TCPSTAT_INC(tcps_sndtotal);
1580 * Data sent (as far as we can tell).
1581 * If this advertises a larger window than any other segment,
1582 * then remember the size of the advertised window.
1583 * Any pending ACK has now been sent.
1585 if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1586 tp->rcv_adv = tp->rcv_nxt + recwin;
1587 tp->last_ack_sent = tp->rcv_nxt;
1588 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1589 if (tcp_timer_active(tp, TT_DELACK))
1590 tcp_timer_activate(tp, TT_DELACK, 0);
1593 * This completely breaks TCP if newreno is turned on. What happens
1594 * is that if delayed-acks are turned on on the receiver, this code
1595 * on the transmitter effectively destroys the TCP window, forcing
1596 * it to four packets (1.5Kx4 = 6K window).
1598 if (sendalot && --maxburst)
1607 tcp_setpersist(struct tcpcb *tp)
1609 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1612 tp->t_flags &= ~TF_PREVVALID;
1613 if (tcp_timer_active(tp, TT_REXMT))
1614 panic("tcp_setpersist: retransmit pending");
1616 * Start/restart persistance timer.
1618 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1619 tcp_persmin, tcp_persmax);
1620 tcp_timer_activate(tp, TT_PERSIST, tt);
1621 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1626 * Insert TCP options according to the supplied parameters to the place
1627 * optp in a consistent way. Can handle unaligned destinations.
1629 * The order of the option processing is crucial for optimal packing and
1630 * alignment for the scarce option space.
1632 * The optimal order for a SYN/SYN-ACK segment is:
1633 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1634 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1636 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1637 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1638 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1639 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1640 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1643 tcp_addoptions(struct tcpopt *to, u_char *optp)
1645 u_int mask, optlen = 0;
1647 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1648 if ((to->to_flags & mask) != mask)
1650 if (optlen == TCP_MAXOLEN)
1652 switch (to->to_flags & mask) {
1654 while (optlen % 4) {
1655 optlen += TCPOLEN_NOP;
1656 *optp++ = TCPOPT_NOP;
1658 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1660 optlen += TCPOLEN_MAXSEG;
1661 *optp++ = TCPOPT_MAXSEG;
1662 *optp++ = TCPOLEN_MAXSEG;
1663 to->to_mss = htons(to->to_mss);
1664 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1665 optp += sizeof(to->to_mss);
1668 while (!optlen || optlen % 2 != 1) {
1669 optlen += TCPOLEN_NOP;
1670 *optp++ = TCPOPT_NOP;
1672 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1674 optlen += TCPOLEN_WINDOW;
1675 *optp++ = TCPOPT_WINDOW;
1676 *optp++ = TCPOLEN_WINDOW;
1677 *optp++ = to->to_wscale;
1680 while (optlen % 2) {
1681 optlen += TCPOLEN_NOP;
1682 *optp++ = TCPOPT_NOP;
1684 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1686 optlen += TCPOLEN_SACK_PERMITTED;
1687 *optp++ = TCPOPT_SACK_PERMITTED;
1688 *optp++ = TCPOLEN_SACK_PERMITTED;
1691 while (!optlen || optlen % 4 != 2) {
1692 optlen += TCPOLEN_NOP;
1693 *optp++ = TCPOPT_NOP;
1695 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1697 optlen += TCPOLEN_TIMESTAMP;
1698 *optp++ = TCPOPT_TIMESTAMP;
1699 *optp++ = TCPOLEN_TIMESTAMP;
1700 to->to_tsval = htonl(to->to_tsval);
1701 to->to_tsecr = htonl(to->to_tsecr);
1702 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1703 optp += sizeof(to->to_tsval);
1704 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1705 optp += sizeof(to->to_tsecr);
1707 #ifdef TCP_SIGNATURE
1710 int siglen = TCPOLEN_SIGNATURE - 2;
1712 while (!optlen || optlen % 4 != 2) {
1713 optlen += TCPOLEN_NOP;
1714 *optp++ = TCPOPT_NOP;
1716 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
1718 optlen += TCPOLEN_SIGNATURE;
1719 *optp++ = TCPOPT_SIGNATURE;
1720 *optp++ = TCPOLEN_SIGNATURE;
1721 to->to_signature = optp;
1730 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1733 while (!optlen || optlen % 4 != 2) {
1734 optlen += TCPOLEN_NOP;
1735 *optp++ = TCPOPT_NOP;
1737 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1739 optlen += TCPOLEN_SACKHDR;
1740 *optp++ = TCPOPT_SACK;
1741 sackblks = min(to->to_nsacks,
1742 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1743 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1744 while (sackblks--) {
1745 sack_seq = htonl(sack->start);
1746 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1747 optp += sizeof(sack_seq);
1748 sack_seq = htonl(sack->end);
1749 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1750 optp += sizeof(sack_seq);
1751 optlen += TCPOLEN_SACK;
1754 TCPSTAT_INC(tcps_sack_send_blocks);
1762 /* XXX is there any point to aligning this option? */
1763 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1764 if (TCP_MAXOLEN - optlen < total_len)
1766 *optp++ = TCPOPT_FAST_OPEN;
1767 *optp++ = total_len;
1768 if (to->to_tfo_len > 0) {
1769 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1770 optp += to->to_tfo_len;
1772 optlen += total_len;
1777 panic("%s: unknown TCP option type", __func__);
1782 /* Terminate and pad TCP options to a 4 byte boundary. */
1784 optlen += TCPOLEN_EOL;
1785 *optp++ = TCPOPT_EOL;
1788 * According to RFC 793 (STD0007):
1789 * "The content of the header beyond the End-of-Option option
1790 * must be header padding (i.e., zero)."
1791 * and later: "The padding is composed of zeros."
1793 while (optlen % 4) {
1794 optlen += TCPOLEN_PAD;
1795 *optp++ = TCPOPT_PAD;
1798 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));