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/hhook.h>
44 #include <sys/kernel.h>
47 #include <sys/mutex.h>
48 #include <sys/protosw.h>
50 #include <sys/socket.h>
51 #include <sys/socketvar.h>
52 #include <sys/sysctl.h>
55 #include <net/route.h>
58 #include <netinet/cc.h>
59 #include <netinet/in.h>
60 #include <netinet/in_kdtrace.h>
61 #include <netinet/in_systm.h>
62 #include <netinet/ip.h>
63 #include <netinet/in_pcb.h>
64 #include <netinet/ip_var.h>
65 #include <netinet/ip_options.h>
67 #include <netinet6/in6_pcb.h>
68 #include <netinet/ip6.h>
69 #include <netinet6/ip6_var.h>
72 #include <netinet/tcp_fsm.h>
73 #include <netinet/tcp_seq.h>
74 #include <netinet/tcp_timer.h>
75 #include <netinet/tcp_var.h>
76 #include <netinet/tcpip.h>
78 #include <netinet/tcp_debug.h>
81 #include <netinet/tcp_offload.h>
85 #include <netipsec/ipsec.h>
88 #include <machine/in_cksum.h>
90 #include <security/mac/mac_framework.h>
92 VNET_DEFINE(int, path_mtu_discovery) = 1;
93 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
94 &VNET_NAME(path_mtu_discovery), 1,
95 "Enable Path MTU Discovery");
97 VNET_DEFINE(int, tcp_do_tso) = 1;
98 #define V_tcp_do_tso VNET(tcp_do_tso)
99 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
100 &VNET_NAME(tcp_do_tso), 0,
101 "Enable TCP Segmentation Offload");
103 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
104 #define V_tcp_sendspace VNET(tcp_sendspace)
105 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
106 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
108 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
109 #define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)
110 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
111 &VNET_NAME(tcp_do_autosndbuf), 0,
112 "Enable automatic send buffer sizing");
114 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
115 #define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
117 &VNET_NAME(tcp_autosndbuf_inc), 0,
118 "Incrementor step size of automatic send buffer");
120 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
121 #define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
122 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
123 &VNET_NAME(tcp_autosndbuf_max), 0,
124 "Max size of automatic send buffer");
126 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
127 struct tcphdr *th, struct tcpopt *to,
129 static void inline cc_after_idle(struct tcpcb *tp);
132 * Wrapper for the TCP established output helper hook.
135 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
136 struct tcpopt *to, long len, int tso)
138 struct tcp_hhook_data hhook_data;
140 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
144 hhook_data.len = len;
145 hhook_data.tso = tso;
147 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
153 * CC wrapper hook functions
156 cc_after_idle(struct tcpcb *tp)
158 INP_WLOCK_ASSERT(tp->t_inpcb);
160 if (CC_ALGO(tp)->after_idle != NULL)
161 CC_ALGO(tp)->after_idle(tp->ccv);
165 * Tcp output routine: figure out what should be sent and send it.
168 tcp_output(struct tcpcb *tp)
170 struct socket *so = tp->t_inpcb->inp_socket;
171 long len, recwin, sendwin;
172 int off, flags, error = 0; /* Keep compiler happy */
174 struct ip *ip = NULL;
175 struct ipovly *ipov = NULL;
177 u_char opt[TCP_MAXOLEN];
178 unsigned ipoptlen, optlen, hdrlen;
180 unsigned ipsec_optlen = 0;
183 int sack_rxmit, sack_bytes_rxmt;
188 int maxburst = TCP_MAXBURST;
191 struct ip6_hdr *ip6 = NULL;
194 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
197 INP_WLOCK_ASSERT(tp->t_inpcb);
200 if (tp->t_flags & TF_TOE)
201 return (tcp_offload_output(tp));
205 * Determine length of data that should be transmitted,
206 * and flags that will be used.
207 * If there is some data or critical controls (SYN, RST)
208 * to send, then transmit; otherwise, investigate further.
210 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
211 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
213 tp->t_flags &= ~TF_LASTIDLE;
215 if (tp->t_flags & TF_MORETOCOME) {
216 tp->t_flags |= TF_LASTIDLE;
222 * If we've recently taken a timeout, snd_max will be greater than
223 * snd_nxt. There may be SACK information that allows us to avoid
224 * resending already delivered data. Adjust snd_nxt accordingly.
226 if ((tp->t_flags & TF_SACK_PERMIT) &&
227 SEQ_LT(tp->snd_nxt, tp->snd_max))
232 off = tp->snd_nxt - tp->snd_una;
233 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
235 flags = tcp_outflags[tp->t_state];
237 * Send any SACK-generated retransmissions. If we're explicitly trying
238 * to send out new data (when sendalot is 1), bypass this function.
239 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
240 * we're replacing a (future) new transmission with a retransmission
241 * now, and we previously incremented snd_cwnd in tcp_input().
244 * Still in sack recovery , reset rxmit flag to zero.
250 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
251 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
254 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
257 /* Do not retransmit SACK segments beyond snd_recover */
258 if (SEQ_GT(p->end, tp->snd_recover)) {
260 * (At least) part of sack hole extends beyond
261 * snd_recover. Check to see if we can rexmit data
264 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
266 * Can't rexmit any more data for this hole.
267 * That data will be rexmitted in the next
268 * sack recovery episode, when snd_recover
269 * moves past p->rxmit.
272 goto after_sack_rexmit;
274 /* Can rexmit part of the current hole */
275 len = ((long)ulmin(cwin,
276 tp->snd_recover - p->rxmit));
278 len = ((long)ulmin(cwin, p->end - p->rxmit));
279 off = p->rxmit - tp->snd_una;
280 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
285 TCPSTAT_INC(tcps_sack_rexmits);
286 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
287 min(len, tp->t_maxseg));
292 * Get standard flags, and add SYN or FIN if requested by 'hidden'
295 if (tp->t_flags & TF_NEEDFIN)
297 if (tp->t_flags & TF_NEEDSYN)
300 SOCKBUF_LOCK(&so->so_snd);
302 * If in persist timeout with window of 0, send 1 byte.
303 * Otherwise, if window is small but nonzero
304 * and timer expired, we will send what we can
305 * and go to transmit state.
307 if (tp->t_flags & TF_FORCEDATA) {
310 * If we still have some data to send, then
311 * clear the FIN bit. Usually this would
312 * happen below when it realizes that we
313 * aren't sending all the data. However,
314 * if we have exactly 1 byte of unsent data,
315 * then it won't clear the FIN bit below,
316 * and if we are in persist state, we wind
317 * up sending the packet without recording
318 * that we sent the FIN bit.
320 * We can't just blindly clear the FIN bit,
321 * because if we don't have any more data
322 * to send then the probe will be the FIN
325 if (off < sbused(&so->so_snd))
329 tcp_timer_activate(tp, TT_PERSIST, 0);
335 * If snd_nxt == snd_max and we have transmitted a FIN, the
336 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
337 * a negative length. This can also occur when TCP opens up
338 * its congestion window while receiving additional duplicate
339 * acks after fast-retransmit because TCP will reset snd_nxt
340 * to snd_max after the fast-retransmit.
342 * In the normal retransmit-FIN-only case, however, snd_nxt will
343 * be set to snd_una, the offset will be 0, and the length may
346 * If sack_rxmit is true we are retransmitting from the scoreboard
347 * in which case len is already set.
349 if (sack_rxmit == 0) {
350 if (sack_bytes_rxmt == 0)
351 len = ((long)ulmin(sbavail(&so->so_snd), sendwin) -
357 * We are inside of a SACK recovery episode and are
358 * sending new data, having retransmitted all the
359 * data possible in the scoreboard.
361 len = ((long)ulmin(sbavail(&so->so_snd), tp->snd_wnd) -
364 * Don't remove this (len > 0) check !
365 * We explicitly check for len > 0 here (although it
366 * isn't really necessary), to work around a gcc
367 * optimization issue - to force gcc to compute
368 * len above. Without this check, the computation
369 * of len is bungled by the optimizer.
372 cwin = tp->snd_cwnd -
373 (tp->snd_nxt - tp->sack_newdata) -
377 len = lmin(len, cwin);
383 * Lop off SYN bit if it has already been sent. However, if this
384 * is SYN-SENT state and if segment contains data and if we don't
385 * know that foreign host supports TAO, suppress sending segment.
387 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
388 if (tp->t_state != TCPS_SYN_RECEIVED)
394 * Be careful not to send data and/or FIN on SYN segments.
395 * This measure is needed to prevent interoperability problems
396 * with not fully conformant TCP implementations.
398 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
405 * If FIN has been sent but not acked,
406 * but we haven't been called to retransmit,
407 * len will be < 0. Otherwise, window shrank
408 * after we sent into it. If window shrank to 0,
409 * cancel pending retransmit, pull snd_nxt back
410 * to (closed) window, and set the persist timer
411 * if it isn't already going. If the window didn't
412 * close completely, just wait for an ACK.
414 * We also do a general check here to ensure that
415 * we will set the persist timer when we have data
416 * to send, but a 0-byte window. This makes sure
417 * the persist timer is set even if the packet
418 * hits one of the "goto send" lines below.
421 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
422 (off < (int) sbavail(&so->so_snd))) {
423 tcp_timer_activate(tp, TT_REXMT, 0);
425 tp->snd_nxt = tp->snd_una;
426 if (!tcp_timer_active(tp, TT_PERSIST))
431 /* len will be >= 0 after this point. */
432 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
435 * Automatic sizing of send socket buffer. Often the send buffer
436 * size is not optimally adjusted to the actual network conditions
437 * at hand (delay bandwidth product). Setting the buffer size too
438 * small limits throughput on links with high bandwidth and high
439 * delay (eg. trans-continental/oceanic links). Setting the
440 * buffer size too big consumes too much real kernel memory,
441 * especially with many connections on busy servers.
443 * The criteria to step up the send buffer one notch are:
444 * 1. receive window of remote host is larger than send buffer
445 * (with a fudge factor of 5/4th);
446 * 2. send buffer is filled to 7/8th with data (so we actually
447 * have data to make use of it);
448 * 3. send buffer fill has not hit maximal automatic size;
449 * 4. our send window (slow start and cogestion controlled) is
450 * larger than sent but unacknowledged data in send buffer.
452 * The remote host receive window scaling factor may limit the
453 * growing of the send buffer before it reaches its allowed
456 * It scales directly with slow start or congestion window
457 * and does at most one step per received ACK. This fast
458 * scaling has the drawback of growing the send buffer beyond
459 * what is strictly necessary to make full use of a given
460 * delay*bandwith product. However testing has shown this not
461 * to be much of an problem. At worst we are trading wasting
462 * of available bandwith (the non-use of it) for wasting some
463 * socket buffer memory.
465 * TODO: Shrink send buffer during idle periods together
466 * with congestion window. Requires another timer. Has to
467 * wait for upcoming tcp timer rewrite.
469 * XXXGL: should there be used sbused() or sbavail()?
471 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
472 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
473 sbused(&so->so_snd) >= (so->so_snd.sb_hiwat / 8 * 7) &&
474 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
475 sendwin >= (sbused(&so->so_snd) -
476 (tp->snd_nxt - tp->snd_una))) {
477 if (!sbreserve_locked(&so->so_snd,
478 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
479 V_tcp_autosndbuf_max), so, curthread))
480 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
485 * Decide if we can use TCP Segmentation Offloading (if supported by
488 * TSO may only be used if we are in a pure bulk sending state. The
489 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
490 * IP options prevent using TSO. With TSO the TCP header is the same
491 * (except for the sequence number) for all generated packets. This
492 * makes it impossible to transmit any options which vary per generated
497 * Pre-calculate here as we save another lookup into the darknesses
498 * of IPsec that way and can actually decide if TSO is ok.
500 ipsec_optlen = ipsec_hdrsiz_tcp(tp);
502 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
503 ((tp->t_flags & TF_SIGNATURE) == 0) &&
504 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
508 tp->t_inpcb->inp_options == NULL &&
509 tp->t_inpcb->in6p_options == NULL)
513 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
516 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
517 sbused(&so->so_snd)))
521 recwin = sbspace(&so->so_rcv);
524 * Sender silly window avoidance. We transmit under the following
525 * conditions when len is non-zero:
527 * - We have a full segment (or more with TSO)
528 * - This is the last buffer in a write()/send() and we are
529 * either idle or running NODELAY
530 * - we've timed out (e.g. persist timer)
531 * - we have more then 1/2 the maximum send window's worth of
532 * data (receiver may be limited the window size)
533 * - we need to retransmit
536 if (len >= tp->t_maxseg)
539 * NOTE! on localhost connections an 'ack' from the remote
540 * end may occur synchronously with the output and cause
541 * us to flush a buffer queued with moretocome. XXX
543 * note: the len + off check is almost certainly unnecessary.
545 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
546 (idle || (tp->t_flags & TF_NODELAY)) &&
547 len + off >= sbavail(&so->so_snd) &&
548 (tp->t_flags & TF_NOPUSH) == 0) {
551 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
553 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
555 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
562 * Sending of standalone window updates.
564 * Window updates are important when we close our window due to a
565 * full socket buffer and are opening it again after the application
566 * reads data from it. Once the window has opened again and the
567 * remote end starts to send again the ACK clock takes over and
568 * provides the most current window information.
570 * We must avoid the silly window syndrome whereas every read
571 * from the receive buffer, no matter how small, causes a window
572 * update to be sent. We also should avoid sending a flurry of
573 * window updates when the socket buffer had queued a lot of data
574 * and the application is doing small reads.
576 * Prevent a flurry of pointless window updates by only sending
577 * an update when we can increase the advertized window by more
578 * than 1/4th of the socket buffer capacity. When the buffer is
579 * getting full or is very small be more aggressive and send an
580 * update whenever we can increase by two mss sized segments.
581 * In all other situations the ACK's to new incoming data will
582 * carry further window increases.
584 * Don't send an independent window update if a delayed
585 * ACK is pending (it will get piggy-backed on it) or the
586 * remote side already has done a half-close and won't send
587 * more data. Skip this if the connection is in T/TCP
590 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
591 !(tp->t_flags & TF_DELACK) &&
592 !TCPS_HAVERCVDFIN(tp->t_state)) {
594 * "adv" is the amount we could increase the window,
595 * taking into account that we are limited by
596 * TCP_MAXWIN << tp->rcv_scale.
601 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
602 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
603 oldwin = (tp->rcv_adv - tp->rcv_nxt);
609 * If the new window size ends up being the same as the old
610 * size when it is scaled, then don't force a window update.
612 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
615 if (adv >= (long)(2 * tp->t_maxseg) &&
616 (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
617 recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
618 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
624 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
625 * is also a catch-all for the retransmit timer timeout case.
627 if (tp->t_flags & TF_ACKNOW)
629 if ((flags & TH_RST) ||
630 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
632 if (SEQ_GT(tp->snd_up, tp->snd_una))
635 * If our state indicates that FIN should be sent
636 * and we have not yet done so, then we need to send.
638 if (flags & TH_FIN &&
639 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
642 * In SACK, it is possible for tcp_output to fail to send a segment
643 * after the retransmission timer has been turned off. Make sure
644 * that the retransmission timer is set.
646 if ((tp->t_flags & TF_SACK_PERMIT) &&
647 SEQ_GT(tp->snd_max, tp->snd_una) &&
648 !tcp_timer_active(tp, TT_REXMT) &&
649 !tcp_timer_active(tp, TT_PERSIST)) {
650 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
654 * TCP window updates are not reliable, rather a polling protocol
655 * using ``persist'' packets is used to insure receipt of window
656 * updates. The three ``states'' for the output side are:
657 * idle not doing retransmits or persists
658 * persisting to move a small or zero window
659 * (re)transmitting and thereby not persisting
661 * tcp_timer_active(tp, TT_PERSIST)
662 * is true when we are in persist state.
663 * (tp->t_flags & TF_FORCEDATA)
664 * is set when we are called to send a persist packet.
665 * tcp_timer_active(tp, TT_REXMT)
666 * is set when we are retransmitting
667 * The output side is idle when both timers are zero.
669 * If send window is too small, there is data to transmit, and no
670 * retransmit or persist is pending, then go to persist state.
671 * If nothing happens soon, send when timer expires:
672 * if window is nonzero, transmit what we can,
673 * otherwise force out a byte.
675 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
676 !tcp_timer_active(tp, TT_PERSIST)) {
682 * No reason to send a segment, just return.
685 SOCKBUF_UNLOCK(&so->so_snd);
689 SOCKBUF_LOCK_ASSERT(&so->so_snd);
691 if (len >= tp->t_maxseg)
692 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
694 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
697 * Before ESTABLISHED, force sending of initial options
698 * unless TCP set not to do any options.
699 * NOTE: we assume that the IP/TCP header plus TCP options
700 * always fit in a single mbuf, leaving room for a maximum
702 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
707 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
710 hdrlen = sizeof (struct tcpiphdr);
713 * Compute options for segment.
714 * We only have to care about SYN and established connection
715 * segments. Options for SYN-ACK segments are handled in TCP
718 if ((tp->t_flags & TF_NOOPT) == 0) {
720 /* Maximum segment size. */
721 if (flags & TH_SYN) {
722 tp->snd_nxt = tp->iss;
723 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
724 to.to_flags |= TOF_MSS;
726 /* Window scaling. */
727 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
728 to.to_wscale = tp->request_r_scale;
729 to.to_flags |= TOF_SCALE;
732 if ((tp->t_flags & TF_RCVD_TSTMP) ||
733 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
734 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
735 to.to_tsecr = tp->ts_recent;
736 to.to_flags |= TOF_TS;
737 /* Set receive buffer autosizing timestamp. */
738 if (tp->rfbuf_ts == 0 &&
739 (so->so_rcv.sb_flags & SB_AUTOSIZE))
740 tp->rfbuf_ts = tcp_ts_getticks();
742 /* Selective ACK's. */
743 if (tp->t_flags & TF_SACK_PERMIT) {
745 to.to_flags |= TOF_SACKPERM;
746 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
747 (tp->t_flags & TF_SACK_PERMIT) &&
748 tp->rcv_numsacks > 0) {
749 to.to_flags |= TOF_SACK;
750 to.to_nsacks = tp->rcv_numsacks;
751 to.to_sacks = (u_char *)tp->sackblks;
755 /* TCP-MD5 (RFC2385). */
756 if (tp->t_flags & TF_SIGNATURE)
757 to.to_flags |= TOF_SIGNATURE;
758 #endif /* TCP_SIGNATURE */
760 /* Processing the options. */
761 hdrlen += optlen = tcp_addoptions(&to, opt);
766 ipoptlen = ip6_optlen(tp->t_inpcb);
769 if (tp->t_inpcb->inp_options)
770 ipoptlen = tp->t_inpcb->inp_options->m_len -
771 offsetof(struct ipoption, ipopt_list);
775 ipoptlen += ipsec_optlen;
779 * Adjust data length if insertion of options will
780 * bump the packet length beyond the t_maxopd length.
781 * Clear the FIN bit because we cut off the tail of
784 if (len + optlen + ipoptlen > tp->t_maxopd) {
789 u_int if_hw_tsomaxsegcount;
790 u_int if_hw_tsomaxsegsize;
795 /* extract TSO information */
796 if_hw_tsomax = tp->t_tsomax;
797 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
798 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
801 * Limit a TSO burst to prevent it from
802 * overflowing or exceeding the maximum length
803 * allowed by the network interface:
805 KASSERT(ipoptlen == 0,
806 ("%s: TSO can't do IP options", __func__));
809 * Check if we should limit by maximum payload
812 if (if_hw_tsomax != 0) {
813 /* compute maximum TSO length */
814 max_len = (if_hw_tsomax - hdrlen);
817 } else if (len > max_len) {
824 * Check if we should limit by maximum segment
827 if (if_hw_tsomaxsegcount != 0 &&
828 if_hw_tsomaxsegsize != 0) {
830 mb = sbsndmbuf(&so->so_snd, off, &moff);
832 while (mb != NULL && max_len < len) {
837 * Get length of mbuf fragment
838 * and how many hardware frags,
839 * rounded up, it would use:
841 mlen = (mb->m_len - moff);
842 frags = howmany(mlen,
843 if_hw_tsomaxsegsize);
845 /* Handle special case: Zero Length Mbuf */
850 * Check if the fragment limit
851 * will be reached or exceeded:
853 if (frags >= if_hw_tsomaxsegcount) {
855 if_hw_tsomaxsegcount *
856 if_hw_tsomaxsegsize);
860 if_hw_tsomaxsegcount -= frags;
866 } else if (len > max_len) {
873 * Prevent the last segment from being
874 * fractional unless the send sockbuf can be
877 max_len = (tp->t_maxopd - optlen);
878 if ((off + len) < sbavail(&so->so_snd)) {
879 moff = len % max_len;
887 * In case there are too many small fragments
890 if (len <= max_len) {
897 * Send the FIN in a separate segment
898 * after the bulk sending is done.
899 * We don't trust the TSO implementations
900 * to clear the FIN flag on all but the
903 if (tp->t_flags & TF_NEEDFIN)
907 len = tp->t_maxopd - optlen - ipoptlen;
913 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
914 ("%s: len > IP_MAXPACKET", __func__));
916 /*#ifdef DIAGNOSTIC*/
918 if (max_linkhdr + hdrlen > MCLBYTES)
920 if (max_linkhdr + hdrlen > MHLEN)
922 panic("tcphdr too big");
926 * This KASSERT is here to catch edge cases at a well defined place.
927 * Before, those had triggered (random) panic conditions further down.
929 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
932 * Grab a header mbuf, attaching a copy of data to
933 * be transmitted, and initialize the header from
934 * the template for sends on this connection.
940 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
941 TCPSTAT_INC(tcps_sndprobe);
942 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
943 tp->t_sndrexmitpack++;
944 TCPSTAT_INC(tcps_sndrexmitpack);
945 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
947 TCPSTAT_INC(tcps_sndpack);
948 TCPSTAT_ADD(tcps_sndbyte, len);
951 if (MHLEN < hdrlen + max_linkhdr)
952 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
955 m = m_gethdr(M_NOWAIT, MT_DATA);
958 SOCKBUF_UNLOCK(&so->so_snd);
964 m->m_data += max_linkhdr;
968 * Start the m_copy functions from the closest mbuf
969 * to the offset in the socket buffer chain.
971 mb = sbsndptr(&so->so_snd, off, len, &moff);
973 if (len <= MHLEN - hdrlen - max_linkhdr) {
974 m_copydata(mb, moff, (int)len,
975 mtod(m, caddr_t) + hdrlen);
978 m->m_next = m_copy(mb, moff, (int)len);
979 if (m->m_next == NULL) {
980 SOCKBUF_UNLOCK(&so->so_snd);
989 * If we're sending everything we've got, set PUSH.
990 * (This will keep happy those implementations which only
991 * give data to the user when a buffer fills or
994 if (off + len == sbused(&so->so_snd))
996 SOCKBUF_UNLOCK(&so->so_snd);
998 SOCKBUF_UNLOCK(&so->so_snd);
999 if (tp->t_flags & TF_ACKNOW)
1000 TCPSTAT_INC(tcps_sndacks);
1001 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1002 TCPSTAT_INC(tcps_sndctrl);
1003 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1004 TCPSTAT_INC(tcps_sndurg);
1006 TCPSTAT_INC(tcps_sndwinup);
1008 m = m_gethdr(M_NOWAIT, MT_DATA);
1015 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1020 m->m_data += max_linkhdr;
1023 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1024 m->m_pkthdr.rcvif = (struct ifnet *)0;
1026 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1030 ip6 = mtod(m, struct ip6_hdr *);
1031 th = (struct tcphdr *)(ip6 + 1);
1032 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1036 ip = mtod(m, struct ip *);
1037 ipov = (struct ipovly *)ip;
1038 th = (struct tcphdr *)(ip + 1);
1039 tcpip_fillheaders(tp->t_inpcb, ip, th);
1043 * Fill in fields, remembering maximum advertised
1044 * window for use in delaying messages about window sizes.
1045 * If resending a FIN, be sure not to use a new sequence number.
1047 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1048 tp->snd_nxt == tp->snd_max)
1051 * If we are starting a connection, send ECN setup
1052 * SYN packet. If we are on a retransmit, we may
1053 * resend those bits a number of times as per
1056 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1057 if (tp->t_rxtshift >= 1) {
1058 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1059 flags |= TH_ECE|TH_CWR;
1061 flags |= TH_ECE|TH_CWR;
1064 if (tp->t_state == TCPS_ESTABLISHED &&
1065 (tp->t_flags & TF_ECN_PERMIT)) {
1067 * If the peer has ECN, mark data packets with
1068 * ECN capable transmission (ECT).
1069 * Ignore pure ack packets, retransmissions and window probes.
1071 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1072 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1075 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1078 ip->ip_tos |= IPTOS_ECN_ECT0;
1079 TCPSTAT_INC(tcps_ecn_ect0);
1083 * Reply with proper ECN notifications.
1085 if (tp->t_flags & TF_ECN_SND_CWR) {
1087 tp->t_flags &= ~TF_ECN_SND_CWR;
1089 if (tp->t_flags & TF_ECN_SND_ECE)
1094 * If we are doing retransmissions, then snd_nxt will
1095 * not reflect the first unsent octet. For ACK only
1096 * packets, we do not want the sequence number of the
1097 * retransmitted packet, we want the sequence number
1098 * of the next unsent octet. So, if there is no data
1099 * (and no SYN or FIN), use snd_max instead of snd_nxt
1100 * when filling in ti_seq. But if we are in persist
1101 * state, snd_max might reflect one byte beyond the
1102 * right edge of the window, so use snd_nxt in that
1103 * case, since we know we aren't doing a retransmission.
1104 * (retransmit and persist are mutually exclusive...)
1106 if (sack_rxmit == 0) {
1107 if (len || (flags & (TH_SYN|TH_FIN)) ||
1108 tcp_timer_active(tp, TT_PERSIST))
1109 th->th_seq = htonl(tp->snd_nxt);
1111 th->th_seq = htonl(tp->snd_max);
1113 th->th_seq = htonl(p->rxmit);
1115 tp->sackhint.sack_bytes_rexmit += len;
1117 th->th_ack = htonl(tp->rcv_nxt);
1119 bcopy(opt, th + 1, optlen);
1120 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1122 th->th_flags = flags;
1124 * Calculate receive window. Don't shrink window,
1125 * but avoid silly window syndrome.
1127 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1128 recwin < (long)tp->t_maxseg)
1130 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1131 recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1132 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1133 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1134 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1137 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1138 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1139 * case is handled in syncache.
1142 th->th_win = htons((u_short)
1143 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1145 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1148 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1149 * a 0 window. This may cause the remote transmitter to stall. This
1150 * flag tells soreceive() to disable delayed acknowledgements when
1151 * draining the buffer. This can occur if the receiver is attempting
1152 * to read more data than can be buffered prior to transmitting on
1155 if (th->th_win == 0) {
1157 tp->t_flags |= TF_RXWIN0SENT;
1159 tp->t_flags &= ~TF_RXWIN0SENT;
1160 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1161 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1162 th->th_flags |= TH_URG;
1165 * If no urgent pointer to send, then we pull
1166 * the urgent pointer to the left edge of the send window
1167 * so that it doesn't drift into the send window on sequence
1168 * number wraparound.
1170 tp->snd_up = tp->snd_una; /* drag it along */
1172 #ifdef TCP_SIGNATURE
1173 if (tp->t_flags & TF_SIGNATURE) {
1174 int sigoff = to.to_signature - opt;
1175 tcp_signature_compute(m, 0, len, optlen,
1176 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1181 * Put TCP length in extended header, and then
1182 * checksum extended header and data.
1184 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1185 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1189 * ip6_plen is not need to be filled now, and will be filled
1192 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1193 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1194 optlen + len, IPPROTO_TCP, 0);
1197 #if defined(INET6) && defined(INET)
1202 m->m_pkthdr.csum_flags = CSUM_TCP;
1203 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1204 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1206 /* IP version must be set here for ipv4/ipv6 checking later */
1207 KASSERT(ip->ip_v == IPVERSION,
1208 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1213 * Enable TSO and specify the size of the segments.
1214 * The TCP pseudo header checksum is always provided.
1217 KASSERT(len > tp->t_maxopd - optlen,
1218 ("%s: len <= tso_segsz", __func__));
1219 m->m_pkthdr.csum_flags |= CSUM_TSO;
1220 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
1224 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1225 ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
1226 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1228 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1229 ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
1230 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1233 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1234 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1240 if (so->so_options & SO_DEBUG) {
1246 save = ipov->ih_len;
1247 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1249 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1253 ipov->ih_len = save;
1255 #endif /* TCPDEBUG */
1258 * Fill in IP length and desired time to live and
1259 * send to IP level. There should be a better way
1260 * to handle ttl and tos; we could keep them in
1261 * the template, but need a way to checksum without them.
1264 * m->m_pkthdr.len should have been set before checksum calculation,
1265 * because in6_cksum() need it.
1269 struct route_in6 ro;
1271 bzero(&ro, sizeof(ro));
1273 * we separately set hoplimit for every segment, since the
1274 * user might want to change the value via setsockopt.
1275 * Also, desired default hop limit might be changed via
1276 * Neighbor Discovery.
1278 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1281 * Set the packet size here for the benefit of DTrace probes.
1282 * ip6_output() will set it properly; it's supposed to include
1283 * the option header lengths as well.
1285 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1287 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss)
1288 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1290 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1292 if (tp->t_state == TCPS_SYN_SENT)
1293 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1295 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1297 /* TODO: IPv6 IP6TOS_ECT bit on */
1298 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
1299 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1300 NULL, NULL, tp->t_inpcb);
1302 if (error == EMSGSIZE && ro.ro_rt != NULL)
1303 mtu = ro.ro_rt->rt_mtu;
1307 #if defined(INET) && defined(INET6)
1314 bzero(&ro, sizeof(ro));
1315 ip->ip_len = htons(m->m_pkthdr.len);
1317 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1318 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1321 * If we do path MTU discovery, then we set DF on every packet.
1322 * This might not be the best thing to do according to RFC3390
1323 * Section 2. However the tcp hostcache migitates the problem
1324 * so it affects only the first tcp connection with a host.
1326 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1328 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) {
1329 ip->ip_off |= htons(IP_DF);
1330 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1332 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1335 if (tp->t_state == TCPS_SYN_SENT)
1336 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1338 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1340 error = ip_output(m, tp->t_inpcb->inp_options, &ro,
1341 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1344 if (error == EMSGSIZE && ro.ro_rt != NULL)
1345 mtu = ro.ro_rt->rt_mtu;
1352 * In transmit state, time the transmission and arrange for
1353 * the retransmit. In persist state, just set snd_max.
1355 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1356 !tcp_timer_active(tp, TT_PERSIST)) {
1357 tcp_seq startseq = tp->snd_nxt;
1360 * Advance snd_nxt over sequence space of this segment.
1362 if (flags & (TH_SYN|TH_FIN)) {
1365 if (flags & TH_FIN) {
1367 tp->t_flags |= TF_SENTFIN;
1373 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1374 tp->snd_max = tp->snd_nxt;
1376 * Time this transmission if not a retransmission and
1377 * not currently timing anything.
1379 if (tp->t_rtttime == 0) {
1380 tp->t_rtttime = ticks;
1381 tp->t_rtseq = startseq;
1382 TCPSTAT_INC(tcps_segstimed);
1387 * Set retransmit timer if not currently set,
1388 * and not doing a pure ack or a keep-alive probe.
1389 * Initial value for retransmit timer is smoothed
1390 * round-trip time + 2 * round-trip time variance.
1391 * Initialize shift counter which is used for backoff
1392 * of retransmit time.
1395 if (!tcp_timer_active(tp, TT_REXMT) &&
1396 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1397 (tp->snd_nxt != tp->snd_una))) {
1398 if (tcp_timer_active(tp, TT_PERSIST)) {
1399 tcp_timer_activate(tp, TT_PERSIST, 0);
1402 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1403 } else if (len == 0 && sbavail(&so->so_snd) &&
1404 !tcp_timer_active(tp, TT_REXMT) &&
1405 !tcp_timer_active(tp, TT_PERSIST)) {
1407 * Avoid a situation where we do not set persist timer
1408 * after a zero window condition. For example:
1409 * 1) A -> B: packet with enough data to fill the window
1410 * 2) B -> A: ACK for #1 + new data (0 window
1412 * 3) A -> B: ACK for #2, 0 len packet
1414 * In this case, A will not activate the persist timer,
1415 * because it chose to send a packet. Unless tcp_output
1416 * is called for some other reason (delayed ack timer,
1417 * another input packet from B, socket syscall), A will
1418 * not send zero window probes.
1420 * So, if you send a 0-length packet, but there is data
1421 * in the socket buffer, and neither the rexmt or
1422 * persist timer is already set, then activate the
1430 * Persist case, update snd_max but since we are in
1431 * persist mode (no window) we do not update snd_nxt.
1436 if (flags & TH_FIN) {
1438 tp->t_flags |= TF_SENTFIN;
1440 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1441 tp->snd_max = tp->snd_nxt + len;
1447 * We know that the packet was lost, so back out the
1448 * sequence number advance, if any.
1450 * If the error is EPERM the packet got blocked by the
1451 * local firewall. Normally we should terminate the
1452 * connection but the blocking may have been spurious
1453 * due to a firewall reconfiguration cycle. So we treat
1454 * it like a packet loss and let the retransmit timer and
1455 * timeouts do their work over time.
1456 * XXX: It is a POLA question whether calling tcp_drop right
1457 * away would be the really correct behavior instead.
1459 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1460 !tcp_timer_active(tp, TT_PERSIST)) &&
1461 ((flags & TH_SYN) == 0) &&
1465 tp->sackhint.sack_bytes_rexmit -= len;
1466 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1467 ("sackhint bytes rtx >= 0"));
1471 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1474 tp->t_softerror = error;
1477 if (!tcp_timer_active(tp, TT_REXMT) &&
1478 !tcp_timer_active(tp, TT_PERSIST))
1479 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1480 tp->snd_cwnd = tp->t_maxseg;
1484 * For some reason the interface we used initially
1485 * to send segments changed to another or lowered
1487 * If TSO was active we either got an interface
1488 * without TSO capabilits or TSO was turned off.
1489 * If we obtained mtu from ip_output() then update
1493 tp->t_flags &= ~TF_TSO;
1495 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1503 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1504 tp->t_softerror = error;
1512 TCPSTAT_INC(tcps_sndtotal);
1515 * Data sent (as far as we can tell).
1516 * If this advertises a larger window than any other segment,
1517 * then remember the size of the advertised window.
1518 * Any pending ACK has now been sent.
1520 if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1521 tp->rcv_adv = tp->rcv_nxt + recwin;
1522 tp->last_ack_sent = tp->rcv_nxt;
1523 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1524 if (tcp_timer_active(tp, TT_DELACK))
1525 tcp_timer_activate(tp, TT_DELACK, 0);
1528 * This completely breaks TCP if newreno is turned on. What happens
1529 * is that if delayed-acks are turned on on the receiver, this code
1530 * on the transmitter effectively destroys the TCP window, forcing
1531 * it to four packets (1.5Kx4 = 6K window).
1533 if (sendalot && --maxburst)
1542 tcp_setpersist(struct tcpcb *tp)
1544 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1547 tp->t_flags &= ~TF_PREVVALID;
1548 if (tcp_timer_active(tp, TT_REXMT))
1549 panic("tcp_setpersist: retransmit pending");
1551 * Start/restart persistance timer.
1553 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1554 TCPTV_PERSMIN, TCPTV_PERSMAX);
1555 tcp_timer_activate(tp, TT_PERSIST, tt);
1556 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1561 * Insert TCP options according to the supplied parameters to the place
1562 * optp in a consistent way. Can handle unaligned destinations.
1564 * The order of the option processing is crucial for optimal packing and
1565 * alignment for the scarce option space.
1567 * The optimal order for a SYN/SYN-ACK segment is:
1568 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1569 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1571 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1572 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1573 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1574 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1575 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1578 tcp_addoptions(struct tcpopt *to, u_char *optp)
1580 u_int mask, optlen = 0;
1582 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1583 if ((to->to_flags & mask) != mask)
1585 if (optlen == TCP_MAXOLEN)
1587 switch (to->to_flags & mask) {
1589 while (optlen % 4) {
1590 optlen += TCPOLEN_NOP;
1591 *optp++ = TCPOPT_NOP;
1593 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1595 optlen += TCPOLEN_MAXSEG;
1596 *optp++ = TCPOPT_MAXSEG;
1597 *optp++ = TCPOLEN_MAXSEG;
1598 to->to_mss = htons(to->to_mss);
1599 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1600 optp += sizeof(to->to_mss);
1603 while (!optlen || optlen % 2 != 1) {
1604 optlen += TCPOLEN_NOP;
1605 *optp++ = TCPOPT_NOP;
1607 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1609 optlen += TCPOLEN_WINDOW;
1610 *optp++ = TCPOPT_WINDOW;
1611 *optp++ = TCPOLEN_WINDOW;
1612 *optp++ = to->to_wscale;
1615 while (optlen % 2) {
1616 optlen += TCPOLEN_NOP;
1617 *optp++ = TCPOPT_NOP;
1619 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1621 optlen += TCPOLEN_SACK_PERMITTED;
1622 *optp++ = TCPOPT_SACK_PERMITTED;
1623 *optp++ = TCPOLEN_SACK_PERMITTED;
1626 while (!optlen || optlen % 4 != 2) {
1627 optlen += TCPOLEN_NOP;
1628 *optp++ = TCPOPT_NOP;
1630 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1632 optlen += TCPOLEN_TIMESTAMP;
1633 *optp++ = TCPOPT_TIMESTAMP;
1634 *optp++ = TCPOLEN_TIMESTAMP;
1635 to->to_tsval = htonl(to->to_tsval);
1636 to->to_tsecr = htonl(to->to_tsecr);
1637 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1638 optp += sizeof(to->to_tsval);
1639 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1640 optp += sizeof(to->to_tsecr);
1644 int siglen = TCPOLEN_SIGNATURE - 2;
1646 while (!optlen || optlen % 4 != 2) {
1647 optlen += TCPOLEN_NOP;
1648 *optp++ = TCPOPT_NOP;
1650 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
1652 optlen += TCPOLEN_SIGNATURE;
1653 *optp++ = TCPOPT_SIGNATURE;
1654 *optp++ = TCPOLEN_SIGNATURE;
1655 to->to_signature = optp;
1663 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1666 while (!optlen || optlen % 4 != 2) {
1667 optlen += TCPOLEN_NOP;
1668 *optp++ = TCPOPT_NOP;
1670 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1672 optlen += TCPOLEN_SACKHDR;
1673 *optp++ = TCPOPT_SACK;
1674 sackblks = min(to->to_nsacks,
1675 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1676 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1677 while (sackblks--) {
1678 sack_seq = htonl(sack->start);
1679 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1680 optp += sizeof(sack_seq);
1681 sack_seq = htonl(sack->end);
1682 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1683 optp += sizeof(sack_seq);
1684 optlen += TCPOLEN_SACK;
1687 TCPSTAT_INC(tcps_sack_send_blocks);
1691 panic("%s: unknown TCP option type", __func__);
1696 /* Terminate and pad TCP options to a 4 byte boundary. */
1698 optlen += TCPOLEN_EOL;
1699 *optp++ = TCPOPT_EOL;
1702 * According to RFC 793 (STD0007):
1703 * "The content of the header beyond the End-of-Option option
1704 * must be header padding (i.e., zero)."
1705 * and later: "The padding is composed of zeros."
1707 while (optlen % 4) {
1708 optlen += TCPOLEN_PAD;
1709 *optp++ = TCPOPT_PAD;
1712 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));