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_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_fsm.h>
74 #include <netinet/tcp_seq.h>
75 #include <netinet/tcp_timer.h>
76 #include <netinet/tcp_var.h>
77 #include <netinet/tcpip.h>
79 #include <netinet/tcp_debug.h>
82 #include <netinet/tcp_offload.h>
86 #include <netipsec/ipsec.h>
89 #include <machine/in_cksum.h>
91 #include <security/mac/mac_framework.h>
93 VNET_DEFINE(int, path_mtu_discovery) = 1;
94 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
95 &VNET_NAME(path_mtu_discovery), 1,
96 "Enable Path MTU Discovery");
98 VNET_DEFINE(int, tcp_do_tso) = 1;
99 #define V_tcp_do_tso VNET(tcp_do_tso)
100 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
101 &VNET_NAME(tcp_do_tso), 0,
102 "Enable TCP Segmentation Offload");
104 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
105 #define V_tcp_sendspace VNET(tcp_sendspace)
106 SYSCTL_VNET_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_RW,
107 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
109 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
110 #define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)
111 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
112 &VNET_NAME(tcp_do_autosndbuf), 0,
113 "Enable automatic send buffer sizing");
115 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
116 #define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
117 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
118 &VNET_NAME(tcp_autosndbuf_inc), 0,
119 "Incrementor step size of automatic send buffer");
121 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
122 #define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
123 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
124 &VNET_NAME(tcp_autosndbuf_max), 0,
125 "Max size of automatic send buffer");
127 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
128 struct tcphdr *th, struct tcpopt *to,
130 static void inline cc_after_idle(struct tcpcb *tp);
133 * Wrapper for the TCP established output helper hook.
136 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
137 struct tcpopt *to, long len, int tso)
139 struct tcp_hhook_data hhook_data;
141 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
145 hhook_data.len = len;
146 hhook_data.tso = tso;
148 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
154 * CC wrapper hook functions
157 cc_after_idle(struct tcpcb *tp)
159 INP_WLOCK_ASSERT(tp->t_inpcb);
161 if (CC_ALGO(tp)->after_idle != NULL)
162 CC_ALGO(tp)->after_idle(tp->ccv);
166 * Tcp output routine: figure out what should be sent and send it.
169 tcp_output(struct tcpcb *tp)
171 struct socket *so = tp->t_inpcb->inp_socket;
172 long len, recwin, sendwin;
173 int off, flags, error = 0; /* Keep compiler happy */
175 struct ip *ip = NULL;
176 struct ipovly *ipov = NULL;
178 u_char opt[TCP_MAXOLEN];
179 unsigned ipoptlen, optlen, hdrlen;
181 unsigned ipsec_optlen = 0;
184 int sack_rxmit, sack_bytes_rxmt;
189 int maxburst = TCP_MAXBURST;
192 struct ip6_hdr *ip6 = NULL;
195 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
198 INP_WLOCK_ASSERT(tp->t_inpcb);
201 if (tp->t_flags & TF_TOE)
202 return (tcp_offload_output(tp));
206 * Determine length of data that should be transmitted,
207 * and flags that will be used.
208 * If there is some data or critical controls (SYN, RST)
209 * to send, then transmit; otherwise, investigate further.
211 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
212 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
214 tp->t_flags &= ~TF_LASTIDLE;
216 if (tp->t_flags & TF_MORETOCOME) {
217 tp->t_flags |= TF_LASTIDLE;
223 * If we've recently taken a timeout, snd_max will be greater than
224 * snd_nxt. There may be SACK information that allows us to avoid
225 * resending already delivered data. Adjust snd_nxt accordingly.
227 if ((tp->t_flags & TF_SACK_PERMIT) &&
228 SEQ_LT(tp->snd_nxt, tp->snd_max))
233 off = tp->snd_nxt - tp->snd_una;
234 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
236 flags = tcp_outflags[tp->t_state];
238 * Send any SACK-generated retransmissions. If we're explicitly trying
239 * to send out new data (when sendalot is 1), bypass this function.
240 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
241 * we're replacing a (future) new transmission with a retransmission
242 * now, and we previously incremented snd_cwnd in tcp_input().
245 * Still in sack recovery , reset rxmit flag to zero.
251 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
252 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
255 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
258 /* Do not retransmit SACK segments beyond snd_recover */
259 if (SEQ_GT(p->end, tp->snd_recover)) {
261 * (At least) part of sack hole extends beyond
262 * snd_recover. Check to see if we can rexmit data
265 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
267 * Can't rexmit any more data for this hole.
268 * That data will be rexmitted in the next
269 * sack recovery episode, when snd_recover
270 * moves past p->rxmit.
273 goto after_sack_rexmit;
275 /* Can rexmit part of the current hole */
276 len = ((long)ulmin(cwin,
277 tp->snd_recover - p->rxmit));
279 len = ((long)ulmin(cwin, p->end - p->rxmit));
280 off = p->rxmit - tp->snd_una;
281 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
286 TCPSTAT_INC(tcps_sack_rexmits);
287 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
288 min(len, tp->t_maxseg));
293 * Get standard flags, and add SYN or FIN if requested by 'hidden'
296 if (tp->t_flags & TF_NEEDFIN)
298 if (tp->t_flags & TF_NEEDSYN)
301 SOCKBUF_LOCK(&so->so_snd);
303 * If in persist timeout with window of 0, send 1 byte.
304 * Otherwise, if window is small but nonzero
305 * and timer expired, we will send what we can
306 * and go to transmit state.
308 if (tp->t_flags & TF_FORCEDATA) {
311 * If we still have some data to send, then
312 * clear the FIN bit. Usually this would
313 * happen below when it realizes that we
314 * aren't sending all the data. However,
315 * if we have exactly 1 byte of unsent data,
316 * then it won't clear the FIN bit below,
317 * and if we are in persist state, we wind
318 * up sending the packet without recording
319 * that we sent the FIN bit.
321 * We can't just blindly clear the FIN bit,
322 * because if we don't have any more data
323 * to send then the probe will be the FIN
326 if (off < so->so_snd.sb_cc)
330 tcp_timer_activate(tp, TT_PERSIST, 0);
336 * If snd_nxt == snd_max and we have transmitted a FIN, the
337 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
338 * a negative length. This can also occur when TCP opens up
339 * its congestion window while receiving additional duplicate
340 * acks after fast-retransmit because TCP will reset snd_nxt
341 * to snd_max after the fast-retransmit.
343 * In the normal retransmit-FIN-only case, however, snd_nxt will
344 * be set to snd_una, the offset will be 0, and the length may
347 * If sack_rxmit is true we are retransmitting from the scoreboard
348 * in which case len is already set.
350 if (sack_rxmit == 0) {
351 if (sack_bytes_rxmt == 0)
352 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
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(so->so_snd.sb_cc, 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) so->so_snd.sb_cc)) {
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 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
470 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
471 so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
472 so->so_snd.sb_cc < V_tcp_autosndbuf_max &&
473 sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
474 if (!sbreserve_locked(&so->so_snd,
475 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
476 V_tcp_autosndbuf_max), so, curthread))
477 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
482 * Decide if we can use TCP Segmentation Offloading (if supported by
485 * TSO may only be used if we are in a pure bulk sending state. The
486 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
487 * IP options prevent using TSO. With TSO the TCP header is the same
488 * (except for the sequence number) for all generated packets. This
489 * makes it impossible to transmit any options which vary per generated
494 * Pre-calculate here as we save another lookup into the darknesses
495 * of IPsec that way and can actually decide if TSO is ok.
497 ipsec_optlen = ipsec_hdrsiz_tcp(tp);
499 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
500 ((tp->t_flags & TF_SIGNATURE) == 0) &&
501 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
505 tp->t_inpcb->inp_options == NULL &&
506 tp->t_inpcb->in6p_options == NULL)
510 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
513 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
517 recwin = sbspace(&so->so_rcv);
520 * Sender silly window avoidance. We transmit under the following
521 * conditions when len is non-zero:
523 * - We have a full segment (or more with TSO)
524 * - This is the last buffer in a write()/send() and we are
525 * either idle or running NODELAY
526 * - we've timed out (e.g. persist timer)
527 * - we have more then 1/2 the maximum send window's worth of
528 * data (receiver may be limited the window size)
529 * - we need to retransmit
532 if (len >= tp->t_maxseg)
535 * NOTE! on localhost connections an 'ack' from the remote
536 * end may occur synchronously with the output and cause
537 * us to flush a buffer queued with moretocome. XXX
539 * note: the len + off check is almost certainly unnecessary.
541 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
542 (idle || (tp->t_flags & TF_NODELAY)) &&
543 len + off >= so->so_snd.sb_cc &&
544 (tp->t_flags & TF_NOPUSH) == 0) {
547 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
549 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
551 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
558 * Sending of standalone window updates.
560 * Window updates are important when we close our window due to a
561 * full socket buffer and are opening it again after the application
562 * reads data from it. Once the window has opened again and the
563 * remote end starts to send again the ACK clock takes over and
564 * provides the most current window information.
566 * We must avoid the silly window syndrome whereas every read
567 * from the receive buffer, no matter how small, causes a window
568 * update to be sent. We also should avoid sending a flurry of
569 * window updates when the socket buffer had queued a lot of data
570 * and the application is doing small reads.
572 * Prevent a flurry of pointless window updates by only sending
573 * an update when we can increase the advertized window by more
574 * than 1/4th of the socket buffer capacity. When the buffer is
575 * getting full or is very small be more aggressive and send an
576 * update whenever we can increase by two mss sized segments.
577 * In all other situations the ACK's to new incoming data will
578 * carry further window increases.
580 * Don't send an independent window update if a delayed
581 * ACK is pending (it will get piggy-backed on it) or the
582 * remote side already has done a half-close and won't send
583 * more data. Skip this if the connection is in T/TCP
586 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
587 !(tp->t_flags & TF_DELACK) &&
588 !TCPS_HAVERCVDFIN(tp->t_state)) {
590 * "adv" is the amount we could increase the window,
591 * taking into account that we are limited by
592 * TCP_MAXWIN << tp->rcv_scale.
597 adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale);
598 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
599 oldwin = (tp->rcv_adv - tp->rcv_nxt);
605 * If the new window size ends up being the same as the old
606 * size when it is scaled, then don't force a window update.
608 if (oldwin >> tp->rcv_scale == (adv + oldwin) >> tp->rcv_scale)
611 if (adv >= (long)(2 * tp->t_maxseg) &&
612 (adv >= (long)(so->so_rcv.sb_hiwat / 4) ||
613 recwin <= (long)(so->so_rcv.sb_hiwat / 8) ||
614 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
620 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
621 * is also a catch-all for the retransmit timer timeout case.
623 if (tp->t_flags & TF_ACKNOW)
625 if ((flags & TH_RST) ||
626 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
628 if (SEQ_GT(tp->snd_up, tp->snd_una))
631 * If our state indicates that FIN should be sent
632 * and we have not yet done so, then we need to send.
634 if (flags & TH_FIN &&
635 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
638 * In SACK, it is possible for tcp_output to fail to send a segment
639 * after the retransmission timer has been turned off. Make sure
640 * that the retransmission timer is set.
642 if ((tp->t_flags & TF_SACK_PERMIT) &&
643 SEQ_GT(tp->snd_max, tp->snd_una) &&
644 !tcp_timer_active(tp, TT_REXMT) &&
645 !tcp_timer_active(tp, TT_PERSIST)) {
646 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
650 * TCP window updates are not reliable, rather a polling protocol
651 * using ``persist'' packets is used to insure receipt of window
652 * updates. The three ``states'' for the output side are:
653 * idle not doing retransmits or persists
654 * persisting to move a small or zero window
655 * (re)transmitting and thereby not persisting
657 * tcp_timer_active(tp, TT_PERSIST)
658 * is true when we are in persist state.
659 * (tp->t_flags & TF_FORCEDATA)
660 * is set when we are called to send a persist packet.
661 * tcp_timer_active(tp, TT_REXMT)
662 * is set when we are retransmitting
663 * The output side is idle when both timers are zero.
665 * If send window is too small, there is data to transmit, and no
666 * retransmit or persist is pending, then go to persist state.
667 * If nothing happens soon, send when timer expires:
668 * if window is nonzero, transmit what we can,
669 * otherwise force out a byte.
671 if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) &&
672 !tcp_timer_active(tp, TT_PERSIST)) {
678 * No reason to send a segment, just return.
681 SOCKBUF_UNLOCK(&so->so_snd);
685 SOCKBUF_LOCK_ASSERT(&so->so_snd);
687 if (len >= tp->t_maxseg)
688 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
690 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
693 * Before ESTABLISHED, force sending of initial options
694 * unless TCP set not to do any options.
695 * NOTE: we assume that the IP/TCP header plus TCP options
696 * always fit in a single mbuf, leaving room for a maximum
698 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
703 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
706 hdrlen = sizeof (struct tcpiphdr);
709 * Compute options for segment.
710 * We only have to care about SYN and established connection
711 * segments. Options for SYN-ACK segments are handled in TCP
714 if ((tp->t_flags & TF_NOOPT) == 0) {
716 /* Maximum segment size. */
717 if (flags & TH_SYN) {
718 tp->snd_nxt = tp->iss;
719 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
720 to.to_flags |= TOF_MSS;
722 /* Window scaling. */
723 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
724 to.to_wscale = tp->request_r_scale;
725 to.to_flags |= TOF_SCALE;
728 if ((tp->t_flags & TF_RCVD_TSTMP) ||
729 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
730 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
731 to.to_tsecr = tp->ts_recent;
732 to.to_flags |= TOF_TS;
733 /* Set receive buffer autosizing timestamp. */
734 if (tp->rfbuf_ts == 0 &&
735 (so->so_rcv.sb_flags & SB_AUTOSIZE))
736 tp->rfbuf_ts = tcp_ts_getticks();
738 /* Selective ACK's. */
739 if (tp->t_flags & TF_SACK_PERMIT) {
741 to.to_flags |= TOF_SACKPERM;
742 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
743 (tp->t_flags & TF_SACK_PERMIT) &&
744 tp->rcv_numsacks > 0) {
745 to.to_flags |= TOF_SACK;
746 to.to_nsacks = tp->rcv_numsacks;
747 to.to_sacks = (u_char *)tp->sackblks;
751 /* TCP-MD5 (RFC2385). */
752 if (tp->t_flags & TF_SIGNATURE)
753 to.to_flags |= TOF_SIGNATURE;
754 #endif /* TCP_SIGNATURE */
756 /* Processing the options. */
757 hdrlen += optlen = tcp_addoptions(&to, opt);
762 ipoptlen = ip6_optlen(tp->t_inpcb);
765 if (tp->t_inpcb->inp_options)
766 ipoptlen = tp->t_inpcb->inp_options->m_len -
767 offsetof(struct ipoption, ipopt_list);
771 ipoptlen += ipsec_optlen;
775 * Adjust data length if insertion of options will
776 * bump the packet length beyond the t_maxopd length.
777 * Clear the FIN bit because we cut off the tail of
780 if (len + optlen + ipoptlen > tp->t_maxopd) {
785 u_int if_hw_tsomaxsegcount;
786 u_int if_hw_tsomaxsegsize;
791 /* extract TSO information */
792 if_hw_tsomax = tp->t_tsomax;
793 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
794 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
797 * Limit a TSO burst to prevent it from
798 * overflowing or exceeding the maximum length
799 * allowed by the network interface:
801 KASSERT(ipoptlen == 0,
802 ("%s: TSO can't do IP options", __func__));
805 * Check if we should limit by maximum payload
808 if (if_hw_tsomax != 0) {
809 /* compute maximum TSO length */
810 max_len = (if_hw_tsomax - hdrlen);
813 } else if (len > max_len) {
820 * Check if we should limit by maximum segment
823 if (if_hw_tsomaxsegcount != 0 &&
824 if_hw_tsomaxsegsize != 0) {
826 mb = sbsndmbuf(&so->so_snd, off, &moff);
828 while (mb != NULL && max_len < len) {
833 * Get length of mbuf fragment
834 * and how many hardware frags,
835 * rounded up, it would use:
837 mlen = (mb->m_len - moff);
838 frags = howmany(mlen,
839 if_hw_tsomaxsegsize);
841 /* Handle special case: Zero Length Mbuf */
846 * Check if the fragment limit
847 * will be reached or exceeded:
849 if (frags >= if_hw_tsomaxsegcount) {
851 if_hw_tsomaxsegcount *
852 if_hw_tsomaxsegsize);
856 if_hw_tsomaxsegcount -= frags;
862 } else if (len > max_len) {
869 * Prevent the last segment from being
870 * fractional unless the send sockbuf can be
873 max_len = (tp->t_maxopd - optlen);
874 if ((off + len) < so->so_snd.sb_cc) {
875 moff = len % max_len;
883 * In case there are too many small fragments
886 if (len <= max_len) {
893 * Send the FIN in a separate segment
894 * after the bulk sending is done.
895 * We don't trust the TSO implementations
896 * to clear the FIN flag on all but the
899 if (tp->t_flags & TF_NEEDFIN)
903 len = tp->t_maxopd - optlen - ipoptlen;
909 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
910 ("%s: len > IP_MAXPACKET", __func__));
912 /*#ifdef DIAGNOSTIC*/
914 if (max_linkhdr + hdrlen > MCLBYTES)
916 if (max_linkhdr + hdrlen > MHLEN)
918 panic("tcphdr too big");
922 * This KASSERT is here to catch edge cases at a well defined place.
923 * Before, those had triggered (random) panic conditions further down.
925 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
928 * Grab a header mbuf, attaching a copy of data to
929 * be transmitted, and initialize the header from
930 * the template for sends on this connection.
936 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
937 TCPSTAT_INC(tcps_sndprobe);
938 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
939 tp->t_sndrexmitpack++;
940 TCPSTAT_INC(tcps_sndrexmitpack);
941 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
943 TCPSTAT_INC(tcps_sndpack);
944 TCPSTAT_ADD(tcps_sndbyte, len);
947 if (MHLEN < hdrlen + max_linkhdr)
948 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
951 m = m_gethdr(M_NOWAIT, MT_DATA);
954 SOCKBUF_UNLOCK(&so->so_snd);
960 m->m_data += max_linkhdr;
964 * Start the m_copy functions from the closest mbuf
965 * to the offset in the socket buffer chain.
967 mb = sbsndptr(&so->so_snd, off, len, &moff);
969 if (len <= MHLEN - hdrlen - max_linkhdr) {
970 m_copydata(mb, moff, (int)len,
971 mtod(m, caddr_t) + hdrlen);
974 m->m_next = m_copy(mb, moff, (int)len);
975 if (m->m_next == NULL) {
976 SOCKBUF_UNLOCK(&so->so_snd);
985 * If we're sending everything we've got, set PUSH.
986 * (This will keep happy those implementations which only
987 * give data to the user when a buffer fills or
990 if (off + len == so->so_snd.sb_cc)
992 SOCKBUF_UNLOCK(&so->so_snd);
994 SOCKBUF_UNLOCK(&so->so_snd);
995 if (tp->t_flags & TF_ACKNOW)
996 TCPSTAT_INC(tcps_sndacks);
997 else if (flags & (TH_SYN|TH_FIN|TH_RST))
998 TCPSTAT_INC(tcps_sndctrl);
999 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1000 TCPSTAT_INC(tcps_sndurg);
1002 TCPSTAT_INC(tcps_sndwinup);
1004 m = m_gethdr(M_NOWAIT, MT_DATA);
1011 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1013 MH_ALIGN(m, hdrlen);
1016 m->m_data += max_linkhdr;
1019 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1020 m->m_pkthdr.rcvif = (struct ifnet *)0;
1022 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1026 ip6 = mtod(m, struct ip6_hdr *);
1027 th = (struct tcphdr *)(ip6 + 1);
1028 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1032 ip = mtod(m, struct ip *);
1033 ipov = (struct ipovly *)ip;
1034 th = (struct tcphdr *)(ip + 1);
1035 tcpip_fillheaders(tp->t_inpcb, ip, th);
1039 * Fill in fields, remembering maximum advertised
1040 * window for use in delaying messages about window sizes.
1041 * If resending a FIN, be sure not to use a new sequence number.
1043 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1044 tp->snd_nxt == tp->snd_max)
1047 * If we are starting a connection, send ECN setup
1048 * SYN packet. If we are on a retransmit, we may
1049 * resend those bits a number of times as per
1052 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
1053 if (tp->t_rxtshift >= 1) {
1054 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1055 flags |= TH_ECE|TH_CWR;
1057 flags |= TH_ECE|TH_CWR;
1060 if (tp->t_state == TCPS_ESTABLISHED &&
1061 (tp->t_flags & TF_ECN_PERMIT)) {
1063 * If the peer has ECN, mark data packets with
1064 * ECN capable transmission (ECT).
1065 * Ignore pure ack packets, retransmissions and window probes.
1067 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1068 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1071 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1074 ip->ip_tos |= IPTOS_ECN_ECT0;
1075 TCPSTAT_INC(tcps_ecn_ect0);
1079 * Reply with proper ECN notifications.
1081 if (tp->t_flags & TF_ECN_SND_CWR) {
1083 tp->t_flags &= ~TF_ECN_SND_CWR;
1085 if (tp->t_flags & TF_ECN_SND_ECE)
1090 * If we are doing retransmissions, then snd_nxt will
1091 * not reflect the first unsent octet. For ACK only
1092 * packets, we do not want the sequence number of the
1093 * retransmitted packet, we want the sequence number
1094 * of the next unsent octet. So, if there is no data
1095 * (and no SYN or FIN), use snd_max instead of snd_nxt
1096 * when filling in ti_seq. But if we are in persist
1097 * state, snd_max might reflect one byte beyond the
1098 * right edge of the window, so use snd_nxt in that
1099 * case, since we know we aren't doing a retransmission.
1100 * (retransmit and persist are mutually exclusive...)
1102 if (sack_rxmit == 0) {
1103 if (len || (flags & (TH_SYN|TH_FIN)) ||
1104 tcp_timer_active(tp, TT_PERSIST))
1105 th->th_seq = htonl(tp->snd_nxt);
1107 th->th_seq = htonl(tp->snd_max);
1109 th->th_seq = htonl(p->rxmit);
1111 tp->sackhint.sack_bytes_rexmit += len;
1113 th->th_ack = htonl(tp->rcv_nxt);
1115 bcopy(opt, th + 1, optlen);
1116 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1118 th->th_flags = flags;
1120 * Calculate receive window. Don't shrink window,
1121 * but avoid silly window syndrome.
1123 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1124 recwin < (long)tp->t_maxseg)
1126 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1127 recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1128 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1129 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1130 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1133 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1134 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1135 * case is handled in syncache.
1138 th->th_win = htons((u_short)
1139 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1141 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1144 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1145 * a 0 window. This may cause the remote transmitter to stall. This
1146 * flag tells soreceive() to disable delayed acknowledgements when
1147 * draining the buffer. This can occur if the receiver is attempting
1148 * to read more data than can be buffered prior to transmitting on
1151 if (th->th_win == 0) {
1153 tp->t_flags |= TF_RXWIN0SENT;
1155 tp->t_flags &= ~TF_RXWIN0SENT;
1156 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1157 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1158 th->th_flags |= TH_URG;
1161 * If no urgent pointer to send, then we pull
1162 * the urgent pointer to the left edge of the send window
1163 * so that it doesn't drift into the send window on sequence
1164 * number wraparound.
1166 tp->snd_up = tp->snd_una; /* drag it along */
1168 #ifdef TCP_SIGNATURE
1169 if (tp->t_flags & TF_SIGNATURE) {
1170 int sigoff = to.to_signature - opt;
1171 tcp_signature_compute(m, 0, len, optlen,
1172 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1177 * Put TCP length in extended header, and then
1178 * checksum extended header and data.
1180 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1181 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1185 * ip6_plen is not need to be filled now, and will be filled
1188 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1189 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1190 optlen + len, IPPROTO_TCP, 0);
1193 #if defined(INET6) && defined(INET)
1198 m->m_pkthdr.csum_flags = CSUM_TCP;
1199 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1200 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1202 /* IP version must be set here for ipv4/ipv6 checking later */
1203 KASSERT(ip->ip_v == IPVERSION,
1204 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1209 * Enable TSO and specify the size of the segments.
1210 * The TCP pseudo header checksum is always provided.
1211 * XXX: Fixme: This is currently not the case for IPv6.
1214 KASSERT(len > tp->t_maxopd - optlen,
1215 ("%s: len <= tso_segsz", __func__));
1216 m->m_pkthdr.csum_flags |= CSUM_TSO;
1217 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
1221 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1222 ("%s: mbuf chain shorter than expected: %ld + %u + %u - %u != %u",
1223 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1225 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1226 ("%s: mbuf chain shorter than expected: %ld + %u + %u != %u",
1227 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1230 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1231 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1237 if (so->so_options & SO_DEBUG) {
1243 save = ipov->ih_len;
1244 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1246 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1250 ipov->ih_len = save;
1252 #endif /* TCPDEBUG */
1255 * Fill in IP length and desired time to live and
1256 * send to IP level. There should be a better way
1257 * to handle ttl and tos; we could keep them in
1258 * the template, but need a way to checksum without them.
1261 * m->m_pkthdr.len should have been set before cksum calcuration,
1262 * because in6_cksum() need it.
1266 struct route_in6 ro;
1268 bzero(&ro, sizeof(ro));
1270 * we separately set hoplimit for every segment, since the
1271 * user might want to change the value via setsockopt.
1272 * Also, desired default hop limit might be changed via
1273 * Neighbor Discovery.
1275 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1278 * Set the packet size here for the benefit of DTrace probes.
1279 * ip6_output() will set it properly; it's supposed to include
1280 * the option header lengths as well.
1282 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1284 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss)
1285 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1287 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1289 if (tp->t_state == TCPS_SYN_SENT)
1290 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1292 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1294 /* TODO: IPv6 IP6TOS_ECT bit on */
1295 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
1296 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1297 NULL, NULL, tp->t_inpcb);
1299 if (error == EMSGSIZE && ro.ro_rt != NULL)
1300 mtu = ro.ro_rt->rt_mtu;
1304 #if defined(INET) && defined(INET6)
1311 bzero(&ro, sizeof(ro));
1312 ip->ip_len = htons(m->m_pkthdr.len);
1314 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1315 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1318 * If we do path MTU discovery, then we set DF on every packet.
1319 * This might not be the best thing to do according to RFC3390
1320 * Section 2. However the tcp hostcache migitates the problem
1321 * so it affects only the first tcp connection with a host.
1323 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1325 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss) {
1326 ip->ip_off |= htons(IP_DF);
1327 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1329 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1332 if (tp->t_state == TCPS_SYN_SENT)
1333 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1335 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1337 error = ip_output(m, tp->t_inpcb->inp_options, &ro,
1338 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1341 if (error == EMSGSIZE && ro.ro_rt != NULL)
1342 mtu = ro.ro_rt->rt_mtu;
1349 * In transmit state, time the transmission and arrange for
1350 * the retransmit. In persist state, just set snd_max.
1352 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1353 !tcp_timer_active(tp, TT_PERSIST)) {
1354 tcp_seq startseq = tp->snd_nxt;
1357 * Advance snd_nxt over sequence space of this segment.
1359 if (flags & (TH_SYN|TH_FIN)) {
1362 if (flags & TH_FIN) {
1364 tp->t_flags |= TF_SENTFIN;
1370 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1371 tp->snd_max = tp->snd_nxt;
1373 * Time this transmission if not a retransmission and
1374 * not currently timing anything.
1376 if (tp->t_rtttime == 0) {
1377 tp->t_rtttime = ticks;
1378 tp->t_rtseq = startseq;
1379 TCPSTAT_INC(tcps_segstimed);
1384 * Set retransmit timer if not currently set,
1385 * and not doing a pure ack or a keep-alive probe.
1386 * Initial value for retransmit timer is smoothed
1387 * round-trip time + 2 * round-trip time variance.
1388 * Initialize shift counter which is used for backoff
1389 * of retransmit time.
1392 if (!tcp_timer_active(tp, TT_REXMT) &&
1393 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1394 (tp->snd_nxt != tp->snd_una))) {
1395 if (tcp_timer_active(tp, TT_PERSIST)) {
1396 tcp_timer_activate(tp, TT_PERSIST, 0);
1399 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1400 } else if (len == 0 && so->so_snd.sb_cc &&
1401 !tcp_timer_active(tp, TT_REXMT) &&
1402 !tcp_timer_active(tp, TT_PERSIST)) {
1404 * Avoid a situation where we do not set persist timer
1405 * after a zero window condition. For example:
1406 * 1) A -> B: packet with enough data to fill the window
1407 * 2) B -> A: ACK for #1 + new data (0 window
1409 * 3) A -> B: ACK for #2, 0 len packet
1411 * In this case, A will not activate the persist timer,
1412 * because it chose to send a packet. Unless tcp_output
1413 * is called for some other reason (delayed ack timer,
1414 * another input packet from B, socket syscall), A will
1415 * not send zero window probes.
1417 * So, if you send a 0-length packet, but there is data
1418 * in the socket buffer, and neither the rexmt or
1419 * persist timer is already set, then activate the
1427 * Persist case, update snd_max but since we are in
1428 * persist mode (no window) we do not update snd_nxt.
1433 if (flags & TH_FIN) {
1435 tp->t_flags |= TF_SENTFIN;
1437 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1438 tp->snd_max = tp->snd_nxt + len;
1444 * We know that the packet was lost, so back out the
1445 * sequence number advance, if any.
1447 * If the error is EPERM the packet got blocked by the
1448 * local firewall. Normally we should terminate the
1449 * connection but the blocking may have been spurious
1450 * due to a firewall reconfiguration cycle. So we treat
1451 * it like a packet loss and let the retransmit timer and
1452 * timeouts do their work over time.
1453 * XXX: It is a POLA question whether calling tcp_drop right
1454 * away would be the really correct behavior instead.
1456 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1457 !tcp_timer_active(tp, TT_PERSIST)) &&
1458 ((flags & TH_SYN) == 0) &&
1462 tp->sackhint.sack_bytes_rexmit -= len;
1463 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1464 ("sackhint bytes rtx >= 0"));
1468 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1471 tp->t_softerror = error;
1474 if (!tcp_timer_active(tp, TT_REXMT) &&
1475 !tcp_timer_active(tp, TT_PERSIST))
1476 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1477 tp->snd_cwnd = tp->t_maxseg;
1481 * For some reason the interface we used initially
1482 * to send segments changed to another or lowered
1484 * If TSO was active we either got an interface
1485 * without TSO capabilits or TSO was turned off.
1486 * If we obtained mtu from ip_output() then update
1490 tp->t_flags &= ~TF_TSO;
1492 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1500 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1501 tp->t_softerror = error;
1509 TCPSTAT_INC(tcps_sndtotal);
1512 * Data sent (as far as we can tell).
1513 * If this advertises a larger window than any other segment,
1514 * then remember the size of the advertised window.
1515 * Any pending ACK has now been sent.
1517 if (recwin >= 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1518 tp->rcv_adv = tp->rcv_nxt + recwin;
1519 tp->last_ack_sent = tp->rcv_nxt;
1520 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1521 if (tcp_timer_active(tp, TT_DELACK))
1522 tcp_timer_activate(tp, TT_DELACK, 0);
1525 * This completely breaks TCP if newreno is turned on. What happens
1526 * is that if delayed-acks are turned on on the receiver, this code
1527 * on the transmitter effectively destroys the TCP window, forcing
1528 * it to four packets (1.5Kx4 = 6K window).
1530 if (sendalot && --maxburst)
1539 tcp_setpersist(struct tcpcb *tp)
1541 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1544 tp->t_flags &= ~TF_PREVVALID;
1545 if (tcp_timer_active(tp, TT_REXMT))
1546 panic("tcp_setpersist: retransmit pending");
1548 * Start/restart persistance timer.
1550 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1551 TCPTV_PERSMIN, TCPTV_PERSMAX);
1552 tcp_timer_activate(tp, TT_PERSIST, tt);
1553 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1558 * Insert TCP options according to the supplied parameters to the place
1559 * optp in a consistent way. Can handle unaligned destinations.
1561 * The order of the option processing is crucial for optimal packing and
1562 * alignment for the scarce option space.
1564 * The optimal order for a SYN/SYN-ACK segment is:
1565 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1566 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1568 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1569 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1570 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1571 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1572 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1575 tcp_addoptions(struct tcpopt *to, u_char *optp)
1577 u_int mask, optlen = 0;
1579 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1580 if ((to->to_flags & mask) != mask)
1582 if (optlen == TCP_MAXOLEN)
1584 switch (to->to_flags & mask) {
1586 while (optlen % 4) {
1587 optlen += TCPOLEN_NOP;
1588 *optp++ = TCPOPT_NOP;
1590 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1592 optlen += TCPOLEN_MAXSEG;
1593 *optp++ = TCPOPT_MAXSEG;
1594 *optp++ = TCPOLEN_MAXSEG;
1595 to->to_mss = htons(to->to_mss);
1596 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1597 optp += sizeof(to->to_mss);
1600 while (!optlen || optlen % 2 != 1) {
1601 optlen += TCPOLEN_NOP;
1602 *optp++ = TCPOPT_NOP;
1604 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1606 optlen += TCPOLEN_WINDOW;
1607 *optp++ = TCPOPT_WINDOW;
1608 *optp++ = TCPOLEN_WINDOW;
1609 *optp++ = to->to_wscale;
1612 while (optlen % 2) {
1613 optlen += TCPOLEN_NOP;
1614 *optp++ = TCPOPT_NOP;
1616 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1618 optlen += TCPOLEN_SACK_PERMITTED;
1619 *optp++ = TCPOPT_SACK_PERMITTED;
1620 *optp++ = TCPOLEN_SACK_PERMITTED;
1623 while (!optlen || optlen % 4 != 2) {
1624 optlen += TCPOLEN_NOP;
1625 *optp++ = TCPOPT_NOP;
1627 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1629 optlen += TCPOLEN_TIMESTAMP;
1630 *optp++ = TCPOPT_TIMESTAMP;
1631 *optp++ = TCPOLEN_TIMESTAMP;
1632 to->to_tsval = htonl(to->to_tsval);
1633 to->to_tsecr = htonl(to->to_tsecr);
1634 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1635 optp += sizeof(to->to_tsval);
1636 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1637 optp += sizeof(to->to_tsecr);
1641 int siglen = TCPOLEN_SIGNATURE - 2;
1643 while (!optlen || optlen % 4 != 2) {
1644 optlen += TCPOLEN_NOP;
1645 *optp++ = TCPOPT_NOP;
1647 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
1649 optlen += TCPOLEN_SIGNATURE;
1650 *optp++ = TCPOPT_SIGNATURE;
1651 *optp++ = TCPOLEN_SIGNATURE;
1652 to->to_signature = optp;
1660 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1663 while (!optlen || optlen % 4 != 2) {
1664 optlen += TCPOLEN_NOP;
1665 *optp++ = TCPOPT_NOP;
1667 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1669 optlen += TCPOLEN_SACKHDR;
1670 *optp++ = TCPOPT_SACK;
1671 sackblks = min(to->to_nsacks,
1672 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1673 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1674 while (sackblks--) {
1675 sack_seq = htonl(sack->start);
1676 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1677 optp += sizeof(sack_seq);
1678 sack_seq = htonl(sack->end);
1679 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1680 optp += sizeof(sack_seq);
1681 optlen += TCPOLEN_SACK;
1684 TCPSTAT_INC(tcps_sack_send_blocks);
1688 panic("%s: unknown TCP option type", __func__);
1693 /* Terminate and pad TCP options to a 4 byte boundary. */
1695 optlen += TCPOLEN_EOL;
1696 *optp++ = TCPOPT_EOL;
1699 * According to RFC 793 (STD0007):
1700 * "The content of the header beyond the End-of-Option option
1701 * must be header padding (i.e., zero)."
1702 * and later: "The padding is composed of zeros."
1704 while (optlen % 4) {
1705 optlen += TCPOLEN_PAD;
1706 *optp++ = TCPOPT_PAD;
1709 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));