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>
49 #include <sys/socket.h>
50 #include <sys/socketvar.h>
51 #include <sys/sysctl.h>
54 #include <net/route.h>
57 #include <netinet/cc.h>
58 #include <netinet/in.h>
59 #include <netinet/in_systm.h>
60 #include <netinet/ip.h>
61 #include <netinet/in_pcb.h>
62 #include <netinet/ip_var.h>
63 #include <netinet/ip_options.h>
65 #include <netinet6/in6_pcb.h>
66 #include <netinet/ip6.h>
67 #include <netinet6/ip6_var.h>
70 #include <netinet/tcp_fsm.h>
71 #include <netinet/tcp_seq.h>
72 #include <netinet/tcp_timer.h>
73 #include <netinet/tcp_var.h>
74 #include <netinet/tcpip.h>
76 #include <netinet/tcp_debug.h>
80 #include <netipsec/ipsec.h>
83 #include <machine/in_cksum.h>
85 #include <security/mac/mac_framework.h>
88 extern struct mbuf *m_copypack();
91 VNET_DEFINE(int, path_mtu_discovery) = 1;
92 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
93 &VNET_NAME(path_mtu_discovery), 1,
94 "Enable Path MTU Discovery");
96 VNET_DEFINE(int, ss_fltsz) = 1;
97 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, slowstart_flightsize, CTLFLAG_RW,
98 &VNET_NAME(ss_fltsz), 1,
99 "Slow start flight size");
101 VNET_DEFINE(int, ss_fltsz_local) = 4;
102 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, local_slowstart_flightsize,
103 CTLFLAG_RW, &VNET_NAME(ss_fltsz_local), 1,
104 "Slow start flight size for local networks");
106 VNET_DEFINE(int, tcp_do_tso) = 1;
107 #define V_tcp_do_tso VNET(tcp_do_tso)
108 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
109 &VNET_NAME(tcp_do_tso), 0,
110 "Enable TCP Segmentation Offload");
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) = 256*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");
130 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
131 struct tcphdr *th, struct tcpopt *to,
133 static void inline cc_after_idle(struct tcpcb *tp);
136 * Wrapper for the TCP established ouput helper hook.
139 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
140 struct tcpopt *to, long len, int tso)
142 struct tcp_hhook_data hhook_data;
144 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
148 hhook_data.len = len;
149 hhook_data.tso = tso;
151 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
157 * CC wrapper hook functions
160 cc_after_idle(struct tcpcb *tp)
162 INP_WLOCK_ASSERT(tp->t_inpcb);
164 if (CC_ALGO(tp)->after_idle != NULL)
165 CC_ALGO(tp)->after_idle(tp->ccv);
169 * Tcp output routine: figure out what should be sent and send it.
172 tcp_output(struct tcpcb *tp)
174 struct socket *so = tp->t_inpcb->inp_socket;
175 long len, recwin, sendwin;
176 int off, flags, error;
178 struct ip *ip = NULL;
179 struct ipovly *ipov = NULL;
181 u_char opt[TCP_MAXOLEN];
182 unsigned ipoptlen, optlen, hdrlen;
184 unsigned ipsec_optlen = 0;
187 int sack_rxmit, sack_bytes_rxmt;
192 int maxburst = TCP_MAXBURST;
195 struct ip6_hdr *ip6 = NULL;
198 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
201 INP_WLOCK_ASSERT(tp->t_inpcb);
204 * Determine length of data that should be transmitted,
205 * and flags that will be used.
206 * If there is some data or critical controls (SYN, RST)
207 * to send, then transmit; otherwise, investigate further.
209 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
210 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
212 tp->t_flags &= ~TF_LASTIDLE;
214 if (tp->t_flags & TF_MORETOCOME) {
215 tp->t_flags |= TF_LASTIDLE;
221 * If we've recently taken a timeout, snd_max will be greater than
222 * snd_nxt. There may be SACK information that allows us to avoid
223 * resending already delivered data. Adjust snd_nxt accordingly.
225 if ((tp->t_flags & TF_SACK_PERMIT) &&
226 SEQ_LT(tp->snd_nxt, tp->snd_max))
230 off = tp->snd_nxt - tp->snd_una;
231 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
233 flags = tcp_outflags[tp->t_state];
235 * Send any SACK-generated retransmissions. If we're explicitly trying
236 * to send out new data (when sendalot is 1), bypass this function.
237 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
238 * we're replacing a (future) new transmission with a retransmission
239 * now, and we previously incremented snd_cwnd in tcp_input().
242 * Still in sack recovery , reset rxmit flag to zero.
248 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
249 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
252 cwin = min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt;
255 /* Do not retransmit SACK segments beyond snd_recover */
256 if (SEQ_GT(p->end, tp->snd_recover)) {
258 * (At least) part of sack hole extends beyond
259 * snd_recover. Check to see if we can rexmit data
262 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
264 * Can't rexmit any more data for this hole.
265 * That data will be rexmitted in the next
266 * sack recovery episode, when snd_recover
267 * moves past p->rxmit.
270 goto after_sack_rexmit;
272 /* Can rexmit part of the current hole */
273 len = ((long)ulmin(cwin,
274 tp->snd_recover - p->rxmit));
276 len = ((long)ulmin(cwin, p->end - p->rxmit));
277 off = p->rxmit - tp->snd_una;
278 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
283 TCPSTAT_INC(tcps_sack_rexmits);
284 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
285 min(len, tp->t_maxseg));
290 * Get standard flags, and add SYN or FIN if requested by 'hidden'
293 if (tp->t_flags & TF_NEEDFIN)
295 if (tp->t_flags & TF_NEEDSYN)
298 SOCKBUF_LOCK(&so->so_snd);
300 * If in persist timeout with window of 0, send 1 byte.
301 * Otherwise, if window is small but nonzero
302 * and timer expired, we will send what we can
303 * and go to transmit state.
305 if (tp->t_flags & TF_FORCEDATA) {
308 * If we still have some data to send, then
309 * clear the FIN bit. Usually this would
310 * happen below when it realizes that we
311 * aren't sending all the data. However,
312 * if we have exactly 1 byte of unsent data,
313 * then it won't clear the FIN bit below,
314 * and if we are in persist state, we wind
315 * up sending the packet without recording
316 * that we sent the FIN bit.
318 * We can't just blindly clear the FIN bit,
319 * because if we don't have any more data
320 * to send then the probe will be the FIN
323 if (off < so->so_snd.sb_cc)
327 tcp_timer_activate(tp, TT_PERSIST, 0);
333 * If snd_nxt == snd_max and we have transmitted a FIN, the
334 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
335 * a negative length. This can also occur when TCP opens up
336 * its congestion window while receiving additional duplicate
337 * acks after fast-retransmit because TCP will reset snd_nxt
338 * to snd_max after the fast-retransmit.
340 * In the normal retransmit-FIN-only case, however, snd_nxt will
341 * be set to snd_una, the offset will be 0, and the length may
344 * If sack_rxmit is true we are retransmitting from the scoreboard
345 * in which case len is already set.
347 if (sack_rxmit == 0) {
348 if (sack_bytes_rxmt == 0)
349 len = ((long)ulmin(so->so_snd.sb_cc, sendwin) - off);
354 * We are inside of a SACK recovery episode and are
355 * sending new data, having retransmitted all the
356 * data possible in the scoreboard.
358 len = ((long)ulmin(so->so_snd.sb_cc, tp->snd_wnd)
361 * Don't remove this (len > 0) check !
362 * We explicitly check for len > 0 here (although it
363 * isn't really necessary), to work around a gcc
364 * optimization issue - to force gcc to compute
365 * len above. Without this check, the computation
366 * of len is bungled by the optimizer.
369 cwin = tp->snd_cwnd -
370 (tp->snd_nxt - tp->sack_newdata) -
374 len = lmin(len, cwin);
380 * Lop off SYN bit if it has already been sent. However, if this
381 * is SYN-SENT state and if segment contains data and if we don't
382 * know that foreign host supports TAO, suppress sending segment.
384 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
385 if (tp->t_state != TCPS_SYN_RECEIVED)
391 * Be careful not to send data and/or FIN on SYN segments.
392 * This measure is needed to prevent interoperability problems
393 * with not fully conformant TCP implementations.
395 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
402 * If FIN has been sent but not acked,
403 * but we haven't been called to retransmit,
404 * len will be < 0. Otherwise, window shrank
405 * after we sent into it. If window shrank to 0,
406 * cancel pending retransmit, pull snd_nxt back
407 * to (closed) window, and set the persist timer
408 * if it isn't already going. If the window didn't
409 * close completely, just wait for an ACK.
413 tcp_timer_activate(tp, TT_REXMT, 0);
415 tp->snd_nxt = tp->snd_una;
416 if (!tcp_timer_active(tp, TT_PERSIST))
421 /* len will be >= 0 after this point. */
422 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
425 * Automatic sizing of send socket buffer. Often the send buffer
426 * size is not optimally adjusted to the actual network conditions
427 * at hand (delay bandwidth product). Setting the buffer size too
428 * small limits throughput on links with high bandwidth and high
429 * delay (eg. trans-continental/oceanic links). Setting the
430 * buffer size too big consumes too much real kernel memory,
431 * especially with many connections on busy servers.
433 * The criteria to step up the send buffer one notch are:
434 * 1. receive window of remote host is larger than send buffer
435 * (with a fudge factor of 5/4th);
436 * 2. send buffer is filled to 7/8th with data (so we actually
437 * have data to make use of it);
438 * 3. send buffer fill has not hit maximal automatic size;
439 * 4. our send window (slow start and cogestion controlled) is
440 * larger than sent but unacknowledged data in send buffer.
442 * The remote host receive window scaling factor may limit the
443 * growing of the send buffer before it reaches its allowed
446 * It scales directly with slow start or congestion window
447 * and does at most one step per received ACK. This fast
448 * scaling has the drawback of growing the send buffer beyond
449 * what is strictly necessary to make full use of a given
450 * delay*bandwith product. However testing has shown this not
451 * to be much of an problem. At worst we are trading wasting
452 * of available bandwith (the non-use of it) for wasting some
453 * socket buffer memory.
455 * TODO: Shrink send buffer during idle periods together
456 * with congestion window. Requires another timer. Has to
457 * wait for upcoming tcp timer rewrite.
459 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
460 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
461 so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
462 so->so_snd.sb_cc < V_tcp_autosndbuf_max &&
463 sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
464 if (!sbreserve_locked(&so->so_snd,
465 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
466 V_tcp_autosndbuf_max), so, curthread))
467 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
472 * Decide if we can use TCP Segmentation Offloading (if supported by
475 * TSO may only be used if we are in a pure bulk sending state. The
476 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
477 * IP options prevent using TSO. With TSO the TCP header is the same
478 * (except for the sequence number) for all generated packets. This
479 * makes it impossible to transmit any options which vary per generated
484 * Pre-calculate here as we save another lookup into the darknesses
485 * of IPsec that way and can actually decide if TSO is ok.
487 ipsec_optlen = ipsec_hdrsiz_tcp(tp);
489 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
490 ((tp->t_flags & TF_SIGNATURE) == 0) &&
491 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
495 tp->t_inpcb->inp_options == NULL &&
496 tp->t_inpcb->in6p_options == NULL)
500 if (SEQ_LT(p->rxmit + len, tp->snd_una + so->so_snd.sb_cc))
503 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.sb_cc))
507 recwin = sbspace(&so->so_rcv);
510 * Sender silly window avoidance. We transmit under the following
511 * conditions when len is non-zero:
513 * - We have a full segment (or more with TSO)
514 * - This is the last buffer in a write()/send() and we are
515 * either idle or running NODELAY
516 * - we've timed out (e.g. persist timer)
517 * - we have more then 1/2 the maximum send window's worth of
518 * data (receiver may be limited the window size)
519 * - we need to retransmit
522 if (len >= tp->t_maxseg)
525 * NOTE! on localhost connections an 'ack' from the remote
526 * end may occur synchronously with the output and cause
527 * us to flush a buffer queued with moretocome. XXX
529 * note: the len + off check is almost certainly unnecessary.
531 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
532 (idle || (tp->t_flags & TF_NODELAY)) &&
533 len + off >= so->so_snd.sb_cc &&
534 (tp->t_flags & TF_NOPUSH) == 0) {
537 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
539 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
541 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
548 * Compare available window to amount of window
549 * known to peer (as advertised window less
550 * next expected input). If the difference is at least two
551 * max size segments, or at least 50% of the maximum possible
552 * window, then want to send a window update to peer.
553 * Skip this if the connection is in T/TCP half-open state.
554 * Don't send pure window updates when the peer has closed
555 * the connection and won't ever send more data.
557 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
558 !TCPS_HAVERCVDFIN(tp->t_state)) {
560 * "adv" is the amount we can increase the window,
561 * taking into account that we are limited by
562 * TCP_MAXWIN << tp->rcv_scale.
564 long adv = min(recwin, (long)TCP_MAXWIN << tp->rcv_scale) -
565 (tp->rcv_adv - tp->rcv_nxt);
567 if (adv >= (long) (2 * tp->t_maxseg))
569 if (2 * adv >= (long) so->so_rcv.sb_hiwat)
574 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
575 * is also a catch-all for the retransmit timer timeout case.
577 if (tp->t_flags & TF_ACKNOW)
579 if ((flags & TH_RST) ||
580 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
582 if (SEQ_GT(tp->snd_up, tp->snd_una))
585 * If our state indicates that FIN should be sent
586 * and we have not yet done so, then we need to send.
588 if (flags & TH_FIN &&
589 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
592 * In SACK, it is possible for tcp_output to fail to send a segment
593 * after the retransmission timer has been turned off. Make sure
594 * that the retransmission timer is set.
596 if ((tp->t_flags & TF_SACK_PERMIT) &&
597 SEQ_GT(tp->snd_max, tp->snd_una) &&
598 !tcp_timer_active(tp, TT_REXMT) &&
599 !tcp_timer_active(tp, TT_PERSIST)) {
600 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
604 * TCP window updates are not reliable, rather a polling protocol
605 * using ``persist'' packets is used to insure receipt of window
606 * updates. The three ``states'' for the output side are:
607 * idle not doing retransmits or persists
608 * persisting to move a small or zero window
609 * (re)transmitting and thereby not persisting
611 * tcp_timer_active(tp, TT_PERSIST)
612 * is true when we are in persist state.
613 * (tp->t_flags & TF_FORCEDATA)
614 * is set when we are called to send a persist packet.
615 * tcp_timer_active(tp, TT_REXMT)
616 * is set when we are retransmitting
617 * The output side is idle when both timers are zero.
619 * If send window is too small, there is data to transmit, and no
620 * retransmit or persist is pending, then go to persist state.
621 * If nothing happens soon, send when timer expires:
622 * if window is nonzero, transmit what we can,
623 * otherwise force out a byte.
625 if (so->so_snd.sb_cc && !tcp_timer_active(tp, TT_REXMT) &&
626 !tcp_timer_active(tp, TT_PERSIST)) {
632 * No reason to send a segment, just return.
635 SOCKBUF_UNLOCK(&so->so_snd);
639 SOCKBUF_LOCK_ASSERT(&so->so_snd);
641 * Before ESTABLISHED, force sending of initial options
642 * unless TCP set not to do any options.
643 * NOTE: we assume that the IP/TCP header plus TCP options
644 * always fit in a single mbuf, leaving room for a maximum
646 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
651 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
654 hdrlen = sizeof (struct tcpiphdr);
657 * Compute options for segment.
658 * We only have to care about SYN and established connection
659 * segments. Options for SYN-ACK segments are handled in TCP
662 if ((tp->t_flags & TF_NOOPT) == 0) {
664 /* Maximum segment size. */
665 if (flags & TH_SYN) {
666 tp->snd_nxt = tp->iss;
667 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
668 to.to_flags |= TOF_MSS;
670 /* Window scaling. */
671 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
672 to.to_wscale = tp->request_r_scale;
673 to.to_flags |= TOF_SCALE;
676 if ((tp->t_flags & TF_RCVD_TSTMP) ||
677 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
678 to.to_tsval = ticks + tp->ts_offset;
679 to.to_tsecr = tp->ts_recent;
680 to.to_flags |= TOF_TS;
681 /* Set receive buffer autosizing timestamp. */
682 if (tp->rfbuf_ts == 0 &&
683 (so->so_rcv.sb_flags & SB_AUTOSIZE))
684 tp->rfbuf_ts = ticks;
686 /* Selective ACK's. */
687 if (tp->t_flags & TF_SACK_PERMIT) {
689 to.to_flags |= TOF_SACKPERM;
690 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
691 (tp->t_flags & TF_SACK_PERMIT) &&
692 tp->rcv_numsacks > 0) {
693 to.to_flags |= TOF_SACK;
694 to.to_nsacks = tp->rcv_numsacks;
695 to.to_sacks = (u_char *)tp->sackblks;
699 /* TCP-MD5 (RFC2385). */
700 if (tp->t_flags & TF_SIGNATURE)
701 to.to_flags |= TOF_SIGNATURE;
702 #endif /* TCP_SIGNATURE */
704 /* Processing the options. */
705 hdrlen += optlen = tcp_addoptions(&to, opt);
710 ipoptlen = ip6_optlen(tp->t_inpcb);
713 if (tp->t_inpcb->inp_options)
714 ipoptlen = tp->t_inpcb->inp_options->m_len -
715 offsetof(struct ipoption, ipopt_list);
719 ipoptlen += ipsec_optlen;
723 * Adjust data length if insertion of options will
724 * bump the packet length beyond the t_maxopd length.
725 * Clear the FIN bit because we cut off the tail of
728 if (len + optlen + ipoptlen > tp->t_maxopd) {
732 KASSERT(ipoptlen == 0,
733 ("%s: TSO can't do IP options", __func__));
736 * Limit a burst to IP_MAXPACKET minus IP,
737 * TCP and options length to keep ip->ip_len
740 if (len > IP_MAXPACKET - hdrlen) {
741 len = IP_MAXPACKET - hdrlen;
746 * Prevent the last segment from being
747 * fractional unless the send sockbuf can
750 if (sendalot && off + len < so->so_snd.sb_cc) {
751 len -= len % (tp->t_maxopd - optlen);
756 * Send the FIN in a separate segment
757 * after the bulk sending is done.
758 * We don't trust the TSO implementations
759 * to clear the FIN flag on all but the
762 if (tp->t_flags & TF_NEEDFIN)
766 len = tp->t_maxopd - optlen - ipoptlen;
772 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
773 ("%s: len > IP_MAXPACKET", __func__));
775 /*#ifdef DIAGNOSTIC*/
777 if (max_linkhdr + hdrlen > MCLBYTES)
779 if (max_linkhdr + hdrlen > MHLEN)
781 panic("tcphdr too big");
785 * This KASSERT is here to catch edge cases at a well defined place.
786 * Before, those had triggered (random) panic conditions further down.
788 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
791 * Grab a header mbuf, attaching a copy of data to
792 * be transmitted, and initialize the header from
793 * the template for sends on this connection.
799 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
800 TCPSTAT_INC(tcps_sndprobe);
801 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
802 tp->t_sndrexmitpack++;
803 TCPSTAT_INC(tcps_sndrexmitpack);
804 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
806 TCPSTAT_INC(tcps_sndpack);
807 TCPSTAT_ADD(tcps_sndbyte, len);
810 if ((m = m_copypack(so->so_snd.sb_mb, off,
811 (int)len, max_linkhdr + hdrlen)) == 0) {
812 SOCKBUF_UNLOCK(&so->so_snd);
817 * m_copypack left space for our hdr; use it.
822 MGETHDR(m, M_DONTWAIT, MT_DATA);
824 SOCKBUF_UNLOCK(&so->so_snd);
829 if (MHLEN < hdrlen + max_linkhdr) {
830 MCLGET(m, M_DONTWAIT);
831 if ((m->m_flags & M_EXT) == 0) {
832 SOCKBUF_UNLOCK(&so->so_snd);
839 m->m_data += max_linkhdr;
843 * Start the m_copy functions from the closest mbuf
844 * to the offset in the socket buffer chain.
846 mb = sbsndptr(&so->so_snd, off, len, &moff);
848 if (len <= MHLEN - hdrlen - max_linkhdr) {
849 m_copydata(mb, moff, (int)len,
850 mtod(m, caddr_t) + hdrlen);
853 m->m_next = m_copy(mb, moff, (int)len);
854 if (m->m_next == NULL) {
855 SOCKBUF_UNLOCK(&so->so_snd);
863 * If we're sending everything we've got, set PUSH.
864 * (This will keep happy those implementations which only
865 * give data to the user when a buffer fills or
868 if (off + len == so->so_snd.sb_cc)
870 SOCKBUF_UNLOCK(&so->so_snd);
872 SOCKBUF_UNLOCK(&so->so_snd);
873 if (tp->t_flags & TF_ACKNOW)
874 TCPSTAT_INC(tcps_sndacks);
875 else if (flags & (TH_SYN|TH_FIN|TH_RST))
876 TCPSTAT_INC(tcps_sndctrl);
877 else if (SEQ_GT(tp->snd_up, tp->snd_una))
878 TCPSTAT_INC(tcps_sndurg);
880 TCPSTAT_INC(tcps_sndwinup);
882 MGETHDR(m, M_DONTWAIT, MT_DATA);
888 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
893 m->m_data += max_linkhdr;
896 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
897 m->m_pkthdr.rcvif = (struct ifnet *)0;
899 mac_inpcb_create_mbuf(tp->t_inpcb, m);
903 ip6 = mtod(m, struct ip6_hdr *);
904 th = (struct tcphdr *)(ip6 + 1);
905 tcpip_fillheaders(tp->t_inpcb, ip6, th);
909 ip = mtod(m, struct ip *);
910 ipov = (struct ipovly *)ip;
911 th = (struct tcphdr *)(ip + 1);
912 tcpip_fillheaders(tp->t_inpcb, ip, th);
916 * Fill in fields, remembering maximum advertised
917 * window for use in delaying messages about window sizes.
918 * If resending a FIN, be sure not to use a new sequence number.
920 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
921 tp->snd_nxt == tp->snd_max)
924 * If we are starting a connection, send ECN setup
925 * SYN packet. If we are on a retransmit, we may
926 * resend those bits a number of times as per
929 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn) {
930 if (tp->t_rxtshift >= 1) {
931 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
932 flags |= TH_ECE|TH_CWR;
934 flags |= TH_ECE|TH_CWR;
937 if (tp->t_state == TCPS_ESTABLISHED &&
938 (tp->t_flags & TF_ECN_PERMIT)) {
940 * If the peer has ECN, mark data packets with
941 * ECN capable transmission (ECT).
942 * Ignore pure ack packets, retransmissions and window probes.
944 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
945 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
948 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
951 ip->ip_tos |= IPTOS_ECN_ECT0;
952 TCPSTAT_INC(tcps_ecn_ect0);
956 * Reply with proper ECN notifications.
958 if (tp->t_flags & TF_ECN_SND_CWR) {
960 tp->t_flags &= ~TF_ECN_SND_CWR;
962 if (tp->t_flags & TF_ECN_SND_ECE)
967 * If we are doing retransmissions, then snd_nxt will
968 * not reflect the first unsent octet. For ACK only
969 * packets, we do not want the sequence number of the
970 * retransmitted packet, we want the sequence number
971 * of the next unsent octet. So, if there is no data
972 * (and no SYN or FIN), use snd_max instead of snd_nxt
973 * when filling in ti_seq. But if we are in persist
974 * state, snd_max might reflect one byte beyond the
975 * right edge of the window, so use snd_nxt in that
976 * case, since we know we aren't doing a retransmission.
977 * (retransmit and persist are mutually exclusive...)
979 if (sack_rxmit == 0) {
980 if (len || (flags & (TH_SYN|TH_FIN)) ||
981 tcp_timer_active(tp, TT_PERSIST))
982 th->th_seq = htonl(tp->snd_nxt);
984 th->th_seq = htonl(tp->snd_max);
986 th->th_seq = htonl(p->rxmit);
988 tp->sackhint.sack_bytes_rexmit += len;
990 th->th_ack = htonl(tp->rcv_nxt);
992 bcopy(opt, th + 1, optlen);
993 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
995 th->th_flags = flags;
997 * Calculate receive window. Don't shrink window,
998 * but avoid silly window syndrome.
1000 if (recwin < (long)(so->so_rcv.sb_hiwat / 4) &&
1001 recwin < (long)tp->t_maxseg)
1003 if (recwin < (long)(tp->rcv_adv - tp->rcv_nxt))
1004 recwin = (long)(tp->rcv_adv - tp->rcv_nxt);
1005 if (recwin > (long)TCP_MAXWIN << tp->rcv_scale)
1006 recwin = (long)TCP_MAXWIN << tp->rcv_scale;
1009 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1010 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1011 * case is handled in syncache.
1014 th->th_win = htons((u_short)
1015 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1017 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1020 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1021 * a 0 window. This may cause the remote transmitter to stall. This
1022 * flag tells soreceive() to disable delayed acknowledgements when
1023 * draining the buffer. This can occur if the receiver is attempting
1024 * to read more data than can be buffered prior to transmitting on
1027 if (th->th_win == 0) {
1029 tp->t_flags |= TF_RXWIN0SENT;
1031 tp->t_flags &= ~TF_RXWIN0SENT;
1032 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1033 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1034 th->th_flags |= TH_URG;
1037 * If no urgent pointer to send, then we pull
1038 * the urgent pointer to the left edge of the send window
1039 * so that it doesn't drift into the send window on sequence
1040 * number wraparound.
1042 tp->snd_up = tp->snd_una; /* drag it along */
1044 #ifdef TCP_SIGNATURE
1045 if (tp->t_flags & TF_SIGNATURE) {
1046 int sigoff = to.to_signature - opt;
1047 tcp_signature_compute(m, 0, len, optlen,
1048 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1053 * Put TCP length in extended header, and then
1054 * checksum extended header and data.
1056 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1060 * ip6_plen is not need to be filled now, and will be filled
1063 th->th_sum = in6_cksum(m, IPPROTO_TCP, sizeof(struct ip6_hdr),
1064 sizeof(struct tcphdr) + optlen + len);
1068 m->m_pkthdr.csum_flags = CSUM_TCP;
1069 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1070 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1071 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1073 /* IP version must be set here for ipv4/ipv6 checking later */
1074 KASSERT(ip->ip_v == IPVERSION,
1075 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1079 * Enable TSO and specify the size of the segments.
1080 * The TCP pseudo header checksum is always provided.
1081 * XXX: Fixme: This is currently not the case for IPv6.
1084 KASSERT(len > tp->t_maxopd - optlen,
1085 ("%s: len <= tso_segsz", __func__));
1086 m->m_pkthdr.csum_flags |= CSUM_TSO;
1087 m->m_pkthdr.tso_segsz = tp->t_maxopd - optlen;
1090 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1091 ("%s: mbuf chain shorter than expected", __func__));
1094 * In transmit state, time the transmission and arrange for
1095 * the retransmit. In persist state, just set snd_max.
1097 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1098 !tcp_timer_active(tp, TT_PERSIST)) {
1099 tcp_seq startseq = tp->snd_nxt;
1102 * Advance snd_nxt over sequence space of this segment.
1104 if (flags & (TH_SYN|TH_FIN)) {
1107 if (flags & TH_FIN) {
1109 tp->t_flags |= TF_SENTFIN;
1115 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1116 tp->snd_max = tp->snd_nxt;
1118 * Time this transmission if not a retransmission and
1119 * not currently timing anything.
1121 if (tp->t_rtttime == 0) {
1122 tp->t_rtttime = ticks;
1123 tp->t_rtseq = startseq;
1124 TCPSTAT_INC(tcps_segstimed);
1129 * Set retransmit timer if not currently set,
1130 * and not doing a pure ack or a keep-alive probe.
1131 * Initial value for retransmit timer is smoothed
1132 * round-trip time + 2 * round-trip time variance.
1133 * Initialize shift counter which is used for backoff
1134 * of retransmit time.
1137 if (!tcp_timer_active(tp, TT_REXMT) &&
1138 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1139 (tp->snd_nxt != tp->snd_una))) {
1140 if (tcp_timer_active(tp, TT_PERSIST)) {
1141 tcp_timer_activate(tp, TT_PERSIST, 0);
1144 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1148 * Persist case, update snd_max but since we are in
1149 * persist mode (no window) we do not update snd_nxt.
1154 if (flags & TH_FIN) {
1156 tp->t_flags |= TF_SENTFIN;
1158 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1159 tp->snd_max = tp->snd_nxt + len;
1162 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1163 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1169 if (so->so_options & SO_DEBUG) {
1175 save = ipov->ih_len;
1176 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1178 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1182 ipov->ih_len = save;
1187 * Fill in IP length and desired time to live and
1188 * send to IP level. There should be a better way
1189 * to handle ttl and tos; we could keep them in
1190 * the template, but need a way to checksum without them.
1193 * m->m_pkthdr.len should have been set before cksum calcuration,
1194 * because in6_cksum() need it.
1199 * we separately set hoplimit for every segment, since the
1200 * user might want to change the value via setsockopt.
1201 * Also, desired default hop limit might be changed via
1202 * Neighbor Discovery.
1204 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1206 /* TODO: IPv6 IP6TOS_ECT bit on */
1207 error = ip6_output(m,
1208 tp->t_inpcb->in6p_outputopts, NULL,
1209 ((so->so_options & SO_DONTROUTE) ?
1210 IP_ROUTETOIF : 0), NULL, NULL, tp->t_inpcb);
1214 ip->ip_len = m->m_pkthdr.len;
1216 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1217 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1220 * If we do path MTU discovery, then we set DF on every packet.
1221 * This might not be the best thing to do according to RFC3390
1222 * Section 2. However the tcp hostcache migitates the problem
1223 * so it affects only the first tcp connection with a host.
1225 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1227 if (V_path_mtu_discovery && tp->t_maxopd > V_tcp_minmss)
1228 ip->ip_off |= IP_DF;
1230 error = ip_output(m, tp->t_inpcb->inp_options, NULL,
1231 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1237 * We know that the packet was lost, so back out the
1238 * sequence number advance, if any.
1240 * If the error is EPERM the packet got blocked by the
1241 * local firewall. Normally we should terminate the
1242 * connection but the blocking may have been spurious
1243 * due to a firewall reconfiguration cycle. So we treat
1244 * it like a packet loss and let the retransmit timer and
1245 * timeouts do their work over time.
1246 * XXX: It is a POLA question whether calling tcp_drop right
1247 * away would be the really correct behavior instead.
1249 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1250 !tcp_timer_active(tp, TT_PERSIST)) &&
1251 ((flags & TH_SYN) == 0) &&
1255 tp->sackhint.sack_bytes_rexmit -= len;
1256 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1257 ("sackhint bytes rtx >= 0"));
1262 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1265 tp->t_softerror = error;
1268 if (!tcp_timer_active(tp, TT_REXMT) &&
1269 !tcp_timer_active(tp, TT_PERSIST))
1270 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1271 tp->snd_cwnd = tp->t_maxseg;
1275 * For some reason the interface we used initially
1276 * to send segments changed to another or lowered
1279 * tcp_mtudisc() will find out the new MTU and as
1280 * its last action, initiate retransmission, so it
1281 * is important to not do so here.
1283 * If TSO was active we either got an interface
1284 * without TSO capabilits or TSO was turned off.
1285 * Disable it for this connection as too and
1286 * immediatly retry with MSS sized segments generated
1290 tp->t_flags &= ~TF_TSO;
1291 tcp_mtudisc(tp->t_inpcb, 0);
1297 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1298 tp->t_softerror = error;
1306 TCPSTAT_INC(tcps_sndtotal);
1309 * Data sent (as far as we can tell).
1310 * If this advertises a larger window than any other segment,
1311 * then remember the size of the advertised window.
1312 * Any pending ACK has now been sent.
1314 if (recwin > 0 && SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1315 tp->rcv_adv = tp->rcv_nxt + recwin;
1316 tp->last_ack_sent = tp->rcv_nxt;
1317 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1318 if (tcp_timer_active(tp, TT_DELACK))
1319 tcp_timer_activate(tp, TT_DELACK, 0);
1322 * This completely breaks TCP if newreno is turned on. What happens
1323 * is that if delayed-acks are turned on on the receiver, this code
1324 * on the transmitter effectively destroys the TCP window, forcing
1325 * it to four packets (1.5Kx4 = 6K window).
1327 if (sendalot && --maxburst)
1336 tcp_setpersist(struct tcpcb *tp)
1338 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1341 if (tcp_timer_active(tp, TT_REXMT))
1342 panic("tcp_setpersist: retransmit pending");
1344 * Start/restart persistance timer.
1346 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1347 TCPTV_PERSMIN, TCPTV_PERSMAX);
1348 tcp_timer_activate(tp, TT_PERSIST, tt);
1349 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1354 * Insert TCP options according to the supplied parameters to the place
1355 * optp in a consistent way. Can handle unaligned destinations.
1357 * The order of the option processing is crucial for optimal packing and
1358 * alignment for the scarce option space.
1360 * The optimal order for a SYN/SYN-ACK segment is:
1361 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1362 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1364 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1365 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1366 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1367 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1368 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1371 tcp_addoptions(struct tcpopt *to, u_char *optp)
1373 u_int mask, optlen = 0;
1375 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1376 if ((to->to_flags & mask) != mask)
1378 if (optlen == TCP_MAXOLEN)
1380 switch (to->to_flags & mask) {
1382 while (optlen % 4) {
1383 optlen += TCPOLEN_NOP;
1384 *optp++ = TCPOPT_NOP;
1386 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1388 optlen += TCPOLEN_MAXSEG;
1389 *optp++ = TCPOPT_MAXSEG;
1390 *optp++ = TCPOLEN_MAXSEG;
1391 to->to_mss = htons(to->to_mss);
1392 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1393 optp += sizeof(to->to_mss);
1396 while (!optlen || optlen % 2 != 1) {
1397 optlen += TCPOLEN_NOP;
1398 *optp++ = TCPOPT_NOP;
1400 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1402 optlen += TCPOLEN_WINDOW;
1403 *optp++ = TCPOPT_WINDOW;
1404 *optp++ = TCPOLEN_WINDOW;
1405 *optp++ = to->to_wscale;
1408 while (optlen % 2) {
1409 optlen += TCPOLEN_NOP;
1410 *optp++ = TCPOPT_NOP;
1412 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1414 optlen += TCPOLEN_SACK_PERMITTED;
1415 *optp++ = TCPOPT_SACK_PERMITTED;
1416 *optp++ = TCPOLEN_SACK_PERMITTED;
1419 while (!optlen || optlen % 4 != 2) {
1420 optlen += TCPOLEN_NOP;
1421 *optp++ = TCPOPT_NOP;
1423 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1425 optlen += TCPOLEN_TIMESTAMP;
1426 *optp++ = TCPOPT_TIMESTAMP;
1427 *optp++ = TCPOLEN_TIMESTAMP;
1428 to->to_tsval = htonl(to->to_tsval);
1429 to->to_tsecr = htonl(to->to_tsecr);
1430 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1431 optp += sizeof(to->to_tsval);
1432 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1433 optp += sizeof(to->to_tsecr);
1437 int siglen = TCPOLEN_SIGNATURE - 2;
1439 while (!optlen || optlen % 4 != 2) {
1440 optlen += TCPOLEN_NOP;
1441 *optp++ = TCPOPT_NOP;
1443 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE)
1445 optlen += TCPOLEN_SIGNATURE;
1446 *optp++ = TCPOPT_SIGNATURE;
1447 *optp++ = TCPOLEN_SIGNATURE;
1448 to->to_signature = optp;
1456 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1459 while (!optlen || optlen % 4 != 2) {
1460 optlen += TCPOLEN_NOP;
1461 *optp++ = TCPOPT_NOP;
1463 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1465 optlen += TCPOLEN_SACKHDR;
1466 *optp++ = TCPOPT_SACK;
1467 sackblks = min(to->to_nsacks,
1468 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1469 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1470 while (sackblks--) {
1471 sack_seq = htonl(sack->start);
1472 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1473 optp += sizeof(sack_seq);
1474 sack_seq = htonl(sack->end);
1475 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1476 optp += sizeof(sack_seq);
1477 optlen += TCPOLEN_SACK;
1480 TCPSTAT_INC(tcps_sack_send_blocks);
1484 panic("%s: unknown TCP option type", __func__);
1489 /* Terminate and pad TCP options to a 4 byte boundary. */
1491 optlen += TCPOLEN_EOL;
1492 *optp++ = TCPOPT_EOL;
1495 * According to RFC 793 (STD0007):
1496 * "The content of the header beyond the End-of-Option option
1497 * must be header padding (i.e., zero)."
1498 * and later: "The padding is composed of zeros."
1500 while (optlen % 4) {
1501 optlen += TCPOLEN_PAD;
1502 *optp++ = TCPOPT_PAD;
1505 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));