2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
5 * The Regents of the University of California. All rights reserved.
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31 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_tcpdebug.h"
42 #include <sys/param.h>
43 #include <sys/systm.h>
44 #include <sys/domain.h>
46 #include <sys/hhook.h>
48 #include <sys/kernel.h>
51 #include <sys/mutex.h>
52 #include <sys/protosw.h>
54 #include <sys/socket.h>
55 #include <sys/socketvar.h>
56 #include <sys/sysctl.h>
59 #include <net/route.h>
62 #include <netinet/in.h>
63 #include <netinet/in_kdtrace.h>
64 #include <netinet/in_systm.h>
65 #include <netinet/ip.h>
66 #include <netinet/in_pcb.h>
67 #include <netinet/ip_var.h>
68 #include <netinet/ip_options.h>
70 #include <netinet6/in6_pcb.h>
71 #include <netinet/ip6.h>
72 #include <netinet6/ip6_var.h>
74 #include <netinet/tcp.h>
76 #include <netinet/tcp_fsm.h>
77 #include <netinet/tcp_seq.h>
78 #include <netinet/tcp_timer.h>
79 #include <netinet/tcp_var.h>
80 #include <netinet/tcpip.h>
81 #include <netinet/cc/cc.h>
82 #include <netinet/tcp_fastopen.h>
84 #include <netinet/tcp_pcap.h>
87 #include <netinet/tcp_debug.h>
90 #include <netinet/tcp_offload.h>
93 #include <netipsec/ipsec_support.h>
95 #include <machine/in_cksum.h>
97 #include <security/mac/mac_framework.h>
99 VNET_DEFINE(int, path_mtu_discovery) = 1;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
101 &VNET_NAME(path_mtu_discovery), 1,
102 "Enable Path MTU Discovery");
104 VNET_DEFINE(int, tcp_do_tso) = 1;
105 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
106 &VNET_NAME(tcp_do_tso), 0,
107 "Enable TCP Segmentation Offload");
109 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
110 #define V_tcp_sendspace VNET(tcp_sendspace)
111 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
112 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
114 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
116 &VNET_NAME(tcp_do_autosndbuf), 0,
117 "Enable automatic send buffer sizing");
119 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
120 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
121 &VNET_NAME(tcp_autosndbuf_inc), 0,
122 "Incrementor step size of automatic send buffer");
124 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
126 &VNET_NAME(tcp_autosndbuf_max), 0,
127 "Max size of automatic send buffer");
129 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
130 #define V_tcp_sendbuf_auto_lowat VNET(tcp_sendbuf_auto_lowat)
131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
132 &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
133 "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
136 * Make sure that either retransmit or persist timer is set for SYN, FIN and
139 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
140 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
141 tcp_timer_active((tp), TT_REXMT) || \
142 tcp_timer_active((tp), TT_PERSIST), \
143 ("neither rexmt nor persist timer is set"))
146 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
147 struct tcphdr *th, struct tcpopt *to,
148 uint32_t len, int tso);
150 static void inline cc_after_idle(struct tcpcb *tp);
154 * Wrapper for the TCP established output helper hook.
157 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
158 struct tcpopt *to, uint32_t len, int tso)
160 struct tcp_hhook_data hhook_data;
162 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
166 hhook_data.len = len;
167 hhook_data.tso = tso;
169 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
176 * CC wrapper hook functions
179 cc_after_idle(struct tcpcb *tp)
181 INP_WLOCK_ASSERT(tp->t_inpcb);
183 if (CC_ALGO(tp)->after_idle != NULL)
184 CC_ALGO(tp)->after_idle(tp->ccv);
188 * Tcp output routine: figure out what should be sent and send it.
191 tcp_output(struct tcpcb *tp)
193 struct socket *so = tp->t_inpcb->inp_socket;
195 uint32_t recwin, sendwin;
196 int off, flags, error = 0; /* Keep compiler happy */
198 struct ip *ip = NULL;
200 struct ipovly *ipov = NULL;
203 u_char opt[TCP_MAXOLEN];
204 unsigned ipoptlen, optlen, hdrlen;
205 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
206 unsigned ipsec_optlen = 0;
209 int sack_rxmit, sack_bytes_rxmt;
213 unsigned int wanted_cookie = 0;
214 unsigned int dont_sendalot = 0;
216 int maxburst = TCP_MAXBURST;
219 struct ip6_hdr *ip6 = NULL;
222 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
225 INP_WLOCK_ASSERT(tp->t_inpcb);
228 if (tp->t_flags & TF_TOE)
229 return (tcp_offload_output(tp));
233 * For TFO connections in SYN_RECEIVED, only allow the initial
234 * SYN|ACK and those sent by the retransmit timer.
236 if (IS_FASTOPEN(tp->t_flags) &&
237 (tp->t_state == TCPS_SYN_RECEIVED) &&
238 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN|ACK sent */
239 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */
243 * Determine length of data that should be transmitted,
244 * and flags that will be used.
245 * If there is some data or critical controls (SYN, RST)
246 * to send, then transmit; otherwise, investigate further.
248 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
249 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
251 tp->t_flags &= ~TF_LASTIDLE;
253 if (tp->t_flags & TF_MORETOCOME) {
254 tp->t_flags |= TF_LASTIDLE;
260 * If we've recently taken a timeout, snd_max will be greater than
261 * snd_nxt. There may be SACK information that allows us to avoid
262 * resending already delivered data. Adjust snd_nxt accordingly.
264 if ((tp->t_flags & TF_SACK_PERMIT) &&
265 SEQ_LT(tp->snd_nxt, tp->snd_max))
270 off = tp->snd_nxt - tp->snd_una;
271 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
273 flags = tcp_outflags[tp->t_state];
275 * Send any SACK-generated retransmissions. If we're explicitly trying
276 * to send out new data (when sendalot is 1), bypass this function.
277 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
278 * we're replacing a (future) new transmission with a retransmission
279 * now, and we previously incremented snd_cwnd in tcp_input().
282 * Still in sack recovery , reset rxmit flag to zero.
288 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
289 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
293 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
294 /* Do not retransmit SACK segments beyond snd_recover */
295 if (SEQ_GT(p->end, tp->snd_recover)) {
297 * (At least) part of sack hole extends beyond
298 * snd_recover. Check to see if we can rexmit data
301 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
303 * Can't rexmit any more data for this hole.
304 * That data will be rexmitted in the next
305 * sack recovery episode, when snd_recover
306 * moves past p->rxmit.
309 goto after_sack_rexmit;
311 /* Can rexmit part of the current hole */
312 len = ((int32_t)ulmin(cwin,
313 tp->snd_recover - p->rxmit));
315 len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
316 off = p->rxmit - tp->snd_una;
317 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
322 TCPSTAT_INC(tcps_sack_rexmits);
323 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
324 min(len, tp->t_maxseg));
329 * Get standard flags, and add SYN or FIN if requested by 'hidden'
332 if (tp->t_flags & TF_NEEDFIN)
334 if (tp->t_flags & TF_NEEDSYN)
337 SOCKBUF_LOCK(&so->so_snd);
339 * If in persist timeout with window of 0, send 1 byte.
340 * Otherwise, if window is small but nonzero
341 * and timer expired, we will send what we can
342 * and go to transmit state.
344 if (tp->t_flags & TF_FORCEDATA) {
347 * If we still have some data to send, then
348 * clear the FIN bit. Usually this would
349 * happen below when it realizes that we
350 * aren't sending all the data. However,
351 * if we have exactly 1 byte of unsent data,
352 * then it won't clear the FIN bit below,
353 * and if we are in persist state, we wind
354 * up sending the packet without recording
355 * that we sent the FIN bit.
357 * We can't just blindly clear the FIN bit,
358 * because if we don't have any more data
359 * to send then the probe will be the FIN
362 if (off < sbused(&so->so_snd))
366 tcp_timer_activate(tp, TT_PERSIST, 0);
372 * If snd_nxt == snd_max and we have transmitted a FIN, the
373 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
374 * a negative length. This can also occur when TCP opens up
375 * its congestion window while receiving additional duplicate
376 * acks after fast-retransmit because TCP will reset snd_nxt
377 * to snd_max after the fast-retransmit.
379 * In the normal retransmit-FIN-only case, however, snd_nxt will
380 * be set to snd_una, the offset will be 0, and the length may
383 * If sack_rxmit is true we are retransmitting from the scoreboard
384 * in which case len is already set.
386 if (sack_rxmit == 0) {
387 if (sack_bytes_rxmt == 0)
388 len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
394 * We are inside of a SACK recovery episode and are
395 * sending new data, having retransmitted all the
396 * data possible in the scoreboard.
398 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
401 * Don't remove this (len > 0) check !
402 * We explicitly check for len > 0 here (although it
403 * isn't really necessary), to work around a gcc
404 * optimization issue - to force gcc to compute
405 * len above. Without this check, the computation
406 * of len is bungled by the optimizer.
409 cwin = tp->snd_cwnd -
410 (tp->snd_nxt - tp->sack_newdata) -
414 len = imin(len, cwin);
420 * Lop off SYN bit if it has already been sent. However, if this
421 * is SYN-SENT state and if segment contains data and if we don't
422 * know that foreign host supports TAO, suppress sending segment.
424 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
425 if (tp->t_state != TCPS_SYN_RECEIVED)
428 * When sending additional segments following a TFO SYN|ACK,
429 * do not include the SYN bit.
431 if (IS_FASTOPEN(tp->t_flags) &&
432 (tp->t_state == TCPS_SYN_RECEIVED))
438 * Be careful not to send data and/or FIN on SYN segments.
439 * This measure is needed to prevent interoperability problems
440 * with not fully conformant TCP implementations.
442 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
448 * On TFO sockets, ensure no data is sent in the following cases:
450 * - When retransmitting SYN|ACK on a passively-created socket
452 * - When retransmitting SYN on an actively created socket
454 * - When sending a zero-length cookie (cookie request) on an
455 * actively created socket
457 * - When the socket is in the CLOSED state (RST is being sent)
459 if (IS_FASTOPEN(tp->t_flags) &&
460 (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
461 ((tp->t_state == TCPS_SYN_SENT) &&
462 (tp->t_tfo_client_cookie_len == 0)) ||
467 * If FIN has been sent but not acked,
468 * but we haven't been called to retransmit,
469 * len will be < 0. Otherwise, window shrank
470 * after we sent into it. If window shrank to 0,
471 * cancel pending retransmit, pull snd_nxt back
472 * to (closed) window, and set the persist timer
473 * if it isn't already going. If the window didn't
474 * close completely, just wait for an ACK.
476 * We also do a general check here to ensure that
477 * we will set the persist timer when we have data
478 * to send, but a 0-byte window. This makes sure
479 * the persist timer is set even if the packet
480 * hits one of the "goto send" lines below.
483 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
484 (off < (int) sbavail(&so->so_snd))) {
485 tcp_timer_activate(tp, TT_REXMT, 0);
487 tp->snd_nxt = tp->snd_una;
488 if (!tcp_timer_active(tp, TT_PERSIST))
493 /* len will be >= 0 after this point. */
494 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
496 tcp_sndbuf_autoscale(tp, so, sendwin);
499 * Decide if we can use TCP Segmentation Offloading (if supported by
502 * TSO may only be used if we are in a pure bulk sending state. The
503 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
504 * IP options prevent using TSO. With TSO the TCP header is the same
505 * (except for the sequence number) for all generated packets. This
506 * makes it impossible to transmit any options which vary per generated
509 * IPv4 handling has a clear separation of ip options and ip header
510 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
511 * the right thing below to provide length of just ip options and thus
512 * checking for ipoptlen is enough to decide if ip options are present.
514 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
516 * Pre-calculate here as we save another lookup into the darknesses
517 * of IPsec that way and can actually decide if TSO is ok.
520 if (isipv6 && IPSEC_ENABLED(ipv6))
521 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
527 if (IPSEC_ENABLED(ipv4))
528 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
533 ipoptlen = ip6_optlen(tp->t_inpcb);
536 if (tp->t_inpcb->inp_options)
537 ipoptlen = tp->t_inpcb->inp_options->m_len -
538 offsetof(struct ipoption, ipopt_list);
541 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
542 ipoptlen += ipsec_optlen;
545 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
546 ((tp->t_flags & TF_SIGNATURE) == 0) &&
547 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
548 ipoptlen == 0 && !(flags & TH_SYN))
552 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
555 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
556 sbused(&so->so_snd)))
560 recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
561 (long)TCP_MAXWIN << tp->rcv_scale);
564 * Sender silly window avoidance. We transmit under the following
565 * conditions when len is non-zero:
567 * - We have a full segment (or more with TSO)
568 * - This is the last buffer in a write()/send() and we are
569 * either idle or running NODELAY
570 * - we've timed out (e.g. persist timer)
571 * - we have more then 1/2 the maximum send window's worth of
572 * data (receiver may be limited the window size)
573 * - we need to retransmit
576 if (len >= tp->t_maxseg)
579 * NOTE! on localhost connections an 'ack' from the remote
580 * end may occur synchronously with the output and cause
581 * us to flush a buffer queued with moretocome. XXX
583 * note: the len + off check is almost certainly unnecessary.
585 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
586 (idle || (tp->t_flags & TF_NODELAY)) &&
587 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
588 (tp->t_flags & TF_NOPUSH) == 0) {
591 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
593 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
595 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
602 * Sending of standalone window updates.
604 * Window updates are important when we close our window due to a
605 * full socket buffer and are opening it again after the application
606 * reads data from it. Once the window has opened again and the
607 * remote end starts to send again the ACK clock takes over and
608 * provides the most current window information.
610 * We must avoid the silly window syndrome whereas every read
611 * from the receive buffer, no matter how small, causes a window
612 * update to be sent. We also should avoid sending a flurry of
613 * window updates when the socket buffer had queued a lot of data
614 * and the application is doing small reads.
616 * Prevent a flurry of pointless window updates by only sending
617 * an update when we can increase the advertized window by more
618 * than 1/4th of the socket buffer capacity. When the buffer is
619 * getting full or is very small be more aggressive and send an
620 * update whenever we can increase by two mss sized segments.
621 * In all other situations the ACK's to new incoming data will
622 * carry further window increases.
624 * Don't send an independent window update if a delayed
625 * ACK is pending (it will get piggy-backed on it) or the
626 * remote side already has done a half-close and won't send
627 * more data. Skip this if the connection is in T/TCP
630 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
631 !(tp->t_flags & TF_DELACK) &&
632 !TCPS_HAVERCVDFIN(tp->t_state)) {
634 * "adv" is the amount we could increase the window,
635 * taking into account that we are limited by
636 * TCP_MAXWIN << tp->rcv_scale.
642 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
643 oldwin = (tp->rcv_adv - tp->rcv_nxt);
649 * If the new window size ends up being the same as or less
650 * than the old size when it is scaled, then don't force
653 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
656 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
657 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
658 recwin <= (so->so_rcv.sb_hiwat / 8) ||
659 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
661 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
667 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
668 * is also a catch-all for the retransmit timer timeout case.
670 if (tp->t_flags & TF_ACKNOW)
672 if ((flags & TH_RST) ||
673 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
675 if (SEQ_GT(tp->snd_up, tp->snd_una))
678 * If our state indicates that FIN should be sent
679 * and we have not yet done so, then we need to send.
681 if (flags & TH_FIN &&
682 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
685 * In SACK, it is possible for tcp_output to fail to send a segment
686 * after the retransmission timer has been turned off. Make sure
687 * that the retransmission timer is set.
689 if ((tp->t_flags & TF_SACK_PERMIT) &&
690 SEQ_GT(tp->snd_max, tp->snd_una) &&
691 !tcp_timer_active(tp, TT_REXMT) &&
692 !tcp_timer_active(tp, TT_PERSIST)) {
693 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
697 * TCP window updates are not reliable, rather a polling protocol
698 * using ``persist'' packets is used to insure receipt of window
699 * updates. The three ``states'' for the output side are:
700 * idle not doing retransmits or persists
701 * persisting to move a small or zero window
702 * (re)transmitting and thereby not persisting
704 * tcp_timer_active(tp, TT_PERSIST)
705 * is true when we are in persist state.
706 * (tp->t_flags & TF_FORCEDATA)
707 * is set when we are called to send a persist packet.
708 * tcp_timer_active(tp, TT_REXMT)
709 * is set when we are retransmitting
710 * The output side is idle when both timers are zero.
712 * If send window is too small, there is data to transmit, and no
713 * retransmit or persist is pending, then go to persist state.
714 * If nothing happens soon, send when timer expires:
715 * if window is nonzero, transmit what we can,
716 * otherwise force out a byte.
718 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
719 !tcp_timer_active(tp, TT_PERSIST)) {
725 * No reason to send a segment, just return.
728 SOCKBUF_UNLOCK(&so->so_snd);
732 SOCKBUF_LOCK_ASSERT(&so->so_snd);
734 if (len >= tp->t_maxseg)
735 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
737 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
740 * Before ESTABLISHED, force sending of initial options
741 * unless TCP set not to do any options.
742 * NOTE: we assume that the IP/TCP header plus TCP options
743 * always fit in a single mbuf, leaving room for a maximum
745 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
750 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
753 hdrlen = sizeof (struct tcpiphdr);
756 * Compute options for segment.
757 * We only have to care about SYN and established connection
758 * segments. Options for SYN-ACK segments are handled in TCP
762 if ((tp->t_flags & TF_NOOPT) == 0) {
763 /* Maximum segment size. */
764 if (flags & TH_SYN) {
765 tp->snd_nxt = tp->iss;
766 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
767 to.to_flags |= TOF_MSS;
770 * On SYN or SYN|ACK transmits on TFO connections,
771 * only include the TFO option if it is not a
772 * retransmit, as the presence of the TFO option may
773 * have caused the original SYN or SYN|ACK to have
774 * been dropped by a middlebox.
776 if (IS_FASTOPEN(tp->t_flags) &&
777 (tp->t_rxtshift == 0)) {
778 if (tp->t_state == TCPS_SYN_RECEIVED) {
779 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
781 (u_int8_t *)&tp->t_tfo_cookie.server;
782 to.to_flags |= TOF_FASTOPEN;
784 } else if (tp->t_state == TCPS_SYN_SENT) {
786 tp->t_tfo_client_cookie_len;
788 tp->t_tfo_cookie.client;
789 to.to_flags |= TOF_FASTOPEN;
792 * If we wind up having more data to
793 * send with the SYN than can fit in
794 * one segment, don't send any more
795 * until the SYN|ACK comes back from
802 /* Window scaling. */
803 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
804 to.to_wscale = tp->request_r_scale;
805 to.to_flags |= TOF_SCALE;
808 if ((tp->t_flags & TF_RCVD_TSTMP) ||
809 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
810 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
811 to.to_tsecr = tp->ts_recent;
812 to.to_flags |= TOF_TS;
815 /* Set receive buffer autosizing timestamp. */
816 if (tp->rfbuf_ts == 0 &&
817 (so->so_rcv.sb_flags & SB_AUTOSIZE))
818 tp->rfbuf_ts = tcp_ts_getticks();
820 /* Selective ACK's. */
821 if (tp->t_flags & TF_SACK_PERMIT) {
823 to.to_flags |= TOF_SACKPERM;
824 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
825 (tp->t_flags & TF_SACK_PERMIT) &&
826 tp->rcv_numsacks > 0) {
827 to.to_flags |= TOF_SACK;
828 to.to_nsacks = tp->rcv_numsacks;
829 to.to_sacks = (u_char *)tp->sackblks;
832 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
833 /* TCP-MD5 (RFC2385). */
835 * Check that TCP_MD5SIG is enabled in tcpcb to
836 * account the size needed to set this TCP option.
838 if (tp->t_flags & TF_SIGNATURE)
839 to.to_flags |= TOF_SIGNATURE;
840 #endif /* TCP_SIGNATURE */
842 /* Processing the options. */
843 hdrlen += optlen = tcp_addoptions(&to, opt);
845 * If we wanted a TFO option to be added, but it was unable
846 * to fit, ensure no data is sent.
848 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
849 !(to.to_flags & TOF_FASTOPEN))
854 * Adjust data length if insertion of options will
855 * bump the packet length beyond the t_maxseg length.
856 * Clear the FIN bit because we cut off the tail of
859 if (len + optlen + ipoptlen > tp->t_maxseg) {
864 u_int if_hw_tsomaxsegcount;
865 u_int if_hw_tsomaxsegsize;
870 /* extract TSO information */
871 if_hw_tsomax = tp->t_tsomax;
872 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
873 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
876 * Limit a TSO burst to prevent it from
877 * overflowing or exceeding the maximum length
878 * allowed by the network interface:
880 KASSERT(ipoptlen == 0,
881 ("%s: TSO can't do IP options", __func__));
884 * Check if we should limit by maximum payload
887 if (if_hw_tsomax != 0) {
888 /* compute maximum TSO length */
889 max_len = (if_hw_tsomax - hdrlen -
893 } else if (len > max_len) {
900 * Check if we should limit by maximum segment
903 if (if_hw_tsomaxsegcount != 0 &&
904 if_hw_tsomaxsegsize != 0) {
906 * Subtract one segment for the LINK
907 * and TCP/IP headers mbuf that will
908 * be prepended to this mbuf chain
909 * after the code in this section
910 * limits the number of mbufs in the
911 * chain to if_hw_tsomaxsegcount.
913 if_hw_tsomaxsegcount -= 1;
915 mb = sbsndmbuf(&so->so_snd, off, &moff);
917 while (mb != NULL && max_len < len) {
922 * Get length of mbuf fragment
923 * and how many hardware frags,
924 * rounded up, it would use:
926 mlen = (mb->m_len - moff);
927 frags = howmany(mlen,
928 if_hw_tsomaxsegsize);
930 /* Handle special case: Zero Length Mbuf */
935 * Check if the fragment limit
936 * will be reached or exceeded:
938 if (frags >= if_hw_tsomaxsegcount) {
940 if_hw_tsomaxsegcount *
941 if_hw_tsomaxsegsize);
945 if_hw_tsomaxsegcount -= frags;
951 } else if (len > max_len) {
958 * Prevent the last segment from being
959 * fractional unless the send sockbuf can be
962 max_len = (tp->t_maxseg - optlen);
963 if (((uint32_t)off + (uint32_t)len) <
964 sbavail(&so->so_snd)) {
965 moff = len % max_len;
973 * In case there are too many small fragments
976 if (len <= max_len) {
983 * Send the FIN in a separate segment
984 * after the bulk sending is done.
985 * We don't trust the TSO implementations
986 * to clear the FIN flag on all but the
989 if (tp->t_flags & TF_NEEDFIN)
993 len = tp->t_maxseg - optlen - ipoptlen;
1001 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1002 ("%s: len > IP_MAXPACKET", __func__));
1004 /*#ifdef DIAGNOSTIC*/
1006 if (max_linkhdr + hdrlen > MCLBYTES)
1008 if (max_linkhdr + hdrlen > MHLEN)
1010 panic("tcphdr too big");
1014 * This KASSERT is here to catch edge cases at a well defined place.
1015 * Before, those had triggered (random) panic conditions further down.
1017 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1020 * Grab a header mbuf, attaching a copy of data to
1021 * be transmitted, and initialize the header from
1022 * the template for sends on this connection.
1028 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1029 TCPSTAT_INC(tcps_sndprobe);
1030 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1031 tp->t_sndrexmitpack++;
1032 TCPSTAT_INC(tcps_sndrexmitpack);
1033 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1035 TCPSTAT_INC(tcps_sndpack);
1036 TCPSTAT_ADD(tcps_sndbyte, len);
1039 if (MHLEN < hdrlen + max_linkhdr)
1040 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1043 m = m_gethdr(M_NOWAIT, MT_DATA);
1046 SOCKBUF_UNLOCK(&so->so_snd);
1052 m->m_data += max_linkhdr;
1056 * Start the m_copy functions from the closest mbuf
1057 * to the offset in the socket buffer chain.
1059 mb = sbsndptr(&so->so_snd, off, len, &moff);
1061 if (len <= MHLEN - hdrlen - max_linkhdr) {
1062 m_copydata(mb, moff, len,
1063 mtod(m, caddr_t) + hdrlen);
1066 m->m_next = m_copym(mb, moff, len, M_NOWAIT);
1067 if (m->m_next == NULL) {
1068 SOCKBUF_UNLOCK(&so->so_snd);
1077 * If we're sending everything we've got, set PUSH.
1078 * (This will keep happy those implementations which only
1079 * give data to the user when a buffer fills or
1082 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1085 SOCKBUF_UNLOCK(&so->so_snd);
1087 SOCKBUF_UNLOCK(&so->so_snd);
1088 if (tp->t_flags & TF_ACKNOW)
1089 TCPSTAT_INC(tcps_sndacks);
1090 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1091 TCPSTAT_INC(tcps_sndctrl);
1092 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1093 TCPSTAT_INC(tcps_sndurg);
1095 TCPSTAT_INC(tcps_sndwinup);
1097 m = m_gethdr(M_NOWAIT, MT_DATA);
1104 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1109 m->m_data += max_linkhdr;
1112 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1113 m->m_pkthdr.rcvif = (struct ifnet *)0;
1115 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1119 ip6 = mtod(m, struct ip6_hdr *);
1120 th = (struct tcphdr *)(ip6 + 1);
1121 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1125 ip = mtod(m, struct ip *);
1127 ipov = (struct ipovly *)ip;
1129 th = (struct tcphdr *)(ip + 1);
1130 tcpip_fillheaders(tp->t_inpcb, ip, th);
1134 * Fill in fields, remembering maximum advertised
1135 * window for use in delaying messages about window sizes.
1136 * If resending a FIN, be sure not to use a new sequence number.
1138 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1139 tp->snd_nxt == tp->snd_max)
1142 * If we are starting a connection, send ECN setup
1143 * SYN packet. If we are on a retransmit, we may
1144 * resend those bits a number of times as per
1147 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1148 if (tp->t_rxtshift >= 1) {
1149 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1150 flags |= TH_ECE|TH_CWR;
1152 flags |= TH_ECE|TH_CWR;
1155 if (tp->t_state == TCPS_ESTABLISHED &&
1156 (tp->t_flags & TF_ECN_PERMIT)) {
1158 * If the peer has ECN, mark data packets with
1159 * ECN capable transmission (ECT).
1160 * Ignore pure ack packets, retransmissions and window probes.
1162 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1163 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1166 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1169 ip->ip_tos |= IPTOS_ECN_ECT0;
1170 TCPSTAT_INC(tcps_ecn_ect0);
1174 * Reply with proper ECN notifications.
1176 if (tp->t_flags & TF_ECN_SND_CWR) {
1178 tp->t_flags &= ~TF_ECN_SND_CWR;
1180 if (tp->t_flags & TF_ECN_SND_ECE)
1185 * If we are doing retransmissions, then snd_nxt will
1186 * not reflect the first unsent octet. For ACK only
1187 * packets, we do not want the sequence number of the
1188 * retransmitted packet, we want the sequence number
1189 * of the next unsent octet. So, if there is no data
1190 * (and no SYN or FIN), use snd_max instead of snd_nxt
1191 * when filling in ti_seq. But if we are in persist
1192 * state, snd_max might reflect one byte beyond the
1193 * right edge of the window, so use snd_nxt in that
1194 * case, since we know we aren't doing a retransmission.
1195 * (retransmit and persist are mutually exclusive...)
1197 if (sack_rxmit == 0) {
1198 if (len || (flags & (TH_SYN|TH_FIN)) ||
1199 tcp_timer_active(tp, TT_PERSIST))
1200 th->th_seq = htonl(tp->snd_nxt);
1202 th->th_seq = htonl(tp->snd_max);
1204 th->th_seq = htonl(p->rxmit);
1206 tp->sackhint.sack_bytes_rexmit += len;
1208 th->th_ack = htonl(tp->rcv_nxt);
1210 bcopy(opt, th + 1, optlen);
1211 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1213 th->th_flags = flags;
1215 * Calculate receive window. Don't shrink window,
1216 * but avoid silly window syndrome.
1218 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1219 recwin < tp->t_maxseg)
1221 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1222 recwin < (tp->rcv_adv - tp->rcv_nxt))
1223 recwin = (tp->rcv_adv - tp->rcv_nxt);
1226 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1227 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1228 * case is handled in syncache.
1231 th->th_win = htons((u_short)
1232 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1234 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1237 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1238 * a 0 window. This may cause the remote transmitter to stall. This
1239 * flag tells soreceive() to disable delayed acknowledgements when
1240 * draining the buffer. This can occur if the receiver is attempting
1241 * to read more data than can be buffered prior to transmitting on
1244 if (th->th_win == 0) {
1246 tp->t_flags |= TF_RXWIN0SENT;
1248 tp->t_flags &= ~TF_RXWIN0SENT;
1249 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1250 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1251 th->th_flags |= TH_URG;
1254 * If no urgent pointer to send, then we pull
1255 * the urgent pointer to the left edge of the send window
1256 * so that it doesn't drift into the send window on sequence
1257 * number wraparound.
1259 tp->snd_up = tp->snd_una; /* drag it along */
1262 * Put TCP length in extended header, and then
1263 * checksum extended header and data.
1265 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1266 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1268 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1269 if (to.to_flags & TOF_SIGNATURE) {
1271 * Calculate MD5 signature and put it into the place
1272 * determined before.
1273 * NOTE: since TCP options buffer doesn't point into
1274 * mbuf's data, calculate offset and use it.
1276 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1277 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1279 * Do not send segment if the calculation of MD5
1280 * digest has failed.
1290 * There is no need to fill in ip6_plen right now.
1291 * It will be filled later by ip6_output.
1293 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1294 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1295 optlen + len, IPPROTO_TCP, 0);
1298 #if defined(INET6) && defined(INET)
1303 m->m_pkthdr.csum_flags = CSUM_TCP;
1304 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1305 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1307 /* IP version must be set here for ipv4/ipv6 checking later */
1308 KASSERT(ip->ip_v == IPVERSION,
1309 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1314 * Enable TSO and specify the size of the segments.
1315 * The TCP pseudo header checksum is always provided.
1318 KASSERT(len > tp->t_maxseg - optlen,
1319 ("%s: len <= tso_segsz", __func__));
1320 m->m_pkthdr.csum_flags |= CSUM_TSO;
1321 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1324 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1325 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1326 ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u",
1327 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1329 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1330 ("%s: mbuf chain shorter than expected: %d + %u + %u != %u",
1331 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1335 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1336 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1343 if (so->so_options & SO_DEBUG) {
1349 save = ipov->ih_len;
1350 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1352 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1356 ipov->ih_len = save;
1358 #endif /* TCPDEBUG */
1359 TCP_PROBE3(debug__output, tp, th, m);
1362 * Fill in IP length and desired time to live and
1363 * send to IP level. There should be a better way
1364 * to handle ttl and tos; we could keep them in
1365 * the template, but need a way to checksum without them.
1368 * m->m_pkthdr.len should have been set before checksum calculation,
1369 * because in6_cksum() need it.
1374 * we separately set hoplimit for every segment, since the
1375 * user might want to change the value via setsockopt.
1376 * Also, desired default hop limit might be changed via
1377 * Neighbor Discovery.
1379 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1382 * Set the packet size here for the benefit of DTrace probes.
1383 * ip6_output() will set it properly; it's supposed to include
1384 * the option header lengths as well.
1386 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1388 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1389 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1391 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1393 if (tp->t_state == TCPS_SYN_SENT)
1394 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1396 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1399 /* Save packet, if requested. */
1400 tcp_pcap_add(th, m, &(tp->t_outpkts));
1403 /* TODO: IPv6 IP6TOS_ECT bit on */
1404 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1405 &tp->t_inpcb->inp_route6,
1406 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1407 NULL, NULL, tp->t_inpcb);
1409 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL)
1410 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu;
1413 #if defined(INET) && defined(INET6)
1418 ip->ip_len = htons(m->m_pkthdr.len);
1420 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1421 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1424 * If we do path MTU discovery, then we set DF on every packet.
1425 * This might not be the best thing to do according to RFC3390
1426 * Section 2. However the tcp hostcache migitates the problem
1427 * so it affects only the first tcp connection with a host.
1429 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1431 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1432 ip->ip_off |= htons(IP_DF);
1433 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1435 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1438 if (tp->t_state == TCPS_SYN_SENT)
1439 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1441 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1444 /* Save packet, if requested. */
1445 tcp_pcap_add(th, m, &(tp->t_outpkts));
1448 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1449 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1452 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1453 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1459 * In transmit state, time the transmission and arrange for
1460 * the retransmit. In persist state, just set snd_max.
1462 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1463 !tcp_timer_active(tp, TT_PERSIST)) {
1464 tcp_seq startseq = tp->snd_nxt;
1467 * Advance snd_nxt over sequence space of this segment.
1469 if (flags & (TH_SYN|TH_FIN)) {
1472 if (flags & TH_FIN) {
1474 tp->t_flags |= TF_SENTFIN;
1480 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1481 tp->snd_max = tp->snd_nxt;
1483 * Time this transmission if not a retransmission and
1484 * not currently timing anything.
1486 if (tp->t_rtttime == 0) {
1487 tp->t_rtttime = ticks;
1488 tp->t_rtseq = startseq;
1489 TCPSTAT_INC(tcps_segstimed);
1494 * Set retransmit timer if not currently set,
1495 * and not doing a pure ack or a keep-alive probe.
1496 * Initial value for retransmit timer is smoothed
1497 * round-trip time + 2 * round-trip time variance.
1498 * Initialize shift counter which is used for backoff
1499 * of retransmit time.
1502 if (!tcp_timer_active(tp, TT_REXMT) &&
1503 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1504 (tp->snd_nxt != tp->snd_una))) {
1505 if (tcp_timer_active(tp, TT_PERSIST)) {
1506 tcp_timer_activate(tp, TT_PERSIST, 0);
1509 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1510 } else if (len == 0 && sbavail(&so->so_snd) &&
1511 !tcp_timer_active(tp, TT_REXMT) &&
1512 !tcp_timer_active(tp, TT_PERSIST)) {
1514 * Avoid a situation where we do not set persist timer
1515 * after a zero window condition. For example:
1516 * 1) A -> B: packet with enough data to fill the window
1517 * 2) B -> A: ACK for #1 + new data (0 window
1519 * 3) A -> B: ACK for #2, 0 len packet
1521 * In this case, A will not activate the persist timer,
1522 * because it chose to send a packet. Unless tcp_output
1523 * is called for some other reason (delayed ack timer,
1524 * another input packet from B, socket syscall), A will
1525 * not send zero window probes.
1527 * So, if you send a 0-length packet, but there is data
1528 * in the socket buffer, and neither the rexmt or
1529 * persist timer is already set, then activate the
1537 * Persist case, update snd_max but since we are in
1538 * persist mode (no window) we do not update snd_nxt.
1543 if (flags & TH_FIN) {
1545 tp->t_flags |= TF_SENTFIN;
1547 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1548 tp->snd_max = tp->snd_nxt + xlen;
1554 * We know that the packet was lost, so back out the
1555 * sequence number advance, if any.
1557 * If the error is EPERM the packet got blocked by the
1558 * local firewall. Normally we should terminate the
1559 * connection but the blocking may have been spurious
1560 * due to a firewall reconfiguration cycle. So we treat
1561 * it like a packet loss and let the retransmit timer and
1562 * timeouts do their work over time.
1563 * XXX: It is a POLA question whether calling tcp_drop right
1564 * away would be the really correct behavior instead.
1566 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1567 !tcp_timer_active(tp, TT_PERSIST)) &&
1568 ((flags & TH_SYN) == 0) &&
1572 tp->sackhint.sack_bytes_rexmit -= len;
1573 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1574 ("sackhint bytes rtx >= 0"));
1578 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1581 tp->t_softerror = error;
1584 tp->t_softerror = error;
1587 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1588 tp->snd_cwnd = tp->t_maxseg;
1592 * For some reason the interface we used initially
1593 * to send segments changed to another or lowered
1595 * If TSO was active we either got an interface
1596 * without TSO capabilits or TSO was turned off.
1597 * If we obtained mtu from ip_output() then update
1601 tp->t_flags &= ~TF_TSO;
1603 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1611 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1612 tp->t_softerror = error;
1620 TCPSTAT_INC(tcps_sndtotal);
1623 * Data sent (as far as we can tell).
1624 * If this advertises a larger window than any other segment,
1625 * then remember the size of the advertised window.
1626 * Any pending ACK has now been sent.
1628 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1629 tp->rcv_adv = tp->rcv_nxt + recwin;
1630 tp->last_ack_sent = tp->rcv_nxt;
1631 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1632 if (tcp_timer_active(tp, TT_DELACK))
1633 tcp_timer_activate(tp, TT_DELACK, 0);
1636 * This completely breaks TCP if newreno is turned on. What happens
1637 * is that if delayed-acks are turned on on the receiver, this code
1638 * on the transmitter effectively destroys the TCP window, forcing
1639 * it to four packets (1.5Kx4 = 6K window).
1641 if (sendalot && --maxburst)
1650 tcp_setpersist(struct tcpcb *tp)
1652 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1655 tp->t_flags &= ~TF_PREVVALID;
1656 if (tcp_timer_active(tp, TT_REXMT))
1657 panic("tcp_setpersist: retransmit pending");
1659 * Start/restart persistence timer.
1661 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1662 tcp_persmin, tcp_persmax);
1663 tcp_timer_activate(tp, TT_PERSIST, tt);
1664 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1669 * Insert TCP options according to the supplied parameters to the place
1670 * optp in a consistent way. Can handle unaligned destinations.
1672 * The order of the option processing is crucial for optimal packing and
1673 * alignment for the scarce option space.
1675 * The optimal order for a SYN/SYN-ACK segment is:
1676 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1677 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1679 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1680 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1681 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1682 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1683 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1686 tcp_addoptions(struct tcpopt *to, u_char *optp)
1688 u_int32_t mask, optlen = 0;
1690 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1691 if ((to->to_flags & mask) != mask)
1693 if (optlen == TCP_MAXOLEN)
1695 switch (to->to_flags & mask) {
1697 while (optlen % 4) {
1698 optlen += TCPOLEN_NOP;
1699 *optp++ = TCPOPT_NOP;
1701 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1703 optlen += TCPOLEN_MAXSEG;
1704 *optp++ = TCPOPT_MAXSEG;
1705 *optp++ = TCPOLEN_MAXSEG;
1706 to->to_mss = htons(to->to_mss);
1707 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1708 optp += sizeof(to->to_mss);
1711 while (!optlen || optlen % 2 != 1) {
1712 optlen += TCPOLEN_NOP;
1713 *optp++ = TCPOPT_NOP;
1715 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1717 optlen += TCPOLEN_WINDOW;
1718 *optp++ = TCPOPT_WINDOW;
1719 *optp++ = TCPOLEN_WINDOW;
1720 *optp++ = to->to_wscale;
1723 while (optlen % 2) {
1724 optlen += TCPOLEN_NOP;
1725 *optp++ = TCPOPT_NOP;
1727 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1729 optlen += TCPOLEN_SACK_PERMITTED;
1730 *optp++ = TCPOPT_SACK_PERMITTED;
1731 *optp++ = TCPOLEN_SACK_PERMITTED;
1734 while (!optlen || optlen % 4 != 2) {
1735 optlen += TCPOLEN_NOP;
1736 *optp++ = TCPOPT_NOP;
1738 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1740 optlen += TCPOLEN_TIMESTAMP;
1741 *optp++ = TCPOPT_TIMESTAMP;
1742 *optp++ = TCPOLEN_TIMESTAMP;
1743 to->to_tsval = htonl(to->to_tsval);
1744 to->to_tsecr = htonl(to->to_tsecr);
1745 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1746 optp += sizeof(to->to_tsval);
1747 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1748 optp += sizeof(to->to_tsecr);
1752 int siglen = TCPOLEN_SIGNATURE - 2;
1754 while (!optlen || optlen % 4 != 2) {
1755 optlen += TCPOLEN_NOP;
1756 *optp++ = TCPOPT_NOP;
1758 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1759 to->to_flags &= ~TOF_SIGNATURE;
1762 optlen += TCPOLEN_SIGNATURE;
1763 *optp++ = TCPOPT_SIGNATURE;
1764 *optp++ = TCPOLEN_SIGNATURE;
1765 to->to_signature = optp;
1773 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1776 while (!optlen || optlen % 4 != 2) {
1777 optlen += TCPOLEN_NOP;
1778 *optp++ = TCPOPT_NOP;
1780 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1782 optlen += TCPOLEN_SACKHDR;
1783 *optp++ = TCPOPT_SACK;
1784 sackblks = min(to->to_nsacks,
1785 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1786 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1787 while (sackblks--) {
1788 sack_seq = htonl(sack->start);
1789 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1790 optp += sizeof(sack_seq);
1791 sack_seq = htonl(sack->end);
1792 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1793 optp += sizeof(sack_seq);
1794 optlen += TCPOLEN_SACK;
1797 TCPSTAT_INC(tcps_sack_send_blocks);
1804 /* XXX is there any point to aligning this option? */
1805 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1806 if (TCP_MAXOLEN - optlen < total_len) {
1807 to->to_flags &= ~TOF_FASTOPEN;
1810 *optp++ = TCPOPT_FAST_OPEN;
1811 *optp++ = total_len;
1812 if (to->to_tfo_len > 0) {
1813 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1814 optp += to->to_tfo_len;
1816 optlen += total_len;
1820 panic("%s: unknown TCP option type", __func__);
1825 /* Terminate and pad TCP options to a 4 byte boundary. */
1827 optlen += TCPOLEN_EOL;
1828 *optp++ = TCPOPT_EOL;
1831 * According to RFC 793 (STD0007):
1832 * "The content of the header beyond the End-of-Option option
1833 * must be header padding (i.e., zero)."
1834 * and later: "The padding is composed of zeros."
1836 while (optlen % 4) {
1837 optlen += TCPOLEN_PAD;
1838 *optp++ = TCPOPT_PAD;
1841 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1846 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
1850 * Automatic sizing of send socket buffer. Often the send buffer
1851 * size is not optimally adjusted to the actual network conditions
1852 * at hand (delay bandwidth product). Setting the buffer size too
1853 * small limits throughput on links with high bandwidth and high
1854 * delay (eg. trans-continental/oceanic links). Setting the
1855 * buffer size too big consumes too much real kernel memory,
1856 * especially with many connections on busy servers.
1858 * The criteria to step up the send buffer one notch are:
1859 * 1. receive window of remote host is larger than send buffer
1860 * (with a fudge factor of 5/4th);
1861 * 2. send buffer is filled to 7/8th with data (so we actually
1862 * have data to make use of it);
1863 * 3. send buffer fill has not hit maximal automatic size;
1864 * 4. our send window (slow start and cogestion controlled) is
1865 * larger than sent but unacknowledged data in send buffer.
1867 * The remote host receive window scaling factor may limit the
1868 * growing of the send buffer before it reaches its allowed
1871 * It scales directly with slow start or congestion window
1872 * and does at most one step per received ACK. This fast
1873 * scaling has the drawback of growing the send buffer beyond
1874 * what is strictly necessary to make full use of a given
1875 * delay*bandwidth product. However testing has shown this not
1876 * to be much of an problem. At worst we are trading wasting
1877 * of available bandwidth (the non-use of it) for wasting some
1878 * socket buffer memory.
1880 * TODO: Shrink send buffer during idle periods together
1881 * with congestion window. Requires another timer. Has to
1882 * wait for upcoming tcp timer rewrite.
1884 * XXXGL: should there be used sbused() or sbavail()?
1886 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
1889 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
1890 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
1891 sbused(&so->so_snd) >=
1892 (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
1893 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
1894 sendwin >= (sbused(&so->so_snd) -
1895 (tp->snd_nxt - tp->snd_una))) {
1896 if (!sbreserve_locked(&so->so_snd,
1897 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
1898 V_tcp_autosndbuf_max), so, curthread))
1899 so->so_snd.sb_flags &= ~SB_AUTOSIZE;