2 * SPDX-License-Identifier: BSD-3-Clause
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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_kern_tls.h"
41 #include "opt_tcpdebug.h"
43 #include <sys/param.h>
44 #include <sys/systm.h>
46 #include <sys/domain.h>
48 #include <sys/hhook.h>
50 #include <sys/kernel.h>
56 #include <sys/mutex.h>
57 #include <sys/protosw.h>
58 #include <sys/qmath.h>
60 #include <sys/socket.h>
61 #include <sys/socketvar.h>
62 #include <sys/sysctl.h>
63 #include <sys/stats.h>
66 #include <net/route.h>
67 #include <net/route/nhop.h>
70 #include <netinet/in.h>
71 #include <netinet/in_kdtrace.h>
72 #include <netinet/in_systm.h>
73 #include <netinet/ip.h>
74 #include <netinet/in_pcb.h>
75 #include <netinet/ip_var.h>
76 #include <netinet/ip_options.h>
78 #include <netinet6/in6_pcb.h>
79 #include <netinet/ip6.h>
80 #include <netinet6/ip6_var.h>
82 #include <netinet/tcp.h>
84 #include <netinet/tcp_fsm.h>
85 #include <netinet/tcp_log_buf.h>
86 #include <netinet/tcp_seq.h>
87 #include <netinet/tcp_timer.h>
88 #include <netinet/tcp_var.h>
89 #include <netinet/tcpip.h>
90 #include <netinet/cc/cc.h>
91 #include <netinet/tcp_fastopen.h>
93 #include <netinet/tcp_pcap.h>
96 #include <netinet/tcp_debug.h>
99 #include <netinet/tcp_offload.h>
102 #include <netipsec/ipsec_support.h>
104 #include <netinet/udp.h>
105 #include <netinet/udp_var.h>
106 #include <machine/in_cksum.h>
108 #include <security/mac/mac_framework.h>
110 VNET_DEFINE(int, path_mtu_discovery) = 1;
111 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
112 &VNET_NAME(path_mtu_discovery), 1,
113 "Enable Path MTU Discovery");
115 VNET_DEFINE(int, tcp_do_tso) = 1;
116 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
117 &VNET_NAME(tcp_do_tso), 0,
118 "Enable TCP Segmentation Offload");
120 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
121 #define V_tcp_sendspace VNET(tcp_sendspace)
122 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
123 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
125 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
126 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
127 &VNET_NAME(tcp_do_autosndbuf), 0,
128 "Enable automatic send buffer sizing");
130 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
132 &VNET_NAME(tcp_autosndbuf_inc), 0,
133 "Incrementor step size of automatic send buffer");
135 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
136 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
137 &VNET_NAME(tcp_autosndbuf_max), 0,
138 "Max size of automatic send buffer");
140 VNET_DEFINE(int, tcp_sendbuf_auto_lowat) = 0;
141 #define V_tcp_sendbuf_auto_lowat VNET(tcp_sendbuf_auto_lowat)
142 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto_lowat, CTLFLAG_VNET | CTLFLAG_RW,
143 &VNET_NAME(tcp_sendbuf_auto_lowat), 0,
144 "Modify threshold for auto send buffer growth to account for SO_SNDLOWAT");
147 * Make sure that either retransmit or persist timer is set for SYN, FIN and
150 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
151 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
152 tcp_timer_active((tp), TT_REXMT) || \
153 tcp_timer_active((tp), TT_PERSIST), \
154 ("neither rexmt nor persist timer is set"))
156 static void inline cc_after_idle(struct tcpcb *tp);
160 * Wrapper for the TCP established output helper hook.
163 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
164 struct tcpopt *to, uint32_t len, int tso)
166 struct tcp_hhook_data hhook_data;
168 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
172 hhook_data.len = len;
173 hhook_data.tso = tso;
175 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
182 * CC wrapper hook functions
185 cc_after_idle(struct tcpcb *tp)
187 INP_WLOCK_ASSERT(tp->t_inpcb);
189 if (CC_ALGO(tp)->after_idle != NULL)
190 CC_ALGO(tp)->after_idle(tp->ccv);
194 * Tcp output routine: figure out what should be sent and send it.
197 tcp_output(struct tcpcb *tp)
199 struct socket *so = tp->t_inpcb->inp_socket;
201 uint32_t recwin, sendwin;
202 int off, flags, error = 0; /* Keep compiler happy */
203 u_int if_hw_tsomaxsegcount = 0;
204 u_int if_hw_tsomaxsegsize = 0;
206 struct ip *ip = NULL;
208 struct ipovly *ipov = NULL;
211 u_char opt[TCP_MAXOLEN];
212 unsigned ipoptlen, optlen, hdrlen, ulen;
213 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
214 unsigned ipsec_optlen = 0;
216 int idle, sendalot, curticks;
217 int sack_rxmit, sack_bytes_rxmt;
221 struct udphdr *udp = NULL;
222 unsigned int wanted_cookie = 0;
223 unsigned int dont_sendalot = 0;
225 int maxburst = TCP_MAXBURST;
228 struct ip6_hdr *ip6 = NULL;
231 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
234 const bool hw_tls = (so->so_snd.sb_flags & SB_TLS_IFNET) != 0;
236 const bool hw_tls = false;
240 INP_WLOCK_ASSERT(tp->t_inpcb);
243 if (tp->t_flags & TF_TOE)
244 return (tcp_offload_output(tp));
248 * For TFO connections in SYN_SENT or SYN_RECEIVED,
249 * only allow the initial SYN or SYN|ACK and those sent
250 * by the retransmit timer.
252 if (IS_FASTOPEN(tp->t_flags) &&
253 ((tp->t_state == TCPS_SYN_SENT) ||
254 (tp->t_state == TCPS_SYN_RECEIVED)) &&
255 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN or SYN|ACK sent */
256 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */
260 * Determine length of data that should be transmitted,
261 * and flags that will be used.
262 * If there is some data or critical controls (SYN, RST)
263 * to send, then transmit; otherwise, investigate further.
265 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
266 if (idle && (((ticks - tp->t_rcvtime) >= tp->t_rxtcur) ||
267 (tp->t_sndtime && ((ticks - tp->t_sndtime) >= tp->t_rxtcur))))
269 tp->t_flags &= ~TF_LASTIDLE;
271 if (tp->t_flags & TF_MORETOCOME) {
272 tp->t_flags |= TF_LASTIDLE;
278 * If we've recently taken a timeout, snd_max will be greater than
279 * snd_nxt. There may be SACK information that allows us to avoid
280 * resending already delivered data. Adjust snd_nxt accordingly.
282 if ((tp->t_flags & TF_SACK_PERMIT) &&
283 SEQ_LT(tp->snd_nxt, tp->snd_max))
288 off = tp->snd_nxt - tp->snd_una;
289 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
291 flags = tcp_outflags[tp->t_state];
293 * Send any SACK-generated retransmissions. If we're explicitly trying
294 * to send out new data (when sendalot is 1), bypass this function.
295 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
296 * we're replacing a (future) new transmission with a retransmission
297 * now, and we previously incremented snd_cwnd in tcp_input().
300 * Still in sack recovery , reset rxmit flag to zero.
306 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
307 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
311 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
312 /* Do not retransmit SACK segments beyond snd_recover */
313 if (SEQ_GT(p->end, tp->snd_recover)) {
315 * (At least) part of sack hole extends beyond
316 * snd_recover. Check to see if we can rexmit data
319 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
321 * Can't rexmit any more data for this hole.
322 * That data will be rexmitted in the next
323 * sack recovery episode, when snd_recover
324 * moves past p->rxmit.
327 goto after_sack_rexmit;
329 /* Can rexmit part of the current hole */
330 len = ((int32_t)ulmin(cwin,
331 tp->snd_recover - p->rxmit));
333 len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
334 off = p->rxmit - tp->snd_una;
335 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
340 TCPSTAT_INC(tcps_sack_rexmits);
341 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
342 min(len, tcp_maxseg(tp)));
347 * Get standard flags, and add SYN or FIN if requested by 'hidden'
350 if (tp->t_flags & TF_NEEDFIN)
352 if (tp->t_flags & TF_NEEDSYN)
355 SOCKBUF_LOCK(&so->so_snd);
357 * If in persist timeout with window of 0, send 1 byte.
358 * Otherwise, if window is small but nonzero
359 * and timer expired, we will send what we can
360 * and go to transmit state.
362 if (tp->t_flags & TF_FORCEDATA) {
365 * If we still have some data to send, then
366 * clear the FIN bit. Usually this would
367 * happen below when it realizes that we
368 * aren't sending all the data. However,
369 * if we have exactly 1 byte of unsent data,
370 * then it won't clear the FIN bit below,
371 * and if we are in persist state, we wind
372 * up sending the packet without recording
373 * that we sent the FIN bit.
375 * We can't just blindly clear the FIN bit,
376 * because if we don't have any more data
377 * to send then the probe will be the FIN
380 if (off < sbused(&so->so_snd))
384 tcp_timer_activate(tp, TT_PERSIST, 0);
390 * If snd_nxt == snd_max and we have transmitted a FIN, the
391 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
392 * a negative length. This can also occur when TCP opens up
393 * its congestion window while receiving additional duplicate
394 * acks after fast-retransmit because TCP will reset snd_nxt
395 * to snd_max after the fast-retransmit.
397 * In the normal retransmit-FIN-only case, however, snd_nxt will
398 * be set to snd_una, the offset will be 0, and the length may
401 * If sack_rxmit is true we are retransmitting from the scoreboard
402 * in which case len is already set.
404 if (sack_rxmit == 0) {
405 if (sack_bytes_rxmt == 0)
406 len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
412 * We are inside of a SACK recovery episode and are
413 * sending new data, having retransmitted all the
414 * data possible in the scoreboard.
416 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
419 * Don't remove this (len > 0) check !
420 * We explicitly check for len > 0 here (although it
421 * isn't really necessary), to work around a gcc
422 * optimization issue - to force gcc to compute
423 * len above. Without this check, the computation
424 * of len is bungled by the optimizer.
427 cwin = tp->snd_cwnd -
428 (tp->snd_nxt - tp->snd_recover) -
432 len = imin(len, cwin);
438 * Lop off SYN bit if it has already been sent. However, if this
439 * is SYN-SENT state and if segment contains data and if we don't
440 * know that foreign host supports TAO, suppress sending segment.
442 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
443 if (tp->t_state != TCPS_SYN_RECEIVED)
446 * When sending additional segments following a TFO SYN|ACK,
447 * do not include the SYN bit.
449 if (IS_FASTOPEN(tp->t_flags) &&
450 (tp->t_state == TCPS_SYN_RECEIVED))
456 * Be careful not to send data and/or FIN on SYN segments.
457 * This measure is needed to prevent interoperability problems
458 * with not fully conformant TCP implementations.
460 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
466 * On TFO sockets, ensure no data is sent in the following cases:
468 * - When retransmitting SYN|ACK on a passively-created socket
470 * - When retransmitting SYN on an actively created socket
472 * - When sending a zero-length cookie (cookie request) on an
473 * actively created socket
475 * - When the socket is in the CLOSED state (RST is being sent)
477 if (IS_FASTOPEN(tp->t_flags) &&
478 (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
479 ((tp->t_state == TCPS_SYN_SENT) &&
480 (tp->t_tfo_client_cookie_len == 0)) ||
485 * If FIN has been sent but not acked,
486 * but we haven't been called to retransmit,
487 * len will be < 0. Otherwise, window shrank
488 * after we sent into it. If window shrank to 0,
489 * cancel pending retransmit, pull snd_nxt back
490 * to (closed) window, and set the persist timer
491 * if it isn't already going. If the window didn't
492 * close completely, just wait for an ACK.
494 * We also do a general check here to ensure that
495 * we will set the persist timer when we have data
496 * to send, but a 0-byte window. This makes sure
497 * the persist timer is set even if the packet
498 * hits one of the "goto send" lines below.
501 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
502 (off < (int) sbavail(&so->so_snd))) {
503 tcp_timer_activate(tp, TT_REXMT, 0);
505 tp->snd_nxt = tp->snd_una;
506 if (!tcp_timer_active(tp, TT_PERSIST))
511 /* len will be >= 0 after this point. */
512 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
514 tcp_sndbuf_autoscale(tp, so, sendwin);
517 * Decide if we can use TCP Segmentation Offloading (if supported by
520 * TSO may only be used if we are in a pure bulk sending state. The
521 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
522 * IP options prevent using TSO. With TSO the TCP header is the same
523 * (except for the sequence number) for all generated packets. This
524 * makes it impossible to transmit any options which vary per generated
527 * IPv4 handling has a clear separation of ip options and ip header
528 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
529 * the right thing below to provide length of just ip options and thus
530 * checking for ipoptlen is enough to decide if ip options are present.
532 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
534 * Pre-calculate here as we save another lookup into the darknesses
535 * of IPsec that way and can actually decide if TSO is ok.
538 if (isipv6 && IPSEC_ENABLED(ipv6))
539 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
545 if (IPSEC_ENABLED(ipv4))
546 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
551 ipoptlen = ip6_optlen(tp->t_inpcb);
554 if (tp->t_inpcb->inp_options)
555 ipoptlen = tp->t_inpcb->inp_options->m_len -
556 offsetof(struct ipoption, ipopt_list);
559 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
560 ipoptlen += ipsec_optlen;
563 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
565 ((tp->t_flags & TF_SIGNATURE) == 0) &&
566 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
567 ipoptlen == 0 && !(flags & TH_SYN))
571 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
574 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
575 sbused(&so->so_snd)))
579 recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
580 (long)TCP_MAXWIN << tp->rcv_scale);
583 * Sender silly window avoidance. We transmit under the following
584 * conditions when len is non-zero:
586 * - We have a full segment (or more with TSO)
587 * - This is the last buffer in a write()/send() and we are
588 * either idle or running NODELAY
589 * - we've timed out (e.g. persist timer)
590 * - we have more then 1/2 the maximum send window's worth of
591 * data (receiver may be limited the window size)
592 * - we need to retransmit
595 if (len >= tp->t_maxseg)
598 * As the TCP header options are now
599 * considered when setting up the initial
600 * window, we would not send the last segment
601 * if we skip considering the option length here.
602 * Note: this may not work when tcp headers change
603 * very dynamically in the future.
605 if ((((tp->t_flags & TF_SIGNATURE) ?
606 PADTCPOLEN(TCPOLEN_SIGNATURE) : 0) +
607 ((tp->t_flags & TF_RCVD_TSTMP) ?
608 PADTCPOLEN(TCPOLEN_TIMESTAMP) : 0) +
609 len) >= tp->t_maxseg)
612 * NOTE! on localhost connections an 'ack' from the remote
613 * end may occur synchronously with the output and cause
614 * us to flush a buffer queued with moretocome. XXX
616 * note: the len + off check is almost certainly unnecessary.
618 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
619 (idle || (tp->t_flags & TF_NODELAY)) &&
620 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
621 (tp->t_flags & TF_NOPUSH) == 0) {
624 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
626 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
628 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
635 * Sending of standalone window updates.
637 * Window updates are important when we close our window due to a
638 * full socket buffer and are opening it again after the application
639 * reads data from it. Once the window has opened again and the
640 * remote end starts to send again the ACK clock takes over and
641 * provides the most current window information.
643 * We must avoid the silly window syndrome whereas every read
644 * from the receive buffer, no matter how small, causes a window
645 * update to be sent. We also should avoid sending a flurry of
646 * window updates when the socket buffer had queued a lot of data
647 * and the application is doing small reads.
649 * Prevent a flurry of pointless window updates by only sending
650 * an update when we can increase the advertized window by more
651 * than 1/4th of the socket buffer capacity. When the buffer is
652 * getting full or is very small be more aggressive and send an
653 * update whenever we can increase by two mss sized segments.
654 * In all other situations the ACK's to new incoming data will
655 * carry further window increases.
657 * Don't send an independent window update if a delayed
658 * ACK is pending (it will get piggy-backed on it) or the
659 * remote side already has done a half-close and won't send
660 * more data. Skip this if the connection is in T/TCP
663 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
664 !(tp->t_flags & TF_DELACK) &&
665 !TCPS_HAVERCVDFIN(tp->t_state)) {
667 * "adv" is the amount we could increase the window,
668 * taking into account that we are limited by
669 * TCP_MAXWIN << tp->rcv_scale.
675 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
676 oldwin = (tp->rcv_adv - tp->rcv_nxt);
685 * If the new window size ends up being the same as or less
686 * than the old size when it is scaled, then don't force
689 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
692 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
693 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
694 recwin <= (so->so_rcv.sb_hiwat / 8) ||
695 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
696 adv >= TCP_MAXWIN << tp->rcv_scale))
698 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
704 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
705 * is also a catch-all for the retransmit timer timeout case.
707 if (tp->t_flags & TF_ACKNOW)
709 if ((flags & TH_RST) ||
710 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
712 if (SEQ_GT(tp->snd_up, tp->snd_una))
715 * If our state indicates that FIN should be sent
716 * and we have not yet done so, then we need to send.
718 if (flags & TH_FIN &&
719 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
722 * In SACK, it is possible for tcp_output to fail to send a segment
723 * after the retransmission timer has been turned off. Make sure
724 * that the retransmission timer is set.
726 if ((tp->t_flags & TF_SACK_PERMIT) &&
727 SEQ_GT(tp->snd_max, tp->snd_una) &&
728 !tcp_timer_active(tp, TT_REXMT) &&
729 !tcp_timer_active(tp, TT_PERSIST)) {
730 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
734 * TCP window updates are not reliable, rather a polling protocol
735 * using ``persist'' packets is used to insure receipt of window
736 * updates. The three ``states'' for the output side are:
737 * idle not doing retransmits or persists
738 * persisting to move a small or zero window
739 * (re)transmitting and thereby not persisting
741 * tcp_timer_active(tp, TT_PERSIST)
742 * is true when we are in persist state.
743 * (tp->t_flags & TF_FORCEDATA)
744 * is set when we are called to send a persist packet.
745 * tcp_timer_active(tp, TT_REXMT)
746 * is set when we are retransmitting
747 * The output side is idle when both timers are zero.
749 * If send window is too small, there is data to transmit, and no
750 * retransmit or persist is pending, then go to persist state.
751 * If nothing happens soon, send when timer expires:
752 * if window is nonzero, transmit what we can,
753 * otherwise force out a byte.
755 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
756 !tcp_timer_active(tp, TT_PERSIST)) {
762 * No reason to send a segment, just return.
765 SOCKBUF_UNLOCK(&so->so_snd);
769 SOCKBUF_LOCK_ASSERT(&so->so_snd);
771 if (len >= tp->t_maxseg)
772 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
774 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
777 * Before ESTABLISHED, force sending of initial options
778 * unless TCP set not to do any options.
779 * NOTE: we assume that the IP/TCP header plus TCP options
780 * always fit in a single mbuf, leaving room for a maximum
782 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
787 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
790 hdrlen = sizeof (struct tcpiphdr);
792 if (flags & TH_SYN) {
793 tp->snd_nxt = tp->iss;
797 * Compute options for segment.
798 * We only have to care about SYN and established connection
799 * segments. Options for SYN-ACK segments are handled in TCP
803 if ((tp->t_flags & TF_NOOPT) == 0) {
804 /* Maximum segment size. */
805 if (flags & TH_SYN) {
806 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
808 to.to_mss -= V_tcp_udp_tunneling_overhead;
809 to.to_flags |= TOF_MSS;
812 * On SYN or SYN|ACK transmits on TFO connections,
813 * only include the TFO option if it is not a
814 * retransmit, as the presence of the TFO option may
815 * have caused the original SYN or SYN|ACK to have
816 * been dropped by a middlebox.
818 if (IS_FASTOPEN(tp->t_flags) &&
819 (tp->t_rxtshift == 0)) {
820 if (tp->t_state == TCPS_SYN_RECEIVED) {
821 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
823 (u_int8_t *)&tp->t_tfo_cookie.server;
824 to.to_flags |= TOF_FASTOPEN;
826 } else if (tp->t_state == TCPS_SYN_SENT) {
828 tp->t_tfo_client_cookie_len;
830 tp->t_tfo_cookie.client;
831 to.to_flags |= TOF_FASTOPEN;
834 * If we wind up having more data to
835 * send with the SYN than can fit in
836 * one segment, don't send any more
837 * until the SYN|ACK comes back from
844 /* Window scaling. */
845 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
846 to.to_wscale = tp->request_r_scale;
847 to.to_flags |= TOF_SCALE;
850 if ((tp->t_flags & TF_RCVD_TSTMP) ||
851 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
852 curticks = tcp_ts_getticks();
853 to.to_tsval = curticks + tp->ts_offset;
854 to.to_tsecr = tp->ts_recent;
855 to.to_flags |= TOF_TS;
856 if (tp->t_rxtshift == 1)
857 tp->t_badrxtwin = curticks;
860 /* Set receive buffer autosizing timestamp. */
861 if (tp->rfbuf_ts == 0 &&
862 (so->so_rcv.sb_flags & SB_AUTOSIZE))
863 tp->rfbuf_ts = tcp_ts_getticks();
865 /* Selective ACK's. */
866 if (tp->t_flags & TF_SACK_PERMIT) {
868 to.to_flags |= TOF_SACKPERM;
869 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
870 tp->rcv_numsacks > 0) {
871 to.to_flags |= TOF_SACK;
872 to.to_nsacks = tp->rcv_numsacks;
873 to.to_sacks = (u_char *)tp->sackblks;
876 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
877 /* TCP-MD5 (RFC2385). */
879 * Check that TCP_MD5SIG is enabled in tcpcb to
880 * account the size needed to set this TCP option.
882 if (tp->t_flags & TF_SIGNATURE)
883 to.to_flags |= TOF_SIGNATURE;
884 #endif /* TCP_SIGNATURE */
886 /* Processing the options. */
887 hdrlen += optlen = tcp_addoptions(&to, opt);
889 * If we wanted a TFO option to be added, but it was unable
890 * to fit, ensure no data is sent.
892 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
893 !(to.to_flags & TOF_FASTOPEN))
897 if (V_tcp_udp_tunneling_port == 0) {
898 /* The port was removed?? */
899 SOCKBUF_UNLOCK(&so->so_snd);
900 return (EHOSTUNREACH);
902 hdrlen += sizeof(struct udphdr);
905 * Adjust data length if insertion of options will
906 * bump the packet length beyond the t_maxseg length.
907 * Clear the FIN bit because we cut off the tail of
910 if (len + optlen + ipoptlen > tp->t_maxseg) {
918 /* extract TSO information */
919 if_hw_tsomax = tp->t_tsomax;
920 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
921 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
924 * Limit a TSO burst to prevent it from
925 * overflowing or exceeding the maximum length
926 * allowed by the network interface:
928 KASSERT(ipoptlen == 0,
929 ("%s: TSO can't do IP options", __func__));
932 * Check if we should limit by maximum payload
935 if (if_hw_tsomax != 0) {
936 /* compute maximum TSO length */
937 max_len = (if_hw_tsomax - hdrlen -
941 } else if (len > max_len) {
948 * Prevent the last segment from being
949 * fractional unless the send sockbuf can be
952 max_len = (tp->t_maxseg - optlen);
953 if (((uint32_t)off + (uint32_t)len) <
954 sbavail(&so->so_snd)) {
955 moff = len % max_len;
963 * In case there are too many small fragments
966 if (len <= max_len) {
973 * Send the FIN in a separate segment
974 * after the bulk sending is done.
975 * We don't trust the TSO implementations
976 * to clear the FIN flag on all but the
979 if (tp->t_flags & TF_NEEDFIN)
982 if (optlen + ipoptlen >= tp->t_maxseg) {
984 * Since we don't have enough space to put
985 * the IP header chain and the TCP header in
986 * one packet as required by RFC 7112, don't
987 * send it. Also ensure that at least one
988 * byte of the payload can be put into the
991 SOCKBUF_UNLOCK(&so->so_snd);
996 len = tp->t_maxseg - optlen - ipoptlen;
1004 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1005 ("%s: len > IP_MAXPACKET", __func__));
1007 /*#ifdef DIAGNOSTIC*/
1009 if (max_linkhdr + hdrlen > MCLBYTES)
1011 if (max_linkhdr + hdrlen > MHLEN)
1013 panic("tcphdr too big");
1017 * This KASSERT is here to catch edge cases at a well defined place.
1018 * Before, those had triggered (random) panic conditions further down.
1020 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1023 * Grab a header mbuf, attaching a copy of data to
1024 * be transmitted, and initialize the header from
1025 * the template for sends on this connection.
1029 struct sockbuf *msb;
1032 if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1033 TCPSTAT_INC(tcps_sndprobe);
1035 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1036 stats_voi_update_abs_u32(tp->t_stats,
1037 VOI_TCP_RETXPB, len);
1039 stats_voi_update_abs_u64(tp->t_stats,
1042 } else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1043 tp->t_sndrexmitpack++;
1044 TCPSTAT_INC(tcps_sndrexmitpack);
1045 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1047 stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1051 TCPSTAT_INC(tcps_sndpack);
1052 TCPSTAT_ADD(tcps_sndbyte, len);
1054 stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1059 if (MHLEN < hdrlen + max_linkhdr)
1060 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1063 m = m_gethdr(M_NOWAIT, MT_DATA);
1066 SOCKBUF_UNLOCK(&so->so_snd);
1072 m->m_data += max_linkhdr;
1076 * Start the m_copy functions from the closest mbuf
1077 * to the offset in the socket buffer chain.
1079 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1080 if (len <= MHLEN - hdrlen - max_linkhdr && !hw_tls) {
1081 m_copydata(mb, moff, len,
1082 mtod(m, caddr_t) + hdrlen);
1083 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1084 sbsndptr_adv(&so->so_snd, mb, len);
1087 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1091 m->m_next = tcp_m_copym(mb, moff,
1092 &len, if_hw_tsomaxsegcount,
1093 if_hw_tsomaxsegsize, msb, hw_tls);
1094 if (len <= (tp->t_maxseg - optlen)) {
1096 * Must have ran out of mbufs for the copy
1097 * shorten it to no longer need tso. Lets
1098 * not put on sendalot since we are low on
1103 if (m->m_next == NULL) {
1104 SOCKBUF_UNLOCK(&so->so_snd);
1113 * If we're sending everything we've got, set PUSH.
1114 * (This will keep happy those implementations which only
1115 * give data to the user when a buffer fills or
1118 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1121 SOCKBUF_UNLOCK(&so->so_snd);
1123 SOCKBUF_UNLOCK(&so->so_snd);
1124 if (tp->t_flags & TF_ACKNOW)
1125 TCPSTAT_INC(tcps_sndacks);
1126 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1127 TCPSTAT_INC(tcps_sndctrl);
1128 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1129 TCPSTAT_INC(tcps_sndurg);
1131 TCPSTAT_INC(tcps_sndwinup);
1133 m = m_gethdr(M_NOWAIT, MT_DATA);
1140 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1145 m->m_data += max_linkhdr;
1148 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1149 m->m_pkthdr.rcvif = (struct ifnet *)0;
1151 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1155 ip6 = mtod(m, struct ip6_hdr *);
1157 udp = (struct udphdr *)((caddr_t)ip6 + sizeof(struct ip6_hdr));
1158 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1159 udp->uh_dport = tp->t_port;
1160 ulen = hdrlen + len - sizeof(struct ip6_hdr);
1161 udp->uh_ulen = htons(ulen);
1162 th = (struct tcphdr *)(udp + 1);
1164 th = (struct tcphdr *)(ip6 + 1);
1166 tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip6, th);
1170 ip = mtod(m, struct ip *);
1172 ipov = (struct ipovly *)ip;
1175 udp = (struct udphdr *)((caddr_t)ip + sizeof(struct ip));
1176 udp->uh_sport = htons(V_tcp_udp_tunneling_port);
1177 udp->uh_dport = tp->t_port;
1178 ulen = hdrlen + len - sizeof(struct ip);
1179 udp->uh_ulen = htons(ulen);
1180 th = (struct tcphdr *)(udp + 1);
1182 th = (struct tcphdr *)(ip + 1);
1183 tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip, th);
1187 * Fill in fields, remembering maximum advertised
1188 * window for use in delaying messages about window sizes.
1189 * If resending a FIN, be sure not to use a new sequence number.
1191 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1192 tp->snd_nxt == tp->snd_max)
1195 * If we are starting a connection, send ECN setup
1196 * SYN packet. If we are on a retransmit, we may
1197 * resend those bits a number of times as per
1200 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1201 if (tp->t_rxtshift >= 1) {
1202 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1203 flags |= TH_ECE|TH_CWR;
1205 flags |= TH_ECE|TH_CWR;
1207 /* Handle parallel SYN for ECN */
1208 if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1209 (tp->t_flags2 & TF2_ECN_SND_ECE)) {
1211 tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1214 if (TCPS_HAVEESTABLISHED(tp->t_state) &&
1215 (tp->t_flags2 & TF2_ECN_PERMIT)) {
1217 * If the peer has ECN, mark data packets with
1218 * ECN capable transmission (ECT).
1219 * Ignore pure ack packets, retransmissions and window probes.
1221 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1222 (sack_rxmit == 0) &&
1223 !((tp->t_flags & TF_FORCEDATA) && len == 1 &&
1224 SEQ_LT(tp->snd_una, tp->snd_max))) {
1227 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1230 ip->ip_tos |= IPTOS_ECN_ECT0;
1231 TCPSTAT_INC(tcps_ecn_ect0);
1233 * Reply with proper ECN notifications.
1234 * Only set CWR on new data segments.
1236 if (tp->t_flags2 & TF2_ECN_SND_CWR) {
1238 tp->t_flags2 &= ~TF2_ECN_SND_CWR;
1241 if (tp->t_flags2 & TF2_ECN_SND_ECE)
1246 * If we are doing retransmissions, then snd_nxt will
1247 * not reflect the first unsent octet. For ACK only
1248 * packets, we do not want the sequence number of the
1249 * retransmitted packet, we want the sequence number
1250 * of the next unsent octet. So, if there is no data
1251 * (and no SYN or FIN), use snd_max instead of snd_nxt
1252 * when filling in ti_seq. But if we are in persist
1253 * state, snd_max might reflect one byte beyond the
1254 * right edge of the window, so use snd_nxt in that
1255 * case, since we know we aren't doing a retransmission.
1256 * (retransmit and persist are mutually exclusive...)
1258 if (sack_rxmit == 0) {
1259 if (len || (flags & (TH_SYN|TH_FIN)) ||
1260 tcp_timer_active(tp, TT_PERSIST))
1261 th->th_seq = htonl(tp->snd_nxt);
1263 th->th_seq = htonl(tp->snd_max);
1265 th->th_seq = htonl(p->rxmit);
1268 * Lost Retransmission Detection
1269 * trigger resending of a (then
1270 * still existing) hole, when
1271 * fack acks recoverypoint.
1273 if ((tp->t_flags & TF_LRD) && SEQ_GEQ(p->rxmit, p->end))
1274 p->rxmit = tp->snd_recover;
1275 tp->sackhint.sack_bytes_rexmit += len;
1277 if (IN_RECOVERY(tp->t_flags)) {
1279 * Account all bytes transmitted while
1280 * IN_RECOVERY, simplifying PRR and
1281 * Lost Retransmit Detection
1283 tp->sackhint.prr_out += len;
1285 th->th_ack = htonl(tp->rcv_nxt);
1287 bcopy(opt, th + 1, optlen);
1288 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1290 th->th_flags = flags;
1292 * Calculate receive window. Don't shrink window,
1293 * but avoid silly window syndrome.
1294 * If a RST segment is sent, advertise a window of zero.
1296 if (flags & TH_RST) {
1299 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1300 recwin < tp->t_maxseg)
1302 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1303 recwin < (tp->rcv_adv - tp->rcv_nxt))
1304 recwin = (tp->rcv_adv - tp->rcv_nxt);
1307 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1308 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1309 * case is handled in syncache.
1312 th->th_win = htons((u_short)
1313 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1315 /* Avoid shrinking window with window scaling. */
1316 recwin = roundup2(recwin, 1 << tp->rcv_scale);
1317 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1321 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1322 * a 0 window. This may cause the remote transmitter to stall. This
1323 * flag tells soreceive() to disable delayed acknowledgements when
1324 * draining the buffer. This can occur if the receiver is attempting
1325 * to read more data than can be buffered prior to transmitting on
1328 if (th->th_win == 0) {
1330 tp->t_flags |= TF_RXWIN0SENT;
1332 tp->t_flags &= ~TF_RXWIN0SENT;
1333 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1334 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1335 th->th_flags |= TH_URG;
1338 * If no urgent pointer to send, then we pull
1339 * the urgent pointer to the left edge of the send window
1340 * so that it doesn't drift into the send window on sequence
1341 * number wraparound.
1343 tp->snd_up = tp->snd_una; /* drag it along */
1346 * Put TCP length in extended header, and then
1347 * checksum extended header and data.
1349 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1351 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1352 if (to.to_flags & TOF_SIGNATURE) {
1354 * Calculate MD5 signature and put it into the place
1355 * determined before.
1356 * NOTE: since TCP options buffer doesn't point into
1357 * mbuf's data, calculate offset and use it.
1359 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1360 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1362 * Do not send segment if the calculation of MD5
1363 * digest has failed.
1373 * There is no need to fill in ip6_plen right now.
1374 * It will be filled later by ip6_output.
1377 m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
1378 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1379 udp->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
1380 th->th_sum = htons(0);
1381 UDPSTAT_INC(udps_opackets);
1383 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1384 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1385 th->th_sum = in6_cksum_pseudo(ip6,
1386 sizeof(struct tcphdr) + optlen + len, IPPROTO_TCP,
1391 #if defined(INET6) && defined(INET)
1397 m->m_pkthdr.csum_flags = CSUM_UDP;
1398 m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
1399 udp->uh_sum = in_pseudo(ip->ip_src.s_addr,
1400 ip->ip_dst.s_addr, htons(ulen + IPPROTO_UDP));
1401 th->th_sum = htons(0);
1402 UDPSTAT_INC(udps_opackets);
1404 m->m_pkthdr.csum_flags = CSUM_TCP;
1405 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1406 th->th_sum = in_pseudo(ip->ip_src.s_addr,
1407 ip->ip_dst.s_addr, htons(sizeof(struct tcphdr) +
1408 IPPROTO_TCP + len + optlen));
1411 /* IP version must be set here for ipv4/ipv6 checking later */
1412 KASSERT(ip->ip_v == IPVERSION,
1413 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1418 * Enable TSO and specify the size of the segments.
1419 * The TCP pseudo header checksum is always provided.
1422 KASSERT(len > tp->t_maxseg - optlen,
1423 ("%s: len <= tso_segsz", __func__));
1424 m->m_pkthdr.csum_flags |= CSUM_TSO;
1425 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1428 KASSERT(len + hdrlen == m_length(m, NULL),
1429 ("%s: mbuf chain shorter than expected: %d + %u != %u",
1430 __func__, len, hdrlen, m_length(m, NULL)));
1433 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1434 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1441 if (so->so_options & SO_DEBUG) {
1447 save = ipov->ih_len;
1448 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1450 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1454 ipov->ih_len = save;
1456 #endif /* TCPDEBUG */
1457 TCP_PROBE3(debug__output, tp, th, m);
1459 /* We're getting ready to send; log now. */
1460 TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_OUT, ERRNO_UNK,
1464 * Fill in IP length and desired time to live and
1465 * send to IP level. There should be a better way
1466 * to handle ttl and tos; we could keep them in
1467 * the template, but need a way to checksum without them.
1470 * m->m_pkthdr.len should have been set before checksum calculation,
1471 * because in6_cksum() need it.
1476 * we separately set hoplimit for every segment, since the
1477 * user might want to change the value via setsockopt.
1478 * Also, desired default hop limit might be changed via
1479 * Neighbor Discovery.
1481 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1484 * Set the packet size here for the benefit of DTrace probes.
1485 * ip6_output() will set it properly; it's supposed to include
1486 * the option header lengths as well.
1488 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1490 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1491 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1493 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1495 if (tp->t_state == TCPS_SYN_SENT)
1496 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1498 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1501 /* Save packet, if requested. */
1502 tcp_pcap_add(th, m, &(tp->t_outpkts));
1505 /* TODO: IPv6 IP6TOS_ECT bit on */
1506 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1507 &tp->t_inpcb->inp_route6,
1508 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1509 NULL, NULL, tp->t_inpcb);
1511 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_nh != NULL)
1512 mtu = tp->t_inpcb->inp_route6.ro_nh->nh_mtu;
1515 #if defined(INET) && defined(INET6)
1520 ip->ip_len = htons(m->m_pkthdr.len);
1522 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1523 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1526 * If we do path MTU discovery, then we set DF on every packet.
1527 * This might not be the best thing to do according to RFC3390
1528 * Section 2. However the tcp hostcache migitates the problem
1529 * so it affects only the first tcp connection with a host.
1531 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1533 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1534 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1535 if (tp->t_port == 0 || len < V_tcp_minmss) {
1536 ip->ip_off |= htons(IP_DF);
1539 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1542 if (tp->t_state == TCPS_SYN_SENT)
1543 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1545 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1548 /* Save packet, if requested. */
1549 tcp_pcap_add(th, m, &(tp->t_outpkts));
1552 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1553 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1556 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_nh != NULL)
1557 mtu = tp->t_inpcb->inp_route.ro_nh->nh_mtu;
1563 tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1565 * In transmit state, time the transmission and arrange for
1566 * the retransmit. In persist state, just set snd_max.
1568 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1569 !tcp_timer_active(tp, TT_PERSIST)) {
1570 tcp_seq startseq = tp->snd_nxt;
1573 * Advance snd_nxt over sequence space of this segment.
1575 if (flags & (TH_SYN|TH_FIN)) {
1578 if (flags & TH_FIN) {
1580 tp->t_flags |= TF_SENTFIN;
1586 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1587 tp->snd_max = tp->snd_nxt;
1589 * Time this transmission if not a retransmission and
1590 * not currently timing anything.
1592 tp->t_sndtime = ticks;
1593 if (tp->t_rtttime == 0) {
1594 tp->t_rtttime = ticks;
1595 tp->t_rtseq = startseq;
1596 TCPSTAT_INC(tcps_segstimed);
1599 if (!(tp->t_flags & TF_GPUTINPROG) && len) {
1600 tp->t_flags |= TF_GPUTINPROG;
1601 tp->gput_seq = startseq;
1602 tp->gput_ack = startseq +
1603 ulmin(sbavail(&so->so_snd) - off, sendwin);
1604 tp->gput_ts = tcp_ts_getticks();
1610 * Set retransmit timer if not currently set,
1611 * and not doing a pure ack or a keep-alive probe.
1612 * Initial value for retransmit timer is smoothed
1613 * round-trip time + 2 * round-trip time variance.
1614 * Initialize shift counter which is used for backoff
1615 * of retransmit time.
1618 if (!tcp_timer_active(tp, TT_REXMT) &&
1619 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1620 (tp->snd_nxt != tp->snd_una))) {
1621 if (tcp_timer_active(tp, TT_PERSIST)) {
1622 tcp_timer_activate(tp, TT_PERSIST, 0);
1625 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1626 } else if (len == 0 && sbavail(&so->so_snd) &&
1627 !tcp_timer_active(tp, TT_REXMT) &&
1628 !tcp_timer_active(tp, TT_PERSIST)) {
1630 * Avoid a situation where we do not set persist timer
1631 * after a zero window condition. For example:
1632 * 1) A -> B: packet with enough data to fill the window
1633 * 2) B -> A: ACK for #1 + new data (0 window
1635 * 3) A -> B: ACK for #2, 0 len packet
1637 * In this case, A will not activate the persist timer,
1638 * because it chose to send a packet. Unless tcp_output
1639 * is called for some other reason (delayed ack timer,
1640 * another input packet from B, socket syscall), A will
1641 * not send zero window probes.
1643 * So, if you send a 0-length packet, but there is data
1644 * in the socket buffer, and neither the rexmt or
1645 * persist timer is already set, then activate the
1653 * Persist case, update snd_max but since we are in
1654 * persist mode (no window) we do not update snd_nxt.
1659 if (flags & TH_FIN) {
1661 tp->t_flags |= TF_SENTFIN;
1663 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1664 tp->snd_max = tp->snd_nxt + xlen;
1667 (TCPS_HAVEESTABLISHED(tp->t_state) &&
1668 (tp->t_flags & TF_SACK_PERMIT) &&
1669 tp->rcv_numsacks > 0)) {
1670 /* Clean up any DSACK's sent */
1671 tcp_clean_dsack_blocks(tp);
1674 /* Record the error. */
1675 TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1676 error, 0, NULL, false);
1679 * We know that the packet was lost, so back out the
1680 * sequence number advance, if any.
1682 * If the error is EPERM the packet got blocked by the
1683 * local firewall. Normally we should terminate the
1684 * connection but the blocking may have been spurious
1685 * due to a firewall reconfiguration cycle. So we treat
1686 * it like a packet loss and let the retransmit timer and
1687 * timeouts do their work over time.
1688 * XXX: It is a POLA question whether calling tcp_drop right
1689 * away would be the really correct behavior instead.
1691 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1692 !tcp_timer_active(tp, TT_PERSIST)) &&
1693 ((flags & TH_SYN) == 0) &&
1697 tp->sackhint.sack_bytes_rexmit -= len;
1698 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1699 ("sackhint bytes rtx >= 0"));
1703 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1707 tp->t_softerror = error;
1710 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1711 tp->snd_cwnd = tp->t_maxseg;
1715 * For some reason the interface we used initially
1716 * to send segments changed to another or lowered
1718 * If TSO was active we either got an interface
1719 * without TSO capabilits or TSO was turned off.
1720 * If we obtained mtu from ip_output() then update
1724 tp->t_flags &= ~TF_TSO;
1726 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1734 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1735 tp->t_softerror = error;
1743 TCPSTAT_INC(tcps_sndtotal);
1746 * Data sent (as far as we can tell).
1747 * If this advertises a larger window than any other segment,
1748 * then remember the size of the advertised window.
1749 * Any pending ACK has now been sent.
1751 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1752 tp->rcv_adv = tp->rcv_nxt + recwin;
1753 tp->last_ack_sent = tp->rcv_nxt;
1754 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1755 if (tcp_timer_active(tp, TT_DELACK))
1756 tcp_timer_activate(tp, TT_DELACK, 0);
1759 * This completely breaks TCP if newreno is turned on. What happens
1760 * is that if delayed-acks are turned on on the receiver, this code
1761 * on the transmitter effectively destroys the TCP window, forcing
1762 * it to four packets (1.5Kx4 = 6K window).
1764 if (sendalot && --maxburst)
1773 tcp_setpersist(struct tcpcb *tp)
1775 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1778 tp->t_flags &= ~TF_PREVVALID;
1779 if (tcp_timer_active(tp, TT_REXMT))
1780 panic("tcp_setpersist: retransmit pending");
1782 * Start/restart persistence timer.
1784 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1785 tcp_persmin, tcp_persmax);
1786 tcp_timer_activate(tp, TT_PERSIST, tt);
1787 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1792 * Insert TCP options according to the supplied parameters to the place
1793 * optp in a consistent way. Can handle unaligned destinations.
1795 * The order of the option processing is crucial for optimal packing and
1796 * alignment for the scarce option space.
1798 * The optimal order for a SYN/SYN-ACK segment is:
1799 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1800 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1802 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1803 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1804 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1805 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1806 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1809 tcp_addoptions(struct tcpopt *to, u_char *optp)
1811 u_int32_t mask, optlen = 0;
1813 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1814 if ((to->to_flags & mask) != mask)
1816 if (optlen == TCP_MAXOLEN)
1818 switch (to->to_flags & mask) {
1820 while (optlen % 4) {
1821 optlen += TCPOLEN_NOP;
1822 *optp++ = TCPOPT_NOP;
1824 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1826 optlen += TCPOLEN_MAXSEG;
1827 *optp++ = TCPOPT_MAXSEG;
1828 *optp++ = TCPOLEN_MAXSEG;
1829 to->to_mss = htons(to->to_mss);
1830 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1831 optp += sizeof(to->to_mss);
1834 while (!optlen || optlen % 2 != 1) {
1835 optlen += TCPOLEN_NOP;
1836 *optp++ = TCPOPT_NOP;
1838 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1840 optlen += TCPOLEN_WINDOW;
1841 *optp++ = TCPOPT_WINDOW;
1842 *optp++ = TCPOLEN_WINDOW;
1843 *optp++ = to->to_wscale;
1846 while (optlen % 2) {
1847 optlen += TCPOLEN_NOP;
1848 *optp++ = TCPOPT_NOP;
1850 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1852 optlen += TCPOLEN_SACK_PERMITTED;
1853 *optp++ = TCPOPT_SACK_PERMITTED;
1854 *optp++ = TCPOLEN_SACK_PERMITTED;
1857 while (!optlen || optlen % 4 != 2) {
1858 optlen += TCPOLEN_NOP;
1859 *optp++ = TCPOPT_NOP;
1861 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1863 optlen += TCPOLEN_TIMESTAMP;
1864 *optp++ = TCPOPT_TIMESTAMP;
1865 *optp++ = TCPOLEN_TIMESTAMP;
1866 to->to_tsval = htonl(to->to_tsval);
1867 to->to_tsecr = htonl(to->to_tsecr);
1868 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1869 optp += sizeof(to->to_tsval);
1870 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1871 optp += sizeof(to->to_tsecr);
1875 int siglen = TCPOLEN_SIGNATURE - 2;
1877 while (!optlen || optlen % 4 != 2) {
1878 optlen += TCPOLEN_NOP;
1879 *optp++ = TCPOPT_NOP;
1881 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1882 to->to_flags &= ~TOF_SIGNATURE;
1885 optlen += TCPOLEN_SIGNATURE;
1886 *optp++ = TCPOPT_SIGNATURE;
1887 *optp++ = TCPOLEN_SIGNATURE;
1888 to->to_signature = optp;
1896 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1899 while (!optlen || optlen % 4 != 2) {
1900 optlen += TCPOLEN_NOP;
1901 *optp++ = TCPOPT_NOP;
1903 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1905 optlen += TCPOLEN_SACKHDR;
1906 *optp++ = TCPOPT_SACK;
1907 sackblks = min(to->to_nsacks,
1908 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1909 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1910 while (sackblks--) {
1911 sack_seq = htonl(sack->start);
1912 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1913 optp += sizeof(sack_seq);
1914 sack_seq = htonl(sack->end);
1915 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1916 optp += sizeof(sack_seq);
1917 optlen += TCPOLEN_SACK;
1920 TCPSTAT_INC(tcps_sack_send_blocks);
1927 /* XXX is there any point to aligning this option? */
1928 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1929 if (TCP_MAXOLEN - optlen < total_len) {
1930 to->to_flags &= ~TOF_FASTOPEN;
1933 *optp++ = TCPOPT_FAST_OPEN;
1934 *optp++ = total_len;
1935 if (to->to_tfo_len > 0) {
1936 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1937 optp += to->to_tfo_len;
1939 optlen += total_len;
1943 panic("%s: unknown TCP option type", __func__);
1948 /* Terminate and pad TCP options to a 4 byte boundary. */
1950 optlen += TCPOLEN_EOL;
1951 *optp++ = TCPOPT_EOL;
1954 * According to RFC 793 (STD0007):
1955 * "The content of the header beyond the End-of-Option option
1956 * must be header padding (i.e., zero)."
1957 * and later: "The padding is composed of zeros."
1959 while (optlen % 4) {
1960 optlen += TCPOLEN_PAD;
1961 *optp++ = TCPOPT_PAD;
1964 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1969 * This is a copy of m_copym(), taking the TSO segment size/limit
1970 * constraints into account, and advancing the sndptr as it goes.
1973 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1974 int32_t seglimit, int32_t segsize, struct sockbuf *sb, bool hw_tls)
1977 struct ktls_session *tls, *ntls;
1980 struct mbuf *n, **np;
1983 int32_t len = *plen;
1987 uint32_t mlen, frags;
1990 KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1991 KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1992 if (off == 0 && m->m_flags & M_PKTHDR)
1997 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
2001 if ((sb) && (m == sb->sb_sndptr)) {
2002 sb->sb_sndptroff += m->m_len;
2003 sb->sb_sndptr = m->m_next;
2011 if (hw_tls && (m->m_flags & M_EXTPG))
2019 KASSERT(len == M_COPYALL,
2020 ("tcp_m_copym, length > size of mbuf chain"));
2022 if (pkthdrlen != NULL)
2023 *pkthdrlen = len_cp;
2028 if (m->m_flags & M_EXTPG)
2029 ntls = m->m_epg_tls;
2034 * Avoid mixing TLS records with handshake
2035 * data or TLS records from different
2041 if (pkthdrlen != NULL)
2042 *pkthdrlen = len_cp;
2047 mlen = min(len, m->m_len - off);
2050 * For M_EXTPG mbufs, add 3 segments
2051 * + 1 in case we are crossing page boundaries
2052 * + 2 in case the TLS hdr/trailer are used
2053 * It is cheaper to just add the segments
2054 * than it is to take the cache miss to look
2055 * at the mbuf ext_pgs state in detail.
2057 if (m->m_flags & M_EXTPG) {
2058 fragsize = min(segsize, PAGE_SIZE);
2065 /* Break if we really can't fit anymore. */
2066 if ((frags + 1) >= seglimit) {
2068 if (pkthdrlen != NULL)
2069 *pkthdrlen = len_cp;
2074 * Reduce size if you can't copy the whole
2075 * mbuf. If we can't copy the whole mbuf, also
2076 * adjust len so the loop will end after this
2079 if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2080 mlen = (seglimit - frags - 1) * fragsize;
2082 *plen = len_cp + len;
2083 if (pkthdrlen != NULL)
2086 frags += howmany(mlen, fragsize);
2090 KASSERT(seglimit > 0,
2091 ("%s: seglimit went too low", __func__));
2094 n = m_gethdr(M_NOWAIT, m->m_type);
2096 n = m_get(M_NOWAIT, m->m_type);
2101 if (!m_dup_pkthdr(n, m, M_NOWAIT))
2103 if (len == M_COPYALL)
2104 n->m_pkthdr.len -= off0;
2106 n->m_pkthdr.len = len;
2107 pkthdrlen = &n->m_pkthdr.len;
2112 if (m->m_flags & (M_EXT|M_EXTPG)) {
2113 n->m_data = m->m_data + off;
2116 bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2119 if (sb && (sb->sb_sndptr == m) &&
2120 ((n->m_len + off) >= m->m_len) && m->m_next) {
2121 sb->sb_sndptroff += m->m_len;
2122 sb->sb_sndptr = m->m_next;
2125 if (len != M_COPYALL) {
2138 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2142 * Automatic sizing of send socket buffer. Often the send buffer
2143 * size is not optimally adjusted to the actual network conditions
2144 * at hand (delay bandwidth product). Setting the buffer size too
2145 * small limits throughput on links with high bandwidth and high
2146 * delay (eg. trans-continental/oceanic links). Setting the
2147 * buffer size too big consumes too much real kernel memory,
2148 * especially with many connections on busy servers.
2150 * The criteria to step up the send buffer one notch are:
2151 * 1. receive window of remote host is larger than send buffer
2152 * (with a fudge factor of 5/4th);
2153 * 2. send buffer is filled to 7/8th with data (so we actually
2154 * have data to make use of it);
2155 * 3. send buffer fill has not hit maximal automatic size;
2156 * 4. our send window (slow start and cogestion controlled) is
2157 * larger than sent but unacknowledged data in send buffer.
2159 * The remote host receive window scaling factor may limit the
2160 * growing of the send buffer before it reaches its allowed
2163 * It scales directly with slow start or congestion window
2164 * and does at most one step per received ACK. This fast
2165 * scaling has the drawback of growing the send buffer beyond
2166 * what is strictly necessary to make full use of a given
2167 * delay*bandwidth product. However testing has shown this not
2168 * to be much of an problem. At worst we are trading wasting
2169 * of available bandwidth (the non-use of it) for wasting some
2170 * socket buffer memory.
2172 * TODO: Shrink send buffer during idle periods together
2173 * with congestion window. Requires another timer. Has to
2174 * wait for upcoming tcp timer rewrite.
2176 * XXXGL: should there be used sbused() or sbavail()?
2178 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2181 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2182 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2183 sbused(&so->so_snd) >=
2184 (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2185 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2186 sendwin >= (sbused(&so->so_snd) -
2187 (tp->snd_nxt - tp->snd_una))) {
2188 if (!sbreserve_locked(&so->so_snd,
2189 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2190 V_tcp_autosndbuf_max), so, curthread))
2191 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
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