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.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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>
75 #include <netinet/tcp_fsm.h>
76 #include <netinet/tcp_log_buf.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"))
145 static void inline cc_after_idle(struct tcpcb *tp);
149 * Wrapper for the TCP established output helper hook.
152 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
153 struct tcpopt *to, uint32_t len, int tso)
155 struct tcp_hhook_data hhook_data;
157 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
161 hhook_data.len = len;
162 hhook_data.tso = tso;
164 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
171 * Flags used when sending segments in tcp_output. Basic flags (TH_RST,
172 * TH_ACK,TH_SYN,TH_FIN) are totally determined by state, with the proviso
173 * that TH_FIN is sent only if all data queued for output is included in the
176 u_char tcp_outflags[TCP_NSTATES] = {
177 TH_RST|TH_ACK, /* 0, CLOSED */
179 TH_SYN, /* 2, SYN_SENT */
180 TH_SYN|TH_ACK, /* 3, SYN_RECEIVED */
181 TH_ACK, /* 4, ESTABLISHED */
182 TH_ACK, /* 5, CLOSE_WAIT */
183 TH_FIN|TH_ACK, /* 6, FIN_WAIT_1 */
184 TH_FIN|TH_ACK, /* 7, CLOSING */
185 TH_FIN|TH_ACK, /* 8, LAST_ACK */
186 TH_ACK, /* 9, FIN_WAIT_2 */
187 TH_ACK, /* 10, TIME_WAIT */
191 * CC wrapper hook functions
194 cc_after_idle(struct tcpcb *tp)
196 INP_WLOCK_ASSERT(tp->t_inpcb);
198 if (CC_ALGO(tp)->after_idle != NULL)
199 CC_ALGO(tp)->after_idle(tp->ccv);
203 * Tcp output routine: figure out what should be sent and send it.
206 tcp_output(struct tcpcb *tp)
208 struct socket *so = tp->t_inpcb->inp_socket;
210 uint32_t recwin, sendwin;
211 int off, flags, error = 0; /* Keep compiler happy */
212 u_int if_hw_tsomaxsegcount = 0;
213 u_int if_hw_tsomaxsegsize;
215 struct ip *ip = NULL;
217 struct ipovly *ipov = NULL;
220 u_char opt[TCP_MAXOLEN];
221 unsigned ipoptlen, optlen, hdrlen;
222 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
223 unsigned ipsec_optlen = 0;
225 int idle, sendalot, curticks;
226 int sack_rxmit, sack_bytes_rxmt;
230 unsigned int wanted_cookie = 0;
231 unsigned int dont_sendalot = 0;
233 int maxburst = TCP_MAXBURST;
236 struct ip6_hdr *ip6 = NULL;
239 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
242 INP_WLOCK_ASSERT(tp->t_inpcb);
245 if (tp->t_flags & TF_TOE)
246 return (tcp_offload_output(tp));
250 * For TFO connections in SYN_RECEIVED, only allow the initial
251 * SYN|ACK and those sent by the retransmit timer.
253 if (IS_FASTOPEN(tp->t_flags) &&
254 (tp->t_state == TCPS_SYN_RECEIVED) &&
255 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial 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)
268 tp->t_flags &= ~TF_LASTIDLE;
270 if (tp->t_flags & TF_MORETOCOME) {
271 tp->t_flags |= TF_LASTIDLE;
277 * If we've recently taken a timeout, snd_max will be greater than
278 * snd_nxt. There may be SACK information that allows us to avoid
279 * resending already delivered data. Adjust snd_nxt accordingly.
281 if ((tp->t_flags & TF_SACK_PERMIT) &&
282 SEQ_LT(tp->snd_nxt, tp->snd_max))
287 off = tp->snd_nxt - tp->snd_una;
288 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
290 flags = tcp_outflags[tp->t_state];
292 * Send any SACK-generated retransmissions. If we're explicitly trying
293 * to send out new data (when sendalot is 1), bypass this function.
294 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
295 * we're replacing a (future) new transmission with a retransmission
296 * now, and we previously incremented snd_cwnd in tcp_input().
299 * Still in sack recovery , reset rxmit flag to zero.
305 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
306 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
310 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
311 /* Do not retransmit SACK segments beyond snd_recover */
312 if (SEQ_GT(p->end, tp->snd_recover)) {
314 * (At least) part of sack hole extends beyond
315 * snd_recover. Check to see if we can rexmit data
318 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
320 * Can't rexmit any more data for this hole.
321 * That data will be rexmitted in the next
322 * sack recovery episode, when snd_recover
323 * moves past p->rxmit.
326 goto after_sack_rexmit;
328 /* Can rexmit part of the current hole */
329 len = ((int32_t)ulmin(cwin,
330 tp->snd_recover - p->rxmit));
332 len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
333 off = p->rxmit - tp->snd_una;
334 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
339 TCPSTAT_INC(tcps_sack_rexmits);
340 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
341 min(len, tp->t_maxseg));
346 * Get standard flags, and add SYN or FIN if requested by 'hidden'
349 if (tp->t_flags & TF_NEEDFIN)
351 if (tp->t_flags & TF_NEEDSYN)
354 SOCKBUF_LOCK(&so->so_snd);
356 * If in persist timeout with window of 0, send 1 byte.
357 * Otherwise, if window is small but nonzero
358 * and timer expired, we will send what we can
359 * and go to transmit state.
361 if (tp->t_flags & TF_FORCEDATA) {
364 * If we still have some data to send, then
365 * clear the FIN bit. Usually this would
366 * happen below when it realizes that we
367 * aren't sending all the data. However,
368 * if we have exactly 1 byte of unsent data,
369 * then it won't clear the FIN bit below,
370 * and if we are in persist state, we wind
371 * up sending the packet without recording
372 * that we sent the FIN bit.
374 * We can't just blindly clear the FIN bit,
375 * because if we don't have any more data
376 * to send then the probe will be the FIN
379 if (off < sbused(&so->so_snd))
383 tcp_timer_activate(tp, TT_PERSIST, 0);
389 * If snd_nxt == snd_max and we have transmitted a FIN, the
390 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
391 * a negative length. This can also occur when TCP opens up
392 * its congestion window while receiving additional duplicate
393 * acks after fast-retransmit because TCP will reset snd_nxt
394 * to snd_max after the fast-retransmit.
396 * In the normal retransmit-FIN-only case, however, snd_nxt will
397 * be set to snd_una, the offset will be 0, and the length may
400 * If sack_rxmit is true we are retransmitting from the scoreboard
401 * in which case len is already set.
403 if (sack_rxmit == 0) {
404 if (sack_bytes_rxmt == 0)
405 len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
411 * We are inside of a SACK recovery episode and are
412 * sending new data, having retransmitted all the
413 * data possible in the scoreboard.
415 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
418 * Don't remove this (len > 0) check !
419 * We explicitly check for len > 0 here (although it
420 * isn't really necessary), to work around a gcc
421 * optimization issue - to force gcc to compute
422 * len above. Without this check, the computation
423 * of len is bungled by the optimizer.
426 cwin = tp->snd_cwnd -
427 (tp->snd_nxt - tp->sack_newdata) -
431 len = imin(len, cwin);
437 * Lop off SYN bit if it has already been sent. However, if this
438 * is SYN-SENT state and if segment contains data and if we don't
439 * know that foreign host supports TAO, suppress sending segment.
441 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
442 if (tp->t_state != TCPS_SYN_RECEIVED)
445 * When sending additional segments following a TFO SYN|ACK,
446 * do not include the SYN bit.
448 if (IS_FASTOPEN(tp->t_flags) &&
449 (tp->t_state == TCPS_SYN_RECEIVED))
455 * Be careful not to send data and/or FIN on SYN segments.
456 * This measure is needed to prevent interoperability problems
457 * with not fully conformant TCP implementations.
459 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
465 * On TFO sockets, ensure no data is sent in the following cases:
467 * - When retransmitting SYN|ACK on a passively-created socket
469 * - When retransmitting SYN on an actively created socket
471 * - When sending a zero-length cookie (cookie request) on an
472 * actively created socket
474 * - When the socket is in the CLOSED state (RST is being sent)
476 if (IS_FASTOPEN(tp->t_flags) &&
477 (((flags & TH_SYN) && (tp->t_rxtshift > 0)) ||
478 ((tp->t_state == TCPS_SYN_SENT) &&
479 (tp->t_tfo_client_cookie_len == 0)) ||
484 * If FIN has been sent but not acked,
485 * but we haven't been called to retransmit,
486 * len will be < 0. Otherwise, window shrank
487 * after we sent into it. If window shrank to 0,
488 * cancel pending retransmit, pull snd_nxt back
489 * to (closed) window, and set the persist timer
490 * if it isn't already going. If the window didn't
491 * close completely, just wait for an ACK.
493 * We also do a general check here to ensure that
494 * we will set the persist timer when we have data
495 * to send, but a 0-byte window. This makes sure
496 * the persist timer is set even if the packet
497 * hits one of the "goto send" lines below.
500 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
501 (off < (int) sbavail(&so->so_snd))) {
502 tcp_timer_activate(tp, TT_REXMT, 0);
504 tp->snd_nxt = tp->snd_una;
505 if (!tcp_timer_active(tp, TT_PERSIST))
510 /* len will be >= 0 after this point. */
511 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
513 tcp_sndbuf_autoscale(tp, so, sendwin);
516 * Decide if we can use TCP Segmentation Offloading (if supported by
519 * TSO may only be used if we are in a pure bulk sending state. The
520 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
521 * IP options prevent using TSO. With TSO the TCP header is the same
522 * (except for the sequence number) for all generated packets. This
523 * makes it impossible to transmit any options which vary per generated
526 * IPv4 handling has a clear separation of ip options and ip header
527 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
528 * the right thing below to provide length of just ip options and thus
529 * checking for ipoptlen is enough to decide if ip options are present.
531 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
533 * Pre-calculate here as we save another lookup into the darknesses
534 * of IPsec that way and can actually decide if TSO is ok.
537 if (isipv6 && IPSEC_ENABLED(ipv6))
538 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
544 if (IPSEC_ENABLED(ipv4))
545 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
550 ipoptlen = ip6_optlen(tp->t_inpcb);
553 if (tp->t_inpcb->inp_options)
554 ipoptlen = tp->t_inpcb->inp_options->m_len -
555 offsetof(struct ipoption, ipopt_list);
558 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
559 ipoptlen += ipsec_optlen;
562 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
563 ((tp->t_flags & TF_SIGNATURE) == 0) &&
564 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
565 ipoptlen == 0 && !(flags & TH_SYN))
569 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
572 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
573 sbused(&so->so_snd)))
577 recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
578 (long)TCP_MAXWIN << tp->rcv_scale);
581 * Sender silly window avoidance. We transmit under the following
582 * conditions when len is non-zero:
584 * - We have a full segment (or more with TSO)
585 * - This is the last buffer in a write()/send() and we are
586 * either idle or running NODELAY
587 * - we've timed out (e.g. persist timer)
588 * - we have more then 1/2 the maximum send window's worth of
589 * data (receiver may be limited the window size)
590 * - we need to retransmit
593 if (len >= tp->t_maxseg)
596 * NOTE! on localhost connections an 'ack' from the remote
597 * end may occur synchronously with the output and cause
598 * us to flush a buffer queued with moretocome. XXX
600 * note: the len + off check is almost certainly unnecessary.
602 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
603 (idle || (tp->t_flags & TF_NODELAY)) &&
604 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
605 (tp->t_flags & TF_NOPUSH) == 0) {
608 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
610 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
612 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
619 * Sending of standalone window updates.
621 * Window updates are important when we close our window due to a
622 * full socket buffer and are opening it again after the application
623 * reads data from it. Once the window has opened again and the
624 * remote end starts to send again the ACK clock takes over and
625 * provides the most current window information.
627 * We must avoid the silly window syndrome whereas every read
628 * from the receive buffer, no matter how small, causes a window
629 * update to be sent. We also should avoid sending a flurry of
630 * window updates when the socket buffer had queued a lot of data
631 * and the application is doing small reads.
633 * Prevent a flurry of pointless window updates by only sending
634 * an update when we can increase the advertized window by more
635 * than 1/4th of the socket buffer capacity. When the buffer is
636 * getting full or is very small be more aggressive and send an
637 * update whenever we can increase by two mss sized segments.
638 * In all other situations the ACK's to new incoming data will
639 * carry further window increases.
641 * Don't send an independent window update if a delayed
642 * ACK is pending (it will get piggy-backed on it) or the
643 * remote side already has done a half-close and won't send
644 * more data. Skip this if the connection is in T/TCP
647 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
648 !(tp->t_flags & TF_DELACK) &&
649 !TCPS_HAVERCVDFIN(tp->t_state)) {
651 * "adv" is the amount we could increase the window,
652 * taking into account that we are limited by
653 * TCP_MAXWIN << tp->rcv_scale.
659 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
660 oldwin = (tp->rcv_adv - tp->rcv_nxt);
666 * If the new window size ends up being the same as or less
667 * than the old size when it is scaled, then don't force
670 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
673 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
674 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
675 recwin <= (so->so_rcv.sb_hiwat / 8) ||
676 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
678 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
684 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
685 * is also a catch-all for the retransmit timer timeout case.
687 if (tp->t_flags & TF_ACKNOW)
689 if ((flags & TH_RST) ||
690 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
692 if (SEQ_GT(tp->snd_up, tp->snd_una))
695 * If our state indicates that FIN should be sent
696 * and we have not yet done so, then we need to send.
698 if (flags & TH_FIN &&
699 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
702 * In SACK, it is possible for tcp_output to fail to send a segment
703 * after the retransmission timer has been turned off. Make sure
704 * that the retransmission timer is set.
706 if ((tp->t_flags & TF_SACK_PERMIT) &&
707 SEQ_GT(tp->snd_max, tp->snd_una) &&
708 !tcp_timer_active(tp, TT_REXMT) &&
709 !tcp_timer_active(tp, TT_PERSIST)) {
710 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
714 * TCP window updates are not reliable, rather a polling protocol
715 * using ``persist'' packets is used to insure receipt of window
716 * updates. The three ``states'' for the output side are:
717 * idle not doing retransmits or persists
718 * persisting to move a small or zero window
719 * (re)transmitting and thereby not persisting
721 * tcp_timer_active(tp, TT_PERSIST)
722 * is true when we are in persist state.
723 * (tp->t_flags & TF_FORCEDATA)
724 * is set when we are called to send a persist packet.
725 * tcp_timer_active(tp, TT_REXMT)
726 * is set when we are retransmitting
727 * The output side is idle when both timers are zero.
729 * If send window is too small, there is data to transmit, and no
730 * retransmit or persist is pending, then go to persist state.
731 * If nothing happens soon, send when timer expires:
732 * if window is nonzero, transmit what we can,
733 * otherwise force out a byte.
735 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
736 !tcp_timer_active(tp, TT_PERSIST)) {
742 * No reason to send a segment, just return.
745 SOCKBUF_UNLOCK(&so->so_snd);
749 SOCKBUF_LOCK_ASSERT(&so->so_snd);
751 if (len >= tp->t_maxseg)
752 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
754 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
757 * Before ESTABLISHED, force sending of initial options
758 * unless TCP set not to do any options.
759 * NOTE: we assume that the IP/TCP header plus TCP options
760 * always fit in a single mbuf, leaving room for a maximum
762 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
767 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
770 hdrlen = sizeof (struct tcpiphdr);
773 * Compute options for segment.
774 * We only have to care about SYN and established connection
775 * segments. Options for SYN-ACK segments are handled in TCP
779 if ((tp->t_flags & TF_NOOPT) == 0) {
780 /* Maximum segment size. */
781 if (flags & TH_SYN) {
782 tp->snd_nxt = tp->iss;
783 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
784 to.to_flags |= TOF_MSS;
787 * On SYN or SYN|ACK transmits on TFO connections,
788 * only include the TFO option if it is not a
789 * retransmit, as the presence of the TFO option may
790 * have caused the original SYN or SYN|ACK to have
791 * been dropped by a middlebox.
793 if (IS_FASTOPEN(tp->t_flags) &&
794 (tp->t_rxtshift == 0)) {
795 if (tp->t_state == TCPS_SYN_RECEIVED) {
796 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
798 (u_int8_t *)&tp->t_tfo_cookie.server;
799 to.to_flags |= TOF_FASTOPEN;
801 } else if (tp->t_state == TCPS_SYN_SENT) {
803 tp->t_tfo_client_cookie_len;
805 tp->t_tfo_cookie.client;
806 to.to_flags |= TOF_FASTOPEN;
809 * If we wind up having more data to
810 * send with the SYN than can fit in
811 * one segment, don't send any more
812 * until the SYN|ACK comes back from
819 /* Window scaling. */
820 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
821 to.to_wscale = tp->request_r_scale;
822 to.to_flags |= TOF_SCALE;
825 if ((tp->t_flags & TF_RCVD_TSTMP) ||
826 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
827 curticks = tcp_ts_getticks();
828 to.to_tsval = curticks + tp->ts_offset;
829 to.to_tsecr = tp->ts_recent;
830 to.to_flags |= TOF_TS;
831 if (tp->t_rxtshift == 1)
832 tp->t_badrxtwin = curticks;
835 /* Set receive buffer autosizing timestamp. */
836 if (tp->rfbuf_ts == 0 &&
837 (so->so_rcv.sb_flags & SB_AUTOSIZE))
838 tp->rfbuf_ts = tcp_ts_getticks();
840 /* Selective ACK's. */
841 if (tp->t_flags & TF_SACK_PERMIT) {
843 to.to_flags |= TOF_SACKPERM;
844 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
845 (tp->t_flags & TF_SACK_PERMIT) &&
846 tp->rcv_numsacks > 0) {
847 to.to_flags |= TOF_SACK;
848 to.to_nsacks = tp->rcv_numsacks;
849 to.to_sacks = (u_char *)tp->sackblks;
852 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
853 /* TCP-MD5 (RFC2385). */
855 * Check that TCP_MD5SIG is enabled in tcpcb to
856 * account the size needed to set this TCP option.
858 if (tp->t_flags & TF_SIGNATURE)
859 to.to_flags |= TOF_SIGNATURE;
860 #endif /* TCP_SIGNATURE */
862 /* Processing the options. */
863 hdrlen += optlen = tcp_addoptions(&to, opt);
865 * If we wanted a TFO option to be added, but it was unable
866 * to fit, ensure no data is sent.
868 if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
869 !(to.to_flags & TOF_FASTOPEN))
874 * Adjust data length if insertion of options will
875 * bump the packet length beyond the t_maxseg length.
876 * Clear the FIN bit because we cut off the tail of
879 if (len + optlen + ipoptlen > tp->t_maxseg) {
887 /* extract TSO information */
888 if_hw_tsomax = tp->t_tsomax;
889 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
890 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
893 * Limit a TSO burst to prevent it from
894 * overflowing or exceeding the maximum length
895 * allowed by the network interface:
897 KASSERT(ipoptlen == 0,
898 ("%s: TSO can't do IP options", __func__));
901 * Check if we should limit by maximum payload
904 if (if_hw_tsomax != 0) {
905 /* compute maximum TSO length */
906 max_len = (if_hw_tsomax - hdrlen -
910 } else if (len > max_len) {
916 * Prevent the last segment from being
917 * fractional unless the send sockbuf can be
920 max_len = (tp->t_maxseg - optlen);
921 if (((uint32_t)off + (uint32_t)len) <
922 sbavail(&so->so_snd)) {
923 moff = len % max_len;
931 * In case there are too many small fragments
934 if (len <= max_len) {
941 * Send the FIN in a separate segment
942 * after the bulk sending is done.
943 * We don't trust the TSO implementations
944 * to clear the FIN flag on all but the
947 if (tp->t_flags & TF_NEEDFIN)
950 len = tp->t_maxseg - optlen - ipoptlen;
958 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
959 ("%s: len > IP_MAXPACKET", __func__));
961 /*#ifdef DIAGNOSTIC*/
963 if (max_linkhdr + hdrlen > MCLBYTES)
965 if (max_linkhdr + hdrlen > MHLEN)
967 panic("tcphdr too big");
971 * This KASSERT is here to catch edge cases at a well defined place.
972 * Before, those had triggered (random) panic conditions further down.
974 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
977 * Grab a header mbuf, attaching a copy of data to
978 * be transmitted, and initialize the header from
979 * the template for sends on this connection.
986 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
987 TCPSTAT_INC(tcps_sndprobe);
988 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
989 tp->t_sndrexmitpack++;
990 TCPSTAT_INC(tcps_sndrexmitpack);
991 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
993 TCPSTAT_INC(tcps_sndpack);
994 TCPSTAT_ADD(tcps_sndbyte, len);
997 if (MHLEN < hdrlen + max_linkhdr)
998 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1001 m = m_gethdr(M_NOWAIT, MT_DATA);
1004 SOCKBUF_UNLOCK(&so->so_snd);
1010 m->m_data += max_linkhdr;
1014 * Start the m_copy functions from the closest mbuf
1015 * to the offset in the socket buffer chain.
1017 mb = sbsndptr_noadv(&so->so_snd, off, &moff);
1018 if (len <= MHLEN - hdrlen - max_linkhdr) {
1019 m_copydata(mb, moff, len,
1020 mtod(m, caddr_t) + hdrlen);
1021 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1022 sbsndptr_adv(&so->so_snd, mb, len);
1025 if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1029 m->m_next = tcp_m_copym(mb, moff,
1030 &len, if_hw_tsomaxsegcount,
1031 if_hw_tsomaxsegsize, msb);
1032 if (len <= (tp->t_maxseg - optlen)) {
1034 * Must have ran out of mbufs for the copy
1035 * shorten it to no longer need tso. Lets
1036 * not put on sendalot since we are low on
1041 if (m->m_next == NULL) {
1042 SOCKBUF_UNLOCK(&so->so_snd);
1051 * If we're sending everything we've got, set PUSH.
1052 * (This will keep happy those implementations which only
1053 * give data to the user when a buffer fills or
1056 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1059 SOCKBUF_UNLOCK(&so->so_snd);
1061 SOCKBUF_UNLOCK(&so->so_snd);
1062 if (tp->t_flags & TF_ACKNOW)
1063 TCPSTAT_INC(tcps_sndacks);
1064 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1065 TCPSTAT_INC(tcps_sndctrl);
1066 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1067 TCPSTAT_INC(tcps_sndurg);
1069 TCPSTAT_INC(tcps_sndwinup);
1071 m = m_gethdr(M_NOWAIT, MT_DATA);
1078 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1083 m->m_data += max_linkhdr;
1086 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1087 m->m_pkthdr.rcvif = (struct ifnet *)0;
1089 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1093 ip6 = mtod(m, struct ip6_hdr *);
1094 th = (struct tcphdr *)(ip6 + 1);
1095 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1099 ip = mtod(m, struct ip *);
1101 ipov = (struct ipovly *)ip;
1103 th = (struct tcphdr *)(ip + 1);
1104 tcpip_fillheaders(tp->t_inpcb, ip, th);
1108 * Fill in fields, remembering maximum advertised
1109 * window for use in delaying messages about window sizes.
1110 * If resending a FIN, be sure not to use a new sequence number.
1112 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1113 tp->snd_nxt == tp->snd_max)
1116 * If we are starting a connection, send ECN setup
1117 * SYN packet. If we are on a retransmit, we may
1118 * resend those bits a number of times as per
1121 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1122 if (tp->t_rxtshift >= 1) {
1123 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1124 flags |= TH_ECE|TH_CWR;
1126 flags |= TH_ECE|TH_CWR;
1129 if (tp->t_state == TCPS_ESTABLISHED &&
1130 (tp->t_flags & TF_ECN_PERMIT)) {
1132 * If the peer has ECN, mark data packets with
1133 * ECN capable transmission (ECT).
1134 * Ignore pure ack packets, retransmissions and window probes.
1136 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1137 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1140 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1143 ip->ip_tos |= IPTOS_ECN_ECT0;
1144 TCPSTAT_INC(tcps_ecn_ect0);
1148 * Reply with proper ECN notifications.
1150 if (tp->t_flags & TF_ECN_SND_CWR) {
1152 tp->t_flags &= ~TF_ECN_SND_CWR;
1154 if (tp->t_flags & TF_ECN_SND_ECE)
1159 * If we are doing retransmissions, then snd_nxt will
1160 * not reflect the first unsent octet. For ACK only
1161 * packets, we do not want the sequence number of the
1162 * retransmitted packet, we want the sequence number
1163 * of the next unsent octet. So, if there is no data
1164 * (and no SYN or FIN), use snd_max instead of snd_nxt
1165 * when filling in ti_seq. But if we are in persist
1166 * state, snd_max might reflect one byte beyond the
1167 * right edge of the window, so use snd_nxt in that
1168 * case, since we know we aren't doing a retransmission.
1169 * (retransmit and persist are mutually exclusive...)
1171 if (sack_rxmit == 0) {
1172 if (len || (flags & (TH_SYN|TH_FIN)) ||
1173 tcp_timer_active(tp, TT_PERSIST))
1174 th->th_seq = htonl(tp->snd_nxt);
1176 th->th_seq = htonl(tp->snd_max);
1178 th->th_seq = htonl(p->rxmit);
1180 tp->sackhint.sack_bytes_rexmit += len;
1182 th->th_ack = htonl(tp->rcv_nxt);
1184 bcopy(opt, th + 1, optlen);
1185 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1187 th->th_flags = flags;
1189 * Calculate receive window. Don't shrink window,
1190 * but avoid silly window syndrome.
1192 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1193 recwin < tp->t_maxseg)
1195 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1196 recwin < (tp->rcv_adv - tp->rcv_nxt))
1197 recwin = (tp->rcv_adv - tp->rcv_nxt);
1200 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1201 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1202 * case is handled in syncache.
1205 th->th_win = htons((u_short)
1206 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1208 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1211 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1212 * a 0 window. This may cause the remote transmitter to stall. This
1213 * flag tells soreceive() to disable delayed acknowledgements when
1214 * draining the buffer. This can occur if the receiver is attempting
1215 * to read more data than can be buffered prior to transmitting on
1218 if (th->th_win == 0) {
1220 tp->t_flags |= TF_RXWIN0SENT;
1222 tp->t_flags &= ~TF_RXWIN0SENT;
1223 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1224 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1225 th->th_flags |= TH_URG;
1228 * If no urgent pointer to send, then we pull
1229 * the urgent pointer to the left edge of the send window
1230 * so that it doesn't drift into the send window on sequence
1231 * number wraparound.
1233 tp->snd_up = tp->snd_una; /* drag it along */
1236 * Put TCP length in extended header, and then
1237 * checksum extended header and data.
1239 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1240 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1242 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1243 if (to.to_flags & TOF_SIGNATURE) {
1245 * Calculate MD5 signature and put it into the place
1246 * determined before.
1247 * NOTE: since TCP options buffer doesn't point into
1248 * mbuf's data, calculate offset and use it.
1250 if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1251 (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1253 * Do not send segment if the calculation of MD5
1254 * digest has failed.
1264 * There is no need to fill in ip6_plen right now.
1265 * It will be filled later by ip6_output.
1267 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1268 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1269 optlen + len, IPPROTO_TCP, 0);
1272 #if defined(INET6) && defined(INET)
1277 m->m_pkthdr.csum_flags = CSUM_TCP;
1278 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1279 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1281 /* IP version must be set here for ipv4/ipv6 checking later */
1282 KASSERT(ip->ip_v == IPVERSION,
1283 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1288 * Enable TSO and specify the size of the segments.
1289 * The TCP pseudo header checksum is always provided.
1292 KASSERT(len > tp->t_maxseg - optlen,
1293 ("%s: len <= tso_segsz", __func__));
1294 m->m_pkthdr.csum_flags |= CSUM_TSO;
1295 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1298 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1299 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1300 ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u",
1301 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1303 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1304 ("%s: mbuf chain shorter than expected: %d + %u + %u != %u",
1305 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1309 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1310 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1317 if (so->so_options & SO_DEBUG) {
1323 save = ipov->ih_len;
1324 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1326 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1330 ipov->ih_len = save;
1332 #endif /* TCPDEBUG */
1333 TCP_PROBE3(debug__output, tp, th, m);
1335 /* We're getting ready to send; log now. */
1336 TCP_LOG_EVENT(tp, th, &so->so_rcv, &so->so_snd, TCP_LOG_OUT, ERRNO_UNK,
1340 * Fill in IP length and desired time to live and
1341 * send to IP level. There should be a better way
1342 * to handle ttl and tos; we could keep them in
1343 * the template, but need a way to checksum without them.
1346 * m->m_pkthdr.len should have been set before checksum calculation,
1347 * because in6_cksum() need it.
1352 * we separately set hoplimit for every segment, since the
1353 * user might want to change the value via setsockopt.
1354 * Also, desired default hop limit might be changed via
1355 * Neighbor Discovery.
1357 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1360 * Set the packet size here for the benefit of DTrace probes.
1361 * ip6_output() will set it properly; it's supposed to include
1362 * the option header lengths as well.
1364 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1366 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1367 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1369 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1371 if (tp->t_state == TCPS_SYN_SENT)
1372 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1374 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1377 /* Save packet, if requested. */
1378 tcp_pcap_add(th, m, &(tp->t_outpkts));
1381 /* TODO: IPv6 IP6TOS_ECT bit on */
1382 error = ip6_output(m, tp->t_inpcb->in6p_outputopts,
1383 &tp->t_inpcb->inp_route6,
1384 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1385 NULL, NULL, tp->t_inpcb);
1387 if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_rt != NULL)
1388 mtu = tp->t_inpcb->inp_route6.ro_rt->rt_mtu;
1391 #if defined(INET) && defined(INET6)
1396 ip->ip_len = htons(m->m_pkthdr.len);
1398 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1399 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1402 * If we do path MTU discovery, then we set DF on every packet.
1403 * This might not be the best thing to do according to RFC3390
1404 * Section 2. However the tcp hostcache migitates the problem
1405 * so it affects only the first tcp connection with a host.
1407 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1409 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1410 ip->ip_off |= htons(IP_DF);
1411 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1413 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1416 if (tp->t_state == TCPS_SYN_SENT)
1417 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1419 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1422 /* Save packet, if requested. */
1423 tcp_pcap_add(th, m, &(tp->t_outpkts));
1426 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1427 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1430 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1431 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1437 * In transmit state, time the transmission and arrange for
1438 * the retransmit. In persist state, just set snd_max.
1440 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1441 !tcp_timer_active(tp, TT_PERSIST)) {
1442 tcp_seq startseq = tp->snd_nxt;
1445 * Advance snd_nxt over sequence space of this segment.
1447 if (flags & (TH_SYN|TH_FIN)) {
1450 if (flags & TH_FIN) {
1452 tp->t_flags |= TF_SENTFIN;
1458 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1459 tp->snd_max = tp->snd_nxt;
1461 * Time this transmission if not a retransmission and
1462 * not currently timing anything.
1464 if (tp->t_rtttime == 0) {
1465 tp->t_rtttime = ticks;
1466 tp->t_rtseq = startseq;
1467 TCPSTAT_INC(tcps_segstimed);
1472 * Set retransmit timer if not currently set,
1473 * and not doing a pure ack or a keep-alive probe.
1474 * Initial value for retransmit timer is smoothed
1475 * round-trip time + 2 * round-trip time variance.
1476 * Initialize shift counter which is used for backoff
1477 * of retransmit time.
1480 if (!tcp_timer_active(tp, TT_REXMT) &&
1481 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1482 (tp->snd_nxt != tp->snd_una))) {
1483 if (tcp_timer_active(tp, TT_PERSIST)) {
1484 tcp_timer_activate(tp, TT_PERSIST, 0);
1487 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1488 } else if (len == 0 && sbavail(&so->so_snd) &&
1489 !tcp_timer_active(tp, TT_REXMT) &&
1490 !tcp_timer_active(tp, TT_PERSIST)) {
1492 * Avoid a situation where we do not set persist timer
1493 * after a zero window condition. For example:
1494 * 1) A -> B: packet with enough data to fill the window
1495 * 2) B -> A: ACK for #1 + new data (0 window
1497 * 3) A -> B: ACK for #2, 0 len packet
1499 * In this case, A will not activate the persist timer,
1500 * because it chose to send a packet. Unless tcp_output
1501 * is called for some other reason (delayed ack timer,
1502 * another input packet from B, socket syscall), A will
1503 * not send zero window probes.
1505 * So, if you send a 0-length packet, but there is data
1506 * in the socket buffer, and neither the rexmt or
1507 * persist timer is already set, then activate the
1515 * Persist case, update snd_max but since we are in
1516 * persist mode (no window) we do not update snd_nxt.
1521 if (flags & TH_FIN) {
1523 tp->t_flags |= TF_SENTFIN;
1525 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1526 tp->snd_max = tp->snd_nxt + xlen;
1530 /* Record the error. */
1531 TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1532 error, 0, NULL, false);
1535 * We know that the packet was lost, so back out the
1536 * sequence number advance, if any.
1538 * If the error is EPERM the packet got blocked by the
1539 * local firewall. Normally we should terminate the
1540 * connection but the blocking may have been spurious
1541 * due to a firewall reconfiguration cycle. So we treat
1542 * it like a packet loss and let the retransmit timer and
1543 * timeouts do their work over time.
1544 * XXX: It is a POLA question whether calling tcp_drop right
1545 * away would be the really correct behavior instead.
1547 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1548 !tcp_timer_active(tp, TT_PERSIST)) &&
1549 ((flags & TH_SYN) == 0) &&
1553 tp->sackhint.sack_bytes_rexmit -= len;
1554 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1555 ("sackhint bytes rtx >= 0"));
1559 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1563 tp->t_softerror = error;
1566 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1567 tp->snd_cwnd = tp->t_maxseg;
1571 * For some reason the interface we used initially
1572 * to send segments changed to another or lowered
1574 * If TSO was active we either got an interface
1575 * without TSO capabilits or TSO was turned off.
1576 * If we obtained mtu from ip_output() then update
1580 tp->t_flags &= ~TF_TSO;
1582 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1590 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1591 tp->t_softerror = error;
1599 TCPSTAT_INC(tcps_sndtotal);
1602 * Data sent (as far as we can tell).
1603 * If this advertises a larger window than any other segment,
1604 * then remember the size of the advertised window.
1605 * Any pending ACK has now been sent.
1607 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1608 tp->rcv_adv = tp->rcv_nxt + recwin;
1609 tp->last_ack_sent = tp->rcv_nxt;
1610 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1611 if (tcp_timer_active(tp, TT_DELACK))
1612 tcp_timer_activate(tp, TT_DELACK, 0);
1615 * This completely breaks TCP if newreno is turned on. What happens
1616 * is that if delayed-acks are turned on on the receiver, this code
1617 * on the transmitter effectively destroys the TCP window, forcing
1618 * it to four packets (1.5Kx4 = 6K window).
1620 if (sendalot && --maxburst)
1629 tcp_setpersist(struct tcpcb *tp)
1631 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1634 tp->t_flags &= ~TF_PREVVALID;
1635 if (tcp_timer_active(tp, TT_REXMT))
1636 panic("tcp_setpersist: retransmit pending");
1638 * Start/restart persistence timer.
1640 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1641 tcp_persmin, tcp_persmax);
1642 tcp_timer_activate(tp, TT_PERSIST, tt);
1643 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1648 * Insert TCP options according to the supplied parameters to the place
1649 * optp in a consistent way. Can handle unaligned destinations.
1651 * The order of the option processing is crucial for optimal packing and
1652 * alignment for the scarce option space.
1654 * The optimal order for a SYN/SYN-ACK segment is:
1655 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1656 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1658 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1659 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1660 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1661 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1662 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1665 tcp_addoptions(struct tcpopt *to, u_char *optp)
1667 u_int32_t mask, optlen = 0;
1669 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1670 if ((to->to_flags & mask) != mask)
1672 if (optlen == TCP_MAXOLEN)
1674 switch (to->to_flags & mask) {
1676 while (optlen % 4) {
1677 optlen += TCPOLEN_NOP;
1678 *optp++ = TCPOPT_NOP;
1680 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1682 optlen += TCPOLEN_MAXSEG;
1683 *optp++ = TCPOPT_MAXSEG;
1684 *optp++ = TCPOLEN_MAXSEG;
1685 to->to_mss = htons(to->to_mss);
1686 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1687 optp += sizeof(to->to_mss);
1690 while (!optlen || optlen % 2 != 1) {
1691 optlen += TCPOLEN_NOP;
1692 *optp++ = TCPOPT_NOP;
1694 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1696 optlen += TCPOLEN_WINDOW;
1697 *optp++ = TCPOPT_WINDOW;
1698 *optp++ = TCPOLEN_WINDOW;
1699 *optp++ = to->to_wscale;
1702 while (optlen % 2) {
1703 optlen += TCPOLEN_NOP;
1704 *optp++ = TCPOPT_NOP;
1706 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1708 optlen += TCPOLEN_SACK_PERMITTED;
1709 *optp++ = TCPOPT_SACK_PERMITTED;
1710 *optp++ = TCPOLEN_SACK_PERMITTED;
1713 while (!optlen || optlen % 4 != 2) {
1714 optlen += TCPOLEN_NOP;
1715 *optp++ = TCPOPT_NOP;
1717 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1719 optlen += TCPOLEN_TIMESTAMP;
1720 *optp++ = TCPOPT_TIMESTAMP;
1721 *optp++ = TCPOLEN_TIMESTAMP;
1722 to->to_tsval = htonl(to->to_tsval);
1723 to->to_tsecr = htonl(to->to_tsecr);
1724 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1725 optp += sizeof(to->to_tsval);
1726 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1727 optp += sizeof(to->to_tsecr);
1731 int siglen = TCPOLEN_SIGNATURE - 2;
1733 while (!optlen || optlen % 4 != 2) {
1734 optlen += TCPOLEN_NOP;
1735 *optp++ = TCPOPT_NOP;
1737 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1738 to->to_flags &= ~TOF_SIGNATURE;
1741 optlen += TCPOLEN_SIGNATURE;
1742 *optp++ = TCPOPT_SIGNATURE;
1743 *optp++ = TCPOLEN_SIGNATURE;
1744 to->to_signature = optp;
1752 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1755 while (!optlen || optlen % 4 != 2) {
1756 optlen += TCPOLEN_NOP;
1757 *optp++ = TCPOPT_NOP;
1759 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1761 optlen += TCPOLEN_SACKHDR;
1762 *optp++ = TCPOPT_SACK;
1763 sackblks = min(to->to_nsacks,
1764 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1765 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1766 while (sackblks--) {
1767 sack_seq = htonl(sack->start);
1768 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1769 optp += sizeof(sack_seq);
1770 sack_seq = htonl(sack->end);
1771 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1772 optp += sizeof(sack_seq);
1773 optlen += TCPOLEN_SACK;
1776 TCPSTAT_INC(tcps_sack_send_blocks);
1783 /* XXX is there any point to aligning this option? */
1784 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1785 if (TCP_MAXOLEN - optlen < total_len) {
1786 to->to_flags &= ~TOF_FASTOPEN;
1789 *optp++ = TCPOPT_FAST_OPEN;
1790 *optp++ = total_len;
1791 if (to->to_tfo_len > 0) {
1792 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1793 optp += to->to_tfo_len;
1795 optlen += total_len;
1799 panic("%s: unknown TCP option type", __func__);
1804 /* Terminate and pad TCP options to a 4 byte boundary. */
1806 optlen += TCPOLEN_EOL;
1807 *optp++ = TCPOPT_EOL;
1810 * According to RFC 793 (STD0007):
1811 * "The content of the header beyond the End-of-Option option
1812 * must be header padding (i.e., zero)."
1813 * and later: "The padding is composed of zeros."
1815 while (optlen % 4) {
1816 optlen += TCPOLEN_PAD;
1817 *optp++ = TCPOPT_PAD;
1820 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1825 * This is a copy of m_copym(), taking the TSO segment size/limit
1826 * constraints into account, and advancing the sndptr as it goes.
1829 tcp_m_copym(struct mbuf *m, int32_t off0, int32_t *plen,
1830 int32_t seglimit, int32_t segsize, struct sockbuf *sb)
1832 struct mbuf *n, **np;
1835 int32_t len = *plen;
1839 uint32_t mlen, frags;
1843 KASSERT(off >= 0, ("tcp_m_copym, negative off %d", off));
1844 KASSERT(len >= 0, ("tcp_m_copym, negative len %d", len));
1845 if (off == 0 && m->m_flags & M_PKTHDR)
1850 KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1854 if ((sb) && (m == sb->sb_sndptr)) {
1855 sb->sb_sndptroff += m->m_len;
1856 sb->sb_sndptr = m->m_next;
1865 KASSERT(len == M_COPYALL,
1866 ("tcp_m_copym, length > size of mbuf chain"));
1868 if (pkthdrlen != NULL)
1869 *pkthdrlen = len_cp;
1872 mlen = min(len, m->m_len - off);
1875 * For M_NOMAP mbufs, add 3 segments
1876 * + 1 in case we are crossing page boundaries
1877 * + 2 in case the TLS hdr/trailer are used
1878 * It is cheaper to just add the segments
1879 * than it is to take the cache miss to look
1880 * at the mbuf ext_pgs state in detail.
1882 if (m->m_flags & M_NOMAP) {
1883 fragsize = min(segsize, PAGE_SIZE);
1890 /* Break if we really can't fit anymore. */
1891 if ((frags + 1) >= seglimit) {
1893 if (pkthdrlen != NULL)
1894 *pkthdrlen = len_cp;
1899 * Reduce size if you can't copy the whole
1900 * mbuf. If we can't copy the whole mbuf, also
1901 * adjust len so the loop will end after this
1904 if ((frags + howmany(mlen, fragsize)) >= seglimit) {
1905 mlen = (seglimit - frags - 1) * fragsize;
1907 *plen = len_cp + len;
1908 if (pkthdrlen != NULL)
1911 frags += howmany(mlen, fragsize);
1915 KASSERT(seglimit > 0,
1916 ("%s: seglimit went too low", __func__));
1919 n = m_gethdr(M_NOWAIT, m->m_type);
1921 n = m_get(M_NOWAIT, m->m_type);
1926 if (!m_dup_pkthdr(n, m, M_NOWAIT))
1928 if (len == M_COPYALL)
1929 n->m_pkthdr.len -= off0;
1931 n->m_pkthdr.len = len;
1932 pkthdrlen = &n->m_pkthdr.len;
1937 if (m->m_flags & M_EXT) {
1938 n->m_data = m->m_data + off;
1941 bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
1944 if (sb && (sb->sb_sndptr == m) &&
1945 ((n->m_len + off) >= m->m_len) && m->m_next) {
1946 sb->sb_sndptroff += m->m_len;
1947 sb->sb_sndptr = m->m_next;
1950 if (len != M_COPYALL) {
1963 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
1967 * Automatic sizing of send socket buffer. Often the send buffer
1968 * size is not optimally adjusted to the actual network conditions
1969 * at hand (delay bandwidth product). Setting the buffer size too
1970 * small limits throughput on links with high bandwidth and high
1971 * delay (eg. trans-continental/oceanic links). Setting the
1972 * buffer size too big consumes too much real kernel memory,
1973 * especially with many connections on busy servers.
1975 * The criteria to step up the send buffer one notch are:
1976 * 1. receive window of remote host is larger than send buffer
1977 * (with a fudge factor of 5/4th);
1978 * 2. send buffer is filled to 7/8th with data (so we actually
1979 * have data to make use of it);
1980 * 3. send buffer fill has not hit maximal automatic size;
1981 * 4. our send window (slow start and cogestion controlled) is
1982 * larger than sent but unacknowledged data in send buffer.
1984 * The remote host receive window scaling factor may limit the
1985 * growing of the send buffer before it reaches its allowed
1988 * It scales directly with slow start or congestion window
1989 * and does at most one step per received ACK. This fast
1990 * scaling has the drawback of growing the send buffer beyond
1991 * what is strictly necessary to make full use of a given
1992 * delay*bandwidth product. However testing has shown this not
1993 * to be much of an problem. At worst we are trading wasting
1994 * of available bandwidth (the non-use of it) for wasting some
1995 * socket buffer memory.
1997 * TODO: Shrink send buffer during idle periods together
1998 * with congestion window. Requires another timer. Has to
1999 * wait for upcoming tcp timer rewrite.
2001 * XXXGL: should there be used sbused() or sbavail()?
2003 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2006 lowat = V_tcp_sendbuf_auto_lowat ? so->so_snd.sb_lowat : 0;
2007 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat - lowat &&
2008 sbused(&so->so_snd) >=
2009 (so->so_snd.sb_hiwat / 8 * 7) - lowat &&
2010 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
2011 sendwin >= (sbused(&so->so_snd) -
2012 (tp->snd_nxt - tp->snd_una))) {
2013 if (!sbreserve_locked(&so->so_snd,
2014 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
2015 V_tcp_autosndbuf_max), so, curthread))
2016 so->so_snd.sb_flags &= ~SB_AUTOSIZE;