xref: /freebsd/sys/netinet/tcp_output.c (revision c1d255d3)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
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.
18  *
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
29  * SUCH DAMAGE.
30  *
31  *	@(#)tcp_output.c	8.4 (Berkeley) 5/24/95
32  */
33 
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36 
37 #include "opt_inet.h"
38 #include "opt_inet6.h"
39 #include "opt_ipsec.h"
40 #include "opt_kern_tls.h"
41 #include "opt_tcpdebug.h"
42 
43 #include <sys/param.h>
44 #include <sys/systm.h>
45 #include <sys/arb.h>
46 #include <sys/domain.h>
47 #ifdef TCP_HHOOK
48 #include <sys/hhook.h>
49 #endif
50 #include <sys/kernel.h>
51 #ifdef KERN_TLS
52 #include <sys/ktls.h>
53 #endif
54 #include <sys/lock.h>
55 #include <sys/mbuf.h>
56 #include <sys/mutex.h>
57 #include <sys/protosw.h>
58 #include <sys/qmath.h>
59 #include <sys/sdt.h>
60 #include <sys/socket.h>
61 #include <sys/socketvar.h>
62 #include <sys/sysctl.h>
63 #include <sys/stats.h>
64 
65 #include <net/if.h>
66 #include <net/route.h>
67 #include <net/route/nhop.h>
68 #include <net/vnet.h>
69 
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>
77 #ifdef INET6
78 #include <netinet6/in6_pcb.h>
79 #include <netinet/ip6.h>
80 #include <netinet6/ip6_var.h>
81 #endif
82 #include <netinet/tcp.h>
83 #define	TCPOUTFLAGS
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>
92 #ifdef TCPPCAP
93 #include <netinet/tcp_pcap.h>
94 #endif
95 #ifdef TCPDEBUG
96 #include <netinet/tcp_debug.h>
97 #endif
98 #ifdef TCP_OFFLOAD
99 #include <netinet/tcp_offload.h>
100 #endif
101 
102 #include <netipsec/ipsec_support.h>
103 
104 #include <netinet/udp.h>
105 #include <netinet/udp_var.h>
106 #include <machine/in_cksum.h>
107 
108 #include <security/mac/mac_framework.h>
109 
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");
114 
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");
119 
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");
124 
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");
129 
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");
134 
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");
139 
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");
145 
146 /*
147  * Make sure that either retransmit or persist timer is set for SYN, FIN and
148  * non-ACK.
149  */
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"))
155 
156 static void inline	cc_after_idle(struct tcpcb *tp);
157 
158 #ifdef TCP_HHOOK
159 /*
160  * Wrapper for the TCP established output helper hook.
161  */
162 void
163 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
164     struct tcpopt *to, uint32_t len, int tso)
165 {
166 	struct tcp_hhook_data hhook_data;
167 
168 	if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
169 		hhook_data.tp = tp;
170 		hhook_data.th = th;
171 		hhook_data.to = to;
172 		hhook_data.len = len;
173 		hhook_data.tso = tso;
174 
175 		hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
176 		    tp->osd);
177 	}
178 }
179 #endif
180 
181 /*
182  * CC wrapper hook functions
183  */
184 static void inline
185 cc_after_idle(struct tcpcb *tp)
186 {
187 	INP_WLOCK_ASSERT(tp->t_inpcb);
188 
189 	if (CC_ALGO(tp)->after_idle != NULL)
190 		CC_ALGO(tp)->after_idle(tp->ccv);
191 }
192 
193 /*
194  * Tcp output routine: figure out what should be sent and send it.
195  */
196 int
197 tcp_output(struct tcpcb *tp)
198 {
199 	struct socket *so = tp->t_inpcb->inp_socket;
200 	int32_t len;
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;
205 	struct mbuf *m;
206 	struct ip *ip = NULL;
207 #ifdef TCPDEBUG
208 	struct ipovly *ipov = NULL;
209 #endif
210 	struct tcphdr *th;
211 	u_char opt[TCP_MAXOLEN];
212 	unsigned ipoptlen, optlen, hdrlen, ulen;
213 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
214 	unsigned ipsec_optlen = 0;
215 #endif
216 	int idle, sendalot, curticks;
217 	int sack_rxmit, sack_bytes_rxmt;
218 	struct sackhole *p;
219 	int tso, mtu;
220 	struct tcpopt to;
221 	struct udphdr *udp = NULL;
222 	unsigned int wanted_cookie = 0;
223 	unsigned int dont_sendalot = 0;
224 #if 0
225 	int maxburst = TCP_MAXBURST;
226 #endif
227 #ifdef INET6
228 	struct ip6_hdr *ip6 = NULL;
229 	int isipv6;
230 
231 	isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
232 #endif
233 #ifdef KERN_TLS
234 	const bool hw_tls = (so->so_snd.sb_flags & SB_TLS_IFNET) != 0;
235 #else
236 	const bool hw_tls = false;
237 #endif
238 
239 	NET_EPOCH_ASSERT();
240 	INP_WLOCK_ASSERT(tp->t_inpcb);
241 
242 #ifdef TCP_OFFLOAD
243 	if (tp->t_flags & TF_TOE)
244 		return (tcp_offload_output(tp));
245 #endif
246 
247 	/*
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.
251 	 */
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 */
257 		return (0);
258 
259 	/*
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.
264 	 */
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))))
268 		cc_after_idle(tp);
269 	tp->t_flags &= ~TF_LASTIDLE;
270 	if (idle) {
271 		if (tp->t_flags & TF_MORETOCOME) {
272 			tp->t_flags |= TF_LASTIDLE;
273 			idle = 0;
274 		}
275 	}
276 again:
277 	/*
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.
281 	 */
282 	if ((tp->t_flags & TF_SACK_PERMIT) &&
283 	    SEQ_LT(tp->snd_nxt, tp->snd_max))
284 		tcp_sack_adjust(tp);
285 	sendalot = 0;
286 	tso = 0;
287 	mtu = 0;
288 	off = tp->snd_nxt - tp->snd_una;
289 	sendwin = min(tp->snd_wnd, tp->snd_cwnd);
290 
291 	flags = tcp_outflags[tp->t_state];
292 	/*
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().
298 	 */
299 	/*
300 	 * Still in sack recovery , reset rxmit flag to zero.
301 	 */
302 	sack_rxmit = 0;
303 	sack_bytes_rxmt = 0;
304 	len = 0;
305 	p = NULL;
306 	if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
307 	    (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
308 		uint32_t cwin;
309 
310 		cwin =
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)) {
314 			/*
315 			 * (At least) part of sack hole extends beyond
316 			 * snd_recover. Check to see if we can rexmit data
317 			 * for this hole.
318 			 */
319 			if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
320 				/*
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.
325 				 */
326 				p = NULL;
327 				goto after_sack_rexmit;
328 			} else
329 				/* Can rexmit part of the current hole */
330 				len = ((int32_t)ulmin(cwin,
331 						   tp->snd_recover - p->rxmit));
332 		} else
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",
336 		    __func__, off));
337 		if (len > 0) {
338 			sack_rxmit = 1;
339 			sendalot = 1;
340 			TCPSTAT_INC(tcps_sack_rexmits);
341 			TCPSTAT_ADD(tcps_sack_rexmit_bytes,
342 			    min(len, tcp_maxseg(tp)));
343 		}
344 	}
345 after_sack_rexmit:
346 	/*
347 	 * Get standard flags, and add SYN or FIN if requested by 'hidden'
348 	 * state flags.
349 	 */
350 	if (tp->t_flags & TF_NEEDFIN)
351 		flags |= TH_FIN;
352 	if (tp->t_flags & TF_NEEDSYN)
353 		flags |= TH_SYN;
354 
355 	SOCKBUF_LOCK(&so->so_snd);
356 	/*
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.
361 	 */
362 	if (tp->t_flags & TF_FORCEDATA) {
363 		if (sendwin == 0) {
364 			/*
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.
374 			 *
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
378 			 * itself.
379 			 */
380 			if (off < sbused(&so->so_snd))
381 				flags &= ~TH_FIN;
382 			sendwin = 1;
383 		} else {
384 			tcp_timer_activate(tp, TT_PERSIST, 0);
385 			tp->t_rxtshift = 0;
386 		}
387 	}
388 
389 	/*
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.
396 	 *
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
399 	 * wind up 0.
400 	 *
401 	 * If sack_rxmit is true we are retransmitting from the scoreboard
402 	 * in which case len is already set.
403 	 */
404 	if (sack_rxmit == 0) {
405 		if (sack_bytes_rxmt == 0)
406 			len = ((int32_t)min(sbavail(&so->so_snd), sendwin) -
407 			    off);
408 		else {
409 			int32_t cwin;
410 
411                         /*
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.
415 			 */
416 			len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
417 			    off);
418 			/*
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.
425 			 */
426 			if (len > 0) {
427 				cwin = tp->snd_cwnd -
428 					(tp->snd_nxt - tp->snd_recover) -
429 					sack_bytes_rxmt;
430 				if (cwin < 0)
431 					cwin = 0;
432 				len = imin(len, cwin);
433 			}
434 		}
435 	}
436 
437 	/*
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.
441 	 */
442 	if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
443 		if (tp->t_state != TCPS_SYN_RECEIVED)
444 			flags &= ~TH_SYN;
445 		/*
446 		 * When sending additional segments following a TFO SYN|ACK,
447 		 * do not include the SYN bit.
448 		 */
449 		if (IS_FASTOPEN(tp->t_flags) &&
450 		    (tp->t_state == TCPS_SYN_RECEIVED))
451 			flags &= ~TH_SYN;
452 		off--, len++;
453 	}
454 
455 	/*
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.
459 	 */
460 	if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
461 		len = 0;
462 		flags &= ~TH_FIN;
463 	}
464 
465 	/*
466 	 * On TFO sockets, ensure no data is sent in the following cases:
467 	 *
468 	 *  - When retransmitting SYN|ACK on a passively-created socket
469 	 *
470 	 *  - When retransmitting SYN on an actively created socket
471 	 *
472 	 *  - When sending a zero-length cookie (cookie request) on an
473 	 *    actively created socket
474 	 *
475 	 *  - When the socket is in the CLOSED state (RST is being sent)
476 	 */
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)) ||
481 	     (flags & TH_RST)))
482 		len = 0;
483 	if (len <= 0) {
484 		/*
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.
493 		 *
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.
499 		 */
500 		len = 0;
501 		if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
502 			(off < (int) sbavail(&so->so_snd))) {
503 			tcp_timer_activate(tp, TT_REXMT, 0);
504 			tp->t_rxtshift = 0;
505 			tp->snd_nxt = tp->snd_una;
506 			if (!tcp_timer_active(tp, TT_PERSIST))
507 				tcp_setpersist(tp);
508 		}
509 	}
510 
511 	/* len will be >= 0 after this point. */
512 	KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
513 
514 	tcp_sndbuf_autoscale(tp, so, sendwin);
515 
516 	/*
517 	 * Decide if we can use TCP Segmentation Offloading (if supported by
518 	 * hardware).
519 	 *
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
525 	 * segment or packet.
526 	 *
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.
531 	 */
532 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
533 	/*
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.
536 	 */
537 #ifdef INET6
538 	if (isipv6 && IPSEC_ENABLED(ipv6))
539 		ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
540 #ifdef INET
541 	else
542 #endif
543 #endif /* INET6 */
544 #ifdef INET
545 	if (IPSEC_ENABLED(ipv4))
546 		ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
547 #endif /* INET */
548 #endif /* IPSEC */
549 #ifdef INET6
550 	if (isipv6)
551 		ipoptlen = ip6_optlen(tp->t_inpcb);
552 	else
553 #endif
554 	if (tp->t_inpcb->inp_options)
555 		ipoptlen = tp->t_inpcb->inp_options->m_len -
556 				offsetof(struct ipoption, ipopt_list);
557 	else
558 		ipoptlen = 0;
559 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
560 	ipoptlen += ipsec_optlen;
561 #endif
562 
563 	if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
564 	    (tp->t_port == 0) &&
565 	    ((tp->t_flags & TF_SIGNATURE) == 0) &&
566 	    tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
567 	    ipoptlen == 0 && !(flags & TH_SYN))
568 		tso = 1;
569 
570 	if (sack_rxmit) {
571 		if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
572 			flags &= ~TH_FIN;
573 	} else {
574 		if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
575 		    sbused(&so->so_snd)))
576 			flags &= ~TH_FIN;
577 	}
578 
579 	recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
580 	    (long)TCP_MAXWIN << tp->rcv_scale);
581 
582 	/*
583 	 * Sender silly window avoidance.   We transmit under the following
584 	 * conditions when len is non-zero:
585 	 *
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
593 	 */
594 	if (len) {
595 		if (len >= tp->t_maxseg)
596 			goto send;
597 		/*
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.
604 		 */
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)
610 			goto send;
611 		/*
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
615 		 *
616 		 * note: the len + off check is almost certainly unnecessary.
617 		 */
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) {
622 			goto send;
623 		}
624 		if (tp->t_flags & TF_FORCEDATA)		/* typ. timeout case */
625 			goto send;
626 		if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
627 			goto send;
628 		if (SEQ_LT(tp->snd_nxt, tp->snd_max))	/* retransmit case */
629 			goto send;
630 		if (sack_rxmit)
631 			goto send;
632 	}
633 
634 	/*
635 	 * Sending of standalone window updates.
636 	 *
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.
642 	 *
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.
648 	 *
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.
656 	 *
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
661 	 * half-open state.
662 	 */
663 	if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
664 	    !(tp->t_flags & TF_DELACK) &&
665 	    !TCPS_HAVERCVDFIN(tp->t_state)) {
666 		/*
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.
670 		 */
671 		int32_t adv;
672 		int oldwin;
673 
674 		adv = recwin;
675 		if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
676 			oldwin = (tp->rcv_adv - tp->rcv_nxt);
677 			if (adv > oldwin)
678 				adv -= oldwin;
679 			else
680 				adv = 0;
681 		} else
682 			oldwin = 0;
683 
684 		/*
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
687 		 * a window update.
688 		 */
689 		if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
690 			goto dontupdate;
691 
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))
697 			goto send;
698 		if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
699 			goto send;
700 	}
701 dontupdate:
702 
703 	/*
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.
706 	 */
707 	if (tp->t_flags & TF_ACKNOW)
708 		goto send;
709 	if ((flags & TH_RST) ||
710 	    ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
711 		goto send;
712 	if (SEQ_GT(tp->snd_up, tp->snd_una))
713 		goto send;
714 	/*
715 	 * If our state indicates that FIN should be sent
716 	 * and we have not yet done so, then we need to send.
717 	 */
718 	if (flags & TH_FIN &&
719 	    ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
720 		goto send;
721 	/*
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.
725 	 */
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);
731 		goto just_return;
732 	}
733 	/*
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
740 	 *
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.
748 	 *
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.
754 	 */
755 	if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
756 	    !tcp_timer_active(tp, TT_PERSIST)) {
757 		tp->t_rxtshift = 0;
758 		tcp_setpersist(tp);
759 	}
760 
761 	/*
762 	 * No reason to send a segment, just return.
763 	 */
764 just_return:
765 	SOCKBUF_UNLOCK(&so->so_snd);
766 	return (0);
767 
768 send:
769 	SOCKBUF_LOCK_ASSERT(&so->so_snd);
770 	if (len > 0) {
771 		if (len >= tp->t_maxseg)
772 			tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
773 		else
774 			tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
775 	}
776 	/*
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
781 	 * link header, i.e.
782 	 *	max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
783 	 */
784 	optlen = 0;
785 #ifdef INET6
786 	if (isipv6)
787 		hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
788 	else
789 #endif
790 		hdrlen = sizeof (struct tcpiphdr);
791 
792 	if (flags & TH_SYN) {
793 		tp->snd_nxt = tp->iss;
794 	}
795 
796 	/*
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
800 	 * syncache.
801 	 */
802 	to.to_flags = 0;
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);
807 			if (tp->t_port)
808 				to.to_mss -= V_tcp_udp_tunneling_overhead;
809 			to.to_flags |= TOF_MSS;
810 
811 			/*
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.
817 			 */
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;
822 					to.to_tfo_cookie =
823 					    (u_int8_t *)&tp->t_tfo_cookie.server;
824 					to.to_flags |= TOF_FASTOPEN;
825 					wanted_cookie = 1;
826 				} else if (tp->t_state == TCPS_SYN_SENT) {
827 					to.to_tfo_len =
828 					    tp->t_tfo_client_cookie_len;
829 					to.to_tfo_cookie =
830 					    tp->t_tfo_cookie.client;
831 					to.to_flags |= TOF_FASTOPEN;
832 					wanted_cookie = 1;
833 					/*
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
838 					 * the other end.
839 					 */
840 					dont_sendalot = 1;
841 				}
842 			}
843 		}
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;
848 		}
849 		/* Timestamps. */
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;
858 		}
859 
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();
864 
865 		/* Selective ACK's. */
866 		if (tp->t_flags & TF_SACK_PERMIT) {
867 			if (flags & TH_SYN)
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;
874 			}
875 		}
876 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
877 		/* TCP-MD5 (RFC2385). */
878 		/*
879 		 * Check that TCP_MD5SIG is enabled in tcpcb to
880 		 * account the size needed to set this TCP option.
881 		 */
882 		if (tp->t_flags & TF_SIGNATURE)
883 			to.to_flags |= TOF_SIGNATURE;
884 #endif /* TCP_SIGNATURE */
885 
886 		/* Processing the options. */
887 		hdrlen += optlen = tcp_addoptions(&to, opt);
888 		/*
889 		 * If we wanted a TFO option to be added, but it was unable
890 		 * to fit, ensure no data is sent.
891 		 */
892 		if (IS_FASTOPEN(tp->t_flags) && wanted_cookie &&
893 		    !(to.to_flags & TOF_FASTOPEN))
894 			len = 0;
895 	}
896 	if (tp->t_port) {
897 		if (V_tcp_udp_tunneling_port == 0) {
898 			/* The port was removed?? */
899 			SOCKBUF_UNLOCK(&so->so_snd);
900 			return (EHOSTUNREACH);
901 		}
902 		hdrlen += sizeof(struct udphdr);
903 	}
904 	/*
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
908 	 * the segment.
909 	 */
910 	if (len + optlen + ipoptlen > tp->t_maxseg) {
911 		flags &= ~TH_FIN;
912 
913 		if (tso) {
914 			u_int if_hw_tsomax;
915 			u_int moff;
916 			int max_len;
917 
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;
922 
923 			/*
924 			 * Limit a TSO burst to prevent it from
925 			 * overflowing or exceeding the maximum length
926 			 * allowed by the network interface:
927 			 */
928 			KASSERT(ipoptlen == 0,
929 			    ("%s: TSO can't do IP options", __func__));
930 
931 			/*
932 			 * Check if we should limit by maximum payload
933 			 * length:
934 			 */
935 			if (if_hw_tsomax != 0) {
936 				/* compute maximum TSO length */
937 				max_len = (if_hw_tsomax - hdrlen -
938 				    max_linkhdr);
939 				if (max_len <= 0) {
940 					len = 0;
941 				} else if (len > max_len) {
942 					sendalot = 1;
943 					len = max_len;
944 				}
945 			}
946 
947 			/*
948 			 * Prevent the last segment from being
949 			 * fractional unless the send sockbuf can be
950 			 * emptied:
951 			 */
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;
956 				if (moff != 0) {
957 					len -= moff;
958 					sendalot = 1;
959 				}
960 			}
961 
962 			/*
963 			 * In case there are too many small fragments
964 			 * don't use TSO:
965 			 */
966 			if (len <= max_len) {
967 				len = max_len;
968 				sendalot = 1;
969 				tso = 0;
970 			}
971 
972 			/*
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
977 			 * last segment.
978 			 */
979 			if (tp->t_flags & TF_NEEDFIN)
980 				sendalot = 1;
981 		} else {
982 			if (optlen + ipoptlen >= tp->t_maxseg) {
983 				/*
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
989 				 * TCP segment.
990 				 */
991 				SOCKBUF_UNLOCK(&so->so_snd);
992 				error = EMSGSIZE;
993 				sack_rxmit = 0;
994 				goto out;
995 			}
996 			len = tp->t_maxseg - optlen - ipoptlen;
997 			sendalot = 1;
998 			if (dont_sendalot)
999 				sendalot = 0;
1000 		}
1001 	} else
1002 		tso = 0;
1003 
1004 	KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1005 	    ("%s: len > IP_MAXPACKET", __func__));
1006 
1007 /*#ifdef DIAGNOSTIC*/
1008 #ifdef INET6
1009 	if (max_linkhdr + hdrlen > MCLBYTES)
1010 #else
1011 	if (max_linkhdr + hdrlen > MHLEN)
1012 #endif
1013 		panic("tcphdr too big");
1014 /*#endif*/
1015 
1016 	/*
1017 	 * This KASSERT is here to catch edge cases at a well defined place.
1018 	 * Before, those had triggered (random) panic conditions further down.
1019 	 */
1020 	KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1021 
1022 	/*
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.
1026 	 */
1027 	if (len) {
1028 		struct mbuf *mb;
1029 		struct sockbuf *msb;
1030 		u_int moff;
1031 
1032 		if ((tp->t_flags & TF_FORCEDATA) && len == 1) {
1033 			TCPSTAT_INC(tcps_sndprobe);
1034 #ifdef STATS
1035 			if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1036 				stats_voi_update_abs_u32(tp->t_stats,
1037 				VOI_TCP_RETXPB, len);
1038 			else
1039 				stats_voi_update_abs_u64(tp->t_stats,
1040 				    VOI_TCP_TXPB, len);
1041 #endif /* 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);
1046 #ifdef STATS
1047 			stats_voi_update_abs_u32(tp->t_stats, VOI_TCP_RETXPB,
1048 			    len);
1049 #endif /* STATS */
1050 		} else {
1051 			TCPSTAT_INC(tcps_sndpack);
1052 			TCPSTAT_ADD(tcps_sndbyte, len);
1053 #ifdef STATS
1054 			stats_voi_update_abs_u64(tp->t_stats, VOI_TCP_TXPB,
1055 			    len);
1056 #endif /* STATS */
1057 		}
1058 #ifdef INET6
1059 		if (MHLEN < hdrlen + max_linkhdr)
1060 			m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1061 		else
1062 #endif
1063 			m = m_gethdr(M_NOWAIT, MT_DATA);
1064 
1065 		if (m == NULL) {
1066 			SOCKBUF_UNLOCK(&so->so_snd);
1067 			error = ENOBUFS;
1068 			sack_rxmit = 0;
1069 			goto out;
1070 		}
1071 
1072 		m->m_data += max_linkhdr;
1073 		m->m_len = hdrlen;
1074 
1075 		/*
1076 		 * Start the m_copy functions from the closest mbuf
1077 		 * to the offset in the socket buffer chain.
1078 		 */
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);
1085 			m->m_len += len;
1086 		} else {
1087 			if (SEQ_LT(tp->snd_nxt, tp->snd_max))
1088 				msb = NULL;
1089 			else
1090 				msb = &so->so_snd;
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)) {
1095 				/*
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
1099 				 * mbufs.
1100 				 */
1101 				tso = 0;
1102 			}
1103 			if (m->m_next == NULL) {
1104 				SOCKBUF_UNLOCK(&so->so_snd);
1105 				(void) m_free(m);
1106 				error = ENOBUFS;
1107 				sack_rxmit = 0;
1108 				goto out;
1109 			}
1110 		}
1111 
1112 		/*
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
1116 		 * a PUSH comes in.)
1117 		 */
1118 		if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1119 		    !(flags & TH_SYN))
1120 			flags |= TH_PUSH;
1121 		SOCKBUF_UNLOCK(&so->so_snd);
1122 	} else {
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);
1130 		else
1131 			TCPSTAT_INC(tcps_sndwinup);
1132 
1133 		m = m_gethdr(M_NOWAIT, MT_DATA);
1134 		if (m == NULL) {
1135 			error = ENOBUFS;
1136 			sack_rxmit = 0;
1137 			goto out;
1138 		}
1139 #ifdef INET6
1140 		if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1141 		    MHLEN >= hdrlen) {
1142 			M_ALIGN(m, hdrlen);
1143 		} else
1144 #endif
1145 		m->m_data += max_linkhdr;
1146 		m->m_len = hdrlen;
1147 	}
1148 	SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1149 	m->m_pkthdr.rcvif = (struct ifnet *)0;
1150 #ifdef MAC
1151 	mac_inpcb_create_mbuf(tp->t_inpcb, m);
1152 #endif
1153 #ifdef INET6
1154 	if (isipv6) {
1155 		ip6 = mtod(m, struct ip6_hdr *);
1156 		if (tp->t_port) {
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);
1163 		} else {
1164 			th = (struct tcphdr *)(ip6 + 1);
1165 		}
1166 		tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip6, th);
1167 	} else
1168 #endif /* INET6 */
1169 	{
1170 		ip = mtod(m, struct ip *);
1171 #ifdef TCPDEBUG
1172 		ipov = (struct ipovly *)ip;
1173 #endif
1174 		if (tp->t_port) {
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);
1181 		} else
1182 			th = (struct tcphdr *)(ip + 1);
1183 		tcpip_fillheaders(tp->t_inpcb, tp->t_port, ip, th);
1184 	}
1185 
1186 	/*
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.
1190 	 */
1191 	if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1192 	    tp->snd_nxt == tp->snd_max)
1193 		tp->snd_nxt--;
1194 	/*
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
1198 	 * RFC 3168.
1199 	 */
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;
1204 		} else
1205 			flags |= TH_ECE|TH_CWR;
1206 	}
1207 	/* Handle parallel SYN for ECN */
1208 	if ((tp->t_state == TCPS_SYN_RECEIVED) &&
1209 	    (tp->t_flags2 & TF2_ECN_SND_ECE)) {
1210 			flags |= TH_ECE;
1211 			tp->t_flags2 &= ~TF2_ECN_SND_ECE;
1212 	}
1213 
1214 	if (TCPS_HAVEESTABLISHED(tp->t_state) &&
1215 	    (tp->t_flags2 & TF2_ECN_PERMIT)) {
1216 		/*
1217 		 * If the peer has ECN, mark data packets with
1218 		 * ECN capable transmission (ECT).
1219 		 * Ignore pure ack packets, retransmissions and window probes.
1220 		 */
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))) {
1225 #ifdef INET6
1226 			if (isipv6)
1227 				ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1228 			else
1229 #endif
1230 				ip->ip_tos |= IPTOS_ECN_ECT0;
1231 			TCPSTAT_INC(tcps_ecn_ect0);
1232 			/*
1233 			 * Reply with proper ECN notifications.
1234 			 * Only set CWR on new data segments.
1235 			 */
1236 			if (tp->t_flags2 & TF2_ECN_SND_CWR) {
1237 				flags |= TH_CWR;
1238 				tp->t_flags2 &= ~TF2_ECN_SND_CWR;
1239 			}
1240 		}
1241 		if (tp->t_flags2 & TF2_ECN_SND_ECE)
1242 			flags |= TH_ECE;
1243 	}
1244 
1245 	/*
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...)
1257 	 */
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);
1262 		else
1263 			th->th_seq = htonl(tp->snd_max);
1264 	} else {
1265 		th->th_seq = htonl(p->rxmit);
1266 		p->rxmit += len;
1267 		/*
1268 		 * Lost Retransmission Detection
1269 		 * trigger resending of a (then
1270 		 * still existing) hole, when
1271 		 * fack acks recoverypoint.
1272 		 */
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;
1276 	}
1277 	if (IN_RECOVERY(tp->t_flags)) {
1278 		/*
1279 		 * Account all bytes transmitted while
1280 		 * IN_RECOVERY, simplifying PRR and
1281 		 * Lost Retransmit Detection
1282 		 */
1283 		tp->sackhint.prr_out += len;
1284 	}
1285 	th->th_ack = htonl(tp->rcv_nxt);
1286 	if (optlen) {
1287 		bcopy(opt, th + 1, optlen);
1288 		th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1289 	}
1290 	th->th_flags = flags;
1291 	/*
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.
1295 	 */
1296 	if (flags & TH_RST) {
1297 		recwin = 0;
1298 	} else {
1299 		if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1300 		    recwin < tp->t_maxseg)
1301 			recwin = 0;
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);
1305 	}
1306 	/*
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.
1310 	 */
1311 	if (flags & TH_SYN)
1312 		th->th_win = htons((u_short)
1313 				(min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1314 	else {
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));
1318 	}
1319 
1320 	/*
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
1326 	 * the connection.
1327 	 */
1328 	if (th->th_win == 0) {
1329 		tp->t_sndzerowin++;
1330 		tp->t_flags |= TF_RXWIN0SENT;
1331 	} else
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;
1336 	} else
1337 		/*
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.
1342 		 */
1343 		tp->snd_up = tp->snd_una;		/* drag it along */
1344 
1345 	/*
1346 	 * Put TCP length in extended header, and then
1347 	 * checksum extended header and data.
1348 	 */
1349 	m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1350 
1351 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1352 	if (to.to_flags & TOF_SIGNATURE) {
1353 		/*
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.
1358 		 */
1359 		if (!TCPMD5_ENABLED() || (error = TCPMD5_OUTPUT(m, th,
1360 		    (u_char *)(th + 1) + (to.to_signature - opt))) != 0) {
1361 			/*
1362 			 * Do not send segment if the calculation of MD5
1363 			 * digest has failed.
1364 			 */
1365 			m_freem(m);
1366 			goto out;
1367 		}
1368 	}
1369 #endif
1370 #ifdef INET6
1371 	if (isipv6) {
1372 		/*
1373 		 * There is no need to fill in ip6_plen right now.
1374 		 * It will be filled later by ip6_output.
1375 		 */
1376 		if (tp->t_port) {
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);
1382 		} else {
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,
1387 			    0);
1388 		}
1389 	}
1390 #endif
1391 #if defined(INET6) && defined(INET)
1392 	else
1393 #endif
1394 #ifdef INET
1395 	{
1396 		if (tp->t_port) {
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);
1403 		} else {
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));
1409 		}
1410 
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));
1414 	}
1415 #endif
1416 
1417 	/*
1418 	 * Enable TSO and specify the size of the segments.
1419 	 * The TCP pseudo header checksum is always provided.
1420 	 */
1421 	if (tso) {
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;
1426 	}
1427 
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)));
1431 
1432 #ifdef TCP_HHOOK
1433 	/* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1434 	hhook_run_tcp_est_out(tp, th, &to, len, tso);
1435 #endif
1436 
1437 #ifdef TCPDEBUG
1438 	/*
1439 	 * Trace.
1440 	 */
1441 	if (so->so_options & SO_DEBUG) {
1442 		u_short save = 0;
1443 #ifdef INET6
1444 		if (!isipv6)
1445 #endif
1446 		{
1447 			save = ipov->ih_len;
1448 			ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1449 		}
1450 		tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1451 #ifdef INET6
1452 		if (!isipv6)
1453 #endif
1454 		ipov->ih_len = save;
1455 	}
1456 #endif /* TCPDEBUG */
1457 	TCP_PROBE3(debug__output, tp, th, m);
1458 
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,
1461 	    len, NULL, false);
1462 
1463 	/*
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.
1468 	 */
1469 	/*
1470 	 * m->m_pkthdr.len should have been set before checksum calculation,
1471 	 * because in6_cksum() need it.
1472 	 */
1473 #ifdef INET6
1474 	if (isipv6) {
1475 		/*
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.
1480 		 */
1481 		ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1482 
1483 		/*
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.
1487 		 */
1488 		ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1489 
1490 		if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1491 			tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1492 		else
1493 			tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1494 
1495 		if (tp->t_state == TCPS_SYN_SENT)
1496 			TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1497 
1498 		TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1499 
1500 #ifdef TCPPCAP
1501 		/* Save packet, if requested. */
1502 		tcp_pcap_add(th, m, &(tp->t_outpkts));
1503 #endif
1504 
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);
1510 
1511 		if (error == EMSGSIZE && tp->t_inpcb->inp_route6.ro_nh != NULL)
1512 			mtu = tp->t_inpcb->inp_route6.ro_nh->nh_mtu;
1513 	}
1514 #endif /* INET6 */
1515 #if defined(INET) && defined(INET6)
1516 	else
1517 #endif
1518 #ifdef INET
1519     {
1520 	ip->ip_len = htons(m->m_pkthdr.len);
1521 #ifdef INET6
1522 	if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1523 		ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1524 #endif /* INET6 */
1525 	/*
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.
1530 	 *
1531 	 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1532 	 */
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);
1537 		}
1538 	} else {
1539 		tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1540 	}
1541 
1542 	if (tp->t_state == TCPS_SYN_SENT)
1543 		TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1544 
1545 	TCP_PROBE5(send, NULL, tp, ip, tp, th);
1546 
1547 #ifdef TCPPCAP
1548 	/* Save packet, if requested. */
1549 	tcp_pcap_add(th, m, &(tp->t_outpkts));
1550 #endif
1551 
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,
1554 	    tp->t_inpcb);
1555 
1556 	if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_nh != NULL)
1557 		mtu = tp->t_inpcb->inp_route.ro_nh->nh_mtu;
1558     }
1559 #endif /* INET */
1560 
1561 out:
1562 	if (error == 0)
1563 		tcp_account_for_send(tp, len, (tp->snd_nxt != tp->snd_max), 0, hw_tls);
1564 	/*
1565 	 * In transmit state, time the transmission and arrange for
1566 	 * the retransmit.  In persist state, just set snd_max.
1567 	 */
1568 	if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1569 	    !tcp_timer_active(tp, TT_PERSIST)) {
1570 		tcp_seq startseq = tp->snd_nxt;
1571 
1572 		/*
1573 		 * Advance snd_nxt over sequence space of this segment.
1574 		 */
1575 		if (flags & (TH_SYN|TH_FIN)) {
1576 			if (flags & TH_SYN)
1577 				tp->snd_nxt++;
1578 			if (flags & TH_FIN) {
1579 				tp->snd_nxt++;
1580 				tp->t_flags |= TF_SENTFIN;
1581 			}
1582 		}
1583 		if (sack_rxmit)
1584 			goto timer;
1585 		tp->snd_nxt += len;
1586 		if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1587 			tp->snd_max = tp->snd_nxt;
1588 			/*
1589 			 * Time this transmission if not a retransmission and
1590 			 * not currently timing anything.
1591 			 */
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);
1597 			}
1598 #ifdef STATS
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();
1605 			}
1606 #endif /* STATS */
1607 		}
1608 
1609 		/*
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.
1616 		 */
1617 timer:
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);
1623 				tp->t_rxtshift = 0;
1624 			}
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)) {
1629 			/*
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
1634 			 *    advertisement)
1635 			 * 3) A -> B: ACK for #2, 0 len packet
1636 			 *
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.
1642 			 *
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
1646 			 * persist timer.
1647 			 */
1648 			tp->t_rxtshift = 0;
1649 			tcp_setpersist(tp);
1650 		}
1651 	} else {
1652 		/*
1653 		 * Persist case, update snd_max but since we are in
1654 		 * persist mode (no window) we do not update snd_nxt.
1655 		 */
1656 		int xlen = len;
1657 		if (flags & TH_SYN)
1658 			++xlen;
1659 		if (flags & TH_FIN) {
1660 			++xlen;
1661 			tp->t_flags |= TF_SENTFIN;
1662 		}
1663 		if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1664 			tp->snd_max = tp->snd_nxt + xlen;
1665 	}
1666 	if ((error == 0) &&
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);
1672 	}
1673 	if (error) {
1674 		/* Record the error. */
1675 		TCP_LOG_EVENT(tp, NULL, &so->so_rcv, &so->so_snd, TCP_LOG_OUT,
1676 		    error, 0, NULL, false);
1677 
1678 		/*
1679 		 * We know that the packet was lost, so back out the
1680 		 * sequence number advance, if any.
1681 		 *
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.
1690 		 */
1691 		if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1692 		    !tcp_timer_active(tp, TT_PERSIST)) &&
1693 		    ((flags & TH_SYN) == 0) &&
1694 		    (error != EPERM)) {
1695 			if (sack_rxmit) {
1696 				p->rxmit -= len;
1697 				tp->sackhint.sack_bytes_rexmit -= len;
1698 				KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1699 				    ("sackhint bytes rtx >= 0"));
1700 			} else
1701 				tp->snd_nxt -= len;
1702 		}
1703 		SOCKBUF_UNLOCK_ASSERT(&so->so_snd);	/* Check gotos. */
1704 		switch (error) {
1705 		case EACCES:
1706 		case EPERM:
1707 			tp->t_softerror = error;
1708 			return (error);
1709 		case ENOBUFS:
1710 			TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1711 			tp->snd_cwnd = tp->t_maxseg;
1712 			return (0);
1713 		case EMSGSIZE:
1714 			/*
1715 			 * For some reason the interface we used initially
1716 			 * to send segments changed to another or lowered
1717 			 * its MTU.
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
1721 			 * it and try again.
1722 			 */
1723 			if (tso)
1724 				tp->t_flags &= ~TF_TSO;
1725 			if (mtu != 0) {
1726 				tcp_mss_update(tp, -1, mtu, NULL, NULL);
1727 				goto again;
1728 			}
1729 			return (error);
1730 		case EHOSTDOWN:
1731 		case EHOSTUNREACH:
1732 		case ENETDOWN:
1733 		case ENETUNREACH:
1734 			if (TCPS_HAVERCVDSYN(tp->t_state)) {
1735 				tp->t_softerror = error;
1736 				return (0);
1737 			}
1738 			/* FALLTHROUGH */
1739 		default:
1740 			return (error);
1741 		}
1742 	}
1743 	TCPSTAT_INC(tcps_sndtotal);
1744 
1745 	/*
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.
1750 	 */
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);
1757 #if 0
1758 	/*
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).
1763 	 */
1764 	if (sendalot && --maxburst)
1765 		goto again;
1766 #endif
1767 	if (sendalot)
1768 		goto again;
1769 	return (0);
1770 }
1771 
1772 void
1773 tcp_setpersist(struct tcpcb *tp)
1774 {
1775 	int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1776 	int tt;
1777 
1778 	tp->t_flags &= ~TF_PREVVALID;
1779 	if (tcp_timer_active(tp, TT_REXMT))
1780 		panic("tcp_setpersist: retransmit pending");
1781 	/*
1782 	 * Start/restart persistence timer.
1783 	 */
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)
1788 		tp->t_rxtshift++;
1789 }
1790 
1791 /*
1792  * Insert TCP options according to the supplied parameters to the place
1793  * optp in a consistent way.  Can handle unaligned destinations.
1794  *
1795  * The order of the option processing is crucial for optimal packing and
1796  * alignment for the scarce option space.
1797  *
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.
1801  *
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)).
1807  */
1808 int
1809 tcp_addoptions(struct tcpopt *to, u_char *optp)
1810 {
1811 	u_int32_t mask, optlen = 0;
1812 
1813 	for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1814 		if ((to->to_flags & mask) != mask)
1815 			continue;
1816 		if (optlen == TCP_MAXOLEN)
1817 			break;
1818 		switch (to->to_flags & mask) {
1819 		case TOF_MSS:
1820 			while (optlen % 4) {
1821 				optlen += TCPOLEN_NOP;
1822 				*optp++ = TCPOPT_NOP;
1823 			}
1824 			if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1825 				continue;
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);
1832 			break;
1833 		case TOF_SCALE:
1834 			while (!optlen || optlen % 2 != 1) {
1835 				optlen += TCPOLEN_NOP;
1836 				*optp++ = TCPOPT_NOP;
1837 			}
1838 			if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1839 				continue;
1840 			optlen += TCPOLEN_WINDOW;
1841 			*optp++ = TCPOPT_WINDOW;
1842 			*optp++ = TCPOLEN_WINDOW;
1843 			*optp++ = to->to_wscale;
1844 			break;
1845 		case TOF_SACKPERM:
1846 			while (optlen % 2) {
1847 				optlen += TCPOLEN_NOP;
1848 				*optp++ = TCPOPT_NOP;
1849 			}
1850 			if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1851 				continue;
1852 			optlen += TCPOLEN_SACK_PERMITTED;
1853 			*optp++ = TCPOPT_SACK_PERMITTED;
1854 			*optp++ = TCPOLEN_SACK_PERMITTED;
1855 			break;
1856 		case TOF_TS:
1857 			while (!optlen || optlen % 4 != 2) {
1858 				optlen += TCPOLEN_NOP;
1859 				*optp++ = TCPOPT_NOP;
1860 			}
1861 			if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1862 				continue;
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);
1872 			break;
1873 		case TOF_SIGNATURE:
1874 			{
1875 			int siglen = TCPOLEN_SIGNATURE - 2;
1876 
1877 			while (!optlen || optlen % 4 != 2) {
1878 				optlen += TCPOLEN_NOP;
1879 				*optp++ = TCPOPT_NOP;
1880 			}
1881 			if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1882 				to->to_flags &= ~TOF_SIGNATURE;
1883 				continue;
1884 			}
1885 			optlen += TCPOLEN_SIGNATURE;
1886 			*optp++ = TCPOPT_SIGNATURE;
1887 			*optp++ = TCPOLEN_SIGNATURE;
1888 			to->to_signature = optp;
1889 			while (siglen--)
1890 				 *optp++ = 0;
1891 			break;
1892 			}
1893 		case TOF_SACK:
1894 			{
1895 			int sackblks = 0;
1896 			struct sackblk *sack = (struct sackblk *)to->to_sacks;
1897 			tcp_seq sack_seq;
1898 
1899 			while (!optlen || optlen % 4 != 2) {
1900 				optlen += TCPOLEN_NOP;
1901 				*optp++ = TCPOPT_NOP;
1902 			}
1903 			if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1904 				continue;
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;
1918 				sack++;
1919 			}
1920 			TCPSTAT_INC(tcps_sack_send_blocks);
1921 			break;
1922 			}
1923 		case TOF_FASTOPEN:
1924 			{
1925 			int total_len;
1926 
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;
1931 				continue;
1932 			}
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;
1938 			}
1939 			optlen += total_len;
1940 			break;
1941 			}
1942 		default:
1943 			panic("%s: unknown TCP option type", __func__);
1944 			break;
1945 		}
1946 	}
1947 
1948 	/* Terminate and pad TCP options to a 4 byte boundary. */
1949 	if (optlen % 4) {
1950 		optlen += TCPOLEN_EOL;
1951 		*optp++ = TCPOPT_EOL;
1952 	}
1953 	/*
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."
1958 	 */
1959 	while (optlen % 4) {
1960 		optlen += TCPOLEN_PAD;
1961 		*optp++ = TCPOPT_PAD;
1962 	}
1963 
1964 	KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));
1965 	return (optlen);
1966 }
1967 
1968 /*
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.
1971  */
1972 struct mbuf *
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)
1975 {
1976 #ifdef KERN_TLS
1977 	struct ktls_session *tls, *ntls;
1978 	struct mbuf *start;
1979 #endif
1980 	struct mbuf *n, **np;
1981 	struct mbuf *top;
1982 	int32_t off = off0;
1983 	int32_t len = *plen;
1984 	int32_t fragsize;
1985 	int32_t len_cp = 0;
1986 	int32_t *pkthdrlen;
1987 	uint32_t mlen, frags;
1988 	bool copyhdr;
1989 
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)
1993 		copyhdr = true;
1994 	else
1995 		copyhdr = false;
1996 	while (off > 0) {
1997 		KASSERT(m != NULL, ("tcp_m_copym, offset > size of mbuf chain"));
1998 		if (off < m->m_len)
1999 			break;
2000 		off -= m->m_len;
2001 		if ((sb) && (m == sb->sb_sndptr)) {
2002 			sb->sb_sndptroff += m->m_len;
2003 			sb->sb_sndptr = m->m_next;
2004 		}
2005 		m = m->m_next;
2006 	}
2007 	np = &top;
2008 	top = NULL;
2009 	pkthdrlen = NULL;
2010 #ifdef KERN_TLS
2011 	if (hw_tls && (m->m_flags & M_EXTPG))
2012 		tls = m->m_epg_tls;
2013 	else
2014 		tls = NULL;
2015 	start = m;
2016 #endif
2017 	while (len > 0) {
2018 		if (m == NULL) {
2019 			KASSERT(len == M_COPYALL,
2020 			    ("tcp_m_copym, length > size of mbuf chain"));
2021 			*plen = len_cp;
2022 			if (pkthdrlen != NULL)
2023 				*pkthdrlen = len_cp;
2024 			break;
2025 		}
2026 #ifdef KERN_TLS
2027 		if (hw_tls) {
2028 			if (m->m_flags & M_EXTPG)
2029 				ntls = m->m_epg_tls;
2030 			else
2031 				ntls = NULL;
2032 
2033 			/*
2034 			 * Avoid mixing TLS records with handshake
2035 			 * data or TLS records from different
2036 			 * sessions.
2037 			 */
2038 			if (tls != ntls) {
2039 				MPASS(m != start);
2040 				*plen = len_cp;
2041 				if (pkthdrlen != NULL)
2042 					*pkthdrlen = len_cp;
2043 				break;
2044 			}
2045 		}
2046 #endif
2047 		mlen = min(len, m->m_len - off);
2048 		if (seglimit) {
2049 			/*
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.
2056 			 */
2057 			if (m->m_flags & M_EXTPG) {
2058 				fragsize = min(segsize, PAGE_SIZE);
2059 				frags = 3;
2060 			} else {
2061 				fragsize = segsize;
2062 				frags = 0;
2063 			}
2064 
2065 			/* Break if we really can't fit anymore. */
2066 			if ((frags + 1) >= seglimit) {
2067 				*plen =	len_cp;
2068 				if (pkthdrlen != NULL)
2069 					*pkthdrlen = len_cp;
2070 				break;
2071 			}
2072 
2073 			/*
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
2077 			 * mbuf.
2078 			 */
2079 			if ((frags + howmany(mlen, fragsize)) >= seglimit) {
2080 				mlen = (seglimit - frags - 1) * fragsize;
2081 				len = mlen;
2082 				*plen = len_cp + len;
2083 				if (pkthdrlen != NULL)
2084 					*pkthdrlen = *plen;
2085 			}
2086 			frags += howmany(mlen, fragsize);
2087 			if (frags == 0)
2088 				frags++;
2089 			seglimit -= frags;
2090 			KASSERT(seglimit > 0,
2091 			    ("%s: seglimit went too low", __func__));
2092 		}
2093 		if (copyhdr)
2094 			n = m_gethdr(M_NOWAIT, m->m_type);
2095 		else
2096 			n = m_get(M_NOWAIT, m->m_type);
2097 		*np = n;
2098 		if (n == NULL)
2099 			goto nospace;
2100 		if (copyhdr) {
2101 			if (!m_dup_pkthdr(n, m, M_NOWAIT))
2102 				goto nospace;
2103 			if (len == M_COPYALL)
2104 				n->m_pkthdr.len -= off0;
2105 			else
2106 				n->m_pkthdr.len = len;
2107 			pkthdrlen = &n->m_pkthdr.len;
2108 			copyhdr = false;
2109 		}
2110 		n->m_len = mlen;
2111 		len_cp += n->m_len;
2112 		if (m->m_flags & (M_EXT|M_EXTPG)) {
2113 			n->m_data = m->m_data + off;
2114 			mb_dupcl(n, m);
2115 		} else
2116 			bcopy(mtod(m, caddr_t)+off, mtod(n, caddr_t),
2117 			    (u_int)n->m_len);
2118 
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;
2123 		}
2124 		off = 0;
2125 		if (len != M_COPYALL) {
2126 			len -= n->m_len;
2127 		}
2128 		m = m->m_next;
2129 		np = &n->m_next;
2130 	}
2131 	return (top);
2132 nospace:
2133 	m_freem(top);
2134 	return (NULL);
2135 }
2136 
2137 void
2138 tcp_sndbuf_autoscale(struct tcpcb *tp, struct socket *so, uint32_t sendwin)
2139 {
2140 
2141 	/*
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.
2149 	 *
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.
2158 	 *
2159 	 * The remote host receive window scaling factor may limit the
2160 	 * growing of the send buffer before it reaches its allowed
2161 	 * maximum.
2162 	 *
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.
2171 	 *
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.
2175 	 *
2176 	 * XXXGL: should there be used sbused() or sbavail()?
2177 	 */
2178 	if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
2179 		int lowat;
2180 
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;
2192 		}
2193 	}
2194 }
2195