2 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
3 * Copyright (c) 2004 The DragonFly Project. All rights reserved.
5 * This code is derived from software contributed to The DragonFly Project
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
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15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of The DragonFly Project nor the names of its
17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
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21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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39 * modification, are permitted provided that the following conditions
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63 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
66 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
67 * $FreeBSD: src/sys/netinet/tcp_output.c,v 1.39.2.20 2003/01/29 22:45:36 hsu Exp $
71 #include "opt_inet6.h"
72 #include "opt_ipsec.h"
73 #include "opt_tcpdebug.h"
75 #include <sys/param.h>
76 #include <sys/systm.h>
77 #include <sys/kernel.h>
78 #include <sys/sysctl.h>
80 #include <sys/domain.h>
81 #include <sys/protosw.h>
82 #include <sys/socket.h>
83 #include <sys/socketvar.h>
84 #include <sys/in_cksum.h>
85 #include <sys/thread.h>
86 #include <sys/globaldata.h>
88 #include <net/if_var.h>
89 #include <net/route.h>
91 #include <netinet/in.h>
92 #include <netinet/in_systm.h>
93 #include <netinet/ip.h>
94 #include <netinet/in_pcb.h>
95 #include <netinet/ip_var.h>
96 #include <netinet6/in6_pcb.h>
97 #include <netinet/ip6.h>
98 #include <netinet6/ip6_var.h>
99 #include <netinet/tcp.h>
101 #include <netinet/tcp_fsm.h>
102 #include <netinet/tcp_seq.h>
103 #include <netinet/tcp_timer.h>
104 #include <netinet/tcp_timer2.h>
105 #include <netinet/tcp_var.h>
106 #include <netinet/tcpip.h>
108 #include <netinet/tcp_debug.h>
112 #include <netinet6/ipsec.h>
116 #include <netproto/ipsec/ipsec.h>
118 #endif /*FAST_IPSEC*/
121 extern struct mbuf *m_copypack();
124 int path_mtu_discovery = 0;
125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
126 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
128 static int avoid_pure_win_update = 1;
129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, avoid_pure_win_update, CTLFLAG_RW,
130 &avoid_pure_win_update, 1, "Avoid pure window updates when possible");
132 int tcp_do_autosndbuf = 1;
133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
134 &tcp_do_autosndbuf, 0, "Enable automatic send buffer sizing");
136 int tcp_autosndbuf_inc = 8*1024;
137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
138 &tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer");
140 int tcp_autosndbuf_max = 2*1024*1024;
141 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
142 &tcp_autosndbuf_max, 0, "Max size of automatic send buffer");
144 static int tcp_idle_cwv = 1;
145 SYSCTL_INT(_net_inet_tcp, OID_AUTO, idle_cwv, CTLFLAG_RW,
147 "Congestion window validation after idle period (part of RFC2861)");
149 static int tcp_idle_restart = 1;
150 SYSCTL_INT(_net_inet_tcp, OID_AUTO, idle_restart, CTLFLAG_RW,
151 &tcp_idle_restart, 0, "Reset congestion window after idle period");
153 static int tcp_do_tso = 1;
154 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
155 &tcp_do_tso, 0, "Enable TCP Segmentation Offload (TSO)");
157 static void tcp_idle_cwnd_validate(struct tcpcb *);
159 static int tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen);
162 * Tcp output routine: figure out what should be sent and send it.
165 tcp_output(struct tcpcb *tp)
167 struct inpcb * const inp = tp->t_inpcb;
168 struct socket *so = inp->inp_socket;
169 long len, recvwin, sendwin;
171 int off, flags, error = 0;
178 u_char opt[TCP_MAXOLEN];
179 unsigned int ipoptlen, optlen, hdrlen;
184 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
186 const boolean_t isipv6 = FALSE;
188 boolean_t can_tso = FALSE, use_tso;
189 boolean_t report_sack, idle_cwv = FALSE;
190 u_int segsz, tso_hlen;
192 KKASSERT(so->so_port == &curthread->td_msgport);
195 * Determine length of data that should be transmitted,
196 * and flags that will be used.
197 * If there is some data or critical controls (SYN, RST)
198 * to send, then transmit; otherwise, investigate further.
202 * If we have been idle for a while, the send congestion window
203 * could be no longer representative of the current state of the
204 * link; need to validate congestion window. However, we should
205 * not perform congestion window validation here, since we could
206 * be asked to send pure ACK.
208 if (tp->snd_max == tp->snd_una &&
209 (ticks - tp->snd_last) >= tp->t_rxtcur && tcp_idle_restart)
213 * Calculate whether the transmit stream was previously idle
214 * and adjust TF_LASTIDLE for the next time.
216 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
217 if (idle && (tp->t_flags & TF_MORETOCOME))
218 tp->t_flags |= TF_LASTIDLE;
220 tp->t_flags &= ~TF_LASTIDLE;
222 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
223 !IN_FASTRECOVERY(tp))
224 nsacked = tcp_sack_bytes_below(&tp->scb, tp->snd_nxt);
227 * Find out whether TSO could be used or not
229 * For TSO capable devices, the following assumptions apply to
230 * the processing of TCP flags:
231 * - If FIN is set on the large TCP segment, the device must set
232 * FIN on the last segment that it creates from the large TCP
234 * - If PUSH is set on the large TCP segment, the device must set
235 * PUSH on the last segment that it creates from the large TCP
238 #if !defined(IPSEC) && !defined(FAST_IPSEC)
241 && (tp->t_flags & TF_SIGNATURE) == 0
245 struct rtentry *rt = inp->inp_route.ro_rt;
247 if (rt != NULL && (rt->rt_flags & RTF_UP) &&
248 (rt->rt_ifp->if_hwassist & CSUM_TSO))
252 #endif /* !IPSEC && !FAST_IPSEC */
260 if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
262 (!TAILQ_EMPTY(&tp->t_segq) ||
263 tp->reportblk.rblk_start != tp->reportblk.rblk_end))
268 /* Make use of SACK information when slow-starting after a RTO. */
269 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
270 !IN_FASTRECOVERY(tp)) {
271 tcp_seq old_snd_nxt = tp->snd_nxt;
273 tcp_sack_skip_sacked(&tp->scb, &tp->snd_nxt);
274 nsacked += tp->snd_nxt - old_snd_nxt;
278 off = tp->snd_nxt - tp->snd_una;
279 sendwin = min(tp->snd_wnd, tp->snd_cwnd + nsacked);
280 sendwin = min(sendwin, tp->snd_bwnd);
282 flags = tcp_outflags[tp->t_state];
284 * Get standard flags, and add SYN or FIN if requested by 'hidden'
287 if (tp->t_flags & TF_NEEDFIN)
289 if (tp->t_flags & TF_NEEDSYN)
293 * If in persist timeout with window of 0, send 1 byte.
294 * Otherwise, if window is small but nonzero
295 * and timer expired, we will send what we can
296 * and go to transmit state.
298 if (tp->t_flags & TF_FORCE) {
301 * If we still have some data to send, then
302 * clear the FIN bit. Usually this would
303 * happen below when it realizes that we
304 * aren't sending all the data. However,
305 * if we have exactly 1 byte of unsent data,
306 * then it won't clear the FIN bit below,
307 * and if we are in persist state, we wind
308 * up sending the packet without recording
309 * that we sent the FIN bit.
311 * We can't just blindly clear the FIN bit,
312 * because if we don't have any more data
313 * to send then the probe will be the FIN
316 if (off < so->so_snd.ssb_cc)
320 tcp_callout_stop(tp, tp->tt_persist);
326 * If snd_nxt == snd_max and we have transmitted a FIN, the
327 * offset will be > 0 even if so_snd.ssb_cc is 0, resulting in
328 * a negative length. This can also occur when TCP opens up
329 * its congestion window while receiving additional duplicate
330 * acks after fast-retransmit because TCP will reset snd_nxt
331 * to snd_max after the fast-retransmit.
333 * A negative length can also occur when we are in the
334 * TCPS_SYN_RECEIVED state due to a simultanious connect where
335 * our SYN has not been acked yet.
337 * In the normal retransmit-FIN-only case, however, snd_nxt will
338 * be set to snd_una, the offset will be 0, and the length may
341 len = (long)ulmin(so->so_snd.ssb_cc, sendwin) - off;
344 * Lop off SYN bit if it has already been sent. However, if this
345 * is SYN-SENT state and if segment contains data, suppress sending
346 * segment (sending the segment would be an option if we still
347 * did TAO and the remote host supported it).
349 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
352 if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
353 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
359 * Be careful not to send data and/or FIN on SYN segments.
360 * This measure is needed to prevent interoperability problems
361 * with not fully conformant TCP implementations.
363 if (flags & TH_SYN) {
370 * A negative len can occur if our FIN has been sent but not
371 * acked, or if we are in a simultanious connect in the
372 * TCPS_SYN_RECEIVED state with our SYN sent but not yet
375 * If our window has contracted to 0 in the FIN case
376 * (which can only occur if we have NOT been called to
377 * retransmit as per code a few paragraphs up) then we
378 * want to shift the retransmit timer over to the
381 * However, if we are in the TCPS_SYN_RECEIVED state
382 * (the SYN case) we will be in a simultanious connect and
383 * the window may be zero degeneratively. In this case we
384 * do not want to shift to the persist timer after the SYN
385 * or the SYN+ACK transmission.
388 if (sendwin == 0 && tp->t_state != TCPS_SYN_RECEIVED) {
389 tcp_callout_stop(tp, tp->tt_rexmt);
391 tp->snd_nxt = tp->snd_una;
392 if (!tcp_callout_active(tp, tp->tt_persist))
397 KASSERT(len >= 0, ("%s: len < 0", __func__));
399 * Automatic sizing of send socket buffer. Often the send buffer
400 * size is not optimally adjusted to the actual network conditions
401 * at hand (delay bandwidth product). Setting the buffer size too
402 * small limits throughput on links with high bandwidth and high
403 * delay (eg. trans-continental/oceanic links). Setting the
404 * buffer size too big consumes too much real kernel memory,
405 * especially with many connections on busy servers.
407 * The criteria to step up the send buffer one notch are:
408 * 1. receive window of remote host is larger than send buffer
409 * (with a fudge factor of 5/4th);
410 * 2. send buffer is filled to 7/8th with data (so we actually
411 * have data to make use of it);
412 * 3. send buffer fill has not hit maximal automatic size;
413 * 4. our send window (slow start and cogestion controlled) is
414 * larger than sent but unacknowledged data in send buffer.
416 * The remote host receive window scaling factor may limit the
417 * growing of the send buffer before it reaches its allowed
420 * It scales directly with slow start or congestion window
421 * and does at most one step per received ACK. This fast
422 * scaling has the drawback of growing the send buffer beyond
423 * what is strictly necessary to make full use of a given
424 * delay*bandwith product. However testing has shown this not
425 * to be much of an problem. At worst we are trading wasting
426 * of available bandwith (the non-use of it) for wasting some
427 * socket buffer memory.
429 * TODO: Shrink send buffer during idle periods together
430 * with congestion window. Requires another timer. Has to
431 * wait for upcoming tcp timer rewrite.
433 if (tcp_do_autosndbuf && so->so_snd.ssb_flags & SSB_AUTOSIZE) {
434 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.ssb_hiwat &&
435 so->so_snd.ssb_cc >= (so->so_snd.ssb_hiwat / 8 * 7) &&
436 so->so_snd.ssb_cc < tcp_autosndbuf_max &&
437 sendwin >= (so->so_snd.ssb_cc - (tp->snd_nxt - tp->snd_una))) {
440 newsize = ulmin(so->so_snd.ssb_hiwat +
443 if (!ssb_reserve(&so->so_snd, newsize, so, NULL))
444 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
445 if (newsize >= (TCP_MAXWIN << tp->snd_scale))
446 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
452 * - Congestion window needs validation
453 * - There are SACK blocks to report
454 * - RST or SYN flags is set
458 * Checking for SYN|RST looks overkill, just to be safe than sorry
461 if (report_sack || idle_cwv || (flags & (TH_RST | TH_SYN)))
464 tcp_seq ugr_nxt = tp->snd_nxt;
466 if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) &&
467 tp->snd_nxt == tp->snd_max)
470 if (SEQ_GT(tp->snd_up, ugr_nxt))
476 * Find out segment size and header length for TSO
478 error = tcp_tso_getsize(tp, &segsz, &tso_hlen);
483 segsz = tp->t_maxseg;
484 tso_hlen = 0; /* not used */
488 * Truncate to the maximum segment length if not TSO, and ensure that
489 * FIN is removed if the length no longer contains the last data byte.
496 * Truncate TSO transfers to (IP_MAXPACKET - iphlen -
497 * thoff), and make sure that we send equal size
498 * transfers down the stack (rather than big-small-
501 len = (min(len, (IP_MAXPACKET - tso_hlen)) / segsz) *
510 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.ssb_cc))
513 recvwin = ssb_space(&so->so_rcv);
516 * Sender silly window avoidance. We transmit under the following
517 * conditions when len is non-zero:
519 * - We have a full segment
520 * - This is the last buffer in a write()/send() and we are
521 * either idle or running NODELAY
522 * - we've timed out (e.g. persist timer)
523 * - we have more then 1/2 the maximum send window's worth of
524 * data (receiver may be limiting the window size)
525 * - we need to retransmit
531 * NOTE! on localhost connections an 'ack' from the remote
532 * end may occur synchronously with the output and cause
533 * us to flush a buffer queued with moretocome. XXX
535 * note: the len + off check is almost certainly unnecessary.
537 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
538 (idle || (tp->t_flags & TF_NODELAY)) &&
539 len + off >= so->so_snd.ssb_cc &&
540 !(tp->t_flags & TF_NOPUSH)) {
543 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
545 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
547 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
549 if (tp->t_flags & TF_XMITNOW)
554 * Compare available window to amount of window
555 * known to peer (as advertised window less
556 * next expected input). If the difference is at least two
557 * max size segments, or at least 50% of the maximum possible
558 * window, then want to send a window update to peer.
562 * "adv" is the amount we can increase the window,
563 * taking into account that we are limited by
564 * TCP_MAXWIN << tp->rcv_scale.
566 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
567 (tp->rcv_adv - tp->rcv_nxt);
571 * This ack case typically occurs when the user has drained
572 * the TCP socket buffer sufficiently to warrent an ack
573 * containing a 'pure window update'... that is, an ack that
574 * ONLY updates the tcp window.
576 * It is unclear why we would need to do a pure window update
577 * past 2 segments if we are going to do one at 1/2 the high
578 * water mark anyway, especially since under normal conditions
579 * the user program will drain the socket buffer quickly.
580 * The 2-segment pure window update will often add a large
581 * number of extra, unnecessary acks to the stream.
583 * avoid_pure_win_update now defaults to 1.
585 if (avoid_pure_win_update == 0 ||
586 (tp->t_flags & TF_RXRESIZED)) {
587 if (adv >= (long) (2 * segsz)) {
591 hiwat = (long)(TCP_MAXWIN << tp->rcv_scale);
592 if (hiwat > (long)so->so_rcv.ssb_hiwat)
593 hiwat = (long)so->so_rcv.ssb_hiwat;
594 if (adv >= hiwat / 2)
599 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
600 * is also a catch-all for the retransmit timer timeout case.
602 if (tp->t_flags & TF_ACKNOW)
604 if ((flags & TH_RST) ||
605 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
607 if (SEQ_GT(tp->snd_up, tp->snd_una))
610 * If our state indicates that FIN should be sent
611 * and we have not yet done so, then we need to send.
613 if ((flags & TH_FIN) &&
614 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
618 * TCP window updates are not reliable, rather a polling protocol
619 * using ``persist'' packets is used to insure receipt of window
620 * updates. The three ``states'' for the output side are:
621 * idle not doing retransmits or persists
622 * persisting to move a small or zero window
623 * (re)transmitting and thereby not persisting
625 * tcp_callout_active(tp, tp->tt_persist)
626 * is true when we are in persist state.
627 * The TF_FORCE flag in tp->t_flags
628 * is set when we are called to send a persist packet.
629 * tcp_callout_active(tp, tp->tt_rexmt)
630 * is set when we are retransmitting
631 * The output side is idle when both timers are zero.
633 * If send window is too small, there is data to transmit, and no
634 * retransmit or persist is pending, then go to persist state.
636 * If nothing happens soon, send when timer expires:
637 * if window is nonzero, transmit what we can, otherwise force out
640 * Don't try to set the persist state if we are in TCPS_SYN_RECEIVED
641 * with data pending. This situation can occur during a
642 * simultanious connect.
644 if (so->so_snd.ssb_cc > 0 &&
645 tp->t_state != TCPS_SYN_RECEIVED &&
646 !tcp_callout_active(tp, tp->tt_rexmt) &&
647 !tcp_callout_active(tp, tp->tt_persist)) {
653 * No reason to send a segment, just return.
655 tp->t_flags &= ~TF_XMITNOW;
660 * Before ESTABLISHED, force sending of initial options
661 * unless TCP set not to do any options.
662 * NOTE: we assume that the IP/TCP header plus TCP options
663 * always fit in a single mbuf, leaving room for a maximum
665 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
669 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
671 hdrlen = sizeof(struct tcpiphdr);
672 if (flags & TH_SYN) {
673 tp->snd_nxt = tp->iss;
674 if (!(tp->t_flags & TF_NOOPT)) {
677 opt[0] = TCPOPT_MAXSEG;
678 opt[1] = TCPOLEN_MAXSEG;
679 mss = htons((u_short) tcp_mssopt(tp));
680 memcpy(opt + 2, &mss, sizeof mss);
681 optlen = TCPOLEN_MAXSEG;
683 if ((tp->t_flags & TF_REQ_SCALE) &&
684 (!(flags & TH_ACK) ||
685 (tp->t_flags & TF_RCVD_SCALE))) {
686 *((u_int32_t *)(opt + optlen)) = htonl(
688 TCPOPT_WINDOW << 16 |
689 TCPOLEN_WINDOW << 8 |
690 tp->request_r_scale);
694 if ((tcp_do_sack && !(flags & TH_ACK)) ||
695 tp->t_flags & TF_SACK_PERMITTED) {
696 uint32_t *lp = (uint32_t *)(opt + optlen);
698 *lp = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
699 optlen += TCPOLEN_SACK_PERMITTED_ALIGNED;
705 * Send a timestamp and echo-reply if this is a SYN and our side
706 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
707 * and our peer have sent timestamps in our SYN's.
709 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
711 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
712 u_int32_t *lp = (u_int32_t *)(opt + optlen);
714 /* Form timestamp option as shown in appendix A of RFC 1323. */
715 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
716 *lp++ = htonl(ticks);
717 *lp = htonl(tp->ts_recent);
718 optlen += TCPOLEN_TSTAMP_APPA;
721 /* Set receive buffer autosizing timestamp. */
722 if (tp->rfbuf_ts == 0 && (so->so_rcv.ssb_flags & SSB_AUTOSIZE))
723 tp->rfbuf_ts = ticks;
726 * If this is a SACK connection and we have a block to report,
727 * fill in the SACK blocks in the TCP options.
730 tcp_sack_fill_report(tp, opt, &optlen);
733 if (tp->t_flags & TF_SIGNATURE) {
737 * Initialize TCP-MD5 option (RFC2385)
739 bp = (u_char *)opt + optlen;
740 *bp++ = TCPOPT_SIGNATURE;
741 *bp++ = TCPOLEN_SIGNATURE;
743 for (i = 0; i < TCP_SIGLEN; i++)
745 optlen += TCPOLEN_SIGNATURE;
747 * Terminate options list and maintain 32-bit alignment.
753 #endif /* TCP_SIGNATURE */
754 KASSERT(optlen <= TCP_MAXOLEN, ("too many TCP options"));
758 ipoptlen = ip6_optlen(inp);
760 if (inp->inp_options) {
761 ipoptlen = inp->inp_options->m_len -
762 offsetof(struct ipoption, ipopt_list);
768 ipoptlen += ipsec_hdrsiz_tcp(tp);
772 /* TSO segment length must be multiple of segment size */
773 KASSERT(len >= (2 * segsz) && (len % segsz == 0),
774 ("invalid TSO len %ld, segsz %u", len, segsz));
776 KASSERT(len <= segsz,
777 ("invalid len %ld, segsz %u", len, segsz));
780 * Adjust data length if insertion of options will bump
781 * the packet length beyond the t_maxopd length. Clear
782 * FIN to prevent premature closure since there is still
783 * more data to send after this (now truncated) packet.
785 * If just the options do not fit we are in a no-win
786 * situation and we treat it as an unreachable host.
788 if (len + optlen + ipoptlen > tp->t_maxopd) {
789 if (tp->t_maxopd <= optlen + ipoptlen) {
790 static time_t last_optlen_report;
792 if (last_optlen_report != time_second) {
793 last_optlen_report = time_second;
794 kprintf("tcpcb %p: MSS (%d) too "
795 "small to hold options!\n",
798 error = EHOSTUNREACH;
802 len = tp->t_maxopd - optlen - ipoptlen;
809 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
811 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
815 * Grab a header mbuf, attaching a copy of data to
816 * be transmitted, and initialize the header from
817 * the template for sends on this connection.
820 if ((tp->t_flags & TF_FORCE) && len == 1)
821 tcpstat.tcps_sndprobe++;
822 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
823 if (tp->snd_nxt == tp->snd_una)
824 tp->snd_max_rexmt = tp->snd_max;
826 tcpstat.tcps_sndsackrtopack++;
827 tcpstat.tcps_sndsackrtobyte += len;
829 tcpstat.tcps_sndrexmitpack++;
830 tcpstat.tcps_sndrexmitbyte += len;
832 tcpstat.tcps_sndpack++;
833 tcpstat.tcps_sndbyte += len;
837 tcp_idle_cwnd_validate(tp);
839 /* Update last send time after CWV */
840 tp->snd_last = ticks;
842 if ((m = m_copypack(so->so_snd.ssb_mb, off, (int)len,
843 max_linkhdr + hdrlen)) == NULL) {
848 * m_copypack left space for our hdr; use it.
854 m = m_gethdr(MB_DONTWAIT, MT_HEADER);
856 m = m_getl(hdrlen + max_linkhdr, MB_DONTWAIT, MT_HEADER,
863 m->m_data += max_linkhdr;
865 if (len <= MHLEN - hdrlen - max_linkhdr) {
866 m_copydata(so->so_snd.ssb_mb, off, (int) len,
867 mtod(m, caddr_t) + hdrlen);
870 m->m_next = m_copy(so->so_snd.ssb_mb, off, (int) len);
871 if (m->m_next == NULL) {
880 * If we're sending everything we've got, set PUSH.
881 * (This will keep happy those implementations which only
882 * give data to the user when a buffer fills or
885 if (off + len == so->so_snd.ssb_cc)
888 if (tp->t_flags & TF_ACKNOW)
889 tcpstat.tcps_sndacks++;
890 else if (flags & (TH_SYN | TH_FIN | TH_RST))
891 tcpstat.tcps_sndctrl++;
892 else if (SEQ_GT(tp->snd_up, tp->snd_una))
893 tcpstat.tcps_sndurg++;
895 tcpstat.tcps_sndwinup++;
897 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
903 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
906 m->m_data += max_linkhdr;
909 m->m_pkthdr.rcvif = NULL;
911 ip6 = mtod(m, struct ip6_hdr *);
912 th = (struct tcphdr *)(ip6 + 1);
913 tcp_fillheaders(tp, ip6, th, use_tso);
915 ip = mtod(m, struct ip *);
916 th = (struct tcphdr *)(ip + 1);
917 /* this picks up the pseudo header (w/o the length) */
918 tcp_fillheaders(tp, ip, th, use_tso);
922 * Fill in fields, remembering maximum advertised
923 * window for use in delaying messages about window sizes.
924 * If resending a FIN, be sure not to use a new sequence number.
926 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
927 tp->snd_nxt == tp->snd_max)
932 * If we are doing retransmissions, then snd_nxt will
933 * not reflect the first unsent octet. For ACK only
934 * packets, we do not want the sequence number of the
935 * retransmitted packet, we want the sequence number
936 * of the next unsent octet. So, if there is no data
937 * (and no SYN or FIN), use snd_max instead of snd_nxt
938 * when filling in ti_seq. But if we are in persist
939 * state, snd_max might reflect one byte beyond the
940 * right edge of the window, so use snd_nxt in that
941 * case, since we know we aren't doing a retransmission.
942 * (retransmit and persist are mutually exclusive...)
944 if (len || (flags & (TH_SYN|TH_FIN)) ||
945 tcp_callout_active(tp, tp->tt_persist))
946 th->th_seq = htonl(tp->snd_nxt);
948 th->th_seq = htonl(tp->snd_max);
949 th->th_ack = htonl(tp->rcv_nxt);
951 bcopy(opt, th + 1, optlen);
952 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
954 th->th_flags = flags;
958 * Calculate receive window. Don't shrink window, but avoid
959 * silly window syndrome by sending a 0 window if the actual
960 * window is less then one segment.
962 if (recvwin < (long)(so->so_rcv.ssb_hiwat / 4) &&
963 recvwin < (long)segsz)
965 if (recvwin < (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt))
966 recvwin = (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt);
967 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
968 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
971 * Adjust the RXWIN0SENT flag - indicate that we have advertised
972 * a 0 window. This may cause the remote transmitter to stall. This
973 * flag tells soreceive() to disable delayed acknowledgements when
974 * draining the buffer. This can occur if the receiver is attempting
975 * to read more data then can be buffered prior to transmitting on
979 tp->t_flags |= TF_RXWIN0SENT;
981 tp->t_flags &= ~TF_RXWIN0SENT;
984 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
986 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
987 KASSERT(!use_tso, ("URG with TSO"));
989 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
990 th->th_flags |= TH_URG;
994 * If no urgent pointer to send, then we pull
995 * the urgent pointer to the left edge of the send window
996 * so that it doesn't drift into the send window on sequence
999 tp->snd_up = tp->snd_una; /* drag it along */
1003 #ifdef TCP_SIGNATURE
1004 if (tp->t_flags & TF_SIGNATURE) {
1005 tcpsignature_compute(m, len, optlen,
1006 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1008 #endif /* TCP_SIGNATURE */
1011 * Put TCP length in extended header, and then
1012 * checksum extended header and data.
1014 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1017 * ip6_plen is not need to be filled now, and will be
1018 * filled in ip6_output().
1020 th->th_sum = in6_cksum(m, IPPROTO_TCP,
1021 sizeof(struct ip6_hdr),
1022 sizeof(struct tcphdr) + optlen + len);
1024 m->m_pkthdr.csum_thlen = sizeof(struct tcphdr) + optlen;
1026 m->m_pkthdr.csum_flags = CSUM_TSO;
1027 m->m_pkthdr.tso_segsz = segsz;
1029 m->m_pkthdr.csum_flags = CSUM_TCP;
1030 m->m_pkthdr.csum_data =
1031 offsetof(struct tcphdr, th_sum);
1033 th->th_sum = in_addword(th->th_sum,
1034 htons((u_short)(optlen + len)));
1039 * IP version must be set here for ipv4/ipv6 checking
1042 KASSERT(ip->ip_v == IPVERSION,
1043 ("%s: IP version incorrect: %d",
1044 __func__, ip->ip_v));
1049 * In transmit state, time the transmission and arrange for
1050 * the retransmit. In persist state, just set snd_max.
1052 if (!(tp->t_flags & TF_FORCE) ||
1053 !tcp_callout_active(tp, tp->tt_persist)) {
1054 tcp_seq startseq = tp->snd_nxt;
1057 * Advance snd_nxt over sequence space of this segment.
1059 if (flags & (TH_SYN | TH_FIN)) {
1062 if (flags & TH_FIN) {
1064 tp->t_flags |= TF_SENTFIN;
1068 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1069 tp->snd_max = tp->snd_nxt;
1071 * Time this transmission if not a retransmission and
1072 * not currently timing anything.
1074 if (tp->t_rtttime == 0) {
1075 tp->t_rtttime = ticks;
1076 tp->t_rtseq = startseq;
1077 tcpstat.tcps_segstimed++;
1082 * Set retransmit timer if not currently set,
1083 * and not doing a pure ack or a keep-alive probe.
1084 * Initial value for retransmit timer is smoothed
1085 * round-trip time + 2 * round-trip time variance.
1086 * Initialize shift counter which is used for backoff
1087 * of retransmit time.
1089 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1090 tp->snd_nxt != tp->snd_una) {
1091 if (tcp_callout_active(tp, tp->tt_persist)) {
1092 tcp_callout_stop(tp, tp->tt_persist);
1095 tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
1100 * Persist case, update snd_max but since we are in
1101 * persist mode (no window) we do not update snd_nxt.
1105 panic("tcp_output: persist timer to send SYN");
1106 if (flags & TH_FIN) {
1108 tp->t_flags |= TF_SENTFIN;
1110 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1111 tp->snd_max = tp->snd_nxt + xlen;
1117 if (so->so_options & SO_DEBUG) {
1118 tcp_trace(TA_OUTPUT, tp->t_state, tp,
1119 mtod(m, void *), th, 0);
1124 * Fill in IP length and desired time to live and
1125 * send to IP level. There should be a better way
1126 * to handle ttl and tos; we could keep them in
1127 * the template, but need a way to checksum without them.
1130 * m->m_pkthdr.len should have been set before cksum
1131 * calcuration, because in6_cksum() need it.
1135 * we separately set hoplimit for every segment,
1136 * since the user might want to change the value
1137 * via setsockopt. Also, desired default hop
1138 * limit might be changed via Neighbor Discovery.
1140 ip6->ip6_hlim = in6_selecthlim(inp,
1141 (inp->in6p_route.ro_rt ?
1142 inp->in6p_route.ro_rt->rt_ifp : NULL));
1144 /* TODO: IPv6 IP6TOS_ECT bit on */
1145 error = ip6_output(m, inp->in6p_outputopts,
1146 &inp->in6p_route, (so->so_options & SO_DONTROUTE),
1150 ip->ip_len = m->m_pkthdr.len;
1152 if (INP_CHECK_SOCKAF(so, AF_INET6))
1153 ip->ip_ttl = in6_selecthlim(inp,
1154 (inp->in6p_route.ro_rt ?
1155 inp->in6p_route.ro_rt->rt_ifp : NULL));
1158 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
1160 ip->ip_tos = inp->inp_ip_tos; /* XXX */
1162 * See if we should do MTU discovery.
1163 * We do it only if the following are true:
1164 * 1) we have a valid route to the destination
1165 * 2) the MTU is not locked (if it is,
1166 * then discovery has been disabled)
1168 if (path_mtu_discovery &&
1169 (rt = inp->inp_route.ro_rt) &&
1170 (rt->rt_flags & RTF_UP) &&
1171 !(rt->rt_rmx.rmx_locks & RTV_MTU))
1172 ip->ip_off |= IP_DF;
1174 error = ip_output(m, inp->inp_options, &inp->inp_route,
1175 (so->so_options & SO_DONTROUTE) |
1176 IP_DEBUGROUTE, NULL, inp);
1179 KASSERT(error != 0, ("no error, but th not set"));
1182 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1185 * We know that the packet was lost, so back out the
1186 * sequence number advance, if any.
1188 if (!(tp->t_flags & TF_FORCE) ||
1189 !tcp_callout_active(tp, tp->tt_persist)) {
1191 * No need to check for TH_FIN here because
1192 * the TF_SENTFIN flag handles that case.
1194 if (!(flags & TH_SYN))
1199 if (error == ENOBUFS) {
1201 * If we can't send, make sure there is something
1202 * to get us going again later.
1204 * The persist timer isn't necessarily allowed in all
1205 * states, use the rexmt timer.
1207 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1208 !tcp_callout_active(tp, tp->tt_persist)) {
1209 tcp_callout_reset(tp, tp->tt_rexmt,
1220 if (error == EMSGSIZE) {
1222 * ip_output() will have already fixed the route
1223 * for us. tcp_mtudisc() will, as its last action,
1224 * initiate retransmission, so it is important to
1227 tcp_mtudisc(inp, 0);
1230 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
1231 TCPS_HAVERCVDSYN(tp->t_state)) {
1232 tp->t_softerror = error;
1237 tcpstat.tcps_sndtotal++;
1240 * Data sent (as far as we can tell).
1242 * If this advertises a larger window than any other segment,
1243 * then remember the size of the advertised window.
1245 * Any pending ACK has now been sent.
1247 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv)) {
1248 tp->rcv_adv = tp->rcv_nxt + recvwin;
1249 tp->t_flags &= ~TF_RXRESIZED;
1251 tp->last_ack_sent = tp->rcv_nxt;
1252 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1253 if (tcp_delack_enabled)
1254 tcp_callout_stop(tp, tp->tt_delack);
1261 tcp_setpersist(struct tcpcb *tp)
1263 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1266 if (tp->t_state == TCPS_SYN_SENT ||
1267 tp->t_state == TCPS_SYN_RECEIVED) {
1268 panic("tcp_setpersist: not established yet, current %s",
1269 tp->t_state == TCPS_SYN_SENT ?
1270 "SYN_SENT" : "SYN_RECEIVED");
1273 if (tcp_callout_active(tp, tp->tt_rexmt))
1274 panic("tcp_setpersist: retransmit pending");
1276 * Start/restart persistance timer.
1278 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN,
1280 tcp_callout_reset(tp, tp->tt_persist, tt, tcp_timer_persist);
1281 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1286 tcp_idle_cwnd_validate(struct tcpcb *tp)
1288 u_long initial_cwnd = tcp_initial_window(tp);
1291 tcpstat.tcps_sndidle++;
1293 /* According to RFC5681: RW=min(IW,cwnd) */
1294 min_cwnd = min(tp->snd_cwnd, initial_cwnd);
1297 u_long idle_time, decay_cwnd;
1300 * RFC2861, but only after idle period.
1304 * Before the congestion window is reduced, ssthresh
1305 * is set to the maximum of its current value and 3/4
1306 * cwnd. If the sender then has more data to send
1307 * than the decayed cwnd allows, the TCP will slow-
1308 * start (perform exponential increase) at least
1309 * half-way back up to the old value of cwnd.
1311 tp->snd_ssthresh = max(tp->snd_ssthresh,
1312 (3 * tp->snd_cwnd) / 4);
1315 * Decay the congestion window by half for every RTT
1316 * that the flow remains inactive.
1318 * The difference between our implementation and
1319 * RFC2861 is that we don't allow cwnd to go below
1320 * the value allowed by RFC5681 (min_cwnd).
1322 idle_time = ticks - tp->snd_last;
1323 decay_cwnd = tp->snd_cwnd;
1324 while (idle_time >= tp->t_rxtcur &&
1325 decay_cwnd > min_cwnd) {
1327 idle_time -= tp->t_rxtcur;
1329 tp->snd_cwnd = max(decay_cwnd, min_cwnd);
1332 * Slow-start from scratch to re-determine the send
1333 * congestion window.
1335 tp->snd_cwnd = min_cwnd;
1338 /* Restart ABC counting during congestion avoidance */
1343 tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen0)
1345 struct inpcb * const inp = tp->t_inpcb;
1347 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
1349 const boolean_t isipv6 = FALSE;
1351 unsigned int ipoptlen, optlen;
1354 hlen = sizeof(struct ip) + sizeof(struct tcphdr);
1357 ipoptlen = ip6_optlen(inp);
1359 if (inp->inp_options) {
1360 ipoptlen = inp->inp_options->m_len -
1361 offsetof(struct ipoption, ipopt_list);
1367 ipoptlen += ipsec_hdrsiz_tcp(tp);
1372 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
1373 (tp->t_flags & TF_RCVD_TSTMP))
1374 optlen += TCPOLEN_TSTAMP_APPA;
1377 if (tp->t_maxopd <= optlen + ipoptlen)
1378 return EHOSTUNREACH;
1380 *segsz = tp->t_maxopd - optlen - ipoptlen;