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
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12 * notice, this list of conditions and the following disclaimer.
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15 * documentation and/or other materials provided with the distribution.
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17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
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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, tso_lenmax = 0;
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)) {
250 tso_lenmax = rt->rt_ifp->if_tsolen;
254 #endif /* !IPSEC && !FAST_IPSEC */
262 if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
264 (!TAILQ_EMPTY(&tp->t_segq) ||
265 tp->reportblk.rblk_start != tp->reportblk.rblk_end))
270 /* Make use of SACK information when slow-starting after a RTO. */
271 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
272 !IN_FASTRECOVERY(tp)) {
273 tcp_seq old_snd_nxt = tp->snd_nxt;
275 tcp_sack_skip_sacked(&tp->scb, &tp->snd_nxt);
276 nsacked += tp->snd_nxt - old_snd_nxt;
280 off = tp->snd_nxt - tp->snd_una;
281 sendwin = min(tp->snd_wnd, tp->snd_cwnd + nsacked);
282 sendwin = min(sendwin, tp->snd_bwnd);
284 flags = tcp_outflags[tp->t_state];
286 * Get standard flags, and add SYN or FIN if requested by 'hidden'
289 if (tp->t_flags & TF_NEEDFIN)
291 if (tp->t_flags & TF_NEEDSYN)
295 * If in persist timeout with window of 0, send 1 byte.
296 * Otherwise, if window is small but nonzero
297 * and timer expired, we will send what we can
298 * and go to transmit state.
300 if (tp->t_flags & TF_FORCE) {
303 * If we still have some data to send, then
304 * clear the FIN bit. Usually this would
305 * happen below when it realizes that we
306 * aren't sending all the data. However,
307 * if we have exactly 1 byte of unsent data,
308 * then it won't clear the FIN bit below,
309 * and if we are in persist state, we wind
310 * up sending the packet without recording
311 * that we sent the FIN bit.
313 * We can't just blindly clear the FIN bit,
314 * because if we don't have any more data
315 * to send then the probe will be the FIN
318 if (off < so->so_snd.ssb_cc)
322 tcp_callout_stop(tp, tp->tt_persist);
328 * If snd_nxt == snd_max and we have transmitted a FIN, the
329 * offset will be > 0 even if so_snd.ssb_cc is 0, resulting in
330 * a negative length. This can also occur when TCP opens up
331 * its congestion window while receiving additional duplicate
332 * acks after fast-retransmit because TCP will reset snd_nxt
333 * to snd_max after the fast-retransmit.
335 * A negative length can also occur when we are in the
336 * TCPS_SYN_RECEIVED state due to a simultanious connect where
337 * our SYN has not been acked yet.
339 * In the normal retransmit-FIN-only case, however, snd_nxt will
340 * be set to snd_una, the offset will be 0, and the length may
343 len = (long)ulmin(so->so_snd.ssb_cc, sendwin) - off;
346 * Lop off SYN bit if it has already been sent. However, if this
347 * is SYN-SENT state and if segment contains data, suppress sending
348 * segment (sending the segment would be an option if we still
349 * did TAO and the remote host supported it).
351 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
354 if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
355 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
361 * Be careful not to send data and/or FIN on SYN segments.
362 * This measure is needed to prevent interoperability problems
363 * with not fully conformant TCP implementations.
365 if (flags & TH_SYN) {
372 * A negative len can occur if our FIN has been sent but not
373 * acked, or if we are in a simultanious connect in the
374 * TCPS_SYN_RECEIVED state with our SYN sent but not yet
377 * If our window has contracted to 0 in the FIN case
378 * (which can only occur if we have NOT been called to
379 * retransmit as per code a few paragraphs up) then we
380 * want to shift the retransmit timer over to the
383 * However, if we are in the TCPS_SYN_RECEIVED state
384 * (the SYN case) we will be in a simultanious connect and
385 * the window may be zero degeneratively. In this case we
386 * do not want to shift to the persist timer after the SYN
387 * or the SYN+ACK transmission.
390 if (sendwin == 0 && tp->t_state != TCPS_SYN_RECEIVED) {
391 tcp_callout_stop(tp, tp->tt_rexmt);
393 tp->snd_nxt = tp->snd_una;
394 if (!tcp_callout_active(tp, tp->tt_persist))
399 KASSERT(len >= 0, ("%s: len < 0", __func__));
401 * Automatic sizing of send socket buffer. Often the send buffer
402 * size is not optimally adjusted to the actual network conditions
403 * at hand (delay bandwidth product). Setting the buffer size too
404 * small limits throughput on links with high bandwidth and high
405 * delay (eg. trans-continental/oceanic links). Setting the
406 * buffer size too big consumes too much real kernel memory,
407 * especially with many connections on busy servers.
409 * The criteria to step up the send buffer one notch are:
410 * 1. receive window of remote host is larger than send buffer
411 * (with a fudge factor of 5/4th);
412 * 2. send buffer is filled to 7/8th with data (so we actually
413 * have data to make use of it);
414 * 3. send buffer fill has not hit maximal automatic size;
415 * 4. our send window (slow start and cogestion controlled) is
416 * larger than sent but unacknowledged data in send buffer.
418 * The remote host receive window scaling factor may limit the
419 * growing of the send buffer before it reaches its allowed
422 * It scales directly with slow start or congestion window
423 * and does at most one step per received ACK. This fast
424 * scaling has the drawback of growing the send buffer beyond
425 * what is strictly necessary to make full use of a given
426 * delay*bandwith product. However testing has shown this not
427 * to be much of an problem. At worst we are trading wasting
428 * of available bandwith (the non-use of it) for wasting some
429 * socket buffer memory.
431 * TODO: Shrink send buffer during idle periods together
432 * with congestion window. Requires another timer. Has to
433 * wait for upcoming tcp timer rewrite.
435 if (tcp_do_autosndbuf && so->so_snd.ssb_flags & SSB_AUTOSIZE) {
436 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.ssb_hiwat &&
437 so->so_snd.ssb_cc >= (so->so_snd.ssb_hiwat / 8 * 7) &&
438 so->so_snd.ssb_cc < tcp_autosndbuf_max &&
439 sendwin >= (so->so_snd.ssb_cc - (tp->snd_nxt - tp->snd_una))) {
442 newsize = ulmin(so->so_snd.ssb_hiwat +
445 if (!ssb_reserve(&so->so_snd, newsize, so, NULL))
446 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
447 if (newsize >= (TCP_MAXWIN << tp->snd_scale))
448 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
454 * - Congestion window needs validation
455 * - There are SACK blocks to report
456 * - RST or SYN flags is set
460 * Checking for SYN|RST looks overkill, just to be safe than sorry
463 if (report_sack || idle_cwv || (flags & (TH_RST | TH_SYN)))
466 tcp_seq ugr_nxt = tp->snd_nxt;
468 if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) &&
469 tp->snd_nxt == tp->snd_max)
472 if (SEQ_GT(tp->snd_up, ugr_nxt))
478 * Find out segment size and header length for TSO
480 error = tcp_tso_getsize(tp, &segsz, &tso_hlen);
485 segsz = tp->t_maxseg;
486 tso_hlen = 0; /* not used */
490 * Truncate to the maximum segment length if not TSO, and ensure that
491 * FIN is removed if the length no longer contains the last data byte.
497 if (__predict_false(tso_lenmax < segsz))
498 tso_lenmax = segsz << 1;
501 * Truncate TSO transfers to (IP_MAXPACKET - iphlen -
502 * thoff), and make sure that we send equal size
503 * transfers down the stack (rather than big-small-
506 len = min(len, tso_lenmax);
507 len = (min(len, (IP_MAXPACKET - tso_hlen)) / segsz) *
516 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.ssb_cc))
519 recvwin = ssb_space(&so->so_rcv);
522 * Sender silly window avoidance. We transmit under the following
523 * conditions when len is non-zero:
525 * - We have a full segment
526 * - This is the last buffer in a write()/send() and we are
527 * either idle or running NODELAY
528 * - we've timed out (e.g. persist timer)
529 * - we have more then 1/2 the maximum send window's worth of
530 * data (receiver may be limiting the window size)
531 * - we need to retransmit
537 * NOTE! on localhost connections an 'ack' from the remote
538 * end may occur synchronously with the output and cause
539 * us to flush a buffer queued with moretocome. XXX
541 * note: the len + off check is almost certainly unnecessary.
543 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
544 (idle || (tp->t_flags & TF_NODELAY)) &&
545 len + off >= so->so_snd.ssb_cc &&
546 !(tp->t_flags & TF_NOPUSH)) {
549 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
551 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
553 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
555 if (tp->t_flags & TF_XMITNOW)
560 * Compare available window to amount of window
561 * known to peer (as advertised window less
562 * next expected input). If the difference is at least two
563 * max size segments, or at least 50% of the maximum possible
564 * window, then want to send a window update to peer.
568 * "adv" is the amount we can increase the window,
569 * taking into account that we are limited by
570 * TCP_MAXWIN << tp->rcv_scale.
572 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
573 (tp->rcv_adv - tp->rcv_nxt);
577 * This ack case typically occurs when the user has drained
578 * the TCP socket buffer sufficiently to warrent an ack
579 * containing a 'pure window update'... that is, an ack that
580 * ONLY updates the tcp window.
582 * It is unclear why we would need to do a pure window update
583 * past 2 segments if we are going to do one at 1/2 the high
584 * water mark anyway, especially since under normal conditions
585 * the user program will drain the socket buffer quickly.
586 * The 2-segment pure window update will often add a large
587 * number of extra, unnecessary acks to the stream.
589 * avoid_pure_win_update now defaults to 1.
591 if (avoid_pure_win_update == 0 ||
592 (tp->t_flags & TF_RXRESIZED)) {
593 if (adv >= (long) (2 * segsz)) {
597 hiwat = (long)(TCP_MAXWIN << tp->rcv_scale);
598 if (hiwat > (long)so->so_rcv.ssb_hiwat)
599 hiwat = (long)so->so_rcv.ssb_hiwat;
600 if (adv >= hiwat / 2)
605 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
606 * is also a catch-all for the retransmit timer timeout case.
608 if (tp->t_flags & TF_ACKNOW)
610 if ((flags & TH_RST) ||
611 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
613 if (SEQ_GT(tp->snd_up, tp->snd_una))
616 * If our state indicates that FIN should be sent
617 * and we have not yet done so, then we need to send.
619 if ((flags & TH_FIN) &&
620 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
624 * TCP window updates are not reliable, rather a polling protocol
625 * using ``persist'' packets is used to insure receipt of window
626 * updates. The three ``states'' for the output side are:
627 * idle not doing retransmits or persists
628 * persisting to move a small or zero window
629 * (re)transmitting and thereby not persisting
631 * tcp_callout_active(tp, tp->tt_persist)
632 * is true when we are in persist state.
633 * The TF_FORCE flag in tp->t_flags
634 * is set when we are called to send a persist packet.
635 * tcp_callout_active(tp, tp->tt_rexmt)
636 * is set when we are retransmitting
637 * The output side is idle when both timers are zero.
639 * If send window is too small, there is data to transmit, and no
640 * retransmit or persist is pending, then go to persist state.
642 * If nothing happens soon, send when timer expires:
643 * if window is nonzero, transmit what we can, otherwise force out
646 * Don't try to set the persist state if we are in TCPS_SYN_RECEIVED
647 * with data pending. This situation can occur during a
648 * simultanious connect.
650 if (so->so_snd.ssb_cc > 0 &&
651 tp->t_state != TCPS_SYN_RECEIVED &&
652 !tcp_callout_active(tp, tp->tt_rexmt) &&
653 !tcp_callout_active(tp, tp->tt_persist)) {
659 * No reason to send a segment, just return.
661 tp->t_flags &= ~TF_XMITNOW;
666 * Before ESTABLISHED, force sending of initial options
667 * unless TCP set not to do any options.
668 * NOTE: we assume that the IP/TCP header plus TCP options
669 * always fit in a single mbuf, leaving room for a maximum
671 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
675 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
677 hdrlen = sizeof(struct tcpiphdr);
678 if (flags & TH_SYN) {
679 tp->snd_nxt = tp->iss;
680 if (!(tp->t_flags & TF_NOOPT)) {
683 opt[0] = TCPOPT_MAXSEG;
684 opt[1] = TCPOLEN_MAXSEG;
685 mss = htons((u_short) tcp_mssopt(tp));
686 memcpy(opt + 2, &mss, sizeof mss);
687 optlen = TCPOLEN_MAXSEG;
689 if ((tp->t_flags & TF_REQ_SCALE) &&
690 (!(flags & TH_ACK) ||
691 (tp->t_flags & TF_RCVD_SCALE))) {
692 *((u_int32_t *)(opt + optlen)) = htonl(
694 TCPOPT_WINDOW << 16 |
695 TCPOLEN_WINDOW << 8 |
696 tp->request_r_scale);
700 if ((tcp_do_sack && !(flags & TH_ACK)) ||
701 tp->t_flags & TF_SACK_PERMITTED) {
702 uint32_t *lp = (uint32_t *)(opt + optlen);
704 *lp = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
705 optlen += TCPOLEN_SACK_PERMITTED_ALIGNED;
711 * Send a timestamp and echo-reply if this is a SYN and our side
712 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
713 * and our peer have sent timestamps in our SYN's.
715 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
717 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
718 u_int32_t *lp = (u_int32_t *)(opt + optlen);
720 /* Form timestamp option as shown in appendix A of RFC 1323. */
721 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
722 *lp++ = htonl(ticks);
723 *lp = htonl(tp->ts_recent);
724 optlen += TCPOLEN_TSTAMP_APPA;
727 /* Set receive buffer autosizing timestamp. */
728 if (tp->rfbuf_ts == 0 && (so->so_rcv.ssb_flags & SSB_AUTOSIZE))
729 tp->rfbuf_ts = ticks;
732 * If this is a SACK connection and we have a block to report,
733 * fill in the SACK blocks in the TCP options.
736 tcp_sack_fill_report(tp, opt, &optlen);
739 if (tp->t_flags & TF_SIGNATURE) {
743 * Initialize TCP-MD5 option (RFC2385)
745 bp = (u_char *)opt + optlen;
746 *bp++ = TCPOPT_SIGNATURE;
747 *bp++ = TCPOLEN_SIGNATURE;
749 for (i = 0; i < TCP_SIGLEN; i++)
751 optlen += TCPOLEN_SIGNATURE;
753 * Terminate options list and maintain 32-bit alignment.
759 #endif /* TCP_SIGNATURE */
760 KASSERT(optlen <= TCP_MAXOLEN, ("too many TCP options"));
764 ipoptlen = ip6_optlen(inp);
766 if (inp->inp_options) {
767 ipoptlen = inp->inp_options->m_len -
768 offsetof(struct ipoption, ipopt_list);
774 ipoptlen += ipsec_hdrsiz_tcp(tp);
778 /* TSO segment length must be multiple of segment size */
779 KASSERT(len >= (2 * segsz) && (len % segsz == 0),
780 ("invalid TSO len %ld, segsz %u", len, segsz));
782 KASSERT(len <= segsz,
783 ("invalid len %ld, segsz %u", len, segsz));
786 * Adjust data length if insertion of options will bump
787 * the packet length beyond the t_maxopd length. Clear
788 * FIN to prevent premature closure since there is still
789 * more data to send after this (now truncated) packet.
791 * If just the options do not fit we are in a no-win
792 * situation and we treat it as an unreachable host.
794 if (len + optlen + ipoptlen > tp->t_maxopd) {
795 if (tp->t_maxopd <= optlen + ipoptlen) {
796 static time_t last_optlen_report;
798 if (last_optlen_report != time_second) {
799 last_optlen_report = time_second;
800 kprintf("tcpcb %p: MSS (%d) too "
801 "small to hold options!\n",
804 error = EHOSTUNREACH;
808 len = tp->t_maxopd - optlen - ipoptlen;
815 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
817 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
821 * Grab a header mbuf, attaching a copy of data to
822 * be transmitted, and initialize the header from
823 * the template for sends on this connection.
826 if ((tp->t_flags & TF_FORCE) && len == 1)
827 tcpstat.tcps_sndprobe++;
828 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
829 if (tp->snd_nxt == tp->snd_una)
830 tp->snd_max_rexmt = tp->snd_max;
832 tcpstat.tcps_sndsackrtopack++;
833 tcpstat.tcps_sndsackrtobyte += len;
835 tcpstat.tcps_sndrexmitpack++;
836 tcpstat.tcps_sndrexmitbyte += len;
838 tcpstat.tcps_sndpack++;
839 tcpstat.tcps_sndbyte += len;
843 tcp_idle_cwnd_validate(tp);
845 /* Update last send time after CWV */
846 tp->snd_last = ticks;
848 if ((m = m_copypack(so->so_snd.ssb_mb, off, (int)len,
849 max_linkhdr + hdrlen)) == NULL) {
854 * m_copypack left space for our hdr; use it.
860 m = m_gethdr(MB_DONTWAIT, MT_HEADER);
862 m = m_getl(hdrlen + max_linkhdr, MB_DONTWAIT, MT_HEADER,
869 m->m_data += max_linkhdr;
871 if (len <= MHLEN - hdrlen - max_linkhdr) {
872 m_copydata(so->so_snd.ssb_mb, off, (int) len,
873 mtod(m, caddr_t) + hdrlen);
876 m->m_next = m_copy(so->so_snd.ssb_mb, off, (int) len);
877 if (m->m_next == NULL) {
886 * If we're sending everything we've got, set PUSH.
887 * (This will keep happy those implementations which only
888 * give data to the user when a buffer fills or
891 if (off + len == so->so_snd.ssb_cc)
894 if (tp->t_flags & TF_ACKNOW)
895 tcpstat.tcps_sndacks++;
896 else if (flags & (TH_SYN | TH_FIN | TH_RST))
897 tcpstat.tcps_sndctrl++;
898 else if (SEQ_GT(tp->snd_up, tp->snd_una))
899 tcpstat.tcps_sndurg++;
901 tcpstat.tcps_sndwinup++;
903 MGETHDR(m, MB_DONTWAIT, MT_HEADER);
909 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
912 m->m_data += max_linkhdr;
915 m->m_pkthdr.rcvif = NULL;
917 ip6 = mtod(m, struct ip6_hdr *);
918 th = (struct tcphdr *)(ip6 + 1);
919 tcp_fillheaders(tp, ip6, th, use_tso);
921 ip = mtod(m, struct ip *);
922 th = (struct tcphdr *)(ip + 1);
923 /* this picks up the pseudo header (w/o the length) */
924 tcp_fillheaders(tp, ip, th, use_tso);
928 * Fill in fields, remembering maximum advertised
929 * window for use in delaying messages about window sizes.
930 * If resending a FIN, be sure not to use a new sequence number.
932 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
933 tp->snd_nxt == tp->snd_max)
938 * If we are doing retransmissions, then snd_nxt will
939 * not reflect the first unsent octet. For ACK only
940 * packets, we do not want the sequence number of the
941 * retransmitted packet, we want the sequence number
942 * of the next unsent octet. So, if there is no data
943 * (and no SYN or FIN), use snd_max instead of snd_nxt
944 * when filling in ti_seq. But if we are in persist
945 * state, snd_max might reflect one byte beyond the
946 * right edge of the window, so use snd_nxt in that
947 * case, since we know we aren't doing a retransmission.
948 * (retransmit and persist are mutually exclusive...)
950 if (len || (flags & (TH_SYN|TH_FIN)) ||
951 tcp_callout_active(tp, tp->tt_persist))
952 th->th_seq = htonl(tp->snd_nxt);
954 th->th_seq = htonl(tp->snd_max);
955 th->th_ack = htonl(tp->rcv_nxt);
957 bcopy(opt, th + 1, optlen);
958 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
960 th->th_flags = flags;
964 * Calculate receive window. Don't shrink window, but avoid
965 * silly window syndrome by sending a 0 window if the actual
966 * window is less then one segment.
968 if (recvwin < (long)(so->so_rcv.ssb_hiwat / 4) &&
969 recvwin < (long)segsz)
971 if (recvwin < (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt))
972 recvwin = (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt);
973 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
974 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
977 * Adjust the RXWIN0SENT flag - indicate that we have advertised
978 * a 0 window. This may cause the remote transmitter to stall. This
979 * flag tells soreceive() to disable delayed acknowledgements when
980 * draining the buffer. This can occur if the receiver is attempting
981 * to read more data then can be buffered prior to transmitting on
985 tp->t_flags |= TF_RXWIN0SENT;
987 tp->t_flags &= ~TF_RXWIN0SENT;
990 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
992 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
993 KASSERT(!use_tso, ("URG with TSO"));
995 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
996 th->th_flags |= TH_URG;
1000 * If no urgent pointer to send, then we pull
1001 * the urgent pointer to the left edge of the send window
1002 * so that it doesn't drift into the send window on sequence
1003 * number wraparound.
1005 tp->snd_up = tp->snd_una; /* drag it along */
1009 #ifdef TCP_SIGNATURE
1010 if (tp->t_flags & TF_SIGNATURE) {
1011 tcpsignature_compute(m, len, optlen,
1012 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1014 #endif /* TCP_SIGNATURE */
1017 * Put TCP length in extended header, and then
1018 * checksum extended header and data.
1020 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1023 * ip6_plen is not need to be filled now, and will be
1024 * filled in ip6_output().
1026 th->th_sum = in6_cksum(m, IPPROTO_TCP,
1027 sizeof(struct ip6_hdr),
1028 sizeof(struct tcphdr) + optlen + len);
1030 m->m_pkthdr.csum_thlen = sizeof(struct tcphdr) + optlen;
1032 m->m_pkthdr.csum_flags = CSUM_TSO;
1033 m->m_pkthdr.tso_segsz = segsz;
1035 m->m_pkthdr.csum_flags = CSUM_TCP;
1036 m->m_pkthdr.csum_data =
1037 offsetof(struct tcphdr, th_sum);
1039 th->th_sum = in_addword(th->th_sum,
1040 htons((u_short)(optlen + len)));
1045 * IP version must be set here for ipv4/ipv6 checking
1048 KASSERT(ip->ip_v == IPVERSION,
1049 ("%s: IP version incorrect: %d",
1050 __func__, ip->ip_v));
1055 * In transmit state, time the transmission and arrange for
1056 * the retransmit. In persist state, just set snd_max.
1058 if (!(tp->t_flags & TF_FORCE) ||
1059 !tcp_callout_active(tp, tp->tt_persist)) {
1060 tcp_seq startseq = tp->snd_nxt;
1063 * Advance snd_nxt over sequence space of this segment.
1065 if (flags & (TH_SYN | TH_FIN)) {
1068 if (flags & TH_FIN) {
1070 tp->t_flags |= TF_SENTFIN;
1074 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1075 tp->snd_max = tp->snd_nxt;
1077 * Time this transmission if not a retransmission and
1078 * not currently timing anything.
1080 if (tp->t_rtttime == 0) {
1081 tp->t_rtttime = ticks;
1082 tp->t_rtseq = startseq;
1083 tcpstat.tcps_segstimed++;
1088 * Set retransmit timer if not currently set,
1089 * and not doing a pure ack or a keep-alive probe.
1090 * Initial value for retransmit timer is smoothed
1091 * round-trip time + 2 * round-trip time variance.
1092 * Initialize shift counter which is used for backoff
1093 * of retransmit time.
1095 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1096 tp->snd_nxt != tp->snd_una) {
1097 if (tcp_callout_active(tp, tp->tt_persist)) {
1098 tcp_callout_stop(tp, tp->tt_persist);
1101 tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
1106 * Persist case, update snd_max but since we are in
1107 * persist mode (no window) we do not update snd_nxt.
1111 panic("tcp_output: persist timer to send SYN");
1112 if (flags & TH_FIN) {
1114 tp->t_flags |= TF_SENTFIN;
1116 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1117 tp->snd_max = tp->snd_nxt + xlen;
1123 if (so->so_options & SO_DEBUG) {
1124 tcp_trace(TA_OUTPUT, tp->t_state, tp,
1125 mtod(m, void *), th, 0);
1130 * Fill in IP length and desired time to live and
1131 * send to IP level. There should be a better way
1132 * to handle ttl and tos; we could keep them in
1133 * the template, but need a way to checksum without them.
1136 * m->m_pkthdr.len should have been set before cksum
1137 * calcuration, because in6_cksum() need it.
1141 * we separately set hoplimit for every segment,
1142 * since the user might want to change the value
1143 * via setsockopt. Also, desired default hop
1144 * limit might be changed via Neighbor Discovery.
1146 ip6->ip6_hlim = in6_selecthlim(inp,
1147 (inp->in6p_route.ro_rt ?
1148 inp->in6p_route.ro_rt->rt_ifp : NULL));
1150 /* TODO: IPv6 IP6TOS_ECT bit on */
1151 error = ip6_output(m, inp->in6p_outputopts,
1152 &inp->in6p_route, (so->so_options & SO_DONTROUTE),
1156 ip->ip_len = m->m_pkthdr.len;
1158 if (INP_CHECK_SOCKAF(so, AF_INET6))
1159 ip->ip_ttl = in6_selecthlim(inp,
1160 (inp->in6p_route.ro_rt ?
1161 inp->in6p_route.ro_rt->rt_ifp : NULL));
1164 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
1166 ip->ip_tos = inp->inp_ip_tos; /* XXX */
1168 * See if we should do MTU discovery.
1169 * We do it only if the following are true:
1170 * 1) we have a valid route to the destination
1171 * 2) the MTU is not locked (if it is,
1172 * then discovery has been disabled)
1174 if (path_mtu_discovery &&
1175 (rt = inp->inp_route.ro_rt) &&
1176 (rt->rt_flags & RTF_UP) &&
1177 !(rt->rt_rmx.rmx_locks & RTV_MTU))
1178 ip->ip_off |= IP_DF;
1180 error = ip_output(m, inp->inp_options, &inp->inp_route,
1181 (so->so_options & SO_DONTROUTE) |
1182 IP_DEBUGROUTE, NULL, inp);
1185 KASSERT(error != 0, ("no error, but th not set"));
1188 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1191 * We know that the packet was lost, so back out the
1192 * sequence number advance, if any.
1194 if (!(tp->t_flags & TF_FORCE) ||
1195 !tcp_callout_active(tp, tp->tt_persist)) {
1197 * No need to check for TH_FIN here because
1198 * the TF_SENTFIN flag handles that case.
1200 if (!(flags & TH_SYN))
1205 if (error == ENOBUFS) {
1207 * If we can't send, make sure there is something
1208 * to get us going again later.
1210 * The persist timer isn't necessarily allowed in all
1211 * states, use the rexmt timer.
1213 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1214 !tcp_callout_active(tp, tp->tt_persist)) {
1215 tcp_callout_reset(tp, tp->tt_rexmt,
1226 if (error == EMSGSIZE) {
1228 * ip_output() will have already fixed the route
1229 * for us. tcp_mtudisc() will, as its last action,
1230 * initiate retransmission, so it is important to
1233 tcp_mtudisc(inp, 0);
1236 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
1237 TCPS_HAVERCVDSYN(tp->t_state)) {
1238 tp->t_softerror = error;
1243 tcpstat.tcps_sndtotal++;
1246 * Data sent (as far as we can tell).
1248 * If this advertises a larger window than any other segment,
1249 * then remember the size of the advertised window.
1251 * Any pending ACK has now been sent.
1253 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv)) {
1254 tp->rcv_adv = tp->rcv_nxt + recvwin;
1255 tp->t_flags &= ~TF_RXRESIZED;
1257 tp->last_ack_sent = tp->rcv_nxt;
1258 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1259 if (tcp_delack_enabled)
1260 tcp_callout_stop(tp, tp->tt_delack);
1267 tcp_setpersist(struct tcpcb *tp)
1269 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1272 if (tp->t_state == TCPS_SYN_SENT ||
1273 tp->t_state == TCPS_SYN_RECEIVED) {
1274 panic("tcp_setpersist: not established yet, current %s",
1275 tp->t_state == TCPS_SYN_SENT ?
1276 "SYN_SENT" : "SYN_RECEIVED");
1279 if (tcp_callout_active(tp, tp->tt_rexmt))
1280 panic("tcp_setpersist: retransmit pending");
1282 * Start/restart persistance timer.
1284 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN,
1286 tcp_callout_reset(tp, tp->tt_persist, tt, tcp_timer_persist);
1287 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1292 tcp_idle_cwnd_validate(struct tcpcb *tp)
1294 u_long initial_cwnd = tcp_initial_window(tp);
1297 tcpstat.tcps_sndidle++;
1299 /* According to RFC5681: RW=min(IW,cwnd) */
1300 min_cwnd = min(tp->snd_cwnd, initial_cwnd);
1303 u_long idle_time, decay_cwnd;
1306 * RFC2861, but only after idle period.
1310 * Before the congestion window is reduced, ssthresh
1311 * is set to the maximum of its current value and 3/4
1312 * cwnd. If the sender then has more data to send
1313 * than the decayed cwnd allows, the TCP will slow-
1314 * start (perform exponential increase) at least
1315 * half-way back up to the old value of cwnd.
1317 tp->snd_ssthresh = max(tp->snd_ssthresh,
1318 (3 * tp->snd_cwnd) / 4);
1321 * Decay the congestion window by half for every RTT
1322 * that the flow remains inactive.
1324 * The difference between our implementation and
1325 * RFC2861 is that we don't allow cwnd to go below
1326 * the value allowed by RFC5681 (min_cwnd).
1328 idle_time = ticks - tp->snd_last;
1329 decay_cwnd = tp->snd_cwnd;
1330 while (idle_time >= tp->t_rxtcur &&
1331 decay_cwnd > min_cwnd) {
1333 idle_time -= tp->t_rxtcur;
1335 tp->snd_cwnd = max(decay_cwnd, min_cwnd);
1338 * Slow-start from scratch to re-determine the send
1339 * congestion window.
1341 tp->snd_cwnd = min_cwnd;
1344 /* Restart ABC counting during congestion avoidance */
1349 tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen0)
1351 struct inpcb * const inp = tp->t_inpcb;
1353 const boolean_t isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
1355 const boolean_t isipv6 = FALSE;
1357 unsigned int ipoptlen, optlen;
1360 hlen = sizeof(struct ip) + sizeof(struct tcphdr);
1363 ipoptlen = ip6_optlen(inp);
1365 if (inp->inp_options) {
1366 ipoptlen = inp->inp_options->m_len -
1367 offsetof(struct ipoption, ipopt_list);
1373 ipoptlen += ipsec_hdrsiz_tcp(tp);
1378 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
1379 (tp->t_flags & TF_RCVD_TSTMP))
1380 optlen += TCPOLEN_TSTAMP_APPA;
1383 if (tp->t_maxopd <= optlen + ipoptlen)
1384 return EHOSTUNREACH;
1386 *segsz = tp->t_maxopd - optlen - ipoptlen;