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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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
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62 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
63 * $FreeBSD: src/sys/netinet/tcp_output.c,v 1.39.2.20 2003/01/29 22:45:36 hsu Exp $
67 #include "opt_inet6.h"
68 #include "opt_tcpdebug.h"
70 #include <sys/param.h>
71 #include <sys/systm.h>
72 #include <sys/kernel.h>
73 #include <sys/malloc.h> /* for M_NOWAIT */
74 #include <sys/sysctl.h>
76 #include <sys/domain.h>
77 #include <sys/protosw.h>
78 #include <sys/socket.h>
79 #include <sys/socketvar.h>
80 #include <sys/in_cksum.h>
81 #include <sys/thread.h>
82 #include <sys/globaldata.h>
85 #include <net/if_var.h>
86 #include <net/route.h>
87 #include <net/netmsg2.h>
88 #include <net/netisr2.h>
90 #include <netinet/in.h>
91 #include <netinet/in_systm.h>
92 #include <netinet/ip.h>
93 #include <netinet/in_pcb.h>
94 #include <netinet/ip_var.h>
95 #include <netinet6/in6_pcb.h>
96 #include <netinet/ip6.h>
97 #include <netinet6/ip6_var.h>
98 #include <netinet/tcp.h>
100 #include <netinet/tcp_fsm.h>
101 #include <netinet/tcp_seq.h>
102 #include <netinet/tcp_timer.h>
103 #include <netinet/tcp_timer2.h>
104 #include <netinet/tcp_var.h>
105 #include <netinet/tcpip.h>
107 #include <netinet/tcp_debug.h>
111 extern struct mbuf *m_copypack();
114 int path_mtu_discovery = 1;
115 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
116 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
118 static int avoid_pure_win_update = 1;
119 SYSCTL_INT(_net_inet_tcp, OID_AUTO, avoid_pure_win_update, CTLFLAG_RW,
120 &avoid_pure_win_update, 1, "Avoid pure window updates when possible");
123 * 1 - enabled for increasing and decreasing the buffer size
124 * 2 - enabled only for increasing the buffer size
126 int tcp_do_autosndbuf = 1;
127 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
128 &tcp_do_autosndbuf, 0, "Enable automatic send buffer sizing");
130 int tcp_autosndbuf_inc = 8*1024;
131 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
132 &tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer");
134 int tcp_autosndbuf_min = 32768;
135 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_min, CTLFLAG_RW,
136 &tcp_autosndbuf_min, 0, "Min size of automatic send buffer");
138 int tcp_autosndbuf_max = 2*1024*1024;
139 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
140 &tcp_autosndbuf_max, 0, "Max size of automatic send buffer");
142 int tcp_prio_synack = 1;
143 SYSCTL_INT(_net_inet_tcp, OID_AUTO, prio_synack, CTLFLAG_RW,
144 &tcp_prio_synack, 0, "Prioritize SYN, SYN|ACK and pure ACK");
146 static int tcp_idle_cwv = 1;
147 SYSCTL_INT(_net_inet_tcp, OID_AUTO, idle_cwv, CTLFLAG_RW,
149 "Congestion window validation after idle period (part of RFC2861)");
151 static int tcp_idle_restart = 1;
152 SYSCTL_INT(_net_inet_tcp, OID_AUTO, idle_restart, CTLFLAG_RW,
153 &tcp_idle_restart, 0, "Reset congestion window after idle period");
155 static int tcp_do_tso = 1;
156 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
157 &tcp_do_tso, 0, "Enable TCP Segmentation Offload (TSO)");
159 static int tcp_fairsend = 4;
160 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fairsend, CTLFLAG_RW,
162 "Amount of segments sent before yield to other senders or receivers");
164 static void tcp_idle_cwnd_validate(struct tcpcb *);
166 static int tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen);
167 static void tcp_output_sched(struct tcpcb *tp);
170 * Tcp output routine: figure out what should be sent and send it.
173 tcp_output(struct tcpcb *tp)
175 struct inpcb * const inp = tp->t_inpcb;
176 struct socket *so = inp->inp_socket;
177 long len, recvwin, sendwin;
179 int off, flags, error = 0;
186 u_char opt[TCP_MAXOLEN];
187 unsigned int ipoptlen, optlen, hdrlen;
192 const boolean_t isipv6 = INP_ISIPV6(inp);
194 const boolean_t isipv6 = FALSE;
196 boolean_t can_tso = FALSE, use_tso;
197 boolean_t report_sack, idle_cwv = FALSE;
198 u_int segsz, tso_hlen, tso_lenmax = 0;
200 boolean_t need_sched = FALSE;
202 KKASSERT(so->so_port == &curthread->td_msgport);
205 * Determine length of data that should be transmitted,
206 * and flags that will be used.
207 * If there is some data or critical controls (SYN, RST)
208 * to send, then transmit; otherwise, investigate further.
212 * If we have been idle for a while, the send congestion window
213 * could be no longer representative of the current state of the
214 * link; need to validate congestion window. However, we should
215 * not perform congestion window validation here, since we could
216 * be asked to send pure ACK.
218 if (tp->snd_max == tp->snd_una &&
219 (ticks - tp->snd_last) >= tp->t_rxtcur && tcp_idle_restart)
223 * Calculate whether the transmit stream was previously idle
224 * and adjust TF_LASTIDLE for the next time.
226 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
227 if (idle && (tp->t_flags & TF_MORETOCOME))
228 tp->t_flags |= TF_LASTIDLE;
230 tp->t_flags &= ~TF_LASTIDLE;
232 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
233 !IN_FASTRECOVERY(tp))
234 nsacked = tcp_sack_bytes_below(&tp->scb, tp->snd_nxt);
237 * Find out whether TSO could be used or not
239 * For TSO capable devices, the following assumptions apply to
240 * the processing of TCP flags:
241 * - If FIN is set on the large TCP segment, the device must set
242 * FIN on the last segment that it creates from the large TCP
244 * - If PUSH is set on the large TCP segment, the device must set
245 * PUSH on the last segment that it creates from the large TCP
250 && (tp->t_flags & TF_SIGNATURE) == 0
254 struct rtentry *rt = inp->inp_route.ro_rt;
256 if (rt != NULL && (rt->rt_flags & RTF_UP) &&
257 (rt->rt_ifp->if_hwassist & CSUM_TSO)) {
259 tso_lenmax = rt->rt_ifp->if_tsolen;
270 if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
272 (!TAILQ_EMPTY(&tp->t_segq) ||
273 tp->reportblk.rblk_start != tp->reportblk.rblk_end))
278 /* Make use of SACK information when slow-starting after a RTO. */
279 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
280 !IN_FASTRECOVERY(tp)) {
281 tcp_seq old_snd_nxt = tp->snd_nxt;
283 tcp_sack_skip_sacked(&tp->scb, &tp->snd_nxt);
284 nsacked += tp->snd_nxt - old_snd_nxt;
288 off = tp->snd_nxt - tp->snd_una;
289 sendwin = min(tp->snd_wnd, tp->snd_cwnd + nsacked);
290 sendwin = min(sendwin, tp->snd_bwnd);
292 flags = tcp_outflags[tp->t_state];
294 * Get standard flags, and add SYN or FIN if requested by 'hidden'
297 if (tp->t_flags & TF_NEEDFIN)
299 if (tp->t_flags & TF_NEEDSYN)
303 * If in persist timeout with window of 0, send 1 byte.
304 * Otherwise, if window is small but nonzero
305 * and timer expired, we will send what we can
306 * and go to transmit state.
308 if (tp->t_flags & TF_FORCE) {
311 * If we still have some data to send, then
312 * clear the FIN bit. Usually this would
313 * happen below when it realizes that we
314 * aren't sending all the data. However,
315 * if we have exactly 1 byte of unsent data,
316 * then it won't clear the FIN bit below,
317 * and if we are in persist state, we wind
318 * up sending the packet without recording
319 * that we sent the FIN bit.
321 * We can't just blindly clear the FIN bit,
322 * because if we don't have any more data
323 * to send then the probe will be the FIN
326 if (off < so->so_snd.ssb_cc)
330 tcp_callout_stop(tp, tp->tt_persist);
336 * If snd_nxt == snd_max and we have transmitted a FIN, the
337 * offset will be > 0 even if so_snd.ssb_cc is 0, resulting in
338 * a negative length. This can also occur when TCP opens up
339 * its congestion window while receiving additional duplicate
340 * acks after fast-retransmit because TCP will reset snd_nxt
341 * to snd_max after the fast-retransmit.
343 * A negative length can also occur when we are in the
344 * TCPS_SYN_RECEIVED state due to a simultanious connect where
345 * our SYN has not been acked yet.
347 * In the normal retransmit-FIN-only case, however, snd_nxt will
348 * be set to snd_una, the offset will be 0, and the length may
351 len = (long)ulmin(so->so_snd.ssb_cc, sendwin) - off;
354 * Lop off SYN bit if it has already been sent. However, if this
355 * is SYN-SENT state and if segment contains data, suppress sending
356 * segment (sending the segment would be an option if we still
357 * did TAO and the remote host supported it).
359 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
362 if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
363 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
369 * Be careful not to send data and/or FIN on SYN segments.
370 * This measure is needed to prevent interoperability problems
371 * with not fully conformant TCP implementations.
373 if (flags & TH_SYN) {
380 * A negative len can occur if our FIN has been sent but not
381 * acked, or if we are in a simultanious connect in the
382 * TCPS_SYN_RECEIVED state with our SYN sent but not yet
385 * If our window has contracted to 0 in the FIN case
386 * (which can only occur if we have NOT been called to
387 * retransmit as per code a few paragraphs up) then we
388 * want to shift the retransmit timer over to the
391 * However, if we are in the TCPS_SYN_RECEIVED state
392 * (the SYN case) we will be in a simultanious connect and
393 * the window may be zero degeneratively. In this case we
394 * do not want to shift to the persist timer after the SYN
395 * or the SYN+ACK transmission.
398 if (sendwin == 0 && tp->t_state != TCPS_SYN_RECEIVED) {
399 tcp_callout_stop(tp, tp->tt_rexmt);
401 tp->snd_nxt = tp->snd_una;
402 if (!tcp_callout_active(tp, tp->tt_persist))
407 KASSERT(len >= 0, ("%s: len < 0", __func__));
409 * Automatic sizing of send socket buffer. Often the send buffer
410 * size is not optimally adjusted to the actual network conditions
411 * at hand (delay bandwidth product). Setting the buffer size too
412 * small limits throughput on links with high bandwidth and high
413 * delay (eg. trans-continental/oceanic links). Setting the
414 * buffer size too big consumes too much real kernel memory,
415 * especially with many connections on busy servers.
417 * The criteria to step up the send buffer one notch are:
418 * 1. receive window of remote host is larger than send buffer
419 * (with a fudge factor of 5/4th);
420 * 2. hiwat has not significantly exceeded bwnd (inflight)
421 * (bwnd is a maximal value if inflight is disabled).
422 * 3. send buffer is filled to 7/8th with data (so we actually
423 * have data to make use of it);
424 * 4. hiwat has not hit maximal automatic size;
425 * 5. our send window (slow start and cogestion controlled) is
426 * larger than sent but unacknowledged data in send buffer.
428 * The remote host receive window scaling factor may limit the
429 * growing of the send buffer before it reaches its allowed
432 * It scales directly with slow start or congestion window
433 * and does at most one step per received ACK. This fast
434 * scaling has the drawback of growing the send buffer beyond
435 * what is strictly necessary to make full use of a given
436 * delay*bandwith product. However testing has shown this not
437 * to be much of an problem. At worst we are trading wasting
438 * of available bandwith (the non-use of it) for wasting some
439 * socket buffer memory.
441 * The criteria for shrinking the buffer is based solely on
442 * the inflight code (snd_bwnd). If inflight is disabled,
443 * the buffer will not be shrinked. Note that snd_bwnd already
444 * has a fudge factor. Our test adds a little hysteresis.
446 if (tcp_do_autosndbuf && (so->so_snd.ssb_flags & SSB_AUTOSIZE)) {
447 const int asbinc = tcp_autosndbuf_inc;
448 const int hiwat = so->so_snd.ssb_hiwat;
449 const int lowat = so->so_snd.ssb_lowat;
452 if ((tp->snd_wnd / 4 * 5) >= hiwat &&
453 so->so_snd.ssb_cc >= (hiwat / 8 * 7) &&
454 hiwat < tp->snd_bwnd + hiwat / 10 &&
455 hiwat + asbinc < tcp_autosndbuf_max &&
456 hiwat < (TCP_MAXWIN << tp->snd_scale) &&
457 sendwin >= (so->so_snd.ssb_cc -
458 (tp->snd_nxt - tp->snd_una))) {
459 newsize = ulmin(hiwat + asbinc, tcp_autosndbuf_max);
460 if (!ssb_reserve(&so->so_snd, newsize, so, NULL))
461 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
463 if (newsize >= (TCP_MAXWIN << tp->snd_scale))
464 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
466 } else if ((long)tp->snd_bwnd <
467 (long)(hiwat * 3 / 4 - lowat - asbinc) &&
468 hiwat > tp->t_maxseg * 2 + asbinc &&
469 hiwat + asbinc >= tcp_autosndbuf_min &&
470 tcp_do_autosndbuf == 1) {
471 newsize = ulmax(hiwat - asbinc, tp->t_maxseg * 2);
472 ssb_reserve(&so->so_snd, newsize, so, NULL);
478 * - Congestion window needs validation
479 * - There are SACK blocks to report
480 * - RST or SYN flags is set
484 * Checking for SYN|RST looks overkill, just to be safe than sorry
487 if (report_sack || idle_cwv || (flags & (TH_RST | TH_SYN)))
490 tcp_seq ugr_nxt = tp->snd_nxt;
492 if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) &&
493 tp->snd_nxt == tp->snd_max)
496 if (SEQ_GT(tp->snd_up, ugr_nxt))
502 * Find out segment size and header length for TSO
504 error = tcp_tso_getsize(tp, &segsz, &tso_hlen);
509 segsz = tp->t_maxseg;
510 tso_hlen = 0; /* not used */
514 * Truncate to the maximum segment length if not TSO, and ensure that
515 * FIN is removed if the length no longer contains the last data byte.
524 if (__predict_false(tso_lenmax < segsz))
525 tso_lenmax = segsz << 1;
528 * Truncate TSO transfers to (IP_MAXPACKET - iphlen -
529 * thoff), and make sure that we send equal size
530 * transfers down the stack (rather than big-small-
533 len = min(len, tso_lenmax);
534 nsegs = min(len, (IP_MAXPACKET - tso_hlen)) / segsz;
552 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.ssb_cc))
555 recvwin = ssb_space(&so->so_rcv);
558 * Sender silly window avoidance. We transmit under the following
559 * conditions when len is non-zero:
561 * - We have a full segment
562 * - This is the last buffer in a write()/send() and we are
563 * either idle or running NODELAY
564 * - we've timed out (e.g. persist timer)
565 * - we have more then 1/2 the maximum send window's worth of
566 * data (receiver may be limiting the window size)
567 * - we need to retransmit
573 * NOTE! on localhost connections an 'ack' from the remote
574 * end may occur synchronously with the output and cause
575 * us to flush a buffer queued with moretocome. XXX
577 * note: the len + off check is almost certainly unnecessary.
579 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
580 (idle || (tp->t_flags & TF_NODELAY)) &&
581 len + off >= so->so_snd.ssb_cc &&
582 !(tp->t_flags & TF_NOPUSH)) {
585 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
587 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
589 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
591 if (tp->t_flags & TF_XMITNOW)
596 * Compare available window to amount of window
597 * known to peer (as advertised window less
598 * next expected input). If the difference is at least two
599 * max size segments, or at least 50% of the maximum possible
600 * window, then want to send a window update to peer.
604 * "adv" is the amount we can increase the window,
605 * taking into account that we are limited by
606 * TCP_MAXWIN << tp->rcv_scale.
608 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
609 (tp->rcv_adv - tp->rcv_nxt);
613 * This ack case typically occurs when the user has drained
614 * the TCP socket buffer sufficiently to warrent an ack
615 * containing a 'pure window update'... that is, an ack that
616 * ONLY updates the tcp window.
618 * It is unclear why we would need to do a pure window update
619 * past 2 segments if we are going to do one at 1/2 the high
620 * water mark anyway, especially since under normal conditions
621 * the user program will drain the socket buffer quickly.
622 * The 2-segment pure window update will often add a large
623 * number of extra, unnecessary acks to the stream.
625 * avoid_pure_win_update now defaults to 1.
627 if (avoid_pure_win_update == 0 ||
628 (tp->t_flags & TF_RXRESIZED)) {
629 if (adv >= (long) (2 * segsz)) {
633 hiwat = (long)(TCP_MAXWIN << tp->rcv_scale);
634 if (hiwat > (long)so->so_rcv.ssb_hiwat)
635 hiwat = (long)so->so_rcv.ssb_hiwat;
636 if (adv >= hiwat / 2)
641 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
642 * is also a catch-all for the retransmit timer timeout case.
644 if (tp->t_flags & TF_ACKNOW)
646 if ((flags & TH_RST) ||
647 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
649 if (SEQ_GT(tp->snd_up, tp->snd_una))
652 * If our state indicates that FIN should be sent
653 * and we have not yet done so, then we need to send.
655 if ((flags & TH_FIN) &&
656 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
660 * TCP window updates are not reliable, rather a polling protocol
661 * using ``persist'' packets is used to insure receipt of window
662 * updates. The three ``states'' for the output side are:
663 * idle not doing retransmits or persists
664 * persisting to move a small or zero window
665 * (re)transmitting and thereby not persisting
667 * tcp_callout_active(tp, tp->tt_persist)
668 * is true when we are in persist state.
669 * The TF_FORCE flag in tp->t_flags
670 * is set when we are called to send a persist packet.
671 * tcp_callout_active(tp, tp->tt_rexmt)
672 * is set when we are retransmitting
673 * The output side is idle when both timers are zero.
675 * If send window is too small, there is data to transmit, and no
676 * retransmit or persist is pending, then go to persist state.
678 * If nothing happens soon, send when timer expires:
679 * if window is nonzero, transmit what we can, otherwise force out
682 * Don't try to set the persist state if we are in TCPS_SYN_RECEIVED
683 * with data pending. This situation can occur during a
684 * simultanious connect.
686 if (so->so_snd.ssb_cc > 0 &&
687 tp->t_state != TCPS_SYN_RECEIVED &&
688 !tcp_callout_active(tp, tp->tt_rexmt) &&
689 !tcp_callout_active(tp, tp->tt_persist)) {
695 * No reason to send a segment, just return.
697 tp->t_flags &= ~TF_XMITNOW;
701 if (need_sched && len > 0) {
702 tcp_output_sched(tp);
707 * Before ESTABLISHED, force sending of initial options
708 * unless TCP set not to do any options.
709 * NOTE: we assume that the IP/TCP header plus TCP options
710 * always fit in a single mbuf, leaving room for a maximum
712 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
716 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
718 hdrlen = sizeof(struct tcpiphdr);
719 if (flags & TH_SYN) {
720 tp->snd_nxt = tp->iss;
721 if (!(tp->t_flags & TF_NOOPT)) {
724 opt[0] = TCPOPT_MAXSEG;
725 opt[1] = TCPOLEN_MAXSEG;
726 mss = htons((u_short) tcp_mssopt(tp));
727 memcpy(opt + 2, &mss, sizeof mss);
728 optlen = TCPOLEN_MAXSEG;
730 if ((tp->t_flags & TF_REQ_SCALE) &&
731 (!(flags & TH_ACK) ||
732 (tp->t_flags & TF_RCVD_SCALE))) {
733 *((u_int32_t *)(opt + optlen)) = htonl(
735 TCPOPT_WINDOW << 16 |
736 TCPOLEN_WINDOW << 8 |
737 tp->request_r_scale);
741 if ((tcp_do_sack && !(flags & TH_ACK)) ||
742 tp->t_flags & TF_SACK_PERMITTED) {
743 uint32_t *lp = (uint32_t *)(opt + optlen);
745 *lp = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
746 optlen += TCPOLEN_SACK_PERMITTED_ALIGNED;
752 * Send a timestamp and echo-reply if this is a SYN and our side
753 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
754 * and our peer have sent timestamps in our SYN's.
756 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
758 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
759 u_int32_t *lp = (u_int32_t *)(opt + optlen);
761 /* Form timestamp option as shown in appendix A of RFC 1323. */
762 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
763 *lp++ = htonl(ticks);
764 *lp = htonl(tp->ts_recent);
765 optlen += TCPOLEN_TSTAMP_APPA;
768 /* Set receive buffer autosizing timestamp. */
769 if (tp->rfbuf_ts == 0 && (so->so_rcv.ssb_flags & SSB_AUTOSIZE))
770 tp->rfbuf_ts = ticks;
773 * If this is a SACK connection and we have a block to report,
774 * fill in the SACK blocks in the TCP options.
777 tcp_sack_fill_report(tp, opt, &optlen);
780 if (tp->t_flags & TF_SIGNATURE) {
784 * Initialize TCP-MD5 option (RFC2385)
786 bp = (u_char *)opt + optlen;
787 *bp++ = TCPOPT_SIGNATURE;
788 *bp++ = TCPOLEN_SIGNATURE;
790 for (i = 0; i < TCP_SIGLEN; i++)
792 optlen += TCPOLEN_SIGNATURE;
794 * Terminate options list and maintain 32-bit alignment.
800 #endif /* TCP_SIGNATURE */
801 KASSERT(optlen <= TCP_MAXOLEN, ("too many TCP options"));
805 ipoptlen = ip6_optlen(inp);
807 if (inp->inp_options) {
808 ipoptlen = inp->inp_options->m_len -
809 offsetof(struct ipoption, ipopt_list);
816 /* TSO segment length must be multiple of segment size */
817 KASSERT(len >= (2 * segsz) && (len % segsz == 0),
818 ("invalid TSO len %ld, segsz %u", len, segsz));
820 KASSERT(len <= segsz,
821 ("invalid len %ld, segsz %u", len, segsz));
824 * Adjust data length if insertion of options will bump
825 * the packet length beyond the t_maxopd length. Clear
826 * FIN to prevent premature closure since there is still
827 * more data to send after this (now truncated) packet.
829 * If just the options do not fit we are in a no-win
830 * situation and we treat it as an unreachable host.
832 if (len + optlen + ipoptlen > tp->t_maxopd) {
833 if (tp->t_maxopd <= optlen + ipoptlen) {
834 static time_t last_optlen_report;
836 if (last_optlen_report != time_uptime) {
837 last_optlen_report = time_uptime;
838 kprintf("tcpcb %p: MSS (%d) too "
839 "small to hold options!\n",
842 error = EHOSTUNREACH;
846 len = tp->t_maxopd - optlen - ipoptlen;
853 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
855 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
859 * Grab a header mbuf, attaching a copy of data to
860 * be transmitted, and initialize the header from
861 * the template for sends on this connection.
864 if ((tp->t_flags & TF_FORCE) && len == 1)
865 tcpstat.tcps_sndprobe++;
866 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
867 if (tp->snd_nxt == tp->snd_una)
868 tp->snd_max_rexmt = tp->snd_max;
870 tcpstat.tcps_sndsackrtopack++;
871 tcpstat.tcps_sndsackrtobyte += len;
873 tcpstat.tcps_sndrexmitpack++;
874 tcpstat.tcps_sndrexmitbyte += len;
876 tcpstat.tcps_sndpack++;
877 tcpstat.tcps_sndbyte += len;
881 tcp_idle_cwnd_validate(tp);
883 /* Update last send time after CWV */
884 tp->snd_last = ticks;
886 if ((m = m_copypack(so->so_snd.ssb_mb, off, (int)len,
887 max_linkhdr + hdrlen)) == NULL) {
892 * m_copypack left space for our hdr; use it.
898 m = m_gethdr(M_NOWAIT, MT_HEADER);
900 m = m_getl(hdrlen + max_linkhdr, M_NOWAIT, MT_HEADER,
907 m->m_data += max_linkhdr;
909 if (len <= MHLEN - hdrlen - max_linkhdr) {
910 m_copydata(so->so_snd.ssb_mb, off, (int) len,
911 mtod(m, caddr_t) + hdrlen);
914 m->m_next = m_copy(so->so_snd.ssb_mb, off, (int) len);
915 if (m->m_next == NULL) {
924 * If we're sending everything we've got, set PUSH.
925 * (This will keep happy those implementations which only
926 * give data to the user when a buffer fills or
929 if (off + len == so->so_snd.ssb_cc)
932 if (tp->t_flags & TF_ACKNOW)
933 tcpstat.tcps_sndacks++;
934 else if (flags & (TH_SYN | TH_FIN | TH_RST))
935 tcpstat.tcps_sndctrl++;
936 else if (SEQ_GT(tp->snd_up, tp->snd_una))
937 tcpstat.tcps_sndurg++;
939 tcpstat.tcps_sndwinup++;
941 MGETHDR(m, M_NOWAIT, MT_HEADER);
947 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
950 m->m_data += max_linkhdr;
954 * Prioritize SYN, SYN|ACK and pure ACK.
955 * Leave FIN and RST as they are.
957 if (tcp_prio_synack && (flags & (TH_FIN | TH_RST)) == 0)
958 m->m_flags |= M_PRIO;
960 m->m_pkthdr.rcvif = NULL;
962 ip6 = mtod(m, struct ip6_hdr *);
963 th = (struct tcphdr *)(ip6 + 1);
964 tcp_fillheaders(tp, ip6, th, use_tso);
966 ip = mtod(m, struct ip *);
967 th = (struct tcphdr *)(ip + 1);
968 /* this picks up the pseudo header (w/o the length) */
969 tcp_fillheaders(tp, ip, th, use_tso);
973 * Fill in fields, remembering maximum advertised
974 * window for use in delaying messages about window sizes.
975 * If resending a FIN, be sure not to use a new sequence number.
977 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
978 tp->snd_nxt == tp->snd_max)
983 * If we are doing retransmissions, then snd_nxt will
984 * not reflect the first unsent octet. For ACK only
985 * packets, we do not want the sequence number of the
986 * retransmitted packet, we want the sequence number
987 * of the next unsent octet. So, if there is no data
988 * (and no SYN or FIN), use snd_max instead of snd_nxt
989 * when filling in ti_seq. But if we are in persist
990 * state, snd_max might reflect one byte beyond the
991 * right edge of the window, so use snd_nxt in that
992 * case, since we know we aren't doing a retransmission.
993 * (retransmit and persist are mutually exclusive...)
995 if (len || (flags & (TH_SYN|TH_FIN)) ||
996 tcp_callout_active(tp, tp->tt_persist))
997 th->th_seq = htonl(tp->snd_nxt);
999 th->th_seq = htonl(tp->snd_max);
1000 th->th_ack = htonl(tp->rcv_nxt);
1002 bcopy(opt, th + 1, optlen);
1003 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1005 th->th_flags = flags;
1009 * Calculate receive window. Don't shrink window, but avoid
1010 * silly window syndrome by sending a 0 window if the actual
1011 * window is less then one segment.
1013 if (recvwin < (long)(so->so_rcv.ssb_hiwat / 4) &&
1014 recvwin < (long)segsz)
1016 if (recvwin < (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt))
1017 recvwin = (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt);
1018 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
1019 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
1022 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1023 * a 0 window. This may cause the remote transmitter to stall. This
1024 * flag tells soreceive() to disable delayed acknowledgements when
1025 * draining the buffer. This can occur if the receiver is attempting
1026 * to read more data then can be buffered prior to transmitting on
1030 tp->t_flags |= TF_RXWIN0SENT;
1032 tp->t_flags &= ~TF_RXWIN0SENT;
1035 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
1037 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1038 KASSERT(!use_tso, ("URG with TSO"));
1040 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1041 th->th_flags |= TH_URG;
1045 * If no urgent pointer to send, then we pull
1046 * the urgent pointer to the left edge of the send window
1047 * so that it doesn't drift into the send window on sequence
1048 * number wraparound.
1050 tp->snd_up = tp->snd_una; /* drag it along */
1054 #ifdef TCP_SIGNATURE
1055 if (tp->t_flags & TF_SIGNATURE) {
1056 tcpsignature_compute(m, len, optlen,
1057 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1059 #endif /* TCP_SIGNATURE */
1062 * Put TCP length in extended header, and then
1063 * checksum extended header and data.
1065 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1068 * ip6_plen is not need to be filled now, and will be
1069 * filled in ip6_output().
1071 th->th_sum = in6_cksum(m, IPPROTO_TCP,
1072 sizeof(struct ip6_hdr),
1073 sizeof(struct tcphdr) + optlen + len);
1075 m->m_pkthdr.csum_thlen = sizeof(struct tcphdr) + optlen;
1077 m->m_pkthdr.csum_flags = CSUM_TSO;
1078 m->m_pkthdr.tso_segsz = segsz;
1080 m->m_pkthdr.csum_flags = CSUM_TCP;
1081 m->m_pkthdr.csum_data =
1082 offsetof(struct tcphdr, th_sum);
1084 th->th_sum = in_addword(th->th_sum,
1085 htons((u_short)(optlen + len)));
1090 * IP version must be set here for ipv4/ipv6 checking
1093 KASSERT(ip->ip_v == IPVERSION,
1094 ("%s: IP version incorrect: %d",
1095 __func__, ip->ip_v));
1100 * In transmit state, time the transmission and arrange for
1101 * the retransmit. In persist state, just set snd_max.
1103 if (!(tp->t_flags & TF_FORCE) ||
1104 !tcp_callout_active(tp, tp->tt_persist)) {
1105 tcp_seq startseq = tp->snd_nxt;
1108 * Advance snd_nxt over sequence space of this segment.
1110 if (flags & (TH_SYN | TH_FIN)) {
1113 if (flags & TH_FIN) {
1115 tp->t_flags |= TF_SENTFIN;
1119 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1120 tp->snd_max = tp->snd_nxt;
1122 * Time this transmission if not a retransmission and
1123 * not currently timing anything.
1125 if (tp->t_rtttime == 0) {
1126 tp->t_rtttime = ticks;
1127 tp->t_rtseq = startseq;
1128 tcpstat.tcps_segstimed++;
1133 * Set retransmit timer if not currently set,
1134 * and not doing a pure ack or a keep-alive probe.
1135 * Initial value for retransmit timer is smoothed
1136 * round-trip time + 2 * round-trip time variance.
1137 * Initialize shift counter which is used for backoff
1138 * of retransmit time.
1140 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1141 tp->snd_nxt != tp->snd_una) {
1142 if (tcp_callout_active(tp, tp->tt_persist)) {
1143 tcp_callout_stop(tp, tp->tt_persist);
1146 tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
1148 } else if (len == 0 && so->so_snd.ssb_cc &&
1149 tp->t_state > TCPS_SYN_RECEIVED &&
1150 !tcp_callout_active(tp, tp->tt_rexmt) &&
1151 !tcp_callout_active(tp, tp->tt_persist)) {
1153 * Avoid a situation where we do not set persist timer
1154 * after a zero window condition. For example:
1155 * 1) A -> B: packet with enough data to fill the window
1156 * 2) B -> A: ACK for #1 + new data (0 window
1158 * 3) A -> B: ACK for #2, 0 len packet
1160 * In this case, A will not activate the persist timer,
1161 * because it chose to send a packet. Unless tcp_output
1162 * is called for some other reason (delayed ack timer,
1163 * another input packet from B, socket syscall), A will
1164 * not send zero window probes.
1166 * So, if you send a 0-length packet, but there is data
1167 * in the socket buffer, and neither the rexmt or
1168 * persist timer is already set, then activate the
1176 * Persist case, update snd_max but since we are in
1177 * persist mode (no window) we do not update snd_nxt.
1181 panic("tcp_output: persist timer to send SYN");
1182 if (flags & TH_FIN) {
1184 tp->t_flags |= TF_SENTFIN;
1186 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1187 tp->snd_max = tp->snd_nxt + xlen;
1193 if (so->so_options & SO_DEBUG) {
1194 tcp_trace(TA_OUTPUT, tp->t_state, tp,
1195 mtod(m, void *), th, 0);
1200 * Fill in IP length and desired time to live and
1201 * send to IP level. There should be a better way
1202 * to handle ttl and tos; we could keep them in
1203 * the template, but need a way to checksum without them.
1206 * m->m_pkthdr.len should have been set before cksum
1207 * calcuration, because in6_cksum() need it.
1211 * we separately set hoplimit for every segment,
1212 * since the user might want to change the value
1213 * via setsockopt. Also, desired default hop
1214 * limit might be changed via Neighbor Discovery.
1216 ip6->ip6_hlim = in6_selecthlim(inp,
1217 (inp->in6p_route.ro_rt ?
1218 inp->in6p_route.ro_rt->rt_ifp : NULL));
1220 /* TODO: IPv6 IP6TOS_ECT bit on */
1221 error = ip6_output(m, inp->in6p_outputopts,
1222 &inp->in6p_route, (so->so_options & SO_DONTROUTE),
1227 KASSERT(!INP_CHECK_SOCKAF(so, AF_INET6), ("inet6 pcb"));
1229 ip->ip_len = m->m_pkthdr.len;
1230 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
1231 ip->ip_tos = inp->inp_ip_tos; /* XXX */
1233 * See if we should do MTU discovery.
1234 * We do it only if the following are true:
1235 * 1) we have a valid route to the destination
1236 * 2) the MTU is not locked (if it is,
1237 * then discovery has been disabled)
1239 if (path_mtu_discovery &&
1240 (rt = inp->inp_route.ro_rt) &&
1241 (rt->rt_flags & RTF_UP) &&
1242 !(rt->rt_rmx.rmx_locks & RTV_MTU))
1243 ip->ip_off |= IP_DF;
1245 KASSERT(inp->inp_flags & INP_HASH,
1246 ("inpcb has no hash"));
1247 m_sethash(m, inp->inp_hashval);
1248 error = ip_output(m, inp->inp_options, &inp->inp_route,
1249 (so->so_options & SO_DONTROUTE) |
1250 IP_DEBUGROUTE, NULL, inp);
1253 KASSERT(error != 0, ("no error, but th not set"));
1256 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1259 * We know that the packet was lost, so back out the
1260 * sequence number advance, if any.
1262 if (!(tp->t_flags & TF_FORCE) ||
1263 !tcp_callout_active(tp, tp->tt_persist)) {
1265 * No need to check for TH_FIN here because
1266 * the TF_SENTFIN flag handles that case.
1268 if (!(flags & TH_SYN))
1273 if (error == ENOBUFS) {
1274 KASSERT((len == 0 && (flags & (TH_SYN | TH_FIN)) == 0) ||
1275 tcp_callout_active(tp, tp->tt_rexmt) ||
1276 tcp_callout_active(tp, tp->tt_persist),
1277 ("neither rexmt nor persist timer is set"));
1280 if (error == EMSGSIZE) {
1282 * ip_output() will have already fixed the route
1283 * for us. tcp_mtudisc() will, as its last action,
1284 * initiate retransmission, so it is important to
1287 tcp_mtudisc(inp, 0);
1290 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
1291 TCPS_HAVERCVDSYN(tp->t_state)) {
1292 tp->t_softerror = error;
1297 tcpstat.tcps_sndtotal++;
1300 * Data sent (as far as we can tell).
1302 * If this advertises a larger window than any other segment,
1303 * then remember the size of the advertised window.
1305 * Any pending ACK has now been sent.
1307 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv)) {
1308 tp->rcv_adv = tp->rcv_nxt + recvwin;
1309 tp->t_flags &= ~TF_RXRESIZED;
1311 tp->last_ack_sent = tp->rcv_nxt;
1312 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1313 if (tcp_delack_enabled)
1314 tcp_callout_stop(tp, tp->tt_delack);
1316 if (tcp_fairsend > 0 && (tp->t_flags & TF_FAIRSEND) &&
1317 segcnt >= tcp_fairsend)
1325 tcp_setpersist(struct tcpcb *tp)
1327 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1330 if (tp->t_state == TCPS_SYN_SENT ||
1331 tp->t_state == TCPS_SYN_RECEIVED) {
1332 panic("tcp_setpersist: not established yet, current %s",
1333 tp->t_state == TCPS_SYN_SENT ?
1334 "SYN_SENT" : "SYN_RECEIVED");
1337 if (tcp_callout_active(tp, tp->tt_rexmt))
1338 panic("tcp_setpersist: retransmit pending");
1340 * Start/restart persistance timer.
1342 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN,
1344 tcp_callout_reset(tp, tp->tt_persist, tt, tcp_timer_persist);
1345 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1350 tcp_idle_cwnd_validate(struct tcpcb *tp)
1352 u_long initial_cwnd = tcp_initial_window(tp);
1355 tcpstat.tcps_sndidle++;
1357 /* According to RFC5681: RW=min(IW,cwnd) */
1358 min_cwnd = min(tp->snd_cwnd, initial_cwnd);
1361 u_long idle_time, decay_cwnd;
1364 * RFC2861, but only after idle period.
1368 * Before the congestion window is reduced, ssthresh
1369 * is set to the maximum of its current value and 3/4
1370 * cwnd. If the sender then has more data to send
1371 * than the decayed cwnd allows, the TCP will slow-
1372 * start (perform exponential increase) at least
1373 * half-way back up to the old value of cwnd.
1375 tp->snd_ssthresh = max(tp->snd_ssthresh,
1376 (3 * tp->snd_cwnd) / 4);
1379 * Decay the congestion window by half for every RTT
1380 * that the flow remains inactive.
1382 * The difference between our implementation and
1383 * RFC2861 is that we don't allow cwnd to go below
1384 * the value allowed by RFC5681 (min_cwnd).
1386 idle_time = ticks - tp->snd_last;
1387 decay_cwnd = tp->snd_cwnd;
1388 while (idle_time >= tp->t_rxtcur &&
1389 decay_cwnd > min_cwnd) {
1391 idle_time -= tp->t_rxtcur;
1393 tp->snd_cwnd = max(decay_cwnd, min_cwnd);
1396 * Slow-start from scratch to re-determine the send
1397 * congestion window.
1399 tp->snd_cwnd = min_cwnd;
1402 /* Restart ABC counting during congestion avoidance */
1407 tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen0)
1409 struct inpcb * const inp = tp->t_inpcb;
1411 const boolean_t isipv6 = INP_ISIPV6(inp);
1413 const boolean_t isipv6 = FALSE;
1415 unsigned int ipoptlen, optlen;
1418 hlen = sizeof(struct ip) + sizeof(struct tcphdr);
1421 ipoptlen = ip6_optlen(inp);
1423 if (inp->inp_options) {
1424 ipoptlen = inp->inp_options->m_len -
1425 offsetof(struct ipoption, ipopt_list);
1433 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
1434 (tp->t_flags & TF_RCVD_TSTMP))
1435 optlen += TCPOLEN_TSTAMP_APPA;
1438 if (tp->t_maxopd <= optlen + ipoptlen)
1439 return EHOSTUNREACH;
1441 *segsz = tp->t_maxopd - optlen - ipoptlen;
1447 tcp_output_sched_handler(netmsg_t nmsg)
1449 struct tcpcb *tp = nmsg->lmsg.u.ms_resultp;
1453 lwkt_replymsg(&nmsg->lmsg, 0);
1456 tcp_output_fair(tp);
1460 tcp_output_init(struct tcpcb *tp)
1462 netmsg_init(tp->tt_sndmore, NULL, &netisr_adone_rport, MSGF_DROPABLE,
1463 tcp_output_sched_handler);
1464 tp->tt_sndmore->lmsg.u.ms_resultp = tp;
1468 tcp_output_cancel(struct tcpcb *tp)
1471 * This message is still pending to be processed;
1472 * drop it. Optimized.
1475 if ((tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE) == 0) {
1476 lwkt_dropmsg(&tp->tt_sndmore->lmsg);
1482 tcp_output_pending(struct tcpcb *tp)
1484 if ((tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE) == 0)
1491 tcp_output_sched(struct tcpcb *tp)
1494 if (tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE)
1495 lwkt_sendmsg(netisr_cpuport(mycpuid), &tp->tt_sndmore->lmsg);
1502 * Yield to other senders or receivers on the same netisr if the current
1503 * TCP stream has sent tcp_fairsend segments and is going to burst more
1504 * segments. Bursting large amount of segements in a single TCP stream
1505 * could delay other senders' segments and receivers' ACKs quite a lot,
1506 * if others segments and ACKs are queued on to the same hardware transmit
1507 * queue; thus cause unfairness between senders and suppress receiving
1510 * Fairsend should be performed at the places that do not affect segment
1511 * sending during congestion control, e.g.
1512 * - User requested output
1513 * - ACK input triggered output
1516 * For devices that are TSO capable, their TSO aggregation size limit could
1520 tcp_output_fair(struct tcpcb *tp)
1524 tp->t_flags |= TF_FAIRSEND;
1525 ret = tcp_output(tp);
1526 tp->t_flags &= ~TF_FAIRSEND;