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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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/sysctl.h>
75 #include <sys/domain.h>
76 #include <sys/protosw.h>
77 #include <sys/socket.h>
78 #include <sys/socketvar.h>
79 #include <sys/in_cksum.h>
80 #include <sys/thread.h>
81 #include <sys/globaldata.h>
83 #include <net/if_var.h>
84 #include <net/route.h>
85 #include <net/netmsg2.h>
86 #include <net/netisr2.h>
88 #include <netinet/in.h>
89 #include <netinet/in_systm.h>
90 #include <netinet/ip.h>
91 #include <netinet/in_pcb.h>
92 #include <netinet/ip_var.h>
93 #include <netinet6/in6_pcb.h>
94 #include <netinet/ip6.h>
95 #include <netinet6/ip6_var.h>
96 #include <netinet/tcp.h>
98 #include <netinet/tcp_fsm.h>
99 #include <netinet/tcp_seq.h>
100 #include <netinet/tcp_timer.h>
101 #include <netinet/tcp_timer2.h>
102 #include <netinet/tcp_var.h>
103 #include <netinet/tcpip.h>
105 #include <netinet/tcp_debug.h>
109 extern struct mbuf *m_copypack();
112 int path_mtu_discovery = 1;
113 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_RW,
114 &path_mtu_discovery, 1, "Enable Path MTU Discovery");
116 static int avoid_pure_win_update = 1;
117 SYSCTL_INT(_net_inet_tcp, OID_AUTO, avoid_pure_win_update, CTLFLAG_RW,
118 &avoid_pure_win_update, 1, "Avoid pure window updates when possible");
121 * 1 - enabled for increasing and decreasing the buffer size
122 * 2 - enabled only for increasing the buffer size
124 int tcp_do_autosndbuf = 1;
125 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_RW,
126 &tcp_do_autosndbuf, 0, "Enable automatic send buffer sizing");
128 int tcp_autosndbuf_inc = 8*1024;
129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_RW,
130 &tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer");
132 int tcp_autosndbuf_min = 32768;
133 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_min, CTLFLAG_RW,
134 &tcp_autosndbuf_min, 0, "Min size of automatic send buffer");
136 int tcp_autosndbuf_max = 2*1024*1024;
137 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_RW,
138 &tcp_autosndbuf_max, 0, "Max size of automatic send buffer");
140 int tcp_prio_synack = 1;
141 SYSCTL_INT(_net_inet_tcp, OID_AUTO, prio_synack, CTLFLAG_RW,
142 &tcp_prio_synack, 0, "Prioritize SYN, SYN|ACK and pure ACK");
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 int tcp_fairsend = 4;
158 SYSCTL_INT(_net_inet_tcp, OID_AUTO, fairsend, CTLFLAG_RW,
160 "Amount of segments sent before yield to other senders or receivers");
162 static void tcp_idle_cwnd_validate(struct tcpcb *);
164 static int tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen);
165 static void tcp_output_sched(struct tcpcb *tp);
168 * Tcp output routine: figure out what should be sent and send it.
171 tcp_output(struct tcpcb *tp)
173 struct inpcb * const inp = tp->t_inpcb;
174 struct socket *so = inp->inp_socket;
175 long len, recvwin, sendwin;
177 int off, flags, error = 0;
184 u_char opt[TCP_MAXOLEN];
185 unsigned int ipoptlen, optlen, hdrlen;
190 const boolean_t isipv6 = INP_ISIPV6(inp);
192 const boolean_t isipv6 = FALSE;
194 boolean_t can_tso = FALSE, use_tso;
195 boolean_t report_sack, idle_cwv = FALSE;
196 u_int segsz, tso_hlen, tso_lenmax = 0;
198 boolean_t need_sched = FALSE;
200 KKASSERT(so->so_port == &curthread->td_msgport);
203 * Determine length of data that should be transmitted,
204 * and flags that will be used.
205 * If there is some data or critical controls (SYN, RST)
206 * to send, then transmit; otherwise, investigate further.
210 * If we have been idle for a while, the send congestion window
211 * could be no longer representative of the current state of the
212 * link; need to validate congestion window. However, we should
213 * not perform congestion window validation here, since we could
214 * be asked to send pure ACK.
216 if (tp->snd_max == tp->snd_una &&
217 (ticks - tp->snd_last) >= tp->t_rxtcur && tcp_idle_restart)
221 * Calculate whether the transmit stream was previously idle
222 * and adjust TF_LASTIDLE for the next time.
224 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
225 if (idle && (tp->t_flags & TF_MORETOCOME))
226 tp->t_flags |= TF_LASTIDLE;
228 tp->t_flags &= ~TF_LASTIDLE;
230 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
231 !IN_FASTRECOVERY(tp))
232 nsacked = tcp_sack_bytes_below(&tp->scb, tp->snd_nxt);
235 * Find out whether TSO could be used or not
237 * For TSO capable devices, the following assumptions apply to
238 * the processing of TCP flags:
239 * - If FIN is set on the large TCP segment, the device must set
240 * FIN on the last segment that it creates from the large TCP
242 * - If PUSH is set on the large TCP segment, the device must set
243 * PUSH on the last segment that it creates from the large TCP
248 && (tp->t_flags & TF_SIGNATURE) == 0
252 struct rtentry *rt = inp->inp_route.ro_rt;
254 if (rt != NULL && (rt->rt_flags & RTF_UP) &&
255 (rt->rt_ifp->if_hwassist & CSUM_TSO)) {
257 tso_lenmax = rt->rt_ifp->if_tsolen;
268 if ((tp->t_flags & (TF_SACK_PERMITTED | TF_NOOPT)) ==
270 (!TAILQ_EMPTY(&tp->t_segq) ||
271 tp->reportblk.rblk_start != tp->reportblk.rblk_end))
276 /* Make use of SACK information when slow-starting after a RTO. */
277 if (TCP_DO_SACK(tp) && tp->snd_nxt != tp->snd_max &&
278 !IN_FASTRECOVERY(tp)) {
279 tcp_seq old_snd_nxt = tp->snd_nxt;
281 tcp_sack_skip_sacked(&tp->scb, &tp->snd_nxt);
282 nsacked += tp->snd_nxt - old_snd_nxt;
286 off = tp->snd_nxt - tp->snd_una;
287 sendwin = min(tp->snd_wnd, tp->snd_cwnd + nsacked);
288 sendwin = min(sendwin, tp->snd_bwnd);
290 flags = tcp_outflags[tp->t_state];
292 * Get standard flags, and add SYN or FIN if requested by 'hidden'
295 if (tp->t_flags & TF_NEEDFIN)
297 if (tp->t_flags & TF_NEEDSYN)
301 * If in persist timeout with window of 0, send 1 byte.
302 * Otherwise, if window is small but nonzero
303 * and timer expired, we will send what we can
304 * and go to transmit state.
306 if (tp->t_flags & TF_FORCE) {
309 * If we still have some data to send, then
310 * clear the FIN bit. Usually this would
311 * happen below when it realizes that we
312 * aren't sending all the data. However,
313 * if we have exactly 1 byte of unsent data,
314 * then it won't clear the FIN bit below,
315 * and if we are in persist state, we wind
316 * up sending the packet without recording
317 * that we sent the FIN bit.
319 * We can't just blindly clear the FIN bit,
320 * because if we don't have any more data
321 * to send then the probe will be the FIN
324 if (off < so->so_snd.ssb_cc)
328 tcp_callout_stop(tp, tp->tt_persist);
334 * If snd_nxt == snd_max and we have transmitted a FIN, the
335 * offset will be > 0 even if so_snd.ssb_cc is 0, resulting in
336 * a negative length. This can also occur when TCP opens up
337 * its congestion window while receiving additional duplicate
338 * acks after fast-retransmit because TCP will reset snd_nxt
339 * to snd_max after the fast-retransmit.
341 * A negative length can also occur when we are in the
342 * TCPS_SYN_RECEIVED state due to a simultanious connect where
343 * our SYN has not been acked yet.
345 * In the normal retransmit-FIN-only case, however, snd_nxt will
346 * be set to snd_una, the offset will be 0, and the length may
349 len = (long)ulmin(so->so_snd.ssb_cc, sendwin) - off;
352 * Lop off SYN bit if it has already been sent. However, if this
353 * is SYN-SENT state and if segment contains data, suppress sending
354 * segment (sending the segment would be an option if we still
355 * did TAO and the remote host supported it).
357 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
360 if (len > 0 && tp->t_state == TCPS_SYN_SENT) {
361 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
367 * Be careful not to send data and/or FIN on SYN segments.
368 * This measure is needed to prevent interoperability problems
369 * with not fully conformant TCP implementations.
371 if (flags & TH_SYN) {
378 * A negative len can occur if our FIN has been sent but not
379 * acked, or if we are in a simultanious connect in the
380 * TCPS_SYN_RECEIVED state with our SYN sent but not yet
383 * If our window has contracted to 0 in the FIN case
384 * (which can only occur if we have NOT been called to
385 * retransmit as per code a few paragraphs up) then we
386 * want to shift the retransmit timer over to the
389 * However, if we are in the TCPS_SYN_RECEIVED state
390 * (the SYN case) we will be in a simultanious connect and
391 * the window may be zero degeneratively. In this case we
392 * do not want to shift to the persist timer after the SYN
393 * or the SYN+ACK transmission.
396 if (sendwin == 0 && tp->t_state != TCPS_SYN_RECEIVED) {
397 tcp_callout_stop(tp, tp->tt_rexmt);
399 tp->snd_nxt = tp->snd_una;
400 if (!tcp_callout_active(tp, tp->tt_persist))
405 KASSERT(len >= 0, ("%s: len < 0", __func__));
407 * Automatic sizing of send socket buffer. Often the send buffer
408 * size is not optimally adjusted to the actual network conditions
409 * at hand (delay bandwidth product). Setting the buffer size too
410 * small limits throughput on links with high bandwidth and high
411 * delay (eg. trans-continental/oceanic links). Setting the
412 * buffer size too big consumes too much real kernel memory,
413 * especially with many connections on busy servers.
415 * The criteria to step up the send buffer one notch are:
416 * 1. receive window of remote host is larger than send buffer
417 * (with a fudge factor of 5/4th);
418 * 2. hiwat has not significantly exceeded bwnd (inflight)
419 * (bwnd is a maximal value if inflight is disabled).
420 * 3. send buffer is filled to 7/8th with data (so we actually
421 * have data to make use of it);
422 * 4. hiwat has not hit maximal automatic size;
423 * 5. our send window (slow start and cogestion controlled) is
424 * larger than sent but unacknowledged data in send buffer.
426 * The remote host receive window scaling factor may limit the
427 * growing of the send buffer before it reaches its allowed
430 * It scales directly with slow start or congestion window
431 * and does at most one step per received ACK. This fast
432 * scaling has the drawback of growing the send buffer beyond
433 * what is strictly necessary to make full use of a given
434 * delay*bandwith product. However testing has shown this not
435 * to be much of an problem. At worst we are trading wasting
436 * of available bandwith (the non-use of it) for wasting some
437 * socket buffer memory.
439 * The criteria for shrinking the buffer is based solely on
440 * the inflight code (snd_bwnd). If inflight is disabled,
441 * the buffer will not be shrinked. Note that snd_bwnd already
442 * has a fudge factor. Our test adds a little hysteresis.
444 if (tcp_do_autosndbuf && (so->so_snd.ssb_flags & SSB_AUTOSIZE)) {
445 const int asbinc = tcp_autosndbuf_inc;
446 const int hiwat = so->so_snd.ssb_hiwat;
447 const int lowat = so->so_snd.ssb_lowat;
450 if ((tp->snd_wnd / 4 * 5) >= hiwat &&
451 so->so_snd.ssb_cc >= (hiwat / 8 * 7) &&
452 hiwat < tp->snd_bwnd + hiwat / 10 &&
453 hiwat + asbinc < tcp_autosndbuf_max &&
454 hiwat < (TCP_MAXWIN << tp->snd_scale) &&
455 sendwin >= (so->so_snd.ssb_cc -
456 (tp->snd_nxt - tp->snd_una))) {
457 newsize = ulmin(hiwat + asbinc, tcp_autosndbuf_max);
458 if (!ssb_reserve(&so->so_snd, newsize, so, NULL))
459 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
461 if (newsize >= (TCP_MAXWIN << tp->snd_scale))
462 atomic_clear_int(&so->so_snd.ssb_flags, SSB_AUTOSIZE);
464 } else if ((long)tp->snd_bwnd <
465 (long)(hiwat * 3 / 4 - lowat - asbinc) &&
466 hiwat > tp->t_maxseg * 2 + asbinc &&
467 hiwat + asbinc >= tcp_autosndbuf_min &&
468 tcp_do_autosndbuf == 1) {
469 newsize = ulmax(hiwat - asbinc, tp->t_maxseg * 2);
470 ssb_reserve(&so->so_snd, newsize, so, NULL);
476 * - Congestion window needs validation
477 * - There are SACK blocks to report
478 * - RST or SYN flags is set
482 * Checking for SYN|RST looks overkill, just to be safe than sorry
485 if (report_sack || idle_cwv || (flags & (TH_RST | TH_SYN)))
488 tcp_seq ugr_nxt = tp->snd_nxt;
490 if ((flags & TH_FIN) && (tp->t_flags & TF_SENTFIN) &&
491 tp->snd_nxt == tp->snd_max)
494 if (SEQ_GT(tp->snd_up, ugr_nxt))
500 * Find out segment size and header length for TSO
502 error = tcp_tso_getsize(tp, &segsz, &tso_hlen);
507 segsz = tp->t_maxseg;
508 tso_hlen = 0; /* not used */
512 * Truncate to the maximum segment length if not TSO, and ensure that
513 * FIN is removed if the length no longer contains the last data byte.
522 if (__predict_false(tso_lenmax < segsz))
523 tso_lenmax = segsz << 1;
526 * Truncate TSO transfers to (IP_MAXPACKET - iphlen -
527 * thoff), and make sure that we send equal size
528 * transfers down the stack (rather than big-small-
531 len = min(len, tso_lenmax);
532 nsegs = min(len, (IP_MAXPACKET - tso_hlen)) / segsz;
550 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una + so->so_snd.ssb_cc))
553 recvwin = ssb_space(&so->so_rcv);
556 * Sender silly window avoidance. We transmit under the following
557 * conditions when len is non-zero:
559 * - We have a full segment
560 * - This is the last buffer in a write()/send() and we are
561 * either idle or running NODELAY
562 * - we've timed out (e.g. persist timer)
563 * - we have more then 1/2 the maximum send window's worth of
564 * data (receiver may be limiting the window size)
565 * - we need to retransmit
571 * NOTE! on localhost connections an 'ack' from the remote
572 * end may occur synchronously with the output and cause
573 * us to flush a buffer queued with moretocome. XXX
575 * note: the len + off check is almost certainly unnecessary.
577 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
578 (idle || (tp->t_flags & TF_NODELAY)) &&
579 len + off >= so->so_snd.ssb_cc &&
580 !(tp->t_flags & TF_NOPUSH)) {
583 if (tp->t_flags & TF_FORCE) /* typ. timeout case */
585 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
587 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
589 if (tp->t_flags & TF_XMITNOW)
594 * Compare available window to amount of window
595 * known to peer (as advertised window less
596 * next expected input). If the difference is at least two
597 * max size segments, or at least 50% of the maximum possible
598 * window, then want to send a window update to peer.
602 * "adv" is the amount we can increase the window,
603 * taking into account that we are limited by
604 * TCP_MAXWIN << tp->rcv_scale.
606 long adv = min(recvwin, (long)TCP_MAXWIN << tp->rcv_scale) -
607 (tp->rcv_adv - tp->rcv_nxt);
611 * This ack case typically occurs when the user has drained
612 * the TCP socket buffer sufficiently to warrent an ack
613 * containing a 'pure window update'... that is, an ack that
614 * ONLY updates the tcp window.
616 * It is unclear why we would need to do a pure window update
617 * past 2 segments if we are going to do one at 1/2 the high
618 * water mark anyway, especially since under normal conditions
619 * the user program will drain the socket buffer quickly.
620 * The 2-segment pure window update will often add a large
621 * number of extra, unnecessary acks to the stream.
623 * avoid_pure_win_update now defaults to 1.
625 if (avoid_pure_win_update == 0 ||
626 (tp->t_flags & TF_RXRESIZED)) {
627 if (adv >= (long) (2 * segsz)) {
631 hiwat = (long)(TCP_MAXWIN << tp->rcv_scale);
632 if (hiwat > (long)so->so_rcv.ssb_hiwat)
633 hiwat = (long)so->so_rcv.ssb_hiwat;
634 if (adv >= hiwat / 2)
639 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
640 * is also a catch-all for the retransmit timer timeout case.
642 if (tp->t_flags & TF_ACKNOW)
644 if ((flags & TH_RST) ||
645 ((flags & TH_SYN) && !(tp->t_flags & TF_NEEDSYN)))
647 if (SEQ_GT(tp->snd_up, tp->snd_una))
650 * If our state indicates that FIN should be sent
651 * and we have not yet done so, then we need to send.
653 if ((flags & TH_FIN) &&
654 (!(tp->t_flags & TF_SENTFIN) || tp->snd_nxt == tp->snd_una))
658 * TCP window updates are not reliable, rather a polling protocol
659 * using ``persist'' packets is used to insure receipt of window
660 * updates. The three ``states'' for the output side are:
661 * idle not doing retransmits or persists
662 * persisting to move a small or zero window
663 * (re)transmitting and thereby not persisting
665 * tcp_callout_active(tp, tp->tt_persist)
666 * is true when we are in persist state.
667 * The TF_FORCE flag in tp->t_flags
668 * is set when we are called to send a persist packet.
669 * tcp_callout_active(tp, tp->tt_rexmt)
670 * is set when we are retransmitting
671 * The output side is idle when both timers are zero.
673 * If send window is too small, there is data to transmit, and no
674 * retransmit or persist is pending, then go to persist state.
676 * If nothing happens soon, send when timer expires:
677 * if window is nonzero, transmit what we can, otherwise force out
680 * Don't try to set the persist state if we are in TCPS_SYN_RECEIVED
681 * with data pending. This situation can occur during a
682 * simultanious connect.
684 if (so->so_snd.ssb_cc > 0 &&
685 tp->t_state != TCPS_SYN_RECEIVED &&
686 !tcp_callout_active(tp, tp->tt_rexmt) &&
687 !tcp_callout_active(tp, tp->tt_persist)) {
693 * No reason to send a segment, just return.
695 tp->t_flags &= ~TF_XMITNOW;
699 if (need_sched && len > 0) {
700 tcp_output_sched(tp);
705 * Before ESTABLISHED, force sending of initial options
706 * unless TCP set not to do any options.
707 * NOTE: we assume that the IP/TCP header plus TCP options
708 * always fit in a single mbuf, leaving room for a maximum
710 * max_linkhdr + sizeof(struct tcpiphdr) + optlen <= MCLBYTES
714 hdrlen = sizeof(struct ip6_hdr) + sizeof(struct tcphdr);
716 hdrlen = sizeof(struct tcpiphdr);
717 if (flags & TH_SYN) {
718 tp->snd_nxt = tp->iss;
719 if (!(tp->t_flags & TF_NOOPT)) {
722 opt[0] = TCPOPT_MAXSEG;
723 opt[1] = TCPOLEN_MAXSEG;
724 mss = htons((u_short) tcp_mssopt(tp));
725 memcpy(opt + 2, &mss, sizeof mss);
726 optlen = TCPOLEN_MAXSEG;
728 if ((tp->t_flags & TF_REQ_SCALE) &&
729 (!(flags & TH_ACK) ||
730 (tp->t_flags & TF_RCVD_SCALE))) {
731 *((u_int32_t *)(opt + optlen)) = htonl(
733 TCPOPT_WINDOW << 16 |
734 TCPOLEN_WINDOW << 8 |
735 tp->request_r_scale);
739 if ((tcp_do_sack && !(flags & TH_ACK)) ||
740 tp->t_flags & TF_SACK_PERMITTED) {
741 uint32_t *lp = (uint32_t *)(opt + optlen);
743 *lp = htonl(TCPOPT_SACK_PERMITTED_ALIGNED);
744 optlen += TCPOLEN_SACK_PERMITTED_ALIGNED;
750 * Send a timestamp and echo-reply if this is a SYN and our side
751 * wants to use timestamps (TF_REQ_TSTMP is set) or both our side
752 * and our peer have sent timestamps in our SYN's.
754 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
756 (!(flags & TH_ACK) || (tp->t_flags & TF_RCVD_TSTMP))) {
757 u_int32_t *lp = (u_int32_t *)(opt + optlen);
759 /* Form timestamp option as shown in appendix A of RFC 1323. */
760 *lp++ = htonl(TCPOPT_TSTAMP_HDR);
761 *lp++ = htonl(ticks);
762 *lp = htonl(tp->ts_recent);
763 optlen += TCPOLEN_TSTAMP_APPA;
766 /* Set receive buffer autosizing timestamp. */
767 if (tp->rfbuf_ts == 0 && (so->so_rcv.ssb_flags & SSB_AUTOSIZE))
768 tp->rfbuf_ts = ticks;
771 * If this is a SACK connection and we have a block to report,
772 * fill in the SACK blocks in the TCP options.
775 tcp_sack_fill_report(tp, opt, &optlen);
778 if (tp->t_flags & TF_SIGNATURE) {
782 * Initialize TCP-MD5 option (RFC2385)
784 bp = (u_char *)opt + optlen;
785 *bp++ = TCPOPT_SIGNATURE;
786 *bp++ = TCPOLEN_SIGNATURE;
788 for (i = 0; i < TCP_SIGLEN; i++)
790 optlen += TCPOLEN_SIGNATURE;
792 * Terminate options list and maintain 32-bit alignment.
798 #endif /* TCP_SIGNATURE */
799 KASSERT(optlen <= TCP_MAXOLEN, ("too many TCP options"));
803 ipoptlen = ip6_optlen(inp);
805 if (inp->inp_options) {
806 ipoptlen = inp->inp_options->m_len -
807 offsetof(struct ipoption, ipopt_list);
814 /* TSO segment length must be multiple of segment size */
815 KASSERT(len >= (2 * segsz) && (len % segsz == 0),
816 ("invalid TSO len %ld, segsz %u", len, segsz));
818 KASSERT(len <= segsz,
819 ("invalid len %ld, segsz %u", len, segsz));
822 * Adjust data length if insertion of options will bump
823 * the packet length beyond the t_maxopd length. Clear
824 * FIN to prevent premature closure since there is still
825 * more data to send after this (now truncated) packet.
827 * If just the options do not fit we are in a no-win
828 * situation and we treat it as an unreachable host.
830 if (len + optlen + ipoptlen > tp->t_maxopd) {
831 if (tp->t_maxopd <= optlen + ipoptlen) {
832 static time_t last_optlen_report;
834 if (last_optlen_report != time_uptime) {
835 last_optlen_report = time_uptime;
836 kprintf("tcpcb %p: MSS (%d) too "
837 "small to hold options!\n",
840 error = EHOSTUNREACH;
844 len = tp->t_maxopd - optlen - ipoptlen;
851 KASSERT(max_linkhdr + hdrlen <= MCLBYTES, ("tcphdr too big"));
853 KASSERT(max_linkhdr + hdrlen <= MHLEN, ("tcphdr too big"));
857 * Grab a header mbuf, attaching a copy of data to
858 * be transmitted, and initialize the header from
859 * the template for sends on this connection.
862 if ((tp->t_flags & TF_FORCE) && len == 1)
863 tcpstat.tcps_sndprobe++;
864 else if (SEQ_LT(tp->snd_nxt, tp->snd_max)) {
865 if (tp->snd_nxt == tp->snd_una)
866 tp->snd_max_rexmt = tp->snd_max;
868 tcpstat.tcps_sndsackrtopack++;
869 tcpstat.tcps_sndsackrtobyte += len;
871 tcpstat.tcps_sndrexmitpack++;
872 tcpstat.tcps_sndrexmitbyte += len;
874 tcpstat.tcps_sndpack++;
875 tcpstat.tcps_sndbyte += len;
879 tcp_idle_cwnd_validate(tp);
881 /* Update last send time after CWV */
882 tp->snd_last = ticks;
884 if ((m = m_copypack(so->so_snd.ssb_mb, off, (int)len,
885 max_linkhdr + hdrlen)) == NULL) {
890 * m_copypack left space for our hdr; use it.
896 m = m_gethdr(M_NOWAIT, MT_HEADER);
898 m = m_getl(hdrlen + max_linkhdr, M_NOWAIT, MT_HEADER,
905 m->m_data += max_linkhdr;
907 if (len <= MHLEN - hdrlen - max_linkhdr) {
908 m_copydata(so->so_snd.ssb_mb, off, (int) len,
909 mtod(m, caddr_t) + hdrlen);
912 m->m_next = m_copy(so->so_snd.ssb_mb, off, (int) len);
913 if (m->m_next == NULL) {
922 * If we're sending everything we've got, set PUSH.
923 * (This will keep happy those implementations which only
924 * give data to the user when a buffer fills or
927 if (off + len == so->so_snd.ssb_cc)
930 if (tp->t_flags & TF_ACKNOW)
931 tcpstat.tcps_sndacks++;
932 else if (flags & (TH_SYN | TH_FIN | TH_RST))
933 tcpstat.tcps_sndctrl++;
934 else if (SEQ_GT(tp->snd_up, tp->snd_una))
935 tcpstat.tcps_sndurg++;
937 tcpstat.tcps_sndwinup++;
939 MGETHDR(m, M_NOWAIT, MT_HEADER);
945 (hdrlen + max_linkhdr > MHLEN) && hdrlen <= MHLEN)
948 m->m_data += max_linkhdr;
952 * Prioritize SYN, SYN|ACK and pure ACK.
953 * Leave FIN and RST as they are.
955 if (tcp_prio_synack && (flags & (TH_FIN | TH_RST)) == 0)
956 m->m_flags |= M_PRIO;
958 m->m_pkthdr.rcvif = NULL;
960 ip6 = mtod(m, struct ip6_hdr *);
961 th = (struct tcphdr *)(ip6 + 1);
962 tcp_fillheaders(tp, ip6, th, use_tso);
964 ip = mtod(m, struct ip *);
965 th = (struct tcphdr *)(ip + 1);
966 /* this picks up the pseudo header (w/o the length) */
967 tcp_fillheaders(tp, ip, th, use_tso);
971 * Fill in fields, remembering maximum advertised
972 * window for use in delaying messages about window sizes.
973 * If resending a FIN, be sure not to use a new sequence number.
975 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
976 tp->snd_nxt == tp->snd_max)
981 * If we are doing retransmissions, then snd_nxt will
982 * not reflect the first unsent octet. For ACK only
983 * packets, we do not want the sequence number of the
984 * retransmitted packet, we want the sequence number
985 * of the next unsent octet. So, if there is no data
986 * (and no SYN or FIN), use snd_max instead of snd_nxt
987 * when filling in ti_seq. But if we are in persist
988 * state, snd_max might reflect one byte beyond the
989 * right edge of the window, so use snd_nxt in that
990 * case, since we know we aren't doing a retransmission.
991 * (retransmit and persist are mutually exclusive...)
993 if (len || (flags & (TH_SYN|TH_FIN)) ||
994 tcp_callout_active(tp, tp->tt_persist))
995 th->th_seq = htonl(tp->snd_nxt);
997 th->th_seq = htonl(tp->snd_max);
998 th->th_ack = htonl(tp->rcv_nxt);
1000 bcopy(opt, th + 1, optlen);
1001 th->th_off = (sizeof(struct tcphdr) + optlen) >> 2;
1003 th->th_flags = flags;
1007 * Calculate receive window. Don't shrink window, but avoid
1008 * silly window syndrome by sending a 0 window if the actual
1009 * window is less then one segment.
1011 if (recvwin < (long)(so->so_rcv.ssb_hiwat / 4) &&
1012 recvwin < (long)segsz)
1014 if (recvwin < (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt))
1015 recvwin = (tcp_seq_diff_t)(tp->rcv_adv - tp->rcv_nxt);
1016 if (recvwin > (long)TCP_MAXWIN << tp->rcv_scale)
1017 recvwin = (long)TCP_MAXWIN << tp->rcv_scale;
1020 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1021 * a 0 window. This may cause the remote transmitter to stall. This
1022 * flag tells soreceive() to disable delayed acknowledgements when
1023 * draining the buffer. This can occur if the receiver is attempting
1024 * to read more data then can be buffered prior to transmitting on
1028 tp->t_flags |= TF_RXWIN0SENT;
1030 tp->t_flags &= ~TF_RXWIN0SENT;
1033 th->th_win = htons((u_short) (recvwin>>tp->rcv_scale));
1035 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1036 KASSERT(!use_tso, ("URG with TSO"));
1038 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1039 th->th_flags |= TH_URG;
1043 * If no urgent pointer to send, then we pull
1044 * the urgent pointer to the left edge of the send window
1045 * so that it doesn't drift into the send window on sequence
1046 * number wraparound.
1048 tp->snd_up = tp->snd_una; /* drag it along */
1052 #ifdef TCP_SIGNATURE
1053 if (tp->t_flags & TF_SIGNATURE) {
1054 tcpsignature_compute(m, len, optlen,
1055 (u_char *)(th + 1) + sigoff, IPSEC_DIR_OUTBOUND);
1057 #endif /* TCP_SIGNATURE */
1060 * Put TCP length in extended header, and then
1061 * checksum extended header and data.
1063 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1066 * ip6_plen is not need to be filled now, and will be
1067 * filled in ip6_output().
1069 th->th_sum = in6_cksum(m, IPPROTO_TCP,
1070 sizeof(struct ip6_hdr),
1071 sizeof(struct tcphdr) + optlen + len);
1073 m->m_pkthdr.csum_thlen = sizeof(struct tcphdr) + optlen;
1075 m->m_pkthdr.csum_flags = CSUM_TSO;
1076 m->m_pkthdr.tso_segsz = segsz;
1078 m->m_pkthdr.csum_flags = CSUM_TCP;
1079 m->m_pkthdr.csum_data =
1080 offsetof(struct tcphdr, th_sum);
1082 th->th_sum = in_addword(th->th_sum,
1083 htons((u_short)(optlen + len)));
1088 * IP version must be set here for ipv4/ipv6 checking
1091 KASSERT(ip->ip_v == IPVERSION,
1092 ("%s: IP version incorrect: %d",
1093 __func__, ip->ip_v));
1098 * In transmit state, time the transmission and arrange for
1099 * the retransmit. In persist state, just set snd_max.
1101 if (!(tp->t_flags & TF_FORCE) ||
1102 !tcp_callout_active(tp, tp->tt_persist)) {
1103 tcp_seq startseq = tp->snd_nxt;
1106 * Advance snd_nxt over sequence space of this segment.
1108 if (flags & (TH_SYN | TH_FIN)) {
1111 if (flags & TH_FIN) {
1113 tp->t_flags |= TF_SENTFIN;
1117 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1118 tp->snd_max = tp->snd_nxt;
1120 * Time this transmission if not a retransmission and
1121 * not currently timing anything.
1123 if (tp->t_rtttime == 0) {
1124 tp->t_rtttime = ticks;
1125 tp->t_rtseq = startseq;
1126 tcpstat.tcps_segstimed++;
1131 * Set retransmit timer if not currently set,
1132 * and not doing a pure ack or a keep-alive probe.
1133 * Initial value for retransmit timer is smoothed
1134 * round-trip time + 2 * round-trip time variance.
1135 * Initialize shift counter which is used for backoff
1136 * of retransmit time.
1138 if (!tcp_callout_active(tp, tp->tt_rexmt) &&
1139 tp->snd_nxt != tp->snd_una) {
1140 if (tcp_callout_active(tp, tp->tt_persist)) {
1141 tcp_callout_stop(tp, tp->tt_persist);
1144 tcp_callout_reset(tp, tp->tt_rexmt, tp->t_rxtcur,
1146 } else if (len == 0 && so->so_snd.ssb_cc &&
1147 tp->t_state > TCPS_SYN_RECEIVED &&
1148 !tcp_callout_active(tp, tp->tt_rexmt) &&
1149 !tcp_callout_active(tp, tp->tt_persist)) {
1151 * Avoid a situation where we do not set persist timer
1152 * after a zero window condition. For example:
1153 * 1) A -> B: packet with enough data to fill the window
1154 * 2) B -> A: ACK for #1 + new data (0 window
1156 * 3) A -> B: ACK for #2, 0 len packet
1158 * In this case, A will not activate the persist timer,
1159 * because it chose to send a packet. Unless tcp_output
1160 * is called for some other reason (delayed ack timer,
1161 * another input packet from B, socket syscall), A will
1162 * not send zero window probes.
1164 * So, if you send a 0-length packet, but there is data
1165 * in the socket buffer, and neither the rexmt or
1166 * persist timer is already set, then activate the
1174 * Persist case, update snd_max but since we are in
1175 * persist mode (no window) we do not update snd_nxt.
1179 panic("tcp_output: persist timer to send SYN");
1180 if (flags & TH_FIN) {
1182 tp->t_flags |= TF_SENTFIN;
1184 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1185 tp->snd_max = tp->snd_nxt + xlen;
1191 if (so->so_options & SO_DEBUG) {
1192 tcp_trace(TA_OUTPUT, tp->t_state, tp,
1193 mtod(m, void *), th, 0);
1198 * Fill in IP length and desired time to live and
1199 * send to IP level. There should be a better way
1200 * to handle ttl and tos; we could keep them in
1201 * the template, but need a way to checksum without them.
1204 * m->m_pkthdr.len should have been set before cksum
1205 * calcuration, because in6_cksum() need it.
1209 * we separately set hoplimit for every segment,
1210 * since the user might want to change the value
1211 * via setsockopt. Also, desired default hop
1212 * limit might be changed via Neighbor Discovery.
1214 ip6->ip6_hlim = in6_selecthlim(inp,
1215 (inp->in6p_route.ro_rt ?
1216 inp->in6p_route.ro_rt->rt_ifp : NULL));
1218 /* TODO: IPv6 IP6TOS_ECT bit on */
1219 error = ip6_output(m, inp->in6p_outputopts,
1220 &inp->in6p_route, (so->so_options & SO_DONTROUTE),
1225 KASSERT(!INP_CHECK_SOCKAF(so, AF_INET6), ("inet6 pcb"));
1227 ip->ip_len = m->m_pkthdr.len;
1228 ip->ip_ttl = inp->inp_ip_ttl; /* XXX */
1229 ip->ip_tos = inp->inp_ip_tos; /* XXX */
1231 * See if we should do MTU discovery.
1232 * We do it only if the following are true:
1233 * 1) we have a valid route to the destination
1234 * 2) the MTU is not locked (if it is,
1235 * then discovery has been disabled)
1237 if (path_mtu_discovery &&
1238 (rt = inp->inp_route.ro_rt) &&
1239 (rt->rt_flags & RTF_UP) &&
1240 !(rt->rt_rmx.rmx_locks & RTV_MTU))
1241 ip->ip_off |= IP_DF;
1243 KASSERT(inp->inp_flags & INP_HASH,
1244 ("inpcb has no hash"));
1245 m_sethash(m, inp->inp_hashval);
1246 error = ip_output(m, inp->inp_options, &inp->inp_route,
1247 (so->so_options & SO_DONTROUTE) |
1248 IP_DEBUGROUTE, NULL, inp);
1251 KASSERT(error != 0, ("no error, but th not set"));
1254 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1257 * We know that the packet was lost, so back out the
1258 * sequence number advance, if any.
1260 if (!(tp->t_flags & TF_FORCE) ||
1261 !tcp_callout_active(tp, tp->tt_persist)) {
1263 * No need to check for TH_FIN here because
1264 * the TF_SENTFIN flag handles that case.
1266 if (!(flags & TH_SYN))
1271 if (error == ENOBUFS) {
1272 KASSERT((len == 0 && (flags & (TH_SYN | TH_FIN)) == 0) ||
1273 tcp_callout_active(tp, tp->tt_rexmt) ||
1274 tcp_callout_active(tp, tp->tt_persist),
1275 ("neither rexmt nor persist timer is set"));
1278 if (error == EMSGSIZE) {
1280 * ip_output() will have already fixed the route
1281 * for us. tcp_mtudisc() will, as its last action,
1282 * initiate retransmission, so it is important to
1285 tcp_mtudisc(inp, 0);
1288 if ((error == EHOSTUNREACH || error == ENETDOWN) &&
1289 TCPS_HAVERCVDSYN(tp->t_state)) {
1290 tp->t_softerror = error;
1295 tcpstat.tcps_sndtotal++;
1298 * Data sent (as far as we can tell).
1300 * If this advertises a larger window than any other segment,
1301 * then remember the size of the advertised window.
1303 * Any pending ACK has now been sent.
1305 if (recvwin > 0 && SEQ_GT(tp->rcv_nxt + recvwin, tp->rcv_adv)) {
1306 tp->rcv_adv = tp->rcv_nxt + recvwin;
1307 tp->t_flags &= ~TF_RXRESIZED;
1309 tp->last_ack_sent = tp->rcv_nxt;
1310 tp->t_flags &= ~(TF_ACKNOW | TF_XMITNOW);
1311 if (tcp_delack_enabled)
1312 tcp_callout_stop(tp, tp->tt_delack);
1314 if (tcp_fairsend > 0 && (tp->t_flags & TF_FAIRSEND) &&
1315 segcnt >= tcp_fairsend)
1323 tcp_setpersist(struct tcpcb *tp)
1325 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1328 if (tp->t_state == TCPS_SYN_SENT ||
1329 tp->t_state == TCPS_SYN_RECEIVED) {
1330 panic("tcp_setpersist: not established yet, current %s",
1331 tp->t_state == TCPS_SYN_SENT ?
1332 "SYN_SENT" : "SYN_RECEIVED");
1335 if (tcp_callout_active(tp, tp->tt_rexmt))
1336 panic("tcp_setpersist: retransmit pending");
1338 * Start/restart persistance timer.
1340 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift], TCPTV_PERSMIN,
1342 tcp_callout_reset(tp, tp->tt_persist, tt, tcp_timer_persist);
1343 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1348 tcp_idle_cwnd_validate(struct tcpcb *tp)
1350 u_long initial_cwnd = tcp_initial_window(tp);
1353 tcpstat.tcps_sndidle++;
1355 /* According to RFC5681: RW=min(IW,cwnd) */
1356 min_cwnd = min(tp->snd_cwnd, initial_cwnd);
1359 u_long idle_time, decay_cwnd;
1362 * RFC2861, but only after idle period.
1366 * Before the congestion window is reduced, ssthresh
1367 * is set to the maximum of its current value and 3/4
1368 * cwnd. If the sender then has more data to send
1369 * than the decayed cwnd allows, the TCP will slow-
1370 * start (perform exponential increase) at least
1371 * half-way back up to the old value of cwnd.
1373 tp->snd_ssthresh = max(tp->snd_ssthresh,
1374 (3 * tp->snd_cwnd) / 4);
1377 * Decay the congestion window by half for every RTT
1378 * that the flow remains inactive.
1380 * The difference between our implementation and
1381 * RFC2861 is that we don't allow cwnd to go below
1382 * the value allowed by RFC5681 (min_cwnd).
1384 idle_time = ticks - tp->snd_last;
1385 decay_cwnd = tp->snd_cwnd;
1386 while (idle_time >= tp->t_rxtcur &&
1387 decay_cwnd > min_cwnd) {
1389 idle_time -= tp->t_rxtcur;
1391 tp->snd_cwnd = max(decay_cwnd, min_cwnd);
1394 * Slow-start from scratch to re-determine the send
1395 * congestion window.
1397 tp->snd_cwnd = min_cwnd;
1400 /* Restart ABC counting during congestion avoidance */
1405 tcp_tso_getsize(struct tcpcb *tp, u_int *segsz, u_int *hlen0)
1407 struct inpcb * const inp = tp->t_inpcb;
1409 const boolean_t isipv6 = INP_ISIPV6(inp);
1411 const boolean_t isipv6 = FALSE;
1413 unsigned int ipoptlen, optlen;
1416 hlen = sizeof(struct ip) + sizeof(struct tcphdr);
1419 ipoptlen = ip6_optlen(inp);
1421 if (inp->inp_options) {
1422 ipoptlen = inp->inp_options->m_len -
1423 offsetof(struct ipoption, ipopt_list);
1431 if ((tp->t_flags & (TF_REQ_TSTMP | TF_NOOPT)) == TF_REQ_TSTMP &&
1432 (tp->t_flags & TF_RCVD_TSTMP))
1433 optlen += TCPOLEN_TSTAMP_APPA;
1436 if (tp->t_maxopd <= optlen + ipoptlen)
1437 return EHOSTUNREACH;
1439 *segsz = tp->t_maxopd - optlen - ipoptlen;
1445 tcp_output_sched_handler(netmsg_t nmsg)
1447 struct tcpcb *tp = nmsg->lmsg.u.ms_resultp;
1451 lwkt_replymsg(&nmsg->lmsg, 0);
1454 tcp_output_fair(tp);
1458 tcp_output_init(struct tcpcb *tp)
1460 netmsg_init(tp->tt_sndmore, NULL, &netisr_adone_rport, MSGF_DROPABLE,
1461 tcp_output_sched_handler);
1462 tp->tt_sndmore->lmsg.u.ms_resultp = tp;
1466 tcp_output_cancel(struct tcpcb *tp)
1469 * This message is still pending to be processed;
1470 * drop it. Optimized.
1473 if ((tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE) == 0) {
1474 lwkt_dropmsg(&tp->tt_sndmore->lmsg);
1480 tcp_output_pending(struct tcpcb *tp)
1482 if ((tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE) == 0)
1489 tcp_output_sched(struct tcpcb *tp)
1492 if (tp->tt_sndmore->lmsg.ms_flags & MSGF_DONE)
1493 lwkt_sendmsg(netisr_cpuport(mycpuid), &tp->tt_sndmore->lmsg);
1500 * Yield to other senders or receivers on the same netisr if the current
1501 * TCP stream has sent tcp_fairsend segments and is going to burst more
1502 * segments. Bursting large amount of segements in a single TCP stream
1503 * could delay other senders' segments and receivers' ACKs quite a lot,
1504 * if others segments and ACKs are queued on to the same hardware transmit
1505 * queue; thus cause unfairness between senders and suppress receiving
1508 * Fairsend should be performed at the places that do not affect segment
1509 * sending during congestion control, e.g.
1510 * - User requested output
1511 * - ACK input triggered output
1514 * For devices that are TSO capable, their TSO aggregation size limit could
1518 tcp_output_fair(struct tcpcb *tp)
1522 tp->t_flags |= TF_FAIRSEND;
1523 ret = tcp_output(tp);
1524 tp->t_flags &= ~TF_FAIRSEND;