2 * Copyright (c) 2004 Jeffrey M. Hsu. All rights reserved.
3 * Copyright (c) 2004 The DragonFly Project. All rights reserved.
5 * This code is derived from software contributed to The DragonFly Project
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 * 3. Neither the name of The DragonFly Project nor the names of its
17 * contributors may be used to endorse or promote products derived
18 * from this software without specific, prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
24 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
26 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
27 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
30 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
36 * The Regents of the University of California. All rights reserved.
38 * Redistribution and use in source and binary forms, with or without
39 * modification, are permitted provided that the following conditions
41 * 1. Redistributions of source code must retain the above copyright
42 * notice, this list of conditions and the following disclaimer.
43 * 2. Redistributions in binary form must reproduce the above copyright
44 * notice, this list of conditions and the following disclaimer in the
45 * documentation and/or other materials provided with the distribution.
46 * 3. Neither the name of the University nor the names of its contributors
47 * may be used to endorse or promote products derived from this software
48 * without specific prior written permission.
50 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
51 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
52 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
53 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
54 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
55 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
56 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
57 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
58 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
59 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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_copym(so
->so_snd
.ssb_mb
, off
,
915 (int) len
, M_NOWAIT
);
916 if (m
->m_next
== NULL
) {
925 * If we're sending everything we've got, set PUSH.
926 * (This will keep happy those implementations which only
927 * give data to the user when a buffer fills or
930 if (off
+ len
== so
->so_snd
.ssb_cc
)
933 if (tp
->t_flags
& TF_ACKNOW
)
934 tcpstat
.tcps_sndacks
++;
935 else if (flags
& (TH_SYN
| TH_FIN
| TH_RST
))
936 tcpstat
.tcps_sndctrl
++;
937 else if (SEQ_GT(tp
->snd_up
, tp
->snd_una
))
938 tcpstat
.tcps_sndurg
++;
940 tcpstat
.tcps_sndwinup
++;
942 MGETHDR(m
, M_NOWAIT
, MT_HEADER
);
948 (hdrlen
+ max_linkhdr
> MHLEN
) && hdrlen
<= MHLEN
)
951 m
->m_data
+= max_linkhdr
;
955 * Prioritize SYN, SYN|ACK and pure ACK.
956 * Leave FIN and RST as they are.
958 if (tcp_prio_synack
&& (flags
& (TH_FIN
| TH_RST
)) == 0)
959 m
->m_flags
|= M_PRIO
;
961 m
->m_pkthdr
.rcvif
= NULL
;
963 ip6
= mtod(m
, struct ip6_hdr
*);
964 th
= (struct tcphdr
*)(ip6
+ 1);
965 tcp_fillheaders(tp
, ip6
, th
, use_tso
);
967 ip
= mtod(m
, struct ip
*);
968 th
= (struct tcphdr
*)(ip
+ 1);
969 /* this picks up the pseudo header (w/o the length) */
970 tcp_fillheaders(tp
, ip
, th
, use_tso
);
974 * Fill in fields, remembering maximum advertised
975 * window for use in delaying messages about window sizes.
976 * If resending a FIN, be sure not to use a new sequence number.
978 if (flags
& TH_FIN
&& tp
->t_flags
& TF_SENTFIN
&&
979 tp
->snd_nxt
== tp
->snd_max
)
984 * If we are doing retransmissions, then snd_nxt will
985 * not reflect the first unsent octet. For ACK only
986 * packets, we do not want the sequence number of the
987 * retransmitted packet, we want the sequence number
988 * of the next unsent octet. So, if there is no data
989 * (and no SYN or FIN), use snd_max instead of snd_nxt
990 * when filling in ti_seq. But if we are in persist
991 * state, snd_max might reflect one byte beyond the
992 * right edge of the window, so use snd_nxt in that
993 * case, since we know we aren't doing a retransmission.
994 * (retransmit and persist are mutually exclusive...)
996 if (len
|| (flags
& (TH_SYN
|TH_FIN
)) ||
997 tcp_callout_active(tp
, tp
->tt_persist
))
998 th
->th_seq
= htonl(tp
->snd_nxt
);
1000 th
->th_seq
= htonl(tp
->snd_max
);
1001 th
->th_ack
= htonl(tp
->rcv_nxt
);
1003 bcopy(opt
, th
+ 1, optlen
);
1004 th
->th_off
= (sizeof(struct tcphdr
) + optlen
) >> 2;
1006 th
->th_flags
= flags
;
1010 * Calculate receive window. Don't shrink window, but avoid
1011 * silly window syndrome by sending a 0 window if the actual
1012 * window is less then one segment.
1014 if (recvwin
< (long)(so
->so_rcv
.ssb_hiwat
/ 4) &&
1015 recvwin
< (long)segsz
)
1017 if (recvwin
< (tcp_seq_diff_t
)(tp
->rcv_adv
- tp
->rcv_nxt
))
1018 recvwin
= (tcp_seq_diff_t
)(tp
->rcv_adv
- tp
->rcv_nxt
);
1019 if (recvwin
> (long)TCP_MAXWIN
<< tp
->rcv_scale
)
1020 recvwin
= (long)TCP_MAXWIN
<< tp
->rcv_scale
;
1023 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1024 * a 0 window. This may cause the remote transmitter to stall. This
1025 * flag tells soreceive() to disable delayed acknowledgements when
1026 * draining the buffer. This can occur if the receiver is attempting
1027 * to read more data then can be buffered prior to transmitting on
1031 tp
->t_flags
|= TF_RXWIN0SENT
;
1033 tp
->t_flags
&= ~TF_RXWIN0SENT
;
1036 th
->th_win
= htons((u_short
) (recvwin
>>tp
->rcv_scale
));
1038 if (SEQ_GT(tp
->snd_up
, tp
->snd_nxt
)) {
1039 KASSERT(!use_tso
, ("URG with TSO"));
1041 th
->th_urp
= htons((u_short
)(tp
->snd_up
- tp
->snd_nxt
));
1042 th
->th_flags
|= TH_URG
;
1046 * If no urgent pointer to send, then we pull
1047 * the urgent pointer to the left edge of the send window
1048 * so that it doesn't drift into the send window on sequence
1049 * number wraparound.
1051 tp
->snd_up
= tp
->snd_una
; /* drag it along */
1055 #ifdef TCP_SIGNATURE
1056 if (tp
->t_flags
& TF_SIGNATURE
) {
1057 tcpsignature_compute(m
, len
, optlen
,
1058 (u_char
*)(th
+ 1) + sigoff
, IPSEC_DIR_OUTBOUND
);
1060 #endif /* TCP_SIGNATURE */
1063 * Put TCP length in extended header, and then
1064 * checksum extended header and data.
1066 m
->m_pkthdr
.len
= hdrlen
+ len
; /* in6_cksum() need this */
1069 * ip6_plen is not need to be filled now, and will be
1070 * filled in ip6_output().
1072 th
->th_sum
= in6_cksum(m
, IPPROTO_TCP
,
1073 sizeof(struct ip6_hdr
),
1074 sizeof(struct tcphdr
) + optlen
+ len
);
1076 m
->m_pkthdr
.csum_thlen
= sizeof(struct tcphdr
) + optlen
;
1078 m
->m_pkthdr
.csum_flags
= CSUM_TSO
;
1079 m
->m_pkthdr
.tso_segsz
= segsz
;
1081 m
->m_pkthdr
.csum_flags
= CSUM_TCP
;
1082 m
->m_pkthdr
.csum_data
=
1083 offsetof(struct tcphdr
, th_sum
);
1085 th
->th_sum
= in_addword(th
->th_sum
,
1086 htons((u_short
)(optlen
+ len
)));
1091 * IP version must be set here for ipv4/ipv6 checking
1094 KASSERT(ip
->ip_v
== IPVERSION
,
1095 ("%s: IP version incorrect: %d",
1096 __func__
, ip
->ip_v
));
1101 * In transmit state, time the transmission and arrange for
1102 * the retransmit. In persist state, just set snd_max.
1104 if (!(tp
->t_flags
& TF_FORCE
) ||
1105 !tcp_callout_active(tp
, tp
->tt_persist
)) {
1106 tcp_seq startseq
= tp
->snd_nxt
;
1109 * Advance snd_nxt over sequence space of this segment.
1111 if (flags
& (TH_SYN
| TH_FIN
)) {
1114 if (flags
& TH_FIN
) {
1116 tp
->t_flags
|= TF_SENTFIN
;
1120 if (SEQ_GT(tp
->snd_nxt
, tp
->snd_max
)) {
1121 tp
->snd_max
= tp
->snd_nxt
;
1123 * Time this transmission if not a retransmission and
1124 * not currently timing anything.
1126 if (tp
->t_rtttime
== 0) {
1127 tp
->t_rtttime
= ticks
;
1128 tp
->t_rtseq
= startseq
;
1129 tcpstat
.tcps_segstimed
++;
1134 * Set retransmit timer if not currently set,
1135 * and not doing a pure ack or a keep-alive probe.
1136 * Initial value for retransmit timer is smoothed
1137 * round-trip time + 2 * round-trip time variance.
1138 * Initialize shift counter which is used for backoff
1139 * of retransmit time.
1141 if (!tcp_callout_active(tp
, tp
->tt_rexmt
) &&
1142 tp
->snd_nxt
!= tp
->snd_una
) {
1143 if (tcp_callout_active(tp
, tp
->tt_persist
)) {
1144 tcp_callout_stop(tp
, tp
->tt_persist
);
1147 tcp_callout_reset(tp
, tp
->tt_rexmt
, tp
->t_rxtcur
,
1149 } else if (len
== 0 && so
->so_snd
.ssb_cc
&&
1150 tp
->t_state
> TCPS_SYN_RECEIVED
&&
1151 !tcp_callout_active(tp
, tp
->tt_rexmt
) &&
1152 !tcp_callout_active(tp
, tp
->tt_persist
)) {
1154 * Avoid a situation where we do not set persist timer
1155 * after a zero window condition. For example:
1156 * 1) A -> B: packet with enough data to fill the window
1157 * 2) B -> A: ACK for #1 + new data (0 window
1159 * 3) A -> B: ACK for #2, 0 len packet
1161 * In this case, A will not activate the persist timer,
1162 * because it chose to send a packet. Unless tcp_output
1163 * is called for some other reason (delayed ack timer,
1164 * another input packet from B, socket syscall), A will
1165 * not send zero window probes.
1167 * So, if you send a 0-length packet, but there is data
1168 * in the socket buffer, and neither the rexmt or
1169 * persist timer is already set, then activate the
1177 * Persist case, update snd_max but since we are in
1178 * persist mode (no window) we do not update snd_nxt.
1182 panic("tcp_output: persist timer to send SYN");
1183 if (flags
& TH_FIN
) {
1185 tp
->t_flags
|= TF_SENTFIN
;
1187 if (SEQ_GT(tp
->snd_nxt
+ xlen
, tp
->snd_max
))
1188 tp
->snd_max
= tp
->snd_nxt
+ xlen
;
1194 if (so
->so_options
& SO_DEBUG
) {
1195 tcp_trace(TA_OUTPUT
, tp
->t_state
, tp
,
1196 mtod(m
, void *), th
, 0);
1201 * Fill in IP length and desired time to live and
1202 * send to IP level. There should be a better way
1203 * to handle ttl and tos; we could keep them in
1204 * the template, but need a way to checksum without them.
1207 * m->m_pkthdr.len should have been set before cksum
1208 * calcuration, because in6_cksum() need it.
1212 * we separately set hoplimit for every segment,
1213 * since the user might want to change the value
1214 * via setsockopt. Also, desired default hop
1215 * limit might be changed via Neighbor Discovery.
1217 ip6
->ip6_hlim
= in6_selecthlim(inp
,
1218 (inp
->in6p_route
.ro_rt
?
1219 inp
->in6p_route
.ro_rt
->rt_ifp
: NULL
));
1221 /* TODO: IPv6 IP6TOS_ECT bit on */
1222 error
= ip6_output(m
, inp
->in6p_outputopts
,
1223 &inp
->in6p_route
, (so
->so_options
& SO_DONTROUTE
),
1228 KASSERT(!INP_CHECK_SOCKAF(so
, AF_INET6
), ("inet6 pcb"));
1230 ip
->ip_len
= htons(m
->m_pkthdr
.len
);
1231 ip
->ip_ttl
= inp
->inp_ip_ttl
; /* XXX */
1232 ip
->ip_tos
= inp
->inp_ip_tos
; /* XXX */
1234 * See if we should do MTU discovery.
1235 * We do it only if the following are true:
1236 * 1) we have a valid route to the destination
1237 * 2) the MTU is not locked (if it is,
1238 * then discovery has been disabled)
1240 if (path_mtu_discovery
&&
1241 (rt
= inp
->inp_route
.ro_rt
) &&
1242 (rt
->rt_flags
& RTF_UP
) &&
1243 !(rt
->rt_rmx
.rmx_locks
& RTV_MTU
))
1245 ip
->ip_off
|= htons(IP_DF
);
1248 KASSERT(inp
->inp_flags
& INP_HASH
,
1249 ("inpcb has no hash"));
1250 m_sethash(m
, inp
->inp_hashval
);
1251 error
= ip_output(m
, inp
->inp_options
, &inp
->inp_route
,
1252 (so
->so_options
& SO_DONTROUTE
) |
1253 IP_DEBUGROUTE
, NULL
, inp
);
1256 KASSERT(error
!= 0, ("no error, but th not set"));
1259 tp
->t_flags
&= ~(TF_ACKNOW
| TF_XMITNOW
);
1262 * We know that the packet was lost, so back out the
1263 * sequence number advance, if any.
1265 if (!(tp
->t_flags
& TF_FORCE
) ||
1266 !tcp_callout_active(tp
, tp
->tt_persist
)) {
1268 * No need to check for TH_FIN here because
1269 * the TF_SENTFIN flag handles that case.
1271 if (!(flags
& TH_SYN
))
1276 if (error
== ENOBUFS
) {
1277 KASSERT((len
== 0 && (flags
& (TH_SYN
| TH_FIN
)) == 0) ||
1278 tcp_callout_active(tp
, tp
->tt_rexmt
) ||
1279 tcp_callout_active(tp
, tp
->tt_persist
),
1280 ("neither rexmt nor persist timer is set"));
1283 if (error
== EMSGSIZE
) {
1285 * ip_output() will have already fixed the route
1286 * for us. tcp_mtudisc() will, as its last action,
1287 * initiate retransmission, so it is important to
1290 tcp_mtudisc(inp
, 0);
1293 if ((error
== EHOSTUNREACH
|| error
== ENETDOWN
) &&
1294 TCPS_HAVERCVDSYN(tp
->t_state
)) {
1295 tp
->t_softerror
= error
;
1300 tcpstat
.tcps_sndtotal
++;
1303 * Data sent (as far as we can tell).
1305 * If this advertises a larger window than any other segment,
1306 * then remember the size of the advertised window.
1308 * Any pending ACK has now been sent.
1310 if (recvwin
> 0 && SEQ_GT(tp
->rcv_nxt
+ recvwin
, tp
->rcv_adv
)) {
1311 tp
->rcv_adv
= tp
->rcv_nxt
+ recvwin
;
1312 tp
->t_flags
&= ~TF_RXRESIZED
;
1314 tp
->last_ack_sent
= tp
->rcv_nxt
;
1315 tp
->t_flags
&= ~(TF_ACKNOW
| TF_XMITNOW
);
1316 if (tcp_delack_enabled
)
1317 tcp_callout_stop(tp
, tp
->tt_delack
);
1319 if (tcp_fairsend
> 0 && (tp
->t_flags
& TF_FAIRSEND
) &&
1320 segcnt
>= tcp_fairsend
)
1328 tcp_setpersist(struct tcpcb
*tp
)
1330 int t
= ((tp
->t_srtt
>> 2) + tp
->t_rttvar
) >> 1;
1333 if (tp
->t_state
== TCPS_SYN_SENT
||
1334 tp
->t_state
== TCPS_SYN_RECEIVED
) {
1335 panic("tcp_setpersist: not established yet, current %s",
1336 tp
->t_state
== TCPS_SYN_SENT
?
1337 "SYN_SENT" : "SYN_RECEIVED");
1340 if (tcp_callout_active(tp
, tp
->tt_rexmt
))
1341 panic("tcp_setpersist: retransmit pending");
1343 * Start/restart persistance timer.
1345 TCPT_RANGESET(tt
, t
* tcp_backoff
[tp
->t_rxtshift
], TCPTV_PERSMIN
,
1347 tcp_callout_reset(tp
, tp
->tt_persist
, tt
, tcp_timer_persist
);
1348 if (tp
->t_rxtshift
< TCP_MAXRXTSHIFT
)
1353 tcp_idle_cwnd_validate(struct tcpcb
*tp
)
1355 u_long initial_cwnd
= tcp_initial_window(tp
);
1358 tcpstat
.tcps_sndidle
++;
1360 /* According to RFC5681: RW=min(IW,cwnd) */
1361 min_cwnd
= min(tp
->snd_cwnd
, initial_cwnd
);
1364 u_long idle_time
, decay_cwnd
;
1367 * RFC2861, but only after idle period.
1371 * Before the congestion window is reduced, ssthresh
1372 * is set to the maximum of its current value and 3/4
1373 * cwnd. If the sender then has more data to send
1374 * than the decayed cwnd allows, the TCP will slow-
1375 * start (perform exponential increase) at least
1376 * half-way back up to the old value of cwnd.
1378 tp
->snd_ssthresh
= max(tp
->snd_ssthresh
,
1379 (3 * tp
->snd_cwnd
) / 4);
1382 * Decay the congestion window by half for every RTT
1383 * that the flow remains inactive.
1385 * The difference between our implementation and
1386 * RFC2861 is that we don't allow cwnd to go below
1387 * the value allowed by RFC5681 (min_cwnd).
1389 idle_time
= ticks
- tp
->snd_last
;
1390 decay_cwnd
= tp
->snd_cwnd
;
1391 while (idle_time
>= tp
->t_rxtcur
&&
1392 decay_cwnd
> min_cwnd
) {
1394 idle_time
-= tp
->t_rxtcur
;
1396 tp
->snd_cwnd
= max(decay_cwnd
, min_cwnd
);
1399 * Slow-start from scratch to re-determine the send
1400 * congestion window.
1402 tp
->snd_cwnd
= min_cwnd
;
1405 /* Restart ABC counting during congestion avoidance */
1410 tcp_tso_getsize(struct tcpcb
*tp
, u_int
*segsz
, u_int
*hlen0
)
1412 struct inpcb
* const inp
= tp
->t_inpcb
;
1414 const boolean_t isipv6
= INP_ISIPV6(inp
);
1416 const boolean_t isipv6
= FALSE
;
1418 unsigned int ipoptlen
, optlen
;
1421 hlen
= sizeof(struct ip
) + sizeof(struct tcphdr
);
1424 ipoptlen
= ip6_optlen(inp
);
1426 if (inp
->inp_options
) {
1427 ipoptlen
= inp
->inp_options
->m_len
-
1428 offsetof(struct ipoption
, ipopt_list
);
1436 if ((tp
->t_flags
& (TF_REQ_TSTMP
| TF_NOOPT
)) == TF_REQ_TSTMP
&&
1437 (tp
->t_flags
& TF_RCVD_TSTMP
))
1438 optlen
+= TCPOLEN_TSTAMP_APPA
;
1441 if (tp
->t_maxopd
<= optlen
+ ipoptlen
)
1442 return EHOSTUNREACH
;
1444 *segsz
= tp
->t_maxopd
- optlen
- ipoptlen
;
1450 tcp_output_sched_handler(netmsg_t nmsg
)
1452 struct tcpcb
*tp
= nmsg
->lmsg
.u
.ms_resultp
;
1456 lwkt_replymsg(&nmsg
->lmsg
, 0);
1459 tcp_output_fair(tp
);
1463 tcp_output_init(struct tcpcb
*tp
)
1465 netmsg_init(tp
->tt_sndmore
, NULL
, &netisr_adone_rport
, MSGF_DROPABLE
,
1466 tcp_output_sched_handler
);
1467 tp
->tt_sndmore
->lmsg
.u
.ms_resultp
= tp
;
1471 tcp_output_cancel(struct tcpcb
*tp
)
1474 * This message is still pending to be processed;
1475 * drop it. Optimized.
1478 if ((tp
->tt_sndmore
->lmsg
.ms_flags
& MSGF_DONE
) == 0) {
1479 lwkt_dropmsg(&tp
->tt_sndmore
->lmsg
);
1485 tcp_output_pending(struct tcpcb
*tp
)
1487 if ((tp
->tt_sndmore
->lmsg
.ms_flags
& MSGF_DONE
) == 0)
1494 tcp_output_sched(struct tcpcb
*tp
)
1497 if (tp
->tt_sndmore
->lmsg
.ms_flags
& MSGF_DONE
)
1498 lwkt_sendmsg(netisr_cpuport(mycpuid
), &tp
->tt_sndmore
->lmsg
);
1505 * Yield to other senders or receivers on the same netisr if the current
1506 * TCP stream has sent tcp_fairsend segments and is going to burst more
1507 * segments. Bursting large amount of segements in a single TCP stream
1508 * could delay other senders' segments and receivers' ACKs quite a lot,
1509 * if others segments and ACKs are queued on to the same hardware transmit
1510 * queue; thus cause unfairness between senders and suppress receiving
1513 * Fairsend should be performed at the places that do not affect segment
1514 * sending during congestion control, e.g.
1515 * - User requested output
1516 * - ACK input triggered output
1519 * For devices that are TSO capable, their TSO aggregation size limit could
1523 tcp_output_fair(struct tcpcb
*tp
)
1527 tp
->t_flags
|= TF_FAIRSEND
;
1528 ret
= tcp_output(tp
);
1529 tp
->t_flags
&= ~TF_FAIRSEND
;