* Copyright (c) 1982, 1986 Regents of the University of California.
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley. The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
* @(#)tcp_timer.c 7.14 (Berkeley) %G%
#include "../net/route.h"
int tcp_keepidle
= TCPTV_KEEP_IDLE
;
int tcp_keepintvl
= TCPTV_KEEPINTVL
;
* Fast timeout routine for processing delayed acks
register struct inpcb
*inp
;
register struct tcpcb
*tp
;
for (; inp
!= &tcb
; inp
= inp
->inp_next
)
if ((tp
= (struct tcpcb
*)inp
->inp_ppcb
) &&
(tp
->t_flags
& TF_DELACK
)) {
tp
->t_flags
&= ~TF_DELACK
;
tp
->t_flags
|= TF_ACKNOW
;
* Tcp protocol timeout routine called every 500 ms.
* Updates the timers in all active tcb's and
* causes finite state machine actions if timers expire.
register struct inpcb
*ip
, *ipnxt
;
register struct tcpcb
*tp
;
tcp_maxidle
= TCPTV_KEEPCNT
* tcp_keepintvl
;
* Search through tcb's and update active timers.
for (; ip
!= &tcb
; ip
= ipnxt
) {
for (i
= 0; i
< TCPT_NTIMERS
; i
++) {
if (tp
->t_timer
[i
] && --tp
->t_timer
[i
] == 0) {
(void) tcp_usrreq(tp
->t_inpcb
->inp_socket
,
PRU_SLOWTIMO
, (struct mbuf
*)0,
(struct mbuf
*)i
, (struct mbuf
*)0);
if (ipnxt
->inp_prev
!= ip
)
tcp_iss
+= TCP_ISSINCR
/PR_SLOWHZ
; /* increment iss */
* Cancel all timers for TCP tp.
for (i
= 0; i
< TCPT_NTIMERS
; i
++)
int tcp_backoff
[TCP_MAXRXTSHIFT
+ 1] =
{ 1, 2, 4, 8, 16, 32, 64, 64, 64, 64, 64, 64, 64 };
register struct tcpcb
*tp
;
* 2 MSL timeout in shutdown went off. If we're closed but
* still waiting for peer to close and connection has been idle
* too long, or if 2MSL time is up from TIME_WAIT, delete connection
* control block. Otherwise, check again in a bit.
if (tp
->t_state
!= TCPS_TIME_WAIT
&&
tp
->t_idle
<= tcp_maxidle
)
tp
->t_timer
[TCPT_2MSL
] = tcp_keepintvl
;
* Retransmission timer went off. Message has not
* been acked within retransmit interval. Back off
* to a longer retransmit interval and retransmit one segment.
if (++tp
->t_rxtshift
> TCP_MAXRXTSHIFT
) {
tp
->t_rxtshift
= TCP_MAXRXTSHIFT
;
tcpstat
.tcps_timeoutdrop
++;
tp
= tcp_drop(tp
, ETIMEDOUT
);
tcpstat
.tcps_rexmttimeo
++;
rexmt
= ((tp
->t_srtt
>> 2) + tp
->t_rttvar
) >> 1;
rexmt
*= tcp_backoff
[tp
->t_rxtshift
];
TCPT_RANGESET(tp
->t_rxtcur
, rexmt
, TCPTV_MIN
, TCPTV_REXMTMAX
);
tp
->t_timer
[TCPT_REXMT
] = tp
->t_rxtcur
;
* If losing, let the lower level know and try for
* a better route. Also, if we backed off this far,
* our srtt estimate is probably bogus. Clobber it
* so we'll take the next rtt measurement as our srtt;
* move the current srtt into rttvar to keep the current
* retransmit times until then.
if (tp
->t_rxtshift
> TCP_MAXRXTSHIFT
/ 4) {
tp
->t_rttvar
+= (tp
->t_srtt
>> 2);
tp
->snd_nxt
= tp
->snd_una
;
* If timing a segment in this window, stop the timer.
* Close the congestion window down to one segment
* (we'll open it by one segment for each ack we get).
* Since we probably have a window's worth of unacked
* data accumulated, this "slow start" keeps us from
* dumping all that data as back-to-back packets (which
* might overwhelm an intermediate gateway).
* There are two phases to the opening: Initially we
* open by one mss on each ack. This makes the window
* size increase exponentially with time. If the
* window is larger than the path can handle, this
* exponential growth results in dropped packet(s)
* almost immediately. To get more time between
* drops but still "push" the network to take advantage
* of improving conditions, we switch from exponential
* to linear window opening at some threshhold size.
* For a threshhold, we use half the current window
* size, truncated to a multiple of the mss.
* (the minimum cwnd that will give us exponential
* growth is 2 mss. We don't allow the threshhold
u_int win
= MIN(tp
->snd_wnd
, tp
->snd_cwnd
) / 2 / tp
->t_maxseg
;
tp
->snd_cwnd
= tp
->t_maxseg
;
tp
->snd_ssthresh
= win
* tp
->t_maxseg
;
* Persistance timer into zero window.
* Force a byte to be output, if possible.
tcpstat
.tcps_persisttimeo
++;
* Keep-alive timer went off; send something
* or drop connection if idle for too long.
tcpstat
.tcps_keeptimeo
++;
if (tp
->t_state
< TCPS_ESTABLISHED
)
if (tp
->t_inpcb
->inp_socket
->so_options
& SO_KEEPALIVE
&&
tp
->t_state
<= TCPS_CLOSE_WAIT
) {
if (tp
->t_idle
>= tcp_keepidle
+ tcp_maxidle
)
* Send a packet designed to force a response
* if the peer is up and reachable:
* either an ACK if the connection is still alive,
* or an RST if the peer has closed the connection
* due to timeout or reboot.
* Using sequence number tp->snd_una-1
* causes the transmitted zero-length segment
* to lie outside the receive window;
* by the protocol spec, this requires the
* correspondent TCP to respond.
tcpstat
.tcps_keepprobe
++;
* The keepalive packet must have nonzero length
* to get a 4.2 host to respond.
tcp_respond(tp
, tp
->t_template
,
tp
->rcv_nxt
- 1, tp
->snd_una
- 1, 0);
tcp_respond(tp
, tp
->t_template
,
tp
->rcv_nxt
, tp
->snd_una
- 1, 0);
tp
->t_timer
[TCPT_KEEP
] = tcp_keepintvl
;
tp
->t_timer
[TCPT_KEEP
] = tcp_keepidle
;
tcpstat
.tcps_keepdrops
++;
tp
= tcp_drop(tp
, ETIMEDOUT
);