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/*
 * INET		An implementation of the TCP/IP protocol suite for the LINUX
 *		operating system.  INET is implemented using the  BSD Socket
 *		interface as the means of communication with the user level.
 *
 *		Implementation of the Transmission Control Protocol(TCP).
 *
 * Version:	@(#)tcp.c	1.0.16	05/25/93
 *
 * Authors:	Ross Biro, <bir7@leland.Stanford.Edu>
 *		Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *		Mark Evans, <evansmp@uhura.aston.ac.uk>
 *		Corey Minyard <wf-rch!minyard@relay.EU.net>
 *		Florian La Roche, <flla@stud.uni-sb.de>
 *		Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
 *		Linus Torvalds, <torvalds@cs.helsinki.fi>
 *		Alan Cox, <gw4pts@gw4pts.ampr.org>
 *		Matthew Dillon, <dillon@apollo.west.oic.com>
 *		Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *		Jorge Cwik, <jorge@laser.satlink.net>
 *
 * Fixes:
 *
 *		Eric Schenk	: Fix retransmission timeout counting.
 */
 
#include <net/tcp.h>
 
void tcp_delack_timer(unsigned long data)
{
	tcp_send_ack((struct sock *) data);
}
 
/*
 *	Reset the retransmission timer
 */
 
void tcp_reset_xmit_timer(struct sock *sk, int why, unsigned long when)
{
	del_timer(&sk->retransmit_timer);
	sk->ip_xmit_timeout = why;
	if (why == TIME_WRITE) {
		/* In this case we want to timeout on the first packet
		 * in the resend queue. If the resend queue is empty,
		 * then the packet we are sending hasn't made it there yet,
		 * so we timeout from the current time.
		 */
		if (sk->send_head) {
			sk->retransmit_timer.expires =
				sk->send_head->when + when;
		} else {
			/* This should never happen!
		 	 */
			printk(KERN_ERR "Error: send_head NULL in xmit_timer\n");
			sk->ip_xmit_timeout = 0;
			return;
		}
	} else {
		sk->retransmit_timer.expires = jiffies+when;
	}
 
	if (sk->retransmit_timer.expires < jiffies) {
		/* We can get here if we reset the timer on an event
		 * that could not fire because the interrupts were disabled.
		 * make sure it happens soon.
		 */
		sk->retransmit_timer.expires = jiffies+2;
	}
	add_timer(&sk->retransmit_timer);
}
 
/*
 *	POLICY:
 *
 * 	This is the normal code called for timeouts.  It does the retransmission
 * 	and then does backoff.  tcp_do_retransmit is separated out because
 * 	tcp_ack needs to send stuff from the retransmit queue without
 * 	initiating a backoff.
 */
 
 
static void tcp_retransmit_time(struct sock *sk, int all)
{
	/*
	 * record how many times we've timed out.
	 * This determines when we should quite trying.
	 * This needs to be counted here, because we should not be
	 * counting one per packet we send, but rather one per round
	 * trip timeout.
	 */
	sk->retransmits++;
 
	tcp_do_retransmit(sk, all);
 
	/*
	 * Increase the timeout each time we retransmit.  Note that
	 * we do not increase the rtt estimate.  rto is initialized
	 * from rtt, but increases here.  Jacobson (SIGCOMM 88) suggests
	 * that doubling rto each time is the least we can get away with.
	 * In KA9Q, Karn uses this for the first few times, and then
	 * goes to quadratic.  netBSD doubles, but only goes up to *64,
	 * and clamps at 1 to 64 sec afterwards.  Note that 120 sec is
	 * defined in the protocol as the maximum possible RTT.  I guess
	 * we'll have to use something other than TCP to talk to the
	 * University of Mars.
	 *
	 * PAWS allows us longer timeouts and large windows, so once
	 * implemented ftp to mars will work nicely. We will have to fix
	 * the 120 second clamps though!
	 */
 
	sk->backoff++;
	sk->rto = min(sk->rto << 1, 120*HZ);
 
	/* be paranoid about the data structure... */
	if (sk->send_head)
		tcp_reset_xmit_timer(sk, TIME_WRITE, sk->rto);
	else
		/* This should never happen! */
		printk(KERN_ERR "send_head NULL in tcp_retransmit_time\n");
}
 
/*
 *	POLICY:
 *		Congestion control.
 *
 *	A timer event has trigger a tcp retransmit timeout. The
 *	socket xmit queue is ready and set up to send. Because
 *	the ack receive code keeps the queue straight we do
 *	nothing clever here.
 */
 
void tcp_retransmit(struct sock *sk, int all)
{
	if (all) 
	{
		tcp_retransmit_time(sk, all);
		return;
	}
 
	/* remember window where we lost */
	sk->ssthresh = min(sk->cong_window,
			(sk->window_seq-sk->rcv_ack_seq)/max(sk->mss,1)) >> 1;
	/* sk->ssthresh in theory can be zero.  I guess that's OK */
	sk->cong_count = 0;
	sk->cong_window = 1;
 
	/* Do the actual retransmit. */
	tcp_retransmit_time(sk, all);
}
 
/*
 *	A write timeout has occurred. Process the after effects. BROKEN (badly)
 */
 
static int tcp_write_timeout(struct sock *sk)
{
	/*
	 *	Look for a 'soft' timeout.
	 */
	if ((sk->state == TCP_ESTABLISHED && sk->retransmits && !(sk->retransmits & 7))
		|| (sk->state != TCP_ESTABLISHED && sk->retransmits > TCP_RETR1)) 
	{
		/*
		 *	Attempt to recover if arp has changed (unlikely!) or
		 *	a route has shifted (not supported prior to 1.3).
		 */
		ip_rt_advice(&sk->ip_route_cache, 0);
	}
 
	/*
	 *	Have we tried to SYN too many times (repent repent 8))
	 *	NOTE: we must be careful to do this test for both
	 *	the SYN_SENT and SYN_RECV states, otherwise we take
	 *	23 minutes to timeout on the SYN_RECV state, which
	 *	leaves us (more) open to denial of service attacks
	 *	than we would like.
	 */
 
	if (sk->retransmits > TCP_SYN_RETRIES
	&& (sk->state==TCP_SYN_SENT || sk->state==TCP_SYN_RECV))
	{
		if(sk->err_soft)
			sk->err=sk->err_soft;
		else
			sk->err=ETIMEDOUT;
		sk->error_report(sk);
		del_timer(&sk->retransmit_timer);
		tcp_statistics.TcpAttemptFails++;	/* Is this right ??? - FIXME - */
		tcp_set_state(sk,TCP_CLOSE);
		/* Don't FIN, we got nothing back */
		return 0;
	}
	/*
	 *	Has it gone just too far ?
	 */
	if (sk->retransmits > TCP_RETR2) 
	{
		if(sk->err_soft)
			sk->err = sk->err_soft;
		else
			sk->err = ETIMEDOUT;
		sk->error_report(sk);
		del_timer(&sk->retransmit_timer);
		/*
		 *	Time wait the socket 
		 */
		if (sk->state == TCP_FIN_WAIT1 || sk->state == TCP_FIN_WAIT2 || sk->state == TCP_CLOSING ) 
		{
			tcp_set_state(sk,TCP_TIME_WAIT);
			tcp_reset_msl_timer (sk, TIME_CLOSE, TCP_TIMEWAIT_LEN);
		}
		else
		{
			/*
			 *	Clean up time.
			 */
			tcp_set_state(sk, TCP_CLOSE);
			return 0;
		}
	}
	return 1;
}
 
/*
 *	It could be we got here because we needed to send an ack,
 *	so we need to check for that and not just normal retransmit.
 */
static void tcp_time_write_timeout(struct sock * sk)
{
	/*
	 *	Retransmission
	 */
	sk->prot->retransmit (sk, 0);
	tcp_write_timeout(sk);
}
 
 
/*
 *	The TCP retransmit timer. This lacks a few small details.
 *
 *	1. 	An initial rtt timeout on the probe0 should cause what we can
 *		of the first write queue buffer to be split and sent.
 *	2.	On a 'major timeout' as defined by RFC1122 we shouldn't report
 *		ETIMEDOUT if we know an additional 'soft' error caused this.
 *		tcp_err should save a 'soft error' for us.
 */
 
void tcp_retransmit_timer(unsigned long data)
{
	struct sock *sk = (struct sock*)data;
	int why = sk->ip_xmit_timeout;
 
	/*
	 *	We are reset. We will send no more retransmits.
	 */
 
	if(sk->zapped)
		return;
 
	/* 
	 *	Only process if socket is not in use
	 */
 
	if (sk->users) 
	{
		/* Try again in 1 second */
		sk->retransmit_timer.expires = jiffies+HZ;
		add_timer(&sk->retransmit_timer);
		return;
	}
 
	if (sk->ack_backlog && !sk->dead) 
		sk->data_ready(sk,0);
 
	/* Now we need to figure out why the socket was on the timer. */
 
	switch (why) 
	{
	/* Window probing */
	case TIME_PROBE0:
		tcp_send_probe0(sk);
		tcp_write_timeout(sk);
		break;
 
	/* Retransmitting */
	case TIME_WRITE:
		tcp_time_write_timeout(sk);
		break;
 
	/* Sending Keepalives */
	case TIME_KEEPOPEN:
		/* 
		 * this reset_timer() call is a hack, this is not
		 * how KEEPOPEN is supposed to work.
		 */
		tcp_reset_xmit_timer (sk, TIME_KEEPOPEN, TCP_TIMEOUT_LEN);
		/* Send something to keep the connection open. */
		if (sk->prot->write_wakeup)
			  sk->prot->write_wakeup (sk);
		sk->retransmits++;
		sk->prot->retransmits++;
		tcp_write_timeout(sk);
		break;
 
	default:
		printk (KERN_ERR "rexmit_timer: timer expired - reason unknown\n");
		break;
	}
}