tcp_input.c 122.5 KB
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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:	$Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
 *
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 * Authors:	Ross Biro
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 *		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>
 */

/*
 * Changes:
 *		Pedro Roque	:	Fast Retransmit/Recovery.
 *					Two receive queues.
 *					Retransmit queue handled by TCP.
 *					Better retransmit timer handling.
 *					New congestion avoidance.
 *					Header prediction.
 *					Variable renaming.
 *
 *		Eric		:	Fast Retransmit.
 *		Randy Scott	:	MSS option defines.
 *		Eric Schenk	:	Fixes to slow start algorithm.
 *		Eric Schenk	:	Yet another double ACK bug.
 *		Eric Schenk	:	Delayed ACK bug fixes.
 *		Eric Schenk	:	Floyd style fast retrans war avoidance.
 *		David S. Miller	:	Don't allow zero congestion window.
 *		Eric Schenk	:	Fix retransmitter so that it sends
 *					next packet on ack of previous packet.
 *		Andi Kleen	:	Moved open_request checking here
 *					and process RSTs for open_requests.
 *		Andi Kleen	:	Better prune_queue, and other fixes.
 *		Andrey Savochkin:	Fix RTT measurements in the presnce of
 *					timestamps.
 *		Andrey Savochkin:	Check sequence numbers correctly when
 *					removing SACKs due to in sequence incoming
 *					data segments.
 *		Andi Kleen:		Make sure we never ack data there is not
 *					enough room for. Also make this condition
 *					a fatal error if it might still happen.
 *		Andi Kleen:		Add tcp_measure_rcv_mss to make 
 *					connections with MSS<min(MTU,ann. MSS)
 *					work without delayed acks. 
 *		Andi Kleen:		Process packets with PSH set in the
 *					fast path.
 *		J Hadi Salim:		ECN support
 *	 	Andrei Gurtov,
 *		Pasi Sarolahti,
 *		Panu Kuhlberg:		Experimental audit of TCP (re)transmission
 *					engine. Lots of bugs are found.
 *		Pasi Sarolahti:		F-RTO for dealing with spurious RTOs
 */

#include <linux/config.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/sysctl.h>
#include <net/tcp.h>
#include <net/inet_common.h>
#include <linux/ipsec.h>
#include <asm/unaligned.h>

int sysctl_tcp_timestamps = 1;
int sysctl_tcp_window_scaling = 1;
int sysctl_tcp_sack = 1;
int sysctl_tcp_fack = 1;
int sysctl_tcp_reordering = TCP_FASTRETRANS_THRESH;
int sysctl_tcp_ecn;
int sysctl_tcp_dsack = 1;
int sysctl_tcp_app_win = 31;
int sysctl_tcp_adv_win_scale = 2;

int sysctl_tcp_stdurg;
int sysctl_tcp_rfc1337;
int sysctl_tcp_max_orphans = NR_FILE;
int sysctl_tcp_frto;
int sysctl_tcp_nometrics_save;

int sysctl_tcp_moderate_rcvbuf = 1;

#define FLAG_DATA		0x01 /* Incoming frame contained data.		*/
#define FLAG_WIN_UPDATE		0x02 /* Incoming ACK was a window update.	*/
#define FLAG_DATA_ACKED		0x04 /* This ACK acknowledged new data.		*/
#define FLAG_RETRANS_DATA_ACKED	0x08 /* "" "" some of which was retransmitted.	*/
#define FLAG_SYN_ACKED		0x10 /* This ACK acknowledged SYN.		*/
#define FLAG_DATA_SACKED	0x20 /* New SACK.				*/
#define FLAG_ECE		0x40 /* ECE in this ACK				*/
#define FLAG_DATA_LOST		0x80 /* SACK detected data lossage.		*/
#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/

#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
#define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
#define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)

#define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
#define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
#define IsDSack(tp) ((tp)->rx_opt.sack_ok & 4)

#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)

/* Adapt the MSS value used to make delayed ack decision to the 
 * real world.
 */ 
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static inline void tcp_measure_rcv_mss(struct sock *sk,
				       const struct sk_buff *skb)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
	const unsigned int lss = icsk->icsk_ack.last_seg_size; 
	unsigned int len;
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	icsk->icsk_ack.last_seg_size = 0; 
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	/* skb->len may jitter because of SACKs, even if peer
	 * sends good full-sized frames.
	 */
	len = skb->len;
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	if (len >= icsk->icsk_ack.rcv_mss) {
		icsk->icsk_ack.rcv_mss = len;
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	} else {
		/* Otherwise, we make more careful check taking into account,
		 * that SACKs block is variable.
		 *
		 * "len" is invariant segment length, including TCP header.
		 */
		len += skb->data - skb->h.raw;
		if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
		    /* If PSH is not set, packet should be
		     * full sized, provided peer TCP is not badly broken.
		     * This observation (if it is correct 8)) allows
		     * to handle super-low mtu links fairly.
		     */
		    (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
		     !(tcp_flag_word(skb->h.th)&TCP_REMNANT))) {
			/* Subtract also invariant (if peer is RFC compliant),
			 * tcp header plus fixed timestamp option length.
			 * Resulting "len" is MSS free of SACK jitter.
			 */
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			len -= tcp_sk(sk)->tcp_header_len;
			icsk->icsk_ack.last_seg_size = len;
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			if (len == lss) {
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				icsk->icsk_ack.rcv_mss = len;
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				return;
			}
		}
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		icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
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	}
}

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static void tcp_incr_quickack(struct sock *sk)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
	unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
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	if (quickacks==0)
		quickacks=2;
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	if (quickacks > icsk->icsk_ack.quick)
		icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
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}

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void tcp_enter_quickack_mode(struct sock *sk)
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{
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	struct inet_connection_sock *icsk = inet_csk(sk);
	tcp_incr_quickack(sk);
	icsk->icsk_ack.pingpong = 0;
	icsk->icsk_ack.ato = TCP_ATO_MIN;
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}

/* Send ACKs quickly, if "quick" count is not exhausted
 * and the session is not interactive.
 */

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static inline int tcp_in_quickack_mode(const struct sock *sk)
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{
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	const struct inet_connection_sock *icsk = inet_csk(sk);
	return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
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}

/* Buffer size and advertised window tuning.
 *
 * 1. Tuning sk->sk_sndbuf, when connection enters established state.
 */

static void tcp_fixup_sndbuf(struct sock *sk)
{
	int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
		     sizeof(struct sk_buff);

	if (sk->sk_sndbuf < 3 * sndmem)
		sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
}

/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
 *
 * All tcp_full_space() is split to two parts: "network" buffer, allocated
 * forward and advertised in receiver window (tp->rcv_wnd) and
 * "application buffer", required to isolate scheduling/application
 * latencies from network.
 * window_clamp is maximal advertised window. It can be less than
 * tcp_full_space(), in this case tcp_full_space() - window_clamp
 * is reserved for "application" buffer. The less window_clamp is
 * the smoother our behaviour from viewpoint of network, but the lower
 * throughput and the higher sensitivity of the connection to losses. 8)
 *
 * rcv_ssthresh is more strict window_clamp used at "slow start"
 * phase to predict further behaviour of this connection.
 * It is used for two goals:
 * - to enforce header prediction at sender, even when application
 *   requires some significant "application buffer". It is check #1.
 * - to prevent pruning of receive queue because of misprediction
 *   of receiver window. Check #2.
 *
 * The scheme does not work when sender sends good segments opening
 * window and then starts to feed us spagetti. But it should work
 * in common situations. Otherwise, we have to rely on queue collapsing.
 */

/* Slow part of check#2. */
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static int __tcp_grow_window(const struct sock *sk, struct tcp_sock *tp,
			     const struct sk_buff *skb)
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{
	/* Optimize this! */
	int truesize = tcp_win_from_space(skb->truesize)/2;
	int window = tcp_full_space(sk)/2;

	while (tp->rcv_ssthresh <= window) {
		if (truesize <= skb->len)
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			return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
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		truesize >>= 1;
		window >>= 1;
	}
	return 0;
}

static inline void tcp_grow_window(struct sock *sk, struct tcp_sock *tp,
				   struct sk_buff *skb)
{
	/* Check #1 */
	if (tp->rcv_ssthresh < tp->window_clamp &&
	    (int)tp->rcv_ssthresh < tcp_space(sk) &&
	    !tcp_memory_pressure) {
		int incr;

		/* Check #2. Increase window, if skb with such overhead
		 * will fit to rcvbuf in future.
		 */
		if (tcp_win_from_space(skb->truesize) <= skb->len)
			incr = 2*tp->advmss;
		else
			incr = __tcp_grow_window(sk, tp, skb);

		if (incr) {
			tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr, tp->window_clamp);
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			inet_csk(sk)->icsk_ack.quick |= 1;
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		}
	}
}

/* 3. Tuning rcvbuf, when connection enters established state. */

static void tcp_fixup_rcvbuf(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);

	/* Try to select rcvbuf so that 4 mss-sized segments
	 * will fit to window and correspoding skbs will fit to our rcvbuf.
	 * (was 3; 4 is minimum to allow fast retransmit to work.)
	 */
	while (tcp_win_from_space(rcvmem) < tp->advmss)
		rcvmem += 128;
	if (sk->sk_rcvbuf < 4 * rcvmem)
		sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
}

/* 4. Try to fixup all. It is made iimediately after connection enters
 *    established state.
 */
static void tcp_init_buffer_space(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int maxwin;

	if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
		tcp_fixup_rcvbuf(sk);
	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
		tcp_fixup_sndbuf(sk);

	tp->rcvq_space.space = tp->rcv_wnd;

	maxwin = tcp_full_space(sk);

	if (tp->window_clamp >= maxwin) {
		tp->window_clamp = maxwin;

		if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
			tp->window_clamp = max(maxwin -
					       (maxwin >> sysctl_tcp_app_win),
					       4 * tp->advmss);
	}

	/* Force reservation of one segment. */
	if (sysctl_tcp_app_win &&
	    tp->window_clamp > 2 * tp->advmss &&
	    tp->window_clamp + tp->advmss > maxwin)
		tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);

	tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

/* 5. Recalculate window clamp after socket hit its memory bounds. */
static void tcp_clamp_window(struct sock *sk, struct tcp_sock *tp)
{
	struct sk_buff *skb;
	unsigned int app_win = tp->rcv_nxt - tp->copied_seq;
	int ofo_win = 0;

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	inet_csk(sk)->icsk_ack.quick = 0;
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	skb_queue_walk(&tp->out_of_order_queue, skb) {
		ofo_win += skb->len;
	}

	/* If overcommit is due to out of order segments,
	 * do not clamp window. Try to expand rcvbuf instead.
	 */
	if (ofo_win) {
		if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
		    !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
		    !tcp_memory_pressure &&
		    atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0])
			sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
					    sysctl_tcp_rmem[2]);
	}
	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) {
		app_win += ofo_win;
		if (atomic_read(&sk->sk_rmem_alloc) >= 2 * sk->sk_rcvbuf)
			app_win >>= 1;
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		if (app_win > inet_csk(sk)->icsk_ack.rcv_mss)
			app_win -= inet_csk(sk)->icsk_ack.rcv_mss;
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		app_win = max(app_win, 2U*tp->advmss);

		if (!ofo_win)
			tp->window_clamp = min(tp->window_clamp, app_win);
		tp->rcv_ssthresh = min(tp->window_clamp, 2U*tp->advmss);
	}
}

/* Receiver "autotuning" code.
 *
 * The algorithm for RTT estimation w/o timestamps is based on
 * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
 * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
 *
 * More detail on this code can be found at
 * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
 * though this reference is out of date.  A new paper
 * is pending.
 */
static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
{
	u32 new_sample = tp->rcv_rtt_est.rtt;
	long m = sample;

	if (m == 0)
		m = 1;

	if (new_sample != 0) {
		/* If we sample in larger samples in the non-timestamp
		 * case, we could grossly overestimate the RTT especially
		 * with chatty applications or bulk transfer apps which
		 * are stalled on filesystem I/O.
		 *
		 * Also, since we are only going for a minimum in the
		 * non-timestamp case, we do not smoothe things out
		 * else with timestamps disabled convergance takes too
		 * long.
		 */
		if (!win_dep) {
			m -= (new_sample >> 3);
			new_sample += m;
		} else if (m < new_sample)
			new_sample = m << 3;
	} else {
		/* No previous mesaure. */
		new_sample = m << 3;
	}

	if (tp->rcv_rtt_est.rtt != new_sample)
		tp->rcv_rtt_est.rtt = new_sample;
}

static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
{
	if (tp->rcv_rtt_est.time == 0)
		goto new_measure;
	if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
		return;
	tcp_rcv_rtt_update(tp,
			   jiffies - tp->rcv_rtt_est.time,
			   1);

new_measure:
	tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
	tp->rcv_rtt_est.time = tcp_time_stamp;
}

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static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
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{
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	struct tcp_sock *tp = tcp_sk(sk);
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	if (tp->rx_opt.rcv_tsecr &&
	    (TCP_SKB_CB(skb)->end_seq -
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	     TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
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		tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
}

/*
 * This function should be called every time data is copied to user space.
 * It calculates the appropriate TCP receive buffer space.
 */
void tcp_rcv_space_adjust(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int time;
	int space;
	
	if (tp->rcvq_space.time == 0)
		goto new_measure;
	
	time = tcp_time_stamp - tp->rcvq_space.time;
	if (time < (tp->rcv_rtt_est.rtt >> 3) ||
	    tp->rcv_rtt_est.rtt == 0)
		return;
	
	space = 2 * (tp->copied_seq - tp->rcvq_space.seq);

	space = max(tp->rcvq_space.space, space);

	if (tp->rcvq_space.space != space) {
		int rcvmem;

		tp->rcvq_space.space = space;

		if (sysctl_tcp_moderate_rcvbuf) {
			int new_clamp = space;

			/* Receive space grows, normalize in order to
			 * take into account packet headers and sk_buff
			 * structure overhead.
			 */
			space /= tp->advmss;
			if (!space)
				space = 1;
			rcvmem = (tp->advmss + MAX_TCP_HEADER +
				  16 + sizeof(struct sk_buff));
			while (tcp_win_from_space(rcvmem) < tp->advmss)
				rcvmem += 128;
			space *= rcvmem;
			space = min(space, sysctl_tcp_rmem[2]);
			if (space > sk->sk_rcvbuf) {
				sk->sk_rcvbuf = space;

				/* Make the window clamp follow along.  */
				tp->window_clamp = new_clamp;
			}
		}
	}
	
new_measure:
	tp->rcvq_space.seq = tp->copied_seq;
	tp->rcvq_space.time = tcp_time_stamp;
}

/* There is something which you must keep in mind when you analyze the
 * behavior of the tp->ato delayed ack timeout interval.  When a
 * connection starts up, we want to ack as quickly as possible.  The
 * problem is that "good" TCP's do slow start at the beginning of data
 * transmission.  The means that until we send the first few ACK's the
 * sender will sit on his end and only queue most of his data, because
 * he can only send snd_cwnd unacked packets at any given time.  For
 * each ACK we send, he increments snd_cwnd and transmits more of his
 * queue.  -DaveM
 */
static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_buff *skb)
{
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	struct inet_connection_sock *icsk = inet_csk(sk);
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	u32 now;

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	inet_csk_schedule_ack(sk);
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	tcp_measure_rcv_mss(sk, skb);
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	tcp_rcv_rtt_measure(tp);
	
	now = tcp_time_stamp;

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	if (!icsk->icsk_ack.ato) {
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		/* The _first_ data packet received, initialize
		 * delayed ACK engine.
		 */
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		tcp_incr_quickack(sk);
		icsk->icsk_ack.ato = TCP_ATO_MIN;
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	} else {
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		int m = now - icsk->icsk_ack.lrcvtime;
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		if (m <= TCP_ATO_MIN/2) {
			/* The fastest case is the first. */
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			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
		} else if (m < icsk->icsk_ack.ato) {
			icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
			if (icsk->icsk_ack.ato > icsk->icsk_rto)
				icsk->icsk_ack.ato = icsk->icsk_rto;
		} else if (m > icsk->icsk_rto) {
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			/* Too long gap. Apparently sender falled to
			 * restart window, so that we send ACKs quickly.
			 */
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			tcp_incr_quickack(sk);
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			sk_stream_mem_reclaim(sk);
		}
	}
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	icsk->icsk_ack.lrcvtime = now;
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	TCP_ECN_check_ce(tp, skb);

	if (skb->len >= 128)
		tcp_grow_window(sk, tp, skb);
}

/* Called to compute a smoothed rtt estimate. The data fed to this
 * routine either comes from timestamps, or from segments that were
 * known _not_ to have been retransmitted [see Karn/Partridge
 * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
 * piece by Van Jacobson.
 * NOTE: the next three routines used to be one big routine.
 * To save cycles in the RFC 1323 implementation it was better to break
 * it up into three procedures. -- erics
 */
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static void tcp_rtt_estimator(struct tcp_sock *tp, __u32 mrtt, u32 *usrtt)
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{
	long m = mrtt; /* RTT */

	/*	The following amusing code comes from Jacobson's
	 *	article in SIGCOMM '88.  Note that rtt and mdev
	 *	are scaled versions of rtt and mean deviation.
	 *	This is designed to be as fast as possible 
	 *	m stands for "measurement".
	 *
	 *	On a 1990 paper the rto value is changed to:
	 *	RTO = rtt + 4 * mdev
	 *
	 * Funny. This algorithm seems to be very broken.
	 * These formulae increase RTO, when it should be decreased, increase
	 * too slowly, when it should be incresed fastly, decrease too fastly
	 * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
	 * does not matter how to _calculate_ it. Seems, it was trap
	 * that VJ failed to avoid. 8)
	 */
	if(m == 0)
		m = 1;
	if (tp->srtt != 0) {
		m -= (tp->srtt >> 3);	/* m is now error in rtt est */
		tp->srtt += m;		/* rtt = 7/8 rtt + 1/8 new */
		if (m < 0) {
			m = -m;		/* m is now abs(error) */
			m -= (tp->mdev >> 2);   /* similar update on mdev */
			/* This is similar to one of Eifel findings.
			 * Eifel blocks mdev updates when rtt decreases.
			 * This solution is a bit different: we use finer gain
			 * for mdev in this case (alpha*beta).
			 * Like Eifel it also prevents growth of rto,
			 * but also it limits too fast rto decreases,
			 * happening in pure Eifel.
			 */
			if (m > 0)
				m >>= 3;
		} else {
			m -= (tp->mdev >> 2);   /* similar update on mdev */
		}
		tp->mdev += m;	    	/* mdev = 3/4 mdev + 1/4 new */
		if (tp->mdev > tp->mdev_max) {
			tp->mdev_max = tp->mdev;
			if (tp->mdev_max > tp->rttvar)
				tp->rttvar = tp->mdev_max;
		}
		if (after(tp->snd_una, tp->rtt_seq)) {
			if (tp->mdev_max < tp->rttvar)
				tp->rttvar -= (tp->rttvar-tp->mdev_max)>>2;
			tp->rtt_seq = tp->snd_nxt;
			tp->mdev_max = TCP_RTO_MIN;
		}
	} else {
		/* no previous measure. */
		tp->srtt = m<<3;	/* take the measured time to be rtt */
		tp->mdev = m<<1;	/* make sure rto = 3*rtt */
		tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
		tp->rtt_seq = tp->snd_nxt;
	}

613 614
	if (tp->ca_ops->rtt_sample)
		tp->ca_ops->rtt_sample(tp, *usrtt);
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}

/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 * routine referred to above.
 */
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static inline void tcp_set_rto(struct sock *sk)
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{
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	const struct tcp_sock *tp = tcp_sk(sk);
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	/* Old crap is replaced with new one. 8)
	 *
	 * More seriously:
	 * 1. If rtt variance happened to be less 50msec, it is hallucination.
	 *    It cannot be less due to utterly erratic ACK generation made
	 *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
	 *    to do with delayed acks, because at cwnd>2 true delack timeout
	 *    is invisible. Actually, Linux-2.4 also generates erratic
	 *    ACKs in some curcumstances.
	 */
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	inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
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	/* 2. Fixups made earlier cannot be right.
	 *    If we do not estimate RTO correctly without them,
	 *    all the algo is pure shit and should be replaced
	 *    with correct one. It is exaclty, which we pretend to do.
	 */
}

/* NOTE: clamping at TCP_RTO_MIN is not required, current algo
 * guarantees that rto is higher.
 */
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static inline void tcp_bound_rto(struct sock *sk)
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{
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	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
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}

/* Save metrics learned by this TCP session.
   This function is called only, when TCP finishes successfully
   i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
 */
void tcp_update_metrics(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);

	if (sysctl_tcp_nometrics_save)
		return;

	dst_confirm(dst);

	if (dst && (dst->flags&DST_HOST)) {
		int m;

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		if (inet_csk(sk)->icsk_backoff || !tp->srtt) {
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			/* This session failed to estimate rtt. Why?
			 * Probably, no packets returned in time.
			 * Reset our results.
			 */
			if (!(dst_metric_locked(dst, RTAX_RTT)))
				dst->metrics[RTAX_RTT-1] = 0;
			return;
		}

		m = dst_metric(dst, RTAX_RTT) - tp->srtt;

		/* If newly calculated rtt larger than stored one,
		 * store new one. Otherwise, use EWMA. Remember,
		 * rtt overestimation is always better than underestimation.
		 */
		if (!(dst_metric_locked(dst, RTAX_RTT))) {
			if (m <= 0)
				dst->metrics[RTAX_RTT-1] = tp->srtt;
			else
				dst->metrics[RTAX_RTT-1] -= (m>>3);
		}

		if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
			if (m < 0)
				m = -m;

			/* Scale deviation to rttvar fixed point */
			m >>= 1;
			if (m < tp->mdev)
				m = tp->mdev;

			if (m >= dst_metric(dst, RTAX_RTTVAR))
				dst->metrics[RTAX_RTTVAR-1] = m;
			else
				dst->metrics[RTAX_RTTVAR-1] -=
					(dst->metrics[RTAX_RTTVAR-1] - m)>>2;
		}

		if (tp->snd_ssthresh >= 0xFFFF) {
			/* Slow start still did not finish. */
			if (dst_metric(dst, RTAX_SSTHRESH) &&
			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
			    (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
				dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
			if (!dst_metric_locked(dst, RTAX_CWND) &&
			    tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
				dst->metrics[RTAX_CWND-1] = tp->snd_cwnd;
		} else if (tp->snd_cwnd > tp->snd_ssthresh &&
			   tp->ca_state == TCP_CA_Open) {
			/* Cong. avoidance phase, cwnd is reliable. */
			if (!dst_metric_locked(dst, RTAX_SSTHRESH))
				dst->metrics[RTAX_SSTHRESH-1] =
					max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
			if (!dst_metric_locked(dst, RTAX_CWND))
				dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
		} else {
			/* Else slow start did not finish, cwnd is non-sense,
			   ssthresh may be also invalid.
			 */
			if (!dst_metric_locked(dst, RTAX_CWND))
				dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
			if (dst->metrics[RTAX_SSTHRESH-1] &&
			    !dst_metric_locked(dst, RTAX_SSTHRESH) &&
			    tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
				dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
		}

		if (!dst_metric_locked(dst, RTAX_REORDERING)) {
			if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
			    tp->reordering != sysctl_tcp_reordering)
				dst->metrics[RTAX_REORDERING-1] = tp->reordering;
		}
	}
}

/* Numbers are taken from RFC2414.  */
__u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
{
	__u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);

	if (!cwnd) {
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		if (tp->mss_cache > 1460)
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			cwnd = 2;
		else
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			cwnd = (tp->mss_cache > 1095) ? 3 : 4;
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	}
	return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
}

/* Initialize metrics on socket. */

static void tcp_init_metrics(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct dst_entry *dst = __sk_dst_get(sk);

	if (dst == NULL)
		goto reset;

	dst_confirm(dst);

	if (dst_metric_locked(dst, RTAX_CWND))
		tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
	if (dst_metric(dst, RTAX_SSTHRESH)) {
		tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
		if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
			tp->snd_ssthresh = tp->snd_cwnd_clamp;
	}
	if (dst_metric(dst, RTAX_REORDERING) &&
	    tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
		tp->rx_opt.sack_ok &= ~2;
		tp->reordering = dst_metric(dst, RTAX_REORDERING);
	}

	if (dst_metric(dst, RTAX_RTT) == 0)
		goto reset;

	if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
		goto reset;

	/* Initial rtt is determined from SYN,SYN-ACK.
	 * The segment is small and rtt may appear much
	 * less than real one. Use per-dst memory
	 * to make it more realistic.
	 *
	 * A bit of theory. RTT is time passed after "normal" sized packet
	 * is sent until it is ACKed. In normal curcumstances sending small
	 * packets force peer to delay ACKs and calculation is correct too.
	 * The algorithm is adaptive and, provided we follow specs, it
	 * NEVER underestimate RTT. BUT! If peer tries to make some clever
	 * tricks sort of "quick acks" for time long enough to decrease RTT
	 * to low value, and then abruptly stops to do it and starts to delay
	 * ACKs, wait for troubles.
	 */
	if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
		tp->srtt = dst_metric(dst, RTAX_RTT);
		tp->rtt_seq = tp->snd_nxt;
	}
	if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
		tp->mdev = dst_metric(dst, RTAX_RTTVAR);
		tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
	}
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	tcp_set_rto(sk);
	tcp_bound_rto(sk);
	if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
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		goto reset;
	tp->snd_cwnd = tcp_init_cwnd(tp, dst);
	tp->snd_cwnd_stamp = tcp_time_stamp;
	return;

reset:
	/* Play conservative. If timestamps are not
	 * supported, TCP will fail to recalculate correct
	 * rtt, if initial rto is too small. FORGET ALL AND RESET!
	 */
	if (!tp->rx_opt.saw_tstamp && tp->srtt) {
		tp->srtt = 0;
		tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
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		inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
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	}
}

static void tcp_update_reordering(struct tcp_sock *tp, int metric, int ts)
{
	if (metric > tp->reordering) {
		tp->reordering = min(TCP_MAX_REORDERING, metric);

		/* This exciting event is worth to be remembered. 8) */
		if (ts)
			NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
		else if (IsReno(tp))
			NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
		else if (IsFack(tp))
			NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
		else
			NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
#if FASTRETRANS_DEBUG > 1
		printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
		       tp->rx_opt.sack_ok, tp->ca_state,
		       tp->reordering,
		       tp->fackets_out,
		       tp->sacked_out,
		       tp->undo_marker ? tp->undo_retrans : 0);
#endif
		/* Disable FACK yet. */
		tp->rx_opt.sack_ok &= ~2;
	}
}

/* This procedure tags the retransmission queue when SACKs arrive.
 *
 * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
 * Packets in queue with these bits set are counted in variables
 * sacked_out, retrans_out and lost_out, correspondingly.
 *
 * Valid combinations are:
 * Tag  InFlight	Description
 * 0	1		- orig segment is in flight.
 * S	0		- nothing flies, orig reached receiver.
 * L	0		- nothing flies, orig lost by net.
 * R	2		- both orig and retransmit are in flight.
 * L|R	1		- orig is lost, retransmit is in flight.
 * S|R  1		- orig reached receiver, retrans is still in flight.
 * (L|S|R is logically valid, it could occur when L|R is sacked,
 *  but it is equivalent to plain S and code short-curcuits it to S.
 *  L|S is logically invalid, it would mean -1 packet in flight 8))
 *
 * These 6 states form finite state machine, controlled by the following events:
 * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
 * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
 * 3. Loss detection event of one of three flavors:
 *	A. Scoreboard estimator decided the packet is lost.
 *	   A'. Reno "three dupacks" marks head of queue lost.
 *	   A''. Its FACK modfication, head until snd.fack is lost.
 *	B. SACK arrives sacking data transmitted after never retransmitted
 *	   hole was sent out.
 *	C. SACK arrives sacking SND.NXT at the moment, when the
 *	   segment was retransmitted.
 * 4. D-SACK added new rule: D-SACK changes any tag to S.
 *
 * It is pleasant to note, that state diagram turns out to be commutative,
 * so that we are allowed not to be bothered by order of our actions,
 * when multiple events arrive simultaneously. (see the function below).
 *
 * Reordering detection.
 * --------------------
 * Reordering metric is maximal distance, which a packet can be displaced
 * in packet stream. With SACKs we can estimate it:
 *
 * 1. SACK fills old hole and the corresponding segment was not
 *    ever retransmitted -> reordering. Alas, we cannot use it
 *    when segment was retransmitted.
 * 2. The last flaw is solved with D-SACK. D-SACK arrives
 *    for retransmitted and already SACKed segment -> reordering..
 * Both of these heuristics are not used in Loss state, when we cannot
 * account for retransmits accurately.
 */
static int
tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_una)
{
	struct tcp_sock *tp = tcp_sk(sk);
	unsigned char *ptr = ack_skb->h.raw + TCP_SKB_CB(ack_skb)->sacked;
	struct tcp_sack_block *sp = (struct tcp_sack_block *)(ptr+2);
	int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE)>>3;
	int reord = tp->packets_out;
	int prior_fackets;
	u32 lost_retrans = 0;
	int flag = 0;
	int i;

	/* So, SACKs for already sent large segments will be lost.
	 * Not good, but alternative is to resegment the queue. */
	if (sk->sk_route_caps & NETIF_F_TSO) {
		sk->sk_route_caps &= ~NETIF_F_TSO;
		sock_set_flag(sk, SOCK_NO_LARGESEND);
924
		tp->mss_cache = tp->mss_cache;
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	}

	if (!tp->sacked_out)
		tp->fackets_out = 0;
	prior_fackets = tp->fackets_out;

	for (i=0; i<num_sacks; i++, sp++) {
		struct sk_buff *skb;
		__u32 start_seq = ntohl(sp->start_seq);
		__u32 end_seq = ntohl(sp->end_seq);
		int fack_count = 0;
		int dup_sack = 0;

		/* Check for D-SACK. */
		if (i == 0) {
			u32 ack = TCP_SKB_CB(ack_skb)->ack_seq;

			if (before(start_seq, ack)) {
				dup_sack = 1;
				tp->rx_opt.sack_ok |= 4;
				NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
			} else if (num_sacks > 1 &&
				   !after(end_seq, ntohl(sp[1].end_seq)) &&
				   !before(start_seq, ntohl(sp[1].start_seq))) {
				dup_sack = 1;
				tp->rx_opt.sack_ok |= 4;
				NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
			}

			/* D-SACK for already forgotten data...
			 * Do dumb counting. */
			if (dup_sack &&
			    !after(end_seq, prior_snd_una) &&
			    after(end_seq, tp->undo_marker))
				tp->undo_retrans--;

			/* Eliminate too old ACKs, but take into
			 * account more or less fresh ones, they can
			 * contain valid SACK info.
			 */
			if (before(ack, prior_snd_una - tp->max_window))
				return 0;
		}

		/* Event "B" in the comment above. */
		if (after(end_seq, tp->high_seq))
			flag |= FLAG_DATA_LOST;

		sk_stream_for_retrans_queue(skb, sk) {
			u8 sacked = TCP_SKB_CB(skb)->sacked;
			int in_sack;

			/* The retransmission queue is always in order, so
			 * we can short-circuit the walk early.
			 */
			if(!before(TCP_SKB_CB(skb)->seq, end_seq))
				break;

			fack_count += tcp_skb_pcount(skb);

			in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
				!before(end_seq, TCP_SKB_CB(skb)->end_seq);

			/* Account D-SACK for retransmitted packet. */
			if ((dup_sack && in_sack) &&
			    (sacked & TCPCB_RETRANS) &&
			    after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
				tp->undo_retrans--;

			/* The frame is ACKed. */
			if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) {
				if (sacked&TCPCB_RETRANS) {
					if ((dup_sack && in_sack) &&
					    (sacked&TCPCB_SACKED_ACKED))
						reord = min(fack_count, reord);
				} else {
					/* If it was in a hole, we detected reordering. */
					if (fack_count < prior_fackets &&
					    !(sacked&TCPCB_SACKED_ACKED))
						reord = min(fack_count, reord);
				}

				/* Nothing to do; acked frame is about to be dropped. */
				continue;
			}

			if ((sacked&TCPCB_SACKED_RETRANS) &&
			    after(end_seq, TCP_SKB_CB(skb)->ack_seq) &&
			    (!lost_retrans || after(end_seq, lost_retrans)))
				lost_retrans = end_seq;

			if (!in_sack)
				continue;

			if (!(sacked&TCPCB_SACKED_ACKED)) {
				if (sacked & TCPCB_SACKED_RETRANS) {
					/* If the segment is not tagged as lost,
					 * we do not clear RETRANS, believing
					 * that retransmission is still in flight.
					 */
					if (sacked & TCPCB_LOST) {
						TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
						tp->lost_out -= tcp_skb_pcount(skb);
						tp->retrans_out -= tcp_skb_pcount(skb);
					}
				} else {
					/* New sack for not retransmitted frame,
					 * which was in hole. It is reordering.
					 */
					if (!(sacked & TCPCB_RETRANS) &&
					    fack_count < prior_fackets)
						reord = min(fack_count, reord);

					if (sacked & TCPCB_LOST) {
						TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
						tp->lost_out -= tcp_skb_pcount(skb);
					}
				}

				TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
				flag |= FLAG_DATA_SACKED;
				tp->sacked_out += tcp_skb_pcount(skb);

				if (fack_count > tp->fackets_out)
					tp->fackets_out = fack_count;
			} else {
				if (dup_sack && (sacked&TCPCB_RETRANS))
					reord = min(fack_count, reord);
			}

			/* D-SACK. We can detect redundant retransmission
			 * in S|R and plain R frames and clear it.
			 * undo_retrans is decreased above, L|R frames
			 * are accounted above as well.
			 */
			if (dup_sack &&
			    (TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS)) {
				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
				tp->retrans_out -= tcp_skb_pcount(skb);
			}
		}
	}

	/* Check for lost retransmit. This superb idea is
	 * borrowed from "ratehalving". Event "C".
	 * Later note: FACK people cheated me again 8),
	 * we have to account for reordering! Ugly,
	 * but should help.
	 */
	if (lost_retrans && tp->ca_state == TCP_CA_Recovery) {
		struct sk_buff *skb;

		sk_stream_for_retrans_queue(skb, sk) {
			if (after(TCP_SKB_CB(skb)->seq, lost_retrans))
				break;
			if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
				continue;
			if ((TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_RETRANS) &&
			    after(lost_retrans, TCP_SKB_CB(skb)->ack_seq) &&
			    (IsFack(tp) ||
			     !before(lost_retrans,
				     TCP_SKB_CB(skb)->ack_seq + tp->reordering *
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				     tp->mss_cache))) {
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				TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
				tp->retrans_out -= tcp_skb_pcount(skb);

				if (!(TCP_SKB_CB(skb)->sacked&(TCPCB_LOST|TCPCB_SACKED_ACKED))) {
					tp->lost_out += tcp_skb_pcount(skb);
					TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
					flag |= FLAG_DATA_SACKED;
					NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
				}
			}
		}
	}

	tp->left_out = tp->sacked_out + tp->lost_out;

	if ((reord < tp->fackets_out) && tp->ca_state != TCP_CA_Loss)
		tcp_update_reordering(tp, ((tp->fackets_out + 1) - reord), 0);

#if FASTRETRANS_DEBUG > 0
	BUG_TRAP((int)tp->sacked_out >= 0);
	BUG_TRAP((int)tp->lost_out >= 0);
	BUG_TRAP((int)tp->retrans_out >= 0);
	BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
#endif
	return flag;
}

/* RTO occurred, but do not yet enter loss state. Instead, transmit two new
 * segments to see from the next ACKs whether any data was really missing.
 * If the RTO was spurious, new ACKs should arrive.
 */
void tcp_enter_frto(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;

	tp->frto_counter = 1;

	if (tp->ca_state <= TCP_CA_Disorder ||
            tp->snd_una == tp->high_seq ||
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            (tp->ca_state == TCP_CA_Loss && !inet_csk(sk)->icsk_retransmits)) {
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		tp->prior_ssthresh = tcp_current_ssthresh(tp);
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		tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
		tcp_ca_event(tp, CA_EVENT_FRTO);
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	}

	/* Have to clear retransmission markers here to keep the bookkeeping
	 * in shape, even though we are not yet in Loss state.
	 * If something was really lost, it is eventually caught up
	 * in tcp_enter_frto_loss.
	 */
	tp->retrans_out = 0;
	tp->undo_marker = tp->snd_una;
	tp->undo_retrans = 0;

	sk_stream_for_retrans_queue(skb, sk) {
		TCP_SKB_CB(skb)->sacked &= ~TCPCB_RETRANS;
	}
	tcp_sync_left_out(tp);

	tcp_set_ca_state(tp, TCP_CA_Open);
	tp->frto_highmark = tp->snd_nxt;
}

/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
 * which indicates that we should follow the traditional RTO recovery,
 * i.e. mark everything lost and do go-back-N retransmission.
 */
static void tcp_enter_frto_loss(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	int cnt = 0;

	tp->sacked_out = 0;
	tp->lost_out = 0;
	tp->fackets_out = 0;

	sk_stream_for_retrans_queue(skb, sk) {
		cnt += tcp_skb_pcount(skb);
		TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {

			/* Do not mark those segments lost that were
			 * forward transmitted after RTO
			 */
			if (!after(TCP_SKB_CB(skb)->end_seq,
				   tp->frto_highmark)) {
				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
				tp->lost_out += tcp_skb_pcount(skb);
			}
		} else {
			tp->sacked_out += tcp_skb_pcount(skb);
			tp->fackets_out = cnt;
		}
	}
	tcp_sync_left_out(tp);

	tp->snd_cwnd = tp->frto_counter + tcp_packets_in_flight(tp)+1;
	tp->snd_cwnd_cnt = 0;
	tp->snd_cwnd_stamp = tcp_time_stamp;
	tp->undo_marker = 0;
	tp->frto_counter = 0;

	tp->reordering = min_t(unsigned int, tp->reordering,
					     sysctl_tcp_reordering);
	tcp_set_ca_state(tp, TCP_CA_Loss);
	tp->high_seq = tp->frto_highmark;
	TCP_ECN_queue_cwr(tp);
}

void tcp_clear_retrans(struct tcp_sock *tp)
{
	tp->left_out = 0;
	tp->retrans_out = 0;

	tp->fackets_out = 0;
	tp->sacked_out = 0;
	tp->lost_out = 0;

	tp->undo_marker = 0;
	tp->undo_retrans = 0;
}

/* Enter Loss state. If "how" is not zero, forget all SACK information
 * and reset tags completely, otherwise preserve SACKs. If receiver
 * dropped its ofo queue, we will know this due to reneging detection.
 */
void tcp_enter_loss(struct sock *sk, int how)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	int cnt = 0;

	/* Reduce ssthresh if it has not yet been made inside this window. */
	if (tp->ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
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	    (tp->ca_state == TCP_CA_Loss && !inet_csk(sk)->icsk_retransmits)) {
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		tp->prior_ssthresh = tcp_current_ssthresh(tp);
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		tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
		tcp_ca_event(tp, CA_EVENT_LOSS);
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	}
	tp->snd_cwnd	   = 1;
	tp->snd_cwnd_cnt   = 0;
	tp->snd_cwnd_stamp = tcp_time_stamp;

	tcp_clear_retrans(tp);

	/* Push undo marker, if it was plain RTO and nothing
	 * was retransmitted. */
	if (!how)
		tp->undo_marker = tp->snd_una;

	sk_stream_for_retrans_queue(skb, sk) {
		cnt += tcp_skb_pcount(skb);
		if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
			tp->undo_marker = 0;
		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
			tp->lost_out += tcp_skb_pcount(skb);
		} else {
			tp->sacked_out += tcp_skb_pcount(skb);
			tp->fackets_out = cnt;
		}
	}
	tcp_sync_left_out(tp);

	tp->reordering = min_t(unsigned int, tp->reordering,
					     sysctl_tcp_reordering);
	tcp_set_ca_state(tp, TCP_CA_Loss);
	tp->high_seq = tp->snd_nxt;
	TCP_ECN_queue_cwr(tp);
}

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static int tcp_check_sack_reneging(struct sock *sk)
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{
	struct sk_buff *skb;

	/* If ACK arrived pointing to a remembered SACK,
	 * it means that our remembered SACKs do not reflect
	 * real state of receiver i.e.
	 * receiver _host_ is heavily congested (or buggy).
	 * Do processing similar to RTO timeout.
	 */
	if ((skb = skb_peek(&sk->sk_write_queue)) != NULL &&
	    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
		NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);

		tcp_enter_loss(sk, 1);
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		inet_csk(sk)->icsk_retransmits++;
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		tcp_retransmit_skb(sk, skb_peek(&sk->sk_write_queue));
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		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
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					  inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
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		return 1;
	}
	return 0;
}

static inline int tcp_fackets_out(struct tcp_sock *tp)
{
	return IsReno(tp) ? tp->sacked_out+1 : tp->fackets_out;
}

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static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
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{
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	return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
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}

static inline int tcp_head_timedout(struct sock *sk, struct tcp_sock *tp)
{
	return tp->packets_out &&
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	       tcp_skb_timedout(sk, skb_peek(&sk->sk_write_queue));
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}

/* Linux NewReno/SACK/FACK/ECN state machine.
 * --------------------------------------
 *
 * "Open"	Normal state, no dubious events, fast path.
 * "Disorder"   In all the respects it is "Open",
 *		but requires a bit more attention. It is entered when
 *		we see some SACKs or dupacks. It is split of "Open"
 *		mainly to move some processing from fast path to slow one.
 * "CWR"	CWND was reduced due to some Congestion Notification event.
 *		It can be ECN, ICMP source quench, local device congestion.
 * "Recovery"	CWND was reduced, we are fast-retransmitting.
 * "Loss"	CWND was reduced due to RTO timeout or SACK reneging.
 *
 * tcp_fastretrans_alert() is entered:
 * - each incoming ACK, if state is not "Open"
 * - when arrived ACK is unusual, namely:
 *	* SACK
 *	* Duplicate ACK.
 *	* ECN ECE.
 *
 * Counting packets in flight is pretty simple.
 *
 *	in_flight = packets_out - left_out + retrans_out
 *
 *	packets_out is SND.NXT-SND.UNA counted in packets.
 *
 *	retrans_out is number of retransmitted segments.
 *
 *	left_out is number of segments left network, but not ACKed yet.
 *
 *		left_out = sacked_out + lost_out
 *
 *     sacked_out: Packets, which arrived to receiver out of order
 *		   and hence not ACKed. With SACKs this number is simply
 *		   amount of SACKed data. Even without SACKs
 *		   it is easy to give pretty reliable estimate of this number,
 *		   counting duplicate ACKs.
 *
 *       lost_out: Packets lost by network. TCP has no explicit
 *		   "loss notification" feedback from network (for now).
 *		   It means that this number can be only _guessed_.
 *		   Actually, it is the heuristics to predict lossage that
 *		   distinguishes different algorithms.
 *
 *	F.e. after RTO, when all the queue is considered as lost,
 *	lost_out = packets_out and in_flight = retrans_out.
 *
 *		Essentially, we have now two algorithms counting
 *		lost packets.
 *
 *		FACK: It is the simplest heuristics. As soon as we decided
 *		that something is lost, we decide that _all_ not SACKed
 *		packets until the most forward SACK are lost. I.e.
 *		lost_out = fackets_out - sacked_out and left_out = fackets_out.
 *		It is absolutely correct estimate, if network does not reorder
 *		packets. And it loses any connection to reality when reordering
 *		takes place. We use FACK by default until reordering
 *		is suspected on the path to this destination.
 *
 *		NewReno: when Recovery is entered, we assume that one segment
 *		is lost (classic Reno). While we are in Recovery and
 *		a partial ACK arrives, we assume that one more packet
 *		is lost (NewReno). This heuristics are the same in NewReno
 *		and SACK.
 *
 *  Imagine, that's all! Forget about all this shamanism about CWND inflation
 *  deflation etc. CWND is real congestion window, never inflated, changes
 *  only according to classic VJ rules.
 *
 * Really tricky (and requiring careful tuning) part of algorithm
 * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
 * The first determines the moment _when_ we should reduce CWND and,
 * hence, slow down forward transmission. In fact, it determines the moment
 * when we decide that hole is caused by loss, rather than by a reorder.
 *
 * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
 * holes, caused by lost packets.
 *
 * And the most logically complicated part of algorithm is undo
 * heuristics. We detect false retransmits due to both too early
 * fast retransmit (reordering) and underestimated RTO, analyzing
 * timestamps and D-SACKs. When we detect that some segments were
 * retransmitted by mistake and CWND reduction was wrong, we undo
 * window reduction and abort recovery phase. This logic is hidden
 * inside several functions named tcp_try_undo_<something>.
 */

/* This function decides, when we should leave Disordered state
 * and enter Recovery phase, reducing congestion window.
 *
 * Main question: may we further continue forward transmission
 * with the same cwnd?
 */
static int tcp_time_to_recover(struct sock *sk, struct tcp_sock *tp)
{
	__u32 packets_out;

	/* Trick#1: The loss is proven. */
	if (tp->lost_out)
		return 1;

	/* Not-A-Trick#2 : Classic rule... */
	if (tcp_fackets_out(tp) > tp->reordering)
		return 1;

	/* Trick#3 : when we use RFC2988 timer restart, fast
	 * retransmit can be triggered by timeout of queue head.
	 */
	if (tcp_head_timedout(sk, tp))
		return 1;

	/* Trick#4: It is still not OK... But will it be useful to delay
	 * recovery more?
	 */
	packets_out = tp->packets_out;
	if (packets_out <= tp->reordering &&
	    tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
	    !tcp_may_send_now(sk, tp)) {
		/* We have nothing to send. This connection is limited
		 * either by receiver window or by application.
		 */
		return 1;
	}

	return 0;
}

/* If we receive more dupacks than we expected counting segments
 * in assumption of absent reordering, interpret this as reordering.
 * The only another reason could be bug in receiver TCP.
 */
static void tcp_check_reno_reordering(struct tcp_sock *tp, int addend)
{
	u32 holes;

	holes = max(tp->lost_out, 1U);
	holes = min(holes, tp->packets_out);

	if ((tp->sacked_out + holes) > tp->packets_out) {
		tp->sacked_out = tp->packets_out - holes;
		tcp_update_reordering(tp, tp->packets_out+addend, 0);
	}
}

/* Emulate SACKs for SACKless connection: account for a new dupack. */

static void tcp_add_reno_sack(struct tcp_sock *tp)
{
	tp->sacked_out++;
	tcp_check_reno_reordering(tp, 0);
	tcp_sync_left_out(tp);
}

/* Account for ACK, ACKing some data in Reno Recovery phase. */

static void tcp_remove_reno_sacks(struct sock *sk, struct tcp_sock *tp, int acked)
{
	if (acked > 0) {
		/* One ACK acked hole. The rest eat duplicate ACKs. */
		if (acked-1 >= tp->sacked_out)
			tp->sacked_out = 0;
		else
			tp->sacked_out -= acked-1;
	}
	tcp_check_reno_reordering(tp, acked);
	tcp_sync_left_out(tp);
}

static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
{
	tp->sacked_out = 0;
	tp->left_out = tp->lost_out;
}

/* Mark head of queue up as lost. */
static void tcp_mark_head_lost(struct sock *sk, struct tcp_sock *tp,
			       int packets, u32 high_seq)
{
	struct sk_buff *skb;
	int cnt = packets;

	BUG_TRAP(cnt <= tp->packets_out);

	sk_stream_for_retrans_queue(skb, sk) {
		cnt -= tcp_skb_pcount(skb);
		if (cnt < 0 || after(TCP_SKB_CB(skb)->end_seq, high_seq))
			break;
		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
			tp->lost_out += tcp_skb_pcount(skb);
		}
	}
	tcp_sync_left_out(tp);
}

/* Account newly detected lost packet(s) */

static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
{
	if (IsFack(tp)) {
		int lost = tp->fackets_out - tp->reordering;
		if (lost <= 0)
			lost = 1;
		tcp_mark_head_lost(sk, tp, lost, tp->high_seq);
	} else {
		tcp_mark_head_lost(sk, tp, 1, tp->high_seq);
	}

	/* New heuristics: it is possible only after we switched
	 * to restart timer each time when something is ACKed.
	 * Hence, we can detect timed out packets during fast
	 * retransmit without falling to slow start.
	 */
	if (tcp_head_timedout(sk, tp)) {
		struct sk_buff *skb;

		sk_stream_for_retrans_queue(skb, sk) {
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			if (tcp_skb_timedout(sk, skb) &&
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			    !(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
				tp->lost_out += tcp_skb_pcount(skb);
			}
		}
		tcp_sync_left_out(tp);
	}
}

/* CWND moderation, preventing bursts due to too big ACKs
 * in dubious situations.
 */
static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
{
	tp->snd_cwnd = min(tp->snd_cwnd,
			   tcp_packets_in_flight(tp)+tcp_max_burst(tp));
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

/* Decrease cwnd each second ack. */
static void tcp_cwnd_down(struct tcp_sock *tp)
{
	int decr = tp->snd_cwnd_cnt + 1;

	tp->snd_cwnd_cnt = decr&1;
	decr >>= 1;

1548
	if (decr && tp->snd_cwnd > tp->ca_ops->min_cwnd(tp))
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		tp->snd_cwnd -= decr;

	tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

/* Nothing was retransmitted or returned timestamp is less
 * than timestamp of the first retransmission.
 */
static inline int tcp_packet_delayed(struct tcp_sock *tp)
{
	return !tp->retrans_stamp ||
		(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
		 (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
}

/* Undo procedures. */

#if FASTRETRANS_DEBUG > 1
static void DBGUNDO(struct sock *sk, struct tcp_sock *tp, const char *msg)
{
	struct inet_sock *inet = inet_sk(sk);
	printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
	       msg,
	       NIPQUAD(inet->daddr), ntohs(inet->dport),
	       tp->snd_cwnd, tp->left_out,
	       tp->snd_ssthresh, tp->prior_ssthresh,
	       tp->packets_out);
}
#else
#define DBGUNDO(x...) do { } while (0)
#endif

static void tcp_undo_cwr(struct tcp_sock *tp, int undo)
{
	if (tp->prior_ssthresh) {
1585 1586
		if (tp->ca_ops->undo_cwnd)
			tp->snd_cwnd = tp->ca_ops->undo_cwnd(tp);
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		else
			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1);

		if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
			tp->snd_ssthresh = tp->prior_ssthresh;
			TCP_ECN_withdraw_cwr(tp);
		}
	} else {
		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
	}
	tcp_moderate_cwnd(tp);
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

static inline int tcp_may_undo(struct tcp_sock *tp)
{
	return tp->undo_marker &&
		(!tp->undo_retrans || tcp_packet_delayed(tp));
}

/* People celebrate: "We love our President!" */
static int tcp_try_undo_recovery(struct sock *sk, struct tcp_sock *tp)
{
	if (tcp_may_undo(tp)) {
		/* Happy end! We did not retransmit anything
		 * or our original transmission succeeded.
		 */
		DBGUNDO(sk, tp, tp->ca_state == TCP_CA_Loss ? "loss" : "retrans");
		tcp_undo_cwr(tp, 1);
		if (tp->ca_state == TCP_CA_Loss)
			NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
		else
			NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
		tp->undo_marker = 0;
	}
	if (tp->snd_una == tp->high_seq && IsReno(tp)) {
		/* Hold old state until something *above* high_seq
		 * is ACKed. For Reno it is MUST to prevent false
		 * fast retransmits (RFC2582). SACK TCP is safe. */
		tcp_moderate_cwnd(tp);
		return 1;
	}
	tcp_set_ca_state(tp, TCP_CA_Open);
	return 0;
}

/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
static void tcp_try_undo_dsack(struct sock *sk, struct tcp_sock *tp)
{
	if (tp->undo_marker && !tp->undo_retrans) {
		DBGUNDO(sk, tp, "D-SACK");
		tcp_undo_cwr(tp, 1);
		tp->undo_marker = 0;
		NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
	}
}

/* Undo during fast recovery after partial ACK. */

static int tcp_try_undo_partial(struct sock *sk, struct tcp_sock *tp,
				int acked)
{
	/* Partial ACK arrived. Force Hoe's retransmit. */
	int failed = IsReno(tp) || tp->fackets_out>tp->reordering;

	if (tcp_may_undo(tp)) {
		/* Plain luck! Hole if filled with delayed
		 * packet, rather than with a retransmit.
		 */
		if (tp->retrans_out == 0)
			tp->retrans_stamp = 0;

		tcp_update_reordering(tp, tcp_fackets_out(tp)+acked, 1);

		DBGUNDO(sk, tp, "Hoe");
		tcp_undo_cwr(tp, 0);
		NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);

		/* So... Do not make Hoe's retransmit yet.
		 * If the first packet was delayed, the rest
		 * ones are most probably delayed as well.
		 */
		failed = 0;
	}
	return failed;
}

/* Undo during loss recovery after partial ACK. */
static int tcp_try_undo_loss(struct sock *sk, struct tcp_sock *tp)
{
	if (tcp_may_undo(tp)) {
		struct sk_buff *skb;
		sk_stream_for_retrans_queue(skb, sk) {
			TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
		}
		DBGUNDO(sk, tp, "partial loss");
		tp->lost_out = 0;
		tp->left_out = tp->sacked_out;
		tcp_undo_cwr(tp, 1);
		NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
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		inet_csk(sk)->icsk_retransmits = 0;
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		tp->undo_marker = 0;
		if (!IsReno(tp))
			tcp_set_ca_state(tp, TCP_CA_Open);
		return 1;
	}
	return 0;
}

static inline void tcp_complete_cwr(struct tcp_sock *tp)
{
1698
	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
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	tp->snd_cwnd_stamp = tcp_time_stamp;
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	tcp_ca_event(tp, CA_EVENT_COMPLETE_CWR);
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}

static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag)
{
	tp->left_out = tp->sacked_out;

	if (tp->retrans_out == 0)
		tp->retrans_stamp = 0;

	if (flag&FLAG_ECE)
		tcp_enter_cwr(tp);

	if (tp->ca_state != TCP_CA_CWR) {
		int state = TCP_CA_Open;

		if (tp->left_out || tp->retrans_out || tp->undo_marker)
			state = TCP_CA_Disorder;

		if (tp->ca_state != state) {
			tcp_set_ca_state(tp, state);
			tp->high_seq = tp->snd_nxt;
		}
		tcp_moderate_cwnd(tp);
	} else {
		tcp_cwnd_down(tp);
	}
}

/* Process an event, which can update packets-in-flight not trivially.
 * Main goal of this function is to calculate new estimate for left_out,
 * taking into account both packets sitting in receiver's buffer and
 * packets lost by network.
 *
 * Besides that it does CWND reduction, when packet loss is detected
 * and changes state of machine.
 *
 * It does _not_ decide what to send, it is made in function
 * tcp_xmit_retransmit_queue().
 */
static void
tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
		      int prior_packets, int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int is_dupack = (tp->snd_una == prior_snd_una && !(flag&FLAG_NOT_DUP));

	/* Some technical things:
	 * 1. Reno does not count dupacks (sacked_out) automatically. */
	if (!tp->packets_out)
		tp->sacked_out = 0;
        /* 2. SACK counts snd_fack in packets inaccurately. */
	if (tp->sacked_out == 0)
		tp->fackets_out = 0;

        /* Now state machine starts.
	 * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
	if (flag&FLAG_ECE)
		tp->prior_ssthresh = 0;

	/* B. In all the states check for reneging SACKs. */
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	if (tp->sacked_out && tcp_check_sack_reneging(sk))
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		return;

	/* C. Process data loss notification, provided it is valid. */
	if ((flag&FLAG_DATA_LOST) &&
	    before(tp->snd_una, tp->high_seq) &&
	    tp->ca_state != TCP_CA_Open &&
	    tp->fackets_out > tp->reordering) {
		tcp_mark_head_lost(sk, tp, tp->fackets_out-tp->reordering, tp->high_seq);
		NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
	}

	/* D. Synchronize left_out to current state. */
	tcp_sync_left_out(tp);

	/* E. Check state exit conditions. State can be terminated
	 *    when high_seq is ACKed. */
	if (tp->ca_state == TCP_CA_Open) {
		if (!sysctl_tcp_frto)
			BUG_TRAP(tp->retrans_out == 0);
		tp->retrans_stamp = 0;
	} else if (!before(tp->snd_una, tp->high_seq)) {
		switch (tp->ca_state) {
		case TCP_CA_Loss:
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			inet_csk(sk)->icsk_retransmits = 0;
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			if (tcp_try_undo_recovery(sk, tp))
				return;
			break;

		case TCP_CA_CWR:
			/* CWR is to be held something *above* high_seq
			 * is ACKed for CWR bit to reach receiver. */
			if (tp->snd_una != tp->high_seq) {
				tcp_complete_cwr(tp);
				tcp_set_ca_state(tp, TCP_CA_Open);
			}
			break;

		case TCP_CA_Disorder:
			tcp_try_undo_dsack(sk, tp);
			if (!tp->undo_marker ||
			    /* For SACK case do not Open to allow to undo
			     * catching for all duplicate ACKs. */
			    IsReno(tp) || tp->snd_una != tp->high_seq) {
				tp->undo_marker = 0;
				tcp_set_ca_state(tp, TCP_CA_Open);
			}
			break;

		case TCP_CA_Recovery:
			if (IsReno(tp))
				tcp_reset_reno_sack(tp);
			if (tcp_try_undo_recovery(sk, tp))
				return;
			tcp_complete_cwr(tp);
			break;
		}
	}

	/* F. Process state. */
	switch (tp->ca_state) {
	case TCP_CA_Recovery:
		if (prior_snd_una == tp->snd_una) {
			if (IsReno(tp) && is_dupack)
				tcp_add_reno_sack(tp);
		} else {
			int acked = prior_packets - tp->packets_out;
			if (IsReno(tp))
				tcp_remove_reno_sacks(sk, tp, acked);
			is_dupack = tcp_try_undo_partial(sk, tp, acked);
		}
		break;
	case TCP_CA_Loss:
		if (flag&FLAG_DATA_ACKED)
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			inet_csk(sk)->icsk_retransmits = 0;
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		if (!tcp_try_undo_loss(sk, tp)) {
			tcp_moderate_cwnd(tp);
			tcp_xmit_retransmit_queue(sk);
			return;
		}
		if (tp->ca_state != TCP_CA_Open)
			return;
		/* Loss is undone; fall through to processing in Open state. */
	default:
		if (IsReno(tp)) {
			if (tp->snd_una != prior_snd_una)
				tcp_reset_reno_sack(tp);
			if (is_dupack)
				tcp_add_reno_sack(tp);
		}

		if (tp->ca_state == TCP_CA_Disorder)
			tcp_try_undo_dsack(sk, tp);

		if (!tcp_time_to_recover(sk, tp)) {
			tcp_try_to_open(sk, tp, flag);
			return;
		}

		/* Otherwise enter Recovery state */

		if (IsReno(tp))
			NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
		else
			NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);

		tp->high_seq = tp->snd_nxt;
		tp->prior_ssthresh = 0;
		tp->undo_marker = tp->snd_una;
		tp->undo_retrans = tp->retrans_out;

		if (tp->ca_state < TCP_CA_CWR) {
			if (!(flag&FLAG_ECE))
				tp->prior_ssthresh = tcp_current_ssthresh(tp);
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			tp->snd_ssthresh = tp->ca_ops->ssthresh(tp);
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			TCP_ECN_queue_cwr(tp);
		}

		tp->snd_cwnd_cnt = 0;
		tcp_set_ca_state(tp, TCP_CA_Recovery);
	}

	if (is_dupack || tcp_head_timedout(sk, tp))
		tcp_update_scoreboard(sk, tp);
	tcp_cwnd_down(tp);
	tcp_xmit_retransmit_queue(sk);
}

/* Read draft-ietf-tcplw-high-performance before mucking
 * with this code. (Superceeds RFC1323)
 */
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static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
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{
	/* RTTM Rule: A TSecr value received in a segment is used to
	 * update the averaged RTT measurement only if the segment
	 * acknowledges some new data, i.e., only if it advances the
	 * left edge of the send window.
	 *
	 * See draft-ietf-tcplw-high-performance-00, section 3.3.
	 * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
	 *
	 * Changed: reset backoff as soon as we see the first valid sample.
	 * If we do not, we get strongly overstimated rto. With timestamps
	 * samples are accepted even from very old segments: f.e., when rtt=1
	 * increases to 8, we retransmit 5 times and after 8 seconds delayed
	 * answer arrives rto becomes 120 seconds! If at least one of segments
	 * in window is lost... Voila.	 			--ANK (010210)
	 */
1909 1910
	struct tcp_sock *tp = tcp_sk(sk);
	const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
1911
	tcp_rtt_estimator(tp, seq_rtt, usrtt);
1912 1913 1914
	tcp_set_rto(sk);
	inet_csk(sk)->icsk_backoff = 0;
	tcp_bound_rto(sk);
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}

1917
static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
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{
	/* We don't have a timestamp. Can only use
	 * packets that are not retransmitted to determine
	 * rtt estimates. Also, we must not reset the
	 * backoff for rto until we get a non-retransmitted
	 * packet. This allows us to deal with a situation
	 * where the network delay has increased suddenly.
	 * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
	 */

	if (flag & FLAG_RETRANS_DATA_ACKED)
		return;

1931 1932 1933 1934
	tcp_rtt_estimator(tcp_sk(sk), seq_rtt, usrtt);
	tcp_set_rto(sk);
	inet_csk(sk)->icsk_backoff = 0;
	tcp_bound_rto(sk);
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}

1937 1938
static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
				      const s32 seq_rtt, u32 *usrtt)
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{
1940
	const struct tcp_sock *tp = tcp_sk(sk);
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	/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
	if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
1943
		tcp_ack_saw_tstamp(sk, usrtt, flag);
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	else if (seq_rtt >= 0)
1945
		tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
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}

1948 1949
static inline void tcp_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,
				  u32 in_flight, int good)
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{
1951
	tp->ca_ops->cong_avoid(tp, ack, rtt, in_flight, good);
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	tp->snd_cwnd_stamp = tcp_time_stamp;
}

/* Restart timer after forward progress on connection.
 * RFC2988 recommends to restart timer to now+rto.
 */

static inline void tcp_ack_packets_out(struct sock *sk, struct tcp_sock *tp)
{
	if (!tp->packets_out) {
1962
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
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	} else {
1964
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
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	}
}

static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
			 __u32 now, __s32 *seq_rtt)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
	__u32 seq = tp->snd_una;
	__u32 packets_acked;
	int acked = 0;

	/* If we get here, the whole TSO packet has not been
	 * acked.
	 */
	BUG_ON(!after(scb->end_seq, seq));

	packets_acked = tcp_skb_pcount(skb);
	if (tcp_trim_head(sk, skb, seq - scb->seq))
		return 0;
	packets_acked -= tcp_skb_pcount(skb);

	if (packets_acked) {
		__u8 sacked = scb->sacked;

		acked |= FLAG_DATA_ACKED;
		if (sacked) {
			if (sacked & TCPCB_RETRANS) {
				if (sacked & TCPCB_SACKED_RETRANS)
					tp->retrans_out -= packets_acked;
				acked |= FLAG_RETRANS_DATA_ACKED;
				*seq_rtt = -1;
			} else if (*seq_rtt < 0)
				*seq_rtt = now - scb->when;
			if (sacked & TCPCB_SACKED_ACKED)
				tp->sacked_out -= packets_acked;
			if (sacked & TCPCB_LOST)
				tp->lost_out -= packets_acked;
			if (sacked & TCPCB_URG) {
				if (tp->urg_mode &&
				    !before(seq, tp->snd_up))
					tp->urg_mode = 0;
			}
		} else if (*seq_rtt < 0)
			*seq_rtt = now - scb->when;

		if (tp->fackets_out) {
			__u32 dval = min(tp->fackets_out, packets_acked);
			tp->fackets_out -= dval;
		}
		tp->packets_out -= packets_acked;

		BUG_ON(tcp_skb_pcount(skb) == 0);
		BUG_ON(!before(scb->seq, scb->end_seq));
	}

	return acked;
}


/* Remove acknowledged frames from the retransmission queue. */
2026
static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
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{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb;
	__u32 now = tcp_time_stamp;
	int acked = 0;
	__s32 seq_rtt = -1;
2033 2034 2035 2036 2037
	struct timeval usnow;
	u32 pkts_acked = 0;

	if (seq_usrtt)
		do_gettimeofday(&usnow);
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	while ((skb = skb_peek(&sk->sk_write_queue)) &&
	       skb != sk->sk_send_head) {
		struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 
		__u8 sacked = scb->sacked;

		/* If our packet is before the ack sequence we can
		 * discard it as it's confirmed to have arrived at
		 * the other end.
		 */
		if (after(scb->end_seq, tp->snd_una)) {
2049 2050
			if (tcp_skb_pcount(skb) > 1 &&
			    after(tp->snd_una, scb->seq))
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				acked |= tcp_tso_acked(sk, skb,
						       now, &seq_rtt);
			break;
		}

		/* Initial outgoing SYN's get put onto the write_queue
		 * just like anything else we transmit.  It is not
		 * true data, and if we misinform our callers that
		 * this ACK acks real data, we will erroneously exit
		 * connection startup slow start one packet too
		 * quickly.  This is severely frowned upon behavior.
		 */
		if (!(scb->flags & TCPCB_FLAG_SYN)) {
			acked |= FLAG_DATA_ACKED;
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			++pkts_acked;
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		} else {
			acked |= FLAG_SYN_ACKED;
			tp->retrans_stamp = 0;
		}

		if (sacked) {
			if (sacked & TCPCB_RETRANS) {
				if(sacked & TCPCB_SACKED_RETRANS)
					tp->retrans_out -= tcp_skb_pcount(skb);
				acked |= FLAG_RETRANS_DATA_ACKED;
				seq_rtt = -1;
			} else if (seq_rtt < 0)
				seq_rtt = now - scb->when;
2079 2080 2081 2082
			if (seq_usrtt)
				*seq_usrtt = (usnow.tv_sec - skb->stamp.tv_sec) * 1000000
					+ (usnow.tv_usec - skb->stamp.tv_usec);

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			if (sacked & TCPCB_SACKED_ACKED)
				tp->sacked_out -= tcp_skb_pcount(skb);
			if (sacked & TCPCB_LOST)
				tp->lost_out -= tcp_skb_pcount(skb);
			if (sacked & TCPCB_URG) {
				if (tp->urg_mode &&
				    !before(scb->end_seq, tp->snd_up))
					tp->urg_mode = 0;
			}
		} else if (seq_rtt < 0)
			seq_rtt = now - scb->when;
		tcp_dec_pcount_approx(&tp->fackets_out, skb);
		tcp_packets_out_dec(tp, skb);
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		__skb_unlink(skb, &sk->sk_write_queue);
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		sk_stream_free_skb(sk, skb);
	}

	if (acked&FLAG_ACKED) {
2101
		tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
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		tcp_ack_packets_out(sk, tp);
2103 2104 2105

		if (tp->ca_ops->pkts_acked)
			tp->ca_ops->pkts_acked(tp, pkts_acked);
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	}

#if FASTRETRANS_DEBUG > 0
	BUG_TRAP((int)tp->sacked_out >= 0);
	BUG_TRAP((int)tp->lost_out >= 0);
	BUG_TRAP((int)tp->retrans_out >= 0);
	if (!tp->packets_out && tp->rx_opt.sack_ok) {
		if (tp->lost_out) {
			printk(KERN_DEBUG "Leak l=%u %d\n",
			       tp->lost_out, tp->ca_state);
			tp->lost_out = 0;
		}
		if (tp->sacked_out) {
			printk(KERN_DEBUG "Leak s=%u %d\n",
			       tp->sacked_out, tp->ca_state);
			tp->sacked_out = 0;
		}
		if (tp->retrans_out) {
			printk(KERN_DEBUG "Leak r=%u %d\n",
			       tp->retrans_out, tp->ca_state);
			tp->retrans_out = 0;
		}
	}
#endif
	*seq_rtt_p = seq_rtt;
	return acked;
}

static void tcp_ack_probe(struct sock *sk)
{
2136 2137
	const struct tcp_sock *tp = tcp_sk(sk);
	struct inet_connection_sock *icsk = inet_csk(sk);
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	/* Was it a usable window open? */

	if (!after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
		   tp->snd_una + tp->snd_wnd)) {
2143 2144
		icsk->icsk_backoff = 0;
		inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
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		/* Socket must be waked up by subsequent tcp_data_snd_check().
		 * This function is not for random using!
		 */
	} else {
2149
		inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2150 2151
					  min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
					  TCP_RTO_MAX);
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	}
}

static inline int tcp_ack_is_dubious(struct tcp_sock *tp, int flag)
{
	return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
		tp->ca_state != TCP_CA_Open);
}

static inline int tcp_may_raise_cwnd(struct tcp_sock *tp, int flag)
{
	return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
		!((1<<tp->ca_state)&(TCPF_CA_Recovery|TCPF_CA_CWR));
}

/* Check that window update is acceptable.
 * The function assumes that snd_una<=ack<=snd_next.
 */
2170 2171
static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
					const u32 ack_seq, const u32 nwin)
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{
	return (after(ack, tp->snd_una) ||
		after(ack_seq, tp->snd_wl1) ||
		(ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
}

/* Update our send window.
 *
 * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
 * and in FreeBSD. NetBSD's one is even worse.) is wrong.
 */
static int tcp_ack_update_window(struct sock *sk, struct tcp_sock *tp,
				 struct sk_buff *skb, u32 ack, u32 ack_seq)
{
	int flag = 0;
	u32 nwin = ntohs(skb->h.th->window);

	if (likely(!skb->h.th->syn))
		nwin <<= tp->rx_opt.snd_wscale;

	if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
		flag |= FLAG_WIN_UPDATE;
		tcp_update_wl(tp, ack, ack_seq);

		if (tp->snd_wnd != nwin) {
			tp->snd_wnd = nwin;

			/* Note, it is the only place, where
			 * fast path is recovered for sending TCP.
			 */
			tcp_fast_path_check(sk, tp);

			if (nwin > tp->max_window) {
				tp->max_window = nwin;
				tcp_sync_mss(sk, tp->pmtu_cookie);
			}
		}
	}

	tp->snd_una = ack;

	return flag;
}

static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)
{
	struct tcp_sock *tp = tcp_sk(sk);
	
	tcp_sync_left_out(tp);
	
	if (tp->snd_una == prior_snd_una ||
	    !before(tp->snd_una, tp->frto_highmark)) {
		/* RTO was caused by loss, start retransmitting in
		 * go-back-N slow start
		 */
		tcp_enter_frto_loss(sk);
		return;
	}

	if (tp->frto_counter == 1) {
		/* First ACK after RTO advances the window: allow two new
		 * segments out.
		 */
		tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
	} else {
		/* Also the second ACK after RTO advances the window.
		 * The RTO was likely spurious. Reduce cwnd and continue
		 * in congestion avoidance
		 */
		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
		tcp_moderate_cwnd(tp);
	}

	/* F-RTO affects on two new ACKs following RTO.
	 * At latest on third ACK the TCP behavor is back to normal.
	 */
	tp->frto_counter = (tp->frto_counter + 1) % 3;
}

/* This routine deals with incoming acks, but not outgoing ones. */
static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 prior_snd_una = tp->snd_una;
	u32 ack_seq = TCP_SKB_CB(skb)->seq;
	u32 ack = TCP_SKB_CB(skb)->ack_seq;
	u32 prior_in_flight;
	s32 seq_rtt;
2260
	s32 seq_usrtt = 0;
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	int prior_packets;

	/* If the ack is newer than sent or older than previous acks
	 * then we can probably ignore it.
	 */
	if (after(ack, tp->snd_nxt))
		goto uninteresting_ack;

	if (before(ack, prior_snd_una))
		goto old_ack;

	if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
		/* Window is constant, pure forward advance.
		 * No more checks are required.
		 * Note, we use the fact that SND.UNA>=SND.WL2.
		 */
		tcp_update_wl(tp, ack, ack_seq);
		tp->snd_una = ack;
		flag |= FLAG_WIN_UPDATE;

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		tcp_ca_event(tp, CA_EVENT_FAST_ACK);

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		NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
	} else {
		if (ack_seq != TCP_SKB_CB(skb)->end_seq)
			flag |= FLAG_DATA;
		else
			NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);

		flag |= tcp_ack_update_window(sk, tp, skb, ack, ack_seq);

		if (TCP_SKB_CB(skb)->sacked)
			flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);

		if (TCP_ECN_rcv_ecn_echo(tp, skb->h.th))
			flag |= FLAG_ECE;

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		tcp_ca_event(tp, CA_EVENT_SLOW_ACK);
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	}

	/* We passed data and got it acked, remove any soft error
	 * log. Something worked...
	 */
	sk->sk_err_soft = 0;
	tp->rcv_tstamp = tcp_time_stamp;
	prior_packets = tp->packets_out;
	if (!prior_packets)
		goto no_queue;

	prior_in_flight = tcp_packets_in_flight(tp);

	/* See if we can take anything off of the retransmit queue. */
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	flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
				    tp->ca_ops->rtt_sample ? &seq_usrtt : NULL);
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	if (tp->frto_counter)
		tcp_process_frto(sk, prior_snd_una);

	if (tcp_ack_is_dubious(tp, flag)) {
		/* Advanve CWND, if state allows this. */
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		if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(tp, flag))
			tcp_cong_avoid(tp, ack,  seq_rtt, prior_in_flight, 0);
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		tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
	} else {
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		if ((flag & FLAG_DATA_ACKED))
			tcp_cong_avoid(tp, ack, seq_rtt, prior_in_flight, 1);
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	}

	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag&FLAG_NOT_DUP))
		dst_confirm(sk->sk_dst_cache);

	return 1;

no_queue:
	tp->probes_out = 0;

	/* If this ack opens up a zero window, clear backoff.  It was
	 * being used to time the probes, and is probably far higher than
	 * it needs to be for normal retransmission.
	 */
	if (sk->sk_send_head)
		tcp_ack_probe(sk);
	return 1;

old_ack:
	if (TCP_SKB_CB(skb)->sacked)
		tcp_sacktag_write_queue(sk, skb, prior_snd_una);

uninteresting_ack:
	SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
	return 0;
}


/* Look for tcp options. Normally only called on SYN and SYNACK packets.
 * But, this can also be called on packets in the established flow when
 * the fast version below fails.
 */
void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx, int estab)
{
	unsigned char *ptr;
	struct tcphdr *th = skb->h.th;
	int length=(th->doff*4)-sizeof(struct tcphdr);

	ptr = (unsigned char *)(th + 1);
	opt_rx->saw_tstamp = 0;

	while(length>0) {
	  	int opcode=*ptr++;
		int opsize;

		switch (opcode) {
			case TCPOPT_EOL:
				return;
			case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
				length--;
				continue;
			default:
				opsize=*ptr++;
				if (opsize < 2) /* "silly options" */
					return;
				if (opsize > length)
					return;	/* don't parse partial options */
	  			switch(opcode) {
				case TCPOPT_MSS:
					if(opsize==TCPOLEN_MSS && th->syn && !estab) {
						u16 in_mss = ntohs(get_unaligned((__u16 *)ptr));
						if (in_mss) {
							if (opt_rx->user_mss && opt_rx->user_mss < in_mss)
								in_mss = opt_rx->user_mss;
							opt_rx->mss_clamp = in_mss;
						}
					}
					break;
				case TCPOPT_WINDOW:
					if(opsize==TCPOLEN_WINDOW && th->syn && !estab)
						if (sysctl_tcp_window_scaling) {
							__u8 snd_wscale = *(__u8 *) ptr;
							opt_rx->wscale_ok = 1;
							if (snd_wscale > 14) {
								if(net_ratelimit())
									printk(KERN_INFO "tcp_parse_options: Illegal window "
									       "scaling value %d >14 received.\n",
									       snd_wscale);
								snd_wscale = 14;
							}
							opt_rx->snd_wscale = snd_wscale;
						}
					break;
				case TCPOPT_TIMESTAMP:
					if(opsize==TCPOLEN_TIMESTAMP) {
						if ((estab && opt_rx->tstamp_ok) ||
						    (!estab && sysctl_tcp_timestamps)) {
							opt_rx->saw_tstamp = 1;
							opt_rx->rcv_tsval = ntohl(get_unaligned((__u32 *)ptr));
							opt_rx->rcv_tsecr = ntohl(get_unaligned((__u32 *)(ptr+4)));
						}
					}
					break;
				case TCPOPT_SACK_PERM:
					if(opsize==TCPOLEN_SACK_PERM && th->syn && !estab) {
						if (sysctl_tcp_sack) {
							opt_rx->sack_ok = 1;
							tcp_sack_reset(opt_rx);
						}
					}
					break;

				case TCPOPT_SACK:
					if((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
					   !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
					   opt_rx->sack_ok) {
						TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
					}
	  			};
	  			ptr+=opsize-2;
	  			length-=opsize;
	  	};
	}
}

/* Fast parse options. This hopes to only see timestamps.
 * If it is wrong it falls back on tcp_parse_options().
 */
static inline int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
					 struct tcp_sock *tp)
{
	if (th->doff == sizeof(struct tcphdr)>>2) {
		tp->rx_opt.saw_tstamp = 0;
		return 0;
	} else if (tp->rx_opt.tstamp_ok &&
		   th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
		__u32 *ptr = (__u32 *)(th + 1);
		if (*ptr == ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
				  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
			tp->rx_opt.saw_tstamp = 1;
			++ptr;
			tp->rx_opt.rcv_tsval = ntohl(*ptr);
			++ptr;
			tp->rx_opt.rcv_tsecr = ntohl(*ptr);
			return 1;
		}
	}
	tcp_parse_options(skb, &tp->rx_opt, 1);
	return 1;
}

static inline void tcp_store_ts_recent(struct tcp_sock *tp)
{
	tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
	tp->rx_opt.ts_recent_stamp = xtime.tv_sec;
}

static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
{
	if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
		/* PAWS bug workaround wrt. ACK frames, the PAWS discard
		 * extra check below makes sure this can only happen
		 * for pure ACK frames.  -DaveM
		 *
		 * Not only, also it occurs for expired timestamps.
		 */

		if((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
		   xtime.tv_sec >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
			tcp_store_ts_recent(tp);
	}
}

/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
 *
 * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
 * it can pass through stack. So, the following predicate verifies that
 * this segment is not used for anything but congestion avoidance or
 * fast retransmit. Moreover, we even are able to eliminate most of such
 * second order effects, if we apply some small "replay" window (~RTO)
 * to timestamp space.
 *
 * All these measures still do not guarantee that we reject wrapped ACKs
 * on networks with high bandwidth, when sequence space is recycled fastly,
 * but it guarantees that such events will be very rare and do not affect
 * connection seriously. This doesn't look nice, but alas, PAWS is really
 * buggy extension.
 *
 * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
 * states that events when retransmit arrives after original data are rare.
 * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
 * the biggest problem on large power networks even with minor reordering.
 * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
 * up to bandwidth of 18Gigabit/sec. 8) ]
 */

2513
static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
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{
2515
	struct tcp_sock *tp = tcp_sk(sk);
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	struct tcphdr *th = skb->h.th;
	u32 seq = TCP_SKB_CB(skb)->seq;
	u32 ack = TCP_SKB_CB(skb)->ack_seq;

	return (/* 1. Pure ACK with correct sequence number. */
		(th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&

		/* 2. ... and duplicate ACK. */
		ack == tp->snd_una &&

		/* 3. ... and does not update window. */
		!tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&

		/* 4. ... and sits in replay window. */
2530
		(s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
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}

2533
static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
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{
2535
	const struct tcp_sock *tp = tcp_sk(sk);
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	return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
		xtime.tv_sec < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
2538
		!tcp_disordered_ack(sk, skb));
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}

/* Check segment sequence number for validity.
 *
 * Segment controls are considered valid, if the segment
 * fits to the window after truncation to the window. Acceptability
 * of data (and SYN, FIN, of course) is checked separately.
 * See tcp_data_queue(), for example.
 *
 * Also, controls (RST is main one) are accepted using RCV.WUP instead
 * of RCV.NXT. Peer still did not advance his SND.UNA when we
 * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
 * (borrowed from freebsd)
 */

static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
	return	!before(end_seq, tp->rcv_wup) &&
		!after(seq, tp->rcv_nxt + tcp_receive_window(tp));
}

/* When we get a reset we do this. */
static void tcp_reset(struct sock *sk)
{
	/* We want the right error as BSD sees it (and indeed as we do). */
	switch (sk->sk_state) {
		case TCP_SYN_SENT:
			sk->sk_err = ECONNREFUSED;
			break;
		case TCP_CLOSE_WAIT:
			sk->sk_err = EPIPE;
			break;
		case TCP_CLOSE:
			return;
		default:
			sk->sk_err = ECONNRESET;
	}

	if (!sock_flag(sk, SOCK_DEAD))
		sk->sk_error_report(sk);

	tcp_done(sk);
}

/*
 * 	Process the FIN bit. This now behaves as it is supposed to work
 *	and the FIN takes effect when it is validly part of sequence
 *	space. Not before when we get holes.
 *
 *	If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
 *	(and thence onto LAST-ACK and finally, CLOSE, we never enter
 *	TIME-WAIT)
 *
 *	If we are in FINWAIT-1, a received FIN indicates simultaneous
 *	close and we go into CLOSING (and later onto TIME-WAIT)
 *
 *	If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
 */
static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
{
	struct tcp_sock *tp = tcp_sk(sk);

2601
	inet_csk_schedule_ack(sk);
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	sk->sk_shutdown |= RCV_SHUTDOWN;
	sock_set_flag(sk, SOCK_DONE);

	switch (sk->sk_state) {
		case TCP_SYN_RECV:
		case TCP_ESTABLISHED:
			/* Move to CLOSE_WAIT */
			tcp_set_state(sk, TCP_CLOSE_WAIT);
2611
			inet_csk(sk)->icsk_ack.pingpong = 1;
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			break;

		case TCP_CLOSE_WAIT:
		case TCP_CLOSING:
			/* Received a retransmission of the FIN, do
			 * nothing.
			 */
			break;
		case TCP_LAST_ACK:
			/* RFC793: Remain in the LAST-ACK state. */
			break;

		case TCP_FIN_WAIT1:
			/* This case occurs when a simultaneous close
			 * happens, we must ack the received FIN and
			 * enter the CLOSING state.
			 */
			tcp_send_ack(sk);
			tcp_set_state(sk, TCP_CLOSING);
			break;
		case TCP_FIN_WAIT2:
			/* Received a FIN -- send ACK and enter TIME_WAIT. */
			tcp_send_ack(sk);
			tcp_time_wait(sk, TCP_TIME_WAIT, 0);
			break;
		default:
			/* Only TCP_LISTEN and TCP_CLOSE are left, in these
			 * cases we should never reach this piece of code.
			 */
			printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
			       __FUNCTION__, sk->sk_state);
			break;
	};

	/* It _is_ possible, that we have something out-of-order _after_ FIN.
	 * Probably, we should reset in this case. For now drop them.
	 */
	__skb_queue_purge(&tp->out_of_order_queue);
	if (tp->rx_opt.sack_ok)
		tcp_sack_reset(&tp->rx_opt);
	sk_stream_mem_reclaim(sk);

	if (!sock_flag(sk, SOCK_DEAD)) {
		sk->sk_state_change(sk);

		/* Do not send POLL_HUP for half duplex close. */
		if (sk->sk_shutdown == SHUTDOWN_MASK ||
		    sk->sk_state == TCP_CLOSE)
			sk_wake_async(sk, 1, POLL_HUP);
		else
			sk_wake_async(sk, 1, POLL_IN);
	}
}

static __inline__ int
tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, u32 end_seq)
{
	if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
		if (before(seq, sp->start_seq))
			sp->start_seq = seq;
		if (after(end_seq, sp->end_seq))
			sp->end_seq = end_seq;
		return 1;
	}
	return 0;
}

static inline void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
	if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
		if (before(seq, tp->rcv_nxt))
			NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
		else
			NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);

		tp->rx_opt.dsack = 1;
		tp->duplicate_sack[0].start_seq = seq;
		tp->duplicate_sack[0].end_seq = end_seq;
		tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1, 4 - tp->rx_opt.tstamp_ok);
	}
}

static inline void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
{
	if (!tp->rx_opt.dsack)
		tcp_dsack_set(tp, seq, end_seq);
	else
		tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
}

static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
	    before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
2709
		tcp_enter_quickack_mode(sk);
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		if (tp->rx_opt.sack_ok && sysctl_tcp_dsack) {
			u32 end_seq = TCP_SKB_CB(skb)->end_seq;

			if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
				end_seq = tp->rcv_nxt;
			tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
		}
	}

	tcp_send_ack(sk);
}

/* These routines update the SACK block as out-of-order packets arrive or
 * in-order packets close up the sequence space.
 */
static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
{
	int this_sack;
	struct tcp_sack_block *sp = &tp->selective_acks[0];
	struct tcp_sack_block *swalk = sp+1;

	/* See if the recent change to the first SACK eats into
	 * or hits the sequence space of other SACK blocks, if so coalesce.
	 */
	for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; ) {
		if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
			int i;

			/* Zap SWALK, by moving every further SACK up by one slot.
			 * Decrease num_sacks.
			 */
			tp->rx_opt.num_sacks--;
			tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
			for(i=this_sack; i < tp->rx_opt.num_sacks; i++)
				sp[i] = sp[i+1];
			continue;
		}
		this_sack++, swalk++;
	}
}

static __inline__ void tcp_sack_swap(struct tcp_sack_block *sack1, struct tcp_sack_block *sack2)
{
	__u32 tmp;

	tmp = sack1->start_seq;
	sack1->start_seq = sack2->start_seq;
	sack2->start_seq = tmp;

	tmp = sack1->end_seq;
	sack1->end_seq = sack2->end_seq;
	sack2->end_seq = tmp;
}

static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct tcp_sack_block *sp = &tp->selective_acks[0];
	int cur_sacks = tp->rx_opt.num_sacks;
	int this_sack;

	if (!cur_sacks)
		goto new_sack;

	for (this_sack=0; this_sack<cur_sacks; this_sack++, sp++) {
		if (tcp_sack_extend(sp, seq, end_seq)) {
			/* Rotate this_sack to the first one. */
			for (; this_sack>0; this_sack--, sp--)
				tcp_sack_swap(sp, sp-1);
			if (cur_sacks > 1)
				tcp_sack_maybe_coalesce(tp);
			return;
		}
	}

	/* Could not find an adjacent existing SACK, build a new one,
	 * put it at the front, and shift everyone else down.  We
	 * always know there is at least one SACK present already here.
	 *
	 * If the sack array is full, forget about the last one.
	 */
	if (this_sack >= 4) {
		this_sack--;
		tp->rx_opt.num_sacks--;
		sp--;
	}
	for(; this_sack > 0; this_sack--, sp--)
		*sp = *(sp-1);

new_sack:
	/* Build the new head SACK, and we're done. */
	sp->start_seq = seq;
	sp->end_seq = end_seq;
	tp->rx_opt.num_sacks++;
	tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
}

/* RCV.NXT advances, some SACKs should be eaten. */

static void tcp_sack_remove(struct tcp_sock *tp)
{
	struct tcp_sack_block *sp = &tp->selective_acks[0];
	int num_sacks = tp->rx_opt.num_sacks;
	int this_sack;

	/* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
2817
	if (skb_queue_empty(&tp->out_of_order_queue)) {
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		tp->rx_opt.num_sacks = 0;
		tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
		return;
	}

	for(this_sack = 0; this_sack < num_sacks; ) {
		/* Check if the start of the sack is covered by RCV.NXT. */
		if (!before(tp->rcv_nxt, sp->start_seq)) {
			int i;

			/* RCV.NXT must cover all the block! */
			BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));

			/* Zap this SACK, by moving forward any other SACKS. */
			for (i=this_sack+1; i < num_sacks; i++)
				tp->selective_acks[i-1] = tp->selective_acks[i];
			num_sacks--;
			continue;
		}
		this_sack++;
		sp++;
	}
	if (num_sacks != tp->rx_opt.num_sacks) {
		tp->rx_opt.num_sacks = num_sacks;
		tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack, 4 - tp->rx_opt.tstamp_ok);
	}
}

/* This one checks to see if we can put data from the
 * out_of_order queue into the receive_queue.
 */
static void tcp_ofo_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	__u32 dsack_high = tp->rcv_nxt;
	struct sk_buff *skb;

	while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
		if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
			break;

		if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
			__u32 dsack = dsack_high;
			if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
				dsack_high = TCP_SKB_CB(skb)->end_seq;
			tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
		}

		if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
			SOCK_DEBUG(sk, "ofo packet was already received \n");
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			__skb_unlink(skb, &tp->out_of_order_queue);
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			__kfree_skb(skb);
			continue;
		}
		SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
			   TCP_SKB_CB(skb)->end_seq);

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		__skb_unlink(skb, &tp->out_of_order_queue);
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		__skb_queue_tail(&sk->sk_receive_queue, skb);
		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
		if(skb->h.th->fin)
			tcp_fin(skb, sk, skb->h.th);
	}
}

static int tcp_prune_queue(struct sock *sk);

static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
{
	struct tcphdr *th = skb->h.th;
	struct tcp_sock *tp = tcp_sk(sk);
	int eaten = -1;

	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
		goto drop;

	__skb_pull(skb, th->doff*4);

	TCP_ECN_accept_cwr(tp, skb);

	if (tp->rx_opt.dsack) {
		tp->rx_opt.dsack = 0;
		tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
						    4 - tp->rx_opt.tstamp_ok);
	}

	/*  Queue data for delivery to the user.
	 *  Packets in sequence go to the receive queue.
	 *  Out of sequence packets to the out_of_order_queue.
	 */
	if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
		if (tcp_receive_window(tp) == 0)
			goto out_of_window;

		/* Ok. In sequence. In window. */
		if (tp->ucopy.task == current &&
		    tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
		    sock_owned_by_user(sk) && !tp->urg_data) {
			int chunk = min_t(unsigned int, skb->len,
							tp->ucopy.len);

			__set_current_state(TASK_RUNNING);

			local_bh_enable();
			if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
				tp->ucopy.len -= chunk;
				tp->copied_seq += chunk;
				eaten = (chunk == skb->len && !th->fin);
				tcp_rcv_space_adjust(sk);
			}
			local_bh_disable();
		}

		if (eaten <= 0) {
queue_and_out:
			if (eaten < 0 &&
			    (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
			     !sk_stream_rmem_schedule(sk, skb))) {
				if (tcp_prune_queue(sk) < 0 ||
				    !sk_stream_rmem_schedule(sk, skb))
					goto drop;
			}
			sk_stream_set_owner_r(skb, sk);
			__skb_queue_tail(&sk->sk_receive_queue, skb);
		}
		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
		if(skb->len)
			tcp_event_data_recv(sk, tp, skb);
		if(th->fin)
			tcp_fin(skb, sk, th);

2950
		if (!skb_queue_empty(&tp->out_of_order_queue)) {
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			tcp_ofo_queue(sk);

			/* RFC2581. 4.2. SHOULD send immediate ACK, when
			 * gap in queue is filled.
			 */
2956
			if (skb_queue_empty(&tp->out_of_order_queue))
2957
				inet_csk(sk)->icsk_ack.pingpong = 0;
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		}

		if (tp->rx_opt.num_sacks)
			tcp_sack_remove(tp);

		tcp_fast_path_check(sk, tp);

		if (eaten > 0)
			__kfree_skb(skb);
		else if (!sock_flag(sk, SOCK_DEAD))
			sk->sk_data_ready(sk, 0);
		return;
	}

	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
		/* A retransmit, 2nd most common case.  Force an immediate ack. */
		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
		tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);

out_of_window:
2978 2979
		tcp_enter_quickack_mode(sk);
		inet_csk_schedule_ack(sk);
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drop:
		__kfree_skb(skb);
		return;
	}

	/* Out of window. F.e. zero window probe. */
	if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
		goto out_of_window;

2989
	tcp_enter_quickack_mode(sk);
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	if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		/* Partial packet, seq < rcv_next < end_seq */
		SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
			   tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
			   TCP_SKB_CB(skb)->end_seq);

		tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
		
		/* If window is closed, drop tail of packet. But after
		 * remembering D-SACK for its head made in previous line.
		 */
		if (!tcp_receive_window(tp))
			goto out_of_window;
		goto queue_and_out;
	}

	TCP_ECN_check_ce(tp, skb);

	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
	    !sk_stream_rmem_schedule(sk, skb)) {
		if (tcp_prune_queue(sk) < 0 ||
		    !sk_stream_rmem_schedule(sk, skb))
			goto drop;
	}

	/* Disable header prediction. */
	tp->pred_flags = 0;
3018
	inet_csk_schedule_ack(sk);
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	SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
		   tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);

	sk_stream_set_owner_r(skb, sk);

	if (!skb_peek(&tp->out_of_order_queue)) {
		/* Initial out of order segment, build 1 SACK. */
		if (tp->rx_opt.sack_ok) {
			tp->rx_opt.num_sacks = 1;
			tp->rx_opt.dsack     = 0;
			tp->rx_opt.eff_sacks = 1;
			tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
			tp->selective_acks[0].end_seq =
						TCP_SKB_CB(skb)->end_seq;
		}
		__skb_queue_head(&tp->out_of_order_queue,skb);
	} else {
		struct sk_buff *skb1 = tp->out_of_order_queue.prev;
		u32 seq = TCP_SKB_CB(skb)->seq;
		u32 end_seq = TCP_SKB_CB(skb)->end_seq;

		if (seq == TCP_SKB_CB(skb1)->end_seq) {
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David S. Miller 已提交
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			__skb_append(skb1, skb, &tp->out_of_order_queue);
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			if (!tp->rx_opt.num_sacks ||
			    tp->selective_acks[0].end_seq != seq)
				goto add_sack;

			/* Common case: data arrive in order after hole. */
			tp->selective_acks[0].end_seq = end_seq;
			return;
		}

		/* Find place to insert this segment. */
		do {
			if (!after(TCP_SKB_CB(skb1)->seq, seq))
				break;
		} while ((skb1 = skb1->prev) !=
			 (struct sk_buff*)&tp->out_of_order_queue);

		/* Do skb overlap to previous one? */
		if (skb1 != (struct sk_buff*)&tp->out_of_order_queue &&
		    before(seq, TCP_SKB_CB(skb1)->end_seq)) {
			if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
				/* All the bits are present. Drop. */
				__kfree_skb(skb);
				tcp_dsack_set(tp, seq, end_seq);
				goto add_sack;
			}
			if (after(seq, TCP_SKB_CB(skb1)->seq)) {
				/* Partial overlap. */
				tcp_dsack_set(tp, seq, TCP_SKB_CB(skb1)->end_seq);
			} else {
				skb1 = skb1->prev;
			}
		}
		__skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
		
		/* And clean segments covered by new one as whole. */
		while ((skb1 = skb->next) !=
		       (struct sk_buff*)&tp->out_of_order_queue &&
		       after(end_seq, TCP_SKB_CB(skb1)->seq)) {
		       if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
			       tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, end_seq);
			       break;
		       }
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		       __skb_unlink(skb1, &tp->out_of_order_queue);
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		       tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq, TCP_SKB_CB(skb1)->end_seq);
		       __kfree_skb(skb1);
		}

add_sack:
		if (tp->rx_opt.sack_ok)
			tcp_sack_new_ofo_skb(sk, seq, end_seq);
	}
}

/* Collapse contiguous sequence of skbs head..tail with
 * sequence numbers start..end.
 * Segments with FIN/SYN are not collapsed (only because this
 * simplifies code)
 */
static void
D
David S. Miller 已提交
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tcp_collapse(struct sock *sk, struct sk_buff_head *list,
	     struct sk_buff *head, struct sk_buff *tail,
	     u32 start, u32 end)
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{
	struct sk_buff *skb;

	/* First, check that queue is collapsable and find
	 * the point where collapsing can be useful. */
	for (skb = head; skb != tail; ) {
		/* No new bits? It is possible on ofo queue. */
		if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
			struct sk_buff *next = skb->next;
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David S. Miller 已提交
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			__skb_unlink(skb, list);
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			__kfree_skb(skb);
			NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
			skb = next;
			continue;
		}

		/* The first skb to collapse is:
		 * - not SYN/FIN and
		 * - bloated or contains data before "start" or
		 *   overlaps to the next one.
		 */
		if (!skb->h.th->syn && !skb->h.th->fin &&
		    (tcp_win_from_space(skb->truesize) > skb->len ||
		     before(TCP_SKB_CB(skb)->seq, start) ||
		     (skb->next != tail &&
		      TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
			break;

		/* Decided to skip this, advance start seq. */
		start = TCP_SKB_CB(skb)->end_seq;
		skb = skb->next;
	}
	if (skb == tail || skb->h.th->syn || skb->h.th->fin)
		return;

	while (before(start, end)) {
		struct sk_buff *nskb;
		int header = skb_headroom(skb);
		int copy = SKB_MAX_ORDER(header, 0);

		/* Too big header? This can happen with IPv6. */
		if (copy < 0)
			return;
		if (end-start < copy)
			copy = end-start;
		nskb = alloc_skb(copy+header, GFP_ATOMIC);
		if (!nskb)
			return;
		skb_reserve(nskb, header);
		memcpy(nskb->head, skb->head, header);
		nskb->nh.raw = nskb->head + (skb->nh.raw-skb->head);
		nskb->h.raw = nskb->head + (skb->h.raw-skb->head);
		nskb->mac.raw = nskb->head + (skb->mac.raw-skb->head);
		memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
		TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
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		__skb_insert(nskb, skb->prev, skb, list);
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Linus Torvalds 已提交
3162 3163 3164 3165 3166 3167 3168 3169 3170 3171 3172 3173 3174 3175 3176 3177 3178 3179
		sk_stream_set_owner_r(nskb, sk);

		/* Copy data, releasing collapsed skbs. */
		while (copy > 0) {
			int offset = start - TCP_SKB_CB(skb)->seq;
			int size = TCP_SKB_CB(skb)->end_seq - start;

			if (offset < 0) BUG();
			if (size > 0) {
				size = min(copy, size);
				if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
					BUG();
				TCP_SKB_CB(nskb)->end_seq += size;
				copy -= size;
				start += size;
			}
			if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
				struct sk_buff *next = skb->next;
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				__skb_unlink(skb, list);
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				__kfree_skb(skb);
				NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
				skb = next;
				if (skb == tail || skb->h.th->syn || skb->h.th->fin)
					return;
			}
		}
	}
}

/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
 * and tcp_collapse() them until all the queue is collapsed.
 */
static void tcp_collapse_ofo_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);
	struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
	struct sk_buff *head;
	u32 start, end;

	if (skb == NULL)
		return;

	start = TCP_SKB_CB(skb)->seq;
	end = TCP_SKB_CB(skb)->end_seq;
	head = skb;

	for (;;) {
		skb = skb->next;

		/* Segment is terminated when we see gap or when
		 * we are at the end of all the queue. */
		if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
		    after(TCP_SKB_CB(skb)->seq, end) ||
		    before(TCP_SKB_CB(skb)->end_seq, start)) {
D
David S. Miller 已提交
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			tcp_collapse(sk, &tp->out_of_order_queue,
				     head, skb, start, end);
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			head = skb;
			if (skb == (struct sk_buff *)&tp->out_of_order_queue)
				break;
			/* Start new segment */
			start = TCP_SKB_CB(skb)->seq;
			end = TCP_SKB_CB(skb)->end_seq;
		} else {
			if (before(TCP_SKB_CB(skb)->seq, start))
				start = TCP_SKB_CB(skb)->seq;
			if (after(TCP_SKB_CB(skb)->end_seq, end))
				end = TCP_SKB_CB(skb)->end_seq;
		}
	}
}

/* Reduce allocated memory if we can, trying to get
 * the socket within its memory limits again.
 *
 * Return less than zero if we should start dropping frames
 * until the socket owning process reads some of the data
 * to stabilize the situation.
 */
static int tcp_prune_queue(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk); 

	SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);

	NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);

	if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
		tcp_clamp_window(sk, tp);
	else if (tcp_memory_pressure)
		tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);

	tcp_collapse_ofo_queue(sk);
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	tcp_collapse(sk, &sk->sk_receive_queue,
		     sk->sk_receive_queue.next,
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		     (struct sk_buff*)&sk->sk_receive_queue,
		     tp->copied_seq, tp->rcv_nxt);
	sk_stream_mem_reclaim(sk);

	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
		return 0;

	/* Collapsing did not help, destructive actions follow.
	 * This must not ever occur. */

	/* First, purge the out_of_order queue. */
3267 3268
	if (!skb_queue_empty(&tp->out_of_order_queue)) {
		NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
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Linus Torvalds 已提交
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		__skb_queue_purge(&tp->out_of_order_queue);

		/* Reset SACK state.  A conforming SACK implementation will
		 * do the same at a timeout based retransmit.  When a connection
		 * is in a sad state like this, we care only about integrity
		 * of the connection not performance.
		 */
		if (tp->rx_opt.sack_ok)
			tcp_sack_reset(&tp->rx_opt);
		sk_stream_mem_reclaim(sk);
	}

	if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
		return 0;

	/* If we are really being abused, tell the caller to silently
	 * drop receive data on the floor.  It will get retransmitted
	 * and hopefully then we'll have sufficient space.
	 */
	NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);

	/* Massive buffer overcommit. */
	tp->pred_flags = 0;
	return -1;
}


/* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
 * As additional protections, we do not touch cwnd in retransmission phases,
 * and if application hit its sndbuf limit recently.
 */
void tcp_cwnd_application_limited(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

	if (tp->ca_state == TCP_CA_Open &&
	    sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
		/* Limited by application or receiver window. */
		u32 win_used = max(tp->snd_cwnd_used, 2U);
		if (win_used < tp->snd_cwnd) {
			tp->snd_ssthresh = tcp_current_ssthresh(tp);
			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
		}
		tp->snd_cwnd_used = 0;
	}
	tp->snd_cwnd_stamp = tcp_time_stamp;
}

3317 3318 3319 3320 3321 3322 3323 3324 3325 3326 3327 3328 3329 3330 3331 3332 3333 3334 3335 3336 3337 3338
static inline int tcp_should_expand_sndbuf(struct sock *sk, struct tcp_sock *tp)
{
	/* If the user specified a specific send buffer setting, do
	 * not modify it.
	 */
	if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
		return 0;

	/* If we are under global TCP memory pressure, do not expand.  */
	if (tcp_memory_pressure)
		return 0;

	/* If we are under soft global TCP memory pressure, do not expand.  */
	if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
		return 0;

	/* If we filled the congestion window, do not expand.  */
	if (tp->packets_out >= tp->snd_cwnd)
		return 0;

	return 1;
}
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/* When incoming ACK allowed to free some skb from write_queue,
 * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
 * on the exit from tcp input handler.
 *
 * PROBLEM: sndbuf expansion does not work well with largesend.
 */
static void tcp_new_space(struct sock *sk)
{
	struct tcp_sock *tp = tcp_sk(sk);

3350
	if (tcp_should_expand_sndbuf(sk, tp)) {
3351
 		int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
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3352 3353 3354 3355 3356 3357 3358 3359 3360 3361 3362 3363 3364 3365 3366 3367 3368 3369 3370 3371 3372 3373
			MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
		    demanded = max_t(unsigned int, tp->snd_cwnd,
						   tp->reordering + 1);
		sndmem *= 2*demanded;
		if (sndmem > sk->sk_sndbuf)
			sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
		tp->snd_cwnd_stamp = tcp_time_stamp;
	}

	sk->sk_write_space(sk);
}

static inline void tcp_check_space(struct sock *sk)
{
	if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
		sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
		if (sk->sk_socket &&
		    test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
			tcp_new_space(sk);
	}
}

3374
static __inline__ void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
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Linus Torvalds 已提交
3375
{
3376
	tcp_push_pending_frames(sk, tp);
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	tcp_check_space(sk);
}

/*
 * Check if sending an ack is needed.
 */
static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
{
	struct tcp_sock *tp = tcp_sk(sk);

	    /* More than one full frame received... */
3388
	if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
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	     /* ... and right edge of window advances far enough.
	      * (tcp_recvmsg() will send ACK otherwise). Or...
	      */
	     && __tcp_select_window(sk) >= tp->rcv_wnd) ||
	    /* We ACK each frame or... */
3394
	    tcp_in_quickack_mode(sk) ||
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	    /* We have out of order data. */
	    (ofo_possible &&
	     skb_peek(&tp->out_of_order_queue))) {
		/* Then ack it now */
		tcp_send_ack(sk);
	} else {
		/* Else, send delayed ack. */
		tcp_send_delayed_ack(sk);
	}
}

static __inline__ void tcp_ack_snd_check(struct sock *sk)
{
3408
	if (!inet_csk_ack_scheduled(sk)) {
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		/* We sent a data segment already. */
		return;
	}
	__tcp_ack_snd_check(sk, 1);
}

/*
 *	This routine is only called when we have urgent data
 *	signalled. Its the 'slow' part of tcp_urg. It could be
 *	moved inline now as tcp_urg is only called from one
 *	place. We handle URGent data wrong. We have to - as
 *	BSD still doesn't use the correction from RFC961.
 *	For 1003.1g we should support a new option TCP_STDURG to permit
 *	either form (or just set the sysctl tcp_stdurg).
 */
 
static void tcp_check_urg(struct sock * sk, struct tcphdr * th)
{
	struct tcp_sock *tp = tcp_sk(sk);
	u32 ptr = ntohs(th->urg_ptr);

	if (ptr && !sysctl_tcp_stdurg)
		ptr--;
	ptr += ntohl(th->seq);

	/* Ignore urgent data that we've already seen and read. */
	if (after(tp->copied_seq, ptr))
		return;

	/* Do not replay urg ptr.
	 *
	 * NOTE: interesting situation not covered by specs.
	 * Misbehaving sender may send urg ptr, pointing to segment,
	 * which we already have in ofo queue. We are not able to fetch
	 * such data and will stay in TCP_URG_NOTYET until will be eaten
	 * by recvmsg(). Seems, we are not obliged to handle such wicked
	 * situations. But it is worth to think about possibility of some
	 * DoSes using some hypothetical application level deadlock.
	 */
	if (before(ptr, tp->rcv_nxt))
		return;

	/* Do we already have a newer (or duplicate) urgent pointer? */
	if (tp->urg_data && !after(ptr, tp->urg_seq))
		return;

	/* Tell the world about our new urgent pointer. */
	sk_send_sigurg(sk);

	/* We may be adding urgent data when the last byte read was
	 * urgent. To do this requires some care. We cannot just ignore
	 * tp->copied_seq since we would read the last urgent byte again
	 * as data, nor can we alter copied_seq until this data arrives
	 * or we break the sematics of SIOCATMARK (and thus sockatmark())
	 *
	 * NOTE. Double Dutch. Rendering to plain English: author of comment
	 * above did something sort of 	send("A", MSG_OOB); send("B", MSG_OOB);
	 * and expect that both A and B disappear from stream. This is _wrong_.
	 * Though this happens in BSD with high probability, this is occasional.
	 * Any application relying on this is buggy. Note also, that fix "works"
	 * only in this artificial test. Insert some normal data between A and B and we will
	 * decline of BSD again. Verdict: it is better to remove to trap
	 * buggy users.
	 */
	if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
	    !sock_flag(sk, SOCK_URGINLINE) &&
	    tp->copied_seq != tp->rcv_nxt) {
		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
		tp->copied_seq++;
		if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
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David S. Miller 已提交
3479
			__skb_unlink(skb, &sk->sk_receive_queue);
L
Linus Torvalds 已提交
3480 3481 3482 3483 3484 3485 3486 3487 3488 3489 3490 3491 3492 3493 3494 3495 3496 3497 3498 3499 3500 3501 3502 3503 3504 3505 3506 3507 3508 3509 3510 3511 3512 3513 3514 3515 3516 3517 3518 3519 3520 3521 3522 3523 3524 3525 3526 3527 3528 3529 3530 3531 3532 3533 3534 3535 3536 3537 3538 3539 3540 3541 3542 3543 3544 3545 3546 3547 3548 3549 3550 3551 3552 3553 3554 3555 3556 3557 3558 3559 3560 3561 3562 3563 3564 3565 3566 3567 3568 3569 3570 3571 3572 3573 3574 3575 3576 3577 3578 3579 3580 3581 3582 3583 3584 3585 3586 3587 3588 3589 3590 3591 3592 3593 3594 3595 3596 3597 3598 3599 3600 3601 3602 3603 3604 3605 3606 3607 3608 3609 3610 3611 3612 3613 3614 3615 3616 3617 3618 3619 3620 3621 3622 3623 3624 3625 3626 3627 3628 3629 3630 3631 3632 3633 3634 3635 3636 3637 3638 3639 3640 3641 3642 3643 3644 3645 3646 3647 3648 3649 3650 3651 3652 3653 3654 3655 3656 3657 3658 3659 3660 3661
			__kfree_skb(skb);
		}
	}

	tp->urg_data   = TCP_URG_NOTYET;
	tp->urg_seq    = ptr;

	/* Disable header prediction. */
	tp->pred_flags = 0;
}

/* This is the 'fast' part of urgent handling. */
static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/* Check if we get a new urgent pointer - normally not. */
	if (th->urg)
		tcp_check_urg(sk,th);

	/* Do we wait for any urgent data? - normally not... */
	if (tp->urg_data == TCP_URG_NOTYET) {
		u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
			  th->syn;

		/* Is the urgent pointer pointing into this packet? */	 
		if (ptr < skb->len) {
			u8 tmp;
			if (skb_copy_bits(skb, ptr, &tmp, 1))
				BUG();
			tp->urg_data = TCP_URG_VALID | tmp;
			if (!sock_flag(sk, SOCK_DEAD))
				sk->sk_data_ready(sk, 0);
		}
	}
}

static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int chunk = skb->len - hlen;
	int err;

	local_bh_enable();
	if (skb->ip_summed==CHECKSUM_UNNECESSARY)
		err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
	else
		err = skb_copy_and_csum_datagram_iovec(skb, hlen,
						       tp->ucopy.iov);

	if (!err) {
		tp->ucopy.len -= chunk;
		tp->copied_seq += chunk;
		tcp_rcv_space_adjust(sk);
	}

	local_bh_disable();
	return err;
}

static int __tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
{
	int result;

	if (sock_owned_by_user(sk)) {
		local_bh_enable();
		result = __tcp_checksum_complete(skb);
		local_bh_disable();
	} else {
		result = __tcp_checksum_complete(skb);
	}
	return result;
}

static __inline__ int
tcp_checksum_complete_user(struct sock *sk, struct sk_buff *skb)
{
	return skb->ip_summed != CHECKSUM_UNNECESSARY &&
		__tcp_checksum_complete_user(sk, skb);
}

/*
 *	TCP receive function for the ESTABLISHED state. 
 *
 *	It is split into a fast path and a slow path. The fast path is 
 * 	disabled when:
 *	- A zero window was announced from us - zero window probing
 *        is only handled properly in the slow path. 
 *	- Out of order segments arrived.
 *	- Urgent data is expected.
 *	- There is no buffer space left
 *	- Unexpected TCP flags/window values/header lengths are received
 *	  (detected by checking the TCP header against pred_flags) 
 *	- Data is sent in both directions. Fast path only supports pure senders
 *	  or pure receivers (this means either the sequence number or the ack
 *	  value must stay constant)
 *	- Unexpected TCP option.
 *
 *	When these conditions are not satisfied it drops into a standard 
 *	receive procedure patterned after RFC793 to handle all cases.
 *	The first three cases are guaranteed by proper pred_flags setting,
 *	the rest is checked inline. Fast processing is turned on in 
 *	tcp_data_queue when everything is OK.
 */
int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
			struct tcphdr *th, unsigned len)
{
	struct tcp_sock *tp = tcp_sk(sk);

	/*
	 *	Header prediction.
	 *	The code loosely follows the one in the famous 
	 *	"30 instruction TCP receive" Van Jacobson mail.
	 *	
	 *	Van's trick is to deposit buffers into socket queue 
	 *	on a device interrupt, to call tcp_recv function
	 *	on the receive process context and checksum and copy
	 *	the buffer to user space. smart...
	 *
	 *	Our current scheme is not silly either but we take the 
	 *	extra cost of the net_bh soft interrupt processing...
	 *	We do checksum and copy also but from device to kernel.
	 */

	tp->rx_opt.saw_tstamp = 0;

	/*	pred_flags is 0xS?10 << 16 + snd_wnd
	 *	if header_predition is to be made
	 *	'S' will always be tp->tcp_header_len >> 2
	 *	'?' will be 0 for the fast path, otherwise pred_flags is 0 to
	 *  turn it off	(when there are holes in the receive 
	 *	 space for instance)
	 *	PSH flag is ignored.
	 */

	if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
		TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
		int tcp_header_len = tp->tcp_header_len;

		/* Timestamp header prediction: tcp_header_len
		 * is automatically equal to th->doff*4 due to pred_flags
		 * match.
		 */

		/* Check timestamp */
		if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
			__u32 *ptr = (__u32 *)(th + 1);

			/* No? Slow path! */
			if (*ptr != ntohl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
					  | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
				goto slow_path;

			tp->rx_opt.saw_tstamp = 1;
			++ptr; 
			tp->rx_opt.rcv_tsval = ntohl(*ptr);
			++ptr;
			tp->rx_opt.rcv_tsecr = ntohl(*ptr);

			/* If PAWS failed, check it more carefully in slow path */
			if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
				goto slow_path;

			/* DO NOT update ts_recent here, if checksum fails
			 * and timestamp was corrupted part, it will result
			 * in a hung connection since we will drop all
			 * future packets due to the PAWS test.
			 */
		}

		if (len <= tcp_header_len) {
			/* Bulk data transfer: sender */
			if (len == tcp_header_len) {
				/* Predicted packet is in window by definition.
				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
				 * Hence, check seq<=rcv_wup reduces to:
				 */
				if (tcp_header_len ==
				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
				    tp->rcv_nxt == tp->rcv_wup)
					tcp_store_ts_recent(tp);

3662
				tcp_rcv_rtt_measure_ts(sk, skb);
L
Linus Torvalds 已提交
3663 3664 3665 3666 3667 3668

				/* We know that such packets are checksummed
				 * on entry.
				 */
				tcp_ack(sk, skb, 0);
				__kfree_skb(skb); 
3669
				tcp_data_snd_check(sk, tp);
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3670 3671 3672 3673 3674 3675 3676 3677 3678 3679 3680 3681 3682 3683 3684 3685 3686 3687 3688 3689 3690 3691 3692 3693 3694
				return 0;
			} else { /* Header too small */
				TCP_INC_STATS_BH(TCP_MIB_INERRS);
				goto discard;
			}
		} else {
			int eaten = 0;

			if (tp->ucopy.task == current &&
			    tp->copied_seq == tp->rcv_nxt &&
			    len - tcp_header_len <= tp->ucopy.len &&
			    sock_owned_by_user(sk)) {
				__set_current_state(TASK_RUNNING);

				if (!tcp_copy_to_iovec(sk, skb, tcp_header_len)) {
					/* Predicted packet is in window by definition.
					 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
					 * Hence, check seq<=rcv_wup reduces to:
					 */
					if (tcp_header_len ==
					    (sizeof(struct tcphdr) +
					     TCPOLEN_TSTAMP_ALIGNED) &&
					    tp->rcv_nxt == tp->rcv_wup)
						tcp_store_ts_recent(tp);

3695
					tcp_rcv_rtt_measure_ts(sk, skb);
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3696 3697 3698 3699 3700 3701 3702 3703 3704 3705 3706 3707 3708 3709 3710 3711 3712 3713 3714 3715

					__skb_pull(skb, tcp_header_len);
					tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
					NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
					eaten = 1;
				}
			}
			if (!eaten) {
				if (tcp_checksum_complete_user(sk, skb))
					goto csum_error;

				/* Predicted packet is in window by definition.
				 * seq == rcv_nxt and rcv_wup <= rcv_nxt.
				 * Hence, check seq<=rcv_wup reduces to:
				 */
				if (tcp_header_len ==
				    (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
				    tp->rcv_nxt == tp->rcv_wup)
					tcp_store_ts_recent(tp);

3716
				tcp_rcv_rtt_measure_ts(sk, skb);
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Linus Torvalds 已提交
3717 3718 3719 3720 3721 3722 3723 3724 3725 3726 3727 3728 3729 3730 3731 3732 3733 3734

				if ((int)skb->truesize > sk->sk_forward_alloc)
					goto step5;

				NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);

				/* Bulk data transfer: receiver */
				__skb_pull(skb,tcp_header_len);
				__skb_queue_tail(&sk->sk_receive_queue, skb);
				sk_stream_set_owner_r(skb, sk);
				tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
			}

			tcp_event_data_recv(sk, tp, skb);

			if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
				/* Well, only one small jumplet in fast path... */
				tcp_ack(sk, skb, FLAG_DATA);
3735
				tcp_data_snd_check(sk, tp);
3736
				if (!inet_csk_ack_scheduled(sk))
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Linus Torvalds 已提交
3737 3738 3739
					goto no_ack;
			}

3740
			__tcp_ack_snd_check(sk, 0);
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no_ack:
			if (eaten)
				__kfree_skb(skb);
			else
				sk->sk_data_ready(sk, 0);
			return 0;
		}
	}

slow_path:
	if (len < (th->doff<<2) || tcp_checksum_complete_user(sk, skb))
		goto csum_error;

	/*
	 * RFC1323: H1. Apply PAWS check first.
	 */
	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
3758
	    tcp_paws_discard(sk, skb)) {
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Linus Torvalds 已提交
3759 3760 3761 3762 3763 3764 3765 3766 3767 3768 3769 3770 3771 3772 3773 3774 3775 3776 3777 3778 3779 3780 3781 3782 3783 3784 3785 3786 3787 3788 3789 3790 3791 3792 3793 3794 3795 3796 3797 3798 3799 3800 3801 3802 3803 3804
		if (!th->rst) {
			NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
			tcp_send_dupack(sk, skb);
			goto discard;
		}
		/* Resets are accepted even if PAWS failed.

		   ts_recent update must be made after we are sure
		   that the packet is in window.
		 */
	}

	/*
	 *	Standard slow path.
	 */

	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
		/* RFC793, page 37: "In all states except SYN-SENT, all reset
		 * (RST) segments are validated by checking their SEQ-fields."
		 * And page 69: "If an incoming segment is not acceptable,
		 * an acknowledgment should be sent in reply (unless the RST bit
		 * is set, if so drop the segment and return)".
		 */
		if (!th->rst)
			tcp_send_dupack(sk, skb);
		goto discard;
	}

	if(th->rst) {
		tcp_reset(sk);
		goto discard;
	}

	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);

	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		TCP_INC_STATS_BH(TCP_MIB_INERRS);
		NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
		tcp_reset(sk);
		return 1;
	}

step5:
	if(th->ack)
		tcp_ack(sk, skb, FLAG_SLOWPATH);

3805
	tcp_rcv_rtt_measure_ts(sk, skb);
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	/* Process urgent data. */
	tcp_urg(sk, skb, th);

	/* step 7: process the segment text */
	tcp_data_queue(sk, skb);

3813
	tcp_data_snd_check(sk, tp);
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Linus Torvalds 已提交
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	tcp_ack_snd_check(sk);
	return 0;

csum_error:
	TCP_INC_STATS_BH(TCP_MIB_INERRS);

discard:
	__kfree_skb(skb);
	return 0;
}

static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
					 struct tcphdr *th, unsigned len)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int saved_clamp = tp->rx_opt.mss_clamp;

	tcp_parse_options(skb, &tp->rx_opt, 0);

	if (th->ack) {
		/* rfc793:
		 * "If the state is SYN-SENT then
		 *    first check the ACK bit
		 *      If the ACK bit is set
		 *	  If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
		 *        a reset (unless the RST bit is set, if so drop
		 *        the segment and return)"
		 *
		 *  We do not send data with SYN, so that RFC-correct
		 *  test reduces to:
		 */
		if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
			goto reset_and_undo;

		if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
		    !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
			     tcp_time_stamp)) {
			NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
			goto reset_and_undo;
		}

		/* Now ACK is acceptable.
		 *
		 * "If the RST bit is set
		 *    If the ACK was acceptable then signal the user "error:
		 *    connection reset", drop the segment, enter CLOSED state,
		 *    delete TCB, and return."
		 */

		if (th->rst) {
			tcp_reset(sk);
			goto discard;
		}

		/* rfc793:
		 *   "fifth, if neither of the SYN or RST bits is set then
		 *    drop the segment and return."
		 *
		 *    See note below!
		 *                                        --ANK(990513)
		 */
		if (!th->syn)
			goto discard_and_undo;

		/* rfc793:
		 *   "If the SYN bit is on ...
		 *    are acceptable then ...
		 *    (our SYN has been ACKed), change the connection
		 *    state to ESTABLISHED..."
		 */

		TCP_ECN_rcv_synack(tp, th);
		if (tp->ecn_flags&TCP_ECN_OK)
			sock_set_flag(sk, SOCK_NO_LARGESEND);

		tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
		tcp_ack(sk, skb, FLAG_SLOWPATH);

		/* Ok.. it's good. Set up sequence numbers and
		 * move to established.
		 */
		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;

		/* RFC1323: The window in SYN & SYN/ACK segments is
		 * never scaled.
		 */
		tp->snd_wnd = ntohs(th->window);
		tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);

		if (!tp->rx_opt.wscale_ok) {
			tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
			tp->window_clamp = min(tp->window_clamp, 65535U);
		}

		if (tp->rx_opt.saw_tstamp) {
			tp->rx_opt.tstamp_ok	   = 1;
			tp->tcp_header_len =
				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
			tp->advmss	    -= TCPOLEN_TSTAMP_ALIGNED;
			tcp_store_ts_recent(tp);
		} else {
			tp->tcp_header_len = sizeof(struct tcphdr);
		}

		if (tp->rx_opt.sack_ok && sysctl_tcp_fack)
			tp->rx_opt.sack_ok |= 2;

		tcp_sync_mss(sk, tp->pmtu_cookie);
		tcp_initialize_rcv_mss(sk);

		/* Remember, tcp_poll() does not lock socket!
		 * Change state from SYN-SENT only after copied_seq
		 * is initialized. */
		tp->copied_seq = tp->rcv_nxt;
		mb();
		tcp_set_state(sk, TCP_ESTABLISHED);

		/* Make sure socket is routed, for correct metrics.  */
		tp->af_specific->rebuild_header(sk);

		tcp_init_metrics(sk);

3937 3938
		tcp_init_congestion_control(tp);

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		/* Prevent spurious tcp_cwnd_restart() on first data
		 * packet.
		 */
		tp->lsndtime = tcp_time_stamp;

		tcp_init_buffer_space(sk);

		if (sock_flag(sk, SOCK_KEEPOPEN))
3947
			inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
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3948 3949 3950 3951 3952 3953 3954 3955 3956 3957 3958

		if (!tp->rx_opt.snd_wscale)
			__tcp_fast_path_on(tp, tp->snd_wnd);
		else
			tp->pred_flags = 0;

		if (!sock_flag(sk, SOCK_DEAD)) {
			sk->sk_state_change(sk);
			sk_wake_async(sk, 0, POLL_OUT);
		}

3959
		if (sk->sk_write_pending || tp->defer_accept || inet_csk(sk)->icsk_ack.pingpong) {
L
Linus Torvalds 已提交
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			/* Save one ACK. Data will be ready after
			 * several ticks, if write_pending is set.
			 *
			 * It may be deleted, but with this feature tcpdumps
			 * look so _wonderfully_ clever, that I was not able
			 * to stand against the temptation 8)     --ANK
			 */
3967 3968 3969 3970 3971
			inet_csk_schedule_ack(sk);
			inet_csk(sk)->icsk_ack.lrcvtime = tcp_time_stamp;
			inet_csk(sk)->icsk_ack.ato	 = TCP_ATO_MIN;
			tcp_incr_quickack(sk);
			tcp_enter_quickack_mode(sk);
3972 3973
			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
						  TCP_DELACK_MAX, TCP_RTO_MAX);
L
Linus Torvalds 已提交
3974 3975 3976 3977 3978 3979 3980 3981 3982 3983 3984 3985 3986 3987 3988 3989 3990 3991 3992 3993 3994 3995 3996 3997 3998 3999 4000 4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4011 4012 4013 4014 4015 4016 4017 4018 4019 4020 4021 4022 4023 4024 4025 4026 4027 4028 4029 4030 4031 4032 4033 4034 4035 4036 4037 4038 4039 4040 4041 4042 4043 4044 4045 4046 4047 4048 4049 4050 4051 4052 4053 4054 4055 4056 4057 4058 4059 4060 4061 4062 4063 4064 4065 4066 4067 4068 4069 4070 4071 4072 4073 4074 4075 4076 4077 4078 4079 4080 4081 4082 4083 4084 4085 4086 4087 4088 4089 4090 4091 4092 4093 4094 4095 4096 4097 4098 4099 4100 4101 4102 4103 4104 4105 4106 4107 4108 4109 4110 4111 4112 4113 4114 4115 4116 4117 4118 4119 4120 4121 4122 4123

discard:
			__kfree_skb(skb);
			return 0;
		} else {
			tcp_send_ack(sk);
		}
		return -1;
	}

	/* No ACK in the segment */

	if (th->rst) {
		/* rfc793:
		 * "If the RST bit is set
		 *
		 *      Otherwise (no ACK) drop the segment and return."
		 */

		goto discard_and_undo;
	}

	/* PAWS check. */
	if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && tcp_paws_check(&tp->rx_opt, 0))
		goto discard_and_undo;

	if (th->syn) {
		/* We see SYN without ACK. It is attempt of
		 * simultaneous connect with crossed SYNs.
		 * Particularly, it can be connect to self.
		 */
		tcp_set_state(sk, TCP_SYN_RECV);

		if (tp->rx_opt.saw_tstamp) {
			tp->rx_opt.tstamp_ok = 1;
			tcp_store_ts_recent(tp);
			tp->tcp_header_len =
				sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
		} else {
			tp->tcp_header_len = sizeof(struct tcphdr);
		}

		tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
		tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;

		/* RFC1323: The window in SYN & SYN/ACK segments is
		 * never scaled.
		 */
		tp->snd_wnd    = ntohs(th->window);
		tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
		tp->max_window = tp->snd_wnd;

		TCP_ECN_rcv_syn(tp, th);
		if (tp->ecn_flags&TCP_ECN_OK)
			sock_set_flag(sk, SOCK_NO_LARGESEND);

		tcp_sync_mss(sk, tp->pmtu_cookie);
		tcp_initialize_rcv_mss(sk);


		tcp_send_synack(sk);
#if 0
		/* Note, we could accept data and URG from this segment.
		 * There are no obstacles to make this.
		 *
		 * However, if we ignore data in ACKless segments sometimes,
		 * we have no reasons to accept it sometimes.
		 * Also, seems the code doing it in step6 of tcp_rcv_state_process
		 * is not flawless. So, discard packet for sanity.
		 * Uncomment this return to process the data.
		 */
		return -1;
#else
		goto discard;
#endif
	}
	/* "fifth, if neither of the SYN or RST bits is set then
	 * drop the segment and return."
	 */

discard_and_undo:
	tcp_clear_options(&tp->rx_opt);
	tp->rx_opt.mss_clamp = saved_clamp;
	goto discard;

reset_and_undo:
	tcp_clear_options(&tp->rx_opt);
	tp->rx_opt.mss_clamp = saved_clamp;
	return 1;
}


/*
 *	This function implements the receiving procedure of RFC 793 for
 *	all states except ESTABLISHED and TIME_WAIT. 
 *	It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
 *	address independent.
 */
	
int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
			  struct tcphdr *th, unsigned len)
{
	struct tcp_sock *tp = tcp_sk(sk);
	int queued = 0;

	tp->rx_opt.saw_tstamp = 0;

	switch (sk->sk_state) {
	case TCP_CLOSE:
		goto discard;

	case TCP_LISTEN:
		if(th->ack)
			return 1;

		if(th->rst)
			goto discard;

		if(th->syn) {
			if(tp->af_specific->conn_request(sk, skb) < 0)
				return 1;

			/* Now we have several options: In theory there is 
			 * nothing else in the frame. KA9Q has an option to 
			 * send data with the syn, BSD accepts data with the
			 * syn up to the [to be] advertised window and 
			 * Solaris 2.1 gives you a protocol error. For now 
			 * we just ignore it, that fits the spec precisely 
			 * and avoids incompatibilities. It would be nice in
			 * future to drop through and process the data.
			 *
			 * Now that TTCP is starting to be used we ought to 
			 * queue this data.
			 * But, this leaves one open to an easy denial of
		 	 * service attack, and SYN cookies can't defend
			 * against this problem. So, we drop the data
			 * in the interest of security over speed.
			 */
			goto discard;
		}
		goto discard;

	case TCP_SYN_SENT:
		queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
		if (queued >= 0)
			return queued;

		/* Do step6 onward by hand. */
		tcp_urg(sk, skb, th);
		__kfree_skb(skb);
4124
		tcp_data_snd_check(sk, tp);
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4125 4126 4127 4128
		return 0;
	}

	if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4129
	    tcp_paws_discard(sk, skb)) {
L
Linus Torvalds 已提交
4130 4131 4132 4133 4134 4135 4136 4137 4138 4139 4140 4141 4142 4143 4144 4145 4146 4147 4148 4149 4150 4151 4152 4153 4154 4155 4156 4157 4158 4159 4160 4161 4162 4163 4164 4165 4166 4167 4168 4169 4170 4171 4172 4173 4174 4175 4176 4177 4178 4179 4180 4181 4182 4183 4184 4185 4186 4187 4188 4189 4190 4191 4192 4193 4194 4195 4196 4197
		if (!th->rst) {
			NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
			tcp_send_dupack(sk, skb);
			goto discard;
		}
		/* Reset is accepted even if it did not pass PAWS. */
	}

	/* step 1: check sequence number */
	if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
		if (!th->rst)
			tcp_send_dupack(sk, skb);
		goto discard;
	}

	/* step 2: check RST bit */
	if(th->rst) {
		tcp_reset(sk);
		goto discard;
	}

	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);

	/* step 3: check security and precedence [ignored] */

	/*	step 4:
	 *
	 *	Check for a SYN in window.
	 */
	if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
		NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
		tcp_reset(sk);
		return 1;
	}

	/* step 5: check the ACK field */
	if (th->ack) {
		int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);

		switch(sk->sk_state) {
		case TCP_SYN_RECV:
			if (acceptable) {
				tp->copied_seq = tp->rcv_nxt;
				mb();
				tcp_set_state(sk, TCP_ESTABLISHED);
				sk->sk_state_change(sk);

				/* Note, that this wakeup is only for marginal
				 * crossed SYN case. Passively open sockets
				 * are not waked up, because sk->sk_sleep ==
				 * NULL and sk->sk_socket == NULL.
				 */
				if (sk->sk_socket) {
					sk_wake_async(sk,0,POLL_OUT);
				}

				tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
				tp->snd_wnd = ntohs(th->window) <<
					      tp->rx_opt.snd_wscale;
				tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
					    TCP_SKB_CB(skb)->seq);

				/* tcp_ack considers this ACK as duplicate
				 * and does not calculate rtt.
				 * Fix it at least with timestamps.
				 */
				if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
				    !tp->srtt)
4198
					tcp_ack_saw_tstamp(sk, 0, 0);
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Linus Torvalds 已提交
4199 4200 4201 4202 4203 4204 4205 4206 4207 4208 4209

				if (tp->rx_opt.tstamp_ok)
					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;

				/* Make sure socket is routed, for
				 * correct metrics.
				 */
				tp->af_specific->rebuild_header(sk);

				tcp_init_metrics(sk);

4210 4211
				tcp_init_congestion_control(tp);

L
Linus Torvalds 已提交
4212 4213 4214 4215 4216 4217 4218 4219 4220 4221 4222 4223 4224 4225 4226 4227 4228 4229 4230 4231 4232 4233 4234 4235 4236 4237 4238 4239 4240 4241 4242 4243 4244
				/* Prevent spurious tcp_cwnd_restart() on
				 * first data packet.
				 */
				tp->lsndtime = tcp_time_stamp;

				tcp_initialize_rcv_mss(sk);
				tcp_init_buffer_space(sk);
				tcp_fast_path_on(tp);
			} else {
				return 1;
			}
			break;

		case TCP_FIN_WAIT1:
			if (tp->snd_una == tp->write_seq) {
				tcp_set_state(sk, TCP_FIN_WAIT2);
				sk->sk_shutdown |= SEND_SHUTDOWN;
				dst_confirm(sk->sk_dst_cache);

				if (!sock_flag(sk, SOCK_DEAD))
					/* Wake up lingering close() */
					sk->sk_state_change(sk);
				else {
					int tmo;

					if (tp->linger2 < 0 ||
					    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
					     after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
						tcp_done(sk);
						NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
						return 1;
					}

4245
					tmo = tcp_fin_time(sk);
L
Linus Torvalds 已提交
4246
					if (tmo > TCP_TIMEWAIT_LEN) {
4247
						inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
L
Linus Torvalds 已提交
4248 4249 4250 4251 4252 4253 4254
					} else if (th->fin || sock_owned_by_user(sk)) {
						/* Bad case. We could lose such FIN otherwise.
						 * It is not a big problem, but it looks confusing
						 * and not so rare event. We still can lose it now,
						 * if it spins in bh_lock_sock(), but it is really
						 * marginal case.
						 */
4255
						inet_csk_reset_keepalive_timer(sk, tmo);
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4256 4257 4258 4259 4260 4261 4262 4263 4264 4265 4266 4267 4268 4269 4270 4271 4272 4273 4274 4275 4276 4277 4278 4279 4280 4281 4282 4283 4284 4285 4286 4287 4288 4289 4290 4291 4292 4293 4294 4295 4296 4297 4298 4299 4300 4301 4302 4303 4304 4305 4306 4307 4308 4309 4310 4311 4312 4313 4314
					} else {
						tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
						goto discard;
					}
				}
			}
			break;

		case TCP_CLOSING:
			if (tp->snd_una == tp->write_seq) {
				tcp_time_wait(sk, TCP_TIME_WAIT, 0);
				goto discard;
			}
			break;

		case TCP_LAST_ACK:
			if (tp->snd_una == tp->write_seq) {
				tcp_update_metrics(sk);
				tcp_done(sk);
				goto discard;
			}
			break;
		}
	} else
		goto discard;

	/* step 6: check the URG bit */
	tcp_urg(sk, skb, th);

	/* step 7: process the segment text */
	switch (sk->sk_state) {
	case TCP_CLOSE_WAIT:
	case TCP_CLOSING:
	case TCP_LAST_ACK:
		if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
			break;
	case TCP_FIN_WAIT1:
	case TCP_FIN_WAIT2:
		/* RFC 793 says to queue data in these states,
		 * RFC 1122 says we MUST send a reset. 
		 * BSD 4.4 also does reset.
		 */
		if (sk->sk_shutdown & RCV_SHUTDOWN) {
			if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
			    after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
				NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
				tcp_reset(sk);
				return 1;
			}
		}
		/* Fall through */
	case TCP_ESTABLISHED: 
		tcp_data_queue(sk, skb);
		queued = 1;
		break;
	}

	/* tcp_data could move socket to TIME-WAIT */
	if (sk->sk_state != TCP_CLOSE) {
4315
		tcp_data_snd_check(sk, tp);
L
Linus Torvalds 已提交
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		tcp_ack_snd_check(sk);
	}

	if (!queued) { 
discard:
		__kfree_skb(skb);
	}
	return 0;
}

EXPORT_SYMBOL(sysctl_tcp_ecn);
EXPORT_SYMBOL(sysctl_tcp_reordering);
EXPORT_SYMBOL(tcp_parse_options);
EXPORT_SYMBOL(tcp_rcv_established);
EXPORT_SYMBOL(tcp_rcv_state_process);