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tcp_input.c

/*
 * 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 $
 *
 * Authors: Ross Biro
 *          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 presence 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/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>
#include <net/netdma.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;
int sysctl_tcp_abc;

#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.
 */ 
static void tcp_measure_rcv_mss(struct sock *sk,
                        const struct sk_buff *skb)
{
      struct inet_connection_sock *icsk = inet_csk(sk);
      const unsigned int lss = icsk->icsk_ack.last_seg_size; 
      unsigned int len;

      icsk->icsk_ack.last_seg_size = 0; 

      /* skb->len may jitter because of SACKs, even if peer
       * sends good full-sized frames.
       */
      len = skb->len;
      if (len >= icsk->icsk_ack.rcv_mss) {
            icsk->icsk_ack.rcv_mss = len;
      } 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.
                   */
                  len -= tcp_sk(sk)->tcp_header_len;
                  icsk->icsk_ack.last_seg_size = len;
                  if (len == lss) {
                        icsk->icsk_ack.rcv_mss = len;
                        return;
                  }
            }
            icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
      }
}

static void tcp_incr_quickack(struct sock *sk)
{
      struct inet_connection_sock *icsk = inet_csk(sk);
      unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);

      if (quickacks==0)
            quickacks=2;
      if (quickacks > icsk->icsk_ack.quick)
            icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
}

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

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

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

/* 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 spaghetti. But it should work
 * in common situations. Otherwise, we have to rely on queue collapsing.
 */

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

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

            truesize >>= 1;
            window >>= 1;
      }
      return 0;
}

static 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);
                  inet_csk(sk)->icsk_ack.quick |= 1;
            }
      }
}

/* 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 corresponding 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 immediately 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 inet_connection_sock *icsk = inet_csk(sk);

      icsk->icsk_ack.quick = 0;

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


/* Initialize RCV_MSS value.
 * RCV_MSS is an our guess about MSS used by the peer.
 * We haven't any direct information about the MSS.
 * It's better to underestimate the RCV_MSS rather than overestimate.
 * Overestimations make us ACKing less frequently than needed.
 * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
 */
void tcp_initialize_rcv_mss(struct sock *sk)
{
      struct tcp_sock *tp = tcp_sk(sk);
      unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);

      hint = min(hint, tp->rcv_wnd/2);
      hint = min(hint, TCP_MIN_RCVMSS);
      hint = max(hint, TCP_MIN_MSS);

      inet_csk(sk)->icsk_ack.rcv_mss = hint;
}

/* 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 smooth things out
             * else with timestamps disabled convergence 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 measure. */
            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;
}

static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, const struct sk_buff *skb)
{
      struct tcp_sock *tp = tcp_sk(sk);
      if (tp->rx_opt.rcv_tsecr &&
          (TCP_SKB_CB(skb)->end_seq -
           TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
            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 &&
                !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
                  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)
{
      struct inet_connection_sock *icsk = inet_csk(sk);
      u32 now;

      inet_csk_schedule_ack(sk);

      tcp_measure_rcv_mss(sk, skb);

      tcp_rcv_rtt_measure(tp);
      
      now = tcp_time_stamp;

      if (!icsk->icsk_ack.ato) {
            /* The _first_ data packet received, initialize
             * delayed ACK engine.
             */
            tcp_incr_quickack(sk);
            icsk->icsk_ack.ato = TCP_ATO_MIN;
      } else {
            int m = now - icsk->icsk_ack.lrcvtime;

            if (m <= TCP_ATO_MIN/2) {
                  /* The fastest case is the first. */
                  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) {
                  /* Too long gap. Apparently sender failed to
                   * restart window, so that we send ACKs quickly.
                   */
                  tcp_incr_quickack(sk);
                  sk_stream_mem_reclaim(sk);
            }
      }
      icsk->icsk_ack.lrcvtime = now;

      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
 */
static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
{
      struct tcp_sock *tp = tcp_sk(sk);
      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 increased quickly, decrease too quickly
       * 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;
      }
}

/* Calculate rto without backoff.  This is the second half of Van Jacobson's
 * routine referred to above.
 */
static inline void tcp_set_rto(struct sock *sk)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      /* 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 circumstances.
       */
      inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;

      /* 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 exactly, which we pretend to do.
       */
}

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

/* 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)) {
            const struct inet_connection_sock *icsk = inet_csk(sk);
            int m;

            if (icsk->icsk_backoff || !tp->srtt) {
                  /* 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 &&
                     icsk->icsk_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) {
            if (tp->mss_cache > 1460)
                  cwnd = 2;
            else
                  cwnd = (tp->mss_cache > 1095) ? 3 : 4;
      }
      return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
}

/* Set slow start threshold and cwnd not falling to slow start */
void tcp_enter_cwr(struct sock *sk)
{
      struct tcp_sock *tp = tcp_sk(sk);

      tp->prior_ssthresh = 0;
      tp->bytes_acked = 0;
      if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
            tp->undo_marker = 0;
            tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
            tp->snd_cwnd = min(tp->snd_cwnd,
                           tcp_packets_in_flight(tp) + 1U);
            tp->snd_cwnd_cnt = 0;
            tp->high_seq = tp->snd_nxt;
            tp->snd_cwnd_stamp = tcp_time_stamp;
            TCP_ECN_queue_cwr(tp);

            tcp_set_ca_state(sk, TCP_CA_CWR);
      }
}

/* 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 circumstances 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);
      }
      tcp_set_rto(sk);
      tcp_bound_rto(sk);
      if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
            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;
            inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
      }
}

static void tcp_update_reordering(struct sock *sk, const int metric,
                          const int ts)
{
      struct tcp_sock *tp = tcp_sk(sk);
      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, inet_csk(sk)->icsk_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)
{
      const struct inet_connection_sock *icsk = inet_csk(sk);
      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 dup_sack = 0;
      int i;

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

      /* SACK fastpath:
       * if the only SACK change is the increase of the end_seq of
       * the first block then only apply that SACK block
       * and use retrans queue hinting otherwise slowpath */
      flag = 1;
      for (i = 0; i< num_sacks; i++) {
            __u32 start_seq = ntohl(sp[i].start_seq);
            __u32 end_seq =    ntohl(sp[i].end_seq);

            if (i == 0){
                  if (tp->recv_sack_cache[i].start_seq != start_seq)
                        flag = 0;
            } else {
                  if ((tp->recv_sack_cache[i].start_seq != start_seq) ||
                      (tp->recv_sack_cache[i].end_seq != end_seq))
                        flag = 0;
            }
            tp->recv_sack_cache[i].start_seq = start_seq;
            tp->recv_sack_cache[i].end_seq = end_seq;

            /* 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;
            }
      }

      if (flag)
            num_sacks = 1;
      else {
            int j;
            tp->fastpath_skb_hint = NULL;

            /* order SACK blocks to allow in order walk of the retrans queue */
            for (i = num_sacks-1; i > 0; i--) {
                  for (j = 0; j < i; j++){
                        if (after(ntohl(sp[j].start_seq),
                                ntohl(sp[j+1].start_seq))){
                              sp[j].start_seq = htonl(tp->recv_sack_cache[j+1].start_seq);
                              sp[j].end_seq = htonl(tp->recv_sack_cache[j+1].end_seq);
                              sp[j+1].start_seq = htonl(tp->recv_sack_cache[j].start_seq);
                              sp[j+1].end_seq = htonl(tp->recv_sack_cache[j].end_seq);
                        }

                  }
            }
      }

      /* clear flag as used for different purpose in following code */
      flag = 0;

      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;

            /* Use SACK fastpath hint if valid */
            if (tp->fastpath_skb_hint) {
                  skb = tp->fastpath_skb_hint;
                  fack_count = tp->fastpath_cnt_hint;
            } else {
                  skb = sk->sk_write_queue.next;
                  fack_count = 0;
            }

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

            sk_stream_for_retrans_queue_from(skb, sk) {
                  int in_sack, pcount;
                  u8 sacked;

                  tp->fastpath_skb_hint = skb;
                  tp->fastpath_cnt_hint = fack_count;

                  /* 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;

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

                  pcount = tcp_skb_pcount(skb);

                  if (pcount > 1 && !in_sack &&
                      after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
                        unsigned int pkt_len;

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

                        if (!in_sack)
                              pkt_len = (start_seq -
                                       TCP_SKB_CB(skb)->seq);
                        else
                              pkt_len = (end_seq -
                                       TCP_SKB_CB(skb)->seq);
                        if (tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size))
                              break;
                        pcount = tcp_skb_pcount(skb);
                  }

                  fack_count += pcount;

                  sacked = TCP_SKB_CB(skb)->sacked;

                  /* 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);

                                    /* clear lost hint */
                                    tp->retransmit_skb_hint = NULL;
                              }
                        } 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);

                                    /* clear lost hint */
                                    tp->retransmit_skb_hint = NULL;
                              }
                        }

                        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);
                        tp->retransmit_skb_hint = NULL;
                  }
            }
      }

      /* 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 && icsk->icsk_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 *
                             tp->mss_cache))) {
                        TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
                        tp->retrans_out -= tcp_skb_pcount(skb);

                        /* clear lost hint */
                        tp->retransmit_skb_hint = NULL;

                        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) && icsk->icsk_ca_state != TCP_CA_Loss)
            tcp_update_reordering(sk, ((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)
{
      const struct inet_connection_sock *icsk = inet_csk(sk);
      struct tcp_sock *tp = tcp_sk(sk);
      struct sk_buff *skb;

      tp->frto_counter = 1;

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

      /* 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(sk, 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(sk, TCP_CA_Loss);
      tp->high_seq = tp->frto_highmark;
      TCP_ECN_queue_cwr(tp);

      clear_all_retrans_hints(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)
{
      const struct inet_connection_sock *icsk = inet_csk(sk);
      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 (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
          (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
            tp->prior_ssthresh = tcp_current_ssthresh(sk);
            tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
            tcp_ca_event(sk, CA_EVENT_LOSS);
      }
      tp->snd_cwnd         = 1;
      tp->snd_cwnd_cnt   = 0;
      tp->snd_cwnd_stamp = tcp_time_stamp;

      tp->bytes_acked = 0;
      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(sk, TCP_CA_Loss);
      tp->high_seq = tp->snd_nxt;
      TCP_ECN_queue_cwr(tp);

      clear_all_retrans_hints(tp);
}

static int tcp_check_sack_reneging(struct sock *sk)
{
      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)) {
            struct inet_connection_sock *icsk = inet_csk(sk);
            NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);

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

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

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

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

/* 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 sock *sk, const int addend)
{
      struct tcp_sock *tp = tcp_sk(sk);
      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(sk, tp->packets_out + addend, 0);
      }
}

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

static void tcp_add_reno_sack(struct sock *sk)
{
      struct tcp_sock *tp = tcp_sk(sk);
      tp->sacked_out++;
      tcp_check_reno_reordering(sk, 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(sk, 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;

      BUG_TRAP(packets <= tp->packets_out);
      if (tp->lost_skb_hint) {
            skb = tp->lost_skb_hint;
            cnt = tp->lost_cnt_hint;
      } else {
            skb = sk->sk_write_queue.next;
            cnt = 0;
      }

      sk_stream_for_retrans_queue_from(skb, sk) {
            /* TODO: do this better */
            /* this is not the most efficient way to do this... */
            tp->lost_skb_hint = skb;
            tp->lost_cnt_hint = cnt;
            cnt += tcp_skb_pcount(skb);
            if (cnt > packets || 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);

                  /* clear xmit_retransmit_queue hints
                   *  if this is beyond hint */
                  if(tp->retransmit_skb_hint != NULL &&
                     before(TCP_SKB_CB(skb)->seq,
                          TCP_SKB_CB(tp->retransmit_skb_hint)->seq)) {

                        tp->retransmit_skb_hint = NULL;
                  }
            }
      }
      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 (!IsReno(tp) && tcp_head_timedout(sk, tp)) {
            struct sk_buff *skb;

            skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
                  : sk->sk_write_queue.next;

            sk_stream_for_retrans_queue_from(skb, sk) {
                  if (!tcp_skb_timedout(sk, skb))
                        break;

                  if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
                        TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
                        tp->lost_out += tcp_skb_pcount(skb);

                        /* clear xmit_retrans hint */
                        if (tp->retransmit_skb_hint &&
                            before(TCP_SKB_CB(skb)->seq,
                                 TCP_SKB_CB(tp->retransmit_skb_hint)->seq))

                              tp->retransmit_skb_hint = NULL;
                  }
            }

            tp->scoreboard_skb_hint = 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;
}

/* Lower bound on congestion window is slow start threshold
 * unless congestion avoidance choice decides to overide it.
 */
static inline u32 tcp_cwnd_min(const struct sock *sk)
{
      const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;

      return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
}

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

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

      if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
            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 sock *sk, const int undo)
{
      struct tcp_sock *tp = tcp_sk(sk);

      if (tp->prior_ssthresh) {
            const struct inet_connection_sock *icsk = inet_csk(sk);

            if (icsk->icsk_ca_ops->undo_cwnd)
                  tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
            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;

      /* There is something screwy going on with the retrans hints after
         an undo */
      clear_all_retrans_hints(tp);
}

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, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
            tcp_undo_cwr(sk, 1);
            if (inet_csk(sk)->icsk_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(sk, 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(sk, 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(sk, tcp_fackets_out(tp) + acked, 1);

            DBGUNDO(sk, tp, "Hoe");
            tcp_undo_cwr(sk, 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;
            }

            clear_all_retrans_hints(tp);

            DBGUNDO(sk, tp, "partial loss");
            tp->lost_out = 0;
            tp->left_out = tp->sacked_out;
            tcp_undo_cwr(sk, 1);
            NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
            inet_csk(sk)->icsk_retransmits = 0;
            tp->undo_marker = 0;
            if (!IsReno(tp))
                  tcp_set_ca_state(sk, TCP_CA_Open);
            return 1;
      }
      return 0;
}

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

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(sk);

      if (inet_csk(sk)->icsk_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 (inet_csk(sk)->icsk_ca_state != state) {
                  tcp_set_ca_state(sk, state);
                  tp->high_seq = tp->snd_nxt;
            }
            tcp_moderate_cwnd(tp);
      } else {
            tcp_cwnd_down(sk);
      }
}

static void tcp_mtup_probe_failed(struct sock *sk)
{
      struct inet_connection_sock *icsk = inet_csk(sk);

      icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
      icsk->icsk_mtup.probe_size = 0;
}

static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
{
      struct tcp_sock *tp = tcp_sk(sk);
      struct inet_connection_sock *icsk = inet_csk(sk);

      /* FIXME: breaks with very large cwnd */
      tp->prior_ssthresh = tcp_current_ssthresh(sk);
      tp->snd_cwnd = tp->snd_cwnd *
                   tcp_mss_to_mtu(sk, tp->mss_cache) /
                   icsk->icsk_mtup.probe_size;
      tp->snd_cwnd_cnt = 0;
      tp->snd_cwnd_stamp = tcp_time_stamp;
      tp->rcv_ssthresh = tcp_current_ssthresh(sk);

      icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
      icsk->icsk_mtup.probe_size = 0;
      tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
}


/* 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 inet_connection_sock *icsk = inet_csk(sk);
      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. */
      if (tp->sacked_out && tcp_check_sack_reneging(sk))
            return;

      /* C. Process data loss notification, provided it is valid. */
      if ((flag&FLAG_DATA_LOST) &&
          before(tp->snd_una, tp->high_seq) &&
          icsk->icsk_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 (icsk->icsk_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 (icsk->icsk_ca_state) {
            case TCP_CA_Loss:
                  icsk->icsk_retransmits = 0;
                  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(sk);
                        tcp_set_ca_state(sk, 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(sk, 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(sk);
                  break;
            }
      }

      /* F. Process state. */
      switch (icsk->icsk_ca_state) {
      case TCP_CA_Recovery:
            if (prior_snd_una == tp->snd_una) {
                  if (IsReno(tp) && is_dupack)
                        tcp_add_reno_sack(sk);
            } 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)
                  icsk->icsk_retransmits = 0;
            if (!tcp_try_undo_loss(sk, tp)) {
                  tcp_moderate_cwnd(tp);
                  tcp_xmit_retransmit_queue(sk);
                  return;
            }
            if (icsk->icsk_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(sk);
            }

            if (icsk->icsk_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;
            }

            /* MTU probe failure: don't reduce cwnd */
            if (icsk->icsk_ca_state < TCP_CA_CWR &&
                icsk->icsk_mtup.probe_size &&
                tp->snd_una == tp->mtu_probe.probe_seq_start) {
                  tcp_mtup_probe_failed(sk);
                  /* Restores the reduction we did in tcp_mtup_probe() */
                  tp->snd_cwnd++;
                  tcp_simple_retransmit(sk);
                  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 (icsk->icsk_ca_state < TCP_CA_CWR) {
                  if (!(flag&FLAG_ECE))
                        tp->prior_ssthresh = tcp_current_ssthresh(sk);
                  tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
                  TCP_ECN_queue_cwr(tp);
            }

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

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

/* Read draft-ietf-tcplw-high-performance before mucking
 * with this code. (Supersedes RFC1323)
 */
static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
{
      /* 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 overestimated 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)
       */
      struct tcp_sock *tp = tcp_sk(sk);
      const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
      tcp_rtt_estimator(sk, seq_rtt);
      tcp_set_rto(sk);
      inet_csk(sk)->icsk_backoff = 0;
      tcp_bound_rto(sk);
}

static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
{
      /* 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;

      tcp_rtt_estimator(sk, seq_rtt);
      tcp_set_rto(sk);
      inet_csk(sk)->icsk_backoff = 0;
      tcp_bound_rto(sk);
}

static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
                              const s32 seq_rtt)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      /* 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)
            tcp_ack_saw_tstamp(sk, flag);
      else if (seq_rtt >= 0)
            tcp_ack_no_tstamp(sk, seq_rtt, flag);
}

static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
                     u32 in_flight, int good)
{
      const struct inet_connection_sock *icsk = inet_csk(sk);
      icsk->icsk_ca_ops->cong_avoid(sk, ack, rtt, in_flight, good);
      tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
}

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

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

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;
}

static u32 tcp_usrtt(const struct sk_buff *skb)
{
      struct timeval tv, now;

      do_gettimeofday(&now);
      skb_get_timestamp(skb, &tv);
      return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
}

/* Remove acknowledged frames from the retransmission queue. */
static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
{
      struct tcp_sock *tp = tcp_sk(sk);
      const struct inet_connection_sock *icsk = inet_csk(sk);
      struct sk_buff *skb;
      __u32 now = tcp_time_stamp;
      int acked = 0;
      __s32 seq_rtt = -1;
      u32 pkts_acked = 0;
      void (*rtt_sample)(struct sock *sk, u32 usrtt)
            = icsk->icsk_ca_ops->rtt_sample;

      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)) {
                  if (tcp_skb_pcount(skb) > 1 &&
                      after(tp->snd_una, scb->seq))
                        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;
                  ++pkts_acked;
            } else {
                  acked |= FLAG_SYN_ACKED;
                  tp->retrans_stamp = 0;
            }

            /* MTU probing checks */
            if (icsk->icsk_mtup.probe_size) {
                  if (!after(tp->mtu_probe.probe_seq_end, TCP_SKB_CB(skb)->end_seq)) {
                        tcp_mtup_probe_success(sk, skb);
                  }
            }

            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;
                        if (rtt_sample)
                              (*rtt_sample)(sk, tcp_usrtt(skb));
                  }
                  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;
                  if (rtt_sample)
                        (*rtt_sample)(sk, tcp_usrtt(skb));
            }
            tcp_dec_pcount_approx(&tp->fackets_out, skb);
            tcp_packets_out_dec(tp, skb);
            __skb_unlink(skb, &sk->sk_write_queue);
            sk_stream_free_skb(sk, skb);
            clear_all_retrans_hints(tp);
      }

      if (acked&FLAG_ACKED) {
            tcp_ack_update_rtt(sk, acked, seq_rtt);
            tcp_ack_packets_out(sk, tp);

            if (icsk->icsk_ca_ops->pkts_acked)
                  icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
      }

#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) {
            const struct inet_connection_sock *icsk = inet_csk(sk);
            if (tp->lost_out) {
                  printk(KERN_DEBUG "Leak l=%u %d\n",
                         tp->lost_out, icsk->icsk_ca_state);
                  tp->lost_out = 0;
            }
            if (tp->sacked_out) {
                  printk(KERN_DEBUG "Leak s=%u %d\n",
                         tp->sacked_out, icsk->icsk_ca_state);
                  tp->sacked_out = 0;
            }
            if (tp->retrans_out) {
                  printk(KERN_DEBUG "Leak r=%u %d\n",
                         tp->retrans_out, icsk->icsk_ca_state);
                  tp->retrans_out = 0;
            }
      }
#endif
      *seq_rtt_p = seq_rtt;
      return acked;
}

static void tcp_ack_probe(struct sock *sk)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      struct inet_connection_sock *icsk = inet_csk(sk);

      /* Was it a usable window open? */

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

static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
{
      return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
            inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
}

static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
            !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
}

/* Check that window update is acceptable.
 * The function assumes that snd_una<=ack<=snd_next.
 */
static inline int tcp_may_update_window(const struct tcp_sock *tp, const u32 ack,
                              const u32 ack_seq, const u32 nwin)
{
      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.
                   */
                  tp->pred_flags = 0;
                  tcp_fast_path_check(sk, tp);

                  if (nwin > tp->max_window) {
                        tp->max_window = nwin;
                        tcp_sync_mss(sk, inet_csk(sk)->icsk_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 behavior 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 inet_connection_sock *icsk = inet_csk(sk);
      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;
      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 (sysctl_tcp_abc) {
            if (icsk->icsk_ca_state < TCP_CA_CWR)
                  tp->bytes_acked += ack - prior_snd_una;
            else if (icsk->icsk_ca_state == TCP_CA_Loss)
                  /* we assume just one segment left network */
                  tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
      }

      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;

            tcp_ca_event(sk, CA_EVENT_FAST_ACK);

            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;

            tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
      }

      /* 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. */
      flag |= tcp_clean_rtx_queue(sk, &seq_rtt);

      if (tp->frto_counter)
            tcp_process_frto(sk, prior_snd_una);

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

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

      return 1;

no_queue:
      icsk->icsk_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 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) ]
 */

static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
{
      struct tcp_sock *tp = tcp_sk(sk);
      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. */
            (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
}

static inline int tcp_paws_discard(const struct sock *sk, const struct sk_buff *skb)
{
      const struct tcp_sock *tp = tcp_sk(sk);
      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 &&
            !tcp_disordered_ack(sk, skb));
}

/* 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);

      inet_csk_schedule_ack(sk);

      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);
                  inet_csk(sk)->icsk_ack.pingpong = 1;
                  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 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 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);
            tcp_enter_quickack_mode(sk);

            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. */
      if (skb_queue_empty(&tp->out_of_order_queue)) {
            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");
                  __skb_unlink(skb, &tp->out_of_order_queue);
                  __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);

            __skb_unlink(skb, &tp->out_of_order_queue);
            __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);

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

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

            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:
            tcp_enter_quickack_mode(sk);
            inet_csk_schedule_ack(sk);
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;

      tcp_enter_quickack_mode(sk);

      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;
      inet_csk_schedule_ack(sk);

      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) {
                  __skb_append(skb1, skb, &tp->out_of_order_queue);

                  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;
                   }
                   __skb_unlink(skb1, &tp->out_of_order_queue);
                   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
tcp_collapse(struct sock *sk, struct sk_buff_head *list,
           struct sk_buff *head, struct sk_buff *tail,
           u32 start, u32 end)
{
      struct sk_buff *skb;

      /* First, check that queue is collapsible 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;
                  __skb_unlink(skb, list);
                  __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;
            __skb_insert(nskb, skb->prev, skb, list);
            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;

                  BUG_ON(offset < 0);
                  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;
                        __skb_unlink(skb, list);
                        __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)) {
                  tcp_collapse(sk, &tp->out_of_order_queue,
                             head, skb, start, end);
                  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);
      tcp_collapse(sk, &sk->sk_receive_queue,
                 sk->sk_receive_queue.next,
                 (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. */
      if (!skb_queue_empty(&tp->out_of_order_queue)) {
            NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
            __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 (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
          sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
            /* Limited by application or receiver window. */
            u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
            u32 win_used = max(tp->snd_cwnd_used, init_win);
            if (win_used < tp->snd_cwnd) {
                  tp->snd_ssthresh = tcp_current_ssthresh(sk);
                  tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
            }
            tp->snd_cwnd_used = 0;
      }
      tp->snd_cwnd_stamp = tcp_time_stamp;
}

static 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;
}

/* 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);

      if (tcp_should_expand_sndbuf(sk, tp)) {
            int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
                  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 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);
      }
}

static inline void tcp_data_snd_check(struct sock *sk, struct tcp_sock *tp)
{
      tcp_push_pending_frames(sk, tp);
      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... */
      if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
           /* ... 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... */
          tcp_in_quickack_mode(sk) ||
          /* 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)
{
      if (!inet_csk_ack_scheduled(sk)) {
            /* We sent a data segment already. */
            return;
      }
      __tcp_ack_snd_check(sk, 1);
}

/*
 *    This routine is only called when we have urgent data
 *    signaled. 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 semantics 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)) {
                  __skb_unlink(skb, &sk->sk_receive_queue);
                  __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);
}

#ifdef CONFIG_NET_DMA
static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb, int hlen)
{
      struct tcp_sock *tp = tcp_sk(sk);
      int chunk = skb->len - hlen;
      int dma_cookie;
      int copied_early = 0;

      if (tp->ucopy.wakeup)
            return 0;

      if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
            tp->ucopy.dma_chan = get_softnet_dma();

      if (tp->ucopy.dma_chan && skb->ip_summed == CHECKSUM_UNNECESSARY) {

            dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
                  skb, hlen, tp->ucopy.iov, chunk, tp->ucopy.pinned_list);

            if (dma_cookie < 0)
                  goto out;

            tp->ucopy.dma_cookie = dma_cookie;
            copied_early = 1;

            tp->ucopy.len -= chunk;
            tp->copied_seq += chunk;
            tcp_rcv_space_adjust(sk);

            if ((tp->ucopy.len == 0) ||
                (tcp_flag_word(skb->h.th) & TCP_FLAG_PSH) ||
                (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
                  tp->ucopy.wakeup = 1;
                  sk->sk_data_ready(sk, 0);
            }
      } else if (chunk > 0) {
            tp->ucopy.wakeup = 1;
            sk->sk_data_ready(sk, 0);
      }
out:
      return copied_early;
}
#endif /* CONFIG_NET_DMA */

/*
 *    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_prediction 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);

                        /* We know that such packets are checksummed
                         * on entry.
                         */
                        tcp_ack(sk, skb, 0);
                        __kfree_skb(skb); 
                        tcp_data_snd_check(sk, tp);
                        return 0;
                  } else { /* Header too small */
                        TCP_INC_STATS_BH(TCP_MIB_INERRS);
                        goto discard;
                  }
            } else {
                  int eaten = 0;
                  int copied_early = 0;

                  if (tp->copied_seq == tp->rcv_nxt &&
                      len - tcp_header_len <= tp->ucopy.len) {
#ifdef CONFIG_NET_DMA
                        if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
                              copied_early = 1;
                              eaten = 1;
                        }
#endif
                        if (tp->ucopy.task == current && sock_owned_by_user(sk) && !copied_early) {
                              __set_current_state(TASK_RUNNING);

                              if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
                                    eaten = 1;
                        }
                        if (eaten) {
                              /* 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);

                              tcp_rcv_rtt_measure_ts(sk, skb);

                              __skb_pull(skb, tcp_header_len);
                              tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
                              NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
                        }
                        if (copied_early)
                              tcp_cleanup_rbuf(sk, skb->len);
                  }
                  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);

                        tcp_rcv_rtt_measure_ts(sk, skb);

                        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);
                        tcp_data_snd_check(sk, tp);
                        if (!inet_csk_ack_scheduled(sk))
                              goto no_ack;
                  }

                  __tcp_ack_snd_check(sk, 0);
no_ack:
#ifdef CONFIG_NET_DMA
                  if (copied_early)
                        __skb_queue_tail(&sk->sk_async_wait_queue, skb);
                  else
#endif
                  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 &&
          tcp_paws_discard(sk, skb)) {
            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);

      tcp_rcv_rtt_measure_ts(sk, skb);

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

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

      tcp_data_snd_check(sk, tp);
      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);
      struct inet_connection_sock *icsk = inet_csk(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);

            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_mtup_init(sk);
            tcp_sync_mss(sk, icsk->icsk_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.  */
            icsk->icsk_af_ops->rebuild_header(sk);

            tcp_init_metrics(sk);

            tcp_init_congestion_control(sk);

            /* 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))
                  inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));

            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);
            }

            if (sk->sk_write_pending ||
                icsk->icsk_accept_queue.rskq_defer_accept ||
                icsk->icsk_ack.pingpong) {
                  /* 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
                   */
                  inet_csk_schedule_ack(sk);
                  icsk->icsk_ack.lrcvtime = tcp_time_stamp;
                  icsk->icsk_ack.ato       = TCP_ATO_MIN;
                  tcp_incr_quickack(sk);
                  tcp_enter_quickack_mode(sk);
                  inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
                                      TCP_DELACK_MAX, TCP_RTO_MAX);

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);

            tcp_mtup_init(sk);
            tcp_sync_mss(sk, icsk->icsk_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);
      struct inet_connection_sock *icsk = inet_csk(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 (icsk->icsk_af_ops->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);
            tcp_data_snd_check(sk, tp);
            return 0;
      }

      if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
          tcp_paws_discard(sk, skb)) {
            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)
                              tcp_ack_saw_tstamp(sk, 0);

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

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

                        tcp_init_metrics(sk);

                        tcp_init_congestion_control(sk);

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

                        tcp_mtup_init(sk);
                        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;
                              }

                              tmo = tcp_fin_time(sk);
                              if (tmo > TCP_TIMEWAIT_LEN) {
                                    inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
                              } 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.
                                     */
                                    inet_csk_reset_keepalive_timer(sk, tmo);
                              } 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) {
            tcp_data_snd_check(sk, tp);
            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);
EXPORT_SYMBOL(tcp_initialize_rcv_mss);

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