/*
   *  Copyright (c) 2005, 2006 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
   *
   *  Changes to meet Linux coding standards, and DCCP infrastructure fixes.
   *
   *  Copyright (c) 2006 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
   *
   *  This program is free software; you can redistribute it and/or modify
   *  it under the terms of the GNU General Public License as published by
   *  the Free Software Foundation; either version 2 of the License, or
   *  (at your option) any later version.
   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to the Free Software
   *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
   */
  
  /*
   * This implementation should follow RFC 4341
   */
  #include <linux/slab.h>
  #include "../feat.h"
  #include "ccid2.h"
  
  
  #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
  static bool ccid2_debug;
  #define ccid2_pr_debug(format, a...)	DCCP_PR_DEBUG(ccid2_debug, format, ##a)
  #else
  #define ccid2_pr_debug(format, a...)
  #endif
  
  static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hc)
  {
  	struct ccid2_seq *seqp;
  	int i;
  
  	/* check if we have space to preserve the pointer to the buffer */
  	if (hc->tx_seqbufc >= (sizeof(hc->tx_seqbuf) /
  			       sizeof(struct ccid2_seq *)))
  		return -ENOMEM;
  
  	/* allocate buffer and initialize linked list */
  	seqp = kmalloc(CCID2_SEQBUF_LEN * sizeof(struct ccid2_seq), gfp_any());
  	if (seqp == NULL)
  		return -ENOMEM;
  
  	for (i = 0; i < (CCID2_SEQBUF_LEN - 1); i++) {
  		seqp[i].ccid2s_next = &seqp[i + 1];
  		seqp[i + 1].ccid2s_prev = &seqp[i];
  	}
  	seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = seqp;
  	seqp->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
  
  	/* This is the first allocation.  Initiate the head and tail.  */
  	if (hc->tx_seqbufc == 0)
  		hc->tx_seqh = hc->tx_seqt = seqp;
  	else {
  		/* link the existing list with the one we just created */
  		hc->tx_seqh->ccid2s_next = seqp;
  		seqp->ccid2s_prev = hc->tx_seqh;
  
  		hc->tx_seqt->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
  		seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = hc->tx_seqt;
  	}
  
  	/* store the original pointer to the buffer so we can free it */
  	hc->tx_seqbuf[hc->tx_seqbufc] = seqp;
  	hc->tx_seqbufc++;
  
  	return 0;
  }
  
  static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
  {
  	if (ccid2_cwnd_network_limited(ccid2_hc_tx_sk(sk)))
  		return CCID_PACKET_WILL_DEQUEUE_LATER;
  	return CCID_PACKET_SEND_AT_ONCE;
  }
  
  static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
  {
  	u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);
  
  	/*
  	 * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
  	 * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
  	 * acceptable since this causes starvation/deadlock whenever cwnd < 2.
  	 * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
  	 */
  	if (val == 0 || val > max_ratio) {
  		DCCP_WARN("Limiting Ack Ratio (%u) to %u
  ", val, max_ratio);
  		val = max_ratio;
  	}
  	dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
  				   min_t(u32, val, DCCPF_ACK_RATIO_MAX));
  }
  
  static void ccid2_check_l_ack_ratio(struct sock *sk)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  
  	/*
  	 * After a loss, idle period, application limited period, or RTO we
  	 * need to check that the ack ratio is still less than the congestion
  	 * window. Otherwise, we will send an entire congestion window of
  	 * packets and got no response because we haven't sent ack ratio
  	 * packets yet.
  	 * If the ack ratio does need to be reduced, we reduce it to half of
  	 * the congestion window (or 1 if that's zero) instead of to the
  	 * congestion window. This prevents problems if one ack is lost.
  	 */
  	if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
  		ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
  }
  
  static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
  {
  	dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
  				   clamp_val(val, DCCPF_SEQ_WMIN,
  						  DCCPF_SEQ_WMAX));
  }
  
  static void ccid2_hc_tx_rto_expire(unsigned long data)
  {
  	struct sock *sk = (struct sock *)data;
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
  
  	bh_lock_sock(sk);
  	if (sock_owned_by_user(sk)) {
  		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
  		goto out;
  	}
  
  	ccid2_pr_debug("RTO_EXPIRE
  ");
  
  	/* back-off timer */
  	hc->tx_rto <<= 1;
  	if (hc->tx_rto > DCCP_RTO_MAX)
  		hc->tx_rto = DCCP_RTO_MAX;
  
  	/* adjust pipe, cwnd etc */
  	hc->tx_ssthresh = hc->tx_cwnd / 2;
  	if (hc->tx_ssthresh < 2)
  		hc->tx_ssthresh = 2;
  	hc->tx_cwnd	= 1;
  	hc->tx_pipe	= 0;
  
  	/* clear state about stuff we sent */
  	hc->tx_seqt = hc->tx_seqh;
  	hc->tx_packets_acked = 0;
  
  	/* clear ack ratio state. */
  	hc->tx_rpseq    = 0;
  	hc->tx_rpdupack = -1;
  	ccid2_change_l_ack_ratio(sk, 1);
  
  	/* if we were blocked before, we may now send cwnd=1 packet */
  	if (sender_was_blocked)
  		tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
  	/* restart backed-off timer */
  	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
  out:
  	bh_unlock_sock(sk);
  	sock_put(sk);
  }
  
  /*
   *	Congestion window validation (RFC 2861).
   */
  static bool ccid2_do_cwv = true;
  module_param(ccid2_do_cwv, bool, 0644);
  MODULE_PARM_DESC(ccid2_do_cwv, "Perform RFC2861 Congestion Window Validation");
  
  /**
   * ccid2_update_used_window  -  Track how much of cwnd is actually used
   * This is done in addition to CWV. The sender needs to have an idea of how many
   * packets may be in flight, to set the local Sequence Window value accordingly
   * (RFC 4340, 7.5.2). The CWV mechanism is exploited to keep track of the
   * maximum-used window. We use an EWMA low-pass filter to filter out noise.
   */
  static void ccid2_update_used_window(struct ccid2_hc_tx_sock *hc, u32 new_wnd)
  {
  	hc->tx_expected_wnd = (3 * hc->tx_expected_wnd + new_wnd) / 4;
  }
  
  /* This borrows the code of tcp_cwnd_application_limited() */
  static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	/* don't reduce cwnd below the initial window (IW) */
  	u32 init_win = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache),
  	    win_used = max(hc->tx_cwnd_used, init_win);
  
  	if (win_used < hc->tx_cwnd) {
  		hc->tx_ssthresh = max(hc->tx_ssthresh,
  				     (hc->tx_cwnd >> 1) + (hc->tx_cwnd >> 2));
  		hc->tx_cwnd = (hc->tx_cwnd + win_used) >> 1;
  	}
  	hc->tx_cwnd_used  = 0;
  	hc->tx_cwnd_stamp = now;
  
  	ccid2_check_l_ack_ratio(sk);
  }
  
  /* This borrows the code of tcp_cwnd_restart() */
  static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	u32 cwnd = hc->tx_cwnd, restart_cwnd,
  	    iwnd = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache);
  
  	hc->tx_ssthresh = max(hc->tx_ssthresh, (cwnd >> 1) + (cwnd >> 2));
  
  	/* don't reduce cwnd below the initial window (IW) */
  	restart_cwnd = min(cwnd, iwnd);
  	cwnd >>= (now - hc->tx_lsndtime) / hc->tx_rto;
  	hc->tx_cwnd = max(cwnd, restart_cwnd);
  
  	hc->tx_cwnd_stamp = now;
  	hc->tx_cwnd_used  = 0;
  
  	ccid2_check_l_ack_ratio(sk);
  }
  
  static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
  {
  	struct dccp_sock *dp = dccp_sk(sk);
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	const u32 now = ccid2_time_stamp;
  	struct ccid2_seq *next;
  
  	/* slow-start after idle periods (RFC 2581, RFC 2861) */
  	if (ccid2_do_cwv && !hc->tx_pipe &&
  	    (s32)(now - hc->tx_lsndtime) >= hc->tx_rto)
  		ccid2_cwnd_restart(sk, now);
  
  	hc->tx_lsndtime = now;
  	hc->tx_pipe    += 1;
  
  	/* see whether cwnd was fully used (RFC 2861), update expected window */
  	if (ccid2_cwnd_network_limited(hc)) {
  		ccid2_update_used_window(hc, hc->tx_cwnd);
  		hc->tx_cwnd_used  = 0;
  		hc->tx_cwnd_stamp = now;
  	} else {
  		if (hc->tx_pipe > hc->tx_cwnd_used)
  			hc->tx_cwnd_used = hc->tx_pipe;
  
  		ccid2_update_used_window(hc, hc->tx_cwnd_used);
  
  		if (ccid2_do_cwv && (s32)(now - hc->tx_cwnd_stamp) >= hc->tx_rto)
  			ccid2_cwnd_application_limited(sk, now);
  	}
  
  	hc->tx_seqh->ccid2s_seq   = dp->dccps_gss;
  	hc->tx_seqh->ccid2s_acked = 0;
  	hc->tx_seqh->ccid2s_sent  = now;
  
  	next = hc->tx_seqh->ccid2s_next;
  	/* check if we need to alloc more space */
  	if (next == hc->tx_seqt) {
  		if (ccid2_hc_tx_alloc_seq(hc)) {
  			DCCP_CRIT("packet history - out of memory!");
  			/* FIXME: find a more graceful way to bail out */
  			return;
  		}
  		next = hc->tx_seqh->ccid2s_next;
  		BUG_ON(next == hc->tx_seqt);
  	}
  	hc->tx_seqh = next;
  
  	ccid2_pr_debug("cwnd=%d pipe=%d
  ", hc->tx_cwnd, hc->tx_pipe);
  
  	/*
  	 * FIXME: The code below is broken and the variables have been removed
  	 * from the socket struct. The `ackloss' variable was always set to 0,
  	 * and with arsent there are several problems:
  	 *  (i) it doesn't just count the number of Acks, but all sent packets;
  	 *  (ii) it is expressed in # of packets, not # of windows, so the
  	 *  comparison below uses the wrong formula: Appendix A of RFC 4341
  	 *  comes up with the number K = cwnd / (R^2 - R) of consecutive windows
  	 *  of data with no lost or marked Ack packets. If arsent were the # of
  	 *  consecutive Acks received without loss, then Ack Ratio needs to be
  	 *  decreased by 1 when
  	 *	      arsent >=  K * cwnd / R  =  cwnd^2 / (R^3 - R^2)
  	 *  where cwnd / R is the number of Acks received per window of data
  	 *  (cf. RFC 4341, App. A). The problems are that
  	 *  - arsent counts other packets as well;
  	 *  - the comparison uses a formula different from RFC 4341;
  	 *  - computing a cubic/quadratic equation each time is too complicated.
  	 *  Hence a different algorithm is needed.
  	 */
  #if 0
  	/* Ack Ratio.  Need to maintain a concept of how many windows we sent */
  	hc->tx_arsent++;
  	/* We had an ack loss in this window... */
  	if (hc->tx_ackloss) {
  		if (hc->tx_arsent >= hc->tx_cwnd) {
  			hc->tx_arsent  = 0;
  			hc->tx_ackloss = 0;
  		}
  	} else {
  		/* No acks lost up to now... */
  		/* decrease ack ratio if enough packets were sent */
  		if (dp->dccps_l_ack_ratio > 1) {
  			/* XXX don't calculate denominator each time */
  			int denom = dp->dccps_l_ack_ratio * dp->dccps_l_ack_ratio -
  				    dp->dccps_l_ack_ratio;
  
  			denom = hc->tx_cwnd * hc->tx_cwnd / denom;
  
  			if (hc->tx_arsent >= denom) {
  				ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
  				hc->tx_arsent = 0;
  			}
  		} else {
  			/* we can't increase ack ratio further [1] */
  			hc->tx_arsent = 0; /* or maybe set it to cwnd*/
  		}
  	}
  #endif
  
  	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
  
  #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
  	do {
  		struct ccid2_seq *seqp = hc->tx_seqt;
  
  		while (seqp != hc->tx_seqh) {
  			ccid2_pr_debug("out seq=%llu acked=%d time=%u
  ",
  				       (unsigned long long)seqp->ccid2s_seq,
  				       seqp->ccid2s_acked, seqp->ccid2s_sent);
  			seqp = seqp->ccid2s_next;
  		}
  	} while (0);
  	ccid2_pr_debug("=========
  ");
  #endif
  }
  
  /**
   * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
   * This code is almost identical with TCP's tcp_rtt_estimator(), since
   * - it has a higher sampling frequency (recommended by RFC 1323),
   * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
   * - it is simple (cf. more complex proposals such as Eifel timer or research
   *   which suggests that the gain should be set according to window size),
   * - in tests it was found to work well with CCID2 [gerrit].
   */
  static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	long m = mrtt ? : 1;
  
  	if (hc->tx_srtt == 0) {
  		/* First measurement m */
  		hc->tx_srtt = m << 3;
  		hc->tx_mdev = m << 1;
  
  		hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
  		hc->tx_rttvar   = hc->tx_mdev_max;
  
  		hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
  	} else {
  		/* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
  		m -= (hc->tx_srtt >> 3);
  		hc->tx_srtt += m;
  
  		/* Similarly, update scaled mdev with regard to |m| */
  		if (m < 0) {
  			m = -m;
  			m -= (hc->tx_mdev >> 2);
  			/*
  			 * This neutralises RTO increase when RTT < SRTT - mdev
  			 * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
  			 * in Linux TCP", USENIX 2002, pp. 49-62).
  			 */
  			if (m > 0)
  				m >>= 3;
  		} else {
  			m -= (hc->tx_mdev >> 2);
  		}
  		hc->tx_mdev += m;
  
  		if (hc->tx_mdev > hc->tx_mdev_max) {
  			hc->tx_mdev_max = hc->tx_mdev;
  			if (hc->tx_mdev_max > hc->tx_rttvar)
  				hc->tx_rttvar = hc->tx_mdev_max;
  		}
  
  		/*
  		 * Decay RTTVAR at most once per flight, exploiting that
  		 *  1) pipe <= cwnd <= Sequence_Window = W  (RFC 4340, 7.5.2)
  		 *  2) AWL = GSS-W+1 <= GAR <= GSS          (RFC 4340, 7.5.1)
  		 * GAR is a useful bound for FlightSize = pipe.
  		 * AWL is probably too low here, as it over-estimates pipe.
  		 */
  		if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
  			if (hc->tx_mdev_max < hc->tx_rttvar)
  				hc->tx_rttvar -= (hc->tx_rttvar -
  						  hc->tx_mdev_max) >> 2;
  			hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
  			hc->tx_mdev_max = tcp_rto_min(sk);
  		}
  	}
  
  	/*
  	 * Set RTO from SRTT and RTTVAR
  	 * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
  	 * This agrees with RFC 4341, 5:
  	 *	"Because DCCP does not retransmit data, DCCP does not require
  	 *	 TCP's recommended minimum timeout of one second".
  	 */
  	hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;
  
  	if (hc->tx_rto > DCCP_RTO_MAX)
  		hc->tx_rto = DCCP_RTO_MAX;
  }
  
  static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
  			  unsigned int *maxincr)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	struct dccp_sock *dp = dccp_sk(sk);
  	int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;
  
  	if (hc->tx_cwnd < dp->dccps_l_seq_win &&
  	    r_seq_used < dp->dccps_r_seq_win) {
  		if (hc->tx_cwnd < hc->tx_ssthresh) {
  			if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) {
  				hc->tx_cwnd += 1;
  				*maxincr    -= 1;
  				hc->tx_packets_acked = 0;
  			}
  		} else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
  			hc->tx_cwnd += 1;
  			hc->tx_packets_acked = 0;
  		}
  	}
  
  	/*
  	 * Adjust the local sequence window and the ack ratio to allow about
  	 * 5 times the number of packets in the network (RFC 4340 7.5.2)
  	 */
  	if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
  		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2);
  	else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2)
  		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U);
  
  	if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
  		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2);
  	else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2)
  		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2);
  
  	/*
  	 * FIXME: RTT is sampled several times per acknowledgment (for each
  	 * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
  	 * This causes the RTT to be over-estimated, since the older entries
  	 * in the Ack Vector have earlier sending times.
  	 * The cleanest solution is to not use the ccid2s_sent field at all
  	 * and instead use DCCP timestamps: requires changes in other places.
  	 */
  	ccid2_rtt_estimator(sk, ccid2_time_stamp - seqp->ccid2s_sent);
  }
  
  static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  
  	if ((s32)(seqp->ccid2s_sent - hc->tx_last_cong) < 0) {
  		ccid2_pr_debug("Multiple losses in an RTT---treating as one
  ");
  		return;
  	}
  
  	hc->tx_last_cong = ccid2_time_stamp;
  
  	hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
  	hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);
  
  	ccid2_check_l_ack_ratio(sk);
  }
  
  static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
  				     u8 option, u8 *optval, u8 optlen)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  
  	switch (option) {
  	case DCCPO_ACK_VECTOR_0:
  	case DCCPO_ACK_VECTOR_1:
  		return dccp_ackvec_parsed_add(&hc->tx_av_chunks, optval, optlen,
  					      option - DCCPO_ACK_VECTOR_0);
  	}
  	return 0;
  }
  
  static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
  {
  	struct dccp_sock *dp = dccp_sk(sk);
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
  	struct dccp_ackvec_parsed *avp;
  	u64 ackno, seqno;
  	struct ccid2_seq *seqp;
  	int done = 0;
  	unsigned int maxincr = 0;
  
  	/* check reverse path congestion */
  	seqno = DCCP_SKB_CB(skb)->dccpd_seq;
  
  	/* XXX this whole "algorithm" is broken.  Need to fix it to keep track
  	 * of the seqnos of the dupacks so that rpseq and rpdupack are correct
  	 * -sorbo.
  	 */
  	/* need to bootstrap */
  	if (hc->tx_rpdupack == -1) {
  		hc->tx_rpdupack = 0;
  		hc->tx_rpseq    = seqno;
  	} else {
  		/* check if packet is consecutive */
  		if (dccp_delta_seqno(hc->tx_rpseq, seqno) == 1)
  			hc->tx_rpseq = seqno;
  		/* it's a later packet */
  		else if (after48(seqno, hc->tx_rpseq)) {
  			hc->tx_rpdupack++;
  
  			/* check if we got enough dupacks */
  			if (hc->tx_rpdupack >= NUMDUPACK) {
  				hc->tx_rpdupack = -1; /* XXX lame */
  				hc->tx_rpseq    = 0;
  #ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
  				/*
  				 * FIXME: Ack Congestion Control is broken; in
  				 * the current state instabilities occurred with
  				 * Ack Ratios greater than 1; causing hang-ups
  				 * and long RTO timeouts. This needs to be fixed
  				 * before opening up dynamic changes. -- gerrit
  				 */
  				ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
  #endif
  			}
  		}
  	}
  
  	/* check forward path congestion */
  	if (dccp_packet_without_ack(skb))
  		return;
  
  	/* still didn't send out new data packets */
  	if (hc->tx_seqh == hc->tx_seqt)
  		goto done;
  
  	ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
  	if (after48(ackno, hc->tx_high_ack))
  		hc->tx_high_ack = ackno;
  
  	seqp = hc->tx_seqt;
  	while (before48(seqp->ccid2s_seq, ackno)) {
  		seqp = seqp->ccid2s_next;
  		if (seqp == hc->tx_seqh) {
  			seqp = hc->tx_seqh->ccid2s_prev;
  			break;
  		}
  	}
  
  	/*
  	 * In slow-start, cwnd can increase up to a maximum of Ack Ratio/2
  	 * packets per acknowledgement. Rounding up avoids that cwnd is not
  	 * advanced when Ack Ratio is 1 and gives a slight edge otherwise.
  	 */
  	if (hc->tx_cwnd < hc->tx_ssthresh)
  		maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);
  
  	/* go through all ack vectors */
  	list_for_each_entry(avp, &hc->tx_av_chunks, node) {
  		/* go through this ack vector */
  		for (; avp->len--; avp->vec++) {
  			u64 ackno_end_rl = SUB48(ackno,
  						 dccp_ackvec_runlen(avp->vec));
  
  			ccid2_pr_debug("ackvec %llu |%u,%u|
  ",
  				       (unsigned long long)ackno,
  				       dccp_ackvec_state(avp->vec) >> 6,
  				       dccp_ackvec_runlen(avp->vec));
  			/* if the seqno we are analyzing is larger than the
  			 * current ackno, then move towards the tail of our
  			 * seqnos.
  			 */
  			while (after48(seqp->ccid2s_seq, ackno)) {
  				if (seqp == hc->tx_seqt) {
  					done = 1;
  					break;
  				}
  				seqp = seqp->ccid2s_prev;
  			}
  			if (done)
  				break;
  
  			/* check all seqnos in the range of the vector
  			 * run length
  			 */
  			while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
  				const u8 state = dccp_ackvec_state(avp->vec);
  
  				/* new packet received or marked */
  				if (state != DCCPAV_NOT_RECEIVED &&
  				    !seqp->ccid2s_acked) {
  					if (state == DCCPAV_ECN_MARKED)
  						ccid2_congestion_event(sk,
  								       seqp);
  					else
  						ccid2_new_ack(sk, seqp,
  							      &maxincr);
  
  					seqp->ccid2s_acked = 1;
  					ccid2_pr_debug("Got ack for %llu
  ",
  						       (unsigned long long)seqp->ccid2s_seq);
  					hc->tx_pipe--;
  				}
  				if (seqp == hc->tx_seqt) {
  					done = 1;
  					break;
  				}
  				seqp = seqp->ccid2s_prev;
  			}
  			if (done)
  				break;
  
  			ackno = SUB48(ackno_end_rl, 1);
  		}
  		if (done)
  			break;
  	}
  
  	/* The state about what is acked should be correct now
  	 * Check for NUMDUPACK
  	 */
  	seqp = hc->tx_seqt;
  	while (before48(seqp->ccid2s_seq, hc->tx_high_ack)) {
  		seqp = seqp->ccid2s_next;
  		if (seqp == hc->tx_seqh) {
  			seqp = hc->tx_seqh->ccid2s_prev;
  			break;
  		}
  	}
  	done = 0;
  	while (1) {
  		if (seqp->ccid2s_acked) {
  			done++;
  			if (done == NUMDUPACK)
  				break;
  		}
  		if (seqp == hc->tx_seqt)
  			break;
  		seqp = seqp->ccid2s_prev;
  	}
  
  	/* If there are at least 3 acknowledgements, anything unacknowledged
  	 * below the last sequence number is considered lost
  	 */
  	if (done == NUMDUPACK) {
  		struct ccid2_seq *last_acked = seqp;
  
  		/* check for lost packets */
  		while (1) {
  			if (!seqp->ccid2s_acked) {
  				ccid2_pr_debug("Packet lost: %llu
  ",
  					       (unsigned long long)seqp->ccid2s_seq);
  				/* XXX need to traverse from tail -> head in
  				 * order to detect multiple congestion events in
  				 * one ack vector.
  				 */
  				ccid2_congestion_event(sk, seqp);
  				hc->tx_pipe--;
  			}
  			if (seqp == hc->tx_seqt)
  				break;
  			seqp = seqp->ccid2s_prev;
  		}
  
  		hc->tx_seqt = last_acked;
  	}
  
  	/* trim acked packets in tail */
  	while (hc->tx_seqt != hc->tx_seqh) {
  		if (!hc->tx_seqt->ccid2s_acked)
  			break;
  
  		hc->tx_seqt = hc->tx_seqt->ccid2s_next;
  	}
  
  	/* restart RTO timer if not all outstanding data has been acked */
  	if (hc->tx_pipe == 0)
  		sk_stop_timer(sk, &hc->tx_rtotimer);
  	else
  		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
  done:
  	/* check if incoming Acks allow pending packets to be sent */
  	if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
  		tasklet_schedule(&dccp_sk(sk)->dccps_xmitlet);
  	dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
  }
  
  static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
  {
  	struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
  	struct dccp_sock *dp = dccp_sk(sk);
  	u32 max_ratio;
  
  	/* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
  	hc->tx_ssthresh = ~0U;
  
  	/* Use larger initial windows (RFC 4341, section 5). */
  	hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
  	hc->tx_expected_wnd = hc->tx_cwnd;
  
  	/* Make sure that Ack Ratio is enabled and within bounds. */
  	max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
  	if (dp->dccps_l_ack_ratio == 0 || dp->dccps_l_ack_ratio > max_ratio)
  		dp->dccps_l_ack_ratio = max_ratio;
  
  	/* XXX init ~ to window size... */
  	if (ccid2_hc_tx_alloc_seq(hc))
  		return -ENOMEM;
  
  	hc->tx_rto	 = DCCP_TIMEOUT_INIT;
  	hc->tx_rpdupack  = -1;
  	hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_time_stamp;
  	hc->tx_cwnd_used = 0;
  	setup_timer(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire,
  			(unsigned long)sk);
  	INIT_LIST_HEAD(&hc->tx_av_chunks);
  	return 0;
  }
  
  static void ccid2_hc_tx_exit(struct sock *sk)
  {
  	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
  	int i;
  
  	sk_stop_timer(sk, &hc->tx_rtotimer);
  
  	for (i = 0; i < hc->tx_seqbufc; i++)
  		kfree(hc->tx_seqbuf[i]);
  	hc->tx_seqbufc = 0;
  }
  
  static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
  {
  	struct ccid2_hc_rx_sock *hc = ccid2_hc_rx_sk(sk);
  
  	if (!dccp_data_packet(skb))
  		return;
  
  	if (++hc->rx_num_data_pkts >= dccp_sk(sk)->dccps_r_ack_ratio) {
  		dccp_send_ack(sk);
  		hc->rx_num_data_pkts = 0;
  	}
  }
  
  struct ccid_operations ccid2_ops = {
  	.ccid_id		  = DCCPC_CCID2,
  	.ccid_name		  = "TCP-like",
  	.ccid_hc_tx_obj_size	  = sizeof(struct ccid2_hc_tx_sock),
  	.ccid_hc_tx_init	  = ccid2_hc_tx_init,
  	.ccid_hc_tx_exit	  = ccid2_hc_tx_exit,
  	.ccid_hc_tx_send_packet	  = ccid2_hc_tx_send_packet,
  	.ccid_hc_tx_packet_sent	  = ccid2_hc_tx_packet_sent,
  	.ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
  	.ccid_hc_tx_packet_recv	  = ccid2_hc_tx_packet_recv,
  	.ccid_hc_rx_obj_size	  = sizeof(struct ccid2_hc_rx_sock),
  	.ccid_hc_rx_packet_recv	  = ccid2_hc_rx_packet_recv,
  };
  
  #ifdef CONFIG_IP_DCCP_CCID2_DEBUG
  module_param(ccid2_debug, bool, 0644);
  MODULE_PARM_DESC(ccid2_debug, "Enable CCID-2 debug messages");
  #endif