path: root/net/dccp/ccids/ccid2.c

/*
 *  net/dccp/ccids/ccid2.c
 *
 *  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: draft-ietf-dccp-ccid2-10.txt
 *
 * BUGS:
 * - sequence number wrapping
 */

#include "../ccid.h"
#include "../dccp.h"
#include "ccid2.h"

static int ccid2_debug;

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
#define ccid2_pr_debug(format, a...) \
        do { if (ccid2_debug) \
                printk(KERN_DEBUG "%s: " format, __FUNCTION__, ##a); \
        } while (0)
#else
#define ccid2_pr_debug(format, a...)
#endif

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
static void ccid2_hc_tx_check_sanity(const struct ccid2_hc_tx_sock *hctx)
{
	int len = 0;
	int pipe = 0;
	struct ccid2_seq *seqp = hctx->ccid2hctx_seqh;

	/* there is data in the chain */
	if (seqp != hctx->ccid2hctx_seqt) {
		seqp = seqp->ccid2s_prev;
		len++;
		if (!seqp->ccid2s_acked)
			pipe++;

		while (seqp != hctx->ccid2hctx_seqt) {
			struct ccid2_seq *prev = seqp->ccid2s_prev;

			len++;
			if (!prev->ccid2s_acked)
				pipe++;

			/* packets are sent sequentially */
			BUG_ON(seqp->ccid2s_seq <= prev->ccid2s_seq);
			BUG_ON(time_before(seqp->ccid2s_sent,
					   prev->ccid2s_sent));

			seqp = prev;
		}
	}

	BUG_ON(pipe != hctx->ccid2hctx_pipe);
	ccid2_pr_debug("len of chain=%d\n", len);

	do {
		seqp = seqp->ccid2s_prev;
		len++;
	} while (seqp != hctx->ccid2hctx_seqh);

	ccid2_pr_debug("total len=%d\n", len);
	BUG_ON(len != hctx->ccid2hctx_seqbufc * CCID2_SEQBUF_LEN);
}
#else
#define ccid2_hc_tx_check_sanity(hctx) do {} while (0)
#endif

static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hctx, int num,
				 gfp_t gfp)
{
	struct ccid2_seq *seqp;
	int i;

	/* check if we have space to preserve the pointer to the buffer */
	if (hctx->ccid2hctx_seqbufc >= (sizeof(hctx->ccid2hctx_seqbuf) /
					sizeof(struct ccid2_seq*)))
		return -ENOMEM;

	/* allocate buffer and initialize linked list */
	seqp = kmalloc(sizeof(*seqp) * num, gfp);
	if (seqp == NULL)
		return -ENOMEM;

	for (i = 0; i < (num - 1); i++) {
		seqp[i].ccid2s_next = &seqp[i + 1];
		seqp[i + 1].ccid2s_prev = &seqp[i];
	}
	seqp[num - 1].ccid2s_next = seqp;
	seqp->ccid2s_prev = &seqp[num - 1];

	/* This is the first allocation.  Initiate the head and tail.  */
	if (hctx->ccid2hctx_seqbufc == 0)
		hctx->ccid2hctx_seqh = hctx->ccid2hctx_seqt = seqp;
	else {
		/* link the existing list with the one we just created */
		hctx->ccid2hctx_seqh->ccid2s_next = seqp;
		seqp->ccid2s_prev = hctx->ccid2hctx_seqh;

		hctx->ccid2hctx_seqt->ccid2s_prev = &seqp[num - 1];
		seqp[num - 1].ccid2s_next = hctx->ccid2hctx_seqt;
	}

	/* store the original pointer to the buffer so we can free it */
	hctx->ccid2hctx_seqbuf[hctx->ccid2hctx_seqbufc] = seqp;
	hctx->ccid2hctx_seqbufc++;

	return 0;
}

static int ccid2_hc_tx_send_packet(struct sock *sk,
				   struct sk_buff *skb, int len)
{
	struct ccid2_hc_tx_sock *hctx;

	switch (DCCP_SKB_CB(skb)->dccpd_type) {
	case 0: /* XXX data packets from userland come through like this */
	case DCCP_PKT_DATA:
	case DCCP_PKT_DATAACK:
		break;
	/* No congestion control on other packets */
	default:
		return 0;
	}

        hctx = ccid2_hc_tx_sk(sk);

	ccid2_pr_debug("pipe=%d cwnd=%d\n", hctx->ccid2hctx_pipe,
		       hctx->ccid2hctx_cwnd);

	if (hctx->ccid2hctx_pipe < hctx->ccid2hctx_cwnd) {
		/* OK we can send... make sure previous packet was sent off */
		if (!hctx->ccid2hctx_sendwait) {
			hctx->ccid2hctx_sendwait = 1;
			return 0;
		}
	}

	return 1; /* XXX CCID should dequeue when ready instead of polling */
}

static void ccid2_change_l_ack_ratio(struct sock *sk, int val)
{
	struct dccp_sock *dp = dccp_sk(sk);
	/*
	 * XXX I don't really agree with val != 2.  If cwnd is 1, ack ratio
	 * should be 1... it shouldn't be allowed to become 2.
	 * -sorbo.
	 */
	if (val != 2) {
		const struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
		int max = hctx->ccid2hctx_cwnd / 2;

		/* round up */
		if (hctx->ccid2hctx_cwnd & 1)
			max++;

		if (val > max)
			val = max;
	}

	ccid2_pr_debug("changing local ack ratio to %d\n", val);
	WARN_ON(val <= 0);
	dp->dccps_l_ack_ratio = val;
}

static void ccid2_change_cwnd(struct sock *sk, int val)
{
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

	if (val == 0)
		val = 1;

	/* XXX do we need to change ack ratio? */
	ccid2_pr_debug("change cwnd to %d\n", val);

	BUG_ON(val < 1);
	hctx->ccid2hctx_cwnd = val;
}

static void ccid2_start_rto_timer(struct sock *sk);

static void ccid2_hc_tx_rto_expire(unsigned long data)
{
	struct sock *sk = (struct sock *)data;
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
	long s;

	bh_lock_sock(sk);
	if (sock_owned_by_user(sk)) {
		sk_reset_timer(sk, &hctx->ccid2hctx_rtotimer,
			       jiffies + HZ / 5);
		goto out;
	}

	ccid2_pr_debug("RTO_EXPIRE\n");

	ccid2_hc_tx_check_sanity(hctx);

	/* back-off timer */
	hctx->ccid2hctx_rto <<= 1;

	s = hctx->ccid2hctx_rto / HZ;
	if (s > 60)
		hctx->ccid2hctx_rto = 60 * HZ;

	ccid2_start_rto_timer(sk);

	/* adjust pipe, cwnd etc */
	hctx->ccid2hctx_pipe = 0;
	hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd >> 1;
	if (hctx->ccid2hctx_ssthresh < 2)
		hctx->ccid2hctx_ssthresh = 2;
	ccid2_change_cwnd(sk, 1);

	/* clear state about stuff we sent */
	hctx->ccid2hctx_seqt	= hctx->ccid2hctx_seqh;
	hctx->ccid2hctx_ssacks	= 0;
	hctx->ccid2hctx_acks	= 0;
	hctx->ccid2hctx_sent	= 0;

	/* clear ack ratio state. */
	hctx->ccid2hctx_arsent	 = 0;
	hctx->ccid2hctx_ackloss  = 0;
	hctx->ccid2hctx_rpseq	 = 0;
	hctx->ccid2hctx_rpdupack = -1;
	ccid2_change_l_ack_ratio(sk, 1);
	ccid2_hc_tx_check_sanity(hctx);
out:
	bh_unlock_sock(sk);
	sock_put(sk);
}

static void ccid2_start_rto_timer(struct sock *sk)
{
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

	ccid2_pr_debug("setting RTO timeout=%ld\n", hctx->ccid2hctx_rto);

	BUG_ON(timer_pending(&hctx->ccid2hctx_rtotimer));
	sk_reset_timer(sk, &hctx->ccid2hctx_rtotimer,
		       jiffies + hctx->ccid2hctx_rto);
}

static void ccid2_hc_tx_packet_sent(struct sock *sk, int more, int len)
{
	struct dccp_sock *dp = dccp_sk(sk);
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
	struct ccid2_seq *next;
	u64 seq;

	ccid2_hc_tx_check_sanity(hctx);

	BUG_ON(!hctx->ccid2hctx_sendwait);
	hctx->ccid2hctx_sendwait = 0;
	hctx->ccid2hctx_pipe++;
	BUG_ON(hctx->ccid2hctx_pipe < 0);

	/* There is an issue.  What if another packet is sent between
	 * packet_send() and packet_sent().  Then the sequence number would be
	 * wrong.
	 * -sorbo.
	 */
	seq = dp->dccps_gss;

	hctx->ccid2hctx_seqh->ccid2s_seq   = seq;
	hctx->ccid2hctx_seqh->ccid2s_acked = 0;
	hctx->ccid2hctx_seqh->ccid2s_sent  = jiffies;

	next = hctx->ccid2hctx_seqh->ccid2s_next;
	/* check if we need to alloc more space */
	if (next == hctx->ccid2hctx_seqt) {
		int rc;

		ccid2_pr_debug("allocating more space in history\n");
		rc = ccid2_hc_tx_alloc_seq(hctx, CCID2_SEQBUF_LEN, GFP_KERNEL);
		BUG_ON(rc); /* XXX what do we do? */

		next = hctx->ccid2hctx_seqh->ccid2s_next;
		BUG_ON(next == hctx->ccid2hctx_seqt);
	}
	hctx->ccid2hctx_seqh = next;

	ccid2_pr_debug("cwnd=%d pipe=%d\n", hctx->ccid2hctx_cwnd,
		       hctx->ccid2hctx_pipe);

	hctx->ccid2hctx_sent++;

	/* Ack Ratio.  Need to maintain a concept of how many windows we sent */
	hctx->ccid2hctx_arsent++;
	/* We had an ack loss in this window... */
	if (hctx->ccid2hctx_ackloss) {
		if (hctx->ccid2hctx_arsent >= hctx->ccid2hctx_cwnd) {
			hctx->ccid2hctx_arsent	= 0;
			hctx->ccid2hctx_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 = hctx->ccid2hctx_cwnd * hctx->ccid2hctx_cwnd / denom;

			if (hctx->ccid2hctx_arsent >= denom) {
				ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
				hctx->ccid2hctx_arsent = 0;
			}
		} else {
			/* we can't increase ack ratio further [1] */
			hctx->ccid2hctx_arsent = 0; /* or maybe set it to cwnd*/
		}
	}

	/* setup RTO timer */
	if (!timer_pending(&hctx->ccid2hctx_rtotimer))
		ccid2_start_rto_timer(sk);

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
	ccid2_pr_debug("pipe=%d\n", hctx->ccid2hctx_pipe);
	ccid2_pr_debug("Sent: seq=%llu\n", seq);
	do {
		struct ccid2_seq *seqp = hctx->ccid2hctx_seqt;

		while (seqp != hctx->ccid2hctx_seqh) {
			ccid2_pr_debug("out seq=%llu acked=%d time=%lu\n",
			       	       seqp->ccid2s_seq, seqp->ccid2s_acked,
				       seqp->ccid2s_sent);
			seqp = seqp->ccid2s_next;
		}
	} while (0);
	ccid2_pr_debug("=========\n");
	ccid2_hc_tx_check_sanity(hctx);
#endif
}

/* XXX Lame code duplication!
 * returns -1 if none was found.
 * else returns the next offset to use in the function call.
 */
static int ccid2_ackvector(struct sock *sk, struct sk_buff *skb, int offset,
			   unsigned char **vec, unsigned char *veclen)
{
        const struct dccp_hdr *dh = dccp_hdr(skb);
        unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
        unsigned char *opt_ptr;
        const unsigned char *opt_end = (unsigned char *)dh +
                                        (dh->dccph_doff * 4);
        unsigned char opt, len;
        unsigned char *value;

	BUG_ON(offset < 0);
	options += offset;
	opt_ptr = options;
	if (opt_ptr >= opt_end)
		return -1;

	while (opt_ptr != opt_end) {
                opt   = *opt_ptr++;
                len   = 0;
                value = NULL;

                /* Check if this isn't a single byte option */
                if (opt > DCCPO_MAX_RESERVED) {
                        if (opt_ptr == opt_end)
                                goto out_invalid_option;

                        len = *opt_ptr++;
                        if (len < 3)
                                goto out_invalid_option;
                        /*
                         * Remove the type and len fields, leaving
                         * just the value size
                         */
                        len     -= 2;
                        value   = opt_ptr;
                        opt_ptr += len;

                        if (opt_ptr > opt_end)
                                goto out_invalid_option;
                }

		switch (opt) {
		case DCCPO_ACK_VECTOR_0:
		case DCCPO_ACK_VECTOR_1:
			*vec	= value;
			*veclen = len;
			return offset + (opt_ptr - options);
		}
	}

	return -1;

out_invalid_option:
	BUG_ON(1); /* should never happen... options were previously parsed ! */
	return -1;
}

static void ccid2_hc_tx_kill_rto_timer(struct sock *sk)
{
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

	sk_stop_timer(sk, &hctx->ccid2hctx_rtotimer);
	ccid2_pr_debug("deleted RTO timer\n");
}

static inline void ccid2_new_ack(struct sock *sk,
			         struct ccid2_seq *seqp,
				 unsigned int *maxincr)
{
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

	/* slow start */
	if (hctx->ccid2hctx_cwnd < hctx->ccid2hctx_ssthresh) {
		hctx->ccid2hctx_acks = 0;

		/* We can increase cwnd at most maxincr [ack_ratio/2] */
		if (*maxincr) {
			/* increase every 2 acks */
			hctx->ccid2hctx_ssacks++;
			if (hctx->ccid2hctx_ssacks == 2) {
				ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);
				hctx->ccid2hctx_ssacks = 0;
				*maxincr = *maxincr - 1;
			}
		} else {
			/* increased cwnd enough for this single ack */
			hctx->ccid2hctx_ssacks = 0;
		}
	} else {
		hctx->ccid2hctx_ssacks = 0;
		hctx->ccid2hctx_acks++;

		if (hctx->ccid2hctx_acks >= hctx->ccid2hctx_cwnd) {
			ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);
			hctx->ccid2hctx_acks = 0;
		}
	}

	/* update RTO */
	if (hctx->ccid2hctx_srtt == -1 ||
	    time_after(jiffies, hctx->ccid2hctx_lastrtt + hctx->ccid2hctx_srtt)) {
		unsigned long r = (long)jiffies - (long)seqp->ccid2s_sent;
		int s;

		/* first measurement */
		if (hctx->ccid2hctx_srtt == -1) {
			ccid2_pr_debug("R: %lu Time=%lu seq=%llu\n",
			       	       r, jiffies, seqp->ccid2s_seq);
			hctx->ccid2hctx_srtt = r;
			hctx->ccid2hctx_rttvar = r >> 1;
		} else {
			/* RTTVAR */
			long tmp = hctx->ccid2hctx_srtt - r;
			if (tmp < 0)
				tmp *= -1;

			tmp >>= 2;
			hctx->ccid2hctx_rttvar *= 3;
			hctx->ccid2hctx_rttvar >>= 2;
			hctx->ccid2hctx_rttvar += tmp;

			/* SRTT */
			hctx->ccid2hctx_srtt *= 7;
			hctx->ccid2hctx_srtt >>= 3;
			tmp = r >> 3;
			hctx->ccid2hctx_srtt += tmp;
		}
		s = hctx->ccid2hctx_rttvar << 2;
		/* clock granularity is 1 when based on jiffies */
		if (!s)
			s = 1;
		hctx->ccid2hctx_rto = hctx->ccid2hctx_srtt + s;

		/* must be at least a second */
		s = hctx->ccid2hctx_rto / HZ;
		/* DCCP doesn't require this [but I like it cuz my code sux] */
#if 1
		if (s < 1)
			hctx->ccid2hctx_rto = HZ;
#endif
		/* max 60 seconds */
		if (s > 60)
			hctx->ccid2hctx_rto = HZ * 60;

		hctx->ccid2hctx_lastrtt = jiffies;

		ccid2_pr_debug("srtt: %ld rttvar: %ld rto: %ld (HZ=%d) R=%lu\n",
		       	       hctx->ccid2hctx_srtt, hctx->ccid2hctx_rttvar,
		       	       hctx->ccid2hctx_rto, HZ, r);
		hctx->ccid2hctx_sent = 0;
	}

	/* we got a new ack, so re-start RTO timer */
	ccid2_hc_tx_kill_rto_timer(sk);
	ccid2_start_rto_timer(sk);
}

static void ccid2_hc_tx_dec_pipe(struct sock *sk)
{
	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

	hctx->ccid2hctx_pipe--;
	BUG_ON(hctx->ccid2hctx_pipe < 0);

	if (hctx->ccid2hctx_pipe == 0)
		ccid2_hc_tx_kill_rto_timer(sk);
}

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 *hctx = ccid2_hc_tx_sk(sk);
	u64 ackno, seqno;
	struct ccid2_seq *seqp;
	unsigned char *vector;
	unsigned char veclen;
	int offset = 0;
	int done = 0;
	int loss = 0;
	unsigned int maxincr = 0;

	ccid2_hc_tx_check_sanity(hctx);
	/* 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 (hctx->ccid2hctx_rpdupack == -1) {
		hctx->ccid2hctx_rpdupack = 0;
		hctx->ccid2hctx_rpseq = seqno;
	} else {
		/* check if packet is consecutive */
		if ((hctx->ccid2hctx_rpseq + 1) == seqno)
			hctx->ccid2hctx_rpseq++;
		/* it's a later packet */
		else if (after48(seqno, hctx->ccid2hctx_rpseq)) {
			hctx->ccid2hctx_rpdupack++;

			/* check if we got enough dupacks */
			if (hctx->ccid2hctx_rpdupack >=
			    hctx->ccid2hctx_numdupack) {
				hctx->ccid2hctx_rpdupack = -1; /* XXX lame */
				hctx->ccid2hctx_rpseq = 0;

				ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio << 1);
			}
		}
	}

	/* check forward path congestion */
	/* still didn't send out new data packets */
	if (hctx->ccid2hctx_seqh == hctx->ccid2hctx_seqt)
		return;

	switch (DCCP_SKB_CB(skb)->dccpd_type) {
	case DCCP_PKT_ACK:
	case DCCP_PKT_DATAACK:
		break;
	default:
		return;
	}

	ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
	seqp = hctx->ccid2hctx_seqh->ccid2s_prev;

	/* If in slow-start, cwnd can increase at most Ack Ratio / 2 packets for
	 * this single ack.  I round up.
	 * -sorbo.
	 */
	maxincr = dp->dccps_l_ack_ratio >> 1;
	maxincr++;

	/* go through all ack vectors */
	while ((offset = ccid2_ackvector(sk, skb, offset,
					 &vector, &veclen)) != -1) {
		/* go through this ack vector */
		while (veclen--) {
			const u8 rl = *vector & DCCP_ACKVEC_LEN_MASK;
			u64 ackno_end_rl;

			dccp_set_seqno(&ackno_end_rl, ackno - rl);
			ccid2_pr_debug("ackvec start:%llu end:%llu\n", ackno,
				       ackno_end_rl);
			/* 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 == hctx->ccid2hctx_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 = *vector &
						 DCCP_ACKVEC_STATE_MASK;

				/* new packet received or marked */
				if (state != DCCP_ACKVEC_STATE_NOT_RECEIVED &&
				    !seqp->ccid2s_acked) {
				    	if (state ==
					    DCCP_ACKVEC_STATE_ECN_MARKED) {
						loss = 1;
					} else
						ccid2_new_ack(sk, seqp,
							      &maxincr);

					seqp->ccid2s_acked = 1;
					ccid2_pr_debug("Got ack for %llu\n",
					       	       seqp->ccid2s_seq);
					ccid2_hc_tx_dec_pipe(sk);
				}
				if (seqp == hctx->ccid2hctx_seqt) {
					done = 1;
					break;
				}
				seqp = seqp->ccid2s_next;
			}
			if (done)
				break;


			dccp_set_seqno(&ackno, ackno_end_rl - 1);
			vector++;
		}
		if (done)
			break;
	}

	/* The state about what is acked should be correct now
	 * Check for NUMDUPACK
	 */
	seqp = hctx->ccid2hctx_seqh->ccid2s_prev;
	done = 0;
	while (1) {
		if (seqp->ccid2s_acked) {
			done++;
			if (done == hctx->ccid2hctx_numdupack)
				break;
		}
		if (seqp == hctx->ccid2hctx_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 == hctx->ccid2hctx_numdupack) {
		struct ccid2_seq *last_acked = seqp;

		/* check for lost packets */
		while (1) {
			if (!seqp->ccid2s_acked) {
				loss = 1;
				ccid2_hc_tx_dec_pipe(sk);
			}
			if (seqp == hctx->ccid2hctx_seqt)
				break;
			seqp = seqp->ccid2s_prev;
		}

		hctx->ccid2hctx_seqt = last_acked;
	}

	/* trim acked packets in tail */
	while (hctx->ccid2hctx_seqt != hctx->ccid2hctx_seqh) {
		if (!hctx->ccid2hctx_seqt->ccid2s_acked)
			break;

		hctx->ccid2hctx_seqt = hctx->ccid2hctx_seqt->ccid2s_next;
	}

	if (loss) {
		/* XXX do bit shifts guarantee a 0 as the new bit? */
		ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd >> 1);
		hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;
		if (hctx->ccid2hctx_ssthresh < 2)
			hctx->ccid2hctx_ssthresh = 2;
	}

	ccid2_hc_tx_check_sanity(hctx);
}

static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
{
        struct ccid2_hc_tx_sock *hctx = ccid_priv(ccid);

	hctx->ccid2hctx_cwnd	  = 1;
	/* Initialize ssthresh to infinity.  This means that we will exit the
	 * initial slow-start after the first packet loss.  This is what we
	 * want.
	 */
	hctx->ccid2hctx_ssthresh  = ~0;
	hctx->ccid2hctx_numdupack = 3;
	hctx->ccid2hctx_seqbufc   = 0;

	/* XXX init ~ to window size... */
	if (ccid2_hc_tx_alloc_seq(hctx, CCID2_SEQBUF_LEN, GFP_ATOMIC) != 0)
		return -ENOMEM;

	hctx->ccid2hctx_sent	 = 0;
	hctx->ccid2hctx_rto	 = 3 * HZ;
	hctx->ccid2hctx_srtt	 = -1;
	hctx->ccid2hctx_rttvar	 = -1;
	hctx->ccid2hctx_lastrtt  = 0;
	hctx->ccid2hctx_rpdupack = -1;

	hctx->ccid2hctx_rtotimer.function = &ccid2_hc_tx_rto_expire;
	hctx->ccid2hctx_rtotimer.data	  = (unsigned long)sk;
	init_timer(&hctx->ccid2hctx_rtotimer);

	ccid2_hc_tx_check_sanity(hctx);
	return 0;
}

static void ccid2_hc_tx_exit(struct sock *sk)
{
        struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
	int i;

	ccid2_hc_tx_kill_rto_timer(sk);

	for (i = 0; i < hctx->ccid2hctx_seqbufc; i++)
		kfree(hctx->ccid2hctx_seqbuf[i]);
	hctx->ccid2hctx_seqbufc = 0;
}

static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
{
	const struct dccp_sock *dp = dccp_sk(sk);
	struct ccid2_hc_rx_sock *hcrx = ccid2_hc_rx_sk(sk);

	switch (DCCP_SKB_CB(skb)->dccpd_type) {
	case DCCP_PKT_DATA:
	case DCCP_PKT_DATAACK:
		hcrx->ccid2hcrx_data++;
		if (hcrx->ccid2hcrx_data >= dp->dccps_r_ack_ratio) {
			dccp_send_ack(sk);
			hcrx->ccid2hcrx_data = 0;
		}
		break;
	}
}

static struct ccid_operations ccid2 = {
	.ccid_id		= 2,
	.ccid_name		= "ccid2",
	.ccid_owner		= THIS_MODULE,
	.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_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,
};

module_param(ccid2_debug, int, 0444);
MODULE_PARM_DESC(ccid2_debug, "Enable debug messages");

static __init int ccid2_module_init(void)
{
	return ccid_register(&ccid2);
}
module_init(ccid2_module_init);

static __exit void ccid2_module_exit(void)
{
	ccid_unregister(&ccid2);
}
module_exit(ccid2_module_exit);

MODULE_AUTHOR("Andrea Bittau <a.bittau@cs.ucl.ac.uk>");
MODULE_DESCRIPTION("DCCP TCP-Like (CCID2) CCID");
MODULE_LICENSE("GPL");
MODULE_ALIAS("net-dccp-ccid-2");