[CCID2]: Disable broken Ack Ratio adaptation algorithm

[firewire-audio.git] / 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 RFC 4341
 */

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


#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
static int ccid2_debug;
#define ccid2_pr_debug(format, a...)    DCCP_PR_DEBUG(ccid2_debug, format, ##a)

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(dccp_delta_seqno(seqp->ccid2s_seq,
                                                prev->ccid2s_seq ) >= 0);
                        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_pr_debug(format, a...)
#define ccid2_hc_tx_check_sanity(hctx)
#endif

static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hctx)
{
        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(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 (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[CCID2_SEQBUF_LEN - 1];
                seqp[CCID2_SEQBUF_LEN - 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)
{
        struct ccid2_hc_tx_sock *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, u32 val)
{
        struct dccp_sock *dp = dccp_sk(sk);
        u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->ccid2hctx_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\n", val, max_ratio);
                val = max_ratio;
        }
        if (val > 0xFFFF)               /* RFC 4340, 11.3 */
                val = 0xFFFF;

        if (val == dp->dccps_l_ack_ratio)
                return;

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

static void ccid2_change_cwnd(struct ccid2_hc_tx_sock *hctx, u32 val)
{
        hctx->ccid2hctx_cwnd = val? : 1;
        ccid2_pr_debug("changed cwnd to %u\n", hctx->ccid2hctx_cwnd);
}

static void ccid2_change_srtt(struct ccid2_hc_tx_sock *hctx, long val)
{
        ccid2_pr_debug("change SRTT to %ld\n", val);
        hctx->ccid2hctx_srtt = val;
}

static void ccid2_change_pipe(struct ccid2_hc_tx_sock *hctx, long val)
{
        hctx->ccid2hctx_pipe = 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 */
        ccid2_change_pipe(hctx, 0);
        hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd >> 1;
        if (hctx->ccid2hctx_ssthresh < 2)
                hctx->ccid2hctx_ssthresh = 2;
        ccid2_change_cwnd(hctx, 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_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, unsigned 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;
        ccid2_change_pipe(hctx, hctx->ccid2hctx_pipe + 1);
        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) {
                if (ccid2_hc_tx_alloc_seq(hctx)) {
                        DCCP_CRIT("packet history - out of memory!");
                        /* FIXME: find a more graceful way to bail out */
                        return;
                }
                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++;

        /*
         * 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 */
        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*/
                }
        }
#endif

        /* 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", (unsigned long long)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",
                                       (unsigned long long)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:
        DCCP_BUG("Invalid option - this should not happen (previous parsing)!");
        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(hctx, 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(hctx, 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,
                                       (unsigned long long)seqp->ccid2s_seq);
                        ccid2_change_srtt(hctx, r);
                        hctx->ccid2hctx_rttvar = r >> 1;
                } else {
                        /* RTTVAR */
                        long tmp = hctx->ccid2hctx_srtt - r;
                        long srtt;

                        if (tmp < 0)
                                tmp *= -1;

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

                        /* SRTT */
                        srtt = hctx->ccid2hctx_srtt;
                        srtt *= 7;
                        srtt >>= 3;
                        tmp = r >> 3;
                        srtt += tmp;
                        ccid2_change_srtt(hctx, srtt);
                }
                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);

        ccid2_change_pipe(hctx, hctx->ccid2hctx_pipe-1);
        BUG_ON(hctx->ccid2hctx_pipe < 0);

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

static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
{
        struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);

        if (time_before(seqp->ccid2s_sent, hctx->ccid2hctx_last_cong)) {
                ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
                return;
        }

        hctx->ccid2hctx_last_cong = jiffies;

        ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd >> 1);
        hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;
        if (hctx->ccid2hctx_ssthresh < 2)
                hctx->ccid2hctx_ssthresh = 2;

        /* Avoid spurious timeouts resulting from Ack Ratio > cwnd */
        if (dccp_sk(sk)->dccps_l_ack_ratio > hctx->ccid2hctx_cwnd)
                ccid2_change_l_ack_ratio(sk, hctx->ccid2hctx_cwnd);
}

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;
        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 (dccp_delta_seqno(hctx->ccid2hctx_rpseq, seqno) == 1)
                        hctx->ccid2hctx_rpseq = seqno;
                /* 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, 2 * dp->dccps_l_ack_ratio);
                        }
                }
        }

        /* 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;
        if (after48(ackno, hctx->ccid2hctx_high_ack))
                hctx->ccid2hctx_high_ack = ackno;

        seqp = hctx->ccid2hctx_seqt;
        while (before48(seqp->ccid2s_seq, ackno)) {
                seqp = seqp->ccid2s_next;
                if (seqp == hctx->ccid2hctx_seqh) {
                        seqp = hctx->ccid2hctx_seqh->ccid2s_prev;
                        break;
                }
        }

        /* 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 = SUB48(ackno, rl);

                        ccid2_pr_debug("ackvec start:%llu end:%llu\n",
                                       (unsigned long long)ackno,
                                       (unsigned long long)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) {
                                                ccid2_congestion_event(sk,
                                                                       seqp);
                                        } else
                                                ccid2_new_ack(sk, seqp,
                                                              &maxincr);

                                        seqp->ccid2s_acked = 1;
                                        ccid2_pr_debug("Got ack for %llu\n",
                                                       (unsigned long long)seqp->ccid2s_seq);
                                        ccid2_hc_tx_dec_pipe(sk);
                                }
                                if (seqp == hctx->ccid2hctx_seqt) {
                                        done = 1;
                                        break;
                                }
                                seqp = seqp->ccid2s_prev;
                        }
                        if (done)
                                break;

                        ackno = SUB48(ackno_end_rl, 1);
                        vector++;
                }
                if (done)
                        break;
        }

        /* The state about what is acked should be correct now
         * Check for NUMDUPACK
         */
        seqp = hctx->ccid2hctx_seqt;
        while (before48(seqp->ccid2s_seq, hctx->ccid2hctx_high_ack)) {
                seqp = seqp->ccid2s_next;
                if (seqp == hctx->ccid2hctx_seqh) {
                        seqp = hctx->ccid2hctx_seqh->ccid2s_prev;
                        break;
                }
        }
        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) {
                                ccid2_pr_debug("Packet lost: %llu\n",
                                               (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);
                                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;
        }

        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);
        struct dccp_sock *dp = dccp_sk(sk);
        u32 max_ratio;

        /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
        hctx->ccid2hctx_ssthresh  = ~0;
        hctx->ccid2hctx_numdupack = 3;

        /*
         * RFC 4341, 5: "The cwnd parameter is initialized to at most four
         * packets for new connections, following the rules from [RFC3390]".
         * We need to convert the bytes of RFC3390 into the packets of RFC 4341.
         */
        hctx->ccid2hctx_cwnd = min(4U, max(2U, 4380U / dp->dccps_mss_cache));

        /* Make sure that Ack Ratio is enabled and within bounds. */
        max_ratio = DIV_ROUND_UP(hctx->ccid2hctx_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(hctx))
                return -ENOMEM;

        hctx->ccid2hctx_rto      = 3 * HZ;
        ccid2_change_srtt(hctx, -1);
        hctx->ccid2hctx_rttvar   = -1;
        hctx->ccid2hctx_rpdupack = -1;
        hctx->ccid2hctx_last_cong = jiffies;
        setup_timer(&hctx->ccid2hctx_rtotimer, ccid2_hc_tx_rto_expire,
                        (unsigned long)sk);

        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                = DCCPC_CCID2,
        .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,
};

#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
module_param(ccid2_debug, bool, 0444);
MODULE_PARM_DESC(ccid2_debug, "Enable debug messages");
#endif

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");