[DCCP] CCID2: Initial CCID2 (TCP-Like) implementation

Original work by Andrea Bittau, Arnaldo Melo cleaned up and fixed several
issues on the merge process.

For now CCID2 was turned the default for all SOCK_DCCP connections, but this
will be remedied soon with the merge of the feature negotiation code.

Signed-off-by: Andrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 947 insertions, 3 deletions

diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig
index 7684d83946a4..422af197171d 100644
--- a/net/dccp/ccids/Kconfig
+++ b/net/dccp/ccids/Kconfig
@@ -1,6 +1,34 @@
 menu "DCCP CCIDs Configuration (EXPERIMENTAL)"
         depends on IP_DCCP && EXPERIMENTAL
 
+config IP_DCCP_CCID2
+        tristate "CCID2 (TCP) (EXPERIMENTAL)"
+        depends on IP_DCCP
+        select IP_DCCP_ACKVEC
+        ---help---
+          CCID 2, TCP-like Congestion Control, denotes Additive Increase,
+          Multiplicative Decrease (AIMD) congestion control with behavior
+          modelled directly on TCP, including congestion window, slow start,
+          timeouts, and so forth [RFC 2581].  CCID 2 achieves maximum
+          bandwidth over the long term, consistent with the use of end-to-end
+          congestion control, but halves its congestion window in response to
+          each congestion event.  This leads to the abrupt rate changes
+          typical of TCP.  Applications should use CCID 2 if they prefer
+          maximum bandwidth utilization to steadiness of rate.  This is often
+          the case for applications that are not playing their data directly
+          to the user.  For example, a hypothetical application that
+          transferred files over DCCP, using application-level retransmissions
+          for lost packets, would prefer CCID 2 to CCID 3.  On-line games may
+          also prefer CCID 2.
+
+          CCID 2 is further described in:
+          http://www.icir.org/kohler/dccp/draft-ietf-dccp-ccid2-10.txt
+
+          This text was extracted from:
+          http://www.icir.org/kohler/dccp/draft-ietf-dccp-spec-13.txt
+
+          If in doubt, say M.
+
 config IP_DCCP_CCID3
         tristate "CCID3 (TFRC) (EXPERIMENTAL)"
         depends on IP_DCCP
@@ -15,10 +43,15 @@ config IP_DCCP_CCID3
           suitable than CCID 2 for applications such streaming media where a
           relatively smooth sending rate is of importance.
 
-          CCID 3 is further described in [CCID 3 PROFILE]. The TFRC
-          congestion control algorithms were initially described in RFC 3448.
+          CCID 3 is further described in:
+
+          http://www.icir.org/kohler/dccp/draft-ietf-dccp-ccid3-11.txt.
+
+          The TFRC congestion control algorithms were initially described in
+          RFC 3448.
 
-          This text was extracted from draft-ietf-dccp-spec-11.txt.
+          This text was extracted from:
+          http://www.icir.org/kohler/dccp/draft-ietf-dccp-spec-13.txt
           
           If in doubt, say M.
 
diff --git a/net/dccp/ccids/Makefile b/net/dccp/ccids/Makefile
index 956f79f50743..438f20bccff7 100644
--- a/net/dccp/ccids/Makefile
+++ b/net/dccp/ccids/Makefile
@@ -2,4 +2,8 @@ obj-$(CONFIG_IP_DCCP_CCID3) += dccp_ccid3.o
 
 dccp_ccid3-y := ccid3.o
 
+obj-$(CONFIG_IP_DCCP_CCID2) += dccp_ccid2.o
+
+dccp_ccid2-y := ccid2.o
+
 obj-y += lib/
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
new file mode 100644
index 000000000000..4a7b87512560
--- /dev/null
+++ b/net/dccp/ccids/ccid2.c
@@ -0,0 +1,838 @@
+/*
+ *  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
+ * - jiffies wrapping
+ */
+
+#include <linux/config.h>
+#include "../ccid.h"
+#include "../dccp.h"
+#include "ccid2.h"
+
+static int ccid2_debug;
+
+#if 0
+#define CCID2_DEBUG
+#endif
+
+#ifdef 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
+
+static const int ccid2_seq_len = 128;
+
+static inline struct ccid2_hc_tx_sock *ccid2_hc_tx_sk(const struct sock *sk)
+{
+        return dccp_sk(sk)->dccps_hc_tx_ccid_private;
+}
+
+static inline struct ccid2_hc_rx_sock *ccid2_hc_rx_sk(const struct sock *sk)
+{
+        return dccp_sk(sk)->dccps_hc_rx_ccid_private;
+}
+
+#ifdef CCID2_DEBUG
+static void ccid2_hc_tx_check_sanity(const struct ccid2_hc_tx_sock *hctx)
+{
+        int len = 0;
+        struct ccid2_seq *seqp;
+        int pipe = 0;
+
+        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;
+
+                        prev = seqp->ccid2s_prev;
+                        len++;
+                        if (!prev->ccid2s_acked)
+                                pipe++;
+
+                        /* packets are sent sequentially */
+                        BUG_ON(seqp->ccid2s_seq <= prev->ccid2s_seq);
+                        BUG_ON(seqp->ccid2s_sent < prev->ccid2s_sent);
+                        BUG_ON(len > ccid2_seq_len);
+
+                        seqp = prev;
+                }
+        }
+
+        BUG_ON(pipe != hctx->ccid2hctx_pipe);
+        ccid2_pr_debug("len of chain=%d\n", len);
+
+        do {
+                seqp = seqp->ccid2s_prev;
+                len++;
+                BUG_ON(len > ccid2_seq_len);
+        } while(seqp != hctx->ccid2hctx_seqh);
+
+        BUG_ON(len != ccid2_seq_len);
+        ccid2_pr_debug("total len=%d\n", len);
+}
+#else
+#define ccid2_hc_tx_check_sanity(hctx) do {} while (0)
+#endif
+
+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 100; /* XXX */
+}
+
+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) {
+                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;
+
+        /* XXX I don't think i'm locking correctly
+         * -sorbo.
+         */
+        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);
+        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;
+        hctx->ccid2hctx_seqh = hctx->ccid2hctx_seqh->ccid2s_next;
+
+        ccid2_pr_debug("cwnd=%d pipe=%d\n", hctx->ccid2hctx_cwnd,
+                       hctx->ccid2hctx_pipe);
+
+        if (hctx->ccid2hctx_seqh == hctx->ccid2hctx_seqt) {
+                /* XXX allocate more space */
+                WARN_ON(1);
+        }
+
+        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;
+                }
+        }
+        /* No acks lost up to now... */
+        else {
+                /* decrease ack ratio if enough packets were sent */
+                if (dp->dccps_l_ack_ratio > 1) {
+                        /* XXX don't calculate denominator each time */
+                        int denom;
+
+                        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;
+                        }
+                }
+                /* we can't increase ack ratio further [1] */
+                else {
+                        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 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);
+                        break;
+                }
+        }
+
+        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 ccid2_hc_tx_sock *hctx)
+{
+        if (del_timer(&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;
+                        }
+                }
+                /* increased cwnd enough for this single ack */
+                else {
+                        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 ||
+            (jiffies - hctx->ccid2hctx_lastrtt) >= hctx->ccid2hctx_srtt) {
+                unsigned long r = jiffies - 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(hctx);
+        ccid2_start_rto_timer(sk);
+}
+
+static void ccid2_hc_tx_dec_pipe(struct ccid2_hc_tx_sock *hctx)
+{
+        hctx->ccid2hctx_pipe--;
+        BUG_ON(hctx->ccid2hctx_pipe < 0);
+
+        if (hctx->ccid2hctx_pipe == 0)
+                ccid2_hc_tx_kill_rto_timer(hctx);
+}
+
+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) >> 6;
+
+                                /* 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(hctx);
+                                }
+                                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(hctx);
+                        }
+                        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 sock *sk)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+        struct ccid2_hc_tx_sock *hctx;
+        int seqcount = ccid2_seq_len;
+        int i;
+
+        dp->dccps_hc_tx_ccid_private = kzalloc(sizeof(*hctx), gfp_any());
+        if (dp->dccps_hc_tx_ccid_private == NULL)
+                return -ENOMEM;
+
+        hctx = ccid2_hc_tx_sk(sk);
+
+        /* XXX init variables with proper values */
+        hctx->ccid2hctx_cwnd      = 1;
+        hctx->ccid2hctx_ssthresh  = 10;
+        hctx->ccid2hctx_numdupack = 3;
+
+        /* XXX init ~ to window size... */
+        hctx->ccid2hctx_seqbuf = kmalloc(sizeof(*hctx->ccid2hctx_seqbuf) *
+                                         seqcount, gfp_any());
+        if (hctx->ccid2hctx_seqbuf == NULL) {
+                kfree(dp->dccps_hc_tx_ccid_private);
+                dp->dccps_hc_tx_ccid_private = NULL;
+                return -ENOMEM;
+        }
+        for (i = 0; i < (seqcount - 1); i++) {
+                hctx->ccid2hctx_seqbuf[i].ccid2s_next =
+                                        &hctx->ccid2hctx_seqbuf[i + 1];
+                hctx->ccid2hctx_seqbuf[i + 1].ccid2s_prev =
+                                        &hctx->ccid2hctx_seqbuf[i];
+        }
+        hctx->ccid2hctx_seqbuf[seqcount - 1].ccid2s_next =
+                                        hctx->ccid2hctx_seqbuf;
+        hctx->ccid2hctx_seqbuf->ccid2s_prev =
+                                        &hctx->ccid2hctx_seqbuf[seqcount - 1];
+
+        hctx->ccid2hctx_seqh     = hctx->ccid2hctx_seqbuf;
+        hctx->ccid2hctx_seqt     = hctx->ccid2hctx_seqh;
+        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 dccp_sock *dp = dccp_sk(sk);
+        struct ccid2_hc_tx_sock *hctx = dp->dccps_hc_tx_ccid_private;
+
+        ccid2_hc_tx_kill_rto_timer(hctx);
+
+        kfree(hctx->ccid2hctx_seqbuf);
+
+        kfree(dp->dccps_hc_tx_ccid_private);
+        dp->dccps_hc_tx_ccid_private = NULL;
+}
+
+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 int ccid2_hc_rx_init(struct sock *sk)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+        dp->dccps_hc_rx_ccid_private = kzalloc(sizeof(struct ccid2_hc_rx_sock),
+                                               gfp_any());
+        return dp->dccps_hc_rx_ccid_private == NULL ? -ENOMEM : 0;
+}
+
+static void ccid2_hc_rx_exit(struct sock *sk)
+{
+        struct dccp_sock *dp = dccp_sk(sk);
+
+        kfree(dp->dccps_hc_rx_ccid_private);
+        dp->dccps_hc_rx_ccid_private = NULL;
+}
+
+static struct ccid ccid2 = {
+        .ccid_id                = 2,
+        .ccid_name              = "ccid2",
+        .ccid_owner             = THIS_MODULE,
+        .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_init        = ccid2_hc_rx_init,
+        .ccid_hc_rx_exit        = ccid2_hc_rx_exit,
+        .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 CCID2 CCID");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("net-dccp-ccid-2");
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
new file mode 100644
index 000000000000..0b08c90955a9
--- /dev/null
+++ b/net/dccp/ccids/ccid2.h
@@ -0,0 +1,69 @@
+/*
+ *  net/dccp/ccids/ccid2.h
+ *
+ *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
+ *
+ *  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.
+ */
+#ifndef _DCCP_CCID2_H_
+#define _DCCP_CCID2_H_
+
+struct ccid2_seq {
+        u64                     ccid2s_seq;
+        unsigned long           ccid2s_sent;
+        int                     ccid2s_acked;
+        struct ccid2_seq        *ccid2s_prev;
+        struct ccid2_seq        *ccid2s_next;
+};
+
+/** struct ccid2_hc_tx_sock - CCID2 TX half connection
+ *
+ * @ccid2hctx_ssacks - ACKs recv in slow start
+ * @ccid2hctx_acks - ACKS recv in AI phase
+ * @ccid2hctx_sent - packets sent in this window
+ * @ccid2hctx_lastrtt -time RTT was last measured
+ * @ccid2hctx_arsent - packets sent [ack ratio]
+ * @ccid2hctx_ackloss - ack was lost in this win
+ * @ccid2hctx_rpseq - last consecutive seqno
+ * @ccid2hctx_rpdupack - dupacks since rpseq
+*/
+struct ccid2_hc_tx_sock {
+        int                     ccid2hctx_cwnd;
+        int                     ccid2hctx_ssacks;
+        int                     ccid2hctx_acks;
+        int                     ccid2hctx_ssthresh;
+        int                     ccid2hctx_pipe;
+        int                     ccid2hctx_numdupack;
+        struct ccid2_seq        *ccid2hctx_seqbuf;
+        struct ccid2_seq        *ccid2hctx_seqh;
+        struct ccid2_seq        *ccid2hctx_seqt;
+        long                    ccid2hctx_rto;
+        long                    ccid2hctx_srtt;
+        long                    ccid2hctx_rttvar;
+        int                     ccid2hctx_sent;
+        unsigned long           ccid2hctx_lastrtt;
+        struct timer_list       ccid2hctx_rtotimer;
+        unsigned long           ccid2hctx_arsent;
+        int                     ccid2hctx_ackloss;
+        u64                     ccid2hctx_rpseq;
+        int                     ccid2hctx_rpdupack;
+        int                     ccid2hctx_sendwait;
+};
+
+struct ccid2_hc_rx_sock {
+        int     ccid2hcrx_data;
+};
+
+#endif /* _DCCP_CCID2_H_ */