[DCCP] CCID2: Initial CCID2 (TCP-Like) implementation (2a91aa39) · Commits · EulixOS / Software / Kernel

include/linux/dccp.h

+5 −3

Original line number	Original line	Diff line number	Diff line
	@@ -314,9 +314,9 @@ static inline unsigned int dccp_hdr_len(const struct sk_buff *skb)

	/* initial values for each feature */		/* initial values for each feature */
	#define DCCPF_INITIAL_SEQUENCE_WINDOW 100		#define DCCPF_INITIAL_SEQUENCE_WINDOW 100
	/* FIXME: for now we're using CCID 3 (TFRC) */		/* FIXME: for now we're using CCID 2 (TCP-Like) */
	#define DCCPF_INITIAL_CCID 3		#define DCCPF_INITIAL_CCID 2
	#define DCCPF_INITIAL_SEND_ACK_VECTOR 0		#define DCCPF_INITIAL_SEND_ACK_VECTOR 1
	/* FIXME: for now we're default to 1 but it should really be 0 */		/* FIXME: for now we're default to 1 but it should really be 0 */
	#define DCCPF_INITIAL_SEND_NDP_COUNT 1		#define DCCPF_INITIAL_SEND_NDP_COUNT 1

	@@ -430,6 +430,8 @@ struct dccp_sock {
	struct timeval dccps_timestamp_time;		struct timeval dccps_timestamp_time;
	__u32 dccps_timestamp_echo;		__u32 dccps_timestamp_echo;
	__u32 dccps_packet_size;		__u32 dccps_packet_size;
			__u16 dccps_l_ack_ratio;
			__u16 dccps_r_ack_ratio;
	unsigned long dccps_ndp_count;		unsigned long dccps_ndp_count;
	__u32 dccps_mss_cache;		__u32 dccps_mss_cache;
	struct dccp_options dccps_options;		struct dccp_options dccps_options;

net/dccp/Kconfig

+4 −0

Original line number	Original line	Diff line number	Diff line
	@@ -24,6 +24,10 @@ config INET_DCCP_DIAG
	def_tristate y if (IP_DCCP = y && INET_DIAG = y)		def_tristate y if (IP_DCCP = y && INET_DIAG = y)
	def_tristate m		def_tristate m

			config IP_DCCP_ACKVEC
			depends on IP_DCCP
			def_bool N

	source "net/dccp/ccids/Kconfig"		source "net/dccp/ccids/Kconfig"

	menu "DCCP Kernel Hacking"		menu "DCCP Kernel Hacking"

net/dccp/ccids/Kconfig

+36 −3

Original line number	Original line	Diff line number	Diff line
	menu "DCCP CCIDs Configuration (EXPERIMENTAL)"		menu "DCCP CCIDs Configuration (EXPERIMENTAL)"
	depends on IP_DCCP && 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		config IP_DCCP_CCID3
	tristate "CCID3 (TFRC) (EXPERIMENTAL)"		tristate "CCID3 (TFRC) (EXPERIMENTAL)"
	depends on IP_DCCP		depends on IP_DCCP
	@@ -15,10 +43,15 @@ config IP_DCCP_CCID3
	suitable than CCID 2 for applications such streaming media where a		suitable than CCID 2 for applications such streaming media where a
	relatively smooth sending rate is of importance.		relatively smooth sending rate is of importance.

	CCID 3 is further described in [CCID 3 PROFILE]. The TFRC		CCID 3 is further described in:
	congestion control algorithms were initially described in RFC 3448.
			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.		If in doubt, say M.

net/dccp/ccids/Makefile

+4 −0

Original line number	Original line	Diff line number	Diff line
	@@ -2,4 +2,8 @@ obj-$(CONFIG_IP_DCCP_CCID3) += dccp_ccid3.o

	dccp_ccid3-y := ccid3.o		dccp_ccid3-y := ccid3.o

			obj-$(CONFIG_IP_DCCP_CCID2) += dccp_ccid2.o

			dccp_ccid2-y := ccid2.o

	obj-y += lib/		obj-y += lib/

net/dccp/ccids/ccid2.c

0 → 100644

+838 −0

Original line number	Original line	Diff line number	Diff line
			/*
			* 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");