[DCCP]: Initial implementation

Development to this point was done on a subversion repository at:

http://oops.ghostprotocols.net:81/cgi-bin/viewcvs.cgi/dccp-2.6/

This repository will be kept at this site for the foreseable future,
so that interested parties can see the history of this code,
attributions, etc.

If I ever decide to take this offline I'll provide the full history at
some other suitable place.
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/in.h

@@ -32,6 +32,7 @@ enum {
   IPPROTO_PUP = 12,		/* PUP protocol				*/
   IPPROTO_UDP = 17,		/* User Datagram Protocol		*/
   IPPROTO_IDP = 22,		/* XNS IDP protocol			*/
+  IPPROTO_DCCP = 33,		/* Datagram Congestion Control Protocol */
   IPPROTO_RSVP = 46,		/* RSVP protocol			*/
   IPPROTO_GRE = 47,		/* Cisco GRE tunnels (rfc 1701,1702)	*/
 

include/linux/net.h

@@ -84,6 +84,7 @@ enum sock_type {
 	SOCK_RAW	= 3,
 	SOCK_RDM	= 4,
 	SOCK_SEQPACKET	= 5,
+	SOCK_DCCP	= 6,
 	SOCK_PACKET	= 10,
 };
 

include/linux/socket.h

@@ -271,6 +271,7 @@ struct ucred {
 #define SOL_IRDA        266
 #define SOL_NETBEUI	267
 #define SOL_LLC		268
+#define SOL_DCCP	269
 
 /* IPX options */
 #define IPX_TYPE	1

net/Kconfig

@@ -147,6 +147,7 @@ source "net/bridge/netfilter/Kconfig"
 
 endif
 
+source "net/dccp/Kconfig"
 source "net/sctp/Kconfig"
 source "net/atm/Kconfig"
 source "net/bridge/Kconfig"

net/Makefile

@@ -42,6 +42,7 @@ obj-$(CONFIG_ATM)		+= atm/
 obj-$(CONFIG_DECNET)		+= decnet/
 obj-$(CONFIG_ECONET)		+= econet/
 obj-$(CONFIG_VLAN_8021Q)	+= 8021q/
+obj-$(CONFIG_IP_DCCP)		+= dccp/
 obj-$(CONFIG_IP_SCTP)		+= sctp/
 
 ifeq ($(CONFIG_NET),y)

net/dccp/Kconfig

+menu "DCCP Configuration (EXPERIMENTAL)"
+	depends on INET && EXPERIMENTAL
+
+config IP_DCCP
+	tristate "The DCCP Protocol (EXPERIMENTAL)"
+	---help---
+	  Datagram Congestion Control Protocol
+
+	  From draft-ietf-dccp-spec-11 <http://www.icir.org/kohler/dcp/draft-ietf-dccp-spec-11.txt>.
+
+	  The Datagram Congestion Control Protocol (DCCP) is a transport
+	  protocol that implements bidirectional, unicast connections of
+	  congestion-controlled, unreliable datagrams. It should be suitable
+	  for use by applications such as streaming media, Internet telephony,
+	  and on-line games
+
+	  To compile this protocol support as a module, choose M here: the
+	  module will be called dccp.
+
+	  If in doubt, say N.
+
+source "net/dccp/ccids/Kconfig"
+
+endmenu

net/dccp/Makefile

+obj-$(CONFIG_IP_DCCP) += dccp.o
+
+dccp-y := ccid.o input.o ipv4.o minisocks.o options.o output.o proto.o timer.o
+
+obj-y += ccids/

net/dccp/ccid.c

+/*
+ *  net/dccp/ccid.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ *  CCID infrastructure
+ *
+ *	This program is free software; you can redistribute it and/or modify it
+ *	under the terms of the GNU General Public License version 2 as
+ *	published by the Free Software Foundation.
+ */
+
+#include "ccid.h"
+
+static struct ccid *ccids[CCID_MAX];
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
+static atomic_t ccids_lockct = ATOMIC_INIT(0);
+static DEFINE_SPINLOCK(ccids_lock);
+
+/*
+ * The strategy is: modifications ccids vector are short, do not sleep and
+ * veeery rare, but read access should be free of any exclusive locks.
+ */
+static void ccids_write_lock(void)
+{
+	spin_lock(&ccids_lock);
+	while (atomic_read(&ccids_lockct) != 0) {
+		spin_unlock(&ccids_lock);
+		yield();
+		spin_lock(&ccids_lock);
+	}
+}
+
+static inline void ccids_write_unlock(void)
+{
+	spin_unlock(&ccids_lock);
+}
+
+static inline void ccids_read_lock(void)
+{
+	atomic_inc(&ccids_lockct);
+	spin_unlock_wait(&ccids_lock);
+}
+
+static inline void ccids_read_unlock(void)
+{
+	atomic_dec(&ccids_lockct);
+}
+
+#else
+#define ccids_write_lock() do { } while(0)
+#define ccids_write_unlock() do { } while(0)
+#define ccids_read_lock() do { } while(0)
+#define ccids_read_unlock() do { } while(0)
+#endif
+
+int ccid_register(struct ccid *ccid)
+{
+	int err;
+
+	if (ccid->ccid_init == NULL)
+		return -1;
+
+	ccids_write_lock();
+	err = -EEXIST;
+	if (ccids[ccid->ccid_id] == NULL) {
+		ccids[ccid->ccid_id] = ccid;
+		err = 0;
+	}
+	ccids_write_unlock();
+	if (err == 0)
+		pr_info("CCID: Registered CCID %d (%s)\n",
+			ccid->ccid_id, ccid->ccid_name);
+	return err;
+}
+
+EXPORT_SYMBOL_GPL(ccid_register);
+
+int ccid_unregister(struct ccid *ccid)
+{
+	ccids_write_lock();
+	ccids[ccid->ccid_id] = NULL;
+	ccids_write_unlock();
+	pr_info("CCID: Unregistered CCID %d (%s)\n",
+		ccid->ccid_id, ccid->ccid_name);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(ccid_unregister);
+
+struct ccid *ccid_init(unsigned char id, struct sock *sk)
+{
+	struct ccid *ccid;
+
+#ifdef CONFIG_KMOD
+	if (ccids[id] == NULL)
+		request_module("net-dccp-ccid-%d", id);
+#endif
+	ccids_read_lock();
+
+	ccid = ccids[id];
+	if (ccid == NULL)
+		goto out;
+
+	if (!try_module_get(ccid->ccid_owner))
+		goto out_err;
+
+	if (ccid->ccid_init(sk) != 0)
+		goto out_module_put;
+out:
+	ccids_read_unlock();
+	return ccid;
+out_module_put:
+	module_put(ccid->ccid_owner);
+out_err:
+	ccid = NULL;
+	goto out;
+}
+
+EXPORT_SYMBOL_GPL(ccid_init);
+
+void ccid_exit(struct ccid *ccid, struct sock *sk)
+{
+	if (ccid == NULL)
+		return;
+
+	ccids_read_lock();
+
+	if (ccids[ccid->ccid_id] != NULL) {
+		if (ccid->ccid_exit != NULL)
+			ccid->ccid_exit(sk);
+		module_put(ccid->ccid_owner);
+	}
+
+	ccids_read_unlock();
+}
+
+EXPORT_SYMBOL_GPL(ccid_exit);

net/dccp/ccid.h

+#ifndef _CCID_H
+#define _CCID_H
+/*
+ *  net/dccp/ccid.h
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ *  CCID infrastructure
+ *
+ *	This program is free software; you can redistribute it and/or modify it
+ *	under the terms of the GNU General Public License version 2 as
+ *	published by the Free Software Foundation.
+ */
+
+#include <net/sock.h>
+#include <linux/dccp.h>
+#include <linux/list.h>
+#include <linux/module.h>
+
+#define CCID_MAX 255
+
+struct ccid {
+	unsigned char	ccid_id;
+	const char	*ccid_name;
+	struct module	*ccid_owner;
+	int		(*ccid_init)(struct sock *sk);
+	void		(*ccid_exit)(struct sock *sk);
+	int		(*ccid_hc_rx_init)(struct sock *sk);
+	int		(*ccid_hc_tx_init)(struct sock *sk);
+	void		(*ccid_hc_rx_exit)(struct sock *sk);
+	void		(*ccid_hc_tx_exit)(struct sock *sk);
+	void		(*ccid_hc_rx_packet_recv)(struct sock *sk, struct sk_buff *skb);
+	int		(*ccid_hc_rx_parse_options)(struct sock *sk,
+						    unsigned char option,
+						    unsigned char len, u16 idx,
+						    unsigned char* value);
+	void		(*ccid_hc_rx_insert_options)(struct sock *sk, struct sk_buff *skb);
+	void		(*ccid_hc_tx_insert_options)(struct sock *sk, struct sk_buff *skb);
+	void		(*ccid_hc_tx_packet_recv)(struct sock *sk, struct sk_buff *skb);
+	int		(*ccid_hc_tx_parse_options)(struct sock *sk,
+						    unsigned char option,
+						    unsigned char len, u16 idx,
+						    unsigned char* value);
+	int		(*ccid_hc_tx_send_packet)(struct sock *sk,
+						  struct sk_buff *skb, int len,
+						  long *delay);
+	void		(*ccid_hc_tx_packet_sent)(struct sock *sk, int more, int len);
+};
+
+extern int	   ccid_register(struct ccid *ccid);
+extern int	   ccid_unregister(struct ccid *ccid);
+
+extern struct ccid *ccid_init(unsigned char id, struct sock *sk);
+extern void	   ccid_exit(struct ccid *ccid, struct sock *sk);
+
+static inline void __ccid_get(struct ccid *ccid)
+{
+	__module_get(ccid->ccid_owner);
+}
+
+static inline int ccid_hc_tx_send_packet(struct ccid *ccid, struct sock *sk,
+					 struct sk_buff *skb, int len,
+					 long *delay)
+{
+	int rc = 0;
+	if (ccid->ccid_hc_tx_send_packet != NULL)
+		rc = ccid->ccid_hc_tx_send_packet(sk, skb, len, delay);
+	return rc;
+}
+
+static inline void ccid_hc_tx_packet_sent(struct ccid *ccid, struct sock *sk,
+					  int more, int len)
+{
+	if (ccid->ccid_hc_tx_packet_sent != NULL)
+		ccid->ccid_hc_tx_packet_sent(sk, more, len);
+}
+
+static inline int ccid_hc_rx_init(struct ccid *ccid, struct sock *sk)
+{
+	int rc = 0;
+	if (ccid->ccid_hc_rx_init != NULL)
+		rc = ccid->ccid_hc_rx_init(sk);
+	return rc;
+}
+
+static inline int ccid_hc_tx_init(struct ccid *ccid, struct sock *sk)
+{
+	int rc = 0;
+	if (ccid->ccid_hc_tx_init != NULL)
+		rc = ccid->ccid_hc_tx_init(sk);
+	return rc;
+}
+
+static inline void ccid_hc_rx_exit(struct ccid *ccid, struct sock *sk)
+{
+	if (ccid->ccid_hc_rx_exit != NULL)
+		ccid->ccid_hc_rx_exit(sk);
+}
+
+static inline void ccid_hc_tx_exit(struct ccid *ccid, struct sock *sk)
+{
+	if (ccid->ccid_hc_tx_exit != NULL)
+		ccid->ccid_hc_tx_exit(sk);
+}
+
+static inline void ccid_hc_rx_packet_recv(struct ccid *ccid, struct sock *sk,
+					  struct sk_buff *skb)
+{
+	if (ccid->ccid_hc_rx_packet_recv != NULL)
+		ccid->ccid_hc_rx_packet_recv(sk, skb);
+}
+
+static inline void ccid_hc_tx_packet_recv(struct ccid *ccid, struct sock *sk,
+					  struct sk_buff *skb)
+{
+	if (ccid->ccid_hc_tx_packet_recv != NULL)
+		ccid->ccid_hc_tx_packet_recv(sk, skb);
+}
+
+static inline int ccid_hc_tx_parse_options(struct ccid *ccid, struct sock *sk,
+					   unsigned char option,
+					   unsigned char len, u16 idx,
+					   unsigned char* value)
+{
+	int rc = 0;
+	if (ccid->ccid_hc_tx_parse_options != NULL)
+		rc = ccid->ccid_hc_tx_parse_options(sk, option, len, idx, value);
+	return rc;
+}
+
+static inline int ccid_hc_rx_parse_options(struct ccid *ccid, struct sock *sk,
+					   unsigned char option,
+					   unsigned char len, u16 idx,
+					   unsigned char* value)
+{
+	int rc = 0;
+	if (ccid->ccid_hc_rx_parse_options != NULL)
+		rc = ccid->ccid_hc_rx_parse_options(sk, option, len, idx, value);
+	return rc;
+}
+
+static inline void ccid_hc_tx_insert_options(struct ccid *ccid, struct sock *sk,
+					     struct sk_buff *skb)
+{
+	if (ccid->ccid_hc_tx_insert_options != NULL)
+		ccid->ccid_hc_tx_insert_options(sk, skb);
+}
+
+static inline void ccid_hc_rx_insert_options(struct ccid *ccid, struct sock *sk,
+					     struct sk_buff *skb)
+{
+	if (ccid->ccid_hc_rx_insert_options != NULL)
+		ccid->ccid_hc_rx_insert_options(sk, skb);
+}
+#endif /* _CCID_H */

net/dccp/ccids/Kconfig

+menu "DCCP CCIDs Configuration (EXPERIMENTAL)"
+	depends on IP_DCCP && EXPERIMENTAL
+
+config IP_DCCP_CCID3
+	tristate "CCID3 (TFRC) (EXPERIMENTAL)"
+	depends on IP_DCCP
+	---help---
+	  CCID 3 denotes TCP-Friendly Rate Control (TFRC), an equation-based
+	  rate-controlled congestion control mechanism.  TFRC is designed to
+	  be reasonably fair when competing for bandwidth with TCP-like flows,
+	  where a flow is "reasonably fair" if its sending rate is generally
+	  within a factor of two of the sending rate of a TCP flow under the
+	  same conditions.  However, TFRC has a much lower variation of
+	  throughput over time compared with TCP, which makes CCID 3 more
+	  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.
+
+	  This text was extracted from draft-ietf-dccp-spec-11.txt.
+	  
+	  If in doubt, say M.
+
+endmenu

net/dccp/ccids/Makefile

+obj-$(CONFIG_IP_DCCP_CCID3) += dccp_ccid3.o
+
+dccp_ccid3-y := ccid3.o

net/dccp/ccids/ccid3.h

+/*
+ *  net/dccp/ccids/ccid3.h
+ *
+ *  Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
+ *
+ *  An implementation of the DCCP protocol
+ *
+ *  This code has been developed by the University of Waikato WAND
+ *  research group. For further information please see http://www.wand.net.nz/
+ *  or e-mail Ian McDonald - iam4@cs.waikato.ac.nz
+ *
+ *  This code also uses code from Lulea University, rereleased as GPL by its
+ *  authors:
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ *
+ *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
+ *  and to make it work as a loadable module in the DCCP stack written by
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
+ *
+ *  Copyright (c) 2005 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.
+ */
+#ifndef _DCCP_CCID3_H_
+#define _DCCP_CCID3_H_
+
+#include <linux/types.h>
+#include <linux/list.h>
+#include <linux/timer.h>
+
+struct ccid3_tx_hist_entry {
+	struct list_head	ccid3htx_node;
+	u64			ccid3htx_seqno:48,
+				ccid3htx_win_count:8,
+				ccid3htx_sent:1;
+	struct timeval		ccid3htx_tstamp;
+};
+
+struct ccid3_options_received {
+	u64 ccid3or_seqno:48,
+	    ccid3or_loss_intervals_idx:16;
+	u16 ccid3or_loss_intervals_len;
+	u32 ccid3or_loss_event_rate;
+	u32 ccid3or_receive_rate;
+};
+
+/** struct ccid3_hc_tx_sock - CCID3 sender half connection congestion control block
+ *
+  * @ccid3hctx_state - Sender state
+  * @ccid3hctx_x - Current sending rate
+  * @ccid3hctx_x_recv - Receive rate
+  * @ccid3hctx_x_calc - Calculated send (?) rate
+  * @ccid3hctx_s - Packet size
+  * @ccid3hctx_rtt - Estimate of current round trip time in usecs
+  * @@ccid3hctx_p - Current loss event rate (0-1) scaled by 1000000
+  * @ccid3hctx_last_win_count - Last window counter sent
+  * @ccid3hctx_t_last_win_count - Timestamp of earliest packet with last_win_count value sent
+  * @ccid3hctx_no_feedback_timer - Handle to no feedback timer
+  * @ccid3hctx_idle - FIXME
+  * @ccid3hctx_t_ld - Time last doubled during slow start
+  * @ccid3hctx_t_nom - Nominal send time of next packet
+  * @ccid3hctx_t_ipi - Interpacket (send) interval
+  * @ccid3hctx_delta - Send timer delta
+  * @ccid3hctx_hist - Packet history
+  */
+struct ccid3_hc_tx_sock {
+	u32				ccid3hctx_x;
+	u32				ccid3hctx_x_recv;
+	u32				ccid3hctx_x_calc;
+	u16				ccid3hctx_s;
+	u32				ccid3hctx_rtt;
+	u32				ccid3hctx_p;
+  	u8				ccid3hctx_state;
+	u8				ccid3hctx_last_win_count;
+	u8				ccid3hctx_idle;
+	struct timeval			ccid3hctx_t_last_win_count;
+	struct timer_list		ccid3hctx_no_feedback_timer;
+	struct timeval			ccid3hctx_t_ld;
+	struct timeval			ccid3hctx_t_nom;
+	u32				ccid3hctx_t_ipi;
+	u32				ccid3hctx_delta;
+	struct list_head		ccid3hctx_hist;
+	struct ccid3_options_received	ccid3hctx_options_received;
+};
+
+struct ccid3_loss_interval_hist_entry {
+	struct list_head	ccid3lih_node;
+	u64			ccid3lih_seqno:48,
+				ccid3lih_win_count:4;
+	u32			ccid3lih_interval;
+};
+
+struct ccid3_rx_hist_entry {
+	struct list_head	ccid3hrx_node;
+	u64			ccid3hrx_seqno:48,
+				ccid3hrx_win_count:4,
+				ccid3hrx_type:4;
+	u32			ccid3hrx_ndp; /* In fact it is from 8 to 24 bits */
+	struct timeval		ccid3hrx_tstamp;
+};
+
+struct ccid3_hc_rx_sock {
+  	u64			ccid3hcrx_seqno_last_counter:48,
+				ccid3hcrx_state:8,
+				ccid3hcrx_last_counter:4;
+	unsigned long		ccid3hcrx_rtt;
+  	u32			ccid3hcrx_p;
+  	u32			ccid3hcrx_bytes_recv;
+  	struct timeval		ccid3hcrx_tstamp_last_feedback;
+  	struct timeval		ccid3hcrx_tstamp_last_ack;
+	struct list_head	ccid3hcrx_hist;
+	struct list_head	ccid3hcrx_loss_interval_hist;
+  	u16			ccid3hcrx_s;
+  	u32			ccid3hcrx_pinv;
+  	u32			ccid3hcrx_elapsed_time;
+  	u32			ccid3hcrx_x_recv;
+};
+
+#define ccid3_hc_tx_field(s,field) (s->dccps_hc_tx_ccid_private == NULL ? 0 : \
+				    ((struct ccid3_hc_tx_sock *)s->dccps_hc_tx_ccid_private)->ccid3hctx_##field)
+
+#define ccid3_hc_rx_field(s,field) (s->dccps_hc_rx_ccid_private == NULL ? 0 : \
+				    ((struct ccid3_hc_rx_sock *)s->dccps_hc_rx_ccid_private)->ccid3hcrx_##field)
+
+#endif /* _DCCP_CCID3_H_ */

net/dccp/minisocks.c

+/*
+ *  net/dccp/minisocks.c
+ *
+ *  An implementation of the DCCP protocol
+ *  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.
+ */
+
+#include <linux/config.h>
+#include <linux/dccp.h>
+#include <linux/skbuff.h>
+#include <linux/timer.h>
+
+#include <net/sock.h>
+#include <net/xfrm.h>
+#include <net/inet_timewait_sock.h>
+
+#include "ccid.h"
+#include "dccp.h"
+
+void dccp_time_wait(struct sock *sk, int state, int timeo)
+{
+	/* FIXME: Implement */
+	dccp_pr_debug("Want to help? Start here\n");
+	dccp_set_state(sk, state);
+}
+
+/* This is for handling early-kills of TIME_WAIT sockets. */
+void dccp_tw_deschedule(struct inet_timewait_sock *tw)
+{
+	dccp_pr_debug("Want to help? Start here\n");
+	__inet_twsk_kill(tw, &dccp_hashinfo);
+}
+
+struct sock *dccp_create_openreq_child(struct sock *sk,
+				       const struct request_sock *req,
+				       const struct sk_buff *skb)
+{
+	/*
+	 * Step 3: Process LISTEN state
+	 *
+	 * // Generate a new socket and switch to that socket
+	 * Set S := new socket for this port pair
+	 */
+	struct sock *newsk = inet_csk_clone(sk, req, GFP_ATOMIC);
+
+	if (newsk != NULL) {
+		const struct dccp_request_sock *dreq = dccp_rsk(req);
+		struct inet_connection_sock *newicsk = inet_csk(sk);
+		struct dccp_sock *newdp = dccp_sk(newsk);
+
+		newdp->dccps_hc_rx_ackpkts = NULL;
+		newdp->dccps_role = DCCP_ROLE_SERVER;
+		newicsk->icsk_rto = TCP_TIMEOUT_INIT;
+
+		if (newdp->dccps_options.dccpo_send_ack_vector) {
+			newdp->dccps_hc_rx_ackpkts = dccp_ackpkts_alloc(DCCP_MAX_ACK_VECTOR_LEN,
+									GFP_ATOMIC);
+			/*
+			 * XXX: We're using the same CCIDs set on the parent, i.e. sk_clone
+			 * copied the master sock and left the CCID pointers for this child,
+			 * that is why we do the __ccid_get calls.
+			 */
+			if (unlikely(newdp->dccps_hc_rx_ackpkts == NULL))
+				goto out_free;
+		}
+
+		if (unlikely(ccid_hc_rx_init(newdp->dccps_hc_rx_ccid, newsk) != 0 ||
+			     ccid_hc_tx_init(newdp->dccps_hc_tx_ccid, newsk) != 0)) {
+			dccp_ackpkts_free(newdp->dccps_hc_rx_ackpkts);
+			ccid_hc_rx_exit(newdp->dccps_hc_rx_ccid, newsk);
+			ccid_hc_tx_exit(newdp->dccps_hc_tx_ccid, newsk);
+out_free:
+			/* It is still raw copy of parent, so invalidate
+			 * destructor and make plain sk_free() */
+			newsk->sk_destruct = NULL;
+			sk_free(newsk);
+			return NULL;
+		}
+
+		__ccid_get(newdp->dccps_hc_rx_ccid);
+		__ccid_get(newdp->dccps_hc_tx_ccid);
+
+		/*
+		 * Step 3: Process LISTEN state
+		 *
+		 *	Choose S.ISS (initial seqno) or set from Init Cookie
+		 *	Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
+		 */
+
+		/* See dccp_v4_conn_request */
+		newdp->dccps_options.dccpo_sequence_window = req->rcv_wnd;
+
+		newdp->dccps_gar = newdp->dccps_isr = dreq->dreq_isr;
+		dccp_update_gsr(newsk, dreq->dreq_isr);
+
+		newdp->dccps_iss = dreq->dreq_iss;
+		dccp_update_gss(newsk, dreq->dreq_iss);
+
+		dccp_init_xmit_timers(newsk);
+
+		DCCP_INC_STATS_BH(DCCP_MIB_PASSIVEOPENS);
+	}
+	return newsk;
+}
+
+/* 
+ * Process an incoming packet for RESPOND sockets represented
+ * as an request_sock.
+ */
+struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
+			    struct request_sock *req,
+			    struct request_sock **prev)
+{
+	struct sock *child = NULL;
+
+	/* Check for retransmitted REQUEST */
+	if (dccp_hdr(skb)->dccph_type == DCCP_PKT_REQUEST) {
+		if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dccp_rsk(req)->dreq_isr)) {
+			struct dccp_request_sock *dreq = dccp_rsk(req);
+
+			dccp_pr_debug("Retransmitted REQUEST\n");
+			/* Send another RESPONSE packet */
+			dccp_set_seqno(&dreq->dreq_iss, dreq->dreq_iss + 1);
+			dccp_set_seqno(&dreq->dreq_isr, DCCP_SKB_CB(skb)->dccpd_seq);
+			req->rsk_ops->rtx_syn_ack(sk, req, NULL);
+		}
+		/* Network Duplicate, discard packet */
+		return NULL;
+	}
+
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;
+
+	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_ACK &&
+	    dccp_hdr(skb)->dccph_type != DCCP_PKT_DATAACK)
+		goto drop;
+
+	/* Invalid ACK */
+	if (DCCP_SKB_CB(skb)->dccpd_ack_seq != dccp_rsk(req)->dreq_iss) {
+		dccp_pr_debug("Invalid ACK number: ack_seq=%llu, dreq_iss=%llu\n",
+			      DCCP_SKB_CB(skb)->dccpd_ack_seq, dccp_rsk(req)->dreq_iss);
+		goto drop;
+	}
+
+	child = dccp_v4_request_recv_sock(sk, skb, req, NULL);
+	if (child == NULL)
+		goto listen_overflow;
+
+	/* FIXME: deal with options */
+
+	inet_csk_reqsk_queue_unlink(sk, req, prev);
+	inet_csk_reqsk_queue_removed(sk, req);
+	inet_csk_reqsk_queue_add(sk, req, child);
+out:
+	return child;
+listen_overflow:
+	dccp_pr_debug("listen_overflow!\n");
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
+drop:
+	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_RESET)
+		req->rsk_ops->send_reset(skb);
+
+	inet_csk_reqsk_queue_drop(sk, req, prev);
+	goto out;
+}
+
+/*
+ *  Queue segment on the new socket if the new socket is active,
+ *  otherwise we just shortcircuit this and continue with
+ *  the new socket.
+ */
+int dccp_child_process(struct sock *parent, struct sock *child,
+		       struct sk_buff *skb)
+{
+	int ret = 0;
+	const int state = child->sk_state;
+
+	if (!sock_owned_by_user(child)) {
+		ret = dccp_rcv_state_process(child, skb, dccp_hdr(skb), skb->len);
+
+		/* Wakeup parent, send SIGIO */
+		if (state == DCCP_RESPOND && child->sk_state != state)
+			parent->sk_data_ready(parent, 0);
+	} else {
+		/* Alas, it is possible again, because we do lookup
+		 * in main socket hash table and lock on listening
+		 * socket does not protect us more.
+		 */
+		sk_add_backlog(child, skb);
+	}
+
+	bh_unlock_sock(child);
+	sock_put(child);
+	return ret;
+}

net/dccp/timer.c

+/*
+ *  net/dccp/timer.c
+ * 
+ *  An implementation of the DCCP protocol
+ *  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.
+ */
+
+#include <linux/config.h>
+#include <linux/dccp.h>
+#include <linux/skbuff.h>
+
+#include "dccp.h"
+
+static void dccp_write_timer(unsigned long data);
+static void dccp_keepalive_timer(unsigned long data);
+static void dccp_delack_timer(unsigned long data);
+
+void dccp_init_xmit_timers(struct sock *sk)
+{
+	inet_csk_init_xmit_timers(sk, &dccp_write_timer, &dccp_delack_timer,
+				  &dccp_keepalive_timer);
+}
+
+static void dccp_write_err(struct sock *sk)
+{
+	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
+	sk->sk_error_report(sk);
+
+	dccp_v4_send_reset(sk, DCCP_RESET_CODE_ABORTED);
+	dccp_done(sk);
+	DCCP_INC_STATS_BH(DCCP_MIB_ABORTONTIMEOUT);
+}
+
+/* A write timeout has occurred. Process the after effects. */
+static int dccp_write_timeout(struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	int retry_until;
+
+	if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
+		if (icsk->icsk_retransmits != 0)
+			dst_negative_advice(&sk->sk_dst_cache);
+		retry_until = icsk->icsk_syn_retries ? :  /* FIXME! */ 3 /* FIXME! sysctl_tcp_syn_retries */;
+	} else {
+		if (icsk->icsk_retransmits >= /* FIXME! sysctl_tcp_retries1 */ 5 /* FIXME! */) {
+			/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu black
+			   hole detection. :-(
+
+			   It is place to make it. It is not made. I do not want
+			   to make it. It is disguisting. It does not work in any
+			   case. Let me to cite the same draft, which requires for
+			   us to implement this:
+
+   "The one security concern raised by this memo is that ICMP black holes
+   are often caused by over-zealous security administrators who block
+   all ICMP messages.  It is vitally important that those who design and
+   deploy security systems understand the impact of strict filtering on
+   upper-layer protocols.  The safest web site in the world is worthless
+   if most TCP implementations cannot transfer data from it.  It would
+   be far nicer to have all of the black holes fixed rather than fixing
+   all of the TCP implementations."
+
+                           Golden words :-).
+		   */
+
+			dst_negative_advice(&sk->sk_dst_cache);
+		}
+
+		retry_until = /* FIXME! */ 15 /* FIXME! sysctl_tcp_retries2 */;
+		/*
+		 * FIXME: see tcp_write_timout and tcp_out_of_resources
+		 */
+	}
+
+	if (icsk->icsk_retransmits >= retry_until) {
+		/* Has it gone just too far? */
+		dccp_write_err(sk);
+		return 1;
+	}
+	return 0;
+}
+
+/* This is the same as tcp_delack_timer, sans prequeue & mem_reclaim stuff */
+static void dccp_delack_timer(unsigned long data)
+{
+	struct sock *sk = (struct sock *)data;
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later. */
+		icsk->icsk_ack.blocked = 1;
+		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOCKED);
+		sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN);
+		goto out;
+	}
+
+	if (sk->sk_state == DCCP_CLOSED || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
+		goto out;
+	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout);
+		goto out;
+	}
+
+	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
+
+	if (inet_csk_ack_scheduled(sk)) {
+		if (!icsk->icsk_ack.pingpong) {
+			/* Delayed ACK missed: inflate ATO. */
+			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1, icsk->icsk_rto);
+		} else {
+			/* Delayed ACK missed: leave pingpong mode and
+			 * deflate ATO.
+			 */
+			icsk->icsk_ack.pingpong = 0;
+			icsk->icsk_ack.ato = TCP_ATO_MIN;
+		}
+		dccp_send_ack(sk);
+		NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKS);
+	}
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+/*
+ *	The DCCP retransmit timer.
+ */
+static void dccp_retransmit_timer(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	/*
+	 * sk->sk_send_head has to have one skb with
+	 * DCCP_SKB_CB(skb)->dccpd_type set to one of the retransmittable DCCP
+	 * packet types (REQUEST, RESPONSE, the ACK in the 3way hanshake
+	 * (PARTOPEN timer), etc).
+	 */
+	BUG_TRAP(sk->sk_send_head != NULL);
+
+	/* 
+	 * More than than 4MSL (8 minutes) has passed, a RESET(aborted) was
+	 * sent, no need to retransmit, this sock is dead.
+	 */
+	if (dccp_write_timeout(sk))
+		goto out;
+
+	/*
+	 * We want to know the number of packets retransmitted, not the
+	 * total number of retransmissions of clones of original packets.
+	 */
+	if (icsk->icsk_retransmits == 0)
+		DCCP_INC_STATS_BH(DCCP_MIB_TIMEOUTS);
+
+	if (dccp_retransmit_skb(sk, sk->sk_send_head) < 0) {
+		/*
+		 * Retransmission failed because of local congestion,
+		 * do not backoff.
+		 */
+		if (icsk->icsk_retransmits == 0)
+			icsk->icsk_retransmits = 1;
+		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+					  min(icsk->icsk_rto,
+					      TCP_RESOURCE_PROBE_INTERVAL),
+					  TCP_RTO_MAX);
+		goto out;
+	}
+
+	icsk->icsk_backoff++;
+	icsk->icsk_retransmits++;
+
+	icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
+	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
+	if (icsk->icsk_retransmits > 3 /* FIXME: sysctl_dccp_retries1 */)
+		__sk_dst_reset(sk);
+out:;
+}
+
+static void dccp_write_timer(unsigned long data)
+{
+	struct sock *sk = (struct sock *)data;
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	int event = 0;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later */
+		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20));
+		goto out;
+	}
+
+	if (sk->sk_state == DCCP_CLOSED || !icsk->icsk_pending)
+		goto out;
+
+	if (time_after(icsk->icsk_timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout);
+		goto out;
+	}
+
+	event = icsk->icsk_pending;
+	icsk->icsk_pending = 0;
+
+	switch (event) {
+	case ICSK_TIME_RETRANS:
+		dccp_retransmit_timer(sk);
+		break;
+	}
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+/*
+ *	Timer for listening sockets
+ */
+static void dccp_response_timer(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	const int max_retries = icsk->icsk_syn_retries ? : TCP_SYNACK_RETRIES /* FIXME sysctl_tcp_synack_retries */;
+
+	reqsk_queue_prune(&icsk->icsk_accept_queue, sk, TCP_SYNQ_INTERVAL,
+			  DCCP_TIMEOUT_INIT, DCCP_RTO_MAX, max_retries);
+}
+
+static void dccp_keepalive_timer(unsigned long data)
+{
+	struct sock *sk = (struct sock *)data;
+
+	/* Only process if socket is not in use. */
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later. */ 
+		inet_csk_reset_keepalive_timer(sk, HZ / 20);
+		goto out;
+	}
+
+	if (sk->sk_state == DCCP_LISTEN) {
+		dccp_response_timer(sk);
+		goto out;
+	}
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}