net/l2tp/l2tp_core.h - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0-only */
 /* L2TP internal definitions.
  *
  * Copyright (c) 2008,2009 Katalix Systems Ltd
  */
 #include <linux/refcount.h>

 #ifndef _L2TP_CORE_H_
 #define _L2TP_CORE_H_

 #include <net/dst.h>
 #include <net/sock.h>

 #ifdef CONFIG_XFRM
 #include <net/xfrm.h>
 #endif

 /* Random numbers used for internal consistency checks of tunnel and session structures */
 #define L2TP_TUNNEL_MAGIC	0x42114DDA
 #define L2TP_SESSION_MAGIC	0x0C04EB7D

 /* Per tunnel session hash table size */
 #define L2TP_HASH_BITS	4
 #define L2TP_HASH_SIZE	BIT(L2TP_HASH_BITS)

 /* System-wide session hash table size */
 #define L2TP_HASH_BITS_2	8
 #define L2TP_HASH_SIZE_2	BIT(L2TP_HASH_BITS_2)

 struct sk_buff;

 struct l2tp_stats {
 	atomic_long_t		tx_packets;
 	atomic_long_t		tx_bytes;
 	atomic_long_t		tx_errors;
 	atomic_long_t		rx_packets;
 	atomic_long_t		rx_bytes;
 	atomic_long_t		rx_seq_discards;
 	atomic_long_t		rx_oos_packets;
 	atomic_long_t		rx_errors;
 	atomic_long_t		rx_cookie_discards;
 	atomic_long_t		rx_invalid;
 };

 struct l2tp_tunnel;

 /* L2TP session configuration */
 struct l2tp_session_cfg {
 	enum l2tp_pwtype	pw_type;
 	unsigned int		recv_seq:1;	/* expect receive packets with sequence numbers? */
 	unsigned int		send_seq:1;	/* send packets with sequence numbers? */
 	unsigned int		lns_mode:1;	/* behave as LNS?
 						 * LAC enables sequence numbers under LNS control.
 						 */
 	u16			l2specific_type; /* Layer 2 specific type */
 	u8			cookie[8];	/* optional cookie */
 	int			cookie_len;	/* 0, 4 or 8 bytes */
 	u8			peer_cookie[8];	/* peer's cookie */
 	int			peer_cookie_len; /* 0, 4 or 8 bytes */
 	int			reorder_timeout; /* configured reorder timeout (in jiffies) */
 	char			*ifname;
 };

 /* Represents a session (pseudowire) instance.
  * Tracks runtime state including cookies, dataplane packet sequencing, and IO statistics.
  * Is linked into a per-tunnel session hashlist; and in the case of an L2TPv3 session into
  * an additional per-net ("global") hashlist.
  */
 #define L2TP_SESSION_NAME_MAX 32
 struct l2tp_session {
 	int			magic;		/* should be L2TP_SESSION_MAGIC */
 	long			dead;

 	struct l2tp_tunnel	*tunnel;	/* back pointer to tunnel context */
 	u32			session_id;
 	u32			peer_session_id;
 	u8			cookie[8];
 	int			cookie_len;
 	u8			peer_cookie[8];
 	int			peer_cookie_len;
 	u16			l2specific_type;
 	u16			hdr_len;
 	u32			nr;		/* session NR state (receive) */
 	u32			ns;		/* session NR state (send) */
 	struct sk_buff_head	reorder_q;	/* receive reorder queue */
 	u32			nr_max;		/* max NR. Depends on tunnel */
 	u32			nr_window_size;	/* NR window size */
 	u32			nr_oos;		/* NR of last OOS packet */
 	int			nr_oos_count;	/* for OOS recovery */
 	int			nr_oos_count_max;
 	struct hlist_node	hlist;		/* hash list node */
 	refcount_t		ref_count;

 	char			name[L2TP_SESSION_NAME_MAX]; /* for logging */
 	char			ifname[IFNAMSIZ];
 	unsigned int		recv_seq:1;	/* expect receive packets with sequence numbers? */
 	unsigned int		send_seq:1;	/* send packets with sequence numbers? */
 	unsigned int		lns_mode:1;	/* behave as LNS?
 						 * LAC enables sequence numbers under LNS control.
 						 */
 	int			reorder_timeout; /* configured reorder timeout (in jiffies) */
 	int			reorder_skip;	/* set if skip to next nr */
 	enum l2tp_pwtype	pwtype;
 	struct l2tp_stats	stats;
 	struct hlist_node	global_hlist;	/* global hash list node */

 	/* Session receive handler for data packets.
 	 * Each pseudowire implementation should implement this callback in order to
 	 * handle incoming packets.  Packets are passed to the pseudowire handler after
 	 * reordering, if data sequence numbers are enabled for the session.
 	 */
 	void (*recv_skb)(struct l2tp_session *session, struct sk_buff *skb, int data_len);

 	/* Session close handler.
 	 * Each pseudowire implementation may implement this callback in order to carry
 	 * out pseudowire-specific shutdown actions.
 	 * The callback is called by core after unhashing the session and purging its
 	 * reorder queue.
 	 */
 	void (*session_close)(struct l2tp_session *session);

 	/* Session show handler.
 	 * Pseudowire-specific implementation of debugfs session rendering.
 	 * The callback is called by l2tp_debugfs.c after rendering core session
 	 * information.
 	 */
 	void (*show)(struct seq_file *m, void *priv);

 	u8			priv[];		/* private data */
 };

 /* L2TP tunnel configuration */
 struct l2tp_tunnel_cfg {
 	enum l2tp_encap_type	encap;

 	/* Used only for kernel-created sockets */
 	struct in_addr		local_ip;
 	struct in_addr		peer_ip;
 #if IS_ENABLED(CONFIG_IPV6)
 	struct in6_addr		*local_ip6;
 	struct in6_addr		*peer_ip6;
 #endif
 	u16			local_udp_port;
 	u16			peer_udp_port;
 	unsigned int		use_udp_checksums:1,
 				udp6_zero_tx_checksums:1,
 				udp6_zero_rx_checksums:1;
 };

 /* Represents a tunnel instance.
  * Tracks runtime state including IO statistics.
  * Holds the tunnel socket (either passed from userspace or directly created by the kernel).
  * Maintains a hashlist of sessions belonging to the tunnel instance.
  * Is linked into a per-net list of tunnels.
  */
 #define L2TP_TUNNEL_NAME_MAX 20
 struct l2tp_tunnel {
 	int			magic;		/* Should be L2TP_TUNNEL_MAGIC */

 	unsigned long		dead;

 	struct rcu_head rcu;
 	spinlock_t		hlist_lock;	/* write-protection for session_hlist */
 	bool			acpt_newsess;	/* indicates whether this tunnel accepts
 						 * new sessions. Protected by hlist_lock.
 						 */
 	struct hlist_head	session_hlist[L2TP_HASH_SIZE];
 						/* hashed list of sessions, hashed by id */
 	u32			tunnel_id;
 	u32			peer_tunnel_id;
 	int			version;	/* 2=>L2TPv2, 3=>L2TPv3 */

 	char			name[L2TP_TUNNEL_NAME_MAX]; /* for logging */
 	enum l2tp_encap_type	encap;
 	struct l2tp_stats	stats;

 	struct list_head	list;		/* list node on per-namespace list of tunnels */
 	struct net		*l2tp_net;	/* the net we belong to */

 	refcount_t		ref_count;
 	void (*old_sk_destruct)(struct sock *sk);
 	struct sock		*sock;		/* parent socket */
 	int			fd;		/* parent fd, if tunnel socket was created
 						 * by userspace
 						 */

 	struct work_struct	del_work;
 };

 /* Pseudowire ops callbacks for use with the l2tp genetlink interface */
 struct l2tp_nl_cmd_ops {
 	/* The pseudowire session create callback is responsible for creating a session
 	 * instance for a specific pseudowire type.
 	 * It must call l2tp_session_create and l2tp_session_register to register the
 	 * session instance, as well as carry out any pseudowire-specific initialisation.
 	 * It must return >= 0 on success, or an appropriate negative errno value on failure.
 	 */
 	int (*session_create)(struct net *net, struct l2tp_tunnel *tunnel,
 			      u32 session_id, u32 peer_session_id,
 			      struct l2tp_session_cfg *cfg);

 	/* The pseudowire session delete callback is responsible for initiating the deletion
 	 * of a session instance.
 	 * It must call l2tp_session_delete, as well as carry out any pseudowire-specific
 	 * teardown actions.
 	 */
 	void (*session_delete)(struct l2tp_session *session);
 };

 static inline void *l2tp_session_priv(struct l2tp_session *session)
 {
 	return &session->priv[0];
 }

 /* Tunnel and session refcounts */
 void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel);
 void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel);
 void l2tp_session_inc_refcount(struct l2tp_session *session);
 void l2tp_session_dec_refcount(struct l2tp_session *session);

 /* Tunnel and session lookup.
  * These functions take a reference on the instances they return, so
  * the caller must ensure that the reference is dropped appropriately.
  */
 struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id);
 struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth);
 struct l2tp_session *l2tp_tunnel_get_session(struct l2tp_tunnel *tunnel,
 					     u32 session_id);

 struct l2tp_session *l2tp_session_get(const struct net *net, u32 session_id);
 struct l2tp_session *l2tp_session_get_nth(struct l2tp_tunnel *tunnel, int nth);
 struct l2tp_session *l2tp_session_get_by_ifname(const struct net *net,
 						const char *ifname);

 /* Tunnel and session lifetime management.
  * Creation of a new instance is a two-step process: create, then register.
  * Destruction is triggered using the *_delete functions, and completes asynchronously.
  */
 int l2tp_tunnel_create(int fd, int version, u32 tunnel_id,
 		       u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
 		       struct l2tp_tunnel **tunnelp);
 int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
 			 struct l2tp_tunnel_cfg *cfg);
 void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);

 struct l2tp_session *l2tp_session_create(int priv_size,
 					 struct l2tp_tunnel *tunnel,
 					 u32 session_id, u32 peer_session_id,
 					 struct l2tp_session_cfg *cfg);
 int l2tp_session_register(struct l2tp_session *session,
 			  struct l2tp_tunnel *tunnel);
 void l2tp_session_delete(struct l2tp_session *session);

 /* Receive path helpers.  If data sequencing is enabled for the session these
  * functions handle queuing and reordering prior to passing packets to the
  * pseudowire code to be passed to userspace.
  */
 void l2tp_recv_common(struct l2tp_session *session, struct sk_buff *skb,
 		      unsigned char *ptr, unsigned char *optr, u16 hdrflags,
 		      int length);
 int l2tp_udp_encap_recv(struct sock *sk, struct sk_buff *skb);

 /* Transmit path helpers for sending packets over the tunnel socket. */
 void l2tp_session_set_header_len(struct l2tp_session *session, int version);
 int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb);

 /* Pseudowire management.
  * Pseudowires should register with l2tp core on module init, and unregister
  * on module exit.
  */
 int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, const struct l2tp_nl_cmd_ops *ops);
 void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);

 /* IOCTL helper for IP encap modules. */
 int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);

 /* Extract the tunnel structure from a socket's sk_user_data pointer,
  * validating the tunnel magic feather.
  */
 struct l2tp_tunnel *l2tp_sk_to_tunnel(struct sock *sk);

 static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
 {
 	switch (session->l2specific_type) {
 	case L2TP_L2SPECTYPE_DEFAULT:
 		return 4;
 	case L2TP_L2SPECTYPE_NONE:
 	default:
 		return 0;
 	}
 }

 static inline u32 l2tp_tunnel_dst_mtu(const struct l2tp_tunnel *tunnel)
 {
 	struct dst_entry *dst;
 	u32 mtu;

 	dst = sk_dst_get(tunnel->sock);
 	if (!dst)
 		return 0;

 	mtu = dst_mtu(dst);
 	dst_release(dst);

 	return mtu;
 }

 #ifdef CONFIG_XFRM
 static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
 {
 	struct sock *sk = tunnel->sock;

 	return sk && (rcu_access_pointer(sk->sk_policy[0]) ||
 		      rcu_access_pointer(sk->sk_policy[1]));
 }
 #else
 static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
 {
 	return false;
 }
 #endif

 static inline int l2tp_v3_ensure_opt_in_linear(struct l2tp_session *session, struct sk_buff *skb,
 					       unsigned char **ptr, unsigned char **optr)
 {
 	int opt_len = session->peer_cookie_len + l2tp_get_l2specific_len(session);

 	if (opt_len > 0) {
 		int off = *ptr - *optr;

 		if (!pskb_may_pull(skb, off + opt_len))
 			return -1;

 		if (skb->data != *optr) {
 			*optr = skb->data;
 			*ptr = skb->data + off;
 		}
 	}

 	return 0;
 }

 #define MODULE_ALIAS_L2TP_PWTYPE(type) \
 	MODULE_ALIAS("net-l2tp-type-" __stringify(type))

 #endif /* _L2TP_CORE_H_ */
	/* SPDX-License-Identifier: GPL-2.0-only */
	/* L2TP internal definitions.
	*
	* Copyright (c) 2008,2009 Katalix Systems Ltd
	*/
	#include <linux/refcount.h>

	#ifndef _L2TP_CORE_H_
	#define _L2TP_CORE_H_

	#include <net/dst.h>
	#include <net/sock.h>

	#ifdef CONFIG_XFRM
	#include <net/xfrm.h>
	#endif

	/* Random numbers used for internal consistency checks of tunnel and session structures */
	#define L2TP_TUNNEL_MAGIC 0x42114DDA
	#define L2TP_SESSION_MAGIC 0x0C04EB7D

	/* Per tunnel session hash table size */
	#define L2TP_HASH_BITS 4
	#define L2TP_HASH_SIZE BIT(L2TP_HASH_BITS)

	/* System-wide session hash table size */
	#define L2TP_HASH_BITS_2 8
	#define L2TP_HASH_SIZE_2 BIT(L2TP_HASH_BITS_2)

	struct sk_buff;

	struct l2tp_stats {
	atomic_long_t tx_packets;
	atomic_long_t tx_bytes;
	atomic_long_t tx_errors;
	atomic_long_t rx_packets;
	atomic_long_t rx_bytes;
	atomic_long_t rx_seq_discards;
	atomic_long_t rx_oos_packets;
	atomic_long_t rx_errors;
	atomic_long_t rx_cookie_discards;
	atomic_long_t rx_invalid;
	};

	struct l2tp_tunnel;

	/* L2TP session configuration */
	struct l2tp_session_cfg {
	enum l2tp_pwtype pw_type;
	unsigned int recv_seq:1; /* expect receive packets with sequence numbers? */
	unsigned int send_seq:1; /* send packets with sequence numbers? */
	unsigned int lns_mode:1; /* behave as LNS?
	* LAC enables sequence numbers under LNS control.
	*/
	u16 l2specific_type; /* Layer 2 specific type */
	u8 cookie[8]; /* optional cookie */
	int cookie_len; /* 0, 4 or 8 bytes */
	u8 peer_cookie[8]; /* peer's cookie */
	int peer_cookie_len; /* 0, 4 or 8 bytes */
	int reorder_timeout; /* configured reorder timeout (in jiffies) */
	char *ifname;
	};

	/* Represents a session (pseudowire) instance.
	* Tracks runtime state including cookies, dataplane packet sequencing, and IO statistics.
	* Is linked into a per-tunnel session hashlist; and in the case of an L2TPv3 session into
	* an additional per-net ("global") hashlist.
	*/
	#define L2TP_SESSION_NAME_MAX 32
	struct l2tp_session {
	int magic; /* should be L2TP_SESSION_MAGIC */
	long dead;

	struct l2tp_tunnel tunnel; / back pointer to tunnel context */
	u32 session_id;
	u32 peer_session_id;
	u8 cookie[8];
	int cookie_len;
	u8 peer_cookie[8];
	int peer_cookie_len;
	u16 l2specific_type;
	u16 hdr_len;
	u32 nr; /* session NR state (receive) */
	u32 ns; /* session NR state (send) */
	struct sk_buff_head reorder_q; /* receive reorder queue */
	u32 nr_max; /* max NR. Depends on tunnel */
	u32 nr_window_size; /* NR window size */
	u32 nr_oos; /* NR of last OOS packet */
	int nr_oos_count; /* for OOS recovery */
	int nr_oos_count_max;
	struct hlist_node hlist; /* hash list node */
	refcount_t ref_count;

	char name[L2TP_SESSION_NAME_MAX]; /* for logging */
	char ifname[IFNAMSIZ];
	unsigned int recv_seq:1; /* expect receive packets with sequence numbers? */
	unsigned int send_seq:1; /* send packets with sequence numbers? */
	unsigned int lns_mode:1; /* behave as LNS?
	* LAC enables sequence numbers under LNS control.
	*/
	int reorder_timeout; /* configured reorder timeout (in jiffies) */
	int reorder_skip; /* set if skip to next nr */
	enum l2tp_pwtype pwtype;
	struct l2tp_stats stats;
	struct hlist_node global_hlist; /* global hash list node */

	/* Session receive handler for data packets.
	* Each pseudowire implementation should implement this callback in order to
	* handle incoming packets. Packets are passed to the pseudowire handler after
	* reordering, if data sequence numbers are enabled for the session.
	*/
	void (recv_skb)(struct l2tp_session session, struct sk_buff *skb, int data_len);

	/* Session close handler.
	* Each pseudowire implementation may implement this callback in order to carry
	* out pseudowire-specific shutdown actions.
	* The callback is called by core after unhashing the session and purging its
	* reorder queue.
	*/
	void (session_close)(struct l2tp_session session);

	/* Session show handler.
	* Pseudowire-specific implementation of debugfs session rendering.
	* The callback is called by l2tp_debugfs.c after rendering core session
	* information.
	*/
	void (show)(struct seq_file m, void *priv);

	u8 priv[]; /* private data */
	};

	/* L2TP tunnel configuration */
	struct l2tp_tunnel_cfg {
	enum l2tp_encap_type encap;

	/* Used only for kernel-created sockets */
	struct in_addr local_ip;
	struct in_addr peer_ip;
	#if IS_ENABLED(CONFIG_IPV6)
	struct in6_addr *local_ip6;
	struct in6_addr *peer_ip6;
	#endif
	u16 local_udp_port;
	u16 peer_udp_port;
	unsigned int use_udp_checksums:1,
	udp6_zero_tx_checksums:1,
	udp6_zero_rx_checksums:1;
	};

	/* Represents a tunnel instance.
	* Tracks runtime state including IO statistics.
	* Holds the tunnel socket (either passed from userspace or directly created by the kernel).
	* Maintains a hashlist of sessions belonging to the tunnel instance.
	* Is linked into a per-net list of tunnels.
	*/
	#define L2TP_TUNNEL_NAME_MAX 20
	struct l2tp_tunnel {
	int magic; /* Should be L2TP_TUNNEL_MAGIC */

	unsigned long dead;

	struct rcu_head rcu;
	spinlock_t hlist_lock; /* write-protection for session_hlist */
	bool acpt_newsess; /* indicates whether this tunnel accepts
	* new sessions. Protected by hlist_lock.
	*/
	struct hlist_head session_hlist[L2TP_HASH_SIZE];
	/* hashed list of sessions, hashed by id */
	u32 tunnel_id;
	u32 peer_tunnel_id;
	int version; /* 2=>L2TPv2, 3=>L2TPv3 */

	char name[L2TP_TUNNEL_NAME_MAX]; /* for logging */
	enum l2tp_encap_type encap;
	struct l2tp_stats stats;

	struct list_head list; /* list node on per-namespace list of tunnels */
	struct net l2tp_net; / the net we belong to */

	refcount_t ref_count;
	void (old_sk_destruct)(struct sock sk);
	struct sock sock; / parent socket */
	int fd; /* parent fd, if tunnel socket was created
	* by userspace
	*/

	struct work_struct del_work;
	};

	/* Pseudowire ops callbacks for use with the l2tp genetlink interface */
	struct l2tp_nl_cmd_ops {
	/* The pseudowire session create callback is responsible for creating a session
	* instance for a specific pseudowire type.
	* It must call l2tp_session_create and l2tp_session_register to register the
	* session instance, as well as carry out any pseudowire-specific initialisation.
	* It must return >= 0 on success, or an appropriate negative errno value on failure.
	*/
	int (session_create)(struct net net, struct l2tp_tunnel *tunnel,
	u32 session_id, u32 peer_session_id,
	struct l2tp_session_cfg *cfg);

	/* The pseudowire session delete callback is responsible for initiating the deletion
	* of a session instance.
	* It must call l2tp_session_delete, as well as carry out any pseudowire-specific
	* teardown actions.
	*/
	void (session_delete)(struct l2tp_session session);
	};

	static inline void l2tp_session_priv(struct l2tp_session session)
	{
	return &session->priv[0];
	}

	/* Tunnel and session refcounts */
	void l2tp_tunnel_inc_refcount(struct l2tp_tunnel *tunnel);
	void l2tp_tunnel_dec_refcount(struct l2tp_tunnel *tunnel);
	void l2tp_session_inc_refcount(struct l2tp_session *session);
	void l2tp_session_dec_refcount(struct l2tp_session *session);

	/* Tunnel and session lookup.
	* These functions take a reference on the instances they return, so
	* the caller must ensure that the reference is dropped appropriately.
	*/
	struct l2tp_tunnel l2tp_tunnel_get(const struct net net, u32 tunnel_id);
	struct l2tp_tunnel l2tp_tunnel_get_nth(const struct net net, int nth);
	struct l2tp_session l2tp_tunnel_get_session(struct l2tp_tunnel tunnel,
	u32 session_id);

	struct l2tp_session l2tp_session_get(const struct net net, u32 session_id);
	struct l2tp_session l2tp_session_get_nth(struct l2tp_tunnel tunnel, int nth);
	struct l2tp_session l2tp_session_get_by_ifname(const struct net net,
	const char *ifname);

	/* Tunnel and session lifetime management.
	* Creation of a new instance is a two-step process: create, then register.
	* Destruction is triggered using the *_delete functions, and completes asynchronously.
	*/
	int l2tp_tunnel_create(int fd, int version, u32 tunnel_id,
	u32 peer_tunnel_id, struct l2tp_tunnel_cfg *cfg,
	struct l2tp_tunnel **tunnelp);
	int l2tp_tunnel_register(struct l2tp_tunnel tunnel, struct net net,
	struct l2tp_tunnel_cfg *cfg);
	void l2tp_tunnel_delete(struct l2tp_tunnel *tunnel);

	struct l2tp_session *l2tp_session_create(int priv_size,
	struct l2tp_tunnel *tunnel,
	u32 session_id, u32 peer_session_id,
	struct l2tp_session_cfg *cfg);
	int l2tp_session_register(struct l2tp_session *session,
	struct l2tp_tunnel *tunnel);
	void l2tp_session_delete(struct l2tp_session *session);

	/* Receive path helpers. If data sequencing is enabled for the session these
	* functions handle queuing and reordering prior to passing packets to the
	* pseudowire code to be passed to userspace.
	*/
	void l2tp_recv_common(struct l2tp_session session, struct sk_buff skb,
	unsigned char ptr, unsigned char optr, u16 hdrflags,
	int length);
	int l2tp_udp_encap_recv(struct sock sk, struct sk_buff skb);

	/* Transmit path helpers for sending packets over the tunnel socket. */
	void l2tp_session_set_header_len(struct l2tp_session *session, int version);
	int l2tp_xmit_skb(struct l2tp_session session, struct sk_buff skb);

	/* Pseudowire management.
	* Pseudowires should register with l2tp core on module init, and unregister
	* on module exit.
	*/
	int l2tp_nl_register_ops(enum l2tp_pwtype pw_type, const struct l2tp_nl_cmd_ops *ops);
	void l2tp_nl_unregister_ops(enum l2tp_pwtype pw_type);

	/* IOCTL helper for IP encap modules. */
	int l2tp_ioctl(struct sock *sk, int cmd, unsigned long arg);

	/* Extract the tunnel structure from a socket's sk_user_data pointer,
	* validating the tunnel magic feather.
	*/
	struct l2tp_tunnel l2tp_sk_to_tunnel(struct sock sk);

	static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
	{
	switch (session->l2specific_type) {
	case L2TP_L2SPECTYPE_DEFAULT:
	return 4;
	case L2TP_L2SPECTYPE_NONE:
	default:
	return 0;
	}
	}

	static inline u32 l2tp_tunnel_dst_mtu(const struct l2tp_tunnel *tunnel)
	{
	struct dst_entry *dst;
	u32 mtu;

	dst = sk_dst_get(tunnel->sock);
	if (!dst)
	return 0;

	mtu = dst_mtu(dst);
	dst_release(dst);

	return mtu;
	}

	#ifdef CONFIG_XFRM
	static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
	{
	struct sock *sk = tunnel->sock;

	return sk && (rcu_access_pointer(sk->sk_policy[0]) \|\|
	rcu_access_pointer(sk->sk_policy[1]));
	}
	#else
	static inline bool l2tp_tunnel_uses_xfrm(const struct l2tp_tunnel *tunnel)
	{
	return false;
	}
	#endif

	static inline int l2tp_v3_ensure_opt_in_linear(struct l2tp_session session, struct sk_buff skb,
	unsigned char ptr, unsigned char optr)
	{
	int opt_len = session->peer_cookie_len + l2tp_get_l2specific_len(session);

	if (opt_len > 0) {
	int off = ptr - optr;

	if (!pskb_may_pull(skb, off + opt_len))
	return -1;

	if (skb->data != *optr) {
	*optr = skb->data;
	*ptr = skb->data + off;
	}
	}

	return 0;
	}

	#define MODULE_ALIAS_L2TP_PWTYPE(type) \
	MODULE_ALIAS("net-l2tp-type-" __stringify(type))

	#endif /* _L2TP_CORE_H_ */