text: /*-
   * Copyright (c) 2001-2002 Packet Design, LLC.
   * All rights reserved.
   * 
   * Subject to the following obligations and disclaimer of warranty,
   * use and redistribution of this software, in source or object code
   * forms, with or without modifications are expressly permitted by
   * Packet Design; provided, however, that:
   * 
   *    (i)  Any and all reproductions of the source or object code
   *         must include the copyright notice above and the following
   *         disclaimer of warranties; and
   *    (ii) No rights are granted, in any manner or form, to use
   *         Packet Design trademarks, including the mark "PACKET DESIGN"
   *         on advertising, endorsements, or otherwise except as such
   *         appears in the above copyright notice or in the software.
   * 
   * THIS SOFTWARE IS BEING PROVIDED BY PACKET DESIGN "AS IS", AND
   * TO THE MAXIMUM EXTENT PERMITTED BY LAW, PACKET DESIGN MAKES NO
   * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING
   * THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED
   * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
   * OR NON-INFRINGEMENT.  PACKET DESIGN DOES NOT WARRANT, GUARANTEE,
   * OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS
   * OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY,
   * RELIABILITY OR OTHERWISE.  IN NO EVENT SHALL PACKET DESIGN BE
   * LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE
   * OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT,
   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL
   * DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF
   * USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF
   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
   * THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF
   * THE POSSIBILITY OF SUCH DAMAGE.
   * 
   * Author: Archie Cobbs <archie@freebsd.org>
   *
   * $FreeBSD: src/sys/netgraph/ng_l2tp.c,v 1.25 2008/03/16 21:33:12 mav Exp $
   * $DragonFly: src/sys/netgraph7/ng_l2tp.c,v 1.2 2008/06/26 23:05:35 dillon Exp $
   */
  
  /*
   * L2TP netgraph node type.
   *
   * This node type implements the lower layer of the
   * L2TP protocol as specified in RFC 2661.
   */
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/kernel.h>
  #include <sys/time.h>
  #include <sys/conf.h>
  #include <sys/mbuf.h>
  #include <sys/malloc.h>
  #include <sys/errno.h>
  #include <sys/libkern.h>
  
  #include <netgraph7/ng_message.h>
  #include <netgraph7/netgraph.h>
  #include <netgraph7/ng_parse.h>
  #include "ng_l2tp.h"
  
  #ifdef NG_SEPARATE_MALLOC
  MALLOC_DEFINE(M_NETGRAPH_L2TP, "netgraph_l2tp", "netgraph l2tp node");
  #else
  #define M_NETGRAPH_L2TP M_NETGRAPH
  #endif
  
  /* L2TP header format (first 2 bytes only) */
  #define L2TP_HDR_CTRL		0x8000			/* control packet */
  #define L2TP_HDR_LEN		0x4000			/* has length field */
  #define L2TP_HDR_SEQ		0x0800			/* has ns, nr fields */
  #define L2TP_HDR_OFF		0x0200			/* has offset field */
  #define L2TP_HDR_PRIO		0x0100			/* give priority */
  #define L2TP_HDR_VERS_MASK	0x000f			/* version field mask */
  #define L2TP_HDR_VERSION	0x0002			/* version field */
  
  /* Bits that must be zero or one in first two bytes of header */
  #define L2TP_CTRL_0BITS		0x030d			/* ctrl: must be 0 */
  #define L2TP_CTRL_1BITS		0xc802			/* ctrl: must be 1 */
  #define L2TP_DATA_0BITS		0x800d			/* data: must be 0 */
  #define L2TP_DATA_1BITS		0x0002			/* data: must be 1 */
  
  /* Standard xmit ctrl and data header bits */
  #define L2TP_CTRL_HDR		(L2TP_HDR_CTRL | L2TP_HDR_LEN \
  				    | L2TP_HDR_SEQ | L2TP_HDR_VERSION)
  #define L2TP_DATA_HDR		(L2TP_HDR_VERSION)	/* optional: len, seq */
  
  /* Some hard coded values */
  #define L2TP_MAX_XWIN		128			/* my max xmit window */
  #define L2TP_MAX_REXMIT		5			/* default max rexmit */
  #define L2TP_MAX_REXMIT_TO	30			/* default rexmit to */
  #define L2TP_DELAYED_ACK	((hz + 19) / 20)	/* delayed ack: 50 ms */
  
  /* Default data sequence number configuration for new sessions */
  #define L2TP_CONTROL_DSEQ	1			/* we are the lns */
  #define L2TP_ENABLE_DSEQ	1			/* enable data seq # */
  
  /* Compare sequence numbers using circular math */
  #define L2TP_SEQ_DIFF(x, y)	((int)((int16_t)(x) - (int16_t)(y)))
  
  #define SESSHASHSIZE		0x0020
  #define SESSHASH(x)		(((x) ^ ((x) >> 8)) & (SESSHASHSIZE - 1))
  
  /* Hook private data (data session hooks only) */
  struct ng_l2tp_hook_private {
  	struct ng_l2tp_sess_config	conf;	/* hook/session config */
  	struct ng_l2tp_session_stats	stats;	/* per sessions statistics */
  	hook_p				hook;	/* hook reference */
  	u_int16_t			ns;	/* data ns sequence number */
  	u_int16_t			nr;	/* data nr sequence number */
  	LIST_ENTRY(ng_l2tp_hook_private) sessions;
  };
  typedef struct ng_l2tp_hook_private *hookpriv_p;
  
  /*
   * Sequence number state
   *
   * Invariants:
   *    - If cwnd < ssth, we're doing slow start, otherwise congestion avoidance
   *    - The number of unacknowledged xmit packets is (ns - rack) <= seq->wmax
   *    - The first (ns - rack) mbuf's in xwin[] array are copies of these
   *	unacknowledged packets; the remainder of xwin[] consists first of
   *	zero or more further untransmitted packets in the transmit queue
   *    - We try to keep the peer's receive window as full as possible.
   *	Therefore, (i < cwnd && xwin[i] != NULL) implies (ns - rack) > i.
   *    - rack_timer is running iff (ns - rack) > 0 (unack'd xmit'd pkts)
   *    - If xack != nr, there are unacknowledged recv packet(s) (delayed ack)
   *    - xack_timer is running iff xack != nr (unack'd rec'd pkts)
   */
  struct l2tp_seq {
  	u_int16_t		ns;		/* next xmit seq we send */
  	u_int16_t		nr;		/* next recv seq we expect */
  	u_int16_t		inproc;		/* packet is in processing */
  	u_int16_t		rack;		/* last 'nr' we rec'd */
  	u_int16_t		xack;		/* last 'nr' we sent */
  	u_int16_t		wmax;		/* peer's max recv window */
  	u_int16_t		cwnd;		/* current congestion window */
  	u_int16_t		ssth;		/* slow start threshold */
  	u_int16_t		acks;		/* # consecutive acks rec'd */
  	u_int16_t		rexmits;	/* # retransmits sent */
  	struct callout		rack_timer;	/* retransmit timer */
  	struct callout		xack_timer;	/* delayed ack timer */
  	struct mbuf		*xwin[L2TP_MAX_XWIN];	/* transmit window */
  	struct mtx		mtx;			/* seq mutex */
  };
  
  /* Node private data */
  struct ng_l2tp_private {
  	node_p			node;		/* back pointer to node */
  	hook_p			ctrl;		/* hook to upper layers */
  	hook_p			lower;		/* hook to lower layers */
  	struct ng_l2tp_config	conf;		/* node configuration */
  	struct ng_l2tp_stats	stats;		/* node statistics */
  	struct l2tp_seq		seq;		/* ctrl sequence number state */
  	ng_ID_t			ftarget;	/* failure message target */
  	LIST_HEAD(, ng_l2tp_hook_private) sesshash[SESSHASHSIZE];
  };
  typedef struct ng_l2tp_private *priv_p;
  
  /* Netgraph node methods */
  static ng_constructor_t	ng_l2tp_constructor;
  static ng_rcvmsg_t	ng_l2tp_rcvmsg;
  static ng_shutdown_t	ng_l2tp_shutdown;
  static ng_newhook_t	ng_l2tp_newhook;
  static ng_rcvdata_t	ng_l2tp_rcvdata;
  static ng_rcvdata_t	ng_l2tp_rcvdata_lower;
  static ng_rcvdata_t	ng_l2tp_rcvdata_ctrl;
  static ng_disconnect_t	ng_l2tp_disconnect;
  
  /* Internal functions */
  static int	ng_l2tp_xmit_ctrl(priv_p priv, struct mbuf *m, u_int16_t ns);
  
  static void	ng_l2tp_seq_init(priv_p priv);
  static int	ng_l2tp_seq_set(priv_p priv,
  			const struct ng_l2tp_seq_config *conf);
  static int	ng_l2tp_seq_adjust(priv_p priv,
  			const struct ng_l2tp_config *conf);
  static void	ng_l2tp_seq_reset(priv_p priv);
  static void	ng_l2tp_seq_failure(priv_p priv);
  static void	ng_l2tp_seq_recv_nr(priv_p priv, u_int16_t nr);
  static void	ng_l2tp_seq_xack_timeout(node_p node, hook_p hook,
  		    void *arg1, int arg2);
  static void	ng_l2tp_seq_rack_timeout(node_p node, hook_p hook,
  		    void *arg1, int arg2);
  
  static hookpriv_p	ng_l2tp_find_session(priv_p privp, u_int16_t sid);
  static ng_fn_eachhook	ng_l2tp_reset_session;
  
  #ifdef INVARIANTS
  static void	ng_l2tp_seq_check(struct l2tp_seq *seq);
  #endif
  
  /* Parse type for struct ng_l2tp_seq_config. */
  static const struct ng_parse_struct_field
  	ng_l2tp_seq_config_fields[] = NG_L2TP_SEQ_CONFIG_TYPE_INFO;
  static const struct ng_parse_type ng_l2tp_seq_config_type = {
  	&ng_parse_struct_type,
  	&ng_l2tp_seq_config_fields
  };
  
  /* Parse type for struct ng_l2tp_config */
  static const struct ng_parse_struct_field
  	ng_l2tp_config_type_fields[] = NG_L2TP_CONFIG_TYPE_INFO;
  static const struct ng_parse_type ng_l2tp_config_type = {
  	&ng_parse_struct_type,
  	&ng_l2tp_config_type_fields,
  };
  
  /* Parse type for struct ng_l2tp_sess_config */
  static const struct ng_parse_struct_field
  	ng_l2tp_sess_config_type_fields[] = NG_L2TP_SESS_CONFIG_TYPE_INFO;
  static const struct ng_parse_type ng_l2tp_sess_config_type = {
  	&ng_parse_struct_type,
  	&ng_l2tp_sess_config_type_fields,
  };
  
  /* Parse type for struct ng_l2tp_stats */
  static const struct ng_parse_struct_field
  	ng_l2tp_stats_type_fields[] = NG_L2TP_STATS_TYPE_INFO;
  static const struct ng_parse_type ng_l2tp_stats_type = {
  	&ng_parse_struct_type,
  	&ng_l2tp_stats_type_fields
  };
  
  /* Parse type for struct ng_l2tp_session_stats. */
  static const struct ng_parse_struct_field
  	ng_l2tp_session_stats_type_fields[] = NG_L2TP_SESSION_STATS_TYPE_INFO;
  static const struct ng_parse_type ng_l2tp_session_stats_type = {
  	&ng_parse_struct_type,
  	&ng_l2tp_session_stats_type_fields
  };
  
  /* List of commands and how to convert arguments to/from ASCII */
  static const struct ng_cmdlist ng_l2tp_cmdlist[] = {
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_SET_CONFIG,
  	  "setconfig",
  	  &ng_l2tp_config_type,
  	  NULL
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GET_CONFIG,
  	  "getconfig",
  	  NULL,
  	  &ng_l2tp_config_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_SET_SESS_CONFIG,
  	  "setsessconfig",
  	  &ng_l2tp_sess_config_type,
  	  NULL
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GET_SESS_CONFIG,
  	  "getsessconfig",
  	  &ng_parse_hint16_type,
  	  &ng_l2tp_sess_config_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GET_STATS,
  	  "getstats",
  	  NULL,
  	  &ng_l2tp_stats_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_CLR_STATS,
  	  "clrstats",
  	  NULL,
  	  NULL
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GETCLR_STATS,
  	  "getclrstats",
  	  NULL,
  	  &ng_l2tp_stats_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GET_SESSION_STATS,
  	  "getsessstats",
  	  &ng_parse_int16_type,
  	  &ng_l2tp_session_stats_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_CLR_SESSION_STATS,
  	  "clrsessstats",
  	  &ng_parse_int16_type,
  	  NULL
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_GETCLR_SESSION_STATS,
  	  "getclrsessstats",
  	  &ng_parse_int16_type,
  	  &ng_l2tp_session_stats_type
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_ACK_FAILURE,
  	  "ackfailure",
  	  NULL,
  	  NULL
  	},
  	{
  	  NGM_L2TP_COOKIE,
  	  NGM_L2TP_SET_SEQ,
  	  "setsequence",
  	  &ng_l2tp_seq_config_type,
  	  NULL
  	},
  	{ 0 }
  };
  
  /* Node type descriptor */
  static struct ng_type ng_l2tp_typestruct = {
  	.version =	NG_ABI_VERSION,
  	.name =		NG_L2TP_NODE_TYPE,
  	.constructor =	ng_l2tp_constructor,
  	.rcvmsg =	ng_l2tp_rcvmsg,
  	.shutdown =	ng_l2tp_shutdown,
  	.newhook =	ng_l2tp_newhook,
  	.rcvdata =	ng_l2tp_rcvdata,
  	.disconnect =	ng_l2tp_disconnect,
  	.cmdlist =	ng_l2tp_cmdlist,
  };
  NETGRAPH_INIT(l2tp, &ng_l2tp_typestruct);
  
  /* Sequence number state sanity checking */
  #ifdef INVARIANTS
  #define L2TP_SEQ_CHECK(seq)	ng_l2tp_seq_check(seq)
  #else
  #define L2TP_SEQ_CHECK(x)	do { } while (0)
  #endif
  
  /* memmove macro */
  #define memmove(d, s, l)	bcopy(s, d, l)
  
  /* Whether to use m_copypacket() or m_dup() */
  #define L2TP_COPY_MBUF		m_copypacket
  
  #define ERROUT(x)	do { error = (x); goto done; } while (0)
  
  /************************************************************************
  			NETGRAPH NODE STUFF
  ************************************************************************/
  
  /*
   * Node type constructor
   */
  static int
  ng_l2tp_constructor(node_p node)
  {
  	priv_p priv;
  	int	i;
  
  	/* Allocate private structure */
  	priv = kmalloc(sizeof(*priv), M_NETGRAPH_L2TP,
  		       M_WAITOK | M_NULLOK | M_ZERO);
  	if (priv == NULL)
  		return (ENOMEM);
  	NG_NODE_SET_PRIVATE(node, priv);
  	priv->node = node;
  
  	/* Apply a semi-reasonable default configuration */
  	priv->conf.peer_win = 1;
  	priv->conf.rexmit_max = L2TP_MAX_REXMIT;
  	priv->conf.rexmit_max_to = L2TP_MAX_REXMIT_TO;
  
  	/* Initialize sequence number state */
  	ng_l2tp_seq_init(priv);
  
  	for (i = 0; i < SESSHASHSIZE; i++)
  	    LIST_INIT(&priv->sesshash[i]);
  
  	/* Done */
  	return (0);
  }
  
  /*
   * Give our OK for a hook to be added.
   */
  static int
  ng_l2tp_newhook(node_p node, hook_p hook, const char *name)
  {
  	const priv_p priv = NG_NODE_PRIVATE(node);
  
  	/* Check hook name */
  	if (strcmp(name, NG_L2TP_HOOK_CTRL) == 0) {
  		if (priv->ctrl != NULL)
  			return (EISCONN);
  		priv->ctrl = hook;
  		NG_HOOK_SET_RCVDATA(hook, ng_l2tp_rcvdata_ctrl);
  	} else if (strcmp(name, NG_L2TP_HOOK_LOWER) == 0) {
  		if (priv->lower != NULL)
  			return (EISCONN);
  		priv->lower = hook;
  		NG_HOOK_SET_RCVDATA(hook, ng_l2tp_rcvdata_lower);
  	} else {
  		static const char hexdig[16] = "0123456789abcdef";
  		u_int16_t session_id;
  		hookpriv_p hpriv;
  		uint16_t hash;
  		const char *hex;
  		int i;
  		int j;
  
  		/* Parse hook name to get session ID */
  		if (strncmp(name, NG_L2TP_HOOK_SESSION_P,
  		    sizeof(NG_L2TP_HOOK_SESSION_P) - 1) != 0)
  			return (EINVAL);
  		hex = name + sizeof(NG_L2TP_HOOK_SESSION_P) - 1;
  		for (session_id = i = 0; i < 4; i++) {
  			for (j = 0; j < 16 && hex[i] != hexdig[j]; j++);
  			if (j == 16)
  				return (EINVAL);
  			session_id = (session_id << 4) | j;
  		}
  		if (hex[i] != '\0')
  			return (EINVAL);
  
  		/* Create hook private structure */
  		hpriv = kmalloc(sizeof(*hpriv), M_NETGRAPH_L2TP,
  				M_WAITOK | M_NULLOK | M_ZERO);
  		if (hpriv == NULL)
  			return (ENOMEM);
  		hpriv->conf.session_id = htons(session_id);
  		hpriv->conf.control_dseq = L2TP_CONTROL_DSEQ;
  		hpriv->conf.enable_dseq = L2TP_ENABLE_DSEQ;
  		hpriv->hook = hook;
  		NG_HOOK_SET_PRIVATE(hook, hpriv);
  		hash = SESSHASH(hpriv->conf.session_id);
  		LIST_INSERT_HEAD(&priv->sesshash[hash], hpriv, sessions);
  	}
  
  	/* Done */
  	return (0);
  }
  
  /*
   * Receive a control message.
   */
  static int
  ng_l2tp_rcvmsg(node_p node, item_p item, hook_p lasthook)
  {
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	struct ng_mesg *resp = NULL;
  	struct ng_mesg *msg;
  	int error = 0;
  
  	NGI_GET_MSG(item, msg);
  	switch (msg->header.typecookie) {
  	case NGM_L2TP_COOKIE:
  		switch (msg->header.cmd) {
  		case NGM_L2TP_SET_CONFIG:
  		    {
  			struct ng_l2tp_config *const conf =
  				(struct ng_l2tp_config *)msg->data;
  
  			/* Check for invalid or illegal config */
  			if (msg->header.arglen != sizeof(*conf)) {
  				error = EINVAL;
  				break;
  			}
  			conf->enabled = !!conf->enabled;
  			conf->match_id = !!conf->match_id;
  			conf->tunnel_id = htons(conf->tunnel_id);
  			conf->peer_id = htons(conf->peer_id);
  			if (priv->conf.enabled
  			    && ((priv->conf.tunnel_id != 0
  			       && conf->tunnel_id != priv->conf.tunnel_id)
  			      || ((priv->conf.peer_id != 0
  			       && conf->peer_id != priv->conf.peer_id)))) {
  				error = EBUSY;
  				break;
  			}
  
  			/* Save calling node as failure target */
  			priv->ftarget = NGI_RETADDR(item);
  
  			/* Adjust sequence number state */
  			if ((error = ng_l2tp_seq_adjust(priv, conf)) != 0)
  				break;
  
  			/* Update node's config */
  			priv->conf = *conf;
  			break;
  		    }
  		case NGM_L2TP_GET_CONFIG:
  		    {
  			struct ng_l2tp_config *conf;
  
  			NG_MKRESPONSE(resp, msg, sizeof(*conf), M_WAITOK | M_NULLOK);
  			if (resp == NULL) {
  				error = ENOMEM;
  				break;
  			}
  			conf = (struct ng_l2tp_config *)resp->data;
  			*conf = priv->conf;
  
  			/* Put ID's in host order */
  			conf->tunnel_id = ntohs(conf->tunnel_id);
  			conf->peer_id = ntohs(conf->peer_id);
  			break;
  		    }
  		case NGM_L2TP_SET_SESS_CONFIG:
  		    {
  			struct ng_l2tp_sess_config *const conf =
  			    (struct ng_l2tp_sess_config *)msg->data;
  			hookpriv_p hpriv;
  
  			/* Check for invalid or illegal config. */
  			if (msg->header.arglen != sizeof(*conf)) {
  				error = EINVAL;
  				break;
  			}
  
  			/* Put ID's in network order */
  			conf->session_id = htons(conf->session_id);
  			conf->peer_id = htons(conf->peer_id);
  
  			/* Find matching hook */
  			hpriv = ng_l2tp_find_session(priv, conf->session_id);
  			if (hpriv == NULL) {
  				error = ENOENT;
  				break;
  			}
  
  			/* Update hook's config */
  			hpriv->conf = *conf;
  			break;
  		    }
  		case NGM_L2TP_GET_SESS_CONFIG:
  		    {
  			struct ng_l2tp_sess_config *conf;
  			u_int16_t session_id;
  			hookpriv_p hpriv;
  
  			/* Get session ID */
  			if (msg->header.arglen != sizeof(session_id)) {
  				error = EINVAL;
  				break;
  			}
  			memcpy(&session_id, msg->data, 2);
  			session_id = htons(session_id);
  
  			/* Find matching hook */
  			hpriv = ng_l2tp_find_session(priv, session_id);
  			if (hpriv == NULL) {
  				error = ENOENT;
  				break;
  			}
  
  			/* Send response */
  			NG_MKRESPONSE(resp, msg, sizeof(hpriv->conf), M_WAITOK | M_NULLOK);
  			if (resp == NULL) {
  				error = ENOMEM;
  				break;
  			}
  			conf = (struct ng_l2tp_sess_config *)resp->data;
  			*conf = hpriv->conf;
  
  			/* Put ID's in host order */
  			conf->session_id = ntohs(conf->session_id);
  			conf->peer_id = ntohs(conf->peer_id);
  			break;
  		    }
  		case NGM_L2TP_GET_STATS:
  		case NGM_L2TP_CLR_STATS:
  		case NGM_L2TP_GETCLR_STATS:
  		    {
  			if (msg->header.cmd != NGM_L2TP_CLR_STATS) {
  				NG_MKRESPONSE(resp, msg,
  				    sizeof(priv->stats), M_WAITOK | M_NULLOK);
  				if (resp == NULL) {
  					error = ENOMEM;
  					break;
  				}
  				memcpy(resp->data,
  				    &priv->stats, sizeof(priv->stats));
  			}
  			if (msg->header.cmd != NGM_L2TP_GET_STATS)
  				memset(&priv->stats, 0, sizeof(priv->stats));
  			break;
  		    }
  		case NGM_L2TP_GET_SESSION_STATS:
  		case NGM_L2TP_CLR_SESSION_STATS:
  		case NGM_L2TP_GETCLR_SESSION_STATS:
  		    {
  			uint16_t session_id;
  			hookpriv_p hpriv;
  
  			/* Get session ID. */
  			if (msg->header.arglen != sizeof(session_id)) {
  				error = EINVAL;
  				break;
  			}
  			bcopy(msg->data, &session_id, sizeof(uint16_t));
  			session_id = htons(session_id);
  
  			/* Find matching hook. */
  			hpriv = ng_l2tp_find_session(priv, session_id);
  			if (hpriv == NULL) {
  				error = ENOENT;
  				break;
  			}
  
  			if (msg->header.cmd != NGM_L2TP_CLR_SESSION_STATS) {
  				NG_MKRESPONSE(resp, msg,
  				    sizeof(hpriv->stats), M_WAITOK | M_NULLOK);
  				if (resp == NULL) {
  					error = ENOMEM;
  					break;
  				}
  				bcopy(&hpriv->stats, resp->data,
  					sizeof(hpriv->stats));
  			}
  			if (msg->header.cmd != NGM_L2TP_GET_SESSION_STATS)
  				bzero(&hpriv->stats, sizeof(hpriv->stats));
  			break;
  		    }
  		case NGM_L2TP_SET_SEQ:
  		    {
  			struct ng_l2tp_seq_config *const conf =
  				(struct ng_l2tp_seq_config *)msg->data;
  
  			/* Check for invalid or illegal seq config. */
  			if (msg->header.arglen != sizeof(*conf)) {
  				error = EINVAL;
  				break;
  			}
  			conf->ns = htons(conf->ns);
  			conf->nr = htons(conf->nr);
  			conf->rack = htons(conf->rack);
  			conf->xack = htons(conf->xack);
  
  			/* Set sequence numbers. */
  			error = ng_l2tp_seq_set(priv, conf);
  			break;
  		    }
  		default:
  			error = EINVAL;
  			break;
  		}
  		break;
  	default:
  		error = EINVAL;
  		break;
  	}
  
  	/* Done */
  	NG_RESPOND_MSG(error, node, item, resp);
  	NG_FREE_MSG(msg);
  	return (error);
  }
  
  /*
   * Destroy node
   */
  static int
  ng_l2tp_shutdown(node_p node)
  {
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	struct l2tp_seq *const seq = &priv->seq;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  
  	/* Reset sequence number state */
  	ng_l2tp_seq_reset(priv);
  
  	/* Free private data if neither timer is running */
  	ng_uncallout(&seq->rack_timer, node);
  	ng_uncallout(&seq->xack_timer, node);
  
  	mtx_uninit(&seq->mtx);
  
  	kfree(priv, M_NETGRAPH_L2TP);
  
  	/* Unref node */
  	NG_NODE_UNREF(node);
  	return (0);
  }
  
  /*
   * Hook disconnection
   */
  static int
  ng_l2tp_disconnect(hook_p hook)
  {
  	const node_p node = NG_HOOK_NODE(hook);
  	const priv_p priv = NG_NODE_PRIVATE(node);
  
  	/* Zero out hook pointer */
  	if (hook == priv->ctrl)
  		priv->ctrl = NULL;
  	else if (hook == priv->lower)
  		priv->lower = NULL;
  	else {
  		const hookpriv_p hpriv = NG_HOOK_PRIVATE(hook);
  		LIST_REMOVE(hpriv, sessions);
  		kfree(hpriv, M_NETGRAPH_L2TP);
  		NG_HOOK_SET_PRIVATE(hook, NULL);
  	}
  
  	/* Go away if no longer connected to anything */
  	if (NG_NODE_NUMHOOKS(node) == 0 && NG_NODE_IS_VALID(node))
  		ng_rmnode_self(node);
  	return (0);
  }
  
  /*************************************************************************
  			INTERNAL FUNCTIONS
  *************************************************************************/
  
  /*
   * Find the hook with a given session ID (in network order).
   */
  static hookpriv_p
  ng_l2tp_find_session(priv_p privp, u_int16_t sid)
  {
  	uint16_t	hash = SESSHASH(sid);
  	hookpriv_p	hpriv = NULL;
  
  	LIST_FOREACH(hpriv, &privp->sesshash[hash], sessions) {
  		if (hpriv->conf.session_id == sid)
  			break;
  	}
  
  	return (hpriv);
  }
  
  /*
   * Reset a hook's session state.
   */
  static int
  ng_l2tp_reset_session(hook_p hook, void *arg)
  {
  	const hookpriv_p hpriv = NG_HOOK_PRIVATE(hook);
  
  	if (hpriv != NULL) {
  		hpriv->conf.control_dseq = 0;
  		hpriv->conf.enable_dseq = 0;
  		bzero(&hpriv->conf, sizeof(struct ng_l2tp_session_stats));
  		hpriv->nr = 0;
  		hpriv->ns = 0;
  	}
  	return (-1);
  }
  
  /*
   * Handle an incoming frame from below.
   */
  static int
  ng_l2tp_rcvdata_lower(hook_p h, item_p item)
  {
  	static const u_int16_t req_bits[2][2] = {
  		{ L2TP_DATA_0BITS, L2TP_DATA_1BITS },
  		{ L2TP_CTRL_0BITS, L2TP_CTRL_1BITS },
  	};
  	const node_p node = NG_HOOK_NODE(h);
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	hookpriv_p hpriv = NULL;
  	hook_p hook = NULL;
  	u_int16_t ids[2];
  	struct mbuf *m;
  	u_int16_t hdr;
  	u_int16_t ns;
  	u_int16_t nr;
  	int is_ctrl;
  	int error;
  	int len, plen;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(&priv->seq);
  
  	/* If not configured, reject */
  	if (!priv->conf.enabled) {
  		NG_FREE_ITEM(item);
  		ERROUT(ENXIO);
  	}
  
  	/* Grab mbuf */
  	NGI_GET_M(item, m);
  
  	/* Remember full packet length; needed for per session accounting. */
  	plen = m->m_pkthdr.len;
  
  	/* Update stats */
  	priv->stats.recvPackets++;
  	priv->stats.recvOctets += plen;
  
  	/* Get initial header */
  	if (m->m_pkthdr.len < 6) {
  		priv->stats.recvRunts++;
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(EINVAL);
  	}
  	if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  		priv->stats.memoryFailures++;
  		NG_FREE_ITEM(item);
  		ERROUT(EINVAL);
  	}
  	hdr = ntohs(*mtod(m, u_int16_t *));
  	m_adj(m, 2);
  
  	/* Check required header bits and minimum length */
  	is_ctrl = (hdr & L2TP_HDR_CTRL) != 0;
  	if ((hdr & req_bits[is_ctrl][0]) != 0
  	    || (~hdr & req_bits[is_ctrl][1]) != 0) {
  		priv->stats.recvInvalid++;
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(EINVAL);
  	}
  	if (m->m_pkthdr.len < 4				/* tunnel, session id */
  	    + (2 * ((hdr & L2TP_HDR_LEN) != 0))		/* length field */
  	    + (4 * ((hdr & L2TP_HDR_SEQ) != 0))		/* seq # fields */
  	    + (2 * ((hdr & L2TP_HDR_OFF) != 0))) {	/* offset field */
  		priv->stats.recvRunts++;
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(EINVAL);
  	}
  
  	/* Get and validate length field if present */
  	if ((hdr & L2TP_HDR_LEN) != 0) {
  		if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  			priv->stats.memoryFailures++;
  			NG_FREE_ITEM(item);
  			ERROUT(EINVAL);
  		}
  		len = (u_int16_t)ntohs(*mtod(m, u_int16_t *)) - 4;
  		m_adj(m, 2);
  		if (len < 0 || len > m->m_pkthdr.len) {
  			priv->stats.recvInvalid++;
  			NG_FREE_ITEM(item);
  			NG_FREE_M(m);
  			ERROUT(EINVAL);
  		}
  		if (len < m->m_pkthdr.len)		/* trim extra bytes */
  			m_adj(m, -(m->m_pkthdr.len - len));
  	}
  
  	/* Get tunnel ID and session ID */
  	if (m->m_len < 4 && (m = m_pullup(m, 4)) == NULL) {
  		priv->stats.memoryFailures++;
  		NG_FREE_ITEM(item);
  		ERROUT(EINVAL);
  	}
  	memcpy(ids, mtod(m, u_int16_t *), 4);
  	m_adj(m, 4);
  
  	/* Check tunnel ID */
  	if (ids[0] != priv->conf.tunnel_id
  	    && (priv->conf.match_id || ids[0] != 0)) {
  		priv->stats.recvWrongTunnel++;
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(EADDRNOTAVAIL);
  	}
  
  	/* Check session ID (for data packets only) */
  	if ((hdr & L2TP_HDR_CTRL) == 0) {
  		hpriv = ng_l2tp_find_session(priv, ids[1]);
  		if (hpriv == NULL) {
  			priv->stats.recvUnknownSID++;
  			NG_FREE_ITEM(item);
  			NG_FREE_M(m);
  			ERROUT(ENOTCONN);
  		}
  		hook = hpriv->hook;
  	}
  
  	/* Get Ns, Nr fields if present */
  	if ((hdr & L2TP_HDR_SEQ) != 0) {
  		if (m->m_len < 4 && (m = m_pullup(m, 4)) == NULL) {
  			priv->stats.memoryFailures++;
  			NG_FREE_ITEM(item);
  			ERROUT(EINVAL);
  		}
  		memcpy(&ns, &mtod(m, u_int16_t *)[0], 2);
  		ns = ntohs(ns);
  		memcpy(&nr, &mtod(m, u_int16_t *)[1], 2);
  		nr = ntohs(nr);
  		m_adj(m, 4);
  	}
  
  	/* Strip offset padding if present */
  	if ((hdr & L2TP_HDR_OFF) != 0) {
  		u_int16_t offset;
  
  		/* Get length of offset padding */
  		if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  			priv->stats.memoryFailures++;
  			NG_FREE_ITEM(item);
  			ERROUT(EINVAL);
  		}
  		memcpy(&offset, mtod(m, u_int16_t *), 2);
  		offset = ntohs(offset);
  
  		/* Trim offset padding */
  		if ((2+offset) > m->m_pkthdr.len) {
  			priv->stats.recvInvalid++;
  			NG_FREE_ITEM(item);
  			NG_FREE_M(m);
  			ERROUT(EINVAL);
  		}
  		m_adj(m, 2+offset);
  	}
  
  	/* Handle control packets */
  	if ((hdr & L2TP_HDR_CTRL) != 0) {
  		struct l2tp_seq *const seq = &priv->seq;
  
  		/* Handle receive ack sequence number Nr */
  		ng_l2tp_seq_recv_nr(priv, nr);
  
  		/* Discard ZLB packets */
  		if (m->m_pkthdr.len == 0) {
  			priv->stats.recvZLBs++;
  			NG_FREE_ITEM(item);
  			NG_FREE_M(m);
  			ERROUT(0);
  		}
  
  		mtx_lock(&seq->mtx);
  		/*
  		 * If not what we expect or we are busy, drop packet and
  		 * send an immediate ZLB ack.
  		 */
  		if (ns != seq->nr || seq->inproc) {
  			if (L2TP_SEQ_DIFF(ns, seq->nr) <= 0)
  				priv->stats.recvDuplicates++;
  			else
  				priv->stats.recvOutOfOrder++;
  			mtx_unlock(&seq->mtx);
  			ng_l2tp_xmit_ctrl(priv, NULL, seq->ns);
  			NG_FREE_ITEM(item);
  			NG_FREE_M(m);
  			ERROUT(0);
  		}
  		/*
  		 * Until we deliver this packet we can't receive next one as
  		 * we have no information for sending ack.
  		 */
  		seq->inproc = 1;
  		mtx_unlock(&seq->mtx);
  
  		/* Prepend session ID to packet. */
  		M_PREPEND(m, 2, MB_DONTWAIT);
  		if (m == NULL) {
  			seq->inproc = 0;
  			priv->stats.memoryFailures++;
  			NG_FREE_ITEM(item);
  			ERROUT(ENOBUFS);
  		}
  		memcpy(mtod(m, u_int16_t *), &ids[1], 2);
  
  		/* Deliver packet to upper layers */
  		NG_FWD_NEW_DATA(error, item, priv->ctrl, m);
  		
  		mtx_lock(&seq->mtx);
  		/* Ready to process next packet. */
  		seq->inproc = 0;
  
  		/* If packet was successfully delivered send ack. */
  		if (error == 0) {
  			/* Update recv sequence number */
  			seq->nr++;
  			/* Start receive ack timer, if not already running */
  			if (!callout_active(&seq->xack_timer)) {
  				ng_callout(&seq->xack_timer, priv->node, NULL,
  				    L2TP_DELAYED_ACK, ng_l2tp_seq_xack_timeout,
  				    NULL, 0);
  			}
  		}
  		mtx_unlock(&seq->mtx);
  
  		ERROUT(error);
  	}
  
  	/* Per session packet, account it. */
  	hpriv->stats.recvPackets++;
  	hpriv->stats.recvOctets += plen;
  
  	/* Follow peer's lead in data sequencing, if configured to do so */
  	if (!hpriv->conf.control_dseq)
  		hpriv->conf.enable_dseq = ((hdr & L2TP_HDR_SEQ) != 0);
  
  	/* Handle data sequence numbers if present and enabled */
  	if ((hdr & L2TP_HDR_SEQ) != 0) {
  		if (hpriv->conf.enable_dseq
  		    && L2TP_SEQ_DIFF(ns, hpriv->nr) < 0) {
  			NG_FREE_ITEM(item);	/* duplicate or out of order */
  			NG_FREE_M(m);
  			priv->stats.recvDataDrops++;
  			ERROUT(0);
  		}
  		hpriv->nr = ns + 1;
  	}
  
  	/* Drop empty data packets */
  	if (m->m_pkthdr.len == 0) {
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(0);
  	}
  
  	/* Deliver data */
  	NG_FWD_NEW_DATA(error, item, hook, m);
  done:
  	/* Done */
  	L2TP_SEQ_CHECK(&priv->seq);
  	return (error);
  }
  
  /*
   * Handle an outgoing control frame.
   */
  static int
  ng_l2tp_rcvdata_ctrl(hook_p hook, item_p item)
  {
  	const node_p node = NG_HOOK_NODE(hook);
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	struct l2tp_seq *const seq = &priv->seq;
  	struct mbuf *m;
  	int error;
  	int i;
  	u_int16_t	ns;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(&priv->seq);
  
  	/* If not configured, reject */
  	if (!priv->conf.enabled) {
  		NG_FREE_ITEM(item);
  		ERROUT(ENXIO);
  	}
  
  	/* Grab mbuf and discard other stuff XXX */
  	NGI_GET_M(item, m);
  	NG_FREE_ITEM(item);
  
  	/* Packet should have session ID prepended */
  	if (m->m_pkthdr.len < 2) {
  		priv->stats.xmitInvalid++;
  		m_freem(m);
  		ERROUT(EINVAL);
  	}
  
  	/* Check max length */
  	if (m->m_pkthdr.len >= 0x10000 - 14) {
  		priv->stats.xmitTooBig++;
  		m_freem(m);
  		ERROUT(EOVERFLOW);
  	}
  
  	mtx_lock(&seq->mtx);
  
  	/* Find next empty slot in transmit queue */
  	for (i = 0; i < L2TP_MAX_XWIN && seq->xwin[i] != NULL; i++);
  	if (i == L2TP_MAX_XWIN) {
  		mtx_unlock(&seq->mtx);
  		priv->stats.xmitDrops++;
  		m_freem(m);
  		ERROUT(ENOBUFS);
  	}
  	seq->xwin[i] = m;
  
  	/* If peer's receive window is already full, nothing else to do */
  	if (i >= seq->cwnd) {
  		mtx_unlock(&seq->mtx);
  		ERROUT(0);
  	}
  
  	/* Start retransmit timer if not already running */
  	if (!callout_active(&seq->rack_timer))
  		ng_callout(&seq->rack_timer, node, NULL,
  		    hz, ng_l2tp_seq_rack_timeout, NULL, 0);
  	
  	ns = seq->ns++;
  	
  	mtx_unlock(&seq->mtx);
  
  	/* Copy packet */
  	if ((m = L2TP_COPY_MBUF(m, MB_DONTWAIT)) == NULL) {
  		priv->stats.memoryFailures++;
  		ERROUT(ENOBUFS);
  	}
  
  	/* Send packet and increment xmit sequence number */
  	error = ng_l2tp_xmit_ctrl(priv, m, ns);
  done:
  	/* Done */
  	L2TP_SEQ_CHECK(&priv->seq);
  	return (error);
  }
  
  /*
   * Handle an outgoing data frame.
   */
  static int
  ng_l2tp_rcvdata(hook_p hook, item_p item)
  {
  	const priv_p priv = NG_NODE_PRIVATE(NG_HOOK_NODE(hook));
  	const hookpriv_p hpriv = NG_HOOK_PRIVATE(hook);
  	struct mbuf *m;
  	u_int16_t hdr;
  	int error;
  	int i = 1;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(&priv->seq);
  
  	/* If not configured, reject */
  	if (!priv->conf.enabled) {
  		NG_FREE_ITEM(item);
  		ERROUT(ENXIO);
  	}
  
  	/* Get mbuf */
  	NGI_GET_M(item, m);
  
  	/* Check max length */
  	if (m->m_pkthdr.len >= 0x10000 - 12) {
  		priv->stats.xmitDataTooBig++;
  		NG_FREE_ITEM(item);
  		NG_FREE_M(m);
  		ERROUT(EOVERFLOW);
  	}
  
  	/* Prepend L2TP header */
  	M_PREPEND(m, 6
  	    + (2 * (hpriv->conf.include_length != 0))
  	    + (4 * (hpriv->conf.enable_dseq != 0)),
  	    MB_DONTWAIT);
  	if (m == NULL) {
  		priv->stats.memoryFailures++;
  		NG_FREE_ITEM(item);
  		ERROUT(ENOBUFS);
  	}
  	hdr = L2TP_DATA_HDR;
  	if (hpriv->conf.include_length) {
  		hdr |= L2TP_HDR_LEN;
  		mtod(m, u_int16_t *)[i++] = htons(m->m_pkthdr.len);
  	}
  	mtod(m, u_int16_t *)[i++] = priv->conf.peer_id;
  	mtod(m, u_int16_t *)[i++] = hpriv->conf.peer_id;
  	if (hpriv->conf.enable_dseq) {
  		hdr |= L2TP_HDR_SEQ;
  		mtod(m, u_int16_t *)[i++] = htons(hpriv->ns);
  		mtod(m, u_int16_t *)[i++] = htons(hpriv->nr);
  		hpriv->ns++;
  	}
  	mtod(m, u_int16_t *)[0] = htons(hdr);
  
  	/* Update per session stats. */
  	hpriv->stats.xmitPackets++;
  	hpriv->stats.xmitOctets += m->m_pkthdr.len;
  
  	/* And the global one. */
  	priv->stats.xmitPackets++;
  	priv->stats.xmitOctets += m->m_pkthdr.len;
  
  	/* Send packet */
  	NG_FWD_NEW_DATA(error, item, priv->lower, m);
  done:
  	/* Done */
  	L2TP_SEQ_CHECK(&priv->seq);
  	return (error);
  }
  
  /*
   * Send a message to our controlling node that we've failed.
   */
  static void
  ng_l2tp_seq_failure(priv_p priv)
  {
  	struct ng_mesg *msg;
  	int error;
  
  	NG_MKMESSAGE(msg, NGM_L2TP_COOKIE, NGM_L2TP_ACK_FAILURE, 0, M_WAITOK | M_NULLOK);
  	if (msg == NULL)
  		return;
  	NG_SEND_MSG_ID(error, priv->node, msg, priv->ftarget, 0);
  }
  
  /************************************************************************
  			SEQUENCE NUMBER HANDLING
  ************************************************************************/
  
  /*
   * Initialize sequence number state.
   */
  static void
  ng_l2tp_seq_init(priv_p priv)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  
  	KASSERT(priv->conf.peer_win >= 1,
  	    ("%s: peer_win is zero", __func__));
  	memset(seq, 0, sizeof(*seq));
  	seq->cwnd = 1;
  	seq->wmax = priv->conf.peer_win;
  	if (seq->wmax > L2TP_MAX_XWIN)
  		seq->wmax = L2TP_MAX_XWIN;
  	seq->ssth = seq->wmax;
  	ng_callout_init(&seq->rack_timer);
  	ng_callout_init(&seq->xack_timer);
  	mtx_init(&seq->mtx);
  	L2TP_SEQ_CHECK(seq);
  }
  
  /*
   * Set sequence number state as given from user.
   */
  static int
  ng_l2tp_seq_set(priv_p priv, const struct ng_l2tp_seq_config *conf)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  
  	/* If node is enabled, deny update to sequence numbers. */
  	if (priv->conf.enabled)
  		return (EBUSY);
  
  	/* We only can handle the simple cases. */
  	if (conf->xack != conf->nr || conf->ns != conf->rack)
  		return (EINVAL);
  
  	/* Set ns,nr,rack,xack parameters. */
  	seq->ns = conf->ns;
  	seq->nr = conf->nr;
  	seq->rack = conf->rack;
  	seq->xack = conf->xack;
  
  	return (0);
  }
  
  /*
   * Adjust sequence number state accordingly after reconfiguration.
   */
  static int
  ng_l2tp_seq_adjust(priv_p priv, const struct ng_l2tp_config *conf)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  	u_int16_t new_wmax;
  
  	/* If disabling node, reset state sequence number */
  	if (!conf->enabled) {
  		ng_l2tp_seq_reset(priv);
  		return (0);
  	}
  
  	/* Adjust peer's max recv window; it can only increase */
  	new_wmax = conf->peer_win;
  	if (new_wmax > L2TP_MAX_XWIN)
  		new_wmax = L2TP_MAX_XWIN;
  	if (new_wmax == 0)
  		return (EINVAL);
  	if (new_wmax < seq->wmax)
  		return (EBUSY);
  	seq->wmax = new_wmax;
  
  	/* Done */
  	return (0);
  }
  
  /*
   * Reset sequence number state.
   */
  static void
  ng_l2tp_seq_reset(priv_p priv)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  	hook_p hook;
  	int i;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  
  	/* Stop timers */
  	ng_uncallout(&seq->rack_timer, priv->node);
  	ng_uncallout(&seq->xack_timer, priv->node);
  
  	/* Free retransmit queue */
  	for (i = 0; i < L2TP_MAX_XWIN; i++) {
  		if (seq->xwin[i] == NULL)
  			break;
  		m_freem(seq->xwin[i]);
  	}
  
  	/* Reset session hooks' sequence number states */
  	NG_NODE_FOREACH_HOOK(priv->node, ng_l2tp_reset_session, NULL, hook);
  
  	/* Reset node's sequence number state */
  	seq->ns = 0;
  	seq->nr = 0;
  	seq->rack = 0;
  	seq->xack = 0;
  	seq->wmax = L2TP_MAX_XWIN;
  	seq->cwnd = 1;
  	seq->ssth = seq->wmax;
  	seq->acks = 0;
  	seq->rexmits = 0;
  	bzero(seq->xwin, sizeof(seq->xwin));
  
  	/* Done */
  	L2TP_SEQ_CHECK(seq);
  }
  
  /*
   * Handle receipt of an acknowledgement value (Nr) from peer.
   */
  static void
  ng_l2tp_seq_recv_nr(priv_p priv, u_int16_t nr)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  	struct mbuf	*xwin[L2TP_MAX_XWIN];	/* partial local copy */
  	int		nack;
  	int		i, j;
  	uint16_t	ns;
  
  	mtx_lock(&seq->mtx);
  
  	/* Verify peer's ACK is in range */
  	if ((nack = L2TP_SEQ_DIFF(nr, seq->rack)) <= 0) {
  		mtx_unlock(&seq->mtx);
  		return;				/* duplicate ack */
  	}
  	if (L2TP_SEQ_DIFF(nr, seq->ns) > 0) {
  		mtx_unlock(&seq->mtx);
  		priv->stats.recvBadAcks++;	/* ack for packet not sent */
  		return;
  	}
  	KASSERT(nack <= L2TP_MAX_XWIN,
  	    ("%s: nack=%d > %d", __func__, nack, L2TP_MAX_XWIN));
  
  	/* Update receive ack stats */
  	seq->rack = nr;
  	seq->rexmits = 0;
  
  	/* Free acknowledged packets and shift up packets in the xmit queue */
  	for (i = 0; i < nack; i++)
  		m_freem(seq->xwin[i]);
  	memmove(seq->xwin, seq->xwin + nack,
  	    (L2TP_MAX_XWIN - nack) * sizeof(*seq->xwin));
  	memset(seq->xwin + (L2TP_MAX_XWIN - nack), 0,
  	    nack * sizeof(*seq->xwin));
  
  	/*
  	 * Do slow-start/congestion avoidance windowing algorithm described
  	 * in RFC 2661, Appendix A. Here we handle a multiple ACK as if each
  	 * ACK had arrived separately.
  	 */
  	if (seq->cwnd < seq->wmax) {
  
  		/* Handle slow start phase */
  		if (seq->cwnd < seq->ssth) {
  			seq->cwnd += nack;
  			nack = 0;
  			if (seq->cwnd > seq->ssth) {	/* into cg.av. phase */
  				nack = seq->cwnd - seq->ssth;
  				seq->cwnd = seq->ssth;
  			}
  		}
  
  		/* Handle congestion avoidance phase */
  		if (seq->cwnd >= seq->ssth) {
  			seq->acks += nack;
  			while (seq->acks >= seq->cwnd) {
  				seq->acks -= seq->cwnd;
  				if (seq->cwnd < seq->wmax)
  					seq->cwnd++;
  			}
  		}
  	}
  
  	/* Stop xmit timer */
  	if (callout_active(&seq->rack_timer))
  		ng_uncallout(&seq->rack_timer, priv->node);
  
  	/* If transmit queue is empty, we're done for now */
  	if (seq->xwin[0] == NULL) {
  		mtx_unlock(&seq->mtx);
  		return;
  	}
  
  	/* Start restransmit timer again */
  	ng_callout(&seq->rack_timer, priv->node, NULL,
  	    hz, ng_l2tp_seq_rack_timeout, NULL, 0);
  
  	/*
  	 * Send more packets, trying to keep peer's receive window full.
  	 * Make copy of everything we need before lock release.
  	 */
  	ns = seq->ns;
  	j = 0;
  	while ((i = L2TP_SEQ_DIFF(seq->ns, seq->rack)) < seq->cwnd
  	    && seq->xwin[i] != NULL) {
  		xwin[j++] = seq->xwin[i];
  		seq->ns++;
  	}
  
  	mtx_unlock(&seq->mtx);
  
  	/*
  	 * Send prepared.
  	 * If there is a memory error, pretend packet was sent, as it
  	 * will get retransmitted later anyway.
  	 */
  	for (i = 0; i < j; i++) {
  		struct mbuf 	*m;
  		if ((m = L2TP_COPY_MBUF(xwin[i], MB_DONTWAIT)) == NULL)
  			priv->stats.memoryFailures++;
  		else
  			ng_l2tp_xmit_ctrl(priv, m, ns);
  		ns++;
  	}
  }
  
  /*
   * Handle an ack timeout. We have an outstanding ack that we
   * were hoping to piggy-back, but haven't, so send a ZLB.
   */
  static void
  ng_l2tp_seq_xack_timeout(node_p node, hook_p hook, void *arg1, int arg2)
  {
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	struct l2tp_seq *const seq = &priv->seq;
  
  	/* Make sure callout is still active before doing anything */
  	if (callout_pending(&seq->xack_timer) ||
  	    (!callout_active(&seq->xack_timer)))
  		return;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  
  	/* Send a ZLB */
  	ng_l2tp_xmit_ctrl(priv, NULL, seq->ns);
  
  	/* callout_deactivate() is not needed here 
  	    as ng_uncallout() was called by ng_l2tp_xmit_ctrl() */
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  }
  
  /* 
   * Handle a transmit timeout. The peer has failed to respond
   * with an ack for our packet, so retransmit it.
   */
  static void
  ng_l2tp_seq_rack_timeout(node_p node, hook_p hook, void *arg1, int arg2)
  {
  	const priv_p priv = NG_NODE_PRIVATE(node);
  	struct l2tp_seq *const seq = &priv->seq;
  	struct mbuf *m;
  	u_int delay;
  
  	/* Make sure callout is still active before doing anything */
  	if (callout_pending(&seq->rack_timer) ||
  	    (!callout_active(&seq->rack_timer)))
  		return;
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  
  	priv->stats.xmitRetransmits++;
  
  	/* Have we reached the retransmit limit? If so, notify owner. */
  	if (seq->rexmits++ >= priv->conf.rexmit_max)
  		ng_l2tp_seq_failure(priv);
  
  	/* Restart timer, this time with an increased delay */
  	delay = (seq->rexmits > 12) ? (1 << 12) : (1 << seq->rexmits);
  	if (delay > priv->conf.rexmit_max_to)
  		delay = priv->conf.rexmit_max_to;
  	ng_callout(&seq->rack_timer, node, NULL,
  	    hz * delay, ng_l2tp_seq_rack_timeout, NULL, 0);
  
  	/* Do slow-start/congestion algorithm windowing algorithm */
  	seq->ns = seq->rack;
  	seq->ssth = (seq->cwnd + 1) / 2;
  	seq->cwnd = 1;
  	seq->acks = 0;
  
  	/* Retransmit oldest unack'd packet */
  	if ((m = L2TP_COPY_MBUF(seq->xwin[0], MB_DONTWAIT)) == NULL)
  		priv->stats.memoryFailures++;
  	else
  		ng_l2tp_xmit_ctrl(priv, m, seq->ns++);
  
  	/* callout_deactivate() is not needed here 
  	    as ng_callout() is getting called each time */
  
  	/* Sanity check */
  	L2TP_SEQ_CHECK(seq);
  }
  
  /*
   * Transmit a control stream packet, payload optional.
   * The transmit sequence number is not incremented.
   */
  static int
  ng_l2tp_xmit_ctrl(priv_p priv, struct mbuf *m, u_int16_t ns)
  {
  	struct l2tp_seq *const seq = &priv->seq;
  	u_int16_t session_id = 0;
  	int error;
  
  	mtx_lock(&seq->mtx);
  
  	/* Stop ack timer: we're sending an ack with this packet.
  	   Doing this before to keep state predictable after error. */
  	if (callout_active(&seq->xack_timer))
  		ng_uncallout(&seq->xack_timer, priv->node);
  
  	seq->xack = seq->nr;
  
  	mtx_unlock(&seq->mtx);
  
  	/* If no mbuf passed, send an empty packet (ZLB) */
  	if (m == NULL) {
  
  		/* Create a new mbuf for ZLB packet */
  		MGETHDR(m, MB_DONTWAIT, MT_DATA);
  		if (m == NULL) {
  			priv->stats.memoryFailures++;
  			return (ENOBUFS);
  		}
  		m->m_len = m->m_pkthdr.len = 12;
  		m->m_pkthdr.rcvif = NULL;
  		priv->stats.xmitZLBs++;
  	} else {
  
  		/* Strip off session ID */
  		if (m->m_len < 2 && (m = m_pullup(m, 2)) == NULL) {
  			priv->stats.memoryFailures++;
  			return (ENOBUFS);
  		}
  		memcpy(&session_id, mtod(m, u_int16_t *), 2);
  		m_adj(m, 2);
  
  		/* Make room for L2TP header */
  		M_PREPEND(m, 12, MB_DONTWAIT);
  		if (m == NULL) {
  			priv->stats.memoryFailures++;
  			return (ENOBUFS);
  		}
  	}
  
  	/* Fill in L2TP header */
  	mtod(m, u_int16_t *)[0] = htons(L2TP_CTRL_HDR);
  	mtod(m, u_int16_t *)[1] = htons(m->m_pkthdr.len);
  	mtod(m, u_int16_t *)[2] = priv->conf.peer_id;
  	mtod(m, u_int16_t *)[3] = session_id;
  	mtod(m, u_int16_t *)[4] = htons(ns);
  	mtod(m, u_int16_t *)[5] = htons(seq->nr);
  
  	/* Update sequence number info and stats */
  	priv->stats.xmitPackets++;
  	priv->stats.xmitOctets += m->m_pkthdr.len;
  
  	/* Send packet */
  	NG_SEND_DATA_ONLY(error, priv->lower, m);
  	return (error);
  }
  
  #ifdef INVARIANTS
  /*
   * Sanity check sequence number state.
   */
  static void
  ng_l2tp_seq_check(struct l2tp_seq *seq)
  {
  	int self_unack, peer_unack;
  	int i;
  
  #define CHECK(p)	KASSERT((p), ("%s: not: %s", __func__, #p))
  
  	mtx_lock(&seq->mtx);
  
  	self_unack = L2TP_SEQ_DIFF(seq->nr, seq->xack);
  	peer_unack = L2TP_SEQ_DIFF(seq->ns, seq->rack);
  	CHECK(seq->wmax <= L2TP_MAX_XWIN);
  	CHECK(seq->cwnd >= 1);
  	CHECK(seq->cwnd <= seq->wmax);
  	CHECK(seq->ssth >= 1);
  	CHECK(seq->ssth <= seq->wmax);
  	if (seq->cwnd < seq->ssth)
  		CHECK(seq->acks == 0);
  	else
  		CHECK(seq->acks <= seq->cwnd);
  	CHECK(self_unack >= 0);
  	CHECK(peer_unack >= 0);
  	CHECK(peer_unack <= seq->wmax);
  	CHECK((self_unack == 0) ^ callout_active(&seq->xack_timer));
  	CHECK((peer_unack == 0) ^ callout_active(&seq->rack_timer));
  	for (i = 0; i < peer_unack; i++)
  		CHECK(seq->xwin[i] != NULL);
  	for ( ; i < seq->cwnd; i++)	    /* verify peer's recv window full */
  		CHECK(seq->xwin[i] == NULL);
  
  	mtx_unlock(&seq->mtx);
  
  #undef CHECK
  }
  #endif	/* INVARIANTS */
  