text: 
  /*
   * ng_UI.c
   *
   * Copyright (c) 1996-1999 Whistle Communications, Inc.
   * 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 Whistle Communications;
   * provided, however, that:
   * 1. Any and all reproductions of the source or object code must include the
   *    copyright notice above and the following disclaimer of warranties; and
   * 2. No rights are granted, in any manner or form, to use Whistle
   *    Communications, Inc. trademarks, including the mark "WHISTLE
   *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
   *    such appears in the above copyright notice or in the software.
   * 
   * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
   * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS 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.
   * WHISTLE COMMUNICATIONS 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 WHISTLE COMMUNICATIONS 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 WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
   * OF SUCH DAMAGE.
   *
   * Author: Julian Elischer <julian@freebsd.org>
   *
   * $FreeBSD: src/sys/netgraph/ng_UI.c,v 1.6.2.2 2000/10/24 18:36:44 julian Exp $
   * $Whistle: ng_UI.c,v 1.14 1999/11/01 09:24:51 julian Exp $
   */
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/errno.h>
  #include <sys/kernel.h>
  #include <sys/malloc.h>
  #include <sys/mbuf.h>
  
  #include <netgraph/ng_message.h>
  #include <netgraph/netgraph.h>
  #include "ng_UI.h"
  
  /*
   * DEFINITIONS
   */
  
  /* Everything, starting with sdlc on has defined UI as 0x03 */
  #define HDLC_UI	0x03
  
  /* Node private data */
  struct ng_UI_private {
  	hook_p  downlink;
  	hook_p  uplink;
  };
  typedef struct ng_UI_private *priv_p;
  
  /* Netgraph node methods */
  static ng_constructor_t	ng_UI_constructor;
  static ng_rcvmsg_t	ng_UI_rcvmsg;
  static ng_shutdown_t	ng_UI_rmnode;
  static ng_newhook_t	ng_UI_newhook;
  static ng_rcvdata_t	ng_UI_rcvdata;
  static ng_disconnect_t	ng_UI_disconnect;
  
  /* Node type descriptor */
  static struct ng_type typestruct = {
  	NG_VERSION,
  	NG_UI_NODE_TYPE,
  	NULL,
  	ng_UI_constructor,
  	ng_UI_rcvmsg,
  	ng_UI_rmnode,
  	ng_UI_newhook,
  	NULL,
  	NULL,
  	ng_UI_rcvdata,
  	ng_UI_rcvdata,
  	ng_UI_disconnect,
  	NULL
  };
  NETGRAPH_INIT(UI, &typestruct);
  
  /************************************************************************
  			NETGRAPH NODE STUFF
   ************************************************************************/
  
  /*
   * Create a newborn node. We start with an implicit reference.
   */
  
  static int
  ng_UI_constructor(node_p *nodep)
  {
  	priv_p  priv;
  	int     error;
  
  	/* Allocate private structure */
  	priv = kmalloc(sizeof(*priv), M_NETGRAPH, M_NOWAIT | M_ZERO);
  	if (priv == NULL)
  		return (ENOMEM);
  
  	/* Call generic node constructor */
  	if ((error = ng_make_node_common(&typestruct, nodep))) {
  		kfree(priv, M_NETGRAPH);
  		return (error);
  	}
  	(*nodep)->private = priv;
  
  	/* Done */
  	return (0);
  }
  
  /*
   * Give our ok for a hook to be added
   */
  static int
  ng_UI_newhook(node_p node, hook_p hook, const char *name)
  {
  	const priv_p priv = node->private;
  
  	if (!strcmp(name, NG_UI_HOOK_DOWNSTREAM)) {
  		if (priv->downlink)
  			return (EISCONN);
  		priv->downlink = hook;
  	} else if (!strcmp(name, NG_UI_HOOK_UPSTREAM)) {
  		if (priv->uplink)
  			return (EISCONN);
  		priv->uplink = hook;
  	} else
  		return (EINVAL);
  	return (0);
  }
  
  /*
   * Receive a control message
   */
  static int
  ng_UI_rcvmsg(node_p node, struct ng_mesg *msg,
  	     const char *raddr, struct ng_mesg **rp)
  {
  	kfree(msg, M_NETGRAPH);
  	return (EINVAL);
  }
  
  #define MAX_ENCAPS_HDR	1
  #define ERROUT(x)	do { error = (x); goto done; } while (0)
  
  /*
   * Receive a data frame
   */
  static int
  ng_UI_rcvdata(hook_p hook, struct mbuf *m, meta_p meta)
  {
  	const node_p node = hook->node;
  	const priv_p priv = node->private;
  	int error = 0;
  
  	if (hook == priv->downlink) {
  		u_char *start, *ptr;
  
  		if (!m || (m->m_len < MAX_ENCAPS_HDR
  		    && !(m = m_pullup(m, MAX_ENCAPS_HDR))))
  			ERROUT(ENOBUFS);
  		ptr = start = mtod(m, u_char *);
  
  		/* Must be UI frame */
  		if (*ptr++ != HDLC_UI)
  			ERROUT(0);
  
  		m_adj(m, ptr - start);
  		NG_SEND_DATA(error, priv->uplink, m, meta);	/* m -> NULL */
  	} else if (hook == priv->uplink) {
  		M_PREPEND(m, 1, M_NOWAIT);	/* Prepend IP NLPID */
  		if (!m)
  			ERROUT(ENOBUFS);
  		mtod(m, u_char *)[0] = HDLC_UI;
  		NG_SEND_DATA(error, priv->downlink, m, meta);	/* m -> NULL */
  	} else
  		panic(__func__);
  
  done:
  	NG_FREE_DATA(m, meta);	/* does nothing if m == NULL */
  	return (error);
  }
  
  /*
   * Shutdown node
   */
  static int
  ng_UI_rmnode(node_p node)
  {
  	const priv_p priv = node->private;
  
  	/* Take down netgraph node */
  	node->flags |= NG_INVALID;
  	ng_cutlinks(node);
  	ng_unname(node);
  	bzero(priv, sizeof(*priv));
  	kfree(priv, M_NETGRAPH);
  	node->private = NULL;
  	ng_unref(node);
  	return (0);
  }
  
  /*
   * Hook disconnection
   */
  static int
  ng_UI_disconnect(hook_p hook)
  {
  	const priv_p priv = hook->node->private;
  
  	if (hook->node->numhooks == 0)
  		ng_rmnode(hook->node);
  	else if (hook == priv->downlink)
  		priv->downlink = NULL;
  	else if (hook == priv->uplink)
  		priv->uplink = NULL;
  	else
  		panic(__func__);
  	return (0);
  }
  
  