#ifndef _PPP_CHANNEL_H_
  #define _PPP_CHANNEL_H_
  /*
   * Definitions for the interface between the generic PPP code
   * and a PPP channel.
   *
   * A PPP channel provides a way for the generic PPP code to send
   * and receive packets over some sort of communications medium.
   * Packets are stored in sk_buffs and have the 2-byte PPP protocol
   * number at the start, but not the address and control bytes.
   *
   * Copyright 1999 Paul Mackerras.
   *
   *  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.
   *
   * ==FILEVERSION 20000322==
   */
  
  #include <linux/list.h>
  #include <linux/skbuff.h>
  #include <linux/poll.h>

  #include <net/net_namespace.h>

  
  struct ppp_channel;
  
  struct ppp_channel_ops {
  	/* Send a packet (or multilink fragment) on this channel.
  	   Returns 1 if it was accepted, 0 if not. */
  	int	(*start_xmit)(struct ppp_channel *, struct sk_buff *);
  	/* Handle an ioctl call that has come in via /dev/ppp. */
  	int	(*ioctl)(struct ppp_channel *, unsigned int, unsigned long);
  };
  
  struct ppp_channel {
  	void		*private;	/* channel private data */

  	const struct ppp_channel_ops *ops; /* operations for this channel */

  	int		mtu;		/* max transmit packet size */
  	int		hdrlen;		/* amount of headroom channel needs */
  	void		*ppp;		/* opaque to channel */

  	int		speed;		/* transfer rate (bytes/second) */

  	/* the following is not used at present */

  	int		latency;	/* overhead time in milliseconds */
  };
  
  #ifdef __KERNEL__
  /* Called by the channel when it can send some more data. */
  extern void ppp_output_wakeup(struct ppp_channel *);
  
  /* Called by the channel to process a received PPP packet.
     The packet should have just the 2-byte PPP protocol header. */
  extern void ppp_input(struct ppp_channel *, struct sk_buff *);
  
  /* Called by the channel when an input error occurs, indicating
     that we may have missed a packet. */
  extern void ppp_input_error(struct ppp_channel *, int code);

  /* Attach a channel to a given PPP unit in specified net. */
  extern int ppp_register_net_channel(struct net *, struct ppp_channel *);

  /* Attach a channel to a given PPP unit. */
  extern int ppp_register_channel(struct ppp_channel *);
  
  /* Detach a channel from its PPP unit (e.g. on hangup). */
  extern void ppp_unregister_channel(struct ppp_channel *);
  
  /* Get the channel number for a channel */
  extern int ppp_channel_index(struct ppp_channel *);
  
  /* Get the unit number associated with a channel, or -1 if none */
  extern int ppp_unit_number(struct ppp_channel *);

  /* Get the device name associated with a channel, or NULL if none */
  extern char *ppp_dev_name(struct ppp_channel *);

  /*
   * SMP locking notes:
   * The channel code must ensure that when it calls ppp_unregister_channel,
   * nothing is executing in any of the procedures above, for that
   * channel.  The generic layer will ensure that nothing is executing
   * in the start_xmit and ioctl routines for the channel by the time
   * that ppp_unregister_channel returns.
   */
  
  #endif /* __KERNEL__ */
  #endif