/* dummy.c: a dummy net driver
      
      	The purpose of this driver is to provide a device to point a
      	route through, but not to actually transmit packets.
      
      	Why?  If you have a machine whose only connection is an occasional
      	PPP/SLIP/PLIP link, you can only connect to your own hostname
      	when the link is up.  Otherwise you have to use localhost.
      	This isn't very consistent.
      
      	One solution is to set up a dummy link using PPP/SLIP/PLIP,
      	but this seems (to me) too much overhead for too little gain.
      	This driver provides a small alternative. Thus you can do
      	
      	[when not running slip]
      		ifconfig dummy slip.addr.ess.here up
      	[to go to slip]
      		ifconfig dummy down
      		dip whatever
      
      	This was written by looking at Donald Becker's skeleton driver
      	and the loopback driver.  I then threw away anything that didn't
      	apply!	Thanks to Alan Cox for the key clue on what to do with
      	misguided packets.
      
      			Nick Holloway, 27th May 1994
      	[I tweaked this explanation a little but that's all]
      			Alan Cox, 30th May 1994
      */
      
      /* To have statistics (just packets sent) define this */
      
      #include <linux/config.h>
      #include <linux/module.h>
      #include <linux/kernel.h>
      #include <linux/netdevice.h>
      #include <linux/init.h>
      
      static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
      static struct net_device_stats *dummy_get_stats(struct net_device *dev);
      
      /* fake multicast ability */
  43  static void set_multicast_list(struct net_device *dev)
      {
      }
      
      #ifdef CONFIG_NET_FASTROUTE
      static int dummy_accept_fastpath(struct net_device *dev, struct dst_entry *dst)
      {
      	return -1;
      }
      #endif
      
  54  static int __init dummy_init(struct net_device *dev)
      {
      	/* Initialize the device structure. */
      	dev->hard_start_xmit	= dummy_xmit;
      
      	dev->priv = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
  60  	if (dev->priv == NULL)
  61  		return -ENOMEM;
      	memset(dev->priv, 0, sizeof(struct net_device_stats));
      	dev->get_stats	= dummy_get_stats;
      
      	dev->set_multicast_list = set_multicast_list;
      
      	/* Fill in the fields of the device structure with ethernet-generic values. */
      	ether_setup(dev);
      	dev->tx_queue_len = 0;
      	dev->flags |= IFF_NOARP;
      	dev->flags &= ~IFF_MULTICAST;
      #ifdef CONFIG_NET_FASTROUTE
      	dev->accept_fastpath = dummy_accept_fastpath;
      #endif
      
  76  	return 0;
      }
      
  79  static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
      {
      	struct net_device_stats *stats;
      
      	stats = (struct net_device_stats *)dev->priv;
      	stats->tx_packets++;
      	stats->tx_bytes+=skb->len;
      
      	dev_kfree_skb(skb);
  88  	return 0;
      }
      
  91  static struct net_device_stats *dummy_get_stats(struct net_device *dev)
      {
  93  	return dev->priv;
      }
      
      static struct net_device dev_dummy;
      
  98  static int __init dummy_init_module(void)
      {
      	int err;
      
      	dev_dummy.init = dummy_init;
 103  	SET_MODULE_OWNER(&dev_dummy);
      
      	/* Find a name for this unit */
      	err=dev_alloc_name(&dev_dummy,"dummy%d");
 107  	if(err<0)
 108  		return err;
 109  	if (register_netdev(&dev_dummy) != 0)
 110  		return -EIO;
 111  	return 0;
      }
      
 114  static void __exit dummy_cleanup_module(void)
      {
      	unregister_netdev(&dev_dummy);
      	kfree(dev_dummy.priv);
      
      	memset(&dev_dummy, 0, sizeof(dev_dummy));
      	dev_dummy.init = dummy_init;
      }
      
      module_init(dummy_init_module);
      module_exit(dummy_cleanup_module);