drivers/net/dummy.c

   1 /* dummy.c: a dummy net driver
   2
   3         The purpose of this driver is to provide a device to point a
   4         route through, but not to actually transmit packets.
   5
   6         Why?  If you have a machine whose only connection is an occasional
   7         PPP/SLIP/PLIP link, you can only connect to your own hostname
   8         when the link is up.  Otherwise you have to use localhost.
   9         This isn't very consistent.
  10
  11         One solution is to set up a dummy link using PPP/SLIP/PLIP,
  12         but this seems (to me) too much overhead for too little gain.
  13         This driver provides a small alternative. Thus you can do
  14
  15         [when not running slip]
  16                 ifconfig dummy slip.addr.ess.here up
  17         [to go to slip]
  18                 ifconfig dummy down
  19                 dip whatever
  20
  21         This was written by looking at Donald Becker's skeleton driver
  22         and the loopback driver.  I then threw away anything that didn't
  23         apply!  Thanks to Alan Cox for the key clue on what to do with
  24         misguided packets.
  25
  26                         Nick Holloway, 27th May 1994
  27         [I tweaked this explanation a little but that's all]
  28                         Alan Cox, 30th May 1994
  29 */
  30
  31 /* To have statistics (just packets sent) define this */
  32
  33 #include <linux/config.h>
  34 #include <linux/module.h>
  35 #include <linux/kernel.h>
  36 #include <linux/netdevice.h>
  37 #include <linux/init.h>
  38
  39 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
  40 static struct net_device_stats *dummy_get_stats(struct net_device *dev);
  41
  42 /* fake multicast ability */
  43 static void set_multicast_list(struct net_device *dev)
  44 {
  45 }
  46
  47 #ifdef CONFIG_NET_FASTROUTE
  48 static int dummy_accept_fastpath(struct net_device *dev, struct dst_entry *dst)
  49 {
  50         return -1;
  51 }
  52 #endif
  53
  54 static void __init dummy_setup(struct net_device *dev)
  55 {
  56         /* Initialize the device structure. */
  57         dev->get_stats = dummy_get_stats;
  58         dev->hard_start_xmit = dummy_xmit;
  59         dev->set_multicast_list = set_multicast_list;
  60 #ifdef CONFIG_NET_FASTROUTE
  61         dev->accept_fastpath = dummy_accept_fastpath;
  62 #endif
  63
  64         /* Fill in device structure with ethernet-generic values. */
  65         ether_setup(dev);
  66         dev->tx_queue_len = 0;
  67         dev->flags |= IFF_NOARP;
  68         dev->flags &= ~IFF_MULTICAST;
  69         SET_MODULE_OWNER(dev);
  70 }
  71
  72 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  73 {
  74         struct net_device_stats *stats = dev->priv;
  75
  76         stats->tx_packets++;
  77         stats->tx_bytes+=skb->len;
  78
  79         dev_kfree_skb(skb);
  80         return 0;
  81 }
  82
  83 static struct net_device_stats *dummy_get_stats(struct net_device *dev)
  84 {
  85         return dev->priv;
  86 }
  87
  88 static struct net_device *dev_dummy;
  89
  90 static int __init dummy_init_module(void)
  91 {
  92         int err;
  93
  94         dev_dummy = alloc_netdev(sizeof(struct net_device_stats),
  95                                  "dummy%d", dummy_setup);
  96
  97         if (!dev_dummy)
  98                 return -ENOMEM;
  99
 100         if ((err = register_netdev(dev_dummy))) {
 101                 kfree(dev_dummy);
 102                 dev_dummy = NULL;
 103         }
 104         return err;
 105 }
 106
 107 static void __exit dummy_cleanup_module(void)
 108 {
 109         unregister_netdev(dev_dummy);
 110         kfree(dev_dummy);
 111         dev_dummy = NULL;
 112 }
 113
 114 module_init(dummy_init_module);
 115 module_exit(dummy_cleanup_module);
 116 MODULE_LICENSE("GPL");