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 #include <linux/module.h>
  32 #include <linux/kernel.h>
  33 #include <linux/netdevice.h>
  34 #include <linux/etherdevice.h>
  35 #include <linux/init.h>
  36 #include <linux/moduleparam.h>
  37
  38 static int numdummies = 1;
  39
  40 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
  41 static struct net_device_stats *dummy_get_stats(struct net_device *dev);
  42
  43 static int dummy_set_address(struct net_device *dev, void *p)
  44 {
  45         struct sockaddr *sa = p;
  46
  47         if (!is_valid_ether_addr(sa->sa_data))
  48                 return -EADDRNOTAVAIL;
  49
  50         memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN);
  51         return 0;
  52 }
  53
  54 /* fake multicast ability */
  55 static void set_multicast_list(struct net_device *dev)
  56 {
  57 }
  58
  59 static void __init dummy_setup(struct net_device *dev)
  60 {
  61         /* Initialize the device structure. */
  62         dev->get_stats = dummy_get_stats;
  63         dev->hard_start_xmit = dummy_xmit;
  64         dev->set_multicast_list = set_multicast_list;
  65         dev->set_mac_address = dummy_set_address;
  66
  67         /* Fill in device structure with ethernet-generic values. */
  68         ether_setup(dev);
  69         dev->tx_queue_len = 0;
  70         dev->change_mtu = NULL;
  71         dev->flags |= IFF_NOARP;
  72         dev->flags &= ~IFF_MULTICAST;
  73         SET_MODULE_OWNER(dev);
  74         random_ether_addr(dev->dev_addr);
  75 }
  76
  77 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  78 {
  79         struct net_device_stats *stats = netdev_priv(dev);
  80
  81         stats->tx_packets++;
  82         stats->tx_bytes+=skb->len;
  83
  84         dev_kfree_skb(skb);
  85         return 0;
  86 }
  87
  88 static struct net_device_stats *dummy_get_stats(struct net_device *dev)
  89 {
  90         return netdev_priv(dev);
  91 }
  92
  93 static struct net_device **dummies;
  94
  95 /* Number of dummy devices to be set up by this module. */
  96 module_param(numdummies, int, 0);
  97 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
  98
  99 static int __init dummy_init_one(int index)
 100 {
 101         struct net_device *dev_dummy;
 102         int err;
 103
 104         dev_dummy = alloc_netdev(sizeof(struct net_device_stats),
 105                                  "dummy%d", dummy_setup);
 106
 107         if (!dev_dummy)
 108                 return -ENOMEM;
 109
 110         if ((err = register_netdev(dev_dummy))) {
 111                 free_netdev(dev_dummy);
 112                 dev_dummy = NULL;
 113         } else {
 114                 dummies[index] = dev_dummy;
 115         }
 116
 117         return err;
 118 }
 119
 120 static void dummy_free_one(int index)
 121 {
 122         unregister_netdev(dummies[index]);
 123         free_netdev(dummies[index]);
 124 }
 125
 126 static int __init dummy_init_module(void)
 127 {
 128         int i, err = 0;
 129         dummies = kmalloc(numdummies * sizeof(void *), GFP_KERNEL);
 130         if (!dummies)
 131                 return -ENOMEM;
 132         for (i = 0; i < numdummies && !err; i++)
 133                 err = dummy_init_one(i);
 134         if (err) {
 135                 i--;
 136                 while (--i >= 0)
 137                         dummy_free_one(i);
 138         }
 139         return err;
 140 }
 141
 142 static void __exit dummy_cleanup_module(void)
 143 {
 144         int i;
 145         for (i = 0; i < numdummies; i++)
 146                 dummy_free_one(i);
 147         kfree(dummies);
 148 }
 149
 150 module_init(dummy_init_module);
 151 module_exit(dummy_cleanup_module);
 152 MODULE_LICENSE("GPL");