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 #include <linux/rtnetlink.h>
  38 #include <net/rtnetlink.h>
  39
  40 static int numdummies = 1;
  41
  42 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
  43
  44 static int dummy_set_address(struct net_device *dev, void *p)
  45 {
  46         struct sockaddr *sa = p;
  47
  48         if (!is_valid_ether_addr(sa->sa_data))
  49                 return -EADDRNOTAVAIL;
  50
  51         memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN);
  52         return 0;
  53 }
  54
  55 /* fake multicast ability */
  56 static void set_multicast_list(struct net_device *dev)
  57 {
  58 }
  59
  60 static void dummy_setup(struct net_device *dev)
  61 {
  62         /* Initialize the device structure. */
  63         dev->hard_start_xmit = dummy_xmit;
  64         dev->set_multicast_list = set_multicast_list;
  65         dev->set_mac_address = dummy_set_address;
  66         dev->destructor = free_netdev;
  67
  68         /* Fill in device structure with ethernet-generic values. */
  69         ether_setup(dev);
  70         dev->tx_queue_len = 0;
  71         dev->change_mtu = NULL;
  72         dev->flags |= IFF_NOARP;
  73         dev->flags &= ~IFF_MULTICAST;
  74         SET_MODULE_OWNER(dev);
  75         random_ether_addr(dev->dev_addr);
  76 }
  77
  78 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  79 {
  80         dev->stats.tx_packets++;
  81         dev->stats.tx_bytes += skb->len;
  82
  83         dev_kfree_skb(skb);
  84         return 0;
  85 }
  86
  87 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
  88 {
  89         if (tb[IFLA_ADDRESS]) {
  90                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
  91                         return -EINVAL;
  92                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
  93                         return -EADDRNOTAVAIL;
  94         }
  95         return 0;
  96 }
  97
  98 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
  99         .kind           = "dummy",
 100         .setup          = dummy_setup,
 101         .validate       = dummy_validate,
 102 };
 103
 104 /* Number of dummy devices to be set up by this module. */
 105 module_param(numdummies, int, 0);
 106 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 107
 108 static int __init dummy_init_one(void)
 109 {
 110         struct net_device *dev_dummy;
 111         int err;
 112
 113         dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 114         if (!dev_dummy)
 115                 return -ENOMEM;
 116
 117         err = dev_alloc_name(dev_dummy, dev_dummy->name);
 118         if (err < 0)
 119                 goto err;
 120
 121         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 122         err = register_netdevice(dev_dummy);
 123         if (err < 0)
 124                 goto err;
 125         return 0;
 126
 127 err:
 128         free_netdev(dev_dummy);
 129         return err;
 130 }
 131
 132 static int __init dummy_init_module(void)
 133 {
 134         int i, err = 0;
 135
 136         rtnl_lock();
 137         err = __rtnl_link_register(&dummy_link_ops);
 138
 139         for (i = 0; i < numdummies && !err; i++)
 140                 err = dummy_init_one();
 141         if (err < 0)
 142                 __rtnl_link_unregister(&dummy_link_ops);
 143         rtnl_unlock();
 144
 145         return err;
 146 }
 147
 148 static void __exit dummy_cleanup_module(void)
 149 {
 150         rtnl_link_unregister(&dummy_link_ops);
 151 }
 152
 153 module_init(dummy_init_module);
 154 module_exit(dummy_cleanup_module);
 155 MODULE_LICENSE("GPL");
 156 MODULE_ALIAS_RTNL_LINK("dummy");