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         random_ether_addr(dev->dev_addr);
  75 }
  76
  77 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  78 {
  79         dev->stats.tx_packets++;
  80         dev->stats.tx_bytes += skb->len;
  81
  82         dev_kfree_skb(skb);
  83         return 0;
  84 }
  85
  86 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
  87 {
  88         if (tb[IFLA_ADDRESS]) {
  89                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
  90                         return -EINVAL;
  91                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
  92                         return -EADDRNOTAVAIL;
  93         }
  94         return 0;
  95 }
  96
  97 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
  98         .kind           = "dummy",
  99         .setup          = dummy_setup,
 100         .validate       = dummy_validate,
 101 };
 102
 103 /* Number of dummy devices to be set up by this module. */
 104 module_param(numdummies, int, 0);
 105 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 106
 107 static int __init dummy_init_one(void)
 108 {
 109         struct net_device *dev_dummy;
 110         int err;
 111
 112         dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 113         if (!dev_dummy)
 114                 return -ENOMEM;
 115
 116         err = dev_alloc_name(dev_dummy, dev_dummy->name);
 117         if (err < 0)
 118                 goto err;
 119
 120         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 121         err = register_netdevice(dev_dummy);
 122         if (err < 0)
 123                 goto err;
 124         return 0;
 125
 126 err:
 127         free_netdev(dev_dummy);
 128         return err;
 129 }
 130
 131 static int __init dummy_init_module(void)
 132 {
 133         int i, err = 0;
 134
 135         rtnl_lock();
 136         err = __rtnl_link_register(&dummy_link_ops);
 137
 138         for (i = 0; i < numdummies && !err; i++)
 139                 err = dummy_init_one();
 140         if (err < 0)
 141                 __rtnl_link_unregister(&dummy_link_ops);
 142         rtnl_unlock();
 143
 144         return err;
 145 }
 146
 147 static void __exit dummy_cleanup_module(void)
 148 {
 149         rtnl_link_unregister(&dummy_link_ops);
 150 }
 151
 152 module_init(dummy_init_module);
 153 module_exit(dummy_cleanup_module);
 154 MODULE_LICENSE("GPL");
 155 MODULE_ALIAS_RTNL_LINK("dummy");