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