LXR linux/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
  40static int numdummies = 1;
  41
  42static 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 */
  54static void set_multicast_list(struct net_device *dev)
  55{
  56}
  57
  58
  59static 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
  68static 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
  75static 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}
  89static 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
 100static 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. */
 107module_param(numdummies, int, 0);
 108MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 109
 110static 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
 129err:
 130        free_netdev(dev_dummy);
 131        return err;
 132}
 133
 134static 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
 150static void __exit dummy_cleanup_module(void)
 151{
 152        rtnl_link_unregister(&dummy_link_ops);
 153}
 154
 155module_init(dummy_init_module);
 156module_exit(dummy_cleanup_module);
 157MODULE_LICENSE("GPL");
 158MODULE_ALIAS_RTNL_LINK("dummy");
 159