linux/drivers/net/dummy.c
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   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#include <linux/u64_stats_sync.h>
  40
  41static int numdummies = 1;
  42
  43/* fake multicast ability */
  44static void set_multicast_list(struct net_device *dev)
  45{
  46}
  47
  48struct pcpu_dstats {
  49        u64                     tx_packets;
  50        u64                     tx_bytes;
  51        struct u64_stats_sync   syncp;
  52};
  53
  54static struct rtnl_link_stats64 *dummy_get_stats64(struct net_device *dev,
  55                                                   struct rtnl_link_stats64 *stats)
  56{
  57        int i;
  58
  59        for_each_possible_cpu(i) {
  60                const struct pcpu_dstats *dstats;
  61                u64 tbytes, tpackets;
  62                unsigned int start;
  63
  64                dstats = per_cpu_ptr(dev->dstats, i);
  65                do {
  66                        start = u64_stats_fetch_begin_bh(&dstats->syncp);
  67                        tbytes = dstats->tx_bytes;
  68                        tpackets = dstats->tx_packets;
  69                } while (u64_stats_fetch_retry_bh(&dstats->syncp, start));
  70                stats->tx_bytes += tbytes;
  71                stats->tx_packets += tpackets;
  72        }
  73        return stats;
  74}
  75
  76static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  77{
  78        struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);
  79
  80        u64_stats_update_begin(&dstats->syncp);
  81        dstats->tx_packets++;
  82        dstats->tx_bytes += skb->len;
  83        u64_stats_update_end(&dstats->syncp);
  84
  85        dev_kfree_skb(skb);
  86        return NETDEV_TX_OK;
  87}
  88
  89static int dummy_dev_init(struct net_device *dev)
  90{
  91        dev->dstats = alloc_percpu(struct pcpu_dstats);
  92        if (!dev->dstats)
  93                return -ENOMEM;
  94
  95        return 0;
  96}
  97
  98static void dummy_dev_uninit(struct net_device *dev)
  99{
 100        free_percpu(dev->dstats);
 101}
 102
 103static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
 104{
 105        if (new_carrier)
 106                netif_carrier_on(dev);
 107        else
 108                netif_carrier_off(dev);
 109        return 0;
 110}
 111
 112static const struct net_device_ops dummy_netdev_ops = {
 113        .ndo_init               = dummy_dev_init,
 114        .ndo_uninit             = dummy_dev_uninit,
 115        .ndo_start_xmit         = dummy_xmit,
 116        .ndo_validate_addr      = eth_validate_addr,
 117        .ndo_set_rx_mode        = set_multicast_list,
 118        .ndo_set_mac_address    = eth_mac_addr,
 119        .ndo_get_stats64        = dummy_get_stats64,
 120        .ndo_change_carrier     = dummy_change_carrier,
 121};
 122
 123static void dummy_setup(struct net_device *dev)
 124{
 125        ether_setup(dev);
 126
 127        /* Initialize the device structure. */
 128        dev->netdev_ops = &dummy_netdev_ops;
 129        dev->destructor = free_netdev;
 130
 131        /* Fill in device structure with ethernet-generic values. */
 132        dev->tx_queue_len = 0;
 133        dev->flags |= IFF_NOARP;
 134        dev->flags &= ~IFF_MULTICAST;
 135        dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 136        dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 137        dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 138        eth_hw_addr_random(dev);
 139}
 140
 141static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 142{
 143        if (tb[IFLA_ADDRESS]) {
 144                if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 145                        return -EINVAL;
 146                if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 147                        return -EADDRNOTAVAIL;
 148        }
 149        return 0;
 150}
 151
 152static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 153        .kind           = "dummy",
 154        .setup          = dummy_setup,
 155        .validate       = dummy_validate,
 156};
 157
 158/* Number of dummy devices to be set up by this module. */
 159module_param(numdummies, int, 0);
 160MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 161
 162static int __init dummy_init_one(void)
 163{
 164        struct net_device *dev_dummy;
 165        int err;
 166
 167        dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 168        if (!dev_dummy)
 169                return -ENOMEM;
 170
 171        dev_dummy->rtnl_link_ops = &dummy_link_ops;
 172        err = register_netdevice(dev_dummy);
 173        if (err < 0)
 174                goto err;
 175        return 0;
 176
 177err:
 178        free_netdev(dev_dummy);
 179        return err;
 180}
 181
 182static int __init dummy_init_module(void)
 183{
 184        int i, err = 0;
 185
 186        rtnl_lock();
 187        err = __rtnl_link_register(&dummy_link_ops);
 188
 189        for (i = 0; i < numdummies && !err; i++) {
 190                err = dummy_init_one();
 191                cond_resched();
 192        }
 193        if (err < 0)
 194                __rtnl_link_unregister(&dummy_link_ops);
 195        rtnl_unlock();
 196
 197        return err;
 198}
 199
 200static void __exit dummy_cleanup_module(void)
 201{
 202        rtnl_link_unregister(&dummy_link_ops);
 203}
 204
 205module_init(dummy_init_module);
 206module_exit(dummy_cleanup_module);
 207MODULE_LICENSE("GPL");
 208MODULE_ALIAS_RTNL_LINK("dummy");
 209
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