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 const struct net_device_ops dummy_netdev_ops = {
 104        .ndo_init               = dummy_dev_init,
 105        .ndo_uninit             = dummy_dev_uninit,
 106        .ndo_start_xmit         = dummy_xmit,
 107        .ndo_validate_addr      = eth_validate_addr,
 108        .ndo_set_rx_mode        = set_multicast_list,
 109        .ndo_set_mac_address    = eth_mac_addr,
 110        .ndo_get_stats64        = dummy_get_stats64,
 111};
 112
 113static void dummy_setup(struct net_device *dev)
 114{
 115        ether_setup(dev);
 116
 117        /* Initialize the device structure. */
 118        dev->netdev_ops = &dummy_netdev_ops;
 119        dev->destructor = free_netdev;
 120
 121        /* Fill in device structure with ethernet-generic values. */
 122        dev->tx_queue_len = 0;
 123        dev->flags |= IFF_NOARP;
 124        dev->flags &= ~IFF_MULTICAST;
 125        dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 126        dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 127        dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 128        eth_hw_addr_random(dev);
 129}
 130
 131static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 132{
 133        if (tb[IFLA_ADDRESS]) {
 134                if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 135                        return -EINVAL;
 136                if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 137                        return -EADDRNOTAVAIL;
 138        }
 139        return 0;
 140}
 141
 142static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 143        .kind           = "dummy",
 144        .setup          = dummy_setup,
 145        .validate       = dummy_validate,
 146};
 147
 148/* Number of dummy devices to be set up by this module. */
 149module_param(numdummies, int, 0);
 150MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 151
 152static int __init dummy_init_one(void)
 153{
 154        struct net_device *dev_dummy;
 155        int err;
 156
 157        dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 158        if (!dev_dummy)
 159                return -ENOMEM;
 160
 161        dev_dummy->rtnl_link_ops = &dummy_link_ops;
 162        err = register_netdevice(dev_dummy);
 163        if (err < 0)
 164                goto err;
 165        return 0;
 166
 167err:
 168        free_netdev(dev_dummy);
 169        return err;
 170}
 171
 172static int __init dummy_init_module(void)
 173{
 174        int i, err = 0;
 175
 176        rtnl_lock();
 177        err = __rtnl_link_register(&dummy_link_ops);
 178
 179        for (i = 0; i < numdummies && !err; i++) {
 180                err = dummy_init_one();
 181                cond_resched();
 182        }
 183        if (err < 0)
 184                __rtnl_link_unregister(&dummy_link_ops);
 185        rtnl_unlock();
 186
 187        return err;
 188}
 189
 190static void __exit dummy_cleanup_module(void)
 191{
 192        rtnl_link_unregister(&dummy_link_ops);
 193}
 194
 195module_init(dummy_init_module);
 196module_exit(dummy_cleanup_module);
 197MODULE_LICENSE("GPL");
 198MODULE_ALIAS_RTNL_LINK("dummy");
 199
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