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 #include <linux/u64_stats_sync.h>
  40
  41 static int numdummies = 1;
  42
  43 /* fake multicast ability */
  44 static void set_multicast_list(struct net_device *dev)
  45 {
  46 }
  47
  48 struct pcpu_dstats {
  49         u64                     tx_packets;
  50         u64                     tx_bytes;
  51         struct u64_stats_sync   syncp;
  52 };
  53
  54 static 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
  76 static 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
  89 static 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
  98 static void dummy_dev_uninit(struct net_device *dev)
  99 {
 100         free_percpu(dev->dstats);
 101 }
 102
 103 static 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
 112 static 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
 123 static 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
 141 static 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
 152 static 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. */
 159 module_param(numdummies, int, 0);
 160 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 161
 162 static 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
 177 err:
 178         free_netdev(dev_dummy);
 179         return err;
 180 }
 181
 182 static 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         if (err < 0)
 189                 goto out;
 190
 191         for (i = 0; i < numdummies && !err; i++) {
 192                 err = dummy_init_one();
 193                 cond_resched();
 194         }
 195         if (err < 0)
 196                 __rtnl_link_unregister(&dummy_link_ops);
 197
 198 out:
 199         rtnl_unlock();
 200
 201         return err;
 202 }
 203
 204 static void __exit dummy_cleanup_module(void)
 205 {
 206         rtnl_link_unregister(&dummy_link_ops);
 207 }
 208
 209 module_init(dummy_init_module);
 210 module_exit(dummy_cleanup_module);
 211 MODULE_LICENSE("GPL");
 212 MODULE_ALIAS_RTNL_LINK("dummy");