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 static int dummy_set_address(struct net_device *dev, void *p)
  44 {
  45         struct sockaddr *sa = p;
  46
  47         if (!is_valid_ether_addr(sa->sa_data))
  48                 return -EADDRNOTAVAIL;
  49
  50         memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN);
  51         return 0;
  52 }
  53
  54 /* fake multicast ability */
  55 static void set_multicast_list(struct net_device *dev)
  56 {
  57 }
  58
  59 struct pcpu_dstats {
  60         u64                     tx_packets;
  61         u64                     tx_bytes;
  62         struct u64_stats_sync   syncp;
  63 };
  64
  65 static struct rtnl_link_stats64 *dummy_get_stats64(struct net_device *dev,
  66                                                    struct rtnl_link_stats64 *stats)
  67 {
  68         int i;
  69
  70         for_each_possible_cpu(i) {
  71                 const struct pcpu_dstats *dstats;
  72                 u64 tbytes, tpackets;
  73                 unsigned int start;
  74
  75                 dstats = per_cpu_ptr(dev->dstats, i);
  76                 do {
  77                         start = u64_stats_fetch_begin(&dstats->syncp);
  78                         tbytes = dstats->tx_bytes;
  79                         tpackets = dstats->tx_packets;
  80                 } while (u64_stats_fetch_retry(&dstats->syncp, start));
  81                 stats->tx_bytes += tbytes;
  82                 stats->tx_packets += tpackets;
  83         }
  84         return stats;
  85 }
  86
  87 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  88 {
  89         struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);
  90
  91         u64_stats_update_begin(&dstats->syncp);
  92         dstats->tx_packets++;
  93         dstats->tx_bytes += skb->len;
  94         u64_stats_update_end(&dstats->syncp);
  95
  96         dev_kfree_skb(skb);
  97         return NETDEV_TX_OK;
  98 }
  99
 100 static int dummy_dev_init(struct net_device *dev)
 101 {
 102         dev->dstats = alloc_percpu(struct pcpu_dstats);
 103         if (!dev->dstats)
 104                 return -ENOMEM;
 105
 106         return 0;
 107 }
 108
 109 static void dummy_dev_free(struct net_device *dev)
 110 {
 111         free_percpu(dev->dstats);
 112         free_netdev(dev);
 113 }
 114
 115 static const struct net_device_ops dummy_netdev_ops = {
 116         .ndo_init               = dummy_dev_init,
 117         .ndo_start_xmit         = dummy_xmit,
 118         .ndo_validate_addr      = eth_validate_addr,
 119         .ndo_set_multicast_list = set_multicast_list,
 120         .ndo_set_mac_address    = dummy_set_address,
 121         .ndo_get_stats64        = dummy_get_stats64,
 122 };
 123
 124 static void dummy_setup(struct net_device *dev)
 125 {
 126         ether_setup(dev);
 127
 128         /* Initialize the device structure. */
 129         dev->netdev_ops = &dummy_netdev_ops;
 130         dev->destructor = dummy_dev_free;
 131
 132         /* Fill in device structure with ethernet-generic values. */
 133         dev->tx_queue_len = 0;
 134         dev->flags |= IFF_NOARP;
 135         dev->flags &= ~IFF_MULTICAST;
 136         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 137         dev->features   |= NETIF_F_NO_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 138         random_ether_addr(dev->dev_addr);
 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         err = dev_alloc_name(dev_dummy, dev_dummy->name);
 172         if (err < 0)
 173                 goto err;
 174
 175         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 176         err = register_netdevice(dev_dummy);
 177         if (err < 0)
 178                 goto err;
 179         return 0;
 180
 181 err:
 182         free_netdev(dev_dummy);
 183         return err;
 184 }
 185
 186 static int __init dummy_init_module(void)
 187 {
 188         int i, err = 0;
 189
 190         rtnl_lock();
 191         err = __rtnl_link_register(&dummy_link_ops);
 192
 193         for (i = 0; i < numdummies && !err; i++)
 194                 err = dummy_init_one();
 195         if (err < 0)
 196                 __rtnl_link_unregister(&dummy_link_ops);
 197         rtnl_unlock();
 198
 199         return err;
 200 }
 201
 202 static void __exit dummy_cleanup_module(void)
 203 {
 204         rtnl_link_unregister(&dummy_link_ops);
 205 }
 206
 207 module_init(dummy_init_module);
 208 module_exit(dummy_cleanup_module);
 209 MODULE_LICENSE("GPL");
 210 MODULE_ALIAS_RTNL_LINK("dummy");