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 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
 113 static 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
 131 static 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
 142 static 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. */
 149 module_param(numdummies, int, 0);
 150 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 151
 152 static 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
 167 err:
 168         free_netdev(dev_dummy);
 169         return err;
 170 }
 171
 172 static 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
 190 static void __exit dummy_cleanup_module(void)
 191 {
 192         rtnl_link_unregister(&dummy_link_ops);
 193 }
 194
 195 module_init(dummy_init_module);
 196 module_exit(dummy_cleanup_module);
 197 MODULE_LICENSE("GPL");
 198 MODULE_ALIAS_RTNL_LINK("dummy");