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         int i;
  92         dev->dstats = alloc_percpu(struct pcpu_dstats);
  93         if (!dev->dstats)
  94                 return -ENOMEM;
  95
  96         for_each_possible_cpu(i) {
  97                 struct pcpu_dstats *dstats;
  98                 dstats = per_cpu_ptr(dev->dstats, i);
  99                 u64_stats_init(&dstats->syncp);
 100         }
 101         return 0;
 102 }
 103
 104 static void dummy_dev_uninit(struct net_device *dev)
 105 {
 106         free_percpu(dev->dstats);
 107 }
 108
 109 static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
 110 {
 111         if (new_carrier)
 112                 netif_carrier_on(dev);
 113         else
 114                 netif_carrier_off(dev);
 115         return 0;
 116 }
 117
 118 static const struct net_device_ops dummy_netdev_ops = {
 119         .ndo_init               = dummy_dev_init,
 120         .ndo_uninit             = dummy_dev_uninit,
 121         .ndo_start_xmit         = dummy_xmit,
 122         .ndo_validate_addr      = eth_validate_addr,
 123         .ndo_set_rx_mode        = set_multicast_list,
 124         .ndo_set_mac_address    = eth_mac_addr,
 125         .ndo_get_stats64        = dummy_get_stats64,
 126         .ndo_change_carrier     = dummy_change_carrier,
 127 };
 128
 129 static void dummy_setup(struct net_device *dev)
 130 {
 131         ether_setup(dev);
 132
 133         /* Initialize the device structure. */
 134         dev->netdev_ops = &dummy_netdev_ops;
 135         dev->destructor = free_netdev;
 136
 137         /* Fill in device structure with ethernet-generic values. */
 138         dev->tx_queue_len = 0;
 139         dev->flags |= IFF_NOARP;
 140         dev->flags &= ~IFF_MULTICAST;
 141         dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 142         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 143         dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 144         eth_hw_addr_random(dev);
 145 }
 146
 147 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 148 {
 149         if (tb[IFLA_ADDRESS]) {
 150                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 151                         return -EINVAL;
 152                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 153                         return -EADDRNOTAVAIL;
 154         }
 155         return 0;
 156 }
 157
 158 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 159         .kind           = "dummy",
 160         .setup          = dummy_setup,
 161         .validate       = dummy_validate,
 162 };
 163
 164 /* Number of dummy devices to be set up by this module. */
 165 module_param(numdummies, int, 0);
 166 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 167
 168 static int __init dummy_init_one(void)
 169 {
 170         struct net_device *dev_dummy;
 171         int err;
 172
 173         dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 174         if (!dev_dummy)
 175                 return -ENOMEM;
 176
 177         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 178         err = register_netdevice(dev_dummy);
 179         if (err < 0)
 180                 goto err;
 181         return 0;
 182
 183 err:
 184         free_netdev(dev_dummy);
 185         return err;
 186 }
 187
 188 static int __init dummy_init_module(void)
 189 {
 190         int i, err = 0;
 191
 192         rtnl_lock();
 193         err = __rtnl_link_register(&dummy_link_ops);
 194         if (err < 0)
 195                 goto out;
 196
 197         for (i = 0; i < numdummies && !err; i++) {
 198                 err = dummy_init_one();
 199                 cond_resched();
 200         }
 201         if (err < 0)
 202                 __rtnl_link_unregister(&dummy_link_ops);
 203
 204 out:
 205         rtnl_unlock();
 206
 207         return err;
 208 }
 209
 210 static void __exit dummy_cleanup_module(void)
 211 {
 212         rtnl_link_unregister(&dummy_link_ops);
 213 }
 214
 215 module_init(dummy_init_module);
 216 module_exit(dummy_cleanup_module);
 217 MODULE_LICENSE("GPL");
 218 MODULE_ALIAS_RTNL_LINK("dummy");