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 #define DRV_NAME        "dummy"
  42 #define DRV_VERSION     "1.0"
  43
  44 static int numdummies = 1;
  45
  46 /* fake multicast ability */
  47 static void set_multicast_list(struct net_device *dev)
  48 {
  49 }
  50
  51 struct pcpu_dstats {
  52         u64                     tx_packets;
  53         u64                     tx_bytes;
  54         struct u64_stats_sync   syncp;
  55 };
  56
  57 static struct rtnl_link_stats64 *dummy_get_stats64(struct net_device *dev,
  58                                                    struct rtnl_link_stats64 *stats)
  59 {
  60         int i;
  61
  62         for_each_possible_cpu(i) {
  63                 const struct pcpu_dstats *dstats;
  64                 u64 tbytes, tpackets;
  65                 unsigned int start;
  66
  67                 dstats = per_cpu_ptr(dev->dstats, i);
  68                 do {
  69                         start = u64_stats_fetch_begin_irq(&dstats->syncp);
  70                         tbytes = dstats->tx_bytes;
  71                         tpackets = dstats->tx_packets;
  72                 } while (u64_stats_fetch_retry_irq(&dstats->syncp, start));
  73                 stats->tx_bytes += tbytes;
  74                 stats->tx_packets += tpackets;
  75         }
  76         return stats;
  77 }
  78
  79 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  80 {
  81         struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);
  82
  83         u64_stats_update_begin(&dstats->syncp);
  84         dstats->tx_packets++;
  85         dstats->tx_bytes += skb->len;
  86         u64_stats_update_end(&dstats->syncp);
  87
  88         dev_kfree_skb(skb);
  89         return NETDEV_TX_OK;
  90 }
  91
  92 static int dummy_dev_init(struct net_device *dev)
  93 {
  94         dev->dstats = netdev_alloc_pcpu_stats(struct pcpu_dstats);
  95         if (!dev->dstats)
  96                 return -ENOMEM;
  97
  98         return 0;
  99 }
 100
 101 static void dummy_dev_uninit(struct net_device *dev)
 102 {
 103         free_percpu(dev->dstats);
 104 }
 105
 106 static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
 107 {
 108         if (new_carrier)
 109                 netif_carrier_on(dev);
 110         else
 111                 netif_carrier_off(dev);
 112         return 0;
 113 }
 114
 115 static const struct net_device_ops dummy_netdev_ops = {
 116         .ndo_init               = dummy_dev_init,
 117         .ndo_uninit             = dummy_dev_uninit,
 118         .ndo_start_xmit         = dummy_xmit,
 119         .ndo_validate_addr      = eth_validate_addr,
 120         .ndo_set_rx_mode        = set_multicast_list,
 121         .ndo_set_mac_address    = eth_mac_addr,
 122         .ndo_get_stats64        = dummy_get_stats64,
 123         .ndo_change_carrier     = dummy_change_carrier,
 124 };
 125
 126 static void dummy_get_drvinfo(struct net_device *dev,
 127                               struct ethtool_drvinfo *info)
 128 {
 129         strlcpy(info->driver, DRV_NAME, sizeof(info->driver));
 130         strlcpy(info->version, DRV_VERSION, sizeof(info->version));
 131 }
 132
 133 static const struct ethtool_ops dummy_ethtool_ops = {
 134         .get_drvinfo            = dummy_get_drvinfo,
 135 };
 136
 137 static void dummy_setup(struct net_device *dev)
 138 {
 139         ether_setup(dev);
 140
 141         /* Initialize the device structure. */
 142         dev->netdev_ops = &dummy_netdev_ops;
 143         dev->ethtool_ops = &dummy_ethtool_ops;
 144         dev->destructor = free_netdev;
 145
 146         /* Fill in device structure with ethernet-generic values. */
 147         dev->tx_queue_len = 0;
 148         dev->flags |= IFF_NOARP;
 149         dev->flags &= ~IFF_MULTICAST;
 150         dev->priv_flags |= IFF_LIVE_ADDR_CHANGE;
 151         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 152         dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 153         eth_hw_addr_random(dev);
 154 }
 155
 156 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 157 {
 158         if (tb[IFLA_ADDRESS]) {
 159                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 160                         return -EINVAL;
 161                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 162                         return -EADDRNOTAVAIL;
 163         }
 164         return 0;
 165 }
 166
 167 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 168         .kind           = DRV_NAME,
 169         .setup          = dummy_setup,
 170         .validate       = dummy_validate,
 171 };
 172
 173 /* Number of dummy devices to be set up by this module. */
 174 module_param(numdummies, int, 0);
 175 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 176
 177 static int __init dummy_init_one(void)
 178 {
 179         struct net_device *dev_dummy;
 180         int err;
 181
 182         dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_UNKNOWN, dummy_setup);
 183         if (!dev_dummy)
 184                 return -ENOMEM;
 185
 186         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 187         err = register_netdevice(dev_dummy);
 188         if (err < 0)
 189                 goto err;
 190         return 0;
 191
 192 err:
 193         free_netdev(dev_dummy);
 194         return err;
 195 }
 196
 197 static int __init dummy_init_module(void)
 198 {
 199         int i, err = 0;
 200
 201         rtnl_lock();
 202         err = __rtnl_link_register(&dummy_link_ops);
 203         if (err < 0)
 204                 goto out;
 205
 206         for (i = 0; i < numdummies && !err; i++) {
 207                 err = dummy_init_one();
 208                 cond_resched();
 209         }
 210         if (err < 0)
 211                 __rtnl_link_unregister(&dummy_link_ops);
 212
 213 out:
 214         rtnl_unlock();
 215
 216         return err;
 217 }
 218
 219 static void __exit dummy_cleanup_module(void)
 220 {
 221         rtnl_link_unregister(&dummy_link_ops);
 222 }
 223
 224 module_init(dummy_init_module);
 225 module_exit(dummy_cleanup_module);
 226 MODULE_LICENSE("GPL");
 227 MODULE_ALIAS_RTNL_LINK(DRV_NAME);
 228 MODULE_VERSION(DRV_VERSION);