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->flags |= IFF_NOARP;
 148         dev->flags &= ~IFF_MULTICAST;
 149         dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
 150         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 151         dev->features   |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 152         eth_hw_addr_random(dev);
 153 }
 154
 155 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 156 {
 157         if (tb[IFLA_ADDRESS]) {
 158                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 159                         return -EINVAL;
 160                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 161                         return -EADDRNOTAVAIL;
 162         }
 163         return 0;
 164 }
 165
 166 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 167         .kind           = DRV_NAME,
 168         .setup          = dummy_setup,
 169         .validate       = dummy_validate,
 170 };
 171
 172 /* Number of dummy devices to be set up by this module. */
 173 module_param(numdummies, int, 0);
 174 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 175
 176 static int __init dummy_init_one(void)
 177 {
 178         struct net_device *dev_dummy;
 179         int err;
 180
 181         dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_UNKNOWN, dummy_setup);
 182         if (!dev_dummy)
 183                 return -ENOMEM;
 184
 185         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 186         err = register_netdevice(dev_dummy);
 187         if (err < 0)
 188                 goto err;
 189         return 0;
 190
 191 err:
 192         free_netdev(dev_dummy);
 193         return err;
 194 }
 195
 196 static int __init dummy_init_module(void)
 197 {
 198         int i, err = 0;
 199
 200         rtnl_lock();
 201         err = __rtnl_link_register(&dummy_link_ops);
 202         if (err < 0)
 203                 goto out;
 204
 205         for (i = 0; i < numdummies && !err; i++) {
 206                 err = dummy_init_one();
 207                 cond_resched();
 208         }
 209         if (err < 0)
 210                 __rtnl_link_unregister(&dummy_link_ops);
 211
 212 out:
 213         rtnl_unlock();
 214
 215         return err;
 216 }
 217
 218 static void __exit dummy_cleanup_module(void)
 219 {
 220         rtnl_link_unregister(&dummy_link_ops);
 221 }
 222
 223 module_init(dummy_init_module);
 224 module_exit(dummy_cleanup_module);
 225 MODULE_LICENSE("GPL");
 226 MODULE_ALIAS_RTNL_LINK(DRV_NAME);
 227 MODULE_VERSION(DRV_VERSION);