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 #include <linux/sched.h>
  41
  42 static int numdummies = 1;
  43
  44 static int dummy_set_address(struct net_device *dev, void *p)
  45 {
  46         struct sockaddr *sa = p;
  47
  48         if (!is_valid_ether_addr(sa->sa_data))
  49                 return -EADDRNOTAVAIL;
  50
  51         memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN);
  52         return 0;
  53 }
  54
  55 /* fake multicast ability */
  56 static void set_multicast_list(struct net_device *dev)
  57 {
  58 }
  59
  60 struct pcpu_dstats {
  61         u64                     tx_packets;
  62         u64                     tx_bytes;
  63         struct u64_stats_sync   syncp;
  64 };
  65
  66 static struct rtnl_link_stats64 *dummy_get_stats64(struct net_device *dev,
  67                                                    struct rtnl_link_stats64 *stats)
  68 {
  69         int i;
  70
  71         for_each_possible_cpu(i) {
  72                 const struct pcpu_dstats *dstats;
  73                 u64 tbytes, tpackets;
  74                 unsigned int start;
  75
  76                 dstats = per_cpu_ptr(dev->dstats, i);
  77                 do {
  78                         start = u64_stats_fetch_begin(&dstats->syncp);
  79                         tbytes = dstats->tx_bytes;
  80                         tpackets = dstats->tx_packets;
  81                 } while (u64_stats_fetch_retry(&dstats->syncp, start));
  82                 stats->tx_bytes += tbytes;
  83                 stats->tx_packets += tpackets;
  84         }
  85         return stats;
  86 }
  87
  88 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
  89 {
  90         struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats);
  91
  92         u64_stats_update_begin(&dstats->syncp);
  93         dstats->tx_packets++;
  94         dstats->tx_bytes += skb->len;
  95         u64_stats_update_end(&dstats->syncp);
  96
  97         dev_kfree_skb(skb);
  98         return NETDEV_TX_OK;
  99 }
 100
 101 static int dummy_dev_init(struct net_device *dev)
 102 {
 103         dev->dstats = alloc_percpu(struct pcpu_dstats);
 104         if (!dev->dstats)
 105                 return -ENOMEM;
 106
 107         return 0;
 108 }
 109
 110 static void dummy_dev_uninit(struct net_device *dev)
 111 {
 112         free_percpu(dev->dstats);
 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    = dummy_set_address,
 122         .ndo_get_stats64        = dummy_get_stats64,
 123 };
 124
 125 static void dummy_setup(struct net_device *dev)
 126 {
 127         ether_setup(dev);
 128
 129         /* Initialize the device structure. */
 130         dev->netdev_ops = &dummy_netdev_ops;
 131         dev->destructor = free_netdev;
 132
 133         /* Fill in device structure with ethernet-generic values. */
 134         dev->tx_queue_len = 0;
 135         dev->flags |= IFF_NOARP;
 136         dev->flags &= ~IFF_MULTICAST;
 137         dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
 138         dev->features   |= NETIF_F_NO_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
 139         random_ether_addr(dev->dev_addr);
 140 }
 141
 142 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[])
 143 {
 144         if (tb[IFLA_ADDRESS]) {
 145                 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
 146                         return -EINVAL;
 147                 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
 148                         return -EADDRNOTAVAIL;
 149         }
 150         return 0;
 151 }
 152
 153 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
 154         .kind           = "dummy",
 155         .setup          = dummy_setup,
 156         .validate       = dummy_validate,
 157 };
 158
 159 /* Number of dummy devices to be set up by this module. */
 160 module_param(numdummies, int, 0);
 161 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
 162
 163 static int __init dummy_init_one(void)
 164 {
 165         struct net_device *dev_dummy;
 166         int err;
 167
 168         dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup);
 169         if (!dev_dummy)
 170                 return -ENOMEM;
 171
 172         dev_dummy->rtnl_link_ops = &dummy_link_ops;
 173         err = register_netdevice(dev_dummy);
 174         if (err < 0)
 175                 goto err;
 176         return 0;
 177
 178 err:
 179         free_netdev(dev_dummy);
 180         return err;
 181 }
 182
 183 static int __init dummy_init_module(void)
 184 {
 185         int i, err = 0;
 186
 187         rtnl_lock();
 188         err = __rtnl_link_register(&dummy_link_ops);
 189
 190         for (i = 0; i < numdummies && !err; i++) {
 191                 err = dummy_init_one();
 192                 cond_resched();
 193         }
 194         if (err < 0)
 195                 __rtnl_link_unregister(&dummy_link_ops);
 196         rtnl_unlock();
 197
 198         return err;
 199 }
 200
 201 static void __exit dummy_cleanup_module(void)
 202 {
 203         rtnl_link_unregister(&dummy_link_ops);
 204 }
 205
 206 module_init(dummy_init_module);
 207 module_exit(dummy_cleanup_module);
 208 MODULE_LICENSE("GPL");
 209 MODULE_ALIAS_RTNL_LINK("dummy");