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_irq(&dstats->syncp); 67 tbytes = dstats->tx_bytes; 68 tpackets = dstats->tx_packets; 69 } while (u64_stats_fetch_retry_irq(&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 = netdev_alloc_pcpu_stats(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 int dummy_change_carrier(struct net_device *dev, bool new_carrier) 104 { 105 if (new_carrier) 106 netif_carrier_on(dev); 107 else 108 netif_carrier_off(dev); 109 return 0; 110 } 111 112 static const struct net_device_ops dummy_netdev_ops = { 113 .ndo_init = dummy_dev_init, 114 .ndo_uninit = dummy_dev_uninit, 115 .ndo_start_xmit = dummy_xmit, 116 .ndo_validate_addr = eth_validate_addr, 117 .ndo_set_rx_mode = set_multicast_list, 118 .ndo_set_mac_address = eth_mac_addr, 119 .ndo_get_stats64 = dummy_get_stats64, 120 .ndo_change_carrier = dummy_change_carrier, 121 }; 122 123 static void dummy_setup(struct net_device *dev) 124 { 125 ether_setup(dev); 126 127 /* Initialize the device structure. */ 128 dev->netdev_ops = &dummy_netdev_ops; 129 dev->destructor = free_netdev; 130 131 /* Fill in device structure with ethernet-generic values. */ 132 dev->tx_queue_len = 0; 133 dev->flags |= IFF_NOARP; 134 dev->flags &= ~IFF_MULTICAST; 135 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE; 136 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO; 137 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 138 eth_hw_addr_random(dev); 139 } 140 141 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[]) 142 { 143 if (tb[IFLA_ADDRESS]) { 144 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 145 return -EINVAL; 146 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 147 return -EADDRNOTAVAIL; 148 } 149 return 0; 150 } 151 152 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 153 .kind = "dummy", 154 .setup = dummy_setup, 155 .validate = dummy_validate, 156 }; 157 158 /* Number of dummy devices to be set up by this module. */ 159 module_param(numdummies, int, 0); 160 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 161 162 static int __init dummy_init_one(void) 163 { 164 struct net_device *dev_dummy; 165 int err; 166 167 dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup); 168 if (!dev_dummy) 169 return -ENOMEM; 170 171 dev_dummy->rtnl_link_ops = &dummy_link_ops; 172 err = register_netdevice(dev_dummy); 173 if (err < 0) 174 goto err; 175 return 0; 176 177 err: 178 free_netdev(dev_dummy); 179 return err; 180 } 181 182 static int __init dummy_init_module(void) 183 { 184 int i, err = 0; 185 186 rtnl_lock(); 187 err = __rtnl_link_register(&dummy_link_ops); 188 if (err < 0) 189 goto out; 190 191 for (i = 0; i < numdummies && !err; i++) { 192 err = dummy_init_one(); 193 cond_resched(); 194 } 195 if (err < 0) 196 __rtnl_link_unregister(&dummy_link_ops); 197 198 out: 199 rtnl_unlock(); 200 201 return err; 202 } 203 204 static void __exit dummy_cleanup_module(void) 205 { 206 rtnl_link_unregister(&dummy_link_ops); 207 } 208 209 module_init(dummy_init_module); 210 module_exit(dummy_cleanup_module); 211 MODULE_LICENSE("GPL"); 212 MODULE_ALIAS_RTNL_LINK("dummy"); 213