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