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 int i; 92 dev->dstats = alloc_percpu(struct pcpu_dstats); 93 if (!dev->dstats) 94 return -ENOMEM; 95 96 for_each_possible_cpu(i) { 97 struct pcpu_dstats *dstats; 98 dstats = per_cpu_ptr(dev->dstats, i); 99 u64_stats_init(&dstats->syncp); 100 } 101 return 0; 102 } 103 104 static void dummy_dev_uninit(struct net_device *dev) 105 { 106 free_percpu(dev->dstats); 107 } 108 109 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 110 { 111 if (new_carrier) 112 netif_carrier_on(dev); 113 else 114 netif_carrier_off(dev); 115 return 0; 116 } 117 118 static const struct net_device_ops dummy_netdev_ops = { 119 .ndo_init = dummy_dev_init, 120 .ndo_uninit = dummy_dev_uninit, 121 .ndo_start_xmit = dummy_xmit, 122 .ndo_validate_addr = eth_validate_addr, 123 .ndo_set_rx_mode = set_multicast_list, 124 .ndo_set_mac_address = eth_mac_addr, 125 .ndo_get_stats64 = dummy_get_stats64, 126 .ndo_change_carrier = dummy_change_carrier, 127 }; 128 129 static void dummy_setup(struct net_device *dev) 130 { 131 ether_setup(dev); 132 133 /* Initialize the device structure. */ 134 dev->netdev_ops = &dummy_netdev_ops; 135 dev->destructor = free_netdev; 136 137 /* Fill in device structure with ethernet-generic values. */ 138 dev->tx_queue_len = 0; 139 dev->flags |= IFF_NOARP; 140 dev->flags &= ~IFF_MULTICAST; 141 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE; 142 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO; 143 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 144 eth_hw_addr_random(dev); 145 } 146 147 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[]) 148 { 149 if (tb[IFLA_ADDRESS]) { 150 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 151 return -EINVAL; 152 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 153 return -EADDRNOTAVAIL; 154 } 155 return 0; 156 } 157 158 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 159 .kind = "dummy", 160 .setup = dummy_setup, 161 .validate = dummy_validate, 162 }; 163 164 /* Number of dummy devices to be set up by this module. */ 165 module_param(numdummies, int, 0); 166 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 167 168 static int __init dummy_init_one(void) 169 { 170 struct net_device *dev_dummy; 171 int err; 172 173 dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup); 174 if (!dev_dummy) 175 return -ENOMEM; 176 177 dev_dummy->rtnl_link_ops = &dummy_link_ops; 178 err = register_netdevice(dev_dummy); 179 if (err < 0) 180 goto err; 181 return 0; 182 183 err: 184 free_netdev(dev_dummy); 185 return err; 186 } 187 188 static int __init dummy_init_module(void) 189 { 190 int i, err = 0; 191 192 rtnl_lock(); 193 err = __rtnl_link_register(&dummy_link_ops); 194 if (err < 0) 195 goto out; 196 197 for (i = 0; i < numdummies && !err; i++) { 198 err = dummy_init_one(); 199 cond_resched(); 200 } 201 if (err < 0) 202 __rtnl_link_unregister(&dummy_link_ops); 203 204 out: 205 rtnl_unlock(); 206 207 return err; 208 } 209 210 static void __exit dummy_cleanup_module(void) 211 { 212 rtnl_link_unregister(&dummy_link_ops); 213 } 214 215 module_init(dummy_init_module); 216 module_exit(dummy_cleanup_module); 217 MODULE_LICENSE("GPL"); 218 MODULE_ALIAS_RTNL_LINK("dummy"); 219