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 static int dummy_set_address(struct net_device *dev, void *p) 44 { 45 struct sockaddr *sa = p; 46 47 if (!is_valid_ether_addr(sa->sa_data)) 48 return -EADDRNOTAVAIL; 49 50 dev->addr_assign_type &= ~NET_ADDR_RANDOM; 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_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 139 eth_hw_addr_random(dev); 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 if (err < 0) 193 __rtnl_link_unregister(&dummy_link_ops); 194 rtnl_unlock(); 195 196 return err; 197 } 198 199 static void __exit dummy_cleanup_module(void) 200 { 201 rtnl_link_unregister(&dummy_link_ops); 202 } 203 204 module_init(dummy_init_module); 205 module_exit(dummy_cleanup_module); 206 MODULE_LICENSE("GPL"); 207 MODULE_ALIAS_RTNL_LINK("dummy"); 208