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 40 static int numdummies = 1; 41 42 static int dummy_set_address(struct net_device *dev, void *p) 43 { 44 struct sockaddr *sa = p; 45 46 if (!is_valid_ether_addr(sa->sa_data)) 47 return -EADDRNOTAVAIL; 48 49 memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN); 50 return 0; 51 } 52 53 /* fake multicast ability */ 54 static void set_multicast_list(struct net_device *dev) 55 { 56 } 57 58 59 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) 60 { 61 dev->stats.tx_packets++; 62 dev->stats.tx_bytes += skb->len; 63 64 dev_kfree_skb(skb); 65 return NETDEV_TX_OK; 66 } 67 68 static const struct net_device_ops dummy_netdev_ops = { 69 .ndo_start_xmit = dummy_xmit, 70 .ndo_validate_addr = eth_validate_addr, 71 .ndo_set_multicast_list = set_multicast_list, 72 .ndo_set_mac_address = dummy_set_address, 73 }; 74 75 static void dummy_setup(struct net_device *dev) 76 { 77 ether_setup(dev); 78 79 /* Initialize the device structure. */ 80 dev->netdev_ops = &dummy_netdev_ops; 81 dev->destructor = free_netdev; 82 83 /* Fill in device structure with ethernet-generic values. */ 84 dev->tx_queue_len = 0; 85 dev->flags |= IFF_NOARP; 86 dev->flags &= ~IFF_MULTICAST; 87 random_ether_addr(dev->dev_addr); 88 } 89 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[]) 90 { 91 if (tb[IFLA_ADDRESS]) { 92 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 93 return -EINVAL; 94 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 95 return -EADDRNOTAVAIL; 96 } 97 return 0; 98 } 99 100 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 101 .kind = "dummy", 102 .setup = dummy_setup, 103 .validate = dummy_validate, 104 }; 105 106 /* Number of dummy devices to be set up by this module. */ 107 module_param(numdummies, int, 0); 108 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 109 110 static int __init dummy_init_one(void) 111 { 112 struct net_device *dev_dummy; 113 int err; 114 115 dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup); 116 if (!dev_dummy) 117 return -ENOMEM; 118 119 err = dev_alloc_name(dev_dummy, dev_dummy->name); 120 if (err < 0) 121 goto err; 122 123 dev_dummy->rtnl_link_ops = &dummy_link_ops; 124 err = register_netdevice(dev_dummy); 125 if (err < 0) 126 goto err; 127 return 0; 128 129 err: 130 free_netdev(dev_dummy); 131 return err; 132 } 133 134 static int __init dummy_init_module(void) 135 { 136 int i, err = 0; 137 138 rtnl_lock(); 139 err = __rtnl_link_register(&dummy_link_ops); 140 141 for (i = 0; i < numdummies && !err; i++) 142 err = dummy_init_one(); 143 if (err < 0) 144 __rtnl_link_unregister(&dummy_link_ops); 145 rtnl_unlock(); 146 147 return err; 148 } 149 150 static void __exit dummy_cleanup_module(void) 151 { 152 rtnl_link_unregister(&dummy_link_ops); 153 } 154 155 module_init(dummy_init_module); 156 module_exit(dummy_cleanup_module); 157 MODULE_LICENSE("GPL"); 158 MODULE_ALIAS_RTNL_LINK("dummy"); 159