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_xmit(struct sk_buff *skb, struct net_device *dev); 43 44 static int dummy_set_address(struct net_device *dev, void *p) 45 { 46 struct sockaddr *sa = p; 47 48 if (!is_valid_ether_addr(sa->sa_data)) 49 return -EADDRNOTAVAIL; 50 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 static const struct net_device_ops dummy_netdev_ops = { 61 .ndo_start_xmit = dummy_xmit, 62 .ndo_validate_addr = eth_validate_addr, 63 .ndo_set_multicast_list = set_multicast_list, 64 .ndo_set_mac_address = dummy_set_address, 65 }; 66 67 static void dummy_setup(struct net_device *dev) 68 { 69 ether_setup(dev); 70 71 /* Initialize the device structure. */ 72 dev->netdev_ops = &dummy_netdev_ops; 73 dev->destructor = free_netdev; 74 75 /* Fill in device structure with ethernet-generic values. */ 76 dev->tx_queue_len = 0; 77 dev->flags |= IFF_NOARP; 78 dev->flags &= ~IFF_MULTICAST; 79 random_ether_addr(dev->dev_addr); 80 } 81 82 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev) 83 { 84 dev->stats.tx_packets++; 85 dev->stats.tx_bytes += skb->len; 86 87 dev_kfree_skb(skb); 88 return 0; 89 } 90 91 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[]) 92 { 93 if (tb[IFLA_ADDRESS]) { 94 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 95 return -EINVAL; 96 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 97 return -EADDRNOTAVAIL; 98 } 99 return 0; 100 } 101 102 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 103 .kind = "dummy", 104 .setup = dummy_setup, 105 .validate = dummy_validate, 106 }; 107 108 /* Number of dummy devices to be set up by this module. */ 109 module_param(numdummies, int, 0); 110 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 111 112 static int __init dummy_init_one(void) 113 { 114 struct net_device *dev_dummy; 115 int err; 116 117 dev_dummy = alloc_netdev(0, "dummy%d", dummy_setup); 118 if (!dev_dummy) 119 return -ENOMEM; 120 121 err = dev_alloc_name(dev_dummy, dev_dummy->name); 122 if (err < 0) 123 goto err; 124 125 dev_dummy->rtnl_link_ops = &dummy_link_ops; 126 err = register_netdevice(dev_dummy); 127 if (err < 0) 128 goto err; 129 return 0; 130 131 err: 132 free_netdev(dev_dummy); 133 return err; 134 } 135 136 static int __init dummy_init_module(void) 137 { 138 int i, err = 0; 139 140 rtnl_lock(); 141 err = __rtnl_link_register(&dummy_link_ops); 142 143 for (i = 0; i < numdummies && !err; i++) 144 err = dummy_init_one(); 145 if (err < 0) 146 __rtnl_link_unregister(&dummy_link_ops); 147 rtnl_unlock(); 148 149 return err; 150 } 151 152 static void __exit dummy_cleanup_module(void) 153 { 154 rtnl_link_unregister(&dummy_link_ops); 155 } 156 157 module_init(dummy_init_module); 158 module_exit(dummy_cleanup_module); 159 MODULE_LICENSE("GPL"); 160 MODULE_ALIAS_RTNL_LINK("dummy"); 161