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