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