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 38 static int numdummies = 1; 39 40 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev); 41 static struct net_device_stats *dummy_get_stats(struct net_device *dev); 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 memcpy(dev->dev_addr, sa->sa_data, ETH_ALEN); 51 return 0; 52 } 53 54 /* fake multicast ability */ 55 static void set_multicast_list(struct net_device *dev) 56 { 57 } 58 59 static void __init dummy_setup(struct net_device *dev) 60 { 61 /* Initialize the device structure. */ 62 dev->get_stats = dummy_get_stats; 63 dev->hard_start_xmit = dummy_xmit; 64 dev->set_multicast_list = set_multicast_list; 65 dev->set_mac_address = dummy_set_address; 66 67 /* Fill in device structure with ethernet-generic values. */ 68 ether_setup(dev); 69 dev->tx_queue_len = 0; 70 dev->change_mtu = NULL; 71 dev->flags |= IFF_NOARP; 72 dev->flags &= ~IFF_MULTICAST; 73 SET_MODULE_OWNER(dev); 74 random_ether_addr(dev->dev_addr); 75 } 76 77 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev) 78 { 79 struct net_device_stats *stats = netdev_priv(dev); 80 81 stats->tx_packets++; 82 stats->tx_bytes+=skb->len; 83 84 dev_kfree_skb(skb); 85 return 0; 86 } 87 88 static struct net_device_stats *dummy_get_stats(struct net_device *dev) 89 { 90 return netdev_priv(dev); 91 } 92 93 static struct net_device **dummies; 94 95 /* Number of dummy devices to be set up by this module. */ 96 module_param(numdummies, int, 0); 97 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 98 99 static int __init dummy_init_one(int index) 100 { 101 struct net_device *dev_dummy; 102 int err; 103 104 dev_dummy = alloc_netdev(sizeof(struct net_device_stats), 105 "dummy%d", dummy_setup); 106 107 if (!dev_dummy) 108 return -ENOMEM; 109 110 if ((err = register_netdev(dev_dummy))) { 111 free_netdev(dev_dummy); 112 dev_dummy = NULL; 113 } else { 114 dummies[index] = dev_dummy; 115 } 116 117 return err; 118 } 119 120 static void dummy_free_one(int index) 121 { 122 unregister_netdev(dummies[index]); 123 free_netdev(dummies[index]); 124 } 125 126 static int __init dummy_init_module(void) 127 { 128 int i, err = 0; 129 dummies = kmalloc(numdummies * sizeof(void *), GFP_KERNEL); 130 if (!dummies) 131 return -ENOMEM; 132 for (i = 0; i < numdummies && !err; i++) 133 err = dummy_init_one(i); 134 if (err) { 135 i--; 136 while (--i >= 0) 137 dummy_free_one(i); 138 } 139 return err; 140 } 141 142 static void __exit dummy_cleanup_module(void) 143 { 144 int i; 145 for (i = 0; i < numdummies; i++) 146 dummy_free_one(i); 147 kfree(dummies); 148 } 149 150 module_init(dummy_init_module); 151 module_exit(dummy_cleanup_module); 152 MODULE_LICENSE("GPL"); 153