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
38static int numdummies = 1;
39
40static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
41static struct net_device_stats *dummy_get_stats(struct net_device *dev);
42
43static 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 */
55static void set_multicast_list(struct net_device *dev)
56{
57}
58
59static 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
77static 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
88static struct net_device_stats *dummy_get_stats(struct net_device *dev)
89{
90	return netdev_priv(dev);
91}
92
93static struct net_device **dummies;
94
95/* Number of dummy devices to be set up by this module. */
96module_param(numdummies, int, 0);
97MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
98
99static 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
120static void dummy_free_one(int index)
121{
122	unregister_netdev(dummies[index]);
123	free_netdev(dummies[index]);
124}
125
126static 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
142static 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
150module_init(dummy_init_module);
151module_exit(dummy_cleanup_module);
152MODULE_LICENSE("GPL");
153