xref: /linux/drivers/net/dummy.c (revision f3d9478b2ce468c3115b02ecae7e975990697f15)
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/config.h>
32 #include <linux/module.h>
33 #include <linux/kernel.h>
34 #include <linux/netdevice.h>
35 #include <linux/etherdevice.h>
36 #include <linux/init.h>
37 #include <linux/moduleparam.h>
38 
39 static int numdummies = 1;
40 
41 static int dummy_xmit(struct sk_buff *skb, struct net_device *dev);
42 static struct net_device_stats *dummy_get_stats(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 __init dummy_setup(struct net_device *dev)
61 {
62 	/* Initialize the device structure. */
63 	dev->get_stats = dummy_get_stats;
64 	dev->hard_start_xmit = dummy_xmit;
65 	dev->set_multicast_list = set_multicast_list;
66 	dev->set_mac_address = dummy_set_address;
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 	struct net_device_stats *stats = netdev_priv(dev);
81 
82 	stats->tx_packets++;
83 	stats->tx_bytes+=skb->len;
84 
85 	dev_kfree_skb(skb);
86 	return 0;
87 }
88 
89 static struct net_device_stats *dummy_get_stats(struct net_device *dev)
90 {
91 	return netdev_priv(dev);
92 }
93 
94 static struct net_device **dummies;
95 
96 /* Number of dummy devices to be set up by this module. */
97 module_param(numdummies, int, 0);
98 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
99 
100 static int __init dummy_init_one(int index)
101 {
102 	struct net_device *dev_dummy;
103 	int err;
104 
105 	dev_dummy = alloc_netdev(sizeof(struct net_device_stats),
106 				 "dummy%d", dummy_setup);
107 
108 	if (!dev_dummy)
109 		return -ENOMEM;
110 
111 	if ((err = register_netdev(dev_dummy))) {
112 		free_netdev(dev_dummy);
113 		dev_dummy = NULL;
114 	} else {
115 		dummies[index] = dev_dummy;
116 	}
117 
118 	return err;
119 }
120 
121 static void dummy_free_one(int index)
122 {
123 	unregister_netdev(dummies[index]);
124 	free_netdev(dummies[index]);
125 }
126 
127 static int __init dummy_init_module(void)
128 {
129 	int i, err = 0;
130 	dummies = kmalloc(numdummies * sizeof(void *), GFP_KERNEL);
131 	if (!dummies)
132 		return -ENOMEM;
133 	for (i = 0; i < numdummies && !err; i++)
134 		err = dummy_init_one(i);
135 	if (err) {
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