1// SPDX-License-Identifier: GPL-2.0-only
2/* dummy.c: a dummy net driver
3
4	The purpose of this driver is to provide a device to point a
5	route through, but not to actually transmit packets.
6
7	Why?  If you have a machine whose only connection is an occasional
8	PPP/SLIP/PLIP link, you can only connect to your own hostname
9	when the link is up.  Otherwise you have to use localhost.
10	This isn't very consistent.
11
12	One solution is to set up a dummy link using PPP/SLIP/PLIP,
13	but this seems (to me) too much overhead for too little gain.
14	This driver provides a small alternative. Thus you can do
15
16	[when not running slip]
17		ifconfig dummy slip.addr.ess.here up
18	[to go to slip]
19		ifconfig dummy down
20		dip whatever
21
22	This was written by looking at Donald Becker's skeleton driver
23	and the loopback driver.  I then threw away anything that didn't
24	apply!	Thanks to Alan Cox for the key clue on what to do with
25	misguided packets.
26
27			Nick Holloway, 27th May 1994
28	[I tweaked this explanation a little but that's all]
29			Alan Cox, 30th May 1994
30*/
31
32#include <linux/module.h>
33#include <linux/kernel.h>
34#include <linux/netdevice.h>
35#include <linux/etherdevice.h>
36#include <linux/ethtool.h>
37#include <linux/init.h>
38#include <linux/moduleparam.h>
39#include <linux/rtnetlink.h>
40#include <linux/net_tstamp.h>
41#include <net/rtnetlink.h>
42#include <linux/u64_stats_sync.h>
43
44#define DRV_NAME	"dummy"
45
46static int numdummies = 1;
47
48/* fake multicast ability */
49static void set_multicast_list(struct net_device *dev)
50{
51}
52
53static void dummy_get_stats64(struct net_device *dev,
54			      struct rtnl_link_stats64 *stats)
55{
56	dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes);
57}
58
59static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
60{
61	dev_lstats_add(dev, skb->len);
62
63	skb_tx_timestamp(skb);
64	dev_kfree_skb(skb);
65	return NETDEV_TX_OK;
66}
67
68static int dummy_dev_init(struct net_device *dev)
69{
70	dev->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS;
71
72	netdev_lockdep_set_classes(dev);
73	return 0;
74}
75
76static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
77{
78	if (new_carrier)
79		netif_carrier_on(dev);
80	else
81		netif_carrier_off(dev);
82	return 0;
83}
84
85static const struct net_device_ops dummy_netdev_ops = {
86	.ndo_init		= dummy_dev_init,
87	.ndo_start_xmit		= dummy_xmit,
88	.ndo_validate_addr	= eth_validate_addr,
89	.ndo_set_rx_mode	= set_multicast_list,
90	.ndo_set_mac_address	= eth_mac_addr,
91	.ndo_get_stats64	= dummy_get_stats64,
92	.ndo_change_carrier	= dummy_change_carrier,
93};
94
95static const struct ethtool_ops dummy_ethtool_ops = {
96	.get_ts_info		= ethtool_op_get_ts_info,
97};
98
99static void dummy_setup(struct net_device *dev)
100{
101	ether_setup(dev);
102
103	/* Initialize the device structure. */
104	dev->netdev_ops = &dummy_netdev_ops;
105	dev->ethtool_ops = &dummy_ethtool_ops;
106	dev->needs_free_netdev = true;
107
108	/* Fill in device structure with ethernet-generic values. */
109	dev->flags |= IFF_NOARP;
110	dev->flags &= ~IFF_MULTICAST;
111	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
112	dev->features	|= NETIF_F_SG | NETIF_F_FRAGLIST;
113	dev->features	|= NETIF_F_GSO_SOFTWARE;
114	dev->features	|= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
115	dev->features	|= NETIF_F_GSO_ENCAP_ALL;
116	dev->hw_features |= dev->features;
117	dev->hw_enc_features |= dev->features;
118	eth_hw_addr_random(dev);
119
120	dev->min_mtu = 0;
121	dev->max_mtu = 0;
122}
123
124static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
125			  struct netlink_ext_ack *extack)
126{
127	if (tb[IFLA_ADDRESS]) {
128		if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
129			return -EINVAL;
130		if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
131			return -EADDRNOTAVAIL;
132	}
133	return 0;
134}
135
136static struct rtnl_link_ops dummy_link_ops __read_mostly = {
137	.kind		= DRV_NAME,
138	.setup		= dummy_setup,
139	.validate	= dummy_validate,
140};
141
142/* Number of dummy devices to be set up by this module. */
143module_param(numdummies, int, 0);
144MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
145
146static int __init dummy_init_one(void)
147{
148	struct net_device *dev_dummy;
149	int err;
150
151	dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
152	if (!dev_dummy)
153		return -ENOMEM;
154
155	dev_dummy->rtnl_link_ops = &dummy_link_ops;
156	err = register_netdevice(dev_dummy);
157	if (err < 0)
158		goto err;
159	return 0;
160
161err:
162	free_netdev(dev_dummy);
163	return err;
164}
165
166static int __init dummy_init_module(void)
167{
168	int i, err = 0;
169
170	down_write(&pernet_ops_rwsem);
171	rtnl_lock();
172	err = __rtnl_link_register(&dummy_link_ops);
173	if (err < 0)
174		goto out;
175
176	for (i = 0; i < numdummies && !err; i++) {
177		err = dummy_init_one();
178		cond_resched();
179	}
180	if (err < 0)
181		__rtnl_link_unregister(&dummy_link_ops);
182
183out:
184	rtnl_unlock();
185	up_write(&pernet_ops_rwsem);
186
187	return err;
188}
189
190static void __exit dummy_cleanup_module(void)
191{
192	rtnl_link_unregister(&dummy_link_ops);
193}
194
195module_init(dummy_init_module);
196module_exit(dummy_cleanup_module);
197MODULE_LICENSE("GPL");
198MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");
199MODULE_ALIAS_RTNL_LINK(DRV_NAME);
200