1 // SPDX-License-Identifier: GPL-2.0-only
2 /* dummy.c: a dummy net driver
4 The purpose of this driver is to provide a device to point a
5 route through, but not to actually transmit packets.
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.
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
16 [when not running slip]
17 ifconfig dummy slip.addr.ess.here up
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
27 Nick Holloway, 27th May 1994
28 [I tweaked this explanation a little but that's all]
29 Alan Cox, 30th May 1994
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>
44 #define DRV_NAME "dummy"
46 static int numdummies = 1;
48 /* fake multicast ability */
49 static void set_multicast_list(struct net_device *dev)
53 static void dummy_get_stats64(struct net_device *dev,
54 struct rtnl_link_stats64 *stats)
56 dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes);
59 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
61 dev_lstats_add(dev, skb->len);
63 skb_tx_timestamp(skb);
68 static int dummy_dev_init(struct net_device *dev)
70 dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
77 static void dummy_dev_uninit(struct net_device *dev)
79 free_percpu(dev->lstats);
82 static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
85 netif_carrier_on(dev);
87 netif_carrier_off(dev);
91 static const struct net_device_ops dummy_netdev_ops = {
92 .ndo_init = dummy_dev_init,
93 .ndo_uninit = dummy_dev_uninit,
94 .ndo_start_xmit = dummy_xmit,
95 .ndo_validate_addr = eth_validate_addr,
96 .ndo_set_rx_mode = set_multicast_list,
97 .ndo_set_mac_address = eth_mac_addr,
98 .ndo_get_stats64 = dummy_get_stats64,
99 .ndo_change_carrier = dummy_change_carrier,
102 static const struct ethtool_ops dummy_ethtool_ops = {
103 .get_ts_info = ethtool_op_get_ts_info,
106 static void dummy_setup(struct net_device *dev)
110 /* Initialize the device structure. */
111 dev->netdev_ops = &dummy_netdev_ops;
112 dev->ethtool_ops = &dummy_ethtool_ops;
113 dev->needs_free_netdev = true;
115 /* Fill in device structure with ethernet-generic values. */
116 dev->flags |= IFF_NOARP;
117 dev->flags &= ~IFF_MULTICAST;
118 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
119 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST;
120 dev->features |= NETIF_F_GSO_SOFTWARE;
121 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
122 dev->features |= NETIF_F_GSO_ENCAP_ALL;
123 dev->hw_features |= dev->features;
124 dev->hw_enc_features |= dev->features;
125 eth_hw_addr_random(dev);
131 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
132 struct netlink_ext_ack *extack)
134 if (tb[IFLA_ADDRESS]) {
135 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
137 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
138 return -EADDRNOTAVAIL;
143 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
145 .setup = dummy_setup,
146 .validate = dummy_validate,
149 /* Number of dummy devices to be set up by this module. */
150 module_param(numdummies, int, 0);
151 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
153 static int __init dummy_init_one(void)
155 struct net_device *dev_dummy;
158 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
162 dev_dummy->rtnl_link_ops = &dummy_link_ops;
163 err = register_netdevice(dev_dummy);
169 free_netdev(dev_dummy);
173 static int __init dummy_init_module(void)
177 down_write(&pernet_ops_rwsem);
179 err = __rtnl_link_register(&dummy_link_ops);
183 for (i = 0; i < numdummies && !err; i++) {
184 err = dummy_init_one();
188 __rtnl_link_unregister(&dummy_link_ops);
192 up_write(&pernet_ops_rwsem);
197 static void __exit dummy_cleanup_module(void)
199 rtnl_link_unregister(&dummy_link_ops);
202 module_init(dummy_init_module);
203 module_exit(dummy_cleanup_module);
204 MODULE_LICENSE("GPL");
205 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");
206 MODULE_ALIAS_RTNL_LINK(DRV_NAME);