dummy.c

  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/netdev_lock.h>
 42#include <net/rtnetlink.h>
 43#include <linux/u64_stats_sync.h>
 44
 45#define DRV_NAME	"dummy"
 46
 47static int numdummies = 1;
 48
 49/* fake multicast ability */
 50static void set_multicast_list(struct net_device *dev)
 51{
 52}
 53
 54static void dummy_get_stats64(struct net_device *dev,
 55			      struct rtnl_link_stats64 *stats)
 56{
 57	dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes);
 58}
 59
 60static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev)
 61{
 62	dev_lstats_add(dev, skb->len);
 63
 64	skb_tx_timestamp(skb);
 65	dev_kfree_skb(skb);
 66	return NETDEV_TX_OK;
 67}
 68
 69static int dummy_dev_init(struct net_device *dev)
 70{
 71	dev->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS;
 72
 73	netdev_lockdep_set_classes(dev);
 74	return 0;
 75}
 76
 77static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
 78{
 79	if (new_carrier)
 80		netif_carrier_on(dev);
 81	else
 82		netif_carrier_off(dev);
 83	return 0;
 84}
 85
 86static const struct net_device_ops dummy_netdev_ops = {
 87	.ndo_init		= dummy_dev_init,
 88	.ndo_start_xmit		= dummy_xmit,
 89	.ndo_validate_addr	= eth_validate_addr,
 90	.ndo_set_rx_mode	= set_multicast_list,
 91	.ndo_set_mac_address	= eth_mac_addr,
 92	.ndo_get_stats64	= dummy_get_stats64,
 93	.ndo_change_carrier	= dummy_change_carrier,
 94};
 95
 96static const struct ethtool_ops dummy_ethtool_ops = {
 97	.get_ts_info		= ethtool_op_get_ts_info,
 98};
 99
100static void dummy_setup(struct net_device *dev)
101{
102	ether_setup(dev);
103
104	/* Initialize the device structure. */
105	dev->netdev_ops = &dummy_netdev_ops;
106	dev->ethtool_ops = &dummy_ethtool_ops;
107	dev->needs_free_netdev = true;
108	dev->request_ops_lock = true;
109
110	/* Fill in device structure with ethernet-generic values. */
111	dev->flags |= IFF_NOARP;
112	dev->flags &= ~IFF_MULTICAST;
113	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
114	dev->lltx = true;
115	dev->features	|= NETIF_F_SG | NETIF_F_FRAGLIST;
116	dev->features	|= NETIF_F_GSO_SOFTWARE;
117	dev->features	|= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA;
118	dev->features	|= NETIF_F_GSO_ENCAP_ALL;
119	dev->hw_features |= dev->features;
120	dev->hw_enc_features |= dev->features;
121	eth_hw_addr_random(dev);
122
123	dev->min_mtu = 0;
124	dev->max_mtu = 0;
125}
126
127static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
128			  struct netlink_ext_ack *extack)
129{
130	if (tb[IFLA_ADDRESS]) {
131		if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
132			return -EINVAL;
133		if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
134			return -EADDRNOTAVAIL;
135	}
136	return 0;
137}
138
139static struct rtnl_link_ops dummy_link_ops __read_mostly = {
140	.kind		= DRV_NAME,
141	.setup		= dummy_setup,
142	.validate	= dummy_validate,
143};
144
145/* Number of dummy devices to be set up by this module. */
146module_param(numdummies, int, 0);
147MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
148
149static int __init dummy_init_one(void)
150{
151	struct net_device *dev_dummy;
152	int err;
153
154	dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
155	if (!dev_dummy)
156		return -ENOMEM;
157
158	dev_dummy->rtnl_link_ops = &dummy_link_ops;
159	err = register_netdevice(dev_dummy);
160	if (err < 0)
161		goto err;
162	return 0;
163
164err:
165	free_netdev(dev_dummy);
166	return err;
167}
168
169static int __init dummy_init_module(void)
170{
171	int i, err = 0;
172
173	err = rtnl_link_register(&dummy_link_ops);
174	if (err < 0)
175		return err;
176
177	rtnl_net_lock(&init_net);
178
179	for (i = 0; i < numdummies && !err; i++) {
180		err = dummy_init_one();
181		cond_resched();
182	}
183
184	rtnl_net_unlock(&init_net);
185
186	if (err < 0)
187		rtnl_link_unregister(&dummy_link_ops);
188
189	return err;
190}
191
192static void __exit dummy_cleanup_module(void)
193{
194	rtnl_link_unregister(&dummy_link_ops);
195}
196
197module_init(dummy_init_module);
198module_exit(dummy_cleanup_module);
199MODULE_LICENSE("GPL");
200MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");
201MODULE_ALIAS_RTNL_LINK(DRV_NAME);