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 
46 static int numdummies = 1;
47 
48 /* fake multicast ability */
set_multicast_list(struct net_device * dev)49 static void set_multicast_list(struct net_device *dev)
50 {
51 }
52 
dummy_get_stats64(struct net_device * dev,struct rtnl_link_stats64 * stats)53 static 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 
dummy_xmit(struct sk_buff * skb,struct net_device * dev)59 static 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 
dummy_dev_init(struct net_device * dev)68 static int dummy_dev_init(struct net_device *dev)
69 {
70 	dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
71 	if (!dev->lstats)
72 		return -ENOMEM;
73 
74 	return 0;
75 }
76 
dummy_dev_uninit(struct net_device * dev)77 static void dummy_dev_uninit(struct net_device *dev)
78 {
79 	free_percpu(dev->lstats);
80 }
81 
dummy_change_carrier(struct net_device * dev,bool new_carrier)82 static int dummy_change_carrier(struct net_device *dev, bool new_carrier)
83 {
84 	if (new_carrier)
85 		netif_carrier_on(dev);
86 	else
87 		netif_carrier_off(dev);
88 	return 0;
89 }
90 
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,
100 };
101 
dummy_get_drvinfo(struct net_device * dev,struct ethtool_drvinfo * info)102 static void dummy_get_drvinfo(struct net_device *dev,
103 			      struct ethtool_drvinfo *info)
104 {
105 	strlcpy(info->driver, DRV_NAME, sizeof(info->driver));
106 }
107 
108 static const struct ethtool_ops dummy_ethtool_ops = {
109 	.get_drvinfo            = dummy_get_drvinfo,
110 	.get_ts_info		= ethtool_op_get_ts_info,
111 };
112 
dummy_setup(struct net_device * dev)113 static void dummy_setup(struct net_device *dev)
114 {
115 	ether_setup(dev);
116 
117 	/* Initialize the device structure. */
118 	dev->netdev_ops = &dummy_netdev_ops;
119 	dev->ethtool_ops = &dummy_ethtool_ops;
120 	dev->needs_free_netdev = true;
121 
122 	/* Fill in device structure with ethernet-generic values. */
123 	dev->flags |= IFF_NOARP;
124 	dev->flags &= ~IFF_MULTICAST;
125 	dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
126 	dev->features	|= NETIF_F_SG | NETIF_F_FRAGLIST;
127 	dev->features	|= NETIF_F_GSO_SOFTWARE;
128 	dev->features	|= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;
129 	dev->features	|= NETIF_F_GSO_ENCAP_ALL;
130 	dev->hw_features |= dev->features;
131 	dev->hw_enc_features |= dev->features;
132 	eth_hw_addr_random(dev);
133 
134 	dev->min_mtu = 0;
135 	dev->max_mtu = 0;
136 }
137 
dummy_validate(struct nlattr * tb[],struct nlattr * data[],struct netlink_ext_ack * extack)138 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
139 			  struct netlink_ext_ack *extack)
140 {
141 	if (tb[IFLA_ADDRESS]) {
142 		if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
143 			return -EINVAL;
144 		if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
145 			return -EADDRNOTAVAIL;
146 	}
147 	return 0;
148 }
149 
150 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
151 	.kind		= DRV_NAME,
152 	.setup		= dummy_setup,
153 	.validate	= dummy_validate,
154 };
155 
156 /* Number of dummy devices to be set up by this module. */
157 module_param(numdummies, int, 0);
158 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
159 
dummy_init_one(void)160 static int __init dummy_init_one(void)
161 {
162 	struct net_device *dev_dummy;
163 	int err;
164 
165 	dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
166 	if (!dev_dummy)
167 		return -ENOMEM;
168 
169 	dev_dummy->rtnl_link_ops = &dummy_link_ops;
170 	err = register_netdevice(dev_dummy);
171 	if (err < 0)
172 		goto err;
173 	return 0;
174 
175 err:
176 	free_netdev(dev_dummy);
177 	return err;
178 }
179 
dummy_init_module(void)180 static int __init dummy_init_module(void)
181 {
182 	int i, err = 0;
183 
184 	down_write(&pernet_ops_rwsem);
185 	rtnl_lock();
186 	err = __rtnl_link_register(&dummy_link_ops);
187 	if (err < 0)
188 		goto out;
189 
190 	for (i = 0; i < numdummies && !err; i++) {
191 		err = dummy_init_one();
192 		cond_resched();
193 	}
194 	if (err < 0)
195 		__rtnl_link_unregister(&dummy_link_ops);
196 
197 out:
198 	rtnl_unlock();
199 	up_write(&pernet_ops_rwsem);
200 
201 	return err;
202 }
203 
dummy_cleanup_module(void)204 static void __exit dummy_cleanup_module(void)
205 {
206 	rtnl_link_unregister(&dummy_link_ops);
207 }
208 
209 module_init(dummy_init_module);
210 module_exit(dummy_cleanup_module);
211 MODULE_LICENSE("GPL");
212 MODULE_ALIAS_RTNL_LINK(DRV_NAME);
213