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
47 static int numdummies = 1;
48
49 /* fake multicast ability */
set_multicast_list(struct net_device * dev)50 static void set_multicast_list(struct net_device *dev)
51 {
52 }
53
dummy_get_stats64(struct net_device * dev,struct rtnl_link_stats64 * stats)54 static 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
dummy_xmit(struct sk_buff * skb,struct net_device * dev)60 static 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
dummy_dev_init(struct net_device * dev)69 static 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
dummy_change_carrier(struct net_device * dev,bool new_carrier)77 static 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
86 static 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
96 static const struct ethtool_ops dummy_ethtool_ops = {
97 .get_ts_info = ethtool_op_get_ts_info,
98 };
99
dummy_setup(struct net_device * dev)100 static 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
109 /* Fill in device structure with ethernet-generic values. */
110 dev->flags |= IFF_NOARP;
111 dev->flags &= ~IFF_MULTICAST;
112 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE;
113 dev->lltx = true;
114 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST;
115 dev->features |= NETIF_F_GSO_SOFTWARE;
116 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA;
117 dev->features |= NETIF_F_GSO_ENCAP_ALL;
118 dev->hw_features |= dev->features;
119 dev->hw_enc_features |= dev->features;
120 eth_hw_addr_random(dev);
121
122 dev->min_mtu = 0;
123 dev->max_mtu = 0;
124 }
125
dummy_validate(struct nlattr * tb[],struct nlattr * data[],struct netlink_ext_ack * extack)126 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[],
127 struct netlink_ext_ack *extack)
128 {
129 if (tb[IFLA_ADDRESS]) {
130 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN)
131 return -EINVAL;
132 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS])))
133 return -EADDRNOTAVAIL;
134 }
135 return 0;
136 }
137
138 static struct rtnl_link_ops dummy_link_ops __read_mostly = {
139 .kind = DRV_NAME,
140 .setup = dummy_setup,
141 .validate = dummy_validate,
142 };
143
144 /* Number of dummy devices to be set up by this module. */
145 module_param(numdummies, int, 0);
146 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");
147
dummy_init_one(void)148 static int __init dummy_init_one(void)
149 {
150 struct net_device *dev_dummy;
151 int err;
152
153 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup);
154 if (!dev_dummy)
155 return -ENOMEM;
156
157 dev_dummy->rtnl_link_ops = &dummy_link_ops;
158 err = register_netdevice(dev_dummy);
159 if (err < 0)
160 goto err;
161 return 0;
162
163 err:
164 free_netdev(dev_dummy);
165 return err;
166 }
167
dummy_init_module(void)168 static int __init dummy_init_module(void)
169 {
170 int i, err = 0;
171
172 err = rtnl_link_register(&dummy_link_ops);
173 if (err < 0)
174 return err;
175
176 rtnl_net_lock(&init_net);
177
178 for (i = 0; i < numdummies && !err; i++) {
179 err = dummy_init_one();
180 cond_resched();
181 }
182
183 rtnl_net_unlock(&init_net);
184
185 if (err < 0)
186 rtnl_link_unregister(&dummy_link_ops);
187
188 return err;
189 }
190
dummy_cleanup_module(void)191 static void __exit dummy_cleanup_module(void)
192 {
193 rtnl_link_unregister(&dummy_link_ops);
194 }
195
196 module_init(dummy_init_module);
197 module_exit(dummy_cleanup_module);
198 MODULE_LICENSE("GPL");
199 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");
200 MODULE_ALIAS_RTNL_LINK(DRV_NAME);
201