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