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 */ |
49 | static void set_multicast_list(struct net_device *dev) |
50 | { |
51 | } |
52 | |
53 | static void dummy_get_stats64(struct net_device *dev, |
54 | struct rtnl_link_stats64 *stats) |
55 | { |
56 | dev_lstats_read(dev, packets: &stats->tx_packets, bytes: &stats->tx_bytes); |
57 | } |
58 | |
59 | static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) |
60 | { |
61 | dev_lstats_add(dev, len: skb->len); |
62 | |
63 | skb_tx_timestamp(skb); |
64 | dev_kfree_skb(skb); |
65 | return NETDEV_TX_OK; |
66 | } |
67 | |
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 | |
77 | static void dummy_dev_uninit(struct net_device *dev) |
78 | { |
79 | free_percpu(pdata: dev->lstats); |
80 | } |
81 | |
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 | |
102 | static const struct ethtool_ops dummy_ethtool_ops = { |
103 | .get_ts_info = ethtool_op_get_ts_info, |
104 | }; |
105 | |
106 | static void dummy_setup(struct net_device *dev) |
107 | { |
108 | ether_setup(dev); |
109 | |
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; |
114 | |
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); |
126 | |
127 | dev->min_mtu = 0; |
128 | dev->max_mtu = 0; |
129 | } |
130 | |
131 | static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], |
132 | struct netlink_ext_ack *extack) |
133 | { |
134 | if (tb[IFLA_ADDRESS]) { |
135 | if (nla_len(nla: tb[IFLA_ADDRESS]) != ETH_ALEN) |
136 | return -EINVAL; |
137 | if (!is_valid_ether_addr(addr: nla_data(nla: tb[IFLA_ADDRESS]))) |
138 | return -EADDRNOTAVAIL; |
139 | } |
140 | return 0; |
141 | } |
142 | |
143 | static struct rtnl_link_ops dummy_link_ops __read_mostly = { |
144 | .kind = DRV_NAME, |
145 | .setup = dummy_setup, |
146 | .validate = dummy_validate, |
147 | }; |
148 | |
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" ); |
152 | |
153 | static int __init dummy_init_one(void) |
154 | { |
155 | struct net_device *dev_dummy; |
156 | int err; |
157 | |
158 | dev_dummy = alloc_netdev(0, "dummy%d" , NET_NAME_ENUM, dummy_setup); |
159 | if (!dev_dummy) |
160 | return -ENOMEM; |
161 | |
162 | dev_dummy->rtnl_link_ops = &dummy_link_ops; |
163 | err = register_netdevice(dev: dev_dummy); |
164 | if (err < 0) |
165 | goto err; |
166 | return 0; |
167 | |
168 | err: |
169 | free_netdev(dev: dev_dummy); |
170 | return err; |
171 | } |
172 | |
173 | static int __init dummy_init_module(void) |
174 | { |
175 | int i, err = 0; |
176 | |
177 | down_write(sem: &pernet_ops_rwsem); |
178 | rtnl_lock(); |
179 | err = __rtnl_link_register(ops: &dummy_link_ops); |
180 | if (err < 0) |
181 | goto out; |
182 | |
183 | for (i = 0; i < numdummies && !err; i++) { |
184 | err = dummy_init_one(); |
185 | cond_resched(); |
186 | } |
187 | if (err < 0) |
188 | __rtnl_link_unregister(ops: &dummy_link_ops); |
189 | |
190 | out: |
191 | rtnl_unlock(); |
192 | up_write(sem: &pernet_ops_rwsem); |
193 | |
194 | return err; |
195 | } |
196 | |
197 | static void __exit dummy_cleanup_module(void) |
198 | { |
199 | rtnl_link_unregister(ops: &dummy_link_ops); |
200 | } |
201 | |
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); |
207 | |