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, &stats->tx_packets, &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, 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(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(tb[IFLA_ADDRESS]) != ETH_ALEN) 136 return -EINVAL; 137 if (!is_valid_ether_addr(nla_data(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_dummy); 164 if (err < 0) 165 goto err; 166 return 0; 167 168 err: 169 free_netdev(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(&pernet_ops_rwsem); 178 rtnl_lock(); 179 err = __rtnl_link_register(&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(&dummy_link_ops); 189 190 out: 191 rtnl_unlock(); 192 up_write(&pernet_ops_rwsem); 193 194 return err; 195 } 196 197 static void __exit dummy_cleanup_module(void) 198 { 199 rtnl_link_unregister(&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