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 netdev_lockdep_set_classes(dev); 75 return 0; 76 } 77 78 static void dummy_dev_uninit(struct net_device *dev) 79 { 80 free_percpu(dev->lstats); 81 } 82 83 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 84 { 85 if (new_carrier) 86 netif_carrier_on(dev); 87 else 88 netif_carrier_off(dev); 89 return 0; 90 } 91 92 static const struct net_device_ops dummy_netdev_ops = { 93 .ndo_init = dummy_dev_init, 94 .ndo_uninit = dummy_dev_uninit, 95 .ndo_start_xmit = dummy_xmit, 96 .ndo_validate_addr = eth_validate_addr, 97 .ndo_set_rx_mode = set_multicast_list, 98 .ndo_set_mac_address = eth_mac_addr, 99 .ndo_get_stats64 = dummy_get_stats64, 100 .ndo_change_carrier = dummy_change_carrier, 101 }; 102 103 static const struct ethtool_ops dummy_ethtool_ops = { 104 .get_ts_info = ethtool_op_get_ts_info, 105 }; 106 107 static void dummy_setup(struct net_device *dev) 108 { 109 ether_setup(dev); 110 111 /* Initialize the device structure. */ 112 dev->netdev_ops = &dummy_netdev_ops; 113 dev->ethtool_ops = &dummy_ethtool_ops; 114 dev->needs_free_netdev = true; 115 116 /* Fill in device structure with ethernet-generic values. */ 117 dev->flags |= IFF_NOARP; 118 dev->flags &= ~IFF_MULTICAST; 119 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 120 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 121 dev->features |= NETIF_F_GSO_SOFTWARE; 122 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 123 dev->features |= NETIF_F_GSO_ENCAP_ALL; 124 dev->hw_features |= dev->features; 125 dev->hw_enc_features |= dev->features; 126 eth_hw_addr_random(dev); 127 128 dev->min_mtu = 0; 129 dev->max_mtu = 0; 130 } 131 132 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 133 struct netlink_ext_ack *extack) 134 { 135 if (tb[IFLA_ADDRESS]) { 136 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 137 return -EINVAL; 138 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 139 return -EADDRNOTAVAIL; 140 } 141 return 0; 142 } 143 144 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 145 .kind = DRV_NAME, 146 .setup = dummy_setup, 147 .validate = dummy_validate, 148 }; 149 150 /* Number of dummy devices to be set up by this module. */ 151 module_param(numdummies, int, 0); 152 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 153 154 static int __init dummy_init_one(void) 155 { 156 struct net_device *dev_dummy; 157 int err; 158 159 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 160 if (!dev_dummy) 161 return -ENOMEM; 162 163 dev_dummy->rtnl_link_ops = &dummy_link_ops; 164 err = register_netdevice(dev_dummy); 165 if (err < 0) 166 goto err; 167 return 0; 168 169 err: 170 free_netdev(dev_dummy); 171 return err; 172 } 173 174 static int __init dummy_init_module(void) 175 { 176 int i, err = 0; 177 178 down_write(&pernet_ops_rwsem); 179 rtnl_lock(); 180 err = __rtnl_link_register(&dummy_link_ops); 181 if (err < 0) 182 goto out; 183 184 for (i = 0; i < numdummies && !err; i++) { 185 err = dummy_init_one(); 186 cond_resched(); 187 } 188 if (err < 0) 189 __rtnl_link_unregister(&dummy_link_ops); 190 191 out: 192 rtnl_unlock(); 193 up_write(&pernet_ops_rwsem); 194 195 return err; 196 } 197 198 static void __exit dummy_cleanup_module(void) 199 { 200 rtnl_link_unregister(&dummy_link_ops); 201 } 202 203 module_init(dummy_init_module); 204 module_exit(dummy_cleanup_module); 205 MODULE_LICENSE("GPL"); 206 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 207