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 void dummy_get_drvinfo(struct net_device *dev, 103 struct ethtool_drvinfo *info) 104 { 105 strlcpy(info->driver, DRV_NAME, sizeof(info->driver)); 106 } 107 108 static const struct ethtool_ops dummy_ethtool_ops = { 109 .get_drvinfo = dummy_get_drvinfo, 110 .get_ts_info = ethtool_op_get_ts_info, 111 }; 112 113 static void dummy_setup(struct net_device *dev) 114 { 115 ether_setup(dev); 116 117 /* Initialize the device structure. */ 118 dev->netdev_ops = &dummy_netdev_ops; 119 dev->ethtool_ops = &dummy_ethtool_ops; 120 dev->needs_free_netdev = true; 121 122 /* Fill in device structure with ethernet-generic values. */ 123 dev->flags |= IFF_NOARP; 124 dev->flags &= ~IFF_MULTICAST; 125 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 126 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 127 dev->features |= NETIF_F_GSO_SOFTWARE; 128 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 129 dev->features |= NETIF_F_GSO_ENCAP_ALL; 130 dev->hw_features |= dev->features; 131 dev->hw_enc_features |= dev->features; 132 eth_hw_addr_random(dev); 133 134 dev->min_mtu = 0; 135 dev->max_mtu = 0; 136 } 137 138 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 139 struct netlink_ext_ack *extack) 140 { 141 if (tb[IFLA_ADDRESS]) { 142 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 143 return -EINVAL; 144 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 145 return -EADDRNOTAVAIL; 146 } 147 return 0; 148 } 149 150 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 151 .kind = DRV_NAME, 152 .setup = dummy_setup, 153 .validate = dummy_validate, 154 }; 155 156 /* Number of dummy devices to be set up by this module. */ 157 module_param(numdummies, int, 0); 158 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 159 160 static int __init dummy_init_one(void) 161 { 162 struct net_device *dev_dummy; 163 int err; 164 165 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 166 if (!dev_dummy) 167 return -ENOMEM; 168 169 dev_dummy->rtnl_link_ops = &dummy_link_ops; 170 err = register_netdevice(dev_dummy); 171 if (err < 0) 172 goto err; 173 return 0; 174 175 err: 176 free_netdev(dev_dummy); 177 return err; 178 } 179 180 static int __init dummy_init_module(void) 181 { 182 int i, err = 0; 183 184 down_write(&pernet_ops_rwsem); 185 rtnl_lock(); 186 err = __rtnl_link_register(&dummy_link_ops); 187 if (err < 0) 188 goto out; 189 190 for (i = 0; i < numdummies && !err; i++) { 191 err = dummy_init_one(); 192 cond_resched(); 193 } 194 if (err < 0) 195 __rtnl_link_unregister(&dummy_link_ops); 196 197 out: 198 rtnl_unlock(); 199 up_write(&pernet_ops_rwsem); 200 201 return err; 202 } 203 204 static void __exit dummy_cleanup_module(void) 205 { 206 rtnl_link_unregister(&dummy_link_ops); 207 } 208 209 module_init(dummy_init_module); 210 module_exit(dummy_cleanup_module); 211 MODULE_LICENSE("GPL"); 212 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 213