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 #define DRV_VERSION "1.0" 46 47 static int numdummies = 1; 48 49 /* fake multicast ability */ 50 static void set_multicast_list(struct net_device *dev) 51 { 52 } 53 54 static void dummy_get_stats64(struct net_device *dev, 55 struct rtnl_link_stats64 *stats) 56 { 57 dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes); 58 } 59 60 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) 61 { 62 dev_lstats_add(dev, skb->len); 63 64 skb_tx_timestamp(skb); 65 dev_kfree_skb(skb); 66 return NETDEV_TX_OK; 67 } 68 69 static int dummy_dev_init(struct net_device *dev) 70 { 71 dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats); 72 if (!dev->lstats) 73 return -ENOMEM; 74 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 void dummy_get_drvinfo(struct net_device *dev, 104 struct ethtool_drvinfo *info) 105 { 106 strlcpy(info->driver, DRV_NAME, sizeof(info->driver)); 107 strlcpy(info->version, DRV_VERSION, sizeof(info->version)); 108 } 109 110 static const struct ethtool_ops dummy_ethtool_ops = { 111 .get_drvinfo = dummy_get_drvinfo, 112 .get_ts_info = ethtool_op_get_ts_info, 113 }; 114 115 static void dummy_setup(struct net_device *dev) 116 { 117 ether_setup(dev); 118 119 /* Initialize the device structure. */ 120 dev->netdev_ops = &dummy_netdev_ops; 121 dev->ethtool_ops = &dummy_ethtool_ops; 122 dev->needs_free_netdev = true; 123 124 /* Fill in device structure with ethernet-generic values. */ 125 dev->flags |= IFF_NOARP; 126 dev->flags &= ~IFF_MULTICAST; 127 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 128 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 129 dev->features |= NETIF_F_ALL_TSO; 130 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 131 dev->features |= NETIF_F_GSO_ENCAP_ALL; 132 dev->hw_features |= dev->features; 133 dev->hw_enc_features |= dev->features; 134 eth_hw_addr_random(dev); 135 136 dev->min_mtu = 0; 137 dev->max_mtu = 0; 138 } 139 140 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 141 struct netlink_ext_ack *extack) 142 { 143 if (tb[IFLA_ADDRESS]) { 144 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 145 return -EINVAL; 146 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 147 return -EADDRNOTAVAIL; 148 } 149 return 0; 150 } 151 152 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 153 .kind = DRV_NAME, 154 .setup = dummy_setup, 155 .validate = dummy_validate, 156 }; 157 158 /* Number of dummy devices to be set up by this module. */ 159 module_param(numdummies, int, 0); 160 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 161 162 static int __init dummy_init_one(void) 163 { 164 struct net_device *dev_dummy; 165 int err; 166 167 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 168 if (!dev_dummy) 169 return -ENOMEM; 170 171 dev_dummy->rtnl_link_ops = &dummy_link_ops; 172 err = register_netdevice(dev_dummy); 173 if (err < 0) 174 goto err; 175 return 0; 176 177 err: 178 free_netdev(dev_dummy); 179 return err; 180 } 181 182 static int __init dummy_init_module(void) 183 { 184 int i, err = 0; 185 186 down_write(&pernet_ops_rwsem); 187 rtnl_lock(); 188 err = __rtnl_link_register(&dummy_link_ops); 189 if (err < 0) 190 goto out; 191 192 for (i = 0; i < numdummies && !err; i++) { 193 err = dummy_init_one(); 194 cond_resched(); 195 } 196 if (err < 0) 197 __rtnl_link_unregister(&dummy_link_ops); 198 199 out: 200 rtnl_unlock(); 201 up_write(&pernet_ops_rwsem); 202 203 return err; 204 } 205 206 static void __exit dummy_cleanup_module(void) 207 { 208 rtnl_link_unregister(&dummy_link_ops); 209 } 210 211 module_init(dummy_init_module); 212 module_exit(dummy_cleanup_module); 213 MODULE_LICENSE("GPL"); 214 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 215 MODULE_VERSION(DRV_VERSION); 216