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->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS; 71 72 netdev_lockdep_set_classes(dev); 73 return 0; 74 } 75 76 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 77 { 78 if (new_carrier) 79 netif_carrier_on(dev); 80 else 81 netif_carrier_off(dev); 82 return 0; 83 } 84 85 static const struct net_device_ops dummy_netdev_ops = { 86 .ndo_init = dummy_dev_init, 87 .ndo_start_xmit = dummy_xmit, 88 .ndo_validate_addr = eth_validate_addr, 89 .ndo_set_rx_mode = set_multicast_list, 90 .ndo_set_mac_address = eth_mac_addr, 91 .ndo_get_stats64 = dummy_get_stats64, 92 .ndo_change_carrier = dummy_change_carrier, 93 }; 94 95 static const struct ethtool_ops dummy_ethtool_ops = { 96 .get_ts_info = ethtool_op_get_ts_info, 97 }; 98 99 static void dummy_setup(struct net_device *dev) 100 { 101 ether_setup(dev); 102 103 /* Initialize the device structure. */ 104 dev->netdev_ops = &dummy_netdev_ops; 105 dev->ethtool_ops = &dummy_ethtool_ops; 106 dev->needs_free_netdev = true; 107 108 /* Fill in device structure with ethernet-generic values. */ 109 dev->flags |= IFF_NOARP; 110 dev->flags &= ~IFF_MULTICAST; 111 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 112 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 113 dev->features |= NETIF_F_GSO_SOFTWARE; 114 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 115 dev->features |= NETIF_F_GSO_ENCAP_ALL; 116 dev->hw_features |= dev->features; 117 dev->hw_enc_features |= dev->features; 118 eth_hw_addr_random(dev); 119 120 dev->min_mtu = 0; 121 dev->max_mtu = 0; 122 } 123 124 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 125 struct netlink_ext_ack *extack) 126 { 127 if (tb[IFLA_ADDRESS]) { 128 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 129 return -EINVAL; 130 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 131 return -EADDRNOTAVAIL; 132 } 133 return 0; 134 } 135 136 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 137 .kind = DRV_NAME, 138 .setup = dummy_setup, 139 .validate = dummy_validate, 140 }; 141 142 /* Number of dummy devices to be set up by this module. */ 143 module_param(numdummies, int, 0); 144 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 145 146 static int __init dummy_init_one(void) 147 { 148 struct net_device *dev_dummy; 149 int err; 150 151 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 152 if (!dev_dummy) 153 return -ENOMEM; 154 155 dev_dummy->rtnl_link_ops = &dummy_link_ops; 156 err = register_netdevice(dev_dummy); 157 if (err < 0) 158 goto err; 159 return 0; 160 161 err: 162 free_netdev(dev_dummy); 163 return err; 164 } 165 166 static int __init dummy_init_module(void) 167 { 168 int i, err = 0; 169 170 down_write(&pernet_ops_rwsem); 171 rtnl_lock(); 172 err = __rtnl_link_register(&dummy_link_ops); 173 if (err < 0) 174 goto out; 175 176 for (i = 0; i < numdummies && !err; i++) { 177 err = dummy_init_one(); 178 cond_resched(); 179 } 180 if (err < 0) 181 __rtnl_link_unregister(&dummy_link_ops); 182 183 out: 184 rtnl_unlock(); 185 up_write(&pernet_ops_rwsem); 186 187 return err; 188 } 189 190 static void __exit dummy_cleanup_module(void) 191 { 192 rtnl_link_unregister(&dummy_link_ops); 193 } 194 195 module_init(dummy_init_module); 196 module_exit(dummy_cleanup_module); 197 MODULE_LICENSE("GPL"); 198 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it"); 199 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 200