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/netdev_lock.h> 42 #include <net/rtnetlink.h> 43 #include <linux/u64_stats_sync.h> 44 45 #define DRV_NAME "dummy" 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->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS; 72 73 netdev_lockdep_set_classes(dev); 74 return 0; 75 } 76 77 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 78 { 79 if (new_carrier) 80 netif_carrier_on(dev); 81 else 82 netif_carrier_off(dev); 83 return 0; 84 } 85 86 static const struct net_device_ops dummy_netdev_ops = { 87 .ndo_init = dummy_dev_init, 88 .ndo_start_xmit = dummy_xmit, 89 .ndo_validate_addr = eth_validate_addr, 90 .ndo_set_rx_mode = set_multicast_list, 91 .ndo_set_mac_address = eth_mac_addr, 92 .ndo_get_stats64 = dummy_get_stats64, 93 .ndo_change_carrier = dummy_change_carrier, 94 }; 95 96 static const struct ethtool_ops dummy_ethtool_ops = { 97 .get_ts_info = ethtool_op_get_ts_info, 98 }; 99 100 static void dummy_setup(struct net_device *dev) 101 { 102 ether_setup(dev); 103 104 /* Initialize the device structure. */ 105 dev->netdev_ops = &dummy_netdev_ops; 106 dev->ethtool_ops = &dummy_ethtool_ops; 107 dev->needs_free_netdev = true; 108 dev->request_ops_lock = true; 109 110 /* Fill in device structure with ethernet-generic values. */ 111 dev->flags |= IFF_NOARP; 112 dev->flags &= ~IFF_MULTICAST; 113 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 114 dev->lltx = true; 115 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 116 dev->features |= NETIF_F_GSO_SOFTWARE; 117 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA; 118 dev->features |= NETIF_F_GSO_ENCAP_ALL; 119 dev->hw_features |= dev->features; 120 dev->hw_enc_features |= dev->features; 121 eth_hw_addr_random(dev); 122 123 dev->min_mtu = 0; 124 dev->max_mtu = 0; 125 } 126 127 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 128 struct netlink_ext_ack *extack) 129 { 130 if (tb[IFLA_ADDRESS]) { 131 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 132 return -EINVAL; 133 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 134 return -EADDRNOTAVAIL; 135 } 136 return 0; 137 } 138 139 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 140 .kind = DRV_NAME, 141 .setup = dummy_setup, 142 .validate = dummy_validate, 143 }; 144 145 /* Number of dummy devices to be set up by this module. */ 146 module_param(numdummies, int, 0); 147 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 148 149 static int __init dummy_init_one(void) 150 { 151 struct net_device *dev_dummy; 152 int err; 153 154 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 155 if (!dev_dummy) 156 return -ENOMEM; 157 158 dev_dummy->rtnl_link_ops = &dummy_link_ops; 159 err = register_netdevice(dev_dummy); 160 if (err < 0) 161 goto err; 162 return 0; 163 164 err: 165 free_netdev(dev_dummy); 166 return err; 167 } 168 169 static int __init dummy_init_module(void) 170 { 171 int i, err = 0; 172 173 err = rtnl_link_register(&dummy_link_ops); 174 if (err < 0) 175 return err; 176 177 rtnl_net_lock(&init_net); 178 179 for (i = 0; i < numdummies && !err; i++) { 180 err = dummy_init_one(); 181 cond_resched(); 182 } 183 184 rtnl_net_unlock(&init_net); 185 186 if (err < 0) 187 rtnl_link_unregister(&dummy_link_ops); 188 189 return err; 190 } 191 192 static void __exit dummy_cleanup_module(void) 193 { 194 rtnl_link_unregister(&dummy_link_ops); 195 } 196 197 module_init(dummy_init_module); 198 module_exit(dummy_cleanup_module); 199 MODULE_LICENSE("GPL"); 200 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it"); 201 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 202