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 struct netdev_hw_addr_list *uc, 52 struct netdev_hw_addr_list *mc) 53 { 54 } 55 56 static void dummy_get_stats64(struct net_device *dev, 57 struct rtnl_link_stats64 *stats) 58 { 59 dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes); 60 } 61 62 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) 63 { 64 dev_lstats_add(dev, skb->len); 65 66 skb_tx_timestamp(skb); 67 dev_kfree_skb(skb); 68 return NETDEV_TX_OK; 69 } 70 71 static int dummy_dev_init(struct net_device *dev) 72 { 73 dev->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS; 74 75 netdev_lockdep_set_classes(dev); 76 return 0; 77 } 78 79 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 80 { 81 if (new_carrier) 82 netif_carrier_on(dev); 83 else 84 netif_carrier_off(dev); 85 return 0; 86 } 87 88 static const struct net_device_ops dummy_netdev_ops = { 89 .ndo_init = dummy_dev_init, 90 .ndo_start_xmit = dummy_xmit, 91 .ndo_validate_addr = eth_validate_addr, 92 .ndo_set_rx_mode_async = set_multicast_list, 93 .ndo_set_mac_address = eth_mac_addr, 94 .ndo_get_stats64 = dummy_get_stats64, 95 .ndo_change_carrier = dummy_change_carrier, 96 }; 97 98 static const struct ethtool_ops dummy_ethtool_ops = { 99 .get_ts_info = ethtool_op_get_ts_info, 100 }; 101 102 static void dummy_setup(struct net_device *dev) 103 { 104 ether_setup(dev); 105 106 /* Initialize the device structure. */ 107 dev->netdev_ops = &dummy_netdev_ops; 108 dev->ethtool_ops = &dummy_ethtool_ops; 109 dev->needs_free_netdev = true; 110 dev->request_ops_lock = true; 111 112 /* Fill in device structure with ethernet-generic values. */ 113 dev->flags |= IFF_NOARP; 114 dev->flags &= ~IFF_MULTICAST; 115 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 116 dev->lltx = true; 117 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 118 dev->features |= NETIF_F_GSO_SOFTWARE; 119 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA; 120 dev->features |= NETIF_F_GSO_ENCAP_ALL; 121 dev->hw_features |= dev->features; 122 dev->hw_enc_features |= dev->features; 123 eth_hw_addr_random(dev); 124 125 dev->min_mtu = 0; 126 dev->max_mtu = 0; 127 } 128 129 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 130 struct netlink_ext_ack *extack) 131 { 132 if (tb[IFLA_ADDRESS]) { 133 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 134 return -EINVAL; 135 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 136 return -EADDRNOTAVAIL; 137 } 138 return 0; 139 } 140 141 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 142 .kind = DRV_NAME, 143 .setup = dummy_setup, 144 .validate = dummy_validate, 145 }; 146 147 /* Number of dummy devices to be set up by this module. */ 148 module_param(numdummies, int, 0); 149 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 150 151 static int __init dummy_init_one(void) 152 { 153 struct net_device *dev_dummy; 154 int err; 155 156 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 157 if (!dev_dummy) 158 return -ENOMEM; 159 160 dev_dummy->rtnl_link_ops = &dummy_link_ops; 161 err = register_netdevice(dev_dummy); 162 if (err < 0) 163 goto err; 164 return 0; 165 166 err: 167 free_netdev(dev_dummy); 168 return err; 169 } 170 171 static int __init dummy_init_module(void) 172 { 173 int i, err = 0; 174 175 err = rtnl_link_register(&dummy_link_ops); 176 if (err < 0) 177 return err; 178 179 rtnl_net_lock(&init_net); 180 181 for (i = 0; i < numdummies && !err; i++) { 182 err = dummy_init_one(); 183 cond_resched(); 184 } 185 186 rtnl_net_unlock(&init_net); 187 188 if (err < 0) 189 rtnl_link_unregister(&dummy_link_ops); 190 191 return err; 192 } 193 194 static void __exit dummy_cleanup_module(void) 195 { 196 rtnl_link_unregister(&dummy_link_ops); 197 } 198 199 module_init(dummy_init_module); 200 module_exit(dummy_cleanup_module); 201 MODULE_LICENSE("GPL"); 202 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it"); 203 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 204