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; 108 109 /* Fill in device structure with ethernet-generic values. */ 110 dev->flags |= IFF_NOARP; 111 dev->flags &= ~IFF_MULTICAST; 112 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 113 dev->lltx = true; 114 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 115 dev->features |= NETIF_F_GSO_SOFTWARE; 116 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA; 117 dev->features |= NETIF_F_GSO_ENCAP_ALL; 118 dev->hw_features |= dev->features; 119 dev->hw_enc_features |= dev->features; 120 eth_hw_addr_random(dev); 121 122 dev->min_mtu = 0; 123 dev->max_mtu = 0; 124 } 125 126 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 127 struct netlink_ext_ack *extack) 128 { 129 if (tb[IFLA_ADDRESS]) { 130 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 131 return -EINVAL; 132 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 133 return -EADDRNOTAVAIL; 134 } 135 return 0; 136 } 137 138 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 139 .kind = DRV_NAME, 140 .setup = dummy_setup, 141 .validate = dummy_validate, 142 }; 143 144 /* Number of dummy devices to be set up by this module. */ 145 module_param(numdummies, int, 0); 146 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 147 148 static int __init dummy_init_one(void) 149 { 150 struct net_device *dev_dummy; 151 int err; 152 153 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 154 if (!dev_dummy) 155 return -ENOMEM; 156 157 dev_dummy->rtnl_link_ops = &dummy_link_ops; 158 err = register_netdevice(dev_dummy); 159 if (err < 0) 160 goto err; 161 return 0; 162 163 err: 164 free_netdev(dev_dummy); 165 return err; 166 } 167 168 static int __init dummy_init_module(void) 169 { 170 int i, err = 0; 171 172 err = rtnl_link_register(&dummy_link_ops); 173 if (err < 0) 174 return err; 175 176 rtnl_net_lock(&init_net); 177 178 for (i = 0; i < numdummies && !err; i++) { 179 err = dummy_init_one(); 180 cond_resched(); 181 } 182 183 rtnl_net_unlock(&init_net); 184 185 if (err < 0) 186 rtnl_link_unregister(&dummy_link_ops); 187 188 return err; 189 } 190 191 static void __exit dummy_cleanup_module(void) 192 { 193 rtnl_link_unregister(&dummy_link_ops); 194 } 195 196 module_init(dummy_init_module); 197 module_exit(dummy_cleanup_module); 198 MODULE_LICENSE("GPL"); 199 MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it"); 200 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 201