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->lltx = true; 113 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 114 dev->features |= NETIF_F_GSO_SOFTWARE; 115 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA; 116 dev->features |= NETIF_F_GSO_ENCAP_ALL; 117 dev->hw_features |= dev->features; 118 dev->hw_enc_features |= dev->features; 119 eth_hw_addr_random(dev); 120 121 dev->min_mtu = 0; 122 dev->max_mtu = 0; 123 } 124 125 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 126 struct netlink_ext_ack *extack) 127 { 128 if (tb[IFLA_ADDRESS]) { 129 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 130 return -EINVAL; 131 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 132 return -EADDRNOTAVAIL; 133 } 134 return 0; 135 } 136 137 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 138 .kind = DRV_NAME, 139 .setup = dummy_setup, 140 .validate = dummy_validate, 141 }; 142 143 /* Number of dummy devices to be set up by this module. */ 144 module_param(numdummies, int, 0); 145 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 146 147 static int __init dummy_init_one(void) 148 { 149 struct net_device *dev_dummy; 150 int err; 151 152 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 153 if (!dev_dummy) 154 return -ENOMEM; 155 156 dev_dummy->rtnl_link_ops = &dummy_link_ops; 157 err = register_netdevice(dev_dummy); 158 if (err < 0) 159 goto err; 160 return 0; 161 162 err: 163 free_netdev(dev_dummy); 164 return err; 165 } 166 167 static int __init dummy_init_module(void) 168 { 169 int i, err = 0; 170 171 down_write(&pernet_ops_rwsem); 172 rtnl_lock(); 173 err = __rtnl_link_register(&dummy_link_ops); 174 if (err < 0) 175 goto out; 176 177 for (i = 0; i < numdummies && !err; i++) { 178 err = dummy_init_one(); 179 cond_resched(); 180 } 181 if (err < 0) 182 __rtnl_link_unregister(&dummy_link_ops); 183 184 out: 185 rtnl_unlock(); 186 up_write(&pernet_ops_rwsem); 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