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 int set_multicast_list(struct net_device *dev, 51 struct netdev_hw_addr_list *uc, 52 struct netdev_hw_addr_list *mc) 53 { 54 return 0; 55 } 56 57 static void dummy_get_stats64(struct net_device *dev, 58 struct rtnl_link_stats64 *stats) 59 { 60 dev_lstats_read(dev, &stats->tx_packets, &stats->tx_bytes); 61 } 62 63 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) 64 { 65 dev_lstats_add(dev, skb->len); 66 67 skb_tx_timestamp(skb); 68 dev_kfree_skb(skb); 69 return NETDEV_TX_OK; 70 } 71 72 static int dummy_dev_init(struct net_device *dev) 73 { 74 dev->pcpu_stat_type = NETDEV_PCPU_STAT_LSTATS; 75 76 netdev_lockdep_set_classes(dev); 77 return 0; 78 } 79 80 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 81 { 82 if (new_carrier) 83 netif_carrier_on(dev); 84 else 85 netif_carrier_off(dev); 86 return 0; 87 } 88 89 static const struct net_device_ops dummy_netdev_ops = { 90 .ndo_init = dummy_dev_init, 91 .ndo_start_xmit = dummy_xmit, 92 .ndo_validate_addr = eth_validate_addr, 93 .ndo_set_rx_mode_async = set_multicast_list, 94 .ndo_set_mac_address = eth_mac_addr, 95 .ndo_get_stats64 = dummy_get_stats64, 96 .ndo_change_carrier = dummy_change_carrier, 97 }; 98 99 static const struct ethtool_ops dummy_ethtool_ops = { 100 .get_ts_info = ethtool_op_get_ts_info, 101 }; 102 103 static void dummy_setup(struct net_device *dev) 104 { 105 ether_setup(dev); 106 107 /* Initialize the device structure. */ 108 dev->netdev_ops = &dummy_netdev_ops; 109 dev->ethtool_ops = &dummy_ethtool_ops; 110 dev->needs_free_netdev = true; 111 dev->request_ops_lock = true; 112 113 /* Fill in device structure with ethernet-generic values. */ 114 dev->flags |= IFF_NOARP; 115 dev->flags &= ~IFF_MULTICAST; 116 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 117 dev->lltx = true; 118 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 119 dev->features |= NETIF_F_GSO_SOFTWARE; 120 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA; 121 dev->features |= NETIF_F_GSO_ENCAP_ALL; 122 dev->hw_features |= dev->features; 123 dev->hw_enc_features |= dev->features; 124 eth_hw_addr_random(dev); 125 126 dev->min_mtu = 0; 127 dev->max_mtu = 0; 128 } 129 130 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 131 struct netlink_ext_ack *extack) 132 { 133 if (tb[IFLA_ADDRESS]) { 134 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 135 return -EINVAL; 136 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 137 return -EADDRNOTAVAIL; 138 } 139 return 0; 140 } 141 142 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 143 .kind = DRV_NAME, 144 .setup = dummy_setup, 145 .validate = dummy_validate, 146 }; 147 148 /* Number of dummy devices to be set up by this module. */ 149 module_param(numdummies, int, 0); 150 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 151 152 static int __init dummy_init_one(void) 153 { 154 struct net_device *dev_dummy; 155 int err; 156 157 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 158 if (!dev_dummy) 159 return -ENOMEM; 160 161 dev_dummy->rtnl_link_ops = &dummy_link_ops; 162 err = register_netdev(dev_dummy); 163 if (err < 0) 164 goto err; 165 return 0; 166 167 err: 168 free_netdev(dev_dummy); 169 return err; 170 } 171 172 static int __init dummy_init_module(void) 173 { 174 int i, err = 0; 175 176 err = rtnl_link_register(&dummy_link_ops); 177 if (err < 0) 178 return err; 179 180 for (i = 0; i < numdummies && !err; i++) { 181 err = dummy_init_one(); 182 cond_resched(); 183 } 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