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 #define DRV_VERSION "1.0" 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 struct pcpu_dstats { 55 u64 tx_packets; 56 u64 tx_bytes; 57 struct u64_stats_sync syncp; 58 }; 59 60 static void dummy_get_stats64(struct net_device *dev, 61 struct rtnl_link_stats64 *stats) 62 { 63 int i; 64 65 for_each_possible_cpu(i) { 66 const struct pcpu_dstats *dstats; 67 u64 tbytes, tpackets; 68 unsigned int start; 69 70 dstats = per_cpu_ptr(dev->dstats, i); 71 do { 72 start = u64_stats_fetch_begin_irq(&dstats->syncp); 73 tbytes = dstats->tx_bytes; 74 tpackets = dstats->tx_packets; 75 } while (u64_stats_fetch_retry_irq(&dstats->syncp, start)); 76 stats->tx_bytes += tbytes; 77 stats->tx_packets += tpackets; 78 } 79 } 80 81 static netdev_tx_t dummy_xmit(struct sk_buff *skb, struct net_device *dev) 82 { 83 struct pcpu_dstats *dstats = this_cpu_ptr(dev->dstats); 84 85 u64_stats_update_begin(&dstats->syncp); 86 dstats->tx_packets++; 87 dstats->tx_bytes += skb->len; 88 u64_stats_update_end(&dstats->syncp); 89 90 skb_tx_timestamp(skb); 91 dev_kfree_skb(skb); 92 return NETDEV_TX_OK; 93 } 94 95 static int dummy_dev_init(struct net_device *dev) 96 { 97 dev->dstats = netdev_alloc_pcpu_stats(struct pcpu_dstats); 98 if (!dev->dstats) 99 return -ENOMEM; 100 101 return 0; 102 } 103 104 static void dummy_dev_uninit(struct net_device *dev) 105 { 106 free_percpu(dev->dstats); 107 } 108 109 static int dummy_change_carrier(struct net_device *dev, bool new_carrier) 110 { 111 if (new_carrier) 112 netif_carrier_on(dev); 113 else 114 netif_carrier_off(dev); 115 return 0; 116 } 117 118 static const struct net_device_ops dummy_netdev_ops = { 119 .ndo_init = dummy_dev_init, 120 .ndo_uninit = dummy_dev_uninit, 121 .ndo_start_xmit = dummy_xmit, 122 .ndo_validate_addr = eth_validate_addr, 123 .ndo_set_rx_mode = set_multicast_list, 124 .ndo_set_mac_address = eth_mac_addr, 125 .ndo_get_stats64 = dummy_get_stats64, 126 .ndo_change_carrier = dummy_change_carrier, 127 }; 128 129 static void dummy_get_drvinfo(struct net_device *dev, 130 struct ethtool_drvinfo *info) 131 { 132 strlcpy(info->driver, DRV_NAME, sizeof(info->driver)); 133 strlcpy(info->version, DRV_VERSION, sizeof(info->version)); 134 } 135 136 static const struct ethtool_ops dummy_ethtool_ops = { 137 .get_drvinfo = dummy_get_drvinfo, 138 .get_ts_info = ethtool_op_get_ts_info, 139 }; 140 141 static void dummy_setup(struct net_device *dev) 142 { 143 ether_setup(dev); 144 145 /* Initialize the device structure. */ 146 dev->netdev_ops = &dummy_netdev_ops; 147 dev->ethtool_ops = &dummy_ethtool_ops; 148 dev->needs_free_netdev = true; 149 150 /* Fill in device structure with ethernet-generic values. */ 151 dev->flags |= IFF_NOARP; 152 dev->flags &= ~IFF_MULTICAST; 153 dev->priv_flags |= IFF_LIVE_ADDR_CHANGE | IFF_NO_QUEUE; 154 dev->features |= NETIF_F_SG | NETIF_F_FRAGLIST; 155 dev->features |= NETIF_F_ALL_TSO; 156 dev->features |= NETIF_F_HW_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX; 157 dev->features |= NETIF_F_GSO_ENCAP_ALL; 158 dev->hw_features |= dev->features; 159 dev->hw_enc_features |= dev->features; 160 eth_hw_addr_random(dev); 161 162 dev->min_mtu = 0; 163 dev->max_mtu = 0; 164 } 165 166 static int dummy_validate(struct nlattr *tb[], struct nlattr *data[], 167 struct netlink_ext_ack *extack) 168 { 169 if (tb[IFLA_ADDRESS]) { 170 if (nla_len(tb[IFLA_ADDRESS]) != ETH_ALEN) 171 return -EINVAL; 172 if (!is_valid_ether_addr(nla_data(tb[IFLA_ADDRESS]))) 173 return -EADDRNOTAVAIL; 174 } 175 return 0; 176 } 177 178 static struct rtnl_link_ops dummy_link_ops __read_mostly = { 179 .kind = DRV_NAME, 180 .setup = dummy_setup, 181 .validate = dummy_validate, 182 }; 183 184 /* Number of dummy devices to be set up by this module. */ 185 module_param(numdummies, int, 0); 186 MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices"); 187 188 static int __init dummy_init_one(void) 189 { 190 struct net_device *dev_dummy; 191 int err; 192 193 dev_dummy = alloc_netdev(0, "dummy%d", NET_NAME_ENUM, dummy_setup); 194 if (!dev_dummy) 195 return -ENOMEM; 196 197 dev_dummy->rtnl_link_ops = &dummy_link_ops; 198 err = register_netdevice(dev_dummy); 199 if (err < 0) 200 goto err; 201 return 0; 202 203 err: 204 free_netdev(dev_dummy); 205 return err; 206 } 207 208 static int __init dummy_init_module(void) 209 { 210 int i, err = 0; 211 212 down_write(&pernet_ops_rwsem); 213 rtnl_lock(); 214 err = __rtnl_link_register(&dummy_link_ops); 215 if (err < 0) 216 goto out; 217 218 for (i = 0; i < numdummies && !err; i++) { 219 err = dummy_init_one(); 220 cond_resched(); 221 } 222 if (err < 0) 223 __rtnl_link_unregister(&dummy_link_ops); 224 225 out: 226 rtnl_unlock(); 227 up_write(&pernet_ops_rwsem); 228 229 return err; 230 } 231 232 static void __exit dummy_cleanup_module(void) 233 { 234 rtnl_link_unregister(&dummy_link_ops); 235 } 236 237 module_init(dummy_init_module); 238 module_exit(dummy_cleanup_module); 239 MODULE_LICENSE("GPL"); 240 MODULE_ALIAS_RTNL_LINK(DRV_NAME); 241 MODULE_VERSION(DRV_VERSION); 242