201 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/* dummy.c: a dummy net driver3 4 The purpose of this driver is to provide a device to point a5 route through, but not to actually transmit packets.6 7 Why? If you have a machine whose only connection is an occasional8 PPP/SLIP/PLIP link, you can only connect to your own hostname9 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 do15 16 [when not running slip]17 ifconfig dummy slip.addr.ess.here up18 [to go to slip]19 ifconfig dummy down20 dip whatever21 22 This was written by looking at Donald Becker's skeleton driver23 and the loopback driver. I then threw away anything that didn't24 apply! Thanks to Alan Cox for the key clue on what to do with25 misguided packets.26 27 Nick Holloway, 27th May 199428 [I tweaked this explanation a little but that's all]29 Alan Cox, 30th May 199430*/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 46static int numdummies = 1;47 48/* fake multicast ability */49static void set_multicast_list(struct net_device *dev)50{51}52 53static 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 59static 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 68static 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 76static int dummy_change_carrier(struct net_device *dev, bool new_carrier)77{78 if (new_carrier)79 netif_carrier_on(dev);80 else81 netif_carrier_off(dev);82 return 0;83}84 85static 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 95static const struct ethtool_ops dummy_ethtool_ops = {96 .get_ts_info = ethtool_op_get_ts_info,97};98 99static 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 125static 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 137static 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. */144module_param(numdummies, int, 0);145MODULE_PARM_DESC(numdummies, "Number of dummy pseudo devices");146 147static 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 162err:163 free_netdev(dev_dummy);164 return err;165}166 167static 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 184out:185 rtnl_unlock();186 up_write(&pernet_ops_rwsem);187 188 return err;189}190 191static void __exit dummy_cleanup_module(void)192{193 rtnl_link_unregister(&dummy_link_ops);194}195 196module_init(dummy_init_module);197module_exit(dummy_cleanup_module);198MODULE_LICENSE("GPL");199MODULE_DESCRIPTION("Dummy netdevice driver which discards all packets sent to it");200MODULE_ALIAS_RTNL_LINK(DRV_NAME);201