drivers/net/dummy.c

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