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