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 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);