linux/drivers/net/loopback.c
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   1/*
   2 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3 *              operating system.  INET is implemented using the  BSD Socket
   4 *              interface as the means of communication with the user level.
   5 *
   6 *              Pseudo-driver for the loopback interface.
   7 *
   8 * Version:     @(#)loopback.c  1.0.4b  08/16/93
   9 *
  10 * Authors:     Ross Biro
  11 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12 *              Donald Becker, <becker@scyld.com>
  13 *
  14 *              Alan Cox        :       Fixed oddments for NET3.014
  15 *              Alan Cox        :       Rejig for NET3.029 snap #3
  16 *              Alan Cox        :       Fixed NET3.029 bugs and sped up
  17 *              Larry McVoy     :       Tiny tweak to double performance
  18 *              Alan Cox        :       Backed out LMV's tweak - the linux mm
  19 *                                      can't take it...
  20 *              Michael Griffith:       Don't bother computing the checksums
  21 *                                      on packets received on the loopback
  22 *                                      interface.
  23 *              Alexey Kuznetsov:       Potential hang under some extreme
  24 *                                      cases removed.
  25 *
  26 *              This program is free software; you can redistribute it and/or
  27 *              modify it under the terms of the GNU General Public License
  28 *              as published by the Free Software Foundation; either version
  29 *              2 of the License, or (at your option) any later version.
  30 */
  31#include <linux/kernel.h>
  32#include <linux/jiffies.h>
  33#include <linux/module.h>
  34#include <linux/interrupt.h>
  35#include <linux/fs.h>
  36#include <linux/types.h>
  37#include <linux/string.h>
  38#include <linux/socket.h>
  39#include <linux/errno.h>
  40#include <linux/fcntl.h>
  41#include <linux/in.h>
  42#include <linux/init.h>
  43
  44#include <asm/uaccess.h>
  45#include <asm/io.h>
  46
  47#include <linux/inet.h>
  48#include <linux/netdevice.h>
  49#include <linux/etherdevice.h>
  50#include <linux/skbuff.h>
  51#include <linux/ethtool.h>
  52#include <net/sock.h>
  53#include <net/checksum.h>
  54#include <linux/if_ether.h>     /* For the statistics structure. */
  55#include <linux/if_arp.h>       /* For ARPHRD_ETHER */
  56#include <linux/ip.h>
  57#include <linux/tcp.h>
  58#include <linux/percpu.h>
  59#include <net/net_namespace.h>
  60#include <linux/u64_stats_sync.h>
  61
  62struct pcpu_lstats {
  63        u64                     packets;
  64        u64                     bytes;
  65        struct u64_stats_sync   syncp;
  66};
  67
  68/*
  69 * The higher levels take care of making this non-reentrant (it's
  70 * called with bh's disabled).
  71 */
  72static netdev_tx_t loopback_xmit(struct sk_buff *skb,
  73                                 struct net_device *dev)
  74{
  75        struct pcpu_lstats *lb_stats;
  76        int len;
  77
  78        skb_orphan(skb);
  79
  80        skb->protocol = eth_type_trans(skb, dev);
  81
  82        /* it's OK to use per_cpu_ptr() because BHs are off */
  83        lb_stats = this_cpu_ptr(dev->lstats);
  84
  85        len = skb->len;
  86        if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
  87                u64_stats_update_begin(&lb_stats->syncp);
  88                lb_stats->bytes += len;
  89                lb_stats->packets++;
  90                u64_stats_update_end(&lb_stats->syncp);
  91        }
  92
  93        return NETDEV_TX_OK;
  94}
  95
  96static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev,
  97                                                      struct rtnl_link_stats64 *stats)
  98{
  99        u64 bytes = 0;
 100        u64 packets = 0;
 101        int i;
 102
 103        for_each_possible_cpu(i) {
 104                const struct pcpu_lstats *lb_stats;
 105                u64 tbytes, tpackets;
 106                unsigned int start;
 107
 108                lb_stats = per_cpu_ptr(dev->lstats, i);
 109                do {
 110                        start = u64_stats_fetch_begin_bh(&lb_stats->syncp);
 111                        tbytes = lb_stats->bytes;
 112                        tpackets = lb_stats->packets;
 113                } while (u64_stats_fetch_retry_bh(&lb_stats->syncp, start));
 114                bytes   += tbytes;
 115                packets += tpackets;
 116        }
 117        stats->rx_packets = packets;
 118        stats->tx_packets = packets;
 119        stats->rx_bytes   = bytes;
 120        stats->tx_bytes   = bytes;
 121        return stats;
 122}
 123
 124static u32 always_on(struct net_device *dev)
 125{
 126        return 1;
 127}
 128
 129static const struct ethtool_ops loopback_ethtool_ops = {
 130        .get_link               = always_on,
 131};
 132
 133static int loopback_dev_init(struct net_device *dev)
 134{
 135        dev->lstats = alloc_percpu(struct pcpu_lstats);
 136        if (!dev->lstats)
 137                return -ENOMEM;
 138
 139        return 0;
 140}
 141
 142static void loopback_dev_free(struct net_device *dev)
 143{
 144        free_percpu(dev->lstats);
 145        free_netdev(dev);
 146}
 147
 148static const struct net_device_ops loopback_ops = {
 149        .ndo_init      = loopback_dev_init,
 150        .ndo_start_xmit= loopback_xmit,
 151        .ndo_get_stats64 = loopback_get_stats64,
 152};
 153
 154/*
 155 * The loopback device is special. There is only one instance
 156 * per network namespace.
 157 */
 158static void loopback_setup(struct net_device *dev)
 159{
 160        dev->mtu                = (16 * 1024) + 20 + 20 + 12;
 161        dev->hard_header_len    = ETH_HLEN;     /* 14   */
 162        dev->addr_len           = ETH_ALEN;     /* 6    */
 163        dev->tx_queue_len       = 0;
 164        dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
 165        dev->flags              = IFF_LOOPBACK;
 166        dev->priv_flags        &= ~IFF_XMIT_DST_RELEASE;
 167        dev->hw_features        = NETIF_F_ALL_TSO | NETIF_F_UFO;
 168        dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
 169                | NETIF_F_ALL_TSO
 170                | NETIF_F_UFO
 171                | NETIF_F_HW_CSUM
 172                | NETIF_F_RXCSUM
 173                | NETIF_F_HIGHDMA
 174                | NETIF_F_LLTX
 175                | NETIF_F_NETNS_LOCAL
 176                | NETIF_F_VLAN_CHALLENGED
 177                | NETIF_F_LOOPBACK;
 178        dev->ethtool_ops        = &loopback_ethtool_ops;
 179        dev->header_ops         = &eth_header_ops;
 180        dev->netdev_ops         = &loopback_ops;
 181        dev->destructor         = loopback_dev_free;
 182}
 183
 184/* Setup and register the loopback device. */
 185static __net_init int loopback_net_init(struct net *net)
 186{
 187        struct net_device *dev;
 188        int err;
 189
 190        err = -ENOMEM;
 191        dev = alloc_netdev(0, "lo", loopback_setup);
 192        if (!dev)
 193                goto out;
 194
 195        dev_net_set(dev, net);
 196        err = register_netdev(dev);
 197        if (err)
 198                goto out_free_netdev;
 199
 200        net->loopback_dev = dev;
 201        return 0;
 202
 203
 204out_free_netdev:
 205        free_netdev(dev);
 206out:
 207        if (net_eq(net, &init_net))
 208                panic("loopback: Failed to register netdevice: %d\n", err);
 209        return err;
 210}
 211
 212/* Registered in net/core/dev.c */
 213struct pernet_operations __net_initdata loopback_net_ops = {
 214       .init = loopback_net_init,
 215};
 216
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