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        /* Before queueing this packet to netif_rx(),
  81         * make sure dst is refcounted.
  82         */
  83        skb_dst_force(skb);
  84
  85        skb->protocol = eth_type_trans(skb, dev);
  86
  87        /* it's OK to use per_cpu_ptr() because BHs are off */
  88        lb_stats = this_cpu_ptr(dev->lstats);
  89
  90        len = skb->len;
  91        if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
  92                u64_stats_update_begin(&lb_stats->syncp);
  93                lb_stats->bytes += len;
  94                lb_stats->packets++;
  95                u64_stats_update_end(&lb_stats->syncp);
  96        }
  97
  98        return NETDEV_TX_OK;
  99}
 100
 101static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev,
 102                                                      struct rtnl_link_stats64 *stats)
 103{
 104        u64 bytes = 0;
 105        u64 packets = 0;
 106        int i;
 107
 108        for_each_possible_cpu(i) {
 109                const struct pcpu_lstats *lb_stats;
 110                u64 tbytes, tpackets;
 111                unsigned int start;
 112
 113                lb_stats = per_cpu_ptr(dev->lstats, i);
 114                do {
 115                        start = u64_stats_fetch_begin_bh(&lb_stats->syncp);
 116                        tbytes = lb_stats->bytes;
 117                        tpackets = lb_stats->packets;
 118                } while (u64_stats_fetch_retry_bh(&lb_stats->syncp, start));
 119                bytes   += tbytes;
 120                packets += tpackets;
 121        }
 122        stats->rx_packets = packets;
 123        stats->tx_packets = packets;
 124        stats->rx_bytes   = bytes;
 125        stats->tx_bytes   = bytes;
 126        return stats;
 127}
 128
 129static u32 always_on(struct net_device *dev)
 130{
 131        return 1;
 132}
 133
 134static const struct ethtool_ops loopback_ethtool_ops = {
 135        .get_link               = always_on,
 136};
 137
 138static int loopback_dev_init(struct net_device *dev)
 139{
 140        dev->lstats = alloc_percpu(struct pcpu_lstats);
 141        if (!dev->lstats)
 142                return -ENOMEM;
 143
 144        return 0;
 145}
 146
 147static void loopback_dev_free(struct net_device *dev)
 148{
 149        dev_net(dev)->loopback_dev = NULL;
 150        free_percpu(dev->lstats);
 151        free_netdev(dev);
 152}
 153
 154static const struct net_device_ops loopback_ops = {
 155        .ndo_init      = loopback_dev_init,
 156        .ndo_start_xmit= loopback_xmit,
 157        .ndo_get_stats64 = loopback_get_stats64,
 158};
 159
 160/*
 161 * The loopback device is special. There is only one instance
 162 * per network namespace.
 163 */
 164static void loopback_setup(struct net_device *dev)
 165{
 166        dev->mtu                = 64 * 1024;
 167        dev->hard_header_len    = ETH_HLEN;     /* 14   */
 168        dev->addr_len           = ETH_ALEN;     /* 6    */
 169        dev->tx_queue_len       = 0;
 170        dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
 171        dev->flags              = IFF_LOOPBACK;
 172        dev->priv_flags        &= ~IFF_XMIT_DST_RELEASE;
 173        dev->hw_features        = NETIF_F_ALL_TSO | NETIF_F_UFO;
 174        dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
 175                | NETIF_F_ALL_TSO
 176                | NETIF_F_UFO
 177                | NETIF_F_HW_CSUM
 178                | NETIF_F_RXCSUM
 179                | NETIF_F_HIGHDMA
 180                | NETIF_F_LLTX
 181                | NETIF_F_NETNS_LOCAL
 182                | NETIF_F_VLAN_CHALLENGED
 183                | NETIF_F_LOOPBACK;
 184        dev->ethtool_ops        = &loopback_ethtool_ops;
 185        dev->header_ops         = &eth_header_ops;
 186        dev->netdev_ops         = &loopback_ops;
 187        dev->destructor         = loopback_dev_free;
 188}
 189
 190/* Setup and register the loopback device. */
 191static __net_init int loopback_net_init(struct net *net)
 192{
 193        struct net_device *dev;
 194        int err;
 195
 196        err = -ENOMEM;
 197        dev = alloc_netdev(0, "lo", loopback_setup);
 198        if (!dev)
 199                goto out;
 200
 201        dev_net_set(dev, net);
 202        err = register_netdev(dev);
 203        if (err)
 204                goto out_free_netdev;
 205
 206        BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
 207        net->loopback_dev = dev;
 208        return 0;
 209
 210
 211out_free_netdev:
 212        free_netdev(dev);
 213out:
 214        if (net_eq(net, &init_net))
 215                panic("loopback: Failed to register netdevice: %d\n", err);
 216        return err;
 217}
 218
 219/* Registered in net/core/dev.c */
 220struct pernet_operations __net_initdata loopback_net_ops = {
 221       .init = loopback_net_init,
 222};
 223
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