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![Eric Dumazet](/assets/img/avatar_default.png)
loopback current mtu of 16436 bytes allows no more than 3 MSS TCP segments per frame, or 48 Kbytes. Changing mtu to 64K allows TCP stack to build large frames and significantly reduces stack overhead. Performance boost on bulk TCP transferts can be up to 30 %, partly because we now have one ACK message for two 64KB segments, and a lower probability of hitting /proc/sys/net/ipv4/tcp_reordering default limit. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
216 lines
5.4 KiB
C
216 lines
5.4 KiB
C
/*
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* INET An implementation of the TCP/IP protocol suite for the LINUX
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* operating system. INET is implemented using the BSD Socket
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* interface as the means of communication with the user level.
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*
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* Pseudo-driver for the loopback interface.
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*
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* Version: @(#)loopback.c 1.0.4b 08/16/93
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*
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* Authors: Ross Biro
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* Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
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* Donald Becker, <becker@scyld.com>
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*
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* Alan Cox : Fixed oddments for NET3.014
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* Alan Cox : Rejig for NET3.029 snap #3
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* Alan Cox : Fixed NET3.029 bugs and sped up
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* Larry McVoy : Tiny tweak to double performance
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* Alan Cox : Backed out LMV's tweak - the linux mm
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* can't take it...
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* Michael Griffith: Don't bother computing the checksums
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* on packets received on the loopback
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* interface.
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* Alexey Kuznetsov: Potential hang under some extreme
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* cases removed.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <linux/kernel.h>
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#include <linux/jiffies.h>
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#include <linux/module.h>
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#include <linux/interrupt.h>
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#include <linux/fs.h>
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/socket.h>
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#include <linux/errno.h>
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#include <linux/fcntl.h>
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#include <linux/in.h>
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#include <linux/init.h>
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#include <asm/uaccess.h>
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#include <asm/io.h>
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#include <linux/inet.h>
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#include <linux/netdevice.h>
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#include <linux/etherdevice.h>
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#include <linux/skbuff.h>
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#include <linux/ethtool.h>
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#include <net/sock.h>
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#include <net/checksum.h>
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#include <linux/if_ether.h> /* For the statistics structure. */
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#include <linux/if_arp.h> /* For ARPHRD_ETHER */
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#include <linux/ip.h>
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#include <linux/tcp.h>
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#include <linux/percpu.h>
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#include <net/net_namespace.h>
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#include <linux/u64_stats_sync.h>
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struct pcpu_lstats {
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u64 packets;
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u64 bytes;
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struct u64_stats_sync syncp;
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};
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/*
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* The higher levels take care of making this non-reentrant (it's
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* called with bh's disabled).
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*/
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static netdev_tx_t loopback_xmit(struct sk_buff *skb,
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struct net_device *dev)
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{
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struct pcpu_lstats *lb_stats;
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int len;
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skb_orphan(skb);
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skb->protocol = eth_type_trans(skb, dev);
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/* it's OK to use per_cpu_ptr() because BHs are off */
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lb_stats = this_cpu_ptr(dev->lstats);
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len = skb->len;
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if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
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u64_stats_update_begin(&lb_stats->syncp);
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lb_stats->bytes += len;
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lb_stats->packets++;
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u64_stats_update_end(&lb_stats->syncp);
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}
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return NETDEV_TX_OK;
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}
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static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev,
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struct rtnl_link_stats64 *stats)
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{
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u64 bytes = 0;
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u64 packets = 0;
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int i;
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for_each_possible_cpu(i) {
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const struct pcpu_lstats *lb_stats;
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u64 tbytes, tpackets;
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unsigned int start;
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lb_stats = per_cpu_ptr(dev->lstats, i);
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do {
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start = u64_stats_fetch_begin_bh(&lb_stats->syncp);
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tbytes = lb_stats->bytes;
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tpackets = lb_stats->packets;
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} while (u64_stats_fetch_retry_bh(&lb_stats->syncp, start));
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bytes += tbytes;
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packets += tpackets;
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}
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stats->rx_packets = packets;
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stats->tx_packets = packets;
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stats->rx_bytes = bytes;
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stats->tx_bytes = bytes;
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return stats;
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}
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static u32 always_on(struct net_device *dev)
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{
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return 1;
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}
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static const struct ethtool_ops loopback_ethtool_ops = {
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.get_link = always_on,
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};
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static int loopback_dev_init(struct net_device *dev)
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{
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dev->lstats = alloc_percpu(struct pcpu_lstats);
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if (!dev->lstats)
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return -ENOMEM;
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return 0;
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}
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static void loopback_dev_free(struct net_device *dev)
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{
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free_percpu(dev->lstats);
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free_netdev(dev);
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}
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static const struct net_device_ops loopback_ops = {
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.ndo_init = loopback_dev_init,
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.ndo_start_xmit= loopback_xmit,
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.ndo_get_stats64 = loopback_get_stats64,
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};
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/*
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* The loopback device is special. There is only one instance
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* per network namespace.
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*/
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static void loopback_setup(struct net_device *dev)
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{
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dev->mtu = 64 * 1024;
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dev->hard_header_len = ETH_HLEN; /* 14 */
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dev->addr_len = ETH_ALEN; /* 6 */
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dev->tx_queue_len = 0;
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dev->type = ARPHRD_LOOPBACK; /* 0x0001*/
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dev->flags = IFF_LOOPBACK;
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dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
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dev->hw_features = NETIF_F_ALL_TSO | NETIF_F_UFO;
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dev->features = NETIF_F_SG | NETIF_F_FRAGLIST
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| NETIF_F_ALL_TSO
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| NETIF_F_UFO
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| NETIF_F_HW_CSUM
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| NETIF_F_RXCSUM
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| NETIF_F_HIGHDMA
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| NETIF_F_LLTX
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| NETIF_F_NETNS_LOCAL
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| NETIF_F_VLAN_CHALLENGED
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| NETIF_F_LOOPBACK;
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dev->ethtool_ops = &loopback_ethtool_ops;
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dev->header_ops = ð_header_ops;
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dev->netdev_ops = &loopback_ops;
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dev->destructor = loopback_dev_free;
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}
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/* Setup and register the loopback device. */
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static __net_init int loopback_net_init(struct net *net)
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{
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struct net_device *dev;
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int err;
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err = -ENOMEM;
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dev = alloc_netdev(0, "lo", loopback_setup);
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if (!dev)
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goto out;
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dev_net_set(dev, net);
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err = register_netdev(dev);
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if (err)
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goto out_free_netdev;
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BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
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net->loopback_dev = dev;
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return 0;
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out_free_netdev:
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free_netdev(dev);
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out:
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if (net_eq(net, &init_net))
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panic("loopback: Failed to register netdevice: %d\n", err);
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return err;
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}
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/* Registered in net/core/dev.c */
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struct pernet_operations __net_initdata loopback_net_ops = {
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.init = loopback_net_init,
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};
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