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.
6 * Pseudo-driver for the loopback interface.
8 * Version: @(#)loopback.c 1.0.4b 08/16/93
11 * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12 * Donald Becker, <becker@scyld.com>
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
20 * Michael Griffith: Don't bother computing the checksums
21 * on packets received on the loopback
23 * Alexey Kuznetsov: Potential hang under some extreme
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.
31 #include <linux/kernel.h>
32 #include <linux/jiffies.h>
33 #include <linux/module.h>
34 #include <linux/interrupt.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>
42 #include <linux/init.h>
44 #include <asm/uaccess.h>
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>
53 #include <net/checksum.h>
54 #include <linux/if_ether.h> /* For the statistics structure. */
55 #include <linux/if_arp.h> /* For ARPHRD_ETHER */
57 #include <linux/tcp.h>
58 #include <linux/percpu.h>
59 #include <net/net_namespace.h>
60 #include <linux/u64_stats_sync.h>
65 struct u64_stats_sync syncp;
69 * The higher levels take care of making this non-reentrant (it's
70 * called with bh's disabled).
72 static netdev_tx_t loopback_xmit(struct sk_buff *skb,
73 struct net_device *dev)
75 struct pcpu_lstats *lb_stats;
80 /* Before queueing this packet to netif_rx(),
81 * make sure dst is refcounted.
85 skb->protocol = eth_type_trans(skb, dev);
87 /* it's OK to use per_cpu_ptr() because BHs are off */
88 lb_stats = this_cpu_ptr(dev->lstats);
91 if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
92 u64_stats_update_begin(&lb_stats->syncp);
93 lb_stats->bytes += len;
95 u64_stats_update_end(&lb_stats->syncp);
101 static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev,
102 struct rtnl_link_stats64 *stats)
108 for_each_possible_cpu(i) {
109 const struct pcpu_lstats *lb_stats;
110 u64 tbytes, tpackets;
113 lb_stats = per_cpu_ptr(dev->lstats, i);
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));
122 stats->rx_packets = packets;
123 stats->tx_packets = packets;
124 stats->rx_bytes = bytes;
125 stats->tx_bytes = bytes;
129 static u32 always_on(struct net_device *dev)
134 static const struct ethtool_ops loopback_ethtool_ops = {
135 .get_link = always_on,
138 static int loopback_dev_init(struct net_device *dev)
140 dev->lstats = alloc_percpu(struct pcpu_lstats);
147 static void loopback_dev_free(struct net_device *dev)
149 free_percpu(dev->lstats);
153 static const struct net_device_ops loopback_ops = {
154 .ndo_init = loopback_dev_init,
155 .ndo_start_xmit= loopback_xmit,
156 .ndo_get_stats64 = loopback_get_stats64,
160 * The loopback device is special. There is only one instance
161 * per network namespace.
163 static void loopback_setup(struct net_device *dev)
165 dev->mtu = 64 * 1024;
166 dev->hard_header_len = ETH_HLEN; /* 14 */
167 dev->addr_len = ETH_ALEN; /* 6 */
168 dev->tx_queue_len = 0;
169 dev->type = ARPHRD_LOOPBACK; /* 0x0001*/
170 dev->flags = IFF_LOOPBACK;
171 dev->priv_flags &= ~IFF_XMIT_DST_RELEASE;
172 dev->hw_features = NETIF_F_ALL_TSO | NETIF_F_UFO;
173 dev->features = NETIF_F_SG | NETIF_F_FRAGLIST
180 | NETIF_F_NETNS_LOCAL
181 | NETIF_F_VLAN_CHALLENGED
183 dev->ethtool_ops = &loopback_ethtool_ops;
184 dev->header_ops = ð_header_ops;
185 dev->netdev_ops = &loopback_ops;
186 dev->destructor = loopback_dev_free;
189 /* Setup and register the loopback device. */
190 static __net_init int loopback_net_init(struct net *net)
192 struct net_device *dev;
196 dev = alloc_netdev(0, "lo", loopback_setup);
200 dev_net_set(dev, net);
201 err = register_netdev(dev);
203 goto out_free_netdev;
205 BUG_ON(dev->ifindex != LOOPBACK_IFINDEX);
206 net->loopback_dev = dev;
213 if (net_eq(net, &init_net))
214 panic("loopback: Failed to register netdevice: %d\n", err);
218 /* Registered in net/core/dev.c */
219 struct pernet_operations __net_initdata loopback_net_ops = {
220 .init = loopback_net_init,