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
10 * Authors: Ross Biro, <bir7@leland.Stanford.Edu>
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/system.h>
45 #include <asm/uaccess.h>
48 #include <linux/inet.h>
49 #include <linux/netdevice.h>
50 #include <linux/etherdevice.h>
51 #include <linux/skbuff.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>
60 static DEFINE_PER_CPU(struct net_device_stats, loopback_stats);
62 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
64 /* KISS: just allocate small chunks and copy bits.
66 * So, in fact, this is documentation, explaining what we expect
67 * of largesending device modulo TCP checksum, which is ignored for loopback.
70 static void emulate_large_send_offload(struct sk_buff *skb)
72 struct iphdr *iph = skb->nh.iph;
73 struct tcphdr *th = (struct tcphdr*)(skb->nh.raw + (iph->ihl * 4));
74 unsigned int doffset = (iph->ihl + th->doff) * 4;
75 unsigned int mtu = skb_shinfo(skb)->tso_size + doffset;
76 unsigned int offset = 0;
77 u32 seq = ntohl(th->seq);
78 u16 id = ntohs(iph->id);
80 while (offset + doffset < skb->len) {
81 unsigned int frag_size = min(mtu, skb->len - offset) - doffset;
82 struct sk_buff *nskb = alloc_skb(mtu + 32, GFP_ATOMIC);
86 skb_reserve(nskb, 32);
87 nskb->mac.raw = nskb->data - 14;
88 nskb->nh.raw = nskb->data;
90 memcpy(nskb->data, skb->nh.raw, doffset);
91 if (skb_copy_bits(skb,
96 skb_put(nskb, doffset + frag_size);
97 nskb->ip_summed = CHECKSUM_UNNECESSARY;
99 nskb->priority = skb->priority;
100 nskb->protocol = skb->protocol;
101 nskb->dst = dst_clone(skb->dst);
102 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
103 nskb->pkt_type = skb->pkt_type;
105 th = (struct tcphdr*)(nskb->nh.raw + iph->ihl*4);
106 iph->tot_len = htons(frag_size + doffset);
109 iph->check = ip_fast_csum((unsigned char *) iph, iph->ihl);
110 th->seq = htonl(seq);
111 if (offset + doffset + frag_size < skb->len)
112 th->fin = th->psh = 0;
123 * The higher levels take care of making this non-reentrant (it's
124 * called with bh's disabled).
126 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
128 struct net_device_stats *lb_stats;
132 skb->protocol=eth_type_trans(skb,dev);
134 #ifndef LOOPBACK_MUST_CHECKSUM
135 skb->ip_summed = CHECKSUM_UNNECESSARY;
138 if (skb_shinfo(skb)->tso_size) {
139 BUG_ON(skb->protocol != htons(ETH_P_IP));
140 BUG_ON(skb->nh.iph->protocol != IPPROTO_TCP);
142 emulate_large_send_offload(skb);
146 dev->last_rx = jiffies;
148 lb_stats = &per_cpu(loopback_stats, get_cpu());
149 lb_stats->rx_bytes += skb->len;
150 lb_stats->tx_bytes += skb->len;
151 lb_stats->rx_packets++;
152 lb_stats->tx_packets++;
160 static struct net_device_stats *get_stats(struct net_device *dev)
162 struct net_device_stats *stats = dev->priv;
169 memset(stats, 0, sizeof(struct net_device_stats));
171 for (i=0; i < NR_CPUS; i++) {
172 struct net_device_stats *lb_stats;
174 if (!cpu_possible(i))
176 lb_stats = &per_cpu(loopback_stats, i);
177 stats->rx_bytes += lb_stats->rx_bytes;
178 stats->tx_bytes += lb_stats->tx_bytes;
179 stats->rx_packets += lb_stats->rx_packets;
180 stats->tx_packets += lb_stats->tx_packets;
186 struct net_device loopback_dev = {
188 .mtu = (16 * 1024) + 20 + 20 + 12,
189 .hard_start_xmit = loopback_xmit,
190 .hard_header = eth_header,
191 .hard_header_cache = eth_header_cache,
192 .header_cache_update = eth_header_cache_update,
193 .hard_header_len = ETH_HLEN, /* 14 */
194 .addr_len = ETH_ALEN, /* 6 */
196 .type = ARPHRD_LOOPBACK, /* 0x0001*/
197 .rebuild_header = eth_rebuild_header,
198 .flags = IFF_LOOPBACK,
199 .features = NETIF_F_SG|NETIF_F_FRAGLIST
200 |NETIF_F_NO_CSUM|NETIF_F_HIGHDMA
204 /* Setup and register the of the LOOPBACK device. */
205 int __init loopback_init(void)
207 struct net_device_stats *stats;
209 /* Can survive without statistics */
210 stats = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
212 memset(stats, 0, sizeof(struct net_device_stats));
213 loopback_dev.priv = stats;
214 loopback_dev.get_stats = &get_stats;
217 return register_netdev(&loopback_dev);
220 EXPORT_SYMBOL(loopback_dev);