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>
60 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
62 /* KISS: just allocate small chunks and copy bits.
64 * So, in fact, this is documentation, explaining what we expect
65 * of largesending device modulo TCP checksum, which is ignored for loopback.
68 static void emulate_large_send_offload(struct sk_buff *skb)
70 struct iphdr *iph = skb->nh.iph;
71 struct tcphdr *th = (struct tcphdr*)(skb->nh.raw + (iph->ihl * 4));
72 unsigned int doffset = (iph->ihl + th->doff) * 4;
73 unsigned int mtu = skb_shinfo(skb)->tso_size + doffset;
74 unsigned int offset = 0;
75 u32 seq = ntohl(th->seq);
76 u16 id = ntohs(iph->id);
78 while (offset + doffset < skb->len) {
79 unsigned int frag_size = min(mtu, skb->len - offset) - doffset;
80 struct sk_buff *nskb = alloc_skb(mtu + 32, GFP_ATOMIC);
84 skb_reserve(nskb, 32);
85 nskb->mac.raw = nskb->data - 14;
86 nskb->nh.raw = nskb->data;
88 memcpy(nskb->data, skb->nh.raw, doffset);
89 if (skb_copy_bits(skb,
94 skb_put(nskb, doffset + frag_size);
95 nskb->ip_summed = CHECKSUM_UNNECESSARY;
97 nskb->priority = skb->priority;
98 nskb->protocol = skb->protocol;
99 nskb->dst = dst_clone(skb->dst);
100 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
101 nskb->pkt_type = skb->pkt_type;
103 th = (struct tcphdr*)(nskb->nh.raw + iph->ihl*4);
104 iph->tot_len = htons(frag_size + doffset);
107 iph->check = ip_fast_csum((unsigned char *) iph, iph->ihl);
108 th->seq = htonl(seq);
109 if (offset + doffset + frag_size < skb->len)
110 th->fin = th->psh = 0;
121 * The higher levels take care of making this non-reentrant (it's
122 * called with bh's disabled).
124 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
126 struct net_device_stats *stats = dev->priv;
130 skb->protocol=eth_type_trans(skb,dev);
132 #ifndef LOOPBACK_MUST_CHECKSUM
133 skb->ip_summed = CHECKSUM_UNNECESSARY;
136 if (skb_shinfo(skb)->tso_size) {
137 BUG_ON(skb->protocol != htons(ETH_P_IP));
138 BUG_ON(skb->nh.iph->protocol != IPPROTO_TCP);
140 emulate_large_send_offload(skb);
144 dev->last_rx = jiffies;
146 stats->rx_bytes+=skb->len;
147 stats->tx_bytes+=skb->len;
157 static struct net_device_stats *get_stats(struct net_device *dev)
159 return (struct net_device_stats *)dev->priv;
162 struct net_device loopback_dev = {
164 .mtu = (16 * 1024) + 20 + 20 + 12,
165 .hard_start_xmit = loopback_xmit,
166 .hard_header = eth_header,
167 .hard_header_cache = eth_header_cache,
168 .header_cache_update = eth_header_cache_update,
169 .hard_header_len = ETH_HLEN, /* 14 */
170 .addr_len = ETH_ALEN, /* 6 */
172 .type = ARPHRD_LOOPBACK, /* 0x0001*/
173 .rebuild_header = eth_rebuild_header,
174 .flags = IFF_LOOPBACK,
175 .features = NETIF_F_SG|NETIF_F_FRAGLIST
176 |NETIF_F_NO_CSUM|NETIF_F_HIGHDMA,
179 /* Setup and register the of the LOOPBACK device. */
180 int __init loopback_init(void)
182 struct net_device_stats *stats;
184 /* Can survive without statistics */
185 stats = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
187 memset(stats, 0, sizeof(struct net_device_stats));
188 loopback_dev.priv = stats;
189 loopback_dev.get_stats = &get_stats;
192 return register_netdev(&loopback_dev);
195 EXPORT_SYMBOL(loopback_dev);