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/sched.h>
33 #include <linux/interrupt.h>
35 #include <linux/types.h>
36 #include <linux/string.h>
37 #include <linux/socket.h>
38 #include <linux/errno.h>
39 #include <linux/fcntl.h>
41 #include <linux/init.h>
43 #include <asm/system.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>
52 #include <linux/if_ether.h> /* For the statistics structure. */
53 #include <linux/if_arp.h> /* For ARPHRD_ETHER */
55 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
58 * The higher levels take care of making this non-reentrant (it's
59 * called with bh's disabled).
61 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
63 struct net_device_stats *stats = (struct net_device_stats *)dev->priv;
66 * Optimise so buffers with skb->free=1 are not copied but
67 * instead are lobbed from tx queue to rx queue
70 if(atomic_read(&skb->users) != 1)
72 struct sk_buff *skb2=skb;
73 skb=skb_clone(skb, GFP_ATOMIC); /* Clone the buffer */
83 skb->protocol=eth_type_trans(skb,dev);
85 #ifndef LOOPBACK_MUST_CHECKSUM
86 skb->ip_summed = CHECKSUM_UNNECESSARY;
89 dev->last_rx = jiffies;
90 stats->rx_bytes+=skb->len;
91 stats->tx_bytes+=skb->len;
100 static struct net_device_stats *get_stats(struct net_device *dev)
102 return (struct net_device_stats *)dev->priv;
105 /* Initialize the rest of the LOOPBACK device. */
106 int __init loopback_init(struct net_device *dev)
108 dev->mtu = (16 * 1024) + 20 + 20 + 12;
109 dev->hard_start_xmit = loopback_xmit;
110 dev->hard_header = eth_header;
111 dev->hard_header_cache = eth_header_cache;
112 dev->header_cache_update= eth_header_cache_update;
113 dev->hard_header_len = ETH_HLEN; /* 14 */
114 dev->addr_len = ETH_ALEN; /* 6 */
115 dev->tx_queue_len = 0;
116 dev->type = ARPHRD_LOOPBACK; /* 0x0001 */
117 dev->rebuild_header = eth_rebuild_header;
118 dev->flags = IFF_LOOPBACK;
119 dev->features = NETIF_F_SG|NETIF_F_FRAGLIST|NETIF_F_NO_CSUM|NETIF_F_HIGHDMA;
120 dev->priv = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
121 if (dev->priv == NULL)
123 memset(dev->priv, 0, sizeof(struct net_device_stats));
124 dev->get_stats = get_stats;
127 * Fill in the generic fields of the device structure.