drivers/net/loopback.c

   1 /*
   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.
   5  *
   6  *              Pseudo-driver for the loopback interface.
   7  *
   8  * Version:     @(#)loopback.c  1.0.4b  08/16/93
   9  *
  10  * Authors:     Ross Biro, <bir7@leland.Stanford.Edu>
  11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
  12  *              Donald Becker, <becker@scyld.com>
  13  *
  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
  19  *                                      can't take it...
  20  *              Michael Griffith:       Don't bother computing the checksums
  21  *                                      on packets received on the loopback
  22  *                                      interface.
  23  *              Alexey Kuznetsov:       Potential hang under some extreme
  24  *                                      cases removed.
  25  *
  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.
  30  */
  31 #include <linux/kernel.h>
  32 #include <linux/jiffies.h>
  33 #include <linux/module.h>
  34 #include <linux/interrupt.h>
  35 #include <linux/fs.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>
  41 #include <linux/in.h>
  42 #include <linux/init.h>
  43
  44 #include <asm/system.h>
  45 #include <asm/uaccess.h>
  46 #include <asm/io.h>
  47
  48 #include <linux/inet.h>
  49 #include <linux/netdevice.h>
  50 #include <linux/etherdevice.h>
  51 #include <linux/skbuff.h>
  52 #include <linux/ethtool.h>
  53 #include <net/sock.h>
  54 #include <net/checksum.h>
  55 #include <linux/if_ether.h>     /* For the statistics structure. */
  56 #include <linux/if_arp.h>       /* For ARPHRD_ETHER */
  57 #include <linux/ip.h>
  58 #include <linux/tcp.h>
  59 #include <linux/percpu.h>
  60
  61 static DEFINE_PER_CPU(struct net_device_stats, loopback_stats);
  62
  63 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
  64
  65 /* KISS: just allocate small chunks and copy bits.
  66  *
  67  * So, in fact, this is documentation, explaining what we expect
  68  * of largesending device modulo TCP checksum, which is ignored for loopback.
  69  */
  70
  71 static void emulate_large_send_offload(struct sk_buff *skb)
  72 {
  73         struct iphdr *iph = skb->nh.iph;
  74         struct tcphdr *th = (struct tcphdr*)(skb->nh.raw + (iph->ihl * 4));
  75         unsigned int doffset = (iph->ihl + th->doff) * 4;
  76         unsigned int mtu = skb_shinfo(skb)->tso_size + doffset;
  77         unsigned int offset = 0;
  78         u32 seq = ntohl(th->seq);
  79         u16 id  = ntohs(iph->id);
  80
  81         while (offset + doffset < skb->len) {
  82                 unsigned int frag_size = min(mtu, skb->len - offset) - doffset;
  83                 struct sk_buff *nskb = alloc_skb(mtu + 32, GFP_ATOMIC);
  84
  85                 if (!nskb)
  86                         break;
  87                 skb_reserve(nskb, 32);
  88                 nskb->mac.raw = nskb->data - 14;
  89                 nskb->nh.raw = nskb->data;
  90                 iph = nskb->nh.iph;
  91                 memcpy(nskb->data, skb->nh.raw, doffset);
  92                 if (skb_copy_bits(skb,
  93                                   doffset + offset,
  94                                   nskb->data + doffset,
  95                                   frag_size))
  96                         BUG();
  97                 skb_put(nskb, doffset + frag_size);
  98                 nskb->ip_summed = CHECKSUM_UNNECESSARY;
  99                 nskb->dev = skb->dev;
 100                 nskb->priority = skb->priority;
 101                 nskb->protocol = skb->protocol;
 102                 nskb->dst = dst_clone(skb->dst);
 103                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
 104                 nskb->pkt_type = skb->pkt_type;
 105
 106                 th = (struct tcphdr*)(nskb->nh.raw + iph->ihl*4);
 107                 iph->tot_len = htons(frag_size + doffset);
 108                 iph->id = htons(id);
 109                 iph->check = 0;
 110                 iph->check = ip_fast_csum((unsigned char *) iph, iph->ihl);
 111                 th->seq = htonl(seq);
 112                 if (offset + doffset + frag_size < skb->len)
 113                         th->fin = th->psh = 0;
 114                 netif_rx(nskb);
 115                 offset += frag_size;
 116                 seq += frag_size;
 117                 id++;
 118         }
 119
 120         dev_kfree_skb(skb);
 121 }
 122
 123 /*
 124  * The higher levels take care of making this non-reentrant (it's
 125  * called with bh's disabled).
 126  */
 127 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
 128 {
 129         struct net_device_stats *lb_stats;
 130
 131         skb_orphan(skb);
 132
 133         skb->protocol=eth_type_trans(skb,dev);
 134         skb->dev=dev;
 135 #ifndef LOOPBACK_MUST_CHECKSUM
 136         skb->ip_summed = CHECKSUM_UNNECESSARY;
 137 #endif
 138
 139         if (skb_shinfo(skb)->tso_size) {
 140                 BUG_ON(skb->protocol != htons(ETH_P_IP));
 141                 BUG_ON(skb->nh.iph->protocol != IPPROTO_TCP);
 142
 143                 emulate_large_send_offload(skb);
 144                 return 0;
 145         }
 146
 147         dev->last_rx = jiffies;
 148
 149         lb_stats = &per_cpu(loopback_stats, get_cpu());
 150         lb_stats->rx_bytes += skb->len;
 151         lb_stats->tx_bytes += skb->len;
 152         lb_stats->rx_packets++;
 153         lb_stats->tx_packets++;
 154         put_cpu();
 155
 156         netif_rx(skb);
 157
 158         return(0);
 159 }
 160
 161 static struct net_device_stats *get_stats(struct net_device *dev)
 162 {
 163         struct net_device_stats *stats = dev->priv;
 164         int i;
 165
 166         if (!stats) {
 167                 return NULL;
 168         }
 169
 170         memset(stats, 0, sizeof(struct net_device_stats));
 171
 172         for (i=0; i < NR_CPUS; i++) {
 173                 struct net_device_stats *lb_stats;
 174
 175                 if (!cpu_possible(i))
 176                         continue;
 177                 lb_stats = &per_cpu(loopback_stats, i);
 178                 stats->rx_bytes   += lb_stats->rx_bytes;
 179                 stats->tx_bytes   += lb_stats->tx_bytes;
 180                 stats->rx_packets += lb_stats->rx_packets;
 181                 stats->tx_packets += lb_stats->tx_packets;
 182         }
 183
 184         return stats;
 185 }
 186
 187 static u32 loopback_get_link(struct net_device *dev)
 188 {
 189         return 1;
 190 }
 191
 192 static struct ethtool_ops loopback_ethtool_ops = {
 193         .get_link               = loopback_get_link,
 194         .get_tso                = ethtool_op_get_tso,
 195         .set_tso                = ethtool_op_set_tso,
 196 };
 197
 198 struct net_device loopback_dev = {
 199         .name                   = "lo",
 200         .mtu                    = (16 * 1024) + 20 + 20 + 12,
 201         .hard_start_xmit        = loopback_xmit,
 202         .hard_header            = eth_header,
 203         .hard_header_cache      = eth_header_cache,
 204         .header_cache_update    = eth_header_cache_update,
 205         .hard_header_len        = ETH_HLEN,     /* 14   */
 206         .addr_len               = ETH_ALEN,     /* 6    */
 207         .tx_queue_len           = 0,
 208         .type                   = ARPHRD_LOOPBACK,      /* 0x0001*/
 209         .rebuild_header         = eth_rebuild_header,
 210         .flags                  = IFF_LOOPBACK,
 211         .features               = NETIF_F_SG|NETIF_F_FRAGLIST
 212                                   |NETIF_F_NO_CSUM|NETIF_F_HIGHDMA
 213                                   |NETIF_F_LLTX,
 214         .ethtool_ops            = &loopback_ethtool_ops,
 215 };
 216
 217 /* Setup and register the of the LOOPBACK device. */
 218 int __init loopback_init(void)
 219 {
 220         struct net_device_stats *stats;
 221
 222         /* Can survive without statistics */
 223         stats = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
 224         if (stats) {
 225                 memset(stats, 0, sizeof(struct net_device_stats));
 226                 loopback_dev.priv = stats;
 227                 loopback_dev.get_stats = &get_stats;
 228         }
 229
 230         return register_netdev(&loopback_dev);
 231 };
 232
 233 EXPORT_SYMBOL(loopback_dev);