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
  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 struct pcpu_lstats {
  62         unsigned long packets;
  63         unsigned long bytes;
  64 };
  65
  66 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
  67
  68 /* KISS: just allocate small chunks and copy bits.
  69  *
  70  * So, in fact, this is documentation, explaining what we expect
  71  * of largesending device modulo TCP checksum, which is ignored for loopback.
  72  */
  73
  74 #ifdef LOOPBACK_TSO
  75 static void emulate_large_send_offload(struct sk_buff *skb)
  76 {
  77         struct iphdr *iph = ip_hdr(skb);
  78         struct tcphdr *th = (struct tcphdr *)(skb_network_header(skb) +
  79                                               (iph->ihl * 4));
  80         unsigned int doffset = (iph->ihl + th->doff) * 4;
  81         unsigned int mtu = skb_shinfo(skb)->gso_size + doffset;
  82         unsigned int offset = 0;
  83         u32 seq = ntohl(th->seq);
  84         u16 id  = ntohs(iph->id);
  85
  86         while (offset + doffset < skb->len) {
  87                 unsigned int frag_size = min(mtu, skb->len - offset) - doffset;
  88                 struct sk_buff *nskb = alloc_skb(mtu + 32, GFP_ATOMIC);
  89
  90                 if (!nskb)
  91                         break;
  92                 skb_reserve(nskb, 32);
  93                 skb_set_mac_header(nskb, -ETH_HLEN);
  94                 skb_reset_network_header(nskb);
  95                 iph = ip_hdr(nskb);
  96                 skb_copy_to_linear_data(nskb, skb_network_header(skb),
  97                                         doffset);
  98                 if (skb_copy_bits(skb,
  99                                   doffset + offset,
 100                                   nskb->data + doffset,
 101                                   frag_size))
 102                         BUG();
 103                 skb_put(nskb, doffset + frag_size);
 104                 nskb->ip_summed = CHECKSUM_UNNECESSARY;
 105                 nskb->dev = skb->dev;
 106                 nskb->priority = skb->priority;
 107                 nskb->protocol = skb->protocol;
 108                 nskb->dst = dst_clone(skb->dst);
 109                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
 110                 nskb->pkt_type = skb->pkt_type;
 111
 112                 th = (struct tcphdr *)(skb_network_header(nskb) + iph->ihl * 4);
 113                 iph->tot_len = htons(frag_size + doffset);
 114                 iph->id = htons(id);
 115                 iph->check = 0;
 116                 iph->check = ip_fast_csum((unsigned char *) iph, iph->ihl);
 117                 th->seq = htonl(seq);
 118                 if (offset + doffset + frag_size < skb->len)
 119                         th->fin = th->psh = 0;
 120                 netif_rx(nskb);
 121                 offset += frag_size;
 122                 seq += frag_size;
 123                 id++;
 124         }
 125
 126         dev_kfree_skb(skb);
 127 }
 128 #endif /* LOOPBACK_TSO */
 129
 130 /*
 131  * The higher levels take care of making this non-reentrant (it's
 132  * called with bh's disabled).
 133  */
 134 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
 135 {
 136         struct pcpu_lstats *pcpu_lstats, *lb_stats;
 137
 138         skb_orphan(skb);
 139
 140         skb->protocol = eth_type_trans(skb,dev);
 141 #ifndef LOOPBACK_MUST_CHECKSUM
 142         skb->ip_summed = CHECKSUM_UNNECESSARY;
 143 #endif
 144
 145 #ifdef LOOPBACK_TSO
 146         if (skb_is_gso(skb)) {
 147                 BUG_ON(skb->protocol != htons(ETH_P_IP));
 148                 BUG_ON(ip_hdr(skb)->protocol != IPPROTO_TCP);
 149
 150                 emulate_large_send_offload(skb);
 151                 return 0;
 152         }
 153 #endif
 154         dev->last_rx = jiffies;
 155
 156         /* it's OK to use __get_cpu_var() because BHs are off */
 157         pcpu_lstats = netdev_priv(dev);
 158         lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());
 159         lb_stats->bytes += skb->len;
 160         lb_stats->packets++;
 161
 162         netif_rx(skb);
 163
 164         return 0;
 165 }
 166
 167 static struct net_device_stats *get_stats(struct net_device *dev)
 168 {
 169         const struct pcpu_lstats *pcpu_lstats;
 170         struct net_device_stats *stats = &dev->stats;
 171         unsigned long bytes = 0;
 172         unsigned long packets = 0;
 173         int i;
 174
 175         pcpu_lstats = netdev_priv(dev);
 176         for_each_possible_cpu(i) {
 177                 const struct pcpu_lstats *lb_stats;
 178
 179                 lb_stats = per_cpu_ptr(pcpu_lstats, i);
 180                 bytes   += lb_stats->bytes;
 181                 packets += lb_stats->packets;
 182         }
 183         stats->rx_packets = packets;
 184         stats->tx_packets = packets;
 185         stats->rx_bytes = bytes;
 186         stats->tx_bytes = bytes;
 187         return stats;
 188 }
 189
 190 static u32 always_on(struct net_device *dev)
 191 {
 192         return 1;
 193 }
 194
 195 static const struct ethtool_ops loopback_ethtool_ops = {
 196         .get_link               = always_on,
 197         .set_tso                = ethtool_op_set_tso,
 198         .get_tx_csum            = always_on,
 199         .get_sg                 = always_on,
 200         .get_rx_csum            = always_on,
 201 };
 202
 203 static int loopback_dev_init(struct net_device *dev)
 204 {
 205         struct pcpu_lstats *lstats;
 206
 207         lstats = alloc_percpu(struct pcpu_lstats);
 208         if (!lstats)
 209                 return -ENOMEM;
 210
 211         dev->priv = lstats;
 212         return 0;
 213 }
 214
 215 static void loopback_dev_free(struct net_device *dev)
 216 {
 217         struct pcpu_lstats *lstats = netdev_priv(dev);
 218
 219         free_percpu(lstats);
 220         free_netdev(dev);
 221 }
 222
 223 /*
 224  * The loopback device is special. There is only one instance and
 225  * it is statically allocated. Don't do this for other devices.
 226  */
 227 static void loopback_setup(struct net_device *dev)
 228 {
 229         dev->get_stats          = &get_stats;
 230         dev->mtu                = (16 * 1024) + 20 + 20 + 12;
 231         dev->hard_start_xmit    = loopback_xmit;
 232         dev->hard_header        = eth_header;
 233         dev->hard_header_cache  = eth_header_cache;
 234         dev->header_cache_update = eth_header_cache_update;
 235         dev->hard_header_len    = ETH_HLEN;     /* 14   */
 236         dev->addr_len           = ETH_ALEN;     /* 6    */
 237         dev->tx_queue_len       = 0;
 238         dev->type               = ARPHRD_LOOPBACK;      /* 0x0001*/
 239         dev->rebuild_header     = eth_rebuild_header;
 240         dev->flags              = IFF_LOOPBACK;
 241         dev->features           = NETIF_F_SG | NETIF_F_FRAGLIST
 242 #ifdef LOOPBACK_TSO
 243                 | NETIF_F_TSO
 244 #endif
 245                 | NETIF_F_NO_CSUM
 246                 | NETIF_F_HIGHDMA
 247                 | NETIF_F_LLTX
 248                 | NETIF_F_NETNS_LOCAL,
 249         dev->ethtool_ops        = &loopback_ethtool_ops;
 250         dev->init = loopback_dev_init;
 251         dev->destructor = loopback_dev_free;
 252 }
 253
 254 /* Setup and register the loopback device. */
 255 static int __init loopback_init(void)
 256 {
 257         struct net_device *dev;
 258         int err;
 259
 260         err = -ENOMEM;
 261         dev = alloc_netdev(0, "lo", loopback_setup);
 262         if (!dev)
 263                 goto out;
 264
 265         err = register_netdev(dev);
 266         if (err)
 267                 goto out_free_netdev;
 268
 269         err = 0;
 270         loopback_dev = dev;
 271
 272 out:
 273         if (err)
 274                 panic("loopback: Failed to register netdevice: %d\n", err);
 275         return err;
 276
 277 out_free_netdev:
 278         free_netdev(dev);
 279         goto out;
 280 }
 281
 282 fs_initcall(loopback_init);
 283
 284 struct net_device *loopback_dev;
 285 EXPORT_SYMBOL(loopback_dev);