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