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/interrupt.h>
  34 #include <linux/fs.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>
  40 #include <linux/in.h>
  41 #include <linux/init.h>
  42
  43 #include <asm/system.h>
  44 #include <asm/uaccess.h>
  45 #include <asm/io.h>
  46
  47 #include <linux/inet.h>
  48 #include <linux/netdevice.h>
  49 #include <linux/etherdevice.h>
  50 #include <linux/skbuff.h>
  51 #include <net/sock.h>
  52 #include <net/checksum.h>
  53 #include <linux/if_ether.h>     /* For the statistics structure. */
  54 #include <linux/if_arp.h>       /* For ARPHRD_ETHER */
  55 #include <linux/ip.h>
  56 #include <linux/tcp.h>
  57
  58 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
  59
  60 /* KISS: just allocate small chunks and copy bits.
  61  *
  62  * So, in fact, this is documentation, explaining what we expect
  63  * of largesending device modulo TCP checksum, which is ignored for loopback.
  64  */
  65
  66 static void emulate_large_send_offload(struct sk_buff *skb)
  67 {
  68         struct iphdr *iph = skb->nh.iph;
  69         struct tcphdr *th = (struct tcphdr*)(skb->nh.raw + (iph->ihl * 4));
  70         unsigned int doffset = (iph->ihl + th->doff) * 4;
  71         unsigned int mtu = skb_shinfo(skb)->tso_size + doffset;
  72         unsigned int offset = 0;
  73         u32 seq = ntohl(th->seq);
  74         u16 id  = ntohs(iph->id);
  75
  76         while (offset + doffset < skb->len) {
  77                 unsigned int frag_size = min(mtu, skb->len - offset) - doffset;
  78                 struct sk_buff *nskb = alloc_skb(mtu + 32, GFP_ATOMIC);
  79
  80                 if (!nskb)
  81                         break;
  82                 skb_reserve(nskb, 32);
  83                 nskb->mac.raw = nskb->data - 14;
  84                 nskb->nh.raw = nskb->data;
  85                 iph = nskb->nh.iph;
  86                 memcpy(nskb->data, skb->nh.raw, doffset);
  87                 if (skb_copy_bits(skb,
  88                                   doffset + offset,
  89                                   nskb->data + doffset,
  90                                   frag_size))
  91                         BUG();
  92                 skb_put(nskb, doffset + frag_size);
  93                 nskb->ip_summed = CHECKSUM_UNNECESSARY;
  94                 nskb->dev = skb->dev;
  95                 nskb->priority = skb->priority;
  96                 nskb->protocol = skb->protocol;
  97                 nskb->dst = dst_clone(skb->dst);
  98                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
  99                 nskb->pkt_type = skb->pkt_type;
 100
 101                 th = (struct tcphdr*)(nskb->nh.raw + iph->ihl*4);
 102                 iph->tot_len = htons(frag_size + doffset);
 103                 iph->id = htons(id);
 104                 iph->check = 0;
 105                 iph->check = ip_fast_csum((unsigned char *) iph, iph->ihl);
 106                 th->seq = htonl(seq);
 107                 if (offset + doffset + frag_size < skb->len)
 108                         th->fin = th->psh = 0;
 109                 netif_rx(nskb);
 110                 offset += frag_size;
 111                 seq += frag_size;
 112                 id++;
 113         }
 114
 115         dev_kfree_skb(skb);
 116 }
 117
 118 /*
 119  * The higher levels take care of making this non-reentrant (it's
 120  * called with bh's disabled).
 121  */
 122 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
 123 {
 124         struct net_device_stats *stats = (struct net_device_stats *)dev->priv;
 125
 126         /*
 127          *      Optimise so buffers with skb->free=1 are not copied but
 128          *      instead are lobbed from tx queue to rx queue
 129          */
 130
 131         if(atomic_read(&skb->users) != 1)
 132         {
 133                 struct sk_buff *skb2=skb;
 134                 skb=skb_clone(skb, GFP_ATOMIC);         /* Clone the buffer */
 135                 if(skb==NULL) {
 136                         kfree_skb(skb2);
 137                         return 0;
 138                 }
 139                 kfree_skb(skb2);
 140         }
 141         else
 142                 skb_orphan(skb);
 143
 144         skb->protocol=eth_type_trans(skb,dev);
 145         skb->dev=dev;
 146 #ifndef LOOPBACK_MUST_CHECKSUM
 147         skb->ip_summed = CHECKSUM_UNNECESSARY;
 148 #endif
 149
 150         if (skb_shinfo(skb)->tso_size) {
 151                 struct iphdr *iph = skb->nh.iph;
 152
 153                 if (skb->protocol != htons(ETH_P_IP))
 154                         BUG();
 155                 if (iph->protocol != IPPROTO_TCP)
 156                         BUG();
 157
 158                 emulate_large_send_offload(skb);
 159                 return 0;
 160         }
 161
 162         dev->last_rx = jiffies;
 163         stats->rx_bytes+=skb->len;
 164         stats->tx_bytes+=skb->len;
 165         stats->rx_packets++;
 166         stats->tx_packets++;
 167
 168         netif_rx(skb);
 169
 170         return(0);
 171 }
 172
 173 static struct net_device_stats *get_stats(struct net_device *dev)
 174 {
 175         return (struct net_device_stats *)dev->priv;
 176 }
 177
 178 /* Initialize the rest of the LOOPBACK device. */
 179 int __init loopback_init(struct net_device *dev)
 180 {
 181         dev->mtu                = (16 * 1024) + 20 + 20 + 12;
 182         dev->hard_start_xmit    = loopback_xmit;
 183         dev->hard_header        = eth_header;
 184         dev->hard_header_cache  = eth_header_cache;
 185         dev->header_cache_update= eth_header_cache_update;
 186         dev->hard_header_len    = ETH_HLEN;             /* 14                   */
 187         dev->addr_len           = ETH_ALEN;             /* 6                    */
 188         dev->tx_queue_len       = 0;
 189         dev->type               = ARPHRD_LOOPBACK;      /* 0x0001               */
 190         dev->rebuild_header     = eth_rebuild_header;
 191         dev->flags              = IFF_LOOPBACK;
 192         dev->features           = NETIF_F_SG|NETIF_F_FRAGLIST|NETIF_F_NO_CSUM|NETIF_F_HIGHDMA;
 193
 194         /* Current netfilter will die with oom linearizing large skbs,
 195          * however this will be cured before 2.5.x is done.
 196          */
 197         dev->features          |= NETIF_F_TSO;
 198
 199         dev->priv = kmalloc(sizeof(struct net_device_stats), GFP_KERNEL);
 200         if (dev->priv == NULL)
 201                         return -ENOMEM;
 202         memset(dev->priv, 0, sizeof(struct net_device_stats));
 203         dev->get_stats = get_stats;
 204
 205         /*
 206          *      Fill in the generic fields of the device structure.
 207          */
 208
 209         return(0);
 210 };