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skbuff.c

/*
 *    Routines having to do with the 'struct sk_buff' memory handlers.
 *
 *    Authors:    Alan Cox <iiitac@pyr.swan.ac.uk>
 *                Florian La Roche <rzsfl@rz.uni-sb.de>
 *
 *    Version:    $Id: skbuff.c,v 1.90 2001/11/07 05:56:19 davem Exp $
 *
 *    Fixes:
 *          Alan Cox    :     Fixed the worst of the load
 *                            balancer bugs.
 *          Dave Platt  :     Interrupt stacking fix.
 *    Richard Kooijman  :     Timestamp fixes.
 *          Alan Cox    :     Changed buffer format.
 *          Alan Cox    :     destructor hook for AF_UNIX etc.
 *          Linus Torvalds    :     Better skb_clone.
 *          Alan Cox    :     Added skb_copy.
 *          Alan Cox    :     Added all the changed routines Linus
 *                            only put in the headers
 *          Ray VanTassle     :     Fixed --skb->lock in free
 *          Alan Cox    :     skb_copy copy arp field
 *          Andi Kleen  :     slabified it.
 *          Robert Olsson     :     Removed skb_head_pool
 *
 *    NOTE:
 *          The __skb_ routines should be called with interrupts
 *    disabled, or you better be *real* sure that the operation is atomic
 *    with respect to whatever list is being frobbed (e.g. via lock_sock()
 *    or via disabling bottom half handlers, etc).
 *
 *    This program is free software; you can redistribute it and/or
 *    modify it under the terms of the GNU General Public License
 *    as published by the Free Software Foundation; either version
 *    2 of the License, or (at your option) any later version.
 */

/*
 *    The functions in this file will not compile correctly with gcc 2.4.x
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/inet.h>
#include <linux/slab.h>
#include <linux/netdevice.h>
#ifdef CONFIG_NET_CLS_ACT
#include <net/pkt_sched.h>
#endif
#include <linux/string.h>
#include <linux/skbuff.h>
#include <linux/cache.h>
#include <linux/rtnetlink.h>
#include <linux/init.h>
#include <linux/scatterlist.h>

#include <net/protocol.h>
#include <net/dst.h>
#include <net/sock.h>
#include <net/checksum.h>
#include <net/xfrm.h>

#include <asm/uaccess.h>
#include <asm/system.h>

#include "kmap_skb.h"

static struct kmem_cache *skbuff_head_cache __read_mostly;
static struct kmem_cache *skbuff_fclone_cache __read_mostly;

/*
 *    Keep out-of-line to prevent kernel bloat.
 *    __builtin_return_address is not used because it is not always
 *    reliable.
 */

/**
 *    skb_over_panic    -     private function
 *    @skb: buffer
 *    @sz: size
 *    @here: address
 *
 *    Out of line support code for skb_put(). Not user callable.
 */
void skb_over_panic(struct sk_buff *skb, int sz, void *here)
{
      printk(KERN_EMERG "skb_over_panic: text:%p len:%d put:%d head:%p "
                    "data:%p tail:%#lx end:%#lx dev:%s\n",
             here, skb->len, sz, skb->head, skb->data,
             (unsigned long)skb->tail, (unsigned long)skb->end,
             skb->dev ? skb->dev->name : "<NULL>");
      BUG();
}

/**
 *    skb_under_panic   -     private function
 *    @skb: buffer
 *    @sz: size
 *    @here: address
 *
 *    Out of line support code for skb_push(). Not user callable.
 */

void skb_under_panic(struct sk_buff *skb, int sz, void *here)
{
      printk(KERN_EMERG "skb_under_panic: text:%p len:%d put:%d head:%p "
                    "data:%p tail:%#lx end:%#lx dev:%s\n",
             here, skb->len, sz, skb->head, skb->data,
             (unsigned long)skb->tail, (unsigned long)skb->end,
             skb->dev ? skb->dev->name : "<NULL>");
      BUG();
}

void skb_truesize_bug(struct sk_buff *skb)
{
      printk(KERN_ERR "SKB BUG: Invalid truesize (%u) "
             "len=%u, sizeof(sk_buff)=%Zd\n",
             skb->truesize, skb->len, sizeof(struct sk_buff));
}
EXPORT_SYMBOL(skb_truesize_bug);

/*    Allocate a new skbuff. We do this ourselves so we can fill in a few
 *    'private' fields and also do memory statistics to find all the
 *    [BEEP] leaks.
 *
 */

/**
 *    __alloc_skb -     allocate a network buffer
 *    @size: size to allocate
 *    @gfp_mask: allocation mask
 *    @fclone: allocate from fclone cache instead of head cache
 *          and allocate a cloned (child) skb
 *    @node: numa node to allocate memory on
 *
 *    Allocate a new &sk_buff. The returned buffer has no headroom and a
 *    tail room of size bytes. The object has a reference count of one.
 *    The return is the buffer. On a failure the return is %NULL.
 *
 *    Buffers may only be allocated from interrupts using a @gfp_mask of
 *    %GFP_ATOMIC.
 */
struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
                      int fclone, int node)
{
      struct kmem_cache *cache;
      struct skb_shared_info *shinfo;
      struct sk_buff *skb;
      u8 *data;

      cache = fclone ? skbuff_fclone_cache : skbuff_head_cache;

      /* Get the HEAD */
      skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
      if (!skb)
            goto out;

      size = SKB_DATA_ALIGN(size);
      data = kmalloc_node_track_caller(size + sizeof(struct skb_shared_info),
                  gfp_mask, node);
      if (!data)
            goto nodata;

      /*
       * See comment in sk_buff definition, just before the 'tail' member
       */
      memset(skb, 0, offsetof(struct sk_buff, tail));
      skb->truesize = size + sizeof(struct sk_buff);
      atomic_set(&skb->users, 1);
      skb->head = data;
      skb->data = data;
      skb_reset_tail_pointer(skb);
      skb->end = skb->tail + size;
      /* make sure we initialize shinfo sequentially */
      shinfo = skb_shinfo(skb);
      atomic_set(&shinfo->dataref, 1);
      shinfo->nr_frags  = 0;
      shinfo->gso_size = 0;
      shinfo->gso_segs = 0;
      shinfo->gso_type = 0;
      shinfo->ip6_frag_id = 0;
      shinfo->frag_list = NULL;

      if (fclone) {
            struct sk_buff *child = skb + 1;
            atomic_t *fclone_ref = (atomic_t *) (child + 1);

            skb->fclone = SKB_FCLONE_ORIG;
            atomic_set(fclone_ref, 1);

            child->fclone = SKB_FCLONE_UNAVAILABLE;
      }
out:
      return skb;
nodata:
      kmem_cache_free(cache, skb);
      skb = NULL;
      goto out;
}

/**
 *    __netdev_alloc_skb - allocate an skbuff for rx on a specific device
 *    @dev: network device to receive on
 *    @length: length to allocate
 *    @gfp_mask: get_free_pages mask, passed to alloc_skb
 *
 *    Allocate a new &sk_buff and assign it a usage count of one. The
 *    buffer has unspecified headroom built in. Users should allocate
 *    the headroom they think they need without accounting for the
 *    built in space. The built in space is used for optimisations.
 *
 *    %NULL is returned if there is no free memory.
 */
struct sk_buff *__netdev_alloc_skb(struct net_device *dev,
            unsigned int length, gfp_t gfp_mask)
{
      int node = dev->dev.parent ? dev_to_node(dev->dev.parent) : -1;
      struct sk_buff *skb;

      skb = __alloc_skb(length + NET_SKB_PAD, gfp_mask, 0, node);
      if (likely(skb)) {
            skb_reserve(skb, NET_SKB_PAD);
            skb->dev = dev;
      }
      return skb;
}

static void skb_drop_list(struct sk_buff **listp)
{
      struct sk_buff *list = *listp;

      *listp = NULL;

      do {
            struct sk_buff *this = list;
            list = list->next;
            kfree_skb(this);
      } while (list);
}

static inline void skb_drop_fraglist(struct sk_buff *skb)
{
      skb_drop_list(&skb_shinfo(skb)->frag_list);
}

static void skb_clone_fraglist(struct sk_buff *skb)
{
      struct sk_buff *list;

      for (list = skb_shinfo(skb)->frag_list; list; list = list->next)
            skb_get(list);
}

static void skb_release_data(struct sk_buff *skb)
{
      if (!skb->cloned ||
          !atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
                         &skb_shinfo(skb)->dataref)) {
            if (skb_shinfo(skb)->nr_frags) {
                  int i;
                  for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
                        put_page(skb_shinfo(skb)->frags[i].page);
            }

            if (skb_shinfo(skb)->frag_list)
                  skb_drop_fraglist(skb);

            kfree(skb->head);
      }
}

/*
 *    Free an skbuff by memory without cleaning the state.
 */
static void kfree_skbmem(struct sk_buff *skb)
{
      struct sk_buff *other;
      atomic_t *fclone_ref;

      switch (skb->fclone) {
      case SKB_FCLONE_UNAVAILABLE:
            kmem_cache_free(skbuff_head_cache, skb);
            break;

      case SKB_FCLONE_ORIG:
            fclone_ref = (atomic_t *) (skb + 2);
            if (atomic_dec_and_test(fclone_ref))
                  kmem_cache_free(skbuff_fclone_cache, skb);
            break;

      case SKB_FCLONE_CLONE:
            fclone_ref = (atomic_t *) (skb + 1);
            other = skb - 1;

            /* The clone portion is available for
             * fast-cloning again.
             */
            skb->fclone = SKB_FCLONE_UNAVAILABLE;

            if (atomic_dec_and_test(fclone_ref))
                  kmem_cache_free(skbuff_fclone_cache, other);
            break;
      }
}

/* Free everything but the sk_buff shell. */
static void skb_release_all(struct sk_buff *skb)
{
      dst_release(skb->dst);
#ifdef CONFIG_XFRM
      secpath_put(skb->sp);
#endif
      if (skb->destructor) {
            WARN_ON(in_irq());
            skb->destructor(skb);
      }
#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
      nf_conntrack_put(skb->nfct);
      nf_conntrack_put_reasm(skb->nfct_reasm);
#endif
#ifdef CONFIG_BRIDGE_NETFILTER
      nf_bridge_put(skb->nf_bridge);
#endif
/* XXX: IS this still necessary? - JHS */
#ifdef CONFIG_NET_SCHED
      skb->tc_index = 0;
#ifdef CONFIG_NET_CLS_ACT
      skb->tc_verd = 0;
#endif
#endif
      skb_release_data(skb);
}

/**
 *    __kfree_skb - private function
 *    @skb: buffer
 *
 *    Free an sk_buff. Release anything attached to the buffer.
 *    Clean the state. This is an internal helper function. Users should
 *    always call kfree_skb
 */

void __kfree_skb(struct sk_buff *skb)
{
      skb_release_all(skb);
      kfree_skbmem(skb);
}

/**
 *    kfree_skb - free an sk_buff
 *    @skb: buffer to free
 *
 *    Drop a reference to the buffer and free it if the usage count has
 *    hit zero.
 */
void kfree_skb(struct sk_buff *skb)
{
      if (unlikely(!skb))
            return;
      if (likely(atomic_read(&skb->users) == 1))
            smp_rmb();
      else if (likely(!atomic_dec_and_test(&skb->users)))
            return;
      __kfree_skb(skb);
}

static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
{
      new->tstamp       = old->tstamp;
      new->dev          = old->dev;
      new->transport_header   = old->transport_header;
      new->network_header     = old->network_header;
      new->mac_header         = old->mac_header;
      new->dst          = dst_clone(old->dst);
#ifdef CONFIG_INET
      new->sp                 = secpath_get(old->sp);
#endif
      memcpy(new->cb, old->cb, sizeof(old->cb));
      new->csum_start         = old->csum_start;
      new->csum_offset  = old->csum_offset;
      new->local_df           = old->local_df;
      new->pkt_type           = old->pkt_type;
      new->ip_summed          = old->ip_summed;
      skb_copy_queue_mapping(new, old);
      new->priority           = old->priority;
#if defined(CONFIG_IP_VS) || defined(CONFIG_IP_VS_MODULE)
      new->ipvs_property      = old->ipvs_property;
#endif
      new->protocol           = old->protocol;
      new->mark         = old->mark;
      __nf_copy(new, old);
#if defined(CONFIG_NETFILTER_XT_TARGET_TRACE) || \
    defined(CONFIG_NETFILTER_XT_TARGET_TRACE_MODULE)
      new->nf_trace           = old->nf_trace;
#endif
#ifdef CONFIG_NET_SCHED
      new->tc_index           = old->tc_index;
#ifdef CONFIG_NET_CLS_ACT
      new->tc_verd            = old->tc_verd;
#endif
#endif
      skb_copy_secmark(new, old);
}

static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
{
#define C(x) n->x = skb->x

      n->next = n->prev = NULL;
      n->sk = NULL;
      __copy_skb_header(n, skb);

      C(len);
      C(data_len);
      C(mac_len);
      n->hdr_len = skb->nohdr ? skb_headroom(skb) : skb->hdr_len;
      n->cloned = 1;
      n->nohdr = 0;
      n->destructor = NULL;
      C(iif);
      C(tail);
      C(end);
      C(head);
      C(data);
      C(truesize);
      atomic_set(&n->users, 1);

      atomic_inc(&(skb_shinfo(skb)->dataref));
      skb->cloned = 1;

      return n;
#undef C
}

/**
 *    skb_morph   -     morph one skb into another
 *    @dst: the skb to receive the contents
 *    @src: the skb to supply the contents
 *
 *    This is identical to skb_clone except that the target skb is
 *    supplied by the user.
 *
 *    The target skb is returned upon exit.
 */
struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
{
      skb_release_all(dst);
      return __skb_clone(dst, src);
}
EXPORT_SYMBOL_GPL(skb_morph);

/**
 *    skb_clone   -     duplicate an sk_buff
 *    @skb: buffer to clone
 *    @gfp_mask: allocation priority
 *
 *    Duplicate an &sk_buff. The new one is not owned by a socket. Both
 *    copies share the same packet data but not structure. The new
 *    buffer has a reference count of 1. If the allocation fails the
 *    function returns %NULL otherwise the new buffer is returned.
 *
 *    If this function is called from an interrupt gfp_mask() must be
 *    %GFP_ATOMIC.
 */

struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
{
      struct sk_buff *n;

      n = skb + 1;
      if (skb->fclone == SKB_FCLONE_ORIG &&
          n->fclone == SKB_FCLONE_UNAVAILABLE) {
            atomic_t *fclone_ref = (atomic_t *) (n + 1);
            n->fclone = SKB_FCLONE_CLONE;
            atomic_inc(fclone_ref);
      } else {
            n = kmem_cache_alloc(skbuff_head_cache, gfp_mask);
            if (!n)
                  return NULL;
            n->fclone = SKB_FCLONE_UNAVAILABLE;
      }

      return __skb_clone(n, skb);
}

static void copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
{
#ifndef NET_SKBUFF_DATA_USES_OFFSET
      /*
       *    Shift between the two data areas in bytes
       */
      unsigned long offset = new->data - old->data;
#endif

      __copy_skb_header(new, old);

#ifndef NET_SKBUFF_DATA_USES_OFFSET
      /* {transport,network,mac}_header are relative to skb->head */
      new->transport_header += offset;
      new->network_header   += offset;
      new->mac_header         += offset;
#endif
      skb_shinfo(new)->gso_size = skb_shinfo(old)->gso_size;
      skb_shinfo(new)->gso_segs = skb_shinfo(old)->gso_segs;
      skb_shinfo(new)->gso_type = skb_shinfo(old)->gso_type;
}

/**
 *    skb_copy    -     create private copy of an sk_buff
 *    @skb: buffer to copy
 *    @gfp_mask: allocation priority
 *
 *    Make a copy of both an &sk_buff and its data. This is used when the
 *    caller wishes to modify the data and needs a private copy of the
 *    data to alter. Returns %NULL on failure or the pointer to the buffer
 *    on success. The returned buffer has a reference count of 1.
 *
 *    As by-product this function converts non-linear &sk_buff to linear
 *    one, so that &sk_buff becomes completely private and caller is allowed
 *    to modify all the data of returned buffer. This means that this
 *    function is not recommended for use in circumstances when only
 *    header is going to be modified. Use pskb_copy() instead.
 */

struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
{
      int headerlen = skb->data - skb->head;
      /*
       *    Allocate the copy buffer
       */
      struct sk_buff *n;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      n = alloc_skb(skb->end + skb->data_len, gfp_mask);
#else
      n = alloc_skb(skb->end - skb->head + skb->data_len, gfp_mask);
#endif
      if (!n)
            return NULL;

      /* Set the data pointer */
      skb_reserve(n, headerlen);
      /* Set the tail pointer and length */
      skb_put(n, skb->len);

      if (skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len))
            BUG();

      copy_skb_header(n, skb);
      return n;
}


/**
 *    pskb_copy   -     create copy of an sk_buff with private head.
 *    @skb: buffer to copy
 *    @gfp_mask: allocation priority
 *
 *    Make a copy of both an &sk_buff and part of its data, located
 *    in header. Fragmented data remain shared. This is used when
 *    the caller wishes to modify only header of &sk_buff and needs
 *    private copy of the header to alter. Returns %NULL on failure
 *    or the pointer to the buffer on success.
 *    The returned buffer has a reference count of 1.
 */

struct sk_buff *pskb_copy(struct sk_buff *skb, gfp_t gfp_mask)
{
      /*
       *    Allocate the copy buffer
       */
      struct sk_buff *n;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      n = alloc_skb(skb->end, gfp_mask);
#else
      n = alloc_skb(skb->end - skb->head, gfp_mask);
#endif
      if (!n)
            goto out;

      /* Set the data pointer */
      skb_reserve(n, skb->data - skb->head);
      /* Set the tail pointer and length */
      skb_put(n, skb_headlen(skb));
      /* Copy the bytes */
      skb_copy_from_linear_data(skb, n->data, n->len);

      n->truesize += skb->data_len;
      n->data_len  = skb->data_len;
      n->len           = skb->len;

      if (skb_shinfo(skb)->nr_frags) {
            int i;

            for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
                  skb_shinfo(n)->frags[i] = skb_shinfo(skb)->frags[i];
                  get_page(skb_shinfo(n)->frags[i].page);
            }
            skb_shinfo(n)->nr_frags = i;
      }

      if (skb_shinfo(skb)->frag_list) {
            skb_shinfo(n)->frag_list = skb_shinfo(skb)->frag_list;
            skb_clone_fraglist(n);
      }

      copy_skb_header(n, skb);
out:
      return n;
}

/**
 *    pskb_expand_head - reallocate header of &sk_buff
 *    @skb: buffer to reallocate
 *    @nhead: room to add at head
 *    @ntail: room to add at tail
 *    @gfp_mask: allocation priority
 *
 *    Expands (or creates identical copy, if &nhead and &ntail are zero)
 *    header of skb. &sk_buff itself is not changed. &sk_buff MUST have
 *    reference count of 1. Returns zero in the case of success or error,
 *    if expansion failed. In the last case, &sk_buff is not changed.
 *
 *    All the pointers pointing into skb header may change and must be
 *    reloaded after call to this function.
 */

int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
                 gfp_t gfp_mask)
{
      int i;
      u8 *data;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      int size = nhead + skb->end + ntail;
#else
      int size = nhead + (skb->end - skb->head) + ntail;
#endif
      long off;

      if (skb_shared(skb))
            BUG();

      size = SKB_DATA_ALIGN(size);

      data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
      if (!data)
            goto nodata;

      /* Copy only real data... and, alas, header. This should be
       * optimized for the cases when header is void. */
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      memcpy(data + nhead, skb->head, skb->tail);
#else
      memcpy(data + nhead, skb->head, skb->tail - skb->head);
#endif
      memcpy(data + size, skb_end_pointer(skb),
             sizeof(struct skb_shared_info));

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
            get_page(skb_shinfo(skb)->frags[i].page);

      if (skb_shinfo(skb)->frag_list)
            skb_clone_fraglist(skb);

      skb_release_data(skb);

      off = (data + nhead) - skb->head;

      skb->head     = data;
      skb->data    += off;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      skb->end      = size;
      off           = nhead;
#else
      skb->end      = skb->head + size;
#endif
      /* {transport,network,mac}_header and tail are relative to skb->head */
      skb->tail         += off;
      skb->transport_header += off;
      skb->network_header   += off;
      skb->mac_header         += off;
      skb->csum_start       += nhead;
      skb->cloned   = 0;
      skb->hdr_len  = 0;
      skb->nohdr    = 0;
      atomic_set(&skb_shinfo(skb)->dataref, 1);
      return 0;

nodata:
      return -ENOMEM;
}

/* Make private copy of skb with writable head and some headroom */

struct sk_buff *skb_realloc_headroom(struct sk_buff *skb, unsigned int headroom)
{
      struct sk_buff *skb2;
      int delta = headroom - skb_headroom(skb);

      if (delta <= 0)
            skb2 = pskb_copy(skb, GFP_ATOMIC);
      else {
            skb2 = skb_clone(skb, GFP_ATOMIC);
            if (skb2 && pskb_expand_head(skb2, SKB_DATA_ALIGN(delta), 0,
                                   GFP_ATOMIC)) {
                  kfree_skb(skb2);
                  skb2 = NULL;
            }
      }
      return skb2;
}


/**
 *    skb_copy_expand   -     copy and expand sk_buff
 *    @skb: buffer to copy
 *    @newheadroom: new free bytes at head
 *    @newtailroom: new free bytes at tail
 *    @gfp_mask: allocation priority
 *
 *    Make a copy of both an &sk_buff and its data and while doing so
 *    allocate additional space.
 *
 *    This is used when the caller wishes to modify the data and needs a
 *    private copy of the data to alter as well as more space for new fields.
 *    Returns %NULL on failure or the pointer to the buffer
 *    on success. The returned buffer has a reference count of 1.
 *
 *    You must pass %GFP_ATOMIC as the allocation priority if this function
 *    is called from an interrupt.
 */
struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
                        int newheadroom, int newtailroom,
                        gfp_t gfp_mask)
{
      /*
       *    Allocate the copy buffer
       */
      struct sk_buff *n = alloc_skb(newheadroom + skb->len + newtailroom,
                              gfp_mask);
      int oldheadroom = skb_headroom(skb);
      int head_copy_len, head_copy_off;
      int off;

      if (!n)
            return NULL;

      skb_reserve(n, newheadroom);

      /* Set the tail pointer and length */
      skb_put(n, skb->len);

      head_copy_len = oldheadroom;
      head_copy_off = 0;
      if (newheadroom <= head_copy_len)
            head_copy_len = newheadroom;
      else
            head_copy_off = newheadroom - head_copy_len;

      /* Copy the linear header and data. */
      if (skb_copy_bits(skb, -head_copy_len, n->head + head_copy_off,
                    skb->len + head_copy_len))
            BUG();

      copy_skb_header(n, skb);

      off                  = newheadroom - oldheadroom;
      n->csum_start       += off;
#ifdef NET_SKBUFF_DATA_USES_OFFSET
      n->transport_header += off;
      n->network_header   += off;
      n->mac_header         += off;
#endif

      return n;
}

/**
 *    skb_pad                 -     zero pad the tail of an skb
 *    @skb: buffer to pad
 *    @pad: space to pad
 *
 *    Ensure that a buffer is followed by a padding area that is zero
 *    filled. Used by network drivers which may DMA or transfer data
 *    beyond the buffer end onto the wire.
 *
 *    May return error in out of memory cases. The skb is freed on error.
 */

int skb_pad(struct sk_buff *skb, int pad)
{
      int err;
      int ntail;

      /* If the skbuff is non linear tailroom is always zero.. */
      if (!skb_cloned(skb) && skb_tailroom(skb) >= pad) {
            memset(skb->data+skb->len, 0, pad);
            return 0;
      }

      ntail = skb->data_len + pad - (skb->end - skb->tail);
      if (likely(skb_cloned(skb) || ntail > 0)) {
            err = pskb_expand_head(skb, 0, ntail, GFP_ATOMIC);
            if (unlikely(err))
                  goto free_skb;
      }

      /* FIXME: The use of this function with non-linear skb's really needs
       * to be audited.
       */
      err = skb_linearize(skb);
      if (unlikely(err))
            goto free_skb;

      memset(skb->data + skb->len, 0, pad);
      return 0;

free_skb:
      kfree_skb(skb);
      return err;
}

/* Trims skb to length len. It can change skb pointers.
 */

int ___pskb_trim(struct sk_buff *skb, unsigned int len)
{
      struct sk_buff **fragp;
      struct sk_buff *frag;
      int offset = skb_headlen(skb);
      int nfrags = skb_shinfo(skb)->nr_frags;
      int i;
      int err;

      if (skb_cloned(skb) &&
          unlikely((err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC))))
            return err;

      i = 0;
      if (offset >= len)
            goto drop_pages;

      for (; i < nfrags; i++) {
            int end = offset + skb_shinfo(skb)->frags[i].size;

            if (end < len) {
                  offset = end;
                  continue;
            }

            skb_shinfo(skb)->frags[i++].size = len - offset;

drop_pages:
            skb_shinfo(skb)->nr_frags = i;

            for (; i < nfrags; i++)
                  put_page(skb_shinfo(skb)->frags[i].page);

            if (skb_shinfo(skb)->frag_list)
                  skb_drop_fraglist(skb);
            goto done;
      }

      for (fragp = &skb_shinfo(skb)->frag_list; (frag = *fragp);
           fragp = &frag->next) {
            int end = offset + frag->len;

            if (skb_shared(frag)) {
                  struct sk_buff *nfrag;

                  nfrag = skb_clone(frag, GFP_ATOMIC);
                  if (unlikely(!nfrag))
                        return -ENOMEM;

                  nfrag->next = frag->next;
                  kfree_skb(frag);
                  frag = nfrag;
                  *fragp = frag;
            }

            if (end < len) {
                  offset = end;
                  continue;
            }

            if (end > len &&
                unlikely((err = pskb_trim(frag, len - offset))))
                  return err;

            if (frag->next)
                  skb_drop_list(&frag->next);
            break;
      }

done:
      if (len > skb_headlen(skb)) {
            skb->data_len -= skb->len - len;
            skb->len       = len;
      } else {
            skb->len       = len;
            skb->data_len  = 0;
            skb_set_tail_pointer(skb, len);
      }

      return 0;
}

/**
 *    __pskb_pull_tail - advance tail of skb header
 *    @skb: buffer to reallocate
 *    @delta: number of bytes to advance tail
 *
 *    The function makes a sense only on a fragmented &sk_buff,
 *    it expands header moving its tail forward and copying necessary
 *    data from fragmented part.
 *
 *    &sk_buff MUST have reference count of 1.
 *
 *    Returns %NULL (and &sk_buff does not change) if pull failed
 *    or value of new tail of skb in the case of success.
 *
 *    All the pointers pointing into skb header may change and must be
 *    reloaded after call to this function.
 */

/* Moves tail of skb head forward, copying data from fragmented part,
 * when it is necessary.
 * 1. It may fail due to malloc failure.
 * 2. It may change skb pointers.
 *
 * It is pretty complicated. Luckily, it is called only in exceptional cases.
 */
unsigned char *__pskb_pull_tail(struct sk_buff *skb, int delta)
{
      /* If skb has not enough free space at tail, get new one
       * plus 128 bytes for future expansions. If we have enough
       * room at tail, reallocate without expansion only if skb is cloned.
       */
      int i, k, eat = (skb->tail + delta) - skb->end;

      if (eat > 0 || skb_cloned(skb)) {
            if (pskb_expand_head(skb, 0, eat > 0 ? eat + 128 : 0,
                             GFP_ATOMIC))
                  return NULL;
      }

      if (skb_copy_bits(skb, skb_headlen(skb), skb_tail_pointer(skb), delta))
            BUG();

      /* Optimization: no fragments, no reasons to preestimate
       * size of pulled pages. Superb.
       */
      if (!skb_shinfo(skb)->frag_list)
            goto pull_pages;

      /* Estimate size of pulled pages. */
      eat = delta;
      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            if (skb_shinfo(skb)->frags[i].size >= eat)
                  goto pull_pages;
            eat -= skb_shinfo(skb)->frags[i].size;
      }

      /* If we need update frag list, we are in troubles.
       * Certainly, it possible to add an offset to skb data,
       * but taking into account that pulling is expected to
       * be very rare operation, it is worth to fight against
       * further bloating skb head and crucify ourselves here instead.
       * Pure masohism, indeed. 8)8)
       */
      if (eat) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;
            struct sk_buff *clone = NULL;
            struct sk_buff *insp = NULL;

            do {
                  BUG_ON(!list);

                  if (list->len <= eat) {
                        /* Eaten as whole. */
                        eat -= list->len;
                        list = list->next;
                        insp = list;
                  } else {
                        /* Eaten partially. */

                        if (skb_shared(list)) {
                              /* Sucks! We need to fork list. :-( */
                              clone = skb_clone(list, GFP_ATOMIC);
                              if (!clone)
                                    return NULL;
                              insp = list->next;
                              list = clone;
                        } else {
                              /* This may be pulled without
                               * problems. */
                              insp = list;
                        }
                        if (!pskb_pull(list, eat)) {
                              if (clone)
                                    kfree_skb(clone);
                              return NULL;
                        }
                        break;
                  }
            } while (eat);

            /* Free pulled out fragments. */
            while ((list = skb_shinfo(skb)->frag_list) != insp) {
                  skb_shinfo(skb)->frag_list = list->next;
                  kfree_skb(list);
            }
            /* And insert new clone at head. */
            if (clone) {
                  clone->next = list;
                  skb_shinfo(skb)->frag_list = clone;
            }
      }
      /* Success! Now we may commit changes to skb data. */

pull_pages:
      eat = delta;
      k = 0;
      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            if (skb_shinfo(skb)->frags[i].size <= eat) {
                  put_page(skb_shinfo(skb)->frags[i].page);
                  eat -= skb_shinfo(skb)->frags[i].size;
            } else {
                  skb_shinfo(skb)->frags[k] = skb_shinfo(skb)->frags[i];
                  if (eat) {
                        skb_shinfo(skb)->frags[k].page_offset += eat;
                        skb_shinfo(skb)->frags[k].size -= eat;
                        eat = 0;
                  }
                  k++;
            }
      }
      skb_shinfo(skb)->nr_frags = k;

      skb->tail     += delta;
      skb->data_len -= delta;

      return skb_tail_pointer(skb);
}

/* Copy some data bits from skb to kernel buffer. */

int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
{
      int i, copy;
      int start = skb_headlen(skb);

      if (offset > (int)skb->len - len)
            goto fault;

      /* Copy header. */
      if ((copy = start - offset) > 0) {
            if (copy > len)
                  copy = len;
            skb_copy_from_linear_data_offset(skb, offset, to, copy);
            if ((len -= copy) == 0)
                  return 0;
            offset += copy;
            to     += copy;
      }

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            int end;

            BUG_TRAP(start <= offset + len);

            end = start + skb_shinfo(skb)->frags[i].size;
            if ((copy = end - offset) > 0) {
                  u8 *vaddr;

                  if (copy > len)
                        copy = len;

                  vaddr = kmap_skb_frag(&skb_shinfo(skb)->frags[i]);
                  memcpy(to,
                         vaddr + skb_shinfo(skb)->frags[i].page_offset+
                         offset - start, copy);
                  kunmap_skb_frag(vaddr);

                  if ((len -= copy) == 0)
                        return 0;
                  offset += copy;
                  to     += copy;
            }
            start = end;
      }

      if (skb_shinfo(skb)->frag_list) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;

            for (; list; list = list->next) {
                  int end;

                  BUG_TRAP(start <= offset + len);

                  end = start + list->len;
                  if ((copy = end - offset) > 0) {
                        if (copy > len)
                              copy = len;
                        if (skb_copy_bits(list, offset - start,
                                      to, copy))
                              goto fault;
                        if ((len -= copy) == 0)
                              return 0;
                        offset += copy;
                        to     += copy;
                  }
                  start = end;
            }
      }
      if (!len)
            return 0;

fault:
      return -EFAULT;
}

/**
 *    skb_store_bits - store bits from kernel buffer to skb
 *    @skb: destination buffer
 *    @offset: offset in destination
 *    @from: source buffer
 *    @len: number of bytes to copy
 *
 *    Copy the specified number of bytes from the source buffer to the
 *    destination skb.  This function handles all the messy bits of
 *    traversing fragment lists and such.
 */

int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len)
{
      int i, copy;
      int start = skb_headlen(skb);

      if (offset > (int)skb->len - len)
            goto fault;

      if ((copy = start - offset) > 0) {
            if (copy > len)
                  copy = len;
            skb_copy_to_linear_data_offset(skb, offset, from, copy);
            if ((len -= copy) == 0)
                  return 0;
            offset += copy;
            from += copy;
      }

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
            int end;

            BUG_TRAP(start <= offset + len);

            end = start + frag->size;
            if ((copy = end - offset) > 0) {
                  u8 *vaddr;

                  if (copy > len)
                        copy = len;

                  vaddr = kmap_skb_frag(frag);
                  memcpy(vaddr + frag->page_offset + offset - start,
                         from, copy);
                  kunmap_skb_frag(vaddr);

                  if ((len -= copy) == 0)
                        return 0;
                  offset += copy;
                  from += copy;
            }
            start = end;
      }

      if (skb_shinfo(skb)->frag_list) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;

            for (; list; list = list->next) {
                  int end;

                  BUG_TRAP(start <= offset + len);

                  end = start + list->len;
                  if ((copy = end - offset) > 0) {
                        if (copy > len)
                              copy = len;
                        if (skb_store_bits(list, offset - start,
                                       from, copy))
                              goto fault;
                        if ((len -= copy) == 0)
                              return 0;
                        offset += copy;
                        from += copy;
                  }
                  start = end;
            }
      }
      if (!len)
            return 0;

fault:
      return -EFAULT;
}

EXPORT_SYMBOL(skb_store_bits);

/* Checksum skb data. */

__wsum skb_checksum(const struct sk_buff *skb, int offset,
                    int len, __wsum csum)
{
      int start = skb_headlen(skb);
      int i, copy = start - offset;
      int pos = 0;

      /* Checksum header. */
      if (copy > 0) {
            if (copy > len)
                  copy = len;
            csum = csum_partial(skb->data + offset, copy, csum);
            if ((len -= copy) == 0)
                  return csum;
            offset += copy;
            pos   = copy;
      }

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            int end;

            BUG_TRAP(start <= offset + len);

            end = start + skb_shinfo(skb)->frags[i].size;
            if ((copy = end - offset) > 0) {
                  __wsum csum2;
                  u8 *vaddr;
                  skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

                  if (copy > len)
                        copy = len;
                  vaddr = kmap_skb_frag(frag);
                  csum2 = csum_partial(vaddr + frag->page_offset +
                                   offset - start, copy, 0);
                  kunmap_skb_frag(vaddr);
                  csum = csum_block_add(csum, csum2, pos);
                  if (!(len -= copy))
                        return csum;
                  offset += copy;
                  pos    += copy;
            }
            start = end;
      }

      if (skb_shinfo(skb)->frag_list) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;

            for (; list; list = list->next) {
                  int end;

                  BUG_TRAP(start <= offset + len);

                  end = start + list->len;
                  if ((copy = end - offset) > 0) {
                        __wsum csum2;
                        if (copy > len)
                              copy = len;
                        csum2 = skb_checksum(list, offset - start,
                                         copy, 0);
                        csum = csum_block_add(csum, csum2, pos);
                        if ((len -= copy) == 0)
                              return csum;
                        offset += copy;
                        pos    += copy;
                  }
                  start = end;
            }
      }
      BUG_ON(len);

      return csum;
}

/* Both of above in one bottle. */

__wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset,
                            u8 *to, int len, __wsum csum)
{
      int start = skb_headlen(skb);
      int i, copy = start - offset;
      int pos = 0;

      /* Copy header. */
      if (copy > 0) {
            if (copy > len)
                  copy = len;
            csum = csum_partial_copy_nocheck(skb->data + offset, to,
                                     copy, csum);
            if ((len -= copy) == 0)
                  return csum;
            offset += copy;
            to     += copy;
            pos   = copy;
      }

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            int end;

            BUG_TRAP(start <= offset + len);

            end = start + skb_shinfo(skb)->frags[i].size;
            if ((copy = end - offset) > 0) {
                  __wsum csum2;
                  u8 *vaddr;
                  skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

                  if (copy > len)
                        copy = len;
                  vaddr = kmap_skb_frag(frag);
                  csum2 = csum_partial_copy_nocheck(vaddr +
                                            frag->page_offset +
                                            offset - start, to,
                                            copy, 0);
                  kunmap_skb_frag(vaddr);
                  csum = csum_block_add(csum, csum2, pos);
                  if (!(len -= copy))
                        return csum;
                  offset += copy;
                  to     += copy;
                  pos    += copy;
            }
            start = end;
      }

      if (skb_shinfo(skb)->frag_list) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;

            for (; list; list = list->next) {
                  __wsum csum2;
                  int end;

                  BUG_TRAP(start <= offset + len);

                  end = start + list->len;
                  if ((copy = end - offset) > 0) {
                        if (copy > len)
                              copy = len;
                        csum2 = skb_copy_and_csum_bits(list,
                                                 offset - start,
                                                 to, copy, 0);
                        csum = csum_block_add(csum, csum2, pos);
                        if ((len -= copy) == 0)
                              return csum;
                        offset += copy;
                        to     += copy;
                        pos    += copy;
                  }
                  start = end;
            }
      }
      BUG_ON(len);
      return csum;
}

void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to)
{
      __wsum csum;
      long csstart;

      if (skb->ip_summed == CHECKSUM_PARTIAL)
            csstart = skb->csum_start - skb_headroom(skb);
      else
            csstart = skb_headlen(skb);

      BUG_ON(csstart > skb_headlen(skb));

      skb_copy_from_linear_data(skb, to, csstart);

      csum = 0;
      if (csstart != skb->len)
            csum = skb_copy_and_csum_bits(skb, csstart, to + csstart,
                                    skb->len - csstart, 0);

      if (skb->ip_summed == CHECKSUM_PARTIAL) {
            long csstuff = csstart + skb->csum_offset;

            *((__sum16 *)(to + csstuff)) = csum_fold(csum);
      }
}

/**
 *    skb_dequeue - remove from the head of the queue
 *    @list: list to dequeue from
 *
 *    Remove the head of the list. The list lock is taken so the function
 *    may be used safely with other locking list functions. The head item is
 *    returned or %NULL if the list is empty.
 */

struct sk_buff *skb_dequeue(struct sk_buff_head *list)
{
      unsigned long flags;
      struct sk_buff *result;

      spin_lock_irqsave(&list->lock, flags);
      result = __skb_dequeue(list);
      spin_unlock_irqrestore(&list->lock, flags);
      return result;
}

/**
 *    skb_dequeue_tail - remove from the tail of the queue
 *    @list: list to dequeue from
 *
 *    Remove the tail of the list. The list lock is taken so the function
 *    may be used safely with other locking list functions. The tail item is
 *    returned or %NULL if the list is empty.
 */
struct sk_buff *skb_dequeue_tail(struct sk_buff_head *list)
{
      unsigned long flags;
      struct sk_buff *result;

      spin_lock_irqsave(&list->lock, flags);
      result = __skb_dequeue_tail(list);
      spin_unlock_irqrestore(&list->lock, flags);
      return result;
}

/**
 *    skb_queue_purge - empty a list
 *    @list: list to empty
 *
 *    Delete all buffers on an &sk_buff list. Each buffer is removed from
 *    the list and one reference dropped. This function takes the list
 *    lock and is atomic with respect to other list locking functions.
 */
void skb_queue_purge(struct sk_buff_head *list)
{
      struct sk_buff *skb;
      while ((skb = skb_dequeue(list)) != NULL)
            kfree_skb(skb);
}

/**
 *    skb_queue_head - queue a buffer at the list head
 *    @list: list to use
 *    @newsk: buffer to queue
 *
 *    Queue a buffer at the start of the list. This function takes the
 *    list lock and can be used safely with other locking &sk_buff functions
 *    safely.
 *
 *    A buffer cannot be placed on two lists at the same time.
 */
void skb_queue_head(struct sk_buff_head *list, struct sk_buff *newsk)
{
      unsigned long flags;

      spin_lock_irqsave(&list->lock, flags);
      __skb_queue_head(list, newsk);
      spin_unlock_irqrestore(&list->lock, flags);
}

/**
 *    skb_queue_tail - queue a buffer at the list tail
 *    @list: list to use
 *    @newsk: buffer to queue
 *
 *    Queue a buffer at the tail of the list. This function takes the
 *    list lock and can be used safely with other locking &sk_buff functions
 *    safely.
 *
 *    A buffer cannot be placed on two lists at the same time.
 */
void skb_queue_tail(struct sk_buff_head *list, struct sk_buff *newsk)
{
      unsigned long flags;

      spin_lock_irqsave(&list->lock, flags);
      __skb_queue_tail(list, newsk);
      spin_unlock_irqrestore(&list->lock, flags);
}

/**
 *    skb_unlink  -     remove a buffer from a list
 *    @skb: buffer to remove
 *    @list: list to use
 *
 *    Remove a packet from a list. The list locks are taken and this
 *    function is atomic with respect to other list locked calls
 *
 *    You must know what list the SKB is on.
 */
void skb_unlink(struct sk_buff *skb, struct sk_buff_head *list)
{
      unsigned long flags;

      spin_lock_irqsave(&list->lock, flags);
      __skb_unlink(skb, list);
      spin_unlock_irqrestore(&list->lock, flags);
}

/**
 *    skb_append  -     append a buffer
 *    @old: buffer to insert after
 *    @newsk: buffer to insert
 *    @list: list to use
 *
 *    Place a packet after a given packet in a list. The list locks are taken
 *    and this function is atomic with respect to other list locked calls.
 *    A buffer cannot be placed on two lists at the same time.
 */
void skb_append(struct sk_buff *old, struct sk_buff *newsk, struct sk_buff_head *list)
{
      unsigned long flags;

      spin_lock_irqsave(&list->lock, flags);
      __skb_append(old, newsk, list);
      spin_unlock_irqrestore(&list->lock, flags);
}


/**
 *    skb_insert  -     insert a buffer
 *    @old: buffer to insert before
 *    @newsk: buffer to insert
 *    @list: list to use
 *
 *    Place a packet before a given packet in a list. The list locks are
 *    taken and this function is atomic with respect to other list locked
 *    calls.
 *
 *    A buffer cannot be placed on two lists at the same time.
 */
void skb_insert(struct sk_buff *old, struct sk_buff *newsk, struct sk_buff_head *list)
{
      unsigned long flags;

      spin_lock_irqsave(&list->lock, flags);
      __skb_insert(newsk, old->prev, old, list);
      spin_unlock_irqrestore(&list->lock, flags);
}

static inline void skb_split_inside_header(struct sk_buff *skb,
                                 struct sk_buff* skb1,
                                 const u32 len, const int pos)
{
      int i;

      skb_copy_from_linear_data_offset(skb, len, skb_put(skb1, pos - len),
                               pos - len);
      /* And move data appendix as is. */
      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
            skb_shinfo(skb1)->frags[i] = skb_shinfo(skb)->frags[i];

      skb_shinfo(skb1)->nr_frags = skb_shinfo(skb)->nr_frags;
      skb_shinfo(skb)->nr_frags  = 0;
      skb1->data_len             = skb->data_len;
      skb1->len            += skb1->data_len;
      skb->data_len              = 0;
      skb->len             = len;
      skb_set_tail_pointer(skb, len);
}

static inline void skb_split_no_header(struct sk_buff *skb,
                               struct sk_buff* skb1,
                               const u32 len, int pos)
{
      int i, k = 0;
      const int nfrags = skb_shinfo(skb)->nr_frags;

      skb_shinfo(skb)->nr_frags = 0;
      skb1->len           = skb1->data_len = skb->len - len;
      skb->len            = len;
      skb->data_len             = len - pos;

      for (i = 0; i < nfrags; i++) {
            int size = skb_shinfo(skb)->frags[i].size;

            if (pos + size > len) {
                  skb_shinfo(skb1)->frags[k] = skb_shinfo(skb)->frags[i];

                  if (pos < len) {
                        /* Split frag.
                         * We have two variants in this case:
                         * 1. Move all the frag to the second
                         *    part, if it is possible. F.e.
                         *    this approach is mandatory for TUX,
                         *    where splitting is expensive.
                         * 2. Split is accurately. We make this.
                         */
                        get_page(skb_shinfo(skb)->frags[i].page);
                        skb_shinfo(skb1)->frags[0].page_offset += len - pos;
                        skb_shinfo(skb1)->frags[0].size -= len - pos;
                        skb_shinfo(skb)->frags[i].size      = len - pos;
                        skb_shinfo(skb)->nr_frags++;
                  }
                  k++;
            } else
                  skb_shinfo(skb)->nr_frags++;
            pos += size;
      }
      skb_shinfo(skb1)->nr_frags = k;
}

/**
 * skb_split - Split fragmented skb to two parts at length len.
 * @skb: the buffer to split
 * @skb1: the buffer to receive the second part
 * @len: new length for skb
 */
void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len)
{
      int pos = skb_headlen(skb);

      if (len < pos)    /* Split line is inside header. */
            skb_split_inside_header(skb, skb1, len, pos);
      else        /* Second chunk has no header, nothing to copy. */
            skb_split_no_header(skb, skb1, len, pos);
}

/**
 * skb_prepare_seq_read - Prepare a sequential read of skb data
 * @skb: the buffer to read
 * @from: lower offset of data to be read
 * @to: upper offset of data to be read
 * @st: state variable
 *
 * Initializes the specified state variable. Must be called before
 * invoking skb_seq_read() for the first time.
 */
void skb_prepare_seq_read(struct sk_buff *skb, unsigned int from,
                    unsigned int to, struct skb_seq_state *st)
{
      st->lower_offset = from;
      st->upper_offset = to;
      st->root_skb = st->cur_skb = skb;
      st->frag_idx = st->stepped_offset = 0;
      st->frag_data = NULL;
}

/**
 * skb_seq_read - Sequentially read skb data
 * @consumed: number of bytes consumed by the caller so far
 * @data: destination pointer for data to be returned
 * @st: state variable
 *
 * Reads a block of skb data at &consumed relative to the
 * lower offset specified to skb_prepare_seq_read(). Assigns
 * the head of the data block to &data and returns the length
 * of the block or 0 if the end of the skb data or the upper
 * offset has been reached.
 *
 * The caller is not required to consume all of the data
 * returned, i.e. &consumed is typically set to the number
 * of bytes already consumed and the next call to
 * skb_seq_read() will return the remaining part of the block.
 *
 * Note: The size of each block of data returned can be arbitary,
 *       this limitation is the cost for zerocopy seqeuental
 *       reads of potentially non linear data.
 *
 * Note: Fragment lists within fragments are not implemented
 *       at the moment, state->root_skb could be replaced with
 *       a stack for this purpose.
 */
unsigned int skb_seq_read(unsigned int consumed, const u8 **data,
                    struct skb_seq_state *st)
{
      unsigned int block_limit, abs_offset = consumed + st->lower_offset;
      skb_frag_t *frag;

      if (unlikely(abs_offset >= st->upper_offset))
            return 0;

next_skb:
      block_limit = skb_headlen(st->cur_skb);

      if (abs_offset < block_limit) {
            *data = st->cur_skb->data + abs_offset;
            return block_limit - abs_offset;
      }

      if (st->frag_idx == 0 && !st->frag_data)
            st->stepped_offset += skb_headlen(st->cur_skb);

      while (st->frag_idx < skb_shinfo(st->cur_skb)->nr_frags) {
            frag = &skb_shinfo(st->cur_skb)->frags[st->frag_idx];
            block_limit = frag->size + st->stepped_offset;

            if (abs_offset < block_limit) {
                  if (!st->frag_data)
                        st->frag_data = kmap_skb_frag(frag);

                  *data = (u8 *) st->frag_data + frag->page_offset +
                        (abs_offset - st->stepped_offset);

                  return block_limit - abs_offset;
            }

            if (st->frag_data) {
                  kunmap_skb_frag(st->frag_data);
                  st->frag_data = NULL;
            }

            st->frag_idx++;
            st->stepped_offset += frag->size;
      }

      if (st->frag_data) {
            kunmap_skb_frag(st->frag_data);
            st->frag_data = NULL;
      }

      if (st->cur_skb->next) {
            st->cur_skb = st->cur_skb->next;
            st->frag_idx = 0;
            goto next_skb;
      } else if (st->root_skb == st->cur_skb &&
               skb_shinfo(st->root_skb)->frag_list) {
            st->cur_skb = skb_shinfo(st->root_skb)->frag_list;
            goto next_skb;
      }

      return 0;
}

/**
 * skb_abort_seq_read - Abort a sequential read of skb data
 * @st: state variable
 *
 * Must be called if skb_seq_read() was not called until it
 * returned 0.
 */
void skb_abort_seq_read(struct skb_seq_state *st)
{
      if (st->frag_data)
            kunmap_skb_frag(st->frag_data);
}

#define TS_SKB_CB(state)      ((struct skb_seq_state *) &((state)->cb))

static unsigned int skb_ts_get_next_block(unsigned int offset, const u8 **text,
                                struct ts_config *conf,
                                struct ts_state *state)
{
      return skb_seq_read(offset, text, TS_SKB_CB(state));
}

static void skb_ts_finish(struct ts_config *conf, struct ts_state *state)
{
      skb_abort_seq_read(TS_SKB_CB(state));
}

/**
 * skb_find_text - Find a text pattern in skb data
 * @skb: the buffer to look in
 * @from: search offset
 * @to: search limit
 * @config: textsearch configuration
 * @state: uninitialized textsearch state variable
 *
 * Finds a pattern in the skb data according to the specified
 * textsearch configuration. Use textsearch_next() to retrieve
 * subsequent occurrences of the pattern. Returns the offset
 * to the first occurrence or UINT_MAX if no match was found.
 */
unsigned int skb_find_text(struct sk_buff *skb, unsigned int from,
                     unsigned int to, struct ts_config *config,
                     struct ts_state *state)
{
      unsigned int ret;

      config->get_next_block = skb_ts_get_next_block;
      config->finish = skb_ts_finish;

      skb_prepare_seq_read(skb, from, to, TS_SKB_CB(state));

      ret = textsearch_find(config, state);
      return (ret <= to - from ? ret : UINT_MAX);
}

/**
 * skb_append_datato_frags: - append the user data to a skb
 * @sk: sock  structure
 * @skb: skb structure to be appened with user data.
 * @getfrag: call back function to be used for getting the user data
 * @from: pointer to user message iov
 * @length: length of the iov message
 *
 * Description: This procedure append the user data in the fragment part
 * of the skb if any page alloc fails user this procedure returns  -ENOMEM
 */
int skb_append_datato_frags(struct sock *sk, struct sk_buff *skb,
                  int (*getfrag)(void *from, char *to, int offset,
                              int len, int odd, struct sk_buff *skb),
                  void *from, int length)
{
      int frg_cnt = 0;
      skb_frag_t *frag = NULL;
      struct page *page = NULL;
      int copy, left;
      int offset = 0;
      int ret;

      do {
            /* Return error if we don't have space for new frag */
            frg_cnt = skb_shinfo(skb)->nr_frags;
            if (frg_cnt >= MAX_SKB_FRAGS)
                  return -EFAULT;

            /* allocate a new page for next frag */
            page = alloc_pages(sk->sk_allocation, 0);

            /* If alloc_page fails just return failure and caller will
             * free previous allocated pages by doing kfree_skb()
             */
            if (page == NULL)
                  return -ENOMEM;

            /* initialize the next frag */
            sk->sk_sndmsg_page = page;
            sk->sk_sndmsg_off = 0;
            skb_fill_page_desc(skb, frg_cnt, page, 0, 0);
            skb->truesize += PAGE_SIZE;
            atomic_add(PAGE_SIZE, &sk->sk_wmem_alloc);

            /* get the new initialized frag */
            frg_cnt = skb_shinfo(skb)->nr_frags;
            frag = &skb_shinfo(skb)->frags[frg_cnt - 1];

            /* copy the user data to page */
            left = PAGE_SIZE - frag->page_offset;
            copy = (length > left)? left : length;

            ret = getfrag(from, (page_address(frag->page) +
                      frag->page_offset + frag->size),
                      offset, copy, 0, skb);
            if (ret < 0)
                  return -EFAULT;

            /* copy was successful so update the size parameters */
            sk->sk_sndmsg_off += copy;
            frag->size += copy;
            skb->len += copy;
            skb->data_len += copy;
            offset += copy;
            length -= copy;

      } while (length > 0);

      return 0;
}

/**
 *    skb_pull_rcsum - pull skb and update receive checksum
 *    @skb: buffer to update
 *    @start: start of data before pull
 *    @len: length of data pulled
 *
 *    This function performs an skb_pull on the packet and updates
 *    update the CHECKSUM_COMPLETE checksum.  It should be used on
 *    receive path processing instead of skb_pull unless you know
 *    that the checksum difference is zero (e.g., a valid IP header)
 *    or you are setting ip_summed to CHECKSUM_NONE.
 */
unsigned char *skb_pull_rcsum(struct sk_buff *skb, unsigned int len)
{
      BUG_ON(len > skb->len);
      skb->len -= len;
      BUG_ON(skb->len < skb->data_len);
      skb_postpull_rcsum(skb, skb->data, len);
      return skb->data += len;
}

EXPORT_SYMBOL_GPL(skb_pull_rcsum);

/**
 *    skb_segment - Perform protocol segmentation on skb.
 *    @skb: buffer to segment
 *    @features: features for the output path (see dev->features)
 *
 *    This function performs segmentation on the given skb.  It returns
 *    the segment at the given position.  It returns NULL if there are
 *    no more segments to generate, or when an error is encountered.
 */
struct sk_buff *skb_segment(struct sk_buff *skb, int features)
{
      struct sk_buff *segs = NULL;
      struct sk_buff *tail = NULL;
      unsigned int mss = skb_shinfo(skb)->gso_size;
      unsigned int doffset = skb->data - skb_mac_header(skb);
      unsigned int offset = doffset;
      unsigned int headroom;
      unsigned int len;
      int sg = features & NETIF_F_SG;
      int nfrags = skb_shinfo(skb)->nr_frags;
      int err = -ENOMEM;
      int i = 0;
      int pos;

      __skb_push(skb, doffset);
      headroom = skb_headroom(skb);
      pos = skb_headlen(skb);

      do {
            struct sk_buff *nskb;
            skb_frag_t *frag;
            int hsize;
            int k;
            int size;

            len = skb->len - offset;
            if (len > mss)
                  len = mss;

            hsize = skb_headlen(skb) - offset;
            if (hsize < 0)
                  hsize = 0;
            if (hsize > len || !sg)
                  hsize = len;

            nskb = alloc_skb(hsize + doffset + headroom, GFP_ATOMIC);
            if (unlikely(!nskb))
                  goto err;

            if (segs)
                  tail->next = nskb;
            else
                  segs = nskb;
            tail = nskb;

            nskb->dev = skb->dev;
            skb_copy_queue_mapping(nskb, skb);
            nskb->priority = skb->priority;
            nskb->protocol = skb->protocol;
            nskb->dst = dst_clone(skb->dst);
            memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
            nskb->pkt_type = skb->pkt_type;
            nskb->mac_len = skb->mac_len;

            skb_reserve(nskb, headroom);
            skb_reset_mac_header(nskb);
            skb_set_network_header(nskb, skb->mac_len);
            nskb->transport_header = (nskb->network_header +
                                skb_network_header_len(skb));
            skb_copy_from_linear_data(skb, skb_put(nskb, doffset),
                                doffset);
            if (!sg) {
                  nskb->csum = skb_copy_and_csum_bits(skb, offset,
                                              skb_put(nskb, len),
                                              len, 0);
                  continue;
            }

            frag = skb_shinfo(nskb)->frags;
            k = 0;

            nskb->ip_summed = CHECKSUM_PARTIAL;
            nskb->csum = skb->csum;
            skb_copy_from_linear_data_offset(skb, offset,
                                     skb_put(nskb, hsize), hsize);

            while (pos < offset + len) {
                  BUG_ON(i >= nfrags);

                  *frag = skb_shinfo(skb)->frags[i];
                  get_page(frag->page);
                  size = frag->size;

                  if (pos < offset) {
                        frag->page_offset += offset - pos;
                        frag->size -= offset - pos;
                  }

                  k++;

                  if (pos + size <= offset + len) {
                        i++;
                        pos += size;
                  } else {
                        frag->size -= pos + size - (offset + len);
                        break;
                  }

                  frag++;
            }

            skb_shinfo(nskb)->nr_frags = k;
            nskb->data_len = len - hsize;
            nskb->len += nskb->data_len;
            nskb->truesize += nskb->data_len;
      } while ((offset += len) < skb->len);

      return segs;

err:
      while ((skb = segs)) {
            segs = skb->next;
            kfree_skb(skb);
      }
      return ERR_PTR(err);
}

EXPORT_SYMBOL_GPL(skb_segment);

void __init skb_init(void)
{
      skbuff_head_cache = kmem_cache_create("skbuff_head_cache",
                                    sizeof(struct sk_buff),
                                    0,
                                    SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                                    NULL);
      skbuff_fclone_cache = kmem_cache_create("skbuff_fclone_cache",
                                    (2*sizeof(struct sk_buff)) +
                                    sizeof(atomic_t),
                                    0,
                                    SLAB_HWCACHE_ALIGN|SLAB_PANIC,
                                    NULL);
}

/**
 *    skb_to_sgvec - Fill a scatter-gather list from a socket buffer
 *    @skb: Socket buffer containing the buffers to be mapped
 *    @sg: The scatter-gather list to map into
 *    @offset: The offset into the buffer's contents to start mapping
 *    @len: Length of buffer space to be mapped
 *
 *    Fill the specified scatter-gather list with mappings/pointers into a
 *    region of the buffer space attached to a socket buffer.
 */
static int
__skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
{
      int start = skb_headlen(skb);
      int i, copy = start - offset;
      int elt = 0;

      if (copy > 0) {
            if (copy > len)
                  copy = len;
            sg_set_buf(sg, skb->data + offset, copy);
            elt++;
            if ((len -= copy) == 0)
                  return elt;
            offset += copy;
      }

      for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
            int end;

            BUG_TRAP(start <= offset + len);

            end = start + skb_shinfo(skb)->frags[i].size;
            if ((copy = end - offset) > 0) {
                  skb_frag_t *frag = &skb_shinfo(skb)->frags[i];

                  if (copy > len)
                        copy = len;
                  sg_set_page(&sg[elt], frag->page, copy,
                              frag->page_offset+offset-start);
                  elt++;
                  if (!(len -= copy))
                        return elt;
                  offset += copy;
            }
            start = end;
      }

      if (skb_shinfo(skb)->frag_list) {
            struct sk_buff *list = skb_shinfo(skb)->frag_list;

            for (; list; list = list->next) {
                  int end;

                  BUG_TRAP(start <= offset + len);

                  end = start + list->len;
                  if ((copy = end - offset) > 0) {
                        if (copy > len)
                              copy = len;
                        elt += __skb_to_sgvec(list, sg+elt, offset - start,
                                          copy);
                        if ((len -= copy) == 0)
                              return elt;
                        offset += copy;
                  }
                  start = end;
            }
      }
      BUG_ON(len);
      return elt;
}

int skb_to_sgvec(struct sk_buff *skb, struct scatterlist *sg, int offset, int len)
{
      int nsg = __skb_to_sgvec(skb, sg, offset, len);

      sg_mark_end(&sg[nsg - 1]);

      return nsg;
}

/**
 *    skb_cow_data - Check that a socket buffer's data buffers are writable
 *    @skb: The socket buffer to check.
 *    @tailbits: Amount of trailing space to be added
 *    @trailer: Returned pointer to the skb where the @tailbits space begins
 *
 *    Make sure that the data buffers attached to a socket buffer are
 *    writable. If they are not, private copies are made of the data buffers
 *    and the socket buffer is set to use these instead.
 *
 *    If @tailbits is given, make sure that there is space to write @tailbits
 *    bytes of data beyond current end of socket buffer.  @trailer will be
 *    set to point to the skb in which this space begins.
 *
 *    The number of scatterlist elements required to completely map the
 *    COW'd and extended socket buffer will be returned.
 */
int skb_cow_data(struct sk_buff *skb, int tailbits, struct sk_buff **trailer)
{
      int copyflag;
      int elt;
      struct sk_buff *skb1, **skb_p;

      /* If skb is cloned or its head is paged, reallocate
       * head pulling out all the pages (pages are considered not writable
       * at the moment even if they are anonymous).
       */
      if ((skb_cloned(skb) || skb_shinfo(skb)->nr_frags) &&
          __pskb_pull_tail(skb, skb_pagelen(skb)-skb_headlen(skb)) == NULL)
            return -ENOMEM;

      /* Easy case. Most of packets will go this way. */
      if (!skb_shinfo(skb)->frag_list) {
            /* A little of trouble, not enough of space for trailer.
             * This should not happen, when stack is tuned to generate
             * good frames. OK, on miss we reallocate and reserve even more
             * space, 128 bytes is fair. */

            if (skb_tailroom(skb) < tailbits &&
                pskb_expand_head(skb, 0, tailbits-skb_tailroom(skb)+128, GFP_ATOMIC))
                  return -ENOMEM;

            /* Voila! */
            *trailer = skb;
            return 1;
      }

      /* Misery. We are in troubles, going to mincer fragments... */

      elt = 1;
      skb_p = &skb_shinfo(skb)->frag_list;
      copyflag = 0;

      while ((skb1 = *skb_p) != NULL) {
            int ntail = 0;

            /* The fragment is partially pulled by someone,
             * this can happen on input. Copy it and everything
             * after it. */

            if (skb_shared(skb1))
                  copyflag = 1;

            /* If the skb is the last, worry about trailer. */

            if (skb1->next == NULL && tailbits) {
                  if (skb_shinfo(skb1)->nr_frags ||
                      skb_shinfo(skb1)->frag_list ||
                      skb_tailroom(skb1) < tailbits)
                        ntail = tailbits + 128;
            }

            if (copyflag ||
                skb_cloned(skb1) ||
                ntail ||
                skb_shinfo(skb1)->nr_frags ||
                skb_shinfo(skb1)->frag_list) {
                  struct sk_buff *skb2;

                  /* Fuck, we are miserable poor guys... */
                  if (ntail == 0)
                        skb2 = skb_copy(skb1, GFP_ATOMIC);
                  else
                        skb2 = skb_copy_expand(skb1,
                                           skb_headroom(skb1),
                                           ntail,
                                           GFP_ATOMIC);
                  if (unlikely(skb2 == NULL))
                        return -ENOMEM;

                  if (skb1->sk)
                        skb_set_owner_w(skb2, skb1->sk);

                  /* Looking around. Are we still alive?
                   * OK, link new skb, drop old one */

                  skb2->next = skb1->next;
                  *skb_p = skb2;
                  kfree_skb(skb1);
                  skb1 = skb2;
            }
            elt++;
            *trailer = skb1;
            skb_p = &skb1->next;
      }

      return elt;
}

EXPORT_SYMBOL(___pskb_trim);
EXPORT_SYMBOL(__kfree_skb);
EXPORT_SYMBOL(kfree_skb);
EXPORT_SYMBOL(__pskb_pull_tail);
EXPORT_SYMBOL(__alloc_skb);
EXPORT_SYMBOL(__netdev_alloc_skb);
EXPORT_SYMBOL(pskb_copy);
EXPORT_SYMBOL(pskb_expand_head);
EXPORT_SYMBOL(skb_checksum);
EXPORT_SYMBOL(skb_clone);
EXPORT_SYMBOL(skb_copy);
EXPORT_SYMBOL(skb_copy_and_csum_bits);
EXPORT_SYMBOL(skb_copy_and_csum_dev);
EXPORT_SYMBOL(skb_copy_bits);
EXPORT_SYMBOL(skb_copy_expand);
EXPORT_SYMBOL(skb_over_panic);
EXPORT_SYMBOL(skb_pad);
EXPORT_SYMBOL(skb_realloc_headroom);
EXPORT_SYMBOL(skb_under_panic);
EXPORT_SYMBOL(skb_dequeue);
EXPORT_SYMBOL(skb_dequeue_tail);
EXPORT_SYMBOL(skb_insert);
EXPORT_SYMBOL(skb_queue_purge);
EXPORT_SYMBOL(skb_queue_head);
EXPORT_SYMBOL(skb_queue_tail);
EXPORT_SYMBOL(skb_unlink);
EXPORT_SYMBOL(skb_append);
EXPORT_SYMBOL(skb_split);
EXPORT_SYMBOL(skb_prepare_seq_read);
EXPORT_SYMBOL(skb_seq_read);
EXPORT_SYMBOL(skb_abort_seq_read);
EXPORT_SYMBOL(skb_find_text);
EXPORT_SYMBOL(skb_append_datato_frags);

EXPORT_SYMBOL_GPL(skb_to_sgvec);
EXPORT_SYMBOL_GPL(skb_cow_data);

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