[deliverable/linux.git] / net / core / 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/splice.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;

static void sock_pipe_buf_release(struct pipe_inode_info *pipe,
                                  struct pipe_buffer *buf)
{
        struct sk_buff *skb = (struct sk_buff *) buf->private;

        kfree_skb(skb);
}

static void sock_pipe_buf_get(struct pipe_inode_info *pipe,
                                struct pipe_buffer *buf)
{
        struct sk_buff *skb = (struct sk_buff *) buf->private;

        skb_get(skb);
}

static int sock_pipe_buf_steal(struct pipe_inode_info *pipe,
                               struct pipe_buffer *buf)
{
        return 1;
}


/* Pipe buffer operations for a socket. */
static struct pipe_buf_operations sock_pipe_buf_ops = {
        .can_merge = 0,
        .map = generic_pipe_buf_map,
        .unmap = generic_pipe_buf_unmap,
        .confirm = generic_pipe_buf_confirm,
        .release = sock_pipe_buf_release,
        .steal = sock_pipe_buf_steal,
        .get = sock_pipe_buf_get,
};

/*
 *      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;
}

/**
 *      dev_alloc_skb - allocate an skbuff for receiving
 *      @length: length to allocate
 *
 *      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. Although this function
 *      allocates memory it can be called from an interrupt.
 */
struct sk_buff *dev_alloc_skb(unsigned int length)
{
        return __dev_alloc_skb(length, GFP_ATOMIC);
}
EXPORT_SYMBOL(dev_alloc_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;
}

/**
 *      skb_put - add data to a buffer
 *      @skb: buffer to use
 *      @len: amount of data to add
 *
 *      This function extends the used data area of the buffer. If this would
 *      exceed the total buffer size the kernel will panic. A pointer to the
 *      first byte of the extra data is returned.
 */
unsigned char *skb_put(struct sk_buff *skb, unsigned int len)
{
        unsigned char *tmp = skb_tail_pointer(skb);
        SKB_LINEAR_ASSERT(skb);
        skb->tail += len;
        skb->len  += len;
        if (unlikely(skb->tail > skb->end))
                skb_over_panic(skb, len, __builtin_return_address(0));
        return tmp;
}
EXPORT_SYMBOL(skb_put);

/**
 *      skb_push - add data to the start of a buffer
 *      @skb: buffer to use
 *      @len: amount of data to add
 *
 *      This function extends the used data area of the buffer at the buffer
 *      start. If this would exceed the total buffer headroom the kernel will
 *      panic. A pointer to the first byte of the extra data is returned.
 */
unsigned char *skb_push(struct sk_buff *skb, unsigned int len)
{
        skb->data -= len;
        skb->len  += len;
        if (unlikely(skb->data<skb->head))
                skb_under_panic(skb, len, __builtin_return_address(0));
        return skb->data;
}
EXPORT_SYMBOL(skb_push);

/**
 *      skb_pull - remove data from the start of a buffer
 *      @skb: buffer to use
 *      @len: amount of data to remove
 *
 *      This function removes data from the start of a buffer, returning
 *      the memory to the headroom. A pointer to the next data in the buffer
 *      is returned. Once the data has been pulled future pushes will overwrite
 *      the old data.
 */
unsigned char *skb_pull(struct sk_buff *skb, unsigned int len)
{
        return unlikely(len > skb->len) ? NULL : __skb_pull(skb, len);
}
EXPORT_SYMBOL(skb_pull);

/**
 *      skb_trim - remove end from a buffer
 *      @skb: buffer to alter
 *      @len: new length
 *
 *      Cut the length of a buffer down by removing data from the tail. If
 *      the buffer is already under the length specified it is not modified.
 *      The skb must be linear.
 */
void skb_trim(struct sk_buff *skb, unsigned int len)
{
        if (skb->len > len)
                __skb_trim(skb, len);
}
EXPORT_SYMBOL(skb_trim);

/* 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;
}

/*
 * Callback from splice_to_pipe(), if we need to release some pages
 * at the end of the spd in case we error'ed out in filling the pipe.
 */
static void sock_spd_release(struct splice_pipe_desc *spd, unsigned int i)
{
        struct sk_buff *skb = (struct sk_buff *) spd->partial[i].private;

        kfree_skb(skb);
}

/*
 * Fill page/offset/length into spd, if it can hold more pages.
 */
static inline int spd_fill_page(struct splice_pipe_desc *spd, struct page *page,
                                unsigned int len, unsigned int offset,
                                struct sk_buff *skb)
{
        if (unlikely(spd->nr_pages == PIPE_BUFFERS))
                return 1;

        spd->pages[spd->nr_pages] = page;
        spd->partial[spd->nr_pages].len = len;
        spd->partial[spd->nr_pages].offset = offset;
        spd->partial[spd->nr_pages].private = (unsigned long) skb_get(skb);
        spd->nr_pages++;
        return 0;
}

/*
 * Map linear and fragment data from the skb to spd. Returns number of
 * pages mapped.
 */
static int __skb_splice_bits(struct sk_buff *skb, unsigned int *offset,
                             unsigned int *total_len,
                             struct splice_pipe_desc *spd)
{
        unsigned int nr_pages = spd->nr_pages;
        unsigned int poff, plen, len, toff, tlen;
        int headlen, seg;

        toff = *offset;
        tlen = *total_len;
        if (!tlen)
                goto err;

        /*
         * if the offset is greater than the linear part, go directly to
         * the fragments.
         */
        headlen = skb_headlen(skb);
        if (toff >= headlen) {
                toff -= headlen;
                goto map_frag;
        }

        /*
         * first map the linear region into the pages/partial map, skipping
         * any potential initial offset.
         */
        len = 0;
        while (len < headlen) {
                void *p = skb->data + len;

                poff = (unsigned long) p & (PAGE_SIZE - 1);
                plen = min_t(unsigned int, headlen - len, PAGE_SIZE - poff);
                len += plen;

                if (toff) {
                        if (plen <= toff) {
                                toff -= plen;
                                continue;
                        }
                        plen -= toff;
                        poff += toff;
                        toff = 0;
                }

                plen = min(plen, tlen);
                if (!plen)
                        break;

                /*
                 * just jump directly to update and return, no point
                 * in going over fragments when the output is full.
                 */
                if (spd_fill_page(spd, virt_to_page(p), plen, poff, skb))
                        goto done;

                tlen -= plen;
        }

        /*
         * then map the fragments
         */
map_frag:
        for (seg = 0; seg < skb_shinfo(skb)->nr_frags; seg++) {
                const skb_frag_t *f = &skb_shinfo(skb)->frags[seg];

                plen = f->size;
                poff = f->page_offset;

                if (toff) {
                        if (plen <= toff) {
                                toff -= plen;
                                continue;
                        }
                        plen -= toff;
                        poff += toff;
                        toff = 0;
                }

                plen = min(plen, tlen);
                if (!plen)
                        break;

                if (spd_fill_page(spd, f->page, plen, poff, skb))
                        break;

                tlen -= plen;
        }

done:
        if (spd->nr_pages - nr_pages) {
                *offset = 0;
                *total_len = tlen;
                return 0;
        }
err:
        return 1;
}

/*
 * Map data from the skb to a pipe. Should handle both the linear part,
 * the fragments, and the frag list. It does NOT handle frag lists within
 * the frag list, if such a thing exists. We'd probably need to recurse to
 * handle that cleanly.
 */
int skb_splice_bits(struct sk_buff *__skb, unsigned int offset,
                    struct pipe_inode_info *pipe, unsigned int tlen,
                    unsigned int flags)
{
        struct partial_page partial[PIPE_BUFFERS];
        struct page *pages[PIPE_BUFFERS];
        struct splice_pipe_desc spd = {
                .pages = pages,
                .partial = partial,
                .flags = flags,
                .ops = &sock_pipe_buf_ops,
                .spd_release = sock_spd_release,
        };
        struct sk_buff *skb;

        /*
         * I'd love to avoid the clone here, but tcp_read_sock()
         * ignores reference counts and unconditonally kills the sk_buff
         * on return from the actor.
         */
        skb = skb_clone(__skb, GFP_KERNEL);
        if (unlikely(!skb))
                return -ENOMEM;

        /*
         * __skb_splice_bits() only fails if the output has no room left,
         * so no point in going over the frag_list for the error case.
         */
        if (__skb_splice_bits(skb, &offset, &tlen, &spd))
                goto done;
        else if (!tlen)
                goto done;

        /*
         * now see if we have a frag_list to map
         */
        if (skb_shinfo(skb)->frag_list) {
                struct sk_buff *list = skb_shinfo(skb)->frag_list;

                for (; list && tlen; list = list->next) {
                        if (__skb_splice_bits(list, &offset, &tlen, &spd))
                                break;
                }
        }

done:
        /*
         * drop our reference to the clone, the pipe consumption will
         * drop the rest.
         */
        kfree_skb(skb);

        if (spd.nr_pages) {
                int ret;

                /*
                 * Drop the socket lock, otherwise we have reverse
                 * locking dependencies between sk_lock and i_mutex
                 * here as compared to sendfile(). We enter here
                 * with the socket lock held, and splice_to_pipe() will
                 * grab the pipe inode lock. For sendfile() emulation,
                 * we call into ->sendpage() with the i_mutex lock held
                 * and networking will grab the socket lock.
                 */
                release_sock(__skb->sk);
                ret = splice_to_pipe(pipe, &spd);
                lock_sock(__skb->sk);
                return ret;
        }

        return 0;
}

/**
 *      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 1: 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 2: 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
 *      @len: length of data pulled
 *
 *      This function performs an skb_pull on the packet and updates
 *      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;
}

/**
 * skb_partial_csum_set - set up and verify partial csum values for packet
 * @skb: the skb to set
 * @start: the number of bytes after skb->data to start checksumming.
 * @off: the offset from start to place the checksum.
 *
 * For untrusted partially-checksummed packets, we need to make sure the values
 * for skb->csum_start and skb->csum_offset are valid so we don't oops.
 *
 * This function checks and sets those values and skb->ip_summed: if this
 * returns false you should drop the packet.
 */
bool skb_partial_csum_set(struct sk_buff *skb, u16 start, u16 off)
{
        if (unlikely(start > skb->len - 2) ||
            unlikely((int)start + off > skb->len - 2)) {
                if (net_ratelimit())
                        printk(KERN_WARNING
                               "bad partial csum: csum=%u/%u len=%u\n",
                               start, off, skb->len);
                return false;
        }
        skb->ip_summed = CHECKSUM_PARTIAL;
        skb->csum_start = skb_headroom(skb) + start;
        skb->csum_offset = off;
        return true;
}

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);
EXPORT_SYMBOL_GPL(skb_partial_csum_set);